Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS FOR PRODUCING RIGID POLYURETHANE FOAMS
The invention relates to a process for producing rigid polyurethane foams and
to rigid
polyurethane foams produced by the process of the invention and also to a
polyol
component.
Rigid polyurethane foams have been known for a long time and have been
described
widely. Rigid polyurethane foams are used predominantly for thermal
insulation, for
example in refrigeration appliances, transport means or buildings and for
producing
structural elements, in particular sandwich elements.
An important field of use of rigid polyurethane foams is composite elements.
The
production of composite elements composed of, in particular, metallic covering
layers and a
core of foams based on isocyanates, usually polyurethane (PUR) or
polyisocyanurate (PIR)
foams, frequently also referred to as sandwich elements, on continuously
operating double
belt plants is at present practiced on a large scale. Apart from sandwich
elements for
coolstore insulation, elements having colored covering layers are becoming
ever more
important for construction of façades of a variety of buildings. Apart from
coated steel
sheets, stainless steel sheets, copper sheets or aluminum sheets are used as
covering
layers.
It is important that the rigid polyurethane foams fill the hollow spaces
uniformly and without
voids, so that very good bonding to the covering layers gives a stable
construction which
ensures good thermal insulation. To prevent foam defects, the foamable PU
reaction
mixture has to be introduced within a short time into the hollow space to be
insulated. Low-
pressure or preferably high-pressure machines are usually used for filling
such articles with
foam.
A summary overview of the production of rigid polyurethane foams and their use
as
covering layer or core layer in composite elements and also their use as
insulating layer in
refrigeration or heating engineering may be found, for example, in
"Polyurethane",
Kunststoff-Handbuch, volume 7, 3rd edition 1993, edited by Dr. Gunter Oertel,
Carl-
Hanser-Verlag, Munich/Vienna.
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Suitable rigid polyurethane foams can be produced in a known manner by
reacting organic
polyisocyanates with one or more compounds having at least two reactive
hydrogen atoms
in the presence of blowing agents, catalysts and optionally auxiliaries and/or
additives.
As compounds having at least two hydrogen atoms which are reactive toward
isocyanate
groups, preference is given to using polyether alcohols and/or polyester
alcohols for
producing the polyurethanes. The choice of polyols is made, in particular, on
the basis of
costs and the desired use properties (e.g. EP-A 1 632 511, US-B 6,495,722, WO
2006/108833).
However, the surface properties of the known rigid polyurethane foams are
still capable of
improvement, especially in the production of composite elements since these
properties
have a substantial influence on the adhesion of the covering layers to the
foam. In the
production of foams by the spray foam process, too, a good surface is of great
importance.
EP 0 728 783 A1, EP 0 826 708 A1 and WO 2010/106067 describe processes for
producing rigid PU foams, in which the polyol component comprises castor oil.
Castor oil
can be advantageous for the surface properties of the foam. On the other hand,
castor oil
can in the presence of water lead, due to phase separation, to instability of
the polyol
component, which can lead to problems in processing. Water is frequently used
as an
inexpensive and environmentally friendly blowing agent in the polyol
component. A
disadvantage of the process described in EP 0 826 708 A1 is, in addition to
the high
viscosity of the polyol component, the very poor adhesion of the rigid PU
foams formed.
The rigid PU foams produced by the process described EP 0 728 783 A1 are also
still
capable of improvement in respect of their surface properties and adhesion.
The rigid PU
foams produced as described in WO 2010/106067 A1 display good adhesion and
have a
good surface but are still capable of improvement in respect of the storage
stability of the
polyol component in the case of relatively large amounts of water (> 1.5 parts
by weight).
It is an object of the invention to develop a process for producing rigid
polyurethane foams
which leads to foams having good adhesion, good curing and surface quality and
whose
polyol component has good storage stability and thus good processing
properties.
The object has surprisingly been able to be achieved by a process for
producing rigid
polyurethane foams by reacting
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a) organic polyisocyanates with
b) compounds having at least two hydrogen atoms which are reactive toward
isocyanate
groups in the presence of
c) blowing agents,
d) catalysts and, if appropriate,
e) auxiliaries and additives,
wherein a mixture of
b1) from 20 to 60 parts by weight of one or more high-functionality polyether
alcohols
having functionalities of from 3.5 to 5.5 and a hydroxyl number of from 400 to
550 mg
KOH/g,
b2) from 5 to 25 parts by weight of one or more polyether alcohols based on
aromatic
and/or aliphatic amines and having functionalities of from 3.5 to 4.5 and a
hydroxyl
number of from 350 to 500 mg KOH/g,
b3) from 5 to 25 parts by weight of one or more polyether alcohols having
functionalities
of from 2 to 4 and a hydroxyl number of from 150 to 450 mg KOH/g
b4) from 1 to 15 parts by weight of one or more low molecular weight chain
extenders and/or
crosslinkers having functionalities of from 2 to 3 and a molecular weight M,
of < 400 g/mol
and optionally
b5) from 1 to 5 parts by weight of water
is used as component b).
The total parts by weight of b1) to b5) in the polyol component b) by
definition do not
exceed 100 parts by weight. The polyol component b) can also comprise
catalysts,
stabilizers and customary auxiliaries and additives.
The hydroxyl number is determined in accordance with DIN 53240.
The invention further provides the polyol component b) comprising a mixture of
b1) from 20 to 60 parts by weight of one or more high-functionality polyether
alcohols
having functionalities of from 3.5 to 5.5 and a hydroxyl number of from 400 to
550 mg
KOH/g,
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b2) from 5 to 25 parts by weight of one or more polyether alcohols based on
aromatic
and/or aliphatic amines and having functionalities of from 3.5 to 4.5 and a
hydroxyl
number of from 350 to 500 mg KOH/g,
b3) from 5 to 25 parts by weight of one or more polyether alcohols having
functionalities
of from 2 to 4 and a hydroxyl number of from 150 to 450 mg KOH/g
b4) from 1 to 15 parts by weight of one or more low molecular weight chain
extenders
and/or crosslinkers having functionalities of from 2 to 3 and a molecular
weight !Ow of
< 400 g/mol and optionally
b5) from 1 to 5 parts by weight of water.
As regards the individual components used in the process of the invention and
for the
polyol component b) of the invention, the following may be said:
a) Possible organic polyisocyanates are the aliphatic, cycloaliphatic,
araliphatic and
preferably aromatic polyfunctional isocyanates known per se.
Specific examples are: alkylene diisocyanates having from 4 to 12 carbon atoms
in the
alkylene radical, e.g. dodecane 1,12-diisocyanate, 2-ethyltetramethylene 1,4-
diisocyanate,
2-methylpentamethylene 1,5-diisocyanate, tetramethylene 1,4-diisocyanate and
preferably
hexamethylene 1,6-diisocyanate; cycloaliphatic diisocyanates, e.g. cyclohexane
1,3- and
1,4-diisocyanate and also any mixtures of these isomers, 1-isocyanato-3,3,5-
trimethy1-5-
isocyanatomethylcyclohexane (isophorone diisocyanate), hexahydrotolylene 2,4-
and 2,6-
diisocyanate and also the corresponding isomer mixtures, dicyclohexylmethane
4,4'-, 2,2'-
and 2,4'-diisocyanate and also the corresponding isomer mixtures, and
preferably aromatic
diisocyanates and polyisocyanates, e.g. tolylene 2,4- and 2,6-diisocyanate and
the
corresponding isomer mixtures, diphenylmethane 4,4'-, 2,4'- and 2,2'-
diisocyanate and the
corresponding isomer mixtures, mixtures of diphenylmethane 4,4'- and 2,4'-
diisocyanates,
polyphenylpolymethylene polyisocyanates, mixtures of diphenylmethane 4,4'-,
2,4'- and
2,2'-diisocyanates and polyphenylpolymethylene polyisocyanates (crude MDI) and
mixtures
of crude MDI and tolylene diisocyanates. The organic diisocyanates and
polyisocyanates
can be used individually or in the form of their mixtures.
Use is frequently also made of modified polyfunctional isocyanates, i.e.
products which are
obtained by chemical reaction of organic diisocyanates and/or polyisocyanates.
Mention
may be made by way of example of diisocyanates and/or polyisocyanates
comprising
ester, urea, biuret, allophanate, carbodiimide, isocyanurate, uretdione and/or
urethane
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groups.
Specific examples are: organic, preferably aromatic polyisocyanates comprising
urethane
groups and having NCO contents of from 33.6 to 15% by weight, preferably from
31 to 21%
by weight, based on the total weight, for example reaction products of low
molecular weight
diols, triols, dialkylene glycols, trialkylene glycols or polyoxyalkylene
glycols, and having
molecular weights up to 6000, in particular molecular weights up to 1500,
modified
diphenylmethane 4,4'-diisocyanate, modified diphenylmethane 4,4'- and 2,4'-
diisocyanate
mixtures or modified crude MDI or tolylene 2,4- or 2,6-diisocyanate, with
examples of
dialkylene glycols or polyoxyalkylene glycols, which can be used individually
or as
mixtures, being: diethylene glycol, dipropylene glycol, polyoxyethylene,
polyoxypropylene
and polyoxypropylene-polyoxyethylene glycols, triols and/or tetrols. Also
suitable are
prepolymers comprising NCO groups and having NCO contents of from 25 to 3.5%
by
weight, preferably from 21 to 14% by weight, based on the total weight, and
prepared from
the polyester polyols and/or preferably polyether polyols described below and
diphenylmethane 4,4'-diisocyanate, mixtures of diphenylmethane 2,4'- and 4,4'-
diisocyanate, tolylene 2,4- and/or 2,6- diisocyanates or crude MDI.
Liquid polyisocyanates comprising carbodiimide groups and/or isocyanurate
rings and
having NCO contents of from 33.6 to 15% by weight, preferably from 31 to 21%
by weight,
based on the total weight, e.g. compounds based on diphenylmethane 4,4'-, 2,4'-
and/or
2,2'-diisocyanate and/or tolylene 2,4- and/or 2,6-diisocyanate, have also been
found to be
useful.
The modified polyisocyanates can optionally be mixed with one another or with
unmodified
organic polyisocyanates such as diphenylmethane 2,4'-, 4,4'-diisocyanate,
crude MDI,
tolylene 2,4- and/or 2,6- diisocyanate.
The following polyisocyanates have been found to be particularly useful and
are preferably
employed: mixtures of tolylene diisocyanates and crude MDI or mixtures of
modified
organic polyisocyanates comprising urethane groups and having an NCO content
of from
33.6 to 15% by weight, in particular ones based on tolylene diisocyanates,
diphenylmethane 4,4'-diisocyanate, diphenylmethane diisocyanate isomer
mixtures or
crude MDI and in particular crude MDI having a diphenylmethane diisocyanate
isomer
content of from 25 to 80% by weight, preferably from 30 to 55% by weight.
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b) The polyether polyols b1), b2) and b3) used 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 2 to 6, 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.
It is also
possible to use multimetal cyanide compounds, known as DMC catalysts. Tertiary
amines
such as triethylamine, tributylamine, trimethylamine, dimethylethanolamine
and/or
dimethylcyclohexylamine can also be used as catalyst.
Suitable alkylene oxides for preparing the polyether polyols b1), b2) and b3)
are, for
example, ethylene oxide, 1,2-propylene oxide, 1,3-propylene oxide, 1,2- or 2,3-
butylene
oxide, tetrahydrofuran, styrene oxide, preferably ethylene oxide and 1,2-
propylene oxide.
The alkylene oxides can be used individually, alternately in succession or as
mixtures.
Possible starter molecules for the polyether alcohols b1), b2) and b3) used
according to the
invention are the following compounds:
b1) Use is made, in particular, of hydroxyl-comprising high-functionality
compounds, in
particular sugars, starches or lignin, as starter substances. Glucose, sucrose
and sorbitol
are of particular practical importance here. Since these compounds are present
in solid
form under the usual reaction conditions of alkoxylation, it is generally
customary to
alkoxylate these compounds together with coinitiators. Suitable coinitiators
are, in
particular, water and polyfunctional lower alcohols, e.g. glycerol,
trimethylolpropane,
pentaerythritol, ethylene glycol, diethylene glycol, propylene glycol and
homologues
thereof.
b2) As starter molecules having at least two primary amino groups in the
molecule,
preference is given to using aromatic diamines and/or polyamines, for example
phenylenediamines, 2,3-, 2,4-, 3,4- and 2,6-tolylenediamine (TDA) and 4,4'-,
2,4'- and 2,2'-
diaminodiphenylmethane.
Aliphatic starter molecules used are, in particular, ammonia, polyfunctional
aliphatic
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amines, in particular those having from 2 to 6 carbon atoms and primary and
secondary
amino groups, and also amino alcohols having from 2 to 6 carbon atoms in the
main chain.
Preference is given to using ethylenediamine, monoalkylethylenediamines, 1,3-
propylenediamine and also various butylenediamines and hexamethylenediamines;
and
ethanolamine, diethanolamine and triethanolamine as amino alcohols.
b3) Water and/or low molecular weight bifunctional or trifunctional alcohols
are used as
starter substances. In particular, linear or branched alcohols, especially
those having from
2 to 6 carbon atoms in the main chain, are used. Compounds preferably used as
starter
substances are water and, for example, glycerol, trimethylolpropane, ethylene
glycol,
propylene glycol, diethylene glycol, dipropylene glycol, 1,4-butanediol, 1,6-
hexanediol and
homologues thereof. As starter molecules having at least two primary amino
groups in the
molecule, preference is given to using aromatic diamines and/or polyamines,
for example
phenylenediamines, 2,3-, 2,4-, 3,4- and 2,6-toluenediamine (TDA) and 4,4'-,
2,4'- and 2,2'-
diaminodiphenylmethane.
The polyether alcohols b1) preferably have functionalities of from 3.7 to 5.2
and a hydroxyl
number of from 400 to 520 mg KOH/g and particularly preferably functionalities
of from 3.9
to 5 and a hydroxyl number of from 400 to 500 mg KOH/g and very particularly
preferably
functionalities of from 4 to 4.5 and a hydroxyl number of from 450 to 500 mg
KOH/g.
The proportion of the component b1) is preferably from 30 to 60 parts by
weight,
particularly preferably from 35 to 55 parts by weight.
Polyether alcohols b2) based on aromatic amines are preferred. Very particular
preference
is given to polyether alcohols b2) based on aromatic amines and having
functionalities of
from 3.7 to 4.1 and a hydroxyl number of from 360 to 420 mg KOH/g.
The proportion of the component b2) is preferably from 5 to 20 parts by
weight, particularly
preferably from 5 to 15 parts by weight.
Polyether alcohols b3) having functionalities of from 3 to 4 and a hydroxyl
number of from
150 to 430 mg KOH/g, in particular from 150 to 200 mg KOH/g, are preferred.
Preference is given to polyether alcohols b3) based on aromatic amines and
having
functionalities of from 3.8 to 4 and a hydroxyl number of 150-200 mg KOH/g.
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Preference is likewise given to polyether alcohols b3) having a functionality
of 3 and a
hydroxyl number of 150-200 mg KOH/g.
The proportion of the component b3) is preferably from 5 to 20 parts by
weight.
Further information regarding the polyether alcohols b1), b2) and b3) used and
also their
preparation may be found, for example, in Kunststoffhandbuch, volume 7
"Polyurethane",
edited by GOnter Oertel, Carl-Hanser-Verlag, Munich, 3rd edition, 1993.
As low molecular weight chain extenders and/or crosslinkers b4), use is made
of diols
and/or triols and also amino alcohols having molecular weights of less than
400, preferably
from 60 to 300.
Possibilities are, for example, aliphatic, cycloaliphatic and/or araliphatic
diols having from 2
to 14 carbon atoms, preferably from 2 to 10 carbon atoms, e.g. ethylene
glycol, 1,2-
propylene glycol, 1,3-propanediol, 1,10-decanediol, o-, m-, p-
dihydroxycyclohexane,
diethylene glycol, dipropylene glycol, 1,4-butanediol, 1,6-hexanediol and
bis(2-
hydroxyethyl)hydroquinone, triols such as 1,2,4-, 1,3,5-trihydroxycyclohexane,
glycerol and
trimethylolpropane and low molecular weight hydroxyl-comprising polyalkylene
oxides
based on ethylene oxide and/or 1,2-propylene oxide and the abovementioned
diols and/or
triols as starter molecules and also amino alcohols such as diethanolamine and
triethanolamine.
The use an aliphatic diol having 2-6 carbon atoms, in particular 1,2-propylene
glycol, as
chain extender b4) is particularly preferred.
The abovementioned low molecular weight chain extenders and/or crosslinkers
b4) are
advantageously used in an amount of from 1 to 15% by weight, preferably from 2
to 10%
by weight, based on the weight of the polyol compound (b).
The component b) can comprise from 1 to 5 parts by weight, in particular from
1.5 to 5
parts by weight, of water b5). In one embodiment, the proportion of water b5)
is from 2 to
5% by weight. This embodiment can be combined with other embodiments of the
process
of the invention.
c) As blowing agent for the process of the invention, it is possible to use
the blowing
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agents customary for producing rigid polyurethane foams.
As blowing agents c), it is possible to use water and additionally generally
known
chemically and/or physically acting compounds. For the purposes of the present
invention,
chemical blowing agents are compounds which react with isocyanate to form
gaseous
products, for example water or formic acid. 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, halogenated hydrocarbons and other compounds, for example
perfluorinated alkanes such as perfluorohexane, chlorofluorocarbons, and
ethers, esters,
ketones, acetals and also inorganic and organic compounds which liberate
nitrogen on
heating, or mixtures thereof, for example (cyclo)aliphatic hydrocarbons having
from 4 to 8
carbon atoms or fluorinated hydrocarbons such as 1,1,1,3,3-pentafluoropropane
(HFC 245
fa), trifluoromethane, difluoromethane, 1,1,1,3,3-pentafluorobutane (HFC 365
mfc), 1,1,1,2-
tetrafluoroethane, difluoroethane and heptafluoropropane.
Low-boiling aliphatic hydrocarbons, preferably n-pentane and/or isopentane, in
particular n-
pentane, are advantageously used as blowing agents.
n-Pentane has a boiling point of 36 C, isopentane a boiling point of 28 C. The
boiling points
are therefore in a range which is favorable for the blowing process.
Since the aliphatic hydrocarbons which are suitable as blowing agents are
flammable and
explosive, the foaming plants have to be equipped with the appropriate safety
devices as
are also necessary when using n-pentane as blowing agent.
It is advantageous to use the aliphatic hydrocarbons together with water as
blowing agent.
The amount of aliphatic hydrocarbons used is from 2 to 25% by weight,
preferably from 5 to
15% by weight, based on the component b). The proportion of water depends on
the
desired foam density of the rigid polyurethane foam and is generally from 2 to
2.5%.
d) Catalysts (d) used for producing the rigid polyurethane foams are, in
particular,
compounds which strongly accelerate the reaction of the compounds comprising
reactive
hydrogen atoms, in particular hydroxyl groups, of the component (b) with the
organic,
optionally modified polyisocyanates (a).
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Suitable catalysts (d) are strongly basic amines, for example amidines such as
2,3-dimethy1-3,4,5,6-tetrahydropyrimidine, tertiary amines such as
triethylamine,
tributylamine, dimethylcyclohexylamine, dimethylbenzylamine, N-
methylmorpholine,
N-ethylmorpholine, N-cyclohexylmorpholine, N,N,N',N'-
tetramethylethylenediamine,
N,N,N',N'-tetramethylbutanediamine,
N,N,N',N'-tetramethy1-1,6-hexanediamine,
pentamethyldiethylenetriamine, tetramethyldiamino(ethyl ether), bis(2-
dimethylaminoethyl)
ether, bis(dimethylaminopropyl)urea, dimethylpiperazine, 1,2-
dimethylimidazole, 1-
azabicyclo[3.3.0]octane and preferably 1,4-diazabicyclo[2.2.2]octane, and
alkanolamine
compounds such as triethanolamine, triisopropanolamine, N-methyldiethanolamine
and N-
ethyldiethanolamine, N,N-dimethylaminoethoxyethanol,
N,N,N'-
trimethylaminoethylethanolamine and dimethylethanolamine.
Further possible catalysts are: tris(dialkylaminoalkyl)-s-hexahydrotriazines,
in particular
tris(N,N-dimethylaminopropy1)-s-hexahydrotriazine, tetraalkylammonium
hydroxides such
as tetramethylammonium hydroxide, alkali metal hydroxides such as sodium
hydroxide and
alkali metal alkoxides such as sodium methoxide and potassium isopropoxide and
also
alkali metal salts of long-chain fatty acids having from 10 to 20 carbon atoms
and optionally
lateral OH groups.
If isocyanurate groups are to be incorporated into the rigid foam, specific
catalysts are
required. As isocyanurate catalysts, use is usually made of metal
carboxylates, in particular
potassium acetate and solutions thereof. The catalysts can, depending on
requirements, be
used either alone or in any mixtures with one another.
Preference is given to using from 0.001 to 7% by weight, in particular from
0.05 to 5% by
weight, of catalyst or catalyst combination, based on the weight of the
component (b).
e) Auxiliaries and/or additives (e) can optionally be incorporated into
the reaction mixture
for producing the rigid polyurethane foams. Mention may be made by way of
example of
surface-active substances, foam stabilizers, cell regulators, fillers, dyes,
pigments, flame
retardants, hydrolysis inhibitors, fungistatic and bacteriostatic substances.
Possible surface-active substances are, for example, compounds which serve to
aid the
homogenization of the starting materials and may also be suitable for
regulating the cell
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structure of the plastics. Mention may be made by way of example of
emulsifiers such as
the sodium salts of castor oil sulfates or of fatty acids and also salts of
fatty acids with
amines, e.g. diethylamine oleate, diethanolamine stearate, diethanolamine
ricinoleate, salts
of sulfonic acids, e.g. alkali metal or ammonium salts of
dodecylbenzenesulfonic acid or
dinaphthylmethanedisulfonic acid and ricinoleic acid; foam stabilizers such as
siloxane-
oxyalkylene copolymers and other organopolysiloxanes, ethoxylated
alkylphenols,
ethoxylated fatty alcohols, paraffin oils, castor oil esters and ricinoleic
esters, Turkey red oil
and peanut oil and cell regulators such as paraffins, fatty alcohols and
dimethylpolysiloxanes. The above-described oligomeric acrylates having
polyoxyalkylene
and fluoroalkane radicals as side groups are also suitable for improving the
emulsifying
action, the cell structure and/or for stabilizing the foam. The surface-active
substances are
usually employed in amounts of from 0.01 to 5 parts by weight, based on 100
parts by
weight of the component (b).
For the purposes of the present invention, fillers, in particular reinforcing
fillers, are the
customary organic and inorganic fillers, reinforcing materials, weighting
agents, agents for
improving the abrasion behavior in paints, coating compositions, etc., known
per se.
Specific examples are: inorganic fillers such as siliceous minerals, for
example sheet
silicates such as antigorite, serpentine, horn blendes, amphiboles,
chrysotile, talc; metal
oxides such as kaolin, aluminum oxides, titanium oxides and iron oxides, metal
salts such
as chalk, barite and inorganic pigments such as cadmium sulfide, zinc sulfide
and also
glass, etc. Preference is given to using kaolin (china clay), aluminum
silicate and
coprecipitates of barium sulfate and aluminum silicate and also natural and
synthetic
fibrous minerals such as wollastonite, metal fibers and in particular glass
fibers of various
lengths which may be coated with a size. Possible organic fillers are, for
example: carbon,
melamine, rosin, cyclopentadienyl resins and graft polymers and also cellulose
fibers,
polyamide, polyacrylonitrile, polyurethane, polyester fibers based on aromatic
and/or
aliphatic dicarboxylic esters and in particular carbon fibers.
The inorganic and organic fillers can be used individually or as mixtures and
are
advantageously incorporated into the reaction mixture in amounts of from 0.5
to 50% by
weight, preferably from 1 to 40% by weight, based on the weight of the
components (a) and
(b), but the content of mats, nonwovens and woven fabrics of natural and
synthetic fibers
can reach values of up to 80% by weight.
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As flame retardants, it is possible to employ organic phosphoric esters and/or
phosphonic
esters. Preference is given to using compounds which are not reactive toward
isocyanate
groups. Chlorine-comprising phosphoric esters are also among the preferred
compounds.
Suitable flame retardants are, for example, tris(2-chloropropyl) phosphate,
triethyl
phosphate, diphenyl cresyl phosphate, diethyl ethanephosphinate, tricresyl
phosphate,
tris(2-chloroethyl) phosphate, tris(1,3-dichloropropyl) phosphate, tris(2,3-
dibromopropyl)
phosphate, tetrakis(2-chloroethyl) ethylene diphosphate, dimethyl
methanephosphonate,
diethyl diethanolaminomethylphosphonate and also commercial halogen-comprising
flame
retardant polyols.
In addition, it is also possible to use bromine-comprising flame retardants.
As bromine-
comprising flame retardants, preference is given to using compounds which are
reactive
toward the isocyanate group. Such compounds are, for example, esters of
tetrabromophthalic acid with aliphatic diols and alkoxylation products of
dibromobutenediol.
Compounds derived from the group of brominated neopentyl compounds comprising
OH
groups can also be employed.
Apart from the abovementioned halogen-substituted phosphates, it is also
possible to use
inorganic or organic flame retardants such as red phosphorus, aluminum oxide
hydrate,
antimony trioxide, arsenic oxide, ammonium polyphosphate and calcium sulfate,
expandable graphite or cyanuric acid derivatives such as melamine, or mixtures
of at least
two flame retardants such as ammonium polyphosphates and melamine and
optionally
maize starch or ammonium polyphosphate, melamine and expandable graphite
and/or
aromatic or nonaromatic polyesters for making the polyisocyanate polyaddition
products
flame resistant. In general, it has been found to be advantageous to use from
5 to 50 parts
by weight, preferably from 5 to 25 parts by weight, of the flame retardants
mentioned per
100 parts by weight of the component (b).
Further details regarding the abovementioned other customary auxiliaries and
additives
may be found in the specialist literature, for example the monograph by J.H.
Saunders and
K.C. Frisch "High Polymers", volume XVI, Polyurethanes, parts 1 and 2,
Interscience
Publishers 1962 and 1964, or Kunststoff-Handbuch, Polyurethane, volume VII,
Hanser-
Verlag, Munich, Vienna, 3rd edition, 1993.
To produce the rigid polyurethane foams, the polyisocyanates a) and the polyol
component
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b) are reacted in such amounts that the isocyanate index is in the range from
100 to 150,
preferably from 105 to 140, and particularly preferably from 110 to 130. The
isocyanate
index is the molar ratio of isocyanate groups to groups which are reactive
toward
isocyanate groups, multiplied by 100.
The rigid foams of the invention are preferably produced on continuously
operating double
belt plants. Here, the polyol component and the isocyanate component are
metered by
means of a high-pressure machine and mixed in a mixing head. Catalysts and/or
blowing
agents can be added to the polyol mixture beforehand by means of separate
pumps. The
reaction mixture is applied continuously to the lower covering layer. The
lower covering
layer with the reaction mixture and the upper covering layer run into the
double belt. Here,
the reaction mixture foams and cures. After leaving the double belt, the
continuous strip is
cut into the desired dimensions. In this way, it is possible to produce
sandwich elements
having metallic covering layers or insulation elements having flexible
covering layers.
The starting components are mixed at a temperature of from 15 to 90 C,
preferably from 20
to 60 C, in particular from 20 to 45 C. The reaction mixture can be cast into
closed support
tools by means of high- or low-pressure metering machines. Discontinuous
sandwich
elements, for example, are manufactured by this technology.
The invention further provides rigid polyurethane foams produced by the
process of the
invention.
The rigid polyurethane foams produced by the process of the invention have a
density of
from 0.02 to 0.75 g/cm3, preferably from 0.025 to 0.24 g/cm3 and in particular
from 0.03 to
0.1 g/cm3. They are particularly suitable as insulation material in the
building and
refrigeration sector, e.g. as intermediate layer for sandwich elements or for
filling housings
of refrigerators and freezer chests with foam.
The rigid PUR foams produced by the process of the invention have good
surfaces with
few defects and display good adhesion and good curing. The polyol component
(b) at the
same time has good storage stability at 20 C or 5 C over several months.
The invention is illustrated by the examples below.
Comparative example 1
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A polyol component was produced by mixing
42.4 parts by weight of a polyether alcohol having a hydroxyl number of 490 mg
KOH/g and
based on propylene oxide and a mixture of sucrose and glycerol as starter,
15 parts by weight of a polyether alcohol having a hydroxyl number of 390 mg
KOH/g and
based on ethylene oxide/propylene oxide and vicinal TDA as starter,
20 parts by weight of castor oil,
8 parts by weight of 1,2-propylene glycol,
parts by weight of tris-2-chloroisopropyl phosphate,
10 2 parts by weight of Tegostab B8496 from Goldschmidt,
0.5 part by weight of potassium acetate in ethylene glycol, 50% strength
solution, and
2.1 parts by weight of water.
The polyol component is not stable at 20 C and also at 5 C and separates into
two phases
after 24 hours.
Comparative example 2
A polyol component was produced by mixing
70.4 parts by weight of a polyether alcohol having a hydroxyl number of 490 mg
KOH/g and
based on propylene oxide and a mixture of sucrose and glycerol as starter,
15 parts by weight of a polyether alcohol having a hydroxyl number of 390 mg
KOH/g and
based on ethylene oxide/propylene oxide and vicinal TDA as starter,
10 parts by weight of tris-2-chloroisopropyl phosphate,
2 parts by weight of Tegostab B8496 from Goldschmidt,
0.5 part by weight of potassium acetate in ethylene glycol, 50% strength
solution, and
2.1 parts by weight of water.
The polyol component is stable at 20 C and also at 5 C. This was reacted with
a polymeric
MDI having an NCO content of 30.9% by weight (Lupranat M50 from BASF SE) in
the
presence of n-pentane (7 parts by weight), dimethylcyclohexylamine and water
at an
isocyanate index of 120. The amounts of dimethylcyclohexylamine and water were
selected so that the gel time was 45 seconds and the resulting foam had a
density of 36 g/I.
Example 1
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= ,=
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A polyol component was produced by mixing
42.4 parts by weight of a polyether alcohol having a hydroxyl number of 490 mg
KOH/g and
based on propylene oxide and a mixture of sucrose and glycerol as starter,
15 parts by weight of a polyether alcohol having a hydroxyl number of 390 mg
KOH/g and
based on ethylene oxide/propylene oxide and vicinal TDA as starter,
20 parts by weight of a polyether alcohol having a hydroxyl number of 160 mg
KOH/g and
based on ethylene oxide/propylene oxide and vicinal TDA as starter,
8 parts by weight of 1,2-propylene glycol,
parts by weight of tris-2-chloroisopropyl phosphate,
10 2 parts by weight of Tegostab B8496 from Goldschmidt,
0.5 part by weight of potassium acetate in ethylene glycol, 50% strength
solution, and
2.1 parts by weight of water.
The polyol component is stable at 20 C and also at 5 C. This was reacted with
a polymeric
MDI having an NCO content of 30.9% by weight (Lupranat M50 from BASF SE) in
the
presence of n-pentane (7 parts by weight), dimethylcyclohexylamine and water
at an
isocyanate index of 120. The amounts of dimethylcyclohexylamine and water were
selected so that the gel time was 45 seconds and the resulting foam had a
density of 36 g/I.
Example 2
A polyol component was produced by mixing
42.4 parts by weight of a polyether alcohol having a hydroxyl number of 490 mg
KOH/g and
based on propylene oxide and a mixture of sucrose and glycerol as starter,
15 parts by weight of a polyether alcohol having a hydroxyl number of 390 mg
KOH/g and
based on ethylene oxide/propylene oxide and vicinal TDA as starter,
20 parts by weight of a polyether alcohol having a hydroxyl number of 160 mg
KOH/g and
based on propylene oxide and trimethylolpropane as starter,
8 parts by weight of 1,2-propylene glycol,
10 parts by weight of tris-2-chloroisopropyl phosphate,
2 parts by weight of Tegostab B8496 from Goldschmidt,
0.5 part by weight of potassium acetate in ethylene glycol, 50% strength
solution, and
2.1 parts by weight of water.
The polyol component is stable at 20 C and also at 5 C. This was reacted with
a polymeric
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MDI having an NCO content of 30.9% by weight (Lupranate M50 from BASF SE) in
the
presence of n-pentane (7 parts by weight), dimethylcyclohexylamine and water
at an
isocyanate index of 120. The amounts of dimethylcyclohexylamine and water were
selected so that the gel time was 45 seconds and the resulting foam had a
density of 36 g/I.
Curing was determined by means of the indenter test. For this purpose, a steel
indenter
having a hemispherical end having a radius of 10 mm was pressed to a depth of
10 mm
into the foam formed by means of a tensile/compressive testing machine at 3,
4, 5 and 6
minutes after mixing of the components in a polystyrene cup. The maximum force
required
in N is a measure of the curing of the foam. The sum of curing after 3, 4, 5
and 6 minutes is
reported.
For the adhesion experiments, sandwich elements (200x200x80 mm) having
metallic
covering layers were foamed in the laboratory in a closed heated mold. The
temperature of
the mold was 40 C and the total density of the foam was 36 g/I. After curing
of the system,
test specimens having dimensions of 100x100x80 mm were sawn and the adhesion
of the
foam to the covering layer (tensile strength in Table 1) was determined in
accordance with
DIN EN ISO 527-1 / DIN 53292.
The frequency of surface defects was determined quantitatively by an optical
method. For
this purpose, a foam specimen was cut down to a plane one millimeter from the
lower
covering layer, i.e. the covering layer to which the polyurethane reaction
solution had been
applied in the double belt process.
In the quantitative assessment of the surface, the surface of the foam was
illuminated from
the right and then from the left and in each case photographed. The images
were
superimposed and analyzed by means of image analysis software. The defects on
the
surface appear as black areas. The percentage of the black areas based on the
total
surface area is a measure of the frequency of surface defects in the foam.
Furthermore, an additional qualitative assessment of the nature of the surface
of the foams
was carried out by removing the covering layer from a lm x 2m foam specimen
and
visually assessing the surface.
The results are shown in Table 1.
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Table 1
Comparative Comparative Example 1 Example 2
example 1 example 2
Stability of the polyol unstable stable stable stable
component at 20 C
Stability of the polyol unstable stable stable stable
component at 5 C
Total curing after 3, 4, 5 and 330 351 352
6 min [NI]
Tensile strength [N/mm2] 0.24 0.34 0.33
Surface (qualitative) poor very good very good
Surface (quantitative) [%] 5.9 0.7 1
The results in Table 1 show that the stability of the polyol component is good
at 20 C and
5 C and the surface properties, the curing and the adhesion of the foams
produced by the
process of the invention are very good.
The storage stability of the polyol components used in the process of the
invention is very
good; polyol components corresponding to examples 1 and 2, which each comprise
5 parts
by weight of water, are even stable for months at 20 C and also at 5 C.
The PU foams obtained according to comparative example 2 display a
significantly lower
tensile strength and poorer surface properties.
