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Description  |
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The present invention relates to a process for the production of cellular
plastics by the polyisocyanate polyaddition process, which plastics are
also referred to as polyisocyanate polyaddition products below, in which
the blowing agent used is a low-boiling, fluorinated or perfluorinated,
tertiary alkylamine (d1) or a mixture of (d1) and at least one further
physical and/or chemical blowing agent (d2) which is different from (d1),
and in which the blowing agent (d1) is usually sparingly soluble or
insoluble, in the necessary amounts, in the organic polyisocyanate or the
compound containing at least two reactive hydrogen atoms and is therefore
emulsified in at least one of these starting components, and to blowing
agent-containing emulsions of the abovementioned blowing agent (d1) or a
mixture of (d1) and (d2) and at least one starting component (a), (b) or
(c) for the production of the polyisocyanate polyaddition products.
The production of cellular polyisocyanate polyaddition products, for
example cellular polyurethane elastomers and flexible, semi-rigid or rigid
polyurethane foams, by reacting organic polyisocyanates and/or modified
organic polyisocyanates with relatively high-molecular-weight compounds
containing at least two reactive hydrogen atoms, for example
polyoxyalkylenepolyamines and/or preferably organic polyhydroxyl compounds
having molecular weights of, for example, from 500 to 12,000 and, if
desired, chain extenders and/or crosslinking agents having molecular
weights of approximately 500 in the presence of catalysts, blowing agents,
assistants and/or additives has been disclosed in numerous patents and
other publications. A suitable choice of the starting components
polyisocyanate, relatively high-molecular-weight compound containing
reactive hydrogen atoms and, if desired, chain extender and/or
crosslinking agent allows elastic or rigid, cellular polyisocyanate
polyaddition products and all modifications in between to be produced by
this method.
A review on the production of cellular polyurethane (PU) elastomers,
polyurethane (PU) foams and polyisocyanurate (PIR) foams, their mechanical
properties and their use is given, for example, in the monographs High
Polymers, Volume XVI, Polyurethanes, Parts I and II, by J. H. Saunders and
K. C. Frisch (Interscience Publishers, New York, 1962 and 1964
respectively), Kunststoff-Handbuch, Volume VII, Polyurethane, 1st Edition,
1966, edited by Dr. R. Vieweg and Dr. A. Hochtlen, and 2nd Edition, 1983,
edited Dr. G. Oertel (Carl Hanser Verlag, Munich) and
Integralschaumstoffe, edited by Dr. H. Piechota and Dr. H. Rohr (Carl
Hanser Verlag, Munich, Vienna, 1975).
Cellular plastics are produced by the polyisocyanate polyaddition process
using essentially two types of blowing agent:
low-boiling, inert liquids which evaporate under the conditions of the
exothermic polyaddition reaction, for example, alkanes, such as butane,
pentane, inter alia, or preferably halogenated hydrocarbons, such as
methylene chloride, dichloromonofluoromethane, trichlorofluoromethane,
inter alia, and chemical compounds which form blowing gases by a chemical
reaction or thermal decomposition. Examples which may be mentioned are the
reaction of water with isocyanates to form amines and carbon dioxide,
which proceeds synchronously with the polyurethane preparation, and the
cleavage of thermally labile compounds, e.g. azoisobutyronitrile, which,
as a cleavage product, in addition to nitrogen, gives toxic
tetramethylsuccinonitrile or azodicarbonamide, whose use as a constituent
of a blowing agent combination is described in EP-A 0 092 740 (CA
1,208,912). While the last-mentioned method, in which thermally labile
compounds, e.g. azo compounds, hydrazides, semicarbazides, N-nitroso
compounds, benzoxazines, inter alia (Kunststoffe 66 (1976), 10, pages 698
to 701) are usually incorporated into a previously prepared polymer or
drum-coated onto the polymer granules and are foamed by extrusion, has
remained of minor importance in industry, physical low-boiling liquids, in
particular chlorofluoroalkanes, are used worldwide on a large scale for
the production of polyurethane and polyisocyanurate foams. The only
disadvantage of these blowing gases is environmental pollution. By
contrast, the formation of blowing gases by thermal cleavage or chemical
reaction gives cleavage products and/or reactive byproducts which are
included in or chemically bonded to the polyaddition product and can
result in an undesired modification of the mechanical properties of the
plastic. In the case of the formation of carbon dioxide from water and
isocyanate, urea groups are formed in the polyaddition product and can
result in an improvement in the compressive strength or even embrittlement
of the polyurethane, depending on their amount.
According to EP-A-351 614, it is furthermore possible to use as blowing
agents fluorinated hydrocarbons, perfluorinated hydrocarbons, sulfur
hexafluoride or mixtures of at least two of these compounds. Since these
fluorinated or perfluorinated blowing agents are sparingly soluble or
insoluble in the starting components for the production of the
polyisocyanate polyaddition products, they are emulsified in at least one
organic and/or modified organic polyisocyanate, at least one relatively
high-molecular-weight compound containing at least two reactive hydrogen
atoms or a mixture of at least one relatively high-molecular-weight
compound containing at least two reactive hydrogen atoms and a
low-molecular-weight chain extender and/or crosslinking agent. This method
allows the production of cellular plastics having a uniform and fine cell
structure. The only disadvantages of this process are the narrow choice of
suitable fluorinated or perfluorinated compounds having a boiling point in
the necessary range and the high price of these blowing agents. The
production of cellular plastics having the cell structure required in
industry is restricted to a narrow choice of mixtures of perfluoropentane
and perfluorohexane.
Low-boiling hydrocarbons which can be used as blowing agents are soluble i
the starting components for the preparation of the polyisocyanate
polyaddition products and give cellular plastics having a relatively
coarse, frequently non-uniform cell structure and increased thermal
conductivity.
The mechanism of foam formation in the preparation of polyisocyanate
polyaddition products and the effect of surface-active assistants based on
siloxaneoxyalkylene copolymers on this reaction has been described by B.
Kanner et al. (J. of cellular Plastics, January, 1969, pages 32 to 39).
It is an object of the present invention to replace all or at least some of
the chlorofluorocarbons known as blowing agents for the production of
cellular plastics by the polyisocyanate polyaddition process by other,
environmentally friendly blowing agents without adversely effecting the
fine-celled foam structure, as can be achieved using emulsions based on
fluorinated hydrocarbons. It is a further object of the present invention
to improve the processing properties of the reaction mixtures containing
the blowing agents and to minimize their sensitivity in a variety of
foaming equipment.
We have found that, surprisingly, this object is achieved with the aid of
low-boiling, fluorinated or perfluorinated, tertiary alkylamines.
The present invention accordingly provides a process for the production of
cellular plastics by the polyisocyanate polyaddition process, by reacting
a) an organic and/or modified organic polyisocyanate with
b) at least one relatively high-molecular-weight compound containing at
least two reactive hydrogen atoms, and, if desired,
c) a low-molecular-weight chain extender and/or cross-linking agent,
in the presence of
d) a blowing agent
e) a catalyst and
f) assistants and/or additives,
wherein the blowing agent (d) used is a low-boiling, fluorinated or
preferably perfluorinated, tertiary alkylamine.
In a modified embodiment of the process according to the invention, blowing
agent (d) used may furthermore be a mixture which contains
d1) at least one low-boiling, fluorinated and/or preferably perfluorinated,
tertiary alkylamine, and
d2) at least one further physical or chemical blowing agent which is
different from (d1), or a mixture of at least one such physical blowing
agent and at least one such chemical blowing agent.
The present invention furthermore provides blowing agent-containing
emulsions which contain
i) at least one low-boiling, fluorinated or preferably perfluorinated,
tertiary alkylamine having 3 to 9 carbon atoms which is sparingly soluble
or insoluble in the starting components (a), (b) and (c), and
ii) at least one organic and/or modified organic polyisocyanate (a) or at
least one relatively high-molecular-weight compound containing at least
two reactive hydrogen atoms (b) or at least one low-molecular-weight chain
extender and/or crosslinking agent (c), or a mixture of (b) and (c).
Since the fluorinated or preferably perfluorinated, tertiary alkylamines
which can be used according to the invention are, in the amounts necessary
as blowing agents, usually sparingly soluble or insoluble in the starting
components for the production of the polyisocyanate polyaddition products,
these alkylamines are expediently emulsified in at least one of the
starting components (a), (b) and (c), preferably in (b) or a mixture of
(b) and (c).
Surprisingly, it has been found that emulsions of this type are simple to
prepare, relatively stable and easy to handle under a very wide range of
processing conditions and are distinguished by improved processing
properties. The polyisocyanate polyaddition products produced according to
the invention have a uniform, fine-celled structure and good mechanical
properties. Particularly noteworthy is their extremely low thermal
conductivity. A further advantage is the good chemical degradability of
the fluorinated and perfluorinated, tertiary alkylamines in the
atmosphere.
The following details apply to the starting components (a) to (f), in
particular to the blowing agent or blowing agent mixture (d) which can be
used according to the invention for the production of the cellular
polyisocyanate polyaddition products, preferably the foams containing
urethane groups or urethane and isocyanurate groups:
suitable organic polyisocyanates (a) are conventional aliphatic,
cycloaliphatic, araliphatic and preferably aromatic polyisocyanates.
The following may be mentioned as examples: alkylene diisocyanates having
from 4 to 12 carbon atoms in the alkylene moiety, such as 1,12-dodecane
diisocyanate, 2-ethyltetramethylene 1,4-diisocyanate,
2-methylpentamethylene 1,5-diisocyanate, tetramethylene 1,4-diisocyanate
and preferably hexamethylene 1,6-diisocyanate; cycloaliphatic
diisocyanates, such as cyclohexane 1,3- and 1,4-diisocyanate and any
desired mixtures of these isomers,
1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophorone
diisocyanate), 2,4- and 2,6-hexahydrotolylene diisocyanate, and the
corresponding isomer mixtures, 4,4'-, 2,2'- and 2,4'-dicyclohexylmethane
diisocyanate and the corresponding isomer mixtures, and preferably
aromatic diisocyanates and polyisocyanates, e.g. 2,4- and 2,6-tolylene
diisocyanate and the corresponding isomer mixtures, 4,4'-, 2,4'- and
2,2'-diphenylmethane diisocyanate and the corresponding isomer mixtures,
mixtures of 4,4'- and 2,4'-diphenylmethane diisocyanates,
polyphenyl-polymethylene polyisocyanates, mixtures of 4,4'-, 2,4'- and
2,2'-diphenylmethane diisocyanates and polyphenyl-polymethylene
polyisocyanates (crude MDI), and mixtures of crude MDI and tolylene
diisocyanates. The organic diisocyanates and polyisocyanates may be
employed individually or in the form of mixtures.
Frequently, modified polyisocyanates are also used, i.e. products which are
obtained by chemical reaction of organic diisocyanates and/or
polyisocyanates. Specific examples are ester-, urea-, biuret-,
allophanate-, carbodiimide-, isocyanurate-, uretdione- and/or
urethane-containing diisocyanates and/or polyisocyanates. Individual
examples are urethane-containing organic, preferably aromatic,
polyisocyanates containing from 33.6 to 15% by weight, preferably from 31
to 21% by weight, of NCO, based on the total weight, for example
4,4'-diphenylmethane diisocyanate, 4,4'- or 2,4'diphenylmethane
diisocyanate mixtures, crude MDI or 2,4- or 2,6-tolylene diisocyanate
modified by means of low-molecular-weight diols, triols, dialkylene
glycols, trialkylene glycols or polyoxyalkylene glycols having molecular
weights of up to 6000, specific examples of di- and polyoxyalkylene
glycols, which can be employed individually or as mixtures, being
diethylene glycol, dipropylene glycol, polyoxyethylene glycol, triol
and/or tetrol, polyoxypropylene glycol, triol and/or tetrol and
polyoxypropylene-polyoxyethylene glycol, triol and/or tetrol.
NCO-containing prepolymers containing from 25 to 3.5% by weight,
preferably from 21 to 14% by weight, of NCO, based on the total weight,
and prepared from the polyester- and/or preferably polyether-polyols
described below and 4,4'-diphenylmethane diisocyanate, mixtures of 2,4'-
and 4,4'-diphenylmethane diisocyanate, 2,4- and/or 2,6-tolylene
diisocyanates or crude MDI are also suitable. Furthermore, liquid
polyisocyanates containing carbodiimide groups and/or isocyanurate rings
and containing from 33.6 to 15% by weight, preferably from 31 to 21% by
weight, of NCO, based on the total weight, e.g. based on 4,4'-, 2,4'-
and/or 2,2'-diphenylmethane diisocyanate and/or 2,4- and/or 2,6-tolylene
diisocyanate, have also proven successful.
The modified polyisocyanates may be mixed with one another or with
unmodified organic polyisocyanates, e.g. 2,4'- or 4,4'-diphenylmethane
diisocyanate, crude MDI or 2,4- and/or 2,6-tolylene diisocyanate.
Organic polyisocyanates which have proven particularly successful and are
preferred for use for the production of cellular elastomers are
NCO-containing prepolymers containing from 25 to 9% by weight of NCO, in
particular based on polyether- or polyester-polyols and one or more
diphenylmethane diisocyanate isomers, advantageously 4,4'-diphenylmethane
diisocyanate and/or modified urethane-containing organic polyisocyanates
containing from 33.6 to 15% by weight of NCO, in particular based on
4,4'-diphenylmethane diisocyanate or diphenylmethane diisocyanate isomer
mixtures; those for the production of flexible polyurethane foams are
mixtures of 2,4- and 2,6-tolylene diisocyanates, mixtures of tolylene
diisocyanates and crude MDI or, in particular, mixtures of the
abovementioned prepolymers based on diphenylmethane diisocyanate isomers
and crude MDI; and that for the production of rigid polyurethane or
polyurethane polyisocyanate foams is crude MDI.
The relatively high-molecular-weight compound (b) containing at least two
reactive hydrogen atoms expediently has a functionality of from 2 to 8,
preferably from 2 to 6, and a molecular weight of from 400 to 8000,
preferably from 1200 to 6000. Particular success has been achieved using,
for example, polyether-polyamines and/or preferably polyols selected from
the group comprising the polyether-polyols, polyester-polyols,
polythioetherpolyols, polyester-amides, hydroxyl-containing polyacetals
and hydroxyl-containing aliphatic polycarbonates, or mixtures of at least
two of said polyols. Particular preference is given to polyester-polyols
and/or polyether-polyols.
Suitable polyester-polyols may be prepared, for example, from organic
dicarboxylic acids having from 2 to 12 carbon atoms, preferably aliphatic
dicarboxylic acids having from 4 to 6 carbon atoms and polyhydric
alcohols, preferably diols, having from 2 to 12 carbon atoms, preferably
from 2 to 6 carbon atoms. Examples of suitable dicarboxylic acids are
succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid,
sebacic acid, decanedicarboxylic acid, maleic acid, fumaric acid, phthalic
acid, isophthalic acid and terephthalic acid. The dicarboxylic acids may
be used either individually or mixed with one another. The free
dicarboxylic acids may also be replaced by the corresponding dicarboxylic
acid derivatives, for example dicarboxylic acid esters of alcohols having
1 to 4 carbon atoms or dicarboxylic anhydrides. Preference is given to
dicarboxylic acid mixtures comprising succinic acid, glutaric acid and
adipic acid in ratios of, for example, from 20 to 35:35 to 50:20 to 32
parts by weight, and in particular adipic acid. Examples of dihydric and
polyhydric alcohols, in particular alkanediols and dialkylene glycols, are
ethanediol, diethylene glycol, 1,2- and 1,3-propanediol, dipropylene
glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,10-decanediol,
glycerol and trimethylolpropane. Preference is given to ethanediol,
diethylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol and
mixtures of at least two of said diols, in particular mixtures of
1,4-butanediol, 1,5-pentanediol and 1,6-hexanediol. Furthermore,
polyester-polyols made from lactones, e.g. .epsilon.-caprolactone or
hydroxycarboxylic acids, e.g. .omega.-hydroxycaproic acid, may also be
employed.
The polyester-polyols may be prepared by polycondensing the organic, e.g.
aromatic and preferably aliphatic polycarboxylic acids and/or derivatives
thereof and polyhydric alcohols without using a catalyst or preferably in
the presence of an esterification catalyst, expediently in an inert gas
atmosphere, e.g. nitrogen, carbon monoxide, helium, argon, inter alia, in
the melt at from 150.degree. to 250.degree. C., preferably from
180.degree. to 220.degree. C., at atmospheric pressure or under reduced
pressure until the desired acid number, which is advantageously less than
10, preferably less than 2, is reached. In a preferred embodiment, the
esterification mixture is polycondensed at the abovementioned temperatures
under atmospheric pressure and subsequently under a pressure of less than
500 mbar, preferably from 50 to 150 mbar, until an acid number of from 80
to 30, preferably from 40 to 30, has been reached. Examples of suitable
esterification catalysts are iron, cadmium, cobalt, lead, zinc, antimony,
magnesium, titanium and tin catalysts in the form of metals, metal oxides
or metal salts. However, the polycondensation may also be carried out in
the liquid phase in the presence of diluents and/or entrainers, e.g.
benzene, toluene, xylene or chlorobenzene, for removal of the water of
condensation by azeotropic distillation.
The polyester-polyols are advantageously prepared by polycondensing the
organic polycarboxylic acids and/or derivatives thereof with polyhydric
alcohols in a molar ratio of from 1:1 to 1.8, preferably from 1:1.05 to
1.2.
The polyester-polyols obtained preferably have a functionality of from 2 to
4, in particular from 2 to 3, and a molecular weight of from 480 to 3000,
preferably from 1200 to 3000, in particular from 1800 to 2500.
However, the preferred polyols are polyetherpolyols prepared by
conventional processes, for example by anionic polymerization using alkali
metal hydroxides, such as sodium hydroxide or potassium hydroxide, or
alkali metal alkoxides, such as sodium methoxide, sodium ethoxide,
potassium ethoxide or potassium isopropoxide as catalysts and with
addition of at least one initiator molecule containing 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, inter alia, or bleaching earth as catalysts, from
one or more alkylene oxides having from 2 to 4 carbon atoms in the
alkylene moiety.
Examples of suitable alkylene oxides are tetrahydrofuran, 1,3-propylene
oxide, 1,2- and 2,3-butylene oxide, styrene oxide and preferably ethylene
oxide and 1,2-propylene oxide. The alkylene oxides may be used
individually, alternately one after the other or as mixtures. Examples of
suitable initiator molecules are water, organic dicarboxylic acids, such
as succinic acid, adipic acid, phthalic acid and terephthalic acid,
aliphatic and aromatic, unsubstituted or N-mono-, N,N- and
N,N'-dialkyl-substituted diamines having from 1 to 4 carbon atoms in the
alkyl moiety, such as unsubstituted or mono- or dialkyl-substituted
ethylenediamine, diethylenetriamine, triethylenetetramine,
1,3-propylenediamine, 1,3- and 1,4-butylenediamine, 1,2-, 1,3-, 1,4-, 1,5-
and 1,6-hexamethylenediamine, phenylenediamines, 2,3-, 2,4- and
2,6-tolylenediamine and 4,4'-, 2,4'- and 2,2'-diaminodiphenylmethane.
Other suitable initiator molecules are alkanolamines, e.g. ethanolamine,
N-methyl- and N-ethylethanolamine, dialkanolamines, e.g. diethanolamine,
N-methyl- and N-ethyl-diethanolamine, and trialkanolamines, e.g.
triethanolamine, and ammonia. Preference is given to polyhydric alcohols,
in particular dihydric and/or trihydric alcohols, such as ethanediol, 1,2-
and 1,3-propanediol, diethylene glycol, dipropylene glycol,
1,4-butanediol, 1,6-hexanediol, glycerol, trimethylolpropane,
pentaerythritol, sorbitol and sucrose.
The polyether-polyols, preferably polyoxypropylene- and
polyoxypropylene-polyoxyethylene-polyols, have a functionality of from 2
to 6, in particular from 2 to 4, and molecular weights of from 400 to
8000, preferably from 1200 to 6000, in particular from 1800 to 4000, and
suitable polyoxytetramethylene glycols have a molecular weight of up to
approximately 3500.
Other suitable polyether-polyols are polymer-modified polyether-polyols,
preferably graft polyetherpolyols, in particular those based on styrene
and/or acrylonitrile and prepared by in-situ polymerization of
acrylonitrile, styrene or preferably mixtures of styrene and
acrylonitrile, for example in a weight ratio of from 90:10 to 10:90,
preferably from 70:30 to 30:70, expediently in the abovementioned
polyether-polyols by a method similar to that of German Pat. No(s). 11 11
394, 12 22 669 (U.S. Pat. No(s). 3,304,273, 3,383,351 and 3,523,093), 11
52 536 (GB No. 1,040,452) and 11 52 537 (GB No. 987,618), and
polyether-polyol dispersions which contain, as the disperse phase, usually
in an amount of from 1 to 50% by weight, preferably from 2 to 25% by
weight, for example polyureas, polyhydrazides, polyurethanes containing
tertamino groups in bound form, and/or melamine and are described, for
example, in EP-B-011 752 (U.S. Pat. No. 4,304,708), U.S. Pat. No.
4,374,209 and DE-A-32 31 497.
Like the polyester-polyols, the polyether-polyols can be used individually
or in the form of mixtures. Furthermore, they may be mixed with the graft
polyetherpolyols or polyester-polyols and the hydroxyl-containing
polyester-amides, polyacetals, polycarbonates and/or polyether-polyamines.
Examples of suitable hydroxyl-containing polyacetals are the compounds
which can be prepared from glycols, such as diethylene glycol, triethylene
glycol, 4,4'-dihydroxyethoxydiphenyldimethylmethane, hexanediol and
formaldehyde. Suitable polyacetals can also be prepared by polymerizing
cyclic acetals.
Suitable hydroxyl-containing polycarbonates are those of a conventional
type, which can be prepared, for example, by reacting diols, such as
1,3-propanediol, 1,4-butanediol and/or 1,6-hexanediol, diethylene glycol,
triethylene glycol or tetraethylene glycol, with diaryl carbonates, e.g.
diphenyl carbonate, or phosgene.
The polyester-amides include, for example, the predominantly linear
condensates obtained from polybasic, saturated and/or unsaturated
carboxylic acids or anhydrides thereof and polyhydric, saturated and/or
unsaturated amino alcohols, or mixtures of polyhydric alcohols and amino
alcohols and/or polyamines.
Suitable polyether-polyamines can be prepared from the abovementioned
polyether-polyols by known processes. The examples which may be mentioned
are the cyanoalkylation of polyoxyalkylene-polyols and a subsequent
hydrogenation of the resultant nitrile (U.S. Pat. No. 3,267,050) or the
partial or complete amination of polyoxyalkylene-polyols using amines or
ammonia in the presence of hydrogen and catalysts (DE No. 12 15 373).
The polyisocyanate polyaddition products, and preferably urethane- or
urethane- and isocyanurate-containing foams, may be prepared with or
without the use of chain extenders and/or crosslinking agents (c).
However, it may prove advantageous, in order to modify the mechanical
properties, for example the hardness, to add chain extenders, crosslinking
agents or, if desired, mixtures thereof. The chain extenders and/or
crosslinking agents used are diols and/or triols, having a molecular
weight of less than 400, preferably from 60 to 300. Examples are
dialkylene glycols and aliphatic, cycloaliphatic and/or araliphatic diols
having from 2 to 14 carbon atoms, preferably from 4 to 10 carbon atoms,
e.g. ethylene glycol, 1,3-propanediol, 1,10-decanediol, o-, m- and
p-dihydroxycyclohexane, diethylene glycol, dipropylene glycol and
preferably 1,4-butanediol, 1,6-hexanediol and
bis(2-hydroxyethyl)hydroquinone, triols, such as 1,2,4- and
1,3,5-trihydroxycyclohexane, glycerol and trimethylolpropane, and
low-molecular-weight hydroxyl-containing polyalkylene oxides, based on
ethylene oxide and/or 1,2-propylene oxide, and the above-mentioned diols
and/or triols as initiator molecules.
Cellular polyurethane-polyurea elastomers can also be prepared using
secondary aromatic diamines, primary aromatic diamines, 3,3'-di- and/or
3,3',5,5'-tetraalkyl-substituted diaminodiphenylmethanes as chain
extenders or crosslinking agents instead of or mixed with the
abovementioned diols and/or triols.
Examples of secondary aromatic diamines are N,N'- dialkyl-substituted
aromatic diamines, which are unsubstituted or substituted on the aromatic
radical by alkyl radicals, having 1 to 20, preferably 1 to 4, carbon atoms
in the N-alkyl radical, e.g. N,N'-diethyl-, N,N'-di- sec-pentyl-,
N,N'-di-sec-hexyl-, N,N'-di-sec-decyl- and N,N'-dicyclohexyl-p- and
m-phenylenediamine, N,N'-dimethyl-, N,N'-diethyl-, N,N'-diisopropyl-,
N,N'-di-sec-butyl- and N,N'-dicyclohexyl-4,4'-diaminodiphenylmethane and
N,N'-di-sec-butylbenzidine.
The aromatic diamines used are expediently those which have at least one
alkyl substituent in the orthoposition to the amino groups, are liquid at
room temperature and are miscible with component (b), in particular the
polyether-polyols. Furthermore, alkyl-substituted meta-phenylenediamines
of the formulae
##STR1##
where R.sup.3 and R.sup.2 are identical or different and are methyl,
ethyl, propyl or isopropyl, and R.sup.1 is linear or branched alkyl having
1 to 10 carbon atoms, preferably 4 to 6 carbon atoms, have proven
successful.
Particularly successful are those alkyl radicals R.sup.1 in which the
branching point is on the C.sup.1 carbon atom. Specific examples of
radicals R.sup.1 are methyl, ethyl, isopropyl, 1-methyloctyl,
2-ethyloctyl, 1-methylhexyl, 1,1-dimethylpentyl, 1,3,3-trimethylhexyl,
1-ethylpentyl, 2-ethylpentyl and preferably cyclohexyl, 1-methyl-n-propyl,
tert-butyl, 1-ethyl-n-propyl, 1-methyl-n-butyl and 1,1-dimethyl-n-propyl.
Examples of suitable alkyl-substituted m-phenylenediamines are
2,4-dimethyl-6-cyclohexyl-, 2-cyclohexyl-4,6-diethyl-,
2-cyclohexyl-2,6-isopropyl-, 2,4-dimethyl-6-(1-ethyl-n-propyl)-,
2,4-dimethyl-6-(1,1-dimethyl-n-propyl)- and
2-(1-methyl-n-butyl)-4,6-dimethyl-1,3-phenylenediamine. Preference is
given to 1-methyl-3,5-diethyl-2,4- and -2,6-phenylenediamines,
2,4-dimethyl-6-tert-butyl-, 2,4-dimethyl-6-isooctyl- and
2,4-dimethyl-6-cyclohexyl-1,3-phenylenediamine.
Examples of suitable 3,3'-di- and 3,3',5,5'-tetra-n-alkyl-substituted
4,4'-diaminodiphenylmethanes are 3,3'-di-, 3,3',5,5'-tetramethyl-,
3,3'-di-, 3,3',5,5'-tetraethyl-, 3,3'-di- and
3,3',5,5'-tetra-n-propyl-4,4'-diaminodiphenylmethane.
Preference is given to diaminodiphenylmethanes of the formula
##STR2##
where R.sup.4, R.sup.5, R.sup.6 and R.sup.7 are identical or different and
are methyl, ethyl, propyl, isopropyl, sec-butyl or tert-butyl, but where
at least one of the radicals must be isopropyl or sec-butyl. The
4,4'-diaminodiphenylmethanes may also be used in a mixture with isomers of
the formulae
##STR3##
where R.sup.4, R.sup.5, R.sup.6 and R.sup.7 are as defined above.
Preference is given to 3,5-dimethyl-3', 5'-diisopropyl- and
3,3',5,5'-tetraisopropyl-4,4'diaminodiphenylmethane. The
diaminodiphenylmethanes can be employed individually or in the form of
mixtures.
Said chain extenders and/or crosslinking agents (c) can be used
individually or as mixtures of identical or different types of compounds.
The amount of chain extender, crosslinking agent or mixture thereof used,
if any, is expediently from 2 to 60% by weight, preferably from 8 to 50%
by weight, in particular from 10 to 40% by weight, based on the weight of
components (b) and (c).
The blowing agent (d) used according to the invention is a low-boiling,
fluorinated or preferably perfluorinated, tertiary alkylamine (d1) or a
mixture of such alkylamines. The fluorinated, tertiary alkylamine used is
preferably predominantly, i.e. at least 50%, preferably at least 80%, in
particular at least 90%, fluorinated and expediently has at least one,
preferably one, bonded hydrogen atom. As stated above, fluorinated or
perfluorinated, tertiary alkylamines of this type in the amounts necessary
for formation of foams preferably containing urethane or urethane and
isocyanurate groups are sparingly soluble or insoluble in the starting
components (a), (b) and (c) or in mixtures of (b) and (c), and they are
therefore emulsified in at least one of these starting components (a), (b)
and (c), preferably in (b) or a mixture of (b) and (c) or the liquid
reaction mixture comprising (a), (b), (d) to (f) and, if used, (c). Highly
suitable blowing agents are the fluorinated or perfluorinated, tertiary
alkylamines having 3 to 9 carbon atoms, preferably 4 to 6 carbon atoms,
which are liquid at room temperature, particularly preferably the
perfluorinated, tertiary alkylamines.
Specific examples of suitable (per)fluorinated, tertiary alkylamines are
perfluorodimethylethylamine, perfluorodiethylmethylamine,
perfluorotrimethylamine, perfluorotriethylamine,
perfluorodimethyl-n-propylamine, perfluorodiethyl-n-propylamine,
perfluoro-tri-n-propylamine and perfluorodimethylisopropylamine, and the
corresponding partially fluorinated tertiary alkylamines. The fluorinated
and/or preferably perfluorinated, tertiary amines may be employed
individually or in the form of mixtures. The preferred blowing agent (d)
is perfluorodimethylisopropylamine.
The blowing agent (d) for the production of the cellular plastics by the
process according to the invention may alternatively be a mixture
containing or preferably comprising
d1) at least one low-boiling, fluorinated or preferably perfluorinated,
tertiary alkylamine, or a mixture of such alkylamines nd
d2) at least one further physical blowing agent and/or chemical blowing
agent which is different from (d1), or a mixture of such physical and
chemical blowing agents.
Examples of suitable physical blowing agents which are different from (d1)
are:
alkanes having 4 to 12 carbon atoms, preferably 5 or 6 carbon atoms,
cycloalkanes having 4 to 6 carbon atoms, preferably 5 or 6 carbon atoms,
linear or cyclic, saturated or olefinically unsaturated ethers having 2 to
5 carbon atoms,
aliphatic carboxylic acid esters having a maximum boiling point of
142.degree. C., preferably below 80.degree. C.,
aliphatic and/or cycloaliphatic ketones having 3 to 5 carbon atoms,
partially halogenated chlorofluorocarbons having 1 or 2 carbon atoms,
perfluorinated, linear or cyclic ethers having 4 to 12 carbon atoms,
preferably 4 to 6 carbon atoms, and
preferably fluorinated or perfluorinated, advantageously aliphatic or
cycloaliphatic hydrocarbons having 3 to 8 carbon atoms, preference being
given to aliphatic or cycloaliphatic, fluorinated hydrocarbons having 3 to
6 carbon atoms which are liquid at room temperature and contain at least
one bonded hydrogen atom and aliphatic or cycloaliphatic, perfluorinated
hydrocarbons having 4 to 7 carbon atoms.
Specific examples of physical blowing agents (d2) of the said type are
gaseous or preferably liquid, linear or branched alkanes, e.g. butane, n-
and isopentane and technical-grade pentane mixtures, n- and isohexanes, n-
and isoheptanes, n- and isooctanes, n- and isononanes, n- and isodecanes,
n- and isoundecanes and n- and isododecanes. Since very good results with
respect to the stability of the emulsions, the processing properties of
the reaction mixture and the mechanical properties of the cellular
polisocyanate polyaddition products produced are achieved when n-pentane,
isopentane or n-hexane, or a mixture thereof, is used, these alkanes are
preferably employed. Furthermore, specific examples of cycloalkanes are
cyclobutane, preferably cyclopentane, cyclohexane or mixtures thereof,
specific examples of linear or cyclic ethers are dimethyl ether, diethyl
ether, methyl ethyl ether, vinyl methyl ether, vinyl ethyl ether, divinyl
ether, tetrahydrofuran and furan, specific examples of aliphatic
carboxylic acid esters are methyl, ethyl, n-propyl, isopropyl and butyl
acetate and preferably methyl and ethyl formate, specific examples of
ketones are acetone, methyl ethyl ketone and cyclopentanone, specific
examples of partially halogenated chlorofluorocarbons are
difluoromonochloromethane (R 22), 1,1,1-trifluoro-2,2-dichloroethane (R
123) and 1,1,1-dichloromonofluoroethane (R 141b), specific examples of
perfluorinated, linear or cyclic ethers are perfluorodiethyl ether,
perfluorodipropyl ether and perfluoroethyl propyl ether, oligomers of
perfluoropropylene oxide having a maximum boiling point of 135.degree. C.,
perfluorotetrahydrofuran, perfluoroalkyltetrahydrofurans and
perfluorofuran. Aliphatic or cycloaliphatic, fluorinated or perfluorinated
hydrocarbons which are gases at room temperature e.g. perfluoropropane,
perfluorobutane and perfluorocyclobutane, which can be liquefied under
pressure, for example up to about 25 bar, mixed and emulsified are also
highly suitable.
However, physical blowing agents (d2) which have proven eminently suitable
and are therefore preferred are aliphatic or cycloaliphatic, fluorinated
or perfluorinated hydrocarbons which are liquid at room temperature. The
fluorinated hydrocarbons used are expediently those which are
predominantly, for example at least 85%, fluorinated and contain at least
one, preferably one, bonded hydrogen atom. Examples of suitable
fluorinated hydrocarbons are trifluoromethane, difluoromethane,
difluoroethane, tetrafluoroethane and preferably hexafluoropropane,
heptafluoropropane, 1-H-perfluorobutane and 1-H-perfluorohexane. Examples
of suitable perfluorinated hydrocarbons are perfluoropentane,
perfluorohexane, perfluoroheptane, perfluorooctane, perfluorocyclopentane
and perfluorocyclohexane. The fluorinated or perfluorinated hydrocarbons
or mixtures thereof, like the other suitable physical blowing agents, can
be employed individually or in the form of mixtures. It is also possible
to use mixtures of the different physical blowing agents.
The blowing agent mixtures (d) which can be used according to the invention
advantageously contain the low-boiling, fluorinated and/or perfluorinated,
tertiary alkylamine (d1) and the further physical blowing agent (d2) which
is different from (d1), preferably the fluorinated and/or perfluorinated
hydrocarbon, in a weight ratio of from 90:10 to 10:90, preferably from
80:20 to 60:40. If the physical blowing agent is insoluble in the starting
components (a), (b) and (c) in the necessary amounts, it is expediently
emulsified in at least one of the starting components together with the
low-boiling, fluorinated and/or perfluorinated, tertiary alkylamine.
In addition to the low-boiling, fluorinated and/or perfluorinated, tertiary
alkylamine (d1) which can be used according to the invention as blowing
agent, or a mixture of (d1) and the other physical blowing agent which is
different from (d1), or in place of the physical blowing agent which is
different from (d1), it is also possible to use a chemical blowing agent.
A particularly proven chemical blowing agent is water, which reacts with
the organic, modified or unmodified polyisocyanate (a) to form carbon
dioxide, the actual blowing agent, and urea groups, and thus effects the
compressive strength of the end products. Other suitable chemical blowing
agents are organic mono- and polycarboxylic acids having a molecular
weight of from 60 to 300 and preferably formic acid, and ammonium and/or
amine salts of formic acid and/or of the abovementioned mono- and/or
polycarboxylic acids, so long as these react with isocyanates under the
reaction conditions and form carbon dioxide.
The organic carboxylic acids used are advantageously aliphatic mono- and
polycarboxylic acids, e.g. dicarboxylic acids. However, other organic
mono- and polycarboxylic acids are also suitable. The organic carboxylic
acids may, if desired, also contain substituents which are inert under the
reaction conditions of the polyisocyanate polyaddition or are reactive
with isocyanate, and/or may contain olefinically unsaturated groups.
Specific examples of chemically inert substituents are halogen atoms, such
as fluorine and/or chlorine, and alkyl, e.g. methyl or ethyl. The
substituted organic carboxylic acids expediently contain at least one
further group which is reactive toward isocyanates, e.g. a mercapto group,
a primary and/or secondary amino group or preferably a primary and/or
secondary hydroxyl group.
Suitable carboxylic acids are thus substituted or unsubstituted
monocarboxylic acids, e.g. acetic acid, propionic acid, 2-chloropropionic
acid, 3-chloropropionic acid, 2,2-dichloropropionic acid, hexanoic acid,
2-ethylhexanoic acid, cyclohexanecarboxylic acid, dodecanoic acid,
palmitic acid, stearic acid, oleic acid, 3-mercaptopropionic acid,
glycolic acid, 3-hydroxypropionic acid, lactic acid, ricinoleic | | |
