This invention is related to the preparation of coloured
polyethylene pipe resins suitable for transporting cold and/or hot water containing
Polymer materials are frequently used for preparing pipes
that are suitable for transporting fluid such as liquid or gas. The fluid may be
pressurised and its temperature may range between 0 and 90 °C. These pipes
were ususally prepared from medium or high density monomodal or multimodal polyethylene.
For example, WO00/01765
discloses the use of a multimodal polyethylene resin having a density of 0.930 to
0.965 g/cc and a M15 of from 0.2 to 1.2 dg/min for transporting cold, pressurised
The transport of hot water requires other types of resin
than conventional polyethylene as the service life of a typical polyethylene pipe
decreases by about 50 % when the temperature of the transported fluid increases
by 10°C and as it is subject to stress cracking at elevated temperature.
Several multimodal polyethylene resins were disclosed for
the transport of hot fluid. For example, EP-A-1448702
discloses a polyethylene resin useful for the preparation of hot water pipes. That
polyethylene resin is multimodal with a high molecular weight fraction having a
density of at least 0.920 g/cc and a low molecular weight fraction. Its density
ranges between 0.921 and 0.950 g/cc. Its time to failure at a temperature of 95
°C and at a pressure of 3.6 MPa is of at least 165 h and its modulus of elasticity
is of at most 900 MPa.
also discloses a multimodal polyethylene resin that can be used for hot water pipes.
It has a density of from 0.925 to 0.950 g/cc and a MI2 of from 0.1 to 5 dg/min.
It comprises a high molecular weight fraction having a density of from 0.910 to
0.935 g/cc and a MI2 of at most 1 dg/min and a low molecular weight fraction having
a density of from 0.945 to 0.965 g/cc and a MI2 of from 2 to 200 dg/min.
Water for domestic use also transports disinfectants. The
service life of pipes prepared from the prior art polyethylene resins was substantially
decreased by the addition of disinfectants.
Cross-linked polyethylene resins have also been used to
improve the performances of the pipes. The cross linking was achieved either chemically
with silane or peroxides or physically by irradiation.
discloses the use of a high density polyethylene resin comprising a combination
of at least two antioxidant additives to prepare pipes for transporting water containing
There is thus a need for coloured polyethylene pipes that
are able to transport hot or cold water containing such aggressive chemical compound,
that do not require the addition of specific combinations of antioxidants.
It is an aim of the present invention to prepare coloured
polyethylene resins suitable for preparing pipes for the transport of hot or cold
water containing disinfectant.
It is also an aim of the present invention to prepare coloured
polyethlene pipe resins that have good mechanical properties.
It is another aim of the present invention, to prepare
coloured polyethylene pipe resins that can be processed easily.
Any one of these aims is at least partially fulfilled by
the present invention.
The pipe of the present invention is prepared from a bi-
or multi-modal polyethylene resin produced either by two or more single site catalyst
systems in a single reactor or by a single site catalyst system in two serially
connected reactors, wherein at least one of the single site catalyst systems is
a metallocene catalyst system comprising a bisindenyl or a bis tetrahydroindenyl
catalyst component of formula R" (Ind)2 MQ2 wherein Ind is
a substituted or unsubstituted indenyl or tetrahydroindenyl group, R" is a structural
bridge imparting stereorigidity to the complex, M is a metal Group 4 of the Periodic
Table and Q is a hydrocarbyl having from 1 to 20 carbon atom or a halogen. The polyethylene
resin further comprises blue pigments and anti-UV additive.
The catalyst system comprises a metallocene component,
and more preferably it comprise a bridged bis-indenyl or bistetrahydro-indenyl catalyst
component described by general formula
wherein Ind is a substituted or unsubstituted indenyl or tetrahydroindenyl group,
R" is a structural bridge imparting stereorigidity to the complex, M is a metal
Group 4 of the Periodic Table and Q is a hydrocarbyl having from 1 to 20 carbon
atom or a halogen.
If Ind is an indenyl group it is preferably unsubstituted
or substituted at position 4 with a bulky substituent and at position 2 with a small
substituent. A bulky substituent is at least as bulky as t-butyl. A small substituent
is preferably methyl.
If Ind is a tetrahydroindenyl group, it is preferably unsubstituted.
M is preferably Ti or Zr, more preferably Zr.
Each Q is preferably selected from aryl, alkyl, alkenyl,
alkylaryl or arylalkyl having at most 6 carbon atoms, or halogen. More preferably
both Q are the same and are chlorine.
Structural bridge R" is selected from C1-C4
alkylene radical, a dialkyl germanium or silicon or siloxane, or an alkyl phosphine
or amine radical, which bridge is substituted or unsubstituted. Preferably it is
ethylene, isopropylidene, dimethylsilyl or diphenyl.
The most preferred catalyst components are ethylenebistetrahydroindenyl
zirconium dichloride and ethylenebis(4-phenyl-2-methyl-indenyl) zirconium dichloride.
The metallocene catalyst component used in the present invention can be prepared
by any known method. A preferred preparation method is described in J.
Organomet. Chem. 288, 63-67 (1985).
The catalyst system also comprises an activating agent
having an ionising action and optionally an inert support. The activating agent
is preferably selected from aluminoxane or boron-containing compound and the inert
support is preferably selected from mineral oxide, more preferably, silica. Alternatively,
the activating agent is a fluorinated activating support.
The polyethylene resin that can be used in the present
invention is either bi- or multi-modal and is prepared by any method known in the
art. Its density preferably ranges from 0.915 to 0.965 g/cc.
The polyethylene resin is a bi- or multi-modal resin prepared
in two or more serially connected loop reactors. It comprises a high molecular weight
(HMW), low density fraction and a low molecular weight (LMW), high density fraction.
The high molecular weight, low density fraction has a density
of at least 0.908 g/cc, preferably of at least 0.912 g/cc and of at most 0.928 g/cc,
more preferably of at most 0.926 g/cc. Most preferably it is of about 0.922 g/cc.
It has a high load melt index HLMI of at least 2 dg/min, more preferably of at least
5 dg/min and most preferably of at least 7 dg/min and of at most 12 dg/min, more
preferably of at most 10 dg/min. Most preferably, it is of 8 to 9 dg/min. The melt
index MI2 is of from 0.05 to 2 dg/min, more preferably of from 0.1 to 0.5 dg/min
and most preferably of about 0.2 dg/min.
The low molecular weight, high density fraction has a density
of at least 0.930 g/cc, more preferably of at least 0.940 g/cc, and of at most 0.975
g/cm3, more preferably of at most 0.962 g/cc. Most preferably it is of
about 0.945 to 0.955 g/cc. It has a melt index Ml2 of at least 0.5 dg/min, more
preferably of at least 1 dg/min, and of at most 10 dg/min, more preferably of at
most 6 dg/min. Most preferably, it is of from 2 to 3 dg/min.
The final resin comprises 50 to 60 wt% of HMW fraction,
preferably from 50 to 55 wt%, more preferably from 52 to 53 wt% and from 40 to 50
wt% of LMW fraction, preferably from 45 to 50 wt% and most preferably from 47 to
48 wt%. It has a broad or multimodal molecular weight distribution of from 2 to
5, a density of from 0.930 to 0.949 g/cc and a melt index Ml2 of from 0.3 to 1 dg/min.
The most preferred polyethylene resin according to the present invention has a density
of about 0.935 g/cc, a melt index MI2 of 0.6 dg/min and a polydispersity of about
The molecular weight distribution is fully described by
the polydispersity index D defined by the ratio Mw/Mn of the weight average molecular
weight Mw to the number average molecular weight Mn as determined by gel permeation
The density is measured according to the method of standard
test ASTM 1505 at a temperature of 23 °C. The melt index and high load melt
indices are measured by the method of standard test ASTM D 1238 respectively under
a load of 2.16 kg and 21.6 kg and at a temperature of 190 °C.
The polyethylene resins according to the invention can
be prepared by any method suitable therefore. They can be prepared by physically
blending the high density and the low density polyethylene fractions, prepared separately,
or they can be prepared by polymerising ethylene in the presence of a mixture of
catalysts. Preferably, the high density and low density fractions are produced in
two serially connected loop reactors with the same catalyst system. In such a case,
the LMW, high density fraction is preferably prepared in the first reactor, so that
the HMW, low density fraction is prepared in the presence of the high density fraction.
Preferably, the same catalyst system is used in both steps of the cascade polymerisation
process to produce a chemical blend of the high and low molecular weight fractions.
The catalyst system may be employed in a solution polymerisation process, which
is homogeneous, or in a slurry process, which is heterogeneous or in a gas phase
process. Preferably a slurry process is used. The most preferred polymerisation
process is carried out in two serially connected slurry loop reactors.
In a preferred arrangement, the product of a first cascade
reaction zone, including the olefin monomer, is contacted with the second co-reactant
and the catalyst system in a second cascade reaction zone to produce and mix the
second polyolefin with the first polyolefin in the second reaction zone. The first
and second reaction zones are conveniently interconnected reactors such as interconnected
loop reactors. It is also possible to introduce into the second reaction zone fresh
olefin monomer as well as the product of the first reaction zone.
Because the second polyolefin is produced in the presence
of the first polyolefin a multimodal or at least bimodal molecular weight distribution
In one embodiment of the invention, the first co-reactant
is hydrogen, to produce the LMW fraction and the second co-reactant is the comonomer
to produce the HMW fraction. Typical comonomers include hexene, butene, octene or
methylpentene, preferably hexene.
In an alternative embodiment, the first co-reactant is
the comonomer, preferably hexene. Because the metallocene catalyst components of
the present invention exhibit good comonomer response as well as good hydrogen response,
substantially all of the comonomer is consumed in the first reaction zone in this
embodiment. Homopolymerisation takes place in the second reaction zone with little
or no interference from the comonomer.
The temperature of each reactor may be in the range of
from 60°C to 110°C, preferably from 70°C to 90°C.
The pigment used to colour pipe resins is generally carbon
black. It has the dual advantage of simultaneously colouring the pipe and resisting
ultra-violet radiations and thus serves as pigment and as anti-UV additive.
It has now been found that the present polyethylene resin,
additivated with blue pigments combined with at least one anti-UV, offers a much
higher resistance to disinfectant-containing water than the same resin additivated
with carbon black, all other additives being identical for both resins.
The amount of blue pigment added to the resin is of from
1 to 3000 ppm, preferably of from 500 to 2000 ppm. The amount of anti-UV additive
is of from 1 to 5000 ppm, preferably of from 1000 to 3500 ppm.
The blue pigment and anti-UV may be added to the resin
either by compounding or by dry blending.
The disinfectants typically used in domestic water can
be selected from chlorine, chlorine dioxide and chloramine.
The present invention further provides the use of such
blue polyethylene resin for the manufacture of pipes for transporting cold or hot
water, especially containing disinfectant.
The blue polyethylene resins according to the invention,
having such a specific composition, molecular weight and density, can lead to a
marked improvement of the processing properties when the resin is used as a pipe
resin, while conserving or improving mechanical behaviour as compared to known pipe
In particular, the blue polyethylene resins in accordance
with the invention have impact resistance and slow crack resistance at least equivalent
to, often higher than current available pipe resins.
The blue resins of the invention are endowed with excellent
The blue resin in accordance with the invention is characterised
by a high shear-thinning behaviour. This means good injection-moulding capability
for the resins when used to produce injection-moulded pipes and pipe fittings.
Generally, the pipes are manufactured by extrusion or by
injection moulding, preferably by extrusion in an extruder. The pipes made of the
multimodal polyethylene resin according to the present invention may be single layer
pipes or be part of multilayer pipes that include further layers of other resins.
In another embodiment according to the present invention,
the pipe is a multilayer pipe comprising at least one layer of pipe resin prepared
by any method known in the art and at least one other layer of polyethylene resin
additivated with blue pigment and anti-UV additive, wherein said other polyethylene
resin may or may not be a pipe resin.
The pipes of the present invention offer an excellent resistance
to degradation when used for transporting hot or cold water containing disinfectant.
The water temperature ranges from 0 to 90 °C and the amount of disinfectant
in the water is of from the smallest detectable amount, typically of from 0.1 mg/L,
up to the existing upper tolerance. Said upper tolerance is of 1 mg per litre of
water for chlorine dioxide and of 4 mg per litre for chlorine and chloramine. Generally
the amount of disinfectant in domestic water is of 0.3 to 0.4 mg/L. It must be noted
that the blue pipes according to the present invention can sustain higher percentage
of disinfectant than the upper limit tolerated for domestic water.
Two different resins were extruded into pipes that were
tested for transporting water containing chlorine dioxide.
Resin R1, according to the present invention, was prepared
with ethylene bistetrahydroindenyl zirconium dichloride catalyst component in a
double slurry loop reactor. The density was of 0.935 g/cc and the melt flow rate
MI2 was of 0.7 dg/min. It was additivated with 1150 ppm of blue pigment and 2800
ppm of HALS-type anti-UV additive.
Resin R2 is the same polyethylene resin as that of R1 but
it was additivated with carbon black instead of blue pigment and anti-UV additive.
Resin R3 is a commercial resin sold by Total Petrochemicals
under the name XS10H. It was prepared with a Ziegler-Natta catalyst system. It was
additivated with 1150 ppm of blue pigment and 2800 ppm of HALS-type anti-UV additive.
Resin R4 is the same resin as that of R3 but it was additivated
with carbon black instead of blue pigment and anti-UV.
Resin R5 is a commercial resin sold by Total Petrochemicals
under the name XSC50H. It was prepared with a Ziegler-Natta catalyst system. It
was additivated with 1150 ppm of blue pigment and 2800 ppm of HALS-type anti-UV
All resins contain in addition a standard antioxidant package.
These pipes were tested following according to the JANALAB
procedure and under the following conditions:
- chlorine dioxide: 4 ppm
- fluid temperature : 70 °C
- stress : 1.9 MPa
The results are presented in Table I
average time to failure (hours)
As can be seen from Table I resins R3 and R5, additivated
with blue pigments and anti-UV, according to the present invention, have a much
higher resistance to degradation by disinfectant-containing water than the same
resin additivated with carbon black.