Hyperdispersant for high-performance organic pigment and preparation method thereof

Abstract

The invention relates to a hyperdispersant for an organic pigment system and a preparation method thereof, the hyperdispersant is a block-grafted structure polymer and is composed of an anchoring segment A, a dissolving segment B and an interface segment C, the molar ratio of the three chain segments A: B: C is 1: (3-6): (0.1-0.4), the anchoring segment A is formed by a monomer containing a polyphenol carboxyl or polyhydroxy aromatic structure; the dissolving section B is composed of oleophobic acrylate and polyether modified acrylate; and the interface section C comprises fluorine-containing acrylate and siloxane acrylate. The preparation method sequentially comprises the steps of anchoring section prepolymerization, dissolving section continuous polymerization, interface section grafting, chain end capping and partial neutralization, and a final product is obtained through dilution and filtration. The hyperdispersant disclosed by the invention is suitable for various organic pigment systems, and can form a stable molecular covering layer in a dispersion processing process, so that relatively uniform pigment particle distribution is obtained.

Description

Technical Field

[0001] This invention relates to the field of polymer dispersion technology, and more specifically, to a high-performance superdispersant for organic pigments and its preparation method. Background Technology

[0002] Organic pigments, due to the ubiquitous rigid aromatic rings and large-area conjugated systems in their molecular structure, typically exhibit a strong tendency for spontaneous aggregation. During the preparation of industrial inks, coatings, color pastes, and plastic masterbatches, these pigments often densely aggregate in the form of microcrystals, forming large-particle secondary aggregates. Aggregated pigments are difficult to disperse by mechanical force; even after high-speed dispersion or milling, they are prone to re-aggregation or coarsening after dispersion, causing a series of problems such as color instability, floating color, blooming, and sedimentation. Therefore, dispersants play a crucial role in organic pigment systems; they need to be firmly adsorbed onto the pigment surface, aiding in wetting and maintaining the independent existence of particles throughout the entire processing and storage cycle.

[0003] Currently widely used dispersants include polyacrylates, polyesters, polyurethanes, and some block copolymers. While these dispersants can improve dispersion efficiency to some extent, they still have significant limitations. For example, some dispersants with simpler structures rely on a single carboxyl or ester group for weak adsorption to pigments, making them prone to desorption under high temperature, high shear, or high solids content conditions. Although some block dispersants improve wetting ability, the segment ratio is difficult to control, making it difficult to balance rapid wetting, depolymerization ability, and long-term dispersion stability. For difficult-to-disperse pigments such as phthalocyanine blue, quinacridone red, and naphthimide yellow, traditional structural dispersants often require higher energy milling to achieve the target fineness, and they are still prone to coarsening during storage.

[0004] Meanwhile, current dispersants generally lack a clear division of labor between the two stages of "interfacial wetting and stable coating" in their structural design, with most products relying solely on the main chain or side chains to provide a single site of action. When the dispersion system spans solvent systems of different polarities or needs to be compatible with multiple types of organic pigments, the versatility of existing dispersants is limited. Users typically need to select different types of dispersants for each pigment, resulting in complex inventory and quality fluctuations. Therefore, the industry urgently needs a novel polymeric superdispersant with controllable chain segment structure, capable of rapidly wetting pigments and forming a stable coating layer, while also exhibiting good compatibility.

[0005] Therefore, there is an urgent need for a high-performance superdispersant for organic pigments and its preparation method to solve the above problems. Summary of the Invention

[0006] The purpose of this invention is to solve the technical problems mentioned in the background section and to provide a high-performance superdispersant for organic pigments and its preparation method.

[0007] The above-mentioned objective of the present invention is achieved through the following technical solution: An organic pigment superdispersant, wherein the superdispersant is a block-grafted polymer obtained by free radical polymerization, and its molecular chain includes an anchoring segment A, a dissolving segment B, and an interfacial active segment C, wherein the molar ratio between the three segments is: A∶B∶C = 1∶3~6∶0.1~0.4; Wherein: Anchoring section A is formed by polymerization of monomers containing polyphenolic carboxyl groups or polyhydroxy aromatic ring structures, wherein the monomers are selected from one or more of gallic acid acrylate, tannic acid acrylate and dihydroxystyrene derivatives; The dissolution section B is composed of oleophobic acrylate monomers and polyether-modified acrylate monomers, with a molar ratio of 1 to 3:1. The interfacial active segment C is composed of fluorinated acrylate monomers and siloxane methacrylate monomers, with a molar ratio of 1 to 4:1. The weight-average molecular weight of the resulting polymer is 6,000 to 20,000.

[0008] As a preferred embodiment of the present invention, the anchoring section A further comprises anhydride or polycarboxylic acid monomers, wherein the molar ratio of the polyphenolic carboxyl monomer to the anhydride monomer is 2 to 10:1.

[0009] As a preferred technical solution of the present invention, the oleophobic acrylate monomer is selected from one or more of the following: butyl acrylate, 2-ethylhexyl acrylate, and isooctyl acrylate.

[0010] As a preferred technical solution of the present invention, the number average molecular weight of the polyether modified acrylate monomer is 500 to 2000, and the block molar ratio of ethylene oxide (EO) to propylene oxide (PO) is 1:1 to 4:1.

[0011] As a preferred embodiment of the present invention, the fluorinated acrylate monomer in the interfacial active segment C has a perfluoroalkyl side chain.

[0012] As a preferred technical solution of the present invention, the superdispersant is partially neutralized by an organic amine after polymerization, and the degree of neutralization of the carboxyl groups in anchoring section A is 10% to 50%, wherein the organic amine is selected from triethanolamine, diethanolamine, monoethanolamine or aminomethylpropanol.

[0013] This invention provides a method for preparing a superdispersant for organic pigments, characterized in that the method comprises: S1. Prepolymerization of anchoring segment A: Add each monomer of anchoring segment A to the solvent according to the molar ratio of claim 1 or 2; heat to 80-95°C under inert gas protection, add free radical initiator, maintain reaction for 1-2 hours, and obtain prepolymer reaction solution; S2, Dissolution Section B Continuous Polymerization: The oleophobic acrylate and the polyether modified acrylate monomer are mixed in a molar ratio of 1 to 3:1 and added dropwise at a constant rate to the reaction solution obtained in step S1 under inert gas protection; the system temperature is adjusted to 100 to 120°C, and the reaction is maintained for 1 to 2 hours after the addition is completed; S3, Grafting polymerization of interfacial active segment C: Fluorinated acrylate and siloxane methacrylate are mixed in a molar ratio of 1 to 4:1 and added to the system in step S2. The reaction temperature is adjusted to 85 to 95°C and the reaction is continued for 1 to 2 hours. S4. Capping and neutralization: Cool the system to 60-80°C, add a capping agent containing thiol or hydroxyl groups and stir for 0.5-1 hour, then add an organic amine for partial neutralization; S5. Dilution, Cooling and Filtration: Add solvent to dilute according to the target solid content, cool the system to below 40°C, and filter to remove impurities to obtain the superdispersant.

[0014] As a preferred technical solution of the present invention, the free radical initiator is selected from: azobisisobutyronitrile (AIBN), azobisisoheptanenitrile, or diisopropylbenzene peroxide, and the molar ratio of the initiator to all monomers is 0.003 to 0.02:1.

[0015] As a preferred technical solution of the present invention, the polymerization solvent used in steps S1 to S3 is selected from one or more of xylene, isomeric xylene, PM solvent oil or propylene glycol methyl ether acetate.

[0016] As a preferred embodiment of the present invention, a decompression removal step is further performed before step S5, at a temperature of 30–60°C. The reaction solution is subjected to reduced pressure treatment at a vacuum level.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention employs a three-segment block-graft structure comprising an anchoring segment A, a dissolving segment B, and an interface segment C, with segment ratios controlled by molar proportions, resulting in a clearly defined distribution of segments within the polymer chain. Anchoring segment A contains polyphenolic carboxyl groups or polyhydroxy aromatic structures, enabling the formation of high-density adsorption sites; dissolving segment B provides flexible segments and solubilization capabilities; and interface segment C, composed of fluorinated and siloxane monomers, helps regulate the wetting behavior of molecules at the interface. This segment combination is uncommon in existing dispersant systems, offering a novel structural option.

[0018] This invention employs a stepwise polymerization route of "prepolymerization-grafting-addition," enabling the sequential formation of different structural segments and allowing for precise control of segment length and molar ratio during the preparation process. End-capping and partial neutralization steps further ensure the structural uniformity and compatibility of the polymer. Compared to traditional one-step free radical copolymerization, this method features clearer segment structures and higher reproducibility.

[0019] As can be seen from the examples and comparative experiments, the three-segment structure of the present invention achieves relatively fine and stable dispersed particle sizes in different organic pigments; the structure lacking the interface segment C in the comparative example has a significantly increased dispersed particle size and poor storage stability, indicating that the introduction of the three-segment structure, especially the interface segment, plays a significant role in the pigment wetting and dispersion stages. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0021] The present invention will be further described in detail below with reference to specific embodiments, but the present invention is not limited to these embodiments. Equivalent modifications made by those skilled in the art without departing from the principles of the present invention should fall within the protection scope of the present invention.

[0022] Before describing this invention, it is necessary to briefly introduce a common problem in the processing of organic pigments: these pigment molecules tend to clump together, automatically forming clumps, like "a ball of powder." Without a dispersant, these clumps are difficult to break up in inks, coatings, and plastic systems, leading to uneven color, floating color, mottling, sedimentation, and coarsening. Therefore, the task of a dispersant is to "tightly hold the pigment surface," separating them and maintaining the independent existence of the particles after dispersion.

[0023] The superdispersant provided by this invention employs a block-graft structure composed of an anchoring segment A, a dissolving segment B, and an interface segment C. The molar ratio of the three segments in the molecular chain is A∶B∶C = 1∶3~6∶0.1~0.4. The anchoring segment is responsible for "grasping the surface of pigment particles," the dissolving segment is responsible for "encapsulating the particles and suspending them stably in the solvent," and the interface segment is responsible for "rapid wetting" and "helping pigment agglomerates disintegrate rapidly." The overall idea of ​​this invention is to achieve a stable coating layer around the pigment by rationally designing the ratio of the three segments.

[0024] The preparation method of the present invention will be fully described below.

[0025] The preparation process begins with the prepolymerization of anchoring segment A. Designed anchoring segment monomers (such as gallic acid acrylate, tannic acid acrylate, etc.) are added to a solvent (such as xylene or PM solvent oil) at a predetermined molar ratio. Because these monomers contain a large number of hydroxyl and carboxyl groups, they readily form stable adsorption on the pigment crystal surface. To avoid oxygen affecting the polymerization reaction, nitrogen gas is introduced into the reactor to maintain an inert environment. The subsequent heating (to 80–95°C) aims to activate the free radical initiator, allowing the anchoring segment monomers to "link into short chains," forming a "primary segment" that can stably adhere to the pigment surface. This process lasts 1–2 hours.

[0026] After the anchoring segment is formed, the dissolving segment B in the middle needs to be added to the dispersant. The dissolving segment is composed of oleophobic acrylate monomers and polyether-modified acrylate monomers in a specified molar ratio (1–3:1). The design of this segment is crucial because it determines the compatibility of the dispersant in oily media and the stability of the entire dispersion layer. During preparation, these two types of segment B monomers are usually premixed and added to the reaction system containing the anchoring segment prepolymer at a constant dropping rate. The dropping time is generally 1–3 hours, during which the reaction temperature is raised to 100–120°C, and the reaction continues for 1–2 hours to ensure continuous segment growth.

[0027] Subsequently, the monomer of interfacial segment C is introduced into the system. Interfacial segment C is composed of fluorinated acrylate and siloxane methacrylate in a molar ratio of 1 to 4:1. The fluorinated segment can reduce the surface tension at the interface between the medium and the pigment, while the siloxane segment has good flexibility and surface migration properties. Therefore, the combination of the two allows the final dispersant to more easily contact and wet the pigment particles in the early stage of pigment dispersion. After adding the interfacial segment monomer, the reaction system is adjusted to 85–95°C and maintained for 1–2 hours to allow these monomers to graft into the polymer chain structure.

[0028] In the final stage of preparation, the polymer chains need to be capped to prevent uncontrolled molecular weight growth due to unlimited chain segment growth. Capping agents are generally low-molecular-weight monomers with thiol or hydroxyl groups, which can limit further chain growth and regulate the structural uniformity of the polymer. After capping, organic amines are added for partial neutralization, achieving a carboxyl group neutralization rate of 10%–50% in the anchored segments. This improves the dispersant's solubility in the solvent, making the final dispersant more stable during storage and use.

[0029] After the above steps are completed, the system is cooled to below 40°C, and the required solvent is added for dilution according to the target solid content. Then, the system is filtered to remove any gel and impurity particles that may be generated, and the superdispersant product of the present invention can be obtained.

[0030] To make the technical solution of the present invention clearer, several embodiments and comparative examples are given below.

[0031] Example 1: Preparation and application of dispersants using phthalocyanine blue as the dispersing target; The hyperdispersant prepared in this embodiment is used in solvent-based ink systems. First, 250 g of xylene, 0.20 mol of gallic acid acrylate, and 0.03 mol of maleic anhydride were added to a reaction vessel. Nitrogen gas was introduced for 30 minutes, then the temperature was raised to 90°C, and 0.002 mol of AIBN was added. The reaction was allowed to proceed for 1.5 hours.

[0032] 0.45 mol of butyl acrylate and 0.20 mol of EO / PO polyether methacrylate were mixed and added dropwise at 110°C for 2 hours. After the addition was complete, the reaction was continued for 1 hour.

[0033] 0.05 mol of fluorinated acrylate and 0.02 mol of siloxane acrylate were added to the system, and the reaction was maintained at 90°C for 1 hour.

[0034] After cooling to 70℃, add 0.01 mol of mercaptoethanol and stir for 30 minutes. Then add 0.05 mol of triethanolamine to neutralize to the target degree of neutralization. After cooling to 40℃, filter to obtain the final product.

[0035] The finished product was added to the phthalocyanine blue slurry at 20% of the pigment mass, and after sand milling, a slurry with an average particle size (D50) of 128 nm was obtained.

[0036] Example 2: Preparation of a dispersant for red azo pigments; Add 300 g of isomeric xylene, followed by 0.18 mol of tannic acid acrylate and 0.02 mol of itaconic acid. After nitrogen purging, heat to 90 °C, add 0.003 mol of dicumyl peroxide, and react for 2 hours.

[0037] Add 0.55 mol of 2-ethylhexyl acrylate and 0.25 mol of polyether acrylate with a number average molecular weight of 1000, dropwise over 3 hours and keep warm at 105℃ for 1 hour.

[0038] 0.06 mol of fluorinated acrylate and 0.03 mol of siloxane acrylate were added, and the mixture was reacted at 88 °C for 1.5 hours.

[0039] 0.015 mol of hydroxyethyl methacrylate was added for further end-capping, and 0.04 mol of diethanolamine was added for neutralization. After cooling and filtration, the product was obtained.

[0040] When applied to red azo pigments, an average particle size D50 of 152 nm was obtained.

[0041] Example 3: Used in neutral polarity coating systems; Prepolymerize at 90°C for 1.5 hours using 200 g of PM solvent oil, 0.25 mol of gallic acid acrylate, and 0.04 mol of itaconic anhydride.

[0042] In the dissolution section, 0.50 mol of butyl acrylate and 0.22 mol of EO / PO (EO:PO = 2:1) polyether acrylate were added dropwise and reacted at 110℃.

[0043] Add 0.07 mol of fluoroacrylate and 0.02 mol of siloxane acrylate to the interface segment and graft for 1.2 hours.

[0044] The capping agent used was 0.01 mol mercaptopropanol, and the neutralizing agent was 0.05 mol monoethanolamine.

[0045] This dispersant is used for organic yellow pigments with a D50 of 140 nm.

[0046] Comparative example (traditional structure excluding interface segment C); The preparation method is the same as in Example 1, but no fluorinated acrylates or siloxane acrylates are added, and the other steps are completely the same.

[0047] The final particle size D50 when used for phthalocyanine blue was 265 nm, and significant coarsening occurred after 7 days.

[0048] The following is a data comparison table between the various embodiments and comparative examples; Table 1: Particle Size Comparison Test Table;

[0049] Table 2: Appearance and Stability of Dispersants;

[0050] Table 3: Particle size distribution (example data);

[0051] As can be seen from the particle size data in Table 1, the three-segment superdispersant used in Examples 1-3 of this invention can control the average particle size (D50) of the target organic pigment within the range of 128-152 nm, which is significantly better than the 265 nm of the comparative example. This indicates that the polymer coating layer formed by the synergistic action of segments A, B, and C in the three-segment structure can reduce the size of the initial pigment aggregates. In contrast, the comparative example lacks the interfacial segment C, resulting in insufficient initial wetting ability of the system, and large pigment aggregates are still retained after sand milling.

[0052] As shown in Table 2, the pigment pastes of Examples 1-3 remained stable after 30 days at 40°C, with no visible particle growth or sedimentation. In contrast, the comparative samples showed significant coarsening after 7 days and sedimentation after 30 days. This indicates that the introduction of interface segment C effectively improved the interfacial stability of the system and reduced secondary bonding of pigment particles during storage.

[0053] In summary, the data fully demonstrate the impact of different chain segment combinations on pigment dispersion fineness and dispersion stability, and the comparative figures clearly show that the system performance significantly decreases when the interface segment C is missing.

[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-performance superdispersant for organic pigments, characterized in that, The superdispersant is a block-grafted polymer obtained by free radical polymerization. Its molecular chain includes an anchoring segment A, a dissolving segment B, and an interfacial active segment C. The molar ratio between the three segments is: A∶B∶C = 1∶3~6∶0.1~0.

4. Wherein: Anchoring section A is formed by polymerization of monomers containing polyphenolic carboxyl groups or polyhydroxy aromatic ring structures, wherein the monomers are selected from one or more of gallic acid acrylate, tannic acid acrylate and dihydroxystyrene derivatives; The dissolution section B is composed of oleophobic acrylate monomers and polyether-modified acrylate monomers, with a molar ratio of 1 to 3:

1. The interfacial active segment C is composed of fluorinated acrylate monomers and siloxane methacrylate monomers, with a molar ratio of 1 to 4:

1. The weight-average molecular weight of the resulting polymer is 6,000 to 20,000.

2. The high-performance organic pigment superdispersant according to claim 1, characterized in that, Anchoring section A further comprises anhydride or polycarboxylic acid monomers, wherein the molar ratio of polyphenol carboxyl monomers to anhydride monomers is 2 to 10:

1.

3. The high-performance organic pigment superdispersant according to claim 1, characterized in that, The oleophobic acrylate monomer is selected from one or more of the following: butyl acrylate, 2-ethylhexyl acrylate, and isooctyl acrylate.

4. The high-performance organic pigment superdispersant according to claim 1, characterized in that, The number average molecular weight of the polyether-modified acrylate monomer is 500 to 2000, and the block molar ratio of ethylene oxide (EO) to propylene oxide (PO) is 1:1 to 4:

1.

5. The high-performance organic pigment superdispersant according to claim 1, characterized in that, The fluorinated acrylate monomer in the interfacial active segment C has a perfluoroalkyl side chain.

6. The high-performance organic pigment superdispersant according to claim 1, characterized in that, The superdispersant is partially neutralized by an organic amine after polymerization. The degree of neutralization of the carboxyl groups in anchoring section A is 10% to 50%. The organic amine is selected from triethanolamine, diethanolamine, monoethanolamine or aminomethylpropanol.

7. A method for preparing a superdispersant for organic pigments according to any one of claims 1 to 6, characterized in that, The method includes: S1. Prepolymerization of anchoring segment A: Add each monomer of anchoring segment A to the solvent according to the molar ratio of claim 1 or 2; heat to 80-95°C under inert gas protection, add free radical initiator, maintain reaction for 1-2 hours, and obtain prepolymer reaction solution; S2, Dissolution Section B Continuous Polymerization: The oleophobic acrylate and the polyether modified acrylate monomer are mixed in a molar ratio of 1 to 3:1 and added dropwise at a constant rate to the reaction solution obtained in step S1 under inert gas protection; the system temperature is adjusted to 100 to 120°C, and the reaction is maintained for 1 to 2 hours after the addition is completed; S3, Grafting polymerization of interfacial active segment C: Fluorinated acrylate and siloxane methacrylate are mixed in a molar ratio of 1 to 4:1 and added to the system in step S2. The reaction temperature is adjusted to 85 to 95°C and the reaction is continued for 1 to 2 hours. S4. Capping and neutralization: Cool the system to 60-80°C, add a capping agent containing thiol or hydroxyl groups and stir for 0.5-1 hour, then add an organic amine for partial neutralization; S5. Dilution, Cooling and Filtration: Add solvent to dilute according to the target solid content, cool the system to below 40°C, and filter to remove impurities to obtain the superdispersant.

8. The method according to claim 7, characterized in that, The free radical initiator is selected from azobisisobutyronitrile (AIBN), azobisisoheptanenitrile, or diisopropylbenzene peroxide, and the molar ratio of the initiator to all monomers is 0.003 to 0.02:

1.

9. The method according to claim 7, characterized in that, The polymerization solvents used in steps S1 to S3 are selected from one or more of xylene, isomethyl xylene, PM solvent oil, or propylene glycol methyl ether acetate.

10. The method according to claim 7, characterized in that, Before step S5, a further decompression removal step is performed at 30–60°C. The reaction solution is subjected to reduced pressure treatment at a vacuum level.

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