Preparation method of water-based pigment dispersant for painting and dispersant

Abstract

The present invention provides a preparation method and dispersant for a water-based pigment dispersant for painting, which belongs to the field of pigments. A block copolymer solution is synthesized using four monomers: styrene, diallyl maleate, allyl maleate-based quaternary ammonium salt monomer, and acrylic acid. The block copolymer solution is then modified using fatty alcohol polyoxyethylene ether as a graft modifier. The allyl maleate-based quaternary ammonium salt monomer is prepared from N-methylamine and allyl maleate-based ethylene oxide to obtain an intermediate, which is then recrystallized and purified with a brominated alkyl compound. Because it has the same structural units as diallyl maleate, the polymer molecular structure is more stable, and it has a hydrophobic tail and a positively charged head composed of an alkyl chain, which contributes to the binding stability of the polymer with pigment particles in an aqueous medium. The branched alkyl group and polyoxyethylene chain in the structure of the fatty alcohol polyoxyethylene ether itself have both hydrophilic and hydrophobic properties, further improving the dispersion effect and storage stability of the dispersant.

Description

Technical Field

[0001] The invention belongs to the field of pigments, and in particular relates to a preparation method of a water-based pigment dispersant for painting and the dispersant. Background Art

[0002] The ingredients of water-based pigments include granular pigments, dispersants, wetting agents, and other fillers and additives. Water-based pigments are liquid mixtures of the above ingredients. Among them, pigments are divided into organic pigments and inorganic pigments, which are used as colorants to color various systems. Organic pigments are generally taken from plants and marine animals, such as madder indigo, gamboge, and purple extracted from shellfish in ancient Rome. Organic pigments are often used in art painting.

[0003] Dispersants help pigments adhere better to substrates, improving their coloring and hiding power. They also prevent floating and settling, maintaining pigment uniformity and stability by preventing the sedimentation and agglomeration of pigment particles. Furthermore, dispersants ensure the storage stability of coatings and significantly impact the performance of pigment preparations. Styrene-maleic anhydride copolymers are widely used due to their excellent performance and low price.

[0004] Patent publication number US6336966 discloses a method for preparing star-shaped pigment dispersions using atom transfer radical polymerization (ATRP). However, the complex and costly ATRP process hinders large-scale industrial application. Existing dispersants typically suffer from drawbacks such as high dosage, high color paste viscosity, high cost, insufficient dispersion, and poor stability. Summary of the Invention

[0005] In response to the deficiencies in the prior art, the present invention proposes a method for preparing a water-based pigment dispersant for painting and a dispersant. The dispersant is a graft-modified styrene-diallyl maleate-allyl maleate quaternary ammonium salt monomer-acrylic acid block copolymer. Through graft modification, a dispersant with good dispersibility in aqueous media, strong relative tinting power, and good storage stability is obtained, thereby solving the problems of poor pigment dispersibility, low color paste tinting power, poor storage stability, and insufficient adhesion of the dispersant to the substrate.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A water-based pigment dispersant for painting, which is a graft-modified styrene-diallyl maleate-allyl maleate quaternary ammonium salt monomer-acrylic acid block copolymer, and the preparation method includes the following steps:

[0008] S1: Styrene, diallyl maleate, allyl maleate quaternary ammonium salt monomer, acrylic acid and solvent are mixed to obtain a mixed solution; a mixture of an initiator, a chain transfer agent and a solvent is added dropwise to the mixed solution to react under nitrogen protection. After the addition is completed, the mixture is kept warm for 1-3 hours to obtain a block copolymer solution;

[0009] S2: performing a grafting reaction on the block copolymer solution obtained in step S1, a graft modifier and a catalyst to obtain a water-based pigment dispersant for painting.

[0010] In step S1, the mass ratio of styrene, diallyl maleate, allyl maleate quaternary ammonium salt monomer and acrylic acid is 12-20:15-25:18-28:10-15;

[0011] The solvent in step S1 is 1,4-dioxane or cyclohexane;

[0012] The reaction temperature in step S1 is 70-90° C., and the reaction time is 2-6 hours;

[0013] The initiator in step S1 is benzoyl peroxide or dicumyl peroxide, and the amount of the initiator is 3-8% of the total mass of styrene, diallyl maleate, allyl maleate quaternary ammonium salt monomer and acrylic acid;

[0014] The chain transfer agent in step S1 is dodecanethiol or α-methylstyrene linear dimer, and the amount of the chain transfer agent is 2-3% of the total mass of styrene, diallyl maleate, allyl maleate quaternary ammonium salt monomer and acrylic acid;

[0015] The structural formula of the allyl maleate quaternary ammonium salt monomer in step S1 is as follows:

[0016] ,

[0017] Wherein, R1 is butyl, pentyl, hexyl, heptyl or octyl, and the value of n is a positive integer from 3 to 5;

[0018] The preparation method of the allyl maleate quaternary ammonium salt monomer in step S1 comprises the following steps:

[0019] (1) Add methanol, N-methylamine, and allyl maleate oxirane to a reactor equipped with a condenser reflux tube, heat to 55-60°C, react for 48-60 hours, remove methanol, wash, and dry to obtain an intermediate;

[0020] (2) adding isopropyl alcohol, the intermediate obtained in step (1) and the bromoalkyl compound to a reaction vessel equipped with a condenser reflux tube, mixing and reacting with stirring, removing the isopropyl alcohol, and purifying the product by recrystallization in water to obtain an allyl maleate quaternary ammonium salt monomer;

[0021] The reaction formula is as follows:

[0022] ;

[0023] The N-methylamine in step S1 (1) is N-methylbutylamine, N-methylpentylamine, N-methylhexylamine, N-methylheptylamine or N-methyloctylamine, and the molar ratio of the N-methylamine to allyl maleate oxirane is 2.5-3:1;

[0024] The molecular formula of the bromoalkane compound in step S1 (2) is BrC n H 2n+1 , n is any positive integer between 3 and 5;

[0025] The molar ratio of the intermediate to the bromoalkyl compound in step S1 (2) is 1:2.6-2.8; the stirring reaction temperature is 70-90° C., and the stirring reaction time is 36-48 hours.

[0026] The graft modifier in step S2 is fatty alcohol polyoxyethylene ether, and the general structural formula is:

[0027] ,

[0028] Wherein, R is an alkyl group containing 12 to 18 carbon atoms, and a is a positive integer between 10 and 30; the amount of the graft modifier used is 35 to 85% of the molar amount of the acrylic acid in step S1;

[0029] The catalyst in step S2 includes one of p-toluenesulfonic acid, aluminum chloride, triethylamine, 4-dimethylaminopyridine, and pyridine;

[0030] The grafting reaction temperature in step S2 is 60-90° C. and the time is 3-6 hours.

[0031] A water-based pigment dispersant prepared by the above-mentioned method for preparing a water-based pigment dispersant for painting.

[0032] The beneficial effects of the present invention are:

[0033] 1. The water-based pigment dispersant prepared by the present invention is a block copolymer of styrene-diallyl maleate-allyl maleate quaternary ammonium salt monomer and acrylic acid. This is a polymer containing carboxyl groups and terminal addition-polymerizable double bonds. It has a low softening point and exhibits flexibility and low viscosity in aqueous media, which enhances its hydrophilicity as a water-soluble dispersant and, in turn, improves the dispersion stability of the pigment in the aqueous medium. The block copolymer can be adsorbed on the surface of the pigment particles and has strong compatibility with the pigment, thereby improving the overall solubility and dispersibility of the dispersant in the aqueous medium.

[0034] 2. The block copolymer proposed in this invention comprises polymer segments with different properties, combining the advantageous characteristics of multiple polymers. This multi-block copolymer offers richer functionality and microstructure. The hydrophobic segment is formed by the polymerization of styrene and diallyl maleate monomers, while the hydrophilic segment is acrylic acid. The allyl maleate quaternary ammonium salt monomer and diallyl maleate share the same structural unit (the allyl maleate group), which further stabilizes the polymer's molecular structure. The allyl maleate quaternary ammonium salt monomer has a hydrophobic tail and a positively charged head composed of an alkyl chain, which contributes to the polymer's stable binding to pigment particles in aqueous media.

[0035] 3. The four monomers are polymerized in a defined ratio to control the ratio of hydrophilic and hydrophobic groups in the block polymer. If the polymer is too hydrophilic, its adsorption capacity for pigment molecules will be weakened, resulting in poor storage stability of the pigment. If it is too hydrophobic, it will cause flocculation and aggregation of pigment molecules.

[0036] 4. The graft-modified block copolymer dispersant containing a styrene-diallyl maleate-allyl maleate quaternary ammonium salt monomer-acrylic acid structure prepared by the present invention, by grafting a fatty alcohol polyoxyethylene ether modifier onto the block copolymer, has both hydrophilic and hydrophobic properties based on the alkyl and polyoxyethylene chains in the modifier's own structure, and has both wetting and dispersing properties, which can further improve the dispersing effect and storage stability of the dispersant. DETAILED DESCRIPTION

[0037] The preparation process of allyl maleate oxirane refers to the document "Process for the preparation and isolation of polyglycidyl compounds", Bayer Aktiengesellschaft, US04562274A1.

[0038] To 5 mol of diallyl maleate, add 2.89 kg of a 21.8% peroxypropionic acid solution in benzene, and reflux at 60° C. for 8.5 hours. After the reaction is complete, cool, concentrate, and then wash to obtain allyl maleate oxirane.

[0039] The structural formula and related information of the graft modifiers used in the Examples and Comparative Examples are as follows:

[0040] Graft modifier A

[0041] , decaethylene glycol monododecyl ether;

[0042] Graft modifier B

[0043] , polyethylene glycol (12) tridecyl ether;

[0044] Graft modifier C

[0045] , polyethylene glycol 23 lauryl ether;

[0046] The above graft modifier is a commercially available product purchased from KMIC Company.

[0047] Example 1

[0048] Add 15 ml of methanol, 5.7 mmol of N-methylbutylamine, and 2.2 mmol of allyl maleate oxirane to a reactor equipped with a reflux condenser, raise the temperature to 55°C, react for 48 hours, remove the methanol by rotary evaporation, wash with petroleum ether, and dry to obtain an intermediate;

[0049] 15 ml of isopropanol, 2.5 mmol of the intermediate, and 6.5 mmol of bromobutane were added to a reaction vessel equipped with a condenser reflux tube, and the mixture was stirred at 70° C. for 48 h. The isopropanol was removed by rotary evaporation, and the mixture was purified by recrystallization in water to obtain a maleic acid allyl ester quaternary ammonium salt monomer with the following structural formula:

[0050] .

[0051] 18.5 g of styrene, 22.4 g of diallyl maleate, 26.6 g of allyl maleate quaternary ammonium salt monomer, and 10.8 g of acrylic acid were placed in a reactor, 100 ml of 1,4-dioxane solvent was added to dissolve the above four monomers, and the temperature was raised to 70°C under nitrogen protection. 2.8 g of benzoyl peroxide was dissolved in 10 ml of 1,4-dioxane and thoroughly mixed with 2.1 g of dodecyl mercaptan, and then added dropwise to the reactor and reacted at 70°C for 2 h. After the addition was completed, the reaction was continued for 1 h to obtain a block copolymer solution;

[0052] 75 g of graft modifier A and 4 g of 4-dimethylaminopyridine were added to the block copolymer solution for graft reaction at 60° C. for 3 h. After the reaction was completed, the solvent was removed and the solution was cooled to room temperature to obtain a water-based pigment dispersant for painting.

[0053] Example 2

[0054] Add 10 ml of methanol, 5.2 mmol of N-methyloctylamine, and 1.7 mmol of allyl maleate oxirane to a reactor equipped with a reflux condenser, raise the temperature to 60°C, react for 60 h, remove the methanol by rotary evaporation, wash with petroleum ether, and dry to obtain an intermediate;

[0055] 15 ml of isopropanol, 1.5 mmol of the intermediate, and 4.2 mmol of bromobutane were added to a reaction vessel equipped with a condenser reflux tube, and the mixture was stirred at 90° C. for 36 h. The isopropanol was removed by rotary evaporation, and the mixture was purified by recrystallization in water to obtain a maleic acid allyl ester quaternary ammonium salt monomer with the following structural formula:

[0056] .

[0057] 19.5 g of styrene, 26.2 g of diallyl maleate, 24.5 g of allyl maleate quaternary ammonium salt monomer, and 20.7 g of acrylic acid were placed in a reactor, 100 ml of 1,4-dioxane solvent was added to dissolve the above four monomers, and the temperature was raised to 90°C under nitrogen protection. 7.2 g of dicumyl peroxide was dissolved in 10 ml of 1,4-dioxane and the mixture was thoroughly mixed with 1.86 g of α-methylstyrene linear dimer, and then the mixture was dropped into the reactor and reacted at 70°C for 6 h. After the addition was completed, the reaction was continued for 3 h to obtain a block copolymer solution;

[0058] 220 g of graft modifier B and 4 g of 4-dimethylaminopyridine were added to the block copolymer solution for graft reaction at 90° C. for 3 h. After the reaction was completed, the solvent was removed and the solution was cooled to room temperature to obtain a water-based pigment dispersant for painting.

[0059] Example 3

[0060] Add 15 ml of methanol, 4.2 mmol of N-methyloctylamine, and 1.6 mmol of allyl maleate oxirane to a reactor equipped with a reflux condenser, raise the temperature to 60°C, react for 60 h, remove the methanol by rotary evaporation, wash with petroleum ether, and dry to obtain an intermediate;

[0061] 15 ml of isopropanol, 2.0 mmol of the intermediate, and 4.2 mmol of bromopropane were added to a reaction vessel equipped with a condenser reflux tube, and the mixture was stirred at 80° C. for 48 h. The isopropanol was removed by rotary evaporation, and the mixture was purified by recrystallization in water to obtain a maleic acid allyl ester quaternary ammonium salt monomer with the following structural formula:

[0062] .

[0063] 17.5 g of styrene, 20.1 g of diallyl maleate, 22.8 g of allyl maleate quaternary ammonium salt monomer and 15.6 g of acrylic acid were placed in a reactor, 90 ml of cyclohexane solvent was added to dissolve the above four monomers, and the temperature was raised to 90° C. under nitrogen protection. 3.8 g of dicumyl peroxide was dissolved in 10 ml of cyclohexane and thoroughly mixed with 1.52 g of α-methylstyrene linear dimer, and then added dropwise to the reactor and reacted at 75° C. for 6 h. After the addition was completed, the reaction was continued for 2 h to obtain a block copolymer solution;

[0064] 241 g of graft modifier C and 4 g of triethylamine were added to the block copolymer solution for graft reaction at 90° C. for 6 h. After the reaction was completed, the solvent was removed and the solution was cooled to room temperature to obtain a water-based pigment dispersant for painting.

[0065] Comparative Example 1

[0066] 17.5 g of styrene, 20.1 g of diallyl maleate, and 15.6 g of acrylic acid were placed in a reactor, cyclohexane solvent was added to dissolve the above monomers, and the temperature was raised to 70°C under nitrogen protection. 1.8 g of dicumyl peroxide was dissolved in cyclohexane and thoroughly mixed with 1.06 g of α-methylstyrene linear dimer. The mixture was then added dropwise to the reactor and reacted at 70°C for 2 h. After the addition was complete, the reaction was continued for 1 h to obtain a block copolymer solution.

[0067] 241 g of graft modifier C and 4 g of triethylamine were added to the block copolymer solution for graft reaction at 60° C. for 3 h. After the reaction was completed, the solvent was removed and the solution was cooled to room temperature to obtain a graft-modified block copolymer dispersant.

[0068] Comparative Example 2

[0069] A block copolymer solution was prepared using the allyl maleate quaternary ammonium salt monomer obtained in Example 2, and then 75 g of polyethyleneimine and 4 g of 4-dimethylaminopyridine were added to the block copolymer solution for grafting reaction at 60° C. for 3 h. After the reaction was completed, the solvent was removed and the mixture was cooled to room temperature to obtain a grafted modified block copolymer dispersant.

[0070] Comparative Example 3

[0071] Add 15 ml of methanol, 4.2 mmol of N-methylnonylamine, and 1.6 mmol of allyl maleate oxirane to a reactor equipped with a reflux condenser, raise the temperature to 60°C, react for 60 h, remove the methanol by rotary evaporation, wash with petroleum ether, and dry to obtain an intermediate;

[0072] 15 ml of isopropanol, 2.0 mmol of the intermediate, and 4.2 mmol of bromobutane were added to a reaction vessel equipped with a condenser reflux tube, and the mixture was stirred at 80° C. for 48 h. The isopropanol was removed by rotary evaporation, and the mixture was purified by recrystallization in water to obtain an allyl maleate quaternary ammonium salt monomer having the following structural formula:

[0073] .

[0074] 19.5 g of styrene, 24.9 g of diallyl maleate, 25.8 g of allyl maleate quaternary ammonium salt monomer, and 15.6 g of acrylic acid were placed in a reactor, cyclohexane solvent was added to dissolve the above four monomers, and the temperature was raised to 90° C. under nitrogen protection. 4.3 g of dicumyl peroxide was dissolved in cyclohexane and thoroughly mixed with 2.6 g of α-methylstyrene linear dimer. The mixture was then added dropwise to the reactor and reacted at 75° C. for 6 h. After the addition was complete, the reaction was continued for 2 h to obtain a block copolymer solution.

[0075] 275 g of graft modifier C and 4 g of triethylamine were added to the block copolymer solution and subjected to graft reaction at 90° C. for 6 h. After the reaction was completed, the solvent was removed and the solution was cooled to room temperature to obtain a graft-modified block copolymer dispersant.

[0076] The definition of tinting strength in the national standard GB / T 13451.2-1992 - Relative Tinting Strength of Coloring Pigments (Photometric Method) is: it refers to the ability of a pigment to absorb incident light, thereby having the ability to, for example, tint or darken the white paint to which it is added; tinting strength is expressed as a percentage, and the standard sample is generally taken as 100% in the measurement. If the sample's tinting strength is less than 100, it means that the sample's tinting strength is lower than the standard sample; otherwise, it is higher than the standard sample.

[0077] The graft-modified block copolymer dispersants synthesized in Examples 1-3 and Comparative Examples 1-3 were used to prepare water-based color pastes. The preparation process is as follows:

[0078] The raw material composition of the water-based color paste is as follows: 15% pigment, 8% dispersant, 15% water-based acrylic resin, 7% glycerol, and the balance is water. The above materials except water are first mixed and ground to a mixture with a fineness of less than 15μm. The mixture is then dispersed with water using an oscillator for 60 minutes to obtain the water-based color paste. The water-based acrylic resin is BASF brand, model 678, and the pigment is Pigment Yellow 83.

[0079] The white paste is composed of the following proportions by weight: 25% titanium dioxide, 8% dispersant, 15% water-based acrylic resin, 7% glycerol, and the balance water. The preparation process is the same as that of the water-based color paste. The brand of the water-based acrylic resin is BASF, model number 678.

[0080] The water-based color pastes prepared with the dispersants of Examples 1-3 were used as samples 1-3, and the water-based color pastes prepared with the dispersants of Comparative Examples 1-3 were used as standard samples 1-3 corresponding to samples 1-3. The water-based color pastes were subjected to tinting power test, color intensity test and stability test.

[0081] According to the method for determining relative tinting strength by visual inspection as described in the national standard HG / T3951-2007, water-based color paste and white paste are blended at a mass ratio of 1:20 to obtain diluted color pastes for the sample and the standard. When there is a color difference between the water-based color paste of the sample and the standard, adjustments are made. If the color of the sample is darker or thicker than that of the standard, the amount of white paste is increased. If the color of the sample is lighter than that of the standard, the amount of white paste is reduced until the colors of the two are consistent.

[0082] The tinting strength of the diluted color paste of the sample is calculated according to the following formula:

[0083] TS= ×100%

[0084] Where: TS = tinting strength percentage of diluted color paste of the sample;

[0085] b = amount of standard color paste, in grams (g);

[0086] a = The mass of the test color paste that achieves the same tinting strength as the standard diluted color paste, in grams (g).

[0087] During the test, the value of b is equal to the mass of the white slurry used to dilute the standard sample, and the value of a is equal to the mass of the white slurry used to dilute the test sample;

[0088] The color intensity of the water-based color paste prepared with the dispersants of Examples 1-3 was measured using an X-Rite colorimeter, with the water-based color paste prepared with the dispersants of Comparative Examples 1-3 being used as the standard; where L represents the brightness of the color. When comparing color differences, A positive value indicates that the sample is lighter than the standard color, and a negative value indicates the opposite; the b value indicates the yellow-blue value. A positive value indicates that the sample is yellower than the standard color, while a negative value indicates the opposite;

[0089] Specifically, the stability test is as follows: after the water-based color pastes of Examples 1-3 and Comparative Examples 1-3 are placed under sealed conditions at 25°C for 30 days and 90 days respectively, visual observation is made to see whether there is obvious pigment particle precipitation, flocculation, and other conditions that seriously affect the stability, so as to judge the storage stability of the dispersant used in the water-based color paste. Among them, "√" indicates that there is no abnormality in visual observation, and "×" indicates that there is obvious pigment particle precipitation, flocculation, etc. in visual observation. The results are shown in Table 1 below:

[0090] Table 1 Performance test results of water-based color pastes of Examples and Comparative Examples

[0091]

[0092] As can be seen from the above table, in the aqueous pastes of Examples 1-3, the block copolymer dispersant of styrene-diallyl maleate-allyl maleate quaternary ammonium salt monomer-acrylic acid graft modification of the present invention is adopted and polymerized in a limited ratio, and has good tinting power and stability. This is because the block copolymer with different chain segments of different properties can be adsorbed on the surface of the pigment particles and has a strong compatibility with the pigment, thereby improving the overall solubility and dispersibility of the dispersant in the aqueous medium. The hydrophobic segment is formed by polymerization of monomers of styrene and diallyl maleate, and the hydrophilic segment is acrylic acid. The allyl maleate quaternary ammonium salt monomer and diallyl maleate have the same structural unit, which can make the molecular structure of the polymer more stable. The allyl maleate quaternary ammonium salt monomer has a hydrophobic tail and a positively charged head composed of an alkyl chain, which contributes to the binding stability of the polymer with the pigment particles in an aqueous medium. The dispersant in Comparative Example 1 does not have an added allyl maleate quaternary ammonium salt monomer, so that the synthesized polymer molecular structure lacks stability.

[0093] The dispersant in Comparative Example 2, synthesized using a conventional graft modifier, resulted in decreased tinting power and storage stability of the water-based color paste. However, the modifiers used in Examples 1-3, which were obtained by grafting branched fatty alcohol polyoxyethylene ether modifiers onto the block copolymers, possessed both hydrophilic and hydrophobic properties based on the alkyl and polyoxyethylene chains in the modifiers' own structures, and had both wetting and dispersing properties, thereby further improving the dispersing effect and storage stability of the dispersant.

[0094] In Comparative Example 3, the N-methylamine used in the dispersant synthesis of the allyl maleate quaternary ammonium salt monomer is N-methylnonylamine, which exceeds the specified chain length. This results in the synthesized dispersant being structurally unstable, thus affecting the stability of the water-based color paste.

[0095] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a water-based pigment dispersant for painting, characterized in that: The following steps are included: S1: Styrene, diallyl maleate, allyl maleate quaternary ammonium salt monomer, acrylic acid and solvent are mixed to obtain a mixed solution; a mixture of an initiator, a chain transfer agent and a solvent is added dropwise to the mixed solution to react under nitrogen protection. After the addition is completed, the mixture is kept warm for 1-3 hours to obtain a block copolymer solution; The structural formula of the allyl maleate quaternary ammonium salt monomer in step S1 is as follows: ， Wherein, R1 is butyl, pentyl, hexyl, heptyl or octyl, and the value of n is a positive integer from 3 to 5; S2: performing a grafting reaction on the block copolymer solution obtained in step S1, a graft modifier, and a catalyst to obtain a water-based pigment dispersant for painting; The graft modifier in step S2 is fatty alcohol polyoxyethylene ether, and the general structural formula is: ， Wherein, R is an alkyl group containing 12 to 18 carbon atoms, and a is a positive integer between 10 and 30; The amount of the graft modifier used is 35-85% of the molar amount of the acrylic acid in step S1.

2. The method for preparing a water-based pigment dispersant for painting according to claim 1, characterized in that: In step S1, the mass ratio of styrene, diallyl maleate, allyl maleate quaternary ammonium salt monomer and acrylic acid is 12-20:15-25:18-28:10-15.

3. The method for preparing a water-based pigment dispersant for painting according to claim 1, characterized in that: In step S1, the solvent is 1,4-dioxane or cyclohexane, the reaction temperature is 70-90° C., and the reaction time is 2-6 hours.

4. The method for preparing a water-based pigment dispersant for painting according to claim 1, characterized in that: The initiator in step S1 is benzoyl peroxide or dicumyl peroxide, and the amount of the initiator used is 3-8% of the total mass of styrene, diallyl maleate, allyl maleate quaternary ammonium salt monomer and acrylic acid.

5. The method for preparing a water-based pigment dispersant for painting according to claim 1, characterized in that: In step S1, the chain transfer agent is dodecanethiol or α-methylstyrene linear dimer, and the amount of the chain transfer agent is 2-3% of the total mass of styrene, diallyl maleate, allyl maleate quaternary ammonium salt monomer and acrylic acid.

6. The method for preparing a water-based pigment dispersant for painting according to claim 1, characterized in that: The catalyst in step S2 includes p-toluenesulfonic acid, aluminum chloride, triethylamine, 4-dimethylaminopyridine or pyridine; The grafting reaction temperature is 60-90° C. and the time is 3-6 hours.

7. The method for preparing a water-based pigment dispersant for painting according to claim 1, characterized in that: The preparation method of the allyl maleate quaternary ammonium salt monomer in step S1 comprises the following steps: (1) Add methanol, N-methylamine, and allyl maleate oxirane to a reactor equipped with a condenser reflux tube, heat to 55-60°C, react for 48-60 hours, remove methanol, wash, and dry to obtain an intermediate; (2) adding isopropyl alcohol, the intermediate obtained in step (1) and the bromoalkyl compound to a reaction vessel equipped with a condenser reflux tube, mixing and reacting with stirring, removing the isopropyl alcohol, and purifying the product by recrystallization in water to obtain an allyl maleate quaternary ammonium salt monomer; The molecular formula of the bromoalkane compound is BrC n H 2n+1 , n is any positive integer between 3 and 5.

8. The method for preparing a water-based pigment dispersant for painting according to claim 7, characterized in that: The N-methylamine in step (1) is N-methylbutylamine, N-methylpentylamine, N-methylhexylamine, N-methylheptylamine or N-methyloctylamine; The molar ratio of N-methylamine to allyl maleate oxirane is 2.5-3:1; The molar ratio of the intermediate to the bromoalkane compound in step (2) is 1:2.6-2.8, the temperature of the stirring reaction is 70-90° C., and the time of the stirring reaction is 36-48 hours.

9. A water-based pigment dispersant prepared by the method for preparing a water-based pigment dispersant according to any one of claims 1 to 8.

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