Note: Descriptions are shown in the official language in which they were submitted.
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WO 00/44797 - 1 - PCT/EP00/00528
Description
Tetrafluoroethylene/Hexafluoropropylene Copolymers with Higher Drawability
Field of the Invention
The invention relates to melt-processable tetrafluoroethylene
(TFE)/hexafluoropropylene
(HFP) copolymer melt pellets having improved processability for wire and cable
applications and to a process for using this polymer to coat wire and cable
conductors.
Back round
Melt-processable copolymers with TFE and HFP are best known under the name
FEP. As
perfluorinated thermoplastics, such copolymers have unique end-use properties
like
chemical resistance, weathering resistance, low flammability, thermal
stability and
outstanding electrical properties. Like other thermoplastics, FEP is easily
molded to give
coated wires, tubes, pipes, foils and films.
Because it has excellent thermal stability and is practically non-flammable,
FEP is
frequently used in the design of multiple-occupancy rooms and meeting halls,
to meet
stringent fire protection requirements. FEP is also the natural choice in data
transmission
cables due to its excellent dielectric properties (EP-A-423 995).
High processing speeds are desired when wires and cables are extrusion coated.
However,
melt fracture limits these high extrusion rates in the case of many
thermoplastics. Melt-
fracture results in surface roughness and/or uneven wall thickness. To
increase the
extrusion speed it is therefore assumed that the molecular weight distribution
of the
copolymer used should be very broad as disclosed, for example, for the FEPs in
US-A-4,552,925.
For substantial broadening of the molecular weight distribution, use is mostly
made of a
mixture of at least two FEPs with markedly differing molecular weights. The
molecular
weights are usually characterized by the melt viscosity or the melt flow index
(MFI value).
The mixtures desired are often produced by polymerizing the components
separately and
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mixing them in the form of latices, beads or unconsolidated products before
melt
pelletizing. Thus the manufacture of these mixtures is a cumbersome and costly
process.
Other FEP mixtures are disclosed in DE 26 13 642 and DE 26 13 795.
These mixtures are claimed to be advantageous therein for suppressing foaming
during the
FEP stabilization. This process is carned out by treating the resin at high
temperatures (up
to 400° C), preferably with water vapor. This process removes the
thermally unstable end
groups, mostly COOH and CONHZ groups. These end groups may easily be detected
by
IR spectroscopy.
These mixtures have a very broad molecular weight distribution, and this is
generally
understood by the skilled worker to give improved extrudability.
Removal of thermally unstable end groups is required for the processing of
FEP, in
particular for wire coatings. The decomposition reaction of the unstable end
groups,
described in Modern Fluoropolymers, editor John Scheirs, Wiley & Sons, 1997,
page 228
leads to bubbles and holes in the final products. Melt pelletizing of
unstabilized polymer
resins results in corrosion of the equipment used and in metal contamination
of the melt
pellets produced. However, the stabilization processes of DE 26 13 642 and DE
26 13 795
are very difficult to carry out, since they give rise to problems of corrosion
of the
equipment used, due to the use of water vapor.
Metal contaminants are difficult to control and may result in degradation and
decomposition of the copolymer at high processing temperatures. This
decomposition
generally leads to discoloration and degradation, and to a build up of die
deposits. Die
deposits are accumulations of molecular fractions of the polymer on the
surface of the die
orifice, and adversely affect the coating process. The phenomenon known as
cone fracture
can also occur. During the process of coating a wire, the molten polymer is
extruded as a
tube or sheath and drawn by vacuum onto the wire. Cone fracture is
discontinuity or
fracture that occurs during this process. Every time this type of cone
fracture occurs, the
coating process has to be re-initiated and there is a waiting time for the
system to reach
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equilibrium again. Thus long operating times are difficult to achieve.
Productivity is also
reduced.
Furthermore, extrusion temperatures have to be kept as low as possible to
inhibit
decomposition reactions and the resultant evolution of toxic gases, the rate
of which
substantially increases as the temperature rises. On the other hand, lower
extrusion
temperatures result in higher melt viscosities and thus earlier onset of melt
fracture.
Lowering the intrinsic melt viscosity by lowering the molecular weight results
in poorer
mechanical properties.
To render the material more thermally stable, therefore, it is necessary not
only to
eliminate the thermally unstable end groups but also to avoid metal
contamination and Mw
fractions which are relatively prone to shear degradation and/or to thermal
degradation.
Another way to eliminate unstable end groups is postfluorination, for example
as disclosed
in GB-A-1 210 794, US-A-4 743 658 and EP-B-457 255. This process generally
uses
elemental fluorine diluted with nitrogen at elevated temperatures up to the
melting range
of the polymer. When subjected to fluorination the polymer here may be in the
form of
melt pellets, agglomerates or unconsolidated material. Here, too, excessive
metal
contamination should be avoided.
EP-B-222 945 discloses the fluorination of hardened agglomerates, there called
granules.
The fluorination leads to perfluorinated end groups whereas the humid heat
treatment
described above cannot mechanistically result in a fully fluorinated polymer
resin. It is
believed that inserted double bonds are present here in the main chain of the
polymer and
lead to inherent thermal instability. These bonds may lead to the
discoloration seen on
long exposure to high temperatures.
Another degradation reaction of FEP is disclosed in US-A-4 626 587. The onset
of this
reaction is supposed to occur firstly by splitting of the HFP diads in the
middle of the
chain at temperatures above the melting point. These diads are formed in the
free-radical
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polymerization reaction by recombination of the corresponding polymer radicals
in a
termination step. The destruction of the diads under processing conditions
leads to halving
of the molecular weight of these polymer chains, adversely affecting
mechanical
properties of the polymer, and to formation of end groups which are more
unstable. As
US-A-4 626 587 teaches, these diads are destroyed by subjecting the material
to very high
shear rates at a temperature markedly above the melting point. This process is
also very
costly.
Another process for reducing the instability of the main chain is disclosed in
EP-A-789 038.
The process uses relatively large amounts of a chain transfer agent to
suppress termination
of polymer radicals.
Summary of the Invention
The present invention provides a material which can be used for wire and cable
coatings
1 S and which can be processed at higher speeds and at higher temperatures,
giving longer
running times for machinery. The invention furthermore provides a
manufacturing process
which is more economical and more controllable for consistency of quality.
Still further,
the invention provides a process for reducing die deposits and the frequency
of cone
fracture during the extrusion coating of wires or cables.
Detailed Description
The polymer according to the invention is a copolymer of TFE and HFP. It has
an HFP
content in the range from 5 to 22% by weight, preferably from 10 to 18% by
weight, a
TFE content of from 95 to 78% by weight, preferably from 90 to 82% by weight,
and
optionally contains up to 3 mol% of a fluorinated monomer copolymerizable with
HFP
and TFE. The optional comonomer is preferably a perfluoro alkyl vinyl ether as
is
disclosed in EP-A-789 038 and DE-C-27 10 501. The monomer content may be
measured
via IR spectroscopy as described in US-A-4 552 925. The polymers of the
invention
typically have a melting point of from 240 to 275°C, preferably 245 to
265°C.
The polymer of the invention is essentially free of thermally unstable end
groups, these
being removed via postfluorination of the agglomerates. "Essentially free of
end groups"
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means fewer than 80 end groups per million carbon atoms, preferably fewer than
40 end
groups and particularly preferably fewer than 30 end groups per million carbon
atoms. The
material is essentially of high purity with respect to metals, i.e. the total
amount of iron,
chromium and nickel is less than 200 parts per billion (ppb), preferably less
than 100 ppb.
The polymer of the invention used to coat wire and cable conductors has a very
narrow
molecular weight distribution, i.e. a ratio of Mw to Mn of less than 2 (Mw =
weight
average, Mn = number average molecular weight). This ratio may be as low as
1.5. This
is in contrast to FEP grades recommended for wire coating with high extrusion
rates, a
broad molecular weight distribution being recommended for those grades. The
broadness
of the molecular weight distribution is measured according by the method of
W. H. Tuminello in Polym. Eng. Sci 26, 1339 (1986). For high speed wire
extrusion the
MFI of the polymer is >_ 15. Lower MFIs are useful for other applications,
such as foamed
coaxial cable. This polymer is preferably essentially free of unstable end
groups. It is very
particularly preferably the polymer of the invention.
A melt pelletized copolymer according to the invention with an MFI value of 24
and 15%
of HFP may be produced as described below. This polymer can be extruded with a
wire
coating extruder at, for example, 390°C (735°F) at a rate of 454
m/min (1500 feet/min)
over a machinery running time of 6 hours without discoloration and without
producing any
substantial amount of die deposit and with less cone fracture than commercial
FEP grades.
The surprisingly good performance is not fully understood.
Despite narrow molecular weight distribution, high processing rates can be
achieved. As
has been discussed above, the art teaches that broad molecular weight
distribution is
needed to achieve such high processing rates. It has now been discovered that
narrow
molecular weight distribution is better, thus overcoming a well-established
prejudice.
Furthermore, no discoloration occurs during processing. This is an indication
of the
absence of any decomposition reaction. The MFI value of the extruded material
is
practically unchanged. The amount of IR-detectable end groups does not
increase. Both
findings indicate that there is no significant chain degradation. This
observation indicates
~
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that the material has no weak linkages in its main chain, for example HFP
diads (US-A-
4 626 587).
The non-occurrence of discoloration, the almost unchanged MFI value and the
almost
unchanged number of end groups are evidence of the absence of any significant
decomposition even at relatively high processing temperatures. It is believed
that this
results in reduced die deposits and the markedly reduced frequency of cone
fracture.
Hence, the copolymer according to the invention exhibits surprisingly high
thermal
stability even under shear. The polymer of the invention can therefore also be
used
advantageously in other applications.
The evidence of the absence of decomposition reactions is surprising and not
fully
understood. It is believed that metal contaminants, in particular heavy
metals, such as
iron, nickel or chromium, may induce a decomposition reaction. Indeed, neutron
activation
analysis showed that the amount of ions of iron, nickel and chromium in the
material used
was very low: below 50 ppb. Thus the copolymer according to the invention can
be
classified as of high purity.
The polymer of the invention may be produced by the process described below.
The polymerization may be carried out as free-radical aqueous emulsion
polymerization of
the prior art (see US-A-2 946 763). Ammonium or potassium peroxodisulfate may
be
used as initiators. As emulsifiers, use may be made of standard emulsifiers,
such as the
ammonium salt of perfluorooctanoic acid. Buffers, such as NH3, (NH4)ZC03 or
NaHC03,
may be added to the formulation. Typical chain transfer agents, such as H2,
lower alkanes,
methylene fluoride or methylene chloride are used. Chlorine- or bromine-
containing chain
transfer agents should be avoided. These components may cause marked corrosion
during
fluorination. The polymerization temperature can range from 40 to
120°C, preferably from
50 to 80°C; the polymerization pressure may range from 8 to 25 bar,
preferably from 10 to
20 bar. HFP forms as initial charge and is fed into the reactor according to
the rules of
copolymerization [see, for example, "Modern Fluoropolymers", editor John
Scheirs,
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Wiley & Sons, 1997, page 241). The preferred polymerization formulation is
free from
alkali metal salts.
Furthermore, it is preferable to carry out the copolymerisation without use of
any chain
transfer agent, in contrast to EP-A-789 038. Chain transfer agents
intrinsically broaden the
molecular weight distribution. The polymerization rate/time curve should have
the shape
as published in "Modern Fluoropolymers", editor Johns Scheirs, Wiley & Sons,
1997,
page 226. As stated in that publication, the Mw/Mn ratio can be easily
calculated from the
rate/time curves in the absence of any chain transfer agent via equation (6),
page 230 and
assuming that termination occurs solely via recombination. Recombination leads
to an
Mw/Mn ratio of 1.5 for small conversions. Termination primarily via chain
transfer leads
to an Mw/Mn ratio of 2.
The free-radical polymerization may also be carned out in a nonaqueous medium,
such as
1 S R 113, as disclosed in US-A-3 528 954. This nonaqueous process is not
preferred,
however, because it is believed that it also generates relatively small
amounts of high-
molecular-weight products due to the gel effect arising in this "suspension
polymerization". It is more likely that the gel effect gives rise to weak
bonds in the main
chain (HFP diads). A gel effect is most unlikely to occur in the aqueous
emulsion
polymerization because chain propagation and chain termination take place on
the surface
of the latex particles.
The dispersion obtained from the polymerization is mechanically coagulated
using a
homogenizer (see EP-B-591 888) and agglomerated using a water-immiscible
organic
liquid, such as gasoline, a technique well known in the art (see "Modern
Fluoropolymers",
editor John Scheirs, Wiley & Sons, 1997, page 227). The agglomerates are free-
flowing
beads with a diameter of from 0.5 to 2 mm. The free flowability is preferred
for technical
reliability in carrying out the subsequent work-up steps. The agglomerate is
dried by
flushing with nitrogen and then under moderate vacuum at temperatures up to
180°C.
Chemical coagulation of the agglomerate may also be employed. However, this is
generally done using acids. This is not preferred, since it results in very
high levels of
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metal contaminants at all subsequent work-up steps. The agglomerate may then
be
fluorinated at temperatures of from 60 to 150°C, preferably at from 100
to 140°C with a
mixture of fluorine in nitrogen. The mixture generally comprises 10% by weight
of
fluorine. Fluorination continues until at least 90 to 95% of the end groups of
the original
agglomerate have been eliminated. Higher fluorination temperatures can lead to
a change
in the MFI value which can be up to 30% and is difficult to control. This can
lead to
broadening of molecular weight distribution and adversely affect performance.
The result
is lack of reproducibility with an adverse effect on the quality and
consistency of wires
and cables coated with the polymer. Reaction times were not substantially
shortened by
higher temperatures, and higher fluorinating temperatures are therefore not
considered to
be advantageous. Moreover higher temperatures can lead to presintering or even
sintering
of the agglomerate, and sticking of the material to the walls of the
equipment. The
fluorination is carried out in a tumble drier which keeps the material in
motion. This gives
more homogeneous reaction conditions. The free-flowable agglomerate has to be
as free as
possible of fines and mechanically sufficiently stable enough for no
substantial production
of fines during post-treatment. Fines may impair the reliability of operation
of the process.
The agglomerate does not require the hardening which is disclosed in EP-B-222
945.
The fluorination of the agglomerate has two advantages. It is not diffusion-
controlled,
since the end groups reside on the surface of the latex particles. Reaction
times are
therefore relatively short. The unhardened agglomerate is sufficiently soft
not to abrade
metal contaminants from the wall of the tumble drier. Thus the level of metal
contaminants is reduced. Neither feature holds for the fluorination of melt
pellets. In this
case the fluorination process requires higher temperatures and much longer
reaction times
to allow for diffusion control of the reaction. Furthermore, the hard, sharp
melt pellets
abrade a considerable amount of metal from the wall of the tumble drier.
Increasing the
reaction time results in higher levels of metal contamination. This
contamination is
difficult to remove. The level of metal contamination increased by up to two
orders of
magnitude when the pellet process was used.
The fluorinated agglomerate is subsequently melt pelletized.
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Some comminution of the agglomerate takes place during drying and
fluorination. This
produces fines, which inhibit free flow of the material. It is advantageous to
compact the
fluorinated agglomerate before melt pelletizing. This gives a more reliable
constant feed
rate.
Melt pelletizing of fluorinated agglomerates provides many advantages over
melt
pelletizing of nonfluorinated agglomerates. Melt pelletizing proceeds
practically without
decomposition. The MFI value remains almost unchanged. This finding suggests
that there
is no substantial presence of weak linkages in the main chain. Corrosion of
the equipment
used is substantially reduced. The amount of metal contamination picked up is
therefore
insignificant. The emission of gaseous decomposition products at the die
orifice is
significantly reduced (e.g. by four orders of magnitudes). Thus the whole
process becomes
substantially more reliable. Die deposits are substantially reduced. Thus the
process needs
less attention. The melt pellets do not exhibit any discoloration, in contrast
to melt pellets
originating from non-fluorinated agglomerates, which are typically coffee
brown in color
when they leave the extruder.
The MFI value of the melt pellets produced via the process described above is
only
slightly increased by about 10%, compared to the MFI value of the copolymer
from
polymerization. It is therefore easier to achieve uniform quality.
As described in DE-A-195 47 909, the melt pellets are subsequently subjected
to an
aqueous treatment to remove volatiles and COF groups. Here too, the near
absence of
gaseous decomposition products and acidic end groups considerably reduces
corrosion of
the stainless steel water-treatment vessel. There is a reduction in further
heavy metal
contamination. Furthermore, water soluble salts originating from the
production process
are removed. The amount of extractable fluoride is reduced to less than 1 ppm.
Test Methods
The MFI value is measured according to ASTM D 1238 (DIN 53735) at 372°C
with a load
of 5 kg. T'he MFI value can be converted to the melt viscosity value in 0.1
Pas (Poise) by
dividing 53150 by the MFI value (g/min).
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The HFP content is measured via FTIR spectroscopy as disclosed in US-A-4 552
925. The
absorbances at wave numbers 980 cm' and 2350 cm', respectively, are measured
on a
film of 0.05 ~ 0.01 mm thickness, produced at 350°C, with a FTIR-
Nicolet Magna 560
FTIR spectrometer. The HFP content is calculated according to the following
equation:
HFP content (% by weight) = A98dA23so x 3.2.
The end groups (-COOH, -COF, -CONHZ) are determined via FTIR spectroscopy as
disclosed in EP-B-226 668 and US-A-3 085 083. A film of thickness 0.1 mm
produced at
350°C is used together with a reference film of a material containing
none of the end
groups to be analyzed. A Nicolet Magna 560 FTIR spectrometer was used, with
software
in interactive subtraction mode. When the number of end groups is stated, this
is the sum
of isolated and associated COOH, CONHZ and COF groups.
Melting points of the copolymers were determined by DSC by the method of ASTM
D
4591-87 at a heating rate of 10 K/min. The melting point stated here is the
peak
temperature of the endotherm during the second melting process.
The beadth of the molecular weight distribution, characterized by the Mw/Mn
ratio, was
measured via rheological spectroscopy with an Advanced Rheometer Expansion
System
CARES) supplied by Rheometric Scientific. Measurements were carried out at
372°C and
evaluated by the method of W. H. Tuminello, Polym. Eng. Sci., 26, 1339 (1989).
Metal contents were measured by extracting the samples with 3% strength HN03
for 72
hours at room temperature and subjecting the extracts to atomic absorption
spectroscopy.
The extractable fluoride ion content of the melt pellets was measured by the
method given
in EP-B-220 910. However, extraction was carried out only with water.
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Example 1
A 15001 stainless steel reactor was charged with 10001 of deionized water with
3 kg of
the ammonium salt of perfluorooctanoic acid. Air was removed by evacuation and
flushing with nitrogen. The reactor was heated to 70°C and the
temperature kept constant.
2 kg of 25% strength aqueous ammonia solution were added.
The reactor was pressurized with TFE and HFP to 17 bar total pressure, the
partial
pressure of HFP being 12.5 bar. The polymerization was started within 10 min
by adding
1600 g of ammonium persulfate in solution in 5 1 of deionized water. The
pressure was
kept constant by feeding a gaseous mixture of TFE/HFP into the reactor. The
TFE/HFP
weight ratio was 0.14. After 6 hours the reaction was stopped by interrupting
the monomer
feed. The monomers were vented off. The reactor was cooled to room temperature
and
then the contents were discharged. The solids content of the polymer
dispersion was 29%.
The dispersion was practically free of coagulum. The MFI value was 20 g/min.
The HFP
content of the copolymer was 13% by weight. The melting point was
255°C. The
copolymer had 660 COOH end groups per 106 carbon atoms. Mw/Mn was measured as
1.7, while an Mw/Mn value of 1.6 was calculated from the polymerization
rate/time curve.
The dispersion was coagulated using a homogenizes and agglomerated using
gasoline. The
agglomerate was washed three times with deionized water and dried for 6 hours
at 180°C
in a tumble drier, first by purging with nitrogen and then under vacuum.
The resulting agglomerate was divided into two parts. One part was then melt-
pelletized,
water-washed and dried giving a coffee brown color. It was fluorinated and
again water-
treated to remove residual COF end groups, whereupon the discoloration
disappeared.
This sample is called A0. The material had 43 end groups per million carbon
atoms. The
other part of the agglomerate was first fluorinated, then melted pelletized,
treated with
water and dried. This sample is called A1 and had only 18 end groups per
million carbon
atoms.
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At each processing step the content of iron, nickel and chromium was measured
using the
extraction method. Table 1 shows the results together with the amount of end
groups.
Table 1:
Metal contaminations for samples AO and Al after the various steps of work-up.
The
agglomerate had 660 end groups.
Sample A0: Fluorination of the Melt Pellets (Comparison)
Steps of
work-up
metal ions melt water-treatedFluorinatedFinal product:
agglomerate ellets b melt elletswater-washed
app ~
[ppb] ~ p melt pellets
~
ppb~ ~p b
b~
Fe 10 247 198 892 550
Ni > 10 41 22 56 21
Cr > 10 38 19 71 27
T' 43 end groups per million carbon atoms
Sample A1: Fluorination of the Agglomerate (Invention)
Steps of
work-up
metal ions fluorinatedMelt Final product:
agglomerate water-washed
agglomeratepellets *
~
[ppb] melt pellets
~ppb~ ~ppb~
b
Fe 10 14 18 14
Ni >5 >5 >S >5
Cr >5 >5 >5 >5
T' 18 end groups per million carbon atoms
The fluorination was carried out in a 3001 stainless steel tumble drier using
a mixture of
10% fluorine in nitrogen, at 140°C (sample AO) and at from 100 to
140°C (sample A1).
Details are listed in Table 2. The fluorine mixture had to be replaced several
times
(replenishment). At the end of the fluorination, excess fluorine was removed
by flushing
air through the reactor. The excess fluorine was adsorbed by passing the air
stream
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through a bed of A1z03 granules and through a scrubber comprising an aqueous
slurry of
CaC03.
Table 2:
Fluorination Conditions for Samples AO and A1.
*> overall Final""~~
sample material reaction temp.Number of
form C replenishmentsreaction number of
time end rou
[h] s
AO Melt pellets200 16 8.5 43
A 1 Agglomerate 140 7 4 12
replenishment every half hour, except for the last hour
**~ end groups are the total of COOH, COF and CONHZ per million carbon atoms
Water treatment of the melt pellets (see DE-A-195 47 909) was carried out in a
10001
stainless steel reactor. 200 kg of melt pellets and 4001 of deionized water
with 1 1 of 25%
ammonia solution were charged to the reactor. The reactor was heated to
100°C and kept
at this temperature for 4 hours for the nonfluorinated melt pellets and for 1
hour for the
fluorinated melt pellets. This reaction time is required to bring the content
of COF end
groups to below 5 ppm. The reactor was cooled by replacing the water twice.
The product
was dried by injecting hot air into the reactor. The melt pellets had an
extractable fluoride
ion content of 0.1 ppm.
Example 2
Sample A11 was run through a wire coating extruder under two different sets of
conditions together with a commercial product designated C 1. The production
of sample
Al 1 resembled that of A1, but the product had an MFI value of 24 g/min.
Polymerization
and work-up of Al 1 and A1 were identical. A11 has 28 end groups and an iron
content of
18 ppb. The Mw/Mn ratio was 1.6. The calculated value was 1.7. The extractable
fluoride
ion content was 0.2 ppm.
The coating conditions are listed in Table 3.
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Table 3
Coating performance of the material according to the invention in comparison
with a
commercial product C 1 and with sample AO
Run No. 1 2 3
Sample Al l Al l C1
MFI g/min 24 24 21
Copper wire temp. 176 (350 193 (380 177 (350 F)
[C] F) F)
Cone length [cm) 5.1 (2.0 3.8 (1.5 5.1 (2.0 inches)
inches) inches)
Die temperature 380 (716 391 (735 380 (716 F)
[C] F) F)
Extruder speed 21.3 24.7 18.5
[rpm]
Line speed [m/min]521 611 427
(1710 f/min)(2006 f/min)(1402 f/min)
The temperature profiles, not given in the table, were slightly adjusted to
maximize the
line output while maintaining the insulation eccentricity deviation between
0.00076 and
0.0018 cm (0.0003 and 0.0007 inches).
In runs l and 2 there were no marked die deposits and no cone fractures during
the run
time. In run 3 there was a considerable level of die deposits and cone
fracture during an
identical run time. When C 1 was aged above its melting point (i.e.,
250°C), it showed
noticeable brownish discoloration.
Example 3
Samples Al 1, A12 and commercial products were run through a slightly
different wire-
coating extruder.
The coating conditions are listed in Tab. 4.
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Table 4
Coating performance of the material according to the invention in comparison
to two
commercial products
Run No. 1 2
Sample A 11 /A 12 C2
MFI g/min 24/23 25
Copper wire temp. 193/190 (380 F/375177 (350 F)
[C] F)
Cone length [cm] 5.1 (2.0 inches) 5.1 (2.0 inches)
Die temp. [C] 404 (760 F) 404 (760 F)
Extruder speed [rpm]42.5 32.0
Line speed [m/min] 518 (1700 f/min) 415/417 (1390
f/min)
The temperature profiles were slightly adjusted to maximize the line output
while
maintaining the insulation eccentricity deviation between 0.00076 and 0.0018
cm (0.0003
and 0.0007 inches).
Run No. 1 did not show any noticeable die deposits, and only two cone
fractures, during a
period of 29 hours of extruding wires which were blue, green, orange, brown
and white in
color.
Run No. 2 showed a considerable level of die deposits and averaged 6 to 8 cone
fractures
during a run time of 24 hours.
