Black direct dye as well as preparation method and application thereof

Abstract

The invention provides a black direct dye as well as a preparation method and application thereof. The preparation method of the black direct dye disclosed by the invention comprises the following steps: acquiring polyaniline: performing oxidative polymerization on aniline hydrochloride by using an oxidizing agent to obtain polyaniline; obtaining a condensation product: carrying out condensation reaction on polyaniline and p-nitrotoluene o-sulfonic acid and / or 2-methyl-5-nitrobenzoic acid to obtain the condensation product; and a post-treatment step: carrying out post-treatment on the condensation product to obtain the black direct dye. The preparation method of the black direct dye is simple and easy to implement, few in three wastes in the production process and environmentally friendly. The black direct dye prepared by the preparation method is bright in color, good in water solubility, high in dye-uptake and excellent in dyeing performance.

Description

Technical Field

[0001] The invention relates to a black direct dye and a preparation method and application thereof, belonging to the field of dye synthesis. Background Art

[0002] Direct dyes are water-soluble dyes with sulfonic acid or carboxyl groups. They can be used to dye a wide range of materials, including but not limited to cotton, linen, and leather. They have a wide range of applications and a high market demand.

[0003] Currently, the most popular black direct dyes on the market are primarily used for dyeing fabrics such as cotton, linen, and leather. Chinese Patent CN 108485306A discloses a method for synthesizing Solvent Black 7, a dye suitable for leather, coatings, paper, and other materials. This dye has wide applicability, excellent performance, and a production process that reduces waste, waste products, and energy consumption, offering advantages in industrial production. Chinese Patent CN 101580650A also discloses a method for preparing Direct Sunfast Black 22, a dye with good water solubility and a pollution-free production process.

[0004] However, Solvent Black 7 dye has problems such as poor water solubility, low dyeing rate, and dull color; Direct Sun-Fast Black 22 has problems such as complex production process, low color fastness, low UV fastness and other poor dyeing properties, and it is suitable for fabric dyeing but not for paper and paper fiber dyeing.

[0005] Therefore, it is an urgent technical problem to develop a black direct dye that has a simple preparation method, good water solubility, bright color, high dye uptake, high light fastness and is suitable for dyeing paper and paper fibers. Summary of the Invention

[0006] Problems to be solved by the invention

[0007] In view of the technical problems existing in the prior art, based on the requirements of environmentally friendly dyes (low production of three wastes and low energy consumption), poor water solubility, low dye uptake, dull color, and poor dyeing performance, the present invention first provides a method for preparing a black direct dye. The preparation method of the black direct dye of the present invention is simple and easy to implement, the raw materials are easily available, and it is suitable for mass production. The prepared black direct dye has the characteristics of good water solubility, high dye uptake, bright color, excellent dyeing performance, environmentally friendly production process, and is suitable for paper dyeing.

[0008] Solutions for solving problems

[0009] The present invention first provides a method for preparing a black direct dye, which comprises the following steps:

[0010] The steps of obtaining polyaniline are as follows: using an oxidant to oxidatively polymerize aniline hydrochloride to obtain polyaniline;

[0011] The step of obtaining a condensation product comprises: subjecting polyaniline to a condensation reaction with p-nitrotoluene o-sulfonic acid and / or 2-methyl-5-nitrobenzoic acid to obtain a condensation product;

[0012] Post-processing step: post-processing the condensation product to obtain a black direct dye.

[0013] According to the preparation method of the present invention, the step of obtaining polyaniline includes: mixing an oxidant with an aniline hydrochloride solution and then performing an oxidative polymerization reaction.

[0014] According to the preparation method of the present invention, the temperature of the oxidative polymerization reaction is 25 to 40° C., and the time of the oxidative polymerization reaction is 3 to 5 hours.

[0015] According to the preparation method of the present invention, the oxidant includes one or a combination of two or more of potassium persulfate, sodium persulfate, hydrogen peroxide, potassium dichromate, and hydrogen persulfate; preferably, the aniline hydrochloride solution is a solution obtained by reacting a hydrochloric acid solution with aniline.

[0016] According to the preparation method of the present invention, the time for adding the oxidant to the aniline hydrochloride solution is 1.5 to 2 hours; preferably, the temperature of mixing the oxidant and the aniline hydrochloride solution is 5 to 10°C, and then the temperature is raised to 25 to 40°C over 2-3 hours to carry out the oxidative polymerization reaction.

[0017] According to the preparation method of the present invention, the p-nitrotoluene o-sulfonic acid and / or 2-methyl-5-nitrobenzoic acid are dehydrated to obtain molten p-nitrotoluene o-sulfonic acid and / or 2-methyl-5-nitrobenzoic acid; preferably, the temperature of the dehydration treatment is 100-160° C., and the time of the dehydration treatment is 1-3 hours.

[0018] According to the preparation method of the present invention, the temperature of the condensation reaction is 100 to 230° C., and the time of the condensation reaction is 4 to 6 hours;

[0019] Preferably, the pH value of the polyaniline is 6-8.

[0020] According to the preparation method of the present invention, the post-treatment step includes cooling the condensation product to 20-30° C. to dissolve unreacted p-nitrotoluene o-sulfonic acid or 2-methyl-5-nitrobenzoic acid to obtain a black direct dye.

[0021] The present invention also provides a black direct dye, which is prepared according to the preparation method of the present invention.

[0022] The present invention also provides use of the black direct dye according to the present invention for dyeing or printing paper fibers.

[0023] Effects of the Invention

[0024] The preparation method of the black direct dye of the present invention is simple and easy to implement, has little three wastes in the production process, and is environmentally friendly. The black direct dye prepared by the preparation method of the present invention has bright color, good water solubility, high dye uptake, and excellent dyeing performance. DETAILED DESCRIPTION

[0025] Various exemplary embodiments, features, and aspects of the present invention will be described in detail below. The word "exemplary" is used herein to mean "serving as an example, embodiment, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as superior or preferred over other embodiments.

[0026] In addition, numerous specific details are provided in the following detailed description to better illustrate the present invention. Those skilled in the art will appreciate that the present invention can be practiced without certain specific details. In other instances, methods, means, equipment, and steps well known to those skilled in the art are not described in detail in order to highlight the main points of the present invention.

[0027] Unless otherwise stated, the units used in this specification are international standard units, and the numerical values and numerical ranges appearing in the present invention should be understood to include the inevitable systematic errors in industrial production.

[0028] In this specification, the use of "may" includes both the meaning of performing a certain process and the meaning of not performing a certain process.

[0029] In this specification, references to "some specific / preferred embodiments," "other specific / preferred embodiments," "embodiments," etc., mean that the specific elements (e.g., features, structures, properties, and / or characteristics) described in connection with the embodiments are included in at least one embodiment described herein, and may or may not be present in other embodiments. In addition, it should be understood that the elements may be combined in various embodiments in any suitable manner.

[0030] In this specification, the numerical range represented by "value A to value B" refers to a range including the endpoint values A and B. The present invention provides a method for preparing a black direct dye according to the first aspect of the present invention, which comprises the following steps:

[0031] The steps of obtaining polyaniline are as follows: using an oxidant to oxidatively polymerize aniline hydrochloride to obtain polyaniline;

[0032] The step of obtaining a condensation product comprises: subjecting polyaniline to a condensation reaction with p-nitrotoluene o-sulfonic acid and / or 2-methyl-5-nitrobenzoic acid to obtain a condensation product;

[0033] Post-processing step: post-processing the condensation product to obtain a black direct dye.

[0034] The preparation method of the black direct dye of the invention is simple, has little three wastes in the production process, and is environmentally friendly.

[0035] Steps to obtain polyaniline

[0036] The invention uses an oxidant to oxidatively polymerize aniline hydrochloride to obtain polyaniline.

[0037] Specifically, an oxidizing agent is mixed with an aniline hydrochloride solution to conduct an oxidative polymerization reaction. In the present invention, the aniline hydrochloride solution is a solution obtained by reacting a hydrochloric acid solution with aniline. Specifically, polyaniline can be prepared by mixing aniline monomer, hydrochloric acid, and a solvent to obtain an aniline hydrochloride solution. The amount of solvent used is not particularly limited in the present invention and can be added as needed.

[0038] The amount of hydrochloric acid used is 1.5-4 times the mass of aniline, for example, 1.8 times, 2 times, 2.2 times, 2.5 times, 2.8 times, 3 times, 3.2 times, 3.5 times, 3.8 times, etc. In the presence of hydrochloric acid, aniline is protonated to form aniline cations, which is a necessary process for subsequent oxidation to form cationic free radicals.

[0039] Furthermore, the amount of the oxidant is 2-4 times the mass of aniline, for example, 2.2 times, 2.5 times, 2.8 times, 3 times, 3.2 times, 3.5 times, 3.8 times, etc.; in the presence of the oxidant, the aniline cation is oxidized to generate aniline cation radicals, the two aniline cation radicals couple to form a dimer, and the dimer is subsequently further oxidized to generate polyaniline with a higher degree of polymerization.

[0040] Furthermore, in order to facilitate the oxidative polymerization reaction, the oxidant may be pre-dissolved in a solvent and then mixed with the aniline hydrochloride solution. The concentration of the oxidant in the solvent is not particularly limited and may be selected as needed.

[0041] In some specific embodiments, the temperature of the oxidative polymerization reaction is 25-40°C, for example: 28°C, 30°C, 32°C, 35°C, 38°C, etc.; the time of the oxidative polymerization reaction is 3-5 hours, for example: 3.2 hours, 3.5 hours, 3.8 hours, 4 hours, 4.2 hours, 4.5 hours, 4.8 hours, etc.

[0042] Specifically, the oxidant includes one or a combination of two or more of potassium persulfate, sodium persulfate, hydrogen peroxide, potassium dichromate, hydrogen persulfate, etc.

[0043] In some specific embodiments, the time for adding the oxidant to the aniline hydrochloride solution is 1.5 to 2 hours, for example, 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours, etc.; preferably, the temperature of mixing the oxidant and the aniline hydrochloride solution is 5 to 10°C, for example, 6°C, 7°C, 8°C, 9°C, etc., and then after 2-3 hours, for example, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours, etc., the temperature is raised to 25 to 40°C for oxidative polymerization reaction.

[0044] In the present invention, when the temperature of mixing the oxidant and the aniline hydrochloride solution is 5-10° C., the reaction is mild and controllable, with fewer side reactions. At the same time, the polyaniline obtained under low temperature conditions has a uniform structure and can subsequently participate in a condensation reaction to obtain a black direct dye with excellent quality.

[0045] Steps for obtaining condensation products

[0046] The polyaniline is subjected to a condensation reaction with p-nitrotoluene o-sulfonic acid and / or 2-methyl-5-nitrobenzoic acid to obtain a condensation product.

[0047] In some specific embodiments, the p-nitrotoluene o-sulfonic acid and / or 2-methyl-5-nitrobenzoic acid are dehydrated to obtain molten p-nitrotoluene o-sulfonic acid and / or 2-methyl-5-nitrobenzoic acid. The molten p-nitrotoluene o-sulfonic acid and 2-methyl-5-nitrobenzoic acid obtained after dehydration have higher activity and higher concentration, which can improve the reaction rate and efficiency during the reaction process. Dehydration also makes the reaction environment conditions controllable and reduces the production of by-products.

[0048] Specifically, the temperature of the dehydration treatment is 100-160°C, for example, 110°C, 120°C, 130°C, 140°C, 150°C, etc.; the time of the dehydration treatment is 1-3 hours, for example: 1.2 hours, 1.5 hours, 1.8 hours, 2 hours, 2.2 hours, 2.5 hours, 2.8 hours, etc.

[0049] In some specific embodiments, the condensation reaction temperature is 100-230°C, for example, 120°C, 150°C, 180°C, 200°C, 220°C, etc.; the condensation reaction time is 4-6 hours, for example, 4.2 hours, 4.5 hours, 4.8 hours, 5 hours, 5.2 hours, 5.5 hours, 5.8 hours, etc. In addition, in the present invention, the amount of p-nitrotoluene o-sulfonic acid is not particularly limited and can be adjusted according to the needs of the reaction. Generally, the mass ratio of aniline to p-nitrotoluene o-sulfonic acid is 1:5-1:6, for example, 1:5.2, 1:5.4, 1:5.6, 1:5.8, etc.

[0050] Furthermore, the pH value of the polyaniline is 6 to 8, such as 6.5, 7, 7.5, etc. When the pH value of polyaniline is 6 to 8, the molecular structure of polyaniline is stable and the reaction activity is stable, which avoids excessive reaction activity due to excessive acidity and inactivation due to excessive alkalinity, thereby improving the purity of the product.

[0051] Post-processing steps

[0052] The present invention obtains the black direct dye of the present invention through post-treatment.

[0053] In some specific embodiments, the post-treatment step includes cooling the condensation product to 20-30°C, for example, 22°C, 24°C, 26°C, 28°C, etc.; dissolving unreacted p-nitrotoluene o-sulfonic acid or 2-methyl-5-nitrobenzoic acid to obtain a black direct dye.

[0054] By cooling the condensation product to 20-30°C, unreacted p-nitrotoluene o-sulfonic acid or 2-methyl-5-nitrobenzoic acid can be dissolved. A black direct dye can then be obtained through solid-liquid separation. Furthermore, the dissolved p-nitrotoluene o-sulfonic acid / 2-methyl-5-nitrobenzoic acid can be dried and reused in the condensation reaction.

[0055] <Second Aspect>

[0056] The second aspect of the present invention provides a black direct dye. In the present invention, the black direct dye is prepared by the above-mentioned preparation method.

[0057] The black direct dye of the invention has bright color, good water solubility, high dye uptake and excellent dyeing performance.

[0058] <Third Aspect>

[0059] The third aspect of the present invention provides a use of the black direct dye according to the second aspect of the present invention for dyeing or printing paper fibers.

[0060] Example

[0061] The embodiments of the present invention will be described in detail below with reference to the examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present invention and should not be construed as limiting the scope of the invention. Where specific conditions are not specified in the examples, the methods were performed according to conventional conditions or the conditions recommended by the manufacturer. Where the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be obtained commercially.

[0062] Example 1

[0063] (1) Place 10 g of aniline, 100 g of water, and 30 g of dilute hydrochloric acid in a beaker and stir until the aniline is completely dissolved. Then cool the system to 5°C to obtain an aniline hydrochloride solution for later use. Dissolve 20 g of potassium persulfate in 100 g of water and add the solution dropwise to the aniline solution over 1.5 hours. After the addition is complete, heat the system to 25°C within 2 hours. After heating, keep the temperature for 3 hours until the reaction reaches the end point, thereby obtaining polyaniline.

[0064] (2) 50 g of p-nitrotoluene o-sulfonic acid was placed in a three-necked flask, stirring was started, and the system was heated to 160° C. and kept warm for 2 hours until it was in a molten state; the polyaniline obtained in (1) was filtered and washed with water until the pH of the system was about 7, and then added to p-nitrotoluene o-sulfonic acid, the system was heated to 200° C., and the reaction was kept warm for 4 hours until the reaction reached the end point to obtain a condensation product.

[0065] (3) The condensation product obtained in (2) was kept at 20°C for 1 hour to dissolve the incompletely reacted p-nitrotoluene o-sulfonic acid in (2). After the reaction, the condensation product was filtered and spray-dried to obtain a black direct dye, which was recorded as S1.

[0066] Example 2

[0067] (1) Place 10 g of aniline, 100 g of water, and 30 g of dilute hydrochloric acid in a beaker and stir until the aniline is completely dissolved. Then cool the system to 8°C to obtain an aniline hydrochloride solution for later use. Dissolve 20 g of potassium persulfate in 100 g of water and add the solution to the aniline hydrochloride solution over a 1.5 hour dropwise addition period. After the addition is complete, heat the system to 25°C within 2.5 hours. After heating, heat the system for 3 hours until the reaction reaches the endpoint, thereby obtaining polyaniline.

[0068] (2) 55 g of 2-methyl-5-nitrobenzoic acid was placed in a three-necked flask, stirred, and the system was heated to 100° C. and kept warm for 2 hours until it was in a molten state; the polyaniline obtained in (1) was filtered and washed with water until the pH of the system was about 7, and then added to the 2-methyl-5-nitrobenzoic acid and the system was heated to 180° C. and kept warm for 4 hours until the reaction reached the end point to obtain a condensation product.

[0069] (3) The condensation product obtained in (2) was kept at 20°C for 1 hour to dissolve the unreacted 2-methyl-5-nitrobenzoic acid in (2). After the reaction, the condensation product was filtered and spray-dried to obtain a black direct dye, which was recorded as S2.

[0070] Example 3

[0071] (1) Place 10 g of aniline, 100 g of water, and 30 g of dilute hydrochloric acid in a beaker and stir until the aniline is completely dissolved. Then cool the system to 5°C to obtain an aniline hydrochloride solution for later use. Dissolve 20 g of potassium persulfate in 100 g of water and add the solution dropwise to the aniline solution over 1.5 hours. After the addition is complete, heat the system to 40°C within 3 hours. After heating, keep the temperature for 4 hours until the reaction reaches the end point, thereby obtaining polyaniline.

[0072] (2) 50 g of p-nitrotoluene o-sulfonic acid was placed in a three-necked flask, stirring was started, and the system was heated to 150° C. and kept warm for 2 hours until it was in a molten state; the polyaniline obtained in (1) was filtered and washed with water until the pH of the system was about 7, and then added to p-nitrotoluene o-sulfonic acid, and the system was heated to 230° C. and kept warm for 4 hours until the reaction reached the end point to obtain a condensation product.

[0073] (3) The condensation product obtained in (2) was kept at 25°C for 1 hour to dissolve the incompletely reacted p-nitrotoluene o-sulfonic acid in (2). After the reaction, the condensation product was filtered and spray-dried to obtain a black direct dye, which was recorded as S3.

[0074] Example 4

[0075] (1) Place 10 g of aniline, 100 g of water, and 30 g of dilute hydrochloric acid in a beaker and stir until the aniline is completely dissolved. Then cool the system to 10°C to obtain an aniline hydrochloride solution for later use. Dissolve 20 g of potassium persulfate in 100 g of water and add the solution to the aniline hydrochloride solution over a 2-hour dropwise addition period. After the addition is complete, heat the system to 40°C within 2.5 hours. After heating, heat the system for 4.5 hours until the reaction reaches the endpoint, thereby obtaining polyaniline.

[0076] (2) 55 g of 2-methyl-5-nitrobenzoic acid was placed in a three-necked flask, stirred, and the system was heated to 120° C. and kept warm for 2 hours until it was molten. The polyaniline obtained in (1) was filtered and washed with water until the pH of the system was about 7. The polyaniline was then added to the 2-methyl-5-nitrobenzoic acid and the system was heated to 180° C. The reaction was kept warm for 4 hours until the reaction reached the end point to obtain a condensation product.

[0077] (3) The condensation product obtained in (2) was kept at 25°C for 1 hour to dissolve the unreacted 2-methyl-5-nitrobenzoic acid in (2). After the reaction, the condensation product was filtered and spray-dried to obtain a black direct dye, which was recorded as S4.

[0078] Example 5

[0079] (1) Place 10 g of aniline, 100 g of water, and 30 g of dilute hydrochloric acid in a beaker and stir until the aniline is completely dissolved. Then cool the system to 5°C to obtain an aniline hydrochloride solution for later use. Dissolve 20 g of potassium persulfate in 100 g of water and add the solution dropwise to the aniline solution over 1.5 hours. After the addition is complete, heat the system to 30°C within 3 hours. After heating, keep the temperature for 5 hours until the reaction reaches the end point, thereby obtaining polyaniline.

[0080] (2) 55 g of p-nitrotoluene o-sulfonic acid was placed in a three-necked flask, stirred and heated to 160° C. for 2 hours until the flask was melted. The polyaniline obtained in (1) was filtered and washed with water until the pH of the system was neutral. The polyaniline was then added to the p-nitrotoluene o-sulfonic acid and the system was heated to 230° C. The reaction was carried out at this temperature for 4 hours until the reaction reached the end point to obtain a condensation product.

[0081] (3) The condensation product obtained in (2) was kept at 30°C for 1 hour to dissolve the incompletely reacted p-nitrotoluene o-sulfonic acid in (2). After the reaction, the condensation product was filtered and spray-dried to obtain a black direct dye, which was recorded as S5.

[0082] Example 6

[0083] (1) Place 10 g of aniline, 100 g of water, and 30 g of dilute hydrochloric acid in a beaker and stir until the aniline is completely dissolved. Then cool the system to 10°C to obtain an aniline hydrochloride solution for later use. Dissolve 20 g of potassium persulfate in 100 g of water and add the solution to the aniline hydrochloride solution over a 2-hour dropwise addition period. After the addition is complete, heat the system to 40°C within 2 hours. After heating, heat the mixture for 3.5 hours until the reaction reaches the endpoint, thereby obtaining polyaniline.

[0084] (2) 60 g of 2-methyl-5-nitrobenzoic acid was placed in a three-necked flask, stirred, and the system was heated to 120° C. and kept warm for 2 hours until it was molten. The polyaniline obtained in (1) was filtered and washed with water until the pH of the system was neutral. The polyaniline was then added to the 2-methyl-5-nitrobenzoic acid and the system was heated to 200° C. The reaction was kept warm for 4 hours until the reaction reached the end point to obtain a condensation product.

[0085] (3) The condensation product obtained in (2) was kept at 30°C for 1 hour to dissolve the unreacted 2-methyl-5-nitrobenzoic acid in (2). After the reaction, the condensation product was filtered and spray-dried to obtain a black direct dye, which was recorded as S6.

[0086] Comparative Example 1

[0087] The preparation method of Comparative Example 1 refers to the method disclosed in Chinese Patent CN 108485306A, and the specific preparation process is as follows:

[0088] (1) Place 80 g of aniline, 5 g of ferric chloride, and 2 g of potassium ferrate in a 500 ml four-necked flask. Stir and heat to 40°C. Then slowly add 50 g of 30 w% hydrochloric acid dropwise over 2 hours. After the addition is complete, heat to 120°C and maintain the reaction at this temperature. Stop heating when water droplets condense on the flask wall, indicating the end point of the reaction.

[0089] (2) 96 g of nitrobenzene and 4 g of polyethylene glycol were added to the above reaction system, stirred evenly, and then heated to 200° C., kept at this temperature for 4 hours, and then cooled to 70° C. 160 g of dimethylacetamide was added to the reaction system, and the temperature was lowered to 25° C. while stirring. The reaction system was then filtered, washed with hot water, and dried to obtain the finished product of Solvent Black 7 dye, which was recorded as D1.

[0090] Comparative Example 2

[0091] The preparation method of Comparative Example 2 refers to the method disclosed in Chinese Patent CN 101580650A, and the specific preparation conditions are as follows:

[0092] (1) Add 100g of bottom water to a beaker and then add 33.5g of sodium nitrite. Stir until completely dissolved to obtain a sodium nitrite solution, which is then allowed to stand for use. Add 300g of bottom water to a three-necked flask and then add 65g of 4,4'-diaminodiphenylamine-2-sulfonic acid. Start stirring and add 60g of hydrochloric acid. After stirring for 1 hour, add 300g of ice-water mixture to cool the mixture. Slowly drop the sodium nitrite solution in, ensuring that the system temperature is 3°C during the addition process. After the addition is complete, maintain the system temperature at 5°C for 1.5 hours. After the reaction is complete, a primary diazo product is obtained.

[0093] (2) Dissolve 102 g of gamma acid in 700 g of water, stir for 1 hour, and then adjust the pH of the system to 8.0 with a 30% by mass alkali solution to obtain a gamma acid solution. Cool the gamma acid solution to 5°C, add the primary diazo product dropwise to the gamma acid solution, and after the addition is complete, adjust the pH of the system to 8 with a 30% by mass alkali solution. Maintain the system temperature at 0°C and react for 8 hours. After the reaction is complete, obtain the primary coupling product.

[0094] (3) Add 100 g of bottom water to a beaker and then add 31 g of sodium nitrite. Stir until completely dissolved to obtain a sodium nitrite solution, which is then allowed to stand for later use. Add 260 g of a 30% hydrochloric acid solution to the primary coupling product, stir evenly, then cool the system to 0°C and dropwise add the obtained sodium nitrite solution. After the addition is complete, keep the temperature at 0°C and react for 2 hours to obtain a secondary diazo product.

[0095] (4) Put 300g of bottom water in a beaker, add 40g of m-phenylenediamine and stir until it is completely dissolved to obtain a m-phenylenediamine solution. Use a 30% by mass liquid alkali solution to adjust the pH of the system to 8, and cool the system to 20°C for use. Turn on the stirring, add the secondary diazo product obtained in (3) to the m-phenylenediamine solution for coupling reaction, and after the addition, keep the pH of the system at 7 and the temperature at 10°C for 4h. After the reaction, a black direct dye solution is obtained. The black direct dye solution is directly spray-dried to obtain a black direct dye product, which is recorded as D2.

[0096] Dyeing method

[0097] Take 1g each of the black direct dyes obtained in Example 1-6 and Comparative Example 1-2, 20g of paper, and 4g of alum, add them into 100g of water, stir evenly and keep for 1 hour, then make paper and set it.

[0098] Performance Testing

[0099] The dried dyed paper was taken to measure its dry rubbing resistance, sunlight fastness, ultraviolet color fastness and solubility. The method used was based on GB / T 31479-2015, and the dye uptake was detected by spectrophotometry. The chromaticity value was detected by a colorimeter. At the same time, 50 g of the dyed wastewater was taken to measure the Abs value and COD value of the foot water. The methods used were UV-visible spectrophotometry (wavelength 380 nm to 750 nm) and GB11914-89 chemical oxygen demand-dichromate method, respectively. The properties of the black direct dyes prepared in Examples 1-6 and Comparative Examples 1-2 are shown in Table 1 below:

[0100] Table 1

[0101]

[0102] Note: / indicates not detected

[0103] As can be seen from Table 1, the solubility of the black direct dyes prepared in Examples 1-6 is better than that in Comparative Example 1, indicating that the black direct dyes in Examples 1-6 have good water solubility. At the same time, the dye uptake in the examples is higher than that in the comparative example, indicating that the black direct dyes in the examples have a higher and stronger bond with the paper and paper fibers, which can reduce dye waste during the dyeing process, improve utilization rate, and save use costs.

[0104] In terms of chromaticity, the dyes in Examples 1-6 have higher L*, a*, and b* than the dyes in Comparative Examples 1-2, indicating that the dyes in the examples have brighter color and a reddish-yellow hue. When combined with other dyes, they can make up for the lack of red and yellow wavelengths and have a wider range of applications.

[0105] In terms of dyeing performance, the dry abrasion resistance, sunlight resistance and UV resistance of the dyes in Examples 1-6 are better than those in the comparative examples, indicating that the dyes prepared in the examples have better dyeing performance; at the same time, in terms of wastewater, the foot water ABS and foot water COD of the products in Examples 1-6 and Comparative Example 2 were not detected, while both were still present in Comparative Example 1, proving that the dyes prepared by this method have no pollutant residues in the wastewater after dyeing, saving wastewater treatment costs for downstream manufacturers and reducing environmental pollution.

[0106] Therefore, the black direct dye of the present invention improves various properties of the dye while also reducing production wastewater, thereby protecting the environment and facilitating clean and green production.

[0107] It should be noted that, although the technical solutions of the present invention are described with specific examples, those skilled in the art will appreciate that the present invention should not be limited thereto.

[0108] While various embodiments of the present invention have been described above, the above descriptions are intended to be illustrative, non-exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is selected to best explain the principles of the embodiments, their practical applications, or technological improvements in the marketplace, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for preparing a black direct dye, characterized in that: The following steps are involved: The steps of obtaining polyaniline are as follows: using an oxidant to oxidatively polymerize aniline hydrochloride to obtain polyaniline; The step of obtaining a condensation product comprises: subjecting polyaniline to a condensation reaction with p-nitrotoluene o-sulfonic acid and / or 2-methyl-5-nitrobenzoic acid to obtain a condensation product; Post-processing step: post-processing the condensation product to obtain a black direct dye.

2. The preparation method according to claim 1, characterized in that The step of obtaining polyaniline comprises: mixing an oxidant with an aniline hydrochloride solution and then performing an oxidative polymerization reaction.

3. The preparation method according to claim 2, characterized in that The temperature of the oxidative polymerization reaction is 25 to 40° C., and the time of the oxidative polymerization reaction is 3 to 5 hours.

4. The preparation method according to claim 2 or 3, characterized in that The oxidant includes one or a combination of two or more of potassium persulfate, sodium persulfate, hydrogen peroxide, potassium dichromate, and hydrogen persulfate; preferably, the aniline hydrochloride solution is a solution obtained by reacting hydrochloric acid solution with aniline.

5. The preparation method according to any one of claims 2 to 4, characterized in that The time for adding the oxidant to the aniline hydrochloride solution is 1.5 to 2 hours; preferably, the temperature of mixing the oxidant and the aniline hydrochloride solution is 5 to 10° C., and then the temperature is raised to 25 to 40° C. over 2-3 hours to carry out oxidative polymerization reaction.

6. The preparation method according to any one of claims 1 to 5, characterized in that The p-nitrotoluene o-sulfonic acid and / or 2-methyl-5-nitrobenzoic acid are subjected to a dehydration treatment to obtain molten p-nitrotoluene o-sulfonic acid and / or 2-methyl-5-nitrobenzoic acid; preferably, the dehydration treatment temperature is 100-160° C., and the dehydration treatment time is 1-3 hours.

7. The preparation method according to any one of claims 1 to 6, characterized in that The condensation reaction temperature is 100 to 230° C., and the condensation reaction time is 4 to 6 hours; Preferably, the pH value of the polyaniline is 6-8.

8. The preparation method according to any one of claims 1 to 6, characterized in that The post-treatment step comprises cooling the condensation product to 20-30° C. to dissolve unreacted p-nitrotoluene o-sulfonic acid or 2-methyl-5-nitrobenzoic acid, thereby obtaining a black direct dye.

9. A black direct dye, characterized in that Prepared according to the preparation method according to any one of claims 1 to 8.

10. Use of the black direct dye according to claim 9 for dyeing or printing paper fibers.

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