Note: Descriptions are shown in the official language in which they were submitted.
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Thermoplastic Bay
This invention relates to thermoplastic shipping bags
and in particular to bags used for packaging fine powders.
Plastics shipping bags are suitable for the packaging,
5 transportation and storage of a wide variety of products in
granular, bead, or pellet form. However, there are many
products such as cement, clays/ powdered coal and pigments,
for instance, which cannot be readily packaged in plastic bags
because of the inability of plastic films to provide a
filtering action in order to release the air which has become
entrained inside the package during the high-speed filling
operation. Plastic bags are known having perforations
directly in their walls to provide the necessary air release.
However, this can result in excessive environmental contain-
anion and/or product loss from the package. This means that for powdered products having a particle size in the range of
10 microns or less, resort is generally had to the use of
paper or paper-like packaging materials for generally
acceptable finished packages. Paper bags are commonly used for
these applications with the inner ply of the paper supplying
the necessary filtering action. Such packaging materials,
however, are limited by the end use of these packaged goods in
several ways.
One drawback is that paper bags are extremely sensitive
to environmental extremes and require special care in high
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humidity or low temperature conditions. Also, paper fibre
contamination may result when the package's contents are
emptied into sensitive chemical mixtures. Further, with the
growing concern for environmental safety in the workplace,
there is an increasing need for packages which can be added
to, and thermally or mechanically dispersed within, industrial
processes. Multi-wall paper bags, and, to some degree,
plastic bags using contaminating adhesives or glues are
generally incompatible, particularly in the plastics and
rubber industry.
Some of these problems can be overcome by using a
plastic bag made from a spun bonded plastic in the form of a
mat of compressed thermoplastic fires, such as TYVEK~, which
has high strength characteristics while still retaining the
air permeable characteristics of paper. Alternatively, a
plastic film bag lined with paper achieves the same results.
However, these bags have the disadvantage of high cost and,
like paper bags, they have the further disadvantage of being
unsuitable for use in applications where the bag as well as
the product is thrown into rubber or plastic mixes where the
bag is expected to mix and incorporate as part of the
finished product.
One particularly useful type of plastics shipping bag is
that known as a valved bag, which is generally used for
packaging granular materials such as fertilizers and polymer
resins. One such embodiment is described in our United States
Patent No. 3,833,166. These bags possess the important
commercial advantage of being easily filled through a valve
structure with the self-closing of this valve structure
after filling. When filled and stored with the valve in the
down or sealed position the effectiveness of the valve is so
good that entrapped air is difficult to expel from the bags.
To avoid the problem it is common practice to place a row of
10 or so 0.6 mm diameter perforations down each side of the
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bag to allow the air to escape. This is satisfactory for
coarse granular product, but for finer materials of a
particle size of less than 100 microns this practice is
unsatisfactory since the product can readily leak through the
holes. This disadvantage is somewhat overcome by offsetting
the inner perforation layers of the bag from the outer layers
and trapping any escaping materials between the inner and
outer layers of the bag while readily allowing the air to
escape.
By using this system of offset perforations typically
with perforations at 2.5 cm centers over the entire body of
the bag, product with particle size of down to 1.0 micron may
be packaged. However, with powders of smaller particle
sizes the product will flow into these holes forming plugs
which prevent further flow of air.
It has now been found that a suitable shipping bag can
be obtained by providing the bag with a perforated wall and
an inner lining of a thermoplastic mesh adjacent said
perforated wall. This inner lining constitutes an inner
lining for the bag which permits adequate filtering and air
release during and after the filling operation.
Accordingly, the invention provides a thermoplastic
shipping bag having a front wall and a back wall correct-
erased in that at least one of said walls is perforated to
permit the passage of air there through, said perforated wall
having adjacent thereto an inner lining comprising a thermos
plastic mesh whereby said inner lining constitutes a powdered
product retaining inner lining of the bag.
The invention is of use when applied in the conventional
open-top bag.
Accordingly, in one feature the invention provides a
plastic shipping bag of the open-top type having a 'Deck
wall and a front wall joined together around the periphery of
the bag at its bottom and both sides characterlsed in that at
least one of said walls is perforated to permit the passage
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of ax there through, said perforated wall having joined
around all or part of its periphery an inner lining comprising
a thermoplastic mesh, whereby said inner lining constitutes a
powdered product retaining inner lining of the bag.
The utility of the open-topped bag according to the
invention resides in the fact that the bag may be filled with
the upper inner opposing faces of the meshed lining and its
opposing wall substantially contacting each other or the
filler spout of the powder feeding machine. Entrained air may
then escape through the thermoplastic mesh during the filling
operation but vainly after the bag is sealed, with reduced
product loss.
The invention is of particular use when applied in a
valved bag.
Accordingly, in a preferred feature the invention
provides a thermoplastic shipping bag of the valved bag type
having a back wall and a front wall joined together
around the entire periphery of the bag and a filling aperture
characterized in that at least one of said walls is purrer-
axed to permit the passage of air there through, said perform
axed wall having joined thereto an inner lining comprising a
thermoplastic mesh whereby said inner lining constitutes a
powdered product retaining inner lining of the bag.
In a more preferred feature the invention provides, a
thermoplastics valved bag of the type having a back
wall and a front wall joined together around the entire
periphery of the bag, the front wall consisting of a first
panel and a second panel, of greater combined width than the
width of the back wall, said first panel at least partially
overlapping said second panel throughout the length of the
bag and said panels in their common area being joined together
along a fine substantially parallel with and at a distance
from one end of the bag, thus forming a tubular self-closing
filling sleeve having inner and outer walls and extending
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transversely of the bag adjacent to said one end thereof, with
said first panel forming the outer wall and said second panel
forming the inner wall of said filling sleeve, and being also
joined together along at least one line extending from said
S first-mentioned line substantially to the opposite end of the
bag, said second panel consisting of at least two plies that
are non-coextensive with each other so that at least the
inner end portion of the inner wall of said filling sleeve is
formed of a number of plies that is less than the total
number ox plies in said second panel, characterized in that
at least one of said walls is perforated to permit the passage
ox air there through, said perforated wall having joined
thereto an inner lining comprising a thermoplastic mesh
whereby said inner lining constitutes a powdered product
lo retaining inner lining of the bag.
The inner lining comprising a thermoplastic mesh is
preferably joined to the perforated wall at the periphery of
the wall. However, this inner lining may be joined by
intermediate tack seals, spot welds or by adhesives at other
selected places throughout the area of the perforated wall.
It can be readily seen that the advantages of the
valved bag according to the invention reside in the fact that
entrained air can exit through the mesh of the inner lining
and vent to atmosphere through the perforated wall, instead
of via the filling sleeve as the bag is being filled, and
most important after the valve has self-sealed with entrained
air still in the bag.
By the term "thermoplastic", as used herein is meant any
polymeric material that will repeatedly soften when heated
and harden when cooled which is capable of providing a film,
ply, layer, or mesh of suitable thickness and strength for
shipping bags. Of particular use are thermoplastics of the
polyethylene and polybutadiene family of polymers. As
examples, high density, low density, linear low density
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polyethylene, ethylene-vinyl acetate copolymers and 1,2 posy
butadienes may be mentioned.
By the term "mesh" is meant an air porous film or ply
having pores which constitute discrete regular or irregular
5 apertures arranged in the form of a net or sieve. The mesh
may generally be formed by the perforation of a hot thermos
plastic film or by the weaving of a thermoplastic yarn
It will be readily appreciated that the selected pore
size of use in the practice of the invention will be dependent
lo upon the particle size of the powdered product for which the
bag is used and that it is well within the skill of the art
or a porous inner lining having pore sizes suitable for a
particular product to be readily selected and manufactured.
The pores are of a size suitable to cause retention of
15 substantially all of the particular powdered product while
permitting release of the entrained air. Generally, the pore
size will be of a diameter of from 0.1 mm to 1.0 mm. A density
ox at least 5~cm2 is essential, preferably >25 pores~cm', and
more preferably, 300 pores/cm2.
As the pore density (number of pores/cm2~ increases the
pore size is reduced to approach the desirable lower limit.
However, provided the pore size is not of the size of a
particular powdered product, such as to cause excessive pore
blockage, pore sizes lower than 0.1 mm may be of use.
Z5 It has been found that the air filtering improvement
which occurs as the pore density increases is much greater
than would have been expected if due simply to the increase in
the number of pores. It is believed that as the density of
the pores increases such that adjacent pores become closer
30 together pyramidal plugging formation is reduced by the
turbulence of air flows through adjacent pores of the mesh.
Depending on the severity of product aeration of the
material being poured into the bag, the thermoplastic mesh
may constitute the complete and full inner lining or only some
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portion thereof. Preferably, for speed of air release through
the mesh it constitutes the whole of the inner lining.
Generally, a bag according to the invention comprises a
single inner lining comprising a mesh at one side only of the
5 bag. However, it can be readily seen that both walls of the
bag may each be perforated and joined to its respective inner
lining However, where a valved bag according to the
invention has a meshed lining joined to the front wall of the
bag, it is necessary that this lining be joined to the front
10 wall in such a manner as to not prevent or hinder the entry
of the powdered product into the bag proper, i.e. it must
allow entry into the space between the back wall and the
inner meshed lining. This can be achieved, for example, by
having the lining joined to the front wall below the filling
15 sleeve.
While both the front and back walls may be perforated,
provided that the wall to which the inner meshed lining is
joined is perforated, this is generally sufficient to effect
air release. The perforations may take the form of holes
20 and/or slits and the desired number, shapes, distributions,
and sizes of the perforations in the wall Jill be determined
by the strength and thickness of the heavy-gauge film and the
volume of air to be released, but should no be such that the
strength of the bag is unacceptably weakened. Optionally,
25 the wall further consists of two heavy-gauge plies which are
perforated together and subsequently separated and displaced
so that the perforations of each ply are offset one to the
other by a prescribed distance. Such an arrangement assists
in reducing moisture ingress.
It should be understood that the principles of the
invention are applicable also to the fabrication of bags
having walls individually comprising more than one ply, erg.
two plies, three plies, four plies, etc. In general, however,
the back and front walls have the same number of plies,
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preferably, two plies. The important feature is that in
addition, one or both walls must also have an inner meshed
lining associated therewith.
It will be understood that the term "inner lining" as
used in this specification is not to be restricted solely to
a lining which is adjacent to and contacts the powdered
product when the bag is full, but also embraces that lining
comprising a thermoplastic mesh which may be separated from
the product by an interposed perforated ply.
Thus, also falling within the scope of the invention is
a bag, as herein before described J provided with an inner
perforated film or ply which constitutes a true inner ply of
the bag and contacts the powder product and which permits air
and fine powder to exit via its perforations prior to this
air and fine powder contacting the inner ply comprising a
thermoplastic mesh.
It is not necessary for all plies and the inner meshed
lining of the bag to be made of the same material. In the
case of a two-ply bag it may be found advantageous to make
the innermost ply of the perforated wall and the inner meshed
lining of a plastics material that melts at a different
temperature than the plastics material of the outermost plies.
Such bags are particularly useful in applications in which
materials such as, for example, crystalline or powdered
chemicals or pigments, are packed into the bags while hot.
Three embodiments of the bag of this invention will now
be more particularly described by way of example with reference
to the accompanying drawings, in which:
Fig. 1 is an elevation Al view of a first embodiment of
a valved bag according to the invention:
Fig. 2 is a sectional view along line Isle of Fig. l;
Fig. 3 is an elevation Al view of a second and preferred
embodiment of a valved bag according to the invention;
Fig. 4 is a sectional view along IV-IV of Fig. 3;
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Fig. 5 is an elevation Al view of a third embodiment of
an open-ended bag according to the invention; and
Fig. 6 is a sectional view along line VI-VI of Fig. 5.
Corresponding reference characters indicate corresponding
5 parts throughout the several views of the drawings.
In Figs. 1 and 2 is shown a generally rectangular pillow-
type bag 10, formed of heavy-gauge (6 mill polyethylene film,
and having a single-ply back wall 11 and a front wall made of
first and second partially overlapping panels 12 and 13. Wall
10 11 has a multiplicity of perforations constituted as 0.6 mm
diameter holes Z3 at Z.5 cm centers over the wall's entire
area. As shown, the first panel 12 is single-ply while the
second panel 13 has two plies 16 and 17. Panel 12 and outer
ply 17 of panel 13 are integral with back wall 11 and thus form
15 with the back wall a flattened single-ply tube, which is
close at both ends by transverse seals 14 and 15. Panel 13
lies beneath panel 12 in the area of overlap, and the free
edge of its inner ply 16 which is a strip of film extending
the whole length of the bag and being somewhat wider than ply
17, projects somewhat beyond the free edge of outer ply 17.
A seal 18 unites both plies of panel 13 with panel 12, and a
seal 19 unites the projecting end of ply 16 of panel 13 with
panel 12. The portion left unsealed in the common area of
overlap at the top end of the bag constitutes a tubular valve
sleeve suitable for insertion of a filling spout. The top
ends of seals 18 and 19, together with dot seals 20 delineate
the tubular valve sleeve. When the bag has been filled, the
projecting end portion of the inner ply 16 ox panel 13 acts
as a sift-proof closing flap or the valve.
also integral with back wall 11 at its inner periphery
is an inner polyethylene mesh 24 of 1.25 mix thickness, having
a pore density of 300 pores/cm2 and pore size of 0.2 mm
diameter, (formed from "VISPO~E"~ film, ethylene-vinyl acetate
I copolymer, melt index of 0.3, - Ethyl Corporation).
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In Figs. 3 and 4 again is shown a generally rectangular
pillow-type bag 10, formed of 3 mix polyethylene film. It
has a two-ply back wall 21, each ply of which has a multiply-
city of 0.6 mm diameter holes 23 at 2.5 cm centers over its
S entire width and area. The arrangement of holes in one ply
is offset from the arrangement of holes in the outer ply.
sack wall 21, at the inner periphery of its innermost ply,
is integral with an inner polyethylene mesh 24 of 1.25 mill
thickness ("VESPER" film).
Bag 10 also has a front wall made of two-ply 3 mix
polyethylene partially overlapping panels, the said first
panel being shown at 22 and the second at 13. Panels 22 and
13 are integral with back wall 21 and thus form with the
back wall a flattened two-ply tube, which is closed at both
ends by transverse seals 14 and 15. Panel 13 lies beneath
panel 22 in the area of overlap, and the free edge of its
inter ply 16 projects somewhat beyond the free edge of its
outer ply 17. A seal 18, unites both plies of panel 13 with
the two plies of panel 22, and a seal 19, unites the
projecting end of ply 16 ox panel 13 with the two plies of
panel 22. The portion left unsealed in the common axe of
overlap at the top end of the bag constitutes a tubular valve
sleeve, suitable for insertion of a filling spout. The top
ends of seals 18 and 19, together with dot seals 20, delineate
the tubular valve sleeve. When the bag has been willed, the
projecting end portion of the inner ply 16 of panel 13 acts as
a sift proof closing flap for the valve.
Although in the particular embodiment of the invention
described with reference to Figs. 1 to 4, the end of the valve
sleeve is shown as being formed out of a projecting portion of
the inner ply 16 of panel 13, it should be understood that it
can alternatively be formed by a portion of outer ply 17
projecting beyond the edge of inner ply 16. In other words,
either one of plies 16 and 17 can project beyond the edge of
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the other to form the valve closing flap. Seal 19, while not
being essential prevents the contents of the filled bag from
entering the space between the panels, from which it might not
be easily emptied. Dot seals 20 may be replaced by a
continuous seal extending substantially parallel to transverse
seal 14 from the top end of seal 18 to be inward edge of ply
16.
While, in the drawings, the valve opening of each bag is
shown as being located close to one side of the bag, it should
be understood that it can be located anywhere adjacent to the
end seal 14 of the bag, provided that sufficient space is
left between its inner mouth and the side of the bag facing it
to allow insertion of a reasonably long filling spout and
free delivery of filling material therefrom. Generally, it is
preferred to arrange the front panels so that the valve
opening is located within one vertical half of the bag, with
thy valve sleeve extending into or towards the other vertical
half. The width of the wider front panel will not signify-
gently exceed, and preferably is less than, the width of the
back wall.
It is preferred that the longitudinal seals between the
front panels, shown at 18 and 19 in Figs. 1 and 3, stop short
of and thus do not intersect transverse seal 15 at the bottom
of tune bag. Such intersection might result in weakening of
the end seal at the points of intersection, and thus in winnowing
of the bottom of the bag.
The bags are preferably made from a thermoplastics
tubular film of appropriate width. Preferably the plastics
film is readily heat sealable, or is provided with a heat-
sealable coating. Film of low-denslty polyethylene is
particularly suitable because of its inherent heat-sealability,
its toughness, and its low cost.
Bags according to the invention may be constructed by
suitably incorporating a sheet of a thermoplastic mesh as an
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inner lining brought into contact with a sheet of suitably
perforated heavy gauge film to produce a 2-ply structure
composition, and subsequently folding opposite sides of the
lengths of films inwardly so that the mesh component is
contained with the edge portions overlapping one another
Heat sealing of the overlapping portions and the meshed
fining film together along the length of the overlapping
region and transverse of one of the open ends of the folded
film provides the bag.
By employing analogous methods but sealing the over-lapped
edges of the sheets along their whole length and making only
a single transverse seal, a simple open ended bag can be
constructed. Such a bag is shown in Figs. 5 and 6, wherein
a generally rectangular pillow-type bag 10, formed of heavy
gauge (3 mill polyethylene film comprises a single ply back
wall 31 and a single ply front wall 32. The back wall 31 is
perforated with a multiplicity of 0.6 mm diameter holes 23 at
2.5 cm centers aver its entire area and has joined at its
periphery an inner polyethylene mesh lining 24 having a pore
density of 300 pores/cm2.
Where the object of the invention is a self-sealing bag,
a section of the overlapping region will be left unsealed to
constitute the valve opening and a second transverse seal
made at the opposite end of the bag.
A preferred method of making a valved bag according to
the invention is that described in United States Patent No.
3,812,769 suitably modified in that a sheet of a thermoplastic
mesh film is fed jointly with the heavy gauge~~llm to the
fabricating machine described therein. It is advantageous to
unite the thermoplastic mesh and heavy-gauge films as the
latter passes from realistic to the point of folding and
bag making, for reasons which are apparent to those versed in
the art. However, this modification can also be done suitably
well at a point where the heavy-gauge film is passing by from
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its point ox manufacture, or on separate machines adequately
redesigned to facilitate the hot-air sealing stage and the
drawing of plastic films from rolls rotating freely to a
point where film can again be accumulated on rolls.
The bags may be constructed from one or more plies of
film. When constructed of two-ply film, it is convenient to
employ a length of flattened tubing as the starting heavy-
gauge film rather than two separate single-ply lengths placed
in contact.
The thermoplastic mesh constituting the inner lining can
be made from a thermoplastic film by several techniques. Hot
micro-perforation of the film by hot air jet, laser or needle
perforation is preferred, while the weaving of thermoplastic
yarns is optional.
A preferred inner lining consists of an ethylene-vinyl
acetate copolymer OIL "633"* EVA copolymer in the form of a
mesh. However, because ox the elastic nature of this film,
with its inherent loss of lateral strength as a result of
such modification, it cannot be readily processed on high-speed
shipping bag manufacturing equipment. It is desirable
therefore to unite this film to the heavy-gauge film to
facilitate passage over a suitable folding frame to complete
the bag-making operation.
There are several methods by which the heavy-gauge and
meshed films can be combined. They can be combined by
contacting the films with a resistance type heating element,
or through the use of contact adhesives, or, preiexably,
because of the relatively thin and temperature sensitive
nature of the meshed film by heat sealing with a hot air jet.
The heat seals resulting from hot air jets are optionally
made at the margins of the inner lining, continuously along
it length, and additional seals running parallel with and
inside these margins as necessary to marry this film to the
heavy film preparatory to folding.
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Perforation of the heavy-gauge film constituting the
perforated wall may be done using mechanical perforators, on
all or any part of the film surface, preferably, prior to its
incorporation with the meshed film. Optimally, two heavy-
gauge plies are used, which are perforated together and subsequently separated so that the perforations of each ply
are offset to the other by a prescribed distance, continuously
along the length of film. This provides the additional
benefits of a reduction in moisture ingress or other
environmental contamination of the contents, thereby increasing
shelf life, and further reduces loss of packaged product to
the atmosphere.
In an alternative embodiment the perforated wall of the
bag has perforations adjacent its outer edge only.
It has been demonstrated that a preferred thermoplastic
valved bag according to the invention and described herein
would decorate, after being sealed, in an equivalent amount
of time, generally of the order of 30 seconds, as a typical
multi-wall paper bag. In contrast, a conventional thermos
plastic valved bag would require an indefinite time period to
decorate after normal industrial filling speeds for
cementitious products; while a similar bag with simple
perforations made directly through its walls would have
improved decoration but with excessive product loss and
environmental contamination.
