Flame retardants for water-based fire-retardant coatings for steel structures and water-based fire-retardant coatings for steel structures

Abstract

This invention provides a flame retardant for water-based fire-retardant coatings for steel structures, prepared from the following raw materials: urea, phosphoric acid, acidic lignin, and pentaerythritol; the weight ratio of urea, phosphoric acid, acidic lignin, and pentaerythritol is 1:(0.8-1):(0.1-0.5):(0.01-0.05). Applying this flame retardant to water-based fire-retardant coatings for steel structures achieves both moisture resistance and flame retardancy.

Description

Technical Field

[0001] This invention relates to the field of coatings, and in particular to flame retardants for water-based fire-retardant coatings for steel structures, water-based fire-retardant coatings for steel structures, and methods for their preparation. Background Technology

[0002] Currently, ammonium polyphosphate, melamine, and pentaerythritol are the most commonly used flame-retardant systems in water-based fire-retardant coatings for steel structures. However, these systems struggle to achieve the ideal fire resistance rating for steel structures and are prone to moisture absorption, which is detrimental to the corrosion resistance of steel materials. Therefore, developing flame retardants for water-based fire-retardant coatings for steel structures that offer ideal flame retardancy and are non-hygroscopic or have low moisture absorption is of significant social and economic importance. Summary of the Invention

[0003] The purpose of this invention is to provide a flame retardant for water-based fireproof coatings for steel structures. Applying the flame retardant to water-based fireproof coatings for steel structures can achieve the effects of being non-hygroscopic and flame retardant.

[0004] To achieve the above objectives, the technical solution of the present invention is as follows:

[0005] This invention provides a flame retardant for water-based fireproof coatings for steel structures, which is prepared from the following raw materials: urea, phosphoric acid, acidic lignin, and pentaerythritol.

[0006] Optionally, the weight ratio of urea, phosphoric acid, acid lignin, and pentaerythritol is 1:(0.8-1):(0.1-0.5):(0.01-0.05).

[0007] Optionally, the acidic lignin is obtained by the following steps: boiling and stirring crude acidic lignin in hot water, filtering and washing while hot, and drying to obtain the acidic lignin;

[0008] The ratio of crude acidic lignin to water is (0-10)g:100ml.

[0009] Optional steps include the following:

[0010] Step 1: Add phosphoric acid and urea to the reactor, stir and heat. After the urea is completely dissolved, add acidic lignin and pentaerythritol, stir, and add defoamer.

[0011] Step 2: While stirring, heat to 95-115℃ and react, keep the temperature constant until bubbles are produced, then stop the reaction;

[0012] Step 3: Transfer the product obtained in Step 2 into a ceramic container and react at 190-220℃ for 3-5 hours to obtain the flame retardant for water-based fireproof coatings for steel structures.

[0013] The present invention also provides a water-based fireproof coating for steel structures, which is prepared from the following raw materials in parts by weight: 15-35 parts of flame retardant for water-based fireproof coatings for steel structures as described in any of claims 1-3, 20-30 parts of water, 25-35 parts of styrene-acrylic emulsion, 0.1-0.4 parts of thickener, 0.4-1 parts of dispersant, 5-15 parts of lignin maleate, 3-10 parts of expandable graphite, 3-10 parts of hollow glass microspheres, and 5-20 parts of inorganic filler.

[0014] Optionally, the preparation method of the styrene-acrylic emulsion includes the following steps:

[0015] (1) Monomer purification: Styrene and butyl acrylate were purified separately to obtain purified styrene / butyl acrylate.

[0016] (2) Solution preparation:

[0017] First component: Add emulsifier NP-40, sodium dodecyl sulfate and deionized water to the first container in sequence, stir until completely dissolved, let stand to defoam, and obtain the first component;

[0018] Second component: Add purified styrene, purified butyl acrylate, and part of the first component to the second container in sequence, and stir until no layering occurs to obtain the second component;

[0019] Third component: Add lignin maleate, acrylic acid, and the remaining first component to the third container in sequence, and then perform ultrasonic treatment. The ultrasonic treatment needs to be repeated 3 times, and after each ultrasonic treatment, the particles on the wall of the third container need to be cleaned with a glass rod to obtain the third component.

[0020] The ultrasonic treatment is performed by placing the third container containing the mixture of lignin maleate, acrylic acid, and the first component into an ultrasonic vibrator and ultrasonically treating it for 1-3 minutes.

[0021] Fourth component: Add a portion of ammonium persulfate and an appropriate amount of deionized water to the fourth container in sequence to completely dissolve the solid and obtain the fourth component;

[0022] Fifth component: Add the remaining ammonium persulfate and an appropriate amount of deionized water to the fifth container in sequence to completely dissolve the solid and obtain the fifth component;

[0023] (3) Emulsion polymerization:

[0024] a. Install the four-necked flask, condenser, and stirring rod. Pour part of the third component directly into the reaction vessel, turn on the electric stirrer (electric stirring is carried out throughout the emulsion polymerization process), set the stirring speed to the first preset speed of 400 RPM, and heat up.

[0025] b. Once the temperature reaches the first preset temperature of 55-65℃, add part of the fourth component under constant temperature and continue to heat up;

[0026] c. Heat to the second preset temperature of 75-85℃, adjust the stirring speed to the second preset speed of 600RPM, and add the remaining third and fourth components dropwise using a dropping funnel. The third and fourth components are added dropwise within 0.8-1.2 hours.

[0027] d. After the third and fourth components are added, the reaction is kept at a constant temperature. Then, the second and fifth components are added dropwise using a dropping funnel. The second and fifth components are added dropwise over 1.8-2.2 hours. After the second and fifth components are added, the reaction is kept at a constant temperature for another 1.8-2.2 hours to obtain the reaction solution.

[0028] e. Stop the reaction, pour the reaction solution into the sixth container, add sodium hydroxide solution to adjust the pH to 8, and obtain the styrene-acrylic emulsion. The concentration of the sodium hydroxide solution added is 4.5-5.5 mol / L.

[0029] This invention also provides a method for preparing a water-based fire-retardant coating for steel structures, comprising the following steps:

[0030] Step 1: Mix the flame retardant, lignin maleate and inorganic filler for the water-based fireproof coating for steel structures in a high-speed mixer, and then ball mill the mixture at high speed in a ball mill to obtain a pulverizing aid.

[0031] Step 2: Add water, styrene-acrylic emulsion, thickener, dispersant, pulverizing aid, expandable graphite, and hollow glass microspheres to a container in sequence, and stir at a uniform speed for 30-60 minutes to obtain the water-based fireproof coating for steel structures.

[0032] Optionally, before ball milling, the particle size of the mixture is controlled by the following process: the ratio of large balls, medium balls, and small balls is 1:6:20;

[0033] The ball milling time is 3-6 hours, and the rotation speed is 400-600 rpm.

[0034] Optionally, the particle size of the mixture of flame retardant, lignin maleate and inorganic filler in the ball-milled water-based fireproof coating for steel structures is 2-15 micrometers, preferably 5-10 micrometers.

[0035] Optionally, the lignin maleate is prepared by the following steps:

[0036] First, add ethylene glycol dimethyl ether to the first container containing a thermometer and a condenser, heat it to the preset temperature, and stir.

[0037] The second step involves sequentially adding acidic lignin and maleic anhydride to the ethylene glycol dimethyl ether. When the temperature inside the first container reaches the preset temperature, the reaction proceeds for 5-7 hours.

[0038] The third step is to cool the reaction solution to room temperature and pour it into a second container containing deionized water, thereby precipitating a solid.

[0039] The fourth step involves solid filtration, followed by washing with water until the pH of the filtrate reaches 5-6, and then drying to obtain the lignin maleate.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] 1. This invention provides a flame retardant for water-based fireproof coatings for steel structures. Applying the flame retardant to water-based fireproof coatings for steel structures can achieve the effects of being non-hygroscopic and flame retardant.

[0042] 2. Lignin is a renewable biomass material with excellent char-forming ability. In this invention, acidic lignin and pentaerythritol are used as the char source, phosphoric acid as the acid source, and urea as the gas source. These are chemically combined to prepare a carbon-phosphorus-nitrogen ternary synergistic intumescent flame retardant with high flame retardant efficiency and low moisture absorption.

[0043] 3. Lignin maleate, as a substitute for pentaerythritol, offers better charring performance and is less hygroscopic. Containing both benzene rings and maleic acid, lignin maleate promotes the dispersion of flame retardants in styrene-acrylic acid emulsions, acting as a compatibilizer. Its three-dimensional structure and numerous polar groups further enhance the dispersion of hollow glass microspheres in coatings, resulting in superior flame retardant performance.

[0044] 4. Expandable graphite can increase the expansion coefficient of the carbon layer, and hollow glass microspheres can delay heat conduction. When used in combination with flame retardants, they can play a synergistic and synergistic role, which can greatly improve the fire resistance time of steel structures.

[0045] 5. Since the acidic lignin used in this invention is derived from waste materials in the papermaking industry, it is widely available and inexpensive. Therefore, its introduction can reduce the cost of water-based fire-retardant coatings for steel structures and realize the high-value application of lignin, resulting in significant socio-economic benefits.

[0046] 6. This water-based fireproof coating for steel structures incorporates lignin and chemically integrated flame retardants, giving it superior fire resistance as well as better water resistance and environmental friendliness.

[0047] 7. Traditional fire-retardant coatings use a physical mixture of ammonium polyphosphate, melamine, and pentaerythritol, which is prone to moisture absorption. In this invention, urea, phosphoric acid, acidic lignin, and pentaerythritol undergo a chemical reaction to generate a flame retardant for water-based fire-retardant coatings for steel structures. The hydroxyl groups are reacted, making the coating less hygroscopic and less prone to rusting. This invention uses a flame retardant for water-based fire-retardant coatings for steel structures instead of ammonium polyphosphate and melamine, and lignin maleate instead of pentaerythritol. Lignin maleate can serve as a carbon source and also aids in dispersion.

[0048] 8. The ball milling process used in the embodiments of the present invention employs large, medium, and small balls with specific particle sizes. Through extensive experiments, the inventors discovered that using three different types of balls with different particle sizes, in a ratio of 1:6:20 for large, medium, and small balls, can reduce the gap between the balls. By using the optimal ratio, the finest particles can be obtained in the shortest ball milling time. Attached Figure Description

[0049] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0050] Figure 1 Photograph of the water-based fireproof coating for steel structures prepared in Example 1 of this invention;

[0051] Figure 2 Photograph of the water-based fireproof coating for steel structures prepared in Example 2 of this invention;

[0052] Figure 3 This is a photograph of the water-based fireproof coating for steel structures prepared in Example 3 of the present invention. Detailed Implementation

[0053] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] Embodiments of the present invention:

[0055] Embodiment 1 of the present invention provides a method for preparing acidic lignin, wherein crude acidic lignin is stirred in hot water at 70-90°C for 1-2 hours, filtered while hot, washed, and dried to obtain acidic lignin;

[0056] The ratio of crude acidic lignin to water is (0-10)g:100ml.

[0057] Embodiment 2 of the present invention provides a flame retardant for water-based fireproof coatings for steel structures, which is prepared from the following raw materials: urea, phosphoric acid, acidic lignin, and pentaerythritol. The weight ratio of urea, phosphoric acid, acidic lignin, and pentaerythritol is 1:(0.8-1):(0.1-0.5):(0.01-0.05).

[0058] Embodiment 3 of the present invention provides a method for preparing a flame retardant for a water-based fire-retardant coating for steel structures, comprising the following steps:

[0059] a. Stir the crude acidic lignin in hot water at 70-90℃ for 1-2 hours, filter while hot, wash, and dry to obtain acidic lignin;

[0060] The ratio of crude acidic lignin to water is (0-10) g: 100 ml;

[0061] b. Add phosphoric acid and urea to the reactor (a reaction vessel can be used in this embodiment of the invention), and heat to 55-65°C while stirring at low speed. After the urea is completely dissolved, add acidic lignin and pentaerythritol; after stirring, add an appropriate amount of defoamer; in this embodiment of the invention, dimethyl silicone oil is used as the defoamer;

[0062] In this embodiment of the invention, the high-speed mixer is divided into a low-speed setting and a high-speed setting. Low-speed mixing is simply adjusting the high-speed mixer to the low-speed setting.

[0063] c. While stirring, gradually increase the temperature to 95-115℃ and maintain the temperature until bubbles are produced, then stop the reaction.

[0064] d. Transfer the product obtained in step c into a ceramic container and react at 190-220℃ for 3-5 hours to obtain the flame retardant for water-based fireproof coatings for steel structures.

[0065] Embodiment 4 of the present invention also provides a water-based fireproof coating for steel structures, which is prepared from the following raw materials in parts by weight: 15-35 parts of flame retardant for water-based fireproof coating for steel structures, 20-30 parts of water, 25-35 parts of styrene-acrylic emulsion, 0.1-0.4 parts of thickener, 0.4-1 parts of dispersant, 5-15 parts of lignin maleate, 3-10 parts of expandable graphite, 3-10 parts of hollow glass microspheres, and 5-20 parts of inorganic filler.

[0066] The inorganic filler is conventional and includes calcium carbonate, talc, titanium dioxide, and barium sulfate.

[0067] Embodiment 5 of the present invention provides a method for preparing a water-based fire-retardant coating for steel structures, comprising the following steps:

[0068] Step 1: Preparation of lignin maleate;

[0069] The crude acidic lignin is stirred in hot water at 70-90℃ for 1-2 hours, filtered while hot, washed, and dried to obtain acidic lignin; the ratio of crude acidic lignin to water is (0-10)g:100ml.

[0070] Add 120-180 mL of ethylene glycol dimethyl ether to a three-necked flask equipped with a thermometer and a condenser. Heat the flask to a preset temperature (90-110°C) and stir. Then add 25-35 g of acidic lignin and 10-15 g of maleic anhydride. When the temperature inside the flask reaches the preset temperature, react for 5-7 hours. After the reaction is complete, there will be a black liquid and a black viscous solid in the flask. Cool the black liquid to room temperature and then pour it into a beaker containing 0.8-1.2 L of deionized water while stirring, so that a solid precipitates out. Filter the precipitated solid and wash it with water 2-3 times until the pH of the filtrate is 5-6. Dry the filtrate to obtain the lignin maleate ester.

[0071] Step 2: Mix the flame retardant, lignin maleate and inorganic filler for the water-based fireproof coating for steel structures in a high-speed mixer, and then ball mill the mixture at high speed for 3-6 hours at a speed of 400-600 rpm to obtain the pulverizing aid.

[0072] Before ball milling, the particle size of the mixture of flame retardant, lignin maleate and inorganic filler used in water-based fireproof coatings for steel structures is controlled by the following process: the ratio of large balls, medium balls and small balls is 1:6:20. In this embodiment of the invention, the particle size of large balls, medium balls and small balls are all in accordance with the national standard of the purchased ball mill.

[0073] After ball milling, the particle size of the mixture of flame retardant, lignin maleate and inorganic filler used in water-based fireproof coatings for steel structures is 2-15 micrometers, preferably 5-10 micrometers.

[0074] Step 3: Add water, styrene-acrylic emulsion, thickener, dispersant, pulverizing aid, expandable graphite, and hollow glass microspheres sequentially to a container, and stir at a uniform speed for 30-60 minutes to obtain the water-based fireproof coating for steel structures. The particle size of the hollow glass microspheres is 10-30 micrometers, preferably 15-25 micrometers.

[0075] The following provides specific embodiments.

[0076] Example 1

[0077] Preparation of flame retardants for water-based fire-retardant coatings for steel structures:

[0078] The crude acidic lignin was boiled in hot water at 80℃ for 1.5 hours, filtered while hot, washed, and dried to obtain purified acidic lignin; the concentration of crude acidic lignin in water was 5g / 100ml.

[0079] Phosphoric acid and urea are added to a reactor, the temperature is raised to 60°C, and the temperature is maintained until the solid melts. After 2 minutes, acidic lignin and pentaerythritol are added to the reactor. After stirring for 1 minute, an appropriate amount of dimethyl silicone oil is added. The temperature is raised to 95°C and maintained until small bubbles are generated. The reactants in the reactor are transferred to a ceramic container and the reaction is continued at 200°C for 4 hours. The reaction is stopped, and the mixture is cooled and pulverized to obtain a flame retardant for water-based fireproof coatings for steel structures. The weight ratio of phosphoric acid, urea, acidic lignin, and pentaerythritol is 1:1:0.2:0.05.

[0080] The water-based fireproof coating for steel structures is prepared from the following raw materials in parts by weight: 15 parts flame retardant, 20 parts water, 25 parts styrene-acrylic emulsion, 0.1 parts thickener, 0.4 parts dispersant, 5 parts lignin maleate, 3 parts expandable graphite, 3 parts hollow glass microspheres, and 5 parts inorganic filler.

[0081] Preparation of water-based fire-retardant coatings for steel structures:

[0082] Step 1: Prepare lignin maleate;

[0083] (1) Boil crude acidic lignin in hot water at 80℃ for 1.5 hours, filter while hot, wash and dry to obtain purified acidic lignin; the concentration of crude acidic lignin in water is 5g / 100ml.

[0084] (2) Add 150 mL of ethylene glycol dimethyl ether to a 250 mL three-necked flask equipped with a thermometer and a condenser, heat to the preset temperature (90 °C), stir, and add 30 g of acidic lignin and 12 g of maleic anhydride in sequence. When the temperature inside the flask reaches the preset temperature of 90 °C, react for 6 h. After the reaction is completed, cool the above reaction solution to room temperature, and then pour it into a beaker containing 1 L of deionized water while stirring, so that a solid is precipitated. Filter the precipitated solid, wash it with water twice until the pH of the filtrate is 5-6, and dry it to obtain the lignin maleate ester.

[0085] Step 2: Mix the flame retardant, lignin maleate and inorganic filler for the water-based fireproof coating for steel structures in a high-speed mixer, and then ball mill the mixture at high speed in a ball mill to obtain a pulverizing aid.

[0086] Before ball milling, the particle size of the mixture of flame retardant, lignin maleate and inorganic filler used in water-based fireproof coatings for steel structures is controlled by the following process: the ratio of large balls, medium balls and small balls is 1:6:20.

[0087] The ball milling time was 3 hours, and the rotation speed was 600 rpm.

[0088] After ball milling, the particle size of the mixture of flame retardant, lignin maleate and inorganic filler used in water-based fireproof coatings for steel structures, i.e. the pulverizing aid, is 5 micrometers.

[0089] Step 3: Add water, styrene-acrylic emulsion, thickener, dispersant, pulverizing aid, expandable graphite, and hollow glass microspheres sequentially to a container, and stir at a uniform speed for 30 minutes to obtain the water-based fireproof coating for steel structures. The hollow glass microspheres have a particle size of 15 micrometers.

[0090] Example 2

[0091] Preparation of flame retardants for water-based fire-retardant coatings for steel structures:

[0092] The crude acidic lignin was boiled in hot water at 90℃ for 1 hour, filtered while hot, washed, and dried to obtain purified acidic lignin; the concentration of crude acidic lignin in water was 10g / 100ml.

[0093] Phosphoric acid and urea are added to a reactor, the temperature is raised to 65°C, and the temperature is maintained until the solid melts. After 2 minutes, acidic lignin and pentaerythritol are added to the reactor. After stirring for 1 minute, an appropriate amount of dimethyl silicone oil is added. The temperature is raised to 100°C and maintained until small bubbles are generated. The reactants in the reactor are transferred to a ceramic container and the reaction is continued at 220°C for 3 hours. The reaction is stopped, and the mixture is cooled and pulverized to obtain a flame retardant for water-based fireproof coatings for steel structures. The weight ratio of phosphoric acid, urea, acidic lignin, and pentaerythritol is 0.8:1:0.1:0.01.

[0094] The water-based fireproof coating for steel structures is prepared from the following raw materials in parts by weight: 35 parts flame retardant, 30 parts water, 35 parts styrene-acrylic emulsion, 0.4 parts thickener, 1 part dispersant, 15 parts lignin maleate, 10 parts expandable graphite, 10 parts hollow glass microspheres, and 20 parts inorganic filler.

[0095] Preparation of water-based fire-retardant coatings for steel structures:

[0096] Step 1: Prepare lignin maleate;

[0097] (1) Boil crude acidic lignin in hot water at 90℃ for 1 hour, filter while hot, wash and dry to obtain purified acidic lignin; the concentration of crude acidic lignin in water is 10g / 100ml.

[0098] (2) Add 150 mL of ethylene glycol dimethyl ether to a 250 mL three-necked flask equipped with a thermometer and a condenser, heat to the preset temperature (90 °C), stir, and add 30 g of acidic lignin and 12 g of maleic anhydride in sequence. When the temperature inside the flask reaches the preset temperature of 90 °C, react for 6 h. After the reaction is completed, cool the above reaction solution to room temperature, and then pour it into a beaker containing 1 L of deionized water while stirring, so that a solid is precipitated. Filter the precipitated solid, wash it with water twice until the pH of the filtrate is 5-6, and dry it to obtain the lignin maleate ester.

[0099] Step 2: Mix the flame retardant, lignin maleate and inorganic filler for the water-based fireproof coating for steel structures in a high-speed mixer, and then ball mill the mixture at high speed in a ball mill to obtain a pulverizing aid.

[0100] Before ball milling, the particle size of the mixture of flame retardant, lignin maleate and inorganic filler used in water-based fireproof coatings for steel structures is controlled by the following process: the ratio of large balls, medium balls and small balls is 1:6:20.

[0101] The ball milling time was 6 hours, and the rotation speed was 400 rpm.

[0102] After ball milling, the particle size of the mixture of flame retardant, lignin maleate and inorganic filler used in water-based fireproof coatings for steel structures, i.e. the pulverizing aid, is 5 micrometers.

[0103] Step 3: Add water, styrene-acrylic emulsion, thickener, dispersant, pulverizing aid, expandable graphite, and hollow glass microspheres sequentially to a container, and stir at a uniform speed for 60 minutes to obtain the water-based fireproof coating for steel structures. The hollow glass microspheres have a particle size of 25 micrometers.

[0104] Example 3

[0105] Preparation of flame retardants for water-based fire-retardant coatings for steel structures:

[0106] The crude acidic lignin was boiled in hot water at 70℃ for 2 hours, filtered while hot, washed, and dried to obtain purified acidic lignin; the ratio of crude acidic lignin to water was 8g / 100ml.

[0107] Phosphoric acid and urea are added to a reactor, the temperature is raised to 55°C, and the temperature is maintained until the solid melts. After 2 minutes, acidic lignin and pentaerythritol are added to the reactor. After stirring for 1 minute, an appropriate amount of dimethyl silicone oil is added. The temperature is raised to 110°C and maintained until small bubbles are generated. The reactants in the reactor are transferred to a ceramic container and the reaction is continued at 190°C for 5 hours. The reaction is stopped, and the mixture is cooled and pulverized to obtain a flame retardant for water-based fireproof coatings for steel structures. The weight ratio of phosphoric acid, urea, acidic lignin, and pentaerythritol is 1 / 1 / 0.5 / 0.01.

[0108] The water-based fireproof coating for steel structures is prepared from the following raw materials in parts by weight: 25 parts flame retardant, 25 parts water, 30 parts styrene-acrylic emulsion, 0.2 parts thickener, 0.8 parts dispersant, 10 parts lignin maleate, 7 parts expandable graphite, 8 parts hollow glass microspheres, and 15 parts inorganic filler.

[0109] Preparation of water-based fire-retardant coatings for steel structures:

[0110] Step 1: Prepare lignin maleate;

[0111] (1) Boil crude acidic lignin in hot water at 70°C for 2 hours, filter while hot, wash and dry to obtain purified acidic lignin; the ratio of crude acidic lignin to water is 8g / 100ml.

[0112] (2) Add 150 mL of ethylene glycol dimethyl ether to a 250 mL three-necked flask equipped with a thermometer and a condenser, heat to the preset temperature (90 °C), stir, and add 30 g of acidic lignin and 12 g of maleic anhydride in sequence. When the temperature inside the flask reaches the preset temperature of 90 °C, react for 6 h. After the reaction is completed, cool the above reaction solution to room temperature, and then pour it into a beaker containing 1 L of deionized water while stirring, so that a solid is precipitated. Filter the precipitated solid, wash it with water twice until the pH of the filtrate is 5-6, and dry it to obtain the lignin maleate ester.

[0113] Step 2: Mix the flame retardant, lignin maleate and inorganic filler for the water-based fireproof coating for steel structures in a high-speed mixer, and then ball mill the mixture at high speed in a ball mill to obtain a pulverizing aid.

[0114] Before ball milling, the particle size of the mixture of flame retardant, lignin maleate and inorganic filler used in water-based fireproof coatings for steel structures is controlled by the following process: the ratio of large balls, medium balls and small balls is 1:6:20.

[0115] The ball milling time was 4 hours, and the rotation speed was 500 rpm.

[0116] After ball milling, the particle size of the mixture of flame retardant, lignin maleate and inorganic filler used in water-based fireproof coatings for steel structures, i.e. the pulverizing aid, is 5 micrometers.

[0117] Step 3: Add water, styrene-acrylic emulsion, thickener, dispersant, pulverizing aid, expandable graphite, and hollow glass microspheres sequentially to a container, and stir at a uniform speed for 40 minutes to obtain the water-based fireproof coating for steel structures. The hollow glass microspheres have a particle size of 20 micrometers.

[0118] Example 4

[0119] Examples 1-3 all used commercially available ordinary styrene-acrylic emulsions;

[0120] The only difference between Example 4 and Example 1 is that the styrene-acrylic emulsion in Example 1 is replaced with the styrene-acrylic emulsion prepared by the following method, and everything else is the same as in Example 1.

[0121] The preparation method of the styrene-acrylic emulsion in Example 4 can be as follows:

[0122] The instruments required for preparing styrene-acrylic emulsion in this embodiment of the invention are: stirrer, water bath, condenser, dropping funnel, 250mL three-necked flask, thermometer, beaker, glass rod, rubber stopper, glass stopper, and separatory funnel.

[0123] This invention provides a method for preparing a styrene-acrylic emulsion, comprising the following steps:

[0124] (1) Monomer purification: Styrene and butyl acrylate were purified separately to obtain purified styrene / butyl acrylate.

[0125] The styrene purification process specifically involves:

[0126] Styrene was washed once with a 10% sodium hydroxide solution in a separatory funnel, and the mixture was separated. The lower alkaline layer was discharged, and the upper liquid was the monomer.

[0127] Add an appropriate amount of deionized water to the upper liquid, then wash with water, separate the liquid, and release the lower wastewater. Repeat the water washing operation until the pH of the wastewater is 7-8 to obtain the purified styrene.

[0128] The purification of butyl acrylate specifically involves:

[0129] Wash butyl acrylate once with a 10% sodium hydroxide solution in a separatory funnel, separate the layers, release the lower alkaline solution, and the upper liquid is the monomer.

[0130] Add an appropriate amount of deionized water to the upper liquid, then wash with water, separate the liquid, and release the lower wastewater. Repeat the water washing operation until the pH of the wastewater is 7-8 to obtain the purified butyl acrylate.

[0131] (2) Solution preparation: (Theoretical solid content: 50%)

[0132] First component: Add emulsifier NP-40, sodium dodecyl sulfate and deionized water to the first container in sequence, stir until completely dissolved, let stand to defoam, and obtain the first component;

[0133] Second component: Add purified styrene, purified butyl acrylate, and part of the first component to the second container in sequence, and stir until no layering occurs to obtain the second component;

[0134] Third component: Add lignin maleate, acrylic acid, and the remaining first component to the third container in sequence, and then perform ultrasonic treatment. The ultrasonic treatment needs to be repeated 3 times, and after each ultrasonic treatment, the particles on the wall of the third container need to be cleaned with a glass rod to obtain the third component.

[0135] The ultrasonic treatment is performed by placing the third container containing the mixture of lignin maleate, acrylic acid, and the first component into an ultrasonic vibrator and ultrasonically treating it for 1-3 minutes.

[0136] Fourth component: Add a portion of ammonium persulfate and an appropriate amount of deionized water to the fourth container in sequence to completely dissolve the solid and obtain the fourth component;

[0137] Fifth component: Add the remaining ammonium persulfate and an appropriate amount of deionized water to the fifth container in sequence to completely dissolve the solid and obtain the fifth component;

[0138] (3) Emulsion polymerization:

[0139] a. Install the four-necked flask, condenser, and stirring rod. Pour part of the third component directly into the reaction vessel, turn on the electric stirrer (electric stirring is carried out throughout the emulsion polymerization process), set the stirring speed to the first preset speed of 400 RPM, and heat up.

[0140] b. Once the temperature reaches the first preset temperature of 55-65℃, add part of the fourth component under constant temperature and continue to heat up;

[0141] c. Heat to the second preset temperature of 75-85℃, adjust the stirring speed to the second preset speed of 600RPM, and add the remaining third and fourth components dropwise using a dropping funnel. The third and fourth components are added dropwise within 0.8-1.2 hours.

[0142] d. After the third and fourth components are added, the reaction is kept at a constant temperature. Then, the second and fifth components are added dropwise using a dropping funnel. The second and fifth components are added dropwise over 1.8-2.2 hours. After the second and fifth components are added, the reaction is kept at a constant temperature for another 1.8-2.2 hours to obtain the reaction solution.

[0143] e. Stop the reaction, pour the reaction solution into the sixth container, add sodium hydroxide solution to adjust the pH to 8, and obtain the styrene-acrylic emulsion. The concentration of the sodium hydroxide solution added is 4.5-5.5 mol / L.

[0144] Specifically, the raw materials for preparing the styrene-acrylic emulsion include the following components in parts by weight: 9-10.62 parts styrene, 0.18-1.8 parts lignin maleate, 7.2-18 parts butyl acrylate, 7.2-18 parts acrylic acid, 0.11-0.9 parts ammonium persulfate, 0.72-1.8 parts emulsifier NP-40, and 0.7-1.8 parts sodium dodecyl sulfate.

[0145] In this embodiment of the invention, lignin maleate is obtained through the following steps:

[0146] The crude acidic lignin is stirred in hot water at 70-90℃ for 1-2 hours, filtered while hot, washed, and dried to obtain acidic lignin; the ratio of crude acidic lignin to water is (0-10)g:100ml.

[0147] Add 120-180 mL of ethylene glycol dimethyl ether to a three-necked flask equipped with a thermometer and a condenser. Heat the flask to a preset temperature (90-110°C) and stir. Then add 25-35 g of acidic lignin and 10-15 g of maleic anhydride. When the temperature inside the flask reaches the preset temperature, react for 5-7 hours. After the reaction is complete, there will be a black liquid and a black viscous solid in the flask. Cool the black liquid to room temperature and then pour it into a beaker containing 0.8-1.2 L of deionized water while stirring, so that a solid precipitates out. Filter the precipitated solid and wash it with water 2-3 times until the pH of the filtrate is 5-6. Dry the filtrate to obtain the lignin maleate ester.

[0148] Example 4 uses the following preparation method:

[0149] Example 4 of this invention provides a method for preparing a styrene-acrylic emulsion, comprising the following steps:

[0150] (1) Monomer purification:

[0151] Styrene was purified to:

[0152] Styrene was washed once with a 10% sodium hydroxide solution in a separatory funnel, separated, and the lower alkaline layer was discharged, while the upper liquid was monomer. An appropriate amount of deionized water was added to the upper liquid, followed by washing, separation, and discharge of the lower wastewater. The washing operation was repeated until the pH of the wastewater was 7-8 to obtain the purified styrene.

[0153] Butyl acrylate was purified to:

[0154] The butyl acrylate was washed once with a 10% sodium hydroxide solution in a separatory funnel, separated, and the lower alkaline layer was discharged, while the upper liquid was the monomer. An appropriate amount of deionized water was added to the upper liquid, and then the mixture was washed with water, separated, and the lower wastewater was discharged. The water washing operation was repeated until the pH of the wastewater was 7-8 to obtain the purified butyl acrylate.

[0155] (2) Solution preparation:

[0156] First component: Add 0.72g of emulsifier NP-40, 1.08g of sodium dodecyl sulfate, and 21g of deionized water to the first beaker in sequence, stir with a glass rod until the solid is completely dissolved, let stand to defoam, and obtain the first component;

[0157] Second component: Add 9.0g of purified styrene, 7.2g of purified butyl acrylate and 10.7g of the first component to the second beaker in sequence, stir with a magnetic stirrer at 450 rpm until no layering is formed, and the second component is obtained;

[0158] Third component: Add 1.8g of lignin maleate, 18.0g of acrylic acid and 12.1g of the first component to the third beaker in sequence, and then sonicate for 2 minutes. The sonication needs to be repeated 3 times, and after each sonication, the particles on the wall of the third container need to be cleaned with a glass rod to obtain the third component.

[0159] The ultrasonic treatment is performed by placing the third container, which contains a mixture of lignin maleate, acrylic acid, and the first component, into an ultrasonic vibrator and ultrasonically treating it for 2 minutes.

[0160] Fourth component: Add 0.50g of ammonium persulfate and 8.00g of deionized water to the fourth beaker in sequence until the solid is completely dissolved to obtain the fourth component;

[0161] Fifth component: Add 0.4g of ammonium persulfate and 8.00g of deionized water to the fifth beaker in sequence, shake the beaker to completely dissolve the solid, and obtain the fifth component;

[0162] (3) Emulsion polymerization:

[0163] a. Install the four-necked flask, condenser, and stir bar. Pour half of the third component directly into the reaction flask, turn on the electric stirrer (electric stirring is carried out throughout the emulsion polymerization process), set the stirring speed to the first preset speed of 400 RPM, and heat up.

[0164] b. Once the temperature reaches the first preset temperature of 60℃, add half of the fourth component into the titration funnel under constant temperature. After the addition is complete, continue to raise the temperature.

[0165] c. Heat to the second preset temperature of 85℃, adjust the stirring speed to the second preset speed of 600RPM, and add the remaining third and fourth components dropwise using a dropping funnel. The third and fourth components are added dropwise in about 1 hour.

[0166] d. After adding the third and fourth components, maintain the temperature for 1 hour. Then, add the second and fifth components dropwise using a dropping funnel. The second and fifth components are added in about 2 hours. After the second and fifth components are added, maintain the temperature for another 2 hours to obtain the reaction solution.

[0167] e. Stop the reaction, pour the reaction solution into the sixth container, add 5 mol / L sodium hydroxide solution to adjust the pH to 8, and obtain the styrene-acrylic emulsion. Measure the solid content.

[0168] The preparation method of lignin maleate in Example 4 is as follows:

[0169] (1) Boil crude acidic lignin in hot water at 70°C for 2 hours, filter while hot, wash and dry to obtain purified acidic lignin; the ratio of crude acidic lignin to water is 8g / 100ml.

[0170] (2) Add 150 mL of ethylene glycol dimethyl ether to a 250 mL three-necked flask equipped with a thermometer and a condenser, heat to the preset temperature (90 °C), stir, and add 30 g of acidic lignin and 12 g of maleic anhydride in sequence. When the temperature inside the flask reaches the preset temperature of 90 °C, react for 6 h. After the reaction is completed, cool the above reaction solution to room temperature, and then pour it into a beaker containing 1 L of deionized water while stirring, so that a solid is precipitated. Filter the precipitated solid, wash it with water twice until the pH of the filtrate is 5-6, and dry it to obtain the lignin maleate ester.

[0171] Comparative Example 1

[0172] The only difference from Example 1 is that the coating prepared in Comparative Example 1 did not contain any flame retardant; everything else was the same as in Example 1.

[0173] Comparative Example 2

[0174] The only difference from Example 1 is that acidic lignin was not used as the flame retardant in Comparative Example 2; otherwise, they are the same as in Example 1.

[0175] Preparation of flame retardants (using phosphoric acid, urea, and pentaerythritol):

[0176] Phosphoric acid and urea were added to a reactor, and the temperature was raised to 60°C and kept constant until the solid melted. After 2 minutes, pentaerythritol was added to the reactor, and after stirring for 1 minute, an appropriate amount of dimethyl silicone oil was added. The temperature was raised to 95°C and kept constant until small bubbles were generated. The reactants in the reactor were transferred to a ceramic container and the reaction was continued at 200°C for 4 hours. The reaction was stopped, and the mixture was cooled and pulverized to obtain the flame retardant. The weight ratio of phosphoric acid, urea and pentaerythritol was 1:1:0.05.

[0177] Preparation of coating: The flame retardant of Comparative Example 2 was used, and the rest was the same as in Example 1.

[0178] Comparative Example 3

[0179] The only difference from Example 1 is that the flame retardant used in Comparative Example 3 is crude acidic lignin that has not been boiled in water; otherwise, it is the same as in Example 1.

[0180] Preparation of flame retardants (using phosphoric acid, urea, pentaerythritol, and crude acidic lignin):

[0181] Phosphoric acid and urea were added to a reactor, and the temperature was raised to 60°C and kept constant until the solid melted. After 2 minutes, crude acidic lignin and pentaerythritol were added to the reactor. After stirring for 1 minute, an appropriate amount of dimethyl silicone oil was added. The temperature was raised to 95°C and kept constant until small bubbles were generated. The reactants in the reactor were transferred to a ceramic container and the reaction was continued at 200°C for 4 hours. The reaction was stopped, and the mixture was cooled and pulverized to obtain the flame retardant. The weight ratio of phosphoric acid, urea, crude acidic lignin, and pentaerythritol was 1:1:0.2:0.05.

[0182] Preparation of coating: The flame retardant of Comparative Example 3 was used, and the rest was the same as in Example 1.

[0183] Comparative Example 4

[0184] The only difference from Example 1 is that the flame retardant in Comparative Example 4 was not pentaerythritol; everything else was the same as in Example 1.

[0185] Preparation of flame retardants (using phosphoric acid, urea, and acidic lignin):

[0186] The crude acidic lignin was boiled in hot water at 80℃ for 1.5 hours, filtered while hot, washed, and dried to obtain purified acidic lignin; the concentration of crude acidic lignin in water was 5g / 100ml.

[0187] Phosphoric acid and urea are added to a reactor, the temperature is raised to 60°C, and the temperature is maintained until the solid melts. After 2 minutes, acidic lignin is added to the reactor, and after stirring for 1 minute, an appropriate amount of dimethyl silicone oil is added. The temperature is raised to 95°C and maintained until small bubbles are generated. The reactants in the reactor are transferred to a ceramic container and the reaction is continued at 200°C for 4 hours. The reaction is stopped, and the mixture is cooled and pulverized to obtain the flame retardant. The weight ratio of phosphoric acid, urea, and acidic lignin is 1:1:0.2.

[0188] Preparation of coating: The flame retardant of Comparative Example 4 was used, and the rest was the same as in Example 1.

[0189] Comparative Example 5

[0190] The only difference from Example 1 is that the flame retardant in Comparative Example 5 did not use pentaerythritol and acid lignin; otherwise, it was the same as Example 1.

[0191] Preparation of flame retardants (using phosphoric acid and urea):

[0192] Phosphoric acid and urea are added to the reactor, the temperature is raised to 60°C, and the temperature is kept constant until the solid melts. After 2 minutes, stirring is started. After stirring for 1 minute, an appropriate amount of dimethyl silicone oil is added. The temperature is raised to 95°C and kept constant until small bubbles are generated. The reactants in the reactor are transferred to a ceramic container and the reaction is continued at 200°C for 4 hours. The reaction is stopped, and the mixture is cooled and crushed to obtain the flame retardant. The weight ratio of phosphoric acid to urea is 1:1.

[0193] Preparation of coating: The flame retardant of Comparative Example 5 was used, and the rest was the same as in Example 1.

[0194] Comparative Example 6

[0195] The only difference from Example 1 is that in the preparation of the coating in Comparative Example 6, the particle size of the mixture of flame retardant, lignin maleate and inorganic filler was ball-milled into large balls, while the rest was the same as in Example 1.

[0196] Preparation of flame retardants:

[0197] The crude acidic lignin was boiled in hot water at 80℃ for 1.5 hours, filtered while hot, washed, and dried to obtain purified acidic lignin; the concentration of crude acidic lignin in water was 5g / 100ml.

[0198] Phosphoric acid and urea were added to a reactor, and the temperature was raised to 60°C and kept constant until the solid melted. After 2 minutes, acidic lignin and pentaerythritol were added to the reactor. After stirring for 1 minute, an appropriate amount of dimethyl silicone oil was added. The temperature was raised to 95°C and kept constant until small bubbles were generated. The reactants in the reactor were transferred to a ceramic container and the reaction was continued at 200°C for 4 hours. The reaction was stopped, and the mixture was cooled and pulverized to obtain the flame retardant. The weight ratio of phosphoric acid, urea, acidic lignin, and pentaerythritol was 1:1:0.2:0.05.

[0199] The coating was prepared by ball milling large balls containing flame retardants, lignin maleate, and inorganic fillers without controlling the particle size ratio.

[0200] Comparative Example 7

[0201] The only difference from Example 1 is that in the preparation of the coating in Comparative Example 7, the particle size of the mixture of flame retardant, lignin maleate and inorganic filler is small balls that are ball-milled; the rest is the same as in Example 1.

[0202] Preparation of flame retardants:

[0203] The crude acidic lignin was boiled in hot water at 80℃ for 1.5 hours, filtered while hot, washed, and dried to obtain purified acidic lignin; the concentration of crude acidic lignin in water was 5g / 100ml.

[0204] Phosphoric acid and urea were added to a reactor, and the temperature was raised to 60°C and kept constant until the solid melted. After 2 minutes, acidic lignin and pentaerythritol were added to the reactor. After stirring for 1 minute, an appropriate amount of dimethyl silicone oil was added. The temperature was raised to 95°C and kept constant until small bubbles were generated. The reactants in the reactor were transferred to a ceramic container and the reaction was continued at 200°C for 4 hours. The reaction was stopped, and the mixture was cooled and pulverized to obtain the flame retardant. The weight ratio of phosphoric acid, urea, acidic lignin, and pentaerythritol was 1:1:0.2:0.05.

[0205] The coating was prepared by ball milling small balls containing flame retardants, lignin maleate, and inorganic fillers without controlling the particle size ratio.

[0206] Comparative Example 8

[0207] The only difference from Example 1 is that in Comparative Example 8, the coating preparation, flame retardant, lignin maleate and inorganic filler mixture were all ball-milled with medium-sized balls, while the rest was the same as in Example 1.

[0208] Preparation of flame retardants:

[0209] The crude acidic lignin was boiled in hot water at 80℃ for 1.5 hours, filtered while hot, washed, and dried to obtain purified acidic lignin; the concentration of crude acidic lignin in water was 5g / 100ml.

[0210] Phosphoric acid and urea were added to a reactor, and the temperature was raised to 60°C and kept constant until the solid melted. After 2 minutes, acidic lignin and pentaerythritol were added to the reactor. After stirring for 1 minute, an appropriate amount of dimethyl silicone oil was added. The temperature was raised to 95°C and kept constant until small bubbles were generated. The reactants in the reactor were transferred to a ceramic container and the reaction was continued at 200°C for 4 hours. The reaction was stopped, and the mixture was cooled and pulverized to obtain the flame retardant. The weight ratio of phosphoric acid, urea, acidic lignin, and pentaerythritol was 1:1:0.2:0.05.

[0211] Preparation of coatings: The particle size of the mixture of flame retardant, lignin maleate and inorganic filler was ball-milled with medium-sized balls, and the particle size ratio was not controlled.

[0212] Comparative Example 9

[0213] The only difference from Example 1 is that lignin maleate was not used; everything else is the same as in Example 1.

[0214] Comparative Example 10

[0215] Fire-retardant coatings are obtained by physically mixing ammonium polyphosphate, melamine, and pentaerythritol, a process known to those skilled in the art.

[0216] Experiments revealed that, in Comparative Examples 6-8, using only one type of ball for ball milling, regardless of the milling time, the minimum particle size of the mixture (flame retardant, lignin maleate, and inorganic filler) could only reach 14 micrometers; while the embodiments of the present invention could mill to a minimum particle size of 5 micrometers in the shortest time.

[0217] Experimental test:

[0218] The water-based fire-retardant coatings for steel structures prepared in the examples and the coatings prepared in the comparative examples were cured into films. The fire resistance time of the samples was tested according to the national standard GB / T 14907; the oxygen index of the samples was tested according to the national standard GB / T 2406.2; the water absorption rate was tested by placing the samples at 25°C and 80% humidity for 24 hours. The results are shown in Table 1.

[0219] Table 1

[0220]

[0221]

[0222] In summary:

[0223] Comparative Example 1, no flame retardant added;

[0224] Comparative Example 2, without the use of acidic lignin;

[0225] Comparative Example 3 used crude acidic lignin boiled in unheated water;

[0226] Comparative Example 4, pentaerythritol was not used;

[0227] Comparative Example 5, without the use of pentaerythritol and acid lignin;

[0228] In Comparative Example 6, the particle size of the mixture of flame retardant, lignin maleate and inorganic filler was ball-milled using large balls, without controlling the particle size ratio.

[0229] In Comparative Example 7, the particle size of the mixture of flame retardant, lignin maleate and inorganic filler was all determined by ball milling with small balls, without controlling the particle size ratio.

[0230] In Comparative Example 8, the particle size of the mixture of flame retardant, lignin maleate and inorganic filler was all ball-milled using medium-sized balls, without controlling the particle size ratio.

[0231] Comparative Example 9, without the use of lignin maleate;

[0232] Comparative Example 10: Fire-retardant coating was obtained by physically mixing currently known conventional ammonium polyphosphate, melamine, and pentaerythritol.

[0233] In summary, compared to Example 1, Example 4 exhibits significantly enhanced fire resistance time and limiting oxygen index, resulting in a substantial performance improvement. Therefore, it can be concluded that the fire-retardant coating prepared using the styrene-acrylic emulsion of Example 4 of this invention demonstrates significantly improved performance compared to commercially available ordinary styrene-acrylic emulsions.

[0234] Compared with Comparative Examples 1-10, Example 1 has a significantly enhanced fire resistance time and limiting oxygen index. Therefore, it can be seen that phosphoric acid, urea, pentaerythritol and acid lignin are indispensable raw materials for the flame retardant of the present invention, and they interact, react and have synergistic effects with each other.

[0235] Compared to the traditional Comparative Example 10, Examples 1-4 show a significantly reduced water absorption rate, are less prone to moisture absorption, and have greatly enhanced fire resistance time and limiting oxygen index.

[0236] Compared to Comparative Examples 6-8, which used spheres of varying sizes, Example 1 used three types of spheres: large, medium, and small, with strict control over their particle size. This resulted in a significant enhancement in refractory time and limiting oxygen index, leading to a substantial improvement in performance.

[0237] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0238] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A water-based fire-retardant coating for steel structures, characterized in that, It is prepared from the following raw materials in parts by weight: 15-35 parts flame retardant, 20-30 parts water, 25-35 parts styrene-acrylic emulsion, 0.1-0.4 parts thickener, 0.4-1 parts dispersant, 5-15 parts lignin maleate, 3-10 parts expandable graphite, 3-10 parts hollow glass microspheres, and 5-20 parts inorganic filler; The preparation method of the styrene-acrylic emulsion includes the following steps: (1) Monomer purification: Styrene and butyl acrylate were purified separately to obtain purified styrene / butyl acrylate; (2) Solution preparation: First component: Add emulsifier NP-40, sodium dodecyl sulfate and deionized water to the first container in sequence, stir until completely dissolved, let stand to defoam, and obtain the first component; Second component: Add purified styrene, purified butyl acrylate, and part of the first component to the second container in sequence, and stir until no layering occurs to obtain the second component; Third component: Add lignin maleate, acrylic acid, and the remaining first component to the third container in sequence, and then perform ultrasonic treatment. The ultrasonic treatment needs to be repeated 3 times, and after each ultrasonic treatment, the particles on the wall of the third container need to be cleaned with a glass rod to obtain the third component. The ultrasonic treatment is as follows: the third container containing the mixture of lignin maleate, acrylic acid and the first component is placed in an ultrasonic vibrator and ultrasonically treated for 1-3 minutes. Fourth component: Add a portion of ammonium persulfate and deionized water sequentially to the fourth container to completely dissolve the solid and obtain the fourth component; Fifth component: Add the remaining ammonium persulfate and deionized water to the fifth container in sequence to completely dissolve the solid and obtain the fifth component; (3) Emulsion polymerization: a. Install the four-necked flask, condenser, and stirring rod. Pour part of the third component directly into the reaction vessel. Turn on the electric stirrer and keep the electric stirrer running throughout the emulsion polymerization process. Set the stirring speed to the first preset speed of 400 RPM and heat up. b. Once the temperature reaches the first preset temperature of 55-65℃, add part of the fourth component under constant temperature and continue to heat up; c. Heat to the second preset temperature of 75-85℃, adjust the stirring speed to the second preset speed of 600 RPM, and add the remaining third and fourth components dropwise using a dropping funnel. The third and fourth components are added dropwise within 0.8-1.2 hours. d. After the third and fourth components are added, maintain the reaction temperature. Then, add the second and fifth components dropwise using a dropping funnel. The second and fifth components are added in 1.8-2.2 hours. After the second and fifth components are added dropwise, the reaction is carried out at a constant temperature for 1.8-2.2 hours to obtain the reaction solution. e. Stop the reaction, pour the reaction solution into the sixth container, add sodium hydroxide solution to adjust the pH to 8, and obtain the styrene-acrylic emulsion. The concentration of the sodium hydroxide solution is 4.5-5.5 mol / L. The flame retardant is prepared from the following raw materials: urea, phosphoric acid, acidic lignin, and pentaerythritol; The weight ratio of urea, phosphoric acid, acid lignin, and pentaerythritol is 1:(0.8-1):(0.1-0.5):(0.01-0.05).

2. The water-based fireproof coating for steel structures according to claim 1, characterized in that, The acidic lignin is obtained by the following steps: boiling and stirring crude acidic lignin in hot water, filtering and washing while hot, and drying to obtain the acidic lignin; The ratio of crude acidic lignin to water is (5-10) g: 100 ml.

3. The water-based fireproof coating for steel structures according to claim 1, characterized in that, The preparation method of the flame retardant includes the following steps: Step 1: Add phosphoric acid and urea to the reactor, stir and heat. After the urea is completely dissolved, add acidic lignin and pentaerythritol, stir, and add defoamer. Step 2: While stirring, heat to 95-115℃ and react, keep the temperature constant until bubbles are produced, then stop the reaction; Step 3: Transfer the product obtained in Step 2 into a porcelain container and react at 190-220℃ for 3-5 hours to obtain the flame retardant.

4. The method for preparing the water-based fire-retardant coating for steel structures according to any one of claims 1-3, characterized in that, Includes the following steps: Step 1: Mix the flame retardant, lignin maleate and inorganic filler in a high-speed mixer, and then ball mill the mixture at high speed in a ball mill to obtain a pulverizing aid; Step 2: Add water, styrene-acrylic emulsion, thickener, dispersant, pulverizing aid, expandable graphite, and hollow glass microspheres to a container in sequence, and stir at a uniform speed for 30-60 minutes to obtain the water-based fireproof coating for steel structures.

5. The method for preparing water-based fire-retardant coating for steel structures according to claim 4, characterized in that, Before ball milling, the particle size of the mixture is controlled by the following process: the ratio of large balls, medium balls, and small balls is 1:6:20; The ball milling time is 3-6 hours, and the rotation speed is 400-600 rpm.

6. The method for preparing water-based fire-retardant coating for steel structures according to claim 4, characterized in that, The particle size of the mixture of flame retardant, lignin maleate and inorganic filler after ball milling is 2-15 micrometers.

7. The method for preparing water-based fire-retardant coating for steel structures according to claim 4, characterized in that, The lignin maleate ester is prepared by the following steps: First, add ethylene glycol dimethyl ether to the first container containing a thermometer and a condenser, heat it to the preset temperature, and stir. The second step involves sequentially adding acidic lignin and maleic anhydride to the ethylene glycol dimethyl ether. When the temperature inside the first container reaches the preset temperature, the reaction proceeds for 5-7 hours. The third step is to cool the reaction solution to room temperature and pour it into a second container containing deionized water, thereby precipitating a solid. The fourth step involves solid filtration, followed by washing with water until the pH of the filtrate reaches 5-6, and then drying to obtain the lignin maleate.

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