Synthesis of melamine polyphosphate with low residual melamine

Abstract

The present invention relates to a method for producing melamine-depleted melamine polyphosphate comprising heating crude melamine polyphosphate to a holding temperature of greater than 290° C. for a holding time of at least 1 hour, to melamine-depleted melamine polyphosphate containing residual melamine, the residual melamine concentration being less than 0.2% by weight, and to a polymer composition comprising the melamine-depleted melamine polyphosphate.

Description

[Technical field]

[0001] The present invention relates to a method for producing melamine-depleted melamine polyphosphate comprising heating crude melamine polyphosphate to a holding temperature of greater than 290° C. for a holding time of at least 1 hour, to a melamine-depleted melamine polyphosphate containing residual melamine, the residual melamine concentration being less than 0.2% by weight, and to a polymer composition comprising the melamine-depleted melamine polyphosphate. Combinations of the preferred embodiments with other preferred embodiments are within the scope of the present invention. [Background technology]

[0002] Melamine polyphosphate is a commercially available halogen-free flame retardant that is often used in polyamide 66, 6, 11, 12, thermoplastic polyurethanes, and polyurethanes. This flame retardant undergoes endothermic decomposition above 350°C, acting as a heat sink and cooling the polymer. The released phosphoric acid further reacts with the polymer to form char, suppressing the release of free radical gases into the oxygen phase. At the same time, nitrogen species released by the decomposition of melamine expand the char, further protecting the polymer.

[0003] Melamine polyphosphates generally contain trace amounts of melamine, which is labeled under the United Nations GHS system (Globally Harmonized System of Classification, Labelling and Packaging of Chemicals) as H361f "suspected of impairing fertility." Summary of the Invention [Problem to be solved by the invention]

[0004] The aim was to find a process for the preparation of melamine polyphosphate which results in very low residual melamine concentrations. [Means for solving the problem]

[0005] The object has been solved by a method for producing melamine-free melamine polyphosphate, comprising heating crude melamine polyphosphate to a holding temperature above 290° C. for a holding time of at least 1 hour.

[0006] The object was also solved by a melamine-depleted melamine polyphosphate containing residual melamine, the residual melamine concentration of which is less than 0.2% by weight. The object was also solved by a polymer composition comprising melamine-depleted melamine polyphosphate or by a polymer composition obtainable by a process for producing melamine-depleted melamine polyphosphate comprising heating crude melamine polyphosphate to a holding temperature above 290° C. for a holding time of at least 1 hour. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] A suitable overall reaction scheme is as follows: Melamine + phosphoric acid + water ↓ Melamine phosphate ↓ Crude melamine polyphosphate ↓ Melamine polyphosphate for melamine removal

[0008] Melamine phosphate Crude melamine polyphosphate can be produced by polymerizing melamine phosphate, which can be preferably obtained by the reaction of melamine, phosphoric acid and water.

[0009] The phosphoric acid is usually used in the form of an aqueous phosphoric acid solution, for example at a concentration of at least 50, 60, or 70% by weight or 70-90% by weight. The phosphoric acid usually has less than 1000, 100, or 10 ppm of heavy metals (which may be determined as Pb by the PLC08 method). The aqueous phosphoric acid solution can be added to the melamine all at once or in several portions, or continuously, for example by spraying.

[0010] Melamine is typically used in solid form, such as powder or granules. Melamine generally has a purity of at least 95, 98 or 99%, which can be determined by titration with HClO4. Melamine has the following chemical structure: [ka]

[0011] Water can be added to the reaction in the form of an aqueous phosphoric acid solution, or in the form of water, or in the form of both an aqueous phosphoric acid solution and water. Water can be added to the melamine all at once or in several portions, or continuously, for example by spraying.

[0012] The weight ratio of water to melamine added can be 10:100 to 60:100, preferably 20:100 to 50:100, and especially 30:100 to 45:100. To calculate the weight ratio of water to melamine, add up the total amount of water from the aqueous phosphoric acid solution and water added.

[0013] Typically, melamine phosphate is prepared by heating melamine, phosphoric acid, and water above a reaction temperature of 70, 75, 80, 85, 90, or 95° C. Typically, melamine phosphate is prepared by heating melamine, phosphoric acid, and water below a reaction temperature of 160, 150, 140, 130, 120, 110, or 100° C. Typically, melamine phosphate is prepared by heating melamine, phosphoric acid, and water at a reaction temperature in the range of 70-130° C., 70-120° C., or 75-110° C. The reaction temperature generally refers to the temperature of the reactants.

[0014] The melamine phosphate is prepared by heating melamine, phosphoric acid and water for at least 0.5, 1, 3, 4, 5 or 6 hours, for example 1 to 20 hours or 2 to 12 hours. Water may be removed during the process by applying reduced pressure, such as less than 800, 500, or 400 mbar.

[0015] Preferably, melamine phosphate is prepared by adding phosphoric acid and water to powder of melamine.

[0016] More preferably, the melamine phosphate is prepared by adding an aqueous solution of phosphoric acid and water to melamine powder, and the weight ratio of water to melamine added may be 10:100 to 60:100, preferably 20:100 to 50:100, and particularly 30:100 to 45:100.

[0017] The melamine phosphate is generally dried at elevated temperature, in a vacuum, or at elevated temperature in a vacuum.

[0018] The melamine phosphate may contain melamine and phosphoric acid in a molar ratio of 1:1 to 2:1, 1.2:1 to 1.5:1, 1.25:1 to 1.4:1, or 1.25:1 to 1.35:1. In one embodiment, the melamine phosphate contains melamine and phosphoric acid in a molar ratio of 1.2:1 to 1.5:1. The molar ratio in the melamine phosphate can be adjusted by selecting the appropriate molar amount of the extract.

[0019] The melamine phosphate may have a purity of at least 80, 90, or 95%, which may be determined by HNMR.

[0020] The melamine phosphate may have a moisture content of less than 5, 3, or 1% by weight, which can be determined with a moisture meter equipped with a weighing and halogen heating unit.

[0021] Crude melamine polyphosphate Crude melamine polyphosphate is generally produced by polymerizing melamine phosphate at a polymerization temperature in the range of 200 to 290° C. for a polymerization time of at least 0.5 hours.

[0022] The polymerization temperature may be at least 220, 240, 250, 260, 265 or 270°C. In one embodiment, the polymerization temperature is at least 250°C. In another embodiment, the polymerization temperature is at least 260°C. In another embodiment, the polymerization temperature is at least 265°C. The polymerization temperature may be up to 280, 285 or 290°C. The polymerization temperature may range from 230 to 290°C, preferably from 260 to 290°C, especially from 280 to 290°C. The polymerization temperature generally refers to the temperature of the reactants.

[0023] The polymerization of phosphate units into polyphosphate units is generally an endothermic reaction, which means that the polymerization temperature remains constant even during the addition of thermal energy to the melamine phosphate.

[0024] The polymerization time is at least 0.5 hours, such as 1, 2, 3, 4, or 5 hours. In one embodiment, the polymerization time is at least 2 hours. In another embodiment, the polymerization time is at least 3 hours. In another embodiment, the polymerization time is at least 3 hours. In another embodiment, the polymerization time is at least 4 hours. The polymerization time may be up to 20 hours, such as up to 15 hours, or up to 10 hours. The polymerization time may range from 1 to 20 hours, preferably from 2 to 15 hours, in particular from 3 to 10 hours.

[0025] The polymerization of the melamine phosphate is generally carried out while mixing the melamine phosphate, for example by stirring or by injecting an inert gas, which may be air, nitrogen or a noble gas, with nitrogen being preferred here.

[0026] The polymerization of phosphate units into polyphosphate units normally results in the production of water of reaction, which can be measured by an increase in pressure.

[0027] The water of reaction can be removed during polymerization. The water of reaction can be removed by purging with an inert gas or by applying a vacuum. In one form, the water of reaction is removed by purging with an inert gas.

[0028] The inert gas may be air, nitrogen or a noble gas, with nitrogen being preferred herein. Purging can be carried out by volumetric flow resulting in exchange of the volume above the polymerization product at least 1, 2, 3, 4 or 5 times per hour.

[0029] In another form, the water of reaction is removed by applying a vacuum such as at least 0.9 bar, 0.5 bar or 0.1 bar.

[0030] Melamine phosphate is generally polymerized in an atmosphere without the addition of ammonia. In another embodiment, melamine phosphate is polymerized in an atmosphere from which ammonia has been removed. In another embodiment, melamine phosphate is polymerized in an inert gas atmosphere.

[0031] Typically, a reaction mixture containing at least 60, 70, 80, 90, 95, 96, 97, 98, 99, or 99.5% by weight of melamine phosphate is polymerized. The concentration of melamine phosphate in the reaction mixture generally refers to the concentration before polymerization is initiated. In one form, the reaction mixture is polymerized without containing other compounds such as polymerization catalysts or reactants.

[0032] The reaction mixture may optionally contain a polymerization catalyst such as an alkali metal hydroxide, an alkaline earth metal hydroxide, or a borate (e.g., zinc borate). If a polymerization catalyst is used, the amount used will generally be 0.1% to 10% by weight of the reaction mixture. It is preferred that the reaction mixture does not contain a polymerization catalyst.

[0033] In one embodiment, the reaction mixture may be free of compounds that release water, such as borax, aluminum hydroxide, magnesium hydroxide, and mixtures thereof, hi another embodiment, the reaction mixture may contain less than 5, 3, 2, 1, 0.5, or 0.1 wt. % of compounds that release water.

[0034] In one embodiment, the reaction mixture may be free of urea. In another embodiment, the reaction mixture may contain less than 5, 3, 2, 1, 0.5, or 0.1 wt.% urea. In another embodiment, the reaction mixture may contain less than 0.1, 0.05, or 0.01 moles of urea per mole of phosphoric acid.

[0035] In one embodiment, the reaction mixture may be free of metal oxides, metal hydroxides, metal oxohydroxides, metal (hydroxy)carbonates, or layered double hydroxides (LDHs) of Mg, Zn, and Al, such as MgO, Mg(OH)2, Al2O3, Al(O)OH (boehmite), ZnO, Zn(OH)2, and Mg, Al-, Zn, Al-, and Mg / Zn, hydrotalcite or hydromagnesite, MgCO3, or ZnCO3, etc. In another embodiment, the reaction mixture may contain less than 5, 3, 2, 1, 0.5, or 0.1 wt. % of metal oxides, metal hydroxides, metal oxohydroxides, metal (hydroxy)carbonates, or layered double hydroxides (LDHs) of Mg, Zn, and Al.

[0036] In one aspect, the reaction mixture may be free of organic solvents, hi another aspect, the reaction mixture may contain less than 5, 3, 2, 1, 0.5, or 0.1 wt. % organic solvent.

[0037] The polyphosphate in the crude melamine polyphosphate may have a degree of polymerization of at least 10, 20, 30, or 40; 31 It can be determined by P solid-state NMR.

[0038] At the end of the polymerization time, the resulting crude melamine polyphosphate can be used directly to produce melamine-free melamine polyphosphate, e.g. without further post-treatment steps or cooling. It is preferred to use the crude melamine polyphosphate at the polymerization temperature to produce melamine-free melamine polyphosphate, e.g. by increasing the temperature from the polymerization temperature to a holding temperature.

[0039] In another embodiment, at the end of the polymerization time, the obtained crude melamine polyphosphate can be cooled, for example, to below 150° C., 120° C., or 100° C. The cooling can be achieved by stirring without heating or by injecting cold inert gas. After cooling, the crude melamine polyphosphate can generally be obtained in a solid form, for example as a powder, and can also be further crushed, pulverized, pressed, granulated, or tableted.

[0040] Crude melamine polyphosphate generally has a residual melamine concentration of at least 0.1, 0.2, or 0.25% by weight melamine.

[0041] Melamine polyphosphate for melamine removal The present invention also relates to a melamine-depleted melamine polyphosphate containing residual melamine, the residual melamine concentration being less than 0.2%, 0.1% or 0.05% by weight. The melamine-depleted melamine polyphosphate is obtainable by a process comprising heating crude melamine polyphosphate to a holding temperature of greater than 290° C. for a holding time of at least 1 hour.

[0042] The present invention also relates to a method for producing melamine-depleted melamine polyphosphate comprising heating crude melamine polyphosphate to a holding temperature above 290° C. for a holding time of at least 1 hour.

[0043] The hold temperature can be at least 295°C, 300°C, 305°C, 310°C, 315°C, or 317°C. In one embodiment, the hold temperature is at least 295°C. In another embodiment, the hold temperature is at least 300°C. In another embodiment, the hold temperature is at least 305°C. In another embodiment, the hold temperature is at least 310°C. In another embodiment, the hold temperature is at least 315°C. The hold temperature can be up to 400, 390, 380, or 370, 360, or 350°C.

[0044] The holding temperature is in the range of more than 290 to 400°C, preferably 30 to 370°C, particularly 310 to 350°C.

[0045] The retention time is at least 0.5 hours, such as 1, 2, 3, 4 or 5 hours. In one embodiment, the retention time is at least 2 hours. In another embodiment, the retention time is at least 3 hours. In another embodiment, the retention time is at least 3 hours. In another embodiment, the retention time is at least 4 hours.

[0046] The holding time may be up to 20 hours, such as up to 15 hours, up to 10 hours or up to 8 hours. The holding time may range from 1 to 20 hours, preferably from 2 to 15 hours, especially from 3 to 10 hours.

[0047] In one embodiment, the hold time is at least 2 hours with a hold temperature of at least 295° C. In another embodiment, the hold time is at least 3 hours with a hold temperature of at least 295° C. In another embodiment, the hold time is at least 4 hours with a hold temperature of at least 295° C.

[0048] In one embodiment, the hold time is at least 2 hours with a hold temperature of at least 300° C. In another embodiment, the hold time is at least 3 hours with a hold temperature of at least 300° C. In another embodiment, the hold time is at least 4 hours with a hold temperature of at least 300° C.

[0049] In one embodiment, the hold time is at least 2 hours with a hold temperature of at least 305° C. In another embodiment, the hold time is at least 3 hours with a hold temperature of at least 305° C. In another embodiment, the hold time is at least 4 hours with a hold temperature of at least 305° C.

[0050] In one embodiment, the hold time is at least 2 hours with a hold temperature of at least 310° C. In another embodiment, the hold time is at least 3 hours with a hold temperature of at least 310° C. In another embodiment, the hold time is at least 4 hours with a hold temperature of at least 310° C.

[0051] In one embodiment, the hold time is at least 2 hours with a hold temperature of at least 315° C. In another embodiment, the hold time is at least 3 hours with a hold temperature of at least 315° C. In another embodiment, the hold time is at least 4 hours with a hold temperature of at least 315° C.

[0052] Heating of the crude melamine polyphosphate is generally carried out whilst mixing the melamine phosphate, for example by stirring or by injecting an inert gas, which may be air, nitrogen or a noble gas, with nitrogen being preferred here.

[0053] At the end of the holding period, the resulting melamine polyphosphate can be cooled, for example, to less than 150° C., 120° C., or 100° C. Cooling can be achieved by stirring without heating or by injecting cold inert gas.

[0054] The melamine-depleted melamine polyphosphate is generally obtained in a solid form, such as a powder, and may further be ground, pulverized, pressed, granulated, or tableted.

[0055] During the holding time, the residual water can be distilled off while the crude melamine polyphosphate is heated. The residual water can be removed while the crude melamine polyphosphate is heated, for example, by purging with an inert gas or by applying a vacuum. During the holding time, the crude melamine polyphosphate can be purged with an inert gas or exposed to a vacuum.

[0056] In one embodiment, residual water is removed by purging with an inert gas. The inert gas can be air, nitrogen, or a noble gas, with nitrogen being preferred here. Purging can be performed by a volumetric flow that provides a volumetric exchange above the crude melamine polyphosphate at least once, twice, three times, four times, or five times per hour.

[0057] In another form the residual water is removed by applying a vacuum such as at least 0.9 bar, 0.5 bar or 0.1 bar.

[0058] The crude melamine polyphosphate is generally heated in an atmosphere without the addition of ammonia. In another embodiment, the crude melamine polyphosphate is heated in an atmosphere from which ammonia has been removed. In another embodiment, the crude melamine polyphosphate is heated in an inert gas atmosphere.

[0059] In one form, the crude melamine polyphosphate may be free of compounds that release water, such as borax, aluminum hydroxide, magnesium hydroxide, and mixtures thereof, hi another form, the crude melamine polyphosphate may contain less than 5, 3, 2, 1, 0.5, or 0.1 wt. % of compounds that release water.

[0060] In one embodiment, the crude melamine polyphosphate may be free of urea. In another embodiment, the reaction mixture may contain less than 5, 3, 2, 1, 0.5, or 0.1 wt. % urea. In another embodiment, the crude melamine polyphosphate may contain less than 0.1, 0.05, or 0.01 moles of urea per mole of phosphoric acid.

[0061] In one form, the crude melamine polyphosphate may be free of metal oxides, metal hydroxides, metal oxohydroxides, metal (hydroxy)carbonates, or layered double hydroxides (LDHs) of Mg, Zn, and Al, such as MgO, Mg(OH)2, Al2O3, Al(O)OH (boehmite), ZnO, Zn(OH)2, and Mg, Al-, Zn, Al-, and Mg / Zn, Al-hydrotalcites or hydromagnesites, MgCO3, or ZnCO3, etc. In another form, the crude melamine polyphosphate may contain less than 5, 3, 2, 1, 0.5, or 0.1 wt. % of metal oxides, metal hydroxides, metal oxohydroxides, metal (hydroxy)carbonates, or layered double hydroxides (LDHs) of Mg, Zn, and Al.

[0062] In one aspect, the crude melamine polyphosphate may be free of organic solvents. In another aspect, the crude melamine polyphosphate may contain less than 5, 3, 2, 1, 0.5, or 0.1 wt. % organic solvent.

[0063] The polyphosphate in the melamine-removing polyphosphate melamine may have a degree of polymerization of at least 10, 20, 30 or 40; 31 It can be determined by P solid-state NMR.

[0064] The residual melamine concentration in the melamine-removed melamine polyphosphate is generally less than 0.3%, 0.25%, 0.2%, 0.15%, 0.1%, 0.08%, 0.05%, or 0.03% by weight, which can be determined by HPLC analysis on a strong cation exchange phase using a diode array detector at 210 nm.

[0065] The melamine-depleted melamine polyphosphate may contain 1-30, 5-25, or 10-20% by weight of melam polyphosphate. In another embodiment, the melamine-depleted melamine polyphosphate may contain up to 30, 25, 20, 15, or 10% by weight of melam polyphosphate. In another embodiment, the melamine-depleted melamine polyphosphate may contain at least 1, 5, 10, or 15% by weight of melam polyphosphate. The melam polyphosphate concentration can be determined by HPLC on a cation exchange resin.

[0066] Melam is also known as N2-(4,6-diamino-1,3,5-triazin-2-yl)-1,3,5-triazine-2,4,6-triamine) and has the following chemical structure: [ka]

[0067] The melamine-depleted melamine polyphosphate may contain 0.01-5.0, 0.05-3.0 or 0.1-1.0 wt% melem polyphosphate. In another embodiment, the melamine-depleted melamine polyphosphate may contain up to 15, 10, 5, 2 or 1 wt% melem polyphosphate. In another embodiment, the melamine-depleted melamine polyphosphate may contain at least 0.01, 0.05 or 0.1 wt% melem polyphosphate. The melem polyphosphate concentration may be determined by HPLC on a cation exchange resin.

[0068] Melem is known as 1,3,4,6,7,9,9b-heptaazaphenalene-2,5,8-triamine and has the following chemical structure: [ka]

[0069] In one embodiment, the holding time is at least 2 hours at a holding temperature of at least 300° C., during which the crude melamine polyphosphate is purged with an inert gas or exposed to a vacuum.

[0070] In another embodiment, the holding time is at least 2 hours at a holding temperature of at least 310° C., during which the crude melamine polyphosphate is purged with an inert gas or exposed to a vacuum.

[0071] In another embodiment, the holding time is at least 2 hours at a holding temperature of at least 320° C., during which the crude melamine polyphosphate is purged with an inert gas or exposed to a vacuum.

[0072] In one embodiment, the holding time is at least 2 hours at a holding temperature of at least 300°C, during which the crude melamine polyphosphate is purged with an inert gas or exposed to vacuum, and crude melamine polyphosphate is produced by polymerizing the melamine phosphate at a polymerization temperature in the range of 200 to 290°C for a polymerization time of at least 0.5 hours.

[0073] In one embodiment, the holding time is at least 2 hours at a holding temperature of at least 310°C, during which the crude melamine polyphosphate is purged with an inert gas or exposed to vacuum, and crude melamine polyphosphate is produced by polymerizing the melamine phosphate at a polymerization temperature in the range of 230 to 290°C for a polymerization time of at least 1 hour.

[0074] In one embodiment, the holding time is at least 2 hours at a holding temperature of at least 320°C, during which the crude melamine polyphosphate is purged with an inert gas or exposed to vacuum, and crude melamine polyphosphate is produced by polymerizing the melamine phosphate at a polymerization temperature in the range of 230 to 290°C for a polymerization time of at least 2 hours.

[0075] In one embodiment, the holding time is at least 2 hours at a holding temperature of at least 300°C, during which time the crude melamine polyphosphate is purged with an inert gas or exposed to vacuum, and crude melamine polyphosphate is produced by polymerizing melamine phosphate at a polymerization temperature in the range of 200-290°C for a polymerization time of at least 0.5 hours, and the melamine phosphate is prepared by adding phosphoric acid and water to melamine powder.

[0076] In one embodiment, the holding time is at least 2 hours at a holding temperature of at least 310°C, during which the crude melamine polyphosphate is purged with an inert gas or exposed to vacuum, and crude melamine polyphosphate is produced by polymerizing melamine phosphate at a polymerization temperature in the range of 230-290°C for a polymerization time of at least 1 hour, and the melamine phosphate is prepared by adding phosphoric acid and water to melamine powder.

[0077] In one embodiment, the holding time is at least 2 hours at a holding temperature of at least 320°C, during which the crude melamine polyphosphate is purged with an inert gas or exposed to vacuum, and crude melamine polyphosphate is produced by polymerizing melamine phosphate at a polymerization temperature in the range of 230-290°C for a polymerization time of at least 2 hours, and the melamine phosphate is prepared by adding phosphoric acid and water to melamine powder.

[0078] The present invention also relates to a polymer composition (preferably a polyamide composition) comprising melamine-depleted melamine polyphosphate or a polymer composition (preferably a polyamide composition) comprising melamine-depleted melamine polyphosphate obtainable by a process for producing melamine-depleted melamine polyphosphate comprising heating crude melamine polyphosphate to a holding temperature of at least 300° C. for a holding time of at least 1 hour.

[0079] Melamine polyphosphate can be used as a flame retardant for polymers. A typical flame retardant polymer composition contains 10-50 wt. %, or 20-40 wt. % melamine polyphosphate.

[0080] The flame retardant polymer composition comprises: -35-55% by weight of polymer -15 to 45% by weight of melamine polyphosphate -0 to 50% by weight of reinforcing fibers -0 to 20% by weight of carbon-producing compounds - Catalyst that promotes carbon production of 0 to 10% by weight may include:

[0081] The flame retardant polymer composition may comprise the following polymers: 1. Polymers of mono- and diolefins, such as polypropylene (PP), polyisobutylene, polybutylene-1, polymethylpentene-1, polyisoprene or polybutadiene; polyethylene (optionally crosslinked), including, for example, high density polyethylene (HDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), or mixtures of these polymers. 2. Copolymers of mono- and diolefins, optionally containing other vinyl monomers, such as, for example, ethylene-propylene copolymers, linear low density polyethylene, and mixtures thereof with low density polyethylene, as well as terpolymers of ethylene, propylene and dienes, such as, for example, hexadiene, dicyclopentadiene or ethylidene norbornene; further, mixtures of such copolymers with the polymers listed under 1, such as, for example, polypropylene / ethylene-propylene copolymers. 3. Polystyrene, poly-(p-methyl-styrene), poly-(α-methylstyrene), and copolymers of styrene or α-methylstyrene with dienes or acrylic derivatives, such as styrene-butadiene, styrene-acrylonitrile, styrene-alkyl methacrylate, styrene-butadiene-alkyl acrylate, styrene-maleic anhydride, and styrene-acrylonitrile-methyl acrylate. 4. Polyphenylene oxide and polyphenylene sulfide, and their mixtures with styrene polymers or with polyamides. 5. Polyethers, polyesters, and polyurethanes derived from polybutadienes containing terminal hydroxy groups and aliphatic or aromatic polyisocyanates and their precursors. 6. Polyamides and copolyamides derived from diamines and dicarboxylic acids and / or aminocarboxylic acids or the corresponding lactams, such as polyamide 4, polyamide 6, polyamide 6 / 6, 6 / 10, 6 / 9, 6 / 12, 4 / 6, 66 / 6, 6 / 66, polyamide 11, polyamide 12, aromatic polyamides based on aromatic diamines and adipic acid: polyamides prepared from hexamethylenediamine and iso- and / or terephthalic acid, optionally with an elastomer as modifier, such as poly-2,4,4-trimethylhexamethylene terephthalamide, poly-m-phenylene-isophthalamide, etc. 7. Polyesters derived from dicarboxylic acids and dialcohols and / or hydroxycarboxylic acids or the corresponding lactones, such as polyethylene terephthalate, polybutylene terephthalate, poly-1,4-dimethylolcyclohexane terephthalate and polyhydroxybenzoates. 8. Thermosetting resins, including, for example, unsaturated polyester resins, saturated polyester resins, alkyd resins, polyacrylates or polyethers, or compositions comprising one or more of these polymers and a crosslinker.

[0082] The reinforcing fibers may be selected from the group of inorganic reinforcing materials, such as, for example, mica, clay or glass fibers, or aramid and / or carbon fibers, or combinations thereof.

[0083] Many substances are known to enhance the flame retardant effect and may be included in the polymer composition as carbon-producing compounds. These substances include, for example, phenolic resins, epoxy resins, melamine resins, alkyd resins, allyl resins, unsaturated polyester resins, silicone resins, urethane resins, acrylate resins, starch, glucose, and compounds having at least two hydroxyl groups. Examples of compounds having at least two hydroxyl groups include various alcohols such as pentaerythritol, dipentaerythritol, tripentaerythritol, and mixtures thereof. The concentration of such carbon-producing compounds in the polymer composition is usually less than 20% by weight, preferably 5-15% by weight.

[0084] Various catalysts for promoting carbon production may be incorporated to promote carbon production. These catalysts include, inter alia, metal salts of tungstic acid, complex oxides of tungsten and metalloids, salts of tin oxide, ammonium sulfamate and / or dimers thereof. The metal salts of tungstic acid are preferably alkali metal salts, in particular sodium tungstate. The complex oxides of tungsten and metalloids are understood to be complex oxides formed from tungsten and a metalloid such as silicon or phosphorus. The amount of catalyst used in the polymer composition is generally 0.1-5% by weight, preferably 0.1-2.5% by weight.

[0085] The flame retardant effect of melamine polyphosphate can be further enhanced by adding a second flame retardant component. In principle, other known flame retardants can be used as the second flame retardant component. Examples include antimony oxides, such as antimony trioxide; alkaline earth metal oxides, such as magnesium oxide; other metal oxides, such as alumina, silica, zinc oxide, iron oxide, manganese oxide; metal hydroxides, such as magnesium hydroxide and aluminum hydroxide; metal borates, such as hydrated or non-hydrated zinc borate; and phosphorus-containing compounds.

[0086] Examples of phosphorus-containing compounds include zinc phosphate, ammonium phosphate, ammonium pyrophosphate, ammonium polyphosphate, ethylenediamine phosphate, piperazine phosphate, piperazine pyrophosphate, melamine phosphate, dimelamine phosphate, melamine pyrophosphate, guanidine phosphate, dicyandiamide phosphate and / or urea phosphate. Phosphonates and phosphate esters can also be used. Their content can vary within a wide range, but generally does not exceed the content of the triazine derivative polyphosphate.

[0087] The polymer composition may further contain other conventional additives, such as stabilizers, release agents, flow agents, dispersants, colorants and / or pigments in generally applicable amounts. The additive content of the polymer composition is generally selected so that the desired properties remain within acceptable ranges, the limiting ranges of course depending on the polymer composition and the intended application.

[0088] The polymer compositions can be prepared using most conventional techniques, including dry mixing of all or many of the components in a tumble mixer, followed by melting in a melt mixer, such as a Brabender mixer, a single screw extruder, or preferably a twin screw extruder. EXAMPLES

[0089] Example 1 - Preparation of Melamine Phosphate Melamine powder (6000 kg, 45.57 kmol, purity at least 99%) was heated to 70 °C. Aqueous phosphoric acid solution (75 wt%, 4800 kg, 36.23 kmol) and water (1050 kg) were added to the melamine powder with stirring at 80-100 °C within 7 hours. During the process, reduced pressure (about 300 mbar) was applied to remove the water. The melamine phosphate was dried under vacuum at about 105 °C.

[0090] The yield was about 9550 Kg of melamine phosphate powder containing melamine and phosphoric acid in a molar ratio of about 1.25:1.33. The melamine phosphate had a purity of greater than 95% and a moisture content of less than 1% by weight (measured with a moisture meter equipped with weighing and halogen heating unit).

[0091] Example 2 - Polymerization of Melamine Phosphate Melamine phosphate (9200 Kg, from Example 1) was heated in a stirred reactor from 20° C. to 290° C. Heating was continued but the temperature of the melamine phosphate did not increase further above 290° C. The polymerization temperature was maintained for a polymerization time of 2.5 hours. During the polymerization time, an increase in pressure due to the production of water of reaction was observed.

[0092] Throughout the process, the reactor was stirred and purged with nitrogen at an overpressure of about 30 mbar, so the volume of free gas in the reactor was exchanged about 5-7 times per hour.

[0093] The residual melamine concentration in the crude melamine polyphosphate was 0.3 wt % and was determined as described in Example 3.

[0094] At the end of the polymerization time, crude melamine polyphosphate was obtained and used directly in Example 3.

[0095] Example 3 - Heating of crude melamine polyphosphate The crude melamine polyphosphate produced in Example 2 was used directly at its polymerization temperature without any post-treatment.

[0096] The temperature of the crude melamine polyphosphate was then increased from the polymerization temperature of 290° C. to a holding temperature. Samples were analyzed immediately upon reaching temperatures of 300° C. and then 320° C. (Examples A and B in Table 1).

[0097] The crude melamine polyphosphate was maintained at the holding temperature for the holding time according to Table 1. During the holding time, no pressure increase due to the production of reaction water was observed.

[0098] Example C was repeated twice starting from Example 1, and the results are listed as Examples D and E.

[0099] During the retention time, the reactor was stirred and purged with nitrogen at an overpressure of about 30 mbar, so that the volume of free gas in the reactor was exchanged about 5-7 times per hour.

[0100] At the end of the holding period, the powder was allowed to cool, with stirring, to below 90° C. in 5 hours to yield approximately 7930 Kg.

[0101] In Examples C-F, melamine-free melamine polyphosphate was obtained as a white powder with an acid value of up to 0.6 mg KOH / g (potentiometric titration with 0.1 M NaOH) and a pH of about 5.5-6.5 (saturated solution at 20° C.).

[0102] Residual melamine concentrations are shown in Table 1 in weight percent and were determined by HPLC on Partisil® 10SCX (benzenesulfonic acid based strong cation exchange phase, length 25 cm, particle size 10 μm) at 40° C. The mobile phase (0.7 ml / min) was water, buffer KH2PO4 / H3PO4. Melamine was detected in approximately 5.4 min by a diode array detection DAD detector at 210 nm.

[0103] [Table 1]

[0104] The data in Table 1 show that the process of the present invention can reliably reduce the residual melamine concentration to about 0.01% (Examples C, D and E). In comparison, at lower temperatures or shorter times, the residual melamine concentration is higher.

Claims

1. 1. A method for producing melamine-depleted melamine polyphosphate, comprising heating crude melamine polyphosphate to a holding temperature above 290°C for a holding time of at least 1 hour.

2. 2. The method of claim 1, wherein the crude melamine polyphosphate has a residual melamine concentration of at least 0.2% by weight melamine.

3. 3. The method of claim 1 or 2, wherein the melamine-depleted melamine polyphosphate has a residual melamine concentration of less than 0.2 wt%, less than 0.1 wt%, or less than 0.05 wt%.

4. 3. The method of claim 1 or 2, wherein the holding temperature is at least 295, 300, 305, 310, or 315°C.

5. 3. The method of claim 1 or 2, wherein the hold time is at least 1, 2, 3, 4, or 5 hours.

6. 3. The method of claim 1 or 2, wherein during the holding time the crude melamine polyphosphate is purged with an inert gas or subjected to a vacuum.

7. 3. The method of claim 1 or 2, wherein the crude melamine polyphosphate is produced by polymerizing melamine phosphate at a polymerization temperature in the range of 200 to 290°C for a polymerization time of at least 0.5 hours.

8. 8. The method of claim 7, wherein the melamine phosphate contains melamine and phosphoric acid in a molar ratio of 1:1 to 2:1, preferably 1.2:1 to 1.5:

1.

9. 8. The method of claim 7, wherein the melamine phosphate is prepared by heating melamine, phosphoric acid, and water above 70°C.

10. 8. The method of claim 7, wherein the melamine phosphate is prepared by adding phosphoric acid and water to melamine powder.

11. 3. The method of claim 1, wherein the melamine-depleted melamine polyphosphate contains 1 to 30% by weight of melam polyphosphate.

12. 1. A melamine-depleted melamine polyphosphate containing residual melamine, wherein the residual melamine concentration is less than 0.2 wt %, less than 0.1 wt %, or less than 0.05 wt %.

13. The melamine-depleted melamine polyphosphate of claim 12, containing 1 to 30% by weight of melam polyphosphate.

14. The melamine-removed melamine polyphosphate of claim 12 or 13, containing 0.01 to 5.0% by weight of melem polyphosphate.

15. 14. The melamine-depleted melamine polyphosphate of claim 12 or 13, wherein the melamine-depleted melamine polyphosphate is obtainable by a process as defined in claim 1 or 2, comprising heating the crude melamine polyphosphate to a holding temperature above 290°C for a holding time of at least 1 hour.

16. 14. A polymer composition comprising melamine-depleted melamine polyphosphate as defined in claim 13 or a polymer composition comprising melamine-depleted melamine polyphosphate obtainable by the process defined in claim 1 or 2.