U.S. patent application number 11/650601 was filed with the patent office on 2007-07-05 for cellulose-based substrates encapsulated with polymeric films and adhesive.
This patent application is currently assigned to Weyerhaeuser Co.. Invention is credited to Terry M. Grant, Brian C. Horsfield, H. Donald JR. Muise, Herbert D. SR. Muise, James F. Tadlock, Bruce A. Thompson, Gerald Wilhite, Richard H. Young.
Application Number | 20070151685 11/650601 |
Document ID | / |
Family ID | 39581824 |
Filed Date | 2007-07-05 |
United States Patent
Application |
20070151685 |
Kind Code |
A1 |
Horsfield; Brian C. ; et
al. |
July 5, 2007 |
Cellulose-based substrates encapsulated with polymeric films and
adhesive
Abstract
A cellulose based substrate (20) generally includes a cellulose
based sheet having a corrugated medium (48) spanning between first
and second linerboards (44 and 46), wherein the corrugated medium
includes at least one sizing agent for moisture wicking resistance.
The cellulose based substrate further includes a polymeric film
(43) encapsulating at least a portion of the cellulose based
sheet.
Inventors: |
Horsfield; Brian C.;
(Federal Way, WA) ; Young; Richard H.; (Maple
Valley, WA) ; Muise; Herbert D. SR.; (Tumwater,
WA) ; Muise; H. Donald JR.; (Tumwater, WA) ;
Wilhite; Gerald; (Bowling Green, KY) ; Grant; Terry
M.; (Auburn, WA) ; Tadlock; James F.;
(Olympia, WA) ; Thompson; Bruce A.; (Federal Way,
WA) |
Correspondence
Address: |
WEYERHAEUSER COMPANY;INTELLECTUAL PROPERTY DEPT., CH 1J27
P.O. BOX 9777
FEDERAL WAY
WA
98063
US
|
Assignee: |
Weyerhaeuser Co.
Federal Way
WA
|
Family ID: |
39581824 |
Appl. No.: |
11/650601 |
Filed: |
January 5, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10879846 |
Jun 29, 2004 |
|
|
|
11650601 |
Jan 5, 2007 |
|
|
|
Current U.S.
Class: |
162/125 ;
162/158; 162/164.3; 428/34.2 |
Current CPC
Class: |
B32B 23/04 20130101;
B65D 5/566 20130101; B32B 3/04 20130101; B32B 2439/62 20130101;
B32B 23/08 20130101; Y10T 428/1303 20150115; B32B 7/12 20130101;
B32B 23/18 20130101; B32B 23/14 20130101; B32B 27/10 20130101; B31B
2105/001 20170801; B32B 3/02 20130101; B32B 29/08 20130101; B32B
3/28 20130101; B32B 2307/734 20130101; B32B 2439/00 20130101 |
Class at
Publication: |
162/125 ;
162/158; 162/164.3; 428/034.2 |
International
Class: |
D21F 11/00 20060101
D21F011/00; B65D 5/56 20060101 B65D005/56; B65D 65/40 20060101
B65D065/40 |
Claims
1. A cellulose based substrate, comprising: (a) a cellulose based
sheet having a corrugated medium spanning between first and second
linerboards, wherein the corrugated medium includes at least one
sizing agent for moisture wicking resistance; and (b) a polymeric
film encapsulating at least a portion of the cellulose based
sheet.
2. The cellulose based substrate of claim 1, wherein the at least
one sizing agent includes alum for sizing the natural resins of the
cellulose.
3. The cellulose based substrate of claim 1, wherein the at least
one sizing agent includes a reactive sizing additive.
4. The cellulose based substrate of claim 1, wherein the at least
one sizing agent is a reactive sizing agent selected from the group
consisting of alkyl ketene dimer, alkenyl ketene dimer emulsion,
alkenyl succinic anhydride (ASA), and any blends thereof.
5. The cellulose based substrate of claim 4, wherein the reactive
sizing agent is present in the corrugated medium in an amount
within the range of about 0.1 to about 4.0 lb/ton.
6. The cellulose based substrate of claim 1, wherein the corrugated
medium further includes a cationic crosslinking-type wet strength
resin.
7. The cellulose based substrate of claim 6, wherein the resin is
selected from the group consisting of urea-formaldehyde
condensation products, melamine-urea-formaldehyde condensation
products, and polyamide-epichlorohydrin reaction products.
8. The cellulose based substrate of claim 1, wherein the corrugated
medium includes about 0 to about 30% virgin cellulosic fiber.
9. The cellulose based substrate of claim 1, wherein the polymeric
film encapsulating at least a portion of the cellulose based sheet
is adhesively bonded to the first and second linerboards.
10. The cellulose based substrate of claim 1, wherein corrugated
medium spanning between first and second linerboards is bonded to
the first and second linerboards using a water-resistant
adhesive.
11. A container, comprising: (a) a cellulose based sheet having a
corrugated medium spanning between first and second linerboards,
wherein the corrugated medium includes at least one sizing agent
for moisture wicking resistance; and (b) a polymeric film
encapsulating at least a portion of the cellulose based sheet.
12. A container, comprising: (a) a cellulose based sheet having a
corrugated medium spanning between first and second linerboards,
wherein the corrugated medium includes a sizing agent for moisture
wicking resistance and a reactive cationic cross-linking type resin
for improved wet strength; and (b) a polymeric film encapsulating
at least a portion of the cellulose based sheet.
13. The container of claim 12, wherein the sizing agent is alum for
sizing the natural resins of the cellulose.
14. The container of claim 12, wherein the sizing agent is a
reactive sizing agent selected from the group consisting of alkyl
ketene dimer, alkenyl ketene dimer emulsion, alkenyl succinic
anhydride (ASA), and any blends thereof.
15. The container of claim 14, wherein the reactive sizing agent is
present in the corrugated medium in an amount in the range of about
0.1 to about 4.0 lb/ton.
16. The container of claim 12, wherein the corrugated medium
includes about 0 to about 30% virgin cellulosic fiber.
17. The container of claim 12, wherein corrugated medium spanning
between first and second linerboards is bonded to the first and
second linerboards using a water-resistant adhesive.
18. The container of claim 12, wherein the polymeric film
encapsulating at least a portion of the cellulose based sheet is
adhesively bonded to the first and second linerboards.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part of co-pending
U.S. patent application Ser. No. 10/879,846, filed on Jun. 29,
2004, the disclosure of which is hereby expressly incorporated by
reference.
TECHNICAL FIELD
[0002] Embodiments of the present disclosure relate generally to
cellulose based substrates encapsulated with polymeric films.
BACKGROUND
[0003] Containers made from fibreboard are used widely in many
industries. For example, fibreboard containers are used to ship
products that are moist or packed in ice such as fresh produce or
fresh seafood. It is known that when such containers take up
moisture, they lose strength. To minimize or avoid this loss of
strength, moisture-resistant shipping containers are required.
[0004] Moisture-resistant containers used to date have commonly
been prepared by saturating container blanks with melted wax after
folding and assembly. Wax-saturated containers cannot be
effectively recycled and must generally be disposed of in a
landfill. In addition, wax adds a significant amount of weight to
the container blank, e.g., the wax can add up to 40% by weight to
the container blank.
[0005] Other methods for imparting moisture resistance to container
blanks have included impregnation with a water-resistant synthetic
resin or coating the blank with a thermoplastic material. In the
latter case, forming water-resistant seals around container blank
peripheral edges and edges associated with slots or cutouts in the
container blank has been an issue. When seals along these edges are
not moisture resistant or fail, moisture can be absorbed by the
container blank with an attendant loss of strength. In addition,
obtaining consistent and reproducible bonding of the thermoplastic
material to the container blank and around edges has been a
challenge.
[0006] Faced with the foregoing, the present inventors developed a
cellulose based substrate encapsulated with a polymeric film that
is recyclable and lighter in weight than previous wax-saturated
containers and does not suffer from inconsistent bonding, sealing,
and conformance of a film to the substrate. The encapsulated
container is generally set forth in co-pending U.S. patent
application Ser. No. 10/879,846, filed on Jun. 29, 2004, from which
priority is claimed in the present application.
[0007] Upon further research, the inventors discovered an
additional problem related to cellulose based substrate
encapsulation. While encapsulated cellulose based containers have
improved moisture resistance, their moisture-resistant
characteristics are compromised if the encapsulating film is not
sealed correctly during manufacture or is subsequently punctured
during manufacture or use. Hence, a problem associated with
encapsulated, corrugated, cellulose based containers is that if the
encapsulating polymeric film allows moisture to enter the
encapsulation, the moisture wicks throughout the container and
renders the container weakened or, worse yet, inoperable.
[0008] Therefore, there exists a need for a moisture-resistant
encapsulated container having improved moisture wicking
resistance.
SUMMARY
[0009] This summary is provided to introduce a selection of
concepts in a simplified form that are further described below in
the detailed description. This summary is not intended to identify
key features of the claimed subject matter, nor is it intended to
be used as an aid in determining the scope of the claimed subject
matter.
[0010] In accordance with one embodiment of the present disclosure,
a cellulose based substrate is provided. The cellulose based
substrate includes a cellulose based sheet having a corrugated
medium spanning between first and second linerboards, wherein the
corrugated medium includes at least one sizing agent for moisture
wicking resistance. The cellulose based substrate further includes
a polymeric film encapsulating at least a portion of the cellulose
based sheet.
[0011] In accordance with another embodiment of the present
disclosure, a container is provided. The container includes a
cellulose based sheet having a corrugated medium spanning between
first and second linerboards, wherein the corrugated medium
includes at least one sizing agent for moisture wicking resistance.
The container further includes a polymeric film encapsulating at
least a portion of the cellulose based sheet.
[0012] In accordance with yet another embodiment of the present
disclosure, a container is provided. The container includes a
cellulose based sheet having a corrugated medium spanning between
first and second linerboards, wherein the corrugated medium
includes a sizing agent for moisture wicking resistance and a
reactive cationic cross-linking type resin for improved wet
strength. The container further includes a polymeric film
encapsulating at least a portion of the cellulose based sheet.
DESCRIPTION OF THE DRAWINGS
[0013] The patent or application file contains at least one
photograph executed in color. Copies of this patent or patent
application publication with color photographs will be provided by
the Office upon request and payment of the necessary fee.
[0014] The foregoing aspects and many of the attendant advantages
of this disclosure will become more readily appreciated by
reference to the following detailed description, when taken in
conjunction with the accompanying drawings, wherein:
[0015] FIG. 1 is a perspective view of one surface of a container
blank encapsulated with a polymeric film in accordance with the
present invention;
[0016] FIG. 2 is a perspective view of a container formed from the
container blank of FIG. 1;
[0017] FIG. 3 is a section taken through line 3-3 of FIG. 1;
[0018] FIG. 4 is a perspective view of one surface of a second
embodiment of a container blank encapsulated with polymeric films
in accordance with the present invention;
[0019] FIG. 5 is a perspective view of a container formed from the
container blank of FIG. 4;
[0020] FIG. 6 is a diagrammatic view of a process for producing a
container blank encapsulated with polymeric films in accordance
with the present invention;
[0021] FIG. 7 is a diagrammatic view of a second embodiment of a
process for producing a container blank encapsulated with polymeric
films in accordance with the present invention;
[0022] FIG. 8 is a perspective view photograph showing a wicking
testing apparatus, as described in Example 1;
[0023] FIGS. 9-12 are perspective view photographs showing wicking
testing results, as described in Example 1;
[0024] FIGS. 13 and 14 are perspective view photographs showing a
wicking testing apparatus, as described in Example 2;
[0025] FIG. 15 is a perspective view photograph showing a wicking
testing apparatus, as described in Example 3;
[0026] FIGS. 16-18 are perspective view photographs showing wicking
testing results, as described in Example 3; and
[0027] FIGS. 19-24 are perspective view photographs showing wicking
testing results, as described in Example 4.
DETAILED DESCRIPTION
[0028] As used herein, the following terms have the following
meanings.
[0029] Fibreboard refers to fabricated paperboard used in container
manufacture, including corrugated fibreboard.
[0030] Container refers to a box, receptacle or carton that is used
in packing, storing, and shipping goods.
[0031] Moisture-resistant film refers to polymeric films that are
substantially impervious to moisture. Such films are not
necessarily totally impervious to moisture, although this is
preferred, but the amount of moisture capable of passing through
the film should not be so great that such moisture reduces the
strength or other properties of the cellulose based substrate to
below acceptable levels.
[0032] Thermobondable refers to a property of a material that
allows the material to be bonded to a surface by heating the
material.
[0033] Thermoplastic refers to a material, usually polymeric in
nature, that softens when heated and returns to its original
condition when cooled.
[0034] Panel refers to a face or side of a container.
[0035] Score refers to an impression or crease in a cellulose based
substrate to locate and facilitate folding.
[0036] Flaps refer to closing members of a container.
[0037] Peeling refers to separation of one film from another film
along a bond formed between the films.
[0038] Creep refers to movement of the film-to-film bond line that
occurs when the films peel from each other when the bond is
subjected to stress.
[0039] The present invention provides for the encapsulation of a
cellulose based substrate with polymeric films. Cellulose based
substrates are formed from cellulose materials, such as wood pulp,
straw, cotton, bagasse, and the like. Cellulose based substrates
useful in the present invention come in many forms, such as
fibreboard, containerboard, corrugated containerboard, and
paperboard. The cellulose based substrates can be formed into
structures such as container blanks, tie sheets, slip sheets, and
inner packings for containers. Examples of inner packings include
shells, tubes, partitions, U-boards, H-dividers, and corner
boards.
[0040] The following discussion proceeds with reference to an
exemplary cellulose based substrate in the form of a containerboard
blank, but it should be understood that the present invention is
not limited to containerboard blanks.
[0041] Referring to FIG. 1, a non-limiting example of a cellulose
based substrate includes a container blank 20 having rectangular
panels 21 and 22 that will form sidewalls of a container when the
blank is folded and secured. Panels 21 and 22 are separated by
rectangular panel 24 that will form an end wall of a container when
the blank is folded. Extending from the edge of panel 22 opposite
the edge connected to panel 24 is an additional rectangular panel
26 that will form a second end wall. The sequence of panels 21, 22,
24, and 26 define a lengthwise dimension for container blank 20.
Each panel 21, 22, 24, and 26 includes two rectangular flaps 28
extending from the left edge and right edge thereof. Extending
rearwardly from the rear edge of panel 26 is a narrow rectangular
flap 30. Panels 21, 22, 24, and 26 and flaps 28 and 30 are
separated from each other by either slots 32 defined as cuts formed
in container blank 20 or scores 34. The external peripheral edge
around container blank 20 defines a container blank periphery 36.
As illustrated, container blank 20 has a first surface defined in
FIG. 1 as the upper visible surface and a second opposite surface
forming the underside of the container blank in FIG. 1. Panel 21
and panel 22 include cutouts 42 that serve as ventilation orifices,
drainage orifices, or handles once container blank 20 is formed
into a container by applying adhesive to panel 30 and positioning
panel 30 adjacent to panel 21. While container blank 20 is
illustrated with scores, cutouts and slots, it is understood that
such features are not required and that a cellulose based substrate
without such features may be encapsulated with polymeric films in
accordance with the present invention. In the illustrated
embodiment, the edge of the blank adjacent the container blank
periphery and the blank edges that define the slots and cutouts are
examples of exposed edges adjacent to which the polymeric films are
bonded to each other by an adhesive, as described below in more
detail.
[0042] Overlying and underlying container blank 20 are polymeric
films 43 adhered to the container blank and bonded and sealed to
each other around the container blank periphery 36 by an adhesive.
Polymeric films 43 are also bonded and sealed to each other by an
adhesive adjacent the exposed blank edges that define slots 32 and
cutouts 42. As used herein, the term "sealed" means that
overlapping portions of the film adjacent the top surface and the
film adjacent the bottom surface are bonded to each other by an
adhesive in a manner that substantially prevents moisture from
passing through the seal. Areas 31, identified with the stippling,
correspond to locations on container blank 20 where additional
adhesive can be applied in order to further strengthen and
reinforce films 43, as described below in more detail.
[0043] Container blank 20 can be folded and secured into a
container as illustrated in FIG. 2. The numbering convention of
FIG. 1 is carried forward in FIG. 2. Prior to folding container
blank 20 and securing it to form a container, the portions of
polymeric films 43 within slots 32 are cut. Additionally prior to
folding the container, the excess polymeric film adjacent to the
periphery 36 can be trimmed. Furthermore, the polymeric film
spanning cutouts 42 can be cut in such a manner that a passageway
is made into the interior of the container while at the same time
preserving the film-to-film seal.
[0044] Referring to FIG. 3, container blank 20 is comprised of
upper liner board 44 and lower liner board 46 spaced apart by
flutes 48. An outer surface of liner board 44 is overlaid with an
adhesive layer 45 and polymeric film 43. In the illustrated
embodiment, an outer surface of lower liner board 46 is overlaid
with an adhesive layer 45 and a polymeric film 43. While the
present invention is described in the context of an embodiment
wherein an adhesive is applied to both polymeric films 43, it
should be understood that satisfactory results can be achieved by
applying adhesive only to one of the films. The applied adhesive 45
and polymeric films 43 conform to the topographical features
defined by the peripheral edge 36, scores 34 and cutouts 42. The
adhesive and films conform to the topographical features by
following the elevational changes in the first and second surfaces
of the container blank. Preferably, adhesive 45 and films 43
conform to the shape and encapsulate the exposed edges of the
container blank such as those defining slots and cutouts, and seal
closely against such edges as depicted in FIG. 3. Likewise,
polymeric films 43 adjacent the container blank periphery 36 are
bonded to each other at 37 by adhesive 45 to provide a
moisture-resistant seal. A similar moisture-resistant seal 39 is
provided between the polymeric films 43 within cutout 42.
[0045] Containerboard is one example of a cellulose based substrate
useful in the present invention. Particular examples of
containerboard include single face corrugated fibreboard,
single-wall corrugated fibreboard, double-wall corrugated
fibreboard, triple-wall corrugated fibreboard and corrugated
fibreboard with more walls. The foregoing are examples of cellulose
based substrates and forms the cellulose based substrates may take
that are useful in accordance with the methods of the present
invention; however, the present invention is not limited to the
foregoing forms of cellulose based substrates.
[0046] Portions of the cellulose based substrate can be crushed
before applying the polymeric films. Crushing of the cellulose
based substrate adjacent its peripheral edges, and the edges within
cutouts and slots, has been observed to result in improved
conformance of the film to the shape of the edges. Crushing of the
edges can be achieved by passing the edges through a nip to
temporarily reduce the caliper of the substrate and reduce its
resilience to deformation. Crushing of the edges is commonly
achieved by placing stiff rubber rollers adjacent to cutting
knives.
[0047] Polymeric films useful in accordance with the present
invention include thermobondable and thermoplastic films that are
moisture-resistant. The films should cooperate with the adhesives,
described below in more detail, to bond the films together and
provide moisture-resistant seals between the overlapping portions
of the films. The adhesive may additionally bond the films to the
cellulose based substrate. Useful films may be a single-layer or
may be a multi-layer, e.g., a two or more layer film. Single-layer
films are preferred. The choice of a specific film composition and
structure will depend upon the ultimate needs of the particular
application for the cellulose based substrate. Films should be
chosen so that they provide the proper balance between properties
such as flexibility, moisture resistance, abrasion resistance, tear
resistance, slip resistance, color, printability, and
toughness.
[0048] In certain embodiments, co-extruded multi-layer polymeric
films can be used. Multi-layer films provide the ability to choose
an inner layer composition that cooperates with the adhesive while
at the same time providing an outer layer that has properties more
appropriate for the exposed surfaces of the encapsulated
container.
[0049] Exemplary films include linear low density polyethylene
(LLDPE) blended with low density polyethylene (LDPE), blends of
LLDPE and ethylene vinyl acetate (EVA) copolymer, blends of LLDPE
and ethylene acrylic acid (EAA), coextruded films comprising LLDPE
and EVA layers, coextruded films of an LLDPE-LDPE blend and EVA,
coextruded films having an LLDPE layer and an EAA or ethylene
methacrylic acid (EMA) layer, or coextruded films having an
LLDPE-LDPE layer and an EAA or EMA layer. Examples of other useful
film layers include those made from metallocene, Surlyn.RTM.
thermoplastic resins from DuPont Company, polypropylene,
polyvinylchloride, or polyesters or combination thereof in a
monolayer or multi-layer arrangement.
[0050] Film thickness can vary over a wide range. The film should
not be so thick that when it is applied to a container blank it
will not conform to changes in topography along the surface of the
container blank created by such things as the peripheral edges,
edges defined by the slots, and edges defined by the cutouts. The
films should be thick enough to survive normal use conditions
without losing their moisture-resistance. Exemplary film
thicknesses range from about 0.7 mil (0.018 mm) to about 4.0 mil
(0.10 mm).
[0051] The moisture-resistant polymeric film applied to the inner
and outer surfaces of the container blank can be the same, or
different films can be applied to different surfaces. Choosing
different films for the respective surfaces would be desirable when
the particular properties needed for the respective surfaces of the
container blank differ. Examples of film properties that might be
chosen to be different on the respective surfaces of the container
blank have been described above. In addition to being colored, it
is possible that graphics may be preprinted on the polymeric film.
For food applications, the film is preferably approved for use by
the United States Food and Drug Administration.
[0052] Adhesives useful in accordance with the present invention
include those that cooperate with the films to bond the films
together and optionally to the underlying cellulose based
substrate. The adhesive and film combination should be such that
the two are able to conform to the exposed edges of the container
blank. Preferably, once the adhesive and film are conformed to the
edges of the container blank and the adhesive has set, any peeling
of the films and creep adjacent such edges is minimal. The adhesive
and films should be chosen so that the bond between the films
formed by the adhesive has a cohesive strength that is greater than
the stresses that the bonds are exposed to during manufacturing and
use of the encapsulated container. For example, the film and
adhesive should be chosen so that the bond between the films formed
by the adhesive has a cohesive strength that is greater than the
stresses that promote peeling of the films adjacent the container
blank edges. By choosing the films and adhesives so that the bond
between the films formed by the adhesive has a cohesive strength
greater than the stresses promoting peeling, creep of the peeling
can be minimized. Preferably, the adhesive will remain with the
polymeric films when the encapsulated container blank is re-pulped,
e.g., during recycling. Exemplary types of adhesives are known as
hot melt adhesives, and include elastic styrene-isopropene-styrene
block copolymers. Other useful adhesives include ethylene vinyl
acetate adhesives, amorphous polyolefin adhesives, polypropylene
adhesives, and pressure sensitive adhesives. Preferably, the
adhesives have a viscosity ranging from about 1,000 to 15,000
centipoise at the application temperature. While hot melt adhesives
are preferred, it should be understood that non-hot melt adhesives
may find utility in the present invention and that other
compositions of adhesives may also be used.
[0053] Referring to FIG. 4, in another embodiment of the present
invention a container blank 50 includes panels 21, 22, 24, and 26
that are structurally separated from each other as well as from
flaps 28 and flap 30. In this embodiment, polymeric resistant films
43 function as a hinge between the respective panels of the
container blank. As with FIG. 1, container blank 50 in FIG. 4 is
illustrated with stippled areas 31 that identify locations where
additional adhesive may be added to reinforce films 43.
[0054] Container blank 50 can be folded and secured into a
container as illustrated in FIG. 5. The numbering convention of
FIG. 4 is carried forward in FIG. 5.
[0055] Referring to FIG. 6, a method for producing a cellulose
based substrate encapsulated in a polymeric film on a continuous
basis, as opposed to a batch basis is illustrated and described in
the context of a containerboard blank. In the illustrated
embodiment, a container blank 20 from a source of container blanks
(not shown) is delivered via a conveyance system illustrated as two
sets of rollers 52 to a film application stage 53. At film
application station 53, films 56 and 58 are unrolled from the
supply rolls and delivered to a nip formed by rollers 54. Before
entering the nip at rollers 54, adhesive is applied to the surface
of the respective films that will contact the upper surface 38 and
lower surface 40 of container blank 20. In this embodiment,
adhesive is applied to both films 56 and 58; however, as noted
above, adhesive can be applied to only one of films 56 or 58. The
following description applies equally well to an embodiment wherein
adhesive is applied to only one of the films 56 or 58.
[0056] In the embodiment of FIG. 6, adhesive is applied to
substantially all of the surface of films 56 and 58, particularly
those portions where direct film-to-film bonding is necessary,
e.g., around the container blank periphery and adjacent the edges
defined within cutouts and slots. It should be understood that it
is not required that adhesive be applied to substantially all of
the surfaces of films 56 and 58. Satisfactory film-to-film bonding
can be achieved by applying adhesive only to those portions of the
films that overlap around the container blank periphery and
adjacent the edges defined within cutouts and slots. Adhesive is
preferably provided by a non-contact application method in order to
minimize burn-through or tearing of films 56 and 58. An exemplary
application process includes applying a hot melt adhesive as
carefully controlled extruded fibers filaments of the adhesive
applied in a crossing pattern. Equipment suitable for applying
adhesives in this manner is available from Nordson Corporation of
Dawsonville, Ga. Adhesive can be applied in other manners such as
slot die methods wherein the film contacts a die as the adhesive is
dispensed or spray type application methods.
[0057] The location where the adhesive is applied can vary;
however, when the adhesive is heated, it is preferable to add the
adhesive as close to the nip formed by rollers 54 as possible in
order to avoid premature cooling of the adhesive. In order to
facilitate wetting of the film surfaces by the adhesive, the film
surfaces can be treated such as by corona treatment (not shown).
The adhesive should be applied at temperatures that do not
adversely affect the moisture-resistant properties of the film and
do not damage the film or the underlying container blank. The
application rate for the adhesive can vary. Exemplary application
rates include about 1 gram per square meter to 15 grams per square
meter. When necessary, more adhesive can be applied to those areas
where added bond strength is desirable such as areas prone to tears
or where added thickness can reduce abrasion damage. After the
adhesive is applied, film 56 is provided adjacent upper first
surface 38 of container blank 20, and film 58 is provided adjacent
lower second surface 40 of container blank 20. Films 56 and 58 have
a width dimension measured in the cross-machine direction that is
greater than the width of container blank 20. Thus, portions of the
films 56 and 58 extend beyond the edges of the blanks that are
parallel to the direction that the blanks travel. In the direction
that the blanks travel through the process, individual blanks are
spaced apart. Accordingly, films 56 and 58 bridge the space between
the trailing edge of one blank and the leading edge of the next
blank.
[0058] The combination of container blank 20, first film 56 and
second film 58 passes through the nip formed by rollers 54. The nip
formed by rollers 54 defines an inlet to a pressure chamber 60.
Pressure chamber 60 is in fluid communication with a pump 62
capable of increasing the pressure within pressure chamber 60.
Pressure chamber 60 also includes a plurality of rollers 64 for
supporting the combined container blank 20, first film 56 and
second film 58 through pressure chamber 60. Pressure chamber 60 is
operated at a pressure greater than the pressure outside pressure
chamber 60. As described below in more detail, the elevated
pressure within pressure chamber 60 promotes the conformance of
films 56 and 58 to container blank 20 around the container blank
peripheral edges as well as within any slots or cutouts provided in
the container blank. The container blank 20 and films 56 and 58
exit chamber 60 through the nip created by rollers 66. The nips
created by rollers 54 and 66 are preferably as airtight as possible
in order to maintain the elevated pressure within chamber 60.
Alternative means can be used besides the rollers to prevent
pressure loss from chamber 60, such as air locks and the like. From
pressure chamber 60, container blanks 20 encapsulated by films 56
and 58 pass to trimming stage 78 described below in more
detail.
[0059] As noted above, films 56 and 58 are dimensioned such that
the respective films extend beyond the container blank periphery in
the cross machine direction perpendicular to the travel of the
container blank 20. In this manner, film 56 comes into contact with
film 58 adjacent the container blank periphery and within slots and
cutouts where the films overlap. The presence of adhesive between
these overlapping portions of the film causes the films to be held
together. As the adhesive cools, the cohesive strength of the bond
formed by the adhesive between the films increases. Preferably, the
adhesive bonds the films to each other at substantially all points
where the films overlap. In this manner, the films form an envelope
that substantially encapsulates the container blank. As described
below in more detail, the envelope is formed in a manner such that
a pressure differential may be provided between the environment
inside the envelope and the environment outside the envelope. An
envelope formed around the container blank is suitable so long as
it encapsulates the blank in a manner that is capable of supporting
a pressure differential between the inside of the envelope and the
outside. For example, two films bonded to each other adjacent the
leading and trailing edges of a container blank, but not the
parallel side edges, would not substantially encapsulate a blank so
as to be able to support a pressure differential between an
environment between the films and an environment outside the films;
however, an envelope formed by the films wherein the films are
intermittently or reversibly bonded around all exposed edges of the
container blank would be satisfactory, because a pressure
differential can be created between the interior of the envelope
and the environment exterior to the envelope.
[0060] Conformance of the two films to the container blank
periphery, slots, and cutouts, is promoted by providing a pressure
differential between an environment within the envelope described
above and the environment exterior of such envelope. More
specifically, the container blank and films are treated so that
there is a point in the manufacturing process after the adhesive
has been applied to at least one of the films where the pressure
within the envelope is lower than the pressure exterior to the
envelope. Satisfactory conformance of the films is evidenced by an
absence of air bubbles at the interface between the films and the
container blank, as well as robust and continuous seals around the
exposed edges of the container and the edges exposed within the
cutouts and slots. The degree of the conformance of the films to
the container blank can be evaluated by assessing the distance
between the film-to-film bond line and the exposed edge of the
container blank. As the distance between the film-to-film bond line
and the container blank edge increases, the degree of conformance
of the film to the container blank edge decreases. Shorter
distances between the container blank edge and the film-to-film
bond line are more desirable than larger distances.
[0061] As used herein, the phrase "pressure differential" refers to
a difference in pressure between the inside of the envelope and the
exterior of the envelope that is attributable to more than the
pressure differential that would be observed by simply reducing the
temperature of gas within the envelope without a phase change. For
example, in the context of the present invention, a pressure
differential can be provided by moving the envelope from a low
pressure environment to a higher pressure environment, with or
without cooling of the gas within the envelope.
[0062] Pressure within pressure chamber 60 can vary and should be
chosen so that crushing of the container blank is avoided while at
the same time, conformance of the film to the blanks is high. The
pressure in chamber 60 should not be so high that excessive gas
loss cannot be prevented by rollers 54 and 66. Rollers 54 and 66
should be operated at a pressure that is high enough to minimize
gas loss while at the same time not being so high that unwanted
crushing of the container blank occurs. Examples of suitable
rollers include silicone rubber rollers that are either patterned
or non-patterned. The particular pressure within the chamber will
depend upon a number of factors, including the thickness and
malleability of the film. Thinner more malleable films will conform
to the container blank with less pressure than thicker, stiffer
films. The chamber should be long enough so that the adhesive is
able to gain adequate cohesive strength through cooling as it
passes through pressure chamber 60. As discussed above, an adequate
cohesive strength is one that is greater than the tension force
that promotes peeling of the films from each other. The length of
pressure chamber will also depend upon the speed of the blanks
passing through the chamber. Exemplary pressures within the
pressure chamber can range from about 2 to 20 pounds per square
inch. Blank speeds ranging from about 1 to 500 feet (0.3 to 150
meters) per minute are exemplary.
[0063] Within trimming stage 78, sensor 80 and laser 82 cooperate
to trim away excess polymeric film around the container blank
periphery and within the slots and cutouts without compromising the
water-resistant seals. In order to ensure the accuracy of the film
trimming, trimming stage 78 preferably employs a conveyance system
83, such as a vacuum belt that minimizes movement of the container
blank and films during the laser trimming process. Alternatives to
laser trimming include die cutting or hand trimming.
[0064] By trimming away portions of the polymeric films within the
cutouts, openings can be provided for ventilation, drainage, or for
allowing the cutouts to serve as handles for the container. It is
preferred that trimming of the films within the cutouts and slots
be carried out as soon as possible after the adhesive forms the
film-to-film bonds. Peeling of the films occurs when the tension on
the films is greater than the cohesive strength of the
film-adhesive-film bond. When the films conform to the contour of
the edges of the container blank, the films are put under tension
that can cause peeling. Peeling is evidenced by the films
separating along the line where the upper film meets the lower
film. As the films begin to peel, this line begins to creep away
from the edge of the container blank. As peeling may increase over
time, it is preferable to minimize the time between when the
encapsulated blank leaves the pressure chamber and the time when
the trimming occurs. The films adjacent the exposed edges should be
trimmed as close as possible to the container blank edges without
compromising the film-to-film bond at the time of trimming. The
distance between the edge of the container blank and the edge of
the trimmed film should be great enough that any peeling of the
films does not extend to the trimmed edge of the films and
compromise the seal between the films.
[0065] Referring to FIG. 7, a cellulose based substrate
encapsulated by polymeric films can be produced by a method wherein
pressure chamber 60 of FIG. 6 has been replaced by a vacuum chamber
84. The system illustrated in FIG. 7 includes trimming stage 78
identical to the trimming stage described above with respect to
FIG. 6. The system of FIG. 7 also includes a film application stage
86 that is identical to the film application stage 53 in FIG. 6
with the exception that adhesive applicators 59 are omitted.
[0066] Vacuum chamber 84 is an air tight chamber in fluid
communication with vacuum pump 88. The inlet of vacuum chamber 84
includes rollers 94 defining a nip designed to allow a container
blank 20 and associated films 56 and 58 to pass into chamber 84
without compromising the reduced pressure therein. Upstream from
rollers 94 are a pair of rollers 92 that receive films 56 and 58
and container blank 20. Films 56 and 58 are positioned adjacent to
the upper and lower surface of blank 20 at rollers 92. When
container blank 20 includes corrugated fibreboard and the flutes
are oriented parallel to the direction of travel of the blanks,
when the leading edge of the container enters vacuum chamber 84, a
suction is created at the trailing end of the container blank. This
suction draws films 56 and 58 against the trailing end of container
blank 20 and serves to create a seal that prevents air from being
drawn into vacuum chamber 84 through the corrugated flutes of
container 20.
[0067] Vacuum chamber 84 includes a conveyor belt 96 for
transporting blanks 20 through vacuum chamber 84. Vacuum chamber 84
also includes a combination of rollers 98, 100 and 102 for
separating films 56 and 58 from container blank 20 and delivering
the films to an adhesive applicator 104 where adhesive is applied
to a surface of the films 56 and 58 before they are recombined with
blanks 20. As noted above, in the illustrated embodiment, adhesive
is shown as being applied to surfaces of both films 56 and 58;
however, this embodiment is not limited to applying adhesive to
both films and accordingly, adhesive can be applied to either film
56 or 58. The exit of vacuum chamber 84 includes a pair of rollers
106 defining an air tight nip at the exit of chamber 84.
[0068] In accordance with this process employing a vacuum chamber,
container blanks 20 are combined with films 56 and 58 at film
application stage 86. The web comprising the container blank 20 and
films 56 and 58 enter vacuum chamber 84 at the nip formed by
rollers 94. As films 56 and 58 enter vacuum chamber 84, they are
separated from container blank 20 and delivered to adhesive
applicators 104 where adhesive is applied to the surface of at
least one of the films. As soon as possible after adhesive
applicators 104, films 56 and 58 are recombined with container
blanks 20. The amount of time between when adhesive is applied to
the films and when the films are applied to the container blank
should be minimized in order to avoid the adhesive losing its
adhesive properties due to cooling.
[0069] The combination of films 56 and 58 and the adhesive form an
envelope encapsulating container blank 20. Pressure within this
envelope will be approximately equal to the pressure within vacuum
chamber 84. Accordingly, as the envelope exits vacuum chamber 84,
it will be exposed to the environment outside vacuum chamber 84
which preferably is atmospheric pressure. The pressure differential
between the internal environment within the envelope and the
environment outside the envelope promotes the conformance of the
film to the container blank, including the exposed edges around the
container blank periphery and edges defined within cutouts and
slots. After the adhesive cools, the web of films, adhesive, and
container blank is delivered to trimming stage 78 where the
encapsulated blank is processed as described above.
[0070] In the process illustrated in FIG. 7, it is preferred that
the films as they exit the vacuum chamber adhere to each other at
substantially all points where they overlap so that the films form
an envelope that substantially encapsulates the container blank.
While it is preferred that the films are reversibly or
intermittently bonded to each other adjacent all four edges of the
container blank and within any slots and cutouts of the container
blank, as discussed above, an envelope formed around the container
blank is suitable so long as it is capable of supporting a pressure
differential between the inside of the envelope and the
outside.
[0071] Exemplary vacuum conditions within vacuum chamber 84 can
range from about 200 mm Hg to about 300 mm Hg. Vacuum within vacuum
chamber 84 should be chosen so that it is far enough below the
pressure outside vacuum chamber 84 so that acceptable conformance
of films 56 and 58 to container blank 20 is achieved after the
encapsulated blank exits the vacuum chamber. Vacuum within vacuum
chamber 84 should not be so low that film damage occurs, the
container blank experiences loss of caliper or the vacuum cannot be
maintained by the seals at the inlet and outlet of the vacuum
chamber. The description regarding the types of films, adhesives,
film properties, adhesive properties, adhesive loading, line speeds
and the like described above with respect to FIG. 6 are also
applicable to the process of FIG. 7.
[0072] Although not illustrated, other methods of promoting the
conformance of the polymeric films to the container blank can be
used. One example of such method includes a hot air knife capable
of delivering a focused stream of air at the encapsulated container
blank as it leaves the pressure chamber 60 of FIG. 6 or the vacuum
chamber 84 of FIG. 7.
[0073] With the reference to FIGS. 6 and 7, the inlets and outlets
of the respective vacuum chamber 60 and pressure chamber 84 are
described as including rollers. It should be understood that
combinations of other types of components such as brushes, soft
rollers, and wiper blades that allow for the entry and exit of the
container blanks and films into the vacuum chamber or pressure
chamber without substantially compromising the reduced or increased
pressure within the respective chambers can be utilized. For
example, one alternative includes a combination of a soft roller
and a flexible wiper for sealing the upper surface of the
combination of a container blank and film to the vacuum/pressure
chamber and a brush for sealing the lower surface of the blank and
film to the vacuum/pressure chamber.
[0074] The present invention has been described above in the
context of a containerboard blank encapsulated with a polymeric
film. The containerboard blank can be formed and secured to provide
a moisture-resistant container. In addition, such a
moisture-resistant container can be combined with other structural
components such as inner packings, described above, that may be
encapsulated with a polymeric film, or may not be encapsulated with
a polymeric film. Furthermore, containers can be provided wherein
the container body is not encapsulated with a polymeric film while
certain inner packing structural components are encapsulated with a
polymeric film. In addition, cellulose based inner packings
encapsulated with a polymeric film can be combined with
non-cellulosic based container bodies and cellulose based container
bodies encapsulated with polymeric film can be combined with
non-cellulosic inner packing structural components.
[0075] The moisture wicking resistance properties of the flutes or
corrugated medium 48 in accordance with the present disclosure will
now be described in greater detail. Embodiments of the present
disclosure achieve moisture wicking resistance in the container 20
while maintaining adhesive properties between the corrugated medium
48 and the linerboards 44 and 46. In that regard, the corrugated
medium 48 is treated with at least one additive designed to enhance
the sizing of the corrugated medium 48.
[0076] As described above, the container or container blank 20 is
suitably formed from a cellulose based sheet having flutes or
corrugated medium 48 spanning between the first and second
linerboards 44 and 46. The container or container blank 20 includes
a polymeric film encapsulating at least a portion of the cellulose
based sheet. In some instances, there will be holes in the
container encapsulation films, whether from film manufacturer
defects, the container manufacturing process, or container packing
and handling issues. As described in greater detail in the Examples
provided below, a container that has such a hole (or holes) and is
exposed to free water will wick water, so long as there is free
water to be absorbed or until the total saturation point of the
container is reached, unless the corrugated sheet (including the
linerboard and the corrugated medium) has low-wicking properties.
Moreover, as described in the Examples provided below, encapsulated
containers tend to wick water more readily that unencapsulated
containers.
[0077] Most corrugated cellulose based containers are formed from
cellulose based sheets having a corrugated medium spanning between
the first and second linerboards. The corrugated medium is
typically adhered to the first and second linerboards using a
water-based adhesive. Conventional practice in the field of
corrugated cellulose based containers is to manufacture the first
and second linerboards with a sizing agent, which provides some
moisture-resistance in the first and second linerboards, but to
manufacture the corrugated medium with little to no sizing, as
compared to the first and second linerboards.
[0078] It was believed that such manufacturing processes allow the
water-based adhesive to sufficiently penetrate the corrugated
medium and provide a suitable bonding site between the corrugated
medium and the linerboards. However, such manufacturing processes
allow for water or moisture to wick through the corrugated medium
and spread to the linerboards. After water has wicked throughout an
encapsulated cellulose based container, the container will be
damaged and will likely fail under the load of the contents within
the container.
[0079] Therefore, conventional practice in the field of corrugated
cellulose based containers has been to manufacture the corrugated
medium with little or no sizing agents. Contrary to conventional
practice, the sized corrugated medium, in accordance with the
present disclosure, provides moisture wicking resistance to the
container while still obtaining a suitable adhesive bond. Moreover,
such a bond can be improved by increasing the roughness factor of
the corrugated medium.
[0080] It should further be appreciated that water-resistant
adhesives are also within the scope of the present disclosure.
Water resistant adhesives obtain a suitable bond between the
corrugated medium and linerboards while further improving the
moisture resistance of the corrugated cellulose based containers
described herein.
[0081] In one embodiment, the corrugated medium 48 includes alum,
which is an additive designed to size the natural resins to form
hydrophobic groups within the cellulosic fiber. Alum is generally
added to virgin cellulose fiber, as opposed to recycled fiber.
Regarding recycled fiber, the natural resins in the fiber tend to
break down in the drying and/or repulping process. For this reason,
alternative agents are added to secondary or recycled fiber.
[0082] In another embodiment, the corrugated medium 48 includes a
sizing agent. As a nonlimiting example, the sizing agent is a
reactive sizing agent, such as alkyl ketene dimer (AKD), alkenyl
ketene dimer emulsion (ALKD), alkenyl succinic anhydride (ASA), or
any blends of the foregoing additives, such as ASA/ALKD blends. It
should be appreciated, however, that non-reactive sizing agents
(such as rosin and paraffin wax emulsions) and other surface
treatments (such as styrene maleic anhydride (SMA), styrene acrylic
emulsion (SAE), polyacrylamides (PAE), colloidal silica, and
cellulosics) are also sizing agents within the scope of the
invention.
[0083] In accordance with embodiments described herein, the
reactive sizing agent is present in the corrugated medium in an
amount in the range of about 0.1 to about 10.0 lbs/ton. In another
embodiment, the reactive sizing agent is present in the corrugated
medium in an amount in the range of about 0.1 to about 4.0 lbs/ton.
Variations in the amount of reactive sizing agent are generally a
result of variations in amount of virgin fiber versus secondary or
recycled fiber used in the product, as well as the papermaking
conditions.
[0084] Linerboards of a corrugated substrate generally have
moisture wicking resistance properties similar to the corrugated
medium described herein, whether sized by alum or the sizing agents
described herein.
[0085] It should be apparent that the principles of including a
sizing agent for moisture wicking resistance in the corrugated
medium described herein are not limited to container encapsulation
methods by adhesive bonding, but also extend to other encapsulation
methods. It should further be appreciated that the principles of
including a sizing agent for moisture wicking resistance in the
corrugated medium are not limited to encapsulated containers, but
also extend to unencapsulated containers.
[0086] In another embodiment, the cellulosic pulp is treated with
both a sizing treatment, as discussed above, and a wet strength
resin, such as cationic polyamide-epichlorohydrin reaction products
(PAE resins). Methods of enhancing the strength of cellulosic
products with PAE resins is described in U.S. Pat. No. 5,830,320,
the disclosure of which is hereby expressly incorporated by
reference. As described in U.S. Pat. No. 5,830,320, a cellulosic
fiber product comprises about 5-40% of the cellulosic fiber treated
with 0.5-5.0% of a reactive crosslinking-type wet strength resin
additive substantially uniformly blended with 95-60% of untreated
fiber.
[0087] The PAE resin is at least partially crosslinked and may be
selected from the following: urea-formaldehyde condensation
products, melamine-urea-formaldehyde condensation products, and
polyamide-epichlorohydrin reaction products.
[0088] In addition to improving wet strength, such treatment with
PAE resin increases the dry strength of the cellulosic fiber
product and improves the repulpability of the fibers when recycled.
Therefore, in another embodiment, 10-30% of the cellulosic fiber is
treated with 0.5-5.0% of a reactive crosslinking-type wet strength
resin additive. In another embodiment, the cellulosic fiber product
contains from about 0.1-0.6% by weight of the resin based on the
total amount of cellulosic fiber in the product.
[0089] Advantages of moisture wicking resistance properties in the
corrugated medium in accordance with the present disclosure include
increased container integrity and strength when exposed to water
and/or water migration. For example, in produce-packing
applications, water or ice is added to produce to keep the produce
fresh during transportation. If the encapsulation structure is
damaged and allows moisture to enter the encapsulation, the
embodiments disclosed herein prevent water from wicking throughout
the encapsulated cellulose based substrate or sheet. Therefore, the
wicking resistance properties of the container described herein
provide for wicking prevention and maintain container integrity
even if water enters the encapsulation structure.
[0090] Examples 1-6 that follow illustrate the improved strength of
containers constructed in accordance with embodiments of the
present disclosure as compared to previously developed (or
"control") containers. Specifically, the Examples indicate that
water tends to wick significantly less in Low Wicking Medium
container board, as compared to Control container board. Moreover,
wicking in the Low Wicking Medium was observed to be more prevalent
in encapsulated samples than in unencapsulated samples, indicating
that encapsulation encourages wicking. In addition, the Examples
indicate that the moisture wicking directly impacts the
top-to-bottom strength of the container and that the Low Wicking
Medium containers have superior strength performance over the
Control Medium containers. In that regard, the Low Wicking Medium
encapsulated containers only lost 25% of their top-to-bottom
strength when exposed to a water mist shower for seven days. The
Control Medium encapsulated containers, on the other hand, lost 73%
of their top-to-bottom strength.
EXAMPLE 1
Wicking Testing for Unencapsulated Cellulose Based Sheets
[0091] The basis for the wicking testing provided in this example
is in accordance with the Springfield Wick Test W-30. Several
modifications were made to accommodate the use of combined
corrugated container board rather than the individual paper samples
that the test is designed for. The first modification was to cut
the samples to a size of 11 inches.times.2 inches to be large
enough for the encapsulation process (described below in Example
3). As seen in FIG. 8, the samples were cut such that the flutes of
the corrugated medium were oriented in the vertical direction to
allow for maximum wicking directly up the flutes. The second
modification was to measure only on the sides of the samples for
wicking because the sample sides were the only points for
measurement without opening up the linerboards of the samples to
expose the corrugated medium and thereby destroy the sample. The
third modification was regarding time for testing: one set of
unencapsulated samples was left for 3 hours and a second set was
left for 72 hours.
[0092] The "Control Medium" samples were cut from a C-flute
corrugated container board, having standard low-wicking linerboards
and a standard medium (i.e., without a sizing agent). The
"Low-Wicking Medium" samples were also cut from a C-flute
corrugated container board from the same manufacturer under the
same manufacturing conditions, but having standard low-wicking
linerboards and a low-wicking medium (i.e., with a sizing
agent).
[0093] As seen in FIG. 8, four test samples were set up in the
testing apparatus. The two samples on the left are Control Medium
samples and the two samples on the right are Low-Wicking Medium
samples. Per test protocol, 450 ml of deionized water was added to
the pool at the bottom of the testing apparatus. Accordingly,
approximately 1.3 cm of each sample was submerged in the water pool
at all times.
[0094] During testing, it was observed that the Control Medium
samples began to wick water immediately on contact with the water
pool. The Low-Wicking Medium samples had no immediate wicking. In
all cases, the linerboards of the samples wicked very little water
compared to the corrugated medium. Most of the wicking was
completed within less than 2 hours of testing. Water did continue
to wick after that initial period, but at a significantly reduced
rate.
[0095] The Control Medium samples wicked water a distance of
approximately 5.8 cm above the level of the water pool, while the
Low-Wicking Medium samples wicked approximately 1-2 mm above the
level of the water pool. As seen in FIG. 9, the linerboard of the
Low-Wicking Medium samples wicked water only slightly above the
surface of the pool, approximately 1-2 mm.
[0096] As seen in FIG. 10, the Control Medium sample is situated on
the left and the Low-Wicking Medium sample is situated on the
right. At first glance, it appears that both sets of samples
completed the test with similar results. However, upon closer
examination (see FIG. 11), the Control Medium sample wicked
significantly more water (4.5 cm above pool surface) than the
Low-Wicking Medium sample (2 mm above pool surface). Referring back
to FIG. 10, a thin dark line on the right side of the two Control
Medium samples indicates the wicking level of the sample where the
soaked medium has lost it shape and emerges from the side of the
sample. There is no such line on the Low-Wicking Medium
samples.
[0097] The test that was run over a 72-hour period had similar
results to the 3-hour test. As seen in FIG. 12, there was slightly
more wicking by the linerboards over the longer time period.
However, the test results were substantially similar to the 3-hour
test results. In the 72-hour test, the water wicked up the Control
Medium sample to a distance of approximately 5.0 cm, as compared to
the 4.5 cm in the 3-hour test. The Low-Wicking Medium samples
wicked to distance of approximately 3-4 mm, as compared to 2-3 mm
in the 3-hour test.
EXAMPLE 2
Compression Testing for Encapsulated Containers
[0098] Two sets of nine, 4''.times.4''.times.4'' regular slotted
containers manufactured from the same materials used for the
wicking testing in Example 1 were die cut. (Regular slotted
containers in accordance with the present disclosure include flaps
all having the same length, with the two outer flaps being one half
of the container width to meet in the middle.) The nine Control
Medium containers were marked with a "C" and sent with the nine
Low-Wicking Medium containers to be encapsulated. The bottom flaps
and the manufacturer's joint were closed using hot melt, and two 1
mm holes were punched into consecutive bottom slots of all of the
containers. As seen in FIGS. 13 and 14, the containers were placed
in a tray and filled with ice. The tray was placed in a cooler for
seven days at a temperature of approximately 35.degree. F.
[0099] After seven days the containers were removed from the cooler
and taken directly to be top-to-bottom compression tested. The
results in Table 1 below show a significant difference in
compression results between containers made from the Control Medium
container board (126.67 lbf average) and containers made from the
Low-Wicking Medium container board (171.22 lbf average).
TABLE-US-00001 TABLE 1 COMPRESSION TEST RESULTS Low-Wicking Control
Medium Medium Peak Force Avg. (lbf) 126.67 171.22 Std. Deviation
61.0287 20.0984 Peak Displacement Avg. 0.1918 0.2951 Std. Deviation
0.0932 0.2025
[0100] The largest contributing factor to the Control Medium sample
containers having low average results was that two of the Control
Medium sample containers were completely saturated with water
inside the encapsulation. In that regard, the containers had wicked
water into the whole structure of the container. These two
saturated containers had peak force readings of 23 lbf and 28 lbf.
However, even with those two containers disregarded from the
average test results, the remaining Control Medium sample
containers averaged 155.57 lbf, still significantly less than the
compression strength of the Low-Wicking Medium sample containers at
171.22 lbf. These results suggest that the containers having a
Low-Wicking Medium provide additional strength, as compared to
containers with a medium that wicks, because the Low-Wicking Medium
does not "pull" (or wick) free water into the structure of the
container.
[0101] Therefore, incorporating a medium having low-wicking
properties into an encapsulated container apparently improves the
ability of the finished container to continue to provide structural
strength when the encapsulation is compromised and the container is
exposed to free water.
EXAMPLE 3
Wicking Tests for Encapsulated Cellulose Based Sheets
[0102] An additional wick test was done using the same corrugated
material as used in Example 1, except in encapsulated form (see
FIG. 15). Each sample was encapsulated by a standard encapsulating
process and had two 1 mm holes punched through the encapsulation
film at the bottom of the sample to allow exposure to the
water.
[0103] The basis for the wicking portion of the testing was again
the Springfield Wick Test W-30, with the same modifications
described above in Example 1. Again, 450 ml of deionized water was
added to the pool at the bottom of the testing apparatus.
[0104] From the same materials as the samples used in the previous
examples, the encapsulated Control Medium samples were cut from an
encapsulated C-flute corrugated container board, having standard
linerboards and a standard medium. The encapsulated Low-Wicking
Medium sample were cut from an encapsulated C-flute corrugated
container board, having standard linerboards and a Low-Wicking
Medium. As seen in FIG. 15, the two samples on the left are the
Control Medium samples and the two samples on the right are the
Low-Wicking Medium samples.
[0105] Unlike the unencapsulated samples in Example 1, the
encapsulation materials in this example prevented measurements of
water wicking at interim times during the 72-hour test. FIG. 16
shows the samples immediately after being removed from the test
after 72 hours. The two encapsulated Control Medium samples on the
left have linerboards wetted approximately 2-3 mm above the level
of the pool. However, looking carefully, dark staining is apparent
along the flute lines on the face of the sample. Thus, water
appeared to have wicked along the corrugated medium, transferring
into the linerboards along the adhesive lines between the
corrugated medium and the linerboards. It does not appear, however,
that water entered between the encapsulating film and the
linerboards.
[0106] The encapsulated Low-Wicking Medium samples on the right
include one sample having a water mark approximately 1-2 mm above
the level of the water pool and one sample having no indication of
a water mark. Neither sample has any water staining along the flute
lines, as observed in the Control Medium samples.
[0107] Referring to FIG. 17, the corrugated medium of the
encapsulated Low-Wicking Medium sample that wicked water is
exposed. This sample wicked water at a highest point of
approximately 4.2 cm above the level of the water pool. The
corrugated medium, while wet, was not entirely saturated. In
addition, the water did not permeate the sample along an even water
line across the sample. Rather, the high-water line appeared to be
at the third and fourth flutes from the left. When accessing the
corrugated medium, there was some fiber tear along the left-hand
edge and the third flute line from the right below the high-water
line, indicating that the adhesive bond was still in place and had
not dissolved.
[0108] Referring to FIG. 18, the corrugated medium of one of the
encapsulated Control Medium samples is seen. Both of the
encapsulated Control Medium samples wicked water approximately 21.2
cm above the level of the water pool. Unlike the Low-Wicking Medium
samples, the medium of the Control Medium samples is completely
saturated. Although not evident in FIG. 18, this sample glistened
with free water. No fiber tear was present on the sample below the
high water line, indicating that the adhesive bond was
dissolved.
[0109] Notably, the encapsulated Low-Wicking Medium sample that
wicked water drew considerably more water than the unencapsulated
counterparts previously described in Example 1 (4.2 cm versus 1-2
mm). Both samples were cut from the same piece of container board;
therefore, these results indicate that the encapsulation or the
process of encapsulation encourages wicking. It is believed that
the encapsulated Low-Wicking Medium sample that did not wick water
was not adequately prepared with puncture holes. For example, the
puncture holes may have been closed off by the excess material from
the encapsulating film that deformed when it touched the bottom of
the water pool.
[0110] The encapsulated Control Medium samples also wicked
considerably more water than their unencapsulated counterparts
described in Example 1 (21.2 cm versus 5.0 cm). Again, both samples
were cut from the same piece of board; therefore, these results
further indicate that the encapsulation or the process of
encapsulation has an enhancement effect on water wicking.
EXAMPLE 4
Wicking Testing for Encapsulated Containers
[0111] Two samples of encapsulated broccoli containers were
obtained. A hole was punctured in the top flap locking hole. In an
effort to determine how a large quantity of penetrating water
affects an encapsulated container in terms of container strength
and water migration, 400 ml of deionized water was poured down the
exposed flutes of the container.
[0112] Both sample containers had the same 69# liners from the same
rolls: mottled white on the double back side and standard kraft for
the single face. The difference between the two containers was the
corrugated medium. The first sample container is the Control Medium
container having a 36# FPT Medium (Spec. No. 4490). The second
sample container is the Low-Wicking Medium container having a 36#
FPT Low-Wicking Medium (Spec. No. 4491).
[0113] Using a squeeze bottle, 400 ml of deionized water was
injected into each container over a 10-minute period into one
corner of the container opposite the manufacturer's joint. As seen
in FIGS. 19 and 20, approximately 20 minutes after the water had
been introduced, the Low-Wicking Medium container (FIG. 19) has
only one small spot on the bottom flap that looks wet. The Control
Medium container (FIG. 20), on the other hand, has multiple areas
where the linerboard was wetted out, particularly evident along the
flute lines on the bottom flap. Both containers had water damage in
the form of pock marks in the flutes down the side wall below the
hole locking area where the water was introduced.
[0114] Both containers were allowed to stand for 44 hours.
Referring to FIGS. 21 and 22, the bottom flap directly below the
point of entry of the Low-Wicking Medium container (FIG. 21) was
completely saturated and water had moved fairly evenly up the side
wall approximately 3.5 inches (denoted by the red/black line hand
drawn on the container). Water had just passed the corner on both
short side panels. Where the line goes straight up the side wall is
the area where the water was initially introduced by pouring.
[0115] The Control Medium container (FIG. 22) has significantly
more water damage than the Low-Wicking Medium container (FIG. 21).
The bottom flap directly below the point of entry was completely
saturated. Visual inspection of the Control Medium container showed
that water had completely saturated the linerboards. As seen in
FIG. 22, the water in the Control Medium container moved up the
side walls to a depth of approximately 9.5 inches and had migrated
around the corners to about half way on both side panels.
[0116] Referring to FIGS. 23 and 24, photos taken 235 hours after
the initial wetting show consistent results with the results
described above. In the Low-Wicking Medium container (FIG. 23),
water had not wicked any further into the container structure from
the initial migration (FIG. 21). In the Control Medium container
(FIG. 24), water had continued to wick throughout the container
(compare with FIG. 22). On the original sidewall where the water
was introduced, water wicked beyond the flap score onto the top
flaps (as denoted by the red line). Water also continued to wick up
onto the top flap.
[0117] This example shows that the Low-Wicking Medium container
does not "pull" water into the container much above the level of
the standing pool of water it may be in. On the other hand, the
Control Medium container, when exposed to a constant source of free
water, continues to "pull" that water into the container structure
until equilibrium is reached (i.e., when the container structure
completely saturated). There is a maximum amount of water, which
will produce container failure regardless of the paper combination
used in an encapsulated container.
EXAMPLE 5
Wicking Testing for Encapsulated Containers
[0118] In conjunction with Example 4, a second trial was conducted
with sample containers from the same materials as those described
in Example 4. In this example, ten containers of each of the two
medium types (Control and Low-Wicking Mediums) were placed in a
standing pool of water. Each container stood in approximately 1
inch of water. The pool was continually fed a small stream of water
to maintain a constant depth. Each container had a hole
intentionally created in a bottom corner with sandpaper, not at the
manufacturing joint. All of the containers were weighted from above
to keep them in the water and prevent floating.
[0119] After three plus days, five containers of each type were
removed from the pool with the intention of doing top-to-bottom
compression testing. However, all the containers were so wetted out
on the bottom that doing top-to-bottom tests was infeasible. Upon
removing the containers from the pool, observations were made about
the different wetness areas. In that regard, the containers having
the Low-Wick Medium were completely saturated on all the bottom
flaps and approximately 1 to 1.5 inches up all the sidewalls. These
containers only minimally wicked water above the level of the pool,
which is consistent with the results described in the previous
examples.
[0120] Of the five Control Medium samples, the bottom flaps on all
of these containers were completely saturated as well. In addition,
water wicked up to a minimum of 3 inches on all panels with a
majority of the panels having water halfway or more up the
sidewalls of the panels.
[0121] The other ten samples (five of each type of medium--Control
and Low-Wick) were allowed to soak for three additional days. The
Low-Wick Medium samples had no further take up of water beyond 0.5
inch level above the level of the pool. The remaining Control
Medium containers continued to wick all the way up the sidewall and
onto the top flaps of the containers.
EXAMPLE 6
Compression and Water Take-Up Testing for Encapsulated
Containers
[0122] Ten samples of the encapsulated broccoli container
containing 36# Low-Wick Medium (Spec. No. 4491) and ten sample
containers containing 36# Control Medium (Spec. No. 4490) were
subjected to testing. Holes were formed in two bottom corners of
each container. Each container was then filled with 35 pounds of
roll cores which were enclosed in a plastic bag, and the containers
were closed. Each set of ten containers was then stacked on its own
pallet. Three layers were built using four containers on the bottom
and middle layers and two containers on the top layer. The two
pallets were placed directly underneath their own spray head.
[0123] Initially, each container was hand watered, using a garden
hose to simulate the initial soaking a container would receive in a
spray or a clamshell applicator. Then, the spray nozzles were
turned on at a controlled rate of 0.14 gallons/minute. The
containers were left for seven days under the shower.
[0124] The containers were emptied of the roll cores and taken to
the lab for top-to-bottom compression testing. Table 2 displays the
results of the compression testing. TABLE-US-00002 TABLE 2
COMPRESSION TEST RESULTS Control Low Wicking Dry Medium Medium
Container Peak Force Avg. (lbf) 281.2 787.5 1050 Std. Deviation
161.5067 75.5561 -- Minimum 64 612 -- Maximum 550 867 -- Peak
Displacement Avg. 0.138 0.195 -- Std. Deviation 0.05474 0.02377
--
[0125] Dry containers were also tested to compare to the watered
containers and averaged 1050 pounds force average. Therefore, the
containers with Low-Wick Medium lost an average 25% of their
top-to-bottom strength, while the containers with Control Medium
lost 73% of their top-to-bottom strength.
[0126] The differences between the two types of container were even
more apparent when the containers were handled. The containers with
Control Medium were almost entirely soaked. All panels were
partially, if not completely wet. The containers with Low-Wick
Medium had only small areas of wetness, with the exception of one
container, which had some larger areas of wetness. In the one
exception container, water had penetrated other holes that were in
the container prior to the test and had not been made as a uniform
testing condition. Due to the Low-Wick Medium, however, the water
that entered these holes also did not spread through the entire
panel of the container. The data in Table 2 shows the differences
in water take-up in grams on average. TABLE-US-00003 TABLE 3 WATER
TAKE-UP Control Low Wicking Dry Medium Medium Container Water
Absorbed Avg. (g) 320.23 41.3 0 Std. Deviation 131.93684 58.39825
-- Minimum 149.2 13.3 -- Maximum 545.4 198.1 --
[0127] While illustrative embodiments have been illustrated and
described, it will be appreciated that various changes can be made
therein without departing from the spirit and scope of the
disclosure.
* * * * *