Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1~35~59S
This invention relates to laces and granules of
thermoplastic polymers and their production. In par-ticular
it relates to -the production of laces and granules reinforced
w~th long fibre
Many thermoplastic compositions are compounded
by mixing various additives, e.g stabilisers, fillers and
pigments, with a thermoplastic polymer and extruding the
mixture by means of a screw extruder. The thermoplastic is
heated to above its softening point as it passes through the
screw and while in the screw the melt is mixed. After mi*ing
the melt passes through a die so as to produce what is usually
known as a "lace". In most cases the lace is chopped into
granules, usually after it has been cooled, e.g. by passing
the lace through a cold water bath.
Laces may also be produced by extrusion through a
die without the use of a screw feed For example, United
Kingdom patent No. 1,334,702 published on October 24, 1973
describes a process for making fibre reinforced thermoplastic
material. In this process a roving of the fibres, preferably
glass fibre, is passed through a bed of powdered thermoplastic
material and while the roving is in the bed it is separated
into bundles each of which consists of one or more filaments.
The roving is allowed to regain its
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original state and powder is trapped between the
fibres so that the result is a roving which is im-
preqnated with the powder. The impregnated roving
is heated so as to melt the thermoplastic powder and
while the powder is molten the roving is drawn
through a die to produce a consolidated lace.
It is sometimes desirable to make small
changes in the composition of a lace, e.g. a change
of pigment. In the past this has normally required
thorough cleaning of the whole of the equipment used
to produce the lace and it is an object of this in-
vention to facilitate the making of small changes
in the composition of the lace.
A thermoplastic lace according to the
invention has a thermoplastic coating the composition
of which differs from that of the lace. For example
the bulk is fibre reinforced, preferably glass fibre
reinforced, and the coating is not fibre reinforced.
A thermoplastics granule according to the
invention has at least a partial thermoplastics
coating the composition of which differs from that
of the bulk of the granule. For example the bulk
of the granule but not the coating contains fibre
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reinforcement, preferably glass fibre reinforcement,
the fibres of which are parallel to one another and
which fibres extend the whole length of the granule.
Many granules have flat ends (where they
were severed from a lace) and, according to the in-
vention such granules most suitably have the flat
ends uncoated and the remainder of its surface coated.
Granules are often cylindrical in shape but they can
be any shape which can be achieved by extrusion
through a die followed by cutting.
According to the method of the invention `
the composition of a thermoplastics lace is modified
by exposing the lace while its surface is tacky
to a powdered thermoplastics composition whereby the
powder adheres to the surface of the lace to form a
granular coating.
In a preferred form of the invention the
granular coating is heated so that the coating melts
and becomes more uniform. Most suitably the lace
is passed through a second die in order to make the
molten coating more uniform.
The coating is conveniently applied to the
lace by passing the lace above the surface of a bath
of the powdered thermoplastics composition while a
current of air is directed at the lace from below the
surface of the bath. During its passage through the
bed of powdered material the air picks up powder which
impinges on the surface of the lace.
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Fibre reinforced laces in particular are
highly resistant to bending and this technique is
particularly desirable in that it allows the powder
to be applied to the surface of the lace without
bending the lace.
The surface of the lace can be made tacky
by applying a solvent or adhesive but it is preferred
to make the surface tacky by heating at least the ;~
surface to or maintaining at least the surface at a
temperature at which the surface is tacky.
In most cases laces are hot during the
manufacturing process and they are tacky if the pow-
der is applied before the lace has time to cool;
laces which contain long fibre have sufficient ten-
sile stren~th to pass through a die. ;;
If a non-reinforced lace is to pass through
a die it is necessary to cool the lace because the ;
hot lace has little or no tensile strength. Since
the lace is cooled from the surface inwards it will
usually be necessary to reheat only the surface in
order to make it sufficiently tacky for the powder
to stick.
The method described above is particularly
suitable for making small changes in the composition
of a lace. For example a colour masterbatch contain-
ing a very high proportion of pigment can be coated
onto a lace. When the granules produced by cutting
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the coated lace are remelted to produce the final
product the pigmented layer becomes uniformly dis-
persed in the whole composition so that a uniformly
coloured article is produced. Thus the coated lace
is equivalent to a uniformly coloured lace. How-
ever producing a uniformly coloured lace would
necessitate passing the pigment through the whole
of the lace forming process and when it is desired
to change the colour it is necessary to clean the
whole equipment very thoroughly. In the meth`od ac-
cording to the invention it is necessary to change
only the coating e~uipment which represents a very
small proportion of the total. Thus the invention
facilitates the production of a series of different
coloured compounds.
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It will be appreciated that any additives, e.g.
stabilisers, fillers with small particle size such as
ballotini glass or talc and foaming agents, can be applied
in the same manner as the colour masterbatch In some cases
it is undesirable or impossible to pass an additive through
the main lace forming process, e.g. a foaming agent mi~ht
decompose or a liquid additive might have an undesirable
effect on the powder bath of the process described in said
United Kingdom patent No. 1,334,702 The process according
to the invention enables said additives to be incorporated
since the conditions during the coating stage can be adjusted
to suit the additive.
It will also be appreciated that the polymer used
- in the coating need not be the same as that in the lace.
When laces reinforced with long fibres are chopped
the cutter sometimes fails to sever fibres at or near
the surface of the lace. When this happens the granules
separate by pulling out the unsevered fibre to leave a
"whisker" which protrudes from the end of the granule.
2~ It has been found that the presence of an unfilled sheath
reduces the number of granules which have whiskers.
Thus a method of making granules of fibre, preferably
glass fibre, thermoplastic polymer preferably comprises:
(a) Impregnating a fibrous, preferably glass,
roving with a powdered thermoplastic;
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(b) E-leating the impregnated roving from (a)
to a temperature at which the thermo-
plastic melts;
(c) While the thermoplastic is molten
drawing the roving through a die to
produce a consolidated lace;
(d) Passing the lace from (c), while its :
temperature is still high enough for
its surface to be tacky above the sur-
face of a bath of a powdered thermo-
plastics composition while a current
of air is directed at the lace from
below the surface of the bath whereby
powder from the bath is caused to adhere
to the surface of the lace;
(e) Heating the granular coating applied
in (d) so that it melts;
(f) Passing the lace with the molten coat-
ing through a second die so that the
coa~ing becomes more uniform;
(g) Cooling the lace from (f) and cutting
it into granules.
The polymer of the sheath is most suitably the
same as the polymer used to form the lace. On the other
hand there is the possibility of operating a dual pur-
pose process in which coatings are used as described
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above to modify the composition of -the lace and the coating
also serves to reduce the incidence oE whiskers.
A coating o~ several layers may be applied by
repeated applications of the method described above.
A lace produced as described above is usually
chopped to give granules.
The invention includes laces and granules which
have been prepared as described above. -~
Two methods of carrying out theprocess according
to the invention will now be described by way of example
with reference to the accompanying diagrammatic drawings
in which: ~
Figure 1 illustrates the method of applying ~ -
coatings to a glass fibre reinforced lace, and
Figure 2 illustrates a modification of the process
of Figure 1 which is applicable to lacas which are not
reinforced.
Figure 3 illustrates two granules according to
the invention an~ two other granules.
Figure 1 illustrates the application of a coating
to a fibre reinforced lace 10 which has been produced by
the method described in said United Kingdom patent ~o.
1,334,702, The method of producing the lace is not
part of this invention and it is not illustrated in
Figure 1.
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1039595
T~e l~cc 10 ~as~s t~r~u~h ~ ~c '1 which
is the last step in the process of the preparation of
the lace. Before it has time to cool and while the
surface is still tacky the lace 10 passes over a tray
12 which contains a fluidised bed of powdered polymer
13. A nozzle 14 is situated in the bed and a blast
of air from the nozzle produces a curtain 15 which
contains the powdered polymer. As the lace passes
through this curtain the particles adhere to its
tacky surface so that the surface becomes coated with
particles. The particles which do not contact the ~
lace fall back ~nto the tray 12 so that they are re- `
circulated. The tray may be shielded to prevent
scattering o~ the polymer but the shield is not shown
in any drawings.
~ ter passing over the tray 12 the lace
enters a hot tube 16. The temperature of the tube
is such that the coating (but not the body of the
lace) melts and the molten coating passes ihrough a
second die 17 so that a uniform sheath is produced.
After leaving the second die 17 the lace is cooled
and chopped in conventional ma~nner to produce granules.
Figure 2 shows a modification of the process
for use with laces which are not reinforced with fibre.
The differences are that the lace 10 is produced by
a conventional screw extruder process and on leaving
the die 11 of the extruder the lace passes through a
water bath 18 which cools it so that is has sufficient
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tensile strength to withstand t:he rest of the process.
On leaving the water bath the lace 10 passes throu~h
a small heater 19 which dries and hea-ts the surface
until it is tacky. On leaving the heater 19 the lace
is coated with powder as described with reference to
Figure 1. When the lace passes through the hot tube
16 it is necessary to heat it sufficiently to melt the
adherent powder but care must be taken to avoid heat-
ing it so much that it loses its tensile strength.
The application of three coatings to glass
fibre reinforced laces as described in Figure 1 will ,
now be described. In each case the original lace was
produced by passing glass roving at 5 m per minute
through a bed of pot~dered polypropylene. During its
passage through the bed the roving was spread out and
allowed to reform as an impregnated roving. The im- `
pregnated roving was passed through a hot tube to melt
the polypropylene powder and then through a die to
consolidate the roving into a lace. On leaving the
die the surface temperature of the lace was approxi-
mately 230C.
The lace was chopped (using a conventional
chopper) into granules 1 cm long some of which had
elongated whiskers protruding from one end. The pro- ~
portion of such granules varied between about 25% and ~ -
about 35%.
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EXA~I PLE
A glass reinforced polypropylene lace, con-
taining 23.3% by weight of continuous glass filaments
running parallel to the lace axis and having a surface
temperature of approximately 230C, was pulled at a
rate of 5 m per minute through an atmosphere of air
and polypropylene po~der. The powder adhered to the -
hot lace surface and the granular coating so formed was
melted and consolidated by its passage through a 12 cm
length of heated tube maintained at an average tempera-
ture of 250C and fitted with a die. The resultant lace
was chopped into 1 cm long granules and it was found
that the glass fibre concentration of the coated lace
had been reduced to 21.2% by weight. The number of
granules having elongated glass fibres protruding from
their ends was only 3%, resulting in a much improved
flow and making feeding of the granules into injection
moulding machines easier by eliminating bridging.
EXA~lPLE 2 -
Production of a Pigmented Lace
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A glass fibre reinforced lace as described in
Example 1 was pulled at a rate of 5 m per minute through
an atmosphere of air and polyethylene powder, the poly-
ethylene powder containing 5% by weight of carbon black `
pigment. The granular covering of powder and pigment
which adhered to the lace surface was melted and consol-
idated by its passage through a 12 cm length of heated
tube, maintained at an average temperature of 250~C and
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fitted with a die. The resultin~ lace had a glass
fibre concentration oE 21.2% by weight and on chop-
ping it was found that the number of chips having
glass fibres protruding from their ends had been re-
duced to 2%. When the material was injection moulded
the specimen obtained had an overall pigment concen-tra-
tion of 0.6% by weight based on the total weight of
polymer, and showed excellent colour dispersion.
EXAMPLE 3
Incor oration of Extra Additives into the Surf_ce Coatin~
P ..
A glass fibre reinforced lace as described in
Example 1, but having a glass fibre concentration of
27.~% by weight, was pulled at a rate of 5 m per minute
through an atmosphere of air and polypropylene powder,
the polypropylene powder containing 5% by weight of a
liquid heat stabilising agent. The granular covering
adhering to the lace surface was melted and consolidated
by its passage through a 12 cm length of heated tube, ~`
maintained at an average temperature of 250C and fitted
with a die. The resulting lace had a glass fibre con-
centration of 25.0% by weight and an overall heat stabi- -
liser concentration of 0.5% by weight based on the ``~
total polymer weight. ~hen the lace was chopped the
number of granules having long glass fibres protruding
from their ends had been reduced to 2%. Subsequent in-
jection moulding of these granules yielded a specimen
which showed a significantly increased resistance to
high temperature deformation. ;
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EXAI~IPLE ~ 1039595
Production of lace incorporating a foaming a~ent
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A glass fibre reinforced lace as described in
Example 1 was pulled at the ra~e of 5 m per minute throu~h
an atmosphere of air and low density polyethylene powde~,
the polyethylene powder containing 4% by weight of a
blowing agent (azo-dicarbonamide). The granular cover-
ing of powder and blo~ting agent which adhered to the
lace surface was consolidated by its passage through a
12 cm length of heated tube, maintained at an average
temperature of 160C and fitted with a die. The result-
ing lace had a glass fibre concentration of 20.3% by
weight and was chopped to form a granule suitable for
moulding. About 3% of the granules had long fibres
protruding from the cut ends.
These granules were fed to a 350 tons Bone-
Craven injection moulding machine, fitted with a tray
shaped mould, the cavity of which was 35 cm x 25 cm x
5 cm deep with a wall thickness of 6 mm. The shot size -
was adjusted so that a moulding of a final density of
0.76 g/cm3 was achieved, by virtue of the foaming
action of the decomposing blowing agent.
An important effect of the coating will now
be described with reference to Figure 3.
A sa-tisfactory granule without a coating -
(i.e. a granule not according to the invention) is
shown in Figure 3_. The granule has a wall 20_ (which
in most cases is cylindrical but can be any shape which
can be applied by pulling through a die) and a flat
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face 22_ which was formed by the chopper. The granule
contains fibres which are paral:Lel to one another and
which extend the whole length of the granule. There
may be (at the most) a small tuft 23_ of fibre which
stands proud of the surface 22_ Figure 3b shows an
unsatisfactory granule. Instead of, at the most, a
small tuft there is a whisker 23b of fibre which pro-
trudes from the flat face 22b; the whisker is about as
long as the rest of the granule.
A satisfactory granule according to the
invention is shown in Figure 3c. The granule has a
coating 24c covering the surface 20c. As can be seen
from the drawing the composition of the coating differs
from the composition of the bulk of the granule. The
bulk contains the fibres 21c whereas the coating does ; '
not. (Example l illustrates the case where this is
the only difference. Example 2, 3 and 4 show that ;~ -
there can also be other differences.) The coated gran-
ules may have, at the most, a small tuft 23c of fibre `
standing proud of the flat face 22c; a few granules may
have the elongated whiskers as shown at 23d.
It has been found that the elongated whiskers
(but not the short tufts) have an adverse effect upon
the bulk properties, e.g. feeding from a hopper may be
difficult, and that compositions which contain at least ~ `
90% by weight, preferably 95% by weight, of granules
as shown in Figure 3c give satisfactory bulk properties.
-- (Note: For the purposes of comparison and Claim l9,
granules without any tuft are deemed to be as shown in
103~595
Figure 3c).
Examples 1 to ~ show the production of
coated granules with 2% to 3% having whiskers; in
the comparative example there were 25% to 35% of
such granules. Clearly the application of the
coating substantially improves the bulk properties.
It is emphasised that where tufts or whiskers
occur they protrude through the cut face 22 and no
coating is applied to this face. It is surprising
that the application of a coating to the surface 20
has a beneficial effect upon the whiskers which pro-
trude through an uncoated surface.
Glass fibres are the mos-t commonly used
but the reduction of whiskering according to the
invention can be applied to other t~pes of fibre,
e.g. carbon fibre.
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