An aqueous electroplating silver material, a preparation method and application thereof

Abstract

The present application relates to the technical field of water-based paint, in particular to a water-based silver plating material with high metallic gloss, excellent adhesion and weather resistance, and a preparation method of the material and application of the material in automobile parts and metal surface treatment. The water-based aluminum silver paste with high metallic gloss and porous structure and the core-shell emulsion synergistically act on the aluminum sheet to form a high degree of parallel arrangement on the surface of the coating film, and the 60 degree gloss can reach more than 900 GU, and meanwhile, the water-based aluminum silver paste has excellent stability, the surface pores of the porous structure aluminum silver paste can adsorb resin molecules to form an anchoring effect, and the settling stability can be more than 6 months without hard precipitation.

Description

Technical Field

[0001] This invention relates to the field of water-based coatings technology, specifically to a water-based electroplating silver material with high metallic luster, excellent adhesion and weather resistance, as well as the preparation method of the material and its application in automotive parts and metal surface treatment. Background Technology

[0002] With increasingly stringent global environmental regulations, the coatings industry is undergoing a profound transformation from traditional high-VOC (volatile organic compound) solvent-based coatings to environmentally friendly water-based coatings. In the automotive wheel, exterior trim, and high-end metal decoration sectors, consumers have extremely high demands for "electroplating-grade" high metallic gloss and mirror-like effects.

[0003] However, existing water-based metallic paints still face serious challenges in practical applications: First, the surface tension of water is much higher than that of organic solvents, resulting in poor wettability of water-based systems on the substrate. It is also difficult to achieve perfect parallel orientation of aluminum silver paste in the coating film, which often leads to diffuse reflection rather than specular reflection of light, resulting in low gloss and severe mottled appearance.

[0004] Secondly, conventional aluminum silver pastes are mostly monocrystalline or have a common ball milling structure. The particle surface is smooth, and the binding force with water-based resin is weak. They are prone to agglomeration and sedimentation, and cannot achieve the dense stacking effect required for mirror reflection.

[0005] Finally, in order to ensure the application performance of water-based coatings, film-forming aids are usually added, but this often leads to a decrease in film hardness, and the water resistance and salt spray resistance cannot meet the stringent requirements of automotive parts.

[0006] Therefore, there is an urgent need to develop a water-based electroplating silver material to solve the above problems. Summary of the Invention

[0007] The purpose of this invention is to provide a water-based electroplating silver material, which solves the problems of low gloss, poor adhesion and insufficient corrosion resistance of water-based metallic paints in the prior art by using a specific modified core-shell acrylic emulsion and a porous water-based aluminum silver paste.

[0008] Another object of the present invention is to provide a method for preparing the above-mentioned water-based electroplated silver material.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: The first aspect of this invention provides an aqueous electroplating silver material, comprising the following components in parts by weight: 30-45 parts of modified core-shell acrylic emulsion; 3-8 parts of porous water-based aluminum silver paste; 0.5-2 parts of active cross-linking component; pH adjuster 0.3~1.0 parts; 5-15 parts of film-forming solubilizing medium; 0.1~0.5 parts of interface wetting stabilizer; 25-55 parts deionized water; The modified core-shell acrylic emulsion is composed of a hard core with a high glass transition temperature and a soft shell containing hydrophilic and reactive groups. The porous aqueous aluminum silver paste has micro-nano pores or a polycrystalline lamellar structure on its particle surface, and its average particle size is 5~20μm.

[0010] In some embodiments, the modified core-shell acrylic emulsion has a core polymer with a glass transition temperature of 30-60°C and a shell polymer with a glass transition temperature of -20-10°C, and the shell monomer contains acrylic acid or hydroxyethyl methacrylate; the porous aqueous aluminum silver paste has a porosity of 5-15%.

[0011] In some embodiments, the polycrystalline lamellar structure is an aluminum pigment particle composed of multiple tiny grains with an average grain size of 50~200nm, and clear grain boundaries exist between the grains. In some embodiments, the ratio of the diffraction peak intensity of the (111) crystal plane to the diffraction peak intensity of the (200) crystal plane in the X-ray diffraction pattern of the polycrystalline plate-like aluminum pigment particles, I(111) / I(200), is greater than 2.5, indicating that it has a preferred orientation crystal structure.

[0012] In some embodiments, the polycrystalline lamellar aluminum pigment particles have a surface exhibiting an uneven nanoscale texture formed by grain boundary etching, the texture having a depth of 10~50nm and a width of 20~100nm.

[0013] In some embodiments, the active crosslinking component is at least one of a blocked aliphatic polyurethane crosslinking agent, a high imino-amino resin, or a carbodiimide crosslinking agent.

[0014] In some embodiments, the porous aqueous aluminum silver paste is prepared by the following method: Flake aluminum powder is placed in an inorganic acid solution with a mass concentration of 5-15% and etched for 5-15 minutes with ultrasonic assistance, followed by washing, drying and surface passivation treatment; or, flake aluminum powder is prepared into a polycrystalline structure by high-energy ball milling under inert gas protection.

[0015] In some embodiments, the film-forming solubilizing medium is a mixture of at least two of propylene glycol methyl ether, dipropylene glycol butyl ether, or isophorone.

[0016] In some embodiments, the pH adjuster is selected from one or more of dimethylethanolamine and triethylamine.

[0017] In some embodiments, the interface wetting stabilizer is a polyether-modified polysiloxane or a high molecular weight block copolymer dispersant.

[0018] A second aspect of the present invention provides a method for preparing an aqueous electroplating silver material, comprising the following steps: (1) Pre-dispersion: Add the modified core-shell acrylic emulsion, interfacial wetting stabilizer and 65-75% of the total volume of deionized water into the stirred tank and disperse at a speed of 300-500 r / min for 10-15 minutes. (2) Mixing reaction: Add active crosslinking components, pH adjuster and film-forming solubilizing medium, under nitrogen protection, heat to 35~45℃, stir at 600~800r / min for 20~30 minutes to obtain resin mixture; (3) Paint preparation: Cool the resin mixture obtained in step (2) to 25~30℃, add porous water-based aluminum silver paste, and stir at a low speed of 400~600r / min for 10~20 minutes; (4) Post-treatment: Add the remaining deionized water to adjust the viscosity for application, filter with a 120~200 mesh filter to obtain water-based electroplating silver material.

[0019] The third aspect of the present invention provides the application of water-based electroplating silver materials on the surface of automobile wheel hubs, plastic parts or metal substrates.

[0020] Beneficial effects: (1) The present invention has high metallic gloss, and the porous structure of the water-based aluminum silver paste and the core-shell emulsion work together to make the aluminum sheets form a highly parallel arrangement on the coating surface. The gloss of 60° can reach more than 900 GU. At the same time, it has excellent stability. The pores on the surface of the porous structure aluminum silver paste can adsorb resin molecules to form an anchoring effect. The sedimentation stability reaches more than 6 months without hard precipitation. (2) This invention has a wide application window. The core-shell emulsion with a gradient glass transition temperature, combined with specific film-forming aids, enables the coating to form a uniform film in environments of 20-35℃ and 40-80%RH, and significantly improves weather resistance. The nanoscale texture formed by the grain boundaries of polycrystalline aluminum pigments effectively scatters ultraviolet rays, and the gloss retention rate is >85% after 500 hours of QUV accelerated aging. Detailed Implementation

[0021] The following specific embodiments illustrate the present invention in detail. These embodiments are intended to fully explain the technical implementation of the present invention, rather than to limit its scope of protection.

[0022] I. Raw Material Preparation 1.1 Modified Core-Shell Acrylic Emulsion Preparation process: (1) Core layer pre-emulsification: 100g of deionized water, 0.8g of sodium dodecyl sulfate and 0.3g of ammonium persulfate were added to the reactor, nitrogen was purged 3 times, the temperature was raised to 75℃, 68g of methyl methacrylate, 32g of styrene and 20g of deionized water were mixed and pre-emulsified, and added dropwise at a uniform rate for 2h, and kept warm for 1h. (2) Shell polymerization: 88g of butyl acrylate, 6g of acrylic acid, 4g of hydroxyethyl methacrylate and 30g of deionized water were pre-emulsified and added dropwise at a constant rate for 3 hours, while the temperature was controlled at 80℃ and kept warm for 2 hours. (3) Post-treatment: Cool down to 40℃, adjust pH to 7.8 with 25% ammonia water, and filter with a 120 mesh filter.

[0023] Key parameters: solid content 40.5±0.5 wt%, particle size 95±10 nm (Malvin laser particle size analyzer), shell carboxyl content 1.9 mmol / g (potentiometric titration), core Tg=45℃, shell Tg=-8℃ (DSC determination).

[0024] 1.2 Porous Waterborne Aluminum Silver Paste Option A: Inorganic acid etching method Raw material: 50g of flake aluminum powder (D50=10μm); Etching: 200 mL of 10% hydrochloric acid solution, ultrasonic power 300 W, 40℃ water bath, strictly timed for 10 min (time deviation ±30 s). Post-treatment: Wash with deionized water until pH=7.0±0.2, then vacuum dry at 60℃ for 2h; Passivation: Soak in 1% KH-550 silane coupling agent ethanol solution (pH=4.5, adjusted with acetic acid) for 30 min, then dry at 60℃; Structural verification: BET measurement showed a porosity of 8.2%, and SEM observation showed pore sizes of 80–150 nm, with no interconnected macropores.

[0025] Option B: High-energy ball milling method Conditions: Argon protection (oxygen content <10ppm), cemented carbide balls (Φ5mm), ball-to-material ratio 5:1, rotation speed 800rpm, ball milling 2.0±0.1h; Post-processing: Same as Scheme A, silane passivation; Structural verification: XRD showed I(111) / I(200)=3.0, and SEM showed grain size of 80–120 nm with no oxide layer thickening.

[0026] 1.3 Other components Active crosslinking component: Blocked aliphatic polyurethane crosslinking agent HD-326 (Wanhua Chemical); pH adjuster: dimethylethanolamine (content ≥99%); Film-forming solubilizing medium: propylene glycol methyl ether (PM) and dipropylene glycol butyl ether (DPNB) mixed in a 1:1 ratio; Interface wetting stabilizer: Tego Wet 270 (Evonik); Deionized water: conductivity ≤ 5 μS / cm.

[0027] II. Preparation Method of Water-Based Electroplating Silver Materials Pre-dispersion: Add the modified core-shell acrylic emulsion, interfacial wetting stabilizer and 70% deionized water into a jacketed stirred tank and disperse at 300–500 r / min for 12±2 min. Mixing reaction: Add active crosslinking components, pH adjuster and film-forming solubilizing medium, purge with nitrogen (flow rate 0.5 L / min), heat to 40±2℃, stir at 600–800 r / min for 25±5 min to obtain resin mixture; Paint mixing: Cool to 28±2℃, slowly add porous water-based aluminum silver paste, and stir at a low speed of 400–600 r / min for 15±3 min (avoid shearing and damaging the aluminum sheet). Post-processing: Add the remaining deionized water to adjust to the application viscosity (25℃ Ford Cup 4 viscosity 25±2 s), filter through a 150-mesh stainless steel filter to obtain the product.

[0028] The ambient humidity is controlled to ≤60% throughout the process to prevent early oxidation of aluminum powder.

[0029] Example 1 Modified core-shell acrylic emulsion (core Tg=45℃ / shell Tg=-8℃) 35 parts Porous aqueous aluminum silver paste (prepared according to scheme A, porosity 8.2%) 5 parts HD-326 crosslinking agent 1.2 parts 0.5 parts of dimethylethanolamine PM:DPNB = 1:1 10 servings Tego Wet 270 0.3 servings 48 portions of deionized water Product A1 was obtained.

[0030] Example 2 Modified core-shell acrylic emulsion (core Tg=48℃ / shell Tg=-5℃) 40 parts Porous aqueous aluminum silver paste (prepared according to scheme B, I(111) / I(200)=3.0) 6 parts HD-326 crosslinking agent 1.5 parts 0.7 parts of dimethylethanolamine PM:DPNB=1:1 12 servings Tego Wet 270 0.4 servings 39.4 parts deionized water Product A2 was obtained.

[0031] Example 3 Modified core-shell acrylic emulsion (core Tg=42℃ / shell Tg=-10℃) 45 parts Porous water-based aluminum silver paste (Solution A+B synergy: acid etching for 10 min, followed by argon balloon milling for 1 h, porosity 12%) I(111) / I(200)=3.2) 8 copies HD-326:Carbodiimide = 1:1 2.0 parts 1.0 part of dimethylethanolamine PM:DPNB=1:1 15 servings Tego Wet 270 0.4 servings 28.5 parts deionized water Product A3 was obtained. SEM observation showed that the pore size was 80–150 nm, and TEM observation confirmed that the resin was embedded in the micropores of the aluminum sheet to form an anchoring structure.

[0032] Comparative Example 1 The porous aqueous aluminum silver paste in Example 3 was replaced with ordinary aluminum silver paste (non-porous structure, average particle size 10 μm, Eckart AquaBrite®, Germany), while the other components and preparation process were exactly the same.

[0033] Comparative Example 2 The modified core-shell acrylic emulsion in Example 3 was replaced with a conventional acrylic emulsion (Tg=25℃, solid content 40%, BASF Joncryl® 678), while other components and processes remained unchanged.

[0034] Comparative Example 3 Based on the formulation of Example 3, the active crosslinking components (HD-326 and carbodiimide) were completely removed, while all other conditions remained unchanged.

[0035] Comparative Example 4 The film-forming aid (DPNB: isophorone = 1:1) in Example 3 was replaced with 15 parts of propylene glycol methyl ether (PM), while the other components remained unchanged.

[0036] Comparative Example 5 The core-shell emulsion shell formulation in Example 3 was adjusted by reducing the amount of acrylic acid from 6 parts to 1.5 parts (based on a total shell monomer amount of 100 parts), while the rest of the preparation process remained the same.

[0037] Comparative Example 6 In Example 3, the Tg of the core-shell emulsion shell layer was adjusted from -10℃ to +5℃, while other components remained unchanged.

[0038] Comparative Example 7 The acid etching time of the porous aluminum silver paste in Example 3 was extended from 10 minutes to 20 minutes (other etching conditions remained unchanged), resulting in a porosity increase to 22% and interconnected pores. The subsequent silane passivation process was the same.

[0039] Comparative Example 8 In the preparation of acid-etched aluminum silver paste in Example 3, the silane coupling agent passivation step was omitted (i.e., after etching, washing, and drying, it was used directly), while other components and processes remained unchanged.

[0040] Comparative Example 9 The process for preparing aluminum silver paste by high-energy ball milling in Example 3 was modified to ball milling in air (without argon protection), while the ball-to-material ratio, rotation speed, time and other parameters remained unchanged.

[0041] The products prepared in the examples and comparative examples were tested as follows: Detection method: All tests were conducted strictly in accordance with national standards. Optical performance: 60° gloss (GB / T 9754-2007), metallic feel (5-person blind evaluation on a 1-5 scale), and light and shadow effect (visual rating). Surface properties: Surface tension (GB / T 18445-2012 Dangling drop method, 25℃); Storage stability: 30 days in a 50℃ constant temperature chamber (GB / T 6753.3-1986), record sedimentation status, gloss retention rate, and redispersion time; Interface performance: Cross-cut adhesion (GB / T 9286-2021); Mechanical and durability properties: pencil hardness (GB / T 6739-2022), salt spray resistance (GB / T 1771-2007, corrosion spread width), QUV aging (GB / T 14522-2008, 500h); Construction performance: ABS board is sprayed in a high humidity environment of 35℃ / 80%RH, and blindly evaluated by 3 people (Excellent / Good / Average / Poor).

[0042] Note: The data is the average of three parallel experiments, with an error range of ±3%.

[0043] Table 1: Results of Optical Performance and Surface Wettability Tests (Testing standards: GB / T 9754-2007, GB / T 18445-2012) In summary, the surface tension of the example is ≤31.8 mN / m (significantly lower than 72 mN / m of water), which directly promotes the high parallel alignment of the aluminum sheets and the gloss exceeds 900 GU; the comparative examples 1 / 2 / 5 have poor wettability (>38 mN / m), resulting in a sharp drop in gloss and obvious unevenness on the two sides.

[0044] Table 2: Test Results of Storage Stability and Interfacial Adhesion (Testing standards: GB / T 6753.3-1986, GB / T 9286-2021) In summary, the triple mechanism of "micropore anchoring + cross-linking + passivation" of the present invention ensures long-term stability (no precipitation, level 0 adhesion); comparative examples 7 / 8 suffered from oxidation agglomeration and adhesion degradation to level 4 due to uncontrolled pores or lack of passivation.

[0045] Table 3: Test Results of Mechanical Properties, Durability, and Construction Window (Testing standards: GB / T 6739-2022, GB / T 1771-2007, GB / T 14522-2008) In summary, Example 3 simultaneously achieves high hardness (2H), high corrosion resistance (corrosion spread <0.8mm), high weather resistance (91.8%), and a wide construction window. Meanwhile, Comparative Example 4 has poor construction and its hardness drops to Grade B; Comparative Example 6 (shell Tg=+5℃) has a hardness of 3H, but its construction is poor; Comparative Examples 7 / 8 / 9 have a sharp drop in weather resistance (58.0–68.3%). None of the comparative examples can simultaneously meet the four major indicators of high gloss, high stability, wide construction window, and high durability.

[0046] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A water-based silver plating material, characterized in that, The components include the following parts by weight: 30-45 parts of modified core-shell acrylic emulsion; 3-8 parts of porous water-based aluminum silver paste; 0.5-2 parts of active cross-linking component; pH adjuster 0.3~1.0 parts; 5-15 parts of film-forming solubilizing medium; 0.1~0.5 parts of interface wetting stabilizer; 25-55 parts deionized water; The modified core-shell acrylic emulsion is composed of a hard core with a high glass transition temperature and a soft shell containing hydrophilic and reactive groups. The porous aqueous aluminum silver paste has micro-nano pores or a polycrystalline lamellar structure on its particle surface, and its average particle size is 5~20μm.

2. The water-based electroplating silver material according to claim 1, characterized in that, The modified core-shell acrylic emulsion has a core polymer with a glass transition temperature of 30~60℃ and a shell polymer with a glass transition temperature of -20~10℃, and the shell monomer contains acrylic acid or hydroxyethyl methacrylate; the porous aqueous aluminum silver paste has a porosity of 5~15%.

3. The water-based electroplating silver material according to claim 1, characterized in that, The polycrystalline lamellar structure is an aluminum pigment particle composed of multiple tiny grains with an average grain size of 50~200nm, and clear grain boundaries exist between the grains.

4. The water-based electroplating silver material according to claim 3, characterized in that, In the X-ray diffraction pattern, the ratio of the diffraction peak intensity of the (111) crystal plane to that of the (200) crystal plane, I(111) / I(200), is greater than 2.5, indicating that the polycrystalline plate-like aluminum pigment particles have a preferred orientation crystal structure.

5. The water-based electroplating silver material according to claim 4, characterized in that, The polycrystalline, lamellar aluminum pigment particles exhibit an uneven, nanoscale texture formed by grain boundary etching on their surface. The texture has a depth of 10-50 nm and a width of 20-100 nm.

6. The water-based electroplating silver material according to claim 1, characterized in that, The active crosslinking component is at least one of a blocked aliphatic polyurethane crosslinking agent, a high iminoamine resin, or a carbodiimide crosslinking agent.

7. The water-based electroplating silver material according to claim 1, characterized in that, The porous aqueous aluminum silver paste was prepared by the following method: Flake aluminum powder is placed in an inorganic acid solution with a mass concentration of 5-15% and etched for 5-15 minutes under ultrasonic assistance, followed by washing, drying and surface passivation treatment. Alternatively, aluminum flakes can be prepared into a polycrystalline structure by high-energy ball milling under inert gas protection.

8. The water-based electroplating silver material according to claim 1, characterized in that, The film-forming solubilizing medium is a mixture of at least two of propylene glycol methyl ether, dipropylene glycol butyl ether, or isophorone; The pH adjuster is selected from one or more of dimethylethanolamine and triethylamine; The interface wetting stabilizer is a polyether-modified polysiloxane or a high molecular weight block copolymer dispersant.

9. A method for preparing an aqueous electroplating silver material as described in any one of claims 1 to 8, characterized in that, Includes the following steps: (1) Pre-dispersion: Add the modified core-shell acrylic emulsion, interfacial wetting stabilizer and 65-75% of the total volume of deionized water into the stirred tank and disperse at a speed of 300-500 r / min for 10-15 minutes. (2) Mixing reaction: Add active crosslinking components, pH adjuster and film-forming solubilizing medium, under nitrogen protection, heat to 35~45℃, stir at 600~800r / min for 20~30 minutes to obtain resin mixture; (3) Paint preparation: Cool the resin mixture obtained in step (2) to 25~30℃, add porous water-based aluminum silver paste, and stir at a low speed of 400~600r / min for 10~20 minutes; (4) Post-treatment: Add the remaining deionized water to adjust the viscosity for application, filter with a 120~200 mesh filter to obtain water-based electroplating silver material.

10. The application of the water-based electroplating silver material according to any one of claims 1 to 8 on the surface of automobile wheel hubs, plastic parts or metal substrates.

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