Melamine resin foam by oxidation reaction

Abstract

The invention relates to a method for producing melamine resin foams, comprising foaming an aqueous mixture M comprising at least one melamine-formaldehyde precondensate, an aqueous hydrogen peroxide solution and at least one surfactant.

Description

[0001] The present invention relates to a method for producing melamine resin foam, which method comprises foaming an aqueous mixture M comprising at least one melamine-formaldehyde precondensate, an aqueous hydrogen peroxide solution and at least one surfactant.

[0002] Melamine resin foams are used for different applications such as sound absorption (e.g. in anechoic chambers) and heat insulation (e.g. in building and pipe insulation). In the prior art, melamine foams are generally prepared by reacting a melamine-formaldehyde precondensate with an acid as a curing agent. Additionally, generally, a physical blowing agent, such as a hydrocarbon and in particular pentane, is used. Since the above reaction shows a rather low exothermicity, in the prior art, the reaction / foaming mixture is generally heated in order to ensure curing and foaming of the resin. The heating according to the prior art is carried out using an external heat source such as microwave radiation or hot air.

[0003] However, the application of external heat and in particular microwave radiation as described in the prior art and generally used for producing melamine resin foam can be disadvantageous since, for example, it is challenging to keep the microwave power constant during the production process.

[0004] Furthermore, hydrocarbons used as physical blowing agents, such as pentane as described in the prior art in particular, are combustible and can readily lead to the formation of an explosive atmosphere. Therefore, a high level of safety devices and procedures is required in the production of the described melamine resin foam according to the prior art.

[0005] DE 29 15 467(A1) relates to the preparation of an elastic foam based on a melamine / formaldehyde condensate by foaming an aqueous solution or dispersion containing a melamine / formaldehyde precondensate, an emulsifier, a volatile blowing agent and a curing agent. As curing agents, organic acids and inorganic acids are disclosed. The foaming of the mixture is carried out in a hot air atmosphere at 150 °C. DE 29 15 467(A1) does not disclose a method comprising an aqueous hydrogen peroxide solution in which overheating during foaming can be avoided.

[0006] CN 109 836 548(A) discloses a method for preparing a melamine-based foam, which method comprises preparing a mixture of melamine, paraformaldehyde and water, using n-pentane as a blowing agent, an organic acid as a curing agent, and heating in a microwave oven during foaming. CN 109 836 548 A does not disclose a method comprising an aqueous hydrogen peroxide solution in which microwave heating during foaming can be avoided, nor does it disclose a method without n-pentane.

[0007] EP 3 750 952(A1) relates to a method for producing melamine-formaldehyde foam using a fluorinated blowing agent, the method comprising heating and foaming a mixture comprising at least one melamine-formaldehyde precondensate, at least one curing agent, at least one surfactant and a blowing agent mixture. The curing agent is an acidic compound that catalyzes the condensation selected from inorganic or organic acids, and the blowing agent comprises 5 wt% to 20 wt% of a fluorinated ether and 80 wt% to 95 wt% of a hydrocarbon (such as pentane). The precondensate is foamed by heating the mixture using microwave radiation. EP 3 750 952(A1) does not disclose a method comprising an aqueous hydrogen peroxide solution, in which microwave heating during foaming can be avoided, nor does it disclose a method without n-pentane.

[0008] WO 2018 / 098056(A1) relates to a cleaning tool comprising a melamine-formaldehyde foam for hard surface cleaning (such as tiles, showers and sinks), including a method for producing the foam. A mixture comprising a melamine-formaldehyde precondensate, at least one linear polymer, a curing agent, a dispersant and a blowing agent is heated to foam by means of hot air or high-frequency radiation. The curing agent can be an inorganic or organic acid. Surfactants for cleaning the surface can be impregnated into the foam, such as a mixture of surfactants, biocides, bleaching agents, scale reducing agents, agents for removing grease stains, etc. WO2018 / 098056(A1) does not disclose the preparation of a melamine resin foam according to the method of the present invention, which comprises foaming at least one melamine-formaldehyde precondensate, an aqueous hydrogen peroxide solution and at least one surfactant.

[0009] WO 2014 / 172357(A1) relates to a cleaning article comprising a melamine-formaldehyde foam containing hollow microspheres for removing dirt and stains from hard surfaces. Surfactants for cleaning the surface can be included in the microspheres and impregnated into the foam, such as a mixture of surfactants, biocides, bleaching agents, scale reducing agents, agents for removing grease stains, etc. WO 2014 / 172357(A1) does not disclose the preparation of a melamine resin foam according to the method of the present invention, which comprises foaming at least one melamine-formaldehyde precondensate, an aqueous hydrogen peroxide solution and at least one surfactant.

[0010] WO 2019 / 060647 (A1) relates to a cleaning product, which includes a melamine-formaldehyde foam for removing dirt and stains from hard surfaces. Surfactants for cleaning the surface can be impregnated into the foam, such as a mixture of surfactants, biocides, bleaches, scale reducers, agents for removing oil stains, etc. WO 2019 / 060647 (A1) does not disclose the preparation of melamine resin foam according to the method of the present invention, which includes foaming at least one melamine-formaldehyde precondensate, an aqueous hydrogen peroxide solution, and at least one surfactant.

[0011] US 3,864,137 relates to the production of a foam by mixing an aqueous silicate solution with hydrogen peroxide as a blowing agent, thereby producing a structure consisting essentially of silicate, which may also contain an inorganic filler or an organic filler. US 3,864,137 does not disclose the preparation of melamine resin foam according to the method of the present invention.

[0012] CN 103 553 700 (A) relates to an environmentally friendly magnesium oxide material, wherein the raw materials for foaming contain 80 wt% to 90 wt% of calcined magnesium powder, a filler, and a composite foaming agent, and the composite foaming agent may contain 20 wt% to 40 wt% of peroxide. The raw materials may also contain an organic filler or an inorganic filler, such as zeolite, fly ash, and / or waste tire rubber, and 5 wt% to 10 wt% of melamine resin. CN 103 553 700 A does not disclose the preparation of melamine resin foam according to the method of the present invention, which includes foaming at least one melamine-formaldehyde precondensate, an aqueous hydrogen peroxide solution, and at least one surfactant.

[0013] CN 102 603 353 (A) relates to a foaming agent for foaming concrete, which contains 35 wt% to 45 wt% of hydrogen peroxide. CN 102 603 353 (A) does not disclose any melamine resin foam or the method according to the method of the present invention.

[0014] CN 110 372 995(A) relates to an environmentally friendly modified melamine-formaldehyde-melamine resin foam material, which is obtained from a mixture of the following raw materials in parts by weight: 65 to 80 parts of modified melamine-formaldehyde-melamine resin; 3 to 6 parts of foam stabilizer; 0.2 to 2 parts of foaming agent, 20 to 35 parts of functional powder; 0.2 to 0.5 parts of dispersant; 0.3 to 0.6 parts of accelerator, and 2 to 5 parts of curing agent. The foaming agent preferably comprises industrial hydrogen peroxide and aluminum powder. The method according to CN 110 372 995(A) is disadvantageous because it is based on the forced use of powders, in particular large amounts of functional powder and / or aluminum powder as foaming agents. Due to the reaction with hydrogen peroxide, such powders cause the formation of (higher amounts of) hydrogen, which is problematic in terms of safety considerations. In addition, the method according to CN 110 372 995(A) requires the use of acids such as sulfuric acid, hydrochloric acid, phosphoric acid, oxalic acid, acetic acid and acrylic acid.

[0015] The object of the present invention is to provide a new method for producing melamine resin foam. In addition, the new method should have beneficial properties with respect to avoiding excessive external heating or the use of microwave radiation, in particular with respect to flammable / explosive hydrocarbon blowing agents.

[0016] This object is achieved by a method for producing melamine resin foam, which comprises foaming an aqueous mixture M, said mixture M comprising at least one melamine-formaldehyde precondensate, an aqueous hydrogen peroxide solution and at least one surfactant.

[0017] The method of the present invention can be used to produce melamine resin foam, for example for thermal insulation applications or sound absorption and thermal insulation applications. By using the method of the present invention, certain disadvantages of the methods for producing melamine resin foam disclosed in the prior art can be avoided.

[0018] Surprisingly, it has been found that by applying the method of the present invention, external heating as described in the prior art, such as by using microwave radiation or hot air, can be avoided.

[0019] In addition, surprisingly, it has been found that by applying the method of the present invention, melamine resin foam can be produced without adding physical blowing agents (such as hydrocarbons, for example pentane), or at least by significantly reducing the amount of physical blowing agents added. Therefore, the advantage of the method of the present invention is that during curing by external heating or microwave radiation, the presence of flammable / explosive physical blowing agents (such as pentane) can be avoided, or at least the concentration of such physical blowing agents can be significantly reduced.

[0020] Another advantage of the method according to the invention can be seen in the fact that in the method according to the invention, no curing agent / catalyst in the form of an acid (in particular formic acid as applied in the prior art) needs to be added.

[0021] Furthermore, the method according to the invention produces melamine resin foams with a low Shore hardness, which can be used in some applications. In particular, foams showing a low Shore hardness are of high interest for thermal insulation applications.

[0022] The invention is described in more detail as follows:

[0023] The invention relates to a method for producing melamine resin foams, which method comprises foaming an aqueous mixture M, said mixture M comprising at least one melamine-formaldehyde precondensate, an aqueous hydrogen peroxide solution and at least one surfactant.

[0024] In order to obtain melamine resin foams, the foaming of melamine-formaldehyde precondensates per se is known to the person skilled in the art. The same applies to melamine-precondensates per se.

[0025] The melamine-formaldehyde precondensate can be prepared separately or a commercially available precondensate of the two components (melamine and formaldehyde) can be used.

[0026] Preferably,

[0027] a) the melamine-formaldehyde precondensate has a molar ratio of melamine to formaldehyde in the following range: 1:5 to 1:1.3 [mol / mol], preferably 1:3.5 to 1:1.5 [mol / mol], and / or

[0028] b) the number-average molecular weight M n of the melamine-formaldehyde precondensate ranges from 200 g / mol to 1000 g / mol (determined by gel permeation chromatography).

[0029] Preferably, the melamine-formaldehyde precondensate is unmodified.

[0030] The person skilled in the art knows how to determine the average molecular weight (number-average) of such melamine-formaldehyde precondensates. For example, this can be carried out using gel permeation chromatography. The preparation and characterization of such melamine-formaldehyde precondensates are described, for example, in "W. Woebang, Kunststoffhandbuch 10 th"Duroplaste, Munich, Vienna, 1988", "Encyclopedia of Polymer Science and Technology, 3rd Edition, Volume 1, Chapter 1, amino resins, pages 340 to 370, 2003" or "Ullmann's Encyclopedia of Industrial Chemistry, 6th Edition, Volume 2, Chapter 3, amino resins, pages 537 to 565, Weinheim, 2003".

[0031] Furthermore, in the present invention, it is preferred that the mixture M comprises, based on the total weight of the mixture M, 30% to 90% by weight of at least one melamine - formaldehyde pre - condensate, preferably 40% to 80% by weight of the melamine - formaldehyde pre - condensate, more preferably 51% to 75% by weight of the melamine - formaldehyde pre - condensate, based on the total weight of the mixture M.

[0032] Hydrogen peroxide and aqueous hydrogen peroxide solutions are known to those skilled in the art.

[0033] In the present invention, it is preferred that

[0034] a) The aqueous hydrogen peroxide solution contains (about) 3% to 50% by weight, preferably (about) 6% to 37% by weight, more preferably (about) 25% to 35% by weight of hydrogen peroxide, based on the total weight of the hydrogen peroxide solution.

[0035] Hydrogen peroxide itself and solutions of hydrogen peroxide in water, alcohols or ethers are known to those skilled in the art.

[0036] In the process of the present invention, hydrogen peroxide is preferably applied as an aqueous solution containing (about) 3% to 50% by weight of hydrogen peroxide, preferably (about) 6% to 37% by weight of hydrogen peroxide, more preferably (about) 25% to 35% by weight of hydrogen peroxide, based on the total weight of the hydrogen peroxide solution.

[0037] Furthermore, according to the present invention, it is preferred that the mixture M comprises, based on the total weight of the mixture M, 0.5% to 10% by weight of the hydrogen peroxide contained in the aqueous hydrogen peroxide solution, preferably 1% to 7.5% by weight of hydrogen peroxide, based on the total weight of the mixture M.

[0038] Surfactants themselves are known to those skilled in the art. According to the present invention, anionic, cationic and non - ionic surfactants and mixtures thereof can be used as dispersants / emulsifiers.

[0039] Useful anionic surfactants include, for example, dibenzofuran sulfonates, alkane and alkylbenzene sulfonates, alkylnaphthalene sulfonates, olefin sulfonates, alkyl ether sulfonates, fatty alcohol sulfates, ether sulfates, α-sulfo fatty acid esters, acylaminoalkane sulfonates, acylhydroxyethyl sulfonates, alkyl ether carboxylates, N-acyl sarcosinates, alkyl and alkyl ether phosphates.

[0040] 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 alkyl polyglycosides.

[0041] Useful cationic emulsifiers include, for example, alkyltriammonium salts, alkylbenzyldimethylammonium salts, and alkylpyridinium salts.

[0042] Preferably, in the process according to the invention,

[0043] a) the at least one surfactant is an anionic surfactant, preferably the at least one surfactant is an anionic surfactant selected from the group consisting of dibenzofuran sulfonates, alkane and alkylbenzene sulfonates, alkylnaphthalene sulfonates, olefin sulfonates, alkyl ether sulfonates, fatty alcohol sulfates, ether sulfates, α-sulfo fatty acid esters, acylaminoalkane sulfonates, acylhydroxyethyl sulfonates, alkyl ether carboxylates, N-acyl sarcosinates, alkyl and alkyl ether phosphates, or

[0044] b) the at least one surfactant is a nonionic surfactant, preferably the at least one surfactant is a nonionic surfactant selected from the group consisting of 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 alkyl polyglycosides, and / or

[0045] c) The at least one surfactant is a surfactant mixture of the following substances: i) 50% to 90% by weight of at least one anionic surfactant, preferably the at least one surfactant is an anionic surfactant selected from the group consisting of dibenzofuran sulfonate, alkane and alkylbenzene sulfonate, alkylnaphthalene sulfonate, olefin sulfonate, alkyl ether sulfonate, fatty alcohol sulfate, ether sulfate, α-sulfo fatty acid ester, acylaminoalkane sulfonate, acylhydroxyethyl sulfonate, alkyl ether carboxylate, N-acylsarcosinate, alkyl and alkyl ether phosphate, and ii) 10% to 50% by weight of at least one nonionic surfactant based on the total weight of the surfactant mixture, wherein the at least one nonionic surfactant is preferably selected from alkylphenol polyglycol ether, fatty alcohol polyglycol ether, fatty acid polyglycol ether, fatty acid alkanolamide, ethylene oxide-propylene oxide block copolymer, amine oxide, glycerol fatty acid ester, sorbitan ester and alkylpolyglycoside.

[0046] Furthermore, preferably, the mixture M contains 0.5% to 10% by weight of at least one surfactant based on the total weight of the mixture M, preferably 1% to 7.5% by weight of at least one surfactant based on the total weight of the mixture M.

[0047] In the process of the present invention, the mixture M may additionally contain at least one blowing agent as an optional component. Blowing agents are known to those skilled in the art.

[0048] In the process of the present invention,

[0049] a) Preferably, the blowing agent is at least one physical blowing agent

[0050] i) selected from hydrocarbons, preferably selected from C 5 -C 7 hydrocarbons or halogenated hydrocarbons, more preferably selected from chlorinated hydrocarbons or fluorinated hydrocarbons, and / or

[0051] ii) selected from alcohols, ethers, ketones and esters, and / or

[0052] b) The blowing agent has a boiling point between 0 °C and 80 °C, and / or

[0053] c) The mixture M contains 0.5% to 30% by weight of the blowing agent based on the total weight of the mixture M, preferably 1.5% to 20% by weight of the blowing agent based on the total weight of the mixture M.

[0054] Physical blowing agents are known to those skilled in the art and are described, for example, in Encyclopedia of Polymer Science and Technology, Volume I, 3rd Edition, Additives, pages 203 to 218, 2003.

[0055] Useful physical blowing agents include, for example, hydrocarbons such as butane, n-pentane, isopentane or cyclopentane, hexane; halogenated hydrocarbons, more particularly chlorinated hydrocarbons and / or fluorinated hydrocarbons such as dichloromethane, chloroform, trichloroethane, chlorofluorocarbons, hydrochlorofluorocarbons (HCFC), hydrofluorocarbons (HCF) such as methyl nonafluorobutyl ether, ethyl nonafluorobutyl ether, hydrofluoroolefins (HFO) such as hexafluorobutene; alcohols such as methanol, ethanol, n-propanol or isopropanol; ethers, ketones, and esters such as methyl formate, ethyl formate, methyl acetate or ethyl acetate. Preferred physical blowing agents are those with a boiling point between 0 °C and 80 °C.

[0056] In the process according to the invention, it is preferred that the additional blowing agent is a fluorinated ether.

[0057] Furthermore, in the process according to the invention, it is preferred that the additional blowing agent is a hydrofluoroolefin. More preferably, the hydrofluoroolefin is trans-1-chloro-3,3,3-trifluoropropene.

[0058] The amount of blowing agent in the mixture generally depends on the desired foam density. Preferably, it is selected relative to the amount of the melamine-formaldehyde precondensate such that the density of the foam is 5 kg / m 3 to 150 kg / m 3 、more preferably 10 kg / m 3 to 100 kg / m 3 、most preferably 12.5 kg / m 3 to 75 kg / m 3 of the amount.

[0059] Furthermore, in another embodiment of the invention, it is preferred to add additional water to the mixture M, where 1 wt% to 30 wt% of additional water is added, preferably 5 wt% to 25 wt% of additional water, based on the total weight of the mixture M after the addition of water.

[0060] In the present invention, it is preferred that the mixture M does not contain i) any functional powder, in particular no calcium carbonate powder and no calcined kaolin, ii) any aluminum powder and / or iii) any accelerator, in particular no aqueous cobalt naphthenate, no aqueous cobalt isooctanoate and no aqueous potassium isooctanoate.

[0061] In the context of the present invention, the term "mixture M does not contain any" means that mixture M contains an amount less than 0.01% by weight (based on the total weight of mixture M), preferably an amount less than 0.001% by weight, more preferably an amount less than 0.0001% by weight of the respective component, and most preferably mixture M is completely free of said component (less than 100 ppm).

[0062] In another embodiment of the present invention, mixture M comprises:

[0063] a) based on the total weight of said mixture M, 30% to 90% by weight of said at least one melamine - formaldehyde pre - condensate, preferably based on the total weight of mixture M,

[0064] 40% to 80% by weight of said melamine - formaldehyde pre - condensate, more preferably based on the total weight of mixture M, 51% to 75% by weight of said melamine - formaldehyde pre - condensate, and / or

[0065] b) based on the total weight of said mixture M, 0.5% to 10% by weight of hydrogen peroxide as contained in said aqueous hydrogen peroxide solution, preferably based on the total weight of mixture M, 1% to 7.5% by weight of hydrogen peroxide as contained in said aqueous hydrogen peroxide solution, and / or

[0066] c) based on the total weight of said mixture M, 0.5% to 10% by weight of said at least one surfactant, preferably based on the total weight of mixture M, 1% to 7.5% by weight of said at least one surfactant, and / or

[0067] d) optionally, based on the total weight of said mixture M, 0% to 40% by weight of a blowing agent, preferably based on the total weight of mixture M, 0.5% to 30% by weight of a blowing agent, and / or

[0068] e) based on the total weight of mixture M, 1% to 69% by weight of additional water as contained in and / or additionally added to the aqueous hydrogen peroxide solution.

[0069] It is clear to those skilled in the art that the sum of the weight percentages of the components contained in mixture M generally totals 100% by weight.

[0070] In this embodiment of the present invention, more preferably, the at least one surfactant is a surfactant mixture of the following substances: i) 50% to 90% by weight of at least one anionic surfactant, preferably the at least one surfactant is an anionic surfactant selected from the following: dibenzofuran sulfonate, alkane and alkylbenzene sulfonate, alkylnaphthalene sulfonate, olefin sulfonate, alkyl ether sulfonate, fatty alcohol sulfate, ether sulfate, α-sulfo fatty acid ester, acylaminoalkane sulfonate, acylhydroxyethyl sulfonate, alkyl ether carboxylate, N-acyl sarcosinate, alkyl and alkyl ether phosphate, and ii) based on the total weight of the surfactant mixture, 10% to 50% by weight of at least one nonionic surfactant, wherein the at least one nonionic surfactant is preferably selected from alkylphenol polyglycol ether, fatty alcohol polyglycol ether, fatty acid polyglycol ether, fatty acid alkanolamide, ethylene oxide-propylene oxide block copolymer, amine oxide, glycerol fatty acid ester, sorbitan ester and alkyl polyglycoside.

[0071] In this even more preferred embodiment of the present invention, mixture M does not contain i) any functional powder, in particular no calcium carbonate powder and no calcined kaolin, ii) any aluminum powder and / or iii) any accelerator, in particular no aqueous cobalt naphthenate, no aqueous cobalt isooctanoate and no aqueous potassium isooctanoate.

[0072] According to one embodiment of the present invention, it is particularly preferred that mixture M contains:

[0073] a) 51% to 75% by weight of a melamine-formaldehyde precondensate, based on the total weight of mixture M,

[0074] b) 0.5% to 10% by weight of hydrogen peroxide as contained in the aqueous hydrogen peroxide solution, preferably 1% to 7.5% by weight of hydrogen peroxide as contained in the aqueous hydrogen peroxide solution, based on the total weight of the mixture M, and / or

[0075] c) 1% to 7.5% by weight of at least one surfactant, based on the total weight of mixture M, and / or

[0076] d) Optionally, 0% to 40% by weight of a blowing agent, based on the total weight of mixture M, and / or

[0077] e) 1% to 69% by weight of additional water as contained in and / or additionally added to the aqueous hydrogen peroxide solution, based on the total weight of mixture M.

[0078] It is clear to those skilled in the art that the sum of the weight percentages of the components contained in mixture M generally totals 100% by weight.

[0079] In this embodiment of the present invention, more preferably, the at least one surfactant is a surfactant mixture of the following substances: i) 50% to 90% by weight of at least one anionic surfactant, preferably the at least one surfactant is an anionic surfactant selected from the following: dibenzofuran sulfonate, alkane and alkylbenzene sulfonate, alkylnaphthalene sulfonate, olefin sulfonate, alkyl ether sulfonate, fatty alcohol sulfate, ether sulfate, α-sulfo fatty acid ester, acylaminoalkane sulfonate, acylhydroxyethyl sulfonate, alkyl ether carboxylate, N-acylsarcosinate, alkyl and alkyl ether phosphates, and ii) based on the total weight of the surfactant mixture, 10% to 50% by weight of at least one nonionic surfactant, wherein the at least one nonionic surfactant is preferably selected from 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 alkyl polysaccharides.

[0080] In this even more preferred embodiment of the present invention, mixture M does not contain i) any functional powder, in particular does not contain calcium carbonate powder and does not contain calcined kaolin, ii) any aluminum powder and / or iii) any accelerator, in particular does not contain aqueous cobalt naphthenate, does not contain aqueous cobalt isooctanoate and does not contain aqueous potassium isooctanoate.

[0081] In addition, mixture M according to the present invention may optionally contain at least one halogen-free flame retardant. The at least one halogen-free flame retardant means one halogen-free flame retardant or a mixture of two or more halogen-free flame retardants. The at least one halogen-free flame retardant can be solid or liquid. The halogen-free flame retardant is usually added to mixture M before foaming, or applied as a coating after foam preparation.

[0082] Halogen-free flame retardants are known to those skilled in the art. For example, halogen-free flame retardants are disclosed in European Patent Application No. 21200402.2-1107.

[0083] The halogen-free flame retardant is preferably present in a total amount of 0.5% to 40% by weight, more preferably in a total amount of 2.5% to 25% by weight, and most preferably in a total amount of 5% to 20% by weight based on the melamine resin foam.

[0084] In another embodiment, mixture M does not contain silicate. In the context of the present invention, the term "does not contain silicate" means that the mixture contains no more than 1% by weight of silicate based on the total amount of mixture M, no more than 0.1% by weight of silicate based on the total amount of mixture M in another embodiment, and in another embodiment, mixture M substantially does not contain silicate, such as does not contain silicate at all.

[0085] In another embodiment, no acidic compound is added to the mixture M as a curing agent to catalyze the further condensation of the melamine resin. Preferably, no acidic compound selected from the following is added to the mixture M: formic acid, hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, acetic acid, oxalic acid, toluenesulfonic acid, sulfamic acid, acid anhydrides, and mixtures thereof. Most preferably, no formic acid is added to the mixture M.

[0086] In another embodiment according to the present invention, preferably, the melamine resin foam has a bulk density in the following range: 5 kg / m 3 to 150 kg / m 3 , more preferably 10 kg / m 3 to 100 kg / m 3 and most preferably 12.5 kg / m 3 to 75 kg / m 3 .

[0087] Those skilled in the art know how to determine / measure the corresponding density. This can be done by the method according to DIN EN ISO845:2009.

[0088] In another embodiment according to the present invention, preferably, the melamine resin foam has a Shore hardness of 10 to 100, more preferably 10 to 60.

[0089] Those skilled in the art know how to determine / measure the corresponding Shore hardness. This can be done, for example, by the method according to ASTM D2240:2015. According to the present invention, for the measurement of low-density foams, the 000 scale (sphere diameter 2.4 mm, spring force 1.111 N) is used.

[0090] Finally, the resulting foamed material can be dried to remove residual water and blowing agent from the foam. The drying is preferably carried out in an oven at a temperature in the range of 40 °C to 200 °C, particularly preferably 100 °C to 150 °C, until constant weight. The described method provides blocks or plates of foamed material, which can be cut into dimensions of any desired shape.

[0091] The melamine resin foam prepared by the method according to the present invention can be post-treated by the following methods:

[0092] 1. Thermal compression to obtain foams with higher density, better durability, and cleaning behavior. These foams can be produced according to EP2922901.

[0093] 2. Hydrophobization to obtain foams with lower water intake and

[0094] 3. Optionally, impregnate with a flame retardant to further improve the FST properties (flame, smoke, toxicity) in case of fire.

[0095] As described in WO 2007 / 023118, hydrophilization can be achieved by impregnating with a fluorocarbon resin and / or a silicone resin and additionally impregnating with a flame retardant substance such as a silicate, borate, hydroxide or phosphate.

[0096] In another preferred embodiment of the present invention, the method for producing melamine foam comprises the following steps:

[0097] a) adding the at least one melamine - formaldehyde pre - condensate, hydrogen peroxide solution, the at least one surfactant, optionally additional water and optionally the at least one blowing agent at a temperature between 50 °C and 80 °C to obtain an aqueous mixture M,

[0098] b) foaming the aqueous mixture M at a temperature between 50 °C and 80 °C,

[0099] c) optionally, tempering the resulting foam from step b) at 50 °C to 80 °C for 50 minutes to 70 minutes.

[0100] Another subject of the present invention is a melamine resin foam obtainable by the method as defined in detail above.

[0101] Another subject of the present invention is the use of a melamine resin foam obtainable by the method as described in detail above for sound insulation and / or heat insulation, construction and building, furniture and cushioning applications, packaging applications, cleaning applications, filter and / or agricultural applications.

[0102] In particular, the melamine resin foam obtained by the method of the present invention can be used in construction and / or building, i.e., for cushioning and furniture (such as seats, sofas, mattresses) in leisure or office environments or for transportation (such as seats, headrests and armrests) in trains, airplanes and cars. Further applications are in packaging, i.e., as packaging materials for protecting delivered items; cleaning applications, such as cleaning sponges; floor mats; hand pads; as filter media; or in acoustic applications in construction and / or building, such as absorbers for indoor acoustics in offices, schools, restaurants, anechoic chambers, furniture, partition walls; acoustic elements in walls and ceilings; and mufflers in air - conditioning or transportation applications, such as absorbers in cars, under - hood absorbers for noise reduction, or indoor absorbers such as roof liners, sun visors or hat racks. Further applications include heat insulation in industrial applications, such as insulation of pipes or air - conditioning units or insulation of walls and roofs in buildings and / or construction. Applications in agriculture include growth substrates and flower foams.

[0103] The present invention will be explained in more detail below by way of examples, but the present invention is not limited to these examples. Examples

[0104] Hereinafter, the present invention will be described in more detail and specifically with reference to examples. However, these examples are not intended to limit the present invention.

[0105] Method

[0106] Shore hardness

[0107] Measurements were carried out in accordance with ASTM D 2240-15. For the measurement of low-density foams, a scale of 000 was used (sphere diameter 2.4 mm, spring force 1.111 N).

[0108] Density

[0109] Measurements were carried out in accordance with DIN EN ISO 845-2009.

[0110] Material

[0111] MF Melamine-formaldehyde precondensate with an average molecular weight (number average) M of 350 g / mol and a molar ratio of melamine:formaldehyde of 1:3, which does not contain additional thermosetting formers other than melamine, and does not contain additional aldehydes other than formaldehyde, and which does not contain sulfite groups.

[0112] SM Surfactant mixture: Hostapur SAS-30, Clariant / Lutensol AT80 (BASF) in a ratio of 80 / 20

[0113] 30 wt% of H 2 O 2 aqueous solution (Sigma Aldrich)

[0114] trans-1-chloro-3,3,3-trifluoropropene, pentane

[0115] Comparative Examples 1-14

[0116] C1 .

[0117] Dissolve 225 of spray-dried melamine-formaldehyde precondensate MF (molar ratio 1:3) in 90 g of water, and then mix 3.375 g of a surfactant mixture: Hostapur SAS-30, Clariant / Lutensol AT80 (BASF) in a ratio of 80 / 20, 6.75 g of sodium formate, and 6.85 g of formic acid and 6 g of pentane at a temperature of 20 °C to 35 °C. Subsequently introduce this mixture into a polypropylene mold for foaming and irradiate it with microwave energy in a microwave oven. After the foaming is completed, anneal the obtained body in a circulating air oven at 200 °C for 20 minutes.

[0118] C2-C14

[0119] Prepare samples C2 to C14 according to the procedure described in detail for C1, but with different pentane contents as visible in Table 1.

[0120] Table 1: Comparative Examples C1-C14

[0121] # Pentane / g <![CDATA[Density / kg / m 3 > Shore hardness 000 C1 6 45 112 C2 7 42.5 99 C3 8 40 99 C4 9 37.5 93 C5 10 35 88 C6 11 32.5 86 C7 12 30 84 C8 13 27.5 83 C9 14 25 81 C10 16 22.5 70 C11 17 20 68 C12 18 17.5 67 C13 22 15 63 C14 30 12.5 52

[0122] Examples I1-I18 of the present invention

[0123] I1

[0124] In a temperature-controlled 10-L glass container at 60 °C, mix 35 g of solid MF resin, 7.5 g of water, 7 g of 30 wt% hydrogen peroxide solution, and 2 g of surfactant mixture SM and stir for 30 s. The atmosphere in the container is flowed with nitrogen. After a few minutes, foaming starts. Keep the obtained foam in the container at 60 °C for 60 minutes to fully cure. Then, apply a release agent for demolding to remove the foam from the container.

[0125] O2-O5

[0126] Prepare samples O2 to O5 according to the procedure described in detail for O1, but with different hydrogen peroxide solution contents as visible in Table 2.

[0127] I6

[0128] In a temperature-controlled 10-L glass container at 60 °C, mix 35 g of solid MF resin, 7.5 g of water, 11 g of 30 wt% hydrogen peroxide solution, 2 g of surfactant mixture SM, and 1 g of HFO blowing agent and stir for 30 s. The atmosphere in the container is flowed with nitrogen. After a few minutes, foaming starts. Keep the obtained foam in the container at 60 °C for 60 minutes to fully cure. Then, apply a release agent for demolding to remove the foam from the container.

[0129] I7-I18

[0130] Samples I7 to I18 were prepared according to the procedure described in detail for I6, but with different hydrogen peroxide solution and HFO blowing agent contents as visible in Table 2.

[0131] Table 2: Examples of the present invention

[0132] # <![CDATA[30 wt% H 2 P 2 solution / g]]> HFO blowing agent / g <![CDATA[Density / kg / m 3 > Shore hardness 000 I1 7 0 94 95 I2 8 0 78 88 I3 9 0 72 76 I4 10 0 65 72 I5 11 0 56 59 I6 11 1 44 52 I7 11 2 34 46 I8 11 3 33 44 I9 11 4 28 39 I10 11 5 27 39 I11 11 6 25 37 I12 11 7 23 34 I13 11 8 21 32 I14 11 9 20 29 I15 11 10 17 27 I16 11 11 16 26 I17 11 12 12 23 I18 11 13 11 22

[0133] As visible in Tables 1 and 2, the method of the present invention yields density and Shore hardness values comparable to those of the comparative examples. However, according to the method of the present invention, it is not necessary to apply pentane and microwave heating.

Claims

1. A method for producing melamine resin foam, the method comprising foaming an aqueous mixture M, the mixture M comprising at least one melamine-formaldehyde precondensate, an aqueous hydrogen peroxide solution, and at least one surfactant.

2. The method according to claim 1, wherein a) the melamine-formaldehyde precondensate has a molar ratio of melamine to formaldehyde in the range of 1:5 to 1:1.3 [mol / mol], preferably 1:3.5 to 1:1.5 [mol / mol], and / or b) The number-average molecular weight M of the melamine-formaldehyde precondensate n is in the range of 200 g / mol to 1000 g / mol (determined by gel permeation chromatography).

3. The method according to claim 1 or 2, wherein the aqueous hydrogen peroxide solution comprises 3 wt% to 50 wt%, preferably 6 wt% to 37 wt%, more preferably 25 wt% to 35 wt% of hydrogen peroxide based on the total weight of the hydrogen peroxide solution.

4. The method according to any one of claims 1 to 3, wherein a) the at least one surfactant is an anionic surfactant, preferably the at least one surfactant is an anionic surfactant selected from the group consisting of dibenzofuran sulfonates, alkane and alkylbenzene sulfonates, alkylnaphthalene sulfonates, olefin sulfonates, alkyl ether sulfonates, fatty alcohol sulfates, ether sulfates, α-sulfo fatty acid esters, acylaminoalkane sulfonates, acylhydroxyethyl sulfonates, alkyl ether carboxylates, N-acyl sarcosinates, alkyl and alkyl ether phosphates, or b) the at least one surfactant is a nonionic surfactant, preferably the at least one surfactant is a nonionic surfactant selected from the group consisting of 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 alkyl polyglycosides, and / or c) the at least one surfactant is a surfactant mixture of at least one anionic surfactant in an amount of 50 wt% to 90 wt% and at least one nonionic surfactant in an amount of 10 wt% to 50 wt% based on the total weight of the surfactant mixture.

5. The method according to any one of claims 1 to 4, wherein the mixture M comprises an additional blowing agent, wherein a) preferably, the blowing agent is at least one physical blowing agent i) selected from hydrocarbons, preferably selected from C 5 -C 7 hydrocarbons or halogenated hydrocarbons, more preferably selected from chlorinated hydrocarbons or fluorinated hydrocarbons, and / or ii) selected from alcohols, ethers, ketones, and esters, and / or b) the blowing agent has a boiling point between 0 °C and 80 °C, and / or c) the mixture M comprises 0.5 wt% to 30 wt% of the blowing agent based on the total weight of the mixture M, preferably 1.5 wt% to 20 wt% of the blowing agent based on the total weight of the mixture M.

6. The method according to any one of claims 1 to 5, wherein additional water is added to the mixture M, wherein 1 wt% to 30 wt% of additional water is added based on the total weight of the mixture M after the addition of water, preferably 5 wt% to 25 wt% of additional water is added based on the total weight of the mixture M after the addition of water.

7. The method according to any one of claims 1 to 6, wherein no acidic compound selected from the following is added to the mixture M: formic acid, hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, acetic acid, oxalic acid, toluenesulfonic acid, sulfamic acid, acid anhydrides, and mixtures thereof, in particular, formic acid is not added to the mixture M.

8. The method according to any one of claims 1 to 7, wherein the mixture M comprises a) based on the total weight of the mixture M, 30% to 90% by weight of the at least one melamine - formaldehyde pre - condensate, preferably based on the total weight of the mixture M, 40% to 80% by weight of the melamine - formaldehyde pre - condensate, more preferably based on the total weight of the mixture M, 51% to 75% by weight of the melamine - formaldehyde pre - condensate, and / or b) based on the total weight of the mixture M, 0.5% to 10% by weight of hydrogen peroxide as contained in the aqueous hydrogen peroxide solution, preferably based on the total weight of the mixture M, 1% to 7.5% by weight of hydrogen peroxide as contained in the aqueous hydrogen peroxide solution, and / or c) based on the total weight of the mixture M, 0.5% to 10% by weight of the at least one surfactant, preferably based on the total weight of the mixture M, 1% to 7.5% by weight of the at least one surfactant, and / or d) optionally, based on the total weight of the mixture M, 0% to 40% by weight of a blowing agent, preferably based on the total weight of the mixture M, 0.5% to 30% by weight of a blowing agent, and / or e) based on the total weight of the mixture M, 1% to 69% by weight of additional water as contained in and / or additionally added to the aqueous hydrogen peroxide solution.

9. The method according to any one of claims 1 to 8, wherein the mixture M does not contain i) any functional powder, in particular does not contain calcium carbonate powder and does not contain calcined kaolin, ii) any aluminum powder and / or iii) any accelerator, in particular does not contain aqueous cobalt naphthenate, does not contain aqueous cobalt isooctanoate, and does not contain aqueous potassium isooctanoate.

10. The method according to any one of claims 1 to 9, wherein the melamine resin foam has a bulk density in the following range: 5 kg / m 3 to 150 kg / m 3 , more preferably 10 kg / m 3 to 100 kg / m 3 , and most preferably 12.5 kg / m 3 to 75 kg / m 3 .

11. The method according to any one of claims 1 to 10, wherein the melamine resin foam has a Shore hardness of 10 to 100, more preferably 10 to 60 (determined according to ASTM D2240:2015).

12. A method for producing a melamine resin foam according to any one of claims 1 to 11, the method comprising the following steps: a) adding the at least one melamine - formaldehyde pre - condensate, hydrogen peroxide solution, the at least one surfactant, optionally additional water, and optionally the at least one blowing agent at a temperature between 50°C and 80°C to obtain an aqueous mixture M, b) foaming the aqueous mixture M at a temperature between 50°C and 80°C, c) optionally, tempering the resulting foam from step b) at 50°C to 80°C for 50 minutes to 70 minutes.

13. A melamine resin foam, which can be obtained by the method according to any one of claims 1 to 12.

14. Use of the melamine resin foam according to any one of claims 1 to 13 for sound insulation and / or thermal insulation, construction and building, furniture and cushioning applications, packaging applications, cleaning applications, filters and / or agricultural applications.