Preparation method and application of flaky aluminum powder without mineral oil

Abstract

The invention discloses a preparation method of flaky aluminum powder without mineral oil. A plasma-assisted ball milling method is adopted. The main raw material is aluminum powder with the particle size of 1-20 microns; alcohol is used as an organic solvent, and fatty acid is used as a surface treating agent; the ball milling atmosphere is carbon dioxide, and the temperature and the pressure are adjusted, so that the carbon dioxide in the ball milling tank is in a supercritical state during ball milling; applying voltage to excite the plasma; and after ball milling, collecting the obtained powder to obtain the product. The invention also comprises application of the flaky aluminum powder prepared by the preparation method in pigments. The flaky aluminum powder prepared by the method has good covering power, metallic feeling and dispersity, and meets application requirements; compared with an existing preparation method, pollution to the environment and possible adverse effects on human health are reduced.

Description

Technical Field

[0001] The present invention relates to a preparation method and application of flaky aluminum powder, and in particular to a preparation method and application of flaky aluminum powder that does not contain mineral oil. Background Art

[0002] As society progresses, people are increasingly concerned about their health and environmental safety. The packaging and plastics industries are implementing restrictions on hazardous substances, and domestic and international standards for raw materials such as inks, masterbatches, and pigments are becoming increasingly refined and stringent. As a key pigment, metallic aluminum pigments must meet the hazardous substance requirements of their applications. This requires hazardous substance management, optimization and upgrading of traditional products, and development of new products to meet regulatory standards for inks, masterbatches, and aluminum pigments.

[0003] For example, the regulation of mineral oil residues primarily focuses on mineral oil hydrocarbons (MOH). These compounds are primarily derived from crude oil but may also be synthesized from coal, natural gas, and biomass. MOH can enter food through various pathways, including environmental pollution, mechanical lubricants used during harvesting and food production, processing aids, food additives, and food contact materials. Mineral oil aromatic hydrocarbons (MOAH) and mineral oil saturated hydrocarbons (MOSH) are of particular concern, as MOAH may be genotoxic and carcinogenic, while MOSH can accumulate in human tissues and may adversely affect the liver.

[0004] Aluminum pigments are produced from pure aluminum metal. Aluminum pigment particles are actually flakes with pigment properties covered with a fatty acid film on the surface. This form gives them excellent corrosion resistance and decorative properties, and they are widely used. The main method for manufacturing aluminum pigments is ball milling: by placing steel balls, aluminum powder and lubricants in a ball mill, and using the steel balls to crush the aluminum powder to obtain flake aluminum powder with a smaller particle size. Existing aluminum pigment preparation methods mainly include dry production and wet production. The ball mill and pipeline are filled with inert gas, which is called "dry production"; while adding organic solvents to the ball mill instead of inert gas is called "wet production". Existing wet production includes: (1) mixing aluminum powder with mineral oil, lubricants, etc. in a certain proportion and then grinding them in a ball mill; (2) the ball-milled material is screened and filtered to form a filter cake; (3) the filter cake is kneaded and surface-treated to become aluminum pigment. Existing aluminum pigment production methods basically use wet ball milling technology. The existing dry-process aluminum pigments have less than ideal hiding power, metallic feel and dispersibility; while the existing wet-process aluminum pigments contain a certain amount of mineral oil and cannot meet the application performance requirements of industries such as inks and plastics. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the above-mentioned defects of the prior art and provide a method for preparing flaky aluminum powder that does not contain mineral oil and its application, so that the aluminum pigment does not contain mineral oil while having good hiding power and metallic feel.

[0006] The technical solution adopted by the present invention to solve the technical problem is as follows: a method for preparing flaky aluminum powder without mineral oil, using a plasma-assisted ball milling method; the main raw material is aluminum powder with a particle size of 1 to 20 μm; alcohols are used as organic solvents during ball milling, and fatty acids are used as surface treatment agents during ball milling; the amount of the surface treatment agent used is 0.05% to 3% of the total mass of the powder; Before ball milling, replace the air in the ball mill with carbon dioxide, then adjust the pressure in the ball mill to 7.3MPa~100MPa and the temperature to 31℃~100℃, so that the carbon dioxide in the ball mill is in a supercritical state during ball milling; adjust the peak-to-peak amplitude of the vibration platform to 10mm~15mm during ball milling; the excitation voltage of the plasma during ball milling is 10kV~20kV; collect the obtained powder after ball milling.

[0007] Preferably, the aluminum powder has a particle size of 1 to 2 μm.

[0008] Preferably, the ball-to-material mass ratio of the ball mill is 30:1-50.

[0009] Preferably, metal grinding balls are used for ball milling.

[0010] Preferably, after adding the grinding balls, grinding materials, organic solvent and surface treatment agent, the filling volume ratio in the ball mill jar is 30% to 60%.

[0011] Preferably, the surface treatment agent is one or more of oleic acid, isostearic acid, stearic acid, and lauric acid.

[0012] Preferably, ethanol is used as the organic solvent.

[0013] Preferably, the amount of the surface treatment agent is 0.1% to 2% of the total mass of the powder.

[0014] Preferably, the mass ratio of the surface treatment agent to the organic solvent is 1:0.5-5.

[0015] Preferably, the ball milling time is 2 to 4 hours.

[0016] Preferably, the vibration acceleration of the ball mill is 280~410m / s 2 .

[0017] Preferably, the operating current of the plasma power supply is 0.5A~3A.

[0018] Preferably, the purity of the aluminum powder is above 99.9%.

[0019] Based on the same inventive concept, the present invention also provides the application of the preparation method of the mineral oil-free flaky aluminum powder in pigments.

[0020] The present invention has the following beneficial effects: the present invention adopts mineral oil-free ball milling technology to prepare flaky aluminum powder that does not contain mineral oil. The product has good hiding power, metallic feel and dispersibility, and meets application requirements; compared with existing preparation methods, the present invention reduces pollution to the environment and possible adverse effects on human health.

[0021] In addition to the above-described objects, features and advantages, the present invention has other objects, features and advantages. The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings: Figure 1 is a SEM image of the flaky aluminum powder obtained after passing through a 200-mesh sieve in Example 1 of the present invention; Figure 2 This is a SEM image of the flaky aluminum powder obtained after passing through a 200-mesh sieve in Comparative Example 1; Figure 3 Figures (a) and (b) are the actual effect diagrams of the flaky aluminum powder after application of Example 1 of the present invention and Comparative Example 1, respectively; Figure 4 This is a SEM image of the flaky aluminum powder obtained after passing through a 200-mesh sieve in Comparative Example 2; Figure 5 Figure (a) and Figure (b) are the actual effect pictures of the flaky aluminum powder after application of Example 1 and Comparative Example 2 of the present invention, respectively. DETAILED DESCRIPTION

[0023] In order to make the purpose, scheme and beneficial technology of the present invention clearer, the present invention is further described in detail below with reference to the embodiments and drawings. It should be noted that the embodiments described in this specification are only for explaining the present invention and are not intended to limit the present invention.

[0024] For simplicity, only some numerical ranges are explicitly disclosed herein. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, and similarly, any upper limit can be combined with any other upper limit to form an unspecified range. In addition, although not explicitly stated, each point or individual value between the endpoints of a range is included in the range. Thus, each point or individual value can serve as its own lower limit or upper limit and be combined with any other point or individual value, or with other lower limits or upper limits, to form an unspecified range.

[0025] In the description of this article, it should be noted that, unless otherwise specified, "above" and "below" are inclusive of the number itself, and the "multiple" in "one or more" means two or more, and the "multiple" in "one or more" means two or more.

[0026] The present invention provides a method for preparing flaky aluminum powder without mineral oil, using plasma-assisted ball milling. The main raw material is aluminum powder with a particle size of 1 to 20 μm. Alcohols are used as organic solvents during ball milling, and fatty acids are used as surface treatment agents during ball milling. The amount of the surface treatment agent used is 0.05% to 3% of the total mass of the powder. Before ball milling, replace the air in the ball mill with carbon dioxide, then adjust the pressure in the ball mill to 7.3MPa~100MPa and the temperature to 31℃~100℃, so that the carbon dioxide in the ball mill is in a supercritical state during ball milling; adjust the peak-to-peak amplitude of the vibration platform to 10mm~15mm during ball milling; the excitation voltage of the plasma during ball milling is 10kV~20kV; collect the obtained powder after ball milling.

[0027] In this invention, aluminum powder is flaked through mineral oil-free ball milling. During the milling process, the powder particles are continuously pulverized, increasing their specific surface area and surface energy, making them prone to agglomeration or sedimentation in liquid media. A surface treatment agent reduces surface tension, making the aluminum powder more wettable by the liquid and reducing interparticle adsorption, thereby improving the dispersibility of the product during and after ball milling.

[0028] Supercritical carbon dioxide technology enables better mixing of aluminum powder and surface treatment agents. Supercritical carbon dioxide fluid refers to the state of carbon dioxide above its supercritical temperature and supercritical pressure. In this state, supercritical carbon dioxide fluid has a density close to that of a liquid, approximately 0.9-1.0 g / cm³, enabling it to dissolve many substances like a liquid. Its viscosity, approximately 0.2-0.3 mPa·s, is close to that of a gas. This low viscosity provides excellent fluidity and mass transfer properties, allowing it to flow through materials rapidly with minimal pressure drop. Its diffusion coefficient is intermediate between that of a gas and a liquid, approximately 1 / 10-1 / 20 that of a gas and 10-100 times greater than that of a liquid, enabling it to penetrate and diffuse into materials more rapidly. Its surface tension is similar to that of a gas, almost zero, enabling it to effectively penetrate the interiors of solid particles and tiny pores, enabling efficient treatment of complex structures. Carbon dioxide itself is non-toxic, harmless, and non-flammable. It is a naturally occurring substance that is environmentally friendly and meets the requirements of sustainable development. Supercritical carbon dioxide is chemically stable and does not readily react with other substances, making it relatively safe to use and producing no harmful byproducts. After ball milling, the carbon dioxide can be converted into gas by adjusting the pressure and temperature, thereby efficiently separating the products.

[0029] During the ball milling process, high voltage is applied to excite the carbon dioxide within the mill, generating a low-temperature CO2 plasma discharge, achieving plasma-assisted ball milling under glow discharge. During plasma milling, two discharge modes occur within the mill. One is caused by gas excitation, generating a glow discharge that permeates the mill space and is the primary source of energy for gas and powder activation, known as the external electric field. The other discharge mode is caused by discharge between the milling balls and powder particles, known as the internal electric field. This internal electric field exhibits a nonlinear relationship with the external electric field, and the resulting electric field strength, resulting from the superposition of the two, can be very large, resulting in a high breakdown current. Plasma-assisted ball milling can shorten ball milling time, rapidly yielding the target product and improving production efficiency.

[0030] The unique reaction environment of the present invention is very different from the traditional wet production environment, which can fully mix the materials. By controlling factors such as the ball milling time, rotation speed, size and material of the grinding balls, the size, morphology and structure of the aluminum flakes can be effectively controlled.

[0031] In an embodiment of the present invention, the aluminum powder may be selected from nitrogen atomization fine aluminum powder and / or air atomization fine aluminum powder.

[0032] In an embodiment of the present invention, the aluminum powder has a particle size of 1-2 μm.

[0033] In an embodiment of the present invention, the ball-to-material mass ratio of the ball mill is 30:1-50.

[0034] In an embodiment of the present invention, metal grinding balls are used for ball milling.

[0035] In some embodiments of the present invention, the grinding balls of the ball mill are high carbon steel balls.

[0036] In an embodiment of the present invention, after the grinding balls, grinding materials, organic solvent and surface treatment agent are added, the filling volume ratio in the ball mill jar is 30% to 60%.

[0037] In an embodiment of the present invention, the surface treatment agent is one or more of oleic acid, isostearic acid, stearic acid, and lauric acid.

[0038] In the embodiment of the present invention, ethanol is used as the organic solvent.

[0039] In an embodiment of the present invention, the amount of the surface treatment agent is 0.1% to 2% of the total mass of the powder.

[0040] In an embodiment of the present invention, the mass ratio of the surface treatment agent to the organic solvent is 1:0.5-5.

[0041] In some embodiments of the present invention, the air in the ball mill is replaced by carbon dioxide by evacuating the ball mill and then introducing high-purity carbon dioxide.

[0042] In an embodiment of the present invention, the ball milling time is 2 to 4 hours.

[0043] In the embodiment of the present invention, the vibration acceleration of the ball mill is 280~410m / s 2 .

[0044] In an embodiment of the present invention, the operating current of the plasma power supply is 0.5A~3A.

[0045] In an embodiment of the present invention, the purity of the aluminum powder is above 99.9%.

[0046] In some embodiments of the present invention, the product is sieved through a 150-400 mesh sieve after ball milling to separate the product from the milling balls.

[0047] The method for preparing the mineral oil-free flaky aluminum powder described in the embodiment of the present invention is used in pigments. The flaky aluminum powder obtained by the preparation method is a flake material with pigment properties coated with a fatty acid film on the surface and can be directly used as an aluminum pigment.

[0048] Example The following examples describe the present disclosure in more detail and are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by weight. Unless otherwise stated, all reagents used in the examples are available through conventional commercial sources or synthesized according to conventional methods and can be used directly without further processing. Unless otherwise stated, all instruments used in the examples are available through conventional commercial sources.

[0049] Example 1 The method for preparing flaky aluminum powder without mineral oil in this embodiment adopts plasma-assisted ball milling; the main raw material is aluminum powder with a particle size of 1-2 μm; oleic acid is used as a surface treatment agent, and ethanol is used as an organic solvent for ball milling; (1) Place the ball mill on the ball mill, weigh high-purity aluminum powder (purity ≥99.9%) and put it into the ball mill, add high-carbon steel grinding balls; the ball-to-material ratio is controlled at 30:1; (2) Add a mixture of oleic acid and anhydrous ethanol to the ball mill. The mass ratio of oleic acid to anhydrous ethanol is 1:1, and the total mass of oleic acid and anhydrous ethanol accounts for 0.5% of the total mass of aluminum powder. At this time, the filling ratio in the ball mill is 30%. (3) The ball mill is vacuumed to a pressure of 5×10 -3 Pa, then high-purity CO2 (99.99%) is introduced and the temperature is adjusted to 7.39 MPa and 32°C in the ball mill; this temperature and pressure condition can make the carbon dioxide in the ball mill in a supercritical state during ball milling; (4) Perform discharge plasma ball milling for 2 hours; during ball milling, adjust the peak-to-peak amplitude of the vibration platform to 10 mm, and the vibration acceleration of the ball mill is set to 280 m / s²; during ball milling, the operating current of the plasma power supply is 0.5 A, and the plasma excitation voltage is 10 kV; (5) After the ball milling is completed, the pressure is released to discharge the carbon dioxide, and the aluminum powder is sieved through 200 mesh to obtain flakes with a diameter of 5μm~8μm and a thickness of 0.2μm~0.8μm (diameter-to-thickness ratio>75). The electron microscope photo is shown in Figure 1 As can be seen from the figure, the aluminum flakes are thin and uniform. After further classification, flake aluminum powder with a particle size range of 6 to 8 μm is obtained, with a yield of 96%. The aluminum pigment of this example has excellent hiding power and a good metallic feel.

[0050] Example 2 The method for preparing flaky aluminum powder without mineral oil in this embodiment adopts plasma-assisted ball milling; the main raw material is aluminum powder with a particle size of 1-2 μm; oleic acid is used as a surface treatment agent, and ethanol is used as an organic solvent for ball milling; (1) Place the ball mill on the ball mill, weigh high-purity aluminum powder (purity ≥99.9%) and put it into the ball mill, add high-carbon steel grinding balls; the ball-to-material ratio is controlled at 50:1; (2) Add a mixture of oleic acid and anhydrous ethanol to the ball mill. The mass ratio of oleic acid to anhydrous ethanol is 1:1, and the total mass accounts for 3% of the total mass of the aluminum powder. At this time, the filling ratio in the ball mill is 30%. (3) The ball mill is vacuumed to a pressure of 5×10 -3 Pa, then high-purity CO2 (99.99%) is introduced and the temperature is adjusted to 100 MPa and 45°C in the ball mill; this temperature and pressure condition can make the carbon dioxide in the ball mill in a supercritical state during ball milling; (4) Conduct discharge plasma ball milling for 4 hours; during ball milling, adjust the peak-to-peak amplitude of the vibration platform to 15 mm, and set the ball mill vibration acceleration to 410 m / s²; during ball milling, the operating current of the plasma power supply is 3 A, and the plasma excitation voltage is 20 kV; (5) After the ball milling is completed, the pressure is released to discharge the carbon dioxide, and the aluminum powder is sieved through a 300-mesh screen to obtain flake aluminum powder with a flake diameter of 5 μm to 8 μm and a thickness of 0.2 μm to 0.8 μm (diameter-to-thickness ratio > 75). After further classification, aluminum powder flakes with a particle size range of 6 to 8 μm are obtained, with a yield of 95%. The aluminum pigment of this embodiment has excellent hiding power and a good metallic feel.

[0051] Example 3 The method for preparing flaky aluminum powder without mineral oil in this embodiment adopts plasma-assisted ball milling; the main raw material is aluminum powder with a particle size of 1-2 μm; oleic acid is used as a surface treatment agent, and ethanol is used as an organic solvent for ball milling; (1) Place the ball mill on the ball mill, weigh high-purity aluminum powder (purity ≥99.9%) and put it into the ball mill, add high-carbon steel grinding balls; the ball-to-material ratio is controlled at 40:1; (2) Add a mixture of oleic acid and anhydrous ethanol to the ball mill. The mass ratio of oleic acid to anhydrous ethanol is 1:1, and the total mass of oleic acid and anhydrous ethanol accounts for 1.5% of the total mass of aluminum powder. At this time, the filling ratio in the ball mill is 45%. (3) The ball mill is vacuumed to a pressure of 5×10 -3 Pa, then high-purity CO2 (99.99%) is introduced and the temperature is adjusted to 50 MPa and 60°C in the ball mill; this temperature and pressure condition can make the carbon dioxide in the ball mill in a supercritical state during ball milling; (4) Discharge plasma ball milling was performed for 3 hours; during ball milling, the peak-to-peak amplitude of the vibration platform was adjusted to 12 mm, and the vibration acceleration of the ball mill was set to 345 m / s²; during ball milling, the operating current of the plasma power supply was 1.5 A, and the plasma excitation voltage was 15 kV; (5) After the ball milling is completed, the pressure is released to discharge the carbon dioxide, and the aluminum powder is sieved through a 200-mesh screen to obtain flake aluminum powder with a flake diameter of 5 μm to 8 μm and a thickness of 0.2 μm to 0.8 μm (diameter-to-thickness ratio > 75). After further classification, aluminum powder flakes with a particle size range of 6 to 8 μm are obtained, with a yield of 96%. The aluminum pigment of this embodiment has excellent hiding power and a good metallic feel.

[0052] Comparative Example 1 The preparation method of this comparative example does not use plasma assistance compared to Example 1, and other processes are basically the same. The specific method is as follows: The main raw material is aluminum powder with a particle size of 1~2μm; oleic acid is used as the surface treatment agent and ethanol is used as the organic solvent for ball milling; (1) Place the ball mill on the ball mill, weigh high-purity aluminum powder (purity ≥99.9%) and put it into the ball mill, add high-carbon steel grinding balls; the ball-to-material ratio is controlled at 30:1; (2) Add a mixture of oleic acid and anhydrous ethanol to the ball mill. The mass ratio of oleic acid to anhydrous ethanol is 1:1, and the total mass of oleic acid and anhydrous ethanol accounts for 0.5% of the total mass of aluminum powder. At this time, the filling ratio in the ball mill is 30%. (3) The ball mill is vacuumed to a pressure of 5×10 -3 Pa, then high-purity CO2 (99.99%) is introduced and the temperature is adjusted to 7.39 MPa and 35°C in the ball mill; this temperature and pressure condition can make the carbon dioxide in the ball mill in a supercritical state during ball milling; (4) Ball milling was performed for 2 hours; during ball milling, the peak-to-peak amplitude of the vibration platform was adjusted to 10 mm, and the vibration acceleration of the ball mill was set to 280 m / s²; (5) After the ball milling is completed, the pressure is released to discharge the carbon dioxide, and the aluminum powder is sieved through 200 mesh to obtain flakes with a diameter of 4μm~6μm and a thickness of 0.4μm~1μm (diameter-to-thickness ratio>100). The electron microscope photo is shown in Figure 2 As can be seen from the figure, the aluminum flakes are relatively thick; the final obtained flaky aluminum powder has a particle size range of 4 to 6 μm. The output rate of flaky aluminum powder ≥ 6 μm is below 80%, which will cause the product pigment effect to be unsatisfactory.

[0053] The actual effect of the aluminum flakes after application of comparative example 1 and example 1 is compared. Figure 3 ; Apply the coating on the surface of coated paper by drawing method, with a coating thickness of about 15 microns; Figure 3 (a) is the application effect of Example 1, Figure 3 (b) is the application effect of Comparative Example 1; Figure 3 It can be seen that the sample of Example 1 has a strong covering ability on the background and a strong metallic feel, while the sample of Comparative Example 1 has a weak covering ability on the background, the background pattern can be seen through the pigment layer, and the metallic feel is weak.

[0054] Comparative Example 2 The preparation method of this comparative example is compared with Example 1, except that carbon dioxide is replaced by nitrogen, and other processes are basically the same. The specific method is as follows: The main raw material is aluminum powder with a particle size of 1~2μm; oleic acid is used as the surface treatment agent and ethanol is used as the organic solvent for ball milling; (1) Place the ball mill on the ball mill, weigh high-purity aluminum powder (purity ≥99.9%) and put it into the ball mill, add high-carbon steel grinding balls; the ball-to-material ratio is controlled at 30:1; (2) Add a mixture of oleic acid and anhydrous ethanol to the ball mill. The mass ratio of oleic acid to anhydrous ethanol is 1:1, and the total mass of oleic acid and anhydrous ethanol accounts for 0.5% of the total mass of aluminum powder. At this time, the filling ratio in the ball mill is 30%. (3) The ball mill is vacuumed to a pressure of 5×10 -3 Pa, then introduce high-purity nitrogen (99.99%) and adjust the temperature until the pressure in the ball mill is 7.39 MPa and the temperature is 32°C; (4) Perform discharge plasma ball milling for 2 hours; during ball milling, adjust the peak-to-peak amplitude of the vibration platform to 10 mm and the vibration acceleration of the ball mill to 280 m / s. 2 During ball milling, the operating current of the plasma power supply was 0.5 A, and the plasma excitation voltage was 10 kV; (5) After the ball milling is completed, the nitrogen is released and the aluminum powder is sieved through 200 mesh to obtain flakes with a diameter of 4 μm to 6 μm and a thickness of 0.5 μm to 1 μm (diameter-to-thickness ratio>100). The electron microscope photo is shown in Figure 4 As can be seen from the figure, the aluminum flakes are agglomerated and thick; the final obtained flaky aluminum powder has a particle size range of 4 to 6 μm. The output rate of flaky aluminum powder ≥ 6 μm is below 80%, which will cause the product pigment effect to be unsatisfactory.

[0055] The actual effect of the aluminum flakes after application of comparative example 2 and example 1 is compared. Figure 5 ; Apply the coating on the surface of coated paper by drawing method, with a coating thickness of about 15 microns; Figure 5 (a) is the application effect of Example 1, Figure 5 (b) is the application effect of comparative example 2; Figure 5 It can be seen that the sample of Example 1 has a strong covering ability on the background and a strong metallic feel, while the sample of Comparative Example 2 has a weak covering ability on the background, the background pattern can be seen through the pigment layer, and the metallic feel is weak.

Claims

1. A method for preparing flaky aluminum powder without mineral oil, characterized in that: The plasma-assisted ball milling method is used; the main raw material is aluminum powder with a particle size of 1 to 20 μm; alcohols are used as organic solvents during ball milling, and fatty acids are used as surface treatment agents during ball milling; the amount of the surface treatment agent is 0.05% to 3% of the total mass of the powder; Before ball milling, replace the air in the ball mill with carbon dioxide, then adjust the pressure in the ball mill to 7.3MPa~100MPa and the temperature to 31℃~100℃, so that the carbon dioxide in the ball mill is in a supercritical state during ball milling; adjust the peak-to-peak amplitude of the vibration platform to 10mm~15mm during ball milling; the excitation voltage of the plasma during ball milling is 10kV~20kV; collect the obtained powder after ball milling.

2. The method for preparing flaky aluminum powder free of mineral oil according to claim 1, characterized in that: The ball-to-material mass ratio of ball milling is 30:1~50; the ball mill uses metal grinding balls.

3. The method for preparing flaky aluminum powder free of mineral oil according to claim 1 or 2, characterized in that: After adding the grinding balls, grinding materials, organic solvent and surface treatment agent, the filling volume ratio in the ball mill jar is 30%~60%.

4. The method for preparing flaky aluminum powder free of mineral oil according to claim 1 or 2, characterized in that: The surface treatment agent is one or more of oleic acid, isostearic acid, stearic acid, and lauric acid; Ethanol was used as the organic solvent; The amount of the surface treatment agent used is 0.1% to 2% of the total mass of the powder.

5. The method for preparing flaky aluminum powder free of mineral oil according to claim 1 or 2, characterized in that: The mass ratio of the surface treatment agent to the organic solvent is 1:0.5-5.

6. The method for preparing flaky aluminum powder free of mineral oil according to claim 1 or 2, characterized in that: The ball milling time is 2~4h.

7. The method for preparing flaky aluminum powder free of mineral oil according to claim 1 or 2, characterized in that: The vibration acceleration of the ball mill is 280~410m / s 2 .

8. The method for preparing flaky aluminum powder free of mineral oil according to claim 1 or 2, characterized in that: The operating current of the plasma power supply is 0.5A~3A.

9. The method for preparing flaky aluminum powder free of mineral oil according to claim 1 or 2, characterized in that: The purity of the aluminum powder is above 99.9%.

10. Use of the method for preparing flaky aluminum powder free of mineral oil according to any one of claims 1 to 9 in pigments.

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