Note: Descriptions are shown in the official language in which they were submitted.
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TITLE
Stabilized Ethylene/Tetrafluoroethylene
Copolymers
- FIELD OF THE INVENTION
This invention relates to an
ethylene-tetrafluoroethylene copolymer which is
stabilized against thermal deqradation, and more
particularly to an ethylene~tetrafluoroethylene
copolymer which is stabilized against thermal
degradation by addition of CuI or CuCl.
BACKGROUND OF THE INVENTION
Ethylene-tetrafluoroethylene copolymers have
good thermal, chemical, electrical and mechanical
properties and are melt-processible. These
copolymers are known to be heat-resistant
thermoplastic resins which have a melting point of
260 to 300C. ~owev~r, the copolymers thermally
deteriorate and become colored, brittle and foamed
when heated to a temperature higher than the melting
point for a long period of time. Accordingly, it is
desirable to prevent the thermal deterioration of
ethylene-tetrafluoroethylene copolymers during the
conventional operation of injectlon molding and
extrusion molding processes.
U.S. Patent ~,110,30~ discloses that a
copper compound, such as metallic copper, cupric
oxide or cuprous oxide, cupric nitrate, cupric
chloride or copper alloys, stabilize the copolymers
against degradation at elevated temperatures.
SUM~ARY OF THE INVENTION
It has now been found that cuprous chloride
or cuprous iodide provide better protection to
ethylene-tetrafluoroethylene copolymers (E/TFE
copolymers hereinafter~ against thermal degradation
than the metallic copper or cupric oxides disclosed
AD5155
~ l7~ 57 ~
in U.S. Patent 4,110,308, and therefore can be
employed at lower concentrations, thus avoiding
detrimental pigmentation and the like.
- Addition o cuprous chloride or iodide to an
E/TFE copolymer allows the copolymer to be exposed to
very high temperatures in air without rapid loss in
weight, molecular weight deterioration, color or
bubble generation. Such protection greatly improves
E~TFE copolymers utility for such applications as
rotomolding, surface coating, molding, and wire
insulation, where high temperatures are involved in
manufacture and/or use.
For example, in rotomolding the E/TFE powder
is subjected to temperatures well above the melting
15 point for up to an hour with oxygen generally
present. Under such conditions, untreated E/TFE
powders turn brown, foam, and become exceedingly
brittle because of molecular weight reduction. The
addition of small amounts of cuprous chloride or
20 iodide prevents such degradation.
DESCRIPTION
The ethylene-tetrafluoroethylene copolymers
used in the invention can be prepared by various
well-known polymerization methods such as emulsion
25 polymerization in an aqueous medium or suspension
polymerization. The ratio of ethylene to
tetrafluoroethyle~e units can be conventionally
varied and it i~ possible to combine a small amount
(e.g., up to 20 mole percent) of a copolymerizable
30 ethylenically unsaturated comonomer of 3-12 carbon
atoms~ such 2s propylene, isobutylene, vinyl
fluoride, hexafluoropropylene,
chlorotrifluoroethylene, acrylic acid, alkyl esters
thereof, chloroethyl vinyl ether, perfluoroalkyl
` ` ' 11'~.~.5~
perfluorovinyl ethers, hexafluoroacetone,
perfluorobutyl ethylene, and the like. The ratio of
ethylene to tetra1uoroethylene units in the
- copolymer may vary over wide limits. For example,
the mole ratio of tetrafluoroethylene to ethylene
units may be from 40/60-70/30, and preferably from
about 45/55-60/40.
The cuprous chloride or iodide provides
outstanding oxidation inhibition for E/TFE resins
over the concentration range of 0.05 to 500ppm,
preferably 5-50ppm, as copper. The protection is the
same through this range whether at Sppm or 50ppm.
Copper in other forms is not as potent at lower
concentrations; for example, Cu powder, Cu2O, and
CuO all provide protection but become effective only
at higher concentrations of 50ppm or more. There are
important advantages gained at the lower
~oncentrations: (1) pismentation by the additive is
minimized, (2) conversion of the halide to black
20 ~upric oxide at high temperatures is not as
noticeable, (3) problems such as surface roughening,
haziness, and electrical flaws are avoided.
E/TFE resins stabilized with CuI or CuCl can
be heated in air above their melting point and
25 maintained there for 2 hours and more without
significant losses in molecular weight (toughness) or
color.
Another advantage of using the halides~ and
particularly CuI, is their ability to greatly
30 stabilize E/TFE melts during processing; thereby
allowing greater holdup times without losses in
end-product molecular weight.
Inclusion of the cuprous halides in E/rFE
resins also improves stress cracking resistance in
a.~t~6
high temperature applications. Color degradation is
also slowed remarkably. For example, 5ppm CuI
retains 90 percent of its initial room temperature
- elongation after 215 hours of aging at 230C, whereas
5 a control tno Cu) lasts for only 27 hours, and a
sample containing 50ppm Cu metal powder lasts just 70
hours. Use of cuprous chloride or iodide in E/TFE
finished articles provides good prote~tion agains
thermally induced cracking for up to 400 hours of
10 aging at 230C. Better protection shouid be expected
at lower temperatures.
It is preferable to optimize the particle
size, the specific surface area, and the particle
distribution of the cuprous halide in accordance with
15 the desired properties of the copolymer composition.
For example, it is preferable to use a cuprous halide
having a relatively small average particle diameter,
usually less than 100 micron and preferably about
1-50 micron. It is also preferable to have a sharp
20 particle distribution.
Various methods can be employed for blending
the cuprous halide with the E/TFE. Eor example~
commercially available CuI or CuCl powder can be
blended with the copolymer in a mixer. An aqueous
25 slurry or organic solvent slurry of
ethylene-tetrafluoroethylene copolymer and CuI or
CuCl can also be prepared.
EXAMPLES
In the Examples, the E/TFE copolymer
30 designated E/TFE-I was a copolymer of
ethylene/tetrafluoroethylene/hexafluoroacetone
(21.3/72.9/5.8 wt percent) having a melt viscosity of
18 X 10 poise and a melting point of 262C. The
copolymer was in the form of a partially compacted
35 friable powder.
~'7~1.Ss7~
The E/TFE copolymer designated E/TE~E-II was
a copolymer of ethylene~tetrafluoroethylene/per-
fluorobutyl ethylene (18.9/79.35/1.75) having a melt
viscosity of 5.85 X 104 poise, in powder form.
EXAMPLE 1 AND COMPARISONS
The following powdered additiYes were
employed:
~1) cuprous iodide, CuI
(2) copper metal
(3) cupric oxide, CuO
(4) ~-A12O3
(5) ZnO
(6) CuI/KI mixture adsorbed on ~-A12O3
(7) cupric nitrate adsorbed on ~-A12O3
(8) CuI/KI mixture
The different powdered additives were added
to E/TFE-I powder in a blender along with enough
trifluoro-1,1,2-tri~chloroethane (F-113) solvent to
produce a fluid slurry. After mixing at high speed
20 for 1 minute, the slurry was poured into a pan ~nd
the F-113 was allowed to evaporate. The resultan~
powder cake was then dried for 1 hour under vacuum a~
120C.
Evaluations - Two grams of each mixture were
?S weighed onto a watch glass and all the mixtures
prepared were heated together at 300C for two hours
in an oven using constantly circulating air. At
300C, the E/TFE-I powder is well above its melting
point of 262C. The cooled mixtures were examined
30 for signs of degradation such as color generation,
foaming, and cracking.
Results - The results are tabulated below in
order of good to bad performance:
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These results show cuprous iodide
(Example 13 give outstanding protection against
oxidation. Its performance is much better than that
~ for any of the other tested additives (Comparisons
5 A-~). Based on the visual observations, CuI,
CuI/KI/~12O3, Cu(NO3)2 adsorbed on
~-A1~03 in unwashed form, and copper metal powder
rendered some protection, but CuO, Cu(NO3)2
adsorbed on ~ ~12O3 in washed form, ~A12O3,
ZnO, and CuI/KI actually accelerated E/TFE-I
degradation.
~ EXAMPLE 2
Experimental - E/TFE~I powder samples were
prepared in the same way described in Example 1.
15 Samples containing CuI, CuCl, CuBr, Cu, Cu2O, CuO,
at 5, 50, 500, and 1000ppm as copper were studied.
Other additives tested were CuC12.2H2O and
CuBr2 at 5, 50, and 500 ppm as copper plus
CuF2.2H2O as 50ppm coppex mixed with 749ppm XI,
20 1000 and 300ppm ~-A12O3, 100 ppm of
Cu(NO3)2fi~-A12O3 mixtures both washed ~nd
unwashed, and 1000ppm of CuI~KI/~-A12O3 mixtures
both washed and unwashed.
The additive particle size distributions
25 were measured using the Sedigraph and Coulter Counter
techniques. The average particle size in microns for
each additive type follows: Cu metal powder, 42 ;
Cu2O, 13 ; CuO, 7 ; CuI, 19.7 ; CuC12 2H2O,
14.6 ; ~-A1~03, 11.4 .
Each sample, in the amount of 2 grams, was
placed on a watch glass, weighed, and then subjected
to two hours of heat aging at 300C in circulating
air.. Once cooled, each sample was photographed and
then weighed to determine the amount of any weight
as7~
loss. The samples, as a group, were then subjected
to another 2 hour aging in the 300C oven, cooled,
photographed, and weighed again. This procedure was
repeated six times giving the samples 12 hours of
exposure time in the 300C oven.
Results - Wide differences in sta~iLity were
evident after the first two hour exposure. The
control resln with no additives turned dark brown and
foamed excessively. Of those samples containing 5ppm
copperr the CuI and CuCl ones exhibited no color
change or foaming. The CuC12~2H~O sample
displayed no foaming but incurred slight yellowing
and some weight lossO Of the remaining samples, CuBr
prevented foaming but allowed some yellowing, while
15 Cu metal, Cu2O, CuO, and CuBr2 allowed some
foaming and considerable color development.
At 50ppm copper, all the additives except
Cu2O, CuO, CuF2.2H2O and Cu metal prevented
both color and bubble formation. At 500 and lOOOppm,
20 all the additives gave good protection.
The CuI sa~ples containing 500 and lOOOppm
copper turned grey and black, respectively, after the
first two hour aging~ The darkening is due not to
degradation of the polymer, but is instead the result
25 of cupric oxide (black) formation. These samples did
not darken further with continued oven exposures.
Evidence for CuO formation was also seen in the CuCl,
CuBr, and Cu~O samples. Vf these, the CuI was the
most reactive toward oxygen.
The weight loss with time for the various
samples is tabulated in Table 1.
At 5ppm copper, Table 1 shows a wide range
of additive effectiveness with CuI being the most
powerful inhibitor followed in order of decreasing
76
activity by CuCl, CuC12.2H2Or CuBr, Cu2O,
CuBr2 and CuO. The CuI and CuCl compounds are by
far the most effective additives: (1) they protect
the longest against color forma~ion t4 6 hours), (2)
5 prevent foaming up to 6 hours for CuI and 4 hours for
CuCl, (3) maintain the initial low rate of weight
loss the longest and (4) give the lowest ultimate (12
hours) weight loss.
At 50ppm, the order of effectiveness remains
10 essentially the same. Here the sample containing
copper metal gives the least protection. The overall
order of effectiveness from best to poorest:
CuI CuCl, CuBr CuC12.2H2O, Cu2O CuBr2, CuO,
and Cu metal.
At 500ppm, all the additives showed some
effectiveness. However, at this loading, many of the
additives pigment the resin. This pigmentation is
undesirable in many applications. The CuO turns the
resin geey, the CuI tan, and the Cu2O pink. From
20 the pigmentation standpoint, CuCl lends the least
- color with the maximum protection and does not
! J
blacken to CuO nearly as much as the CuI. Of all the
additives, copper metal pigments least but does not
render ade~uate protection for the E/TFE-I.
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13
EXAMPLE 3
Expe imental - E/TFE-I samples were the same
ones used in Example 2. Stabilized E/TFE-II samples
were prepared the same way as the E~TFE-I samples
tsee Example 1), but several changes were made from
the Example 1 procedure: (1) the powder samples were
weighed directly into heat-cleaned (300C for 2
hours) aluminum weighing dishes rather than into
watch glasses, in order to allow easy removal of the
polymer discs after heat aging; (2) a larger sample
(S.5 grams) was used to supply enough polymer for MV
measurements; and (2) the samples were photographed
a~ainst a white b.~ckground in order to better compare
color changes and differences.
Each sample was weighed into its aluminum
dish usin~ a gravimetric balance. All the samples
were heat aged together in an air circulation oven
set at 300~C. After aging, the samples were again
weighed to determine the degree of weight loss. Each
sample was then separated from the aluminum dish,
photographed with the other samp]es.
Results - The weight loss results are
tabulated in Tables 2 and 3.
The weight loss results for both E/TFE-I and
E/TFE-II are largely parallel. A concentration
dependence is evident for the Cu, Cu2O and CuO
additives, whereas CuI and CuCl show no concentration
dependence over the wide range of 5 to 500ppm
30 copper. More important, the CuI and CuCl are far
more potent stabilizers than copper or its oxides at
low concentrations.
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16
EXAMPLE 4
Experimental - CuI or CuCl was blended with
E,'TFE-I or II powder by tumble blending for 1 hour.
- The blends were then extruded through a 28mm twin
screw extruder.
The extruded samples were compression molded
(at 300C) into 4" X 4" ~ 0.010" films. These films
were cut into 2" X 4" halves, and one half were
subjected to thermal agin~ in air at 230C for a
10 specif ied time. The other half were not aged and
served as a control. A new film sample was molded
for each aging cycle. The unaged and aged samples
were measured for color, degree of oxidation by
absorption in the 1755 cm 1 region (carbonyl
region), and percent elongation at both room
temperature and 200C.
The E/TFE-I sampies extruded were ones
containing: a control ~no additive), 5ppm Cu as CuI,
50ppm Cu as CuI, 500ppm Cu as CuI, 5ppm Cu as CuCl,
20 50ppm Cu as CuCl, 50ppm Cu metal powder, 50ppm Cu as
Cu2O. The E/TFE-II samples extruded were ones
containing: 0.25ppm Cu as CuI, 5ppm Cu as CuI, 5ppm
Cu as Cu2O, and 50ppm Cu as Cu2O. The E/TFE-II
powder served as a control.
Results - are shown in Table 4.
: 16
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