Note: Descriptions are shown in the official language in which they were submitted.
110~7Z6
METHOD OF CO-EXTRUSION WITH FOAM CORE
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
This invention relates to a method of manufacturing
integrally formed plastic sandwiches. More particularly, the
invention relates to a process for the extrusion of integral
plastic members having solid skins and a cellular inner portion.
DESCRIPTION OF THE PRIOR ART
Attempts have been made in the past to provide for the
production of plastic sandwich structural elements by bonding
solid plastic skin members to the top and bottom surfaces of a
cellular plastic core. However, this method of fabrication is
costly since it requires the individual fabrication of the indi-
vidual skin and core members, the application of a relatively
costly adhesive material and the clamping of the bonded struc-
tural element until the adhesive is set. In addition, the
difficulty in obtaining a high strength bond over an extended
surface using an adhesive results in a product having a less
than desirable level of reliability.
Other methods for the fabrication of plastic sandwich
members have in the past included a molding process in which
inert gas is dispersed in a polymer melt, the polymer melt is
introduced into a mold and as the mold fills, the gas expands
within the material forming a cellular core while a solid plastic
skin forms along the walls of the mold. This method has the
disadvantages of not permitting close control over the skin
thickness, not permitting variations in material between the
skin and the core and requiring a large and consequently expen-
sive mold for the production of large plastic members.
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Attempts have been made to co-extrude a multi-layer
plastic sandwich such as disclosed in the U.S. patent to
Chisholm et al, No. 3,557,265. This patent nowhere discloses
the concept of providing a foamed core. In Thomas, U.S.
No. 3,331,900 there is disclosed a skin coated foamed plastic
article. Shippers, U.S.No. 3,782,870 discloses an apparatus
for partially foaming a portion of extruded ma-terial by
separating melt streams and then rejoining the separate melt
streams and partially foaming one of the melt streams.
SUMMARY OF THE INVENTION
The present invention contemplates control of the
cellular core characteristics co-extruding method utilizing the
concept of temperature differences in the materials being co-
extruded.
In one broad aspect, the invention comprehends a method
of manufacturing a co-extruded article, which comprises the steps
of mixing ingredients for a cellular plastic including a
chemical blowing agent and a thermoplastic resin in a plastic
state for forming a core, and at a temperature range of 300F.
to 400F. Other ingredients for at least one solid thermo-
plastic resin are mixed in a plastic state at a temperaturediffering from the temperature by at least 25F. for forming
the skin for the core, and then simultaneously co-extruding
the cellular plastic and solid plastic through a die.
More particularly, a first extruder is charged with
essential ingredients for production of cellular plastic at
a predetermined temperature. At least one second extruder is
charged with essential ingredients for production of solid
plastic at a temperature differing from said predetermined
temperature by at least 2~ degrees Farenheit. Control means
are provided for the simultaneous operation of the first and
second extruders thus resulting in the extrusion of a sandwich
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member having a core of cellular plastic and one or more
integrally forrned skin members of solid plastlc. The
characteristics of the resulting plastic sandwich element
can be controlled to feature, as desired, high flexural
strength, hardness, relatively hiyh flexural rigidity,
relatively low weight and relatively low cost. By increasing
and decreasing the speed of operation of the second extruders,
the thickness of skin members may be increased or decreased.
It is therefore an object of the present invention
to provide a method for the manufacture of an integrally
formed co-extruded plastic member having a core of cellular
plastic and skin members of solid plastic.
Some of the advantages of the present invention
are that the plastic sandwich material so produced is desirable
for use as a cap liner. The product prevents product
penetration in to the liner when used as a liner for caps,
and any product penetration stagnating behind the liner
and attracting germs. The final product assures a smooth
surface in contact with the contents of the product. The
concept of temperature differential co-extrusion of the
foam core provides for different degrees of resilience while
also greatly providing for price advantage in that less mat-
erial can be used.- Further, the layers enable a better stamped
liner allowing a sharp definition while providing for a
stronger product. The layers encasing the foam core at a
various temperature when co extruded provide for a desired
cell structure while in the event some cells blow too much and
are open, the layers will seal these open cells thus forming a
very resilient liner.
These, together with various ancillary aspects of the
present invention, are obtained by this method of manufacture
of plastic sandwich elements, preferred embodiments being shown
in the accompanying drawing by way of example only, wherein:
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BRIEF DESCRIPTION OF THE DRAWING
_
Fig. l is a longitudinal sectional view through a
portion of an embodiment of an apparatus which can be used
according to the present invention;
Fig. 2 is a cross sectional view illustrating sche-
matically the construction of a co-extruded plastic sandwich with
a retaining thick skin at a temperature of at least 25 degrees
Farenheit hotter than the core shown immediately after co-extrusion;
Fig. 2A is a view similar to Fig. 2 after the core
has additionally foamedî
~ igs. 3 and 3A are views similar to Fig5. 2 and 2A but
illustrating the co-extruded plastic sandwich having a relatively
thin skin co-extruded at a temperature of at least 25 degrees
Farenheit hotter than the core;
Figs. 4 and 4A are views similar to Figs. 2 and 2A
but illustrating the co-extruded plastic sandwich having a relative-
ly thick skin co-extruded at a temperature of at least 25 degrees
Farenheit cooler than the core;
Figs. 5 and 5A are views similar to Figs. 2 and 2A
but illustrate the co-extruded plastic sandwich having the same re-
latively thin skin as Figs. 3 and 3A co-extruded at a temperature
of at least 25 degrees Farenheit cooler than the core.
DETAILED DESCRIPTION OF THE INVENTION
With continuing reference to the accompanying
drawing, whexein like reference numerals designate similar parts
throughout the various views, reference numeral 10 is used to
generally designate a typical apparatus which can be used for the
co-extruding of the plastic sandwich.
As shown three extruders are employed arranged with
the extruder 12 for the core being arranged horizontally with its
auger 14 feeding longitudinally. The extruders 16 and 20 and their
augers 18 and 22 are shown arranged vertically. It is to be
understood that while this is a space saving and convenient typical
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installation, in accordance Wit31 the concePts of the present
invention the extruders can be dlsposed in any suita~le arrangement
such as side by side, angularly clisposed, or even remote from
each other, the material to be co-extruded being fed to a size-
able die 24.
In the illustrated embodiment, the first extruder 12
includes a perforated plate 26 and a tapered nozzle 29 through
which core ma-terial C to be extruded is fed to the die 24. Like-
wise, skin material A fed by auger 18 passes through a perforated
plate 30 and throuqh tapered nozzle 32 onto the foamed core mat-
erial C and thence through die 24. The skin material B fed by
auger 22 passes through perforated plate 34 and tapered nozzle 36
onto the core material C and thence through die 24. This facilitat-
es the formation of top skin A of solid plastic and a bottom skin
B of solid plastic on the center core C of cellular plastic of
the integral plastic sandwich member 100. The extruder 12 is
charged with essential ingredients for the production of cellular
plastic and the second extruder 16 and the third extruder 20 are
each charged with essential ingredients for the production of
solid plastics.
Control means are provided to control the relative
speeds of rotation of the augers 14, 18 and 22 to provide for del-
ivery of selected and sufficient quantities of tlle esse3ltial in~red-
ients to provide core material C and skin material A and B.
The present invention is adapted to use practically all
thermoplastic materials. The thickness of the material may range
from between .010 inches to an inch or two while the thickness of
the skin material A and for B is in the order of .001 to .010 in-
ches, the balance being in the thickness of core material C. A
material for the integrally formed plastic sandwich element 100 maybe polyethylene which forms A and B of solid polyethylene and a core
C of closed cell foam polyethylene. The use of polyethylene is
indicated by way of example only, and other thermoplastics materials
having properties adapted for fabrication by an extrusion process
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and which can be formed into a foam or cellular state may be util~
ized using the process and apparatus according to the present in-
vention. Of course, two, three, or more layers may be used to
obtain the desired thickness and properties where this material is
used as a cap liner.
EXAMPLE I
As shown in Fig. 2, a plastic sandwich 100 is formed
with the core material C being formed from a mixture of melted
polyethylene, and zinc powder such as zinc stearate in amounts as
conventionally employed as a stabilizer and activator. A product
sold by Uni-Royal under the trade mark of "CELOGEN" is employed as
a foaming agent. Other conventional foaming agents may alternativ-
ely be employed. The extrusion temperature of the core material C
may range from 300 to 400 degrees Fahrenheit at optimum operation
and in this example the core material tempe~ature selected is 300
degrees Farenheit. The skin material A and B employed is delivered
at a rate so that the thickness is .010 inches and is relatively
thick. The temperature of this polyethylene may range from 200
to 450 degrees Farenheit.
The use of thick skin permits for reasonable tensile
strength while the added heat of the skin will promote further ex-
pansion in a controlled manner of the cellular material C because
of free release of pressure after passing through the die. The
thick layer promotes eveness of the final sandwich even if the
added heat will expand the resiliency of the material, allow for
sufficient tensile stress and hardness while permitting expansion
of the thickness of material in the order of 240% as compared to
the thickness of an equal amount of material without foaming.
EXAMPLE 2
In Figs. 3 and 3A there is shown an embodiment of the
invention wherein a thin skin of a thickness of .001 inch is used
at the same temperature as set for-th in Example 1. This embodiment
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causes an expansion factor in the order o~ 600% with great
resiliency, a shore hardness of 65 on a durometer and sufficient
tensile stress to function well as a cap liner. The added heat
of the thin skin unexpectedly enhances tensile strength rather
than inhibits the tensile strength by providing intimate
coexistance of the skin and core.
EXAMPLE 3
In Figs. 4 and 4~ the followin~ are the charac~eristics
of the materials used:
Core material C is at temperature of 300F; skin
materials A and B are each of .010 inch thickness and at a
temperature of 250F. This gives great tensile strength and a
shore hardness of 90 on the durometer. Further, the thick cool
skin inhibits further expansion after extrusion permitting rapid
and accurate extrusion.
EXAMPLE 4
In Figs. 5 and ~A, the characteristics are the same as
Example 3, except that the skin materials A and B are relatively
thin being .001 inch thick. While this thin skin at a cooler
temperature will permit the core to expand, this expansion is un~
expected even and the cooler skin prevents blowing of cells even
though a gooa expanslon factor is obtained.
It is to be understood that the skin thickness may be
increased or decreased as desired by increasing or decreasing
the output (speed) of the extruder for the skin material without
making any changes in the temperature of extruding.
A latitude of modification, substitution and change is
intended in the foregoing disclosure, and in some instances, some
features of the present invention may be employed without a
corresponding use of other features.
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