Method for recovering melamino-formaldehyde resins from waste materials produced during production and processing of artificial panels

Abstract

The invention relates to a method for degrading melamino-formaldehyde resins from waste products produced during the production and processing of artificial panels, comprising the following steps: providing waste products which are produced during the production and processing of artificial panels and contain polycondensed melamino-formaldehyde resins; optionally, the waste material product containing the melamino-formaldehyde resin is crushed; mixing the waste product containing melamine formaldehyde resin with water and adding at least one reducing sulfur-containing compound selected from the group consisting of meta-disulfite, bisulfite and / or dithionite, sulfinate or sulfinate analogue; heating an aqueous mixture / suspension consisting of the waste product containing the melamine formaldehyde resin and at least one reducing sulfur-containing compound to a temperature of between 60 DEG C and 120 DEG C, preferably between 80 DEG C and 100 DEG C, with controlled reaction until a clear solution is obtained; separating impurities from the clear solution; optionally further heating the mixture of the waste product containing melamine formaldehyde resin and at least one reducing sulfur compound, from which impurities have been removed, at a temperature of between 60 DEG C and 120 DEG C, preferably between 80 DEG C and 110 DEG C under the condition of reaction control, and optionally at a temperature of between 60 DEG C and 120 DEG C, preferably between 80 DEG C and 110 DEG C, until it can be confirmed that the polycondensed melamine formaldehyde resin is not (re) present in the reaction mixture; and cooling the reaction mixture and separating the mixture of melamine derivatives precipitated in the process, in particular melamine hydroxymethyl alcohol and melamine sulfonate.

Description

Technical Field

[0001] The present invention relates to a method for recovering or decomposing melamine formaldehyde resin from waste generated during the manufacture, processing and recycling of wood-based panels. The present invention also relates to the use of melamine derivatives recovered from waste products containing melamine formaldehyde resin. Background Art

[0002] In all industrial fields, the question of how to recycle residues or products after their end-of-use is being raised more and more frequently. Since the European Union has stipulated future reuse / recycling for all products, this topic has received significant practical impetus. It can also be found that due to the substantial increase in the prices of these raw materials, recycling has become increasingly interesting. Additionally, the cost of residue disposal has increased significantly. Furthermore, the following aspect is also becoming increasingly important: all producers want to produce as ecologically as possible. This means that raw materials should be used effectively, emissions should be avoided, and waste should be generated in small amounts.

[0003] These developments are particularly important for products that contain starting materials based on oil or gas. These products are mainly plastics, which are also important in terms of quantity. Recycling of thermoplastics (polyethylene, polypropylene, polyvinyl chloride) has been practiced for decades, yet the concept of recycling thermosetting plastics / thermosetting resins (phenolic resins, melamine resins, urea resins, etc.) has not been able to be implemented.

[0004] This is particularly related to the difficult-to-crack crosslinked structure of thermosetting plastics / thermosetting resins, which is regarded as a special advantage of the products because the products are thus considered resistant to thermal or chemical erosion. However, this is also related to the sometimes very low prices of raw materials in the past.

[0005] Preliminary methods for recycling urea-formaldehyde glue, which is particularly used as glue in wood materials, have been developed. After curing, these glues are very sensitive to the erosion of moisture / water at higher temperatures. Here, materials (such as particle boards) may decompose due to hydrolysis. The hydrolyzed glue basically remains in the generated wood chips and is used as the basis for the added glue when remanufacturing wood materials. However, it must be confirmed that this method is rather a recycling of the wood matrix compared to recycling the glue components.

[0006] However, there have also been initiatives in the past that have demonstrated that recycling thermosetting plastics should be feasible. DD 155779 describes how to clean production facilities contaminated / clogged with cured melamine resin.

[0007] The decomposition and utilization of cured melamine resins (fibers) are described in EP 0612 793B1. However, only residues from the production of molded articles / fibers and the recycling of said products are referred to here. The cured melamine residues / waste materials are processed by means of reductive decomposition with bisulfites, metabisulfites or dithionites. Here, the vast majority of melamine methyl sulfone is produced. Feasible applications of such sulfones are also described in the publications. However, the sulfones can only be used in small amounts in the applications. In addition, because of working with a large excess of reducing agent, a large amount of waste in the form of inorganic sulfates is also produced. Said waste must be removed after separation. In addition, the reaction time is at least eight hours.

[0008] Another method is described in CN 111675827. There, the cured melamine resins from different sources are heated and decomposed in a mixture consisting of water and an organic solvent in the presence of an acid or a Lewis acid under reflux. Here, the ratio of the solvent to the melamine waste is at least 80 to 1. A relatively long reaction time of up to twenty-four hours is also given here. The reaction is also carried out under pressure at a temperature above 100 °C. In addition to the melamine produced, a relatively large amount of a mixture consisting of the solvent, the acid and salts remains. Said residue must be removed again. All of these make the method costly, expensive and problematic in terms of recycling.

[0009] CN 111 777 566 and CN 111 875 843 describe similar methods for recovering melamine from tableware made of melamine formaldehyde resins. For this purpose, the tableware is first comminuted and then treated with an aqueous organic solvent and an acidic catalyst such as HCl, HNO3, H2SO4, AlCl3, etc. at a temperature between 80 °C and 150 °C. The significant amount of organic solvent combined with water required by the method makes the method more ecologically disadvantageous. In addition, the acids that are equally problematic are also present in the aqueous phase.

[0010] However, so far, the recovery of thermosetting resins from wood materials, impregnates or laminates has not been described. During the production and further processing of wood materials, waste materials containing melamine resins are generated at many stages of the value chain.

[0011] In the case of the manufacture of wood-based panels and their further processing into floorboards or furniture components, impregnated decorative papers, covering papers and balancing papers are particularly pressed onto the wood-based panels. These papers are impregnated with thermosetting resins (urea resins, melamine resins) in impregnation facilities or impregnation channels. When starting up the facilities, changing products, making operating errors or changing production parameters due to technical reasons, a large number of impregnations that are imperfect in terms of quality are produced. The impregnations are removed (e.g. by heat utilization) and have an average loss of 3% - 8% depending on the coating size, duration of the interference, etc. Since modern impregnation channels operate at speeds of 80 m / min and greater, millions of square meters of waste are generated annually as a result. Usually, the impregnations contain approximately 50% by weight of resin, and thus a significant amount of urea / melamine resin is also lost. Additionally, due to trimming and dust formation of the impregnations, resin waste is produced during impregnation. These residues are also removed. Residual resin is also produced during impregnation, which is currently removed and can also amount to a significant number of tons in a year.

[0012] When further processing the impregnations, for example, by pressing them onto the wood-based panels, waste is generated at the press due to scraping equipment for removing the impregnation overhangs at the edges of the panels, and superposed impregnations that can no longer be used for production are also removed. All of these residues or waste have the advantage that the melamine resin has not fully cured, making it more recyclable without problems.

[0013] When manufacturing wood-based panels (such as particle boards, fiber boards), adhesives highly reinforced with melamine are also often used. The same applies to the impregnations as for the panels: waste that must be removed is generated at all stages of the value chain.

[0014] The disadvantages resulting from the hitherto practice of waste removal are especially high material losses, high removal costs and waste problems.

[0015] As has been shown, the European Union expects a consistent recycling concept for all products. This means that for the wood materials industry, and also for products containing melamine, recycling paths are needed. This should only apply to products containing significant amounts of melamine. Summary of the Invention

[0016] Therefore, the technical object on which the present invention is based is to develop a method that enables the recovery of melamine by means of residues and waste from different stages of the value chain, namely impregnation, wood-based panel manufacture and recycling products. The method should provide products that can be used for manufacturing impregnations, coatings or wood materials. Here, it should be considered that due to the recycling costs, rather higher-value utilization should become preferred. Here, special attention should be paid to generating as little waste as possible or no waste at all. Additionally, the method should be a solution that is as fast as possible and less energy-intensive.

[0017] This object is achieved by a method having the features of claim 1.

[0018] Correspondingly, a method is provided for degrading or decomposing or depolymerizing melamine formaldehyde resin from waste products generated during the manufacture and processing of wood-based panels. The melamine formaldehyde resin to be decomposed is in particular incorporated in the waste or waste products of paper layers and wood-based material bearing plates generated in production facilities for the manufacture and further processing of wood-based panels.

[0019] The method comprises the following steps:

[0020] - providing waste products generated during the manufacture and processing of wood-based panels, said waste products containing condensed melamine formaldehyde resin,

[0021] - optionally comminuting the waste products containing melamine formaldehyde resin,

[0022] - mixing the waste products containing melamine formaldehyde resin with water and adding at least one reducing sulfur-containing compound selected from metabisulfites, bisulfites and / or dithionites, sulfinates or sulfinate analogues,

[0023] - heating the aqueous mixture / suspension composed of the waste products containing melamine formaldehyde resin and at least one reducing sulfur-containing compound to a temperature between 60 °C and 120 °C, preferably between 80 °C and 100 °C, under reaction control until a clear solution is obtained,

[0024] - separating impurities from the clear solution,

[0025] - optionally further heating the mixture composed of the waste products containing melamine formaldehyde resin and at least one reducing sulfur compound from which impurities have been removed to a temperature between 60 °C and 120 °C, preferably between 80 °C and 110 °C, under reaction control until it is verified that no (longer) condensed melamine formaldehyde resin is present in the reaction mixture, and

[0026] - cooling the reaction mixture and separating the mixture of melamine derivatives precipitated therefrom, in particular separating melamine hydroxymethyl alcohol and melamine sulfonate.

[0027] Accordingly, a method is provided in which a thermosetting resin matrix is decomposed into different waste products by means of bisulfite / metabisulfite / dithionite or sulfinate. Here, the more or less crosslinked melamine resin contained in the residue is reductively decomposed by means of a sulfur-containing reducing agent.

[0028] Melamine hydroxymethanol and melamine sulfonate and a small amount of melamine are produced as reaction products, where melamine sulfonate is the main component (more than 70%). The formed melamine sulfonate has the following structure:

[0029]

[0030] During or after the reaction, impurities contained in different residues or products can be easily separated. It is advantageous to filter off or skim off floating fibers, etc. This can be carried out (continuously) already during the decomposition reaction or at the end. However, it must be considered that, for example, fibers may cause additional consumption of the reducing agent. This is not necessary when processing the resin, where the impurities should also be separated in the purification step.

[0031] When decomposing while boiling under reflux, the melamine resin matrix is separated, and the water-insoluble residues dissolve slowly. Here, auxiliaries that vary according to the waste / product are also removed. Here, it involves auxiliaries usually present in the resin, such as curing agents, elastifiers, corundum, glass balls, pigments, etc. However, other resins or adhesives are also removed (urea resins / adhesives).

[0032] The melamine derivatives released from the polycondensate precipitate out upon cooling and can then be filtered off and washed. Here, auxiliaries that vary according to the waste / product are also removed. Here, it involves auxiliaries usually present in the resin, such as curing agents, elastifiers, corundum, glass balls, pigments, etc. However, other resins or adhesives are also removed (urea resins / adhesives).

[0033] After separating the components, the melamine derivatives can be used for different applications. After adding ammonia or other amines, the melamine sulfonate can be converted into the corresponding ammonium salt. The ammonium salt can be used as a curing agent. However, the melamine sulfonate itself can also be used. Melamine hydroxymethanol can be used again to prepare melamine resins / adhesives for different applications. When manufacturing wood materials using urea-formaldehyde glue as an adhesive, melamine hydroxymethanol can also be used as a formaldehyde scavenger. It is also considered for use as a glue component for reducing swelling. Generally, this component can also be used as a flame retardant or a flame retardant / adhesive combination in different products (wood materials, laminates, etc.).

[0034] Therefore, this method enables (almost) complete recycling of melamine resins. Thereby, raw materials can be saved, waste can be avoided, and costs can be reduced.

[0035] In a first aspect, this method comprises the following steps:

[0036] - Providing a waste product generated during the manufacture and processing of wood-based panels, the waste product containing a condensed melamine formaldehyde resin,

[0037] - Optionally, crush the waste product containing melamine formaldehyde resin.

[0038] - Mix the waste product containing melamine formaldehyde resin with an aqueous solution of 20% to 70% by weight, preferably 40% to 60% by weight, of at least one metabisulfite, bisulfite, and / or dithionite.

[0039] - Heat the mixture composed of the waste product containing melamine formaldehyde resin and at least one metabisulfite, bisulfite, and / or dithionite to a temperature between 60 °C and 120 °C, preferably between 80 °C and 100 °C, until a clear solution is obtained.

[0040] - Separate the non-hydrolyzable impurities (as contaminants) from the clear solution.

[0041] - Further heat the mixture composed of the waste product containing melamine formaldehyde resin and at least one metabisulfite, bisulfite, and / or dithionite from which the impurities have been removed at a temperature between 60 °C and 120 °C, preferably between 80 °C and 110 °C, under reaction control until it can be verified that no (longer) condensed melamine formaldehyde resin is present in the reaction mixture.

[0042] - Cool the reaction mixture and separate the mixture of melamine derivatives, especially melamine hydroxymethyl alcohol and melamine sulfonate, which precipitates out here.

[0043] According to a first aspect, a method is hereby provided in which the thermosetting resin matrix in different waste products is decomposed by means of bisulfite / metabisulfite / dithionite.

[0044] The method according to the first aspect does not require the use of organic solvents or strong acids. More precisely, metabisulfite or bisulfite is used, which can also be used as a preservative in the food industry, so it is not a concern in terms of toxicology and ecology. The alkali metal sulfate produced during the hydrolysis decomposition can also be utilized.

[0045] In an embodiment of the method, the waste product containing melamine formaldehyde resin is mixed with an aqueous solution of 20% to 70% by weight, preferably 40% to 60% by weight, of at least one metabisulfite, bisulfite, and / or dithionite of an alkali metal or alkaline earth metal.

[0046] In particular, the waste product containing melamine formaldehyde resin is mixed with at least one sodium metabisulfite solution or sodium bisulfite solution, which has a pH value between 3.0 and 6, preferably between 3.5 and 5.5. Sodium metabisulfite (Na2S2O5), also known as sodium pyrosulfite or sodium metabisulfite, is the sodium salt of unstable dithionous acid in the free state. Sodium bisulfite (NaHSO3), also known as sodium bisulfite, is the sodium salt of sulfurous acid. It is unstable outside the aqueous solution.

[0047] In a particularly preferred embodiment, the waste product containing melamine formaldehyde resin is mixed with at least one sodium bisulfite (or sodium bisulfite) solution of 40% to 60% by weight, especially 50% by weight.

[0048] As mentioned above, in the next step, the mixture composed of the waste product containing melamine formaldehyde resin and at least one metabisulfite, bisulfite and / or dithionite is heated to a temperature between 60 °C and 120 °C, preferably between 80 °C and 100 °C, until a clear solution is obtained.

[0049] Currently, a clear solution should be understood as one in which no turbidity is visible (i.e., the solution is transparent), and only solids contained as contaminants can be seen.

[0050] In an intermediate step, the mentioned impurities are separated from the clear solution. The separation of the solids contained as contaminants in the reaction mixture is carried out by filtration, preferably hot filtration and / or skimming. Therefore, the fibers released from the paper layer or the wood-based panel and floating can be skimmed off, and other particles such as corundum and / or glass beads can be separated by hot filtration.

[0051] Subsequently, the mixture composed of the waste product containing melamine formaldehyde resin and at least one metabisulfite, bisulfite and / or dithionite, from which the impurities have been removed, is further heated at a temperature between 60 °C and 120 °C, preferably between 80 °C and 110 °C, under reaction control until it can be verified that no melamine formaldehyde resin oligomers are present in the reaction mixture.

[0052] The depolymerization or hydrolysis degradation of melamine formaldehyde resin is controlled by reaction using suitable analytical methods such as thin layer chromatography (DC), HPLC or gas chromatography. Preferably, thin layer chromatography (DC) is used, where water and / or alcohol such as methanol, ethanol or a mixture thereof is used as a suitable mobile phase. Preferably, a mixture composed of water / ethanol (1:1) is used as the mobile phase.

[0053] After the depolymerization of melamine formaldehyde resin, the reaction mixture is cooled. During the cooling of the reaction mixture, a product mixture precipitates from the monomeric melamine derivatives.

[0054] The mixture from monomeric melamine derivatives comprises melamine hydroxymethyl alcohols, in particular monohydroxymethyl melamine and dihydroxymethyl melamine, and melamine sulfonates. The share of melamine hydroxymethyl alcohols is about 10 wt% - 30 wt%, and the share of melamine sulfonates is about 70 wt% - 90 wt%.

[0055] In a final step, the mixture consisting of monomeric melamine derivatives is separated into melamine hydroxymethyl alcohols and melamine sulfonates.

[0056] The melamine hydroxymethyl alcohols and melamine sulfonates obtained from melamine formaldehyde resins can be used for different purposes. The melamine sulfonates (after concentration of the liquid mixture) precipitate and can be separated. By adding ammonia or an amine, the melamine sulfonates can be converted into a soluble form.

[0057] Thus, the melamine derivatives recovered or obtained from waste products containing melamine formaldehyde resins can be used as curing agents, flame retardants and / or for the preparation of melamine resins for resins.

[0058] In one embodiment, the recovered melamine derivatives comprise a mixture consisting of monomeric melamine hydroxymethyl alcohols and melamine sulfonates, and the monomeric melamine hydroxymethyl alcohols and melamine sulfonates can be separated as described.

[0059] In one embodiment, it is proposed that melamine sulfonates be used as curing agents for formaldehyde resins, in particular melamine formaldehyde resins or urea formaldehyde resins. Melamine sulfonates are particularly suitable as latent curing agents. Preferably, the solution containing melamine sulfonates is used as a curing agent after separation of the melamine hydroxymethyl alcohols.

[0060] When using melamine sulfonates as curing agents, the suitable amount of melamine sulfonates in the resin to be cured is between 0.4 wt% and 3 wt%, preferably between 0.5 wt% and 2.0 wt%.

[0061] In another embodiment, it is proposed that the melamine hydroxymethyl alcohols (separated from the mixture) be used for the preparation of melamine resins, in particular for the preparation of melamine resins for use as adhesives or impregnating agents.

[0062] In this case, the recovered melamine hydroxymethyl alcohols are preferably mixed with melamine and formaldehyde. In one embodiment, the melamine hydroxymethyl alcohols are used in a ratio of monohydroxymethyl melamine to dihydroxymethyl melamine of 1 / 1. Formaldehyde and melamine are added in a ratio of 1 / 1. The condensation to form the melamine formaldehyde resin is preferably carried out until the water dilution is 1 to 3.

[0063] In another embodiment, melamine hydroxymethyl alcohol and melamine sulfonate are used as a mixture or separately as a flame retardant. In the case of being used as a flame retardant, an ammonium salt of a melamine derivative is preferably used.

[0064] In a second aspect, the method comprises the following steps:

[0065] - Providing a waste product generated during the manufacture and processing of wood-based panels, the waste product containing a condensed melamine formaldehyde resin,

[0066] - Optionally crushing the waste product containing the melamine formaldehyde resin,

[0067] - Mixing the waste product containing the melamine formaldehyde resin with water and adding at least one sulfite or sulfite analogue (as a reducing agent),

[0068] - Heating the aqueous mixture / suspension composed of the waste product containing the melamine formaldehyde resin and at least one sulfite or sulfite analogue to a temperature between 60 °C and 120 °C, preferably between 80 °C and 100 °C, under reaction control until a clear solution is obtained, - Separating impurities from the clear solution,

[0069] - Optionally further heating the mixture composed of the waste product containing the melamine formaldehyde resin and at least one sulfite or sulfite analogue from which impurities have been removed to a temperature between 60 °C and 120 °C, preferably between 80 °C and 110 °C, under reaction control until it is confirmed that there is no (longer) condensed melamine formaldehyde resin present in the reaction mixture, and

[0070] - Cooling the reaction mixture and separating the melamine sulfonate that precipitates out in the form of a salt here.

[0071] According to the second aspect, the thermosetting resin matrix in different products is decomposed by a sulfite or sulfite analogue, especially formamidine sulfinic acid (FAS), as a reducing agent. The reaction is carried out with water as the solvent. The material to be recovered boils under reflux here. Particularly advantageously, in this method, the reaction ends after 90 min to 120 min, different from the prior art. The ratio between the reducing agent and the melamine waste is also significantly lower. In EP 0612793B1 mentioned above, the ratio is approximately 4 to 1. The ratio can be reduced to 2 to 1 with FAS.

[0072] When the melamine waste reacts with a sulfite or sulfite analogue such as FAS, when FAS is used as an ammonium salt having the structure listed above, melamine sulfonate is produced as the main product as a decomposition product:

[0073] The yield of the melamine sulfonate depends on the waste product containing melamine-formaldehyde resin to be decomposed and is between 70% and 95%, preferably between 75% and 90%, based on the waste product containing melamine-formaldehyde resin used.

[0074] It is surprising that decomposing the waste product containing melamine-formaldehyde resin results in essentially one main product, because when using metabisulfite as a reducing agent in the manner known from the prior art, a mixture consisting of melamine, melamine hydroxymethyl alcohol, and hydroxymethyl melamine sulfonate is usually produced (EP 612 793B1).

[0075] After the end of the reaction and the separation of the impurities already mentioned, the reaction solution is cooled. Here, the melamine sulfonate precipitates and can be separated, washed, and dried from the reaction solution. Not only the precipitated melamine sulfonate but also the supernatant can be reused.

[0076] The method according to the second aspect also does not require the use of organic solvents. More precisely, an aqueous solution of sulfite or a sulfite analogue such as FAS is used.

[0077] As already mentioned, the sulfite or sulfite analogue is used as a reducing agent. The sulfite analogue formamidine sulfinic acid (FAS) is used as the preferred reducing agent.

[0078] Formamidine sulfinic acid (FAS), also known as aminoiminomethanesulfinic acid, is a white to yellow odorless solid that can be prepared in situ from thiourea and hydrogen peroxide. The reducing effect of FAS comes from the sulfite ions generated during hydrolysis. Currently, FAS is widely used for the decolorization of recycled paper and is thus abundantly available.

[0079] In another embodiment of the method, the weight ratio of the reducing agent to the waste product containing melamine-formaldehyde resin is between 2:1 and 0.5:1, preferably between 1.5:1 and 0.8:1. Preferably, FAS is added portion by portion because FAS does not dissolve well even in warm water, thus ensuring reasonable mixing.

[0080] In a preferred embodiment of the method, the reaction time until the complete degradation of the melamine-formaldehyde resin is between 60 min and 240 min, preferably between 90 min and 120 min. In particular, in view of the significantly longer reaction times known from the prior art, the relatively short reaction time is surprising. Thereby, a time-advantageous and thus low-cost variant for recycling melamine resin waste is provided.

[0081] As mentioned, in the next step, the aqueous mixture / suspension consisting of the waste product containing melamine formaldehyde resin and at least one sulfite is heated to a temperature between 60 °C and 120 °C, preferably between 80 °C and 100 °C, under reaction control until a clear solution is obtained.

[0082] Currently, a clear solution should be understood as one in which no turbidity is visible (i.e., the solution is transparent), and only the solids contained as contaminants can be seen.

[0083] In an intermediate step, the impurities mentioned are separated from the clear solution. The separation of the solids contained as contaminants in the reaction mixture is carried out by filtration, preferably hot filtration, and / or skimming. Thus, the fibers released from the paper layer or the wood-based panel and floating can be skimmed off, and other particles such as corundum and / or glass beads can be separated by hot filtration.

[0084] Optionally, subsequently, the mixture consisting of the waste product containing melamine formaldehyde resin and at least one sulfite, from which the impurities have been removed, is further heated at a temperature between 60 °C and 120 °C, preferably between 80 °C and 110 °C, under reaction control until it is confirmed that no melamine formaldehyde resin oligomers are present in the reaction mixture.

[0085] The depolymerization or hydrolysis degradation of the melamine formaldehyde resin is controlled by means of suitable analytical methods such as thin-layer chromatography, HPLC or gas chromatography. In the case of thin-layer chromatography, water and / or an alcohol such as methanol, ethanol or a mixture thereof is used as a suitable mobile phase. Preferably, methanol is used as the mobile phase.

[0086] After the depolymerization of the melamine formaldehyde resin, the reaction mixture is cooled. During the cooling of the reaction mixture, monomeric melamine sulfonate (C4H7N6SO3) precipitates.

[0087] In particular, when using FAS as a reducing agent, melamine sulfonate precipitates as an ammonium salt.

[0088] If FAS is used as a reducing agent, the aqueous supernatant (after separating the precipitated melamine sulfonate) contains a solution consisting of ammonium sulfite and ammonium sulfate. Both the ammonium sulfite and ammonium sulfate are formed due to the decomposition of FAS into urea and sulfonic acid, where urea further decomposes into ammonia and carbon dioxide. The sulfonic acid is oxidized to sulfite and / or sulfate. This solution (or supernatant) can be used as a curing agent for melamine resins and urea resins. Thus, the whole decomposition is utilized.

[0089] Use melamine sulfonate (precipitated and separated as a solid) as a curing agent for resins, in particular formaldehyde resins such as melamine formaldehyde resins and urea formaldehyde resins. When using melamine sulfonate as a curing agent, the suitable amount of melamine sulfonate in the resin to be cured is between 0.2% by weight and 3% by weight, preferably between 0.5% by weight and 2.0% by weight.

[0090] In one embodiment of the method, the waste products containing melamine formaldehyde resin generated during the manufacture and processing of wood-based panels include stacked melamine resins, melamine resin dust, overlay impregnates, decorative impregnates, balance impregnates, kraft paper impregnates, uncoated or coated wood-based panels such as HDF boards, and / or laminates such as thin laminates.

[0091] Here, the stacked melamine resin is understood as a melamine formaldehyde resin that has at least partially condensed and has turbidity. In particular, when either the viscosity increases significantly (measured with a 4 mm DIN cup according to EN ISO 2431:2011: fresh resin 20 s to 30 s, stacked resin: >50 s) or the resin becomes turbid, stacking exists in the melamine resin.

[0092] Melamine resin dust is generated at different locations during the processing of impregnates and wood-based panels, for example, at the shearing machine and during trimming. The melamine resin dust generated here has a particle size of >50 μm and a maximum of 100 μm - 300 μm. The trimming material is a small piece (Schnipsel) with a width of approximately 10 mm and a length variable according to the effectiveness of the scraper.

[0093] Overlay impregnates, decorative impregnates, balance impregnates, and kraft paper impregnates are based on paper layers that are completely or partially impregnated (soaked) with a resin, preferably a melamine formaldehyde resin.

[0094] Correspondingly, not only partially impregnated, i.e., single-sided impregnated paper, but also fully impregnated paper can be used. In the case of single-sided impregnated paper, only the entire surface of one side of the paper is uniformly provided with the impregnating resin. In this case, the amount of resin applied is between 30% by weight and 70% by weight, preferably between 40% by weight and 60% by weight, and particularly preferably 50% by weight, based on the grammage of the paper. In contrast, in the case of fully impregnated paper, the resin amount is 80% - 400% by weight, preferably 90% - 120% by weight, and particularly preferably 100% - 110% by weight, based on the grammage of the paper.

[0095] The overlay paper is a thin paper that is usually impregnated with a conventional melamine resin. The overlay paper is also commercially available, in which wear-resistant particles, such as corundum particles, have been incorporated into the resin of the overlay layer or sprinkled onto the overlay layer wetted with resin to improve wear resistance. For the impregnation of the overlay paper, a resin coating with up to 400% by weight of melamine resin is common.

[0096] The decorative paper is a special paper for the surface finishing of wood materials, which achieves a high decorative variety. Thus, in addition to the typical imprints of various wood reproductions, extensive imprints of geometric shapes or extensive imprints of artistic products are commercially available. In fact, there are no restrictions in the choice of themes. To ensure optimal printability, the paper used must have a suitable smoothness and dimensional stability and also be suitable for the penetration of the necessary impregnation with artificial resins. The resin coating of the decorative impregnation is 100% to 120% by weight.

[0097] The balance paper is a high-quality impregnated paper used as a balancing material for compensating tensile stresses on the upper side of the carrier plate, for example, a high-quality impregnated paper for single-sided veneered panels and other single-sided claddings.

[0098] The kraft paper has high strength and is composed of cellulose fibers added with starch, alum, and glue to achieve surface effects and strength improvement. The resin coating in the kraft paper impregnation is 45% to 90%. The kraft paper is used as the core layer of HPL (High Pressure Laminate) and CPL (Continuous Pressed Laminate). Phenolic resin is used in the HPL core layer, while in the CPL, it is impregnated with a mixture composed of melamine and phenolic resin.

[0099] The impregnation can be carried out, for example, in an impregnation bath by roll coating, by anilox roll coating, by knife coating, or also by spraying. In one embodiment variant, the paper layer is treated in such a way that first (e.g., in a soaking tank) the reverse side of the paper layer is impregnated with a resin having a solids content between 50% and 70% by weight, preferably 60% by weight. After passing through a breathing section, immersion impregnation is carried out with the resin. The excess resin is removed in a doctor blade system / pressure roll pair, and optionally (in the case of an overlay paper layer), the wear-resistant particles are sprinkled onto the impregnated paper layer. A drying step is carried out until the residual humidity is about 6%. Then the impregnate is pressed together with the wood-based panel, for example, in a short-cycle press.

[0100] Wood-based panels such as wood particle boards and wood fiber boards, e.g., MDF boards, HDF boards are made of wood chips or wood fibers, which can be obtained by cutting wood chips in a cutting machine or the fiber separation process (Zerfaserungsprozess) of wood chips in a refining mill. The wood fibers used together in wood fiber boards have a length between 1.5 mm and 20 mm and a thickness between 0.05 mm and 1 mm. The size of the wood chips used in wood particle boards depends on whether they are used for the top layer or the middle layer. In the middle layer, the screening width of the chips is > 0.125 mm, and in the top layer, the screening width of the chips is > 0.8 mm - 1.0 mm.

[0101] Preferred adhesives for wood-based panels are formaldehyde-containing adhesives such as melamine formaldehyde resin and urea formaldehyde resin. The amount of adhesive used in wood-based panels usually ranges from 5 wt% to 25 wt%, preferably 8 wt% to 20 wt%, and particularly preferably between 10 wt% and 15 wt%. In specific applications, the amount of adhesive in wood-based panels can also exceed 25 wt%, e.g., up to 30 wt% - 50 wt%.

[0102] In the case of a clad wood-based panel, the paper impregnates listed above are laid on the wood-based panel and pressed. Usually, the impregnated decorative paper is first applied to the upper side of the wood-based panel. Subsequently, at least one cover layer impregnate is applied to the decorative impregnate. The balance impregnate is pressed against the wood-based panel on the lower side. The typical structure of a clad HDF board from top to bottom is: cover layer impregnate, decorative impregnate, HDF carrier, balance impregnate.

[0103] A laminate is a laminated material composed of paper impregnates pressed against each other on a carrier board.

[0104] For example, flexible laminates are known in the prior art, in which the laminate composite is provided with at least one impregnated paper layer such as a decorative impregnate, at least one transparent paper layer (cellophane) such as cellophane treated with sulfuric acid, and / or at least one plastic film layer. Cellophane is a transparent paper made of finely ground cellulose, which is largely oil-impermeable but not moisture-resistant. Its high transparency is obtained through a very sharp glazing finish. Different sub-layers or layers can be included in the laminate structure multiple times, alternately or exchanging their positions.

[0105] The plastic film layer used in the laminate is composed of a polymer, especially polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), thermoplastic polyurethane (TPU) or polyurethane. Such plastic films can especially be used as protective films on sensitive surfaces.

[0106] In addition to cellulose fibers, wood fibers and wood chips, waste products containing melamine formaldehyde resin can also contain inorganic wear-resistant particles, glass balls, colored pigments, other binders such as urea resin, and other additives. The cellulose fibers here are from impregnated paper, such as the decorative impregnation, covering impregnation, and balance impregnation as described. Inorganic particles such as wear-resistant particles (corundum) are contained in the covering impregnation. The wood fibers are from wood-based panels (such as HDF boards, MDF boards), and the wood chips are from particle boards. Colored pigments are preferably present in the decorative impregnation. Other additives include flame retardants, curing agents, elasticizers, and waxes.

[0107] The solid substances listed as being contained in the waste products containing melamine formaldehyde resin accumulate as impurities or contaminants during the decomposition process and are separated during the decomposition process as mentioned.

[0108] As can be seen, the composition of the waste products containing melamine formaldehyde resin to be decomposed varies, such that optional further adjustment and modification of the method are feasible.

[0109] Decomposing melamine resin dust does not require further comminution of the waste products before mixing with at least one solution of metabisulfite, bisulfite, and / or dithionite, as shown in other waste products.

[0110] Therefore, in the case of using decorative impregnation, covering impregnation, balance impregnation, clad and unclad wood-based panels, and laminates, however, it is necessary to comminute the waste products. Correspondingly, in one embodiment, the waste products containing melamine formaldehyde resin are comminuted to a particle size between 0.1 mm and 10 mm, preferably between 0.5 mm and 3 mm. Decomposition proceeds optimally in the case of very finely ground materials with a particle size less than 3 mm.

[0111] Furthermore, in the case of wood-based panels (such as wood fiber boards or wood particle boards) clad with covering impregnation, decorative impregnation, and / or balance impregnation, it is advantageous to first only pre-comminute the clad wood-based panels (for example, pre-comminute to a specification of 5×5 cm). The pre-comminuted fragments are first treated in a steam environment in order to hydrolyze additional binders (preferably, urea formaldehyde resin) present in the wood-based panels.

[0112] The residue obtained after hydrolysis (preferably from the impregnation and wood fibers or wood chips) is separated and further comminuted, and only then is it incorporated into at least one solution of metabisulfite, bisulfite, and / or dithionite to hydrolytically degrade the melamine formaldehyde resin according to the method.

[0113] The melamine formaldehyde resin contained in the waste product and to be decomposed has a molar ratio of melamine / formaldehyde of 1 / 1.5 to 1 / 2.5, preferably 1 / 1.6 to 1 / 2.3, and particularly preferably 1 / 1.6 to 1 / 1.8.

[0114] In one embodiment of the method, the polycondensed melamine formaldehyde resin to be decomposed in the waste product is not fully cured; that is, the condensate is not fully crosslinked. This particularly applies to superimposed resins and impregnated paper layers (which have not yet undergone the pressing step).

[0115] In contrast, in another embodiment of the method, the polycondensed melamine formaldehyde resin to be decomposed in the waste product is fully cured. This particularly applies to compacted uncoated and coated wood-based panels and laminates.

[0116] The different polymerization states and crosslinking states of the melamine formaldehyde resin are briefly shown below.

[0117] Melamine and formaldehyde first react to form a water-soluble monomer product (see Scheme I) in the case of forming hydroxymethyl groups at the amino groups of melamine. The melamine formaldehyde monomer is also called melamine hydroxymethyl alcohol.

[0118] Scheme I

[0119]

[0120] After adding a suitable catalyst, preferably an acid, the melamine formaldehyde monomer undergoes polycondensation, in which the monomers are linked via ether groups and methylene groups and high molecular weight pre-condensates and condensates are formed (see Scheme II).

[0121] Scheme II

[0122]

[0123] The pre-condensates and condensates differ in their molar mass and their solubility. Thus, the low molecular weight pre-condensates still have limited water solubility, while the high molecular weight condensates are insoluble. The limited water solubility of the pre-condensates is particularly caused by the still free hydroxymethyl groups and the low degree of crosslinking of the generally still linear oligomers. Thus, the pre-condensates are polymerization intermediates.

[0124] In the complete curing of the condensate, strong crosslinking occurs in the case of the splitting of the still existing hydroxymethyl groups, in which a tightly crosslinked plastic is formed via methylene groups (see Scheme III).

[0125] Scheme III

[0126]

[0127] Therefore, in synthetic resins hardened via a condensation reaction, the following resin states are distinguished:

[0128] - State A: readily soluble in solvents, fusible, curable;

[0129] - State B: only partially soluble in solvents, fusible, curable;

[0130] - State C: insoluble, cured.

[0131] Due to the relatively low crosslinking degree of the resin, it is preferable to decompose the resin that has not been fully hardened (i.e., the resin in the partially crosslinked State B). BRIEF DESCRIPTION OF THE DRAWINGS

[0132] The present invention will be described in detail below with reference to the accompanying drawings according to embodiments. The drawings show:

[0133] Figure 1 The curing curves of melamine sulfonate from metabisulfite decomposition and a commercially available curing agent when used as a curing agent for melamine formaldehyde resin;

[0134] Figure 2 The curing curves of melamine sulfonate from metabisulfite decomposition and ammonium sulfate when used as a curing agent for urea formaldehyde resin;

[0135] Figure 3 The curing curves of the supernatant from FAS decomposition and a commercially available curing agent when used as a curing agent for melamine formaldehyde resin;

[0136] Figure 4 The curing curves of the ammonium salt of melamine sulfonate from FAS decomposition and a commercially available curing agent when used as a curing agent for melamine formaldehyde resin. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0137] General situation:

[0138] In the embodiments, the progress of the reaction was traced via thin layer chromatography. Here, for comparison, melamine resin / precursor was allowed to proceed together, which allowed the evaluation of the degradation progress. Melamine, monohydroxymethyl melamine, dihydroxymethyl melamine, and melamine resin were involved herein.

[0139] Example 1: Decomposition of the melamine residue of resin waste with a sodium metabisulfite solution

[0140] 100 g of a liquid melamine resin that had become turbid due to superposition (solid content: 55 wt%, melamine / formaldehyde molar ratio: approximately 1:1.8) was transferred to a 1000 ml three-necked round-bottom flask and admixed with 300 g of a 50% sodium metabisulfite solution.

[0141] The mixture is boiled under reflux, whereupon the turbidity dissolves after approximately 3 h. The progress of the reaction is monitored by thin-layer chromatography (mobile phase: water / ethanol (1 / 1)). After it has been verified by thin-layer chromatography that no resin oligomers are present any longer (6 h), the reaction solution is cooled, the precipitated product is suctioned off via a vacuum filter, washed with cold water and then dried.

[0142] The pale yellow product is a mixture consisting of monohydroxymethylmelamine and dihydroxymethylmelamine and melamine sulfonate. The filtrate is again concentrated by half, and the precipitated melamine sulfonate is likewise washed and dried. The yield is 95% taking into account approximately 10 wt% auxiliaries (plasticizers, curing agents, etc.) in the resin.

[0143] Example 2: Decomposition of melamine residues with sodium bisulfite solution

[0144] 100 g of solid melamine dust (melamine / formaldehyde molar ratio: approximately 1 / 1.8) from melamine resin dust produced at the shearing machine and trimming device during impregnation are transferred to a 2000 ml three-necked round-bottom flask and admixed with 600 g of a 50% sodium bisulfite solution.

[0145] The mixture is boiled under reflux, whereupon the resin dissolves slowly. After a clear solution has formed, the floating fibres (paper and cellulose) are first skimmed off, and then hot filtration is carried out in order to separate the corundum and glass beads. After washing, these corundum and glass beads can be reused. Subsequently, boiling is continued under reflux. The progress of the reaction is monitored by thin-layer chromatography (mobile phase: water / ethanol (1 / 1)). After it has been verified by thin-layer chromatography that no resin oligomers are present any longer (12 h), the reaction solution is cooled, the precipitated product is suctioned off via a vacuum filter, washed with cold water and then dried.

[0146] The pale yellow product is a mixture consisting of monohydroxymethylmelamine and dihydroxymethylmelamine and monohydroxymethylmelamine sulfonate and dihydroxymethylmelamine sulfonate. The yield is 91% taking into account approximately 10 wt% auxiliaries (plasticizers, curing agents, etc.) in the resin. In a further experiment, the amount of sodium bisulfite is reduced to 150 g in 300 ml of water. No difference was found with regard to the yield.

[0147] Example 3: Decomposition of melamine residues of the coating with sodium metabisulfite solution

[0148] In a laboratory mill, the overlay impregnation that can no longer be used for production due to superposition is ground into powder under cooling. 100 g of the solid overlay impregnation (resin: molar ratio of melamine / formaldehyde: approximately 1 / 1.8) in the overlay impregnation is transferred to a 2000 ml three-necked round-bottom flask and admixed with 400 g of a 50% sodium metabisulfite solution.

[0149] The mixture is boiled under reflux. After a clear solution is produced, hot filtration is carried out to separate paper fibers, corundum, etc. Subsequently, boiling is continued under reflux. The progress of the reaction is monitored by thin-layer chromatography (mobile phase: water / ethanol (1 / 1)). After it can be confirmed by thin-layer chromatography that no resin oligomers are present any longer (12 h), the reaction solution is cooled, the precipitated product is suctioned via a vacuum filter, washed with cold water and then dried.

[0150] The pale yellow product is a mixture consisting of monohydroxymethylmelamine and dihydroxymethylmelamine as well as monohydroxymethylmelamine sulfonate and dihydroxymethylmelamine sulfonate. Taking into account approximately 20 wt% of auxiliaries (elasticizer, corundum, curing agent, etc.) in the overlay impregnation, the yield is 86%.

[0151] Example 4: Decomposition of the decorative impregnation with a sodium metabisulfite solution

[0152] In a laboratory mill, the decorative impregnation that can no longer be used for production due to superposition is ground into powder under cooling. This involves an impregnation with a core impregnation by means of a urea resin (resin coating: approximately 50 wt%) and a second covering impregnation by means of a melamine resin (resin coating: approximately 50 wt%). 200 g of the solid decorative impregnation (resin: molar ratio of melamine / formaldehyde: approximately 1 / 1.8) in the decorative impregnation is transferred to a 2000 ml three-necked round-bottom flask and admixed with 400 g of a 30% sodium metabisulfite solution.

[0153] The mixture is boiled under reflux. After a clear solution is produced, hot filtration is carried out to separate paper fibers, corundum, etc. Subsequently, boiling is continued under reflux. The progress of the reaction is monitored by thin-layer chromatography (mobile phase: water / ethanol (1 / 1)). After it can be confirmed by thin-layer chromatography that no resin oligomers are present any longer (12 h), the reaction solution is cooled, the precipitated product is suctioned via a vacuum filter, washed with cold water and then dried.

[0154] The pale yellow product is a mixture composed of monohydroxymethylmelamine and dihydroxymethylmelamine, as well as monohydroxymethylmelamine sulfonate and dihydroxymethylmelamine sulfonate. Considering approximately 10 wt% of auxiliaries (elasticizers, curing agents, etc.) in the resin and approximately 50 wt% of urea resin in the core layer, the yield is 78%.

[0155] Example 5: Decomposition of HDF with a high melamine fraction using a sodium metabisulfite solution

[0156] In a laboratory grinder, the HDF containing approximately 50 wt% of binder and approximately 80 wt% of melamine resin was ground into powder while cooling. 200 g of the solid powder in the said powder was transferred to a 2000 ml three-necked round-bottom flask, and 400 g of 30% sodium metabisulfite solution was incorporated.

[0157] The mixture was boiled under reflux (for approximately 6 h). Then, hot filtration was carried out to separate fibers, etc. Subsequently, boiling was continued under reflux. The progress of the reaction was monitored by thin-layer chromatography (mobile phase: water / ethanol (1 / 1)). After it was confirmed by thin-layer chromatography that no resin oligomers were present anymore (12 h), the reaction solution was cooled, the precipitated product was suction-filtered through a vacuum filter, washed with cold water and then dried.

[0158] The pale yellow product is a mixture composed of monohydroxymethylmelamine and dihydroxymethylmelamine, as well as monohydroxymethylmelamine sulfonate and dihydroxymethylmelamine sulfonate. Considering approximately 10 wt% of auxiliaries (elasticizers, curing agents, etc.) in the resin, the yield is 55%.

[0159] Example 6: Decomposition of a laminate using a sodium metabisulfite solution

[0160] In a laboratory grinder, the laminate (decoration and parchment paper) was crushed into powder while cooling. The laminate consists of a decorative impregnate (paper weight: 100 g / m 2 , resin coating: 120%) and parchment paper: paper weight: 40 g / m 2 ). 200 g of the crushed laminate was transferred to a 2000 ml three-necked round-bottom flask, and 600 g of 30% sodium metabisulfite solution was incorporated.

[0161] Boil the mixture under reflux. After a clear solution is produced, perform hot filtration to separate the paper fibers. Subsequently, continue boiling under reflux. Monitor the progress of the reaction by thin-layer chromatography (mobile phase: water / ethanol (1 / 1)). After it can be confirmed by thin-layer chromatography that no resin oligomers are present anymore (12 h), cool the reaction solution, suction-filter the precipitated product via a vacuum filter, wash it with cold water and then dry it.

[0162] The pale yellow product is a mixture consisting of monohydroxymethyl melamine and dihydroxymethyl melamine, as well as monohydroxymethyl melamine sulfonate and dihydroxymethyl melamine sulfonate. Considering approximately 10 wt% of auxiliaries (elasticizers, curing agents, etc.) in the resin, the yield is 81%.

[0163] Example 7: Decomposition of the direct cladding of a floor structure with a sodium metabisulfite solution

[0164] Pre-crush the laminated floor with an HDF carrier from recycling in a crushing device (chipper) into a specification of approximately 5×5 cm. The cladding of the laminated floor consists of a cover layer impregnate (paper weight: 25 g / m 2 , resin coating: 400% melamine resin), a decorative impregnate (paper weight: 60 g / m 2 , resin coating: 100%) and a balance part (paper weight: 80 g / m 2 , resin coating: 120% melamine resin). Subsequently, carry out the hydrolysis of the urea-formaldehyde glue of the HDF in a vapor environment in a boiler under elevated pressure.

[0165] Sieve out the wood fibers of the cladding and grind them into powder in a laboratory grinder while cooling. The humidity of the cladding is approximately 20%. Transfer 200 g of the ground cladding dry into a 2000 ml three-necked round-bottom flask and incorporate 400 g of a 30% sodium metabisulfite solution.

[0166] Boil the mixture under reflux. After a clear solution is produced, perform hot filtration to separate the paper fibers, wood fibers, corundum, etc. Subsequently, continue boiling under reflux. Monitor the progress of the reaction by thin-layer chromatography (mobile phase: water / ethanol (1 / 1)). After it can be confirmed by thin-layer chromatography that no resin oligomers are present anymore (12 h), cool the reaction solution, suction-filter the precipitated product via a vacuum filter, wash it with cold water and then dry it.

[0167] The pale yellow product is a mixture consisting of monohydroxymethylmelamine and dihydroxymethylmelamine as well as monohydroxymethylmelamine sulfonate and dihydroxymethylmelamine sulfonate. Taking into account approximately 20% by weight of auxiliaries (elasticizers, curing agents, etc.) in the resin, the yield is 65%.

[0168] Example 8: The melamine sulfonate decomposed with a sodium metabisulfite solution is used as a curing agent for melamine formaldehyde resin

[0169] Dissolve the melamine sulfonate from Example 1 in warm water (50 °C, 20% solution).

[0170] Use the clear solution as a curing agent for melamine resin (BASF Kauramin 796). Here, compare the curing performance with the curing agent already in use (see Table 1 and Figure 1 the chart).

[0171]

[0172] As confirmed by the comparison, classify the melamine sulfonate curing agent as a latent curing agent (similar to XXL). Currently, it is preferably used because pre-curing during the process is avoided when using it.

[0173] Example 9: The melamine sulfonate decomposed with a sodium metabisulfite solution is used as a curing agent for urea formaldehyde resin

[0174] Dissolve the precipitated melamine sulfonate from Example 1 in warm water (50 °C, 20% solution).

[0175] Use the clear solution as a curing agent for urea resin. Here, compare the curing performance with the curing agent already in use (see Figure 2 the chart).

[0176] As confirmed by the values, the curing performance of the melamine sulfonate curing agent is similar to that of ammonium chloride curing agent. However, due to very different molar weights, the dosage is different. Compared with in melamine resin, the sulfonate curing agent is significantly more effective in urea formaldehyde glue.

[0177] Example 10: Use the melamine hydroxymethyl alcohol decomposed with a sodium metabisulfite solution for condensation

[0178] The light yellow pasty product from Example 1 (before the precipitation of melamine sulfonate) was placed in warm water (30 °C). Then concentrated ammonia was metered into the slurry until the pH value reached 7.5. Here, the melamine sulfonate began to dissolve. The melamine sulfonate can be used as a curing agent for melamine resins (see Example 7). Then suction was carried out. The filter with melamine hydroxymethanol was dried. According to the molar ratio (melamine to formaldehyde), the share of melamine hydroxymethanol in the recovered melamine resin was 10 wt% to 30 wt%. In this case, the share was 20 wt%.

[0179] Subsequently, melamine hydroxymethanol was used to prepare melamine resin, where the share of the recovered melamine hydroxymethanol was 20 wt%. Here, it was assumed that the ratio of melamine to formaldehyde was 1 to 1.5.

[0180] It was assumed that the ratio of monohydroxymethyl to dihydroxymethyl was 1 to 1. Formaldehyde and melamine for the remaining process were added in the same ratio. Formaldehyde was provided in the form of a 33% solution. 10 wt% of ethylene glycol was added as an elastomer by solid content. The pH value was set to approximately 8.5 with sodium hydroxide solution. Melamine and melamine hydroxymethanol were added slowly as powders under stirring. The condensation was carried out at 95 °C for about 20 min. Subsequently, the temperature was returned to 85 °C. The condensation was carried out for about 30 min to 40 min until the water dilution was 1 to 3. Subsequently, it was cooled to room temperature.

[0181] Example 11: Decomposition of melamine residues with FAS

[0182] 100 g of solid melamine dust (melamine / formaldehyde molar ratio: approximately 1 / 1.8) in the melamine resin dust generated at the shearing machine and trimming device during impregnation was transferred to a 1000 ml three-necked round-bottom flask containing 600 ml of water. The aqueous solution was heated to boiling under stirring. Then 117 g of FAS (in four equal parts (about 30 g of formamidine sulfinic acid each)) was added at 10 min intervals respectively.

[0183] The mixture was boiled under reflux, where the resin and FAS slowly dissolved. The progress of the reaction was monitored by thin-layer chromatography (mobile phase: methanol). After a clear light yellow solution was produced after about two hours, hot filtration was carried out to separate the contaminants. Then the reaction solution was cooled, the precipitated product was suctioned through a vacuum filter, washed with cold water and then dried.

[0184] Upon analysis, the white product consisted only of melamine sulfonate as an ammonium salt. Considering approximately 10 wt% of additives (elastomer, curing agent, etc.) in the resin, the yield was 90%.

[0185] Example 12: Decomposition of melamine residues in the overlay with FAS

[0186] In a laboratory grinder, the overlay impregnate that can no longer be used for production due to superposition is ground into powder while being cooled. An α-cellulose paper with a grammage of 25 g / m 2 is used to prepare the overlay. In addition to the resin, about 25 g of corundum per m 2 is also contained in the impregnate. 100 g of the overlay impregnate in the overlay impregnate (resin: molar ratio of melamine / formaldehyde: approximately 1 / 1.8) is transferred to a 1000 ml three-necked round-bottom flask and suspended with 600 ml of water. Then the solution is heated to boiling with stirring, and then 82 g of FAS is incorporated in four equal portions.

[0187] The mixture is kept boiling under reflux. After a clear solution is produced, hot filtration is carried out to separate the paper fibers, corundum, etc. Subsequently, boiling is continued under reflux. The progress of the reaction is monitored by thin-layer chromatography (mobile phase: methanol). After about 2 h, the reaction solution is cooled, the precipitated product is suctioned through a vacuum filter, washed with cold water and then dried.

[0188] The white product is the ammonium salt of melamine sulfonate. Considering about 20 wt% of auxiliaries (elasticizer, corundum, curing agent, etc.) and cellulose fibers in the overlay impregnate, the yield is 89%.

[0189] Example 13: Decomposition of decorative impregnate with FAS

[0190] In a laboratory grinder, the decorative impregnate that can no longer be used for production due to superposition is ground into powder while being cooled. Here, it involves an impregnate with a core impregnation by means of urea resin (resin coating: approximately 50 wt%) and a second covering impregnation by means of melamine resin (resin coating: approximately 50 wt%, molar ratio of melamine resin to melamine / formaldehyde: about 1 / 1.8). The grammage of the paper of the impregnate used is 80 g / m 2 . 100 g of the decorative impregnate is transferred to a 1000 ml three-necked round-bottom flask and 600 g of water is incorporated. Then it is heated to boiling with stirring. Then 54 g of FAS is added in four equal portions.

[0191] The mixture is kept boiling under reflux for about 1 h. After a clear solution is produced, hot filtration is carried out to separate the paper fibers, corundum, etc. Subsequently, boiling is continued under reflux for one hour. The progress of the reaction is monitored by thin-layer chromatography (mobile phase: methanol). Subsequently, the reaction solution is cooled, the precipitated product (melamine sulfonate as ammonium salt) is suctioned through a vacuum filter, washed with cold water and then dried.

[0192] With consideration of approximately 10 wt% of additives (elasticizers, curing agents, etc.) in the resin, paper fibers, and approximately 50 wt% of urea resin in the core, the yield is 78%.

[0193] Example 14: Using the supernatant from the FAS decomposition as a curing agent

[0194] Using the decomposed yellow solution from Example 11 as a curing agent. The yellow solution consists of a mixture composed of ammonium sulfite and ammonium sulfate. The solid content is approximately 20%.

[0195] Comparison with other commercially available curing agents (Curing agents 528, 1448, and XXL) was carried out to determine and compare the curing of the melamine resin Kauramin 796 (see Table 2 and Figure 3 the chart in). The supernatant composed of ammonium sulfite and ammonium sulfate was used at different concentrations or in different purification stages (purified FAS product liquid / liquid (w = 15%); FAS product solid / liquid).

[0196]

[0197]

[0198] Table 2

[0199] As confirmed by the data in Table 2 and Figure 3 the curing agent curves in the table in, the recovered curing agent from the supernatant (FAS product) has a similar reactivity to the standard curing agents used, and is significantly more reactive than the latent curing agent XXL.

[0200] Example 15: Using the melamine sulfonate from the FAS decomposition as a curing agent

[0201] The white product from Example 11 was dissolved in warm water (50 °C, 20% solution). The white product contains the ammonium salt of melamine sulfonate. The melamine sulfonate was used at different concentrations (sulfonate product w = 20% liquid / liquid; sulfonate product solid / liquid).

[0202] The clear solution was used as a curing agent for the melamine resin. Here, the curing performance was compared with the curing agents already in use (Curing agents 528, 1448, and XXL) (see Table 3 and Figure 4 the chart in).

[0203]

[0204] Table 3

[0205] As confirmed by the hardener curve, the ammonium salt of melamine sulfonate should be classified as rather a potential hardener (similar to XXL). Currently, the hardener is preferably used because pre-curing during the process should be avoided when using it. Of course, the hardener can be used in combination with other hardeners in order to achieve a customized reactivity of the resin using the hardener.

Claims

1. A method for degrading melamine formaldehyde resin from waste products generated during the manufacture and processing of wood-based panels, characterized in that, The following steps are provided: - Provide a waste product generated during the manufacture and processing of wood-based panels, the waste product containing a condensed melamine formaldehyde resin, - Optionally crush the waste product containing the melamine formaldehyde resin, - Mix the waste product containing the melamine formaldehyde resin with water and add at least one reducing sulfur-containing compound selected from metabisulfites, bisulfites and / or dithionites, sulfinates or sulfinate analogues, - Heat the aqueous mixture / suspension composed of the waste product containing the melamine formaldehyde resin and at least one reducing sulfur-containing compound to a temperature between 60 °C and 120 °C, preferably between 80 °C and 100 °C, under reaction control until a clear solution is obtained, - Separate impurities from the clear solution, - Optionally further heat, under reaction control, the mixture composed of the waste product containing the melamine formaldehyde resin and at least one reducing sulfur compound, from which impurities have been removed, to a temperature between 60 °C and 120 °C, preferably between 80 °C and 110 °C, until it can be verified that no (longer) condensed melamine formaldehyde resin is present in the reaction mixture, and - Cool the reaction mixture and separate the mixture of melamine derivatives precipitated therefrom, in particular melamine hydroxymethyl alcohol and melamine sulfonate.

2. The method for degrading melamine formaldehyde resin from waste products generated during the manufacture and processing of wood-based panels according to claim 1, characterized in that, The following steps are provided: - Provide a waste product generated during the manufacture and processing of wood-based panels, the waste product containing a condensed melamine formaldehyde resin, - Optionally crush the waste product containing the melamine formaldehyde resin, - Mix the waste product containing the melamine formaldehyde resin with an aqueous solution of 20% to 70% by weight, preferably 40% to 60% by weight, of at least one metabisulfite, bisulfite and / or dithionite, - Heat the mixture composed of the waste product containing the melamine formaldehyde resin and at least one metabisulfite, bisulfite and / or dithionite to a temperature between 60 °C and 120 °C, preferably between 80 °C and 100 °C, until a clear solution is obtained, - Separate impurities from the clear solution, - Further heat, under reaction control, the mixture composed of the waste product containing the melamine formaldehyde resin and at least one metabisulfite, bisulfite and / or dithionite, from which impurities have been removed, to a temperature between 60 °C and 120 °C, preferably between 80 °C and 110 °C, until it can be verified that no condensed melamine formaldehyde resin is present in the reaction mixture, - Cool the reaction mixture and separate the mixture of melamine derivatives, in particular melamine hydroxymethyl alcohol and melamine sulfonate, precipitated therefrom.

3. The method according to any one of the above claims, characterized in that, Mix the waste product containing melamine formaldehyde resin with an aqueous alkali metal or alkaline earth metal solution containing 20% to 70% by weight, preferably 40% to 60% by weight, of at least one metabisulfite, bisulfite, and / or dithionite, especially with an aqueous sodium bisulfite solution containing 40% to 60% by weight, especially 50% by weight.

4. The method according to any one of the above claims, characterized in that, Mix the waste product containing melamine formaldehyde resin with at least one sodium metabisulfite solution or sodium bisulfite solution having a pH value between 3.0 and 6, preferably between 3.5 and 5.

5.

5. The method for degrading melamine formaldehyde resin from waste products generated during the manufacture and processing of wood-based panels according to claim 1, characterized in that, The following steps are provided: - Provide a waste product generated during the manufacture and processing of wood-based panels, the waste product containing a condensed melamine formaldehyde resin, - Optionally crush the waste product containing melamine formaldehyde resin, - Mix the waste product containing melamine formaldehyde resin with water and add at least one sulfite or sulfite analogue, - Heat the aqueous mixture / suspension composed of the waste product containing melamine formaldehyde resin and at least one sulfite or sulfite analogue to a temperature between 60°C and 120°C, preferably between 80°C and 100°C, under reaction control until a clear solution is obtained, - Separate impurities from the clear solution, - Optionally further heat the mixture composed of the waste product containing melamine formaldehyde resin and at least one sulfite from which impurities have been removed to a temperature between 60°C and 120°C, preferably between 80°C and 110°C, under reaction control until it can be confirmed that there is no (longer) condensed melamine formaldehyde resin in the reaction mixture, and - Cool the reaction mixture and separate the melamine sulfonate precipitated as a salt therein.

6. The method according to claim 5, characterized in that, Add the at least one sulfite or sulfite analogue as a solid to the aqueous solution / suspension composed of the waste product containing melamine formaldehyde resin.

7. The method according to any one of claims 5 to 6, characterized in that,The at least one sulfite can be prepared from formamidine sulfinic acid (FAS).

8. The method according to any one of claims 5 to 7, characterized in that, The ratio of the reducing agent to the waste product containing melamine formaldehyde resin is between 2:1 and 0.5:1, preferably between 1.5:1 and 0.8:

1.

9. The method according to any one of claims 5 to 8, characterized in that, The reaction time until the complete degradation of the melamine formaldehyde resin is between 60 min and 240 min, preferably between 90 min and 120 min.

10. The method according to any one of claims 5 to 9, characterized in that, The melamine sulfonate precipitated as a salt after the reaction mixture is cooled is an ammonium salt.

11. The method according to any one of claims 5 to 10, characterized in that, The supernatant obtained after the precipitation and separation of the melamine sulfonate contains ammonium sulfate (NH4)2SO4 and ammonium sulfite (NH4)2SO3.

12. The method according to any one of the above claims, characterized in that, The waste product containing melamine formaldehyde resin generated during the manufacture and processing of wood-based panels includes stacked melamine resins, melamine resin dust, overlay impregnates, decorative impregnates, uncoated or coated wood-based panels such as HDF boards, and / or laminates such as thin laminates.

13. The method according to any one of the above claims, characterized in that, The waste product containing melamine formaldehyde resin contains cellulose fibers, wood fibers, inorganic wear-resistant particles, glass balls, colored pigments, additional binders, and other additives.

14. The method according to any one of the above claims, characterized in that, The melamine formaldehyde resin contained in the waste product has a melamine / formaldehyde molar ratio of from 1 / 1.5 to 1 / 2.5, preferably from 1 / 1.6 to 1 / 2.3, and particularly preferably from 1 / 1.6 to 1 / 1.

8.

15. The method according to any one of the above claims, characterized in that, The waste product containing the melamine formaldehyde resin is comminuted to a particle size between 0.1 mm and 10 mm, preferably between 0.5 mm and 3 mm.

16. The method according to any one of the above claims, characterized in that, The separation of the impurities contained in the reaction mixture is carried out by filtration, preferably hot filtration and / or skimming.

17. The method according to any one of the above claims, characterized in that, The reaction control of the degradation of the melamine formaldehyde resin is carried out using suitable analytical methods such as thin layer chromatography, HPLC or gas chromatography.

18. Use of a melamine sulfonate or melamine sulfonates obtained by the method according to any one of claims 1 to 17 as a curing agent for resins, in particular formaldehyde resins such as melamine formaldehyde resins and urea formaldehyde resins.

19. Use of melamine hydroxymethyl alcohol obtained by the method according to any one of claims 1 to 17 for the preparation of melamine resins, in particular as an adhesive or impregnating agent.

20. Use of melamine hydroxymethyl alcohol and melamine sulfonate obtained by the method according to any one of claims 1 to 17 as a flame retardant and / or adhesive.

21. Use of the supernatant liquid containing ammonium sulfate (NH4)2SO4 and ammonium sulfite (NH4)2SO3, which is produced after precipitation and separation of melamine sulfonate in the method according to any one of claims 5 to 17, as a curing agent for resins, in particular as a curing agent for formaldehyde resins such as melamine formaldehyde resins and urea formaldehyde resins.

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