Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Method for producing insulated casing pipes in a continuous production process
Description
The present invention relates to a continuous process for producing insulated
pipes
comprising a conveying pipe, a jacketing pipe, a layer made of at least one
polyurethane
between conveying pipe and jacketing pipe, and a foil tube between the at
least one
polyurethane and the jacketing pipe, comprising at least the steps of (A) in a
gripper-belt
system, providing a foil tube formed continuously from a foil, and providing a
conveying pipe,
where the arrangement has the conveying pipe within the foil tube in such a
way that an
annular gap is formed between conveying pipe and foil tube, (B) charging a
polyurethane
system comprising at least one isocyanate component (a) and at least one
polyol mixture (b)
to the annular gap, (C) foaming the polyurethane system and allowing the same
to harden,
and (D) applying a layer made of at least one thermoplastic to the foil tube
via extrusion, in
order to form the jacketing pipe, which comprises using a multiple nozzle
system having
curvature corresponding to the radius of the annular gap to charge the
material in step (B).
Pipes insulated with polyurethane foams are known in the prior art and are
described by way
of example in EP-A-865 893 and DE-A-197 42 012. Insulated pipeline systems are
assembled from individual pipe segments. The standard procedures here use pipe
lengths of
6 m, 12 m, and 16 m. Necessary additional lengths are manufactured separately
or are cut to
size from existing semifinished product. The individual pipe segments are
welded and the
existing sleeve technique is then used to apply insulation in the region of
the weld. These
sleeve connections are more susceptible to damage than the actual pipe
product. This
difference results from the fact that the pipe lengths are produced under
defined, controllable
conditions in production facilities. The sleeve connections are often produced
in situ at the
construction site under time pressure with exposure to wind and weather. The
quality of the
sleeve connections is often affected by, for example, temperature,
contamination, and
moisture. Furthermore, the number of sleeve connections is a major factor in
the costs of
installation of pipeline systems.
It is therefore desirable, in the pipe-processing industry, to minimize the
number of sleeve
connections installed, based on the length of a line. This is achieved by
using relatively long
individual pipe segments, but production of these is more demanding and
frequently leads to
technical problems.
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Most individual pipes are produced by batchwise pipe-in-pipe production. In
this process, the
conveying pipe, generally made of steel, is provided with star-shaped spacers
which serve to
center the interior pipe. The conveying pipe is inserted into the exterior
jacketing pipe,
generally made of polyethylene, in such a way as to give an annular gap
between the two
pipes. Polyurethane foam is charged to said annular gap, because this has
excellent
insulation properties. To this end, the slightly inclined double pipe is
provided with end caps,
equipped with static ventilation holes. A polyurethane metering machine is
then used to
charge the liquid reaction mixture to the annular gap, and this mixture
continues to flow
downward in liquid form within the gap between the pipes until the reaction
begins. From this
juncture, the viscosity of the foam slowly rises, and the distribution process
continues by
virtue of flow of the foam, until reaction of the material is complete.
EP 1 552 915 A2 discloses a process for producing insulated pipes where a
polyurethane
system comprising an isocyanate component and a polyol component with low
viscosity
smaller than 3000 mPas is charged to the annular gap formed by conveying pipe
and
jacketing pipe. After the charging procedure, the polyurethane system foams
and
simultaneously cures.
EP 1 783 152 A2 likewise discloses a process for producing insulated pipes
where a
polyurethane system comprising an isocyanate component and a polyol component
with
particularly low viscosity of less than 1300 mPas is charged to the annular
gap formed by
conveying pipe and jacketing pipe.
EP 1 552 915 A2 and EP 1 783 152 A2 accordingly describe processes for
producing
insulated pipes in which the problem of complete filling of the pipe prior to
foaming and
hardening is solved by using polyol components with particularly low viscosity
and therefore
good flowability.
Another important factor for the quality of the pipes is uniform density
distribution in the foam.
However, this quality is not advantageous when the processes known from the
prior art are
used. The resultant density is usually lower at the ends and higher in the
middle of the pipe.
As the length of the pipe increases, the required overall density of the foam
in the annular
gap increases, for reasons of production technology.
Another essential factor for uniform density distribution is that the liquid
polyurethane system
is introduced uniformly into the annular gap between jacketing pipe and
conveying pipe. The
processes known from the prior art cannot necessarily ensure uniform
distribution.
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A disadvantage of continuous processes known from the prior art is that large
amounts of
polyurethane-precursor mixture have to be introduced continuously into a
moving double
pipe formed from conveying pipe and jacketing pipe, which is formed by joining
an elongate
foil. It is sometimes not possible to convey said mixture onward at sufficient
speed, and the
foam can therefore escape from the front of the pipe.
It was an object of the invention to provide a continuous process for
producing insulated
pipes, where pipes are obtained which feature low and uniformly distributed
overall density,
and also small cell diameters of the resultant polyurethane foam, and
therefore low thermal
conductivity. Another object of the present invention is to provide a process
which ensures
that the polyurethane system introduced does not escape laterally from the
resultant pipe but
instead remains completely within the annular gap. Another intention is to
obtain an insulated
pipe which has a particularly uniform density distribution of the polyurethane
foam to the
greatest possible extent over the entire length.
Said objects are achieved in the invention via a continuous process for
producing insulated
pipes comprising a conveying pipe, a jacketing pipe, a layer made of at least
one
polyurethane between conveying pipe and jacketing pipe, and a foil tube
between the at least
one polyurethane and the jacketing pipe, comprising at least the following
steps:
(A) in a gripper-belt system, providing a foil tube formed continuously
from a foil, and
providing a conveying pipe, where the arrangement has the conveying pipe
within the
foil tube in such a way that an annular gap is formed between conveying pipe
and foil
tube,
(B) charging a polyurethane system comprising at least one isocyanate
component (a) and
at least one polyol mixture (b) to the annular gap,
(C) foaming the polyurethane system and allowing the same to harden, and
(D) applying a layer made of at least one thermoplastic to the foil tube
via extrusion, in
order to form the jacketing pipe,
which comprises using a multiple nozzle system having curvature corresponding
to the
radius of the annular gap to charge the material in step (B).
The process of the invention is carried out continuously. This means in
particular that each
individual step of the process is carried out continuously.
A detailed explanation is provided below of the individual steps of the
process of the
invention.
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Step (A):
Step (A) of the process of the invention comprises, in a gripper-belt system,
providing a foil
tube formed continuously from a foil, and providing a conveying pipe, where
the arrangement
has the conveying pipe within the foil tube in such a way that an annular gap
is formed
between conveying pipe and foil tube.
The arrangement of the conveying pipe, the diameter of which in the invention
is smaller than
that of the foil tube and than that of the jacketing pipe formed in step (D)
of the process of the
invention, within the jacketing pipe, is such that an annular gap is formed
between conveying
pipe and jacketing pipe. The polyurethane system is charged to said annular
gap in step (B)
of the invention.
The conveying pipe used in the invention is generally a steel pipe with
external diameter of,
for example, from 1 to 120 cm, preferably from 4 to 110 cm. The length of the
conveying pipe
is, for example, from 1 to 24 meters, preferably from 6 to 16 meters. In one
preferred
embodiment of the process of the invention, the conveying pipe used comprises
a wind-and-
fold metal sheet.
In the continuous conduct of the process of the invention, the conveying pipe
is provided, for
example, in the form of material on a roll. It is also possible to provide the
conveying pipe in
linear form.
In step (A) of the process of the invention, in a gripper-belt system, a foil
tube formed
continuously from a foil is provided, and a conveying pipe is provided.
To this end, it is preferable to unwind an elongate foil continuously from a
roll and to use
processes known to the person skilled in the art, for example welding, to join
said foil to give
a foil tube. In one preferred embodiment of the process of the invention, said
joining takes
place in the gripper-belt system within which the conveying pipe is also
continuously
introduced. The foil is preferably introduced here by way of a shaping guide
or foil guide. It is
preferable to form a circular foil tube.
The width of the foil used in the invention is preferably suitable for forming
an appropriate foil
tube which has an internal diameter that is generally from 6 to 140 cm,
preferably from 10 to
120 cm. Said foil is preferably provided in the form of material on a roll.
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The foil used in the invention can be composed of any material that appears to
the person
skilled in the art to be suitable, for example polyethylene.
The thickness of the foil used in the invention is generally any thickness
that appears to the
5 person skilled in the art to be suitable, for example from 5 pm to 10 pm.
Step (A) of the process of the invention is preferably carried out at a
temperature which
permits joining of the edges of the foil to give an appropriate foil tube. It
is preferable in the
invention that an appropriate temperature is present only at the point at
which the foil is
joined to give a tube and that the remainder of step (A) is carried out at a
temperature of from
10 C to 30 C, for example ambient temperature.
A gripper-belt system used in the invention is known per se to the person
skilled in the art.
This generally involves two circulating caterpillar systems, bearing aluminum
shaping jaws as
required by the dimensions of the pipe. Said aluminum jaws are, for example,
pipe half-shells
which when they meet form the complete cross section of the pipe. By way of
example, there
are up to 180 individual segments incorporated within each circulating
caterpillar.
The arrangement of the conveying pipe within the foil tube in step (A) of the
process of the
invention is such that an annular gap is formed between conveying pipe and
foil tube. It is
particularly preferable here that the arrangement has the conveying pipe
centrally in the,
preferably, circular, foil tube, so that a concentric annular gap is formed.
Step (B):
Step (B) of the process of the invention comprises the charging of a
polyurethane system
comprising at least one isocyanate component (a) and at least one polyol
mixture (b) to the
annular gap, where the charging procedure in step (B) uses a multiple nozzle
system having
curvature corresponding to the radius of the annular gap.
In the invention, the charging procedure for the polyurethane system in step
(B) of the
process of the invention uses a multiple nozzle system having curvature
corresponding to the
radius of the annular gap.
In one possible embodiment of the invention, the multiple nozzle system used
is by way of
example a piece of pipe which has been curved to correspond to the radius,
preferably to
correspond to the average radius, of the gap between the pipes. The expression
"average
radius" means in the invention a radius which lies between the radius of the
conveying pipe
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and the radius of the foil tube, preferably a radius corresponding to the
average value of the
radius of the conveying pipe and the radius of the foil tube, with possible
deviation by 20%,
preferably 10%, upward and downward from said average value. In the invention,
the pipe
having corresponding curvature has at least one aperture for introducing the
polyurethane
system into the annular gap. In another preferred embodiment, the pipe having
corresponding curvature has from 1 to 40, preferably from 2 to 30,
particularly preferably
from 2 to 20, apertures. The apertures can be of any type known to the person
skilled in the
art, but the intention here is to ensure that the polyurethane system used in
the invention can
be charged through the apertures into the annular gap. Examples of suitable
apertures are
slits and holes.
The present invention therefore preferably provides the process of the
invention where the
multiple nozzle system is formed from a pipe having curvature corresponding to
the radius,
preferably to the average radius, of the annular gap, and having at least one
aperture for
introducing the polyurethane system into the annular gap.
The length of the pipe having curvature according to the invention
corresponding to the
radius of the annular gap depends on the diameters of the conveying pipe and
of the foil
tube. The pipe preferably has circular curvature. The length of the pipe
having circular
curvature can generally be described by way of the annular-gap arc section
comprised by the
curved pipe. In one preferred embodiment, the curved pipe comprises an arc
section of from
20 to 180 , preferably from 30 to 170 , particularly preferably from 40 to 160
, for example
one third of a full circle, of the annular gap. An arc section of, for
example, 180 here
corresponds to one half of a full circle, and an arc section of, for example,
900 corresponds to
one quarter of a full circle.
The apertures present in the pipe can generally point in any direction that
appears to the
person skilled in the art to be suitable. In one preferred embodiment of the
process of the
invention, the arrangement has the apertures of the multiple nozzle system in
such a way
that the polyurethane system is charged in the direction of the foil tube. It
is possible in the
invention, but less preferred, that the arrangement has the apertures of the
multiple nozzle
system in such a way that the polyurethane system is charged in the direction
of the
conveying pipe.
In the invention, the multiple nozzle system used in the invention has all of
the apparatuses
necessary for operation, for example in- and outlet lines, in particular for
supplying the
polyurethane system. It is preferable that the multiple nozzle system of the
invention is
attached to a mixing head known to the person skilled in the art.
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In one preferred embodiment of the process of the invention, the conveying
pipe is
introduced continuously, and a foil which, via welding, forms the foil tube is
likewise
introduced continuously, and mutually superposed on a gripper-belt system for
the welding
procedure, and the arrangement has, in the vicinity of the gripper-belt
system, preferably
within the annular gap that is formed, the multiple nozzle system used in the
invention. This
arrangement ensures that the polyurethane system charged is distributed
particularly
uniformly, and that no material escapes from, or drips from, the annular gap.
In step (B) of the process of the invention it is generally possible to use
any polyurethane
system that appears to the person skilled in the art to be suitable.
Polyurethane systems
used with preference are explained in detail below.
lsocyanate component (a) used comprises the usual aliphatic, cycloaliphatic,
and in
particular aromatic di- and/or polyisocyanates. It is preferable to use
tolylene diisocyanate
(TDI), diphenylmethane diisocyanate (MDI), and in particular a mixture of
diphenylmethane
diisocyanate and polyphenylene polymethylene polyisocyanates (crude MDI). The
isocyanates can also have been modified, for example via incorporation of
uretdione groups,
carbamate groups, isocyanurate groups, carbodiimide groups, allophanate
groups, and in
particular urethane groups.
It is also possible to use isocyanate component (a) in the form of
polyisocyanate
prepolymers. These prepolymers are known from the prior art. They are produced
in a
manner known per se, by reacting polyisocyanates (a) described above, for
example at
temperatures of about 80 C, with compounds having hydrogen atoms reactive
toward
isocyanates, preferably with polyols, to give polyisocyanate prepolymers. The
polyol:
polyisocyanate ratio is generally selected in such a way that the NCO content
of the
prepolymer is from 8 to 25% by weight, preferably from 10 to 22% by weight,
particularly
preferably from 13 to 20% by weight.
It is particularly preferable in the invention to use crude MD1 as isocyanate
component (a).
In one preferred embodiment, isocyanate component (a) is selected in such a
way that its
viscosity is less than 800 mPas, preferably from 100 to 650 mPas, particularly
preferably
from 120 to 400 mPas, in particular from 180 to 350 mPas, measured in
accordance with
DIN 53019 at 20 C.
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For the purposes of this invention it is preferable that the polyurethane
systems and
polyurethane foams of the invention are in essence free from isocyanurate
groups. The ratio
isocyanurate group: urethane group in the foam is preferably smaller than
1:10, particularly
preferably smaller than 1:100. In particular, there are in essence no
isocyanurate groups
present in the polyurethane foam used in the invention.
The polyol mixture (b) in the polyurethane system used in the invention
generally comprises
polyols as constituent (b1), and optionally chemical blowing agents as
constituent (b2). The
polyol mixture (b) generally comprises physical blowing agents (b3).
The viscosity of the polyol mixture (b) used in the invention (but without
physical blowing
agents (b3)) is generally from 200 to 10 000 mPas, preferably from 500 to 9500
mPas,
particularly preferably from 1000 to 9000 mPas, very particularly preferably
from 2500 to
8500 mPas, in particular from 3100 to 8000 mPas, measured in each case in
accordance
with DIN 53019 at 20 C. In one particularly preferred embodiment, the process
of the
invention uses a polyol mixture (b) (but without physical blowing agents (b3))
of which the
viscosity is more than 3000 mPas, for example from 3100 to 8000 mPas, measured
in each
case in accordance with DIN 53019 at 20 C.
The present invention therefore preferably provides the process of the
invention where a
polyol mixture (b) (but without physical blowing agents (b3)) is used of which
the viscosity is
more than 3000 mPas, for example from 3100 to 8000 mPas, in each case measured
in
accordance with DIN 53019 at 20 C.
The polyol mixture (b) generally comprises physical blowing agents (b3).
However, the
addition of physical blowing agent causes a significant lowering of viscosity.
An essential
point in the invention means therefore that the statements made above relating
to the
viscosity of the polyol mixture (b) refer to the viscosity of the polyol
mixture (b) without
addition of physical blowing agents (b3), even when the mixture comprises
physical blowing
agents.
Polyols (constituent b1) that can be used are generally compounds having at
least two
groups reactive toward isocyanate, i.e. having at least two hydrogen atoms
reactive toward
isocyanate groups. Examples of these are compounds having OH groups, SH
groups, NH
groups, and/or NH2 groups.
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Preferred polyols (constituent b1) used are compounds based on polyesterols or
on
polyetherols. The functionality of the polyetherols and/or polyesterols is
generally from 1.9 to
8, preferably from 2.4 to 7, particularly preferably from 2.9 to 6.
The hydroxy number of the polyols (b1) is generally greater than 100 mg KOH/g,
preferably
greater than 150 mg KOH/g, particularly preferably greater than 200 mg KOH/g.
An upper
limit which has proven successful for the hydroxy number is generally 1000 mg
KOH/g,
preferably 800 mg KOH/g, particularly 700 mg KOH/g, very particularly 600
KOH/g. The OH
numbers stated above relate to the entirety of the polyols (b1), and this does
not exclude the
possibility that individual constituents of the mixture have higher or lower
values.
It is preferable that component (b1) comprises polyether polyols, where these
are produced
by known processes, for example via anionic polymerization with alkali metal
hydroxides,
such as sodium hydroxide or potassium hydroxide, or with alkali metal
alcoholates, such as
sodium methoxide, sodium ethoxide, or potassium ethoxide, or potassium
isopropoxide, as
catalysts, and with addition of at least one starter molecule which comprises
from 2 to 8,
preferably from 3 to 8, reactive hydrogen atoms, or via cationic
polymerization with Lewis
acids, such as antimony pentachloride, boron fluoride etherate, etc., or
bleaching earth, as
catalysts, starting from one or more alkylene oxides having from 2 to 4 carbon
atoms in the
alkylene moiety.
Examples of suitable alkylene oxides are tetrahydrofuran, propylene 1,3-oxide,
butylene 1,2-
or 2,3-oxide, styrene oxide, and preferably ethylene oxide and propylene 1,2-
oxide. The
alkylene oxides can be used individually, in alternation, or in the form of a
mixture.
Starter molecules that can be used are alcohols, such as glycerol,
trimethylolpropane (TMP),
pentaerythritol, sucrose, or sorbitol, or else amines, such as methylamine,
ethylamine,
isopropylamine, butylannine, benzylamine, aniline, toluidine, toluenediamine,
naphthylamine,
ethylenediamine (EDA), diethylenetriamine, 4,4'-methylenedianiline, 1,3-
propanediamine,
1,6-hexanediamine, ethanolamine, diethanolamine, triethanolamine, and the
like.
Other starter molecules that can be used are condensates of formaldehyde,
phenol, and
diethanolamine or ethanolamine, formaldehyde, alkylphenols, and diethanolamine
or
ethanolamine, formaldehyde, bisphenol A, and diethanolamine or ethanolamine,
formaldehyde, aniline, and diethanolamine or ethanolamine, formaldehyde,
cresol, and
diethanolamine or ethanolamine, formaldehyde, toluidine, and diethanolamine or
ethanolamine, or else formaldehyde, toluenediamine (TDA), and diethanolamine
or
ethanolamine; similar compounds can also be used.
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Starter molecules preferably used are glycerol, sucrose, sorbitol, and EDA.
The polyol mixture can moreover optionally comprise chemical blowing agents as
constituent
5 (b2). Preferred chemical blowing agents are water and carboxylic acids,
and formic acid is
particularly preferred as chemical blowing agent. The amount generally used of
the chemical
blowing agent is from 0.1 to 5% by weight, in particular from 1.0 to 3.0% by
weight, based on
the weight of component (b).
10 As mentioned above, the polyol mixture (b) generally comprises a
physical blowing agent
(b3). These are compounds emulsified or dissolved in the starting materials
for polyurethane
production, and they vaporize under the conditions of polyurethane formation.
By way of
example, they involve hydrocarbons, such as cyclopentane, halogenated
hydrocarbons, and
other compounds such as perfluorinated alkanes, e.g. perfluorohexane,
fluorochlorocarbons,
or else ethers, esters, ketones, and/or acetals. The amount usually used of
these, based on
the total weight of components (b), is from 1 to 30% by weight, preferably
from 2 to 25% by
weight, particularly preferably from 3 to 20% by weight.
The present invention therefore preferably provides the process of the
invention where the
polyurethane system is foamed with cyclopentane as physical blowing agent.
In one preferred embodiment, the polyol mixture (b) comprises, as constituent
(b4),
crosslinking agents. Crosslinking agents are compounds of molar mass from 60
to less than
400 g/mol, having at least 3 hydrogen atoms reactive toward isocyanates.
Glycerol is an
example here.
The amount generally used of the crosslinking agents (b4) is from 1 to 10% by
weight,
preferably from 2 to 6% by weight, based on the total weight of the polyol
mixture (b) (but
without physical blowing agents (b3)).
In another preferred embodiment, the polyol mixture (b) comprises, as
constituent (b5), chain
extenders, where these serve to increase the density of crosslinking. Chain
extenders are
compounds of molar mass from 60 to less than 400 g/mol, having 2 hydrogen
atoms reactive
toward isocyanates. Examples here are butanediol, diethylene glycol,
dipropylene glycol, and
also ethylene glycol.
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The amounts generally used of the chain extenders (b5) are from 2 to 20% by
weight,
preferably from 4 to 15% by weight, based on the total weight of the polyol
mixture (b) (but
without physical blowing agents (b3)).
Components (b4) and (b5) can be used individually or in combination in the
polyol mixture.
The polyurethane foams present as insulating material in the invention are
obtainable via
reaction of the polyurethane system of the invention.
The amounts reacted during the reaction of the polyisocyanates (a) and the
polyol mixture
(b) are generally such that the isocyanate index of the foam is from 90 to
240, preferably
from 90 to 200, particularly preferably from 95 to 180, very particularly
preferably from 95 to
160, in particular from 100 to 149.
In one preferred embodiment, components (a) and (b) of the polyurethane system
are
selected in such a way that the compressive strength of the resultant foam
(for density
60 kg/m3) is greater than 0.2 N/mm2, preferably greater than 0.25 N/mm2,
particularly
preferably greater than 0.3 N/mm2, measured in accordance with DIN 53421.
The overall shot density in the process of the invention is generally less
than 80 kg/m3,
preferably less than 75 kg/m3, particularly preferably less than 70 kg/m3,
very particularly
preferably less than 65 kg/m3, in particular less than 60 kg/m3. The overall
shot density
generally means the total amount of liquid polyurethane material charged,
based on the total
volume of the foam-filled annular gap.
The process of the invention can generally take place at any compaction level
that appears
to the person skilled in the art to be suitable. Compaction level means the
quotient calculated
from the overall density of the material charged to the annular gap divided by
the free-
foamed core density determined on an uncompacted foam.
It is preferable that the present invention provides the process of the
invention where the
reaction is carried out with a compaction level smaller than 4.0, preferably
smaller than 3.5,
particularly preferably smaller than 3.0, and very particularly preferably
smaller than 2.5.
The polyurethane system used in step (B) of the process of the invention
preferably
comprises a catalyst. It is generally possible in the invention to use any of
the catalysts that
appear to the person skilled in the art to be suitable.
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Catalysts preferably used in the invention catalyze the blowing reaction, i.e.
the reaction of
diisocyanate with water. This reaction takes place predominantly prior to
actual
polyurethane-chain formation, i.e. prior to the polymerization reaction, and
therefore gives
the polyurethane system a fast reaction profile.
Examples of catalysts that can be used in the invention are those selected
from the group
consisting of organotin compounds, such as tin(II) salts of organic carboxylic
acids, and/or
basic amine compounds, preferably tertiary amines, such as triethylamine,
and/or 1,4-
diazabicyclo[2.2.2]octane, potassium acetate, potassium formate, and/or
potassium octoate,
glycine, N-((2-hydroxy-5-nonylphenyl)methyl)-N-methyl monosodium salt (CAS
number
56968-08-2), (2-hydroxypropyI)-trimethylammonium 2-ethylhexanoate (CAS number
62314-
22-1), 1-propylammonium-2-hydroxy-N,N-trimethyl formate,
trimethylhydroxypropyl-
ammonium formate, 2-((2-(dimethylamino)ethyl)methylamino)ethanol (CAS number
2212-32-
0), and/or N,N',N"-tris(dimethylaminopropyl)hexahydrotriazine (CAS number
15875-13-5),
and mixtures thereof.
The catalysts preferred in the invention can be added to the polyurethane
system in any
manner known to the person skilled in the art, for example in bulk or in the
form of solution,
for example in the form of aqueous solution.
The amount added of the at least one catalyst in the invention, based on
polyol components
(b), is from 0.01 to 1.5% by weight, preferably from 0.05 to 1.0% by weight,
particularly
preferably from 0.05 to 0.5% by weight, very particularly preferably from 0.1
to 0.3% by
weight.
It is also optionally possible to add additional substances (b6) to the
polyurethane system
used in the invention. Additional substances (b6) are the usual auxiliaries
and additional
substances known in the prior art, but without physical blowing agents.
Examples that may
be mentioned are surfactant substances, foam stabilizers, cell regulators,
fillers, dyes,
pigments, flame retardants, antistatic agents, hydrolysis stabilizers, and/or
substances
having fungistatic and bacteriostatic action. It should be noted that the
general and preferred
viscosity ranges stated above for component (b) refer to a polyol mixture (b)
inclusive of any
additional substances (b6) added (but exclusive of optional physical blowing
agent (b3)
added).
The present invention therefore preferably provides the process of the
invention where the at
least one polyol mixture (b) comprises polyols (b1), optionally chemical
blowing agents (b2),
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physical blowing agents (b3), crosslinking agents (b4), chain extenders (b5),
and/or
optionally additional substances (b6).
The present invention therefore in particular provides the process of the
invention where from
1 to 25% by weight of flame retardant, based on the total weight of the polyol
mixture, is used
as additional substance (b6).
Step (C):
Step (C) of the process of the invention comprises the foaming of the
polyurethane system
and allowing same to harden.
The foaming and hardening in the invention generally takes place at a
component
temperature of from 18 to 35 C, preferably from 20 to 30 C, particularly
preferably from 22 to
28 C.
The foaming and hardening in the invention generally takes place at surface
temperatures of
from 15 to 50 C, preferably from 20 to 50 C, particularly preferably from 25
to 45 C.
In step (C) of the process of the invention, gaseous substances arising under
the reaction
conditions during the reaction, and/or blowing agents, optionally escape
through the open
ends of the pipe produced.
Step (C) of the process of the invention gives an insulated pipe comprising at
least one
conveying pipe, one foil tube, and one insulating layer made of polyurethane
foam between
conveying pipe and foil tube.
The thickness of the insulating layer is generally from 1 to 20 cm, preferably
from 5 to 20 cm,
particularly preferably from 7 to 20 cm.
In another preferred embodiment, the thermal conductivity of the insulating
layer comprising
polyurethane foam is less than 27 mW/mK, preferably from 22 to 26.7 mW/mK,
measured in
accordance with EN ISO 8497.
Step (D):
Step (D) of the process of the invention comprises applying a layer made of at
least one
thermoplastic to the foil tube via extrusion, in order to form the jacketing
pipe.
CA 02857081 2014-05-27
14
Step (C) of the process of the invention gives a conveying pipe surrounded by
an insulating
layer made of at least one polyurethane foam, surrounded in turn by the foil
tube produced in
step (A). In order to form the jacketing pipe made of at least one
thermoplastic, said pipe is
applied via extrusion in step (D) of the process of the invention.
The extrusion of thermoplastics to produce a layer, in this case the jacketing
pipe, is known
per se to the person skilled in the art.
The application procedure in step (D) of the process of the invention is
generally carried out
at a temperature which appears suitable to the person skilled in the art of
extrusion of
thermoplastics, for example a temperature higher than the melting point of the
thermoplastic
used. Examples of suitable temperatures are from 180 to 220 C, preferably from
190 to
230 C.
The thickness of the jacketing pipe formed in step (D) of the process of the
invention is
generally from 1 to 30 mm. The internal diameter of the jacketing pipe depends
in the
invention on the diameter of the foil tube and by way of example is from 6 to
140 cm,
preferably from 10 to 120 cm.
The jacketing pipe can optionally be composed of a plurality of layers, where
these can be
joined during the extrusion procedure for producing the jacketing pipe. An
example here is
the introduction of multiple-ply foils between polyurethane foam and jacketing
pipe, where
the foil comprises at least one metallic ply in order to improve barrier
effect. EP-A-960 723
describes suitable jacketing pipes of this type. Said additional layer
optionally present is
preferably introduced before the end of step (A), together with the foil. By
way of example,
multiple-ply foils with aluminum as diffusion barrier can be used in the
invention.
Any of the thermoplastics which have properties advantageous for an
appropriate insulated
pipe are generally suitable in the invention. Examples of thermoplastics that
can be used in
the invention are those selected from the group consisting of polyethylene,
polypropylene,
and mixtures thereof, and it is preferable to use polyethylene.
After step (D) of the process of the invention, the insulated pipe formed can
be further treated
by processes known to the person skilled in the art, for example via cutting-
to-size of the
insulated pipe, which has been produced continuously and is therefore in
principle
continuous, to give desired lengths, for example 6, 12, or 75 m.
CA 02857081 2014-05-27
In one particularly preferred embodiment, the insulated pipe produced in the
invention is an
insulated composite jacketed pipe which is suitable for underground district-
heating networks
and which complies with the requirements of DIN EN 253:2009.
5 The present invention also provides an insulated pipe which can be
produced via the process
of the invention. The details mentioned for the insulated pipe produced in
relation to the
process of the invention apply correspondingly. The pipe produced in the
invention features
particularly uniform density distribution over the entire length and therefore
low lambda
values for far better physical properties.
The present invention also provides an apparatus for producing an insulated
pipe,
comprising an apparatus for introducing a conveying pipe, an apparatus for
introducing a foil
for forming a foil tube, a gripper-belt system, an apparatus for extruding the
at least one
plastic, and a multiple nozzle system having curvature corresponding to the
radius of the
annular gap between conveying pipe and foil tube, preferably for carrying out
the process of
the invention.
The individual apparatuses mentioned are known per se to the person skilled in
the art.
These apparatuses known per se have to be arranged appropriately for the
process of the
invention.
The apparatus of the invention also comprises the multiple nozzle system of
the invention.
Details and preferred embodiments relating to this multiple nozzle system are
mentioned in
relation to the process of the invention, and these are also intended to apply
to the apparatus
of the invention.
The present invention also provides the use of the apparatus of the invention
for carrying out
the process of the invention, in particular for producing the insulated pipe
of the invention.
Figure
Figure 1 is a diagram of a distributor pipe of the invention in an annular gap
derived from
steel pipe and PE foil. The meanings of the reference symbols here are as
follows:
1 Mixing head
2 Distributor pipe with varying number of holes, for example 6 holes
3 Steel pipe
4 Polyurethane foam
5 Supportive LD-PE foil
