Note: Descriptions are shown in the official language in which they were submitted.
CA 02170769 2004-04-30
BAGS AND METHOD OF MAKING BAGS
Field of Invention
This invention relates to chains of interconnected, pre-opened bags used in
packaging and more particularly relates to a novel and improved method of
making chains of bags.
Backs~round of the Invention
U.S. Patent 3,254,828, issued June 7, 1966, to Hershey Lerner under the
title Flexible Container Strips is directed to so called bags on a roll (here
the
AutoBag patent). This patent discloses a web of bags interconnected by lines
of
weakness, preferably in the form of perforations, with each of the bags being
open
on one face. In use the bags are sequentially fed to a loading station. When
at
the loading station, each bag is blown open, a product is inserted and
thereafter
separated from the web and, if desired, the bag is then sealed to form a
package.
These container strips in the form of chains of pre-opened bags are
supplied either on a roll as taught in the AutoBag patent or festooned in a
carton
in the manner taught in Patent 4,201,029, issued May 6, 1980, to Bernard
Lerner
et al. under the title Method and Apparatus for Packaging, (here the Wig-Wag
patent). Such container strips have been sold by Automated Packaging Systems,
Inc. of Streetsboro, Ohio, the assignee of the present case, under the
trademark
AutoBag and have enjoyed great commercial success.
Both AutoBag and competitive products have usually been made by feeding
a tube through a converting machine. Such a machine forms transverse seals to
delineate the bottoms of the bags and transverse lines of weakness by
perforating
both layers of the tube to delineate contiguous ends of adjacent bags. After
the
perforations are formed, a "zinging" operation is performed on each bag to
open the
front of the bag while leaving the perforations of the back intact.
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Relatively recently a market has developed for these chains of bags made
from two layers of plastic, so that the plastic of the front of the bag is
different
from that of the back of the bag. For example, some customers for such bags
may
wish the back of the bag to be white to enhance the legibility of information
imprinted on it such as instructions on how to use a product packaged in the
bag.
The front of the bag is clear, so that the contents of a package are readily
visible.
To accomplish this two single layer webs of plastic are fed from respective
supplies
in a manner similar to that taught in U.S. patent 4,337,058 issued June 29,
1982 to
Bernard Lerner under the title Method of Making a Container Strip Having
Inserts. Marginal edges of the two webs are then fused together to form a tube
and remainder of the container strip manufacture is identical to that when the
supplied work piece is a flattened tube.
So called "multiple up" production has also become quite customary. With
multiple up, the work piece may be either a relatively wide flattened tube or
two
relatively wide single ply sheets fed together and fused. In either event hot
knives
are used to sever the work piece into two or more elongate tubes and
thereafter
each new tube is made into a chain of pre-opened bags.
When bags are made from two single ply webs, every effort has been made
to provide identical tension on the two webs, so that once made into a tube
the
only difference of the tube from one provided as a tubular work piece is that
the
front and back are not identical, such as the back may be pigmented while the
front is clear. With the two single ply approach, if the bag making machine
was
not adjusted properly, once opened the bags would not lie flat with the
separated
edges which delineate the openings lying in closely juxtaposed positions. The
resultant product was often scrap. If the edges were not juxtaposed but rather
there was a gap between them, these "gap" bags were rejected because they were
perceived to be unacceptable to customers as unsightly and bags which would
produce packages with malaligned top edges. If the top edge of an opened bag
overlapped the bottom of the adjacent bag, they were not subject to a policy
of
universal rejection as were the gap bags but all too often the spark gap
detector
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used for bag registration in a bagging machine would not function properly.
Such
a bagging machine is disclosed in Patent 4,014,154, issued March 29, 1977, to
Bernard Lerner and related patents identified therein (here the H-100
patents).
SummarEr of the Invention
As taught in the Parent Case, it has now been recognized for the first time
that if chains of bags are made from single ply webs that are differentially
tensioned an improved and superior product can be produced.
The improved product is a flexible container strip formed of an elongated
flexible tube of plastic material capable of bonding to itself at a
predetermined
temperature on application of pressure but being otherwise non-adherent to
material of identical composition. The tube is longitudinally collapsed with
face
and back plies joined together along their longitudinal side edges. A
plurality of
spaced, transversely disposed bottom seals each secure the plies together and
delineate ends of fillable bag spaces. Each seal extends transversely from one
side
edge of the tube to another such that the tube is separated into a chain of
connected bags. The face ply of each bag has a transverse end opening
extending
substantially from one side edge of the bag to the other and extending
longitudinally a distance sufficient to facilitate bag opening and loading and
to
provide detection access to aligned lines of weakness in the back ply. Each
opening is adjacent the end of the bag remote from its bottom seal forming the
filling space end of that bag such that the bags of the chain are all oriented
in the
same direction.
The openings all formed in the face ply and are at longitudinally spaced
intervals equal to the spacing of the bottom seals. The back ply of each bag
has a
transversely weakened tearable portion extending substantially from one side
edge
to another to permit facile separation of the bags while maintaining the
integrity of
the back ply and the tube. Each tearable portion is aligned with and
accessible
through the end opening of its bag. Thus, the improved strip is a chain of
collapsed bags which may be fed serially along a path from a supply to bag
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opening and load stations, may be readily and accurately registered at a load
station through spark detector location of the tearable portions and may be
opened by a blast of air directed longitudinally of the path and then loaded
and
separated from the chain sequentially and one at a time.
In the preferred method of manufacture of the Parent Case the tension on
the web which will become the face of the bags is carefully differentially
tensioned
to stretch it, without exceeding its elastic limit, more than the web which
will
become the back of the bags. Alternatively the back web is tensioned more than
the front and the back to exceed its elastic limit. While the differential
tensioning
is maintained, side seams are formed to produce a tube. Preferably the balance
of
the container strip formation operation is that which has been employed in the
past, so that existing manufacturing equipment can be used without
modification.
With the preferred process of the Parent Case, the improved product
results when the face of a bag is "zung" to form a transverse opening
delineating
the top of the bag. The formation of the opening releases the tension in the
face
of the bag, so that the face of the bag will shrink relative to the back with
the
result that the top edge of the just opened bag will be at least about 1J~
(one
sixty fourth) of an inch from the bottom edge of the following adjacent bag.
The
resultant product not only facilitates bag opening at a load station, but also
assists
in reliably producing appropriate bag registration at a load station.
Registration is
enhanced because the perforations in the back face, being aligned with and
accessible through the elongated opening, are readily, precisely and reliably
detected by a spark detector.
In an alternate system for making the improved chain of bags, bottom seals
and perforations are formed and the web is "zung" to separate perforations of
the
face web. Thereafter side seals are formed while the back web is maintained
under controlled tension to produce bags having top openings of consistent and
desired longitudinal extent.
The process of this invention includes feeding face and back plastic web
sections along respective paths of travel and as they are fed forming
transversely
PCT/IJS94/11346
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extending lines of weakness in the back section. Spaced pairs of transversely
extending lines of severance are formed in the front section at longitudinally
spaced intervals corresponding to the spacing of the lines of weakness. The
sections are superposed with the lines of severance positioned with an
associated
one of the lines of weakness longitudinally located between the lines of
severance
of the associated pair. Transverse seals are formed between the sections at
least
some of which delineate bag bottoms each near a line of weakness and its
associated pair of lines of severance. A side edge seal is formed between the
sections which is spaced from a second side edge delineated by a selected one
of a
longitudinally extending fold or a second side edge seal. Bag openings are
formed
by removing portions of the face section between the lines of severance of
each
pair.
The spacing of the lines of severance of each pair is sufficient to assure
that
the associated line of weakness may be readily detected as by a spark gap
detector
when the lines of weakness are perforations. Preferably the spacing of the
lines of
s~° rv erance is at least about 1/64 inch.
~~.s suggested previously the sections may be either independent, separate
webs or alternately formed by a single wide web folded to produce the two
sections. Optionally, the face section may be in the form of a series of
independently precut portions which are secured to the back section with each
portion forming the front of an individual bag of the chain of bags being
formed.
With all of the options, although the sections may be folded from a single
web, it is considered that prior to juxtaposing the sections together the face
and
back sections traverse respective paths of travel and following juxtaposition
the
sections traverse a common path of travel.
Accordingly, the objects of the invention are to provide a novel and
improved methods of making chains of interconnected but pre-opened bags.
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6
In the Drawings
Figure 1 is a fragmentary plan view of a section of a chain of
interconnected bags made in accordance with invention;
Figure 2 is a sectional view of the chain of Figure 1 as seen from the plane
indicated by the line 2-2 of Figure 1;
Figure 3 is an enlarged sectional view of a section of the chain indicated by
the circle 3 of Figure 2;
Figure 4 is a side elevational, schematic view of a process of making a
chain;
Figure 5 is a schematic plan view of the machine of Figure 4;
Figure 6 is a schematic perspective view of a method of forming a chain of
bags from a single web in which the web sections are joined by a fold;
Figure 7 is a schematic perspective view of a method of forming a chain of
interconnected bags from independent sections; and,
Figure 8 is a schematic perspective view of a method of forming bags from
independent web sections wherein the face section is severed into independent
portions prior to securement to the back section.
Description of the Preferred Embodiments
Referring now to the drawings and to Figures 4 and 5 in particular where
the process of The Parent Case is shown. With this process, a pair of single
ply
individual web supplies 10, 12 are provided which are face and back webs
respectively. Webs from the supplies 10, 12 are respectively fed along
individual
paths of travel 14, 15 to a juncture at juncture nip rolls 17. Tension control
nip
roll sets 18, 20 are provided. The set 18 is positioned along the path 14 to
tension
the face web 10 while the set 20 is along the path 15 to tension the back web
12.
When in operation the nip roll set 18 will be set to tension the face web to a
higher level than the back web, in that the web from the supply 10 will form
the ,
face of fronts of bags being produced.
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The webs are fed from the juncture nip rolls 17 along a common path of
travel 28. Hot knives 22, 23 are positioned downstream from the juncture nips
17
to form bead seals along side edges of the webs and convert the webs into a
tube.
Trim strips 25, 26 formed by the hot knives are removed for collection and
recycling.
Once formed into a tube the combined webs pass through a sealer 30 which
forms transverse seals to become the bottoms of the bags being produced. Next
a
perforator 32 forms transverse lines of weakness in the tube to delineate, in
each
case, a bag bottom adjacent a transverse seal and the top of an adjoining bag.
A rotating finger known as a "zinger" 34 is provided. The zinger has a
surface speed slightly greater than the speed of the web so that as the zinger
34
strikes a section of the web that will be the front of a bag, acting against
the
resistance of an anvil roll 35, it separates the perforations of the front web
to form
a bag opening. Thereafter the web, now formed into a container strip of
intercon-
nected but open bags, is collected at a take up 38. Apart from the adjustment
of
the tension control nips 18, 20 to provide differential tensioning, the
machine and
the process thus far described are now conventional and well known to those in
the art.
Deferring now to Figures 1 through 3, the novel container strip of The
Parent Case is shown generally at 40. The strip includes a plurality of
intercon-
nected bags 42 joined together in a back ply 43 by lines of weakness 44 in the
form of ~rforations. Transverse seals 46 delineate the bottoms of bags.
The face ply formed by the web from the supply 10 is separated into
individual bag face sections 48. A transversely extending bag opening 50 is
adjacent the top of each bag face section 48. Each opening 50 extends
completely
across tine web from one side edge 52 to the other 53, while the perforations
in
the back 43 remain intact. Each bag opening extends longitudinally of the web
preferably at least 1/64 (one sixty fourth) of an inch.
The importance of the longitudinal extent of these openings is besE
understood by reference to Figure 3. A conventional spark detector is shown
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schematically at 55. Assuming the web is moving from right to left in Figure 3
so
that the bags are being fed closed end first in a bagging machine, as is
conven-
tional, it will be seen that the detector 55 will readily be able to locate
the per- ,
forations 44 once the spark path indicated schematically at 58 is aligned with
the
perforations.
Referring now to Figure 6, a web 60 is fed along a path of travel indicated
by an arrow 61. Transverse lines of weakness in the form of perforations 62
and
spaced pairs lines of severance 64 are shown as concurrently formed in the
web.
The lines of weakness and severance are formed by coacting cutting and anvil
rolls
65, 66.
As the web 60 proceeds along its path of travel a fold 68 is formed in a
known manner as by a well known V board. Through the folding process a face
section 69 of the web 60 is superposed over a back section 70.
The parts of the base section 69 between each of the pairs of lines of
severance 64 is removed as by a vacuum head shown schematically at 72 to
produce a bag opening aligned with and superposed over an associated line of
weakness 62.
Transverse seals 74 are formed by a heat sealer shown schematically at 75.
Each of the seals shown in Figure 6, delineates a bottom of one of the chain
of
bags being formed. A hot knife 77 forms a bead seal 78 along the web side edge
opposite the fold 68 to complete the chain of bags. Optionally a second hot
knife
80 may form an opposed bead seal 81 to assure that the openings delineated by
the lines of severance 64 extend fully from one side edge to the other of each
bag,
if that is desired. Alternatively, the lines of severance may extend to the
fold and
use of the second hot knife 80 is not required.
Referring now to Figure 7, face and back webs 10, 12, as in the
embodiment of Figures 4 and 5, are fed along individual paths. Lines of
weakness
62 and lines of severance 64 are respectively formed in a manner similar to
the
embodiment of Figure 6 but with separate cutter and anvil rolls (not shown)
rather
than the dual cutter and anvil rolls 65, 66 of Figure 6. Thereafter, they are
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PCT/LTS94/11346
9
juxtaposed and the transverse seals 74 and the bead seal 78, 81 are formed in
a
manner corresponding to the embodiment of Figure 6.
With the embodiment of Figure 8, the upper face section 10 is severed into
individual parts 83 by cutter and anvil rolls 84, 85 which form lines of
severance 64
extending across the full width of web. Thereafter the individual parts 83 are
suitably fed by a conventional mechanism, not shown, into juxtaposition with
the
back web 12. Transverse lines of weakness 62 are formed in the back web by
coacting cutter and anvil rolls 87, 88, shown at a location prior to wet
juxtaposition but they may be located at down stream locations along the path
of
travel. Once the parts 83 are juxtaposed with the back web 12, the transverse
seals 24 and the bead seals 78, 81 are formed in the manner described in
connection with Figure 6.
Operation
hi operation as depicted in Figures 4 and 5, coils of single ply plastic are
mounted to provide the front and back supplies 10, 12. The materials of the
webs
may be other than identical so long as they are capable of being sealed
together.
For example, one web may be pigmented such that it is translucent or opaque
while the other web is clear. Typically the plastic will be polyethylene,
although
other thermal softenable plastics capable of adherence together on application
of
heat and pressure are sometimes employed.
Webs from the supplies 10, 12 are fed along their respective independent
paths of travel through the tension control nip rolls 18, 20 to the juncture
nips 17.
They are then fed along the path 28 past the hot knives 22, 23, the transverse
sealer 30, the perforator 32, the zinger 34 and thence to the take up 38.
Once the machine is set up and operation commences and the nips 18, 20
are adjusted to provide differential tension along the paths 14, 15. The
appropriate tension is a function of the material, its thickness and its
width.
Once appropriate tension has been at least provisionally established and
temperatures of the hot knives and transverse sealer are adjusted to
appropriate
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to
levels, production commences. Tension is further adjusted as the machine
operates until desired finished products are consistently produced. During
production the two plies are fed past the hot knives to create a tube with a
front
face stretched more than the back. This differential stretching is maintained
as
the now formed tube passes the transverse sealer and the perforator. Once the
face web is opened by the zinging operation, the tension in the just opened
web
face section is released and it will shrink longitudinally of the web relative
to the
back preferably to produce the desired opening of at least 1/64 (one sixty
fourth)
of an inch measured longitudinally of the web.
With the embodiments of Figures 6 - 8, relative tension of the web sections
is not critical in that bag openings of sufficient width are formed by
producing the
pairs of lines of severance 74 in each of those embodiments in the manner
described. In the three embodiments shown once the lines of severance 64 and
the lines of weakness 62 are formed, the front and back sections are
juxtaposed.
Thereafter, the bead seals 78 and the transverse seal 74 are formed. While in
each embodiment the schematic drawings depict the formation of the transverse
seals before the bead seals, the sequence can obviously be reversed.
Similarly,
removal of web parts between lines of severance is shown in Figure 6 to occur
as
the webs are juxtaposed, but this operation may also be performed at other
locations along the path of travel. After juxtaposition of the front and back
sections, the bead seal 81 is formed in the embodiments of Figures 7 and 8 and
may be formed in the embodiment of Figure 6 if desired. With all three
embodiments, a chain of bags is produced in which each bag opening, as in the
embodiment depicted in Figures 4 and 5, has sufficient longitudinal extent to
assure facile detection of the associated line of weakness.
Although the invention has been described in its preferred form with a
certain degree of particularity, it is understood that the present disclosure
of the
preferred form has been made only by way of example and that numerous changes
in the details of construction, operation and the combination and arrangement
of
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parts may be resorted to without departing from the spirit and the scope of
the
invention as hereinafter claimed.
