Patent Application
20250122349
The present invention relates to melamine resin foams with an open-celled structure comprising halogen-free flame retardants, selected from phosphine oxide, phosphinate or phosphonate, a process for producing such melamine resin foams and their use for acoustic and/or thermal insulation.
EP 1 146 070 A2 relates to an open-cell melamine resin foam with improved fire properties, in which the surface of the cell skeleton is coated with an ammonium salt of the phosphoric acid, in particular ammonium orthophosphate and ammonium polyphosphate as flame retardants. The melamine resin foams with the flame-retardant coating often show a higher formaldehyde-emission.
CN 107987466 A discloses the preparation of a melamine formaldehyde foam by using a com-bination of petroleum ether and diphenylmethane diisocyanate as a foaming auxiliary agent, a vulcanized rubber, cell opener and a phosphate as flame retardant. Preferably, the flame retardant is tributyl phosphate, tris (2-ethylhexyl) phosphate, tris (2-chloroethyl) phosphate, tris (2,3-dichloropropyl) phosphate, tris (2,3-dibromopropyl) phosphate, cresyl-diphenyl phosphate, tricresyl phosphate, triphenyl phosphate, or (2-ethylhexyl) -diphenyl phosphate.
CN 107903579 A discloses a hot-compressed melamine resin foam good fireproof and flame-retardant properties, tensile strength and sound insulation properties. The preparation method comprises the steps of taking melamine formaldehyde resin, sequentially adding a foaming agent, a surfactant, a flame retardant, a cell opening agent and a curing agent, mixing, uniform-ly stirring, placing into a microwave foaming furnace for foaming, then cutting foam, carrying out hot pressing compression.
WO 2017/125414 discloses polyurethane aerogels having a high porosity, a low density and a sufficiently high mechanical stability combined with good flame resistance by adding a phospho-rous compound with at least one functional group reactive toward isocyanate to the gel forming composition.
EP 1 142 939 A2 relates to a halogen-free, water-blown, flame-retardant rigid polyurethane foam and to a process for its production and the use of oxalkylated alkylphosphonic acids as flame retardants.
US 2011-023057 relates to a flame-retardant composite foam comprising foamed particles comprising 24-95% by weight of styrene polymer and from 1 to 65% by weight of a cured modified or foamed aminoplastic resin and from 0.1 to 20% by weight of an organic phospho-rous compound as flame retardant. The density of the resultant composite foam is in the range from 35 to 50 g/l.
Flame retardants are generally added to the mixture of resin and blowing agent before foaming or applied as coating after foam preparation. The addition of solid flame retardants to melamine-formaldehyde prepolymer mixture often disturbs the cell formation and cell opening during foaming resulting in low mechanical performance or foam collapse. Impregnation of solid flame retardants to the foam by spraying or dipping makes a further impregnation step and preparation of a suspension necessary. Suspension stability, calandering and drying are often difficult with thick foam samples.
The object of the present invention is to provide a halogen-free, flame-retardant, open-celled melamine resin foam with sufficient mechanical stability, low density and low formaldehyde emission.
To solve the problem, the present invention provides melamine resin foams with an open-celled structure comprising a halogen-free flame retardant; selected from phosphine oxide, phosphinate or phosphonate and a process for producing the melamine resin foam with an open-celled structure 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 curative, at least one surfactant, at least one liquid halogen-free flame-retardant, selected from phosphine oxide, phosphinate or phosphonate and at least one blowing agent.
The melamine resin foam according to the invention comprises at least one halogen-free flame retardant, selected from phosphine oxide, phosphinate or phosphonate. At least one means one or mixtures of two or more halogen-free flame retardants. Preferably the melamine resin foam is halogen-free and does not contain any halogenated flame retardant or other halogenated addi-tives.
Preferably the at least one halogen-free flame retardant is chemically bond to the melamine resin. The following properties of the halogen free flame retardants refer to the properties before chemically bonding to the melamine resin. Liquid means that the halogen-free flame retardant is liquid at ambient conditions (25° C., 101.325 kPa) before chemically bonding to the melamine resin. Preferably the viscosity is in the range from 100 to 700 mPa*s, determined with a Brookfield viscosimeter at 25° C. Preferably the hydroxyl number is in the range from 400-500 mg KOH/g determined by double Karl-Fischer titration. Preferably the phosphorus content of the halogen-free flame retardants is in the range from 10-13% (w/w) as determined by photome-try after oxidative dissolution.
Preferably the at least one halogen-free flame retardant is a liquid phosphine oxide, phosphinate or phosphonate compound. Liquid means the organophosphorus compound is liquid at ambient conditions (25° C., 101.325 kPa) before incorporation into the melamine resin foam. More preferably the at least one halogen-free flame retardant is a liquid phosphine oxide, phosphinate or phosphonate and phosphorus in oxidation states between +2 and +4. More preferably the at least one halogen-free flame retardant is selected from the following structures I-III
Preferably R1, R2 and R3 are
Most preferably the at least one halogen-free flame retardant is selected from tris (hydroxy methyl) phosphine oxide, Bis(polyoxyethylene) methylphosphonate, Bis(3-hydroxypropyl) isobutylphosphine, Diethyl bis(hydroxyethyl) aminomethyl phosphonate.
The halogen-free flame retardants are preferably present in a total amount of 0.5 to 40 wt.-%, more preferably in a total amount of 2.5 to 25 wt.-%, most preferably in a total amount of 5 to 20 wt.-%, based on the melamine resin foam.
Preferably the open-celled melamine resin foam comprises 75 to 99 wt.-%, more preferably of 80 to 95 wt.-% of a cured melamine resin. Most preferably the open-celled melamine resin consists essentially of 80 to 95 wt.-% of cured melamine resin and 5 to 20 wt.-% of the halogen-free flame retardant.
The melamine resin foam has preferably an open-celled structure and an open-cell content measured according to DIN ISO 4590 of more than 50%, preferable of 95% or higher, most preferably of 98 to 100%.
Preferably the density of the melamine resin foam is in the range from 5 to 15 kg/m3, more preferably 6 to 12 kg/m3.
Preferably the shore hardness 000 of the open-celled melamine resin foam is in the range from 35 to 75 N, measured according to ASTM D 2240.
Preferably the formaldehyde emission of the open-celled melamine resin is in the range from 5 to 15 mg FA/kg sample foam, measured according to EN 14184.
The melamine foam can be produced as described in WO 2009/021963. The melamine-resin foam according to the invention is preferably produced by a process comprising heating and foaming an aqueous mixture M using microwave radiation, said mixture M comprising at least one melamine-formaldehyde precondensate, at least one liquid halogen-free flame retardant, at least one curative, at least one surfactant and at least one blowing agent. The melamine resin foam can be tempered at a temperature between 120-300° C.
In order to achieve bonding to the melamine resin the at least one halogen-free flame retardant used in the process according to the invention is reactive towards the melamine resin or mela-mine resin precursor. Preferably the at least one halogen-free flame retardant has functional groups, which are capable to react with the melamine-formaldehyde precondensate. Preferably the at least one halogen-free flame retardant has hydroxyl groups as functional groups, most preferably 2 or 3 functional groups per molecule. The at least one halogen-free flame retardant used in the process has preferably the properties as described above and is used in a total amount of 0.5 to 40 wt.-%, more preferably in a total amount of 5 to 20 wt.-%, based on the melamine melamine-formaldehyde precondensate.
The melamine/formaldehyde precondensates may be prepared separately or commercially available precondensates of the two components, melamine and formaldehyde may be used.
Preferably a melamine-formaldehyde precondensate having a molar ratio of melamine to formaldehyde ranging from 1:5 to 1:1.3, more preferably from 1:3, 5 to: 1:1, 5 is used. Preferably the number average molecular weight Mn ranges from 200 g/mol to 1000 g/mol. Preference is given to unmodified melamine/formaldehyde precondensates.
Anionic, cationic and nonionic surfactants and also mixtures thereof can be used as disper-sant/emulsifier.
Useful anionic surfactants include for example diphenylene oxide sulfonates, alkane and al-kylbenzenesulfonates, alkylnaphthalenesulfonates, olefinsulfonates, alkyl ether sulfonates, fatty alcohol sulfates, ether sulfates, α-sulfo fatty acid esters, acylaminoalkanesulfonates, acyl isethi-onates, alkyl ether carboxylates, N-acylsarcosinates, alkyl and alkylether phosphates. Useful nonionic surfactants include alkylphenol polyglycol ethers, fatty alcohol polyglycol ethers, fatty acid polyglycol ethers, fatty acid alkanolamides, ethylene oxide-propylene oxide block copoly-mers, amine oxides, glycerol fatty acid esters, sorbitan esters and alkylpolyglycosides. Useful cationic emulsifiers include for example alkyltriammonium salts, alkylbenzyldimethylammonium salts and alkylpyridinium salts.
The dispersants/emulsifiers can be added in amounts from 0.2% to 5% by weight, based on the melamine-formaldehyde precondensate.
Preferably the mixture M comprises a surfactant mixture comprising a mixture of 50 to 90 wt % of at least one anionic surfactant and 10 to 50 wt % of at least one nonionic surfactant, wherein the weight percentages are each based on the total weight of the surfactant mixture.
As curatives it is possible to use acidic compounds which catalyze the further condensation of the melamine resin. The amount of these curatives is generally in the range from 0.01% to 20% by weight and preferably in the range from 0.05% to 5% by weight, all based on the precondensate. Useful acidic compounds include organic and inorganic acids, for example selected from the group consisting of hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, formic acid, acetic acid, oxalic acid, toluene sulfonic acids, amido sulfonic acids, acid anhydrides and mixtures thereof. Preferably formic acid is used as curative.
The mixture further comprises at least one blowing agent. Useful physical blowing agents include for example hydrocarbons, such as pentane, hexane, halogenated, more particularly chlo-rinated and/or fluorinated, hydrocarbons, for example methylene chloride, chloroform, trichloro-ethane, chlorofluorocarbons, hydrochlorofluorocarbons (HCFCs), alcohols, for example metha-nol, ethanol, n propanol or isopropanol, ethers, ketones and esters, for example methyl formate, ethyl formate, methyl acetate or ethyl acetate, in liquid form or air, nitrogen or carbon dioxide as gases.
The amount of blowing agent in the mixture generally depends on the desired density for the foam. Preferably the amount in relation to the melamine-formaldehyde precondensate is chosen in an amount that the density of the foam is 5 to 15 kg/m3, more preferably 6 to 12 kg/m3. The blowing agent is preferably present in the mixture in an amount of 0.5% to 60% by weight, preferably 1% to 40% by weight and more preferably 1.5% to 30% by weight, based on the mela-mine-formaldehyde precondensate. It is preferable to add a physical blowing agent having a boiling point between 0 and 80° C. Most preferably pentane is used as blowing agent.
The precondensate being foamed up generally by heating the suspension of the melamine-formaldehyde precondensate to obtain a foamed material.
The introduction of energy may preferably be effectuated via electromagnetic radiation, for example via high-frequency radiation at 5 to 400 kW, preferably 5 to 200 kW and more preferably 9 to 120 kW per kilogram of the mixture used in a frequency range from 0.2 to 100 GHz, preferably 0.5 to 10 GHz. Magnetrons are a useful source of dielectric radiation, and one magnetron can be used or two or more magnetrons at the same time.
The foamed materials produced can be finally dried, removing residual water and blowing agent from the foam. Drying is carried out preferably in a drying oven at a temperature in the range of 40 to 200° C., particularly preferably 100 to 150° C. until a constant weight. The process described provides blocks or slabs of foamed material, which can be cut to size in any desired shapes.
Preferably the process is used for recycling melamine resin foam scrap, preferably from mela-mine resin foam from the production plant, which was produced with properties outside the desired specification. A further subject to the present invention is a process for recycling melamine resin foam comprising the steps:
The melamine resin foam prepared by the method according to the invention may be post-treated by the following methods:
A process for producing resilient compressed foamed materials having anisotropic mechanical properties on the basis of melamine-formaldehyde resins comprising a step of compressing the soft, uncured melamine-formaldehyde foamed material and curing and drying the foamed material obtained is described in WO 2011/134778.
Hydrophilization by impregnation with a fluorocarbon resin and/or silicon resin and additional impregnation with flame-retardant substances, such as silicates, borate, hydroxides or phosphates can be achieved as described in WO 2007/023118.
With the use of at least one liquid halogen-free flame retardant, which is reactive towards the melamine resin or melamine resin precursor a melamine resin foam with high char formation in case of a fire can be produced. The melamine resin foams according to the invention surprisingly have a low formaldehyde emission. They can be used for acoustic and/or thermal insulation.
Hereinafter, the present invention is described in more detail and specifically with reference to the Examples, which however are not intended to limit the present invention.
Ram pressure measurements for evaluating the mechanical quality of the melamine resin foams were all carried out as follows. A cylindrical ram having a diameter of 8 mm and a height of 10 cm was pressed into a cylindrical sample having a diameter of 11 cm and a height of 5 cm in the direction of foaming at an angle of 90% until the sample tore. The tearing force [N], hereinafter also referred to as ram pressure value, provides information as to the quality of the foam.
The measurements were run according to ASTM D 2240. For the measurement of low density foams the scale of 000 was used (2.4 mm diameter of the sphere, spring force 1.111 N).
The formaldehyde emission measurement was performed according to EN 14184. The result is given by mg FA/kg sample.
Char formation was measured by cone calorimetry after flame retardancy testing according to ISO 5660-1. Char residue was calculated as difference of initial mass minus mass loss in weight percent. The higher the char residue the better is the flame retardancy effect. The following test assembly is used:
Production of the melamine resin foam in the lab: 100 g of a spray-dried melamine-formaldehyde precondensate (molar ratio 1:3) were dissolved in 40 g of water, then 1.5 g of a sodium C12/C14-alkyl sulfonate and 3 g of sodium formiate were added. Thereafter the flame retardants FR1 to FR4 were added in amounts listed in Table 3 to the mixture and the aqueous mixture was stirred for 60 s. Afterwards, 17.8 g of pentane as blowing agent and 3.1 g formic acid are added t0 the mixture. The mixture is stirred for 30 min and subsequently transferred to a propylene mold for foaming. The foaming is supported by microwave energy. After the foaming is accomplished, the foam is demolded and dried in the oven for 6 hours at 100° C.,
The melamine resin foams of Examples 1 to 4 show surprisingly low formaldehyde (FA) emis-sions and better mechanical properties compared to comparative example C1 and C2 with FR 5 and FR6. Char formation of 5% or more should be high in order to build as sufficient protective carbon layer.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21200402.2 | Oct 2021 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/076916 | 9/28/2022 | WO |
