WO2025172138A1 - Process for producing improved rigid polyurethane and/or polyisocyanurate foams with low volume expansion and good curing characteristics after setting - Google Patents

Abstract

The present invention relates to a process for producing polyurethane-based rigid foams, in which (a) aromatic polyisocyanate, (b) compounds having hydrogen atoms reactive toward isocyanate groups, (c) catalyst, (d) blowing agent, (e) optionally flame retardant, and (f) optionally auxiliaries and adjuvants are mixed to form a reaction mixture and reacted to give the polyurethane-based rigid foam, wherein the catalyst (c) comprises at least the catalysts (c1) and (c2), and catalyst (c1) consists of at least one amine catalyst having at least one tertiary amino group and catalyst (c2) consists of at least one alkali metal, alkaline earth metal or ammonium salt of 3,5,5-trimethylhexanoic acid. The present invention further relates to the use of a catalyst (c) comprising the catalysts (c1) and (c2) for producing polyurethanes, to a polyurethane obtainable by a process of the invention, and to the use of such a polyurethane for producing sandwich elements.

Description

Process for the production of improved polyurethane and/or polyisocyanurate rigid foams with low volume expansion and good curing behavior after setting

The present invention relates to a process for the production of polyurethane-based rigid foams, in which (a) aromatic polyisocyanate, (b) compounds having hydrogen atoms reactive towards isocyanate groups, (c) catalyst, (d) blowing agent, (e) optionally flame retardant and (f) optionally auxiliaries and additives are mixed to form a reaction mixture and reacted to give the polyurethane-based rigid foam, wherein the compounds having hydrogen atoms reactive towards isocyanate groups (b) contain more than 50 wt. %, based on the total weight of component (b), aromatic polyester polyols (b1) which have an average total functionality of > 1.7 and < 2.5 and an OH number of > 180 and < 260 mg KOH/g and wherein the catalyst (c) contains at least the catalysts (c1) and (c2) and catalyst (c1) consists of at least one amine catalyst having at least one tertiary amino group and Catalyst (c2) consists of at least one alkali metal, alkaline earth metal, or ammonium salt of 3,5,5-trimethylhexanoic acid. The present invention further relates to the use of a catalyst (c) comprising catalysts (c1) and (c2) for producing polyurethanes, a polyurethane obtainable by a process according to the invention, and the use of such a polyurethane for producing sandwich elements.

Polyurethane-based rigid foams, such as polyurethane or polyisocyanurate rigid foams, have long been known and widely described. These are frequently used as insulation materials for heat and cold insulation, for example, in refrigerators, hot water tanks, district heating pipes, or in construction, for example, in sandwich elements.

A comprehensive overview of the production of polyurethane-based rigid foams and their use as cover or core layers in composite elements, as well as their application as insulation layers in cooling or heating technology, can be found, for example, in "Polyurethane", Kunststoff-Handbuch, Volume 7, 3rd edition 1993, Chapter 6, edited by Dr. Günter Oertel, Carl-Hanser-Verlag, Munich/Vienna.

A key application for polyurethane-based rigid foams is their use in the manufacture of composite elements. The production of composite elements, particularly with metallic cover layers and a core made of isocyanate-based foams, mostly polyurethane (PUR) or polyisocyanurate (PIR) foams, often referred to as sandwich elements, on continuously operating double-belt systems is currently being carried out in This is practiced on a large scale. For the continuous production of the composite elements, the liquid reaction mixture is applied to a continuously moving lower layer. The lower layer containing the reaction mixture and the upper cover layer enter the double belt, where the reaction mixture foams and hardens. After leaving the double belt, the continuous strand is cut to the desired dimensions. In this way, sandwich elements with rigid or flexible cover layers can be produced.

For the discontinuous production of sandwich elements, cooling units, hot water tanks or district heating pipes, the liquid reaction mixture is introduced into closed support tools, where it then foams, bonds with the covering layer and hardens.

For both the continuous and discontinuous production of polyurethane-based rigid foams, it is crucial that the reaction mixture cures quickly. Rapid curing enables increased productivity in the manufacturing process because continuous double belts can be operated at higher speeds and discontinuously produced components can be demolded and refilled more quickly.

In addition to good curing, it is also essential in the manufacturing processes described above that the polyurethane-based rigid foam expands as little as possible, i.e. that it increases in volume as little as possible after the setting process.

A significant increase in volume after setting during continuous production results in the foam pressing with great force against the upper facing layer, resulting in the increased formation of horizontal cells. "Horizontal cells" are cells whose largest horizontal axis is larger than the largest vertical axis. Horizontal cells lead to significantly reduced foam compressive strength in the direction of rise and thus to a reduced load-bearing capacity of the composite element under load. Likewise, the increased shear of the foam increases the occurrence of surface defects beneath the facing materials. This increased formation of blowholes and, when flexible facing materials are used, leads to a poorer visual appearance of the manufactured insulation panels. When rigid metal facings are used, blowholes lead to an increased likelihood of blistering in the sandwich element after installation and to reduced adhesion of the facing layer to the foam.

In the continuous manufacturing process, slow curing and a strong increase in volume after setting also lead to the manufactured composite elements expanding more after leaving the double belt and having a greater thickness in the center than on the sides (tongue/groove). This difference persists even when cooled, resulting in undesirable effects, e.g. poor stackability of the composite elements during packaging or a reduced fit of the tongue/groove connection when joining multiple elements. In continuous manufacturing processes, this behavior means that double-belt systems must be operated at reduced speeds in order to extend the residence time of the curing reaction mixture in the supporting double belt. This means that the composite elements are again produced with improved plane-parallelism of the cover layer materials. This, however, has a negative impact on the productivity of the manufacturing process.

Even in the discontinuous production of rigid foam components, significant post-expansion after the foam has set is extremely unfavorable. Depending on the flow direction of the reaction material, this also results in locally pronounced cell orientations and thus different foam compressive strengths, which leads to faster component failure due to increased anisotropy. Increased post-expansion after the foam has set creates strong shear and thrust zones, particularly near the face layers, which cause increased shrinkage cavities.

Likewise, a strong volume expansion after setting results in the component being cured having to remain in the mold longer to cure. Discontinuous component production also results in increased foam expansion, which increases the tendency for foam cracking in the component.

An ideal polyurethane-based rigid foam therefore has the best possible curing process with the lowest possible volume expansion after setting.

BE1027812 discloses a kit for producing polyurethane foams, the kit comprising an isocyanate component, a polyol component, a blowing agent, and a catalyst. The isocyanate component and the polyol component are present in the kit in a weight ratio of 15:10 to 18:10, and the polyol component comprises at least three different polyether polyols, the polyether polyols together being present in a concentration of at least 75.0 wt.%, based on the total weight of the polyol component. Potassium isononanoate is mentioned as a possible catalyst.

BE 1027823 discloses a kit for the production of polyisocyanurate foams, the kit comprising an isocyanate component, a polyol component, a blowing agent and a catalyst, and the isocyanate component and the polyol component in the kit in a weight ratio between 18:10 and 22:10, with the polyol component being a mixture of a polyether polyol and a polyester polyol in a weight ratio of 2:7 to 4:7. Potassium isononanoate is mentioned as a possible catalyst.

WO2023001687 discloses the production of a rigid polyurethane foam based on polyester polyol and a mixture of bis(2-dimethylaminoethyl) ether and potassium formate as a catalyst. Also disclosed is the production of sandwich elements using the double-belt process.

It is known that improved foam curing can be achieved by adding catalysts to the reaction mixture that promote the PIR reaction. Due to their low toxicity profile compared to many amine catalysts, alkali metal salts of short-chain linear carboxylic acids are particularly popular for this purpose. Although the use of these salt compounds results in very rapid curing, their use often causes excessive volume expansion of the foam after setting.

To achieve improved curing with reduced volume expansion, potassium 2-ethylhexanoate is used when necessary. In direct comparison with the previously described short-chain unbranched potassium salts, this leads to reduced volume expansion after setting. Due to new toxicological findings, potassium 2-ethylhexanoate is to be classified as reprotoxic Category 1 under European Chemicals Regulation as of November 23, 2023. This makes handling the catalyst more difficult due to increased protective measures.

The object of the invention was therefore to find a catalyst for the production of polyurethane-based rigid foam, which reduces the use of tertiary amine catalysts, leads to improved curing and a low volume expansion of the foam after setting and, according to current knowledge, is not reprotoxic according to category 1.

This object is achieved by a process for the production of polyurethane-based rigid foams, in which (a) aromatic polyisocyanate, (b) compounds having hydrogen atoms reactive towards isocyanate groups, (c) catalyst, (d) blowing agent, (e) optionally flame retardant and (f) optionally auxiliaries and additives are mixed to form a reaction mixture and reacted to give the polyurethane-based rigid foam, wherein the compounds having hydrogen atoms reactive towards isocyanate groups (b) comprise more than 50 wt.%, based on the total weight of component (b), aromatic polyester polyo- le (b1) which have an average total functionality of > 1.7 and < 2.5 and an OH number of > 180 and < 260 mg KOH/g and wherein the catalyst (c) contains at least the catalysts (c1) and (c2) and catalyst (c1) consists of at least one amine catalyst having at least one tertiary amino group and catalyst (c2) consists of at least one alkali metal, alkaline earth metal or ammonium salt of 3,5,5-trimethylhexanoic acid.

Furthermore, the present invention relates to the use of a catalyst (c) comprising the catalysts (c1) and (c2) for producing polyurethanes, a polyurethane obtainable by a process according to the invention and the use of such a polyurethane for producing sandwich elements.

Polyurethane-based rigid foams according to the present invention comprise polyurethane rigid foams and polyisocyanurate foams. Polyurethane-based rigid foams are typically obtained by reacting compounds containing isocyanate groups with compounds containing isocyanate-reactive hydrogens. For the purposes of the invention, the term "rigid polyurethane foam" refers to polyurethane-based foams produced with an isocyanate index of 90 to below 180. Rigid polyisocyanurate foams are understood to mean polyurethane-based rigid foams produced with an isocyanate index of at least 180. The isocyanate index is the ratio of isocyanate groups to isocyanate-reactive groups multiplied by 100. An isocyanate index of 100 corresponds to an equimolar ratio of the isocyanate groups used in component (a) to the isocyanate-reactive groups of components (b) to (f). Polyisocyanurate rigid foams usually contain isocyanurate groups.

For the purposes of the invention, polyurethane-based rigid foams are understood to mean foams according to DIN 7726 that have a compressive strength according to DIN 53 421 / DIN EN ISO 604 of greater than or equal to 80 kPa, preferably greater than or equal to 150 kPa, particularly preferably greater than or equal to 180 kPa. Furthermore, the polyurethane-based rigid foam according to DIN ISO 4590 has a closed-cell content of greater than 50%, preferably greater than 85%, and particularly preferably greater than 90%. Further details on polyurethane-based rigid foams according to the invention can be found in the "Kunststoffhandbuch, Volume 7, Polyurethane", Carl Hanser Verlag, 3rd edition 1993, Chapter 6, in particular Chapters 6.2.2 and 6.5.2.2.

Suitable polyisocyanates (a) are the known aromatic polyfunctional isocyanates. Such polyfunctional isocyanates are known per se or can be prepared by known methods. The polyfunctional isocyanates can be used in particular They can also be used as mixtures, so that component (a) in this case contains various polyfunctional isocyanates. Polyfunctional isocyanates considered as polyisocyanates have two (hereinafter referred to as diisocyanates) or more than two isocyanate groups per molecule.

In particular, the following should be mentioned: 2,4- and 2,6-toluene diisocyanate and the corresponding isomer mixtures (TDI), 4,4’-, 2,4’-, 2,2’- diphenylmethane diisocyanate and higher-nuclear homologues of diphenylmethane diisocyanate and the corresponding mixtures (MDI), mixtures of 4,4’-, 2,4’- and 2,2’-diphenylmethane diisocyanates and polyphenylpolymethylene polyisocyanates (polymer MDI) and mixtures of MDI and TDI.

Particularly suitable are 2,2'-, 2,4'- and/or 4,4'-diphenylmethane diisocyanate, as well as higher-nuclear homologues of diphenylmethane diisocyanate (MDI), 1,5-naphthylene diisocyanate (NDI), 2,4- and/or 2,6-tolylene diisocyanate (TDI), 3,3'-dimethyldiphenyl diisocyanate, 1,2-diphenylethane diisocyanate and/or p-phenylene diisocyanate (PPDI).

Modified polyisocyanates, i.e., products obtained by chemically converting organic polyisocyanates and containing at least two reactive isocyanate groups per molecule, are also frequently used. Polyisocyanates containing ester, urea, biuret, allophanate, carbodiimide, isocyanurate, uretdione, carbamate, and/or urethane groups are particularly mentioned, often together with unreacted polyisocyanates.

The polyisocyanates of component (a) particularly preferably contain 2,2'-MDI or 2,4'-MDI or 4,4'-MDI (also referred to as monomeric diphenylmethane or MMDI) or oligomeric MDI consisting of higher-nuclear homologues of MDI which have at least 3 aromatic nuclei and a functionality of at least 3, or mixtures of at least two of these isomers, optionally also mixtures of at least one isomer of MDI with at least one higher-nuclear homologue of MDI, or crude MDI which arises during the production of MDI, or preferably mixtures of at least one higher-nuclear homologue of MDI and at least one of the aforementioned low-molecular-weight MDI derivatives 2,2'-MDI, 2,4'-MDI or 4,4'-MDI (also referred to as polymeric MDI). The isomers and homologues of MDI are usually obtained by distillation of crude MDI.

Polymeric MDI is particularly preferably used as isocyanate (a). The average functionality of a polymeric MDI preferably varies in the range from 2.2 to 4, particularly preferably from 2.4 to 3.8 and especially from 2.6 to 3.0. Polymeric MDI is used, for example,

BASF Polyurethanes GmbH markets it under the name Lupranat® M20 or Lupranat® M50.

Component (a) preferably contains at least 70, particularly preferably at least 90, and especially 100 wt. %, based on the total weight of component (a), of one or more isocyanates selected from the group consisting of 2,2'-MDI, 2,4'-MDI, 4,4'-MDI, and oligomers of MDI. The content of oligomeric MDI is preferably at least 20 wt. %, particularly preferably greater than 30 to less than 80 wt. %, based on the total weight of component (a).

As compounds having hydrogen atoms reactive towards isocyanate groups (b), it is possible to use all compounds having isocyanate-reactive groups known in polyurethane chemistry, preferably compounds having on average at least 1.5 isocyanate-reactive groups, such as hydroxyl groups, -NH groups, NH2 groups 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) with respect to isocyanate groups is in the range of at least 1.5, preferably 1.7 to 8.0, particularly preferably 1.9 to 3.0 and in particular 2.0 to 2.5. The compounds (b) particularly preferably have polyesterols and/or polyetherols. Polyester films and polyether films preferably each have a number-average molecular weight of 150 to 15,000 g/mol, more preferably 150 to 5,000 g/mol, and particularly preferably 200 to 2,000 g/mol. In addition to polyether films and polyester films, low-molecular-weight chain extenders and/or crosslinking agents known, for example, in polyurethane chemistry can also be used. Compounds (b) preferably have a number-average molecular weight of 62 to 15,000 g/mol.

Polyether polyols are produced, for example, from epoxides such as propylene oxide and/or ethylene oxide, or from tetrahydrofuran with hydrogen-active starter compounds such as aliphatic alcohols, phenols, amines, carboxylic acids, water, or natural product-based compounds such as sucrose, sorbitol, or mannitol, using a catalyst. Examples include basic catalysts or double metal cyanide catalysts, as described, for example, in PCT/EP2005/010124, EP 90444, or WO 05/090440. Within the scope of the present invention, it is assumed that the functionality of the polyether polyols is equal to that of the starter molecule. If mixtures of starter molecules with different functionalities are used, fractional functionalities can be obtained. Influences on the functionality, e.g., due to side reactions, are not taken into account in the target functionality. Polyesterols are produced, for example, from aliphatic or aromatic dicarboxylic acids and polyhydric alcohols, polythioether polyols, polyesteramides, hydroxyl-containing polyacetals, and/or hydroxyl-containing aliphatic polycarbonates, preferably in the presence of an esterification catalyst. Other possible polyols are listed, for example, in "Kunststoffhandbuch, Volume 7, Polyurethane," Carl Hanser Verlag, 3rd edition 1993, Chapter 3.1.

The compounds having hydrogen atoms (b) reactive towards isocyanate groups contain greater than 50% by weight, based on the total weight of component (b), of at least one aromatic polyester polyol (b1) which has an average total functionality of > 1.7 and < 2.5 and an OH number of > 180 and < 260 mg KOH/g.

This can be prepared by esterification of (b1.1) 10 to 50 mol% of a dicarboxylic acid composition containing aromatic dicarboxylic acids, (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 cycloaliphatic diols having 2 to 18 C atoms or alkoxylates thereof and (b1.4) 0 to 50 mol% of a higher-functional polyol selected from the group consisting of glycerol, alkoxylated glycerol, trimethylolpropane, alkoxylated trimethylolpropane, pentaerythrol, alkoxylated pentaerythrol.

The dicarboxylic acid composition (b1.1) contains dicarboxylic acids and/or their derivatives, which can typically be used to produce 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. Component (b1.1) particularly preferably contains phthalic anhydride, phthalic acid, terephthalic acid, or polyethylene terephthalate (PET), and in particular phthalic anhydride or terephthalic acid, specifically phthalic anhydride. In general, component (b1.1) can also contain aliphatic dicarboxylic acids or aliphatic dicarboxylic acid derivatives. If aliphatic dicarboxylic acids are used, they are generally present in an amount of 0.5-40 mol%, preferably 0.5 to 20 mol%, based in each case on component (b1.1). Adipic acid or dicarboxylic acid mixtures of succinic, glutaric, and adipic acid are preferably used as aliphatic dicarboxylic acids. The dicarboxylic acid composition (b1.1) preferably contains no aliphatic dicarboxylic acids or derivatives thereof and thus consists of 100 mol% of one or more aromatic dicarboxylic acids or derivatives thereof. In general, component (b1.1) is used in amounts of 10 to 50 mol%, preferably in amounts of 20 to 45 mol%, based on the components (b1.1), (b1.2), (b1.3) and (b1.4) used to prepare the aromatic polyester polyol (b1).

One or more fatty acids and/or fatty acid derivatives (b1.2) can also be used to produce the aromatic polyester polyol (b1). The acids and/or fatty acid derivatives can be of either biological or petrochemical origin. Examples of fatty acids are caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, myristic 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, clupanodonic acid, cervonic acid, ricinoleic acid, and mixtures thereof. Examples of fatty acid derivatives are glycerol esters of fatty acids such as castor oil, grape seed oil, black cumin oil, pumpkin seed oil, borage seed oil, soybean oil, wheat seed 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 oil, hazelnut oil, primrose oil, wild rose oil, safflower oil, walnut oil.

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, animal tallow such as beef tallow, alkyl or especially methyl esters of fatty acids such as biodiesel.

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

In a particularly preferred embodiment of the present 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, specifically oleic acid, and is used in an amount of 5 to 15 mol%. The fatty acid or fatty acid derivative improves, among other things, the blowing agent solubility in the production of rigid polyurethane or polyisocyanurate foams. Very particularly preferably, component (b1.2) does not comprise any triglyceride, in particular any oil or fat. The glycerol released from the triglyceride by esterification or transesterification impairs the dimensional stability of the rigid foam. Component (b1.3) comprises one or more aliphatic or cycloaliphatic diols having 2 to 18 carbon atoms or their alkoxylates. Component (b1.3) preferably 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. The aliphatic diol (b1.3) is particularly preferably monoethylene glycol or diethylene glycol, especially diethylene glycol. In general, component (b1.3) is used in amounts of 10 to 80 mol%, preferably in amounts of 20 to 75 mol%, particularly preferably in amounts of 30 to 60 mol%, based on all components used for preparing the aromatic polyester polyol (b1).

Any polyols with a functionality greater than 2 can be used as the higher-functionality polyol (b1.4) for preparing the aromatic polyester polyol (b1). Preferably, the higher-functionality polyol (b1.4) is selected from the group consisting of glycerol, alkoxylated glycerol, trimethylolpropane, alkoxylated trimethylolpropane, pentaerythritol, alkoxylated pentaerythritol, and mixtures of two or more of these higher-functionality polyols. The higher-functionality polyol (b1.4) is particularly preferably glycerol, alkoxylated glycerol, or mixtures thereof.

The higher-functional polyol (b1.4) is used in amounts of 0 to 50 mol%, preferably in amounts of 5 to 40 mol%, particularly preferably in amounts of 10 to 25 mol%, based on all components used for preparing the aromatic polyester polyol (b1).

According to the invention, the aromatic polyester polyol (b1) has a number-weighted average functionality of > 1.7 to < 2.5, particularly preferably > 1.75 to < 2.2, and a hydroxyl number of 180 to 260 mg KOH/g, preferably 200 to 250 mg KOH/g. In a particularly preferred embodiment, the aromatic polyester polyol (b1) has an OH number of 180 to 260 mg KOH/g and a functionality of 1.7 to 2.5.

To prepare the aromatic polyester polyol (b1), the dicarboxylic acids (b1.1), fatty acids and/or fatty acid derivatives (b1.2), the aliphatic or cycloaliphatic diols having 2 to 18 C atoms or alkoxylates thereof (b1.3) and the higher-functionality polyols (b1.4) can be polycondensed catalyst-free or preferably in the presence of esterification catalysts, advantageously in an atmosphere of inert gas such as nitrogen in the melt at temperatures of 150 to 280°C, preferably 180 to 260°C, optionally under reduced pressure, to the desired acid number, 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 number of 80 to 20, preferably 40 to 20, under atmospheric pressure and subsequently under a pressure of less than 500 mbar, preferably 40 to 400 mbar. Suitable esterification catalysts include, for example, iron, cadmium, cobalt, lead, zinc, antimony, magnesium, titanium, and tin catalysts in the form of metals, metal oxides, or metal salts. However, the polycondensation can also be carried out in the liquid phase in the presence of diluents and/or entrainers, such as benzene, toluene, xylene, or chlorobenzene, for azeotropic distillation of the condensation water.

The proportion of the polyester polyols (b1) according to the invention is at least 50% by weight, preferably at least 65% by weight and particularly preferably at least 80% by weight, in each case based on the total weight of component (b).

Component (b) preferably contains, in addition to the polyester polyol (b1), at least one polyether polyol (b2), which preferably has a hydroxyl number of 160-350 mg KOH/g and is prepared by alkoxylation of a starter or starter mixture. Preferably, at least 80% by weight of ethylene oxide is used as the alkylene oxide for preparing polyether polyol (b2), and the polyether polyol (b2) preferably has at least 90%, more preferably at least 95%, particularly preferably at least 99%, and in particular exclusively primary hydroxyl end groups.

The polyether polyols (b2) are prepared by known processes, for example by anionic polymerization of one or more alkylene oxides having 2 to 4 carbon atoms, containing ethylene oxide, with conventional catalysts, such as alkali metal hydroxides, such as sodium or potassium hydroxide, alkali metal alkoxides, such as sodium methylate, sodium or potassium ethylate, or potassium isopropylate, or aminic alkoxylation catalysts, such as dimethylethanolamine (DMEOA), imidazole, and/or imidazole derivatives, using at least one starter molecule or starter molecule mixture which preferably contains on average < 3.5 and > 1.5, particularly preferably < 3.0 and > 2.0, and in particular 2 reactive hydrogen atoms. In addition to the anionic polymerization of the starter molecules, the preparation can also be carried out by cationic polymerization, using Lewis acids, such as antimony pentachloride, boron fluoride etherate, or bleaching earth, as catalysts.

Preferred alkoxylation catalysts are KOH and aminic alkoxylation catalysts. Since, when using KOH as the alkoxylation catalyst, the polyether must first be neutralized and the resulting potassium salt must be separated, the use of aminic alkoxylation catalysts is particularly preferred. Preferred aminic alkoxylation catalysts are selected from the group consisting of dimethyl ethane, nolamine (DMEOA), imidazole and imidazole derivatives and mixtures thereof, particularly preferably imidazole.

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, ethylene oxide is used exclusively as the alkylene oxide. The alkylene oxides can be used individually, alternately one after the other or as mixtures. According to the invention, at least 80% by weight of ethylene oxide, preferably at least 90% by weight of ethylene oxide, more preferably at least 95% by weight and especially at least 98% by weight of ethylene oxide is used as the alkylene oxide for preparing polyether polyol (b2). Very particularly preferably, ethylene oxide is used exclusively as the alkylene oxide for preparing the polyether polyol (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 must be ensured according to the invention that the polyether polyol produced therefrom has the content of primary hydroxyl end groups according to the invention.

Examples of suitable starter molecules are: water, organic dicarboxylic acids such as succinic acid, adipic acid, phthalic acid and terephthalic acid, aliphatic and aromatic, optionally N-mono-, N, N- and N, N'-dialkyl-substituted diamines having 1 to 4 carbon atoms in the alkyl radical, such as optionally mono- 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-tolylenediamine and 4,4'-, 2,4'- and 2,2'-diaminodiphenylmethane. Particularly preferred are the diprimary amines mentioned, preferably ethylenediamine. Other suitable starter molecules are alkanolamines, such as ethanolamine, N-methyl-, and N-ethylethanolamine; dialkanolamines, such as diethanolamine, N-methyl-, and N-ethyldiethanolamine; and trialkanolamines, such as triethanolamine; and ammonia.

Preferred starter molecules are two or more alcohols, such as ethanediol, 1,2- and 1,3-propanediol, diethylene glycol (DEG), dipropylene glycol, 1,4-butanediol, 1,6-hexanediol, glycerol, trimethylolpropane, bisphenol A, bisphenol F, pentaerythritol, sorbitol and sucrose; particular preference is given to using diethylene glycol, monoethylene glycol, 1,2-propanediol and glycerol, especially diethylene glycol.

In a preferred embodiment, the starter molecules do not contain fatty acids. According to the invention, the polyether polyol (b2) has a hydroxyl number of 160 - 350 mg KOH/g, preferably 170 - 290 mg KOH/g, particularly preferably 175 - 225 mg KOH/g.

When polyether polyol (b2) is used, the proportion of component (b2) is preferably from 0 to 50 wt.%, particularly preferably from 5 to 35 wt.%, and in particular from 10 to 25 wt.%, based on the total weight of component (b).

According to the invention, the sum of the mass fractions of component (b1) and component (b2) based on component (b) is > 80 wt. %, preferably > 90 wt. %, particularly preferably > 95 wt. The sum of the mass fractions of component (b1) and component (b2) based on component (b) is very particularly preferably 100 wt. %, i.e., in this embodiment, no further compounds containing hydrogen atoms reactive toward isocyanate groups are used as component (b1) and component (b2).

According to the invention, catalyst (c) contains at least catalysts (c1) and (c2), wherein catalyst (c1) consists of at least one amine catalyst having at least one tertiary amino group and catalyst (c2) consists of at least one alkali metal, alkaline earth metal or ammonium salt of 3,5,5-trimethylhexanoic acid.

As amine catalysts (c1) it is possible to use all known compounds having at least one tertiary amino group which are usually used for the preparation of polyurethanes and which greatly accelerate the reaction of the compounds of component (b) containing reactive hydrogen atoms, in particular hydroxyl groups, with the polyisocyanates (a). Examples are tertiary amines such as triethylamine, tributylamine, dimethylbenzylamine, dicyclohexylmethylamine, dimethylcyclohexylamine, N,N,N',N'-tetramethyldiaminodiethyl ether, bis-(dimethylaminopropyl)-urea, N-methyl- or N-ethylmorpholine, N-cyclohexylmorpholine, N,N,N',N'-tetramethylethylenediamine, N,N,N,N-tetramethylbutanediamine, N,N,N,N-tetramethylhexanediamine-1,6,-pentamethyldiethylenetriamine, bis(2-dimethylaminoethyl) ether, dimethylpiperazine, 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-methyl- and N-ethyldiethanolamine, dimethylaminoethanol, 2-(N,N-dimethylaminoethoxy)ethanol, N,N',N"-tris-(dialkylaminoalkyl)hexahydrotriazines, e.g. N,N',N"-tris-(dimethylaminopropyl)-s-hexahydrotriazines, and triethylenediamine. Preferably, the catalyst (c1) is selected from the group consisting of dimethylcyclohexylamine, 1,4-diazobicyclo(2,2,2)octane, 1,3,4-tris(dimethylaminopropyl)hexahydro-s-triazine, bis(2-dimethylaminoethyl)methylamine, bis(dimethylaminoethyl)ether or mixtures of two or more of these catalysts. The catalyst (c2) particularly preferably contains bis(2-dimethylaminoethyl)methylamine and/or bis(dimethylaminoethyl)ether.

According to the invention, the catalyst (c2) contains at least one alkali metal, alkaline earth metal, or ammonium salt of 3,5,5-trimethylhexanoic acid; preferably, the catalyst (c2) contains at least potassium 3,5,5-trimethylhexanoate. The catalyst (c2) can be obtained, for example, by reacting 3,5,5-trimethylhexanoic acid with alkali metal or alkaline earth metal hydroxide, for example in aqueous solution or ammonia or an ammonia-containing solution. The reaction is preferably carried out in an amount such that the free residual acid content of 3,5,5-trimethylhexanoic acid, based on the total weight of the catalyst (c2), is less than 20% by weight, more preferably less than 10% by weight, further preferably less than 4% by weight, even more preferably less than 3% by weight, and in particular less than 1% by weight. The pH of the catalyst (c2) after addition of water is preferably less than 8, more preferably less than 7 and in particular less than 6. The catalyst (c2) is preferably used in the form of a solution, the solution preferably containing at least 35% by weight, more preferably at least 45% by weight and in particular at least 55% by weight of catalyst (c2) and the OH number of the solution of the catalyst (c2) is preferably less than 350 mg KOH/g, more preferably less than 150 mg KOH/g and in particular 0 mg KOH/g, the presence of water not being taken into account in the OH number determination.

Preferably, 0.001 to 10 parts by weight of catalyst or catalyst combination are used, based on 100 parts by weight of component (b). The proportion of catalysts (c1) and (c2) is preferably at least 50% by weight, more preferably at least 80% by weight, and in particular, only catalysts (c1) and (c2) are used. The mass ratio of catalysts (c1) and (c2) is preferably 1:8 to 8:1, more preferably 1:6 to 6:1, and in particular 1:3 to 3:1.

Blowing agents (d) used to produce the inventive rigid polyisocyanurate foams include formic acid and formic acid-water mixtures. These react with isocyanate groups to form carbon dioxide and carbon monoxide. Since these blowing agents release the gas through a chemical reaction with the isocyanate groups, they are referred to as chemical blowing agents. Physical blowing agents, such as low-boiling hydrocarbons, are also used. Particularly suitable physical blowing agents are liquids that are inert toward the polyisocyanates (a) and have boiling points below 100°C, preferably below 50°C, at atmospheric pressure. pressure so that they evaporate under the influence of the exothermic polyaddition reaction.

Examples of physical blowing agents that can be used are alkanes such as heptane, hexane, n- and isopentane, preferably technical mixtures of n- and isopentanes, n- 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, carboxylic acid alkyl esters such as methyl formate, dimethyl oxalate and ethyl acetate and halogenated saturated and unsaturated hydrocarbons such as methylene chloride, dichloromonofluoromethane, difluoromethane, trifluoromethane, difluoroethane, tetrafluoroethane, chlorodifluoroethane, 1,1-dichloro-2,2,2-trifluoroethane, 2,2-dichloro-2-fluoroethane and heptafluoropropane, and unsaturated hydrocarbons such as trifluoropropenes and tetrafluoropropenes, such as (HFO-1234), pentafluoropropenes, such as (HFO-1225), chlorotrifluoropropenes, such as (HFO-1233), chlorodifluoropropenes, chlorotetrafluoropropenes and hexafluorobutenes, as well as mixtures of one or more of these components. Preference is given to tetrafluoropropenes, pentafluoropropenes, chlorotrifluoropropenes and hexafluorobutenes, where the unsaturated, terminal carbon atom carries at least one chlorine or fluorine 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 can also be used.

Also suitable are organic carboxylic acids such as formic acid, acetic acid, oxalic acid, ricinoleic acid and compounds containing carboxyl groups.

Preferably, no halogenated hydrocarbons are used as blowing agents. Water, formic acid-water mixtures, or formic acid are used as chemical blowing agents. Pentane isomers or mixtures of pentane isomers are preferably used as physical blowing agents. The chemical blowing agents are preferably used together with physical blowing agents; particularly preferably, water or formic acid-water mixtures are used together with pentane isomers or mixtures of pentane isomers. The physical blowing agent preferably contains at least 30 mol% cyclopentane. The amount of blowing agent or blowing agent mixture used is from 0.1 to 45% by weight, preferably from 1 to 30% by weight, particularly preferably from 1 to 20% by weight, and in particular from 1.5 to 20% by weight, based in each case on the sum of components (b) to (f). The blowing agents are preferably used in an amount such that the reaction mixture is converted into polyurethane-based rigid foams having a density of preferably less than 45 kg/m ³ , more preferably less than 40 kg/m ³ , particularly preferably less than 35 kg/m ³ , and in particular less than 33 kg/m ³ .

Flame retardants known from the prior art can generally be used as flame retardants. Suitable flame retardants include, 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, dimethyl methanephosphonate, diethyl diethanolaminomethylphosphonate, and commercially available halogen-containing flame retardant polyols. Other phosphates or phosphonates that can be used as liquid flame retardants include diethyl ethane phosphonate (DEEP), triethyl phosphate (TEP), dimethylpropyl phosphonate (DMPP), and diphenyl cresyl phosphate (DPK). Compounds containing phosphorus, chlorine, or bromine atoms that also contain isocyanate-reactive groups are not considered compounds containing isocyanate-reactive hydrogen atoms (B) in the context of the present invention and are not considered to be part of component (B) when calculating proportions.

In addition to the flame retardants already mentioned, inorganic or organic flame retardants, such as red phosphorus, red phosphorus-containing dressings, aluminum oxide hydrate, antimony trioxide, arsenic oxide, ammonium polyphosphate and calcium sulfate, expanded graphite or cyanuric acid derivatives, such as melamine, or mixtures of at least two flame retardants, such as ammonium polyphosphates and melamine and optionally corn starch or ammonium polyphosphate, melamine, expanded graphite and optionally aromatic polyesters, can also be used to flame-retard the rigid polyisocyanurate foams. Preferred flame retardants do not contain any groups reactive toward isocyanate groups. The flame retardants are preferably liquid at room temperature. TCPP, DEEP, TEP, DMPP and DPK are preferred, particularly TCPP and TEP, especially TCPP.

In general, the proportion of flame retardants (e) is 1 to 20 wt.%, preferably 2 to

15 wt.%, particularly preferably 3 to 10 wt.% based on the sum of the weight quantities of components (b) to (f). Preferably, the flame retardant (e) contains at least one phosphorus-containing flame retardant, the phosphorus content, based on the total weight of components (a) to (f), being <1 wt. %, preferably <0.6 wt. %, particularly preferably <0.4 wt. Particular preference is given to using no halogen-containing flame retardants in addition to the phosphorus-containing flame retardant.

If desired, further auxiliaries and/or additives (f) may be added to the reaction mixture for producing the rigid polyisocyanurate foams of the invention. Examples include surfactants, foam stabilizers, cell regulators, fillers, light stabilizers, dyes, pigments, hydrolysis inhibitors, and fungistatic and bacteriostatic substances.

Suitable surfactants include compounds that support the homogenization of the starting materials and, where appropriate, are also suitable for regulating the cell structure of the plastics. Examples include emulsifiers such as the sodium salts of castor oil sulfates or fatty acids, as well as salts of fatty acids with amines, e.g., oleic diethylamine, stearic diethanolamine, ricinoleic diethanolamine; salts of sulfonic acids, e.g., alkali or ammonium salts of dodecylbenzene- or dinaphthylmethanedisulfonic acid and ricinoleic acid; foam stabilizers such as siloxaneoxyalkylene copolymers and other organopolysiloxanes and dimethylpolysiloxanes. Oligomeric acrylates with polyoxyalkylene and fluoroalkane residues as side groups are also suitable for improving the emulsifying effect, the cell structure, and/or stabilizing the foam. The surfactants are typically used in amounts of 0.01 to 10 parts by weight, based on 100 parts by weight of component (B). Conventional foam stabilizers, for example silicone-based ones such as siloxaneoxyalkylene copolymers and other organopolysiloxanes, can be used as foam stabilizers.

Fillers, in particular reinforcing fillers, are understood to mean the conventional organic and inorganic fillers, reinforcing agents, weighting agents, agents for improving abrasion properties in paints, coatings, etc. Examples include: inorganic fillers such as silicate minerals, for example phyllosilicates such as antigorite, serpentine, hornblende, amphiboles, chrysotile and talc, metal oxides such as kaolin, aluminum oxides, titanium oxides and iron oxides, metal salts such as chalk, barite and inorganic pigments such as cadmium sulfide and zinc sulfide, as well as glass, among others. 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 and especially glass fibers of various lengths, which are may optionally be sized. Suitable organic fillers include, for example: carbon, melamine, rosin, cyclopentadienyl resins and graft polymers, as well as cellulose fibers, polyamide, polyacrylonitrile, polyurethane, polyester fibers based on aromatic and/or aliphatic dicarboxylic acid esters and in particular carbon fibers. The inorganic and organic fillers can be used individually or as mixtures and are advantageously added to the reaction mixture in amounts of 0.5 to 50% by weight, preferably 1 to 40% by weight, based on the weight of components (a) to (f), although the content of mats, nonwovens and woven fabrics made of natural and synthetic fibers can reach values of up to 80% by weight, based on the weight of components (a) to (f).

According to the invention, the rigid polyisocyanurate foams are produced by mixing components (a) to (d) and, if present, (e) and (f), to form a reaction mixture. To reduce complexity, premixes can also be prepared. These comprise at least one isocyanate component containing polyisocyanates (a) and a polyol component containing isocyanate-reactive compounds (b). All or part of the further components (c) to (f) can be added in whole or in part to the isocyanate component and polyol component. Due to the high reactivity of the isocyanates, components (c) to (f) are often added to the polyol component to avoid side reactions. However, physical blowing agents, in particular, can also be added to the isocyanate component (a). Formic acid-water mixtures or formic acid are usually present in whole or in part in the polyol component, and the physical blowing agent (e.g., pentane) and, if present, the remainder of the chemical blowing agent are metered directly "online" during production. Preferably, catalysts (c1) and (c2) are also fed online in a separate stream to the reaction mixture, and particularly preferably, the remaining components (e) and (f) are added to the polyol component. The catalyst is usually added online, but it can also be partially or completely dissolved in the polyol component.

The polyol component for producing the rigid polyisocyanurate foams according to the invention preferably contains 70 to 90% by weight of the compounds having at least 1.5 hydrogen atoms reactive toward isocyanate groups (b), 1 to 5% by weight of catalysts (c), 1 to 20% by weight of blowing agent (d), 0 to 18% by weight of flame retardant (e), and 0 to 20% by weight of further auxiliaries and additives (f), each based on the total weight of components (b) to (f). In a particularly preferred embodiment, the proportions of components (b) to (f) add up to 100% by weight. The reaction mixture is then allowed to react to form the rigid polyisocyanurate foam. For the purposes of the present invention, a reaction mixture refers to the mixture of polyisocyanates (a) with the isocyanate-reactive compounds (b) and all other components (c), (d), and optionally (e) and (f), with reaction conversions of less than 90%, based on the isocyanate groups.

The components are preferably mixed to form the reaction mixture at an isocyanate index of greater than 180, particularly preferably 240 to 800, more preferably 260 to 600, even more preferably 300 to 500, and especially 340 to 400. The starting components are mixed at a temperature 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 high- or low-pressure metering machines. The isocyanate index is the molar ratio of isocyanate groups to isocyanate-reactive groups multiplied by 100.

The reaction mixture can, for example, be placed in a mold for complete reaction. Discontinuous sandwich elements, for example, are produced using this technology. The polyurethane-based rigid foams according to the invention are preferably produced on continuously operating double-belt systems. The polyol and isocyanate components are preferably 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 to a continuously moving, lower cover layer. The lower cover layer containing the reaction mixture and the upper cover layer enter the double belt, where the reaction mixture foams and cures. After leaving the double belt, the continuous strand is cut to the desired dimensions. In this way, sandwich elements with metallic cover layers or with flexible cover layers can be produced, for example. The lower and upper cover layers, which can be the same or different, can be flexible or rigid cover layers, which are commonly used in the double-belt process. These include metal facings such as aluminum or steel, bitumen facings, paper, nonwovens, plastic sheets such as polystyrene, plastic films such as polyethylene films, or wooden facings. The facings can also be coated, for example, with a conventional varnish or adhesion promoter. Particularly preferred are facings that are diffusion-tight to the cell gas of the polyisocyanurate rigid foam.

Such processes are known and described, for example, in the "Plastics Handbook, Volume

7, Polyurethane", Carl Hanser Verlag, 3rd edition 1993, Chapter 6.2.2 or EP 2234732. Closing The present invention relates to a polyisocyanate-based rigid foam obtainable by a process according to the invention and to a polyurethane sandwich element comprising such a polyisocyanate-based rigid foam according to the invention.

The present invention further relates to a polyurethane-based rigid foam obtainable by the process of the invention. The polyurethane-based rigid foam of the invention is preferably used as part of a composite element, which is preferably obtained using a double belt.

The invention is further illustrated by the following examples:

Examples:

The following materials were used:

Polyols:

Polyesterol 1: Esterification product of phthalic anhydride and diethylene glycol with a hydroxyl functionality of 2.0 and a hydroxyl number of 240 mg KOH/g.

Polyesterol 2: Esterification product of terephthalic acid, oleic acid, diethylene glycol and ethoxylated glycerol, with a hydroxyl functionality of 2.5, a hydroxyl number of 240 mg KOH/g and an oleic acid content of 15 wt%.

Polyetherol 1 : Polyether polyol produced by ethoxylation of ethylene glycol with a hydroxyl functionality of 2 and a hydroxyl number of 190 mg KOH/g.

Flame retardants:

Flame retardant 1 : Tris(2-chloroisopropyl)phosphate with a chlorine content of 32.5 wt% and a phosphorus content of 9.5 wt%.

Flame retardant 2: Triethyl phosphate with a phosphorus content of 17.0 wt.%

Foam stabilizers:

Foam stabilizer 1: Tegostab B 8498 (silicone-containing foam stabilizer from Evonik).

Catalysts:

Cat. 1: Catalyst, 23.1 wt% bis(2-dimethylaminoethyl) ether in 76.9 wt% dipropylene glycol.

Cat. 2: Catalyst, 70.0 wt% potassium acetate dissolved in 30.0 wt% water

Cat. 3: Catalyst, 70.0 wt% potassium 2-ethylhexanoate, dissolved in 26.6 wt% diethylene glycol and 3.4 wt% water

Cat. 4: Catalyst obtained by reacting 3,5,5-trimethylhexanoic acid in diethylene glycol and water with potassium hydroxide. Theoretical content: 57.1 wt% potassium 3,5,5-trimethylhexanoate, 30.5 wt% diethylene glycol, 9.8 wt% water, and 2.5 wt% 3,5,5-trimethylhexanoic acid. Cat. 5: Catalyst obtained by reacting 3,5,5-trimethylhexanoic acid in diethylene glycol and water with potassium hydroxide. Theoretical content: 43.2 wt% potassium 3,5,5-trimethylhexanoate, 44.4 wt% diethylene glycol, 7.7 wt% water, and 4.7 wt% 3,5,5-trimethylhexanoic acid.

Cat. 6: Catalyst obtained by reacting 3,5,5-trimethylhexanoic acid in diethylene glycol and water with potassium hydroxide. Theoretical content: 35.4 wt% potassium 3,5,5-trimethylhexanoate, 45.6 wt% diethylene glycol, 7.0 wt% water, and 12.0 wt% 3,5,5-trimethylhexanoic acid.

Cat. 7: Catalyst consisting of 42.6 wt% potassium 2,2-dimethylpropionate, 45.5 wt%

Diethylene glycol, 8.9 wt% water and 3 wt% 2,2-dimethylpropanoic acid

Cat. 8: Catalyst consisting of 55 wt% potassium neodecanoate in 45 wt% water

Cat. 9: Catalyst consisting of 30 wt% potassium sorbate, 40 wt% diethylene glycol, 24

wt% monoethylene glycol and 6 wt% water

Cat. 10: Catalyst consisting of 37.6 wt% potassium propionate, 60 wt% monoethylene glycol and 2.4 wt% water.

Cat. 11: Catalyst consisting of 48.5 wt% dodecanoate, 40 wt% diethylene glycol, 9.0 wt% water and 2.5 wt% dodecanoic acid.

Cat. 12: Catalyst consisting of 48.5 wt% potassium hexanoate, 40 wt% diethylene glycol, 9.0 wt% water and 2.5 wt% hexanoic acid.

Cat. 13: Catalyst consisting of 68.5 wt% potassium 3-methylbutanoate, 20 wt% diethylene glycol, 9.0 wt% water and 2.5 wt% 3-methylbutanoic acid.

Cat. 14: Catalyst obtained by reacting 3,5,5-trimethylhexanoic acid in dimethyl sulfoxide and water with potassium hydroxide. Theoretical content: 57.1 wt% potassium 3,5,5-trimethylhexanoate, 30.5 wt% dimethyl sulfoxide, 9.8 wt% water, and 2.5 wt% 3,5,5-trimethylhexanoic acid.

Chemical blowing agents:

Propellant 1 : Water

Physical blowing agents:

Propellant 2: Propellant mixture consisting of 40 mol% cyclopentane and 60 mol% isopentane.

Isocyanates:

Isocyanate 1: Lupranat® M 50, polymeric methylene diphenyl diisocyanate (PMDI) from BASF, with a viscosity of approx. 550 mPa*s at 25°C. Using the described starting materials, the polyol component described below was produced:

Polyesterol 1: 44.4 wt.% Polyesterol 2: 30.0 wt.% Polyetherol 1 : 7 wt.% Flame retardant 1: 12 wt.% Flame retardant 2: 4 wt.% Foam stabilizer 1 : 2 wt.% Blowing agent 1 : approx. 0.6 wt.%

Laboratory foaming:

This polyol component was subsequently used for laboratory foaming experiments in which catalysts 2 - 14 were compared.

For this purpose, catalysts 1 - 14 and blowing agents 1 - 2 were added to the polyol component, and the resulting mixture was then heated to 20°C and reacted with isocyanate 1, also heated to 20°C, in a mixing ratio such that the isocyanate index of all foams produced was 280 ± 10. The ambient temperature at which all foamings were carried out was 21 ± 1.0 °C. For the foamings, blowing agent 2 was added in an amount such that the content, based on the foam, was 3.95 ± 0.05 wt.%. Furthermore, the amount of catalyst 1 for all foamings was selected such that the content, based on the foam, was 0.44 ± 0.05 wt.%. By varying blowing agent 1 and catalyst 2-14, all foams were subsequently adjusted to comparable setting times of 45 s ± 1 s and cup foam densities of 33 kg/ ^m³ ± 1 kg/ ^m³ . The absolute amounts of the starting materials were selected to yield 80 g of reaction mixture. For this purpose, the starting materials were mixed intensively in a paper cup for 6 seconds using a laboratory stirrer at 1500 rpm.

The reaction mixtures, thus adjusted to comparable setting times and foam densities, were then used to determine the foam curing and foam rise profile.

The setting time is the time from the start of mixing until the point at which threads can be pulled from the rising reaction mixture by immersing a rod (thread pulling time).

Measuring foam hardening:

The foam curing of the laboratory foams, which were adjusted to identical reaction times and foam densities, was determined using the bolt test. For this purpose, 4, 5, and 6 minutes after intensive mixing of 80 g of reaction component (at 1500 rpm) in a 1.15 In a 10-liter polypropylene cup, a steel bolt with a spherical cap of 10 mm radius was pressed 10 mm deep into the foam using a tensile/compression testing machine. The required maximum force in N is a measure of the foam's curing at that time. Each curing measurement was performed at a new foam location at the same distance from the foam edge. The mean of the maximum forces can be found as a force value in Table 1 [0 foam curing 4;5;6 min in N].

Measuring the foam rise profile:

The foam height as a function of time was recorded using the Format Foamat device. Before each measurement, a zero-point height calibration of the cup was performed by placing the empty cup centrally below the ultrasonic sensor and normalizing the measured height to 0 mm.

The beaker was then filled with 60 g of reaction mixture, mixed thoroughly for 5 seconds at 1400 rpm, and placed centrally under the Foamat device to measure the foam height as a function of time. Using the factor: foam height at setting time (RT) / maximum foam height (120 seconds), the percentage foam height at setting time could be calculated, which is proportional to the foam's volume expansion at setting time. This value can be found in Table 1 [foam height at setting time in %].

Table 1: Examples and comparative examples As can be seen from Table 1, the use of catalyst 2 (Example 1, not according to the invention) leads to very good foam curing, but the foam has a significantly lower foam height at the time of setting, which leads to the disadvantages already described in the continuous and discontinuous production of components (horizontal cells, poorer foam compressive strengths, increased void formation due to increased shear of the foam and reduced plane parallelism of the cover layer materials of composite elements in continuous processing using the double-belt process, as well as increased anisotropy and longer demolding times in discontinuous processing).

Catalyst 3 (Example 2, not according to the invention) shows a significant advantage over Catalyst 2 (Example 1) in terms of the foam height achieved at setting time and results in a slightly reduced, but still acceptable, foam cure. Due to new toxicological findings, potassium 2-ethylhexanoate has been classified as reprotoxic, Category 1, under European Chemicals Regulation since November 23, 2023, which complicates handling of the catalyst.

According to current knowledge, catalysts 4, 5, 6, and 14 (according to the invention) are less toxicologically critical than catalyst 3. Furthermore, in direct comparison with catalyst 3, catalysts 4, 5, 6, and 14 demonstrate an advantage in foam curing, as well as a comparable (catalyst 5) and higher foam height (catalysts 4 and 14) at the time of setting. In addition to the toxicological advantage, the three catalysts also demonstrate a property advantage over the established catalyst 3.

The use of catalyst 7 (Example 6, not according to the invention) leads to slightly poorer foam curing and a higher foam height at the time of setting compared to the catalysts according to the invention. The use of catalyst 8 (Example 7, not according to the invention) leads to foams that have an advantageously high foam height at the time of setting, but these foams also show very weak curing. The use of catalysts 9, 10, 11, 12 and 13 (Examples 8, 9, 10, 11, 12, each not according to the invention) leads to comparable to better curing compared to catalyst 3, but all catalysts lead to a significantly lower foam height at the time of setting. In addition to the described property disadvantages, the use of catalysts 7, 10, 12, and 13 also leads to a strong odor nuisance during the foaming process, especially when formic acid is used as a chemical co-blowing agent. No odor nuisance was detected from the inventive catalysts from Examples 3, 4, 5, and 13.

Claims

Claims 1 . Process for the production of polyurethane-based - Rigid foams, in which a) aromatic polyisocyanate, b) compounds with hydrogen atoms reactive towards isocyanate groups c) catalyst d) blowing agent e) optionally flame retardant f) optionally auxiliaries and additives are mixed to a reaction mixture and reacted to give the polyurethane-based rigid foam, wherein the compounds with hydrogen atoms reactive towards isocyanate groups (b) contain > 50 wt. %, based on the total weight of component (b), aromatic polyester polyols (b1) which have an average total functionality of > 1.7 and < 2.5 and an OH number of > 180 and < 260 mg KOH/g and wherein the catalyst (c) contains at least the catalysts (c1) and (c2) and catalyst (c1) consists of at least one amine catalyst having at least one tertiary amino group and catalyst (c2) consists of at least one alkali metal, alkaline earth metal or ammonium salt of 3,5,5-trimethylhexanoic acid. 2. Process according to claim 1, characterized in that the mixing to form the reaction mixture takes place at an isocyanate index of at least 180. 3. Process according to one or more of claims 1 to 2, characterized in that the catalyst c1 is selected from the group consisting of dimethylcyclohexylamine, 1,4-diazobicyclo (2,2,2) octane, 1,3,4 tris (dimethylaminopropyl) hexahydro-s-triazine, bis (2-dimethylaminoethyl) methylamine, bis (dimethylaminoethyl) ether. 4. Process according to one or more of claims 1 to 3, characterized in that the catalyst (c2) contains at least potassium 3,5,5-trimethylhexanoate. 5. Method according to one or more of claims 1 to 4, characterized in that that the catalyst (c2) contains a free residual acid content of 3,5,5-trimethylhexanoic acid of < 10 wt.%, based on the total weight of the catalyst (c2). 6. Process according to one or more of claims 1 to 5, characterized in that catalyst (c2) is present in dissolved form and that the solution contains > 45% by weight of catalyst (c2) and the OH number of the solution of catalyst (c2) is < 350 mg KOH/g, the presence of water not being taken into account in the OH number determination. 7. Process according to one of claims 1 to 6, characterized in that the reaction mixture leads to polyurethane-based rigid foams which have a foam density of < 45 kg/m ³ . 8. Process according to one of claims 1 to 7, characterized in that the blowing agent (d) contains chemical and physical blowing agents, wherein the chemical blowing agent contains water and the physical blowing agent contains at least 30 mol% cyclopentane. 9. Process according to one of claims 1 to 8, characterized in that at least one phosphorus-containing flame retardant is used as flame retardant (e) and the phosphorus content, based on the total weight of components (a) to (f), is < 1 wt.%. 10. Process according to one of claims 1 to 9, characterized in that the reaction mixture for producing sandwich elements is applied to a continuously moving cover layer using a double-belt system. 11. Polyurethane-based rigid foam obtainable by the process according to one or more of claims 1 to 10. 12. Use of a polyurethane-based rigid foam according to claim 11 for the production of composite elements. 13. A composite element obtainable or obtained by a process according to claim 10.