Note: Descriptions are shown in the official language in which they were submitted.
106~671
This invention relates to method of packaging and,
more particularly, to a method of packaging with metal containers
having a body wall thickness less than that conventionally used
in the packaging industry.
In the manufacture of containers for use in the packing of
a variety of food and non-food products in metal containers, it is
desirable, from the standpoint of both economy and convenience, to
employ metal plate as thin and as light weight as possible.
Presently, containers formed from metal plate having a thickness o-f
10-15 mils are conventionally used for packaging solid food products,
oils and non-carbonated beverages. The major drawback to the
extensive use of thinner lighter weight plate, e.g. plate having
a thickness of 6 mils or less is that the conventional smooth
surfaced cylindrical containers made therefrom do not ordinarily
have sufficient wall strength to withstand the substantial vacuum
created in the container after the product is packed therein and
the container hermetically sealed. For example, food products
such as non-carbonated beverages are packaged in metal containers
or placed in the container while the product is still heated in
order to prevent bacterial contamination. Motor oils are hot
when placed in containers as the oil is heated to make it less
viscous for filling. As either of these hot liquid products cools
in the sealed container, the product is reduced in volume and an
internal vacuum, in order of about minus 10 psig, is created in
the container, i.e. the pressure inside the container after the
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packaged product has cooled to room temperature is about 10 psig
less than the pressure outside the container. The result of this
condition is a 10 psi external pressure on the container side-
walls which tends to force or flex the sidewalls of the
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~062671
container inwardly and buckle them. This buckling of the side-
walls is referred to in the art as "panellng". When this condi- -
tion occurs, the container frequently assumes an undesirably
distorted appearance and sometimes deforms to such an extent
that it will not support another container that may be stacked
on top of it.
In order to reinforce and strengthen the container
body against paneling and to maintain its original shape, and
yet avoid the use of heavy body plate, the art has devised a
number of methods to prevent paneling. These methods however
are not without disadvantages. For example, it is common
practice in the manufacture of containers used in packaging
hot food products to provide the container body with one or
more circumferential beads. The use of such beading provides
the necessary paneling resistance in containers made from thin
light weight metal plate but has a detrimental effect upon
the axial strength or resistance of the container to crushing
under high container stacking conditions in storage. Because
the circumferential beads reduce the axial strength of the
container body, the use of metal plate of 10 mils thickness
is still required to compensate for the loss in axial strength.
In accordance with the present invention, there is
provided a method for the packaging a variety of heated products
in containers having wall thicknesses of 6 mils or less wherein
paneling of the container after sealing is prevented or sub-
stantially retarded which method is accomplished by imposing
; within a hermetically sealed container a superatmospheric
pressure in the order of about 5 to about 25 psig with an --
inert gas having low absorption in liquids.
According to a broad aspect of the present invention
there is provided a process for packaging articles in thin
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106Z671
walled containers having improved resistance to paneling. The
process comprises providing a container having sidewalls which
undergo paneling when the container is filled with a product
which undergoes a reduction in volume upon cooling. An inert
gas forming material is metered into the filled container, -~
; the gas forming material having a coefficient of absorption
of less than 0.02. The container is then hermetically sealed
and the product packaged therein is allowed to cool and the
gas to expand so that a superatmospheric internal pressure in
the range of about 5 to about 25 psig is imposed at room
temperature upon the sidewalls of the cooled container whereby
paneling due to atmospheric pressure is substantially prevented.
By the practice of the present invention containers
having a body wall thickness of 4 to 6 mils can be employed
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for the packaging of hot fill products where 10 mil thickness
plate is now presently required.
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106Z671
The container bodies used in the packaging method of the
present invention are preferably made of rigid, gas impermeable
.; materials such as metals as steel or aluminum. Containers whose
.~ body walls are fabricated from commercially available thermo-
plastic resins such as polyethylene or polypropylene are not
generally preferred in the practice of the present invention as '`
due~to the relative gas permeability of these materials as compared
to metals ~the pressure originally induced in the sealed container ''
may~be reduced during the time of storage by the escape of the
0 ~ pressuri~zing gas from the container which will thereafter render
the container susceptible to paneling. ;
: It is essential to the practice of the present invention
that the gas used to pressurize the container be inert to the '
contcnts~o~the container and~have low absorption in liquids. If
th.e~gas is~not inert or has~high absorption in liquids such as
do'es~C02, upon storage~, the~chemic:al reaction of the gas or the '.
ab ~ tion of the gas: by liquid;protuct will cause the total
: ~ essure:~within tbe contsiner to drop and as a result, the sidewalls :~
of the~container will~panel~:due~to~atmospheric pressure in order to '.
,~ ~ 20~co~mpensate~for this~internal pressure drop.:~
.~ ~ '~ G~enerally~,~a~gas~having~an~absorption coefficient t~ )
, ~ at;~atmospheric~.pressure'~and~room~temperature (70F) of less than ;.
'0~02~is~sui~table fo:r use~in~the practice of the present invention.
'~` ~ itr ~ n-which is~ the pre~ferred inert gas for use in the practice '"
'of~thé p'résent; invention~has an ~ value of 0.01475.
In~pressurizing;~tho:~container,~the gas may be introduced
o: ~ '.container~in~.any~convenient~-anner.~ For example, the
. ~ gaseo~us~mat~rial~can:.~.~be:~charged as~a~gas into the vapor space of
' the~o ~ ner~throug~:a~holo in the~closure l~id of the container
. ~ ~ ~using~a~press~re~syringe.~'Thereafter the~hole is sealed with a
rubber p~lug~or~;spot~wélded to~hermetically seal the cdntainer.
Gases~which -ay liquify or solidify at low temperaturcs and
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1~6Z67~
thereafter vaporize and expand at room temperature are pre-
ferred because of their ease of handling. When such liquid
gaseous materials are used, droplets of the liquid gaseous
material are metered into the container onto the exposed surface
of the packaged product and sealing of the container is carried out
rapidly and soon as possible after the liquid gaseous material
has been introduced into the container. Liquid nitrogen has
been found to perform very satisfactorily under normal conditions
and is an excellent example of a liquid gaseous material which is
preferred in the practice of the present invention.
The containers used in the practice of the present
invention can be formed from metal plate ranging in thickness
from about 0.004 inches (4 mils) to about 0.006 inches (6 mils).
The container walls are preferably smooth surfaced and free of any
structural reinforcement such as beading.
In packaging heated products in containers in accordance
with the practice of the present invention, the heated product
is first dispensed into the container and a gas producing
material such as liquid nitrogen is metered into the product
filled container, The container is then sealed with minimum
delay to entrap the gas producing medium in the vapor space or
headspace of the container and prevent any appreciable loss of
gaseous material.
The amount of gas which is metered into the container
; 25 prior to hermetic sealing of the container is determined by the
amount of vapor space remaining in the container after the heated
product has cooled to room temperature and the internal pressure
required after cooling. For example 0.071 grams of liquid nitrogen
when vaporized at 70F exerts a pressure of 7 psig per cubic inch
(cu. in.) of volume. The vapor space remaining in a container
after a heated product has cooled can be readily ascertained.
For example, the vapor space remaining in a 48 ounce 404 (4 4/16")
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106Z671
diameter fruit drink container after filling at 90F is about 6.5
cu. in. Thus, a charge of 0.46 grams of liquid nitrogen confined in
such a container filled with fruit drink heated to 190F is sufficient
to produce the necessary pressure to pressurize the container between
5 psig and 25 psig after the fruit drink has cooled to room
temperature.
After the gas has been metered into the product filled
container and the container hermetically sealed, the container is
ready for storage. The gas producing material metered into the
container expands to fill the headspace area created by the product
as it cools and thereafter pressurizes the container sidewalls
against buckling from the external atmospheric pressure.
It is critical to the practice of the present invention
that sufficient gas be metered into the vapor space of the container
to create an internal pressure of about 5 to about 25 psig at room
temperature. If the container is pressurized to a pressure less
than about 5 psig the sidewalls are spongy and lack paneling
resistance and if the internal pressure of the container is raised
to substantially more than about 25 psig, during filling, conventional
r' 20 end closure units may be permanently deformed at the higher pressures
encountered when the hot filled container is initially sealed.
The practice of the present invention is illustrated by
the following Examples:
EXAMPLE I
Several 211 (2 11/16") x 413 (4 13/16") 2 piece, drawn
and wall ironed steel containers having unbeaded sidewalls of 4 mil
thickness were filled with 12 ounces of water heated to 200F.
The containers were hermetically sealed by double flanging with a
steel lid equipped with a self-sealing gas valve. The headspace
in the container was pressurized immediately to 70 psig with
nitrogen which was injected into the container by means of a
hypodermic needle inserted through the valve. The needle was
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iO~ '71
withdrawn and the valve sealed. Immediately after the pressurized
nitrogen gas addition, the container and its contents were allowed
to cool to room temperature. The internal pressure of the
container at room temperature (75F) was determined to be approxi-
mately 25 psig with a Beckman Head Space Sampler. An axial load
of 730 pounds was applied to the pressurized container on an
Instron Universal Testing Machine with little or no paneling
observed in the container sidewalls. In addition to this
resistance to paneling, the container sidewalls returned to their
original condition after the axial load was removed.
Substantially the same results were observed when by
following the above procedure, equivalent containers were
pressurized to an internal pressure of 10 psig and 15 psig at
room temperature with nitrogen.
By way of contrast when the procedure of Example I was
repeated with the exception that nitrogen was metered into the
containers in amounts sufficient to raise the internal pressure
of the sealed, cooled (75F) containers to 1 psig and 2 psig, the
sidewalls of the container could be easily hand deformed and they
collapsed under an axial load of 600 pounds.
By way of further contrast when the procedure of
Example I was repeated with the exception that no nitrogen was
metered into the container after sealing, a vacuum ranging from
minus 1 psig to minus 2 psig was measured in the containers and
modest to severe paneling of the sealed containers was observed
when the containers had cooled to room temperature.
EXAMPLE II
Several 211 x 413 3 piece steel containers having
unbeaded sidewalls of 6 mil thickness were filled with 12 ounces
of water heated to 190F. To the surface of the heated water in
the container was added 1.0 gram of liquid nitrogen. The con-
tainer was hermetically sealed by double flanging with a steel
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~ 06Z671
lid immediately after the liquid nitrogen addition and the con-
tainer and its contents were allowed to cool to room temperature.
The internal pressure of the container was determined to be
approximately 25 psig ~75F) with a Beckman Head Space Sampler.
An axial load of 1,200 pounds was applied to the
pressurized container on an Instron Universal Testing Machine with
no paneling observed in the container sidewalls.
EXAMPLE III
Several 404 ~4 4/6") x 700 t7") 3 piece steel containers
having unbeaded sidewalls of 6 mil thickness were filled with 46
ounces of water heated to 190F. To the surface of the heated water
in the container was added 2.5 grams of liquid nitrogen. The con-
tainer was hermetically sealed by double flanging with a steel lid
immediately after the liquid nitrogen addition and the container
and its contents were allowed to cool to room temperature. The
internal pressure of the container was determined to be approxi-
mately 11 psig (75F) with a Beckman Head Space Sampler.
An axial load of approximately 1,140 pounds was applied
to the pressurized container on an Instron Universal Testing
Machine with no paneling observed in the container sidewalls.
- By way of contrast when the procedure of Example III was
repeated with the exception that liquid nitrogen was added to the
containers in amounts sufficient to raise the internal pressure
of the sealed, cooled containers to 1 psig and 2 psig at room
temperature, the sidewalls of the container could be easily hand
deformed and they collapsed under an axial load of 900 pounds.
By way of further contrast when the procedure of
Example III was repeated with the exception that no nitrogen was
added to the container after sealing, a vacuum of approximately
minus 10 psig was created in the container (at 75F) and severe
paneling of the sealed containers was observed when the containers
had cooled to room temperature.
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1062671
EXAMPLE IV
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Several 404 x 700 3 piece, steel containers having
unbeaded sidewalls of 6 mil thickness were filled with 46 ounces
of water heated to l90~F. The containers were hermetically
sealed by double flanging with a steel lid equipped with a self-
sealing gas valve. The headspace in the container was pressurized
immediately to 25 psig with nitrogen which was injected into the
container by means of a hypodermic needle inserted through the
valve. The needle was withdrawn and the valve sealed. Immediately
after the pressurized nitrogen gas addition, the container and its
contents were allowed to cool to room temperature. The internal
pressure of the container at room temperature t75F) was determined
to be approximately 10 psig with a Beckman Head Space Sampler. An
axial load of 1,140 pounds was applied to the pressurized containers
on an Instron Universal Testing Machine with little or no paneling
observed in the container sidewalls.
By way of contrast when the procedure o~ Example IV was
repeated with the exception that nitrogen was metered into the
containers in amounts sufficient to raise the internal pressure
of the sealed, cooled (75F) containers to 1 psig and 2 psig, the
sidewalls of the container could be easily hand deformed.
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~06Z67~
SUPPLEME~TARY DISCLOSURE
The process for packaging articles in thin walled
containers of the Supplementary Disclosure is concerned with
filling the container with a product heated to above room
temperature and which undergoes a reduction in volume upon
cooling to room temperature. Also, the inert gas forming
material is filled in a container in an amount sufficient to
cause an increase in the internal pressure of the container of
at least 3 psi.
; 10 According to a broad aspect of the present invention
there is provided a process for packaging article~ in thin
walled containers having improved resistance to paneling.
The process comprises the steps of providing a container having
sidewalls which undergo paneling when the container is filled
with a product heated to above roo~ temperature which undergoes
a reduction in volume upon cooling to room temperature. The
container is filled with the heated product and an inert gas
forming material is metered into the filled container in an
amount sufficient to cause an increase in the internal pressure
of the container of at least 3 psi. The gas forming material
has a coefficient of absorption of less than 0.02. The con-
tainer is then hermetically sealed and the product packaged
therein is allowed to cool to room temperature and the gas to
expand so that the internal pressure of the container increases
by at least 3 psi at room temperature and imposes a sufficient
force upon the sidewalls of the cooled container whereby pànel-
ing due to atmospheric pressure is substantially prevented.
By the practice of the present invention containers
' having a body wall thickness of 4 to 6 mils can be employed for
30 the packaging of hot fill products where 10 mil thickness plate
is now presently utilized.
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lO~iZ671
In pressurizing the container, the g~s may be intro-
duced into the container in any convenient manner, and for
example, the gaseous material can be charged as a gas into
the vapor space of the container. The containers used in the
practice of the present invention can be formed from metal
plate ranging in thickness from about 0.004 inches (4 mils)
to about 0.006 inches (6 mils). The container walls are
preferably smooth surfaced and free of any structural reinforce-
ment such as beading.
Generally, to prevent paneling in metal containers
having a wall thickness of 4 to 8 mils which are used to pack-
age liquid products which are at elevated temperatures at the
time of filling and particularly at temperatures above
pasteurization temperatures (e.g. 140 - 160F) a sufficient
amount of gaseous material, is metered into the container to
increase the internal pressure in the container when at room
temperature in the order of at least 3 psi. Hereinafter, this
increase in internal pressure in the container at room temper-
ature (70F) will be referred to as ~P.
It has been determined that if the ~P effected by
the incorporation of the gaseous material in the vapor space
of the container is at least 3 psi containers having sidewalls
of reduced thickness can be employed for the packaging of
liquids which are introduced into the container at elévated
temperatures and shrink in volume when cooled to room temper-
ature. A ~P of about 5 to about 35 psi is generally employed
, in the practice of the present invention and a ~P of about 8
to about 25 p9i iS preferred. A ~P higher than 35 psi can be
employed in the practice of the present invention, but impos-
ing such higher pressures does not materially improve the
resistance of the container to sidewall paneling. Further, in
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106Z671
the case of metal containers sealed with flat metal end
closures, the imposition of a QP in excess of 35 psi in the
sealed container can cause the end to bulge outwardly from
the container creating the false impression that the end has
bulged due to a build-up of pressure resulting from the
' deterioration of the packaged product.
The incorporation of the gaseous material in the con-
tainer may function to reduce the negative pressure of vacuum
within the container to impose a substantial positive pressure,
that is, a pressure above atmospheric, within the container.
Thus, within the ~P range of 5 to 35 psi, the actual internal
pressure created in the hermetically sealed container at room
temperature effected by the addition of the gaseous material
may vary, depending on the dimensions of the container, from
small negative pressures e.g. -1.0 to -2.0 psig to relatively
' high positive pressures in the order of S to 25 psig. For
example, as will hereinafter be illustrated, a 404 (4-4/16")
x 700 (7") container having a sidewall thickness of 8 mils
~i filled with 48 ounces of a hot (190 - 200F) liquid can be
pressurized with a liquid nitrogen addition and paneling is
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avoided at an internal pressure of -1.7 psig, whereas in a
207,5 (2-7,5/16") x 410.5 (4-10.5/16") container having a
6 mil wall thickness, filled with 10 ounces of the same hot
liquid, an internal pressure of 12.9 psig is required to avoid
paneling.
, By following the practice of the present invention,
containers having sidewall thickness in the order of 4 to 8
,. .~ .
Jj mils can be substituted for containers of identical size having
sidewall thickness in the order of 9 to 11 mils in the packag-
, 30 ing of hot fill products without undergoing sidewall paneling
`', thereby effecting a substantial cost reduction in the price of
the container used to package the hot fill item.
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1062671
The practice of the present invention is illustrated
by the following additio.~al Examples other than those of the
Principal Disclosure.
XAMPLE I
Several hundred 404 (4 4/16") x 700 (7") 3 piece steel
containers having unbeaded sid~walls of 8 mils thickness were
-filled with 48 ounces of apple juice heated 190F - 200F on a
commercial juice packaging line. Liquid nitrogen was added to
the surface o~ the heated julce and the container was hermetic-
ally sealed by double seaming with a steel lid immediately
after the liquid nitrogen addition. ~he container and its con- -
tents were allowed to cool to room temperature (70F). The
internal pressure of the cooled, juice filled container was
determined to be approximately -1.7 psig. No paneling was
observed in the sidewalls of any of the containers. The juice
had previously b~en packaged in 40~4 x 700 containers having a
sidewall thickness of 10 mils. ;
When it was attempted to package hot apple juice in
the containers used in Example I without liquid nitrogen addi-
tion, severe paneling of the container sidewalls was observed.
It was determined that paneling in the hot juice filled con-
tainers used in Example I was initiated at -6.0 to -7.0 psig
and that severe paneling occured at vacuums in the order of
-9.0 to -10 psig.
EXAMPLE II
Several hundred 207.5 (2-7,5/16") x 410.5 (4-10.5/16")
3 piece steel containers having unbeaded sidewalls of 6 mil
thickness were filled with 10 ounces of apple juice heated to
190F - 200F on a commercial juice packaging line. Liquid
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nitrogen was added to the surface of the heated apple juice
`~ and the container was hermetically sealed by double seaming
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10~;2671
with a steel lid i~ediately after the liquid nitrogen addition
and the container and its contents were allowed to cool to
room temperature (70F). The internal pressure of the con-
tainer was determined to be approximately 12.9 psig. No panel-
ing was observe~ in the sidewalls of any of the containers.
reviously 207,5 x 410.5 containers having a wall thickness of
8.9 mils had been used for the packaging of the juice.
When it was attempted to package hot apple juice in
the 6 mil containers used in Example II without liquid nitro-
gen addition, severe paneling of the container sidewalls wereobserved. It was determined that paneling in the hot juice
filled containers used in Example II occurred at a vacuum of
about -10.0 psig.
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