Composite articles

A composite article comprising a body of semi-rigid polyurethane foam in contact with a layer of sheet of polymeric material, the foam having been prepared by reacting an organic polyisocyanate with a polymeric polyol having a hydroxyl number in the range from 20 to 80 and a crosslinking agent or chain extender having a hydroxyl number of at least 250 in the presence of water and a catalytically effective amount of an alkali metal or alkaline earth metal salt of an acid of the formula: EQU R--A--COOH wherein R represents R'OCO--, R'COO-- or R'O--, R' represents an optionally substituted hydrocarbon or heterocyclic radical and A represents an optionally substituted C.sub.1 -C.sub.3 chain.

This invention relates to composite articles containing semi-rigid 
polyurethane foams and to methods for their production. 
The manufacture of polyurethane foams has been well established for over 
thirty years, the general method being to react an organic polyisocyanate 
with an organic polyol in the presence of a foaming agent and, usually, 
other beneficial additives such as catalysts and surface active agents. 
By suitable choice of components and conditions, foams are made which vary 
in properties from the soft flexible type used in upholstery applications 
to the hard rigid type used as structural members. Thus, flexible foams 
are generally made from polymeric diols or triols having hydroxyl numbers 
of from 20 to 80 using water as the principal foaming agent. The much 
higher crosslink density required in rigid foams is provided by the use of 
higher functionality polyols and/or polyisocyanates and here the principal 
foaming agent is usually a halogenated hydrocarbon such as 
trichlorofluoromethane. 
Between the extremes of flexibility on the one hand and rigidity on the 
other, there exists another useful type of foam generally classified as 
semi-rigid. These foams, which are used as shock-absorbing materials in 
the passenger compartments of automobiles and elsewhere, are usually made 
by reacting a polyisocyanate with a mixture of a flexible foam polyol and 
a crosslinking agent such as trimethylolpropane. 
Whilst the production of all polyurethane foams, flexible, rigid or 
semi-rigid, involves the same basic chemical reaction, that between 
isocyanate groups and hydroxyl groups, each type of foam presents 
different problems to the manufacturer. The differences are often 
associated with the balance which must always be achieved between gas 
generation and polymer gelation. Clearly, for example, the balance in a 
water-blown flexible foam system is different from that in a solvent-blown 
highly crosslinked rigid foam system. Many of these problems can be 
solved, at least partially, by appropriate choice of auxiliary agents, for 
example catalysts, surfactants, foam stabilisers and the like. 
The catalysts conventionally used in the production of polyurethane foams 
are tertiary amines. From among the very large number that have been 
proposed there may be mentioned low molecular weight aliphatic amines such 
as triethylamine, long chain aliphatic amines such as 
N,N-dimethylcetylamine, cycloaliphatic amines such as 
N,N-dimethylcyclohexylamine, arylaliphatic amines such as 
N,N-dimethylbenzylamine, isocyanate-reactive amines such as 
N,N-dimethylaminoethanol, polyamines such as bis-(2-dimethylaminoethyl) 
ether and more complex heterocyclic compounds such as N-ethylmorpholine, 
N,N'-diethylpiperazine and 1,4- diazabicyclo[2.2.2]octane. Tin compounds 
such as stannous octoate and dibutyltin dilaurate are also widely used as 
catalysts, often in conjunction with tertiary amines. 
In addition to tertiary amines, other basic materials are known to catalyse 
urethane formation and many such materials have been proposed as 
alternatives to the amines, which often have disagreeable odours. Examples 
of such materials include alkali metal salts of carboxylic acids but 
whilst certain salts, for example potassium acetate, have been used as 
trimerisation catalysts in polyisocyanurate foam formulations, they have 
not been used to any appreciable extent in conventional urethane systems. 
Other salts have been proposed as catalysts for foam production. Thus, 
GB-A-2 064 567 describes a process for the production of rigid 
polyisocyanurate foam by reacting a polyisocyanate with a reaction product 
of a dibasic carboxylic acid anhydride and a polyether polyol, the latter 
being partially in the form of an alkali metal or alkaline earth metal 
alcoholate. Since the reaction product can function as polyol component 
and trimerisation catalyst simultaneously, it overcomes the problem of 
using a carboxylate having only limited solubility in the polyols normally 
used in polyisocyanurate formulations. 
EP-A-0 220 697 is concerned with a quite different problem, namely the 
production of flexible polyurethane foams having improved foam stability 
from formulations having water contents. This publication describes 
formulations containing as "foam modifier" an alkali metal or alkaline 
earth metal salt of a Bronsted acid having a pKa greater than 1. As 
examples of suitable foam modifiers, there are mentioned alkali and 
alkaline earth metal hydroxides and alkoxides, alkali and alkaline earth 
metal salts of certain inorganic acids and alkali and alkaline earth metal 
carboxylates which may be simple acetates, for example, or the salts of 
more complex carboxylic acids such as may be obtained by reacting a cyclic 
anhydride of a dicarboxylic acid with one of the hydroxyl groups of a base 
polyol. 
Another disadvantage which can arise with tertiary amines in addition to 
the odour problem is migration to adjacent materials. Thus, semi-rigid 
foams enclosed in a layer of a plastics material such as plasticised 
polyvinyl chloride are now widely used as automobile crashpads, that is 
the large moulded panel surrounding the instruments situated in front of 
the driver and front seat passenger. In these crashpads, it is often found 
that the PVC layer in contact with the foam becomes discoloured and it is 
believed that one of the causes of this discolorisation is the migration 
of tertiary amine from the foam into the PVC followed by reaction of the 
amine with the PVC and/or the plasticiser. This problem has been discussed 
by Wilson et al (Rubber and Plastics International, Vol. 13, No. 1, page 
23, February 1988) who concluded that close co-operation between the PVC 
and polyurethane industries is required to solve the problem. The 
complexity of the problem is illustrated by Wilson et al's finding that, 
under certain conditions, deterioration of the PVC occurred even when the 
foam contained non-migratory (isocyanate-reactive) tertiary amines.

When tertiary amine catalysts in semi-rigid foam formulations are replaced 
by simple alkali metal carboxylates such as potassium acetate the staining 
of adjacent plastics materials is substantially reduced but, in general, 
the catalytic balance is adversely affected. In particular, when potassium 
acetate is used in an amount to give an acceptable cream time, the foam 
cures at an unacceptably slow rate resulting in long demould or jig dwell 
times. 
It has now been found that satisfactory catalysis in the production of 
these composite articles can be achieved by the use of the salts 
hereinafter defined. 
Accordingly, the invention provides a composite article comprising a body 
of semi-rigid polyurethane foam in contact with a layer or sheet of 
polymeric material, the foam having been prepared by reacting an organic 
polyisocyanate with a polymeric polyol having a hydroxyl number in the 
range from 20 to 80 and a crosslinking agent or chain extender having a 
hydroxyl number of at least 250 in the presence of water and a 
catalytically effective amount of an alkali metal or alkaline earth metal 
salt of an acid of the formula: 
EQU R--A--COOH (1) 
wherein R represents R'OCO--, R'COO-- or R'O--, R' represents an optionally 
substituted hydrocarbon or heterocyclic radical and A represents an 
optionally substituted C.sub.1 -C.sub.3 chain. 
The salt of the acid of formula 1 may be a salt of any metal of Groups IA 
and IIA of the Periodic Table but, in general, the alkali metal salts, 
that is to say the Groups IA metal salts, are preferred, especially the 
potassium salts. If desired, mixtures of such salts may be used, for 
example a mixture of potassium and sodium salts, or mixtures of one or 
more of the salts with a free acid of formula 1. 
Optionally substituted hydrocarbon radicals which may be represented by R' 
include optionally substituted alkyl, cycloalkyl, aralkyl and aryl 
radicals. Examples of suitable substituents include hydroxy groups. 
Particularly suitable radicals include hydroxy terminated polyoxyalkylene 
radicals, for example hydroxy terminated polyoxyethylene radicals. 
Divalent radicals which may be represented by A include 
##STR1## 
radicals, wherein R.sup.2 is hydrogen or lower alkyl as well as radicals of 
the formula: 
##STR2## 
In general, salts of acids of formula 1 wherein A is an optionally 
substituted C.sub.1 -C.sub.2 radical are preferred on account of their 
superior catalytic activity, especially salts of maleic acid, A then being 
a radical of the formula --CH.dbd.CH--. Also on the ground of superior 
activity, it is preferred that R is a radical of the formula R'OCO--. The 
acids of formula 1 wherein R is R'OCO-- may be prepared by reacting an 
alcohol of the formula: 
EQU R'--OH (2) 
with an acid anhydride of the formula: 
##STR3## 
wherein R' and A have the meanings given above. 
Examples of compounds of formula 2 which may be used include alcohols, for 
example 2-octanol, cyclohexanol or benzyl alcohol, phenols, polylactic 
acid and polyoxyalkylene polyols such as polyethylene glycols, especially 
polyethylene glycols having molecular weights below 500, for example 200. 
Examples of suitable acid anhydrides include succinic, glutaric, maleic, 
phthalic and itaconic anhydrides and the anhydrides of 1,2-cyclohexane and 
1,2-cyclohexene dicarboxylic acids. 
Acids of formula 1 wherein R is R'COO-- may be prepared by reacting an acid 
of the formula R'COOH with a hydroxy acid of the formula HOACOOH. Acids of 
formula 1 wherein R is R'O-- may be prepared as for instance described in 
Beilstein Handbuch der Organischen Chemie, 3, 232 and 3, 233. The salts 
may be formed from the free acids in conventional manner, for example by 
reacting an acid of formula 1 with the appropriate metal carbonate. If 
desired, a deficiency of metal carbonate may be used so that the product 
is a mixture of salt and free acid. 
A catalytically effective amount of the salt will usually be in the range 
from 2 to 30 milliequivalents, preferably from 5 to 12 milliequivalents 
based on 100 grams of polymeric polyol. 
Organic polyisocyanates which may be employed in preparing the semi-rigid 
polyurethane foam include aromatic diisocyanates, especially those which 
are commercially available such as tolylene and diphenylmethane 
diisocyanates. Since liquid polyisocyanates are preferred, it is 
convenient to use MDI isomer mixtures or MDI variants containing urethane, 
allophanate, urea, biuret, carbodiimide or uretonimine residues. Also 
useful are polymethylene polyphenylene polyisocyanates commonly known as 
"crude" or "polymeric" MDI. Suitable forms of urethane modified MDI 
include polyester or polyether based prepolymers. 
Polymeric polyols which may be used in preparing the foam include the 
polyether and polyester polyols conventionally employed in the manufacture 
of flexible foams. Particular mention may be made of polyoxypropylene and 
poly(oxypropylene-oxyethylene) diols and triols having molecular weight of 
from 1500 to 8000, especially ethylene oxide capped polyoxypropylene diols 
and triols. If desired, polymer polyols formed by the polymerisation of 
one or more olefinic monomers in a polyether or polyester polyol may be 
used. 
Crosslinking agents which may be used include non-polymeric polyols having 
three or more hydroxyl groups and their lower molecular weight 
oxyalkylation products. A preferred crosslinking agent is 
trimethylolpropane. Chain extenders include diols such as ethylene glycol 
in 1,4-butanediol. The degree of flexibility/rigidity in the foamed 
product can be varied on known manner by varying the proportion of 
crosslinking agent or chain extender to polymeric polyol. In general, the 
crosslinking agent or chain extender should provide from about 10 to 75%, 
especially from about 25 to 75% of the hydroxyl groups in the foam forming 
reaction mixtures. Preferred crosslinking agents and chain extenders have 
hydroxyl numbers of at least 300. 
The water used as blowing agent is suitably present in the foam forming 
reaction mixture in amounts of from 0.1 to 4.5% by weight, especially from 
1.5 to 3.5% by weight, based on the weight of polymeric polyol. Other 
blowing agents such as trichlorofluoromethane may be included, if desired, 
to provide additional foaming. 
The amount of polyisocyanate used relative to the polyols and water is 
usually such as to provide an isocyanate index in the range 80 to 130, 
especially 90 to 130, an index of about 100 being preferred. 
The foam-forming reaction mixture may also contain other conventional 
ingredients of polyurethane foam formulations, for example surface active 
agents which may be of either the silicone or the non-silicone type. 
Tertiary amine catalysts may also be included but are preferably excluded 
if staining of adjacent polymeric materials is to be avoided. Other useful 
additives cell openers. 
In practising the invention, it is usually convenient to incorporate the 
catalytic salt in the polyol component prior to reaction with the 
polyisocyanate. 
Accordingly, the invention also provides a reaction system for use in the 
preparation of the polyurethane semi-rigid foam component of the composite 
articles comprising: 
(A) an organic polyisocyanate, and 
(B) a polyol component comprising: 
(i) a polymeric polyol having a hydroxyl number in the range from 20 to 80; 
(ii) a crosslinking agent or chain extender having a hydroxyl number of at 
least 250; 
(iii) water, and 
(iv) a catalytically effective amount of an alkali metal or alkaline earth 
metal salt of an acid of formula 1. 
The polymeric material which is in contact with the foam in the composite 
articles of the invention may be, for example, a decorative and/or 
protective facing material. As examples of such materials, there may be 
mentioned textile materials, paper and plastics materials, for example 
polyvinyl chloride which may contain plasticisers. 
The composite articles of the invention may be prepared by bonding a 
pre-formed semi-rigid polurethane foam to the polymeric material but, in 
general, it is preferred to form the foam in contact with the polymeric 
material. 
Thus, in a further aspect of the invention, there is provided a method for 
the preparation of a composite article which comprises contacting a layer 
or sheet of polymeric material with a reaction system as hereinbefore 
described whereby to form a body of semi-rigid polyurethane foam in 
contact with the polymeric material. 
The invention is illustrated but not limited by the following Examples: 
EXAMPLE 1 
A 3-neck round-bottomed flask fitted with stirrer, thermometer and 
condenser was charged with two moles of polyethylene glycol (mol. weight 
200) and the temperature was raised to 50 Deg. C. One mole of acid 
anhydride was added portionwise at such rate that each portion had reacted 
before the addition of a further amount. When the reaction was completed, 
as indicated by acid titration, half a mole of potassium carbonate was 
added as a 50% aqueous solution. After completion of this reaction, water 
was removed at 100 Deg. C under vacuum. A typical analysis of the product 
is a water content of approximately 1-2% and an acid value of 4-10 mg 
KOH/g. In this way, catalysts A and B were prepared using maleic anhydride 
and itaconic anhydride respectively. 
Free acid B was then prepared by reacting one mole of the polyethylene 
glycol with one mole of itaconic anhydride at 50 Deg. C. 
EXAMPLE 2 
A 3-neck round-bottomed flask fitted with stirrer, thermometer and 
condenser was charged with one mole of ethoxyethoxyethane and the 
temperature was raised to 50 Deg. C. One mole of maleic anhydride was 
added portionwise at such a rate that each portion had reacted before the 
addition of a further amount. When the reaction was completed, as 
indicated by acid titration, the reaction temperature was decreased to 
30.degree. C. Subsequently 50% by weight of the content of the flask of 
methanol was added. Then, half a mole of an alkali metal carbonate was 
added portionwise at such a rate that the frothing due to carbondioxide 
liberation was controllable. After the completion of this saponification 
reaction, a 50/50 by weight mixture of dipropylene glycol and ethylene 
glycol was added. The amount of glycol mixture added was equal to the 
weight of the synthesized salt, i.e. the weight of the diol mixture was 
equal to the (total) weight of one mole of ethoxyethoxyethanol, maleic 
anhydride and one mole of alkali metal. The methanol and water were 
removed under vacuum in a rotary evaporator at a water bath temperature of 
approximately 80.degree. C. A typical analysis of the alkali carboxylates 
produced by this method is a water content of approximately 0.2-0.4% and 
an acid value of 1-3 mg KOH/g. In this way, catalysts C, D and E were 
prepared using sodium carbonate, potassium carbonate and rubidium 
carbonate, respectively. 
EXAMPLE 3 
700 gram of 2-lactic acid (lactic acid containing approximately 10% of 
water, obtained from CCA biochem bv, Gorinchem. Holland) was charged to a 
three neck-flask equipped with a stirrer, a N.sub.2 purge and a take-off 
condenser and heated up to 140.degree.-150.degree.. After six hours of 
polymerization, the thus formed poly(lactic acid) had an acid value of 150 
mg KOH/g. 420 l gram of the viscous poly(lactic acid) was charged into a 
3-necked flask, equipped with a stirrer and a condenser and the 
temperature was raised to 60.degree. C. Subsequently, 83 gram of maleic 
anhydride was added portionwise and reacted for 3 hours. Then 300 ml of 
methanol was added and the mixture was cooled to 30.degree. C. To this 
mixture 183 gram of potassium carbonate had to be added in order to obtain 
an acid value of 1 mg KOH/g. Prior to evaporation (rotary evaporator, water 
bath temperature 80.degree. C.) of the methanol and water, 450 gram of a 
mixture of dipropylene glycol and Renex 688 (ethoxylated nonylphenol, 
Atlas) in a ratio of 65/35 by weight was added in order to obtain a free 
flowing catalyst. This catalyst is referred to in the following Tables as 
catalyst F. 
EXAMPLE 4 
The potassium salt of ethoxyacetic acid (Aldrich) was obtained from 
straightforward neutralization of ethoxyacetic acid with aqueous potassium 
hydroxide. The catalyst was used as a 60% solution in water and called 
catalyst G in the following. 
EXAMPLE 5 
A non-pigmented lead-stabilised PVC foil (1 mm thickness) was placed in an 
aluminum mould (15.times.30.times.1 cm) at 40 Deg. C and a 70 g reaction 
mixture was foamed thereon. Twelve foam/PVC composites were made in this 
way, the formulations and foaming characteristics being given in Table 1. 
Formulations 9 and 10 using conventional tertiary amine catalysts (Dabco 
33LV and Niax A-1) and Formulations 11 and 12 using potassium acetate and 
potassium formate have been included for comparative purposes. The 
potassium acetate was used as a 50% solution in ethylene glycol and the 
potassium formated as a 44% solution in a 13:1 mixture of ethylene glycol 
and water. 
Of each of the foam/PVC composites so made, three dogbone shaped specimen 
with dimensions according to DIN 530504 S2 were cut. The three specimen 
thus prepared were ptu into a Petri dish with a diameter of approximately 
10 cm and held at 120.degree. C. in an air circulation oven. After 100, 
250 and 500 hours of ageing each time one of the samples was taken of the 
Petri dish. The staining results given in Table 2 show that the tertiary 
amine catalysts caused much more discoloration than the salts. Potassium 
acetate exhibits good staining characteristics but the cure is 
unacceptably slow whilst potassium formate is a good cure catalyst but 
provides unacceptable staining. 
TABLE 1 
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Formulation 
1 2 3 4 5 6 
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Polyol 100.00 100.0 100.00 
100.0 100.00 
100.0 
Trimethylol- 
2.8 2.8 2.8 2.8 2.8 2.8 
propane 
Water 2.5 2.5 2.5 2.5 2.5 2.5 
Surfactant 
1.0 1.0 1.0 1.0 1.0 1.0 
Catalyst A 
5.0 -- -- -- -- -- 
Catalyst B 
-- 2.0 5.3 -- -- -- 
Acid B -- -- 1.9 -- -- -- 
Catalyst C 
-- -- -- 4.0 -- -- 
Catalyst D 
-- -- -- -- 2.5 -- 
Catalyst E 
-- -- -- -- -- 2.9 
Polyiso- 58.0 55.3 58.9 59.5 57.6 58.2 
cyanate 
Cream time 
19 17 17 30 18 18 
(s) 
Gel time (s) 
44 72 57 65 57 53 
Rise time (s) 
62 150 95 115 120 120 
Demold time 
4 8 5 5 6 5 
(min) 
______________________________________ 
Formulation 
7 8 9 10 11 12 
______________________________________ 
Polyol 100.00 100.0 100.00 
100.0 100.00 
100.0 
Trimethylol- 
2.8 2.8 2.8 2.8 2.8 2.8 
propane 
Water 2.5 2.1 2.5 2.5 2.5 2.5 
Surfactant 
1.0 1.0 1.0 1.0 1.0 1.0 
Catalyst F 
1.8 -- -- -- -- -- 
Catalyst G 
-- 0.9 -- -- -- -- 
Dabco 33LV 
-- -- 0.45 -- -- -- 
Niax A-1 -- -- -- 0.15 -- -- 
Potassium 
-- -- -- -- 0.45 -- 
acetate 
Potassium 
-- -- -- -- -- 0.80 
formate 
Polyiso- 54.5 53.5 54.1 54.0 53.6 55.5 
cyanate 
Cream time 
18 18 17 19 17 17 
(s) 
Gel time (s) 
62 90 86 95 80 65 
Rise time (s) 
140 200 175 200 195 140 
Demold time 
7 9 10 9 13 7 
(min) 
______________________________________ 
The polyol used in these formulations was an ethylene oxide tipped 
oxypropylated glycerol having a hydroxyl number of 28. The surfactant was 
Silicone B 4113 (Goldschmidt). The polyisocyanate was a liquid MDI. 
TABLE 2 
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Discoloration of PVC skin as a function of time at 
120.degree. C. 
Time 100 h. 250 h. 500 h 
______________________________________ 
Composite 1 
slight slight/moderate 
moderate 
Composite 2 
very slight slight slight/moderate 
Composite 3 
very slight slight slight/moderate 
Composite 4 
slight slight/moderate 
moderate/strong 
Composite 5 
slight slight/moderate 
moderate 
Composite 6 
slight slight/moderate 
moderate 
Composite 7 
slight slight/moderate 
moderate/strong 
Composite 8 
slight slight/moderate 
moderate/strong 
Composite 9 
strong very strong total 
discoloration 
Composite 10 
moderate strong very strong 
Composite 11 
slight slight/moderate 
moderate 
Composite 12 
slight/moderate 
moderate strong 
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