A water-resistant polyurethane emulsion, its preparation method and application

Abstract

The present invention provides a water-resistant polyurethane emulsion, a preparation method thereof and an application. The raw materials for preparing the water-resistant polyurethane emulsion include the following components in parts by weight: 20-40 parts of isocyanate monomer, 50-75 parts of polyol, 5-11 parts of hydrophilic chain extender, 1.2-2.4 parts of small molecule alcohol chain extender, 0.1-0.3 parts of organometallic catalyst, 10-30 parts of solvent A, 3-6 parts of neutralizer and 100-170 parts of water. In the hydrophilic chain extender, carboxymethyl is connected to sulfonyl group. The water-resistant polyurethane emulsion provided in the present invention has good emulsion stability, and the formed coating has excellent water resistance, light transmittance, adhesion, scratch resistance and hardness.

Description

Technical Field

[0001] The present invention belongs to the technical field of polyurethane materials, and particularly relates to a water-resistant polyurethane emulsion, a preparation method thereof, and an application thereof. Background Art

[0002] With the continuous improvement of global environmental awareness, regulations have been successively introduced in various countries and regions to strictly control the emissions of volatile organic compounds (VOCs), promoting the accelerated transformation of the emulsion industry towards environmentally friendly products. Among them, waterborne polyurethane (WPU), with water as the solvent, has environmental advantages such as low VOC content and non-flammability, showing the potential to replace traditional solvent-based emulsions. In addition, WPU also has excellent adhesion, outstanding flexibility, and convenient construction, and has received extensive attention in the past few decades.

[0003] In order to stably disperse polyurethane in an aqueous system, monomers containing hydrophilic groups such as carboxyl groups are usually introduced into the polyurethane main chain as internal emulsifiers. However, due to the presence of hydrophilic groups such as carboxyl groups, the waterborne polyurethane emulsion has poor water resistance after the film is dried and is easily eroded by water vapor.

[0004] In the prior art, hydrophobic modification or introduction of nano-fillers has been disclosed to improve the water resistance of WPU. For example, Gharieh et al. (Gharieh, A.; Pourghasem, M. Eco-friendly UV-curable polyurethane-silica superhydrophobic coating with superb mechanical durability. Polym. Adv. Technol. 2022, 33, 3312-3322.) improved the water resistance of the WPU coating by modifying it with hydroxyl-terminated polydimethylsiloxane with low surface energy. Using hydroxyl-terminated polydimethylsiloxane as a hydrophobic segment can improve water resistance, but its introduction may reduce the dispersion stability and mechanical properties. And the modification method of introducing nano-fillers will cause the problem of decreased light transmittance, making it difficult to be applied in fields such as automotive glass coatings and electronic product screen protection coatings.

[0005] Therefore, there is an urgent need to develop a waterborne polyurethane emulsion that has good emulsion stability, mechanical properties, and light transmittance while improving water resistance to meet the needs of practical applications. Summary of the Invention

[0006] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a water-resistant polyurethane emulsion, a preparation method and an application thereof. The water-resistant polyurethane emulsion has good emulsion stability, and the coating formed by the water-resistant polyurethane emulsion has excellent water resistance, light transmittance, mechanical strength, scratch resistance and hardness.

[0007] To achieve this purpose, the present invention adopts the following technical solutions:

[0008] In the first aspect, the present invention provides a water-resistant polyurethane emulsion. The raw materials for preparing the water-resistant polyurethane emulsion include the following components in parts by weight: 20-40 parts of isocyanate monomer (such as 22 parts, 24 parts, 26 parts, 28 parts, 30 parts, 32 parts, 34 parts, 36 parts or 38 parts, etc.), 50-75 parts of polyol (53 parts, 56 parts, 59 parts, 62 parts, 65 parts, 68 parts, 71 parts or 74 parts, etc.), 5-11 parts of hydrophilic chain extender (such as 6 parts, 7 parts, 8 parts, 9 parts or 10 parts, etc.), 1.2-2.4 parts of small molecule alcohol chain extender (such as 1.4 parts, 1.6 parts, 1.8 parts, 2.0 parts or 2.2 parts, etc.), 0.1-0.3 parts of organometallic catalyst (such as 0.12 parts, 0.14 parts, 0.16 parts, 0.18 parts, 0.20 parts, 0.22 parts, 0.24 parts, 0.26 parts or 0.28 parts, etc.), 10-30 parts of solvent A (such as 12 parts, 14 parts, 16 parts, 18 parts, 20 parts, 22 parts, 24 parts, 26 parts or 28 parts, etc.), 3-6 parts of neutralizer (such as 3.3 parts, 3.6 parts, 3.9 parts, 4.2 parts, 4.5 parts, 4.8 parts, 5.1 parts, 5.4 parts or 5.7 parts, etc.) and 100-170 parts of water (such as 110 parts, 120 parts, 130 parts, 140 parts, 150 parts or 160 parts, etc.);

[0009] The hydrophilic chain extender has the structure shown in Formula I;

[0010] Formula I;

[0011] In Formula I, R is an alkyl group with 1-5 carbon atoms (such as 2, 3 or 4, etc.) substituted by two or more hydroxyl groups.

[0012] In the present invention, in the raw materials for preparing the water-resistant polyurethane emulsion, the hydroxyl group in the hydrophilic chain extender reacts with the isocyanate group to achieve chain extension, and the carboxymethyl group is connected to the sulfone group, enhancing the overall polarity of the molecule and improving the dispersion stability of the polyurethane in the aqueous phase in the prepared water-resistant polyurethane emulsion. When the water-resistant polyurethane emulsion is coated into a film, during the heat curing process, the carboxyl group connected to the sulfone group undergoes a decarboxylation reaction to generate carbon dioxide, which is removed from the polyurethane molecular chain, so that the polyurethane chain segment does not contain the hydrophilic group carboxyl, and finally the water resistance of the cured film-forming coating is significantly improved. The water-resistant polyurethane emulsion has good emulsion stability, and the coating formed by the water-resistant polyurethane emulsion has excellent water resistance, light transmittance, mechanical strength, scratch resistance and hardness.

[0013] Preferably, the weight parts of the polyol are 55-65 parts.

[0014] Preferably, the weight parts of the hydrophilic chain extender are 8-11 parts.

[0015] Preferably, the isocyanate monomer includes any one or a combination of at least two of isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI) or tetramethylxylylene diisocyanate (TMXDI).

[0016] Preferably, the polyol includes polyether polyol and / or polyester polyol.

[0017] Preferably, the polyether polyol includes any one or a combination of at least two of polytetrahydrofuran ether glycol (PTMEG), polypropylene glycol (PPG) or polyethylene glycol (PEG).

[0018] Preferably, the polyester polyol includes polycaprolactone diol (PCL).

[0019] Preferably, the number average molecular weight of the polyol is 2000-3000, such as 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800 or 2900, etc.

[0020] Preferably, the hydrophilic chain extender is prepared by the following method:

[0021] (1) React mercapto diol with chloroacetate to obtain a compound having the structure shown in Formula II.

[0022] Formula II.

[0023] In Formula II, R is an alkyl group with 1-5 carbon atoms (such as 2, 3 or 4, etc.) substituted by two or more hydroxyl groups, and Y is sodium or potassium.

[0024] (2) Mix the compound having the structure shown in Formula II prepared in step (1) with an acid and adjust the pH to 1 - 6 (such as 2, 3, 4, or 5, etc.) to obtain a compound having the structure shown in Formula III.

[0025] Formula III.

[0026] In Formula III, R is an alkyl group with 1 - 5 carbon atoms (such as 2, 3, or 4, etc.) substituted by two or more hydroxyl groups.

[0027] (3) React the compound having the structure shown in Formula III prepared in step (2) with an oxidizing agent to obtain a hydrophilic chain extender.

[0028] Preferably, step (1) includes mixing mercapto diol, chloroacetate, and solvent B, adding a base to adjust the pH to 9 - 11 (such as 9.3, 9.6, 9.9, 10.2, 10.5, or 10.8, etc.) for reaction to obtain a compound having the structure shown in Formula II.

[0029] Preferably, the mercapto diol includes any one or a combination of at least two of 3 - mercapto - 1,2 - propanediol, 2 - mercapto - 1,3 - propanediol, 3 - mercapto - 1,2 - butanediol, or 4 - mercapto - 1,3 - butanediol.

[0030] Preferably, the chloroacetate includes sodium chloroacetate and / or potassium chloroacetate.

[0031] Preferably, the solvent B includes water and / or ethanol.

[0032] Preferably, the water is deionized water.

[0033] Preferably, the base includes sodium hydroxide (NaOH) and / or potassium hydroxide.

[0034] Preferably, the molar ratio of the mercapto diol to the chloroacetate is 1:(1.1 - 1.5), such as 1:1.15, 1:1.2, 1:1.25, 1:1.3, 1:1.35, 1:1.4, or 1:1.45, etc.

[0035] Preferably, the volume ratio of the mixture of the mercapto diol and the chloroacetate to the volume of solvent B is 1:(3 - 5), such as 1:3.2, 1:3.4, 1:3.6, 1:3.8, 1:4.0, 1:4.2, 1:4.4, 1:4.6, or 1:4.8, etc.

[0036] Preferably, the temperature of the reaction in step (1) is 30 - 65°C (such as 35°C, 40°C, 45°C, 50°C, 55°C or 60°C, etc.), and the time is 1 - 2 h (such as 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h or 1.9 h, etc.).

[0037] Preferably, the acid in step (2) includes any one or a combination of at least two of hydrochloric acid (HCl), sulfuric acid, nitric acid or perchloric acid.

[0038] Preferably, the oxidant includes any one or a combination of at least two of potassium permanganate, potassium persulfate (K 2 S 2 O 8 ), or sodium persulfate.

[0039] Preferably, the molar ratio of the mercapto diol to the oxidant is 1:(1.1 - 1.2), such as 1:1.11, 1:1.12, 1:1.13, 1:1.14, 1:1.15, 1:1.16, 1:1.17, 1:1.18 or 1:1.19, etc.

[0040] Preferably, the temperature of the reaction in step (3) is 20 - 30°C (such as 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C or 29°C, etc.), and the reaction time is 1 - 2 h (such as 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h or 1.9 h, etc.).

[0041] Preferably, the small molecule alcohol chain extender includes any one or a combination of at least two of ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, butylene glycol or hexylene glycol.

[0042] Preferably, the organometallic catalyst includes an organobismuth catalyst and / or an organotin catalyst.

[0043] Preferably, the solvent A includes any one or a combination of at least two of acetone, methyl ethyl ketone or N-methylpyrrolidone.

[0044] Preferably, the neutralizing agent includes a low-boiling tertiary amine.

[0045] In the present invention, the low-boiling tertiary amine is a tertiary amine with a boiling point ≤ 150°C (such as 20°C, 40°C, 60°C, 80°C, 100°C, 120°C or 140°C, etc.) at 1 atm.

[0046] Preferably, the low-boiling tertiary amine includes any one or a combination of at least two of triethylamine (TEA), dimethylethanolamine (DMEA), or N,N-dimethylethylamine.

[0047] In a second aspect, the present invention provides a method for preparing a water-resistant polyurethane emulsion as described in the first aspect, and the preparation method includes the following steps:

[0048] (a) Mixing an isocyanate monomer, a polyol, a solvent A, and an organometallic catalyst, and reacting to obtain a first prepolymer.

[0049] (b) Mixing the first prepolymer obtained in step (a) with a hydrophilic chain extender and reacting to obtain a second prepolymer.

[0050] (c) Mixing the second prepolymer obtained in step (b), a small molecule alcohol chain extender, and an organometallic catalyst, and reacting to obtain a third prepolymer.

[0051] (d) Mixing the third prepolymer obtained in step (c) with a neutralizing agent, adding water for emulsification to obtain the water-resistant polyurethane emulsion.

[0052] Preferably, the reactions in steps (a), (b), and (c) are carried out under nitrogen protection.

[0053] Preferably, the temperature of the reaction in step (a) is 75-85 °C (such as 76 °C, 77 °C, 78 °C, 79 °C, 80 °C, 81 °C, 82 °C, 83 °C, or 84 °C, etc.), and the reaction time is 2-3 h (such as 2.1 h, 2.2 h, 2.3 h, 2.4 h, 2.5 h, 2.6 h, 2.7 h, 2.8 h, or 2.9 h, etc.).

[0054] Preferably, the temperature of the reaction in step (b) is 75-85 °C (such as 76 °C, 77 °C, 78 °C, 79 °C, 80 °C, 81 °C, 82 °C, 83 °C, or 84 °C, etc.), and the reaction time is 0.5-1 h (such as 0.55 h, 0.6 h, 0.65 h, 0.7 h, 0.75 h, 0.8 h, 0.85 h, 0.9 h, or 0.95 h, etc.).

[0055] Preferably, the temperature of the reaction in step (c) is 60-65 °C (such as 60.5 °C, 61 °C, 61.5 °C, 62 °C, 62.5 °C, 63 °C, 63.5 °C, 64 °C, or 64.5 °C, etc.), and the reaction time is 1-2 h (such as 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h, or 1.9 h, etc.).

[0056] Thirdly, the present invention provides an application of the water-resistant polyurethane emulsion as described in the first aspect, and the water-resistant polyurethane emulsion is used to prepare a water-resistant polyurethane coating after curing.

[0057] Preferably, the curing temperature is 90-100 °C, such as 91 °C, 92 °C, 93 °C, 94 °C, 95 °C, 96 °C, 97 °C, 98 °C or 99 °C, etc.

[0058] Preferably, the curing time is 30-60 min, such as 33 min, 36 min, 39 min, 42 min, 45 min, 48 min, 51 min, 54 min or 57 min, etc.

[0059] Compared with the prior art, the present invention has the following beneficial effects:

[0060] In the preparation raw materials of the water-resistant polyurethane emulsion of the present invention, the hydroxyl group in the hydrophilic chain extender reacts with the isocyanate group to achieve chain extension, and the carboxymethyl group is connected to the strong electron-withdrawing sulfone group, which enhances the overall polarity of the molecule and improves the dispersion stability of the polyurethane in the water phase in the prepared water-resistant polyurethane emulsion. When the water-resistant polyurethane emulsion is coated into a film, during the heating and curing process, the carboxyl group connected to the strong electron-withdrawing sulfone group undergoes a decarboxylation reaction to generate carbon dioxide, which is removed from the polyurethane molecular chain, so that the polyurethane chain segment does not contain the hydrophilic group carboxyl, and finally the water resistance of the formed coating after curing is significantly improved. The water-resistant polyurethane emulsion has good emulsion stability, and the coating formed by the water-resistant polyurethane emulsion has excellent water resistance, light transmittance, adhesion, scratch resistance and hardness. The light transmittance of the coating formed by the water-resistant polyurethane emulsion is ≥78%, the water absorption rate is ≤5%, the adhesion is ≤2 grades, the scratch resistance is ≥600 g, and the hardness is 2H-4H. Preferably, the light transmittance is ≥86%, the water absorption rate is ≤4%, the adhesion is ≤1 grade, the scratch resistance is ≥800 g, and the hardness is 3H-4H. Description of the Drawings

[0061] Figure 1 The reaction flow chart of the hydrophilic chain extender provided for Preparation Example 1. Detailed Embodiments

[0062] The technical solutions of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0063] Preparation Example 1

[0064] This preparation example provides a hydrophilic chain extender, specifically hydrophilic chain extender A1, which has the structure shown in Formula I-1 and is prepared by the following method. The reaction flow chart is asFigure 1 。

[0065] Formula Ⅰ-1;

[0066] (1)Mix 3-mercapto-1,2-propanediol and sodium chloroacetate at a molar ratio of 1:1.3, dissolve them in deionized water, the volume ratio of the mixture of 3-mercapto-1,2-propanediol and sodium chloroacetate to deionized water is 1:4, adjust the pH to 10 with sodium hydroxide, then heat the system to 60 °C and react continuously for 1.5 hours to produce a compound with the structure shown in Formula Ⅱ-1;

[0067] Formula Ⅱ-1;

[0068] (2)After the reaction in step (1) is completed, add hydrochloric acid (mass percentage concentration of 10%) to adjust the pH to 3 to obtain a compound with the structure shown in Formula Ⅲ-1;

[0069] Formula Ⅲ-1;

[0070] (3)After the reaction in step (2) is completed, cool the system to 25 °C, add potassium persulfate for oxidation reaction according to the molar ratio of 3-mercapto-1,2-propanediol to potassium persulfate of 1:1.2, and continuously react at 25 °C for 1.5 hours to obtain the hydrophilic chain extender A1.

[0071] Preparation Example 2

[0072] This preparation example provides a hydrophilic chain extender, specifically hydrophilic chain extender A2, which has the structure shown in Formula Ⅰ-1 and is prepared by the following method.

[0073] Formula Ⅰ-1;

[0074] (1)Mix 3-mercapto-1,2-propanediol and sodium chloroacetate at a molar ratio of 1:1.1, dissolve them in ethanol, the volume ratio of the mixture of 3-mercapto-1,2-propanediol and sodium chloroacetate to ethanol is 1:4, and adjust the pH to 11 with sodium hydroxide, then heat the system to 55 °C and react continuously for 2 hours to produce a compound with the structure shown in Formula Ⅱ-1;

[0075] Formula Ⅱ-1;

[0076] (2)After the reaction in step (1) is completed, add hydrochloric acid (mass percentage concentration of 10%) to adjust the pH to 2 to obtain a compound with the structure shown in Formula Ⅲ-1;

[0077] Formula Ⅲ-1;

[0078] After the reaction in step (2) is completed, the temperature of the system is lowered to 25 °C. Potassium persulfate is added for an oxidation reaction according to a molar ratio of 3-mercapto-1,2-propanediol to potassium persulfate of 1:1.2, and the reaction is continued at 25 °C for 2 hours to obtain the hydrophilic chain extender A2.

[0079] Preparation Example 3

[0080] This preparation example provides a hydrophilic chain extender, specifically hydrophilic chain extender A3, which has the structure shown in Formula I-1 and is prepared by the following method.

[0081] Formula I-1;

[0082] (1) 3-Mercapto-1,2-propanediol and sodium chloroacetate are mixed in a molar ratio of 1:1.5 and dissolved in ethanol. The volume ratio of the mixture of 3-mercapto-1,2-propanediol and sodium chloroacetate to ethanol is 1:4, and the pH is adjusted to 9 using sodium hydroxide. Subsequently, the system is heated to 65 °C and the reaction is continued for 1 hour to form a compound having the structure shown in Formula II-1;

[0083] Formula II-1;

[0084] (2) After the reaction in step (1) is completed, hydrochloric acid (mass percentage concentration of 10%) is added to adjust the pH to 1 to obtain a compound having the structure shown in Formula III-1;

[0085] Formula III-1;

[0086] (3) After the reaction in step (2) is completed, the temperature of the system is lowered to 25 °C. Potassium persulfate is added for an oxidation reaction according to a molar ratio of 3-mercapto-1,2-propanediol to potassium persulfate of 1:1.2, and the reaction is continued at 25 °C for 2 hours to obtain the hydrophilic chain extender A3.

[0087] Preparation Example 4

[0088] This preparation example provides a hydrophilic chain extender, specifically hydrophilic chain extender A4. The difference from Preparation Example 1 is that it has the structure shown in Formula I-2,

[0089] Formula I-2

[0090] In the preparation method, 3-mercapto-1,2-propanediol is replaced with 4-mercapto-1,3-butanediol in the same molar amount. In step (1), a compound having the structure shown in Formula II-2 is formed; in step (2), a compound having the structure shown in Formula III-2 is formed;

[0091] Formula II-2;

[0092] Formula Ⅲ-2;

[0093] Other conditions are the same as those in Preparation Example 1.

[0094] Example 1

[0095] This example provides a water-resistant polyurethane emulsion and a preparation method thereof. The raw materials for preparing the water-resistant polyurethane emulsion include the following components by weight: 28 parts of isocyanate monomer (IPDI and HDI with a mass ratio of 5:2), 55 parts of polyol (polytetrahydrofuran ether diol with a number average molecular weight of 2000), 9 parts of hydrophilic chain extender (hydrophilic chain extender A1 provided in Preparation Example 1), 2 parts of small molecule alcohol chain extender (1,4-butanediol), 0.2 part of organometallic catalyst (organobismuth catalyst, manufacturer: Guangzhou Yourun Synthetic Materials, grade: BCAT-E16), 20 parts of solvent A (N-methylpyrrolidone), 5 parts of neutralizer (triethylamine), and 150 parts of deionized water;

[0096] The preparation method includes the following steps:

[0097] (a) Put the isocyanate monomer, polyol, solvent A, and organometallic catalyst into a four-necked flask and mix them. Protect with nitrogen and heat up to 80 °C. Add the organometallic catalyst and react for 2.5 h to obtain a first prepolymer;

[0098] (b) Mix the first prepolymer obtained in step (a) with the hydrophilic chain extender and react at 80 °C for 40 min under nitrogen protection to obtain a second prepolymer;

[0099] (c) Cool down to 62 °C, mix the second prepolymer obtained in step (b), the small molecule alcohol chain extender, and the organometallic catalyst, and react for 1.5 h under nitrogen protection to obtain a third prepolymer;

[0100] (d) Mix the third prepolymer obtained in step (c) with the neutralizer, and slowly add deionized water for emulsification under high-speed stirring at 1000 rpm to obtain the water-resistant polyurethane emulsion.

[0101] Example 2

[0102] This example provides a water - resistant polyurethane emulsion and its preparation method. The raw materials for preparing the water - resistant polyurethane emulsion include the following components by weight: 25 parts of isocyanate monomer (HDI), 65 parts of polyol (polycaprolactone diol with a number - average molecular weight of 2000), 10 parts of hydrophilic chain extender (hydrophilic chain extender A2 provided in Preparation Example 2), 2 parts of small - molecule alcohol chain extender (1,4 - butanediol), 0.1 part of organometallic catalyst (organobismuth catalyst, manufacturer: Guangzhou Yourun Synthetic Materials, brand: BCAT - E16), 20 parts of solvent A (N - methylpyrrolidone), 5.5 parts of neutralizer (triethylamine), and 150 parts of deionized water;

[0103] The preparation method includes the following steps:

[0104] (a) Put the isocyanate monomer, polyol, solvent A, and organometallic catalyst into a four - necked flask and mix them. Protect with nitrogen and heat up to 75°C. Add the organometallic catalyst and react for 3 h to obtain a first prepolymer;

[0105] (b) Mix the first prepolymer obtained in step (a) with the hydrophilic chain extender and react at 75°C for 40 min under nitrogen protection to obtain a second prepolymer;

[0106] (c) Cool down to 60°C, mix the second prepolymer obtained in step (b), the small - molecule alcohol chain extender, and the organometallic catalyst, and react for 1.5 h under nitrogen protection to obtain a third prepolymer;

[0107] (d) Mix the third prepolymer obtained in step (c) with the neutralizer, and slowly add deionized water for emulsification under high - speed stirring at 1000 rpm to obtain the water - resistant polyurethane emulsion.

[0108] Example 3

[0109] This example provides a water - resistant polyurethane emulsion and its preparation method. The raw materials for preparing the water - resistant polyurethane emulsion include the following components by weight: 30 parts of isocyanate monomer (IPDI), 55 parts of polyol (polycaprolactone diol with a number - average molecular weight of 2000), 8 parts of hydrophilic chain extender (hydrophilic chain extender A3 provided in Preparation Example 3), 2 parts of small - molecule alcohol chain extender (1,4 - butanediol), 0.1 part of organometallic catalyst (organobismuth catalyst, manufacturer: Guangzhou Yourun Synthetic Materials, brand: BCAT - E16), 20 parts of solvent A (N - methylpyrrolidone), 4 parts of neutralizer (triethylamine), and 150 parts of deionized water;

[0110] The preparation method includes the following steps:

[0111] (a) Put the isocyanate monomer, polyol, solvent A, and organometallic catalyst into a four-necked flask and mix them. Purge with nitrogen and heat to 85 °C. Add the organometallic catalyst and react for 2 h to obtain the first prepolymer;

[0112] (b) Mix the first prepolymer obtained in step (a) with the hydrophilic chain extender, and react at 85 °C for 40 min under nitrogen protection to obtain the second prepolymer;

[0113] (c) Cool down to 65 °C, mix the second prepolymer obtained in step (b), the small molecule alcohol chain extender, and the organometallic catalyst, and react for 1.5 h under nitrogen protection to obtain the third prepolymer;

[0114] (d) Mix the third prepolymer obtained in step (c) with the neutralizing agent, and slowly add deionized water for emulsification under high-speed stirring at 1000 rpm to obtain the water-resistant polyurethane emulsion.

[0115] Example 4

[0116] This example provides a water-resistant polyurethane emulsion and its preparation method. The difference from Example 1 is that the hydrophilic chain extender A1 provided in Preparation Example 1 is replaced with the hydrophilic chain extender A4 provided in Preparation Example 4 with the same molar amount, and other conditions are the same as those in Example 1.

[0117] Example 5

[0118] This example provides a water-resistant polyurethane emulsion and its preparation method. The difference from Example 1 is that the weight fraction of the polyol (polytetrahydrofuran glycol, number average molecular weight of 2000) is adjusted to 70 parts, and other conditions are the same as those in Example 1.

[0119] Example 6

[0120] This example provides a water-resistant polyurethane emulsion and its preparation method. The difference from Example 1 is that the weight fraction of the polyol (polytetrahydrofuran glycol, number average molecular weight of 2000) is adjusted to 50 parts, and other conditions are the same as those in Example 1.

[0121] Example 7

[0122] This example provides a water-resistant polyurethane emulsion and its preparation method. The difference from Example 1 is that the weight fraction of the hydrophilic chain extender (the hydrophilic chain extender A1 provided in Preparation Example 1) is adjusted to 7 parts, and other conditions are the same as those in Example 1.

[0123] Example 8

[0124] This example provides a water-resistant polyurethane emulsion and its preparation method. The difference from Example 1 is that the weight fraction of the hydrophilic chain extender (hydrophilic chain extender A1 provided in Preparation Example 1) is adjusted to 11 parts, and other conditions are the same as those in Example 1.

[0125] Example 9

[0126] This example provides a water-resistant polyurethane emulsion and its preparation method. The difference from Example 1 is that the polyol (polytetrahydrofuran glycol with a number-average molecular weight of 2000) is replaced with the same mass of polyol (polytetrahydrofuran glycol with a number-average molecular weight of 1000), and other conditions are the same as those in Example 1.

[0127] Example 10

[0128] This example provides a water-resistant polyurethane emulsion and its preparation method. The difference from Example 1 is that the polyol (polytetrahydrofuran glycol with a number-average molecular weight of 2000) is replaced with the same mass of polyol (polytetrahydrofuran glycol with a number-average molecular weight of 3000), and other conditions are the same as those in Example 1.

[0129] Comparative Example 1

[0130] This comparative example provides a polyurethane emulsion and its preparation method. The difference from Example 1 is that the hydrophilic chain extender (hydrophilic chain extender A1 provided in Preparation Example 1) is replaced with the same mass of 2,2-dimethylolpropionic acid, and other conditions are the same as those in Example 1.

[0131] Comparative Example 2

[0132] This comparative example provides a polyurethane emulsion and its preparation method. The difference from Example 1 is that the weight fraction of the hydrophilic chain extender (hydrophilic chain extender A1 provided in Preparation Example 1) is adjusted to 3 parts, and other conditions are the same as those in Example 1.

[0133] Comparative Example 3

[0134] This comparative example provides a polyurethane emulsion and its preparation method. The difference from Example 1 is that the weight fraction of the hydrophilic chain extender (hydrophilic chain extender A1 provided in Preparation Example 1) is adjusted to 15 parts, and other conditions are the same as those in Example 1.

[0135] Performance Test

[0136] (1) Emulsion Appearance: Observe the appearances of the water-resistant polyurethane emulsions provided in Examples 1 to 10 and the polyurethane emulsions provided in Comparative Examples 1 to 3. Pour the water-resistant polyurethane emulsion and the polyurethane emulsion into colorless transparent containers respectively, and let them stand for 24 h, then observe the color, transparency, and uniformity.

[0137] (2)Water absorption rate: The water-resistant polyurethane emulsions provided in Examples 1 to 10 and the polyurethane emulsions provided in Comparative Examples 1 to 3 were respectively dropped into cleaned glassware, and the thickness after film formation was controlled within the range of 0.7 to 1 mm. They were baked at 100 °C for 30 min to be completely cured, and then cut into 3 cm × 3 cm specimens. Referring to T / CWA 206-2021, the mass of the specimen was weighed and recorded as m 0 , soaked in deionized water for 24 h, taken out and the surface moisture was blotted dry with filter paper, and the mass was weighed and recorded as m 1 , and the water absorption rate was calculated as (m 1 - m 0 ) / m 0 ×100%.

[0138] (3)The water-resistant polyurethane emulsions provided in Examples 1 to 10 and the polyurethane emulsions provided in Comparative Examples 1 to 3 were respectively poured onto the surface of a clean glass substrate, and a gap coater was used to scrape the emulsion, controlling the wet film thickness to be 150 μm. Subsequently, it was left standing at room temperature for 10 min to ensure leveling, and then baked at 100 °C for 30 min to be completely cured to form a uniform coating, and the light transmittance, adhesion, scratch resistance, and pencil hardness were tested. The test methods are as follows:

[0139] Light transmittance: Tested in accordance with GB / T 2410-2008;

[0140] Adhesion: Tested in accordance with GB / T 9286-2021;

[0141] Scratch resistance: Tested in accordance with ASTMD 5178-1998;

[0142] Pencil hardness: Tested in accordance with GB / T 6739-2022.

[0143] The test results are shown in Table 1.

[0144] Table 1

[0145]

[0146] As can be seen from the content of Table 1, the water-resistant polyurethane emulsions provided in Examples 1 to 10 have good emulsion stability. The light transmittance of the formed coating is ≥78%, the water absorption rate is ≤5%, the adhesion is ≤2 levels, the scratch resistance is ≥600 g, and the hardness is 2H to 4H.

[0147] Compared with Example 1, if the weight fraction of the polyol is on the high side (Example 5), the hardness and scratch resistance of the coating formed by the water-resistant polyurethane emulsion prepared are significantly decreased, but the water absorption rate increases slightly. The reason is that the higher soft segment ratio leads to a decrease in crosslinking density and an increase in micropores, resulting in a slight increase in water absorption rate.

[0148] Compared with Example 1, if the weight fraction of the polyol is on the low side (Example 6), the crosslinking density increases, the scratch resistance of the coating formed by the aqueous polyurethane emulsion is significantly increased, the water molecule penetration path is blocked, the water absorption rate decreases, but the light transmittance decreases.

[0149] Compared with Example 1, if the weight fraction of the hydrophilic chain extender is on the low side (Example 7), the light transmittance and scratch resistance of the coating formed by the water-resistant polyurethane emulsion prepared both decrease, and the water absorption rate remains basically unchanged.

[0150] Compared with Example 1, if the weight fraction of the hydrophilic chain extender is on the high side (Example 8), the light transmittance and scratch resistance of the coating formed by the water-resistant polyurethane emulsion prepared increase, and the water absorption rate decreases slightly. This is because the increase in the hydrophilic chain extender leads to an increase in the proportion of hydrophobic sulfone groups and a reduction in the water absorption channels.

[0151] Compared with Example 1, if the number average molecular weight of the polyol is too low (Example 9), all the properties of the water-resistant polyurethane emulsion prepared decrease. This is because the low molecular weight of the polyol results in a short soft segment structure, a decrease in the chain segment flexibility, and it is difficult to form a regular and ordered stacking structure between the polyurethane main chains, leading to a decrease in the compactness of the formed coating and a significant increase in the water absorption rate. Secondly, the chain segments are unevenly arranged and the structure is loose, which is easy to form micro-light scattering regions, thus reducing the light transmittance of the coating and deteriorating the transparency. In addition, due to insufficient flexibility, the matching between the coating and the substrate surface decreases, the adhesion decreases, and in the scratch resistance test, it shows a lower tolerance load. The insufficient aggregation of the hard segments also reduces the pencil hardness after film formation.

[0152] Compared with Example 1, if the number average molecular weight of the polyol is on the high side (Example 10), the water resistance of the water-resistant polyurethane emulsion prepared is improved, but the light transmittance, hardness and scratch resistance decrease. This is because the high molecular weight polytetrahydrofuran ether glycol forms long-chain polyether segments, enhancing the hydrophobicity. After forming the coating, the water absorption rate is slightly improved, but due to the easy entanglement of the long-chain polyether, the chain segment stacking is uneven, resulting in a decrease in the light transmittance. In addition, the relatively high softness of the coating leads to a decrease in hardness and scratch resistance.

[0153] Compared with Example 1, if the hydrophilic chain extender (hydrophilic chain extender A1 provided in Preparation Example 1) is replaced with the same mass of 2,2-dimethylolpropionic acid (Comparative Example 1), the water absorption rate of the coating formed by the prepared polyurethane emulsion increases significantly, and the hardness and scratch resistance decrease significantly. This is because the formed coating contains hydrophilic groups of carboxyl, resulting in poor water resistance.

[0154] Compared with Example 1, if the weight fraction of the hydrophilic chain extender is too low (Comparative Example 2), the stability of the prepared water-resistant polyurethane emulsion is poor, and stratification occurs after standing for 24 h. The light transmittance, hardness and scratch resistance of the formed coating are all low, and the water absorption rate is high. This is because the weight fraction of the water chain extender is too low, resulting in uneven latex particle sizes and poor fluidity during film formation, and a continuous and dense coating cannot be formed.

[0155] Compared with Example 1, if the weight fraction of the hydrophilic chain extender is too high (Comparative Example 3), the sulfone group accounts for a relatively high proportion, and the high polarity leads to excessive cross-linking of the molecular chain. The stability of the prepared water-resistant polyurethane emulsion is poor, and stratification occurs after standing for 24 h. The high polarity and excessive cross-linking result in an increase in the hardness of the formed coating but an increase in brittleness, and the light transmittance and scratch resistance are low; at the same time, the residual carboxyl groups increase after high-temperature curing, and the water absorption rate increases.

[0156] The applicant declares that the present invention uses the above examples to illustrate the process method of the present invention, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvement of the present invention, the equivalent replacement of the raw materials selected for the present invention, the addition of auxiliary components, and the selection of specific methods, etc., all fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A water-resistant polyurethane emulsion, characterized in that: The raw materials for preparing the water-resistant polyurethane emulsion include the following components by weight: 20-40 parts of isocyanate monomer, 50-75 parts of polyol, 5-11 parts of hydrophilic chain extender, 1.2-2.4 parts of small molecule alcohol chain extender, 0.1-0.3 parts of organic metal catalyst, 10-30 parts of solvent A, 3-6 parts of neutralizer and 100-170 parts of water; The hydrophilic chain extender has a structure shown in Formula I; Formula I; In formula I, R is an alkyl group having 1 to 5 carbon atoms substituted with two or more hydroxyl groups.

2. The water-resistant polyurethane emulsion according to claim 1, characterized in that: The isocyanate monomer includes any one of isophorone diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, toluene diisocyanate or tetramethylxylylene diisocyanate, or a combination of at least two thereof; The polyols include polyether polyols and / or polyester polyols; The polyether polyol includes any one of polytetramethylene glycol, polypropylene glycol or polyethylene glycol, or a combination of at least two thereof; The polyester polyol includes polycaprolactone diol; The number average molecular weight of the polyol is 2000-3000.

3. The water-resistant polyurethane emulsion according to claim 1, characterized in that: The hydrophilic chain extender is prepared by the following method: (1) reacting mercaptodiol and chloroacetate to obtain a compound having a structure shown in Formula II; Formula II; In Formula II, R is an alkyl group having 1 to 5 carbon atoms substituted with two or more hydroxyl groups, and Y is sodium or potassium; (2) mixing the compound having the structure shown in Formula II obtained in step (1) with an acid and adjusting the pH to 1 to 6 to obtain a compound having the structure shown in Formula III; Formula III; In Formula III, R is an alkyl group having 1 to 5 carbon atoms substituted with two or more hydroxyl groups; (3) reacting the compound having the structure shown in formula III obtained in step (2) with an oxidant to obtain the hydrophilic chain extender.

4. The water-resistant polyurethane emulsion according to claim 3, characterized in that: The step (1) comprises mixing mercaptodiol, chloroacetate and solvent B, adding alkali to adjust the pH to 9-11 for reaction, and obtaining a compound having a structure shown in formula II; The mercapto diol includes any one of 3-mercapto-1,2-propanediol, 2-mercapto-1,3-propanediol, 3-mercapto-1,2-butanediol or 4-mercapto-1,3-butanediol, or a combination of at least two thereof; The chloroacetate includes sodium chloroacetate and / or potassium chloroacetate; The solvent B comprises water and / or ethanol; The base includes sodium hydroxide and / or potassium hydroxide; The molar ratio of the mercaptodiol to the chloroacetate is 1:(1.1-1.5); The ratio of the volume of the mixture of the mercaptodiol and the chloroacetate to the volume of the solvent B is 1:(3-5); The reaction temperature of step (1) is 30-65°C and the reaction time is 1-2 h.

5. The water-resistant polyurethane emulsion according to claim 4, characterized in that: The acid in step (2) includes any one of hydrochloric acid, sulfuric acid, nitric acid or perchloric acid, or a combination of at least two thereof; The oxidant in step (3) comprises any one of potassium permanganate, potassium persulfate or sodium persulfate, or a combination of at least two thereof; The molar ratio of the mercapto diol to the oxidant is 1:(1.1-1.2); The reaction temperature in step (3) is 20-30°C, and the reaction time is 1-2 h.

6. The water-resistant polyurethane emulsion according to claim 1, characterized in that: The small molecule alcohol chain extender includes any one of ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, butanediol or hexanediol, or a combination of at least two thereof; The organic metal catalyst includes an organic bismuth catalyst and / or an organic tin catalyst.

7. The water-resistant polyurethane emulsion according to claim 1, characterized in that: The solvent A comprises any one of acetone, butanone or N-methylpyrrolidone or a combination of at least two thereof; The neutralizing agent includes a low boiling point tertiary amine; The low boiling point tertiary amine includes any one of triethylamine, dimethylethanolamine or N,N-dimethylethylamine or a combination of at least two thereof.

8. A method for preparing a water-resistant polyurethane emulsion according to any one of claims 1 to 7, characterized in that: The preparation method comprises the following steps: (a) mixing an isocyanate monomer, a polyol, a solvent A and an organic metal catalyst, and reacting them to obtain a first prepolymer; (b) mixing the first prepolymer prepared in step (a) and a hydrophilic chain extender, and reacting them to obtain a second prepolymer; (c) mixing the second prepolymer prepared in step (b), a small molecule alcohol chain extender and an organic metal catalyst, and reacting them to obtain a third prepolymer; (d) mixing the third prepolymer obtained in step (c) with a neutralizing agent, and emulsifying with water to obtain the water-resistant polyurethane emulsion.

9. The preparation method according to claim 8, characterized in that: The reactions in step (a), step (b) and step (c) are carried out under nitrogen protection; The reaction temperature of step (a) is 75-85°C and the reaction time is 2-3 h; The reaction temperature in step (b) is 75-85°C and the reaction time is 0.5-1 h; The reaction temperature in step (c) is 60-65° C., and the reaction time is 1-2 h.

10. An application of the water-resistant polyurethane emulsion according to any one of claims 1 to 7, characterized in that: The water-resistant polyurethane emulsion is used to prepare a water-resistant polyurethane coating after being cured.

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