U.S. patent application number 12/820532 was filed with the patent office on 2010-10-07 for high processing temperature foaming polymer composition.
Invention is credited to Mikael Abeguile, Jerome Alric, Thierry Auvray, Susanne Brix, Alfred Gemmel, Paul Kroushl, Christian Lankes, Friedrich Muller, Olivier Pinto.
Application Number | 20100252947 12/820532 |
Document ID | / |
Family ID | 39472519 |
Filed Date | 2010-10-07 |
United States Patent
Application |
20100252947 |
Kind Code |
A1 |
Brix; Susanne ; et
al. |
October 7, 2010 |
HIGH PROCESSING TEMPERATURE FOAMING POLYMER COMPOSITION
Abstract
A foaming composition comprising a melt processible
fluoropolymer, and a chemical foaming agent, where the chemical
foaming agent is ammonium polyphosphate.
Inventors: |
Brix; Susanne; (Eckental,
DE) ; Muller; Friedrich; (Lauf, DE) ; Lankes;
Christian; (Feucht, DE) ; Gemmel; Alfred;
(Kalchreuth, DE) ; Pinto; Olivier; (Lyon, FR)
; Abeguile; Mikael; (Chaponost, FR) ; Alric;
Jerome; (L'Isle D'Abeau, FR) ; Auvray; Thierry;
(Lancaster, PA) ; Kroushl; Paul; (Lancaster,
PA) |
Correspondence
Address: |
SOFER & HAROUN LLP.
317 MADISON AVENUE, SUITE 910
NEW YORK
NY
10017
US
|
Family ID: |
39472519 |
Appl. No.: |
12/820532 |
Filed: |
June 22, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12315077 |
Nov 26, 2008 |
7767725 |
|
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12820532 |
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Current U.S.
Class: |
264/54 |
Current CPC
Class: |
B29C 48/07 20190201;
C08J 9/122 20130101; B29C 48/022 20190201; B29K 2027/18 20130101;
C08J 2327/12 20130101; C08J 9/06 20130101; H01B 3/445 20130101;
C08J 2201/03 20130101 |
Class at
Publication: |
264/54 |
International
Class: |
C08J 9/06 20060101
C08J009/06 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 29, 2007 |
EP |
07291426 |
Jun 19, 2008 |
EP |
08305287.8 |
Claims
1. A method for extruding a foaming composition, said method
comprising the steps of: blending a foaming composition of a melt
processible fluoropolymer, and ammonium polyphosphate as a chemical
foaming agent above the temperature needed to melt the
fluoropolymer and below the temperature needed to decompose the
chemical foaming agent; and extruding said composition above the
temperature needed to decompose the chemical foaming agent.
Description
RELATED APPLICATION
[0001] This application is a continuation application of U.S.
patent application Ser. No. 12/315,077, filed on Nov. 26, 2008,
which claims the benefit of priority from European Patent
Application No. 07 291 426.0, filed on Nov. 29, 2007 and European
Patent Application No. 08 305 287.8, filed on Jun. 19, 2008, the
entirety of which are incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to a foaming fluoropolymer
composition, an extrusion process of said composition, an
electrical cable comprising an insulated layer and/or a cross
spacer obtained by said process.
[0003] More particularly this composition is for use in the
manufacture of dielectric insulated material for electrical cables
(power or communication cables), such as Local Area Network (LAN)
cables, aeronautic cables, Bus cables and automotive cables.
BACKGROUND
[0004] Fluoropolymers have generally excellent suitability for
electrical applications since they present a low dielectric
constant and a low dissipation factor, but they are quite
expensive. Hence it is desirable to minimize the amount of
insulated material in providing a foaming fluoropolymer
composition.
[0005] In addition, even at high temperatures, fluoropolymers are
stable and do not burn, and they can therefore in principle be used
not only for electrical purposes but in all fields of
engineering.
[0006] However no chemical foaming agent providing a decomposition
temperature superior to the melting point of fluoropolymer exists
on the market.
[0007] Document U.S. Pat. No. 6,064,008 proposes a flame retardant
communication cable comprising elongated electrical conductor
surrounded by a layer of insulating material, said insulating
material comprising a chemically blown fluorinated polymer having a
melting point of greater than about 248.degree. C.
[0008] The insulated material is foamed using a chemical foaming
agent, which decomposes at a temperature above the temperature
needed to melt the fluorinated polymer and the gas evolved from the
chemical foaming agent.
[0009] A particularly suitable chemical foaming agent is the barium
salt of 5-phenyltetrazole.
[0010] However such chemical foaming agent presents a decomposition
temperature below the fluorinated polymer having a melting point
greater than about 248.degree. C.
[0011] According to Plastic Additive Handbook, 5.sup.th edition, H.
Zweifel, pp. 711, the barium salt of 5-phenyltetrazole begins to
decompose at a temperature below 248.degree. C., i.e. 240.degree.
C.
[0012] In the case of said prior art document, the decomposition of
the barium salt of 5-phenyltetrazole occurs too early during the
extrusion process and thus released gaseous products are not
efficiently diluted and voids are not dispersed into the molten
fluorinated polymer.
[0013] Therefore the composition with such chemical foaming agent
cannot provide a chemically foamed fluorinated polymer with
homogeneous aspect presenting good mechanical and electrical
properties due to the difficulty of controlling the foaming
process.
OBJECTS AND SUMMARY
[0014] The present invention seeks to solve the above-mentioned
problems of the prior art.
[0015] To this end, an object of the present invention is to
provide a foaming composition comprising a melt processible
fluoropolymer, and a chemical foaming agent, characterized in that
said chemical foaming agent is ammonium polyphosphate.
[0016] By means of the invention, said composition leads to stable
foaming process, more particularly during extrusion, in terms of
diameter control, void degree and capacitance consistency.
[0017] Furthermore, once said composition foamed, it provides high
performances dielectric properties in improving the electrical
transmission characteristics of the resulting cables, in particular
in the domain of LAN cables.
[0018] Fluoropolymer of the present invention is thermoplastically
processible. Hence, it can be melted and therefore extruded by a
conventional technique.
[0019] The thermoplastic extrudable fluoropolymer of the present
invention has preferably a melting temperature above 250.degree. C.
and is advantageously a tetrafluoroethylene copolymer.
[0020] For example, said tetrafluoroethylene copolymer can be
selected from the group of: [0021] tetrafluoroethylene and
hexafluoropropylene copolymers (FEP); [0022] tetrafluoroethylene
perfluoroalkoxy vinyl ether copolymers such as tetrafluoroethylene
perfluoromethyl vinyl ether copolymers (MFA), tetrafluoroethylene
perfluoropropyl vinyl ether copolymers (PFA); [0023] ethylene
tetrafluoroethylene copolymers (ETFE); [0024] ethylene
chlorotrifluoroethylene copolymers (ECTFE); and [0025]
polytetrafluoroethylene (PTFE); or mixtures thereof.
[0026] Furthermore, such foaming composition further allows to
minimize the amount of fluoropolymers required, which are
expensive.
[0027] In another embodiment of the present invention, the
composition comprises less than 3% by weight of the ammonium
polyphosphate based on 100% by weight of polymer in the
composition, more preferably less than 1% by weight of the ammonium
polyphosphate based on 100% by weight of polymer in the
composition.
[0028] In another embodiment of the present invention, the
composition comprises more than 0.05% by weight of the ammonium
polyphosphate based on 100% by weight of polymer in the
composition, more preferably more than 0.5% by weight of ammonium
polyphosphate based on 100% by weight of polymer in the
composition.
[0029] In a variant, said composition further comprises a
nucleating agent, more particularly said nucleating agent is boron
nitride.
[0030] In addition, it is preferable that the amount of the
nucleating agent is from 0.5% to 2% by weight based on 100% by
weigh of polymer in the composition in order that the extruded
composition keeps good mechanical properties.
[0031] Another object is an extrusion process of a foaming
composition comprising the following steps: [0032] blending a
foaming composition according to the present invention above the
temperature needed to melt the fluoropolymer and below the
temperature needed to decompose the chemical foaming agent, and
[0033] extruding said composition above the temperature needed to
decompose the chemical foaming agent.
[0034] The chemical foaming agent of the present invention, i.e.
ammonium polyphosphate, decomposes typically from 340.degree. C. in
the fluoropolymer composition.
[0035] In the case of extrudable PTFE, it starts to melt at a
temperature of about 320.degree. C. and at temperatures higher than
that it can be processed thermoplastically. The foamed PTFE leads
to a reduction in the viscosity of the PTFE.
[0036] The invention therefore permits production of extrudate
composed of foamed fluoropolymer by means of commercially available
extruders. After discharge of the extrudate from the extruder, no
further measures relating to the foaming procedure are required,
since the reactants for the foaming process are already present in
the extruder or are introduced into the same, and the extruder
possesses the heat required to decompose the chemical foaming
agent, thus yielding a foamed extrudate.
[0037] An extrudate thus obtained can then be directly introduced
to further operations, among which is by way of example winding
onto a reel.
[0038] Examples of extrudates that can be produced by the process
according to the invention are rods, pipes, tapes, and insulation
and sheathing for lines.
[0039] Another object is an electrical cable comprising a
dielectric insulating layer obtained by the extrusion process
according to the present invention. Said electrical cable can
advantageously be a coaxial high-frequency cable or LAN cable.
[0040] Another object is an electrical cable comprising a cross
spacer obtained by the extrusion process according to the present
invention. Cross spacer is used in LAN cable construction in order
to reduce crosstalks between twisted pairs.
BRIEF DESCRIPTION OF THE DRAWINGS
[0041] Other characteristics and advantages of the invention are
described below in detail in the following description, which is
given by way of non-limiting illustration, taken in conjunction
with the drawings, in which:
[0042] FIG. 1 is a schematic view of an extrusion process according
to the present invention,
[0043] FIG. 2 is a cross sectional view of an isolated electrical
wire according to the present invention,
[0044] FIG. 3 is a cross sectional view of a Profibus cable
according to the present invention, and
[0045] FIG. 4 is a cross sectional view of a LAN cable according to
the present invention.
DETAILED DESCRIPTION
[0046] The polymer melting temperatures as well as the chemical
foaming agent decomposition temperature, mentioned all over the
present description, can be determined by method well known in the
art.
[0047] The polymer melting temperatures is by example determined by
the melt enthalpy provided by Differential Scanning Calorimetry
(DSC) with a ramp T.degree. C. of 10.degree. C./mn.
[0048] The chemical foaming agent decomposition temperature is by
example determined by Differential Scanning Calorimetry (DSC) with
a ramp T.degree. C. of 10.degree. C./mn, 340.degree. C. being the
onset of the decomposition enthalpy peak of ammonium polyphosphate.
Dynamic rheology analysis can be used as well (T.degree. C. sweep
at constant frequency: plot of viscosity vs. T.degree. C., and
comparison with solid composition), 340.degree. C. being the onset
of viscosity drop of ammonium polyphosphate versus solid viscosity
behaviour. Both methods lead to comparable results.
[0049] In order to control the structure of the foam such as void
degree and void size, the thermal decomposition of the chemical
foaming agent must take place in a processing window temperature
from 340.degree. C. to 380.degree. C. In said decomposition
temperature ranges, ammonium polyphosphate releases gaseous
products such as by example ammonia.
[0050] The chemical foaming agent decomposition of the present
invention occurs in the polymer melt inside the compression zone of
the extruder and bubble growth and void dispersion are controlled
in the processing window temperature of said compression zone.
[0051] The following non-limiting example shows the potential of
ammonium polyphosphate as chemical blowing agents in fluoropolymer
composition.
[0052] For that, an extruded composition according to the invention
is prepared in using an extrudable PTFE commercialized by ELRING
KLINGER under the reference Moldflon, ammonium polyphosphate (APP)
commercialized by Buddenheim under the reference FR CROSS S10, and
boron nitride commercialized by Momentive Performance under the
reference BN AC6004.
[0053] In a first step of compounding, a first compound (Compound
1) is prepared on a Berrstoff ZE-25 twin-screw extruder. The
Compound 1 is detailed in Table 1 as below.
TABLE-US-00001 TABLE 1 Amount Compound 1 (% by weight) Extrudable
PTFE 80 APP masterbatch 20 (10% by weight of APP in extrudable
PTFE)
[0054] According to FIG. 1, extrudable PTFE is introduced in a
first feed hopper 101a and the APP masterbatch is introduced in a
second feed hopper 102a of the twin-screw extruder 100a to obtain
first compound pellets 110 by a pelletizer 103a.
[0055] The temperature range of the twin-screw extruder is above
the temperature needed to melt the extrudable PTFE and is below the
temperature needed to decompose the ammonium polyphosphate, i.e.
below 340.degree. C. The pellets 110 obtained from the first
compound are thus unfoamed.
[0056] In a second step of compounding, a second compound (Compound
2) is prepared in the same conditions used during the first step of
compounding. The Compound 2 is detailed in Table 2 as below.
TABLE-US-00002 TABLE 2 Amount Compound 2 (% by weight) Extrudable
PTFE 98 Boron nitride 2
[0057] According to FIG. 1, extrudable PTFE is introduced in a
first feed hopper 101b and the boron nitride is introduced in a
second feed hopper 102b of the twin-screw extruder 100b to obtain
second compound pellets 111 by a pelletizer 103b.
[0058] Finally, a composition (Composition 1) comprising the first
and second compound pellets 110, 111 is then introduced in the feed
hopper 201 of a single-screw extruder 200 (FIG. 1) with a screw of
30 mm in diameter and an L/D ratio of 30. The Composition 1 is
detailed in Table 3 as below and comprises finally 0.15% by weight
of ammonium polyphosphate and 1.85% by weight of boron nitride.
TABLE-US-00003 TABLE 3 Amount Composition 1 (% by weight) Compound
1 7.5 Compound 2 92.5
[0059] In another embodiment, the fluoropolymer, the chemical
foaming agent and the nucleating agent used in the composition
according to the invention can directly be weighted and introduced
at the same time in the feed hopper of a single-screw extruder, the
preparation method of the composition according to the invention
being not limited.
[0060] The temperature extrusion profile of the Composition 1 is
shown in Table 4 as below.
TABLE-US-00004 TABLE 4 Temperature Zone (.degree. C.) Zone 1 330
Zone 2 350 Zone 3 370 Zone 4 380 Zone 5 380 Clamp 370 Head 370 Die
330
[0061] The temperature of the single-screw extruder is above the
temperature needed to melt the fluoropolymer (Zone 1) and to blend
the Composition 1 without decomposing the chemical foaming
agent.
[0062] Then, said temperature increases (Zone 2 to Zone 5) to
decompose the ammonium polyphosphate in the extruder once the
extrudable PTFE is completely melted. Hence, ammonia is efficiently
diluted in said melted extrudable PTFE.
[0063] Finally, the Composition 1 is extruded with a thickness of
0.95 mm around a copper wire with a diameter of 0.64 mm to obtain
an insulated electrical wire 10 as represented in FIG. 2.
[0064] Said insulated electric 10 comprises in a general manner an
electric wire 1 surrounded by a dielectric foamed insulating layer
2 according to the present invention.
[0065] The line speed and the single-screw speed of the extruded
processing conditions are respectively of 15 m/mn and 85 rpm.
[0066] Said extrusion step easily allows to control the foaming
process in order to optimise the quality of the foamed composition.
The dielectric foamed insulating layer presents a homogeneous
structure such as its concentricity is of 91%.
[0067] Hence, ammonium polyphosphate avoids any anticipated
decomposition in said extrusion step, said anticipated
decomposition resulting of an inhomogeneous mixture, and thus an
inhomogeneous foamed structure.
[0068] In addition, the capacitance of the dielectric foamed
insulating layer obtained from Composition 1 is measured on line
during extrusion using a high speed capacitance measuring
instrument. The capacitance measurement device is a tube where an
electronic unit supplies the measuring tube with a high frequency
sinusoidal voltage. The isolated electric wire, which passes trough
the measuring tube, is earthed and generates a capacitive current
measured by the electronic unit.
[0069] The online capacitance specification of said dielectric
foamed insulating layer is about 67.+-.1.5 picofarads/meter. Thus
it complies with dielectric requirement for LAN insulated conductor
wire.
[0070] The cable of FIG. 3 represents an electrical communication
cable 20, such as a Profibus cable, comprising two isolated
electrical wire 10 according to the present invention, twisted to a
pair with fillers 3 in gaps.
[0071] In addition, said cable 20 comprises an aluminium laminate
foil 4 overlapping the twisted pair of isolated electrical wire and
fillers, and optionally a jacket 5, well known in the art,
surrounding the foil 4.
[0072] From this example of cable embodiment, the attenuation and
the impedance is determined according to EN 50289-1 (part 11 and
part 8) standards.
[0073] Impedance results are mentioned is the Table 5 as below.
TABLE-US-00005 TABLE 5 Impedance Frequency (Ohm) 3-20 MHz 150 .+-.
15 31.25-38.4 MHz 185 .+-. 18.5 9.6 kHz 270 .+-. 27
[0074] Attenuation results are mentioned is the Table 6 as
below.
TABLE-US-00006 TABLE 6 Attenuation Frequency (dB/km) 16 MHz
.ltoreq.42 4 MHz .ltoreq.22 38.4 kHz .ltoreq.4 9.6 kHz
.ltoreq.2.5
[0075] Extrusion temperatures, line speed and screw speed mentioned
in the present invention vary depending on extruder type,
particular material, desired properties and applications.
Temperatures generally range from about 250 to 500.degree. C., and
preferably range from about 300 to 450.degree. C., according to the
desired application. Line speed generally ranges from about 30 m/mm
to 500 m/mm according to the desired application. Screw speed
generally ranges from about 10 to 100 rpm, according to the desired
application.
[0076] The cable of FIG. 4 represents an electrical communication
cable 30 such as a category 6 LAN cable. It comprises four twisted
pairs 11, 12, 13, 14 of isolated electrical wires 10 according to
the present invention.
[0077] A sheath 6, made by example of halogen free fire resistant
polyethylene (HFFR PE), polyvinyl chloride (PVC) or any type of
limited combustible material, surrounds the whole of said four
twisted pairs.
[0078] In addition, a cross spacer 7 separates the four pairs 11,
12, 13, 14 of conductors from each other.
[0079] It is well known that cross spacer improves the crosstalk
performance and the impedance of electrical communication
cable.
[0080] Advantageously, said cross spacer 7 can be made by extrusion
from the foaming composition according to the present invention,
providing optimised performance of said electrical communication
cable.
[0081] While some embodiments of the present invention have been
described above, it should be understood that it has been presented
by way of examples only and not meant to limit the invention.
[0082] In this way, the electrical cables according to the
invention can comprise at least one extruded element obtained from
the foaming composition according to the invention such as by
example a dielectric insulating layer or a cross spacer.
* * * * *