Semi-gloss nickel luster agent, and preparation method and application thereof

Abstract

This invention discloses a semi-bright nickel brightener, its preparation method, and its application. The semi-bright nickel brightener comprises water-soluble components of the following mass concentrations: chloral hydrate 200-320 g / L, salicylic acid 60-90 g / L, sodium saccharin 25-45 g / L, lithium chloride 0.3-0.8 g / L, and cerium salt and / or lanthanum salt 0.02-0.5 g / L. It is a homogeneous and transparent concentrated solution with a pH value of 3.0-4.5 at room temperature. Prepared by a gradient cooling stepwise dissolution method, this method achieves the homogeneous and stable coexistence of soluble rare earth ions and organic additives. The semi-bright nickel plating agent can stably control the potential difference between the semi-bright nickel plating layer and the bright nickel plating layer within the range of 125-155mV with a fluctuation range of no more than ±5mV. The sulfur content of the plating layer is no higher than 0.002%, the internal stress is 20-40MPa, the grain size is 15-40nm, the neutral salt spray test can reach more than 240 hours, and the CASS test can reach more than 48 hours. It is particularly suitable for double-layer or multi-layer nickel electroplating systems for hardware and plastic parts.

Description

Technical Field

[0001] This invention relates to the field of electroplating technology, specifically to a semi-bright nickel brightener, its preparation method and application, which is particularly suitable for double-layer or multi-layer nickel electroplating systems for hardware and plastic parts. Background Technology

[0002] Nickel electroplating is one of the most widely used processes in the field of metal surface treatment. Nickel plating has excellent corrosion resistance, wear resistance, and decorative properties, and is widely used in hardware and sanitary ware, automotive parts, home appliances, aerospace, and other fields. In multilayer nickel plating systems, a semi-bright nickel plating layer is used as the bottom layer in conjunction with a bright nickel plating layer or a high-sulfur nickel plating layer, achieving electrochemical corrosion protection through the interlayer potential difference.

[0003] The quality of the semi-bright nickel plating directly determines the overall corrosion resistance of the multi-layer nickel plating. Semi-bright nickel plating requires a sulfur content not exceeding 0.005%, fine crystal structure, and good leveling and dispersing ability. An ideal semi-bright nickel plating should have a columnar structure, be sulfur-free or have extremely low sulfur content, and possess a stable and sufficiently large potential difference (typically above 120mV) between itself and the bright nickel layer, thereby achieving excellent electrochemical corrosion protection.

[0004] However, existing semi-bright nickel brightener products generally suffer from the following technical defects: First, the sulfur content of the coating is unstable. The sulfur components in existing semi-bright nickel brighteners are difficult to control precisely during electroplating, resulting in significant fluctuations in the sulfur content of the coating. This instability directly affects the potential difference between the semi-bright nickel layer and the bright nickel layer, thereby weakening the electrochemical corrosion resistance of the multilayer nickel system.

[0005] Second, the potential difference is unstable. The potential difference between semi-bright nickel and bright nickel is a key parameter determining the corrosion resistance of multilayer nickel plating. In existing products, due to the lack of synergistic interaction between additive components, the potential difference easily drifts with the extension of electroplating time, making it difficult to maintain long-term stability.

[0006] Third, the coating is brittle and prone to blistering. While pursuing brightness and levelness, existing semi-bright nickel brighteners often lead to increased internal stress in the coating, making it brittle and reducing the adhesion between the coating and the bright nickel layer. In severe cases, quality problems such as blistering and peeling may occur.

[0007] Fourth, poor appearance after chrome plating. Semi-bright nickel plating prepared with existing semi-bright nickel brighteners is prone to yellowing, darkening, and other appearance defects after chrome plating, affecting the decorative effect of the product.

[0008] To address the aforementioned issues, researchers have attempted to add chloral hydrate as a potential difference stabilizer to the nickel plating solution, or use saccharin as a stress reliever. CN102953094A discloses an additive for a semi-bright nickel plating solution, a semi-bright nickel plating solution, and a semi-bright nickel plating method, but it does not address the synergistic control of the sulfur content and internal stress of the plating layer. CN116288555A discloses a semi-bright nickel plating solution with controllable internal stress in the plating layer and a method for electroplating using this solution, which controls the internal stress of the plating layer through coumarin, but its potential difference stability still needs improvement. In addition, CN102383151A discloses a nano-semi-bright nickel plating solution, in which rare earth oxides (lanthanum oxide and / or yttrium oxide) are added, but it only involves the combination of rare earth oxides and the base plating solution, and does not involve the compounding of rare earths and organic additives.

[0009] As is well known, soluble rare earth ions readily react with organic additives in nickel plating solutions, especially sodium saccharin containing sulfonyl groups and salicylic acid containing phenolic hydroxyl groups, to form precipitates. Therefore, there has long been a prejudice in the industry that "rare earth ions are not suitable for homogeneous bright nickel systems containing organic additives". Summary of the Invention

[0010] This invention addresses the technical defects of existing semi-bright nickel brighteners, such as unstable sulfur content in the coating, large potential difference fluctuations, brittle coating prone to blistering, and poor appearance after chromium plating, by providing a semi-bright nickel brightener, its preparation method, and its application.

[0011] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a semi-bright nickel brightener, mainly composed of the following water-soluble components at the following mass concentrations: Chloral hydrate 200-320 g / L; Salicylic acid 60-90g / L; Sodium saccharin 25-45 g / L; Lithium chloride 0.3-0.8 g / L; And cerium salts and / or lanthanum salts at 0.02-0.5 g / L; The semi-bright nickel brightener is a homogeneous and transparent concentrated solution with a pH value of 3.0-4.5 at room temperature.

[0012] In this invention, chloral hydrate acts as a potential difference stabilizer, effectively regulating the potential difference between semi-bright and bright nickel. Salicylic acid, as an auxiliary leveling agent and complexing agent, adsorbs onto the cathode surface, inhibiting rapid reduction of metal ions and promoting uniform nucleation. Sodium saccharin functions as both a primary brightener and a stress reliever, refining the coating grains and reducing internal stress. Lithium chloride, as a conductive salt and coordination buffer, improves the conductivity of the plating solution and assists in refining the coating crystallization. Cerium salts and / or lanthanum salts, as grain refiners and coating modifiers, with their unique 4f electron layer structure, adsorb onto the cathode surface, altering the electrocrystallization process of nickel ions.

[0013] This invention, through in-situ testing with an electrochemical workstation and characterization of the coating's microstructure, reveals that the five components exhibit a significant synergistic structure-activity relationship when coexisting within the specified proportions. Particularly noteworthy is that this synergistic effect is not a simple summation of the known functions of each component, but rather, through the characteristic adsorption of rare earth ions at the cathode interface, it alters the competitive reduction pathway between chloral hydrate and sodium saccharin, thereby unexpectedly and significantly eliminating lattice distortion internal stress while simultaneously improving potential difference stability.

[0014] Secondly, the present invention provides a semi-bright nickel plating solution, comprising a base plating solution and the aforementioned semi-bright nickel brightener.

[0015] The base plating solution contains 250-350 g / L nickel sulfate, 35-55 g / L nickel chloride, and 35-50 g / L boric acid; the amount of semi-bright nickel brightener added is 0.5-5 mL / L.

[0016] Thirdly, the present invention provides a method for preparing the above-mentioned semi-bright nickel brightener, comprising the following steps: (1) Heat deionized water to 55-65℃, add chloral hydrate and stir until completely dissolved to obtain the first solution; (2) Add salicylic acid to the first solution and stir until completely dissolved to obtain the second solution; (3) Cool the second solution to 30-40℃, add sodium saccharin and lithium chloride, and stir until completely dissolved to obtain the third solution; (4) Add cerium salt and / or lanthanum salt to the third solution and stir until completely dissolved; (5) Adjust the pH to 3.0-4.5 with citric acid, and add deionized water to the target volume to obtain the semi-bright nickel brightener.

[0017] This invention employs a stepwise dissolution and gradient cooling preparation method. Following a specific order of addition—chloral hydrate → salicylic acid → sodium saccharin + lithium chloride → rare earth salts—and controlled gradient cooling, it avoids uneven precipitation or decomposition caused by differences in dissolution rates and temperature sensitivity among the components. In particular, adding the rare earth salts at a lower temperature effectively prevents the hydrolysis of rare earth ions at high temperatures.

[0018] Fourthly, the present invention provides an electroplating method, comprising the following steps: The substrate is subjected to degreasing and activation treatments in sequence; The substrate, after degreasing and activation treatment, is placed in the above-mentioned semi-bright nickel plating solution for semi-bright nickel plating under the following conditions: plating solution temperature 50-65℃, pH value 3.8-4.4, cathode current density 2-8A / dm², and plating time 10-40 minutes. After electroplating, a bright nickel layer and a chromium layer are electroplated on the resulting semi-bright nickel plating.

[0019] Fifthly, the present invention provides a double-layer nickel plating layer prepared by the above-mentioned electroplating method, wherein the grain size of the semi-bright nickel plating layer is 15-40 nm, the internal stress is 20-40 MPa, the sulfur content is not higher than 0.002%, and the potential difference between the semi-bright nickel plating layer and the bright nickel plating layer is 125-155 mV.

[0020] Sixthly, the present invention provides the application of the above-mentioned double-layer nickel plating in the anti-corrosion treatment of hardware or plastic parts.

[0021] Compared with the prior art, the present invention has the following beneficial effects: (1) It can stably control the sulfur content of semi-bright nickel plating to below 0.002%, which is much lower than the existing products' 0.003%-0.005%, and the batch-to-batch fluctuation is minimal.

[0022] (2) Semi-bright nickel brightener can stabilize the potential difference between the semi-bright nickel plating and the bright nickel plating in the range of 125-155mV, with a fluctuation range of no more than ±5mV, which is significantly better than existing products.

[0023] (3) The internal stress of the coating is 20-40MPa, which is much lower than the 60-80MPa of existing products. This eliminates the brittleness of the coating. The semi-bright nickel coating and the bright nickel coating are tightly bonded and will not cause quality problems such as blistering or peeling.

[0024] (4) The grain size of the semi-bright nickel coating is refined to 15-40nm, which is much finer than the 50-80nm of the existing products, giving the coating higher density and lower porosity.

[0025] (5) After chrome plating, the coating is clean and bright, does not turn yellow or black, and has a good decorative effect.

[0026] (6) The neutral salt spray test can reach more than 240 hours and the CASS test can reach more than 48 hours, which is significantly better than existing products. Attached Figure Description

[0027] Figure 1 A scanning electron microscope image of the surface of the semi-bright nickel coating prepared in Example 1; Figure 2 The X-ray diffraction comparison diagrams are shown for the semi-bright nickel coatings of Example 1 and Comparative Example 1. Figure 3 This is a comparison diagram of the potential difference stability of semi-bright nickel plating and bright nickel plating in Examples 1-3 and Comparative Examples 1-4; Figure 4 A surface photograph of the double-layer nickel plating prepared in Example 1 after 48 hours of CASS testing; Figure 5 A surface photograph of the double-layer nickel plating prepared for Comparative Example 1 after 24 hours of CASS testing; Figure 6 This is a bar chart comparing the grain size of the semi-bright nickel coatings in Examples 1-3 and Comparative Examples 1-4 of the present invention. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to the embodiments. The embodiments are only intended to provide a clearer understanding of the technical features, objectives and effects of the present invention.

[0029] This application discloses a semi-bright nickel brightener, comprising the following water-soluble components at the following mass concentrations: Chloral hydrate 200-320 g / L; Salicylic acid 60-90g / L; Sodium saccharin 25-45 g / L; Lithium chloride 0.3-0.8 g / L; And cerium salts and / or lanthanum salts at 0.02-0.5 g / L; The semi-bright nickel brightener is a homogeneous and transparent concentrated solution with a pH value of 3.0-4.5 at room temperature.

[0030] The cerium salt is at least one of cerium nitrate, cerium sulfate, and cerium chloride; the lanthanum salt is at least one of lanthanum nitrate, lanthanum sulfate, and lanthanum chloride.

[0031] In some embodiments, the components comprise the following mass concentrations: Chloral hydrate 230-290 g / L; Salicylic acid 68-82 g / L; Sodium saccharin 30-40g / L; Lithium chloride 0.4-0.6 g / L; Cerium salts and / or lanthanum salts: 0.05-0.3 g / L.

[0032] The mass ratio of chloral hydrate, salicylic acid, sodium saccharin, lithium chloride, and cerium salt and / or lanthanum salt is: 400-600:120-180:50-80:1:0.05-0.8.

[0033] The base plating solution contains 250-350 g / L nickel sulfate, 35-55 g / L nickel chloride, and 35-50 g / L boric acid; the amount of semi-bright nickel brightener added is 0.5-5 mL / L.

[0034] The preparation method of the semi-bright nickel brightener of this application includes the following steps: (1) Heat deionized water to 55-65℃, add chloral hydrate and stir until completely dissolved to obtain the first solution; (2) Add salicylic acid to the first solution and stir until completely dissolved to obtain the second solution; (3) Cool the second solution to 30-40℃, add sodium saccharin and lithium chloride, and stir until completely dissolved to obtain the third solution; (4) Add cerium salt and / or lanthanum salt to the third solution and stir until completely dissolved; (5) Adjust the pH to 3.0-4.5 with citric acid, and add deionized water to the target volume to obtain the semi-bright nickel brightener.

[0035] An electroplating method according to this application includes the following steps: The substrate is subjected to degreasing and activation treatments in sequence; The substrate after degreasing and activation treatment is placed in the semi-bright nickel plating solution described in claim 5 for semi-bright nickel plating. The process conditions are: plating solution temperature 50-65℃, pH value 3.8-4.4, cathode current density 2-8A / dm², and plating time 10-40 minutes. After electroplating, a bright nickel layer and a chromium layer are electroplated on the resulting semi-bright nickel plating.

[0036] During the semi-bright nickel plating process, the semi-bright nickel brightener is added according to the electroplating ampere-hours, with an addition amount of 80-200 mL per 1000 Ah.

[0037] This invention discloses a double-layer nickel plating layer prepared by the aforementioned electroplating method. The semi-bright nickel plating layer has a grain size of 15-40 nm, an internal stress of 20-40 MPa, a sulfur content not exceeding 0.002%, and a potential difference of 125-155 mV between the semi-bright and bright nickel plating layers. This double-layer nickel plating layer is used in the anti-corrosion treatment of hardware or plastic parts.

[0038] Example 1

[0039] I. Preparation of Semi-Bright Nickel Brightener Prepare a semi-bright nickel brightener (total volume 1L) according to the following formula: Chloral hydrate: 260g Salicylic acid: 75.8g Sodium saccharin: 34.2g Lithium chloride: 0.5g Cerium nitrate (Ce(NO3)3·6H2O): 0.1g Deionized water: Balance The preparation steps are as follows: (1) Add about 600 mL of deionized water to the preparation container, heat to 60-65 °C, add 260 g of chloral hydrate, and stir at 300-400 rpm until completely dissolved to obtain the first solution; (2) Add 75.8g of salicylic acid to the first solution and continue stirring until completely dissolved. After complete dissolution, continue stirring for about 15 minutes to obtain the second solution. (3) Cool the second solution naturally to 35~40℃, add 34.2g sodium saccharin and 0.5g lithium chloride, and continue stirring until completely dissolved to obtain the third solution; (4) Add 0.1g of cerium nitrate to the third solution and continue stirring until completely dissolved. The solution is uniform and transparent, without any precipitate or turbidity. (5) Adjust the pH to 3.5–4.0 with citric acid; (6) Add deionized water to a total volume of 1L, stir well, and you will get a semi-bright nickel brightener.

[0040] II. Preparation of Semi-Bright Nickel Plating Solution Prepare a semi-bright nickel plating solution (total volume 1L) according to the following formula: Nickel sulfate (NiSO4·6H2O): 300g / L Nickel chloride (NiCl2·6H2O): 45g / L Boric acid (H3BO3): 45g / L Semi-bright nickel brightener prepared in Example 1: 2 mL / L The preparation steps are as follows: (1) Add about 600 mL of deionized water to the plating tank and heat it to 60-65 °C; (2) Add 300g of nickel sulfate and 45g of nickel chloride, and stir until completely dissolved; (3) Add 45g of boric acid and stir until completely dissolved; (4) Adjust the pH value to 4.0 using 10% dilute sulfuric acid or 4% sodium hydroxide solution; (5) Add 2 mL of the semi-bright nickel brightener prepared in Example 1, add deionized water to the total volume of 1 L, and stir evenly.

[0041] III. Electroplating Process Substrate: Brass sheet (50mm×50mm×1mm) Pre-processing flow: (1) Chemical degreasing: Soak in alkaline degreasing solution at 60℃ for 5 minutes; (2) Hot water wash: Soak in 60℃ hot water for 1 minute; (3) Acid activation: Immerse in 5% dilute sulfuric acid solution for 30 seconds; (4) Wash with deionized water: Wash twice with deionized water.

[0042] Semi-bright nickel plating process conditions: Plating bath temperature: 55℃ pH value: 4.0 Cathode current density: 4.5 A / dm² Electroplating time: 20 minutes Mixing method: Air mixing After electroplating, the workpiece is removed, cleaned with deionized water, and then transferred to a bright nickel plating bath to electroplat a bright nickel layer (approximately 10 μm thick), and finally a chromium layer (approximately 0.3 μm thick).

[0043] Example 2

[0044] Semi-bright nickel brightener formulation: Chloral hydrate: 230g / L Salicylic acid: 82g / L Sodium saccharin: 30g / L Lithium chloride: 0.6 g / L Lanthanum nitrate (La(NO3)3·6H2O): 0.2 g / L Deionized water: Balance The preparation method is the same as in Example 1.

[0045] The preparation method of the semi-bright nickel plating solution is the same as in Example 1, and the amount of semi-bright nickel brightener added is 1.5 mL / L.

[0046] The electroplating process conditions are the same as in Example 1.

[0047] Example 3

[0048] Semi-bright nickel brightener formulation: Chloral hydrate: 290g / L Salicylic acid: 68g / L Sodium saccharin: 40g / L Lithium chloride: 0.4 g / L Cerium sulfate (Ce2(SO4)3): 0.08 g / L Deionized water: Balance The preparation method is the same as in Example 1.

[0049] The preparation method of the semi-bright nickel plating solution is the same as in Example 1, and the amount of semi-bright nickel brightener added is 2.5 mL / L.

[0050] The electroplating process conditions are the same as in Example 1.

[0051] Example 4

[0052] Semi-bright nickel brightener formulation: Chloral hydrate: 310g / L Salicylic acid: 62g / L Sodium saccharin: 42g / L Lithium chloride: 0.35 g / L Lanthanum chloride (LaCl3·7H2O): 0.3 g / L Deionized water: Balance The preparation method is the same as in Example 1.

[0053] The preparation method of the semi-bright nickel plating solution is the same as in Example 1, and the amount of semi-bright nickel brightener added is 3 mL / L.

[0054] The electroplating process conditions are the same as in Example 1, except that the cathode current density is 6 A / dm².

[0055] Example 5

[0056] Semi-bright nickel brightener formulation: Chloral hydrate: 210g / L Salicylic acid: 88g / L Sodium saccharin: 28g / L Lithium chloride: 0.7 g / L Cerium nitrate: 0.4 g / L Deionized water: Balance The preparation method is the same as in Example 1.

[0057] The preparation method of the semi-bright nickel plating solution is the same as in Example 1, and the amount of semi-bright nickel brightener added is 1 mL / L.

[0058] The electroplating process conditions are the same as in Example 1, except that the cathode current density is 3A / dm².

[0059] Comparative Example 1 The additives for semi-bright nickel plating solutions (containing brightener, hydrated trichloroacetaldehyde and wetting agent) were prepared using the formulation of Example 1 in CN102953094A. The other plating solution formulations (nickel sulfate 300g / L, nickel chloride 45g / L, boric acid 45g / L) and plating process conditions were the same as in Example 1.

[0060] Comparative Example 2 The semi-bright nickel brightener formulation does not contain salicylic acid; the remaining components and their contents are the same as in Example 1 (chloral hydrate 260 g / L, sodium saccharin 34.2 g / L, lithium chloride 0.5 g / L, cerium nitrate 0.1 g / L). The preparation method, electroplating solution preparation, and electroplating process conditions are the same as in Example 1.

[0061] Comparative Example 3 The semi-bright nickel brightener formulation does not contain rare earth metal salts; the remaining components and their contents are the same as in Example 1 (chloral hydrate 260 g / L, salicylic acid 75.8 g / L, sodium saccharin 34.2 g / L, lithium chloride 0.5 g / L). The preparation method, electroplating solution preparation, and electroplating process conditions are the same as in Example 1.

[0062] Comparative Example 4 The semi-bright nickel brightener formulation does not contain lithium chloride; the remaining components and their contents are the same as in Example 1 (chloral hydrate 260 g / L, salicylic acid 75.8 g / L, sodium saccharin 34.2 g / L, cerium nitrate 0.1 g / L). The preparation method, electroplating solution preparation, and electroplating process conditions are the same as in Example 1.

[0063] Performance testing I. Determination of Sulfur Content in Coating The sulfur content of the semi-bright nickel coatings obtained in each example and comparative example was determined using a LECO CS-230 carbon-sulfur analyzer (combustion infrared absorption method). Measurements were taken at three different locations for each sample, and the average value and standard deviation were calculated.

[0064] The sulfur content determination results showed that the sulfur content of the semi-bright nickel plating in Examples 1 to 5 of this invention was no higher than 0.002%, with Example 3 having the lowest (approximately 0.0015%). The standard deviation of each example did not exceed 0.0003%, indicating excellent batch-to-batch consistency. In contrast, the sulfur content of Comparative Example 1 fluctuated between 0.0052% and 0.0085%, with a standard deviation as high as 0.0015%; the sulfur content of Comparative Example 2 (without salicylic acid) was approximately 0.0051%; the sulfur content of Comparative Example 3 (without rare earth salts) was approximately 0.0035%; and the sulfur content of Comparative Example 4 (without lithium chloride) was approximately 0.0042%. The latter three not only had significantly higher sulfur content, but their standard deviations were also much larger than those of the examples. The absence of any component—salicylic acid, rare earth salts, or lithium chloride—led to a significant increase in sulfur content and a decrease in stability, which fully demonstrates the crucial role of the synergistic effect of the five components in controlling sulfur content.

[0065] II. Potential Difference Test The potential difference between the semi-bright nickel plating and the bright nickel plating obtained in each example and comparative example was measured using a ZF-9 potentiometer. The bright nickel plating was obtained by electroplating the same substrate in a standard bright nickel plating solution (280 g / L nickel sulfate, 50 g / L nickel chloride, 45 g / L boric acid, and appropriate amount of bright nickel additives). The initial potential difference and the change in potential difference during 24 hours of continuous plating were recorded.

[0066] The potential difference test results show (see) Figure 3 The initial potential difference of the semi-bright nickel plating in Examples 1 to 5 of this invention ranges from 135 mV to 150 mV, all within the preferred range of 125 to 155 mV. After 24 hours of continuous plating, the potential difference decay in each example did not exceed 5 mV, exhibiting excellent anti-drift characteristics. Example 3 showed the best performance, with an initial potential difference of approximately 148 mV, which remained at around 145 mV after 24 hours. In contrast, Comparative Examples 1 to 4 not only had lower initial potential differences (only 108 to 128 mV), but also exhibited significant negative shifts ranging from 15 mV to 22 mV within the same time period, with Comparative Example 4, lacking lithium chloride, showing the most drastic fluctuations (fluctuation range of approximately ±20 mV). This comparison directly confirms the indispensable synergistic effect of lithium chloride and rare earth salts in maintaining the stability of the interfacial electric double layer.

[0067] III. Coating Internal Stress Test The internal stress of the semi-bright nickel coatings obtained in each example and comparative example was determined using the spiral shrinkage tester method (ASTM B636 standard). Three specimens were prepared for each sample, and the average value was taken.

[0068] The internal stress test results showed that the internal stress of the semi-bright nickel plating in Examples 1 to 5 of this invention ranged from 20 MPa to 40 MPa, with Example 3 having the lowest stress (approximately 25 MPa) and Example 4 having the highest stress (approximately 35 MPa), both significantly lower than that of Comparative Example 1 (approximately 68 MPa) and Comparative Example 2 (approximately 62 MPa). Of particular note are Comparative Example 3 (without rare earth salts, approximately 58 MPa) and Comparative Example 4 (without lithium chloride, approximately 75 MPa). The internal stress of Comparative Example 4 increased by nearly 168% compared to Example 1 (approximately 28 MPa). This drastic change clearly demonstrates that lithium chloride is not simply a conductive salt, but rather exhibits a significant synergistic stress-reducing effect with sodium saccharin—the absence of lithium chloride significantly reduces the stress-relief effect of sodium saccharin.

[0069] IV. Determination of Coating Grain Size The average grain size of the semi-bright nickel coatings obtained in each embodiment and comparative example was calculated using X-ray diffraction and the Scherrer formula.

[0070] The results of grain size measurement show (see...) Figure 6The average grain size of the semi-bright nickel coatings in Examples 1 to 5 of this invention ranges from 15 nm to 40 nm, with Example 3 having the smallest (approximately 20 nm) and Example 4 having the largest (approximately 35 nm), both significantly finer than the approximately 65 nm of Comparative Example 1. The grain size of Comparative Example 3 (without rare earth salts) is approximately 52 nm, about 2.4 times that of Example 1 (approximately 22 nm), confirming the decisive role of rare earth salts in grain refinement. The grain size of Comparative Example 4 (without lithium chloride) is even coarser, approximately 70 nm, with a significant deterioration in coating density.

[0071] V. Bonding Strength Test The adhesion between the semi-bright nickel plating and the bright nickel plating obtained in each embodiment and comparative example was tested using bending and filing tests. The bending test involved repeatedly bending the plated part 180° along a 5mm diameter round bar until it broke, and observing the peeling and flaking of the plating at the fracture surface and the bent area. The filing test involved filing from the substrate towards the plating with a flat file, and observing whether the plating showed peeling or flaking.

[0072] The adhesion test results showed that the coatings of Examples 1 to 5 did not exhibit peeling or flaking after bending tests, and the edges did not lift during file tests. The coatings of Comparative Examples 1 to 4 all showed varying degrees of microcracks during bending tests, with Comparative Examples 2 and 4 also exhibiting significant peeling. Comparative Example 4 (without lithium chloride) showed the most severe peeling, indicating that the absence of lithium chloride not only increased internal stress but also severely degraded interlayer adhesion.

[0073] VI. Salt spray corrosion test Neutral salt spray test (NSS) and copper accelerated acetic acid salt spray test (CASS) were conducted according to GB / T 10125 standard. The sample was a brass sheet plated with a double layer of nickel (approximately 15 μm of semi-bright nickel + approximately 10 μm of bright nickel). Three parallel samples were taken for each sample, and the average value was taken as the result.

[0074] Salt spray test results show (see) Figure 4 , Figure 5 The salt spray corrosion resistance of Examples 1 to 5 of this invention is significantly better than that of the comparative examples. Example 3 showed the best performance, with NSS withstanding more than 270 hours and CASS withstanding more than 52 hours; Example 1's NSS withstood more than 260 hours and CASS withstood more than 50 hours. Comparative Example 1's NSS withstood only about 120 hours and CASS only about 24 hours. Comparative Example 4 (without lithium chloride) showed the worst corrosion resistance, with NSS only about 105 hours and CASS only about 20 hours, further confirming the significant contribution of lithium chloride to the coating's density and corrosion resistance.

[0075] VII. Evaluation of Chrome Plating Appearance Visually observe the appearance of each embodiment and comparative example after chrome plating. Evaluation criteria include brightness, color uniformity, and whether it turns yellow or dark.

[0076] The appearance evaluation results show that the chromium plating layers of Examples 1 to 5 are all clean, bright, and uniform in color, with no yellowing or blackening observed. The chromium plating layers of Comparative Examples 1 to 4 all exhibit varying degrees of yellowing or darkening, with Comparative Example 4 (without lithium chloride) showing the most significant darkening, followed by Comparative Example 1. This indicates that the synergistic effect of the five components of this invention has a positive effect on improving the surface condition of the plating layer and enhancing the quality of subsequent chromium plating.

[0077] VIII. Stability Test of Light Agent The semi-bright nickel brighteners prepared in each embodiment were sealed and stored in the dark at room temperature (25±5℃), and the presence of precipitation, layering, discoloration and other phenomena were observed periodically.

[0078] The stability test results of the brighteners showed that the semi-bright nickel brighteners prepared in Examples 1 to 5 of this invention remained uniformly transparent after being stored at room temperature for 6 months, without any precipitation or stratification. After 12 months of storage, only Example 4 showed a trace amount of precipitation, while the other examples remained clear and transparent. This indicates that the present invention, through a gradient cooling stepwise dissolution method combined with citric acid pH adjustment, can effectively inhibit the complexation and precipitation of rare earth ions and organic ligands, ensuring that the brighteners have good long-term storage stability.

[0079] The semi-bright nickel brightener of Example 1 of this invention was applied to the electroplating production line (rack plating line) of zinc alloy faucet body of a sanitary ware company. The production process is as follows: dewaxing → degreasing → acid activation → pre-plating copper → acid copper → semi-bright nickel (this invention) → bright nickel → nickel sealing → chromium plating.

[0080] The production line application parameters are as follows: plating tank volume 3000L, semi-bright nickel brightener addition amount 2mL / L, plating solution temperature controlled at 55±2℃, pH value controlled at 4.0±0.2, cathode current density controlled at 4~5A / dm², electroplating time 25 minutes, brightener replenishment amount is 120mL per 1000Ah.

[0081] The production line operated stably for four consecutive months without significant degradation of the plating solution performance, and no major treatment was required during this period. The potential difference between the semi-bright nickel plating layer and the bright nickel plating layer was measured weekly, for a total of 16 times, remaining stable within the range of 132–148 mV with minimal fluctuations. The product CASS test showed no corrosion spots after 48 hours, and a 100% pass rate was achieved out of 50 batches sampled during this period. The chrome plating had a uniform and bright appearance, without yellowing or darkening. The overall product yield improved from 92% with the original process to over 97.5%. The consumption of brightener in the semi-bright nickel plating remained stable at approximately 110–130 mL per 1000 Ah, indicating that the decomposition and carry-over loss of brightener in the plating solution were within normal levels.

[0082] CN102383151A adds insoluble rare earth oxide particles (typically in the micrometer range), and its mechanism of action is physical suspension co-deposition. This document explicitly mentions the negative impact of particle agglomeration on the stability of the plating solution. It is generally accepted in the field that soluble rare earth ions (such as Ce³⁺ and La³⁺) readily undergo coordination reactions with organic additives in nickel plating solutions (especially sodium saccharin containing sulfonyl groups and salicylic acid containing phenolic hydroxyl groups), forming insoluble flocculent precipitates. Therefore, the industry has long held the technical prejudice that "rare earth ions are not suitable for homogeneous bright nickel systems containing organic additives."

[0083] The present invention utilizes five components—chloral hydrate, salicylic acid, sodium saccharin, lithium chloride, and rare earth salts—to form the core technical solution of the invention. The absence of any one component will lead to a significant deterioration of multiple key performance indicators. This fully demonstrates that there is a complex synergistic mechanism among the five components. The technical effect is not a simple superposition of the known functions of each component, but rather produces a synergistic effect of "1+1>2".

[0084] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A semi-bright nickel brightener, characterized in that, It consists of water-soluble components at the following mass concentrations: Chloral hydrate 200-320 g / L; Salicylic acid 60-90g / L; Sodium saccharin 25-45 g / L; Lithium chloride 0.3-0.8 g / L; And cerium salts and / or lanthanum salts at 0.02-0.5 g / L; The semi-bright nickel brightener is a homogeneous and transparent concentrated solution with a pH value of 3.0-4.5 at room temperature.

2. The semi-bright nickel brightener according to claim 1, characterized in that, The cerium salt is at least one of cerium nitrate, cerium sulfate, and cerium chloride; the lanthanum salt is at least one of lanthanum nitrate, lanthanum sulfate, and lanthanum chloride.

3. The semi-bright nickel brightener according to claim 1, characterized in that, Components containing the following mass concentrations: Chloral hydrate 230-290 g / L; Salicylic acid 68-82 g / L; Sodium saccharin 30-40 g / L; Lithium chloride 0.4-0.6 g / L; Cerium salts and / or lanthanum salts: 0.05-0.3 g / L.

4. The semi-bright nickel brightener according to claim 1, characterized in that, The mass ratio of chloral hydrate, salicylic acid, sodium saccharin, lithium chloride, and cerium and / or lanthanum salts is: 400-600:120-180:50-80:1:0.05-0.8。 5. A semi-bright nickel plating solution, characterized in that, The plating solution comprises a base plating bath and a semi-bright nickel brightener as described in any one of claims 1-4; the base plating bath comprises 250-350 g / L nickel sulfate, 35-55 g / L nickel chloride and 35-50 g / L boric acid; the amount of the semi-bright nickel brightener added is 0.5-5 mL / L.

6. A method for preparing the semi-bright nickel brightener according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Heat deionized water to 55-65℃, add chloral hydrate and stir until completely dissolved to obtain the first solution; (2) Add salicylic acid to the first solution and stir until completely dissolved to obtain the second solution; (3) Cool the second solution to 30-40℃, add sodium saccharin and lithium chloride, and stir until completely dissolved to obtain the third solution; (4) Add cerium salt and / or lanthanum salt to the third solution and stir until completely dissolved; (5) Adjust the pH to 3.0-4.5 with citric acid, and add deionized water to the target volume to obtain the semi-bright nickel brightener.

7. An electroplating method, characterized in that, Includes the following steps: The substrate is subjected to degreasing and activation treatments in sequence; The substrate after degreasing and activation treatment is placed in the semi-bright nickel plating solution described in claim 5 for semi-bright nickel plating. The process conditions are: plating solution temperature 50-65℃, pH value 3.8-4.4, cathode current density 2-8A / dm², and plating time 10-40 minutes. After electroplating, a bright nickel layer and a chromium layer are electroplated on the resulting semi-bright nickel plating.

8. The electroplating method according to claim 7, characterized in that, During the semi-bright nickel electroplating process, the semi-bright nickel brightener is added according to the electroplating ampere-hours, with an addition amount of 80-200 mL per 1000 Ah.

9. A double-layer nickel plating, characterized in that, The semi-bright nickel plating layer is prepared by the electroplating method according to claim 7 or 8, wherein the grain size of the semi-bright nickel plating layer is 15-40 nm, the internal stress is 20-40 MPa, the sulfur content is not higher than 0.002%, and the potential difference between the semi-bright nickel plating layer and the bright nickel plating layer is 125-155 mV.

10. The application of the double-layer nickel plating as described in claim 9 in the anti-corrosion treatment of hardware or plastic parts.

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