U.S. patent application number 10/180036 was filed with the patent office on 2003-04-03 for process for rigid polyurethane foams.
This patent application is currently assigned to Imperial Chemical Industries PLC. Invention is credited to Hamilton, Alan James.
Application Number | 20030065046 10/180036 |
Document ID | / |
Family ID | 8231702 |
Filed Date | 2003-04-03 |
United States Patent
Application |
20030065046 |
Kind Code |
A1 |
Hamilton, Alan James |
April 3, 2003 |
Process for rigid polyurethane foams
Abstract
Process for the preparation of open celled rigid polyurethane or
urethane-modified polyisocyanurate foams by reaction of a
polyfunctional isocyanate-reactive composition with a
polyisocyanate composition comprising a prepolymer of NCO-value
21-30% based on a high molecular weight oxyethylene-containing
polyol.
Inventors: |
Hamilton, Alan James;
(Leefdaal, BE) |
Correspondence
Address: |
Intellectual Property Group
Pillsbury Winthrop LLP
1600 Tysons Boulevard
McLean
VA
22102
US
|
Assignee: |
Imperial Chemical Industries
PLC
London
GB
|
Family ID: |
8231702 |
Appl. No.: |
10/180036 |
Filed: |
June 27, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10180036 |
Jun 27, 2002 |
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09280479 |
Mar 30, 1999 |
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6433032 |
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Current U.S.
Class: |
521/159 |
Current CPC
Class: |
C08J 9/0028 20130101;
Y10T 428/239 20150115; C08J 2205/10 20130101; C08G 18/10 20130101;
C08G 2330/50 20130101; C08G 2110/0025 20210101; C08J 2375/04
20130101; Y10T 428/231 20150115; C08G 18/3848 20130101; C08J
2205/05 20130101; Y10T 428/233 20150115; Y10T 428/249987 20150401;
Y10T 428/249984 20150401; C08G 18/10 20130101; C08G 18/3848
20130101 |
Class at
Publication: |
521/159 |
International
Class: |
C08G 018/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 2, 1998 |
EP |
98106031.2 |
Claims
1. Process for the preparation of an open-celled (semi-)rigid
polyurethane or urethane-modified polyisocyanurate foam by reaction
of a polyisocyanate composition with a polyfunctional
isocyanate-reactive composition under foam-forming conditions,
characterised in that the polyisocyanate composition has a free
NCO-value of 21 to 30% by weight and comprises the reaction product
of a stoichiometric excess of an organic polyisocyanate and an
isocyanate-reactive material comprising a polyether polyol having a
number average molecular weight between 1000 and 10000 and an
average nominal hydroxyl functionality of from 2 to 6 and
containing from 10 to 50% by weight of oxyethylene units.
2. Process according to claim 1 wherein the free NCO-value of the
polyisocyanate composition is between 23 and 29 wt %.
3. Process according to claim 2 wherein the free NCO-value of the
polyisocyanate composition is between 24 and 26 wt %.
4. Process according to any one of the preceding claims wherein the
polyether polyol has a number average molecular weight between 1000
and 6000.
5. Process according to any one of the preceding claims wherein the
polyether polyol has an average nominal hydroxyl functionality of
from 2 to 4.
6. Process according to any one of the preceding claims wherein the
polyether polyol has an oxyethylene content of between 15 and 35%
by weight.
7. Process according to any one of the preceding claims wherein the
polyether polyol is a poly(oxyethylene-oxypropylene) polyol.
8. Process according to any one of the preceding claims wherein at
least 50% of the oxyethylene groups are present at the end of the
polyether polyol.
9. Process according to any one of the preceding claims wherein the
isocyanate-reactive material in the reaction product is used in an
amount from 2 to 25% by weight based on the reaction product.
10. Process according to any one of the preceding claims wherein
the organic polyisocyanate is polymethylene polyphenylene
polyisocyanate.
11. Process according to any one of the preceding claims carried
out in the presence of an isocyanate-reactive cyclic compound
corresponding to the formula : 3wherein Y is O or NR.sup.1 wherein
each R.sup.1 independently is a lower alkyl radical of
C.sub.1-C.sub.6 or a lower alkyl radical substituted with an
isocyanate-reactive group; each R independently is hydrogen, a
lower alkyl radical of C.sub.1-C.sub.6 or (CH.sub.2).sub.m--X
wherein X is an isocyanate-reactive group which is OH or NH.sub.2
and m is 0, 1 or 2; and n is 1 or 2; with the proviso that at least
one of R.sup.1 or R is or comprises an isocyanate-reactive
group.
12. Process according to claim 11 wherein the isocyanate-reactive
cyclic compound corresponds to the formula (II) or (III): 4 5
13. (Semi-)rigid open-celled polyurethane or urethane-modified
polyisocyanurate foam obtainable by a process as defined in any one
of claims 1 to 12.
14. Evacuated insulation panel comprising a filler material and
vessel formed of a gastight film enveloping said filler,
characterised in that said filler material comprises a (semi-)rigid
open-celled polyurethane or urethane-modified polyisocyanurate foam
as defined in claim 13.
15. Polyisocyanate composition having a free NCO-value of 21 to 30%
by weight comprising the reaction product of a stoichiometric
excess of an organic polyisocyanate and an isocyanate-reactive
material comprising a polyether polyol having a number average
molecular weight between 1000 and 10000 and an average nominal
hydroxyl functionality of from 2 to 6 and containing from 10 to 50%
by weight of oxyethylene units.
Description
[0001] This invention relates to a process for the preparation of
open-celled rigid polyurethane or urethane-modified
polyisocyanurate foams, to foams prepared thereby, to the use of
these foams in evacuated insulation panels and to certain novel
polyisocyanate compositions useful in the process.
[0002] Rigid polyurethane and urethane-modified polyisocyanurate
foams are in general prepared by reacting the appropriate
polyisocyanate and polyol in the presence of a blowing agent. They
can be open- or closed-celled.
[0003] One use of open-celled rigid polyurethane or
urethane-modified polyisocyanurate foams is as a thermal insulation
medium, for example, in evacuated insulation panels used in the
construction of refrigerated storage devices.
[0004] Evacuated insulation panels generally comprise a low thermal
conductivity filler material (such as open-celled polyurethane
foam) and a vessel formed of a gastight film enveloping said
filler, the whole being evacuated to an internal pressure of about
5 mbar or less and then hermetically sealed.
[0005] Open-celled polyurethane foams suitable as low thermal
conductivity filler material for evacuated insulation panels can
advantageously be produced by reacting an organic polyisocyanate
with an isocyanate-reactive material comprising at least one
isocyanate-reactive cyclic compound, as described in, for example,
EP-A-498628, EP-A-498629, EP-A-419114, EP-A-662494, WO 95/15355, WO
95/02620, WO 96/25455, WO 96/32605, WO 96/36655, WO 98/54239 and GB
2324798, all incorporated herein by reference.
[0006] General descriptions of the construction of evacuated
insulation panels and their use in thermal devices can be found in
U.S. Pat. Nos. 5,066,437, 5,032,439 and 5,076,984 and European
Patent Publications Nos. 434266, 434225 and 181778, all
incorporated herein by reference as well as the references
mentioned therein.
[0007] EP 547515 describes a method for producing open cell rigid
polyurethane foam for use in a vacuum insulating material by
reacting polymethylene polyphenylisocyanate prepolymer with polyol
at an NCO/OH equivalent ratio of 1.3 to 3.0 using water as blowing
agent. The prepolymer is obtained by reacting polymethylene
polyphenyllsocyanate (p-MDI) with a polyol (oxypropylene based) and
has an amine equivalent of 140 to 200 (which corresponds to an NCO
value of 21 to 30%).
[0008] The obtained open cell rigid polyurethane foam has a fine
cell structure due to the presence of the p-MDI prepolymer and no
scorching due to the index range employed.
[0009] EP 581191 describes a method for producing an open cell
rigid polyurethane foam for use in vacuum insulating material by
reacting a polyol with a polymethylene polyphenyl polyisocyanate
prepolymer derived from a monol by use of a substitute for
trichlorofluoromethane as blowing agent.
[0010] The use of a prepolymer leads to a very fine cell structure
of the cotained foam.
[0011] The present Applicant has now developed an improved process
for the preparation of open-celled rigid polyurethane and
urethane-modified polyisocyanurate foams derived from certain
polyisocyanate compositions comprising specific prepolymers (i.e.
reaction products of a stoichiometric excess of a polyisocyanate
and an isocyanate-reactive material).
[0012] Accordingly the invention provides a process for the
preparation of an open-celled (semi-)rigid polyurethane or
urethane-modified polyisocyanurate foam by reaction of a
polyisocyanate composition with a polyfunctional
isocyanate-reactive composition under foam-forming conditions,
characterised in that the polyisocyanate composition has a free
NCO-value of 21 to 30% by weight and comprises the reaction product
of a stoichiometric excess of an organic polyisocyanate and an
isocyanate-reactive material comprising a polyether polyol having a
number average molecular weight between 1000 and 10000 and an
average nominal hydroxyl functionality of from 2 to 6 and
containing from 10 to 50% by weight of oxyethylene units.
[0013] The process of the invention is suitable for the preparation
of open-celled rigid polyurethane or urethane-modified
polyisocyanurate foams having improved cell-opening and finer
cells.
[0014] Closed cell contents of below 5% for the core of the foam
are generally obtained by using the process of the present
invention. Generally the closed cell content is below 2%, even more
generally below 1%.
[0015] The open-celled foams according to the invention are
characterised by excellent thermal insulation properties with no
degradation of mechanical properties and are therefore particularly
suitable for thermal insulation purposes.
[0016] Foam blocks at a thickness of greater than 30 cm and even
greater than 45 cm can be prepared without scorching or splitting
of the foam by using the process of the present invention.
[0017] Prepolymers of the claimed range of NCO values lead to lower
exotherms within the foam thereby reducing the scorching of the
foam and the tendency to split.
[0018] Preferably the NCO value of the polyisocyanate composition
is between 23 and 29 wt %, more preferably between 24 and 26 wt
%.
[0019] The viscosity of the polyisocyanate composition is
preferably below 2000 cps, more preferably below 1500 cps at
25.degree. C. to allow easy processing.
[0020] The use of a polyfunctional isocyanate-reactive material to
prepare the prepolymer is preferred over the use of a
monofunctional isocyanate-reactive material. The use of prepolymers
derived from monofunctional isocyanate-reactive material (such as a
monohydric alcohol, preferably having a molecular weight of at
least 340, for example a polyalkylene glycol monoalkyl ether of
molecular weight 350 to 750) still leads to splitting of the foam
especially in the production of thick foam blocks.
[0021] The isocyanate-reactive material which is reacted with a
stoichiometric excess of an organic polyisocyanate to form the
reaction product which is present in the polyisocyanate composition
(hereinafter called the `isocyanate-reactive material`) is
preferably a polyether polyol having a number average molecular
weight between 1000 to 6000 and an average nominal hydroxyl
functionality of from 2 to 4 and an oxyethylene content of between
10 and 50%.
[0022] Preferably the polyether polyol has a molecular weight
between 3000 and 5000, a functionality between 2.5 and 3.5 and an
oxyethylene content of between 15 and 35%.
[0023] The term "average nominal hydroxyl functionality" is used
herein to indicate the average functionality (number of hydroxyl
groups per molecule) of the polyol composition on the assumption
that this is the average functionality (number of active hydrogen
atoms per molecule) of the initiator(s) used in their preparation
although in practice it will often be somewhat less because of some
terminal unsaturation.
[0024] Suitable polyether polyols for use in the
isocyanate-reactive material have been fully described in the prior
art and include reaction products of alkylene oxides, for example
ethylene oxide and/or propylene oxide, with initiators containing
from 2 to 6 active hydrogen atoms per molecule. Suitable initiators
include water and polyols, for example ethylene glycol, propylene
glycol, diethylene glycol, dipropylene glycol, cyclohexane
dimethanol, resorcinol, bisphenol A, glycerol, trimethylolpropane,
1,2,6-hexanetriol, triethanolamine, pentaerythritol and sorbitol;
polyamines, for example ethylene diamine, tolylene diamine,
diaminodiphenylmethane and polymethylene polyphenylene polyamines;
and aminoalcohols, for example ethanolamine and diethanolamine, and
mixtures of such initiators.
[0025] Preferred polyether polyols are
poly(oxyethylene-oxypropylene) polyols containing preferably 10 to
50%, and more preferably 15 to 35% by weight, based on the total
weight of the polyol, of oxyethylene groups.
[0026] Preferably, at least 50%, more preferably at least 75%, of
these oxyethylene groups are present at the end of the polyether
polyol.
[0027] If the oxyethylene content of the polyether polyol used in
preparing the prepolymer is below 10 wt % the foam cell texture
becomes coarse; if the oxyethylene content of the polyether polyol
is above 50 wt % the closed cell content of the foam becomes too
high.
[0028] In the preparation of the reaction product of the organic
polyisocyanate and the isocyanate-reactive material it is preferred
to react the organic polyisocyanate and the isocyanate-reactive
material in such a ratio that the isocyanate-reactive material is
present in the reaction product in an amount from 2 to 25%, and
more preferably from 10 to 20%, by weight based on the total weight
of the reaction product.
[0029] Organic polyisocyanates which may be used in the present
invention include aliphatic, cycloaliphatic, araliphatic and
aromatic polyisocyanates, but especially the polyisocyanates
proposed in the literature for use in the production of foams. Of
particular importance are aromatic diisocyanates such as tolylene
and diphenylmethane diisocyanates in the well known pure, modified
or crude forms. Special mention may be made of the so-called MDI
variants (diphenylmethane diisocyanate modified by the introduction
of urethane, allophanate, urea, biuret, carbodiimide, uretonimine
or isocyanurate residues) and the mixtures of diphenylmethane
diisocyanate(s) and oligomers thereof known in the art as "crude"
or "polymeric" MDI (polymethylene polyphenylene
polyisocyanates).
[0030] Polyfunctional isocyanate-reactive compositions with which
the polyisocyanate composition may be reacted to form open-celled
rigid polyurethane or urethane-modified polyisocyanurate foams
include any of those known in the art for that purpose.
[0031] Of particular importance for the preparation of rigid foams
are polyols and polyol mixtures having average hydroxyl numbers of
from 300 to 1000, especially from 300 to 700 mg KOH/g, and hydroxyl
functionality's of from 2 to 8, especially from 3 to 8.
[0032] Suitable polyols have been fully described in the prior art
and include reaction products of alkylene oxides, for example
ethylene oxide and/or propylene oxide, with initiators containing
from 2 to 8 active hydrogen atoms per molecule. Suitable initiators
include: polyols, for example glycerol, trimethylolpropane,
triethanolamine, pentaerythritol, sorbitol and sucrose; polyamines,
for example ethylene diamine, tolylene diamine,
diaminodiphenylmethane and polymethylene polyphenylene polyamines;
and aminoalcohols, for example ethanolamine and diethanolamine, and
mixtures of such initiators.
[0033] Other suitable polymeric polyols include polyesters obtained
by the condensation of appropriate proportions of glycols and
higher functionality polyols with dicarboxylic or polycarboxylic
acids. Still further suitable polymeric polyols include
hydroxyl-terminated polythiOethers, polyamides, polyesteramides,
polycarbonates, polyacetals, polyolefins and polysiloxanes.
[0034] The quantities of the polyisocyanate compositions and the
polyfunctional isocyanate-reactive compositions to be reacted will
depend upon the nature of the rigid polyurethane or
urethane-modified polyisocyanurate foam to be produced and will be
readily determined by those skilled in the art.
[0035] The process of the invention may be carried out in the
presence of any of the blowing agents known in the art for the
preparation of rigid polyurethane or urethane-modified
polyisocyanurate foams. Such blowing agents include water or other
carbon dioxide-evolving compounds, such as isocyanate-reactive
cyclic compounds, or inert low boiling compounds having a boiling
point of above -70.degree. C. at atmospheric pressure.
[0036] Suitable inert blowing agents include, for example,
hydrocarbons, dialkyl ethers, alkyl alkanoates, aliphatic and
cycloaliphatic hydrofluorocarbons, hydrochlorofluorocarbons,
chlorofluorocarbons, and fluorine-containing ethers. Suitable
hydrocarbon blowing agents include lower aliphatic or cyclic
hydrocarbons such as n-pentane, isopentane, cyclopentane,
neopentane, hexane and cyclohexane.
[0037] Where water is used as blowing agent, the amount may be
selected in known manner to provide foams of the desired density,
typical amounts being in the range from 0.05 to 5% by weight based
on the total reaction ingredients, although it may be a particular
embodiment of the present invention to incorporate up to 10% by
weight or even up to 20% by weight of water.
[0038] The total quantity of blowing agent to be used in a reaction
system for producing cellular polymeric materials will be readily
determined by those skilled in the art, but will typically be from
2 to 25% by weight based on the total reaction system.
[0039] In order to further lower the thermal conductivity open
celled rigid polyurethane foams having decreased cell sizes (in the
range 50 to 150 micron) can be prepared.
[0040] These fine-celled open-celled rigid polyurethane foams can
be obtained by incorporating an insoluble fluorinated compound into
the foam-forming mixture or by air-nucleation.
[0041] The term insoluble as used herein with reference to the
insoluble fluorinated compound to be used in the preparation of
these fine-celled open-celled rigid polyurethane foams is defined
as showing a solubility in either the isocyanate-reactive
composition or the polyisocyanate composition with which it is to
be blended of less than 500 ppm by weight at 25.degree. C. and
atmospheric pressure.
[0042] Insoluble fluorinated compounds for use in the preparation
of fine-celled open-celled rigid polyurethane foam include any of
those disclosed in U.S. Pat. No. 4,981,897, U.S. Pat. No.
5,034,424, U.S. Pat. No. 4,972,002, EP-A-0508649, EP-A-0498628 and
WO 95/18176, incorporated herein by reference.
[0043] The term substantially fluorinated as used herein with
reference to the insoluble, substantially fluorinated compound to
be used in the preparation of these fine-celled open-celled rigid
polyurethane foams is to be understood to embrace compounds in
which at least 50% of the hydrogen atoms of the unfluorinated
compounds are replaced by fluorine.
[0044] Suitable compounds include substantially fluorinated or
perfluorinated hydrocarbons, substantially fluorinated or
perfluorinated ethers, substantially fluorinated or perfluorinated
tertiary amines, substantially fluorinated or perfluorinated
amino-ethers and substantially fluorinated or perfluorinated
sulphones.
[0045] Preferred insoluble perfluorinated compounds include
perfluoro-n-pentane, perfluoro-n-hexane, perfluoro
N-methylmorpholine and perfluoro(4-methylpent-2-ene).
[0046] Certain insoluble fluorinated compounds suitable for use in
the preparation of these fine-celled open-celled rigid polyurethane
foams may themselves act as blowing agents under the conditions
pertaining to the foam-forming reaction, particularly where their
boiling point is lower than the exotherm temperature achieved by
the reaction mixture. For the avoidance of doubt, such materials
may, partly or completely, fulfil the function of blowing agent in
addition to that of insoluble fluorinated compound.
[0047] The amount of the insoluble fluorinated compound to be used
in the preparation of these fine-celled open-celled rigid
polyurethane foams ranges from 0.05 to 10%, preferably from 0.1 to
5%, most preferably from 0.6 to 2.3% by weight based on the total
foam-forming composition.
[0048] The insoluble fluorinated compound will usually be
incorporated in the foam-forming reaction mixture in the form of an
emulsion or preferably a microemulsion in one of the major
components, that is to say in the isocyanate-reactive component
and/or the polyisocyanate component. Such emulsions or
microemulsions may be prepared using conventional techniques and
suitable emulsifying agents.
[0049] Emulsifying agents suitable for preparing stable emulsions
or microemulsions of fluorinated liquid compounds in organic
polyisocyanates and/or isocyanate-reactive compounds include
surfactants chosen from the group of nonionic, ionic (anionic or
cationic) and amphoteric surfactants. Preferred surfactants are
fluoro surfactants, silicone surfactants and/or alkoxylated
alkanes.
[0050] The amount of emulsifying agent used is between 0.02 and 5
pbw per 100 pbw of foam-forming reaction system and between 0.05
and 10 pbw per 100 pbw of polyisocyanate or polyol composition.
[0051] In addition to the polyisocyanate and polyfunctional
isocyanate-reactive compositions and the blowing agent, the
foam-forming reaction mixture will commonly contain one or more
other auxiliaries or additives conventional to formulations for the
production of open-celled rigid polyurethane and urethane-modified
polyisocyanurate foams. Such optional additives include
crosslinking agents, for example low molecular weight polyols such
as triethanolamine, foam-stabilising agents or surfactants, for
example siloxane-oxyalkylene copolymers, urethane catalysts, for
example tin compounds such as stannous octoate or dibutyltin
dilaurate or tertiary amines such as dimethylcyclohexylamine or
triethylene diamine, fire retardants, for example halogenated alkyl
phosphates such as tris chloropropyl phosphate or alkyl
phosphonates, smoke suppressants, organic or inorganic fillers,
thixotropic agents, dyes, pigments, mould release agents, cell
opening agents such as inert particles, polymer particles (such as
polymer polyols), specific surfactants, incompatible liquids such
as solvents or polyols, inorganic fillers such as bentonite clays,
silica particles (particularly fumed silica), metal flakes and
stearates.
[0052] A particularly preferred process according to the present
invention comprises the step of reacting the claimed organic
polyisocyanate composition comprising the prepolymer with a
polyfunctional isocyanate-reactive composition in the presence of
an isocyanate-reactive cyclic compound of formula: 1
[0053] wherein
[0054] Y is O or NR.sup.1 wherein each R.sup.1 independently is a
lower alkyl radical of C.sub.1-C.sub.6 or a lower alkyl radical
substituted with an isocyanate-reactive group;
[0055] each R independently is hydrogen, a lower alkyl radical of
C.sub.1-C.sub.6 or (CH.sub.2).sub.m--X wherein X is an
isocyanate-reactive group which is OH or NH.sub.2 and
[0056] m is 0, 1 or 2; and
[0057] n is 1 or 2;
[0058] with the proviso that at least one of R.sup.1 or R is or
comprises an isocyanate-reactive group.
[0059] A preferred compound of formula (I) wherein Y is O is an
isocyanate-reactive cyclic carbonate which is glycerol
carbonate.
[0060] Preferred compounds of formula (I) wherein Y is NR.sub.1 are
isocyanate-reactive cyclic ureas of formula : 2
[0061] The isocyanate-reactive cyclic blowing promoter is used in
amounts ranging from 0.1 to 99%, preferably from 0.5 to 60%, more
preferably from 1 to 10% by weight based on the total
isocyanate-reactive material.
[0062] The process is preferably carried out in the presence of a
metal salt catalyst. Preferred metal salt catalysts are those
selected among group Ia and group IIa metal salts, more preferably
among group Ia and group IIa metal carboxylates.
[0063] Particularly suitable metal salt catalysts are potassium
acetate and potassium ethylhexoate (for example, Catalyst LB
available from Imperial Chemical Industries).
[0064] The metal salt is used in amounts ranging from 0.01 to 3% by
weight based on the total reaction system.
[0065] Alternatively aminoalcohol catalysts can be used in the
above process as described in WO 98/54239, incorporated herein by
reference. A preferred aminoalcohol catalyst is
2-(2-dimethylaminoethoxy)ethanol. The aminoalcohol catalyst is
generally used in amounts varying between 0.1 and 3% by weight
based on total reaction system.
[0066] Amine catalysts can be used together with the metal salt
catalyst or the aminoalcohol catalyst described above. Examples of
suitable tertiary amine catalysts include dimethylcyclohexylamine,
bis(dimethylaminoethyl)ether, tetramethylhexane diamine,
triethylenediamine, N-methylmorpholine,
pentamethyldiethylenetriamine, tetramethylethylenediamine,
1-methyl-4-dimethylaminoethylpiperazine,
3-methoxy-N-dimethylpropylamine, N-ethylmorpholine,
diethylethanolamine, N-cocomorpholine,
N,N-dimethylyl-N',N'-dimethyl isopropylpropylenediamine- ,
N,N-diethyl-3-diethylaminopropylamine, dimethylbenzylamine. The
amine catalyst is used in amounts ranging from 0.1 to 1.5% by
weight based on the total foam.
[0067] In order to decrease the closed cell content particularly in
conditions of overpack as during the filling of a refrigerator
cavity a supplemental cell opening agent selected from the group
consisting of fatty acids, fatty acid amines, fatty acid amides and
fatty acid esters can be used as described in GB 2324798,
incorporated herein by reference.
[0068] Examples of suitable fatty acid derivative cell opening
agents include tallow diamines (which are complex mixtures of
C.sub.16-C.sub.30 diamines), mixtures of tallow diamines with fatty
acid esters such as the commercially available products INT
494/792/0, 494/792/1, 494/792/2 and 494/792/4 available from Munch
Chemie-Labor and the following fatty acid diamines
C.sub.19H.sub.38(NH.sub.2).sub.2, C.sub.23H.sub.46(NH.sub.2).sub-
.2 and C.sub.22H.sub.50(NH.sub.2).sub.2.
[0069] These fatty acid based additional cell opening agents are
used in amounts of between 0.1 and 20% by weight, preferably
between 0.5 and 5% by weight and most preferably between 0.5 and 2%
by weight based on the foam.
[0070] Further useful additives for use in the above described
process include polyethylene glycols containing from 1 to 10
ethyleneoxy units, antioxidants such as Irganox 1135, Irganox 1010
and Irgafos TNPP, additional silicone-based cell opening agents
such as Ortagol 501 and Tegostab B8919 (both available from
Goldschmidt), Additive 6164 (available from OSI) and silicones of
the DC-200 series (available from Dow Corning).
[0071] Isocyanate indices of from 70 to 140 will typically be used
in operating the method of the present invention but lower indices
may be used if desired. Higher indices, for example 150 to 500 or
even up to 3000, may be used in conjunction with trimerisation
catalysts to make foams containing isocyanurate linkages.
[0072] Preferred indices lie in the range 90 to 250, more
preferably 100 to 120.
[0073] In operating the process for making rigid foams according to
the invention, the known one-shot, prepolymer or semi-prepolymer
techniques may be used together with conventional mixing methods
and the rigid foam may be produced in the form of slabstock,
mouldings, cavity fillings, sprayed foam, frothed foam or laminates
with other materials such as hardboard, plasterboard, plastics,
paper or metals.
[0074] Open-celled rigid polyurethane foams prepared in accordance
with the process of the invention are characterised by having open
cells (closed cell content below 1%) and are of particular use for
evacuated insulation panel applications where they show superior
thermal insulation properties. Further outgassing (i.e. gases such
as air, water vapour or blowing agent diffusing gradually from
closed cell portions) of an open-celled rigid polyurethane foam of
the present invention is decreased compared to foams with higher
closed cell content and thus internal pressure increase with lapse
of time of evacuated insulation panels filled with the present
foams is decreased leading to improved thermal insulation. Further
the time needed to evacuate a panel to the desired pressure level
is decreased owing to the lower closed cell content of the present
foam.
[0075] Preferably the open-celled rigid polyurethane foam of the
present invention is preconditioned prior to placement in the
gastight envelope.
[0076] This preconditioning involves heating and agitating the
filler material preferably under reduced pressure in order to
remove contaminants.
[0077] To improve the performance of the evacuated insulation
panel, materials are provided within the sealed panels to absorb or
otherwise interact with gases and vapours that remain due to
imperfect evacuation, that permeate the enclosure from the outside
atmosphere or evolve from the polyurethane foam filler itself. Such
materials are known as getters and may include, for example,
activated carbon, molecular sieves and zeolites to adsorb volatiles
evolving from the polyurethane foam filler.
[0078] The above described polyisocyanate composition can also be
used in a process for making closed celled rigid polyurethane or
urethane-modified polyisocyanurate foam such as the foam used to
encapsulate an evacuated insulation panels within the cavity of a
refrigerator.
[0079] The invention is illustrated but not limited by the
following examples in which all parts, percentages and ratios are
by weight.
[0080] The following glossary of materials is included to identify
reaction components not otherwise identified in the examples.
[0081] Glossary
[0082] Polyol A is a sorbitol-initiated polyether polyol of OH
value 500 mg KOH/g.
[0083] Polyol B is a sorbitol-initiated polyether polyol of OH
value 350 mg KOH/g.
[0084] PEG 200 is polyethylene glycol of molecular weight 200.
[0085] Surfactant is a siloxane-based surfactant.
[0086] IMR 494/792/2 is a cell-opening agent available from Munch
Chemie.
[0087] Cell opening agent is a silicone-based cell-opening
agent.
[0088] Blow catalyst is an amine-based catalyst.
[0089] DMAEE is a catalyst available from Huntsman Chemicals under
the tradename ZR 70.
[0090] Fixapret NF is a cyclic urea available from BASF.
[0091] Additive is a scorch-preventing compound.
EXAMPLES
[0092] Rigid open celled polyurethane foams were made from an
isocyanate-reactive composition containing the ingredients listed
in table 1 below and a polyisocyanate composition containing a
prepolymer prepared by reacting polymeric MDI with a polyol as
identified in table 2 below (NCO value of prepolymer, molecular
weight, functionality, oxyethylene content of the polyol). The two
compositions were reacted at a NCO index of 110. The closed cell
content (CCC in %) of the obtained foams was measured using a
Micromeretic Accupyc 1330 Closed Cell Measuring.
[0093] The foam cell size was also evaluated.
[0094] The results are listed in table 2 below.
[0095] As a reference example a foam was made using polymeric MDI
instead of a prepolymer as polyisocyanate.
[0096] These results show that using a prepolymer derived from a
polyether polyol with a very low EO content leads to coarse cell
texture (examples 6 to 8) whereas using prepolymers derived from a
polyether polyol with high EO content leads to a higher closed cell
content (examples 11 and 12).
1 TABLE 1 Polyol A 24 Polyol B 60 PEG 200 10 Surfactant 1 IMR
494/792/2 1 Cell opening agent 0.5 Blow catalyst 0.05 DMAEE 1.2
Fixapret NF 2.8 Additive 1
[0097]
2TABLE 2 EO NCO MW Funct. content CCC Example prepolymer polyol
Polyol polyol (%) Cell size Ref. 30.8 80 Fine 1 28.5 4500 2 27 0.6
Very fine 2 26.9 6000 3 16 0.3 Very fine 3 23.5 650 6 0 76 Fine 4
28.5 500 3 0 1.2 Coarse 5 28.7 500 3 50 30 Slightly coarse 6 27.5
1000 3 0 0.6 Coarse 7 24.5 3500 3 0 0.4 Coarse 8 24.5 3500 3 10 0.2
Slightly coarse 9 24.8 3500 3 16 0.5 Fine 10 25 3500 3 25 0.3 Very
fine 11 23.9 3500 3 50 10 Very fine 12 28.4 1000 3 50 8 Fine
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