Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Fine cell, water-blown rigid uolyurethane foams
The invention relates to a process for the production of water-blown, fine
cell rigid
foams containing urethane groups and/or isocyanurate groups by the reaction of
polyisocyanates with a polyol component in the form of an emulsion. The
invention
also relates to open-cell polyurethane foams which are foamable in the mould.
According to prior art, rigid polyurethane foams are produced from polyols
having on
average at least three hydroxyl groups per molecule, from isocyanates which
are at least
difunctional, catalysts, blowing agents and polysiloxane-polyoxyalkylene block
mixed
polymers and optionally the conventional additives.
A summary of the prior art, the raw materials used and the relevant processes
may be
found in G. Oertel (Ed.): "Kunststoffhandbuch", Volume VII, C. Hanser Verlag,
Munich, 1983, in Houben-Weyl: "Methoden der organischen Chemie", Volume E20,
Thieme Verlag, Stuttgart, 1987, pp. 1561 to 1757, and in "Ullmann's
Encyclopedia of
Industrial Chemistry", Vol. A21, VCH, Weinheim, 4th Edition,1992, pp. 665 to
715.
In general, polyether polyols or polyester polyols or mixtures of these are
used; there
are on average at least three hydroxyl groups per molecule in the polyol
mixture used
and the hydroxyl value of the polyol mixture used is between 100 and 900.
The rigid polyurethane foams formed are for the most part predominantly closed-
cell.
Their bulk densities are between 5 and 950 kgnri 3, mostly between 10 and 350
kgnri 3,
with bulk densities of between 20 and 70 kg~rri 3 being used particularly
frequently.
Recent developments in the field of rigid polyurethane foams are related to
the
specifically controlled production of predominantly open-cell polyurethane- or
polyisocyanurate-modified rigid polyurethane foams which are used as
insulating
materials for example in vacuum panels. When the above-mentioned open-cell
rigid
foams are to be used in vacuum panels, a cell diameter as small as possible is
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particularly important, as it determines the efficiency of the insulation. The
smaller the
cell diameter, the less evacuation is necessary in order to achieve a specific
insulating
effect. The average cell diameter of the water-blown rigid polyurethane foams
obtained
by prior art is generally greater than 150 Eun; foams having such a cell
diameter are
generally unsuitable for vacuum applications.
The production of open-cell rigid polyurethane foams is in principle known.
Thus
US-A 5 350 777 describes the use of alkaline-earth salts of long-chain fatty
acids as
cell openers.
EP-A 498 628 describes the production of open-cell rigid foams by the usage of
a
thermally activated blowing agent. The disadvantage of this process is that
the cells of
the foam can be opened only when a minimum temperature is exceeded in the
course of
the foaming process, so that the resulting foams do not have a uniform
proportion of
open cells throughout the volume filled with the foam.
DE-A 43 03 809 discloses a process for the production of rigid foams having an
increased proportion of open cells which utilises the cell-opening properties
of a liquid
polyolefin additive. This process has the disadvantage of a narrow field of
application
and the further disadvantage that the cells coarsen rapidly as the amount of
polyolefin
additive is increased.
In US-A 5 250 579 and US-A 5 312 846, cell-opening substances having a surface
tension of less than 23 mJ~m z are disclosed. These have the disadvantage that
they
contain organically bound halogen.
The objective of the present invention was to find a process for the
production of water-
blown, fine cell and optionally open-cell rigid polyurethane foams, wherein
the rigid
polyurethane foams according to the invention retain the required final
properties
- open cell and fine cells content - even during a foaming in the mould.
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It has been found that fine cell and optionally open-cell rigid polyurethane
foams are
obtained when a polyisocyanate is foamed with a water-containing polyol
formulation
in the form of an emulsion.
The invention accordingly provides a process for the production of fine cell
rigid
polyurethane and/or polyisocyanurate foams by the reaction of
A) a polyisocyanate having an NCO content of 20 to 48 wt.% with
B) a polyol component in the form of an emulsion, having on average at least
two
groups which are reactive with isocyanate and containing
1 ) at least one at least difiznctional polyol,
2) water,
3) catalyst,
4) optionally auxiliary substances and additives.
The invention also provides a polyurethane or polyisocyanurate foam produced
in the
mould having an open cells content, measured in accordance with DIN ISO 4590-
92, of
>85%, preferably >90%, with an overpacking of >3%, based on the minimum amount
of filling. This foam can be produced by the process according to the
invention.
Polyol formulations according to the invention contain at least one polymer
which is
immiscible with water, possesses at least one functional group which is
reactive with
isocy~ate and contains hydrogen atoms, and has a number average molecular
weight
of 150 to 12,500 g/mol, preferably 200 to 1500 g/mol. Examples of this are:
trigly-
cerides, for example, castor oil, or castor oil modified by
transesterification/amidation
reactions with monohydric or polyhydric alcohols or amines, or fatty acids
such as
stearic acid, oleic acid, linoleic acid or ricinoleic acid. The polyol
formulation contains
5 to 99 parts by weight, preferably 20 to 80 parts by weight, of this
component. The
polymer which is immiscible with water is preferably an at least difimctional
polyol.
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In order to have the functionality necessary for the foaming, the polyol
formulations
according to the invention contain at least one polyol which has at least two
hydrogen
atoms which are reactive with isocyanates and a number average molecular
weight of
150 to 12,500 g/mol, preferably 200 to 1500 g/mol. Such polyols can be
obtained by
polyaddition of alkylene oxides such as, for example, ethylene oxide,
propylene oxide,
butylene oxide, dodecyl oxide or styrene oxide, preferably propylene oxide or
ethylene
oxide, to starter compounds such as water or polyhydric alcohols such as
sucrose,
sorbitol, pentaerythritol, trimethylolpropane, glycerol, propylene glycol,
ethylene
glycol, diethylene glycol as well as mixtures of the above-mentioned starter
compounds. The starter compound used may also be ammonia, or compounds having
at least one primary, secondary or tertiary amino group, for example,
aliphatic amines
such as ethylenediamine, oligomers of ethylenediamine (for example, diethylene-
triamine, triethylenetetramine or pentaethylenehexamine), ethanolamine,
diethanol-
amine, triethanolamine, N-methyl- or N-ethyldiethanolamine, 1,3-
propylenediamine,
1,3- or 1,4-butylenediarnine, 1,2-hexamethylenediamine, 1;3-
hexamethylenediamine,
1,4-hexamethylenediamine, 1,5-hexamethylenediamine or 1,6-
hexamethylenediamine,
aromatic amines such as phenylenediamines, tolylenediamines (2,3-
tolylenediamine,
3,4-tolylenediamine, 2,4-tolylenediamine, 2,5-tolylenediamine, 2,6-
tolylenediamine or
mixtures of the above-mentioned isomers), 2,2'-diaminodiphenyhnethane, 2,4'-
diaminodiphenyhnethane, 4,4'-diaminodiphenylmethane or mixtures of these
isomers.
The polyol formulation contains 0 to 95 parts by weight, preferably 10 to 40
parts by
weight, of this component.
Polyol formulations according to the invention can also contain polyester
polyols
having a number average molecular weight of 100 to 30,000 g/mol, preferably
150 to
10,000 g/rnol, particularly preferably 200 to 600 g/mol, which can be prepared
from
aromatic and/or aliphatic dicarboxylic acids and polyols having at least two
hydroxyl
groups. Examples of dicarboxylic acids are phthalic acid, fumaric acid,
malefic acid,
azelaic acid, glutaric acid, adipic acid, suberic acid, terephthalic acid,
isophthalic acid,
decanedicarboxylic acid, malonic acid, glutaric acid and succinic acid.
Individual
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dicarboxylic acids or any mixtures of different dicarboxylic acids can be
used. Instead
of the free dicarboxylic acids, the corresponding dicarboxylic acid
derivatives such as,
for example, dicarboxylic mono- or diesters of alcohols having one to four
carbon
atoms, or dicarboxylic anhydrides, can also be used. The following are
preferably used
as alcohol component for the esterification: ethylene glycol, diethylene
glycol,
triethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-propanediol,
1,4-butane-
diol, 1,5-pentanediol, 1,6-hexanediol, 1,10-decanediol, glycerol,
trimethylolpropane, or
mixtures of these. The polyol formulations according to the invention can also
contain
polyether esters, which are obtained, for example, as described in EP-A 250
967, by
reaction of phthalic anhydride with diethylene glycol and subsequently with
ethylene
oxide. The polyol formulation can contain 0 to 90 parts by weight, preferably
5 to 30
parts by weight, of polyester polyol.
The polyol formulations according to the invention also contain at least one
catalyst in
quantities of 0 to 10 parts by weight, preferably 0.5 to 5 parts by weight.
The
conventional catalysts of polyurethane chemistry can be used according to the
invention. Examples of such catalysts are: triethylenediamine, N,N-
dimethylcyclohe-
xylamine, tetramethylenediamine, 1-methyl-4-dimethylaminoethylpiperazine,
triethyl-
amine, tributylamine, dimethylbenzylamine, N,N',N"-tris(dimethylaminopropyl)-
hexahydrotriazine, dimethylaminopropylformamide, N,N,N,N'-tetramethylethylene-
diamine, N,N,N,N'-tetramethylbutanediamine, tetramethylhexanediamine,
pentameth-
yldiethylenetriamine, tetramethyl diaminoethyl ether, dimethylpiperazine, 1,2-
dimethylimidazole, 1-azabicyclo[3.3.0]octane, bis(dimethylaminopropyl)urea, N-
methylinorpholine, N-ethylinorpholine, N-cyclohexylmorpholine, 2,3-dimethyl-
3,4,5,6-tetrahydropyrimidine, triethanolamine, diethanolamine,
triisopropanolamine, N-
methyldiethanolamine, N-ethyldiethanolamine, dimethylethanolamine, tin(II)
acetate,
tin(11) octanoate, tin(II) ethylhexanoate, tin(Il7 laurate, dibutyltin
diacetate, dibutyltin
dilaurate, dibutyltin maleate, dioctyltin diacetate, tris(N,N-
dimethylaminopropyl)-s-
hexahydrotriazine, tetramethylammonium hydroxide, potassium acetate, sodium
acetate, sodium hydroxide or mixtures of these or similar catalysts.
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According to the invention, ionic and non-ionic emulsifiers can also be used
in
quantities of 0 to 10 parts by weight, preferably 0.5 to 2 parts by weight.
Such
emulsifiers are described, for example, in "Rompp Chemie Lexikon", Volume 2,
Thieme Verlag, Stuttgart, 9th Edition, 1991, p. 1156 ff.
The polyol component according to the invention contains 0.1 to 10 parts by
weight,
preferably 0.5 to 5 parts by weight, of water.
It is essential for the process according to the invention that the polyol
component be
used in the form of an emulsion. This means that at least one of the
components of the
polyol component must not be miscible with the rest of the formulation; i.e.
as a rule,
that at least one compound is included which is neither water-soluble nor
miscible with
water and which optionally has hydrogen atoms which are reactive with
isocyanate. It
has been found that the use of a polyol component in the form of an emulsion
results in
foams having a considerably greater cell fineness.
Aromatic polyisocyanates of the type described in Justus Liebigs Annalen der
Chemie,
562 (1949) 75 can be used as the isocyanate component, for example those
corresponding to the formula
Q(NCO)n,
wherein
n can have values of 2 to 4, preferably 2, and
Q denotes an aliphatic hydrocarbon group having 2 to 18, preferably 6 to 10
carbon atoms, a cycloaliphatic hydrocarbon group having 4 to 15, preferably 5
to 10 carbon atoms, an aromatic hydrocarbon group having 8 to 15, preferably 8
to 13 carbon atoms.
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Polyisocyanates of the type described in DE-OS 28 32 253 are particularly
preferred.
As a rule the technically readily accessible polyisocyanates are particularly
preferred,
for example, tolylene 2,4- and 2,6-diisocyanate and any mixtures of these
isomers
("TDI"), polyphenyl polymethylene polyisocyanates, which are prepared by
aniline-
s formaldehyde condensation and subsequent phosgenation ("crude MDI") and
polyisocyanates containing carbodiimide groups, urethane groups, allophanate
groups,
isocyanurate groups, urea groups or biuret groups ("modified
polyisocyanates"), in
particular modified polyisocyanates which are derived from tolylene 2,4- and
2,6-
diisocyanate or from diphenylinethane 4,4'- and/or 2,4'-diisocyanate.
Prepolymers of the above-mentioned isocyanates and of organic compounds having
at
least one hydroxyl group can also be used. By way of example, one may mention
polyols or polyesters having one to four hydroxyl groups and (number average)
molecular weights of 60 to 1,400.
Other substances which may be used concomitantly are paraffins or fatty
alcohols or
dimethylpolysiloxanes and pigments or dyes, also stabilisers against ageing
and
weathering influences, plasticisers and fungistatic and bacteriostatic
substances as well
as fillers such as barium sulphate, kieselguhr, carbon black or prepared
chalk. These are
mostly added to the polyol component in quantities of 0 to 10 parts by weight,
preferably 0 to 5 parts by weight.
Further examples of optionally used surface-active additives and foam
stabilisers as
well as cell regulators, reaction inhibitors, stabilisers, flame retardants,
dyes and fillers,
as well as fungistatic and bacteriostatic substances, together with details of
the method
of use and mode of action of these additives are given in Vieweg/Hochtlen
(Eds.):
"Kunststoff Handbuch", Volume VII, Carl Hanser Verlag, Munich 1966, pages 121
to
205, and G. Oertel (Ed.): "Kunststoffhandbuch", Volume VII, Carl Hanser
Verlag, 2nd
Edition, Munich, 1983.
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The polyurethane or polyisocyanurate foams produced in the mould according to
the
invention have a proportion of open cells, measured in accordance with DIN ISO
4590-
92, of >85%, preferably >90%, and a degree of compression of >3%, based on the
minimum amount of filling. The minimum amount of filling of a moulding is the
amount of finally reacted rigid polyurethane foam necessary to just fill the
mould.
The invention also provides the use of the rigid foams according to the
invention as an
intermediate layer for composite elements, as filling substrates for vacuum
insulating
panels and for the foaming of cavities of cold stores as well as in the
construction of
containers.
The process according to the invention is preferably used for the foaming of
cavities of
refiigeration and freezing equipment. It can also be used in the heat
insulation, for
example, of hot-water tanks or long-distance heating pipes. Foams can, of
course, also
be produced by block foaming or by the known per se double transport process
(see
"Kunststoffhandbuch", Volume 7: Polyurethane, Carl Hanser Verlag, Munich,
Vienna,
3rd Edition, 1993, p. 148).
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Eaamules
Polyol A: polyethylene oxide polyether (M" = 300) based on trimethylolpropane
Polyol B: polyether ester (Mn = 375) based on phthalic anhydride, diethylene
glycol and ethylene oxide
Polyol C: Castor oil [from the firm Alberding + Boley, Krefeld]
Isocyanate: polyphenyl polymethylene polyisocyanate, NCO content 31.5 wt.%
(Desmodur~ 44V20, Bayer AG)
Stabiliser: silicone stabiliser (Tegostab B 8404, Th. Goldschmidt AG, Essen)
Emulsifier: sodium sulfate salt of an ethoxylated fatty acid alcohol, 30 wt.%
in
water (from the firm Servo, NL-Delden)
Catalyst l: dimethylcyclohexylarnine
Catalyst 2: potassium acetate (25 wt.% in diethylene glycol)
The foaming was carried out in high-pressure machine HK 165 from the firm
Hennecke. In each case two test pieces were produced:
Test piece 1: freely foamed block having the dimensions 50 x 50 x 40 cm3
Test piece 2: foamed in a mould; dimensions of test piece
9 x 40 x 70 cm3; degree of compression 8%
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Ezamnle 1 (according to the invention)
100 parts by weight of a mixture of 92 parts by weight polyol C, 2.5 parts by
weight
catalyst 1, 1 part by weight catalyst 2, 2.5 parts by weight water and 2 parts
by weight
stabiliser was reacted with 145 parts by weight of isocyanate. The polyol
mixture was a
white emulsion.
Test piece 1: bulk density 52 kg/m3;
proportion of open cells (DIN ISO 4590-92): 95%
cell size from micrograph (using light microscopy): 100 pm
Test piece 2: bulk density 75 kg/m3;
proportion of open cells (DIN ISO 4590-92): 93%
cell size from micrograph (using light microscopy): 90 Eun
Ezamnle 2 (accordins to the invention)
100 parts by weight of a mixture of 19.2 parts by weight polyol A, 19.7 parts
by weight
polyol B, 57.7 parts by weight polyol C, 0.8 parts by weight catalyst 1, 0.9
parts by
weight catalyst 2, 3.6 parts by weight emulsifier, 0.9 parts by weight water
and 1.4
parts by weight stabiliser was reacted with 127 parts by weight of isocyanate.
The
polyol mixture was a white emulsion.
Test piece 1: bulk density 46 kg/m3;
proportion of open cells (DIN ISO 4590-92): 98%
cell size from micmgraph (using light microscopy): 90 pxn
Test piece 2: bulk density 69 kg/m3;
proportion of open cells (DIN ISO 4590-92): 96%
cell size from micrograph (using light microscopy): 80 E.irn
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Example 3 (Comuarison Ezamnlel
100 parts by weight of a mixture of 46.3 parts by weight polyol A, 46.3 parts
by weight
polyol B, 2.5 parts by weight catalyst 1, 1 part by weight catalyst 2, 2 parts
by weight
water and 2 parts by weight stabiliser was reacted with 127 parts by weight of
isocyanate. The polyol mixture was a clear solution.
Test piece 1: bulk density 46 kg/m3;
proportion of open cells (DIN ISO 4590-92): 9%
cell size from micrograph (using light microscopy): 160 p.m
Test piece 2: bulk density 69 kg/m3;
proportion of open cells (DIN ISO 4590-92): 9%
cell size from micrograph (using light microscopy): 150 p,m
The Examples show that rigid foams of a particular cell fineness are obtained
by using
polyol emulsions.
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