Note: Descriptions are shown in the official language in which they were submitted.
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POLYMERIC COMPOSITION USEFUL FOR HOT WATER PIPE SERVICE
Background of the I_vention
Field of the Invention
The present invention relates to a polymeric composition which
has particular utility for hot water pipe service. In particular, the
present invention relates to a polymeric composition comprising a
butene-l homopolymer and a particular group of additive components.
Description of the Prior Art
Since its introduction in the United States in the early
1970's, the major market for butene-l polymers has been in hot water
extruded pipe applications. For the most part, these prior art butene-l
polymer compositions comprised a butene-l polymer along with various
standard antioxidants. In these plumbing applications, the flexibility
of the butene-l polymers, its good creep resistance over a wide range of
temperatures and high hydrostatic design stress rating were very useful
properties. However, one drawback of the prior art polybutylene plumb-
ing resins is the deactivation of stabilizer due to hot water aging,
leading to partial loss of stability. Especially for more demanding
applications such as district heating where the pipes are continuously
exposed to hot (80C) water, improvements were required in the prior art
plumbing grade resins. The present invention deals with a combination
of ingredients in a butene-l polymer composition that is a significant
improvement in the art.
Summary of the Invention
The present invention relates to a butene-l homopolymer
composition having particular utility in hot water pipe service. In
particular, the present invention comprises a polymeric composition
consisting essentially o~ an intimate blend ot:
a) about 93 to about 98 percent by weight o-f an isotactic butene-l
homopolymer;
if~4.~3~3'~
,
b) about 0.05 to about n.s percent by weiyht Gf
1,3,5-Tris(4-tert-butyl-3-hydroxy-2,6-dimethyl-benzyl)-1,3,5-triaz-
ine-2,4,6-(lH,3H,5H)-trione antioxidant;
c) about 0.2 tn about 0.7 percent by weight of lamyl-stearyl thio-
dipropionate;
d) about 0.02 to about 0.6 percent by weight of a nucleating agent;
e) about 0.5 to about 3.0 percent by weight of filler component
comprising a mineral filler coated with an acid acceptor; and
f) zero to about 3.0 percent by weight pigment.
While each of the ingredients (a) through (e) are significant
in achieving the overall balance of excellent properties, it is
important to note that the invention is directed to a combination of
ingredients. This combination of ingredients could not have been
synthesized by just picking and choosing, for example, the best anti-
oxidant and the best nucleant, etc. A significant aspect of the present
invention is how the various ingredients work together, therein result-
ing in a superior product. The butene-l homopolymer, of course, is
important in providing good creep resistance over a wide range of
temperatures and high hydrostatic design stress rating which is based on
high hoop stress. The sterically hindered phenolic antioxidant provides
oxidative stability. The lauryl-stearyl thiodipropionate is a co-
stabilizer and acts as a hydroperoxide decomposer. While this is
normally used as a processing stabilizer, it has been found here that in
combination with the particular antioxidant claimed, a significant
effect on long term s-tability is obtained. The nucleating agent results
in faster pipe extrusion speed and an overall improvement in pipe
properties. Further, the presence of a high density polyethylene
nucleant in the formulation results in higher elongation and break
strength in the machine direction.
The resulting overall polymeric composition has an excellent,
superior balance of properties not available in prior art formulations.
38'3'7
-- 3 --
Of most significance, the formulations of the present invention
possess an estimated long term stability in hot water (95C)
service which is considerably improved over that for prior art
formulations.
Detailed Description of the Invention
The butene-l homopolymer employed herein is an iso-
tactic butene-l homopolymer. The polymers used herein are
suitably crystallizable thermoplastic butene-l polymers with
number average molecular weights above 15,000, preferably above
20,000 and an isotactic content above 85%, preferably above 90%,
and more preferably above 95%, determined as the diethyl ether-
insoluble component. Suitable isotactic butene-l polymers are
commercially available and methods for their preparation are
well known in the art, as shown in, for example, United States
Patent 3,362,940. Illustrative of butene-l polymers suitable
for use in the present invention (if the above requirements are
met) are those known in the industry as pipe grades. Especial-
ly preferred are Shell butene-l homopolymer.
The antioxidant employed herein is a sterically hin-
dered phenolic antioxidant. Such antioxidants are disclosedin United States Patents Nos. 3,285,855 and 3,644,482. Pre-
ferred antioxidants are HOSTANOX ~ 03, available from American
Hoechst Corp. and Cyanox ~ 1790, available from American
Cyanamide Corp.
HOSTANOX ~ 03 is bis[3,3-bis(4'hydroxy-3'tert.butyl-
phenyl)-butanoic acid]-glycolester and has the structure:
(CH3)3c
3 2 COo CH2
(CH3)3C _ ~ ~ 2
3~'7
Cyanox ~ 1790 is 1,3,5-Tris(4-tert-butyl)-3-hydroxy-
2,6-dimethylbenzyl)-1,3,5-triazine-2,4,6-(lH,3H,5H)-trione.
Lauryl-stearyl thiodipropionate has the structure
O O
,. ..
H37cl8o-c-cH2cH2-s-cH2cH2-c-ocl2H25
Another necessary component of the present invention
is a nucleating agent. Nucleating agents contemplated in this
invention include by way of example:
high density polyethylene;
graphitic non-turbostatic carbon;
fatty acid amides;
anthraquinones;
and amides;
Other nucleating agents are also contemplated for use in this
invention. GraphitiC non-turbostatic carbon nucleating agents
are disclosed in United States Patent 4,321,334. Fatty acid
amide nucleating agents are disclosed in United States Patent
4,322,503 and include specifically N,N'-ethylene-bis-stearamide
and stearamide. Anthraquinone nucleating agents include speci-
fically 1,2-dihydroxy-9,10-anthraquinone; 1,4-dihydroxy-9,10-
anthraquinone; 1,5-dihydroxy-9,10-anthraquinone; 12,5,8-
tetrahydroxy-9,10-anthraquinone; 9,10-anthraquinone; and
sodium 2-anthraquinone sulfonate. Amide nucleating agents are
disclosed in United States Patent 4,320,209 and include speci-
fically l-naphthalene acetamide; N-stearoyl-p-aminophenol;
mercapto-N-2-naphthylacetamide; malonamide; nicotinamide;
isonicotinamide; benzamide; phthalimide; salicylamide;
anthranilamide; and 1,8-naphthalimide.
A much preferred nucleating agent is high density
polyethylene. The high density polyethylene employed in the
composition of this invention is characterized by a density
1;~4.~3~
above about 0.93 g/cc and preferably at least about 0.95 g/cc.
An HDPE with a melt index of from about 0.1 to 20, as measured
by ASTM D1238, Condition E, is typically employed; HDPE of
higher melt index may al~o be suitable. The melt index and
molecular weight of HDPE are inversely related; the corresponding
molecular weight for a polymer with a given melt index may be
readily determined by routine experimentation. A particularly
suitable HDPE, for example has a melt index of 0.45 g/10 min.,
a weight average molecular weight of about 166,000 and a density
of 0.950 grams/cm3. A high density polyethylene with a vis-
cosity at mixing temperatures approximating that of the butene-
l-homopolymer facilities intimate mixing in conventional
extrusion compounding equipment. A wide variety of suitable
high density polyethylenes are commercially available and methods
for their preparation are well known in the art. They may be
prepared by polymerization processes employing Ziegler type
coordination catalysts or supported chromium oxide catalysts.
Commercially available HDPE of either type is suitable. "HDPE"
refers to high density polyethylene of the type described. As
shown in the examples, the HDPE significantly increases the
pipe extrusion speed. Also, as shown in the Illustrative
Embodiments, the HDPE unexpectedly increases the elongation
(MD) of the composition.
The filler component employed in this invention is a
coated mineral filler, in particular a magnesium silicate coated
with an acid acceptor. The preferred magnesium silicate is talc
which is described in Kirk-Othmer, "Encyclopedia of Chemical
Technology", Second Edition, Volume 19, page 608 et seq. The
acid acceptors which are coated on the mineral filler are pre-
ferably stearates of weak bases, such as alkaline earth metalstearates. A preferred acid acceptor is zinc stearate.
'.'3~'7
Accordingly, the preferred filler component is zinc stearate coated
talc. Such materials are well known, con~nercially available fillers.
In addition to adding certain strenyth properties to the
composition of the invention, the particular fillers employed herein
also unexpectedly improve the long term stability of the blends.
Pigments are added as desired to achieve a particular color
for the resin. Iypical pigments include carbon blacks, ti-tanium
dioxide, and iron oxide.
The relative amounts of each of the various ingredients in the
polymeric composition of the present invention, are listed below in
percent by weight (the total for a particular composition adding up, of
course, to 100 percent):
PreferredMore Preferred
Butene-1 homopolymer 93 to 9~ 95 to 97
Antioxidant 0.05 to 0.5 0.1 to 0.3
Costabilizer 0.2 to 0.7 0.3 to 0.5
Nucleating Agent 0.02 to 0.60.025 to 0.5
Filler 0.5 to 3.0 1.0 to 2.0
Pigment 0 to 3.0 1.0 to 2.0
The relative amounts of these various ingredients are
important in achie~ing the overall balance of superior properties. For
example, it has been shown that if too much stabilizer is added some of
the stabilizer will bloom to the surface. If desired, various other
ingredients such as conventional fillers, thermal and ultraviolet
stabilizers, processing agents, tracer compounds and/or other additives
may be incorporated into the polymer composition so long as their
addition does not significantly effect the properties of the present
composition. In this event, it is understood that these other materials
are excluded when calculating the added concentration of tne various
ingredients of this invention.
~ 3~7
In a preferred embodiment, the various ingredients are
blended or intimately mixed in an intensive mixing device such
as a twin-screw extruder or a Banbury-type mixer. The resulting
blends have particular utility as extruded pipe for hot water
service in view of the long-term stability of such resins in
hot water.
The invention is further illustrated by reference to
the following Illustrative Embodiments, which are given for the
purpose of illustration only and are not meant to limit the
invention to the particular reactants and conditions employed
therein.
llustrative Embodiment I
In Illustrative Embodiment I, twelve different formu-
lations were examined. The various ingredients employed in
the five formulations were:
lZ ~89 ~
-- 8
Ingredient Trade Name Description
utene-l homopolymer Shell* polybutylene Pipe grade, butene-l
homopolymer with
melt index of 0.4
dg/min and number
average molecular
weight of 73,000
hindered phenolic HOSTANOX (~)03 See earlier des-
antioxidant cription
hindered phenolic IRGANOX (~1010 (3',5'-di-tert-butyl-
antioxidant 4'-hydroxyphenyl)
propionate methane
or tetrakis (methy-
lene (3,5-di-tert-
butyl-4-hydroxy-
hydrocinnamate)
methane
hindered phenolic CYANOX (~)1790 1,3,5-Tris(4-tert-
antioxidant butyl-3-hydroxy-2,6-
dimethylbenzyl)-
1,3,5-triazine-2,4,6-
(lH,3H,5H)-trione
hindered phenolic NAUGARD (~)XL-l 2,2'-oxamidobis-
antioxidant [ethyl 3-(3.5-di-
tert-butyl-4-hydroxy-
phenyl) propionate]
Costabilizer CYANOX(~)1212 1 amyl-stearyl di-
thiopropionate
Costabilizer SEENOX 412S Pentaerythritol
tetrakis (~-lauryl
thiopropionate)
Costabilizer HOSTANOX SE-10 Dioctadecyl disul-
phide
*
HDPE DUPGnt 7815 High density poly--
ethylene
Filler ComponentMistron ZSC Zinc stearate coated
talc
Other ingredients employed in the formulations were standard
carbon blacks, TiO2 and tracer compounds.
The various ingredients were prepared by first master-
batching the ingredients in a Banbury-type mixer. Then the
masterbatch was let down with the remaining butene homopolymer
in an extruder at about 200C. The formulations are presented
below in Table 1 (relative amounts are expressed in weight per-
cent):
*Trade mark
38'3'7
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-- 10 --
Each of the four hindered phenolic antioxidants
(Cyanox 1790, Hostanox 03, Irganox 1010 and Naugard XL-l) was
used in combination with one of the three co-stabilizers (Cyanox
1212, Seenox 412S and Hostanox SE-10). The same gray pigment
system was used in all the twelve formulations. The resins were
compounded in a Brabender mixing head at 175C at 60 RPM for
five minutes under nitrogen purge in order to avoid oxidative
degradation. Each resin was then compression-molded into 60
mil thick plaque. After transformation in at least 7 days to
the stable hexagonal crystal form I of PB, the plaques were im-
mersed in a 95C water bath to evaluate long term stability in
hot water. Periodically samples were withdrawn and hot air oven
stability at 150C was determined. The time to reach character-
istic tackiness and color change (to yellow-brownish) was taken
as the failure point in the oven. The exudation or blooming of
stabilizers to the plaque surface was also monitored as a
function of storage time in ambient air (23C).
Table II shows the oven life after hot water aging as
a measure of long term stability for the twelve formulations.
Among these formulations 127-4 through 127-8 and 12 showed lower
stability than the other seven resins. In later experiments,
resins 127-3 and 127-10 showed stabilizer blooming to the plaque
surface after 24 days (from compression molding) at ambient
temperature and pressure. Due to observation of the blooming
tendency of Hostanox SE-10 in gray and black PB formulations,
and because Cyanox 1212 is potentially more acceptable than
Hostanox SE-10 in a PB resin for potable water pipe, resins 127-
9 through 127-12 were not chosen for further development. After
considering all the relevant factors, formulations 127-1 and
127-2 showed the best combination of properties. Plaques of
127-1 and 127-2 have not bloomed in air up to four months.
*Trade mark
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