Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a process for
producing parboil spherical segment-shaped packing
material particles made of a plastic material which
have an external convex and an internal concave
surface, where the plastic material is mixed with
additives such as bubble-forming agents, coloring
pigments or similar substances, and by means of a
feeding funnel, is fed into an ex~ruder through an
opening in a bush surrounding the extrusion screw,
where the plastic material is plasticized in the
course of the extrude and, because of the difference
in speed existing over the cross section of the mass,
comes out of an opening in the die with a bent surface,
and the extruded plastic material is cut off directly
at the opening of the die and before any considerable
expansion has taken place.
A process of this type is known from U.S.
Patent No. 3,961,000. In the case of this process,
the e~pandible polystyrene (ENS) is mixed with add-
lives. The additives consist of bubble-forming-agents-
such as bicarbonate of ammonia and sodium bicarbonate
or similar substances and coloring pigments
Via a supply funnel, the mixture is fed into
an extrusion device. An extrusion screw transports
the mixture through the extrude, where because of the
special design of the extrusion screw, i.e. an inquiry-
sing core diameter as well as a suitable temperature
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program, the plastic material is plasticized in the
course of the extrude. Immediately after the plastic
material comes out of an opening in the die, it is cut
off by means of a cutting device, in which case it is
made possible for the cut-off particles to expand in
a first expansion process into the special shape with
a convex outside and a concave inside surface. The
packing material particles are processed to their
final condition in several subsequent expanding
processes.
Polystyrene is a polymerization product of
the Bunsen derivative styrenes and according to the
conditions of representation, has polymers of varying
chain lengths. The chain length is significantly
determined by how many styrenes units were "chained to
one another" during the polymerization.
polymerization j
CH=cH2 2 OH -
monomeric styrenes polystyrene
The chain length essentially determines the
physical characteristics of the plastic material. In
order for the plastic material to be processed in an
extrude, it must by "thermoplastic". This means that
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the plastic material which is firm at a certain
temperature (usually at room temperature) becomes
plastic (soft, moldable) when the temperature is in-
creased and can then be processed to a certain shape
and after cooling resumes its firm condition.
For the processing in the extrude, two
different basic types of polystyrene are available:
a the so-called standard polystyrene
) a polystyrene containing an expanding
agent.
The standard polystyrene is a pure polymer,
ire., a pure polystyrene without additives. In the
case of the polystyrene containing an expanding
agent, an expanding agent is included in the polymer
matrix which boils at an increased temperature and
foams the polymer. Such expanding agents are prefer
rawly low-boiling hydrocarbons, fluorohydro-carbons
or water.
Standard polystyrene types as well as polyp
styrenes types containing expanding agents are suitable for processing into foamed materials on the extrude.
When standard polystyrene is used, it is necessary to
add an expanding agent to the extrude during process
sing In that case, one speaks of a so-called direct
gassing.
The expanding agent causes the plasticized
material to foam after leaving the extrude.
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The expanding agent, in the extrude, is
released under pressure in gaseous fox in the pies-
ticized plastic mass. The plastic mass is supers-
turated with gas, i.e., because of the conditions
(pressure, temperature existing in the extrude,
more gas is released than under normal conditions.
After leaving the extrude, the expanding
agent tries to burble down and to expand to normal
pressure. The stick plastic mass surrounding the
expanding agent prevents the propellant gas from
escaping into the atmosphere and therefore results
in the foamed structure.
By cooling the plastic material in the
indicated shapes, the typical structure of the blocks
of foamed material is obtained.
In the case of large-volume blocks of foamed
material, such as insulating boards, the size of the
foam bubbles is relatively large, and the diameter of
these bubbles fluctuates over a considerable range.
In the case of the present process, however,
small packing material particles are produced, the
diameter of which is about up to three centimeters.
In the case of these small packing particles, the
size of the bubbles must naturally be much smaller
than in the above-described case in order to ensure
the stability of the packing particle material. Only
a few large bubbles in these small packing particles
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decrease stability and even under little stress
result in a breaking of the particles. Larger
bumbles, especially in the edge area of the packing
particles having a surface that is convex on the
outside and concave on the inside lead to a consider
fable danger of "crumbling" in this edge area, so
that because of the constant friction during the
transport a fine rubbed of snow will be created.
There is also the danger that during the
re-expandiny processes, such as they are carried out
in the process of the initially mentioned type, if
individual larger bubbles are created, these become
larger and the packing particles are destroyed during
these expanding processes.
In order to achieve a more uniform formation
of bubbles, so-called "nucleation agents" may be
added. These nucleation agents cause a nucleation ox
bubbles in the plasticized plastic material. From a
chemical point of view, this takes place by the fact
that the solid nucleation agents decompose in the
extrude while forming gas.
The released gas has the objective of forming
in the plasticized plastic material a larger number of
nuclei of bubbles. This resulting gas, as far as the
term it concerned, must be clearly separated from the
propellant gas, The propellant gas which under
pressure is released in the plastic material, diffuses
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into the small bubbles and causes the expansion of
the nuclei of the bubbles created by the decomposition
of the nucleation agent.
In the technique, nucleation agents are
preferably used that do no carry harmful gases,
decomposing into carbon dioxide, nitrogen or similar
gases
The raw materials used in the process must
correspond to the German Food Law. According to FDA
requirements, all components must be GRAS (GENERALLY
RECOGNIZED AS SAFE). The most often used materials
are carbonates, such as carbonate of ammonia or sodium
carbonate. Sodium hydrogen carbonate has, for exam-
pie, also teen used widely as a propellant in backing
powders since at an increased temperature it separates
carbon dioxide.
The required quantity of nucleation agent
is determined by the decomposition behavior of the
nucleation agent at a rising temperature The so-
called theoretical gas yield in-this case plays a
significant role. The theoretical gas yield is
determined by the released quantity of gas (such as
carbon dioxide per unit of weight. wince the gas
yield increases with rising temperature, small
quantities of nucleation agent art required at high
processing temperatures.
In the case of relatively low processing
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temperatures of about 110 - 130C, the conventional
nucleation agents cannot be used economically because
they have an optimal processing temperature range of
180 - 230C. In addition, the formation of bubbles
in regard to their size and their spatial distribution
per volume element of plasticized plastic mass
is very irregular, which after leaving the extrude
results in an irregular cell structure of the expand
dyed plastic material.
It is the objective of the invention to improve
a process of the initially mentioned type in such a
way that in the case of a relatively low processing
temperature of the plastic material in the extrude
and small additions of nucleation agent, an even format
lion of a large number of bubbles is made possible.
This objective is achieved by the fact that
on the surface of the plastic granules, before their
processing in the extrude, the bubble forming agent
(nucleation agent) is applied.
In accordance with the present invention,
there is thus provided a process for producing parboil
spherical-segment-shaped packing material particles
made of plastic and having an external convex and an
internal concave surface, in which the plastic-materialis
mixed with additives and fed by means of a feeding
funnel into an extrude through an opening in a bush
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surïc)undinq an extrusion screw, where the plastic
material is plasticized in the course of extrusion and
comes out of an opening in a die with a bent surface,
and the extruded plastic material is cut off directly
at the opening of the die and before any considerable
expansion has taken place. The process according to
the invention is characterized in that a bubble-forming
agent having a grain size of less than about 40 mu is
uniformly distributed on the surface of the plastic
particles before their processing in the extrude in
an amount less than 0.2 percent by weight based on the
weight of said particles.
The finely ground nucleation agent, in a drum,
is "drummed" onto the plastic granules. The quantity
of the "drummed-on" nucleation agent is preferably
about 0.1-0.2 percent by weight with respect to the
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weight of the granules.
The nucleation agent may especially ad van-
tageously consist of a carbonate and an acid combo-
next n The acid component, in addition to the effect
of the heat, by the chemical effect on the carbonate
component, makes possible a development of carbon
dioxide. the acid component consists of citric acid
and there are therefore no reservations based on the
food law,
Of decisive significance in regard to a
uniform quality of the packing material particles
produced according to this process is the formation
and the expansion of gas bubbles.
The formation ox bubbles takes place by the
fact that the nucleation agent releases a gas in the
plasticized plastic material. The release of gas,
as mentioned before, can take place only by the then-
mix splitting-up of the carbonate, or in addition by
reactions between the acid component and the carbonate
component. Since the carbonates are salts of the
weak acid carbonic acid, the carbonic acid can be
pushed out o their compounds by stronger acids, in
this case citric acids.
The conventional propellants are swilled
exothermal systems, during the decomposition of which
large quantities ox heat are released. The danger of
the formation of heat accumulation, i.e. local over-
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heating, leads to an uneven formation of bubbles.
The propellant used in this process is an
endothermally effective system. With an increasing
temperature, an even decomposition of the propellant
and thus more finely celled and more uniform foamed
structures are obtained. The decomposition behavior
of the nucleation agent depends essentially on the
added quantity of heat (temperature stress through
outside heating and inside friction.
The solid nucleation agent must be evenly
and finely distributed in the plasticized plastic
material so that per volume element potential nuclei
exist that are as numerous as possible and as small
as possible. It is then ensured that when the for-
motion of gas occurs, a uniform fine-celled foam will
be created in the extrude.
According to the invention, this it achieved
by the tact that the nucleation agent, before the
plastic material granules are pulled into the extrude,
is distributed on these granules so that it adheres to
them evenly, in which case the grain size is of very
decisive significance.
The finely ground nucleation agent (grain
size about 40 I) is "drummed onto" the granules of
plastic material in a drum. The term "drummed onto"
is used here in order to differentiate it clearly
from the mixing of the granules of plastic material
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with the nucleation agent, as it is carried out in
the state of the art. This mixing may also take
place in mixing drums so that a clear difference must
be made between the two processes, as far as the
terminology is concerned.
Figuratively, the granules of plastic
material, after they have left the drum, are different
from one another because of the fact that after the
"drumming-on" the granule s of plastic material look
like, for example, an apple iced with confectioners
sugar, whereas after the mixing, the granules look
as if an apple had been sprinkled with sugar crystals.
The adherence of the swigger crystals" in the state of
the art is achieved by adding bonding agents, such as
talc to the mixture. In the case of the drur~ming-on,
no bonding agents are required since the fine "powder"
adheres well to the surface.
When one follows the path of the differently
treated (mixed or drurmmed-on) granules from the
mixing drum through the extrude, the difference can
be made particularly clear using the "apple example'`.
The granules (apples) in the tunnel are in
a constant movement and in the pull-in zone of the
extrude, where they are not yet plasticized, are
turned into different directions and rubbed against
one another. The granule (apple first carries out
an essentially vertical movement through the funnel
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and subsequently in the extrude, by the propelling
sides of the extrusion screw, is moved into a direct
lion that can be divided into two components. One
movement is the axial movement through the extrude
and the other movement is the circular movement
around the axis of the extrude.
Over the course of the extrude, because of
the increase of the core diameter of toe screw, the
space for the granules (apples decreases continuously.
Through the rubbing-against-one-another of
the individual granules (apples) because of the
advancing and rotating movement and because of the
increasing densification. a relatively extensive
rubbing-off takes place on the granules with the
coarse nucleation agent (apples with sugar crystals),
the rubbed-off material collecting especially in the
hollow spaces between the granules.
In the case of the granules with the drummed-
on nucleation agent (apples with confectioners sugar
icing), a layer exists that adheres firmly because
of the adhesive forces and is distributed evenly over
the surface. The rubbing-off of nucleation agent on
the path of the granule (apple) through the funnel
and the material pull-in zone is much less, and
therefore hardly any material is collected in the
spaces between the granules (apples).
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In the plasticizing zone of the extrude,
i.e., in the zone where the granules become sot, the
granules no longer rub against one another but are
squeezed together or kneaded together. However, this
kneading-through in the extrude is only a rough
mixing of components.
In the microscopic range, a certain "close
order" is still maintained despite this mixing.
In the case of the drummed-on granules of
plastic material, after the collapse of the solid
phase by plasticizing, the spatial distribution of the
still firm nucleation agent it very regular. This
means that in any volume element, numerous very fine
nuclei of bubbles are evenly distributed.
In contrast, in the cave of the originally
only mixed granules (i.e., the plastic material and
the nucleation agent are only mixed and not drummed
on), there are in certain areas many and relatively
large solid matter particles of the bubble nuclei
present, whereas in other areas there are almost no
bubble nuclei present, but only much plasticized
plastic material with the propellant released in said
material.
Because of the small grain size and the fine
distribution, even at low processing temperatures of
about 110 130~C - thus far below the processing
range of 180 _ 230C considered as optimal in the
I
state of the art - a sufficient decomposition of
the nucleation agent takes place with the formation
of numerous and very small bubbles.
The first phase, i.e., the formation of the
nuclei and thus of the bubbles, is improved decisively
by the drumming-on of the nucleation agent, and con-
siderable costs are saved because of the low process
sing temperature.
The second important aspect concerning the
quality of the end product is the increase in the
size of the gas bubbles. In the initial phase, the
increase in size of the gas bubbles still takes place
by means of the occurring gas of the nucleation
agent. However, the further increase in size, espy-
Shelley during the re-expanding processes, takes place
by means of the propellant released in the plastic
material.
Decisive for the growth of the bubbles is
the pressure within the bubbles and the pressure of
the released agent in the extrude and the pressure
in the extrude itself. The relationship between
these pressures can be described by means of the
following reaction equations
UP Pi Pi (1)
UP = 2 OR I
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In these equations,
Pi is the existing pressure on the inside of the
bubble,
Pi is the partial pressure of the released
propellant gas in the melted plastic material,
UP is the difference in pressure (ire. the
"driving pharisee,
is the surface tension of the burble,
R is the radius of the bubble.
While the bubble grows, the pressure in the
bubble decreases, while the radius increases keynote-
nuzzle. At the beginning" it grows very fast until
a large part of the excessive released gas was used
up in the adjacent area to expand the polymer.
The growth of the bubbles is influenced by
the diffusion rate of the released propellant in the
melted plastic material in the direction of the bubble
as well as by the degree of supersaturation and the
viscosity of the melted mass. In the state of equip
librium, the balance of forces exists that is desert-
bed by equations (1) and (2).
In the case of a starting material that is
only mixed (apple with sugar crystals), uneven growth
rates of the bubbles exist because of the irregular
spatial distribution. Zones with a lot of plastic
material and muck released propellant alternated with
other zones which contained relatively large amounts
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of nucleation agent and where gas bubbles were
created that are relatively large and grew rapidly
end in regard to the pressure of the propellant have
no vacuum in the gas bubbles. They cause an inquiry-
sod diffusion of the propellant into the bubble no-
suiting in an increased rate of growth of these
already large bubbles. The mixing or the "fraction-
lion" taking place in the extrude my means of the
screw, to e. a milling-through of the plasticized mass
with an occasional cell collapse of the foam struck
lure is not sufficient for controlling an uneven
foam structure in regard to arrangement and size.
Further features and advantages of the
invention will become more readily apparent from the
following description of preferred embodiments, with
reference to the appended drawings, in which Figure 1
is a diagrammatic side view of a device for producing
packing material particles.
The device required to carry out the process
is shown in diagram form in Figure 1 and has a drum
5 provided with openings 6 and 7 through which the
plastic material and the finely ground nucleation
agent are added. From the drum 5, the drummed-on
plastic granules, by means of a conveying device 8
and a conveying pipe 9, are fed into an extrusion
device 10.
The extrusion device 10 consists of a drip
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vying motor 11, a gear 12, a material pull-in zone 13
and an extrude 14. A cutting device 16 it arranged
directly in front of an opening 15 of the die of the
extrude 14.
The drummed-on granules, via a feeding
funnel 17, reach the extrude 14 through the material
entrance zone 13.
The plastic material is plasticized over the
longitudinal course of the extrude: the nucleation
agent decomposes while forming gas, and the plastic
material comes out of the opening 15 in the form of a
mass of melted foam. Because of the difference in
speed existing over the mass cross section, the pies-
tic foam squeezes out of the inside area of the open
nine 15 of the die with a bent surface.
The extruded plastic is cut off by means of
the cutting device 16 directly at the opening 15.
The cut-off plastic particles expand in the
free fall in a first expanded condition, already taking
their shape of having a surface that is concave on
the inside an convex on the outside A collecting
container 19 collects the solidified and cooled
plastic particles 18.
The initially expanded foamed particles by
means of a blower 20 are transported through a pipe
I into a storage container 22.
After a certain storage period, the initially
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expanded plastic particles 18 are conveyed from the
storage container 22 into a re-expansion unit 23
where the plastic particles are re-expanded.
After leaving the re-expansion unit 23, the
re-expanded plastic particles 18 are conveyed to a
storage container 24. This storage container 24
preferably consists of a sieve material or any other
open mesh material permitting a free circulation of
air and thus an easier drying of the newly expanded
plastic particles 18.
The plastic packing particles that are
expanded to their final condition have an even and
uniform cell structure. The particles have such
stability that the pressure affecting the packing
material during transport does not result in a
breaking of the packing material particles. In
addition, the individual particles are closed off in
themselves by a relatively smooth surface so that not
much "crumb formation" takes place when the individual
packing material particles rub against one another.
When carrying out this process, the nuclear
lion agent is first ground to a grain size of 40 p.
The nucleation agent is based on the multi-component
nucleation agent that is known under the trademark of
"Hydrocerol". The acid component consists either of
water-repellent anhydrocitric acid or of citric acid
MindWrite. The acid component is treated or coated
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in such a way that it is water-repellent and can thus
be mixed with the carbonate component (sodium hydrogen
carbonate) and can be stored for long periods without
drawing humidity from the environment.
The nucleation agent OF 0556 is a fine,
odorless, white, free-flowing, non-dusty powder.
According to FDA requirements, all components of OF
0556 are GRAS (Generally Recognized As Safe). CF0556
can be stored well without clotting or sticking-to-
getter because of moisture absorption.
The plastic granules consisting of expandable polystyrene (ENS), i.e., polystyrene with incorporated
propellant (for example, pontoon) are fed into the
drum 5.
For each 70 kg ENS granules, 100 g CF0~56
nucleation agent are drummed on. In the case of this
process which must not be confused with a pure mixing,
an evenly distributed layer of the fine nucleation
agent places itself on the plastic granules. The
addition of so-called bonding agents in the form of
talc or similar substances is not necessary, because
the very fine coating adheres well to the granules.
The proportion of nucleation agent is 0.14 percent by
weight.
The drummed-on granules, by means of the
conveying advice 8, via conveying pipe 9, are fed
into the feeding funnel 17. Coloring pigments or
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other desirable additives may be added to the
feeding funnel. The mixture is pulled into the
material pull in zone 13 of the extrude 14 by means
of the extrusion screw. Over the course of the ox-
truer 14, the material, because of an increase of
the core diameter of the extrude screw, is plastic
cited by the friction and by heat supplied cores-
pondingly from the outside.
The drummed-on granules, on their surface,
lo have the evenly distributed about 40 large solid
matter particles of the nucleation agent. In the
transition phase from the solid to the plasticized
condition, the granules are squeezed against one
another, without significantly destroying the close
order of the particles arranged on the surface. When
the plastic particles are squeezed and sheared, the
overall mixing is still somewhat improved. This can
be remonstrated by imagining that a softly chewed
piece of chewing gum is made into a ball and this ball
is then pulled apart between two fingers. The strut-
eking will take place so evenly that the regularity
of particles on-the surface will be maintained -
The processing temperature of the plastic material is approximately between 110 - 130C. Even
at these low temperatures, the nucleation agent OF
0~56 develops carbon dioxide Because of the fine
distribution, considering the overall volume, an
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evenly distributed formation of bumbles that increases
at a uniform speed is achieved The size of the
hubbies also depends on the dimensions of the extrude
and the speed of the extrude screw. Immediately
after the extruded plastic comes out and is cut elf,
a rapid expansion of the plastic particles will take
place because the compressed gasses in the bubbles can
expand to almost normal pressure.
At the same time, the plastic particles are
colored and are maintained in a first expanded shape,
In this first expanded shape, the initially expanded
packing material particles have a bulk density of
about 22 kgJm3. They have an extremely fine-celled
structure making the surface of the packing material
particles very smooth. the packing material part-
ales, after a rest, will then be re-expanded.
During this rest period, the propellant
existing in the plastic material diffuses from the
plastic material into the bubbles. The inside
pressure within the bubbles, because of the rapid
expansion after leaving the extrusion screw, is much
less than the partial pressure of the released pro-
pollinate in the plastic material, in which case this
difference in pressure is the driving force for the
diffusion and also determines the direction.
The further expansion processes are carried
out in such a way that the packing particles are
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exposed to a vapor atmosphere, pausing the propellant
that had diffused into the bubbles to expand and
expanding the plastic particle. The storage periods
between the individual expanding processes become
continuously longer, because less and less propellant
gas is released in the plastic material and less can
therefore diffuse into the bubbles. After several
expanding processes, the packing particles have a
bulk density of only about 4.5 kg/m3.
Despite the numerous expanding processes,
the packing material particles have a relatively
smooth surface and, because of the fine-celled struck
lure have sufficient stability. Especially at the
edge zones, the packing particles are smooth and
round so that there is no danger of a crumb formation
between the parts that are stacked into one another
under stress.
By means of the drumming-on of the 40
nucleation particles on the plastic granules, the basis
is created for the quality of the end product.
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