U.S. patent number 3,769,056 [Application Number 05/085,358] was granted by the patent office on 1973-10-30 for container surface and method of obtaining same.
This patent grant is currently assigned to Ilikon Corporation. Invention is credited to Thomas F. Sincock.
United States Patent |
3,769,056 |
Sincock |
October 30, 1973 |
**Please see images for:
( Certificate of Correction ) ** |
CONTAINER SURFACE AND METHOD OF OBTAINING SAME
Abstract
Vendability of nestable, resilient, plastic containers is
improved by coating outside surface portions with a lubricant.
These portions preferably are the nesting means and/or the lower
sidewall area of the container. A process is provided for
depositing the lubricant on the container which, in the case of a
partially foamed container, may occur simultaneously with its
exposure to a foaming agent.
Inventors: |
Sincock; Thomas F. (Simsburg,
CT) |
Assignee: |
Ilikon Corporation (Natick,
MA)
|
Family
ID: |
22191083 |
Appl.
No.: |
05/085,358 |
Filed: |
October 30, 1970 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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760911 |
Sep 19, 1968 |
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Current U.S.
Class: |
427/259; D7/523;
264/DIG.5; 264/45.6; 264/53; 264/130; 427/230; 427/272; 427/275;
427/373; D11/152 |
Current CPC
Class: |
B29C
44/56 (20130101); B05D 1/32 (20130101); Y10S
264/05 (20130101) |
Current International
Class: |
B05D
1/32 (20060101); B44d 001/52 () |
Field of
Search: |
;117/8.5,5.5,161ZA,155UA,10,11,94,98 ;220/97C ;264/48,45 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Martin; William D.
Assistant Examiner: Davis; Theodore G.
Parent Case Text
This is a division of copending application Ser. No. 760,911, filed
Sept. 19, 1968, and now abandoned.
Claims
I claim:
1. A method of forming a partially foamed, plastic container having
a predetermined, lubricated, non-foamed external surface portion
which comprises:
a. dissolving a lubricant in a medium which is absorbable by the
plastic and convertible to a gaseous state below the melting point
temperature of the plastic used to form the container, to form a
solution of lubricant in the absorbable medium;
b. masking a portion of said foamable plastic container which is to
be non-foamed;
c. exposing at least part of said masked portion along with another
portion of said container which is to be foamed to said solution to
simultaneously coat said exposed masked portion with said lubricant
and permit said medium to be absorbed into the portion of the
plastic to be foamed; and
d. heating the plastic container to a temperature below the melting
point temperature of the plastic but above the temperature at which
the medium converts to the gaseous state to produce a foam covering
having a boundary along the edge of one of said container
portions.
2. The method of claim 1 wherein masking is accomplished by coating
with a liquid chemical composition which is substantially insoluble
in the absorbable medium.
3. A method of forming a partially foamed, plastic container having
a predetermined, lubricated, non-foamed external surface portion
which comprises:
a. dissolving a lubricant in a medium which is absorbable by the
plastic and convertible to a gaseous state below the melting point
temperature of the plastic used to form the container, to form a
solution of lubricant in the absorbable medium;
b. depositing a chemical masking composition which is substantially
insoluble in said absorbable medium on an outer surface portion of
a container which is to be non-foamed;
c. entirely exposing said masked outer surface portion of said
container along with another outer surface portion of said
container to be foamed to said solution of lubricant in absorbable
medium, to coat said previously chemically masked surface portion
with said lubricant to form said predetermined, lubricated
non-foamed external surface portion without the absorbable medium
portion of the solution dissolving said chemical masking
composition, while concurrently permitting said absorbable medium
to be absorbed into the surface portion of the plastic to be
foamed; and
d. applying heat to the inside of the container to cause said outer
surface portion of the container which had absorbed said medium to
foam.
4. The method of claim 3 wherein:
a. the masking composition is a resinous ester dissolved in
alcohol;
b. the lubricant is silicone oil; and
c. the absorbable medium is trichlorofluoromethane.
Description
This invention relates to containers and more particularly to
nestable containers for use in coin operated dispensing
machines.
Thin wall containers made of non-foamed as well as of entirely and
partially foamed plastic, such as those described in U.S. Pat. No.
3,374,922, are being increasingly used in vending machines for
containing hot and cold beverages of all types. These containers
usually have stacking or nesting means formed in a wall portion
thereof which function to maintain adjacent walls spaced from each
other when a number of such containers are nested together to form
a stack. The stacking means usually comprises a series of
cooperating shoulders or shelves having close dimensional
tolerances, since these portions must be accurately and
consistently reproduced with a minimum of variation or otherwise
the supported surface of the stacking means of one container may
proceed beyond the supporting surface of the stacking means of an
immediately adjacent nested container during stacking or in
subsequent handling of a plurality of such containers. This results
in a wedging together of two or more containers, with the result
that they do not consistently feed freely from a nested
relationship within a vending machine when a coin is inserted
therein by a customer. Such high tolerance requirements often
result in numerous container rejects, thereby lowering the
economics of a high speed, large volume container producing
operation.
This problem of nestable container vendability is aggravated with
the more recently developed type container having a foam band
integrally along its sidewall for insulating purposes. During
formation of this foam covering, the portion of the container which
is not to be foamed is usually masked to prevent the foaming agent
from contacting it. However, in high speed production operations,
foam breakthrough often occurs in the container portion which is to
be non-foamed. This foam has an unusually high coefficient of
friction, and since portions of the non-foamed surface are usually
those which contact the next adjacent container within the stack,
as well as chute surfaces within the vending maching during
movement of the container into its filling position, vendability of
this type of container as limited by minute patches of foam
breakthrough presents an unusual problem. In addition, in the
process of producing these containers, masking is usually carried
out by coating the surface to be non-foamed with a chemical
composition, such as that set out in copending application Ser. No.
695,359, filed Jan. 3, 1968, now U.S. Pat. No. 3,565,660, and
assigned to the assignee of the present invention. The non-volatile
portion of this composition which remains on the surface of the
container after foaming also has a coefficient of friction which is
greater than that of the basic plastic substrate, and thus also
tends to retard swift movement of the container along surfaces with
which it comes into sliding contact.
Now there has been developed for use with either a non-foamed,
partially foamed or entirely foamed nestable container of the type
used in vending machines, means for improving behavior of such
containers within a stack and for reducing frictional resistance of
these containers when in sliding contact with the internal surfaces
of automated vending machines.
Accordingly, it is a principle object of this invention to improve
the vendability of nestable containers.
It is another object of this invention to provide a container
having improved resistance against wedging within another container
when a plurality of like containers are nested together within a
stack.
It is an additional object of this invention to reduce the
frictional effect between surfaces of a vending machine and a
plastic container in contact with the surfaces.
It is a further object of this invention to provide a container
exhibiting improved stacking performance yet permitting a
relaxation of the tolerances of the stacking means by which the
nesting is accomplished.
It is an additional object of this invention to provide an
improved, partially foamed, nestable and vendable container as well
as a method of producing such a container.
It is a still further object of this invention to decrease the
frictional effects of a foamed surface on vendability of a
partially or completely foamed, nestable container.
It is an additional object of this invention to decrease the
effects of friction on vendability of a previously chemically
masked portion of a partially foamed container.
It is yet a further object of this invention to provide a container
and a method of forming such a container which overcomes the prior
art difficulties discussed above.
Other objects of this invention will in part be obvious and will in
part appear hereinafter.
These and other objects are accomplished by providing, in the
broadest aspect of the invention, a nestable, thin wall, cup-like
thermoplastic container having nesting means formed in its sidewall
for maintaining the sidewall spaced from that of a similar
container when nested there within, the sidewall having on at least
a portion of its outer surface, a thin coating of lubricant to
reduce frictional resistance to sliding between the coated surface
and a supporting surface with which it comes into contact.
In a preferred embodiment of the invention, the sidewall of the
nestable container has a gripping portion of major extent having a
foamed, slip resistant covering on its outer surface, a lower,
non-foamed section intermediate the base and the gripping portion,
and an upper, non-foamed section intermediate the gripping portion
and the upper end, the upper and lower non-foamed sections having
portions off-set laterally with respect to the gripping portion
defining points of contact between the container and a planar
surface when the non-foamed sections are placed against said
surface with the foamed slip resistant covering located inwardly of
this surface, nesting means formed in the sidewall for maintaining
the foamed, gripping, slip resistant surface of the sidewall of the
container spaced from the sidewall of a similar container when
nested therewith, the outer surface of the lower section having a
coating of lubricant thereon to enhance sliding contact of the
container along the planar surface.
A method is provided for forming the previously mentioned partially
foamed plastic container having a predetermined, lubricated,
non-foamed external surface portion which comprises: masking a
portion of the surface of a plastic container which is to be
non-foamed; exposing at least part of the masked portion along with
another surface portion of the container which is to be foamed to a
medium which is absorbable by the plastic and convertible to a
gaseous state below the melting point temperature of the plastic
used to form the container; heating the plastic container to a
temperature below the melting point temperature of the plastic but
above the temperature at which the medium converts to the gaseous
state to produce a foam covering having a boundary along the edge
of one of said surface portions; and applying a thin coating of
lubricant to at least a portion of the external surface of the
container portion to be non-foamed.
In a preferred form of the method, the lubricant is dissolved in
the absorbable medium and coated on the masked surface at the same
time the portion to be foamed is exposed to the absorbable
medium.
In describing the overall invention, reference will be made to
preferred embodiments depicted in the accompanying drawings in
which:
FIG. 1 is a perspective view of a container embodying the present
invention;
FIG. II is a partially sectioned, elevational view taken along the
axis of the container of FIG. I;
FIG. III is a partial, sectional view of two nested containers of
the type shown in FIGS. I and II; and
FIG. IV is a diagrammatical view illustrating the operational steps
for producing the container of FIGS. I and II.
With reference to the drawings, wherein identical numerals refer to
identical parts, there is shown in FIGS. I-III a thin wall,
nestable, cup-like thermoplastic container for beverages, foods and
the like, which is of the throw-away type and is broadly identified
as 10. Container 10 generally comprises base 12, sidewall 14
generally extending upwardly and outwardly from base 12 in a
frustro-conical manner, forming open upper end 17 at the free end
of sidewall 14. Sidewall 14 comprises middle finger gripping
portion 16 having a relatively even outer surface of major extent,
which diverges outwardly relative to the container axis at a
substantially constant angle. The length of finger gripping surface
16 may range between about 40 to 90 percent of the sidewall axial
length. Though not essential, surface 16 may have a partially
foamed outer covering 18, obtained in a manner to be hereinafter
described. Sidewall 14 further comprises lower section 20
intermediate base 12 and gripping surface 16, and upper section 22,
intermediate gripping surface 16 and open upper end 17. Upper
section 22 has portions offset from the angle of gripping surface
16 to define nesting means formed therein, which, together with a
corner chime 40 at the peripheral joint between lower section 20
and base 12, cooperate with similar structure in a like container
as illustrated in FIG. III, to maintain a radial clearance between
the sidewalls of two adjacently nested containers.
Nesting means of upper section 22 of sidewall 14 comprises
outwardly flaring arcuately spaced supporting shoulder 24, the
upper edge of which integrally merges into an upwardly and inwardly
inclined spacing skirt 26. Spacing skirt 26 is integrally formed
with an upwardly and outwardly formed stacking shoulder 28 along
its upper margin. As shown in FIG. III the point of integral
adjoinment of stacking shoulder 28 and spacing skirt 26 forms an
annular stacking edge 30. Stacking shoulder 28 integrally merges at
its upper end into an upwardly extending sidewall portion 31. Rim
32 flares outwardly and consists of an upper rim forming wall 34
which merges into reversely bent flange 36, thereby defining an
outer rim margin 38 as typically shown in FIGS. II and III.
Slide line 54 of container 10 as depicted in FIG. II, is defined by
a plane tangent at one point to the outer surface of the container
at the point of maximum diameter in an upper section above the
midpoint of the sidewall, and at another point tangent to the outer
surface of the radially outermost extremity of the section of the
container below the sidewall midpoint. These points need not
necessarily be at the upper sidewall extremity or at the lower
joint between the sidewall and base though they are located at
these points in the embodiment of FIGS. I-III. Corner chime as used
herein is meant to include the radially outermost extremity of the
lower end of the container. In FIG. II, slide line 54 is
represented by a plane tangent to outer rim margin 38 of upper
section 22, and to the outside surface of corner chime 40 of lower
section 20.
In the form of the invention depicted in FIGS. I-III, the annularly
extending foam covering 18 of sidewall 14 extends from about
three-eighths inch above corner chime 40, to about one inch below
its uppermost peripheral margin. By further reference to FIG. II,
and slide line 54, it can be seen that foamed section 18 of
container 10 is radially inward of slide line 54, and is so located
along the sidewall that it will never come in contact with a
straight surface against which the container is placed.
Consequently, a container 10 passing along the inclined dispensing
tube of a vending machine will never contact the wall of the
dispensing tube except tangentially at corner chime 40 and outer
rim margin 38.
In accordance with the present invention, container 10 has on at
least a portion of its outer surface, a thin adherent coating 19 of
a lubricant such as silicone oil, which functions to reduce the
frictional resistance between the coated surface and any other
surface with which it comes into sliding contact, such as the inner
surface(s) of an adjacently stacked container or any of the
surface(s) of the cup dispensing portions of an automated vending
machine. Lubricant 19 in the embodiment of FIGS. I - III is present
on the outer surface of the nesting means in the upper portion 22
of the container sidewall between the top edge of the foamed
gripping portion 18 and rim 32, on the lower portion of the
sidewall 20 between the base 12 and the lower end of foam covering
18 including chime 40 and also on the outer surface of the margin
of base 12.
In use, container 10 is readily adaptable to be nested or stacked
together with a plurality of like containers in the manner depicted
in FIG. III. When placed in nested position, it can be seen that
the outer surface of supporting shoulder 24 is engaged by the
annular stacking edge 30 of stacking shoulder 28.
In the event of the tendency of the inner non-foamed surface of an
outer cup to move inward toward the foamed surface portion of the
inner cup or vice versa, because for example, of a drag movement
during transfer of nested stacks within the vending machine,
non-foamed, outer anti-rub corner chime 40 of the inner cup will
contact the non-foamed inner surface of the bottom section of the
outer cup as depicted in FIG. III, to maintain the desired sidewall
clearance of the foamed portion of the inner cup from the
non-foamed portion of the outer cup. Contact between the chime and
the inner surface of the next adjacent cup is in an edgewise manner
rather than surface to surface, in order to minimize frictional
drag between the non-foamed portions of the lower sections.
Lubricant film 19 is interposed (FIG. III) between the outer
surface of supporting shoulder 24 of the inner container and the
inner surface of stacking edge 30 of the outer container in the
limited peripheral areas of contact in the upper sidewall portions
of each. Lubricant 19 is likewise disposed between the outer and
inner surfaces of immediately adjacent stacked containers at the
lower contacting portions of the sidewalls. When it is desired to
release the lowermost container (or to raise the uppermost
container) from a stack of a plurality of similarly constructed
units, the lubricant film acts in a sense like a ball bearing to
insure uniform and rapid separation of the outer and inner
containers around the peripheries of each at their upper ends,
i.e., between edge 30 of the outer container and shoulder 24 of the
inner container. Lubricant 19 also functions to minimize the
frictional resistance against sliding of the inner surface of
sidewall 18 of an outer cup along chime 40 at the lower end of the
sidewall of the inner cup as the outer cup moves away from the
stack. Since the lubricant utilized must in all cases bear approval
for use with comestibles by the Food and Drug Administration, trace
amounts of the lubricant appearing on the inner surfaces of a
container, which may have been rubbed off of the outer surface of
an adjacent stacked unit are not objectionable from the standpoint
of food or beverage contamination.
Container 10 must subsequently fall by gravity along an inclined
chute from a lower position within a nested stack in the upper
section of an automated vending machine into place in the filling
station below. Contact during travel along the chute, which may not
be entirely smooth, is along slide line 54. In so doing, lubricant
19 on chime 40 in the lowermost portion of the sidewall again aids
in reducing frictional resistance to sliding, thereby facilitating
rapid and trouble free movement of the cup into its dispensing
position within the machine.
Referring now to FIG. IV, an expeditious process is illustrated by
which a partially foamed, plastic container having a predetermined,
lubricated, non-foamed external surface portion is obtained.
Initially, a solution 60 is prepared (FIG. IVa) of a non-volatile
lubricant 61 dissolved in a medium which is absorbable by the
plastic and convertible to a gaseous state below the melting point
of the plastic of the container being treated. The solution may be
stirred by means of a suitable stirrer 64 in tank 65 to insure
complete dissolution. A completely non-foamed thermoformed cup 62
of the type depicted in FIG. I is obtained, which it is desired to
lubricate and to partially foam by providing previously described
foam covering 18 along the major extent of its sidewall. To prevent
absorption of the foaming agent into the plastic in the
predetermined portions to be non-foamed, i.e., the upper and lower
portions of the sidewall on either side of the foam band, these
portions are coated with a chemical lacquer composition comprising
a non-volatile resinous ester dissolved in an alcohol as described
in copending application Ser. No. 695,359 filed Jan. 3, 1968, now
U.S. Pat. No. 3,565,660, and assigned to the assignee of the
present invention. This coating is accomplished by moving cup 62
into contact with a porous material 64 which is saturated with the
chemical masking agent. The chemical masking agent is supplied to
porous material 64 by means of a conduit connecting to a
pressurized supply source of the composition. Porous applicator
material 64 is supported in holder 66. Cup 62 is rotated as
depicted at (b) while its upper and lower surfaces are in contact
with porous material 64, thereby resulting in a coating of the
exterior of the bottom chime and the nesting means with the
chemical masking composition, as well as the areas immediately
adjacent thereto. The chemical masking agent utilized is considered
to a liquid which when coated on the surface of the plastic and
dried thereon to evaporate the solvent when the masking agent is a
lacquer, acts as a barrier against absorption into the plastic of
the absorbable foaming agent. The cup, having preselected exterior
portions thereof coated with the chemical masking agent, is then
immersed in tank 65, which contains the solution of lubricant
dissolved in the absorbable medium, as schematically depicted at
(c) for a predetermined interval of time. At the end of this
interval of time, cup 62 is withdrawn from tank 65 and subjected to
a heat source as depicted at (d) which involves circulating a
fluid, e.g., air or steam at elevated temperature through an inlet
conduit 68 into the interior of cup 62. The heated fluid exits from
the cup through outlet conduit 70 which has a diameter greater than
that of inlet conduit 68, and which is equipped with a flange 72
adpated to rest against the upper surface of the rim of cup 62
while the gas is being circulated. The heat, which as shown is
applied to the inner side of the cup, i.e., that which is opposite
to the side which had been exposed to the absorbable medium,
results in the formation of foam covering 18 along the area which
was previously in contact with the medium and which had not
initially been coated with the chemical masking agent. The cup 62
is shown at (e) with the foam covering thereon.
Also, as a result of exposure to the solution of lubricant and
absorbable medium, a coating 19 of lubricant is left on top of the
previously chemically masked upper and lower portions of the
sidewall, on the nesting means and on the corner chime portions
thereof. The lubricant is also present on the surface of the
plastic portion which was subsequently foamed, and therefore
results in the lubricant being interspersed throughout the foam
cells after the foaming step. Lubricant 19 functions as previously
described to enhance the stack release and vending properties of
cup 62. Since the chemical masking agent is insoluble in the
solution of lubricant and absorbable medium, the non-volatile
portion of the masking agent is not disturbed from its place as a
coating on the preselected portions of the container sidewall
during the exposure step. Since the lubricant is relatively
non-volatile, it remains on the cup surface and does not evaporate
as does the absorbable medium during the heating step.
The above description and particularly the drawings are set forth
for purposes of illustration only and should not be taken in a
limited sense.
The following examples are given to illustrate the invention and
are not intended as limitation thereof. Unless otherwise specified,
quantities are mentioned on a weight basis.
EXAMPLE 1
A solution of lubricant dissolved in a liquid foaming agent was
prepared by adding ten parts of liquid Dow Corning DC 200 silicone
oil (polydiemethyl siloxane characterized by a viscosity of 500
centistokes, a specific gravity of 0.973 at 25.degree. C. and a
surface tension of 21 dynes/cm..sup.2 at 25.degree. C.) to 1990
parts of Freon-11 (trichloromonofluoro methane). The mixture was
stirred until a clear homogeneous solution was obtained.
A rubber-modified styrene polymer blend having a Staudinger
molecular weight of approximately 50,000, i.e., a physical blend of
7.5 parts of styrene-butadiene graft copolymer with 92.5 parts of
styrene polymer wherein the graft copolymer contains 28 percent by
weight of styrene based on the weight of the copolymer, was
thermoformed into a smooth, tapered cup approximately 4 inches in
height and having an average inside diameter of 2 inches. The cup
had nesting means formed in the upper sidewall portion thereof
similar to that depicted in FIG. I.
The cup formed by the above described operation was coated by
contacting 1 inch of the lower outer portion of the cup sidewall as
well as the outer surface of the nesting means in the upper portion
of the cup sidewall with a porous pad saturated with a resinous
ester dissolved in alcohol. This latter composition was prepared by
adding 35 parts by weight of "Amberol 750" (a resinous ester formed
by esterifying the reaction product of maleic anhydride and rosin
acid with glycerol) to 60 parts of methanol. After a 3 second
interval the cup was separated from contact with the pad and
allowed to dry for 45 seconds.
The cup, chemically masked in this manner, was then immersed in the
previously prepared solution of polydimethyl siloxane and Freon-11
up to within about one-half inch of the top of the sidewall. The
cup was maintained in this immersed condition for a period of 10
seconds after which it was withdrawn from the solution. After a 20
second interval at dry room temperature conditions, hot air at a
temperature of 250.degree. F. was circulated through the interior
of the cup for a period of 10 seconds.
The resulting cup had a foamed outer surface throughout the area of
immersion in the solution of foaming agent and lubricant, extending
into the body of the cup for approximately one-third of its overall
thickness, except for those portions of the cup which had been
previously coated with the resinous ester masking composition.
These latter preselected portions were non-foamed and had a thin
coating of the polydimethyl siloxane lubricant deposited thereon.
Examination of the cup disclosed that its overall structural
properties were not seriously altered by the steeping operation
while at the same time the insulating properties of the cup were
increased several fold. The foam was of excellent quality, the
cells being fine in size and uniform in appearance.
Additional cups were thermoformed as set out above for test
purposes to be hereafter described. Certain of these cups were
chemically masked and foamed as set out above, except that the
lubricant was not added to the Freon-11 foaming agent. The entirely
non-foamed cups, the partially foamed, non-lubricated cups and
additionally prepared cups partially foamed and lubricated in the
manner set out above, were passed down an inclined hollow
cylindrical chute of the type utilized in automated vending
machines, which made an angle with the horizontal of about
60.degree., and observed for speed relative to each other. The
following results were obtained. Numbers refer to the quantity of
cups falling into the categories identified by the key below.
##SPC1##
As can be seen from the above, 100 percent of the chemically
masked, lubricated, partially foamed cups tested were considered to
have adequate or better speed while sliding down the vending tube,
with about 77 percent of this category considered to have fast
speed, thereby producing excellent vendability. Results were
slightly better with the unmasked and non-foamed control cups and
substantially poorer with the chemically masked and partially
foamed cups.
EXAMPLE II
A solution of lubricant dissolved in a liquid foaming agent is
prepared by adding thirty parts of liquid Dow Corning DC 200
silicone oil to 1970 parts of Freon-11. The mixture was stirred
until a clear homogeneous solution was obtained. Chemical masking,
exposing, foaming and testing are carried out in the same manner as
in Example I utilizing similarly shaped initially thermoformed
cups. Substantially equivalent results are obtained.
In general, the plastics used in the practice of this invention are
substantially thermoplastic materials which have been fabricated
into containers having nesting means simultaneously formed therein,
and include such materials as polystyrene,
styrene-buta-diene-acrylonitrile graft and/or mechanical
polyblends, other rubber-modified graft and mechanically blended
styrene polymers, vinyl chloride, vinyl acetate copolymers,
polyethylene, chlorosulfonated polyethylene, chlorinated
polyethylene and ethylene-vinyl acetate copolymers which are graft
and/or mechanically blended with polyvinyl chloride homopolymers
and copolymers, polyvinyl halide homopolymers and copolymers
including interpolymers, mixtures and plasticized versions of the
same.
The plastic solvent foaming agent may be any material which is (1)
at least a partial solvent for the plastic being processed, and (2)
convertible to a gaseous state at a temperature below the melting
point temperature of the plastic. Freon-11 (trichlorofluoromethane)
is generally preferred for polystyrene homopolymers and
rubber-modified interpolymers, with methylene chloride, acetone,
dichloro-ethylene, xylene, carbon tetrachloride, methyl ethyl
ketone, benzol, toluol, chloroform and the like being likewise
effective depending on the particular plastic being used.
The masking step of the above-described process of the present
invention may be achieved by either coating with a chemical
composition as set forth in the preferred embodiment or by
mechanical means. Typical of the latter approach is the use of a
sealed chamber imposed around the cup surface(s) to be non-foamed
to shield these portions during exposure of the cup to the
absorbable medium. Also useful for effective masking are the
utilization of cooled surfaces in contact with either side of the
surface to be non-foamed, while the surface to be foamed is heated.
This may be accomplished by means of cooling rings in contact with
the outside surface portion of the cup which is to be non-foamed or
by means of a composite mandrel placed against the wall of the
interior of the cup prior to exposure to the absorbable medium, the
mandrel having both heated portions for creating foam and cooled
portions for retarding foaming.
In the preferred chemical masking approach the coating materials
employed may be any fluid substances which will serve as a barrier
against absorption of the medium by the plastic. The choice of the
fluid substance, utilized will, of course, depend on the medium
employed in the process. In some instances, it may be desirable to
employ fluid substances which are considered insoluble in the
particular medium employed. Preferentially, the coating composition
is a lacquer comprising a resinous ester which is a derivative of
rosin or rosin acids, a modified rosin or a modified tarpene
hydrocarbon, which is soluble in alcohol and generally insoluble in
aliphatic and petroleum hydrocarbons. This composition has been
found to effectively shield the portions to be non-foamed from the
absorbable medium. However, the non-volatile resinous ester portion
of the composition, after evaporation of the solvent, is rather
rough and slip resistant which, as mentioned, causes vending and
stack separation problems with the cups. The problem is unusually
overcome by the present invention wherein these slip resistant
surfaces are subsequently coated with a slip promoting type of
release agent during the exposure step.
Regardless of the manner in which the masking is achieved in the
present invention, patches of almost imperceptible foam
breakthrough often appear in the area of the cup which was meant to
be non-foamed. This is especially true in high speed production
operations because of incomplete masking, whether it be a result of
a slight discontinuity in the coating of chemical masking agent or
incomplete shielding or surface contact if one of the other methods
of masking is used. This foam, as mentioned, has a rather high
coefficient of friction which may cause cup sliding problems.
However, the effect of this deficiency is diminished by the manner
of coating of the preferred embodiment wherein a film of lubricant
has already been deposited on the surface prior to the foaming step
when the patches are generated. Thus the present invention can
reduce the criticality of the masking step since foam patch
breakthrough is no longer as much of a problem.
In general, the plastic article is permitted to dry for a short
interval of time after exposure to the foaming agent -- lubricant
solution and prior to heating. This drying interval allows deeper
diffusion and serves to harden the outer surface of the cup
somewhat, forming a skin which aids considerably in the formation
of the closed cell structures which are necessary for good
insulating properties. If desired, the drying, interval may be
accelerated by forced air blasts, moderate heating conditions,
etc.
After the drying interval, the plastic article is heated to foam
the outermost portions of the plastic article. The heating means
utilized may vary, the final results being affected by the
uniformity of heating, rate of heating and temperature level at
which it is conducted. Heating may be on either the same or the
opposite side of the cup surface which had been exposed to the
absorbable medium. An especially uniform foam has been obtained by
exposing the side opposite to that which had been exposed to the
foaming agent.
Though it is preferred for operational simplicity to coat the
container portion to be non-foamed with the lubricant
simultaneously with immersion in the medium, any suitable equipment
may be employed to coat the portion of the plastic container to be
non-foamed as a separate step either before or after exposure to
the foaming agent. For example, this could even occur by utilizing
a brush, roll or similar device either with or without a partial
foaming step.
The quantity of coating applied should be such that the dry coating
weight is from about 0.1 to 1.5 parts of lubricant per 98.5 to 99.9
parts of liquid foaming agent, and preferably 0.1 to 0.5 parts of
lubricant per 99.5 to 99.9 parts of foaming agent.
The lubricant utilized on the container surfaces of the present
invention must have clearance of the Food and Drug Administration
for use in food packaging applications, since this is the type of
container contemplated by the invention. Consequently, it should be
inert, clear and non-toxic, but may be either a solid or liquid at
room temperature conditions prior to dissolution. It must have the
ability to reduce friction between the plastic container and
another surface along which the container is sliding. When utilized
in conjunction with the partial foaming process wherein coating
takes place during exposure to the absorbable medium as in the
preferred embodiment, the lubricant should be miscible in the
absorbable medium. It must be highly efficient at low
concentrations, be soluble in water or organic solvents and have no
effect on the quality of the foam produced during the heating step.
It should be relatively non-volatile at temperatures up to about
200.degree. C, in order to avoid evaporating during the foaming
step. Effective lubricants include fatty materials such as fatty
acids having from 8 to 24 C atoms, ethers, alcohols and amides such
as oleamide, palmitamide, linoleamide and stearamide; polyethylene
glycols having average molecular weights in the range of between
about 400 to 4,000; fully refined paraffin waxes melting at between
about 145.degree. to 180.degree. F.; petrolatum, glycerine, castor
oil, mineral oil, fluorocarbon polymers and fluorocarbon
surfactants. Particularly preferred when the lubricant is applied
during the partial foaming process are polymeric silicone materials
characterized by a repeating siloxane linkage, i.e., ##SPC2##
wherein R.sub.1 and R.sub.2 are either C.sub.1 or C.sub.2 alkyl
groups.
Polydimethyl siloxane is particularly preferred since it has been
found to have no effect on the quality of foam produced on the
finished container, with the resulting cell size being equivalent
to that obtained without use of the lubricant. Also, off grade
scrap cups having this type of lubricant coated on their surfaces
showed no signs of incompatibility or other adverse processing
behavior when reground and re-extruded.
It should be noted that the present invention is applicable to
deposition of lubricant on any exterior surface portion of a
nestable container of a type wherein it is desirable to increase
its sliding properties. It is preferred however that the coating be
applied on the lower portion of the sidewall in the area of its
joint with the base and on the surfaces of the nesting means.
Satisfactory results are obtained by coating at either or both of
these sections of the cup.
As an advantageous side effect of the lubricated exterior surface
portions of the containers of the present invention, it has been
noted that minor amounts of the lubricant are rubbed off the
surfaces of the cups onto various cup supporting surfaces of the
vending machines over a period of time. This also decreases the
effect on cup dispensing speed of sticky internal surfaces of these
machines which may be caused by vapors condensing from hot liquids
within the machine which are present as parts of the constituents
of the beverage being dispensed.
The nestable containers of the present invention are formed from
resilient thermoplastic materials. The structures are used in coin
operated beverage dispensing machines and broadly where space
requirements require that a plurality of containers be nested
together within a stack. The lubricated surfaces of the invention
are especially applicable in insulated containers for holding hot
or cold substances having integral non-foamed wall portions which
provide improved structural properties. The invention is likewise
applicable, however, to entirely foamed and entirely non-foamed
containers.
It is obvious that many variations may be made in the products and
processes set forth above without departing from the spirit and
scope of the invention as hereinafter claimed.
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