Preparation process of water-based passivated aluminum silver paste for injection molding

Abstract

The invention belongs to the field of water-based passivated aluminum paste preparation processes, and relates to a preparation process of water-based passivated aluminum paste for injection molding, which comprises the following steps: obtaining spherical aluminum powder; carrying out ball milling treatment; performing water bath treatment. The process disclosed by the invention can meet the requirements of the market on high-performance, environment-friendly and low-cost injection molding paint.

Description

Technical Field

[0001] The invention belongs to the field of injection coating preparation technology, and relates to a preparation technology of water-based passivation aluminum-silver paste for injection molding. Background Art

[0002] With the rapid development of science and technology and modern industry, the application areas of aluminum flake powder are constantly expanding, and its importance in many fields such as injection molding coatings is becoming increasingly prominent. In order to meet the urgent market demand for high-performance injection molding coatings, the quality requirements for aluminum flake powder are also constantly increasing.

[0003] Flake aluminum powder offers significant performance advantages over traditional spherical aluminum powder. Its surface area is significantly larger than that of spherical aluminum powder. At the same injection molding volume, flake aluminum powder achieves significantly better surface color than spherical aluminum powder of the same type, significantly enhancing the color of molded objects. However, compatibility issues with organic plastics have been a key factor hindering further performance improvements. With the pursuit of high-performance injection molding coatings and increasingly stringent environmental requirements, the development of flake aluminum powder with specialized properties has become increasingly urgent.

[0004] Water-based passivated aluminum paste is a flake aluminum paste that has undergone a surface passivation treatment and is produced by pure water-based ball milling. Unlike traditional aluminum pastes, the WAG (Wag series) aluminum pastes currently available on the market are produced by direct ball milling with an oily solvent to produce an oily product. This product is then filtered through a filter press to produce a paste. This product is then washed with an aqueous solvent multiple times, approximately 2-3 times. Certain additives are added during the washing process to achieve the desired effect, converting the oil-to-water ratio to the final finished water-based aluminum paste. This type of water-based aluminum paste is produced by washing the oily aluminum paste with water. This paste is initially ball milled with an oily solvent and is essentially an oily paste. However, the subsequent washing step with an aqueous solvent results in a water-based finished product. This type of aluminum paste is highly polluting and environmentally unfriendly, and the multiple washing steps with aqueous solvents can lead to waste.

[0005] Water-based ball-milled aluminum paste for passivation and injection molding has wide application in a wide range of industries, including refrigerator doors, plastics, and automotive wheels, paving the way for its widespread application. However, several pressing challenges remain. While my country has developed water-based aluminum pastes with excellent corrosion resistance, most of these pastes are oil-to-water conversions, which are inherently expensive and leave significant room for improvement in crystal structure, adhesion, hydrogen evolution rate, color, hiding power, environmental protection, and experimental hazards. Summary of the Invention

[0006] This application addresses the above-mentioned issues and provides a process for preparing a water-based passivated aluminum-silver paste for injection molding to meet the market demand for high-performance, high-hiding, and low-cost injection molding coatings. The aluminum-silver paste produced in this application does not require the introduction of oily solvents from the beginning of the production process, and directly uses aqueous solvents for ball milling and subsequent operations, which is more environmentally friendly.

[0007] In order to achieve the above technical objectives, the technical solution adopted in this application is a preparation process of a water-based passivation aluminum silver paste for injection molding, comprising the following steps: 1) Obtain spherical aluminum powder; 2) Ball milling: Put spherical aluminum powder into the ball mill; Adding 1.5-3 times the mass of dipropylene glycol monobutyl ether to the spherical aluminum powder put into the ball mill; adding 3-5% of the mass of the spherical aluminum powder as a titanate coupling agent, 0.5-1.5% of the mass of the spherical aluminum powder as oleic acid, and 1.5%-3% of the mass of the spherical aluminum powder as phosphomolybdic acid; Ball milling was performed, and the ball milling speed was set to 24 r / min; when the particle size approached 2.5 times the initial particle size, the speed was changed to 12 r / min; the ball milling was continued until the target particle size was reached and the mill was stopped; flake aluminum powder was obtained; 3) Water bath stirring and heating treatment Weigh the aluminum flake powder, dilute it with 2-3 times the amount of BCS as the aluminum flake powder, and stir it manually; Add 6%-15% of the mass of the flake aluminum powder to the phosphate passivator and 10%-18% of the mass of the flake aluminum powder to the BYK-192 and place them in a water bath. Set the stirring temperature of the water bath to 50-70°C. The mixture was stirred in a water bath using an electromagnetic stirrer, and after the stirring in the water bath was completed, suction filtration was performed to obtain a finished aqueous passivation aluminum-silver paste.

[0008] As an improved technical solution of the present application, when a ball mill is used to process spherical aluminum powder, stainless steel balls and tungsten carbide balls are used for grinding.

[0009] As an improved technical solution of this application, during the ball milling process, the mass ratio of stainless steel balls to tungsten carbide steel balls is 5:1; the mass ratio of the total mass of tungsten carbide steel balls and stainless steel balls to the mass of spherical aluminum powder is 225:(6-9).

[0010] As an improved technical solution of the present application, the stirring speed is set to 250r / min-400r / min; the water bath stirring time is 3-5 hours.

[0011] As an improved technical solution of the present application, the particle size of the spherical aluminum powder is 3-4 microns.

[0012] As an improved technical solution of the present application, the radius of the flaky aluminum powder is 12-13 microns.

[0013] Beneficial effects The technical solution applied in this application uses a ball milling passivation process to produce a high-performance, environmentally friendly, water-based passivated aluminum-silver paste with strong hiding power and low hydrogen evolution efficiency. This process uses spherical aluminum powder with a particle size of 1 / 8 in a ball milling process to produce flake aluminum powder. During the ball milling process, appropriate amounts of grinding aids and passivating agents are added to produce a flake aluminum-silver paste with a radius of 12-13 microns. The solid material is then filtered to obtain a solid material. This solid material is then stirred in a water bath. A phosphate passivating agent and a dispersant are added during the stirring process to obtain a raw slurry. After filtration, the finished product is obtained.

[0014] The most environmentally friendly feature of this process is that the solvent used from the ball milling stage is water-based, not oil-based. This makes it more environmentally friendly than traditional aluminum powder coatings. When used in injection molding, its hiding power and color rendering capabilities are superior to other similar aluminum powders.

[0015] The most significant benefit of this product is that it uses aqueous solvents for ball milling, eliminating the need for material washing and producing no oily solvents, making it environmentally friendly. Unlike WAG8005 and Silver Arrow 622F, this method simplifies raw material selection. The subsequent water bath agitation and filtration process significantly reduces sample viscosity, minimizing dust generation and facilitating safe production. Furthermore, the low hydrogen evolution value of this experimental sample, even allowing for a small amount of hydrogen volatilization after thermal storage, enhances safety and reliability during transportation.

[0016] Since this product only uses water-based solvents and does not require washing, it greatly reduces production costs. The actual unit price of the finished product is also lower than that of wag8005 and silver arrow 622f, and has strong commercial value. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The preparation process flow chart of this application is shown. DETAILED DESCRIPTION

[0018] In this article: BCS: ethylene glycol monobutyl ether.

[0019] Phosphate ester passivating agent options: dodecyl phosphate, bis-2-ethylhexyl phosphate.

[0020] like Figure 1 As shown, a preparation process of a water-based passivation aluminum silver paste for injection molding comprises the following steps 1) Obtain spherical aluminum powder with a particle size of 3-4 microns.

[0021] 2) Ball milling: Put spherical aluminum powder into the ball mill; Adding 1.5-3 times the mass of dipropylene glycol monobutyl ether to the spherical aluminum powder put into the ball mill; adding 3-5% of the mass of the spherical aluminum powder as a titanate coupling agent, 0.5-1.5% of the mass of the spherical aluminum powder as oleic acid, and 1.5%-3% of the mass of the spherical aluminum powder as phosphomolybdic acid; When using a ball mill to process spherical aluminum powder, stainless steel balls and tungsten carbide balls are used for grinding; during the ball milling process, the mass ratio of stainless steel balls to tungsten carbide steel balls is 5:1; the total mass of tungsten carbide steel balls and stainless steel balls to the mass of spherical aluminum powder is 225: (6-9); the purpose is to make the aluminum flakes more uniform during ball milling.

[0022] Ball milling was performed, and the ball milling speed was set to 24 r / min; when the ball milling speed was close to 2.5 times the initial particle size, it was switched to 12 r / min; the ball milling was continued until the target particle size was reached and the machine was stopped; and flaky aluminum powder was obtained, and the radius of the flaky aluminum powder was 12-13 microns.

[0023] 3) Water bath stirring and heating treatment Weigh the aluminum flake powder, dilute it with 2-3 times the amount of BCS as the aluminum flake powder, and stir it manually; Add 6%-15% of the mass of the flake aluminum powder to the phosphate passivator and 10%-18% of the mass of the flake aluminum powder to the BYK-192 and place them in a water bath. Set the stirring temperature of the water bath to 50-70°C. An electromagnetic stirrer is used for water bath stirring, and the stirring speed is set at 250r / min-400r / min; the water bath stirring time is 3-5 hours, and after the water bath stirring is completed, suction filtration is performed to obtain a finished water-based passivated aluminum silver paste. Example

[0024] A preparation process of aqueous passivation aluminum silver paste for injection molding, comprising the following steps 1) Obtain 6 kg of spherical aluminum powder with a particle size of 4 μm.

[0025] 2) Ball milling: 17 kg of dipropylene glycol monobutyl ether was added to the spherical aluminum powder; 2% of phosphomolybdic acid by weight of the spherical aluminum powder, 0.5% of oleic acid by weight of the spherical aluminum powder, and 3.5% of BYK-102A (titanate coupling agent) by weight of the spherical aluminum powder were added, and the mixture was stirred and mixed to prepare an aluminum powder slurry.

[0026] Put the mixed slurry into a clean and well-sealed ball mill.

[0027] After sealing the ball mill lid and setting the speed to 24 rpm, start the mill and begin ball milling. The spherical aluminum powder is milled, and mechanical force is added during the milling process to grind it into flake aluminum powder. When the particle size reaches approximately 10 microns, the speed is slowed to 12 rpm. Once the aluminum powder in the ball mill reaches the target particle size, the mill is stopped and allowed to stand for 1-2 hours. After the aluminum powder reacts completely, the material is removed and filtered to obtain flake aluminum powder (with a smooth surface and uniform structure). During the ball milling process, stainless steel balls and tungsten carbide balls are used for grinding. The mass ratio of stainless steel balls to tungsten carbide steel balls is 5:1. The mass ratio of the total steel balls (the combined mass of the stainless steel balls and tungsten carbide balls) to the spherical aluminum powder is 225:6.

[0028] If the ball milling process is not reduced, uneven pits will appear on the surface of the resulting aluminum flakes, resulting in uneven light reflection. This reduces the color of the aluminum-silver paste, resulting in poor tinting power and reduced hiding power. Furthermore, because the passivating agent tends to aggregate in surface pits, it exerts a greater effect, making the aluminum powder surface more uneven and creating an uneven passivation film. This step ensures the spherical aluminum powder remains in a non-fragmented state during ball milling, maintaining a high specific surface area and helping to improve the state and integrity of the aluminum flakes. This step is crucial for converting spherical aluminum powder into flakes.

[0029] The ball milling process is the core step of aluminum powder deformation. This process uses ball milling to remove the oxide film on the surface of the aluminum powder, and then adds phosphomolybdic acid to make the solution acidic. Since the molybdenum in phosphomolybdic acid is in a high valence state, the molybdenum ions in a high valence state have extremely strong oxidizing properties; and because the oxidizing properties of the ion surface are strong, its own ability to obtain electrons is strong, which can snatch electrons from metallic aluminum. Aluminum itself is an amphoteric substance. Therefore, metallic aluminum can separate the electrons in the outer electron orbit and reduce the potential of the molybdenum ion itself; and because the chloride ion loses electrons, its own surface activity decreases, making the aluminum more stable (Al+H3PMo 12 O 40 →Al 3+ +Mo 5+ +H + +H2O). Due to the effect of the acidic solution, the surface of the aluminum powder can be slightly dissolved to form a passivation film, and the molybdate and phosphate generated during the decomposition of molybdenum phosphate react with aluminum ions to produce a dense surface film attached to the surface of the aluminum powder (Al 3+ +PO4 3- +MoO4 2-→Al3(PO4)2·MoO4). This metal passivation film adsorbed on the surface of the aluminum powder increases the surface electron density of the aluminum ions, hindering anodic dissolution. The molybdate ions adsorbed on the surface are incorporated into the surface crystals, reducing their surface activity. Combined with the mechanical force of the ball mill, the originally spherical aluminum powder is transformed into flakes. The impact and compaction of the steel balls within the ball mill removes the surface oxide film, thereby reducing the aluminum oxide content in the aluminum-silver paste and improving the sample's color.

[0030] 3) Water bath stirring Take 50g of effective amount of flake aluminum powder out of the machine (because the aluminum-silver paste contains water, the effective amount here refers to the aluminum content), dilute it with about 100g of ethylene glycol monobutyl ether (BCS) and add it to a glass beaker; stir manually until no large pieces of solid aluminum-silver paste appear, then stir in a water bath.

[0031] 5 g of Lubrizol 2062H (phosphate passivator) and 8 g of BYK-192 were added and stirred in a water bath at a speed of 300 r / min to modify the hydrophilicity and self-hiding power of the aluminum powder; the stirring temperature was maintained at 55°C for 4 h; after the water bath stirring was completed, the obtained slurry was filtered to obtain the finished product.

[0032] A phosphate-based passivating agent is added to the aluminum powder during water bath stirring to passivate the aluminum powder surface, resulting in flaky aluminum powder. A passivation film forms on the aluminum powder surface, and the temperature reaches the semi-tempering temperature of aluminum metal at 70°C. This slight adjustment to the aluminum powder's crystal structure increases surface smoothness and reduces contact between the aluminum powder and the medium, resulting in improved performance.

[0033] Lubrizol 2062H: This product is a phosphate ester passivating agent that can form a chemical bond with aluminum metal through the phosphate ester group. This bond is easy to form a film, so this product can form a metal film on the surface of the aluminum metal that is isolated from the outside world, thereby reducing the contact between the aluminum metal and the external environment and effectively improving the corrosion resistance of the finished product.

[0034] BYK-192 dispersant: Because flake aluminum powders are prone to segregation and self-aggregation in solution, complete dispersion is difficult with mechanical stirring alone. Therefore, to prevent this aggregation, a dispersant is used to form a shell around the aluminum powder, increasing the distance between the flake particles and maintaining coating stability. Furthermore, during the dispersion process, the dispersant adheres to the surface of the flakes, influencing the van der Waals and electrostatic forces between the particles, shifting the spatial phase of the particles and preventing segregation. This also prevents pigment agglomeration or aggregation when shear forces are removed. This type of dispersant also improves hydrophilicity and contributes to improved surface leveling.

[0035] Preparation of finished product samples to be tested: Component A: filtered outlet material; Component B: BCS: water = 1:1 mixture; Component C: water-based baking varnish resin (acrylic resin) (Guangdong Hongke).

[0036] Components A, B, and C were mixed in a mass ratio of 1:3:15 to preliminarily obtain a water-based passivated aluminum coating.

[0037] The tinplate that has been polished and alkaline washed to have no pollution and oxide layer on the surface is used as the spraying substrate, sprayed with the prepared water-based passivation aluminum coating, and dried for subsequent performance testing.

[0038] Control group: Silver Arrow 622f Silver Arrow Metallic Pigments Co., Ltd., WAG5008 Anhui Xuyang Group (WAG series products).

[0039] Detection method: 1. For 14-day hydrogen evolution, the base material used was Amazon resin with a pH range of approximately 7.5-8.6, and water was used in parallel testing.

[0040] 2. Surface morphology and structure analysis: To test whether the aluminum powder is passivated, the surface morphology is observed using a SU1000 scanning electron microscope; the coating element content and the crystal surface morphology are analyzed using an MSP-2S ion diffractometer.

[0041] 3. Adhesion: To test the adhesion of the sample, first prepare the sprayed substrate and use a knife to cross-scribe the substrate into a grid. Then, use a special tape to cut a piece of tape about 75 mm long and flatten it on top of the grid. Then, quickly tear off the tape at a 60° angle. Observe the cut area of ​​the coating with a magnifying glass. The adhesion is judged based on the coating peeling within the cut area grid.

[0042] 4. Hiding power test: Mechanically stir the prepared black base material with the finished product and the reference sample to mix them evenly and compare the tinting power (using the 5.0 Wag8005 sample as the standard for testing the tinting power); prepare the sample and press it into sheets with the Wag8005 sample and the Silver Arrow 622f sample respectively, observe the hiding power of the two small sheets and use the equipment to measure the L value.

[0043] 5. Stability test: After sealing the prepared raw materials, place them in an oven at 50°C for 14 days to observe the changes in hydrogen evolution, hue, appearance and viscosity over time.

[0044] Test results: Table 1 Test results

[0045]

[0046] The aluminum-silver paste used in this process uses an aqueous organic solvent from the beginning of the ball milling stage, which not only reduces the oil-to-water washing process, but also reduces environmental pollution. Compared with the wag series products, this product not only has a very stable hydrogen release rate, but also releases less than 10ml of hydrogen in 7 days and less than 15ml of hydrogen in 30 days; while the wag sample releases less than 15ml of hydrogen in 7 days and less than 30ml of hydrogen in 30 days. Regarding the L value, when compared with wag-related finished products, this product's L value is generally above 78.41, while the wag series products generally have an L value between 78-79. In terms of injection molding metal hue, this product's metallic color is superior to wag-related products.

[0047] This finished product is a metallic aluminum-silver paste with a flaky structure. The excellent structure of the aluminum flakes allows for superior hiding during injection molding and adhesion. This superior hiding power also enhances hiding power during hiding tests. Compared to flaky aluminum powder, the flaky aluminum powder's layered structure provides a denser structure. This unique, closely packed structure effectively enhances the paste's hiding power. Furthermore, the addition of a passivating agent during the waterbath heating process creates a dense passivation film on the paste's surface. This film not only effectively isolates the paste from direct contact with the external environment but also reduces oxidation.

[0048] Because aluminum flakes form a stacked structure during injection molding, the finished product's particle size is three to four times that of the raw aluminum powder, significantly reducing the amount of aluminum paste required and ensuring a more uniform color for the molded product. However, most commercially available aluminum pastes, due to their high gassing, develop numerous tiny pores, damaging the plastic's structure and reducing the product's lifespan.

[0049] This product has low outgassing volume, so it can effectively reduce the appearance of bubbles in the finished product due to the outgassing of aluminum-silver paste due to heating during injection molding, which leads to a reduction in service life.

[0050] The process of this application not only solves the problem of lack of pure water-based passivation aluminum-silver paste on the market, but also improves traditional indicators such as hydrogen evolution and L value coverage to obtain a water-based passivation aluminum-silver paste with better performance, and is more suitable for use in injection molding processes.

Claims

1. A preparation process for aqueous passivation aluminum silver paste for injection molding, characterized in that: Includes the following steps 1) Obtain spherical aluminum powder; 2) Ball milling: Put spherical aluminum powder into the ball mill; Adding 1.5-3 times the mass of dipropylene glycol monobutyl ether to the spherical aluminum powder put into the ball mill; adding 3-5% of the mass of the spherical aluminum powder as a titanate coupling agent, 0.5-1.5% of the mass of the spherical aluminum powder as oleic acid, and 1.5%-3% of the mass of the spherical aluminum powder as phosphomolybdic acid; Ball milling was performed, and the ball milling speed was set to 24 r / min; when the particle size approached 2.5 times the initial particle size, the speed was changed to 12 r / min; the ball milling was continued until the target particle size was reached and the mill was stopped; flake aluminum powder was obtained; Water bath stirring and heating treatment Weigh the aluminum flake powder, dilute it with 2-3 times the amount of BCS as the aluminum flake powder, and stir it manually; Add 6%-15% of the mass of the flake aluminum powder to the phosphate passivator and 10%-18% of the mass of the flake aluminum powder to the BYK-192 and place them in a water bath. Set the stirring temperature of the water bath to 50-70°C. The mixture was stirred in a water bath using an electromagnetic stirrer, and after the stirring in the water bath was completed, suction filtration was performed to obtain a finished aqueous passivation aluminum-silver paste.

2. The preparation process of a water-based passivation aluminum-silver paste for injection molding according to claim 1, characterized in that: When using a ball mill to process spherical aluminum powder, stainless steel balls and tungsten carbide balls are used for grinding.

3. The preparation process of a water-based passivation aluminum-silver paste for injection molding according to claim 2, characterized in that: During the ball milling process, the mass ratio of stainless steel balls to tungsten carbide steel balls was 5:1; the mass ratio of the total mass of tungsten carbide steel balls and stainless steel balls to the mass of spherical aluminum powder was 225:(6-9).

4. The preparation process of a water-based passivation aluminum-silver paste for injection molding according to claim 1, characterized in that: The stirring speed is set at 250r / min-400r / min; the water bath stirring time is 3-5 hours.

5. The preparation process of a water-based passivation aluminum-silver paste for injection molding according to claim 1, characterized in that: The particle size of the spherical aluminum powder is 3-4 microns.

6. The process for preparing a water-based passivation aluminum-silver paste for injection molding according to claim 1, characterized in that: The radius of the flaky aluminum powder is 12-13 microns.

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