Cyanide-free electrolyte for hard gold electroforming and preparation process thereof

Abstract

The invention provides a cyanide-free electrolyte for hard gold electroforming and a preparation process of the cyanide-free electrolyte, and belongs to the technical field of gold plating processes. The preparation process comprises the following steps: adding 4-dimethylaminopyridine for reaction to prepare an additive A; adding lithium tert-butoxide for reaction to prepare an additive B; preparing an AuCl3 solution; 5, 5-dimethyl hydantoin is dissolved, and all the components are added. The preparation method comprises the following steps: stirring and mixing N-acetyl-L-cysteine, triphenyl methanol and dichloromethane, mixing trifluoroacetic acid, performing reduced pressure distillation, purification and elution, then adding triethylamine, 4-dimethylaminopyridine and acetic anhydride for reaction, and adding trifluoroacetic acid and triethyl silane for reaction to prepare an additive A; after being added into a cyanide-free electrolyte, in the process of electroplating a gold layer, the gold plating solution can effectively promote the formation of crystal nucleuses, prevent the overgrowth of crystal grains and promote the refinement of gold crystal grains, and the fine and uniformly distributed crystal grain structure can remarkably improve the hardness and wear resistance of the plating layer.

Description

Technical Field

[0001] The invention relates to the technical field of gold plating technology, and in particular to a cyanide-free electrolyte for hard gold electroforming and a preparation process thereof. Background Art

[0002] Gold plating has excellent corrosion resistance, stable conductivity and low contact resistance. It is often used as a functional plating layer and is widely used in printed circuit boards (PCBs), precision electronic devices, electronic interconnects, plug-and-play devices and other fields. It is usually electroplated using a gold plating electroforming solution. In the traditional electroforming process, cyanide is widely used as the main component in the electroplating solution because it can effectively promote metal deposition and ensure the smoothness and continuity of the coating. However, the high toxicity of cyanide poses a serious threat to production safety, environmental protection and worker health. It must strictly comply with environmental protection regulations during its storage, transportation, use and waste disposal, resulting in increased costs and risks that cannot be ignored.

[0003] In recent years, with the increasingly stringent environmental regulations and the urgent need of society for sustainable development, the development of cyanide-free electroplating technology has become an inevitable trend in the development of the industry. Cyanide-free electroplating liquid can not only avoid the hazards of cyanide, but also meet the requirements of modern production for high efficiency and environmental protection, and promote the green transformation of the gold electroplating industry. Although some cyanide-free electroplating liquids have been developed and applied, these solutions often have limitations in electroplating efficiency, coating hardness, wear resistance and stability, and it is difficult to completely replace traditional cyanide electroplating liquids, resulting in a relatively short service life of the gold coating obtained by electroplating with cyanide-free electroplating liquid.

[0004] In view of this, it is necessary to propose a cyanide-free electrolyte for hard gold electroforming and a preparation process thereof, which can improve the hardness and wear resistance of the gold plating layer, so as to extend the service life of the gold plating layer. Summary of the invention

[0005] In view of the shortcomings of the prior art, the object of the present invention is to provide a cyanide-free electrolyte for hard gold electroforming and a preparation process thereof.

[0006] A cyanide-free electrolyte for hard gold electroforming, comprising, by weight:

[0007] 10-12 parts of AuCl3 solution, 30-35 parts of 5,5-dimethylhydantoin, 70-80 parts of potassium chloride, 20-30 parts of anhydrous ethanol, 10-20 parts of additive A, 10-20 parts of additive B, 1-3 parts of cinnamaldehyde, 8-10 parts of polyacrylamide, 30-35 parts of composite buffer and 50-60 parts of deionized water, wherein the composite buffer is prepared by mixing citric acid and disodium hydrogen phosphate in a mass ratio of (1-3):1.

[0008] A process for preparing a cyanide-free electrolyte for hard gold electroforming comprises the following steps:

[0009] S1: Add 4-dimethylaminopyridine to react and prepare additive A

[0010] N-acetyl-L-cysteine ​​and triphenylmethanol are stirred and mixed with dichloromethane, and then trifluoroacetic acid is added, and then the mixture is distilled under reduced pressure, purified and eluted, and then dissolved in dichloromethane, and triethylamine, 4-dimethylaminopyridine and acetic anhydride are added to react, and finally the mixture is mixed with trifluoroacetic acid and triethylsilane to react, so as to obtain additive A;

[0011] S2: Add lithium tert-butoxide to react and prepare additive B

[0012] Ethylene oxide and 1,3-dimethyl-2-imidazolidinone are stirred and mixed with dimethylformamide, and then lithium tert-butoxide is added, heated for reaction, and then poured into deionized water, stirred, filtered and recrystallized to obtain additive B;

[0013] S3: Preparation of AuCl3 solution

[0014] After pretreatment, pure gold is added to aqua regia, heated and stirred to dissolve, then added to deionized water to prepare a gold-containing solution, and then sodium hydroxide solution is added to adjust the pH to obtain an AuCl3 solution;

[0015] S4: Dissolve 5,5-dimethylhydantoin and add the components

[0016] Dissolve 5,5-dimethylhydantoin in deionized water, add sodium hydroxide solution to adjust pH, and then add the AuCl3 solution, the additive A, the additive B, potassium chloride, cinnamaldehyde, polyacrylamide and a composite buffer to obtain a cyanide-free electrolyte.

[0017] Furthermore, S1 specifically includes the following steps:

[0018] S1.1: Add N-acetyl-L-cysteine ​​and triphenylmethanol to dichloromethane at a solid-liquid ratio of 1 g: (1.6-2) g: (13-15) mL, stir and mix well to obtain a mixed solution;

[0019] S1.2: Add trifluoroacetic acid to the mixed solution, continue stirring for 2-3 hours, then remove the solvent by distillation under reduced pressure, purify by silica gel column chromatography and elute with an eluent to obtain intermediate A;

[0020] S1.3: Add the intermediate A to dichloromethane at a solid-liquid ratio of 1 g: (30-40) mL, stir and mix, place in an ice-water bath at 1-3°C, add triethylamine, 4-dimethylaminopyridine and acetic anhydride, stir and react for 10-12 hours, then remove the solvent by distillation under reduced pressure, purify by silica gel column chromatography and elute with an eluent to obtain intermediate B;

[0021] S1.4: Dissolve the intermediate B in dichloromethane at a solid-liquid ratio of 1 g: (40-50) mL, add trifluoroacetic acid and triethylsilane, stir and react for 3-4 hours, then remove the solvent by distillation under reduced pressure, purify by silica gel column chromatography and elute with an eluent to obtain additive A.

[0022] Furthermore, S2 specifically includes the following steps:

[0023] S2.1: Add equimolar amounts of ethylene oxide and 1,3-dimethyl-2-imidazolidinone to dimethylformamide, stir and mix thoroughly to obtain a mixed solution;

[0024] S2.2: Add lithium tert-butoxide to the mixed solution, stir and mix thoroughly, heat to 60-70°C, and keep the temperature to react for 1-2 hours to obtain a precursor solution;

[0025] S2.3: Pour the above precursor solution into deionized water, stir at a rate of 200-300 r / min for 10-20 min, and then filter and recrystallize to obtain additive B.

[0026] Furthermore, S3 specifically includes the following steps:

[0027] S3.1: Cut the pure gold into small pieces, wash and dry them, then add them into aqua regia at a solid-liquid ratio of 1g:(11-13)mL, heat and stir at 80-90℃ to dissolve until a blood-red viscous substance is formed;

[0028] S3.2: Add deionized water to the above blood-red viscous material to prepare a gold-containing solution with a mass fraction of 20-30%, and add sodium hydroxide solution to adjust the pH to 6-7 to obtain an AuCl3 solution.

[0029] Furthermore, S4 specifically includes the following steps:

[0030] S4.1: Add 5,5-dimethylhydantoin to deionized water, heat to 40-50°C and stir to dissolve, then add sodium hydroxide solution to adjust the pH to 10-11 to obtain solution A;

[0031] S4.2: Add the AuCl3 solution obtained in step S3.2 to the above solution A while stirring, and heat at 40-50°C until the solution becomes colorless to obtain solution B;

[0032] S4.3: Add anhydrous ethanol, additive A obtained in step S1.4 and additive B obtained in step S2.3 to the above liquid B, stir and mix evenly, then add potassium chloride, cinnamaldehyde and polyacrylamide, continue to stir and mix, then add a composite buffer to adjust the pH to 9-10 to obtain a cyanide-free electrolyte.

[0033] Furthermore, the volume ratio of trifluoroacetic acid to dichloromethane is 1:(3-5), and the eluent is dichloromethane and methanol in a volume ratio of (70-80):1.

[0034] Furthermore, the mass ratio of 4-dimethylaminopyridine and acetic anhydride to intermediate A is 1:(9-11):(30-36), and the solid-liquid ratio of intermediate A to triethylamine is 1 g:(0.8-1) mL.

[0035] Furthermore, the solid-liquid ratio of intermediate B to trifluoroacetic acid and triethylsilane is 1 g: (6-8) mL: (0.6-0.8) mL.

[0036] Furthermore, the solid-liquid ratio of ethylene oxide to dimethylformamide is 1 g:(40-50) mL, and the mass ratio of lithium tert-butoxide to ethylene oxide is (1.5-2.5):1.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. The present invention prepares additive A by stirring and mixing N-acetyl-L-cysteine, triphenylmethanol and dichloromethane and mixing trifluoroacetic acid, performing reduced pressure distillation, purification and elution, and then adding triethylamine, 4-dimethylaminopyridine and acetic anhydride to react and adding trifluoroacetic acid and triethylsilane to react. After adding the additive A to a cyanide-free electrolyte, the additive A can effectively promote the formation of crystal nuclei, prevent excessive growth of crystal grains, and promote the refinement of gold grains during the electroplating of a gold layer. The fine and evenly distributed grain structure can significantly improve the hardness and wear resistance of the coating.

[0039] 2. The present invention prepares an additive B by stirring and mixing equimolar amounts of ethylene oxide and 1,3-dimethyl-2-imidazolidinone with dimethylformamide, and then adding lithium tert-butoxide to react, and adding the additive B to a cyanide-free electrolyte. Since the additive B has good surface activity, an effective adsorption layer can be formed between the cyanide-free electrolyte and the substrate, and the adsorption can change the double electric layer structure of the electrode interface, affect the charge distribution, thereby promoting the uniform deposition of gold ions during the electroplating process, reducing uneven growth, making the coating smoother, and affecting the crystallization process, prompting the metal deposition to appear in the form of smaller and more uniform grains, reducing scattering between crystal planes, and enhancing the reflection effect, thereby increasing the glossiness of the coating. In addition, by adding the additive B and the additive A to the cyanide-free electrolyte at the same time, the hardness and corrosion resistance of the gold coating formed by electroplating can be improved while ensuring high deposition efficiency.

[0040] 3. After adding cinnamaldehyde to the cyanide-free electrolyte, the present invention adjusts the electrodeposition process through complexation with gold ions, promotes the formation of a more uniform and fine grain structure, thereby enhancing the wear resistance of the coating. In addition, cinnamaldehyde and additive A have a synergistic effect, and the two further improve the hardness and wear resistance of the coating through the synergistic effect.

[0041] 4. After adding polyacrylamide to the cyanide-free electrolyte, the active groups on the polyacrylamide molecules can adsorb to the surface of solid particles in the electrolyte, so that the surface of the particles is fully wetted, the mutual attraction between the particles is reduced, and the uniform dispersion of the particles is promoted. At the same time, the surface tension of the system is reduced, and the dynamic stability of the system is increased, thereby helping the gold ions to be more evenly deposited on the surface of the substrate to form a denser and smoother coating, which can effectively resist the penetration of corrosive media and improve the corrosion resistance of the formed gold coating. DETAILED DESCRIPTION

[0042] The following is a detailed description of a cyanide-free electrolyte for hard gold electroforming and its preparation process provided by the present invention in conjunction with specific embodiments. At the same time, it is explained here that in order to make the embodiments more detailed, the following embodiments are the best and preferred embodiments, and those skilled in the art may also adopt other alternative methods to implement some known technologies.

[0043] Example 1

[0044] A process for preparing a cyanide-free electrolyte for hard gold electroforming comprises the following steps:

[0045] S1: Add 4-dimethylaminopyridine to react and prepare additive A

[0046] N-acetyl-L-cysteine ​​and triphenylmethanol were added to dichloromethane at a solid-liquid ratio of 1g:1.6g:13mL, and the mixture was stirred to obtain a mixed solution. Trifluoroacetic acid was then added to the mixed solution, and the stirring was continued for 2h. The solvent was then removed by distillation under reduced pressure. The mixture was purified by silica gel column chromatography and eluted with an eluent to obtain an intermediate A, wherein the volume ratio of trifluoroacetic acid to dichloromethane was 1:3. The intermediate A was then added to dichloromethane at a solid-liquid ratio of 1g:30mL, and the mixture was stirred and mixed. The mixture was placed in an ice water bath at 1°C, and triethylamine, 4-dimethylaminopyridine and acetic anhydride were added. The mixture was stirred for reaction for 10h, and the solvent was then removed by distillation under reduced pressure. The mixture was purified by silica gel column chromatography and eluted with an eluent to obtain an intermediate A. Purification by column chromatography and elution with an eluent to obtain intermediate B, wherein the mass ratio of 4-dimethylaminopyridine and acetic anhydride to intermediate A is 1:9:30, and the solid-liquid ratio of intermediate A to triethylamine is 1g:0.8mL. Subsequently, intermediate B is dissolved in dichloromethane at a solid-liquid ratio of 1g:40mL, and trifluoroacetic acid and triethylsilane are added, and the reaction is stirred for 3h, wherein the solid-liquid ratio of intermediate B to trifluoroacetic acid and triethylsilane is 1g:6mL:0.6mL, and then the solvent is removed by reduced pressure distillation, and the additive A is obtained by purification by silica gel column chromatography and elution with an eluent, wherein the eluent is dichloromethane and methanol at a volume ratio of 70:1;

[0047] S2: Add lithium tert-butoxide to react and prepare additive B

[0048] Equimolar amounts of ethylene oxide and 1,3-dimethyl-2-imidazolidinone were added to dimethylformamide, and the mixture was stirred to obtain a mixed solution. Lithium tert-butoxide was added to the mixed solution, and the mixture was stirred to obtain a mixed solution. The mixture was heated to 60°C and kept warm for 1 hour to obtain a precursor solution, wherein the solid-liquid ratio of ethylene oxide to dimethylformamide was 1 g:40 mL, and the mass ratio of lithium tert-butoxide to ethylene oxide was 1.5:1. The precursor solution was then poured into deionized water, stirred at a rate of 200 r / min for 10 minutes, and then filtered and recrystallized to obtain additive B.

[0049] S3: Preparation of AuCl3 solution

[0050] Cut the pure gold into small pieces, wash and dry them, then add them into aqua regia at a solid-liquid ratio of 1g:11mL, heat and stir at 80℃ to dissolve until a blood-red viscous substance is formed, then add deionized water into the blood-red viscous substance to prepare a gold-containing solution with a mass fraction of 20%, and add sodium hydroxide solution to adjust the pH to 6-7 to obtain AuCl3 solution;

[0051] S4: Dissolve 5,5-dimethylhydantoin and add the components

[0052] 30 parts of 5,5-dimethylhydantoin are added to 50 parts of deionized water by weight, heated to 40°C and stirred to dissolve, and then sodium hydroxide solution is added to adjust the pH to 10 to obtain liquid A, and then 10 parts of the AuCl3 solution prepared in step S3 are added to liquid A while stirring, and heated at 40°C until the solution becomes colorless to obtain liquid B, and then 20 parts of anhydrous ethanol, 10 parts of additive A prepared in step S1 and 10 parts of additive B prepared in step S2 are added to liquid B, and stirred to mix evenly, and then 70 parts of potassium chloride, 1 part of cinnamaldehyde and 8 parts of polyacrylamide are added, and stirring and mixing are continued, and then 30 parts of a composite buffer are added to adjust the pH to 9 to obtain a cyanide-free electrolyte, wherein the composite buffer is a mixture of citric acid and disodium hydrogen phosphate in a mass ratio of 1:1.

[0053] Then, a copper sheet is used as a substrate, the copper sheet is wrapped with a polyimide tape, a plating area of ​​10 mm×10 mm is reserved in the middle, and the above-mentioned cyanide-free electrolyte is used as a plating solution to electroplate gold to obtain a gold-plated copper sheet, wherein the process conditions for electroplating gold are: temperature 40°C, magnetic stirring rate 400 r / min, current density 0.5 A / dm 2 , time: 10 minutes.

[0054] The performance test results are shown in Table 1 below:

[0055] 1. Make small cuts on the surface of the gold-plated layer, touching the base material when making cuts. The distance between the cuts is less than 2mm. After making cuts, stick them firmly with 3M tape, tear them off quickly, and observe whether the gold-plated layer falls off.

[0056] 2. According to GB / T10125-2021 "Artificial atmosphere corrosion test salt spray test", a neutral salt spray (NSS) test was carried out on an LX-60A salt spray tester, using 5% NaCl solution for continuous spraying, temperature 35°C, pressure 197.2kPa, and test time 48h;

[0057] 3. Use the Junnengda MM6 gloss meter to measure the gloss of the gold-plated layer at a measuring angle of 60°;

[0058] 4. Use HXD-1000B microhardness tester to measure the hardness of the gold-plated layer. The test conditions are: load 25g, load time 15s.

[0059] Example 2

[0060] S1: Add 4-dimethylaminopyridine to react and prepare additive A

[0061] N-acetyl-L-cysteine ​​and triphenylmethanol were added to dichloromethane at a solid-liquid ratio of 1g:1.8g:14mL, and the mixture was stirred to obtain a mixed solution. Trifluoroacetic acid was then added to the mixed solution, and the stirring was continued for 2.5h. The solvent was then removed by distillation under reduced pressure. The mixture was purified by silica gel column chromatography and eluted with an eluent to obtain an intermediate A, wherein the volume ratio of trifluoroacetic acid to dichloromethane was 1:4. The intermediate A was then added to dichloromethane at a solid-liquid ratio of 1g:35mL, and the mixture was stirred and mixed. The mixture was placed in an ice-water bath at 2°C, and triethylamine, 4-dimethylaminopyridine and acetic anhydride were added. The mixture was stirred for 11h, and the solvent was then removed by distillation under reduced pressure. The mixture was purified by silica gel column chromatography and eluted with an eluent to obtain an intermediate A. Purification by column chromatography and elution with an eluent to obtain intermediate B, wherein the mass ratio of 4-dimethylaminopyridine and acetic anhydride to intermediate A is 1:10:33, and the solid-liquid ratio of intermediate A to triethylamine is 1g:0.9mL. Subsequently, intermediate B is dissolved in dichloromethane at a solid-liquid ratio of 1g:45mL, and trifluoroacetic acid and triethylsilane are added, and the reaction is stirred for 3.5h, wherein the solid-liquid ratio of intermediate B to trifluoroacetic acid and triethylsilane is 1g:7mL:0.7mL, and then the solvent is removed by reduced pressure distillation, and purification by silica gel column chromatography and elution with an eluent to obtain additive A, wherein the eluent is dichloromethane and methanol at a volume ratio of 75:1;

[0062] S2: Add lithium tert-butoxide to react and prepare additive B

[0063] Equimolar amounts of ethylene oxide and 1,3-dimethyl-2-imidazolidinone were added to dimethylformamide, and the mixture was stirred to obtain a mixed solution. Lithium tert-butoxide was added to the mixed solution, and the mixture was stirred to obtain a mixed solution. The mixture was heated to 65°C and kept warm for 1.5 hours to obtain a precursor solution, wherein the solid-liquid ratio of ethylene oxide to dimethylformamide was 1 g:45 mL, and the mass ratio of lithium tert-butoxide to ethylene oxide was 2:1. The precursor solution was poured into deionized water, stirred at a rate of 250 r / min for 15 minutes, and then filtered and recrystallized to obtain additive B.

[0064] S3: Preparation of AuCl3 solution

[0065] Cut the pure gold into small pieces, wash and dry them, then add them into aqua regia at a solid-liquid ratio of 1g:12mL, heat and stir at 80-90℃ to dissolve until a blood-red viscous substance is formed, then add deionized water into the blood-red viscous substance to prepare a gold-containing solution with a mass fraction of 25%, and add sodium hydroxide solution to adjust the pH to 6.5 to obtain an AuCl3 solution;

[0066] S4: Dissolve 5,5-dimethylhydantoin and add the components

[0067] 33 parts of 5,5-dimethylhydantoin are added to 55 parts of deionized water by weight, heated to 45°C and stirred to dissolve, and then sodium hydroxide solution is added to adjust the pH to 10.5 to obtain liquid A, and then 11 parts of the AuCl3 solution prepared in step S3 are added to liquid A while stirring, and heated at 45°C until the solution becomes colorless to obtain liquid B, and then 25 parts of anhydrous ethanol, 15 parts of additive A prepared in step S1 and 15 parts of additive B prepared in step S2 are added to liquid B, and stirred to mix evenly, and then 75 parts of potassium chloride, 2 parts of cinnamaldehyde and 9 parts of polyacrylamide are added, and stirring and mixing is continued, and then 33 parts of a composite buffer is added to adjust the pH to 9.5 to obtain a cyanide-free electrolyte, wherein the composite buffer is a mixture of citric acid and disodium hydrogen phosphate in a mass ratio of 2:1.

[0068] Then, the performance test was performed according to the performance test method in Example 1.

[0069] Example 3

[0070] S1: Add 4-dimethylaminopyridine to react and prepare additive A

[0071] N-acetyl-L-cysteine ​​and triphenylmethanol were added to dichloromethane at a solid-liquid ratio of 1g:2g:15mL, and the mixture was stirred to obtain a mixed solution. Trifluoroacetic acid was then added to the mixed solution, and the stirring was continued for 3h. The solvent was then removed by distillation under reduced pressure. The mixture was purified by silica gel column chromatography and eluted with an eluent to obtain an intermediate A, wherein the volume ratio of trifluoroacetic acid to dichloromethane was 1:5. The intermediate A was then added to dichloromethane at a solid-liquid ratio of 1g:40mL, and the mixture was stirred and mixed. The mixture was placed in an ice-water bath at 3°C, and triethylamine, 4-dimethylaminopyridine and acetic anhydride were added. The mixture was stirred for 12h, and the solvent was then removed by distillation under reduced pressure. The mixture was purified by silica gel column chromatography and eluted with an eluent to obtain an intermediate A. Purification by column chromatography and elution with an eluent to obtain intermediate B, wherein the mass ratio of 4-dimethylaminopyridine and acetic anhydride to intermediate A is 1:11:36, and the solid-liquid ratio of intermediate A to triethylamine is 1g:1mL. Subsequently, intermediate B is dissolved in dichloromethane at a solid-liquid ratio of 1g:50mL, and trifluoroacetic acid and triethylsilane are added, and the reaction is stirred for 4h, wherein the solid-liquid ratio of intermediate B to trifluoroacetic acid and triethylsilane is 1g:8mL:0.8mL, and then the solvent is removed by reduced pressure distillation, and purification by silica gel column chromatography and elution with an eluent to obtain additive A, wherein the eluent is dichloromethane and methanol at a volume ratio of 80:1;

[0072] S2: Add lithium tert-butoxide to react and prepare additive B

[0073] Equimolar amounts of ethylene oxide and 1,3-dimethyl-2-imidazolidinone were added to dimethylformamide, and the mixture was stirred to obtain a mixed solution. Lithium tert-butoxide was added to the mixed solution, and the mixture was stirred to obtain a mixed solution. The mixture was heated to 70°C and kept warm for 2 hours to obtain a precursor solution, wherein the solid-liquid ratio of ethylene oxide to dimethylformamide was 1 g:50 mL, and the mass ratio of lithium tert-butoxide to ethylene oxide was 2.5:1. The precursor solution was then poured into deionized water, stirred at a rate of 300 r / min for 20 minutes, and then filtered and recrystallized to obtain additive B.

[0074] S3: Preparation of AuCl3 solution

[0075] The pure gold was chopped, washed and dried, and then added to aqua regia at a solid-liquid ratio of 1g:13mL, heated and stirred at 90°C to dissolve until a blood-red viscous substance was formed, and then deionized water was added to the blood-red viscous substance to prepare a gold-containing solution with a mass fraction of 30%, and sodium hydroxide solution was added to adjust the pH to 7 to obtain an AuCl3 solution;

[0076] S4: Dissolve 5,5-dimethylhydantoin and add the components

[0077] 35 parts of 5,5-dimethylhydantoin are added to 60 parts of deionized water by weight, heated to 50°C and stirred to dissolve, and then sodium hydroxide solution is added to adjust the pH to 11 to obtain liquid A, and then 12 parts of the AuCl3 solution prepared in step S3 are added to liquid A while stirring, and heated at 50°C until the solution becomes colorless to obtain liquid B, and then 30 parts of anhydrous ethanol, 20 parts of additive A prepared in step S1 and 20 parts of additive B prepared in step S2 are added to liquid B, and stirred to mix evenly, and then 80 parts of potassium chloride, 3 parts of cinnamaldehyde and 10 parts of polyacrylamide are added, and stirring and mixing are continued, and then 35 parts of a composite buffer is added to adjust the pH to 10 to obtain a cyanide-free electrolyte, wherein the composite buffer is a mixture of citric acid and disodium hydrogen phosphate in a mass ratio of 3:1.

[0078] Then, a copper sheet is used as a substrate, the copper sheet is wrapped with a polyimide tape, a plating area of ​​10 mm×10 mm is reserved in the middle, and the above-mentioned cyanide-free electrolyte is used as a plating solution to electroplate gold to obtain a gold-plated copper sheet, wherein the process conditions for electroplating gold are: temperature 40°C, magnetic stirring rate 400 r / min, current density 0.5 A / dm 2 , time: 10 minutes.

[0079] The performance test results are shown in Table 1 below:

[0080] 1. Make small cuts on the surface of the gold-plated layer, touching the base material when making cuts. The distance between the cuts is less than 2mm. After making cuts, stick them firmly with 3M tape, tear them off quickly, and observe whether the gold-plated layer falls off.

[0081] 2. According to GB / T10125-2021 "Artificial atmosphere corrosion test salt spray test", a neutral salt spray (NSS) test was carried out on an LX-60A salt spray tester, using 5% NaCl solution for continuous spraying, temperature 35°C, pressure 197.2kPa, and test time 48h;

[0082] 3. Use the Junnengda MM6 gloss meter to measure the gloss of the gold-plated layer at a measuring angle of 60°;

[0083] 4. Use HXD-1000B microhardness tester to measure the hardness of the gold-plated layer. The test conditions are: load 25g, load time 15s.

[0084] Table 1: Summary of performance test results of Examples 1-3

[0085]

[0086] Comparative Example 1

[0087] The difference between this comparative example and Example 1 is that step S1 is removed, and the additive A in step S4 is removed, and then the performance test is performed according to the performance test method in Example 1, and the results are shown in Table 2 below.

[0088] Table 2: Comparative Example 1 and Example 1 Performance Test Results Comparison Table

[0089] Test items Gold plating bonding strength Gold plating corrosion Hardness value (HV) Example 1 Not falling off No corrosion 82.65 Comparative Example 1 Local shedding More pitting 74.52

[0090] As shown in Table 2 above, the gold-plated layer of Comparative Example 1 partially falls off after the tape is quickly torn off, indicating that the bonding force between the gold-plated layer and the substrate is poor, and the hardness value of the gold-plated layer in Comparative Example 1 is 74.52HV, which is relatively small compared with the gold-plated layer in Example 1. That is to say, the bonding force and hardness value of the gold-plated layer and the substrate in Example 1 are relatively high, so that the wear resistance of the gold-plated layer in Example 1 is excellent. It can be seen that by stirring and mixing N-acetyl-L-cysteine, triphenylmethanol and dichloromethane and mixing them with trifluoroacetic acid, after reduced pressure distillation, purification and elution, triethylamine, 4-dimethylaminopyridine and acetic anhydride are added to react, and trifluoroacetic acid and triethylsilane are added to react to prepare additive A. After adding it to the cyanide-free electrolyte, in the process of electroplating the gold layer, it can effectively promote the formation of crystal nuclei, prevent excessive growth of grains, and promote the refinement of gold grains, and the fine and evenly distributed grain structure can significantly improve the hardness and wear resistance of the coating.

[0091] Comparative Example 2

[0092] The difference between this comparative example and Example 1 is that step S2 is removed, and the additive B in step S4 is removed, and then the performance test is carried out according to the performance test method in Example 1, and the results are shown in Table 3 below.

[0093] Table 3: Comparison of performance test results between Comparative Example 2 and Example 1

[0094] Test items Gold plating corrosion Gloss (GU) Hardness value (HV) Example 1 No corrosion 96.26 82.65 Comparative Example 2 More pitting 74.62 75.18

[0095] As shown in Table 3 above, the gloss of the gold-plated layer in Comparative Example 2 is 74.62GU, which is less than that in Example 1. It can be seen that by stirring and mixing equimolar amounts of ethylene oxide and 1,3-dimethyl-2-imidazolidinone with dimethylformamide, and then adding lithium tert-butoxide to react, an additive B is obtained, and after adding the additive B to the cyanide-free electrolyte, the additive B has good surface activity and can form an effective adsorption layer between the cyanide-free electrolyte and the substrate. This adsorption can change the double electric layer structure of the electrode interface and affect the charge distribution, thereby promoting the uniform deposition of gold ions during the electroplating process, reducing uneven growth, making the coating smoother, and affecting the crystallization process, prompting the metal deposition to appear in the form of smaller and more uniform grains, reducing the scattering between crystal planes, and enhancing the reflection effect, thereby increasing the gloss of the coating;

[0096] In addition, more pitting appeared on the surface of the gold-plated layer in Comparative Examples 1 and 2, and the hardness values ​​were both lower than those in Example 1, indicating that adding Additive B and Additive A to the cyanide-free electrolyte at the same time can ensure high deposition efficiency while also improving the hardness and corrosion resistance of the gold-plated layer formed by electroplating.

[0097] Comparative Example 3

[0098] The difference between this comparative example and Example 1 is that the cinnamaldehyde in step S4 is replaced by an equal amount of additive A, and then the performance test is carried out according to the performance test method in Example 1. The results are shown in Table 4 below.

[0099] Comparative Example 4

[0100] The difference between this comparative example and Example 1 is that the additive A in step S4 is replaced with an equal amount of cinnamaldehyde, and then the performance test is carried out according to the performance test method in Example 1. The results are shown in Table 4 below.

[0101] Table 4: Comparative Example 3-4 and Example 1 Performance Test Results Comparison Table

[0102]

[0103] As shown in Table 4 above, the gold-plated layers in Comparative Examples 3 and 4 both show slight detachment, and the hardness values ​​of the two are both less than those in Example 1, indicating that the addition of a single additive A and a single cinnamaldehyde, the binding force and hardness of the gold-plated layer are not as good as the addition of cinnamaldehyde and additive A at the same time. It can be seen that after adding cinnamaldehyde to the cyanide-free electrolyte, it is complexed with gold ions to adjust the electrodeposition process, promote the formation of a more uniform and fine grain structure, thereby enhancing the wear resistance of the coating, and cinnamaldehyde and additive A have a synergistic effect, and the two further improve the hardness and wear resistance of the coating through the synergistic effect.

[0104] Comparative Example 5

[0105] The difference between this comparative example and Example 1 is that the polyacrylamide in step S4 is removed, and then the performance test is performed according to the performance test method in Example 1. The results are shown in Table 5 below.

[0106] Table 5: Comparative Example 5 and Example 1 Performance Test Results Comparison Table

[0107] Test items Gold plating corrosion Example 1 No corrosion Comparative Example 5 Slight pitting

[0108] As shown in Table 5 above, slight pitting occurs on the surface of the gold-plated layer in Comparative Example 5, indicating that after polyacrylamide is added to the cyanide-free electrolyte, the active groups on the polyacrylamide molecules can adsorb to the surface of the solid particles in the electrolyte, so that the surface of the particles is fully wetted, the mutual attraction between the particles is reduced, and the uniform dispersion of the particles is promoted. At the same time, the surface tension of the system is reduced, and the dynamic stability of the system is increased, thereby helping the gold ions to be more evenly deposited on the surface of the substrate to form a denser and smoother coating, which can effectively resist the penetration of corrosive media and improve the corrosion resistance of the formed gold coating.

[0109] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A cyanide-free electrolyte for hard gold electroforming, characterized in that: By weight, including: 10-12 parts of AuCl3 solution, 30-35 parts of 5,5-dimethylhydantoin, 70-80 parts of potassium chloride, 20-30 parts of anhydrous ethanol, 10-20 parts of additive A, 10-20 parts of additive B, 1-3 parts of cinnamaldehyde, 8-10 parts of polyacrylamide, 30-35 parts of composite buffer and 50-60 parts of deionized water, wherein the composite buffer is prepared by mixing citric acid and disodium hydrogen phosphate in a mass ratio of (1-3):

1.

2. A process for preparing a cyanide-free electrolyte for hard gold electroforming, characterized in that: The steps include: S1: Add 4-dimethylaminopyridine to react and prepare additive A N-acetyl-L-cysteine ​​and triphenylmethanol are stirred and mixed with dichloromethane, and then trifluoroacetic acid is added, and then the mixture is distilled under reduced pressure, purified and eluted, and then dissolved in dichloromethane, and triethylamine, 4-dimethylaminopyridine and acetic anhydride are added to react, and finally the mixture is mixed with trifluoroacetic acid and triethylsilane to react, so as to obtain additive A; S2: Add lithium tert-butoxide to react and prepare additive B Ethylene oxide and 1,3-dimethyl-2-imidazolidinone are stirred and mixed with dimethylformamide, and then lithium tert-butoxide is added, heated for reaction, and then poured into deionized water, stirred, filtered and recrystallized to obtain additive B; S3: Preparation of AuCl3 solution After pretreatment, pure gold is added to aqua regia, heated and stirred to dissolve, then added to deionized water to prepare a gold-containing solution, and then sodium hydroxide solution is added to adjust the pH to obtain an AuCl3 solution; S4: Dissolve 5,5-dimethylhydantoin and add the components Dissolve 5,5-dimethylhydantoin in deionized water, add sodium hydroxide solution to adjust pH, and then add the AuCl3 solution, the additive A, the additive B, potassium chloride, cinnamaldehyde, polyacrylamide and a composite buffer to obtain a cyanide-free electrolyte.

3. The process for preparing a cyanide-free electrolyte for hard gold electroforming according to claim 2, characterized in that: S1 specifically includes the following steps: S1.1: Add N-acetyl-L-cysteine ​​and triphenylmethanol to dichloromethane at a solid-liquid ratio of 1 g: (1.6-2) g: (13-15) mL, stir and mix well to obtain a mixed solution; S1.2: Add trifluoroacetic acid to the mixed solution, continue stirring for 2-3 hours, then remove the solvent by distillation under reduced pressure, purify by silica gel column chromatography and elute with an eluent to obtain intermediate A; S1.3: Add the intermediate A to dichloromethane at a solid-liquid ratio of 1 g: (30-40) mL, stir and mix, place in an ice-water bath at 1-3°C, add triethylamine, 4-dimethylaminopyridine and acetic anhydride, stir and react for 10-12 hours, then remove the solvent by distillation under reduced pressure, purify by silica gel column chromatography and elute with an eluent to obtain intermediate B; S1.4: Dissolve the intermediate B in dichloromethane at a solid-liquid ratio of 1 g: (40-50) mL, add trifluoroacetic acid and triethylsilane, stir and react for 3-4 hours, then remove the solvent by distillation under reduced pressure, purify by silica gel column chromatography and elute with an eluent to obtain additive A.

4. The process for preparing a cyanide-free electrolyte for hard gold electroforming according to claim 3, characterized in that: S2 specifically includes the following steps: S2.1: Add equimolar amounts of ethylene oxide and 1,3-dimethyl-2-imidazolidinone to dimethylformamide, stir and mix thoroughly to obtain a mixed solution; S2.2: Add lithium tert-butoxide to the mixed solution, stir and mix thoroughly, heat to 60-70°C, and keep the temperature to react for 1-2 hours to obtain a precursor solution; S2.3: Pour the above precursor solution into deionized water, stir at a rate of 200-300 r / min for 10-20 min, and then filter and recrystallize to obtain additive B.

5. The process for preparing a cyanide-free electrolyte for hard gold electroforming according to claim 4, characterized in that: S3 specifically includes the following steps: S3.1: Cut the pure gold into small pieces, wash and dry them, then add them into aqua regia at a solid-liquid ratio of 1g:(11-13)mL, heat and stir at 80-90℃ to dissolve until a blood-red viscous substance is formed; S3.2: Add deionized water to the above blood-red viscous material to prepare a gold-containing solution with a mass fraction of 20-30%, and add sodium hydroxide solution to adjust the pH to 6-7 to obtain an AuCl3 solution.

6. The process for preparing a cyanide-free electrolyte for hard gold electroforming according to claim 5, characterized in that: S4 specifically includes the following steps: S4.1: Add 5,5-dimethylhydantoin to deionized water, heat to 40-50°C and stir to dissolve, then add sodium hydroxide solution to adjust the pH to 10-11 to obtain solution A; S4.2: Add the AuCl3 solution obtained in step S3.2 to the above solution A while stirring, and heat at 40-50°C until the solution becomes colorless to obtain solution B; S4.3: Add anhydrous ethanol, additive A obtained in step S1.4 and additive B obtained in step S2.3 to the above liquid B, stir and mix evenly, then add potassium chloride, cinnamaldehyde and polyacrylamide, continue to stir and mix, then add a composite buffer to adjust the pH to 9-10 to obtain a cyanide-free electrolyte.

7. The process for preparing a cyanide-free electrolyte for hard gold electroforming according to claim 6, characterized in that: The volume ratio of trifluoroacetic acid to dichloromethane is 1:(3-5), and the eluent is dichloromethane and methanol in a volume ratio of (70-80):

1.

8. The process for preparing a cyanide-free electrolyte for hard gold electroforming according to claim 7, characterized in that: The mass ratio of 4-dimethylaminopyridine and acetic anhydride to intermediate A is 1:(9-11):(30-36), and the solid-liquid ratio of intermediate A to triethylamine is 1g:(0.8-1)mL.

9. The process for preparing a cyanide-free electrolyte for hard gold electroforming according to claim 8, characterized in that: The solid-liquid ratio of intermediate B to trifluoroacetic acid and triethylsilane is 1 g: (6-8) mL: (0.6-0.8) mL.

10. The process for preparing a cyanide-free electrolyte for hard gold electroforming according to claim 9, characterized in that: The solid-liquid ratio of ethylene oxide to dimethylformamide is 1 g:(40-50) mL, and the mass ratio of lithium tert-butoxide to ethylene oxide is (1.5-2.5):1.

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