Compressed open-cell, fine-cell PUR / PIR rigid foams

Abstract

The invention relates to a method for producing compressed open-cell, fine-cell polyurethane rigid foams, to the polyurethane rigid foams obtained and to the use thereof.

Description

[0001] The invention relates to a method for producing compressed open-cell and fine-cell polyurethane rigid foams, the obtained polyurethane rigid foams and their use.

[0002] Polyurethane rigid foams may contain not only urethane groups (PUR) but also isocyanurate groups (PIR). In the present application, unless otherwise stated, the designations polyurethane rigid foam or PUR / PIR rigid foam are to be understood as meaning not only rigid foams essentially containing urethane groups but also rigid foams containing both urethane groups and isocyanurate groups.

[0003] Rigid polyurethane foams have been known for a long time. Thermal insulation is an important field of application. Insulation using vacuum insulation panels (VIP) containing rigid polyurethane foam is becoming increasingly important here. The foam quality has a decisive influence on the insulating properties of the foam used for vacuum insulation: On the one hand, the smallest possible cell size and the most uniform possible cell size are advantageous, and on the other hand, a high proportion of open cells is advantageous in order to enable the foam to be easily evacuated.

[0004] The production of open-cell rigid polyurethane foams is also known in principle. Usually certain cell-opening substances are added to the reaction mixture in order to open the cells during the foaming process.

[0005] WO 2018 / 162372 A1 discloses a method for producing fine-pored, open-cell polyurethane rigid foams. Here, a reaction mixture containing supercritical CO2 is introduced into a mold under counterpressure and then rapidly decompressed. Due to the special composition of the reaction mixture, a foam with a particularly low density, a high open porosity and a small cell size is obtained.

[0006] There is a constant effort to achieve an improved combination of properties in rigid polyurethane foams, such as further improving (ie, reducing) the thermal conductivity of the foam without having to make significant sacrifices in mechanical properties.

[0007] Although compressed open-cell polyurethane rigid foams have been proposed many times. For example, DE 102005021994A1 discloses a method in which a polyurethane rigid foam for VIP is compressed after curing and before evacuation. However, neither the chemical composition of the polyurethane rigid foam nor the open porosity, cell size or density is disclosed. Due to the fact that WO 2018 / 162372A1 discloses for the first time a polyurethane rigid foam (which exhibits low density and low cell size and a large proportion of open cells), the foam of DE 102005021994 A1 cannot be such a foam. The document particularly teaches that compression of polyurethane foams will inevitably lead to deterioration of mechanical properties.

[0008] The object of the present invention is to further reduce the thermal conductivity of the low-density open-cell and fine-cell polyurethane foams known from the prior art, in particular without accepting significant losses in mechanical properties, such as compressive strength parallel and / or transverse to the foaming direction.

[0009] Surprisingly, this object can be achieved by a process for producing a compressed open-cell PUR / PIR rigid foam, which comprises the following steps:

[0010] i. preparing a reaction mixture R), which comprises

[0011] - an isocyanate-reactive composition A) comprising

[0012] a polyol component A1) having a functionality f>2.5, comprising at least one polyether polyol, polyester polyol, polycarbonate polyol, polyether-polycarbonate polyol, polyetherester polyol or a mixture thereof,

[0013] optional catalyst component A2),

[0014] Optional auxiliaries and additives component A3);

[0015] - polyisocyanate component B); and

[0016] - a blowing agent component C) comprising CO2 in a supercritical state,

[0017] ii. introducing the reaction mixture R) in step i. into a closed mold, wherein the back pressure in the closed mold during introduction is 2.0 to 90 bar,

[0018] iii. foaming the reaction mixture R) in a closed mold along a foaming direction to obtain a film having a thickness D in a dimension substantially perpendicular to the foaming direction. e PUR / PIR rigid foam,

[0019] iv. Demolding of PUR / PIR rigid foam,

[0020] v. Set the thickness D of PUR / PIR rigid foam e Compressed to thickness D k , to obtain compressed PUR / PIR rigid foam, where D k 0.05·D e To 0.95·D e And wherein step v. can be performed before or after step iv.

[0021] In step i, a reaction mixture is prepared by mixing at least supercritical CO2 as a blowing agent, an isocyanate-reactive composition A) and a polyisocyanate component B). The isocyanate-reactive composition A) contains at least one polyol component A1) with a functionality of 2.5, which contains at least one polyether polyol, polyester polyol, polycarbonate polyol, polyether-polycarbonate polyol, polyetherester polyol or a mixture thereof. The composition A) may also contain a catalyst component A2), an auxiliary and additive component A3), or both the catalyst component A2) and the auxiliary and additive component A3). The composition A) may finally also contain low molecular weight isocyanate-reactive compounds A4) and / or other isocyanate-reactive compounds A5), such as graft polyols, polyamines, polyamino alcohols and polythiols. Comprising here are all combinations of A1) with A2), A3), A4) and / or A5), i.e. A1) with A2); A1) with A3); A1) with A4); A1) with A5); A1) with A2) and A3); A1) with A2) and A4); A1) with A2) and A5); A1) with A3) and A4); A1) with A3) and A5); A1) with A4) and A5); A1) with A2), A3) and A4); A1) with A3) and A5); A1) with A4) and A5); A1) with A2), A3) and A4); A1) with A2), A3) and A5); A1) with A2), A4) and A5); A1) with A3), A4) and A5).

[0022] In step ii., the reaction mixture obtained in step i. is introduced into a closed mold, wherein a counterpressure of 2.0 to 90 bar prevails in the closed mold.

[0023] In step iii., the reaction mixture is foamed in a closed mold and a PUR / PIR rigid foam is obtained. The foaming takes place in a specific direction, the so-called foaming direction. If, for example, the reaction mixture is located at the bottom of a cuboid before foaming and the foam formed during the foaming rises vertically upward, the vertical direction pointing upward is the foaming direction. The resulting foam has a thickness D substantially perpendicular to the foaming direction. e In the context of the present application, a direction Y that is "substantially perpendicular to" a direction X is a direction Y that makes an angle of (90±10)° with the direction X.

[0024] In step iv., the PUR / PIR rigid foam is demoulded.

[0025] In step v., the PUR / PIR rigid foam is compressed. The compression can be carried out in a closed mold after demoulding or before demoulding. Thickness D e Here it is compressed to a thickness of D k , which is 0.05·D e To 0.95·D e .

[0026] This solution is surprising, since the foams on which it is based are already very fine-porous, i.e. the cell size of the polyurethane foam is very small, in some cases less than 100 μm. On the one hand, it was surprising that such fine-porous foams could withstand the compression according to the invention without destroying the cell structure at all. On the other hand, it was surprising that in such fine-porous foams compression would lead to a reduction in thermal conductivity, since for a given foam the thermal conductivity generally increases likewise with increasing density. It was expected that in the compression of fine-porous foams in particular the electrical conductivity of the polymer material would dominate and the electrical conductivity of the foam would increase. Finally, it was surprising that the mechanical properties of the resulting foam, in particular the compressive strength, were maintained.

[0027] In one embodiment, the proportion of all primary OH functions present in the polyol component A1) to the total number of terminal OH functions in the polyol component A1) is at least 30%.

[0028] In another embodiment, the thickness D e Compressed to thickness D k , which is 0.20 to 0.95·D e , preferably 0.35 to 0.95·D e , or 0.35 to 0.95·D e , more preferably 0.50 to 0.95·D e or 0.50 to 0.90·D e .

[0029] In one embodiment, the number of NCO groups in the isocyanate component B) and the number of isocyanate-reactive hydrogen atoms in the isocyanate-reactive composition A) have a numerical ratio of ≧110:100 to ≦300:100 to one another.

[0030] In another embodiment, the reaction mixture R) is substantially free of pore-opening compounds or comprises no pore-opening compounds. The expression "substantially free" here means that the reaction mixture R) comprises pore-opening compounds in an amount that corresponds at most to unintentional contaminants, for example less than 0.1% by weight, based on the total amount of isocyanate-reactive composition A.

[0031] In another embodiment, step i) is carried out under supercritical conditions of CO 2. In a preferred embodiment, both step i. and step ii. are carried out under supercritical conditions of CO 2.

[0032] In another embodiment, in step iii., the back pressure is maintained for a time period 1 of 1 to 40 seconds after the end of step ii., and then the back pressure is reduced in a time period 2 at a reduction rate of 1 to 90 bar / s.

[0033] In another embodiment, the polyol component A1) has a hydroxyl number of 280 to 600 mg KOH / g, measured according to DIN 53240-2:2007.

[0034] In one embodiment, at least 65% by weight of the isocyanate-reactive composition A) consists of a polyol component A1) having a hydroxyl number of 280 to 600 mg KOH / g and a functionality of ≥2.8 to ≤6.0, measured in accordance with DIN 53240-2:2007. In another embodiment, the proportion of primary OH functional groups present in the isocyanate-reactive composition A) to the total number of all terminal OH functional groups in the isocyanate-reactive composition A) is at least 35%. In a preferred embodiment, at least 65% by weight of the isocyanate-reactive composition A), based on the total amount of A) excluding A2) and A3), consists of a polyol component A1) having a hydroxyl number of 280 to 600 mg KOH / g and a functionality of ≥2.8 to ≤6.0, measured in accordance with DIN 53240-2:2007, and the proportion of primary OH functional groups present in the isocyanate-reactive composition A) to the total number of all terminal OH functional groups in the isocyanate-reactive composition A) is at least 35%.

[0035] In a further embodiment, at least 60% by weight of the isocyanate-reactive composition A) consists of polyether polyols.

[0036] The isocyanate-reactive composition A) contains at least one polyol component A1) selected from the group consisting of polyether polyols, polyester polyols, polyether ester polyols, polycarbonate polyols and polyether-polycarbonate polyols.

[0037] The proportion of primary OH functions in the polyol component A1) to the total number of terminal OH functions is preferably at least 30%, more preferably at least 35%, particularly preferably at least 38%.

[0038] The polyol component A1) is further characterized by a functionality f of >2.5, preferably ≥2.6 to ≤6.5, particularly preferably ≥2.8 to ≤6.1. Isocyanate-reactive compositions of the polyol component A1) having a functionality within these ranges exhibit an optimal viscosity increase during injection until the back pressure is reduced and allow faster demoulding of the foam.

[0039] The hydroxyl number of the polyol component A1) is preferably from 280 to 600 mg KOH / g, particularly preferably from 300 to 580 mg KOH / g, particularly preferably from 350 to 540 mg KOH / g. This has a particularly favorable effect on the mechanical properties of the foam.

[0040] In the context of the present application, a "polyether polyol" may also be a mixture of different polyether polyols, which also applies analogously to the other polyols described herein.

[0041] The polyether polyols which can be used according to the invention are the polyether polyols which are known to the person skilled in the art and which can be used for polyurethane synthesis.

[0042] Useful polyether polyols include, for example, polytetramethylene glycol polyethers obtainable by cationic ring-opening polymerization of tetrahydrofuran.

[0043] Likewise suitable polyether polyols include adducts of styrene oxide, ethylene oxide, propylene oxide, butylene oxide and / or epichlorohydrin with difunctional or polyfunctional starter molecules. Particularly preferred are adducts of ethylene oxide and propylene oxide. Suitable starter molecules are, for example, water, ethylene glycol, diethylene glycol, butyl diethylene glycol, glycerol, diethylene glycol, trimethylolpropane, propylene glycol, pentaerythritol, sorbitol, sucrose, ethylenediamine, toluenediamine, triethanolamine, bisphenols, in particular 4,4'-methylenebisphenol, 4,4'-(1-methylethylidene)bisphenol, 1,4-butanediol, 1,6-hexanediol and low molecular weight hydroxyl-containing esters of such polyols with dicarboxylic acids and oligoethers of such polyols.

[0044] Preferably, the isocyanate-reactive composition A) comprises at least 50% by weight, preferably at least 60% by weight, particularly preferably at least 70% by weight of polyether polyols, based on its total weight. In a preferred embodiment, 100% by weight of component A1) consists of polyether polyols. These preferred embodiments are characterized by particularly good hydrolytic stability.

[0045] Available polyetherester polyols are compounds containing ether groups, ester groups and OH groups. Organic dicarboxylic acids with a maximum of 12 carbon atoms are suitable for producing polyetherester polyols, preferably aliphatic dicarboxylic acids or aromatic dicarboxylic acids with ≥4 to ≤6 carbon atoms, which are used alone or in combination. Examples include suberic acid, azelaic acid, decanedicarboxylic acid, maleic acid, malonic acid, phthalic acid, pimelic acid and sebacic acid, and particularly glutaric acid, fumaric acid, succinic acid, adipic acid, phthalic acid, terephthalic acid and m-terephthalic acid. Except for organic dicarboxylic acids, derivatives of these acids can also be used, such as their anhydrides and esters and half esters of low molecular weight monofunctional alcohols with ≥1 to ≤4 carbon atoms. It is possible to partially use the above-mentioned bio-based starting materials, particularly fatty acids or fatty acid derivatives (oleic acid, soybean oil, etc.), and can have advantages, such as in the storage stability of polyol formulations, the dimensional stability of foams, fire retardant behavior and compression strength.

[0046] The polyether polyols obtained by alkoxylation of starter molecules (eg polyols) are used as a further component for preparing polyetherester polyols. The starter molecules are at least difunctional, but may optionally also contain a certain proportion of higher-functional starter molecules, in particular trifunctional starter molecules.

[0047] The starter molecules are, for example, diols having a number average molecular weight Mn of preferably ≥18 g / mol to ≤400 g / mol, preferably ≥62 g / mol to ≤200 g / mol, such as 1,2-ethanediol, 1,3-propylene glycol, 1,2-propylene glycol, 1,4-butanediol, 1,5-pentene diol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,10-decanediol, 2- Methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2-butyl-2-ethyl-1,3-propanediol, 2-butene-1,4-diol and 2-butyne-1,4-diol, ether diols, for example diethylene glycol, triethylene glycol, tetraethylene glycol, dibutylene glycol, tributylene glycol, tetrabutylene glycol, dihexanediol, trihexanediol, tetrahexanediol and oligomeric mixtures of alkylene glycols, for example diethylene glycol. Starter molecules having functional groups other than OH can also be used alone or in the form of mixtures.

[0048] In addition to diols, compounds having >2 Zerewitinoff-active hydrogens (in particular having a number-average functionality of >2 to ≤8, in particular ≥3 to ≤6) can also be used as starter molecules for the preparation of polyethers, for example 1,1,1-trimethylolpropane, triethanolamine, glycerol, sorbitan and pentaerythritol and triol- or tetraol-started polyethylene oxide polyols, whose average molar mass Mn is preferably ≥62 g / mol to ≤400 g / mol, in particular ≥92 g / mol to ≤200 g / mol.

[0049] Polyetherester polyols can also be prepared by alkoxylation (especially ethoxylation and / or propoxylation) of the reaction products obtained by reacting organic dicarboxylic acids and their derivatives with components having Zerevitenov-active hydrogen (especially diols and polyols). Derivatives of these acids that can be used include, for example, their anhydrides, such as phthalic anhydride.

[0050] Suitable polyester polyols are in particular the polycondensates of diols, triols and tetraols with dicarboxylic acids, tricarboxylic acids and tetracarboxylic acids or hydroxycarboxylic acids or lactones. Instead of the free polycarboxylic acids, the corresponding polycarboxylic anhydrides or corresponding lower alcohol polycarboxylic esters can also be used to prepare the polyesters.

[0051] Examples of suitable diols are ethylene glycol, butanediol, diethylene glycol, triethylene glycol, polyalkylene glycols such as polyethylene glycol and 1,2-propylene glycol, 1,3-propylene glycol, 1,3- and 1,4-butylene glycol, 1,6-hexanediol and isomers, neopentyl glycol or neopentyl glycol hydroxypivalate. In addition, polyols such as trimethylolpropane, glycerol, erythritol, pentaerythritol, trimethylolbenzene or trishydroxyethyl isocyanurate can also be used.

[0052] Furthermore, a monohydric alkanol may be additionally co-used.

[0053] Examples of polycarboxylic acids include phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, cyclohexanedicarboxylic acid, adipic acid, azelaic acid, sebacic acid, glutaric acid, tetrachlorophthalic acid, maleic acid, fumaric acid, itaconic acid, malonic acid, suberic acid, succinic acid, 2-methylsuccinic acid, 3,3-diethylglutaric acid, 2,2-dimethylsuccinic acid, dodecanedioic acid, endomethylenetetrahydrophthalic acid, dimer fatty acids, trimer fatty acids, citric acid or trimellitic acid. The corresponding anhydrides can also be used as acid sources.

[0054] Monocarboxylic acids such as benzoic acid and alkanecarboxylic acids may also be used together.

[0055] Hydroxycarboxylic acids which can be used as reaction partners for preparing polyester polyols having terminal hydroxyl groups are, for example, hydroxycaproic acid, hydroxybutyric acid, hydroxydecanoic acid, hydroxystearic acid, etc. Suitable lactones are, in particular, caprolactone, butyrolactone and homologues.

[0056] Also suitable for preparing the polyester polyols are, in particular, biobased starting materials and / or derivatives thereof, such as castor oil, polyhydroxy fatty acids, ricinoleic acid, hydroxyl-modified oils, grape seed oil, black cumin oil, pumpkin kernel oil, borage seed oil, soybean oil, wheat germ oil, rapeseed oil, sunflower seed oil, peanut oil, almond oil, pistachio oil, almond oil, olive oil, macadamia oil, avocado oil, sea buckthorn oil, sesame oil, hemp oil, hazelnut oil, primrose oil, wild rose oil, safflower oil, walnut oil, fatty acids, hydroxyl-modified and epoxidized fatty acids and fatty acid esters, such as those based on myristoleic acid, palmitoleic acid, oleic acid, octadecenoic acid, petroselinic acid, gadoleic acid, erucic acid, nervonic acid, linoleic acid, α- and γ-linolenic acid, octadecatenic acid, arachidonic acid, eicosatetraenoic acid, docosapentaenoic acid and docosahexaenoic acid. Particular preference is given to esters of ricinoleic acid with polyfunctional alcohols, such as glycerol. It is also preferred to use mixtures of such biobased acids with other carboxylic acids, such as phthalic acid.

[0057] Useful polycarbonate polyols are polycarbonates with hydroxyl groups, such as polycarbonate diols. These can be obtained by reaction of carbonic acid derivatives (such as diphenyl carbonate, dimethyl carbonate or phosgene) with polyols (preferably diols), or by copolymerization of alkylene oxides (such as propylene oxide) with CO2.

[0058] Examples of such diols are ethylene glycol, 1,2- and 1,3-propylene glycol, 1,3- and 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol, neopentyl glycol, 1,4-bishydroxymethylcyclohexane, 2-methylpropane-1,3-diol, 2,2,4-trimethylpentane-1,3-diol, dipropylene glycol, polypropylene glycol, dibutylene glycol, polybutylene glycol, bisphenol A and lactone-modified diols of the abovementioned type.

[0059] Instead of or in addition to the pure polycarbonate diols, it is also possible to use polyether polycarbonate diols which are obtainable, for example, by copolymerization of alkylene oxides, such as propylene oxide, with CO 2 .

[0060] Methods for preparing polyols are described, for example, by Ionescu, "Chemistry and Technology of Polyols for Polyurethanes", Rapra Technology Limited, Shawbury 2005, pages 55 et seq. (Chapter 4: Oligo-Polyols for Elastic Polyurethanes), pages 263 et seq. (Chapter 8: Polyester Polyols for Elastic Polyurethanes), in particular pages 321 et seq. (Chapter 13: Polyether Polyols for Rigid Polyurethane Foams) and pages 419 et seq. (Chapter 16: Polyester Polyols for Rigid Polyurethane Foams). Polyester polyols and polyether polyols can also be obtained by glycolysis of suitable polymer recyclates. Suitable polyether-polycarbonate polyols and methods for their preparation are described, for example, in EP 2910585 A,

[0024] -

[0041] . Examples relating to polycarbonate polyols and processes for their preparation are found, inter alia, in EP 1359177 A. Processes for the preparation of suitable polyetherester polyols are described, inter alia, in WO 2010 / 043624 A and EP 1923417 A.

[0061] When the alkylene oxide used for alkoxylation has a high proportion of ethylene oxide, polyether polyols, polyether carbonate polyols and polyether ester polyols with a high proportion of primary OH functional groups are obtained. The molar proportion of ethylene oxide structures is in particular at least 50 mol%, based on the sum of the alkylene oxide structures present in the polyols of component A1. The use of 100 mol% of ethylene oxide is likewise a preferred embodiment.

[0062] The isocyanate-reactive composition A) may also contain low molecular weight isocyanate-reactive compounds A4), in particular difunctional or trifunctional amines and alcohols, particularly preferably diols and / or triols having a molar mass Mn of less than 400 g / mol, preferably from 60 to 300 g / mol, such as triethanolamine, diethylene glycol, ethylene glycol, glycerol. If such low molecular weight isocyanate-reactive compounds are used for the production of rigid polyurethane foams, for example as chain extenders and / or crosslinkers, and they do not fall within the definition of polyol component A1), they are advantageously used in an amount of up to 5% by weight, based on the total weight of the composition A).

[0063] In addition to the above-mentioned polyols and isocyanate-reactive compounds, the composition A) may also contain other isocyanate-reactive compounds A5), such as graft polyols, polyamines, polyamino alcohols and polythiols. It is to be understood that the isocyanate-reactive component also includes such compounds with mixed functionalities.

[0064] Preferred isocyanate-reactive compositions A) comprise a polyol component A1) having a hydroxyl number of 280 to 600 mg KOH / g and a functionality of ≥2.8 to ≤6.0, a content of at least 65% by weight, in particular at least 80% by weight, very particularly preferably more than 90% by weight, based on the total amount of A) (excluding components A2) and A3)), and a proportion of primary OH functions in the composition A) of at least 35% (based on all terminal OH functions in the composition A).

[0065] In the preparation of PUR / PIR rigid foams, supercritical CO2 is used as blowing agent component C). The amount of blowing agent component C) is sufficient to achieve a dimensionally stable foam matrix and the desired apparent density. This is usually 0.5 to 30 parts by weight of blowing agent, based on 100 parts by weight of composition A) (excluding A2) and A3)).

[0066] CO2 as a physical blowing agent is used in a supercritical or near-critical state. In the present invention, near-critical conditions exist when the following conditions are met: (Tc-T) / T≤0.4 and / or (pc-p) / p≤0.4. Wherein, T is the temperature existing in the method, Tc is the critical temperature of the blowing agent or the blowing agent mixture, p is the pressure existing in the method, and pc is the critical pressure of the blowing agent or the blowing agent mixture. Near-critical conditions are preferably when the following conditions are met: (Tc-T) / T≤0.3 and / or (pc-p) / p≤0.3, and (Tc-T) / T≤0.2 and / or (pc-p) / p≤0.2 are particularly preferred.

[0067] Particularly suitable conditions for carrying out the process of the invention when using CO2 are pressures and temperatures above the critical point of CO2, i.e. ≥73.7 bar and ≥30.9°C, preferably 74 to 350 bar and 31 to 100°C, particularly preferably 75 to 200 bar and 32 to 60°C.

[0068] In addition to critical CO 2 , physical blowing agents can also be used as additional blowing agents. In the present invention, “physical blowing agents” are understood to be compounds which, due to their physical properties, tend to volatilize and do not react with the polyisocyanate component B).

[0069] The additional physical blowing agent may be selected from hydrocarbons (e.g. n-pentane, isopentane, cyclopentane, butane, isobutane, propane), ethers (e.g. methylal), halogenated ethers, perfluorinated and partially fluorinated hydrocarbons having 1 to 8 carbon atoms (e.g. perfluorohexane), HFC245fa (1,1,1,3,3-pentafluoropropane), HFC 365mfc (1,1,1,3,3-pentafluorobutane), HFC 134a or mixtures thereof, and (hydro)fluorinated olefins, such as HFO 1233zd(E) (trans-1-chloro-3,3,3-trifluoro-1-propene) or HFO 1336mzz(Z) (cis-1,1,1,4,4,4-hexafluoro-2-butene) or additives such as FA from 3M. 188(1,1,1,2,3,4,5,5,5-nonafluoro-4-(trifluoromethyl)pent-2-ene), and mixtures thereof.

[0070] When further blowing agents are added, in one embodiment the blowing agent component C) preferably contains more than 60% by weight of supercritical CO 2 , particularly preferably more than 75% by weight.

[0071] In addition to or instead of physical blowing agents, chemical blowing agents (also called "co-blowing agents") can also be used. These chemical blowing agents are particularly preferably water and / or formic acid. Co-blowing agents are preferably used in an amount of 0 to 6% by weight, particularly preferably 0.5 to 4% by weight, based on the total amount of compounds having hydrogen atoms reactive toward isocyanate groups in the foam-forming reaction mixture R).

[0072] The proportion of blowing agent C) is preferably ≥1% by weight to ≤30% by weight, more preferably ≥4% by weight to ≤20% by weight, particularly preferably ≥6% by weight to ≤16% by weight, in each case based on the total amount of components A) and C); the proportion of blowing agent in the reaction mixture R) is 0.5% by weight to 15% by weight, preferably 2% by weight to 10% by weight, particularly preferably ≥3% by weight to ≤8% by weight, in each case based on the total amount of R).

[0073] In another embodiment, the isocyanate-reactive composition A) comprises the catalyst component A2), preferably in an amount of ≥0.01 to <2.0 wt. %, based on the total weight of the isocyanate-reactive composition A).

[0074] Compounds which accelerate the reaction of the compounds of composition A) containing hydroxyl groups or isocyanate-reactive groups with the isocyanate groups of component B are generally used as catalyst components A2).

[0075] The catalyst component A2) may contain A2a) at least one catalytically active amine compound having a functional group which has a Zerewitinoff-active hydrogen and can therefore react with isocyanates (so-called “incorporable catalysts”). Examples of catalysts that can be used and can be incorporated are bis(dimethylaminopropyl)urea, bis(N,N-dimethylaminoethoxyethyl)urethane, dimethylaminopropyl urea, N,N,N-trimethyl-N-hydroxyethylbis(aminopropyl ether), N,N,N-trimethyl-N-hydroxyethylbis(aminoethyl ether), diethylethanolamine, bis(N,N-dimethyl-3-aminopropyl)amine, dimethylaminopropylamine, 3-dimethylaminopropyl-N,N-dimethylpropane-1,3-diamine, dimethyl-2-(2-aminoethoxyethanol) and (1,3-bis(dimethylamino)propan-2-ol), N,N-bis(3-dimethylaminopropyl)-N-isopropanolamine, bis(dimethylaminopropyl)-2-hydroxyethylamine, N,N,N-trimethyl-N-(3-aminopropyl)-bis(aminoethyl ether), 3-dimethylaminoisopropyldiisopropanolamine or mixtures thereof.

[0076] It is also possible to use one or more further compounds A2b), in particular catalytically active compounds known for PUR / PIR chemistry, including not only further amine compounds but also salts, for example tin(II) acetate, tin(II) octoate, tin(II) ethylhexanoate, tin(II) laurate, dibutyltin diacetate, dibutyltin dilaurate, dibutyltin maleate, dioctyltin diacetate, tris(N,N-dimethylaminopropyl)-s-hexahydrotriazine, tetramethylammonium hydroxide, sodium acetate, sodium octoate, potassium acetate, potassium octoate, sodium hydroxide.

[0077] The catalyst component A2) is generally used in an amount of 0.001 to 5% by weight, in particular 0.05 to 2.5% by weight, based on the weight of the composition A). Particularly preferably, the catalyst component A2) contains both an incorporable catalyst A2a) and a non-incorporable catalyst A2b). Particularly preferably, an incorporable amine compound and a catalytically active salt are used in combination.

[0078] Catalysts A2a) and A2b) are preferably used in a molar ratio A2a) / A2b) of 0.1 to 16.3, particularly preferably 0.3 to 10, very particularly preferably 0.8 to 6.0. The catalyst component A2) preferably comprises an amine compound that can be incorporated into the polyurethane as a catalytically active compound A2a) and a catalytically active compound A2b), which is a catalytically active salt that cannot be incorporated into the polyurethane, and the molar ratio of A2a) / A2b) is 0.1 to 16.3, particularly preferably 0.3 to 10, very particularly preferably 0.8 to 6.0. In a particularly preferred embodiment, 3-(dimethylamino)propyl urea and potassium acetate are used in a molar ratio A2a) / A2b) of 0.1 to 6.0, particularly preferably 0.3 to 10, very particularly preferably 0.8 to 6.0. The preferred catalyst ratio or catalyst particularly advantageously leads to a specific viscosity increase.

[0079] In one embodiment, the isocyanate-reactive composition A) comprises an auxiliary and additive component A3) which comprises a stabilizer, preferably in an amount of ≥0.05 wt. % to <5 wt. %, based on the total weight of the isocyanate-reactive composition A).

[0080] In another embodiment, the reaction mixture R) comprises essentially no pore-opening compounds or no pore-opening compounds. The expression "essentially free" means here that the reaction mixture R) comprises pore-opening compounds in an amount that corresponds at most to unintentional contaminants, for example less than 0.1% by weight, based on the total amount of isocyanate-reactive composition A.

[0081] The reaction mixture R) may contain auxiliaries and additives A3). The auxiliaries and additives may contain pore-opening compounds, but preferably contain essentially no or no pore-opening compounds. Cell-opening compounds are described, for example, in Kunststoff-Handbuch, Volume 7, Polyurethane, Carl Hanser Verlag, München / Wien, 3rd edition, 1993, pages 104-127. These are, for example, silicones, for example polyether-polydimethylsiloxane copolymers, or organic polymers, for example polymers based on polybutadiene (for example Ortegol 500 and 501 from Evonik Industries), surfactants, for example the sodium salt of ethoxylated and sulfated isotridecanol, which is available under the trade name Sermul EA266 (Elementis Specialties, The Netherlands), and mixtures of different components, for example mixtures of amine-stabilized, macromolecular, unsaturated hydrocarbons and phthalates.

[0082] Further auxiliaries and additives A3) which can be used in the process according to the invention are the customary auxiliaries and additives known to the prior art and to the person skilled in the art. These include, for example, surface-active substances, stabilizers, in particular foam stabilizers, cell regulators, fillers, dyes, pigments, flame retardants, antistatic agents, antihydrolysis agents and / or fungistatic and bacteriostatic substances.

[0083] Polyether-polydimethylsiloxane copolymers are frequently used as foam stabilizers, preferably polyethylene oxide-polyethers with oligodimethylsiloxane end groups, the number of dimethylsiloxane units preferably being ≤5.

[0084] Useful stabilizers also include saturated and unsaturated hydrocarbons, such as paraffins, polybutadienes, fatty alcohols and esters, such as carboxylic esters. Preference is given to using stabilizers, in particular foam stabilizers, which do not have a cell-opening effect.

[0085] Composition A) preferably contains a total of not more than 3% by weight of silicone and polybutadiene.

[0086] Also useful as stabilizers are surfactants, for example alkoxylated alkanols, for example ethers of linear or branched alkanols having ≥6 to ≤30 carbon atoms and polyalkylene glycols having ≥5 to ≤100 alkylene oxide units, alkoxylated alkylphenols, alkoxylated fatty acids, carboxylic acid esters of alkoxylated anhydrous sorbitan (especially polysorbate 80), fatty acid esters, polyalkyleneamines, alkyl sulfates, phosphatidylinositols, fluorinated surfactants, surfactants containing polysiloxane groups and / or bis(2-ethyl-1-hexyl)sulfosuccinate. Fluorinated surfactants may be perfluorinated or partially fluorinated. Examples thereof are partially fluorinated ethoxylated alkanols or carboxylic acids.

[0087] The composition A) preferably contains a total of not more than 5% by weight of surfactants, particularly preferably not more than 3% by weight, more preferably less than 2% by weight, particularly preferably not more than 1.6% by weight, based on the total weight of the composition A).

[0088] The reaction mixture R) comprises a polyisocyanate component B), i.e. an isocyanate having an NCO functionality of ≥ 2. Examples of suitable polyisocyanates of this type include 1,4-butylene diisocyanate, 1,5-pentane diisocyanate, 1,6-hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), 2,2,4- and / or 2,4,4-trimethylhexamethylene diisocyanate, isomeric bis(4,4′-isocyanatocyclohexyl)methane or mixtures thereof with any isomeric content, 1,4-cyclohexyl diisocyanate, 1,4-phenylene diisocyanate, 2,4- and / or 2,4,4-trimethylhexamethylene diisocyanate. 2,6-toluene diisocyanate (TDI), 1,5-naphthalene diisocyanate, 2,2'- and / or 2,4'- and / or 4,4'-diphenylmethane diisocyanate (MDI) and / or higher homologues, 1,3- and / or 1,4-bis(2-isocyanatoprop-2-yl)benzene (TMXDI), 1,3-bis(isocyanatomethyl)benzene (XDI) and 2,6-diisocyanatocyclohexanoic acid alkyl esters having a C1 to C6 alkyl group (lysine diisocyanate).

[0089] The isocyanate component B) preferably used is a mixture of isomers of diphenylmethane diisocyanate ("monomeric MDI", abbreviated to "mMDI") and its oligomers ("oligomeric MDI"). The mixture of monomeric MDI and oligomeric MDI is usually called "polymeric MDI" (pMDI). The oligomers of MDI are polyphenyl polymethylene polyisocyanates with a high ring content, i.e. mixtures of high-ring homologues of diphenylmethane diisocyanate with an NCO functionality f>2 and having the following structural formula: C15H10N2O2[C8H5NO]n, where n=>0 integers, preferably n=1, 2, 3 and 4. The high-ring homologues C15H10N2O2[C8H5NO]m, where m=>4 integers) can likewise be included in the mixture of organic polyisocyanates a). Likewise preferred as isocyanate component B) are mixtures of mMDI and / or pMDI which comprise up to 20% by weight, more preferably up to 10% by weight, of other aliphatic, cycloaliphatic and in particular aromatic polyisocyanates known for producing polyurethanes, very particularly TDI.

[0090] In addition to the above-mentioned polyisocyanates, modified diisocyanates having a uretdione, isocyanurate, urethane, carbodiimide, uretonimine, allophanate, biuret, amide, iminooxadiazinedione and / or oxadiazinedione structure, and unmodified polyisocyanates having more than two NCO groups per molecule, for example 4-isocyanatomethyl-1,8-octane diisocyanate (nonane triisocyanate) or triphenylmethane 4,4',4"-triisocyanate, can also be used in part.

[0091] Instead of or in addition to the polyisocyanates mentioned above, suitable NCO prepolymers can also be used as organic isocyanate component B). The prepolymers can be prepared by reacting one or more polyisocyanates with one or more polyols corresponding to the polyols mentioned under components A1) and A2).

[0092] The isocyanate may be a prepolymer obtainable by reacting an isocyanate having an NCO functionality of ≧2 with a polyol having a molecular weight of ≧62 g / mol to ≦8000 g / mol and an OH functionality of ≧1.5 to ≦6.

[0093] The NCO content is preferably ≧29.0 wt % to ≦32.0 wt %, and the viscosity at 25° C. is preferably ≧80 mPas to ≦2000 mPas, particularly preferably ≧100 mPas to ≦800 mPas (dynamic viscosity determined at 25° C. in accordance with DIN 53019).

[0094] The number of NCO groups in the polyisocyanate component B) and the number of isocyanate-reactive groups in the composition A) can have a numerical ratio of, for example, ≥50:100 to ≤300:100 to each other. In order to prepare a rigid polyurethane foam, components A) and B) are usually reacted in an amount such that the isocyanate index in the formulation is 80-150, preferably 90-130, particularly preferably 95-125. Within this range, preferably urethane groups are formed. In another preferred embodiment, the isocyanate index is 150-300. Within this range, the foam has a high proportion of isocyanurate functional groups, which, for example, achieves the inherent flame retardancy of the foam.

[0095] The method of the present invention consists of at least steps i. to v.

[0096] In step i. of the process according to the invention, a reaction mixture R) is prepared from components A), B) and C).

[0097] For this purpose, for example, the composition A) can be precharged in a container and subsequently mixed with the blowing agent component C) and the polyisocyanate B) can be added. The mixing of the components can also be carried out in a mixing head.

[0098] Mixing, in particular with components C) and B), can be carried out under pressure. In a preferred embodiment, components A) and C) are mixed with component B) in a high-pressure mixing head.

[0099] The blowing agent component C) is CO2 in a supercritical state, and the reaction of the components is preferably carried out under CO2 supercritical conditions. In this case, suitable pressures in the mixing head and / or in the discharge pipe or discharge pipes for producing the polyurethane foam are, for example, ≥73.7 bar to ≤350 bar, preferably ≥75 bar to ≤200 bar. Suitable temperatures are, for example, ≥30.9°C to ≤100°C, preferably ≥32°C to ≤60°C. At such pressures, supercritical conditions of the blowing agent used can be maintained.

[0100] In another embodiment, the residence time of the mixture in the mixing head under supercritical conditions of the blowing agent is >0 seconds to ≤20 seconds, preferably ≥0.1 seconds to ≤10 seconds, particularly preferably ≥0.5 seconds to ≤5 seconds. This results in the mixture being able to polymerize under supercritical conditions. The residence time can be determined by dividing the volume of the reaction chamber (=mixing chamber and / or pipeline) in which supercritical conditions exist by the volume of the mixture conveyed per a specific unit of time.

[0101] In step ii. of the process according to the invention, the reaction mixture R) according to the invention consisting of components A), B) and C) is introduced into a closed mold, wherein the counterpressure in the mold during the introduction is 2.0 to 90 bar, preferably 2.0 to 80 bar, particularly preferably 5.0 to 40 bar.

[0102] Possible embodiments in this regard are as follows: counterpressure is achieved by applying gas (compressed air or nitrogen) to the mold directly and / or via a floating seal that divides the pressurized space into a gas space and a reaction space, and is regulated, maintained and finally decompressed by a proportional valve.

[0103] In step iii. of the process, the reaction mixture is foamed.

[0104] A preferred embodiment of step iii) is as follows: After step ii. has ended, the counterpressure in the mold is kept constant for a time period 1, which is preferably 1-40 seconds, particularly preferably 5-20 seconds, very particularly preferably 8-17 seconds, wherein the viscosity of the reaction mixture initially increases without the reaction mixture foaming. It has been found that maintaining the pressure during the preferred time period leads to a viscosity range of the mixture that is particularly favorable for this reaction phase. After the end of time period 1, the mold is depressurized. The mold is depressurized in a time period 2 at a decompression rate of 1-90 bar / s, preferably 1-80 bar / s, particularly preferably 2-70 bar / s. The decompression can be carried out in particular by a proportional valve. The reaction mixture foams in time period 2. Too fast a decompression has a negative impact on the stability of the foam cells, and too slow a decompression has a negative impact on the foaming reaction.

[0105] In step iv. of the process, the PUR / PIR rigid foam is demoulded.

[0106] In step v. of the method, the PUR / PIR rigid foam is compressed. This compression can be carried out before or after step iv. To this end, the thickness of the PUR / PIR rigid foam is reduced.

[0107] This can be achieved by reducing the volume of the reaction mold, for example by inserting a plate and reclosing the mold containing the rigid foam. The volume of the reaction mold can be reduced by 5-95%, preferably by 40-70%. e Reduce by 40% to D k Equivalent to a reduction to D e (100-40)% = 60%, that is, thickness D e = 100mm rigid foam is compressed by 40% which is equivalent to compression to thickness D k =(100-0.4*100)mm=60mm compressed rigid foam.

[0108] After a certain period of time after the reaction mixture has been foamed, compression can be carried out in the reduced-volume mold. This period of time can be from 10 seconds to 30 minutes, preferably from 1 to 10 minutes. Compression can also be carried out before or after the foam has solidified. The duration of the compression, i.e. the maintenance of the reduced volume in the closed mold, is from 1 to 30 minutes, preferably from 2 to 15 minutes. The time and duration of the compression influence the thickness D of the resulting compressed foam. k , the thickness is measured 24 hours after the end of compression.

[0109] Alternatively, the rigid foam can also be compressed in a hydraulic press after step iv.

[0110] The subject of the present invention is also an open-cell PUR / PIR rigid foam obtainable or obtained by the process according to the invention. The foam according to the invention has good mechanical properties, in particular good dimensional stability at high temperatures and preferably also good compressive strength.

[0111] Preferably, the open-cell PUR / PIR rigid foam has an apparent density according to ISO 845:2006 of 30-90 kg / m 3 , preferably 30-120kg / m 3 , an open porosity of >90%, preferably ≥94%, according to ISO 4590:2002, an average (arithmetic mean) cell diameter of 70-130 μm as evaluated by optical microscopy. The value for the average cell diameter is based on the foam which has not yet been compressed in step v.

[0112] The PUR / PIR foams according to the invention make it possible to produce foamed moldings and composite systems containing these moldings in a preferred manner. The composite system is usually delimited on both the top and bottom sides by a decorative layer. Conceivable decorative layers include, in particular, metal, plastic, wood and paper. Fields of application of such discontinuously produced PUR / PIR composite systems include, in particular, the technical insulation of electrical appliances such as refrigerators, freezers, combined refrigerator-freezers, and boilers, refrigerated containers and refrigerators, and also pipes.

[0113] The use of PUR / PIR foams in these areas is already known in principle to the person skilled in the art and has been described many times. The PUR / PIR foams of the invention are extremely suitable for these purposes, since they are characterized by high dimensional stability and advantageously also by high compressive strength and low thermal conductivity, which can be further enhanced by applying a vacuum.

[0114] Finally, the present invention also provides a refrigerator, freezer or combined refrigerator-freezer comprising a PUR / PIR rigid foam obtainable by the process according to the invention.

[0115] The terms used in this application have the following meanings:

[0116] The index (also called isocyanate index, isocyanate characteristic value or characteristic value) is understood to be the quotient of the molar amount [mol] of isocyanate groups actually used and the molar amount [mol] of isocyanate-reactive hydrogen atoms actually used, multiplied by 100:

[0117] Index = (isocyanate groups [mol] / isocyanate reactive hydrogen atoms [mol]) · 100

[0118] In the context of the present application, the "functionality" or "f" of a compound refers to the theoretical functionality: for example, for a polyol started exclusively with glycerol, the functionality f=3, while for a polyol started exclusively with ethylenediamine, f=4. In the context of the present application, the "functionality" or "f" of a mixture of components refers to the number-average functionality of the mixture on which these data are based. Thus, for example, the functionality of a polyol component A1) refers to the number-average functionality of the mixture of polyols contained in component A1, based on all the isocyanate-reactive hydrogen atoms contained.

[0119] In the context of the present application, "molar weight" or "molar mass" or "Mn", respectively, means the number-weighted mean molar mass.

[0120] In the case of a single added polyol, the OH number (also called: hydroxyl number) denotes the OH number of the polyol in question. Data on the OH number of a mixture refer to the number-average OH number of the mixture, which is calculated from the OH numbers of the individual components in their respective molar ratios. The OH number denotes the amount of potassium hydroxide in milligrams which is equivalent to the amount of acetic acid which binds to one gram of substance during acetylation. In the context of the present invention, it is determined in accordance with the DIN 53240-2 standard of November 2007.

[0121] The present invention will now be described in more detail with reference to the following Examples and Comparative Examples, but the scope thereof is not limited to the Examples. Example:

[0122] Standards or measuring instruments used:

[0123] Determination of apparent density: Rubber and plastic foams - Determination of apparent density (ISO 845:2006); German version DIN EN ISO 845:2009

[0124] Open porosity determination: Determination of the volume ratio of open and closed cells (ISO 4590:2002); German version DIN EN ISO 4590:2003

[0125] Compression strength determination: Rigid foams - Determination of compression properties (ISO 844:2014); German version DIN EN ISO844:2014

[0126] OH value determination: Determination of hydroxyl value - Part 2: Method with catalyst according to DIN 53240-2 (November 2007 edition)

[0127] Cell size determination: Optical microscopy evaluation was performed using a VHX 5000 optical microscope; the specimen to be measured was examined at three different locations on a circular area with a diameter of 5 mm. The observation was performed transversely to the foaming direction. The resolution was chosen so that more than 100 cells could be captured in the selected area. All cells were subsequently evaluated using the freely available ImageJ software, and the arithmetic mean cell diameter was calculated from the resulting ECD values ​​(equivalent circular diameter).

[0128] The numerical value of the primary OH functional group ratio in Table 1 (expressed in [%) refers to the ratio of primary OH functional groups to the total number of OH functional groups in the mixture of polyols contained in the formulation.

[0129] Examples 1-3 and Comparative Examples 1-2:

[0130] According to the formulation listed in Table 1 below, polyurethane foams blown with supercritical CO2 were produced.

[0131] Unless otherwise stated, the amounts are to be understood as parts by weight. The following substances were used:

[0132] Polyol 1: trimethylol initiated polyether polyol, with propylene oxide as the alkylene oxide, hydroxyl value of 880 mgKOH / g, functionality of 3, viscosity of 6100 mPa·s at 25°C

[0133] Polyol 2: trimethylol initiated polyether polyol, with ethylene oxide as the alkylene oxide, hydroxyl value of 550 mgKOH / g, functionality of 3, viscosity of 505 mPa·s at 25°C

[0134] Polyol 3: Polyether polyol initiated by 1,2-propylene glycol, with propylene oxide as the alkylene oxide, hydroxyl value of 56 mgKOH / g, functionality of 2, viscosity of 310 mPa·s at 25°C

[0135] Polyol 4: Polyether polyol initiated by 1,2-propylene glycol, with propylene oxide as the alkylene oxide, hydroxyl value of 112 mgKOH / g, functionality of 2, viscosity of 140 mPa·s at 25°C

[0136] Polyol 5: trimethylolpropane-initiated polyether polyol, with propylene oxide as the alkylene oxide, hydroxyl value of 235 mgKOH / g, functionality of 3, viscosity of 350 mPa·s at 25°C

[0137] Polyol 6: Hydroxy functional fatty acid ester, hydroxyl value of 160 mg KOH / g, functionality of 3.

[0138] Tegostab B 8443: Polyether polydimethylsiloxane copolymer foam stabilizer (Evonik). DesmorapidPU 1792: Catalyst, potassium acetate in diethylene glycol (Covestro)

[0139] Amine ZZ: Catalyst, N'-(3-(dimethylamino)propyl)-N,N-dimethylpropane-1,3-diamine, Air Products

[0140] Isocyanate: mixture of MDI and PMDI, functionality of about 2.8, NCO content of about 31.5% by weight, viscosity at 25°C of about 200 mPa·s (Desmodur 44V20L, Covestro)

[0141] Preparation of polyurethane molded foam on high-pressure equipment:

[0142] In order to prepare polyurethane molded foams on a high-pressure device, a polyol formulation is prepared from the isocyanate-reactive compounds, stabilizers, catalysts listed in Table 1 below. The formulation is used as a polyol component in a standard high-pressure mixing device and mixed with CO2 at a pressure of 160 bar and a temperature of 50°C. Supercritical conditions for the blowing agent exist here (supercritical CO2, also called "scCO2"). In the high-pressure mixing head, the mixture is mixed with a polyisocyanate delivered at a pressure of 160 bar and a temperature of 35°C. The injection volume is 180 g / s, corresponding to a volume flow of 95 ml / s (density of the mixture is 1.2 g / ml). The resulting reaction mixture is metered into a closed mold pre-pressurized with a counterpressure of 11 bar and a mold temperature of 55°C. After the injection is completed, the pre-pressurized counterpressure is maintained for another 8 seconds before being rapidly depressurized to ambient pressure in <2 seconds.

[0143] In the method according to the invention, the mold is opened after a predetermined time (see Table 1) and, for compression, a plate of the desired thickness (Example 1, Example 2: 38% of the foam thickness) is inserted into the mold and the mold is closed again. The foam is subsequently compressed in the mold with reduced volume for a predetermined time (Examples 1-2: 5 minutes, Example 3: 10 minutes) and then demolded. In the method not according to the invention (Comparative Example 1), the mold is opened only after a predetermined time and the obtained foam is demolded. Here, the foams of Examples 1-3 before compression correspond to the foam of Comparative Example 1. The amount of scCO2 used in Comparative Example 2 is smaller, so that the resulting foam without compression has a higher apparent density than Example 1 and an apparent density comparable to that of Example 2.

[0144] Example 3 demonstrates that even fully cured foam can have its thermal conductivity improved by compression, ie, the thermal conductivity is reduced by compression.

[0145] Examples 1-3 show that compression produces a higher apparent density while reducing the arithmetic mean cell size. Very fine-pored foams with elliptical cell shapes are thus formed, which surprisingly have low thermal conductivity under vacuum. The compressed foam is characterized in that its mechanical properties are not worse than those of the uncompressed foam (Comparative Example 1).

[0146] Uncompressed foams, such as the starting foam in Comparative Example 1, have higher thermal conductivity despite lower apparent density. Comparison of foams with similar apparent density to the compressed foam (Comparative Example 2 with Examples 1-3) clearly shows that without compression, very fine-cell foams cannot be prepared and thermal conductivity is significantly increased.

[0147] Table 1

[0148]

[0149]

Claims

1. A method for producing compressed open-cell PUR / PIR rigid foam comprising the following steps i. preparing a reaction mixture R), which comprises - an isocyanate-reactive composition A) comprising a polyol component A1) having a functionality f>2.5, comprising at least one polyether polyol, polyester polyol, polycarbonate polyol, polyether-polycarbonate polyol, polyetherester polyol or a mixture thereof, optional catalyst component A2), Optional auxiliaries and additives component A3); - polyisocyanate component B); and - a blowing agent component C) comprising CO2 in a supercritical state, ii. introducing the reaction mixture R) in step i. into a closed mold, wherein the back pressure in the closed mold during introduction is 2.0 to 90 bar, iii. foaming the reaction mixture R) in a closed mold along a foaming direction to obtain a film having a thickness D in a dimension substantially perpendicular to the foaming direction. e PUR / PIR rigid foam, iv. Demolding of PUR / PIR rigid foam, v. Set the thickness D of PUR / PIR rigid foam e Compressed to thickness D k , to obtain compressed PUR / PIR rigid foam, where D k 0.05·D e To 0.95·D e And wherein step v. can be performed before or after step iv. 2 . The process according to claim 1 , wherein the proportion of all primary OH functions present in the polyol component A1) to the total number of terminal OH functions in the polyol component A1) is at least 30%.

3. The process according to any one of claims 1 to 2, wherein the reaction mixture R) contains essentially no pore-opening compounds or no pore-opening compounds.

4. The process according to any one of claims 1 to 3, wherein steps i. and optionally ii. are carried out under supercritical conditions for CO2.

5. The method according to any one of claims 1 to 4, wherein in step iii., the back pressure is maintained for a time period 1 of 1 to 40 seconds after the end of step ii., and then the back pressure is reduced in a time period 2 at a reduction rate of 1 to 90 bar / s. 6 . The process according to claim 1 , wherein the polyol component A1) has a hydroxyl number of 280 to 600 mg KOH / g, measured according to DIN 53240-2:2007.

7. The process according to claim 1 , wherein at least 65% by weight of the isocyanate-reactive composition A) consists of a polyol component A1) having a hydroxyl number of 280 to 600 mg KOH / g and a functionality of ≥2.8 to ≤6.0, measured in accordance with DIN 53240-2:2007, and the proportion of primary OH functional groups present in the isocyanate-reactive composition A) to the total number of all terminal OH functional groups in the isocyanate-reactive composition A) is at least 35%.

8. The method according to any one of claims 1 to 7, wherein the compressive strength of the PUR / PIR rigid foam measured in accordance with DIN EN ISO 844:2014 parallel to and transverse to its foaming direction is not less than 40%, preferably not less than 30%, more preferably not less than 20% of the compressive strength of a PUR / PIR rigid foam produced by the same method and having the same apparent density but not compressed, measured in accordance with DIN EN ISO 844:2014.

9. The process according to any one of claims 1 to 8, wherein the content of blowing agent component C) is 0.5% to 15% by weight, based on the total weight of R).

10. The process according to claim 1, wherein the isocyanate-reactive composition A) comprises the catalyst component A2), preferably in an amount of ≥0.01 to <2.0 wt. %, based on the total weight of the isocyanate-reactive composition A).

11. The process according to claim 1, wherein the isocyanate-reactive composition A) comprises an auxiliary and additive component A3 which comprises a stabilizer, preferably ≥0.05 to <5% by weight of stabilizer, based on the total weight of the isocyanate-reactive composition A).

12. Compressed open-cell PUR / PIR rigid foam obtainable by the process according to any one of claims 1 to 11.

13. The compressed open-cell PUR / PIR rigid foam according to claim 12, having an apparent density according to ISO 845:2006 of 30-120 kg / m 3 , preferably 30-70kg / m 3 , the open porosity according to ISO 4590:2002 is >90%, preferably ≥94%, and the average pore size evaluated according to optical microscopy is 40-130 μm.

14. Vacuum insulation panel comprising the PUR / PIR rigid foam according to claim 13.

15. A refrigerator, freezer or combined refrigerator-freezer comprising a compressed open-cell PUR / PIR rigid foam according to claim 12 or 13 or a vacuum insulation panel according to claim 14.

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