Note: Descriptions are shown in the official language in which they were submitted.
CA 0222101~ 1997-12-22
' 0050/47638
Pressurized, isocyanate-terminated prepolymers containing
oxazolidone and urethane groups for one-component foams
The present invention relates to pressurized,
isocyanate-terminated prepolymers containing oxazolidone and
urethane groups which can be processed into one-component
polyurethane foams.
One-component polyurethane foams, also known as in-situ foams,
are frequently-used construction materials which are employed
mainly in the building industry, for example for the installation
of doors and windows in buildings or as filler material for
15 hollow spaces resulting from the method of construction or for
openings in walls for pipe installations.
The in-situ foams are formed by isocyanate-terminated prepolymers
present in pressure containers being discharged by means of
20 blowing agents, foamed by frothing action and cured by means of
atmospheric moisture.
To prepare the pressurized prepolymers, two principal methods are
known;
1. The isocyanate component and the polyol component are
introduced into the pressure container in the desired ratio,
the container is closed and the blowing agent is injected.
The prepolymer which forms and the blowing agent are
intensively mixed with one another in a shaking or tumbling
apparatus.
2. The prepolymer is formed from the isocyanate and polyol
components in a reactor and then introduced into the pressure
container, the container is closed and the blowing agent is
injected. The prepolymer is intensively mixed with the
blowing agent in shaking or tumbling apparatus.
40 In order to achieve an optimum distribution of the foam in the
joints and hollow spaces to be filled with foam, a low prepolymer
viscosity is desirable. In the past, the chlorofluorocarbons
customary as blowing agents contributed to lowering the
viscosity. ~ince continued use of such compounds is not possible
45 for environmental reasons, plasticizers or solvents have
fre~uently been added to the prepolymers, as described, for
example, in DE-A-4 025 843 or EP-A-480 342. However, the use of
0050/47638 CA 0222l0l~ l997-l2-22
.
such compounds leads, since they are not built into the foam, to
considerable shrinkage of the foams. DE-A-33 17 193,
DE-A-39 11 784 and DE-A-38 29 104 also describe the addition of
compounds which are said to lower the viscosity of the
5 prepolymers. However, here too, considerable shrinkage and
embrittlement of the foams result.
In addition, in the case of the foams of the prior art, the
different property requirements for the foam, particularly the
10 ratio of open to closed cells, had to be taken into account for
the two possible ways of discharging the in-situ foam from the
aerosol can, viz. discharge via a foaming gun and discharge via a
foaming tube, customarily designated as elbow discharge.
Thus, a conventional, largely closed-celled foam permits only gun
processing, while in the case of elbow processing it would have
additional and thus excessive shrinkage. On the other hand, a
largely open-celled foam can only be satisfactorily processed by
20 elbow discharge, while the bubbles in it would be too large if
discharged by means of a gun.
For this reason, specific foam formulations have hitherto been
prepared for the two methods of discharge.
It is an object of the present invention to provide a prepolymer
for one-component polyurethane foams which, owing to its low
viscosity, is readily processible and can be processed into foams
having low shrinkage, an optimum ratio of open to closed cells
30 and improved mechanical properties and which permits discharge
both via a gun and via an elbow.
We have found that this object is achieved by an isocyanate-
35 terminated prepolymer containing oxazolidone and urethane groups
which can be prepared by reacting an isocyanate component with a
polyol component, wherein the isocyanate component (A) used is a
reaction product containing terminal isocyanate groups and
obtained by reacting at least one isocyanate containing at least
40 two isocyanate groups in the molecule with a mixture of at least
one compound containing at least two functional groups which
react with isocyanate and at least one epoxide group in the
molecule and at least one polyester polyol and the polyol
component (B) used comprises at least one polyether terminated by
45 primary hydroxyl groups and having a functionality of >2.
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The present invention accordingly provides isocyanate-terminated
prepolymers containing oxazolidone and urethane groups as
described above.
5 The present invention further provides a process for preparing
the isocyanate-terminated prepolymers, provides for their use for
producing one-component polyurethane foams and also provides the
one-component polyurethane foams.
As regards the isocyanate components (A) used according to the
present invention and their formative components, the following
may be said:
15 As isocyanates containing at least two isocyanate groups in the
molecule, it is possible to use the customary and known
diisocyanates and polyisocyanates, for example aliphatic
isocyanates such as hexamethylene l,6-diisocyanate (HDI),
isophorone diisocyanate, aromatic isocyanates such as tolylene
20 diisocyanate (TDI), diphenylmethane diisocyanate (MDI) and
mixtures of diphenylmethane diisocyanate and
polyphenylene-polymethylene polyisocyanates (raw MDI). The
isocyanates can also be modified by incorporation of, for
example, uretdione, isocyanurate and allophanate groups.
For one-component polyurethane foam, preference is given to using
raw MDI.
The polyester polyols used according to the present invention are
30 prepared in a known manner by polycondensation of polybasic
carboxylic acids with polyhydric alcohols. Such products are
described, for example, in the Kunststoff-Handbuch, Volume 7,
"Polyurethane", edited by Gunter Oertel, Carl-Hauser-Verlag
Munich, 3rd edition 1993, pages 67 to 74.
Polyester polyols derived from dibasic carboxylic acids, in
particular aliphatic dicarboxylic acids, and diols are
particularly advantageous for preparing the prepolymers of the
40 present invention. Polyesterols based on adipic acid and
diethylene glycol have been found to be particularly useful. The
molecular weight of these polyesterols should be from 100 to
2000 g/mol (weight average). If the molecular weights are too
high, the viscosity of the polyesterols increases excessively.
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As compounds containlng at least two groups which react with
isocyanate and at least one epoxide group in the molecule, it is
possible to use polyols obtained by epoxidation of natural
materials, for example epoxidized soyabean oil but in particular
5 epoxidized polybutadienediols. The molecular weight should be
from 600 to 4000 g/mol (weight average) since in this weight
range they can, despite their incompatibility with the
polyesterpolyol, be built into the urethane/oxazolidone-modified
isocyanate to form oxazolidone structures.
The polyester polyol and the epoxidized compound are preferably
used in a weight ratio of from 100:1 to 1:100, in particualr from
50:1 to 1:5. Furthermore, it has been found to be useful to use
the mixture of polyester polyol and epoxidized compound in an
15 amount of from 0.1 to 20 % by weight, preferably from 2 to 10 %
by weight, based on the isocyanate used.
The polyisocyanate modified as described with oxazolidone and
20 urethane groups is reacted with the polyol component (B) to give
the prepolymer of the present invention. According to the present
invention, the polyol component comprises at least one high
molecular weight polyether terminated by primary hydroxyl groups
and having a functionality of >2 and a molecular weight of
25 >1500 g/mol, preferably from 3000 to 20,000 g/mol. These
polyether polyols provided with primary OH groups and having a
high molecular weight are particularly advantageous since as
reactive polyols they form high molecular weight reaction
products and thus effect, in the cured one-component foam, not
30 only good elasticity behavior but also optimum low-temperature
curing without embrittlement.
Among the pure polyether polyols having the abovementioned
characteristics, polyethylene glycols are particularly useful.
35 These are used in combination with customary polyhydroxyl
compounds and additives in such a way that, despite their melting
point above 20~C, they give a polyol component which is liquid at
room temperature. Apart from the advantages mentioned, the use of
these polyether polyols gives additional advantages via their
40 physically cell-opening high molecular weight reaction products
with the isocyanate in the aerosol can. The pure polyether
polyols having a high molecular weight and primary OH groups also
include the polyethers derived from more than one alkylene oxide.
Here, suitable polyols are those in whose preparation ethylene
45 oxide as final addition generates primary OH groups.
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Other particularly useful polyether polyols are those which have
the abovementioned characteristics and which are prepared using a
polyesterpolyol, in particular a fatty acid ester having
OH functionality, as initiator.
Ethoxylated castor oil which can also be partially propoxylated
is particularly useful. The mean molecular weight (weight
average) is preferably >1500 g/mol, in particular from 1500 to
8000 g/mol. Higher molecular weights lead to increased prepolymer
10 viscosities-
Apart from the ethoxylated fatty acid esters, the polyolcomponent comprises the hydroxy-functional compounds customary
15 for the production of rigid polyurethane foams, usually polyether
polyols and/or polyester polyols as are described, for example,
in Kunststoff-Handbuch, loc sit., and also, if desired,
short-chain diols such as ethylene glycol, propylene glycol,
1,4-butanediol as chain extenders, short-chain at least trihydric
alcohols such as glycerol or trimethylolpropane as crosslinkers
and also catalysts and, if desired, stabilizers, colorants and/or
monools as molecular weight regulators.
Catalysts used are preferably strongly basic amines or organic
25 metal compounds, in particular tin compounds or synergistically
acting mixtures of strongly basic amines and organic metal
compounds. Examples of strongly basic amines are: amidines such
as
2,3-dimethyl-3,4,5,6-tetrahydropyrimidine,
30 tris(dialkylaminoalkyl)-s-hexahydrotriazines such as
tris(N,N-dimethylaminopropyl)-s-hexahydrotriazine, but preferably
tertiary amines such as triethylamine, tributylamine,
dimethylbenzylamine, N-methylmorpholine, N-ethylmorpholine,
N-cyclohexylmorpholine, bis(morpholinoethyl) ether,
35 N,N,N',N'-tetramethylethylenediamine,
N,N,N',N'-tetramethylbutanediamine,
N,N,N',N'-tetramethylhexane-1,6-diamine,
pentamethyldiethylenetriamine, bis(dimethylaminoethyl) ether,
bis(di-methylaminopropyl)urea, dimethylpiperazine,
40 1,2-dimethylimidazole, bis(4-N,N-dimethylaminocyclohexyl)methane,
1-aza-bicyclo(3.3.0)octane and 1,4-diazabicyclo(2.2.2)octane.
Suitable organic tin compounds are, for example: tin(II) salts of
organic carboxylic acids, eg. tin(II) diacetate, tinn(II)
45 dioctoate, tin(II) diethylhexoate and tin(II) dilaurate, and also
dialkyl tin(IV) salts of carboxylic acids, eg. dibutyltin
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diacetate, dibutyltin dilaurate, dibutyltin maleate, dibutyltin
dimercaptide and dioctyltin diacetate.
Particularly suitable stabilizers are siloxane-oxyalkylene
5 copolymers.
The prepolymer of the present invention is present in a pressure
container and is dissolved in a liquefied gas or liquefied gas
10 mixture which functions as blowing agent. Suitable blowing agents
are customary liquefied gases and also other substances having a
boiling point of <50~C. Examples which may be mentioned are:
Dimethyl ether, propane, n- or iso-butane, pentane, methyl
15 isobutyl ether and also halogenated hydrocarbons such as
dichlorofluoromethane, monofluorotrichloromethane,
trifluorotrichloroethane, trifluoromethane,
1,1-dichloro-l,fluoroethane, monochlororifluoroethane,
monochlorodifluoroethane, difluoroethane,
20 dichlorotrifluoroethane, monochlorotetrafluoroethane,
pentafluoroethane, tetrafluoroethane, dichloromonofluoroethane.
Particularly suitable blowing agents are alkanes and also
mixtures of alkanes, fluorinated alkanes and dimethyl ether.
The preparation of the prepolymers of the present invention is
preferably carried out in two stages: firstly, the
urethane-/oxazolidone-modified polyisocyanate is prepared. For
this purpose, the necessary amounts of isocyanate are initially
30 charged and the mixture of polyesterol and epoxidized polyol is
metered in. Since the two compounds are not miscible with one
other, they are preferably added in the form of an emulsion. The
reaction is carried out at from 60 to 110~C, preferably from 80 to
90~C, while stirring. After a reaction time of from about 2 to
35 6 hours, the modification is complete and the reaction mixture is
cooled to room temperature.
The reaction of the isocyanate component thus prepared with the
40 polyol component can be carried out in two possible ways:
1. The polyol component is metered into aerosol cans. The
isocyanate component is then metered in, the aerosol can is
closed by means of a valve and the blowing agent is metered
in. The mixture constituents in the aerosol can are then
intensively mixed and homogenized in a subsequent shaking or
tumbling apparatus. The subsequent reaction forms the
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prepolymer in the aerosol cans. After warm storage at about
50~C for about 24 hours or storage at room temperature for
about 3 days, the foam is ready to use.
5 2. The isocyanate component is reacted with the polyol component
in a reactor, the reaction mixture is introduced into an
aerosol can, the latter is closed by means of a valve and the
blowing agent is introduced. The subsequent procedure is as
described above.
The weight ratio of polyol component to isocyanate component is
about 100:~140 or an index of >400.
15 Compared with the prior art, the prepolymer of the present
invention has the following advantages:
The built-in oxazolidone groups have a cell-opening action in the
foam and thus reduce the shrinkage. On the other hand, the
20 solubility of the reaction product in excess isocyanate is
improved. This is particularly surprising when epoxidized
polybutadienediol is used, since this compound is extremely
hydrophobic and normally does not mix with the other constituents
of the reaction mixture. The resulting foams cure readily, have
25 very good mechanical properties, in particular display no
embrittlement, and have an excellent low-temperature behavior.
The foams can be discharged from the pressure container either
via a gun or via an elbow.
The invention is illustrated by the following examples.
Examples
Example 1
1.1 Preparation of the urethane-/oxazolidone-modified isocyanate
A stirred reactor provided with a heating and cooling
facility and a temperature measurement device was charged
with 95 kg of a raw diphenylmethane diisocyanate. In a
separate mixing vessel, 6 kg of an adipic acid/diethylene
glycol polyester alcohol having a molecular weight of
450 g/mol (OH number = 250 mg KOH/g) were mixed with 0.67 kg
of an epoxidized polybutadienediol having an OH number of
180 mg KOH/g. The mixture gave a stable emulsion of the
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otherwise immiscible liquids. With the stirrer running, 5 kg
of this emulsion were added to the raw diphenylmethane
diisocyanate and thoroughly mixed. The contents of the
reactor were then slowly heated to about 80~C while
continuing the stirring. After reaching 80~C, this
temperature was held for about 2 hours and the reaction
product was then slowly cooled to room temperature. The
urethane-/oxazolidone-modified isocyanate obtained had the
following properties:
Isocyanate content: 28.7 % of NCO
Viscosity (25~C): 350 mPa s
15 1.2 Preparation of the polyol component
1750 g of a polyester alcohol based on a dicarboxylic acid
mixture (glutaric acid, succinic acid, adipic acid) and
ethylene glycol and having an OH number of 56 mg KOH/g, 300 g
of a polyether alcohol based on
sucrose/pentaerythritol/propylene oxide and having an OH
number of 410 mg KOH/g, 350 g of a polyether based on
glycerol/propylene oxide/ethylene oxide and having an OH
number of 35 mg KOH/g, 400 g of a polyethylene glycol having
a molecular weight of 600 g/mol, 325 g of an ethoxylated
castor oil having a molecular weight of 4200 g/mol (OH number
of 40 mg KOH/g), 125 g of a siloxane-oxyalkylene copolymer as
foam stabilizer, 40 g of bis(morpholinoethyl) ether, 10 g of
4-methyl-4-hydroxypentan-2-one, 50 g of 1,4-butanediol and
1650 g of trichloropropyl phosphate were weighed one after
the other into a mixing vessel and were homogenized by
subsequent thorough mixing to give a polyol component.
1.3 Preparation of the prepolymers in aerosol cans having
universal valves
280 g of the above-described polyol component were introduced
into a 1 1 aerosol can. After addition of 434 g of the
urethane-/oxazolidone-modified raw diphenylmethane
diisocyanate as described in 1.1, the aerosol can was closed
with a universal valve. Immediately after closing the can,
40 g of dimethyl ether, 72 g of tetrafluoroethane and 24 g of
a gas mixture consisting of 80 % of butane and 20 % of
propane were introduced one after the other through the valve
into the aerosol can by means of a gas-metering apparatus.
After metering in each individual gas or the gas mixture, the
contents of the aerosol can were homogenized by intensive
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shaking. After warm storage at 50~C for 24 hours, the
prepolymer reaction was sufficiently complete for the aerosol
can to be ready for producing the one-component foam.
5 1.4 Production of the one-component foams
The prepolymers were discharged from the above-described
aerosol cans both by means of a gun and by means of an elbow.
This was achieved by mounting the aerosol can on the
respective dlscharge apparatus. The discharged prepolymers
displayed very good frothing action and cured in the presence
of atmospheric moisture or moisture from the substrate to
give a foam having a very well structured surface, thin foam
skin and very fine foam cells ln each case. The cured
one-component foam displayed very good mechanical properties,
as shown in the table below.
Foams as described in Example 1
Gun dischargeElbow discharge
Density in kg/m3 14 16
Tensile strength in 11.5 12
N/cm2
Elongation at break 34 34
in %
Shear strength in N/ 6 7
cm2
Compressive stress at 5.8 6,7
10 % deformation in
30 N/cm2
In addition, the shrinkage of the foam after storage under
controlled conditions (40~C/90 % relative humidity) was very
low.
Shrinkage of the foam as described in Example 1
Gun discharge Elbow discharge
- 1.46 % - 1.75 %
The foams as described in Example 1 were also cold-stable,
ie. they displayed no embrittlement at all at processing
temperatures of about 5~C.
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The foam was classlfied in the burning class B2 as specified
in DIN 4102.
Example 2
2.1 Preparation of the urethane-/oxazolidone-modified isocyanate
A stirred reactor provided with a heating and cooling
facility and a temperature measurement device was charged
with 94.8 kg of a raw diphenylmethane diisocyanate. In a
separate mixing vessel, 6 kg of an adipic acid/diethylene
glycol polyester alcohol having a molecular weight of
450 g/mol (OH number = 250 mg KOH/g) and 0.93 kg of an
epoxidized polybutadienediol having an OH number of 120 mg
KOH/g were mixed. The mixture gave a stable emulsion of the
otherwise immiscible liquids. With the stirrer running,
5.2 kg of this emulsion were added to the raw diphenylmethane
diisocyanate and thoroughly mixed. The contents of the
reactor were then slowly warmed to about 80~C while
continuing the stirring. After reaching 80~C, this
temperature was held for about 2 hours and the reaction
product was then slowly cooled to room temperature. The
urethane-/oxazolidone-modified isocyanate obtained had the
following properties:
Isocyanate content: 28.5 % of NCO
Viscositity (25~C): 370 mPa s
30 2.2 Preparation of the polyol component
3400 g of a reaction product of a dicarboxylic acid mixture
(glutaric acid, succinic acid, adipic acid) and a
polypropylene glycol polyether having a molecular weight of
450 g/mol and an OH number of 50 mg KOH/g, 300 g of a
polyether alcohol based on sucrose/pentaerythritol/propylene
oxide and having an OH number of 410 mg KOH/g, 350 g of a
polyether alcohol based on glycerol/propylene oxide/ethylene
oxide and having an OH number of 35 mg KOH/g, 400 g of a
polyethylene glycol having a molecular weight of 600 g/mol,
325 g of an ethoxylated castor oil having a molecular weight
of 4200 g/mol (OH number = 40 mg KOH/g), 125 g of a
siloxane-oxyalkylene copolymer as foam stabilizer, 40 g of
bis(morpholinoethyl) ether and 60 g of 1,4-butanediol were
weighed one after the other into a mixing vessel and
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homogenized by subsequent thorough mixing to give a polyol
component.
2.3 Preparation of the prepolymer in aerosol cans having
universal valves
245 g of the above-described polyol component were introduced
into a 1 l aerosol can. After additlon of 380 g of the
urethane-/oxazolidone-modified raw diphenylmethane
diisocyanate as described in 2.1, the aerosol can was closed
with a universal valve. Immediately after closing the can,
44 g of dimethyl ether, 36 g of tetrafluoroethane and 66 g of
a gas mixture consisting of 80 % of butane and 20 % of
propane were introduced one after the other through the valve
into the aerosol can by means of a gas-metering apparatus.
After metering in each individual gas or the gas mixture, the
contents of the aerosol can were homogenized by intensive
shaking. After warm storage at 50~C for 24 hours, the
prepolymer reaction was sufficiently complete for the
prepolymer to be ready for production of the one-component
polyurethane foam.
2.4 Production of the one-component polyurethane foams
The prepolymers were discharged from the above-described
aerosol cans both by means of a gun and by means of an elbow.
This was achieved by mounting the aerosol can on the
respective discharge apparatus. The discharged prepolymers
displayed very good frothing action and cured in the presence
of atmospheric moisture or moisture from the substrate to
give in each case a foam having a very well structured
surface, thin foam skin and very fine foam cells. The cured
one-component foam displayed good mechanical properties, as
shown in the table below.
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Foams as described in Example 2
Gun discharge Elbow discharge
Density in kg/m3 15 16
5 Tensile strength in 9.5 11
N/cm2
Elongation at break 32 28
in %
Shear strength in N/ 6 7
cm2
Compressive stress at 5.6 6.2
10 % deformation in
N/cm2
In addition, the shrinkage of the foam after storage under
controlled conditions (40~C/90 % relative humidity) was very
low.
Shrinkage of the foam as described in Example 2
Gun discharge Elbow discharge
- 1.15 % - 1.28 %
The foams as described in Example 2 were also cold-stable,
ie. they displayed no embrittlement at all at processing
temperatures of about 5~C.
