Binder for metal powder molding and method for preparing the same

Abstract

This invention discloses a binder for metal powder molding and its preparation method, belonging to the field of metal powder molding technology. First, modified silicon nitride powder and nano-silica powder are combined to obtain a composite powder, which is then calcined to form a porous composite powder. Then, polyacrylic acid, porous composite powder, polyethylene glycol and magnesium chloride are polymerized together. The silicon nitride powder modified with isostearyl titanate isopropyl ester has a stronger bonding force with the nano-silica powder. After calcination, the modified silicon nitride powder and nano-silica powder can be uniformly mixed together. During the degreasing process of the metal blank, organic matter will generate carbon dioxide and water and evaporate. Since both silicon nitride powder and nano-silica are inorganic fillers, they can not only reduce the residual carbon content, but also be uniformly embedded in the metal blank, increasing the strength of the blank. In addition, silicon nitride has good thermal conductivity.

Description

Technical Field

[0001] This invention belongs to the field of metal powder forming technology, specifically a binder for metal powder forming and its preparation method. Background Technology

[0002] Metal powder forming technology (such as powder injection molding, compression molding, 3D printing, etc.) is a key process for manufacturing complex-shaped, high-precision metal parts. Its core lies in temporarily binding metal powder particles into a specific shape using a binder, followed by debinding and sintering to obtain the final, densified product. The performance of the binder directly determines the green strength, debinding efficiency, product dimensional accuracy, and defect control, making it a core factor affecting the feasibility of the forming process and the performance of the parts.

[0003] Chinese invention patent application CN102115606B discloses a method for preparing a binder and a feedstock for injection molding of metal powder. The binder comprises olefin thermoplastic elastomers, brassica wax, industrial paraffin wax, high-density polyethylene, polypropylene, and stearic acid. The feedstock is produced through processes such as mixing, extrusion, cooling and crushing, and vacuum packaging according to the material ratio. During molding, the liquid and solid phases are not easily separated, the injection preform has uniform density, high debinding efficiency, and high sintered preform density.

[0004] During the debinding process of metal powder sintering, if the density of the sintered blank is too high, the gas formed by the binder cannot be discharged in time, resulting in excessive local stress concentration, and even microcracks, leading to a decline in product quality. Summary of the Invention

[0005] The purpose of this invention is to provide a binder for metal powder molding and its preparation method. The binder is made by combining silicon nitride and silicon dioxide to obtain a composite powder, which is then calcined and polymerized with a polymer and magnesium chloride to obtain a modified polymer. The modified polymer is then mixed with other raw materials to obtain a binder that can increase the strength of the metal blank during the degreasing process.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for preparing a binder for metal powder molding includes the following steps:

[0008] Step 1: Modify silicon nitride powder with triisostearoyl titanate to obtain modified silicon nitride powder. Then, use the sol-gel method to coat silicon dioxide on the modified silicon nitride powder to obtain composite powder. After calcination, obtain porous composite powder.

[0009] Step 2: Polymerize polyacrylic acid, porous composite powder and polyethylene glycol together, and then chelate with magnesium chloride to obtain modified polymer.

[0010] Step 3: Mix the modified polymer, deionized water, glycerin, isopropanol, ethylene glycol butyl ether and Tween 80 evenly to obtain a binder for metal powder molding.

[0011] Furthermore, the modified silicon nitride powder is prepared through the following steps:

[0012] Silicon nitride powder with a particle size of less than 15 nm and toluene were added to a reaction vessel. Under nitrogen protection and at a speed of 800-1000 r / min, triisostearoyl titanate isopropyl ester was added. The mixture was refluxed at 65-70℃ for 2.5-3 h, filtered, purified, dried, and ground to obtain modified silicon nitride powder.

[0013] Furthermore, the ratio of silicon nitride powder, toluene, and triisostearoyl titanate is 5-6g: 200-300mL: 0.5-0.6g.

[0014] Furthermore, the composite powder is prepared through the following steps:

[0015] Modified silicon nitride powder, deionized water, and anhydrous ethanol were added to a reaction vessel, followed by the addition of 1 mol / L triethylenetetramine. The pH was adjusted to 10-11 with ammonia. Tetraethyl orthosilicate was added at 35-45℃ and 200-400 r / min. The reaction was carried out for 3-5 hours, filtered, washed, and dried to obtain the composite powder.

[0016] Furthermore, the ratio of modified silicon nitride powder, deionized water, anhydrous ethanol, triethylenetetramine and tetraethyl orthosilicate is 1-2g: 10-15mL: 50-60mL: 4-6mL: 4-6mL.

[0017] Furthermore, the porous composite powder is prepared through the following steps:

[0018] The composite powder was placed in a muffle furnace and heated to 300-450℃ at a rate of 5℃ / min under nitrogen protection. The temperature was held for 2-3 hours, cooled to room temperature, and then ground to obtain porous composite powder.

[0019] Furthermore, the modified polymer is prepared through the following steps:

[0020] Polyacrylic acid, porous composite powder, deionized water and polyethylene glycol were added to a reaction vessel and reacted at 95-100℃ and 300-500 r / min for 3-4 h. Then, a magnesium chloride aqueous solution with a concentration of 0.1 g / mL was added and reacted for another 3-4 h to obtain the modified polymer.

[0021] Furthermore, the ratio of polyacrylic acid, porous composite powder, deionized water, polyethylene glycol and magnesium chloride aqueous solution is 60-80mL: 5-10g: 800-1000mL: 100-120g: 150-200mL.

[0022] Furthermore, the binder for metal powder molding is prepared through the following steps:

[0023] The modified polymer and deionized water are added to a reaction vessel and stirred for 8-12 minutes at 20-25℃ and 300-500 r / min. After standing, glycerol, isopropanol, ethylene glycol butyl ether, and Tween 50 are added sequentially at 65-70℃ and 300-500 r / min and stirred for 0.5-1 h to obtain a binder for metal powder molding.

[0024] Furthermore, the mass ratio of the modified polymer, deionized water, glycerol, isopropanol, ethylene glycol butyl ether, and Tween 80 is 140-160:20-30:2-3:2.5-5:2.5-5:0.5-1.

[0025] The beneficial effects of this invention are:

[0026] 1. In this invention, the binder for metal powder molding is first made by combining modified silicon nitride powder and nano-silica powder together to obtain a composite powder, which is then calcined to form a porous composite powder. Then, polyacrylic acid, porous composite powder, polyethylene glycol, and magnesium chloride are polymerized together. The silicon nitride powder modified with isopropyl isostearyl titanate has a stronger bonding force with the nano-silica powder. After calcination, the modified silicon nitride powder and nano-silica powder can be uniformly mixed together. During the degreasing process of the metal blank, organic matter will generate carbon dioxide and water and evaporate. Since both silicon nitride powder and nano-silica are inorganic fillers, they can not only reduce the amount of residual carbon, but also be uniformly embedded in the metal blank, increasing the strength of the blank. In addition, silicon nitride has good thermal conductivity, which makes the heat distribution of the metal blank uniform. The porous composite powder, as a pore-forming agent, can timely discharge the gas formed by the polymer, avoiding affecting the strength of the metal product. At the same time, magnesium chloride generates magnesium oxide during sintering, which can inhibit abnormal grain growth, refine the grains, and further improve the sintering strength.

[0027] 2. In this invention, the modified polymer is formed by reacting the carboxyl groups on polyacrylic acid and the hydroxyl groups on polyethylene glycol to generate weakly hydrophilic ester bonds, forming a micro-crosslinked network structure. This reacts some of the hydroxyl groups, preventing the formation of hydrogen bonds between hydroxyl groups and water molecules. Then, it chelates with magnesium ions in a magnesium chloride aqueous solution to form metal coordination bonds. This mixture is then mixed with other raw materials to obtain a binder for metal powder molding. The junction between magnesium chloride and the polymer forms some fine pores, which work synergistically with the porous structure of the porous composite powder. This facilitates the entry of water molecules into the interior and the expulsion of water molecules from the interior, exhibiting good moisture absorption and release properties. This achieves a dynamic balance between moisture absorption and release, allowing the binder for metal powder molding to be stored for a longer time in high humidity environments without a decrease in viscosity.

[0028] 3. The triisostearoyl titanate isopropyl ester in the modified silicon nitride powder of this invention has organic segments, which can increase the bonding force between the polymer and the polymer during subsequent crosslinking, reduce the agglomeration of the porous composite powder, and also increase the crosslinking density of the polyacrylic acid and polyethylene glycol crosslinking network, increase the cohesive force of the modified polymer, and improve the viscosity of the binder. In addition, the small molecule structure of glycerol may be inserted between polymer chains to increase toughness, and Tween 80 can improve wettability and dispersibility, ensuring that the binder for metal powder molding can maintain uniform flowability. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1: This example provides a binder for metal powder molding, which is prepared through the following steps:

[0031] S1: 5.5g of silicon nitride powder with a particle size of less than 15nm and 250mL of toluene were added to a reaction vessel. Under nitrogen protection and at 900r / min, 0.55g of triisostearoyl titanate isopropyl ester was added. The mixture was refluxed at 67℃ for 2.5h. The polar bonds of triisostearoyl titanate are easily physically or chemically bonded to the hydroxyl groups on the surface of silicon nitride, thus coating the surface of the nano-silicon nitride powder, reducing the surface energy of the nano-silicon nitride powder particles, and inhibiting agglomeration. The mixture was filtered, extracted with ethanol as solvent using a Soxhlet extractor for 60h, vacuum dried at 62℃ for 11h, ground, and passed through a 400-mesh sieve to obtain modified silicon nitride powder.

[0032] S2: Add 1.5g of modified silicon nitride powder, 12mL of deionized water and 55mL of anhydrous ethanol to a reaction vessel, then add 5mL of 1mol / L triethylenetetramine, adjust the pH to 10 with ammonia, and add 5mL of tetraethyl orthosilicate dropwise to the reaction vessel at 40℃ and 300r / min. React for 4h, centrifuge and filter, wash 4 times alternately with deionized water and anhydrous ethanol, and vacuum dry at 65℃ to constant weight to obtain composite powder.

[0033] S3: Place the composite powder in a muffle furnace, raise the temperature to 375°C at a rate of 5°C / min under nitrogen protection, hold for 2.5 hours, cool to room temperature, grind, and pass through a 200-mesh sieve to obtain porous composite powder.

[0034] S4: Add 70 mL of polyacrylic acid (preferably with a molecular weight of 50,000-75,000), 7.5 g of porous composite powder, 900 mL of deionized water, and 110 g of polyethylene glycol (preferably with a molecular weight of 400-500) to a reactor and react at 97 °C and 400 r / min for 3.5 h. The carboxyl groups on the polyacrylic acid and the hydroxyl groups on the polyethylene glycol react to form weakly hydrophilic ester bonds, forming a micro-crosslinked structure. The interpenetrating and interactive molecular chains of polyethylene glycol and polyacrylic acid give the polymer larger porosity and allow it to reach moisture absorption and desorption equilibrium more quickly. Add 175 mL of magnesium chloride aqueous solution with a concentration of 0.1 g / mL and perform a complexation reaction for 3.5 h. The carboxyl groups of polyacrylic acid chelate with magnesium chloride. The introduction of magnesium ions makes it easier for water molecules to be released, exhibiting good moisture release performance, and thus obtaining the modified polymer.

[0035] S5: 150g of modified polymer as the matrix and 25g of deionized water were added to a reaction vessel and stirred for 10min at 22℃ and 400r / min. After standing for 4.5h, 2.5g of glycerol as a plasticizer, 3.7g of isopropanol as a fast-drying agent, 3.7g of ethylene glycol butyl ether as a penetrant, and 0.7g of Tween 80 as a surfactant were added sequentially at 67℃ and 400r / min. The mixture was stirred for 0.5h to obtain a binder for metal powder molding.

[0036] Example 2: This example provides a binder for metal powder molding, which is prepared through the following steps:

[0037] S1: Add 5g of silicon nitride powder with a particle size of less than 15nm and 200mL of toluene to a reaction vessel. Under nitrogen protection and at 800r / min, add 0.5g of triisostearoyl titanate isopropyl ester. Reflux at 65℃ for 2.5h. The polar bonds of triisostearoyl titanate isopropyl ester and the hydroxyl groups on the surface of silicon nitride can easily form physical or chemical bonds to coat the surface of the nano silicon nitride powder, reducing the surface energy of the nano silicon nitride powder particles and inhibiting agglomeration. After filtration, extract with ethanol as solvent using a Soxhlet extractor for 48h. Vacuum dry at 60℃ for 10h, grind, and pass through a 400-mesh sieve to obtain modified silicon nitride powder.

[0038] S2: Add 1g of modified silicon nitride powder, 10mL of deionized water and 50mL of anhydrous ethanol to a reaction vessel, then add 4mL of 1mol / L triethylenetetramine, adjust the pH to 10 with ammonia, and add 4mL of tetraethyl orthosilicate dropwise to the reaction vessel at 35℃ and 200r / min. React for 3h, centrifuge and filter, wash three times alternately with deionized water and anhydrous ethanol, and vacuum dry at 60℃ to constant weight to obtain composite powder.

[0039] S3: Place the composite powder in a muffle furnace, raise the temperature to 300°C at a rate of 5°C / min under nitrogen protection, hold for 2 hours, cool to room temperature, grind, and pass through a 200-mesh sieve to obtain porous composite powder.

[0040] S4: Add 60 mL of polyacrylic acid (preferably with a molecular weight of 50,000-75,000), 5 g of porous composite powder, 800 mL of deionized water, and 100 g of polyethylene glycol (preferably with a molecular weight of 400-500) to a reaction vessel and react for 3 h at 95 °C and 300 r / min. The carboxyl groups on the polyacrylic acid and the hydroxyl groups on the polyethylene glycol react to form weakly hydrophilic ester bonds, forming a micro-crosslinked structure. The interpenetrating and interactive molecular chains of polyethylene glycol and polyacrylic acid give the polymer larger porosity and allow it to reach moisture absorption and desorption equilibrium more quickly. Add 150 mL of magnesium chloride aqueous solution with a concentration of 0.1 g / mL and perform a complexation reaction for 3 h. The carboxyl groups of polyacrylic acid chelate with magnesium chloride. The introduction of magnesium ions makes it easier for water molecules to be released, exhibiting good moisture release performance, and thus obtaining the modified polymer.

[0041] S5: 140g of modified polymer as the matrix and 20g of deionized water were added to a reaction vessel and stirred for 8min at 20℃ and 300r / min. After standing for 4h, 2g of glycerol as a plasticizer, 2.5g of isopropanol as a fast-drying agent, 2.5g of ethylene glycol butyl ether as a penetrant, and 0.5g of Tween 80 as a surfactant were added sequentially at 65℃ and 300r / min. The mixture was stirred for 0.5h to obtain a binder for metal powder molding.

[0042] Example 3: This example provides a binder for metal powder molding, which is prepared through the following steps:

[0043] S1: 6g of silicon nitride powder with a particle size of less than 15nm and 300mL of toluene were added to a reaction vessel. Under nitrogen protection and at 1000r / min, 0.6g of triisostearoyl titanate isopropyl ester was added. The mixture was refluxed at 70℃ for 3h. The polar bonds of triisostearoyl titanate are easily physically or chemically bonded to the hydroxyl groups on the surface of silicon nitride, thus coating the surface of the nano-silicon nitride powder, reducing the surface energy of the nano-silicon nitride powder particles, and inhibiting agglomeration. The mixture was filtered, extracted with ethanol as solvent using a Soxhlet extractor for 72h, vacuum dried at 65℃ for 12h, ground, and passed through a 400-mesh sieve to obtain modified silicon nitride powder.

[0044] S2: Add 2g of modified silicon nitride powder, 15mL of deionized water and 60mL of anhydrous ethanol to a reaction vessel, then add 6mL of 1mol / L triethylenetetramine, adjust the pH to 11 with ammonia, and add 6mL of tetraethyl orthosilicate dropwise to the reaction vessel at 45℃ and 400r / min. React for 5h, centrifuge and filter, wash 5 times alternately with deionized water and anhydrous ethanol, and vacuum dry at 70℃ to constant weight to obtain composite powder.

[0045] S3: Place the composite powder in a muffle furnace and heat it to 450°C at a rate of 5°C / min under nitrogen protection. Hold the temperature for 3 hours, cool it to room temperature, grind it, and pass it through a 200-mesh sieve to obtain porous composite powder.

[0046] S4: Add 80 mL of polyacrylic acid (preferably with a molecular weight of 50,000-75,000), 10 g of porous composite powder, 1000 mL of deionized water, and 120 g of polyethylene glycol (preferably with a molecular weight of 400-500) to a reaction vessel and react at 100 °C and 500 r / min for 4 h. The carboxyl groups on the polyacrylic acid and the hydroxyl groups on the polyethylene glycol react to form weakly hydrophilic ester bonds, forming a micro-crosslinked structure. The interpenetrating and interactive molecular chains of polyethylene glycol and polyacrylic acid give the polymer larger pores, allowing it to reach moisture absorption and desorption equilibrium more quickly. Add 200 mL of magnesium chloride aqueous solution with a concentration of 0.1 g / mL and perform a complexation reaction for 4 h. The carboxyl groups of polyacrylic acid chelate with magnesium chloride. The introduction of magnesium ions makes it easier for water molecules to be released, exhibiting good moisture release performance, and thus obtaining the modified polymer.

[0047] S5: Add 160g of modified polymer as the matrix and 30g of deionized water to a reaction vessel, stir for 12min at 25℃ and 500r / min, let stand for 5h, and then add 3g of glycerol as a plasticizer, 5g of isopropanol as a fast-drying agent, 5g of ethylene glycol butyl ether as a penetrant, and 1g of Tween 80 as a surfactant in sequence at 70℃ and 500r / min. Stir for 1h to obtain a binder for metal powder molding.

[0048] Comparative Example 1: Based on Example 1, the porous composite powder was removed in step S4, while the other steps remained unchanged, to prepare a binder for metal powder molding.

[0049] Comparative Example 2: Based on Example 1, the magnesium chloride aqueous solution was removed in step S4, while the other steps remained unchanged, to prepare a binder for metal powder molding.

[0050] Comparative Example 3: Based on Example 1, in step S4, the modified silicon nitride powder prepared in step S1 was used instead of the porous composite powder, while the other steps remained unchanged, to prepare a binder for metal powder molding.

[0051] The performance of the binders used for metal powder molding in Examples 1-3 and Comparative Examples 1-3 was tested:

[0052] Bending strength: Using the EASY-Ⅱ type BJ equipment (Wuhan Yizhi Technology Co., Ltd.), 60×6×4mm were printed at room temperature. 3 The strip samples were used for bending strength testing. The printing parameters were set as follows: layer thickness 50-350μm, white ink concentration 10-100%, resolution 360×1080, 3 passes, ink pressurization time 420ms. After printing, the samples were transferred to an oven for curing at 190℃ for 3 hours. After the oven cooled to room temperature, the supporting powder around the samples was removed with a brush, and the surface powder was blown off with an air compressor gun. The samples cured at 190℃ are called 316L stainless steel green blanks.

[0053] Viscosity test: A rotational viscometer (NDJ-5S, Shanghai Hengping Scientific Instruments Co., Ltd.) is used to test the viscosity of the liquid. First, the liquid to be tested and the cylinder are preheated in a 20°C water bath. Then, the rotor is selected according to the viscosity range of the liquid to be tested (rotors No. 0 and No. 1 are commonly used) and the rotation speed is adjusted until the reading is within the range of 30-70%. After the reading on the instrument stabilizes, the viscosity data of the liquid is read.

[0054] Storage stability test: The samples were stored at 22℃ and 80% humidity for 3 months. The morphology of the samples was observed and the viscosity was measured. The test results are as follows:

[0055] Table 1 Performance Test Overview

[0056]

[0057] As shown in Table 1, the bending strength in Examples 1-3 is greater than that in Comparative Examples 1 and 3. In Comparative Example 1, step S4 involves removing the porous composite powder; in Comparative Example 2, step S4 involves removing the magnesium chloride aqueous solution; and in Comparative Example 3, step S4 involves replacing the porous composite powder with the modified silicon nitride powder prepared in step S1. This indicates that the porous composite powder can enhance the bending strength of the green body after metal powder molding, and that silicon dioxide, modified silicon nitride powder, and magnesium chloride have a certain synergistic effect in improving the strength of the metal green body.

[0058] The viscosity of Examples 1-3 is higher than that of Comparative Examples 1 and 3. In Comparative Example 1, step S4 removes the porous composite powder. In Comparative Example 3, step S4 uses the modified silicon nitride powder prepared in step S1 to replace the porous composite powder. This shows that the addition of porous composite powder can increase the viscosity of the binder for metal powder molding.

[0059] In Examples 1-3, the viscosity was higher than that in Comparative Examples 1-3 after 6 months. In Comparative Example 1, the porous composite powder was removed in step S4. In Comparative Example 2, the magnesium chloride aqueous solution was removed in step S4. In Comparative Example 3, the modified silicon nitride powder prepared in step S1 was used to replace the porous composite powder in step S4. This shows that magnesium chloride and silicon dioxide have a synergistic effect in extending the shelf life of the binder for metal powder molding.

[0060] It should be noted that, in this document, terms such as “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0061] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for preparing a binder for metal powder molding, characterized in that, Includes the following steps: Step 1: Modify silicon nitride powder with triisostearoyl titanate to obtain modified silicon nitride powder, then coat the modified silicon nitride powder with silicon dioxide using the sol-gel method to obtain composite powder, and then calcine to obtain porous composite powder. Step 2: Polyacrylic acid, porous composite powder and polyethylene glycol are polymerized together, and then chelated with magnesium chloride to obtain the modified polymer; Step 3: Mix the modified polymer, deionized water, glycerin, isopropanol, ethylene glycol butyl ether and Tween 80 evenly to obtain a binder for metal powder molding; The modified silicon nitride powder mentioned in step one is prepared through the following steps: Silicon nitride powder with a particle size of less than 15 nm and toluene were added to a reaction vessel. Under nitrogen protection and at a speed of 800-1000 r / min, triisostearoyl titanate isopropyl ester was added. The mixture was refluxed at 65-70℃ for 2.5-3 h, filtered, purified, dried, and ground to obtain modified silicon nitride powder.

2. The method for preparing a binder for metal powder molding according to claim 1, characterized in that, The ratio of silicon nitride powder, toluene, and triisostearoyl titanate is 5-6g: 200-300mL: 0.5-0.6g.

3. The method for preparing a binder for metal powder molding according to claim 1, characterized in that, The composite powder described in step one is prepared through the following steps: Modified silicon nitride powder, deionized water, and anhydrous ethanol were added to a reaction vessel, followed by the addition of 1 mol / L triethylenetetramine. The pH was adjusted to 10-11 with ammonia. Tetraethyl orthosilicate was added at 35-45℃ and 200-400 r / min. The reaction was carried out for 3-5 hours, filtered, washed, and dried to obtain the composite powder.

4. The method for preparing a binder for metal powder molding according to claim 3, characterized in that, The ratio of modified silicon nitride powder, deionized water, anhydrous ethanol, triethylenetetramine and tetraethyl orthosilicate is 1-2g: 10-15mL: 50-60mL: 4-6mL: 4-6mL.

5. The method for preparing a binder for metal powder molding according to claim 1, characterized in that, The porous composite powder described in step one is prepared through the following steps: The composite powder was placed in a muffle furnace and heated to 300-450℃ at a rate of 5℃ / min under nitrogen protection. The temperature was held for 2-3 hours, cooled to room temperature, and then ground to obtain porous composite powder.

6. The method for preparing a binder for metal powder molding according to claim 1, characterized in that, The modified polymer described in step two is prepared through the following steps: Polyacrylic acid, porous composite powder, deionized water and polyethylene glycol were added to a reaction vessel and reacted at 95-100℃ and 300-500 r / min for 3-4 h. Then, a magnesium chloride aqueous solution with a concentration of 0.1 g / mL was added and reacted for another 3-4 h to obtain the modified polymer.

7. The method for preparing a binder for metal powder molding according to claim 6, characterized in that, The ratio of polyacrylic acid, porous composite powder, deionized water, polyethylene glycol and magnesium chloride aqueous solution is 60-80mL: 5-10g: 800-1000mL: 100-120g: 150-200mL.

8. The method for preparing a binder for metal powder molding according to claim 1, characterized in that, The binder for metal powder molding mentioned in step three is prepared through the following steps: The modified polymer and deionized water are added to a reaction vessel and stirred for 8-12 minutes at 20-25℃ and 300-500 r / min. After standing, glycerol, isopropanol, ethylene glycol butyl ether and Tween 50 are added sequentially at 65-70℃ and 300-500 r / min and stirred for 0.5-1 h to obtain a binder for metal powder molding. The mass ratio of the modified polymer, deionized water, glycerol, isopropanol, ethylene glycol butyl ether, and Tween 80 is 140-160:20-30:2-3:2.5-5:2.5-5:0.5-1.

9. A binder for metal powder molding, characterized in that, It is prepared by the method for preparing a binder for metal powder molding according to any one of claims 1-8.

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