A flaky zinc powder suitable for waterborne zinc-rich paint and a method for preparing the same

Abstract

This invention provides a flake-shaped zinc powder suitable for water-based zinc-rich coatings and its preparation method. The preparation method includes the following steps: preparing spherical fine zinc powder with a particle size ≤74μm; mixing the spherical fine zinc powder, additive A, and additive B, and then feeding them into a drum ball mill for ball milling under a protective gas atmosphere to obtain flake-shaped powder; the sum of the mass of additive A and additive B is 1-3% of the mass of the spherical fine zinc powder; under a protective gas atmosphere, further polishing and shaping the flake-shaped powder obtained in step S2 in a drum ball mill, and then discharging the powder; the rotation speed of the drum ball mill in this step is not greater than the rotation speed of the ball mill in step S2. The flake-shaped zinc powder obtained by the technical solution of this invention has good flowability and dispersibility, less cold welding, is easy to disperse in coatings, and is not prone to sedimentation; the powder has good flake-shaped structure and a smooth surface, and does not oxidize or generate heat even when the product is completely exposed to air.

Description

Technical Field

[0001] This invention relates to the field of materials technology, and in particular to a flake zinc powder suitable for water-based zinc-rich coatings and its preparation method. Background Technology

[0002] Existing zinc powders used in long-lasting anti-corrosion zinc-rich coatings with sacrificial anode function include spherical zinc powder and flake zinc powder. Due to the long-lasting anti-corrosion performance, thinner coating thickness, higher strength and toughness, and other mechanical properties of zinc-rich coatings using flake zinc powder, as well as the energy-saving and environmentally friendly advantages of flake zinc powder, the application of flake zinc powder in long-lasting anti-corrosion zinc-rich coatings is becoming more and more widespread, and its share of replacing spherical zinc powder is increasing. In some coatings, such as the Jumite coating for automobiles and the high-strength Dacromet coating for bolts, flake zinc powder is difficult to replace.

[0003] There are two common manufacturing processes for flake zinc powder: wet ball milling and dry ball milling. Wet ball milling for producing flake zinc powder requires a large amount of additives such as aviation kerosene, increasing VOC emissions and production safety risks. Furthermore, the process necessitates additional filtration and drying steps, increasing production management complexity. It also prolongs the time the zinc powder is exposed to air, making it prone to oxidation and blackening. Therefore, wet ball milling is rarely used.

[0004] Currently, the mainstream production of flake zinc powder uses a dry ball milling process. This involves adding raw spherical zinc powder and additives to a ball mill in a specific ratio, and then producing flake zinc powder according to set milling speed, duration, and temperature conditions. This process is short, has no VOC emissions, ensures safe and controllable production, and allows for immediate packaging. The zinc powder also has a low oxidation degree. The additives used are mostly low-activity coating agents such as stearic acid and paraffin wax, which primarily focus on dispersing.

[0005] However, existing dry ball milling processes still produce flake zinc powder with issues such as zinc powder agglomeration (possibly caused by cold welding between zinc powder particles), difficulty in controlling particle size, and a low aspect ratio. Furthermore, as the required particle size of flake zinc powder decreases, the higher the oxidation level of the zinc powder, the more severe the agglomeration becomes, resulting in significant differences in particle size distribution between production batches and poor consistency among flake zinc powder products. The main reasons for this are twofold: first, the auxiliary agents used in the production of flake zinc powder are functionally limited and cannot meet the requirements; second, the ball milling process lacks specificity and fails to meet the requirements for low oxidation, fine particle size, high aspect ratio, and high dispersion of flake zinc powder. Summary of the Invention

[0006] To address the above technical problems, this invention discloses a flake zinc powder suitable for water-based zinc-rich coatings and its preparation method. The obtained flake zinc powder has fine particle size, high aspect ratio, good dispersibility, and good consistency.

[0007] The technical solution adopted by this invention is as follows: A method for preparing flake zinc powder suitable for water-based zinc-rich coatings includes the following steps: Step S1: Prepare spherical fine zinc powder, wherein the particle size of the spherical fine zinc powder is ≤74μm; Step S2: The spherical fine zinc powder, additive A, and additive B are mixed and fed into a drum ball mill, and ball milled under a protective gas atmosphere to obtain flake-shaped powder. Additive A includes at least one of stearic acid, zinc fatty acid, paraffin wax, polytetrafluoroethylene micro powder, and fumed silica. Additive B includes at least one of salicylic acid, salicylic acid derivatives, salicylic acid polymers, triethylhexylphosphonic acid, sodium dodecyl sulfate, polydimethylsiloxane, polyether-modified polydimethylsiloxane, and long-chain alkyl-modified chain siloxane. The sum of the masses of additive A and additive B is 1-3% of the mass of the spherical fine zinc powder. Step S3: Under a protective gas atmosphere, the flake-shaped powder obtained in step S2 is further polished and shaped in a drum ball mill and then discharged; the rotational speed of the drum ball mill in this step is not greater than the rotational speed of the ball mill in step S2.

[0008] In this technical solution, during the ball milling process, additives A and B are used to modify the surface of the spherical fine zinc powder, which improves the dispersibility and oxidation resistance of the zinc powder, making it less prone to agglomeration. The resulting zinc powder has fine particle size, high aspect ratio, and high dispersion.

[0009] As a further improvement of the present invention, in step S2, the rotation speed of the drum ball mill is 40~80 rpm, the ball milling time is 1~3 hours, and the operating temperature is -30~50℃.

[0010] As a further improvement of the present invention, in step S3, the rotation speed of the drum ball mill is 20~40 rpm, the ball milling time is 2~5 hours, and the operating temperature is -30~50℃.

[0011] As a further improvement of the present invention, the protective gas is nitrogen or an inert gas.

[0012] As a further improvement of the present invention, in step S2, the drum ball mill is first evacuated and then filled with nitrogen. After evacuation, the pressure inside the drum ball mill is 0.003~0.01MPa, and after filling with nitrogen, the pressure inside the drum ball mill is 0.1~0.13MPa.

[0013] As a further improvement of the present invention, the mass of additive A is 0.5-2% of the mass of the spherical fine zinc powder, and the mass of additive B is 0.1-2% of the mass of the spherical fine zinc powder. Further, the mass of additive A is 1-2% of the mass of the spherical fine zinc powder; and the mass of additive B is 0.6-1% of the mass of the spherical fine zinc powder.

[0014] As a further improvement of the present invention, the additive A is stearic acid, a mixture of stearic acid and zinc stearate, or a mixture of stearic acid and polytetrafluoroethylene micro powder.

[0015] As a further improvement of the present invention, the auxiliary agent B is a mixture of salicylic acid, triethylhexyl phosphoric acid and polydimethylsiloxane, a mixture of salicylic acid and sodium dodecyl sulfate, or a mixture of salicylic acid and polyether-modified polydimethylsiloxane.

[0016] As a further improvement of the present invention, in step S1, the neutral particle size D50 of the spherical fine zinc powder is 5~20μm, and the total zinc content is ≥98%.

[0017] The present invention also discloses a flake zinc powder suitable for water-based zinc-rich coatings, which is prepared by the preparation method of flake zinc powder suitable for water-based zinc-rich coatings as described in any one of the above.

[0018] As a further improvement of the present invention, the total zinc content of the flake zinc powder suitable for water-based zinc-rich coatings is ≥96%, the particle size distribution is normally distributed, the neutral particle size D50 is 10~25μm, the flake thickness is 0.1~0.4μm, and the aspect ratio is 30~80.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: The flake zinc powder of this invention exhibits good flowability and dispersibility, requires minimal cold welding, and is easy to disperse in coatings, with minimal sedimentation. The powder has excellent flake structure, a smooth surface, and a flake thickness of 0.1-0.4 micrometers, which is adjustable and controllable. The aspect ratio is 30-80, also adjustable and controllable. It provides excellent coating performance, preventing oxidation and heat generation even when fully exposed to air, and exhibits good storage properties. Zinc-rich coatings prepared using flake zinc powder as filler show significantly improved corrosion resistance, with an increase in corrosion protection efficiency of over 30%. The resulting Dacromet coating has a salt spray resistance time exceeding 1000 hours (compared to approximately 400 hours for similar domestic products), and the zinc-rich coating has a salt spray resistance time exceeding 2000 hours. Furthermore, the flake zinc powder product of this invention has a metallic luster, and the Dacromet coating is bright white. It is widely applicable to various zinc-rich coatings, not only suitable for Dacromet, Jumex, and other heat-curing zinc-rich coatings, but also showing significant corrosion resistance in room-temperature curing water-based zinc-rich coatings. It produces no VOCs, making it energy-saving and environmentally friendly. Attached Figure Description

[0020] Figure 1 This is a flowchart of a method for preparing flake zinc powder suitable for water-based zinc-rich coatings according to an embodiment of the present invention.

[0021] Figure 2 This is a particle size distribution diagram of the flaky zinc powder obtained in Example 1 of the present invention.

[0022] Figure 3This is a SEM image of the flake zinc powder obtained in Example 1 of the present invention.

[0023] Figure 4 This is a particle size distribution diagram of the flake zinc powder obtained in Example 2 of the present invention.

[0024] Figure 5 This is a SEM image of the flake zinc powder obtained in Example 2 of the present invention.

[0025] Figure 6 This is a particle size distribution diagram of the flake zinc powder obtained in Example 3 of the present invention.

[0026] Figure 7 This is a SEM image of the flake zinc powder obtained in Example 3 of the present invention.

[0027] Figure 8 This is a particle size distribution diagram of the flaky zinc powder obtained in Example 4 of the present invention.

[0028] Figure 9 This is a SEM image of the flake zinc powder obtained in Example 4 of the present invention. Detailed Implementation

[0029] The preferred embodiments of the present invention will be described in further detail below.

[0030] A type of flake zinc powder suitable for water-based zinc-rich coatings is prepared using a dry ball milling process, such as... Figure 1 As shown.

[0031] Step S1: Prepare spherical fine zinc powder, wherein the particle size of the spherical fine zinc powder is ≤74μm, the neutral particle size D50 is 5~20μm, and the total zinc content is ≥98%; Step S2: The spherical fine zinc powder, additive A, and additive B are mixed and then fed into a drum ball mill for ball milling under a nitrogen atmosphere to obtain flake-shaped powder. The additives are A+B type mixed additives, with the mixed additives accounting for 1-3% of the mass of the spherical fine zinc powder. Additive A includes at least one of stearic acid, zinc fatty acid, paraffin wax, polytetrafluoroethylene micro powder, and fumed silica. Additive B includes at least one of salicylic acid, salicylic acid derivatives, salicylic acid polymers, triethylhexylphosphonic acid, sodium dodecyl sulfate, polydimethylsiloxane, polyether-modified polydimethylsiloxane, and long-chain alkyl-modified chain siloxane. Further, the mass of additive A is 0.5-2% of the mass of the spherical fine zinc powder, and the mass of additive B is 0.1-2% of the mass of the spherical fine zinc powder.

[0032] This step is the "ball milling to form flakes" process. The ball milling equipment is a drum ball mill with a diameter of Φ=1.2~2m. The process requirements are: ball mill speed 40~80 rpm, ball milling time 1~3 hours, and operating temperature control -30~50℃.

[0033] The nitrogen atmosphere is achieved by first evacuating the drum ball mill and then filling it with nitrogen. The vacuuming requires a pressure of 0.003~0.01MPa inside the drum ball mill, and the pressure inside the drum ball mill after filling with nitrogen is 0.1~0.13MPa.

[0034] Step S3: Under a nitrogen atmosphere, the flake-like powder obtained in step S2 is further polished and shaped in a drum ball mill before being discharged; the rotational speed of the drum ball mill in this step is not greater than the rotational speed of the ball mill in step S2.

[0035] This step is the "polishing and shaping" process. The equipment is still the same drum ball mill used in the "ball milling and flake forming" process. The process requirements are: ball mill speed 20~40 rpm, ball milling time 2~5 hours, and operating temperature control -30~50℃.

[0036] The key technical indicators of the flake zinc powder prepared using the above processes and requirements include, but are not limited to: total zinc ≥ 96%, normal particle size distribution, neutral particle size D50 = 10~25μm, flake thickness = 0.1~0.4μm, and aspect ratio = 30~80.

[0037] The following description uses specific examples to illustrate the point. Example 1

[0038] The flake zinc powder was prepared according to the above production process and process parameters. The specific parameters are: 1000 kg of spherical fine zinc powder, 20 kg of stearic acid as auxiliary agent A, and 6 kg of salicylic acid as auxiliary agent B.

[0039] The diameter of the drum ball mill is Φ=1.5m. In the "ball milling and flake forming" process of step S2, the drum ball mill speed is 40~80 rpm and the ball milling time is 2 hours. In the "polishing and shaping" process of step S3, the drum ball mill speed is 18~36 rpm and the ball milling time is 1.5 hours.

[0040] The obtained flake zinc powder has a total zinc content of 97.3% and a particle size distribution as follows: Figure 2 As shown, the SEM image is as follows: Figure 3 As shown, the particles exhibit a normal distribution, with a neutral particle size D50 of 24 μm, a sheet thickness of 0.21 μm, and an aspect ratio of 37. Example 2

[0041] The flake zinc powder was prepared according to the above production process and process parameters. The specific parameters are: 1000 kg of spherical fine zinc powder, A is 10 kg of stearic acid and 5 kg of zinc fatty acid, and B is 4 kg of triethylhexyl phosphate and 4 kg of polydimethylsiloxane.

[0042] The diameter of the drum ball mill is Φ=1.5m. In the "ball milling and flake forming" process of step S2, the drum ball mill speed is 40~80 rpm and the ball milling time is 1.5 hours. In the "polishing and shaping" process of step S3, the drum ball mill speed is 18~36 rpm and the ball milling time is 2.5 hours.

[0043] The obtained flake zinc powder has a total zinc content of 97.8% and a particle size distribution as shown in the figure. Figure 4 As shown, the SEM image is as follows: Figure 5 As shown, the neutral particle size D50 is 24.1 μm, the sheet thickness is 0.17 μm, and the aspect ratio is 56. Example 3

[0044] The flake zinc powder was prepared according to the above production process and process parameters. The specific parameters are: 1000 kg of spherical fine zinc powder, 10 kg of stearic acid and 6 kg of polytetrafluoroethylene micro powder as auxiliary agent A, and 6 kg of salicylic acid and 4 kg of sodium dodecyl sulfate as auxiliary agent B.

[0045] The diameter of the drum ball mill is Φ=1.5m. In the "ball milling and flake forming" process of step S2, the drum ball mill speed is 40~80 rpm and the ball milling time is 2.5 hours. In the "polishing and shaping" process of step S3, the drum ball mill speed is 18~36 rpm and the ball milling time is 2 hours.

[0046] The obtained flaky zinc powder has a total zinc content of 97.4% and a particle size distribution as shown in the figure. Figure 6 As shown, the SEM image is as follows: Figure 7 As shown, the neutral particle size D50 = 20 μm, the sheet thickness = 0.13 μm, and the aspect ratio = 71. Example 4

[0047] The flake zinc powder was prepared according to the above production process and process parameters. The specific parameters are: 1000 kg of spherical fine zinc powder, A is 10 kg of stearic acid and 4 kg of zinc fatty acid, B is 8 kg of salicylic acid and 2 kg of polyether modified polydimethylsiloxane.

[0048] The diameter of the drum ball mill is Φ=1.5m. In the "ball milling and flake forming" process of step S2, the drum ball mill speed is 40~80 rpm and the ball milling time is 1.5 hours. In the "polishing and shaping" process of step S3, the drum ball mill speed is 18~36 rpm and the ball milling time is 4 hours.

[0049] The obtained flake zinc powder has a total zinc content of 97.7% and a particle size distribution as shown in the figure. Figure 8 As shown, the SEM image is as follows: Figure 9 As shown, the neutral particle size D50 is 16.8 μm, the sheet thickness is 0.12 μm, and the aspect ratio is 69.

[0050] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A process for the production of flaky zinc powder suitable for use in aqueous zinc-rich coatings, characterized in that: Includes the following steps: Step S1: Prepare spherical fine zinc powder, wherein the particle size of the spherical fine zinc powder is ≤74μm; Step S2: The spherical fine zinc powder, additive A, and additive B are mixed and fed into a drum ball mill, and ball milled under a protective gas atmosphere to obtain flake-shaped powder. Additive A includes at least one of stearic acid, zinc fatty acid, paraffin wax, polytetrafluoroethylene micro powder, and fumed silica. Additive B includes at least one of salicylic acid, salicylic acid derivatives, salicylic acid polymers, triethylhexylphosphonic acid, sodium dodecyl sulfate, polydimethylsiloxane, polyether-modified polydimethylsiloxane, and long-chain alkyl-modified chain siloxane. The sum of the masses of additive A and additive B is 1-3% of the mass of the spherical fine zinc powder. Step S3: Under a protective gas atmosphere, the flake-like powder obtained in step S2 is further polished and shaped in a drum ball mill and then discharged; the rotational speed of the drum ball mill in this step is not greater than the rotational speed of the ball mill in step S2. In step S2, the rotation speed of the drum ball mill is 40~80 rpm, the ball milling time is 1~3 hours, and the operating temperature is -30~50℃.

2. The process for the preparation of a flaky zinc powder suitable for use in waterborne zinc-rich paints according to claim 1, characterized in that: In step S3, the rotation speed of the drum ball mill is 20~40 rpm, the ball milling time is 2~5 hours, and the operating temperature is -30~50℃.

3. The method for preparing flake zinc powder suitable for water-based zinc-rich coatings according to claim 1, characterized in that: The protective gas is nitrogen or an inert gas.

4. The method for preparing flake zinc powder suitable for water-based zinc-rich coatings according to claim 3, characterized in that: In step S2, the drum ball mill is first evacuated and then filled with nitrogen. After evacuation, the pressure inside the drum ball mill is 0.003~0.01MPa. After filling with nitrogen, the pressure inside the drum ball mill is 0.1~0.13MPa.

5. The method for preparing flake zinc powder suitable for water-based zinc-rich coatings according to claim 1, characterized in that: The mass of additive A is 0.5-2% of the mass of the spherical fine zinc powder, and the mass of additive B is 0.1-2% of the mass of the spherical fine zinc powder.

6. The method for preparing flake zinc powder suitable for water-based zinc-rich coatings according to claim 5, characterized in that: The mass of additive A is 1-2% of the mass of the spherical fine zinc powder, and the mass of additive B is 0.6-1% of the mass of the spherical fine zinc powder.

7. The method for preparing flake zinc powder suitable for water-based zinc-rich coatings according to any one of claims 1 to 6, characterized in that: In step S1, the neutral particle size D50 of the spherical fine zinc powder is 5~20μm, and the total zinc content is ≥98%.

8. A flake zinc powder suitable for water-based zinc-rich coatings, characterized in that: The zinc powder is prepared using the method for preparing flake zinc powder suitable for water-based zinc-rich coatings as described in any one of claims 1 to 7.

9. The flake zinc powder suitable for water-based zinc-rich coatings according to claim 8, characterized in that: The flake zinc powder suitable for water-based zinc-rich coatings has a total zinc content of ≥96%, a normally distributed particle size distribution, a neutral particle size D50 of 10~25μm, a flake thickness of 0.1~0.4μm, and an aspect ratio of 30~80.

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