Melamine resin foam produced by oxidation reaction

Abstract

The present invention relates to a method for producing a melamine resin foam, comprising 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.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a melamine resin foam, comprising 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.

[0002] Melamine resin foams are used in a variety of applications, including sound absorption in acoustic chambers and thermal insulation in buildings and pipes. In the current state of the art, melamine foams are generally prepared by reacting a melamine-formaldehyde precondensate with an acid as a curing agent. Additionally, a physical blowing agent, such as a hydrocarbon, especially pentane, is typically used. Because the aforementioned reaction is fairly low in exothermicity, the reaction / foaming mixture is typically heated to ensure the resin cures and foams. Heating in the current state of the art is accomplished using an external heat source, such as microwave irradiation or hot air.

[0003] However, the application of external heat and especially microwave radiation as described in the prior art and commonly applied to produce melamine resin foams can have drawbacks, for example because it is difficult to keep the microwave power constant during the course of production.

[0004] Furthermore, as described in the prior art, hydrocarbons used as physical blowing agents, particularly pentane, are flammable and can easily lead to the formation of an explosive atmosphere. Therefore, the production of the described melamine resin foams according to the state of the art requires advanced safety equipment and procedures.

[0005] German Patent Application Publication No. 2915467 relates to the preparation of elastic foams based on melamine-formaldehyde condensates by foaming an aqueous solution or dispersion containing a melamine-formaldehyde precondensate, an emulsifier, a volatile blowing agent, and a curing agent. Organic and inorganic acids are disclosed as curing agents. The mixture is foamed in a hot air atmosphere at 150°C. German Patent Application Publication No. 2915467 does not disclose a method involving aqueous hydrogen peroxide, which would avoid excessive heating during foaming.

[0006] CN109836548 discloses a method for preparing a melamine-based foam, which includes 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. CN109836548 does not disclose a method involving aqueous hydrogen peroxide or a method not involving n-pentane, which can avoid microwave heating during foaming.

[0007] EP 3750952 A1 relates to a method for producing melamine-formaldehyde foam using a fluorinated blowing agent, which involves heating and foaming a mixture containing 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 selected from inorganic or organic acids that catalyzes condensation, and the blowing agent contains 5 to 20% by weight of a fluorinated ether and 80 to 95% by weight of a hydrocarbon such as pentane. The precondensate is foamed by heating the mixture using microwave irradiation. EP 3750952 A1 does not disclose a method involving aqueous hydrogen peroxide or a method not involving n-pentane, which would avoid microwave heating during foaming.

[0008] WO 2018 / 098056 relates to cleaning implements containing melamine-formaldehyde foam for cleaning hard surfaces such as tiles, showers, and sinks, including a method for producing the foam. A mixture containing a melamine-formaldehyde precondensate, at least one linear polymer, a curing agent, a dispersant, and a foaming agent is heated by either hot air or high-frequency radiation to foam. The curing agent may be either an inorganic or organic acid. The foam may be impregnated with an active agent for cleaning surfaces, such as a mixture of surfactants, biocides, bleaching agents, limescale reducers, greasy stain removers, and the like. WO 2018 / 098056 does not disclose the preparation of melamine resin foams by 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 relates to cleaning articles containing melamine-formaldehyde foams containing hollow microspheres for removing dirt and stains from hard surfaces. Surface-cleaning active agents, such as mixtures of surfactants, biocides, bleaching agents, limescale reducers, greasy soil removers, etc., can be contained in the microspheres and impregnated into the foam. WO 2014 / 172357 does not disclose the preparation of melamine resin foams by 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 relates to cleaning articles comprising melamine-formaldehyde foams for removing dirt and stains from hard surfaces. The foams can be impregnated with active agents for cleaning surfaces, such as mixtures of surfactants, biocides, bleaching agents, limescale reducers, greasy soil removers, etc. WO 2019 / 060647 does not disclose the preparation of melamine resin foams by 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.

[0011] U.S. Patent No. 3,864,137 relates to the production of foams by mixing an aqueous silicate solution with hydrogen peroxide as a blowing agent to obtain a structure consisting essentially of silicate, which may also contain inorganic or organic fillers. U.S. Patent No. 3,864,137 does not disclose the preparation of melamine resin foams by the method of the present invention.

[0012] Chinese Patent No. 103553700 relates to an environmentally friendly magnesium oxide material, in which the raw materials for foaming contain 80-90% by weight of calcined magnesium powder, a filler, and a composite blowing agent, and the composite blowing agent may contain 20-40% by weight of peroxide. The raw materials may also contain organic or inorganic fillers such as zeolite, fly ash, and / or waste tire rubber, and 5-10% by weight of melamine resin. Chinese Patent No. 103553700 does not disclose the preparation of melamine resin foam by 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] Chinese Patent No. 102603353 relates to a foaming agent for foaming concrete, which contains 35-45% by weight of hydrogen peroxide. Chinese Patent No. 102603353 does not disclose melamine resin foam or the method according to the present invention.

[0014] Chinese Patent No. 110372995 relates to an environmentally friendly modified melamine-formaldehyde-melamine resin foam material obtained from a mixture of the following weight parts of raw materials: 65-80 parts modified melamine-formaldehyde melamine resin; 3-6 parts foam stabilizer; 0.2-2 parts blowing agent; 20-35 parts functional powder; 0.2-0.5 parts dispersant; 0.3-0.6 parts accelerator; and 2-5 parts curing agent. The blowing agent preferably includes industrial hydrogen peroxide and aluminum powder. The method according to Chinese Patent No. 110372995 is disadvantageous because it relies on the essential use of powders, particularly large amounts of functional powder and / or aluminum powder as a blowing agent. Such powders are problematic from a safety standpoint, as they react with hydrogen peroxide to form (larger amounts of) hydrogen. Furthermore, the method according to Chinese Patent No. 110372995 requires the use of acids such as sulfuric acid, hydrochloric acid, phosphoric acid, oxalic acid, acetic acid, and acrylic acid.

[0015] The present invention aims to provide a novel method for producing melamine resin foams. Furthermore, the novel method should have beneficial properties with respect to avoiding the use of excessive external heating or microwave irradiation, especially in connection with flammable / explosive hydrocarbon blowing agents.

[0016] This object relates to a method for producing a 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 foams for thermal insulation or sound-absorbing and thermal insulation applications, for example. By using the method of the present invention, certain drawbacks of the methods of producing melamine resin foams disclosed in the prior art can be avoided.

[0018] Surprisingly, it has been found that by applying the method of the present invention, it is possible to avoid external heating as described in the prior art, such as by using microwave irradiation or hot air.

[0019] Furthermore, it has surprisingly been found that by applying the method of the present invention, melamine resin foams can be produced without adding physical blowing agents such as hydrocarbons, e.g., pentane, or at least by significantly reducing the amount of physical blowing agent added. Thus, an advantage of the method of the present invention is that the presence of flammable / explosive physical blowing agents such as pentane during curing by external heating or microwave irradiation can be avoided, or at least the concentration of such physical blowing agents can be significantly reduced.

[0020] A further advantage of the process of the invention can be seen in the fact that it does not require the addition of hardeners / catalysts in the form of acids, in particular formic acid as applied in the state of the art.

[0021] Furthermore, the method of the present invention results in melamine resin foams having low Shore hardness, which can be useful in several applications. In particular, foams exhibiting low Shore hardness are very important for thermal insulation applications.

[0022] The present invention is more specifically as follows.

[0023] The present invention relates to a method for producing a melamine resin foam, comprising 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] The foaming of melamine-formaldehyde precondensates to obtain such melamine resin foams is known to those skilled in the art, as is the case with melamine precondensates.

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

[0026] Preferably, a) the melamine-formaldehyde precondensate has a molar ratio of melamine to formaldehyde ranging from 1:5 to 1:1.3 [mol / mol], preferably from 1:3.5 to 1:1.5 [mol / mol], and / or b) Number average molecular weight M of melamine-formaldehyde precondensate n is in the range of 200 g / mol to 1000 g / mol (measured by gel permeation chromatography).

[0027] Unmodified melamine-formaldehyde precondensates are preferred.

[0028] Those skilled in the art know how to determine the average molecular weight (number average) of such melamine-formaldehyde precondensates. For example, this can be done using gel permeation chromatography. The preparation and characterization of such melamine-formaldehyde precondensates are described, for example, in W. Woebang's Kunststoffhandbuch, Vol. 10, Duroplast, Munich, Vienna, 1988; Encyclopedia of Polymer Science and Technology, 3rd Edition, Vol. 1, Chapter 1, Amino Resins, pp. 340-370, 2003; or Ullmann's Encyclopedia of Industrial Chemistry, 6th Edition, Vol. 2, Chapter 3, Amino Resins, pp. 537-565, Weinheim, 2003.

[0029] Furthermore, in the present invention, it is preferred that the mixture M comprises 30 to 90% by weight of at least one melamine-formaldehyde precondensate relative to the total weight of the mixture M, preferably 40 to 80% by weight of melamine-formaldehyde precondensate relative to the total weight of the mixture M, more preferably 51 to 75% by weight of melamine-formaldehyde precondensate relative to the total weight of the mixture M.

[0030] Hydrogen peroxide and aqueous hydrogen peroxide solutions are known to those skilled in the art.

[0031] Within the scope of the present invention, a) The aqueous hydrogen peroxide solution contains (about) 3 to 50 wt %, preferably (about) 6 to 37 wt %, and more preferably (about) 25 to 35 wt % of hydrogen peroxide based on the total weight of the hydrogen peroxide solution.

[0032] Hydrogen peroxide itself as well as solutions of hydrogen peroxide in water, alcohol or ether are known to those skilled in the art.

[0033] In the method of the present invention, hydrogen peroxide is preferably applied as an aqueous solution of about 3 to 50% by weight hydrogen peroxide, preferably about 6 to 37% by weight hydrogen peroxide, more preferably about 25 to 35% by weight hydrogen peroxide, based on the total weight of the hydrogen peroxide solution.

[0034] Furthermore, according to the present invention, it is preferred that the mixture M contains 0.5 to 10 wt % of hydrogen peroxide contained in an aqueous hydrogen peroxide solution relative to the total weight of the mixture M, and preferably 1 to 7.5 wt % of hydrogen peroxide relative to the total weight of the mixture M.

[0035] Such surfactants are known to those skilled in the art. According to the present invention, anionic, cationic and nonionic surfactants and mixtures thereof can also be used as dispersing / emulsifying agents.

[0036] Useful anionic surfactants include, for example, diphenylene oxide sulfonates, alkane sulfonates, alkyl benzene sulfonates, alkyl naphthalene sulfonates, olefin sulfonates, alkyl ether sulfonates, fatty alcohol sulfates, ether sulfates, α-sulfofatty acid esters, acylaminoalkane sulfonates, acyl isethionates, alkyl ether carboxylates, N-acyl sarcosinates, alkyl phosphates, and alkyl ether phosphates.

[0037] 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.

[0038] Useful cationic emulsifiers include, for example, alkyltriammonium salts, alkylbenzyldimethylammonium salts, and alkylpyridinium salts.

[0039] According to the method of the present invention, a) at least one surfactant is an anionic surfactant, preferably at least one surfactant is an anionic surfactant selected from the group of diphenylene oxide sulfonates, alkanesulfonates, alkylbenzenesulfonates, alkylnaphthalenesulfonates, olefinsulfonates, alkyl ether sulfonates, fatty alcohol sulfates, ether sulfates, α-sulfofatty acid esters, acylaminoalkanesulfonates, acyl isethionates, alkyl ether carboxylates, N-acyl sarcosinates, alkyl, and alkyl ether phosphates, or b) at least one surfactant is a non-ionic surfactant, preferably at least one surfactant is a non-ionic surfactant selected from the group 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 preferably a surfactant mixture of: i) 50 to 90 wt. % of at least one anionic surfactant, preferably at least one surfactant selected from the group consisting of diphenylene oxide sulfonates, alkanesulfonates, alkylbenzenesulfonates, alkylnaphthalenesulfonates, olefinsulfonates, alkyl ether sulfonates, fatty alcohol sulfates, ether sulfates, α-sulfofatty acid esters, acylaminoalkanesulfonates, acyl isethionates, alkyl ether carboxylates, N-acylsarcosinates, alkyl phosphates, and alkyl ether phosphates; and ii) 10 to 50 wt. % of at least one nonionic surfactant, based on the total weight of the surfactant mixture, 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.

[0040] Furthermore, it is preferred that the mixture M contains 0.5 to 10% by weight of at least one surfactant relative to the total weight of the mixture M, preferably 1 to 7.5% by weight of at least one surfactant relative to the total weight of the mixture M.

[0041] In the process of the present invention, the mixture M may optionally further comprise at least one blowing agent, such blowing agents being known to those skilled in the art.

[0042] In the method of the present invention, a) Preferably, the blowing agent is i) selected from the group of hydrocarbons, preferably selected from the group of C5-C7 hydrocarbons or halogenated hydrocarbons, more preferably selected from the group of chlorinated or fluorinated hydrocarbons, and / or ii) at least one physical blowing agent selected from the group of alcohols, ethers, ketones and esters; and / or b) the blowing agent has a boiling point of 0 to 80°C, and / or c) Mixture M contains 0.5 to 30% by weight of a blowing agent relative to the total weight of mixture M, preferably 1.5 to 20% by weight of a blowing agent relative to the total weight of mixture M.

[0043] Physical blowing agents are known to those skilled in the art and are described, for example, in Encyclopedia of Polymer Science and Technology, Vol. I, 3rd Edition, Supplement, pp. 203-218, 2003.

[0044] Useful physical blowing agents include, for example, hydrocarbons such as butane, n-, iso-, or cyclopentane, hexane, halogenated, more specifically chlorinated and / or fluorinated hydrocarbons such as methylene chloride, chloroform, trichloroethane, chlorofluorocarbons, hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HCFs) such as methyl nonafluorobutyl ether and ethyl nonafluorobutyl ether, hydrofluoroolefins (HFOs) 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 have a boiling point of 0 to 80°C.

[0045] According to the method of the present invention, the additional blowing agent is preferably a fluorinated ether.

[0046] Further, according to the method of the present invention, the additional blowing agent is preferably a hydrofluoroolefin, more preferably trans-1-chloro-3,3,3-trifluoropropene.

[0047] The amount of blowing agent in the mixture generally depends on the desired density of the foam. Preferably, the amount of melamine-formaldehyde precondensate is such that the foam density is between 5 and 150 kg / m. 3 , more preferably 10 to 100 kg / m 3 , and most preferably 12.5 to 75 kg / m 3 The amount is selected.

[0048] Furthermore, in another embodiment of the present invention, additional water is added to the mixture M, and it is preferred that 1 to 30% by weight of additional water is added based on the total weight of the mixture M after the addition of water, and preferably 5 to 25% by weight of additional water is added based on the total weight of the mixture M after the addition of water.

[0049] In the present invention, it is preferred that the mixture M i) does not contain any functional powder, in particular does not contain calcium carbonate powder and calcined kaolin, ii) does not contain any aluminum powder, and / or iii) does not contain any accelerator, in particular does not contain an aqueous solution of cobalt naphthenate, cobalt isooctanoate, or potassium isooctanoate.

[0050] Within the context of the present invention, the term "free of mixture M" means that mixture M contains the respective component in an amount of less than 0.01% by weight (relative to the total weight of mixture M), preferably less than 0.001% by weight, more preferably less than 0.0001% by weight, and most preferably mixture M is completely free of said component (less than 100 ppm).

[0051] In a further embodiment of the invention, the mixture M is a) from 30 to 90% by weight, relative to the total weight of the mixture M, of at least one melamine-formaldehyde precondensate, preferably from 40 to 80% by weight, relative to the total weight of the mixture M, more preferably from 51 to 75% by weight, relative to the total weight of the mixture M, and / or b) 0.5 to 10% by weight of hydrogen peroxide in an aqueous hydrogen peroxide solution relative to the total weight of the mixture M, preferably 1 to 7.5% by weight of hydrogen peroxide in an aqueous hydrogen peroxide solution relative to the total weight of the mixture M, and / or c) 0.5 to 10% by weight of at least one surfactant, relative to the total weight of the mixture M, preferably 1 to 7.5% by weight of at least one surfactant, relative to the total weight of the mixture M, and / or d) optionally 0 to 40% by weight of a blowing agent, relative to the total weight of the mixture M, preferably 0.5 to 30% by weight of a blowing agent, relative to the total weight of the mixture M, and / or e) 1 to 69% by weight of additional water contained in the aqueous hydrogen peroxide solution and / or additionally added, based on the total weight of the mixture M.

[0052] It will be apparent to those skilled in the art that the weight percentages of the components contained within mixture M generally add up to 100% by weight.

[0053] In this embodiment of the invention, the at least one surfactant is i) 50 to 90 wt. % of at least one anionic surfactant, preferably the at least one surfactant is selected from the group consisting of diphenylene oxide sulfonates, alkanesulfonates, alkylbenzenesulfonates, alkylnaphthalenesulfonates, olefinsulfonates, alkyl ether sulfonates, fatty alcohol sulfates, ether sulfates, α-sulfofatty acid esters, acylaminoalkanesulfonates, acyl isethionates, alkyl ether carboxylates, N-acyl sarcosinates, alkyl phosphates, and More preferred is a surfactant mixture of an anionic surfactant selected from the group of alkyl ether phosphates and ii) 10 to 50 wt. % of at least one nonionic surfactant, based on the total weight of the surfactant mixture, 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.

[0054] In this embodiment of the invention, it is even more preferred that mixture M i) does not comprise any functional powders, in particular does not comprise calcium carbonate powder and calcined kaolin, ii) does not comprise any aluminum powder, and / or iii) does not comprise any accelerators, in particular does not comprise aqueous cobalt naphthenate, cobalt isooctanoate and potassium isooctanoate solutions.

[0055] According to one embodiment of the present invention, the mixture M comprises: a) 51 to 75% by weight of a melamine-formaldehyde precondensate, based on the total weight of the mixture M; b) 0.5 to 10% by weight of hydrogen peroxide in an aqueous hydrogen peroxide solution relative to the total weight of the mixture M, preferably 1 to 7.5% by weight of hydrogen peroxide in an aqueous hydrogen peroxide solution relative to the total weight of the mixture M, and / or c) 1 to 7.5% by weight, relative to the total weight of the mixture M, of at least one surfactant, and / or d) optionally 0 to 40% by weight of a blowing agent, relative to the total weight of the mixture M, and / or e) 1 to 69% by weight of additional water contained in the aqueous hydrogen peroxide solution and / or additionally added, based on the total weight of the mixture M.

[0056] It will be apparent to those skilled in the art that the weight percentages of the components contained within mixture M generally add up to 100% by weight.

[0057] In this embodiment of the present invention, it is more preferred that the at least one surfactant is a surfactant mixture of: i) 50 to 90 wt. % of at least one anionic surfactant, preferably at least one surfactant selected from the group consisting of diphenylene oxide sulfonates, alkanesulfonates, alkylbenzenesulfonates, alkylnaphthalenesulfonates, olefinsulfonates, alkyl ether sulfonates, fatty alcohol sulfates, ether sulfates, α-sulfofatty acid esters, acylaminoalkanesulfonates, acyl isethionates, alkyl ether carboxylates, N-acylsarcosinates, alkyl phosphates, and alkyl ether phosphates; and ii) 10 to 50 wt. % of at least one nonionic surfactant, based on the total weight of the surfactant mixture, 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.

[0058] In this embodiment of the invention, it is even more preferred that mixture M i) does not comprise any functional powders, in particular does not comprise calcium carbonate powder and calcined kaolin, ii) does not comprise any aluminum powder, and / or iii) does not comprise any accelerators, in particular does not comprise aqueous cobalt naphthenate, cobalt isooctanoate and potassium isooctanoate solutions.

[0059] Furthermore, the mixture M according to the present invention may optionally contain at least one halogen-free flame retardant. 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 may be solid or liquid. The halogen-free flame retardant is generally added to the mixture M before foaming or applied as a coating after foam preparation.

[0060] 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.

[0061] The halogen-free flame retardant is preferably present in a total amount of 0.5 to 40% by weight, more preferably 2.5 to 25% by weight, and most preferably 5 to 20% by weight, based on the melamine resin foam.

[0062] In a further embodiment, the mixture M is silicate-free. In the context of the present invention, the term "silicate-free" means essentially free of silicates, such as containing 1% or less by weight of silicates relative to the total amount of the mixture M, in another embodiment 0.1% or less by weight of silicates relative to the total amount of the mixture M, and in a further embodiment the mixture M is completely free of silicates.

[0063] In a further embodiment, no acidic compound is added to mixture M as a curing agent to catalyze further condensation of the melamine resin. Preferably, no acidic compound selected from the group consisting of formic acid, hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, acetic acid, oxalic acid, toluenesulfonic acid, amidosulfonic acid, acid anhydrides, and mixtures thereof is added to mixture M. Most preferably, no formic acid is added to mixture M.

[0064] In a further embodiment according to the invention, the melamine resin foam has a viscosity of 5 to 150 kg / m 3 , more preferably 10 to 100 kg / m 3 , and most preferably 12.5 to 75 kg / m 3 It is preferred that the bulk density be in the range of 1000 .mu.m.sup.2.

[0065] A person skilled in the art knows how to determine / measure the respective density, which can be done by the method according to DIN EN ISO 845:2009.

[0066] In a further embodiment according to the present invention, the melamine resin foam preferably has a Shore hardness of 10-100, more preferably 10-60.

[0067] Those skilled in the art know how to determine / measure the respective Shore hardness. This can be done, for example, by the method described in ASTM D2240:2015. According to the present invention, for the measurement of low density foam, a scale of 000 was used (sphere diameter 2.4 mm, spring force 1.111 N).

[0068] The resulting foamed material can then be dried to remove residual water and blowing agent from the foam. Drying is preferably carried out in a drying oven at temperatures between 40 and 200°C, more preferably between 100 and 150°C, until a constant weight is reached. The described method provides blocks or slabs of foamed material that can be cut to any desired shape or size.

[0069] The melamine resin foams prepared by the process according to the invention can be post-treated by the following methods: 1. Hot compression to obtain foams with higher density, better durability and cleaning behavior. These foams can be produced according to EP 2922901. 2. Hydrophobization to obtain foams with lower water absorption and 3. Possibly impregnation with flame retardants to further improve the FST properties (flame, smoke, toxicity) in case of fire.

[0070] As described in WO 2007 / 023118, hydrophilization can be achieved by impregnation with fluorocarbon and / or silicone resins, as well as additional impregnation with flame-retardant substances such as silicates, borates, hydroxides or phosphates.

[0071] In a further preferred embodiment of the present invention, the method for producing melamine foam comprises the steps of: a) adding at a temperature of 50-80°C at least one melamine-formaldehyde precondensate, a hydrogen peroxide solution, at least one surfactant, optionally additional water, and optionally at least one blowing agent to obtain an aqueous mixture M; b) foaming the aqueous mixture M at a temperature between 50 and 80°C; c) optionally tempering the foam obtained from step b) at 50-80°C for 50-70 minutes.

[0072] Another subject of the present invention is a melamine resin foam obtainable by the process defined in detail above.

[0073] Another subject of the present invention is the use of the melamine resin foam obtained by the process described in detail above for acoustic and / or thermal insulation, building and construction, furniture and cushioning applications, packaging applications, cleaning applications, filters and / or agricultural applications.

[0074] In particular, the melamine resin foam obtained by the method of the present invention can be used in buildings and / or structures, i.e., for cushioning and furniture in leisure or office environments, such as seats, sofas, mattresses, or seats, headrests, and armrests in trains, airplanes, and automobiles. Further applications include packaging, i.e., packaging materials for protecting deliveries; cleaning applications, such as cleaning sponges, floor pads, and hand pads; filter media; and acoustic applications in buildings and / or structures, such as offices, schools, restaurants, noise chambers, furniture, separation walls, and acoustic elements in walls and ceilings; and sound absorbers in air conditioning or transportation applications, such as automobile sound absorbers, under-hood motors for noise reduction, or indoor sound absorbers, such as headliners, sun visors, or hat racks. Further applications include industrial insulation, such as pipe insulation or insulation for air conditioning units, or wall and roof insulation in buildings and / or structures. Agricultural applications include cultivation substrates and floral foams.

[0075] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. [Example]

[0076] The present invention will be described in more detail and specifically below with reference to examples, but these are not intended to limit the present invention.

[0077] [method] Shore hardness Measurements were made according to ASTM D 2240-15. For measurements of low density foams, a 000 scale was used (sphere diameter 2.4 mm, spring force 1.111 N).

[0078] ·density The measurements were carried out in accordance with DIN EN ISO 845-2009.

[0079] [material] MF A melamine-formaldehyde precondensate having a molar ratio of melamine:formaldehyde of 1:3 and an average molecular weight (number average) M of 350 g / mol, which contains no further thermoset formers besides melamine, no further aldehydes besides formaldehyde and no sulfite groups. SM surfactant mixture: Hostapur SAS-30, Clariant / Lutensol AT80, BASF, ratio 80 / 20 30 wt% H2O2 aqueous solution, Sigma Aldrich trans-1-chloro-3,3,3-trifluoropropene, pentane

[0080] [Comparative examples C1 to C14] C1 225 g of spray-dried melamine-formaldehyde precondensate MF (1:3 molar ratio) was dissolved in 90 g of water and then mixed with 3.375 g of a surfactant mixture (80 / 20 ratio): Hostapur SAS-30, Clariant / Lutensol AT80, BASF, 6.75 g of sodium formate, 6.85 g of formic acid, and 6 g of pentane at a temperature of 20-35 °C. The mixture was then introduced into a foaming polypropylene mold and irradiated with microwave energy in a microwave oven. After foaming was complete, the resulting mass was annealed in a circulating air oven at 200 °C for 20 minutes.

[0081] C2~C14 Samples C2-C14 were prepared according to the procedure detailed for C1, but with varying pentane content as seen in Table 1. [Table 1]

[0082] [Examples I1 to I18 of the present invention] I1 In a 10 L temperature-controlled glass container at 60°C, 35 g of solid MF resin, 7.5 g of water, 7 g of a 30 wt% hydrogen peroxide solution, and 2 g of surfactant mixture SM were mixed and stirred for 30 seconds. The atmosphere in the container was flushed with nitrogen. After a few minutes, foaming began. The resulting foam was kept in the container at 60°C for 60 minutes to fully cure. After that, a mold release agent was applied and the foam was removed from the container.

[0083] I2~I5 Samples I2-I5 were prepared according to the procedure detailed for I1, but with varying hydrogen peroxide solution content as seen in Table 2.

[0084] I6 In a 10-liter glass container controlled at 60°C, 35 g of solid MF resin, 7.5 g of water, 11 g of a 30 wt% hydrogen peroxide solution, 2 g of surfactant mixture SM, and 1 g of HFO blowing agent were mixed and stirred for 30 seconds. The atmosphere in the container was flushed with nitrogen. After a few minutes, foaming began. The resulting foam was kept in the container at 60°C for 60 minutes to fully cure. After that, a mold release agent was applied and the foam was removed from the container.

[0085] I7~I18 Samples I7-I18 were prepared according to the procedure detailed for I6, but with varying hydrogen peroxide solution and HFO blowing agent contents as seen in Table 2. [Table 2]

[0086] As can be seen from Tables 1 and 2, the method of the present invention results in density and Shore hardness values ​​comparable to the comparative examples, however, with the method of the present invention, it is not necessary to apply pentane and microwave heating.

Claims

1. 1. A method for producing a melamine resin foam, comprising 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.

2. a) the melamine-formaldehyde precondensate has a molar ratio of melamine to formaldehyde ranging from 1:5 to 1:1.3 [mol / mol], preferably from 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 (measured by gel permeation chromatography); The method of claim 1.

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

4. a) the at least one surfactant is an anionic surfactant, preferably the at least one surfactant is an anionic surfactant selected from the group of diphenylene oxide sulfonates, alkanesulfonates, alkylbenzenesulfonates, alkylnaphthalenesulfonates, olefinsulfonates, alkyl ether sulfonates, fatty alcohol sulfates, ether sulfates, α-sulfofatty acid esters, acylaminoalkanesulfonates, acyl isethionates, alkyl ether carboxylates, N-acylsarcosinates, alkyl phosphates, and alkyl ether phosphates, or b) the at least one surfactant is a non-ionic surfactant, preferably the at least one surfactant is a non-ionic 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 50 to 90 wt. % of at least one anionic surfactant and 10 to 50 wt. % of at least one nonionic surfactant, based on the total weight of the surfactant mixture; 4. The method according to any one of claims 1 to 3.

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

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

7. 7. The method according to claim 1, wherein no acidic compound selected from the group consisting of formic acid, hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, acetic acid, oxalic acid, toluenesulfonic acid, amidosulfonic acid, acid anhydrides, and mixtures thereof is added to the mixture M, in particular no formic acid is added to the mixture M.

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

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

10. The melamine resin foam has a compressive strength of 5 to 150 kg / m ３ , more preferably 10 to 100 kg / m ３ , most preferably 12.5 to 75 kg / m ３ 10. The method of claim 1, wherein the bulk density is in the range of

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

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

13. A melamine resin foam obtainable by the method according to any one of claims 1 to 12.

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

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