Melamine formaldehyde resin and production process thereof

Abstract

The invention discloses melamine formaldehyde resin and a production process thereof, and belongs to the technical field of high polymer materials. The production process comprises the following steps: carrying out a reaction on melamine and 2, 5-furandicarbonyl chloride to generate an intermediate, carrying out a condensation polymerization reaction on the intermediate, the melamine and formaldehyde, and adding a polyvinyl alcohol-metal complex for common condensation polymerization to form the melamine formaldehyde resin. 2, 5-furandicarbonyl chloride of a biological source is used for replacing part of formaldehyde, the content of methanol is reduced, meanwhile, a hydroxymethyl crosslinking site at one end of a furan ring can be closed, the crosslinking density is reduced, and the toughness is improved. Under the condition that the reaction energy is reduced by the metal ions, the polyvinyl alcohol and the formaldehyde are subjected to aldolization to block free formaldehyde; the coordination effect of metal ions and furan rings further promotes the crosslinking of polyvinyl alcohol and melamino-formaldehyde molecular chains, and the flexible long chain of the introduced polyvinyl alcohol reduces the brittleness of the resin material.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, and particularly relates to a melamine formaldehyde resin and its production process. Background Art

[0002] Melamine formaldehyde resin, abbreviated as melamine resin, is an important triazine ring compound, which is obtained by first carrying out a hydroxylation reaction between melamine and formaldehyde and then dehydration polycondensation. Melamine resin has excellent aging resistance, flame retardancy, heat resistance, chemical corrosion resistance and insulation performance, and can be used to manufacture materials such as molding compounds, artificial boards and foam plastics.

[0003] Melamine formaldehyde resin is a polymer formed by the reaction of melamine and formaldehyde under specific conditions. This reaction is usually carried out in the presence of an acidity regulator and a stabilizer to ensure the smooth progress of the reaction and the stability of the product. The specific reaction process is divided into two stages: the first stage is the addition reaction of melamine and formaldehyde. Under neutral or alkaline conditions, melamine undergoes hydroxymethylation to generate 9 different hydroxymethyl melamines; the second stage is the condensation reaction, where melamine reacts with hydroxymethylated melamine, or hydroxymethylated melamine undergoes self-condensation to form a polymer.

[0004] Its preparation uses melamine and formaldehyde as the core raw materials. Melamine formaldehyde resin will generate formaldehyde gas during the high-temperature curing process, which not only pollutes the environment but also may be harmful to human health. Therefore, environmentally friendly alternative raw materials have become the focus of attention in the industry. Summary of the Invention

[0005] The present invention provides a melamine formaldehyde resin and its production process, which can solve the problem of formaldehyde environmental pollution existing in the preparation of melamine formaldehyde resin in the prior art.

[0006] The object of the present invention can be achieved by the following technical solutions:

[0007] A production process of a melamine formaldehyde resin includes the following steps:

[0008] S1. Mix melamine, triethylamine and DMF and stir to form a reaction solution, add 2,5-furandicarbonyl chloride, and the molar ratio of 2,5-furandicarbonyl chloride to melamine is 1-1.2:3. React at 10-20 °C for 8-12 h to obtain an intermediate;

[0009] The reaction formula of the above reaction is as follows:

[0010]

[0011] S2. Mix the formaldehyde solution and the organic amine. The organic amine adjusts the pH to 8 - 9.5. Add melamine and the intermediate, heat to 80 - 90 °C, react at a constant temperature for 4 - 6 h, cool to 60 - 70 °C, add the polyvinyl alcohol-metal complex solution, adjust the pH to 6 - 7, and stir and react for 2 - 4 h to obtain melamine formaldehyde resin.

[0012] In S2, part of the formaldehyde and melamine react under alkaline conditions to obtain a pre-condensate, namely the trimethylol compound of melamine. Part of the formaldehyde reacts with the intermediate to obtain a furan-based melamine dimethylol compound. At this time, since the furan ring in the intermediate will block one end of the hydroxymethyl crosslinking site, reducing the crosslinking density and improving the toughness of the material. The furan-based acyl chloride in the intermediate replaces part of the formaldehyde to react with melamine, reducing the content of free formaldehyde in the melamine formaldehyde resin. And the bio-derived 2,5-furandicarbonyl chloride is biodegradable and environmentally friendly. The introduced furan ring in the intermediate is more stable at high temperatures than formaldehyde and will not cause environmental pollution.

[0013] In the subsequently added polyvinyl alcohol-metal complex solution, the hydroxyl groups in polyvinyl alcohol form coordination bonds with metal ions. The polyvinyl alcohol-metal complex participates in the crosslinking polycondensation reaction in the reaction system of melamine formaldehyde. The hydroxyl groups of polyvinyl alcohol undergo acetalization reaction with free formaldehyde, restricting the pollution of formaldehyde to the environment. The metal ions in it form complexes that can reduce the reaction energy and promote the progress of the acetalization reaction. In addition, the metal ions can form coordination bonds with the oxygen atoms of the furan ring, enhancing the crosslinking of polyvinyl alcohol and the melamine formaldehyde condensate, and using the flexible long chain of polyvinyl alcohol to reduce the brittleness of the material.

[0014] Furthermore, the concentration of melamine in the reaction solution is 3 - 5 mol / L, and the concentration of triethylamine is 3 - 5 mol / L. Triethylamine can adjust the reaction system to be alkaline and neutralize the generated HCl, promoting the forward progress of the reaction.

[0015] Furthermore, the organic amine is one of diethanolamine, triethanolamine, and triethylamine. As a pH regulator, the organic amine compound can be dissolved in an organic solvent, while inorganic basic compounds usually require water as a solvent, and the introduction of water will cause side reactions.

[0016] Furthermore, the concentration of the formaldehyde solution is 30 - 40 wt%. The concentration of the formaldehyde solution affects the reaction efficiency. A high-concentration formaldehyde solution can promote the condensation reaction, but a too-high concentration of the formaldehyde solution has the problem of easy volatilization, which is not conducive to maintaining the safety of the production environment.

[0017] Furthermore, in S2, the ratio of the molar amount of formaldehyde in the formaldehyde solution to the total molar amount of melamine in S1 and S2 is 2 - 3:1.

[0018] Further, in S2, the melamine is added according to a molar ratio of melamine to the melamine for preparing the intermediate in S1 of 5:1-2.

[0019] Further, the metal ions contained in the polyvinyl alcohol-metal complex solution are one of zinc ions and aluminum ions. The raw materials of the metal ions zinc ions and aluminum ions have relatively low prices, relatively low biological toxicity, and can improve the thermal stability and electrical conductivity of the resin, and improve the antistatic performance when applied in specific fields.

[0020] Further, the preparation steps of the polyvinyl alcohol-metal complex solution are as follows:

[0021] Heat and dissolve polyvinyl alcohol in water to form a polyvinyl alcohol solution with a concentration of 0.1-0.5 mol / L, add an aqueous solution of zinc chloride or aluminum chloride with a concentration of 0.01-0.05 mol / L, with a volume ratio of 1:0.5-1, add hydrochloric acid to adjust the pH to 3-4, and stir and react for 2-4 h to obtain a polyvinyl alcohol-metal complex solution.

[0022] Further, the polyvinyl alcohol-metal complex solution is added according to a molar ratio of polyvinyl alcohol to formaldehyde of 0.1-0.2:1.

[0023] Further, the basic regulator used to adjust the pH to 6-7 is an organic amine, and the acidic regulator is hydrochloric acid. Adjusting the pH to weakly acidic in the later stage of the reaction can, on the one hand, improve the polycondensation efficiency in the later stage of the reaction, and on the other hand, promote the acetal reaction of polyvinyl alcohol and formaldehyde to avoid the free formaldehyde.

[0024] The present invention also provides a melamine formaldehyde resin prepared by using the above production process.

[0025] The beneficial effects of the present invention:

[0026] (1) In the present invention, 2,5-furandicarbonyl chloride of biological origin is used to replace part of formaldehyde to participate in the preparation of melamine formaldehyde resin. While reducing the methanol content, the furan ring on the intermediate containing the furan ring will block one end of the hydroxymethyl cross-linking site, reducing the cross-linking density in the subsequent polycondensation reaction and improving the toughness.

[0027] (2) In the present invention, the polyvinyl alcohol-metal coordination compound participates in the polycondensation reaction of melamine formaldehyde. Under the condition that the metal ions reduce the reaction energy, the acetal reaction of polyvinyl alcohol and formaldehyde occurs in a weak acid condition to block the free formaldehyde; the coordination effect of the metal ions and the furan ring further promotes the cross-linking of the polyvinyl alcohol and melamine formaldehyde molecular chains, and the introduced flexible long chain of polyvinyl alcohol reduces the brittleness of the resin material.

[0028] (3) The metal ions introduced in the present invention can not only improve the thermal stability of the material, but also enhance the antistatic performance of the resin and expand its application fields. Detailed implementation manners

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0030] Example 1

[0031] The steps for preparing melamine formaldehyde resin are as follows:

[0032] S1. Add 200 mL of DMF into a flask, then add 75.7 g of melamine (0.6 mol) and 60.7 g of triethylamine (0.6 mol). Start stirring, and after mixing evenly, a reaction solution is formed. Weigh 38.6 g of 2,5-furandicarbonyl chloride (0.2 mol) and add it to the reaction solution. The molar ratio of 2,5-furandicarbonyl chloride to melamine is 1:3. Control the reaction temperature at 15 °C and keep the reaction at a constant temperature for 10 h to obtain an intermediate.

[0033] S2. Take 600 g of formaldehyde solution with a concentration of 35 wt%, the molar amount of formaldehyde is 7.0 mol, add triethylamine and mix, adjust the pH to 8.5. Weigh 378.36 g of melamine (3 mol) and add it to the reaction system together with the intermediate prepared in S1. Heat to 85 °C and keep the reaction at a constant temperature for 5 h. Then cool down to 60 °C, add a polyvinyl alcohol-Zn complex solution. The molar amount of polyvinyl alcohol is 0.72 mol. Adjust the pH to 6.5 with triethylamine and hydrochloric acid, and stir and react for 3 h to obtain melamine formaldehyde resin. The preparation of the polyvinyl alcohol-Zn complex solution is as follows:

[0034] Heat to 90 °C, dissolve polyvinyl alcohol in water to form a 0.1 mol / L polyvinyl alcohol solution, add a 0.01 mol / L zinc chloride aqueous solution. The volume ratio of the polyvinyl alcohol solution to the zinc chloride aqueous solution is 1:0.5. Add hydrochloric acid to adjust the pH to 3.0 and stir and react for 3 h to obtain the polyvinyl alcohol-Zn complex solution.

[0035] Example 2

[0036] It is only different from Example 1 in that the addition amount of 35wt% formaldehyde solution in S2 is reduced to 446 g, the molar amount of formaldehyde is 5.2 mol, the melamine is reduced to 252.24 g (2 mol), and the polyvinyl alcohol-Zn complex solution is added according to the molar amount of polyvinyl alcohol of 0.52 mol.

[0037] The steps for preparing melamine formaldehyde resin are as follows:

[0038] S1. Add 200 mL of DMF to a flask, then add 75.7 g of melamine (0.6 mol) and 60.7 g of triethylamine (0.6 mol). Start stirring, and after mixing evenly, a reaction solution is formed. Weigh 38.6 g of 2,5-furandicarbonyl chloride (0.2 mol) and add it to the reaction solution. The molar ratio of 2,5-furandicarbonyl chloride to melamine is 1:3. Control the reaction temperature at 15 °C and react at a constant temperature for 10 h to obtain an intermediate.

[0039] S2. Take 446 g of 35wt% formaldehyde solution, with the molar amount of formaldehyde being 5.2 mol. Add triethylamine and mix, adjust the pH to 8.5. Weigh 252.24 g of melamine (2 mol) and add it to the reaction system together with the intermediate prepared in S1. Heat to 85 °C and react at a constant temperature for 5 h. Then cool to 60 °C, add the polyvinyl alcohol-Zn complex solution with the molar amount of polyvinyl alcohol being 0.52 mol. Adjust the pH to 6.5 with triethylamine and hydrochloric acid, and stir and react for 3 h to obtain melamine formaldehyde resin. The preparation of the polyvinyl alcohol-Zn complex solution is as follows:

[0040] Heat to 90 °C, dissolve polyvinyl alcohol in water to form a 0.1 mol / L polyvinyl alcohol solution, add a 0.01 mol / L zinc chloride aqueous solution. The volume ratio of the polyvinyl alcohol solution to the zinc chloride aqueous solution is 1:0.5. Add hydrochloric acid to adjust the pH to 3.0 and stir and react for 3 h to obtain the polyvinyl alcohol-Zn complex solution.

[0041] Example 3

[0042] It is only different from Example 1 in that the addition amount of 35wt% formaldehyde solution in S2 is reduced to 360 g, the molar amount of formaldehyde is 4.2 mol, the melamine is reduced to 189.18 g (1.5 mol), and the polyvinyl alcohol-Zn complex solution is added according to the molar amount of polyvinyl alcohol of 0.36 mol.

[0043] The steps for preparing melamine formaldehyde resin are as follows:

[0044] S1. Add 200 mL of DMF to a flask, then add 75.7 g of melamine (0.6 mol) and 60.7 g of triethylamine (0.6 mol). Start stirring and mix evenly to form a reaction solution. Weigh 38.6 g of 2,5-furandicarbonyl chloride (0.2 mol) and add it to the reaction solution. The molar ratio of 2,5-furandicarbonyl chloride to melamine is 1:3. Control the reaction temperature at 15 °C and react at a constant temperature for 10 h to obtain an intermediate.

[0045] S2. Take 360 g of a 35 wt% formaldehyde solution. The molar amount of formaldehyde is 4.2 mol. Add triethylamine and mix, adjust the pH to 8.5. Weigh 189.18 g of melamine (1.5 mol) and add it to the reaction system together with the intermediate prepared in S1. Heat to 85 °C and react at a constant temperature for 5 h. Cool down to 60 °C, add a polyvinyl alcohol-Zn complex solution. The molar amount of polyvinyl alcohol is 0.36 mol. Adjust the pH to 6.5 with triethylamine and hydrochloric acid, and stir and react for 3 h to obtain a melamine formaldehyde resin. The preparation of the polyvinyl alcohol-Zn complex solution is as follows:

[0046] Heat to 90 °C, dissolve polyvinyl alcohol in water to form a 0.1 mol / L polyvinyl alcohol solution, add a 0.01 mol / L zinc chloride aqueous solution. The volume ratio of the polyvinyl alcohol solution to the zinc chloride aqueous solution is 1:0.5. Add hydrochloric acid to adjust the pH to 3.0 and stir and react for 3 h to obtain a polyvinyl alcohol-Zn complex solution.

[0047] Example 4

[0048] The difference from Example 2 is only that the addition amount of the 35 wt% formaldehyde solution in S2 is increased to 557 g, the molar amount of formaldehyde is 6.5 mol, and the polyvinyl alcohol-Zn complex solution is added according to the molar amount of polyvinyl alcohol of 0.65 mol.

[0049] The steps for preparing the melamine formaldehyde resin are as follows:

[0050] S1. Add 200 mL of DMF to a flask, then add 75.7 g of melamine (0.6 mol) and 60.7 g of triethylamine (0.6 mol). Start stirring and mix evenly to form a reaction solution. Weigh 38.6 g of 2,5-furandicarbonyl chloride (0.2 mol) and add it to the reaction solution. The molar ratio of 2,5-furandicarbonyl chloride to melamine is 1:3. Control the reaction temperature at 15 °C and react at a constant temperature for 10 h to obtain an intermediate.

[0051] S2. Take 557 g of formaldehyde solution with a concentration of 35 wt%, the molar amount of formaldehyde is 6.5 mol, add triethylamine and mix, adjust the pH to 8.5, weigh 252.24 g of melamine (2 mol), and add it to the reaction system together with the intermediate prepared in S1. Heat to 85 °C, keep the temperature constant for reaction for 5 h, cool down to 60 °C, add the polyvinyl alcohol-Zn complex solution, the molar amount of polyvinyl alcohol is 0.65 mol, adjust the pH to 6.5 with triethylamine and hydrochloric acid, and stir and react for 3 h to obtain melamine formaldehyde resin. The preparation of the polyvinyl alcohol-Zn complex solution is as follows:

[0052] Heat to 90 °C, dissolve polyvinyl alcohol in water to form a 0.1 mol / L polyvinyl alcohol solution, add a 0.01 mol / L zinc chloride aqueous solution, the volume ratio of the polyvinyl alcohol solution to the zinc chloride aqueous solution is 1:0.5, add hydrochloric acid to adjust the pH to 3.0, and stir and react for 3 h to obtain the polyvinyl alcohol-Zn complex solution.

[0053] Example 5

[0054] The difference from Example 2 is only that the addition amount of the 35 wt% formaldehyde solution in S2 is increased to 669 g, the molar amount of formaldehyde is 7.8 mol, and the polyvinyl alcohol-Zn complex solution is added according to the molar amount of polyvinyl alcohol of 0.78 mol.

[0055] The steps for preparing melamine formaldehyde resin are as follows:

[0056] S1. Add 200 mL of DMF to a flask, then add 75.7 g of melamine (0.6 mol) and 60.7 g of triethylamine (0.6 mol), start stirring, and form a reaction solution after mixing evenly. Weigh 38.6 g of 2,5-furandicarbonyl chloride (0.2 mol), add it to the reaction solution, the molar ratio of 2,5-furandicarbonyl chloride to melamine is 1:3, control the reaction temperature at 15 °C, keep the temperature constant for reaction for 10 h, and obtain an intermediate.

[0057] S2. Take 669 g of formaldehyde solution with a concentration of 35 wt%, the molar amount of formaldehyde is 7.8 mol, add triethylamine and mix, adjust the pH to 8.5, weigh 252.24 g of melamine (2 mol), and add it to the reaction system together with the intermediate prepared in S1. Heat to 85 °C, keep the temperature constant for reaction for 5 h, cool down to 60 °C, add the polyvinyl alcohol-Zn complex solution, the molar amount of polyvinyl alcohol is 0.78 mol, adjust the pH to 6.5 with triethylamine and hydrochloric acid, and stir and react for 3 h to obtain melamine formaldehyde resin. The preparation of the polyvinyl alcohol-Zn complex solution is as follows:

[0058] Heat to 90 °C, dissolve polyvinyl alcohol in water to form a 0.1 mol / L polyvinyl alcohol solution, add a 0.01 mol / L zinc chloride aqueous solution, the volume ratio of the polyvinyl alcohol solution to the zinc chloride aqueous solution is 1:0.5, add hydrochloric acid to adjust the pH to 3.0, and stir and react for 3 h to obtain a polyvinyl alcohol-Zn complex solution.

[0059] Example 6

[0060] The difference from Example 4 is only that the polyvinyl alcohol-Zn complex solution is added according to the molar amount of polyvinyl alcohol of 0.975 mol.

[0061] The steps for preparing melamine formaldehyde resin are as follows:

[0062] S1. Add 200 mL of DMF to a flask, then add 75.7 g of melamine (0.6 mol) and 60.7 g of triethylamine (0.6 mol), start stirring, and after mixing evenly, form a reaction solution. Weigh 38.6 g of 2,5-furandicarbonyl chloride (0.2 mol) and add it to the reaction solution. The molar ratio of 2,5-furandicarbonyl chloride to melamine is 1:3. Control the reaction temperature at 15 °C and react at a constant temperature for 10 h to obtain an intermediate.

[0063] S2. Take 557 g of a 35 wt% formaldehyde solution, the molar amount of formaldehyde is 6.5 mol, add triethylamine and mix, adjust the pH to 8.5, weigh 252.24 g of melamine (2 mol), and add it to the reaction system together with the intermediate prepared in S1. Heat to 85 °C and react at a constant temperature for 5 h. Cool to 60 °C, add the polyvinyl alcohol-Zn complex solution, the molar amount of polyvinyl alcohol is 0.975 mol, adjust the pH to 6.5 with triethylamine and hydrochloric acid, and stir and react for 3 h to obtain melamine formaldehyde resin. The preparation of the polyvinyl alcohol-Zn complex solution is as follows:

[0064] Heat to 90 °C, dissolve polyvinyl alcohol in water to form a 0.1 mol / L polyvinyl alcohol solution, add a 0.01 mol / L zinc chloride aqueous solution, the volume ratio of the polyvinyl alcohol solution to the zinc chloride aqueous solution is 1:0.5, add hydrochloric acid to adjust the pH to 3.0, and stir and react for 3 h to obtain a polyvinyl alcohol-Zn complex solution.

[0065] Example 7

[0066] The difference from Example 4 is only that the polyvinyl alcohol-Zn complex solution is added according to the molar amount of polyvinyl alcohol of 1.3 mol.

[0067] The steps for preparing melamine formaldehyde resin are as follows:

[0068] S1. Add 200 mL of DMF to a flask, then add 75.7 g of melamine (0.6 mol) and 60.7 g of triethylamine (0.6 mol). Start stirring. After mixing evenly, a reaction solution is formed. Weigh 38.6 g of 2,5-furandicarbonyl chloride (0.2 mol) and add it to the reaction solution. The molar ratio of 2,5-furandicarbonyl chloride to melamine is 1:3. Control the reaction temperature at 15 °C and carry out a constant-temperature reaction for 10 h to obtain an intermediate.

[0069] S2. Take 557 g of a formaldehyde solution with a concentration of 35 wt%, the molar amount of formaldehyde is 6.5 mol. Add triethylamine and mix, adjust the pH to 8.5. Weigh 252.24 g of melamine (2 mol) and add it to the reaction system together with the intermediate prepared in S1. Heat to 85 °C and carry out a constant-temperature reaction for 5 h. Then cool down to 60 °C, add a polyvinyl alcohol-Zn complex solution. The molar amount of polyvinyl alcohol is 1.3 mol. Adjust the pH to 6.5 with triethylamine and hydrochloric acid, and stir and react for 3 h to obtain a melamine formaldehyde resin. The preparation of the polyvinyl alcohol-Zn complex solution is as follows:

[0070] Heat to 90 °C, dissolve polyvinyl alcohol in water to form a 0.1 mol / L polyvinyl alcohol solution, add a 0.01 mol / L zinc chloride aqueous solution. The volume ratio of the polyvinyl alcohol solution to the zinc chloride aqueous solution is 1:0.5. Add hydrochloric acid to adjust the pH to 3.0 and stir and react for 3 h to obtain a polyvinyl alcohol-Zn complex solution.

[0071] Example 8

[0072] The difference from Example 6 is only that the polyvinyl alcohol-Zn complex solution is replaced with a polyvinyl alcohol-Al complex solution.

[0073] The steps for preparing the melamine formaldehyde resin are as follows:

[0074] S1. Add 200 mL of DMF to a flask, then add 75.7 g of melamine (0.6 mol) and 60.7 g of triethylamine (0.6 mol). Start stirring. After mixing evenly, a reaction solution is formed. Weigh 38.6 g of 2,5-furandicarbonyl chloride (0.2 mol) and add it to the reaction solution. The molar ratio of 2,5-furandicarbonyl chloride to melamine is 1:3. Control the reaction temperature at 15 °C and carry out a constant-temperature reaction for 10 h to obtain an intermediate.

[0075] S2. Take 557 g of formaldehyde solution with a concentration of 35 wt%, the molar amount of formaldehyde is 6.5 mol, add triethylamine and mix, adjust the pH to 8.5, weigh 252.24 g of melamine (2 mol), and add it together with the intermediate prepared in S1 into the reaction system. Heat to 85 °C, keep the temperature constant for reaction for 5 h, cool down to 60 °C, add polyvinyl alcohol-Al complex solution, the molar amount of polyvinyl alcohol is 0.975 mol, adjust the pH to 6.5 with triethylamine and hydrochloric acid, and stir and react for 3 h to obtain melamine formaldehyde resin. The preparation of the polyvinyl alcohol-Al complex solution is as follows:

[0076] Heat to 90 °C, dissolve polyvinyl alcohol in water to form a 0.1 mol / L polyvinyl alcohol solution, add a 0.01 mol / L aluminum chloride aqueous solution, the volume ratio of the polyvinyl alcohol solution to the aluminum chloride aqueous solution is 1:0.5, add hydrochloric acid to adjust the pH to 3.0, and stir and react for 3 h to obtain the polyvinyl alcohol-Al complex solution.

[0077] Comparative Example 1

[0078] The difference from Example 1 is that the melamine formaldehyde resin in this comparative example is a liquid melamine formaldehyde resin (MF resin) purchased conventionally in the market.

[0079] Comparative Example 2

[0080] The difference from Example 1 is that 2,5-furandicarbonyl chloride is not added in the preparation of melamine formaldehyde resin in this comparative example.

[0081] The steps for preparing melamine formaldehyde resin are as follows:

[0082] S1. Take 618 g of formaldehyde solution with a concentration of 35 wt%, the molar amount of formaldehyde is 7.2 mol, add triethylamine and mix, adjust the pH to 8.5, weigh 454.03 g of melamine (3.6 mol), add it into the reaction system, heat to 85 °C, keep the temperature constant for reaction for 5 h, cool down to 60 °C, add polyvinyl alcohol-Zn complex solution, the molar amount of polyvinyl alcohol is 0.72 mol, adjust the pH to 6.5 with triethylamine and hydrochloric acid, and stir and react for 3 h to obtain melamine formaldehyde resin. The preparation of the polyvinyl alcohol-Zn complex solution is as follows:

[0083] Heat to 90 °C, dissolve polyvinyl alcohol in water to form a 0.1 mol / L polyvinyl alcohol solution, add a 0.01 mol / L zinc chloride aqueous solution, the volume ratio of the polyvinyl alcohol solution to the zinc chloride aqueous solution is 1:0.5, add hydrochloric acid to adjust the pH to 3.0, and stir and react for 3 h to obtain the polyvinyl alcohol-Zn complex solution.

[0084] Comparative Example 3

[0085] The difference from Example 1 is that no polyvinyl alcohol-metal complex solution is added in the preparation of melamine formaldehyde resin in this comparative example.

[0086] The steps for preparing melamine formaldehyde resin are as follows:

[0087] S1. Add 200 mL of DMF into a flask, then add 75.7 g of melamine (0.6 mol) and 60.7 g of triethylamine (0.6 mol). Start stirring, and after mixing evenly, a reaction solution is formed. Weigh 38.6 g of 2,5-furandicarbonyl chloride (0.2 mol) and add it to the reaction solution. The molar ratio of 2,5-furandicarbonyl chloride to melamine is 1:3. Control the reaction temperature at 15 °C and carry out a constant-temperature reaction for 10 h to obtain an intermediate.

[0088] S2. Take 618 g of formaldehyde solution with a concentration of 35 wt%, the molar amount of formaldehyde is 7.2 mol, add triethylamine and mix, adjust the pH to 8.5. Weigh 378.36 g of melamine (3 mol) and add it together with the intermediate prepared in S1 into the reaction system. Heat to 85 °C and carry out a constant-temperature reaction for 8 h to obtain melamine formaldehyde resin.

[0089] Comparative Example 4

[0090] The difference from Example 1 is that neither 2,5-furandicarbonyl chloride nor polyvinyl alcohol-metal complex solution is added in the preparation of melamine formaldehyde resin in this comparative example.

[0091] The steps for preparing melamine formaldehyde resin are as follows:

[0092] S1. Take 618 g of formaldehyde solution with a concentration of 35 wt%, the molar amount of formaldehyde is 7.2 mol, add triethylamine and mix, adjust the pH to 8.5. Weigh 454.03 g of melamine (3.6 mol) and add it into the reaction system. Heat to 85 °C and carry out a constant-temperature reaction for 8 h to obtain melamine formaldehyde resin.

[0093] Perform performance tests on the melamine formaldehyde resins prepared in Examples 1 - 8 and Comparative Examples 1 - 4. The results are shown in Table 1:

[0094] Bending strength detection: Apply the melamine formaldehyde resins of the examples and comparative examples as coatings on the upper and lower surfaces of the artificial board, dry at 60 °C, and measure the bending strength of the artificial board (record the bending strength when the coating cracks).

[0095] Table 1

[0096]

[0097]

[0098] As can be seen from Table 1, as the proportion of the intermediate increases, the free formaldehyde content of the resin decreases, and its toughness is significantly improved; when the amount of formaldehyde used increases, the free formaldehyde content also increases, and the amount of formaldehyde used should not be too low, as it is not conducive to the formation of polycondensates, and the viscosity of the resin is relatively low. The polyvinyl alcohol-metal complex solution can block free formaldehyde through the reaction of polyvinyl alcohol and formaldehyde, and the free formaldehyde content will be significantly reduced. The comprehensive performance of the melamine formaldehyde resin in the comparative example is far inferior to that of the resin prepared in the examples. The melamine formaldehyde resin prepared in the examples of the present invention has a low free formaldehyde content and excellent toughness, and can be applied to various industries such as wood processing, coatings, and construction.

[0099] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variation thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device.

[0100] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A production process of melamine formaldehyde resin, characterized in that, It includes the following steps: S1. Mix melamine, triethylamine and DMF and stir to form a reaction solution. Add 2,5-furandicarbonyl chloride. The molar ratio of 2,5-furandicarbonyl chloride to melamine is 1 - 1.2:

3. React at 10 - 20 °C for 8 - 12 h to obtain an intermediate. S2. Mix a formaldehyde solution and an organic amine. Adjust the pH to 8 - 9.5 with the organic amine. Add melamine and the intermediate. Heat to 80 - 90 °C and react at a constant temperature for 4 - 6 h. Cool to 60 - 70 °C. Add a polyvinyl alcohol-metal complex solution. Adjust the pH to 6 - 7 and stir to react for 2 - 4 h to obtain melamine formaldehyde resin.

2. The production process of a melamine formaldehyde resin according to claim 1, characterized in that, The concentration of melamine in the reaction solution is 3 - 5 mol / L, and the concentration of triethylamine is 3 - 5 mol / L.

3. The production process of a melamine formaldehyde resin according to claim 1, characterized in that, The organic amine is one of diethanolamine, triethanolamine and triethylamine.

4. The production process of a melamine formaldehyde resin according to claim 1, characterized in that, The concentration of the formaldehyde solution is 30 - 40 wt%.

5. The production process of a melamine formaldehyde resin according to claim 1, characterized in that, In S2, the molar ratio of formaldehyde in the formaldehyde solution to the total molar amount of melamine in S1 and S2 is 2 - 3:

1.

6. The production process of a melamine formaldehyde resin according to claim 1, characterized in that, In S2, the melamine is added according to the molar ratio of melamine to the melamine for preparing the intermediate in S1 of 5:1 - 2.

7. The production process of a melamine formaldehyde resin according to claim 1, characterized in that, The metal ions contained in the polyvinyl alcohol-metal complex solution are one of zinc ions and aluminum ions.

8. The production process of a melamine formaldehyde resin according to claim 1, characterized in that, The preparation steps of the polyvinyl alcohol-metal complex solution are as follows: Heat polyvinyl alcohol and dissolve it in water to form a 0.1 - 0.5 mol / L polyvinyl alcohol solution. Add a 0.01 - 0.05 mol / L zinc chloride or aluminum chloride aqueous solution with a volume ratio of 1:0.5 - 1. Add hydrochloric acid to adjust the pH to 3 - 4 and stir to react for 2 - 4 h to obtain the polyvinyl alcohol-metal complex solution.

9. The production process of a melamine formaldehyde resin according to claim 1, characterized in that, The polyvinyl alcohol-metal complex solution is added according to the molar ratio of polyvinyl alcohol to formaldehyde of 0.1 - 0.2:

1.

10. A melamine formaldehyde resin, characterized in that, The melamine formaldehyde resin is prepared by using the production process described in any one of claims 1 - 9.

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