"Process for the preparation of flexible polyurethane foam and foam
obtained thereby."
The present invention is directed to a process for the
preparation of a flexible polyurethane foam and to the polyurethane foam
prepared by that process. The foam is in particular a flexible polyurethane
foam which has a density of between 25 and 120 kg/m3, a resilience,
measured at 20°C in accordance with ASTM D 3574 H, higher than 35%,
and an ILD 40% hardness, measured in accordance with ISO 2439 B, of
between 60 and 500 N.
Flexible polyurethane foams are widely used for body
support applications, such as mattresses, mattress toppers, pillows,
cushions of any types for use in beds, seats or other applications such as
floor mats, etc. Besides providing functional support to the human body,
the body supporting material should also provide a good pressure
distribution, a sufficient physiological comfort, as well as an adequate
breathability.
High resilience (HR) polyurethane foams have been widely
used for body support applications, due to their superior support and
resilience characteristics. They have in particular a quite high SAG factor
and also a high resilience. However, the uniformity of the pressure
distribution on such kind of foams is not optimal, which may lead to
pressure-points, and making them thus not suitable for people requiring
pressure-relief, for instance in hospitals where long-term patients often
suffer from pressure sores.
Visco-elastic (VE) foams have found wide acceptance as
body support materials. In contrast to conventional polyurethane foams
and high resilience polyurethane foam they have resilience figures which
are markedly lower than 40%, and which are usually even lower than
15%. VE foams are rather soft but supportive foam materials,
characterised by a very slow recovery and an indentation hardness which
is temperature sensitive. This property allows the body to sink more
deeply into the foam, while still maintaining the firm feel of a good quality
resilient foam. VE foams thus gently conform to the shape of the user's
body, allowing pressure to be absorbed uniformly and distributed more
evenly, which is of particular benefit in the prevention and healing of
pressure sores. A disadvantage of VE foams is however that their
hardness increases with decreasing temperature, which makes them very
uncomfortable for use in cold rooms or areas. Further, VE foams are
denser and more closed-celled than conventional HR foams, leading to a
worse breathability and thus decreased thermophysiological comfort.
Another class of materials used for body support materials
are gels. Gels are very well-known for their excellent balanced pressure
distribution, due to their three dimensional deformation properties leading
to flattening pressure points. They further provide a good physical
comfort, such as a low hardness and a good elasticity, and provide the
user with a good "feel". However, gels, such as polyurethane gels,
exhibit a relatively high thermal conductivity as well as a very high heat
capacity. This leads to a cool feel as heat is removed from the body when
in contact with the gel. A further disadvantage of gels is that they have a
very high dead weight (specific weight usually between 600-1 100 kg/m3) .
In order to decrease the specific weight of gels, cellular gels, such as
cellular polyurethane gels, have been developed, as disclosed in
US 4 404 296. They are blown with an inert gas such as air, N2 or CO2.
Besides the reduced specific weight, their heat capacity is reduced as
well. However, cellular gels have the disadvantage that under influence
of compression, the cells of the foamed gel stick to each other because of
the undercrosslinked matrix, and that the foamed gel has bad mechanical
properties, especially a very bad elasticity. Besides their very low
resiliency, they are not breathable at all since they don't allow any air
transfer. Foamed gels are thus not at all suitable as body support
materials.
Because of their very high specific weight and their high
thermal capacity, gel layers are preferably used with one or more
additional body supporting layers, such as foam layers, spring layers and
the like. Mattress or mattress toppers comprising polyurethane gel layers
overlying foam layers are for instance known from WO 2006/100558, US
2001/0018466 and US 2005/0017396. Gel layers may be integrally
attached to the additional support layers, for instance by gluing, sewing,
welding or by chemical bonding. Gel layers can also be separate bodies
inserted in foam layers, as illustrated in US2007/022691 1. In order to
enable the gel layers to develop their pressure distributing effect, they
need a complete envelopment by means of a relatively thin highly elastic
cover, which should be impermeable to prevent penetration of the tacky
gel material through the cover. Such cover is disadvantageous for air
passage and thus breathability. Furthermore, it increases the production
cost of the body support manufacturing process. Due to the minimum
thickness required to achieve the desired pressure distribution properties,
the obtained mattresses with integrated gel layers are still very heavy and
thus difficult to handle.
In order to lower the weight, the overall rate of thermal
transfer and the overall thermal mass of a gel mattress which consists of
a gel layer covered with an upper and a lower foam layer, US
2005/0017396 discloses an extruded gel layer which has vertical hollow
columns. These hollow columns have walls which partially or completely
buckle when a person is lying on the mattress. A drawback of this
mattress is that its weight is still substantially larger than the weight of a
polyurethane foam mattress. The gel layer has indeed to be relatively
thick in order to provide the desired improved pressure distribution
effects. Moreover, due to the vertical hollow columns in the gel layer,
these pressure distribution properties are lost to some extent and, what's
more, the load bearing properties of the mattress are getting worse. In
this respect the SAG factor is an important parameter of a body
supporting foam. This SAG factor or support factor is the compressive
strength at 65% indentation divided by the compressive strength at 25%
indentation. A good support and a comfortable feeling is provided by
foams such as HR foams and latex foams which have a relatively high
SAG factor, more particularly a SAG factor higher than 2.5. A drawback
of the hollow columns in the gel layer is that when the walls thereof
buckle under the load of a person lying on the mattress, the compressive
strength provided by these walls is reduced so that the person is not or
less optimally supported.
It is an object of the invention to provide a new process for
preparing a flexible polyurethane foam which is resilient and breathable
but which still enables to provide improved foam properties without
showing however the drawbacks of a gel layer.
To this end, the process for the preparation of a flexible
polyurethane foam according to the present invention, comprises the step
of allowing a reaction mixture, which comprises a blowing agent, to foam
to produce the polyurethane foam, and is characterised in that before the
reaction mixture is allowed to foam, at least one organogel material is
dispersed therein. The organogel material is thus incorporated in the
polyurethane foam upon foam expansion to form at least part of the cell
ribs and/or cell walls of this polyurethane foam.
Incorporating a gel material in a polyurethane coating
material is already known per se from WO 01/32791 . The polyurethane
coating material is not a flexible polyurethane foam but is a rigid foam or
a microcellular elastomer and has a density which is generally higher
than 200 kg/m3. The gel material is incorporated in this polyurethane
coating material to improve the insulating properties thereof. In contrast
to the present invention, the gel material is therefore an aerogel or
xerogel, which contains no liquid and which is thus a solid material.
The organogel material used in the process of the present
invention is on the contrary a dimensionally stable, jelly-like material.
Gels are defined as a substantially dilute cross-linked system which
exhibits no flow when in the steady state. Gels are mostly liquid, yet they
behave like solids due to the three-dimensional crosslinked network
within the liquid. Apart from the xerogels, which are dried to form a
porous product which is not jelly-like anymore, there are two main types
of gels namely hydrogels and organogels. Hydrogels contain water as the
dispersion medium (liquid). Organogels are composed of a liquid organic
phase entrapped in a three-dimensionally cross-linked network. They are
highly elastic. In the flexible polyurethane foam according to the
invention, the organogel material forms part of the cell ribs and/or cell
walls so that the physical properties of the foam are modified thereby.
The incorporation of the organogel material in the polyurethane material
of the foam may in particular reduce the tensile stress in the foam
material when locally compressing this material. In this way, a better
pressure distribution can be achieved without the drawbacks of a gel
layer and while maintaining the desired support and resilient properties of
the polyurethane foam. Such advantageous effect cannot be achieved
when simply coating the cell ribs and/or the cell walls of a polyurethane
foam with an organogel material, for example by impregnation the foam
therewith.
In a preferred embodiment of the process according to the
invention, the organogel material is dispersed in the reaction mixture in
an amount of at least 0.1 wt. %, preferably at least 1 wt. %, more
preferably at least 5 wt. % and most preferably at least 10 wt. %,
calculated on the total weight of the polyurethane foam prepared from the
reaction mixture.
In a further preferred embodiment of the process according
to the invention, the organogel material is dispersed in the reaction
mixture in an amount of less than 40 wt. %, preferably less than 30 wt. %
and more preferably less than 20 wt. %, calculated on the total weight of
the polyurethane foam prepared from the reaction mixture.
Advantageously, the organogel is a gel selected from the
group consisting of polyurethane gels, oil extended thermoplastic block
copolymer gels, in particular SEBS gels, silicone gels and PVC plastisol
gels, the organogel material being preferably a polyurethane gel.
In a particular embodiment, which is especially suited for
body support applications, the flexible polyurethane foam obtained by the
process according to the invention has a density of between 25 and 120
kg/m3, a resilience, measured at 20°C in accordance with
ASTM D 3574 H, higher than 35%, and an ILD 40% hardness, measured
in accordance with ISO 2439 B, between 60 and 500 N.
To provide good support properties, the SAG factor of the
foam is preferably greater than 1.8, more preferably greater than 2.0 and
most preferably greater than 2.2.
The invention also relates to the flexible polyurethane foam
obtained by the process according to the invention. This foam may
comprise cell ribs and cell walls, the organogel material being
incorporated in the foam to form at least part of these cell ribs and/or cell
walls, or the foam may comprise substantially only cell ribs (being in
particular a reticulated foam), the organogel material being incorporated
in the foam to form at least part of these cell ribs. In a preferred
embodiment, the organogel material forms gel inclusions in the cell ribs
and/or cell walls. The physical properties of the foam are thus changed
by the presence of the organogel inclusions in the cell ribs and/or in the
cell walls.
Other particularities and advantages of the invention will
become apparent from the following description of some particular
embodiments of the process for preparing a flexible polyurethane foam
according to the present invention.
The invention is directed to a process for the preparation of
a flexible polyurethane foam. The term polyurethane foam embraces not
only pure polyurethane foam but also polyurea modified polyurethane
foams. The term "flexible" indicates a foam which has an ILD 40%
hardness of less than 500 N and thus embraces also soft or hypersoft
foams. The flexible polyurethane foam can be intended for several
applications but is especially intended for seating and bedding
applications. It has preferably an ILD 40% hardness, measured in
accordance with ISO 2439 B, between 60 and 500 N, and more
preferably between 90 and 200 N. The resilience or ball rebound of the
foam, measured at 20°C in accordance with ASTM D 3574 H, is
preferably higher than 35% and more preferably higher than 45%. The
density of the foam is preferably between 25 and 120 kg/m3 and is more
preferably lower than 100 kg/m3 and most preferably lower than 80 kg/m3.
The foam is preferably an open cell foam.
The flexible polyurethane foam is prepared by allowing a
reaction mixture, which comprises a blowing agent, to foam. The blowing
agent preferably comprises water which reacts with isocyanate groups to
produce carbon dioxide gas. The known one-shot, semi-prepolymer or
full prepolymer techniques may be used together with conventional
mixing equipment and the foams may be produced in the form of
slabstock, mouldings and the like. In the full prepolymer techniques, the
reaction mixture is prepared by mixing an isocyanate prepolymer with an
aqueous mixture (comprising a surfactant) to produce the polyurethane
foam. This technique is used in particular for preparing hydrophilic
polyurethane foam. For producing flexible polyurethane foam for seating
and bedding applications, the one-shot or the semi-prepolymer
techniques are usually applied. In these techniques a polyurethane
reaction mixture is composed by mixing at least an isocyanate
component and an isocyanate reactive component. In the semiprepolymer
techniques, the isocyanate component comprises an
isocyanate prepolymer and/or the isocyanate reactive component
comprises an isocyanate reactive prepolymer, in particular a polyol
prepolymer.
An essential feature of the process according to the
invention is that before the reaction mixture is allowed to foam, at least
one organogel material is dispersed therein. The organogel material is in
other words distributed substantially evenly throughout the liquid reaction
mixture. The organogel can be dispersed in the reaction mixture by
adding it separately to that reaction mixture. When the reaction mixture is
composed by mixing at least an isocyanate component and an
isocyanate reactive component, it can be dispersed in one or both of
these components, preferably in the isocyanate reactive component.
The organogel is a dimensionally stable, jelly-like material. It
consists mainly of a liquid but it behaves like a solid due to the presence
of a three-dimensional crosslinked network within the liquid. The liquid in
an organogel is an organic liquid whilst the liquid in a hydrogel is water.
An important drawback of hydrogels is that they easily dry out because of
the evaporation of water, which leads to hardening of hydrogels. In the
process according to the invention this cannot be prevented by encasing
the gel material in an elastic film since the gel material is to be dispersed
in the reaction mixture. Hydrogels are further disadvanteous in the
process according to the invention, because the big amount of water
entrapped in the hydrogel, might interfere with the polyurethane foam
forming reaction, which is undesired. Consequently, use is made in the
process according to the present invention of organogels which contain
an organic liquid. This organic liquid is less volatile than water and/or is
bonded in the gel so that it will not or substantially not evaporate from the
gel material. The gel is preferably an anhydrous gel which contains
substantially no water.
One physical property of the gel is the gel strength or gel
rigidity. The gel rigidity, expressed in gram Bloom, is determined by the
gram weight required to depress a gel a distance of 4 mm with a circular
piston having a cross-sectional area of 1 square centimetre at 23°C. It
can be determined in accordance with the British Standard BS 757
( 1975). The organogel used in the process of the present invention has
preferably a gel rigidity of at least 5 grams, more preferably of at least 10
grams and most preferably of at least 20 grams. Such gel rigidities are
high enough to support a three-dimensional gel configuration, which is
not the case for pre-polymers which may also be contained as explained
hereabove in the reaction mixture and which may be quite viscous but
which don't show any gel rigidity at all. The organogel has preferably a
gel rigidity which is smaller than 700 grams, more preferably smaller than
500 grams and most preferably smaller than 350 grams.
The organogel material may be of different compositions. It
may comprise for example a silicone gel, in particular an organosiloxane
gel. Suitable examples of such a gel are described in US 4 072 635,
which is incorporated herein by way of reference. The organogel material
may also comprise a PVC plastisol gel. Examples of such a gel are
described in US 5 330 249, which is incorporated herein by way of
reference. Oil extended thermoplastic block copolymer gels are also
suitable gels. Examples of these oil gels, more particularly of SEBS gels
(poly(styrene-ethylene-butylene-styrene) gels), are described in
US 5 508 334 and US 5 336 708, which are incorporated herein by way
of reference. These oil gels contain high levels of a plasticizing oil to
achieve the gelatinous properties.
The organogel material used in the process of the present
invention preferably comprises a polyurethane gel. Examples of such
polyurethane gels are described in US 4 404 296, US 4 456 642 and in
US 5 362 834, which are incorporated herein by way of reference.
Polyurethane gels, are materials of gel-like consistency,
which contain one or more polyols within a certain molecular weight
range as the coherent dispersing agent in which a polymeric network
which is covalently linked via urethane bonds, is dispersed. They can for
instance be obtained by reacting one or more higher-functional highermolecular
weight polyols with a quantity of an organic di- or
polyisocyanate in the presence of appropriate polyurethane forming
catalysts, provided that an isocyanate index between 15-60 is applied
and provided that the isocyanate component or polyol component has a
certain minimum functionality and that the polyol is essentially free of any
polyol having an OH number greater than 112 or a molecular weight
below 800. The anhydrous polyurethane gels prepared in this way consist
of a high-molecular weight covalently crosslinked polyurethane matrix,
dispersed in a liquid dispersing agent (polyol) firmly bonded in the matrix.
The liquid dispersing agent is a polyhydroxy (poylol) compound having a
molecular weight between 1000 and 12000 and an OH number between
20 and 112, and is free of hydroxy compounds having a molecular weight
below 800. The advantage of these polyurethane gels is that their
consistency can be varied between a jelly-like or gelatine state and a
solid jelly by varying the isocyanate index and the functionality of the
starting materials, and that they have an exceptional stability, even at
high temperatures, due to the fact that the polyol dispersing agent is
firmly bonded in the gel. The preparation of the gels can be obtained by
the so-called one-shot process or by a prepolymer process, as is clearly
disclosed in US 4 456 642. The obtained gels can be used in a wide
variety of forms, such as granulates, foils, molded articles. A gel
granulate is particularly preferred when the gel is to be admixed to a
polyurethane forming composition.
Up to 50 % of an active ingredient may be included in the
gel-forming composition. Active ingredients refer to any additive capable
of providing a benefit to a user, such as for instance biocides, fragrances,
anti-allergic agents, fungicides, phase change materials (PCM). . . They
are preferably mixed or dispersed in the polyol component before the
other reactants are combined with the polyol. Organogels containing
active ingredients have the advantage over the known polyurethane
foams, that the outward migration of even solid or low volatile active
ingredients, remains active over a long time period. Other filler types can
be added as well to the gel, such as powders, nanoparticles,
microspheres of synthetic or natural materials.
The organogel is preferably dispersed in the reaction
mixture in an amount of at least 0.1 wt. %, preferably at least 1 wt. %,
more preferably at least 5 wt. % and most preferably at least 10 wt. %.
The amount of organogel dispersed in the reaction mixture is preferably
smaller than 40 wt. %, more preferably smaller than 30 wt. % and most
preferably smaller than 20 wt. %. These percentages are calculated on
the total weight of the polyurethane foam prepared from the reaction
mixture.
The organogel is preferably dispersed in the reaction
mixture in the form of particles having an average volume of between
0.001 and 10 mm3, which average volume is preferably larger than
0.01 mm3, more preferably larger than 0.1 mm3, and preferably smaller
than 2 mm3, more preferably smaller than 0.5 mm3. Such particle size can
be achieved by adding the organogel in a particulate form, more
particularly in a granular of powder form or it can be achieved by adding
larger pieces of gel material and by homogenizing these pieces of gel
material. This can be done in the reaction mixture itself and/or in one or
more of the components which are mixed with one another to compose
the reaction mixture.
Due to the fact that the organogel material is dispersed in
the reaction mixture, and does not dissolve entirely therein, the dispersed
particles of the organogel are incorporated in the flexible polyurethane
foam during foam expansion, more particularly in the cell ribs and/or cell
walls thereof. The organogel forms inclusions in these cell ribs and/or cell
walls. At the interface between the polyurethane material and the
organogel material, some of the reaction components of the polyurethane
material may have penetrated somewhat into the organogel material,
which may provide for an increased adhesion between both materials.
When the organogel material comprises reactive groups which may react
with one or more of the reaction components of the polyurethane
material, a chemical bond can also be achieved between both materials,
leading to a strong immobilisation of the PU gel in the PU foam.
The presence of the organogel inclusions in the cell ribs
and/or cell walls of the polyurethane foam influences the physical and/or
thermophysiological properties of the foam. They may for example
reduce the tensile stresses in the foam thus improving the pressure
distribution properties. On the other hand, they can give the foam also a
softer, gel-like feel and thus improve the comfort feeling of the foam.
They may also have an effect on the heat capacity of the foam and even
on the thermal conductivity, thus giving the foam a cooler feel. Since the
gel particles will also have some effect on the foam formation, they may
also increase the open cell content of the foam.
The presence of inclusions of another material in the
polyurethane material of the flexible foam, may also reduce some
physical foam properties such as the wet compression set. It has
however been found that the wet compression set of the foam can be
improved by the use of a polyol having a high oxyethylene unit content.
As explained already hereabove, the reaction mixture is
preferably composed by mixing at least an isocyanate component and an
isocyanate reactive component. The organogel can be dispersed in the
reaction mixture itself, in the isocyanate component and/or in the
isocyanate reactive component.
The polyisocyanate component comprises usually only one
but may comprise more than one polyisocyanate compounds (=
polyisocyanates). Organic polyisocyanates which are conventionally used
in the preparation of flexible polyurethane foams include aliphatic,
cycloaliphatic and araliphatic polyisocyanates, as well as aromatic
polyisocyanates, such as the commercial TDI (toluene diisocyanate), MDI
(diphenylmethane diisocyanate), and crude or polymeric MDI.
Polymeric MDI may contain at least 70 % by weight of pure
MDI (4,4'-isomer or isomer mixture) and up to 30 % by weight of the socalled
polymeric MDI containing from 25 to 65 % by weight of
diisocyanates, the remainder being largely polymethylene polyphenylene
polyisocyanates having isocyanate functionalities greater than 2 . Mixtures
may also be used of pure MDI and polymeric MDI compositions
containing higher proportions (up to 100 %) of the said higher
functionality polyisocyanates.
Modified isocyanates are also useful. Such isocyanates are
generally prepared through the reaction of a commercial isocyanate, for
example TDI or MDI, with a low molecular weight diol or amine. Modified
isocyanates can also be prepared through the reaction of the isocyanates
with themselves, producing isocyanates containing allophanate,
uretonimine, carbodiimide or isocyanurate linkages. Modified forms of
MDI including polyurea dispersions in MDI have for instance been
described in EP-A-0 103 996.
The isocyanate reactive com ponent may comprise
moreover one or more solid polymers, which are no organogels, stably
dispersed in this component. The production of stably dispersed
polymers within polyols to make polymer polyols is known in the art. The
basic patents in the field are US 3 383 351 and US 3 304 273. Such
compositions can be produced by polymerizing one or more ethylenically
unsaturated monomers dissolved or dispersed in a polyol in the presence
of a free radical catalyst to form a stable dispersion of polymer particles in
the polyol. These polymer polyol compositions have the valuable property
of imparting to polyurethane foams produced therefrom higher loadbearing
properties than are provided by the corresponding unmodified
polyols. Also included are the polyols like those taught in US 3 325 421
and US 4 374 209.
A wide variety of monomers may be utilized in the
preparation of the polymer polyol. Numerous ethylenically unsaturated
monomers are disclosed in the prior patents and polyurea and
polyurethane suspension polymers can also been utilized. Exemplary
monomers include styrene and its derivatives such as paramethylstyrene,
acrylates, methacrylates such as methyl methacrylate,
acrylonitrile and other nitrile derivatives such as methacrylonitrile, and the
like. Vinylidene chloride may also be employed. The preferred monomer
mixtures used to make the polymer polyol are mixtures of acrylonitrile
and styrene (SAN polyols) or acrylonitrile, styrene and vinylidene
chloride.
In order to avoid the negative influence of the organogel
particles and of the solid polymer particles on the wet compression set of
the foam, the isocyanate reactive component comprises preferably
isocyanate reactive compounds which include, per 100 parts by weight
thereof (not including the water and any organogel or any solid polymer
dispersed therein):
a) 50 to 80 parts of one or more polyoxyalkylene polyols having an
oxyethylene unit content of at least 40 wt. % of the oxyalkylene units of
the polyoxyalkylene polyol, a hydroxyl number of between 20 and 100,
preferably of between 20 and 60, and a nominal functionality of 2 to 4;
and
b) 20 to 50 parts of one or more further polyoxyalkylene polyols
containing no oxyethylene units or having an oxyethylene unit content
lower than 40 wt. % of the oxyalkylene units of the further
polyoxyalkylene polyol, and having a hydroxyl number of between 20 and
100, preferably of between 20 and 60, and a nominal functionality of 2 to
4 .
The term "nominal functionality" is used herein to indicate
the functionality (number of hydroxyl groups per molecule) of the polyol
on the assumption that the functionality of the polyoxyalkylene polyol is
equal to the functionality (= number of active hydrogen atoms per
molecule) of the initiator used in its preparation, although in practice it will
often be somewhat less because of some terminal unsaturation. When
two or more initiators are used so that a mixture of polyoxyalkylene
polyols is obtained, each of the different polyols of this mixture is to be
considered as a separate polyol (isocyanate reactive compound). The
initiator may be for example glycerine, trimethylolpropane or diethylene
triamine.
The parts and percentages mentioned in the present
specification are all by weight.
The term "hydroxyl number" indicates the number of
milligrams KOH which are equivalent to one gram of polyol sample so
that the equivalent weight of the polyol = 561 00 / hydroxyl number.
The polyoxyalkylene polyols of type a which have an
oxyethylene unit content of at least 40 wt. %, i.e. the EO rich polyol or
polyols, are preferably used in an amount of at least 55 parts, more
preferably in an amount of at least 60 parts, and most preferably in an
amount of at least 65 parts per 100 parts of the isocyanate reactive
groups containing compounds. Preferably, they are used in an amount of
less than 75 parts per 100 parts of the isocyanate reactive groups
containing compounds in view of the better mechanical properties which
can be achieved and also in view of maintaining a good processability.
The high amount of the EO rich polyol or polyols, also
increases the open cell content of the foam. An advantage of an open cell
foam is that it does not shrink after its production, and does not require a
separate crushing or reticulation step, as is usually required with the
conventional HR polyurethane foams. The EO rich polyol or polyols
preferably have an oxyethylene unit content of at least 50 wt. %, more
preferably of at least 60 wt. % and most preferably of at least 70 wt. %, of
the oxyalkylene units of the polyoxyalkylene polyol. Advantagously, the
EO rich polyol or polyols have an oxyethylene unit content of less than 90
wt. %, preferably of less than 85 wt. % and more preferably of less than
80 wt. %, of the oxyalkylene units of the polyoxyalkylene polyol.
In addition to the oxyethylene units, the oxyalkylene chains
usually comprise oxypropylene units. A portion of the ethylene oxide (in
particular less than 25% of the oxylkylene units) may be used for end
capping the oxyalkylene chains so that the polyol has a higher primary
hydroxyl content, for example a primary OH content higher than 50%. In
this way, the polyol is more reactive towards the isocyanates. The
remaining part of the oxyethylene units should be distributed over the
oxyalkylene chain and this preferably randomly.
The isocyanate reactive compounds may contain, in
addition to the EO rich polyol or polyols of type a and the further polyol or
polyols of type b (which have a lower EO content), other compounds
which have a relatively large equivalent weight, more particularly an
equivalent weight higher than 561 (=561 00/1 00). These compounds
include for example polyesters containing primary or secondary hydroxyl
groups or also polyamines. However, the isocyanate reactive compounds
preferably comprise, per 100 parts, at least 85 parts, more preferably at
least 95 parts, of the EO rich polyol or polyols of type a and of the further
polyol or polyols of type b (which are polyether polyols).
By the process according to the invention, foams can be
produced having a tear resistance, measured in accordance with ASTM
D3574 F, higher than 1 N/cm, an elongation, measured in accordance
with EN ISO 1798, higher than 100 %, and a tensile strength, measured
in accordance with EN ISO 1798 , higher than 50 kPa, preferably higher
than 70 kPa.
The preferred foaming agent for use in the process of the
invention is water, optionally in conjunction with a physical blowing agent,
for example a low boiling organofluoro compound. As is known to the
skilled person, the amount of foaming agent may be varied in order to
achieve the desired foam density. Preferably water is the only foaming
agent. The isocyanate index (NCO index) of the reaction system may
vary between 80 and 120, but is preferably higher than 90 and more
preferably higher than 100. A higher isocyanate index can assist in
achieving a higher foam hardness.
The foam formulation may contain one or more of the
additives conventional to polyurethane foam formulations. Such additives
include catalysts, for example tertiary amines and tin compounds,
surface-active agents and foam stabilisers, for example siloxaneoxyalkylene
copolymers, flame retardants, organic and inorganic fillers,
pigments, agents for suppressing the so-called boiling-foam effect such
as poly-dimethyl siloxanes, and internal mould release agents for
moulding applications.

CLAIMS

1. A process for the preparation of a flexible polyurethane
foam wherein a reaction mixture, which comprises a blowing agent, is
allowed to foam to produce the polyurethane foam, characterised in that
before allowing said reaction mixture to foam, at least one organogel
material is dispersed therein.

2 . A process according to claim 1, characterised in that said
organogel material is dispersed in the reaction mixture in an amount of at
least 0.1 wt. %, preferably at least 1 wt. %, more preferably at least 5 wt.
% and most preferably at least 10 wt. %, calculated on the total weight of
the polyurethane foam prepared from the reaction mixture.

3 . A process according to claim 1 or 2, characterised in that
said organogel material is dispersed in the reaction mixture in an amount
of less than 40 wt. %, preferably less than 30 wt. % and more preferably
less than 20 wt. %, calculated on the total weight of the polyurethane
foam prepared from the reaction mixture.

4 . A process according to any one of the claims 1 to 3,
characterised in that said organogel material is a gel selected from the
group consisting of polyurethane gels, oil extended thermoplastic block
copolymer gels, in particular SEBS gels, silicone gels and PVC plastisol
gels, and the organogel material being preferably a polyurethane gel.

5 . A process according to any one of the claims 1 to 4,
characterised in that said organogel material is dispersed in said reaction
mixture in the form of particles having an average volume of between
0.001 and 10 mm3, which average volume is preferably larger than
0.01 mm3, more preferably larger than 0.1 mm3, and preferably smaller
than 2 mm3, more preferably smaller than 0.5 mm3.

6 . A process according to any one of the claims 1 to 5,
characterised in that said reaction mixture is a polyurethane reaction
mixture composed by mixing at least an isocyanate component and an
isocyanate reactive component, at least a portion of said organogel
material being dispersed in said isocyanate reactive component before
mixing it with the isocyanate component.

7 . A process according to any one of the claims 1 to 6,
characterised in that said reaction mixture is a polyurethane reaction
mixture composed by mixing at least an isocyanate component and an
isocyanate reactive component, the isocyanate reactive component
comprising isocyanate reactive compounds including, per 100 parts by
weight thereof,
a) 50 to 80 parts of one or more polyoxyalkylene polyols having an
oxyethylene unit content of at least 40 wt. % preferably of at least 50
wt. %, more preferably of at least 60 wt. % and most preferably of at
least 70 wt. %, of the oxyalkylene units of the polyoxyalkylene polyol, a
hydroxyl number of between 20 and 100, preferably of between 20 and
60, and a nominal functionality of 2 to 4, the oxyethylene unit content
being preferably smaller than 90 wt. %, preferably smaller than 85 wt.
% and more preferably smaller than 80 wt. %, of the oxyalkylene units
of the polyoxyalkylene polyol; and
b) 20 to 50 parts of one or more further polyoxyalkylene polyols
containing no oxyethylene units or having an oxyethylene unit content
lower than 40 wt. % of the oxyalkylene units of the further
polyoxyalkylene polyol, and having a hydroxyl number of between 20
and 100, preferably of between 20 and 60, and a nominal functionality
of 2 to 4,
the isocyanate reactive compounds comprising, per 100 parts by weight
thereof, preferably at least 85 parts, and more preferably at least 95
parts, of said one or more polyoxyalkylene polyols and said one or more
further polyoxyalkylene polyols.

8 . A process according to claim 7, characterised in that the
isocyanate reactive compounds comprise, per 100 parts by weight
thereof, at least 55 parts, preferably at least 60 parts, more preferably at
least 65 parts of said one or more polyoxyalkylene polyols which have an
oxyethylene unit content of at least 40 wt. %.

9 . A process as claimed in claim 7 or 8, characterised in
that the isocyanate reactive compounds comprise, per 100 parts by
weight thereof, less than 75 parts of said one or more polyoxyalkylene
polyols which have an oxyethylene unit content of at least 40 wt. %.

10 . A flexible polyurethane foam prepared by a process
according to any one of the claims 1 to 9 .

11. A flexible polyurethane foam according to claim 10
characterised in that said organogel material is incorporated in the foam
to form at least part of the cell ribs, the organogel material forming in
particular inclusions in said cell ribs.

12 . A flexible polyurethane foam according to claim 10
characterised in that said organogel material is incorporated in the foam
to form at least part of the cell ribs and/or cell walls, the organogel
material forming in particular inclusions in said cell ribs and/or cell walls.

13 . A flexible polyurethane foam according to any one of
the claims 10 to 12, characterised in that the reaction mixture comprises
such an amount of said blowing agent that the prepared polyurethane
foam has a density of between 25 and 120 kg/m3, the density of the
prepared polyurethane foam being preferably lower than 100 kg/m3 and
more preferably lower than 80 kg/m3.

14. A flexible polyurethane foam according to any one of
the claims 10 to 13, characterised in that the prepared polyurethane foam
has a resilience, measured at 20°C in accordance with ASTM D 3574 H,
higher than 35% and preferably higher than 45%.

15 . A flexible polyurethane foam according to any one of
the claims 10 to 14, characterised in that the prepared polyurethane foam
has an ILD 40% hardness, measured in accordance with ISO 2439 B,
between 60 and 500 N, and preferably between 75 and 200 N.