Continuous Plating Method and Continuous Plating System

Abstract

The present invention relates to a continuous plating method for preventing appearance defects in a plating layer formed on the surface of a workpiece, comprising: a pretreatment step for cleaning and activating the surface of a workpiece; a plating step for forming a metal plating layer by passing the pretreated workpiece through a plating solution; and a posttreatment step for cleaning the workpiece with the plating layer formed thereon using a cleaning solution. Therefore, through a process in which pretreatment, plating, and post-treatment steps are sequentially combined, organic components, plating solution components, and fine impurities that may remain on the surface of the workpiece after plating can be reliably removed during the cleaning step, thereby effectively preventing appearance defects such as white spots, stains, and cloudiness that occur after heat treatment.

Description

Technology Field

[0001] The present invention relates to a continuous plating method and a continuous plating system. Background Technology

[0002] Generally, the continuous plating process for steel sheets involves a pretreatment step to remove surface contaminants, a plating step to precipitate metal ions, and a subsequent drying step to produce the product. However, conventional continuous plating facilities typically do not include a separate post-treatment process after plating, and a method of immediately transferring the sheet to a drying or heat treatment step after forming the plating layer is widely used. In this method, trace amounts of plating solution, additives, or fine contaminants used during the plating process may remain on the surface of the steel sheet; however, since these are not visible to the naked eye immediately after plating, additional processing is often not performed.

[0003] However, in actual production environments, issues have been reported regarding appearance defects on the steel sheet surface, such as white spots, fine contamination marks, and organic residues, occurring during the subsequent annealing or heating processes after plating. This phenomenon is presumed to occur when organic components, plating solution components, or fine foreign substances remaining from the plating process vaporize due to heat, leaving marks on the surface. These defects adversely affect the quality of the final product and, in some cases, lead to line stoppages or increased scrap rates, thereby reducing the efficiency of the manufacturing process.

[0004] In particular, conventional facilities, such as existing continuous plating production lines, adopted a structure that performed no post-plating treatment whatsoever; consequently, they could not effectively prevent appearance defects caused by residual plating solution or surface impurities. Consequently, while the need for post-plating cleaning or post-treatment processes was raised to resolve quality issues, such processes did not become widespread in the industry due to reasons such as increased process costs and equipment complexity inherent in the characteristics of the continuous plating process.

[0005] Due to the limitations and quality issues of such conventional technologies, an improved post-treatment process is required to effectively remove contaminants remaining on the surface after plating and prevent appearance defects. Prior art literature

[0006] Republic of Korea Registered Patent No. 10-2868031 (Published Oct. 14, 2025) Republic of Korea Registered Patent No. 10-0326394 (Published Mar. 12, 2002) The problem to be solved

[0007] The present invention provides a technology that can fundamentally prevent appearance defects occurring during subsequent heat treatment caused by impurities or organic components remaining on the surface of a steel sheet after plating in a continuous plating process. means of solving the problem

[0008] A continuous plating method according to one embodiment of the present invention, for preventing appearance defects of a plating layer formed on the surface of a workpiece, comprises a pretreatment step for cleaning and activating the surface of a workpiece, a plating step for forming a metal plating layer by passing the pretreated workpiece through a plating solution, and a posttreatment step for cleaning the workpiece with a cleaning solution.

[0009] The pH of the cleaning solution used in the above post-treatment step may be 7 to 9.

[0010] The above cleaning solution may be sodium hydroxide (NaOH) or sodium carbonate (Na₂CO₃).

[0011] The above post-processing step can be carried out at a temperature of 30℃ to 60℃.

[0012] The above post-processing step can be performed for 1 to 5 minutes.

[0013] A continuous plating system according to one embodiment of the present invention is a continuous plating system for performing a continuous plating method as described above, and comprises a pretreatment tank, a plating tank, and a posttreatment tank, wherein a cleaning solution having a pH of 7 to 9 may be stored in the posttreatment tank.

[0014] The above post-treatment tank may include a post-treatment tank body capable of accommodating a cleaning solution and allowing a workpiece with a plating layer formed thereon to pass through, and a guide roll disposed inside the post-treatment tank body and guiding the movement path of the workpiece passing through.

[0015] A diagonal groove is formed on the outer circumference of the guide roll, and the diagonal groove can be opened at both ends of the guide roll.

[0016] The above post-treatment tank may further include a pH control unit that detects the pH of the cleaning solution in the main body of the above post-treatment tank and controls the pH of the cleaning solution to be maintained in the range of 7 to 9.

[0017] The above post-treatment tank may further include a cleaning liquid supply pipe positioned above the guide roll inside the main body of the above post-treatment tank to spray a cleaning liquid in the direction of the guide roll.

[0018] The above post-treatment tank may further include a scraper disposed in the main body of the post-treatment tank to wipe the surface of the plated object discharged from the main body of the post-treatment tank. Effects of the invention

[0019] According to an embodiment of the present invention, through a process in which pretreatment, plating, and posttreatment steps are sequentially combined, organic components, plating solution components, and fine impurities that may remain on the surface of a plated object after plating can be stably removed during the cleaning step, thereby effectively preventing appearance defects such as white spots, stains, and cloudiness that occur after heat treatment.

[0020] According to an embodiment of the present invention, by maintaining the pH of the cleaning solution used in the post-treatment step in a weak alkaline range of 7 to 9, organic additive residues contained in the plating solution can be efficiently decomposed and removed without chemically damaging the plating layer, thereby significantly improving the uniformity of appearance quality and cleaning efficiency.

[0021] According to an embodiment of the present invention, by using sodium hydroxide or sodium carbonate as the cleaning solution, the alkalinity and buffering action of the cleaning solution are stably maintained, thereby improving the removal rate of organic additives and minimizing quality variations caused by changes in the composition of the cleaning solution.

[0022] According to an embodiment of the present invention, by performing post-treatment cleaning at a temperature of 30°C to 60°C, the reactivity of the cleaning solution is optimized so that residual organic components are effectively removed, and the effect of preventing a decrease in cleaning power or damage to the plating layer that occurs under low or high temperature conditions is achieved.

[0023] According to an embodiment of the present invention, by limiting the post-treatment cleaning time to 1 to 5 minutes, sufficient contact time between the cleaning solution and the plated body is secured, thereby improving cleaning efficiency and preventing micro-dissolution or discoloration of the plating layer due to prolonged contact.

[0024] According to an embodiment of the present invention, optimal cleaning, plating, and post-treatment conditions are maintained as the workpiece moves continuously through a continuous plating system comprising a pretreatment tank, a plating tank, and a post-treatment tank, thereby improving process stability and productivity and having the effect of significantly reducing the occurrence rate of appearance defects.

[0025] According to an embodiment of the present invention, the post-treatment tank body and the guide roll inside it are configured so that the workpiece is stably transported while uniformly passing through the cleaning liquid, and the diagonal groove structure of the guide roll prevents the accumulation of contaminants and secondary contamination, thereby greatly improving the quality of post-treatment cleaning.

[0026] According to an embodiment of the present invention, a pH control unit is included that detects and automatically controls the pH of the cleaning solution in real time in the main body of the post-treatment tank, thereby continuously maintaining the pH of the cleaning solution in the range of 7 to 9, preventing fluctuations in cleaning power and significantly improving the reproducibility and stability of the post-treatment cleaning.

[0027] According to an embodiment of the present invention, by directly spraying a cleaning solution onto the surface of a guide roll through a cleaning solution supply pipe positioned above the guide roll, contaminants or alkaline components that may adhere to the surface of the guide roll can be removed in real time, thereby preventing secondary contamination through the guide roll and maintaining the quality of post-treatment cleaning.

[0028] According to an embodiment of the present invention, by adding a scraper that wipes the surface of a workpiece discharged from the post-treatment tank body, cleaning liquid droplets, aggregates, or fine contaminants that may remain on the surface of the workpiece are physically removed, thereby having the effect of preventing appearance defects from occurring in advance at the stage prior to heat treatment. Brief explanation of the drawing

[0029] FIG. 1 is a schematic diagram showing a continuous plating system according to one embodiment of the present invention. FIG. 2 is a schematic diagram showing a guide roll of FIG. 1. FIG. 3 is a schematic diagram showing a state in which a scraper is installed on a post-processing body of FIG. 2. FIG. 4 is a block diagram showing a continuous plating method according to one embodiment of the present invention. Specific details for implementing the invention

[0030] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings so that those skilled in the art can easily implement the present invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein. Throughout the specification, similar parts are denoted by the same reference numerals.

[0031] Then, a continuous plating system according to one embodiment of the present invention will be described with reference to FIG. 1.

[0032] Referring to FIGS. 1 to 3, a continuous plating system according to one embodiment of the present invention is a system for forming a metal plating layer on a surface while a workpiece moves continuously and for removing impurities that may remain after plating, and includes a pretreatment tank (10), a plating tank (20), and a posttreatment tank (100). The continuous plating system is configured to prevent appearance defects such as white spots, haze, and stains that occur when residual substances, such as plating solution components, metal ions, and organic additive residues, vaporize or decompose during subsequent heat treatment in the continuous plating process.

[0033] The pretreatment tank (10) performs a pretreatment process to remove organic contaminants, processing oil, oxide scale, etc., from the surface and to activate the surface before the workpiece enters the plating tank. The pretreatment tank (10) may include multiple treatment tanks, such as an electrolytic degreasing tank, a rinsing tank, a pickling tank, and a neutralization tank. The workpiece is transported along guide rolls within each treatment tank and comes into contact with the treatment liquid. Through this, the surface of the workpiece is prepared in a state where a plating layer can be uniformly formed.

[0034] In the plating tank (20), a pre-treated workpiece passes through a plating solution to form a metal plating layer through an electrochemical reaction. The plating tank stores a plating solution containing various organic additives such as metal ions, brighteners, levelers, and wetting agents. The workpiece undergoes a process in which metal ions are deposited on the surface under a constant current condition within the plating tank. However, some additives or fine impurities in the plating solution may remain on the surface of the plating layer, and these components may cause appearance defects during subsequent heat treatment.

[0035] The detailed structure of the pretreatment tank (10) and plating tank (20) described above can be applied to the configuration of the pretreatment tank and plating tank in a widely known continuous plating system, so a detailed description of the structure is omitted.

[0036] The post-treatment tank (100) includes a post-treatment body (110) and a guide roll (120), and removes plating solution residue, organic components, and other impurities from the surface of the plated object after plating is completed, thereby preventing appearance defects that may occur after heat treatment. The post-treatment tank (100) may further include a pH control unit (200), a cleaning solution supply pipe (130), and a scraper (140).

[0037] The post-treatment body (110) may store a cleaning solution inside. The cleaning solution may be a weakly alkaline composition containing sodium hydroxide (NaOH) or sodium carbonate (Na₂CO₃).

[0038] Sodium hydroxide is a basic compound that exhibits strong alkalinity when dissolved in water. Upon dissolution, it becomes completely ionized, providing a high concentration of hydroxide ions (OH-). Sodium hydroxide reacts with organic contaminants to promote saponification and is effective in removing organic additives, such as brighteners, levers, and wetting agents, that remain on the surface of the workpiece during the plating process.

[0039] Sodium carbonate is a salt that exhibits weak alkalinity in cleaning solutions. Compared to sodium hydroxide, it has a lower degree of ionization and a higher buffering capacity, characterized by a gradual change in pH. Sodium carbonate is suitable for decomposing and removing residual organic components generated during the plating process under mild alkaline conditions, providing a cleaning effect while minimizing chemical damage to the plating layer.

[0040] Surface residues can be removed by sufficiently contacting the cleaning solution while the plated body (W) passes through the inside of the post-treatment body (110). The cleaning solution may have a pH of 7 to 9.

[0041] If the pH of the cleaning solution falls within the acidic range of less than 7, there is a risk that the acidic components will chemically attack the plating layer, potentially causing partial dissolution of the metal plating or micro-corrosion. This can lead to quality degradation, such as increased surface roughness, grain non-uniformity, and surface spots. Furthermore, under acidic conditions, organic additive components remaining on the surface of the workpiece during the plating process are not effectively saponified or decomposed. Consequently, the removal efficiency of residual organic components is reduced, and as these components vaporize and decompose during subsequent heat treatment, the likelihood of appearance defects such as white spots, stains, and haze increases. Moreover, the acidic environment can corrode guide rolls or metal components inside the post-treatment tank, leading to a shortened equipment lifespan and increased maintenance costs.

[0042] Meanwhile, if the pH of the cleaning solution forms a strong alkaline region exceeding 9, the strong alkaline solution may excessively attack the surface of the plating layer, causing the plating layer to dissolve slightly or the surface to over-etch. This leads to a decrease in gloss, discoloration, and increased surface roughness of the plating layer, thereby impairing the appearance quality of the plated product. Furthermore, if the pH is excessively high, there is a possibility that the protective film or the surface of the plating layer may be damaged during the removal of organic components, which can reduce the corrosion resistance and stability of the plating layer. Strong alkaline conditions increase the risk of worker safety issues, equipment corrosion, and aging, and there is also the problem of reduced process stability due to the difficulty in maintaining the solution composition and concentration.

[0043] Therefore, by maintaining the pH of the cleaning solution in a weak alkaline range of 7 to 9, residual organic components and impurities can be effectively removed while preventing damage to the plating layer, and appearance defects that may occur after heat treatment can be reliably suppressed.

[0044] The pH control unit (200) detects the pH of the cleaning solution of the post-treatment tank body (110) and maintains the pH of the cleaning solution in the range of 7 to 9.

[0045] As plating solution residue, organic components, and fine contaminants are continuously introduced into the cleaning solution of the post-treatment tank body (110) during the process of the plated workpiece passing through, the pH of the cleaning solution may fluctuate over time. Accordingly, the pH control unit (200) detects the pH of the cleaning solution of the post-treatment tank body (110) in real time and maintains it within a set pH range.

[0046] The pH control unit (200) includes a pH sensor installed inside or outside the post-treatment tank body (110), a supply unit for supplying or diluting the cleaning solution, and a controller that receives the signal from the pH sensor and outputs a control signal for the composition of the cleaning solution.

[0047] The pH sensor comes into direct contact with the cleaning solution inside the post-treatment tank body (110) to continuously measure the pH value of the cleaning solution, and the measured pH value is transmitted to the controller.

[0048] The controller controls the cleaning solution supply unit based on the input pH value when the pH of the cleaning solution deviates from the set range, thereby supplying a solution such as sodium hydroxide, sodium carbonate, or diluted water to the post-treatment tank body (110). This ensures that the pH of the cleaning solution in the post-treatment tank body (110) is always maintained in a weak alkaline range of 7 to 9.

[0049] Additionally, the pH control unit (200) can operate in conjunction with the cleaning solution circulation piping or auxiliary tank. The pH control unit (200) can be configured to be combined with a temperature, concentration, and level control system for the cleaning solution as needed to improve the stability and quality reproducibility of the entire post-processing process.

[0050] The pH control unit (200) formed in this way prevents a decrease in cleaning power, damage to the plating layer, or defects in appearance caused by changes in the pH of the cleaning solution.

[0051] The guide roll (120) is rotatably positioned in the lower inner part of the post-processing body (110). The guide roll (120) guides the movement path of the workpiece (W) inside the post-processing body (110). That is, the guide roll (120) supports the workpiece (W) so that it can stably pass through the inside of the post-processing body (110) containing the cleaning solution.

[0052] Meanwhile, a diagonal groove (121) is formed along the longitudinal direction on the outer surface of the guide roll (120). Both sides of the diagonal groove (121) are formed in a structure that is open toward both ends of the guide roll (120). Accordingly, foreign substances that enter the surface of the guide roll (120) or detach from the workpiece can be discharged through the open ends by the rotation of the guide roll (120) and the flow of the cleaning liquid that enters the diagonal groove (121). Accordingly, the accumulation of contamination on the surface of the guide roll (120) can be prevented, thereby suppressing the re-attachment of contamination to the surface of the workpiece.

[0053] The cleaning liquid supply pipe (130) is positioned above the guide roll (120) inside the post-treatment tank body (110) and can spray cleaning liquid in the direction of the guide roll (120). The cleaning liquid supply pipe (130) can supply fresh cleaning liquid to the surface of the guide roll (120) to remove contaminants or residual alkaline components from the outer surface of the guide roll (120). The cleaning liquid supply pipe (130) maintains the cleanliness of the guide roll (120) throughout the post-treatment process.

[0054] Meanwhile, the cleaning solution supply pipe (130) may be connected to the supply section of the pH control unit (200) to supply the cleaning solution.

[0055] A scraper (140) is positioned at the outlet side of the post-treatment tank body (110) and can come into contact with the surface of the workpiece (W) that has passed through the post-treatment tank body (110). The scraper (140) can physically remove residual cleaning liquid, droplets, or fine contaminants from the workpiece (W).

[0056] The scraper (140) can be implemented in various forms, such as a blade type or a brush type, and suppresses additional stains or surface defects that may occur during the subsequent drying process or heat treatment process.

[0057] In this way, the continuous plating system can provide a plated product with stable appearance quality even after heat treatment by forming a uniform plating layer in the plating tank (20) on a workpiece (W) whose surface is activated in the pretreatment tank (10), and effectively removing impurities remaining on the surface of the plating layer through the combined action of a weak alkaline solution, a guide roll (120), a cleaning solution supply pipe (130), a scraper (140), etc. in the posttreatment tank (100).

[0058] Next, a continuous plating method will be described with further reference to Fig. 4.

[0059] Referring further to FIG. 4, the continuous plating method according to the present embodiment utilizes a continuous plating system according to the embodiments of FIG. 1 to FIG. 3.

[0060] The continuous plating method according to the present embodiment prevents defects in the appearance of the plating layer formed on the surface of a workpiece and includes a pretreatment step (S10) for cleaning and activating the surface of the workpiece, a plating step (S20) for forming a plating layer on the activated surface, and a posttreatment step (S30) for removing contaminants remaining on the surface after plating. The pretreatment step (S10), the plating step (S20), and the posttreatment step (S30) are arranged continuously on a line so that each step operates continuously as the workpiece moves without interruption.

[0061] Accordingly, the continuous plating method according to the present embodiment solves the problem in which organic components such as brighteners, levelers, and wetting agents, which remain in small amounts on the surface of the plated body due to the characteristics of the plating process, as well as fine precipitates of metal ions or foreign substances in the plating solution, vaporize and decompose during the subsequent heat treatment process, causing appearance defects such as white spots, haze, and stains.

[0062] In the pretreatment step (S10), the plated body (W) passes through processes such as electrolytic degreasing, rinsing, pickling, and final rinsing, thereby removing oil, processing oil, roll marks, oxide scale, etc. from the surface.

[0063] In particular, electrolytic degreasing and pickling effectively remove inert layers, such as organic contaminants or oxide layers remaining on the surface, thereby forming new active sites on the surface of the workpiece. This is a critical factor that directly influences the metal ion deposition rate, the crystal structure of the plating layer, and the adhesion of the plating layer during subsequent plating steps.

[0064] The pretreatment step (S10) also plays a decisive role in preventing defects such as pinholes and blisters that may occur during the plating step, and helps ensure the stability of the overall plating quality by ensuring that the surface reaction occurs uniformly when the workpiece (W) enters the plating solution.

[0065] In the plating step (S20), the pre-treated workpiece (W) passes through the plating tank (20), and metal ions in the plating solution are precipitated through an electrochemical reaction.

[0066] In addition to metal ions, plating solutions may contain various organic additives such as brighteners, particle size regulators, and aggregation inhibitors, which affect the flatness, gloss, and grain structure of the plating layer.

[0067] However, these organic additives are prone to remaining in trace amounts on the surface of the plated object after plating is completed, and there is also a possibility that metal microparticles or plating byproducts present in the plating solution may adhere to the surface.

[0068] These residual organic and impurities are not visible to the naked eye immediately after plating, but they can leave defects such as fine dots, stains, and cloudiness on the surface as they vaporize and decompose in a high-temperature environment during subsequent heat treatment.

[0069] Therefore, chemical and physical residues remaining from the plating step can be properly removed in the post-treatment step (S30).

[0070] The post-treatment step (S30) removes organic residues and impurities remaining on the surface by passing the plated body (W) on which plating has been formed through a post-treatment tank body (110) in which a cleaning solution with a pH of 7 to 9 is stored. The pH range of 7 to 9 induces saponification, solubilization, and detachment of organic additives without chemically damaging the plating layer.

[0071] The temperature of the cleaning solution in the post-treatment tank body (110) may be 30°C to 60°C. The workpiece (W) may pass through the post-treatment tank body (110) for 1 to 5 minutes. At this time, impurities on the workpiece (W) may be removed.

[0072] Here, if the temperature of the cleaning solution is lowered to below 30°C, the reactivity of the alkaline component in the cleaning solution is reduced, and the decomposition and detachment effects of the organic component remaining on the surface of the plated body (W) may not be sufficiently exerted. In particular, organic additives such as brighteners and levers remaining in the plating process are accelerated to dissolve and saponify as the temperature rises; therefore, if the temperature of the cleaning solution is low, the organic removal rate is significantly reduced. As a result, there is a risk that residual components will vaporize and carbonize during the heat treatment step after cleaning, causing appearance defects such as white spots, haze, and surface stains.

[0073] On the other hand, if the temperature of the cleaning solution exceeds 60°C, there is a possibility that the metal surface of the plating layer may be chemically attacked or micro-etching may occur due to the excessive temperature. In particular, metal plating layers such as nickel or zinc may experience quality degradation, such as reduced surface gloss, discoloration, or yellowing, in high-temperature alkaline environments. Furthermore, if the cleaning solution temperature becomes excessively high, its stability decreases, accelerating pH changes and potentially increasing costs for managing the solution's composition and maintaining equipment. High-temperature alkaline solutions can also increase risks in terms of operational safety.

[0074] In addition, if the time the workpiece (W) passes through the post-treatment tank body (110) is too short, less than 1 minute, there is a concern that the surface of the workpiece (W) may not secure sufficient contact time with the cleaning solution, and thus the decomposition, dissolution, and detachment reactions of organic components may not be completely carried out. Consequently, residual organic components or plating solution residues may remain on the workpiece (W) without being removed, and said residues may cause surface defects again during the subsequent heat treatment stage. Therefore, an excessively short residence time is a factor that significantly reduces the cleaning effect.

[0075] On the other hand, if the workpiece (W) stays in the post-treatment tank for an excessively long time exceeding 5 minutes, the surface of the plating layer may be chemically affected due to excessive alkali contact, which may result in micro-dissolution, increased surface roughness, or discoloration. In particular, under strong alkali or high temperature conditions, the possibility of reduced gloss and fine surface damage to the plating layer increases, which becomes a factor in degrading the appearance quality of the final product. In addition, an excessively long residence time may reduce the line speed, thereby reducing productivity.

[0076] Therefore, it can be seen that maintaining the cleaning solution temperature of the post-treatment tank body (110) at 30°C or higher and 60°C or lower is most desirable in terms of the reactivity of the cleaning solution, the stability of the plating layer, and the appearance quality, and maintaining the residence time of the plated body at 1 minute or higher and 5 minutes or lower is the optimal condition for ensuring a balance between the efficiency of removing organic components and productivity.

[0077] When the workpiece (W) passes through the post-treatment tank body (110), the guide roll (120) stably supports the path of the workpiece (W) inside the post-treatment tank body (110), and the diagonal groove (121) is open at both ends in the longitudinal direction of the guide roll (120) to induce foreign substances that escape during the cleaning process to be discharged in the axial direction of the guide roll (120) and prevent contaminants from accumulating on the surface of the guide roll (120), thereby preventing secondary contamination from occurring on the surface of the workpiece.

[0078] The diagonal groove (121) of the guide roll (120) is very effective in suppressing the accumulation of surface contamination on the guide roll (120) during long-term operation inside the post-treatment tank (100) and maintaining continuous cleaning quality.

[0079] Then, the cleaning solution supply pipe (130) sprays fresh cleaning solution toward the guide roll (120). This has the effect of removing alkaline components, plating residues, etc. that may adhere to the guide roll (120) in real time, thereby helping to maintain the cleanliness of the guide roll (120) for a long time and stabilize the cleaning quality.

[0080] The scraper (140) physically removes residual cleaning solution, moisture, and fine contaminants from the surface of the plated body (W) that has passed through the post-treatment tank (100). Accordingly, droplet marks and stains can be prevented before the drying step.

[0081] The pH control unit (200) detects the pH of the cleaning solution in the post-treatment tank body (110) in real time while the workpiece (W) is being cleaned, and if the measured pH value deviates from the set range, it controls the supply or dilution of the cleaning solution so that the pH of the cleaning solution is always maintained within the range of 7 to 9. Through this, the alkalinity of the cleaning solution is maintained at a constant level, so that residual organic components and impurities on the surface of the workpiece can be stably removed, and the decrease in cleaning power or damage to the plating layer caused by changes in the composition of the cleaning solution can be prevented.

[0082] In this embodiment, in order to verify the effect of post-treatment cleaning conditions (pH, cleaning solution temperature, cleaning time) on the post-treatment cleaning effect on a plated body after plating is completed, the pH of the cleaning solution was varied to 5, 7, 8, 9, and 11, the temperature of the cleaning solution was varied to 25℃, 45℃, and 70℃, and the cleaning time was varied to 30 seconds, 3 minutes, and 8 minutes to construct the example and comparative example.

[0083] After post-treating the workpieces under each condition, they were heat-treated under the same conditions (400℃ × 60 seconds). Subsequently, the amount of organic residue on the surface of the workpiece was quantitatively analyzed, and the cleaning efficiency was evaluated by measuring the area ratios of white spots, stains, and haze occurring after heat treatment.

[0084] In addition, the stability of the plating layer was confirmed by observing whether discoloration, gloss degradation, or micro-dissolution occurred on the surface of the plating layer.

[0085] The results of these examples and comparative examples are shown in [Table 1].

[0086] [Table 1]

[0087]

[0088] As a result of evaluating the examples and comparative examples, it was confirmed that differences in post-treatment cleaning conditions have a significant impact on the efficiency of removing residual organic components from the surface of the plated body and on the appearance quality after heat treatment. First, in the example where the pH of the cleaning solution was in the range of 7 to 9, the amount of organic residue on the surface of the plated body was maintained at a low level of 0.7 to 0.9 μg / cm², which is significantly lower than under acidic conditions (pH less than 7) or strong alkaline conditions (pH greater than 9). These results indicate that the saponification and decomposition reactions of organic additives occur most efficiently in the weak alkaline region, and as a result, appearance defects such as white spots, cloudiness, and stains caused by the carbonization or vaporization of organic residue after heat treatment were significantly reduced.

[0089] In addition, the same trend was observed in the comparison regarding the cleaning solution temperature. In the examples where the cleaning solution temperature was maintained within the range of 30°C to 60°C, residue removal was sufficient, and appearance defects after heat treatment remained at a very low level of 1-2% or less. On the other hand, in the comparative examples where the cleaning solution temperature was lower than 30°C, the reactivity of the alkaline solution was insufficient, resulting in reduced dissolution and detachment efficiency of organic components; consequently, the amount of residue and the occurrence of appearance defects increased significantly. Conversely, in the comparative examples where the temperature exceeded 60°C, while cleaning power was maintained at a certain level, the excessive high-temperature alkaline environment caused discoloration, yellowing, and a decrease in gloss in the nickel plating layer, resulting in compromised plating layer stability.

[0090] Similar results were confirmed in the evaluation of cleaning time. In the cleaning time range of 1 to 5 minutes, the cleaning solution and the surface of the plated workpiece came into sufficient contact, allowing for stable detachment and dissolution of organic components, and a uniform cleaning effect was ensured without damage to the surface of the plating layer. However, in comparative examples with a cleaning time of less than 1 minute, the reaction time was insufficient, so residual components were not removed and remained, resulting in increased appearance defects after heat treatment. Conversely, in comparative examples exposed to the cleaning solution for a long time exceeding 5 minutes, the alkaline solution excessively attacked the plating layer, causing surface damage such as micro-etching and a decrease in gloss.

[0091] As such, the post-treatment cleaning effect was found to be the best when all three conditions—cleaning solution pH (7–9), cleaning solution temperature (30–60℃), and cleaning time (1–5 min)—were within the optimal range, and it was confirmed that the organic residue removal rate, appearance quality after heat treatment, and chemical stability of the plating layer were simultaneously ensured. When these conditions were not met, insufficient cleaning power or damage to the plating layer occurred, resulting in a significant decrease in post-treatment efficiency.

[0092] Therefore, it has been clearly confirmed that the cleaning condition range of the present invention is not merely a simple process selection, but an optimal condition derived through technical and experimental verification to simultaneously satisfy the efficiency of post-treatment cleaning and the quality of the plating layer.

[0093] Although preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention as defined in the following claims also fall within the scope of the present invention. Explanation of the symbols

[0094] 10: Pretreatment tank 20: Plating tank 100: Post-treatment tank 110: Post-treatment main body 120: Guide Roll 121: Diagonal Groove 130: Cleaning solution supply pipe 140: Scraper 200: pH control unit W: Workpiece

Claims

Claim 1 A continuous plating method for preventing appearance defects of a plating layer formed on the surface of a workpiece, comprising: a pretreatment step for cleaning and activating the surface of a workpiece; a plating step for forming a metal plating layer by passing the pretreated workpiece through a plating solution; and a posttreatment step for removing impurities from the workpiece on which the plating layer is formed by cleaning with a sodium hydroxide (NaOH) or sodium carbonate (Na₂CO₃) cleaning solution having a pH of 7 to 9 at a temperature of 30°C to 60°C for 1 to 5 minutes. Claim 2 delete Claim 3 delete Claim 4 delete Claim 5 delete Claim 6 A continuous plating system for performing a continuous plating method according to claim 1, comprising a pretreatment tank, a plating tank, and a posttreatment tank, wherein a cleaning solution having a pH of 7 to 9 is stored in the posttreatment tank, and the posttreatment tank comprises a posttreatment tank body capable of receiving the cleaning solution and through which a workpiece having a plating layer formed thereon can pass, a guide roll disposed inside the posttreatment tank body and guiding the movement path of the workpiece passing through, and a cleaning solution supply pipe disposed above the guide roll inside the posttreatment tank body and spraying the cleaning solution in the direction of the guide roll. Claim 7 A continuous plating system according to claim 6, wherein a diagonal groove is formed on the outer circumference of the guide roll, and the diagonal groove is open to both ends of the guide roll. Claim 8 In claim 6, the continuous plating system further comprises a pH control unit that detects the pH of the cleaning solution of the main body of the post-treatment tank and controls the pH of the cleaning solution to be maintained in the range of 7 to 9. Claim 9 delete Claim 10 In claim 6, the continuous plating system further comprises a scraper disposed in the main body of the post-treatment tank for wiping the surface of the workpiece discharged from the main body of the post-treatment tank.

Images