Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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CONTAINERS
This invention relates to a foam cup which has been
treated to improve the strength thereo~. The cup is made
from a foam resin sheet produced by the blown bubble
technique to which a solid resin layer is applied to one
or both sides of the foam.
Foam cups are widely used for individual servings of
hot beverages, such as coffee and soup, and cold bever-
ages such as soft drinks. Many millions are used everyday. Obviously, the cup must have sufficient strength to
permit handling by the user, but, at the same time, use a
minimum amount of resin for the product. Polystyrene and
other resins can be used to produce the cup although the
majority are now made from polystyrene.
Broadly, our invention resides in a method of
treating a cup having a closed cell foam wall and a solid
plastic film coating on at least the outer surface
thereof, said cup having been formed from roll stock,
comprising contacting the inner wall of said cup but not
the bottom with a heated mandrel at a temperature and for
a time sufficient to expand said wall, said heating
increasing the wall strength and removing wrinkles on the
inside of the wall of the cup.
Briefly, the cup is held on the mandrel, maintained
at a temperature of 180 to 260~F, for a contact time of
5 to 8 seconds. Best results have resulted from a man-
drel temperature of 230F using a 6 second contact time.
In another aspect, our invention resides in appa-
ratus for treating closed cell foam cups to improve the
characteristics of the wall of the cup comprising a
rotatable turret, means to drive said turret, a plurality
of mandrels mounted on said turret, means to heat said
mandrels, means to apply vacuum and gas under pressure to
each of saicl mandrels at preselected positions on said
turret, means to feed cups to a mandrel in a fixst posi-
tion, and means to convey cups from a mandrel in a second
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position.
I~ the preferred apparatus, the mandrels are elec-
trically heated and contain means for temperature con-
trol. Any suitable power source can be used.
The cups are fed to the mandrel and contained
thereon by vacuum applied to the mandrel and removed by
forcing a gas under pressure between the mandrel and the
cup. This gas may be heated and preferably is air.
The sidewall prior to heating has a thickness of
0.02 to 0.0S inch and heating provides an increase in
thickness of 10 to 50 percent. The cups produced by us
in the work reported herein were produced in a Gl000 ~II
machine of Paper Machinery Corporation of Milwaukee, Wis-
consin. This company is widely known as a producer of
machines for the production of paper cups.
In the production system, the cups of this invention
were prepared from singl'e sidewalled rolled stock pro-
duced according to the disclosure of Mazur 3,669,794.
Double coated stock can also be used, a production method
being shown in Whelan et al. 3,616,020.
Heating foam cups has been disclosed as a method of
improving the strength of containers. One example of
this is Shapiro et al. 3,344,2~2 tl967). In this patent,
foam cups produced by extrusion of foamable sheets of
polystyrene are made, no solid layer being present, and
the foam cups treated while holding the cup between
restraining surfaces. This is said to provide a density
gradient with denser foam near the surface of the cup,
thus increasing the strength of the cup. According to
the patentees, the thickness of the wall or walls of the
container does not apparently change. The patentee also
states that a wall gradient of two or three times the
original thickness will severely impair the formation of
the dense surface walls and the heat-insulating interior
zones.
Another patent which reguires an increase in thick-
ness when a foam cup is heated, is Myer~, et al.,
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4,359,160 (1982), this patent being directed to a
thermoformed cup or container. The sheet for the thermo-
forming operation is produced by extrusion of molten
polystyrene containing a blowing agent and a nucleating
agent from a slit-ring orifice. This product, like the
product of the invention, contains closed, generally
spherical closed cells as extruded. In the process of
Myers, et al., this sheet is thermoformed by a plug-
system method which stretches the cells and produces a
product containing "pancake"-shaped cells. Upon heating
this thermoformed cup, as when hot beverage is added
thereto, the cells tend to return to spherical shape.
Another system which has been developed is that of
Schneider, et al. S.N. 540,318, filed October 11, 1983,
wherein cups are heated in the unrestrained condition.
This invention differs therefrom in that the wide walls
of the cup are restrained during the heating operation.
From the foregoing, it is obvious that the object of
this invention is to provide a coated foam cup of
~0 improved strength.
Further, an ob,ect of this invention is to provide a
method for producing the container.
Further, an object of this invention is to provide
apparatus for carrying out the method.
Other objects o this invention will become apparent
to those skilled in the art upon reading this di~closure.
An additional result obtained through the use of our
invention is the improved internal surface characteris-
tics of the cup. When formed on the Paper Machinery Cor-
poration apparatus, wrinkles are produced in the inside
surface of the cup. These wrinkles detract from the
aesthetics of the cup and these wrinkles are removed in
the heat treatment of this invention.
Accompanying and forming part of the disclosure is a
drawing comprising:
Fig. 1, a cross-section of the apparatus of this
invention for treating cups, and
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Fig. 2, a cross-section of the turret and mandrel on
line 2-2 of Fig. 1.
While various types o4 apparatus can be used in the
practice of our invention, one suitable system i6 shown
in this drawing.
10 represents an arm around which rotates turret 12.
This turret is provided with a plurality of mandrels 14,
16, 18, 20, 22, 24, 26 and 28. The cups C fit upon each
mandrel with contact over substantially all of the side
wall leaving a space 30 (see Fig. 2) between the mandrel
and the bottom of the cup. Each mandrel is provided with
a central bore 32 in Fig. 1 and in the cross-section of
Fig. 2. Between arm 10 and the inner surface of turret
12 there is provided an open space 34 which connects with
15 the bore 32 in each mandrel. Stationary blocks 36, 38
and 40 serve to separate the space 34 into 3 distinct
chambers. By means not shown, a vacuum is applied to
space 34 between barriers 36 and 40 extending for most of
the circumference of arm 10. Gas under pressure is pro-
vided in the space between barriers 38 and 40. A chute(not shown) guides cups C onto mandrel 16 in a first
position and guide means (not shown) are positioned above
mandrel 28 to guide cups removed from the turret. More
specific details are shown in Fig. 2, this drawing also
illustrating a heating coil 42 in the mandrel. The
heating coil temperature is controlled in ways known to
the art. For instance, one can use a control thermo-
couple to record actual temperature or by the use of a
properly calibrated variable voltage transformer. Fig. 2
also shows the stationary arm 10 and rotating turret 12.
To maintain vacuum or pressure in the space 34, teflon
plastic rings 44 and 46 are provided.
In the operation, cups are supplied to mandrel 16 in
a first position and held thereon by the vacuum until the
turret reaches the position shown for turret 28. At this
stage, the gas under pressure blows the cup off of the
mandrel. Heated gas can be used if furth~r heat
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treatment is desired. For reasons of economy, air is the
preferred gas.
Turrets with different sized mandrels can be used
for the various cups produced, 6 through 16 ounce being
the normal range o size.
To improve the cup release from the mandrel and to
increase the abrasive resistance, the mandrel can be
coated with a TEFLoNiceramic coating. The speed of the
treatment and the number of manclrels depend upon the time
for the desired time of contact. The range of 4 to 8
seconds is most generally used.
* trade mark.
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The following examples set forth preferred embodi-
ments of the invention, but the examples should not be
considered unduly limiting.
EXAMPLE I
Amoco R2 polystyrene resin was extruded by the blown
bubble technique using butane in an amount of 4 wt. per-
cent as a blowing agent and a talc nucleating agent in an
amount of 0.5 to 0.75 wt. percent, all weights being
based upon the amount of polystyrene. The production
system is well-known. After slitting and opening of the
sheet to a flat structure, the sheet was fed between nip
rollers into which nip was extruded a polystyrene solid
resin. The solid resin was a 50-50 mixture of Amoco R2
and Amoco H2R polystyrene, the mixture containing, as a
pigment, 2 to 4 wt.-percent of TiO2. A good bond was
obtained with this system. The foam thickness was
slightly less than 0.03 inch and the solid resin thick-
ness was approximately 0.002 inch.
Using a heated mandrel maintained at 230F, cups
were treated thereon for the time shown in the following
table.
Thickness RangeAverage Increase in
Seconds Inch Thickness Perce _
0 .030 - .032 0
3 .034 - .036 16
4 .035 - .037 20
.03~ - .040 30
6 .0~9 - .041 33
7 .040 - .042 36
8 .041 - .043 40
Best results were obtained using treatment time of 6 sec-
onds.
EXAMPLE II
Another series of cups were tested to establish the
increase in strength of the sidewalls. The sidewall
deflective strength was tested on a complete cup. Each
was placed on a platform to which sidewall pressure was
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applied 1 inch from below this rim. A gram scale was
provided to apply a gradually increased weight to the rim
and the deflection measured. The data show the load
required for a 1/2 inch deflection using a 9 ounce cup. The data are shown in the following table.
Gram deflection
Time of
Heating (Sec) Run 1 Run 2 Run 3 Run 4 Ave.
0 345 350 330 465 348
3 395 4~5 465 455 438 26
4 400 475 g95 475 461 32
495 490 475 485 486 39
6 550 475 520 505 513 47
7 525 530 490 515 515 48
From the foregoing descri~tion, those skilled in
that art will appreciate that the modification can be
made without departing from the broad scope of the inven-
tion. It is not intended to limit the broad scope of the
invention to those embodiments illustrated and described,
but reasonable modifications can be made.
WE CLAIM:
