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Description  |
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This invention relates to a process for making molded foam resins having
improved properties which facilitate release of the foam from a mold.
Foam resins based on organic polyisocyanates, e.g. polyurethane foams which
have a dense outer skin and a cellular core as obtained by the method of
foaming in the mold (German Auslegeschrift No. 1,196,864 and French Pat.
Specification No. 1,559,325) are eminently suitable for the series
production of lightweight constructions, e.g. for the manufacture of
furniture, vehicles and buildings.
To produce the molded polyurethane products, a foamable reaction mixture
containing an organic polyisocyanate, compounds which contain at least two
hydrogen atoms capable of reacting with isocyanates and additives is
introduced into closed, heatable molds in which the mixture foams up and
then solidifies in a very compressed state. The resin completely fills the
mold and accurately reproduces the internal surfaces of the mold.
The molds are preferably made of a material with a high thermal capacity
and high thermal conductivity, the material used being preferably metal
although other materials such as synthetic resins, glass, wood, etc. may
also be used.
The mold is usually covered with a mold release agent so that parts of the
foam resin will not adhere to the surface when the foam resin product is
released from the mold. Waxes, soaps or oils, for example, are among the
various mold release agents in use. These mold release agents form a thin
film between the surface of the mold and the foam resin product. This film
does not adhere either to the mold or to the synthetic resinous product
and therefore facilitates release of the product from the mold.
This prior art method has various disadvantages for the production of a
series of molded products. The mold release agent must be applied
repeatedly at regular intervals and, during this time, the mold is
unavailable for production. Fine engravings in the mold, for example to
imitate the structure of wood or grain of leather, become covered with
residues of mold release agent in the course of time. Removal of these
firmly adhering residues from the molds which frequently have a very
complex internal surface requires considerable effort. The molded products
also become coated with a thin film of the release agent, to which lacquer
systems will not adhere. The surfaces of the molded product must therefore
be ground or cleaned with solvents before they are lacquered in order that
the lacquer will adhere sufficiently firmly to the synthetic resin.
In U.S. Pat. No. 3,726,952, it has been disclosed that the application of a
mold release agent to the mold can be obviated by mixing the foamable
reaction mixture with certain additives which modify the properties of the
finished synthetic resin product so that it can easily be released from
metal molds without any damage to its surface. Among the additives which
have been proposed for this purpose are salts of aliphatic carboxylic
acids containing at least 25 carbon atoms with amines, perferably primary
amines, or amines which contain amide or ester groups.
In German Offenlegungsschrift No. 2,121,670 there is disclosed a process
for the production of foam resins by foaming a reaction mixture of organic
polyisocyanates, compounds which contain reactive hydrogen atoms, water
and/or organic blowing agents and additives in a closed mold, the
additives used being, e.g. a mixture of (a) salts of aliphatic carboxylic
acids containing at least 20 aliphatic carbon atoms with amines which may
contain amide and/or ester groups and (b) natural and/or synthetic oils,
fats, or waxes.
Since these additives have an internal lubricating effect on the synthetic
resin mixture they also impart excellent flow properties to the synthetic
resin in the mold and reduce the formation of bubbles on the surface of
the synthetic resin. In addition, these internal mold release agents have
an antistatic effect and they impart excellent mold release properties
even in metal molds which have a very complicated surface. Although
excellent mold release effects can be obtained by these disclosed methods,
it has been found in practice that the esters of higher fatty acids or
their mixed esters frequently used as synthetic oils or waxes are
insufficiently compatible with the isocyanate or polyol components used as
starting materials for the foams, i.e. mixtures of these starting
components with the fatty acid esters used as mold release agents are
frequently unstable in storage and separate into their individual phases.
Although this process of separation can be prevented by stirring the
contents in the storage containers, this is not a satisfactory commercial
solution to the problem because the storage containers are in most cases
not equipped with stirrers. Moreover, the separation process may have
already occurred during the transport of the material.
The problem of finding internal mold release agents which will form a
stable mixture with at least one of the starting components of the foam so
that the mixture will have no tendency to undergo phase separation has
existed.
It is therefore an object of this invention to provide an improved process
for molding foamable reaction mixtures containing an organic
polyisocyanate. Another object of this invention is to provide a process
for molding foamable mixtures containing an organic polyisocyanate and an
internal mold release agent which is devoid of the foregoing
disadvantages. Still another object of this invention is to provide a
foamable reaction mixture containing an organic polyisocyanate and an
effective internal release agent which is miscible with the other
components of the mixture. A further object of the invention is to provide
a foamable reaction mixture containing an organic polyisocyanate adapted
for molding a series of products one after the other without interruption
for the application of a mold release to the surface of the mold.
The foregoing objects and others are accomplished in accordance with this
invention, generally speaking, by providing a process for molding a
foamable reaction mixture containing an organic polyisocyanate and a
reaction product of an organic polyisocyanate with an ester or mixed ester
of a higher fatty acid which contains active hydrogen atoms as a mold
release agent. It has now surprisingly been found that reaction products
of organic polyisocyanates with esters or mixed esters of higher fatty
acids which contain active hydrogen atoms (hereinafter referred to as
"fatty acid esters") used either alone or in combination with other mold
release agents or systems of mold release agents provide excellent mold
release properties in the molding of a foamable reaction mixture
containing an organic polyisocyanate and, that, moreover, these fatty acid
esters will dissolve in the foamable mixture and will not undergo phase
separation.
A process in which foams are produced by foaming a reaction mixture
containing an organic polyisocyanate, an organic compound containing
hydrogen atoms reactive with a polyisocyanate and having a molecular
weight of at least 62, preferably 62 to about 10,000, water and/or organic
blowing agents and optionally other additives together with a reaction
product of a fatty acid ester and a polyisocyanate in a closed mold is
preferred.
The mold release effect can be measured by the force in kp/cm.sup.2 which
is required to open the mold when removing the molded product. It can also
be assessed subjectively by opening a suitable mold by hand and removing
the foam panel (20.times.20.times.1 cm) which has partly foamed. The mold
release forces required for foams which have been treated with the mold
release reaction products provided by the invention are considerably lower
than those required for comparable foams which have been produced by
foaming reaction mixtures without these additives.
For the purpose of this invention, foam resins based on organic
polyisocyanates are understood to mean both foams which are produced from
an organic polyisocyanate alone and those which can be obtained by
addition of an organic polyisocyanate with an organic compound which
contains at least two Zerewitinow active hydrogen atoms, e.g.
polycarbodiimide foam, polyisocyanurate foam, polyurea foam, polybiuret
foam, polyamide foam, polyallophanate foam or polyurethane foam, or foams
containing a mixture of urethane, urea, allophanate, biuret, amide,
carbodiimide and/or isocyanurate groups and any other foam based on a
polyisocyanate. The process described here is particularly suitable for
the production of foams which contain urethane groups prepared from a
foamable reaction mixture containing an organic polyisocyanate.
Any suitable organic polyisocyanate may be used such as, for example, an
aliphatic, cycloaliphatic, araliphatic, aromatic or heterocyclic
polyisocyanate including those described by W. Siefgen in Justus Liebigs
Annalen der Chemie, 562, pages 75 to 136. Examples of suitable
polyisocyanates are ethylene diisocyanate,
tetramethylene-1,4-diisocyanate, hexamethylene-1,6-diisocyanate,
dodecane-1,12-diisocyanate, cyclobutane-1,3-diisocyanate,
cyclohexane-1,3-diisocyanate, cyclohexane-1,4-diisocyanate and any
mixtures of these isomer,
1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl-cyclohexane (German
Auslegeschrift No. 1,202,785), hexahydrotolylene-2,4-diisocyanate and
hexahydrotolylene-2,6-diisocyanate and any mixtures of these isomers,
hexahydrophenylene-1,3-diisocyanate, hexahydrophenylene-1,4-diisocyanate,
perhydrodiphenylmethane-1,4'-diisocyanate,
perhydrodiphenylmethane-4,4'-diisocyanate, phenylene-1,3-diisocyanate,
phenylene-1,4-diisocyanate, tolylene-2,4-diisocyanate,
tolylene-2,6-diisocyanate and any mixtures of these isomers,
diphenylmethane-2,4'-diisocyanate, diphenylmethane-4,4'-diisocyanate,
naphthylene-1,5-diisocyanate, triphenylmethane-4,4',4"-triisocyanate,
polyphenyl-polymethylene polyisocyanates which may be obtained by
aniline-formaldehyde condensation followed by phosgenation and which have
been described, e.g. in British Pat. No. 874,430 and 848,671;
perchlorinated aryl polyisocyanates as described e.g. in German
Auslegeschrift No. 1,157,601; polyisocyanates which contain carbodiimide
groups as described in German Patent Specification No. 1,092,007; the
diisocyanates described in U.S. Pat. Specification No. 3,492,330;
polyisocyanates which contain allophanate groups as described e.g. in
British Patent Specification No. 994,890; Belgian Pat. Specification No.
761,626 and published Dutch Patent Application No. 7,102,524,
polyisocyanates which contain isocyanurate groups as described e.g. in
German Pat. Specifications No. 1,022,789; 1,222,067 and 1,027,394 and in
German Offenlegungsschriften No. 1,929,034 and 2,004,048; polyisocyanates
which contain urethane groups as described e.g. in Belgian Patent
Specification No. 752,261 or in U.S. Pat. Specification No. 3,394,164;
polyisocyanates which contain acylated urea groups as described in German
Patent Specification No. 1,230,778, polyisocyanates which contain biuret
groups as described e.g. in German Pat. Specification No. 1,101,394; in
British Pat. Specification No. 889,050 and in French Pat. Specification
No. 7,017,514; polyisocyanates prepared by telomerisation reactions as
described e.g. in Belgian Pat. Specification No. 723,640; polyisocyanates
which contain ester groups as described e.g. in British Pat. Specification
Nos. 965,474 and 1,072,956; in U.S. Pat. Specification No. 3,567,763 and
in German Patent Specification No. 1,231,688 and reaction products of the
above mentioned isocyanates with acetals according to German Pat.
Specification No. 1,072,385.
The distillation residues obtained from the commercial production of
isocyanates, which still contain isocyanate groups, may also be used, if
desired in the form of solutions in one or more of the above mentioned
polyisocyanates. Any mixtures of the above mentioned polyisocyanates may
also be used.
It is generally preferred to use commercially readily available
polyisocyanates, e.g. tolylene-2,4-diisocyanate and
tolylene-2,6-diisocyanate and any mixtures of these isomers ("TDI")
polyphenyl-polymethylene-polyisocyanates obtained by aniline-formaldehyde
condensation followed by phosgenation ("crude MDI") and polyisocyanates
which contain carbodiimide groups, urethane groups, allophanate groups,
isocyanurate groups, urea groups or biuret groups ("modified
polyisocyanates").
Organic compounds with a molecular weight generally between 62 and 10,000
which contain at least two hydrogen atoms capable of reacting with
isocyanates may also be used as one of the starting components of the
foamable reaction mixture. These may be compounds which contain amino
groups, thiol groups or carboxyl groups but are preferably organic
polyhydroxyl compounds, in particular polyhydric alcohols containing 2 to
8 hydroxyl groups and especially those having a molecular weight of 800 to
10,000, preferably 1000 to 6000, e.g. the polyesters, polyethers,
polythioethers, polyacetals, polycarbonates and polyester amides
containing at least two, generally 2 to 8, but preferably 2 to 4 hydroxyl
groups which are known per se for the production of homogeneous and
cellular polyurethanes.
Any suitable polyester containing hydroxyl groups may be used, e.g. the
reaction products of polyhydric alcohols, preferably dihydric alcohols to
which trihydric alcohols may be added, with polybasic carboxylic acids,
preferably dibasic carboxylic acids. Instead of using free polycarboxylic
acids, the corresponding polycarboxylic acid anhydrides or polycarboxylic
acid esters of lower alcohols or mixtures thereof may be used for
producing the polyesters. The polycarboxylic acids may be aliphatic,
cycloaliphatic, aromatic and/or heterocyclic and may be substituted, e.g.
by halogen atoms, and/or unsaturated. The following are mentioned as
examples: succinic acid, adipic acid, suberic acid, azelaic acid, sebacic
acid, phthalic acid, isophthalic acid, trimellitic acid, phthalic acid
anhydride, tetrahydrophthalic acid anhydride, hexahydrophthalic acid
anhydride, tetrachlorophthalic acid anhydride, endomethylene
tetrahydrophthalic acid anhydride, glutaric acid anhydride, maleic acid,
maleic acid anhydride, fumaric acid, dimeric and trimeric fatty acids such
as oleic acid optionally mixed with monomeric fatty acids, dimethyl
terephthalate and bis-glycol terephthalate. The following are examples of
suitable polyhydric alcohols: ethylene glycol, propylene-1,2-glycol
propylene-1,3-glycol, butylene-1,4-glycol, butylene-2,3-glycol,
hexane-1,6-diol, octane-1,8-diol, neopentyl glycol, cyclohexane dimethanol
(1,4-bis-hydroxy-methylcyclohexane), 2-methyl-propane-1,3-diol, glycerol,
trimethylolpropane, hexane-1,2,6-triol, butane-1,2,4-triol,
trimethylolethane, pentaerythritol, quinitol, mannitol, sorbitol, methyl
glycoside, diethylene glycol, triethylene glycol, tetraethylene glycol,
polyethylene glycols, dipropylene glycol, polypropylene glycols,
dibutylene glycol and polybutylene glycols. The polyesters may also
contain terminal carboxyl groups. Polyesters of lactones such as
.epsilon.-caprolactone or of hydrocarboxylic acids such as
.omega.-hydroxycaproic acid may also be used. The low molecular weight
polyhydric alcohols mentioned above may also be used as such.
Polyethers used according to the invention which contain at least 2 and
generally 2 to 8, preferably 2 or 3 hydroxyl groups are also known per se
and may be prepared, e.g. by the polymerisation of epoxides such as
ethylene oxide, propylene oxide, butylene oxide, tetrahydrofuran, styrene
oxide or epichlorohydrin, each with itself, e.g. in the presence of
BF.sub.3, or by the addition of these epoxides, either alone, as mixtures
or successively, to starting components which contain reactive hydrogen
atoms such as alcohols or amines, e.g. water, ethylene glycol,
propylene-1,3-glycol, propylene-1,2-glycol, trimethylolpropane,
4,4'-dihydroxydiphenylpropane, aniline, ammonia, ethanolamine or ethylene
diamine. Sucrose polyethers such as those described, e.g. in German
Auslegeschrfit No. 1,176,358 and 1,064,938 may also be used according to
the invention. It is frequently preferred to use polyethers which contain
predominantly primary hydroxyl groups (up to 90% by weight, based on all
the hydroxyl groups present in the polyether). Polyethers which have been
modified by vinyl polymers are also suitable, e.g. the polyethers obtained
by the polymerisation of styrene or acrylonitrile in the presence of
polyethers (U.S. Pat. Specification Nos. 3,383,351; 3,304,273; 3,523,093
and 3,110,695 and German Patent Specification No. 1,152,536).
Polybutadienes which contain hydroxyl groups may also be used.
Among the polythioethers there should be particularly mentioned the
condensation products of thiodiglycol with itself and/or with other
glycols, dicarboxylic acids, formaldehyde, aminocarboxylic acids or
aminoalcohols. These products are either polythio mixed ethers, polythio
ether esters or polythio ether ester amides, depending on the
cocomponents.
The polyacetals used may be, for example, compounds prepared from glycols
such as diethylene glycol, triethylene glycol,
4,4'-dioxethoxy-diphenyldimethylmethane, hexanediol and formaldehyde.
Polyacetals suitable for the invention may also be prepared by
polymerising cyclic acetals.
The polycarbonates with hydroxyl groups may be those known per se which can
be prepared, for example, by reacting diols such as propane-1,3-diol,
butane-1,4-diol and/or hexane-1,6-diol, diethylene glycol, triethylene
glycol or tetraethylene glycol with diarylcarbonates such as diphenyl
carbonate or phosgene.
Suitable polyester amides and polyamides include, for example, the
predominantly linear condensates obtained from polybasic saturated and
unsaturated carboxylic acids or their anhydrides and polyvalent saturated
and unsaturated amino alcohols, diamines, polyamines and their mixtures.
Polyhydroxyl compounds which already contain urethane or urea groups and
modified or unmodified natural polyols such as castor oil, carbohydrates
or starch may also be used. Addition products of alkylene oxides with
phenol formaldehyde resins or with urea formaldehyde resins may also be
used for the process of the invention.
Representatives of these compounds are described, for example, in High
Polymers, Volume XVI, "Polyurethanes, Chemistry and Technology", by
Saunders and Frisch, published by Interscience Publishers, New York,
London, Volume I, 1962, pages 32-34 and pages 44-54 and Volume II, 1964,
pages 5-6 and 198-199 and in Kunststoff-Handbuch, Volume VII,
Vieweg-Hochtlen, Carl-Hanser-Verlag, Munich, 1966, e.g. on pages 45 to 71.
Water and/or readily volatile organic substances may be used as blowing
agents according to the invention. Suitable organic blowing agents are
e.g. acetone, ethyl acetate, halogenated alkanes, such as methylene
chloride, chloroform, ethylidene chloride, vinylidene chloride,
monofluorotrichloromethane, chlorodifluoromethane, dichlorodifluoromethane
and trichloro trifluoroethane, as well as butane, hexane, heptane or
diethylether. A blowing effect can also be obtained by adding compounds
which decompose at temperatures above room temperature to liberate gases
such as nitrogen, e.g. azo compounds such as azo isobutyric acid nitrile.
Other examples of blowing agents and details of their methods of use have
been described in Kunststoff-Handbuch, Volume VII, published by Vieweg and
Hochtlen, Carl-Hanser-Verlag, Munich 1966, e.g. on pages 108 to 109, 453
to 455 and 507 to 510.
Catalysts are frequently used in the process according to the invention.
The catalysts used may be known per se, e.g. tertiary amines such as
triethylamine, tributylamine, N-methyl-morpholine, N-ethyl-morpholine,
N-cocomorpholine, N,N,N',N'-tetramethyl-ethylenediamine,
1,4-diaza-bicyclo-(2,2,2)-octane,
N-methyl-N'-dimethylaminoethyl-piperazine,
N,N-dimethylbenzylamine-bis-(N-diethylaminoethyl)-adipate,
N,N-diethylbenzylamine, pentamethyldiethylenetriamine,
N,N-dimethyl-cyclohexylamine, N,N,N',N'-tetramethyl-1,3-butanediamine,
N,N-dimethyl-.beta.-phenylethylamine, 1,2-dimethylimidazole,
2-methylimidazole and tetramethylguanidine.
Triethanolamine, triisopropanolamine, N-methyl-diethanolamine,
N-ethyl-diethanolamine, N,N-dimethyl-ethanolamine and their reaction
products with alkylene oxides such as propylene oxide and/or ethylene
oxide are examples of suitable tertiary amines which contain hydrogen
atoms which are reactive with isocyanate groups.
Silaamines which contain carbon-silicon bonds may also be used as
catalysts, e.g. the compounds described in German Pat. Specification No.
1,229,290 such as 2,2,4-trimethyl-2-silamorpholine and
1,3-diethylaminomethyl-tetramethyldisiloxane.
Bases which contain nitrogen, such as tetralkylammonium hydroxides, and
alkali metal hydroxides such as sodium hydroxide, alkali metal phenolates
such as sodium phenolate and alkali metal alcoholates such as sodium
methylate are also suitable catalysts. Hexahydrotriazines may also be used
as catalysts.
Organic metal compounds may also be used as catalysts, especially organic
tin compounds.
The organic tin compounds used are preferably tin(II) salts (stannous
salts) of carboxylic acids such as tin(II) acetate, tin(II) octoate,
tin(II) ethyl hexoate and tin(II) laurate and the dialkyl tin salts of
carboxylic acids such as dibutyl tin diacetate, dibutyl tin dilaurate,
dibutyl tin maleate or dioctyl tin diacetate.
Other examples of catalysts which may be used according to the invention
and details of their mode of action are described in Kunststoff-Handbuch,
Volume VII, published by Vieweg and Hochtlen, Carl-Hanser-Verlag, Munich,
1966, e.g. on pages 96 to 102.
Any catalytic amount of the catalyst may be used. The catalysts are
generally used in quantities of between about 0.001% and 10% by weight,
based on the weight of the organic compound having at least two hydrogen
atoms capable of reacting with isocyanates and, preferably, a molecular
weight of 62 to about 10,000.
Any suitable surface active additive may also be used in the process
according to the invention (emulsifiers and foam stabilizers). Suitable
emulsifiers are e.g. the sodium salts of ricinoleic sulphonates or the
sodium salts of fatty acids or salts of fatty acids with amines such as
oleic acid diethylamine or stearic acid diethanolamine. Alkali metal salts
or ammonium salts of sulphonic acids such as dodecylbenzene sulphonic acid
or dinaphthylmethane disulphonic acid or alkali metal or ammonium salts of
fatty acids such as ricinoleic acid or of polymeric fatty acids may also
be used as surface active additives.
The main foam stabilizers used are water-soluble polyether siloxanes. The
structure of these compounds is generally such that a copolymer of
ethylene oxide and propylene oxide is linked to a polydimethylsiloxane
group. Foam stabilizers of this type have been described e.g. in U.S. Pat.
Specification No. 3,201,272, Column 3, line 60 to Column 4, line 3.
Reaction retarders may also be used according to the invention, e.g.
substances which are acid in reaction such as hydrochloric acid, sulphuric
acid, phosphoric acid or organic acid halides, as well as cell regulators
of known type such as paraffins or fatty alcohols or
dimethylpolysiloxanes; in addition there may be used pigments or dyes and
flame-retarding agents known per se, e.g. tris-chloroethyl phosphate or
ammonium phosphate and polyphosphate, age resisters and stabilizers to
protect against weathering, plasticizers, fungistatic and bacteriostatic
substances, fillers such as barium sulphate, kieselguhr, carbon black or
whiting.
Other examples of surface active additives, foam stabilizers and cell
regulators, reaction retarders, stabilizers, flame retarding substances,
plasticizers, dyes, fillers and fungistatic and bacteriostatic substances
and details of their mode of action and methods of using these additives
have been described in Kunststoff-Handbuch Volume VI, published by Vieweg
and Hochtlen, Carl-Hanser-Verlag, Munich, 1966, e.g. on pages 103 to 113.
The foaming process is preferably carried out in molds. Foaming in the mold
is carried out by introducing the reaction mixture into a mold suitably
made of a metal such as aluminium or a synthetic resin, e.g. epoxy resin.
The foamable reaction mixture reacts and expands inside the closed mold to
form the molded product. Foaming may either be carried out so that the
molded product has a cellular structure on its surface or it may be
carried out to produce a molded product with a compact skin and cellular
core. According to the invention the foamable reaction mixture may be
introduced into the mold in such an amount that the resulting foam only
just fills the closed mold. Alternatively, a larger quantity of reaction
mixture than would be required for filling the interior of the closed mold
with solidified cellular product may be introduced. This second method is
known as over-charging. It has been disclosed, e.g. in U.S. Pat.
Specification Nos. 3,178,490 and 3,182,104.
When foaming is carried out in molds, mold release agents already know per
se may be used in addition.
The process according to the invention may also be used for producing cold
setting foams (see British Pat. Specification No. 1,162,517 and German
Offenlegungeschrift No. 2,153,086).
According to the invention, reaction products of fatty acid esters and
organic polyisocyanates are added.
Suitable fatty acid esters are in particular those in which at least one
aliphatic acid which contains more than 8 carbon atoms is built into the
molecule and which have acid numbers of between 0 and 100, preferably
between 0 and 40 and hydroxyl numbers between 0 and 150, preferably
between 0 and 75, at least one of those two values being greater than 0.
The fatty acid esters used may also have the character of polyesters or
mixed esters which may be prepared both from monofunctional and from
polyfunctional carboxylic acids and/or alcohols. The fatty acid esters may
be prepared from several different types of fatty acids or carboxylic
acids and/or alcohols so that complicated fatty acid esters with an
average molecular weight generally between 500 and 5000 and preferably
between 800 and 3000 are obtained by a process of mixed condensation.
Amines or amino alcohols may also be used in the preparation of the fatty
acid esters to produce fatty acid mixed esters which contain basic or
amide groups. These mixed esters are suitable for the process according to
the invention. Such mixed esters can be obtained, for example, by adding
ammonia, monoalkylamines or dialkylamines or their alkoxylation products,
for example with ethylene oxide, propylene oxide or higher epoxides or by
using acid amides which contain carboxyl groups or alcohol groups. These
acid amides may be obtained, for example, by the amidation of carboxylic
acids with monoalkanolamines or dialkanolamines such as ethanolamine,
diethanolamine, propanolamine, or dipropanolamine or the like.
The fatty acid esters used for the reaction with the polyisocyanates are
preferably those which can be prepared by esterifying carboxylic acids
with alcohols or which can be obtained from natural substrates. The
following are examples of suitable carboxylic acids and alcohols: butanol,
hexanol, octanol-isomers, dodecanol, oleyl alcohol, other fatty alcohols,
natural or synthetic steroid alcohols, ricinoleic acid, ethylene gly | | |
