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

Abstract

The invention discloses a preparation method of a waterborne polyurethane dispersion with excellent corrosion resistance, which comprises the following steps: (1) firstly carrying out vacuum dehydration on polyol, a micromolecular polyhydroxy chain extender and a hydrophilic chain extender, and then adding polyisocyanate to carry out polymerization reaction; the preparation method comprises the following steps: firstly, adding an alkynyl silane coupling agent into a reaction kettle, then adding micromolecular diol, diol containing an alkynyl side chain and a micromolecular diamine chain extender, carrying out a chain extension reaction, and finally, adding a monoamino silane coupling agent, and carrying out an end capping reaction, so as to prepare a polyurethane polymer; (2) dispersing the polyurethane polymer solution into water to obtain a polymer emulsion; and (3) adding a dithiol compound and an initiator into the polymer emulsion, so that an alkyne group on a polymer side chain and a sulfydryl of thiol are subjected to a click coupling reaction, and the waterborne polyurethane dispersion with the side chain containing free sulfydryl is obtained. According to the invention, the micromolecular mercaptan corrosion inhibitor is grafted to a side chain of a waterborne polyurethane molecule, and the obtained waterborne polyurethane has significantly improved corrosion resistance.

Description

Technical Field

[0001] The invention relates to the field of waterborne polyurethane coatings, and in particular to a waterborne urethane resin containing free mercapto groups (-SH) in the side chain and used for corrosion prevention and protection of metal substrates, and a preparation method thereof. Background Art

[0002] The corrosion of metal materials is a common problem that seriously affects all aspects of human life, including economy, environment and health and safety. Protecting metals from corrosion is of great significance. Coating technology is one of the most effective technologies for protecting metal materials. 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.

[0003] Waterborne polyurethane combines environmental benefits, ease of use and versatility, and is increasingly used in various industries such as coatings, adhesives, inks (inks) and textile finishing agents. It is also an attractive choice in the field of metal anti-corrosion coatings. However, the water-based ability of waterborne polyurethane is obtained by introducing many hydrophilic groups into its own molecular chain. The presence of these hydrophilic groups will seriously affect the water resistance and anti-corrosion properties of waterborne polyurethane coatings. Therefore, improving the water resistance of waterborne polyurethane is one of the key challenges faced in the design and manufacturing of waterborne polyurethane anti-corrosion coatings.

[0004] Cross-linking modification is an effective method to improve the water resistance of waterborne polyurethane. Through cross-linking modification, waterborne polyurethane molecules with a three-dimensional network structure can be formed, thereby reducing its solubility in water and its affinity with water. At the same time, this dense cross-linking structure will also hinder the penetration of water molecules. Therefore, the water resistance of the waterborne polyurethane latex film after cross-linking modification is improved. Silane coupling agent is a commonly used cross-linking agent. Silane containing terminal hydroxyl or amino groups is introduced into the molecular structure of waterborne polyurethane through reaction with isocyanate, and the characteristics of siloxane groups hydrolyzing to form active silanol (-Si-OH) are used to react to form a cross-linking structure of -Si-O-Si-, thereby improving the cross-linking degree of the waterborne polyurethane resin itself. In addition, the silanol formed after the hydrolysis of silane can also undergo condensation reaction with the hydroxyl formed by oxidation of the metal surface, thereby improving the interaction between the coating and the metal surface, thereby improving the anti-corrosion performance of the waterborne polyurethane coating.

[0005] In addition, one of the outstanding advantages of waterborne polyurethane is its strong functionality and easy modification. Various groups or structural units with innovative characteristics can be introduced into the molecular structure of waterborne polyurethane to improve the performance of waterborne polyurethane, especially its anti-corrosion performance. Through molecular design, the introduction of groups or links of elements such as S, P, N, and Si into waterborne polyurethane can improve the anti-corrosion performance of waterborne polyurethane. Among them, there are lone pairs of electrons on sulfur atoms, which are easy to form complex adsorption with metal atoms. The stronger the adsorption, the more stable the complex formed, the stronger the interaction between the sulfur-containing component and the metal matrix, and the better the corrosion inhibition effect. Therefore, the molecular structure of sulfur-containing waterborne polyurethane has aroused great interest. The sulfur element can be introduced into the waterborne polyurethane system in many different ways.

[0006] 1) By means of physical blending, sulfur-containing small molecule compounds are added to the coating formula of waterborne polyurethane, and used as anti-corrosion inhibitors to improve the anti-corrosion performance of waterborne polyurethane coatings. For example, patents CN105176346A, CN118146710A and CN109836999A respectively add dodecyl mercaptan, hexadecyl mercaptan and 2-mercaptobenzoimidazole as corrosion inhibitors to the coating formula of waterborne polyurethane, which effectively improve the anti-corrosion performance of the coating. However, such small molecule sulfur-containing compounds have high requirements for the waterborne polyurethane coating formula, and most of them have toxicity or unpleasant odors, and will slowly migrate and seep out in the coating film, affecting the durability of the anti-corrosion coating.

[0007] 2) Introduce sulfur-containing components into the molecular structure of waterborne polyurethane through chemical reactions to improve the anti-corrosion performance of its coating. According to the way sulfur atoms are introduced into waterborne polyurethane through chemical reactions and their characteristics in the molecular structure of waterborne polyurethane, sulfur-modified waterborne polyurethane can be divided into two categories: block copolymers (sulfur atoms are located in the main chain of waterborne polyurethane molecules) and graft copolymers (sulfur atoms are located in the side chains of waterborne polyurethane molecules).

[0008] In block copolymers, sulfur-containing components, including sulfur-containing polyol oligomers, polythiol oligomers (such as liquid polysulfide rubber), sulfur-containing small molecule polyols or polyamines, and small molecule dithiols or polythiols, react with isocyanates to form a typical block structure of waterborne polyurethane, in which sulfur atoms mainly exist in the form of thiocarbamate bonds (-NH-CO-S-), disulfide bonds (-SS-), thioether bonds (-S-), etc. This type of sulfur-containing waterborne polyurethane has good adhesion to metal substrates, low oxygen permeability and water permeability, and thus has enhanced anti-corrosion performance. For example, the waterborne polyurethane dispersion prepared by patent CN105778039A using 3,6-dioxa-1,8-octanedithiol as a chain extender has the characteristics of high solid content, good stability, low toxicity, environmental protection and good bonding performance, and can be used as a film-forming polymer for anti-corrosion coatings. In addition, thiocarbamate bonds (-NH-CO-S-) and disulfide bonds (-SS-) have the characteristics of dynamic cross-linking, and waterborne polyurethane coatings containing these dynamic cross-linking bonds have certain self-healing functions. For example, patent CN117004310A uses 2,2'-diaminodiphenyl disulfide and trimethylolpropane tris(3-mercaptopropionic acid) ester as chain extenders to synthesize waterborne polyurethane macromolecules with self-healing effects, and the resulting coating has good mechanical properties. However, since the sulfur atom is in the main chain of the waterborne polyurethane molecule, the movement of the sulfur-containing chain segment is hindered, making it difficult to fully diffuse and migrate into the interface between the coating and the metal substrate and produce effective adsorption, which is not conducive to the corrosion protection of the metal. In addition, due to the relatively large radius of the sulfur atom (larger than that of oxygen), the sulfur atom in the main chain will reduce the mechanical strength of the waterborne polyurethane coating to a certain extent. In particular, compared with the urethane bonds (-NH-CO-O-) in general waterborne polyurethanes, the ability to form hydrogen bonds between thiol urethane bonds (-NH-CO-S-) is poor, which greatly reduces the ability of waterborne polyurethane molecules to undergo physical crosslinking by forming hydrogen bonds.

[0009] For waterborne polyurethane graft copolymers with sulfur-containing side chains, one method is to use polyols or polyamines with sulfur-containing side chains as chain extenders to react with waterborne polyurethane prepolymers terminated with isocyanate groups. Due to the high reactivity between thiol (-SH) and isocyanate groups (-NCO), it is difficult to prepare waterborne polyurethanes containing free thiol (-SH) side chains by this method. Another possible method is to first introduce certain specific groups, such as carbon-carbon double bonds (olefin groups) or carbon-carbon triple bonds (alkyne groups), on the main chain or side chain of waterborne polyurethane, and then use the "click reaction" between these unsaturated bonds and thiol groups to graft the sulfur-containing side chains onto the skeleton of waterborne polyurethane. This grafting method can be expected to graft the side chains containing terminal thiol groups onto the skeleton of waterborne polyurethane and make them evenly distributed in a comb shape. This structure is conducive to the migration of the terminal thiol of the side chain of waterborne polyurethane and its strong interaction with the metal surface, and is conducive to the balance of the reversible exchange dynamic cross-linking reaction between the disulfide bond-thiol and the disulfide bond itself, thereby promoting the self-repair of the damage of the waterborne polyurethane coating, which is conducive to improving the anti-corrosion performance of waterborne polyurethane. However, the implementation of this method is relatively complicated, involving more reactants, and the reaction process is also difficult to control, so there is little research at present. Summary of the invention

[0010] As mentioned above, it is very necessary to develop a waterborne polyurethane resin for metal anticorrosion coatings, the molecular structure of which contains a certain concentration of cross-linking groups and terminal free thiol groups, and the terminal thiol groups can be distributed in a comb-like manner on the side chains of the waterborne polyurethane molecules, and can migrate more freely to the metal-coating interface to form strong chemical adsorption, thereby enhancing the water resistance, adhesion and anti-corrosion properties of the waterborne polyurethane, and can be produced by an effective synthesis method.

[0011] In order to solve the above technical problems, the present invention provides a method for preparing a cross-linked aqueous polyurethane dispersion having an anti-corrosion property and containing terminal mercapto groups in the side chains.

[0012] Another object of the present invention is to provide a cross-linked aqueous polyurethane dispersion having excellent anti-corrosion performance prepared by the above method.

[0013] The present invention is implemented by the following technical solutions:

[0014] A method for preparing a cross-linked aqueous polyurethane dispersion having an anti-corrosion property and a side chain containing a terminal thiol group, specifically comprising the following steps:

[0015] (1) Adding 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, heating to 110-120° C., and vacuum dehydrating for 60-120 min; then cooling to 75° C., opening nitrogen protection, adding polyisocyanate component, and reacting at 80-85° C. for 180-210 min to obtain a terminal-NCO polyurethane prepolymer;

[0016] (2) 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 and a diol containing a terminal alkyne group side chain as a chain extender, and continuing the reaction for 120-150 minutes to obtain a polyurethane prepolymer terminated with an -NCO group having an alkyne group at the end of the side chain.

[0017] (3) cooling the polyurethane prepolymer solution to 30-35° C., adding an organic solvent to adjust the viscosity, then adding a small molecule diamine chain extender to carry out a chain extension reaction, adding a monoamine silane coupling agent as a capping agent to carry out a capping reaction, and reacting for 30-40 minutes to allow the -NCO groups in the molecules to react completely, thereby obtaining a polyurethane capped with a silane coupling agent and containing an acetylenic side chain;

[0018] Add a measured neutralizing agent and a proper amount of deionized water to a mixed solution, and emulsify for 5 to 15 minutes at a high-speed shear force of 5000 to 7000 r / min to obtain a polyurethane dispersion aqueous solution with a main molecular chain terminated by aminosilane and a side chain containing a terminal acetylenic group;

[0019] (4) heating the polyurethane dispersion aqueous solution to 65-70° C., adding a mixture of dithiol and acetone under stirring, and simultaneously starting to drop a mixed solution of a free radical initiator and acetone; controlling the dropping rate so that the initiator is dropped completely within 60-80 minutes; and then continuing the reaction for 120-150 minutes to obtain a polyurethane dispersion aqueous solution having a terminal thiol group in the side chain;

[0020] (5) Removing the organic solvent from the aqueous dispersion by vacuum distillation to obtain an aqueous polyurethane dispersion.

[0021] The polymer polyol in the above step (1) includes polyether polyol and polycarbonate polyol. Polyether polyol includes polytetramethylene carbonate diol (PTMG) and polypropylene glycol (PPG). Polycarbonate polyol includes polyhexamethylene carbonate diol and polytetramethylene carbonate diol generated by condensation reaction of 1,4-butanediol and 1,6-hexanediol with dialkyl carbonate. Preferably, one of the above polyols with a molecular weight of 2000 or a mixture of two or more polyols is used, and more preferably, polycarbonate diol (PCDL) with a molecular weight of 2000 prepared from 1,6-hexanediol and polytetramethylene carbonate diol (PTMG) with a molecular weight of 2000 are mixed and used, and their usage ratio is PCDL / PTMG=1.0~3.0 (mass ratio), and the total usage of the two accounts for 55.0~63.0% of the total solid matter in the aqueous polyurethane dispersion.

[0022] The small molecule polyhydroxy chain extender (crosslinking agent) 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 crosslinking agent, and its added amount accounts for 0.5-1.0% of the total solid matter in the aqueous polyurethane dispersion.

[0023] The hydrophilic chain extender described in the above step (1) includes anionic carboxylic acid chain extenders and sulfonate chain extenders, preferably at least one of dimethylol lactic acid, dimethylol propionic acid (DMPA), dimethylol butyric acid (DMBA) and dimethylol valeric acid containing a carboxylic acid group, more preferably dimethylol propionic acid (DMPA) is the hydrophilic chain extender of the present invention, and its added amount accounts for 3.0 to 4.5% of the total solid matter in the aqueous polyurethane dispersion.

[0024] The polyisocyanate in the above step (1) 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, any diisocyanate including HDI, IPDI and H12MDI is used alone or in combination of two or more; more preferably, isophorone diisocyanate (IPDI) is used as the polyisocyanate component of the present invention, and its amount accounts for 25.0-28.0% of the total solid matter in the aqueous polyurethane dispersion.

[0025] The small molecule diol chain extender described in the above step (2) includes ethylene glycol, propylene glycol, 1,4-butanediol (BDO), neopentyl glycol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,3- or 1,4-cyclohexanedimethanol (CHDM), 1,3- or 1,4-cyclohexanediol, hydrogenated bisphenol A, etc. Any one of the above small molecule diols or a mixture of two or more thereof can be selected for use; preferably, 1,4-butanediol (BDO) is the small molecule diol chain extender of the present invention, and its addition amount accounts for 1.6 to 2.3% of the total solid matter in the aqueous polyurethane dispersion.

[0026] The diol containing a terminal alkyne group side chain in the above step (2) includes any one of 2,2-di(prop-2-ynyl)propane-1,3-diol (DPPD), 3-(prop-2-yn-1-yloxy)propane-1,2-diol (POPDH), 2-methyl-2-propargyl-1,3-propanediol (MPPD), 3,5-bis(hydroxymethyl)-1-propargyloxybenzene (PBM), propargyl 2,2-bis(hydroxymethyl)propionate (PBMP), and propargyl 2,2-bis(hydroxymethyl)butyrate (PBMB), or a mixture of two or more thereof; preferably, propargyl 2,2-bis(hydroxymethyl)propionate (PBMP) is the alkyne group-containing diol chain extender of the present invention, and its addition amount accounts for 0.9 to 1.7% of the total solid matter in the aqueous polyurethane dispersion.

[0027] The small molecule diamine chain extender described in the above step (3) includes one or a combination of two or more of ethylenediamine, 1,4-butanediamine, 1,6-hexanediamine, 2-methyl-1,5-pentanediamine (MPMD), piperazine, N-aminoethylpiperazine (AEP), and isophorone diamine; preferably, N-aminoethylpiperazine (AEP) is used as the post-chain extender, and its amount accounts for 1.9 to 2.6% of the total solid matter in the aqueous polyurethane dispersion.

[0028] The monoaminosilane coupling agent described in the above step (3) acts as an end-capping agent, and reacts completely with the terminal free -NCO group in the polyurethane prepolymer in an equivalent ratio to obtain a polyurethane polymer with a silane coupling agent group at the molecular end. The silane coupling agent preferably contains only one amino group and at least two methoxy and / or ethoxy groups connected to the silicon atom, including one or more of 4-aminobutyltriethoxysilane, aminophenyltrimethoxysilane, 3-aminopropyltrimethoxysilane (APTMS), 3-aminopropyltriethoxysilane (APTES), and 3-aminopropylmethyldiethoxysilane (APMDES). Preferably, 3-aminopropyltriethoxysilane (APTES) is used as the end-capping agent, and its amount accounts for 1.5-2.0% of the total solid matter in the aqueous polyurethane dispersion.

[0029] The organic solvent in the above 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 of the present invention, an appropriate amount of organic solvent can be added as needed to adjust the viscosity of the system; acetone is preferably used as the solvent, and its amount generally accounts for 100-200% of the total solid matter in the aqueous polyurethane dispersion.

[0030] The neutralizing agent in the above step (3) 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 100% (molar percentage) of the carboxyl groups in the hydrophilic chain extender dimethylolpropionic acid (DMPA).

[0031] The dithiol compounds described in the above step (4) mainly include 1,2-ethanedithiol, 1,4-butanedithiol, 1,5-pentanedithiol, 1,6-hexanedithiol, 1,8-octanedithiol (OCT), 1,10-decanedithiol, 2,3-butanedithiol, 2,2′-thiobis(ethanethiol), 1,2-benzenedithiol, 1,4-benzenedithiol, 1,3-benzenedithiol, 1,4-benzenedithiol, 4,4 Any one of '-biphenyl dithiol, 1,5-naphthalenedithiol, p-terphenyl-4,4″-dithiol, (methylenedi-1,4-phenylene) dimethylthiol (MPhET) or a mixture of two or more thereof is used; preferably 1,8-octanedithiol (OCT), the amount of which added is related to the amount of propargyl 2,2-bis(hydroxymethyl)propionate (PBMP), and the molar ratio of the two is OCT / PBMP=1.75-2.0.

[0032] The free radical initiator described in the above step (4) includes azobisisobutyronitrile (AIBN), ammonium persulfate, etc., preferably oil-soluble azobisisobutyronitrile (AIBN) is used as the initiator of the reaction, and its added amount is 3-5% of the total mass of the monomers participating in the reaction (i.e., the total mass of 1,8-octanedithiol (OCT) and propargyl 2,2-bis(hydroxymethyl)propionate (PBMP)).

[0033] The conditions for removing acetone in the above step (5) are a temperature of 40 to 60° C. and a vacuum degree of 0.05 to 0.1 MPa.

[0034] The method is used to prepare a waterborne polyurethane dispersion with excellent anti-corrosion performance. The average particle size of the waterborne polyurethane dispersion prepared by the method is 90-130 nm, and the solid content is about 31%-34%.

[0035] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0036] (1) The reaction of synthesizing the aqueous polyurethane dispersion containing free mercapto side chains in the present invention is easy to control, and the obtained product is not only safe and environmentally friendly, does not contain organic solvents, but also has good stability, water resistance and corrosion resistance.

[0037] (2) The present invention firstly adopts the acetone method to synthesize a polyurethane dispersion containing terminal alkynyl groups in the side chain, and then introduces the thiol segment into the side chain of the waterborne polyurethane molecule through the click reaction between the alkynyl group and the thiol, thereby preparing a waterborne polyurethane molecule containing a terminal thiol side chain. Therefore, the thiol group at the end of the side chain can migrate more freely to the metal-coating interface to form a strong chemical adsorption, thereby enhancing the adhesion and anti-corrosion performance of the waterborne polyurethane. When the free thiol concentration (FTD) at the end of the side chain of the waterborne polyurethane is 0.8 to 1.6 x 104 mol / g (relative to the total solid mass of PU), the obtained waterborne polyurethane has excellent anti-corrosion performance. The click reaction between the alkynyl group and thiol in the side chain of the waterborne polyurethane is as follows:

[0038]

[0039] (3) The present invention uses a mixed polyol of polycarbonate diol and polytetramethylene glycol 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 flexibility of the waterborne polyurethane chain, which is conducive to the adsorption of the thiol group of the side chain of the waterborne polyurethane molecule on the surface of the metal substrate.

[0040] (4) The present invention selects trimethylolpropane (TMP) and silane coupling agent as crosslinking agents for waterborne polyurethane, and adds them respectively at different synthesis stages, which not only ensures the smooth progress of the waterborne polyurethane synthesis process (gel will not be caused due to the high amount of crosslinking agent used in the prepolymerization stage), but also obtains the required crosslinking density. The prepared waterborne polyurethane has good water resistance and mechanical strength, which further improves the anti-corrosion performance of the waterborne polyurethane prepared by the present invention.

[0041] (5) The waterborne anti-corrosion coating prepared by using the waterborne polyurethane resin synthesized in the present invention as a film-forming polymer has good formula adjustability and adaptability, and anti-corrosion pigments and fillers or other additives that are beneficial to improving the anti-corrosion performance can be added thereto, which can further improve the anti-corrosion performance of the waterborne polyurethane coating. DETAILED DESCRIPTION

[0042] The following examples are used to illustrate the present invention, but the present invention is not limited thereto. Parameters and conditions not particularly noted in the present invention can be carried out with reference to conventional techniques.

[0043] Example 1

[0044] 60.0 g of polycarbonate diol (PCDL) with a molecular weight of 2000, 30.0 g of polytetramethylene glycol (PTMG) with a molecular weight of 2000, 1.1 g of trimethylolpropane (TMP) and 6.2 g of dimethylolpropionic acid (DMPA) were added to a 500 mL four-necked flask, heated to 120° C., and vacuum dehydrated for 60 min. Then the temperature was lowered to 75° C., and 40.0 g of isophorone diisocyanate (IPDI) was added under a nitrogen atmosphere, and reacted at 80° C. for 200 min to obtain a polyurethane prepolymer with an end group of -NCO group. The prepolymer was cooled to 65°C, 30.0g of acetone was added to reduce the viscosity of the system, and then a mixed solution of 3.2g of 1,4-butanediol (BDO), 2.1g of propargyl 2,2-bis(hydroxymethyl) propionate (PBMP) and 30g of acetone was slowly added, and the reaction was continued at 65°C for 120min to obtain a polyurethane prepolymer containing an alkyne group side chain and -NCO group end-capping. The obtained prepolymer solution was cooled to 35°C, 90.0g of acetone was added to reduce the viscosity of the system, and then a mixed solution of 3.0g of N-aminoethylpiperazine (AEP) and 10g of acetone, and a mixed solution of 2.3g of 3-aminopropyltriethoxysilane (APTES) and 10g of acetone were added in sequence to carry out chain extension reaction for 30min. Then, a mixed solution of 4.8 g of triethylamine and 310 ml of deionized water was added, the speed of the high-speed disperser was increased to 6000 r / min, and high-speed shear emulsification was performed for 10 minutes to obtain a silane-terminated aqueous polyurethane dispersion containing an acetylenic group side chain.

[0045] The polyurethane dispersion solution was heated to 65°C, and a mixture of 4.3g of 1,8-octanedithiol (OCT) and 10g of acetone was added under stirring, and a mixed solution of 0.2g of azobisisobutyronitrile (AIBN) and 30g of acetone was added dropwise. The dropping rate was controlled so that the initiator was dripped within 60min. The reaction was then continued for 120min to obtain a polyurethane dispersion aqueous solution having a terminal thiol group in the side chain.

[0046] 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 containing no organic solvent and having a solid content of 32.6 wt %.

[0047] Example 2

[0048] 55.0 g of polycarbonate diol (PCDL) with a molecular weight of 2000, 40.0 g of polytetramethylene glycol (PTMG) with a molecular weight of 2000, 1.3 g of trimethylolpropane (TMP) and 5.3 g of dimethylol propionic acid (DMPA) were added to a 500 mL four-necked flask, heated to 110° C., and vacuum dehydrated for 90 min. Then the temperature was lowered to 75° C., and 39.0 g of isophorone diisocyanate (IPDI) was added under a nitrogen atmosphere, and reacted at 80° C. for 210 min to obtain a polyurethane prepolymer with an end group of -NCO group. The prepolymer was cooled to 60°C, 30.0g of acetone was added to reduce the viscosity of the system, and then a mixed solution of 2.9g of 1,4-butanediol (BDO), 1.8g of propargyl 2,2-bis(hydroxymethyl) propionate (PBMP) and 30g of acetone was slowly added, and the reaction was continued at 60°C for 150min to obtain a polyurethane prepolymer containing an alkyne group side chain and -NCO group end-capping. The obtained prepolymer solution was cooled to 33°C, 90.0g of acetone was added to reduce the viscosity of the system, and then a mixed solution of 3.2g of N-aminoethylpiperazine (AEP) and 10g of acetone, and a mixed solution of 2.8g of 3-aminopropyltriethoxysilane (APTES) and 10g of acetone were added in sequence to carry out chain extension reaction for 35min. Then, a mixed solution of 4.0 g of triethylamine and 310 ml of deionized water was added, the speed of the high-speed disperser was increased to 7000 r / min, and high-speed shear emulsification was performed for 5 minutes to obtain a silane-terminated aqueous polyurethane dispersion containing an acetylenic group side chain.

[0049] The polyurethane dispersion solution was heated to 70°C, and a mixture of 3.3 g of 1,8-octanedithiol (OCT) and 10 g of acetone was added under stirring, and a mixed solution of 0.21 g of azobisisobutyronitrile (AIBN) and 30 g of acetone was added dropwise. The dropping rate was controlled so that the initiator was dripped within 70 min. The reaction was then continued for 130 min to obtain a polyurethane dispersion aqueous solution having a terminal thiol group in the side chain.

[0050] Finally, acetone was removed by reduced pressure distillation at a temperature of 50° C. and a vacuum degree of 0.08 MPa to obtain an aqueous polyurethane dispersion containing no organic solvent and having a solid content of 33.0 wt %.

[0051] Example 3

[0052] 70.0 g of polycarbonate diol (PCDL) with a molecular weight of 2000, 24.0 g of polytetramethylene glycol (PTMG) with a molecular weight of 2000, 1.5 g of trimethylolpropane (TMP) and 5.5 g of dimethylol propionic acid (DMPA) were added to a 500 mL four-necked flask, heated to 110° C., and vacuum dehydrated for 120 min. Then the temperature was lowered to 75° C., and 41.0 g of isophorone diisocyanate (IPDI) was added under a nitrogen atmosphere, and reacted at 85° C. for 180 min to obtain a polyurethane prepolymer with an end group of -NCO group. The prepolymer was cooled to 63°C, 30.0g of acetone was added to reduce the viscosity of the system, and then a mixed solution of 3.5g of 1,4-butanediol (BDO), 1.4g of propargyl 2,2-bis(hydroxymethyl) propionate (PBMP) and 30g of acetone was slowly added, and the reaction was continued at 63°C for 150min to obtain a polyurethane prepolymer containing an alkyne group side chain and -NCO group end-capping. The obtained prepolymer solution was cooled to 30°C, 90.0g of acetone was added to reduce the viscosity of the system, and then a mixed solution of 3.3g of N-aminoethylpiperazine (AEP) and 10g of acetone, and a mixed solution of 3.1g of 3-aminopropyltriethoxysilane (APTES) and 10g of acetone were added in sequence, and the chain extension reaction was carried out for 40min. Then, a mixed solution of 4.1 g of triethylamine and 310 ml of deionized water was added, the speed of the high-speed disperser was increased to 5000 r / min, and high-speed shear emulsification was performed for 15 minutes to obtain a silane-terminated aqueous polyurethane dispersion containing an acetylenic group side chain.

[0053] The polyurethane dispersion solution was heated to 65°C, and a mixture of 2.6 g of 1,8-octanedithiol (OCT) and 10 g of acetone was added under stirring, and a mixed solution of 0.26 g of azobisisobutyronitrile (AIBN) and 30 g of acetone was added dropwise. The dropping rate was controlled so that the initiator was dripped in 80 min. The reaction was then continued for 120 min to obtain a polyurethane dispersion aqueous solution having a terminal thiol group in the side chain.

[0054] Finally, acetone was removed by reduced pressure distillation at a temperature of 60° C. and a vacuum degree of 0.05 MPa to obtain an aqueous polyurethane dispersion containing no organic solvent and having a solid content of 33.0 wt %.

[0055] Example 4

[0056] 43.0 g of polycarbonate diol (PCDL) with a molecular weight of 2000, 43.0 g of polytetramethylene glycol (PTMG) with a molecular weight of 2000, 1.0 g of trimethylolpropane (TMP) and 6.6 g of dimethylol propionic acid (DMPA) were added to a 500 mL four-necked flask, heated to 110° C., and vacuum dehydrated for 90 min. Then the temperature was lowered to 75° C., and 43.0 g of isophorone diisocyanate (IPDI) was added under a nitrogen atmosphere, and reacted at 85° C. for 200 min to obtain a polyurethane prepolymer with a terminal group of -NCO group. The prepolymer was cooled to 60°C, 30.0g of acetone was added to reduce the viscosity of the system, and then a mixed solution of 3.5g of 1,4-butanediol (BDO), 2.6g of propargyl 2,2-bis(hydroxymethyl) propionate (PBMP) and 30g of acetone was slowly added, and the reaction was continued at 60°C for 150min to obtain a polyurethane prepolymer containing an acetylenic group side chain and -NCO group termination. The obtained prepolymer solution was cooled to 35°C, 90.0g of acetone was added to reduce the viscosity of the system, and then a mixed solution of 3.9g of N-aminoethylpiperazine (AEP) and 10g of acetone, and a mixed solution of 2.6g of 3-aminopropyltriethoxysilane (APTES) and 10g of acetone were added in sequence to carry out chain extension reaction for 35min. Then, a mixed solution of 5.0 g of triethylamine and 310 ml of deionized water was added, the speed of the high-speed disperser was increased to 6000 r / min, and high-speed shear emulsification was performed for 15 minutes to obtain a silane-terminated aqueous polyurethane dispersion containing an acetylenic group side chain.

[0057] The polyurethane dispersion solution was heated to 70°C, and a mixture of 4.9 g of 1,8-octanedithiol (OCT) and 10 g of acetone was added under stirring, and a mixed solution of 0.25 g of azobisisobutyronitrile (AIBN) and 30 g of acetone was added dropwise. The dropping rate was controlled so that the initiator was dripped within 70 min. The reaction was then continued for 120 min to obtain a polyurethane dispersion aqueous solution having a terminal thiol group in the side chain.

[0058] 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 containing no organic solvent and having a solid content of 32.9 wt %.

[0059] Comparative Example 1

[0060] Compared with Example 1, there are two differences: 1) the propargyl 2,2-bis(hydroxymethyl) propionate (PBMP) in Example 1 is replaced by 1,4-butanediol (BDO) in the same mole number, that is, no alkynyl side chain is introduced into the molecule of the waterborne polyurethane; 2) the final product is obtained after emulsification with water. No subsequent operation is required, that is, no dithiol, azobisisobutyronitrile, etc. need to be added for related click reactions.

[0061] The rest is exactly the same as in Example 1. An aqueous polyurethane dispersion with a solid content of 31.8 wt % is obtained.

[0062] Comparative Example 2

[0063] Isopropanolamine with the same molar number was used instead of 3-aminopropyltriethoxysilane (APTES) as the end-capping agent, that is, no silane unit was introduced at the end of the waterborne polyurethane molecule. The other components and operations were exactly the same as those in Example 1. A waterborne polyurethane dispersion with a solid content of 32.3 wt% was obtained.

[0064] The above-mentioned Examples 1-4 and Comparative Examples 1 and 2 were analyzed and tested for performance. The results are shown in Table 1.

[0065] Table 1 Performance comparison of aqueous polyurethane dispersions of Examples 1-4 and Comparative Examples 1-2

[0066]

[0067]

[0068] The above results were obtained by referring to the following test methods or standards:

[0069] APTES (wt%): mass percentage of 3-aminopropyltriethoxysilane (relative to the total solid content of the waterborne polyurethane resin).

[0070] FTD (mol / g): The concentration of free thiol groups at the end of the side chain of waterborne polyurethane (relative to the total solid mass of PU). It is estimated based on the amount of 1,8-octanedithiol (OCT) and propargyl 2,2-bis(hydroxymethyl) propionate (PBMP) used as the raw materials for synthesizing waterborne polyurethane dispersion and the stoichiometric ratio of the click reaction between them. The calculation method is as follows:

[0071] FTD = [(the number of moles of OCT - the number of moles of PBMP) × 2] / total solid mass of waterborne polyurethane resin

[0072] 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.

[0073] Membrane water absorption: According to the standard JC / T 1017-2006 "Polymer emulsion for building waterproof coatings", the water absorption of water-based polyurethane latex membrane is tested.

[0074] 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.

[0075] Water resistance: According to the standard GB / 1733-1993 "Determination of water resistance of paint films", the water resistance of water-based polyurethane latex film is tested.

[0076] Salt spray resistance test: According to the national standard GB / T 1771-2007 "Determination of neutral salt spray resistance of paints and varnishes", the salt spray resistance of water-based polyurethane emulsion varnish is tested.

[0077] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing an aqueous polyurethane resin containing a thiol group in a side chain, characterized in that: The following steps are involved: (1) Add 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, heat to 110-120° C., and vacuum dehydrate for 60-120 min; then cool to 75° C., open nitrogen protection, add polyisocyanate, and react at 80-85° C. for 180-210 min to obtain a terminal-NCO polyurethane prepolymer; (2) 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 and a diol containing a terminal alkyne group side chain as a chain extender, and continuing the reaction for 120-150 minutes to obtain a polyurethane prepolymer terminated with an -NCO group having an alkyne group at the end of the side chain; (3) cooling the obtained polyurethane prepolymer solution terminated with -NCO group and having an alkyne group at the end of the side chain to 30-35° C., adding an organic solvent to adjust the viscosity, then adding a small molecule diamine chain extender to carry out a chain extension reaction, adding a monoamine silane coupling agent as a capping agent to carry out a capping reaction, and reacting for 30-40 minutes to allow the -NCO group in the molecule to react completely, thereby obtaining a polyurethane terminated with a silane coupling agent and containing an alkyne side chain; adding a mixed solution of a certain amount of a neutralizing agent and an appropriate amount of deionized water, and emulsifying for 5-15 minutes at a high-speed shear force of 5000-7000 r / min to obtain a polyurethane dispersion aqueous solution with a molecular main chain capped with amino silane and a side chain containing a terminal alkyne group; (4) heating the polyurethane dispersion aqueous solution to 65-70° C., adding a mixture of dithiol and acetone under stirring, and simultaneously starting to drop a mixed solution of a free radical initiator and acetone; controlling the dropping rate so that the initiator is completely dropped within 60-80 minutes; and then continuing the reaction for 120-150 minutes to obtain a polyurethane dispersion aqueous solution having a terminal thiol group in the side chain; (5) Removing the organic solvent from the aqueous dispersion by vacuum distillation to obtain an aqueous polyurethane dispersion.

2. The method for preparing an aqueous polyurethane resin containing a thiol group in the side chain according to claim 1, characterized in that: The polymer polyol in step (1) is that the polycarbonate diol with a molecular weight of 2000 and the polytetrahydrofuran diol with a molecular weight of 2000 are mixed and used, and their mass ratio is PCDL / PTMG=1.0~3.0, and the two combined consumption accounts for 55.0~63.0% of the total solid matter amount in the aqueous polyurethane dispersion.

3. The method for preparing an aqueous polyurethane resin containing a thiol group in the side chain according to claim 1, characterized in that: The small molecule polyhydroxy chain extender described in step (1) is trimethylolpropane, and its added amount accounts for 0.5-1.0% of the total solid matter in the aqueous polyurethane dispersion.

4. The method for preparing an aqueous polyurethane resin containing a thiol group in the side chain according to claim 1, characterized in that: The hydrophilic chain extender described in step (1) is dimethylol propionic acid, and its added amount accounts for 3.0-4.5% of the total solid matter in the aqueous polyurethane dispersion.

5. The method for preparing an aqueous polyurethane resin containing a thiol group in the side chain according to claim 1, characterized in that: The polyisocyanate in step (1) is isophorone diisocyanate, and its usage accounts for 25.0-28.0% of the total solid matter in the aqueous polyurethane dispersion.

6. The method for preparing an aqueous polyurethane resin containing a thiol group in the side chain according to claim 1, characterized in that: The small molecule diol chain extender described in step (2) is 1,4-butanediol, and its addition amount accounts for 1.6-2.3% of the total solid matter in the aqueous polyurethane dispersion; the diol containing a terminal alkyne group side chain is propargyl 2,2-bis(hydroxymethyl)propionate, and its addition amount accounts for 0.9-1.7% of the total solid matter in the aqueous polyurethane dispersion.

7. The method for preparing an aqueous polyurethane resin containing a mercapto group in the side chain according to claim 1, characterized in that: The monoaminosilane coupling agent described in step (3) is 3-aminopropyltriethoxysilane, and its usage accounts for 1.5-2.0% of the total solid matter in the aqueous polyurethane dispersion; the organic solvent is acetone, and its usage accounts for 100-200% of the total solid matter in the aqueous polyurethane dispersion; the neutralizing agent is triethylamine, and its usage is calculated based on the number of moles required to neutralize 100 mol% of the carboxyl groups in the hydrophilic chain extender dihydroxymethylpropionic acid.

8. The method for preparing an aqueous polyurethane resin containing a mercapto group in the side chain according to claim 1, characterized in that: The free radical initiator described in step (4) is azobisisobutyronitrile, and its added amount is 3-5% of the total mass of the monomers participating in the reaction.

9. The method for preparing an aqueous polyurethane resin containing a mercapto group in the side chain according to claim 1, characterized in that: The conditions for removing acetone in step (5) are a temperature of 40 to 60° C. and a vacuum degree of 0.05 to 0.1 MPa.

10. An aqueous polyurethane resin containing a mercapto group in the side chain, characterized in that: The preparation method according to any one of claims 1 to 9, wherein the average particle size of the obtained waterborne polyurethane resin is 90 to 130 nm and the solid content is 31% to 34%.

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