Preparation method and application of light-resistant core-shell structure composite pigment

Abstract

This invention discloses a method for preparing a lightfast core-shell composite pigment. Barium sulfate is used as the inorganic core material, and a cationic lake pigment prepared with heteropolyacid as a precipitant is used as the organic shell. The two are bonded together by electrostatic interactions between the core and shell, resulting in a core-shell composite pigment with excellent lightfastness and long-lasting light stability. Compared to pure pigment-printed fabrics, the lightfastness of this type of pigment is significantly improved. It can withstand 24 hours of sunlight exposure in a photoresist tester without fading or discoloration. The pigment prepared by this invention can withstand ultraviolet radiation for up to 73 days or even longer. The prepared lightfast core-shell composite pigment has excellent application prospects in pigment printing, inkjet printing, food coloring, and painting inks.

Description

Technical Field

[0001] This invention relates to the field of pigment production, and in particular to a method for preparing lightfast core-shell composite pigments and their applications. Background Technology

[0002] Organic pigments, as colorants, are used in various fields due to their bright colors and strong tinting strength, such as inks, coatings, doping of synthetic fibers, coating printing on fabrics, and coloring of plastics, rubber, and leather. With the development of organic pigments, specific performance requirements are increasingly needed in different application areas. For example, in automotive paints, industrial coatings, and building materials, these pigments need excellent lightfastness to provide durable and aesthetically pleasing finishes and applicability. However, due to their own structure, environmental factors, or particle morphology, organic pigments cannot always meet the requirements for durability and aesthetics during application. For instance, xanthracene cationic pigments, characterized by bright colors and high tinting strength, have wide applications in various fields. These pigments are typically insoluble pigment products obtained by combining soluble xanthracene cationic dyes with a precipitant under acidic conditions and then settling. However, the limited lightfastness of these pigments is often due to the restricted structure of the xanthracene matrix, which contains a large number of aromatic rings, thus limiting the application of xanthracene lake pigments in the printing and dyeing industry. Therefore, in order to make pigments more widely used in various fields, it is necessary to improve their lightfastness.

[0003] Currently, most industrial production methods improve the lightfastness of pigments by using doping agents or introducing specific groups into the pigments to enhance their lightfastness. For example, patent CN 201711445530.7 improves the lightfastness of organic pigments by adding hindered amine fragments to the pigment paste component; patent CN 201410183476.3 inserts dye anions and light stabilizer anions together into the interlayer of hydrotalcite, utilizing the UV absorption, energy transfer, and excited-state annihilation of the light stabilizer anions to improve the lightfastness of the interlayer dye anions. While these existing methods can improve the lightfastness of pigments to some extent, they all achieve this by introducing chemical finishing agents. In practice, these methods often suffer from poor compatibility with the pigment itself and short lightfastness. Furthermore, they can drastically alter the pigment's color and hue, failing to meet actual production requirements.

[0004] Core-shell composite pigments have long been considered an effective strategy to address the poor photostability of organic pigments in practical applications. Inorganic materials such as silica (SiO2), titanium dioxide (TiO2), and sepiolite, due to their small size and quantum size effects, can effectively absorb, reflect, and scatter ultraviolet light, exhibiting significant advantages in UV resistance. Currently, there are numerous methods for combining inorganic materials like silica with organic pigments to form core-shell structures, thereby improving the thermal stability and weather resistance of organic pigments. For example, patent CN110776756B discloses a modified sepiolite composite pigment and its preparation method. By combining chitosan-modified sepiolite with organic pigments, the chromaticity of the organic pigments is improved, while simultaneously enhancing their heat and weather resistance. However, the inorganic materials prepared by this method lack sufficient mechanical strength, making them prone to coating peeling during application. Patent CN116462990A discloses an inorganic-organic coated pigment and its preparation method, which improves the heat resistance and weather resistance of organic pigments by coating silica inside azo pigments of the naphthol AS type. However, its tinting strength changes significantly and cannot meet the actual needs of its application.

[0005] Barium sulfate is a common inorganic chemical component found in nature, primarily exhibiting a barite structure. This white solid is often considered a crucial non-gold ore source due to its outstanding chemical stability and relatively low toxicity in various industrial environments. Furthermore, barium sulfate demonstrates excellent lightfastness due to its extremely high physical density and porosity, making it particularly suitable for applications where light stability is critical. Currently, there is limited research in the industry on combining barium sulfate with organic pigments to improve their stability and lightfastness. Therefore, exploring its combination with organic pigments, especially anthracene lake pigments, to enhance their lightfastness is of significant importance. Summary of the Invention

[0006] To address the aforementioned problems, the present invention aims to provide a method for preparing a lightfast core-shell composite pigment. Using barium sulfate as the core and a cationic pigment as the shell, the two are adsorbed together through electrostatic attraction to form a core-shell composite pigment, thereby solving the problems of poor lightfastness and low lightfastness stability found in existing composite pigments.

[0007] To achieve the above objectives, this invention provides a method for preparing a lightfast core-shell composite pigment. The method uses barium sulfate as the inorganic core material and a cationic lake pigment prepared with heteropolyacid as a precipitant as the organic shell. The two are combined using electrostatic interactions between the core and shell to obtain a core-shell composite pigment with good lightfastness and long-lasting lightfastness.

[0008] This invention first provides a method for preparing a lightfast core-shell composite pigment, comprising the following steps:

[0009] (1) Slowly add aluminum sulfate solution to barium chloride solution, let it react and stir under hot water bath conditions, let the reactants stand, filter under reduced pressure, dry at 60°C and normal pressure, and grind to obtain barium sulfate;

[0010] (2) Add glacial acetic acid and deionized water to the cationic organic dye, stir to allow it to react, and obtain an organic dye solution.

[0011] (3) Take sodium tungstate, sodium molybdate and disodium hydrogen phosphate, add them to hot water at 50-80℃, stir at 250r / min to make them react fully, adjust the pH value to 1.6-1.8 to obtain a heteropoly acid solution; slowly add the dye solution obtained in step (2) to the heteropoly acid solution and stir for 1-2h to prepare an organic lake pigment suspension;

[0012] (4) Disperse the barium sulfate obtained in step (1) in water to obtain a barium sulfate dispersion. Add the barium sulfate dispersion to the organic lake pigment suspension obtained in step (3) and stir to obtain a mixed solution. Let it stand and filter, wash with water, and dry at 60°C under normal pressure to obtain a light-resistant core-shell composite pigment.

[0013] In one embodiment of the present invention, the concentration of the barium chloride solution in step (1) is 0.3 to 0.6 mol / L. The barium chloride solution is obtained by reacting a mixture of barium chloride and water under hot water bath conditions. The temperature of the hot water bath is 60 to 90°C and the reaction time is 2 hours.

[0014] In one embodiment of the present invention, the concentration of the aluminum sulfate solution in step (1) is 0.07-0.20 mol / L, and the aluminum sulfate solution is obtained by reacting a mixture of aluminum sulfate and water under stirring conditions for 1 hour.

[0015] In one embodiment of the present invention, the volume ratio of barium chloride solution and aluminum sulfate solution in step (1) is 1 to 3:1.

[0016] In one embodiment of the present invention, the temperature of the hot water bath in step (1) is 60-90°C, the stirring speed is 100-300 r / min, the reaction time is 1-2 h, and the reaction product is allowed to stand for 0.5-1 h.

[0017] In one embodiment of the present invention, the barium sulfate obtained in step (1) has a particle size of 800 nm-5 μm.

[0018] In one embodiment of the present invention, the cationic organic dye in step (2) is an oxane dye, which includes at least one of rose ore B, basic red, and rhodamine 6G.

[0019] In one embodiment of the present invention, the cationic organic dye in step (2) is a mixture of rose extract B and basic red, wherein the molar ratio of rose extract to basic red is 1-5:0.5-1.

[0020] In one embodiment of the present invention, in step (2), the mass ratio of the cationic organic dye, water and glacial acetic acid is 1:20-50:0.01-1, preferably 1:20-50:0.5-1.

[0021] In one embodiment of the present invention, the stirring speed in step (2) is 100-800 r / min, the stirring time is 0.5-1 h, and the reaction temperature is 50-90℃.

[0022] In one embodiment of the present invention, the molar ratio of sodium tungstate, sodium molybdate and disodium hydrogen phosphate in step (3) is 1-5:1-5:0.5-2, and the reaction time is 1-2 hours.

[0023] In one embodiment of the present invention, the volume ratio of the dye solution and the heteropolyacid solution in step (3) is 1-3:1-2, the stirring temperature is 30-90℃, and the reaction time is 1-3h.

[0024] In one embodiment of the present invention, the mass fraction of the barium sulfate dispersion in step (4) is 1-10%, and the barium sulfate solution is prepared by stirring and reacting barium sulfate and water at 20-100°C and then ultrasonically treating the mixture, with a reaction time of 30-180 min.

[0025] In one embodiment of the present invention, the mass ratio of barium sulfate solution to organic suspension in step (4) is 0.5-2:1-2.

[0026] In one embodiment of the present invention, the stirring temperature in step (4) is 20 to 100°C and the stirring time is 30 to 180 min.

[0027] The second objective of this invention is to provide a lightfast core-shell composite pigment prepared according to the above method.

[0028] The present invention also provides an application of the above-mentioned lightfast core-shell structured composite pigment in pigment printing, inkjet printing, food coloring and painting ink.

[0029] Beneficial effects:

[0030] (1) This invention uses barium sulfate as the core and an organic pigment as the shell, and the two adsorb each other through electrostatic attraction to obtain a composite pigment. By adjusting the preparation method of barium sulfate, the size and surface properties of the inorganic core are precisely controlled to give it excellent porosity, thereby enhancing the pigment's dispersion ability in various media. At the same time, the inorganic core has the ability to absorb, reflect and scatter ultraviolet light, which can concentrate the ultraviolet light energy absorbed by the composite pigment into the core layer, thereby reducing the damage of energy to the pigment structure, improving the lightfastness of the organic pigment and achieving the result that there is no obvious fading or discoloration after 24 hours of exposure to sunlight in a photoreactor.

[0031] (2) Inorganic substances have excellent compatibility with organic pigments and low production costs, giving them an advantage in actual production. This solves the problems caused by traditional methods such as adding dopants, which result in poor compatibility with pigments, low biosafety, weak resistance to ultraviolet light, and the impact of large-scale use on pigment color and hue.

[0032] (3) In the preparation of composite pigments, the present invention uses heteropolyacids as precipitants to prepare cationic lake dyes, which effectively improves the bonding ability between inorganic materials and cationic dyes and greatly enhances the performance of the prepared composite pigments.

[0033] (4) The composite pigment prepared by the method of the present invention can withstand ultraviolet irradiation for up to 73 days or even longer, and has excellent lightfastness and lightfastness. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of a lightfast core-shell composite pigment. Detailed Implementation

[0035] The preferred embodiments of the present invention are described below. It should be understood that the embodiments are for better explanation of the present invention and are not intended to limit the present invention.

[0036] Test method:

[0037] Powder K / S test: The test was conducted using a DataColor colorimeter. Weigh 1g of the core-shell composite pigment and gently spread it evenly on the sample tray, avoiding air bubbles or accumulation. Press the measurement button and wait for the measurement result to be automatically displayed on the screen. Record the measurement result as needed for subsequent analysis and processing.

[0038] Fabric sample K / S test:

[0039] Weigh 1g of core-shell composite pigment into a beaker, then weigh 2g of DM-5211G thickener, 10g of DM-5128 binder, and 10mL of deionized water. Stir thoroughly to form a viscous pigment paste. Print the pigment paste evenly onto polyester-cotton fabric using a screen printing method. Dry at 100℃ and pre-dry at 140℃ for 3 minutes to obtain the printed fabric sample.

[0040] Cut the printed fabric sample into a 5cm x 5cm square, test it with a DataColor colorimeter, press the measurement button, wait for the measurement result to be automatically displayed on the screen, and record the measurement result as needed for subsequent analysis and processing.

[0041] Lightfastness test: Cut the above printed fabric sample into a 5cm×5cm square and irradiate it under a CEL-S250 ultraviolet lamp. Take it out every 10 minutes to test the color value. Calculate the rate of change of color difference ΔE of the printed fabric sample after 12 hours of ultraviolet irradiation, i.e., the fading rate.

[0042] Lightfastness test: Spread the pigment powder evenly on the sample plate and place it in direct sunlight. Record the time required for fading (i.e., the time when the color difference ΔE changes by more than 1).

[0043] Example 1

[0044] A method for preparing a lightfast core-shell composite pigment includes the following steps:

[0045] (1) Add 12.48 g of barium chloride to a 500 mL beaker, then add 200 mL of deionized water, and place it in a 70 °C water bath for 30 min to prepare a barium chloride solution with a concentration of 0.3 mol / L; take 6.86 g of aluminum sulfate, add 200 mL of deionized water, and stir for 30 min to prepare an aluminum sulfate solution with a concentration of 0.1 mol / L; slowly add aluminum sulfate solution to barium chloride solution, cover with plastic wrap, and stir and react for 1 h in a 70 °C hot water bath. Let the reactants stand for 30 min, filter under reduced pressure, dry at 60 °C under normal pressure, and grind to obtain barium sulfate;

[0046] (2) Add 23.95g of rose essence B and 4.79g of basic red to a 500mL beaker, then add 1.26g of glacial acetic acid and 150mL of deionized water to the beaker, stir at 90℃ for 20min to obtain an organic dye solution.

[0047] (3) Take 23g sodium tungstate, 16.4g sodium molybdate and 10.1g disodium hydrogen phosphate, add them to hot water at 80℃, stir at 300r / min for 10min to allow them to react fully, add 2mol / L hydrochloric acid to adjust the pH value to 1.7, continue stirring for 10min to obtain a heteropoly acid solution; cool the organic dye solution obtained in step (2) to 70℃, and slowly add it to the heteropoly acid solution at a volume ratio of 1:1, stir at 300r / min for 1h to obtain an organic lake pigment suspension.

[0048] (4) The barium sulfate obtained in step (1) is ultrasonically dispersed in water to obtain a barium sulfate dispersion with a mass fraction of 5%. An equal volume of barium sulfate dispersion is added to the suspension in step (3). After stirring and reacting for 2 hours, the mixture is allowed to stand for 30 minutes, filtered, washed with water, and dried at 60°C under normal pressure to obtain a light-resistant core-shell composite pigment.

[0049] Example 2

[0050] The difference between Example 2 and Example 1 is that the concentration of barium chloride is different. In Example 2, the concentration of barium chloride is 0.4 mol / L.

[0051] Example 3

[0052] The difference between Example 3 and Example 1 is that the concentration of barium chloride is different. In Example 3, the concentration of barium chloride is 0.5 mol / L.

[0053] Example 4

[0054] The difference between Example 4 and Example 1 is that the concentration of barium chloride is different. In Example 4, the concentration of barium chloride is 0.6 mol / L.

[0055] Example 5

[0056] The difference between Example 5 and Example 1 is that the temperature of the hot water bath is different during the preparation of barium sulfate. In Example 5, the temperature of the hot water bath during the preparation of barium sulfate is 60°C.

[0057] Example 6

[0058] The difference between Example 6 and Example 1 is that the temperature of the hot water bath is different during the preparation of barium sulfate. In Example 6, the temperature of the hot water bath during the preparation of barium sulfate is 80°C.

[0059] Example 7

[0060] The difference between Example 7 and Example 1 is that the temperature of the hot water bath during the preparation of barium sulfate is different. In Example 7, the temperature of the hot water bath during the preparation of barium sulfate is 90°C.

[0061] Example 8

[0062] The difference between Example 8 and Example 1 is that the molar ratio of sodium tungstate, sodium molybdate and disodium hydrogen phosphate in step (3) is 2:1:1.

[0063] Example 9

[0064] The difference between Example 9 and Example 1 is that the volume ratio of the dye solution and the heteropolyacid solution in step (3) is 2:1.

[0065] Example 10

[0066] The difference between Example 10 and Example 1 is that the volume ratio of barium sulfate solution and organic pigment suspension in step (4) is 2:1.

[0067] Comparative Example 1

[0068] The difference between Comparative Example 1 and Example 1 is that steps (1) and (4) are omitted, and the composite pigment is prepared directly by mixing organic pigment suspension and heteropoly acid solution. The amounts of rose extract B and basic red in the organic pigment suspension are different, with the mass of rose extract B being 11.97g and the mass of basic red being 2.39g.

[0069] Comparative Example 2

[0070] The difference between Comparative Example 2 and Comparative Example 1 is that Rose Essence B and Basic Red were replaced with 23.95g of Pigment Red 48, while everything else remained the same.

[0071] Comparative Example 3

[0072] The difference between Comparative Example 3 and Comparative Example 2 is that the reaction temperature of pigment red and glacial acetic acid is different; the reaction temperature of Comparative Example 3 is 60℃.

[0073] Table 2. Lightfastness of pigments and printed fabric samples from Examples 1-10 and Comparative Examples 1-3

[0074] 1 4.8 5.9 14.9 49 2 4.9 6.2 16.4 47 3 4.9 6.8 5.5 65 4 4.7 6.4 8.9 54 5 4.9 7.2 10.2 52 6 4.8 6.8 20 45 7 4.8 6.6 7.6 57 8 4.9 7.0 5.9 66 9 4.6 6.9 7.2 59 10 4.5 4.2 1.9 73 Comparative Example 1 4.8 5.2 56 18 Comparative Example 2 3.2 4.8 48 30 Comparative Example 3 3.5 5.0 62 22

[0075] As shown in Table 2, compared with Comparative Examples 1-3, the lightfastness of Examples 1-10 was significantly increased after the formation of the core-shell structure composite pigment. Simultaneously, the powder color did not change significantly, compensating for the previous defect that inorganic materials altered the pigment hue. The lightfastness could reach up to 73 days, which is largely related to the inorganic materials and their synthesis, the preparation of the organic pigment suspension, and the proportion of inorganic materials in the composite material. Examples 1-4 show that the concentration of barium chloride during the inorganic material synthesis process has a significant impact on the lightfastness of the pigment. The concentration of barium chloride mainly affects the particle size and surface properties of the synthesized barium sulfate, thus affecting the lightfastness of the composite pigment. With increasing barium chloride concentration, the lightfastness of the pigment first increases and then decreases, reaching its maximum when the barium chloride concentration is 0.5 mol / L. Similarly, the synthesis temperature of barium sulfate has a significant impact on its particle size and surface properties, thus affecting the lightfastness of the composite pigment. This is evident from the data in Examples 1 and 5-7, where the composite pigment prepared at a synthesis temperature of 90℃ exhibits the best lightfastness. During the synthesis of the composite pigment, the proportion of raw materials in the synthesis of phosphotungstic molybdenum acid affects the adsorption capacity of the precipitant for the dye, resulting in differences in the crystal structure of the organic pigment, which in turn affects the crystal structure of the composite pigment, leading to differences in its lightfastness. Furthermore, the amount of inorganic material added also affects the pigment's performance; specifically, the more inorganic material added, the better the lightfastness. However, the amount of inorganic material added needs to be controlled within a certain level; otherwise, it will affect the hue of the pigment, resulting in a lighter color in the final fabric and making it difficult to obtain vibrant colors. In Comparative Examples 2 and 3, due to the different properties of the dyes, adjusting their dissolution temperature indirectly affects whether they are completely in a molecular state in the solvent, thus affecting their coating ability.

[0076] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for preparing a lightfast core-shell composite pigment, characterized in that, Includes the following steps: (1) Slowly add aluminum sulfate solution to barium chloride solution, let it react and stir under hot water bath conditions, let the reactants stand, filter under reduced pressure, dry at 60°C and normal pressure, and grind to obtain barium sulfate; the concentration of the barium chloride solution is 0.5~0.6 mol / L, the barium chloride solution is obtained by reacting a mixture of barium chloride and water under hot water bath conditions, the temperature of the hot water bath is 90°C, the reaction time is 2h, the concentration of the aluminum sulfate solution is 0.07-0.20 mol / L, the aluminum sulfate solution is obtained by reacting a mixture of aluminum sulfate and water under stirring conditions, the stirring time is 1h; (2) Add glacial acetic acid and deionized water to the cationic organic dye, stir to react, and obtain an organic dye solution; the cationic organic dye is an oxane dye, and the oxane dye includes at least one of rose rin B, basic red, and rhodamine 6G. (3) Take sodium tungstate, sodium molybdate and disodium hydrogen phosphate, add them to hot water at 50-80℃, stir at 250r / min to make them react fully, adjust the pH value to 1.6-1.8 to obtain a heteropoly acid solution; slowly add the dye solution obtained in step (2) to the heteropoly acid solution and stir for 1-2h to prepare an organic lake pigment suspension; (4) Disperse the barium sulfate obtained in step (1) in water to obtain a barium sulfate dispersion. Add the barium sulfate dispersion to the organic lake pigment suspension obtained in step (3) and stir to obtain a mixed solution. Let it stand and filter, wash with water, and dry at 60°C under normal pressure to obtain a light-resistant core-shell composite pigment.

2. The preparation method according to claim 1, characterized in that, In step (1), the volume ratio of barium chloride solution to aluminum sulfate solution is 1~3:1, the temperature of the hot water bath is 60~90℃, the stirring speed is 100-300r / min, the reaction time is 1-2h, and the reaction product is allowed to stand for 0.5-1h.

3. The preparation method according to claim 1, characterized in that, The cationic organic dye in step (2) is a mixture of rose extract B and basic red, with a molar ratio of rose extract to basic red of 1~5:0.5~1. The mass ratio of the cationic organic dye, water and glacial acetic acid is 1:20~50:0.01~1. The stirring speed is 100-800 r / min, the stirring time is 0.5-1 h, and the reaction temperature is 50~90℃.

4. The preparation method according to claim 1, characterized in that, In step (3), the molar ratio of sodium tungstate, sodium molybdate, and disodium hydrogen phosphate is 1-5:1-5:0.5-2, the reaction time is 1-2 h, the volume ratio of the dye solution and the heteropolyacid solution is 1-3:1-2, the stirring temperature is 30-90℃, and the reaction time is 1-3 h.

5. The preparation method according to claim 1, characterized in that, The mass fraction of the barium sulfate dispersion in step (4) is 1~10%, and the barium sulfate solution is prepared by stirring barium sulfate and water at 20~100℃ and then subjecting them to ultrasonic treatment. The reaction time is 30~180min.

6. The preparation method according to claim 1, characterized in that, In step (4), the mass ratio of barium sulfate solution to organic suspension is 0.5-2:1-2, the stirring temperature is 20~100℃, and the stirring time is 30~180min.

7. The lightfast core-shell composite pigment prepared by the preparation method according to any one of claims 1 to 6.

8. The application of the lightfast core-shell composite pigment as described in claim 7 in pigment printing, inkjet printing, food coloring and painting ink.

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