Method for producing melamine resin foam using ground melamine foam particles

Abstract

The present invention provides a method for producing melamine resin foam comprising heating and foaming an aqueous mixture M using microwave radiation, said mixture M comprising melamine resin foam particles, at least one melamine-formaldehyde precondensate, at least one curing agent, at least one surfactant and at least one blowing agent, and a method for recycling melamine resin foam scrap.

Description

[Technical field]

[0001] The present invention relates to a method for producing melamine resin foam using ground melamine foam particles and to the melamine resin foam obtainable by this method. In particular, the present invention relates to a method for recycling melamine resin foam scraps.

[0002] Related Prior Art WO 2010 / 039574 relates to a liquid hard surface cleaning composition comprising melamine foam fibers and a formaldehyde scavenger.

[0003] CN 103030924 A discloses a fiber material modified melamine formaldehyde foam with improved mechanical properties such as flexibility and compressive strength, in which the fibrous material, such as glass fiber, polyester fiber, polyamide fiber, carbon fiber or cotton fiber, is added in an amount of 0.2-10% by weight of the formaldehyde solution and melamine before polymerization of the resin solution.

[0004] DE 10 2007 009 127 A1 relates to open-cell foams based on amino resins which contain 0.5 to 50% by weight of fibrous fillers, such as melamine fibers, in order to increase the mechanical properties of the open-cell foams, in particular the compressive strength.

[0005] WO 2011 / 061178 relates to a melamine resin foam having improved sound absorption and sound deadening properties in the frequency range of about 300-1600 Hz, comprising 40-85% by weight of open-cell polymer foam and 15-60% by weight of hollow microbeads having a flexible outer layer, based on the total weight of the polymer foam and the hollow microbeads, wherein the hollow microbeads have a D50 value of at least 70 μm and at most 250 μm. The melamine resin foam is impregnated with a liquid dispersion containing expandable hollow microbeads.

[0006] WO 2009 / 021963 relates to a method for producing an abrasive foam based on melamine-formaldehyde condensates containing inorganic nanoparticles, comprising the following steps: (1) producing a solution or dispersion containing a precondensate of the foam to be produced and inorganic nanoparticles, (2) foaming the precondensate by heating the solution or dispersion from step (1) to obtain a foam containing inorganic nanoparticles, and, if applicable, (3) heat-treating the foam obtained in step (2), which results in an increased abrasion rate when abrading delicate surfaces.

[0007] US 8 937 106 B2 relates to open-cell foams with improved thermal conductivity and sound absorption, filled with nanoporous particles, in particular aerogel or aerosil. In a first embodiment, the melamine resin foam is impregnated with nanoporous, preferably inorganic, particles. In a second embodiment, the nanoporous granular particles are mixed with a melamine-formaldehyde precondensate before foaming.

[0008] CN 112 795 053 A discloses a method for recycling melamine formaldehyde resin waste and producing flame retardants therefrom.

[0009] EP 2 703 074 A1 discloses a method for producing melamine resin foams having an improved combination of mechanical and acoustical properties and for producing moulded articles.

[0010] The object of the present invention is to provide a method for recycling melamine foam scraps, in particular to produce melamine foams with low density, improved cleaning behavior and sound absorption properties.

[0011] In order to solve the above problems, the present invention provides a method for producing a melamine resin foam, comprising heating and foaming an aqueous mixture M using microwave radiation, said mixture M comprising melamine resin foam particles, at least one melamine-formaldehyde precondensate, at least one curing agent, at least one surfactant and at least one blowing agent.

[0012] The melamine foam particles can be obtained by milling the melamine resin foam scraps. Preferably, the melamine foam particles are milled in a two-step process. In the first step, the melamine resin foam blocks are milled into foam flakes. The maximum dimension of the foam flakes is preferably in the range of 2-5 cm. In the second step, the foam flakes are further milled into foam particles. The average particle size of the foam particles is preferably in the range of 1-250 μm.

[0013] In a preferred embodiment, the melamine resin foam particles have an average particle size in the range of 1 to 250 μm; more preferably 10 to 200 μm; and most preferably 25 to 150 μm. The average particle size is measured by optical or electron microscopy in combination with image analysis or sieving, as a number average, D 10 , D 50 and D. 90The sieving can be carried out using an air jet sieve. Preferably, the total distribution of the melamine resin particle size is D 90 The number of particles is less than 150 μm, more preferably less than 125 μm, and most preferably between 50 μm and 110 μm, as measured by optical microscopy. 90 50% of the particles have a diameter less than the median diameter D 50 and 50% have a diameter smaller than the median diameter D 50 has a diameter greater than

[0014] In a preferred embodiment, the melamine resin foam particles have a density of 10 to 500 kg / m 3 ; More preferably 15 to 250 kg / m 3 and most preferably 20 to 150 kg / m 3 The bulk density is in the range of

[0015] In a preferred embodiment, the weight ratio of melamine resin foam particles to melamine-formaldehyde precondensate is in the range of 0.01 / 100 to 50 / 100; more preferably in the range of 0.1 / 100 to 25 / 100; and most preferably in the range of 0.5 / 100 to 10 / 100.

[0016] The density of the melamine resin foam produced by the method of the present invention is preferably 5 to 30 kg / m 3 within the range of 8 to 20 kg / m 3 is within the range.

[0017] The melamine foam can be produced as described in WO 2009 / 021963. Preferably, the melamine resin foam particles are premixed with at least one melamine resin in powder form or in an aqueous solution. To this melamine resin premix, at least one hardener, at least one surfactant and at least one blowing agent are added to form an aqueous mixture M. The melamine resin foam is obtained by heating and foaming the aqueous mixture M using microwave radiation. The melamine resin foam may be heat treated at a temperature of 120 to 300°C.

[0018] The melamine / formaldehyde precondensate may be prepared separately or a commercially available precondensate of the two components, i.e. melamine and formaldehyde, may be used. Preferably, a melamine-formaldehyde precondensate is used having a molar ratio of melamine to formaldehyde ranging from 5:1 to 1.3:1, more preferably from 3.5:1 to 1.5:1. Preferably, its number average molecular weight Mn ranges from 200 g / mol to 1000 g / mol. Preference is given to unmodified melamine / formaldehyde precondensates.

[0019] Anionic, cationic and nonionic surfactants and mixtures thereof can be used as dispersing / emulsifying agents.

[0020] Useful anionic surfactants include, for example, diphenylene oxide sulfonates, alkane and alkylbenzene sulfonates, alkylnaphthalene sulfonates, olefin sulfonates, alkyl ether sulfonates, fatty alcohol sulfates, ether sulfates, α-sulfo fatty acid esters, acylaminoalkane sulfonates, acyl isethionates, alkyl ether carboxylates, N-acylsarcosinates, alkyl and alkyl ether 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, glycerin fatty acid esters, sorbitan esters, and alkyl polyglycosides. Useful cationic emulsifiers include, for example, alkyltriammonium salts, alkylbenzyldimethylammonium salts, and alkylpyridinium salts.

[0021] The dispersant / emulsifier can be added in an amount of 0.2% to 5% by weight based on the melamine-formaldehyde precondensate.

[0022] Preferably, the mixture M comprises a surfactant mixture comprising a mixture of 50-90% by weight of at least one anionic surfactant and 10-50% by weight of at least one nonionic surfactant, wherein the weight percentages are each based on the total weight of the surfactant mixture.

[0023] As hardeners, it is possible to use acidic compounds that catalyze the further condensation of the melamine resin. The amount of these hardeners is generally in the range of 0.01% to 20% by weight and preferably in the range of 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, toluenesulfonic acid, amidosulfonic acid, acid anhydrides and mixtures thereof. Preferably, formic acid is used as the hardener.

[0024] The mixture further comprises at least one blowing agent. Useful physical blowing agents include, for example, in liquid form, hydrocarbons such as pentane, hexane, halogenated, more particularly chlorinated and / or fluorinated, hydrocarbons such as methylene chloride, chloroform, trichloroethane, chlorofluorocarbons, hydrochlorofluorocarbons (HCFCs), alcohols such as methanol, ethanol, n-propanol or isopropanol, ethers, ketones and esters such as methyl formate, ethyl formate, methyl acetate or ethyl acetate, or air, nitrogen or carbon dioxide as a gas.

[0025] The amount of blowing agent in the mixture generally depends on the density desired for the foam. Preferably, the amount of blowing agent relative to the melamine-formaldehyde precondensate is such that the foam has a density of 5 to 15 kg / m 3 , more preferably 6 to 12 kg / m 3 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 preferred to add a physical blowing agent having a boiling point of 0 to 80° C. Most preferably pentane is used as the blowing agent.

[0026] The precondensate is generally foamed by heating a suspension of the melamine-formaldehyde precondensate to obtain a foamed material.

[0027] The introduction of energy is preferably carried out by electromagnetic radiation, for example by radio frequency radiation, in the frequency range of 0.2-100 GHz, preferably 0.5-10 GHz, at 5-400 kW, preferably 5-200 kW and more preferably 9-120 kW per kg of mixture used. Magnetrons are a useful source of dielectric radiation, and one magnetron or two or more magnetrons can be used simultaneously.

[0028] The produced foamed material can finally be dried to remove residual water and blowing agent from the foam. Drying is preferably carried out in an oven at a temperature in the range of 40-200° C., particularly preferably 100-150° C., to constant weight. The above process provides blocks or slabs of foamed material, which can be cut to size and of any desired shape.

[0029] Preferably, the method is used to recycle melamine resin foam scrap, preferably from melamine resin foam produced from its manufacturing plant with properties outside the desired specification range. A further subject of the present invention is a method for recycling melamine resin foam, comprising the steps of: a) milling melamine foam scraps into foam flakes having a maximum dimension in the range of 2-5 cm; b) The foam flakes from step a) are measured by optical microscopy or sieving to have a D 90 milling into foam particles having a particle size distribution having a value; c) forming an aqueous mixture M from the foam particles from step b), at least one melamine-formaldehyde precondensate, at least one curing agent, at least one surfactant and at least one blowing agent; d) heating and foaming the aqueous mixture M using microwave radiation to produce a melamine resin foam; and e) optionally, heat treating the melamine resin foam obtained in step d) at a temperature between 120 and 300°C.

[0030] A further subject of the present invention is a melamine resin foam obtainable by the process of the present invention, the melamine resin foam particles being homogeneously distributed throughout the melamine foam.

[0031] The melamine resin foams produced by the process according to the invention can be after-treated by the following methods: 1. Hot compressing to obtain foams with higher density, better durability and cleaning behavior. 2. Hydrophobizing to obtain a foam with lower water absorption; and 3. Impregnated with flame retardants to improve FST properties (flame, smoke, toxicity) in the event of fire.

[0032] A method for producing a resilient compressed foam material based on melamine-formaldehyde resin having anisotropic mechanical properties, comprising the steps of compressing said soft, uncured melamine-formaldehyde foam material and curing and drying the resulting foam material, is described in WO 2011 / 134778.

[0033] Hydrophilization by impregnation with fluorocarbon resins and / or silicone resins and impregnation with flame retardant substances such as silicates, borates, hydroxides or phosphates can be achieved as described in WO 2007 / 023118.

[0034] Preferably, the density of the melamine resin foam is 5 to 15 kg / m 3 , more preferably 6 to 12 kg / m 3 is within the range.

[0035] The melamine resin foams produced according to the invention can be used for sound and / or heat insulation or in cleaning, grinding or scouring sponges. [Brief description of the drawings]

[0036] [Figure 1] Micrograph of melamine resin foam according to the present invention

[0037] The particles are fragments of the former cellular strut network and show the respective shapes (struts and nodes). During the foaming process, the particles can be wetted by the MF resin and build up porous or dense substructures (SEM photos).

[0038] Implementation The present invention includes the following embodiments, including specific combinations of embodiments: 1. A method for producing a melamine resin foam comprising heating and foaming an aqueous mixture M using microwave radiation, said mixture M comprising melamine resin foam particles, at least one melamine-formaldehyde precondensate, at least one curing agent, at least one surfactant and at least one blowing agent. 2. The melamine resin foam particles have a D of less than 150 μm as measured by microscopy. 90 2. The method of embodiment 1, having a particle size distribution having a value. 3. The melamine resin foam particles have a density of 10 to 500 kg / m 3 3. The method of claim 1 or 2, wherein the powder has a bulk density in the range of 4. The method of any one of the preceding claims, wherein the weight ratio of the melamine resin foam particles to the melamine-formaldehyde precondensate is in the range of 1 / 100 to 10 / 100. 5. The method of any of the preceding claims, wherein mixture M comprises a surfactant mixture comprising a mixture of 50-90 wt. % of at least one anionic surfactant and 10-50 wt. % of at least one nonionic surfactant, wherein the weight percentages are each based on the total weight of the surfactant mixture. 6. The process according to any one of the preceding embodiments, wherein formic acid is used as a curing agent. 7. The method of any one of the preceding embodiments, wherein pentane is used as the blowing agent. 8. A method for recycling melamine resin foam, comprising using milled melamine resin foam scrap as the melamine resin foam particles in the method of embodiment 1. 9. The density of the melamine resin foam is 5 to 30 kg / m 3 The method according to any one of embodiments 1 to 8, wherein the range is 8. A method for recycling melamine resin foam, comprising the steps of: a) milling melamine foam scraps into foam flakes having a maximum dimension in the range of 2-5 cm; b) The foam flakes from step a) are sieved into particles having a diameter of less than 150 μm. 90 milling into foam particles having a particle size distribution having a value; c) forming an aqueous mixture M from the foam particles from step b), at least one melamine-formaldehyde precondensate, at least one curing agent, at least one surfactant and at least one blowing agent; d) heating and foaming the aqueous mixture M using microwave radiation to produce a melamine resin foam; and e) optionally, heat treating the melamine resin foam obtained in step d) at a temperature of 120 to 300° C. The method comprising: 9. A melamine resin foam obtainable by the method according to any one of embodiments 1 to 9. 10. Use of the melamine resin foam according to embodiment 9 for sound and / or heat insulation or for cleaning, grinding or scouring sponges. EXAMPLES

[0039] In the following, the invention will be described in more detail with specific reference to examples which, however, are not intended to limit the invention.

[0040] Measurement method: Ram pressure value [N]: Ram pressure measurements for evaluating the mechanical quality of melamine resin foams were all carried out as follows: a cylindrical ram with a diameter of 8 mm and a height of 10 cm was pressed into a cylindrical sample with a diameter of 11 cm and a height of 5 cm in the foaming direction at an angle of 90% until the sample broke. The tear force [N], hereinafter also called the ram pressure value, provides information about the quality of the foam.

[0041] Cleaning test: The lipid emulsion consists of a mixture of Physioderm Creme 100, 6 g of Physioderm and 0.2 g of Active Char (activated carbon, granular, ashless 1.5 mm), Merck, in 100 mL of 2-propanol, which is applied in strips of approximately 80 mm on a ceramic tile with a film thickness of approximately 400 μm and dried at 160° C. for 15 minutes. Melamine foam specimens (geometry: 140 mm x 80 mm x 30 mm) were placed in water for 10 seconds and subsequently squeezed out by hand. Evaluation criteria: number of manual strokes (up and down = 1 stroke) of the wet foam specimen required to remove a 2 cm wide dirty film coating. The fewer strokes required, the better the cleaning efficiency.

[0042] Sound absorption Sound absorption was measured according to ISO 10534-2 using an impedance tube and a melamine foam sample with a thickness of 30 mm and a diameter of 100 mm. The absorption value at 1250 Hz is given (a value of 1.000 = 100% absorption).

[0043] Materials used: A melamine-formaldehyde precondensate having an average molecular weight (number average) M of 350 g / mol, a molar ratio of melamine:formaldehyde of 1:3, containing no further thermoset formers besides melamine and no further aldehydes besides formaldehyde and being sulfite group-free. T1C 12 / C 14 -Alkyl sulfates, sodium salts. T2 Linear saturation C 16 / C 18 Alkyl polyethylene glycol ethers made from fatty alcohols. MF-P Milled melamine-formaldehyde foam particles (average particle size 60-120 μm, bulk density 27 g / L).

[0044] Particle size distribution measurement: Particle size distribution was measured by optical microscopy using an Olympus BX 60. For each sample, 100 individual particles were measured. The resulting data were calculated as the total number distribution D10, D50 and D90. 90% of the particles have a diameter less than the D90 value. 50% of the particles have a diameter smaller than the median diameter D50 and 50% have a diameter larger than the median diameter D50.

[0045] The particle size distribution was measured by an air jet sieve ALPINE Luftstrahlsieb® 200 LS-N under the following conditions: Sample weight: 10g Sieves: 125, 90 and 60 μm Vacuum (below the sieve): 40mbar Air flow rate: 50m 3 / h.

[0046] Preparation of melamine-formaldehyde foam particles MF-P1: Melamine-formaldehyde foam blocks (Basotect®) were ground into foam flakes (10-100 mm) on a laboratory scale using a cutting mill Pallmann PS 3.5 and sieved through a 15 mm square hole sieve. The flakes were further cut with a cutting mill Retsch SM 2000 and sieved by gravity through a Condidur sieve 1 mm. The throughput was 1.4 kg / h. The particle size was 60-100 μm as determined by microscopy. The particle size distribution as determined by air jet sieving is summarized in Table 1.

[0047] Preparation of melamine-formaldehyde foam particles MF-P2: Melamine-formaldehyde foam blocks (Basotect®) were ground into foam flakes (10-100 mm) using a cutting mill Pallmann PS 3.5 and passed through a sieve with square holes of 15 mm. The flakes were weighed out by hand and milled on a production scale using a cutting mill Netzsch, SecoMy 37 (rotation speed: 1072 min-1 The pulp was further cut using a sieve (engine power 37 kW) and sieved through a 315 m sieve. The throughput was 300 kg per hour. The particle size was measured by microscope to be 40-60 μm. The particle size distribution measured by microscope and air jet sieve are summarized in Tables 1 and 2. The bulk density was 97 kg / m at 8% (±1%) humidity. 3 (±2.5kg / m 3 ) was.

[0048] Preparation of melamine-formaldehyde foam particles MF-P3: Melamine-formaldehyde foam blocks (Basotect®) were ground into foam flakes (10-100 mm) using a cutting mill Pallmann PS 3.5 and passed through a sieve with square holes of 15 mm. The flakes were weighed out by hand and milled on a production scale using a cutting mill Netzsch, SecoMy 50 S (3000 min -1 Air classifier at 1072min -1 The pulp was further cut using a 315 m sieve (engine power 37 kW) and sieved through a 315 m sieve. The throughput was 160 kg / h. The particle size distributions measured by microscope and air jet sieving are summarized in Tables 1 and 2.

[0049] Table 1: Particle size distribution of MF-P1 to MF-P3 by optical microscope [Table 1]

[0050] Table 2: Particle size distribution of MF-P1 to MF-P3 by air jet sieving [Table 2]

[0051] Comparative Example C1: In the first step, 100 parts by weight of the melamine-formaldehyde precondensate MF, 38 parts by weight of water, 1.2 parts by weight of anionic surfactant T1, 0.3 parts by weight of nonionic surfactant T2, 2.5 parts by weight of sodium formate, 3.0 parts by weight of formic acid, and 19.5 parts by weight of pentane were mixed together at a temperature of 20 to 35°C. The mixture was introduced into a polypropylene foaming mold and irradiated with microwaves in a microwave oven. The foam obtained after microwave irradiation was annealed in a circulating air oven at 200°C for 20 min. The density of the foam was 10.2 g / L, and the ram pressure value was 28.0 N.

[0052] Comparative Example C2: In the first step, 100 parts by weight of the melamine-formaldehyde precondensate MF, 38 parts by weight of water, 1.2 parts by weight of anionic surfactant T1, 0.3 parts by weight of nonionic surfactant T2, 2.5 parts by weight of sodium formate, 3.0 parts by weight of formic acid, and 17.8 parts by weight of pentane were mixed together at a temperature of 20 to 35°C. The mixture was introduced into a polypropylene foaming mold and irradiated with microwaves in a microwave oven. The foam obtained after microwave irradiation was annealed in a circulating air oven at 200°C for 20 min. The density of the foam was 8.6 g / L, and the ram pressure value was 24.9 N.

[0053] Examples 1-4: In the first step, 100 parts by weight of the melamine-formaldehyde precondensate MF, 2.5-10 parts by weight of melamine-formaldehyde foam particles MF-P1 (amounts according to Table 3), 38 parts by weight of water, 1.2 parts by weight of anionic surfactant T1, 0.3 parts by weight of nonionic surfactant T2, 2.5 parts by weight of sodium formate, 3.0 parts by weight of formic acid and 19.5 parts by weight of pentane were mixed together at a temperature of 20-35° C. The mixture was introduced into a polypropylene foaming mold and irradiated with microwaves in a microwave oven. The foam obtained after microwave irradiation was annealed at 200° C. for 20 min in a circulating air oven. The density of the foam was about 10 g / L and the ram pressure value was 20-25 N (see Table 3).

[0054] [Table 3]

[0055] Examples 5-8: Examples 1-4 were repeated using melamine-formaldehyde foam particles MF-P2. The amount of MP-P2 added per 100 parts of MF precondensate and the resulting foam properties are summarized in Table 4.

[0056] Table 4: Amount of recycled MF-P2 foam particles and MF foam properties for Examples 5-8 [Table 4]

[0057] Examples 9-12: Examples 1-4 were repeated using melamine-formaldehyde foam particles MF-P3. The amount of MP-P2 added per 100 parts of MF precondensate and the resulting foam properties are summarized in Table 5.

[0058] Table 5: Amount of recycled MF-P3 foam particles and MF foam properties for Examples 9-12 [Table 5]

Claims

1. A method for producing a melamine resin foam having a density in the range of 5 to 30 kg / m³, comprising heating and foaming an aqueous mixture M using microwave radiation, wherein the mixture M comprises melamine resin foam particles, at least one melamine-formaldehyde precondensate, at least one curing agent, at least one surfactant, and at least one blowing agent. ３ ​

2. The melamine resin foam particles have a particle size distribution having a D value of less than 150 μm as measured by microscopy, the method according to claim 1. ９０ value, the method according to claim 1.

3. The melamine resin foam particles have a bulk density in the range of 10 to 500 kg / m ３ The method according to claim 1 or 2, wherein the melamine resin foam particles have a bulk density in the range of 10 to 500 kg / m

4. The method according to claim 1 or 2, wherein the weight ratio of the melamine resin foam particles to the melamine - formaldehyde initial condensate is in the range of 0.5 / 100 to 10 / 100.

5. The method according to claim 1 or 2, wherein the mixture M comprises a surfactant mixture containing a mixture of 50 to 90% by weight of at least one anionic surfactant and 10 to 50% by weight of at least one nonionic surfactant, where the weight percentages are based on the total weight of the surfactant mixture respectively.

6. The method according to claim 1 or 2, wherein formic acid is used as a curing agent.

7. The method according to claim 1 or 2, wherein pentane is used as a blowing agent.

8. A method for recycling a melamine resin foam, wherein milled melamine resin foam scrap is used as the melamine resin foam particles in the method according to claim 1.

9. The density of the melamine resin foam is in the range of 8 to 20 kg / m ３ The method according to claim 1 or 2, wherein the density is within the range of

10. A method for recycling a melamine resin foam, comprising the following steps: a) milling the melamine resin foam scrap into foam flakes having a maximum dimension in the range of 2 to 5 cm; b) Measuring the form flakes from step a) by optical microscopy or sieving, and milling and pulverizing the form particles having a particle size distribution with a D value of less than 150 μm ９０ into a process where the form particles having a particle size distribution with a D value of less than 150 μm are milled and pulverized; c) forming an aqueous mixture M from the foam particles from step b), at least one melamine - formaldehyde initial condensate, at least one curing agent, at least one surfactant, and at least one blowing agent; d) heating and foaming the aqueous mixture M using microwave radiation to produce a melamine resin foam; and e) optionally, heat - treating the melamine resin foam obtained in step d) at a temperature of 120 to 300°C. The method as described above.

11. A melamine resin foam obtainable by the method according to claim 1 or 2.

12. Use of the melamine resin foam according to claim 9 for sound insulation and / or heat insulation or for cleaning sponges, grinding sponges or polishing sponges.