Waterborne polyurethane resin with side chain containing heterocyclic group and preparation method of waterborne polyurethane resin

Abstract

The invention discloses a water-based polyurethane dispersion containing a heterocyclic group side chain and having an excellent anti-corrosion function and a preparation method of the water-based polyurethane dispersion. The key technology is that a benzothiazole group is introduced into a side chain structure of a waterborne polyurethane molecule to form a benzothiazole group side chain which is uniformly distributed and can rotate freely, and the benzothiazole group side chain can be oriented on the surface of a metal substrate and form tight adsorption. Besides, a component with a linear symmetric annular skeleton structure is selected to reinforce the cohesive strength of the waterborne polyurethane, a proper cross-linking agent and a synthesis process thereof are determined, and when the density of a cross-linking point is in a range of 2.0-2.6 * 10 <-4 > mol / g, the water resistance, the heat resistance and the mechanical strength of the obtained waterborne polyurethane dispersion are all enhanced, and the water resistance, the heat resistance and the mechanical strength of the waterborne polyurethane dispersion are improved. And the characteristics cooperate with the corrosion inhibition effect of the benzothiazole side chain group, so that the corrosion resistance of the waterborne polyurethane coating film is further improved. The waterborne polyurethane resin synthesized by the invention can be used as a film-forming polymer for preparing waterborne anticorrosive paint with excellent performance.

Description

Technical Field

[0001] The 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 and a preparation method thereof, which is used for corrosion prevention and protection of metal substrates. Background Art

[0002] Metal corrosion is a common problem faced by all mankind, which seriously affects all aspects of human life, including economy, environment and health and safety. The total cost of corrosion in my country accounts for about 4% of GDP, and the cost of corrosion is greater than the sum of all natural disaster losses. In order to protect metal materials, inhibit their corrosion and extend their service life, the application of high-performance anti-corrosion coatings is a simple and effective method. Polyurethane coatings have received high attention due to their excellent comprehensive properties such as excellent durability, chemical resistance and flexibility, and have become one of the main varieties of anti-corrosion coatings. Polyurethane can adhere well to various metal substrates to form a solid protective layer, which can protect the substrate from corrosive agents (such as moisture, salt and industrial chemicals), can withstand harsh environmental conditions and mechanical stress, ensure lasting protection and reduce maintenance costs. These characteristics make it the first choice for extending the service life of metal structures and equipment. In recent years, polyurethane anti-corrosion coatings have developed rapidly and have been widely used in a variety of corrosive environments, producing obvious economic and social benefits.

[0003] With the increasingly stringent environmental regulations of various countries and the continuous enhancement of people's environmental awareness, the emission of volatile organic compounds (VOC) in traditional solvent-based polyurethane coatings is subject to increasingly strict restrictions. Therefore, environmentally friendly water-based polyurethane anti-corrosion coatings have developed rapidly and are showing a trend of gradually replacing solvent-based polyurethane anti-corrosion coatings. However, for a long time in the future, if water-based polyurethane coatings want to replace solvent-based polyurethane and gain competitive advantages with solvent-based polyurethane coatings, the key is to continuously improve their own anti-corrosion performance.

[0004] The corrosion process in which metal materials undergo electrochemical reactions with the environment, causing them to slowly decompose or be destroyed, is essentially an oxidation reaction between metals and water and oxygen, which requires the coexistence of water and oxygen, because without water and oxygen, corrosion is generally difficult to occur. In response to this corrosion mechanism of metals, people have mainly conducted research in the following two directions to improve the anti-corrosion performance of waterborne polyurethane.

[0005] First, improve the shielding and barrier properties of waterborne polyurethane protective coatings, shield or hinder the penetration of water and oxygen through the waterborne polyurethane coating to the metal substrate. This is an important way to improve the anti-corrosion performance of waterborne polyurethane coatings. Since hydrophilic groups are introduced into waterborne polyurethane molecules during the synthesis process, the coating film is water-sensitive, so its water resistance and anti-corrosion performance are poorer than those of solvent-based polyurethane coatings. By optimizing the raw material composition of synthetic waterborne polyurethanes and introducing polyols and chain extenders with hydrophobic and hydrolysis-resistant properties, the water absorption and water resistance of waterborne polyurethanes and their coatings can be improved. For example, patent CN118109159A obtains waterborne polyurethanes with excellent mechanical properties and water resistance by preferably selecting polytetrahydrofuran ether diol and linseed oil polyol as polyol components. Patent CN202210997635.8 uses dihydroxylated isobornyl methacrylate (IBA(OH)2) as a chain extender, and introduces its specific alicyclic molecular structure into the side chain of the polyurethane molecular skeleton, which enhances the hydrophobicity of the product, improves the water resistance of waterborne polyurethane coatings, and expands the scope of application of waterborne polyurethane coatings. In addition, increasing the crosslinking density of waterborne polyurethane resin molecules, adding internal crosslinking agents, or adding external crosslinking agents in the process of synthesizing polyurethane are all effective methods to improve the water resistance of waterborne polyurethane coatings.

[0006] Second, by forming a well-adherent waterborne polyurethane protective coating on the surface of the metal substrate, the electrochemical reaction between the metal substrate and water and oxygen is hindered or delayed. To achieve this goal, the main method at present is to add effective anti-corrosion components, such as active anti-rust pigments, corrosion inhibitors, etc., to the waterborne polyurethane coating. Organic corrosion inhibitors have the advantages of a wide variety, a wide range of adaptability, and high corrosion inhibition efficiency, and are therefore widely used. Heterocyclic compounds containing elements such as N, S, and P, such as heterocyclic compounds containing groups such as imidazole, thiazole, and thiophene, are the most widely studied type in the field of corrosion inhibitors. Usually, this type of corrosion inhibitor can be adsorbed on the metal surface, can form coordination bonds with metal ions, and form complexes on the metal surface. The stronger the adsorption, the more stable the complex, the stronger the interaction between the corrosion inhibitor and the metal matrix, and the better the corrosion inhibition effect. However, this type of small molecule heterocyclic corrosion inhibitor has high requirements for the metal substrate and the waterborne coating formulation, and most of them are toxic, and will migrate and seep out in the coating film, affecting the durability of the anti-corrosion coating. These facts show that organic small molecule corrosion inhibitors have serious pollution problems both in the synthesis and application process, and are no longer in line with the current trend of green, low-carbon and sustainable development. Recent studies have shown that in the synthesis process of waterborne polyurethane, the heterocyclic groups of organic heterocyclic corrosion inhibitors can be introduced into the molecular structure of waterborne polyurethane through small molecule chain extension reactions, thereby improving or enhancing the performance of waterborne polyurethane. For example, patent CN201510349614.5 uses a diamine compound containing an imidazole group (such as 5-(3-aminopropyl)-1H-imidazole-2-amine, etc.) as a chain extender to introduce the imidazole group into the main chain molecular structure of waterborne polyurethane, thereby producing 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 main chain molecular structure of waterborne polyurethane to produce waterborne polyurethane coatings with good adhesion, water resistance, wear resistance, and excellent mechanical properties. Patent CN202410748386.8 uses dihydroxybenzoxazine as a chain extender to produce waterborne polyurethane with excellent mechanical properties, high adhesion and water resistance, which greatly broadens the application scope of waterborne polyurethane materials and gives it broad application prospects in the fields of anti-corrosion, adhesives, electronics industry, and aerospace. Patent CN202310534843.9 first synthesized mercaptobenzimidazole, and then introduced benzimidazole groups by conjugated grafting, which effectively prevented the occurrence of flash rust on the metal substrate during the film-forming 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 matter is 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 reaction, grafting reaction, etc. will enhance the water resistance, adhesion or corrosion resistance of polyurethane. However, these patents also show 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 anticorrosion 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 for chain activity is small, and it can work synergistically with other groups in the waterborne polyurethane molecule to achieve anti-corrosion, obtain a suitable 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 having an anti-corrosion property and containing heterocyclic groups in the side chains.

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

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

[0011] (1) adding a polymer polyol, a small molecular weight polyhydroxy chain extender (crosslinking agent), and a 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 the above hydroxyl components;

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

[0013] (3) adding an appropriate amount of organic solvent to adjust the viscosity, 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 -NCO group-terminated polyurethane prepolymer solution with a low viscosity;

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

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

[0016] (6) Removing the organic solvent from the dispersion solution by vacuum distillation to obtain an aqueous polyurethane dispersion.

[0017] The polymer polyols in the above step (1) include polyether polyols, polyester polyols, polycarbonate polyols and polyolefin polyols, etc., and the molecular weights are all 1000, 2000 or 3000. Polyester polyols include poly-ε-caprolactone diol (PCL), poly-1,4-butylene adipate (PBA), 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 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 in a ratio of PCDL / HTPB=0.5 to 2.0 (mass ratio), and the total amount of the two accounts for 54.40 to 62.38% of the total solid matter 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 the small molecule polyhydroxy crosslinker, and its added 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 added amount accounts for 3.24-4.99% of the total solid matter in the aqueous polyurethane dispersion.

[0020] The polyisocyanate in the above step (2) includes 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 carbocyclic rings and small molecule diols without carbocyclic rings. Small molecule diol chain extenders containing carbocyclic rings include 1,3- or 1,4-cyclohexanedimethanol (CHDM), 1,3- or 1,4-cyclohexanediol, hydrogenated bisphenol A, etc.; small molecule chain extenders without carbocyclic 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 to 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 the above step (3) refers to a compound containing heterocyclic groups such as imidazole, thiophene, thiazole, pyridine, etc. 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-benzothiazole-2-methylamino)ethanol, 2-hydrazinebenzothiazole, etc., or a mixture of any two or more thereof can be selected; preferably, 2-(1,3-benzothiazole-2-methylamino)ethanol is the heterocyclic compound chain extender of the present invention, and its addition amount accounts for 1.50 to 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 other steps of preparing the polyurethane prepolymer of the present invention, an appropriate amount of organic solvent can be added as needed to adjust the viscosity of the system, and the amount generally accounts for 60 to 100% of the total solid matter in the aqueous polyurethane dispersion. Acetone is preferably used as the solvent.

[0024] The neutralizing agent in the above step (4) is one of trimethylamine, triethylamine, dimethylethanolamine, methyldiethanolamine, triethanolamine, ammonia water, 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 dimethylol propionic acid (DMPA);

[0025] The diamine post-chain extender described 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), isophordiamine, and N-methyl-3,3′-diaminopropylamine; preferably, N-aminoethylpiperazine (AEP) is used as the diamine post-chain extender, which accounts for 0.53 to 0.86% of the total solid matter in the aqueous polyurethane dispersion.

[0026] The polyamine crosslinking agent described 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 to 1.95% of the total solid matter in the aqueous polyurethane dispersion.

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

[0028] A waterborne polyurethane dispersion with excellent anti-corrosion performance is prepared by the above method. The average particle size of the waterborne polyurethane dispersion prepared by the above method is 92-128 nm, and the solid content is about 33.5wt%.

[0029] The principle of the present invention is to introduce a benzothiazole heterocyclic group with a corrosion inhibition function into the molecular structure of polyurethane by means of a chain extension reaction, and form a suspended heterocyclic group side chain on the main chain of the polyurethane. This side chain heterocyclic group is connected to the main chain of the polyurethane through a freely rotatable NCC single bond, which reduces the 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 tight 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, so it has 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 linear symmetrical cyclic skeleton structure of MDI, small molecule chain extender 1,4-cyclohexanedimethanol (CHDM) and post-chain extender N-aminoethylpiperazine (AEP) leads to the tight directional arrangement and enhanced cohesive strength of the polyurethane molecular chains, and the appropriate cross-linking density formed by trimethylolpropane (TMP) and diethylenetriamine (DETA), all of which further improve the water resistance, heat resistance and mechanical strength of the waterborne polyurethane prepared by the present invention. These characteristics work synergistically with the corrosion inhibition effect of the benzothiazole side chain group to further improve 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 waterborne polyurethane molecules with a specific structure. The obtained product has greatly improved anti-corrosion performance compared with general waterborne polyurethane dispersion products on the market.

[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 selects diisocyanate H 12 MDI, small molecule chain extender 1,4-cyclohexanedimethanol (CHDM) and post-chain extender N-aminoethylpiperazine (AEP) are the main structural components of the hard segment of waterborne polyurethane. The linear symmetrical ring skeleton structure of these substances not only improves the cohesive strength of polyurethane and the water resistance of waterborne polyurethane, but also promotes the close directional arrangement of polyurethane molecular chains, creating good environmental conditions for the interaction between 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. -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 hardness composition, molecular structure, and cross-linking density of the waterborne polyurethane of the present invention cooperate with the side chain heterocyclic groups in the polyurethane molecules to jointly promote 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 in conjunction with 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, then cooled to 75 ° C, and 66.0 g of 4,4'-dicyclohexylmethane diisocyanate (H 12 MDI), react at 80℃ for 200min to obtain a polyurethane prepolymer with -NCO end group. The prepolymer was cooled to 65℃, 30.0g acetone was added to reduce the viscosity of the system, and then a mixed solution of 2.2g 1,4-cyclohexanedimethanol (CHDM) and 10g acetone was added. After 30min of reaction, a mixture of 4.3g 2-(1,3-benzothiazole-2-methylamino)ethanol and 10g acetone was added, and the reaction was continued at 65℃ for 120min to obtain a polyurethane prepolymer solution. The obtained prepolymer solution was cooled to 35℃, 6.8g triethylamine was added for neutralization for 15min, and then 380ml deionized water was added and the speed of the high-speed disperser was increased to 6000r / min, and water was sheared and emulsified at high speed for 10min. The rotation speed was appropriately reduced, and then a mixed solution of 1.8 g N-aminoethylpiperazine (AEP) and 10 g water, and a mixed solution of 3.5 g diethylenetriamine (DETA) and 10 g water were added in sequence to carry out a post-chain extension reaction for 80 min. Finally, acetone was removed by reduced pressure distillation at a temperature of 40° C. and a vacuum degree of 0.1 MPa to obtain an aqueous polyurethane dispersion with a solid content of 33.3 wt%.

[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, then cooled to 75 ° C, and 65.0 g of 4,4'-dicyclohexylmethane diisocyanate (H 12MDI), react at 80℃ for 200min to obtain a polyurethane prepolymer with -NCO end group. The prepolymer was cooled to 60℃, 30.0g acetone was added to reduce the viscosity of the system, and then a mixed solution of 2.6g 1,4-cyclohexanedimethanol (CHDM) and 10g acetone was added. After reacting for 30min, a mixture of 3.8g 2-(1,3-benzothiazole-2-methylamino)ethanol and 10g acetone was added, and the reaction was continued at 60℃ for 150min to obtain a polyurethane prepolymer solution. The obtained prepolymer solution was cooled to 40℃, 6.5g triethylamine was added for neutralization for 20min, and then 380ml deionized water was added and the speed of the high-speed disperser was increased to 6000r / min, and water was sheared and emulsified at high speed for 5min. The rotation speed was appropriately reduced, and then a mixed solution of 1.6 g N-aminoethylpiperazine (AEP) and 10 g water, and a mixed solution of 3.5 g diethylenetriamine (DETA) and 10 g water were added in sequence to carry out a post-chain extension reaction for 90 min. Finally, acetone was removed by reduced pressure distillation at a temperature of 40° C. and a vacuum degree of 0.1 MPa to obtain an aqueous polyurethane dispersion with a solid 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, then cooled to 75 ° C, and 75.0 g of 4,4'-dicyclohexylmethane diisocyanate (H 12MDI), react at 83°C for 200min to obtain a polyurethane prepolymer with -NCO end group. The prepolymer was cooled to 65°C, 30.0g acetone was added to reduce the viscosity of the system, and then a mixed solution of 3.4g 1,4-cyclohexanedimethanol (CHDM) and 10g acetone was added. After reacting for 30min, a mixture of 3.3g 2-(1,3-benzothiazole-2-methylamino)ethanol and 10g acetone was added, and the reaction was continued at 63°C for 130min to obtain a polyurethane prepolymer solution. The obtained prepolymer solution was cooled to 40°C, 7.9g triethylamine was added for neutralization for 15min, and then 390ml deionized water was added and the speed of the high-speed disperser was increased to 5000r / min, and water was sheared and emulsified at high speed for 15min. The rotation speed was appropriately reduced, and then a mixed solution of 1.5 g N-aminoethylpiperazine (AEP) and 10 g water, and a mixed solution of 4.3 g diethylenetriamine (DETA) and 10 g water were added in sequence to carry out a post-chain extension reaction for 80 min. Finally, acetone was removed by reduced pressure distillation at a temperature of 40° C. and a vacuum degree of 0.1 MPa to obtain an aqueous polyurethane dispersion with a solid 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, then cooled to 75 ° C, and 61.0 g of 4,4'-dicyclohexylmethane diisocyanate (H 12MDI), react at 80℃ for 210min to obtain a polyurethane prepolymer with -NCO end group. The prepolymer was cooled to 65℃, 30.0g acetone was added to reduce the viscosity of the system, and then a mixed solution of 2.4g 1,4-cyclohexanedimethanol (CHDM) and 10g acetone was added. After 30min of reaction, a mixture of 3.7g 2-(1,3-benzothiazole-2-methylamino)ethanol and 10g acetone was added, and the reaction was continued at 62℃ for 150min to obtain a polyurethane prepolymer solution. The obtained prepolymer solution was cooled to 38℃, 4.9g triethylamine was added for neutralization for 20min, and then 380ml deionized water was added and the speed of the high-speed disperser was increased to 6000r / min, and water was sheared and emulsified at high speed for 5min. The rotation speed was appropriately reduced, and then a mixed solution of 1.3 g N-aminoethylpiperazine (AEP) and 10 g water, and a mixed solution of 2.8 g diethylenetriamine (DETA) and 10 g water were added in sequence to carry out a post-chain extension reaction for 90 min. Finally, acetone was removed by reduced pressure distillation at a temperature of 40° C. and a vacuum degree of 0.1 MPa to obtain an aqueous polyurethane dispersion with a solid 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, then cooled to 75 ° C, and 68.0 g of 4,4'-dicyclohexylmethane diisocyanate (H 12MDI), react at 85°C for 180min to obtain a polyurethane prepolymer with -NCO terminal group. The prepolymer was cooled to 65°C, 30.0g acetone was added to reduce the viscosity of the system, and then a mixed solution of 2.2g 1,4-cyclohexanedimethanol (CHDM) and 10g acetone was added. After reacting for 30min, a mixture of 5.0g 2-(1,3-benzothiazole-2-methylamino)ethanol and 10g acetone was added, and the reaction was continued at 60°C for 150min to obtain a polyurethane prepolymer solution. The obtained prepolymer solution was cooled to 45°C, 6.0g triethylamine was added for neutralization for 10min, and then 410ml deionized water was added and the speed of the high-speed disperser was increased to 7000r / min, and water was sheared and emulsified at high speed for 5min. The rotation speed was appropriately reduced, and then a mixed solution of 1.2 g N-aminoethylpiperazine (AEP) and 10 g water, and a mixed solution of 3.9 g diethylenetriamine (DETA) and 10 g water were added in sequence to carry out a post-chain extension reaction for 60 min. Finally, acetone was removed by reduced pressure distillation at a temperature of 40° C. and a vacuum degree of 0.1 MPa to obtain an aqueous polyurethane dispersion with a solid 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, then cooled to 75 ° C, and 68.0 g of 4,4'-dicyclohexylmethane diisocyanate (H 12MDI), react at 85°C for 180min to obtain a polyurethane prepolymer with -NCO terminal group. The prepolymer was cooled to 63°C, 30.0g acetone was added to reduce the viscosity of the system, and then a mixed solution of 3.6g 1,4-cyclohexanedimethanol (CHDM) and 10g acetone was added. After reacting for 30min, a mixture of 3.6g 2-(1,3-benzothiazole-2-methylamino)ethanol and 10g acetone was added, and the reaction was continued at 63°C for 150min to obtain a polyurethane prepolymer solution. The obtained prepolymer solution was cooled to 45°C, 6.1g triethylamine was added for neutralization for 20min, and then 380ml deionized water was added and the speed of the high-speed disperser was increased to 7000r / min, and water was sheared and emulsified at high speed for 10min. The rotation speed was appropriately reduced, and then a mixed solution of 1.0 g N-aminoethylpiperazine (AEP) and 10 g water, and a mixed solution of 3.8 g diethylenetriamine (DETA) and 10 g water were added in sequence to carry out a post-chain extension reaction for 90 min. Finally, acetone was removed by reduced pressure distillation at a temperature of 40° C. and a vacuum degree of 0.1 MPa to obtain an aqueous polyurethane dispersion with a solid content of 33.8 wt%.

[0053] Comparative Example 1

[0054] The hybrid compound chain extender 2-(4-hydroxyphenyl)benzo[b]thiophene-6-ol (HBT) was used in place of the 2-(1,3-benzothiazole-2-methylamino)ethanol (BTA) in Example 1, and the rest was the same as Example 1. An aqueous polyurethane dispersion with a solid content of 33.5 wt % was obtained.

[0055] Comparative Example 2

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

[0057] The above-mentioned 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 Performance comparison 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] Crosslinking point density (DCP): The molar concentration (mol / g) of crosslinking points is estimated based on the amount of each raw material used in the waterborne polyurethane dispersion. The calculation method is as follows:

[0062] DCP = [(functionality of cross-linking agent 1 - 2) * moles of cross-linking agent 1 + (functionality of cross-linking agent 2 - 2) * moles of cross-linking agent 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 mass concentration of the emulsion to 0.1% using a MALVERN laser scattering particle size analyzer.

[0064] Adhesion: According to the standard GB / T 9286-1998 "Cross-cut test for paint and varnish films", the cross-cut method is used to test the adhesion of waterborne polyurethane dispersion coatings.

[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, immerse the Q235 steel plate coated with water-based polyurethane latex coating in a 3.5% NaCl solution by mass for 10 days (d), then use it as the working electrode, the platinum electrode as the counter electrode, and the saturated calomel electrode as the reference electrode to construct a three-electrode system, and use an electrochemical workstation to perform a polarization curve test in a 3.5% NaCl solution. 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 0V, the better the corrosion resistance of the coating. The corrosion potential Ecorr of the products of 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. It can be seen 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 a person skilled in the art can make several improvements and modifications without departing from the principle 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 a polymer polyol, a small molecular weight polyhydroxy chain extender, and a 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 the above hydroxyl components; (2) opening nitrogen protection, adding a polyisocyanate component to the four-necked flask containing the liquid mixture of the hydroxyl component, and reacting at 80 to 85° C. for 180 to 210 minutes to obtain a terminal-NCO polyurethane prepolymer; (3) adding an appropriate amount of organic solvent to adjust the viscosity, 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 -NCO group-terminated polyurethane prepolymer solution with a low viscosity; (4) cooling the prepolymer solution to 35-45° C., adding a neutralizing agent, stirring vigorously for 10-20 min, then adding an appropriate amount of deionized water, and emulsifying for 5-15 min at a high shear force of 5000-7000 r / min to obtain a polyurethane dispersion aqueous solution; (5) adding a small molecule diamine post-chain extender and a polyamine cross-linking agent to the above polyurethane dispersion aqueous solution and reacting for 60 to 90 minutes; (6) Removing the organic solvent from the dispersion solution by vacuum distillation to obtain an aqueous polyurethane dispersion.

2. The method for preparing a waterborne polyurethane resin containing a heterocyclic group in the side chain according to claim 1, characterized in that: 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 the side chain according to claim 1, characterized in that: The small molecule polyhydroxy chain extender described in step (1) is trimethylolpropane (TMP), and its added amount accounts for 0.58-0.98% of the total solid matter in the aqueous polyurethane dispersion.

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

5. The method for preparing a waterborne polyurethane resin containing a heterocyclic group in the side chain according to claim 1, characterized in that: The polyisocyanate described in step (2) is 4,4'-dicyclohexylmethane diisocyanate (H 12 MDI), the amount of which accounts for 28.61-34.0% of the total solid matter in the aqueous polyurethane dispersion.

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

7. The method for preparing a waterborne polyurethane resin having a side chain containing a heterocyclic group as claimed in claim 1, characterized in that: The heterocyclic compound chain extender containing two active groups described in step (3) is 2-(1,3-benzothiazole-2-methylamino)ethanol, and its added amount accounts for 1.50-2.21% of the total solid matter in the aqueous polyurethane dispersion.

8. The method for preparing a waterborne polyurethane resin containing a heterocyclic group in the side chain according to claim 4, characterized in that: The neutralizing agent described in step (4) is triethylamine, 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 dimethylol propionic acid (DMPA).

9. The method for preparing a waterborne polyurethane resin containing a heterocyclic group in the side chain according to claim 1, characterized in that: The small molecule diamine post-chain extender described in step (5) is selected from N-aminoethylpiperazine (AEP), which accounts for 0.53-0.86% of the total solid matter in the aqueous polyurethane dispersion; the polyamine cross-linking agent described in step (5) is diethylenetriamine (DETA), which accounts for 1.31-1.95% of the total solid matter in the aqueous polyurethane dispersion.

10. An aqueous polyurethane resin containing a heterocyclic group in the side chain, characterized in that: Prepared by the method described in any one of claims 1 to 9.

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