Cyanide-free electroplating cadmium solution and preparation method thereof

Abstract

The invention discloses a cyanide-free cadmium electroplating solution and a preparation method thereof, and the cyanide-free cadmium electroplating solution comprises the following components: a cadmium source; the main complexing agent adopts 1-hydroxyethylidene-1, 1-diphosphonic acid; 5, 5-dimethyl hydantoin is adopted as the second complexing agent; beta-D-glucose pyranoloxy octyl polyethylene glycol ether is adopted as the additive. The additive of beta-D-glucose pyranoloxyoctyl polyethylene glycol ether is added into the plating solution, so that the plating solution has the properties of accelerating the deposition speed of a plating layer, improving the uniform plating capacity of the plating solution, improving the deep plating capacity of the plating solution and improving the glossiness of the plating layer; the problems existing in the application of the existing ammonia carboxylic acid complexing agent system, HEDP system and pyrophosphate system plating solution are well solved.

Description

Technical Field

[0001] This invention belongs to the field of surface treatment technology, specifically relating to a cyanide-free cadmium electroplating solution and its preparation method. Background Technology

[0002] Cadmium electroplating is a widely used electroplating process in the aerospace industry. Due to its superior comprehensive performance, it is applied to fasteners, springs, and other components requiring high corrosion resistance. Since cyanide is a highly toxic substance and poses a significant safety hazard to human health, cyanide-free electroplating is an inevitable trend. Currently, existing cyanide-free electroplating processes mainly include ammonium carboxyl complexing agent systems, HEDP systems, and pyrophosphate systems. While these systems can replace cyanide electroplating to some extent, they each have their own problems in application. In ammonium carboxyl complexing systems, the ammonium is easily volatile, leading to significant pH fluctuations in the plating solution and affecting plating quality. The HEDP system has a small current density window, resulting in a very slow plating speed. In pyrophosphate systems, the main complexing agent undergoes natural degradation, affecting the service life of the plating solution and making it unsuitable for long-term use. Summary of the Invention

[0003] The purpose of this invention is to provide a cyanide-free cadmium electroplating solution and its preparation method, so as to solve the above-mentioned problems existing in the application of the ammonium carboxyl complexing agent system, HEDP system and pyrophosphate system plating solution used in the existing cyanide-free electroplating process.

[0004] This invention is achieved through the following technical solution:

[0005] Cyanide-free cadmium electroplating solution, comprising the following components:

[0006] Cadmium source;

[0007] The main complexing agent is hydroxyethylidene diphosphonic acid;

[0008] The second complexing agent is 5,5-dimethylhydantoin;

[0009] The additive is β-D-glucopyranoxyoctyl polyethylene glycol ether.

[0010] In some embodiments, the content of each component in the cyanide-free cadmium electroplating solution is as follows:

[0011] Cadmium source, 0.015M-0.025M;

[0012] Primary complexing agent, 0.25M-0.35M;

[0013] Second complexing agent, 0.08M-0.12M;

[0014] Additives, 0.001M-0.002M.

[0015] In some embodiments, the cyanide-free cadmium plating solution also includes a pH adjuster for adjusting the pH value of the cyanide-free cadmium plating solution to 8.8-9.5.

[0016] In some embodiments, the cyanide-free cadmium electroplating solution also includes a buffer, the buffer having a component content of 0.05M-0.1M.

[0017] In some embodiments, the cyanide-free cadmium electroplating solution also includes a surfactant, wherein the surfactant content is 0.001M-0.003M.

[0018] In some embodiments, the β-D-glucose pyranoxyoctyl polyethylene glycol ether is prepared using octylphenol, chloroethanol, ethylene oxide, an alkaline catalyst, β-D-glucose, trifluoromethanesulfonic anhydride, dichloromethane, tetrabutylammonium bromide, and sodium carbonate.

[0019] In some embodiments, the preparation of the β-D-glucopyranooxyoctyl polyethylene glycol ether includes the following steps:

[0020] Etherification reaction: Octylphenol and chloroethanol are mixed, and an alkaline catalyst is added to react and generate an octyl ether intermediate;

[0021] Polymerization reaction: Ethylene oxide is added to an octyl ether intermediate, and the reaction produces polyethylene glycol chains.

[0022] Grafting reaction: β-D-glucose and trifluoromethanesulfonic anhydride were used in anhydrous conditions with anhydrous dichloromethane as solvent to carry out the grafting reaction.

[0023] Additive synthesis: The product of the polymerization reaction is mixed with the product of the grafting reaction, and β-D-glucopyranoxyoctyl polyethylene glycol ether is generated by using tetrabutylammonium bromide and sodium carbonate as catalysts.

[0024] In some embodiments, the etherification reaction is carried out at 50°C for 12 hours.

[0025] And / or, in the polymerization reaction, the reaction is carried out at 90°C and 2-4 atmospheres for 24 hours;

[0026] And / or, in the grafting group reaction, the reaction is carried out at 0°C for 2-4 hours.

[0027] In some embodiments, the electroplating current density of the cyanide-free cadmium plating solution at room temperature is 1-4 A / dm². 2 The ratio of yin to yang area is 1:2 to 1:3.

[0028] On the other hand, the present invention also provides a method for preparing a cyanide-free cadmium electroplating solution, comprising the following steps:

[0029] The cadmium source is dissolved in distilled water to form a basic solution;

[0030] Add the primary complexing agent and the second complexing agent to the base solution and stir until completely dissolved;

[0031] The pH value of the solution is adjusted to the set range using a pH adjuster;

[0032] A buffer is added to the solution for buffering, followed by the addition of surfactants and additives;

[0033] The solution is filtered and transferred to an electroplating tank, where it is electrolyzed for a set time at a set current to obtain a cyanide-free cadmium electroplating solution.

[0034] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0035] This invention is based on a HEDP cyanide-free cadmium plating process formulation with small pH changes and stable complexes, avoiding the problems of large pH changes in the aminocarboxylic acid complex system and the instability of the pyrophosphate complex system. DMH is used as an auxiliary complexing agent to increase the stability of the plating solution and expand the current density range of the plating solution. On this basis, by adding β-D-glucopyranoxyoctyl polyethylene glycol ether as an additive to the plating solution, the plating solution has the properties of accelerating the coating deposition rate, improving the plating uniformity, improving the plating depth, and improving the coating gloss. It effectively solves the problems existing in the application of existing aminocarboxylic acid complexing agent systems, HEDP systems, and pyrophosphate system plating solutions. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0037] Certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that hardware manufacturers may use different names to refer to the same component. This specification and claims do not distinguish components based on differences in name, but rather on differences in function. The terms "comprising" and "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising / including but not limited to". "Approximately" means that within an acceptable margin of error, those skilled in the art can solve the technical problem and substantially achieve the technical effect within a certain margin of error. The following descriptions in the specification are preferred embodiments for carrying out this application; however, these descriptions are for the purpose of illustrating the general principles of this application and are not intended to limit the scope of this application. The scope of protection of this application shall be determined by the appended claims.

[0038] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a product or system comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a product or system. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the product or system that includes said element.

[0039] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0040] To address the problems of existing plating solutions using aminocarboxylic acid complexing agents, HEDP systems, and pyrophosphate systems, this invention is based on a HEDP cyanide-free cadmium plating process formulation that exhibits minimal pH changes and stable complexes. This avoids the issues of large pH changes in aminocarboxylic acid complex systems and the instability of complexes in pyrophosphate systems.

[0041] To address the slow electroplating speed of the HEDP system, this invention uses DMH as an auxiliary complexing agent to increase the stability of the plating solution and improve its current density range. However, its improvement on the current density range is relatively limited, only increasing it from the original 0.5–1.0 A / dm³. 2 Increased to 0.5–1.5 A / dm 2 .

[0042] Therefore, based on this, an additive is added to the plating solution components in this application. Specifically, the additive is β-D-glucopyranoxyoctyl polyethylene glycol ether. Studies have found that the additive can play the following roles in the plating solution:

[0043] 1) Accelerate the coating deposition rate

[0044] Before adding additives to the plating bath, the current density of the plating bath ranged from 0.5 to 1.5 A / dm³. 2 The deposition rate at the medium current density is approximately 10–15 μm / h;

[0045] With the addition of additives, its current density range can be extended to 1–4 A / dm². 2 The deposition rate at the medium current density is approximately 20–40 μm / h.

[0046] 2) Improve the uniform plating ability of the plating solution

[0047] The uniform plating ability of the plating bath was tested using the Hull cell method. Before the addition of additives, the uniform plating ability was approximately 50%; after the addition of additives, the uniform plating ability could be increased to 55%.

[0048] 3) Improve the deep plating capability of the plating solution.

[0049] The plating uniformity of the plating solution was tested using the copper tube method. Before the addition of additives, a coating was present in the depth-to-diameter ratio of approximately 1.2; after the addition of additives, a coating was present in the depth-to-diameter ratio of approximately 1.5.

[0050] 4) Improve coating gloss

[0051] The gloss of the cadmium plating was tested using a gloss meter. Before the addition of additives, the gloss of the plating at an incident angle of 85° was 5–10; after the addition of additives, the gloss of the plating was 10–20.

[0052] The pH value of the solution of this invention can remain stable between 8.8 and 9.5 for a long time; the electroplating speed even exceeds that of cyanide electroplating, reaching 20 to 40 μm / h, and the main components of the electroplating solution do not change significantly after standing for more than half a year.

[0053] In some embodiments of the present invention, the components of the cyanide-free cadmium electroplating solution include:

[0054] A cadmium source, with a concentration of 0.015M-0.025M, is used to provide the required cadmium ions for the coating; cadmium sulfate can be used as an example.

[0055] The main complexing agent, with a content of 0.25M-0.35M, can stabilize cadmium ions in the solution and reduce deposition in the plating bath; the main complexing agent is hydroxyethylidene diphosphonic acid (HEDP);

[0056] The second complexing agent, with a content of 0.08M-0.12M, can enhance the stability of the plating solution and the gloss of the coating; the second complexing agent is 5,5-dimethylhydantoin (DMH);

[0057] And, additives, in a content of 0.001M-0.002M, the additives being β-D-glucosepyranoxyoctyl polyethylene glycol ether.

[0058] The materials used to prepare the additive are as follows:

[0059] Octylphenol;

[0060] Ethylene Chlorohydrin;

[0061] Ethylene oxide;

[0062] Alkaline catalysts, such as sodium hydroxide, can be used.

[0063] β-D-glucose;

[0064] Trifluoromethanesulfonic anhydride;

[0065] Dichloromethane;

[0066] Tetrabutylammonium bromide (TEBA);

[0067] Sodium carbonate.

[0068] Equipment used for preparing additives:

[0069] The reaction vessel is equipped with temperature control and stirring functions;

[0070] High-performance liquid chromatography (HPLC);

[0071] Mass spectrometer (MS).

[0072] The additive can be prepared using the following methods:

[0073] 1. Etherification reaction;

[0074] In a reaction vessel, octylphenol and an appropriate amount of chloroethanol are mixed; an alkaline catalyst (such as sodium hydroxide) is added; and the mixture is reacted at 50°C for 12 hours to generate an octyl ether intermediate.

[0075] The reaction equation for the etherification reaction is as follows:

[0076] C8H 17 C6H4OH + ClCH2CH2OH → C8H 17 C6H4OCH2CH2OH+HCl.

[0077] 2. Polymerization reaction;

[0078] Ethylene oxide was slowly added to a reactor containing octyl ether intermediate; the temperature was maintained at 90°C and the reaction was continued for 24 hours under high pressure (approximately 2-4 atmospheres) to promote the formation of polyethylene glycol chains; after the reaction was completed, the mixture was cooled to room temperature.

[0079] The reaction equation for the polymerization reaction is as follows:

[0080] nCH2CH2O+H(OCH2CH2) n-1 H→HO(CH2CH2O) n H.

[0081] 3. Grafting group reaction;

[0082] β-D-glucose and trifluoromethanesulfonic anhydride (Tf2O) were slowly added to a reaction vessel; the reaction was carried out under anhydrous conditions, using anhydrous dichloromethane (DCM) as a solvent, and the reaction was carried out at 0°C for 2-4 hours.

[0083] The reaction equation for the grafting group reaction is as follows:

[0084] Glucose-OH+Tf2O→Glucose-OTf+TfOH.

[0085] 4. Additive synthesis;

[0086] The product of the polymerization reaction in step 2 and the product of the grafting reaction in step 3 were slowly added into a reactor; using tetrabutylammonium bromide (TEBA) and sodium carbonate as catalysts, the reaction was carried out at room temperature for 6-12 hours to synthesize β-D-glucopyranoxyoctyl polyethylene glycol ether.

[0087] The reaction equation for the synthesis reaction is as follows:

[0088] Octvl-PEG-OH+Glucose-OTf→Octvl-PEG-O-Glucose+TfOH.

[0089] In some embodiments, the components of the cyanide-free cadmium electroplating solution also include a pH adjuster to adjust the pH of the composition solution to 8.8-9.5 to ensure the activity of the complexing agent; sodium carbonate may be used for example.

[0090] In some embodiments, the cyanide-free cadmium electroplating solution also includes a buffer agent, the content of which is 0.05M-0.1M, to maintain the acid-base stability of the plating solution; for example, boric acid can be used.

[0091] In some embodiments, the cyanide-free cadmium electroplating solution also includes a surfactant, the surfactant content of which is 0.001M-0.003M, to improve the surface smoothness of the coating and reduce surface tension; for example, sodium dodecyl sulfate can be used.

[0092] In some embodiments of the present invention, the preparation method of cyanide-free cadmium electroplating solution includes the following steps:

[0093] Cadmium sulfate is dissolved in distilled water to form a basic solution;

[0094] Add HEDP and DMH gradually to the base solution, stirring constantly to ensure complete dissolution;

[0095] Add sodium carbonate to adjust the pH of the solution to the desired range;

[0096] Boric acid is added for buffering, followed by the addition of surfactants and additives;

[0097] The solution was filtered and transferred to an electroplating tank, where it was electrolyzed for about 24 hours under a low current to obtain a cyanide-free cadmium electroplating solution.

[0098] The cyanide-free cadmium electroplating solution in this embodiment of the invention can avoid the problems existing in current plating solutions and has the characteristics of stable pH of the plating solution, fast coating deposition speed, and long plating solution life.

[0099] The electroplating process parameters of the cyanide-free cadmium plating solution in this embodiment of the invention mainly include:

[0100] Electroplating temperature: room temperature;

[0101] Electroplating current density: 1~4A / dm 2 ;

[0102] Yin-Yang area ratio: 1:2 to 1:3.

[0103] The following detailed description, with reference to specific embodiments, illustrates the cyanide-free cadmium electroplating solution of the present invention, its preparation, and its application.

[0104] Example 1

[0105] Components of a cyanide-free cadmium electroplating solution:

[0106] Cadmium source (cadmium sulfate): 0.015M;

[0107] Main chelating agent (hydroxyethylidene diphosphonic acid / HEDP): 0.25M;

[0108] Second chelating agent (5,5-dimethylhydantoin / DMH): 0.08M;

[0109] Buffer (boric acid): 0.05M;

[0110] Surfactant (sodium dodecyl sulfate): 0.001M;

[0111] β-D-glucosepyranoxyoctyl polyethylene glycol ether: 0.001M.

[0112] Control the pH value of the plating solution to 9.5.

[0113] The methods used to synthesize additives:

[0114] 1. Etherification reaction;

[0115] In a reaction vessel, 10 kg of octylphenol and 6 kg of chloroethanol are mixed; 6 kg of alkaline catalyst (such as sodium hydroxide) is added; and the reaction is carried out at 50°C for 12 hours to produce about 14 kg of octyl ether intermediate, with a reaction yield of about 80%.

[0116] 2. Polymerization reaction;

[0117] 35 kg of ethylene oxide was slowly added to a reactor containing 15 kg of octyl ether intermediate; the temperature was maintained at 90 °C and the reaction was continued for 24 hours under high pressure (approximately 2-4 atmospheres) to promote the formation of polyethylene glycol chains; after the reaction was completed, the mixture was cooled to room temperature.

[0118] The reaction produces approximately 25 kg of polymer, with a yield of approximately 50%.

[0119] 3. Grafting group reaction;

[0120] 12 kg of β-D-glucose and 10 kg of trifluoromethanesulfonic anhydride (Tf2O) were slowly added into a reaction vessel; the reaction was carried out under anhydrous conditions, using 75 L of anhydrous dichloromethane (DCM) as a solvent, and the reaction was carried out at 0 °C for 2-4 hours.

[0121] The reaction produces approximately 10 kg of reaction product, with a yield of approximately 45%.

[0122] 4. Final product reaction;

[0123] 12.5 kg of the product from the polymerization reaction in step 2 and 10 kg of the product from the grafting reaction in step 3 were slowly added into a reactor. Using 10 g of tetrabutylammonium bromide (TEBA) and 60 g of sodium carbonate as catalysts, the reaction was carried out at room temperature for 6-12 hours to synthesize approximately 10 kg of β-D-glucosepyranoxyoctyl polyethylene glycol ether, with a reaction yield of approximately 60%.

[0124] A cyanide-free cadmium plating solution was prepared using the above-mentioned components and preparation method. Electroplating was performed using the prepared cyanide-free cadmium plating solution, and the performance of the cyanide-free cadmium plating solution was tested.

[0125] Electroplating process adopted:

[0126] 1. Pretreatment;

[0127] Cleaning is performed to remove grease and organic contaminants from the sample surface;

[0128] Pickling: Use a 10% sulfuric acid solution to remove oxides from the sample surface;

[0129] Activation is achieved by treating the sample with dilute hydrochloric acid to enhance the adhesion of the coating.

[0130] 2. Electroplating treatment;

[0131] The workpiece is immersed in the prepared solution; the current density is set to 1 A / dm³. 2 The electroplating treatment time is set to 30 minutes.

[0132] 3. Post-processing;

[0133] Rinse with cold water to remove surface residue.

[0134] Passivation: The process involves a triacid hexavalent chromium passivation process for 3–5 seconds.

[0135] Heat treatment: Bake at 60℃ for 20 minutes to enhance coating performance.

[0136] The performance of the plating solution was tested, and the results are as follows:

[0137] a) Plating solution life test

[0138] After the plating solution was left exposed for 180 days, the solution appeared clear and transparent with no sediment at the bottom and the pH value decreased from 9.5 to 9.3, indicating that the plating solution had good stability.

[0139] b) Plating rate test of plating solution

[0140] The plating solution is used at a current density of 1.0 A / dm³. 2 At that time, after 30 minutes of electroplating, the coating thickness was close to 15 μm; when the current density was 2.5 A / dm 2 At that time, after 30 minutes of electroplating, the coating thickness was close to 30 μm; when the current density was 4 A / dm 2 When the plating solution was used, after 30 minutes of electroplating, the coating thickness was close to 40μm, indicating that the electroplating speed of the plating solution was relatively fast.

[0141] c) Plating solution uniformity test

[0142] The uniform plating ability of the plating bath was tested using the Hull cell method when an applied current of 2.5 A / dm² was applied. 2 At that time, the plating capacity was approximately 55%.

[0143] d) Deep plating capability test of plating solution

[0144] The uniform plating ability of the plating solution was tested using the copper tube method when an applied current of 2.5 A / dm² was applied. 2 At that time, the aspect ratio of the coating was greater than 1.5.

[0145] The properties of the formed coating were tested, and the results are as follows:

[0146] a) Appearance

[0147] The coating has a uniform silver-white appearance and good surface quality.

[0148] b) Corrosion resistance

[0149] The 8-12μm coating exhibits good corrosion resistance, with red rust appearing over 2000 hours under neutral salt spray testing.

[0150] Example 2

[0151] Components of a cyanide-free cadmium electroplating solution:

[0152] Cadmium source (cadmium sulfate): 0.0175M;

[0153] Main chelating agent (hydroxyethylidene diphosphonic acid / HEDP): 0.30M;

[0154] Second chelating agent (5,5-dimethylhydantoin / DMH): 0.10M;

[0155] Buffer (boric acid): 0.05M;

[0156] Surfactant (sodium dodecyl sulfate): 0.001M;

[0157] β-D-glucosepyranoxyoctyl polyethylene glycol ether: 0.0015M.

[0158] Control the pH value of the plating solution to 9.0.

[0159] The synthesis of the additives and the electroplating process in this embodiment are the same as in Example 1.

[0160] The performance of the plating solution was tested, and the results are as follows:

[0161] a) Plating solution life test

[0162] After the plating solution was left exposed for 180 days, the solution appeared clear and transparent with no sediment at the bottom and the pH value decreased from 9.0 to 8.8, indicating that the plating solution had good stability.

[0163] b) Plating rate test of plating solution

[0164] The plating solution is used at a current density of 1.0 A / dm³. 2 At that time, after 30 minutes of electroplating, the coating thickness was close to 16 μm; when the current density was 2.5 A / dm 2 At that time, after 30 minutes of electroplating, the coating thickness was close to 31 μm; when the current density was 4 A / dm 2 When the plating solution was used, after 30 minutes of electroplating, the coating thickness was close to 40μm, indicating that the electroplating speed of the plating solution was relatively fast.

[0165] c) Plating solution uniformity test

[0166] The uniform plating ability of the plating bath was tested using the Hull cell method when an applied current of 2.5 A / dm² was applied. 2 At that time, the plating capacity was approximately 53%.

[0167] d) Deep plating capability test of plating solution

[0168] The uniform plating ability of the plating solution was tested using the copper tube method when an applied current of 2.5 A / dm² was applied. 2 At that time, the aspect ratio of the coating was greater than 1.4.

[0169] The properties of the formed coating were tested, and the results are as follows:

[0170] a) Appearance

[0171] The coating has a uniform silver-white appearance and good surface quality.

[0172] b) Corrosion resistance

[0173] The 8-12μm coating exhibits good corrosion resistance, with red rust appearing over 2000 hours under neutral salt spray testing.

[0174] Example 3

[0175] Components of a cyanide-free cadmium electroplating solution:

[0176] Cadmium source (cadmium sulfate): 0.020M;

[0177] Main chelating agent (hydroxyethylidene diphosphonic acid / HEDP): 0.35M;

[0178] Second chelating agent (5,5-dimethylhydantoin / DMH): 0.12M;

[0179] Buffer (boric acid): 0.05M;

[0180] Surfactant (sodium dodecyl sulfate): 0.001M;

[0181] β-D-glucosepyranoxyoctyl polyethylene glycol ether: 0.0020M.

[0182] Control the pH value of the plating solution to 8.5.

[0183] The synthesis of the additives and the electroplating process in this embodiment are the same as in Example 1.

[0184] The performance of the plating solution was tested, and the results are as follows:

[0185] a) Plating solution life test

[0186] After the plating solution was left exposed for 180 days, the solution appeared clear and transparent with no sediment at the bottom and the pH value decreased from 8.5 to 8.0, indicating that the plating solution had good stability.

[0187] b) Plating rate test of plating solution

[0188] The plating solution is used at a current density of 1.0 A / dm³. 2 At that time, after 30 minutes of electroplating, the coating thickness was close to 18 μm; when the current density was 2.5 A / dm 2 At that time, after 30 minutes of electroplating, the coating thickness was close to 32 μm; when the current density was 4 A / dm2 When the plating solution was used, after 30 minutes of electroplating, the coating thickness was close to 40μm, indicating that the electroplating speed of the plating solution was relatively fast.

[0189] c) Plating solution uniformity test

[0190] The uniform plating ability of the plating bath was tested using the Hull cell method when an applied current of 2.5 A / dm² was applied. 2 At that time, the plating capacity was approximately 52%.

[0191] d) Deep plating capability test of plating solution

[0192] The uniform plating ability of the plating solution was tested using the copper tube method when an applied current of 2.5 A / dm² was applied. 2 At that time, the aspect ratio of the coating was greater than 1.2.

[0193] The properties of the formed coating were tested, and the results are as follows:

[0194] a) Appearance

[0195] The coating has a uniform silver-white appearance and good surface quality.

[0196] b) Corrosion resistance

[0197] The 8-12μm coating exhibits good corrosion resistance, with red rust appearing over 2000 hours under neutral salt spray testing.

[0198] Comparative Example 1

[0199] The process formula for the electroplating bath solution in Comparative Example 1 (HEDP cadmium electroplating process) is as follows:

[0200] Cadmium chloride (CdCl2), 0–70 g / L;

[0201] 60% HEDP aqueous solution, 180-250 mL / L;

[0202] Polyethylene glycol 20000 (PEG), 0.01~0.2g / L;

[0203] Thiourea, 0.01–0.2 g / L;

[0204] Control the pH value of the plating solution to 12.0–12.5.

[0205] Electroplating process used:

[0206] 1) Pretreatment;

[0207] Cleaning: Removes grease and organic contaminants.

[0208] Pickling: Use a 10% sulfuric acid solution to remove oxides.

[0209] Activation: Treat with dilute hydrochloric acid to enhance coating adhesion.

[0210] 2) Electroplating process:

[0211] After the plating solution is prepared, immerse the workpiece in it.

[0212] The current density is set to 1 A / dm 2 The electroplating time is set to 30 minutes.

[0213] 3) Post-processing:

[0214] Rinse with cold water to remove surface residue.

[0215] Passivation: The process involves a triacid hexavalent chromium passivation process for 3–5 seconds.

[0216] Heat treatment: Bake at 60℃ for 20 minutes to enhance coating performance.

[0217] The performance of the plating solution was tested, and the results are as follows:

[0218] a) Plating solution life test

[0219] After the plating solution was left exposed for 180 days, it remained clear and transparent with no sediment at the bottom and the pH value remained above 12.0, indicating that the plating solution had good stability.

[0220] b) Plating rate test of plating solution

[0221] The plating solution is used at a current density of 1.0 A / dm³. 2 At that time, after 30 minutes of electroplating, the coating thickness was close to 5μm. The plating rate of the plating solution was relatively slow.

[0222] c) Plating solution uniformity test

[0223] The plating uniformity was measured using the Hull cell method and was approximately 48%.

[0224] d) Deep plating capability test of plating solution

[0225] The plating uniformity of the plating solution was tested using the copper tube method when an applied current of 1 A / dm² was applied. 2 At that time, the aspect ratio of the coating was greater than 1.5.

[0226] The properties of the formed coating were tested, and the results are as follows:

[0227] a) Appearance

[0228] The coating has a uniform silver-white appearance.

[0229] b) Corrosion resistance

[0230] The 8-12μm coating typically develops red rust after 1000 hours under neutral salt spray testing, indicating poor corrosion resistance.

[0231] Comparative Example 2

[0232] The process formula for the electroplating bath solution in Comparative Example 2 (DMH cadmium electroplating process) is as follows:

[0233] Cadmium oxide (CdO), 25–35 g / L;

[0234] DMH (5,5-dimethylhydantoin), 160–200 g / L;

[0235] Sodium hydroxide (NaOH), 80–120 g / L;

[0236] Thiourea, 0.05–0.2 g / L;

[0237] Control the pH value of the plating solution: pH 8.5~9.5.

[0238] Electroplating process used:

[0239] 1) Pretreatment;

[0240] Cleaning: Removes grease and organic contaminants.

[0241] Pickling: Use a 10% sulfuric acid solution to remove oxides.

[0242] Activation: Treat with dilute hydrochloric acid to enhance coating adhesion.

[0243] 2) Electroplating process;

[0244] After the plating solution is prepared, immerse the workpiece in it.

[0245] The current density is set to 1 A / dm 2 The electroplating time is set to 30 minutes.

[0246] 3) Post-processing;

[0247] Rinse with cold water to remove surface residue.

[0248] Passivation: The process involves a triacid hexavalent chromium passivation process for 3–5 seconds.

[0249] Heat treatment: Bake at 60℃ for 20 minutes to enhance coating performance.

[0250] The performance of the plating solution was tested, and the results are as follows:

[0251] a) Plating solution life test

[0252] After the plating solution was left exposed for 180 days, it remained clear and transparent with no sediment at the bottom and the pH value remained around 9.0, indicating that the plating solution had good stability.

[0253] b) Plating rate test of plating solution

[0254] The plating solution is used at a current density of 1.0 A / dm³. 2 At that time, after 30 minutes of electroplating, the coating thickness was close to 5μm. The plating rate of the plating solution was relatively slow.

[0255] c) Plating solution uniformity test

[0256] The plating uniformity was measured using the Hull cell method, and the plating uniformity was approximately 53%.

[0257] d) Deep plating capability test of plating solution

[0258] The plating uniformity of the plating solution was tested using the copper tube method when an applied current of 1 A / dm² was applied. 2 At that time, the aspect ratio of the coating was about 1.0, and the plating solution had the ability to deep plate.

[0259] The properties of the formed coating were tested, and the results are as follows:

[0260] a) Appearance

[0261] The coating has a uniform silver-white appearance.

[0262] b) Corrosion resistance

[0263] The 8-12μm coating showed red rust after about 1000 hours under neutral salt spray testing, indicating poor corrosion resistance.

[0264] Comparative Example 3

[0265] The process formula for the electroplating bath solution in Comparative Example 3 (ammonia-carboxylic acid complex electroplating of cadmium) is as follows:

[0266] Cadmium chloride (CdCl2·2.5H2O), 40–50 g / L;

[0267] Ammonium chloride (NH4Cl), 180–220 g / L;

[0268] N-aminotriacetic acid (NTA), 60–80 g / L;

[0269] EDTA (ethylenediaminetetraacetic acid), 20–30 g / L;

[0270] Control the pH value of the plating solution to 6-7.

[0271] Electroplating process used:

[0272] 1) Pretreatment;

[0273] Cleaning: Removes grease and organic contaminants.

[0274] Pickling: Use a 10% sulfuric acid solution to remove oxides.

[0275] Activation: Treat with dilute hydrochloric acid to enhance coating adhesion.

[0276] 2) Electroplating process;

[0277] After the plating solution is prepared, immerse the workpiece in it.

[0278] The current density is set to 1 A / dm 2 The electroplating time is set to 30 minutes.

[0279] 3) Post-processing;

[0280] Rinse with cold water to remove surface residue.

[0281] Passivation: The process involves a triacid hexavalent chromium passivation process for 3–5 seconds.

[0282] Heat treatment: Bake at 60℃ for 20 minutes to enhance coating performance.

[0283] The performance of the plating solution was tested, and the results are as follows:

[0284] a) Plating solution life test

[0285] After the plating solution was left exposed for 180 days, the solution appeared clear and transparent with no sediment at the bottom, and the pH dropped from 6.5 to 5.5, indicating that the pH stability of the plating solution was poor.

[0286] b) Plating rate test of plating solution

[0287] The plating solution is used at a current density of 1.0 A / dm³. 2 At that time, after 30 minutes of electroplating, the coating thickness was close to 12μm. The plating rate of the plating solution was relatively fast.

[0288] c) Plating solution uniformity test

[0289] The plating uniformity was measured using the Hull cell method, and the plating uniformity was approximately 50%.

[0290] d) Deep plating capability test of plating solution

[0291] The plating uniformity of the plating solution was tested using the copper tube method when an applied current of 1 A / dm² was applied. 2 At that time, the aspect ratio of the coating was approximately 1.2.

[0292] The properties of the formed coating were tested, and the results are as follows:

[0293] a) Appearance

[0294] The coating has a uniform silver-white appearance.

[0295] b) Corrosion resistance

[0296] The 8-12μm coating takes approximately 2000 hours to develop red rust under a neutral salt spray test.

[0297] The performance test results of the plating solution and coating in the examples and comparative examples are shown in Table 1.

[0298] Table 1

[0299] Serial Number Plating solution life test Plating speed test Plating uniformity Deep plating capability Appearance corrosion resistance Example 1 No change in 180 days Faster better better silver-white better Example 2 No change in 180 days Faster better better silver-white better Example 3 No change in 180 days Faster better better silver-white better Comparative Example 1 No change in 180 days Slower better better silver-white Poor Comparative Example 2 No change in 180 days Slower better Poor silver-white Poor Comparative Example 3 pH change Faster better better silver-white better

[0300] The results above show that Examples 1-3 have better overall performance than Comparative Documents 1-3, indicating that the method of the present invention can effectively solve the problems of poor plating solution stability, slow plating speed, poor plating depth capability, and poor corrosion resistance of existing cyanide-free electroplating solutions.

[0301] The foregoing description illustrates and describes several preferred embodiments of this application. However, as previously stated, it should be understood that this application is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the application concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of this application should be within the protection scope of the appended claims.

Claims

1. A cyanide-free cadmium electroplating solution, characterized in that, Includes the following components: Cadmium source; The main complexing agent is hydroxyethylidene diphosphonic acid; The second complexing agent is 5,5-dimethylhydantoin; The additive is β-D-glucopyranoxyoctyl polyethylene glycol ether.

2. The cyanide-free cadmium electroplating solution according to claim 1, characterized in that, The content of each component in the cyanide-free cadmium electroplating solution is as follows: Cadmium source, 0.015M-0.025M; Primary complexing agent, 0.25M-0.35M; Second complexing agent, 0.08M-0.12M; Additives, 0.001M-0.002M.

3. The cyanide-free cadmium electroplating solution according to claim 1 or 2, characterized in that, The cyanide-free cadmium electroplating solution also includes a pH adjuster to adjust the pH value of the cyanide-free cadmium electroplating solution to 8.8-9.

5.

4. The cyanide-free cadmium electroplating solution according to claim 1 or 2, characterized in that, The cyanide-free cadmium electroplating solution also includes a buffer, with the buffer component content ranging from 0.05M to 0.1M.

5. The cyanide-free cadmium electroplating solution according to claim 1 or 2, characterized in that, The cyanide-free cadmium electroplating solution also contains surfactants, with surfactant content ranging from 0.001M to 0.003M.

6. The cyanide-free cadmium electroplating solution according to claim 1, characterized in that, The β-D-glucose pyranoxyoctyl polyethylene glycol ether was prepared using octylphenol, chloroethanol, ethylene oxide, an alkaline catalyst, β-D-glucose, trifluoromethanesulfonic anhydride, dichloromethane, tetrabutylammonium bromide, and sodium carbonate.

7. The cyanide-free cadmium electroplating solution according to claim 6, characterized in that, The preparation of the β-D-glucopyranoxyoctyl polyethylene glycol ether includes the following steps: Etherification reaction: Octylphenol and chloroethanol are mixed, and an alkaline catalyst is added to react and generate an octyl ether intermediate; Polymerization reaction: Ethylene oxide is added to an octyl ether intermediate, and the reaction produces polyethylene glycol chains. Grafting reaction: β-D-glucose and trifluoromethanesulfonic anhydride were used in anhydrous conditions with anhydrous dichloromethane as solvent to carry out the grafting reaction. Additive synthesis: The product of the polymerization reaction is mixed with the product of the grafting reaction, and β-D-glucopyranoxyoctyl polyethylene glycol ether is generated by using tetrabutylammonium bromide and sodium carbonate as catalysts.

8. The cyanide-free cadmium electroplating solution according to claim 6, characterized in that, In the etherification reaction, the reaction is carried out at 50°C for 12 hours; And / or, in the polymerization reaction, the reaction is carried out at 90°C and 2-4 atmospheres for 24 hours; And / or, in the grafting group reaction, the reaction is carried out at 0°C for 2-4 hours.

9. The cyanide-free cadmium electroplating solution according to claim 1, characterized in that, The cyanide-free cadmium plating solution has an electroplating current density of 1-4 A / dm³ at room temperature. 2 The ratio of yin to yang area is 1:2 to 1:

3.

10. A method for preparing the cyanide-free cadmium electroplating solution according to any one of claims 1-9, characterized in that, Includes the following steps: The cadmium source is dissolved in distilled water to form a basic solution; Add the primary complexing agent and the second complexing agent to the base solution and stir until completely dissolved; The pH value of the solution is adjusted to the set range using a pH adjuster; A buffer is added to the solution for buffering, followed by the addition of surfactants and additives; The solution is filtered and transferred to an electroplating tank, where it is electrolyzed for a set time at a set current to obtain a cyanide-free cadmium electroplating solution.