Aqueous polyurethane resin containing heterocyclic groups in side chains and preparation method thereof

Abstract

This invention discloses a waterborne polyurethane dispersion containing heterocyclic side chains and exhibiting excellent corrosion resistance, as well as a method for its preparation. The key technology involves introducing benzothiazole groups into the side chain structure of the waterborne polyurethane molecules, forming uniformly distributed, freely rotatable benzothiazole side chains that can be oriented and tightly adsorbed onto the surface of a metal substrate. Furthermore, components with a linearly symmetrical cyclic backbone structure are selected to enhance the cohesive strength of the waterborne polyurethane. A suitable crosslinking agent and its synthesis process are identified. When the crosslinking point density is between 2.0 and 2.6 x 10 ‑4 When the concentration of benzothiazole in the aqueous polyurethane dispersion is within the 1% to 2% mol / g range, the water resistance, heat resistance, and mechanical strength of the resulting aqueous polyurethane dispersion are enhanced. These properties, in synergistic relationship with the corrosion inhibition effect of the benzothiazole side chain groups, further enhance the corrosion resistance of the aqueous polyurethane coating. Using the aqueous polyurethane resin synthesized in the present invention as a film-forming polymer, a water-based anti-corrosion coating with excellent performance can be formulated.

Description

Technical Field

[0001] The present invention relates to the field of waterborne polyurethane coatings, in particular to a waterborne urethane resin containing N and S heterocyclic groups in the side chain for corrosion prevention and protection of metal substrates and a preparation method thereof. Background Art

[0002] To protect metal materials, inhibit corrosion, and extend their service life, the application of high-performance anti-corrosion coatings is a simple and effective method. Polyurethane coatings have gained significant attention for their excellent overall performance, including durability, chemical resistance, and flexibility, and have become a leading type of anti-corrosion coating. Polyurethane adheres well to various metal substrates, forming a robust protective layer that shields them from corrosive agents such as moisture, salt, and industrial chemicals. Its ability to withstand harsh environmental conditions and mechanical stresses ensures long-lasting protection and reduces maintenance costs, making it a preferred choice for extending the service life of metal structures and equipment. In recent years, polyurethane anti-corrosion coatings have experienced rapid development and are widely used in a variety of corrosive environments, generating significant economic and social benefits.

[0003] With increasingly stringent environmental regulations and growing public awareness, emissions of volatile organic compounds (VOCs) from traditional solvent-based polyurethane coatings are subject to increasingly stringent restrictions. Consequently, environmentally friendly waterborne polyurethane anticorrosive coatings have experienced rapid development and are poised to gradually replace solvent-based coatings. However, for waterborne polyurethane coatings to replace solvent-based coatings and achieve competitive advantages over them for a considerable period of time, they must continuously improve their anticorrosion properties.

[0004] The corrosion process, in which metal materials undergo an electrochemical reaction with their environment, leading to their slow decomposition or destruction, is essentially an oxidation reaction between the metal and water and oxygen. This requires the simultaneous presence of both water and oxygen, as corrosion generally does not occur without them. To address this corrosion mechanism in metals, research is focusing on two main areas to improve the corrosion resistance of waterborne polyurethanes.

[0005] First, it improves the shielding and barrier properties of waterborne polyurethane protective coatings, shielding or hindering the penetration of water and oxygen through the waterborne polyurethane coating into the metal substrate. This is an important approach to improving the corrosion resistance of waterborne polyurethane coatings. Because hydrophilic groups are introduced into waterborne polyurethane molecules during the synthesis process, the coating becomes water-sensitive, resulting in inferior water resistance and corrosion resistance compared to solvent-based polyurethane coatings. By optimizing the raw material composition of the waterborne polyurethane and introducing polyols and chain extenders with hydrophobic and hydrolysis-resistant properties, the water absorption and water resistance of the waterborne polyurethane and its coating can be improved. For example, patent CN118109159A uses polytetramethylene glycol and linseed oil polyol as the preferred polyol components to produce a waterborne polyurethane with excellent mechanical properties and water resistance. Patent CN202210997635.8 uses dihydroxylated isobornyl methacrylate (IBA(OH)2) as a chain extender, introducing its specific alicyclic molecular structure into the side chains of the polyurethane molecular backbone. This enhances the hydrophobicity of the product, improves the water resistance of waterborne polyurethane coatings, and expands the application range of waterborne polyurethane coatings. Furthermore, increasing the crosslinking density of waterborne polyurethane resin molecules and adding internal or external crosslinking agents during the polyurethane synthesis process are all effective methods for improving the water resistance of waterborne polyurethane coatings.

[0006] Second, by forming a well-adherent waterborne polyurethane protective coating on the metal substrate, the electrochemical reaction between the metal substrate and water and oxygen can be inhibited or delayed. Currently, the main approach to achieving this goal is to add effective anti-corrosion components, such as reactive rust-inhibiting pigments and corrosion inhibitors, to the waterborne polyurethane coating. Organic corrosion inhibitors are widely used due to their diverse variety, wide applicability, and high corrosion inhibition efficiency. Heterocyclic compounds containing elements such as nitrogen, sulfur, and phosphorus, such as those containing imidazole, thiazole, and thiophene groups, are the most extensively studied class of corrosion inhibitors. These corrosion inhibitors typically adsorb on metal surfaces, forming coordination bonds with metal ions and forming complexes on the metal surface. The stronger the adsorption and the more stable the complex, the stronger the interaction between the corrosion inhibitor and the metal substrate, and the superior the corrosion inhibition effect. However, these small-molecule heterocyclic corrosion inhibitors have high requirements for the metal substrate and waterborne coating formulation. Furthermore, most are toxic and can migrate and seep out of the coating film, compromising the durability of the anti-corrosion coating. These facts indicate that organic small molecule corrosion inhibitors pose serious pollution problems both during synthesis and application, and are no longer in line with current trends toward green, low-carbon, and sustainable development. Recent studies have shown that during the synthesis of waterborne polyurethanes, through small molecule chain extension reactions, the heterocyclic groups of organic heterocyclic corrosion inhibitors can be introduced into the molecular structure of waterborne polyurethanes, thereby improving or enhancing the performance of waterborne polyurethanes. For example, patent CN201510349614.5 uses imidazole-containing diamine compounds (such as 5-(3-aminopropyl)-1H-imidazole-2-amine) as chain extenders to introduce imidazole groups into the main chain molecular structure of waterborne polyurethanes, resulting in a waterborne polyurethane waterproof coating with excellent performance. Patent CN201810720005.X also uses the diamine compound 2-(4-aminophenyl)-5-aminobenzimidazole (DAPBI) as a chain extender to introduce imidazole groups into the backbone molecular structure of a waterborne polyurethane, producing a waterborne polyurethane coating with excellent adhesion, water resistance, abrasion resistance, and mechanical properties. Patent CN202410748386.8 uses dihydroxybenzoxazine as a chain extender to produce a waterborne polyurethane with excellent mechanical properties, high adhesion, and water resistance. This significantly expands the application range of waterborne polyurethane materials, giving them broad application prospects in fields such as corrosion protection, adhesives, electronics, and aerospace. Patent CN202310534843.9 first synthesized mercaptobenzimidazole and then introduced benzimidazole groups through conjugated grafting, which effectively prevented the occurrence of flash rust on the metal substrate during the film formation process and expanded the commercial application field of water-based polymer coatings. However, its synthesis process is complicated, the operation time is long and difficult, the process is difficult to control, and a large amount of acid, alkali and other organic substances are used in the synthesis process, which is not conducive to environmental protection.Therefore, it can be seen that during the synthesis of waterborne polyurethane, the introduction of heterocyclic groups such as imidazole into the molecular structure of waterborne polyurethane through chain extension reactions, grafting reactions, and other methods can enhance the polyurethane's water resistance, adhesion, or corrosion resistance. However, these patents also indicate that the introduction of heterocyclic groups does not necessarily improve the corrosion resistance of waterborne polyurethane.

[0007] As mentioned above, there is an urgent need to develop a waterborne polyurethane resin for metal anti-corrosion coatings, the molecular structure of which contains a heterocyclic group of a general organic heterocyclic corrosion inhibitor, and the steric hindrance of the heterocyclic group in chain link activity is small, which can work together with other groups in the waterborne polyurethane molecule to achieve anti-corrosion synergy, obtain appropriate orientation and sufficient adsorption at the metal-coating interface, thereby enhancing the water resistance, adhesion and anti-corrosion performance of the waterborne polyurethane, and can be produced by an effective synthesis method. Summary of the Invention

[0008] In view of the shortcomings and deficiencies of the above prior art, the primary purpose of the present invention is to provide a method for preparing a cross-linked aqueous polyurethane dispersion with anti-corrosion properties and containing heterocyclic groups in the side chains.

[0009] The present invention is implemented through the following technical solutions:

[0010] A method for preparing a waterborne polyurethane resin containing a heterocyclic group in a side chain comprises the following steps:

[0011] (1) Add polymer polyol, small molecule polyhydroxy chain extender (crosslinking agent), and hydrophilic chain extender into a four-necked flask equipped with a stirrer, a thermometer, and a vacuum valve, heat to 110-120°C, vacuum dehydrate for 1-2 hours, and then cool to 75°C to obtain a liquid mixture of the above hydroxy components;

[0012] (2) Opening nitrogen protection, adding the polyisocyanate component to the four-necked flask containing the liquid mixture of the hydroxyl component, and reacting at 80-85°C for 180-210 minutes to obtain a terminal-NCO polyurethane prepolymer;

[0013] (3) Add an appropriate amount of organic solvent to adjust the viscosity, and lower the system temperature to 60-65 °C, then add a small molecule diol chain extender, wait for 30 minutes, then add a heterocyclic compound chain extender containing two active groups, continue the reaction for 120-150 minutes, and finally add an organic solvent to adjust the viscosity to obtain a low-viscosity -NCO group-terminated polyurethane prepolymer solution;

[0014] (4) Cooling the prepolymer solution to 35-45°C, adding a neutralizing agent, and vigorously stirring for 10-20 minutes, then adding an appropriate amount of deionized water, and emulsifying at a high shear force of 5000-7000 r / min for 5-15 minutes to obtain a polyurethane dispersion aqueous solution;

[0015] (5) Adding a small molecule diamine post-chain extender and a polyamine crosslinker to the above polyurethane dispersion aqueous solution and reacting for 60 to 90 minutes;

[0016] (6) The organic solvent in the dispersion solution is removed by vacuum distillation to obtain an aqueous polyurethane dispersion.

[0017] The polymer polyols in step (1) above include polyether polyols, polyester polyols, polycarbonate polyols and polyolefin polyols, all of which have a molecular weight of 1000, 2000 or 3000. Polyester polyols include poly-ε-caprolactone diol (PCL), poly-1,4-butylene adipate (PBA) and poly-1,6-hexanediol adipate (PDA). Polyether polyols include polytetramethylene glycol (PTMG) and polypropylene glycol (PPG). Polycarbonate polyols include polyhexamethylene carbonate diol and polytetramethylene carbonate diol generated by the condensation reaction of 1,4-butylene glycol and 1,6-hexanediol with dialkyl carbonate. Polyolefin polyols mainly include hydroxyl-terminated polybutadiene diol. Preferably, one of the above-mentioned polyols, or a mixture of two or more polyols, each having a molecular weight of 2000, is used. More preferably, a mixture of polycarbonate diol (PCDL) prepared from 1,6-hexanediol and hydroxyl-terminated polybutadiene diol (HTPB), each having a molecular weight of 2000, is used. The ratio of PCDL to HTPB is 0.5 to 2.0 (mass ratio), and the total amount of the PCDL and HTPB accounts for 54.40 to 62.38% of the total solids in the aqueous polyurethane dispersion.

[0018] The small molecule polyhydroxy chain extender (crosslinker) described in the above step (1) includes a small molecule polyol containing three or more hydroxyl groups, such as a mixture of one or more of glycerol, trimethylolethane, trimethylolpropane, triisopropanolamine and pentaerythritol; preferably, trimethylolpropane (TMP) is used as the small molecule polyhydroxy crosslinker, and its addition amount accounts for 0.58~0.98% of the total solid matter in the aqueous polyurethane dispersion.

[0019] The hydrophilic chain extender described in the above step (1) can be selected from at least one of dimethylol lactic acid, dimethylol propionic acid (DMPA), dimethylol butyric acid (DMBA) and dimethylol valeric acid containing a carboxylic acid group; preferably, dimethylol propionic acid (DMPA) is the hydrophilic chain extender of the present invention, and its addition amount accounts for 3.24-4.99% of the total solid matter amount in the aqueous polyurethane dispersion.

[0020] The polyisocyanates in the above step (2) include aromatic polyisocyanates, aromatic aliphatic polyisocyanates, aliphatic polyisocyanates, etc. Aromatic polyisocyanates include toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), etc.; aromatic aliphatic polyisocyanates include xylene diisocyanate (XDI), tetramethylxylene diisocyanate (TMXDI), etc.; aliphatic polyisocyanates include isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), 4,4'-dicyclohexylmethane diisocyanate (HDI), etc. 12 MDI) etc. Preferably include HDI, IPDI and H 12 Any diisocyanate including MDI can be used alone or in combination of two or more; more preferably 4,4'-dicyclohexylmethane diisocyanate (H 12 MDI) is used as the polyisocyanate component of the present invention, and its usage accounts for 28.61-34.0% of the total solid matter in the aqueous polyurethane dispersion.

[0021] The small molecule diol chain extender described in the above step (3) includes small molecule diols containing carbon rings and small molecule diols without carbon rings. Small molecule diol chain extenders containing carbon rings include 1,3- or 1,4-cyclohexanedimethanol (CHDM), 1,3- or 1,4-cyclohexanediol, hydrogenated bisphenol A, etc.; small molecule chain extenders without carbon rings include ethylene glycol, propylene glycol, dipropylene glycol, 1,4-butanediol (BDO), neopentyl glycol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,4-hexanediol and 1,6-hexanediol, etc. Any one of the above small molecule diols or a mixture of two or more can be selected for use; preferably, 1,4-cyclohexanedimethanol (CHDM) is the small molecule diol chain extender of the present invention, and its addition amount accounts for 0.97~1.54% of the total solid matter in the aqueous polyurethane dispersion.

[0022] The heterocyclic compound chain extender containing two active groups (hydroxyl or amino) described in step (3) above refers to a compound containing a heterocyclic group such as imidazole, thiophene, thiazole, pyridine, and at least two other active groups (-OH or -NH2 groups, which can react with isocyanate). At least one of 3-imidazolyl-1-propane-1,2-diol, N,N-bis(2-hydroxyethyl)isonicotinamide, 2-((tetrahydro-3-thienyl)amino)-1,3-propanediol, 2-(1,3-benzothiazol-2-methylamino)ethanol, 2-hydrazinobenzothiazole, etc., or a mixture of any two or more thereof can be used; preferably, 2-(1,3-benzothiazol-2-methylamino)ethanol is used as the heterocyclic compound chain extender of the present invention, and its addition amount accounts for 1.50-2.21% of the total solid matter in the aqueous polyurethane dispersion.

[0023] The organic solvent in step (3) is at least one of acetone, methyl ethyl ketone, ethyl acetate, and acetonitrile, or a mixture of any two or more thereof. In the other steps of preparing the polyurethane prepolymer of the present invention, an appropriate amount of organic solvent may be added as needed to adjust the viscosity of the system. The amount of organic solvent generally accounts for 60% to 100% of the total solids in the aqueous polyurethane dispersion. Acetone is preferably used as the solvent.

[0024] The neutralizing agent in step (4) is one of trimethylamine, triethylamine, dimethylethanolamine, methyldiethanolamine, triethanolamine, aqueous ammonia, sodium hydroxide, potassium hydroxide, etc.; preferably, triethylamine is used as the neutralizing agent, and its amount is calculated based on the number of moles required to neutralize 95% (molar percentage) of the carboxyl groups of the hydrophilic chain extender dimethylolpropionic acid (DMPA);

[0025] The diamine post-chain extender in the above step (5) is one or a combination of two or more of ethylenediamine, 1,4-butanediamine, 1,6-hexanediamine, 2-methyl-1,5-pentanediamine, piperazine, N-aminoethylpiperazine (AEP), isophorone diamine, and N-methyl-3,3′-diaminopropylamine; preferably, N-aminoethylpiperazine (AEP) is used as the diamine post-chain extender, which accounts for 0.53-0.86% of the total solid matter in the aqueous polyurethane dispersion.

[0026] The polyamine crosslinking agent in the above step (5) is one or a combination of two or more of diethylenetriamine (DETA), bis(3-aminopropyl)amine, triethylenetetramine (TETA), tripropylenetetramine, and tetraethylenepentamine; preferably, diethylenetriamine (DETA) is used as the polyamine crosslinking agent, which accounts for 1.31-1.95% of the total solid matter in the aqueous polyurethane dispersion.

[0027] The conditions for removing acetone in step (6) above are a temperature of 40-60°C and a vacuum degree of 0.05-0.1 MPa.

[0028] A waterborne polyurethane dispersion with excellent corrosion resistance is prepared by the above method. The waterborne polyurethane dispersion prepared by the above method has an average particle size of 92 to 128 nm and a solid content of approximately 33.5 wt%.

[0029] The principle of the present invention is to introduce a benzothiazole heterocyclic group with corrosion inhibition function into the molecular structure of polyurethane through a chain extension reaction, and form a suspended heterocyclic group side chain on the polyurethane main chain. This side chain heterocyclic group is connected to the polyurethane main chain through a freely rotatable NCC single bond, which reduces steric hindrance. Therefore, the side chain heterocyclic group has a large free activity space and can migrate and diffuse to a certain extent. When the water-based polyurethane forms a film, this benzothiazole side chain can be relatively freely oriented on the surface of the metal substrate and form a close adsorption with the metal surface; and the strong complexation force between the delocalized large π bond formed by the planar resonance structure of the benzothiazole heterocyclic group and the metal atom further strengthens the interaction between the benzothiazole heterocyclic group and the metal, thus having excellent anti-corrosion performance. The molecular structure of the 2-(1,3-benzothiazole-2-methylamino)ethanol chain extender selected by the present invention is as follows:

[0030]

[0031] In addition, the polycarbonate polyol and polybutadiene polyol selected in the present invention have excellent water resistance, chemical resistance and mechanical properties, and diisocyanate H 12 The linearly symmetrical cyclic skeleton structure of MDI, the small molecule chain extender 1,4-cyclohexanedimethanol (CHDM), and the post-chain extender N-aminoethylpiperazine (AEP), resulting in a tight directional arrangement of the polyurethane molecular chains and enhanced cohesive strength, as well as the appropriate crosslinking density formed by trimethylolpropane (TMP) and diethylenetriamine (DETA), further enhances the water resistance, heat resistance, and mechanical strength of the waterborne polyurethane prepared by the present invention. These properties, together with the corrosion inhibition effect of the benzothiazole side chain groups, synergize to further enhance the corrosion resistance of the waterborne polyurethane coating.

[0032] Compared with the prior art, the characteristics and advantages of the present invention are:

[0033] (1) The present invention starts from the molecular structure and improves its own anti-corrosion performance by synthesizing water-based polyurethane molecules with a specific structure. Compared with the general water-based polyurethane dispersion products on the market, the anti-corrosion performance of the obtained product has been greatly improved.

[0034] (2) The present invention introduces the benzothiazole group of the heterocyclic corrosion inhibitor into the molecular structure of the waterborne polyurethane through a chain extension reaction. Instead of becoming a part of the polyurethane main chain, the benzothiazole group forms a uniformly distributed, suspended and freely rotatable heterocyclic group side chain on the main chain. Therefore, the side chain benzothiazole group can be relatively freely oriented on the surface of the metal substrate and form a tight adsorption. In addition, the strong complexation force between the delocalized π bond formed by the planar resonance structure of the benzothiazole heterocyclic group and the metal atom further strengthens the interaction between the benzothiazole heterocyclic group and the metal.

[0035] (3) The present invention uses a mixed polyol of polycarbonate diol and polybutadiene diol as the soft segment of the waterborne polyurethane, which not only can obtain a waterborne polyurethane with excellent water resistance, heat resistance, chemical resistance and other properties, but also takes into account the strength and softness of the waterborne polyurethane chain, which promotes the adsorption of the benzothiazole side chain group of the waterborne polyurethane on the surface of the metal substrate.

[0036] (4) The present invention uses diisocyanate H 12 MDI, the small molecule chain extender 1,4-cyclohexanedimethanol (CHDM), and the post-chain extender N-aminoethylpiperazine (AEP) serve as the primary structural components of the waterborne polyurethane hard segment. The linearly symmetrical cyclic skeleton of these substances not only enhances the polyurethane's cohesive strength and improves its water resistance, but also promotes the tight alignment of the polyurethane molecular chains, creating favorable conditions for interaction between the polyurethane molecules and metal surfaces.

[0037] (5) The present invention selects trimethylolpropane (TMP) and diethylenetriamine (DETA) as crosslinking agents in the polyurethane prepolymer formation stage and the post-chain extension stage, which not only ensures the smooth progress of the waterborne polyurethane synthesis process (it will not cause gelation due to the high amount of crosslinking agent used in the prepolymerization stage), but also obtains the required crosslinking density. When the crosslinking point density is higher than 2.6×10 -4 mol / g, the resulting waterborne polyurethane coating is rigid, the activity of the polymer molecular chain is hindered, and it is not conducive to the interaction between the polymer and the metal atoms. -4 mol / g, the water resistance and mechanical properties of waterborne polyurethane are poor. Therefore, when the range is 2.0~2.6 × 10 -4 mol / g, the prepared waterborne polyurethane has good water resistance, heat resistance and mechanical strength, which further improves the anti-corrosion performance of the waterborne polyurethane prepared by the present invention.

[0038] (6) The soft and hard composition, molecular structure, and cross-linking density of the waterborne polyurethane of the present invention work synergistically with the side chain heterocyclic groups in the polyurethane molecules, thereby jointly promoting the improvement of the anti-corrosion performance of the waterborne polyurethane coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Polarization curves of the aqueous polyurethane dispersion coatings obtained in Example 1 and Comparative Example 1 (the substrate is a steel plate, tested after being immersed in a 3.5% by mass NaCl solution for 10 days). DETAILED DESCRIPTION

[0040] The technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention, but this does not constitute a limitation on the protection scope of the present invention.

[0041] Example 1

[0042] 80.0 g of polycarbonate diol (PCDL) with a molecular weight of 2000, 40.0 g of hydroxyl-terminated polybutadiene diol (HTPB) with a molecular weight of 2000, 1.2 g of trimethylolpropane (TMP) and 9.5 g of dimethylolpropionic acid (DMPA) were added to a 500 mL four-necked flask, heated to 120 ° C, and vacuum dehydrated for 1.0 h to obtain a uniform liquid mixture of the above hydroxyl components. The mixture was then cooled to 75 ° C and 66.0 g of 4,4'-dicyclohexylmethane diisocyanate (HDI) was added under nitrogen atmosphere. 12 MDI) and reacted at 80°C for 200 minutes to produce a polyurethane prepolymer with -NCO terminal groups. The prepolymer was cooled to 65°C, and 30.0g of acetone was added to reduce the viscosity of the system. A mixed solution of 2.2g of 1,4-cyclohexanedimethanol (CHDM) and 10g of acetone was then added. After reacting for 30 minutes, a mixture of 4.3g of 2-(1,3-benzothiazol-2-methylamino)ethanol and 10g of acetone was added. The reaction was continued at 65°C for 120 minutes to produce a polyurethane prepolymer solution. The resulting prepolymer solution was cooled to 35°C and neutralized with 6.8g of triethylamine for 15 minutes. Then, 380ml of deionized water was added and the high-speed disperser speed was increased to 6000 r / min. High-speed shear emulsification with water was performed for 10 minutes. The rotation speed was appropriately reduced, and then a mixed solution of 1.8g N-aminoethylpiperazine (AEP) and 10g water, followed by a mixed solution of 3.5g diethylenetriamine (DETA) and 10g water, were added sequentially, allowing post-chain extension to proceed for 80 minutes. Finally, acetone was removed by reduced pressure distillation at 40°C and a vacuum of 0.1 MPa to obtain an aqueous polyurethane dispersion with a solids content of 33.3wt%.

[0043] Example 2

[0044] 70.0 g of polycarbonate diol (PCDL) with a molecular weight of 2000, 50.0 g of hydroxyl-terminated polybutadiene diol (HTPB) with a molecular weight of 2000, 1.3 g of trimethylolpropane (TMP) and 9.0 g of dimethylolpropionic acid (DMPA) were added to a 500 mL four-necked flask, heated to 115 ° C, and vacuum dehydrated for 1.5 h to obtain a uniform liquid mixture of the above hydroxyl components. The mixture was then cooled to 75 ° C and 65.0 g of 4,4'-dicyclohexylmethane diisocyanate (HDI) was added under nitrogen atmosphere. 12MDI) and reacted at 80°C for 200 minutes to produce a polyurethane prepolymer with -NCO terminal groups. The prepolymer was cooled to 60°C, and 30.0g of acetone was added to reduce the viscosity of the system. A mixed solution of 2.6g of 1,4-cyclohexanedimethanol (CHDM) and 10g of acetone was then added. After reacting for 30 minutes, a mixture of 3.8g of 2-(1,3-benzothiazol-2-methylamino)ethanol and 10g of acetone was added. The reaction was continued at 60°C for 150 minutes to produce a polyurethane prepolymer solution. The resulting prepolymer solution was cooled to 40°C and neutralized with 6.5g of triethylamine for 20 minutes. Then, 380ml of deionized water was added and the high-speed disperser speed was increased to 6000 r / min. High-speed shear emulsification with water was performed for 5 minutes. The rotation speed was appropriately reduced, and then a mixed solution of 1.6 g N-aminoethylpiperazine (AEP) and 10 g water, followed by a mixed solution of 3.5 g diethylenetriamine (DETA) and 10 g water, were added sequentially for a post-chain extension reaction for 90 minutes. Finally, the acetone was removed by reduced pressure distillation at 40°C and a vacuum of 0.1 MPa to obtain a waterborne polyurethane dispersion with a solids content of 33.2 wt%.

[0045] Example 3

[0046] 40.0 g of polycarbonate diol (PCDL) with a molecular weight of 2000, 80.0 g of hydroxyl-terminated polybutadiene diol (HTPB) with a molecular weight of 2000, 2.0 g of trimethylolpropane (TMP) and 11.0 g of dimethylolpropionic acid (DMPA) were added to a 500 mL four-necked flask, heated to 115 ° C, and vacuum dehydrated for 2.0 h to obtain a uniform liquid mixture of the above hydroxyl components. The mixture was then cooled to 75 ° C and 75.0 g of 4,4'-dicyclohexylmethane diisocyanate (HDI) was added under nitrogen atmosphere. 12MDI) and reacted at 83°C for 200 minutes to produce a polyurethane prepolymer with -NCO terminal groups. The prepolymer was cooled to 65°C, and 30.0g of acetone was added to reduce the viscosity of the system. A mixed solution of 3.4g of 1,4-cyclohexanedimethanol (CHDM) and 10g of acetone was then added. After reacting for 30 minutes, a mixture of 3.3g of 2-(1,3-benzothiazol-2-methylamino)ethanol and 10g of acetone was added. The reaction was continued at 63°C for 130 minutes to produce a polyurethane prepolymer solution. The resulting prepolymer solution was cooled to 40°C and neutralized with 7.9g of triethylamine for 15 minutes. Then, 390ml of deionized water was added and the high-speed disperser speed was increased to 5000 rpm. High-speed shear emulsification was performed with water for 15 minutes. The rotation speed was appropriately reduced, and then a mixed solution of 1.5 g N-aminoethylpiperazine (AEP) and 10 g water, followed by a mixed solution of 4.3 g diethylenetriamine (DETA) and 10 g water, were added sequentially for post-chain extension for 80 minutes. Finally, the acetone was removed by reduced pressure distillation at 40°C and a vacuum of 0.1 MPa to obtain an aqueous polyurethane dispersion with a solids content of 34.0 wt%.

[0047] Example 4

[0048] 56.0 g of polycarbonate diol (PCDL) with a molecular weight of 2000, 77.0 g of hydroxyl-terminated polybutadiene diol (HTPB) with a molecular weight of 2000, 2.1 g of trimethylolpropane (TMP) and 6.9 g of dimethylolpropionic acid (DMPA) were added to a 500 mL four-necked flask, heated to 120 ° C, and vacuum dehydrated for 1.5 h to obtain a uniform liquid mixture of the above hydroxyl components. The mixture was then cooled to 75 ° C and 61.0 g of 4,4'-dicyclohexylmethane diisocyanate (HDI) was added under nitrogen atmosphere. 12MDI) and reacted at 80°C for 210 minutes to produce a polyurethane prepolymer with -NCO terminal groups. The prepolymer was cooled to 65°C, and 30.0g of acetone was added to reduce the viscosity. A mixed solution of 2.4g of 1,4-cyclohexanedimethanol (CHDM) and 10g of acetone was then added. After reacting for 30 minutes, a mixture of 3.7g of 2-(1,3-benzothiazol-2-methylamino)ethanol and 10g of acetone was added. The reaction was continued at 62°C for 150 minutes to produce a polyurethane prepolymer solution. The resulting prepolymer solution was cooled to 38°C and neutralized with 4.9g of triethylamine for 20 minutes. Then, 380ml of deionized water was added and the high-speed disperser speed was increased to 6000 r / min. Water high-speed shear emulsification was performed for 5 minutes. The rotation speed was appropriately reduced, and then a mixed solution of 1.3 g N-aminoethylpiperazine (AEP) and 10 g water, followed by a mixed solution of 2.8 g diethylenetriamine (DETA) and 10 g water, were added sequentially for a post-chain extension reaction for 90 minutes. Finally, the acetone was removed by reduced pressure distillation at 40°C and a vacuum of 0.1 MPa to obtain a waterborne polyurethane dispersion with a solids content of 33.9 wt%.

[0049] Example 5

[0050] 68.0 g of polycarbonate diol (PCDL) with a molecular weight of 2000, 68.0 g of hydroxyl-terminated polybutadiene diol (HTPB) with a molecular weight of 2000, 1.6 g of trimethylolpropane (TMP) and 8.3 g of dimethylolpropionic acid (DMPA) were added to a 500 mL four-necked flask, heated to 110 ° C, and vacuum dehydrated for 1.5 h to obtain a uniform liquid mixture of the above hydroxyl components. The mixture was then cooled to 75 ° C and 68.0 g of 4,4'-dicyclohexylmethane diisocyanate (HDI) was added under nitrogen atmosphere. 12MDI) and reacted at 85°C for 180 minutes to produce a polyurethane prepolymer with -NCO terminal groups. The prepolymer was cooled to 65°C, and 30.0 g of acetone was added to reduce the viscosity. A mixed solution of 2.2 g of 1,4-cyclohexanedimethanol (CHDM) and 10 g of acetone was then added. After reacting for 30 minutes, a mixture of 5.0 g of 2-(1,3-benzothiazol-2-methylamino)ethanol and 10 g of acetone was added. The reaction was continued at 60°C for 150 minutes to produce a polyurethane prepolymer solution. The resulting prepolymer solution was cooled to 45°C and neutralized with 6.0 g of triethylamine for 10 minutes. Then, 410 ml of deionized water was added and the high-speed disperser speed was increased to 7000 r / min. High-speed shear emulsification with water was performed for 5 minutes. The rotation speed was appropriately reduced, and then a mixed solution of 1.2 g N-aminoethylpiperazine (AEP) and 10 g water, followed by a mixed solution of 3.9 g diethylenetriamine (DETA) and 10 g water, were added sequentially, allowing post-chain extension to proceed for 60 minutes. Finally, acetone was removed by reduced pressure distillation at 40°C and a vacuum of 0.1 MPa to obtain an aqueous polyurethane dispersion with a solids content of 33.6 wt%.

[0051] Example 6

[0052] 46.0 g of polycarbonate diol (PCDL) with a molecular weight of 2000, 70.0 g of hydroxyl-terminated polybutadiene diol (HTPB) with a molecular weight of 2000, 2.0 g of trimethylolpropane (TMP) and 8.5 g of dimethylolpropionic acid (DMPA) were added to a 500 mL four-necked flask, heated to 120 ° C, and vacuum dehydrated for 1.0 h to obtain a uniform liquid mixture of the above hydroxyl components. The mixture was then cooled to 75 ° C and 68.0 g of 4,4'-dicyclohexylmethane diisocyanate (HDI) was added under nitrogen atmosphere. 12MDI) and reacted at 85°C for 180 minutes to produce a polyurethane prepolymer with -NCO terminal groups. The prepolymer was cooled to 63°C, and 30.0g of acetone was added to reduce the viscosity. A mixed solution of 3.6g of 1,4-cyclohexanedimethanol (CHDM) and 10g of acetone was then added. After reacting for 30 minutes, a mixture of 3.6g of 2-(1,3-benzothiazol-2-methylamino)ethanol and 10g of acetone was added. The reaction was continued at 63°C for 150 minutes to produce a polyurethane prepolymer solution. The resulting prepolymer solution was cooled to 45°C and neutralized with 6.1g of triethylamine for 20 minutes. Then, 380ml of deionized water was added and the high-speed disperser speed was increased to 7000 r / min. High-speed shear emulsification with water was performed for 10 minutes. The speed was appropriately reduced, and then a mixed solution of 1.0 g N-aminoethylpiperazine (AEP) and 10 g water, followed by a mixed solution of 3.8 g diethylenetriamine (DETA) and 10 g water, were added sequentially for a post-chain extension reaction for 90 minutes. Finally, the acetone was removed by reduced pressure distillation at 40°C and a vacuum of 0.1 MPa to obtain a waterborne polyurethane dispersion with a solids content of 33.8 wt%.

[0053] Comparative Example 1

[0054] The 2-(1,3-benzothiazole-2-methylamino)ethanol (BTA) in Example 1 was replaced with the same molar amount of the hybrid compound chain extender 2-(4-hydroxyphenyl)benzo[b]thiophene-6-ol (HBT). Other conditions were the same as in Example 1. A waterborne polyurethane dispersion with a solid content of 33.5 wt% was obtained.

[0055] Comparative Example 2

[0056] Instead of using diethylenetriamine (DETA), a polyamine crosslinker used in the post-chain extension step, N-aminoethylpiperazine (AEP) with the same molar number of amino groups was used. The other components were identical to those in Example 1. An aqueous polyurethane dispersion with a solid content of 33.7 wt% was obtained.

[0057] The above Examples 1-6 and Comparative Examples 1 and 2 were analyzed and tested for performance. The results are shown in Table 1.

[0058] Table 1 Comparison of properties of aqueous polyurethane dispersions of Examples 1-6 and Comparative Examples 1-2

[0059]

[0060] The above results were obtained by referring to the following test methods or standards:

[0061] Crosslink density (DCP): The molar concentration of crosslinks (mol / g) is estimated based on the amount of each raw material in the waterborne polyurethane dispersion. The calculation method is as follows:

[0062] DCP = [(functionality of cross-linker 1 - 2) * moles of cross-linker 1 + (functionality of cross-linker 2 - 2) * moles of cross-linker 2 + ...] / total solid mass of waterborne polyurethane resin

[0063] Average particle size of waterborne polyurethane dispersion: The particle size was measured at 25°C by diluting the emulsion to 0.1% using a MALVERN laser scattering particle size analyzer.

[0064] Adhesion: Adhesion of waterborne polyurethane dispersion coatings was tested using the cross-cut method according to the standard GB / T 9286-1998 "Cross-cut test for paint and varnish films".

[0065] Water absorption rate: According to the standard JC / T 1017-2006 "Polymer emulsion for building waterproof coatings", the water absorption rate of water-based polyurethane latex film is tested.

[0066] Polarization curve test: First, the Q235 steel plate coated with waterborne polyurethane latex coating was immersed in a 3.5% mass fraction NaCl solution for 10 days (d). Then, a three-electrode system was constructed using the working electrode, the platinum electrode as the counter electrode, and the saturated calomel electrode as the reference electrode. The polarization curve test was performed on the plate in a 3.5% NaCl solution using an electrochemical workstation. In the polarization curve test, it is generally believed that the lower the density of the corrosion current, the better the corrosion resistance of the coating, and the closer the corrosion potential is to 0 V, the better the corrosion resistance of the coating. The corrosion potential Ecorr of the products in Examples 1 to 6 is closer to 0V, which is much greater than the Ecorr of the comparative example (see Figure 1 The corrosion current icorr of Examples 1 to 6 is on the order of 10 -9 , while the corrosion current icorr of Comparative Examples 1 and 2 is on the order of 10 -6 and 10 -7 , the former is 2 to 3 orders of magnitude greater than the latter. This shows that the aqueous polyurethane dispersion prepared by the present invention has better anti-corrosion performance.

[0067] The above is 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 principles of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing an aqueous polyurethane resin containing a heterocyclic group in the side chain, characterized in that: The following steps are involved: (1) Adding polymer polyol, small molecule polyhydroxy chain extender and hydrophilic chain extender into a four-necked flask equipped with a stirrer, a thermometer and a vacuum valve, heating to 110-120°C, vacuum dehydrating for 1-2 hours, and then cooling to 75°C to obtain a liquid mixture of hydroxy components; the small molecule polyhydroxy chain extender is trimethylolpropane, and its addition amount accounts for 0.58-0.98% of the total solid matter in the aqueous polyurethane dispersion; (2) Opening nitrogen protection, adding the polyisocyanate component to the four-necked flask containing the liquid mixture of the hydroxyl component, and reacting at 80-85°C for 180-210 minutes to obtain a terminal-NCO polyurethane prepolymer; (3) Adding an appropriate amount of organic solvent to adjust the viscosity, and lowering the system temperature to 60-65°C, then adding a small molecule diol chain extender, and after reacting for 30 minutes, adding a heterocyclic compound chain extender containing two active groups, and continuing the reaction for 120-150 minutes, and finally adding an organic solvent to adjust the viscosity to obtain a low-viscosity -NCO group-terminated polyurethane prepolymer solution; the molecular structure of the heterocyclic compound chain extender containing two active groups described in step (3) is: , its addition amount accounts for 1.50~2.21% of the total solid matter in the waterborne polyurethane dispersion; (4) Cooling the prepolymer solution to 35-45°C, adding a neutralizing agent, and vigorously stirring for 10-20 minutes, then adding an appropriate amount of deionized water, and emulsifying at a high shear force of 5000-7000 r / min for 5-15 minutes to obtain a polyurethane dispersion aqueous solution; (5) adding a small molecule diamine post-chain extender and a polyamine crosslinker to the aqueous polyurethane dispersion and reacting for 60 to 90 minutes; the polyamine crosslinker is diethylenetriamine, which accounts for 1.31 to 1.95% of the total solid matter in the aqueous polyurethane dispersion; (6) The organic solvent in the aqueous dispersion solution is removed by vacuum distillation to obtain an aqueous polyurethane dispersion.

2. The method for preparing a waterborne polyurethane resin having a side chain containing a heterocyclic group as claimed in claim 1, wherein: The polymer polyol described in step (1) is a mixture of polycarbonate diol PCDL prepared from 1,6-hexanediol and hydroxyl-terminated polybutadiene diol HTPB, with a mass ratio of PCDL / HTPB = 0.5~2.0, and the total amount of the two accounts for 54.40~62.38% of the total solid matter in the aqueous polyurethane dispersion.

3. The method for preparing a waterborne polyurethane resin containing a heterocyclic group in a side chain according to claim 1, wherein: The hydrophilic chain extender described in step (1) is dimethylolpropionic acid, and its added amount accounts for 3.24~4.99% of the total solid matter in the aqueous polyurethane dispersion.

4. The method for preparing a waterborne polyurethane resin having a side chain containing a heterocyclic group as claimed in claim 1, wherein: The polyisocyanate described in step (2) is 4,4'-dicyclohexylmethane diisocyanate, and its amount accounts for 28.61-34.0% of the total solid matter in the aqueous polyurethane dispersion.

5. The method for preparing a waterborne polyurethane resin containing a heterocyclic group in a side chain according to claim 1, wherein: The small molecule diol chain extender described in step (3) is 1,4-cyclohexanedimethanol, and its added amount accounts for 0.97~1.54% of the total solid matter in the aqueous polyurethane dispersion.

6. The method for preparing a waterborne polyurethane resin having a side chain containing a heterocyclic group as claimed in claim 1, wherein: The neutralizing agent in step (4) is triethylamine, and its amount is calculated based on the number of moles required to neutralize 95 mol percent of the carboxyl groups of the hydrophilic chain extender dimethylolpropionic acid.

7. The method for preparing a waterborne polyurethane resin containing a heterocyclic group in a side chain according to claim 1, wherein: The small molecule diamine post-chain extender described in step (5) is selected from N-aminoethylpiperazine, which accounts for 0.53-0.86% of the total solid matter in the aqueous polyurethane dispersion.

8. A waterborne polyurethane resin containing a heterocyclic group in the side chain, characterized in that: Prepared by the preparation method according to any one of claims 1 to 7.

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