A polyether siloxane defoamer for water-based coatings and preparation method thereof

Abstract

The present invention discloses a polyether siloxane defoamer for water-based coatings and a preparation method thereof, relating to the technical field of defoamers. The polyether siloxane defoamer for water-based coatings comprises the following raw materials in parts by weight: 60-75 parts of polyether-modified silicone oil, 5-8 parts of silicone paste, 3-5 parts of dispersant, 2-4 parts of silicon dioxide, 5-10 parts of emulsifier, and 2-5 parts of surfactant. The polyether siloxane defoamer for water-based coatings prepared by the present invention exhibits excellent defoaming and anti-foaming properties and stability.

Description

Technical Field

[0001] The present invention relates to the technical field of defoamers, and in particular to a polyether siloxane defoamer for water-based coatings and a preparation method thereof. Background Art

[0002] With the acceleration of industrialization and increasingly stringent environmental standards, water-based paints are gradually replacing traditional oil-based paints in the market, becoming the mainstream choice due to their low volatile organic compound (VOC) emissions, good safety, and ease of use. However, water-based paints are prone to bubbles during production and application. These bubbles can cause defects in the paint film, affecting its appearance and performance.

[0003] To address this issue, defoamers are widely used in water-based coatings. They disrupt the stability of bubbles through the principle of incompatibility, causing them to burst quickly. However, the carrier materials of traditional defoamers are not fully compatible with the coating system, making it difficult for the two to blend evenly. The coating system will regard the defoamer as a "foreign substance," resulting in defects such as craters on the paint film surface. In addition, defoamers have poor dispersion in the coating and tend to accumulate in localized areas, preventing them from exerting their effect evenly. This in turn affects the stability and sustainability of the defoaming effect, making it difficult to meet the water-based coatings' requirements for high compatibility, good stability, and excellent dispersibility of defoamers. This can lead to surface defects such as craters and pinholes in the paint film, which not only affects the coating's aesthetics but can also weaken its protective properties and shorten its service life.

[0004] Chinese invention patent publication number CN119097962A discloses a polyether siloxane defoamer for water-based coatings and its preparation method. The defoamer comprises polyether-modified silicone oil, silicone paste, an emulsifier, and an additive, the latter including a perfluoroalkylethanol polyoxyethylene ether. The defoamer in this patent effectively reduces defects such as craters and pinholes in water-based coatings, but its antibacterial properties are poor. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the present invention aims to provide a polyether siloxane defoamer for water-based coatings and a preparation method thereof.

[0006] To achieve the above object, the present invention is implemented through the following technical solutions:

[0007] A polyether siloxane defoamer for water-based coatings, comprising the following raw materials in parts by weight:

[0008] Polyether modified silicone oil: 60-75 parts, silicone paste: 5-8 parts, dispersant: 3-5 parts, silicon dioxide: 2-4 parts, emulsifier: 5-10 parts, surfactant: 2-5 parts;

[0009] The emulsifier is prepared by the following method:

[0010] S1: N-(4-(2,5-dioxo-4-oxazolidinyl)butyl)-2,2,2-trifluoroacetamide undergoes a ring-opening reaction under the action of n-hexylamine to obtain a fluorine-containing amide polymer;

[0011] S2: Fluoroamide polymer reacts with sodium azide to form azide;

[0012] S3: An azide compound reacts with N,N,N-trimethylpent-4-yn-1-amine quaternary ammonium salt under the action of cuprous bromide to form an emulsifier.

[0013] In step S1, the mass ratio of N-(4-(2,5-dioxo-4-oxazolidinyl)butyl)-2,2,2-trifluoroacetamide and n-hexylamine is (18-20):1.

[0014] The mass ratio of the fluorine-containing amide polymer to sodium azide in step S2 is (2-3):1.

[0015] In the step S3, the mass ratio of the azide compound to the N,N,N-trimethylpent-4-yn-1-amine quaternary ammonium salt is (2-4):1.

[0016] The dispersant is prepared by the following method:

[0017] A1: Lignin reacts with concentrated sulfuric acid to form sulfonated lignin;

[0018] A2: Sulfonated lignin reacts with dodecane bromide in the presence of sodium hydroxide to produce alkyl-modified lignin;

[0019] A3: Alkyl-modified lignin reacts with propylene oxide in the presence of phosphoric acid to form a dispersant.

[0020] The mass ratio of lignin to concentrated sulfuric acid in step A1 is 6:1.

[0021] In step A2, the mass ratio of sulfonated lignin to brominated dodecane is 3:1.

[0022] In step A3, the feed mass ratio of the alkyl-modified lignin to propylene oxide is 7:1.

[0023] The surfactant is prepared by compounding perfluoroalkylethanol polyoxyethylene ether and polyethylene glycol phosphate in a weight ratio of 4:1.

[0024] A method for preparing a polyether siloxane defoamer for water-based coatings comprises the following steps:

[0025] (1) Weigh by weight: polyether modified silicone oil: 60-75 parts, silicone paste: 5-8 parts, dispersant: 3-5 parts, silicon dioxide: 2-4 parts, emulsifier: 5-10 parts, surfactant: 2-5 parts;

[0026] (2) The polyether modified silicone oil, silicone paste, dispersant, silicon dioxide, emulsifier and surfactant are mixed in proportion and emulsified in an emulsifying disperser for 20-40 minutes to obtain a polyether silicone defoamer for water-based coatings.

[0027] Due to the adoption of the above technical solution, the beneficial effects of the present invention include:

[0028] (1) The emulsifier prepared by the present invention achieves dual optimization of dispersibility and compatibility: its amphiphilic structure and cationic properties significantly improve the dispersion efficiency, while the polar / non-polar groups ensure high compatibility with the polyether siloxane system.

[0029] (2) The dispersant prepared by the present invention has amphiphilic properties through the hydrophilicity of the sulfonic acid group and the hydrophobicity of the dodecyl group, which significantly reduces the interfacial tension and promotes the uniform dispersion of the polyether siloxane. In terms of defoaming performance, the strong affinity between the dodecyl group and the hydrophobic group of the siloxane accelerates the spreading of the defoamer on the surface of the foam liquid film, and the rigid skeleton of lignin is embedded in the liquid film to destroy the continuity, and the electrostatic repulsion of the sulfonic acid group cooperates to achieve efficient foam breaking. DETAILED DESCRIPTION

[0030] The present invention will be further described below with reference to the embodiments, but the present invention is not limited to these embodiments.

[0031] Example 1 Preparation of emulsifier:

[0032] S1: Under an ice bath, 1000 g of DMF and 180 g of N-(4-(2,5-dioxo-4-oxazolidinyl)butyl)-2,2,2-trifluoroacetamide were added to a reactor, followed by 10 g of n-hexylamine. The mixture was stirred and mixed, and reacted at 4°C for 20 h. Then, 5000 ml of a mixed solution of cold n-hexane and diethyl ether (n-hexane: diethyl ether (V / V) = 1:1) was added, stirred and mixed, and allowed to stand to precipitate. The precipitate was filtered and dried under vacuum at 70°C for 3 h to obtain a fluorine-containing amide polymer. The reaction equation is shown below:

[0033]

[0034] S2: Add 100 ml of DMF, 20 g of fluorine-containing amide polymer, and 10 g of sodium azide to the reactor, stir and mix, heat to 50°C, react for 50 h, cool to room temperature, filter, and distill under reduced pressure at 60°C for 2 h. Then, add 100 ml of dichloromethane and stir to dissolve. Filter again, add 100 ml of methanol, stir for 10 min, precipitate, centrifuge, and dry in vacuo at 70°C for 4 h to obtain the azide compound. The reaction equation is as follows:

[0035]

[0036] S3: Under sealed conditions, 300 ml of DMF, 20 g of an azide compound, and 10 g of N,N,N-trimethylpent-4-yn-1-amine quaternary ammonium salt were added to a reactor and stirred to mix. Then, 7 g of cuprous bromide and 8 g of N,N,N′,N′′,N′′-pentamethyldiethylenetriamine were added. The mixture was reacted at room temperature for 24 h, and then exposed to air for 1 h to quench the reaction. The mixture was dialyzed against a 2 wt% EDTA solution in DMF (MwCO = 5 KDa) for 24 h, and then dialyzed against deionized water (MwCO = 5 KDa) for 24 h. The emulsifier was freeze-dried at -20°C for 12 h to obtain the emulsifier. The reaction equation is shown below:

[0037]

[0038] Example 2 Preparation of emulsifier:

[0039] S1: In an ice bath, 1000 g of DMF and 190 g of N-(4-(2,5-dioxo-4-oxazolidinyl)butyl)-2,2,2-trifluoroacetamide were added to a reactor, followed by 10 g of n-hexylamine. The mixture was stirred and mixed, and the mixture was reacted at 4°C for 22 h. Then, 5000 ml of a mixed solution of cold n-hexane and diethyl ether (n-hexane:diethyl ether (V / V) = 1:1) was added, the mixture was stirred and mixed, and the mixture was allowed to stand to precipitate. The precipitate was filtered and dried under vacuum at 70°C for 3 h to obtain a fluorine-containing amide polymer.

[0040] S2: Add 100 ml of DMF, 25 g of fluorine-containing amide polymer, and 10 g of sodium azide to the reactor, stir and mix, heat to 60°C, react for 48 hours, cool to room temperature, filter, and distill under reduced pressure at 60°C for 2 hours. Then, add 100 ml of dichloromethane and stir to dissolve. Filter again, add 100 ml of methanol, stir for 10 minutes, precipitate, centrifuge, and dry in vacuo at 70°C for 4 hours to obtain the azide compound.

[0041] S3: Under closed conditions, 300 ml of DMF, 30 g of an azide compound, and 10 g of N,N,N-trimethylpent-4-yn-1-amine quaternary ammonium salt were added to the reactor and stirred to mix. Then, 7 g of cuprous bromide and 8 g of N,N,N′,N′′,N′′-pentamethyldiethylenetriamine were added. The mixture was reacted at room temperature for 22 h, and then exposed to air for 1 h to quench the reaction. The mixture was dialyzed against a 2 wt% EDTA solution in DMF (MwCO = 5 KDa) for 24 h, and then dialyzed against deionized water (MwCO = 5 KDa) for 24 h. The mixture was freeze-dried at -20°C for 12 h to obtain an emulsifier.

[0042] Example 3 Preparation of emulsifier:

[0043] S1: In an ice bath, 1000 g of DMF and 200 g of N-(4-(2,5-dioxo-4-oxazolidinyl)butyl)-2,2,2-trifluoroacetamide were added to a reactor, followed by 10 g of n-hexylamine, and the mixture was stirred and mixed. After reacting at 4°C for 24 h, 5000 ml of a mixed solution of cold n-hexane and diethyl ether (n-hexane: diethyl ether (V / V) = 1:1) was added, and the mixture was stirred and mixed. The mixture was allowed to stand to precipitate, which was filtered and dried under vacuum at 70°C for 3 h to obtain a fluorine-containing amide polymer.

[0044] S2: Add 100 ml of DMF, 30 g of fluorine-containing amide polymer, and 10 g of sodium azide to the reactor, stir and mix, heat to 70°C, react for 45 h, cool to room temperature, filter, and distill under reduced pressure at 60°C for 2 h. Then, add 100 ml of dichloromethane and stir to dissolve. Filter again, add 100 ml of methanol, stir for 10 min, precipitate, centrifuge, and dry in vacuo at 70°C for 4 h to obtain the azide compound.

[0045] S3: Under closed conditions, 300 ml of DMF, 40 g of an azide compound, and 10 g of N,N,N-trimethylpent-4-yn-1-amine quaternary ammonium salt were added to the reactor and stirred to mix. Then, 7 g of cuprous bromide and 8 g of N,N,N′,N′′,N′′-pentamethyldiethylenetriamine were added. The mixture was reacted at room temperature for 20 h, and then exposed to air for 1 h to quench the reaction. The mixture was dialyzed against a 2 wt% EDTA solution in DMF (MwCO = 5 KDa) for 24 h, and then dialyzed against deionized water (MwCO = 5 KDa) for 24 h. The mixture was freeze-dried at -20°C for 12 h to obtain an emulsifier.

[0046] Example 4 Preparation of dispersant:

[0047] A1: Add 300ml of deionized water and 60g of lignin to a reactor and stir to form a suspension. Slowly add 10g of 95wt% concentrated sulfuric acid (control the temperature <50°C) dropwise over 20 minutes. After heating to 60°C, add 150ml of deionized water and stir to mix. After reacting for 2 hours, slowly add 500ml of cold water and adjust the pH to neutral with 10wt% NaOH solution. The solid precipitates and is centrifuged. Wash with deionized water three times (200ml each time) and dry under vacuum at 60°C for 12 hours to obtain sulfonated lignin. In this reaction, some of the hydroxyl groups in the lignin are sulfonated into sulfonic acid groups.

[0048] A2: 200 ml of anhydrous ethanol, 30 g of sulfonated lignin, 10 g of bromododecane, and 4 g of sodium hydroxide were added to a reactor, stirred and mixed, and the mixture was refluxed for 4 h. The mixture was cooled to room temperature and distilled under reduced pressure at 70°C for 2 h to obtain a crude product. The crude product was dissolved in 200 ml of 50°C hot ethanol and filtered while hot. The filtrate was cooled to precipitate a solid, which was then dried under vacuum at 40°C for 6 h to obtain an alkyl-modified lignin. In this reaction, some of the unreacted hydroxyl groups in the lignin underwent a substitution reaction with the bromine atoms in the bromododecane.

[0049] A3: Under nitrogen protection, 300 ml of anhydrous ethanol, 70 g of alkyl-modified lignin, 50 g of propylene oxide, and 8 g of 85 wt% phosphoric acid were added to a reactor with stirring. The mixture was heated to 60°C for 4 h, and then 200 ml of ice water was slowly added to terminate the reaction. A 5 wt% sodium bicarbonate solution was then added to adjust the pH to neutral. The solid was separated by centrifugation and washed three times with deionized water (200 ml each time). The solid was then dried under vacuum at 50°C for 24 h to obtain a dispersant. In this reaction, the unreacted hydroxyl groups in the lignin underwent a ring-opening reaction with the epoxy groups in the propylene oxide.

[0050] Example 5 Preparation of polyether siloxane defoamer for water-based coatings:

[0051] (1) Weigh: polyether-modified silicone oil: 600 g, silicone paste: 50 g, dispersant (prepared in Example 4): 30 g, silicon dioxide: 20 g, emulsifier (prepared in Example 1): 50 g, surfactant (16 g perfluoroalkylethanol polyoxyethylene ether + 4 g polyethylene glycol phosphate): 20 g;

[0052] (2) The polyether modified silicone oil, silicone paste, dispersant, silicon dioxide, emulsifier and surfactant were mixed in proportion and emulsified at 2700 r / min for 20 min using an emulsifying disperser to obtain a polyether silicone defoamer for water-based coatings.

[0053] Example 6 Preparation of polyether siloxane defoamer for water-based coatings:

[0054] (1) Weigh: polyether-modified silicone oil: 700 g, silicone paste: 60 g, dispersant (prepared in Example 4): 40 g, silicon dioxide: 30 g, emulsifier (prepared in Example 2): 80 g, surfactant (24 g perfluoroalkylethanol polyoxyethylene ether + 6 g polyethylene glycol phosphate): 30 g;

[0055] (2) The polyether modified silicone oil, silicone paste, dispersant, silicon dioxide, emulsifier and surfactant were mixed in proportion and emulsified at 2700 r / min for 30 min using an emulsifying disperser to obtain a polyether silicone defoamer for water-based coatings.

[0056] Example 7 Preparation of polyether siloxane defoamer for water-based coatings:

[0057] (1) Weigh: polyether-modified silicone oil: 750 g, silicone paste: 80 g, dispersant (prepared in Example 4): 50 g, silicon dioxide: 40 g, emulsifier (prepared in Example 3): 100 g, surfactant (40 g perfluoroalkylethanol polyoxyethylene ether + 10 g polyethylene glycol phosphate): 50 g;

[0058] (2) The polyether modified silicone oil, silicone paste, dispersant, silicon dioxide, emulsifier and surfactant were mixed in proportion and emulsified at 2700 r / min for 40 min using an emulsifying disperser to obtain a polyether silicone defoamer for water-based coatings.

[0059] Comparative Example 1

[0060] The preparation method of the polyether siloxane defoamer for water-based coatings is basically the same as that in Example 6, except that the emulsifier is replaced by an equal weight of an emulsifier prepared by the following method:

[0061] S1: Under ice bath, 30 mL of anhydrous THF was added to the reactor, and 10 mL of phosgene solution (15% by weight dissolved in toluene) was added via syringe. Then, 2.37 g of γ-benzyl L-glutamate was added and stirred. The mixture was placed in an oil bath at 50°C for 2 h, and then distilled under reduced pressure at 50°C for 30 min. The crude product was dissolved in 10 mL of dry THF and recrystallized from 100 mL of n-hexane. It was then dried under vacuum at 60°C for 2 h to obtain intermediate 1.

[0062] S2: In an ice bath, 1000 g of DMF and 190 g of intermediate 1 were added to a reactor, followed by 10 g of n-hexylamine, and the mixture was stirred and mixed. After reacting at 4°C for 22 h, 5000 ml of a mixed solution of cold n-hexane and diethyl ether (n-hexane: diethyl ether (V / V) = 1:1) was added, stirred and mixed, and the mixture was allowed to stand to precipitate. The precipitate was filtered and dried in a vacuum at 70°C for 3 h to obtain intermediate 2.

[0063] S3: 2000 ml of dichloromethane, 160 g of intermediate 2, 10 g of catalyst 18-crown ether-6, 120 ml of pH = 7 phosphate buffer and 250 g of N-(4-(2,5-dioxo-4-oxazolidinyl)butyl)-2,2,2-trifluoroacetamide were added to the reactor, stirred and mixed, reacted at room temperature for 24 h, extracted to remove water, then dried with 300 g of anhydrous sodium sulfate for 1 h, filtered, and distilled under reduced pressure at 30°C for 40 min. Then, 2000 ml of cold n-hexane / diethyl ether (v / v = 1 / 1) was slowly added to precipitate, centrifuged and filtered, and dried in vacuo at 60°C for 6 h to obtain intermediate 3;

[0064] S4: 100 ml of DMF, 25 g of intermediate 3, and 10 g of sodium azide were added to the reactor, stirred and mixed, and the temperature was raised to 60°C. After reaction for 48 h, the temperature was lowered to room temperature, filtered, and distilled under reduced pressure at 60°C for 2 h. Then, 100 ml of dichloromethane was added and stirred to dissolve. The mixture was filtered again, and 100 ml of methanol was added. The mixture was stirred for 10 min to separate the precipitate. The mixture was centrifuged and dried under vacuum at 70°C for 4 h to obtain intermediate 4.

[0065] S5: Under closed conditions, 300 ml of DMF, 30 g of intermediate 4, and 10 g of N,N,N-trimethylpent-4-yn-1-amine quaternary ammonium salt were added to the reactor and stirred to mix. Then, 7 g of cuprous bromide and 8 g of N,N,N′,N′′,N′′-pentamethyldiethylenetriamine were added. The mixture was reacted at room temperature for 22 h, and then exposed to air for 1 h to quench the reaction. The mixture was dialyzed against a 2 wt% EDTA solution in DMF (MwCO = 5 KDa) for 24 h, and then dialyzed against deionized water (MwCO = 5 KDa) for 24 h. The emulsifier was freeze-dried at -20°C for 12 h to obtain the emulsifier.

[0066] Comparative Example 2

[0067] The preparation method of the polyether siloxane defoamer for water-based coatings is basically the same as that in Example 6, except that the emulsifier is replaced by an equal weight of an emulsifier prepared by the following method:

[0068] S1: Add 100 ml of DMF, 25 g of N-(4-(2,5-dioxo-4-oxazolidinyl)butyl)-2,2,2-trifluoroacetamide, and 10 g of sodium azide to a reactor, stir and mix, heat to 50°C, react for 50 h, cool to room temperature, filter, and distill under reduced pressure at 60°C for 2 h. Then, add 100 ml of dichloromethane and stir to dissolve. Filter again, add 100 ml of methanol, stir for 10 min, precipitate, centrifuge, and dry in vacuo at 70°C for 4 h to obtain an azide compound.

[0069] S2: Under closed conditions, 300 ml of DMF, 30 g of an azide compound, and 10 g of N,N,N-trimethylpent-4-yn-1-amine quaternary ammonium salt were added to the reactor and stirred to mix. Then, 7 g of cuprous bromide and 8 g of N,N,N′,N′′,N′′-pentamethyldiethylenetriamine were added. The mixture was reacted at room temperature for 24 h, and then exposed to air for 1 h to quench the reaction. The mixture was dialyzed against a 2 wt% EDTA solution in DMF (MwCO = 5 KDa) for 24 h, and then dialyzed against deionized water (MwCO = 5 KDa) for 24 h. The emulsifier was freeze-dried at -20°C for 12 h.

[0070] Comparative Example 3

[0071] The preparation method of the polyether siloxane defoamer for water-based coatings is basically the same as that in Example 6, except that the emulsifier is replaced by an equal weight of an emulsifier prepared by the following method:

[0072] The preparation method of the emulsifier is basically the same as that in Example 2, except that the amount of N-(4-(2,5-dioxo-4-oxazolidinyl)butyl)-2,2,2-trifluoroacetamide added in step S1 is 300 g, and the reaction time at 4°C is increased from 22 h to 30 h.

[0073] Comparative Example 4

[0074] The preparation method of the polyether siloxane defoamer for water-based coatings is basically the same as that in Example 6, except that the dispersant is replaced by an equal weight of a dispersant prepared by the following method:

[0075] The preparation method of the dispersant is basically the same as that of Example 4, except that the brominated dodecane in step A2 is replaced by an equal weight of brominated butylene.

[0076] Comparative Example 5

[0077] The preparation method of the polyether silicone defoamer for water-based coatings is basically the same as that of Example 6, except that the dispersant is replaced by an equal weight of the alkyl-modified lignin prepared in step A2.

[0078] Comparative Example 6

[0079] A polyether siloxane defoamer for water-based coatings was prepared using the raw materials and proportions described in Example 4 of the Chinese invention patent publication number CN119097962A.

[0080] The preparation steps of N,N,N-trimethylpent-4-yn-1-amine quaternary ammonium salt are as follows:

[0081] Dissolve 10 g of N,N-dimethylpent-4-yn-1-amine in 100 mL of acetonitrile and stir to dissolve. Slowly add 31 g of iodomethane dropwise for 20 min. Heat to reflux and react for 24 hours. Cool to room temperature and perform rotary evaporation at 70 °C for 3 h. Then add 50 mL of cold ether and stir to precipitate a white solid. Filter and wash with ether three times (20 mL each time). Dry in a vacuum at 40 °C for 12 h to obtain N,N,N-trimethylpent-4-yn-1-amine quaternary ammonium salt.

[0082] The polyether-modified silicone oil used in the examples and comparative examples of the present application is Dow Corning OFX-0400; the silicone paste model is Dow Corning DC4; the perfluoroalkylethanol polyoxyethylene ether model is FEO-300; the polyethylene glycol phosphate is PEG400MO phosphate, produced by Hai'an Petrochemical Plant in Jiangsu Province; the lignin used is guaiacyl lignin with a molecular weight of 2000.

[0083] Dispersibility test: The polyether silicone defoamer prepared in the examples and comparative examples was diluted with water and stirred to form a 10 wt % solution. The solution was stored at (70±5)°C for 48 h, and the emulsion was observed for precipitation and oil floating.

[0084] Defoaming test: Add 100 mL of a 0.2% (mass fraction) sodium dodecylbenzenesulfonate aqueous solution to a 1 L graduated cylinder as the foaming solution. Heat the mixture to 70°C in a water bath and introduce nitrogen at a rate of 2 L / min. When the foam volume reaches 500 mL, add 1 mL of a 10% (mass fraction) polyether siloxane defoamer prepared in the Examples and Comparative Examples. Simultaneously, start a timer and record the time it takes for all the foam to disappear. A shorter time indicates better defoaming performance. Continue bubbling and record the time it takes for the foam height to reach 500 mL again. A longer time indicates better anti-foaming performance.

[0085] Paint film performance test:

[0086] 1. Weigh the following water-based coating components by weight: resin wantipro® 0626: 88.3 g, polyether siloxane defoamer (prepared in the example or comparative example): 0.1 g, film-forming aid Texanol: 6.6 g, film-forming aid DPM: 4.6 g, anti-flash rust additive FA-179: 0.4 g;

[0087] 2. Add the above components into the mixer in sequence under stirring conditions and stir evenly to prepare the water-based paint;

[0088] 3. Place the water-based paint at a constant temperature of 25°C for 24 hours, then scrape the film on a transparent glass plate. After the paint film is dry, observe whether there are shrinkage holes. Use the index of 1-5 to qualitatively express it, where:

[0089] Level 1: Densely distributed obvious shrinkage holes (diameter> 1mm) appear on the paint film surface, with obvious depressions or pinholes visible to the naked eye, and the distribution area exceeds 50%;

[0090] Level 2: There are a large number of shrinkage holes (diameter 0.5-1mm), which appear in patches in local areas, affecting the surface smoothness, and the distribution area is 20%-50%;

[0091] Level 3: A small number of isolated shrinkage cavities (diameter <0.5mm), scattered and can only be found by close observation, with a distribution area of <10%;

[0092] Level 4: Almost no visible shrinkage cavities, with only a few tiny defects (diameter <0.2mm) found under specific light angles;

[0093] Level 5: The paint film is completely smooth and flat, without any shrinkage holes, depressions or orange peel phenomena, and the surface is evenly reflective.

[0094] Antibacterial test: refer to GB / T21866-2008.

[0095] Table 1

[0096]

[0097] The emulsifier prepared by the present invention has a strong polar quaternary ammonium group, which can effectively reduce the interfacial tension between polyether siloxane and aqueous / oily medium, and promote the uniform dispersion of silicone oil droplets. The cationic characteristic of the quaternary ammonium salt gives the emulsifier positive charge, prevents reunion through electrostatic repulsion, and significantly improves the kinetic stability of the dispersion system. The polar head group of the quaternary ammonium salt combines with the polyether segment in the polyether siloxane through hydrogen bonds or dipole interactions, enhancing the compatibility of the emulsifier and the defoamer main structure and reducing the phase separation risk. In addition, the triazole structure contained in the emulsifier can form specific interactions with bacterial target proteins through hydrogen bonds, inhibit key enzyme activity, and have a certain antibacterial effect.

[0098] The dispersant prepared by this invention imparts strong hydrophilicity to lignin through the introduction of sulfonic acid groups via sulfonation. The grafting of dodecane bromide into a long-chain alkyl hydrophobic group creates an amphiphilic structure, which aligns the dispersant within the polyether siloxane system, reducing interfacial tension, preventing defoamer aggregation, and improving system stability. The epoxy groups of propylene oxide undergo ring opening under acidic conditions, undergoing a nucleophilic addition reaction with the phenolic hydroxyl groups of lignin to form polyether side chains. The steric hindrance of the polyether side chains prevents particle aggregation and improves dispersion efficiency. They also reduce surface tension, improving wettability and interfacial compatibility. The introduction of ether bonds (COC) enhances molecular chain flexibility and reduces the risk of chain breakage at high temperatures.

[0099] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. However, any equivalent changes, modifications and evolutions made by ordinary technicians in this field without departing from the scope of the technical solution of the present invention by using the technical content disclosed above are all equivalent embodiments of the present invention. At the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present invention are still within the scope of protection of the technical solution of the present invention.

Claims

1. A polyether siloxane defoamer for water-based coatings, characterized in that: The composition comprises the following raw materials in parts by weight: Polyether modified silicone oil: 60-75 parts, silicone paste: 5-8 parts, dispersant: 3-5 parts, silicon dioxide: 2-4 parts, emulsifier: 5-10 parts, surfactant: 2-5 parts; The emulsifier is prepared by the following method: S1: Under an ice bath, DMF and N-(4-(2,5-dioxo-4-oxazolidinyl)butyl)-2,2,2-trifluoroacetamide were added to a reactor, followed by n-hexylamine, and the mixture was stirred and mixed. After reaction at 4°C, a mixed solution of cold n-hexane and diethyl ether was added, wherein the ratio of n-hexane to diethyl ether was 1:1 (V / V). The mixture was stirred and mixed, and the mixture was allowed to stand to precipitate. The precipitate was filtered and dried under vacuum to obtain a fluorine-containing amide polymer. S2: DMF, fluorine-containing amide polymer, and sodium azide were added to the reactor, stirred and mixed, heated to react, cooled to room temperature, filtered, and distilled under reduced pressure. Then, dichloromethane was added and stirred to dissolve, filtered again, methanol was added, stirred, a precipitate was precipitated, centrifuged, and dried in vacuo to obtain the azide compound; S3: Under closed conditions, DMF, an azide compound, and N,N,N-trimethylpent-4-yn-1-amine quaternary ammonium salt are added to a reactor and stirred to mix. Cuprous bromide and N,N,N′,N′′,N′′-pentamethyldiethylenetriamine are then added and reacted at room temperature. The reaction is then quenched by exposing the mixture to air, followed by dialyzing against a 2 wt % EDTA solution in DMF and then against deionized water. The mixture is freeze-dried to obtain an emulsifier. The mass ratio of N-(4-(2,5-dioxo-4-oxazolidinyl)butyl)-2,2,2-trifluoroacetamide and n-hexylamine in S1 is (18-20):1; The mass ratio of the fluorine-containing amide polymer to sodium azide in S2 is (2-3):1; The mass ratio of the azide compound to the N,N,N-trimethylpent-4-yn-1-amine quaternary ammonium salt in S3 is (2-4):1; The dispersant is prepared by the following method: A1: Deionized water and lignin were added to the reactor and stirred to form a suspension; 95 wt% concentrated sulfuric acid was slowly added dropwise, with the temperature controlled at <50°C, for 20 min. After the temperature was raised to 60°C, deionized water was added and stirred to mix. After the reaction, cold water was slowly added and the pH was adjusted to neutral with 10 wt% NaOH solution. The solid was precipitated, centrifuged, washed three times with deionized water, and vacuum dried to obtain sulfonated lignin. A2: Add anhydrous ethanol, sulfonated lignin, dodecane bromide, and sodium hydroxide to a reactor, stir and mix, heat to reflux for reaction, cool to room temperature, and distill under reduced pressure to obtain a crude product. The crude product is dissolved in 50°C hot ethanol and filtered while hot. The filtrate is cooled to precipitate a solid, which is then vacuum dried to obtain an alkyl-modified lignin. A3: Under nitrogen protection, anhydrous ethanol, alkyl-modified lignin, propylene oxide, and 85 wt% phosphoric acid were added to a reactor, stirred and mixed, and the temperature was raised to 60°C for reaction. Ice water was slowly added to terminate the reaction, and then 5 wt% sodium bicarbonate solution was added to adjust the pH to neutral. The solid was separated by centrifugation, washed three times with deionized water, and vacuum dried to obtain a dispersant. The mass ratio of lignin and concentrated sulfuric acid in A1 is 6:1; The mass ratio of sulfonated lignin and brominated dodecane in A2 is 3:1; The mass ratio of the alkyl-modified lignin to propylene oxide in A3 is 7:

10.

2. A polyether siloxane defoamer for water-based coatings according to claim 1, characterized in that: The surfactant is prepared by compounding perfluoroalkylethanol polyoxyethylene ether and polyethylene glycol phosphate in a weight ratio of 4:

1.

3. A method for preparing a polyether siloxane defoamer for water-based coatings according to any one of claims 1 to 2, characterized in that: The following steps are involved: (1) Weigh by weight: polyether modified silicone oil: 60-75 parts, silicone paste: 5-8 parts, dispersant: 3-5 parts, silicon dioxide: 2-4 parts, emulsifier: 5-10 parts, surfactant: 2-5 parts; (2) The polyether modified silicone oil, silicone paste, dispersant, silicon dioxide, emulsifier and surfactant are mixed in proportion and emulsified in an emulsifying disperser for 20-40 minutes to obtain a polyether silicone defoamer for water-based coatings.

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