Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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1 This invention concerns a moulding material, moulding
processes and articles obtained by the processes.
Numerous injection moulding processes are already
known.In one such process a fluid plastics material is
injected into a mould and allowed to cool, the mould being
"topped up" with further quantities of the plastics material
as the moulding cools and contracts in the mould. Articles
produced by this process are expensive in v;ew of the high
cost of the raw plastics material. In order to reduce the
cost of articles produced by this process, a relatively
cheap inert filler is commonly mixed with the plastics
material prior to moulding. Conventional fillers are in
the form of solid particles and have a high specific gravity,
usually in the range of 2.0 to 4.5. Accordingly, articles
made by this modified process are relatively heavy. Attempts
have been made to reduce the weight of articles produced
by this process by using fillers in the form of hollow
particles, which thus have a lower density. However, the
high moulding pressures required in the process result in
breakdown of the filler particles which can become abrasive
when broken, both in the moulding machine and in the mould
itself, and the benefits derived from the low density
of the filler are reduced.
In a further process, a plastics material is
moulded with the addition of a blowing agent to create
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1 what is known as a "structural foam system". The blowing
agent may be a chemical agent mixed with the plastics material
before injection and which creates gas within the plastics
material at a predetermined temperature to form a cellular
structure within the plastics material. Alternatively, the same
effect may be obtained by blowing an inert gas such as nitrogen
into the plastics material during the moulding process. The
resulting moulded article has a cellular structure and is light
in weight.
An object of the present invention is to provide a
relatively inexpensive moulding material, and an extrusion or
injection process which can result in the extruded or moulded
article having an intermediate weight and firm surface texture
without sink, a uniform foam structure, increased rigidity,
and a reduction of strain in the finished article.
With this object in view, the present invention pro-
vides a moulding material comprising a thermoplastic or
thermosetting polymer mixed with an inorganic filler material
in the form of hollow particles.
With the same object in view, the present invention
also provides an extrusion or injection moulding process
comprising mixing a thermoplastic or thermosetting polymer with
an inorganic filler material in the form of hollow particles,
and extruding or moulding the resultant mixture with the
addition of a blowing agent to form a structural foam system.
The particles of filler material may be in the form
of hollow spheres, preferably of aluminium silicate, and
preferably mixed in a ratio of 5% to 70% by weight of the total
mix.
The invention further provides a structural foam
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1 extrusion or injection moulding material comprising a thermo-
plastic or thermosetting polymer mixed with an inorganic filler
material in the form of hollow particles and with a blowing
agent, the inorganic filler material having a specific gravity
in the range of 0.5 to 1.5 and having a chémical composition
comprising silica as sio2 between 46~ and 68% by weiyht, and
alumina as A1203 between 20% and 38% by weight, the remainder
comprising alkalies in the form Na20 and K20 and iron oxide
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The particles of filler material are preferably of
substantially the same size as particles of the polymer and may
have a chemical composition of silica as SiO2 between 46% and
68% by weight, and alumina as A1203 between 20% and 38% by
weight, the remainder being made up of alkalies in the form
Na20 and K20 and iron oxide as Fe203. Such hollow particles
are commercially available from Fillite (~uncorn) Limited under
the trade mark FILLITE*.
However! the particles of filler materlal may be
considerably smaller than the polymer particles, in which case
a wetting agent is added during the mixing and before the
moulding operation to ensure a uniform mixture and avoid se-
paration of the filler and polymer particles.
Mixing may be performed immediately before the extrusion
or moulding operation and at the point of feed to the extrusion
or moulding machine by means of metering devices.
Preferably the filler material has a specific gravity
in the range of from 0.5 to 1.5.
The blowing agent may be a chemical agent or an inert
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gas such as nitrogen.
*Trade Mark 4
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1 At the present -time, the cost per ton of aluminum
silicate filler material in the form of hollow spheres is
about 2 to 3 times as much as that of a conventional filler
material. However, conventional filler material is between
4 and 5 times as dense as the aluminum silicate filler, and
so the use of the aluminum silicate filler is cheaper on a
volumetric basis. In view of this, the process of the present
invention offers improved economics of material costs as
compared with known extrusion or injection moulding processes.
There is a further significant cost saving, as
compared with known injection moulding processes, as a result
of a reduction in moulding production time cycles resulting
from faster setting up in the mould of the mouldings enabling
them to be ejected from the mould after a shorter period of
time. This is a direct result of the inclusion of the filler.
The process of the invention also makes it easier
to produ~e mouldings on both struc ~ 1 foam injection
moulding machines and more conventional moulding machines.
Mouldi~gs hitherto not considered suitable as structural
foam mouldings are now suitable for and benefit from
this process because of increased rigidity, freedom from
sinkage and faster time cycles.
The process of injection moulding in accordance
with the invention facilitates the production of
mouldings without the use of injection hold-on or
1 back-up pressure in 'he material after injection into the
mould in order to fill the mould during cooling and
contraction of the material. It is normally necessary to
force more material into the mould in order to compensate
for such contraction, but resulting movement of the material
in a semi-molten state introduces strain into the moulding
which can result in distortion of the moulding after
ejection from the mould. Inclusion of the blowing agent and
filler material ensures filling of the mould without further
material injection and therefore the introduction of strain
into the material is substantially reduced. It is thus
only necessary to introduce a metered volume of material
into the mould. The productior of mouldings of a high
quality is thus made more consistent.
A further use of the process of the invention
involves the addition of the filler material to a two-
component mixture of a thermosetting foam such as poly-
urethane. The foam is created by chemical reaction, and
combination of the two components such as polyol and
isocyanate will produce the foam with the filler dispersed
therein. The resulting foam has similar advantages to those
obtained for the plastics material foam.
It will be appreciated that the process may
include other additives, for example reinforcements
such as glass fibre which are mixed with the moulding
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1 material at the same time as the filler. The combination
of the filler and glass fibre produces a combination of
improved physical properties which include increased tensile
strength, increased rigidity and heat distortion whilst still
retaining the advantages of a more uniform foam structure
and good surface finish which result from the use of the
filler.
A further improvement in the adhesion of the
plastic between the filler and the thermoplastic can be
obtained, with the use of a coupling agent such as silane.
This will result in further improvement in physical properties
such as tensile and impact strengths and resistance to
creep under load.
A further use of the process is in the extrusion
of these material mixtures into profiled shapes. Advantages
derived are similar to those of the injection moulded parts
and include cost savings in raw material resulting from
reduced weight of the extrusion and reduced material costs
and increased extrudate output, increased rigidity, freedom
from sinkages and dimensional stability. The extrusion of
sections of 5 mm or more in thickness is made more feasible.
The cost of extrusion as a result becomes more competitive
with timber.
The moulded material obtained by the process
of the invention has the following advantages as compared
with conventional injection moulding processes:-
1 (a) Raw material costs are r~duced by the inclusion of thefiller material at a very much lower cost than that of the
polymer;
(b) Reduced moulding time as a result of reduced coolin`g time
in the mould before the moulding reaches a rlgidity sufficient
for the moulding to be ejected from the mould, resulting in
lower costs of production;
lc) A weight and surfàce texture similar to that of wood can be
obtained by appropriate proportioning of the polymer and the
filler material;
(d) The surface texture obtained by inclusion of the filler
material facilitates painting or similar post-moulding
operations such as printing and metallising. It has been found
that printing can be undertaken almost immediately after moulding
whereas conventional mouldings have to be stored for several
days before printing. The.only surface preparation normally
needed after this process is the application of a primer (in
the case of polypropylenel. Surface imperfections such as "tear"
marks normally evident in polypropylene foam mouldings are
eliminated;
(e) The inclusion of the filler material reduces the thermal
conductivity of the moulding;
(f) The rigidity, flexural strength, dimensional stability
and temperature distortion point of the plastics are increased
as a result of inclusion of the filler;
(g] The mouldings are free from sinkage so that mouldings of
varying thickness can be easily made by this process;
(h) The abrasion resistance of mouldings is improved;
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1 (i) The foam structure is much more uniform throughout the
moulding as a result of the filler acting as a nucleating
agent duriny flow of material into the mould. The occurrence
of large voids in the foam is reduced; and
(j) The residual strain in the moulding is reduced, so forming
a more dimensionally stable moulding conforming more accurately
to the shape of the mou]d.
The invention will be described further, by way of
example, with reference to the following typical mixes wherein
the material proportions are all by weight.
EXAMPLE 1:
Polypropylene 67.0
FILLITE* filler 32.5~
Chemical blowing agent 0.5%
EXAMPLE 2:
Polystyxene 67.0~
FILLITE* filler 32.5%
Chemical blowing agent 0.5%
EXAMPLE 3:
Polyacetol 75.0%
FILLITE* filler 24.5%
Chemical blowing agent 0.5
EXAMPLE 4:
Nylon 80.0~
FILLITE* filler 19.8%
Chemical blowing agent 0.2%
*Trade Mark 9
1 ExAMpLE 5:
Polypropylene 80.0%
FILLITE* filler 20.0~
In this example an inert gas such as nitrogen is used
as a blowing agent.
EXAMPLE 6:
Polypropylene 80.0~
FILLITE* filler 19.5%
Chemical blowing agent 0.5%
This mixture is particularly suitable for extrusion
into Eorm sheet.
EXAMPLE 7:
Polypropylene 94.5%
FILLITE* filler 5.0
Chemical blowing agent 0.5
EXAMPLE 8:
Polystyrene 29.5%
FILLITE* filler 70.0%
Chemical blowing agent 0.5%
It will be appreciated that the chemical blowing agents
may be replaced by an inert gas blowing agent such as nitrogen,
resultant with minor modification of the proportions of the
plastics and filler materials. However, where a chemical blowing
agent is used, that marketed by Fisons Limited under the registered
trade mark GENITRON* has been found to be particularly suitable.
Although the disclosure describes and illustrates a
preferred embodiment of the invention, it is to be understood
the invention is not restricted to this particular embodiment.
*Trade Mark
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