Nickel-free cobalt-free cyanide-free electroplating solution capable of forming gun-color plating layer, electroplating method thereof and composite plating layer

Abstract

The invention discloses nickel-free, cobalt-free and cyanide-free electroplating liquid capable of forming a gun-color plating layer. The nickel-free, cobalt-free and cyanide-free electroplating liquid comprises zinc salt with the concentration being 30-50 g / L, divalent tin salt with the concentration being larger than or equal to 4 g / L and copper salt with the concentration being larger than or equal to 0.5 g / L; the electroplating liquid further comprises 1-hydroxyethylidene-1, 1-diphosphonic acid with the concentration of 100-150 g / L and serves as a first complexing agent, under the condition that the electroplating liquid does not contain nickel salt, cobalt salt and sulfur-containing amino acid, zinc salt, divalent tin salt and copper salt are specifically blended, the ideal cold light gun color is formed, the plating layer performance is excellent, and the electroplating liquid is cyanide-free, does not contain highly toxic cyanide and is free of pollution. The environmental protection pursuit in the electroplating field is met; hEDP serves as a first complexing agent and can form a stable complex with zinc ions, tin ions and copper ions at the same time, uneven deposition in the electroplating process is prevented, and the uniformity and adhesive force of a gun-color plating layer can be improved; the invention further discloses an electroplating method of the nickel-free, cobalt-free and cyanide-free electroplating solution and a gun-color composite coating.

Description

Technical Field

[0001] The invention belongs to the technical field of electroplating, and in particular relates to a nickel-free, cobalt-free, and cyanide-free electroplating solution capable of forming a gun-color coating, an electroplating method thereof, and a composite coating. Background Art

[0002] For high-end products designed with metal accessories (such as clothing, luggage, etc.), metal accessories (zippers, buckles, chains, etc.) as part of the product need to show special colors and textures in line with the product design and concept. In order to make metal accessories meet more product design requirements, manufacturers usually use electroplating, chemical plating, anodizing and other methods to color metal accessories and / or achieve a certain texture, such as frosted, matte, reflective and other texture presentations.

[0003] Gun color is an iron black color with a cold sheen. It has a unique decorative effect and usually gives people a solemn and elegant visual experience. It is one of the more popular design colors. In the electroplating field, to achieve a gun color or a gray-black coating with a cold sheen, the main salt of the electroplating solution generally contains two or more of nickel salts, cobalt salts, and tin salts, and generally also includes sulfur-containing amino acids.

[0004] For example, the patent document with publication number CN 104152956 A discloses a micro-cobalt gunmetal color electroplating solution and an electroplating method thereof. The micro-cobalt gunmetal color electroplating solution contains the following components: 0.2-1.0 g / L of tin salt, 0.5-2.5 g / L of cobalt salt, 100-250 g / L of conductive salt, 0.5-10 g / L of additives, and the remainder is water; the additives are selected from substances containing amino, sulfhydryl or thiocyanate groups.

[0005] For example, the patent document with publication number CN 117004998 A discloses a plating solution, an electroplating method and electroplating of gun nickel alloy, wherein the plating solution comprises raw materials with the following concentrations: 0.1-10 g / L nickel ions, 5-20 g / L tetravalent tin ions, 0.02-50 g / L metal ions, 5-100 g / L complexing agent, 100-200 g / L conductive salt, 5-100 g / L pH buffer, 0.1-20 g / L blackening agent, and the solvent is water; the blackening agent is an amino acid and its salt or a sulfur-containing amino acid, or a sulfur-containing inorganic substance.

[0006] The above-mentioned existing technologies all present a relatively ideal gun-colored color and texture, but the applicant's main market is Europe and the United States. The EU has clear nickel ban regulations for hardware products that come into contact with the skin. At the same time, downstream distributors have reported that cobalt is also a harmful metal, and they hope that gun-colored metal accessories do not contain cobalt. On the other hand, sulfur-containing amino acids are necessary additives for gun-colored coatings, but their addition will reduce the corrosion resistance of the coating, and they also have a strong odor, which has an adverse effect on the production environment.

[0007] The applicant has been deeply engaged in the field of electroplating for many years. Based on the above market demand and the current technical problems in this field, the present invention aims to provide a nickel-free, cobalt-free and cyanide-free electroplating solution that can form a gun-color coating. Summary of the invention

[0008] In view of the problems in the related art, the present invention proposes a nickel-free, cobalt-free, and cyanide-free electroplating solution that can form a gun-color coating to overcome the above-mentioned technical problems existing in the existing related technology. The present invention also relates to an electroplating method and a composite coating of the electroplating solution.

[0009] The technical solution of the present invention is achieved in this way:

[0010] A nickel-free, cobalt-free, and cyanide-free electroplating solution capable of forming a gun-colored coating, comprising a zinc salt having a concentration of 30 to 50 g / L, a divalent tin salt having a concentration of ≥4 g / L, and a copper salt having a concentration of ≥0.5 g / L;

[0011] The invention also contains 100-150 g / L of hydroxyethylidene diphosphonic acid (HEDP) as a first complexing agent.

[0012] Firstly, compared with the prior art, the present invention forms an ideal cold-light gun color with excellent coating performance by specifically blending zinc salt, divalent tin salt and copper salt under the condition that the electroplating solution does not contain nickel salt, cobalt salt and sulfur-containing amino acid.

[0013] Secondly, the present invention is a cyanide-free electroplating solution, does not contain highly toxic cyanide, and meets the environmental protection pursuit in the electroplating field; compared with chemical plating, the electroplating solution system of the present invention is streamlined, the electroplating cost is lower, the throwing power and covering power are strong, and the stability is high.

[0014] Finally, the present invention specifically selects HEDP as the first complexing agent, which can form a stable complex with zinc ions, tin ions and copper ions at the same time, prevents uneven deposition during the electroplating process, and helps to improve the uniformity and adhesion of the gun-color coating. Moreover, HEDP is a more environmentally friendly reagent, which matches the environmental protection pursuit of this application.

[0015] Preferably, the nickel-free, cobalt-free, and cyanide-free electroplating solution further comprises a second complexing agent, and the second complexing agent is ethylenediaminetetramethylenephosphonic acid (EDTMPA) with a concentration of 30 to 50 g / L.

[0016] Preferably, the nickel-free, cobalt-free, and cyanide-free electroplating solution further comprises a third complexing agent, and the third complexing agent is tetrasodium iminodisuccinate (IDS) with a concentration of 20 to 40 g / L.

[0017] Preferably, the nickel-free, cobalt-free, and cyanide-free electroplating solution further comprises a pH buffer, which is a weak acid such as acetic acid or boric acid. More preferably, the pH buffer is boric acid at a concentration of 30 to 40 g / L.

[0018] Preferably, the nickel-free, cobalt-free, and cyanide-free electroplating solution further comprises a citrate at a concentration of 15 to 30 g / L, which can make the color distribution of the gun-colored coating more uniform. More preferably, the citrate is ammonium citrate with a purity of >99.5%. Generally speaking, the purity requirement of the ammonium citrate in the electroplating solution is basically "chemically pure", but the inventors found in the research and development process that the trace oxalic acid impurities contained in the ammonium citrate product with a purity lower than "chemically pure" have an adverse effect on the quality of the gun-colored coating, and it is necessary to carry out specific strict quality control on the material.

[0019] Preferably, the nickel-free, cobalt-free, and cyanide-free electroplating solution further comprises 0.5-1 g / L of ascorbic acid and 0.5-1 g / L of hydroquinone, which work together as stabilizers for divalent tin, can effectively control the reduction rate of divalent tin, optimize the bonding force between the gun-colored coating and the substrate, reduce pores and cracks, make the coating more uniform, and improve the corrosion resistance of the gun-colored coating. More preferably, the hydroquinone is hydroquinone.

[0020] Preferably, the nickel-free, cobalt-free, and cyanide-free electroplating solution further comprises 15-30 ppm octadecyl dimethyl benzyl ammonium chloride, which can make the gun-colored coating darker and brighter.

[0021] Preferably, the zinc salt is zinc sulfate or zinc chloride; the divalent tin salt is stannous sulfate or stannous chloride; and the copper salt is copper sulfate or copper chloride.

[0022] Most preferably, the nickel-free, cobalt-free, and cyanide-free electroplating solution consists of the following components in concentration:

[0023] 30-50 g / L zinc sulfate or zinc chloride;

[0024] 4-10 g / L stannous sulfate or stannous chloride;

[0025] 1-5 g / L copper sulfate or copper chloride;

[0026] 100-150 g / L of hydroxyethylidene diphosphonic acid (HEDP);

[0027] 30-50 g / L ethylenediaminetetramethylenephosphonic acid (EDTMPA);

[0028] 20-40 g / L tetrasodium iminodisuccinate (IDS);

[0029] 15-30 g / L ammonium citrate, concentration > 99.5%;

[0030] 0.5-1 g / L ascorbic acid;

[0031] 0.5-1 g / L hydroquinone;

[0032] 15-30 ppm of octadecyl dimethyl benzyl ammonium chloride;

[0033] 30-40 g / L of boric acid;

[0034] The rest was deionized water.

[0035] Based on the above-mentioned electroplating solution design, it is necessary to control the electroplating environmental parameters, so the present invention also discloses an electroplating method of the above-mentioned electroplating solution, using the above-mentioned nickel-free, cobalt-free, and cyanide-free electroplating solution capable of forming a gun-colored coating for electroplating;

[0036] The pH is controlled within the range of 4≤pH≤6. If it is lower than the specified range of the present invention, the plating solution will produce white precipitation and the coating will be red. If the pH is higher than the specified range of the present invention, the plating solution will be easily turbid and ineffective, and the brightness will be insufficient.

[0037] The electroplating temperature is controlled at 20-35°C. If the temperature is too low, the coating will be insufficiently bright and dull. If the temperature is too high, the plating solution will be unstable and divalent tin will be easily oxidized to tetravalent tin.

[0038] Specifically, when the electroplating process is adopted, the main salt is a zinc salt with a concentration of 30-45 g / L, a divalent tin salt with a concentration of 4-8 g / L, and a copper salt with a concentration of 1-4 g / L, the pH is controlled at 4≤pH≤6, and the current density is set at 0.1-1.5 A / dm 2 , speed 6~10r / min, barrel plating time 30~120min, anode is carbon plate;

[0039] Alternatively, when the electroplating is performed by rack plating, the main salt is a zinc salt with a concentration of 35 to 50 g / L, a divalent tin salt with a concentration of 6 to 10 g / L, and a copper salt with a concentration of 2 to 5 g / L, the pH is controlled at 4 ≤ pH ≤ 6, and the current density is set at 0.2 to 2.5 A / dm 2 The plating time is 15 to 60 minutes, and the anode is a carbon plate.

[0040] A light gun-color composite coating comprises a bright copper coating and a gun-color coating in order from the surface of a substrate to be electroplated outwards, wherein the gun-color coating is formed by electroplating with the nickel-free, cobalt-free, and cyanide-free electroplating solution capable of forming the gun-color coating.

[0041] Preferably, the thickness of the bright copper plating layer is 5 to 15 μm, and the thickness of the gunmetal color plating layer is 1 to 3 μm.

[0042] Specifically, the gun-colored coating contains the following proportions of metal elements:

[0043] Cu 60~65wt%;

[0044] Zn 30-35wt%;

[0045] Sn 5-8wt%;

[0046] Total 100%.

[0047] The present invention adjusts the ratio of each component in the electroplating solution system and designs the composite coating and process parameters so that the gun-color composite coating of the present invention contains three metal elements of copper, zinc and tin in a specific ratio, forms a specific light gun-color and cold light texture, the coating is firmly and smoothly bonded to the metal matrix, has a dense structure, and has good comprehensive properties such as water washing resistance and salt spray resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is a real picture of the electroplated slider of the present invention;

[0049] Figure 2 It is a schematic structural diagram of the gun-colored composite coating of the present invention;

[0050] Figure 3 This is one of the electron microscope scanning images of the gun-colored coating of the present invention;

[0051] Figure 4 This is the second electron microscope scanning image of the gun-colored coating of the present invention;

[0052] Figure 5 This is one of the XFR element analysis results of Example 2 of the present invention;

[0053] Figure 6 This is the second XFR element analysis result of Example 2 of the present invention;

[0054] Figure 7 This is the third XFR element analysis result of Example 2 of the present invention;

[0055] Figure 8 The figures are the physical pictures of the embodiments 5 and 6 of the present invention;

[0056] Fig. 9 The figures are for comparative examples 1 to 4.

[0057] Reference numerals

[0058] 1. Gun color plating; 2. Bright copper plating; 3. Alkaline copper plating; 4. Slider. DETAILED DESCRIPTION

[0059] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0060] Example 1

[0061] (1) The slider to be electroplated (zinc alloy slider blank) is degreased and activated, primed with alkaline copper, and then plated with acid copper to increase brightness.

[0062] (2) Configure a nickel-free, cobalt-free, and cyanide-free plating solution that can form a gunmetal-colored coating

[0063] The nickel-free, cobalt-free, and cyanide-free plating solution contains the following raw materials:

[0064]

[0065] Configuration Operation:

[0066] A. According to the starting concentration and tank volume, weigh the HEDP as designed in the table above and pour it into the electroplating tank, add water to 1 / 2 of the tank volume, add KOH to adjust the pH to 4.5-5.5, stir thoroughly until completely dissolved and set aside;

[0067] B. Dissolve EDTMPA, IDS, ammonium citrate and boric acid as designed in the above table in 1 / 4 of the tank volume of water, then slowly pour into the electrolytic tank in step A and stir evenly;

[0068] C. Slowly pour the copper sulfate and zinc sulfate as designed in the table above into the electrolytic cell and stir until they are completely dissolved;

[0069] D. Slowly add stannous sulfate to the electrolytic cell in small amounts and multiple times, stirring while adding, and finally dilute to the target volume with water, and adjust the pH to 4 with boric acid;

[0070] E. Dissolve ascorbic acid, hydroquinone and octadecyl dimethyl benzyl ammonium chloride in water respectively as designed in the above table, and then add them into the electrolytic cell respectively, and electrolyze with low-density current to remove impurities.

[0071] (3) The slider is small in size and requires batch electroplating, so this embodiment adopts a roller plating process.

[0072] The slider pretreated in step (1) is subjected to roller plating using the electroplating solution of step (2). During the electroplating process, the pH is controlled at 4≤pH≤4.5, the concentration of zinc sulfate is controlled at 30-35 g / L, the concentration of stannous sulfate is controlled at 4-6 g / L, and the concentration of copper sulfate is controlled at 1-3 g / L. The pH and main salt concentration of the dynamic changes are monitored in real time. If they are lower than the specified range, they are adjusted in time. The electroplating temperature is 20°C, and the cathode current density is set to 0.1 A / dm 2 The anode is a carbon plate, the rotation speed is 6r / min, and the roller plating time is 60min.

[0073] (4) Clean the roller-plated slider and blow dry.

[0074] The surface of the slider after electroplating in this embodiment is covered with a composite coating. Figure 2 From the surface of the slider 4 outward, there are a base copper plating layer 3, a bright copper plating layer 2 with a thickness of 5 μm, and a light gun-colored plating layer 1 with a thickness of 1.5 μm.

[0075] Example 2

[0076] (1) The slider to be electroplated (zinc alloy slider blank) is degreased and activated, primed with alkaline copper, and then plated with acid copper to increase brightness.

[0077] (2) Configure a nickel-free, cobalt-free, and cyanide-free plating solution that can form a gunmetal-colored coating

[0078] The nickel-free, cobalt-free, and cyanide-free plating solution contains the following raw materials:

[0079]

[0080] Configuration Operation:

[0081] A. According to the starting concentration and tank volume, weigh the HEDP as designed in the table above and pour it into the electroplating tank, add water to 1 / 2 of the tank volume, add KOH to adjust the pH to 4.5-5.5, stir thoroughly until completely dissolved and set aside;

[0082] B. Dissolve EDTMPA, IDS, ammonium citrate and boric acid as designed in the above table in 1 / 4 of the tank volume of water, then slowly pour into the electrolytic tank in step A and stir evenly;

[0083] C. Slowly pour the copper sulfate and zinc sulfate as designed in the table above into the electrolytic cell and stir until they are completely dissolved;

[0084] D. Slowly add stannous sulfate to the electrolytic cell in small amounts and multiple times, stirring while adding, and finally dilute to the target volume with water, and adjust the pH to 5 with boric acid;

[0085] E. Dissolve ascorbic acid, hydroquinone and octadecyl dimethyl benzyl ammonium chloride in water respectively as designed in the above table, and then add them into the electrolytic cell respectively, and electrolyze with low-density current to remove impurities.

[0086] (3) The slider is small in size and requires batch electroplating, so this embodiment adopts a roller plating process.

[0087] The slider pretreated in step (1) is subjected to roller plating with the electroplating solution of step (2), wherein the pH is controlled at 5 ≤ pH ≤ 5.5, the concentration of zinc sulfate is controlled at 40-45 g / L, the concentration of stannous sulfate is controlled at 7-9 g / L, and the concentration of copper sulfate is controlled at 3-4 g / L. The pH and main salt concentration of the dynamic changes are monitored in real time. If the concentration is lower than the specified range, it is adjusted in time. The electroplating temperature is 30° C., and the cathode current density is set to 1.0 A / dm 2 The anode is a carbon plate, the rotation speed is 8r / min, and the roller plating time is 60min.

[0088] (4) Clean the roller-plated slider and blow dry.

[0089] The surface of the slider after electroplating in this embodiment is covered with a composite coating. Figure 2 From the surface of the slider 4 outward, there are a base copper plating layer 3, a bright copper plating layer 2 with a thickness of 6 μm, and a light gun-colored plating layer 1 with a thickness of 1.5 μm.

[0090] Example 3

[0091] (1) The slider to be electroplated (zinc alloy slider blank) is degreased and activated, primed with alkaline copper, and then plated with acid copper to increase brightness.

[0092] (2) Configure a nickel-free, cobalt-free, and cyanide-free plating solution that can form a gunmetal-colored coating

[0093] The nickel-free, cobalt-free, and cyanide-free plating solution contains the following raw materials:

[0094]

[0095]

[0096] Configuration Operation:

[0097] A. According to the starting concentration and tank volume, weigh the HEDP as designed in the table above and pour it into the electroplating tank, add water to 1 / 2 of the tank volume, add KOH to adjust the pH to 4.5-5.5, stir thoroughly until completely dissolved and set aside;

[0098] B. Dissolve EDTMPA, IDS, ammonium citrate and boric acid as designed in the above table in 1 / 4 of the tank volume of water, then slowly pour into the electrolytic tank in step A and stir evenly;

[0099] C. Slowly pour the copper sulfate and zinc sulfate as designed in the table above into the electrolytic cell and stir until they are completely dissolved;

[0100] D. Slowly add stannous sulfate to the electrolytic cell in small amounts and multiple times, stirring while adding, and finally dilute to the target volume with water, and adjust the pH to 6 with boric acid;

[0101] E. Dissolve ascorbic acid, hydroquinone and octadecyl dimethyl benzyl ammonium chloride in water respectively as designed in the above table, and then add them into the electrolytic cell respectively, and electrolyze with low-density current to remove impurities.

[0102] (3) The slider is small in size and requires batch electroplating, so this embodiment adopts a roller plating process.

[0103] The slider pretreated in step (1) is subjected to roller plating with the electroplating solution of step (2), wherein the pH is controlled at 5.5 ≤ pH ≤ 6, the concentration of zinc sulfate is controlled at 45-50 g / L, the concentration of stannous sulfate is controlled at 8-10 g / L, and the concentration of copper sulfate is controlled at 4-5 g / L. The pH and main salt concentration of the dynamic changes are monitored in real time. If the concentration is lower than the specified range, it is adjusted in time. The electroplating temperature is 35° C., and the cathode current density is set to 1.5 A / dm 2 The anode is a carbon plate, the rotation speed is 10r / min, and the roller plating time is 60min.

[0104] (4) Clean the roller-plated slider and blow dry.

[0105] The surface of the slider after electroplating in this embodiment is covered with a composite coating. Figure 2 From the surface of the slider 4 outward, there are a base copper plating layer 3, a bright copper plating layer 2 with a thickness of 6 μm, and a dark gunmetal color plating layer 1 with a thickness of 1.5 μm.

[0106] Example 4

[0107] Compared with Example 2, this example does not contain octadecyl dimethyl benzyl ammonium chloride; the remaining operations are the same as those in Example 2.

[0108] Example 5

[0109] Compared with Example 3, the concentrations of copper sulfate in this example are 0.5 g / L and stannous sulfate are 15 g / L; the remaining operations are the same as those in Example 3.

[0110] Example 6

[0111] Compared with Example 2, this example uses chemically pure (CP) ammonium citrate from the same manufacturer with a purity of 99.5%; the remaining operations are the same as in Example 2.

[0112] Comparative Example 1

[0113] Compared with Example 1, this comparative example does not contain copper sulfate; the remaining operations are the same as those in Example 1.

[0114] Comparative Example 2

[0115] Compared with Example 2, this comparative example does not contain ascorbic acid and hydroquinone; the remaining operations are the same as those in Example 2.

[0116] Comparative Example 3

[0117] Compared with Example 1, the electroplating temperature of this comparative example is 18°C; the rest of the operations are the same as those of Example 1.

[0118] Comparative Example 4

[0119] Compared with Example 1, the pH of this comparative example was maintained at ≤3; the remaining operations were the same as those of Example 1.

[0120] (1) Coating morphology

[0121] The coating morphologies of Examples 1 to 6 and Comparative Examples 1 to 4 were observed. Figure 1 As shown, the electron microscope photos of different positions of the gun-colored coating in Example 2 are as follows Figure 3 and Figure 4 As shown, the gunmetal coating is smooth and densely structured with very few pores.

[0122] -- Coating morphology Example 1 Lighter gun-colored coating, smooth, with cold luster Example 2 Light gun-colored coating, smooth, with cold light Example 3 Dark gunmetal color coating, smooth, with cold light Example 4 Gun color coating, smooth, black and bright effect is slightly insufficient Example 5 Gunmetal coating color is white Example 6 Light gunmetal color coating but slightly yellowish Comparative Example 1 Matt white coating Comparative Example 2 After the plating solution is left for three days, tetravalent tin is likely to be produced, and the gun-colored coating turns into matte yellow. Comparative Example 3 There are crystals in the plating solution, and the color of the coating is dull Comparative Example 4 Produce white zinc salt precipitation, the coating is red

[0123] Comparative Examples 1 to 4 were unable to form a gun-colored coating, and no further performance testing was performed.

[0124] (2) Taking Example 2 as an example, the light gun-colored coating of Example 2 was subjected to XRF analysis (X-ray fluorescence spectrometer).

[0125] The results are as follows Figures 5 to 7 As shown, the light gun-colored coating of Example 2 contains 61.080% Cu, 32.916% Zn and 6.004% Sn, which indicates that a specific metal ratio of copper, zinc and tin can achieve an ideal gun-colored coating with a cold luster.

[0126] (3) Performance testing

[0127] A. Test according to the washing procedure established by ISO 6330 international standard (*Standard judgment: 1 to 3 are unqualified; 4 to 5 are qualified).

[0128] The results of Examples 1 to 6 are as follows, that is, all passed the test and were judged to be qualified.

[0129] ◆Appearance Durability to Laundering(International standard)

[0130]

[0131] Note:

[0132] scale of 1 to 5, where 1 is bad and 5 is good.

[0133] 5-----Negligible or no change.

[0134] 4-----Slightly changed.

[0135] 3-----Noticeable changed.

[0136] 2-----Considerable changed.

[0137] 1-----Heavy changed.

[0138] B. Refer to the American standard washing machine water washing test of AATCC 61, that is, the wear-resistant water washing test of detergent and steel balls, to detect the performance of the coating of the present invention (* standard judgment: 1 to 3 are unqualified; 4 to 5 are qualified).

[0139] The results of Examples 1 to 4 and Example 6 are as follows:

[0140] ◆Appearance Durability to Washing

[0141]

[0142] The results of Example 5 are as follows:

[0143] ◆Appearance Durability to Washing

[0144]

[0145] Note:

[0146] scale of 1 to 5, where 1 is bad and 5 is good.

[0147] 5------Negligible or no change.

[0148] 4------Slight changed

[0149] 3------Noticeable changed

[0150] 2------Considerable changed

[0151] 1------Heavy changed

[0152] It can be seen from the above test results that the gun-color plated slider prepared in Example 5 did not pass the wear-resistant water washing test. This may be because the tin ion concentration in the electroplating solution of the present invention should not be too high. Although the gun-color coating can be achieved, it may cause the brittleness of the gun-color coating to increase, which has an adverse effect on the protective performance.

[0153] C. Salt spray test: refer to ASTM B368 acid salt spray test standard to detect the corrosion resistance of the coating of the present invention (* standard judgment: 2 to 6 is unqualified; 8 to 10 is qualified).

[0154] The test results of Examples 1 to 5 are as follows:

[0155] ◆Acid Salt Spray (CASS Test)

[0156]

[0157] Note:

[0158] Rating coated metal color change:

[0159] 10-no change

[0160] 9-very slightly changed

[0161] 8-slightly changed

[0162] 6-moderate changed

[0163] 4-Noticeable changed

[0164] 2-severe changed

[0165] The test results of Example 6 are as follows:

[0166] ◆Acid Salt Spray (CASS Test)

[0167]

[0168] Note:

[0169] Rating coated metal color change:

[0170] 10-no change

[0171] 9-very slightly changed

[0172] 8-slightly changed

[0173] 6-moderate changed

[0174] 4-Noticeable changed

[0175] 2-severe changed

[0176] It can be seen from the above test results that the gun-colored coated slider prepared in Example 6 did not pass the acid salt spray test. After repeated studies, the inventors found that chemically pure (CP, purity 99.5%) ammonium citrate contains trace oxalic acid impurities, which are allowable and qualified for chemically pure ammonium citrate products, but have an adverse effect on the gun-colored coating performance of the present invention. This problem was eliminated after replacing it with analytically pure (AR, purity > 99.7%) ammonium citrate from the same producer.

[0177] According to the disclosure and teaching of the above specification, those skilled in the art to which the present invention belongs can also change and modify the above implementation mode. Therefore, the present invention is not limited to the specific implementation modes disclosed and described above, and some modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention. In addition, although some specific terms are used in this specification, these terms are only for the convenience of description and do not constitute any limitation to the present invention.

Claims

1. A nickel-free, cobalt-free, and cyanide-free electroplating solution capable of forming a gun-colored coating, characterized in that: Containing zinc salts with a concentration of 30 to 50 g / L, divalent tin salts with a concentration of ≥4 g / L, and copper salts with a concentration of ≥0.5 g / L; The invention also contains 100-150 g / L of hydroxyethylidene diphosphonic acid as the first complexing agent.

2. The nickel-free, cobalt-free, and cyanide-free electroplating solution capable of forming a gun-colored coating according to claim 1, characterized in that: Also comprising a second complexing agent, a third complexing agent and a pH buffer; The second complexing agent is ethylenediaminetetramethylenephosphonic acid at a concentration of 30 to 50 g / L; The third complexing agent is tetrasodium iminodisuccinate with a concentration of 20 to 40 g / L.

3. The nickel-free, cobalt-free, and cyanide-free electroplating solution capable of forming a gun-colored coating according to claim 1 or 2, characterized in that: It also contains citrate in a concentration of 15 to 30 g / L, ascorbic acid in a concentration of 0.5 to 1 g / L, and hydroquinone in a concentration of 0.5 to 1 g / L.

4. The nickel-free, cobalt-free, and cyanide-free electroplating solution capable of forming a gun-colored coating according to claim 3, characterized in that: Also contains octadecyl dimethyl benzyl ammonium chloride at a concentration of 15 to 30 ppm; The pH buffer is boric acid at a concentration of 30 to 40 g / L; The citrate is ammonium citrate with a purity of more than 99.5%.

5. The nickel-free, cobalt-free, and cyanide-free electroplating solution capable of forming a gun-colored coating according to claim 4, characterized in that: Composed of the following components in the following concentrations: 30-50 g / L zinc sulfate or zinc chloride; 4-10 g / L stannous sulfate or stannous chloride; 1-5 g / L copper sulfate or copper chloride; 100-150 g / L of hydroxyethylidene diphosphonic acid; 30-50 g / L of ethylenediaminetetramethylenephosphonic acid; 20-40 g / L tetrasodium iminodisuccinate; 15-30 g / L ammonium citrate, concentration > 99.5%; 0.5-1 g / L ascorbic acid; 0.5-1 g / L hydroquinone; 15-30 ppm of octadecyl dimethyl benzyl ammonium chloride; 30-40 g / L of boric acid; The rest was deionized water.

6. The electroplating method of any one of claims 1 to 5 using a nickel-free, cobalt-free, and cyanide-free electroplating solution capable of forming a gun-colored coating, characterized in that: The pH is controlled at 4≤pH≤6, and the electroplating temperature is controlled at 20~35℃.

7. The electroplating method according to claim 6, characterized in that: When the electroplating process is adopted, the main salt is 30-45g / L zinc salt, 4-8g / L divalent tin salt and 1-4g / L copper salt, the pH is controlled at 4≤pH≤6, and the current density is set at 0.1-1.5A / dm 2 , speed 6~10r / min, barrel plating time 30~120min, anode is carbon plate; Alternatively, when the electroplating is performed by rack plating, the main salt is a zinc salt with a concentration of 35 to 50 g / L, a divalent tin salt with a concentration of 6 to 10 g / L, and a copper salt with a concentration of 2 to 5 g / L, the pH is controlled at 4 ≤ pH ≤ 6, and the current density is set at 0.2 to 2.5 A / dm 2 The plating time is 15 to 60 minutes, and the anode is a carbon plate.

8. A light gun-colored composite coating, characterized in that: From the surface of the substrate to be electroplated outward, there are bright copper plating layers and gun-color plating layers in order, and the gun-color plating layers are formed by electroplating with the nickel-free, cobalt-free, and cyanide-free electroplating solution capable of forming gun-color plating layers as claimed in any one of claims 1 to 5.

9. The light gunmetal color composite coating according to claim 8, characterized in that: The thickness of the bright copper plating layer is 5 to 15 μm, and the thickness of the gunmetal color plating layer is preferably 1 to 3 μm.

10. The light gun-colored composite coating according to claim 8 or 9, characterized in that: The gunmetal color coating contains the following proportions of metal elements: Cu 60~65wt%; Zn 30-35wt%; Sn 5-8wt%; Total 100%.

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