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Description  |
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This invention relates to the production of polyurethane foam sheetings by
frothing non-ionic polyurethane dispersions and to composite materials
produced from such mechanical foams and textile substrates or microporous
or homogeneous plastics sheet.
It is known to coat textile materials with polymer plastics. The purpose of
such coating is to obtain a synergistic effect in the composite material
with regard to its hard wearing qualities by combination of the properties
of the textile base and its coating.
In principle, the polymers can be applied homogeneously to the substrate
without an interlayer but it has been found advisable to separate the
plastics surface layer from the substrate by an interlayer. The object of
this interlayer is to act as a buffer between the abrasion-resistant top
layer and the base which serves as reinforcement so that the composite
material as a whole will have a softer handle and the component layers
will adhere more firmly to each other.
The buffer materials used in the past were napped fabrics or compact foam
layers. The napped fabrics in most cases consist of short staple fibers
which are teased out of the weft threads of the support fabric or out of
the filling threads in the case of a knitted support fabric by the usual
napping processes of the textile industry. The manufacture of such a
napped fabric requires close technical control of the process and is not
very economical because the process includes several stages. On the other
hand, it is essential to provide a buffer layer in the composite material,
especially for the purpose of bonding the plastics layer to the textile
substrate and especially if composite materials with good textile
properties are to be produced from inferior textiles. Numerous attempts
have therefore been made to replace the napped fabric by a suitable buffer
layer of polymer material.
On a large commercial scale, PVC foams have previously been used for this
purpose. Composite materials of this kind are widely used in the
manufacture of bags, suitcases and the like and in upholstery manufacture.
A serious disadvantage of these materials, however, is that due to their
plasticizer content they are not resistant to chemical cleaning agents
and, moreover, migration of the plasticizer causes undesirable changes in
the properties.
Polyurethanes are basically particularly suitable for coating textiles
because in suitable formulations they are extremely resistant to chemical
cleaning agents and to abrasion. Homogeneous and even microporous
polyurethane coatings, e.g. in sheet form, have been known for some time
and used on high-quality napped woven or knitted fabrics serving as the
textile substrate. It is known to slice polyurethane foams into thin
sheets and fix these to the substrates by a backing or laminating process.
It is also known to coat such composite foam materials with other polymers
either by direct coating or by reversal process. Although these processes
have numerous advantages, they also have the disadvantage that they
require a selection of various kinds of foam sheeting with high unit
densities to be kept in stock. Another disadvantage of the use of foam
laminates from cut sheets of polyurethane foams and textile bases is that
when the laminate is coated with polyurethanes dissolved in organic
solvents, the foam swells or is partly dissolved. With a view to
overcoming these disadvantages, it has been proposed to produce the
polyurethane foams directly in situ on the textile by the foaming process
by means of a propellant but attempts to achieve this have hitherto failed
because it was not possible to produce coatings with a uniform thickness.
For this reason, attempts have also been made to apply aqueous polyurethane
dispersions in the form of so-called mechanical foam to textile
substrates. Thus, in German Offenlegungsschrift No. 2,012,662 it has been
proposed to convert polyurethane dispersions which have been produced with
the aid of emulsifiers into finely porous layers of foam by adding porous
fillers which contain air. It is obvious that this process is commercially
unattractive because the introduction of air in this way can only be
achieved with relatively heavy fillers which would eliminate one of the
advantages of the foam, namely its low density combined with its high
mechanical strength. Moreover, the polyurethane dispersions used in the
Offenlegungsscrift mentioned above, which are produced in known manner in
the presence of emulsifiers, are not sufficiently mechanically stable to
be worked up into stable spread-coatable polyurethane foams by frothing
the latex with stable spread-coatable polyurethane foams by frothing the
latex with a frothing apparatus, i.e. by introducing air mechanically into
the polyurethane dispersion.
In German Offenlegungsschrift No. 1,495,745, it has been proposed to
convert polyurethane ionomer dispersions which are free from emulsifiers
into polyurethane mechanical foams by a frothing or churning process.
Ionomer dispersions of this kind which are free from emulsifiers can be
obtained by known methods, e.g. those described in German Pat. No.
1,237,306; German Offenlegungsschrifts No. 1,495,745; 1,495,847 and
2,035,732. It has been found in practice, however, that difficulties arise
when these dispersions are foamed by a frothing process, especially if a
finely porous, stiff, spreadcoatable foam is to be obtained for producing
thin sheets or interlayers which can be applied to the textile substrate
or separating layer without collapsing when dried. Although a porous foam
is obtained when ionomer polyurethane dispersions produced by the methods
referred to above are foamed by stirring air into them mechanically this
foam is not three-dimensionally stable but collapses to a liquid mass,
e.g. under the coating knife, and, when this liquid mass is dried, only a
thin, cracked sheet with a network-like structure remains. Although a
frothed foam produced from the above mentioned ionomer polyurethane
dispersions can be applied as a laminating coating to a substrate in the
same way as an ionomer polyurethane dispersion which has not been churned,
all that is obtained after drying is a thin polyurethane sheet with a
so-called crow's-foot structure and not a finely porous, compact
polyurethane foam sheet of the kind which would be necessary to obtain the
improvement in the handle and the bonding between the layers of the
composite materials described at the beginning of this text.
According to an earlier proposal of the Applicants (U.S. Pat. Application
No. 373,354 filed June 25, 1973 entitled "Composite Materials and process
for Their Production") self-supporting foam sheets or foams which can be
used for textile coating can be produced from ionomeric polyurethane
dispersions which are free from emulsifiers. The dispersions used for this
purpose must be finely divided (particle size less than 1.0 .mu.), highly
fluid (viscosity approximately 2 - 12 Poises) and highly concentrated
(solids content above 45%) and they must contain foaming agents,
stabilizers and cross-linking agents. One disadvantage of foam foils
produced by this process is their low tensile strength and, in addition,
the many additives required reduce the water resistance of the foam.
It is therefore an object of this invention to provide a process for making
polyurethane foams for use as an interlayer for composite materials which
is devoid of the foregoing disadvantages. Another object of the invention
is to provide a composite material having an improved polyurethane foam
buffer layer between a polymer layer and a textile layer. A more specific
object of the invention is to provide a method for making self-supporting,
finely porous, smooth foam sheets having high-tensile stengths and good
water resistance by the frothing process.
The foregoing objects and others are accomplished in accordance with this
invention, generally speaking, by providing a process for making
polyurethane foams suitable for buffer layers between a polymer layer and
a textile layer of a composite material wherein from about 0.1 to about
10% by weight of a thickening agent is included in an aqueous, non-ionic
polyurethane dispersion free from emulsifiers and having a polyurethane
solids content of more than 45% by weight, a viscosity of from about 2 to
about 12 poises and a particle size of less than 1 .mu..
It has now surprisingly been found that polyurethane foams which are
eminently suitable for use as buffer layers for the composite materials
described above can very well be produced by a mechanical frothing
process, even from aqueous, non-ionic polyurethane dispersions which are
free from emulsifiers and which contain as their only additive merely
about 0.1 to about 10% by weight, preferably about 0.6 to about 5.0% by
weight (based on the polyurethane solid) of thickener if the dispersions
have certain macroscopic properties, namely the following:
1. The dispersion must have a solids content of more than about 45% by
weight of polyurethane. The solids content is preferably from about 48% to
about 55% by weight.
2. The dispersion should have a viscosity of about 10 to about 70 seconds,
preferably about 20 to about 50 seconds outflow time from a Ford cup with
a 4 mm nozzle, i.e. about 2 to about 12 Poises, determined with a HAAKE
viscotester VT 180 at stage 4.
3. The dispersion must be so finely divided that it shows the TYNDALL
effect by reflected and transmitted light. This means that the diameter of
the particles must be less than about 1.0 .mu., preferably between about
0.07 and about 0.3 .mu., determined by the method of measuring the
variation of the angle with the slope of the light scatter curve.
It has also been found that layers which after drying in a drying channel
give rise to self-supporting, finely porous, smooth foam sheets which have
very high tensile strengths and which have excellent resistance wo water
owing to the absence of foaming agents and stabilizers can be obtained
from the churned polyurethane foams by the ordinary methods of brush or
spread coating.
These self-supporting foam sheets can be produced with very small
thicknesses (up to about 0.3 mm). These very thin sheets nevertheless have
considerable mechanical strength and can therefore be rolled up safely and
transported with suitable care. The foams are particularly easy to handle
and transport if they are painted on self-supporting sheets. It is well
known from the coating industry that polyurethane films from a weight per
square meter of about 40 g upwards can be used for coatings which have
such high abrasion resistance that they can be compared favorably with
coatings of other high-molecular weight polymers which have more than
three times their weight per square meter. There has always been a desire
to produce self-supporting sheets with such a low weight per square meter
in a transportable form. This wish has in the past been left unfulfilled
because such thin films were difficult to handle without a reinforcing
layer. There have been several attempts to stabilize the films by backing
them on to supporting fabrics or supporting layers of non-woven
substrates. This method, however, inevitably affected the properties of
the films, in most cases disadvantageously. It has now been found,
however, that the combination of sheet made of frothed polyurethane latex
and film surprisingly results in a material which is distictly easy to
handle without the advantageous properties of the foam or of the film
being in any way deleteriously affected.
This invention therefore provides a self-supporting polyurethane foam sheet
which has been produced by frothing a nonionic, aqueous polyurethane
dispersion of the kind mentioned above which is free from emulsifiers,
which dispersion in addition contains about 0.1 to about 10% by weight,
preferably about 0.6 to about 5.0% by weight, of thickener, based on the
polyurethane solids content.
This invention provides a composite material having at least the following
layers:
a. a plastics sheet, preferably a homogeneous or microporous polyurethane
sheet or a PVC sheet; and
b. a nonionic polyurethane dispersion foam having a density of about 0.04
to about 0.40 g/cm.sup.3 (determined according to DIN 53 420) obtained by
a churning process.
This invention also provides a composite material having at least the
following layers:
a. a plastics sheet, preferably a homogeneous or microporous polyurethane
sheet or a PVC sheet;
b. a nonionic polyurethane dispersion foam having a density of about 0.04
to about 0.40 g/cm.sup.3 (determined according to DIN 53 420) obtained by
the churning process; and
c. a woven or knitted textile layer or fleece manufactured from a fibrous
material.
The invention also provides a composite material having at least the
following layers:
a. a nonionic polyurethane dispersion foam having a density of about 0.04
to about 0.40 g/cm.sup.3 obtained by the churning process; and
b. a woven or knitted textile layer or fleece manufactured from a fibrous
material.
The necessity for fineness of subdivision, low viscosity and high solids
content in the nonionic polyurethane dispersions used according to the
invention arises from the following factors:
The introduction of air into the polyurethane dispersion produces,
effectively, a phase of air-containing cells in a continuous phase
comprising the cell membrane formed by the dispersion. If the viscosity of
the polyurethane dispersion is too high, the air cannot be stirred in
sufficiently homogeneously, with the result that a foam with an irregular
structure is obtained. In addition, high viscosity renders the transport
of the dispersion through the churning apparatus more difficult. Moreover,
if the dispersed polyurethane particles are not sufficiently finely
divided, their film-forming capacity is limited so that on drying, i.e. on
removal of water from the cell membrane, the particles can no longer
coalesce sufficiently and consequently the cell membrane breaks. Instead
of a smooth foam, a foam with a cracked surface is obtained. The same
effect results if the solids content of the nonionic polyurethane
dispersion is too low because the continuous introduction of air into a
given quantity of polyurethane dispersion depletes the cell membrane of
substance since the same quantity of polyurethane must then envelop an
increasing number of pores or pores with an increasing diameter. At a
given point, this progressive depletion of substance will result in the
cell membrane tearing. One must therefore restrict the quantity of air
stirred into the mixture, in which case the foam obtained will differ only
slightly from a homogeneous sheet, or otherwise a foam with a cracked
surface will be obtained.
The preparation of the nonionic, emulsifier-free polyurethane dispersions
suitable for the process according to the invention may be carried out,
for example, by the method according to Canadian Pat. No. 919,329:
1 mol of a trifunctional polyether polyol is reacted with 3 mols of a
diisocyanate. The resulting adduct, which contains isocyanate groups, is
reacted in such a manner with a mixture of
a. a monohydric, low-molecular weight alcohol and
b. a reaction product of a monohydric alcohol or a monocarboxylic acid and
ethylene oxide (molecular weight approximately 600) that a prepolymer
which contains 1 mol of monofunctional polyethylene oxide adduct to
approximately 3000 molecular weight units is obtained. This prepolymer is
emulsified in water with the aid of mechanical dispersing devices without
an emulsifying agent to produce a latex which is polymerized by reaction
with water or some other chain-lengthening agent known from polyurethane
chemistry to produce the final polymer. When preparing the latices, so
little water is used that the solids content will be above about 45% by
weight and preferably above 50% by weight.
Self-dispersible, nonionic polyurethane dispersions which can be used for
the process according to the invention may also be prepared according to
an earlier proposal of the present applicants (U.S. Pat. Application No.
452,180 filed Mar. 18, 1974 entitled "Non-ionic Polyurethane Dispersions")
by introducing side chain polyethylene oxide units attached to allophanate
or biuret groups into linear polyurethanes.
The production of these polyurethanes which can be dispersed in water
without the aid of dispersing agents is carried out according to known
methods of polyurethane chemistry by reacting organic compounds which have
a molecular weight of about 500 to about 6000, preferably about 600 to
about 3000, which contain end groups capable of reacting with isocyanate
groups and which are difunctional for the purpose of the isocyanate
polyaddition reaction, with organic diisocyanates, and, optionally,
difunctional chain-lenghtening agents with a molecular weight below 500
which are known per se in the chemistry of polyurethanes. It is essential
in this reaction to use or include organic diisocyanates of the general
formula
##STR1##
in which R denotes an organic group of the kind which can be obtained by
removing the isocyanate groups from an organic diisocyanate which has a
molecular weight in the range of about 112 to about 1000,
R' denotes a monovalent hydrocarbon group containing 1 to 12 carbon atoms,
X and Y are the same or different and represent oxygen or a group of the
formula -N(R")- in which R" represents a monovalent hydrocarbon group
containing 1 - 12 carbon atoms, and
n denotes an integer of from 9 to 89.
These special diisocyanates are preferably used as mixtures with
conventional unmodified organic diisocyanates of the general formula
R(NCO).sub.2 wherein R is a divalent organic radical. The diisocyanate
mixtures used should contain 5 to 100 mol percent, preferably 10 to 50 mol
percent of modified diisocyanates.
The following are specific examples of suitable difunctional organic
compounds with a molecular weight of about 500 to about 6000, preferably
about 600 to about 3000, which contain end groups capable of reacting with
isocyanates:
1. The dihydroxy polyesters known per se in polyurethane chemistry which
are obtained from dicarboxylic acids such as succinic acid, adipic acid,
suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid,
terephthalic acid, tetrahydrophthalic acid, etc. and diols such as
ethylene glycol, propylene-1,2-glycol, propylene-1,3-glycol, diethylene
glycol, butane-1,4-diol, hexane-1,6-diol, octane-1,8-diol, neopentyl
glycol, 2-methyl propane-1,3-diol or the various isomeric bishydroxymethyl
cyclohexanes;
2. The polylactones known per se in polyurethane chemistry, e.g. polymers
of .epsilon.-caprolactone which have been started on the dihydric alcohols
mentioned above;
3. polycarbonates known per se in polyurethane chemistry of the kind which
can be obtained, for example, by reacting the above mentioned diols with
diaryl carbonates or phosgene;
4. the polyethers known per se in polyurethane chemistry such as, for
example, the polymers or copolymers of styrene oxide, propylene oxide,
tetrahydrofuran, butylene oxide or epichlorohydrin which can be obtained
using divalent starter molecules such as water, the above mentioned diols
or amines which contain 2--N--H-- bonds;
5. the polythioethers, polythio mixed ethers and polythioether esters known
in polyurethane chemistry;
6. the polyacetals known in polyurethane chemistry, for example those
obtained from the above mentioned diols and formaldehyde; and
7. difunctional polyether esters containing end groups which are capable of
reacting with isocyanate groups.
Dihydroxy polyesters, dihydroxy polylactones and dihydroxy polycarbonates
are preferably used.
The chain-lengthening agents with a molecular weight below about 500 may
be, for example, the low-molecular weight diols described for the
preparation of dihydroxy polyesters, or also diamines such as
diaminoethane, 1,6-diaminohexane, piperazine, 2,5-dimethyl piperazine,
1-amino-3-aminomethyl-3,5,5-trimethyl-cyclohexane,
4,4'-diaminodicyclohexylmethane, 1,4-diaminocyclohexane, 1,2-propylene
diamine or also hydrazine, aminoacid hydrazides, hydrazides of
semicarbazidocarboxylic acids, bis-hydrazides and bis-semicarbazides.
Suitable diisocyanates of the general formula R(NCO).sub.2 include the
known diisocyanates of polyurethane chemistry in which R represents a
divalent aliphatic hydrocarbon group preferably containing 2 - 18 carbon
atoms, a divalent cycloaliphatic hydrocarbon group containing preferably 4
- 15 carbon atoms, a divalent aromatic hydrocarbon group containing
preferably 6 - 15 carbon atoms or an araliphatic hydrocarbon group
containing 7 - 15 carbon atoms. The following are typical examples of such
diisocyanates: ethylene diisocyanate, tetramethylene diisocyanate,
hexamethylene diisocyanate, dodecamethylene diisocyanate,
cyclohexane-1,3-and -1,4-diisocyanate,
1-isocyanato-3-isocyanatomethyl-3,5,5-trimethyl cyclohexane,
4,4'-diisocyanatodicyclohexylmethane or also aromatic diisocyanates such
as 2,4-diisocyanatotoluene, 2,6-diisocyanatotoluene, mixtures of these
isomers, 4,4'-diisocyanatodiphenyl methane, 1,5-diisocyanatonaphthalene,
etc.
Examples of suitable organic compounds containing groups reactive with
isocyanato groups and having a molecular weight of about 500 to about
6000, suitable chain lengthening agents and suitable organic diisocyanates
of the formula R(NCO).sub.2 are disclosed by Saunders and Frisch in the
book "Polyurethanes: Chemistry and Technology" published by Interscience
Publishers.
The modified allophanate diisocyanates may be prepared, for example, by
heating 1 mol of a monofunctional alcohol of the general formula
##STR2##
with two mols of one of the above mentioned diisocyanates of the general
formula R(NCO).sub.2, the urethane being formed in a first step of the
reaction and then reacting at an elevated temperature with a second mol of
diisocyanate to form the allophanate diisocyanate. If desired,
trimerization of the diisocyanates may be prevented by the addition of
catalytic quantities of alkylating agents such as p-toluene sulphonic acid
ester in the manner described in U.S. Pat. No. 3,769,318.
Furthermore, allophanatization may be accelerated by the method described
in said patent by the addition of certain metal compounds, e.g. zinc
acetyl acetonate.
To prepare biuret diisocyanates which may be used instead of the
allophanate diisocyanates, the monohydric alcohol of the formula
##STR3##
is first converted into a secondary amine of the general formula
##STR4##
This conversion of the alcohols into the corresponding secondary amines
may be carried out, for example, by the known reaction with N-substituted
ethylene imines or by a condensation reaction of the alcohols with primary
amines in a molar ratio of between 1 : 1 and 1 : 10. In cases where
ethylene imine derivatives are used, the number n is increased to N + 1.
The conversion of the resulting secondary amines which contain
polyethylene oxide units into the biuret diisocyanates which are used for
preparing the self-dispersible dispersions is carried out by reacting one
mol of the secondary amine with at least two mols of diisocyanate of the
general formula R(NCO).sub.2. In this reaction, the urea isocyanate is
first formed from the secondary amine and one mol of diisocyanate, and
this then reacts with a second mol of diisocyanate at an elevated
temperature to produce a biuret diisocyanate. In this reaction also,
trimerization of the diisocyanate can be suppressed by catalytic
quantities of alkylating agents such as p-toluene sulphonic acid esters.
The biuret diisocyanates in the same way as the allophanate diisocyanates
are used as mixtures with unmodified diisocyanates of the formula
R(NCO).sub.2 for preparing the self-dispersible polyurethanes, the
diisocyanate mixtures used containing from 5 to 100 and preferably from 10
to 50 mols percent of modified diisocyanate. If desired, of course,
mixtures of allophanate diisocyanates and biuret diisocyanates may be
used.
Any suitable monohydric alcohol which contains polyethylene oxide units may
be used for preparing the modified diisocyanates. The modified
diisocyanates may be obtained in known manner by ethoxylating monohydric
alcohols or monohydric phenols of the general formula R'-O-H or by
ethoxylating secondary amines of the general formula
##STR5##
In the above formula,
R' and R" represent the same of different hydrocarbon groups, in particular
C.sub.1 -C.sub.10 alkyl groups, C.sub.4 -C.sub.8 cycloalkyl groups,
C.sub.6 -C.sub.12 aryl groups or C.sub.7 -C.sub.10 aralkyl groups. The
following are examples of suitable alcohols or phenols: methanol, ethanol,
n-propanol, n-hexanol, n-decanol, isopropanol, tertiary butanol, phenol,
p-cresol and benzyl alcohol. Suitable secondary amines are, for example,
dimethylamine, diethylamine, dipropylamine, N-methyl-hexylamine,
N-ethyl-decylamine, N-methyl-aniline, N-ethyl-benzylamine and
N-methyl-cyclohexylamine.
The quantity of ethylene oxide to be added by grafting may vary within wide
limits. the polyethylene oxide chain generally consists of 10 to 90 and
preferably 20 to 70 ethylene oxide units.
The conversion of the polyethylene oxide alcohols into the corresponding
secondary amines is carried out in known manner using N-substituted
ethylene imines of the general formula
##STR6##
or primary amines of the general formula R'--NH.sub.2 in which R' has the
meaning specified above.
The preparation of the polyurethanes which are dispersible in water is
carried out according to known methods of polyurethane chemistry by
reacting the higher molecular weight dihydroxyl compounds with the
diisocyanates or diisocyanate mixtures, to which the chain-lengthening
agents mentioned above may be added. The reaction may be carried out by a
single-stage process or by a two-stage process (prepolymer process).
When preparing the self-dispersible polyurethanes, the reactants are used
in proportions corresponding to a ratio of isocyanate groups to groups
which are reactive with isocyanate groups of between 0.8 : 1 and 2.5 : 1,
preferably between 1 : 1 and 1.1 : 1. These proportions do not include any
water which may already be present during the preparation of the
dispersible polyurethanes. If an excess of isocyanate is used then the
reaction products naturally contain isocyanate groups which, when the
products are dispersed in water, react with water to form
polyurethane-polyureas which are free from isocyanate groups. The quantity
of modified diisocyanates used or the quantity of polyethylene oxide units
in these diisocyanates is chosen so that the finished polyurethane
contains 3 to 30 percent by weight, preferably 5 to 20 percent by weight
of polyethylene oxide segments in side chains.
Both the single-stage and the two-stage process may be carried out with or
without solvents. Suitable solvents are water-miscible solvents which are
inert towards isocyanate groups and have a boiling point below 100.degree.
C, e.g. acetone or methyl ethyl ketone.
Conversion of the dissolved polyurethane elastomers into an aqueous
dispersion is preferably carried out by the addition of water to the
stirred solution. In many cases, the phase will pass through a
water-in-oil emulsion which changes into an oil-in-water emulsion after
passing through a viscosity maximum. After removal of the solvent by
distillation, a pure, aqueous stable dispersion is left behind.
The polyurethane elastomers prepared as described above may also be
converted into dispersions by other methods, for example methods of
dispersion without using solvents, e.g. by mixing the elastomer melts with
water in an apparatus which is capable of producing high shearing
gradients or the use of very small quantities of solvents to plasticize
the reaction mixture, using the same apparatus, or methods employing
non-mechanical dispersing means such as sound waves of extremely high
frequency.
Self-dispersible, nonionic polyurethane dispersions can also be obtained by
introducing polyethylene oxide side chains with the diol component. In
addition to the above mentioned higher molecular weight diols,
diisocyanates of the formula R(NCO).sub.2 and, optionally,
chain-lengthening agents, diols of the following general formula
##STR7##
are then also used, in which formula R denotes a divalent group of the
kind obtained by removing the isocyanate groups from a diisocyanate having
a molecular weight of about 112 to about 1000,
X denotes oxygen or --NR"--,
R' and R" which may be the same or different, denote monovalent hydrocarbon
groups containing from 1 to 12 carbon atoms,
R'" denotes hydrogen or a monovalent hydrocarbon group containing from 1 to
8 carbon atoms, and
n denotes an integer of from 4 to 89.
These compounds will be referred to hereinafter as hydrophilic
chain-lengthening agents.
The hydrophilic chain-lengthening agents may be prepared, for example, by
the following method:
Alcohols or monohydric phenols of the general formula R'--O--H (X = O) are
first prepared in known manner as described above or the corresponding
monovalent alcohols which contain polyethylene oxide units, as represented
by the following formula
##STR8##
are prepared by ethoxylating secondary amines of the general formula
##STR9##
The quantity of ethylene oxide introduced by grafting may vary within wide
limits. The polyethylene oxide chains here again generally comprise 5 to
90 and preferably 20 to 70 ethylene oxide units.
The reaction of the resulting monovalent alcohols which contain
polyethylene oxide units with a large excess of one of the diisocyanates
of the general formula R(NCO).sub.2 of which examples are given above,
followed by the removal of the diisocyanate excess to produce the
corresponding monoisocyanate which contains polyethylene oxide units as
represented by the following general formula
##STR10##
then takes place in a second reaction step.
In the second reaction step, the diisocyanate is preferably used in a 2 to
10 times molar excess, preferably a 3 to 4 times molar excess, in order to
prevent the formation of corresponding bis-urethanes which are free from
isocyanate groups. This second reaction step is preferably carried out by
adding the monohydric alcohol which contains polyethylene oxide units to
the diisocyanate in the reaction vessel. The reaction may be carried out
at about 70.degree. to about 130.degree. C. The subsequent removal of the
diisocyanate excess is preferably carried out by thin-layer vacuum
distillation at about 100.degree. to about 180.degree. C.
The hydrophilic chain-lengthening agent is then obtained in a third
reaction step by reacting the above described monoisocyanates which
contain polyethylene oxide units with dialkanolamines of the general
formula
##STR11##
in which R'" has the meaning already indicated above. In this third
reaction step, the reactants are preferably used in stoichiometric
proportions. This third step of the reaction is preferably carried out at
0.degree. to 50.degree. C, preferably at 15.degree. to 30.degree. C.
Suitable dialkanolamines of the above general formula are e.g.
diethanolamine, dipropanolamine (R'" = CH.sub.3) and
bis-(2-hydroxy-2-phenyl-ethyl)-amine.
Preparation of the self-dispersible polyurethanes may be carried out also
in this case by either a single-stage or a two-stage process (prepolymer
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