U.S. patent application number 11/434044 was filed with the patent office on 2007-11-15 for method for forming a container with corrugated wall and rolled lip.
Invention is credited to Robert B. Zadravetz.
Application Number | 20070262129 11/434044 |
Document ID | / |
Family ID | 38684176 |
Filed Date | 2007-11-15 |
United States Patent
Application |
20070262129 |
Kind Code |
A1 |
Zadravetz; Robert B. |
November 15, 2007 |
Method for forming a container with corrugated wall and rolled
lip
Abstract
A method of forming a paper container uses a three-ply
corrugated material having at an outer sheet of paper that may be
stretched circumferentially to permit subsequent rolling of the
corrugated material about a mandrel and an inner sheet of paper
that can be stretched circumferentially to assist in rolling the
lip of the cup and/or attaching the bottom to the cup. An
extensible paper having two axes of extension of over four percent
can be used for one or both of the paper layers.
Inventors: |
Zadravetz; Robert B.; (West
Bend, WI) |
Correspondence
Address: |
BOYLE FREDRICKSON S.C.
840 North Plankinton Avenue
MILWAUKEE
WI
53203
US
|
Family ID: |
38684176 |
Appl. No.: |
11/434044 |
Filed: |
May 15, 2006 |
Current U.S.
Class: |
229/403 ;
229/939 |
Current CPC
Class: |
B31B 2105/0022 20170801;
B31B 2120/002 20170801; B31B 2120/70 20170801; B65D 3/04 20130101;
B31B 50/81 20170801; B31B 2105/00 20170801; B31B 2110/10 20170801;
B31F 1/0038 20130101; B31B 2120/40 20170801; B65D 65/403 20130101;
B31B 50/28 20170801; B31B 2110/20 20170801; B31B 50/25 20170801;
B65D 81/3869 20130101 |
Class at
Publication: |
229/403 ;
229/939 |
International
Class: |
B65D 3/00 20060101
B65D003/00 |
Claims
1. A method of manufacturing a paper container comprising the steps
of: (a) premanufacturing a substantially planar corrugated
paperboard with an outside paper layer providing at least four
percent extensibility along a machine direction of the paper layer,
an inside paper layer providing at least four percent extensibility
along a machine direction of the paper layer, each outside paper
layer glued respectively face toward face, with aligned machine
directions, on either side of a middle corrugated paper layer
having flutes extending along a vertical direction to laminate the
center corrugated paper layer between the first outside paper layer
and the second outside paper layer; (b) cutting a blank from the
premanufactured corrugated paperboard; (c) curving the cut blank of
corrugated paperboard along a circumferential direction crossing
the vertical direction and generally aligned with the machine
directions of the outside and inside paper layers so that the
outside paper layer is on the outside of the curve; and (d)
attaching a bottom wall to a lower curved edge of the curved and
cut corrugated paperboard blank; and (e) rolling an upper curved
edge outward into a lip on the cut and curved corrugated paperboard
blank.
2. The method of claim 1 wherein the outside layer is creped
paper.
3. The method of claim 1 wherein the inside layer is extensible
Kraft paper.
4. The method of claim 1 wherein the middle corrugated paper layer
provides greater than four percent extensibility along a machine
direction of the middle corrugated paper layer as aligned with the
machine directions of the outside paper layer and inside paper
layer.
5. The method of claim 4 wherein the middle corrugated paper layer
is extensible Kraft paper.
6. The method of claim 5 wherein the middle corrugated paper layer
also provides at least four percent extensibility along a cross
direction.
7. The method of claim 1 the inside paper layer further provides at
least four percent extensibility along a cross direction of the
inside paper layer perpendicular to the machine direction.
8. The method of claim 1 the inside paper layer further providing
at least five percent extensibility along the machine
direction.
9. The method of claim 1 including the step of: crushing the upper
curved edge of the corrugated paper board so that the corrugated
paper layer is flattened before rolling the upper curved edge into
a lip.
10. A paper container comprising: an outside paper layer of creped
paper, the creped paper oriented to provide extension
circumferentially around the container; an inside paper layer of
extensible Kraft, the extensible Kraft having a machine direction
oriented circumferentially around the container; a middle
corrugated paper layer having flutes extending from end to end of
the container as laminated between the outside paper layer and the
inside paper layer to form a container wall; a bottom attached to a
lower edge of the container wall; and a lip rolled outward in an
upper edge of the container wall.
11. The container of claim 10 wherein the container wall is
frusto-conical.
12. The container of claim 10 wherein the outside paper layer is
creped paper.
13. The container of claim 10 wherein the inside paper layer is
extensible Kraft paper.
14. The container of claim 10 wherein the middle corrugated paper
layer provides greater than four percent extensibility along a
machine direction of the middle corrugated paper layer as aligned
with the machine directions of the outside paper layer and inside
paper layer.
15. The container of claim 14 wherein the middle corrugated paper
layer is extensible Kraft paper.
16. The container of claim 14 wherein the middle corrugated paper
layer also provides at least four percent extensibility along a
cross direction.
17. The container of claim 10 the inside paper layer further
provides at least four percent extensibility along a cross
direction of the inside paper layer perpendicular to the machine
direction
18. The container of claim 10 the inside paper layer further
providing at least six percent extensibility along the machine
direction.
19. The container of claim 10 including the step of: crushing the
upper curved edge of the corrugated paper board so that the
corrugated paper layer is flattened before rolling the upper curved
edge into a lip.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
Field of the Invention
Cross-Reference to Related Applications
[0001] The invention relates generally to paper containers and in
particular to a container having an insulating wall of corrugated
paper.
BACKGROUND OF THE INVENTION
[0002] Disposable cups for holding hot beverages may be constructed
of expanded polystyrene which provides a cup of relatively low cost
with walls having good thermal insulation. The insulating
properties of the outer walls of the cup allow the cup to be
comfortably held despite the high temperature of its contents. The
disadvantages of polystyrene are that it is not biodegradable,
readily recycled or microwavable.
[0003] In contrast, paper cups are both recyclable and
biodegradable, but such cups, using a single sheet of paper for
their outer walls, provide little thermal insulation. It has
therefore been proposed to construct the outer wall of a paper cup
of multi-ply corrugated paper material. The air trapped between the
flutes of the corrugation and the other plies provides sufficient
thermal insulation to allow the cup to be comfortably held.
Separately cutting and handling the multiple plies needed to form a
multi-ply cup with a corrugated inner layer and assembling the
plies into a single corrugated container requires specialized
machinery, limiting the commercial feasibility of this
approach.
[0004] U.S. Pat. No. 5,839,653, entitled: "Container with
Corrugated Wall" and U.S. Pat. No. 6,126,584, entitled: "Method for
Forming a Container with Corrugated Wall," assigned to the same
assignee as the present invention and hereby incorporated by
reference, teach a simplified method of manufacturing a multi-ply
cup with a corrugated inner layer by premanufacturing a special
corrugated paperboard that can be subsequently rolled into a cup
without tearing, greatly simplifying the manufacture of insulated
wall cups.
[0005] In a first embodiment described in the above patents, the
premanufactured corrugated paperboard has an outside layer on one
side of fluted center layer made from special paper that may expand
to accommodate the distortion inherent in rolling the corrugated
board into a cup. The direction of expansion of the paper is
horizontal with respect to the normal orientation of the completed
cup. The special paper may be creped paper (having small folds that
may unfold under tension to provide expansion) or so-called
"extensible Kraft" a specially prepared Kraft paper that stretches
slightly under tension and is often used for manufacturing bags for
bulk packaged materials such as cement, where the extension can
forestall ripping of the bags under stress.
[0006] One process capable of producing extensible Kraft paper is
described in the "Handbook For Pulp & Paper Technologists" by
G. A. Smook, 1982, page 291, herein incorporated by reference.
Smook describes at page 291, a Clupak compactor that forcibly
shrinks standard Kraft paper along one direction thereby creating
an extensible paper. The Clupak compactor consists of a continuous
rubber belt moving against a heated, chromium-plated and polished
drying cylinder. The web (Kraft) is pressed against the cylinder at
the first point of contact by a non-rotating clamping bar. The
rubber belt is compacted lengthwise (in the machine direction),
which affects the web between it and the cylinder in the same way
thus causing compacting and crimping of the fibers in the web
longitudinally. The compacting is fixed by drying.
[0007] In a second embodiment described in the above patents, the
premanufactured corrugated paperboard has an inside layer on one
side of fluted center layer made from special paper that may
contract to accommodate the distortion inherent in rolling the
corrugated board into a cup. The special paper may be creped paper
or embossed paper having small or large folds that accommodate
compression of the paper. Again, the direction of compression of
the paper is horizontal with respect to the normal orientation of
the completed cup.
[0008] Once the specially manufactured corrugated paperboard is
complete, it is formed into a frusto-conical shape and the edges of
the corrugated board crimped and/or sealed to aid in the rolling of
the upper edge of the cup into a rim and the rolling the lower edge
of the cup about a flange extending downward from a cup bottom. The
rolling to create the rim and to attach the cup bottom is along an
direction perpendicular to the direction of the rolling of the cup
body into a frusto-conical shape and vertical with respect to the
normal orientation of the cup.
[0009] In order that the special corrugated paperboard described in
these patents be readily manufactured on standard equipment in
which the outer and center plies are fed continuously from rolls,
the machine direction of the paper of each ply must be horizontal
in the finished cup when the cup is in a normal orientation.
Correspondingly, the cross direction of the paper of the plies of
each layer will be vertical in the finished cup when the cup is in
a normal orientation
[0010] Despite the generally high extensibility of standard paper
in the cross direction, small tears can form in the rim of the cup
when the cup is formed on standard cup machinery.
SUMMARY OF THE INVENTION
[0011] The present inventor has determined that the use of a paper
with a high degree of extension in machine direction on the inside
of the cup reduces tearing in the rim even though the rim is rolled
along the cross direction. This solution appears to work because
the dominant factor in tearing is not the stretching the paper in a
radial direction about the rim, as one might expect, but the
stretching of the paper along the circumference of the rim. Use of
an expandable material for the center corrugated layer appears to
provide additional benefits in this regard. A combination of an
outer creped ply and an inner ply of extensible Kraft appears to be
particularly advantageous.
[0012] Specifically, the present invention provides a method of
manufacturing a paper container using a premanufactured,
substantially planar corrugated paperboard with a first outside
paper layer providing at least four percent extensibility along a
machine direction, and a second outside paper layer providing at
least four percent extensibility along a machine direction, each
outside paper layer glued respectively face toward face, with
aligned machine directions, on either side of a center corrugated
paper layer having flutes extending along a vertical direction. A
blank is cut from this premanufactured corrugated paperboard and
then curved along a circumferential direction crossing the vertical
direction and generally aligned with the machine directions of the
first and second paper layers. A bottom wall is then attached to a
lower curved edge corrugated paperboard blank and an upper edge is
curved outward into a lip.
[0013] Thus, it is one object of at least one embodiment of the
invention to provide a corrugated paperboard for the manufacture of
containers that allows for the improved formation of a rolled
lip.
[0014] It is another object of least one embodiment of the
invention to provide an improved corrugated paperboard for the
manufacture of containers that can be manufactured with normal
corrugation equipment in which plies have aligned machine
directions and the flutes must run in the cross direction.
[0015] It is yet another object of least one embodiment of the
invention to provide a material that can be used on standard cup
making equipment while resisting tearing of the lip.
[0016] The first outer layer may be creped paper.
[0017] Thus it is one object of at least one embodiment of the
invention to provide an extensible material particularly suited for
a large degree of expansion and appropriate for an outside of a
cup.
[0018] The second outer layer may be extensible Kraft paper.
[0019] Thus, it is one object of at least one embodiment of the
invention to provide an inner extensible material appropriate for
an inside of a cup where it can be coated to resist saturation by a
beverage.
[0020] The center corrugated paper layer may also provides at least
four percent extensibility along a machine direction aligned with
the machine directions of the first outer paper layer and second
outer paper layer.
[0021] It is an object of at least one embodiment of the invention
to provide an extensible intermediate layer between the outer paper
plies that is believed to moderate stress between the plies to
provide tear resistance.
[0022] The center corrugated paper layer may be extensible Kraft
paper.
[0023] Thus it is one object of at least one embodiment of the
invention to an extensible material that can be fluted by standard
equipment.
[0024] One or more of the paper layers may also provide at least
four percent extensibility along a cross direction.
[0025] Thus, it is one object of at least one embodiment of the
invention to provide addition cross direction extension to promote
the rolling of the lip and bottom
[0026] The foregoing and other objects and advantages of the
invention will appear from the following description. In this
description, reference is made to the accompanying drawings which
form a part hereof and in which there is shown by way of
illustration, a preferred embodiment of the invention. Such
embodiment does not necessarily represent the full scope of the
invention, however, and reference must be made therefore to the
claims for interpreting the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a perspective view of a cup manufactured according
to the present invention in partial cut away and showing an outer
paper layer peeled away to reveal an inner corrugated layer;
[0028] FIG. 2 is a plan view of a blank of corrugated material
prior to rolling to form the cup of FIG. 1 showing the direction of
the rolling, and a direction of the flutes of the corrugation and
showing zones in which the corrugations are flattened for
rolling;
[0029] FIG. 3 is a cross section through the blank of FIG. 2 in a
first embodiment showing a creped outer paper layer;
[0030] FIG. 4 is a figure similar to that of FIG. 3 after curvature
as is necessary to construct the cup of FIG. 1 and the expansion of
the outer layer to permit such curvature;
[0031] FIG. 5 is a fragmentary cross section taken along line 5-5
of FIG. 1 showing a forming of the upper lip and attaching of the
bottom of the cup;
[0032] FIG. 6 is a cross section through FIG. 5 taken along line
6-6 showing the flattening of the corrugated material prior to the
forming of FIG. 5;
[0033] FIG. 7 is a cross section taken along line 7-7 of FIG. 5
showing the corrugated material without flattening;
[0034] FIG. 8 is a detailed view of the corrugated material during
rolling to attach to the bottom of the cup showing the slippage
between layers permitted by the crushed corrugated layer such as
reduces internal shear forces and tearing of the outer layer;
[0035] FIG. 9 is a view of slippage of the different lawyers of the
corrugated material in a second embodiment of the invention in
which a slow setting glue may be used to attach the corrugated
elements to one another;
[0036] FIG. 10 is a cross section through a cup forming mandrel of
a cup manufacturing machine showing a forming of the corrugated
material about the mandrel by upwardly moving wings;
[0037] FIG. 11 is a cross section similar to FIG. 3 showing a third
embodiment with an embossed outer layer;
[0038] FIG. 12 is a figure similar to that of FIG. 3 showing a
fourth embodiment showing a creped inner paper layer;
[0039] FIG. 13 is a figure similar to that of FIG. 4 showing
compression of the inner paper layer to permit curvature of the
blank;
[0040] FIG. 14 is a simplified diagram of a machine for making
corrugated paperboard suitable for use with the present
invention;
[0041] FIG. 15 is a top plan view of a sheet of corrugated
paperboard manufactured using the machine of FIG. 14 showing blanks
cut there from and the orientation of the machine direction and
cross-direction on the blanks; and
[0042] FIG. 16 is a cross-sectional view similar to that of FIG. 5
showing the substantial expansion of radius caused by outward
flaring of the upper lip superimposed over a fragmentary top plan
view of the cup showing the extension caused by the outward flaring
and a crack produced in prior art cup designs.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0043] Referring now to FIG. 1, a cup 10, of the present invention
has an upstanding wall 12 rolled into a tube conforming to a
frustum of a cone (hereinafter frusto-conical tube) attached at its
lower edge 14 to a circular bottom (not shown in FIG. 1) to enclose
a beverage receiving volume 16.
[0044] The upstanding wall 12 is composed of a corrugated
paperboard material having an inside paper layer 18 immediately
adjacent to the beverage containing volume 16 which is surrounded
by a middle corrugated paper layer 20 having vertically extending
flutes 22. This, corrugated paper layer is in turn, surrounded by
an outside paper layer 24 which sandwiches the middle corrugated
paper layer 20 between itself and the inside paper layer 18. An
adhesive (not shown) connects the middle corrugated paper layer 20
to the inside paper layer 18 and the outside paper layer 24
according to methods well known in the art. The inside paper layer
18 is coated with a thin water resistant coating 26 to provide
protection of the inside paper layer 18 from hot liquid that may be
held within the volume 16. In the preferred embodiment, the coating
26 is a pulpable acrylic permitting the cup to be easily recycled.
Such coatings are well known in the art and include a variety of
moisture resistant materials including wax and acrylics.
[0045] Referring now to FIG. 4, the upstanding wall 12, before it
is rolled into a cup as shown in FIG. 1, is formed from a blank 28
cut from a premanufactured corrugated paperboard of corrugated
material into a sector of an annulus thereby to roll into the
frusto-conical shape of FIG. 1. The flutes of the corrugations lie
generally along a vertical direction 30 extending along a line of
radius of the annulus whereas the bending of the blank 28 into the
frusto-conical shape is along a circumferential direction 32
crossing the vertical direction 30.
[0046] Referring now to FIG. 3, in a first embodiment, the outside
paper layer 24 of the corrugated blank 28 is constructed of an
extensible paper that will lengthen under tension along the
circumferential direction 32. Such paper may be a creped paper
having multiple randomly formed creases and folds that under
tension straighten to allow the outside paper layer 24 to expand as
described. Alternatively, in a second embodiment (not shown) the
outside paper layer 24 may be a so-called extensible Kraft paper
which provides a stretching at the fiber level of the paper.
Extensible Kraft is commercially available under the trade name of
XKL extensible from Thilmany Pulp and Paper Company of Kaukauna,
Wis. Referring to FIG. 1, in a third embodiment, the outside paper
layer 24 may also be a paper with embossing 25, where the embossing
25 may flatten when the paper is put under tension allowing the
paper to lengthen. Other extensible materials may also be used as
will be apparent from this description to those of ordinary skill
in the art.
[0047] Referring now to FIG. 4, when the blank 28 is rolled as
indicated by arrows 34 into a frusto-conical shape, the outside
paper layer 24 may expand along the circumferential direction 32 to
permit the rolling without tearing of the outside paper layer 24 or
a crushing of the flutes of the middle corrugated paper layer 20.
The expansion of the outside paper layer 24 is necessary because of
the substantially greater thickness of the blank 28 than a single
sheet of paper normally used for the upstanding wall 12 of a cup.
This greater thickness of wall material displaces the outside paper
layer 24 to a greater radius than the inside paper layer 18
requiring a significant increase in the circumferential length of
the outside paper layer 24. An expansion of the outside paper layer
24 of two to fifteen percent is believed to be adequate for most
standard container sizes with necessary thickness of the corrugated
material.
[0048] Referring now to FIGS. 12 and 13, in a fourth embodiment,
the inner layer 18 may be a creped or embossed paper. When the
blank 28 is rolled as indicated by arrows 34 into a frusto-conical
shape, the inside paper layer 18 may compress along the
circumferential direction 32' to permit the rolling without tearing
of the outside paper layer 24 or a crushing of the flutes of the
middle corrugated paper layer 20. In this embodiment, the
compression of the inside paper layer 18, rather than an expansion
of the outside paper layer 24 accommodates the difference in
circumferences of the inside paper layer 18 and outside paper layer
24 as the blank 28 is rolled. Again, a compression of the inside
paper layer 18 of two to fifteen percent is believed to be adequate
for most standard container sizes with necessary thickness of the
corrugated material.
[0049] The ability of the paper layers to change circumferential
dimension, either by expansion or compression, as the cup is rolled
by the requisite amount will be termed circumferential plasticity.
It will be recognized that both the inner and outer paper layers
may be constructed of paper exhibiting circumferential plasticity
and in this case the amount of plasticity for each layer may be
reduced from that required when only a single layer having
circumferential plasticity is used.
[0050] Referring again to FIG. 2, prior to folding the blank 28 and
assembling it into a cup 10, the flutes 22 (not shown in FIG. 2)
are crushed flat in a strip along the lower edge 14 and upper edge
38 of the blank 28. This flattening reduces the thickness of the
middle corrugated paper layer 20 (as shown in FIG. 6) prior to it
being folded into a cup and can be performed in a single operation
during the die cutting of the blank by including anvils within the
knife blade of the die to flatten the edges 14 and 38. Similarly,
the flutes 22 are crushed flat in strips along the left and right
edges 46 and 44 to permit sealing these edges together as will be
described.
[0051] Referring now to FIG. 10, the blank 28 is folded about a
frusto-conical mandrel 40 by conforming wings 42 in a cup making
machine well known in the art. When the folding is complete, left
and right edges 44 and 46 of the blank 28 abut and are sealed
together by a heat-sealing process or adhesive such as is well
known in the art.
[0052] Next, and referring to FIG. 5, the crushed upper edge 38 of
the upstanding wall 12 is rolled outward to form a lip 48 according
to conventional paper cup construction techniques. Also the lower
edge 14 is rolled about a downward extending lip on the periphery
of the disked shaped bottom 51 to form a seal 49 against leakage of
the contained beverage. The seal 49 is formed by heat sealing the
lower edge 14 to the bottom 51 or attaching it with adhesive.
[0053] Referring to FIG. 6, the crushing of the upper and lower
edges 14 and 38 reduces the difference in radius between the inside
paper layer 18 and the outside paper layer 24 in the folding of the
lip 48 and the bottom seal 49 thus reducing the difference in the
circumference of these two layers at the lip 48 and the seal 49 and
the tendency of the outside paper layer 24 in the seal 49 and the
inside paper layer 18 in the lip 48 to tear. With respect to the
seal 49, the extensible material of the outside paper layer 24 may
also expand along the vertical direction 30 further reducing this
tendency of the outside paper layer 24 to tear upon stretching.
[0054] Although the inventor does not wish to be bound by a
particular theory, it is believed that, in both the cases of the
lip 48 and the seal 49, the crushed middle corrugated paper layer
20 facilitates a displacement, upon rolling, between the layers 18
and 24. Referring to FIG. 8, by permitting a degree of displacement
between layers 18 and 24 in the seal 49, the stretching of the
outside paper layer 24 necessary for the folding operation is
reduced. A similar effect occurs with respect to the opposite
direction rolling of the lip 48.
[0055] Referring to FIG. 7, because the crushing of the upper edge
38 and lower edge 14 is restricted to the region of the lip 48 and
seal 49, the thermal properties of the majority of the outer
surface of the upstanding wall 12 are preserved, in particular, the
air spaces between the middle corrugated paper layer 20 and the
layers 18 and 24.
[0056] In another embodiment of the invention, shown generally in
FIG. 9, this same principle of permitting a sliding between the
inside paper layer 18 and outside paper layer 24 may be invoked to
permit the forming of the blank 28 around the mandrel 40 with a
reduced or minimal need for expansion of the outside paper layer
24. In this embodiment, a slow setting adhesive 50 is used to
assemble the components of the blank 28 together. In particular,
the opposed surfaces of layer 18 and layer 24 are coated with a
slow setting adhesive 50 and the blank 28 is rolled about the
mandrel 40. At the time that the wings 42 form the blank 28 around
the mandrel 40, the variation between the circumference necessary
from the inside paper layer 18 and outside paper layer 24 is
accommodated by relative slippage shown by arrows 52 between the
middle corrugated paper layer 20 and the inside paper layer 18 and
the middle corrugated paper layer 20 and the outside paper layer
24. A misalignment in the left and right edges 44 and 46 of the
inside paper layer 18 and outside paper layer 24, respectively, at
a point of seaming, is relatively minor and may be accommodated by
crushing and heat sealing all layers 18 and 24 of both edges 44 and
46 together at the seam line. Alternatively, the outside paper
layer 24 of the blank may be cut to be larger than the inside paper
layer 18 and the middle corrugated paper layer 20. The slight loss
in thermal resistance at this seam caused by the crushing out of
the air space between the layers is offset by the seam which
comprises six layers of paper material.
[0057] Adhesives 50 suitable for this purpose and the control of
the setting time of the adhesives are well understood in the
art.
[0058] Normally moisture protection is required for the outside
paper layer 24 when the cup will be used for cold beverages as a
result of condensation forming on the outer surfaces. However, in
the present cup, the thermal insulating properties of the
corrugated blank greatly reduces such condensation. Nevertheless,
the outer surface of outside paper layer 24 may also be coated with
a water resistant material.
[0059] Referring now to FIG. 14, practical commercial construction
of the blanks 28 may be performed on a commercial corrugation
machine 58 providing for multiple feeder rolls 60 providing paper
for the inside paper layer 18, the middle corrugated paper layer
20, and the outside paper layer 24.
[0060] Each paper layer 18, 20, and 24 will have aligned machine
directions 62 being the direction from which the materials of the
paper layers 18, 20, and 24 are removed from the rolls 60 and
reflecting the fabrication of the paper layers 18, 20, and 24 using
conventional papermaking machines. As will be understood in the
art, the machine direction 62 generally defines a direction in
which the fibers in the paper are aligned and strongly affects the
ability to stretch the paper. Normal papers provide one to three
percent stretch in the machine direction and three to five percent
stretch in the cross-direction perpendicular to the machine
direction.
[0061] Paper removed from roll 60 holding middle corrugated paper
layer 20 is received by corrugating rollers 64 which provide for
fluting extending along the cross-direction. Paper removed from
rolls 60 holding paper layers 18 and 24 are received by adhesive
application rollers 66 that apply adhesive to the inner surfaces of
the paper layers 18 and 24 which are then adhered to the opposite
sides of middle corrugated paper layer 20 as they pass through
combiner rollers 68. The completed paperboard 29 may then be cut
into blanks 28 as has been described above by a die cutter 70.
[0062] Referring now to FIG. 15, the vertical direction 30 for each
blank 28, as previously described, is aligned with the
cross-direction 72 of the paper layers and the circumferential
direction 32 associated with each blank 28 is aligned with the
machine direction 62 of the paper layers. As noted above, with
conventional paper, the machine direction 62 will offer a
relatively low extensibility, however, per the present invention, a
much greater extensibility is provided in the outer sheets by using
a creping or extensible Kraft.
[0063] Referring now to FIG. 16, a conventional cup-forming
machine, operating on the blanks 28 can produce small tears 74 in
the lip 48 extending generally around the circumference of the cup.
While the present inventor does not wish to be bound by a
particular theory, it is believed that these tears 74 are caused by
the outward rolling of the lip 48 such as requires a substantial
circumferential extension 84 of the inner layer 18 as the radius of
the upstanding wall 12 increases at the lip 48 by distance 80.
[0064] Accordingly in the present invention, the inside paper layer
18 may be constructed from an extensible Kraft having a
substantially greater machine direction extension than that found
in normal paper. Preferably, the extensible Kraft provides a
machine direction extension greater than the three percent stretch
found in standard paper and greater than the four percent stretch
normally found in the cross-direction of such paper. Suitable paper
may be obtained from Thilmany under the trade name XKL as has been
described above and provides greater than five percent extension in
both the cross and machine directions and typically extension
values ranging from six to twelve percent.
[0065] Additional resistance against tears 74 may be obtained by
also making the middle corrugated paper layer 20 as shown in FIG.
15 from a similar extensible Kraft. The ability of these inner
layers to expand appears to accommodate the rolling process with
reduced tears possibly by providing better transition between the
distortions of the materials.
[0066] The above description has been that of a preferred
embodiment of the present invention. It will occur to those that
practice the art that many modifications may be made without
departing from the spirit and scope of the invention. In order to
apprise the public of the various embodiments that may fall within
the scope of the invention, the following claims are made:
* * * * *