A waterborne two-component polyurethane coating, its preparation method and application

Abstract

The present application belongs to the technical field of paint, and particularly relates to a water-based two-component polyurethane paint, a preparation method and application thereof. The water-based two-component polyurethane paint comprises component A and component B; the component A comprises resin, pigment and filler, additive, cosolvent, and water; the component B comprises modified polyurethane curing agent; the modified polyurethane curing agent comprises -NCO groups and alkoxysilane functional groups. The -NCO groups in the modified polyurethane curing agent react with the resin, and the hydrolysable and condensable alkoxysilane functional groups introduced at the molecular terminal or side chain can form a firm Si-O-M covalent bond with the surface of inorganic / metal substrate during the curing process of the coating film, so as to improve the adhesion; the self-condensation of the alkoxysilane functional groups can form a dense Si-O-Si hydrophobic network, so as to significantly improve the water resistance; meanwhile, the Si-O-M covalent bond and the Si-O-Si hydrophobic network can interpenetrate with the polyurethane network, so as to improve the crosslinking density and medium resistance of the coating.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, and specifically relates to a water-based two-component polyurethane coating, its preparation method, and its application. Background Technology

[0002] Waterborne polyisocyanate curing agents, typically aliphatic polyisocyanates such as hexamethylene diisocyanate trimer (HDI trimer) and isophorone diisocyanate trimer (IPDI trimer), are the core crosslinking agents for waterborne two-component polyurethane coatings. They react with hydroxyl resins (such as acrylic dispersions, polyester polyols, etc.) to form coatings with excellent performance.

[0003] Currently, traditional water-based curing agents still face the following challenges: 1) Limited adhesion to substrates: Especially on smooth, low surface energy (such as some plastics, clean metals) or inorganic (such as glass, ceramic) substrates, insufficient physical anchoring and polar interaction easily lead to poor coating adhesion; 2) Bottlenecks in hydrolysis / corrosion resistance: Ester bonds and urea bonds in polyurethane coatings may hydrolyze in humid and hot environments, and the interface between the coating and the metal substrate is prone to electrochemical corrosion induced by water vapor penetration, resulting in insufficient corrosion resistance and affecting long-term protective performance.

[0004] In existing technologies, some studies have explored the physical addition of silane coupling agents to coating formulations as adhesion promoters. However, these methods suffer from problems such as easy migration, poor compatibility with the system leading to surface defects (pinholes, orange peel, etc.), and decreased storage stability (silane hydrolysis and self-condensation causing premature failure). Consequently, polyurethane coatings exhibit poor surface finish and performance (adhesion, water resistance, and corrosion resistance). Other studies have investigated silane modification of hydroxyl resins, but these also suffer from insufficient adhesion, water resistance, and corrosion resistance.

[0005] Therefore, providing a polyurethane coating with good adhesion, water resistance, and corrosion resistance is of great significance. Summary of the Invention The present invention aims to solve one or more technical problems existing in the prior art, and at least provide a beneficial alternative. Specifically, the present invention provides a water-based two-component polyurethane coating with good adhesion, water resistance and corrosion resistance.

[0006] The inventive concept of this invention: The waterborne two-component polyurethane coating of this invention comprises component A and component B; component A includes resin, pigments, fillers, additives, co-solvents, and water; component B includes a modified polyurethane curing agent; the modified polyurethane curing agent includes -NCO groups and alkoxysilane functional groups. The -NCO groups in the modified polyurethane curing agent of this invention react with the resin, and the hydrolyzable and condensable alkoxysilane functional groups introduced at the molecular ends or side chains can achieve three major functions during the coating curing process: firstly, they can form strong Si-OM covalent bonds with the surface of inorganic / metallic substrates, greatly improving adhesion; secondly, they can undergo self-condensation to form a dense Si-O-Si hydrophobic network, significantly enhancing water resistance; and thirdly, the Si-OM covalent bonds and the Si-O-Si hydrophobic network can interpenetrate with the polyurethane network, increasing the crosslinking density and media resistance of the coating.

[0007] Therefore, a first aspect of the present invention provides an aqueous two-component polyurethane coating.

[0008] Specifically, the water-based two-component polyurethane coating includes component A and component B; Component A includes resin, pigments, fillers, additives, co-solvents, and water; Component B includes a modified polyurethane curing agent; the modified polyurethane curing agent includes -NCO groups and alkoxysilane functional groups.

[0009] Preferably, the modified polyurethane curing agent is an alkoxysilane-modified waterborne polyurethane curing agent containing active hydrogen.

[0010] Specifically, the modified polyurethane curing agent is obtained by modifying an aqueous polyurethane curing agent with an alkoxysilane containing active hydrogen.

[0011] Preferably, the alkoxysilane containing active hydrogen comprises a silane coupling agent containing active hydrogen.

[0012] Preferably, the silane coupling agent containing active hydrogen includes γ-aminopropyltriethoxysilane (KH550).

[0013] Specifically, the modified polyurethane curing agent is an aqueous polyurethane curing agent that introduces silane coupling agent structural units containing active hydrogen through chemical bonding. By using the active hydrogen-containing silane coupling agent as a capping agent or chain extender, it is chemically bonded to the polyisocyanate backbone, allowing it not only to retain the original -NCO groups that react with the resin, but also to introduce hydrolyzable and condensable alkoxysilane functional groups at the molecular ends or side chains. During the coating curing process, these silane groups help improve adhesion, significantly enhance water resistance, and increase the crosslinking density and media resistance of the coating.

[0014] Preferably, by weight percentage, component A comprises 45-60% resin, 10-30% pigments and fillers, 1-2.5% additives, 2-10% cosolvents, and 12-20% water.

[0015] Preferably, the additives include a dispersant and additive A; additive A includes at least one of an antifoaming agent, a leveling agent, a thickener, and a pH adjuster.

[0016] Specifically, the auxiliary agent A is an aqueous auxiliary agent.

[0017] Preferably, by weight percentage, component A comprises 45-60% resin, 10-30% pigments and fillers, 0.5-1% dispersant, 0.5-1.5% additive A, 2-10% cosolvent, and 12-20% water.

[0018] Preferably, the mass ratio of component A to component B is (5-10):1; for example, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, etc.

[0019] Preferably, the resin comprises a hydroxyl-containing resin; more preferably, the resin comprises a hydroxyl acrylic dispersion.

[0020] Specifically, the resin is an aqueous resin, and the hydroxy acrylic acid dispersion is a secondary hydroxy acrylic acid dispersion.

[0021] Preferably, the molar ratio of -NCO groups in the modified polyurethane curing agent to hydroxyl groups in the resin is 1:(0.8-1.2); for example, 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, etc.

[0022] Preferably, the co-solvent includes at least one of propylene glycol methyl ether, dipropylene glycol butyl ether, ethanol, and butyl acetate.

[0023] Preferably, the pigments and fillers include at least one of titanium dioxide, phthalocyanine blue powder, carbon black powder, and talc powder.

[0024] Specifically, the pigments and fillers are water-soluble pigments and fillers, i.e., water-soluble powders.

[0025] Preferably, the dispersant includes at least one of polyurethane dispersants and acrylic dispersants. The above products can effectively disperse various components in polyurethane coatings, so that the components are evenly dispersed and avoid agglomeration that affects the performance of polyurethane coatings.

[0026] Preferably, the defoamer includes at least one of polyether siloxane copolymer type defoamer and non-silicone water-based defoamer.

[0027] Preferably, the leveling agent includes at least one of silicone-based leveling agents, polyether-based leveling agents, and amino-based leveling agents.

[0028] Preferably, the thickener includes at least one of polyurethane thickeners and alkali-swellable thickeners.

[0029] Preferably, the pH adjuster includes at least one of triethanolamine and borate buffer.

[0030] Preferably, the water includes purified water.

[0031] A second aspect of the present invention provides a method for preparing the waterborne two-component polyurethane coating described in the first aspect of the present invention.

[0032] Specifically, the preparation method of the water-based two-component polyurethane coating includes the following steps: The raw material components of component A are mixed to obtain component A; The components A and B constitute the water-based two-component polyurethane coating.

[0033] Preferably, the method for preparing the water-based two-component polyurethane coating includes the following steps: Water, dispersant, a portion of cosolvent, a portion of defoamer, pigments and fillers are mixed, dispersed and ground into a slurry; the slurry, resin, the remainder of cosolvent, the remainder of defoamer, and the remaining additive A are mixed to obtain component A; The components A and B constitute the water-based two-component polyurethane coating.

[0034] Preferably, the fineness of the slurry is no greater than 50 μm.

[0035] Preferably, the preparation method of the modified polyurethane curing agent includes the following steps: Isocyanate and catalyst are mixed and heated; then alkoxysilane containing active hydrogen is added, and the mixture is reacted to obtain the product.

[0036] Preferably, the isocyanate comprises hexamethylene diisocyanate (HDI).

[0037] Preferably, the catalyst comprises dibutyltin dilaurate.

[0038] Preferably, the amount of catalyst used accounts for 0.01-0.08% of the mass of the isocyanate; for example, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, etc.

[0039] Preferably, the temperature after heating is 40-50℃; for example, 40℃, 41℃, 42℃, 43℃, 44℃, 45℃, 46℃, 47℃, 48℃, 49℃, 50℃, etc.

[0040] Preferably, an alkoxysilane containing active hydrogen is added under stirring conditions.

[0041] Preferably, the alkoxysilane containing active hydrogen comprises a silane coupling agent containing active hydrogen.

[0042] Specifically, during the addition of alkoxysilanes containing active hydrogen, the dropping rate is controlled so that the reaction temperature does not exceed 60°C.

[0043] Preferably, the ratio of the number of moles of active hydrogen in the alkoxysilane containing active hydrogen to the number of moles of -NCO groups participating in the reaction in the isocyanate is (0.05-0.3):1.

[0044] Preferably, the reaction temperature is 50-60℃; for example, 50℃, 51℃, 52℃, 53℃, 54℃, 55℃, 56℃, 57℃, 58℃, 59℃, 60℃, etc.

[0045] Preferably, the reaction proceeds until the -NCO content in the system reaches the theoretical design value, as determined by di-n-butylamine titration.

[0046] A third aspect of the present invention provides an application of the water-based two-component polyurethane coating described in the first aspect of the present invention in the field of engineering machinery.

[0047] Compared with the prior art, the beneficial effects of the technical solution provided by the present invention are as follows: The modified polyurethane curing agent in the polyurethane coating of this invention includes -NCO groups and alkoxysilane functional groups. The -NCO groups can react with the hydroxyl groups in the resin, and the hydrolyzable and condensable alkoxysilane functional groups introduced at the molecular ends or side chains can form strong Si-OM covalent bonds with the surface of inorganic / metal substrates during the coating curing process, greatly improving adhesion. At the same time, self-condensation can occur to form a dense Si-O-Si hydrophobic network, significantly enhancing water resistance. Furthermore, the Si-OM covalent bonds and the Si-O-Si hydrophobic network can interpenetrate with the polyurethane network, increasing the crosslinking density and media resistance of the coating, ultimately giving the polyurethane coating good adhesion, water resistance, and corrosion resistance. Detailed Implementation

[0048] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.

[0049] Unless otherwise specified, the raw materials, reagents or devices used in the following examples are available from conventional commercial sources or can be obtained by existing known methods.

[0050] Example 1 This embodiment provides a water-based two-component polyurethane coating, which consists of component A and component B by weight percentage. Component A consists of 15% water, 0.8% dispersant, 55% water-based resin, 6% cosolvent, 22% pigments and fillers (powder), and 1.2% water-based additives (additive A); component B is 100% modified polyurethane curing agent.

[0051] The mass ratio of component A to component B is 7:1.

[0052] The waterborne resin is Wanhua Chemical's 2033 (hydroxyl content 3.3%); the dispersant is Tigo 740W; the powders are titanium dioxide (15%) and talc (7%); the cosolvents are propylene glycol methyl ether (4%) and dipropylene glycol butyl ether (2%); the defoamer in the waterborne additives is Tigo 901 (0.2%), the leveling agent is Jintuan 387 (0.1%), and the thickener is Wanhua U905 (0.9%). This embodiment also provides a method for preparing the above-mentioned waterborne two-component polyurethane coating, the specific steps of which are as follows: (1) Pre-dispersion of slurry: Add water, propylene glycol methyl ether, and defoamer (1% of the total amount of defoamer) to the reactor and stir for 15 min, controlling the speed at 1500 r / min; add dispersant and stir for 5 min, controlling the speed at 300 r / min; then add powder and disperse at high speed for 10 min, controlling the speed at 2800 r / min; finally add grinding beads and grind the slurry to a fineness of 50 μm at a speed of 3200 r / min to obtain the slurry; (2) Paint preparation: Mix the slurry obtained in step (1) with water-based resin. To prevent demulsification, control the rotation speed at 700 r / min. Then add dipropylene glycol butyl ether, leveling agent, and defoamer (accounting for 1% of the total amount of defoamer). Stir for 30 min. Finally, use thickener to adjust the paint to KU=75±5 to obtain component A. Component A and Component B constitute a water-based two-component polyurethane coating.

[0053] The preparation method of the modified polyurethane curing agent is as follows: (1) Under a dry and inert atmosphere, hexamethylene diisocyanate (HDI) is added to the reaction vessel, and dibutyltin dilaurate catalyst is added at 0.08% of its mass; the reaction system is heated to 50°C, and under stirring conditions, alkoxysilane (KH550) containing active hydrogen is slowly added dropwise to the system, and the dropping rate is controlled so that the reaction temperature does not exceed 60°C. The amount of alkoxysilane added is calculated as 0.08:1 based on the ratio of the number of moles of its active hydrogen to the number of moles of -NCO groups participating in the reaction in the isocyanate. (2) After the addition is complete, keep the reaction at 50°C until the -NCO content in the system reaches the theoretical design value as determined by di-n-butylamine titration. After the reaction is complete, cool down and discharge the material to obtain a portion of the end-capped silane modified polyurethane curing agent, i.e., modified polyurethane curing agent.

[0054] Example 2 The only difference between Example 2 and Example 1 is that the water-based resin used in Example 2 is Wanhua Chemical 2042 (hydroxyl content 4.2%), and everything else is the same as in Example 1.

[0055] Example 3 The only difference between Example 3 and Example 1 is that the waterborne resin used in Example 3 is Tongde 0521W (hydroxyl content 3.3%), while the rest is the same as in Example 1.

[0056] Example 4 The only difference between Example 4 and Example 1 is that the waterborne resin used in Example 4 is Hesongyuan WA219 (hydroxyl content is 1.9%), and everything else is the same as in Example 1.

[0057] Comparative Example 1 (Comparative Examples 1-3 all use polyurethane curing agents) The only difference between Comparative Example 1 and Example 1 is that the waterborne polyurethane curing agent used in Comparative Example 1 is Wanhua Chemical's Antkote 2033, while the rest is the same as in Example 1.

[0058] Comparative Example 2 The only difference between Comparative Example 2 and Comparative Example 1 is that the waterborne polyurethane curing agent used in Comparative Example 2 is Tongde TMA-100, while the rest is the same as in Example 1.

[0059] Comparative Example 3 The only difference between Comparative Example 3 and Example 1 is that the waterborne polyurethane curing agent used in Comparative Example 3 is Lian Gu 3597A, and the rest is the same as in Example 1.

[0060] Performance testing The A and B components of the polyurethane coatings from Examples 1-4 and Comparative Examples 1-3 were mixed at a mass ratio of 7:1 to obtain a water-based two-component polyurethane coating. The polyurethane coating was sprayed onto the substrate (standard sandblasted board) using an air spray gun. The wet film thickness of one coat was 125 μm, and the dry film thickness was 40 μm. The coating was applied in two coats (the next coat was applied after the previous coat had completely dried). After the paint film had completely dried, the coating was placed in a 50°C oven for 48 hours to obtain the test sample. The unpainted areas of the sample were sealed with tape before testing.

[0061] Acid resistance, alkali resistance, salt spray and adhesion tests: Tests were conducted in accordance with HG / T 4761-2014.

[0062] Early water resistance test: The test shall be conducted in accordance with HG / T 5176-2017.

[0063] The performance test results of the waterborne two-component polyurethane coatings of Examples 1-4 and Comparative Examples 1-3 are shown in Table 1.

[0064] Table 1: Performance test results of waterborne two-component polyurethane coatings in Examples 1-4 and Comparative Examples 1-3

[0065] The 3 days, 4 days, etc. times in Table 1 indicate the time after which the anomaly occurred.

[0066] As can be seen from Table 1, the polyurethane coating of the present invention has good water resistance, corrosion resistance and adhesion.

[0067] Comparative Examples 1-3 used other types of polyurethane curing agents, resulting in polyurethane coatings with significantly worse water resistance, corrosion resistance, and adhesion compared to Example 1. This demonstrates that the modified polyurethane curing agent containing -NCO groups and alkoxysilane functional groups used in this invention can improve the water resistance, corrosion resistance, and adhesion of polyurethane coatings.

[0068] In summary, the -NCO groups in the modified polyurethane curing agent of this invention, along with the hydrolyzable and condensable alkoxysilane functional groups introduced at the molecular ends or side chains, enable the polyurethane coating to possess excellent water resistance, corrosion resistance, and adhesion.

[0069] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A polyurethane coating, characterized in that, The polyurethane coating comprises component A and component B; Component A includes resin, pigments, fillers, additives, co-solvents, and water; Component B includes a modified polyurethane curing agent; the modified polyurethane curing agent includes -NCO groups and alkoxysilane functional groups.

2. The polyurethane coating according to claim 1, characterized in that, By weight percentage, component A comprises 45-60% resin, 10-30% pigments and fillers, 1-2.5% additives, 2-10% co-solvent, and 12-20% water; And / or, the additives include dispersants and additive A; additive A includes at least one of defoamers, leveling agents, thickeners, and pH adjusters.

3. The polyurethane coating according to claim 2, characterized in that, By weight percentage, component A comprises 45-60% resin, 10-30% pigments and fillers, 0.5-1% dispersant, 0.5-1.5% additive A, 2-10% cosolvent, and 12-20% water; And / or, the mass ratio of component A to component B is (5-10):

1.

4. The polyurethane coating according to claim 2, characterized in that, The resin includes resins containing hydroxyl groups; And / or, the cosolvent includes at least one of propylene glycol methyl ether, dipropylene glycol butyl ether, ethanol, and butyl acetate; And / or, the pigments and fillers include at least one of titanium dioxide, phthalocyanine blue powder, carbon black powder, and talc.

5. The method for preparing the polyurethane coating according to any one of claims 1-4, characterized in that, The preparation method includes the following steps: The raw material components of component A are mixed to obtain component A; The components A and B constitute the polyurethane coating.

6. The preparation method according to claim 5, characterized in that, The preparation method of the modified polyurethane curing agent includes the following steps: Isocyanate and catalyst are mixed and heated; then alkoxysilane containing active hydrogen is added, and the mixture is reacted to obtain the product.

7. The preparation method according to claim 6, characterized in that, The isocyanate includes hexamethylene diisocyanate; And / or, the catalyst comprises dibutyltin dilaurate; And / or, the amount of the catalyst is 0.01-0.08% of the mass of the isocyanate.

8. The preparation method according to claim 6, characterized in that, The temperature after heating is 40-50℃; And / or, the ratio of the number of moles of active hydrogen in the alkoxysilane containing active hydrogen to the number of moles of -NCO groups participating in the reaction in the isocyanate is (0.05-0.3):

1.

9. The preparation method according to claim 6, characterized in that, The reaction temperature is 50-60℃; And / or, the reaction continues until the -NCO content in the system reaches the theoretical design value as determined by di-n-butylamine titration.

10. The application of the polyurethane coating according to any one of claims 1-4 in the field of engineering machinery.

Images