Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
Mo-3544
LeA 27,641
PROCESS FOR THE PRODUCTION OF MOLDED
POLYURETHANE FOAM ARTICLES AND THE
MOLDED ARTIC OBTAINED THEREBY
BACKGROUND_QF THE INVENTION
The present invention relates to a new process for
the production of molded ar-ticles consisting of polyurethane
foams with a non-cellular surface, in which salts con-taining
water of crystallization are used as blowing agents, and to the
molded articles thus obtained.
The produc-tion of molded articles of polyurethane
foams with a non-cellular surface (i.e., integral skin Foams)
by foaming inside molds is already known (e.g. German
Auslegeschrift 1~196,864). The process is carried out by
introducing a reactive and Foamable mix-ture of organic
polyisocyanates, compounds containing isocyanate reac-tive
groups and the usual auxiliary agents and additives into a mold
in a larger quantity than would be required for completely
filling the mold under conditions of unrestricted foaming and
then foaming up this mixture in the closed mold. It is
possible, by suitable choice of the starting components, in
particular by suitable choice of their molecular weight and
their functionality, to produce flexible, semi-rigid, or rigid
molded products. The dense outer skin is obtained by
introducing into the mold a larger quantity of foamable mixture
than ~ould be required for filling the volume of the mold under
conditions of free foaming and by using fluorochlorohydro-
carbons as blowing agents. These blowing agents condense on
the internal wall of the mold under the prevailing temperature
and pressure conditions so that the blowing reaction is brought
to a standstill at the internal wall of the mold and a solid
outer skin is formed.
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Industrial polyurethane chemistry uses not only the
physical blowing agents mentioned above but also water ~hich
acts as chemical blowing agent by virtue of the carbon dioxide
released by the reaction between water and isocyanates.
Although this chemical blowing agent can be used for producing
polyurethane foams of excellent quality under conditions of
unrestricted foaming, it is not capable of producing high
quality molded foams with a non-cellular surf,ace (i.e.,
integral skin foams). This is due to the fact that carbon
o dioxide does not condense on the internal wall of the mold
under the usual conditions so that the blowing action is not
arrested in the region of the surface skin.
Other chemical or physical blowing agents, for
example blowing agents which release nitrogen, such as
a~o-dicarbonamide or azo-bis-isobutyronitrile, or blowing
agents which release carbon dioxide, such as pyrocarbonic acid
esters and anhydrides (U.S. Patent 4,070,310), and blowing
agents such as air which are dissolved in the reactants, in
particular in the component carrying isocyanate reactive
groups, involve the same problem and are therefore also
unsuitable for the production of high qua`lity integral skin
foams.
The use of compounds containing water of
crystallization in polyurethane systems has already been
described but the teaching given in the relevant publications
does not suggest the use of compounds containing water of
crystallization as blowing agents for the production of molded
foam products with a non~cellular surface. Thus, for example,
salts containing water of crystallization are used according to
British Patent 1,147,695 for the production of polyurethane
pnlymers which are not fnamed. German Offenlegungschrift
1,806,404 discloses the use of salts containing water of
crystallization for the production of molded foam products with
exceptionally uniform properties, which is exactly the opposite
of the effect required according to the invention of obtaining
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a non-uniform structure consisting of a core of foam and a
non-cellular surface skin. Finally, German Offenlegungschrift
2,651,400 descrihes the use of compounds containing water of
crystallization in one-component systems without any reference
to the produotion of integral foams of the type constituting
the products of the process according ~o the present invention.
DESCRIPTTON OF THE INVENTION
It has now surpris;ngly been found that h;gh guality
molded products of polyurethane foams with a non-cellular
surface may be produced from conventional starting materials if
inorganic or organic salts containing water of crystallization
are used. The blow;ng action is produced by the thermally
controlled and delayed splitting off of water followed by the
reaction between isocyanate and water in which carbon dioxide
is released.
The invention is therefore directed to a process for
the production of molded polyurethane foam articles having a
gross density of at least 120 kg/m3 and having a non-cellular
surface by foaming a reaction mixture ~t an isocyanate index of
from 75 to 1500 inside a mold, wherein the reaction mixture
comprises:
a) a poly;socyanate component consisting of a~ least one
aromatic polyisocyanate,
b) a reactive component consisting of at least one
organic compound having at least two isocyanate
reactive groups,
c) blowing agent and optionally
d) other auxiliary agents and additives,
wherein the blowing agent c) comprises a salt containing water
of crystallization, optionally in addition to other chemical or
physical blowing agents. The present invention also relates to
the molded products obtained by this process.
In the context of the present lnvention, the term
"polyurethane foam" is used to denote not only the known foams
containing urethane groups obtained as reaction products of
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polyisocyanates ~nd polyhydroxyl compounds but also other foams
based on polyisocyanates, such as isocyanurate-modified
polyurethane foams as well as polyurea foams which are free
from urethane groups, as obtainable from organ;c poly-
isocyanates and organic polyamines. However, the invention
relates most preferably to products which are urethane group
containing, polyurethanes, optionally ~odified with
isocyanurate.
The polyisocyanate component a) may be any aromatic
polyisocyanates having an isocyante content of at least 20% by
weight. Examples include 2,4-diisocyanato-toluene and
commercial mixtures thereof with 2,6-diisocyanato-toluene or,
preferably, the known polyisocyanates or polyisocyanate
mixtures of the diphenylmethane series such as those obtained~
for example, by the phosgenation of aniline/formaldehyde
condensates optionally followed by distillative working up of
the products of phosgenation. These polyisocyanates or
polyisocyanate mixtures which are particularly suitable for the
process according to the inven~ion generally contain from 50 to
100% by weight of d;isocyanatodiphenylmethane ;somers, the
remainder consisting substantially o~ higher functional
homologues of these diisocyanates. The diisocyanates present
in these mixtures consist substantially of 4,4'-diisocyanato-
diphenylmethane mixed with up to 60% by weight, based on the
total quantity of diisocyanates, of 2,4'-diisocyanato-diphenyl-
methane and opti~a~ly s~a~ ~ua~tities o~ ~,2'-diisocya~ato-
diphenylmethane~ Deri~ati~es o~ these poly~socyanates ~odified
with urethane, carbodiimide or a11Ophanate groups may also be
used as po1yisocydnate component a).
~he reactive component bJ comprises dt 1east one
organic compound containing at least two isocyanate reactive
groups. The component b) is ~enerally a mixtures of several
such compounds. The individual compoun~s of component b) are
preferably organic polyhydroxyl compoun~s known per se from
polyurethane chemistry.
Mo~3544
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Particularly suitable are the known polyhydroxy-
polyethers having molecular weights of from 400 to 10,000,
preferably from 1500 to 6000, containing a~ least 2, preferably
2 to 6 hydroxyl groups per molecule. Polyhydroxypolyethers of
this type are obtained in known manner by ~he alkoxylation of
suitable starter molecules such as, for example, water,
propylene glycol, glycerol, trimethylolpropane, sorbitol, cane
sugar, aminoalcohols such as ethanolamine or diethanolamine or
aliphatic amines such as n hexylamine or 1,6-diaminohexane or
mixtures of such starter molecules. Propylene oxide is a
particularly suitable alkoxylating agent and ethylene oxide may
also be used, optionally introduced together with propylene
oxide or separately in separate reaction steps during the
alkoxylation reaction.
The known modification products of such polyether
polyols, i.e. the known graft polyethers based on the simple
polyether polyols exempl;fied above, and the known polyaddition
products in the form of polyether polyols containing Fillers
are also suitable. The so-called filled polyols include, e.g.,
polyhydrazocarbonamide polyols and polymer polyo1s.
Conventional polyester po1yols in the molecular
weight range of from 400 to 109000, preferably from 1500 to
4000, containing at least 2, preferably 2 to 6 hydroxyl groups
per molecule are also suitable as part or all of component b).
The reaction products known per se of excess quantities of
polyhydric alcohols of the type exemplified above as starter
molecules with polybasic acids such as succinic acid, adipic
acid, phthalic acid, tetrahydrophthalic acid or any mixtures of
such acids are also suitable polyester polyols.
Low molecular weight polyhydroxyl compoundst i.e.
those with molecular weights From ~2 to 399, are also suitable
for use as all or part of component b). These include the low
molecular weight, hydroxyl-containing chain lengthening agents
and cross-linking agents known from polyurethane chemistry,
such as alkane polyols of the type already exemplified above as
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starter molecules, and low molecular weight polyether polyols
obtainable by the alkoxylation of these starter molecules.
Component b~ preferably consists, as already
mentioned above, of organic polyhydroxyl compounds or mixtures
5 of organic polyhydroxyl compounds of the type exemplified
above~ Component b) may consist either of mixtures of the
relatively high molecular we;yht polyhydroxyl compounds
exemplified above and the low molecular weight polyhydroxyl
compounds exemplified above or of low molecular we;ght
o polyhydroxyl compounds on their own.
The reactive component b) may consist, at least in
part, of compounds containing amino groups. These include both
aminopolyethers in the mo1ecular weight range of from 400 to
12,000, preferably from ~OOG to 8000, having at least two
aliphatically and/or aromat;cally bound primary and/or
secondary amino groups, preferably primary amino groups, and
low molecular weight polyamines in the molecular weight range
of from 60 to 399.
Suitable aminopolyethers include those mentioned in
European Patent 0,081,701, U.S. Patents 3,654,370, 3,155,728,
3,236,895, 3,808,250, 3,975,428, 4,016,143, and 3,865,791 and
German Offenlegungschrift 2,948,491. Low molecular weight
polyam;nes include, for example, aliphatic polyamines such as
ethylene diamine or 1,6-diaminohexane and, preferably, aromatic
polyamines, and in particular alkyl substituted phenylene
diamines such as l-methyl-3,5-diethyl-2,4-diaminobenzene,
l-methyl-3,5-diethyl-2,6-diaminobenzene, 4,6-dimethyl-2-ethyl-
1,3-diaminobenzene, 3,5,3'5'-tetraethyl-4,4'-diaminodiphenyl-
methane, 3,5,3',5'-tetraisopropyl-4,4'-diaminodiphenyl-methane,
3,5-diethyl-3',5'-d;isopropyl-4,4'-diamino-diphenylmethane and
mixtures of such compounds.
The blowing agents c) used according to the invention
are salts containing water of crystallization, optionally
together with other known chemical or physical blowing agents.
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The term "salts containing water of crystallization"
is also meant to include hydra~ed oxides or hydroxides of heavy
metals. Salts suitable as blowing agPnts c~ are in particular
salts containing water of crystallization having a solubility
in water of less than 5 g/l at 20G~ Such salts generally also
have the required low solubility in the polyol mixtures used.
It is preferred to use salts which are only slightly
hygroscopic and can easily be ground up into a fine powder,
which is the most suitable form for working up. The salts are
preferably used in the form of powders of which at least 70%
pass through a sieve with a mesh of 100 ~m.
The salts used may be hydrated oxides or hydroxides
of aluminium, barium, calcium, iron, copper or magnesium; or
salts containing water of crystallization of inorganic or
organic acids such as carbonic ac;d, hydrochlor;c acid,
sulphuric acid, hydroFluoric acid, boric acid, oxalic acid,
formic acid, acetic acid, lactic acid or benzoic acid with
metals such as aluminium, barium, calcium, chromium, iron,
potassium, copper, magnesium, manganese, sodium, zinc, tin or
zirconium, e.g. AlKSO4.12H20~ Ba(OH32.8H~0, 2aC24 2H2'
aC4H406.4H20, CaC204.H20, CaS04.2H20, CeS04.4H20,
Ce(C204)3.10H20, CUSO4.5II2O~ Na2B407.10H20, NH4MgAsO4-6H20,
MgC03.3H20, KHC03.MgC03.4H20, A1203.2SiO2.2H20 and
4MgC04.Mg(OH)2.4H20.
It is particularly preferred, however, to use salts
containing water of crystallization of phosphoric acid,
diphosphoric acid and polymeric phosphoric acids such as
M93(P04)2.8H20, AlP04.3H20, CaHP04.~H20, Ca(H2P04)2.H20,
M93(P4)2 8~120~ ~U2P2o7-3H2o~ FeP04-2H20~ Na2HP04-1 2 '
2 P04.2H20, Na2H2P206-6~120~ Na~P04 12~120' M9(t~2PO4)2 4H 0
MgHPO4.2H20 and especially MgNH4P04.6H20. The last mentioned
magnesium ammonium phosphate containing 6 mol oF water of
crystallization is particularly preferred.
In the process according to the invention, the
above mentioned salts containing water of crystallization,
Mo^3544
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which are necessary for the invent;on, may be used in
combinat;on with minor quantities of other, known chemical or
physical blowing agents. These include water, gases such as
air, carbon dioxide or nitrogen physically dissolved in the
starting components, pyrocarbonic acid esters, compounds which
split off nitrogen, and volatile hydrocarbons and halogenated
hydrocarbons. The inclusion of such other blowing agents is,
however, not particularly advantageous, quite apart from the
often unavoidable introduction of water or air by stirring.
o These other blow;ng agents, if used at all, should generally
amount to not more than 50% by we;ght, and preferably not more
than 25% by weight, of 211 the blowing agents present in the
reaction mixture.
The addition of water not bound to salts is
frequently found to be advanta~eous as the flowability and
formation of outer skin can be continuously adjusted by a
careful balance of bound and free water. The quantity of free
water, however, generally does not exceed one third of the
quantity o~ water bound as water of crystallization.
The total quantity of blowing agents used depends, of
course, on the desired density of the molded products. The
weight of component c) generally amounts to 0.1 to 15% by
weight, preferably 1 to 10% by weight, of the total quantity of
reaction mixture composed of components a), b), c) and d).
The other auxiliary agents and additives optionally
used may be, for example, the known catalysts for accelerating
the isocyanate polyaddition r~action, e.g. tertiary amines such
as triethylene dia~ine, N,N-dimethylbenzylamine or N,N-di-
methylcyclohexylamine or organometallic compounds, in
particular tin compounds such as tin(lI)-octoate or dibutyl tin
dilaurate. ~rimerization catalysts, for example, alkali metal
acetates such as sodium or potassium acetate, alkali metal
phenolates such as sodium phenolate or sodium trichloro
phenolate or 2,4,6-tris-(dimethylaminomethyl) phenol or lead
naphthenate, lead benzoate or lead octoate may also be used
Mo-3544
9 2~ 5
according to the invention if the polyurethane foams to be
produced are required to contain isocyanurate groups.
Other auxiliary agents and additives d) optionally
used include, for example, known foam stabilizers, such as
5 those based on polyether-modified polysiloxanes.
Other auxiliary agents and additives d) optionally
used include ;nternal mold release agents, for example those
described in European Patent 081,701, U.5. Patents 3,726,952,
4,098,731, 4,058,492, 4,033,912, 4,024,090, and 4,a98,731,
British Patent 1,365,215 and German Offenlegungschriften
2,319,648 and 2,427,273.
The process according to the invention is generally
carried out by first mixing the starting components b) to d)
and then combining the mixture w;th polyisocyanate component
15 a). The last mentioned mixing may be carried out, for example,
in stirrer mixtures or, preferably, in conYentional high
pressure mixing apparatus of the type conventionally used for
the preparation of polyurethane foams. Immediately aftQr
preparation of the reaction mixture, the latter is introduced
20 into the mold, normally a mold designed to be closed, ~he
quantity introduced into the mold being adjusted to the
required gross density of the molded product. In order to
ensure formation of the required non-cellular outer skin, the
quant;ty of reaction mixture is so chosen that it would fill at
~5 least 1.5 times the volume of the mold if left to foam up
without restriction. The process according to the invention
may be carried out not only by this one-step process but also
by the semi-prepolymer process, in which the total quantity of
polyisocyanate components a) is reacted with part of oomponent
30 b) for example in proportions maintaining an NCO/OH equivalent
ratio of at least 3:1, preferably at least ~:1, to form an
isocyanate semi-prepolymer which is then reacted with a mixture
of the remaining components b) to d). The polyhydroxyl
compounds b) used for the preparation of the isocyanate
semi-proplymers may, of course, be difFerent from the
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polyhydroxyl compounds b) which are subsequently mixed with the
isocyanate semi-prepolymers.
In all the variations of ~he process according to the
invention, the quantitative proportions of the individual
components are so chosen that an isocyanate index from 75 to
1500, preferably from 100 to 150, is obtained. By "isocyanate
index" is meant the quotient of the number of isocyanate groups
d;vided by the number of isocyanate reactive groups, multiplied
by 100. Isocyanate indices substantially above 100 would be
suitable if trimerisation catalysts are used at the same time
for the preparation of ;socyanurate modif;ed polyurethane
foams. The water present in the salts containing water of
crystallization, which are required for this invention, is not
included in the calculation of the isocyanate index.
The gross density of the molded products is at least
120 kg/m3, and is preferably from 180 to 800 kg/m3.
The temperature of the molds used is generally at
least 30~C, preferably at least 50C. The internal walls of
the molds may, if necessary, be coated with known external mold
release agents before the molds are filled.
The process according to the invention enables high
quality molded polyurethane foam products with a solid surFace
free from blisters to be produced even without the aid of the
fluorochlorohydrocarbons which were hitherto always used. The
process accsrding to the invention is suitable in particular
for the production of semi-rigid to rigid integral foams with a
non-cellular surface of the kind widely used in the motor
vehicle and furniture construction industry.
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EXAMPLES
Starting materials:
Component a): Polyisocyanate mixture of the
diphenylmethane series having an isocyanate
content of 31% by weight and containing 55%
by weight Q~ 4,4'-diisocyanatodiphenyl-
methane and abou~ 5% by weight of
2,4'-diisocyanatodiphenylmethane, and 45%
of higher homologues of diisocyanato-
diphenylmethane.
Polyol component bl~: Propoxylation product o~
trimethylolpropane with OH number 860.
Polyol component b2): Propoxylation product of
trimethylolpropane with OH number 42.
Additive dl (stabilizer): Commercially available polyether
siloxane (Tegostab~ OS 5O, manufactured by
Goldschmidt AG, 4300 Essen l).
Additive d2 (catalyst~: N,N-Dimethylcyclohexylamine
The polyol mixtures shown in Table l are worked up
with the quantity of polyisocyanate component a) also shown in
Table l.
Mo-3544
--12--
o o I I o ~t
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_ D ~~ ~ 3 ~ ~ o
3544
-13-
Molded foam products in the form of plates having a
gross density of from 200 to 600 kg/m3 were produced from the
formulations shown in Table 1 (see Table 2). The mold used was
a plate mold measuring 10 x 200 x 200 mm the internal walls of
which were coated with a commercial wax based external mold
release agent (Acmosil ~ 180, manufactured by Acmos, D-2800
Bremen I). Before the polyol mixtures were worked up, they
were briefly loaded with 10 vol-%, based on the atmospheric
pressure, of finely dispersed air by briefly stirring the
mixtures in a high speed stirrer (5 minutes, 1000 revs/mins,
propeller stirrer~.
The reaction mixtures composed of the polyol mixtures
and polyisocyanate component a) were prepared in a conventional
stirrer mixer. The density of the molded produc~s was
determined in each case by the quantity of reaction mixture
introduced into the mold.
Examples:
1, 2 and 3 Examples according to the invention using salt
releasing water of crystallization as a blowing
agent with delayed formation of C02.
4 and 5 Comparison Example using water as C02 releasing
blowing agent.
5 and 7 Comparison Example using monofluorotrichloro
methane (Frigen R11) as blowing agent
(classical integral Foam of great rigidity).
The surface hardness Shore D of the individual molded
Foam products is shown in Table 2 below:
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Table_2
Gross density E x a m p 1 e s
~ m3) 1 2 3 4 __5 6 7
200 - - 44 - 23 - 45
300 54 55 - 42 - ~5
~00 65 65 - 50 - ~6
500 73 74 - 60 - 74
600 76 77 - 66 - 79
The values for sur-face hardness of Examples 1 7 2 and
3 according to the invention are distinctly above those of
comparison Examples 4 and 5 at all gross densities. They are
similar to the surface hardnesses of integral foams 6 and 7
produced anhydrously with Frigen9 Rl1 as blowing agent.
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