Preparation method of high-efficiency defoaming particle-free moisture-curing polyurethane wallboard glue

Abstract

The invention relates to the technical field of polyurethane adhesives, and discloses a preparation method of an efficient defoaming particle-free moisture-curing polyurethane wallboard adhesive, which comprises the following steps: putting amorphous polyester polyol, crystalline polyester polyol and modified hyperbranched polyester into a reaction container, and adding a first part of non-polar organic solvent for azeotropic dehydration; mixing the molten 4, 4 '-diphenylmethane diisocyanate with a second part of non-polar organic solvent in a pressurizing pipeline, spraying the mixture into a negative pressure reaction container through a nozzle, and atomizing and dispersing the 4, 4'-diphenylmethane diisocyanate by utilizing solvent flash evaporation; and reacting and removing the solvent, and then adding auxiliaries such as 2, 2 '-dimorpholine diethyl ether and the like. Deep dehydration is carried out by utilizing an azeotropic effect, so that bubbles are prevented from being generated; through cooperation of pressurized dissolution and a flash evaporation atomization technology, microscopic uniform dispersion of reactants is realized, gel particles are eliminated, and flatness and bonding strength of the adhesive are improved.

Description

Technical Field

[0001] This invention relates to the field of polyurethane adhesive technology, specifically to a method for preparing a high-efficiency defoaming, particle-free, moisture-curing polyurethane wall panel adhesive. Background Technology

[0002] Moisture-curing polyurethane hot melt adhesives are widely used in the coating and lamination processes of integrated wall panels due to their excellent bonding strength and weather resistance. In the actual production process of moisture-curing polyurethane wall panel adhesives, the raw material polyester polyol contains trace amounts of moisture. Because polyester polyol melt has high viscosity and water molecules are easily wrapped by polymer molecular chains or form hydrogen bonds, it is difficult to completely remove the deep moisture of the system by simply relying on traditional heating vacuum dehydration processes. After the subsequent addition of 4,4'-diphenylmethane diisocyanate, the residual moisture will preferentially react with the isocyanate groups to generate carbon dioxide gas. These gases are difficult to escape from the high-viscosity adhesive liquid, resulting in visible bubbles in the final moisture-curing polyurethane wall panel adhesive product, or causing the adhesive layer to blister after application and curing, which weakens the peel strength and appearance quality of the finished wall panel.

[0003] Furthermore, existing technologies employ direct dropwise or flow-addition of molten 4,4'-diphenylmethane diisocyanate. Due to the viscosity difference between 4,4'-diphenylmethane diisocyanate and the polyester polyol melt, and the high reactivity of the isocyanate groups, localized polymerization or excessive cross-linking can easily occur around the high-concentration 4,4'-diphenylmethane diisocyanate droplets when mixing efficiency is insufficient. This uncontrolled local reaction generates insoluble gel particles, i.e., crystal points. These particles not only clog the application equipment but also disrupt the continuity and smoothness of the adhesive layer, becoming stress concentration points under stress and reducing the mechanical properties of the product. Therefore, this invention proposes a method for preparing a highly efficient, defoaming, particle-free, moisture-curing polyurethane wall panel adhesive to address the shortcomings of existing technologies. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for preparing a highly efficient defoaming, particle-free, moisture-curing polyurethane wall panel adhesive. This method solves the problems in existing production processes where incomplete dehydration of polyester polyols leads to the formation of bubbles inside the adhesive layer, and where uneven dispersion of 4,4'-diphenylmethane diisocyanate in high-viscosity systems results in localized reactions that generate gel particles.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a high-efficiency defoaming, particle-free, moisture-curing polyurethane wall panel adhesive, comprising the following steps: Amorphous polyester polyol, crystalline polyester polyol and modified hyperbranched polyester are put into a reaction vessel, and a first part of non-polar organic solvent is added as an azeotropic entrainer. Azeotropic dehydration is carried out under heating and negative pressure conditions. 4,4'-diphenylmethane diisocyanate is heated to a molten state. A second part of non-polar organic solvent is injected into the molten 4,4'-diphenylmethane diisocyanate in a pressurized pipeline. The pressure in the pressurized pipeline is controlled so that the 4,4'-diphenylmethane diisocyanate and the second part of non-polar organic solvent are mixed to form a homogeneous pressurized mixture. Adjust the temperature and vacuum inside the reaction vessel, and inject the homogeneous pressurized mixture into the reaction vessel through a nozzle. Utilize the pressure jump to cause the second part of the nonpolar organic solvent to flash and atomize, dispersing 4,4'-diphenylmethane diisocyanate. After the feeding is completed, the reaction is carried out under negative pressure and constant temperature until the non-polar organic solvent is removed. Add 2,2'-dimorpholine diethyl ether and γ-(2,3-epoxypropoxy)propyltrimethoxysilane to the reaction vessel, mix well, and then filter out the product.

[0006] By adopting the above technical solution, the problems of air bubbles caused by incomplete dehydration and gel particles caused by uneven isocyanate dispersion during the preparation of moisture-curing polyurethane hot melt adhesives can be solved. The specific mechanism of action is as follows: In high-viscosity polyester polyol melts, water can be bound to ester groups through hydrogen bonds or trapped deep within polymer chains. Simple vacuum heating is insufficient to completely remove it. The first part of the non-polar organic solvent vaporizes and nucleates at high temperatures, reducing the vapor partial pressure of water and breaking the binding force between water molecules and polymers. This allows the deep trace amounts of water to be carried out of the system. Thorough dehydration eliminates the potential for subsequent isocyanate to react with water and generate carbon dioxide bubbles, ensuring the density and appearance quality of the adhesive layer. Traditional solid-feeding or simple liquid-drop addition methods result in excessively high local concentrations of isocyanate upon entering the high-temperature reaction system, with the dispersion rate lower than the reaction rate, easily leading to the formation of microscopic gel particles. In this invention, the second part, a non-polar organic solvent, plays a role in diluting and reducing viscosity in the pressurized pipeline. Upon injection into the low-pressure reaction vessel, a dramatic phase change flash occurs due to the sudden pressure change (from pressurized to negative pressure). The instantaneous vaporization and expansion of the solvent generates volume expansion work, tearing the liquid 4,4'-diphenylmethane diisocyanate into micron-sized droplets. This phase change atomization mechanism achieves instantaneous uniform dispersion of reactants at the molecular level, avoiding local over-reaction, thereby eliminating particulate matter in the adhesive solution and improving the thermal stability and mechanical properties of the product. Simultaneously, the non-polar organic solvent does not participate in the chemical reaction, but only acts as a physical medium to assist in dehydration and dispersion, and is ultimately completely removed during the negative pressure polymerization stage, leaving no residue in the final product that would affect environmental performance.

[0007] Preferably, the raw materials used in the preparation process comprise the following components in parts by weight: 400.0 to 550.0 parts of amorphous polyester polyol; 250.0 to 350.0 parts of crystalline polyester polyol; 20.0 to 50.0 parts of modified hyperbranched polyester; 170.0 to 200.0 parts of 4,4'-diphenylmethane diisocyanate; 10.9 to 18.0 parts of nonpolar organic solvent; 0.6 to 1.0 parts of 2,2'-dimorpholine diethyl ether; and 1.2 to 2.0 parts of γ-(2,3-epoxypropoxy)propyltrimethoxysilane.

[0008] By adopting the above technical solution, the specific raw material ratio ensures that the moisture-curing polyurethane wall panel adhesive has a suitable coating viscosity in the molten state, and at the same time has excellent cohesive strength and flexibility after curing.

[0009] Preferably, the modified hyperbranched polyester is prepared from raw materials comprising the following parts by weight: 134.0 to 135.0 parts of trimethylolpropane; 241.4 to 335.3 parts of 2,2-dimethylolpropionic acid; 116.9 to 182.6 parts of adipic acid; and 150.2 to 220.4 parts of lauric acid.

[0010] The preparation process of modified hyperbranched polyester includes: mixing and melting trimethylolpropane, 2,2-dimethylolpropionic acid and adipic acid, adding lauric acid, carrying out esterification reaction at 175℃-185℃, then raising the temperature to 205℃-215℃ and reacting under the action of a catalyst until the acid value of the system decreases to below 10mg potassium hydroxide per gram, and finally obtaining the product by vacuum devolatilization.

[0011] By adopting the above technical solution, the introduction of modified hyperbranched polyester can significantly improve the overall performance of the adhesive. Using trimethylolpropane as the core, combined with 2,2-dimethylolpropionic acid to construct a highly branched molecular skeleton, a large number of terminal hydroxyl reaction sites are provided, increasing the crosslinking density. Simultaneously, the introduction of long-chain fatty acids (lauric acid) partially capsifies the end groups; the introduction of long carbon chains acts as an internal plasticizer, reducing the melt viscosity of the hyperbranched polymer and improving the flexibility of the polymer chain segments. This results in the final wallboard adhesive maintaining high initial tack while possessing better substrate wetting ability. Preferably, the nonpolar organic solvent is selected from cyclohexane or n-heptane; the first part of the nonpolar organic solvent has a weight ratio of 10.0 to 16.0 parts; and the second part of the nonpolar organic solvent has a weight ratio of 0.9 to 2.0 parts.

[0012] By adopting the above technical solution, cyclohexane or n-heptane has a suitable azeotropic point with water and does not react with isocyanate groups. By allocating the ratio of solvent in the azeotropic dehydration stage (first part) and the pressurized delivery stage (second part), both the dehydration efficiency and the vaporization expansion required for flash atomization are ensured, while the total amount of solvent used is controlled at a low level, which facilitates complete removal in the subsequent stage.

[0013] Preferably, the conditions for azeotropic dehydration treatment are: temperature of 105℃-115℃, vacuum degree of -0.090MPa to -0.095MPa, and time of 60min-90min.

[0014] By adopting the above technical solution, it is possible to ensure that the non-polar organic solvent forms a stable azeotrope with water and continues to evaporate, while avoiding the thermal oxidative degradation of polyester polyols due to prolonged high temperature.

[0015] Preferably, the heating temperature for heating 4,4'-diphenylmethane diisocyanate to a molten state is 50°C-55°C; the pressure in the pressurized pipeline is maintained at 0.45MPa-0.55MPa.

[0016] By adopting the above technical solution, low-temperature melting can prevent 4,4'-diphenylmethane diisocyanate from undergoing self-polymerization to form dimers; maintaining a pressure of more than 0.45 MPa in the pressurized pipeline can ensure that the second part of the non-polar organic solvent (such as cyclohexane) remains liquid at a temperature higher than its atmospheric boiling point, thereby forming a homogeneous solution with 4,4'-diphenylmethane diisocyanate, accumulating potential energy for subsequent pressure surge flash evaporation.

[0017] Preferably, the temperature inside the reaction vessel is 80℃-85℃, the vacuum degree inside the reaction vessel is -0.096MPa to -0.099MPa, and the injection time of the homogeneous pressurized mixture is 3min to 5min.

[0018] By adopting the above technical solution, the high vacuum environment increases the pressure difference inside and outside the nozzle, enhances the flash evaporation effect, and the rapid injection feeding can ensure that all reactants start the polymerization reaction almost simultaneously, ensuring the uniformity of molecular weight distribution and avoiding the problem that the materials added first react too much and the materials added later react too little due to the feeding time being too long.

[0019] Preferably, the isothermal reaction temperature is 85℃-90℃, the vacuum degree of the isothermal reaction is less than -0.095MPa, and the isothermal reaction time is 60min-120min.

[0020] By adopting the above technical solution, the chain extension reaction is carried out under negative pressure and suitable temperature. At the same time, the trace amounts of non-polar organic solvents remaining in the system are removed by utilizing the negative pressure environment, ensuring that the volatile organic compound content of the final product meets safety standards.

[0021] Preferably, the homogeneous pressurized mixture is formed by mixing in a static mixer within a pressurized pipeline; the nozzle is an atomizing nozzle.

[0022] By adopting the above technical solution, the static mixer utilizes the division, shearing, rotation and rearrangement of fluids in the pipeline to achieve efficient online mixing of high-viscosity melts and low-viscosity solvents without moving parts; the atomizing nozzle, combined with flash evaporation, further reduces the droplet size and achieves the ultimate dispersion of reactants.

[0023] This invention provides a method for preparing a highly efficient, defoamed, particle-free, moisture-curing polyurethane wall panel adhesive. It has the following beneficial effects: 1. This invention utilizes the characteristic of the first part of the non-polar organic solvent to form a low-boiling-point azeotrope with water molecules to carry out azeotropic dehydration treatment in a mixed system of amorphous polyester polyol, crystalline polyester polyol and modified hyperbranched polyester. This treatment method can destroy the hydrogen bonding between water molecules and polymer chain segments, remove trace amounts of water deep in the system, and block the path of 4,4'-diphenylmethane diisocyanate reacting with water to generate carbon dioxide gas, thereby avoiding the occurrence of bubbles or hollowness in the moisture-cured polyurethane wall panel adhesive layer, and improving the density and bonding strength of the adhesive layer.

[0024] 2. This invention solves the problem of localized gelation caused by uneven dispersion of highly active isocyanates by constructing a feeding system that combines pressurized solvent mixing with flash atomization. In the pressurized pipeline, 4,4'-diphenylmethane diisocyanate forms a homogeneous solution with the second part of non-polar organic solvent. When it is sprayed into the negative pressure environment through the nozzle, the volume expansion force generated by the instantaneous vaporization of the non-polar organic solvent tears the liquid 4,4'-diphenylmethane diisocyanate into micron-sized droplets. This method increases the reaction contact surface area, prevents explosive agglomeration caused by excessively high local concentrations, and ensures that the moisture-cured polyurethane wall panel adhesive has a delicate and particle-free appearance.

[0025] 3. This invention introduces lauric acid-terminated hyperbranched polyester as a key component. The highly branched skeleton constructed by trimethylolpropane and 2,2-dimethylolpropionic acid provides a high density of reactive hydroxyl groups. At the same time, the long carbon chain structure of lauric acid is used to exert an internal plasticizing effect. This method reduces the internal friction of the polymer melt, so that the moisture-curing polyurethane wall panel adhesive has better rheological properties and wetting ability to the substrate at the application temperature. At the same time, it ensures the crosslinking density and cohesive strength after curing, and achieves a balance between application smoothness and final adhesion performance. Detailed Implementation

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the preparation examples, comparative examples, and test examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Raw materials: The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0028] Amorphous polyester polyol, a random copolymer hydroxyl-terminated polyester prepared by polycondensation reaction of adipic acid (CAS No.: 124-04-9), isophthalic acid (CAS No.: 121-91-5), neopentyl glycol (CAS No.: 126-30-7) and ethylene glycol (CAS No.: 107-21-1) as monomers, with a number average molecular weight (Mn) of 2000 g / mol.

[0029] A crystalline polyester polyol, a linear polyhexanediol of adipate, is prepared by polycondensation reaction of adipic acid (CAS No.: 124-04-9) and 1,6-hexanediol (CAS No.: 629-11-8) as repeating units, with a number average molecular weight (Mn) of 3500 g / mol.

[0030] Preparation Examples 1-3: Preparation Example 1: In a four-necked glass flask equipped with a mechanical stirrer, thermometer, nitrogen inlet tube, and water separator with condenser, weigh and add 134.2 g (134.2 parts) of trimethylolpropane, 268.2 g (268.2 parts) of 2,2-dimethylolpropionic acid, and 146.1 g (146.1 parts) of adipic acid. Purge the flask with dry nitrogen to replace the air and set the nitrogen flow protection. Turn on the mechanical stirrer, set the speed to 150 rpm, and heat to 140°C to completely melt the solid raw materials. Then add 180.5 g (180.5 parts) of lauric acid as an end-capping modifier. Continue to slowly heat to 180°C and maintain the reaction at this temperature for 2.5 hours, during which time the water generated in the esterification reaction is removed using the water separator. The temperature was then raised to 210℃, and 0.6g of monobutyltin oxide catalyst was added. The reaction continued until the acid value of the reaction system decreased to below 10mgKOH / g. At this point, a vacuum pump was started to reduce the absolute pressure in the system to between 500Pa and 1000Pa, and negative pressure was maintained for 1.0 hour to remove residual small molecule volatiles. The vacuum was then released, the material was cooled, and the modified hyperbranched polyester, which is a viscous liquid at room temperature, was obtained. The number-average molecular weight (Mn) of the modified hyperbranched polyester was 1850g / mol, the hydroxyl value (OHValue) was 265mgKOH / g, and the viscosity (60℃) was 4500mPa·s.

[0031] Preparation Example 2: In a four-necked glass flask equipped with a mechanical stirrer, thermometer, nitrogen inlet tube, and water separator with condenser, 134.2 g (134.2 parts) of trimethylolpropane, 335.3 g (335.3 parts) of 2,2-dimethylolpropionic acid, and 182.6 g (182.6 parts) of adipic acid were weighed and added. Dry nitrogen was introduced into the flask to replace the air. The mechanical stirrer was turned on and set to 150 rpm. The temperature was raised to 140°C to melt the raw materials. Then, 150.2 g (150.2 parts) of lauric acid was added to the flask. Following the same heating procedure as in Preparation Example 1, the reaction was first carried out at 180°C for 2.5 hours, then the temperature was raised to 210°C and 0.7 g of monobutyltin oxide catalyst was added. After the acid value of the reaction system decreased to below 10 mg KOH / g, vacuum devolatilization was carried out for 1.0 hour under a pressure of 500 Pa to 1000 Pa. The vacuum was then released, the material was cooled, and the modified hyperbranched polyester was obtained. Testing showed that the number-average molecular weight (Mn) of the modified hyperbranched polyester was 2400 g / mol, the hydroxyl value (OHValue) was 195 mg KOH / g, and the viscosity (60℃) was 6200 mPa·s.

[0032] Preparation Example 3: In a four-necked glass flask equipped with a mechanical stirrer, thermometer, nitrogen inlet tube, and water separator with condenser, 134.2 g (i.e., 134.2 parts) of trimethylolpropane, 241.4 g (i.e., 241.4 parts) of 2,2-dimethylolpropionic acid, and 116.9 g (i.e., 116.9 parts) of adipic acid were accurately weighed and added. Dry nitrogen was introduced into the four-necked glass flask to replace the air. The mechanical stirrer was turned on and set to 150 rpm. The temperature was raised to 140°C to melt the raw materials. Then, 220.4 g (i.e., 220.4 parts) of lauric acid was added to the four-necked glass flask. Following the same heating procedure as in Preparation Example 1, the reaction was first carried out at 180°C for 2.0 hours, then the temperature was raised to 210°C and 0.6 g of monobutyltin oxide catalyst was added. After the acid value of the reaction system decreased to below 10 mg KOH / g, vacuum devolatilization was carried out for 1.0 hour under a pressure of 500 Pa to 1000 Pa. The vacuum was then released, the material was cooled, and the modified hyperbranched polyester was obtained. Testing showed that the number-average molecular weight (Mn) of the modified hyperbranched polyester was 1600 g / mol, the hydroxyl value (OHValue) was 285 mg KOH / g, and the viscosity (60℃) was 3200 mPa·s.

[0033] Examples 1-4: Example 1: This embodiment provides a method for preparing a high-efficiency defoaming, particle-free, moisture-curing polyurethane wall panel adhesive. The formulation consists of: 500.0 g (500.0 parts) of amorphous polyester polyol, 300.0 g (300.0 parts) of crystalline polyester polyol, 30.0 g (30.0 parts) of modified hyperbranched polyester obtained in Preparation Example 1, 170.0 g (170.0 parts) of 4,4'-diphenylmethane diisocyanate, 12.5 g (12.5 parts) of cyclohexane, 1.2 g (1.2 parts) of cyclohexane, 0.8 g (0.8 parts) of 2,2'-dimorpholine diethyl ether, and 1.5 g (1.5 parts) of γ-(2,3-epoxypropoxy)propyltrimethoxysilane.

[0034] The preparation method of this embodiment includes the following steps: S1. Add 500.0g (i.e., 500.0 parts) of amorphous polyester polyol, 300.0g (i.e., 300.0 parts) of crystalline polyester polyol and 30.0g (i.e., 30.0 parts) of modified hyperbranched polyester to a 2000mL stainless steel reactor, and add 12.5g (i.e., 12.5 parts) of cyclohexane as an azeotropic entrainer; turn on the anchor stirrer, set the speed to 70rpm, and raise the temperature to 110℃; turn on the vacuum pump, adjust the vacuum degree to -0.092MPa, and maintain the conditions of 110℃ and -0.092MPa for azeotropic dehydration for 75 minutes; S2. In a separate melting tank, heat 170.0 g (i.e., 170.0 parts) of 4,4'-diphenylmethane diisocyanate to 52°C until it is completely melted; use a high-pressure metering pump to deliver the liquid 4,4'-diphenylmethane diisocyanate to the feeding pipeline, inject 1.2 g (i.e., 1.2 parts) of cyclohexane at the front end of the static mixer in the feeding pipeline, and use a back pressure valve to adjust the pressure in the feeding pipeline to maintain it at 0.50 MPa, so that 4,4'-diphenylmethane diisocyanate and cyclohexane form a homogeneous pressurized mixture in the feeding pipeline; S3. Adjust the temperature inside the reactor to 85℃, switch the stirrer inside the reactor to a dispersion disc and set the speed to 450 rpm, and increase the vacuum degree inside the reactor to -0.098 MPa; open the nozzle of the feeding pipeline and spray the prepared homogeneous pressurized mixture into the reactor within 4 minutes, using the pressure change to cause cyclohexane to flash atomize. S4. After the feeding is completed, keep the temperature of the reactor at 88℃ and the vacuum degree of the reactor below -0.095MPa. Adjust the stirring speed to 180rpm and react at a constant temperature for 90 minutes until all the residual cyclohexane in the reaction system is removed and there are no bubbles in the appearance of the liquid. S5. Remove the vacuum, fill the reactor with dry nitrogen, cool to 82°C, add 0.8g (i.e. 0.8 parts) of 2,2'-dimorpholine diethyl ether and 1.5g (i.e. 1.5 parts) of γ-(2,3-epoxypropoxy)propyltrimethoxysilane, stir and mix at 50 rpm for 15 minutes, and filter through a 100-mesh filter to discharge the material.

[0035] Example 2: This embodiment provides a method for preparing a high-efficiency defoaming, particle-free, moisture-curing polyurethane wall panel adhesive. The formulation consists of: 550.0 g (i.e., 550.0 parts) of amorphous polyester polyol, 250.0 g (i.e., 250.0 parts) of crystalline polyester polyol, 20.0 g (i.e., 20.0 parts) of modified hyperbranched polyester obtained in Preparation Example 2, 180.0 g (i.e., 180.0 parts) of 4,4'-diphenylmethane diisocyanate, 10.0 g (i.e., 10.0 parts) of cyclohexane, 0.9 g (i.e., 0.9 parts) of cyclohexane, 0.6 g (i.e., 0.6 parts) of 2,2'-dimorpholine diethyl ether, and 1.2 g (i.e., 1.2 parts) of γ-(2,3-epoxypropoxy)propyltrimethoxysilane.

[0036] The preparation method of this embodiment includes the following steps: S1. Add 550.0g (i.e., 550.0 parts) of amorphous polyester polyol, 250.0g (i.e., 250.0 parts) of crystalline polyester polyol and 20.0g (i.e., 20.0 parts) of modified hyperbranched polyester to a 2000mL stainless steel reactor, and add 10.0g (i.e., 10.0 parts) of cyclohexane; turn on the anchor stirrer, set the speed to 60rpm, and heat to 105℃; turn on the vacuum pump, adjust the vacuum degree to -0.090MPa, and maintain 105℃ and -0.090MPa conditions for azeotropic dehydration for 90 minutes; S2. In a separate melting tank, heat 180.0 g (i.e., 180.0 parts) of 4,4'-diphenylmethane diisocyanate to 50°C until it is completely melted; deliver it through a high-pressure metering pump, and inject 0.9 g (i.e., 0.9 parts) of cyclohexane into the front end of the static mixer in the feeding pipeline. Adjust the pressure in the feeding pipeline by adjusting the back pressure valve to maintain it at 0.45 MPa, so that 4,4'-diphenylmethane diisocyanate and cyclohexane form a homogeneous pressurized mixture in the feeding pipeline; S3. Adjust the temperature inside the reactor to 80℃, set the speed of the dispersion disc to 400rpm, and increase the vacuum degree inside the reactor to -0.096MPa; open the nozzle and spray the homogeneous pressurized mixture into the reactor within 5 minutes, using the pressure change to cause the cyclohexane to flash atomize. S4. After the feeding is complete, keep the temperature of the reactor at 85℃ and the vacuum degree of the reactor below -0.095MPa. Adjust the stirring speed to 150rpm and react at a constant temperature for 120 minutes until the solvent is completely removed. S5. Remove the vacuum, fill with dry nitrogen, cool to 80°C, add 0.6g (i.e. 0.6 parts) of 2,2'-dimorpholine diethyl ether and 1.2g (i.e. 1.2 parts) of γ-(2,3-epoxypropoxy)propyltrimethoxysilane, stir and mix at 50 rpm for 15 minutes, and filter out the material.

[0037] Example 3: This embodiment provides a method for preparing a high-efficiency defoaming, particle-free, moisture-curing polyurethane wall panel adhesive. The formulation consists of: 400.0 g (400.0 parts) of amorphous polyester polyol, 350.0 g (350.0 parts) of crystalline polyester polyol, 50.0 g (50.0 parts) of modified hyperbranched polyester obtained in Preparation Example 3, 200.0 g (200.0 parts) of 4,4'-diphenylmethane diisocyanate, 16.0 g (16.0 parts) of cyclohexane, 2.0 g (2.0 parts) of cyclohexane, 1.0 g (1.0 part) of 2,2'-dimorpholine diethyl ether, and 2.0 g (2.0 parts) of γ-(2,3-epoxypropoxy)propyltrimethoxysilane.

[0038] The preparation method of this embodiment includes the following steps: S1. Add 400.0g (i.e., 400.0 parts) of amorphous polyester polyol, 350.0g (i.e., 350.0 parts) of crystalline polyester polyol and 50.0g (i.e., 50.0 parts) of modified hyperbranched polyester to a 2000mL stainless steel reactor, and add 16.0g (i.e., 16.0 parts) of cyclohexane; turn on the anchor stirrer, set the speed to 80rpm, and raise the temperature to 115℃; adjust the vacuum degree to -0.095MPa, and maintain the conditions of 115℃ and -0.095MPa for azeotropic dehydration for 60 minutes; S2. In a separate melting vessel, heat 200.0 g (i.e., 200.0 parts) of 4,4'-diphenylmethane diisocyanate to 55°C until it is completely melted; deliver it through a high-pressure metering pump, inject 2.0 g of cyclohexane into the feeding line, and adjust the pressure in the feeding line to maintain it at 0.55 MPa through the back pressure valve, so that 4,4'-diphenylmethane diisocyanate and cyclohexane form a homogeneous pressurized mixture in the feeding line; S3. Adjust the temperature inside the reactor to 85℃, set the speed of the dispersion disc to 600rpm, and increase the vacuum degree inside the reactor to -0.099MPa; open the nozzle and spray the homogeneous pressurized mixture into the reactor within 3 minutes, using the pressure change to cause the cyclohexane to flash atomize. S4. After the feeding is complete, keep the temperature of the reactor at 90℃ and the vacuum degree of the reactor below -0.095MPa. Adjust the stirring speed to 200rpm and keep the reaction at a constant temperature for 60 minutes until the solvent is completely removed. S5. Remove the vacuum, fill with dry nitrogen, cool to 85°C, add 1.0g (i.e. 1.0 part) of 2,2'-dimorpholine diethyl ether and 2.0g (i.e. 2.0 part) of γ-(2,3-epoxypropoxy)propyltrimethoxysilane, stir and mix at 60 rpm for 15 minutes, and filter out the material.

[0039] Example 4: This embodiment provides a method for preparing a highly efficient defoaming, particle-free, moisture-curing polyurethane wall panel adhesive. The only difference between this embodiment and Embodiment 1 is that the process solvent is replaced with n-heptane instead of cyclohexane.

[0040] The preparation method of this embodiment includes the following steps: S1. Add 500.0 g (i.e., 500.0 parts) of amorphous polyester polyol, 300.0 g (i.e., 300.0 parts) of crystalline polyester polyol and 30.0 g (i.e., 30.0 parts) of modified hyperbranched polyester to a reactor, and add 12.5 g (i.e., 12.5 parts) of n-heptane; carry out azeotropic dehydration at 115℃ and -0.095 MPa for 80 minutes. S2. Heat 170.0g (i.e. 170.0 parts) of 4,4'-diphenylmethane diisocyanate to 52°C to melt it, and inject 1.2g (i.e. 1.2 parts) of n-heptane into the feeding pipeline, controlling the pressure in the feeding pipeline to be 0.50MPa; S3. Adjust the temperature inside the reactor to 85℃ and increase the vacuum to -0.098MPa. Inject the mixture of 4,4'-diphenylmethane diisocyanate containing n-heptane into the reactor and use the pressure change to cause the n-heptane to flash and atomize. S4. After the feeding is complete, maintain the reaction at 90°C and high vacuum for 100 minutes until all n-heptane is removed. The subsequent processing steps are the same as in Example 1.

[0041] Comparative Examples 1-4: Comparative Example 1: Compared with Example 1, the differences are as follows: In step S1, cyclohexane is not added, but the temperature is raised to 120°C and vacuum dehydration is carried out for 120 minutes under a vacuum of -0.095 MPa; In steps S2 and S3, liquid pressurized conveying and flash atomization feeding are not used, and cyclohexane is not injected into the feeding pipeline. Instead, the feed port of the reactor is opened directly, and the flake solid 4,4'-diphenylmethane diisocyanate is added into the reactor within 2 minutes. The other raw material types, amounts, and subsequent processing steps are the same.

[0042] Comparative Example 2: Compared with Example 1, the difference is that in steps S2 and S3, liquid pressurized conveying and flash atomization feeding are not used, and cyclohexane is not injected into the feeding pipeline. Instead, the feed port of the reactor is opened directly, and the flake solid 4,4'-diphenylmethane diisocyanate is added into the reactor within 2 minutes. All other steps are the same.

[0043] Comparative Example 3: Compared with Example 1, the difference is that cyclohexane is not added in step S1, but the temperature is raised to 120°C and vacuum dehydration is carried out for 120 minutes under a vacuum of -0.095 MPa. All other aspects are the same.

[0044] Comparative Example 4: Compared with Example 1, the difference is that: in step S2, cyclohexane is not injected into the feeding pipeline, but 4,4'-diphenylmethane diisocyanate is heated and melted and then transported to the feeding pipeline; in step S3, pure liquid 4,4'-diphenylmethane diisocyanate is injected into the reactor through a nozzle at a pressure of 0.50 MPa. All other steps are the same.

[0045] Test Example 1-2: Test Example 1: Process Feasibility and Process Indicator Test Test Description and Experimental Procedures: This section of the tests aims to verify the actual performance of the preparation process of this invention in terms of dehydration efficiency, solvent residue control, and production cycle. The specific test methods are as follows: Determination of moisture content at the dehydration endpoint: After the azeotropic or vacuum dehydration process in step S1 is completed, but before the isocyanate is added, use a sampler to extract 5.0 g to 10.0 g of molten sample from the bottom of the reactor. Quickly inject the sample into a pre-dried, sealed sample vial. Detect the moisture content using a Karl Fischer coulometric moisture analyzer. During detection, the sample is heated to 120°C, and the volatilized moisture is carried into the electrolytic cell by a carrier gas for titration. The measured moisture percentage is recorded.

[0046] Determination of volatile organic compound (VOC) residues: After the final product has been filtered and cooled to room temperature, samples are taken for testing. Gas chromatography-mass spectrometry (GC-MS) is performed according to the national standard GB / T33372-2016 "Limits of Volatile Organic Compounds in Adhesives". 2.0 g of sample is weighed and placed in a headspace vial, and equilibrated at 120 °C for 45 minutes. The sample is injected using a headspace sampler, and qualitative and quantitative analysis is performed using a gas chromatograph equipped with a flame ionization detector (FID) or mass spectrometer (MSD) targeting the characteristic peaks of cyclohexane or n-heptane used in the process. The method detection limit is set at 5 mg / kg.

[0047] Total process time statistics: Record the total operation time from the initial addition of the first batch of polyester polyol raw materials to the reactor for heating to the final product filtration and filling. This time includes the entire process duration of heating and melting, dehydration, feeding reaction, degassing, and post-treatment mixing.

[0048] Test data: Table 1 records the measured data of various process indicators of Examples 1 to 4 and Comparative Examples 1 to 4.

[0049] Table 1. Test results of process parameters for the preparation of moisture-curing polyurethane wall panel adhesive

[0050] Note: "Not detected" means the test result is below the method detection limit of 5 mg / kg; "--" means that no solvent was added to the comparative sample, so this test was not performed.

[0051] Results Analysis and Conclusions: Based on the test data in Table 1 and the technical mechanism proposed in this invention, the following conclusions are drawn: The azeotropic entrainment process improves the depth and efficiency of dehydration. Comparative data shows that in Examples 1 to 4, which use cyclohexane or n-heptane to assist azeotropic dehydration, the water content of the dehydrated system is stably controlled between 0.016% and 0.024%, significantly lower than that of Comparative Example 1 (0.048%) and Comparative Example 3 (0.045%), which only use traditional vacuum high-temperature dehydration. This is because the water in the high-viscosity polyester polyol is limited by the diffusion rate, and it is difficult to remove the deep-bound water by relying solely on negative pressure and temperature. However, the non-polar solvent introduced in this invention vaporizes and nucleates inside the polyester melt, reducing the vapor pressure of water and disrupting the hydrogen bonding between water molecules and ester groups, thereby achieving deep dehydration. The reduction in water content directly reduces the side reaction of isocyanate groups being consumed by water, which is beneficial for controlling the molecular weight of subsequent polymerization reactions.

[0052] The combined use of flash evaporation and high vacuum ensured complete solvent removal. Although process solvents were introduced in Examples 1 to 4 during the preparation process, the residual amount of the final product was "not detected". This confirms that the flash evaporation atomization process in step S3 not only utilizes solvent phase change to achieve material dispersion, but also that most of the solvent is vaporized and discharged instantly upon entering the low-pressure environment. The remaining trace amount of solvent is removed in the high-temperature, high-vacuum polymerization stage of step S4. This indicates that the closed-loop process path of introducing, utilizing, and removing solvent constructed in this invention is feasible and will not lead to a decrease in the environmental protection indicators of the product.

[0053] The shortened process cycle reflects the industrialization value. The average total process time of the example group is shorter than that of Comparative Example 1 and Comparative Example 3. This is because the azeotropic dehydration efficiency is higher than that of diffusion dehydration, which shortens the time of the dehydration step. At the same time, the flash feeding method realizes the instantaneous micro-mixing of reactants. Compared with the melting and dispersion process after solid feeding, the time required for the reaction to reach a homogeneous state is shorter.

[0054] Test Example 2: Product Performance Comparison Test Test Description and Experimental Procedures: To objectively evaluate the performance of the moisture-curing polyurethane wallboard adhesive prepared in this invention in terms of dispersibility, appearance quality, thermal stability, and bond strength, the following experimental methods were used to test each group of products: Determination of adhesive fineness (particle size): A scraper fineness meter with a range of 0 to 100 μm was used. The adhesive sample was heated to 120°C in an oven to melt it. A small amount of the molten sample was taken out and immediately poured into the deepest part of the groove of the scraper fineness meter. The sample was scraped towards the shallower part of the groove at a vertical angle and constant speed using a scraper. The surface of the groove was immediately observed under sufficient light, and the scale value of the appearance of continuous linear scratches or dense particle points was recorded. This value reflects the maximum size of unmelted particles, gel particles, or polyurea impurities in the system.

[0055] Appearance rating: A molten adhesive sample was applied to the surface of a high-transparency polyethylene terephthalate (PET) film at a thickness of 0.5 mm. After the adhesive layer cooled and cured, its internal condition was observed using a backlighting method. The scoring criteria are as follows: Grade 5: The adhesive layer has a mirror-like gloss, with no visible bubbles or crystal points; Grade 4: The adhesive layer is transparent, with a very small number of microbubbles and no crystal points; Grade 3: The adhesive layer contains a small amount of dispersed air bubbles or a small amount of tiny particles; Grade 2: Obvious air bubbles or obvious particle aggregation are present in the adhesive layer; Grade 1: The gel layer is cloudy and contains a large number of air bubbles or large particulate impurities.

[0056] 120℃ Thermal Stability (Viscosity Growth Rate) Determination: The initial viscosity of the sample at 120℃ was measured using a rotational viscometer and recorded as follows. The sample was then sealed and placed in a 120℃ drying oven for 4.0 hours. After removal, its viscosity at 120℃ was measured again and recorded as follows. The formula for calculating the viscosity growth rate is: This index is used to characterize the uniformity of the system reaction. The presence of microgels or localized over-reaction centers in the system can lead to abnormal viscosity growth.

[0057] Initial tack test: The adhesive sample was heated to 120℃ and coated onto the surface of polyvinyl chloride (PVC) decorative film by roller coating, with the coating amount controlled at 150g / m². 2 Immediately after applying the adhesive, the PVC film is bonded to the medium-density fiberboard (MDF) substrate, and a pressure of 0.5 MPa is applied by rolling once. After being placed in a standard environment (23°C, 50% humidity) for 1 minute, a 180-degree peel strength test is performed using a universal testing machine with a tensile speed set to 300 mm / min, and the maximum peel force is recorded.

[0058] Test data: Table 2 records the measured data of various physicochemical properties of Examples 1 to 4 and Comparative Examples 1 to 4.

[0059] Table 2. Comparative Test Results of Physicochemical and Adhesive Properties of Moisture-Cure Polyurethane Wall Panel Adhesive

[0060] Note: "<10" indicates that no obvious particles were observed and the reading was below the smallest scale of the fineness gauge; ">100" indicates that the scraper had scratches throughout the entire range.

[0061] Results Analysis and Conclusions: Based on the test data in Table 2 and the technical mechanism proposed in this invention, the following conclusions are drawn: Flash atomization feeding technology eliminated gel particles: the fineness of the gel solutions in Examples 1 to 4 was all less than 10 μm, achieving a submicron level of dispersion. In contrast, Comparative Examples 1 and 2, which used solid feed, had finenesses greater than 100 μm and 65 μm, respectively. This indicates that the solid 4,4'-diphenylmethane diisocyanate formed localized high-concentration regions during melt diffusion, leading to the formation of gel particles. It is particularly noteworthy that although Comparative Example 4 used high-pressure liquid jetting, it did not use cyclohexane or n-heptane for assistance, and its fineness was 35 μm, still inferior to the Example groups. This confirms that mechanical pressure atomization alone is insufficient. This invention utilizes the secondary fragmentation force generated by the phase change expansion of cyclohexane or n-heptane under reduced pressure, which plays a decisive role in achieving the ultimate dispersion of the reactants.

[0062] Azeotropic degassing and flash dispersion synergistically improved the appearance quality: the appearance rating of the example group was 5, showing a bubble-free mirror finish. Although Comparative Example 3 used flash feeding, it omitted the azeotropic dehydration step, resulting in an appearance rating of only 3. This indicates that if there is residual deep trace moisture or microbubbles in the polyester polyol matrix, even if the isocyanate is uniformly dispersed, the carbon dioxide generated in the subsequent reaction will still form macroscopic bubble defects. Only by combining deep azeotropic degassing with flash dispersion can the problems of bubbles caused by moisture and crystal points caused by uneven mixing be solved simultaneously.

[0063] System homogeneity improved thermal stability and adhesive strength. Thermal stability tests showed that the viscosity growth rate of the example groups was controlled at a low level of 3.9% to 5.1%, while the viscosity growth rate of Comparative Example 1, which contained a large number of particles, was as high as 48.2%. This indicates that the microgel particles in the system acted as autocatalytic centers, accelerating the cross-linking and aging of the adhesive solution under heat. In addition, the initial tack of the example groups (17.8 N / 25 mm to 20.5 N / 25 mm) was generally higher than that of the comparative examples. This is because the highly uniform, defect-free adhesive layer can provide a larger contact area and there are no stress concentration defects, thereby improving the cohesive strength and interfacial adhesion of the adhesive.

Claims

1. A method for preparing a high-efficiency defoaming, particle-free, moisture-curing polyurethane wall panel adhesive, characterized in that, Includes the following steps: Amorphous polyester polyol, crystalline polyester polyol and modified hyperbranched polyester are put into a reaction vessel, and a first part of non-polar organic solvent is added as an azeotropic entrainer. Azeotropic dehydration treatment is carried out under heating and negative pressure conditions. 4,4'-diphenylmethane diisocyanate is heated to a molten state, and a second portion of non-polar organic solvent is injected into the molten 4,4'-diphenylmethane diisocyanate in a pressurized pipeline. The pressure in the pressurized pipeline is controlled so that the 4,4'-diphenylmethane diisocyanate and the second portion of non-polar organic solvent are mixed to form a homogeneous pressurized mixture. The temperature and vacuum level inside the reaction vessel are adjusted, and the homogeneous pressurized mixture is injected into the reaction vessel through a nozzle. The pressure change causes the non-polar organic solvent in the second part to flash and atomize, dispersing the 4,4'-diphenylmethane diisocyanate. After the feeding is completed, the reaction is carried out under negative pressure and constant temperature until the non-polar organic solvent is removed. 2,2'-Dimorpholine diethyl ether and γ-(2,3-epoxypropoxy)propyltrimethoxysilane were added to the reaction vessel, mixed thoroughly, and then filtered out.

2. The preparation method of the high-efficiency defoaming, particle-free, moisture-curing polyurethane wall panel adhesive according to claim 1, characterized in that, The raw materials used in the preparation process contain the following components in parts by weight: Amorphous polyester polyol 400.0 parts to 550.0 parts; crystalline polyester polyol 250.0 parts to 350.0 parts; modified hyperbranched polyester 20.0 parts to 50.0 parts; 4,4'-diphenylmethane diisocyanate 170.0 parts to 200.0 parts; nonpolar organic solvent 10.9 parts to 18.0 parts; 2,2'-dimorpholine diethyl ether 0.6 parts to 1.0 parts; γ-(2,3-epoxypropoxy)propyltrimethoxysilane 1.2 parts to 2.0 parts.

3. The preparation method of a high-efficiency defoaming, particle-free, moisture-curing polyurethane wall panel adhesive according to claim 1, characterized in that, The modified hyperbranched polyester is prepared from raw materials comprising the following parts by weight: 134.0 to 135.0 parts of trimethylolpropane; 241.4 to 335.3 parts of 2,2-dimethylolpropionic acid; and 116.9 to 182.6 parts of adipic acid. Lauric acid 150.2 parts to 220.4 parts.

4. The preparation method of a high-efficiency defoaming, particle-free, moisture-curing polyurethane wall panel adhesive according to claim 3, characterized in that, The preparation process of the modified hyperbranched polyester includes: mixing and melting the trimethylolpropane, the 2,2-dimethylolpropionic acid and the adipic acid, adding the lauric acid, carrying out an esterification reaction at 175℃-185℃, then raising the temperature to 205℃-215℃ and reacting under the action of a catalyst until the acid value of the system decreases to below 10 mg potassium hydroxide per gram, and finally obtaining the product by vacuum devolatilization.

5. The preparation method of a high-efficiency defoaming, particle-free, moisture-curing polyurethane wall panel adhesive according to claim 1, characterized in that, The nonpolar organic solvent is selected from either cyclohexane or n-heptane; The first portion of nonpolar organic solvent comprises 10.0 to 16.0 parts by weight; the second portion of nonpolar organic solvent comprises 0.9 to 2.0 parts by weight.

6. The preparation method of a high-efficiency defoaming, particle-free, moisture-curing polyurethane wall panel adhesive according to claim 1, characterized in that, The conditions for the azeotropic dehydration treatment are: temperature of 105℃-115℃, vacuum degree of -0.090MPa to -0.095MPa, and time of 60min-90min.

7. The preparation method of a high-efficiency defoaming, particle-free, moisture-curing polyurethane wall panel adhesive according to claim 1, characterized in that, The heating temperature for heating 4,4'-diphenylmethane diisocyanate to a molten state is 50°C-55°C; the pressure in the pressurized pipeline is maintained at 0.45MPa-0.55MPa.

8. The preparation method of a high-efficiency defoaming, particle-free, moisture-curing polyurethane wall panel adhesive according to claim 1, characterized in that, The temperature inside the reaction vessel is 80℃-85℃, and the vacuum degree inside the reaction vessel is -0.096MPa to -0.099MPa; the injection time of the homogeneous pressurized mixture is 3min to 5min.

9. The preparation method of a high-efficiency defoaming, particle-free, moisture-curing polyurethane wall panel adhesive according to claim 1, characterized in that, The isothermal reaction temperature is 85℃-90℃, the vacuum degree of the isothermal reaction is less than -0.095MPa, and the isothermal reaction time is 60min-120min.

10. The preparation method of a high-efficiency defoaming, particle-free, moisture-curing polyurethane wall panel adhesive according to claim 1, characterized in that, The homogeneous pressurized mixture is formed by mixing in a static mixer within the pressurized pipeline; the nozzle is an atomizing nozzle.

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