Environment-friendly cyanide-free gold-like electroplating solution for automotive interior leather and electroplating method thereof

Abstract

The application discloses an environment-friendly cyanide-free imitation gold electroplating solution for automotive interior leather and an electroplating method thereof, and belongs to the technical field of surface electroplating treatment of metal or nonmetal products. The electroplating solution is mainly composed of potassium pyrophosphate as a main complexing agent, and a multi-element synergistic complexing system is formed by compounding phosphonohydroxyacetic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, potassium sodium tartrate and potassium citrate; the main salt is copper pyrophosphate, zinc sulfate heptahydrate and sodium stannate, and sodium sulfite and sodium erythorbate are simultaneously added as antioxidants, nano SiC microparticles modified by a silane coupling agent, a composite brightener and a composite surfactant are added, and the pH of the electroplating solution is 8.5-9.5. The application further provides a complete electroplating method for PU leather without base cloth, which comprises pretreatment, formation of a conductive layer, pre-plating of nickel, imitation gold electroplating and post-treatment. The application is environment-friendly and efficient, has strong plating layer adhesion, and meets the automotive interior leather vehicle-level use requirements.

Description

Technical Field

[0001] This invention relates to the field of surface electroplating treatment technology for metal or non-metal products, and in particular to an environmentally friendly cyanide-free imitation gold electroplating solution for automotive interior leather and its electroplating method. Background Technology

[0002] With the rapid development of the automotive industry and the increasing demands of consumers for the aesthetics of car interiors, decorative coatings with a golden luster have been widely used in automotive interior parts (such as air conditioning vents, door handles, steering wheel trim, and dashboard bezels). Traditional imitation gold electroplating processes mostly use cyanide systems. Although this system has high stability and uniform coating color, cyanide is highly toxic and poses a serious threat to the environment and the health of operators, and has been gradually restricted by national and industry regulations.

[0003] To replace cyanide-based gold plating, the industry has developed various cyanide-free plating systems, such as pyrophosphate systems, citrate systems, and HEDP (hydroxyethylidene diphosphonic acid) systems. However, existing cyanide-free gold plating processes still face several technical bottlenecks: First, the plating bath composition is too simple, making it difficult to achieve stable co-deposition of metal ions such as copper, zinc, and tin. This results in the plating color being difficult to control within the realistic 18K-24K gold hue range, leading to poor batch-to-batch stability. Second, metal ions in the plating bath are prone to hydrolysis, resulting in low tolerance for impurity ions, short maintenance cycles, and high production costs. Third, the adhesion between the plating layer and the non-woven PU leather substrate is insufficient, and the wear resistance and corrosion resistance are difficult to meet the stringent automotive-grade service life requirements (5-10 years) for automotive interior parts.

[0004] Therefore, developing an environmentally friendly, stable, high-performance, and industrially viable cyanide-free gold plating solution and its supporting plating method is of significant market value. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology by proposing an environmentally friendly, cyanide-free imitation gold electroplating solution and its electroplating method for automotive interior leather.

[0006] The environmentally friendly, cyanide-free, gold-like electroplating solution for automotive interior leather of this invention uses potassium pyrophosphate as the main complexing agent, compounded with phosphonohydroxyacetic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, potassium sodium tartrate, and potassium citrate to form a multi-component synergistic complexing system; the main salts are copper pyrophosphate, zinc sulfate heptahydrate, and sodium stannate, and the coating color is controlled by adjusting the ratio; sodium sulfite and sodium isoascorbate are added as antioxidants, along with nano-SiC particles modified with a silane coupling agent, a composite brightener composed of β-naphthol polyoxyethylene ether and polyethyleneimine, and a composite surfactant composed of dodecyl dimethyl benzyl ammonium bromide and polyethylene glycol isooctylphenol ether; the pH of the electroplating solution is 8.5-9.5.

[0007] Another objective of this invention is to provide an electroplating method for the above-mentioned environmentally friendly cyanide-free imitation gold electroplating solution for automotive interior leather on non-woven PU leather, including a pretreatment process, a conductive layer formation process, a pre-nickel plating process, an imitation gold electroplating process, and a post-treatment process.

[0008] This invention provides an environmentally friendly, cyanide-free, gold-like electroplating solution for automotive interior leather. Each liter of the electroplating solution comprises the following components: 200-260 g / L potassium pyrophosphate, 10-15 g / L phosphonoglycolic acid, 10-15 g / L 2-phosphonobutane-1,2,4-tricarboxylic acid, 8-12 g / L potassium sodium tartrate, 20-30 g / L potassium citrate, 18-24 g / L copper pyrophosphate, 30-45 g / L zinc sulfate heptahydrate, 4-8 g / L sodium stannate, 2-5 g / L sodium sulfite, 0.5-1.5 g / L sodium isoascorbate, 1-3 g / L surface-treated nano-SiC particles, 2-4 g / L composite brightener, and 0.3-0.6 g / L composite surfactant; the pH of the electroplating solution is 8.5-9.5.

[0009] Preferably, the surfactant is a compound of dodecyl dimethyl benzyl ammonium bromide and polyethylene glycol isooctylphenol ether X-100 in a molar ratio of 1:1-2.

[0010] Preferably, the nano-SiC particles have a particle size of 30-60 nm and their surface is modified with a silane coupling agent, KH-560.

[0011] Preferably, the composite brightener is a mixture of β-naphthol polyoxyethylene ether and polyethyleneimine in a mass ratio of 3-5:1, wherein the number-average molecular weight of β-naphthol polyoxyethylene ether is 1000-3000 Da and the number-average molecular weight of polyethyleneimine is 5000-10000 Da.

[0012] An electroplating method using an environmentally friendly, cyanide-free, gold-imitation electroplating solution for automotive interior leather includes the following steps:

[0013] S1. Pretreatment: The baseless PU leather is subjected to degreasing, roughening, cleaning, sensitization and activation treatment in sequence. Degreasing is carried out by ultrasonic degreasing with a weak alkaline degreasing solution at 35-40℃ for 3-5 minutes. Roughening is carried out by soaking in 5-10% ethyl acetate ethanol solution at room temperature for 1-2 minutes. Cleaning is carried out by first cleaning with anhydrous ethanol 2-3 times, then cleaning with warm water at 35-40℃ 2-3 times, and finally cleaning with deionized water 2-3 times. Sensitization is carried out by treating with stannous chloride sensitizing solution at room temperature for 2-3 minutes. Activation is carried out by treating with palladium chloride activation solution at room temperature for 2-3 minutes, and then reducing with 8-12g / L sodium hypophosphite solution at room temperature for 1-2 minutes.

[0014] S2. Formation of conductive layer: Using a chemical nickel plating solution, the pretreated non-backed PU leather is chemically nickel plated at 40-50℃ for 10-15 minutes, and then dried in an oven at 70-80℃ for 10-15 minutes to form a conductive metal layer with a thickness of 0.5-1.0μm.

[0015] S3. Pre-plating nickel: Bright nickel plating solution is used, with a cathode current density of 1.0-1.5 A / dm³. 2 Electroplating is performed at a temperature of 35-40℃ and a pH of 4.0-5.0 for 5-10 minutes to deposit a bright nickel layer on the conductive metal layer, with a nickel layer thickness of 2-4μm.

[0016] S4. Preparation of imitation gold electroplating solution: Dissolve potassium pyrophosphate, phosphonohydroxyacetic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, potassium sodium tartrate, potassium citrate, copper pyrophosphate, zinc sulfate heptahydrate, and sodium stannate in deionized water. At room temperature, mechanically stir at 200-400 rpm for 30-60 min until completely dissolved to form a base plating solution. Add sodium sulfite and sodium isoascorbate and stir for 5-10 min. Dissolve the composite surfactant in deionized water and add it to the base plating solution and stir for 10-20 min. Add surface-treated nano-SiC particles and ultrasonically disperse for 10-30 min to ensure uniform dispersion. Add the composite brightener and continue stirring for 10-30 min. Adjust the pH to 8.5-9.5 with potassium hydroxide. After standing to defoam, the imitation gold electroplating solution is obtained.

[0017] S5. Imitation Gold Electroplating: The baseless PU leather pre-plated with nickel (S3) is first coated with a dilute copper solution at 0.3-0.5 A / dm². 2 After flash plating for 20-30 seconds, the plate is placed in the electroplating solution prepared in S4, with a stainless steel plate as the anode, and a cathode current density of 0.6-1.0 A / dm³. 2 Under conditions of 30-35℃ and pH 8.5-9.5, use a cathode moving and stirring motion of 0.5-1.0 m / min for 3-5 minutes for electroplating;

[0018] S6. Post-treatment: The imitation gold plating is passivated and then sealed with organic varnish.

[0019] Preferably, the non-woven PU leather in S1 refers to a non-woven fiber base fabric and a polyurethane dense film with a thickness of 0.5-1.5mm.

[0020] Preferably, the weakly alkaline degreasing solution in S1 contains 15-25 g / L sodium carbonate, 10-15 g / L trisodium phosphate, and 3-5 g / L nonionic surfactant T102.

[0021] Preferably, the stannous chloride sensitizing solution in S1 is formulated with stannous chloride dihydrate 10-15 g / L, lactic acid 5-10 mL / L, and pH 3.5-4.5.

[0022] Preferably, the palladium chloride activation solution in S1 has the following formulation: palladium chloride 0.1-0.3 g / L, sodium citrate 5-10 g / L, pH 6.5-7.5.

[0023] Preferably, the electroless nickel plating solution in S2 contains 25-30 g / L nickel sulfate, 20-25 g / L sodium hypophosphite, 15-20 g / L sodium citrate, and 10-15 g / L sodium acetate, with a pH of 7.0-8.0.

[0024] Preferably, the bright nickel plating solution in S3 contains 150-180 g / L nickel sulfate, 30-40 g / L nickel chloride, 25-30 g / L boric acid, 0.5-1.0 g / L sodium saccharin, and 1-2 mL / L of 791 brightener.

[0025] Preferably, the dilute copper solution in S5 is 15-20 g / L copper pyrophosphate, 80-100 g / L potassium pyrophosphate, and has a pH of 8.0-9.0.

[0026] Preferably, in step S6, the passivation treatment involves immersing the sample in a 30-50 mL / L trivalent chromium blue-white passivating agent solution at room temperature for 20-30 seconds, followed by rinsing with deionized water. The organic varnish sealing treatment uses a flexible polyurethane transparent varnish with a spray thickness of 8-12 μm, which is then cured at 60-65°C for 30-40 minutes.

[0027] Preferably, the mechanism of action of the environmentally friendly cyanide-free imitation gold electroplating solution for automotive interior leather in this invention is explained as follows:

[0028] This electroplating solution uses potassium pyrophosphate as the main complexing agent, which forms a stable copper pyrophosphate coordination ion with copper ions through pyrophosphate. At the same time, it is compounded with phosphonohydroxyacetic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, potassium sodium tartrate and potassium citrate to form a multi-component synergistic complexing system. Among them, phosphonohydroxyacetic acid and 2-phosphonobutane-1,2,4-tricarboxylic acid, as organophosphonic acid complexing agents, have strong coordination ability with zinc and tin ions, which can effectively inhibit the formation of hydroxide precipitation of zinc and tin under alkaline conditions and prevent the precipitation of metastannic acid colloid generated by the hydrolysis of sodium stannate; potassium sodium tartrate and potassium citrate, as auxiliary complexing agents, further stabilize the metal ions and expand the range of cathode current density; this mixed complexing system realizes the stable co-deposition of copper, zinc and tin metal ions under cyanide-free conditions, avoiding the environmental pollution problems of traditional cyanide systems; sodium sulfite and sodium isoascorbate, as composite reducing agents and antioxidants, prevent the polymerization and precipitation of stannate ions on the one hand, and inhibit the disproportionation reaction of a small amount of Cu⁺ ions that may be generated in the plating solution on the other hand, thereby maintaining the long-term stability of the plating solution.

[0029] After surface treatment, the nano-SiC particles, modified with the silane coupling agent KH-560, possess organophilic functional groups on their surface, improving their dispersibility and suspension stability in the plating bath. During electrodeposition, the nano-SiC particles are adsorbed onto the cathode surface and co-deposited into the alloy coating, significantly enhancing the coating's hardness, wear resistance, and corrosion resistance through dispersion strengthening. In the composite brightener, β-naphthol polyoxyethylene ether, as a nonionic surfactant, can adsorb onto the micro-protrusions on the cathode surface, suppressing tip discharge and thus playing a leveling and brightening role. Polyethyleneimine, on the other hand, is superior... First, it adsorbs onto the active growth points, refining the grains and inhibiting dendrite growth. The combination of the two can obtain a mirror-bright imitation gold coating over a wide current density range. In the composite surfactant, dodecyl dimethyl benzyl ammonium bromide is a cationic surfactant, and polyethylene glycol isooctylphenol ether is a nonionic surfactant. When the two are combined in a certain proportion, on the one hand, it significantly reduces the surface tension of the plating solution, improves the wettability of the cathode, and prevents pinhole formation; on the other hand, the cationic surfactant carries a positive charge and can effectively adsorb onto the negatively charged cathode surface, enhancing the adsorption and co-deposition efficiency of nanoparticles.

[0030] During the electroplating process, the cathode current density is controlled at 0.6-1.0 A / dm³. 2At a temperature of 30-35℃ and a pH of 8.5-9.5, the deposition potentials of the various metal ions are close, forming a copper-zinc-tin alloy co-deposition, resulting in a uniformly colored, gold-like imitation gold plating layer similar to 18-24K gold. Furthermore, the pre-plated nickel layer not only provides a good conductive substrate for the imitation gold plating but also effectively alleviates the internal stress difference between the non-woven PU leather and the metal plating layer, avoiding peeling or cracking problems caused by the mismatch in elastic modulus between the flexible substrate and the hard plating layer, significantly improving the adhesion reliability of the plating layer. The flash copper plating treatment after the pre-plated nickel layer serves to: ensure that the nickel layer surface is in a vacuum... A thin oxide film easily forms in the atmosphere. Flash copper plating can remove the oxide film and provide an active copper surface. At the same time, copper has better lattice matching with the subsequent gold-like plating layer (copper-based alloy), thereby inhibiting the substitution reaction and ensuring the bonding strength and color uniformity. Overall, the electroplating solution of the present invention achieves a stable, environmentally friendly, and high-performance cyanide-free gold-like electrodeposition process through the comprehensive design of multi-component complexing agents, composite antioxidants, nano-reinforcing phases, and synergistic brightening system. The resulting plating layer has bright color, strong bonding strength, and is wear-resistant and corrosion-resistant, making it particularly suitable for surface decoration of plastic parts used in automotive interior leather.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] 1. This invention employs a multi-component synergistic complexation system composed of potassium pyrophosphate, phosphonohydroxyacetic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, potassium sodium tartrate, and potassium citrate, replacing the traditional cyanide system. While achieving stable co-deposition of copper, zinc, and tin ions, it completely avoids the use of cyanide, significantly reducing harm to the environment and operators, and meeting the environmental protection requirements for automotive interior leather production.

[0033] 2. By adding sodium sulfite and sodium isoascorbate as composite reducing agents and antioxidants, this invention effectively inhibits the hydrolysis of sodium stannate and the precipitation of metastannic acid colloids, while preventing the disproportionation reaction of Cu⁺ ions, thus significantly improving the long-term storage stability and service life of the plating solution.

[0034] 3. This invention uses nano-SiC particles modified with silane coupling agent KH-560 to disperse evenly and stably in the plating solution. They are co-embedded in the alloy coating by electrodeposition, and the dispersion strengthening effect significantly improves the hardness, wear resistance and corrosion resistance of the imitation gold coating, enabling the coating to withstand the friction and contact of automotive interior parts during long-term use.

[0035] 4. This invention uses a composite brightener made of β-naphthol polyoxyethylene ether and polyethyleneimine, which can be synergistically adsorbed on the cathode surface, both smoothing and brightening the surface and refining the grains. It can obtain a mirror-like gold plating with uniform color and similarity to 18-24K gold within a wide current density range, which greatly enhances the decorative aesthetics of automotive interior leather.

[0036] 5. The present invention uses a combination of cationic and nonionic surfactants, which not only reduces the surface tension of the plating solution, improves the wettability of the cathode, and prevents pinhole defects, but also enhances the adsorption efficiency of nanoparticles on the cathode surface due to the positive charge of the cationic surfactant, thereby further improving the quality and performance of the composite coating.

[0037] 6. In the optimized electroplating process, the introduction of a pre-plated nickel layer effectively alleviates the difference in thermal expansion coefficients between the baseless PU leather and the imitation gold plating layer. Combined with flash copper plating, it significantly enhances the adhesion between the plating layer and the substrate, avoiding failure problems such as peeling and cracking, and ensuring the reliability of automotive interior leather under temperature change environments. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the process flow for an electroplating method using an environmentally friendly, cyanide-free imitation gold electroplating solution for automotive interior leather, as proposed in this invention. Detailed Implementation

[0039] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0040] Example 1: An environmentally friendly, cyanide-free imitation gold electroplating solution for automotive interior leather, each liter of the electroplating solution comprising the following components: 200g potassium pyrophosphate, 10g phosphonohydroxyacetic acid, 10g 2-phosphonobutane-1,2,4-tricarboxylic acid, 8g potassium sodium tartrate, 20g potassium citrate, 18g copper pyrophosphate, 30g zinc sulfate heptahydrate, 4g sodium stannate, 2g sodium sulfite, 0.5g sodium isoascorbate, 1g nano-SiC particles (30nm particle size) treated with KH-560, 2g composite brightener (1.5g β-naphthol polyoxyethylene ether, molecular weight 1000Da; 0.5g polyethyleneimine, molecular weight 5000Da), 2g composite surfactant (0.12g dodecyl dimethyl benzyl ammonium bromide; 0.18g polyethylene glycol isooctylphenol ether).

[0041] like Figure 1 As shown, an electroplating method using an environmentally friendly, cyanide-free, gold-imitation electroplating solution for automotive interior leather includes the following steps:

[0042] S1. Pretreatment: The 0.5 mm polyurethane dense membrane was subjected to degreasing, roughening, cleaning, sensitization and activation treatments in sequence. Degreasing was performed by ultrasonic degreasing at 35℃ for 5 min using a weak alkaline degreasing solution (sodium carbonate 15 g / L, trisodium phosphate 10 g / L, nonionic surfactant T102 3 g / L). Roughening was performed by soaking in 5% ethyl acetate ethanol solution at room temperature for 2 min. Cleaning was performed by first cleaning twice with anhydrous ethanol, then twice with 35℃ warm water, and finally twice with deionized water. Sensitization was performed by treating with stannous chloride sensitizing solution (stannous chloride dihydrate 10 g / L, lactic acid 5 mL / L, pH 3.5) at room temperature for 3 min. Activation was performed by treating with palladium chloride activating solution (palladium chloride 0.1 g / L, sodium citrate 5 g / L, pH 6.5) at room temperature for 3 min, and then reduced with 8 g / L sodium hypophosphate solution at room temperature for 2 min.

[0043] S2. Formation of conductive layer: Using a chemical nickel plating solution (nickel sulfate 25g / L, sodium hypophosphite 20g / L, sodium citrate 15g / L, sodium acetate 10g / L, pH 7.0), the pretreated polyurethane dense film was chemically nickel plated for 15min at 40℃, and then dried in an oven at 70℃ for 15min to form a conductive metal layer with a thickness of 1.0μm.

[0044] S3. Pre-plating nickel: Using a bright nickel plating solution (nickel sulfate 150g / L, nickel chloride 30g / L, boric acid 25g / L, sodium saccharin 0.5g / L and 791 brightener 1mL / L), at a cathode current density of 1.0A / dm³. 2 At a temperature of 35℃ and pH=4.0, electroplating was performed for 10 minutes to electroplat a bright nickel layer on the conductive metal layer, with a nickel layer thickness of 4μm.

[0045] S4. Preparation of imitation gold electroplating solution: Dissolve the weighed potassium pyrophosphate, phosphonohydroxyacetic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, potassium sodium tartrate, potassium citrate, copper pyrophosphate, zinc sulfate heptahydrate, and sodium stannate in deionized water. At room temperature, mechanically stir at 200 rpm for 60 min until completely dissolved to form a base plating solution. Add sodium sulfite and sodium isoascorbate and stir for 10 min. Dissolve the composite surfactant in deionized water and add it to the base plating solution and stir for 20 min. Add surface-treated nano-SiC particles and ultrasonically disperse for 30 min to ensure uniform dispersion. Add the composite brightener and continue stirring for 30 min. Adjust the pH to 8.5 with potassium hydroxide. After standing to defoam, the imitation gold electroplating solution is obtained.

[0046] S5. Imitation Gold Electroplating: The polyurethane dense film pre-plated with nickel in S3 is first coated with a dilute copper solution (copper pyrophosphate 15g / L, potassium pyrophosphate 80g / L, pH=8.0) at 0.3A / dm³. 2Flash plating for 30 seconds, then immersing in the electroplating solution prepared in S4, using a stainless steel plate as the anode, with a cathode current density of 0.6 A / dm³. 2 Under conditions of 30℃ and pH 8.5, electroplating was performed for 5 minutes with cathode stirring at a speed of 0.5 m / min.

[0047] S6. Post-treatment: The imitation gold plating layer is passivated sequentially using a 30mL / L trivalent chromium blue-white passivating agent solution. It is then immersed at room temperature for 30s and cleaned with deionized water. A layer of flexible polyurethane transparent varnish is then sprayed onto the surface with a thickness of 8μm and cured at 60℃ for 40min.

[0048] Example 2: An environmentally friendly, cyanide-free imitation gold electroplating solution for automotive interior leather, each liter of the electroplating solution comprising the following components: 230g potassium pyrophosphate, 12g phosphonohydroxyacetic acid, 12g 2-phosphonobutane-1,2,4-tricarboxylic acid, 10g potassium sodium tartrate, 25g potassium citrate, 21g copper pyrophosphate, 38g zinc sulfate heptahydrate, 6g sodium stannate, 3.5g sodium sulfite, 1.0g sodium isoascorbate, 2g nano-SiC particles (45nm particle size) treated with KH-560, 3g composite brightener (2.4g β-naphthol polyoxyethylene ether, molecular weight 2000Da; 0.6g polyethyleneimine, molecular weight 8000Da), and 0.45g composite surfactant (0.18g dodecyl dimethyl benzyl ammonium bromide; 0.27g polyethylene glycol isooctylphenol ether).

[0049] An electroplating method using an environmentally friendly, cyanide-free, gold-imitation electroplating solution for automotive interior leather includes the following steps:

[0050] S1. Pretreatment: The 1.0 mm thick polyurethane membrane was subjected to degreasing, roughening, cleaning, sensitization, and activation treatments in sequence. Degreasing was performed using a weakly alkaline degreasing solution (sodium carbonate 20 g / L, trisodium phosphate 12 g / L, nonionic surfactant T102 4 g / L) at 38°C with ultrasonic degreasing for 4 min. Roughening was performed by soaking in an 8% ethyl acetate ethanol solution at room temperature for 1.5 min. Cleaning was performed by first cleaning with anhydrous ethanol 3 times, then with 35°C warm water 3 times, and finally with deionized water 3 times. Sensitization was performed using a stannous chloride sensitizing solution (stannous chloride dihydrate 12 g / L, lactic acid 8 mL / L, pH 4.0) at room temperature for 2.5 min. Activation was performed using a palladium chloride activation solution (palladium chloride 0.2 g / L, sodium citrate 8 g / L, pH 7.0) at room temperature for 2.5 min, and then reduced with a 10 g / L sodium hypophosphate solution at room temperature for 1.5 min.

[0051] S2. Formation of conductive layer: Using a chemical nickel plating solution (nickel sulfate 28g / L, sodium hypophosphite 22g / L, sodium citrate 18g / L, sodium acetate 12g / L, pH 7.5), the pretreated polyurethane dense film was chemically nickel plated for 12 min at 45℃, and then dried in an oven at 75℃ for 12 min to form a conductive metal layer with a thickness of 0.8μm.

[0052] S3. Pre-plating nickel: Using a bright nickel plating solution (nickel sulfate 165g / L, nickel chloride 35g / L, boric acid 28g / L, sodium saccharin 0.8g / L and 791 brightener 1.5mL / L), at a cathode current density of 1.2A / dm³. 2 At a temperature of 38℃ and a pH of 4.5, electroplating was performed for 8 minutes to deposit a bright nickel layer on the conductive metal layer. The nickel layer thickness was 3μm.

[0053] S4. Preparation of imitation gold electroplating solution: Dissolve the weighed potassium pyrophosphate, phosphonohydroxyacetic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, potassium sodium tartrate, potassium citrate, copper pyrophosphate, zinc sulfate heptahydrate, and sodium stannate in deionized water. At room temperature, mechanically stir at 300 rpm for 45 min until completely dissolved to form a base plating solution. Add sodium sulfite and sodium isoascorbate and stir for 7 min. Dissolve the composite surfactant in deionized water and add it to the base plating solution and stir for 15 min. Add surface-treated nano-SiC particles and ultrasonically disperse for 20 min to ensure uniform dispersion. Add the composite brightener and continue stirring for 20 min. Adjust the pH to 9.0 with potassium hydroxide. After standing to defoam, the imitation gold electroplating solution is obtained.

[0054] S5. Imitation Gold Electroplating: The polyurethane dense film pre-plated with nickel in S3 is first treated with a dilute copper solution (copper pyrophosphate 18g / L, potassium pyrophosphate 90g / L, pH=8.5) at 0.4A / dm³. 2 After flash plating for 25 seconds, the plate is placed in the electroplating solution prepared in S4, with a stainless steel plate as the anode, and a cathode current density of 0.8 A / dm³. 2 Under conditions of 32℃ and pH 9.0, electroplating was performed for 4 minutes with cathode stirring at a speed of 0.8 m / min.

[0055] S6. Post-treatment: The gold plating layer was passivated sequentially using a 40mL / L trivalent chromium blue-white passivating agent solution. It was then immersed at room temperature for 25s and cleaned with deionized water. A layer of flexible polyurethane transparent varnish with a thickness of 10μm was then sprayed onto the surface and cured at 65℃ for 35min.

[0056] Example 3: An environmentally friendly, cyanide-free imitation gold electroplating solution for automotive interior leather, each liter of the electroplating solution comprising the following components: 260g potassium pyrophosphate, 15g phosphonohydroxyacetic acid, 15g 2-phosphonobutane-1,2,4-tricarboxylic acid, 12g potassium sodium tartrate, 30g potassium citrate, 24g copper pyrophosphate, 45g zinc sulfate heptahydrate, 8g sodium stannate, 5g sodium sulfite, 1.5g sodium isoascorbate, 3g nano-SiC particles (60nm particle size) treated with KH-560, 4g composite brightener (3.33g β-naphthol polyoxyethylene ether, molecular weight 3000Da; 0.67g polyethyleneimine, molecular weight 10000Da), and 0.6g composite surfactant (0.2g dodecyl dimethyl benzyl ammonium bromide; 0.4g polyethylene glycol isooctylphenol ether).

[0057] An electroplating method using an environmentally friendly, cyanide-free, gold-imitation electroplating solution for automotive interior leather includes the following steps:

[0058] S1. Pretreatment: The 1.5 mm thick polyurethane dense membrane was subjected to degreasing, roughening, cleaning, sensitization and activation treatments in sequence. Degreasing was performed by ultrasonic degreasing at 40℃ for 3 min using a weak alkaline degreasing solution (sodium carbonate 25 g / L, trisodium phosphate 15 g / L, nonionic surfactant T102 5 g / L). Roughening was performed by soaking in 10% ethyl acetate ethanol solution at room temperature for 1 min. Cleaning was performed by first cleaning with anhydrous ethanol 3 times, then with 35℃ warm water 3 times, and finally with deionized water 3 times. Sensitization was performed by treating with stannous chloride sensitizing solution (stannous chloride dihydrate 15 g / L, lactic acid 10 mL / L, pH 4.5) at room temperature for 2 min. Activation was performed by treating with palladium chloride activating solution (palladium chloride 0.3 g / L, sodium citrate 10 g / L, pH 7.5) at room temperature for 2 min, and then reduced with 12 g / L sodium hypophosphite solution at room temperature for 1 min.

[0059] S2. Formation of conductive layer: Using a chemical nickel plating solution (nickel sulfate 30g / L, sodium hypophosphite 25g / L, sodium citrate 20g / L, sodium acetate 15g / L, pH 8.0), the pretreated polyurethane dense film was chemically nickel plated for 10 min at 50℃, and then dried in an oven at 80℃ for 10 min to form a conductive metal layer with a thickness of 0.5μm.

[0060] S3. Pre-plating nickel: Using a bright nickel plating solution (nickel sulfate 180g / L, nickel chloride 40g / L, boric acid 30g / L, sodium saccharin 1.0g / L and 791 brightener 2mL / L), at a cathode current density of 1.5A / dm³. 2 At a temperature of 40℃ and pH=5.0, electroplating was performed for 5 minutes to electroplat a bright nickel layer on the conductive metal layer, with a nickel layer thickness of 2μm.

[0061] S4. Preparation of imitation gold electroplating solution: Dissolve the weighed potassium pyrophosphate, phosphonohydroxyacetic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, potassium sodium tartrate, potassium citrate, copper pyrophosphate, zinc sulfate heptahydrate, and sodium stannate in deionized water. At room temperature, mechanically stir at 400 rpm for 30 min until completely dissolved to form a base plating solution. Add sodium sulfite and sodium isoascorbate and stir for 5 min. Dissolve the composite surfactant in deionized water and add it to the base plating solution and stir for 10 min. Add surface-treated nano-SiC particles and ultrasonically disperse for 10 min to ensure uniform dispersion. Add the composite brightener and continue stirring for 10 min. Adjust the pH to 9.5 with potassium hydroxide. After standing to defoam, the imitation gold electroplating solution is obtained.

[0062] S5. Imitation Gold Electroplating: The polyurethane dense film pre-plated with nickel in S3 is first coated with a dilute copper solution (copper pyrophosphate 20g / L, potassium pyrophosphate 100g / L, pH=9.0) at 0.5A / dm². 2 After flash plating for 20 seconds, the plate is placed in the electroplating solution prepared in S4, with a stainless steel plate as the anode, and a cathode current density of 1.0 A / dm³. 2 Under conditions of 35℃ and pH 9.5, electroplating was performed for 3 minutes with cathode stirring at a speed of 1.0 m / min.

[0063] S6. Post-treatment: The imitation gold plating layer is passivated sequentially using a 50mL / L trivalent chromium blue-white passivating agent solution. It is then immersed at room temperature for 30s and cleaned with deionized water. A layer of flexible polyurethane transparent varnish with a thickness of 12μm is then sprayed onto the surface and cured at 65℃ for 30min.

[0064] Example 4: An environmentally friendly, cyanide-free imitation gold electroplating solution for automotive interior leather, comprising the following components per liter: 215g potassium pyrophosphate, 11g phosphonohydroxyacetic acid, 13g 2-phosphonobutane-1,2,4-tricarboxylic acid, 9g potassium sodium tartrate, 22g potassium citrate, 19g copper pyrophosphate, 33g zinc sulfate heptahydrate, 5g sodium stannate, 2.5g sodium sulfite, 0.8g sodium isoascorbate, 1.5g nano-SiC particles (40nm particle size) treated with KH-560, 2.5g composite brightener (1.94g β-naphthol polyoxyethylene ether, molecular weight 1500Da; 0.56g polyethyleneimine, molecular weight 6000Da), and 0.35g composite surfactant (0.16g dodecyl dimethyl benzyl ammonium bromide; 0.19g polyethylene glycol isooctylphenol ether).

[0065] An electroplating method for an environmentally friendly, cyanide-free imitation gold electroplating solution for automotive interior leather, the same as in Example 2.

[0066] Example 5: An environmentally friendly, cyanide-free imitation gold electroplating solution for automotive interior leather, each liter of the electroplating solution comprising the following components: 245g potassium pyrophosphate, 14g phosphonohydroxyacetic acid, 11g 2-phosphonobutane-1,2,4-tricarboxylic acid, 11g potassium sodium tartrate, 28g potassium citrate, 22g copper pyrophosphate, 42g zinc sulfate heptahydrate, 7g sodium stannate, 4g sodium sulfite, 1.2g sodium isoascorbate, 2.5g nano-SiC particles (50nm particle size) treated with KH-560, 3.5g composite brightener (2.86g β-naphthol polyoxyethylene ether, molecular weight 2500Da; 0.64g polyethyleneimine, molecular weight 7000Da), and 0.5g composite surfactant (0.18g dodecyl dimethyl benzyl ammonium bromide; 0.32g polyethylene glycol isooctylphenol ether).

[0067] An electroplating method for an environmentally friendly, cyanide-free imitation gold electroplating solution for automotive interior leather, the same as in Example 2.

[0068] Example 6: An environmentally friendly, cyanide-free imitation gold electroplating solution for automotive interior leather, each liter of the electroplating solution comprising the following components: 250g potassium pyrophosphate, 13g phosphonohydroxyacetic acid, 14g 2-phosphonobutane-1,2,4-tricarboxylic acid, 10.5g potassium sodium tartrate, 26g potassium citrate, 23g copper pyrophosphate, 40g zinc sulfate heptahydrate, 6.5g sodium stannate, 4.5g sodium sulfite, 1.3g sodium isoascorbate, 2.2g nano-SiC particles (55nm particle size) treated with KH-560, 3.2g composite brightener (2.6g β-naphthol polyoxyethylene ether, molecular weight 2800Da; 0.6g polyethyleneimine, molecular weight 9000Da), and 0.55g composite surfactant (0.21g dodecyl dimethyl benzyl ammonium bromide; 0.34g polyethylene glycol isooctylphenol ether).

[0069] An electroplating method for an environmentally friendly, cyanide-free imitation gold electroplating solution for automotive interior leather, the same as in Example 2.

[0070] Comparative Example 1: Based on Example 2, the difference is that the cyanide-free imitation gold electroplating solution uses a single potassium pyrophosphate complexing agent and does not contain phosphonohydroxyacetic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, potassium sodium tartrate, or potassium citrate. The rest is the same as in Example 2.

[0071] Comparative Example 2: Based on Example 2, the difference is that the cyanide-free gold plating solution does not contain phosphonoglycolic acid and 2-phosphonobutane-1,2,4-tricarboxylic acid, but otherwise it is the same as Example 2.

[0072] Comparative Example 3: Based on Example 2, the difference is that the cyanide-free imitation gold electroplating solution does not contain potassium sodium tartrate and potassium citrate, while the rest is the same as Example 2.

[0073] Comparative Example 4: Based on Example 2, the difference is that the cyanide-free imitation gold electroplating solution does not contain sodium sulfite and sodium isoascorbate, while the rest is the same as Example 2.

[0074] Comparative Example 5: Based on Example 2, the difference is that the cyanide-free imitation gold electroplating solution does not contain surface-treated nano-SiC particles, and the rest is the same as Example 2.

[0075] Comparative Example 6: Based on Example 2, the difference is that the cyanide-free imitation gold electroplating solution does not contain composite brighteners (i.e., it does not contain β-naphthol polyoxyethylene ether and polyethyleneimine), and is otherwise the same as Example 2.

[0076] Performance testing:

[0077] 1. Coating color difference value (ΔE) test: Referring to GB / T 11186-2025 standard, under natural diffused light or standard light source (D65), visually observe the coating surface at a distance of about 300mm from the sample. Use a benchtop colorimeter (CIELAB color space, D65 standard light source, 10° observation angle, 8mm measuring aperture) to test the coating color difference value ΔE. Using the standard imitation gold sample (18K gold sample card) as a reference, measure at 3 different positions on the surface of each sample and calculate the average value.

[0078] 2. Coating adhesion test: Referring to GB / T 9286-2021 standard, the cross-cut test is used. A cross-cut tester is used to cut through the coating surface to the substrate at 1mm intervals, forming 100 small squares (10×10). Special adhesive tape (adhesion of about 10N / 25mm) is tightly attached to the cut area and quickly peeled off. The coating peeling is observed at a magnification of 4×. The adhesion level is rated from 0 to 5 (0 is that the cut edge is completely smooth and no squares are peeled off; 5 is that a large area is peeled off).

[0079] 3. Coating Hardness Test: Referring to GB / T 4340.1-2024 standard, a micro Vickers hardness tester was used. The test force was 0.4903N (50gf), and the holding time was 15s. After cutting and embedding the electroplated sample, it was ground and polished along the direction perpendicular to the coating to the cross-section. Indentation test was performed on the cross-section of the imitation gold coating. Five effective indentation points were selected for each sample (the length of the two diagonals of the indentation is ≥20μm, and the indentation is clear and complete). The length of the diagonal of the indentation was measured, and the Vickers hardness value was calculated according to the formula. The arithmetic mean was taken as the final hardness value, and the result was rounded to the nearest integer (unit: HV).

[0080] 4. Coating Abrasion Resistance Test: Referring to GB / T 1768-2006 standard, a Taber abrasion tester was used, with a CS-10 type grinding wheel (rubber-based grinding wheel) selected. A load of 500g was applied, the rotation speed was 60r / min, and the total wear revolutions were 1000 revolutions. Before the grinding wheel test, it was pre-ground with S-11 sandpaper 25 times to remove the surface passivation layer. The sample was fixed on the turntable, and the equipment was started for abrasion. The grinding wheel was replaced every 500 revolutions, and the surface debris of the sample was removed. The mass of the sample was weighed with an analytical balance (accuracy 0.1mg) before and after abrasion, and the mass loss Δm=m0-m1 was calculated. Each sample was tested 3 times and the average value was taken. The mass loss (mg / 1000 revolutions) was used to characterize the abrasion resistance. The smaller the loss, the better the abrasion resistance.

[0081] 5. Coating Salt Spray Corrosion Resistance Test: Referring to GB / T 10125-2021 standard, the neutral salt spray test (NSS) was adopted. Test conditions: sodium chloride solution concentration (50±5) g / L, pH 6.5-7.2, test chamber temperature (35±2)℃, salt spray deposition rate (1.0-2.0) mL / 80cm 2 • h, the sample is placed in the salt spray chamber at an angle of (20±5)° to the vertical line and sprayed continuously for the specified time (testing three time nodes: 24h, 48h, and 72h respectively). After the time is reached, the sample is taken out, gently rinsed with deionized water, and allowed to air dry or blow dry. The corrosion area and corrosion morphology are observed at a magnification of 4×.

[0082] 6. Plating solution stability test: Seal the newly prepared plating solution and store it in a 45℃ constant temperature water bath for 30 consecutive days. Take a sample every 5 days to observe the appearance of the plating solution (whether there is turbidity, precipitation, or discoloration). Use a dropper to take a small amount of plating solution and drop it onto filter paper to check whether there is any gel-like substance or crystal precipitation.

[0083] Table 1. Performance Test Results

[0084]

[0085] Table 2. Performance Test Results

[0086]

[0087] Data Analysis:

[0088] Examples 1-6 all exhibited excellent comprehensive performance: color difference ΔE ≤ 1.1, visually uniform and realistic color, reaching an 18K-24K imitation gold tone, and adhesion strength of grade 0, indicating excellent adhesion between the pre-plated nickel layer, flash-plated copper layer, and imitation gold plating, as well as between the plating and the non-backed PU leather; hardness ≥ 225HV; and abrasion resistance mass loss ≤ 3.8mg / 1000 rpm. This is directly attributed to the uniformly dispersed nano-SiC particles in the plating solution, which, through electrodeposition, co-embedded into the alloy plating layer, exerted a significant dispersion strengthening effect. All examples passed the 72-hour neutral salt spray test with no or only very slight surface changes. This is attributed to the dense copper-zinc-tin imitation gold alloy coating, the nano-SiC filling coating to improve density through micropores, and the dual protection provided by trivalent chromium passivation and organic varnish sealing layer in the post-treatment process. The plating solution remained clear after 30 days of accelerated aging at 45°C, indicating that the multi-component synergistic complexing system and composite antioxidants effectively inhibited the hydrolysis of metal ions and the decomposition of sodium stannate, giving the plating solution a long maintenance cycle and industrial production potential.

[0089] Comparative Example 1, using only potassium pyrophosphate as a complexing agent, showed a color difference ΔE = 4.5, a bonding strength reduced to level 2, a hardness of only 165 HV, a wear resistance loss as high as 8.5 mg / 1000 rpm, corrosion after 48 hours of salt spray, and extremely poor plating solution stability. Precipitation occurred after 10 days of storage at 45℃, indicating that potassium pyrophosphate alone cannot effectively complex zinc and tin ions, leading to the formation of hydroxide precipitates or stannic acid colloids by zinc and tin under alkaline conditions, causing the plating solution to fail rapidly. At the same time, the alloy composition deviated significantly from the required ratio for gold imitation during co-deposition (too high copper content, insufficient zinc and tin), increasing the internal stress and loosening the structure of the coating, resulting in uncontrolled color, poor bonding strength, and comprehensive deterioration of mechanical properties and corrosion resistance. This fully demonstrates the necessity of a multi-component synergistic complexing system for achieving stable co-deposition of copper-zinc-tin and ensuring the comprehensive performance of the coating.

[0090] Comparative Example 2, without the addition of phosphonoglycolic acid and 2-phosphonobutane-1,2,4-tricarboxylic acid, showed a color difference ΔE = 3.2, an adhesion grade of 1, a hardness of 195 HV, abrasion resistance of 6.2 mg / 1000 rpm, and edge corrosion after 48 hours of salt spray testing. The plating solution exhibited poor stability, with precipitation occurring after 12 days of storage at 45℃. This indicates that while potassium pyrophosphate, potassium sodium tartrate, and potassium citrate have good complexing abilities for copper ions, their complexing stability constants for zinc and tin ions are insufficient. The organic phosphonic acid complexing agents (phosphonoglycolic acid and 2-phosphonobutane-1,2,4-tricarboxylic acid) contain strong complexing agents. Phosphonic acid groups (-PO3H2) with homing ability have a specific strong coordination effect on zinc and tin ions, which can effectively inhibit their hydrolysis under alkaline conditions to form hydroxides or stannic acid precipitates. Without these two, the free concentration of zinc and tin ions in the plating solution is unstable, and the deposition rate of zinc and tin lags behind that of copper during the co-deposition process. This causes the alloy composition to deviate from the optimal gold imitation ratio (high copper content and low zinc and tin content), and the coating appears reddish. At the same time, zinc and tin are prone to forming insoluble basic salts that are mixed in the coating, resulting in a loose structure and increased internal stress, which in turn reduces hardness, wear resistance, adhesion and corrosion resistance.

[0091] Comparative Example 3, without the addition of potassium sodium tartrate and potassium citrate, showed a color difference ΔE=2.5, a bonding strength reduced to grade 1, a hardness of 190HV, an abrasion resistance of 5.8mg / 1000 rpm, and slight discoloration after 48 hours of salt spray resistance. The plating solution showed insufficient stability, and a small amount of precipitation appeared after 20 days of storage at 45℃. This indicates that potassium sodium tartrate and potassium citrate, as auxiliary complexing agents, can further broaden the cathode current density range, refine the grains, and effectively buffer pH fluctuations and inhibit metal ion hydrolysis. Without these two components, even with the presence of the main complexing agent and organophosphonic acid complexing agents, it is still difficult to completely stabilize the co-deposition process, leading to a deviation of the alloy composition from the optimal gold-like ratio (copper deposition too fast, zinc-tin deposition insufficient). The coating structure is loose, and internal stress increases, resulting in a significant decrease in color, bonding strength, hardness, and plating solution life.

[0092] Comparative Example 4, lacking the antioxidants sodium sulfite and sodium isoascorbate (i.e., lacking a composite antioxidant), exhibited a color difference ΔE = 1.5, an adhesion strength of grade 1, a hardness of 218 HV, abrasion resistance of 3.9 mg / 1000 rpm, and significant corrosion after 48 hours of salt spray testing. The plating solution showed extremely poor stability, with flocculent precipitate appearing after only 5 days of storage at 45℃. This indicates that the key role of sodium sulfite and sodium isoascorbate is to prevent the hydrolysis of sodium stannate in alkaline solutions to form metastannic acid colloids and to inhibit the disproportionation reaction of Cu⁺ ions. Without the antioxidants, Sn… 4+Colloidal precipitation leads to turbidity and failure of the plating solution. At the same time, Cu⁺ disproportionation generates copper powder or cuprous oxide, which disrupts the composition of the plating solution. Tin cannot be deposited normally, resulting in low tin content in the coating, changes in the alloy phase structure, reddish color, and decreased corrosion resistance. In addition, instability of the plating solution also causes coarse crystals in the coating, increased internal stress, and reduced hardness and wear resistance. Therefore, composite antioxidants are an indispensable component for maintaining the long-term stability of the plating solution and ensuring the quality of the coating.

[0093] Comparative Example 5, lacking nano-SiC particles, showed a color difference value ΔE = 1.0 and an adhesion grade of 0, indicating that nano-SiC had no significant negative impact on the color and adhesion of the electrodeposition process. Only slight rust spots appeared after 72 hours of salt spray testing, suggesting that the absence of nano-SiC slightly reduced the density of the coating. However, the hardness plummeted to 175 HV, and the wear resistance loss reached 7.0 mg / 1000 rpm. This indicates that nano-SiC particles are co-embedded in the alloy coating through electrodeposition, significantly improving the hardness and wear resistance of the coating through dispersion strengthening. Without nano-SiC, the coating loses its dispersion strengthening phase, resulting in a significant decrease in mechanical properties. However, the electrochemical deposition process (such as alloy composition and crystallization method) remains essentially unchanged, thus maintaining good color and adhesion. This verifies that nano-SiC is the core functional component for improving the mechanical properties of the coating, while having little impact on other properties.

[0094] Comparative Example 6, without the composite brightener, exhibited a color difference value ΔE = 4.0, a bonding strength decreased to level 1, a hardness of 188 HV, abrasion resistance of 6.5 mg / 1000 rpm, and no change in salt spray resistance after 72 hours. The plating solution remained clear and stable. This indicates that the composite brightener, through the leveling effect of β-naphthol polyoxyethylene ether and the grain refinement effect of polyethyleneimine, synergistically adsorbs onto the cathode surface, inhibiting tip discharge and dendrite growth. This results in a mirror-like, uniformly colored coating over a wide current density range. Without the brightener, the coating exhibits coarse crystals and a rough surface, leading to severe light scattering and a sharp increase in color difference. The rough surface also alters the effective contact area with the substrate, increasing internal stress and slightly reducing bonding strength. Since the brightener does not participate in the formation of the main coating structure, it has little impact on hardness, abrasion resistance, and corrosion resistance. Therefore, the composite brightener is a key component for achieving a decorative, imitation gold mirror effect.

[0095] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. An environmentally friendly, cyanide-free, gold-imitation electroplating solution for automotive interior leather, characterized in that, Each liter of electroplating solution comprises the following components: potassium pyrophosphate 200-260 g / L, phosphonoglycolic acid 10-15 g / L, 2-phosphonobutane-1,2,4-tricarboxylic acid 10-15 g / L, potassium sodium tartrate 8-12 g / L, potassium citrate 20-30 g / L, copper pyrophosphate 18-24 g / L, zinc sulfate heptahydrate 30-45 g / L, sodium stannate 4-8 g / L, sodium sulfite 2-5 g / L, sodium isoascorbate 0.5-1.5 g / L, surface-treated nano-SiC particles 1-3 g / L, composite brightener 2-4 g / L, and composite surfactant 0.3-0.6 g / L; the pH of the electroplating solution is 8.5-9.

5.

2. The environmentally friendly, cyanide-free, gold-plating solution for automotive interior leather according to claim 1, characterized in that, The composite surfactant is a mixture of dodecyl dimethyl benzyl ammonium bromide and polyethylene glycol isooctylphenol ether X-100 in a molar ratio of 1:1-2.

3. The environmentally friendly, cyanide-free imitation gold electroplating solution for automotive interior leather according to claim 1, characterized in that, The nano-SiC particles have a particle size of 30-60 nm and their surface is modified with silane coupling agent KH-560.

4. The environmentally friendly, cyanide-free imitation gold electroplating solution for automotive interior leather according to claim 1, characterized in that, The composite brightener is a mixture of β-naphthol polyoxyethylene ether and polyethyleneimine in a mass ratio of 3-5:1, wherein the number-average molecular weight of β-naphthol polyoxyethylene ether is 1000-3000 Da and the number-average molecular weight of polyethyleneimine is 5000-10000 Da.

5. An electroplating method for an environmentally friendly, cyanide-free, imitation gold electroplating solution for automotive interior leather as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Pretreatment: The baseless PU leather is subjected to degreasing, roughening, cleaning, sensitization and activation treatment in sequence. Degreasing is carried out by ultrasonic degreasing with a weak alkaline degreasing solution at 35-40℃ for 3-5 minutes. Roughening is carried out by soaking in 5-10% ethyl acetate ethanol solution at room temperature for 1-2 minutes. Cleaning is carried out by first cleaning with anhydrous ethanol 2-3 times, then cleaning with warm water at 35-40℃ 2-3 times, and finally cleaning with deionized water 2-3 times. Sensitization is carried out by treating with stannous chloride sensitizing solution at room temperature for 2-3 minutes. Activation is carried out by treating with palladium chloride activation solution at room temperature for 2-3 minutes, and then reducing with 8-12g / L sodium hypophosphite solution at room temperature for 1-2 minutes. S2. Formation of conductive layer: Using a chemical nickel plating solution, the pretreated non-backed PU leather is chemically nickel plated at 40-50℃ for 10-15 minutes, and then dried in an oven at 70-80℃ for 10-15 minutes to form a conductive metal layer with a thickness of 0.5-1.0μm. S3. Pre-plating nickel: Bright nickel plating solution is used, with a cathode current density of 1.0-1.5 A / dm³. 2 Electroplating is performed at a temperature of 35-40℃ and a pH of 4.0-5.0 for 5-10 minutes to deposit a bright nickel layer on the conductive metal layer, with a nickel layer thickness of 2-4μm. S4. Preparation of imitation gold electroplating solution: Dissolve potassium pyrophosphate, phosphonohydroxyacetic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, potassium sodium tartrate, potassium citrate, copper pyrophosphate, zinc sulfate heptahydrate, and sodium stannate in deionized water. At room temperature, mechanically stir at 200-400 rpm for 30-60 min until completely dissolved to form a base plating solution. Add sodium sulfite and sodium isoascorbate and stir for 5-10 min. Dissolve the composite surfactant in deionized water and add it to the base plating solution and stir for 10-20 min. Add surface-treated nano-SiC particles and ultrasonically disperse for 10-30 min to ensure uniform dispersion. Add the composite brightener and continue stirring for 10-30 min. Adjust the pH to 8.5-9.5 with potassium hydroxide. After standing to defoam, the imitation gold electroplating solution is obtained. S5. Imitation Gold Electroplating: The baseless PU leather pre-plated with nickel (S3) is first coated with a dilute copper solution at 0.3-0.5 A / dm². 2 After flash plating for 20-30 seconds, the plate is placed in the electroplating solution prepared in S4, with a stainless steel plate as the anode, and a cathode current density of 0.6-1.0 A / dm³. 2 Under conditions of 30-35℃ and pH 8.5-9.5, use a cathode moving and stirring motion of 0.5-1.0 m / min for 3-5 minutes for electroplating; S6. Post-treatment: The imitation gold plating is passivated and then sealed with organic varnish.

6. The electroplating method of the environmentally friendly cyanide-free imitation gold electroplating solution for automotive interior leather according to claim 5, characterized in that, In S1, the non-woven PU leather refers to a non-woven fiber base fabric and a dense polyurethane film with a thickness of 0.5-1.5 mm; the weakly alkaline degreasing solution contains 15-25 g / L sodium carbonate, 10-15 g / L trisodium phosphate, and 3-5 g / L nonionic surfactant T102; the stannous chloride sensitizing solution contains 10-15 g / L stannous chloride dihydrate, 5-10 mL / L lactic acid, and pH 3.5-4.5; the palladium chloride activating solution contains 0.1-0.3 g / L palladium chloride, 5-10 g / L sodium citrate, and pH 6.5-7.

5.

7. The electroplating method of the environmentally friendly cyanide-free imitation gold electroplating solution for automotive interior leather according to claim 5, characterized in that, The electroless nickel plating solution in S2 contains 25-30 g / L nickel sulfate, 20-25 g / L sodium hypophosphite, 15-20 g / L sodium citrate, and 10-15 g / L sodium acetate, with a pH of 7.0-8.

0.

8. The electroplating method of the environmentally friendly cyanide-free imitation gold electroplating solution for automotive interior leather according to claim 5, characterized in that, The bright nickel plating solution in S3 contains 150-180 g / L nickel sulfate, 30-40 g / L nickel chloride, 25-30 g / L boric acid, 0.5-1.0 g / L sodium saccharin and 1-2 mL / L 791 brightener.

9. The electroplating method of the environmentally friendly cyanide-free imitation gold electroplating solution for automotive interior leather according to claim 5, characterized in that, The dilute copper solution in S5 consists of 15-20 g / L copper pyrophosphate, 80-100 g / L potassium pyrophosphate, and has a pH of 8.0-9.

0.

10. The electroplating method of the environmentally friendly cyanide-free imitation gold electroplating solution for automotive interior leather according to claim 5, characterized in that, The passivation treatment in S6 involves immersing the sample in a 30-50 mL / L trivalent chromium blue-white passivating agent solution at room temperature for 20-30 seconds, followed by rinsing with deionized water. The organic varnish sealing treatment uses a flexible polyurethane transparent varnish with a spray thickness of 8-12 μm, which is then cured at 60-65℃ for 30-40 minutes.

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