Note: Descriptions are shown in the official language in which they were submitted.
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POLYOL BLEND FOR THE PREPARATION OF OPEN CELL
RIGID POLYURETHANE FOAMS
The present invention relates to a polyol blend for
the preparation of open cell rigid polyurethane foams, to
a process for preparing open cell rigid polyurethane
foams, to the polyurethane foams obtainable by this
process and to shaped articles comprising these
polyurethane foams.
In general, rigid polyurethane foams are well known
for their excellent heat insulating properties.
Particularly closed cell polyurethane foams, are widely
used as heat insulating material in e.g. pipings, storage
tanks, buildings and refrigerators. Closed cell
polyurethane foams used to be made with blowing agents
based on chlorofluorocarbons (CFC's) of which R-11
(trichlorofluoromethane) was a frequently applied
example. The heat insulating properties were for a large
part determined by the thermal conductivity of CFC gases,
which filled the cells of the foam. However, due to the
ozone depleting effect of CFC's their use has become
subject to strict environmental regulations and hence is
limited nowadays. Alternative blowing agents have been
investigated and are actually used, but is very difficult
to find substitutes for CFC as a blowing agent, which
have equally low thermal conductivity properties.
Although open cell rigid polyurethane foams have not
' 25 such excellent heat insulating properties as closed cell
rigid foams, their thermal conductivity is still
' sufficient to be useful as a heat insulating material.
Furthermore, the dimensional stability at low foam
density of open cell foams is better than that of
closed-cell foams. Open cell rigid polyurethane foams,
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accordingly, are very suitable for application as the
core material in vacuum insulation panels. Such panels
usually comprise a core material enclosed in a vacuum
container of metal and/or plastic films. Furthermore,
open cell rigid polyurethane foams can be used in those
rigid foam applications, which do not require any heat
insulating properties, but which do require some
structural support, for instance, use for automotive
headliners or packaging.
Several methods have been proposed to prepare open
cell rigid polyurethane foams. For instance, in
EP-A-0,547,515 a method for preparing open cell rigid
polyurethane foams is disclosed, wherein a polymethylene
polyphenylisocyanate prepolymer with a polyol at an
NCO/OH equivalent ratio of 1.3 to 3.0 using water as the
sole blowing agent in the presence of a catalyst, a foam
stabiliser and a cell opening agent. The cell opening
agent suitably is a divalent metal salt of a fatty acid,
such as calcium stearate, magnesium stearate, strontium
stearate or calcium myristate.
According to EP-A-0,567,027 open cell rigid
polyurethane foams are prepared by using water as a
blowing agent in combination with a specific polyol
mixture comprising two or three polyols having different
hydroxyl values, said mixture having a hydroxyl value of
160-360 mg KOH/g.
Another method is described in EP-A-0,581,191, where
an open cell rigid polyurethane foam is prepared by
reacting a polyol with a prepolymer obtained by reacting
polymethylene polyphenyl polyisocyanate with a monohydric
alcohol using a CFC-substitute as blowing agent in the
presence of a catalyst, a foam stabiliser and a cell
opening agent. The cell opening agent suitably is a
divalent metal salt of a fatty acid, such as calcium
stearate.
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In G. Burkhart and H. Schator, 35th Annual
Polyurethane Technical/Marketing Conference,
October 9-12, 1994, pp. 311-315 a method for producing
open cell rigid polyurethane foams is disclosed, wherein
the open cell structure is achieved by using a specific
anti-foaming agent (viz. Tegostab 8919; Tegostab is a
trademark) in combination with an appropriate silicone
surfactant.
. US-A-5,248,704 discloses an energy absorbing,
predominantly open-celled, rigid polyurethane foam
prepared using a polyol component which is a mixture of
hydroxyl terminated polyethers.and graft polymer
dispersions. The foam has a density of from 2.0 to
4.5 pounds per square foot, which corresponds with 32 to
288 kg/m3. In Comparative Examples 2 and 3 of
US-A-5,248,704 polyol blends are used consisting of a
rigid polyol having a hydroxyl number of 390 and a
propylene oxide adduct of propylene glycol having an
hydroxyl number of 69 and containing styrene-acrylonitril
polymer particles dispersed therein. In the comparative
examples the amounts of polymer polyo:l-and rigid polyol
are 21.56 parts by weight rigid polyo:l plus 30.81 parts
by weight polymer polyol (Comparative Example 2) and
29.29 parts by weight rigid polyol plus 41.84 parts by
weight polymer polyol (Comparative Example 3). In both
cases this corresponds with about 143 parts by weight per
100 parts by weight of the rigid polyol. The density of
the foams prepared in Comparative Examples 2 and_3 is
2.5-2.8 pounds per cubic foot or 40-45 kg/m3.
US-A-4,866,102 also discloses an energy-absorbing
rigid polyurethane foam, wherein the polyol component
used comprises a polymer polyol. One formulation
disclosed in D2 (Formulation U) comprises 35 parts by
weight of a rigid polyol having a hydroxyl number of 390,
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EP 009903453
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parts by weight a propylene oxide-ethylene oxide adduct
of glycerine having an ethylene oxide content of 75~ and
50 parts by weight of a propylene oxide adduct of
propylene glycol having an hydroxyl number of 69 and
5 containing 50~ of styrene-acrylonitril polymer particles
dispersed therein. The amount of polymer polyol, thus,
corresponds with 143 parts by weight per 100 parts by
weight of rigid polyol. The density of the foam prepared
from this formulation (Example 45) is 1.58 pounds per
cubic foot or 25.3 kg/m3. .
Although these methods are effective in producing
open cell rigid polyurethane foams, there is still room
for improvement. It would be beneficial if open cell
rigid polyurethane foams could be provided having a very
low density in combination with good mechanical or
structural stability, as such low density foams are
attractive for use in a wide variety of applications
including the application as heat insulating material.
The low density is especially desired, because the low
weight of the foam facilitates transportation and
handling of e.g. insulation panels. Moreover, a lower
density also means that less starting material is
necessary to prepare the same volume of foam as compared
to the situation in which a higher density foam is to be
prepared. Clearly this is advantageous from an economic
perspective. Furthermore, it would be attractive if low
density open cell rigid foams could be prepared without
needing any cell-opener or anti-foaming agent, thus
facilitating the manufacture whilst still obtaining
excellent foams.
Accordingly, the present invention relates to a
polyol blend comprising:
(a) a polyol component having an average hydroxyl value
of 150 to 850 mg KOH/g and
(b) a polymer polyol comprising a polymer stably
MCS26/TS6602PCT
AMENDED SHEET
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dispersed in a base polyol medium, which base polyol
medium has an average primary hydroxyl content of less
than 20~.
Essentially, the present invention combines a rigid
polyol component (component (a)) with a particular
polymer polyol (component (b)), which is normally used in
the manufacture of flexible polyurethane foams. This
specific combination of polyols has been found to result
in open cell rigid foams having excellent properties
without the need to apply cell-opening agents or anti-
foaming agents.
The quantities in which the polyol and the polymer
polyol are used may vary within broad limits, but
preferably the polyol blend according to the present
invention comprises 2 to 25 parts by weight, more
preferably 2 to 10 parts by weight, of polymer polyol (b)
per 100 parts by weight of polyol component (a).
The polyol component (a) can be any rigid polyol or
combination of rigid polyols having an average hydroxyl
value of 150 to 850 mg KOH/g. Such rigid polyols are
known in the art. Commonly applied rigid polyols, which
can be suitably applied in the polyol blend of the
present invention, are polyoxyalkylene polyols have a
nominal molecular weight of from 300 to 1500, suitably
500 to 1000, and a nominal average functionality of at
least 2.0, suitably from 2.5 to 6. For the purpose of the
present invention the average hydroxyl number preferably
has a value in the range of from 150 to 650 mg KOH/g. The
polyol component (a) may comprise a single rigid polyol,
but may also comprise two or more rigid poiyols. In a
preferred embodiment the polyol component (a) comprises a
polyol having a hydroxyl value of 150 to 400 mg KOH/g and
a polyol having a hydroxyl value of 900 to 650 mg KOH/g.
An example of a rigid polyol having a lower hydroxyl
value is CARADOL GB250-O1, while examples of rigid
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polyols having a higher hydroxyl value are
CARADOL LP530-03 and CARADOL LP585-Ol (CARADOL is a
trademark) .
The polymer polyol used as component (b) may in
~ 5 principle be any polymer polyol comprising a polymer
stably dispersed in a base polyol medium, provided the
base polyol medium has an average primary hydroxyl
content of less than 20°s based on the total of hydroxyl
groups present on the polyol(s) forming the base polyol
medium. Accordingly, the base polyol medium may consist
of one or more polyols provided the average primary
hydroxyl content of these polyol(s) is less than 20~,
preferably less than 10$ and most preferably less than
5~. The polymer polyol component (b) suitably comprises
such a base polyol medium and a polymer stably dispersed
therein in an amount of 5 to 40~ by weight based on total
weight of polymer polyol. In a further preferred
embodiment the base polyol medium consists of a
polyoxyalkylene polyol having a molecular weight in the
range of from 250 to 12,000, preferably from 500 to
6,500, more preferably from 2,500 to 6,000; an average
nominal functionality (Fn) of at least 2.0, more
preferably from 2.5 to 6.0 and most preferably from 2.5
to 3.5; and a primary hydroxyl content of at most 10~,
more preferably at most 50. Since the base polyol medium
most preferably has a very low average primary hydroxyl
content, very good base polyols are those having a very
low ethylene oxide (EO) content resulting from EO
tipping. Suitably, the ethylene oxide content resulting
,' 30 from ethylene oxide tipping is less than 1°s by weight,
while most suitably the polyol has not been tipped with
EO at all.
The polymer, which is stably dispersed in the base
polyol medium, may in principle be any such polymer known
to be applicable for this purpose. Thus, suitable
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polymers include the polymers based on ethylenically
unsaturated monomers and particularly polymers of vinyl
aromatic hydrocarbons, like styrene, alpha-methyl
styrene, methyl styrene and various other alkyl-
s substituted styrenes. Of these, the use of styrene is
preferred. The vinyl aromatic monomer may be used alone
or in combination with other ethylenically unsaturated
monomers, such as acrylonitrile, methacrylonitrile,
vinylidene chloride, various acrylates and conjugated
dimes like 1,3-butadiene and isoprene. Preferred
polymers, however, are polystyrene and styrene-
acrylonitrile (SAN) copolymers. Another suitable class of
polymers are the polyurea and polyurethane polymers.
Particularly the condensation products of polyhydric
alcohol amines and aromatic diisocyanates are very useful
in this respect. A very much preferred polymer is the
condensation product of triethanol amine and toluene
diisocyanate (TDI). For the purpose of the present
invention it is preferred that the dispersed polymer is
polystyrene, SAN copolymer, polyurea or the polyurethane
polymer obtained as the condensation product of
triethanolamine and toluene diisocyanate.
The dispersed polymer is suitably present in an
amount of from 5 to 40o by weight based on total weight
of polymer polyol. In case the polymer is polystyrene or
SAN polymer, preferred amounts are between 5 and 35o by
weight, whilst in case of polyurea polyurethane polymers
the preferred amount of polymer is between 5 and 20s by
weight.
The polyol blend according to the present invention
is very suitable for the preparation of open cell rigid
polyurethane foams. Thus, the present invention also
relates to a process for the preparation of open cell
rigid polyurethane foams, which process comprises
reacting the polyol blend described herein before with a
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polyisocyanate component in the presence of at least a
catalyst, a foam stabilising agent and a blowing agent.
Polyisocyanates that may be used are those
conventionally applied in the production of rigid
polyurethane foams. Useful polyisocyanates should contain
at least two isocyanate groups and include both aliphatic
-usually alkylene- and aromatic di-, tri-, tetra- and
higher isocyanates known in the art to be suitably
applied in the production of rigid polyurethane foams.
Mixtures of two or more of such aliphatic and/or aromatic
polyisocyanates may also be applied. Examples of suitable
polyisocyanates, then, include 2,4-toluene diisocyanate
(2,4-TDI), 2,6-TDI, mixtures of 2,4-TDI and 2,6-TDI,
1,5-naphthene diisocyanate, 2,4-methoxyphenyl
diisocyanate, 9,4'-diphenylmethane diisocyanate (MDI);
4,4'-biphenylene diisocyanate, 3,3'-dimethoxy-4,4'-bi-
phenylene diisocyanate, 3,3'-dimethyl-4,9'-biphenylene
diisocyanate and 3,3'-dimethyl-4,4'-diphenylmethane
diisocyanate, 4,4',4"-triphenylmethane triisocyanate,
2,4,6-toluene triisocyanate, 9,4'-dimethyl-2,2',
5,5'-diphenylmethane tetraisocyanate, polymethylene-
polyphenylene polyisocyanate and mixtures of two or more
of these. Polymeric MDI, a mixture of polyisocyanates
with MDI as the main component, may also be used. For the
purpose of the present invention it has been found
particularly advantageous to use polymeric MDI.
The quantity of polyisocyanate component to be used
should suitably be such that the isocyanate index has a
value between 50 and 150, most suitably between 80 and
130. However, isocyanate indices outside these ranges may
also be used.
Catalysts for the production of rigid polyurethane
foams are known in the art and include many different
compounds. For the purpose of the present invention
suitable catalysts include tertiary amines, such as, for
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instance, bis(2,2'-dimethylamino)ethyl ether,
trimethylamine, triethylamine, triethylenediamine and
dimethylethanolamine (DMEA). Tin-based catalysts may also
be applied and include tin salts and dialkyl tin salts of
carboxylic acids. Specific examples are dibutyltin
dilaureate, stannous octoate, stannous oleate, dibutyltin
acetate and dibutyltin diacetate. Also trimerisation
catalysts like potassium acetate may be applied. The
catalyst is typically used in an amount of from 0.01 to
7 php (parts by weight per 100 parts of polyol).
The foam stabiliser (or surfactant) used in the
present process may be any polyurethane foam stabiliser
useful in the production of rigid polyurethane foams.
Organosilicone or organopolysiloxane surfactants are most
conventionally applied as foam stabilisers in
polyurethane production. A large variety of such
surfactants is commercially available. Usually, such foam
stabiliser is used in an amount of up to 3 php.
A blowing agent is also present in the process
according to the present invention. Suitable blowing
agents include water, aceton, (liquid) carbon dioxide,
halogenated hydrocarbons, aliphatic alkanes, such as n-
pentane and isopentane, and alicyclic alKanes, such as
cyclopentane and cyclohexane. It will be understood that
these blowing agents may be used singly or in mixtures of
two or more. For the purpose of the present invention, it
has been found particularly advantageous to use water as
the sole blowing agent. The amount in which the water is
used may vary between wide limits, but very good results ,
have been achieved when using water in an amount of
2-12 php.
In addition, other well known auxiliaries, such as
flame retardants, antioxidants, colouring agents and
fillers may also be used.
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PCT/EP99/03453
In a further aspect the present invention relates to
an open cell rigid polyurethane foam obtainable by the
process described herein before, which polyurethane foam
has a density of less than 50 kg/m3 and a closed cell
content of less than 100, preferably of less than 5%.
Preferred foams, which are obtainable by the present
process, have densities of 10 to 30 kg/m3, more
preferably 10 to 25 kg/m3.
The present invention also relates to shaped articles
comprising the open cell rigid polyurethane foam defined
in the preceding paragraph as well as t:o heat insulating
materials comprising this open celled rigid polyurethane
foam in a laminate structure.
The invention is further illustrated by the following
examples, but is by no means limited to the specific
embodiments demonstrated therein.
The components used in the examples are:
Polyol components
Polyol A: A rigid, aromatic, amine-group containing,
propylene oxide(PO)-based polyether polyol
having a hydroxyl value of 530 mg KOH/g.
Polyol B: A rigid, glycerol initiated polyether polyol
having a hydroxyl value of 250 mg KOH/g.
pp-A: A polymer polyol containing ii) a base polyol
being a EO/PO based, glycerol initiated
polyether polyol having a primary hydroxyl
content of essentially Oa, a molecular weight
of 3500 and a hydroxyl value of 37 mg KOH/g
and (ii) stably dispersed therein 20 wt~
polystyrene.
pp-B: A polymer polyol containing (i) the same base
polyol as PP-A, and (ii) stably dispersed
therein 40 wt°s styrene-acrylonitrile
copolymer.
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PP-C: A polymer polyol containing (i) a base polyol
being a EO/PO based, glycerol initiated
polyether polyol having a primary hydroxyl
content of 800, a molecular weight of 4700
and a hydroxyl value of 25 mg KOH/g and '
containing 19 wt°s EO-tip and (ii) stably
dispersed therein 28 wt% polystyrene.
PP-D: A polymer polyol containing (i) the same base
polyol as PP-C, and (ii) stably dispersed
therein 15 wto styrene-acrylonitrile
copolymer.
Ancillary chemicals
DMEA . Dimethylethanolamine
AM58 . trimerisation catalyst ex Resina Chemie
TCPP . tris(chloropropyl)phosphate (flame retardant)
B8404 . Tegostab B8404 (silicone surfactant) ex
Goldschmidt
Isocyanate
MDI . polymeric diphenylmethane diisocyanate
Example 1
A polyol formulation was prepared consisting of
parts by weight (pbw) Polyol A, 70 pbw Polyol B and
10 pbw of PP-A. Subsequently a foaming formulation (Ex-1)
was prepared having a composition as indicated in
25 Table I.
The formulation was allowed to foam in a bag. After
foaming a sample of the foam was taken and density and
closed cell content were determined.
Example 2
30 Example 1 was repeated except that 10 pbw of PP-B
were added (Ex-2) in stead of PP-A.
The composition of the foaming formulation and the
properties of the resulting foam are indicated in
Table I.
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Comparative Examples 1 and 2
Example 1 was repeated except that 10 pbw of PP-C
(CEx-1) or 10 pbw of PP-D (CEx-2) were used in stead of
IO pbw of PP-A.
- 5 The composition of the.foaming formulations and the
properties of the resulting foam are indicated in
Table I.
TABLE I Foaming formulations
Ex-1 Ex-2 CEx-1 CEx-2
Polyol A (pbw) 70 70 70 70
Polyol B (pbw) 30 30 30 30
PP-A (pbw) 10 - - -
PP-B (pbw) - 10 - -
PP-C (pbw) - - 10 -
PP-D (pbw) _ _ - 10
DMEA (pbw) 2.4 2.4 2.9 2.4
AM58 (pbw) 1.6 1.6 1.6 1.6
B8904 (pbw) 2.0 2.0 2.0 2.0
water (pbw) 10.2 10.2 10.2 10.2
TCPP (pbw) 10 10 10 10
MDI (pbw) 208 208 208 208
Isocyanate index 90 90 90 90
Density (kg/m3) 16.8 16.6 17.52 17.5
Closed cell content (%) 2 3 42 60
From Table I it can be seen that the polyol
formulation according to the present invention result in
foams having a slightly lower density and a much lower
closed cell content.
Example 3
A laminate with a open cell polyurethane foam
prepared with a polyol blend according to the present
invention, was made on a continuous laminator machine.
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The laminator machine is a high pressure, multi-
component unit, manufactured by Cannon/Viking UK. The
urethane system, being a blend of four different streams,
was dispensed on the bottom facing through a perforated
pipe, fitted to a traversing mixing head. As the facing,
polyethylene coated kraft paper was used. The machine
output was adjusted to produce 60 mm thick, 600 mm wide
laminates at an overall target density of 22 kg/m3 at a
belt speed of 2.9 m/min. The 6 meter conveyor section was
working in free rise mode.
As stated above, four streams (denoted as "polyol
blend" , "cat 1 blend" , "cat 2 blend" and "MDI" ) are
pumped into the mixing head, where they are thoroughly
mixed and dispensed onto the facing. The MDI stream
consisted of polymeric MDI. The compositions of the other
three streams are indicated in Table II. The amounts are
indicated in parts by weight (pbw).
TABLE II Feed stream compositions
polyol blend cat 1 blend cat 2 blend
Polyol A 30 - -
Polyol B 56.2 15 10
PP-A 10 - -
TCPP 10 - -
B8404 2 - -
DMEA - - 6
AM58 - - 4
water - 15 -
The stream rates were:
Output polyol blend 0.84 1/min
:
Output MDI . 1.08 1/min
Output cat 1 blend 0.136 1/min
.
Output cat 2 blend 0.033 1/min
.
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The temperature of both polyol blend and MDI stream
was 19 C, the temperature of the belt was kept at 35 C.
The properties of the open cel l rigid foam-based
laminate were:
Density . 22 kg/m3
Closed cell content . 2$
Compressive strength
in rise direction . 80 kPa
in production direction . 55 kPa
in side direction . 55 kPa
Dimensional stability at 70 C at 95$ relative humidity
h
2
ours
4
after
in rise direction . 3.5~
in production direction . -0.5~
in side direction . -0.7~
Thermal conductivity at 10 C . 35 mW/(m.K)
Thermal conductivity at 10 C was determined by
putting the laminate between two plates,
one having a
temperature of 0 C and the other having a temperature
of
20 C, and determining the amount of heat transferred
through the laminate from the warm
plate to the cold
plate per second per meter of lami nate per degree Kelvin
temperature difference.
From these data it can be seen that the laminate has
~ a relatively low density and a low closed cell content,
while at the same time exhibiting excellent mechanical
stability and low thermal conducti vity, thus making it
very useful as an insulating mater ial.
