U.S. patent application number 12/435768 was filed with the patent office on 2009-11-12 for cohesive reclosable fasteners for flexible packages.
Invention is credited to Kenneth C. Pokusa, Paul Zerfas.
Application Number | 20090279813 12/435768 |
Document ID | / |
Family ID | 40874692 |
Filed Date | 2009-11-12 |
United States Patent
Application |
20090279813 |
Kind Code |
A1 |
Pokusa; Kenneth C. ; et
al. |
November 12, 2009 |
Cohesive Reclosable Fasteners For Flexible Packages
Abstract
A flexible package having a reclosable fastener with opposing
front and back panels joined together to form a cavity. The
reclosable fastener including opposing cohesive layers supplied
from a solvent dispersion of a thermoplastic elastomer and diluent
disposed on each of the front and back panels effective to form a
reclosable fastener having a cohesive peel strength less than the
bond strength to the front and back panels.
Inventors: |
Pokusa; Kenneth C.; (Indian
Head Park, IL) ; Zerfas; Paul; (Verona, WI) |
Correspondence
Address: |
FITCH EVEN TABIN & FLANNERY
120 SOUTH LASALLE STREET, SUITE 1600
CHICAGO
IL
60603-3406
US
|
Family ID: |
40874692 |
Appl. No.: |
12/435768 |
Filed: |
May 5, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61093901 |
Sep 3, 2008 |
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61052021 |
May 9, 2008 |
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Current U.S.
Class: |
383/211 ;
53/414 |
Current CPC
Class: |
B65D 33/20 20130101 |
Class at
Publication: |
383/211 ;
53/414 |
International
Class: |
B65D 33/28 20060101
B65D033/28 |
Claims
1. A flexible package having a reclosable fastener comprising:
opposing front and back panels joined together to form a cavity; a
reclosable fastener including opposing cohesive layers supplied
from a solvent solution of a blend of a thermoplastic elastomer and
a diluent resin disposed on each of the front and back panels, the
cohesive layers being positioned facing each other on the front and
back panels so that the flexible package can be closed when the
opposing cohesive layers contact each other; and a bond strength of
the cohesive layers to the panels greater than a cohesive bond
strength between opposing cohesive layers so that the front and
back panels can be repeatedly peeled open without substantially
delaminating the cohesive layers from the front and back
panels.
2. The flexible package of claim 1, wherein the cohesive layers
include a major amount of the thermoplastic elastomer including a
styrenic block copolymer or a mixture of styrenic block copolymers
diluted with a minor amount of the diluent resin including ethylene
vinyl acetate copolymer to form the cohesive bond strength.
3. The flexible package of claim 2, wherein the cohesive layers
include about 7 to about 9 parts of the thermoplastic elastomer and
about 0.5 to about 2 parts of the ethylene vinyl acetate
copolymer.
4. The flexible package of claim 2, wherein the styrenic block
copolymer is selected from the group consisting of SIS block
copolymers based on styrene and isoprene, SBS block copolymers
based on styrene and butadiene, SEBS block copolymers with a
hydrogenated midblock of styrene-ethylene/butylenes-styrene, SEPS
block copolymers with a hydrogenated midblock of
styrene-ethylene/propylene-styrene, and mixtures thereof.
5. The flexible package of claim 1, wherein the cohesive bond
strength is about 100 to about 700 g/inch with a residual cohesion
bond strength after contamination about 25 to about 100 percent of
the cohesion bond strength before contamination.
6. The flexible package of claim 5, wherein the cohesive layer has
a tack level not exceeding about 5 psi when preloaded with about
4.5 pounds and not exceeding about 15 psi when preloaded with about
10 pounds.
7. The flexible package of claim 6, wherein the cohesive layer has
a peel strength to the panels of greater than about 700 g/inch.
8. The flexible package of claim 1, wherein the front and back
panels are selected from the group consisting of ethylene vinyl
acetate, polyethylene, polypropylene, polybutylene, nylon,
polyethylene terephthalate, polyvinyl chloride, ethylene vinyl
alcohol, polyvinylidene chloride, polyvinyl alcohol, polystyrene,
or combinations thereof.
9. The flexible package of claim 8, wherein the front and back
panels contain ethylene vinyl acetate in at least their innermost
surfaces.
10. The flexible package of claim 1, wherein at least the innermost
surfaces of the front and back panels include less than about 10
percent of a filler therein.
11. The flexible package of claim 10, wherein the filler is
selected from micro- or nano-sized inorganic materials.
12. The flexible package of claim 11, wherein the filler includes
clay, calcium carbonate, montmorillonite, dolomite, talc, mica, and
mixtures thereof.
13. The flexible package of claim 1, wherein the front and back
panels includes less than about 700 parts per million fatty acid
amide or other additives that can migrate to the panel surface and
decrease the bond strength to the cohesive layers.
14. The flexible package of claim 1, wherein the solvent is an
organic solvent selected from the group consisting of ethyl
acetate, normal propyl acetate, isopropyl acetate, methyl ethyl
ketone, ethyl alcohol, normal propyl alcohol, propylene glycol,
normal propyl ether, butyl acetate, toluene, cyclohexane,
cyclohexanol, and mixtures thereof.
15. The flexible package of claim 1, wherein the reclosable
fastener has less than about 50 parts per million residual organic
solvent.
16. A reclosable fastener suitable for a package, the reclosable
fastener comprising: a cohesive layer applied to a flexible film
and having an exposed cohesive surface; and a non-adhesive spacer
layer having an outer surface and disposed adjacent the cohesive
layer, the non-adhesive spacer layer protruding outwardly beyond
the cohesive surface of the cohesive layer so that the cohesive
surface is recessed from the outer surface of the adjacent
non-adhesive spacer layer.
17. The reclosable fastener of claim 16, wherein the adjacent
non-adhesive spacer layer includes a pair of non-adhesive spacer
layers each positioned adjacent a lateral side of the cohesive
layer.
18. The reclosable fastener of claim 17, wherein each of the pair
of adjacent non-adhesive spacer layers are disposed on the cohesive
surface of the cohesive layer.
19. The reclosable fastener of claim 17, wherein each of the pair
of adjacent non-adhesive spacer layers are disposed on the flexible
film.
20. The reclosable fastener of claim 16, wherein the adjacent
non-adhesive spacer layer includes a polyamide, polyester,
polyethylene, polypropylene, polybutylene, ethylene vinyl acetate,
polyethylene terephthalate, ethylene vinyl alcohol, polyvinyl
chloride, polyvinylidene chloride, polyvinyl alcohol, polystyrene,
and combinations thereof.
21. The reclosable fastener of claim 16, wherein the cohesive layer
includes a thermoplastic elastomer and a diluting resin.
22. The reclosable fastener of claim 21, wherein the thermoplastic
elastomer is a compound including a styrenic block copolymer or a
mixture of styrenic block copolymers and the diluting resin is
ethylene vinyl acetate.
23. The reclosable fastener of claim 22, wherein the compound
includes minor amounts of plasticizers, fillers, antioxidants, or
mixtures thereof.
24. The reclosable fastener of claim 22, wherein the styrenic block
copolymer is selected from the group consisting of SIS block
copolymers based on styrene and isoprene, SBS block copolymers
based on styrene and butadiene, SEBS block copolymers with a
hydrogenated midblock of styrene-ethylene/butylenes-styrene, SEPS
block copolymers with a hydrogenated midblock of
styrene-ethylene/propylene-styrene, and mixtures thereof.
25. The reclosable fastener of claim 16, wherein the cohesive
surface has a cohesive bond strength of about 100 g/inch to about
700 g/inch.
26. The reclosable fastener of claim 25, wherein the cohesive
surface has a tack level not exceeding about 5 psi when preloaded
with about 4.5 pounds and not exceeding about 15 psi when preloaded
with about 10 pounds.
27. The reclosable fastener of claim 16, wherein a gap of about 2.5
to about 50 microns is formed between the outer surface of the
adjacent non-adhesive spacer layer and the cohesive surface of the
cohesive layer.
28. The reclosable fastener of claim 16, further comprising
opposing first and second reclosable fasteners, the cohesive
surface of the first reclosable fastener opposing the cohesive
surface of the second reclosable fastener.
29. A flexible package having a reclosable fastener, the flexible
package comprising: opposing front and back panels; and a
reclosable fastener on each of the front and back panels, each
reclosable fastener including a cohesive layer disposed on the
panel and having an outer surface spaced a first distance from the
panel, a non-adhesive layer adjacent the cohesive layer and having
an outer surface spaced a second distance greater than the first
distance from the panel so that the cohesive layer is substantially
recessed from the outer surface of the non-adhesive layer, and at
least a portion of the outer surfaces of the cohesive layers
cohesively engaged to each other to form a closed package.
30. The flexible container of claim 29, wherein the first distance
the outer surface of the cohesive layer is spaced from the panel is
about 2.5 to about 50 microns.
31. The flexible container of claim 29, wherein the second distance
the outer surface of the non-adhesive layer is spaced from the
panel is about 2.5 to about 100 microns.
32. The reclosable fastener of claim 29, wherein the non-adhesive
layer is disposed on the outer surface of the cohesive layer.
33. The reclosable fastener of claim 29, wherein the non-adhesive
layer is disposed on the panel.
34. The reclosable fastener of claim 33, wherein the thickness of
the cohesive layer is about 2.5 to about 50 microns and the
thickness of the non-adhesive layer is about 5 to about 100
microns.
35. The reclosable fastener of claim 29, wherein the non-adhesive
layer includes a polyolefin, polyamide, polyester, polyethylene,
polypropylene, polybutylene, ethylene vinyl acetate, polyethylene
terephthalate, polyvinyl chloride, ethylene vinyl alcohol,
polyvinylidene chloride, polyvinyl alcohol, polystyrene, and
combinations thereof.
36. The reclosable fastener of claim 29, wherein the cohesive layer
includes a thermoplastic elastomer or a mixture of thermoplastic
elastomers selected from the group consisting of a styrenic block
copolymer or a mixture of styrenic block copolymers.
37. The flexible container of claim 29, wherein the cohesive layer
has a cohesive bond strength of about 100 g/inch to about 700
g/inch.
38. The flexible container of claim 37, wherein the cohesive layer
has a tack level not exceeding about 5 psi when preloaded with
about 4.5 pounds and not exceeding about 15 psi when preloaded with
about 10 pounds.
39. A method of forming a flexible package having a reclosable
fastener, the method comprising: moving a flexible film
longitudinally in a machine direction; applying first and second
strips of a thermoplastic elastomer containing solution
intermittently to the flexible sheet and transverse to the machine
direction, the first and second strips being spaced a first gap
along the machine direction; applying a third strip of the
thermoplastic elastomer containing solution intermittently to the
flexible sheet and parallel to one of the first and second strips,
the third strip being spaced a second gap smaller than the first
gap from one of the first or second strips; applying a strip of a
polyolefin solution adjacent to each of the intermittent
thermoplastic elastomer strips in a manner such that an outer
surface of a dried thermoplastic elastomer strip is recessed from
an outer surface of a dried polyolefin strip; and drying the
thermoplastic elastomer strips and the polyolefin strips.
40. The method of claim 39, further comprising forming the flexible
film into the flexible package such that one of the intermittent
thermoplastic elastomer strips faces another of the intermittent
thermoplastic elastomer strips to form the reclosable fastener.
41. The method of claim 39, wherein a percent solids of the
thermoplastic elastomer containing solution is less than the
percent solids of the polyolefin solution so that the dried
thermoplastic elastomer strip has a smaller thickness than the
dried adjacent polyolefin strip.
42. The method of claim 41, wherein the thermoplastic elastomer
containing solution has a percent solids ranging from about 25 to
about 45 percent.
43. The method of claim 42, wherein the polyolefin solution has a
percent solids ranging from about 45 to about 65 percent.
44. The method of claim 29, wherein the non-adhesive layer is
applied to the outer surface of the cohesive layer.
45. The method of claim 29, wherein the non-adhesive layer is
applied to the flexible film.
46. A method of forming a flexible package having a reclosable
fastener, the method comprising: moving a flexible film
longitudinally in a machine direction; applying first and second
strips of a thermoplastic elastomer containing solution
intermittently to the flexible sheet and transverse to the machine
direction, the first and second strips being spaced a first gap
along the machine direction; applying a third strip of the
thermoplastic elastomer containing solution intermittently to the
flexible sheet and parallel to one of the first and second strips;
and drying the thermoplastic elastomer strips to form the
reclosable fastener.
47. The method of claim 46, wherein the thermoplastic elastomer
containing solution includes about 25 to about 45 percent solids
solution of a styrenic block copolymer and a secondary resin in an
organic solvent.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit of U.S. Provisional
Application No. 61/093,901, filed Sep. 3, 2008, and U.S.
Provisional Application No. 61/052,021, filed May 9, 2008, which
are both hereby incorporated herein by reference in their
entirety.
FIELD
[0002] This disclosure relates generally to reclosable fasteners
for flexible packages and, in particular, to cohesive-based
reclosable fasteners for flexible packages.
BACKGROUND
[0003] Several types of closures or fasteners are available for
reclosing a previously opened flexible package. For example, it is
common to use mechanical reclosable fasteners, such as slider
zippers, clips, tabs, interlocking strips, and the like. These
mechanical closures can be bulky, complexly shaped structures that
require separate molding and fabrication steps prior to being
joined to the flexible film used to form the package. As the
closure itself can be bulky, film rolls incorporating such
structures can be difficult to handle. While mechanical closures
can be applied in form-fill-seal operations, it often requires
complex manufacturing steps to apply, interconnect, and align the
mechanical fastening features of each structure. Therefore,
mechanical reclosable fasteners often add undue complexity, cost,
and expense into the flexible packaging manufacture.
[0004] Adhesive-based reclosable fasteners can be an alternative to
the mechanical fastener, but adhesive-based fasteners present
separate challenges in both manufacturing and forming a
reclosable-type fastener. For example, pressure-sensitive adhesives
(PSA) have been used to form resealable fasteners; however, common
PSA reclosable fasteners have the shortcoming that these types of
adhesives generally have high tack levels. Tack is a property of an
adhesive material that generally enables the material to form a
bond with the surface of another material upon brief or light
pressure. Tack is often considered as a quick stick, an initial
adhesion, or a quick grab characteristic of a material. PSA
materials generally result in a less-desired reclosable fastener
because the adhesive quickly adheres to most surfaces to which it
comes into contact with. As a result, the PSA fastener can adhere
to machine components during package formation, unintended portions
of the packaging film, and even the product (or crumbs thereof)
contained in the package.
[0005] During forming of flexible packaging using PSA, the adhesive
may come into contact with machine components, such as rollers,
cutting blades, folding devices, and the like. Due to the high tack
level of the PSA, contact with these machine parts may result in
transfer or picking of the PSA to these machine components. The
transferred adhesive can then re-transfer from the machine
component to other undesired portions of the packaging film, which
can in some cases result in web tracking problems and other
undesired shortcomings.
[0006] In existing packaging formation machines, the film is often
wound up into large rolls of several hundred or several thousand
yards of material, sometimes called jumbo rolls or jumbos. In these
wound jumbo rolls, the high tack levels of PSAs can result in
adjacently wound film layers sticking to each other, commonly known
in the industry as "blocking." A blocked jumbo roll is difficult
and sometime impossible to unwind, which typically renders the
blocked roll unusable.
[0007] Once formed into the package, the reclosable fasteners using
PSA may also present problems to the consumer using the package. If
the package is used to contain a crumbly or shredded product (i.e.,
shredded cheese and the like), the crumbs or shreds may also stick
to the PSA, which reduces the effectiveness of the adhesive to form
a sufficient closure. An adhesive-based closure that is
sufficiently fouled with product will generally not form an
adequate closure seal because the adhesive is sticking to the
crumbs and not the other side of the package.
[0008] Thermoplastic elastomers (TPE), which are sometimes called
thermoplastic rubber, are another type of adhesive that has been
investigated as a reclosable fastener. Some types of TPE copolymers
(especially certain styrenic block polymers) demonstrate high
cohesive properties, but low tack levels that can be effective at
forming reclosable fasteners; however, such TPEs tend to have
undesirably high cohesive properties that render them difficult for
use as a reclosable fastener in flexible packaging applications
because the TPE can delaminate from the film substrate rather than
peel at the cohesive interface. TPEs also have the shortcoming that
these materials are thermoplastic and, therefore, generally limited
to processing methods using heat (i.e., hot melt extrusion
coating). When processing TPE using heat as a hot melt adhesive,
the material is generally extrusion coated on the web in a machine
direction and in a continuous fashion, which renders the
application method unsuitable for use on some exiting packaging
equipment where the closure needs to be added in a cross-web
direction or transverse to the machine direction. Hot melt
adhesives generally can not be intermittently applied as a strip in
the cross-web direction in an efficient or cost effective
manner.
[0009] Dissolving the TPEs in solvents so that the material may be
printed in a cross-web direction also results in shortcomings when
the packaging material will be used to form food products. In some
cases, organic solvents suitable for use as a carrier with TPE's
may not be acceptable for contact with food items. Dissolving TPEs
in an aqueous carrier can be difficult and presents further
problems in drying the coated product and removing the water
carrier. However, in some cases, even the lower tack levels of the
TPE fastener can result in processing problems on packaging
equipment, such as transfer to machine components and material
blocking as described above with PSA closures.
SUMMARY
[0010] A cohesive-based reclosable fastener and a flexible package
utilizing the cohesive-based reclosable fastener are disclosed. In
one embodiment, the flexible package may include front and back
flexible panels joined together to form a cavity therebetween for
containing an item, such as a food item or other comestible, for
example. Preferably, the cohesive-based reclosable fastener extends
between side edges of the front and back flexible panels about an
opening of the package and is configured to permit the package to
be repeatedly opened and resealed.
[0011] In one aspect, the cohesive-based reclosable fastener may be
supplied in the form of a thermoplastic elastomer (TPE) diluted
with a secondary or diluting compatible resin, such as for example
an ethylene vinyl acetate copolymer (EVA) having a melt flow index
of about 600 or above, dissolved in an organic solvent (or a
mixture of organic solvents). In some cases, TPE, by itself,
generally does not form a suitable reclosable fastener for flexible
packages that can be easily and repeatedly opened and reclosed
because it has too high of a cohesive bond strength, which will not
be peelable or tend to delaminate from the film forming the
flexible substrate of the package before peeling apart at a
cohesive interface. However, by diluting the TPE with effective,
but small amounts of the secondary or diluting resin, such as the
EVA copolymer resin, a desired cohesive peel strength can be
obtained that is suitable for use in flexible packaging
application.
[0012] In one approach, stable solutions of TPE and the secondary
resin of EVA have a sufficiently low viscosity (i.e., about 50 to
about 1200 centipoise at about 23.degree. C.) and high solids
content (i.e., about 20 to about 60 percent) so that they may be
printed or roll coated. Suitable solvents include ethyl acetate,
normal propyl acetate, isopropyl acetate, methyl ethyl ketone,
methyl isobutyl ketone, ethyl alcohol, normal propyl alcohol,
propylene glycol, normal propyl ether, butyl acetate, toluene,
xylene, cyclohexane, cyclohexanol and mixtures thereof. The TPE
solution may be pattern-applied to a flexible film via a
flexographic or rotogravure printing process and subsequently dried
to remove the solvent.
[0013] The pattern-applied cohesive polymer coating may be
configured and registered such that opposing cohesive layers are
disposed on the front and back panels of the package. The
cohesive-based reclosable fastener generally has a configuration
effective so that the fastener can be repeatedly opened and closed
without substantially delaminating, picking, or transferring from
the front and back panels forming the package. In one aspect, such
configuration may be achieved by the cohesive layers having an
enhanced cohesive bond strength to form a seal as the opposing
cohesive layers are engaged together, but also exhibit a greater
bond strength to the front and back panels than the cohesive peel
force needed to open the reclosable fastener.
[0014] In another aspect, the cohesive-based reclosable fastener
may also be configured to enhance adhesion of the fastener to
desired surfaces and at the same time to minimize and, preferably,
to eliminate adhesion and/or transfer of the cohesive fastener to
undesired surfaces. By one approach, the cohesive-based reclosable
fastener may have a relatively low tack level to generally minimize
adhesion to undesired surfaces and, at the same time, also have the
enhanced cohesive bond strength to form the reclosable seal and
still have a relatively high bond strength to the front and back
panels. In one particular form, the cohesive-based reclosable
fastener includes a solvent-based thermoplastic elastomer (TPE)
such as a styrenic block copolymer diluted with a secondary resin
that exhibits low tack and good cohesive bond strength, but a
relatively higher bond strength to the front and back panels than
its cohesive bond strength. To this end, the cohesive-based
reclosable fastener may include a blend of a styrenic block
copolymer and a secondary polymer such as ethylene vinyl acetate.
By one approach, the fastener solution includes a major amount of
the TPE and a minor amount of the EVA.
[0015] In an alternative form, the cohesive-based reclosable
fastener may include a solvent-based cohesive layer of a TPE
material and a secondary resin that has an exposed cohesive surface
in combination with one or more non-adhesive spacer layers adjacent
to the cohesive layer. In this form, an outer surface of the
non-adhesive spacer layer may be configured to protrude outwardly
beyond the cohesive surface of the cohesive layer so that it is
recessed inwardly from the non-adhesive spacer layer outer surface.
Such configuration of the cohesive-based reclosable fastener
generally forms a gap between the cohesive surface and outer
surface of the non-adhesive layer that is effective to allow the
fastener to form bonds to desired surfaces (such as when the
fastener is squeezed closed) and also minimize and, preferably,
eliminate bonds to undesired surfaces (such as when the spacer
layers inhibit contact with the cohesive layer as described in more
detail below).
[0016] For example, the non-adhesive spacer layer generally
functions to limit the contact of the cohesive layer with adjacent
surfaces (such as equipment parts or adjacent package panels) by
maintaining the gap between the cohesive surface and the adjacent
surface because the adjacent surface will first contact the outer
surface of the spacer layer rather than the cohesive surface. To
close the fastener or otherwise engage the cohesive layer, the
adjacent surface will have to span the gap formed by the recessed
cohesive layer. As the substrate film as well as the fastener
materials are typically flexible, the package may be closed by
flexing the package film to traverse the gap to form a bond with a
facing cohesive surface of a matching closure on the opposite panel
of a package. Such engagement may occur when a user pressed
together or squeezes the film with finger pressure or the like.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a perspective view of an exemplary package having
a cohesive-based reclosable fastener thereon illustrated in an open
condition;
[0018] FIG. 2 is a perspective view of the exemplary package of
FIG. 1 illustrated in a closed condition;
[0019] FIG. 3 is a cross-sectional view of an exemplary
cohesive-based reclosable fastener;
[0020] FIG. 4 is a cross-sectional view of another example of a
cohesive-based reclosable fastener illustrated in an open
condition;
[0021] FIG. 5 is a cross-sectional view of the cohesive-based
reclosable fastener of FIG. 4 illustrated in a closed
condition;
[0022] FIG. 6 is a cross-sectional view of another example of a
cohesive-based reclosable fastener illustrated in a partially
closed or unsealed condition;
[0023] FIG. 7 is a cross-sectional view of the cohesive-based
reclosable fastener of FIG. 6 illustrated in a closed or sealed
condition;
[0024] FIG. 8 is a cross-sectional view of another example of a
cohesive-based reclosable fastener;
[0025] FIG. 9 is a schematical view of an exemplary method of
forming a flexible package having a cohesive-based reclosable
fastener thereon;
[0026] FIG. 10 is a cross-sectional view of an exemplary
arrangement of a flexible package showing a cohesive-based
reclosable fastener relative to an adjacent, exemplary machine
component;
[0027] FIG. 11 is a partial, cross-sectional view of an exemplary
film substrate roll showing a cohesive-based reclosable fastener
relative to adjacent film substrate layers in a wound film
roll;
[0028] FIG. 12 is an exemplary process to apply the cohesive based
reclosable fastener to a film substrate;
[0029] FIG. 13 is an exemplary process to form a flexible package
using a cohesive-based reclosable fastener;
[0030] FIG. 14 is a cross-sectional view of another exemplary
cohesive based reclosable fastener.
DETAILED DESCRIPTION OF THE DRAWINGS
[0031] A package 10 having a cohesive-based reclosable fastener 12
is disclosed herein and is generally illustrated in FIGS. 1 to 8.
FIG. 1 generally illustrates an open package 10, and FIG. 2
generally illustrates a sealed or closed package 10. In one
exemplary form, the package 10 is formed from flexible sheet
material or film 14 (sometimes referred herein as a substrate or
film substrate) into opposed front and back flexible panels 16 and
18, respectively. In this exemplary form, the package 10 may also
include a dead fold 20 along a bottom edge 22 thereof and
transverse or side seals 24 along side edges 26 thereof so that the
package 10 forms a cavity 28 between the front panel 16 and back
panel 18 for containing an item, such as a food item, comestible,
or other material. It will be appreciated that the form of package
10 is only an example of but one type of a package suitable for use
with the cohesive-based reclosable fastener 12, and other shapes,
configurations, materials, and container/package types may also be
combined with the cohesive-based reclosable fastener 12. The
package 10 may further include other folds, seals, gussets, and/or
flaps as generally needed for a particular application. Optionally,
the package 10 may also include peel seals 11 either above or below
the reclosable fastener 12 as generally provided in application
Ser. No. 11/267,174, which is hereby incorporated herein by
reference in its entirety.
[0032] In one aspect, the cohesive-based reclosable fastener 12 and
package 10 are generally constructed or have a composition to
minimize the adhesion of the fastener 12 to undesired surfaces and
still function at the same time as an effective reclosable
fastener. That is, the fastener 12 can be opened and closed
multiple times to seal the contents in the cavity 28 during use by
a consumer, but at the same time not delaminate from the film
substrate forming the front and back panels 16 and 16. To this end,
the cohesive-based reclosable fastener 12 generally includes an
adhesive with relatively low tack levels to minimize adhesion to
the unwanted surfaces, but has a selected bonding or opening peel
strength sufficient to enable sealing or reclosure of the package
10 and also enable unbending to allow opening and/or re-opening of
the package. At the same time, the fastener 12 has a strong bond to
the film substrate. By one approach, the fastener may include a
blend of styrenic block copolymers and an ethylene vinyl acetate
copolymer.
[0033] As generally understood, a cohesive-based material typically
adheres more readily to like materials rather than to non-like
materials (that is, self-adhesion). Suitable cohesive materials
used herein generally exhibit a relatively low tack to undesired
surfaces, a good bond strength to desired surfaces (such as no
delaminating from the flexible front and back panels), and
relatively good cohesive or self adhesion bond strength to hold a
flexible package or pouch closed, but still openable or peelable by
hand. It will be appreciated that the selected cohesive-based
materials used herein may, in some cases, exhibit properties of a
pressure sensitive adhesive in that a bond may be formed with the
application of pressure rather than through the application of
heat, solvent, radiation, or the like. The selected cohesive-based
materials also permit debonding or peeling from such like materials
so that the cohesive layers may be repeatedly peeled apart without
substantial damage to the cohesive material and/or any underlying
substrate. When the cohesive material is debonded or peeled apart,
the selected cohesive materials has sufficient internal integrity
and generally peels apart at a cohesive bonding interface
substantially cleanly without substantial material picking,
stringiness, delamination from the substrate, and/or other
substantial disfigurations of the material (i.e., globbing,
pilling, etc.).
[0034] As further discussed below, the cohesive-based material
include blends of a major amount of a thermoplastic elastomer
diluted with minor amounts of a secondary or diluent resin, such as
a relatively low molecular weight (i.e., melt index of about 600 or
greater) ethylene vinyl acetate copolymer (EVA). Diluting the TPE
with an EVA copolymer or the like having a melt index of about 600
or greater, forms an effective reclosable fastener that can still
form an adequate bond with the flexible film forming the front and
back panels. Other diluents are also expected to be functional so
long as they are dissolvable in the target solvent and miscible
with the TPE to form a stable dispersion or solution to be roll
coated or printed.
[0035] In another aspect, the package 10 and fastener formulation
12 are also constructed so that the bond or peel strength of the
cohesive-based reclosable fastener 12 to the package film substrate
14, 16, and 18 is generally greater than the opening peel strength
between the cohesive layers of the fastener 12 itself (layers 32
and 34). In this manner, the reclosable fastener 12 generally
remains adhered to the film substrate 14 and does not substantially
pick, string, or delaminate from the substrate 14, 16, 18 when the
package 10 is opened by a consumer as the fastener 12 is peeled
open. It is believed that the blend of TPE and diluent together
with the construction of the film substrate is effective to form
the desired bonding and peel strengths.
[0036] Referring to FIG. 3, one form of the reclosable fastener 12
is illustrated that includes opposing cohesive layers 30 and 32
with one of the layers disposed on the front panel 16 and the other
layer disposed on the back panel 18. The fastener layers 30 and 32
are generally aligned with each other such that facing outer
surfaces 34 and 36 of each fastener layer 30 and 32, respectively,
oppose each other and are positioned to substantially contact each
other in a closed or sealed condition as the cohesive layers are
engaged together.
[0037] Preferably, the opposing cohesive layers 30 and 32 are each
supplied in the form of a solution consisting of a thermoplastic
elastomer (TPE) diluted with an ethylene vinyl acetate copolymer
(EVA) in an organic solvent or mixture of organic solvents. As
further described below, the use of a solvent-based solution is
advantageous because it permits roll-coating of a dissolved TPE
into intermittent and transverse strips via a web printing or
coating of the cohesive layers 30 and 32 on the film substrate 14
in a manner that simplifies formation of the package 10 in
traditional form, fill, and seal (FFS) machines. As also described
more below, such transverse and intermediate roll-coating or
printing generally can not be achieved using the more traditional
hot melt extrusion coating processes.
[0038] In one form, the fastener includes a major amount of the
thermoplastic elastomer, which may be a styrenic block copolymer
including TPEs such as Kraton.RTM. D SIS block copolymers based on
styrene and isoprene, Kraton.RTM. D SBS block copolymers based on
styrene and butadiene, Kraton.RTM. G SEBS block copolymers with a
hydrogenated midblock of styrene-ethylene/butylenes-styrene, or
Kraton.RTM. SEPS block copolymers with a hydrogenated midblock of
styrene-ethylene/propylene-styrene, or mixtures thereof. In some
cases, additional additives such as plasticizers, fillers,
antioxidants, or other polymers may be necessary in the formulation
of the TPE compound in order to tailor the processing and
performance attributes of the coating.
[0039] By one approach, the fastener may also include a minor
amount of the ethylene vinyl acetate copolymer used to dilute the
TPE. As mentioned, without the use of the EVA, the fastener
generally does not function as a reclosable fastener because the
self-adhesion of the TPE alone is greater that about 700 grams per
inch and, in some cases, even greater than about 1500 grams per
inch, which is undesired for forming a reclosable fastener on
flexible substrates because it tends to delaminate before peeling
apart at the cohesive interface. By one approach, the EVA is a
random copolymer that generally has a melt flow index of about 600
or greater and about 19 percent vinyl acetate and about 81 percent
ethylene. EVA with less vinyl acetate and/or a melt flow index less
than about 500 did not form a stable solution in toluene.
[0040] By one approach, a suitable blend of the fastener includes
may range from about 7 to about 9 parts of the TPE and about 0.5 to
about 2 parts of the EVA, and in a preferred approach, about 8
parts of the TPE and about 1 part of the EVA. However, it is
expected that the EVA diluent may range from about 5 to about 50
percent of the solution. One form of the solution is about 20 to
about 60 percent solids (polymer content) in a compatible solvent
such as methyl ethyl ketone, cyclohexane or toluene, having a
viscosity between 50 and 1200 centipoise at about 23.degree. C.,
which is a composition effective so that the solution can be
printed or roll coated to the flexible substrate. When this
solution is coated onto the film substrate 14 and dried to remove
the solvent, the dried TPE layer 30 or 32 has a coating thickness
of about 0.0001 to about 0.0030 inches. Once dried, the TPE layer
may have a residual amount of the solvent carrier of about 50 ppm
or less. However, other thicknesses and coating weights may be
appropriate depending on the particular application. Depending on
the particular product characteristics desired, suitable TPEs or
TPE-based compounds may be obtained from companies such as GLS
Corporation (a Division of Polyone) (McHenry, Ill.), Dow Chemical
(Midland, Mich.), or Kraton Polymers (Houston, Tex.). Other
suppliers may also provide similar products.
[0041] As mentioned above, the cohesive-based reclosable fastener
generally has a cohesive bond strength to permit the opposing
cohesive layers 30 and 32 to be bonded together in order to close
or seal the package 10. For example, a consumer may press the two
opposing layers into engagement to seal or close the package as
illustrated by the arrows 33 in FIG. 3. By one approach, the bond
between cohesive layers 30 and 32 is generally sufficient to seal
the layers 30 and 32 together and, in some cases, form a hermetic
seal. As used herein, hermetic is understood to mean a generally
air tight seal. In one example, the selected TPE forming the
cohesive layers 30 and 32 may exhibit a cohesive or peel bond
strength of about 100 to about 700 g/inch, and in some cases,
between about 100 to about 400 g/inch as measured by the ASTM peel
test D 3395; however, the reclosable fastener may have other peel
strength values dependent on the particular application or
particular measurement test. Cohesive peel strengths greater than
this level are generally too high when used with flexible packages
to be useful for a peelable and resealable package.
[0042] The cohesive-based materials also preferably have a
relatively low tack level that enables the fastener to minimize
and, preferably, limit the adhesion of the fastener 12 to unwanted
materials and surfaces, such as food particles, forming equipment
surfaces, rollers, and the like. By one approach, the selected TPE
may have a tack level to undesired surfaces of not exceeding about
5 psi when preloaded with about 4.5 pounds and generally not
exceeding about 15 psi when preloaded with about 10 pounds using
the ASTM probe tack test D 2979; however, the tack level may also
vary depending on the particular TPE and application thereof and
measurement test used.
[0043] Even with such relatively low tack levels to undesired
surfaces, the cohesive layers 30 and 32 still form a sufficiently
strong bond with the film substrate forming the front and back
panels 16 and 18 so that the cohesive layers 30 and 32 are not
substantially delaminated therefrom when the package 10 is opened.
By one approach, the bonding strength of the cohesive layers 30 and
32 to the film substrate at an interface 38 thereof is generally
greater than the peel strength of the cohesive material itself. For
example, the peel strength of the selected cohesive material to the
film substrate forming the front and back panels is generally
greater than about 700 g/inch, preferably, greater than about 1000
g/inch and, more preferably, greater than about 1200 g/inch.
However, the peel strength may also vary depending on the film
substrate 14, the TPE, and other factors.
[0044] It is anticipated that the increased bond strength of the
cohesive materials to the film substrate may be achieved through
enhanced interfacial, mechanical or chemical bonding of the
cohesive material to the particular substrate, increased surface
energy of the substrate obtained from a primer coat, surface
treating, and/or combinations of the above. For example, surface
treatments may be used to increase the surface energy (such as
corona treating, plasma treating, flame treating, and the like) or
chemical coatings, such as primers or adhesion promoters may also
be used. These primers may be based on acrylates, polyesters,
vinyls, and alcohols to name but a few. One example of such a
primer coating, described in U.S. Pat. No. 4,493,872 A is a
copolyester comprised of isophthalic acid and at least one
aliphatic dicarboxylic acid, at least one sulfomonomer and an
alkylene glycol. If corona treating, ideally the surface energy
after treatment should be greater than about 40 dynes.
[0045] In addition, it is further anticipated that enhanced
interfacial, mechanical, or chemical bonding of the cohesive
materials 30 and 32 to the substrate 14 may be enhanced through
particular constructions of the substrate materials 14 to increase
bonding surface energy. By one approach, the substrate 14 may be a
single layer or a multi-layer film, and it is preferred that an
innermost layer of the substrate film 14 forming the front and back
panels 16 and 18 may be composed of ethylene vinyl acetate (EVA)
and, more preferably, an EVA having low concentrations of
additives, such as slip or antiblock (commonly added to packaging
film in order to obtain a coefficient of friction suitable to
process the film on form, fill, and seal machines). It is believed
that such additives may include amounts of fatty acid amides, and
it has been discovered that such compounds can affect the bond
strength of cohesive materials to the film.
[0046] By one approach, therefore, the film substrate 14 may have
less than about 700 ppm of fatty acid amides throughout the
innermost layer or, in some cases, throughout the entire substrate
14. While not wishing to be limited by theory, it is believed that
fatty acid amides, which are low molecular weight components, can
migrate or bloom to the surface of the film affecting the strength
of the bond between the film's surface and the cohesive materials.
While corona treating or flame treating may initially burn off any
fatty acid amides on the surface of the film resulting in an
initial good bond strength of the TPE, over time additional fatty
acid amides can migrate or bloom to the film surface, which results
in a reduced bond strength over an extended shelf life. As a
result, it is desired to reduce the fatty acid amide content in the
film (either the inner most layers or the entire film substrate) to
levels below about 700 ppm, which provides for both good initial
bond strength and good long term bond strength because there are
such small amounts of these impurities to bloom to the film surface
over time. Alternatively, such film substrate formulation may also
be combined with use of other surface treatments (corona treating,
plasma treating, flame treating, and the like) or other coatings as
needed for a particular application.
[0047] In yet another aspect, it is anticipated that the enhanced
interfacial, mechanical, or chemical bonding of the cohesive layers
to the flexible film substrate may also be enhanced by including
fillers (such as inorganic materials, minerals, oxides, and the
like) into at least the surface layer(s) of the substrate to
enhance the bonding of the TPE fastener 12 to the substrate 14.
Examples of suitable fillers include micro- or nano-sized fillers
of clay, calcium carbonate, montmorillonite, dolomite,
microcrystalline silica, talc, mica, oxides (silicon oxides,
aluminum oxides, and the like), other additives, and/or
combinations thereof. While not wishing to be limited by theory, it
is believed that such additives may increase the bond strength
between the coating and substrate in at least two ways. First, on a
microscopic level these fillers create a rough surface, increasing
the available contact area between the substrate and the coating,
thereby providing more sites for chemical and/or mechanical bonding
to occur. Secondly, the filler itself, if present at the surface,
may increase the surface energy, thereby promoting a stronger bond
between the coating and the substrate. By one approach,
approximately about 0.5 to about 10 weight percent of the filler in
the film (preferably, montmorillonite) is expected to have a
beneficial impact on bond strength.
[0048] By one approach, suitable flexible films forming the front
and back panels 16 and 18 may be a polyethylene based film about 2
to about 5 mils thick and, in some cases, about 3 mils thick.
Turning to FIG. 14 for a moment, one approach of the flexible film
16 or 18 forming the front and back panels is shown as a
multi-layer, coextruded blown film including a structural base of
one or more layers (two are shown) of a high density polyethylene
702 (HDPE) and an outer or adhesive receiving layer of an EVA heat
seal layer 704 filled with the filler 706. By one approach, the
outer layer may include blends of EVA, linear low density
polyethylene, and the filler. For example, the extruded EVA layer
may include about 60 to about 80 percent EVA, about 5 to about 20
percent polyethylene, and about 3 to about 10 percent of the
filler. With this approach, the cohesive fastener 12 is applied to
the outer EVA heat seal layer 704, which forms the inner surface of
the flexible package 10. By another approach, the multi-layered
film may include multiple layers such that about two-thirds of the
film is about high density polyethylene and about one-third of the
film is organoclay filled EVA.
[0049] As shown in FIG. 14, the filler 706 is generally exaggerated
in size for illustrative purposes, but is expected to be uniformly
dispersed throughout the outer EVA layer 704, and it is expected
that at least some of the filler 708, for example, may have at
least a portion thereof exposed or protruding slightly at an outer
surface 710 of the EVA layer 704. Alternatively, the filler may not
be exposed at the surface 708, but it may create a rougher outer
surface. While not wishing to be limited by theory, the filler 708
at the surface combined with corona treatment may aid in the
bonding of the fastener to the film substrate, which may provide an
effective bond to the film that is greater than the cohesive peel
strength between the two cohesive layers 32 and 34. In generally,
when the cohesive peel force was less than approximately 600 to
about 700 grams per inch, no delamination occurred during repeated
peel/reseal cycles.
[0050] With the cohesive based fastener and film substrates
described herein, an adhesive based reclosable fastener can be
repeatedly opened and closed without delamination from the flexible
backing, can be achieved in a fastener that is stable over time,
and produces generally repeatable results even after fouling or
contamination with product, such as food crumbs. Even if the
cohesive based fastener is fouled with food crumbs or edible oils,
the cohesive based fasteners herein do not exhibit an unusable
drop-off in cohesive properties.
[0051] By one approach, the cohesive fasteners herein maintain a
cohesive or self-adhesion peel strength when contaminated with
product, food crumbs, oils, and the like between about 100 to about
650 g/inch, and exhibit a residual adhesion or residual cohesion
after fouling or contamination between about 25 to about 100
percent of the cohesion levels prior to contamination. As used
herein, adhesion remaining or residual cohesion is a measurement of
the peel strength when fouled or contaminated relative to the peel
strength of a clean or uncontaminated fastener exhibited as a
percentage. As explained further in the Examples, the cohesive
based fasteners herein exhibited a residual cohesion of about 25
percent and about 100 percent, when contaminated with Triscuit and
Wheat Thin crumbs, respectively. A comparable pressure-sensitive
adhesive exhibited residual adhesive values of about 1.2 and about
8 percent when contaminated with similar levels of Triscuit and
Wheat Thin crumbs, respectively.
[0052] Turning back to FIGS. 4 and 5, an alternative form of the
reclosable fastener 112 is illustrated that combines cohesive
layers 30 and 32 together with an adjacent non-adhesive or buffer
spacer layer 140. The adjacent spacer layer 140 is positioned so
that it generally protrudes outwardly beyond the outer surfaces 34
and 36 of the cohesive layers 30 and 32 so that the cohesive layers
30 and 32 are generally recessed from an outer surface 142 of the
spacer layer 140.
[0053] The non-adhesive spacer layer 140 may be formed from a
material that forms a non-sticky or non-adhesive portion of the
package 10 such as a material that does not form a bond with other
materials. By one approach, the non-adhesive spacer layer 140 may
be a polyolefin, a polyamide, or other non-adhesive material. For
example, the spacer layer 140 may include polyester, polyethylene,
polypropylene, polybutylene, ethylene vinyl acetate, nylon,
polyethylene terephthalate, polyvinyl chloride, ethylene vinyl
alcohol, polyvinylidene chloride, polyvinyl alcohol, polystyrene,
and mixtures thereof. In one embodiment, the spacer layer 140 is a
polyolefin. Polyolefins are particularly suitable for use as the
spacer layer materials because they are generally non-adhesive when
dried and they generally lend themselves well to forming aqueous or
solvent dispersions which can be easily pattern coated via
flexographic or rotogravure processes. Preferably, the non-adhesive
spacer layer 140 is supplied from a solvent or aqueous based
dispersion of the non-adhesive material dissolved or dispersed in
the solvent. The dispersion is then intermittently coated or
printed adjacent to the cohesive layers 32. In general, the
thickness of the dried coated layers may range from about 0.1 mils
to about 2 mils.
[0054] As illustrated in FIG. 4, the non-adhesive spacer layer 140
preferably includes a pair of non-adhesive spacer layers 144 and
146 positioned adjacent lateral sides 148 or 150 of each cohesive
layer 30 and 32. In the particular embodiment of FIGS. 4 and 5, the
spacer layers 144 and 146 are positioned on the cohesive layer 32
and spaced at distal ends of the layers 30 and 32 generally
adjacent with the lateral side edges 148 and 150 thereof.
[0055] Preferably, the non-adhesive spacer layer 140 forms a gap
152 between the outer surface 142 of the spacer layer 140 and the
cohesive surface 34 or 36 of the cohesive material. By one
approach, the gap is about 2.5 to about 50 microns. Turning to
FIGS. 10 and 11 for a moment, the gap 152 or otherwise recessed
cohesive surfaces 34 or 36 enables the fastener 112 to limit the
contact of the cohesive layers 30 or 32 with unwanted surfaces. As
illustrated in FIG. 10, the spacer layers 140 and gap 152 tends to
maintain a space between the cohesive layer 32 and an exemplary
machine part, which is illustrated as an exemplary machine roller
154 (but could be any number of machine components, such as
rollers, bars, knives, guides, filling tubes to suggest but a few).
The recession of the cohesive layer 30 or 32 by the spacer layers
140 reduces and, preferably, eliminates the tendency of the
cohesive material to engage with and transfer or pick off adhesive
to the machine part because the cohesive layer 30 or 32 is
generally spaced from these unwanted surfaces due to the spacer
layer 140 contacting the adjacent surface (i.e., machine roller
154) before the cohesive layer 30 or 32 and recession of the
cohesive layer therefrom. As generally illustrated in FIG. 11, the
spacer layer 140 and gap 152 also tends to reduce and, preferably,
eliminate the tendency of the fastener 112 to adhere to other film
layers 14 when the film substrate 14 is wound up in a roll or
jumbo. The formed gap 152 may keep the cohesive layer 32 spaced
from adjacent wound-film layers 14, which generally reduces and,
preferably, eliminates the tendency of the wound roll to block
because, again, the cohesive layer 32 is spaced from the backside
of an adjacent film layer 14 because the spacer 140 engages the
adjacent film layer 14 before the cohesive layer 30 or 32.
[0056] Turning back to FIG. 5, to close the package 10, a user's
fingers (or a machine closing operation during package filing
operations) squeezes the front and back panels 16 and 18 between
the spacer layers 140 to deflect the panels 16 and 18 inwardly
through the gap 152 to intentionally engage the opposing cohesive
layers 30 and 32 to form a cohesive bond therebetween to sealably
close the package 10. To open the package 10, the user peels back
package tabs 156 positioned above the cohesive fastener 112 in
opposite directions 157 to peel the cohesive layer 30 from the
cohesive layer 32. By one approach, the cohesive layers 30 and 32
are configured to be closed and re-opened multiple times and, in
some cases, the cohesive layers 30 and 32 preferably have
sufficient structural and bond integrity to be closed and opened
about 5 to about 10 times; however, particular cohesive layers and
packages can be configured to be opened and closed any number of
times depending on the particular configuration, coating weight,
and other parameters of the cohesive layers and film substrate.
[0057] Referring to FIGS. 6, 7, and 8, alternative embodiments of
the reclosable fastener are illustrated. In FIGS. 6 and 7, a
reclosable fastener 212 is illustrated where the spacer layers 240
are adjacent the cohesive layers 30 and 32 and disposed on the film
substrate 16 and 18. In FIG. 8, the spacer layers 240 are adjacent
the cohesive layers 30 and 32, but spaced therefrom as the spacer
layers 140 do not necessarily need to contact or engage the
cohesive layers 30 or 32 and, in some cases, variability in
manufacturing may result in a space between the layers 140 and
layers 30 and 32.
[0058] In these alternative embodiments, a similar wet coating
weight of both the cohesive layer 30 or 32 and the spacer layer 140
can be applied to the film substrate 14, but the gap 152 and
recession of the cohesive surfaces 34 and 36 can be formed by
varying the percent solids of the cohesive solvent solution and the
spacer layer solvent or aqueous solution used to apply the wet
coating. For example, the cohesive material solution may have a
lower percent solids than the spacer layer solution so that, when
dried and the solvent is substantially removed, the cohesive layers
30 and 32 will form a lower dried coating weight or lower
thickness. By one approach, the cohesive material solution may be
about 25 to about 45 percent solids and the spacer layer solvent
solution may be about 45 to about 65 percent polyolefin solids so
that the cohesive layer forms a coating thickness which is
substantially thinner than the spacer layer. For example, the
cohesive layer may be about 10 to about 20 microns in thickness and
the spacer layer may be between about 20 and about 40 microns in
thickness.
[0059] Turning to FIG. 9, an exemplary process to form the
reclosable fastener 12, 112, or 212 is generally illustrated in
schematic form in which an intermittent indexing process is used.
For instance, a supply of the film substrate 14 may be supplied in
a roll 402 and unwound in a machine direction 404. A first
application station 406 intermittently applies a first strip 408 of
the cohesive dispersion in a transverse or cross web direction. The
first application station 406 may include a flexographic
applicator, a gravure applicator, or other suitable applicator to
apply a solvent dispersion intermittently across a moving web. The
web of film 14 is then indexed or unwound a first distance 410 in
the machine direction and the first application station 406 then
applies a second strip 412 of the cohesive dispersion in a
transverse or cross web direction. The web is then indexed or
unwound a second distance 414, which may be shorter than the first
distance 410, where the application station 406 then applies a
third transverse strip 416 again in a transverse or cross web
direction. This application pattern is then repeated between short
and long indexing as the web 14 is continuously unwound from the
roll 402. Alternatively, the web may be indexed a uniform distance
between each application of transverse strips.
[0060] The web having the coatings 408, 412, and 416 thereon is
then dried, cured, or set using a drying oven or other drying
device 420 to remove the solvent carrier to provide a dried
cohesive strip. The film web 14 may also be finished into the
package 10 by cutting 422, folding 424, forming side seals 426, and
filling 428 an item 430 (such as a foodstuff, for example shredded
cheese).
[0061] If the spacer layers 140 are to be utilized, an optional
second application station 432 may be utilized. If used, the
station 432 will apply a wet coating of the spacer layer dispersion
adjacent to the cohesive material dispersion in a similar fashion
either subsequently to, concurrently, with or prior to the cohesive
layer application using a flexographic applicator, a gravure
applicator, or other suitable applicator to apply a solvent
dispersion intermittently across a moving web. Preferably, the
spacer layers are also applied generally parallel to the cohesive
layer.
[0062] Turning to FIGS. 12 and 13, another example of a suitable
process 500 that may be used to form a substrate having the
reclosable fastener 12, 112, and/or 212 thereon is provided. In
this example, a solvent coating, printing, rotogravure, or
flexographic process is provided to apply the cohesive and/or
spacer layers (if used) to the film substrate. It will be
appreciated that other application processes or methods may also be
used as needed for a particular application. By this alternative
approach, the film substrate having the closure thereon is wound up
into a roll that is later transferred to a form, fill, and seal
machine to form the flexible package.
[0063] In this exemplary process 500, a supply of the film
substrate 14 may be provided in a large jumbo or roll 502 of base
film, which may be a single layer or multi-layer film having EVA as
the inner layer 504 to which the adhesives will be applied. The
film is then unwound and directed to a first application station
506 where the cohesive fastening layer can be applied. By one
approach, the first application station 506 may include a cohesive
polymer solvent solution applicator 508, such as an extrusion die,
solution pan, or other supply of solution. For example, the TPE
containing solvent solution may be applied to a first or plate
cylinder 510 that transfers to the solution to a second or offset
cylinder 512 having an image or impression thereon 514 in the
configuration, size, and shape of the cohesive strip to be applied
to the film 14. The second cylinder 512 then transfers the solvent
solution of the cohesive material to the moving film substrate 14
to form a first strip of the TPE containing material 516 on the
web.
[0064] The web 14 then may be directed to a drying oven 520 to dry,
cure, or remove any residual solvent in the applied fastening
layer. After the fastening layer has been dried to the desired
amount, it may be wound up into an intermediate jumbo or roll 522
for storage or transfer to a subsequent package forming station,
such as a form, fill, and seal process as generally illustrated in
FIG. 13.
[0065] If the fastening layer includes the optional buffer or
spacer layers 140 or 240, then the process 500 may also include a
second solution application station 530. The second application 530
station may be similar to the first station 506, but configured to
apply and register the spacer layer 140 adjacent to the cohesive
layer as discussed previously. To this end, the second application
station 530 may be configured so that the spacer layer 140 or 240
is either applied on top of or adjacent to the cohesive layer as
also discussed previously.
[0066] By one approach, the second application station 530 may also
include a solution applicator 532 (solvent or aqueous), a first or
plate cylinder 534, a second or offset cylinder 536 having an image
or impression 538 thereon of the size, shape, and configuration of
the desired spacer layer or layers 140 and/or 240. The second
cylinder 536 then transfers the strip or strips of the spacer layer
solution to the web in the correct orientation and arrangement
relative to the cohesive layer. Both the cohesive and spacer layers
are then fed to the drying oven 520 to remove residual solvents
prior to being wound up in the intermediate jumbo 522.
Alternatively, the second application station 530 may be located
downstream of the oven 520 so that the spacer layers are applied
adjacent to a dried cohesive layer. In this case, the applied
spacer layers will then be fed into a second drying oven similar to
the oven 520.
[0067] Referring now to FIG. 13, an exemplary form, fill, and seal
machine 600 using the intermediate roll 522 prepared from the
process 500 (which may be slit to an appropriate size prior to
process 600) is illustrated to form a sealed package 602. In this
example, a vertical bagger or flow wrapping process is used that
wraps the film 14 around a filling tube 604. A first heat seal
assembly 606 forms a first machine-direction heat seal 607. A
second transverse-direction heat seal assembly 608 with an integral
trim tool then forms second and third transverse-direction heat
seals 609 and 611 such that these heat seals are located on either
side of the cohesive reclose feature 613. As shown in FIG. 12, seal
609 is below the cohesive closure 613, but seal 609 may also be
above or both above and below seal 613. Finally, the integral trim
tool within the transverse-direction heat seal assembly cuts the
film between the cohesive reclose feature 613 and the bottom seal
611 of an adjacent pouch thereby separating the pouch that was just
filled and sealed from the following pouch that is in the process
of being filled. It will be appreciated that the exemplary
processes of FIGS. 9, 12, and 13 are only but one example of
suitable methods of forming and filling the flexible packaging
having the cohesive-based reclosable fastener thereon. Other
formation methods may also be used as needed for a particular
application.
[0068] Advantages and embodiments of the fastener described herein
are further illustrated by the following examples; however, the
particular conditions, processing schemes, materials, and amounts
thereof recited in these examples, as well as other conditions and
details, should not be construed to unduly limit this method. All
percentages are by weight unless otherwise indicated.
EXAMPLES
[0069] A cohesive-based reclosable fastener was prepared and
compared to a standard pressure-sensitive adhesive fastener
(PSA-Control) obtained from a commercial Nabisco Chips Ahoy Snack'n
Seal package using a pressure sensitive adhesive (Fasson, Avery
Dennison Corporation).
[0070] The cohesive-based fastener was prepared using about 8 parts
of a styrenic block copolymer (TPE, LC347-042B, GLS Corporation)
and about 1 part by weight ethylene vinyl acetate (EVA 1980a, AT
Plastics, Edmonton, Alberta, Canada) and dissolving in toluene. The
EVA had about 19 percent vinyl acetate and a melt flow index of
about 600. The blended and diluted solution had about 22 percent
solids and a Brookfield viscosity of about 155 cP at about
21.degree. C. It was applied on a 2.7 mil multi-layer substrate
using two spaced micrometer controlled notch bars. The coated
substrate was dried by making two passes through an oven at about
150.degree. F. (total drying time about 2.5 to about 3 minutes) to
form about a 3 mil dry coating of the cohesive fastener.
[0071] The substrate film (Pliant Corporation) was a multilayer,
co-extruded film having two layers of a high density polyethylene
and one outer layer of an organoclay filed, ethylene vinyl acetate
(EVA) heat seal layer. The outer EVA heat seal layer of the
coextruded film included about 80 percent EVA, about 10 percent
polyethylene, and about 6 percent organoclay filler. The EVA layer
surface was also corona treated to 40 dynes. The cohesive fastener
was applied to the EVA heat seal layer. With this film, the
cohesive based fasteners of this example did not delaminate or peel
from the film backing so that the bond to the film and the EVA heat
seal layer was greater than the cohesive peel strengths as tested
below.
[0072] Both the cohesive-based fastener and the PSA control were
tested for T-peel in an un-contaminated form, contaminated with
Triscuit-Brand Crumbs (Kraft Foods), Wheat Thin Brand Crumbs (Kraft
Foods), and Coffee beans. As shown in Tables 1-3 below, the T-peel
test results (grams per inch at about 12 inch per minute cross head
speed) with and without exposure to food crumbs are shown. Table 3
provides the residual or percent adhesion remaining (residual
cohesion) after contamination, which is a ratio of the contaminated
peel relative to the un-contaminated peel.
[0073] Each of the cohesive based and control samples were
contaminated by covering the adhesive surface completely with the
food crumbs, and then lifting up and gently shaking the sample to
remove any excess crumbs not adhered to the strip. For the Triscuit
and Wheat Thin crumbs, the crumbs were equivalent to the ground
crumbs found at the bottom of a commercial product box. For the
coffee bean sample, whole coffee beans were placed on the sample
and removed. It is believed that oils from the coffee beans
contaminated the sample.
TABLE-US-00001 TABLE 1 PSA Control and Inventive Cohesive Fastener
contaminated with Food Crumbs Triscuit Crumbs Wheat Thin Crumbs
Coffee Beans PSA Control, Cohesive, PSA Control, Cohesive, PSA
Control, Cohesive, Factor g/in g/in g/in g/in g/in g/in
Contaminated 0 281 7 755 151 572 Contaminated 5 24 16 604 138 621
Contaminated 4 137 4 504 186 615 Contaminated 3 82 69 733 186 471
Avg, g/in 3 131 24 649 208 639
TABLE-US-00002 TABLE 2 PSA Control and Inventive Cohesive Fastener
un-contaminated with Food Crumbs Triscuit Crumbs Wheat Thin Crumbs
Coffee Beans PSA Control, Cohesive, PSA Control, Cohesive, PSA
Control, Cohesive, Factor g/in g/in g/in g/in g/in g/in
Un-contaminated 196 165 259 476 271 652 Un-Contaminated 253 414 248
376 183 642 Un-Contaminated 259 563 330 638 271 820 Un-Contaminated
261 595 -- 697 276 715 AVG, g/in 242 524 279 547 250 707
TABLE-US-00003 TABLE 3 Adhesion remaining after contamination with
Food Crumbs Triscuit Crumbs Wheat Thin Crumbs Coffee Beans PSA
Control, Cohesive, PSA Control, Cohesive, PSA Control, Cohesive,
Factor g/in g/in g/in g/in g/in g/in % adhesion 1.2 25 8.6 118.7 83
90.3 remaining
[0074] As shown above, the cohesive fastener was much more
resistant to contamination by food particles then the PSA adhesive.
The cohesive based fastener exhibited a percent adhesive remaining
(i.e., contaminated peel/un-contaminated peel.times.100) of at
least about 25 percent, and in some cases at least about 100
percent. As a result, the cohesive based fastener did not exhibit
any drop off in peel strength and performed just as well
contaminated with food crumbs as it did when un-contaminated. The
PSA fastener exhibited significant drop-off in peel strength when
contaminated.
[0075] For the T-peel tests above, a slip/peel tester (Model
SP-102B-3M90, Instrumentors, Inc., Strongsville, Ohio) was used.
Set-up included using the machine in the T-peel test mode set to
run at about 12 inch per minute speed. Adhesive samples were cut
into strips about 1 inch wide and about 10 inches long, and two
strips were adhered together with adhesive coated sides facing each
other. The adhered sampled were rolled twice up and back (4 times
total) using a 4.5 pound silicone-coated rubber roller
(Chemsultants International Network, HR100, 4.5 pound hand roller).
The Peel test included taking about 5 second average readings with
about 5-8 readings per strip.
Example 2
[0076] The TPE/EVA cohesive-based fastener of Example 1 in a blend
of about 8 parts TPE to 1 part EVA was tested for variation in
T-peel strength over time. Results are shown below in Table 4.
TABLE-US-00004 TABLE 4 T-Peel Aging Results Time 0 Hour 24 Hours 96
Hours 1 Week T-Peel, g/inch 211 231 205 294 282 327 319 316 270 337
327 362 215 307 306 290 200 335 288 249 250 335 319 290 250 333 343
290 130 326 331 317 Average 240 316 305 301
Example 3
[0077] The TPE/EVA blended cohesive-based fastener of Example 1 was
tested for drop-off in peel strength upon multiple peel/re-seal
cycles in rapid succession using the procedures of Example 1. Each
sample was tested consecutively with no waiting between tests
except to reseal and roll the samples. Wait time between tests was
about 2 minutes or less. Results are shown in Table 5 below. As
shown below, the cohesive peel strength maintained about 80 percent
of its peel strength after repeated re-seal attempts from its
highest level.
TABLE-US-00005 TABLE 5 Multiple Peel/Re-seal Results Iteration 1st
2nd 3rd 4th T-Peel, g/in 177 136 120 119 255 247 237 231 283 309
316 249 280 317 339 283 297 330 362 266 323 378 367 293 310 365 340
303 275 382 350 310 Average: 275 308 304 257
Comparative Example 1
[0078] The film substrate of Example 1 was coated in the manner of
Example 1, but with only the TPE (LC 347-042B) in toluene without
the use of a diluent. In this investigation, the initial peel
strength was about 339 grams per inch (on average), but the peel
strength after 24 hours was unacceptably high at about 1,500 gram
per inch (on average). Results are shown below in Table 6.
TABLE-US-00006 TABLE 6 Undiluted TPE Peel Strength Time Initial 24
Hour T-Peel, g/in 344 366 362 279 1510 343 1544 308 1592 357 1528
353 1625 Average 339 1560
Comparative Example 2
[0079] Other diluents were also tried, but did not result in
acceptable products. First, polyvinyl butyral (PVB) (Wacker
Chemical) was blended with the TPE in toluene in a manner similar
to Example 1 at ratios of about 1:1, about 3:1, and about 7:1
(TPE:PVB). The cohesive peel strength was also tested as in Example
1. No sample produced acceptable results as the cohesive peel was
either too high or too low. At a 1:1 ratio, the sample had a low
initial peel at about 23 g/in, which then increased to about 293
g/in after about 24 hours, but then dropped off again to less than
about 100 g/in after about 96 hours. At a 3:1 ratio, the cohesive
peel had an initial self-adhesion of about 294 g/in, which
increased to greater than 1,100 g/in after 24 hours. Lastly, a 7:1
ratio had an initial cohesion of about 394 g/in, which increased to
greater than about 1,700 g/in after 24 hr. Results are provided in
Tables 7, 8, and 9 below. These samples were not acceptable with
either too low or unacceptable high peel.
TABLE-US-00007 TABLE 7 Initial Peel values (TPE and PVB blends)
TPE/PVB ratio 1/1 3/1 7/1 T-Peel, g/inch 25 306 361 23 318 385 16
328 373 21 295 357 31 268 434 24 277 409 297 395 262 438 Average:
23 294 394
TABLE-US-00008 TABLE 8 24 Hour Peel values (TPE and PVB blends)
TPE/PVB ratio 1/1 3/1 7/1 T-Peel, g/inch 269 1227 1696 342 1272
1867 319 1103 1794 237 1083 1703 309 1091 1745 328 657 1777 269 678
1090 272 569 749 Average: 293 1155 1764
TABLE-US-00009 TABLE 9 96 Hour Peel values (TPE and PVB blends)
TPE/PVB ratio 1/1 3/1 7/1 T-Peel, g/in 68 557 Would not peel 90 498
Would not peel 61 443 Would not peel 74 481 Would not peel 86 426
Would not peel 81 377 Would not peel 64 357 Would not peel 79 419
Would not peel Average: 75 445 Would not peel
Comparative Example 3
[0080] Different ethylene vinyl acetate copolymers were also
evaluated for use as the diluent. An EVA diluent with about 18
percent vinyl acetate and a melt flow index of about 150 (EVA
1850A, AT Plastics) was investigated, but would not dissolve in the
toluene or form a stable solution with the TPE. Another EVA having
about 18 percent vinyl acetate and a melt flow index of about 500
(EVA 1880A, AT Plastics) was investigated, but also would not
dissolve in toluene or form a stable solution with TPE.
[0081] It will be understood that various changes in the details,
materials, and arrangements of the package and process of formation
thereof, which have been herein described and illustrated in order
to explain the nature of the described package, may be made by
those skilled in the art within the principle and scope of the
embodied method as expressed in the appended claims.
* * * * *