Method for producing improved rigid polyisocyanurate foams based on aromatic polyester polyols and ethylene oxide-based polyether polyols

Abstract

The present invention relates to a method for producing a rigid polyisocyanurate foam, comprising mixing (A) a polyisocyanate with (B) a compound having hydrogen atoms reactive with isocyanate groups, (C) a flame retardant, (D) a blowing agent, and (E) a catalyst at an isocyanate index of at least 220 to form a reaction mixture and curing the rigid polyisocyanurate foam, said component (B) comprising at least one aromatic polyester polyol (b1) and at least one polyether polyol (b2), said polyester polyol (b1) having an average total functionality of ≦3.0 and ≧1.7, and said polyether polyol (b2) having an average total functionality of ≦3.0 and ≧1.7. ) is prepared by alkoxylation of an initiator or initiator mixture having a hydroxyl number of 160-350 mg KOH / g and an average total functionality ≦3.5 and ≧1.5, at least 80% by weight of ethylene oxide is used as alkylene oxide for preparing polyether polyol (b2), polyether polyol (b2) has at least 90% primary hydroxyl end groups, the weight ratio of component (b1) to component (b2) is ≦3 and ≧1, and the blowing agent (D) contains a chemical blowing agent and a physical blowing agent, wherein the chemical blowing agent is selected from the group consisting of formic acid-water mixtures and formic acid. The present invention further relates to rigid polyisocyanurate foams obtainable by the process according to the present invention.

Description

[Technical field]

[0001] The present invention relates to a method for producing a rigid polyisocyanurate foam, comprising mixing (A) a polyisocyanate with (B) a compound having hydrogen atoms reactive towards isocyanate groups, (C) a flame retardant, (D) a blowing agent, (E) a catalyst, and (F) optionally further auxiliaries and additives at an isocyanate index of at least 220 to form a reaction mixture and curing to form said rigid polyisocyanurate foam, said component (B) being selected from at least one aromatic polyester polyol (b1) and at least one polyether polyol (b2). (b1.1) 10 to 50 mol % of a dicarboxylic acid composition containing an aromatic dicarboxylic acid, (b1.2) 0 to 20 mol % of one or more fatty acids and / or fatty acid derivatives, (b1.3) 10 to 80 mol % of one or more aliphatic or alicyclic diols having 2 to 18 carbon atoms or alkoxylates thereof, (b1.4) 0 to 50 mol % of glycerin, alkoxylated glycerin, trimethylolpropane, alkoxylated trimethylolpropane, pentaerythritol, glyceryl ether, tert-butyl ether, ... the total amount of components (b1.1) to (b1.4) is 100 mol %, and the polyester polyol (b1) has an average functionality of ≦3.0 and ≧1.7, and the polyether polyol (b2) has a hydroxyl number of 160 to 350 mg KOH / g and is produced by alkoxylation of an initiator or a mixture of initiators having an average functionality of ≦3.5 and ≧1.5, and the polyether polyol (b3) is produced by alkoxylation of an initiator or a mixture of initiators having an average functionality of ≦3.5 and ≧1.5, As the alkylene oxide for preparing polyether polyol (b2), at least 80% by weight of ethylene oxide is used, and polyether polyol (b2) has at least 90% primary hydroxyl end groups, and the mass ratio of component (b1) to component (b2) is ≦3 and ≧1, and the sum of the mass proportions of components (b1) and (b2) based on component (B) is >80% by weight, and the blowing agent (D) contains a chemical blowing agent and a physical blowing agent, wherein the chemical blowing agent is selected from the group consisting of a formic acid-water mixture and formic acid.Furthermore, the present invention relates to rigid polyisocyanurate foams obtainable by the process according to the invention, and to polyol components for use in the process according to the invention.

[0002] Rigid polyurethane or polyisocyanurate foams have been known for a long time. An important application is heat and cold insulation, for example in cooling systems, in storage water heaters, in district heating pipes or in civil engineering, for example in composite elements, also called sandwich elements, consisting of a cover layer and a core made of rigid polyurethane or polyisocyanurate foam. The production of such composite elements, especially when at least one metal cover layer is used, is currently carried out on a large scale, usually on continuously operating double belt plants. In addition to sandwich elements for the insulation of cold storages, sandwich elements for constructing the facades of a wide variety of buildings are becoming increasingly important.

[0003] An essential requirement of the reaction mixture for the continuous production of rigid polyurethane or polyisocyanurate foam-based sandwich elements is, on the one hand, that it allows the production of rigid foams which have good mechanical properties, such as good compressive strength, but nevertheless achieve low surface brittleness and good thermal insulation properties.

[0004] Furthermore, catalysts are almost always added to the reaction mixture for producing rigid polyurethane or polyisocyanurate foams, which make it possible to significantly reduce the required curing times: these are usually tertiary amines, which are often of toxicological and ecological concern and which are released from the foam over time.

[0005] Therefore, it is desirable that the reaction mixture for producing rigid polyurethane or polyisocyanurate foams has a low catalyst content, but still has a short curing time, and these reaction mixtures additionally allow rapid curing to rigid foam.More rapid curing to rigid foam results in much faster achievement of the necessary strength required for cutting this rigid foam, and thus allows, for example, continuous double belt equipment to be operated at a higher speed, which results in increased productivity during the sandwich production.In addition, it is known that more rapid reactivity and foam curing ensures that finer foam cell diameters are obtained, which favors the barrier properties of the rigid foam.

[0006] Furthermore, it is desirable that the resulting foam achieves the necessary flame retardancy requirements with as low a content as possible of flame retardants, which are also often of ecological and toxicological concern.

[0007] Since flame retardants and catalysts are typically much more expensive than polyols, it is also desirable for economic reasons to keep the content of both components as low as possible.

[0008] In particular, during the continuous processing to produce sandwich elements, the reaction mixture should also result in a rigid foam with low surface foam brittleness, so that good adhesion at the interface between the cover layer and the rigid foam is ensured. In this regard, it is known that rigid polyurethane foams, which are usually produced with an isocyanate index of 120 to 160, usually have much lower foam brittleness than rigid polyisocyanurate foams, which are produced with an isocyanate index of more than 180. For this reason, during the continuous production of composite elements of rigid polyisocyanurate foams, adhesion promoters are usually applied between the lower cover layer and the foam, in order to achieve a cover layer adhesion similar to that in the case of, for example, rigid polyurethane foam composite elements. A major disadvantage of rigid polyurethane foams compared to rigid polyisocyanurate foams is that their reaction mixtures must have a much larger proportion of flame retardants, which are often of ecotoxicological concern, in order to meet the necessary flame retardancy requirements.

[0009] Polyisocyanurate foams based on polyesters and polyethers are known. For example, WO 2013 / 139781 and WO 2013 / 102540 describe polyisocyanurate foams in which the weight ratio of polyesterol to polyetherol used is at least 7.

[0010] According to WO 2013 / 107573, the weight ratio of polyesterol to polyetherol used in the preparation of polyisocyanurate foam is less than 1.6. The polyetherol used preferably consists of a mixture, where a part of the polyether polyol is obtained by propoxylation of initiator molecules and the rest of the polyether polyol is obtained by ethoxylation. The ethylene oxide-based polyether polyol preferably has a functionality of more than 4 and the propylene oxide-based polyether polyol has a functionality of less than 5.

[0011] EP3097132 discloses the preparation of polyisocyanurate foams, in which the polyol component has a hydroxyl number of 50-400 mg KOH / g and comprises a polyether polyol obtained by reacting a multifunctional initiator first with ethylene oxide and subsequently with propylene oxide, the degree of propoxylation of the polyether polyol being 0.33-2.

[0012] International Publication No. WO 2021 / 008921 (WO 2021008921), International Publication No. WO 2012 / 083038 (WO2012083038) and European Patent Application Publication No. 2184306 (EP2184306) disclose polyisocyanurate foams starting from mixtures of polyether polyols and polyester polyols as components reactive towards isocyanates, in which water is used as the blowing agent.

[0013] In this connection, there is a need to further improve the properties of the rigid polyisocyanurate foams obtained according to the prior art, in particular the curing behavior, the burning behavior and also the brittleness of the foam surface.

[0014] Accordingly, the object of the present invention was to improve the property profile of the rigid polyisocyanurate foam, in particular to provide rigid polyisocyanurate foams with excellent mechanical properties, such as excellent compressive strength, and at the same time reduced surface brittleness.Furthermore, their production should be possible using as little catalyst as possible, yet with high reaction rate and curing, and good fire resistance should be achieved even with a low flame retardant content.Furthermore, the object is to develop a method for producing such rigid polyisocyanurate foams, which method is suitable for producing sandwich elements, in particular in a continuous production method.

[0015] This problem is solved by a rigid polyisocyanurate foam which can be obtained by the following process, in which (A) a polyisocyanate is mixed with (B) a compound having hydrogen atoms reactive towards isocyanate groups, (C) a flame retardant, (D) a blowing agent, (E) a catalyst, and (F) optionally further auxiliaries and additives at an isocyanate index of at least 220 to form a reaction mixture and cured to form said rigid polyisocyanurate foam, said component (B) being at least one aromatic polyester polyol (b1) and at least one polyether The polyester polyol (b1) contains a polyol (b2), and the polyester polyol (b1) contains the following: (b1.1) 10 to 50 mol % of a dicarboxylic acid composition containing an aromatic dicarboxylic acid, (b1.2) 0 to 20 mol % of one or more fatty acids and / or fatty acid derivatives, (b1.3) 10 to 80 mol % of one or more aliphatic or alicyclic diols having 2 to 18 carbon atoms or alkoxylates thereof, (b1.4) 0 to 50 mol % of glycerin, alkoxylated glycerin, trimethylolpropane, alkoxylated trimethylolpropane, pentaerythritol, tetramethylolpropane ... the total amount of components (b1.1) to (b1.4) is 100 mol %, and the aromatic polyester polyol (b1) has an average functionality of ≦3.0 and ≧1.7, and the polyether polyol (b2) has a hydroxyl number of 160 to 350 mg KOH / g and is produced by alkoxylation of an initiator or a mixture of initiators having an average functionality of ≦3.5 and ≧1.5; At least 80% by weight of ethylene oxide is used as the alkylene oxide for producing the polyether polyol (b2), and the polyether polyol (b2) has at least 90% primary hydroxyl end groups, and the mass ratio of the component (b1) to the component (b2) is ≦3 and ≧1, and the sum of the mass proportions of the components (b1) and (b2) based on the component (B) is >80% by weight, and the blowing agent (D) contains a chemical blowing agent and a physical blowing agent, wherein the chemical blowing agent is selected from the group consisting of a formic acid-water mixture and formic acid.

[0016] Polyisocyanurate rigid foams are generally understood to be foams containing urethane groups as well as isocyanurate groups. In the context of the present invention, the term rigid polyurethane foams also includes rigid polyisocyanurate foams, the production of which is based on an isocyanate index of at least 180. The isocyanate index is then to be understood as the ratio of isocyanate groups to groups reactive with isocyanates multiplied by 100. An isocyanate index of 100 then corresponds to an equimolar ratio of the isocyanate groups used in component (A) to the groups reactive with isocyanates in components (B) to (F).

[0017] The rigid polyisocyanurate foams according to the invention have a compression stress at 10% compression of at least 80 kPa, preferably at least 120 kPa, particularly preferably at least 140 kPa. Furthermore, the rigid isocyanate-based foams according to the invention have a closed cell content of more than 80%, preferably more than 90%, according to DIN ISO 4590. Further details of the rigid polyisocyanurate foams according to the invention can be found in “Kunststoffhandbuch, Band 7, Polyurethane”, Carl Hanser Verlag, 3rd edition, 1993, Chapter 6, in particular Chapters 6.2.2 and 6.5.2.2.

[0018] The embodiments mentioned below under components (B) to (F) relate to the process according to the invention and the rigid foams thus obtainable, as well as to the polyol component according to the invention.

[0019] Component (A) The polyisocyanate (A) is an aromatic polyisocyanate known in the prior art. Such polyfunctional isocyanates are known and can be produced by methods known per se. The polyfunctional isocyanates can also be used, in particular as mixtures, so that the component (A) contains different polyfunctional isocyanates in this case. The polyisocyanate (A) is a polyfunctional isocyanate having two (hereinafter also called diisocyanate) or more than two isocyanate groups per molecule. In particular, the isocyanate (A) is selected from the group consisting of aromatic polyisocyanates, such as 2,4- and 2,6-toluene diisocyanate and the corresponding isomer mixtures, 4,4'-, 2,4'- and 2,2'-diphenylmethane diisocyanate and the corresponding isomer mixtures (also called monomeric diphenylmethane or MMDI), such as mixtures of 4,4'- and 2,4'-diphenylmethane diisocyanate, mixtures of at least one isomer of diphenylmethane diisocyanate with a more polynuclear homologue of diphenylmethane diisocyanate having at least 3 aromatic nuclei and a functionality of at least 3, also called polyphenyl polymethylene polyisocyanate or polymeric MDI. Typically, the isomers and homologues of MDI are obtained by distillation of crude MDI. Polymeric MDI contains, in addition to binuclear MDI (MMDI), preferably one or more polynuclear condensation products of MDI with a functionality of more than 2, especially 3 or 4 or 5. Polymeric MDI is known and is often called polyphenylpolymethylene polyisocyanate. Also usable as isocyanate (A) are mixtures of 4,4'-, 2,4'- and 2,2'-diphenylmethane diisocyanate with polyphenylpolyethylene polyisocyanate (crude MDI) and mixtures of crude MDI with toluene diisocyanate.Particularly preferred are 2,2'-, 2,4'- or 4,4'-diphenylmethane diisocyanate (MDI) and mixtures of two or three of these isomers, 1,5-naphthylene diisocyanate (NDI), 2,4- and / or 2,6-toluene diisocyanate (TDI), 3,3'-dimethyldiphenyl diisocyanate, 1,2-diphenylethane diisocyanate and / or p-phenylene diisocyanate (PPDI).

[0020] Frequently, modified polyisocyanates are also used, i.e. products obtained by chemical reaction of organic polyisocyanates and containing at least two reactive isocyanate groups per molecule. Particular mention should be made of polyisocyanates containing ester, urea, biuret, allophanate, carbodiimide, isocyanurate, uretdione, carbamate and / or urethane groups, often together with unconverted polyisocyanates.

[0021] The polyisocyanates of component (A) particularly preferably contain 2,2'-MDI or 2,4'-MDI or 4,4'-MDI or mixtures of monomeric diphenylmethane diisocyanates or mixtures of monomeric diphenylmethane diisocyanates and higher nuclear homologues of MDI. The average functionality of the polyisocyanates containing polymeric MDI may range from about 2.2 to about 4, preferably from 2.4 to 3.8 and in particular from 2.6 to 3.0. MDI-based polyfunctional isocyanates or mixtures of polyfunctional isocyanates are known and commercially available from BASF Polyurethanes GmbH under the trade names Lupranat® M20, Lupranat® M50 or Lupranat® M70.

[0022] The component (A) preferably contains at least 70% by weight, particularly preferably at least 90% by weight and in particular 100% by weight, of one or more isocyanates selected from the group consisting of 2,2'-MDI, 2,4'-MDI, 4,4'-MDI and higher nuclear homologues of MDI, based on the total weight of the component (A). The content of higher nuclear homologues of MDI is preferably at least 20% by weight, particularly preferably more than 30% by weight and less than 80% by weight, based on the total weight of the component (A).

[0023] The viscosity of the component (A) used may vary over a wide range, preferably having a viscosity at 25° C. of 100 to 3000 mPa·s, particularly preferably 100 to 1000 mPa·s, particularly preferably 100 to 800 mPa·s, particularly preferably 200 to 700 mPa·s and particularly preferably 400 to 650 mPa·s, and is brought about by the selection of the isocyanates (A) and mixtures thereof.

[0024] Ingredient (B) As compounds (B) reactive towards isocyanate groups, it is possible to use all compounds known in polyurethane chemistry which have groups reactive towards isocyanates, preferably compounds which have on average at least 1.5 groups reactive towards isocyanates, such as hydroxyl, -NH, NH2 or carboxylic acid groups, preferably NH2 or OH groups and in particular at least 1.5 OH groups. The average functionality of the compounds of component (B) relative to isocyanate groups is then in the range of at least 1.5, preferably 1.6 to 8.0, particularly preferably 1.7 to 3.0 and in particular 1.8 to 2.5.

[0025] The compound (B) having at least two hydrogen atoms reactive with isocyanate groups contains at least one aromatic polyester polyol (b1) and at least one polyether polyol (b2), wherein the mass ratio of the component (b1) to the component (b2) is ≦3 and ≧1, and the sum of the mass proportions of the components (b1) and (b2) based on the component (B) is more than 80% by weight.

[0026] Within the scope of this disclosure, the terms "polyester polyol" and "polyester ol" are synonymous, similarly the terms "polyether polyol" and "polyether ol" are synonymous.

[0027] According to the present invention, the component (B) contains (b1.1) 10 to 50 mol % of a dicarboxylic acid composition containing an aromatic dicarboxylic acid, (b1.2) 0 to 20 mol % of one or more fatty acids and / or fatty acid derivatives, (b1.3) 10 to 70 mol % of one or more aliphatic or alicyclic diols having 2 to 18 carbon atoms or alkoxylates thereof, and (b1.4) 0 to 50 mol % of at least one aromatic polyester polyol (b1) which can be produced by esterification of a more highly functional polyol selected from the group consisting of glycerin, alkoxylated glycerin, trimethylolpropane, alkoxylated trimethylolpropane, pentaerythritol, and alkoxylated pentaerythritol.

[0028] The dicarboxylic acid composition (b1.1) generally contains dicarboxylic acids and / or their derivatives, which can be used for the preparation of esters. Preferably, the dicarboxylic acid composition (b1.1) contains at least one compound selected from the group consisting of terephthalic acid, dimethyl terephthalate (DMT), polyethylene terephthalate (PET), phthalic acid, phthalic anhydride (PSA) and isophthalic acid. Particularly preferably, the component (b1.1) contains phthalic anhydride, phthalic acid, terephthalic acid or polyethylene terephthalate (PET) and in particular phthalic anhydride or terephthalic acid, in particular phthalic anhydride. In general, the component (b1.1) may also contain aliphatic dicarboxylic acids or aliphatic dicarboxylic acid derivatives. If aliphatic dicarboxylic acids are used, they are generally contained in an amount of 0.5 to 30 mol %, preferably 0.5 to 10 mol %, each based on the component (b1.1). As aliphatic dicarboxylic acids, preferably adipic acid or a dicarboxylic acid mixture of succinic acid, glutaric acid and adipic acid is used. Preferably, the dicarboxylic acid composition (b1.1) does not contain aliphatic dicarboxylic acids or their derivatives, so that 100 mol % consists of one or more aromatic dicarboxylic acids or their derivatives.

[0029] In general, component (b1.1) is used in an amount of 10 to 50 mol %, preferably 20 to 45 mol %, based on the components (b1.1), (b1.2), (b1.3) and (b1.4) used in the preparation of the aromatic polyester polyol (b1).

[0030] For the preparation of the aromatic polyester polyols (b1), one or more fatty acids and / or fatty acid derivatives (b1.2) can also be used. The acids and / or fatty acid derivatives can be of biological and petrochemical origin. Examples of fatty acids are caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, myristoleic acid, palmitic acid, palmitoleic acid, stearic acid, oleic acid, vaccenic acid, petroselinic acid, gadoleic acid, erucic acid, nervonic acid, linoleic acid, linolenic acid, stearidonic acid, arachidonic acid, timnodonic acid, sardine acid, cervonic acid, ricinoleic acid and mixtures thereof. Examples of fatty acid derivatives are glycerol esters of fatty acids, e.g. castor oil, grape seed oil, nigella sativa oil, pumpkin seed oil, borage seed oil, soybean oil, wheat germ oil, rapeseed oil, sunflower seed oil, peanut oil, apricot kernel oil, pistachio oil, almond oil, olive oil, macadamia oil, avocado oil, sea buckthorn oil, sesame oil, hemp seed oil, hazelnut oil, evening primrose oil, wild rose oil, safflower oil, walnut oil.

[0031] Further examples of fatty acid derivatives are hydroxyl modified fats or fatty acids, hydrogenated fats or fatty acids, epoxidized fats or fatty acids, alkyl branched fats or fatty acids, fatty acid amides, tallow, e.g. beef tallow, alkyl esters or especially methyl esters of fatty acids, e.g. biodiesel.

[0032] In general, component (b1.2) is used in an amount of 0 to 20 mol %, preferably in an amount of 5 to 15 mol %, particularly preferably in an amount of 6 to 10 mol %, based on all components (b1.1) to (b1.4) used in the production of the aromatic polyester polyol (b1).

[0033] In a particularly preferred embodiment of the invention, the fatty acid or fatty acid derivative (b1.2) is oleic acid, biodiesel, soybean oil, rapeseed oil or tallow, in particular oleic acid or biodiesel, in particular oleic acid, and is used in an amount of 5 to 15 mol %. The fatty acid or fatty acid derivative improves, inter alia, the solubility of the blowing agent in the production of rigid polyurethane or polyisocyanurate foams. Very particularly preferably, component (b1.2) does not contain triglycerides, in particular oils or fats. Glycerol liberated from the triglycerides by its esterification or transesterification impairs the dimensional stability of the rigid foam.

[0034] As component (b1.3) one or more aliphatic or cycloaliphatic diols having 2 to 18 carbon atoms or alkoxylates thereof are used. Preferably, component (b1.3) contains at least one compound from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2-methyl-1,3-propanediol and 3-methyl-1,5-pentanediol and alkoxylates thereof. Particularly preferably, the aliphatic diol (b1.3) is monoethylene glycol or diethylene glycol, in particular diethylene glycol. In general, component (b1.3) is used in an amount of 10 to 80 mol%, preferably in an amount of 20 to 75 mol%, particularly preferably in an amount of 30 to 60 mol%, based on all components used in the preparation of the aromatic polyester polyol (b1).

[0035] As higher-functionality polyol (b1.4), any polyol having a functionality greater than 2 can be used for the preparation of the aromatic polyester polyol (b1). Preferably, the higher-functionality polyol (b1.4) is selected from the group consisting of glycerin, alkoxylated glycerin, trimethylolpropane, alkoxylated trimethylolpropane, pentaerythritol, alkoxylated pentaerythritol and mixtures of two or more of these higher-functionality polyols. Particularly preferably, the higher-functionality polyol (b1.4) is glycerin, alkoxylated glycerin or a mixture thereof.

[0036] The higher-functional polyol (b1.4) is used in an amount of 0 to 50 mol %, preferably in an amount of 5 to 40 mol %, particularly preferably in an amount of 10 to 25 mol %, based on all components used in the preparation of the aromatic polyester polyol (b1). In a particularly preferred embodiment of the present invention, no higher-functional polyol (b1.4) is used in the preparation of the aromatic polyester.

[0037] According to the invention, said aromatic polyester polyol (b1) has a number-weighted average functionality of ≧1.7 to ≦3.0, preferably ≧1.7 to ≦2.5, particularly preferably ≧1.75 to ≦2.2.

[0038] Preferably, said aromatic polyester polyol (b1) has a hydroxyl number of 190 to 250 mg KOH / g, preferably 200 to 240 mg KOH / g.

[0039] In a particularly preferred embodiment, said aromatic polyester polyol (b1) has an OH number of 190 to 250 mg KOH / g and a functionality of 1.7 to 2.5.

[0040] To prepare the aromatic polyester polyols (b1), the dicarboxylic acids (b1.1), the fatty acids and / or fatty acid derivatives (b1.2), the aliphatic or cycloaliphatic diols having 2 to 18 carbon atoms or their alkoxylates (b1.3) and the more highly functional polyols (b1.4) can be polycondensed in the melt without catalyst or preferably in the presence of an esterification catalyst, expediently in an atmosphere of an inert gas, for example nitrogen, at temperatures of 150 to 280° C., preferably 180 to 260° C., optionally under reduced pressure, to the desired acid value, which is advantageously less than 10 and particularly preferably less than 2. According to a preferred embodiment, the esterification mixture is polycondensed at the abovementioned temperatures to an acid value of 80 to 20, preferably 40 to 20, under standard pressure and subsequently under a pressure of less than 500 mbar, preferably 40 to 400 mbar. As esterification catalysts, for example, iron, cadmium, cobalt, lead, zinc, antimony, magnesium, titanium and tin catalysts in the form of metals, metal oxides or metal salts come into consideration. However, the polycondensation can also be carried out in the liquid phase in the presence of a diluent and / or an azeotropic agent, for example benzene, toluene, xylene or chlorobenzene for removal of the condensed water by azeotropic distillation.

[0041] In general, the proportion of the polyester polyol (b1) according to the invention is at least 20% by weight, preferably at least 30% by weight, particularly preferably at least 40% by weight and in particular at least 50% by weight, based on the sum of the components (B) to (F).

[0042] According to the invention, component (B) contains, in addition to the polyester polyol (b1), at least one polyether polyol (b2) which has a hydroxyl number of 160 to 350 mg KOH / g and is prepared by alkoxylation of an initiator or initiator mixture, in which as alkylene oxide for preparing the polyether polyol (b2) preferably at least 80% by weight of ethylene oxide is used and the polyether polyol (b2) has at least 90%, preferably at least 95%, particularly preferably at least 99% and in particular exclusively primary hydroxyl end groups.

[0043] The polyether polyols (b2) are prepared by known methods, for example by anionic polymerization of one or more alkylene oxides having 2 to 4 carbon atoms, including ethylene oxide, using conventional catalysts, for example alkali hydroxides, such as sodium hydroxide or potassium hydroxide, alkali metal alcoholates, such as sodium methylate, sodium ethylate or potassium ethylate or potassium isopropylate, or amine-based alkoxylation catalysts, such as dimethylethanolamine (DMEOA), imidazole and / or imidazole derivatives, with an average of ≦3.5 and ≧1.5, preferably ≦3.0 and ≧2.0, and particularly preferably at least one initiator molecule or mixture of initiator molecules containing two reactive hydrogen atoms in combination. In addition to the anionic polymerization of the initiator molecules, the preparation can also be carried out on the basis of cationic polymerization, in which Lewis acids, such as antimony pentachloride, boron fluoride etherate or fuller's earth, are used as catalysts.

[0044] Preferred alkoxylation catalysts are KOH and amine-based alkoxylation catalysts.The use of amine-based alkoxylation catalysts is particularly preferred, since when using KOH as alkoxylation catalyst, the polyether must first be neutralized and the resulting potassium salt must be separated.Preferred amine-based alkoxylation catalysts are selected from the group that contains dimethylethanolamine (DMEOA), imidazole and imidazole derivatives and their mixtures, particularly preferably imidazole.

[0045] Suitable alkylene oxides, in addition to ethylene oxide, are, for example, tetrahydrofuran, 1,3- or 1,2-propylene oxide, 1,2- or 2,3-butylene oxide, styrene oxide and preferably 1,2-propylene oxide. In a particularly preferred embodiment, exclusively ethylene oxide is used as alkylene oxide. The alkylene oxides can be used individually, alternately in succession or as a mixture. According to the invention, at least 80% by weight of ethylene oxide, preferably at least 90% by weight of ethylene oxide, particularly preferably at least 95% by weight and in particular at least 98% by weight of ethylene oxide, is used as alkylene oxide for preparing polyether polyols (b2) according to the invention. Very particularly preferably exclusively ethylene oxide is used as alkylene oxide for preparing polyether polyols (b2) according to the invention, i.e. the amount by weight of ethylene oxide based on the total weight of alkylene oxide in component (b2) is 100% by weight in this embodiment. If ethylene oxide is used in a mixture with other alkylene oxides, it should be ensured according to the invention that the polyol ether polyols produced therefrom have the content according to the invention of primary hydroxyl end groups.

[0046] As initiator molecules, the following are, for example, worthy of consideration: water, organic dicarboxylic acids, such as succinic acid, adipic acid, phthalic acid and terephthalic acid, aliphatic and aromatic, optionally N-monodialkyl-substituted, N,N- and N,N'-dialkyl-substituted diamines having 1 to 4 carbon atoms in the alkyl group, such as optionally monoalkyl- and dialkyl-substituted ethylenediamine, diethylenetriamine, triethylenetetramine, 1,3-propylenediamine, 1,3- or 1,4-butylenediamine, 1,2-, 1,3-, 1,4-, 1,5- and 1,6-hexamethylenediamine, phenylenediamines, 2,3-, 2,4- and 2,6-toluylenediamine and 4,4'-, 2,4'- and 2,2'-diamino-diphenylmethane. Particular preference is given to the mentioned diprimary amines, preferably ethylenediamine. As initiator molecules furthermore the following are worthy of consideration: alkanolamines, such as ethanolamine, N-methylethanolamine and N-ethylethanolamine, dialkanolamines, such as diethanolamine, N-methyl and N-ethyldiethanolamine, and trialkanolamines, such as triethanolamine, and ammonia.

[0047] Preferably used are dihydric or higher alcohols, such as ethanediol, 1,2- and 1,3-propanediol, diethylene glycol (DEG), dipropylene glycol, 1,4-butanediol, 1,6-hexanediol, glycerin, trimethylolpropane, bisphenol A, bisphenol F, pentaerythritol, sorbitol and sucrose, particularly preferably diethylene glycol, monoethylene glycol, 1,2-propanediol and glycerin, especially diethylene glycol.

[0048] In a preferred embodiment, the initiator molecule does not contain a fatty acid.

[0049] According to the invention, the polyether polyol (b2) has a hydroxyl number of 160 to 350 mg KOH / g, preferably 170 to 290 mg KOH / g, particularly preferably 175 to 225 mg KOH / g.

[0050] Generally, the proportion of the component (b2) is 20 to 45% by weight, preferably 25 to 40% by weight, and particularly preferably 30 to 38% by weight, based on the total amounts by weight of the components (B) to (F).

[0051] According to the invention, the weight ratio of component (b1) to component (b2) is ≦3 and ≧1, preferably ≦2.5 and ≧1.15 and particularly preferably ≦2.0 and ≧1.3.

[0052] According to the invention, the sum of the mass proportions of components (b1) and (b2) based on component (B) is >80% by weight, preferably >90% by weight, particularly preferably >95% by weight. Very particularly preferably, the sum of the mass proportions of components (b1) and (b2) based on said component (B) is 100% by weight, i.e. in this embodiment, no further compounds having hydrogen atoms reactive with isocyanate groups are used as components (b1) and (b2).

[0053] Ingredients (C) As flame retardant E), flame retardants known from the prior art can generally be used.Suitable flame retardants are, for example, brominated esters, brominated ethers (Ixol) or brominated alcohols, such as dibromoneopentyl alcohol, tribromoneopentyl alcohol and PHT-4-diol, as well as chlorinated phosphates, such as tris(2-chloroethyl)phosphate, tris(2-chloropropyl)phosphate (TCPP), tris(1,3-dichloropropyl)phosphate, tricresyl phosphate, tris(2,3-dibromopropyl)phosphate, tetrakis(2-chloroethyl)ethylene diphosphate, dimethylmethane phosphonate, diethanolaminomethylphosphonic acid diethyl ester, as well as commercially available halogen-containing flame-retardant polyols. As further phosphates or phosphonates, diethylethane phosphonate (DEEP), triethyl phosphate (TEP), dimethylpropyl phosphonate (DMPP), diphenylcresyl phosphate (DPK) can be used as liquid flame retardants.Compounds that contain phosphorus, chlorine or bromine atoms and also have groups reactive with isocyanates are not considered within the scope of the present invention as compounds (B) that have hydrogen atoms reactive with isocyanate groups and are not considered to be included when calculating the quantitative ratio of component (B).

[0054] In addition to the flame retardants already mentioned, inorganic or organic flame retardants, such as red phosphorus, preparations containing red phosphorus, aluminum oxide hydrate, antimony trioxide, arsenic oxide, ammonium polyphosphate and calcium sulfate, expandable graphite or cyanuric acid derivatives, such as melamine, or a mixture of at least two flame retardants, such as ammonium polyphosphate and melamine, and optionally corn starch or ammonium polyphosphate, melamine, expandable graphite and optionally aromatic polyesters, can also be used to impart flame retardancy to the rigid polyisocyanurate foam.Preferred flame retardants do not have groups reactive to isocyanate groups.Preferably, the flame retardants are liquid at room temperature.Preferably, TCPP, DEEP, TEP, DMPP and DPK, particularly preferably TCPP and TEP, especially TCPP.

[0055] Generally, the proportion of the flame retardant (C) is 1 to 20% by weight, preferably 2 to 15% by weight, particularly preferably 3 to 10% by weight, based on the total weight amounts of components (B) to (F).

[0056] Preferably, component (C) comprises a phosphorus-containing flame retardant and the phosphorus content is <0.4 wt. %, preferably <0.3 wt. %, and particularly preferably <0.2 wt. %, based on the total weight of components (A) to (F).

[0057] Ingredients (D) The blowing agents (D) used to prepare the rigid polyisocyanurate foams according to the invention include formic acid and formic acid-water mixtures, which react with isocyanate groups to form carbon dioxide and carbon monoxide. These blowing agents are called chemical blowing agents, since they liberate the gases by chemical reaction with the isocyanate groups. In addition, physical blowing agents can be used, such as low-boiling hydrocarbons. Suitable physical blowing agents are in particular liquids which are inert towards the polyisocyanates (A) and have a boiling point below 100° C., preferably below 50° C., at atmospheric pressure, so that they evaporate under the effect of the exothermic polyaddition reaction.

[0058] Physical blowing agents which can be used are, for example, alkanes such as heptane, hexane, n-pentane and isopentane, preferably technical mixtures of n-pentane and isopentane, n-butane and isobutane and propane, cycloalkanes such as cyclopentane and / or cyclohexane, ethers such as furan, dimethyl ether and diethyl ether, ketones such as acetone and methyl ethyl ketone, alkyl carboxylic acid esters such as methyl formate, dimethyl oxalate and ethyl acetate and halogenated saturated and unsaturated hydrocarbons such as methylene chloride, dichloromonofluoromethane, di ... Examples of suitable fluorocarbons include fluoromethane, trifluoromethane, difluoroethane, tetrafluoroethane, chlorodifluoroethane, 1,1-dichloro-2,2,2-trifluoroethane, 2,2-dichloro-2-fluoroethane and heptafluoropropane, and unsaturated hydrocarbons such as trifluoropropene and tetrafluoropropene, for example (HFO-1234), pentafluoropropene, for example (HFO-1225), chlorotrifluoropropene, for example (HFO-1233), chlorodifluoropropene, chlorotetrafluoropropene and hexafluorobutene, and mixtures of one or more of these components. Preferred are tetrafluoropropene, pentafluoropropene, chlorotrifluoropropene and hexafluorobutene, where the unsaturated terminal carbon atom bears at least one chloro or fluoro substituent. Examples are 1,3,3,3-tetrafluoropropene (HFO-1234ze); 1,1,3,3-tetrafluoropropene; 1,2,3,3,3-pentafluoropropene (HFO-1225ye); 1,1,1-trifluoropropene; 1,1,1,3,3-pentafluoropropene (HFO-1225zc); 1,1,2,3,3-pentafluoropropene (HFO-1225yc); 1-chloro-2,3,3,3-tetrafluoropropene (HFO-1224yd); 1,1,1,2,3-pentafluoropropene (HFO-1225yez); 1-chloro-3,3,3-trifluoropropene (HCFO-1233zd); 1,1,1,4,4,4-hexafluorobut-2-ene (HFO-1336mzz).Mixtures of these low boiling liquids with each other and / or with other substituted or unsubstituted hydrocarbons may also be used.

[0059] Also suitable are organic carboxylic acids, such as formic acid, acetic acid, oxalic acid, ricinoleic acid and carboxyl-containing compounds.

[0060] Preferably, halogenated hydrocarbons are not used as blowing agents. Formic acid-water mixtures or formic acid are used as chemical blowing agents. Preferably, pentane isomers or mixtures of pentane isomers are used as physical blowing agents. In this case, the chemical blowing agent is used together with a physical blowing agent, where the use of formic acid-water mixtures or pure formic acid together with pentane isomers or mixtures of pentane isomers is preferred.

[0061] The amount of the blowing agent or the blowing agent mixture used is 0.1 to 45% by weight, preferably 1 to 30% by weight, particularly preferably 1 to 20% by weight and in particular 1.5 to 20% by weight, based on the total of the components (B) to (F).

[0062] Formic acid or formic acid-water mixtures are preferably used in amounts of 0.2 to 10% by weight, in particular 0.5 to 4% by weight, based on the component (B). If formic acid-water mixtures are used, the proportion of formic acid is preferably more than 40% by weight, particularly preferably 50 to 98% by weight, more preferably 70 to 95% by weight and in particular 80 to 90% by weight, based on the total weight of formic acid and water. Particularly preferably, formic acid or formic acid-water mixtures are used as chemical blowing agents in combination with pentane.

[0063] Ingredient (E) As catalysts (E) for producing the rigid polyisocyanurate foams according to the invention, in particular compounds are used which significantly accelerate the reaction of the compounds of components (B) to (F) which contain reactive hydrogen atoms, in particular hydroxyl groups, with the polyisocyanate (A).

[0064] Suitable polyurethane catalysts include basic polyurethane catalysts, for example tertiary amines, such as triethylamine, tributylamine, dimethylbenzylamine, dicyclohexylmethylamine, dimethylcyclohexylamine, N,N,N',N'-tetramethyldiaminodiethyl ether, bis(dimethylaminopropyl)urea, N-methylmorpholine or N-ethylmorpholine, N-cyclohexylmorpholine, N,N,N',N'-tetramethylethylenediamine, N,N,N,N-tetramethylbutanediamine, N,N,N,N-tetramethylhexane-1,6-diamine, pentamethyldiethylenetriamine, bis(2-dimethylaminoethyl)ether, di Methylpiperazine, N-dimethylaminoethylpiperidine, 1,2-dimethylimidazole, 1-azabicyclo(2,2,0)octane, 1,4-diazabicyclo(2,2,2)octane (Dabco) and alkanolamine compounds such as triethanolamine, triisopropanolamine, N-methyldiethanolamine and N-ethyldiethanolamine, dimethylaminoethanol, 2-(N,N-dimethylaminoethoxy)ethanol, N,N',N"-tris(dialkylaminoalkyl)hexahydrotriazines such as N,N',N"-tris(dimethylaminopropyl)-s-hexahydrotriazine, and triethylenediamine.

[0065] However, metal salts such as iron(II) chloride, zinc chloride, lead octoate and tin salts such as tin dioctoate, tin diethylhexanoate and dibutyltin dilaurate, as well as mixtures of tertiary amines and metal salts, especially organotin salts, are also suitable. Further suitable catalysts include amidines such as 2,3-dimethyl-3,4,5,6-tetrahydropyrimidine, tetraalkylammonium hydroxides such as tetramethylammonium hydroxide, alkali hydroxides such as sodium hydroxide and alkali metal alcoholates such as sodium methylate and potassium isopropylate, alkali metal carboxylates and alkali metal salts of long-chain fatty acids having 8 to 20 carbon atoms and optionally pendant OH groups.

[0066] Furthermore, as catalysts, incorporable amines, i.e. preferably amines having -OH, -NH or -NH2 functional groups, such as ethylenediamine, triethanolamine, diethanolamine, ethanolamine and dimethylethanolamine, are worthy of consideration. Incorporable catalysts can be considered as the compounds of component (B) and component (E).

[0067] It is also possible for the reaction to proceed uncatalyzed, in which case the catalytic activity of the amine-initiated polyol is usually utilized.

[0068] Additionally, catalysts for the trimerization reaction of excess -NCO groups are worthy of consideration: catalysts which form isocyanurate groups, such as ammonium or alkali metal salts, in particular ammonium or alkali metal carboxylates, alone or in combination with tertiary amines. The isocyanurate formation leads to flame-retardant PIR foams, which are preferably used in industrial rigid foams, for example as insulation boards or sandwich elements in civil engineering construction.

[0069] In a preferred embodiment, the catalyst (E) contains an amine catalyst having a tertiary amino group and an ammonium carboxylate catalyst or an alkali metal carboxylate catalyst. In a particularly preferred embodiment, the catalyst (E) contains at least one amine catalyst selected from the group consisting of pentamethyldiethylenetriamine and bis(2-dimethylaminoethyl)ether and at least one alkali metal carboxylate catalyst selected from the group consisting of potassium formate, potassium acetate and potassium-2-ethylhexanoate. Surprisingly, the use of these catalysts during the continuous production of sandwich elements, for example in the double belt, results in sandwich elements with a particularly smooth foam surface on the cover layer side, especially on the lower cover layer side. This results in sandwich elements with excellent adhesion of the foam to the cover layer and a defect-free surface.

[0070] Preferably, from 0.001 to 10 parts by weight of a catalyst or catalyst combination is used, based on 100 parts by weight of said component (B).

[0071] Component (F) The reaction mixture for producing the rigid polyisocyanurate foams according to the invention can optionally further comprise further auxiliaries and / or additives (F), such as, for example, surface-active substances, foam stabilizers, cell regulators, fillers, light stabilizers, dyes, pigments, hydrolysis protection agents, fungistatic and bacteriostatic substances.

[0072] As surface-active substances, for example, compounds that are useful for supporting the homogenization of the starting materials and are also suitable for controlling the cell structure of the plastics are worthy of consideration. Mention may be made, for example, of emulsifiers, such as sodium salts of castor oil sulfate or sodium salts of fatty acids, as well as salts of fatty acids with amines, such as diethylamine oleate, diethanolamine stearate, diethanolamine ricinoleate, salts of sulfonic acids, such as alkali metal or ammonium salts of dodecylbenzenesulfonic acid or dinaphthylmethanedisulfonic acid and ricinoleic acid, foam stabilizers, such as siloxaneoxyalkylene mixed polymers and other organopolysiloxanes and dimethylpolysiloxanes. To improve the emulsification, the cell structure and / or the stabilization of the foam, oligomeric acrylates having polyoxyalkylene and fluoroalkane groups as side groups are furthermore suitable. The surface-active substances are usually used in amounts of 0.01 to 10 parts by weight, based on 100 parts by weight of the component (B). As foam stabilizers it is possible to use the usual foam stabilizers, for example those based on silicones, such as siloxane-oxyalkylene mixed polymers and other organopolysiloxanes.

[0073] Fillers, especially reinforcing fillers, are to be understood as being conventional organic and inorganic fillers, reinforcing agents, extenders, agents for improving the wear behavior in paints, coatings, etc., which are known per se. In particular, examples include: inorganic fillers, such as silicate minerals, such as sheet silicates, for example antigorite, serpentine, hornblende, amphibole, chrysotile and talc, metal oxides, such as kaolin, aluminum oxide, titanium oxide and iron oxide, metal salts, such as chalk, barite and inorganic pigments, for example cadmium sulfide and zinc sulfide, as well as glass. Kaolin (china clay), aluminum silicate and coprecipitates of barium sulfate and aluminum silicate, as well as natural and synthetic fibrous minerals, such as wollastonite, metal fibers of various lengths and especially glass fibers, which may be optionally sized, are preferably used. As organic fillers, for example, the following come into consideration: carbon, melamine, colophony, cyclopentadienyl resins and graft polymers as well as cellulose fibers, polyamide fibers, polyacrylonitrile fibers, polyurethane fibers, polyester fibers based on aromatic and / or aliphatic dicarboxylic esters and especially carbon fibers. The inorganic and organic fillers can be used individually or as mixtures and are added to the reaction mixture in amounts of advantageously 0.5 to 50% by weight, up to 35% by weight, preferably 1 to 40% by weight, based on the weight of the components (A) to (F), whereby the content of mats, nonwovens and woven fabrics made of natural and synthetic fibers can, however, reach values ​​of up to 80% by weight, based on the weight of the components (A) to (F).

[0074] According to the invention, the rigid polyisocyanurate foams are produced by mixing the components (A) to (E) and, if present, (F) to form a reaction mixture. To reduce complexity, premixes can also be produced. These contain at least one isocyanate component (A) containing a polyisocyanate and a polyol component (B) containing a compound reactive towards isocyanates. The further components (C) to (F) can be added completely or partially to the isocyanate and polyol components, where, due to the high reactivity of the isocyanates, the components (C) to (F) are often added to the polyol component to avoid side reactions. However, in particular physical blowing agents can also be mixed into the isocyanate component (A). Usually, a formic acid-water mixture or formic acid is present completely or partially dissolved in the polyol component, and the physical blowing agent (e.g. pentane) and optionally the remainder of the chemical blowing agent are metered in directly "online" during production. Preferably, the physical blowing agent is fed online to the reaction mixture in a separate stream, and particularly preferably, the remaining components (C), (E) and (F) are added to the polyol component. Usually, the catalyst is dosed online, but it may already be present partially or completely dissolved in the polyol component.

[0075] Preferably, the polyol component for producing the rigid polyisocyanurate foam according to the present invention contains, based on the total weight of the components (B) to (F), 70 to 90% by weight of a compound (B) having at least 1.5 hydrogen atoms reactive with isocyanate groups, 2 to 10% by weight of a flame retardant (C), 1 to 20% by weight of a blowing agent (D), 0.5 to 10% by weight of a catalyst (E) and 0.0 to 20% by weight of further auxiliaries and additives (F). In a particularly preferred embodiment, the proportions of the components (B) to (F) total 100% by weight.

[0076] The reaction mixture is then completely reacted to give a rigid polyisocyanurate foam, whereby within the scope of the present invention, reaction mixture refers to a mixture of the polyisocyanate (A) with the compound (B) reactive towards the isocyanate and all further components (C), (D), (E) and optionally (F) at a reaction conversion of less than 90%, based on the isocyanate groups.

[0077] The components are mixed into the reaction mixture at an isocyanate index of 220 to 1000, preferably 260 to 800, preferably 300 to 600, particularly preferably 340 to 500. The starting components are mixed at temperatures of 15 to 90° C., preferably 20 to 60° C., in particular 20 to 45° C. The reaction mixture can be mixed by mixing in a high-pressure or low-pressure dispenser.

[0078] The reaction mixture can be introduced, for example, into a mold to complete the reaction. This technique produces, for example, sandwich elements discontinuously. The rigid foam according to the invention is preferably produced on a continuously operating double belt system. The polyol component and the isocyanate component are metered using a high-pressure machine and mixed in a mixing head. Catalysts and / or blowing agents can be metered into the polyol mixture beforehand using separate pumps. The reaction mixture is applied onto a continuously moving lower cover layer. The lower cover layer with the reaction mixture and the upper cover layer enter the double belt, in which the reaction mixture foams and hardens. After leaving the double belt, the continuous strand is cut to the desired size. In this way, sandwich elements with metal cover layers or with flexible cover layers can be produced. As lower and upper cover layers, which can be the same or different, soft or hard cover layers as are usually used in the double belt process can be used. These include metal cover layers, such as aluminum or steel, asphalt cover layers, paper, nonwoven fabrics, plastic sheets, such as polystyrene, plastic films, such as polyethylene films, or wood cover layers. The cover layers may be coated, for example with conventional lacquers or adhesion promoters. Particularly preferably, a cover layer that is diffusion-resistant to the cell gases of the rigid polyisocyanurate foam is used.

[0079] Such processes are known and are described, for example, in "Kunststoffhandbuch, Band 7, Polyurethane", Carl Hanser Verlag, 3rd Edition, 1993, chapter 6.2.2 or in EP 2234732. Finally, the subject of the present invention is a rigid foam based on polyisocyanates obtainable by the process according to the invention, and a polyurethane sandwich element containing such a rigid foam based on polyisocyanates according to the invention.

[0080] The polyisocyanate-based rigid foams of the present invention are distinguished by good mechanical properties, especially good compressive strength, and at the same time reduced surface brittleness, which is manifested by improved cover layer adhesion, especially in the production of sandwich elements in the continuous double belt process.In addition, the polyisocyanate-based rigid foams of the present invention have good fire resistance, even when using small amounts of ecologically and toxicologically problematic flame retardants.Moreover, the reaction mixtures used for the production of the polyisocyanate-based rigid foams of the present invention make it possible to achieve the reactivity required for improved foam curing when using smaller amounts of ecologically and toxicologically problematic catalysts.

[0081] In the following the invention will be explained on the basis of examples: EXAMPLES

[0082] The following starting materials were used: Polyesterol 1: An esterification product of phthalic anhydride, oleic acid and diethylene glycol having an average hydroxyl functionality of 1.75, a hydroxyl number of 215 mg KOH / g and an oleic acid content of 15% by weight. Polyesterol 2: An esterification product of terephthalic acid, oleic acid, glycerin and diethylene glycol having an average hydroxyl functionality of 2.3, a hydroxyl number of 245 mg KOH / g and an oleic acid content of 18% by weight. Polyesterol 3: An esterification product of phthalic anhydride and diethylene glycol having a hydroxyl functionality of 2.0 and a hydroxyl number of 240 mg KOH / g. Polyetherol 1: A polyether polyol produced by ethoxylation of ethylene glycol and having a hydroxyl functionality of 2 and a hydroxyl value of 190 mg KOH / g. Polyetherol 2: A polyether polyol produced by the ethoxylation of ethylene glycol and having a hydroxyl functionality of 2 and a hydroxyl value of 225 mg KOH / g. Polyetherol 3: A polyether polyol produced by ethoxylation of ethylene glycol and having a hydroxyl functionality of 2 and a hydroxyl value of 280 mg KOH / g. Polyetherol 4: a polyether polyol produced by ethoxylation of ethylene glycol and having a hydroxyl functionality of 2 and a hydroxyl value of 750 mg KOH / g. Polyetherol 5: A polyether polyol produced by ethoxylation of glycerin, having a hydroxyl functionality of 3 and a hydroxyl value of 250 mg KOH / g. Polyetherol 6: a polyether polyol produced by the propoxylation of propylene glycol, having a hydroxyl functionality of 2 and a hydroxyl value of 250 mg KOH / g. Polyetherol 7: A polyether polyol prepared by propoxylation of a mixture of sucrose and glycerin, having a hydroxyl functionality of 4.3 and a hydroxyl number of 490 mg KOH / g. Polyetherol 8: A polyether polyol produced by ethoxylation of a mixture of sucrose and glycerin, having a hydroxyl functionality of 4.8 and a hydroxyl value of 480 mg KOH / g. Polyetherol 9: A polyether polyol consisting of 94% by weight ethylene oxide and 6% by weight propylene oxide, having exclusively primary hydroxyl end groups, a functionality of 2 and a hydroxyl number of 190 mg KOH / g. Polyetherol 10: A polyether polyol produced by the ethoxylation of ethylene glycol and having a hydroxyl functionality of 2 and a hydroxyl value of 115 mg KOH / g. Flame retardant: Tris(2-chloroisopropyl)phosphate (TCPP) Foam stabilizer: Tegostab B 8467 (silicone-containing foam stabilizer from Evonik) Catalyst A: A catalyst consisting of 16.8 wt. % bis(2-dimethylaminoethyl) ether, 76 wt. % polyetherol 6, and 7.2 wt. % dipropylene glycol. Catalyst B: A catalyst consisting of 40% by weight of potassium formate, 54% by weight of monoethylene glycol and 6% by weight of water. Blowing Agent A: A blowing agent mixture consisting of 85% by weight formic acid and 15% by weight water. Blowing Agent B: A blowing agent mixture consisting of 80 mol % n-pentane and 20 mol % isopentane. Blowing agent C: Water PMDI: Polymeric diphenylmethane diisocyanate (Lupranat M50 from BASF).

[0083] Using the starting materials described above, polyol components were produced as shown in Tables 1 and 2, and consisted of polyesterols 1 to 3, polyetherols 1 to 10, a flame retardant, and a foam stabilizer.

[0084] Testing the Polyol Component for Phase Stability and Flowability The polyol components thus produced were examined for phase stability and flowability at 20° C. by filling a small amount of each polyol component into a transparent vial immediately after its production and observing it for several days.

[0085] The polyol components are expanded into rigid foams having comparable indices, reactivities and foam densities. Furthermore, the polyol component was reacted with PMDI in a mix ratio such that the isocyanate index of all produced foams was 340±10. In this case, the amount of flame retardant and the amount of foam stabilizer in the polyol component were selected so that the amounts of flame retardant and foam stabilizer were the same, based on the foams. Furthermore, the amounts of combustible blowing agent B and trimerization catalyst B were selected so that the contents of these compounds, based on the foams, were also the same. By varying blowing agent A or blowing agent C and catalyst A, all foams were subsequently produced with comparable curing times of 55 s±2 s and curing rates of 41 kg / m 3 ±1kg / m 3To this end, 80 g of the reaction mixture was intensively mixed in a paper cup with a laboratory stirrer at 1400 rpm.

[0086] The reaction mixtures thus adjusted to comparable cure times and densities were subsequently used to determine case cure and foam brittleness, as well as to produce rigid foam blocks for further investigation.

[0087] Surface hardening and foam brittleness measurement The surface cure of laboratory foams adjusted to the same reaction time and foam density was determined by bolt testing. For this, after 2.5; 3; 4; 5; 6 and 7 minutes of intensive mixing (at 1500 rpm) of 80 g of reactants in a 1.15 L polystyrene beaker, a steel bolt with a hemispherical head with a radius of 10 mm was pressed into the mushroom-shaped foam to a depth of 10 mm using a tensile / compression tester. The maximum force in N required to do so is a measure of the cure of the foam at each time point. Each cure measurement was performed on a fresh foam site at the same distance from the foam edge.

[0088] As a measure of the brittleness of the rigid polyisocyanurate foam, the time point at which the surface of the rigid foam shows a visible fracture zone during the bolt test was determined (fracture during the bolt test). The earlier visible fracture is recognizable, the more brittle the foam is. Foam fracture during the curing test can be recognized by C (=Crack) in Tables 1 and 2.

[0089] In addition, the brittleness was subjectively determined 8 minutes after mixing the reactive components by pressing the top edge of the foam side (subjective brittleness) and rated according to a rating system of 1 to 5, where 1 means that the foam is not brittle and 5 means that the foam has very high brittleness.

[0090] The foam brittleness was evaluated based on a rating system corresponding to the following criteria: 1. Non-brittle: When the foam is compressed, there are no visible foam cracks and no perceptible cracking sounds. 2. Low brittleness: when the foam is pressed, the foam cracks are not visible, but a slight cracking sound is perceptible. 3. Moderately Brittle: Fine foam cracks are visible and a distinct cracking sound can be perceived when the foam is compressed. 4. High brittleness: when the foam is compressed, obvious foam cracks are visible and a clear cracking sound can be perceived. 5. High brittleness: Upon compression of the foam, obvious foam cracks including material delamination are visible and a clear cracking sound can be perceived.

[0091] Small burner testing according to EN-ISO 11925-2 260 g of the reaction mixture, adjusted to the same reaction time and foam density, were stirred intensively for 10 seconds at 1500 rpm with a laboratory stirrer in a paper cup and transferred to a box mold with internal dimensions 25 cm x 15 cm x 22 cm (length x width x height). After 24 hours of curing of the reaction mixture, the resulting rigid foam block was demolded and all edges were trimmed by 3 cm. The removed specimens with dimensions: 190 x 90 x 20 mm were subsequently conditioned for 24 hours at 20°C and atmospheric humidity of 65%. From each rigid foam block, 5 specimens were removed and tested by flaming at the 90 mm side edge according to DIN EN-ISO 11925-2. The average value of the flame height is reported in Tables 1 and 2 under "Average flame height, EN-ISO 11925-2".

[0092] Determination of compressive strength: 350 g of reaction mixture adjusted to the same reaction time and foam density was reacted in a plastic bucket with a diameter of 21 cm and a height of 20 cm by intensively mixing the mixture for 10 seconds with a laboratory stirrer at 1500 rpm to produce foam blocks.

[0093] Nine specimens with dimensions 50 mm x 50 mm x 50 mm were subsequently removed from the foam block for the determination of the compressive strength according to DIN EN 826. The removal was always carried out at the same location. Of the nine specimens, three specimens were rotated so that the test was carried out towards the upward direction of the foam (top). Of the nine specimens, three specimens were rotated so that the test was carried out perpendicular to the upward direction of the foam (X direction). Of the nine specimens, three specimens were rotated so that the test was carried out perpendicular to the upward direction of the foam (Y direction). From all the measurement results, an average value was subsequently formed and is listed in tables 1 and 2 under "Compressive strength average".

[0094] [Table 1-1] [Table 1-2]

[0095] [Table 2-1] [Table 2-2]

[0096] As can be seen from Tables 1 and 2, the combination of polyester polyol (b1) and polyether polyol (b2) results in particularly advantageous polyol components and rigid polyisocyanurate foams when the weight ratio of component (b1) to component (b2) is within the range according to the invention. Therefore, all polyol components of Examples 1 to 7 are phase-stable and flowable at 20°C. The curing of the polyisocyanurate rigid foams corresponding to Examples 1 to 7 is surprisingly significantly improved compared to all comparative examples, which allows for faster processing on the production equipment and thus considerably increases its productivity. Surprisingly, all foams from Examples 1 to 7 also have a significantly reduced foam brittleness at their surface, which in experience leads to improved foam adhesion on the cover layer material and improved ability of the sandwich elements produced therewith to withstand temperature changes.

[0097] It can further be seen here that all the rigid polyisocyanurate foams according to the invention corresponding to Examples 1 to 7 still have very good compressive strength, despite the reduced foam brittleness. Even with small amounts of flame retardant based on the foams, all the rigid polyisocyanurate foams according to the invention pass the small burner test with a flame height of less than 11.5 cm.

[0098] However, deviations from the formulation according to the invention may result in shortcomings in the polyol component or in the properties of the rigid foam.

[0099] Thus, for example, an increase in the mass ratio of component (b1) to component (b2) causes a clear deterioration in the foam hardening and a clear increase in foam brittleness, as well as a slight deterioration in fire resistance (Comparative Example 5).

[0100] The replacement of the polyether polyol (b2) according to the invention with a polyether polyol not according to the invention leads to similar deterioration. Comparative Examples 1 and 6 therefore show that, based on the polyethylene glycol used, an optimum degree of ethoxylation is obtained for the polyether polyol (b2). A too low degree of ethoxylation (Comparative Example 1) leads to a clear increase in foam brittleness. A too high degree of ethoxylation (Comparative Example 6) leads to solidification of the polyol component at room temperature, so that foaming is no longer possible.

[0101] The replacement of the predominantly ethoxylated polyether polyols (b2) according to the invention with propoxylated polyether polyols (Comparative Example 2) leads to a significant decrease in the foam cure, a significant increase in the flame height according to EN-ISO 11925-2 and a significant increase in foam brittleness.

[0102] The use of higher functional propoxylated and ethoxylated polyether polyols (Comparative Examples 3 and 4) also leads to worse foam properties compared to the polyether polyols (b2) according to the invention.

[0103] In Comparative Examples 7 and 8, water (chemical blowing agent C) was used as the only chemical blowing agent instead of the formic acid-water mixture (blowing agent A) of Examples 1 and 5. This resulted in a significant deterioration of foam cure, deterioration of foam compressive strength and stronger bubble formation at the top of the beaker foam, respectively. In contrast, the exchange of water as a blowing agent in the case of a polyol component not according to the invention (Comparative Example 9) having an increased mass ratio of component (b1) to component (b2) does not result in a significant change in foam cure and compressive strength compared to Comparative Example 5.

[0104] Only the combination of starting materials described in Examples 1-7 can produce a reaction mixture that meets all the requirements.

Claims

1. 1. A method for producing a rigid polyisocyanurate foam, comprising: (A) a polyisocyanate, (B) A compound having a hydrogen atom reactive with an isocyanate group (C) Flame retardant (D) Foaming agent (E) a catalyst; and (F) optionally further auxiliaries and additives, mixing to form a reaction mixture at an isocyanate index of at least 220 and curing to form said rigid polyisocyanurate foam; Here, the component (B) contains at least one aromatic polyester polyol (b1) and at least one polyether polyol (b2), wherein the polyester polyol (b1) is selected from the following: (b1.1) 10 to 50 mol % of a dicarboxylic acid composition containing an aromatic dicarboxylic acid; (b1.2) 0 to 20 mol % of one or more fatty acids and / or fatty acid derivatives, (b1.3) 10 to 80 mol % of one or more aliphatic or cycloaliphatic diols having 2 to 18 carbon atoms or alkoxylates thereof, (b1.4) 0 to 50 mol % of a higher functionality polyol selected from the group consisting of glycerin, alkoxylated glycerin, trimethylolpropane, alkoxylated trimethylolpropane, pentaerythritol, alkoxylated pentaerythritol the total amount of components (b1.1) to (b1.4) totals 100 mol %, and the aromatic polyester polyol (b1) has an average functionality of 3.0 or less and 1.7 or more, and the polyether polyol (b2) has a hydroxyl number of 160 to 350 mg KOH / g and is prepared by alkoxylation of an initiator or a mixture of initiators having an average functionality of 3.5 or less and 1.5 or more; at least 80% by weight of ethylene oxide is used as alkylene oxide for preparing the polyether polyol (b2), and the polyether polyol (b2) has at least 90% primary hydroxyl end groups and a maximum of 10% secondary hydroxyl end groups, the mass ratio of the component (b1) to the component (b2) is 3 or less and 1 or more, and the total mass proportion of the component (b1) and the component (b2) based on the component (B) is more than 80% by weight; and the blowing agent (D) contains a chemical blowing agent and a physical blowing agent, wherein the chemical blowing agent is selected from the group consisting of a formic acid-water mixture and formic acid.

2. 2. The process of claim 1, wherein the aromatic polyester polyol (b1) has an OH number of 190 to 250 mg KOH / g and a functionality of 1.7 to 2.

5.

3. 2. The method according to claim 1, wherein the aromatic polyester polyol (b1) contains 5 to 15 mol % of one or more fatty acids and / or fatty acid derivatives.

4. 2. The process according to claim 1, wherein exclusively diethylene glycol is used as diol (b1.3) having 2 to 18 carbon atoms.

5. 2. The method according to claim 1, wherein the content of (b1.4) is 0 mol%.

6. 2. The process according to claim 1, wherein 2 to 50 mol % of glycerin or ethoxylated glycerin is used as component (b1.4).

7. 2. The method of claim 1, wherein the polyether polyol (b2) has a hydroxyl number of 170 to 290 mg KOH / g.

8. 2. The process of claim 1, wherein the polyether polyol (b2) is prepared by alkoxylation of an initiator or initiator mixture having an average total functionality of less than or equal to 3 and greater than or equal to 2.

9. 2. The process according to claim 1, characterized in that the polyether polyol (b2) is obtained by ethoxylation of diethylene glycol.

10. 2. The method of claim 1, wherein the flame retardant (C) comprises a phosphorus-containing flame retardant and has a phosphorus content of less than 0.4 wt. %, based on the total weight of components (A) through (F).

11. 2. The method of claim 1, wherein the catalyst (E) contains at least one amine catalyst having a tertiary amino group selected from the group consisting of pentamethyldiethylenetriamine and bis(2-dimethylaminoethyl)ether, and at least one alkali metal carboxylate catalyst selected from the group consisting of potassium formate, potassium acetate, and potassium 2-ethylhexanoate.

12. 2. The method according to claim 1, wherein the reaction mixture is applied onto a continuously moving cover layer in a double belt installation for producing sandwich elements.

13. The following amounts are based on the total weight of components (B) to (F): 70 to 90% by weight of a compound (B) having at least 1.7 hydrogen atoms reactive with isocyanate groups, 2 to 10 wt. % of a flame retardant (C), 1 to 20 wt. % of a blowing agent (D), 0.5 to 10% by weight of a catalyst (E), and 0.0 to 20% by weight of further auxiliaries and additives (F) wherein the weight percents total 100 weight percent and wherein components (B) to (F) are as defined in any one of claims 1 to 11.

14. 13. Rigid polyisocyanurate foam obtainable by the process according to any one of claims 1 to 12.