Multipurpose solvent-free polyurethane coating and preparation method thereof

Abstract

The invention discloses a multipurpose solvent-free polyurethane coating and a preparation method thereof, and belongs to the technical field of coatings. The multipurpose solvent-free polyurethane coating comprises a component A and a component B, the component A is prepared from the following raw materials in parts by weight: 25 to 40 parts of hydroxyl-terminated polyurethane prepolymer emulsion, 0.1 to 2 parts of coalescing agent, 0.1 to 2 parts of flatting agent, 0.5 to 2 parts of composite modifier and 0.5 to 1 part of adipic dihydrazide; the component B comprises a water-based blocked isocyanate curing agent; the weight ratio of the component A to the component B is 3: (0.5-1.5); wherein the composite modifier comprises phytate intercalated hydrotalcite and nano boron nitride in a mass ratio of (1.5-3): 1. A coating prepared from the multipurpose solvent-free polyurethane coating has excellent mechanical property, salt fog resistance and corrosion resistance, meanwhile, the coating has good adhesive force with a base material, and the multipurpose solvent-free polyurethane coating can be used for multipurpose scenes.

Description

Technical Field

[0001] The invention belongs to the technical field of coatings, and particularly relates to a multi-purpose solvent-free polyurethane coating and a preparation method thereof. Background Art

[0002] Polyurethane coatings are a common type of coating with excellent properties such as wear resistance, flexibility, adhesion and chemical resistance. They are widely used as wood coatings, architectural coatings, automotive paints and waterproof coatings.

[0003] Current polyurethane coatings primarily include solvent-based and solvent-free polyurethane coatings. Solvent-based polyurethane coatings contain large amounts of organic solvents, which can severely pollute the environment. Solvent evaporation during the curing process can cause pinholes on the coating surface, impacting the coating's corrosion resistance and shielding properties. Solvent-free polyurethane coatings, however, lack solvents and avoid the drawbacks of solvent evaporation during the curing process. However, when used at lower temperatures, their mechanical properties, such as impact resistance and bending resistance, are relatively poor. Furthermore, commonly used solvent-free polyurethane coatings lack good application performance.

[0004] Patent CN101407693B discloses a room-temperature curing solvent-free polyurethane waterproof coating and its preparation method. The coating consists of a prepolymer component A, which includes 2,4-toluene diisocyanate, a polyether diol, a polyether triol, stannous octoate, and H₃PO₄; and a curing agent component B, which includes a polyester diol, a reactive diluent, liquid and solid chain extenders, CaSO₄ whiskers, iron oxide red, a plasticizer, and additives. Components A and B are mixed in a mass ratio of 2:1 to 1:2 and applied to the film. The polypropylene oxide polyol, obtained by anionic ring-opening polymerization, has secondary terminal hydroxyl groups, which easily react with trace amounts of water remaining in component A or atmospheric moisture to produce bubbles, thus affecting the coating's performance. Furthermore, the solvent-free polyurethane coating exhibits poor corrosion resistance. Summary of the Invention

[0005] In view of the deficiencies of the prior art, the object of the present invention is to provide a multi-purpose solvent-free polyurethane coating and a preparation method thereof. The coating prepared from the multi-purpose solvent-free polyurethane coating has excellent mechanical properties, salt spray resistance and corrosion resistance. At the same time, the coating has good adhesion to the substrate and can be used in multi-purpose scenarios.

[0006] To achieve the above-mentioned object, according to one aspect of the present invention, a multi-purpose solvent-free polyurethane coating is provided, comprising a component A and a component B; the component A comprises the following raw materials in parts by weight: 25-40 parts of a hydroxyl-terminated polyurethane prepolymer emulsion, 0.1-2 parts of a film-forming aid, 0.1-2 parts of a leveling agent, 0.5-2 parts of a composite modifier, and 0.5-1 parts of adipic acid dihydrazide; the component B comprises a water-based blocked isocyanate curing agent; the weight ratio of the component A to the component B is 3:(0.5-1.5); wherein the composite modifier comprises phytate-intercalated hydrotalcite and nano-boron nitride in a mass ratio of (1.5-3):1.

[0007] In the present invention, the multi-purpose solvent-free polyurethane coating comprises component A and component B. In component A, the weight percentage of the hydroxyl-terminated polyurethane prepolymer emulsion is 25-40 parts. It is understood that the weight percentage can be any specific value of 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40, or any value within the range of 25-40 parts. In the present invention, the solid content of the hydroxyl-terminated polyurethane prepolymer emulsion is 30-40%. It is understood that the solid content can be any specific value of 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40%, or any value within the range of 30-40%.

[0008] The hydroxyl-terminated polyurethane prepolymer emulsion is prepared by prepolymerizing 2,4-toluene diisocyanate, PTMG1000, dimethylolpropionic acid, 4,4'-dihydroxybenzophenone, and linoleic acid glycerol, adding acetone to adjust viscosity, neutralizing, cooling, and emulsifying the mixture with deionized water, followed by removal of the acetone to obtain the hydroxyl-terminated polyurethane prepolymer emulsion. In the present invention, the PTMG1000 is poly(1,4-butylene glycol) with a number average molecular weight of 1000.

[0009] In the present invention, the mass ratio of the 2,4-toluene diisocyanate, PTMG1000, dimethylol propionic acid, 4,4'-dihydroxybenzophenone and linoleic acid glyceride is 10-12:4:1:1:4.

[0010] The inventors discovered that in the system of the present invention, a triple curing effect is achieved by compounding a specific hydroxyl-terminated polyurethane prepolymer emulsion, adipic acid dihydrazide, and a water-based blocked isocyanate curing agent, further improving the mechanical strength and corrosion resistance of the coating. On the one hand, the molecular chain of the hydroxyl-terminated polyurethane prepolymer of the present invention contains ketone carbonyl groups, hydroxyl groups, and double bonds. The ketone carbonyl groups first undergo a cross-linking reaction with adipic acid dihydrazide. The water-based blocked isocyanate curing agent contains multiple isocyanate groups. The isocyanate groups react with the hydroxyl groups to form urea groups, which in turn react with the isocyanate groups to achieve cross-linking and curing. As the curing time increases, the double bonds on the hydroxyl-terminated polyurethane prepolymer molecular chain come into contact with oxygen in the air, causing oxidative curing of the double bonds, thereby further increasing the degree of cross-linking of the coating, further improving the mechanical strength, corrosion resistance, and salt spray resistance of the coating.

[0011] In the present invention, the weight percentage of the film-forming aid in component A is 0.1-2 parts. It is understood that the weight percentage can be any specific value among 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, or any value within the range of 0.1-2 parts. In the present invention, the film-forming aid is a dodecyl alcohol ester.

[0012] In the present invention, the weight percentage of the leveling agent in component A is 0.1-2 parts. It can be understood that the weight percentage can be any specific value among 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, or any value within the range of 0.1-2 parts. In the present invention, the leveling agent is a polyether-modified organosiloxane.

[0013] In the present invention, the weight percentage of the composite modifier in component A is 0.5-2 parts. It is understood that the weight percentage can be any specific value among 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2, or any value within the range of 0.5-2 parts. In the present invention, the composite modifier comprises phytate-intercalated hydrotalcite and nano-boron nitride in a mass ratio of (1.5-3):1. It is understood that the mass ratio can be any specific value among 1.5:1, 2:1, 2.5:1, or 3:1, or any value within the range of (1.5-3):1.

[0014] The inventors discovered that adding a composite modifier consisting of phytate-intercalated hydrotalcite and nano-boron nitride to the coating system of the present invention creates a synergistic effect, resulting in a coating with both excellent barrier properties and active corrosion protection. The uniform filling of the nano-boron nitride with a specific size within the unique layered structure of the phytate-intercalated hydrotalcite gives the coating excellent barrier properties. Furthermore, the layered structure slowly releases phytate, which chelates with iron ions to form an insoluble protective layer, thereby enhancing the coating's corrosion and salt spray resistance.

[0015] In the present invention, the preparation method of the phytate intercalated hydrotalcite comprises the following steps: adding magnesium nitrate hexahydrate, aluminum nitrate nonahydrate and sodium nitrate to deionized water and mixing them uniformly; adjusting the pH value of the solution to 8.2-8.5; reacting at 110-120° C. for 12-24 hours; washing; and drying to obtain the nitrate intercalated hydrotalcite; and dissolving sodium phytate in deionized water, adding the nitrate intercalated hydrotalcite and mixing them uniformly; reacting at 90-95° C. for 16-20 hours under a nitrogen atmosphere; centrifuging and filtering; and drying to obtain the phytate intercalated hydrotalcite.

[0016] In the present invention, the median particle size D of the nano boron nitride is 50 The present invention controls the particle size of nano-boron nitride to ensure that it is evenly dispersed within the unique layered structure of phytate-intercalated hydrotalcite, achieving optimal synergistic effects. If the particle size of the nano-boron nitride is too large, it will not be evenly dispersed within the unique layered structure of phytate-intercalated hydrotalcite, reducing the synergistic effect. If the particle size of the nano-boron nitride is too small, it will agglomerate, resulting in poor overall performance of the coating.

[0017] In the present invention, in the component A, the weight portion of adipic acid dihydrazide is 0.5-1 part. It can be understood that the weight portion can be any specific value among 0.5, 0.6, 0.7, 0.8, 0.9, 1 or any value within the range of 0.5-1 part.

[0018] In the present invention, the B component includes a water-based blocked isocyanate curing agent. Preferably, the water-based blocked isocyanate curing agent includes BI-40 and BI-70.

[0019] In the present invention, the weight ratio of component A to component B is 3:(0.5-1.5). It is understandable that the weight ratio can be any specific value of 3:0.5, 3:1, 3:1.5 or any value within the range of 3:(0.5-1.5).

[0020] The inventors also found that the contents of the hydroxyl-terminated polyurethane prepolymer emulsion, adipic acid dihydrazide and water-based blocked isocyanate curing agent in the system need to be strictly controlled. When the amount of water-based blocked isocyanate curing agent added is too high, the isocyanate group reacts with the hydroxyl group to form a urea group, and the urea group forms a hydrogen bond with H2O, causing the volatilization of H2O in the system to slow down, and the cross-linking reaction between the ketone carbonyl group and adipic acid dihydrazide is inhibited, resulting in deterioration of the mechanical properties and corrosion resistance of the coating.

[0021] According to one aspect of the present invention, there is also provided a method for preparing the multi-purpose solvent-free polyurethane coating described in any one of the above items, comprising the following steps: (1) Preparing a hydroxyl-terminated polyurethane prepolymer emulsion: prepolymerizing 2,4-toluene diisocyanate, PTMG1000, dihydroxymethyl propionic acid, 4,4'-dihydroxybenzophenone and linoleic acid glyceride, adding acetone to adjust the viscosity, neutralizing, cooling, adding deionized water for emulsification, and removing acetone to obtain the hydroxyl-terminated polyurethane prepolymer emulsion; (2) preparing a composite modifier: mixing the phytate intercalated hydrotalcite and nano boron nitride in proportion and stirring evenly to obtain the composite modifier; (3) mixing the hydroxyl-terminated polyurethane prepolymer emulsion, film-forming aid, leveling agent and composite modifier, adding adipic acid dihydrazide and stirring evenly to obtain component A; (4) Component A and component B are mixed in proportion to obtain the multi-purpose solvent-free polyurethane coating.

[0022] In the present invention, in step (1), a hydroxyl-terminated polyurethane prepolymer emulsion is prepared by prepolymerizing 2,4-toluene diisocyanate, PTMG1000, dimethylol propionic acid, 4,4'-dihydroxybenzophenone, and linoleic acid glyceride, adding acetone to adjust the viscosity, neutralizing, cooling, adding deionized water for emulsification, and removing acetone to obtain the hydroxyl-terminated polyurethane prepolymer emulsion. In the present invention, the mass ratio of 2,4-toluene diisocyanate, PTMG1000, dimethylol propionic acid, 4,4'-dihydroxybenzophenone, and linoleic acid glyceride is 10-12:4:1:1:4. In the present invention, the prepolymerization reaction temperature is 75-80°C, and the prepolymerization reaction time is 3-4h. In the present invention, the neutralization is performed by using triethylamine to neutralize to a neutralization degree of 100%.

[0023] In the present invention, in step (2), a composite modifier is prepared: the phytate intercalated hydrotalcite and nano boron nitride are mixed in proportion and stirred evenly to obtain the composite modifier. In the present invention, the preparation method of the phytate intercalated hydrotalcite is as follows: magnesium nitrate hexahydrate, aluminum nitrate nonahydrate and sodium nitrate are added to deionized water and mixed evenly, the pH value of the solution is adjusted to 8.2-8.5, the reaction is carried out at 110-120°C for 12-24 hours, washed, and dried to obtain nitrate intercalated hydrotalcite; sodium phytate is dissolved in deionized water, the nitrate intercalated hydrotalcite is added and mixed evenly, the reaction is carried out at 90-95°C under a nitrogen atmosphere for 16-20 hours, centrifuged and dried to obtain the phytate intercalated hydrotalcite. Preferably, the mass ratio of the magnesium nitrate hexahydrate, aluminum nitrate nonahydrate and sodium nitrate is 6: (4-5): 1. Preferably, the mass ratio of the sodium phytate and sodium nitrate is (10-11): 1. Preferably, the washing is performed using deionized water.

[0024] In the present invention, in step (3), the hydroxyl-terminated polyurethane prepolymer emulsion, film-forming aid, leveling agent and composite modifier are mixed, adipic acid dihydrazide is added, and stirred evenly to obtain component A.

[0025] In the present invention, in step (4), component A and component B are mixed in proportion to obtain the multi-purpose solvent-free polyurethane coating.

[0026] According to one aspect of the present invention, there is also provided a use of the multi-purpose solvent-free polyurethane coating described above or the multi-purpose solvent-free polyurethane coating prepared according to the above preparation method in exterior coating of industrial products.

[0027] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention achieves a triple curing effect by compounding a specific hydroxyl-terminated polyurethane prepolymer emulsion, adipic acid dihydrazide and a water-based blocked isocyanate curing agent, thereby further improving the mechanical strength and corrosion resistance of the coating. On the one hand, the molecular chain of the hydroxyl-terminated polyurethane prepolymer of the present invention contains ketone carbonyl groups, hydroxyl groups and double bonds. The ketone carbonyl groups first undergo a cross-linking reaction with adipic acid dihydrazide. The water-based blocked isocyanate curing agent contains multiple isocyanate groups. The isocyanate groups react with the hydroxyl groups to form urea groups, which in turn react with the isocyanate groups to achieve cross-linking and curing. As the curing time increases, the double bonds on the hydroxyl-terminated polyurethane prepolymer molecular chain come into contact with oxygen in the air to cause oxidative curing of the double bonds, thereby further increasing the cross-linking degree of the coating, thereby further improving the mechanical strength, corrosion resistance and salt spray resistance of the coating.

[0028] (2) The present invention adds a composite modifier composed of phytate-intercalated hydrotalcite and nano-boron nitride to the coating system of the present invention. The two synergistically enhance the performance of the coating, resulting in an excellent barrier effect and active corrosion protection. On the one hand, the nano-boron nitride is evenly filled in the unique layered structure of the phytate-intercalated hydrotalcite, giving the coating excellent barrier properties. At the same time, the layered structure can slowly release phytate, which chelates with iron ions to form an insoluble protective layer, thereby improving the corrosion resistance and salt spray resistance of the coating.

[0029] (3) The present invention also provides a method for preparing a multi-purpose solvent-free polyurethane coating, which is simple to operate and convenient for industrial production. DETAILED DESCRIPTION

[0030] To facilitate understanding of the features and effects of the present invention by those skilled in the art, the following provides a general description and definition of the terms and expressions used in the specification and claims. Unless otherwise indicated, all technical and scientific terms used herein have the ordinary meanings as understood by those skilled in the art regarding the present invention. In the event of conflict, the definitions in this specification shall prevail.

[0031] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0032] Herein, when describing embodiments or examples, it should be understood that they are not intended to limit the present invention to these embodiments or examples. On the contrary, all alternatives, modifications and equivalents of the methods and materials described herein are encompassed within the scope defined by the claims.

[0033] In this document, for the sake of brevity, not all possible combinations of the various technical features in each embodiment or example are described. Therefore, as long as there are no contradictions in the combination of these technical features, the various technical features in each embodiment or example can be combined in any way, and all possible combinations should be considered to be within the scope of this specification.

[0034] The invention provides a multi-purpose solvent-free polyurethane coating, comprising a component A and a component B; the component A comprises the following raw materials in parts by weight: 25-40 parts of a hydroxyl-terminated polyurethane prepolymer emulsion, 0.1-2 parts of a film-forming aid, 0.1-2 parts of a leveling agent, 0.5-2 parts of a composite modifier, and 0.5-1 parts of adipic acid dihydrazide; the component B comprises a water-based blocked isocyanate curing agent; the weight ratio of the component A to the component B is 3:(0.5-1.5); wherein the composite modifier comprises phytate-intercalated hydrotalcite and nano-boron nitride in a mass ratio of (1.5-3):1.

[0035] In some embodiments, the solid content of the hydroxyl-terminated polyurethane prepolymer emulsion is 30-40%.

[0036] In some embodiments, the film-forming aid is lauryl alcohol ester.

[0037] In some embodiments, the leveling agent is polyether-modified organosiloxane.

[0038] In some embodiments, the preparation method of the hydroxyl-terminated polyurethane prepolymer emulsion is: prepolymerizing 2,4-toluene diisocyanate, PTMG1000, dihydroxymethylpropionic acid, 4,4'-dihydroxybenzophenone and linoleic acid glyceride, adding acetone to adjust the viscosity, neutralizing, cooling, adding deionized water for emulsification, and removing acetone to obtain the hydroxyl-terminated polyurethane prepolymer emulsion.

[0039] In some embodiments, the mass ratio of the 2,4-toluene diisocyanate, PTMG1000, dimethylol propionic acid, 4,4'-dihydroxybenzophenone and linoleic acid glyceride is 10-12:4:1:1:4.

[0040] In some embodiments, the preparation method of the phytate intercalated hydrotalcite is as follows: magnesium nitrate hexahydrate, aluminum nitrate nonahydrate and sodium nitrate are added to deionized water and mixed evenly, the pH value of the solution is adjusted to 8.2-8.5, reacted at 110-120°C for 12-24 hours, washed, and dried to obtain nitrate intercalated hydrotalcite; sodium phytate is dissolved in deionized water, added to the nitrate intercalated hydrotalcite and mixed evenly, kept warm at 90-95°C under a nitrogen atmosphere for 16-20 hours, centrifuged and filtered, and dried to obtain the phytate intercalated hydrotalcite.

[0041] In some embodiments, the median particle size D of the nano boron nitride is 50 80-200nm.

[0042] According to one aspect of the present invention, there is also provided a method for preparing the multi-purpose solvent-free polyurethane coating described in any one of the above items, comprising the following steps: (1) Preparing a hydroxyl-terminated polyurethane prepolymer emulsion: prepolymerizing 2,4-toluene diisocyanate, PTMG1000, dihydroxymethyl propionic acid, 4,4'-dihydroxybenzophenone and linoleic acid glyceride, adding acetone to adjust the viscosity, neutralizing, cooling, adding deionized water for emulsification, and removing acetone to obtain the hydroxyl-terminated polyurethane prepolymer emulsion; (2) preparing a composite modifier: mixing the phytate intercalated hydrotalcite and nano boron nitride in proportion and stirring evenly to obtain the composite modifier; (3) mixing the hydroxyl-terminated polyurethane prepolymer emulsion, film-forming aid, leveling agent and composite modifier, adding adipic acid dihydrazide and stirring evenly to obtain component A; (4) Component A and component B are mixed in proportion to obtain the multi-purpose solvent-free polyurethane coating.

[0043] According to one aspect of the present invention, there is also provided a use of any of the multi-purpose solvent-free polyurethane coatings described above or the multi-purpose solvent-free polyurethane coatings prepared according to the above preparation method in exterior coating of industrial products.

[0044] The present invention will be described in detail below by way of examples. It should be understood that the following examples are only used to further explain and illustrate the present invention, and are not intended to limit the present invention.

[0045] The chemical additives used in the examples and comparative examples of the present invention are all commercially available, and their specific information is as follows: Magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, sodium nitrate, triethylamine, and adipic acid dihydrazide were purchased from Aladdin Reagent Co., Ltd.; sodium phytate was purchased from Shandong Fengtai Biotechnology Co., Ltd.; water-based blocked isocyanate curing agent: BI-40 was purchased from Shaoguan Dongsen Synthetic Materials Co., Ltd.; nano-boron nitride: median particle size D 50 The nanostructured organic siloxane is 80-200 nm and was purchased from Jiangsu Napu Material Technology Co., Ltd.; the dodecanol ester is purchased from Runtai New Materials Co., Ltd.; and the polyether-modified organic siloxane: RH-T1245 is purchased from Ningbo Runhe High-tech Materials Technology Co., Ltd.

[0046] Preparation Example 1: Phytate-intercalated hydrotalcite The preparation method of the phytate intercalated hydrotalcite described in this preparation example is as follows: 6 g of magnesium nitrate hexahydrate, 4.5 g of aluminum nitrate nonahydrate and 1 g of sodium nitrate are added to 200 mL of deionized water and mixed evenly, the pH value of the solution is adjusted to 8.4, the reaction is carried out at 110°C for 24 hours, the solution is washed with deionized water, and the solution is dried to obtain nitrate intercalated hydrotalcite; 10 g of sodium phytate is dissolved in 200 mL of deionized water, the nitrate intercalated hydrotalcite is added and mixed evenly, the reaction is carried out at 90°C under a nitrogen atmosphere for 20 hours, the solution is centrifuged and filtered, and the solution is dried to obtain the phytate intercalated hydrotalcite C1.

[0047] Preparation Example 2: Phytate-intercalated hydrotalcite The preparation method of the phytate intercalated hydrotalcite described in this preparation example is as follows: 6 g of magnesium nitrate hexahydrate, 4 g of aluminum nitrate nonahydrate and 1 g of sodium nitrate are added to deionized water and mixed evenly, the pH value of the solution is adjusted to 8.2, the reaction is carried out at 120°C for 12 hours, the mixture is washed with deionized water, and the mixture is dried to obtain nitrate intercalated hydrotalcite; 11 g of sodium phytate is dissolved in 200 mL of deionized water, the nitrate intercalated hydrotalcite is added and mixed evenly, the mixture is kept warm at 95°C for 16 hours under a nitrogen atmosphere, the mixture is centrifuged and dried to obtain the phytate intercalated hydrotalcite C2.

[0048] Preparation Example 3: Phytate-intercalated hydrotalcite The preparation method of the phytate intercalated hydrotalcite described in this preparation example is as follows: 6 g of magnesium nitrate hexahydrate, 5 g of aluminum nitrate nonahydrate and 1 g of sodium nitrate are added to deionized water and mixed evenly, the pH value of the solution is adjusted to 8.5, the reaction is carried out at 120°C for 12 hours, the mixture is washed with deionized water, and the mixture is dried to obtain nitrate intercalated hydrotalcite; 10.5 g of sodium phytate is dissolved in 200 mL of deionized water, the nitrate intercalated hydrotalcite is added and mixed evenly, the mixture is kept warm at 95°C for 16 hours under a nitrogen atmosphere, the mixture is centrifuged and dried to obtain the phytate intercalated hydrotalcite C3.

[0049] Example 1 A multi-purpose solvent-free polyurethane coating described in this embodiment includes component A and component B; component A includes the following raw materials in parts by weight: 30 parts of a terminal hydroxyl polyurethane prepolymer emulsion, 1 part of a film-forming aid, 0.5 part of a leveling agent, 1.5 parts of a composite modifier, and 0.8 part of adipic acid dihydrazide; component B includes a water-based blocked isocyanate curing agent; the weight ratio of component A to component B is 3:1; wherein the composite modifier includes phytate-intercalated hydrotalcite C1 and nano-boron nitride in a mass ratio of 2:1; the solid content of the terminal hydroxyl polyurethane prepolymer emulsion is 35%; the film-forming aid is dodecyl alcohol ester; and the leveling agent is a polyether-modified organosiloxane.

[0050] The method for preparing the multi-purpose solvent-free polyurethane coating described in this embodiment comprises the following steps: (1) Preparation of a hydroxyl-terminated polyurethane prepolymer emulsion: 11 g of 2,4-toluene diisocyanate, 4 g of PTMG1000, 1 g of dihydroxymethylpropionic acid, 1 g of 4,4'-dihydroxybenzophenone and 4 g of linoleic acid glyceride were subjected to a prepolymerization reaction at 80°C for 3 h, acetone was added to adjust the viscosity, triethylamine was added to neutralize to a neutralization degree of 100%, deionized water was added to emulsify after cooling, and acetone was removed to obtain the hydroxyl-terminated polyurethane prepolymer emulsion; (2) Preparing a composite modifier: mixing the phytate-intercalated hydrotalcite C1 and nano-boron nitride in proportion and stirring evenly to obtain the composite modifier; (3) mixing the hydroxyl-terminated polyurethane prepolymer emulsion, film-forming aid, leveling agent and composite modifier, adding adipic acid dihydrazide and stirring evenly to obtain component A; (4) Component A and component B are mixed in proportion to obtain the multi-purpose solvent-free polyurethane coating.

[0051] Example 2 The multi-purpose solvent-free polyurethane coating described in this embodiment includes component A and component B; the component A includes the following raw materials in parts by weight: 25 parts of terminal hydroxyl polyurethane prepolymer emulsion, 0.1 part of film-forming agent, 0.1 part of leveling agent, 0.5 part of composite modifier and 0.5 part of adipic acid dihydrazide; the component B includes a water-based blocked isocyanate curing agent; the weight ratio of the components A to B is 3:0.5; wherein the composite modifier includes phytate-intercalated hydrotalcite C2 and nano-boron nitride in a mass ratio of 1.5:1; the solid content of the terminal hydroxyl polyurethane prepolymer emulsion is 40%; the film-forming agent is dodecyl alcohol ester; and the leveling agent is polyether-modified organosiloxane.

[0052] The method for preparing the multi-purpose solvent-free polyurethane coating described in this embodiment comprises the following steps: (1) Preparation of a hydroxyl-terminated polyurethane prepolymer emulsion: 10 g of 2,4-toluene diisocyanate, 4 g of PTMG1000, 1 g of dihydroxymethylpropionic acid, 1 g of 4,4'-dihydroxybenzophenone and 4 g of linoleic acid glyceride were subjected to a prepolymerization reaction at 75°C for 4 h, acetone was added to adjust the viscosity, triethylamine was added to neutralize to a neutralization degree of 100%, deionized water was added to emulsify after cooling, and acetone was removed to obtain the hydroxyl-terminated polyurethane prepolymer emulsion; (2) Preparing a composite modifier: mixing the phytate-intercalated hydrotalcite C2 and nano-boron nitride in proportion and stirring evenly to obtain the composite modifier; (3) mixing the hydroxyl-terminated polyurethane prepolymer emulsion, film-forming aid, leveling agent and composite modifier, adding adipic acid dihydrazide and stirring evenly to obtain component A; (4) Component A and component B are mixed in proportion to obtain the multi-purpose solvent-free polyurethane coating.

[0053] Example 3 The multi-purpose solvent-free polyurethane coating described in this embodiment includes component A and component B; the component A includes the following raw materials in parts by weight: 40 parts of a terminal hydroxyl polyurethane prepolymer emulsion, 2 parts of a film-forming aid, 2 parts of a leveling agent, 2 parts of a composite modifier, and 1 part of adipic acid dihydrazide; the component B includes a water-based blocked isocyanate curing agent; the weight ratio of component A to component B is 3:1.5; wherein the composite modifier includes phytate-intercalated hydrotalcite C3 and nano-boron nitride in a mass ratio of 3:1; the solid content of the terminal hydroxyl polyurethane prepolymer emulsion is 30%; the film-forming aid is dodecyl alcohol ester; and the leveling agent is a polyether-modified organosiloxane.

[0054] The method for preparing the multi-purpose solvent-free polyurethane coating described in this embodiment comprises the following steps: (1) Preparation of a hydroxyl-terminated polyurethane prepolymer emulsion: 12 g of 2,4-toluene diisocyanate, 4 g of PTMG1000, 1 g of dihydroxymethylpropionic acid, 1 g of 4,4'-dihydroxybenzophenone and 4 g of linoleic acid glyceride were subjected to a prepolymerization reaction at 80°C for 3.5 h, acetone was added to adjust the viscosity, triethylamine was added to neutralize to a neutralization degree of 100%, deionized water was added to emulsify after cooling, and acetone was removed to obtain the hydroxyl-terminated polyurethane prepolymer emulsion; (2) Preparing a composite modifier: mixing the phytate-intercalated hydrotalcite C3 and nano-boron nitride in proportion and stirring evenly to obtain the composite modifier; (3) mixing the hydroxyl-terminated polyurethane prepolymer emulsion, film-forming aid, leveling agent and composite modifier, adding adipic acid dihydrazide and stirring evenly to obtain component A; (4) Component A and component B are mixed in proportion to obtain the multi-purpose solvent-free polyurethane coating.

[0055] Comparative Example 1 The preparation method of the multi-purpose solvent-free polyurethane coating of this comparative example is exactly the same as that of Example 1, except that the preparation method of the hydroxyl-terminated polyurethane prepolymer emulsion is as follows: 11 g of 2,4-toluene diisocyanate, 4 g of PTMG1000, 1 g of dihydroxymethylpropionic acid and 4 g of linoleic acid glyceride are prepolymerized at 80° C. for 3 h, acetone is added to adjust the viscosity, triethylamine is added to neutralize to a neutralization degree of 100%, deionized water is added after cooling to emulsify, and acetone is removed to obtain the hydroxyl-terminated polyurethane prepolymer emulsion.

[0056] Comparative Example 2 The preparation method of the multi-purpose solvent-free polyurethane coating of this comparative example is exactly the same as that of Example 1, except that the preparation method of the hydroxyl-terminated polyurethane prepolymer emulsion is as follows: 11 g of 2,4-toluene diisocyanate, 4 g of PTMG1000, 1 g of dihydroxymethylpropionic acid and 1 g of 4,4'-dihydroxybenzophenone are prepolymerized at 80° C. for 3 h, acetone is added to adjust the viscosity, triethylamine is added to neutralize to a neutralization degree of 100%, deionized water is added after cooling to emulsify, and acetone is removed to obtain the hydroxyl-terminated polyurethane prepolymer emulsion.

[0057] Comparative Example 3 The preparation method of the multi-purpose solvent-free polyurethane coating of this comparative example is exactly the same as that of Example 1, with the only difference being that the weight ratio of component A to component B is 3:2.

[0058] Comparative Example 4 The preparation method of the multi-purpose solvent-free polyurethane coating of this comparative example is exactly the same as that of Example 1, with the only difference being that the weight ratio of component A to component B is 3:0.2.

[0059] Comparative Example 5 The preparation method of the multi-purpose solvent-free polyurethane coating of this comparative example is exactly the same as that of Example 1, except that the composite modifier includes phytate-intercalated hydrotalcite and nano-boron nitride in a mass ratio of 1:1.

[0060] Comparative Example 6 The preparation method of the multi-purpose solvent-free polyurethane coating of this comparative example is exactly the same as that of Example 1, except that the composite modifier includes phytate-intercalated hydrotalcite and nano-boron nitride in a mass ratio of 4:1.

[0061] Comparative Example 7 The preparation method of the multi-purpose solvent-free polyurethane coating of this comparative example is exactly the same as that of Example 1, with the only difference being that the particle size of the boron nitride is 2-20 μm.

[0062] Performance Testing The multi-purpose solvent-free polyurethane coatings obtained in Examples 1-3 and Comparative Examples 1-7 were evenly coated on the substrate surface and cured at room temperature to obtain a coating with a dry film thickness of 10 μm. Performance tests were conducted according to the following method, and the specific results are shown in Table 1.

[0063] (1) Appearance of coating: visual inspection and hand touch; (2) Adhesion: Tested in accordance with GB / T9286-2021 standard; (3) Hardness: Tested in accordance with GB / T6739-2007 standard; (4) Tensile strength: tested in accordance with GBT23445-2009 standard; (5) Salt spray resistance: Tested in accordance with GB / T1771-2007 standard, in a 5% NaCl solution, pH = 6.5-7.2, 35 ± 2 ° C, salt spray test was carried out to observe the paint film condition; (6) Potentiodynamic polarization curve (Tafel): The coating film was placed in a 3.5% by mass NaCl aqueous solution and the potentiodynamic polarization curve was tested.

[0064] Table 1 Performance data of Examples 1-3 and Comparative Examples 1-7 .

[0065] As shown in Table 1, the multi-purpose solvent-free polyurethanes described in Examples 1-3 of the present invention have good adhesion, high tensile strength, and excellent salt spray resistance after film formation. At the same time, they have a high self-corrosion potential and a low self-corrosion current, indicating that the coatings have strong corrosion resistance. By comparing Example 1 with Comparative Examples 1 and 2, it can be seen that the hydroxyl-terminated polyurethane prepolymer emulsion in Comparative Example 1 does not contain 4,4'-dihydroxybenzophenone, and the tensile strength, corrosion resistance, and salt spray resistance of the coating are all poor; the hydroxyl-terminated polyurethane prepolymer emulsion in Comparative Example 2 does not contain linoleic acid glycerol, and the tensile strength, corrosion resistance, and salt spray resistance of the coating are also poor. By comparing Example 1 with Comparative Examples 3 and 4, it can be seen that the ratio of component A to component B in Comparative Examples 3 and 4 is low or high, and the mechanical properties, corrosion resistance, and salt spray resistance of the coatings are all deteriorated. Comparison of Example 1 with Comparative Examples 5 and 6 shows that the mass ratio of phytate-intercalated hydrotalcite to nano-boron nitride in Comparative Examples 5 and 6 is too low or too high, resulting in poor adhesion, corrosion resistance, and salt spray resistance of the coating. Comparison of Example 1 with Comparative Example 7 shows that the size of the boron nitride in Comparative Example 7 is too large, resulting in poor adhesion, corrosion resistance, and salt spray resistance of the coating.

[0066] It can be seen that the present invention achieves a triple curing effect by compounding a specific hydroxyl-terminated polyurethane prepolymer emulsion, adipic acid dihydrazide and an aqueous blocked isocyanate curing agent, further improving the mechanical strength, salt spray resistance and corrosion resistance of the coating. In addition, the present invention adds a composite modifier of phytic acid intercalated hydrotalcite and nano-boron nitride to the coating system of the present invention, and the two synergize to make the coating have both excellent barrier effect and active anti-corrosion performance. The coating prepared by the multi-purpose solvent-free polyurethane coating of the present invention has excellent mechanical properties, salt spray resistance and corrosion resistance. At the same time, the coating has good adhesion to the substrate and can be used in multi-purpose scenarios.

[0067] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A multi-purpose solvent-free polyurethane coating, characterized in that: The invention comprises a component A and a component B; the component A comprises the following raw materials in parts by weight: 25-40 parts of a hydroxyl-terminated polyurethane prepolymer emulsion, 0.1-2 parts of a film-forming aid, 0.1-2 parts of a leveling agent, 0.5-2 parts of a composite modifier, and 0.5-1 parts of adipic acid dihydrazide; the component B comprises a water-based blocked isocyanate curing agent; the weight ratio of the component A to the component B is 3:(0.5-1.5); wherein the composite modifier comprises phytate-intercalated hydrotalcite and nano-boron nitride in a mass ratio of (1.5-3):

1.

2. A multi-purpose solvent-free polyurethane coating according to claim 1, characterized in that: The solid content of the hydroxyl-terminated polyurethane prepolymer emulsion is 30-40%.

3. The multi-purpose solvent-free polyurethane coating according to claim 1, characterized in that: The film-forming aid is lauryl alcohol ester.

4. The multi-purpose solvent-free polyurethane coating according to claim 1, characterized in that: The leveling agent is polyether-modified organic siloxane.

5. The multi-purpose solvent-free polyurethane coating according to claim 1, characterized in that: The preparation method of the hydroxyl-terminated polyurethane prepolymer emulsion comprises: prepolymerizing 2,4-toluene diisocyanate, PTMG1000, dimethylol propionic acid, 4,4'-dihydroxybenzophenone and linoleic acid glyceride, adding acetone to adjust the viscosity, neutralizing, cooling, adding deionized water for emulsification, and removing acetone to obtain the hydroxyl-terminated polyurethane prepolymer emulsion.

6. The multi-purpose solvent-free polyurethane coating according to claim 5, characterized in that: The mass ratio of the 2,4-toluene diisocyanate, PTMG1000, dimethylol propionic acid, 4,4'-dihydroxybenzophenone and linoleic acid glyceride is 10-12:4:1:1:

4.

7. The multi-purpose solvent-free polyurethane coating according to claim 1, characterized in that: The preparation method of the phytate intercalated hydrotalcite comprises the following steps: adding magnesium nitrate hexahydrate, aluminum nitrate nonahydrate and sodium nitrate into deionized water and mixing them uniformly; adjusting the pH value of the solution to 8.2-8.5; reacting at 110-120° C. for 12-24 hours; washing; and drying to obtain the nitrate intercalated hydrotalcite; and dissolving sodium phytate in deionized water, adding the nitrate intercalated hydrotalcite and mixing them uniformly; reacting at 90-95° C. for 16-20 hours under a nitrogen atmosphere; centrifuging and filtering; and drying to obtain the phytate intercalated hydrotalcite.

8. The multi-purpose solvent-free polyurethane coating according to claim 1, characterized in that: The median particle size D of the nano boron nitride 50 80-200nm.

9. A method for preparing a multi-purpose solvent-free polyurethane coating according to any one of claims 1 to 8, characterized in that: The steps include: (1) Preparing a hydroxyl-terminated polyurethane prepolymer emulsion: prepolymerizing 2,4-toluene diisocyanate, PTMG1000, dihydroxymethyl propionic acid, 4,4'-dihydroxybenzophenone and linoleic acid glyceride, adding acetone to adjust the viscosity, neutralizing, cooling, adding deionized water for emulsification, and removing acetone to obtain the hydroxyl-terminated polyurethane prepolymer emulsion; (2) preparing a composite modifier: mixing the phytate intercalated hydrotalcite and nano boron nitride in proportion and stirring evenly to obtain the composite modifier; (3) mixing the hydroxyl-terminated polyurethane prepolymer emulsion, film-forming aid, leveling agent and composite modifier, adding adipic acid dihydrazide and stirring evenly to obtain component A; (4) Component A and component B are mixed in proportion to obtain the multi-purpose solvent-free polyurethane coating.

10. Use of the multi-purpose solvent-free polyurethane coating according to any one of claims 1 to 8 or the multi-purpose solvent-free polyurethane coating prepared according to the preparation method of claim 9 in exterior coating of industrial products.