Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS FOR THE CONTINUOUS PRODUCTION OF FOAMS IN PIPES
Description
The present invention relates to a continuous process for producing an
insulated pipe
comprising at least one medium pipe, an outer pipe, a layer of at least one
polyurethane
between the at least one medium pipe and outer pipe and a film tube between
the at least one
polyurethane and the outer pipe, which comprises at least the steps (A)
provision, in a jaw
band, of at least one medium pipe and a film tube formed continuously from a
film, where the
at least one medium pipe is arranged within the film tube in such a way that a
gap is formed
between the at least one medium pipe and the film tube, (B) introduction of a
polyurethane
system comprising at least one isocyanate component (a) and at least one
polyol (b) into the
gap, (C) foaming and allowing curing of the polyurethane system and (D)
application of a layer
of at least one material to the film tube in order to form the outer pipe,
where the polyurethane
system has thixotropic properties.
Pipes insulated by means of polyurethane foams are known in the prior art and
are described,
for example, in EP 1 141 613 B1, EP A 865 893, EP 1 777 051 B1, EP 1 595 904
A2, WO
00/39497, WO 01/18087 A1, EP 2 143 539 A1 and EP 1 428 848 B1. Insulated
pipeline
systems are assembled from individual pipe segments. Pipe lengths of 6 m, 12 m
and 16 m
are normally used for this purpose. Transition lengths required are
manufactured specially or
are cut to size from existing prefabricated goods. The individual pipe
segments are welded
together and insulated further in the region of the weld using existing muff
technology. These
muff connections bring about a greater damage potential than the pipes
themselves. This
difference results from the fact that the pipe lengths are produced under
fixed, controllable
conditions in production facilities. The muff connections are often produced
under time
pressure in all kinds of weather on the construction site. Influences such as
temperature,
soiling and moisture often influence the quality of the muff connections.
Furthermore the
number of muff connections represents a large cost factor in the installation
of pipeline
systems.
It is therefore desirable in the pipe processing industry to install as few as
possible muff
connections, based on the length of a line. This is achieved by use of longer
individual pipe
segments, although the production of these involves more demanding
requirements and
frequently leads to technical problems.
The majority of individual pipes are produced by means of the batchwise pipe-
in-pipe
production. In this process, the medium pipe, in general a steel pipe, is
provided with star-
shaped spacers which serve to center the inner pipe. The medium pipe is pushed
into the
CA 02879364 2015-01-16
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outer pipe, in general a polyethylene pipe, so that an annular gap is formed
between the two
pipes. This annular gap is filled with polyurethane foam, since this has
excellent insulating
properties. For this purpose, the slightly inclined double pipe is provided
with closure caps
which are equipped with static venting holes. The liquid reaction mixture is
subsequently
introduced into the annular gap by means of a polyurethane metering machine
and flows
downward in still liquid form in the annular gap until the reaction commences.
From this point
in time onwards, further distribution takes place by flow of the foam whose
viscosity increases
slowly, until the material has fully reacted.
EP 1 552 915 A2 discloses a process for producing insulated pipes, in which a
polyurethane
system comprising an isocyanate component and a polyol component having a low
viscosity of
less than 3000 mPas is introduced into the annular gap formed by the medium
pipe and the
outer pipe. After the introduction, the polyurethane system foams and cures at
the same time.
EP 1 783 152 A2 likewise discloses a process for producing insulated pipes, in
which a
polyurethane system comprising an isocyanate component and a polyol component
having a
particularly low viscosity of less than 1300 mPas is introduced into the
annular gap formed by
the medium pipe and the outer pipe.
The documents 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 before foaming
and curing is solved by use of polyol components having a particularly low
viscosity and thus
good flowability. Although these processes are suitable for producing
insulated pipes having
diameters of greater than 355 mm and/or high foam densities, they display the
known
disadvantages of the batch process, e.g. labor-intensive and costly
manufacture and relatively
coarse cell structure. In addition, pipes manufactured in a batchwise manner
have a relatively
thick outer wall since it has to withstand the internal pressure generated
during foaming. This
causes an undesirable, increased usage of raw material and thus increased
manufacturing
costs.
Furthermore, a uniform foam density distribution of the foam is important for
the quality of the
pipes. However, this is not advantageous when using the processes known from
the prior art.
Usually, a lower foam density is obtained at the ends of the pipe and a higher
foam density is
obtained in the middle. The longer the pipe, the greater is the required foam
density of the
foam in the annular gap due to production reasons.
A disadvantage of the continuous process known from the prior art is that
large amounts of
polyurethane precursor mixture have to be introduced continuously into a
moving double pipe
made up of medium pipe and outer pipe formed by bringing together an elongated
film. Since
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this mixture sometimes cannot be conveyed away quickly enough, the foam can
run out of the
pipe at the front.
Furthermore, the continuous processes known from the prior art have hitherto
not made it
advantageously possible to produce insulated pipes having a pipe diameter of
more than 355
mm. In the production of insulated pipes having pipe diameters of greater than
355 mm using
the processes known from the prior art, a large amount of polyurethane system
has to be
introduced into the film. Owing to the low viscosity of the polyurethane
systems which are
usually used, the polyurethane precursor mixture can, in processes of the
prior art, drip out
from the tube formed at the front and is thus no longer available for the
actual production of
the insulated pipes.
A further problem is to produce insulated pipes having high foam densities of
the polyurethane
foam by means of processes of the prior art. To achieve high foam densities,
it is necessary to
introduce a correspondingly large amount of polyurethane system into the tube
formed from a
film. Here too, the polyurethane system introduced can run out of the tube at
the front and is
thus no longer available to the actual process. The high foam densities are
required for pipes
which are used under water and there have to withstand the respective
hydrostatic pressure.
It is at present difficult to produce insulated pipes which have two or more
pipes for a medium
and have a homogeneous foam structure over the entire pipe cross section by
means of
continuous processes of the prior art. The reason for this is, for example,
the different path
length of the ascending foam when two pipes for a medium are introduced during
production.
It was an object of the present invention to provide a continuous process for
producing
insulated pipes, giving pipes which display a uniformly distributed foam
density over the length
of the pipe and a homogeneous foam structure over the pipe cross section, and
also a small
cell diameter of the polyurethane foam obtained and thus a low thermal
conductivity. It is a
further object of the present invention to provide a process which ensures
that the
polyurethane system introduced does not run out on one side of the pipe formed
but remains
completely in the gap between the at least one medium pipe and the film tube.
It should also
be possible to produce insulated pipes having large diameters and/or high foam
densities of
the insulating material continuously.
These objects are achieved according to the invention by a continuous process
for producing
an insulated pipe comprising at least one medium pipe, an outer pipe, a layer
of at least one
polyurethane between the at least one medium pipe and outer pipe and a film
tube between
the at least one polyurethane and the outer pipe, which comprises at least the
steps:
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(A) provision, in a jaw band, of at least one medium pipe and a film tube
formed
continuously from a film, where the at least one medium pipe is arranged
within the film
tube in such a way that a gap is formed between the at least one medium pipe
and the
film tube,
(B) introduction of a polyurethane system comprising at least one isocyanate
component (a)
and at least one polyol (b) into the gap,
(C) foaming and allowing curing of the polyurethane systems and
(D) application of a layer of at least one material to the film tube in
order to form the outer
pipe,
where the polyurethane system has thixotropic properties.
The process of the invention is carried out continuously. This means, in
particular, that each
individual process step is carried out continuously.
The individual steps of the process of the invention will be described in
detail below.
Step (A):
Step (A) of the process of the invention comprises provision, in a jaw band,
of at least one
medium pipe and a film tube formed continuously from a film, where the at
least one medium
pipe is arranged within the film tube in such a way that a gap is formed
between the at least
one medium pipe and the film tube.
According to the invention, at least one medium pipe, preferably one, two,
three or four pipe(s)
for a medium are present. According to the invention, particular preference is
given to one or
two pipe(s) for a medium, very particularly preferably two pipes for a medium,
being present.
The at least one medium pipe, which according to the invention has a smaller
diameter than
the film tube and than the outer pipe formed in step (D) of the process of the
invention, is
arranged within the outer pipe in such a way that a gap is formed between the
medium pipe
and the outer pipe. The polyurethane system is introduced into this gap in
step (B) according
to the invention. Depending on the number of pipes for a medium which are
present according
to the invention, the gap formed has various shapes. In the particularly
preferred case in which
one medium pipe is present according to the invention, an annular gap is
formed. In the further
preferred embodiment in which two pipes for a medium are present according to
the invention,
a double annular gap is formed.
=
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The at least one medium pipe used according to the invention is generally a
steel pipe having
an external diameter of, for example, from 1 to 70 cm, preferably from 4 to 70
cm, particularly
preferably from 10 to 70 cm and very particularly preferably from 20 to 70 cm.
If more than one
medium pipe is present, these pipes can have identical or different external
diameters.
5 Preference is given to all pipes for media present having the same
diameter. The length of the
at least one medium pipe is, for example, from 3 to 24 m, preferably from 6 to
16 m. More
preferably, the at least one medium pipe is produced as rolled-up product
having a length of,
for example, from 50 to 1500 m.
In the continuous implementation of the process of the invention, the at least
one medium pipe
is provided, for example, in the form of rolled-up product. The at least one
medium pipe can
also be provided as straight lengths of pipe.
In step (A) of the process of the invention, at least one medium pipe and a
film tube formed
continuously from a film are provided in a jaw band.
For this purpose, an elongated film is taken off continuously from a roll and
optionally joined
together by methods known to those skilled in the art, for example welding, to
form a film tube.
This bringing together is, in a preferred embodiment of the process of the
invention, carried out
in the jaw band into which the at least one medium pipe is also continuously
fed. The film is
preferably fed in via a molded shoulder or film shoulder. Preference is given
to a circular film
tube being formed.
The film can comprise at least one layer of thermoplastic polymer which
preferably has a
diffusion-inhibiting effect in respect of the cell gases and oxygen. The film
preferably
additionally comprises at least one layer of metal, e.g. aluminum. Films which
are suitable
according to the invention are known from EP 0 960 723.
The film used according to the invention preferably has a width which allows
formation of a
corresponding film tube which has an internal diameter of generally from 6 to
90 cm,
preferably from 12 to 90 cm, particularly preferably from 19 to 90 cm, very
particularly
preferably from 35 to 90 cm. This film is preferably provided as rolled-up
product.
The film used according to the invention can be made of any material which
appears to be
suitable to a person skilled in the art, for example polyethylene.
The film used according to the invention generally has any thickness which
appears to be
suitable to a person skilled in the art, for example from 5 to 150 pm.
1
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A jaw band used according to the invention is known per se to those skilled in
the art. It
generally comprises two circumferential ridges which, depending on the pipe
dimensions,
carry shape-imparting aluminum jaws. These aluminum jaws are, for example,
pipe half shells
which on coming together form the complete pipe cross section. Up to 180, for
example,
individual segments are installed on each circumferential ridge.
The at least one medium pipe is, in step (A) of the process of the invention,
arranged within
the film tube in such a way that a gap, in the case of one medium pipe being
present an
annular gap, is formed between the at least one medium pipe and the film tube.
Particular
preference is given to the one medium pipe being arranged centrally in the,
preferably circular,
film tube so as to form a concentric annular gap. In the case of more than one
medium pipe
being present, these pipes are preferably arranged symmetrically in the film
tube.
Step (B):
Step (B) of the process of the invention comprises introduction of a
polyurethane system
comprising at least one isocyanate component (a) and at least one polyol (b)
into the gap,
preferably into the annular gap.
The introduction as per step (B) of the process of the invention can generally
be carried out
using any apparatus known to those skilled in the art, for example high-
pressure metering
machines which are freely available on the market, for example from the
companies Hennecke
GmbH, Cannon Deutschland GmbH or Krauss Maffei Kunststofftechnik GmbH.
According to
the invention, it is also possible to use a multiple nozzle bent so as to
correspond to the radius
of the gap formed for the introduction of the polyurethane system as per step
(B) of the
process of the invention.
In step (B) of the process of the invention, a polyurethane system having
thixotropic properties
is introduced. The terms "thixotropy" and "thixotropic properties" are known
per se to those
skilled in the art. For the purposes of the invention, thixotropic properties
mean that the liquid
reaction mixture foams immediately after leaving the mixing head without the
actual reaction
between polyol and isocyanate components having commenced. This prefoaming,
for example
comparable with shaving foam, leads to the material being dimensionally stable
and remaining
at the place of application.
In general, any polyurethane system having thixotropic properties which
appears suitable to a
person skilled in the art can be used in step (B) of the process of the
invention. According to
the invention, the polyurethane systems used can intrinsically have the
thixotropic properties
or the latter are obtained by addition of appropriate additives.
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In a preferred embodiment of the process of the invention, at least one
thixotrope is added to
the polyurethane system before or during step (B).
The present invention therefore preferably provides the process of the
invention in which at
least one thixotrope is added to the polyurethane system before or during step
(B).
Suitable thixotropes are, for example, selected from the group consisting of
inorganic
thixotropes, for example organomodified sheet silicates, hydrophobic or
hydrophilic pyrogenic
silicas, organic thixotropes, for example polyol esters, toluenediamide (TDA)
and derivatives
thereof, liquid thixotropes based on urea-urethanes, for example
isophoronediamine (CAS-No.
2855-13-2), 2,2'-dimethy1-4,4'-methylenebis(cyclohexylamine) (CAS-No. 6864-37-
5),
diethyltoluenediamine (CAS-No. 68479-98-1), triethyleneglycoldiamine (CAS-No.
929-59-9),
polyoxypropylenediamine (CAS-No. 9046-10-0), and mixtures thereof.
The present invention therefore preferably provides the process of the
invention in which the at
least one thixotrope is selected from the group consisting of inorganic
thixotropes, for example
organomodified sheet silicates, hydrophobic or hydrophilic pyrogenic silicas,
organic
thixotropes, for example polyol esters, toluenediamide (TDA) and derivatives
thereof, liquid
thixotropes based on urea-urethanes, for example isophoronediamine (CAS-No.
2855-13-2),
2,2'-dimethy1-4,4'-methylenebis(cyclohexylamine) (CAS-No. 6864-37-5),
diethyltoluenediamine
(CAS-No. 68479-98-1), triethyleneglycoldiamine (CAS-No. 929-59-9),
polyoxypropylenediamine (CAS-No. 9046-10-0), and mixtures thereof.
The at least one thixotrope can, according to the invention, be added to the
polyurethane
system or to the at least one isocyanate component (a) or to the at least one
polyol (b),
preferably to the at least one isocyanate component (a) or to the at least one
polyol (b).
The at least one thixotrope which is preferably present according to the
invention is, for
example, added in an amount of from 0.1 to 20% by weight, preferably from 0.2
to 10% by
weight, particularly preferably from 0.2 to 7% by weight, very particularly
preferably from 0.2 to
5% by weight, in each case based on the at least one isocyanate component (a)
or the at least
one polyol (b).
Polyurethane systems which can be used or are preferably used according to the
invention will
be described in detail below.
As isocyanate component (a), use is made of the customary aliphatic,
cycloaliphatic and in
particular aromatic diisocyanates and/or polyisocyanates. Preference is given
to using
diphenylmethane diisocyanate (MDI) and in particular mixtures of
diphenylmethane
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diisocyanate and polyphenylene-polymethylene polyisocyanates (crude MDI). The
isocyanates
can also be modified, for example by incorporation of uretdione, carbamate,
isocyanurate,
carbodiimide, allophanate and in particular urethane groups.
The isocyanate component (a) can also be used in the form of polyisocyanate
prepolymers.
These prepolymers are known from the prior art. They are prepared in a manner
known per se
by reacting polyisocyanates (a) as described above, for example at
temperatures of about
80 C, with compounds having hydrogen atoms which are reactive toward
isocyanates,
preferably with polyols, to form polyisocyanate prepolymers. The
polyol/polyisocyanate ratio is
generally selected so 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.
According to the invention, particular preference is given to using crude MDI
as isocyanate
component (a).
In a preferred embodiment, the isocyanate component (a) is selected so that it
has a viscosity
of 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
C.
In the polyurethane system used according to the invention, the at least one
polyol is
preferably a polyol mixture (b) which generally comprises polyols as
constituent (b1), and
optionally chemical blowing agents as constituent (b2). In general, the polyol
mixture (b)
comprises physical blowing agents (b3).
The viscosity of the polyol mixture (b) used according to the invention (but
without physical
blowing agents (b3)) is generally from 200 to 10000 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, in each case measured in
accordance with
DIN 53019 at 20 C. In a particularly preferred embodiment, a polyol mixture
(b) (but without
physical blowing agents (b3)) which has a viscosity of more than 3000 mPas,
for example from
3100 to 8000 mPas, in each case measured in accordance with DIN 53019 at 20 C,
is used in
the process of the invention.
The present invention therefore preferably provides the process of the
invention in which a
polyol mixture (b) (but without physical blowing agents (b3)) which has a
viscosity of more than
3000 mPas, for example from 3100 to 8000 mPas, in each case measured in
accordance with
DIN 53019 at 20 C, is used as at least one polyol (b).
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The polyol mixture (b) generally comprises physical blowing agents (b3).
However, the
addition of physical blowing agent leads to a significant decrease in the
viscosity. It is therefore
an important aspect of the invention that the viscosities of the polyol
mixture (b) indicated
above relate, even in the case of the polyol mixture comprising physical
blowing agents, to the
viscosity of the polyol mixture (b) without addition of physical blowing
agents (b3).
Possible polyols (constituent b1) are generally compounds having at least two
groups which
are reactive toward isocyanate, i.e. having at least two hydrogen atoms which
react with
isocyanate groups. Examples thereof are compounds having OH groups, SH groups,
NH
groups and/or NH2groups.
As polyols (constituent b1), preference is given to using compounds based on
polyesterols or
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 polyols (b1) have a hydroxyl number of generally greater than 100 mg
KOH/g, preferably
greater than 150 mg KOH/g, particularly preferably greater than 200 mg KOH/g.
A suitable
upper limit to the hydroxyl number has generally been found to be 1000 mg
KOH/g, preferably
800 mg KOH/g, particularly preferably 700 mg KOH/g, very particularly
preferably 600 KOH/g.
The OH numbers indicated above relate to the totality of the polyols (b1),
which does not rule
out individual constituents of the mixture having higher or lower values.
Component (b1) preferably comprises polyether polyols which are prepared by
known
methods, for example from one or more alkylene oxides having from 2 to 4
carbon atoms in
the alkylene radical by anionic polymerization using alkali metal hydroxides
such as sodium or
potassium hydroxide or alkali metal alkoxides such as sodium methoxide, sodium
or
potassium ethoxide or potassium isopropoxide as catalysts with addition of at
least one starter
molecule comprising from 2 to 8, preferably from 3 to 8, reactive hydrogen
atoms in bound
form or by cationic polymerization using Lewis acids such as antimony
pentachloride, boron
fluoride etherate, etc., or bleaching earth as catalysts.
Suitable alkylene oxides are, for example, tetrahydrofuran, 1,3-propylene
oxide, 1,2- or 2,3-
butylene oxide, styrene oxide and preferably ethylene oxide and 1,2-propylene
oxide. The
alkylene oxides can be used individually, alternately in succession or as
mixtures.
Possible starter molecules are alcohols such as glycerol, trimethylolpropane
(TMP),
pentaerythritol, sugar compounds such as sucrose, sorbitol, and also amines
such as
methylamine, ethylamine, isopropylamine, butylamine, benzylamine, aniline,
toluidine,
toluenediamine, naphthylamine, ethylenediamine (EDA), diethylenetriamine, 4,4'-
,
CA 02879364 2015-01-16
methylenedianiline, 1,3-propanediamine, 1,6-hexanediamine, ethanolamine,
diethanolamine,
triethanolamine and the like.
Further starter molecules which can be used are condensation products of
formaldehyde,
5 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
and also formaldehyde, toluenediamine (TDA) and diethanolamine or ethanolamine
and the
10 like.
Preference is given to using glycerol, sucrose, sorbitol and EDA as starter
molecule.
The polyol mixture can also optionally comprise chemical blowing agents as
constituent (b2).
As chemical blowing agents, preference is given to water or carboxylic acids,
in particular
formic acid. The chemical blowing agent is generally used in an amount of from
0.1 to 4% by
weight, preferably from 0.2 to 2.0% by weight and particularly preferably from
0.3 to 1.5% by
weight, in each case based on the weight of the component (b).
As mentioned above, the polyol mixture (b) generally comprises a physical
blowing agent (b3).
Physical blowing agents are compounds which are dissolved or emulsified in the
starting
materials for polyurethane production and vaporize under the conditions of
polyurethane
formation. These are, for example, hydrocarbons, for example cyclopentane,
halogenated
hydrocarbons and other compounds such as perfluorinated alkanes, e.g.
perfluorohexane,
chlorofluorocarbons and also ethers, esters, ketones and/or acetals. These are
usually used in
an amount of from 1 to 30% by weight, preferably from 2 to 25% by weight,
particularly
preferably from 3 to 20% by weight, based on the total weight of the component
(b).
The present invention therefore preferably provides the process of the
invention in which the
polyurethane system is foamed by means of pentane, preferably cyclopentane, as
physical
blowing agent.
In a preferred embodiment, the polyol mixture (b) comprises crosslinkers as
constituent (b4).
For the purposes of the present invention, crosslinkers are compounds which
have a
molecular weight of from 60 to 400 g/mol and have at least 3 hydrogen atoms
which are
reactive toward isocyanates. An example is glycerol.
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The crosslinkers (b4) are generally used in an amount of from 1 to 10% by
weight, preferably
from 2 to 6% by weight, based on the total weight of the polymer mixture (b)
(but without
physical blowing agents (b3)).
In a further preferred embodiment, the polyol mixture (b) comprises chain
extenders, which
serve to increase the crosslinking density, as constituent (b5). For the
purposes of the present
invention, chain extenders are compounds which have a molecular weight of from
60 to 5
400 g/mol and have 2 hydrogen atoms which are reactive toward isocyanates.
Examples are
butanediol, diethylene glycol, dipropylene glycol and ethylene glycol.
The chain extenders (b5) are generally used in an amount of 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)).
The components (b4) and (b5) can be used individually or in combination in the
polyol mixture.
The polyurethane foams present as insulating material according to the
invention can be
obtained by reaction of the polyurethane system according to the invention.
In the reaction, the at least one isocyanate component (a) and the at least
one polyol (b),
preferably the polyol mixture (b), are generally reacted in such amounts that
the isocyanate
units 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 a preferred embodiment, components (a) and (b) of the polyurethane system
are selected
so that the resulting foam has a compressive strength (at a foam density of 60
kg/m3) of
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.
In general, the overall injected foam density is more than 50 kg/m3,
preferably more than
60 kg/m3, particularly preferably more than 70 kg/m3, very particularly
preferably more than
80 kg/m3, in particular more than 100 kg/m3, in the process of the invention.
The upper limit to
the overall injected foam density is preferably in each case 300 kg/m3. The
overall injected
foam density is generally understood to be the total amount of liquid
polyurethane material
introduced based on the total volume of the annular gap for the foam.
The process of the invention can generally be carried out at any compaction
which appears
suitable to a person skilled in the art. For the purposes of the present
invention, compaction is
CA 02879364 2015-01-16
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the total fill density of the annular gap divided by the free-foamed core foam
density
determined on an uncompacted foam body.
The present invention preferably provides the process of the invention in
which the reaction is
carried out at a compaction of less than 2.0, preferably less than 1.5,
particularly preferably
less than 1.4 and very particularly preferably less than 1.3, in particular
less than 1.2.
The polyurethane system used in step (B) of the process of the invention
preferably comprises
at least one catalyst. According to the invention, it is generally possible to
use all catalysts
which appear to be suitable to a person skilled in the art.
Catalysts which are preferably used according to the invention catalyze the
blowing reaction,
i.e. the reaction of diisocyanate with water. This reaction takes place
predominantly before the
actual polyurethane chain formation, i.e. the polymerization reaction, and
therefore leads to a
fast reaction profile of the polyurethane system. Furthermore, catalysts which
catalyze the
polyurethane gelling reaction or the trimerization reaction of the isocyanate
can preferably be
used.
Examples of catalysts which can be used according to the invention are
selected from the
group consisting of organic tin compounds such as tin(11) salts or organic
carboxylic acids, for
example potassium acetate, potassium formate and/or potassium octoate, basic
amine
compounds such as secondary aliphatic amines, for example
N,N-dimethylaminoethoxyethanol (CAS number 1704-62-7), N,N,N',N'-tetramethy1-
2,2'-oxybis(ethylamine) (CAS number 3033-62-3), imidazoles, amidines,
alkanolamines,
preferably tertiary amines, for example 2[[2-
(dimethylamino)ethyl]methylaminoiethanol (CAS
number 2212-32-0), methylbis(2-dimethylaminoethyl)amine (CAS number 3030-47-
5),
triethylamine, 1,4-diazabicyclo[2.2.2]octane, dimethylbenzylamine,
dimethylcyclohexylamine,
(2-hydroxypropyl)trimethylammonium 2-ethylhexanoate (CAS number 62314-22-1),
N,N,N-
trimethy1-2-hydroxy-1-propaneammonium formate, trimethylhydroxypropylammonium
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), glycine, N-
((2-hydroxy-
5-nonylphenyl)methyl)-N-methyl monosodium salt (CAS number 56968-08-2) and
mixtures
thereof.
The catalysts which are preferred according to the invention can be added to
the polyurethane
system in any way known to those skilled in the art, for example neat or as a
solution, for
example as an aqueous solution.
CA 02879364 2015-01-16
13
Based on the polyol component (b), the at least one catalyst is, according to
the invention,
added in an amount of from 0.01 to 5% by weight, preferably from 0.5 to 5% by
weight,
particularly preferably from 1 to 5% by weight, very particularly preferably
from 1.5 to 5% by
weight, in particular from 2 to 5% by weight.
Additives (b6) can optionally also be added to the polyurethane system used
according to the
invention. For the purposes of the present invention, additives (b6) are the
customary
auxiliaries and additives known in the prior art, but without physical blowing
agents. Mention
may be made by way of example of surface-active substances, foam stabilizers,
cell
regulators, fillers, dyes, pigments, flame retardants, antistatics, hydrolysis
inhibitors and/or
fungistatic and bacteriostatic substances. It may be pointed out that the
general and preferred
viscosity ranges indicated above for the component (b) apply to a polyol
mixture (b) including
any additives (b6) added (but excluding any physical blowing agent (b3)
added).
The present invention therefore preferably provides the process of the
invention in which the at
least one polyol mixture (b) comprises polyols (b1), optionally chemical
blowing agents (b2),
physical blowing agents (b3), crosslinkers (b4), chain extenders (b5),
catalysts and/or
optionally additives (b6).
The present invention therefore provides, in particular, the process of the
invention in which
from 1 to 25% by weight of flame retardants, based on the total weight of the
polyol mixture, is
used as additive (b6).
Step (C):
Step (C) of the process of the invention comprises foaming and allowing curing
of the
polyurethane system.
The foaming and curing is, according to the invention, generally carried out
at a component
temperature of from 18 to 40 C, preferably from 18 to 35 C, particularly
preferably from 22 to
30 C.
The foaming and curing is, according to the invention, generally carried out
at a surface
temperature of from 15 to 50 C, preferably from 20 to 50 C, particularly
preferably from 25 to
45 C.
After step (C) of the process of the invention, an insulated pipe is obtained
comprising at least
one medium pipe, a film tube and an insulating layer composed of polyurethane
foam between
at least one medium pipe and the film tube.
CA 02879364 2015-01-16
14
The insulating layer generally has a thickness of from 1 to 20 cm, preferably
from 3 to 20 cm,
particularly preferably from 5 to 20 cm.
In a further preferred embodiment, the insulating layer comprising
polyurethane foam has a
thermal conductivity of less than 27 mW/mK, preferably less than 26 mW/mK,
particularly
preferably less than 25 mW/mK, very particularly preferably less than 24
mW/mK, in particular
less than 23 mW/mK, in each case measured in accordance with EN ISO 8497.
Step (D):
Step (D) of the process of the invention comprises the application of a layer
of at least one
material to the film tube in order to form the outer pipe.
After step (C) of the process of the invention at least one medium pipe which
is surrounded by
an insulating layer of at least one polyurethane foam which is in turn
surrounded by the film
tube produced in step (A) is obtained. To form the outer pipe composed of at
least one
material, this is applied in step (D) of the process of the invention.
According to the invention,
any suitable material can generally be used as outer pipe.
In a further embodiment of the process of the invention, the material from
which the outer pipe
is formed in step (D) is a thermoplastic polymer.
The present invention therefore preferably provides the process of the
invention in which the
material from which the outer pipe is formed in step (D) is a thermoplastic
polymer, in
particular polyethylene.
The application of thermoplastic polymers can, according to the invention, be
effected by
extrusion. The extrusion of thermoplastic polymers to produce a layer, here
the outer pipe, is
known per se to those skilled in the art.
The application according to step (D) of the process of the invention is
generally carried out at
a temperature which appears suitable to a person skilled in the art for
extrusion of
thermoplastic polymers, for example above the melting temperature of the
thermoplastic
polymer used. Suitable temperatures are, for example, from 180 to 220 C,
preferably from 190
to 230 C or 180 to 230 C, preferably 190 to 220 C.
The outer pipe formed in step (D) of the process of the invention generally
has a thickness of
from 1 to 30 mm. The internal diameter of the outer pipe depends, according to
the invention,
CA 02879364 2015-01-16
on the diameter of the film tube and is, for example, from 6 to 90 cm,
preferably from 12 to
90 cm, particularly preferably from 19 to 90 cm.
The outer pipe can optionally comprise a plurality of layers which can be
brought together
5 during the extrusion process for producing the outer pipe. An example is
the introduction of
multilayer films between polyurethane foam and outer pipe, with the film
comprising at least
one metallic layer in order to improve the barrier action. Suitable outer
pipes of this type are
described in EP-A-960 723. This additional layer which is optionally present
is preferably
introduced together with the film in step (A). For example, it is possible,
according to the
10 invention, to use multilayer films comprising aluminum as diffusion
barrier.
According to the invention, all thermoplastic polymers which have properties
which are
advantageous for a correspondingly insulated pipe are generally suitable.
Examples of
thermoplastic polymers which can be used according to the invention are
selected from the
15 group consisting of polyethylene, polypropylene and mixtures thereof,
with preference being
given to using polyethylene.
After step (D) of the process of the invention the insulated pipe formed can
be treated further
by methods known to those skilled in the art, for example by cutting of the
continuously
produced and thus in principle infinitely long insulated pipe into desired
lengths, for example 6,
12 or 16 m.
In a particularly preferred embodiment, the insulated pipe produced according
to the invention
is an insulated composite outer pipe for district heating networks laid in the
ground, which
meets the requirements of DIN EN 253:2009.
The present invention also provides an insulated pipe which can be produced by
the process
of the invention. The details of the insulated pipe produced which had been
mentioned with
regard to the process of the invention apply analogously. The pipe which has
been produced
continuously according to the invention displays a particularly uniform
density distribution over
the entire length and, as a result of this, low lambda values combined with
better physical
properties. At the same time, the insulated pipe produced according to the
invention has a
large external diameter of, for example, from 125 to 920 mm and/or a
particularly high foam
density of, for example, from 50 to 300 kg/m3.
The present invention also provides an apparatus for producing an insulated
pipe, which
comprises an apparatus for introduction of at least one medium pipe, an
apparatus for the
introduction of a film for forming a film tube, a jaw band, an apparatus for
forming an outer pipe
and an apparatus for addition of at least one thixotrope, preferably for
carrying out the process
" CA 02879364 2015-01-16
16
of the invention. An apparatus for introduction of at least one thixotrope is,
for example, a
multicomponent mixing head or introduction via a static mixer into the high-
pressure circuit.
According to the invention, the at least one thixotrope, as described above,
can be added
during or shortly before production of the polyurethane foam. In a second
embodiment
according to the invention, the at least one thixotrope is mixed into at least
one of the
precursor compounds for production of the same and brought to the location
where the
polyurethane foam is produced and mixed there with the further precursor
compounds.
The individual apparatuses described are known per se to those skilled in the
art. In the case
of the apparatus of the invention, preferably for carrying out the process of
the invention, these
apparatuses known per se have to be arranged according to the invention.
The present invention also provides for the use of the apparatus of the
invention for carrying
out the process of the invention, in particular for producing the insulated
pipe according to the
invention.
