Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates to plastic film
bags or sheets furnished in stacked supplies held on
wickets and which are to be dispensed or removed from the
wicket-held stacks either manually or automatically, one
at a time, for utilization, and more particularly, to
such bags or sheets having specially formed wicket holes
which permit facile removal from the wicket in a desired
tear-removal direction without the incidental production
of contaminating bag material scraps.
Packaging operations in industry are of sig-
nificant import and interest cowards promoting the
rapid, efficient and economical packaging of products
for the market. Food packaging generally and the meat
packing industry in particular require additionally the
strict maintenance of sanitary conditions. Automatic or
semiautomatic packaging techniques have been developed
towards achievement of these desired goals.
Here it should be noted that while the ensuing
discussion treats of plastic film packaging bags towards
illustrative simplification, this invention applies equally
as well to stacked wicket-held plastic film wrapping sheets
and the like.
GJhatever the degree of complexity of the apparatus
and techniques employed in a packaging operation involving
food, meat products in particular, it is of the utmost
importance that the supply of packaging bags be maintained
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in a sanitary condition and that the bag dispensing action
be accomplished with facility and without bag waste or the
incidental production of torn bag scraps which not only
interfere with smooth and efficient operation but also
contaminate the packaged food article. While these
desirable characteristics are very important in even the
simplest modes of semiautomatic packaging, they are of
much greater importance in the more fully automated modes
such as for instance those involving opening the bags one
at a time With an air stream for insertion of a product
unit into each bag sequentially. In these more automated
techniques the relatively higher packaging speed necessitates
a sanitary, continual and consistently reliable bag supply
not liable to produce contaminating bag scraps during
the packaging operation. Towards attaining these disiderata,
the wicket to bag wicket hole relationship is a significantly
important element in the operation. Bags for such use,
irrespective of the complexity of the particular packaging
technique, are usually supplied to the user in bulk packages
which are opened and the bags loaded by hand into the bag
dispensing station or portion of the apparatus or in pre-
wicketed packages.
Criteria for the wicket to bag wicket hole relationship
design dictate that each bag in turn atop a stack of wicketed
bags at a packaging station must be readily removable without
the incidental production of bag scraps and with clean
direct tears through the bag material ~rom the wicket
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holes to the outer open edge of each holed ply of the
bag. Known wickets. used to h,dle stacked lag supplies
in tfie aforedescribed -manner are best described as
inverted U-sfiaped witFL the U having a flat bottom which,
with the wicket' in. place; spans across the top bag of the
stank along a line b etweeri the wicket holes to define a
horizontal bearing -~aember. The heart of the bagging
system, however, is the bag itself. A number of bag
structures have been shown in the patent literature.
Specific reference is made to U.S. patents 3,441,198,
A.E. Ericson, issued 4/29/69 and 3,508,379; B.P. Boyes
et al, issued 4/28/70. Bags have been produced from
tubular film by sealing the tube at one end and from
folded film by sealing at the sides, and others Have
been made by sealing two superimposed films at perimetral
edges. In some bags, the front and rear walls are the
same length. These are called "flush cut" bags. Tn
others, the front wall is shorter than the rear wall.
These are called "lipped" bags . In some tubular bags, the
ends are arcuate and in some the fxont wall has a cut-out
portion less than the flat width of the bag. The bags
may be made of any suitable flexible plastic material.
Seals to fabricate the hag structure may be formed in any
way, heat sealing being convenient, economical, and
preferred. For packaging meats a preferred material is
polyvinylidene chloride. Other suitable materials are:
polyolefins, e.g. polyethylene, or polypropylene; nylon;
polyethylene terephthalate; polystyrene; and the copolymers
of the foregoing materials.
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At first blush it would seem that the wicket
holes of whatever shape desired could be formed multiply
in stacks of such packaging bags by relatively simple
techniques such as straight mechanical punching or by hot
punching, that is with a punch element heated sufficiently
to melt the plastic as the punch pierces the bag stack.
Mechanical punching through stacked bags, however, pro-
daces wicket holes with all sorts of random irregularities
in the preselected shape and in hole edge integrity, with
consequent high incidences of bag rejection in the produc-
tion process and, even more detrimentally, bag failures
through improper wicket tear-offs in use in packaging
operations. The hot mechanical punch techniques are im-
practical for hole formation in stacked bags because the
molten plastic flows from bag to bag in the stack, and the
bags become in effect welded or heat sealed together at
their wicket holes. Wicket hole formation in the bags indi-
vidually, that is one at a time, similarly may utilize
straight mechanical punching or the hot punch techniques.
Bag production, however, is necessarily a high speed oper-
ation and must be so due to the production economics involved.
High speed single bag wicket hole punching with a straight
mechanical punch inherently produces film material scraps,
requires punch replacement from time to time as the punch
die or carting edge dulls, and is thus not as completely
a satisfactory solution as could be hoped for. The wicket
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holes thus formed, even if made to a preselected shape,
have only simple shear cut edges and therefore contribute
less than satisfactorily towards the goal of a wicket to
bag hole relationship which effects the desired clean direct
tears through the bag material from the wicket holes to the
outer open edge of each holed ply of the bag without coin-
cidental random tearing and production of contaminating bag
scraps.
Hot punching the wicket holes in each bag one at
a time, has, up to the time of the present invention, been
the most conventional mode used in the industry. It is
particularly in one at a time bag wicket hole forming with
hot punches that experimental and developmental efforts
have been directed towards making the wicket holes with
directionally tear prone characteristics, that is to say the
hale edge is so formed and/or shaped that the bag tends to
resist tearing from the wicket in all but a preselected
tearing direction.. Hot punching produces a hole of whatever
shape selected having a bead of melted and rehardened plastic
around the hole edge. If the hole is tear drop shaped or
outwardly notched in the desired tear direction, that is
towards the bag mouth outer edge, a linear pulling force
will tend to impose stress concentrations at the hole notch
or tear drop point, and the bag, hopefully, will tend to
tear linearly from the wicket holes to and through the bag
mouth edge. It has been found however that the beads of
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melted and rehardened plastic around the edges of wicket
holes thus formed do not have the consistently reproducible
physical characteristics to meet commercial use standards.
The beads around holes so formed have been found frequently
to include charred particles of resin from the plastic
making for at worst contamination necessitating quality
control rejection, and at best unsightly appearance.
The problems attending wicket hole forming described
hereinabove, particularly when the holes formed have no edge
LO reinforcing whatsoever, are even more serious with oriented
plastic film sheet materials, since any nick, weakness, or
irregularity in a hole edge can cause bag tearing failure
along the weakest orientation line which may be in a completely
unwanted direction.
With this then being the state of the art, the
present invention was conceived and developed to provide a
plastic film packaging bag or sheet for wicket mounting having
a wicket hole which is directionally tear prone in a prese-
lected desired direction.
20 The invention further provides a method for the
production of plastic film packaging bags or sheets having
bead reinforced edge wicket holes which are directionally
tear oriented in a preselected direction unrelated to any
orientation of the plastic film material itself.
Apparatus to practice the aforesaid method to
produce the aforesaid bags or sheets is also comprehended
in this invention.
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these and other features, advantages, and charac-
teristics of this invention will be the more readily under-
stood and appreciated from the ensuing more detailed
description and from the drawings, wherein:
Figure 1 is a perspective view showing apparatus
according to the invention holding a plastic film material
sheet to be wicket holed according to the invention;
Figures Z, 3, and 4 show various forms of apexed
wicket holes in plastic film sheet materials according to
the invention;
Figure 5 is a sectional view through apparatus
according to the invention showing a plastic film sheet in
the process of being wicket holed; and
Figure 6 is a~sectional view through Figure 5
along the section line 6-6.
In general, the invention comprehends a method
of making an apexed hole having a varying thickness hole
edge perimeter of melted and rehardened plastic in a
plastic film sheet material comprising the steps of; masking
the plastic film sheet material with a heat resistant masking
template having an opening therein of a size and apexed shape
substantially congruent with a preselected size and apexed
shape of the hole being formed; disposing the plastic film
sheet material and the masking template on a backing template
having an opening therein substantially similar to the size
and shape of the opening in the masking template and having
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an overall perimetral dimension substantially equal
to the overall perimetral dimension of the opening
in the masking template, the opening in the masking
template and the opening in the backing template being
juxtaposed in substantially concentric alignment; di-
ratting a stream of gas heated to a temperature suf-
ficient to effect rapid melting of the plastic film
material into impingement on the masking template and
the plastic film sheet material between the openings
in the masking template and the backing template for
a time sufficient to melt through the plastic film
sheet material between said openings, the concentric
centerline of said stream being offset epicentrically
from the concentric centerline of the ,juxtaposed open-
ings in the masking and backing templates towards the
apex of the hole being formed; removing the stream of
gas from impipgement on the masking template; and re-
moving the plastic film sheet material from the templates
after the melted plastic film material has at least
partially rehardened,
Wlth reference to the drawings, Figure 1 shows
a plastic film sheet 11 clamped between a masking tem-
plate 13 and a backing template 15, Masking template
13 is provided with an opening 17, generally circular
in form but with an outwardly extending notch or apex
1g, Hacking template 15 is provided with a similar but
slightly larger opening 21 with an outwardly extending
notch or apex 23,
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Here it should be noted that while the form of
wicket hole shown in some of the drawing figures for illus-
trative purposes is tear drop shaped, that is to say generally
circular with a point or apex, other hole shapes axe equally
advantageous, it being necessary only that the hole have a
stress concentration point, herein called an apex, on its
perimeter oriented in the direction of the desired tearing
direction, and that the perimetral bead of melted and re-
hardened plastic film material be somewhat thinner and weaker
at the apex than elsewhere around the hole edge. Figures 2,
3, and 4 of the drawings show, respectively, plastic film
sheets having wicket holes of the tear drop shape, a sharp
pointed inverted V notch, and a keyhole shape, all of which
are apexed in one form or another and yield desired results
according to the invention. Other apexed shapes will work
equally well.
Again with reference to Figure 1, the assembled
arrangement of the plastic film sheet, the masking template
13 and the backing template 15, clamped securely by any
suitable means not shown in the drawings for purposes of
simplification and clearer illustration, is shown positioned
beneath a hole making head comprising a generally tubular
outer housing 25 of any suitable insulative material, having
an electrical heating element 27 disposed interiorly thereof
and connected to electric circuit wires 29, 31 which pass
through a connection bushing 33 mounted atop the housing 25.
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The aircuj.t wj.res in turn connect to a suitable eler~tric
power circuit not shown inthe drawings,
A gas supply conduit 35 connects concentrica3.ly
through a flow control orifice to the top of the housing
25 through a bushing 37, and provides a stream of pres-
surized gas, compressed air for example, from a pressur.-
~:zed gas supply source not shown in the drawings,
The complete hole making head assembly is
commercially available as a unit, one typical such ap-
paratus being a flameless electric torch, known as a
serpentine heater, manufactured and sold by Sylvania,
General Telephone and Electronics of Exeter, Dlew Hampshire,
u.s.A.
Figure 5 is an elevational sectional view
showing a plastic film sheet 11 clamped between a mask-
ing template 13 and a backing Template 15 disposed be-
neath a hole making head assembly comprising an outer
housing 25 and an interiorly mounted electric heating
element 27 with a wicket hole 39 in the process of being
formed by a hot gas stream impinging downwardly as shown
on the masking template and,film material exposed in the
masking template opening 17, In Figure 5, a bottom plate
ail is shown subtending the underside of the backing
template, This arrangement, it has been found, redirects
the hot gas stream upward to the film underside as soon
as hole formation starts and accelerates the melting
process,
As the hole $9 forms; molten plastic film mat-
erial retracts towards the hole edge, forming a bead 43
which, upon rehardening, acts to reinforce the hole edge
against tearing,
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Figure 6, a section through Figure 5, shows the
epiceritric offset of the concentric centerline of the hole
making head assembly from the concentric centerline of the
juxtaposed openings in the masking and backing templates in
a direction towards the apex of the hole being formed. With
this arrangement, the hole edge bead 43 is significantly
thinned as a 43a, thus producing a hole with a reinforced
edge all around except at one relatively weak point, the
apex, which is located in the desired tearing direction.
Example
In practice, the method and apparatus of the in-
vention is automated.
In a typical operation with a production capability
of 260 bags per minute, a commercially available flameless
electric torch, Sylvania model No. DGH116501, was selected
as a hale making head and mounted on a single revolution
clutch drive powered by an electric motor. The hole making
head was connected to a 50 psig compressed air line and a
55 volt A.C. electric supply source. The masking and backing
templates were of 1/8" thick aluminum sheet material, each
apertured for hole forming openings to a 7/32" diameter
circular hole with a keyhole form notch l/16" wide and 1/16"
deep oriented in the desired bag tearing direction. A
bottom plate of 1/8" thick aluminum was disposed and clamped
below the backing template.
In operation, the hole making head moves recipro-
cally between a downward position with its outlet end 1/8"
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above the masking template wherein a 15 millisecond burst
of approximately 1200-1500°F hot air forms the wicket hole,
and an upward position with its outlet end 1 5/8" above the
masking template. The motion of the head was arcuate,
swinging between its upward and downward positions on an arc
of 8 1/2" radius fram a pivot point 3 1/4" above the top
surface of the masking template, and the centerline relation-
ship was arranged so that in the downward or hole forming
position, the centerline of the flameless torch, and thus
the centerline of the hot air stream, was aligned directly
with the tip of the apex of the hole form opening in the
masking template. In the down or hole making position, the
air to the hole making head is on, and is valued off during
each up stroke. The electrical heating energy is on con-
tenuously.
Lipped bags fabricated from tubular stock of
biaxially oriented polyvinylidene chloride and provided with
wicket holes on this arrangement were tested in a commercial
packaging operation in comparison with similar bags wicket
holed by cold punching and by hot punching and found to be
significantly superior in tear proneness from mounting wickets
in the desired direction, to consistently tear more linearly
and cleanly than the other bags, and to tear without pro-
ducing any incidental shards or scraps of bag plastic film
material.
Numerous alternative modes of practicing this
invention will, in the light of the foregoing description,
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undoubtedly occur to persons familiar with the art. The
backing template, fox instance, may be in any form, from a
plate as shown and described to a simple ring grommet or a
tubular brace, it being necessary only that the film being
holed be held up snugly against the masking template opening.
Within practical limits, any hole shape may be used, it
being essential only that the weakest and most tear prone
point on the hole perimeter coincides with the apex which
is oriented in the preselected tearing direction. It is
intended therefore that the foregoing description be taken
as illustrative only, and not construed in any limiting
sense.
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