A castor oil-based waterborne polyurethane curing aid and its preparation method and application

Abstract

The present invention belongs to the technical field of adhesives, and provides a castor oil-based waterborne polyurethane curing aid, and a preparation method and application thereof. The method of the present invention comprises: performing a first step reaction on dihydroxyacetone, a carboxylic anionic hydrophilic chain extender, isophorone diisocyanate and dibutyltin dilaurate, and then performing a second step reaction with castor oil; the second step reaction product and a capping agent perform a capping reaction, and the capping reaction product and triethylamine perform a salt-forming reaction to obtain a prepolymer; the prepolymer and water perform an emulsification reaction, and the waterborne polyurethane emulsion and a cross-linking agent containing a hydrazide group are mixed to obtain a castor oil-based waterborne polyurethane curing aid. Soybean-based adhesives and waterborne polyurethane curing aids form a network interpenetration under the double cross-linking network of soybean protein system and polyurethane system, and the dry bonding strength of plywood pressed by the composite soybean-based adhesive reaches more than 2.25MPa, and the wet bonding strength reaches more than 1.31MPa.

Description

Technical Field

[0001] The invention relates to the technical field of adhesives, and in particular to a castor oil-based waterborne polyurethane curing aid, a preparation method and application thereof. Background Art

[0002] As one of the main types of adhesives for the production of formaldehyde-free artificial boards, soy-based wood adhesives have been industrially applied in the production of artificial boards such as plywood, particleboard, blockboard, and floor substrates.

[0003] However, compared with the current mainstream formaldehyde-based synthetic resin adhesives, the soy protein itself has low group activity and relatively few reaction sites, resulting in low cross-linking density and reduced curing efficiency. Therefore, soy-based adhesives still cannot fully meet the industrial production needs of formaldehyde-free artificial boards in terms of curing speed and hot pressing efficiency. Especially in the low temperature conditions in the Northeast in winter, the problems of reduced curing rate, extended hot pressing time and increased energy consumption are more prominent, hindering their wider industrial application.

[0004] In response to the above problems, the research team has developed a soybean-based adhesive (SA) composed of soybean meal powder, PAE resin (polyamide polyamine-epichlorohydrin) and a cross-linking aid. The cross-linking aid can self-cross-link with soybean meal powder and co-cross-link with PAE resin, which accelerates the curing speed of the soybean-based adhesive and shortens the hot pressing time. Although the problem has been solved to a certain extent, when faced with lower ambient temperatures, especially in winter, in order to meet the needs of industrial production of enterprises, it has become a practical problem to obtain a castor oil-based waterborne polyurethane curing aid that can cure quickly at low temperatures, does not reduce hot pressing efficiency, and improves the stability of the bonding performance of artificial boards. Summary of the invention

[0005] The purpose of the present invention is to provide a castor oil-based waterborne polyurethane curing aid and a preparation method and application thereof in view of the deficiencies in the prior art.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing a castor oil-based waterborne polyurethane curing aid, comprising the following steps:

[0008] 1) subjecting dihydroxyacetone, a carboxylic acid anionic hydrophilic chain extender, isophorone diisocyanate and dibutyltin dilaurate to a first step reaction, and subjecting the first step reaction product to a second step reaction with castor oil to obtain a second step reaction product;

[0009] 2) the second step reaction product and the end-capping agent are subjected to an end-capping reaction, and the end-capping reaction product and triethylamine are subjected to a salt-forming reaction to obtain a prepolymer;

[0010] 3) The prepolymer and water are subjected to an emulsification reaction to obtain an aqueous polyurethane emulsion;

[0011] 4) The waterborne polyurethane emulsion is mixed with a cross-linking agent containing a hydrazide group to obtain a castor oil-based waterborne polyurethane curing aid.

[0012] Preferably, the mass ratio of isophorone diisocyanate to dihydroxyacetone is 9.46-12.62:1;

[0013] The mass ratio of isophorone diisocyanate to dibutyltin dilaurate is 51.36-58.68:1;

[0014] The mass ratio of isophorone diisocyanate to the blocking agent is 1.61 to 14.58:1;

[0015] The mass ratio of isophorone diisocyanate to triethylamine is 8.17-10.89:1;

[0016] The mass ratio of castor oil to carboxylic anionic hydrophilic chain extender is 38-43:5.3-6.3;

[0017] The mass ratio of isophorone diisocyanate to castor oil is 0.89-1.19:1.

[0018] Preferably, the temperature of the first step reaction in step 1) is 55-80°C, the time is 1-2h, and the speed is 200-400rpm;

[0019] The temperature of the second step reaction is 60-80° C., the time is 4-6 hours, and the rotation speed is 200-400 rpm.

[0020] Preferably, the temperature of the end-capping reaction in step 2) is 60-80°C, the time is 2-4h, and the rotation speed is 200-400rpm; the temperature of the salt-forming reaction is 30-40°C, the time is 0.5-1h, and the rotation speed is 100-300rpm.

[0021] Preferably, the solid content of the aqueous polyurethane emulsion in step 3) is 28-35%.

[0022] Preferably, the temperature of the emulsification reaction in step 3) is 20-30° C., the time is 0.5-1 h, and the rotation speed is 1800-2200 rpm.

[0023] Preferably, the molar ratio of the cross-linking agent containing a hydrazide group in step 4) to the dihydroxyacetone in step 1) is 0.8 to 1:1.

[0024] The present invention also provides a castor oil-based waterborne polyurethane curing aid prepared by the preparation method.

[0025] The present invention also provides the use of the castor oil-based waterborne polyurethane curing aid in a composite soybean-based adhesive, wherein the castor oil-based waterborne polyurethane curing aid and the soybean-based adhesive are mixed to obtain a composite soybean-based adhesive;

[0026] The mass ratio of the castor oil-based waterborne polyurethane curing aid to the soybean-based adhesive is 22-28:72-78.

[0027] The beneficial effects of the present invention include the following:

[0028] 1) In the present invention, a self-crosslinking castor oil-based waterborne polyurethane (CWPU) is added as an auxiliary crosslinking agent to the original soy-based adhesive (SA) formula, and the soy-based adhesive and the waterborne polyurethane curing agent are blended and used to form an interpenetrating network under the dual crosslinking network of the soy protein system and the polyurethane system, thereby constructing a dual curing system (SA / CWPU) composite soy-based adhesive. The dry bonding strength of the plywood pressed by the composite soybean-based adhesive reaches more than 2.25MPa, and the wet bonding strength reaches more than 1.31MPa, both of which meet the national standard requirement of 0.7MPa, and are 30-50% higher than that of the single-cure system soybean-based adhesive; the hot pressing time at a hot pressing temperature of 120°C is 3.5min, which is 20-30% shorter than that of the single-cure system soybean-based adhesive; the curing temperature within 4.5min of the hot pressing time is 100°C, which is 10-20°C lower than that of the single-cure system soybean-based adhesive, thereby achieving improved bonding strength of the composite soybean-based adhesive and improved cross-linking curing efficiency, effectively reducing the hot pressing energy consumption in the production process of wood-based panels and improving its overall production efficiency, adapting to low temperature climates, thereby forming a new generation of soybean-based adhesive core technology and promoting the wider application of soybean-based adhesives and their wood-based panel technologies.

[0029] 2) The present invention uses castor oil as a raw material for bio-based waterborne polyurethane, introduces a ketone-hydrazine structure into the waterborne polyurethane structure, and this structure can undergo a crosslinking reaction at room temperature under acidic or neutral conditions, thereby preparing a castor oil-based waterborne polyurethane that can self-crosslink at room temperature, and compounding it with a soybean-based adhesive as an auxiliary crosslinking agent to form a dual-curing crosslinking system, and effectively regulating the curing of the adhesive by controlling the pH value of the system, and being able to simultaneously take into account the low-temperature rapid curing and good storage stability of the soybean-based adhesive, in addition, the bonding performance has also been shown to have a synergistic effect, improve the bonding strength, improve the curing rate, shorten the hot pressing time, and reduce the hot pressing energy consumption of the artificial board, thereby forming a new generation of soybean-based adhesive core technology, and promoting the wider application of soybean-based adhesives and their artificial board technology. The use of the curing aid of the present invention can solve the practical problems of achieving stable bonding performance of artificial boards, rapid curing of adhesives at low temperatures, and not reducing the efficiency of hot pressing under the condition of reduced ambient temperature.

[0030] 3) The castor oil-based waterborne polyurethane curing aid of the present invention has the advantages of being easy to use, not generating wastewater or waste liquid during the synthesis process, significantly improving the cross-linking curing rate of the soybean-based adhesive, and requiring less usage. DETAILED DESCRIPTION

[0031] The present invention provides a method for preparing a castor oil-based waterborne polyurethane curing aid, comprising the following steps:

[0032] 1) subjecting dihydroxyacetone, a carboxylic acid anionic hydrophilic chain extender, isophorone diisocyanate and dibutyltin dilaurate to a first step reaction, and subjecting the first step reaction product to a second step reaction with castor oil to obtain a second step reaction product;

[0033] 2) the second step reaction product and the end-capping agent are subjected to an end-capping reaction, and the end-capping reaction product and triethylamine are subjected to a salt-forming reaction to obtain a prepolymer;

[0034] 3) The prepolymer and water are subjected to an emulsification reaction to obtain an aqueous polyurethane emulsion;

[0035] 4) The waterborne polyurethane emulsion is mixed with a cross-linking agent containing a hydrazide group to obtain a castor oil-based waterborne polyurethane curing aid.

[0036] In the present invention, the mass ratio of isophorone diisocyanate to dihydroxyacetone is preferably 9.46 to 12.62:1, more preferably 10.3 to 12:1, and more preferably 11:1;

[0037] The mass ratio of isophorone diisocyanate to dibutyltin dilaurate is preferably 51.36-58.68:1, more preferably 53-56:1, and more preferably 54-55:1;

[0038] The mass ratio of isophorone diisocyanate to the blocking agent is preferably 1.61 to 14.58:1. When the blocking agent is pentaerythritol triacrylate, the mass ratio of isophorone diisocyanate to the blocking agent is preferably 1.61 to 2.24:1; when the blocking agent is hydroxyethyl acrylate, the mass ratio of isophorone diisocyanate to the blocking agent is preferably 2.56 to 3.36:1; when the blocking agent is dihydroxyacetone, the mass ratio of isophorone diisocyanate to the blocking agent is preferably 6.58 to 14.58:1, and more preferably 8.65 to 10.7:1;

[0039] The mass ratio of isophorone diisocyanate to triethylamine is preferably 8.17 to 10.89:1, more preferably 8.5 to 10:1, and more preferably 9 to 9.5:1;

[0040] The mass ratio of the castor oil to the carboxylic anionic hydrophilic chain extender is preferably 38 to 43:

[0041] 5.3-6.3, more preferably 39-42:5.6-6.0, more preferably 40-41:5.7-5.8;

[0042] The mass ratio of isophorone diisocyanate to castor oil is preferably 0.89 to 1.19:1, more preferably 0.99 to 1.09:1, and even more preferably 1.02 to 1.05:1.

[0043] In the present invention, the carboxylic acid anionic hydrophilic chain extender preferably comprises 2,2-dihydroxymethylpropionic acid and / or 2,2-dihydroxymethylbutyric acid, the end-capping agent preferably comprises one or more of dihydroxyacetone, hydroxyethyl acrylate and pentaerythritol triacrylate, and the hydrazide-containing cross-linking agent preferably comprises one or more of adipic acid dihydrazide, isophthalic acid dihydrazide and succinic acid dihydrazide.

[0044] In the present invention, the temperature of the first step reaction in step 1) is preferably 55-80°C, more preferably 60-75°C, and more preferably 65-70°C; the time of the first step reaction is preferably 1-2h, and more preferably 1.5h; the speed of the first step reaction is preferably 200-400rpm, more preferably 250-350rpm, and more preferably 300rpm;

[0045] The temperature of the second step reaction is preferably 60-80°C, more preferably 65-75°C, and more preferably 70°C; the time of the second step reaction is preferably 4-6h, more preferably 4.5-5.5h, and more preferably 5h; the rotation speed of the second step reaction is preferably 200-400rpm, more preferably 250-350rpm, and more preferably 300rpm.

[0046] In the present invention, the temperature of the end-capping reaction in step 2) is preferably 60-80°C, more preferably 65-75°C, and more preferably 70°C; the time of the end-capping reaction is preferably 2-4h, more preferably 2.5-3.5h, and more preferably 3h; the rotation speed of the end-capping reaction is preferably 200-400rpm, more preferably 250-350rpm, and more preferably 300rpm; the temperature of the salt-forming reaction is preferably 30-40°C, more preferably 32-38°C, and more preferably 34-35°C; the time of the salt-forming reaction is preferably 0.5-1h, and more preferably 0.6-0.8h; the rotation speed of the salt-forming reaction is preferably 100-300rpm, more preferably 150-250rpm, and more preferably 200rpm.

[0047] In the present invention, the solid content of the aqueous polyurethane emulsion in step 3) is preferably 28-35%, more preferably 30-33%, and more preferably 31-32%.

[0048] In the present invention, the temperature of the emulsification reaction in step 3) is preferably 20-30°C, more preferably 22-28°C, and more preferably 24-25°C; the time of the emulsification reaction is preferably 0.5-1h, and more preferably 0.6-0.8h; the rotation speed of the emulsification reaction is preferably 1800-2200rpm, more preferably 1900-2100rpm, and more preferably 2000rpm.

[0049] In the present invention, the molar ratio of the cross-linking agent containing a hydrazide group in step 4) to the dihydroxyacetone in step 1) is preferably 0.8 to 1:1, more preferably 0.85 to 0.95:1, and more preferably 0.9:1.

[0050] The present invention also provides a castor oil-based waterborne polyurethane curing aid prepared by the preparation method.

[0051] The present invention also provides the use of the castor oil-based waterborne polyurethane curing aid in a composite soybean-based adhesive, wherein the castor oil-based waterborne polyurethane curing aid and the soybean-based adhesive are mixed to obtain a composite soybean-based adhesive;

[0052] The mass ratio of the castor oil-based waterborne polyurethane curing aid to the soybean-based adhesive is 22-28:72-78.

[0053] In the present invention, the mass ratio of the castor oil-based waterborne polyurethane curing aid to the soybean-based adhesive is preferably 24-26:74-76, and more preferably 25:75.

[0054] In the present invention, the composite soybean-based adhesive is used to prepare pressed plywood, and the pressed plywood has three layers, wherein the core board is glued on both sides, and the glue application amount of the composite soybean-based adhesive is preferably 190-210g of the composite soybean-based adhesive per square meter of the board, further preferably 195-205g, and more preferably 200g; the process of pressing the plywood is two-step pressing, which is pre-pressing and hot pressing in sequence; the pre-pressing veneer pressure is preferably 0.5-0.7MPa, and more preferably 0.6MPa; the pre-pressing time is preferably 28-32min, and more preferably 30min; the pre-pressing temperature is preferably room temperature; the hot pressing veneer pressure is preferably 0.5-0.7MPa, and more preferably 0.6MPa; the hot pressing time is preferably 100-120°C, and more preferably 105-115°C, and more preferably 110°C; the hot pressing time is preferably 3.5-4.5min, and more preferably 4min.

[0055] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0056] Example 1

[0057] In this embodiment, the mass ratio of isophorone diisocyanate and dihydroxyacetone is 11:1, the mass ratio of isophorone diisocyanate and dibutyltin dilaurate is 55:1, the mass ratio of isophorone diisocyanate and the end-capping agent hydroxyethyl acrylate is 3.36:1, the mass ratio of isophorone diisocyanate and triethylamine is 9.5:1, the mass ratio of castor oil and the carboxylic acid anionic hydrophilic chain extender 2,2-dihydroxymethylpropionic acid is 40:5.8, and the mass ratio of isophorone diisocyanate and castor oil is 1.05:1; the molar ratio of the hydrazide-containing cross-linking agent adipic acid dihydrazide and dihydroxyacetone is 0.9:1.

[0058] The first step reaction of dihydroxyacetone, 2,2-dihydroxymethylpropionic acid, isophorone diisocyanate and dibutyltin dilaurate is carried out at 70°C and 300 rpm for 1.5 hours. The first step reaction product and castor oil are carried out at 70°C and 300 rpm for 5 hours to obtain the second step reaction product. The second step reaction product and hydroxyethyl acrylate are subjected to end-capping reaction at 70°C and 300 rpm for 3 hours. The end-capping reaction product and triethylamine are subjected to salt-forming reaction at 35°C and 200 rpm for 0.8 hours to obtain a prepolymer.

[0059] After the prepolymer and distilled water are mixed, an emulsification reaction is carried out at 25° C. and a rotation speed of 2000 rpm for 0.8 h to obtain an aqueous polyurethane emulsion with a solid content of 32%; the aqueous polyurethane emulsion and adipic acid dihydrazide are mixed evenly to obtain a castor oil-based aqueous polyurethane curing aid.

[0060] Example 2

[0061] In this embodiment, the mass ratio of isophorone diisocyanate to dihydroxyacetone is 9.46:1, the mass ratio of isophorone diisocyanate to dibutyltin dilaurate is 51.36:1, the mass ratio of isophorone diisocyanate to the end-capping agent pentaerythritol triacrylate is 2.24:1, the mass ratio of isophorone diisocyanate to triethylamine is 8.17:1, the mass ratio of castor oil to the carboxylic anionic hydrophilic chain extender 2,2-dihydroxymethylbutyric acid is 43:6.3, and the mass ratio of isophorone diisocyanate to castor oil is 0.89:1; the molar ratio of the hydrazide-containing cross-linking agent isophthalic acid dihydrazide to dihydroxyacetone is 0.8:1.

[0062] The first step reaction of dihydroxyacetone, 2,2-dihydroxymethylbutyric acid, isophorone diisocyanate and dibutyltin dilaurate is carried out at 55°C and 200 rpm for 1 hour. The first step reaction product and castor oil are carried out at 60°C and 200 rpm for 6 hours to obtain the second step reaction product. The second step reaction product and pentaerythritol triacrylate are subjected to end-capping reaction at 60°C and 200 rpm for 4 hours. The end-capping reaction product and triethylamine are subjected to salt-forming reaction at 30°C and 300 rpm for 0.5 hours to obtain a prepolymer.

[0063] After the prepolymer and distilled water are mixed, an emulsification reaction is carried out at 30° C. and a rotation speed of 1800 rpm for 1 hour to obtain an aqueous polyurethane emulsion with a solid content of 30%; the aqueous polyurethane emulsion and isophthalic acid dihydrazide are mixed evenly to obtain a castor oil-based aqueous polyurethane curing aid.

[0064] Example 3

[0065] In this embodiment, the mass ratio of isophorone diisocyanate to dihydroxyacetone is 12.62:1, the mass ratio of isophorone diisocyanate to dibutyltin dilaurate is 58.68:1, the mass ratio of isophorone diisocyanate to the end-capping agent hydroxyethyl acrylate is 2.56:1, the mass ratio of isophorone diisocyanate to triethylamine is 10.89:1, the mass ratio of castor oil to the carboxylic acid anionic hydrophilic chain extender 2,2-dihydroxymethylpropionic acid is 38:5.3, and the mass ratio of isophorone diisocyanate to castor oil is 1.19:1; the molar ratio of the hydrazide-containing cross-linking agent succinic acid dihydrazide to dihydroxyacetone is 0.95:1.

[0066] The first step reaction of dihydroxyacetone, 2,2-dihydroxymethylpropionic acid, isophorone diisocyanate and dibutyltin dilaurate is carried out at 80°C and 400 rpm for 2 hours. The first step reaction product and castor oil are carried out at 80°C and 400 rpm for 4 hours to obtain the second step reaction product. The second step reaction product and hydroxyethyl acrylate are subjected to end-capping reaction at 80°C and 400 rpm for 2 hours. The end-capping reaction product and triethylamine are subjected to salt-forming reaction at 40°C and 100 rpm for 1 hour to obtain a prepolymer.

[0067] After the prepolymer and distilled water are mixed, an emulsification reaction is carried out at 20° C. and a rotation speed of 2200 rpm for 0.5 h to obtain an aqueous polyurethane emulsion with a solid content of 31%; the aqueous polyurethane emulsion and succinic acid dihydrazide are mixed evenly to obtain a castor oil-based aqueous polyurethane curing aid.

[0068] Example 4

[0069] In this embodiment, the mass ratio of isophorone diisocyanate and dihydroxyacetone (non-blocking agent) is 10.3:1, the mass ratio of isophorone diisocyanate and dibutyltin dilaurate is 53:1, the mass ratio of isophorone diisocyanate and the blocking agent (dihydroxyacetone) is 10.7:1, the mass ratio of isophorone diisocyanate and triethylamine is 8.5:1, the mass ratio of castor oil and carboxylic acid anionic hydrophilic chain extender 2,2-dihydroxymethylbutyric acid is 40:5.8, and the mass ratio of isophorone diisocyanate and castor oil is 0.99:1; the molar ratio of the hydrazide-containing cross-linking agent adipic acid dihydrazide and dihydroxyacetone is 0.85:1.

[0070] The first step reaction of dihydroxyacetone, 2,2-dihydroxymethylbutyric acid, isophorone diisocyanate and dibutyltin dilaurate is carried out at 65°C and 350 rpm for 1.5 hours. The first step reaction product and castor oil are carried out at 65°C and 300 rpm for 5 hours to obtain the second step reaction product. The second step reaction product and the end-capping agent are carried out at 75°C and 300 rpm for 3 hours. The end-capping reaction product and triethylamine are carried out at 35°C and 200 rpm for 0.8 hours to obtain a prepolymer.

[0071] After the prepolymer and distilled water are mixed, an emulsification reaction is carried out at 25° C. and a rotation speed of 2000 rpm for 0.8 h to obtain an aqueous polyurethane emulsion with a solid content of 33%; the aqueous polyurethane emulsion and adipic acid dihydrazide are evenly mixed to obtain a castor oil-based aqueous polyurethane curing aid.

[0072] The castor oil-based waterborne polyurethane curing aids of Examples 1 to 4 were mixed with soybean-based adhesives respectively, and the mass ratio of the castor oil-based waterborne polyurethane curing aids to the soybean-based adhesives was 25:75 to obtain a composite soybean-based adhesive, and the composite soybean-based adhesive was used to prepare three-layer plywood, and the amount of adhesive applied was 200g of composite soybean-based adhesive per square meter of board, wherein the core board was double-sidedly glued. Pressing the plywood was divided into two steps, the first step was pre-pressing at room temperature, the pressure of the single board was 0.6MPa, and the pre-pressing time was 30min, and the second step was hot pressing, the pressure of the single board was 0.6MPa, the temperature was 100°C, and the hot pressing time was 4.5min (or the hot pressing temperature was 120°C, and the hot pressing time was 3.5min).

[0073] The dry bonding strengths of the plywood pressed by the composite soy-based adhesive of Examples 1 to 4 are 2.35 MPa, 2.25 MPa, 2.25 MPa, and 2.3 MPa, respectively, and the wet bonding strengths are 1.35 MPa, 1.31 MPa, 1.32 MPa, and 1.33 MPa, respectively, all of which meet the national standard requirement of 0.7 MPa, and are 30-50% higher than that of the single-cure soy-based adhesive; the hot pressing time at a hot pressing temperature of 120°C is 3.5 min, which is 20-30% shorter than that of the single-cure soy-based adhesive; the curing temperature within the hot pressing time of 4.5 min is 100°C, which is 10-20°C lower than that of the single-cure soy-based adhesive, thereby achieving an improvement in the bonding strength of the composite soy-based adhesive and an improvement in the cross-linking curing efficiency.

[0074] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. Application of a castor oil-based waterborne polyurethane curing aid in a composite soybean-based adhesive, characterized in that: Mixing a castor oil-based waterborne polyurethane curing aid and a soybean-based adhesive to obtain a composite soybean-based adhesive; The mass ratio of the castor oil-based waterborne polyurethane curing aid to the soybean-based adhesive is 22-28:72-78; The preparation method of castor oil-based waterborne polyurethane curing aid comprises the following steps: 1) performing a first step reaction on dihydroxyacetone, a carboxylic acid anionic hydrophilic chain extender, isophorone diisocyanate and dibutyltin dilaurate, and performing a second step reaction on the first step reaction product and castor oil to obtain a second step reaction product; 2) The product of the second step reaction and the end-capping agent undergo an end-capping reaction, and the end-capping reaction product and triethylamine undergo a salt-forming reaction to obtain a prepolymer; 3) The prepolymer and water undergo emulsification reaction to obtain a waterborne polyurethane emulsion; 4) The waterborne polyurethane emulsion and the cross-linking agent containing a hydrazide group are mixed to obtain a castor oil-based waterborne polyurethane curing aid.

2. The use according to claim 1, characterized in that: The mass ratio of isophorone diisocyanate to dihydroxyacetone is 9.46-12.62:1; The mass ratio of isophorone diisocyanate to dibutyltin dilaurate is 51.36-58.68:1; The mass ratio of isophorone diisocyanate to the blocking agent is 1.61-14.58:1; The mass ratio of isophorone diisocyanate to triethylamine is 8.17-10.89:1; The mass ratio of castor oil to carboxylic anionic hydrophilic chain extender is 38-43:5.3-6.3; The mass ratio of isophorone diisocyanate to castor oil is 0.89-1.19:

1.

3. The use according to claim 1 or 2, characterized in that: Step 1) The temperature of the first step reaction is 55-80°C, the time is 1-2h, and the speed is 200-400rpm; The temperature of the second step reaction is 60-80°C, the time is 4-6h, and the rotation speed is 200-400rpm.

4. The use according to claim 3, characterized in that: Step 2) The end-capping reaction is carried out at a temperature of 60-80°C, a time of 2-4 hours, and a rotation speed of 200-400 rpm; the salt-forming reaction is carried out at a temperature of 30-40°C, a time of 0.5-1 hour, and a rotation speed of 100-300 rpm.

5. The use according to claim 4, characterized in that: Step 3) The solid content of the aqueous polyurethane emulsion is 28-35%.

6. The use according to claim 5, characterized in that: Step 3) The temperature of the emulsification reaction is 20-30°C, the time is 0.5-1h, and the rotation speed is 1800-2200rpm.

7. The use according to any one of claims 4 to 6, characterized in that: The molar ratio of the cross-linking agent containing a hydrazide group in step 4) to the dihydroxyacetone in step 1) is 0.8-1:1.