Low-VOC (volatile organic compound) modified melamine formaldehyde resin and preparation method thereof

Abstract

The low-VOC modified melamine formaldehyde resin is prepared from the following components in parts by weight: 80 to 100 parts of melamine formaldehyde resin, 5 to 10 parts of hydroxyl-terminated hyperbranched polyester, 8 to 15 parts of epoxy-terminated polybutadiene, 1 to 3 parts of fumed silica, 5 to 15 parts of polyvinyl butyral, 0.1 to 0.2 part of a coupling agent, 1 to 3 parts of a catalyst and 2 to 5 parts of a cross-linking agent, the preparation method comprises the following steps: in a stirring state, adding hydroxyl-terminated hyperbranched polyester, epoxy-terminated polybutadiene, a polyvinyl butyral resin solution and coupling agent modified fumed silica into a melamino-formaldehyde resin solution, heating to 50-70 DEG C, and adding a catalyst and a cross-linking agent; the melamine modified resin prepared by the components and the preparation method has the characteristics of low formaldehyde volatilization, high toughness and durability.

Description

Technical Field

[0001] This application relates to the field of melamine-modified resin technology, and in particular to a low-VOC modified melamine-formaldehyde resin and its preparation method. Background Technology

[0002] Thermosetting films are widely used in laboratory film formation due to their advantages such as low environmental pollution, low processing cost, ease of operation, and high controllability. Traditional melamine resin, as a thermosetting material, can form a highly polymerized three-dimensional network structure under thermosetting conditions. This unique structure endows traditional melamine resin with high hardness, making it suitable for applications requiring high hardness. In past research and development, modification methods for melamine resin have mainly focused on two directions: physical modification and chemical modification. Physical modification involves optimizing resin properties through the introduction of fillers and fiber toughening.

[0003] However, while melamine resin excels in hardness and heat resistance, it has a high formaldehyde content, which is easily volatilized, causing environmental pollution and harm to human health. Current options include reducing formaldehyde content to decrease formaldehyde volatilization and meet environmental protection requirements. However, excessively low formaldehyde content in melamine resin can affect the degree of curing, reduce crosslinking density, and thus weaken toughness and durability, making it difficult to simultaneously achieve low formaldehyde volatilization, high toughness, and excellent durability. Summary of the Invention

[0004] To address the shortcomings of existing melamine resins in simultaneously achieving low formaldehyde volatilization, high toughness, and excellent durability, a low-VOC modified melamine-formaldehyde resin and its preparation method are provided.

[0005] The above-mentioned objective of this invention is achieved through the following technical solutions: A low-VOC modified melamine-formaldehyde resin comprises the following components in parts by weight: 80-100 parts melamine-formaldehyde resin, 5-10 parts hydroxyl-terminated hyperbranched polyester, 8-15 parts epoxy-terminated polybutadiene, 1-3 parts fumed silica, 5-15 parts polyvinyl butyral, 0.1-0.2 parts coupling agent, 1-3 parts catalyst, and 2-5 parts crosslinking agent.

[0006] By adopting the above technical solution, melamine-formaldehyde resin serves as the matrix, providing a basic cross-linking network. The hydroxyl-terminated hyperbranched polyester, with its highly branched three-dimensional structure and abundant terminal hydroxyl groups, undergoes an imine reaction with the imino groups of the melamine-formaldehyde resin to form an interpenetrating network structure, enhancing durability. This structure also encapsulates formaldehyde molecules, reducing formaldehyde diffusion paths. Simultaneously, the flexibility of the hyperbranched structure absorbs internal stress, improving toughness. The epoxy groups of the epoxy-terminated polybutadiene undergo a ring-opening reaction with the terminal hydroxyl groups of the hydroxyl-terminated hyperbranched polyester, resulting in the chemical grafting of flexible polybutadiene long chains. The highly branched structure of end-hydroxyl hyperbranched polyester absorbs and disperses energy through its own deformation and orientation, thereby preventing crack propagation and improving toughness. The epoxy groups can react with free formaldehyde, reducing its content. The polybutadiene backbone is composed of stable C / C single bonds, exhibiting significantly better hydrolysis and heat aging resistance than the inherent methylene ether bonds in melamine resin, enhancing material durability. Fumed silica, with its high specific surface area and surface silanol groups, can form hydrogen bonds with the hydroxyl groups of the hydroxymethyl hyperbranched polyester or dehydrate at high temperatures to form -Si-O-CH groups. 2- Covalent bonds enhance cross-linking density and hinder formaldehyde molecule migration through nano-effects, improving durability. They also alter crack propagation paths, dispersing concentrated impact energy across a broad volume and dissipating it through various physical mechanisms, thus enhancing toughness. The hydroxyl groups of the hyperbranched polyester are tightly bonded to the silica surface via hydrogen bonds, strengthening interfacial adhesion. This allows external forces to be effectively transferred from the relatively flexible resin matrix to the rigid silica nanoparticles. When the material is under stress, it can efficiently induce plastic deformations such as crazes and shear bands, while simultaneously allowing the crack deflection mechanism of silica to fully function. The hyperbranched polyester itself… As a toughening phase, it works synergistically with silica to prevent crack propagation through an energy dissipation mechanism, thereby enhancing the material's toughness. Polyvinyl butyral, with its flexible long chains, forms physical entanglement and van der Waals forces with the resin through the ether bonds of its side groups, absorbing energy through plastic deformation and increasing toughness. Coupling agents improve the interfacial adhesion between inorganic fillers and organic resins, preventing phase separation and improving overall uniformity. Catalysts accelerate condensation reactions, making cross-linking more complete and reducing unreacted monomers. Cross-linking agents increase network density and improve durability. In summary, these components work synergistically through physical and chemical interactions to reduce formaldehyde release and enhance the toughness and durability of the resin.

[0007] Optionally, the melamine-formaldehyde resin is a n-butanol etherified modified melamine-formaldehyde resin.

[0008] By adopting the above technical solutions, etherification modification reduces the free formaldehyde content of the resin. Due to the stability of ether bonds, the resin's durability under high temperature and high humidity conditions is enhanced, its hydrolysis resistance is improved, and its service life is extended. Etherification reduces the rigidity of the resin, making the material easier to deform and absorb energy, and improving its toughness.

[0009] Optionally, the coupling agent is an organozirconate coupling agent.

[0010] By adopting the above technical solution, the organic zirconate molecule contains zirconium atoms. Its inorganic part can react with the silanol groups on the surface of fumed silica to form a strong zirconium-oxygen-silicon covalent bond, while the organic part is compatible with the organic phase of melamine resin. Through van der Waals forces or covalent bonding, the interfacial energy between the filler and the resin is reduced, preventing filler agglomeration, promoting uniform dispersion, improving the toughness of the composite material, and its zirconium-based structure can enhance water resistance and thermal stability.

[0011] Optionally, the crosslinking agent is adipic dihydrazide.

[0012] By adopting the above technical solution, adipic acid dihydrazide contains two highly reactive hydrazide groups, which can undergo nucleophilic addition reactions with free formaldehyde in melamine-formaldehyde resin to generate stable hydrazone compounds, thereby directly reducing the formaldehyde content. The hydrazide groups can also react with the hydroxymethyl groups of hydroxymethyl hyperbranched polyester or the imino groups in the resin to form cross-linking bonds, increasing the density and integrity of the three-dimensional network, improving the thermal stability and durability of the resin. The long, flexible molecular chains of adipic acid dihydrazide introduce toughness into the cross-linking network, enhancing the toughness of the resin.

[0013] Optionally, the catalyst includes p-toluenesulfonic acid and dihydrobutyl phosphate.

[0014] By adopting the above technical solution, toluenesulfonic acid, a strong organic acid, can reduce the activation energy of the reaction through protonation, efficiently promoting the etherification, condensation, and cross-linking reactions of melamine-formaldehyde resin, ensuring rapid curing. Dihydrobutyl phosphate, on the other hand, is a milder acidic catalyst whose phosphate groups may participate in the formation of phosphate ester bonds, providing stability and regulating the reaction rate to avoid uneven curing caused by rapid polymerization. The combined use of the two catalysts allows toluenesulfonic acid to dominate the initial rapid reaction, while dihydrobutyl phosphate acts as a buffer to balance the pH value, making the curing process more stable and controllable, promoting the complete formation of the resin network, reducing free formaldehyde and unreacted monomers, and resulting in better toughness, durability, and thermal stability.

[0015] Optionally, the mass ratio of p-toluenesulfonic acid to dihydrobutyl phosphate is (1-3):1.

[0016] By adopting the above technical solution, toluenesulfonic acid is provided with sufficient catalytic power, while dihydrobutyl phosphate is moderately avoided from over-reacting, so that the etherification, cross-linking and other steps are carried out smoothly, promoting the uniform formation of resin network, so that formaldehyde is effectively consumed in the reaction, reducing residues, and enhancing the toughness, durability and thermal stability of the resin film after formation.

[0017] Optionally, the fumed silica is hydrophobic fumed silica.

[0018] By adopting the above technical solution, the hydrophobic fumed silica has a lower surface energy and is easier to disperse in organic resins, avoiding moisture absorption and agglomeration. The nano-sized particles and large specific surface area can enhance the resin matrix through physical entanglement and surface effects, restrict molecular chain movement, and improve toughness. The hydrophobic surface reduces water adsorption and improves the durability of the composite material.

[0019] The second objective of this invention is achieved through the following technical solution: The preparation method of the above-mentioned low-VOC modified melamine-formaldehyde resin includes the following steps: S1: Dissolve polyvinyl butyral resin in a portion of the solvent to obtain a polyvinyl butyral resin solution, and dissolve melamine-formaldehyde resin in a portion of the solvent to obtain a melamine-formaldehyde resin solution. S2: Under stirring, add hydroxyl-terminated hyperbranched polyester, polyvinyl butyral resin solution, epoxy-terminated polybutadiene, and fumed silica modified with coupling agent to melamine-formaldehyde resin solution, and then add catalyst and crosslinking agent after heating to 50-70℃.

[0020] By adopting the above technical solution, polyvinyl butyral and melamine-formaldehyde resin are first dissolved in solvents to avoid clumping when added directly, ensuring sufficient dispersion of the toughening phase and the base resin. A solution of terminally hydroxyl hyperbranched polyester and polyvinyl alcohol is added first to pre-form a network of the toughening phase. Then, fumed silica treated with a coupling agent is added to optimize the filler interface. After heating to 50-70℃, a catalyst and crosslinking agent are added to control the reaction initiation temperature and avoid premature gelation. This promotes the interaction between components, such as hydrogen bonding between the hyperbranched polyester and the resin, the reinforcing effect of silica, and the efficient crosslinking reaction, resulting in uniform resin, complete reaction, improved resin toughness and durability, and low formaldehyde content.

[0021] In summary, this application has at least the following beneficial effects: (1) The hydroxyl-terminated hyperbranched polyester has a highly branched three-dimensional structure and abundant hydroxyl groups. It reacts with melamine-formaldehyde resin to form an interpenetrating structure, which encapsulates formaldehyde, reduces the internal stress absorbed by formaldehyde, improves toughness and increases durability. (2) Fumed silica has a high specific surface area and contains silanol groups, which can form hydrogen bonds with hydroxymethyl groups or covalent bonds at high temperatures, thereby enhancing cross-linking, hindering formaldehyde migration, changing crack propagation paths, reducing formaldehyde content and improving toughness and durability. (3) Hyperbranched polyester hydroxyl groups and silica are tightly bonded by hydrogen bonds, which enhances interfacial adhesion and induces plastic deformation under stress. The two work together to prevent crack propagation and improve the toughness of the material. Detailed Implementation

[0022] raw material Melamine-formaldehyde resin, specifically melamine-formaldehyde resin powder, 60 mesh, model LG330, purchased from Shijiazhuang Dingshang Chemical Products Co., Ltd. Hexamethylol melamine was purchased from Hubei Jusheng Technology Co., Ltd.

[0023] Hydroxyl-terminated hyperbranched polyester, model HyPer H101, with 5-7 hydroxyl groups / mol and a hydroxyl value of 670 mg KOH / g, was purchased from Wuhan Hyperbranched Resin Technology Co., Ltd. The epoxy-terminated polybutadiene was purchased from Tianyuan Aviation Materials (Yingkou) Technology Co., Ltd. Hydrophobic fumed silica (model HB-132) and hydrophilic fumed silica (model HL-300) were both purchased from Hubei Huifu Nanomaterials Co., Ltd. Adipic acid dihydrazide, purity ≥99.5wt%, purchased from Weifang Kairui Chemical Co., Ltd. Trimethylolpropane, purity ≥98wt%, purchased from Shanghai Maclean Biochemical Technology Co., Ltd. γ-aminopropyltriethoxysilane was purchased from Hangzhou Jessica Chemical Co., Ltd. Polyvinyl butyral resin, model B-98, with an average molecular weight of 40,000, was purchased from Shanghai Coleman Reagent Co., Ltd. The organozirconate, specifically tetrabutyl zirconate, with a purity of 89 wt%, was purchased from Beijing Huawirui Chemical Technology Co., Ltd. p-Toluenesulfonic acid, purity ≥99wt%, purchased from Shanghai Maclean Biochemical Technology Co., Ltd. Butyl dihydrogen phosphate was purchased from Hubei Enxing Biotechnology Co., Ltd. 1-Methoxy-2-propanol, specifically (R)-(-)-1-methoxy-2-propanol, was purchased from Hubei Enxing Biotechnology Co., Ltd. n-Propanol, 36 wt% hydrochloric acid, and 30 wt% sodium hydroxide solution were all commercially available.

[0024] Preparation Example 1 A butanol-etherified modified melamine-formaldehyde resin is prepared as follows: 240 kg of n-butanol and 10 kg of water were added to the reactor as solvents and stirred at 100 rpm. 36 wt% hydrochloric acid was added to adjust the pH to 2.5 ± 0.2. 100 kg of hexamethylol melamine was added, the temperature was raised to 92 °C, and the mixture was refluxed to remove water. The aqueous layer was separated by a separator, and then the temperature was lowered to 40 °C. 30 wt% sodium hydroxide solution was added to adjust the pH to 7.0 ± 0.2. The temperature was raised to 80℃, and the vacuum was reduced to -0.085 MPa at a depressurization rate of 10 kPa / min. The solvent (a mixture of n-butanol and water) was recovered through a condenser until the solvent content was 200 kg. The vacuum was then increased to 101.3 kPa at a pressure increase rate of 5 kPa / min. Heating was stopped, and 160 kg of n-butanol and 6 kg of deionized water were added to the reactor. The pH was adjusted to 2.5 ± 0.2 with 36 wt% hydrochloric acid. The temperature was raised to 92℃ and held for 30 min. The temperature was then lowered to 40℃, and the pH was adjusted to 7.0 with a change of 0.2 by adding 30 wt% sodium hydroxide solution. The temperature was raised to 80℃, and the vacuum was reduced to -0.085 MPa at a depressurization rate of 10 kPa / min. The solvent (a mixture of n-butanol and water) was recovered until the solid content was 96 wt%. The reaction was then stopped, yielding n-butanol etherified melamine-formaldehyde resin.

[0025] Example 1 A low-VOC modified melamine-formaldehyde resin is prepared from the following components by weight: 90 kg of n-butanol etherified modified melamine-formaldehyde resin, 8 kg of hydroxyl-terminated hyperbranched polyester, 10 kg of epoxy-terminated polybutadiene, 10 kg of polyvinyl butyral resin, 0.15 kg of tetrabutyl zirconate, 1.2 kg of p-toluenesulfonic acid, 2 kg of fumed silica, 0.8 kg of dihydrogen phosphate, 3 kg of adipate dihydrazide crosslinking agent, and 57 kg of 1-methoxy-2-propanol solvent; wherein the n-butanol etherified modified melamine-formaldehyde resin is derived from Preparation Example 1.

[0026] Its preparation method is as follows: S1: Add 10 kg of polyvinyl butyral resin to 30 kg of 1-methoxy-2-propanol, stir at 400 rpm, and simultaneously heat to 60°C at a rate of 5°C / min. Continue stirring at this temperature for 45 min, and then naturally cool to 40°C to obtain a polyvinyl butyral resin solution. Add the remaining 20 kg of 1-methoxy-2-propanol to the main reactor. Add the n-butanol etherified modified melamine-formaldehyde resin to the main reactor at a rate of 1 kg / min, and simultaneously stir at 300 rpm. After the addition is complete, add 2 kg of hydrophobic fumed silica, and simultaneously adjust the stirring speed of the main reactor to 500 rpm. Heat to 50°C at a rate of 5°C / min, and maintain this temperature for 30 min to obtain the base solution. S1a: In a pretreatment vessel, add 2 kg of fumed silica, 7 kg of 1-methoxy-2-propanol and 0.1 kg of deionized water, and stir and disperse at 1000 rpm for 20 minutes. Then add 0.15 kg of tetrabutyl zirconate at 100 mL / min. After the addition is complete, heat to 55°C and stir at 1000 rpm for 40 minutes to obtain zirconate ester modified silica slurry. S2: Maintain the main reactor speed at 400 rpm and temperature at 50℃. Add hydroxyl-terminated hyperbranched polyester to the base solution at 1 kg / min. After addition, continue stirring for 20 min. Add 3 kg of adipic acid dihydrazide to the base solution at 500 g / min and continue stirring for 15 min. The hydrazide groups will begin to react with free formaldehyde and hydroxymethyl groups in the resin. Add 10 kg of epoxy-terminated polybutadiene to the base solution at 5 L / min. Add polyvinyl butyral resin solution to the base solution at 5 L / min. After addition, raise the temperature of the main reactor to 60℃ and stir at this temperature for 30 min. Add zirconate ester modified silica slurry to the base solution at 3 L / min and stir for 10 min. Lower the temperature to 40℃ and add 1.2 kg of p-toluenesulfonic acid and 0.8 kg of dihydrogen phosphate to the base solution in sequence. Stir for 30 min after addition to obtain low VOC modified melamine-formaldehyde resin.

[0027] Comparative Example 1 A low-VOC modified melamine-formaldehyde resin differs from Example 1 in that it does not contain terminal hydroxyl hyperbranched polyester, while the rest is the same as Example 1.

[0028] Comparative Example 2 A low-VOC modified melamine-formaldehyde resin differs from Example 1 in that hydrophobic fumed silica is not added, while the rest is the same as Example 1.

[0029] Example 2 A low-VOC modified melamine-formaldehyde resin differs from Example 1 in that: an equal mass of melamine-formaldehyde resin is used to replace the n-butanol etherified modified melamine-formaldehyde resin, while the rest is the same as in Example 1.

[0030] Example 3 A low-VOC modified melamine-formaldehyde resin differs from Example 1 in that γ-aminopropyltriethoxysilane is used in equimolar amounts to replace tetrabutyl zirconate, while the rest is the same as in Example 1.

[0031] Example 4 A low-VOC modified melamine-formaldehyde resin differs from Example 1 in that it uses trimethylolpropane in place of adipate dihydrazide by mass, while the rest is the same as in Example 1.

[0032] Example 5 A low-VOC modified melamine-formaldehyde resin differs from Example 1 in that it does not contain dihydrobutyl phosphate and has 2 kg of p-toluenesulfonic acid, while the rest of the components are the same as in Example 1.

[0033] Example 6 A low-VOC modified melamine-formaldehyde resin differs from Example 1 in that it does not contain p-toluenesulfonic acid and has 2 kg of dihydrobutyl phosphate, while the rest is the same as in Example 1.

[0034] Example 7 A low-VOC modified melamine-formaldehyde resin differs from Example 1 in that: p-toluenesulfonic acid is 1 kg, dihydrobutyl phosphate is 1 kg, and the rest is the same as in Example 1.

[0035] Example 8 A low-VOC modified melamine-formaldehyde resin differs from Example 1 in that: p-toluenesulfonic acid is 1.5 kg, dihydrobutyl phosphate is 0.5 kg, and the rest is the same as in Example 1.

[0036] Example 9 A low-VOC modified melamine-formaldehyde resin differs from Example 1 in that: p-toluenesulfonic acid is 0.8 kg, dihydrobutyl phosphate is 1.2 kg, and the rest is the same as in Example 1.

[0037] Example 10 A low-VOC modified melamine-formaldehyde resin differs from Example 1 in that: p-toluenesulfonic acid is 1.8 kg, dihydrobutyl phosphate is 0.2 kg, and the rest is the same as in Example 1.

[0038] Example 11 A low-VOC modified melamine-formaldehyde resin differs from Example 1 in that hydrophilic fumed silica is used in place of hydrophobic fumed silica by the same mass, while the rest is the same as in Example 1.

[0039] Example 12 A low-VOC modified melamine-formaldehyde resin differs from Example 1 in that: 80 kg of n-butanol etherified modified melamine-formaldehyde resin, 5 kg of hydroxyl-terminated hyperbranched polyester, 8 kg of epoxy-terminated polybutadiene, 5 kg of polyvinyl butyral resin, 1 kg of hydrophobic fumed silica, 0.1 kg of tetrabutyl zirconate, 0.6 kg of p-toluenesulfonic acid, 0.4 kg of dihydrogen phosphate, and 2 kg of adipic acid dihydrazide crosslinking agent are used. The remaining components are the same as in Example 1.

[0040] Example 13 A low-VOC modified melamine-formaldehyde resin differs from Example 1 in that: 100 kg of n-butanol etherified modified melamine-formaldehyde resin, 10 kg of hydroxyl-terminated hyperbranched polyester, 15 kg of epoxy-terminated polybutadiene, 15 kg of polyvinyl butyral resin, 3 kg of hydrophobic fumed silica, 0.2 kg of tetrabutyl zirconate, 1.8 kg of p-toluenesulfonic acid, 1.2 kg of dihydrogen phosphate, and 5 kg of adipic acid dihydrazide crosslinking agent are used. The remaining components are the same as in Example 1.

[0041] Examples 1-13 and Comparative Examples 1-2 were tested, and the results are as follows: According to GB / T 1731-2020 "Test Method for Flexibility of Paint Film and Putty Film", the resins of Examples 1-13 and Comparative Examples 1-2 were coated on tinplate (100mm×50mm×0.3mm), with a wet film thickness controlled at 100μm. The coatings were cured at 140℃ for 30min, and then placed under constant temperature and humidity conditions (23±2℃, 50±5% RH) for 24h. Using a shaft bending tester (shaft diameter gradients of 2mm, 3mm, 4mm, 5mm, 6mm, 8mm, 10mm), the coated plate was bent 180° around the shaft to check for cracking. The minimum shaft diameter (unit: mm) at which the film did not crack was recorded. A smaller diameter indicates better toughness. The test results are shown in Table 1.

[0042] Artificial aging tests were conducted according to GB / T 1865-2009 "Artificial Climate Aging and Artificial Radiation Exposure to Filtered Xenon Arc Radiation for Paints and Varnishes". The resins of Examples 1-13 and Comparative Examples 1-2 were coated on tinplate (100mm×50mm×0.3mm in size), with the wet film thickness controlled at 100μm. The coatings were cured at 140℃ for 30min. After curing, the coatings were placed under constant temperature and humidity conditions (23±2℃, 50±5% RH) for 24h. The coated plates were then placed in a fluorescent ultraviolet aging chamber (UVA-340 lamp) with the following cycle conditions: 8h of UV irradiation (60℃) and 4h of condensation (50℃). The total test time was 200 hours. After aging, the 60° gloss retention rate (gloss retention percentage) was measured using a gloss meter. A higher gloss retention rate indicates better aging resistance. The test results are shown in Table 1.

[0043] According to GB 18582-2020 "Limits of Hazardous Substances in Wall Coatings for Buildings", the resins of Examples 1-13 and Comparative Examples 1-2 were uniformly coated on flat glass plates (150mm×150mm), with the wet film thickness controlled at 100μm. They were then cured in a 140℃ forced-air drying oven for 30 minutes. The cured coating was completely peeled off from the glass plate and cut into small fragments. 50g of the coating fragment was weighed as a sample. A 12cm diameter petri dish was placed at the bottom of a desiccator (40L volume), and 300mL of distilled water was added. The sample was placed on a support inside the desiccator, ensuring it did not contact the absorption liquid. The desiccator was sealed and placed in a dark environment at 23℃ for 24 hours. After standing, the absorption liquid in the petri dish was taken as the test solution, and the formaldehyde content in the test solution was determined using the acetylacetone spectrophotometric method. The test results are shown in Table 1.

[0044] Table 1. Test results of Examples 1-13 and Comparative Examples 1-2 Minimum bending diameter (mm) Artificial aging gloss retention rate (%) Formaldehyde content (mg / kg) Example 1 2 95 5 Comparative Example 1 6 73 30 Comparative Example 2 6 75 28 Example 2 4 80 21 Example 3 4 82 17 Example 4 4 84 15 Example 5 5 78 25 Example 6 5 78 25 Example 7 3 90 10 Example 8 3 92 8 Example 9 4 85 12 Example 10 4 88 10 Example 11 3 90 8 Example 12 4 85 13 Example 13 4 84 15 Based on Table 1, Examples 1-13 and Comparative Examples 1-2 were analyzed, and the analysis is as follows: Compared with Comparative Example 1, the minimum bending diameter and formaldehyde content of the melamine-modified resin in Example 1 are smaller than those of the melamine-modified resin in Comparative Example 1. The artificial aging gloss retention rate of the melamine-modified resin in Example 1 is greater than that of the melamine-modified resin in Comparative Example 1.

[0045] Compared to Comparative Example 1, Example 1 incorporates hydroxyl-terminated hyperbranched polyester. The abundant hydroxyl-terminated hyperbranched polyester reacts with the imino groups of melamine-formaldehyde resin, reducing the formaldehyde diffusion path. Its hyperbranched structure absorbs internal stress and improves toughness. Therefore, the addition of hydroxyl-terminated hyperbranched polyester is necessary.

[0046] Compared with Example 1 and Comparative Example 2, the minimum bending diameter and formaldehyde content of the melamine-modified resin in Example 1 are smaller than those of the melamine-modified resin in Comparative Example 2. The artificial aging gloss retention rate of the melamine-modified resin in Example 1 is greater than that of the melamine-modified resin in Comparative Example 2.

[0047] Compared to Comparative Example 2, Example 1 incorporated fumed silica; the silanol groups in the fumed silica can form hydrogen bonds with the hydroxymethyl groups of the hydroxymethyl hyperbranched polyester or dehydrate at high temperatures to form -Si-O-CH 2- Covalent bonds enhance cross-linking density, hinder the migration of formaldehyde molecules, and improve stability; therefore, the addition of fumed silica is necessary.

[0048] Comparing Example 1 and Example 2, the minimum bending diameter and formaldehyde content of the melamine-modified resin in Example 1 are smaller than those of the melamine-modified resin in Example 2. The artificial aging gloss retention rate of the melamine-modified resin in Example 1 is greater than that of the melamine-modified resin in Example 2.

[0049] Compared to Example 2, the melamine-formaldehyde resin in Example 1 is a n-butanol etherified melamine-formaldehyde resin. Etherification modification reduces the free formaldehyde content of the resin, enhances the resin's durability under high temperature and high humidity conditions, reduces the rigidity of the resin, makes the material easier to deform and absorb energy, and improves toughness. Therefore, n-butanol etherified melamine-formaldehyde resin is superior.

[0050] Comparing Examples 1 and 3, the minimum bending diameter and formaldehyde content of the melamine-modified resin in Example 1 are smaller than those of the melamine-modified resin in Example 3. The artificial aging gloss retention rate of the melamine-modified resin in Example 1 is greater than that of the melamine-modified resin in Example 3.

[0051] Compared to Example 3, the coupling agent in Example 1 is an organozirconate coupling agent. The zirconium atoms of the organozirconate react with the silanol groups on the surface of fumed silica to form zirconium-oxygen-silicon covalent bonds. The organic part is compatible with the organic phase of melamine resin, which reduces the interfacial energy between the filler and the resin, prevents filler agglomeration, promotes uniform dispersion, and improves the toughness of the composite material. In addition, its zirconium-based structure can enhance water resistance and thermal stability. Therefore, organozirconate coupling agents are preferred.

[0052] Comparing Examples 1 and 4, the minimum bending diameter and formaldehyde content of the melamine-modified resin in Example 1 are smaller than those of the melamine-modified resin in Example 4, and the artificial aging gloss retention rate of the melamine-modified resin in Example 1 is greater than that of the melamine-modified resin in Example 4.

[0053] Compared to Example 4, the crosslinking agent in Example 1 was adipic acid dihydrazide. The highly reactive hydrazide group of adipic acid dihydrazide undergoes a nucleophilic addition reaction with the free formaldehyde in the melamine-formaldehyde resin, reducing the formaldehyde content. The hydrazide group can also react with the imino group of the resin, improving the resin's thermal stability and durability. The longer, more flexible molecular chain of adipic acid dihydrazide enhances the resin's toughness. Therefore, choosing adipic acid dihydrazide as the crosslinking agent is preferable.

[0054] Comparing Examples 1 and 5-6, the minimum bending diameter and formaldehyde content of the melamine-modified resin in Example 1 are smaller than those of the melamine-modified resins in Examples 5-6, and the artificial aging gloss retention rate of the melamine-modified resin in Example 1 is greater than that of the melamine-modified resins in Examples 5-6.

[0055] Compared to Examples 5-6, the catalyst in Example 1 was toluenesulfonic acid and butyl dihydrogen phosphate. Toluenesulfonic acid promotes the etherification, condensation, and crosslinking reactions of melamine-formaldehyde resin, ensuring rapid curing. The phosphate groups of butyl dihydrogen phosphate may participate in the formation of phosphate ester bonds, providing stability and regulating the reaction rate to avoid uneven curing caused by rapid polymerization. Toluenesulfonic acid dominates the initial rapid reaction, while butyl dihydrogen phosphate acts as a buffer to balance the pH value, making the curing process more stable and controllable, reducing free formaldehyde and unreacted monomers, resulting in better toughness, durability, and thermal stability after curing. Therefore, toluenesulfonic acid and butyl dihydrogen phosphate are preferred catalysts.

[0056] Comparing Examples 1 and 7-10, the minimum bending diameter and formaldehyde content of the melamine-modified resin in Example 1 are smaller than those in Examples 7-10, and the artificial aging gloss retention rate of the melamine-modified resin in Example 1 is greater than that in Examples 7-10. Similarly, the minimum bending diameter and formaldehyde content of the melamine-modified resins in Examples 7-8 are smaller than those in Examples 9-10, and the artificial aging gloss retention rate of the melamine-modified resins in Examples 7-8 is greater than that in Examples 9-10.

[0057] Compared to Examples 9-10, the mass ratio of p-toluenesulfonic acid to dihydrobutyl phosphate in Examples 1 and 7-8 is (1-3):1. At this ratio, the etherification and crosslinking steps of p-toluenesulfonic acid and dihydrobutyl phosphate proceed smoothly, promote the uniform formation of the resin network, and effectively consume formaldehyde in the reaction, reducing residues and enhancing the toughness, durability and thermal stability of the resin film. Therefore, a mass ratio of p-toluenesulfonic acid to dihydrobutyl phosphate of (1-3):1 is preferred.

[0058] Comparing Example 1 and Example 11, the minimum bending diameter and formaldehyde content of the melamine-modified resin in Example 1 are smaller than those of the melamine-modified resin in Example 11, and the artificial aging gloss retention rate of the melamine-modified resin in Example 1 is greater than that of the melamine-modified resin in Example 11.

[0059] Compared to Example 11, the fumed silica in Example 1 is hydrophobic fumed silica. Hydrophobic fumed silica is easier to disperse in organic resins, avoiding moisture absorption and agglomeration. Its nano-sized particles and large specific surface area enhance the resin matrix, restrict molecular chain movement, improve toughness, and enhance durability due to its hydrophobicity. Therefore, hydrophobic fumed silica is preferred.

[0060] Comparing Examples 1 and 12-13, the minimum bending diameter and formaldehyde content of the melamine-modified resin in Example 1 are smaller than those of the melamine-modified resins in Examples 12-13, and the artificial aging gloss retention rate of the melamine-modified resin in Example 1 is greater than that of the melamine-modified resins in Examples 12-13.

[0061] Compared to Examples 12-13, the mass ratio of n-butanol etherified modified melamine-formaldehyde resin, hydroxyl-terminated hyperbranched polyester, epoxy-terminated polybutadiene, polyvinyl butyral resin, tetrabutyl zirconate, p-toluenesulfonic acid, fumed silica, dihydrobutyl phosphate, and adipate dihydrazide crosslinking agent in Example 1 is 90:8:10:10:0.15:1.2:2:0.8:3. Therefore, the mass ratio of n-butanol etherified modified melamine-formaldehyde resin, hydroxyl-terminated hyperbranched polyester, epoxy-terminated polybutadiene, polyvinyl butyral resin, tetrabutyl zirconate, p-toluenesulfonic acid, fumed silica, dihydrobutyl phosphate, and adipate dihydrazide crosslinking agent in Example 1 is superior.

[0062] This specific embodiment is merely an explanation of the present invention and is not intended to limit the present invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but as long as they are within the scope of protection claimed by the present invention, they are protected by patent law.

Claims

1. A low VOC modified melamine formaldehyde resin characterized in that, The components include the following parts by weight: melamine formaldehyde resin 80-100 parts, hydroxyl-terminated hyperbranched polyester 5-10 parts, epoxy-terminated polybutadiene 8-15 parts, fumed silica 1-3 parts, polyvinyl butyral 5-15 parts, coupling agent 0.1-0.2 parts, catalyst 1-3 parts, crosslinking agent 2-5 parts.

2. The low VOC modified melamine formaldehyde resin according to claim 1, characterized in that, The melamine formaldehyde resin is n-butanol etherification modified melamine formaldehyde resin.

3. The low VOC modified melamine formaldehyde resin according to claim 1, characterized in that, The coupling agent is an organic zirconium ester coupling agent.

4. The low VOC modified melamine formaldehyde resin according to claim 1, characterized in that, The crosslinking agent is adipic acid dihydrazide.

5. The low VOC modified melamine formaldehyde resin according to claim 1, wherein, The catalyst includes p-toluenesulfonic acid and butyl hydrogen phosphate.

6. The low VOC modified melamine formaldehyde resin according to claim 5, characterized in that, The mass ratio of the p-toluenesulfonic acid and butyl hydrogen phosphate is (1-3):

1.

7. The low VOC modified melamine formaldehyde resin according to claim 1, wherein, The fumed silica is hydrophobic fumed silica.

8. A method for producing the low VOC modified melamine formaldehyde resin according to claims 1 to 7, characterized in that, The method includes the following steps: S1: dissolving polyvinyl butyral resin into part of the solvent to obtain a polyvinyl butyral resin solution, and dissolving melamine formaldehyde resin into part of the solvent to obtain a melamine formaldehyde resin solution; S2: under stirring, adding hydroxyl-terminated hyperbranched polyester, epoxy-terminated polybutadiene, the polyvinyl butyral resin solution, fumed silica modified by using a coupling agent, and catalyst and crosslinking agent into the melamine formaldehyde resin solution after being heated to 50-70 DEG C.