Note: Descriptions are shown in the official language in which they were submitted.
Mo3528
LeA 27,398
MIXTURES OF PREPOLYMERS CONTAINING URETHANE GROUPS
AND DIISOCYANATOTOLUENES AND THEIR USE
BACKGROUND ~F THE INVENTION
Field of the Invention
This invention relates to liquid mixtures comprising
prepolymers containing urethane groups based on polyisocyanates
or polyisocyanate mixtures of the diphenylmethane series and
polyester polyols in admixture with diisocyanatotoluenes and/or
polyisocyanates and to the use of these mixtures as isocyanate
components in the production of flexible polyurethane foams,
more part;cularly flexible molded foams.
Brief Description of the Prior Art: The advantageous use
of prepolymers based on polyisocyanates and hydroxy
(OH)-functional compounds such as polyols is known and
described in detail in the literature: DE-PS 1,618,380, GB-PS
1,369,334, DE-OS 2,913,126, DE-OS 2,404,166, DE-AS 2,737,338,
DE-AS 2,624,526, DE-OS 2,513,793, DE-OS 2,513,798, EP-A
0,010,850, EP-A 0,022,617 and EP-A 111,121. The
above-mentioned prepolymers can be made up of various chemical
components. For example, polyethers differing in
functionality, molecular weight, starter molecule, ethylene
oxide content or ethylene oxide/propylene oxide distribution
can be used as the polyol component.
Generally, the quality of the prepolymers can be
determined by the choice of the isocyanate and the polyol
components. Illustratively, DE-A 3,818,769 shows that
variation in the functionality of the polyether for the same or
similar diphenylmethane diisocyanate base can produce a
distinct improvement.
Typically, the prepolymers have higher viscosity and
lower isocyanate (NCO) content than the corresponding,
non-prepolymerized isocyanates. The higher viscosity can
favorably affect metering accuracy of pumps employed in
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processing the prepolymers. The lower NCO content can
adversely affect properties such as hardness of foams prepared
with the prepolymers.
As would be realized, it would be desirable to have
prepolymers that have a higher viscosity and a high NCO content
at the same time. By the present invention, there is provided
l~quid mixtures containing prepolymers which combine high
viscosity with a high NCO content.
SUMMARY OF THE INVENTION
In accordance with the foregoing, the present invention
encompasses a liquid mixture having a viscosity at 25-C of 5 to
100 mPas and an NCO content of 35 to 47% by weight and
comprising
a) a liquid prepolymer containing urethane groups and having
an NCO content of 5 to 30% by weight
which is a reaction product of:
al) a polyisocyanate or a polyisocyanate mixture of the
diphenylmethane series, and
a2) a polyester polyol having a molecular weight of 500 to
10,000 in a substoichiometric quantity,
in admixture with
b) a diisocyanatotoluene and/or component al)
in a ratio by weight of a) to b) of 1:20 to 20:1.
The invention further encompasses an improvement in the
method of preparing foams and foams produced by reacting the
liquid mixture of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The liquid mixtures of the invention are characterized in
that they contain prepolymers which have, at once, high
viscosities and high NCO content. Hence, one is able to
overcome the prior art problem of compromising the des;rable
prepolymer property of high viscosity for a high NCO content,
or vice versa. .
The liquid prepolymer can be prepared by reacting a
component al)~polyisocyanate or polyisocyanate mixtures of the
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diphenylmethane series and, in a substoichiometric quantity,
with a component a2) polyester polyol having a molecular weight
Of S00 to 10.000-
The polyisocyanate component al) can be an aliphatic,
cycloaliphatic, araliphatic or preferably an aromatic
polyisocyanate, i.e., a polyisocyanate in which all of the
isocyanate groups are aromatically bound. Examples of the
aromatic polyisocyanate can include 2,4- and/or
2,6-diisocyanatotoluene; 2,2'-, 2,4'-, and/or 4,4'-
diisocyanatodiphenylmethane, or a mixture of isomers or an
isomeric mixture with a higher homolog of an isomer. A
technical mixture of 4,4'-, 2,4'- and up to 10% and preferably
from < 5 % by weight 2,2'-diisocyanatodiphenyl methane or a
mixture of an isomer or an isomeric mixture with a homolog of
higher functionality, of the type formed in the phosgenation of
an aniline formaldehyde condensate, is preferably used.
The compounds of component a2) contain ;socyanate-reactive
groups and are typically polyesters having a molecular weight
in the range from 500 to 10,000 and preferably in the range
from 1,000 to 7,000 which normally contain at least two,
preferably terminal, isocyanate-reactive groups. These
isocyanate-reactive groups are alcoholic hydroxyl groups
attached to primary or secondary carbon atoms. The molecular
weights mentioned may be determined, for example, by vapor
pressure osmometry.
The polyester polyol of component a2) is preferably a
reaction product of a dicarboxylic acid or an anhydride with an
excess of polyhydric alcohol having a molecular weight of 62 to
200. In a particularly preferred embodiment, the polyester
polyol is a reaction product of adipic acid and/or terephthalic
acid with diethylene glycol and/or glycerol. Accordingly, the
polyester polyols known per se from polyurethane chemistry
which correspond to the foregoing observations may be used as
component a2). The polyester polyols may be produced, for
example, from polybasic carboxylic acids, preferably aliphatic
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dicarboxylic acids, containing 2 to 12 and preferably 4 to 8
carbon atoms in the alkylene radical and polyhydric alcohols,
preferably diols. Examples of suitable polybasic carboxylic
acids are aliphatic dicarboxylic acids~ such as glutaric acid,
5 pimelic acid, suberic acid, azelaic acid, sebacic acid,
undecanedioic acid, dodecanedioic acid and preferably succinic
and adipic acid, and aromatic dicarboxylic acids, such as
phthalic acid and tereph~halic acid. Examples of polyhydric,
more especially di- and trihydric, alcohols are ethylene
10 glycol, diethylene glycol, 1,2- and 1,3-propylene glycol,
dipropylene glycol, decane-l,10-diol, glycerol, trimethylol
propane and preferably butane-1,4-diol and hexane-1,6-diol.
Where polyhydric, particularly trihydric, alcohols are used for
the production of the polyester polyols, their content is best
15 calculated in such a way that the functionality of ~he
polyester polyols obtained is at most 6 and preferably 2 to 4.
Component b) can be a diisocyanatotoluene and/or a
polyisocyanate of component al) in a ratio by weight of a) to
b) of 1:20 to 20:1 and preferably 1:1. Technical mixtures of
20 2,4-diisocyanatotoluene with up to 45% and preferably 20 to 35
by weight 2,6-diisocyanatotoluene are preferably used as the
diisocyanatotoluenes.
The equivalence ratio of the NCO groups of component al)
to the OH groups of component a2) is 20:1 and preferably 1:5.
25 The liquid prepolymer has NCO content of 5 to 30% and
preferably 15 to 25%.
The liquid mixtures have NCO content of 35 to 47% and
preferably 35 to 42%. viscosityof the liquid mixture can range
from 5 to 100 and preferably 20 to 40 ~p~s.
As mentioned above, the liquid mixtures of the
prepolymers with the diisocyanatotoluenes and/or component al)
may be used as the isocyanate components in the production of
elastic, open-cell foams, preferably molded foams. The liquid
mixtures according to the invention are processed to elastic,
open-cell flexible foams by the reaction with:
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1. compounds conta;ning at least two isocyanate-reactive
hydrogen atoms and having a molecular weight in the range from
400 to lO,OOO, preferably from 1,000 to 6,000 and more
preferably from 3,000 to 6,000. Compounds of this type are
preferably compounds containing hydroxyl groups, more
preferably compounds containing 2 to 6 and most preferably 2 to
4 hydroxyl groups. Example thereof can be polyethers or
polyesters containing 2 to 6 and preferably 2 to 4 hydroxyl
groups. Particularly preferred are polyethers of the type known
per se for the production of homogeneous and cellular
polyurethanes as described, for example, in DE-OS 2 832 253,
pages 11 et seq. They preferably have an OH value of 28 to 56;
2. optionally compounds containing at least two
isocyanate-reactive hydragen atoms and having a molecular
weight in the range from 62 to 399. In this case, too, the
compounds in question are compounds containing hydroxyl groups
which serve as chain-extending agents or crosslinking agents.
These compounds generally contain 2 to 4 isocyanate-reactive
hydrogen atoms. Examples of these compounds can be found in
DE-OS 28 32 253, pages 10 et seq.;
3. water as a blowing agent in a quantity of l to 15 parts by
weight per lOO parts by weight of component l.
4. optionally auxiliaries and additives, such as
a) readily volatile organic substances as further
blowing agents,
b) reaction accelerators and reaction retarders known
per se in typical quantities,
c) surface-active additives, such as emulsifiers and
foam stabilizers; cell regulators known per se, such
as paraffins or fatty alcohols or dimethyl
polysiloxanes; pigments or dyes and flameproofing
agents known per se, for example tris-chloroethyl
phosphate, tricresyl phosphate; stabilizers against
the effects of aging and weathering; plasticizers;
fungistatic and bacteriostatic agents; and fillers,
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such as barium sulfate, kieselguhr, carbon black or
whiting.
These optional auxiliaries and additives are descr1bed,
for example, in DE-OS 27 32 292, pages 21 et seq. Further
examples of surface-active additives, foam stabilizers, cell
regulators, reaction retarders, stabilizers, flameproofing
agents, plasticizers, dyes, fillers and fungistatic and
bacteriostatic agents may optionally be used in accordance with
the invention. Information on their use and their mode of
action can be found in Kunststoff-Handbuch, Vol. YII~ edited by
Vieweg and Hochtlen, Carl-Hanser-Verlag, Munchen 1966, for
example on pages 103 to 113.
The reaction components are preferably reacted by the
one-shot process known per se, often using machines, for
example of the type described in US-PS 2,764,565. Particulars
of processing machines can be found in ~unststoff Handbuch,
Vol. VII, edited by Vieweg and Hochtlen, Carl-Hanser-Verlag,
Munchen 1966, for example on pages 121 to 205.
Foaming is preferably carried out in closed molds. To
this end, the reaction components are introduced into a mold
which may be made of metal, for example aluminum, or of
plastic, for example epoxy resin. The resulting reaction
mixture foams in the mold and forms the molding. According to
the invention, foamable reaction mixture may be introduced into
the mold in such a quantity that the foam formed just fills the
mold. However, more foamable reaction mixture may be
introduced into the mold than is necessary to fill the interior
of the mold with foam. This particular technique is known as
overcharging and is known, for example, from US-PSS 3,178,490
and 3,181,104.
The advantages of the mixtures according to the invention
lie in the improvement of the physical properties of the foams
produced with them, in the safety of processing which manifests
in metering accuracy, and in the improvement of foam quality.
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The use of the mixtures according to the invention enables
higher compression hardness to be obtained in the foams. This
means that the processor of the foams does not have to use
expensive filling ethers or additional crosslinking agents in
order to obtain an improved foam hardness. In accordance with
this invention, compression hardness can be improved (i.e.
page 9, table II ) .
The mixtures are distinguished by their high viscosity.
The high viscosity is advantageous in processing because
metering accuracy of pumps is better at high viscosities.
Correct metering of the components is essential for modern
high-quality foam production.
In addition, the high polarity of the polyester polyol
component has an advantageous effect on the foam-forming
reaction. An emulsifying effect on the likewise highly polar
water improves reactivity and leads to stable foams. In
addition, these foams are distinguished by a pleasant and
elastic surface.
The invention is further illustrated by the following
non-limiting examples.
EXAMPLES
Starting materials for foam production:
Prepolymer: 100 parts by weight(wt) of a polyester polyol
prepared by reaction of ethylene glycol and
adipic acid, OH value 55, were reacted while
stirring with pure 4,4'-diphenylmethane
diisocyanate to form a prepolymer having an NCO
content of 17X by weight.
Isocyanate: tolylene diisocyanate (80% by weight 2,4-isomer
and 20% by weight 2,6-isomer)
Polyether A: trifunctional ethylene oxide/propylene oxide
polyether (OH value 30, ethylene oxide content
14% by weight)
Polyether B: polyether A additionally modified with 20%
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by weight styrene/acrylonitrile polymer
Catalyst 1: triethylenediamine, 33% by weight in
d;propylene glycol
Catalyst 2: di-(2-dimethylaminoethyl)-methylam~ne
Catalyst 3: diethanolamine
Stabilizer: B 8629, polysiloxane, a product of Goldschmidt
AG
The foam was produced as stated in the specification. The
results are shown in Tables I and II:
Table I
Content Viscosity NC0 content
(% by wt.) (mPas) at 25CC (% by wt.)
Prepolymer - 3 48.3
Isocyanate 100
Prepolymer 15
13 43.6
Isocyanate 85
Prepolymer 20
22 42.0
Isocyanate 80
Prepolymer 45
Isocyanate 55
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Table II
Example 1 Example 2
Polyether A 80% by wt. 80% by wt.
Polyether B 20 " 20 "
Water 3.2 n 3.2 "
Catalyst 1 0.5 ~ 0-5 "
Catalyst 2 0.06 ~ 0.06 "
Catalyst 3 1.2 n 1.2 ~
Stabilizer 0.5 " 0.5 "
G =.~
prepolvLr~er - 2 n ~
Isocyanate 100 " 80 "
Index* 100 100
Density (kg/m3),
(as measured on the foam) 39 38
Compression hardness at 2.2 2.7
40% compression (kPa), as
measured on the foam
* The index is calculated in accordance with the following
equation: Index = quotient of the number of NC0 groups
divided by the number of NC0-reactive groups multiplied by
100.
The viscosities of the isocyanate and mixtures of the
prepolymer with tolylene diisocyanate and the NC0 contents are
shown in Table I.
The compression hardness of the foam produced using the
prepolymer mixture according to the invention is 22% higher
than that of a conventional foam (see Table II).
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Although the invention has been described in detail in the
foregoing for the purpose of illustration, it is to be
understood that such detail is solely for that purpose and that
variation can be made therein by those skilled in the art
without departing from the spirit and scope of the invention
except as it may be limited by the claims.
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