Note: Descriptions are shown in the official language in which they were submitted.
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CONTAI~ERS
This invention relates to a foam cup which has been
treated to improve the strength thereof. 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 khe 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, the process of our invention resides in a
method of improving the stiffness of a polystyrene foam
container having a sidewall and a bottom, said container
having been prepared from a laminate of polystyrene foam
having generally spherical closed cells, and, on at least
the outer surface thereof, a layer of solid polystyrene,
said method comprising heating said container in the
unrestrained state, said heating being sufficient to
increase the thickness of the sidewall at least 10~.
The sidewall prior to heating has a thickness of
0.02 to 0.05 inch and said heating is carried out under
conditions to provide an increase in thickness of from 10
to 30 percent. The heating can be applied by a variety
of methods such as contact with hot water, steam, hot
air, or infrared radiation. The cups produced by us in
the work reported herein were produced on a G1000 VII
machine of Paper Machinery Corporation of Milwaukee,
Wisconsin. This company is widely known as a major pro-
ducer of machines for the production of paper cups. In
the production system, the cups of this invention were
prepared from single-side-coated roll stock produced
according to the method of disclosure by Mazur 3,669,794
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(1972). Double-coated stock can also be used, this
method being disclosed in Whelan, et al., 3,616,020
(1971).
In the Paper Machinery Corporation machine, a source
of hot air is provided to seal the side seam resulting,
after the sidewall is rolled into shape, and to seal the
bottom of the cup with the si~dewall. In the machine, a
source of air, heated by a flameless torch, blows the
finished cup into a stacking device. It will be recog-
nized that time and temperature of treatment are interre-
lated, runs were made using a treatment time of 3 to 5
seconds with heated air in the range of 250 to 400F.
Heating foam cups has been disclosed as a method of
improving the strength of containers. One example of
this is Shapiro, et al., 3,344,222 (1967). In this
patent~ foam cups produced by extrusion of foamable
sheets of polystyrene are made, no solid layer being pre-
sent, 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 patentee, 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 inte-
rior æones.
It will be seen that the present process which heats
the cup or container in the unrestrained state is
directly contrary to the teaching of Shapirol et al.
Another patent which requires an increase in thick-
ness when a foam cup is heated i8 Myers, et al.,
4,359,160 ~1982), this patent being directed to a thermo-
formed cup or container. The sheet for the thermoforming
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
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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 liquid is added thereto, the cells tend
to return to spherical shape.
Thus, the cup of Myers, et al., while probably being
stronger after filling with hot liquid, is still defi-
cient because it does not have the improved strengthprior to use by the user.
From the above description, it is obvious that the
object of this invention is to provide a coated Eoam cup
of improved strength.
lS A further object of this invention is to provide a
method for producing this container. Other objects of
this invention will become apparent to those skilled in
the art upon reading this disclosure.
The following examples set forth currently preferred
embodiment of the invention, but these examples should
not be considered unduly limited.
EXAMPLE 1
Amoco R2 polystyrene resin was extruded by the blown
bubble technique using butane in an amount of 4 wt% as a
blowing agent and a talc nucleating agent in an amount of
0.5 to 0.75 wt~, 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 struc
ture, 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 poly-
styrene, the mixture containing, as a pigment, 2 to 4 wt%
of TiO2. A good bond was obtained with this system. The
foam thickness was slightly less than 0.03 inch and the
solid resin thickness was approximately 0.002 inch.
The procedure for the showing of sidewall deflective
strength improvement consisted of first measuring the
untreated cup sidewall thickness and the sidewall
deflective strength and then CaLrying out the heating
procedure. For this exampler the heating consisted of
pouring boiling water into the 9-oz. CUp5 brim full and
covering each cup with another cup so that the covering
cup was heated by the steam given off by the hot water.
These pairs of cups were left in -this position for 15
minutes to allow the foam to expand freely. After this
time, the sidewall thickness and deflective strength were
again measured.
The sidewall deElective strength test is made on the
full cup. Each is placed on a platform on its side using
a flat strip pressing against the upper portion of the
rim. A gram scale is provided to apply a gradually
increasing weight to the rim, and the deflection mea-
sured. The data show the load required for a half-inch
deflection of the cup.
The data are shown in the following table, Runs 1-3
being the bottom cups and Runs 4-6 being the upper cups
which were exposed to the steam.
SIDEWALL DEFLECTIVE STRENGTH
SIDEWALL THICKNESS (~rams per 1/2")
Run Untreated Heated ~ ~ntreated Heated ~
1 .028 .032 13 23~ 280 18
2 .027 .~36 25 265 310 15
3 .027 .034 21 260 310 16
~ .028 .037 24 270 315 14
.027 .035 23 260 300 13
6 .027 .035 23 245 235 17
Ave. .027 .035 23 255 302 16
EXAMPLE 2
Cups made according to the procedure set forth in
EXAMPLE 1 were treated wlth air heated with a flameless
torch. With exposure times in the range of 3 to 5 sec-
onds and air temperatures in the range of 250 to 400F,
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increases in wall thickness and increased sidewall
deflective strengths were obtained.
From the foregoing description, those skilled in the
art will appreciate that the modification can be made
without departing from the broad scope of the invention.
It is not intended to limit the broad scope of the inven-
tion to those embodiments illustrated and described, but
reasonable modifications can be made.
