Note: Descriptions are shown in the official language in which they were submitted.
1~5135
o.Z. 0050/033801
Preparation of resilient foams
based on a melamine/formaldehyde condensate
The present invention relates to a process for
the preparation of a resilient foam based on a melamine/
formaldehyde condensate, wherein a very concentrated
aqueous solution or dispersion, which contains a melamine/
formaldehyde precondensate, an emulsifier, a volatile
blowing agent and a curing agent, with or without conven-
tional additives, is foamed and the foam is then cured.
The preparation of foams based on melamine resins
by foaming an aqueous solution of a precondensate is known.
lo According to German Patent 870,027, air is stirred into an
aqueous melamine resin solution which contains an emulsi-
fier and a curing agent. However, the resulting foams
are hard and brittle, and easily break during use.
British Patent 1,161,338 discloses a process for the pre-
paration of foams based on phenolic, urea or melamine
resins, wherein an aqueous resin solution which contains
a blowing agent and a curing catalyst is foamed. On
repeating the E~amples, it is found that the foams
obtained - if any - are brittle, even if the phenolic or
urea resins in the formulations are replaced by melamine
resins. U.S. Patent 3,093,600 describes melamine resin
foams which allegedly have improved resilience and resist-
ance to cracking as a result of the incorporation of
triols, eg. trimethylolpropane However, it is found
that the resilience, and especially the recovery after
compression, of such foams is inadequate for many applica-
tions. Furthermore, on incorporating substantial
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amounts of triols into the foams, the combustibility of
the latter is increased substantially. U.S. Patent
3,06~,953 discloses 2 process for improving the mechani-
cal strength, resilience and softness of aminoplast
resin foams, preferably foams based on urea resins.
Using this process, the above properties of melamine
resin foams produced by prior art methods can be improved
somewhat, but not substantially.
German Laid-Open Application DOS 2,402,441
lo (equivalent to South African Patent Application 403/74)
describes a process for the preparation of
aminoplast foams, wherein a strong acid
is added as a curing agent to an alk~line aminoplast pre-
condensate containing a blowing agent. The heat
liberated by the neutralization causes the blowing agent
to boil and hence to foam. Since, in this process,
curing and foaming take place simultaneously, relatively
- brittle foams result.
It is an object of the present invention to pro-
vide a process by means of which soft and resilient foamswhich are based on melamine/foamaldehyde condensates and
have very low flammability are obtained. We have found
that this object is achieved, according to the invention,
by a process wherein a relatively concentrated solution
or dispersion of a melamine/formaldehyde precondensate is
foamed under conditions such that first there is only a
slight increasein viscosity,and the curing process, accom-
panied by a 13rge increase in viscosity, only commences when
foaming has substantially ended.
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Accordingly, the present invention relates to a
process for the preparation of a resilient foam based on
a melamine/formaldehyde condensate by foaming an aqueous
solution or dispersion, which contains a melamine/form-
aldehyde precondensate, an emulsifier, a volatile blowing
agent and a curing agent, with or without conventional
additives, and then curing the foam, wherein
a) the concentration of the precondensate in the mix-
ture of precondensate and water (without additives) is
selected to be above the salient point of the 1st deriva-
tive of the curve which is obtained when, keeping all
other conditions constant, the amount of water in the
mixture of precondensate and water is varied and the vis-
cosity of the mixture (measured at the boiling point of
the blowing agent under the conditions prevailing at
the start of foaming) is plotted against the concentration
of the precondensate, which concentration must however not
be higher than the value which in the curve described
corresponds to a viscosity of 5,000 dPas, preferably
2,000 dPas and especially 1,000 dPas,
b) during the foaming process, up to the time at
which the foam has reached 80% ~ the maximum attainable rise
height,the viscosity of the aqueous solution or dispersion
must not fall below the value which, in the curve described
under a), corresponds to the minimum concentration defined
there, but must not exceed 6,ooo dPas, preferably 2,500
dPas and especi~lly 1,200 dPas, and
c) after reaching the time defined under b), the vis-
cosity exceeds a value of 10,000 dPas, due to curing of
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the precondensate, within 8 minutes, preferably within 6
minutes and especially within 4 minutes, the viscosities
referred to in b) and c) being measured, in each case, on a
parallel system which is free from blowing agent.
This process surprisingly gives resilient, soft
foams which when used as insulating materials meet the
standards placed by the building trade on such materials,
especially in respect of their heat-insulating and sound-
insulating properties, their mechanical properties and their
behavior on exposure to fire. The foaming of very concen-
trated solutions or dispersions must be regarded as a bold
step into technologically new territory, since the art has
always avoided using melamine resin concentrations which are
so high that, in particular, the dispersions are not stable
on storage.
On microscopic examination of the foams produced
according to the invention it is found that the foam structure t
comprises a plurality of mutually connected three-dimensionally
branched webs.
In order to better understand the invention without
limiting the same, reference is made to the accompanying
drawings wherein:
Figure 1 shows a graph in which the viscosity ~ of a
melamine resin dispersion and its first derivative ~n/~c are
plotted against the concentration c.
Figure 2 shows a graph in which the rise height h and
the viscosity ~ of a foaming m~lamine resin dispersion are
plotted against the time t, and
Figure 3 shows a schematic view of the three-dimensional
structure of the melamine resin foam.
Melamine resin foams are sufficiently resilient only if
~15~350
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the webs conform to the following conditions: L
1. The mean length : width ratio must be greater than
10 : 1, preferably greater than 12 : l and in particular
greater than 15 : 1.
2. The density of the webs must be greater than 1.10,
preferably greater than 1.20, and in particular greater than
1.30 g/cm3.
Webs which are too short (i.e. in which the 1 : d
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llS13S(l
5 - o. z~ 0050~03380
ratio is too low) are obtained if the curing process
commences too early, before foaming has substantially
ended Too low a web density indicates that there are
minor cavities, bubbles and the like in the interior of
the webs, resulting from secondary foaming. Such
secondary foaming occurs if the water content of the
melamine resin precondensate was too high. In both
cases, brittle foams are obtained.
The mean ~ : d ratio is determined microscopi-
cally, the length and width of the webs being determined
by a statistical counting method The web length is
defined as the distance between the centers of two nodes,
and the web width is defined as the narrowest part of a
web, in each case measured on a photomicrograph. To
determine the density of the foam webs, the foam is placed
in a suitable liquid, for example isopropanol, with which
it becomes fully impregnated by virtue of its open-cell
character, The density of the webs is then determined
by the principle of Archimedes
The starting material for the process according to
the invention is a melamine/formaldehyde precondensate.
The molar ratio of melamine to formaldehyde in the precon-
densate can vary within wide limits, namely from l : 1.5
to 1 : 4, but is preferably from l : 2.0 to l : 3.5.
The degree of condensation of the precondensate should be
sufficiently low to allow curing accompanied by further
condensation. The mean molecular weight, measured
osmometrically, can be from 200 to l,000, preferably from
250 to 800,
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The aqueous solution or dispersion of the melamine
resin contains an emulsifier, preferably in an amount of
from 0 5 to 5% by weight, and especially from 1 O to 3.0%
by weight, based on resin. The purpose of the emul-
sifier is to disperse the organic blowing agent homogene-
ously in the aqueous solution or dispersion; accordingly,
the emulsifier ensures the stability of the system and
prevents phase separation during foaming; such phase
separation would result in an inhomogeneous foam. The
o higher the foaming temperature, the more effective the
emulsifier must be, and the higher should be the concen-
tration used. The emulsifier furthermore acts as a
nucleating agent for the foaming process Suitable
materials are anionic co~pounds, especially metal alkyl-
sulfonates and alkylarylsulfonates, where alkyl is of 8
to 20 carbon atoms, the metal preferably being sodium;
metal salts of sulfosuccinic acid esters, sulfonated
castor oils, alkylnaphthalenesulfonic acids, phenol-
sulfonic acids and sulfuric acid esters, for example C12-
C18-alkyl hydrogen sulfates and C16-C18-fatty alcohol
- hydrogen sulfates, are also suitable, as are cationic
compounds, eg. oleic acid triethanolamine ester and lauryl-
pyridinium chloride, and non-ionic compounds, eg. oxy-
ethylated castor oil, oxyethylated tallow alcohols, oxy-
ethylated stearic acid or oleic acid, and oxyethylated
nonylphenol.
The aqueous solution or dispersion additionally
contains a ~olatile blowing agent, preferably boiling at
from -20 to 100C, especially from +20 to +80C.
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Examples are hydrocarbons, halohydrocarbons, alcohols,
ketones, ethers and esters. Preferred blowing agents
are pentane, hexane, trichlorofluoromethane and trichloro-
trifluoroethane The amount of blowing agents depends
on the desired density of the foam and can be from 1 to
50% by weight, preferably from 5 to 40% by weight, based
on resin,
The curing agents employed are compounds which
under the reaction conditions split off, or form, protons,
lo which then catalyze the further condensation of the mel-
amine resin. The amount used is from 0.01 to 20,
preferably from 0.05 to 5, % by weight, based on the resin~
Examples of suitable compounds are inorganic and organic
acids, eg. hydrochloric acid, sulfuric acid, phosphoric
acid, formic acid, acetic acid, oxalic acid, lactic acid
and aminoacids, and latent curing agents, eg s~lts of
halocarboxylic acids, chloroacetamide, hydrogen phosphates,
acid anhydrides and ammonium salts. Formaldehyde it-
self can also undergo disproportionation at elevated tem-
peratures, to form formic acid, and can thus act as a
curing agent,
The aqueous solution or dispersion is preferably
free from additives, For some purposes it can however
be advantageous to add up to 20% by weight, but preferably
less than 10% by weight, based on resin, of conventional
additives, such as fibrous or pulverulent inorganic rein-
forcing agents or fillers, pigments, dyes, flameproofing
agents, plasticizers, agents for reducing the toxicity of
the gas evolved on combustion or agents to promote
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carbonization. Since the foams have an open-cell
structure and can absorb water, it may be necessary, for
some purposes, to add from 0.2 to 5% by weight of a water-
repellent agent. Examples are alkylphenols, where alkyl
is of 5 to 15 carbon atoms, silicones and paraffins,
The additives are mixed homogeneously with the
aqueous solution or dispersion of the melamine resin,
during which mixing the blowing agent can be forced in,
where appropriate under pressure, However, it is
lo also possible to start from a solid, for example spray-
dried, melamine resin and to mix this with the blowing
agent and with an aqueous solution of the emulsifier and
of the curing agent, The sequence of addition of the
components depends on the particular mixing process.
The mixture is brought to the boiling point of the blow-
ing agent in the solution or dispersion at the prevailing
pressure. This may be done by heating, for example
with hot air, steam or high frequency radiation, or by
utilizing the heat of reaction On being brought to
this temperature, the blowing agent is transformed to a
gas and is thus able to cause the mixture to foam.
During the isothermal foaming, the aqueous solution or
dispersion assumes the boiling point of the blowing agent
at the prevailing pressure. Preferably, the process
is carried out under atmospheric pressure, with the mater-
ial at from 20 to 8~C, though the temperature of the
surroundings may be substantially higher.
A critical feature a) of the present invention is
the concentration of the precondensate in its mixture with
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water (without additives). The optimum concentration
is different for every foaming temperature, ie. it
depends on the nature of the blowing agent, According
to the invention, the minimum concentration must conform
to the condition that it should lie above the salient
point of the 1st derivative of the curve which is
o~ned when, keeping all other conditions constant, the
amount of water in the mixture of precondensate and water
is varied and the viscosity of the mixture (measured at
lo the boiling point of the blowing agent under the condi-
tions prevailing at the start of foaming) is plotted
against the concentration of the precondensate,; In
practice, the minimum concentration is determined by pre-
paring mixtures of precondensate and water, containing
various amounts of the latter, and then heating these
mixtures to a temperature at which the blowing agent would
boil under the pressure envisaged for the start of foam-
ing, The corresponding viscosity for each concentra-
tion of the melamine resin is then measured under these
conditions, Thereafter, the measured viscosity is
plotted against the particular concentration, The
initial part of the resulting curve has the shape of` a
straight line of only slight slope, but then rises pro-
gressively more rapidly and ultimately assumes a parabo-
loid course, The 1st derivative of this curve is
obtainedby graphicalmethods, It isinitially inthe formof
a horizontal straight line, followed by a curved salient
region, and ultimately becomes a steep straight line,
The salient region in general extends over a range of at
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most about 1% difference in concentration of the precon-
densate This region represents the minimum concen-
tration of the melamine resin. If it is desired to
locate the salient point even more precisely, the
straight line portions of the curve representing the 1st
derivative are extrapolated and their point of inter-
section is determined. The upper limit of the melamine
resin concentration must conform to the following condi-
tion: it must not exceed the value which, in the curve
lo described, corresponds to a viscosity of 5,000 dPas,
preferably 2,000 dPas and especially 1,000 dPas.
For the preferred blowing agents, the preferred
resin concentrations, which lie within the range defined
above, are as follows:
n-pentane: from 70 to 80, preferably from 72 to 79,
especially from 73 to 78.5, % by weightS
n-hexane: from 73 to 85, preferably from 74 to 84, and
especially from 78 to 83, % by weight;
trichlorofluoromethane: from 68 to 78, preferably from
69 to 77, especially from 70 to 76, % by weight;
trichlorotrifluoroethane: from 72 to 82, preferably from
74 to 80, % by weight.
The above concentrations are again based on the mixture of
precondensate and water, without additives
The second critical feature b) of the i~vention
is that during foaming, up to the time at which the-foam
has reached 80% of the maximum attainable rise height,the
viscosity ofthe aqueous solution or dispersion must not fall
below the value which corresponds, on the curve described
. .
1151~
~ o.z. 0050/033801
under a), to the minimum concentration defined under a),
but must not exceed 6,000 dPas.
The third critical characteristic c) means that
after reaching the time defined under b) the-viscosity
must, due to curing of the precondensate, exceed a value
of 10,000 dPas within 8 minutes, preferably within 6
minutes, especially within 4 minutes, ie the resin must
have cured within this time The two conditions b)
and c~ ensure that foaming and curing are correctly
balanced; for a given blowing agent and hence a given
foaming temperature, the two conditions can be met if the
nature and amount of the curing agent are correctlychosen.
In practice, two aqueous solutions or dispersions are
prepared, of which one contains the melamine resin in the
concentration determined according to a), the emulsifier,
the curing agent, the blowing agent and the additives, if
any, whilst the other contains the same constituents, but
without blowing agent, Both systems are then brought
to the foaming temperature. The parallel batch com-
prising the solution or dispersion which is free fromblowing agent must be prepared since the system containing
blowing agent foams under these conditions and hence its
viscosity cannot be measured. For the first system,
the rise height of the foam is plotted against time in
order to determine the time at which the foam has reached
80% of the maximum attainable rise height. Usingthe second
system, the viscosity is measured as a function of time
The results are then checked as to whether the re~uire-
ments stated under b) and c) are met. Should this not
1~51350
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be the case, the curing conditions must be varied, and
this can best be achieved by varying the nature and
amount of the curing agent and, where necessary, also by
selecting a different blowing agent and hence a different
foaming temperature, In the latter case, however, the
optimum concentration of the melamine resin would have to
be determined afresh, in accordance with a).
A resilient, stable foam of low density is only
obtained if during foaming and curing the conditions
specified under a), b) and c) are observed. If the
initial concentration of melamine resin is too low, or if
the viscosity drops below the defined initial viscosity
before the foam has reached 80% of its maximum rise height,
brittle foams are obtained, as with the prior art pro-
cesses. If solutions or dispersions which are initially
too viscous are employed, or ifthe viscosity increases above
the defined permissible limit before 80% of the maximum
foam rise height has been reached, the foaming pressure no
longer suffices for satisfactory foaming, and the foams
obtained are too dense and insufficiently resilient.
If, after reaching 80% of the maximum rise height of-the
foam, the viscosity increases insufficiently rapidly, ie.
if the foam does not cure sufficiently rapidly, it
collapses and a brittle, inhomogeneous foam having too
high a density is produced,
Preferably, the pressure in the foaming apparatus,
and hence the material temperature during foaming, are
kept constant. However, in special embodiments of the
process these conditions can be varied in the course of
~1513SO
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the foaming process, The foaming process in general
requires from 20 seconds to 20 minutes, preferably from
30 seconds to 10 minutes, depending on the nature and
intensity of heating employed. It is considered to
have finished when the resin has finished foaming and has
cured to the point that it retains its shape,
In a preferred embodiment of the invention, the
finished foam is subjected to a subsequent heat treatment,
In this, it is heated for from 1 minute to 180 minutes,
lo preferably for from 5 to 60 minutes, at from 120 to 300C,
preferably from 150 to 250C, during which time water,
blowing agent and for~aldehyde are substantially removed
and post-curing of the foamed resin occurs, ~his heat
treatment can be carried out immediately following the
production of the foam, in the same apparatus or in a
downstream apparatus, It can however also be carried
out at a later point in time, independently of the foam-
ing process. Heat-treated foams show substantially
less tendency to shrink and to absorb water than do pro-
ducts which have not been heat-treated. The emission
of formaldehyde is also greatly reduced,
In a further preferred embodiment of the inven-
tion, the foam is compressed once or several times, before
or after any heat treatment, by from 40 to 90% of its
original height, and is then allowed to re-expand, It
is presumed that this milling process destroys residual
hard zones in the cell structure, This results in an
increase in the resilience of the foam, and in less
shrinkage on storage at elevated temperatures,
11513SO
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The foams prepared according to the invention
exhibit the following properties-
a) the bulk density, measured according to DIN 53,420,
is from 4 to 80, preferably from 8 to 40, [g l 1];
b) the heat conductivity, measured according to DIN
52,612, is less than 0.06, preferably less than 0,04,
[ l o 1]
c) the compressive strength, measured according to DIN
53,577 at 60% compression, divided by the bulk density,
lo is less than 0.3, preferably lessthan O 2, [N.cm 2/g.l 11 and
in determining the compressive strength at 60% compres-
sion, the foam must recover to at least 70%, preferably
at least 90%,of its original height;
d) the modulus of elasticity, measured by methods simi-
lar to DIN 5~,423, divided by the bulk density is less than
0.25, preferably less than 0.15, [N.mm 2/g l 1];
e) the deflection on break, measured according to DIN
53,423, is greater than 6, preferably greater than 12, [mm];
f) the tensile strength, measured according to DIN 53,571,
is preferably not less than 0.07, in particular not less
than 0.1, [N.mm 2 3; and
g) the foams are of not more than normal flammability,
and preferably of low fl~m~ability, whenassessed according
to DIN 4,102.
The process according to the invention can be
carried out batchwise or continuously. In continuous
operation, which is preferred, the aqueous solution or
dispersion is advantageously applied to a continuously
moving, preferably heated, metal belt, on which it is
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spread uniformly and then foamed and cured in a heated
tunnel. To prevent the formation of a brittle skin on
the surface of the foam, the foaming process can advan-
tageously be carried out between two plastic films
travelling synchronously with the metal belt. This
foaming can be followed directly by the heat treatment
and/or milling treatmen~
The foams can be produced in the form of slabs or
webs having a thickness of 50 cm or more, or in the form
lo of sheets only a few mm thick, In batchwise operation,
molded articles can also be produced. On one or both
sides, the foams can be provided with covering layers or
be laminated with, for example, paper, cardboard, glass
mat, wood, gypsum boards, metal sheets or foils, or
plastic films, which may also be foamed,
The main field of use of the foams produced
according to the invention is heat insulation and sound
insulation in buildings and building components, especi-
ally partitions, but also roofs, facades, doors and floors,
as well as heat insulation and sound insulation in
vehicles and aircraft, and low temperature insul-ation, for
example of cold stores, oil tanks and liquefied gas con-
tainers. Other fields of use are as an insulating
wall cladding and as an insulating and shock-absorbing
packaging material.
In the Examples, parts, percentages and ratios are
by weight.
EXAMPLE 1
A spray-dried melamine/~ormaldehyde precondensate
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(molar ratio L:3, molecular weight about 400) was added,
in an open vessel, to an aqueous so:Lution containing 3%
of formic acid and 1.5% of a mixture of sodium alkyl-
sulfonates, where alkyl is of 12 to 18 carbon atoms, the
percentages being based on me.lamine resin. The concentration
of the resin, based on its mixture with water, was 74.0%.
The mixture was stirred vigorously and 20% of pentane were
then added. Stirring was then continued until, after about
3 minutes, a homogeneous dispersion had formed. This
dispersion was knife-coated onto a PTFE-coated glass fabric D
as the base material and foamed and cured in an oven at an
air temperature of 150C.
Under these conditions, the foam assumed a temperature
equal to the boiling point of pentane, which under these
conditions was 37.0C. After 4 l/2 minutes, the foam had
reached 80% of its maximum rise height, the latter being
ultimately reached after 7 - 8 minutes. The foam was left
for a further 10 minutes in the oven at 150C. It was then
heated for 30 minutes at 180C. The properties of the foam
are shown in Table l.
To determine the optimum melamine resin concentration,
the dependence of the viscosity of the dispersion on the
melamine resin concentration had been measured as follows,
before the foaming process: Mixtures of the melamine resin
precondensate and water in various ratios
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_~J~
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were prepared, The mixtures were then heated at 37,0C
and their viscosity was determined in a rotary viscometer,
The viscosity ~ in dPas was plotted as a graph (see Figure
l) against the concentration c in % by weight of solids.
The 1st derivative ~ ~ of the resulting curve was obtained
~ c
graphically and plotted on the graph in the form of two
straight lines intersecting at the salient point K,
In the present case, this point is at a concentration of
71.7%. The curve asymptotically approaches a concen-
tration of about 80%, so that the preferred m OEimum vis-
cosity of 1,000 dPas corresponds to a concentration of
about 79%. For the foaming procedure described in thé
Example, the concentration chosen was about halfway bet-
ween these values, namely 74.0%. The corresponding
viscosity was 88 dPas,
The ratio of the components in the mixture to be
foamed was then selected to give a ratio of melamine resin
to water (including the water introduced with the curing
agent and the emulsifier) of 74 : 26, Before the
actual foaming process, the maximum rise height and the
dependence of the viscosity on time were determined in
two trial batches. To do this, the mixture described
above, in one case with and in one case without added
- blowing agent, was heated to the foaming temperature.
Figure 2 shows a graph in which the rise height h and the
viscosity ~ have been plotted against time t. The
maximum rise height was 10,25 cm; 80% of the maximum rise
height was reached after 4~ minutes, At that time,
the viscosity was 170 dPas, After a further 3 minutes,
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the ViSCOsity had exceeded a value of 10,000 dPas.
EXAMPLE 2
The procedure followed was as in Example 1, except
that instead of 20% only 13% of pentane was employed,
EXAMPLE 3
The procedure followed was as in Example 1, but
using 3% of sulfuric acid as the acid, 1.5% of sodium
dodecylbenzenesulfonate as the emulsifier and 28% of tri-
chlorotrifluoroethane as the blowing agent, The resin
concentration was 76%. The material temperature,
during foaming, was 47C, The foam was not heat-
lo treated,
EXAMPLE 4
The procedure followed was as in Example 1, butusing 6% of phosphoric acid, 1,5% of sodium laurylsulfon-
ate and 12% of pentane. A melamine resin with a molar
ratio of melamine to formaldehyde equai to 1 : 3,5 was
employed, The resin concentration was 74y. The
foam was not heat-treated,
EXAMPLE 5
2,8% of formic acid and 1.4yo of the alkylsulfon-
ate from Example 1 were added to a solution of a melamine
resin in an open vessel; the percentages are based on
resin, The concentration of resin, based on its mix-
ture with water, was 75,5%, 20yo of pentane was added
with ~igorous stirring. Foamlng, curing and heating
were carried out as in Example 1,
EXAMPLE 6
The procedure followed was as in Example 5, using
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a melamine resin with a molar ratio of melamine to form-
aldehyde equal to 1 : 2,5, The resin concentration
was 76%. 0.20% of formic acid was used as the curing
agent, 3% of the alkylsulfonate from Example 1 plus 0,3%
of an oxyethylated saturated fatty alcohol (with a low
degree of oxyethylation) were used as the emulsifier, and
23% of n-hexane was used as the blowing agent. The
material temperature during foaming was 69,0C. The
foam w~s heat-treated as in Example 1,
EXAMPLE 7
The homogeneous mixture described in Example 1
was applied to a metal belt travelling continuously at a
speed of 0.4 [m,min 1], the belt being heated to about
130C~ The mixture was uniformly spread on the belt,
as a layer about 2 mm thick, by means of a knife coater.
It was then foamed in a foaming tunnel heated by air at
150C, with the material temperature assuming a value of
37.0C, After about 41 minutes, 80% of the ultimate
rise height of the foam was reached, and after about 6
minutes the final height of 15 cm was attained, The
foam was then passed through the foaming tunnel for a
further 7 minutes, during which the material temperature
rose to about 98C. Thereafter the foam was heated
for 15 minutes at a material temperature of about 170C,
and the block was then trimmed,
EXAMPLE 8
The procedure followed was as in Example 6, using
a melamine resin with a molar ratio of melamine to form-
aldehyde equal to 1 : 2,0, The resin concentration
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was 80%. 2.5% of formic acid was used as the curing
agent, a mixture of 0,6% of sodium diisobutyinaphthalene-
sulfonate and 1.6% of an oxyethylated saturated fatty
alcohol (with a low degree of oxyethylation) was used as
the emulsifier and 16% of pentane was used as the blowing
agent.
EXAMPLE 9
The procedure followed was as in Example 1, using
1,8% of formic acid as the acid and 2, 2% of sodium do-
decylbenzenesulfonate as the emulsifier. The heat
lo treatment was carried out at 190C.
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- 21 - 0 ~ Z. 0050/033801
~ O O O O O C~ O O O
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- 22 - o.z. 0050/033801
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- 23 o.z. 0050/033801
TABLE (continuation)
Example Web length Web density
Web thickness g. cm
~1.'3
2 ~10 ~1.3
3 >10 > 1,'3
4 ,~10 >1.3
>12 >1.3
6 >12 >1.'3
7 ~15 >1.'3'
8 ~10 ~1.'3
g >z5 ~ ,
