Flame-retardant low-VOCs aqueous adhesive and preparation method thereof

Abstract

The invention discloses a flame-retardant low-VOCs aqueous adhesive and a preparation method thereof. The preparation method comprises the following steps: S1, preparing a pre-emulsion; S2, synthesizing a resin emulsion; S3, preparing a flame-retardant dispersion; the phosphate flame-retardant monomer participates in the copolymerization reaction of acrylate, and cooperates with hyperbranched ammonium polyphosphate and zinc borate to form a condensed phase and gas phase dual flame-retardant barrier; hydroxyl-containing phosphate is embedded into a solvent-free polyurethane curing agent system, so that aliphatic diisocyanate synchronously completes crosslinking, flame retardance and thickening under the action of an organic tin catalyst, and VOCs introduced by a traditional thickening agent are eliminated from the source; the final value of the NCO content is accurately controlled through a synchronous dropwise adding process and dynamic monitoring of the NCO content, so that the viscosity is stable, and sedimentation and layering are avoided; the long-standing contradiction of high flame retardance, namely high VOCs, and strong adhesion, namely weak constructability, in the field of waterborne adhesives is solved.

Description

Technical Field

[0001] This invention relates to the field of waterborne adhesive preparation technology, specifically to a flame-retardant low-VOCs waterborne adhesive and its preparation method. Background Technology

[0002] Water-based adhesives, with water as the primary dispersion medium and significantly lower organic solvent content than traditional solvent-based adhesives, offer substantial advantages in environmental protection and operational safety, and are widely used in building decoration, wood product processing, packaging and printing, textile lamination, and electronic assembly. As environmental regulations in various countries increasingly restrict volatile organic compound (VOC) emissions, and as the public pays close attention to indoor air quality and fire safety, the development of ultra-low VOC emission water-based adhesives with excellent flame-retardant properties has become an urgent industry need, aiming to meet multiple standards related to safety, environmental protection, and performance.

[0003] Existing technologies have yielded numerous studies on reducing VOCs in water-based adhesives, typically achieved through optimizing resin synthesis processes, selecting environmentally friendly additives, and improving film-forming properties. Regarding flame retardant modification, common methods include adding halogenated flame retardants, phosphorus-nitrogen intumescent flame retardants, or inorganic flame retardant fillers such as aluminum hydroxide and magnesium hydroxide to the adhesive formulation. However, while traditional methods of adding physically mixed flame retardants can improve flame retardancy to some extent, they have several limitations, making it difficult to simultaneously meet the requirements of low VOCs and high performance.

[0004] Specifically, while existing halogenated flame retardants offer advantages in flame retardant efficiency, they may release toxic and harmful gases during use or combustion, and some halogenated flame retardants have potential bioaccumulation, contradicting the development trend of environmental friendliness and health safety. While adding large amounts of inorganic flame retardant fillers is environmentally friendly and safe, it easily leads to a sharp increase in the viscosity of the adhesive system, decreased dispersion stability, shortened shelf life, and poor coating workability, significantly weakening the cohesive strength of the adhesive layer and its adhesion to the substrate, thus failing to guarantee the overall performance of the product. Therefore, there is an urgent need to develop a new strategy to resolve the contradiction between flame retardancy, low VOC emissions, and the basic performance of adhesives. Summary of the Invention

[0005] This invention provides a flame-retardant, low-VOCs water-based adhesive and its preparation method.

[0006] The technical solution of this invention is: a flame-retardant, low-VOCs water-based adhesive, composed of the following raw materials in parts by weight: phosphate ester flame-retardant monomer: 5-12 parts; butyl acrylate: 15-30 parts; methyl methacrylate: 5-15 parts; hydroxyethyl acrylate: 3-10 parts; acrylic acid or methacrylic acid: 1-3 parts; nitrogen-containing vinyl monomer: 0.5-2 parts; vinyltrimethoxysilane: 0.5-2 parts; nonionic emulsifier: 0.5-2 parts; reactive anionic emulsifier: 0.2-0.8 parts; hyperbranched ammonium polyphosphate: 1-5 parts; acrylic acid-acryloyl... Amine copolymer dispersant: 0.3-0.8 parts; hydrophilic polyether diol: 5-12 parts; hydroxyl phosphate ester: 1-4 parts; aliphatic diisocyanate: 0.6-1.5 parts; organotin catalyst: 0.05-0.2 parts; ammonium persulfate: 0.5-1.5 parts; tert-butyl hydroperoxide: 0.1-0.4 parts; sodium metabisulfite: 0.1-0.3 parts; polyether-modified polysiloxane defoamer: 0.1-0.5 parts; polyether-modified siloxane wetting agent: 0.2-0.6 parts; fluorocarbon leveling agent: 0.1-1 parts; zinc borate: 0.1-0.3 parts.

[0007] Note: This adhesive maintains structural integrity under extreme temperature cycling from -40 to 150°C, and has an adhesion strength of over 3.5 MPa to metals, plastics, and wood, perfectly meeting sealing requirements; compared to traditional adhesives, its biodegradability is improved by 30% and it leaves no heavy metal residue.

[0008] A method for preparing a flame-retardant, low-VOCs water-based adhesive includes the following steps: S1. Preparation of preemulsion Take 40-60 parts of the deionized water and add it to the reaction vessel. While stirring at 1500-2500 rpm, add the phosphate flame retardant monomer, butyl acrylate, methyl methacrylate, hydroxyethyl acrylate, acrylic acid or methacrylic acid, nitrogen-containing vinyl monomer, vinyltrimethoxysilane, nonionic emulsifier and reactive anionic emulsifier in sequence according to the formula. Stir and emulsify for 30-60 min to obtain a pre-emulsion. S2, Synthetic resin emulsion Take 20-35 parts of the deionized water and the ammonium persulfate and stir evenly to obtain an ammonium persulfate solution. Heat the ammonium persulfate solution to 75-80℃. Take 10-15% of the total mass of the pre-emulsion and add it dropwise to the reaction system, and keep it at this temperature for 15-30 min. Then, add the remaining pre-emulsion and the ammonium persulfate solution dropwise simultaneously at a reaction vessel temperature of 80-85℃. Let it mature at a reaction vessel temperature of 85-88℃ for 1-1.5 h, and then cool it down to 65-70℃. Add the tert-butyl hydroperoxide and sodium metabisulfite dropwise, and react for 30-60 min. Then cool it down to 50-55℃ and adjust the pH to 7.0-8.0 with a pH adjuster to obtain a resin emulsion. S3. Preparation of flame-retardant dispersion Take 10-20 parts of the deionized water and the acrylic acid-acrylamide copolymer dispersant and mix them evenly. Add the hyperbranched ammonium polyphosphate and continue stirring and dispersing for 45-90 min. Then add the zinc borate and continue dispersing for 15-20 min to obtain a flame retardant dispersion. S4. Preparation of composite emulsion The resin emulsion described in S2 is cooled to 40-45°C, and then the flame retardant dispersion described in S3 is added. After mixing evenly, a composite emulsion is obtained. S5, Synthetic curing agent Under nitrogen protection, the hydrophilic polyether diol and hydroxyl phosphate were placed in a vacuum environment for dehydration, and then cooled to 60-70°C. Simultaneously, the aliphatic diisocyanate and organotin catalyst were added dropwise over a period of 1-2 hours. After the addition was complete, the temperature was raised to 75-85°C. The reaction was terminated when the mass percentage of NCO groups in the system dropped to 8-12%. The mixture was then cooled to 30-40°C and discharged to obtain the curing agent. S6, Final Preparation The composite emulsion obtained in S4 is cooled to 20-30℃. While stirring at 200-400 rpm, the polyether-modified polysiloxane defoamer, polyether-modified siloxane wetting agent, and fluorocarbon leveling agent are added sequentially. After mixing for 20-30 min, the stirring speed is increased to 1000-1500 rpm, and the curing agent described in S5 is added. The mixture is dispersed for 15-30 min. Deionized water is then added to adjust the solid content to 45-55 wt%, and the pH is adjusted to 8.0-9.5 using a pH adjuster. The mixture is stirred and matured at 300-500 rpm for 60-120 min. The viscosity is adjusted, and the mixture is filtered to obtain a flame-retardant low-VOCs waterborne adhesive.

[0009] Note: This preparation method innovatively breaks through the technical bottleneck of water-based adhesives. Through molecular-level bonding of flame-retardant components, innovation of solvent-free curing system, and dynamic and precise process control of NCO, it simultaneously achieves three core indicators: flame retardancy, low VOCs, and suitable application viscosity under zero halogen conditions. It completely solves the performance imbalance problems caused by the toxicity of halogen flame retardants, VOCs release of thickeners, and sedimentation of inorganic fillers in traditional technologies.

[0010] Furthermore, the dropping rate of the pre-emulsion described in S2 is 6-12 g / min.

[0011] Note: This dropping rate range precisely matches the kinetic requirements of emulsion polymerization: below 6 g / min, the reaction rate is insufficient, leading to a broadened molecular weight distribution (PDI > 2.5); above 12 g / min, the local temperature rises sharply, posing a risk of explosive polymerization. Controlling the dropping rate within this range ensures uniform latex particle size (D50 = 110-130 nm), significantly improving the film density of the adhesive and increasing peel strength by 15%.

[0012] Furthermore, the dropping rate of the tert-butyl hydroperoxide and sodium metabisulfite in S2 is 0.5-1.2 g / min.

[0013] Note: Dropping at a low rate of less than 1.2 g / min avoids the instantaneous reaction between tert-butyl hydroperoxide and sodium metabisulfite, which generates a large number of free radicals and prevents emulsion gelation; a rate higher than 0.5 g / min ensures the efficiency of residual monomer removal, resulting in a conversion rate greater than 99.5%. This parameter keeps VOCs stable below 30 g / L, while maintaining the zeta potential of latex particles at -35 mV to -40 mV, thus improving storage stability to 18 months.

[0014] Furthermore, the mixing time of the deionized water and the acrylic acid-acrylamide copolymer dispersant in S3 is 5-7 minutes, and the stirring speed is 800-1200 rpm.

[0015] Note: The minimum rotation speed of 800 rpm ensures that the acrylic acid-acrylamide copolymer is fully hydrated and stretches its molecular chains, while the upper limit of 1200 rpm prevents high-speed shearing from damaging the polymer structure; a mixing time of 5-7 min ensures that the dispersant adsorption rate is greater than 90%, and the particle size of the hyperbranched ammonium polyphosphate is controlled at 200-400 nm, thereby improving the flame retardant efficiency.

[0016] Furthermore, the mixing time of the resin emulsion and the flame retardant dispersion in S4 is 60-90 min, and the stirring speed is 300-500 rpm.

[0017] Note: A minimum speed of 300 rpm avoids resin emulsion demulsification, and an upper limit of 500 rpm prevents the sedimentation of the flame retardant dispersion, namely HBPPA and zinc borate; a mixing time of 60-90 min ensures that the surface of the flame retardant particles is completely coated with resin, enhancing interfacial bonding, and the flame retardant performance degradation rate of the adhesive is less than 5% after heat aging at 150℃.

[0018] Furthermore, the dehydration time of the hydrophilic polyether diol and the hydroxyl phosphate ester described in S5 is 1-2 h, the dehydration temperature is 100-110℃, and the absolute pressure of the vacuum environment is 1.5-2.0 kPa.

[0019] Note: 1.5-2.0 kPa absolute pressure combined with 100-110℃ temperature achieves deep dehydration. The critical dehydration time is 1 hour, and complete dehydration is achieved in 2 hours, with moisture content less than 100 ppm. This ensures that the polyurethane curing agent has a shelf life of more than 24 months and that the NCO content fluctuates by less than 0.5%.

[0020] Furthermore, the method for monitoring NCO groups in the system described in S5 is as follows: during the continuous reaction of the system, a sample is taken every 20 minutes, and the mass percentage of NCO groups in the system is determined according to ASTM D5155 standard.

[0021] Note: The 20-minute monitoring frequency accurately captures the inflection point of NCO decline, i.e. the reaction rate inflection zone, avoiding overshoot or undershoot. The titration error of ASTM D5155 standard is less than 0.5%, which stabilizes the viscosity of the curing agent at 5000±500 mPa·s and extends the application period.

[0022] Further, in S6, the viscosity of the system is adjusted to 3000-8000 mPa·s; wherein, the viscosity value is measured under the following conditions: using a Brookfield DV2T viscometer, selecting an LV3 or LV4 rotor, and measuring at a temperature of 25°C and a rotation speed of 20 rpm.

[0023] Note: The LV3 rotor is suitable for the low viscosity range of 3000-4000 mPa·s, and the LV4 rotor is suitable for the high viscosity range of 4000-8000 mPa·s. The 20 rpm shear rate simulates actual construction conditions. This standardized test eliminates the ±15% error caused by differences in temperature and rotor selection, ensuring that the viscosity fluctuation between batches is less than 5%.

[0024] The beneficial effects of this invention are: This invention utilizes phosphate ester flame-retardant monomers in the copolymerization reaction of acrylates, synergistically forming a dual flame-retardant barrier of condensed and gas phases with hyperbranched ammonium polyphosphate and zinc borate. This achieves UL94 V-0 flame retardancy and an LOI greater than 32% without the need for halogenated flame retardants, overcoming the toxicity release problem caused by the addition of halogenated flame retardants in traditional technologies. By embedding hydroxyl phosphate esters into a solvent-free polyurethane curing agent system, aliphatic diisocyanates simultaneously complete cross-linking, flame retardancy, and thickening functions under the action of an organotin catalyst, eliminating VOCs introduced by thickeners at the source. Combined with oxidation-reduction post-treatment technology, VOCs can be reduced to below 30 g / L. Through a simultaneous dripping process and dynamic monitoring of NCO content, the endpoint value of NCO content is precisely controlled, ensuring viscosity stability and completely solving the problems of drastic viscosity increase and sedimentation caused by the addition of traditional inorganic flame-retardant fillers. This invention also resolves the long-standing contradiction in the field of water-based adhesives: high flame retardancy equals high VOCs, and strong adhesion equals weak workability. Detailed Implementation

[0025] To further illustrate the methods and effects of this invention, the technical solution of this invention will be clearly and completely described below in conjunction with experiments.

[0026] Example 1: A flame-retardant, low-VOCs water-based adhesive is composed of the following raw materials in parts by weight: phosphate ester flame-retardant monomer: 8.5 parts; butyl acrylate: 22.5 parts; methyl methacrylate: 10 parts; hydroxyethyl acrylate: 6.5 parts; acrylic acid or methacrylic acid: 2 parts; nitrogen-containing vinyl monomer: 1.25 parts; vinyltrimethoxysilane: 1.25 parts; nonionic emulsifier: 1.25 parts; reactive anionic emulsifier: 0.5 parts; hyperbranched ammonium polyphosphate: 3 parts; propylene... Acid-acrylamide copolymer dispersant: 0.55 parts; hydrophilic polyether diol: 8.5 parts; hydroxyl phosphate ester: 2.5 parts; aliphatic diisocyanate: 1.05 parts; organotin catalyst: 0.125 parts; ammonium persulfate: 1 part; tert-butyl hydroperoxide: 0.25 parts; sodium metabisulfite: 0.2 parts; polyether-modified polysiloxane defoamer: 0.3 parts; polyether-modified siloxane wetting agent: 0.4 parts; fluorocarbon leveling agent: 0.55 parts; zinc borate: 0.2 parts.

[0027] Example 2: This example describes the flame-retardant, low-VOCs water-based adhesive of Example 1, including the following steps: S1. Preparation of preemulsion Take 50 parts of the deionized water and add it to the reaction vessel. Under stirring at 2000 rpm, add the phosphate flame retardant monomer, butyl acrylate, methyl methacrylate, hydroxyethyl acrylate, acrylic acid or methacrylic acid, nitrogen-containing vinyl monomer, vinyltrimethoxysilane, nonionic emulsifier and reactive anionic emulsifier in sequence according to the formula. Stir and emulsify for 45 min to obtain a pre-emulsion. S2, Synthetic resin emulsion Take 27.5 parts of the deionized water and the ammonium persulfate and stir evenly to obtain an ammonium persulfate solution. Heat the ammonium persulfate solution to 77.5℃. Take 12.5% ​​of the total mass of the pre-emulsion and add it dropwise to the reaction system, and keep it at this temperature for 22.5 min. The dropwise addition rate of the pre-emulsion is 9 g / min. Then, add the remaining pre-emulsion and the ammonium persulfate solution dropwise simultaneously at a reaction vessel temperature of 82.5℃. Let it mature at a reaction vessel temperature of 86.5℃ for 1.25 h, and then cool it down to 67.5℃. Add the tert-butyl hydroperoxide and sodium metabisulfite dropwise at a dropwise addition rate of 0.85 g / min, and react for 45 min. Then, cool it down to 52.5℃ and adjust the pH to 7.5 with a pH adjuster to obtain a resin emulsion. S3. Preparation of flame-retardant dispersion Take 15 parts of the deionized water and the acrylic acid-acrylamide copolymer dispersant and mix them evenly for 6 min at a stirring speed of 1000 rpm. Then add the hyperbranched ammonium polyphosphate and continue stirring and dispersing for 67.5 min. Then add the zinc borate and continue dispersing for 17.5 min to obtain a flame retardant dispersion. S4. Preparation of composite emulsion The resin emulsion described in S2 is cooled to 42.5°C, and then the flame retardant dispersion described in S3 is added. The mixing time is 75 min, the stirring speed is 400 rpm, and the composite emulsion is obtained after uniform mixing. S5, Synthetic curing agent Under nitrogen protection, the hydrophilic polyether diol and hydroxyl phosphate were placed in a vacuum environment for dehydration, then cooled to 65°C, and the aliphatic diisocyanate and organotin catalyst were added dropwise simultaneously over a period of 1.5 h. After the addition was complete, the temperature was raised to 80°C, and the reaction was terminated when the mass percentage of NCO groups in the system dropped to 10%. The mixture was then cooled to 35°C and discharged to obtain the curing agent. The dehydration time of the hydrophilic polyether diol and hydroxyl phosphate was 1.5 h, the dehydration temperature was 105°C, and the absolute pressure of the vacuum environment was 1.75 kPa. The method for monitoring the NCO groups in the system was as follows: during the continuous reaction, samples were taken every 20 min, and the mass percentage of NCO groups in the system was determined according to ASTM D5155 standard. S6, Final Preparation The composite emulsion obtained in S4 was cooled to 25°C. While stirring at 300 rpm, the polyether-modified polysiloxane defoamer, polyether-modified siloxane wetting agent, and fluorocarbon leveling agent were added sequentially. After mixing for 25 min, the stirring speed was increased to 1250 rpm, and the curing agent described in S5 was added. The mixture was dispersed for 22.5 min. Deionized water was then added to adjust the solid content to 50% by mass, and the pH was adjusted to 9.0 using a pH adjuster. The mixture was stirred and matured at 400 rpm for 90 min, and the viscosity of the system was adjusted to 5500 mPa·s. The viscosity value was measured using a Brookfield DV2T viscometer with an LV3 rotor at 25°C and 20 rpm. After filtration, a flame-retardant low-VOCs waterborne adhesive was obtained.

[0028] Example 3: This example is basically the same as Example 1, except that it is composed of the following raw materials in parts by weight: phosphate ester flame retardant monomer: 5 parts; butyl acrylate: 15 parts; methyl methacrylate: 5 parts; hydroxyethyl acrylate: 3 parts; acrylic acid or methacrylic acid: 1 part; nitrogen-containing vinyl monomer: 0.5 parts; vinyltrimethoxysilane: 0.5 parts; nonionic emulsifier: 0.5 parts; reactive anionic emulsifier: 0.2 parts; hyperbranched ammonium polyphosphate: 1 part 0.3 parts; acrylic acid-acrylamide copolymer dispersant; 5 parts; hydroxyl phosphate ester; 0.6 parts; organotin catalyst; 0.05 parts; ammonium persulfate; 0.1 parts; sodium metabisulfite; 0.1 parts; polyether modified polysiloxane defoamer; 0.2 parts; fluorocarbon leveling agent; zinc borate; 0.1 parts.

[0029] Example 4: This example is basically the same as Example 1, except that it is composed of the following raw materials in parts by weight: phosphate ester flame retardant monomer: 12 parts; butyl acrylate: 30 parts; methyl methacrylate: 15 parts; hydroxyethyl acrylate: 10 parts; acrylic acid or methacrylic acid: 3 parts; nitrogen-containing vinyl monomer: 2 parts; vinyltrimethoxysilane: 2 parts; nonionic emulsifier: 2 parts; reactive anionic emulsifier: 0.8 parts; hyperbranched ammonium polyphosphate: 5 parts Acrylic acid-acrylamide copolymer dispersant: 0.8 parts; hydrophilic polyether diol: 12 parts; hydroxyl phosphate ester: 4 parts; aliphatic diisocyanate: 1.5 parts; organotin catalyst: 0.2 parts; ammonium persulfate: 1.5 parts; tert-butyl hydroperoxide: 0.4 parts; sodium metabisulfite: 0.3 parts; polyether modified polysiloxane defoamer: 0.5 parts; polyether modified siloxane wetting agent: 0.6 parts; fluorocarbon leveling agent: 1 part; zinc borate: 0.3 parts.

[0030] Example 5: This example is basically the same as Example 2, except that 40 parts of the deionized water were added to the reaction vessel, and the phosphate flame retardant monomer, butyl acrylate, methyl methacrylate, hydroxyethyl acrylate, acrylic acid or methacrylic acid, nitrogen-containing vinyl monomer, vinyltrimethoxysilane, nonionic emulsifier and reactive anionic emulsifier were added sequentially according to the formula under stirring at 1500 rpm. The mixture was stirred and emulsified for 30 min to obtain a pre-emulsion.

[0031] Example 6: This example is basically the same as Example 2, except that 60 parts of the deionized water were added to the reaction vessel, and the phosphate flame retardant monomer, butyl acrylate, methyl methacrylate, hydroxyethyl acrylate, acrylic acid or methacrylic acid, nitrogen-containing vinyl monomer, vinyltrimethoxysilane, nonionic emulsifier and reactive anionic emulsifier were added sequentially according to the formula under stirring at 2500 rpm. The mixture was stirred and emulsified for 60 min to obtain a pre-emulsion.

[0032] Example 7: This example is basically the same as Example 2, except that 20 parts of the deionized water and the ammonium persulfate are stirred evenly to obtain an ammonium persulfate solution, and the ammonium persulfate solution is heated to 75°C; 10% of the total mass of the pre-emulsion is added dropwise to the reaction system and kept at this temperature for 15 min; then the remaining pre-emulsion and the ammonium persulfate solution are added dropwise simultaneously at a reaction vessel temperature of 80°C; the mixture is matured at a reaction vessel temperature of 85°C for 1 h, and then cooled to 65°C; the tert-butyl hydroperoxide and sodium metabisulfite are added dropwise, and the reaction is carried out for 30 min; then the temperature is lowered to 50°C, and the pH is adjusted to 7.0 with a pH adjuster. The amount of pH adjuster weighed in the raw materials is adjusted accordingly to obtain the resin emulsion.

[0033] Example 8: This example is basically the same as Example 2, except that 35 parts of the deionized water and the ammonium persulfate are stirred evenly to obtain an ammonium persulfate solution, and the ammonium persulfate solution is heated to 80°C; 15% of the total mass of the pre-emulsion is added dropwise to the reaction system and kept at this temperature for 30 min; then the remaining pre-emulsion and the ammonium persulfate solution are added dropwise simultaneously at a reaction vessel temperature of 85°C; the mixture is matured at a reaction vessel temperature of 88°C for 1.5 h, and then cooled to 70°C; the tert-butyl hydroperoxide and sodium metabisulfite are added dropwise, and the reaction is carried out for 60 min; then the temperature is lowered to 55°C, and the pH is adjusted to 8.0 with a pH adjuster. The amount of pH adjuster weighed in the raw materials is adjusted accordingly to obtain a resin emulsion.

[0034] Example 9: This example is basically the same as Example 2, except that 10 parts of the deionized water and the acrylic acid-acrylamide copolymer dispersant are mixed evenly, the hyperbranched ammonium polyphosphate is added, and the mixture is stirred and dispersed for 45 min; then the zinc borate is added, and the mixture is dispersed for 15 min to obtain a flame retardant dispersion; the resin emulsion described in S2 is cooled to 40°C, and then the flame retardant dispersion described in S3 is added and mixed evenly to obtain a composite emulsion.

[0035] Example 10: This example is basically the same as Example 2, except that 20 parts of the deionized water and the acrylic acid-acrylamide copolymer dispersant are mixed evenly, the hyperbranched ammonium polyphosphate is added, and the mixture is stirred and dispersed for 90 min; then the zinc borate is added, and the mixture is dispersed for 20 min to obtain a flame retardant dispersion; the resin emulsion described in S2 is cooled to 45°C, and then the flame retardant dispersion described in S3 is added and mixed evenly to obtain a composite emulsion.

[0036] Example 11: This example is basically the same as Example 2, except that, under nitrogen protection, the hydrophilic polyether diol and hydroxyl phosphate are placed in a vacuum environment for dehydration, and then cooled to 60°C. Simultaneously, the aliphatic diisocyanate and organotin catalyst are added dropwise over a period of 1 hour. After the addition is complete, the temperature is raised to 75°C. The reaction is terminated when the mass percentage of NCO groups in the system drops to 8%. The mixture is then cooled to 30°C and discharged to obtain the curing agent.

[0037] Example 12: This example is basically the same as Example 2, except that, under nitrogen protection, the hydrophilic polyether diol and hydroxyl phosphate are placed in a vacuum environment for dehydration, and then cooled to 70°C. Simultaneously, the aliphatic diisocyanate and organotin catalyst are added dropwise over a period of 2 hours. After the addition is complete, the temperature is raised to 85°C. The reaction is terminated when the mass percentage of NCO groups in the system drops to 12%. The mixture is then cooled to 40°C and discharged to obtain the curing agent.

[0038] Example 13: This example is basically the same as Example 2, except that the composite emulsion obtained in S4 is cooled to 20°C, and the polyether-modified polysiloxane defoamer, polyether-modified siloxane wetting agent, and fluorocarbon leveling agent are added sequentially while stirring at 200 rpm. After mixing for 20 min, the stirring speed is increased to 1000 rpm, and the curing agent described in S5 is added and dispersed for 15 min. Then, deionized water is added to adjust the solid content mass fraction to 45 wt%, and the pH is adjusted to 8.0 with a pH adjuster. The amount of pH adjuster weighed in the raw materials is adjusted accordingly. The mixture is stirred and matured at 300 rpm for 60 min, the viscosity is adjusted, and after filtration, a flame-retardant low-VOCs waterborne adhesive is obtained.

[0039] Example 14: This example is basically the same as Example 2, except that the composite emulsion obtained in S4 is cooled to 30°C, and the polyether-modified polysiloxane defoamer, polyether-modified siloxane wetting agent, and fluorocarbon leveling agent are added sequentially while stirring at 400 rpm. After mixing for 30 min, the stirring speed is increased to 1500 rpm, and the curing agent described in S5 is added and dispersed for 30 min. Then, deionized water is added to adjust the solid content mass fraction to 55 wt%, and the pH is adjusted to 9.5 with a pH adjuster. The amount of pH adjuster weighed in the raw materials is adjusted accordingly. The mixture is stirred and matured at 500 rpm for 120 min, the viscosity is adjusted, and after filtration, a flame-retardant low-VOCs waterborne adhesive is obtained.

[0040] Example 15: This example is basically the same as Example 2, except that the dropping rate of the pre-emulsion in S2 is 6 g / min; and the dropping rate of the tert-butyl hydrogen peroxide and sodium metabisulfite is 0.5 g / min.

[0041] Example 16: This example is basically the same as Example 2, except that the dropping rate of the pre-emulsion in S2 is 12 g / min; and the dropping rate of the tert-butyl hydrogen peroxide and sodium metabisulfite is 1.2 g / min.

[0042] Example 17: This example is basically the same as Example 2, except that the mixing time of the deionized water and the acrylic acid-acrylamide copolymer dispersant in S3 is 5 min and the stirring speed is 800 rpm.

[0043] Example 18: This example is basically the same as Example 2, except that the mixing time of the deionized water and the acrylic acid-acrylamide copolymer dispersant in S3 is 7 min and the stirring speed is 1200 rpm.

[0044] Example 19: This example is basically the same as Example 2, except that the mixing time of the resin emulsion and flame retardant dispersion in S4 is 60 min and the stirring speed is 300 rpm.

[0045] Example 20: This example is basically the same as Example 2, except that the mixing time of the resin emulsion and flame retardant dispersion in S4 is 90 min and the stirring speed is 500 rpm.

[0046] Example 21: This example is basically the same as Example 2, except that the dehydration time of the hydrophilic polyether diol and the hydroxyl phosphate ester in S5 is 1 h, the dehydration temperature is 100℃, and the absolute pressure of the vacuum environment is 1.5 kPa.

[0047] Example 22: This example is basically the same as Example 2, except that the dehydration time of the hydrophilic polyether diol and the hydroxyl phosphate ester in S5 is 2 h, the dehydration temperature is 110℃, and the absolute pressure of the vacuum environment is 2.0 kPa.

[0048] Example 23: This example is basically the same as Example 2, except that in S6 the viscosity of the system is adjusted to 3000 mPa·s; wherein, the viscosity value is tested under the following conditions: using a Brookfield DV2T viscometer, selecting an LV4 rotor, and measuring at a temperature of 25°C and a rotation speed of 20 rpm.

[0049] Example 24: This example is basically the same as Example 2, except that the viscosity of the system is adjusted to 8000 mPa·s in S6.

[0050] Comparative Example 1: Referring to Example 1, the raw materials consisted of the following parts by weight: phosphate ester flame retardant monomer: 3 parts; butyl acrylate: 10 parts; methyl methacrylate: 4 parts; hydroxyethyl acrylate: 15 parts; acrylic acid or methacrylic acid: 4 parts; nitrogen-containing vinyl monomer: 3 parts; vinyltrimethoxysilane: 3 parts; nonionic emulsifier: 3 parts; reactive anionic emulsifier: 1 part; hyperbranched ammonium polyphosphate: 0.5 parts; acrylic acid-acrylamide copolymer dispersant: 0.2 parts; hydrophilic polyether diol: 4 parts; hydroxyl phosphate ester: 5 parts; aliphatic diisocyanate: 2 parts; organotin catalyst: 1 part; ammonium persulfate: 2 parts; tert-butyl hydroperoxide: 1 part; sodium metabisulfite: 0.5 parts; polyether modified polysiloxane defoamer: 0.8 parts; polyether modified siloxane wetting agent: 1 part; fluorocarbon leveling agent: 2 parts; zinc borate: 1 part.

[0051] Comparative Example 2: Referring to Example 2, 40-60 parts of the deionized water were added to a reaction vessel, and the phosphate flame retardant monomer, butyl acrylate, methyl methacrylate, hydroxyethyl acrylate, acrylic acid or methacrylic acid, nitrogen-containing vinyl monomer, vinyltrimethoxysilane, nonionic emulsifier and reactive anionic emulsifier were added sequentially according to the formula while stirring at 1000 rpm. The mixture was stirred and emulsified for 20 min to obtain a pre-emulsion.

[0052] Comparative Example 3: Referring to Example 2, 15 parts of the deionized water and the ammonium persulfate were stirred evenly to obtain an ammonium persulfate solution. The ammonium persulfate solution was heated to 70°C. 20% of the total mass of the pre-emulsion was added dropwise to the reaction system and kept at this temperature for 10 min. Then, the remaining pre-emulsion and the ammonium persulfate solution were added dropwise simultaneously at a reaction vessel temperature of 75°C. The mixture was matured at a reaction vessel temperature of 80°C for 0.5 h, and then cooled to 60°C. The tert-butyl hydroperoxide and sodium metabisulfite were added dropwise, and the reaction was carried out for 25 min. Then, the temperature was lowered to 45°C, and the pH was adjusted to 7.0 with a pH adjuster. The amount of pH adjuster weighed in the raw materials was adjusted accordingly to obtain the resin emulsion.

[0053] Comparative Example 4: Referring to Example 2, under nitrogen protection, the hydrophilic polyether diol and hydroxyl phosphate were placed in a vacuum environment for dehydration, then cooled to 50°C, and the aliphatic diisocyanate and organotin catalyst were added dropwise simultaneously over a period of 0.5 h. After the addition was complete, the temperature was raised to 70°C, and the reaction was terminated when the mass percentage of NCO groups in the system dropped to 7%. The mixture was then cooled to 25°C and discharged to obtain the curing agent.

[0054] Comparative Example 5: Referring to Example 2, the composite emulsion obtained in S4 was cooled to 35°C. While stirring at 450 rpm, the polyether-modified polysiloxane defoamer, polyether-modified siloxane wetting agent, and fluorocarbon leveling agent were added sequentially. After mixing for 35 min, the stirring speed was increased to 1550 rpm, and the curing agent described in S5 was added and dispersed for 35 min. Then, deionized water was added to adjust the solid content to 60 wt%, and the pH was adjusted to 9.5 with a pH adjuster. The amount of pH adjuster weighed in the raw materials was adjusted accordingly. The mixture was stirred and matured at 200 rpm for 50 min, the viscosity was adjusted, and after filtration, a flame-retardant low-VOCs waterborne adhesive was obtained.

[0055] To investigate the performance of the water-based adhesives in the above examples and control examples, the main materials were determined according to the experimental formulations, and samples were obtained for testing. LOI (%) was tested according to GB / T 2406-2009 Oxygen Index Method for Burning Performance of Plastics; VOCs (g / L) was tested according to HJ 2537-2014 Water-based Coatings for Environmental Labeling Products; and peel strength (N / mm²) was tested according to GB / T 2791-1995 Test Method for Peel Strength of Adhesives. The results are shown in Table 1. The specific investigation is as follows: Table 1 Performance test table of samples prepared in Examples 2-24 and Control Examples 1-5

[0056] 1. Investigate the influence of raw material formulation parameters on the performance of water-based adhesives: As shown in Table 1, in Example 4, due to the synergistic effect of 12 parts of phosphate flame retardant monomer and 5 parts of hyperbranched ammonium polyphosphate, the LOI reached 36.5%, which was significantly higher than 28.3% in Control Example 1. This shows that the flame retardant effect was optimal under this formulation. In Example 3, because the amount of flame retardant was the lower limit of the range (5 parts of phosphate and 1 part of hyperbranched ammonium polyphosphate), the LOI was only 32.1%, but it was still better than all the control examples. This indicates that the raw material components need to be strictly matched to the synergistic range defined by this scheme, and changes in the parameters of the raw material formulation have a certain impact on the performance of water-based adhesives.

[0057] 2. Investigate the effect of process parameter adjustment on the performance of water-based adhesives: As shown in Table 1, the process parameters used in Example 2 showed balanced performance. In Control Example 2, it was speculated that the insufficient pre-emulsification speed led to uneven emulsion particle size, with an LOI of only 30.5%. At the same time, the kinetic imbalance of emulsion polymerization caused an increase in residual monomers, and the VOCs of Control Example 2 rose to 37.2 g / L. It can be seen that small deviations in process parameters may cause significant fluctuations in performance.

[0058] As shown in Table 1, in Example 14, due to sufficient redox post-treatment (0.4 parts tert-butyl hydroperoxide, 0.3 parts sodium metabisulfite, and pH control), VOCs decreased to 26.2 g / L. In Control Example 3, it is speculated that the low reaction temperature and insufficient aging time led to an increase in residual monomers. The VOCs in the sample of Control Example 3 reached as high as 42.8 g / L, and the VOCs in Control Example 5 were the highest among all samples. It can be seen that changes in parameters such as temperature and time in the scheme have a significant impact on VOCs removal. Among them, the samples prepared using the process parameters within the range of this scheme have better overall performance.

[0059] 3. Investigate the effect of NCO group content in the system on the performance of water-based adhesives: As shown in Table 1, the sample prepared under the control of stopping the reaction at an NCO content of 7% in Control Example 4 had the worst performance, with a peel strength of only 5.2 N / mm² and a viscosity of 4800 mPa·s. This was mainly due to insufficient crosslinking density leading to cohesive strength defects. The sample prepared under the control of stopping the reaction at an NCO content of 8% in Example 11 had the second best performance, with a peel strength increased to 6.5 N / mm² but a viscosity of 5200 mPa·s, indicating that the crosslinking network had initially formed but had not yet reached optimal equilibrium. In Example 12, the peel strength slightly increased to 6.8 N / mm² and the viscosity increased to 6000 mPa·s when the NCO content was 12%. The peel strength of Example 11 was 6.5 N / mm² and the viscosity was 5200 mPa·s, indicating insufficient crosslinking density and incomplete formation of the hydrogen bond network between molecular chains, thus limiting cohesive strength. In Example 2, the reaction was stopped when the NCO content decreased to 10%, resulting in a peel strength of 6.7 N / mm² and a viscosity of 5500 mPa·s. The cross-linking density and molecular chain extensibility are balanced at mPa·s, which can ensure high strength and maintain low viscosity and fluidity.

Claims

1. A flame-retardant low VOCs water-based adhesive, characterized by, The raw materials are composed of the following weight parts: phosphate ester flame-retardant monomer: 5-12 parts; butyl acrylate: 15-30 parts; methyl methacrylate: 5-15 parts; hydroxyethyl acrylate: 3-10 parts; acrylic acid or methacrylic acid: 1-3 parts; nitrogen-containing vinyl monomer: 0.5-2 parts; vinyl trimethoxysilane: 0.5-2 parts; non-ionic emulsifier: 0.5-2 parts; reactive anionic emulsifier: 0.2-0.8 parts; hyperbranched polyammonium phosphate: 1-5 parts; acrylic acid-acrylamide copolymer dispersant: 0.3-0.8 parts; hydrophilic polyether diol: 5-12 parts; hydroxyl-containing phosphate ester: 1-4 parts; aliphatic diisocyanate: 0.6-1.5 parts; organic tin catalyst: 0.05-0.2 parts; ammonium persulfate: 0.5-1.5 parts; tert-butyl hydroperoxide: 0.1-0.4 parts; sodium metabisulfite: 0.1-0.3 parts; polyether-modified polysiloxane defoamer: 0.1-0.5 parts; polyether-modified silicone wetting agent: 0.2-0.6 parts; fluorocarbon leveling agent: 0.1-1 parts; zinc borate: 0.1-0.3 parts.

2. The preparation method of the fire-retardant low VOCs water-based adhesive according to claim 1, characterized in that, The steps include: S1, preparing a pre-emulsion Take 40-60 parts of the deionized water and add it to the reaction kettle, then add the phosphate ester flame-retardant monomer, butyl acrylate, methyl methacrylate, hydroxyethyl acrylate, acrylic acid or methacrylic acid, nitrogen-containing vinyl monomer, vinyl trimethoxysilane, non-ionic emulsifier, and reactive anionic emulsifier in the order of the formula under the condition of stirring at 1500-2500 rpm, emulsify for 30-60 min to obtain a pre-emulsion; S2, synthesizing a resin emulsion Take 20-35 parts of the deionized water and the ammonium persulfate and stir them uniformly to obtain an ammonium persulfate solution, then heat the ammonium persulfate solution to 75-80℃; take 10-15% of the total mass of the pre-emulsion and add it dropwise to the reaction system, and keep it at temperature for 15-30 min; then add the remaining pre-emulsion and the ammonium persulfate solution to the reaction kettle at a temperature of 80-85℃ simultaneously; mature at a reaction kettle temperature of 85-88℃ for 1-1.5 h, then reduce the temperature to 65-70℃; add the tert-butyl hydroperoxide and sodium metabisulfite and react for 30-60 min; then reduce the temperature to 50-55℃, adjust the pH to 7.0-8.0 with a pH adjuster, and obtain a resin emulsion; S3, preparing a flame-retardant dispersion Take 10-20 parts of the deionized water and mix it uniformly with the acrylic acid-acrylamide copolymer dispersant, then add the hyperbranched polyammonium phosphate and continue to stir and disperse for 45-90 min; then add the zinc borate and continue to disperse for 15-20 min to obtain a flame-retardant dispersion; S4, preparing a composite emulsion Cool the resin emulsion of S2 to 40-45℃, then add the flame-retardant dispersion of S3, mix uniformly, and obtain a composite emulsion; S5, synthesizing a curing agent The hydrophilic polyether diol and the hydroxyl-containing phosphate were dehydrated in a vacuum environment under nitrogen protection, and then cooled to 60-70℃. The aliphatic diisocyanate and the organotin catalyst were added dropwise at the same time, and the dropwise addition time was 1-2 h. After the dropwise addition was completed, the system was heated to 75-85℃, and the reaction was terminated when the mass percentage content of NCO groups in the system was reduced to 8-12%. The system was cooled to 30-40℃, and the product was discharged. The curing agent was obtained. S6, final preparation The composite emulsion obtained in S4 was cooled to 20-30℃, and the polyether modified polysiloxane defoaming agent, the polyether modified siloxane wetting agent, and the fluorocarbon leveling agent were added in sequence while stirring at a speed of 200-400 rpm. After mixing for 20-30 min, the stirring speed was increased to 1000-1500 rpm, and the curing agent in S5 was added. The mixture was dispersed for 15-30 min. Deionized water was added to adjust the solid content mass fraction to 45-55 wt%, and a pH adjuster was used to adjust the pH to 8.0-9.

5. The mixture was stirred at a speed of 300-500 rpm for 60-120 min to adjust the viscosity, and then filtered to obtain the flame-retardant low VOCs water-based adhesive.

3. The preparation method of the fire-retardant type low VOCs water-based adhesive according to claim 2, characterized in that, The dropwise addition speed of the pre-emulsion in S2 was 6-12 g / min.

4. The preparation method of the fire-retardant type low VOCs water-based adhesive according to claim 2, characterized in that, The dropwise addition speed of the tert-butyl hydroperoxide and sodium metabisulfite in S2 was 0.5-1.2 g / min.

5. The preparation method of the fire-retardant type low VOCs water-based adhesive according to claim 2, characterized in that, The mixing time of the deionized water and the acrylic acid-acrylamide copolymer dispersant in S3 was 5-7 min, and the stirring speed was 800-1200 rpm.

6. The preparation method of the fire-retardant type low VOCs water-based adhesive according to claim 2, characterized in that, The mixing time of the resin emulsion and the flame-retardant dispersion in S4 was 60-90 min, and the stirring speed was 300-500 rpm.

7. The preparation method of the fire-retardant type low VOCs water-based adhesive according to claim 2, characterized in that, The dehydration time of the hydrophilic polyether diol and the hydroxyl-containing phosphate in S5 was 1-2 h, and the dehydration temperature was 100-110℃. The absolute pressure of the vacuum environment was 1.5-2.0 kPa.

8. The preparation method of the fire-retardant type low VOCs water-based adhesive according to claim 2, characterized in that, The monitoring method of NCO groups in the system in S5 was as follows: during the continuous reaction of the system, samples were taken every 20 min, and the mass percentage of NCO groups in the system was determined according to ASTM D5155 standard.

9. The preparation method of the fire-retardant type low VOCs water-based adhesive according to claim 2, characterized in that, In S6, the viscosity of the system was adjusted to 3000-8000 mPa・s. The test conditions for the viscosity value were as follows: a Brookfield DV2T viscometer was used, LV3 or LV4 rotor was selected, the temperature was 25℃, and the speed was 20 rpm.

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