CA2323054A1

CA2323054A1 - Process for rigid polyurethane foams

Info

Publication number: CA2323054A1
Application number: CA002323054A
Authority: CA
Inventors: Alan James Hamilton
Original assignee: Individual
Current assignee: Huntsman International LLC
Priority date: 1998-04-02
Filing date: 1999-03-17
Publication date: 1999-10-14
Also published as: WO1999051655A1; AR014797A1; EP1080125A1; TR200002863T2; JP2002510723A; BR9909361A; US6433032B1; CN1296501A; US20030065046A1; AU3517699A; KR20010042355A

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.

Description

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PROCESS FOR RIGID POLYURETHANE FOAMS
Tzis 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.
Rigid polyurethane and urethane-modified polyisocyanurate foams are in general prepared by reacting the appropriate po~_yisocyanate and polyol in the presence of a blowing agent. They can be open- or closed-celled.
One use of open-celled rigid polyurethar,,e or urethane-modified polyisocyanurate foams is as a thermal insulation medium, for example, in e-Tacuated insulation panels used in the construction of refrigerated s~~orage devices.
Evacuated insulation panels generally comprise a. low thermal conductivity f:~ller 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 ~~ mba~or less and then hermetically sealed.
Open-celled polyurethane foams suitable as 7_ow thermal conductivity fa_ller material for evacuated insulation pane:Ls can advantageously be pz-oduced by reacting an organic polyisocyanate with an isocyanate-reactive material comprising at least one i:>ocyanate-reactive cyclic ceampound, as described in, for example, EP-A-4!x8628, EP-A-498629, EP-A-47.9114, EP-A-662494, WO 95/15355, WO 95/02620, ia0 96/25455, WO 96/32605, WC~ 96/36655, WO 98/54239 and GB 2324798, a-~.~ ~Yr~,«~ ~.oro w ~, ".
General descriptions of the construction of evacuated insulation panels and their use in thermal_ devices can be found in US patents Nos 5066437, 5C32439 and 5076984 and European Patent Publications Nos 434266, 434225 :.::::.:.::;:::.:::.::;:..::::::.::::0::::.3:::.3.0:::4 000 -~:.:r <:F:~:C~~:# ~ ~~ ~ ~~:~-.T::.. :.~:.::L~. ,,.:: - 0 9 - O S v~
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EF~ 597515 describes a method for producing opera cell rigid polyurethane fc,am for use in a vacuum insulating material by reacting polymethylene pc~lyphenylisocyanate prepolymer with polyol at an NCO/OH equivalent ratio of 1.3 to 3.0 using water as blowing agent. The prepolymer is obtained b~~ reacting polymethylene polyphenylisocyanate (p-MDI) with a polyol (oxypropylene based) and has an amine equivalent of 190 to 200 (which corresponds to an NCO value of 21 to 30 ~).
T1-e obtained open cell rigid polyurethane foam has a fine cell structure dLe to the presence of the p-MDI prepolymer anc'~ no scorching due to the irdex range employed.
EF 581191 describes a method for producing an open cell rigid polyurethane foam for use in vacuum insulating material by reacting a pclyol with a polymethylene polyphenyl poiyisocyanate prepolymer derived from a monol by use of a substitute for trichlorofluoromethane as blowing agent.
The use of a prepolymer leads to a very fine cell structure of the obtained foam.
The present Applicant has now developed an improved process for the preparation of open-celled rigid polyurethane and urethane-modified poiyisocyanurate foams derived from certain po7_yisocyanate compositions ~~o:nprising specific prepolymers (i.e. reaction products of a stoichiometric excess of a polyisocyanate and an isocyanate-reactive material).
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 co.zditions, characterised in that the polyisoc~~anate 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 iscocyanate-reactive material comprising a pol;yether polyol having a nurlber average molecular weight between 1000 and 10000 and an average .;.::;.:::::.:<.:;.::.:::. :::.:.;.CA::. .: . ::::::.:::.::;:.
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nominal hydroxyl functionality of from 2 to 6 and containing from 10 to 50 % by weight of oxyethylene units.
Tl~e process of the invention is suitable for the preparation of open-s cealled rigid polyurethane or urethane-modified polyisocyanurate foams having improved cell-opening and finer cells.
C~.osed cell contents of below 5 ~ for the core of the foam are generally ot~tained by using the process of the present invention. Generally the c~.osed cell- content is below 2 %, even more generally below 1 %.
The open-celled foams according to the invention are characterised by a}~cellent thermal insulation properties with no degradation of mechanical px-operties and are therefore particularly suitable for thermal insulation pL_rposes .
Fcaam blocks at a thickness of greater than 30 cm and even greater than 45 cnu can be prepared without scorching or splitting of the foam by using tr.e process of the present invention.
Pzepolymers 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.
Preferably the NCO value of the polyisocyanate ~=omposition is between 23 ar.d 29 wt%, more preferably between 24 and 26 wt's.

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The viscosity of the polyisocyanate composition is preferably below 2000 cps, more preferably below 1500,~cp~at 25°C to a:Llow easy processing.
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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, fo~_ 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.
The isocyanate-reactive material which is reacted with a stoichiometric excess of an organic polyisocyanate to form the reaction product which is i::!~: ''...;. ; ..,. ., '.:._ ~ :::~~.A- ~'::~::.::::; ~~ :::::.
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c~resent in the rolyisocvanate ccmpositicn (hereinafter called the isocyanate-reactive material') is preferably a polyether polyei :~:aving a cumber average molecular weight between 1000 t.~ 6000 and an average r;ominal hydroxyl functionality of from ~ to 4 and an oxyethylene content ~:f between 10 and SO ~a.
=referably the poiyether pc':ycl has a molecular weight between 3000 and , :000, a functionality between ~..5 and 3.5 anc. an oxye~:w;ylene content cf ::etween 15 and 35 ~.
l0 '".'he term "average nominal hydroxyl functionality" is used herein to indicate _the average functionality (number of hydroxyl groups per rnolecule) of the polyol co-,aosition on t:~e assumption that this is the :verage functionality (number cf active hydrogen atoms per molecule) of =he ~:itiators) used in their preparation although in practice it will 1~ ;ften be somewhat less because of some terminal unsaturation.
suitable pclyether poiyols for use in the isocyanate-reactive material nave been fully described in the prior art and include reaction products of alkylene oxides, for example ethylene oxide and/or propylene oxide, ?0 pith initiators containing from 2 to 6 active hydrogen atoms per molecule. Suitable initiators include water and polyols, for example =thylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, _yclohexane dimethanol, resorcinol, b~isphenol A, glycerol, ' :.rimethylolpropane, 1,2,6-hexanetriol, triethanolamine, pentaerythritol snd sorbitol; polyamines, for example ethylene diamme, tolylene diamine, ~iami.nodiphenyimethane and polymethylene polyphenylene polyamines; and sminoalcohols, for example ethanolamine and diethanolamine, and mixtures ~f such initiators.
30 P-eferred polyether polyols are poly(oxyethylene-oxypropylene) polyols ~ontair.ing preferably 10 tc 50~, and more preferably 15 to 35$ by weight, _~ased on the total weight e' the polycl, of ox:yethylene groups.
Preferably, at least 50~, more preferably at least 75a, of these ~s ~xyethylene groups are present at the end of the polyether polyol.
:f the cxyethyiene content c' the polyether polyol used in preparing the ~repcil~ner is below 10 wt~ '_~:e foam cell texture becomes coarse; if the W'O 99151655 PCT/EP99/01753 oxyethylene ccntent ~_ the polyether polycl __ above 50 wt~, the closed cell content of the foam becomes too high.
~n the preparaticn of the reaction product of the organic polyisocyanate _ a.nd the i,ocyanate-reactive material it is pr<=ferred to react the organic peiy_sw yanate and the isoc_,ranate-reactive material in such a ratio that the ocyanate-reactive material is present in the rea anon product in an amr ;~t from 2 tc 25a, and more preferably from ',0 to 20~, by weight based the tota'_ weiqht of the reaction product.
rganic polyisocyanates which may be used in the present inventicn vnclude aliphatic, cycloaliphatic, araiiphatic and aromatic polyisocyanates, but especially the polyv~socyanates proposed in the literature fcr use _n r_he production ef teams. Cf particular importance are aromatic diisocyanates such as tol:liene and diphenylmethane diisocvanates 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 ef urethane, allophanate, urea, biuret, carbodiimide, uretonimine or isocyanurate residues) and the ~0 ;-.fixtures of diphenylmethane diisocyanateis) <ind oligomers thereof known in the art as "crude" or "polymeric" MDI (pclymethylene polyphenylene polyisocyanates).
Polyfunctional isocyanate-reactive compositions with which the ~5 oolyisocyanate composition may be reacted tc: term open-celled rigid pclyurethane or urethane-modified polyisocyanurate foams include any cf those known in the art for that purpose.
Of particular importance fcr the preparation of rigid foams are polyols 30 and polyol mixtures having average hydroxyl numbers of from 300 to 1000, especially from 300 to 700 mg KOH/g, and hydrc;xyl functionality's of from to 8, especially from ? to 8.
Suitable polyols have been fully described in the prior art and include =eaction products cf alkylene oxides, for example ethylene oxide and/or cropyiene oxide, with initiators containing from 2 to 8 active hydrogen atcms per molecule. Suitable initiators include: polyols, for example ~aiycerol, trimethylolpropar:e, triethanolamine, pentaerythritol, sorbitol and sucrose; p:.~~~y~mines, f,_r example ethylene diamine, tolylene diamine, WO 99/51655 6 PCTIEP99/Ol?53 diaminodiphenyimethane and peivmethy~ene polypner.ylene poiyamines; end amincalcohols, for example etnanoiamine and diethanclamv~ne, and mixtures cf such initiators.
~ther suitable polyzr.eric polycls ~~:~ciude polyesters obtained ty the , S condensation cf appropriate proportions of giycois ant ::igher functionality polyols with dicarboxylic or polycarbcxylic a=ids.
Still further suitable polymeric polyols include t~ irox.y_-term;:ated polythioethers, polyamides, polyesteramides, cclycarbonates, p vacet. s, polyolefins and polysiloxanes.
The quantities ef the polyisocyanate compositions and the polyfunctio..
isocyanate=reactive compositions to be reacted will depend upon the nature of the rigid polyurethane cr urethane-modified pclyisoc;~ - at-foam tc be produced and will be readi~y determined by those skit t he art .
The process of the invention may be carried out in the presence of any cf the b'_owing agents known in the art for the preparation of rigid polyurethane or urethane-modified polyisocyanurate foams. Such M owing agents include water or other carbon dioxide-evolving compounds, such as isccyanate-reactive cyclic compounds, or inert low boiling compounds having a boiling point cf above -~G°C at atmospheric pressure.
Suitable inert blowing agents include, for example, hydrocarbons, dialkyl ethers, alkyl alkanoates, aliphatic and cycloaiiphatic hydrofluorocarbons, hydrocl:lorofluorocarbons, chlorofluorocarbons, and f'_uorine-containing ethers. Suitable hydrocarbon blowing agents include lower aliphatic or cyclic hydrocarbons such as n-pentane, isopentane, cyclopentane, neopentane, hexane and cyclohexane.
~rihere water is used as blowing agent, the amount may be selected in known manner to provide foams of the desired density, typical amounts beinc in the range from 0.05 to 5 1 by weight based on the total teat' ~n ingredients, although it may be a particular embodiment of the present invention tc incorporate up to i0 ~ by weight cr even up to 20 _ by weight cf water.

WO 99/51655 PCT/EP99/O1 i53 The total qua:~tity cf blowing agent ~_e be used in a reaction system fo.
producing cellular polymeric materials will be readily determined by chose skilled in the art, but will typically be from 2 to 25 $ by weight based on the total reaction system.
;n cider to further lower the thermal conductivity open celled rigid polyurethane foams having decreased cell :sizes (in the range SO to 150 micreni can be prepared.
'ihese fire-celled open-celled rigid polyurethane foams can be obtained by incorporating an insoluble fluorinated compound into the foam-forming mixture or by air-nucleation.
The term insoluble as used herein with reference to the insoluble fluorinated ccmpound to be used in the preparation of these fine-celled IS open-celled rigid polyurethane foams is defined as showing a solubility in either the isocyanate-reactive composit_.on cr the polyisocyanate ~cmposition with which it is to be hlendeo cf less than 500 ppm by weight ~t 25°C and atmospheric pressure.
?0 Inscluble fluorinated compounds for use in the preparation of fine-celled open-celled rigid polyurethane foam include any of those disclosed in US--9981897, US-P-5039929, US-P-49?2002, EP-A-0_';08649, EP-A-0498628 and WO
~5/18176, incorporated herein by reference.
?5 '.'he term substantially fluorinated as used herein with reference to the .nsoluble, substantially fluorinated compound to be used in the preparation of these fine-celled open-celled rigid polyurethane foams is r.o be understood tc embrace compounds in which at least 50 ~ of the iuydrogen atoms of the unfluorinated compounds are replaced by fluorine.
:'uitable compounds include substantially fluorinated or perfluorinated t.ydrocarbons, substantially fluorinated cr perfluorinated ethers, ,ubstantially flucrinated or perfluor,:~nated tertiary amines, substantially fluorinated or perfluorinated amino-ethers and ~ ~vbstar.tialiy fluorinated or perfluorinated sul.phones.

WO 99/5165 PCT/EP99/O1?53 Preferred inso'_ubie perfiucrinated c~cmpounds i::ciude perfl~,:oro-n-pentane, perfluore=n-hexane, perflucrc N-meth~lmorphcline and perfluoro(9-methylpent-~-enel.
O Certain insoluble fluorinated wmpounds suitable for use in the preparation of these fv~ne-celled open-celled rigid polyurethane foams m~;
themselves act as blowing agents _nder 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 cf insoluble fluorinates compound.
The amount of the insoluble fluorinated compound to be used in the I~ preparation of these fine-celled open-celled rigid polyurethane foams ranges from 0.05 to i0 a, preferably from 0.1 to 5 ~S, most preferably from 0.6 to 2.3 ~ by weight based on the total foam-forming composition.
The insoluble fluorinated compound will usually be incorporated in the foam-forming reaction mixture in the form of an emulsion or preferably a microemulsicn 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.
?5 Emulsifying agents suitable for preparing stable emulsions cr microemulsions of fluorinated liquid compounds in organic polyisocyanates and/or isocyanate-reactive compounds include surfactants chosen from the group of nonionic, ionic (anionic or caticnicj and amphoteric surfactants. Preferred surfactants are fluoro surfactants, silicone surfactants and/or aikoxylated alkanes.
The amount of emulsifying agent ~~sed is between O.C~ =nd 5 pbw per 1C0 pbw cf foam-forming reaction system and between 0.05 and 10 pbw per 100 ;5 nbw of polyisocyanate or polyol co::~position.
In addition to the pciyisocyanate and polyfunctional isocyanate-reactive compos'_Lions and the blowing anent, the foam-forming reaction mixture WO 99/516~~ 9 PCT/EP99101753 w___ common'_,,~ ccntai-; ~ne . more ether auxiliaries or additives conventional tc fcrmuiations fcr the production of open-celled rigid pc'_yurethane and urethane-modif'_ed pclyisccya~urate foams. Such optional additives include crossiiaking agents, _cr example low molecular weight poiyols such as triethanclamine, foam-stabi'_ising agents or surfactants, for example siloxane-oxyaikylene copolymers., urethane catalysts, for example tin ccmpounds such as stanncus ectoate or dibu~yltin dilaurate or tertiary amines such as dimethylcyc':ohexylamine or triethylene diamine, fire retardants, for example halogenated alkyl phosphates such as tris l0 chleropropyl phosphate or alkyl phosphonates, smoke suppressants, organic or inorganic fillers, thixotrepic agents, dyes, pigments, mould release aaents, cell openir.~ agents =such as inert particles, polymer particles (suc:~ as polymer polyols;, specific surfact_ar.ts, incompatible liquids such as solvents o_- pclycls, inorganic fillers such as bentonite clays, l~ silica particles (particularly fumed silica;, metal flakes and stearates.
A particularly preferred process according t:o the present invention comprises the step of reacting the claimed organic polyisocyanate compcsitien comprising the prepolymer with a polyfunctional isocyanate-20 reactive composition in the presence cf an isocyanate-reactive cyclic compound cf formula:

I I
C
~5 'f Y (I) (CR2)n CR2 30 wherein Y is O or N R1 wherein. each Hl v_ndependent_y i_; a lower alkyl radical of C1-C6 or a lower alkyl radical sub stituted with an isocyanate-reactive group;
eac:: R independently is hydrcge:n, a lower a1k5~1 radical of C1-C6 or 3~ (CH2)m-X wherein X is an isocyanate-reactive croup which is OH or NH2 and m is G, '_ or 2; and n is 1 or c;

WO 9915165 PCT/EP99/017s3 with the proviso that c_ least one cf P.= or R is or comprv_ses an isocvanate-react:~ae group.
A preferred compound ef formula (I) wherein Y is C is an isocyanate-j reactive cyclic carbonate which is glycerol carbonate.
Preferred compounds cf formula (I) wherein Y is NRl are isocyanate-reactive cyclic areas of formula l0 O
'C
HO-CH2-N // N-CHI-OH (II) lj H-C C-H
1 OH O i and C
CH3-N N-CHj (III) 7j H_C G _H

OH OH
The isocyanate-reactive cyclic blowing promoter is used in amounts ranging from 0.1 to 99 ~, preferably from 0.5 to 60 a, more preferably from 1 ~0 10 o by weight based on the total isocyanate-reactive material.
The process is preferably carried out in the presence of a metal salt r catalyst. Freferred metal salt catalysts are those selected among group as and group IIa metal salts, mere preferably among group Ia and group r IIa metal carboxylates.
Particularly suitable metal salt catalysts are potassium acetate and potassium ethylhexoate (for example, Catalyst ~B available from Imperia-~hemical Tndustries).

VVO 99/51655 1 ~ PCTlEP99/01753 she metal salt is used in amounts ranging f::om 0.01 to 3 ~ by weight used on the total reaction system.
~:lternatively aminoalcohol catalysts can be used in the above process as :iescribed in WO 98/59239, incorporated herein by reference. A preferred ~ aminoalcohol catalyst is 2-(2-dimethylamincethoxy)ethanol.
The aminoalcohol catalyst is generally used in artount~ varying between O.i and 3 $ by weight based on total reaction. system.
~~nine catalysts can be used together with the metal salt catalyst or the aminoalcohol catalyst described above.
Examples of suitable tertiary amine catalysts include dimethylcyciohexyiamine, bis(dimethylaminoethyl)ether, tetramethylhexane diamine, triethyienediamine, N-methylmorpholine, l~ pentamethyldiethy~;enetriamine, tetramethylethyi.enediamine, 1-methyl-9-dimethylaminoethylpiperazine, 3-methoxy-N-dimethylpropylamine, N-ethylmorpholine, diethylethanolamine, N-cocoa,ozphol.ine, N,N-dimethylyl-N',N'-dimethyl isopropylpropylenediami.ne, N,N-diethyl-3-diethylaminopropylamine, dimethylbenzylamine.
The amine catalyst is used in amounts ranging from C.1 to 1.5 ~ by weight based on the total foam.
In order to decrease the closed cell content particularly in conditions of overpack as during the filling of a refr'_gerator cavity a supplemental ~=ell 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.
Examples of suitable fatty acid derivative cell opening agents include sallow diamines iwhich are complex mixtures of C16-C; diamines), mixtures of tallow diamines with fatty acid esters such as the commercially available products INT 499/792/0, 499/792/1, 494/192/2 and 499/79214 available from Munch Chemie-Labor and the following fatty acid diamines Ci9H3e (NHz) z. Cz3Has (NHz) z and CzzHso (NHz) z.
These fatty acid based additional cell opening agents are used in amounts of between C.1 and 20 '~ by weight, preferably between 0.5 and 5 ~ by weight and most preferably between 0.S and 2 ~ by weight based on the foam.

WO 99151655 PCTlEP99/01753 Further useful additi:~es for use in t?-~e above described process include po'_yethyiene glycols containing from 1 to i0 ethyleneoxy units, antioxidants such as Irganox 1135, _rganox iCiO and Irgafos TNPP, additional silicone-based cell opening agents such as Ortagol 501 and , S Tegostab 88919 (both available from Goldschmidt), Additive 616 (available from OSI) and silicones c' the DC-200 series (available frc , i Dcw Corning).
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, fcr example 150 to 500 or even up to 3000, may be used in conjunction with trimerisation catalysts to make foams containing isocyanurate linkages.
Preferred indices lie in the range 90 to 250, more preferably 100 to 120.
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 farm of slabstock, mouldings, cavity fillings, sprayed foam, frothed foam or laminates with other materials such as hardboard, plasterboard, plastics, paper or metals.
Open-celled rigid polyurethane foams prepared in accordance with the process cf 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 cf the present invention is decreased compared to foams with higher closed cell content and thus internal pressure increase with lapse of time cf evacuated insulation panels filled with the present foams is decreased leading to improved thermal insulation. Further the time needed ~o evacuate a panel tc the desired pressure level is decreased owing to the lower closed cell content of the ;~ present foam.
Preferably the open-celled _igid polyurethane foam of the present invent-en is preconditioned prior tc placement ;:, the gastight envelope.

':his preconditioning -involves heating and agitating the filler material preferably under reduced pressure in order to remove contaminants.
To improve the performance of the evacuated :insulation panel, :materials are provided within the sealed panels to absorb or otherwise interact ' with cases and vapours that remain due to imperfect evacuation, that permeate the enclosure from the outside atmosphere of evolve from t:he polyurethane foam filler itself. Such materials are known as Betters and may include, for example, activated carbon, molecular sieves and zeolites to adsorb volatiles evolving from the polyurethane foam filler.
The above described polyisocyanate composition can also be used in a process for making c'_osed 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.
The invention is illustrated but not limited by the following examples in which all parts, percentages and ratios are by weight.
~0 The following glossary of materials is included to identify reaction components not otherwise identified in the examples.
Glossary Polyol 'A is a sorbitoi-initiated polyether pelyo'~ of OH value S00 mg KOH/g.
Polyol B is a sorbitol-initiated polyether polyol of OH value 350 mg KOH/g.
PEG 200 is polyethylene glycol of molecular weight 200.
Surfactant is a siloxane-based surfactant.
IMR 494/792/2 is a cell-opening agent available from Munch Chemie.
Cell opening agent is a silicone-based cell-opening agent.
Blow catalyst is an amine-based catalyst.
DMAEE is a catalyst available from Huntsman Chemicals under the tradename ZR 70.
Fixapret NF is a cyclic urea available from BASF.
Additive is a scorch-preventing compound.

Examples Rigid open celled polyurethane foams were made from an isocyanate-reactive composition containing the ingredients listed _ 'able 1 below and a pelyisocyanate ccmpositior containing a prepolymer prepared y reacting polymeric MDI with a pol_.:1 as identified in table 2 below (NCO
value of prepolymer, molecular weight, functionality, o~Cyethylene content of the polyol). The tro compositions were reacted at a NCO index of~l, ~E
~' The closed cell content (CCC in ~) cf the obtained foams was mea:_.:red using a Micromeretic Accupyc 1330 Closed Cell Measuring.
The foam cell size was also evaluated.
The results are listed in table 2 below.
As a reference example a foam was made using polymeric MDI instead of a prepolymer as polyisocyanate.
1~
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 12 and 12) .
Table i ~ ~ 1 ~ 1 ~~~ ~'~T~~~'99~~"~ ~'~~ PC~E~~'l.~M~

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. ... . ... 1... .. ..

Table 2 Example NCO MW Funct. EO CCC ($) Cell size prepolymerpolyol Polyol content polyol Ref. 30.8 80 Fine 1 2B.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 C 28.5 500 3 0 1.2 Coarse C((p~~ 28.7 500 3 50 30 Slightly coarse _6 27.5 1000 3 0 0.6 Coarse ~

7 C 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 1U 25 3500 3 25 0.3 Very fine _1_~ 23.9 3500 3 _ 50 10 Ver fine 1:_' 28 . 4 1000 3~ ~ 50 ~ 8 Fine ::::::~::,::::>;::::,:,.,:,,:::.~ ~i:
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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 29 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 :

wherein Y is O or NR1 wherein each R1 independently is a lower alkyl radical of C1-C6 or a lower alkyl radical substituted with an isocyanate-reactive group; each R independently is hydrogen, a lower alkyl radical of C1-C6 or (CH2)m-X wherein X is an isocyanate-reactive group which is OH or NH2 and m is 0, 1 or 2;

and n is 1 or 2; with the proviso that at least one of R1 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):

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.