Polyurethane foam and preparation method thereof

Abstract

The invention relates to a process for producing open-cell and very fine-cell PUR / PIR rigid foams, wherein a polyol formulation is used which comprises a specific isocyanate-reactive component, a catalyst component having Zerewitinoff-active hydrogens and a cell-opening component.

Description

[0001] The present invention relates to a method for producing an open-celled polyurethane rigid foam. In addition to urethane groups (PUR), the foam material may also contain isocyanurate groups (PIR). In the present application, unless otherwise stated, the term "PUR / PIR rigid foam" or "PUR / PIR rigid foam material" refers not only to rigid foams which essentially have urethane groups, but also to rigid foams which contain urethane groups as well as isocyanurate groups.

[0002] PUR / PIR rigid foams have been known for a long time. One important field of application is thermal insulation. The use of vacuum insulation panels (VIP) containing PUR / PIR rigid foam for thermal insulation is becoming increasingly important. The foam quality has a decisive influence on the thermal insulation 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 be able to evacuate the foam well.

[0003] EP 905 159 A and EP 905 158 A disclose a method for preparing open-cell polyurethane rigid foam, in which water and hydrocarbons or fluorocarbons are preferably used as blowing agents. The polyol formulation should contain 0.1-80% by weight of polyester alcohol, wherein the reaction product of ricinoleic acid and / or castor oil and / or tall oil fatty acid and polyfunctional alcohol is preferred. These components are used as emulsifying aids for halogen-free blowing agents. In the embodiments, open-cell and closed-cell foams are prepared with the claimed polyols, wherein the open porosity is associated with the presence of additives known as cell openers. Although the cells of the obtained foam are described as fine pores, "extremely fine pores" represent a cell size range of 180-250 μm according to the description. In addition, there is no description about the uniformity of the cell size distribution.

[0004] In the preparation of PUR / PIR rigid foams, a polyol component, which also contains a blowing agent, is reacted with an isocyanate. The reaction of the isocyanate with water forms carbon dioxide, which also serves as a blowing agent. It is also known to add CO2 as a blowing agent to the polyol component or to the reaction mixture.

[0005] The sudden decompression of a reaction mixture containing CO2 is described in WO 2001 / 98389 A1. This patent application relates to a method for preparing polyurethane foam blocks, in which a polyurethane reactive mixture containing carbon dioxide is suddenly decompressed from a pressure higher than the equilibrium solution pressure of carbon dioxide to standard pressure. The dissolved carbon dioxide is released to foam the liquid polyurethane reactive mixture, the foamed mixture is applied to a substrate, and then solidified into a foam block. First, carbon dioxide is completely dissolved in the reaction mixture or at least one of the components polyol and isocyanate at a pressure significantly higher than the equilibrium solution pressure. The pressure is then reduced to a pressure close to the equilibrium solution pressure, during which a small amount of carbon dioxide is released to form a bubble microdispersion, not exceeding the equilibrium solution pressure, the components are optionally mixed, and the pressure is suddenly reduced to standard pressure before the released carbon dioxide is completely dissolved again. However, there is no information about the supercritical conditions of nanocellular foam or blowing agent.

[0006] WO 2011 / 054868 A and WO 2011 / 054873 A disclose methods for preparing fine-celled urethane-group-containing foams using CO 2 as supercritical blowing agent. In both cases, the preparation of a microemulsion from a polyol phase and supercritical CO 2 is essential for carrying out the method. This should be established by using a suitable surfactant component. However, there is no description of how to prepare predominantly open-celled foams using this method.

[0007] WO 2015 / 109488 A likewise describes a process for preparing foams containing urethane groups using CO2 as a supercritical blowing agent. The process is a multistage process in which the polyol component must first be saturated with CO2 under supercritical conditions and the reaction mixture must subsequently be subjected to a pressure of at least 100 bar. The foam produced should have a small cell size and a high porosity. However, foams with a high open porosity are only obtained when using polyethers based on propylene oxide and when using two very specific cell-opening surfactants in a specific ratio. The process provides densities of >> 100 kg / m 3 The total duration of this multi-stage process (saturation, reaction, solidification) in the reactor is >> 1 hour, during which supercritical conditions must be maintained.

[0008] Starting from the prior art, the object of the present invention is therefore to provide a polyol formulation for a reaction mixture with which very fine-pored, open-celled rigid foams containing urethane groups (PUR / PIR rigid foams) can be produced in a simple process that overcomes the disadvantages of the prior art and produces very fine-pored rigid foams containing urethane groups with a high open porosity. The highest possible open porosity combined with a small cell size is of interest for certain applications, wherein this foam property opens up the possibility of reducing the thermal conductivity of the foam by applying a negative pressure.

[0009] In particular, a polyol formulation and a method for its preparation are provided, by which a polyol formulation having an apparent density of 30 to 90 kg / m 3 A polyurethane rigid foam having an open porosity of >90%, wherein the cells have an average diameter of <50 μm.

[0010] The subject of the present invention is a process for producing a PUR / PIR rigid foam material having an apparent density according to ISO 845:2006 of 30-90 kg / m³, preferably 30-70 kg / m³, an open porosity according to ISO 4590:2002 of >90%, preferably ≥94%, and an average cell diameter evaluated by optical microscopy of <50 μm, said process comprising the following steps:

[0011] i) preparing a foam-forming reaction mixture R) comprising a polyol formulation P) comprising

[0012] - an isocyanate-reactive component A), comprising

[0013] at least one polyol component A1) having a functionality f> 2.5, which is selected from polyether polyols, polyester polyols, polycarbonate polyols, polyether-polycarbonate polyols and polyetherester polyols,

[0014] - a catalyst component D), which comprises at least a catalytically active compound D1) having a Zerewitinoff-active hydrogen

[0015] - auxiliaries and additives E), which contain at least cell-opening compounds,

[0016] wherein the proportion of all primary OH functions present in the isocyanate-reactive component A) to the total number of terminal OH functions in component A) is at least 30%,

[0017] polyisocyanate component B), and

[0018] Supercritical CO2 as blowing agent component C)

[0019] ii) introducing the foam-forming reaction mixture R) into the mold,

[0020] iii) causing the reaction mixture R) to foam, and

[0021] iv) De-moulding of PUR / PIR rigid foams.

[0022] The terms used in this application have the following meanings:

[0023] The isocyanate characteristic number (also called characteristic number or isocyanate index) is understood to mean the quotient of the amount of substance of isocyanate groups actually used [mol] and the amount of substance of isocyanate-reactive groups actually used [mol], multiplied by 100:

[0024] Characteristic number = (number of moles of isocyanate groups / number of moles of isocyanate reactive groups) * 100

[0025] In the sense of the present application, the "functionality" or "f" of a component mixture is the number-average functionality of the mixture to which the description relates. Thus, the functionality of a polyol component A1) is the number-average functionality of the mixture of polyols contained in component A1, for example, based on all isocyanate-reactive functional groups contained.

[0026] In the sense of this application, "molar weight" or "molar mass" or "M n ” respectively refer to the number-weighted average molar mass.

[0027] In the case of addition of a polyol, the OH number (also called hydroxyl number) gives its OH number. The OH number data for mixtures relate 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 is expressed as the amount of potassium hydroxide in milligrams, which is equivalent to the amount of acetic acid that is combined with 1 gram of substance in the acetylation. Within the scope of the present invention, it is determined in accordance with standard DIN 53240-2 (edition November 2007).

[0028] The isocyanate-reactive component A) comprises 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.

[0029] The proportion of primary OH functions to the total number of terminal OH functions of all polyols used in component A) is at least 30%, preferably at least 35%, particularly preferably at least 38%.

[0030] The polyol component A1) is further characterized in that it has a functionality f of >2.5, preferably ≥2.6 to ≤6.5, particularly preferably ≥2.8 to ≤6.1. With polyol formulations in which the polyol component A1) has a functionality within these ranges, an optimum viscosity increase is achieved during injection until the counterpressure is reduced, and the foam can be demolded more quickly.

[0031] The polyol component A1) preferably has a hydroxyl number of 280 to 600 mg KOH / g, particularly preferably 300 to 580 mg KOH / g, particularly preferably 350 to 540 mg KOH / g. This has a particularly favorable effect on the mechanical properties of the foam.

[0032] In the sense of the present application, a "polyether polyol" may also be a mixture of different polyether polyols, which also applies analogously to the other polyols listed here.

[0033] The polyether polyols which can be used according to the invention are the polyether polyols known to the person skilled in the art which can be used for polyurethane synthesis.

[0034] Useful polyether polyols are, for example, polytetramethylene glycol polyethers, such as are obtainable by polymerization of tetrahydrofuran with the aid of cationic ring opening.

[0035] Likewise suitable polyether polyols are addition products of styrene oxide, ethylene oxide, propylene oxide, butylene oxide and / or epichlorohydrin onto difunctional or polyfunctional starter molecules. Ethylene oxide and propylene oxide are particularly preferably added. 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-methylethylene)bisphenol, 1,4-butanediol, 1,6-hexanediol and low molecular weight esters of such polyols with dicarboxylic acids having hydroxyl groups and oligoethers of such polyols.

[0036] Preferably, the isocyanate-reactive component 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.

[0037] Useable polyetherester polyols are those compounds comprising ether groups, ester groups and OH groups. Organic dicarboxylic acids with a maximum of 12 carbon atoms are suitable for preparing polyetherester polyols, preferably aliphatic dicarboxylic acids or aromatic dicarboxylic acids with ≥4 to ≤6 carbon atoms, which are used individually or in a mixture. Suberic acid, azelaic acid, decanedioic 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 isophthalic acid can be mentioned as examples. In addition to organic dicarboxylic acids, derivatives of these acids can also be used, such as their anhydrides and their esters and half esters with low molecular weight monofunctional alcohols with ≥1 to ≤4 carbon atoms. It is also feasible and can have advantages to use the above-mentioned bio-based raw materials in proportion, particularly fatty acids or fatty acid derivatives (oleic acid, soybean oil, etc.), for example, in terms of storage stability of polyol formulations, dimensional stability of foams, fire retardant properties and compressive strength.

[0038] As further components for preparing the polyetheresterpolyols, polyetherpolyols obtained by alkoxylation of starter molecules such as polyols are used which are at least difunctional but may optionally also contain proportions of higher-functional, in particular trifunctional, starter molecules.

[0039] 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 such as diethylene glycol, triethylene glycol, tetraethylene glycol, dibutylene glycol, tributylene glycol, tetrabutylene glycol, dihexanediol, trihexanediol, tetrahexanediol and oligomeric mixtures of alkanediols such as diethylene glycol. Starter molecules having a functionality other than OH can also be used individually or in the form of mixtures.

[0040] In addition to diols, compounds having > 2 Zerewitinoff-active hydrogen atoms, in particular having a number-average functionality of > 2 to ≤ 8, in particular ≥ 3 to ≤ 6, such as 1,1,1-trimethylolpropane, triethanolamine, glycerol, sorbitan and pentaerythritol, and also triol- or tetraol-starting polyoxyethylene polyols, whose average molar mass Mn is preferably ≥ 62 g / mol to ≤ 400 g / mol, in particular ≥ 92 g / mol to ≤ 200 g / mol, can be used as starter molecules for the preparation of polyethers.

[0041] The polyetherester polyols can also be prepared by alkoxylation, in particular by ethoxylation and / or propoxylation, of reaction products obtained by reaction of organic dicarboxylic acids and their derivatives with components having Zerewitinoff-active hydrogen, in particular diols and polyols. Derivatives of these acids can be used, for example, their anhydrides, for example phthalic anhydride.

[0042] Suitable polyester polyols are in particular polycondensates of di- and also tri- and tetraols with di- and also tri- and tetracarboxylic acids or hydroxycarboxylic acids or lactones. Instead of free polycarboxylic acids, the corresponding polycarboxylic anhydrides or corresponding polycarboxylic acid esters of lower alcohols can also be used for the preparation of polyesters.

[0043] Examples of suitable diols are ethylene glycol, butanediol, diethylene glycol, triethylene glycol, polyalkylene glycols such as polyethylene glycol, furthermore 1,2-propylene glycol, 1,3-propylene glycol, 1,3-butylene glycol and 1,4-butylene glycol, 1,6-hexanediol and isomers, neopentyl glycol or neopentyl glycol hydroxypivalate. Furthermore, polyols such as trimethylolpropane, glycerol, erythritol, pentaerythritol, trimethylolbenzene or trishydroxyethyl isocyanurate can also be used.

[0044] Furthermore, monohydric alkanols can also be used together.

[0045] As polycarboxylic acids, for example, 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 may be used. As acid sources, the corresponding anhydrides may also be used.

[0046] In addition, monocarboxylic acids such as benzoic acid and alkanecarboxylic acids can also be used together.

[0047] Hydroxycarboxylic acids which can be used together as reaction partners in the preparation of 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.

[0048] Biobased raw materials and / or their derivatives are also suitable for preparing the polyester polyols, for example castor oil, polyhydroxy fatty acids, ricinoleic acid, hydroxyl-modified oils, grape seed oil, black cumin oil, pumpkin seed 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 seed oil, hazelnut oil, primrose oil, wild rose oil, Rose oil, safflower oil, walnut oil, fatty acids, hydroxy-modified and epoxidized fatty acids and fatty acid esters, for example based on myristoleic acid, palmitoleic acid, oleic acid, vaccenic acid, petroselinic acid, oleic acid, erucic acid, nervonic acid, linoleic acid, α- and γ-linolenic acid, stearidonic acid, arachidonic acid, eicosapentaenoic acid, ichthyic acid and docosahexaenoic acid. Particularly preferred are esters of ricinoleic acid with polyfunctional alcohols, for example glycerol. Preference is also given to using mixtures of these biobased acids with other carboxylic acids, for example phthalic acid.

[0049] Polycarbonate polyols that can be used are polycarbonates having hydroxyl groups, such as polycarbonate diols. These can be obtained by reacting 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.

[0050] 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-methyl-1,3-propanediol, 2,2,4-trimethylpentanediol-1,3, dipropylene glycol, polypropylene glycol, dibutylene glycol, polybutylene glycol, bisphenol A and lactone-modified diols of the aforementioned type.

[0051] As an alternative or in addition to pure polycarbonate diols, it is also possible to use polyether polycarbonate diols which are obtainable, for example, by copolymerization of alkylene oxides (for example propylene oxide) with CO 2 .

[0052] Methods for preparing polyols are described, for example, by Ionescu in "Chemistry and Technology of Polyols for Polyurethanes", Rapra Technology Limited, Shawbury 2005, p. 55 et seq. (Chapter 4: Oligo-polyols for Elastic Polyurethanes), p. 263 et seq. (Chapter 8: Polyester Polyols for Elastic Polyurethanes) and in particular p. 321 et seq. (Chapter 13: Polyether Polyols for Rigid Polyurethane Foams) and p. 419 et seq. (Chapter 16: Polyester Polyols for Rigid Polyurethane Foams). Polyester- and polyether polyols can also be obtained by glycolysis of suitable polymer recyclates. Suitable polyether-polycarbonate polyols and their preparation are described, for example, in EP 2910585 A,

[0024] -

[0041] . Examples of polycarbonate polyols and their preparation can be found in particular in EP 1359177 A. The preparation of suitable polyetheresterpolyols is described in WO 2010 / 043624 A and EP 1 923 417 A, among others.

[0053] 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. In particular, the molar proportion of ethylene oxide structures is at least 50 mol%, based on all alkylene oxide structures present in the polyols of component A1. Using 100 mol% of ethylene oxide is likewise a preferred embodiment.

[0054] Furthermore, the isocyanate-reactive component A) may contain low molecular weight isocyanate-reactive compounds A2), in particular difunctional or trifunctional amines and alcohols, particularly preferably compounds with a molar mass M n Less than 400 g / mol, preferably 60 to 300 g / mol of diols and / or triols, for example triethanolamine, diethylene glycol, ethylene glycol, glycerol. If such low molecular weight isocyanate-reactive compounds are used for the preparation of polyurethane rigid foams, for example in terms of function as chain extenders and / or crosslinkers, and these do not also come within the definition of component A1), they are advantageously used in an amount of up to 5% by weight, based on the total weight of component A).

[0055] In addition to the above-mentioned polyols and isocyanate-reactive compounds, further isocyanate-reactive compounds A3) such as graft polyols, polyamines, polyamino alcohols and polythiols may also be present in component A). Of course, the isocyanate-reactive components described also include such compounds with mixed functionality.

[0056] Preferably, at least 65% by weight, in particular at least 80% by weight, very particularly preferably more than 90% by weight, of the isocyanate-reactive component 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, and the proportion of primary OH functions in component A) is at least 35% (based on all terminal OH functions in component A).

[0057] The polyol formulation P) comprises auxiliary agents and additives E). The auxiliary agents and additives include at least one or more cell-opening compounds. Cell-opening compounds are described, for example, in Kunststoff-Handbuch, Volume 7, Polyurethane, Carl Hanser Verlag, Munich / Vienna, 3rd edition, 1993, pages 104-127. They involve, for example, siloxanes, such as polyether-polydimethylsiloxane copolymers, or organic polymers, for example those based on polybutadiene (e.g. 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. Cell openers based on polybutadiene are preferred. The cell-opening component is preferably used in an amount of a maximum of 1% by weight, based on the isocyanate-reactive component A). Particularly preferably, 0.1 to 1.0% by weight, very particularly preferably 0.25 to 0.75% by weight, of an organic polymer based on polybutadiene, based in each case on the total weight of component A) is used.

[0058] Other auxiliaries and additives E) 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. For example, surface-active substances, stabilizers, in particular foam stabilizers, cell regulators, fillers, dyes, pigments, flame retardants, antistatic agents, antihydrolysis agents and / or substances having fungistatic and bacteriostatic effects may be mentioned.

[0059] Some known cell-opening compounds, such as siloxanes, can also simultaneously serve as surfactants, stabilizers or cell regulators. In this case, these components can also be used in amounts higher than the preferred amounts mentioned above for the cell-opening compounds.

[0060] Polyether-polydimethylsiloxane copolymers are generally used, preferably polyoxyalkylene polyethers having oligodimethylsiloxane end groups, the number of dimethylsiloxane units preferably being ≤5.

[0061] As stabilizers, saturated and unsaturated hydrocarbons such as paraffins, polybutadienes, fatty alcohols and esters, for example carboxylic acid esters, may also be used.

[0062] Component A) preferably comprises a total of not more than 3% by weight of siloxane and polybutadiene.

[0063] In addition, surfactants can be used as stabilizers, for example alkoxylated alkanols, such as 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, carboxylates of alkoxylated 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 can be perfluorinated or partially fluorinated. Examples of this are partially fluorinated ethoxylated alkanols or carboxylic acids.

[0064] Preferably, component A) comprises 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 component A).

[0065] Catalysts D are used for the preparation of PUR / PIR rigid foams. Catalysts D) are generally compounds which accelerate the reaction of the compounds of the components mentioned which contain hydroxyl groups or isocyanate-reactive groups with the isocyanate groups of component B.

[0066] The catalyst D) comprises D1) 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 "bindable catalyst"). Examples of bindable catalysts which can be used are, for example, bis-dimethylaminopropyl urea, bis(N,N-dimethylaminoethoxyethyl)carbamate, di-methylamino-propyl 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-dimethylamino Propyl-N,N-dimethylpropane-1,3-diamine, dimethyl-2-(2-aminoethoxyethanol) and (1,3-bis(dimethylamino)propane-2-ol), N,N-bis(3-dimethylamino-propyl)-N-isopropanolamine, bis(dimethylaminopropyl)-2-hydroxyethylamine, N,N,N-trimethyl-N-(3-aminopropyl)-bis(aminoethyl ether), 3-dimethylaminoisopropyl-diisopropanolamine or mixtures thereof.

[0067] In a preferred embodiment, the catalyst D1) is used in an amount of ≥0.01 to <2% by weight, based on the total weight of component A).

[0068] In addition, one or more further catalyst compounds D2) may be used, in particular catalytically active compounds known for use in PUR / PIR chemistry, including, besides further amine compounds, 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.

[0069] The catalyst D) 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 component A. Particularly preferably, the catalyst D) comprises a bindable catalyst D1) and a non-bindable catalyst D2). Particularly preferably, a bindable amine compound and a catalytically active salt are used in combination.

[0070] The catalysts D1 and D2 are preferably used in a molar ratio D1 / D2 of 0.1 to 16.3, particularly preferably 0.3 to 10 and very particularly preferably 0.8 to 6.0. The catalyst component D) preferably comprises an amine compound as catalytically active compound D1) which can be incorporated into the polyurethane and furthermore a catalytically inactive compound D2) which is a catalytically active salt which cannot be incorporated into the polyurethane, and the molar ratio D1 / D2 is 0.1 to 16.3, particularly preferably 0.3 to 10 and very particularly preferably 0.8 to 6.0. In a particularly preferred embodiment, 3-(dimethylamino)propylurea and potassium acetate are used in a molar ratio D1 / D2 of 0.1 to 6.0, particularly preferably 0.3 to 10 and very particularly preferably 0.8 to 6.0. The preferred catalyst ratio or catalyst particularly advantageously influences the defined viscosity increase.

[0071] In the preparation of PUR / PIR rigid foams, supercritical CO2 is used as blowing agent component C). This is used in the amount required 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 component A. Physical blowing agents can be used as additional blowing agents. Within the scope of the present invention, "physical blowing agents" are understood to mean those compounds which, due to their physical properties, are easily volatile and do not react with the isocyanate component.

[0072] 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, such as perfluorohexane, HFC 245fa (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 188 from 3M. (1,1,1,2,3,4,5,5,5-nonafluoro-4-(trifluoromethyl)pent-2-ene), and mixtures thereof.

[0073] CO2 as a physical foaming agent is used in a supercritical or near-critical state. Within the scope of the present invention, when the following conditions are met: (T c - T) / T≤0.4 and / or (p c- p) / p≤0.4, then a near-critical condition exists. Here, T represents the prevailing temperature in the process, Tc represents the critical temperature of the blowing agent or blowing agent mixture, p represents the prevailing pressure in the process and pc represents the critical pressure of the blowing agent or blowing agent mixture. Preferably, when: (T c - T) / T≤0.3 and / or (p c - p) / p≤0.3, particularly preferably (T c - T) / T≤0.2 and / or (p c - p) / p≤0.2, then there is a near-critical condition.

[0074] When using CO2, particularly suitable conditions for carrying out the method according to the invention are those pressures and temperatures above the critical point of CO2, i.e. ≥73.7 bar and ≥30.9°C, preferably 74 bar to 350 bar and 31°C to 100°C, particularly preferably 75 bar to 200 bar and 32°C to 60°C.

[0075] If further blowing agents are added, the blowing agent mixture comprises, in one embodiment, preferably more than 60% by weight of carbon dioxide, particularly preferably more than 75% by weight.

[0076] In addition to or instead of the physical blowing agents added to the CO2, chemical blowing agents (also called "co-blowing agents") can also be used. These are particularly preferably water and / or formic acid. Preferably, the co-blowing agents are 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 isocyanate-reactive hydrogen atoms in the foam-forming reaction mixture R).

[0077] The proportion of blowing agent C) in the mixture of components A), C), D) and E) is ≥1% to ≤30% by weight, preferably ≥4% to ≤20% by weight, particularly preferably ≥6% to ≤16% by weight; the proportion of blowing agent in the foam-forming reaction mixture R) is 0.5% to 15% by weight, preferably 2% to 10% by weight, particularly preferably ≥3% to ≤8% by weight.

[0078] Component B) is a polyisocyanate, i.e. an isocyanate with an NCO functionality of ≥ 2. Examples of suitable polyisocyanates are 1,4-butanediisocyanate, 1,5-pentanediisocyanate, 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-cyclohexylene diisocyanate, 1,4-phenylene diisocyanate, 2,4- and / or 2 ,6-toluene diisocyanate (TDI), 1,5-naphthylene 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-diisocyanatohexanoic acid alkyl esters with C1 to C6-alkyl radicals (lysine diisocyanate).

[0079] Preferred for use as isocyanate component B) are mixtures of isomers of diphenylmethane diisocyanate (“monomeric MDI”, “mMDI” for short) and its oligomers (“oligomeric MDI”). Mixtures of monomeric MDI and oligomeric MDI are often referred to as “polymeric MDI” (pMDI). Oligomers of MDI are mixtures of polycyclic polyphenylpolymethylene polyisocyanates, for example polycyclic homologues of diphenylmethylene diisocyanate, which have an NCO functionality f>2 and have the following formula: 15 H 10 N2O2[C8H5NO] n , wherein n = integer > 0, preferably n = 1, 2, 3 and 4. More cyclic homologues C 15 H 10 N2O2[C8H5NO] m , m = integer ≥ 4) can likewise be present in the mixture of organic polyisocyanates a). As isocyanate component B), preference is furthermore given to mixtures of mMDI and / or pMDI with up to 20% by weight, more preferably up to 10% by weight, of other known aliphatic, cycloaliphatic and in particular aromatic polyisocyanates for the preparation of polyurethanes, very particularly TDI.

[0080] In addition to the above-mentioned polyisocyanates, modified diisocyanates having a uretdione, isocyanurate, urethane, carbodiimide, uretonimine, allophanate, biuret, amide, iminooxadiazinedione and / or oxadiazinetriaone structure, and unmodified polyisocyanates having more than 2 NCO groups per molecule, such as 4-isocyanatomethyl-1,8-octane diisocyanate (nonane triisocyanate) or triphenylmethane-4,4',4''-triisocyanate, can also be used in proportion.

[0081] Instead of or in addition to the polyisocyanates mentioned above, it is also possible to use suitable NCO prepolymers as organic isocyanate component B). The prepolymers can be prepared by reaction of one or more polyisocyanates with one or more polyols corresponding to the polyols mentioned under components A1) and A2).

[0082] The isocyanate may be a prepolymer obtained 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.

[0083] The NCO content is preferably ≧29.0 wt % to ≦32.0 wt % and preferably has a viscosity at 25° C. of ≧80 mPas to ≦2000 mPas, particularly preferably ≧100 mPas to ≦800 mPas (dynamic viscosity determined at 25° C. in accordance with DIN 53019).

[0084] The number of NCO groups in the polyisocyanate component B) and the number of isocyanate-reactive groups in component A) may be present in a quantitative ratio of ≥50:100 to ≤500:100. For the preparation of rigid polyurethane foams, components A) and B) are usually reacted in such amounts that the isocyanate characteristic number of the formulation is 80-150, preferably 90-130, particularly preferably 95-110. Within this range, urethane groups are preferably formed. In another preferred embodiment, the isocyanate characteristic number is 150-400. Within this range, the foam material has a high proportion of isocyanurate functional groups, which produces, for example, the inherent flame retardancy of the foam material.

[0085] In step i) of the process according to the invention, a foam-forming reaction mixture R) is prepared from components A) to E).

[0086] For this purpose, the mixture comprising components A), D), E) can be charged in advance, for example, into a container and then mixed with component C) and with the polyisocyanate B). The mixing of the components can also be carried out in a mixing head.

[0087] Mixing, in particular with components C) and B), can be carried out under pressure. In a preferred embodiment, components A), D), E) and C) are mixed with component B) in a high-pressure mixing head.

[0088] The blowing agent component C) is CO2 in a supercritical state, and the reaction of the components is carried out under supercritical conditions for CO2. In this case, suitable pressures in the mixing head and / or in one or more discharge pipes for the preparation of polyurethane foams are, for example, in the range of ≥73.7 bar to ≤350 bar, and preferably in the range of ≥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 for the blowing agent used can be maintained.

[0089] 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 polymerizable under supercritical conditions. The residence time can be determined by dividing the volume of the reaction chamber (=mixing chamber and / or conduit) in which supercritical conditions exist by the volume of the mixture transported per unit time.

[0090] In step ii) of the process according to the invention, the foam-forming reaction mixture R) according to the invention, composed of components A) to E), is introduced into a mold.

[0091] In a preferred embodiment, the mold is a closed mold, wherein the counterpressure in the mold during injection is 2 to 90 bar, preferably 2 to 80 bar, particularly preferably 5 to 40 bar.

[0092] A possible embodiment for this is as follows: the counterpressure is achieved by charging the mold with gas (compressed air or nitrogen) directly and / or via a floating seal, which divides the pressurized space into a gas space and a reaction space and is regulated, maintained and finally decompressed via a proportional valve.

[0093] In step iii) of the process, the reaction mixture may be foamed.

[0094] For the case where the reaction mixture is injected into the mold under counter pressure, a preferred embodiment of step iii) is as follows:

[0095] After step ii) is terminated, the pressure in the mold is kept constant for a time period 1, preferably 1-40 seconds, particularly preferably 5-20 seconds, very particularly preferably 8-17 seconds, wherein the viscosity of the reaction mixture first increases without foaming. It has been shown that maintaining the pressure during the preferred duration results in a particularly favorable viscosity range for the mixture of the reaction stage. After the end of time period 1, the mold is decompressed. The pressure is released from the mold in time period 2, and the pressure release rate is 1-90 bar / second, preferably 1-80 bar / second, particularly preferably 2-70 bar / second. The release can be achieved in particular by a proportional valve. During time period 2, the reaction mixture foams. Too fast release has a negative impact on the stability of the foam cells, and too slow release has a negative impact on the foaming reaction.

[0096] In step iv) of the process, the PUR / PIR rigid foam is demoulded.

[0097] A particularly preferred embodiment of the method according to the invention comprises the following steps:

[0098] i) Preparation of a foam-forming reaction mixture R consisting of

[0099] an isocyanate-reactive component A) comprising at least one polyol component A1) selected from the group consisting of polyether polyols, polyester polyols, polycarbonate polyols, polyether-polycarbonate polyols and polyetherester polyols, having an OH functionality F of > 2.5,

[0100] - at least one polyisocyanate component B),

[0101] - at least one blowing agent C),

[0102] - a catalyst component D), which comprises at least a catalytically active compound D1) having a Zerewitinoff-active hydrogen

[0103] - auxiliaries and additives E), which contain at least cell-opening compounds,

[0104] wherein the proportion of all primary OH functions present in the isocyanate-reactive component A) to the total number of terminal OH functions in component A) is at least 30%,

[0105] ii) introducing a foam-forming reaction mixture consisting of component A), a blowing agent and a polyisocyanate component B) into a closed mold, wherein the counterpressure in the mold during injection is from 2 to 90 bar,

[0106] iii) maintaining the pressure in the mould for a time period 1 of 1 to 40 seconds after step ii) and subsequently releasing the pressure from the mould during a time period 2 at a pressure release rate of 1 to 90 bar / second.

[0107] iv) De-moulding the PUR / PIR rigid foam.

[0108] A further subject of the present invention is a PUR / PIR rigid foam obtainable or obtained by the process according to the invention.

[0109] By the method according to the invention, an apparent density of 30-90 kg / m 3 , preferably 30-70kg / m 3 PUR / PIR rigid foams having both numerous open cells and particularly small cells. It is thus possible to produce rigid foams having an open porosity of > 90%, in particular > 94%, wherein the cells have an average diameter of < 50 μm. The foams have good mechanical properties, for example good compressive strength.

[0110] From the PUR / PIR foam according to the invention, foamed moldings and composite systems containing these moldings can be produced in a preferred manner. The composite systems are usually limited by decorative layers on the top and bottom sides. Metals, plastics, wood and paper can be considered as decorative layers in particular. As fields of application of such discontinuously produced PUR / PIR composite systems, in particular, the technical insulation of equipment such as refrigerators, refrigerators, refrigerator-freezer combinations and water heaters, refrigerated containers and refrigerated boxes and pipelines can be mentioned.

[0111] The use of PUR / PIR foams in these areas is known in principle to those skilled in the art and has been extensively documented. The PUR / PIR foams according to the invention are particularly well suited for these purposes, since, due to their fine porosity, they are characterized by a low thermal conductivity, which effect can be further enhanced by applying a vacuum.

[0112] The invention further relates to a refrigerator, freezer or refrigerator-freezer combination, comprising a PUR / PIR rigid foam obtained according to the invention, wherein the provided mold is in particular a housing part of a refrigerator, freezer or refrigerator-freezer combination. The invention is intended to be explained in more detail with the aid of the following examples and comparative examples. Example

[0113] Standards or measuring instruments used:

[0114] Determination of apparent density: Cellular materials consisting of rubber and plastics - Determination of apparent density (ISO 845:2006); German version EN ISO 845:2009

[0115] Determination of open porosity:Determination of the volume ratio of open and closed cells (ISO 4590:2002); German version EN ISO 4590:2003

[0116] Determination of compressive strength: Rigid cellular materials - Determination of pressure properties (ISO 844:2014); German version EN ISO844:2014

[0117] Determination of OH value : Determination of the hydroxyl value - Part 2: Method using catalyst according to DIN 53240-2, version November 2007

[0118] Determination of cell size: Optical microscopic evaluation by optical microscope VHX 5000; The sample to be measured was investigated at 3 different locations, each across a circular area with a diameter of 5 mm. The resolution was chosen here so that the selected area included approximately 100 cells. 100 cells were then measured, and the minimum and maximum cell diameters as well as the average cell diameter were calculated.

[0119] Given in Table 1 Functionality f It refers to the number average functionality of the mixture of polyols contained in the formulation.

[0120] Table 1 by[%] Given The proportion of primary OH functional groups It refers to the proportion of primary OH functions to the total number of OH functions in the mixture of polyols contained in the formulation.

[0121] Example 1 and Comparative Examples 2 and 3:

[0122] Polyurethane foams blown with CO2 and n-pentane were prepared according to the recipes listed in Table 1 below. Unless otherwise specified, the amounts given are to be understood as parts by weight. The following materials were used:

[0123] Polyol 1: Polyether polyol based on trimethylolpropane and propylene oxide, with a hydroxyl value of 800 mg KOH / g, a functionality of 3, and a viscosity of 6100 mPas at 25°C

[0124] Polyol 2: Polyether polyol based on trimethylolpropane and ethylene oxide, with a hydroxyl value of 550 mg KOH / g, a functionality of 3, and a viscosity of 505 mPas at 25°C

[0125] Polyol 3: Polyether polyol based on trimethylolpropane and propylene oxide, with a hydroxyl value of 550 mg KOH / g, a functionality of 3, and a viscosity of 1800 mPas at 25°C

[0126] Polyol 4: Polyether polyol based on 1,2-propylene glycol and propylene oxide with a hydroxyl value of 56 mg KOH / g, a functionality of 2, and a viscosity of 310 mPas at 25°C

[0127] Polyol 5: Polyether polyol based on 1,2-propylene glycol and propylene oxide, with a hydroxyl value of 112 mg KOH / g, a functionality of 2, and a viscosity of 140 mPas at 25°C

[0128] Polyol 6: Polyether polyol based on glycerol and propylene oxide, with a hydroxyl value of 231 mg KOH / g, a functionality of 3, and a viscosity of 350 mPas at 20°C

[0129] B 8443: Foam stabilizer (Evonik)

[0130] Ortegol 500: Cell opener (Evonik)

[0131] Desmorapid PU 1972: Catalyst, 25% potassium acetate in diethylene glycol (Covestro)

[0132] Dabco NE1070: Catalyst, 3-(dimethylamino)propyl urea (Air Products)

[0133] Pentane foaming agent

[0134] A mixture of monomeric isocyanates and polymeric MDI with a viscosity of about 290 mPa*s at 20°C (Desmodur 44V20L, Covestro).

[0135] Preparation of polyurethane free foam, comparative example 3:

[0136] To prepare polyurethane free foams in the laboratory, 200 g of the composition was prepared from the respective polyol formulation consisting of the polyols, stabilizers and catalysts listed in Table 1 below and a blowing agent. To prepare the reaction mixture, the composition of polyol formulation and blowing agent was mixed with the corresponding amount of isocyanate at 23° C. by a Pendraulik stirrer for 10 seconds and poured into an upwardly open mold (20 cm×20 cm×18 cm). The exact formulation is summarized in Table 1, the properties of the reaction mixture and the results of the physical investigation of the foam are summarized in Table 2.

[0137] Preparation of polyurethane molded foams, comparative example 2:

[0138] In order to prepare polyurethane molded foams in the laboratory, 100 g of the composition was prepared from the respective polyol formulations consisting of the polyols, stabilizers and catalysts listed in Table 1 below and the blowing agent. To prepare the reaction mixture, the composition of the polyol formulation and the blowing agent was mixed with the corresponding amount of isocyanate at 23°C by a Pendraulik stirrer for 10 seconds and poured into a mold (20 cm×20 cm×6 cm). The mold was firmly closed immediately after pouring. The molded body thus prepared was demolded from the mold after 5 minutes. The exact formulation is summarized in Table 1, and the results of the physical investigation of the foam are summarized in Table 2.

[0139] Preparation of polyurethane molded foam on high pressure equipment, Example 1:

[0140] To produce polyurethane free foams on a high-pressure device, a polyol formulation was prepared from the polyols, stabilizers and catalysts listed in Table 1 below. It was used as the polyol component in a standard high-pressure mixing device and mixed with the blowing agent CO2 at a pressure of 150 bar and a temperature of 50°C. In this case, supercritical conditions exist for the blowing agent. In the high-pressure mixing head, this mixture was mixed with an isocyanate, which was delivered at a pressure of 150 bar and a temperature of 35°C. The injection amount was 40 g / s, corresponding to a volume flow of 48 ml / s (density of the mixture was 1.2 g / ml). The reaction mixture obtained in this way was injected into a closed mold (volume 1 liter) pre-pressurized with a counterpressure of 10 bar, the mold temperature of the mold being 50°C. After the injection was completed, the pre-pressurized counterpressure of 10 bar was still maintained for a further 12 seconds and then only reduced to ambient pressure in < 2 seconds. The molded body prepared in this way was demolded from the mold after 5 minutes. The exact formulation is summarized in Table 1, the results of the physical investigation of the foam are summarized in Table 2.

[0141]

[0142]

[0143] Example 1 shows that very fine-celled rigid foams having a high proportion of open cells can be prepared with the formulation listed.

[0144] Example 1 clearly shows that processing of the formulation on a high-pressure apparatus with supercritical CO 2 as blowing agent and a counterpressure of 10 bar on the mold leads to a rigid foam with finer (compared to, for example, Comparative Example 2 with the same formulation) and simultaneously open cells.

[0145] Although an average cell size of 126 μm can be achieved in Comparative Example 5 by replacing Polyol 2 with Polyol 3, the proportion of open cells is still only 25.6%.

Claims

1. A process for producing a PUR / PIR rigid foam having an apparent density according to ISO 845:2006 of 30 to 90 kg / m 3 , an open porosity of >90% according to ISO 4590:2002, and an average cell diameter of <50 μm as evaluated by optical microscopy, the method comprising the following steps: i) preparing a reaction mixture R) comprising A polyol formulation P) comprising - an isocyanate-reactive component A) comprising at least one polyol component A1) having a functionality f>2.5 selected from the group consisting of polyether polyols, polyester polyols, polycarbonate polyols, polyether-polycarbonate polyols and polyetherester polyols, a catalyst component D) which comprises at least a catalytically active compound D1) having a Zerewitinoff-active hydrogen, - auxiliaries and additional substances E) which contain at least cell-opening compounds, wherein the proportion of all primary OH functions present in the isocyanate-reactive component A) to the total number of terminal OH functions in component A) is at least 30%, polyisocyanate component B), and Supercritical CO2 as blowing agent component C), ii) introducing the foam-forming reaction mixture R) into a mold, iii) foaming the reaction mixture R), and iv) De-moulding of the PUR / PIR rigid foam.

2. The process of claim 1, wherein steps i) and optionally ii) are carried out under supercritical conditions.

3. The process according to claim 1 or 2, wherein step i) is carried out in a high-pressure mixing head.

4. The method according to claim 1 or 2, characterized in that: In step ii), a foam-forming reaction mixture R) composed of component A), blowing agent C) and polyisocyanate component B) is introduced into a closed mold, the counterpressure in the mold being from 2 to 90 bar during injection.

5. The method according to claim 1, characterized in that In step ii), a foam-forming reaction mixture R) consisting of component A), a blowing agent C) and a polyisocyanate component B) is introduced into a closed mold, wherein the counterpressure in the mold during injection is 2 to 90 bar, and In step iii), the pressure in the mold is maintained for a time period 1 of 1 to 40 seconds after the end of step ii), and then the pressure is released from the mold during a time period 2 at a pressure release rate of 1 to 90 bar / second.

6. The method according to claim 1, characterized in that The hydroxyl number of the polyol component A1) is from 280 to 600 mg KOH / g according to DIN 53240-2:2007.

7. The method according to claim 1, characterized in that At least 65% by weight of the isocyanate-reactive component A) consists of a polyol component A1) having a hydroxyl number of 280 to 600 mg KOH / g according to DIN 53240-2:2007 and a functionality of ≥2.8 to ≤6.0, and the proportion of primary OH functions in component A) is at least 35%, based on all terminal OH functions in component A.

8. The method according to claim 1, characterized in that At least 60% by weight of the isocyanate-reactive component A) consists of polyether polyols.

9. The method according to claim 1, characterized in that The content of open-cell component E) is from 0.1 to 1.0% by weight.

10. The method according to claim 1, characterized in that The catalytically active compound D1) is present in an amount of ≥0.01 to <2% by weight, based on the total weight of component A).

11. The process of claim 1, wherein the blowing agent component C) is present in an amount of 0.5% to 15% by weight, based on the total weight of R).

12. The method of claim 1, wherein the rigid foam has an apparent density according to ISO 845:2006 of 30-70 kg / m 3 .

13. The method of claim 1, wherein the rigid foam has an open cell content of >94% according to ISO 4590:2002.

14. Open-cell PUR / PIR rigid foam obtainable by the process according to any one of claims 1 to 13.

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