A silver plating brightener and its preparation method

Abstract

The present invention discloses a silver plating brightener and a preparation method thereof. The main components include deionized water, metal compounds, surfactants, complexing agents, ammonia water and alkaline compounds. This brightener has the advantages of fast silver plating speed, full surface brightness, fine crystal structure of the coating, high hardness, the hardness of the silver coating reaching 160 - 200 HV, excellent conductivity, high bonding strength, etc.; and the preparation process of this brightener is simple, easy to control, and suitable for industrial production applications. The present invention is suitable for preparing silver plating brighteners.

Description

Technical Field

[0001] The invention belongs to the technical field of silver plating and relates to a silver plating brightener and a preparation method thereof. Background Art

[0002] Silver plating is the process of depositing metallic silver on the surface of an object. The surface state after silver plating has a lot to do with the silver plating solution. Only the coating with a smooth, bright surface and a firm bond with the surface of the object can be accepted by the market.

[0003] Theoretical studies have shown that the silver plating process can only obtain an ideal coating under the brightener diffusion control mechanism and at the same time control the size of the silver crystals on the surface of the deposited object. In the presence of a brightener, the brightener (usually a surfactant) can cause the silver ions to first migrate to the depressions in the uneven surface of the object, where they are deposited to fill the surface, and then the silver ions are evenly deposited on the filled surface, so that the surface is flat in theory. However, after silver is deposited on the surface, it will undergo a series of processes such as nucleation-growth to form crystals. If the grains are too large, even a flat surface will have cracks and gaps. Therefore, when electroplating a silver coating, the size of the silver grains must be controlled so that a smooth and bright coating can be formed.

[0004] The current commercially available brighteners are difficult to achieve the above-mentioned effects. Although scholars from all over the world have conducted in-depth and long-term research on silver plating technology, electroplating silver technology has now achieved industrial production and achieved good social and economic effects, but silver plating still has defects such as slow plating speed, insufficient white and bright appearance of the coating, insufficient bonding, and poor coating morphology. Therefore, it is urgent to study a silver plating brightener that can make the coating surface smooth, bright, and highly bonded to meet the needs of actual production. Summary of the invention

[0005] The present invention aims to provide a silver plating brightener and a preparation method thereof. The main components include deionized water, a metal compound, a surfactant, a complexing agent, ammonia water and an alkaline compound. The brightener has the advantages of fast silver plating speed, full bright surface, fine crystallization of the plated layer, high hardness, excellent conductivity, high bonding degree, etc., and the preparation process of the brightener is simple, easy to control, and suitable for industrial production and application.

[0006] The technical solution of the present invention is as follows:

[0007] A silver plating brightener comprises the following components in parts by weight:

[0008] 50-80 parts of deionized water, 1-10 parts of metal compound, 0.1-3 parts of surfactant, 0.5-5 parts of complexing agent, 5-10 parts of ammonia water, 7 parts of alkaline compound.

[0009] As a limitation of the present invention, the metal compound is any two or any three of KCNSe, Sb2O5, Sb2O3 or potassium antimonyl tartrate.

[0010] As the second limitation of the present invention, the surfactant is one or several of betaine, fatty alcohol polyoxyethylene ether, fatty amide phosphate, fatty amide propyl phosphate betaine, diethylenetriamine, polyethyleneimine or N-alkyl alaninate.

[0011] As the third limitation of the present invention, the complexing agent is compounded by glycerol and EDTA with a weight ratio of 1:1.

[0012] As the fourth limitation of the present invention, the alkaline compound is compounded by sodium hydroxide and potassium hydroxide with a weight ratio of 6:1.

[0013] The present invention also provides a preparation method of a silver plating brightener, which is prepared in the following order of steps:

[0014] S1. Add the metal compound to deionized water and stir for 20 min to obtain A.

[0015] S2. Heat A to 40 °C, add the surfactant and the complexing agent thereto, and stir evenly to obtain B.

[0016] S3. After cooling B to room temperature, add ammonia water and the alkaline compound in sequence, and stir until the solution is clear to obtain the silver plating brightener.

[0017] This silver plating brightener is used to add to the silver plating solution to apply a silver layer to the workpiece to be plated. The process parameters in the electroplating process are: the pH value of the silver plating bath solution is 12 - 14, the temperature range is 15 - 35 °C, and the operating current density is 0.3 - 2.0 A / dm 2 , and the content of silver in the bath solution is 30 - 60 g / L.

[0018] The formulation of the brightener has an important impact on the silver plating effect of the brightener, which mainly affects the nucleation and growth of silver grains. In the formulation of the present invention, a metal compound is creatively added for the first time, and the metal compound has a great influence on the growth process of silver grains on the surface of the coating. During the growth of the grains, the metal compound acts as a stress reliever and a brightener. During the electroplating process, since silver is deposited on the cathode surface, electrochemical reactions continuously occur in the electroplating system, and the chemical composition of the plating solution near the electrode continuously changes. As the electroplating progresses, the resistance of the plating solution increases, resulting in the polarization of the electrode and a decrease in the current efficiency. By adding metal ions in a suitable proportion in the brightener and being able to synergistically increase the ion transport efficiency with other substances, the cathode energy is evenly distributed, reducing this polarization effect, that is, the adsorption of the metal compound leads to the even distribution of the cathode energy, so that silver ions can be randomly deposited on the surface of the coating, ensuring the uniformity, smoothness and brightness of the surface of the workpiece. When the brightening solution does not contain the metal compound described in the present application, due to the relatively poor charge transfer ability of the system, the number of silver ions deposited on the cathode surface within the same time is reduced, the silver crystallization nuclei are fewer, and the crystal growth rate is faster, resulting in coarse grains, and the surface of the coating presents a rough granular structure with very low brightness. After the metal compound, surfactant and other substances in the formulation of the present invention are formulated, the surface of the coated layer shows a regular network structure. Under the synergistic action of other substances such as surfactants, complexing agents and alkaline compounds, the metal compound strongly adsorbs on some active sites of the cathode, enabling the crystal orientation growth during silver electrocrystallization, with fine grains, and finally forming a network structure, making the surface flat, bright and with high firmness.

[0019] Surfactants in an appropriate proportion can diffuse and adsorb on the convex parts, active sites and special crystal planes with relatively large surface tension of the object, causing the silver atoms adsorbed on the surface of the object to migrate to the concave parts of the object surface and enter the crystal lattice, thus playing a role in brightening and leveling. The surfactant with polar groups adopted in the present invention has good solubility and diffusion ability in aqueous solution and can adsorb on the convex parts with relatively large surface tension of the electrode. Due to the surface of the cathode, especially the protruding parts of the surface, being affected by the unsaturation of chemical bonds, the polarity is relatively large. Surfactants with polar groups usually preferentially adsorb in these places. At the same time, under the synergistic action of the metal compound in the brightener, they jointly affect the deposition, nucleation, orientation growth and growth of silver ions. In this way, during the electroplating process, silver ions are first deposited in the concave parts of the cathode surface, and after the surface is leveled, they are deposited more evenly on each part of the cathode surface, finally forming a high-quality silver coating.

[0020] The technical effects obtained after adopting the above technical solutions are as follows:

[0021] 1. This brightener has the advantages of fast silver plating speed, full surface brightness, fine grains, fine crystal structure of the coating, high hardness up to 160 - 200 HV, excellent conductivity, and high adhesion;

[0022] 2. The preparation process of this brightener is simple and easy to control, suitable for industrial production applications.

[0023] 3. This brightener can broaden the application ranges of pH, temperature, and current density of the electroplating solution, with a wider applicability;

[0024] 4. This brightener has good dispersibility for the metal particles precipitated during electroplating, which is beneficial to improving the smoothness and brightness of the surface of the plated parts and enhancing the quality of the overall silver - plated layer;

[0025] 5. This brightener can reduce the surface (interface) tension, which is beneficial to the wetting of the plated parts and conducive to the smooth progress of the subsequent electroplating process, resulting in a fast silver deposition speed and a thick coating.

[0026] The present invention is applicable to the preparation of silver - plating brighteners.

[0027] The specific embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings of the specification.

[0028] Accompanying Drawings of the Specification

[0029] Figure 1 It is the micro - structure diagram of the surface of the silver - plated layer in Example 1 of the present invention under a 400 - fold magnification of a metallurgical microscope;

[0030] Figure 2 It is the X - ray photoelectron spectroscopy diagram of the surface of the silver - plated layer in Example 1 of the present invention. Specific Embodiments

[0031] In the following embodiments, unless otherwise specified, the reagents used are all commercially available reagents. Unless otherwise specified, the following experimental methods and detection methods are all existing experimental methods and detection methods.

[0032] Example 1 A Silver - Plating Brightener

[0033] At room temperature, add metal compounds (1 g of KCNSe, 5 g of Sb2O5) to 74 g of deionized water, stir for 20 min, and wait for them to completely dissolve. Heat the solution to 40 °C, and then add 1 g of betaine, 0.25 g of glycerol, 0.25 g of EDTA, 0.1 g of fatty alcohol polyoxyethylene ether CH3(CH2)7O(CH2CH2O)7H, and 0.9 g of fatty amide propyl phosphate betaine in sequence, and stir until completely dissolved. Then cool the solution to room temperature, add 10 g of ammonia water, 6 g of NaOH, and 1 g of KOH in sequence, and stir until the solution is completely clear to obtain the silver - plating brightener.

[0034] The brightener prepared in this example was added to the silver plating solution for electroplating, and the surface of the silver plating layer on the workpiece was tested. As Figure 1 and Figure 2 shown, after adding the brightener of the present invention, the formed plating layer has uniformly distributed grains on the surface, and the grain size is between several micrometers, and the grains are fine.

[0035] From Figure 2 it can be seen that the content of Ag on the surface of the plating layer is 99.6%, and the content of Mg is 0.4%.

[0036] The smoothness, brightness and flatness of the plating layer prepared in this example have all reached a better state. The surface hardness of the plating layer is high, and the surface hardness measured by a Vickers hardness tester is 200 HV. The deposition rate is fast, the plating layer is thick. At a current of 2.0 A, within 2 minutes, the thickness of the plating layer can reach 9.3 micrometers.

[0037] Example 2 A silver plating brightener

[0038] At room temperature, to 50 g of deionized water, metal compounds (0.3 g of KCNSe, 0.7 g of Sb2O 3) , were added and stirred for 20 min until completely dissolved. The solution was heated to 40 °C, and 1 g of betaine, 0.5 g of glycerol, 0.5 g of EDTA, 0.5 g of fatty amide phosphate, 0.5 g of fatty amide propyl phosphate betaine, and 1 g of N-alkyl alaninate were added in sequence and stirred until completely dissolved. Then the solution was cooled to room temperature, and 5 g of ammonia water, 6 g of NaOH and 1 g of KOH were added in sequence and stirred until the solution was completely clear to obtain the silver plating brightener.

[0039] The brightener prepared in this example was added to the silver plating solution for electroplating, and the surface of the silver plating layer on the workpiece was tested. The smoothness, brightness and flatness of the plating layer prepared in this example have all reached a better state. The surface hardness of the plating layer is high, and the surface hardness measured by a Vickers hardness tester is 178 HV. The deposition rate is fast, the plating layer is thick. At a current of 2.0 A, within 2 minutes, the thickness of the plating layer can reach 9.1 micrometers.

[0040] Example 3 A silver plating brightener

[0041] At room temperature, to 80 g of deionized water, metal compounds (2 g of Sb2O5, 3 g of Sb2O3) were added and stirred for 20 min until completely dissolved. The solution was heated to 40 °C, and 0.05 g of polyethyleneimine, 0.05 g of diethylenetriamine, 1 g of glycerol, and 1 g of EDTA were added in sequence and stirred until completely dissolved. Then the solution was cooled to room temperature, and 8 g of ammonia water, 6 g of NaOH and 1 g of KOH were added in sequence and stirred until the solution was completely clear to obtain the silver plating brightener.

[0042] The brightener prepared in this example was added to the silver plating solution for electroplating, and the surface of the silver plating layer on the workpiece was tested. The smoothness, brightness, and flatness of the plating layer prepared in this example all reached a better state. The surface hardness of the plating layer was high, and the surface hardness measured by a Vickers hardness tester was 160 HV. The deposition rate was fast, and the plating layer was thick. At a current of 2.0 A, the thickness of the plating layer could reach 9.0 μm within 2 minutes.

[0043] Example 4 A silver plating brightener

[0044] At room temperature, to 74 g of deionized water, metal compounds [2 g of potassium antimonyl tartrate (C8H4K2O 12 Sb2), 3 g of Sb2O5, 5 g of Sb2O3] were added, and stirred for 20 min until completely dissolved. The solution was heated to 40 °C, and 1 g of betaine, 0.1 g of fatty alcohol polyoxyethylene ether CH3(CH2)7O(CH2CH2O)7H, 0.9 g of fatty amide propyl phosphate betaine, 1 g of N-alkyl alaninate, 2.5 g of glycerol, and 2.5 g of EDTA were added in sequence, and stirred until completely dissolved. Then the solution was cooled to room temperature, and 5 g of ammonia water, 6 g of NaOH, and 1 g of KOH were added in sequence, and stirred until the solution was completely clear to obtain the silver plating brightener.

[0045] The brightener prepared in this example was added to the silver plating solution for electroplating, and the surface of the silver plating layer on the workpiece was tested. The smoothness, brightness, and flatness of the plating layer prepared in this example all reached a better state. The surface hardness of the plating layer was high, and the surface hardness measured by a Vickers hardness tester was 192 HV. The deposition rate was fast, and the plating layer was thick. At a current of 2.0 A, the thickness of the plating layer could reach 9.2 μm within 2 minutes.

[0046] Example 5 Comparative example

[0047] In this example, a series of experimental studies were conducted on the influence of the addition of different metal compounds on the brightener. The preparation process of the brightener was the same as that in Example 1, except that: the metal compounds in the formula of the brightener were different, and the dosages of other components were the same as those in Example 1, specifically as follows:

[0048] Group A: No metal compound was added to this brightener;

[0049] Group B: A sulfur-containing compound (sodium thiosulfate) was added to this brightener to replace the metal compound;

[0050] Group C: Metal compounds (1 g of KCNSe, 5 g of K2Se) were added to this brightener;

[0051] Group D: A single metal compound 1 g of KCNSe was added to this brightener;

[0052] Group E: 5 g of Sb2O5, a single metal compound, is added to the brightener;

[0053] Group F: 1 g of selenious acid, a single metal compound, is added to the brightener;

[0054] Group G: A metal compound (1 g of selenious acid, 5 g of Sb2O5) is added to the brightener

[0055] Group H: 2 g of potassium antimonyl tartrate (C8H4K2O 12 Sb2) is added to the brightener;

[0056] Group I: No complexing agent is added to the brightening solution;

[0057] After the brightening solutions of the above groups are prepared, they are added to the silver plating solution to apply plating on the surface of the workpiece. The results of the silver plating layer are shown in the following table.

[0058] Table 1 Result Comparison Table

[0059] Group Smoothness, Luminance Flatness Hardness (HV) Surface Silver Content % Group A Average Average 130 98.0 Group B Poor Average 125 97.0 Group C Better Very Good 155 99.0 Group D Better Better 152 99.0 Group E Very Good Better 148 99.3 Group F Better Very Good 155 99.1 Group G Very Good Better 157 99.2 Group H Very Good Better 150 99.0 Group I Average Average 130 97.0

[0060] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A silver plating brightener, characterized in that, It includes the following components by weight in grams: 74 g of deionized water, 6 g of metal compound, 2 g of surfactant, 0.5 g of complexing agent, 10 g of ammonia water, 7 g of alkaline compound; The metal compound is composed of 1 g of KCNSe and 5 g of Sb2O5 compounded; The surfactant is composed of 1 g of betaine, 0.1 g of fatty alcohol polyoxyethylene ether and 0.9 g of fatty amide propyl phosphobetaine compounded; The complexing agent is composed of 0.25 g of glycerol and 0.25 g of EDTA compounded; The preparation method of the silver plating brightener is prepared in the following step sequence: S1. Add the metal compound to deionized water and stir for 20 min to obtain A; S2. Heat A to 40 °C, add the surfactant and the complexing agent thereto, and stir evenly to obtain B; S3. After cooling B to room temperature, add ammonia water and alkaline compound in sequence, and stir until the solution is clear to obtain the silver plating brightener.

2. The silver plating brightener according to claim 1, wherein The alkaline compound is composed of 6 g of NaOH and 1 g of KOH compounded.

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