An N-heterocyclic compound grafted lignin sulfonate, its preparation method and application

Abstract

This invention discloses an N-heterocyclic compound-grafted lignin sulfonate, its preparation method, and its applications. The formulation, by mass parts, is as follows: 10-50 parts lignin, 2-8 parts alkali, 10-20 parts epoxy-based olefin monomer, 10-30 parts vinyl-containing N-heterocyclic compound monomer, 0.5-1.5 parts initiator, and 70-250 parts deionized water. The method first prepares a precursor containing an N-heterocyclic compound, then, in an alkaline medium, utilizes the nucleophilic substitution reaction between the epoxy groups of the precursor and the hydroxyl groups in the lignin molecule to graft the precursor onto the lignin molecule, thus obtaining the N-heterocyclic compound-grafted lignin sulfonate. The N-heterocyclic compound-grafted lignin sulfonate prepared by this invention contains 0.5-2.0 mmol / g of N-heterocyclic compound and can be used as a highly efficient dispersant in the field of inorganic nano-pigment pastes.

Description

Technical Field

[0001] This invention belongs to the field of natural polymer materials, and specifically relates to an N-heterocyclic compound grafted lignin sulfonate, its preparation method and application. Background Technology

[0002] Inorganic pigments are colored inorganic compound particles with poor compatibility with resins. They are dispersed in various media in particulate form during use. Pigment particles achieve coloring and decorative effects by adsorbing onto the surface of a material or dispersing within it, aided by the binder. Due to their properties such as hiding power, tinting strength, heat resistance, and light stability, pigments are a major component in the manufacture of coatings, inks, and other products requiring color, playing a crucial role in product performance.

[0003] Inorganic pigments typically have very small particle diameters, generally below 100 μm. However, with the development of science and technology and market demand, pigment powders are becoming increasingly finer, sometimes even below 1 μm. This results in high surface energy of the pigment particles, making them prone to agglomeration. Consequently, dispersibility, tinting strength, and hiding power are affected, directly impacting the performance of the pigments. Adding pigment dispersants adsorbs onto the surface of pigment particles and uses electrostatic repulsion and steric hindrance to disperse and stabilize the pigment particles, preventing problems such as increased particle size, decreased tinting strength, and reduced stability caused by agglomeration.

[0004] Traditional pigment dispersants are divided into inorganic dispersants and organic small-molecule dispersants, which mainly achieve effective dispersion and stabilization through electrostatic repulsion stabilization mechanisms. However, they have low adsorption strength on the pigment particle surface and are prone to detachment, leading to re-flocculation or agglomeration of pigment particles. In recent years, polymeric dispersants, also known as hyperdispersants, have emerged. By providing high steric hindrance, they enable effective dispersion and stability between pigment particles, and the system exhibits low sensitivity to temperature, pH, and other factors, making them ideal dispersants. Currently, commercially available polymeric dispersants include the Solsperse series from ICI (UK), the Disperse-AYD series from Daniel Chemicals (USA), the Disperse BYK series from BYK (Germany), the Hyersol series from KVK (Denmark), and NBZ-3 from my country. Although they exhibit good dispersion effects, their raw materials are all derived from non-renewable fossil-based raw materials, which does not align with current green and sustainable development strategies. Therefore, the preparation of efficient and green hyperdispersants using renewable biomass resources as raw materials has become a research hotspot in the pigment industry.

[0005] Lignin is the most abundant renewable aromatic polymer on Earth, second only to cellulose in reserves. Compared to other biomass molecules, lignin molecules contain numerous carboxyl groups, hydroxyl groups, and benzene rings, which can act as anchoring groups, forming tight adsorption on pigment surfaces through van der Waals forces, hydrogen bonds, and π-π bonds. Secondly, the unique three-dimensional network structure of lignin molecules provides a stronger steric hindrance effect, effectively preventing secondary pigment aggregation. Furthermore, the polyphenolic structure and aromatic skeleton in lignin molecules endow pigments with excellent UV oxidation resistance. Therefore, the preparation of efficient, green biomass-based superdispersants using industrial lignin as raw material has broad market prospects.

[0006] This invention develops a novel functional lignin dispersant and its synthesis process. A precursor is obtained by copolymerizing an epoxy-based olefin monomer and a vinyl-containing N-heterocyclic compound monomer. The precursor is then reacted with a lignin solution under high-temperature alkaline conditions to yield an N-heterocyclic compound-grafted lignin sulfonate. This dispersant is then applied to the preparation of water-based inorganic pigment nano-pastes, improving the D... 90 The particle size was reduced to below 350 nm, and after 7 days of heat storage at 60℃, the pigment paste showed no obvious stratification or precipitation. 90 The particle size increase is less than 15%, exhibiting good thermal storage stability. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings and deficiencies of the prior art and provide an N-heterocyclic compound grafted lignin sulfonate, which has a good grinding aid effect and dispersion stability on inorganic pigment particles, and enables the prepared water-based ceramic ink to be applied to the inkjet printing and ceramic surface decoration industries.

[0008] This invention improves the hydrophilicity and adsorption properties of lignin for inorganic pigment particles by modifying lignin, making it a highly efficient dispersant for preparing inorganic nano-pigment pastes. Specifically, a precursor is first obtained by copolymerizing an epoxy-based olefin monomer and an N-heterocyclic compound monomer containing vinyl groups. Then, the precursor undergoes a nucleophilic substitution reaction with the hydroxyl groups in the lignin molecule under alkaline conditions to obtain an N-heterocyclic compound grafted lignin sulfonate.

[0009] Another object of the present invention is to provide a method for preparing the above-mentioned N-heterocyclic compound grafted lignin sulfonate.

[0010] Another object of the present invention is to provide the application of the above-mentioned N-heterocyclic compound grafted lignin sulfonate.

[0011] The objective of this invention is achieved through the following technical solution:

[0012] A method for preparing an N-heterocyclic compound grafted lignin sulfonate includes the following steps:

[0013] (1) By mass, 10-20 parts of epoxy olefin monomer, 10-30 parts of N-heterocyclic compound monomer containing vinyl and 40-100 parts of water are stirred and dissolved to obtain a solution. 0.5-1.5 parts of initiator are added dropwise to the solution to prepare the precursor by reaction.

[0014] (2) Mix 10-50 parts of lignin and 30-150 parts of water by mass, heat and add 2-8 parts of alkali, stir and dissolve evenly to obtain a lignin aqueous solution, then add the precursor solution prepared in step (1), stir and mix evenly, and after reaction, obtain N-heterocyclic compound grafted lignin sulfonate.

[0015] The epoxy olefin monomer mentioned in step (1) is at least one of glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, and 1,2-epoxy-5-ethylene.

[0016] The N-heterocyclic compound monomer in step (1) is at least one of N-vinylimidazolium, N-vinylcaprolactam, N-vinylcarbazole, N-vinyldiphenylimine, 2-vinylpyridine, 2-vinylpyrazine, 4-vinylpyrimidine, 2-vinylquinoline, and 5-vinylthiazole.

[0017] The initiator mentioned in step (1) is at least one of ammonium persulfate, potassium persulfate, azobisisobutyronitrile, azobisisoheptanenitrile, and dimethyl azobisisobutyrate.

[0018] The dripping in step (1) is completed within 20 to 40 minutes; preferably 40 minutes.

[0019] The addition in step (1) is performed under a protective atmosphere; preferably, it is performed under a nitrogen atmosphere.

[0020] The reaction conditions described in step (1) are 60-80℃ for 1-3 hours.

[0021] The lignin mentioned in step (2) is at least one of sodium lignin sulfonate, potassium lignin sulfonate, ammonium lignin sulfonate, calcium lignin sulfonate, and sulfomethylated lignin.

[0022] The heating conditions described in step (2) are to heat to 70-90°C.

[0023] The reaction conditions described in step (2) are 70-95°C for 1-4 hours.

[0024] The alkali mentioned in step (2) is at least one of sodium hydroxide and potassium hydroxide.

[0025] An N-heterocyclic compound grafted lignin sulfonate was prepared by the above-described preparation method.

[0026] The content of the N-heterocyclic compound in the grafted lignin sulfonate is 0.5–2.0 mmol / g.

[0027] Application of the above-mentioned N-heterocyclic compounds grafted with lignin sulfonates in the preparation of dispersants.

[0028] The application of the above-mentioned N-heterocyclic compound grafted lignin sulfonate as a dispersant in the preparation of inorganic nano-pigment pastes.

[0029] The present invention has the following advantages and effects compared with the prior art:

[0030] 1. This invention synthesizes a functional lignin dispersant by introducing N-heterocyclic compounds with complexing adsorption functions into lignin molecules, which greatly improves the adsorption strength on the surface of inorganic pigments. This enables the production of water-based inorganic nano-pigment pastes from inorganic pigments using a grinding process in an aqueous medium.

[0031] 2. The N-heterocyclic compound grafted with lignin sulfonate of the present invention, as an adsorption group, can undergo high-strength complexation adsorption with the surface of inorganic pigment particles. This anchors the dispersant molecules to the pigment particle surface, preventing desorption during high-frequency Brownian motion collisions. The anionic sulfonic acid groups of the dispersant introduce a negative charge onto the pigment particle surface, thus preventing particle aggregation and sedimentation during collisions. Furthermore, the three-dimensional structure of lignin provides significant steric hindrance, further preventing pigment particle aggregation.

[0032] 3. The N-heterocyclic compound grafted lignin sulfonate of the present invention can be used as a dispersant to prepare inorganic nano-pigment pastes in an aqueous medium via a grinding process. The prepared inorganic nano-pigment pastes exhibit good grinding efficiency and thermal storage stability. 90 Particle size less than 350nm, and after 7 days of heat storage at 60℃, D 90 The particle size increase is less than 15%, there is no water separation or sedimentation, and the overall performance meets the requirements of inorganic nano pigment paste.

[0033] 4. The present invention uses lignin as the main raw material, and the dispersant prepared is environmentally friendly. Attached Figure Description

[0034] Figure 1 The infrared spectrum of vinylimidazolium-grafted lignin sulfonate D1 obtained in Example 1 is shown.

[0035] Figure 2 Potential diagrams of aqueous solutions at different pH values ​​with and without the dispersant obtained in Example 1.

[0036] Figure 3Scanning electron microscope (SEM) images of cadmium red pigment after grinding without dispersant and after grinding with dispersants obtained in Examples 1-3; where (a) is the control group without dispersant, (b) is the experimental group with D1 added, (c) is the experimental group with D2 added, and (d) is the experimental group with D3 added. Detailed Implementation

[0037] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0038] Unless otherwise specified in the following implementation plan, the test conditions are generally as per standard test conditions or the test conditions recommended by the reagent company. Unless otherwise specified, all materials and reagents used are commercially available.

[0039] Example 1

[0040] (1) Add 16.0 g of allyl glycidyl ether, 30.0 g of N-vinylimidazole and 100.0 g of deionized water to a four-necked flask and stir until homogeneous to obtain a mixture. Under nitrogen protection, add 0.7 g of initiator azobisisobutyronitrile dropwise to the solution over 40 min. After the initiator is added, react at a constant temperature of 80 °C for 1 hour to obtain the precursor.

[0041] (2) Add 30.0g of sodium lignin sulfonate and 100.0g of deionized water to a four-necked flask, then heat to 90℃, add 4.0g of sodium hydroxide, stir and dissolve evenly to obtain a lignin aqueous solution. Then add the precursor obtained in step (1), stir and mix evenly, and react at 95℃ for 4 hours to obtain vinylimidazolium-grafted lignin sulfonate.

[0042] The vinylimidazolium grafted lignin sulfonate obtained in Example 1 is named D1, and the content of vinylimidazolium groups in D1 is 1.92 mmol / g.

[0043] Example 2

[0044] (1) Add 12.0 g allyl glycidyl ether, 11.0 g N-vinylcaprolactam and 40.0 g deionized water to a four-necked flask and stir until homogeneous to obtain a mixture. Under nitrogen protection, add 0.5 g of ammonium persulfate as an initiator dropwise to the solution, completing the addition in 20 min. After the initiator addition is complete, react at a constant temperature of 60 °C for 1 hour to obtain the precursor.

[0045] (2) Add 25.0g of potassium lignin sulfonate and 30.0g of deionized water to a four-necked flask, then heat to 70℃, add 3.5g of sodium hydroxide, stir and dissolve evenly to obtain a lignin aqueous solution. Then add the precursor obtained in step (1), stir and mix evenly, and react at 70℃ for 1.5 hours to obtain vinylcaprolactam grafted lignin sulfonate.

[0046] The vinylcaprolactam-grafted lignin sulfonate obtained in Example 2 is named D2, and the content of vinylcaprolactam groups in D2 is 0.57 mmol / g.

[0047] Example 3

[0048] (1) Add 15.0 g glycidyl methacrylate, 20.0 g 2-vinylpyridine and 70.0 g deionized water to a four-necked flask and stir until homogeneous to obtain a mixture. Under nitrogen protection, add 1.0 g of potassium persulfate as an initiator dropwise to the solution, completing the addition in 30 min. After the initiator is added, react at a constant temperature of 70 °C for 1.2 h to obtain the precursor.

[0049] (2) Add 35.0g of sodium lignin sulfonate and 95.0g of deionized water to a four-necked flask, then heat to 70℃, add 4.5g of sodium hydroxide, stir and dissolve evenly to obtain a lignin aqueous solution. Then add the precursor obtained in step (1), stir and mix evenly, and react at 80℃ for 3 hours to obtain vinylpyridine grafted lignin sulfonate.

[0050] The vinylpyridine-grafted lignin sulfonate obtained in Example 3 is named D3, and the content of vinylpyridine groups in D3 is 1.57 mmol / g.

[0051] Example 4

[0052] (1) Add 15.0 g of 1,2-epoxy-5-ethylene, 20.0 g of N-vinyldiphenylimine and 70.0 g of deionized water to a four-necked flask and stir until homogeneous to obtain a mixture. Under nitrogen protection, add 1.0 g of initiator azobisisoheptanenitrile dropwise to the solution over 30 min. After the initiator is added, react at a constant temperature of 70 °C for 2 hours to obtain the precursor.

[0053] (2) Add 37.0g of ammonium lignin sulfonate and 75.0g of deionized water to a four-necked flask, then heat to 70℃, add 6.5g of sodium hydroxide, stir and dissolve evenly to obtain a lignin aqueous solution. Then add 25.0g of the precursor obtained in step (1), stir and mix evenly, and react at 80℃ for 3 hours to obtain vinyl diphenyl grafted lignin sulfonate.

[0054] In Example 4, the content of vinyl diphenylimine groups in vinyl diphenyl grafted lignin sulfonate was 0.84 mmol / g.

[0055] Example 5

[0056] (1) By mass fraction, 10.0 g glycidyl methacrylate, 10.0 g N-vinylcarbazole and 40.0 g deionized water were added to a four-necked flask and stirred until dissolved. Under nitrogen protection, 1.5 g of initiator dimethyl azobisisobutyrate was added dropwise to the solution. The addition was completed in 40 min. The temperature was raised to 80 °C and the reaction was carried out for 1 hour to obtain the precursor.

[0057] (2) By mass, 40.0 g of calcium lignin sulfonate and 100.0 g of deionized water were added to a four-necked flask, heated to 70 °C, and 7.0 g of potassium hydroxide was added. The mixture was stirred until dissolved and homogeneous to obtain an aqueous lignin solution. The precursor solution prepared in step (1) was then added, stirred until homogeneous, and reacted at 95 °C for 4 hours. After cooling to room temperature, the product was purified to obtain vinylcarbazole grafted lignin sulfonate.

[0058] In Example 5, the content of vinylcarbazole groups in vinylcarbazole grafted lignin sulfonate is 0.50 mmol / g.

[0059] Example 6

[0060] (1) By mass fraction, 16.0 g glycidyl acrylate, 20.0 g 2-vinylpyrazine and 100.0 g deionized water were added to a four-necked flask and stirred until dissolved. Under nitrogen protection, 1.5 g of initiator ammonium persulfate was added dropwise to the solution. The addition was completed in 40 min. The temperature was raised to 80 °C and the reaction was carried out for 2 hours to obtain the precursor.

[0061] (2) By mass, 30.0 g of sulfonated lignin and 90.0 g of deionized water were added to a four-necked flask, heated to 70 °C, and 4.4 g of sodium hydroxide were added. The mixture was stirred until dissolved and homogeneous to obtain an aqueous lignin solution. The precursor solution prepared in step (1) was then added, stirred until homogeneous, and reacted at 80 °C for 2 hours. After cooling to room temperature, the product was purified to obtain vinylpyrazine grafted lignin sulfonate.

[0062] In Example 6, the content of vinylpyrazine groups in vinylpyrazine grafted lignin sulfonate is 1.25 mmol / g.

[0063] Example 7

[0064] (1) By mass fraction, 15.0 g of 1,2-epoxy-5-ethylene, 30.0 g of 4-vinylpyrimidine and 80.0 g of deionized water were added to a four-necked flask and stirred until dissolved. Under nitrogen protection, 1.0 g of initiator azobisisobutyronitrile was added dropwise to the solution. The addition was completed in 30 min. The temperature was raised to 70 °C and the reaction was carried out for 2 hours to obtain the precursor.

[0065] (2) By mass, 50.0 g of sodium lignin sulfonate and 30.0 g of deionized water were added to a four-necked flask, heated to 70 °C, and 8.0 g of sodium hydroxide were added. The mixture was stirred until dissolved and homogeneous to obtain an aqueous lignin solution. The precursor solution prepared in step (1) was then added, stirred until homogeneous, and reacted at 95 °C for 3 hours. After cooling to room temperature, the product was purified to obtain vinylpyrimidine-grafted lignin sulfonate.

[0066] In Example 7, the content of vinylpyrimidine groups in vinylpyrimidine grafted lignin sulfonate was 1.06 mmol / g.

[0067] Example 8

[0068] (1) By mass, 20.0 g of allyl glycidyl ether, 25.0 g of 2-vinylquinoline and 100.0 g of deionized water were added to a four-necked flask and stirred until dissolved. Under nitrogen protection, 1.5 g of potassium persulfate initiator was added dropwise to the solution. The addition was completed in 40 min. The temperature was raised to 70 °C and the reaction was carried out for 3 hours to obtain the precursor.

[0069] (2) By mass, 36.0 g of potassium lignin sulfonate and 30.0 g of deionized water were added to a four-necked flask, heated to 80 °C, and 4.8 g of potassium hydroxide were added. The mixture was stirred until dissolved and homogeneous to obtain an aqueous lignin solution. The precursor solution prepared in step (1) was then added, stirred until homogeneous, and reacted at 85 °C for 4 hours. After cooling to room temperature, the product was purified to obtain vinylquinoline grafted lignin sulfonate.

[0070] In Example 8, the content of vinylquinoline groups in vinylquinoline grafted lignin sulfonate was 1.88 mmol / g.

[0071] Example 9

[0072] (1) By mass fraction, 15.0 g of allyl glycidyl ether, 20.0 g of 5-vinylthiazole and 80.0 g of deionized water were added to a four-necked flask and stirred until dissolved. Under nitrogen protection, 1.0 g of initiator azobisisoheptanenitrile was added dropwise to the solution. The addition was completed in 30 min. The temperature was raised to 70 °C and the reaction was carried out for 2 hours to obtain the precursor.

[0073] (2) By mass, 10.0 g of potassium lignin sulfonate and 90.0 g of deionized water were added to a four-necked flask, heated to 70 °C, and 2.0 g of potassium hydroxide was added. The mixture was stirred until dissolved and homogeneous to obtain an aqueous lignin solution. The precursor solution prepared in step (1) was then added, stirred until homogeneous, and reacted at 95 °C for 2 hours. After cooling to room temperature, the product was purified to obtain vinylthiazole grafted lignin sulfonate.

[0074] In Example 9, the content of vinylthiazole groups in vinylthiazole grafted lignin sulfonate is 1.37 mmol / g.

[0075] Example 10

[0076] (1) By mass, 20.0g of epoxy olefin monomer, 30.0g of N-vinylcaprolactam and 100.0g of deionized water were added to a four-necked flask and stirred until dissolved. Under nitrogen protection, 1.3g of initiator dimethyl azobisisobutyrate was added dropwise to the solution. The addition was completed in 40min. The temperature was raised to 80℃ and the reaction was carried out for 1 hour to obtain the precursor.

[0077] (2) By mass, 26.0 g of ammonium lignin sulfonate and 50.0 g of deionized water were added to a four-necked flask, heated to 90 °C, and 5.2 g of potassium hydroxide were added. The mixture was stirred until dissolved and homogeneous to obtain an aqueous lignin solution. The precursor solution prepared in step (1) was then added, stirred until homogeneous, and reacted at 90 °C for 2 hours. After cooling to room temperature, the product was purified to obtain vinylcaprolactam-grafted lignin sulfonate.

[0078] In Example 10, the content of vinylcaprolactam groups in vinylcaprolactam-grafted lignin sulfonate was 1.42 mmol / g.

[0079] Example 11

[0080] (1) By mass fraction, 14.0 g glycidyl acrylate, 28.0 g N-vinylimidazole and 70.0 g deionized water were added to a four-necked flask and stirred until dissolved. Under nitrogen protection, 0.8 g potassium persulfate initiator was added dropwise to the solution. The addition was completed in 20 min. The temperature was raised to 60 °C and the reaction was carried out for 1.4 hours to obtain the precursor.

[0081] (2) By mass, 22.0 g of sodium lignin sulfonate and 60.0 g of deionized water were added to a four-necked flask, heated to 70 °C, and 3.5 g of sodium hydroxide were added. The mixture was stirred until dissolved and homogeneous to obtain an aqueous lignin solution. The precursor solution prepared in step (1) was then added, stirred until homogeneous, and reacted at 85 °C for 3 hours. After cooling to room temperature, the product was purified to obtain vinylimidazolium-grafted lignin sulfonate.

[0082] In Example 11, the content of vinylimidazolium groups in vinylimidazolium-grafted lignin sulfonate is 2.00 mmol / g.

[0083] Example 12

[0084] (1) By mass fraction, 20.0 g of 1,2-epoxy-5-ethylene, 20.0 g of 4-vinylpyrimidine and 80.0 g of deionized water were added to a four-necked flask and stirred until dissolved. Under nitrogen protection, 1.0 g of initiator azobisisobutyronitrile was added dropwise to the solution. The addition was completed in 30 min. The temperature was raised to 70 °C and the reaction was carried out for 2 hours to obtain the precursor.

[0085] (2) By mass, 50.0 g of potassium lignin sulfonate and 150.0 g of deionized water were added to a four-necked flask, heated to 90 °C, and 6.0 g of potassium hydroxide was added. The mixture was stirred until dissolved and homogeneous to obtain an aqueous lignin solution. The precursor solution prepared in step (1) was then added, stirred until homogeneous, and reacted at 95 °C for 1 hour. After cooling to room temperature, the product was purified to obtain vinylpyrimidine grafted lignin sulfonate.

[0086] In Example 12, the content of vinylpyrimidine groups in vinylpyrimidine grafted lignin sulfonate is 0.95 mmol / g.

[0087] Infrared spectroscopy analysis was performed on the purified product D1 obtained from the reaction in Example 1, with sodium lignosulfonate (SL) as a control. The results are as follows: Figure 1 As shown. From Figure 1 It can be seen from this that 2940cm -1 This is the stretching vibration peak of CH on the imidazole ring; 1640 cm⁻¹ -1 The absorption peak at 1350 cm⁻¹ represents the imidazole ring skeleton. -1 The peak at 1120 cm⁻¹ represents the absorption peak of the C=N stretching vibration on the imidazole ring. -1 The characteristic absorption peaks of nitrogen-containing five-membered rings are 752 and 690 cm⁻¹. -1 Attributable to the out-of-plane deformation vibration of the imidazole ring, proving that the vinylimidazolium group was successfully grafted into the lignin molecule. Additionally, 1040 cm⁻¹ -1 The peak at this location is a characteristic absorption peak for sulfonic acid groups, indicating that the product contains a relatively large number of sulfonic acid groups.

[0088] Elemental analysis was performed on SL, D1, D2, and D3. The content of N-heterocyclic groups in D1, D2, and D3 was calculated based on the different nitrogen (N) content. The results are shown in Table 1.

[0089] Table 1

[0090]

[0091] As shown in Table 1, the N content in SL is 0.10%. Calculations show that the contents of N-heterocyclic compound groups in D1, D2, and D3 are 1.92, 0.57, and 1.57 mmol / g, respectively.

[0092] Four commonly used inorganic pigments—cobalt blue (original particle size 4.0 μm), cadmium red (original particle size 1.8 μm), cobalt green (original particle size 0.8 μm), and titanium dioxide (original particle size 5.5 μm)—were selected as research subjects. Using D1, D2, and D3 as dispersants, an inorganic nano-pigment paste with a solid content of 20 wt.% was prepared by water-based milling. The amount of dispersant added was 10 wt.% of the pigment paste. Zirconia beads with a diameter of 0.3 mm were used as the grinding medium, with a zirconium bead to pigment paste mass ratio of 3:1. The nano-pigment paste was ground using a planetary ball mill (Changsha Miqi Instrument Equipment Co., Ltd., YXQM-2L) at a speed of 400 rpm for 10 h. Zirconia beads with a diameter of 0.3 mm were used as the grinding material, with a zirconium bead to pigment paste mass ratio of 3:1. The particle size and thermal storage stability of the prepared water-based nano-pigment paste are shown in Table 2.

[0093] Table 2 shows the D content of four types of water-based nano-pigment pastes prepared by grinding using D1, D2, D3, and SL as dispersants. 90 Particle size, and D after 7 days of heat storage at 60°C 90 Particle size.

[0094] Table 2

[0095]

[0096] (D 90 (The particle size corresponding to a cumulative particle size distribution number of 90% for a sample)

[0097] Table 2 shows that using D1, D2, D3, and SL as dispersants for grinding cobalt blue, cadmium red, cobalt green, and titanium dioxide nano-pastes, among which, using D1, D2, and D3 as dispersants for 10 hours of grinding can significantly improve the D... 90 With particle size reduced to below 200nm, the D of cobalt green and titanium dioxide 90 When the particle size is reduced to below 350 nm, D1 exhibits the highest grinding efficiency, followed by D3 and D2, which is positively correlated with the content of N-heterocyclic groups in its molecule. SL has the worst grinding efficiency, with a larger particle size of the pigment and poor thermal stability.

[0098] After the water-based nano-color paste prepared by grinding was stored at 60℃ for 7 days, the D of the color paste was... 90 The particle size increased, but the D nano-pigment prepared using D1 showed an increase in D... 90 The increase in particle size was generally within 10%, and the nano-pigment pastes prepared using D2 and D3 had a D...90 The increase in particle size is generally within 15%, and the D of the nano-pigment prepared using SL is... 90 The particle size reached the micrometer level. This indicates that the introduction of N-heterocyclic groups improved the adsorption performance of the dispersant on the pigment surface, and enhanced grinding efficiency and heat resistance.

[0099] Using aqueous cadmium red nano-paste as the research object, cadmium red paste without dispersant and cadmium red paste prepared by grinding with D1, D2 and D3 as dispersants were diluted in an aqueous medium, and the zeta potential at different pH values ​​was tested. The results are as follows: Figure 2 As shown. By Figure 2 It is evident that, compared to the cadmium red paste without dispersants, the absolute value of the zeta potential on the surface of pigment particles increased under different pH conditions after the addition of dispersants D1, D2, and D3. The absolute value was the largest at pH 5–10 (40–65 mV), which is greater than the theoretical zeta potential (absolute value of zeta not less than 30 mV) required for particles to remain stable in aqueous solution. This indicates that the nano-pigment particles in the cadmium red nano-paste prepared with D1, D2, and D3 as dispersants can exist stably in aqueous medium.

[0100] Using aqueous cadmium red nanoparticles as the research object, the morphology and particle distribution of nanoparticles in cadmium red particles without dispersant and in cadmium red pastes prepared by grinding with D1, D2, and D3 as dispersants were compared by scanning electron microscopy. Figure 3 As shown. By Figure 3 The SEM images show that in the cadmium red paste prepared without dispersant, the particle size is relatively large, at the micrometer level, and the aggregation between particles is quite severe. In the cadmium red paste prepared with dispersant, the particle size is significantly smaller, at the nanometer level, and the particles are basically in a monodisperse state with less aggregation. Therefore, the addition of dispersant is beneficial to maintaining the dispersion stability of the paste.

[0101] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing an N-heterocyclic compound grafted lignin sulfonate, characterized in that... Includes the following steps: (1) By mass, 10-20 parts of epoxy olefin monomer, 10-30 parts of N-heterocyclic compound monomer containing vinyl and 40-100 parts of water are stirred and dissolved to obtain a solution. 0.5-1.5 parts of initiator are added dropwise to the solution to prepare the precursor by reaction. (2) Mix 10-50 parts of lignin and 30-150 parts of water by mass, heat and add 2-8 parts of alkali, stir and dissolve evenly to obtain lignin aqueous solution, then add the precursor solution prepared in step (1), stir and mix evenly, and after reaction, obtain N-heterocyclic compound grafted lignin sulfonate. The epoxy olefin monomer, the vinyl-containing N-heterocyclic compound monomer, and the initiator mentioned in step (1) are one of the following combinations: Combination I: Allyl glycidyl ether, vinylimidazole, and azobisisobutyronitrile; Combination II: Allyl glycidyl ether, N-vinylcaprolactam, and ammonium persulfate; Combination III: glycidyl methacrylate, 2-vinylpyridine, and potassium persulfate; The dripping in step (1) shall be completed within 20 to 40 minutes; The addition described in step (1) is performed under a protective atmosphere; The reaction conditions described in step (1) are 60-80℃ for 1-3 hours.

2. The preparation method according to claim 1, characterized in that: The lignin mentioned in step (2) is at least one of sodium lignin sulfonate, potassium lignin sulfonate, ammonium lignin sulfonate, calcium lignin sulfonate, and sulfomethylated lignin.

3. The preparation method according to claim 1, characterized in that: The heating condition described in step (2) is to heat to 70-90°C; The reaction conditions described in step (2) are 70–95°C for 1–4 hours; The alkali mentioned in step (2) is at least one of sodium hydroxide and potassium hydroxide.

4. An N-heterocyclic compound grafted lignin sulfonate prepared by any one of the preparation methods according to claims 1 to 3.

5. The use of the N-heterocyclic compound grafted lignin sulfonate according to claim 4 in the preparation of dispersants.

6. The application of the N-heterocyclic compound grafted lignin sulfonate according to claim 4 as a dispersant in the preparation of inorganic nano-pigment pastes.

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