Note: Descriptions are shown in the official language in which they were submitted.
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Packaging material and method for its production
The invention relates to a packaging material according to the preamble of
claim 1.
Furthermore, the invention relates to a method for the production of the
packaging
material according to the invention.
A packaging material with a first film and a woven fabric, which are arranged
one
above the other and are connected together, is known from the applicant's WO
2017/080609. Here, the first film comprises first areas in which the first
film is locally
stretched and second areas in which the first film is not locally stretched;
the first
areas are each arranged between two second areas and run in a first direction,
wherein the woven fabric comprises a thread and wherein a part of the thread
runs in
a direction which intersects the first direction.
In the case of certain applications in which heavy goods are to be packaged,
however, the known packaging material can disadvantageously tear at certain
points
on account of the different high tensile stress between the film and the woven
fabric.
Such packaging materials are used to package pallets, agricultural products,
refuse
etc., so that a high tear strength and protection against weather influences
is
required. Furthermore, such packaging materials should contain as little
plastic as
possible, which on the one hand reduces the environmental burden and on the
other
hand results in more favourable prices for consumers.
The problem of the present invention is to specify a packaging material with
low
weight relative to its dimensioning and high tear strength in the presence of
high
tensile stresses. Furthermore, a method for the production of the packaging
material
according to the invention is to be specified.
This problem is solved by the features of claim 1. A method for the production
of the
packaging material according to the invention is the subject-matter of claim
8. Further
embodiments according to the invention and advantages emerge from the
corresponding sub-claims.
1
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Accordingly, a packaging material is proposed, which comprises a pre-stretched
and
heat-stabilised elastic film and an elastic plastic net arranged flat on the
film, in
particular a plastic net constituted as a Raschel net, wherein the plastic net
is
connected to the film by means of an adhesive layer applied on the film, in
such a
way that a relative movement of the film and the plastic net in relation to
one another
is permitted in the event of high tensile stresses.
As a result of the pre-stretching of the elastic film, the packaging material
advantageously becomes thinner and lighter relative to a predefined length,
wherein
the effect of the heat stabilisation of the pre-stretched film is that the
film does not
exhibit any remaining surface stresses. As a result of the concept according
to the
invention, local excess stresses, which arise at different points of the
packaging
material, can be uniformly distributed by a relative movement of the net and
the film
in relation to one another in the event of high tensile stresses, so that
tearing of the
packaging material is advantageously prevented. This is made possible by the
fact
that the adhesive is a water-soluble adhesive, for example a food-grade
adhesive,
which has a low adhesive strength.
Furthermore, as a result of the prevention of local excess stresses, the
packaging
material can be wound around lightweight and thin winding cores instead of
heavy
winding cylinders made of pressboard.
For the production of the packaging material according to the invention, the
elastic
film is pre-stretched to a defined, predetermined degree and then heat-
stabilised,
wherein an adhesive layer, for example a water-soluble adhesive having a low
adhesive strength, is then applied on the pre-stretched film, for example by
means of
cylinder axes or high-pressure jets. After the pre-stretching of the film, the
latter has a
residual elasticity of 20%. In a subsequent step, the film and the plastic net
are
pressed together by means of rollers, so that a packaging material arises, one
side of
which is constituted as a self-adhesive film covered by a plastic net without
necking
points. The self-adhesive embodiment also gives rise to the advantage that
closing of
the packaging material after receiving the goods is simplified.
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The elastic film can be pre-stretched for example to a thickness of 5 pm,
wherein the
width can be arbitrary, and for example can lie in a range between 40 cm and
380
cm. The elastic film can be produced from LLDPE (linear polyethylene of low
density), LDPE (polyethylene of low density), HDPE (polyethylene of high
density),
VC (polyvinyl chloride), EVA (ethylene vinyl acetate) or from a similar
plastic, in
particular from any polyolefin, or can comprise the latter.
The plastic net can be produced from polyolefins such as for example LLDPE
(linear
polyethylene of low density), LDPE (polyethylene of low density), HDPE
(polyethylene of high density), PVC (polyvinylchloride), EVA (ethylene vinyl
acetate)
or from a similar plastic or can comprise the latter. Its weight can for
example be 2 to
32 g/running metre, wherein the net density can lie for example in a range
between 6
needles/inch to 2 inches needle spacing. The width of the net essentially
corresponds to the width of the elastic film.
The net can consist of fringes extending in the flow direction of the net
(also called
warp threads) and weft threads, which connect the fringes thereby forming a
zigzag
pattern to form a net, which according to the prior art are interwoven with
one
another, wherein the fringes are each formed from a thread. Furthermore,
provision
can be made such that all or part of the fringes, in particular the outer
fringes, are
each formed from two or more threads to increase the strength.
The distance between the fringes can be arbitrary and for example lie in a
range
between 4.2 and 50.8 mm. The plastic threads used for the fringes can have a
thickness from 10 ¨ 60 pm or less.
Furthermore, at least the outer or any fringes can each comprise two or more
partial
fringes to increase the strength, which are connected to one another by means
of at
least one weft thread running in a zigzag manner, in such a way that the
partial
fringes run directly adjacent parallel to one another. In the case of fringes
comprising
two partial fringes, the partial fringes are linked with one another in pairs
by means of
at least one weft thread.
3
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The invention is explained in greater detail below by way of example with the
aid of
the appended figures. In the figures:
Figure la shows a diagrammatic cross-sectional view of a packaging material
constituted according to a first embodiment of the invention;
Figure lb shows a diagrammatic plan view of the packaging material according
to
figure la;
Figure 2 shows a detail view from figure lb;
Figure 3a shows a diagrammatic cross-sectional view of a packaging material
constituted according to a second embodiment of the invention;
Figure 3b shows a diagrammatic plan view of the packaging material according
to
figure 3a; and
Figure 4 shows a detail view from figure 3a.
In the figures lb and 2b, MD denotes the machine direction, i.e. the flow
direction of
the plastic net during production or of the packaging material during winding;
TD
denotes the transverse direction, i.e. the direction at right angles to the
machine
direction or flow direction.
According to the invention and by reference to the example of embodiment
according
to figures la and lb, the packaging material comprises a stretched and heat-
stabilised elastic film 1 and an elastic plastic net of essentially identical
width
arranged flat on film 1, which is connected to film 1 by means of an adhesive
layer 2
applied on film 1, in such a way that a relative movement of film 1 and the
plastic net
in relation to one another is permitted in the event of high tensile stresses.
The plastic
net constantly remains in contact with adhesive layer 2.
The plastic net arranged on film 1 and connected to film 1 can be constituted
as a
Raschel net according to the prior art, comprising fringes 3 extending in the
flow
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direction of the net and weft threads 4 which connect the fringes thereby
forming a
zigzag pattern to form a net. The distance between adjacent fringes 3 can lie
for
example in a range between 4.2 mm and 50.8 mm
The example of embodiment shown in figures 3a, 3b and 4 differs from the
example
of embodiment according to figures la, lb and 2 in that all fringes 3 each
comprise
two partial fringes 3a and 3b for increasing the strength, which are connected
to a
one another by means of a weft thread 4 running in a zigzag manner, in such a
way
that partial fringes 3a, 3b run directly adjacent parallel to one another. The
distance
between partial fringe 3a, 3b of a fringe 3, i.e. the distance between the
virtual central
longitudinal lines of the partial fringes from one another can lie for example
in a range
between 2 mm and 10 mm, preferably in a range between 2 mm and 5 mm. With
such small distances, partial fringes 3a, 3b can come into contact with one
another.
The plastic net can be produced by a Raschel machine, which in each case
comprises at least two guide needles for guiding in each case a plastic thread
for
knitting a fringe in each case, wherein the in each case two guide needles are
supported by a common guide needle support and wherein two needles supported
by
a common needle support can be assigned to the in each case two guide needles.
The distance between two adjacent guide needles and/or between two directly
adjacent needles can lie here in a range between 2 and 10 mm, in particular
between
2 and 5 mm, as a result of which straightforward production of the fringes is
enabled
in the normal operation of the Raschel machine.
