Aqueous dispersant based on styrene maleic anhydride and preparation method thereof

Abstract

The invention discloses an aqueous dispersant based on styrene maleic anhydride and a preparation method thereof, and belongs to the technical field of auxiliary chemicals. In order to solve the problems of weak anchoring force, insufficient viscosity reduction and environmental sensitivity of a traditional SMA dispersing agent, an amphiphilic block (a hydrophilic polyethylene glycol chain segment and a hydrophobic aliphatic / aromatic chain segment) is grafted on an SMA main chain to form a comb-shaped copolymer structure, and the steric hindrance effect and the interface anchoring capacity are synergistically enhanced. According to the design, the wetting dispersity of organic / inorganic pigments and fillers is remarkably improved, the viscosity of a high-solid-content system is greatly reduced, and meanwhile, excellent stability is kept under the conditions of pH fluctuation and high shear. A one-step condensation process is adopted for preparation, a grafting reaction is completed in an anhydrous solvent, and the water-soluble dispersant is directly obtained through neutralization. The viscosity reduction bottleneck of a traditional dispersant is broken through, the production process is simplified, the dispersion efficiency and the system environment adaptability are improved, and the dispersant is suitable for high-solid-content water-based systems in the fields of coatings, printing ink and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of coating additives, and more particularly to an aqueous dispersant based on styrene maleic anhydride and a preparation method thereof. Background Art

[0002] Water-based dispersants are core additives in the fields of coatings, inks, etc. Among them, styrene-maleic anhydride (SMA) copolymer dispersants are widely used because of their readily available raw materials and good environmental protection. However, traditional SMA dispersants have significant defects: (1) Weak anchoring performance: The maleic anhydride unit has insufficient adsorption force on pigments / fillers, especially for non-polar organic pigments (such as carbon black) or high specific surface area fillers (such as talc), which are easily desorbed, resulting in poor dispersion stability. (2) Limited viscosity reduction effect: In high solid content systems, additional viscosity reducers need to be added, which increases costs and affects compatibility. (3) High environmental sensitivity: Under pH fluctuations or high shear processes, the dispersion system is prone to flocculation and sedimentation, limiting its application in slurries with a wide pH range.

[0003] To improve the above problems, the industry has tried various solutions: (1) introducing a single hydrophilic segment, which improves water solubility but further weakens the hydrophobic anchoring force, resulting in a viscosity reduction rate of less than 20%. (2) Increasing the molecular weight leads to a decrease in the dispersant migration rate, reduced wetting efficiency, and easy agglomeration under high shear. (3) Compounding with anionic surfactants, although it can reduce viscosity in the short term, deteriorates long-term storage stability and increases foaming.

[0004] Therefore, developing water-based dispersants with strong anchoring, efficient viscosity reduction and environmental stability remains a technical challenge that needs to be overcome. Summary of the Invention

[0005] The present invention aims to provide an aqueous dispersant based on styrene maleic anhydride and a preparation method thereof, so as to solve the technical problems of weak anchoring, insufficient viscosity reduction and environmental sensitivity of existing aqueous dispersants.

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

[0007] A styrene-maleic anhydride-based aqueous dispersant comprises a styrene-maleic anhydride copolymer main chain and an amphiphilic block grafted to the main chain; the amphiphilic block is composed of a hydrophilic polyethylene glycol segment and a hydrophobic aliphatic or aromatic segment.

[0008] Preferably, the hydrophobic aliphatic segment is selected from at least one of alkyl acrylates and alkyl phenol aldehyde amines; the hydrophobic aliphatic segment is selected from styrene derivatives.

[0009] Preferably, the alkyl acrylate is an alkyl acrylate having a carbon number of C6-C12, preferably isodecyl acrylate.

[0010] Preferably, the hydrophilic polyethylene glycol segment is polyethylene glycol monomethyl ether with a number average molecular weight of 300-2000.

[0011] Preferably, the pH value of the aqueous dispersant system is 6.5-8.5.

[0012] Another object of the present invention is to provide a method for preparing the aforementioned aqueous dispersant, comprising the following steps: reacting a styrene-maleic anhydride copolymer with an amphiphilic block modifier in an anhydrous solvent at 80-120°C for 2-4 hours; adding a neutralizing agent to adjust the pH to 6.5-8.5 to obtain an aqueous dispersant solution.

[0013] Preferably, the anhydrous solvent is N,N-dimethylformamide or N-methylpyrrolidone.

[0014] Preferably, the neutralizing agent is at least one of ammonia water and triethanolamine.

[0015] Preferably, the styrene-maleic anhydride copolymer and the amphiphilic block modifier are subjected to a condensation-catalyzed grafting reaction; wherein the condensation agent is N,N'-dicyclohexylcarbodiimide and the catalyst is 4-dimethylaminopyridine.

[0016] This application has the following beneficial effects:

[0017] (1) Synergistic viscosity reduction: The hydrophilic polyethylene glycol chain segments form a three-dimensional hydration barrier, which synergizes with the steric hindrance effect of the flexible hydrophobic chain to significantly reduce the interaction between particles, greatly reducing the viscosity of the high solid content dispersion system, and completely solving the bottleneck of insufficient viscosity reduction of traditional SMA dispersants.

[0018] (2) Anchoring reinforcement: The hydrophobic block forms multiple adsorption sites on the surface of the pigment / filler, improving the adaptability to interfaces with different polarities, achieving uniform and stable dispersion of organic pigments, inorganic pigments and fillers, and effectively inhibiting flocculation and sedimentation.

[0019] (3) Improved environmental stability: Based on the basic structure of styrene-maleic anhydride copolymer, an amphiphilic block grafting agent is introduced to form a comb-shaped copolymer structure, which gives the system excellent pH buffering capacity and shear stability, maintains dispersion performance under acid-base fluctuations and mechanical stress, and broadens industrial application scenarios. DETAILED DESCRIPTION

[0020] The present invention is further described below with reference to the embodiments, but the scope of protection claimed in the present invention is not limited to the scope described in the embodiments.

[0021] Examples 1-5

[0022] A method for preparing an aqueous dispersant based on styrene maleic anhydride comprises the following steps:

[0023] (1) Pretreatment: 100 parts of styrene-maleic anhydride copolymer (SMA) with an acid value of 180 mgKOH / g was added to a reactor, and 300 mL of anhydrous N,N-dimethylformamide (DMF) was added and stirred at 60°C until completely dissolved to form a uniform and transparent reaction system;

[0024] (2) Hydrophilic block grafting: 30 parts of hydrophilic monomer and 1 part of 4-dimethylaminopyridine (DMAP) were added to the solution, followed by 15 parts of N,N'-dicyclohexylcarbodiimide (DCC), and the temperature was raised to 90 °C for 3 hours;

[0025] (3) Hydrophobic block grafting: cool to 60°C, add 20 parts of hydrophobic monomer dropwise, heat to 100°C and react for 2 hours;

[0026] (4) Reaction termination and neutralization: After the reaction is completed, the mixture is cooled to below 40°C, the by-product dicyclohexylurea (DCU) is filtered out, and a neutralizing agent is slowly added dropwise to neutralize the free acid groups. The pH is controlled at 7.2±0.3, and the mixture is stirred for 30 minutes to form a light yellow transparent aqueous dispersant mother solution.

[0027] Table 1 Difference table

[0028]

[0029]

[0030] The difference between Examples 1-5 lies in the different selections of the hydrophilic monomer, the hydrophobic monomer, and the neutralizing agent.

[0031] Comparative Example 1: Unmodified SMA dispersant: styrene-maleic anhydride copolymer (acid value 180 mgKOH / g) was directly neutralized with ammonia water.

[0032] Comparative Example 2 is a commercially available dispersant.

[0033] Compared with Example 3, Comparative Example 3 does not have a hydrophobic block.

[0034] Compared with Example 3, Comparative Example 4 has no hydrophilic block.

[0035] In Comparative Example 5, compared with Example 3, mPEG1000 was replaced by mPEG300, and the molecular weight of the hydrophilic segment was insufficient.

[0036] In Comparative Example 6, compared with Example 3, propylene stearate (C18) was used instead of isodecyl acrylate, and the polarity of the hydrophobic segment did not match.

[0037] Compared with Example 3, Comparative Example 7 uses low acid value SMA (acid value 50 mgKOH / g) to graft the amphiphilic block.

[0038] Compared with Example 3, Comparative Example 8 uses high acid value SMA (acid value 300 mgKOH / g) to graft the amphiphilic block.

[0039] Compared with Example 3, Comparative Example 9 is a non-one-step grafting process in which hydrophobic grafting is performed first and then hydrophilic grafting is performed.

[0040] Compared with Example 3, Comparative Example 10 is a grafting reaction carried out under the condition that the solvent contains water.

[0041] Test items

[0042] The pigments used included carbon black, phthalocyanine blue, red iron oxide, kaolin, and talc. Color pastes were prepared by sand milling and tested for particle size, viscosity, and storage stability.

[0043] Dispersion Test: Dispersion properties were determined using a Malvern Mastersizer 3000 laser particle size analyzer. The following test conditions were used: pigment solids content was set at 50% carbon black and phthalocyanine blue, 55% red iron oxide / kaolin / talc, and 1.5% dispersant by weight of pigment. The particles were ground using 0.5 mm zirconium beads for 4 hours at 2000 rpm. The initial particle size (D50) and the rate of change in D50 after 30 minutes (ΔD50) were recorded. A ΔD50 ≤ 10% was considered stable.

[0044] Viscosity test: The rheological properties of the system were tested using a Brookfield DV2T viscometer (spindle S64) at 25°C. For high-solids systems (carbon black solids 65%, other pigments 60%), a speed gradient was set from 6 rpm to 60 rpm to 6 rpm to evaluate thixotropic recovery. The viscosity (mPa·s) at 60 rpm was recorded, and the viscosity reduction was calculated based on the dispersant-free system.

[0045] Thermal Storage Stability Test: Seal the color paste in a transparent container and store it in a 50°C thermostat for 7 days (equivalent to 6 months at room temperature). Observe for stratification, sedimentation, and flocculation. After returning to room temperature, re-measure the D50 change rate. A ΔD50 greater than 15% is considered failure.

[0046] pH stability test: The pH value of the color paste was adjusted to the range of 4.0–10.0 using 0.1M HCl / NaOH solution. The particle size change was measured after standing for 48 hours. A high shear simulation group (2000 rpm for 10 minutes) was also set up to record the D50 change rate after extreme pH conditions and mechanical stress. If ΔD50>15%, the system was judged to be unstable.

[0047] Table 2 Dispersibility and viscosity test

[0048]

[0049]

[0050] Note: In Comparative Example 8, the high acid value SMA (300 mgKOH / g) caused molecular chain entanglement, and the viscosity increased instead.

[0051] Table 3 Stability and pH adaptability test (pigment is carbon black)

[0052]

[0053] Combining Tables 2 and 3, it can be seen that the amphiphilic comb copolymer structure designed in the present invention (Examples 1-5) achieves the following performance breakthroughs compared to traditional dispersants:

[0054] (1) Anchoring-dispersion synergy: The static ΔD50 of carbon black in Example 3 is only 7.0% (Table 1), which is much lower than that of unmodified SMA (Comparative Example 1: 38.1%), proving that the hydrophobic block (isodecyl acrylate) and the hydrophilic chain (mPEG2000) synergistically enhance multiple adsorption.

[0055] (2) Highly efficient viscosity reduction: Example 3 has a viscosity of 820 mPa·s (Table 1) in a high solid carbon black system, with a viscosity reduction rate of 46.2%, while the viscosity of Comparative Example 3 (without hydrophobic block) reaches 1800 mPa·s, revealing that steric hindrance and hydration layer synergistically weaken the particle interaction force.

[0056] (3) Environmental stability: Example 3 has a ΔD50 of <7.8% at pH 4.0 / pH 10.0 (Table 2), and a ΔD50 of only 8.1% after high shear, which is significantly better than Comparative Example 10 in which the solvent contains water, confirming that the amphiphilic structure buffers pH fluctuations and shear stress.

[0057] (4) Structural sensitivity: The viscosity reduction rate of SMA with an acid value of 180 mgKOH / g (Example 3, carbon black) is >46%, while the viscosity of SMA with an acid value of 300 mgKOH / g (Comparative Example 8) increases by 15% due to chain entanglement, highlighting the need for precise control of the main chain acid value.

[0058] Conclusion: The aqueous dispersant of the present invention exhibits excellent wetting and dispersing ability in organic pigments such as carbon black and phthalocyanine blue and filler systems such as talc. The system viscosity is significantly lower than that of the comparative dispersant, and there is no obvious sedimentation or particle size growth at high temperature and a wide pH range, breaking through the technical pain points of traditional dispersants in anchoring force, viscosity reduction, and environmental adaptability.

[0059] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiment. All technical solutions based on the concept of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. An aqueous dispersant based on styrene maleic anhydride, characterized in that It comprises a styrene-maleic anhydride copolymer main chain and an amphiphilic block grafted on the main chain; the amphiphilic block is composed of a hydrophilic polyethylene glycol segment and a hydrophobic aliphatic or aromatic segment.

2. The aqueous dispersant according to claim 1, characterized in that The hydrophobic aliphatic chain segment is selected from at least one of alkyl acrylates and alkyl phenol aldehyde amines; the hydrophobic aliphatic chain segment is selected from styrene derivatives.

3. The aqueous dispersant according to claim 2, characterized in that The alkyl acrylate is an alkyl acrylate having a carbon number of C6-C12, and is preferably isodecyl acrylate.

4. The aqueous dispersant according to claim 3, characterized in that The hydrophilic polyethylene glycol segment is polyethylene glycol monomethyl ether with a number average molecular weight of 300-2000.

5. The aqueous dispersant according to claim 1, characterized in that The pH value of the aqueous dispersion system is 6.5–8.

5.

6. A method for preparing the aqueous dispersant according to any one of claims 1 to 5, characterized in that: The following steps are included: In an anhydrous solvent, a styrene-maleic anhydride copolymer is reacted with an amphiphilic block modifier at 80–120°C for 2–4 hours. A neutralizing agent is added to adjust the pH to 6.5–8.5 to obtain an aqueous dispersant solution.

7. The preparation method according to claim 6, characterized in that The anhydrous solvent is N,N-dimethylformamide or N-methylpyrrolidone.

8. The preparation method according to claim 6, characterized in that The neutralizing agent is at least one of ammonia water and triethanolamine.

9. The preparation method according to claim 6, characterized in that The styrene-maleic anhydride copolymer and the amphiphilic block modifier are subjected to a condensation catalytic grafting reaction; wherein the condensation agent is N,N'-dicyclohexylcarbodiimide and the catalyst is 4-dimethylaminopyridine.

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