Note: Descriptions are shown in the official language in which they were submitted.
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The present invention refers to a process for
making reinforced cellular materials from unsaturated
polyester resins by injecting a liquid foam, made from
said resins by mechanical introduction of a gas therein,
into a closed mould con-tai~ing the reinforcing materials
: which will be her.einafter specified.
The present invention also refers to the cellular
materials thus obtained, as well as to the products
made from said cellular materialsu
Moulded cellular materials of reinforced unsaturated
polyester resins are known. Said materials however are
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obtained by impregnating the reinforcing material with
an unsaturated polyester resin in liquid form, which
resin is successively chemically expanded in the mould.
~aid process however has the following disadvantages:
- the chemicals employed as foaming agents are usually
to~ic and further are generall`y unstable at room`
temperature and therefore must be maintained at low
temperatures until their use,
- the process is not economical since the chemical foaming
agent is expensive;
- the process requires moulds suitably relnforced to stand
the pressure produced during the expansion of the liquid
resin
~ method for overcoming these disadvantages has
been proposed in the art. It consists in carrying out the
foaming by mechanical incorporation of the gas lnto the
liquid resin. This method however does not permit to
incorporate a reinforcing material having a length greater
than 1.5 mm before the foaming stage, inasmuch as the
mechanical devices for gas dispersion (nozzles and
turbines) do not permit the passage of larger reinforcing
materials and further such materials also cause a partial
degradation of the foam.
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A ~ethod for overcoming this last difficulty has
also been proposed, which consists in separately
preparing the foam by mechanical means and injecting
it in liquicl form into a closed mould in which a bed
of dry fibres has been previously placed, which fibres
are oonstituted by a mat of glass Pibres cut and disposed
over the entire c.ross-section of the mould or fixed
on the two halves of the mould.
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. However, not even this method is free from
clisadvantages/:
- the styrene contained in the liquid resin dissolves
the binder which keeps the mat together and the
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entering flow of foam removes the glass fibres:
- in the case of a mould containing the rein~orcement
in the for~n of a mat of glass fibres which are cut and
disposed over all the cross-section of the mould, said
reinforcement does not permit the foam to pass through
without breaking it
The Applicant has now surprisingly found a method
for producing cellular mat.erials from unsaturated polyester
resins, reinforced with reinforclng fillers and having
a density lower than 0 7 kg/lt, whereby said
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disadvantages are overcome.
An object of the present invention is therefore
a process for obtaining cellular materials from unsaturated
polyester resins, reinforced with fillers having a density
below 0.7 kg/l by injecting into a closed mould, a liquid
foam of said resins having a density lower than that of
the final cellular material, made by mechanical introduc-
tion of a gas, characterized by the fact that a liquidfoam made from unsaturated polyester resins including
conventional additives, is iniected and subsequently cross-
linked in a closed mould containing a reinforcing agent of
synthetic, artificial, vegetable or mineral fibres in the
form of a monofilament mat, a cut fibre mat, a mono or bi-
directional roving woven mat, rovings, fabrics, the total
amount of reinforcing material used being of from 5 to 50%
by weight of the unsaturated polyester resin.
The liquid foam is made of unsaturated polyester
resins which contain conventional additives, optionally
containing a reinforcement of mineral or organic fibres
having a length lower than 3 mm and more preferably less
than l.S mm, and optionally containing a low boiliny
foaming agent.
In the case that a cut fibre mat is used, it is
convenient to use a product containing a binder which has
a low solubility in styrene, so as to avoid its being
washed away and the consequent displacement of the fibres.
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Preferably glass fibres are used as reinforcing
material.
The reinforced cellular material made of
unsaturated polyester resins having a density up to
0.7 kg/l thus obtained, is also an object of the present
invention. Said cellular material preferably has a
percentage of closed cells above 80~.
If the monofilament mat is employed as
reinforcing agent in the mould, a cellular material is
obtained which is uniformly reinforced along all its
thickness, viz. the fibres are uniformly and homogeneously
distributed through the entire body of the product.
In the case that a woven mat, rovings or fabrics
are used as reinforcing fillers in the mould, a cellular
material is obtained which is uniformly reinforced over
all its surface in a stable ~ay.
The cross-linking in the mould may be carried
out, according to the present invention, both in the
hot and in the cold, preferably between 20 and 80C.
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If glass f;.~res are.used as reinforcing agent in
the moul.d, said fibres have a diameter which is smaller
than 16 micron. If other synthetic, artificial, vegetable
or mineral~fibres, such as e g aramide, carbon, cellulose
ester, polyethyleneterephthalate, acrylic, or regnerated
cellulose fibres are used as reinforcing material, said
fibres have a count lower than 20 deniers
The liquid unsaturated polyester resin foam,
optionally containing the low boiling liquid agent
and/or the reinforcing fibres having the aforesaid
lengths, lS conveniently obtained in a foaming machine
constituted by a turbine having numerous ranks of vanes
having a peripheral speed of 200-500 mt/min, said turbine
being heated by means of suitable jackets and each row
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being separa.ted from the following one by crowns o~
pegs fixed on the jacket of the turbine itself In
the case that a low boiling l1quid agent and/or fibres
of the reinforcing material hereinbefore specified are
used, a stirrer-mixer is conveniently 1nserted before
said turbine, in which stirrer-mixer the solut1on of
unsaturated polyester resin and styrene, containing
suitable additives, is mixed w1th the low bo1ling
liquid agent and/or the fibres Oe reinforcing material.
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A fluid (preferably nitrogen or air) which constitutes
the foaming agent is also introduced into said turbine
at an appropriate pressure. The catalyst is introduced
in the last row of the turbine, wherein the foam has
already been created, in such a way that the foam which
flows out of the turbine already contains the catalyst.
The injection of the liquid foam is conveniently
effected by using a pressuri~ed vessel exploiting the
inner pressure of the vessel and controlling the minimum
and maximum levels according to conventional methods.
The closed moulds (constituted by at least two
halves), into which the liquid foam is injected, may
be of metal or of a composite material~ and in any case
do not require any particular strength, contrary to
what occurs when foams are made by chemical expansion
of the resin where the high pressures which are rached require
especially high resistance and rigidity of the moulds.
It is therefore apparent that the present ivention
is economically convenient, since stronger moulds are
much costlier.
If catalytlc systems which operate in the hot are
used, the moulds may be heated, whereby advantages are
obtained as to polymerization times and surface finish
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of -the products. Before the injection, if synthetic or
artificial, vegetable or mineral fibres having a length
higher than 1.5 mm, such as monofilament mat, cut fibre
mat, woven mat, roving, mono- and bidirectional fabrics,
etc. are used, said rein~orcement fibres, in the dry
state, are preferably previously positioned in the moulds.
The app~opriately catalyzed liquid foam introduced
into the mould~ wets the fibres posi;tioned therein at
the moment of its injection without changing their
disposition in the mould, and subsequently polymerizes.
The polymerization reaction may be primed either
in the cold or in the hot, depending on the catalytic
system employed and on the purposes which are to be attained.
The expression "unsaturated polyester resins" is to be
construed, according to the present invention, as
meaning the resins obtained from an unsaturated polyester,
formed by polycondensation of at least one ~ ~ ~
ethylenically unsaturated dicarboxylic acid and/or at
least one corresponding anhydride with at least one
polyvalent alcohol, and one or more ethylenically
unsaturated monomers, such as e.g. styrene, vinyltoluene,
~ - methylstyrene, methylmethacrylate, diallylphthalate,
etc.
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Examples of ethylenically unsaturatéd dicarboxylic
acids or corresponding anhydrides comprise maleic acid
or its anhydride, fumaric, itaconic and mesaconic acids.
Together with the unsaturated dicarboxylic acids
there may be employed mono or polyfunctional aliphatic,
saturated carboxylic acids such as adipic, succinic,
glutaric acid and the like; mono or polyfunctional
aromatic carboxylic acids such as phthalic, isopthalic,
terephthalic, benzoic acids etc.; anhydrides such as
phthalic, trimellitic anhydride etc.
As polyvalent alcohols there may be employed:
ethylene glycol, propylene glycol, 1,2-butanediol,
diethylene glycol~ dipropylene glycol, 1,6-hexanediol,
1,4-cyclohexanedimethanol, trime*hylolpropane,
pentaerythrite, glycerine, neopentylglycol, etc.
The unsaturated polyester resins may be prepared
by the known processes used for the polyester resins,
both in solvent and in dry phase.
According to a practical preferred embodiment o~ -
the present invention, the unsaturated polyester resin
is obtained by reacting ~rom 1 to 1.3 mols o~ at least
one polyvalent alcohol with from 0.05 to 1 mol of at
least one ethylènically ursaturated dicarboxylic acid
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an anhydride. The polycondensation is continued until
a polymer is obtained having an acid number comprised
between 5 and 90 mg of KOH/g. The preferred acid number
is comprised between 10 and 30 mg of KOH/g and the
molecular weight between 500 and 5000.
Besides the ethylenically unsaturated dicarboxylic
acid or correspondent anhydrides, a saturated dicarboxylic
acid may be present in the mi~ture, in a molar amount
comprised between 5 and 95% with respect to the
unsaturated dicarbo~Yylic acid~ accordlng to the known
art.
The unsaturated polyester thus obtained is mixed
with styrene, in a polyester/styrene ra-tio comprised
between 9:1 and 1:1 preferably between 4:1 and 2.5:t.
Inhibitors and stabilizers adapted to prevent
the prematur0 cross-linking of the mi~re may be added
to the styrene/unsaturated polyester mixture, in amounts
from O.l ppm to 10000 ppm.
The most commonly used inhibitors and stabilizers
are: hydroquinone, quinone, quin1drone, tertiary butyl-
pyrocatecol, toluene hydroquinone, monotertiary butyl-
hydroquinone, ditertiary butylhydroquinone, 1.4-naphthoquinone,
anthraquinone, methyl and/or ehtyl ethers of hydroquinone~
,
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picric acid, trinitrobenzene, paraphenylenediamine, etc.
Further, in order to improve the stability of the
resin, organic or inorganic compounds soluble in the
polyester, quaternary ammonium salts, etc., are added.
In order to improve the stability of the foam,
additives are added to the unsaturated polyester resin
before foaming, such as e.g. surface active agents for
improving the formation Qf the foam and/or agents for
regulating the diameter of the gas bubbles andlor agents
for stabilizing the foams, e.g. surface active agents
based on silicone compounds, block copolymers of silicones
with polyethers, soaps such as ricinooleates, polymercaptanes,
etc.
Any compound or mixture of compounds which generate
free radicals under the particular condltions of the
polymerization may be used as catalytic system
These eompounds are: the peroxides or the
hydroperoxides, such as diacetyl peroxide, ben~oyl peroxide,
hydrogen peroxide, cumene hydroperoxide~ methyltehylketone
peroxide, etc. Other catalysts which generate ~ree
radicals may also be used such as e.g ammonium
persulphate, perborates and percarbonates.
It is preferred to employ, in addition to the
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free radical generating catalyst, an accelerator which
increases the speed of decomposition of the peroxidic
compounds, which thus produces free radicals at higher
speeds. Cobalt naphthenate is generally used as accelerator
and is diluted in styrene until it is brought to a
concentration of about 1-3% of metal.
A complexing agent for increasing the efficency
of the accelerator may also be used. According to a
widely acc~pted interpretation, it is believed that
such agents act to reduce the cobalt naphthenate which
is transoformed into the corresponding cobaltous compound
which is much more reactive.
Generally tertiary aromatic amines, among which
preferably dimethylaniline, are used as compléxing agents. -
Wide variations and changes may be effected in
the details of the embodiment of the present invention
without departing from the spirit and the scope of the
present invention.
In order better to il1ustrate the inventive concept
of the present invention and the way of carrying it into
practice~ some non limitative examples are described.
EXAMPLE 1
100 kg of polyester resin are introduced in a
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steel vessel, which resin has been prepared by reacting
the following components according to the following molar
ratios:
propylene glycol 0.8 mols, diethylene glycol 0 2 mols,
maleic anhydride o. 6 mols, ~hthalic anhydride 0 4 mols,
hydroquinone 100 ppm, styrene 30~ of the tot-al.
500 ml of cobalt octoate having a concentration
of 6% in xylene, l~kg of silicone oil, 5 kg of glass
milled fibres having a nominal length of 1 mm are added
to the aforesaid resin. The whole is mixed with an helical
stirrer for 20 minutes. Said mixture is transferred from
the vessel to a turbine thermostatized at 35C, with
the help of a gear pump having a flow rate of 200 lt/h
The aforesaid turbine is constltut0d by a stator and a
rotor provided with projections having a circular cross-
section. The peripheral speed of the rotor is 250 mt/min.
The foaming gas (air) is Lnjected into the turbine through
a nozzle. The catalyst~methylethylketone peroxide,is
injected at a flow rate 1.6 lt/h before the exit of the
foam from the said turbine.
The liquid foam thus formed is poured into a vessel
adapted to be pressurized Once it has been filled, the
vessel is pressurized and the liquid foam is injected
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through a suitable pipeline into a steel mould heated
at the temperature of 600C. A monofilament mat with a
weight of 600 g/m has been previously positioned in the
mould. The cross-linking is allowed to occur, and it
occurs without development of heat.
Once polymerized, the cellular material thus
obtained is extracted -from the mould. It has the following
characteristics:
Density 0,43 kg/lt
Resistance to tension128 kg/cm
Tension modulus14000 kg/Cm2
Elongation at break1.44%
Resistance to shear 56 kg/cm
Shear modulus 1070 kg/cm
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Minimum height from which a
steel ball of 5kg must fall
to break a sample 300 cm
Thermai conductivity0,031 Kcal/m h C
EXAMPLE 2
The operations are carried out as in Example 1
except that the hardening system is modified inasmuch
as methylethylketone peroxide is still used but in a
percentage of 1.2% of the resin which is further
accelerated with dimethylaniline in an amount of 0.1%
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of the resin. Further, in this case the mould is not
preheated and the injection occurs at room temperature.
Th0 characteristics of the cellular material
obtained are substantially the same as those of Example 1.
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