Water-resistant polyurethane emulsion as well as preparation method and application thereof

Abstract

The invention provides a water-resistant polyurethane emulsion as well as a preparation method and application thereof. The water-resistant polyurethane emulsion is prepared from the following raw materials in parts by weight: 20 to 40 parts of isocyanate monomer, 50 to 75 parts of polyhydric alcohol, 5 to 11 parts of hydrophilic chain extender, 1.2 to 2.4 parts of micromolecular alcohol chain extender, 0.1 to 0.3 part of organic metal catalyst, 10 to 30 parts of solvent A, 3 to 6 parts of neutralizer and 100 to 170 parts of water, wherein carboxymethyl in the hydrophilic chain extender is connected with sulfuryl; the water-resistant polyurethane emulsion provided by the invention has good emulsion stability, and a formed coating has excellent water resistance, light transmittance, adhesive force, scratch resistance and hardness.

Description

Technical Field

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

[0002] As global environmental awareness continues to increase, countries and regions have successively introduced laws and regulations to strictly control the emission of volatile organic compounds (VOCs), which has accelerated the transformation of the emulsion industry to environmentally friendly products. Among them, waterborne polyurethane (WPU) uses water as a solvent, has environmental advantages such as low VOC content and non-flammability, and shows the potential to replace traditional solvent-based emulsions. In addition, WPU also has excellent adhesion, excellent flexibility and convenient construction, and has received widespread attention in the past few decades.

[0003] In order to make polyurethane stably dispersed in water-based systems, monomers containing hydrophilic groups such as carboxyl groups are usually introduced into the polyurethane backbone as internal emulsifiers. However, due to the presence of hydrophilic groups such as carboxyl groups, water-based polyurethane emulsions have poor water resistance after the coating film dries and are easily eroded by water vapor.

[0004] The prior art has disclosed the use of hydrophobic modification or the introduction of nanofillers to improve the water resistance of WPU, such as 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.) by using hydroxyl-terminated polydimethylsiloxane with low surface energy for modification to improve the water resistance of WPU coating. The use of hydroxyl-terminated polydimethylsiloxane as a hydrophobic segment can improve water resistance, but its introduction may reduce dispersion stability and mechanical properties. The introduction of nanofillers in the modification method will cause the problem of decreased transmittance, which is difficult to apply to automotive glass coatings, electronic product screen protection coatings and other fields.

[0005] Therefore, there is an urgent need to develop an aqueous 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] In view of the deficiencies in the prior art, the object of the present invention is to provide a water-resistant polyurethane emulsion and a preparation method and application thereof, wherein the water-resistant polyurethane emulsion has good emulsion stability, and a coating formed by the water-resistant polyurethane emulsion has excellent water resistance, light transmittance, mechanical strength, scratch resistance and hardness.

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

[0008] In a first aspect, the present invention provides a water-resistant polyurethane emulsion, wherein the raw materials for preparing the water-resistant polyurethane emulsion include the following components in parts by weight: 20 to 40 parts (e.g., 22 parts, 24 parts, 26 parts, 28 parts, 30 parts, 32 parts, 34 parts, 36 parts or 38 parts, etc.) of isocyanate monomer, 50 to 75 parts (53 parts, 56 parts, 59 parts, 62 parts, 65 parts, 68 parts, 71 parts or 74 parts, etc.) of polyol, and a hydrophilic Chain extender 5-11 parts (e.g. 6 parts, 7 parts, 8 parts, 9 parts or 10 parts, etc.), small molecule alcohol chain extender 1.2-2.4 parts (e.g. 1.4 parts, 1.6 parts, 1.8 parts, 2.0 parts or 2.2 parts, etc.), organic metal catalyst 0.1-0.3 parts (e.g. 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.), solvent A 10-30 parts (e.g., 12 parts, 14 parts, 16 parts, 18 parts, 20 parts, 22 parts, 24 parts, 26 parts or 28 parts, etc.), 3-6 parts (e.g., 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.) of neutralizer and 100-170 parts (e.g., 110 parts, 120 parts, 130 parts, 140 parts, 150 parts or 160 parts, etc.) of water;

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

[0010] Formula I;

[0011] In formula I, R is an alkyl group having 1 to 5 (eg, 2, 3 or 4) carbon atoms substituted with two or more hydroxyl groups.

[0012] In the present invention, the hydroxyl group in the hydrophilic chain extender in the raw material for preparing the water-resistant polyurethane emulsion reacts with the isocyanate group to achieve chain extension, and the carboxyl group is connected to the sulfone group, so that the overall polarity of the molecule is enhanced, and the dispersion stability of the polyurethane in the water phase in the prepared water-resistant polyurethane emulsion is improved. When the water-resistant polyurethane emulsion is coated to form a film, during the heating and 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 a hydrophilic group carboxyl group, and the water resistance of the coating formed by the final curing film 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 proportion of the polyol is 55-65 parts.

[0014] Preferably, the weight proportion of the hydrophilic chain extender is 8 to 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 comprises polyether polyol and / or polyester polyol.

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

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

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

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

[0021] (1) A mercaptodiol is reacted with chloroacetate to obtain a compound having a structure shown in Formula II.

[0022] Formula II.

[0023] In formula II, R is an alkyl group having 1 to 5 carbon atoms (e.g., 2, 3 or 4, etc.) substituted with two or more hydroxyl groups, and Y is sodium or potassium.

[0024] (2) The compound having the structure represented by Formula II obtained in step (1) is mixed with an acid and the pH is adjusted to 1 to 6 (e.g., 2, 3, 4 or 5) to obtain a compound having the structure represented by Formula III.

[0025] Formula III.

[0026] In formula III, R is an alkyl group having 1 to 5 (eg, 2, 3 or 4) carbon atoms substituted with two or more hydroxyl groups.

[0027] (3) The compound having the structure shown in formula III obtained in step (2) is reacted with an oxidant to obtain a hydrophilic chain extender.

[0028] Preferably, the step (1) comprises mixing mercaptodiol, chloroacetate and solvent B, adding alkali to adjust the pH to 9-11 (e.g., 9.3, 9.6, 9.9, 10.2, 10.5 or 10.8, etc.) to react to obtain a compound having a structure shown in formula II.

[0029] Preferably, 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.

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

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

[0032] Preferably, the water is deionized water.

[0033] Preferably, the base comprises 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), for example, 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 ratio of the volume of the mixed mercaptodiol and chloroacetate to the volume of solvent B is 1:(3-5), for example, 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 reaction temperature in step (1) is 30-65°C (e.g., 35°C, 40°C, 45°C, 50°C, 55°C or 60°C, etc.), and the reaction time is 1-2 h (e.g., 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) comprises any one of hydrochloric acid (HCl), sulfuric acid, nitric acid or perchloric acid, or a combination of at least two thereof.

[0038] Preferably, the oxidant includes any one of potassium permanganate, potassium persulfate (K2S2O8) or sodium persulfate, or a combination of at least two thereof.

[0039] Preferably, the molar ratio of the mercapto diol to the oxidant is 1:(1.1-1.2), for example, 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 reaction temperature in step (3) is 20-30°C (e.g., 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 (e.g., 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 of ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, butanediol or hexanediol, or a combination of at least two thereof.

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

[0043] Preferably, the solvent A comprises any one of acetone, butanone or N-methylpyrrolidone, or a combination of at least two thereof.

[0044] Preferably, the neutralizing agent comprises a low boiling point tertiary amine.

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

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

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

[0048] (a) An isocyanate monomer, a polyol, a solvent A and an organic metal catalyst are mixed and reacted to obtain a first prepolymer.

[0049] (b) mixing the first prepolymer prepared in step (a) with a hydrophilic chain extender, and reacting the mixture to obtain a second prepolymer.

[0050] (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.

[0051] (d) mixing the third prepolymer obtained in step (c) with a neutralizing agent, and emulsifying with water to obtain the water-resistant polyurethane emulsion.

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

[0053] Preferably, the reaction temperature in step (a) is 75-85°C (e.g., 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 (e.g., 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 reaction temperature in step (b) is 75-85°C (e.g., 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 (e.g., 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 reaction temperature in step (c) is 60-65°C (e.g., 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 (e.g., 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] In a third aspect, the present invention provides a use of the water-resistant polyurethane emulsion as described in the first aspect, wherein 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, for example, 91°C, 92°C, 93°C, 94°C, 95°C, 96°C, 97°C, 98°C or 99°C.

[0058] Preferably, the curing time is 30 to 60 min, for example, 33 min, 36 min, 39 min, 42 min, 45 min, 48 min, 51 min, 54 min or 57 min.

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

[0060] The hydroxyl group in the hydrophilic chain extender in the raw materials for preparing the water-resistant polyurethane emulsion of the present invention reacts with the isocyanate group to achieve chain extension, and the carboxyl group is connected to the strong electron-withdrawing sulfone group, so that the overall polarity of the molecule is enhanced, and the dispersion stability of the polyurethane in the water phase in the prepared water-resistant polyurethane emulsion is improved. When the water-resistant polyurethane emulsion is coated to form 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 segment does not contain the hydrophilic group carboxyl group, and the water resistance of the coating formed after the final curing film 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 coating formed by the water-resistant polyurethane emulsion has a transmittance of ≥78%, a water absorption of ≤5%, an adhesion of ≤Level 2, a scratch resistance of ≥600g, and a hardness of 2H~4H. Preferably, the transmittance is ≥86%, the water absorption of ≤4%, the adhesion of ≤Level 1, the scratch resistance of ≥800g, and the hardness of 3H~4H. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 This is the reaction flow diagram of the hydrophilic chain extender provided in Preparation Example 1. DETAILED DESCRIPTION

[0062] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0063] Preparation Example 1

[0064] This preparation example provides a hydrophilic chain extender, specifically a hydrophilic chain extender A1, having a structure shown in Formula I-1, and is prepared by the following method. The reaction flow is as follows: Figure 1 .

[0065] Formula I-1;

[0066] (1) 3-mercapto-1,2-propanediol and sodium chloroacetate are mixed in a molar ratio of 1:1.3 and dissolved in deionized water, wherein the volume ratio of the mixed 3-mercapto-1,2-propanediol and sodium chloroacetate to deionized water is 1:4, and the pH is adjusted to 10 using sodium hydroxide. Subsequently, the system is heated to 60° C. and the reaction is continued for 1.5 hours to generate a compound having a structure shown in Formula II-1;

[0067] Formula II-1;

[0068] (2) After the reaction in step (1) is completed, hydrochloric acid (mass percent concentration is 10%) is added to adjust the pH to 3 to obtain a compound having a structure shown in formula III-1;

[0069] Formula III-1;

[0070] (3) After the reaction in step (2) was completed, the system was cooled to 25° C., potassium persulfate was added at a molar ratio of 3-mercapto-1,2-propanediol to potassium persulfate of 1:1.2 to carry out an oxidation reaction, and the reaction was continued 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 a hydrophilic chain extender A2, having a structure shown in formula Ⅰ-1, and is prepared by the following method.

[0073] Formula I-1;

[0074] (1) 3-mercapto-1,2-propylene glycol and sodium chloroacetate are mixed in a molar ratio of 1:1.1, dissolved in ethanol, the volume ratio of the mixed 3-mercapto-1,2-propylene glycol and sodium chloroacetate to ethanol being 1:4, and the pH is adjusted to 11 using sodium hydroxide, and then the system is heated to 55° C. and the reaction is continued for 2 hours to generate a compound having a structure shown in Formula II-1;

[0075] Formula II-1;

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

[0077] Formula III-1;

[0078] (3) After the reaction in step (2) was completed, the system was cooled to 25° C., potassium persulfate was added at a molar ratio of 3-mercapto-1,2-propanediol to potassium persulfate of 1:1.2 to carry out an oxidation reaction, and the reaction was 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 a hydrophilic chain extender A3, having a structure shown in formula Ⅰ-1, and is prepared by the following method.

[0081] Formula I-1;

[0082] (1) 3-mercapto-1,2-propylene glycol and sodium chloroacetate are mixed in a molar ratio of 1:1.5, dissolved in ethanol, the volume ratio of the mixed 3-mercapto-1,2-propylene glycol and sodium chloroacetate to ethanol being 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 generate a compound having a structure shown in Formula II-1;

[0083] Formula II-1;

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

[0085] Formula III-1;

[0086] (3) After the reaction in step (2) was completed, the system was cooled to 25° C., potassium persulfate was added at a molar ratio of 3-mercapto-1,2-propanediol to potassium persulfate of 1:1.2 to carry out an oxidation reaction, and the reaction was 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, which differs from preparation example 1 in that it has a structure shown in formula I-2,

[0089] Formula I-2

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

[0091] Formula II-2;

[0092] Formula III-2;

[0093] The other conditions were the same as those in Preparation Example 1.

[0094] Example 1

[0095] The present embodiment 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 in parts by weight: 28 parts of isocyanate monomer (IPDI and HDI in a mass ratio of 5:2), 55 parts of polyol (polytetramethylene glycol, 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 parts of organic metal catalyst (organic bismuth catalyst, manufactured by Guangzhou Yourun Synthetic Materials, with a brand name of BCAT-E16), 20 parts of solvent A (N-methylpyrrolidone), 5 parts of neutralizer (triethylamine) and 150 parts of deionized water;

[0096] The preparation method comprises the following steps:

[0097] (a) isocyanate monomer, polyol, solvent A and organometallic catalyst are placed in a four-necked flask and mixed, nitrogen is passed through and the temperature is raised to 80° C., the organometallic catalyst is added, and the reaction is carried out for 2.5 h to obtain a first prepolymer;

[0098] (b) mixing the first prepolymer prepared in step (a) with a hydrophilic chain extender, and reacting them at 80° C. for 40 minutes under nitrogen protection to obtain a second prepolymer;

[0099] (c) cooling to 62° C., mixing the second prepolymer prepared in step (b), a small molecule alcohol chain extender and an organic metal catalyst, and reacting them under nitrogen protection for 1.5 hours to obtain a third prepolymer;

[0100] (d) mixing the third prepolymer prepared in step (c) with a neutralizing agent, and slowly adding deionized water for emulsification under high-speed stirring at 1000 rpm to obtain the water-resistant polyurethane emulsion.

[0101] Example 2

[0102] The present embodiment 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 in parts by weight: 25 parts of isocyanate monomer (HDI), 65 parts of polyol (polycaprolactone diol, 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 parts of organic metal catalyst (organic bismuth catalyst, manufacturer is Guangzhou Yourun Synthetic Materials, brand name 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 comprises the following steps:

[0104] (a) isocyanate monomer, polyol, solvent A and organometallic catalyst are placed in a four-necked flask and mixed, nitrogen is passed through and the temperature is raised to 75° C., the organometallic catalyst is added, and the reaction is carried out for 3 h to obtain a first prepolymer;

[0105] (b) mixing the first prepolymer prepared in step (a) with a hydrophilic chain extender, and reacting at 75° C. for 40 minutes under nitrogen protection to obtain a second prepolymer;

[0106] (c) cooling to 60° C., mixing the second prepolymer prepared in step (b), a small molecule alcohol chain extender and an organic metal catalyst, and reacting them under nitrogen protection for 1.5 h to obtain a third prepolymer;

[0107] (d) mixing the third prepolymer prepared in step (c) with a neutralizing agent, and slowly adding deionized water for emulsification under high-speed stirring at 1000 rpm to obtain the water-resistant polyurethane emulsion.

[0108] Example 3

[0109] The present embodiment 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 in parts by weight: 30 parts of isocyanate monomer (IPDI), 55 parts of polyol (polycaprolactone diol, 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 parts of organic metal catalyst (organic bismuth catalyst, manufacturer is Guangzhou Yourun Synthetic Materials, brand name BCAT-E16), 20 parts of solvent A (N-methylpyrrolidone), 4 parts of neutralizer (triethylamine) and 150 parts of deionized water;

[0110] The preparation method comprises the following steps:

[0111] (a) isocyanate monomer, polyol, solvent A and organometallic catalyst are placed in a four-necked flask and mixed, nitrogen is passed through the flask and the temperature is raised to 85° C., the organometallic catalyst is added, and the reaction is carried out for 2 h to obtain a first prepolymer;

[0112] (b) mixing the first prepolymer prepared in step (a) with a hydrophilic chain extender, and reacting the mixture at 85° C. for 40 minutes under nitrogen protection to obtain a second prepolymer;

[0113] (c) cooling to 65° C., mixing the second prepolymer prepared in step (b), a small molecule alcohol chain extender and an organic metal catalyst, and reacting them under nitrogen protection for 1.5 h to obtain a third prepolymer;

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

[0115] Example 4

[0116] This embodiment provides a water-resistant polyurethane emulsion and a preparation method thereof. The difference between this embodiment and 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 in the same molar amount, and other conditions are the same as in Example 1.

[0117] Example 5

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

[0119] Example 6

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

[0121] Example 7

[0122] This embodiment provides a water-resistant polyurethane emulsion and a preparation method thereof. The difference between this embodiment and Example 1 is that the weight portion of the hydrophilic chain extender (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 embodiment provides a water-resistant polyurethane emulsion and a preparation method thereof. The difference between this embodiment and Example 1 is that the weight portion 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 embodiment provides a water-resistant polyurethane emulsion and a preparation method thereof. The difference between the embodiment 1 and the embodiment 1 is that the polyol (polytetramethylene glycol, number average molecular weight is 2000) is replaced with a polyol (polytetramethylene glycol, number average molecular weight is 1000) of the same mass, and the other conditions are the same as those in the embodiment 1.

[0127] Example 10

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

[0129] Comparative Example 1

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

[0131] Comparative Example 2

[0132] This comparative example provides a polyurethane emulsion and a preparation method thereof. The difference between the comparative example and Example 1 is that the weight portion 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 a preparation method thereof. The difference between the comparative example and Example 1 is that the weight portion 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 Testing

[0136] (1) Emulsion appearance: Observe the appearance 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, let them stand for 24 hours, and 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 added dropwise to clean glassware, and the thickness of the film after formation was controlled to be in the range of 0.7 to 1 mm. The film was baked at 100° C. for 30 min to be completely cured, and cut into 3 cm×3 cm samples. Referring to T / CWA 206-2021, the mass of the sample was weighed and recorded as m0, and the sample was soaked in deionized water for 24 h. The sample was taken out and the surface moisture was absorbed with filter paper, and the mass was weighed and recorded as m1. The water absorption rate was calculated as follows: (m1-m0) / m0×100%.

[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 poured onto the surface of a clean glass substrate, and the emulsions were scraped using a gap-type film applicator to control the wet film thickness to be 150 μm. The coating was then left to stand at room temperature for 10 min to ensure leveling, and then baked at 100° C. for 30 min to completely cure and form a uniform coating. The transmittance, adhesion, scratch resistance and pencil hardness tests were performed 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] It can be seen from the contents of Table 1 that the water-resistant polyurethane emulsions provided in Examples 1 to 10 have good emulsion stability, and the formed coatings have a light transmittance of ≥78%, a water absorption of ≤5%, an adhesion of ≤2, a scratch resistance of ≥600g, and a hardness of 2H to 4H.

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

[0148] Compared with Example 1, if the weight fraction of the polyol is lower (Example 6), the crosslinking density increases, the scratch resistance of the coating formed by the aqueous polyurethane emulsion is significantly improved, 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 lower (Example 7), the light transmittance and scratch resistance of the coating formed by the prepared water-resistant polyurethane emulsion are both reduced, and the water absorption rate remains basically unchanged.

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

[0151] Compared with Example 1, if the number average molecular weight of the polyol is too low (Example 9), the various properties of the prepared water-resistant polyurethane emulsion are reduced. This is because the molecular weight of the polyol is low, the soft segment structure formed is short, the segment flexibility is reduced, and it is difficult to form a regular and orderly stacking structure between the main chains of the formed polyurethane, resulting in a decrease in the density of the formed coating and a significant increase in water absorption. Secondly, the uneven arrangement of the segments and the loose structure easily form microscopic light scattering areas, thereby reducing the light transmittance of the coating and deteriorating the transparency. In addition, due to insufficient flexibility, the matching of the coating with the substrate surface is reduced, the adhesion is reduced, and it shows a lower load tolerance in the scratch resistance test. Insufficient hard segment aggregation also reduces the pencil hardness after film formation.

[0152] Compared with Example 1, if the number average molecular weight of the polyol is high (Example 10), the water resistance of the prepared water-resistant polyurethane emulsion is improved, and the light transmittance, hardness and scratch resistance are reduced. This is because the high molecular weight polytetrahydrofuran ether diol forms a long-chain polyether segment, which enhances the hydrophobicity and slightly improves the water absorption after the coating is formed. However, the long-chain polyether chain is easy to entangle, resulting in uneven accumulation of the segments, resulting in a decrease in light transmittance. In addition, the 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-dihydroxymethylpropionic acid (Comparative Example 1), the water absorption rate of the coating formed by the prepared polyurethane emulsion is greatly increased, and the hardness and scratch resistance are significantly reduced. This is because the formed coating has a hydrophilic group carboxyl, which makes the water resistance worse.

[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 hours. 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 hydrophilic chain extender is too low, resulting in uneven latex particle size, poor fluidity during film formation, and failure to form a continuous and dense coating.

[0155] Compared with Example 1, if the weight fraction of the hydrophilic chain extender is too high (Comparative Example 3), the proportion of sulfone groups is relatively high, the high polarity leads to excessive cross-linking of the molecular chain, and the stability of the prepared water-resistant polyurethane emulsion is poor. After standing for 24 hours, stratification occurs. The high polarity and excessive cross-linking lead to an increase in the hardness of the formed coating but an increase in brittleness, and low light transmittance and scratch resistance. 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 illustrates the process method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned process steps, that is, it does not mean that the present invention must rely on the above-mentioned process steps to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the raw materials selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and 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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