Preparation method of water-based pigment dispersing agent for drawing and dispersing agent

Abstract

The invention provides a preparation method of a water-based pigment dispersing agent for painting and the dispersing agent, and belongs to the field of pigments, four monomers of styrene, diallyl maleate, allyl maleate quaternary ammonium salt monomer and acrylic acid are adopted to synthesize a segmented copolymer solution, and then fatty alcohol-polyoxyethylene ether is used as a grafting modifier for modification. The allyl maleate quaternary ammonium salt monomer is obtained by preparing an intermediate from N-methylamine and allyl maleate ethylene oxide and recrystallizing and purifying the intermediate and a bromoalkane compound, and due to the fact that the allyl maleate quaternary ammonium salt monomer has the same structural unit as diallyl maleate, the molecular structure of the polymer is more stable; the polymer has a hydrophobic tail part and a positively charged head part consisting of an alkyl chain, so that the combination stability of the polymer and pigment particles in an aqueous medium is facilitated; branched alkyl and polyoxyethylene chain in the structure of fatty alcohol-polyoxyethylene ether have hydrophilic and hydrophobic properties at the same time, so that the dispersion effect and storage stability of the dispersant are further improved.

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. 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 can make pigments adhere better to the substrate, thereby improving the coloring and hiding power of the pigments; dispersants can also prevent floating and sedimentation, and maintain the uniformity and stability of the pigments by preventing the sedimentation and agglomeration of pigment particles; in addition, dispersants can also ensure the storage stability of the coating and have a significant impact on the performance of the pigment preparation. Styrene-maleic anhydride copolymers are widely used due to their excellent performance and low price; Patent No. US6336966 discloses a method for preparing star-shaped pigment dispersions using atom transfer radical polymerization technology. However, the preparation process of atom transfer radical polymerization is complicated and costly, making it difficult to apply it industrially on a large scale. Existing dispersants usually have the disadvantages of large dosage, high color paste viscosity, high cost, poor dispersion effect, and poor stability. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a preparation method and a dispersant for a water-based pigment dispersant for painting. The dispersant is a graft-modified styrene-diallyl maleate-allyl maleate quaternary ammonium salt monomer-acrylic acid block copolymer. A dispersant with good dispersibility in an aqueous medium, relatively strong tinting power and good storage stability is obtained through graft modification, thereby solving the problems of poor pigment dispersion ability, low color paste tinting power, poor storage stability, and insufficient adhesion of the dispersant to the substrate.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows: A water-based pigment dispersant for painting is a graft-modified styrene-diallyl maleate-allyl maleate quaternary ammonium salt monomer-acrylic acid block copolymer. The preparation method comprises the following steps: S1: Styrene, diallyl maleate, allyl maleate quaternary ammonium salt monomer, acrylic acid and solvent are mixed to obtain a mixed solution; a mixture consisting of an initiator, a chain transfer agent and a solvent is dripped into the mixed solution, and the mixture is reacted under nitrogen protection. After the dripping is completed, the mixture is kept warm for 1-3 hours to obtain a block copolymer solution; S2: The block copolymer solution obtained in step S1, the graft modifier and the catalyst are subjected to a grafting reaction to obtain a water-based pigment dispersant for painting.

[0006] The mass ratio of styrene, diallyl maleate, allyl maleate quaternary ammonium salt monomer and acrylic acid in step S1 is 12-20:15-25:18-28:10-15; The solvent in step S1 is 1,4-dioxane or cyclohexane; The reaction temperature in step S1 is 70-90°C and the reaction time is 2-6h; 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; 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; 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 of 3-5; The method for preparing 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 isopropanol, the intermediate obtained in step (1) and the bromoalkyl compound into a reaction vessel equipped with a condenser reflux tube, mixing and reacting with stirring, removing the isopropanol, and purifying the product by recrystallization in water to obtain an allyl maleate quaternary ammonium salt monomer; The reaction formula is as follows: ; In step S1 (1), the N-methylamine 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; 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; In step S1 (2), the molar ratio of the intermediate to the bromoalkane compound is 1:2.6-2.8; the stirring reaction temperature is 70-90° C., and the stirring reaction time is 36-48 hours.

[0007] The grafting modifier in step S2 is fatty alcohol polyoxyethylene ether, and the general structural formula is: , Wherein, R is an alkyl group having 12-18 carbon atoms, and a is a positive integer between 10-30; the amount of the graft modifier used is 35-85% of the molar amount of the acrylic acid in step S1; The catalyst in step S2 includes one of p-toluenesulfonic acid, aluminum chloride, triethylamine, 4-dimethylaminopyridine, and pyridine; The grafting reaction temperature in step S2 is 60-90° C. and the time is 3-6 hours.

[0008] A water-based pigment dispersant prepared by the above method for preparing a water-based pigment dispersant for painting.

[0009] The beneficial effects of the present invention are: 1. The water-based pigment dispersant for painting prepared by the present invention is a block copolymer of styrene-diallyl maleate-allyl maleate quaternary ammonium salt monomer-acrylic acid, which is a polymer containing a carboxyl group and a double bond at the end that can be added. It has a lower softening point and shows flexibility and low viscosity in an aqueous medium, thereby improving its hydrophilicity as a water-soluble dispersion, thereby improving 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 a strong compatibility with the pigment, thereby improving the overall solubility and dispersibility of the dispersant in the aqueous medium; 2. The block copolymer proposed in the present invention contains polymer segments with different properties, which can combine the excellent properties of multiple polymers. The multi-block copolymer can provide richer functionality and microscopic phase structure; wherein the hydrophobic segment is polymerized from monomers of styrene and diallyl maleate, the hydrophilic segment is acrylic acid, the allyl maleate quaternary ammonium salt monomer and diallyl maleate have the same structural unit (allyl maleate group), which will make the molecular structure of the polymer more stable, and the allyl maleate quaternary ammonium salt monomer has a hydrophobic tail and a positively charged head composed of an alkyl chain, which helps the polymer to stabilize its binding with pigment particles in an aqueous medium; 3. The four monomers are polymerized in a limited ratio in order to adjust the ratio of hydrophilic groups to hydrophobic groups in the block polymer. If the hydrophilicity of the polymer is too strong, the adsorption capacity of the pigment molecules will be weakened, resulting in poor storage stability of the pigment. If the hydrophobicity is too strong, the pigment molecules will flocculate and agglomerate. 4. The grafted modified block copolymer dispersant containing styrene-diallyl maleate-allyl maleate quaternary ammonium salt monomer-acrylic acid structure prepared by the present invention has both hydrophilic and hydrophobic properties based on the alkyl and polyoxyethylene chains in the structure of the modifier itself, and has both wetting and dispersing properties, which can further improve the dispersing effect and storage stability of the dispersant. DETAILED DESCRIPTION

[0010] The preparation process of allyl maleate oxirane refers to the document “Process for the preparation and isolation of polyglycidyl compounds”, Bayer Aktiengesellschaft, US04562274A1.

[0011] 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 completed, cool, concentrate, and wash to obtain allyl maleate oxirane.

[0012] The structural formula and related information of the graft modifier used in the embodiments and comparative examples are as follows: Graft modifier A , decaethylene glycol monododecyl ether; Graft modifier B , polyethylene glycol (12) tridecyl ether; Graft modifier C , polyethylene glycol 23 dodecyl ether; The above graft modifier is a commercially available product purchased from KMIKE Company.

[0013] Example 1 Add 15 ml of methanol, 5.7 mmol of N-methylbutylamine, and 2.2 mmol of allyl maleate oxirane into a reactor equipped with a condenser reflux tube, heat to 55° C., react for 48 h, remove methanol by rotary evaporation, wash with petroleum ether, and dry to obtain an intermediate; 15 ml of isopropanol, 2.5 mmol of the intermediate, and 6.5 mmol of bromobutyl were added to a reaction vessel equipped with a condenser reflux tube, and the mixture was reacted at 70° C. for 48 h under stirring conditions. 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 having the following structural formula: .

[0014] 18.5g of styrene, 22.4g of diallyl maleate, 26.6g of allyl maleate quaternary ammonium salt monomer and 10.8g of acrylic acid were placed in a reactor, 100ml of 1,4-dioxane solvent was added to dissolve the above four monomers, the temperature was raised to 70°C under nitrogen protection, 2.8g of benzoyl peroxide was dissolved in 10ml of 1,4-dioxane and fully mixed with 2.1g of dodecanethiol, and then dripped into the reactor and reacted at 70°C for 2h. After the dripping was completed, the reaction was continued for 1h to obtain a block copolymer solution; 75 g of graft modifier A 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 solution was cooled to room temperature to obtain a water-based pigment dispersant for painting.

[0015] Example 2 Add 10 ml of methanol, 5.2 mmol of N-methyloctylamine, and 1.7 mmol of allyl maleate oxirane into a reactor equipped with a condenser reflux tube, heat to 60° C., react for 60 h, remove methanol by rotary evaporation, wash with petroleum ether, and dry to obtain an intermediate; 15 ml of isopropanol, 1.5 mmol of the intermediate, and 4.2 mmol of bromobutyl were added to a reaction vessel equipped with a condenser reflux tube, and the mixture was reacted at 90° C. for 36 h under stirring conditions. 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 having the following structural formula: .

[0016] 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, 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 then fully mixed with 1.86 g of α-methylstyrene linear dimer, and then dripped into the reactor for reaction at 70°C for 6 hours, and after the dripping was completed, the reaction was continued for 3 hours to obtain a block copolymer solution; 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.

[0017] Example 3 Add 15 ml of methanol, 4.2 mmol of N-methyloctylamine, and 1.6 mmol of allyl maleate oxirane into a reactor equipped with a condenser reflux tube, heat to 60° C., react for 60 h, remove methanol by rotary evaporation, wash with petroleum ether, and dry to obtain an intermediate; 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 reacted at 80° C. for 48 h under stirring conditions. 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 having the following structural formula: .

[0018] 17.5g of styrene, 20.1g of diallyl maleate, 22.8g of allyl maleate quaternary ammonium salt monomer and 15.6g of acrylic acid were placed in a reactor, 90ml of cyclohexane solvent was added to dissolve the above four monomers, the temperature was raised to 90°C under nitrogen protection, 3.8g of dicumyl peroxide was dissolved in 10ml of cyclohexane and then fully mixed with 1.52g of α-methylstyrene linear dimer, and then dripped into the reactor to react at 75°C for 6h, and the reaction was continued for 2h after the dripping was completed to obtain a block copolymer solution; 241 g of graft modifier C and 4 g of triethylamine were added to the block copolymer solution for grafting 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.

[0019] Comparative Example 1 17.5 g of styrene, 20.1 g of diallyl maleate and 15.6 g of acrylic acid were placed in a reactor, solvent cyclohexane was added to dissolve the above monomers, the temperature was raised to 70°C under nitrogen protection, 1.8 g of dicumyl peroxide was dissolved in cyclohexane and then fully mixed with 1.06 g of α-methylstyrene linear dimer, and then dripped into the reactor to react at 70°C for 2 hours. After the dripping was completed, the reaction was continued for 1 hour to obtain a block copolymer solution; 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.

[0020] Comparative Example 2 The allyl maleate quaternary ammonium salt monomer obtained in Example 2 was used to prepare a block copolymer solution, 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.

[0021] Comparative Example 3 Add 15 ml of methanol, 4.2 mmol of N-methylnonylamine, and 1.6 mmol of allyl maleate oxirane into a reactor equipped with a condenser reflux tube, heat to 60° C., react for 60 h, remove methanol by rotary evaporation, wash with petroleum ether, and dry to obtain an intermediate; 15 ml of isopropanol, 2.0 mmol of the intermediate, and 4.2 mmol of bromobutyl were added to a reaction vessel equipped with a condenser reflux tube, and the mixture was reacted at 80° C. for 48 h under stirring conditions. 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 having the following structural formula: .

[0022] 19.5g of styrene, 24.9g of diallyl maleate, 25.8g of allyl maleate quaternary ammonium salt monomer and 15.6g of acrylic acid are placed in a reactor, solvent cyclohexane is added to dissolve the above four monomers, the temperature is raised to 90°C under nitrogen protection, 4.3g of dicumyl peroxide is dissolved in cyclohexane and then fully mixed with 2.6g of α-methylstyrene linear dimer, and then dripped into the reactor to react at 75°C for 6h, and after the dripping is completed, the reaction is continued for 2h to obtain a block copolymer solution; 275 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 graft modified block copolymer dispersant.

[0023] The definition of tinting strength in the national standard GB / T 13451.2-1992 - Relative tinting strength of coloring pigments (photometer method) is: it refers to the ability of the pigment to absorb incident light, and thus has the ability to, for example, tint or darken the white paint to which the pigment is added; tinting strength is expressed as a percentage, and the standard sample is generally taken as 100% in the measurement. If the sample is lower than 100, it means that the tinting strength of the sample is lower than that of the standard sample, otherwise, it is higher than the standard sample.

[0024] The graft modified block copolymer dispersant synthesized in Examples 1-3 and Comparative Examples 1-3 was used to prepare water-based color paste, and the preparation process was as follows: The raw material composition ratio of the water-based color paste includes, by weight percentage: 15% pigment, 8% dispersant, 15% water-based acrylic resin, 7% glycerol, and the balance is water. The above substances except water are first mixed and ground into a mixture with a fineness of less than 15 μm, and the above mixture and water are dispersed together for 60 minutes using an oscillator to obtain a water-based color paste; wherein the brand of the water-based acrylic resin is BASF, model 678, and the pigment is pigment yellow 83; The composition ratio of the white slurry is as follows: 25% titanium dioxide, 8% dispersant, 15% water-based acrylic resin, 7% propylene glycol, and the balance is water. The preparation process is the same as that of the above-mentioned water-based color paste. The brand of the water-based acrylic resin is BASF, and the model is 678. 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 tests, color intensity tests, and stability tests.

[0025] According to the method for determining relative tinting strength by visual inspection as recorded 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 paste of the sample and diluted color paste of the standard sample; when there is a color difference between the water-based color paste of the sample and the water-based color paste of the standard sample, adjustments are made. If the color of the sample is darker or thicker than that of the standard sample, the amount of white paste is increased; if the color of the sample is lighter than that of the standard sample, the amount of white paste is reduced until the colors of the two are consistent; The tinting strength of the diluted color paste of the sample is calculated according to the following formula: TS= ×100% Where: TS = tinting strength percentage of diluted color paste of the sample; b = amount of standard color paste, in grams (g); a = the mass of the test color paste that achieves the same tinting strength as the standard diluted color paste, in grams (g).

[0026] 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; The color intensity of the water-based color paste prepared with the dispersants of Examples 1-3 was measured using an X-Rite colorimeter, and the water-based color paste prepared with the dispersants of Comparative Examples 1-3 was used as the standard; wherein L represents the brightness of the color. When comparing color differences, A positive value indicates that the sample is lighter than the standard color, while 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; The stability test is specifically to place the water-based color pastes of Examples 1-3 and Comparative Examples 1-3 under closed conditions at 25°C for 30 days and 90 days respectively, and visually observe whether there is obvious precipitation of pigment particles, flocculation, and other conditions that seriously affect the stability, so as to judge the storage stability of the dispersant for the water-based color paste, where "√" indicates that there is no abnormality in visual observation, and "×" indicates that there is obvious precipitation of pigment particles, flocculation, etc. in visual observation. The results are shown in Table 1 below: Table 1 Performance test results of water-based color pastes of examples and comparative examples

[0027] As can be seen from the above table, in the aqueous color paste of Examples 1-3, the block copolymer dispersant of styrene-diallyl maleate-allyl maleate quaternary ammonium salt monomer-acrylic acid grafting modification of the present invention is used, and polymerization is performed in a limited ratio, and has good tinting power and stability. This is because the block copolymer with different segments of 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, wherein the hydrophobic segment is polymerized from styrene and diallyl maleate monomers, and the hydrophilic segment is acrylic acid, and 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, and the allyl maleate quaternary ammonium salt monomer has a hydrophobic tail and a positively charged head composed of an alkyl chain, which helps the polymer to be combined with the pigment particles in the aqueous medium. Stability; and the dispersant in Comparative Example 1, without the addition of the allyl maleate quaternary ammonium salt monomer, makes the synthesized polymer molecular structure lack stability; The dispersant in Comparative Example 2, which is synthesized by using a conventional grafting modifier, leads to a decrease in the tinting power and storage stability of the water-based color paste, while the modifier used in Examples 1-3 is a branched fatty alcohol polyoxyethylene ether modifier grafted onto the block copolymer. Based on the alkyl and polyoxyethylene chains in the modifier's own structure, it has both hydrophilic and hydrophobic properties, and has both wetting and dispersing properties, which can further improve the dispersing effect and storage stability of the dispersant; In Comparative Example 3, the N-methylamine used in the dispersant for synthesizing the allyl maleate quaternary ammonium salt monomer is N-methylnonylamine, which exceeds the specified chain length, resulting in the instability of the synthesized dispersant structure, which affects the stability of the water-based color paste.

[0028] 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 a person skilled in the art can make several improvements and modifications without departing from the technical principles of the present invention, and these improvements and modifications should also be regarded as within 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 consisting of an initiator, a chain transfer agent and a solvent is dripped into the mixed solution, and the mixture is reacted under nitrogen protection. After the dripping 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 of 3-5; S2: The block copolymer solution obtained in step S1, the graft modifier and the catalyst are subjected to a grafting reaction to obtain a water-based pigment dispersant for painting.

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 grafting 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.

7. 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.

8. The method for preparing a water-based pigment dispersant for painting according to claim 1, characterized in that: The method for preparing 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 isopropanol, the intermediate obtained in step (1) and the bromoalkyl compound into a reaction vessel equipped with a condenser reflux tube, mixing and reacting with stirring, removing the isopropanol, 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.

9. The method for preparing a water-based pigment dispersant for painting according to claim 8, 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; In step (2), the molar ratio of the intermediate to the bromoalkane compound is 1:2.6-2.8, the stirring reaction temperature is 70-90° C., and the stirring reaction time is 36-48 hours.

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

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