Note: Descriptions are shown in the official language in which they were submitted.
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TEAR CONTROL CLOSING TAPE AND CONTAINER WITH
TEAR CONTROL CLOSING TAPE
TECHNICAL FIELD
The present invention relates to adhesive tapes and containers. More
particularly, the present invention relates to adhesive tapes for closing
containers
and containers having closing tape.
BACKGROUND OF THE INVENTION
Containers, such as bags and other packages, must be securely closed to
contain their contents. The container must remain closed during storage and
shipping and must withstand vibrations and shocks of rough handling. When
distribution is complete, the consumer or end-user needs to open the container
to
remove the contents. Ideally, a container can be opened without tools or
special
skills. Achieving both secure closure and easy opening is difficult; many
containers can be secure for shipment but are difficult to open. For example,
multiple wall paper bags of dog food or fertilizer often have sewn tops which
remain closed during shipping but are difficult for the end-user to open
without
tools or without damaging the bag and spilling unused contents.
U.S. Patent No. 4,781,296 discloses making a Tyvek spun-bonded olefin
envelope openable. It improves upon the common paperboard envelopes which
are relatively easy to open using conventional tearable tape strip tape
products.
This highly tear-resistant envelope material can be fused by ultrasonic
sealing,
creating lines of weakness. European Patent 447209 discloses an improved
opening for Tyvek envelopes. It uses reinforced strapping tape (or similar
tape)
which is nicked on the ends to control the direction of the tear through the
envelope. It also includes cutting through the Tyvek material, rather than
just
weakening it. These patents describe opening devices for light-weight mailing
envelopes: they function well in this light weight application but are not
readily
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usable to resist splitting when used on a heavier package because the tape is
relatively easy to tear.
European Patent 755868 discloses a paperboard envelope using a single
tape to close and open the envelope. A uniaxially-oriented plastic film is
adhesive-
coated on both sides, allowing it to function as a closing tape as well as an
opening
tape. The tape is nicked to control the direction of tear. The paperboard
material of
the envelope provides the tear resistance.
The Minnesota Mining and Manufacturing Company (3M) has sold tear
strip tapes for many years. One version of tear strip tape (3M # 8612 tape)
has a
polyethylene terephthalate (PET) backing and a reinforcing filament of
polyester
yarn or fiberglass coated with a pressure sensitive adhesive (PSA). This tape
is
applied to the inside of a corrugated box or to the inside of a paperboard
mailing
envelope. The corrugated board or paperboard is nicked on the outside of the
tear
strip to provide a tab which the end-user can pull. During opening, the tape
remains intact and is not split. The tape pulls and tears through the
corrugated
board or paperboard. This tear strip tape can only be used in light-weight
situations because the force required to tear the tape is relatively low.
Other
versions use a tensilized polypropylene tape with a PSA and, optionally, a
reinforced strapping tape. These types of tear strips can also be applied to
the
adhesive side of a wider film tape such as a box sealing tape or a heat
shrinkable
tape. Again, the wide tape is nicked to provide a tab and to initiate tearing.
The
distance between nicks is wider than the tear strip. This is only used for
lightweight packages because the nicks tend to propagate prematurely during
shipping, if used on a heavier shipping container. Using this kind of
conventional
tear strip on a linear low derisity polyethylene (LLDPE) tape backing would
not
function because the tear strength and the elongation of the LLDPE is too
high.
Lightweight film tear strip (with a PSA or with a heat-activated adhesive) is
also applied to film overwraps on packages. One example is a pack of
cigarettes.
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SUMMARY OF THE INVENTION
A container for storing items has a flap for closing the container. The flap
has first and second major surfaces and is formed of a tear resistant film
material.
The container includes means for adhering the first major surface of the flap
to the
container to close the container and a tearable tape strip. The tape strip is
located
on one of the first and second major surfaces of the flap, and permits tearing
of
itself and the flap with a given force notwithstanding that the tear resistant
film
flap is otherwise not cleanly tearable.
The tearable tape strip can be located on the first major surface of the flap
such that tearing the tearable tape strip tears through the flap. The means
for
adhering the first major surface of the flap to the container can include an
adhesive
on at least part of the first major side of the flap, the container, or both.
In another embodiment, a tape for use in closing a container having
opposing ends includes a base layer and a tearable tape strip. The base layer
includes a tear resistant backing having a first side and a second side, and
an
adhesive on at least part of the first side of the backing. The tearable tape
strip is
located on the first side of the backing and has a first side and a second
side. The
tearable tape strip permits tearing of itself and the tear resistant backing
with a
given force notwithstanding that the tear resistant backing is otherwise not
cleanly
tearable. The adhesive can be located between the backing and the tearable
tape
strip and the tearable tape strip tears through the base layer when the tape
is
removed from the container.
The tear resistant backing can be LLDPE, low density polyethylene LDPE,
cast polypropylene, and Kraton/polypropylene blends. The tearable tape strip
can
be one of reinforced strapping tape, tensilized polypropylene, and filament
reinforced tape. The tearable tape strip can have at least one of filaments
and ribs.
The tape can include a tab at one end. The tab is formed by nicks
extending from at least one of the ends of the tape and is located at least
partially
through the tearable tape strip which facilitate beginning tears. In one
version, at
least one nick has a first portion and a second portion. The first portion
extends
from at least one of the ends of the tape and passes through only the base
layer and
the second portion passes through the tearable tape strip. This allows the tab
to
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adhere to the container to reduce the risk of the container
opening before the proper time.
The tape can include a means for indicating
whether the container has been opened and reclosed. Using
linear low density polyethylene as the tear resistant
backing causes the torn edge of the tape to be distorted
such that recovering the opened tape is noticeable even when
covered with additional tape.
According to an aspect of the invention, there is
provided a container for storing items having a flap for
closing the container, wherein the flap has first and second
major surfaces and is formed of a tear resistant film
material, and wherein the container comprises: an adhesive
means for adhering the first major surface of the flap to
the container to close the container; and a tearable tape
strip located on one of the first and second major surfaces
of the flap, wherein the tearable tape strip permits tearing
of itself and the flap with a given force notwithstanding
that the tear resistant film flap is otherwise not cleanly
tearable.
According to another aspect of the invention,
there is provided a tape for use in closing a container
having opposing ends and comprising: a base layer comprising
a tear resistant backing having a first side and a second
side; a tearable tape strip located on the first side of the
backing and having a first side and a second side, wherein
the tearable tape strip permits tearing of itself and the
tear resistant backing with a given force notwithstanding
that the tear resistant backing is otherwise not cleanly
tearable; a first adhesive means for adhering the base layer
to the tearable tape strip; and a second adhesive means for
adhering the tape to the container.
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BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a cross-sectional view of a tape of
the present invention.
Figure 2 is a perspective view of the tape of
Figure 1 applied to a container.
Figure 3 is a partial perspective view of another
embodiment of the tape applied to a container.
Figure 4 is a cross-sectional view of a tape
according to another embodiment of the present invention.
Figure 5 is a cross-sectional view of a tape
according to another embodiment of the present invention.
Figure 6 is a cross-sectional view of a container
according to another embodiment of the present invention.
Figure 7 is a perspective view of the container of
Figure 6.
DETAILED DESCRIPTION
This invention is a tape which functions both to
close a container 9 and also to provide a mechanism to
easily open the container. Although the container 9 can be
any container such as envelopes and boxes, the invention
works particularly well on flexible containers such as bags
like multiple wall paper bags for storing granular material.
As shown in Figure 1, the tear strip tape 10 combines a base
layer 12 which is a tear-resistant tape, with a tearable
tape strip 14. The base layer 12 includes a tear resistant
backing 16 having a first side 18 and a second side 20, and
an adhesive 22 which in the illustrated embodiments is
located on the first side 18 of the backing 16. The
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adhesive 22 can be applied to the backing 16 by any known
method such as knife coating.
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The tearable tape strip 14 can be attached to either the first side 18 or the
second side 20 of the backing 16 of the base layer. In the illustrated
embodiments,
the tearable tape strip 14 is adhered to the first side 18 of the backing 16
using the
adhesive 22. In use, the tearable tape strip 14 is located on the container 9
between
the container and the base layer 12, without adhering to the container. In the
illustrated embodiments, the tearable tape strip 14 includes a base layer 24
and its
own adhesive 26 on one side of the base layer to assist adherence to the base
layer
12 of the tear strip tape 10. In another embodiment, the adhesive 26 is on the
other
side of the tearable tape strip base layer 24 to adhere to the container 9. In
another
embodiment, the tearable tape strip 14 need not include an adhesive.
The backing 16 can be a linear low density polyethylene (LLDPE), low
density polyethylene (LDPE), cast polypropylene, Kraton/polypropylene blends,
or
other tear resistant film. The tearable tape strip 14 can be tearable filament
reinforced tape or a reinforced strapping tape (RST) having filaments or ribs
28.
Suitable RSTs are described in U.S. Patent Nos. 5,079,066 and 5,080,957. The
tearable tape strip 14 could also be tensilized polypropylene or other
oriented or
non-oriented films which tear preferentially in the longitudinal direction.
The ribs
28 constrain the tears in the tearable tape strip 14 to control the direction
of tear.
Nicks 30 in the tearable tape strip 14 form an end tab 32 and initiate points
of tear.
Stress from handling the container 9 is concentrated at these points. The tear
resistant base layer 12 prevents the tear from propagating prematurely, yet
allows a
person to pull the end tab 32 to easily open the container 9. A wide variety
of tear
resistant tapes 12 are available. By balancing the strength, premature
splitting, and
ease of opening, a tape 10 with the desired overall characteristics can be
achieved.
Containers 9 have been closed with this invention and have been subjected to
severe rough handling tests. They have successfully withstood these stresses
yet
have allowed easy opening. This tape 10 uses a weakness of the tearable tape
strip
14, such as RST, (its tendency to split in the longitudinal or machine
direction)
coupled with an inability to tear cleanly through the tear resistant backing
to form a
very functional opening feature for containers. Cleanly tear means to tear
open
consistently, with a relativelv uniform tearing force, without excessive
distortion of
the torn film. There are not extended stretched-out or jagged edges.
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One embodiment of this invention is shown in Figure 2. A backing 16
made of tear resistant film such as LLDPE and an adhesive 22 such as PSA
functions as the base layer 12 which closes the container 9. A narrower
filament
reinforced tape or reinforced strapping tape is the tearable tape strip 14 and
is
laminated to the tear resistant base layer 12. adhesive to adhesive. Nicks 30
through the tape 10 initiate points of tear. The nicks 30 are located through
both
the base layer 12 and the tearable tape strip 14 of the tape 10. The tape 10
is
applied to the container 9. The end tabs 32 formed at the end of the tape
assist
opening the container 9.
In an alternative embodiment, shown in Figure 3, the end tabs 32 can lay
flat against the container 9 during shipping and distribution. In this
version, the
nicks 30 start from the end of the tape 10 at a location such that they pass
through
only the base layer 12. The distance between the nicks 30 is greater than the
width
of the end tab 32. As shown, the nicks are then directed to pass through part
of the
tearable tape strip 14 as well as the base layer. This direction change is
shown as a
smooth curve, but any shape can be used. The key to this feature is that at
the end
of the tape, the end tab 32 includes part of the tape 10 with adhesive 22 to
allow
adhesive of the closure tape to hold lightly onto the bag, while the end tab
32 has at
least a portion that extends through the tearable tape strip 14.
In another embodiment shown in Figure 4, tape 40 includes a tape layer 42
that is a strip of film tape, such as a box sealing tape made of biaxially
oriented
polypropylene. The tape layer 42 includes a backing 44 and an adhesive 46.
This
tape layer 42 is not tear resistant when nicked but provides good closure
strength
at a low cost. The narrower tearable tape strip 14 is laminated to a tear
resistant
tape 12 of a similar width, such as a 3M # 8883 tape. The tearable tape strip
14
includes a base layer 24 and an adhesive 26 and the tear resistant tape 12
includes a
base layer 16' and an adhesive 22' although the adhesive is not required. The
tear
resistant tape 12 is located only in the area where its function is required,
the area
straddling the two portions of the container 9 that are adhered to each other
to close
the container. (Note that if a box sealing tape was used with RST without a
tear
resistant film, nicks in the RST would propagate too easily.) This embodiment,
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like that of Figure 1, prevents a tear from propagating prematurely, yet
allows a
person to pull the end tab 32 to easily open the container 9.
This structure could be formed in several ways. One way is that the tear
resistant tape 12, such as #8883 tape, made by 3M, St. Paul, Minnesota, could
be
laminated between the box sealing tape layer 42 and the tearable tape strip 14
at
the point of application. In another method, an RST tape could be used as the
tearable tape strip 14 and could be laminated to tear resistant tape 12 (3M
#8883
tape) and provided to a customer in roll form. This would be applied to the
box
sealing tape layer 42 at the point of application. Yet another method involves
putting all of the layers together during manufacturing. A tear resistant tape
12 is
coated or laminated to a tearable tape strip 14. This multiple layer
configuration is
then attached to a tape layer 42 which includes a backing 44 and an adhesive
46.
Figure 5 shows an embodiment where there is no adhesive on the tear resistant
layer. The tear resistant base layer 16 only is located between the tape layer
42 and
the tearable tape strip 14 to form tape 50.
In one example, a 20 kg (44 lb) bag of dog food was closed with a 40.6 cm
(16 in) long strip of 48 mm wide tear resistant adhesive base layer 12, such
as 3M
#8883 tape, having a 0.008 cm (3 mil) LLDPE backing 16 and a PSA adhesive 22.
(The 3M #8883 tape is a "stretchable tape" which is used here for its tear
resistant
properties.) A 12 mm wide strip of tearable tape strip 14 (3M # 864 RST tape)
was
applied and nicks 30 were formed in the ends to create end tabs 32. This bag
was
subjected to drop tests according to ASTM D5276 standards. Drops of 76 cm (30
in) were made on the front, back, two sides, and two ends of the bag. The bag
completed the six drops without opening. The bag was then lifted up several
times
by its "ears," the notches formed by the gussets, without opening and without
the
nicks propagating. The bag was easily opened by pulling the tab.
A similar bag of dog food was closed with a tape having 48 mm wide box
sealing tape (3M # 372 tape) laminated to 12 mm wide 3M # 8883 tape and 12 mm
wide 3M #864 tape. Some bags were also closed with a structure of 48 mm wide
box sealing tape and a 12 mm wide lamination of 3M # 864 tape and a 0.008 cm
(3
mil) LLDPE film, and other bags were closed with a 0.010 cm (4 mil) LDPE film.
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This structure also completed the drop tests and lifting tests well, followed
by
being easily opened.
To measure the forces required to open the tape structures, tests were
conducted on a ZPE 1000 High Rate Peel Test System, by Instrumentors, Inc.
Tests were conducted at 0.5 m/s (which is representative of the actual speed
used
by end-users) and the force required to pull a tab (with two tears through the
tape)
was measured in Newtons. The following table summarizes the results. Tests at
other speeds were also conducted. The results at these speeds were
predictable;
lower speeds yielded increased forces and higher speeds yielded decreased
forces.
At all speeds, there were similar force differences among the various tape
samples.
EXAMPLE BASE LAYER TEARABLE TAPE FORCE
NUMBER STRIP (N)
Comparative # 1 #864 RST #864 RST 2.5
Comparative # 2 #372 Box Sealing Tape #864 RST 1.8
Comparative # 3 #372 Box Sealing Tape #8612 (nicks along sides) 0.2
1 #8883 Stretchable Tape #864 RST 12.8
2 #372 Box Sealing Tape #8883 Stretchable Tape / 9.1
#864 RST
3 #372 Box Sealing Tape 4 mil LDPE / #864 RST 5.1
This table illustrates that using a tear resistant film (3M #8883 tape in the
examples) in the structure significantly increases the force required to tear
and thus
decreases the chance of premature opening of the container. If a standard tear
strip
tape such as 3M #8612 (with nicks along the sides) is used with #8883, the
LLDPE
backing deforms and elongates but it does not provide a functional tear.
However,
an example using a single tape construction of #8883 Stretchable Tape did not
work. The tape broke without tearing along its length.
In alternative embodiments, a tape can be made from a tearable tape (such
as 3M #8883). This tape can be made tear resistant at its ends by applying a
tab,
such as a conventional paper tab. In this configuration, nicks or perforations
extend for the entire length of the tape. This version works better when the
tearable tape is strong at least in the region between the two rows of
perforations.
Strengthening the tape can be performed by any known strengthening method. For
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example, ribs or filaments can be used. Also, the material used for the tab
can be
used along the entire length of the tape. -
In another embodiment, shown in Figures 6 and 7, a container 60 includes a
tape for sealing the container. The container 60 can be flexible and can be a
bag.
The tape can be a tearable tape strip 62 and can be part of the container 60
in a way
to simplify the tape. For example the container 60 can have a flap 64 for
closing
the container. The flap 64 has first and second major surfaces and is formed
of a
tear resistant film. Film is defined as being continuous and made from
material
other than sheetstock. (Sheetstock is defined as material that is made of
5bers.
The fibers can be felted, matted, beaten, or refined, and can be made of
cellulose,
as with traditional paper, or of other materials, including synthetic and
plastic
materials that can be bonded together.)
The flap 64 can be weakened (such as by slits, perforations, or score lines)
along subsequent tear lines. As shown, the flap 64 is unweakened. Unweakened
means that there are no slits, perforations, or score lines in the flap, and
the flap is
untreated in any way intended to weaken it. The tearable tape strip 62 and the
flap
64 can have nicks 70 at their ends to facilitate beginning the opening
process.
These nicks 70 can form a tab and do not weaken the flap 64 because the flap
is
made of a tear-resistant plastic. The flap 64 need not be weakened because the
tearable tape strip 62 makes the otherwise tear-resistant film relatively easy
to tear
to open the container. This is a significant difference from the known
sheetstock
envelopes and containers which require weakening in order to function well.
Weakening involves extra manufacturing steps and increased costs.
The container 60 includes a mechanism, such as glue or adhesive 66, that
adheres the first major surface of the flap to the container to close the
container.
The adhesive 66 can be coated on at least part of the first major side of the
flap 64,
or on the other part of the container 60, or on both. The adhesive 66 can
optionally
be protected by a release liner before the container 60 is closed. The
tearable tape
strip 62 is located on either or both of the first and second major surfaces
of the
flap 64. The tearable tape strip 62 permits tearing of itself and the flap 64
with a
given force notwithstanding that the tear resistant film flap 64 is otherwise
not
cleanly tearable.
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If the tearable tape strip 62 is located on the first major surface of the
flap
64, tearing the tearable tape strip tears through the flap. In this version,
an optional
cover tape 68 can be located on the second major surface of the flap 64,
opposite
the tearable tape strip, as shown in Figure 6. The cover tape 68 improves the
ability to tear cleanly through the flap 64, perhaps by constraining the
elongation
of the flap during tearing. This is shown by the decreased force required for
Example 2, which uses a box sealing tape, as compared with Example 1, which
does not. Various tapes can be used as a cover tape 68 including #371
Biaxially
Oriented Polypropylene (BOPP) Box Sealing Tape, #355 PET Box Sealing Tape,
#821 Acetate Tape, and #600 Polyvinyl Chloride (PVC) Tape, all made by 3M, St
Paul, Minnesota. These tapes all have lower elongation than the film used for
the
flap 64.
The flap 64 can be made of LLDPE, LDPE, cast polypropylene, and blends
of Kraton and polypropylene. The tearable tape strip 62 can be RST, tensilized
polypropylene, and filament reinforced tape. Also, the tearable tape strip 62
can
include filaments, ribs, or both, formed on either or both of its first and
second
sides.
