U.S. patent application number 16/523510 was filed with the patent office on 2019-11-14 for process for foaming polyolefin compositions using a fluororesin/azodicarbonamide mixture as a nucleating agent.
The applicant listed for this patent is Dow Global Technologies LLC. Invention is credited to Mohamed ESSEGHIR, Chester J. KMIEC, Gangwei SUN.
Application Number | 20190345304 16/523510 |
Document ID | / |
Family ID | 56073402 |
Filed Date | 2019-11-14 |
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United States Patent
Application |
20190345304 |
Kind Code |
A1 |
SUN; Gangwei ; et
al. |
November 14, 2019 |
Process for Foaming Polyolefin Compositions Using a
Fluororesin/Azodicarbonamide Mixture as a Nucleating Agent
Abstract
The process of foaming a polyolefin, e.g., polyethylene,
composition using as a nucleator a combination an azodicarbonamide
(ADCA) and a fluororesin at a ADCA:fluororesin weight ratio of
60:40 to 20:80. The synergic effect between these two nucleating
agents results in a higher nuclei density and a foamed product with
a smaller cell size as compared to processes using and products
produced by the use of neat PTFE or neat ADCA alone as the
nucleating agent.
Inventors: |
SUN; Gangwei; (Shanghai,
CN) ; ESSEGHIR; Mohamed; (Lawrenceville, NJ) ;
KMIEC; Chester J.; (Phillipsburg, NJ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Dow Global Technologies LLC |
Midland |
MI |
US |
|
|
Family ID: |
56073402 |
Appl. No.: |
16/523510 |
Filed: |
July 26, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15528694 |
May 22, 2017 |
10414892 |
|
|
PCT/CN2014/092557 |
Nov 28, 2014 |
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16523510 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08J 2203/06 20130101;
C08J 2323/06 20130101; C08L 27/18 20130101; C08J 2427/18 20130101;
C08L 23/06 20130101; C08L 23/06 20130101; C08J 2423/06 20130101;
C08J 9/0061 20130101; H01B 3/445 20130101; C08J 9/103 20130101;
C08J 2205/044 20130101; C08L 23/06 20130101; C08L 27/18 20130101;
C08J 2203/04 20130101; C08J 2201/024 20130101; C08L 23/06 20130101;
C08L 23/06 20130101; H01B 3/441 20130101; C08J 2201/03 20130101;
H01B 7/02 20130101; C08J 9/122 20130101; C08J 9/0028 20130101; C08K
5/23 20130101; C08J 2201/022 20130101; C08J 2203/184 20130101; C08J
2207/06 20130101; C08L 23/06 20130101; C08L 27/18 20130101; C08K
5/23 20130101; C08L 23/06 20130101; C08K 5/23 20130101 |
International
Class: |
C08J 9/10 20060101
C08J009/10; H01B 7/02 20060101 H01B007/02; C08J 9/00 20060101
C08J009/00; C08L 23/06 20060101 C08L023/06; C08J 9/12 20060101
C08J009/12; H01B 3/44 20060101 H01B003/44; C08K 5/23 20060101
C08K005/23; C08L 27/18 20060101 C08L027/18 |
Claims
1-12. (canceled)
13. A composition, comprising: (a) a polyolefin; and (b) a
nucleator comprising: (i) azodicarbonamide (ADCA); and (ii) a
fluororesin; wherein an ADCA:fluororesin weight ratio is from 60:40
to 20:80, further wherein the fluororesin is composed of
agglomerates and particles with the fluororesin comprising 80% or
more of particles or agglomerates of less than 1 micron in size
based on the total number of agglomerates and particles of the
fluororesin.
14. The composition of claim 13, wherein the polyolefin comprises
low density polyethylene (LDPE).
15. The composition of claim 14, wherein the polyolefin consists of
LDPE.
16. The composition of claim 13, wherein the fluororesin comprises
polytetrafluoroethylene (PTFE).
17. The composition of claim 16, wherein the fluororesin consists
of PTFE.
18. The composition of claim 13, wherein the nucleator is present
in the composition in an amount from 2 wt % to 10 wt %, based on
the weight of the composition.
19. The composition of claim 1, wherein the composition comprises
high-density polyethylene.
20. The composition of claim 19, wherein the nucleator is present
in the composition in an amount from 0.01 wt % to 1 wt %, based on
the weight of the composition.
21. The composition of claim 13, wherein the composition further
comprises at least one of an antioxidant and a cell stabilizer.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a process of foaming compositions.
In one aspect the invention relates to foaming polyolefin
compositions using a fluororesin as a nucleating agent while in
another aspect, the invention relates to the foamed composition
made from the process. In yet another aspect, the invention relates
to using the foamed compositions as an insulation layer in electric
communication cables, particularly high frequency coaxial
cables.
BACKGROUND OF THE INVENTION
[0002] Typically, the insulation layer of a high frequency telecom
cable is produced by mixing a nucleating agent with a mixture of
high density polyethylene (HDPE) and low density polyethylene
(LDPE). The foamable materials are then extruded in the presence of
a physical foaming agent, like gases such as nitrogen, carbon
dioxide, chlorinated fluorocarbons, freons, helium, neon, argon,
krypton, xenon, and radon, which is injected into the polymer melt
inside of the extruder. Nucleating agents for the foaming can
include but not limited to azodicarbonamide (ADCA) and
4,4'-oxybisbenzenesulfonylhydrazide (OBSH), which thermally
decompose in an extruder and form a number of fine nuclei in the
polymer melt. However, the byproducts of the decomposed ADCA and
OBSH have a high polarity which are well known to have a
significant negative effect on the electrical performance
(dissipation factor) of the cable.
[0003] Compared to ADCA and OBSH, fluororesin powder, such as
polytetrafluoroethylene (PTFE), is a nucleating agent that exhibits
a significantly lesser effect on electrical performance and is free
of the decomposition issues associated with ADCA and OBSH. PTFE has
been and is currently used as a nucleating agent for foaming
compositions for use as insulation in telecom cable but
improvements are still desired, particularly with respect to
dispersion of the nucleating agent within the foamable composition,
i.e., the polymer matrix, and in the formation of small, uniformly
sized cells within the foamed product.
[0004] U.S. Pat. No. 3,554,932 A teaches that finely divided, solid
fluororesins, such as PTFE, fluorinated ethylene-propylene (FEP),
or particle carriers coated with a fluorocarbon functioned as
nucleators for gas-injected, foamed thermoplastic. It also teaches
that the particle size should not exceed 20 microns in diameter,
and it should be used in an amount from 0.01% to 2% by weight.
[0005] CA2523861A1 teaches a low loss foam composition and cable,
such as a coaxial cable. The foam composition is formed by heating
an olefinic polymer, such as a high density polyethylene, medium
density polyethylene, low density polyethylene, linear low density
polyethylene, polypropylene, or a combination thereof, into a
molten state composition, optionally with a nucleating agent. The
molten mixture is extruded under pressure through a die with a
blowing agent comprising an atmospheric gas, such as carbon
dioxide, nitrogen or air, and a co-blowing agent. The nucleating
agent is selected from the group consisting of: azobisformamide,
azodicarbonamide and sodium carbonate, with or without citric acid,
talc, calcium carbonate, mica and combinations thereof.
SUMMARY OF THE INVENTION
[0006] In one embodiment the invention is a process of foaming a
polyolefin composition using as a nucleator a combination of an
azodicarbonamide (ADCA) and a fluororesin and at an
ADCA:fluororesin weight ratio of 60:40 to 20:80.
[0007] In one embodiment the invention is a polyolefin foam made by
a process for foaming a polyolefin composition using as a nucleator
a combination of an ADCA and a fluororesin and at an
ADCA:fluororesin weight ratio of 60:40 to 20:80.
[0008] In one embodiment the invention is a cable comprising an
insulation layer comprising a foam made by a process of foaming a
polyolefin composition using as a nucleator a combination of an
ADCA and a fluororesin and at an ADCA:fluororesin weight ratio of
60:40 to 20:80.
[0009] In one embodiment the invention is a foamable composition
comprising in weight percent based on the weight of the
composition: [0010] (A) 45 to 95% HDPE; [0011] (B) 4 to 54% LDPE;
and [0012] (C) 0.01 to 1% of a combination of an ADCA and a
fluororesin and at an ADCA:fluororesin weight ratio of 60:40 to
20:80.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Definitions
[0013] Unless stated to the contrary, implicit from the context, or
customary in the art, all parts and percents are based on weight
and all test methods are current as of the filing date of this
disclosure. For purposes of United States patent practice, the
contents of any referenced patent, patent application or
publication are incorporated by reference in their entirety (or its
equivalent US version is so incorporated by reference) especially
with respect to the disclosure of definitions (to the extent not
inconsistent with any definitions specifically provided in this
disclosure) and general knowledge in the art.
[0014] The numerical ranges in this disclosure are approximate
unless otherwise indicated. Numerical ranges include all values
from and including the lower and the upper values, in increments of
one unit, provided that there is a separation of at least two units
between any lower value and any higher value. As an example, if a
compositional, physical or other property, such as, for example,
tensile strength, elongation at break, etc., is from 100 to 1,000,
then the intent is that all individual values, such as 100, 101,
102, etc., and sub ranges, such as 100 to 144, 155 to 170, 197 to
200, etc., are expressly enumerated. For ranges containing values
which are less than one or containing fractional numbers greater
than one (e.g., 1.1, 1.5, etc.), one unit is considered to be
0.0001, 0.001, 0.01 or 0.1, as appropriate. For ranges containing
single digit numbers less than ten (e.g., 1 to 5), one unit is
typically considered to be 0.1. These are only examples of what is
specifically intended, and all possible combinations of numerical
values between the lowest value and the highest value enumerated,
are to be considered to be expressly stated in this disclosure.
Numerical ranges are provided within this disclosure for, among
other things, particle size and the amount of individual
ingredients in a mixture.
[0015] "Comprising." "including," "having" and like terms are not
intended to exclude the presence of any additional component, step
or procedure, whether or not the same is specifically disclosed. In
order to avoid any doubt, all processes claimed through use of the
term "comprising" may include one or more additional steps, pieces
of equipment or component parts, and/or materials unless stated to
the contrary. In contrast, the term, "consisting essentially of"
excludes from the scope of any succeeding recitation any other
component, step or procedure, excepting those that are not
essential to operability. The term "consisting of" excludes any
component, step or procedure not specifically delineated or listed.
The term "or," unless stated otherwise, refers to the listed
members individually as well as in any combination.
[0016] "Composition" and like terms mean a mixture of two or more
materials.
[0017] "Polyolefin composition" and like terms mean, in the context
of this invention, a composition comprising at least one
polyolefin.
[0018] "Interpolymer" means a polymer prepared by the
polymerization of at least two different monomers. This generic
term includes copolymers, usually employed to refer to polymers
prepared from two different monomers, and polymers prepared from
more than two different monomers, e.g., terpolymers, tetrapolymers,
etc.
[0019] "Nucleator", "nucleating agent" and like terms mean, in the
context of this invention, a substance, typically a small particle,
that provides a nucleation site or location for bubble formation
within a polymer melt. These nucleating agents are used to enhance
the cell structure of foaming polymers.
[0020] "Agglomerate" and like terms mean a collection of two or
more particles group together to constitute a whole. Agglomerates
can be of various sizes. An agglomerate will always be larger than
the particles from which it is made, but some particles not
associated with a particular agglomerate can be larger than the
agglomerate. In the practice of this invention, agglomerates are
typically and preferably less than one micron is size, more
preferably less than 0.5 micron and even more preferably less than
0.3 micron, in size.
[0021] "Particle" and like terms mean a unitary mass. Particles can
be of various sizes. A fluororesin particle, e.g., a PTFE particle,
is a unitary mass of fluororesin. Two or more fluororesin particles
grouped together. i.e., in contact with one another, form a
fluororesin agglomerate. The fluororesin particles of this
invention are typically and preferably less than one micron is
size, more preferably less than 0.5 micron and even more preferably
less than 0.3 micron, in size.
[0022] "Unagglomerated particle" and like terms mean a particle not
associated with another particle of like kind. Unagglomerated
particles include both particles that have dissociated from an
agglomerate, and particles that have not been associated with an
agglomerate.
[0023] "Masterbatch" and like terms mean a concentrated mixture of
additives in a carrier resin. In the context of this invention, a
masterbatch comprises a concentrated mixture of fluororesin
nucleator in a polyolefin resin. The masterbatch allows for an
efficient addition and dispersion of the nucleator to and in the
polyolefin. The manufacture and use of masterbatches are well known
to those skilled in the art of manufacturing and fabricating
plastics and foam articles.
Polyolefins
[0024] "Polyolefin" and like terms means a polymer derived from one
or more simple olefin monomers, e.g., ethylene, propylene,
1-butene, 1-hexene, 1-octene and the like. The olefin monomers can
be substituted or unsubstituted and if substituted, the
substituents can vary widely. If the polyolefin is to contain
unsaturation, then preferably at least one of the comonomers is at
least one nonconjugated diene such as 1,7-octadiene, 1,9-decadiene,
1,11-dodecadiene, 1,13-tetradecadiene, 7-methyl-1,6-octadiene,
9-methyl-1,8-decadiene and the like. Many polyolefins are
thermoplastic. Polyolefins include but are not limited to
polyethylene, polypropylene, polybutene, polyisoprene and their
various interpolymers.
[0025] In one embodiment of the invention the polyolefin is at
least one, preferably a blend of, high density polyethylene (HDPE)
and low density polyethylene (LDPE). The HDPE resins that can be
used in the practice of this invention are well known, commercially
available, and can be prepared with either Ziegler-Natta,
chromium-based, constrained geometry or metallocene catalysts in
slurry reactors, gas phase reactors or solution reactors. HDPE, as
used herein, is an ethylene-based homopolymer or interpolymer
having a density of at least 0.94 g/cc, or from at least 0.94 g/cc
to 0.98 g/cc, and a melt index from 0.1 g/10 min to 25 g/10
min.
[0026] HDPE can comprise ethylene and one or more C.sub.3-C.sub.20
.alpha.-olefin comonomers. The comonomer(s) can be linear or
branched. Nonlimiting examples of suitable comonomers include
propylene, 1-butene, 1 pentene, 4-methyl-1-pentene, 1-hexene, and
1-octene. HDPE interpolymer includes at least 50 percent by weight
units derived from ethylene, i.e., polymerized ethylene, or at
least 70 percent by weight, or at least 80 percent by weight, or at
least 85 percent by weight, or at least 90 weight percent, or at
least 95 percent by weight ethylene in polymerized form.
[0027] In an embodiment. HDPE is a homopolymer or an
ethylene/.alpha.-olefin copolymer with a density from 0.94 g/cc to
0.98 g/cc, and a melt index from 0.1 g/10 min to 10 g/10 min. In an
embodiment, the HDPE has a density from 0.960 g/cc to 0.980 g/cc,
and a melt index from 0.1 g/10 min to 10 g/10 min. In an
embodiment, HDPE has a density from 0.96 g/cc to 0.97 g/cc and a
melt index from 0.1 g/10 min to 10 g/min. In an embodiment, the
HDPE has a density from 0.96 g/cc to 0.98 g/cc and a melt index
from 1.0 g/10 min to 10.0 g/10 min.
[0028] Nonlimiting examples of suitable, commercially available
HDPE include but are not limited to DOW High Density Polyethylene
resins and CONTINUUM.TM. and UNIVAL.TM. high density polyethylene
resins, ELITE.TM. 5960G, HDPE KT 10000 UE, HDPE KS 10100 UE and
HDPE 35057E, each available from The Dow Chemical Company Midland,
Mich., USA; SURPASS.TM. available from Nova Chemicals Corporation,
Calgary, Alberta, Canada; BS2581 available from Borealis; Hostalen
ACP 5831D available from Lyondell/Basell; RIGIDEX.RTM. HD5502S
available from INEOS Olefins & Polymers Europe; SABIC.RTM.B5823
and SABIC.RTM.B5421 available from Sabic; and HDPE 5802 and BM593
available from Total.
[0029] The LDPE resins that can be used in the practice of this
invention are also well known, commercially available, and made by
any one of a wide variety of processes including, but not limited
to, solution, gas or slurry phase, and high pressure tube or
autoclave. The polyethylene also can be homogeneous or
heterogeneous with respect to comonomer distribution. The
homogeneous polyethylenes usually have an essentially uniform
comonomer distribution. The heterogeneous polyethylenes, on the
other hand, do not have a uniform comonomer distribution. In one
embodiment the LDPE is a linear low density polyethylene (LLDPE).
In one embodiment the LDPE is a very low density polyethylene
(VLDPE).
[0030] The polyethylene can have a broad molecular weight
distribution, characterized by a polydispersity (Mw/Mn) greater
than 3.5, or a narrow molecular weight distribution, characterized
by a polydispersity (Mw/Mn) in the range of about 1.5 to about 3.5.
Mw is defined as weight average molecular weight, and Mn is defined
as number average molecular weight. They can be a single type of
polyethylene or a blend or mixture of more than one type of
polyethylene. Thus, it may be characterized by either single or
multiple DSC melting points. The polyethylenes can have a density
in the range of 0.865 to 0.930 gram per cubic centimeter (g/cc),
and preferably have a density in the range of 0.9000 to 0.925 g/cc.
They also can have a melt index (MI, I.sub.2) in the range of 0.1
to 50 grams per 10 minutes (g/10 min). Typical catalyst systems,
which can be used to prepare these polyethylenes, are
magnesium/titanium based catalyst systems, which can be exemplified
by the catalyst system described in U.S. Pat. No. 4,302,565
(heterogeneous polyethylenes):vanadium based catalyst systems such
as those described in U.S. Pat. No. 4,508,842 (heterogeneous
polyethylenes) and U.S. Pat. No. 5,332,793; 5,342,907; and
5,410,003 (homogeneous polyethylenes); a chromium based catalyst
system such as that described in U.S. Pat. No. 4,101,445; a
metallocene catalyst system such as that described in U.S. Pat.
Nos. 4,937,299 and 5,317,036 (homogeneous polyethylenes); or other
transition metal catalyst systems. Many of these catalyst systems
are often referred to as Ziegler-Natta catalyst systems or Phillips
catalyst systems. Catalyst systems, which use chromium or
molybdenum oxides on silica-alumina supports, can be included here.
Typical processes for preparing the polyethylenes are also
described in the aforementioned patents. Typical in situ
polyethylene blends and processes and catalyst systems for
providing same are described in U.S. Pat. Nos. 5,371,145 and
5,405,901. The various polyethylenes can include low density
homopolymers of ethylene made by high pressure processes (HP-LDPE),
and high density polyethylene (HDPE) having a density greater than
0.940 g/cc. A conventional high pressure process is described in
Introduction to Polymer Chemistry, Stille, Wiley and Sons, New
York, 1962, pages 149 to 151. The high pressure processes are
typically free radical initiated polymerizations conducted in a
tubular reactor or a stirred autoclave. In the stirred autoclave,
the pressure is in the range of about 10,000 to 30,000 psi (about
69 to about 207 MPa) and the temperature is in the range of about
175.degree. C. to about 250.degree. C., and in the tubular reactor,
the pressure is in the range of about 25,000 to about 45,000 psi
(about 170 to about 310 MPa) and the temperature is in the range of
about 200.degree. C. to about 350.degree. C.
[0031] Commercially available LDPE resins include but are not
limited to DOW Low Density Polyethylene resins available from The
Dow Chemical Company such as DFDB-1258 NT and, in general, any
fractional melt flow index (MFI) resin for use in heavy duty bags
or agricultural films such as those available from Borealis, Basel,
Sabic and others.
[0032] The HDPE/LDPE mixtures or blends of the present invention
may be prepared by any suitable means known in the art such as, for
example, dry blending in a pelletized form in desired proportions
followed by melt blending in an apparatus such as a screw extruder
or a BANBURY.TM. mixer. Dry blended pellets may be directly melt
processed into a final solid state article by, for example,
extrusion or injection molding. The blends may also be made by
direct polymerization. Direct polymerization may use, for example,
one or more catalysts in a single reactor or two or more reactors
in series or parallel and vary at least one of operating
conditions, monomer mixtures and catalyst choice.
[0033] The amount of HDPE in the polyolefin composition, based on
the weight of the composition, is typically at least 45 weight
percent (wt %), more typically at least 55 wt % and even more
typically at least 60 wt %. The amount of HDPE in the polyolefin
composition, based on the weight of the composition, typically does
not exceed 95 wt %, more typically it does not exceed 85 wt % and
even more typically it does not exceed 80 wt %.
[0034] The amount of LDPE in the polyolefin composition, based on
the weight of the composition, is typically at least 4 weight
percent (wt %), more typically at least 14 wt % and even more
typically at least 19 wt %. The amount of LDPE in the polyolefin
composition, based on the weight of the composition, typically does
not exceed 54 wt %, more typically it does not exceed 44 wt % and
even more typically it does not exceed 39 wt %.
[0035] The HDPE component of the blend can comprise two or more
grades of HDPE, and the LDPE component of the blend can comprise
two or more grades of LDPE. The HDPE/LDPE blend typically has an
I.sub.2 of 0.1 to 4 g/10 min, more typically 0.15 to 4 g/10
min.
Nucleator
[0036] Fluororesin Component
[0037] Fluororesin particles, particularly those of less than a
micron in size, tend to agglomerate. Some commercially available
fluororesin powders comprise a high concentration of agglomerates
of at least 5 microns (.mu.m) in size. e.g., diameter. Typically
the size of the agglomerates range from 4 to 50 microns, more
typically from 5 to 20 microns and even more typically from 5 to 15
microns. Typically, the amount of fluororesin agglomerates of at
least 5 .mu.m in size in these powders is at least 80%, more
typically at least 82%, and even more typically at least 85%. These
powders do not disperse well in many polyolefins, e.g., HDPE and/or
LDPE.
[0038] While agglomerated fluororesin particles, i.e.,
agglomerates, as described above can be used in the practice of
this invention, in one embodiment unagglomerated particles are
used. In one embodiment the fluororesin components of the
nucleators used in this invention are unagglomerated particles of
less than a micron in size, or less than 0.5 micron in size, or
less than 0.3 micron in size, which may be commingled with
agglomerates that were either originally submicron in size or were
reduced in size from greater than a micron to less than a micron.
In one embodiment the fluororesin component of the nucleator used
in the practice of the invention comprises less than 10 wt %, or 9
wt %, or 8 wt %, or 7 wt %, or 6 wt %, or 5 wt %, or 4 wt %, or 3
wt %, or 2 wt %, or 1 wt % of agglomerates greater than a micron in
size, but the smaller the amount of such agglomerates, and thus the
greater the amount of submicron particles and submicron
agglomerates, the better the dispersion of the fluororesin in the
polyolefin, and the more evenly distributed are the cell sizes in
the foamed product.
[0039] Agglomerated particles can be separated from one another by
any conventional means, e.g., grinding, mixing or stirring
(typically at a relatively high speed), etc. In one embodiment a
fluororesin comprising agglomerates of one micron or greater,
typically of 3, or 4, or 5 microns or greater, is subjected to any
procedure, treatment, etc. that will reduce the majority,
preferably 60%, 70%, 80%, 90% or more, of the such agglomerates to
either unagglomerated particles of less than a micron in size, or
agglomerates of less than a micron in size before the nucleator is
mixed with the polyolefin.
[0040] In one embodiment the fluororesin component of the nucleator
used in the practice of this invention and comprising agglomerates
of one micron or greater, typically of 3, or 4, or 5 microns or
greater, is first mixed with the polyolefin, with or without the
ADCA component of the nucleator, to form a masterbatch, and then
the masterbatch is subjected to any procedure, treatment, etc. that
will reduce the majority, preferably 60%, 70%, 80%, 90% or more, of
the such agglomerates to either unagglomerated particles of less
than a micron in size, or agglomerates of less than a micron in
size. Typically the masterbatch comprises from 1 to 50, more
typically from 5 to 50 and even more typically from 15 to 30 weight
percent (wt %) fluororesin, and from 50 to 99, more typically from
60 to 95 and even more typically from 70 to 85 wt % polyolefin.
After the masterbatch is subjected to the fluororesin size
reduction procedure, treatment, etc., the masterbatch is mixed with
the ADCA component of the nucleator (if it does not already
comprise that component) and the polyolefin to be foamed under
conditions and for a sufficient period of time to uniformly
disperse the unagglomerated particles and agglomerates within the
polyolefin before the start of the foaming process.
[0041] In one embodiment the fluororesin comprising agglomerates of
one micron or greater, typically of 3, or 4, or 5 microns or
greater, is first mixed with the polyolefin, with or without the
ADCA component of the nucleator, in the amount desired for the
practice of the foaming process, and then the polyolefin is
subjected to any procedure, treatment, etc. for a sufficient amount
of time that will both (1) reduce the majority, preferably 60%,
70%, 80%, 90% or more, of the such agglomerates to either
unagglomerated particles of less than a micron in size, or
agglomerates of less than a micron in size, and (2) substantially
uniformly disperse these unagglomerated particles and reduced
agglomerates within the polyolefin before the foaming process
commences. The ADCA component of the nucleator can be added to the
polyolefin before, simultaneously with, or after the addition of
the fluororesin, and before or after the agglomerates of the
fluororesin are subjected to size reduction.
[0042] The nucleator, preferably PTFE comprising particles and
agglomerates of less than a micron in size, can be added to the
polyolefin composition comprising or consisting essentially of HDPE
and LDPE, by any conventional means. The nucleator can be added
neat, in combination with one or more other additives, e.g.,
antioxidant, cell stabilizer, etc., or as part of a masterbatch.
The nucleator is mixed with the polyolefin composition to achieve
an essentially homogeneous dispersion of nucleator in the
polyolefin composition and to this end, batch mixing, e.g., through
the use of a BUSS.TM. kneader, is typically preferred to mixing in
an extruder. If the nucleator is first mixed with the polyolefin
composition in an extruder, then it is typically added to the
polyolefin composition prior to injection of the gas for
foaming.
[0043] Particle size can be determined by any method known in the
art. In one embodiment, the determination of particle size and
proportion (% by number) of fluororesin powder can be determined as
follows. A dispersion comprising a fluororesin powder obtained by a
dispersing treatment for about 2 minutes under ultrasonication of
about 35-40 kHz and ethanol, wherein the fluororesin powder is
contained in an amount to make a laser permeation (proportion of
output light to incident light) of the dispersion 70-95%, is
subjected to a microtrack particle size analyzer under relative
refraction (determination is done based on the ratio of diffraction
ratio (about 0.99) of fluororesin powder to that of ethanol or
according to the measure of the above-mentioned particle size
analyzer which is the nearest to the ratio (e.g., 1.02)) and flow
type cell measurement mode to determine particle size (D.sub.1,
D.sub.2, D.sub.3 . . . ) of individual particles and the number
(N.sub.1, N.sub.2, N.sub.3 . . . ) of particles having each
particle size based on the optical diffraction of the laser. In
this case, the particle size (D) of individual particles is
automatically measured by the microtrack particle size analyzer
wherein particles having various shapes are measured in terms of
the diameters of the corresponding spheres. Therefore, the
proportion (% by number) of the particle size D.sub.1 is expressed
by the percentage of the number of these particles (N.sub.1) to the
number of the entire particles (EN). The proportion of the
particles having a particle size of 0.1-0.5 .mu.m is expressed by
the percentage of the number of the particles having a particle
size of 0.1-0.5 .mu.m to the total number of the existing particles
(EN). Similarly, the proportion of the particles having a particle
size of not less than 5 .mu.m is expressed by the percentage of the
number of the particles having a particle size of not less than 5
.mu.m to the total number of the existing particles (EN). On the
other hand, the average particle size of the nucleator of the
present invention can be calculated using the total number of
existing particles (EN) and the total of the product of the cube of
the particle size of respective particles and the total number of
existing particles (.SIGMA.ND.sup.3), according to the following
formula
Average Particle Size
(.mu.m)=(.SIGMA.ND.sup.3/.SIGMA.N).sup.1/3
Calculation of particle size is further illustrated in U.S. Pat.
No. 6,121,335. The calculation of agglomerate size is determined in
the same manner as that described above for particle size
determination.
[0044] While the shape of the fluororesin particles and
agglomerates is not particularly limited, it is preferable that the
particles and agglomerates are primarily sphere-like in shape to
produce a foam comprising fine cells and superior in uniform
foaming.
[0045] Fluororesin/ADCA Mixture/Nucleator
[0046] In one embodiment of the invention, the nucleator is a
mixture of a fluororesin, preferably PTFE, and azodicarbonamide
(ADCA). The weight ratio of ADCA to fluororesin is typically from
60/40 to 20/80, more typically from 55/45 to 20/80 and even more
typically from 50/50 to 25/75. The particle size distribution and
morphology, e.g., agglomerated or unagglomerated, of the
fluororesin can vary in this embodiment, but preferably both the
particle size distribution and morphology of the fluororesin is as
described above. The amount of the nucleator of this embodiment,
i.e., fluororesin and ADCA, that is added to the polyolefin
composition is typically from 0.01 to 1 wt %, more typically from
0.05 to 0.6 wt % and even more typically from 0.1 to 0.3 wt % based
on the weight of the polyolefin composition.
[0047] The nucleator can be added to the polyolefin composition by
any conventional means. The nucleator can be added neat, in
combination with one or more other additives, e.g., antioxidant,
cell stabilizer, etc., or as part of a masterbatch. The nucleator
is typically added as a mixture of fluororesin and ADCA, but the
fluororesin and ADCA can be added separately and the mixture formed
in situ within the polyolefin composition. The nucleator is mixed
with the polyolefin composition to achieve an essentially
homogeneous dispersion of nucleator in the polyolefin composition
and to this end, batch mixing, e.g., through the use of a
BUSS.TM.kneader, is typically preferred to mixing in an extruder.
If the nucleator is first mixed with the polyolefin composition in
an extruder, then it is typically added to the polyolefin
composition prior to injection of the gas for foaming.
[0048] Use of the fluororesin/ADCA nucleator produces a higher
performance product as compared to a product produced using a
fluororesin, particularly PTFE, alone as the nucleator. The
products exhibit enhanced properties in terms of expansion ratio,
cell size and cell size uniformity as well as surface smoothness.
In this hybrid nucleating agent, the fluororesin is the "passive"
nucleating agent and azodicarbonamide is the "active" nucleating
agent. The synergic effect between these two nucleating agents
results in a higher nuclei density and a foamed product with
smaller cell size as compared to processes using and products
produced by the use of neat PTFE or neat ADCA alone as the
nucleating agent.
Additives
[0049] The polyolefin composition used in this invention may
contain one or more additives as necessary or desired.
Representative additives include but are not limited to, processing
aids, lubricants, stabilizers (antioxidants), foaming aids,
nucleating agents, surfactants, flow aids, viscosity control
agents, coloring agents, copper inhibitors and the like. These
additives can be added to the polymer(s) either before or during
processing. The amount of any particular additive in the polyolefin
composition is typically from 0.01 to 1 wt %, more typically from
0.01 to 0.5 wt % and even more typically from 0.01 to 0.3 wt %, and
the total amount of additives in the polyolefin composition, if
present at all, is typically from 0.01 to 5 wt %, more typically
from 0.01 to 2 wt % and even more typically from 0.01 to 1 wt
%.
Foaming Agent
[0050] The foaming agent is one or more suitable for the extrusion
temperature, foaming conditions, foam forming method and the like.
When an insulating foam layer in the final form is to be formed
simultaneously with extrusion forming, for example, an inert gas
such as nitrogen, a carbon gas (e.g., CO, CO.sub.2, etc.), helium,
argon and the like, hydrocarbon such as methane, propane, butane,
pentane and the like, halogenated hydrocarbons such as
dichlorodifluoromethane, dichloromonofluoromethane,
monochlorodifluoromethane, trichloromonofluoromethane,
monochloropentafluoroethane, trichlorotrifluoroethane and the like
are used. The amount of the foaming agent to be used can vary.
Typically, it is 0.001-0.1 part by weight, more typically
0.005-0.05 part by weight, per 100 parts by weight of the
polyolefin composition to be foamed. The foaming agent may be mixed
with an organic polymer to be foamed in advance or may be supplied
into an extruder from a foaming agent supply opening formed on the
barrel of the extruder.
Foaming Process
[0051] The polyolefin composition of this invention is foamed using
known methods and known equipment. Typically, a foam is produced by
extruding the polyolefin composition containing a nucleator using
an extruder operated under foaming extrusion conditions, e.g.,
injection of a foaming agent while the composition is in a high
pressure zone and then extruding the composition to a low pressure
zone. Foaming process are further described by C. P. Park in
Polyolefin Foam, Chapter 9, Handbook of Polymer Foams and
Technology, edited by D. Klempner and K. C. Frisch, Hanser
Publishers (1991).
[0052] The polyolefin composition of this invention is foamed using
known methods and known equipment. Typically, a foam is produced by
extruding the polyolefin composition containing a nucleator using
an extruder operated under foaming extrusion conditions, e.g.,
injection of a foaming agent while the composition is in a high
pressure zone and then extruding the composition to a low pressure
zone. Foaming process are further described by C. P. Park in
Polyolefin Foam, Chapter 9. Handbook of Polymer Foams and
Technology, edited by D. Klempner and K. C. Frisch, Hanser
Publishers (1991).
[0053] In one embodiment, a typical extrusion foaming process uses
an atmospheric gas (e.g., CO.sub.2) to produce a foamed cable
insulation as described in CA 2 523 861 C, Low Loss Foam
Composition and Cable Having Low Loss Foam Layer. Dissolution of
the foaming gas into the polymer melt is governed by Henry's law as
reported for example in the work of H. Zhang (below) and others.
Solubility is a function of the saturation pressure and the Henry's
law constant, which itself is a function of temperature. /Zhang
Hongtao 201011 MASc thesis.pdf. Also see Foam Extrusion: Principles
and Practice by Shau-Tarng Lee, editor. The MuCell.RTM.
microcellular foam injection molding technology is an example of a
commercially practiced foaming process, and it is described
generally in U.S. Pat. No. 6,284,810.
[0054] Given the above on the importance of adequate pressure
control during foaming extrusion, a suitable process would be the
one commercially referred to as the MuCell process, in which
adequate pressures are built via specific hardware design, for
effective nucleation as reported in U.S. Pat. No. 684,810B1. The
method disclosed in this publication relies solely on high pressure
drops (dP/dt) for self-nucleation of the foaming gas in the absence
of an "auxiliary nucleating agent" (Col. 4, line 25-30).
Embodiments of the Invention
[0055] In one embodiment the polyolefin composition comprises at
least two polyolefins.
[0056] In one embodiment the polyolefin composition comprises two
polyolefin.
[0057] In one embodiment the polyolefins of the polyolefin
composition are an HDPE and a LDPE.
[0058] In one embodiment the polyolefin composition includes at
least one nucleator.
[0059] In one embodiment the polyolefin composition includes at
least one of an antioxidant and a cell stabilizer.
[0060] In one embodiment the polyolefin composition comprises HDPE,
LDPE and a nucleator of PTFE and ADCA.
Specific Embodiments
[0061] The following experiments are provided to illustrate various
embodiments of the invention. They are not intended to limit the
invention as otherwise described and claimed. All numerical values
are approximate.
Examples 1-5 and Comparative Examples 1-2
[0062] Materials
[0063] LDPE-1 is a low density polyethylene (LDPE) with an MI of
2.35 g/10 min (ASTM D-1238. (190.degree. C./2.16 kg)) and a density
of 0.92 g/cc (ASTM D-792).
[0064] PTFE is ZONYL.TM. MP 1400, a white, free-flowing PTFE with
an average particle size of 10 .mu.m and available from DuPont.
[0065] LDPE-2 is DFDB-1258 NT, a low density polyethylene (LDPE)
with an MI of 6 g/10 min (ASTM D-1238, (190.degree. C./2.16 kg))
and a density of 0.922 g/cc (ASTM D-792) available from The Dow
Chemical Company.
[0066] HDPE is DGDA-6944 NT, a high density polyethylene (HDPE)
with an MI of 8 g/10 min (ASTM D-1238, (190.degree. C./2.16 kg))
and a density of 0.965 g/cc (ASTM D-792) available from The Dow
Chemical Company.
[0067] MB-1 is 10 wt % ADCA in LDPE-1.
[0068] MB-2 is 10 wt % PTFE in LDPE-1 with an MI of 2.35 g/10 min
(ASTM D-1238, (190.degree. C./2.16 kg)) and a density of 0.920 g/cc
(ASTM D-792).
[0069] Preparation of Nucleator Masterbatch
[0070] The preparation of a nucleating agent masterbatch is
conducted on single-screw extruder at a temperature of 140.degree.
C. Prior to extrusion, MB-1 and MB-2 are dry blended. The ratio of
MB-1 to MB-2 is adjusted from 60/40 to 20/80.
[0071] Foaming Process
[0072] The physical foaming experiment is conducted on a
single-screw extruder with gas injection system. The screw diameter
is 50 millimeters (mm) with a length to diameter (L/D) ratio of 40.
The gas injection point is located at the middle of screw with
CO.sub.2 as the blowing agent. The temperature profile is
140/175/180(gas injection)/170/145(static mixer)/143(die). HDPE,
LDPE-2 and nucleating agents MB-1 and MB-2 are dry blended first
then fed on the upstream of the extruder. The foamed product is
obtained in the shape of a rod. In one embodiment MB-1 and MB-2 are
compounded into a hybrid nucleating agent MB, and the MB is then
dry blended prior to being fed into the foaming extruder. In one
embodiment HDPE, LDPE-2 and nucleating agents MB- and MB-2 are
compounded into an "all in one" formulation then foamed in the gas
injected extruder.
[0073] Characterization of Extruded Foam Rod
[0074] Expansion Ratio
[0075] The expansion ratio is calculated based on the density of
sample before and after foaming. The density of the foamed article
and solid plaque are measured according to ASTM D792.
Expansionratio=(1-.rho..sub.foam.rho..sub.solid)*100%
[0076] Average Cell Size
[0077] The foamed sample is fractured utilizing liquid nitrogen and
then slices are cut out using a razor blade. The slices are coated
with platinum using an EMITECH.TM. K575X coater before scanning
electron microscopy (SEM) analysis. The SEM images are acquired on
a FEI Nova NanoSEM 630 SEM by Everhart-Thornley detector (ETD) and
Through Lens Detector (TLD) at an accelerating voltage of 5 kV,
working distance around 6.5 mm and spot size of 5. The average cell
size is obtained through the analysis of the SEM photographs.
[0078] The cell density of the foamed article can be calculated by
the following Equation:
N f = ( n c M c 2 A c ) 3 / 2 ##EQU00001##
N.sub.f represents cell number per cubic centimeter volume in the
foamed article, n.sub.c is the cell number in the view area of SEM
picture. A.sub.c is the area of SEM picture, and M.sub.c is the
magnification.
[0079] D, which is the average the cell size, can be calculated by
the following Equation:
D = ( 6 V t 2 .pi. Nf ) 1 / 3 ##EQU00002##
Where, V.sub.t represents that expansion ratio of foamed
article.
[0080] DF measurements: Dissipation Factor measurement is conducted
on a High Frequency Split Post Dielectric Resonator at a frequency
of 2.47 GHz on 50 mil compression molded plaques. Before
measurements, the plaques are conditioned for 24 hours at room
temperature in a desiccant chamber.
[0081] The results are reported in Table 1.
TABLE-US-00001 TABLE 1 Foaming Performance of Hybrid Nucleating
Agents CE1 CE2 IE1 IE2 IE3 IE4 IE5 HDPE 70 70 70 70 70 70 70 LDPE-2
28.5 28.5 28.5 28.5 28.5 28.5 28.5 MB-1 1.5 0.9 0.8 0.6 0.4 0.3
MB-2 1.5 0.6 0.7 0.9 1.1 1.2 Total 100 100 100 100 100 100 100
Porosity, % 77.1 80.8 83.6 81.3 78.4 79.3 78.4 Cell size, mm
0.35-0.55 0.25-0.45 0.27-0.65 0.25-0.45 0.30-0.40 0.30-0.45
0.35-0.46 Avg. cell size, um 0.478 0.392 0.423 0.383 0.343 0.364
0.407 DF of bulk 1.0160E-04 1.0020E-04 1.0590E-04 N/A 9.9350E-05
N/A 1.0178E-04 (unexpanded)
[0082] The results of Table 1 show that the addition of ADCA led to
a better foaming than PTFE (MP1400) alone. In the hybrid system,
the obvious synergy effect between PTFE and ADCA on foaming
performance is found when the ADCA/PTFE ratio varied from 60/40 to
20/80, with a preferred ratio range from 55/45 to 20/80, and an
even more preferred range from 50/50 to 25/75. When the ratio of
ADCA is higher than 60% in the hybrid nucleating agent, no synergy
effect is observed.
* * * * *