Melamine resin foam comprising a hindered amine light stabilizer as heat stabilizer

Abstract

Melamine resin foam comprising a hindered amine light stabilizer as heat stabilizer The present invention relates to a use of a sterically hindered amine for stabilizing a melamine resin foam against heat; and to a melamine resin foam comprising a sterically hindered amine; and to a process for producing the melamine resin foam comprising heating and foaming an aqueous mixture M using microwave radiation, said mixture M comprising at least one melamine-formaldehyde precondensate, at least one sterically hindered amine, at least one curative, at least one surfactant and at least one blowing agent; and to a use of the melamine resin foam for acoustic and / or thermal insulation.

Description

2403931Melamine resin foam comprising a hindered amine light stabilizer as heat stabilizerThe present invention relates to a use of a sterically hindered amine for stabilizing a melamine resin foam against heat; and to a melamine resin foam comprising a sterically hindered amine; and to a process for producing the melamine resin foam comprising heating and foaming an aqueous mixture M using microwave radiation, said mixture M comprising at least one melamine-formaldehyde precondensate, at least one sterically hindered amine, at least one curative, at least one surfactant and at least one blowing agent; and to a use of the melamine resin foam for acoustic and / or thermal insulation.Typically, a melamine-formaldehyde foam, also known as melamine resin foam, has a three-dimensional grid structure with an open cell rate of more than 99%. The foams show a low density, a good flame retardancy, good insulation properties, good sound absorption and a mild abrasiveness. The foam itself or densified foams can be used for the heat and sound insulation of buildings and building parts, for the heat and sound insulation of the interior spaces of vehicles and aircraft, for low temperature insulation, as an insulating wall covering, as an insulating and impact damping packaging material, as abrasively acting cleaning, grinding, and polishing sponges, in the hygiene sector, and as filter material.Especially, for technical applications in heat insulation and sound absorption a high temperature stability of the foam is important. So called-heat stabilizers may be used to further expand the heat stability. This is of high interest for autoclave and vessel applications, pipe insulation, motor test chambers or hood liner applications in automotive. So far, mostly copper salts are applied in the melamine resin foam to promote the heat stability.US4530940 teaches a melamine / formaldehyde foam which contains copper or iron salts as stabilizers against damage by elevated temperatures.US2015 / 0210814 teaches in paragraph

[0074] a melamine / formaldehyde foam which contains basic copper carbonate as preferred heat stabilizer.Unfortunately, the metal salts often led to a decrease in the mechanical properties of the foam. Furthermore, the mostly used substance - alkaline copper carbonate - is harmful to human body and for water organisms.The object of the present invention was to overcome the above problems, e.g. by finding a metal-free heat stabilizer to improve the heat stability of the melamine foam.The object was solved by a use of a sterically hindered amine for stabilizing a melamine resin foam against heat.The object was also solved by a melamine resin foam comprising a sterically hindered amine.2403932The object was also solved by a process for producing the melamine resin foam a comprising heating and foaming an aqueous mixture M using microwave radiation, said mixture M comprising at least one melamine-formaldehyde precondensate, at least one sterically hindered amine, at least one curative, at least one surfactant and at least one blowing agent.The object was also solved a use of the melamine resin foam or the melamine resin foam obtainable by the process for acoustic and / or thermal insulation.The stabilization against heat can be determined by treating the melamine resin foam for 24 h at a temperature of 240 °C. Usually, the RAM pressure value and / or the mass before and after the heat treatment is compared. The descrease in of the Ram pressure value can be expressed in percent and usually is reduced compared to a non- inventive sample. The mass loss can be expressed in percent and usually is reduced compared to a non-inventive sample. Preferably, both the Ram pressure value and the mass loss improved.The sterically hindered amine can be a derivative of tetramethylpiperidine. Suitable sterically hindered amines are for example bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate, bis(2,2,6,6-tetramethyl-4-piperidyl)succinate, bis(1 , 2, 2,6,6- pentamethyl-4-piperidyl)sebacate, bis(1 ,2,2,6,6-pentamethyl-4-piperidyl) n-butyl-3,5-di-tert-butyl-4- hydroxybenzylmalonate, the condensate of 1-(2-hydroxyethyl)-2,2,6,6-tetramethyl-4-hydroxypiperidine and succinic acid, linear or cyclic condensates of N, N'-bis(2,2,6,6-tetramethyl-4-piperidyl)hexamethylenediamine and 4-tert- octylamino-2,6-dichloro-1 ,3,5-triazine, tris(2,2,6,6-tetramethyl-4-piperidyl)nitrilotriacetate, tetrakis(2,2,6,6-tetramethyl- 4-piperidyl)-1,2,3,4-butanetetracarboxylate, 1 ,1'-(1 ,2-ethanediyl)-bis(3,3,5,5-tetramethylpiperazinone), 4-benzoyl-2.2.6.6-tetramethylpiperidine, 4-stearyloxy-2,2,6,6-tetramethylpiperidine, bis(1 , 2,2,6, 6-pentamethylpiperidyl)-2-n- butyl-2-(2-hydroxy-3,5-di-tert-butylbenzyl)malonate, 3-n-octyl-7,7,9,9-tetramethyl-1,3,8-triazaspiro[4.5]decane-2,4- dione, bis(1-octyloxy-2,2,6,6-tetramethylpiperid-4-yl)sebacate, bis(1-octyloxy-2,2,6,6-tetramethylpiperid-4- yljsuccinate, bis-[2,2,6,6-tetramethyl-1-(undecyloxy)-piperidin-4-yl] carbonate, linear or cyclic condensates of N,N'- bis(2,2,6,6-tetramethyl-4-piperidyl)-hexamethylenediamine and 4-morpholino-2,6-dichloro-1 ,3,5-triazine, the condensate of 2-chloro-4,6-bis(4-n-butylamino-2,2,6,6-tetramethylpiperidyl)-1 ,3,5-triazine and 1 ,2-bis(3-aminopropyl- aminojethane, the condensate of 2-chloro-4,6-di-(4-n-butylamino-1,2,2,6,6-pentamethylpiperidyl)-1,3,5-triazine and 1,2-bis(3-aminopropyl-amino)ethane, 8-acetyl-3-dodecyl-7,7,9,9-tetramethyl-1,3,8-triazaspiro[4.5]decane-2,4-dione, 3-dodecyl-1-(2,2,6,6-tetramethyl-4-piperidyl)pyrrolidine-2,5-dione, 3-dodecyl-1-(1,2,2,6,6-pentamethyl-4- piperidyl)pyrrolidine-2, 5-dione, a mixture of 4-hexadecyloxy- and 4-stearyloxy-2,2,6,6-tetramethylpiperidine, a condensate of N,N'-bis(2,2,6,6-tetramethyl-4-piperidyl)hexamethylenediamine and 4-cyclohexylamino-2,6-dichloro-1 ,3,5- triazine, a condensate of 1,2-bis(3-aminopropylamino)ethane and 2,4,6-trichloro-1,3,5-triazine as well as 4- butylamino-2,2,6,6-tetramethylpiperidine (CAS Reg. No. [136504-96-6]); a condensate of 1,6-hexanediamine and2.4.6-trichloro-1,3,5-triazine as well as N,N-dibutylamine and 4-butylamino-2,2,6,6-tetramethylpiperidine (CAS Reg. No. [19226864-7]); reaction products of N6,N6'-hexane-1,6-diylbis[N2,N4-dibutyl-N2,N4,N6-tris(2,2,6,6- tetramethylpiperidin-4-yl)-1,3,5-triazine-2,4,6-triamine], butanal and hydrogen peroxide; N-(2,2,6,6-tetramethyl-4- piperidyl)-n-dodecylsuccinimide, N-(1,2,2,6,6-pentamethyl-4-piperidyl)-n-dodecylsuccinimide, 2-undecyl-7,7,9,9-2403933 tetramethyl-1 -oxa-3,8-diaza-4-oxo-spiro[4,5]decane, a reaction product of 7,7,9,9-tetramethyl-2-cycloundecyl-1 -oxa- 3,8-diaza-4-oxospiro-[4,5]decane and epichlorohydrin, 1,1-bis(1, 2,2,6, 6-pentamethyl-4-piperidyloxycarbonyl)-2-(4- methoxyphenyl)-ethene, N, N'-bis-formyl-N, N'-bis(2,2,6,6-tetramethyl-4-piperidyl)hexamethylenediamine, a diester of 4-methoxymethylenemalonic acid with 1 ,2,2,6,6-pentamethyl-4-hydroxy-piperidine, poly[methylpropyl-3-oxy-4- (2,2,6,6-tetramethyl-4-piperidyl)]siloxane, a reaction product of maleic acid anhydride-D-olefin copolymer with 2, 2,6,6- tetramethyl-4-aminopiperidine or 1 , 2, 2,6, 6-pentamethyl-4-ami nopiperidine, a mixture of oligomeric compounds which are the formal condensation products of N,N'-bis-(2,2,6,6-tetramethyl-1 -propoxy-piperidin-4-yl)-hexane-1 ,6-diamine and 2,4-dichloro-6-{n-butyl-(2,2,6,6-tetramethyl-1 -propoxy-piperidin-4-yl)-amino}-[1 ,3,5]triazine end-capped with 2- chloro-4,6-bis-(di-n-butylamino)-[1 ,3,5]triazine, a mixture of oligomeric compounds which are the formal condensation products of N, N'-bis-(2,2,6,6-tetramethyl-piperidin-4-yl)-hexane-1 ,6-diamine and 2,4-dichloro-6-{n-butyl-(2,2,6,6- tetramethyl-piperidin-4-yl)-amino}-[1,3,5]triazine end-capped with 2-chloro-4,6-bis-(di-n-butylamino)-[1,3,5]triazine, (N2,N4-dibutyl-N2,N4-bis(1,2,2,6,6-pentamethyl-4-piperidinyl)-6-(1-pyrrolidinyl)-[1,3,5]-triazine-2,4-diamine, 2,4- bis[N-(1-cyclohexyloxy-2,2,6,6-tetramethylpiperidine-4-yl)-N-butylamino]-6-(2-hydroxyethyl)amino-1,3,5-triazine, 1-(2- hydroxy-2-methylpropoxy)-4-octadecanoyloxy-2,2,6,6-tetramethylpiperidine, 5-(2-ethylhexanoyl)oxymethyl-3,3,5- trimethyl-2-morpholinone, Sanduvor (Clariant; CAS Reg. No. [106917-31-1]), 5-(2-ethylhexanoyl)-oxymethyl-3,3,5- trimethyl-2-morpholinone, the reaction product of 2,4-bis-[(1 -cyclo-hexyloxy-2,2,6,6-piperidine-4-yl)butylamino]-6- chloro-s-triazine with N,N’-bis-(3-amino-propyl)ethylenediamine), 1 ,3,5-tris(N-cyclohexyl-N-(2,2,6,6-tetramethyl- piperazine-3-one-4-yl)amino)-s-triazine, 1 ,3,5-tris(N-cyclohexyl-N-(1,2,2,6,6-pentamethylpiperazine-3-one-4-yl)- amino)-s-tri azine.The sterically hindered amine may have a solubility in water at 20 °C of below 100 mg / l, preferably below 30 mg / l, and in particular below 10 mg / l.The sterically hindered amine is preferably an oligomeric sterically hindered amine.The oligomeric sterically hindered amine may have a molecular weight Mnof at least 1500 g / mol, preferably of at least 2000 g / mol, and in particular at least 2500 g / mol. In another form oligomeric sterically hindered amine may have a molecular weight Mnof at least 1000, preferably at least 1100, more preferably of at least 1200, still more preferably at least 1300 and most preferably of at least 1400 g / mol.The oligomeric sterically hindered amine may have a molecular weight Mnof up to 30 000 g / mol, preferably of at least 10 000 g / mol, and in particular up to 5 000 g / mol.The oligomeric sterically hindered amine may have a molecular weight Mnin the range from 1500-30000 g / mol, preferably of from 2000-12000 g / mol, and in particular from 2500-7000 g / mol.The molecular weight Mnusually means the number average molecular weight, and may be determined according to DIN 55672-1.2403934The oligomeric sterically hindered amine may have a thermal decomposition temperature of at least 250 °C, preferably at least 300 °C. The thermal decomposition temperature can be determined in an isoperibolic setup in a Liitolf oven.The sterically hindered amine is preferably a compound of formula (I)where n is from 2 to 50, preferably from 2 to 20.In another form the sterically hindered amine is preferably a compound of formula (la)The melamine resin foam may comprise at least 0.01 wt%, preferably at least 0.05 wt%, and in particular at least 0.1 wt% of the sterically hindered amine.The melamine resin foam may comprise up to 5 wt%, preferably up to 3 wt%, and in particular up to 2 wt% of the sterically hindered amine.The melamine resin foam may comprise from 0.01 to 10 wt%, preferably from 0.1 to 5 wt%, and in particular from 0.2 to 3 wt% of the sterically hindered amine.The melamine resin foam may have an open-celled structure. The open-cell content of the melamine resin foam (e.g. measured according to DIN ISO 4590) can be more than 50 %, preferable of 95 % or higher, most preferably of 98 to 100%.The density of the melamine resin foam can be in the range from 5 to 15 kg / m3, more preferably 6 to 12 kg / m3.Preferably the shore hardness 000 of the melamine resin foam is in the range from 35 to 75 N, measured according to ASTM D 2240.The melamine resin foam may comprise at least 75 wt%, preferably at least 80 wt% and in particular at least 85 wt% of cured melamine resin. The melamine resin foam may comprise 75 to 99 wt.-%, preferably of 80 to 97 wt.-% of the cured melamine resin.2403935The melamine-resin foam can be produced by a process comprising heating and foaming an aqueous mixture M using microwave radiation, said mixture M comprising at least one melamine-formaldehyde precondensate, at least one sterically hindered amine, at least one curative, at least one surfactant and at least one blowing agent.The melamine resin foam can be tempered at a temperature between 120 - 300°C.The sterically hindered amine can be used in the process in a total amount of from 0.01 to 10 wt%, preferably from 0.1 to 5 wt%, and in particular from 0.2 to 3 wt%, based on the melamine melamine-formaldehyde precondensate.The melamine / formaldehyde precondensates may be prepared separately or commercially available precondensates of the two components, melamine and formaldehyde may be used. Preferably a melamine-formaldehyde precondensate having a molar ratio of melamine to formaldehyde ranging from 1 : 5 to 1 : 1.3, more preferably from 1 : 3,5 to: 1 : 1,5 is used. Preferably the number average molecular weight Mn ranges from 200 g / mol to 1000 g / mol. Preference is given to unmodified melamine / formaldehyde precondensates.Anionic, cationic and nonionic surfactants and also mixtures thereof can be used as dispersant / emulsifier.Useful anionic surfactants include for example diphenylene oxide sulfonates, alkane and alkylbenzenesulfonates, alkylnaphthalenesulfonates, olefinsulfonates, alkyl ether sulfonates, fatty alcohol sulfates, ether sulfates, a-sulfo fatty acid esters, acylaminoalkanesulfonates, acyl isethionates, alkyl ether carboxylates, N-acylsarcosinates, alkyl and alkylether phosphates.Useful nonionic surfactants include alkylphenol polyglycol ethers, fatty alcohol polyglycol ethers, fatty acid polyglycol ethers, fatty acid alkanolamides, ethylene oxide-propylene oxide block copolymers, amine oxides, glycerol fatty acid esters, sorbitan esters and alkylpolyglycosides.Useful cationic emulsifiers include for example alkyltriammonium salts, alkylbenzyldimethylammonium salts and alkylpyridinium salts.The dispersants / emulsifiers can be added in amounts from 0.2% to 5% by weight, based on the melamine- formaldehyde precondensate.Preferably the mixture M comprises a surfactant mixture comprising a mixture of 50 to 90 wt% of at least one anionic surfactant and 10 to 50 wt% of at least one nonionic surfactant, wherein the weight percentages are each based on the total weight of the surfactant mixture.As curatives it is possible to use acidic compounds which catalyze the further condensation of the melamine resin. The amount of these curatives is generally in the range from 0.01% to 20% by weight and preferably in the range2403936 from 0.05% to 5% by weight, all based on the precondensate. Useful acidic compounds include organic and inorganic acids, for example selected from the group consisting of hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, formic acid, acetic acid, oxalic acid, toluene sulfonic acids, amido sulfonic acids, acid anhydrides and mixtures thereof. Preferably formic acid is used as curative.The mixture further comprises at least one blowing agent. Useful physical blowing agents include for example hydrocarbons, such as pentane, hexane, halogenated, more particularly chlorinated and / or fluorinated, hydrocarbons, for example methylene chloride, chloroform, trichloroethane, chlorofluorocarbons, hydrochlorofluorocarbons (HCFCs), alcohols, for example methanol, ethanol, n propanol or isopropanol, ethers, ketones and esters, for example methyl formate, ethyl formate, methyl acetate or ethyl acetate, in liquid form or air, nitrogen or carbon dioxide as gases.The amount of blowing agent in the mixture generally depends on the desired density for the foam. Preferably the amount in relation to the melamine-formaldehyde precondensate is chosen in an amount that the density of the foam is 5 to 15 kg / m3, more preferably 6 to 12 kg / m3. The blowing agent is preferably present in the mixture in an amount of 0.5% to 60% by weight, preferably 1% to 40% by weight and more preferably 1.5% to 30% by weight, based on the melamine-formaldehyde precondensate. It is preferable to add a physical blowing agent having a boiling point between 0 and 80°C. Most preferably pentane is used as blowing agent.The precondensate being foamed up generally by heating the suspension of the melamine-formaldehyde precondensate to obtain a foamed material.The introduction of energy may preferably be effectuated via electromagnetic radiation, for example via high- frequency radiation at 5 to 400 kW, preferably 5 to 200 kW and more preferably 9 to 120 kW per kilogram of the mixture used in a frequency range from 0.2 to 100 GHz, preferably 0.5 to 10 GHz. Magnetrons are a useful source of dielectric radiation, and at least one magnetron can be used at the same time.The foamed materials produced can be finally dried, removing residual water and blowing agent from the foam. Drying is carried out preferably in a drying oven at a temperature in the range of 40 to 260°C, particularly preferably 100 to 250°C until a constant weight. The process described usually provides blocks or slabs of foamed material, which can be cut to size in any desired shapes.The process for producing the melamine resin foam comprising preferably the steps: a) forming an aqueous mixture M from at least one melamine-formaldehyde precondensate, at least one curative, at least one surfactant, at least one sterically hindered amine and at least one blowing agent, b) heating and foaming the aqueous mixture M using microwave radiation to produce a melamine resin foam, and c) optionally tempering the melamine resin foam obtained in step b) at a temperature between 120 - 300°C.2403937The melamine resin foam may be post-treated by at least one of the following methods:- Thermocompression to obtain foams with higher density, better durability and cleaning behavior.- Hydrophobation to obtain foams with lower water uptake.- Oleophobation to obtain foams with lower oil uptake.- Impregnation with flame retardants to further improve the FST properties (Flame, Smoke, toxicity) in the case of fire.ExamplesRam pressure value:Ram pressure measurements for evaluating the mechanical quality of the melamine resin foams were all carried out as follows: A cylindrical ram having a diameter of 8 mm and a height of 10 cm was pressed into a cylindrical sample having a diameter of 11 cm and a height of 5 cm in the direction of foaming at an angle of 90% until the sample tore. The tearing force [N], hereinafter also referred to as ram pressure value, provided information as to the quality of the foam.Mass Loss:The mass loss measurement is done by weighting the foam before and after the conditioning of 240°C / 24h and expressed in percent.Hindered Amine A: Butanedioic acid, dimethylester, polymer with 4-hydroxy-2, 2, 6, 6-tetramethyl-1 -piperidine ethanol, molecular weight 3100-4000 g / mol, solubility in water (20 °C) = 1.6 mg / l.Example 1Two different foam formulations were prepared: The high-functional resin (M / F ratio of 1 :2.8) is used for the main foam applications whereas the low-functional resin (M / F ratio of 1 :1.6) is used for foam applications with subsequent thermoforming step. Due to the lower crosslinking density the foams based on the low-functional resin shows reduced mechanical properties.A) High-functional resinHigh functional MF melamine-formaldehyde precondensate HF-MF was a spray-dried melamine-formaldehyde precondensate having an average molecular weight (number average) Mn of 350 g / mol, which had a molar ratio of mel- amine:formaldehyde of 1 :2.8.100 g of a spray-dried melamine-formaldehyde precondensate were dissolved in 40 g of water, then 1 .5 g of a sodium C12 / C14-alkyl sulfonate and 3 g of sodium formiate were added. Next, the heat stabilizer Hindered Amine A was added in amounts shown in Table 1. The mixture was stirred for 60 s. Afterwards, 17.8 g of pentane as blowing agent2403938 and 3.1 g formic acid were added to the mixture. The mixture was stirred for 30 min and subsequently transferred to a propylene mold for foaming. The foaming is supported by microwave energy by 6 min of 4 magnetrons with 800W respectively. After the foaming was accomplished, the foam was demolded and dried in the oven for 8 hours at 100°C. The density of the foam was 9 ± 1 kg / m3. Next, the RAM and mass was determined before and then after heating of the foam for 24 hours a 240 °C.Table 1 : Heat stabilization (mean values of 3 measurements)The examples in Table 1 demonstrated that the addition of Hindered Amine A stabilized the foam against heat.Table 2 (All Comparative): Heat stabilization (mean values of 3 measurements)The comparative examples in Table 2 demonstrated that the addition of basic copper carbonate shows low effects on heat stabilization.B) Low-functional resinLow functional melamine-formaldehyde precondensate LF-MF was a spray-dried melamine-formaldehyde precondensate having an average molecular weight (number average) Mn of 320 g / mol, which had a molar ratio of mela- mine:formaldehyde of 1:1.6.2403939100 g of a spray-dried melamine-formaldehyde precondensate (molar ratio 1 : 1.6) were dissolved in 40 g of water, then 1 .5 g of a mixture of 80% sodium C12 / C14-alkyl sulfonate and 20% alkyl polyethylene glycol ether were added. Next, 4.5 g of sodium formiate were added. Next, the heat stabilizer Hindered Amine A was added in amounts shown in Table 3. The mixture was stirred for 60 s. Afterwards, 17.8 g of pentane as blowing agent and 12.3 g formic acid were added to the mixture. The mixture was stirred for 30 min and subsequently transferred to a propylene mold for foaming. The foaming was supported by microwave energy by 6 min of 4 magnetrons with 800W respectively. After the foaming was accomplished, the foam was demolded and dried in the oven for 8 hours at 100°C. The density of the foam was 9 ± 1 kg / m3. Next, the RAM and mass was determined before and then after heating of the foam for 24 hours a 240 °C.Table 3: Heat stabilization (mean values of 3 measurementsThe examples in Table 3 demonstrated that the addition of the Hindered Amine A stabilized the foam against heat.Table 4 (All Comparative): Heat stabilization (mean values of 3 measurements)The comparative examples in Table 4 demonstrated that the addition of basic copper carbonate shows low effects on heat stabilization.

Claims

24039310Claims1. A use of a sterically hindered amine for stabilizing a melamine resin foam against heat.

2. The use according to claim 1 wherein the stabilizing against heat is determined by treating the melamine resin foam for 24 h at a temperature of 240 °C.

3. The use according to claim 1 or 2 wherein the melamine resin foam comprises from 0.01 to 10 wt%, preferably from 0.1 to 5 wt%, and in particular from 0.2 to 3 wt% of the sterically hindered amine.

4. The use according to any of claims 1 to 3 wherein the sterically hindered amine is an oligomeric sterically hindered amine.

5. The use according to any of claims 1 to 4 wherein the sterically hindered amine has a solubility in water at 20 °C of below 100 mg / l.

6. A melamine resin foam comprising a sterically hindered amine.

7. The melamine resin foam according to claim 6 wherein the melamine resin foam comprises from 0.01 to 10 wt%, preferably from 0.1 to 5 wt%, and in particular from 0.2 to 3 wt% of the sterically hindered amine.

8. The melamine resin foam according to claim 6 or 7 wherein the sterically hindered amine is a oligomeric sterically hindered amine.

9. The melamine resin foam according to any of claims 6 to 8 wherein the oligomeric sterically hindered amine has a molecular weight Mnof at least 1500 g / mol, preferably at least 2000 g / mol.

10. The melamine resin foam according to any of claims 6 to 9 wherein the sterically hindered amine has a solubility in water at 20 °C of below 100 mg / l, preferably below 10 mg / l.

11. The melamine resin foam according to any of claims 6 to 10 wherein the sterically hindered amine is a cornpound of formula (I)where n is from 2 to 50, preferably 2 to 20.2403931112. The melamine resin foam according to any of claims 6 to 11 wherein the melamine resin foam has an open- celled structure.

13. A process for producing the melamine resin foam as defined in claims 6 to 12 comprising heating and foaming an aqueous mixture M using microwave radiation, said mixture M comprising at least one melamineformaldehyde precondensate, at least one sterically hindered amine, at least one curative, at least one surfactant and at least one blowing agent.

14. The process according to claim 13 wherein the sterically hindered amine is used in a total amount of from 0.01 to 10 wt%, preferably from 0.1 to 5 wt%, and in particular from 0.2 to 3 wt%, based on the melamine melamineformaldehyde precondensate.

15. The process according to claim 13 or 14 wherein the mixture M comprises a surfactant mixture comprises a mixture of 50 to 90 wt.-% of at least one anionic surfactant and 10 to 50 wt.-% of at least one nonionic surfac- tant, wherein the weight percentages are each based on the total weight of the surfactant mixture.

16. A use of the melamine resin foam as defined in claims 6 to 12 or obtainable by the process as defined in claims 13 to 15 for acoustic and / or thermal insulation.

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