Method For Closing A Tubular Bag Body And A Bag Produced Using It
Field of invention:
The invention relates to a method for sealing a tubular bag body made of a fabric
of monoaxially stretched polymer, more particularly polyolefin or polypropylene,
bands, including the production of a base fold in such a way that the bag
essentially has a rectangular base. The invention also relates to a bag with a
tubular bag body made of a fabric of monoaxially stretched polymer, more
particularly polyolefin or polypropylene bands, at least one end area of which has
a base fold so that the bag has an essentially rectangular base.
Background of invention:
The tubular body of such a bag is usually formed of a tubular round material or a
flat material joined at its longitudinal edges to form a tube. Such bags are roughly
divided into a cushion and box form. Cushion shaped bags are normally produced
by providing the base with a textile seam or a welding seam. The present
invention is concerned with box-shaped bags in which at least one end has a base
fold, so that the bag essentially has a rectangular base. If both ends of the bag
have a base fold, they are known as box bags. Bags which at one end correspond
to a cushion bag and at the other end to the box bag are known as semi-box
shaped.
3
The present invention covers both box bags and semi-box bags. Typical bags have
a filling capacity of 10, 25, 50, 100, 500 and 1000 kg. Bag of plastic fabric
composed of monoaxially stretched bands exhibit the greatest strength and are
dimensionally stable. The fabric comprises monoaxially stretched polymer, more
particularly polyolefin or polypropylene bands. These bands are produced by
stretching polymer, more particularly polyolefin or polypropylene films to usually
four to ten times their length, whereby the molecules are aligned in the
longitudinal direction of the band and in this direction exhibit approximately six
to ten times the strength of the original film. The width of the bands is normally
approximately 1.5 to 10 mm, the thickness 20 to 80 μm. To achieve
impermeability to dust and moisture, a coating of a melt of preferably the same
material as the band can be applied on one or both sides of the fabric.
In connection with box-shaped bags, various methods of sealing the bases are
already known. Usually the folded base is laboriously stuck with a multicomponent
adhesive in accordance with the prior art, as polypropylene and
polyethylene materials, of which the fabric usually consists, can only be stuck
with difficulty. In addition to the laborious sticking procedure, the known
adhesives have further drawbacks as low durability, brittleness as a result of
temperature changes and loss of adhesive effect through the effects of moisture. In
connection with this, in WO95/30598 A1 an improved method is described in
which at least one end of the bag, more particularly a base area, is connected via
an intermediate layer of, more particularly thermoplastic synthetic material, in
4
particular polyolefin, preferably polypropylene material, through the effect of heat
with a cover sheet of monoaxially stretched polymer, more particularly polyolefin,
preferably polypropylene bands, and in which only the external surface area, more
particularly less than 30% of the material thickness of the fabric bands, of the base
area and cover sheet exhibits disorientated molecule as a result of the effect of
heat, whereby in the remaining material area the molecule orientation is retained.
The disadvantage of this method is controlling and limiting the effect of heat so
that only the external surface area is heated and affected by the disorientation of
the molecules.
Compared with areas of molecules orientated by stretching of the material, areas
of the fabric with disorientated molecules are considerably less strong. A further
disadvantage of this method is the either a certain minimum strength of the fabric
or a sufficiently thick coating of the fabric is required in order to allow welding.
This results in a relatively high weight of the bad and higher costs.
Objects of invention:
The aim of the present invention is therefore to provide a bag and a method of
sealing a bag with which the above problems can be avoided and with which a
secure and easily produced bag seal is guaranteed at the same time.
To solve this task the method set out in the introduction is implemented in
accordance with invention so that at least two at least partially overlapping layers
5
of the base are welded to each other with at least one welding seam in the area
where they overlap in order to seal the bag, whereby the at least one welding seam
extends at least over the length of the broad and/or the narrow side of the
rectangular base.
To solve this task the method set out in the introduction is developed further in
accordance with invention in that at least two at least partially overlapping layers
of the base are welded to each other with at least one welding seam in the area
where they overlap in order to seal the bag, whereby the at least one welding seam
extends at least over the length of the broad and/or the narrow side of the
rectangular base.
Detailed description of invention:
In accordance with the invention the layers of the base fold are therefore not
welded over their entire area, but only along at least one discrete welding seam,
whereby preferably several discrete welding seams are provided. This takes into
account that in the area of the at least one welding seam the fabric is weakened
due to the disorientation of the molecules. In spite of the weakening of the fabric
sufficient stability of the welded connection is guaranteed without the risk of
tearing of the fabric, particularly if the welding seams are arranged in such a way
that they are only exposed to shearing forces but not peeling forces.
6
Under shearing loading the forces only act in the plane of the fabric. In the case of
peel loading the forces would act on the welding seam transversely to the plane of
the fabric which can lead to destruction of the welding seam.
In accordance with the present invention a welding seam is understood as a weld
along a longitudinal area, the length of which is many times greater than the
width.
The welding seam does not have to be rectilinear, but can, for example also have
bent/curved areas or changes in direction. It is particularly advantageous if the
welding seam runs obliquely to the band direction or had obliquely running
sections.
The welding seam can, for example, run in zigzag manner. In the case of a zigzag
weld, the individual sections of which runs obliquely to the direction of the fabric
bands, the individual bands are only weakened to a small extent.
The risk of tearing of the fabric can also be advantageously reduced in that the
welding for forming a welding seam is carried out by way of a number of welding
points arranged at intervals from each other.
In this way a continuous welding seam is not produced so that tear continuation
lines are avoided. Preferably the welding seam is produced by way of ultrasonic
7
or laser welding. Ultrasonic welding enables defined welding points to be
produced in a simple manner so that the proportion of the fabric affected by the
welding in the area of welding seam can be reduced.
However, other welding methods are conceivable, such as welding with a hot
stamp (static or as rolling stamp or roller). As the welding seam comprises a
number of welding points arranged at an interval from each other, preferably
consisting of these, the fabric is only weakened in parts by the welding, whereby
the strength between the individual welding points is preserved in full. As the
alignment of the molecule chains is only lost to a small extent through the
welding, the fabric suffers hardly any loss of strength. The effect that melt collects
around the individual welding points and additionally takes up mechanical
stresses can also be utilised.
Preferably the welding points are produced in a punctiform manner, whereby it is
preferred if the welding points are arranged offset with regard to each other
transversely to the band direction. Through the offset arrangement of the welding
points the formation of tear continuation lines is effectively prevented.
The welding points can, for example, be arranged in several rows, whereby the
welding points in one row are arranged by the gap between the welding points in
an adjacent row.
8
In the case of plastic ultrasonic welding, heat is supplied to the welding points of
bands of the fabric to be welded by way of high-frequency mechanical
oscillations, whereby the material is melted or at least softened. The joining force
and the ultrasonic oscillations have the same effect direction. The introduced
longitudinal waves bring about a pulsating stress in the material and joining zone
which leads to plasticisation of the plastic material. On stopping the energy supply
the material cools under pressure at the welding points and a durable,
mechanically stable joint is formed.
Preferably the plurality of welding points arranged at intervals from each other is
applied at a density of at most 15, preferably at most 10, preferably at most 5
welding points per cm2.
Advantageous in the method according to the invention is that there are no weak
points caused by needle perforation of the fabric. Also, welding is associated with
lower costs and is characterised by a high working speed. With the method in
accordance with the invention considerably more bags can be sealed per minute
than with the method known from the prior art. The weld connection is not subject
to ageing or embrittlement.
Disposal is also simple as the bag consists exclusively of single-variety material.
In order to seal the base of the bag solely by means of welding in accordance with
the invention, i.e. without further measures, such as adhesive connections, full
9
area welding etc., a plurality of welding seams is required. More particularly, the
welding seams are arranged so that at least one welding seam essentially extends
over the length of the narrow side of the rectangular base and at least one welding
seam essentially extends over the length of the broad side of the rectangular base.
The welding seams can be produced as individual welding seams separated from
each other. However, it is also conceivable to connect the welding seams to one
another so that in this case a single welding seam with a corresponding number of
adjacent sections is involved. In terms of time the welding seams can be produced
consecutively after each other or also simultaneously.
The reference to the narrow side and the broad side of the bag base also covers
versions with a quadratic base. The terms narrow side and broad side are thus not
to be understood as indications of length, but only serve to differentiate one pair
of opposite sides from the other pair of opposite sides.
Within the scope of the invention a large number of arrangements of the welding
seams is conceivable. In accordance with a first alternative it is envisaged that two
folded over flaps of the base fold are welded along a first welding seam where
they overlap and that said flaps are welded along two second welding seams
running transversely to the first welding seam to the folded-over flap lying
underneath on the narrow sides of the base. An H-shaped weld is thus produced
for example.
10
In accordance with a second alterative it is envisaged that a cover sheet of a fabric
of monoaxially stretched polymer, more particularly polyolefin or polypropylene
bands is connected, more particularly welded, to a folded-over flap of the base
fold on the broad side of the base, whereby the cover sheet essentially corresponds
to the size of the base, that that the cover sheet is the welded to the flap folded
over on the narrow side base along two welding seams, and that the cover sheet is
then welded along a welding seam to the folded-over flap on the base fold on the
other broad side of the base. The externally located cover sheet is thus welded
with all its edges to the folded-over flaps of the base fold and welding is along a
rectangular frame.
In accordance with a second alternative it is envisaged that after folding over the
flaps on the narrow sides of the base and before folding over the flaps on the
broad side of the base a cover sheet is placed on the base fold, which at its four
edges is welded to the base fold by four welding seams, that the flaps on the broad
sides of the base are then folded over together with the welded-on edge of the
cover sheet and the flaps folded over on the broad side are welded together along
a welding seam in the area in which they overlap.
The cover sheet is therefore located internally and welded with all its edge to the
folded over flaps of the base fold, so that welding is produced along a rectangular
frame.
11
In order to avoid welding the folded-over flaps of the base fold or the cover sheet
to the bag body, a separating layer is advantageously placed on the fabric or a
separating layer applied. Preferably the separating layer has a higher thermal
conductivity than the bag fabric. The separating layer, more particularly a metalcontaining
separating layer, is preferably applied by means of a coating process.
Preferably a coating containing metal is used as the separating layer. Due to the
metal content such a separating layer brings about heat removal so that fabric
layer of the bag body facing away from the folded over end section is subject to
reduced or essentially no heat input.
The invention will be described below in more detail with the aid of an example
of embodiment shown schematically in the drawings. Here Figures 1 to 3 show a
first variant of embodiment of the invention, Figures 4 to 7 a second variant of
embodiment of the invention, Figures 8 to 12 a third variant of embodiment of the
invention and Figures 13 to 15 various embodiments of the welding seams.
Fig. 1 shows a tubular bag body in the flat state 1, the base 2 of which is designed
for forming a box shaped bag through folding of the base. The base fold has two
flaps 3 folded over from the two opposite narrow sides of the bag body 1 and two
flaps 4 to be folded over from the opposite broad sides of the bag body 1 along
folding edges 5. After folding the flaps 4 inwards the state shown in Figure 2 is
produced, in which the end sections of the flaps 4 folded inwards from the broad
12
sides overlap each other so that the end section of one flap 4 is shown as a dotted
line. In general it should be stated with regard to the drawings that covered edges
are shown as dotted lines and folding edges are shown a dot-dashed lines.
To seal the base 2 the two flaps 4 folded over on the broad sides of the base 2 are
welded to each other in the area they overlap along a welding seam 7. The flaps 4
are also welded along two welding seams 8, running transversely to the welding
seam 8, to the underlying folded-over flap 3 on the narrow sides of base 2. Here it
is of decisive importance that the welding seams 8 are outside the edges 6 of the
flaps 3 folded over from the narrow sides. In order to avoid that the bag body is
also welded during the production of the welding seams 7 and 8, a separating
layer or a weld-preventing coating must be applied beforehand. For this full-area
coating of the fabric material in the relevant area can be carried out. Alternatively
the coating or the separating layer can only be applied in the area of the
anticipated welding seams. These seams are designated as 9 and 10 in Figure 1.
The areas 9 are on the bag body below the inwards folded flaps 3. The area 10 is
transverse to this.
Figs. 4 to 7 show an alternative embodiment. The initial state is shown in Figure 2
and the flaps folded inwards on the narrow sides of the base are again designated
as 3 and the flaps to be folded over on the broad sides along folding edges 5 are
designated as 4.
13
In contrast to the illustration in Figures 1 to 3, the flaps 3 and 4 are not directly
welded to each other, but a separate cover sheet 11 is used. The cover sheet 11 is
essentially the size of the rectangular base to be produced and in a first step is
welded to one of the two flaps 4 along a welding seam 12. In a second step
(Figure 5) the flap 4 welded to the cover sheet 4, is folded along folding edge 5. In
this way the right and left edge of the cover sheet 11 overlap the flaps 3 folded
over on the narrow sides so that in this area further welding seams 13 can be
produced (Figure 6). In order to prevent the edge area of the folded-over flaps 13
being welded to the underlying bag body while producing the welding seams 13,
before producing welding seams 13 a metal separating sheet or suchlike can be
placed under the flaps which can subsequently be removed. The insertion of a
separating sheet can, for example, take place in the direction of the arrow 14, i.e.
from the side of base 2 which is still open.
In a further processing stage (Figure 7) the upper flap 4 is now folded inwards
along folding edge 5 so that it covers the upper edge area of the cover sheet 11. In
the covering area the last welding seam 15 is then produced so that the base 2 is
fully sealed. In order to prevent the cover sheet 11 being welded to the underlying
bag base while producing the last welding seam 15, at the start of the procedure
(Figure 4) a separating coating or separating layer can be applied in the area 16.
A further embodiment variant is shown in figures 8 to 12. The same reference
numbers are again used for the same parts. In contrast with the illustration in
14
accordance with figures 4 to 7 no external cover sheet 11, but an internal cover
sheet 17 is used. The cover sheet is placed on the base fold before the flaps 4 are
folded over. As can be seen in Figure 9 the cover sheet 17 is of such a size that it
projects over the edges 6 of the flaps 3 folded over on the narrow sides and the
folding edges 5, so that all around a sufficient margin for producing the welding
seams remains. As can be seen in Figure 10 welding seams 18 and 19 are applied
in such a way that the overlapping edge areas of the cover sheet 17 are connected
to the underlying flaps 3 and 4 respectively. To prevent the flaps 3 being welded
to the bag body underneath them, a separating coating or separating layer can be
applied beforehand in area 20 (Figure 8). It is essential that the welding seams 18
are arranged outside the folding edge 5 so that they are subsequently not exposed
to peeling forces but only shearing forces.
The flaps 4 are then folded inwards along the folding edge 5 (Figure 11) whereby
they overlap each other again.
When folding over the flaps 4 the cover sheet 17 is also folded over, whereby the
welding seam 18 is also located in the folded-over area so that in the state shown
in Figure 4 it comes to lie on the inner side.
Finally (Fig. 12) the flaps in the overlapping area are connected to each other by
means of a welding seam 21.
15
In figures 13 to 15 various variants of the welding seams are described. Each of
these variants can be used in the method variants shown in figures 1 to 12. In
figures 13 to 15 only a small section of the generally elongated welding seam is
shown. The bands of bag fabric crossing each other are denoted with 22. In a first
embodiment variant in accordance with Figure 13 the welding seam has a number
of welding points 23 arranged offset with regard to each other. In the illustration
in Figure 14 the welding seam 24 runs in a zigzag manner. In the embodiment in
accordance with Figure 15 the welding seam 24 extends along a wavy line.
Common to all the examples of embodiment is the fact that the welding seams
essentially extend over the longitudinal and/or the lateral length of the rectangular
base 2 so that stable sealing of the bag takes place solely on the basis of these
welding seams.
In principle further measures are not necessary, but are not ruled out within the
context of the invention.
16

We Claim
1. A method for sealing a tubular bag body made from a fabric of
monoaxially stretched polymer, more particularly polyolefin or polypropylene
bands, including the production of a base fold in such a way that the bag
essentially has a rectangular base, characterised in that said method comprises the
step of welding to each other at least two at least partially overlapping layers of
the base with at least one ultrasonic welding seam of defined welding points in the
area where they overlap in order to seal the base, wherein the at least one
ultrasonic welding seam extends at least over the length of the broad and/or the
narrow side of the rectangular base, and wherein in order to prevent the welding
together of the folded over layers of the base fold with the bag body, a separating
layer is placed on the fabric or applied, and wherein the base is sealed only by
using said ultrasonic welding seam.
2. The method in accordance with claim 1 characterised in that the welding is
carried out in order to produce an ultrasonic welding seam which is any non
rectilinear shape, particularly a zig-zag pattern.
3. The method in accordance with claim 1 or 2 characterised in that the ultrasonic
welding is carried out to produce an ultrasonic welding seam with a number of
welding seams arranged at intervals from each other, and that the welding points
in one row are arranged at the gap between the welding points in an adjacent row.
17
4. The method in accordance with any one of claims 1 to 3 characterised in that a
number of ultrasonic welding seams are provided, whereby at least one ultrasonic
welding seam essentially extends over the length of the narrow sides of the
rectangular base and at least one ultrasonic welding seam essentially extends over
the length of the broad side of the rectangular base.
5. The method in accordance with any one of claims 1 to 4 characterised in that
two flaps of the base fold folded over on the broad side of the base are
ultrasonically welded together in the area they overlap along a first welding seam
and that said flaps are welded to the underlying flaps folded over on the narrow
sides of the base along two welding seams running transversely to the first
welding seam.
6. The method in accordance with any one of claims 1 to 4 characterised in that a
cover sheet, preferably made from a fabric of monoaxially stretched polymer,
more particularly polyolefin or polypropylene bands, is welded, to a folded-over
flap of the base fold on the broad side of the base, wherein the cover sheet
essentially corresponds to the size of the base, that the cover sheet is then
ultrasonically welded to the flap folded over on the narrow sides of the base using
two welding seams, and that the cover sheet is then ultrasonically welded using a
welding seam to the folded-over flap on the base fold on the other broad side of
the base.
18
7. The method in accordance with any one of claims 1 to 4 characterised in that
after folding over the flaps on the narrow sides of the base and before folding over
the flaps on the broad side of the base, a cover sheet, preferably made from a
fabric of monoaxially stretched polymer, more particularly polyolefin or
polypropylene bands, is placed on the base fold, followed by ultrasonic welding of
said coversheet at its four edges to the base fold by four welding seams, and that
the flaps on the broad sides of the base are then folded over such that the weldedon
edge of the cover sheet also gets folded over, and the flaps folded over on the
broad side are welded together along a welding seam in the area in which the
broad-side flaps overlap.
8. A bag with a tubular bag body made of a fabric of monoaxially stretched
polymer, more particularly polyolefin or polypropylene bands, at least one end
area of which has a base fold so that the bag has an essentially rectangular base
characterised in that at least two at least partially overlapping layers of the base
are welded to each other with at least one ultrasonic welding seam of defined
welding points in the area where they overlap in order to seal the bag, wherein the
at least one welding seam extends at least over the length of the broad and/or the
narrow side of the rectangular base, and wherein the base is sealed only by using
said ultrasonic welding seam.
9. The bag in accordance with claim 8 characterised in that a separate cover sheet
is applied on the outside of the base produced by the base fold whereby the at
19
least two at least partially overlapping layers are formed by the cover sheet and at
least one folded over flap of the base fold on one side of the bag body.
10. The bag in accordance with claim 8 to 9 characterised in that the ultrasonic
welding seam is a non-rectilinear shaped welding seam, particularly having a zigzag
shape.
11. The bag in accordance with any one of claims 8 to 10 characterised in that the
ultrasonic welding seam consists of a number of welding points arranged at
intervals from each other and wherein the welding points in one row are arranged
at the gap between the welding points in an adjacent row.
12. The bag in accordance with any one of claims 8 to 11 characterised in that a
plurality of ultrasonic welding seams is provided, whereby at least one ultrasonic
welding seam essentially extends over the length of the narrow side of the
rectangular base and at least one ultrasonic welding seam essentially extends over
the length of the broad side of the rectangular base.
13. The bag in accordance with any one of claims 8 to 12, characterised in that in
the area where they overlap, two flaps of the base fold folded over on the broad
side of the base are ultrasonically welded along a first welding seam and that said
flaps are welded along two welding seams running transversely to the first
welding seam to the flaps folded over on the narrow sides of the base.
20
14. The bag in accordance with any one of claims 8 to 12 characterised in that a
cover sheet, made of a fabric of monaxially stretched polymer, more particularly
polyolefin or polypropylene bands is welded, to a folded over flap of the base fold
on the broad side of the base, whereby the cover sheet essentially corresponds to
the size of the base, that the cover sheet is then ultrasonically welded to the flap
folded over on the narrow sides of the base using two welding seams, and that the
cover sheet is ultrasonically welded along a welding seam to the folded-over flap
of the base fold on the other broad side of the base.
15. The bag in accordance with any one of claims 8 to 12 characterised in that
after folding over the flaps on the narrow sides of the base and before folding over
the flaps on the broad side of the base a cover sheet is placed on the base fold,
followed by ultrasonic welding of said coversheet to the base fold by four welding
seams, that the flaps on the broad sides of the base are folded over so that the
welded-on edge of the cover sheet also gets folded over, and the flaps folded over
on the broad side are welded together along a welding seam in the area in which
the broad-side flaps overlap.
16. An apparatus to making a bag from a tubular bag body made from a coated or
an uncoated fabric of monoaxially stretched polymer, more particularly polyolefin
or polypropylene bands, said bag being made in accordance with the method
disclosed in any of claims 1 to 7, characterised in that said apparatus has a feed
21
device for feeding said bag body to a sealing station, and a folding means wherein
said sealing station comprises at least an ultrasonic welding station.
Dated this 3rd day of September 2013
(Tase, Vijay Sharatchandra)
Patent agent for the applicant
Patent agent no IN/PA 987
To,
The Controller of Patents
New Delhi