Note: Descriptions are shown in the official language in which they were submitted.
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F-1398 -1-
NUFACTURING PROCESS FOR CHANNEL SEAL
This invention relates to apparatus for and a method of
applying a channel shaped adhesive strip having ribs along each side
and an adhesive layer between the ribs to a plast$c ~ilm.
Numerous closure arrange~ents have been propssed and employed
for securing plastic bags in a closed condition. Such devices include
rubber bands, twist ties, paper or plastic coated lengths of wire which
are fastened around the gathered and twisted neck of a plastic bag to
sècure a closed position. Such devices do not form an integral part of
a bag structure, and hence may not be readily accessible when it is
desired to effect closure of the bag.
A variety of closures for flexible bags have been developed
including the so-called profile closure having at least one pair of
mating channels, an example of which may be seen in U.S. Reissue
Patent No. 28,969 to Naito which shows the ZIP-LOC storage bag. U.S.
Patent No. 4,186,786 to Kirkpatrick shcws colored channels so that the
user may more easily detect complete occlusion of profile bag
openings. Difficulties have been experienced by the user in closing
these profile types of closures because it is difficult and/or
20 inconvenient to obtain good registration of the two parts of the lock.
The use o~ pressure sensitive adhesives to close plastic bags
is an expedient which is readily accessible and not subject to severe
registration problems. Typically, bags are packaged within a
dispensing carton in either continuous roll form or individually
adjacent to one another. When an exposed and unprotected adhesive
strip adjacent the mouth of such bag structures has been employed, the
bags had a tendency to stick to one another as to exterior objects,
following dispensing of individual bags from the container, thus making
it difficult to use the bags. Also, the adhesives employed were
30 necessarily non-aggressive in an attempt to alleviate the bag-sticking
problem, but this made the closures insecure.
Bag sticking during storage was solved by the arrangement
shown in U.S. Patent No. },990,627 to Olsen, in which a Z-fold in the
*Trademark ~
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F-1398 -~-
bag protects the adhesive strip during shipment and storage. When the
bag is to be used, the Z-fold is pulled out to expose the adhesive.
This arrangement has been successfully used, but the release of the
adhesive strip from its Z-fold protection is not as easy as may be
desired.
A method of making a bag closure comprising perforations may
be seen in U.S. Patent No. 2,899,347 to Kindseth.
Thus, it is an object of the present invention to provide a
bag closure by coextruding a channel shaped strip of thermoplastic with
a layer of pressure sensitive adhesive between the ribs thereof onto a
moving web of plastic film which may be formed into plastic bags.
It is another object of the present invention to maintain a
temperature differential between the molten thermoplastic and the
moving web so that the molten thermoplastic adheres to the moving web
upon contact and thereafter cools to prevent puckering of the moving
web.
It is a further object of the present invention to provide an
apparatus and a method which quickly and economically applies a channel
shaped thermoplastic strip to a polymer film without distortion of the
channel or the film, and which also applies a substantially uniform
adhesive layer between the ribs of the channel.
The present invention relates to apparatus for and a method of
making plastic bags having a channel shaped strip with adhesive between
the ribs. The ribs along each side of the adhesive layer hold the
adhesive strip away from the adjacent layer of plastic film during
shipment and storage of the bags. When the bag is to be used, the film
is pressed down into contact with the pressure sensitive adhesive,
thereby providing a good seal for the bag.
In accordance with the present invention a coextruding
assembly comprising a feed block and a shaping portion is positioned
adjacent to a moving web of film. Molten thermoplastic such as
comprising polyethylene, is supplied to a channel pro~ile extrusion die
in the shaping portion which extrudes a channel shaped strip of
thermoplastic onto the moving web. A dispenser applies a layer of
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F-1398 -3-
adhesive across the width of the strip between the ribs. The molten
thermoplastic is heated to a temperature which is lower than that which
would otherwise be required to obtain good adhesion between the
thermoplastic channel and the moving film, because the moving film is
heated by a backup roller. The temperature differential between the
molten thermoplastic and moving web is such that the molten
thermoplastic adheres to the moving web upon contact and thereafter
cools to set it in the desired channel profile.
The moving web of film is maintained under tension as it moves
past the coextruder so that contraction of the film, upon release,
compensates for the contraction of the channel shaped strip as it
cools. This prevents puckering of the web o~ ~ilm.
In accordance with another aspect of the present invention,
adhesive under pressure is applied across the width of the strip,
preferably as a substantially uniform and continuous layer. In one
embodiment this is accomplished by a plurality of V-shaped notches
which extend from an adhesive reservoir to openings adjacent to the
extruded channel. These V-shaped notches provide the desired pressure
drop between the reservoir and the external openings of the notches and
they are easier to fabricate than a single narrow slot which would
accomplish this purpose. Qlternatively, a slit may be used instead of
the V-shaped notches if properly shaped to~achieve suf~icient pressure
drop or if a spreader overlying the trough of the channel is used to
spread out the glue, preferably into a substantially continuous layer
within the channel strip.
In accordance with another aspect of the present invention,
the dimensions of the die opening are larger than the final desired
dimensions of the channel shaped adhesive strip to be formed. The web
of film moves at a speed greater than the speed of extrusion so that
the channel shaped strip is drawn to its desired dimensions. The large
die opening has the advantage of easier fabrication and servicing~
In accordance with another aspect o~ the present invention the
coextruding assembly comprises a unitary four block construction which
supplies thermoplastic to the shaping portion which shapes the general
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F-1398 ~4~
channel structure through a die opening, and applies adhesive to the
~idth of the strip between the ribs. This fw r piece construction has
i~portant advantages of ~ase of oonstruction and servicing.
In the drawings, which are attached to this
specification and illustrate emb~di~en s of the present
invention:
Figure lA is a perspective of a par~ially constructed bag
having a channel member produced by the apparatus and method of this
invention;
Figure lB is an enlarged cross-section of a channel closure
produced according to this invention in a stored position;
Figure 10 is the embodiment shown in Figure lB in a sealed
position;
Figure 2 is a perspective of a coextruding assembly of this
invention during a production run;
Figure 3 is a diagrammatic cross-section of the apparatus of
this invention;
Figure 4 is a front plan view of a coextruding assembly
constructed in accordance with this invention;
Figure 5 is a sectional view along offset line 5-5 in Figure 4;
Figure 6 is an enlarged view of the adhesive shaping block;
Figure 7 is a sectional view along line 7-7 in Figure 6;
Figure 8 is an exploded view of a coextruding assembly
constructed in accordance with this invention;
Figure 9A is a front plan view of an alternate embodiment of a
shaping block constructed in accordance with this invention;
Figure 98 is a sectional line along line 9B-gB in Figure 9A;
Figure 9C is an enlarged sectional view of the glue channel of
Figure 95;
Figure lOA is a top sectional view of the manifold unit;
Figure lOB is a front view of the manifold unit;
Figure lOC is a section21 view along line lOC-l~C of figure
10~; and
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-4a-
Figure lOD is a sectional view along line laD-lOD of Figure
lûB .
The apparatus of this invention is particularly useful in
forming bag closures comprising a channel shaped strip having adhesive
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F-1398 ~5~
such as a pressure sensitive adhesive in the trough of the strip.
Figure lA shows a partially constructed bag having a first wall 20 and
a second wall 21. A closure comprising a channel shaped adhesive strip
22 is affixed on second wall 21 a preselected distance from edge 23.
As shown more clearly in Figure lB, channel strip 22 comprises ribs 24
and a base 25. The trough formed by ribs 24 and base :25 conta~ns an
adhesive layer 26 therein, the thickness of which should not exceed t~e
interior height of ribs 24. Preferably layer 26 is substantially
continuous. During shipment and storage, ribs 24 protect adhesive
layer 26. Figure lC shows the closure in a sealed pos.ition in which a
substantially flat portion of first wall 20, e.g., an interior flap,
has been pressed into contact with adhesive layer 26. Ribs 24 have
been slightly defoxmed to allow more intimate contact between wall 20
and adhesive layer 26.
An apparatus for making these bags is shown in fi~ures 2 and 3
which depic~ a continuous web of a thermoplastic film 30, e.g.,
polyethylene, mnving between first nip roll 31 and a backup roller 32.
Film 30 passes over backup roller 32 during which it is contacted by a
channel shaped strip 33 containing a pressure sensitive adhesive. The
film then passes over a second or composite roller 34 and on to either
storage or further processing, e.g., heat sealing of the bag sides. A
coextruding assembly is positioned adjacent to backup roller 32 and
moving web 30 to apply the channel shaped adhesive strip to the moving
web ~0 on the side of the film opposite first or backup roller 32. The
coextrudin3 assembly comprises feed block 40, and a shap$ng portion
comprising a channel profile extrusion die block 37 which fits against
a ~lat block 38 to shape the channel structure. The shaping portion
further comprises adhesive dispensing block 39 which fits against
channel die block 37 to apply a layer of adhesive across the width of
the channel strip 33 between the ribs thereof. Channel die block 37 is
connected to the feed block 40 which is fed through pipe 41 by a source
of molten thermoplastic, shown in Figure 3 as a polymer extruder 42
with a heater 43. Adhesive dispensing block 39 is fed through channel
die block 37 by a hose 44 connected to a source of molten adhesive (for
example, hot melt adhesive supplied by using a Nordson model HMXll-A).
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F-1398 6
Figure 3 shows a preferred embodiment in which a heater 35 is
used to maintain backup roller 32 at a desired temperature. This
maintains a temperature differential between the molten thermoplastic
and the moving web of film. To make the channel adhere to the film, it
is necessary to have a sufficiently high temperature where they join
together. This is achieved by the proper combination of molten
thermoplastic temperature and backup roller temperature. The backup
roller must be sufficiently cool to prevent distortion of the film
where it contacts the hot channel. ~owever, it has been found that
when the backup roller 32 is maintained at a warmer temperature, the
required molten thermoplastic temperature is lower. A satisfactory
operation has been achieved with a molten polyethylene temperature of
300CF and a backup roller temperature of 140F at a film speed of 32
ft. per minute. Both the film and the channel comprised low density
polyethylene.
In order to maintain the moving web of film 30 under tension
when the strip is being applied, first nip roller 31 presses the film
30 against the backup roller 32. A second nip roller 45 presses the
moving film against the second roller 34. Alte m atively, the second
roller 34 may be omitted if the first backup roller 32 is adjusted at a
preselected tension to remove any ripples that may occur in the film
30. It is necessary to tension the film at the point ~here the channel
joins it in order to avoid distortion or puckers. If the film tension
is low, then in the final product the film is puckered along the
channel. This is caused by shrinking of the channel as it cools.
Applying tension to the film stretches it elastically, so that when it
is released it contracts. If the amount of tension ~s proper, the
contraction will be the same as the shrinking of the channel and the
product will be smooth. If there is too much tension, then the film
will try to contract more than the channel shrinks, and the channel
will be rippled in large bends.
Figures 4 and 5 show a coextruding assembly comprising a feed
block 50 and a shaping portion or block ccmprising channel die block
52, flat block 53 and adhesive shapi~g block 56. The feed block 50 is
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F-1398 -7-
connected by a pipe 51 to a source of molten thermoplastic, e.g.,
polyethylene supplied by a polymer pump. Mblten plastic enters feed
area 66 and the feed rate for extruding the channel is regulated by
means of screw adjust 67. Feed block 50 has positioned thereon and
bolted thereto a channel shaping block or channel die block 52 and flat
block 53 positioned under channel die block 52. Channel die block 52
has a shaping surface comprising rib forming grooves 54 and a base
forming recessed surface 55 cut into its surfaces. The shaping surface
of channel die block 52 is placed against a ~lat surface of flat block
5~ and bolted thereto with bolts 69 to close the open side of the'
channel profile extrusion die block 52. This two-piece construction
has im,oortant advantages. It is easier to fabricate than a co~parable
one-piece die. Also, it is easier to clean the die because it can be
taken a~,oart for thorough cleaning of the grooves. The shaping portion
of the coextruding assembly also comprises an adhesive shaping block 56
which is bolted onto the assembly through channel die block 52 with
bolts 57. Adhesive shaping block 56 has a cavity therein to form an
adhesive reservoir 58. A plurality of V-shaped notche!s'59-64 extend
between the reservoir 58 and the lower edge of the ad~e~ive shaping
block 56. Adhesive flows from the reservoir 58 through the V-shaped
notches uniformly over the width of the strip and between the ribs.
The adhesive shaping block 56 is positioned against a flat surface of
channel die block 52 orthogonal to the surface having notches 59-64 and
in the direction of the movement of the web. Adhesive from an outside
source, e.g., an adhesive pump, is introduced into the coextruding
assembly by hose 70 and flows through a passage 65 in channel die block
52 and enters reservoir 58. The rate of feed of adhesive is determined
by screw adjust ~8. The V-shaped notches 59-64 (shown in more detail
in Figure 7) in adhesive shaping block 56 allow distribution of the
adhesive uniformly across the width of the channel and easy control of
the flow of adhesive. In a preferred embodiment (explainRd in more
detail in Figures 9A-9C), the application of adhesive can be
accomplished with a single slot having the same cross-sectional area as
the plurality of triangular notches but such a single slot must be
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F-1398 -B-
extremely shallow to effect the pressure drop needed and requires
higher precision in the matching of the adhesive shaping block~ The
use of a single slot allows more even and more uniform distribution of
adhesive. ~ third embodiment may be used which combines the V-shaped
notches and the single slot in a serial construction with the slot
positione~ under the notches and closest to the opening. Thus the
adhesive would flow through the notches (allowing for optimum control
of the flow of the adhesive) and then into a slot and into the channel
(allowing for optimum evenness and uniformity in distribution).
Figures 6 and 7 show more detail for the adhesive shaping
block of Figures 4 and 5. Adhesive shaping block 56 additionally has
machined therein channels 69 to allow the ribs of the extruded channel
structure to pass therethrough.
Figure 8 shows an exploded view of an embodiment of the
coextruding assembly as it would appear in ~ts c ~ ~onent parts. The
assembly comprises feed block 50 with channel die block 52 and flat
block 53 positioned therein. Adhesive shaping block 56 fits over the
front of channel die block 52. In an assembled position flat surface
53a is positioned under channel die block 52 to form a channel shaped
opening through which molten thermoplastic material is extruded to form
a channel strip. Similarly a substantially flat surface 52a of channel
die block 52 is positioned against adhesive shapi~g block 56 to
complete the formation of the notched slots and raiervoir machined
therein.
In operation, a molten thermoplastic, e.gO~ polyethylene, a
copolymer or te~polymer thereof, is fed from a polymer pump into a feed
area 66 at a rate dete m ined by screw adjust member 67. A channel
strip is formed by extruding the molten plastic through the shaped
formed by channel die block 52 and flat block 53. At the point where
front surface 52a of channel die block 52 is contacted by adhesive
shaping block 56 a layer of molten adhesive is deposited between the
ribs of the extruded channel structure. The adhesive is applied by
means of a shaped groove or plurality of grooves through which adhesive
flows from a reservoir 58. Reservoir 58 is fed with adhesive through a
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F-1398 ~9~
passage 65 in channel die block 52 which connects the reservoir 58 with
an adhesive pump.
It has been found that the size of the channel profile
extrusion die opening can be different, e.g. larger, t:han th~ size of
the channel deposited onto the film. The difference can be corrected
by adjusting the linear speed of the film relative to the output of the
die. Running the film faster will draw-down the molten channel more,
making it smaller in cross-section but having essentially the same
proportions. It has been found that a smaller die opening gives a
channel that is more precisely defined, but a larger die opening is
easier to fabricate and service. The size ratio (as measured by width
or height) of the die to the final channel may be varied according to
the type of resin used, the running speed and the temperatures used.
When polyethylene is used to form the channel it is preferred that the
opening in the channel profile extrusion die be about two to about four
times the dimension of the channel shaped strip containing the
adhesive. More particularly, a satisfactory operation was achieved
with a die that had an opening twice the dimensions of the ~inal
channel. That is, for a channel .200 inches wide, the die was .400
inches wide. It was found that if the die opening was too large there
was difficulty in making the ribs stand up straight. When the channel
wraps around the backup roller 32, the vertical ribs tend to flop
over. With a smaller die, this problem was less severe because the
molten channel cooled before the distorting effect of the roll was
presentO Another possible cause of problems with larger die openings
relates to the area of reduction during draw-down. With a greater
reduction in width as is present with the larger die, the web of the
channel contracts more, pulling along with it the portions of the ribs
that adjoin the web. But the exposed portions of the ribs have no
force causing them to move inwardly, so they go straight. The result
is an apparent outward flopping of the ribs.
Figures 9A-9C show an alternate embodiment for the coextruding
assembly. Feed block 80 has positioned thereon a channel die block 81
and flat block 82. In front of a flat portion of channel die block 81
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F-1398 -10-
is adhesive shaping block 83 in which has been formed a single narrow
groove 86 and a cavity or reservoir 35. Molten thermoplastic is
introduced into passage 88 through feed block 80 and extruded through
channel shaped die form 87 as previously explained. Mblten adhesive is
~ntroduced into passage 84 which passes through feed block 80 and
channel die block 81 to supply adhesive to reservoir 85. Glue flows
from reservoir 85 through groove or slit 86 and onto the extruded
channel strip as the channel leaves the extruding die form 87. Bolts
89 are used to join components of the shaping portion of the
coextruding assembly to each other and to the feed block 80.
Figures lGA-lOD show an alternate embodiment of the invention
preferred for more efficient production having a coextruding manifold
assembly comprising a manifold unit lûO and four shaping portions or
blocks (the position of one of such shaping blocks 101 being shown in
phantom in Figure lOA). Manifold unit 100 is a cylindrical shaped
structure having channeled recesses 102 formed therein for receiving
shaping portions or blocks 101. The shapes and areas of the channeled
recesses 102 have been selected to ensure intimate contact between
manifold unit 100 and shaping portions 101 and minimi.ze the effects of
pressures from the adhesive and thermoplastic as they exit the manifold
unit 100 at adhesive ports 103 and thermoplastic ports 104 and enter
shaping portions 101. Manifold unit 100 also has fol~ed therein a bore
105 for thermoplastic to flow through the manifold unit 100 and to each
indiv~dual shaping block 101. Thermoplastic is pumped into the
manifold unit through a hose 116 into bore 105 through which it flows
to each plastic port 104 and then into a shaping portion 101. At each
end of the bore 105 in manifold unit 100, there is a blockage (e.g., a
plate~ a plug or an area where the bore is not formed to the outside of
the manifold unit), so that the only exit for the th~rmoplastic is
through the shaping blocks 101. Manifold unit 100 also comprises an
adhesive or glue feed bore 106 which passes through a substantial
length of the unit and supplies glue to each shaping block 101 through
adhesive ports 103. After the flow of adhesive or glue has passed
through feed bore 106 it is channeled into a return bore 107 to be
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F-1398 -11-
recycled by the adhesive pump into the system. In the embodiment shown
in Figures lOA-lOD, the channeling is accomplished by positioning a
block 108 having a groove 109 fonmed therein and of sufficient
dimension so as to provide a path from the termination of feed bore 106
to the beginning of return bore 107. This groove also serves the need
for creating back pressure in the adh~sive system. Alternatively,
valves could be used to create such back pressure. Thus, adhesive
enters the system through hose 110, flows through feed bore 106 with
portions of the adhesive exiting throu~h adhesive ports 103 and into
shaping portion 101, groove 109, return bore 107 and exits through hose
111, and may then be recirculated into the manifold assembly. In an
alternate embodiment, the groove between the end of glue feed bore 106
and the start of glue return bore 107 could be formed in the end of the
manifold unit 100 and a ~lat plate bolted onto the end to complete the
channeling of the glue. Screw adjust 112 with needle valve 113 is used
to adjust the pressure and feed rate of the glue as it enters shaping
block 101. Similarly screw adjust 114 with needle valve 115 is used to
adjust the pressure and feed rate of the thermoplastic as it enters the
shaping block 101. Since the glue is ~lowing through a recycling
system, individual adjustments of pressure and feed rate may be made
for each shaping block 101 without substantial effect on the other
shaping units. Since the thermoplastic material is not in a recycled
system there is more e~fect on the pressure to the other shaping blocks
when an adjustment is made to one of them. As will be appreciated by
those skilled in the art of thermoplastic polymers and their properties
in~luding their non-Newtonian behavior (i.e~, viscosity is not constant
at a given temperature and change in shear stress is not proportional
to change in shear rate), more care must be taken in selecting and
regulating the ~eed pressures and ~low rates of the thermoplastic used.
Where it is desired to produoe plastic bags in ~hich the
channel shaped adhesive strip is protected by a Z-fold, the apparatus
of the pre~t ~tion may be ino~porated with the a~atus descr~ed
in co,~ ~ C~n Application Ser~ No. 409,973 of F.J. Hbrri~, Jr.,
fi ~ A~t24, 1982, entitled ~Splayed Rolled Folder For Adhesive
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F-1398 -12-
Application". The correspondence between the rollers in this
application and the rolls shown in Figure 1 of that application are as
follows. The nip roller 43 corresponds with nip roller 11; backup
roller 32 corresponds with strip roller 20; second roller 34
corresponds with composite roll ~0; and nip roller 45 corresponds with
nip roller 41. With this correspondence between the rolls, it can be
seen how the apparatus of the present invention can be used to apply a
channel shaped strip which is enclosed within the Z-fold fonmed by the
composite roll 30 in Applicant's aforementioned Canadian
Application No. 409,973.
