High-flame-retardant low-VOC acrylic acid composite resin and preparation method thereof

Abstract

The invention discloses high-flame-retardant low-VOC (volatile organic compound) acrylic acid composite resin and a preparation method thereof. The method comprises the following steps: reacting a melamine resin prepolymer, ammonium polyphosphate and a charring catalyst in an acidic water phase to prepare a microencapsulated synergistic flame retardant with a core-shell structure; then pentaerythritol, phosphorus oxychloride and hydroxyethyl methylacrylate are subjected to a reaction to synthesize a reaction type phosphorus flame-retardant monomer; finally, the monomer, methyl methacrylate, butyl acrylate, acrylic acid and the microencapsulated flame retardant are subjected to emulsion copolymerization in a water phase, and target resin is prepared. Through the synergistic effect of double mechanisms of reactive flame retardance and microencapsulation synergistic flame retardance, the limit oxygen index of the resin is larger than or equal to 32%, and flame-retardant components are stable and do not migrate; a water phase system is adopted in the whole process, the VOC source is controlled from the source, and the VOC content of the product is lower than 40 g / L. The obtained resin has excellent flame retardance, environmental protection property and good mechanical property, and is suitable for the field of high-end coatings and adhesives.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a high flame retardant, low VOC acrylic composite resin and its preparation method. Background Technology

[0002] Acrylic resins are widely used in coatings, adhesives, inks, and plastic modification due to their excellent weather resistance, transparency, film-forming properties, and mechanical properties. However, unmodified ordinary acrylic resins have a low limiting oxygen index and are flammable materials. They burn rapidly upon contact with fire, accompanied by a large number of molten droplets, which can easily cause fires to spread. This severely limits their application in scenarios with strict flame retardancy requirements, such as electronic equipment, transportation, and building interiors. To improve their flame retardancy, traditional technologies mainly rely on physical blending techniques. However, this method has inherent drawbacks, such as the easy migration and precipitation of flame retardants leading to performance degradation, high addition amounts deteriorating the mechanical properties of materials, and the introduction of organic solvents to improve processability, resulting in high VOC content. Although halogen-free intumescent flame retardants and chemically modified reactive flame retardant monomers have been proposed, the former still faces compatibility and dispersibility challenges, while the latter suffers from limited flame retardant efficiency or high costs. Therefore, existing technologies struggle to simultaneously achieve high flame retardant efficiency, excellent overall performance, and ultra-low VOC emissions. Developing an innovative solution has become an urgent technological need in this field. Summary of the Invention

[0003] To address the aforementioned issues, this invention proposes a high flame-retardant, low-VOC acrylic composite resin and its preparation method. This invention successfully constructs a dual high-efficiency flame-retardant mechanism combining "molecular anchoring" and "intelligent triggered expansion" by copolymerizing reactive phosphorus-based flame-retardant monomers into the acrylic resin molecular chain and combining them with a self-synthesized microencapsulated synergistic flame-retardant agent.

[0004] The present invention provides a method for preparing a high flame retardant, low VOC acrylic composite resin, comprising the following steps: Step 1: Add water, melamine resin prepolymer, ammonium polyphosphate, and char catalyst to a flask, adjust the pH to 3-4, stir at 60-80℃ for 1-2 h to form a core-shell structure, filter, wash, and dry to obtain microencapsulated synergistic flame retardant. Step 2: Add water, emulsifier, flame retardant monomer, methyl methacrylate, butyl acrylate, acrylic acid, and microencapsulated synergistic flame retardant to the emulsification kettle, stir, transfer to the reaction kettle, add ammonium persulfate, carry out the polymerization reaction, then cool to below 40°C, adjust the pH to 7-8, filter and discharge to obtain high flame retardant and low VOC acrylic composite resin.

[0005] Preferably, in step 1, the mass ratio of melamine resin prepolymer, ammonium polyphosphate, and char-forming catalyst is (0.5-0.8):1:(0.1-0.3).

[0006] Preferably, the char-forming catalyst in step 1 is pentaerythritol phosphate or melamine polyphosphate.

[0007] Preferably, in step 2, the emulsifier is a compound of sodium allyl hydroxypropanesulfonate and sodium allyl hydroxypropanesulfonate in a mass ratio of (2-2.2):1.

[0008] Preferably, the polymerization reaction in step 2 is carried out at a temperature of 80-90°C for 3-7 hours.

[0009] Preferably, the flame retardant monomer preparation method in step 2 is as follows: under a nitrogen atmosphere, pentaerythritol and phosphorus oxychloride are added to a flask and reacted at 60-80°C for 3-5 h. Then, hydroxyethyl methacrylate and triethylamine are added and reacted at 80-100°C for 4-6 h. After purification, the flame retardant monomer is obtained.

[0010] Preferably, the mass ratio of pentaerythritol, phosphorus oxychloride, hydroxyethyl methacrylate, and triethylamine is 1:(1.8-2.2):(2.5-3.2):(0.02-0.05).

[0011] Preferably, in step 2, the mass ratio of emulsifier, flame retardant monomer, methyl methacrylate, butyl acrylate, acrylic acid, microencapsulated synergistic flame retardant, and ammonium persulfate is (1.5-2):(4-6):(20-25):(26-30):1:(10-12):(0.25-0.35).

[0012] The beneficial effects of this invention are: The composite resin prepared by this invention has a limiting oxygen index (LOI) of over 32%, exhibiting excellent and long-lasting flame retardant properties, effectively overcoming the defects of traditional physical blending methods, such as easy migration and poor durability of flame retardants. Simultaneously, this invention employs a solvent-free aqueous emulsion polymerization process throughout, and selects reactive emulsifiers, eliminating the introduction of organic solvents at the source. This results in an extremely low VOC content (below 40 g / L), far superior to traditional solvent-based or physically blended modified resins, demonstrating significant environmental advantages. Furthermore, this dual flame retardant system exhibits excellent synergistic effects, achieving a high flame retardant rating with extremely low total addition amounts, maximizing and optimizing the resin's overall physical properties, including film-forming properties, adhesion, transparency, and mechanical strength. This invention's process route is green and cost-controllable, providing an ideal solution for preparing acrylic resins with high safety, environmental friendliness, and excellent comprehensive performance, meeting the increasingly stringent requirements of high-end applications for flame retardancy and environmental protection. Attached Figure Description

[0013] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 The values ​​represent the VOC content and LOI of the acrylic composite resin. Detailed Implementation

[0014] The following provides a detailed description of the embodiments of the present invention: These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and processes. However, the scope of protection of the present invention is not limited to the following embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions.

[0015] Example 1 This embodiment describes a method for preparing a high flame-retardant, low-VOC acrylic composite resin, comprising the following steps: Step 1: Add 800 mL of water, 100 g of melamine resin prepolymer, 200 g of ammonium polyphosphate, and 20 g of pentaerythritol phosphate to a flask, adjust the pH to 3, stir at 60°C for 2 h to form a core-shell structure, filter, wash, and dry to obtain a microencapsulated synergistic flame retardant. Step 2: Add 200 mL of water, 40 g of sodium allyl hydroxypropanesulfonate, and 20 g of sodium allyl hydroxypropanesulfonate to the flask and mix well to obtain the emulsifier. Step 3: Under a nitrogen atmosphere, add 30 g pentaerythritol and 54 g phosphorus oxychloride to a flask, react at 60°C for 5 h, then add 75 g hydroxyethyl methacrylate and 0.6 g triethylamine, react at 80°C for 6 h, purify, and obtain the flame retardant monomer. Step 4: Add 2.5 L of water, 75 g of emulsifier, 200 g of flame retardant monomer, 1 kg of methyl methacrylate, 1.3 g of butyl acrylate, 50 g of acrylic acid, and 500 g of microencapsulated synergistic flame retardant to the emulsification tank, stir, transfer to the reaction vessel, add 12.5 g of ammonium persulfate, and carry out the polymerization reaction at 80°C for 7 h. Then cool to below 40°C, adjust the pH to 7, filter and discharge to obtain a high flame retardant and low VOC acrylic composite resin.

[0016] Example 2 This embodiment describes a method for preparing a high flame-retardant, low-VOC acrylic composite resin, comprising the following steps: Step 1: Add 800 mL of water, 160 g of melamine resin prepolymer, 200 g of ammonium polyphosphate, and 60 g of melamine polyphosphate to a flask, adjust the pH to 4, stir at 80°C for 1 h to form a core-shell structure, filter, wash, and dry to obtain a microencapsulated synergistic flame retardant. Step 2: Add 200 mL of water, 44 g of sodium allyl hydroxypropanesulfonate, and 20 g of sodium allyl hydroxypropanesulfonate to the flask and mix well to obtain the emulsifier. Step 3: Under a nitrogen atmosphere, add 30 g pentaerythritol and 66 g phosphorus oxychloride to a flask, react at 80°C for 3 h, then add 96 g hydroxyethyl methacrylate and 1.5 g triethylamine, react at 100°C for 4 h, purify, and obtain the flame retardant monomer. Step 4: Add 2.5 L of water, 85 g of emulsifier, 250 g of flame retardant monomer, 1.1 kg of methyl methacrylate, 1.4 g of butyl acrylate, 50 g of acrylic acid, and 550 g of microencapsulated synergistic flame retardant to the emulsification tank, stir, transfer to the reaction vessel, add 15 g of ammonium persulfate, and carry out the polymerization reaction at 85°C for 5 h. Then cool to below 40°C, adjust the pH to 8, filter and discharge to obtain a high flame retardant and low VOC acrylic composite resin.

[0017] Example 3 This embodiment describes a method for preparing a high flame-retardant, low-VOC acrylic composite resin, comprising the following steps: Step 1: Add 800 mL of water, 130 g of melamine resin prepolymer, 200 g of ammonium polyphosphate, and 40 g of pentaerythritol phosphate to a flask, adjust the pH to 3, stir at 70°C for 1.5 h to form a core-shell structure, filter, wash, and dry to obtain a microencapsulated synergistic flame retardant. Step 2: Add 200 mL of water, 42 g of sodium allyl hydroxypropanesulfonate, and 20 g of sodium allyl hydroxypropanesulfonate to the flask and mix well to obtain the emulsifier. Step 3: Under a nitrogen atmosphere, add 30 g pentaerythritol and 60 g phosphorus oxychloride to a flask, react at 70°C for 4 h, then add 85 g hydroxyethyl methacrylate and 1 g triethylamine, react at 90°C for 5 h, purify, and obtain the flame retardant monomer. Step 4: Add 2.5 L of water, 100 g of emulsifier, 300 g of flame retardant monomer, 1.25 kg of methyl methacrylate, 1.5 g of butyl acrylate, 50 g of acrylic acid, and 600 g of microencapsulated synergistic flame retardant to the emulsification tank, stir, transfer to the reaction vessel, add 17.5 g of ammonium persulfate, and carry out the polymerization reaction at 90°C for 3 h. Then cool to below 40°C, adjust the pH to 7, filter and discharge to obtain a high flame retardant and low VOC acrylic composite resin.

[0018] Comparative Example 1: The difference between this comparative example and Example 1 is that no flame retardant monomer is added.

[0019] The preparation method of the acrylic composite resin in this comparative example includes the following steps: Step 1: Add 800 mL of water, 100 g of melamine resin prepolymer, 200 g of ammonium polyphosphate, and 20 g of pentaerythritol phosphate to a flask, adjust the pH to 3, stir at 60°C for 2 h to form a core-shell structure, filter, wash, and dry to obtain a microencapsulated synergistic flame retardant. Step 2: Add 200 mL of water, 40 g of sodium allyl hydroxypropanesulfonate, and 20 g of sodium allyl hydroxypropanesulfonate to the flask and mix well to obtain the emulsifier. Step 3: Add 2.5 L of water, 75 g of emulsifier, 1 kg of methyl methacrylate, 1.3 g of butyl acrylate, 50 g of acrylic acid, and 500 g of microencapsulated synergistic flame retardant to the emulsification kettle, stir, transfer to the reaction kettle, add 12.5 g of ammonium persulfate, and carry out the polymerization reaction at 80°C for 7 h. Then cool to below 40°C, adjust the pH to 7, filter and discharge to obtain acrylic composite resin.

[0020] Comparative Example 2: The difference between this comparative example and Example 1 is that no microencapsulated synergistic flame retardant is added.

[0021] The preparation method of the acrylic composite resin in this comparative example includes the following steps: Step 1: Add 200 mL of water, 40 g of sodium allyl hydroxypropanesulfonate, and 20 g of sodium allyl hydroxypropanesulfonate to the flask and mix well to obtain the emulsifier. Step 2: Under a nitrogen atmosphere, add 30 g pentaerythritol and 54 g phosphorus oxychloride to a flask, react at 60°C for 5 h, then add 75 g hydroxyethyl methacrylate and 0.6 g triethylamine, react at 80°C for 6 h, purify, and obtain the flame retardant monomer. Step 3: Add 2.5 L of water, 75 g of emulsifier, 200 g of flame retardant monomer, 1 kg of methyl methacrylate, 1.3 g of butyl acrylate, and 50 g of acrylic acid to the emulsification kettle, stir, transfer to the reaction kettle, add 12.5 g of ammonium persulfate, and carry out the polymerization reaction at 80°C for 7 h. Then cool to below 40°C, adjust the pH to 7, filter and discharge to obtain acrylic composite resin.

[0022] Comparative Example 3: The difference between this comparative example and Example 1 is that the flame-retardant acrylic resin was prepared using the traditional physical blending method.

[0023] The preparation method of the acrylic composite resin in this comparative example includes the following steps: Step 1: Add 200 mL of water, 40 g of sodium allyl hydroxypropanesulfonate, and 20 g of sodium allyl hydroxypropanesulfonate to the flask and mix well to obtain the emulsifier. Step 2: Add 2.5 L of water, 75 g of emulsifier, 1 kg of methyl methacrylate, 1.3 g of butyl acrylate, and 50 g of acrylic acid to the emulsification kettle, stir, transfer to the reaction kettle, add 12.5 g of ammonium persulfate, and carry out the polymerization reaction at 80°C for 7 h. Then cool to below 40°C, add 200 g of ammonium polyphosphate, 30 g of pentaerythritol, and 20 g of pentaerythritol phosphate, mix well, adjust the pH to 7, filter and discharge to obtain acrylic composite resin.

[0024] Performance testing 1. Flame retardant performance test The acrylic composite resin was evenly coated on the surface of a sanded wood board (130 mm × 13 mm × 3 mm) and tested using a 5801-A limiting oxygen index instrument according to the ASTM D2863-2017 test standard.

[0025] Table 1 Flame retardant performance test data As shown in Table 1, all embodiments exhibited a limiting oxygen index (LOI) higher than 32%, demonstrating excellent flame retardant performance and meeting the standards for flame-retardant materials. This is mainly due to the dual flame-retardant mechanism of the flame-retardant monomer and the microencapsulated synergistic flame retardant. The flame-retardant monomer exerts its flame-retardant effect in both the gas and condensed phases, while the microencapsulated synergistic flame retardant can efficiently expand to form a dense char layer upon heating. The two work synergistically to greatly enhance the flame-retardant performance. Comparative Example 1, lacking a flame-retardant monomer, relied solely on the microencapsulated synergistic flame retardant, lacking molecular-level anchoring flame-retardant effects, resulting in decreased flame-retardant efficiency and a significantly lower LIO value than the embodiments. Comparative Example 2, lacking the microencapsulated synergistic flame retardant, relied solely on the intrinsic flame-retardant properties of the reactive monomer. Its flame retardant efficiency is limited and it cannot form an efficient expanded char layer. Therefore, its limiting oxygen index value is the lowest, indicating that single chemical modification is insufficient to meet the high flame retardant requirements. Comparative Example 3 uses traditional physical blending. The flame retardant has poor compatibility with the resin matrix and is unevenly dispersed. Moreover, during the combustion process, the components cannot work synergistically and efficiently like microcapsules, resulting in poor flame retardant effect and an LOI value far lower than that of the example.

[0026] 2 VOC content test The VOC content of liquid resin was determined by gas chromatography according to GB / T 23986-2023 standard. First, the sample density and moisture content were determined. Then, all VOC components were analyzed, identified, and quantified using gas chromatography. Finally, the VOC content was calculated, with units of g / L.

[0027] Table 2 VOC content test data As shown in Table 2, the VOC content of Examples 1-3 remained at extremely low levels (<40 g / L), thanks to the green manufacturing process throughout: solvent-free emulsion polymerization was used, along with reactive emulsifiers (whose molecules are bonded to the polymer and do not volatilize), eliminating VOC generation at the source. In contrast, the VOC content of Comparative Example 3 increased sharply. This was because, in the final physical blending step, a large amount of organic solvents (such as ketones and esters) had to be added for dilution in order to evenly disperse a large amount of solid flame retardant powder into the synthesized resin and maintain a suitable application viscosity, resulting in a serious VOC exceedance in the final product. This starkly contrasts with the significant environmental disadvantages of traditional physical blending methods.

[0028] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A high flame-retardant, low-VOC acrylic composite resin and its preparation method, characterized in that, Includes the following steps: Step 1: Add water, melamine resin prepolymer, ammonium polyphosphate, and char catalyst to a flask, adjust the pH to 3-4, stir at 60-80℃ for 1-2 h to form a core-shell structure, filter, wash, and dry to obtain microencapsulated synergistic flame retardant. Step 2: Add water, emulsifier, flame retardant monomer, methyl methacrylate, butyl acrylate, acrylic acid, and microencapsulated synergistic flame retardant to the emulsification kettle, stir, transfer to the reaction kettle, add ammonium persulfate, carry out the polymerization reaction, then cool to below 40°C, adjust the pH to 7-8, filter and discharge to obtain high flame retardant and low VOC acrylic composite resin.

2. The preparation method of the high flame retardant and low VOC acrylic composite resin according to claim 1, characterized in that, In step 1, the mass ratio of melamine resin prepolymer, ammonium polyphosphate, and char-forming catalyst is (0.5-0.8):1:(0.1-0.3).

3. The preparation method of the high flame retardant and low VOC acrylic composite resin according to claim 1, characterized in that, The char-forming catalyst in step 1 is pentaerythritol phosphate or melamine polyphosphate.

4. The preparation method of the high flame retardant and low VOC acrylic composite resin according to claim 1, characterized in that, In step 2, the emulsifier is a compound of sodium allyl hydroxypropanesulfonate and sodium allyl hydroxypropanesulfonate in a mass ratio of (2-2.2):

1.

5. The method for preparing the high flame retardant, low VOC acrylic composite resin according to claim 1, characterized in that, The polymerization reaction in step 2 is carried out at a temperature of 80-90℃ for 3-7 hours.

6. The method for preparing the high flame retardant, low VOC acrylic composite resin according to claim 1, characterized in that, The flame retardant monomer in step 2 is prepared as follows: under a nitrogen atmosphere, pentaerythritol and phosphorus oxychloride are added to a flask and reacted at 60-80℃ for 3-5 h. Then, hydroxyethyl methacrylate and triethylamine are added and reacted at 80-100℃ for 4-6 h. After purification, the flame retardant monomer is obtained.

7. The method for preparing the high flame-retardant, low-VOC acrylic composite resin according to claim 6, characterized in that, The mass ratio of pentaerythritol, phosphorus oxychloride, hydroxyethyl methacrylate, and triethylamine is 1:(1.8-2.2):(2.5-3.2):(0.02-0.05).

8. The method for preparing the high flame-retardant, low-VOC acrylic composite resin according to claim 1, characterized in that, In step 2, the mass ratio of emulsifier, flame retardant monomer, methyl methacrylate, butyl acrylate, acrylic acid, microencapsulated synergistic flame retardant, and ammonium persulfate is (1.5-2):(4-6):(20-25):(26-30):1:(10-12):(0.25-0.35).

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