U.S. patent application number 11/390495 was filed with the patent office on 2006-08-17 for lidded paperboard container.
This patent application is currently assigned to Fort James Corporation. Invention is credited to Margaret P. Hoks, Mark B. Littlejohn, Kevin E. JR. Lutz, Gerald J. Van Handel.
Application Number | 20060180646 11/390495 |
Document ID | / |
Family ID | 34435174 |
Filed Date | 2006-08-17 |
United States Patent
Application |
20060180646 |
Kind Code |
A1 |
Littlejohn; Mark B. ; et
al. |
August 17, 2006 |
Lidded paperboard container
Abstract
This invention relates generally to lidded disposable pressed
paperboard containers and more particularly to a disposable lid
with an engagement profile particularly useful for paperboard
containers comprising evert outer portions. The lid of the present
invention provides a good fit for paperboard container bases having
evert outer portions while still allowing the lid to be removed
from the base without the need for excessive force. The lid profile
is relatively insensitive to size variations of paperboard
container bases having evert outer portions and allows for flexing
of paperboard during application so as to provide an unexpectedly
good seal so as to provide lidded, disposable paperboard
containers.
Inventors: |
Littlejohn; Mark B.;
(Appleton, WI) ; Hoks; Margaret P.; (Neenah,
WI) ; Lutz; Kevin E. JR.; (Laureldale, PA) ;
Van Handel; Gerald J.; (Neenah, WI) |
Correspondence
Address: |
PATENT GROUP GA030-43;GEORGIA-PACIFIC CORPORATION
133 PEACHTREE STREET, N.E.
ATLANTA
GA
30303-1847
US
|
Assignee: |
Fort James Corporation
Atlanta
GA
|
Family ID: |
34435174 |
Appl. No.: |
11/390495 |
Filed: |
March 27, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10963686 |
Oct 13, 2004 |
|
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11390495 |
Mar 27, 2006 |
|
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60512811 |
Oct 20, 2003 |
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Current U.S.
Class: |
229/406 ;
229/125.25; 229/125.36 |
Current CPC
Class: |
B65D 43/0212 20130101;
B65D 2543/00537 20130101; A47G 19/03 20130101; B65D 2543/00092
20130101; B65D 2543/00842 20130101; B65D 2543/00648 20130101; B65D
2543/00805 20130101; A47G 19/02 20130101; B65D 2543/00685 20130101;
B65D 2543/00731 20130101; B65D 2543/00527 20130101; B65D 2543/00361
20130101; B65D 1/34 20130101; B65D 2543/00296 20130101 |
Class at
Publication: |
229/406 ;
229/125.25; 229/125.36 |
International
Class: |
B65D 43/08 20060101
B65D043/08; B65D 1/00 20060101 B65D001/00 |
Claims
1) A disposable container comprising: a) a domed lid having: i) a
central lid portion; ii) a fluted sidewall extending downwardly
from the central lid portion, the fluted sidewall of the domed lid
being provided with a plurality of flutes, such that the fluted
sidewall defines a fluted base at its lower portion; and iii) a rim
extending outwardly and downwardly from the fluted sidewall
providing an annular engagement portion defining a lid engagement
circumference, the rim being further provided with a plurality of
generally equally spaced undercut lugs around the annular
engagement portion of the domed lid; and iv) a pressed paperboard
container having an evert outer portion; wherein the plurality of
undercut lugs of the lid rim are sized to secure the lid to the
container and have a collective undercut span of from about 15% to
about 30% of the lid engagement circumference, and wherein the
perimeter of the base and the annular engagement portion of the lid
rim are sized to engage each other when the lid is installed on the
base.
2) The container of claim 1, wherein the plurality of undercut lugs
of the lid rim define an undercut span of from about 20% to about
25% of the lid engagement circumference.
3) The container of claim 1, wherein the lid rim is provided with
from about 7 to about 15 generally equally spaced undercut lugs
around the annular engagement portion thereof.
4) The container of claim 1, wherein the lid rim is provided with
from about 10 to about 12 generally equally spaced undercut lugs
around the annular engagement portion thereof.
5) The container of claim 1, wherein the undercut lugs of the lid
rim have an undercut depth of from about 25 mils to about 100
mils.
6) The container of claim 1, wherein the undercut lugs of the lid
rim have an undercut circumferential span of from about 1/4'' to
about 1''.
7) The container of claim 1, wherein the lid rim has an outwardly
extending wall adjacent the fluted base of the sidewall and a
downwardly extending engagement wall defining the annular
engagement portion of the rim above the undercut lugs, wherein the
outwardly extending wall defines a headspace of at least about 30
mils above the brim of the container base when the lid is installed
on the base.
8) The container to claim 1, wherein the lid rim has an outwardly
extending wall adjacent the fluted base of the sidewall and a
downwardly extending engagement wall defining the annular
engagement portion of the rim above the undercut lugs, wherein the
outwardly extending wall defines a headspace of from about 30 mils
to about 150 mils when the lid is installed on the base.
9) The container of claim 1, wherein the sidewall of the lid is
provided with a plurality of outwardly convex flutes.
10) The container of claim 9, wherein the flutes have a radius of
curvature of from about 0.125'' to about 1''.
11) The container of claim 9, wherein there is from about 1.5 to
about 1.9 outwardly convex flutes per inch of engagement
circumference of the lid.
12) The container of claim 1, wherein the domed lid is provided
with from about 35 to about 75 generally uniform outwardly convex
flutes.
13) The container of claim 1, wherein the domed lid and container
base are configured and dimensioned such that the perimeter of the
container base is vertically aligned with the fluted base of the
sidewall within an offset distance of about 1/4 to about 3/8'' when
the domed lid is installed on the base.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of co-pending
U.S. patent application Ser. No. 10/963,686, filed Oct. 13, 2004,
entitled "Pressed Paperboard Servingware with Improved Rigidity and
Rim Stiffness", which was based upon Provisional Application Ser.
No. 60/512,811, filed Oct. 20, 2003, of the same title. The
priorities of the above-noted patent applications are hereby
claimed and their disclosures incorporated herein by reference in
their entireties.
TECHNICAL FIELD OF THE INVENTION
[0002] This invention relates generally to lidded disposable
paperboard containers and more particularly to a disposable lid
with an engagement profile particularly useful for paperboard
containers comprising evert outer portions. The lid of the present
invention provides a good fit for pressed paperboard container
bases having evert outer portions while still allowing the lid to
be removed from the base without the need for excessive force. The
lid profile is relatively insensitive to size variations of pressed
paperboard container bases having evert outer portions and allows
for flexing of paperboard during application so as to provide an
unexpectedly good seal so as to provide lidded, disposable pressed
paperboard containers.
BACKGROUND OF THE INVENTION
[0003] Disposable containers with domed lids are widely used in the
food service industry, typically in connection with plastic plates
and platters that are intended for take-out use. U.S. Pat. No.
6,733,852 to Littlejohn et al. (which disclosure is incorporated
herein in its entirety by this reference) discloses a disposable
serving plate with a sidewall-engaged sealing cover. In a
construction of the '852 patent invention, a plate includes a
substantially planar central area, a plate sidewall extending
outwardly and upwardly from the central area, a recessed sealing
area and a container base stop ridge adjacent the sealing area. A
convex outwardly extending rim adjoins the base stop ridge and has
an outer lip or border formed thereabout. A resilient mating domed
lid is fitted to the plate to provide a lidded container.
[0004] A further example of domed lids for use with disposable
plates, here pressed paperboard containers, is disclosed in
co-pending U.S. application Ser. No. 10/170,675, filed Jun. 13,
2002, the disclosure of which is incorporated by reference herein.
As shown in FIG. 1 of the '675 application, a groove defines at its
outer wall an engagement perimeter. This engagement perimeter is
substantially continuous (except for the tab portion) around the
perimeter of the container such that a seal is formed when the lid
is placed on the container for use.
[0005] The design of the '675 application is particularly
well-suited for use with containers having outer perimeters that
terminate in a downward slope, such as the pressed paperboard
container disclosed and claimed in U.S. Pat. No. 6,715,630, (the
disclosure incorporated herein in its entirety by this reference),
for example, see FIG. 1D therein. However, the assignee of the
present invention (Georgia Pacific Corporation, Dixie.RTM.
Business, Atlanta, Ga.) has recently introduced a paperboard
container exhibiting markedly improved rigidity. This paperboard
container is disclosed and claimed in co-pending U.S. patent
application Ser. No. 10/963,686, (disclosure previously
incorporated herein in its entirety by this reference). The pressed
paperboard container of the '686 application comprises a rim that
terminates in an evert outer portion, that is, in an outwardly
and/or upwardly direction.
[0006] The inventors herein have found that the substantially
continuous engagement portion of the '675 application lid provides
an unsatisfactory seal with the '686 application paperboard
container. In particular, the design of the '675 application lid
results in a seal that is overly tight when used with the
paperboard container of the '686 application. While a tight seal is
desirable so that the lid will not inadvertently disengage from the
container in use, if the seal is too tight, the user must apply
considerable force to disengage the lid from the container. During
application of such force, it is quite possible that the user will
apply too much force to result in spilling of the contents. Also,
over exertion can cause the lid to become cracked.
[0007] In addition to the difficulties seen in designing a lid for
a disposable pressed paperboard container having evert outer
portions, lidding of paperboard container bases can be especially
problematic. Unlike plastic containers that are typically
thermoformed or injection molded and which are generally uniform in
final size and shape, paperboard containers are more subject to
size and shape variances, especially pressed paperboard containers
made from paperboard blanks. Sources of variance can include
moisture content, forming conditions, relaxation, spring back and
so forth. As discussed above, lids with continuous or substantially
continuous engagement portions have been disclosed for use on
paperboard plates; however, such lids are frequently difficult to
install properly on a consistent basis due to size variations in
the containers.
[0008] In view of the above, there is a need for a lid for a
disposable pressed paperboard container where the container
comprises a rim that terminates in an evert outer portion so as to
provide a lid with a "just right" fit. Still further, there is a
need for a lid for a disposable paperboard container that provides
a good fit even when the paperboard containers are not of a
consistently uniform size and shape.
SUMMARY OF THE INVENTION
[0009] This invention relates generally to lidded disposable
pressed paperboard containers and, more particularly, to a
disposable lid with an engagement profile particularly useful for
pressed paperboard containers comprising evert outer portions. The
lid of the present invention provides a good fit for pressed
paperboard container bases having evert outer portions while still
allowing the lid to be removed from the base without the need for
excessive force. The lid profile is relatively insensitive to size
variations of pressed paperboard container bases having evert outer
portions and allows for flexing of the base during application so
as to provide an unexpectedly good seal to provide lidded,
disposable pressed paperboard containers. In the engagement of the
lid with the pressed paperboard container, the plurality of
undercut lugs on the lid rim are sized to secure the lid to the
container base. In particular aspects of the invention, the
plurality of lugs are substantially equally distributed around the
perimeter of the lid, and the outer perimeter of the container and
the annular engagement portion of the lid rim are sized to engage
each other when the lid is installed on the base.
[0010] Additional advantages of the invention will be set forth in
part in the detailed description which follows and in part will be
obvious from the description, or may be learned by practice of the
invention. The advantages of the invention will be realized and
attained by means of the elements and combinations particularly
pointed out in the appended claims. It is to be understood that
both the foregoing general description and the following detailed
description are exemplary and explanatory aspects of the invention
and are not restrictive of the invention, as claimed.
BRIEF DESCRIPTION OF DRAWINGS
[0011] The invention is described in detail below with reference to
the drawings wherein like numerals designate like parts. In the
drawings:
[0012] FIG. 1 is an in perspective view of a prior art lid having a
substantially continuous engagement portion.
[0013] FIG. 2 is a view in perspective of a fluted dome lid
configured for use in connection with the present invention;
[0014] FIG. 3 is a top plan view of the domed lid of FIG. 2;
[0015] FIG. 3A is a view in section and elevation of the lid of
FIG. 3 along line 3A-3A;
[0016] FIG. 3B is a schematic view in elevation and section along
line 3B-3B of FIG. 3;
[0017] FIGS. 3C and 3D are enlarged schematics illustrating
features of the lid of FIG. 3;
[0018] FIG. 4 is a view in perspective of a paperboard container
having a horizontal outward projection from its brim;
[0019] FIG. 5 is a schematic view illustrating various angles;
[0020] FIGS. 6 through 8 are schematic views in section showing the
installation of the lid FIG. 2 to a paperboard container base of
the class shown in FIG. 4; and
[0021] FIG. 8A is an enlarged schematic illustrating features of
the inventive containers.
DETAILED DESCRIPTION OF THE INVENTION
[0022] The invention is described in detail below with reference to
the various Figures. Exemplary definitions used in the
specification and claims appear immediately below.
[0023] "Domed" refers to an inverted bowl type structure with a
sidewall and a topwall. It also refers to segmented domed
structures.
[0024] "Evert outer portion" is the portion at the outer perimeter
of the paperboard container. This portion is substantially
ring-shaped where the outer portion of this ring is defined by the
outer edge of the container rim and the inner portion of this ring
is defined by the junction of the evert outer portion and the brim
transition point. In one example, the evert outer portion is
illustrated as element 68 on FIGS. 4 and 5 herein. The evert outer
portion can deviate some from a ring shape (to be substantially
ringed-shaped) if the outer perimeter of the pressed paperboard
container is not exactly circular.
[0025] Referring to FIG. 5, the eversion angle, .beta., is an
outward change in downward slope at the outer flange of a container
and is calculated as the angle between a tangent to the brim
portion at its lower terminus and a tangent to the evert outer
portion at its junction with the brim transition to the evert outer
portion. As used throughout this specification and in the claims,
"slope" refers to inclination as one moves outwardly from the
center of the product. Thus, a sidewall of a container base is
typically referred to as upwardly sloping and a brim has a
downwardly sloping outer portion. A container with a brim sloping
downwardly at 60 degrees from horizontal transitioning to a
horizontal ring (0 slope) has an eversion angle of 60 degrees,
while a container with a brim sloping downwardly at 45 degrees
transitioning to a ring sloping upwardly 5 degrees has an eversion
angle of 50 degrees. Alternatively, the eversion angle can be
conveniently determined by measuring the angle, y, between the
downwardly sloping brim and the outwardly extending evert and
subtracting .gamma. from 180 degrees because .gamma. and .beta. are
supplementary angles as is seen in FIG. 5.
[0026] "Mils" means thousandths of an inch.
[0027] "Rim" as used in connection with the lids of the invention
refers to that portion of the lid flange adapted to engage the
outer border or perimeter of a container base and secure the lid to
the base at the lid's outer flange. The periphery of the rim and
like references are used interchangeably with rim engagement
circumference for circular lids.
[0028] "Thermoforming", "thermoformed" and like terminology is used
herein in accordance with its ordinary meaning. In the simplest
form, thermoforming is the draping of a softened sheet over a
shaped mold. In the more advanced form, thermoforming is the
automatic high speed positioning of a sheet having an accurately
controlled temperature into a pneumatically actuated forming
station whereby the article's shape is defined by the mold,
followed by trimming and regrind collection as is well known in the
art. Still other alternative arrangements include the use of drape,
vacuum, pressure, free blowing, matched die, billow drape, vacuum
snap-back, billow vacuum, plug assist vacuum, reverse draw with
plug assist, pressure bubble immersion, trapped sheet, slip,
diaphragm, twin-sheet cut sheet, twin-sheet roll-fed forming or any
suitable combinations of the above. Details are provided in J. L.
Throne's book, Thermoforming, published in 1987 by Coulthard. Pages
21 through 29 of that book are incorporated herein by reference.
Suitable alternate arrangements also include a pillow forming
technique that creates a positive air pressure between two heat
softened sheets to inflate them against a clamped male/female mold
system to produce a hollow product. Metal molds are etched with
patterns ranging from fine to coarse in order to simulate a natural
or grain like texturized look. Suitable formed articles are trimmed
in line with a cutting die and regrind is optionally reused since
the material is thermoplastic in nature. Other arrangements for
productivity enhancements include the simultaneous forming of
multiple articles with multiple dies in order to maximize
throughput and minimize scrap.
[0029] "Undercut" and like terminology refers to the profile of a
part having a recess, groove or wall that extends laterally under
(or over) a portion of the same part. The "draft" of a thermoformed
part can be thought of in the case of a (female) mold as the
difference between the upper lateral span of a mold cavity and that
span below it. A positive draft allows the pattern to be pulled
cleanly from the mold; however, undercuts inherently have a
negative draft. Articles that are thermoformed must be so designed
as to permit the die section to be parted free of the molded
articles without undue interference with the surfaces of the
articles. Typically, the surfaces of thermoformed articles have a
so-called positive "draft" with respect to the direction in which
the die sections are moved during parting to insure that there is
no interference between the molded article and the interior
surfaces of the die sections during parting. Interference between
the articles and the dies is commonly known as "negative draft" and
occurs when undercuts are molded into a part. In the present
invention, the undercut depth or distance of the lid rim required
to secure the lid to a container base is generally kept to a
minimum.
[0030] "Unfluted" when used to describe a dome sidewall means the
unfluted portion has a curvature equal to or less than the
curvature of the dome sidewall generally.
[0031] "Wall caliper", "caliper" or like terminology refers to the
wall thickness of a lid or container base.
[0032] Typical materials for the lids of the invention include
polystyrene containing compositions, oriented polystyrene sheet and
the like, as well as thermoplastic materials comprising
polypropylene.
[0033] The lids of the invention are used for pressed paperboard
containers, that is, those that are made from paperboard blanks
that are typically cut to size. Coated paperboard can be used. Clay
coated paperboard is typically printed, coated with a functional
grease/water resistant barrier and moistened prior to blanking and
forming. The printed, coated and moistened paperboard roll is then
transferred to a web fed press where the blanks are cut in a
straight across, staggered, or nested pattern (to minimize scrap).
The blanks are transferred to the multi-up forming tool via
individual transfer chutes. The blanks will commonly hit against
blank stops (rigid or pin stops that can rotate) for final
positioning prior to forming. The stop heights and locations are
chosen to accurately locate the blank and allow the formed product
to be removed from the tooling without interference. Typically the
inner portions of the blank stops or inner blank stops are lower in
height since the formed product must pass over them.
[0034] The following U.S. patents contain further information as to
materials, processing techniques and equipment for paperboard
container manufacture and are incorporated by reference into this
application: U.S. Pat. No. 6,715,630, entitled "Disposable Food
Container With A Linear Sidewall Profile and an Arcuate Outer
Flange"; U.S. Pat. No. 6,893,693 entitled "High Gloss Disposable
Pressware"; U.S. Pat. No. 6,585,506, entitled "Side Mounted
Temperature Probe for Pressware Die Set"; U.S. Pat. No. 6,592,357,
entitled "Rotating Inertial Pin Blank Stops for Pressware Die Set";
U.S. Pat. No. 6,589,043, entitled "Punch Stripper Ring Knock-Out
for Pressware Die Sets"; and U.S. application Ser. No. 09/978,484,
entitled "Deep Dish Disposable Pressed Paperboard Container"; Ser.
No. 10/600,814, entitled "Disposable Servingware Containers with
Flange Tabs" See also, U.S. Pat. Nos. 5,249,946; 4,832,676;
4,721,500; and 4,609,140, which are also pertinent and are
disclosed herein in their entireties by this reference.
[0035] For pressed paperboard plate stock of conventional
thicknesses in the range of from about 0.010 to about 0.040 inches,
the springs upon which a lower die half of a forming set is mounted
are typically constructed such that the full stroke of the upper
die results in a force applied between the dies of from about 6000
to about 14,000 pounds or higher. Similar forming forces and
control thereof can likewise be accomplished using hydraulics as
will be appreciated by one of skill in the art. The pressed
paperboard that is formed into the blanks is conventionally
produced by a wet laid paper making process and is typically
available in the form of a continuous web on a roll. The paperboard
stock can have a basis weight in the range of from about 100 pounds
to about 400 pounds per 3000 square foot ream and a thickness or
caliper in the range of from about 0.010 to about 0.040 inches as
noted above. Lower basis weight paperboard stock is generally used
for ease of forming and to save on feedstock costs. Paperboard
stock utilized for forming paper plates is typically formed from
bleached pulp fiber and is usually double clay coated on one side.
Such paperboard stock commonly has a moisture (water) content
varying from about 4.0% to about 8.0% by weight.
[0036] The effect of the compressive forces at the paperboard rim
is greatest when the proper moisture conditions are maintained
within the paperboard: at least about 8% and less than about 12%
water by weight, or from about 9.0 to about 10.5%. Paperboard stock
having moisture in this range has sufficient moisture to deform
under pressure, but not such excessive moisture that water vapor
interferes with the forming operation or that the paperboard is too
weak to withstand the forces applied. To achieve the desired
moisture levels within the paperboard stock as it comes off the
roll, the paperboard is treated by spraying or rolling on a
moistening solution, primarily water, although other components
such as lubricants can be added. The moisture content can be
monitored with a hand held capacitive-type moisture meter to verify
that the desired moisture conditions are being maintained or the
moisture is monitored by other suitable means, such as an infra-red
system. The paperboard plate stock generally will not be formed for
at least about 6 hours after moistening to allow the moisture
within the paperboard to reach equilibrium.
[0037] The paperboard stock is typically impregnated with starch
and coated on one side with a liquid proof layer or layers
comprising a press-applied, water-based coating applied over the
inorganic pigment typically applied to the board during
manufacturing. Carboxylated styrene-butadiene resins can be used
with or without filler if so desired. In addition, for aesthetic
reasons, the paperboard stock is often initially printed before
being coated with an overcoat layer. As an example of typical
coating material, a first layer of latex coating can be applied
over the printed paperboard with a second layer of acrylic coating
applied over the first layer. These coatings can be applied either
using the conventional printing press used to apply the decorative
printing or can be applied using some other form of a conventional
press coater. Coatings utilized in connection with the invention
can include about 2 pigment (clay) containing layers, with a
binder, of about 6 lbs/3000 ft.sup.2 ream or so followed by about 2
acrylic layers of about 0.5-1 lbs/3000 ft.sup.2 ream. The clay
containing layers are generally provided first during board
manufacture and the acrylic layers are then applied by press
coating methods, i.e., gravure, coil coating, flexographic methods
and so forth as opposed to extrusion or film laminating methods
which are expensive and can require offline processing as well as
large amounts of coating material. An extruded film, for example,
can require about 25 lbs/3000 ft.sup.2 ream.
[0038] A layer comprising a latex can contain any suitable latex
known to the art. By way of example, suitable latexes include
styrene-acrylic copolymer, acrylonitrile styrene-acrylic copolymer,
polyvinyl alcohol polymer, acrylic acid polymer, ethylene vinyl
alcohol copolymer, ethylene-vinyl chloride copolymer, ethylene
vinyl acetate copolymer, vinyl acetate acrylic copolymer,
styrene-butadiene copolymer and acetate ethylene copolymer. The
layer can comprise a latex comprising styrene-acrylic copolymer,
styrene-butadiene copolymer, or vinyl acetate-acrylic copolymer.
Still further, the layer comprises a latex containing vinyl acetate
ethylene copolymer. A commercially available vinyl acetate ethylene
copolymer is "AIRFLEX.RTM. 100 HS" latex (Air Products and
Chemicals, Inc., Allentown, Pa.). The layer can comprise a
pigmented latex. Pigmenting the latex increases the coat weight of
the layer comprising a latex thus reducing runnability problems
when using blade cutters to coat the substrate. Pigmenting the
latex also improves the resulting quality of print that can be
applied to the coated paperboard. Suitable pigments or fillers
include kaolin clay, delaminated clays, structured clays, calcined
clays, alumina, silica, aluminosilicates, talc, calcium sulfate,
ground calcium carbonates, and precipitated calcium carbonates.
Other suitable pigments are disclosed, for example, in Kirk-Othmer,
Encyclopedia of Chemical Technology, Third Edition, Vol. 17, pp.
798, 799, 815, 831-836. The pigment can be selected from the group
consisting of kaolin clay and conventional delaminated coating
clay. An available delaminated coating clay is "HYDRAPRINT" slurry,
which is believed to be supplied as a dispersion with a slurry
solids content of about 68%. (J.M. Huber Company, Edison, N.J.).
The layer comprising a latex can also contain other additives that
are well known in the art to enhance the properties of coated
paperboard. By way of example, suitable additives include
dispersants, lubricants, defoamers, film-formers, antifoamers and
crosslinkers. By way of example, "DISPEX N-4" is one suitable
organic dispersant and comprises about 40% solids dispersion of
sodium polycarboxylate (Allied Colloids, Bradford, UK). By way of
example, "BERCHEM 4095" (Bercen, Cranston, R.I.) is one suitable
lubricant and which is believed to comprise 100% active coating
lubricant based on modified glycerides. By way of example,
"Foamaster DF-177NS" is one suitable defoamer (Henkel, Gulph Mills,
Pa.). In one form, the coating comprises multiple layers that each
comprise a latex.
[0039] Typically, paperboard for containers contains up to about 6%
starch; however, the rigidity can be considerably enhanced by using
paperboard with from about 9 to about 12 weight % starch. See, for
example, U.S. Pat. Nos. 5,938,112 and 5,326,020, the disclosures of
which are incorporated herein by this reference.
[0040] The paperboard stock is generally moistened on the uncoated
side after all of the printing and coating steps have been
completed. In a typical forming operation the web of paperboard
stock is fed continuously from a roll through a scoring and cutting
die to form the blanks which are scored and cut before being fed
into position between the upper and lower die halves. The die
halves are heated as described above, to aid in the forming
process. It has been found that good results can be obtained if the
upper die half and lower die half--particularly the surfaces
thereof--are maintained at a temperature in the range of from about
250.degree. F. to about 400.degree. F., or at about 325.degree.
F..+-.25.degree. F. These die temperatures have been found to
facilitate the plastic deformation of paperboard in the rim areas
if the paperboard has suitable moisture levels. At such die
temperatures, the amount of heat applied to the blank is generally
sufficient to liberate the moisture within the blank and thereby
facilitate the deformation of the fibers without overheating the
blank and causing blisters from liberation of steam or scorching
the blank material. It is apparent that the amount of heat applied
to the paperboard stock will generally vary with the amount of time
that the dies dwell in a position pressing the paperboard together.
Suitable die temperatures are based on the usual dwell times
encountered for normal plate production speeds of about 40 to about
60 pressings a minute, and commensurately higher or lower
temperatures in the dies would generally be required for higher or
lower production speeds, respectively.
[0041] In view of the multiplicity of potential sources of
variation in pressed paperboard container dimensions, it is not
surprising that a modicum of size and shape variation occurs, even
under carefully controlled conditions. As will be appreciated from
the foregoing, formation of a pressed paperboard container is a
complex process where stretch, shape relaxation, moisture control
and other factors can each cause some size variation. The inventive
lid design readily accommodates the observed variations, as is
further discussed below.
[0042] In the particular design illustrated, a lid for a nominal 9
inch plate includes about 48 outwardly convex flutes and a lid for
a ten inch plate includes about 54 outwardly convex flutes. The
flutes are generally positioned close to the outer rim of the lid
in order to aid in lid-to-plate application. It has been determined
in accordance with the present invention that a flute position
closer in relation to the outer rim or outer horizontal periphery
area in a plate with a horizontal extension at its outer brim can
significantly increase the ease of the lid application to the
paperboard container base. The number of flutes around the
perimeter of the dome and the relationship of crush resistance is
further explained in U.S. patent application Ser. No. 10/170,675
entitled "Crush-Resistant Disposable Lid", filed on Jun. 13, 2002,
as well as U.S. patent application Ser. No. 11/051,100, filed on
Feb. 4, 2005, entitled "Crush-Resistant Disposable Lid and
Containers Utilizing Same", the disclosures of which are
incorporated herein by reference. The flutes of the sidewall can
consist essentially of outwardly convex flutes, that is, contain
less than about 10% by number inwardly convex flutes. In the
example illustrated herein the flutes are spaced by a substantially
equal number of unfluted areas.
[0043] It has been discovered in accordance with the present
invention that from about 7 to about 15 and more particularly from
about 10 to about 12 evenly-spaced undercut lugs around the domed
rim perimeter provide a particularly suitable combination of
properties in terms of lid application, retention and lid removal
when the container base comprises an evert outer portion. The
inventors herein have determined that the undercut lug design of
the present invention performs much better than a continuous
undercut design as disclosed in the '675 application when used with
a pressed paperboard container having an evert outer portion. In
particular, pressed paperboard containers having evert outer
portions can range in size as a result of varying formation factors
including paper stretch during forming, pleat formation/rim
pressing and subsequent plate shape relaxation and spring back
after forming. Plate diameters can also vary from differing paper
moisture contents as a result of humidity where the plates are
stored. An 11-lug design of the invention created an effective and
flexible lid to fit on a range of pressed paperboard plate
diameters with the plates tested.
[0044] Significantly, the lids could be lifted and transported with
a food load/or weight even if all of the undercut lugs were not
fully engaged. This was found to be important when used with the
pressed paperboard containers comprising an evert outer portion
because the variations in size can make it difficult to fully
engage the continuous undercut design of the '675 application. In
particular, the continuous undercut design requires full engagement
around the container base circumference, otherwise the lid would
readily fall off during lifting with a food load.
[0045] In particular, it was found that pressed paperboard plate
diameters for nominal 9 inch plates range from about 8.48 inches
(loose fit) to about 8.56 inches (tight fit). Most plates were
between about 8.5 inches and about 8.54 inches and fit well with
the lid of the present invention sized for that plate size. The
11-lug design worked well over this range i.e., loose to tight fit,
of pressed paperboard containers. With respect to the nominal 10
inch plates, the pressed paperboard plate diameters ranged from
about 9.90 inches (loose fit) to about 10.10 inches (tight fit).
Most plates were from about 10.03 inches to about 10.060 inches.
These plates all had a good fit with the lid design of the present
invention sized for this plate. Eleven lugs worked well over this
range with the nominal 10 inch plate from loose to tight fit. Thus,
the lid of the present invention is relatively insensitive to
variations in container diameters experienced with pressed
paperboard containers.
[0046] It has been found by the inventors herein that a continuous
undercut design can disengage too easily when used with container
bases having evert outer portions. The release of a single area of
attachment (or incomplete attachment around the entire perimeter of
the container) causes the disengagement of the lid from the
container moving away from the location of disengagement.
Incomplete attachment of the lid to a container base having an
evert outer portion causes the lid to separate from the container
starting from the point of disengagement moving outward from that
point. Once the separation process starts, it is difficult to stop
(especially if there is food on the plate) and the failure of the
lid contact is likely swift. Therefore, upon commercial use of
container bases having evert outer portions, it was found that
prior art lidding solutions for pressed paperboard containers would
not be effective for such containers.
[0047] Many prior art pressed paperboard containers have downward
sloping outer rims. The use of lugged lid designs were not
desirable with the downward sloping pressed paperboard container
design because when one portion of the plate was disengaged from a
lug, the prior art pressed paperboard containers experienced
flexing of the container base which, in turn, caused the portions
of the prior art containers engaged with the remaining lugs to more
tightly engage (e.g. lock) with the lugs. When a lugged lid was
used with a pressed paperboard container having a downward slope
and a user attempted to remove the lid, the act of removing the lid
by pulling on the lid caused the lid to lock tightly on the pressed
paperboard container. This normally resulted in a user needing to
apply considerable force to the lid to get it to come off, which
could result in the food spilling from the container.
[0048] Because the lugs in the lids of the present invention are
distributed around the perimeter of the lid so that from about 15%
to about 30%, or from about 20% to about 25%, of the lid periphery
is available for engagement with the lugs, the lids of the present
invention are more easily removed from pressed paperboard
containers having evert outer portions. It has thus been found that
an excellent (or "just right") seal is possible using the lid
design of the present invention.
[0049] The lidded containers of the present invention are to be
distinguished from the lidded container disclosed in U.S. Design
Pat. No. 415,024 (the disclosure of which is incorporated herein in
its entirety by this reference). As apparent from the number of
"fluted" portions, the plate therein is necessarily formed from a
polymeric material, such as polystyrene or the like. This is
evident because, as would be recognized by one of ordinary skill in
the art, it is not technically possible to form a pressed
paperboard container having the large number of "flutes" (or
pleats) pictured in the '024 patent. Additionally, although FIGS.
1-3 of the '024 patent might, at first glance, appear to show an
evert-type outer portion, the actual shape of the polymeric plates
of the '024 patent are shown in detail in FIG. 4 of the patent. In
that FIG. 4, the plates terminate in a downward slope (like the
paperboard plates of U.S. Pat. No. 6,715,630, discussed previously
herein). As such, when viewing all of the Figures of the '024
patent together, one of ordinary skill in the art would not
interpret the '024 patent to disclose a lidded container for use on
a pressed paperboard container having an evert outer portion.
[0050] Further details will become apparent from the discussion
which follows. It is noted that the lid annular engagement portion
defines a diameter corresponding to its engagement circumference
which is substantially identical to, but slightly smaller than, the
average plate diameter for which the lid is sized. A lid for a
nominal 9 inch plate (average diameter about 8.5 inches) has an
annular engagement portion which defines a diameter of about 8.4
inches, while a lid for a nominal 10 inch plate (average diameter
about 10.0 inches) has an annular engagement portion which defines
a diameter of about 9.9 inches. The optimal lid sizes for pressed
paperboard containers of other sizes can be determined by those of
ordinary skill in the art without undue experimentation.
[0051] Referring to the drawings, in particular, FIGS. 2, 3, 3A and
3B, there is shown a domed lid 10 which includes a central portion
12, a fluted sidewall 14 extending downwardly from the central lid
portion; the fluted sidewall of the domed lid being provided with a
plurality of flutes such as flutes 16, 18, and 20. The fluted
sidewall thus defines a fluted base 22 at its lower portion.
[0052] A rim 24 extends outwardly and downwardly from the fluted
sidewall 14 and defines an annular engagement portion 26. Annular
portion 26 is sized to engage the perimeter of a container having
an evert outer portion (not shown). The rim is further provided
with a plurality of generally equally spaced undercut lugs, such as
28, 30, 32, 34, 36, 38 and so forth around the annular engagement
portion of the domed lid. The lugs are for securing the lid to a
perimeter of a container as noted above. The lugs are generally
equally spaced around the circumference; in other words, the lugs
are separated by an angular displacement which is generally
uniform. Some variation is of course permissible in cases where
other features are disposed around the perimeter of the container
such as removal tab 37, for example. Likewise, the lugs adjacent
removal tab 37 have slightly less arc length, as noted below.
[0053] The plurality of undercut lugs define a collective undercut
span indicated schematically at 40 of from about 15% to about 30%
of the circumference of the annular engagement portion of the rim.
The diameter of annular engagement portion 26 is a minimum internal
diameter of the rim which is measured between opposite undercuts,
that is, at a point of maximum interference with the plate. This
distance is about 8.4 inches for a nominal 9 inch plate and about
9.9 inches for a nominal 10 inch plate as noted above. The about
15% to about 30% refers to the collective undercut span of the
lugs. That is to say, in cases where 11 lugs are present, their
collective undercut span is from about 15% to about 30% of the
total circumference of the annular engagement portion of the rim
based on the diameter of annular engagement portion 26. The lid
engagement circumference is calculated based on the diameter of
annular engagement portion as noted above for purposes of
determining the fraction or percentage of the collective span of
the lugs. The span of individual undercuts is shown as distance 40a
in the various diagrams, while their additive or collective span 40
is the sum of the spans 40a of each individual lug.
[0054] In some examples, the plurality of generally equally spaced
undercut lugs defines a collective (additive) undercut span of from
about 20% to about 25% of the circumference of the annular
engagement portion of the rim.
[0055] While any suitable number of generally equally spaced
undercut lugs can be provided, there is provided in some separate
examples from about 7 to about 15 generally equally spaced undercut
lugs and in some cases from about 10 to about 12 undercut lugs. In
the example illustrated herein, there is provided 11 generally
equally spaced undercut lugs.
[0056] The undercut lugs have an undercut depth 42 (FIG. 3C) of
from about 25 to about 100 mils. The undercut depth is measured
from the inner engagement portion 26 of the lid and the inner edge
42a of the undercut lug. Typically, the undercut lugs have an
undercut depth of from about 40 to about 75 mils.
[0057] The undercut lugs have an individual circumferential span
40a of from about 1/4 inch to about 1 inch, with from about 0.5 to
about 0.75 inches being typical. The individual circumferential
undercut span of the lugs is measured as the arc length from one
edge of the undercut to the other edge of the undercut as is
indicated schematically at 40a in the various diagrams. This
distance is a "circumferential distance". In a suitable example,
each of the lugs has an undercut span of about 0.625 inches except
that the two lugs on either side of a removal tab 37 have a
somewhat shorter undercut span of about 0.5 inches in order to
facilitate lid removal.
[0058] The sidewall of the lid is suitably provided with a
plurality of outwardly convex flutes. These flutes have been found
to provide superior strength characteristics as noted above. The
flutes can have a radius of curvature indicated at 44 of from about
0.125 inches to about 0.5 inch. In the embodiment illustrated, the
flutes have a radius of curvature of about 0.25 inches for nominal
9 and 10 inch lids. The flutes have a flute depth 46 of from about
0.05 inches to about 0.2 inches (see FIG. 3D). The flute depth is
the distance from the outermost portion of the flute to its
innermost portion at the base thereof as indicated schematically in
the diagrams. Curvature can be measured at the base as well. There
is provided in some examples from about 1.5 to about 1.9 outwardly
convex flutes per inch of engagement perimeter of the lid. The
engagement perimeter of the lid is the circumference of an annular
engagement portion 26 as shown in the various diagrams. A
particularly suitable range is from about 1.6 to about 1.85
outwardly convex flutes per inch of engagement circumference of the
lid. In this respect it is noted that a lid for a 9 inch plate has
48 flutes while a lid for a 10 inch plate has 54 flutes. Thus the
domed lid of the invention is typically provided with from about 35
to about 75 generally uniform outwardly convex flutes. In many
cases there is provided from about 45 to about 60 generally uniform
outwardly convex flutes.
[0059] While the inventive lid can be made from a variety of
materials, thermoformed lids made from oriented polystyrene having
a caliper of about 121/2 mils are suitably employed. Other
thicknesses can also be used just so long as the lid does not
become too thick or too thin for efficient use of the lid.
[0060] To improve the usability of the lids of the present
invention on pressed paperboard containers, the domed lids can be
configured such that the fluted base of the sidewall is disposed
near the outer perimeter of the lid. Suitably fitted on a paper
plate the fluted base of the sidewall can be vertically aligned
with the perimeter of a container within an offset distance 48 of
about 3/4 inch or so. An offset distance of from about 1/4 to 3/8
inch or less, for example, is particularly suitable. The offset
distance is measured as the horizontal distance between a vertical
line at the perimeter of the container base and a vertical line at
the base of the fluted sidewall at a point of maximum convexity of
the flutes. See FIG. 8A, in particular.
[0061] A pressed paperboard container base such as plate 50 (FIG.
4) can include a generally planar bottom portion 52, a first
annular transition portion 54 extending upwardly and outwardly from
the generally planar bottom portion of the container. There is
further provided an optional sidewall portion 56 extending upwardly
and outwardly from the first annular transition portion 54. A
second annular transition portion 58 flares outwardly with respect
to the first annular transition portion 54, while an outer flange
portion 60 extends outwardly with respect to the second annular
transition portion.
[0062] Outer flange portion 60 includes a downwardly sloping brim
portion 62 defining a declivity angle .alpha. at its terminus with
respect to a horizontal 53 substantially parallel to the bottom
portion of the container base. The downwardly sloping brim portion
62 transitions to a brim transition portion 66 which, in turn,
transitions to an annular evert outer portion 68 which extends
outwardly with respect to downwardly sloping brim portion 62 at an
eversion angle .beta. (FIG. 5) of at least about 25 degrees. The
evert outer portion 68 thus defines a container base perimeter. The
annular engagement portion of the rim of the domed lid is sized to
engage the base perimeter of the pressed paperboard container and
the lugs are adapted to secure the lid to the container paperboard
base by engaging evert outer portion 68 as is appreciated from the
drawings. The annular evert outer portion is suitably a
substantially horizontal projection which projects outwardly from
the brim. The paperboard which can have a caliper of from about 10
to about 25 mils flexes when the lid is placed on the base.
[0063] FIG. 5 illustrates the various angles .alpha., .beta. and
.gamma. of the outwardly projecting annular portion of containers
that can be used in connection with the present invention. In each
case there is illustrated a profile of a plate 50 having a
substantially planar bottom portion 52 as well as a downwardly
sloping brim portion 62, a brim transition 66 and an evert outer
portion 68. Angle .alpha. is the angle between a tangent 59 at the
terminus of downwardly sloping brim portion 62 and a line 53
generally parallel to bottom portion 52. The eversion angle .beta.
is the angle between a tangent 61 to evert 68 adjacent its junction
with transition portion 66 and tangent line 59 which is tangent to
the terminus of portion 62 as shown. .beta. is an outward change in
downward slope of the outer portion of the article and can be
measured directly or can alternatively be calculated as
180.degree.-.gamma. where the angle, .gamma., is the angle between
tangent line 59 to portion 62 and tangent line 61 to evert outer
portion 68. Angle .beta. is typically anywhere from about
25.degree. to about 160.degree. on an absolute basis. Portion 68
can have an upward slope, a downward slope or have 0 slope as is
shown in FIG. 5 where evert 68 is horizontal, generally in a
parallel direction to the plane of bottom 52. Suitably, .beta. is
from about 30.degree. to about 160.degree.; typically from about
30.degree. to about 90.degree. such as from about 35.degree. to
about 65.degree. or from about 45.degree. to about 55.degree..
Declivity angle .alpha. is typically about 80.degree. or less such
as about 65.degree. or less, but typically more than about
25.degree..
[0064] Referring to the schematic diagrams of FIG. 6 and following,
rim 24 has an outwardly extending wall 72 adjacent the fluted base
22 of sidewall 14. A downwardly extending engagement wall 74
defines annular engagement portion 26 of the rim above the undercut
lugs. Outwardly extending wall 72 thus defines a headspace 76 (FIG.
8A) just outwardly of the uppermost point 78 of the brim. The
headspace is the distance between flute base 22 and a vertically
aligned portion of the brim when the lid is installed on a pressed
paperboard container base as is shown in FIG. 8A. A headspace of at
least about 30 mils or about 50 mils above the brim of the
container base when the lid is installed on the base is desirable
in some embodiments. The headspace can be more than about 150 mils
above the brim and is suitably between about 30 mils and about 250
mils above the brim when the lid is installed on the base. It is
typically desirable to have an outwardly extending wall such as
wall 72 on the brim to provide stiffness to the lid.
[0065] Operation of the domed lid and the cooperation with a
suitable container is better appreciated with reference to FIGS. 6
through 8
[0066] In FIG. 6 the domed lid 10 is shown prior to engaging
container base 50. In FIG. 7 the dome lid is pushed downwardly such
that an outer portion 80 below the engagement portion 26 of the
dome begins to bear upon and flex evert outer portion 68 downwardly
as the dome is installed on the container.
[0067] In FIG. 8, evert outer portion 68 is shown as having
re-flexed outwardly with respect to the dome and is again in a
substantially horizontal position. It will be appreciated from
FIGS. 6 to 8 that the headspace is necessary to allow the flexing
of the container to occur while the lid is being installed such
that a secure fit of the dome and container is achieved as is shown
in FIG. 8.
[0068] While the invention has been described in connection with
various embodiments, modifications within the spirit and scope of
the invention, set forth in the appended claims, will be readily
apparent to those of skill in the art.
* * * * *