Iron electroplating solution and electroplated steel sheet produced using the same

Abstract

The present invention relates to a kind of iron electroplating solution, it comprises: iron ions comprising ferrous ions and ferric ions; chelating agent; and inevitable impurities, wherein the content of ferric ions in the iron ions is 5-60 weight %. According to the present invention, there is high electroplating efficiency, the plating efficiency will not be reduced due to continuous plating operation, and sludge is prevented from being generated, so it is easy to control the plating solution. In addition, burning can also be prevented during the operation of high current density, so a high-quality iron plating layer can be obtained. In addition, since the concentration of the ferric ions generated by the plating reaction remains constant, it is not necessary to replace the plating solution, so it is suitable for a continuous plating process.

Description

Technical Field

[0001] The present invention relates to an iron electroplating solution and an electroplated steel plate manufactured using the iron electroplating solution, and more particularly to an iron electroplating solution and an electroplated steel plate manufactured using the iron electroplating solution. The iron electroplating solution has excellent electroplating efficiency and plating adhesion, and does not generate sludge even when electroplating is performed at a high current density for a long time. Background Art

[0002] Steel plates have excellent mechanical strength, good processability, and abundant resources, so they are widely used as structural parts in automobiles, home appliances, and building materials. However, the corrosion resistance of steel plates themselves is extremely poor, so surface treatments such as plating are mainly performed on the surface to extend their life.

[0003] In particular, iron is a substance that is made into steel plates or steel materials and used as a general structural material, but it is inferior to other metals in corrosion resistance and appearance characteristics, so it is used to form alloys for special purposes by utilizing magnetic properties or electroplating. However, the plating efficiency is extremely low in the process of iron electroplating, and there is a problem of sludge generation when used for a long time, so it is very difficult to apply to industry.

[0004] For example, Patent Document 1 discloses an iron plating solution for an electrogalvanized steel plate substrate. In Patent Document 1, complexing agents such as gluconic acid, nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA), and citric acid are used to prevent sludge. In the above-mentioned case, sludge can be prevented, but there are problems such as increased overvoltage, low plating efficiency, and burning, which makes the coating easy to fall off. In addition, since thiourea, imidazole, etc. are easily electrolyzed during the electroplating process, there is a problem that it is very difficult to control the solution and concentration in a continuous process.

[0005] In patent documentation 2, patent documentation 3 and patent documentation 4, carboxylic acids such as gluconic acid, tartaric acid, citric acid, dicarboxylic acids are also used as complexing agents to prevent sludge, but there are problems such as low plating efficiency, burning, and easy shedding of the coating when operating with high current density. In addition, when ascorbic acid is used, sludge can be temporarily prevented because it plays the role of reducing ferric ions to ferrous ions, but when ascorbic acid is oxidized to generate dehydroascorbic acid (dehydroascorbic acid), it is complexed with iron ions, and the electroplating efficiency is sharply reduced, so it is not suitable for continuous operation.

[0006] In addition, the existing iron plating solution contains ferrous ions (Fe 2+ ), but is oxidized to trivalent iron ions (Fe 3+), the plating efficiency is sharply reduced, and there is a problem of generating sludge. Therefore, the ferric iron ions must be reduced to ferrous ions or the solution must be replaced regularly, but it is difficult to apply in large-scale continuous electroplating processes. In addition, a method for suppressing the formation of ferric iron in solution by using a soluble anode is proposed, but the soluble anode gradually dissolves and is consumed as the plating is performed, so not only the distance between the electrodes and the surface state change, but also needs to be replaced regularly, so it is very difficult to control.

[0007] [Prior art literature]

[0008] [Patent Document]

[0009] Korean Patent Publication No. 10-2009-0112919

[0010] Korean Patent Publication No. 10-2013-0070235

[0011] Japanese Patent Publication No. 1998-204674

[0012] Japanese Patent Publication No. 1994-081188 Summary of the invention

[0013] Technical issues to be solved

[0014] The present invention is proposed in view of the above situation, and its purpose is to provide an iron electroplating solution and an electroplated steel plate manufactured using the iron electroplating solution, wherein the iron electroplating solution can suppress the generation of sludge caused by the oxidation of iron ions even if continuous plating is carried out for a long time, and the plating efficiency can be kept constant, and there is no need to frequently replace the solution.

[0015] Technical Solution

[0016] According to one aspect of the present invention, there is provided an iron electroplating solution comprising: iron ions including ferrous ions and ferric ions; a complexing agent; and inevitable impurities, wherein the content of ferric ions in the iron ions is 5-60 wt %.

[0017] The concentration of the iron ions may be 1-80 g per 1 liter of the iron electroplating solution.

[0018] The molar concentration ratio of the iron ions to the complexing agent may be 1:0.05 to 2.0.

[0019] The complexing agent may be one or more selected from amino acids and amino acid polymers.

[0020] The complexing agent may be one or more selected from alanine, glycine, serine, threonine, arginine, glutamine, glutamic acid and glycylglycine.

[0021] The pH of the iron electroplating solution may be 1.2 to 4.0.

[0022] The iron electroplating solution may further include 200 g or less of a conductive auxiliary agent per 1 liter of the iron electroplating solution.

[0023] The conductive auxiliary agent may be one or more selected from sodium sulfate, potassium sulfate and ammonium sulfate.

[0024] According to another aspect of the present invention, there is provided a plated steel sheet plated with iron using the iron electroplating solution.

[0025] Beneficial Effects

[0026] According to the present invention, the electroplating efficiency is high, the plating efficiency is not reduced due to continuous plating operation, and the generation of sludge is prevented, so that the plating solution is easily controlled.

[0027] Furthermore, burning can be prevented even under operation at high current density, so a high-quality iron plating layer can be obtained.

[0028] Furthermore, since the concentration of trivalent iron ions generated by the plating reaction remains constant, there is no need to replace the plating solution, and thus it is suitable for a continuous plating process. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The plating solution of Example 3 was used at 50 A / dm 2 Scanning electron microscope photograph of the initial stage of the test piece plated at a current density of 0.7 seconds.

[0030] Figure 2 The plating solution of Example 3 was used at 50 A / dm 2 Post-plating scanning electron micrograph of the test piece at a current density of 0.7 s.

[0031] Figure 3 This is a photograph of a test piece plated with the plating solution of Comparative Example 7 observed with a scanning electron microscope.

[0032] Best Mode for Carrying Out the Invention

[0033] Hereinafter, preferred embodiments of the present invention will be described with reference to various embodiments. However, the embodiments of the present invention can be modified into various other embodiments, and the scope of the present invention is not limited to the embodiments described below.

[0034] The present invention relates to an iron electroplating solution and an electroplated steel plate manufactured using the iron electroplating solution, and more particularly to an iron electroplating solution and an electroplated steel plate manufactured using the iron electroplating solution. The iron electroplating solution has excellent electroplating efficiency and plating adhesion, and does not generate sludge even when electroplating is performed at a high current density for a long time.

[0035] As a method for forming a uniform pure iron plating layer in a continuous plating process, an electroplating method is used. However, iron can be formed in the form of ferrous ions (Fe 2+ ) and trivalent iron (Fe 3+ ) exists in the form of trivalent iron ions, and trivalent iron ions are also easy to form sludge in acidic solutions with a pH of more than 2.

[0036] Even if only ferrous ions that have not formed sludge are used as raw materials to prepare electrolytes, ferric ions will naturally form in the solution when in contact with oxygen in the atmosphere or oxygen generated during electroplating. In addition, when an insoluble anode is used, ferrous ions are directly oxidized to ferric ions by the oxidation reaction of the anode. When a soluble anode is used to suppress this problem, the oxidation of ferric ions can be slightly suppressed, but it is impossible to fundamentally suppress the oxidation of ferric ions. Therefore, when ferric iron is formed, a filtering device for removing sludge is essential, and the electrolyte must be replaced regularly to remove the accumulated ferric ions, so serious waste of raw materials is inevitable.

[0037] When the pH of the solution is controlled at a low level below 2, the generation of sludge can be slightly suppressed, but the hydrogen reduction reaction increases, the electroplating efficiency decreases sharply, and the generation of trivalent iron ions cannot be fundamentally suppressed.

[0038] In addition, a complexing agent is added to suppress the generation of sludge in the iron electroplating solution. In the present invention, a complexing agent refers to a substance that strongly combines with metal ions in an aqueous solution to form complex ions, which suppresses the combination of hydroxide ions (OH-) in water with metal ions, thereby preventing the generation of sludge. Therefore, when the combination between the complexing agent and the metal ion is weaker than the binding force between the hydroxide ion and the metal ion, the complexing agent cannot prevent the generation of sludge, but when the combination between the complexing agent and the metal ion is too strong, sludge is prevented from being generated, but the complexing agent and the metal ion are difficult to separate during the plating process, so that the overvoltage of the plating is increased, and therefore there is a problem of reduced plating efficiency.

[0039] Chelating molecules can be considered as effective organic complexing agents to prevent sludge in the solution. Representative chelates include oxalic acid, citric acid, etc., which contain more than two carboxyl groups in one molecule, and NTA, EDTA, etc., which contain multiple carboxyl groups and amines. Complexing agents containing multiple carboxyl groups have more than two carboxyl groups in one complexing agent molecule that form strong bonds with iron ions, thereby inhibiting the bonding of iron ions with hydroxide ions, thereby inhibiting the generation of sludge. However, during the plating process in the cathode, it is difficult to separate the iron ions and the complexing agent molecules, so as to increase the plating overvoltage and reduce the plating efficiency as described above.

[0040] In addition, carboxyl is negatively charged in weak acid because hydrogen is dissociated, and the complexing agent with more than 2 carboxyls forms anions of monovalence or divalence or more in the region where pH is 2 to 4, and the complexing agent is combined with iron ion to form a negatively charged complex ion. When the complexing ion is negatively charged, electric repulsion is generated with the cathode where electroplating reaction occurs, and material transfer is difficult, so the plating efficiency can be reduced, and on the other hand, the anode where oxidation reaction occurs is easier to transfer material due to anionic complex ions, so ferric ion further increases. Especially, compared with ferrous ion, the binding force of ferric ion and complexing agent is stronger, so although the ferric ion generated in the solution does not form sludge, the problem of being completely unable to be used for plating reaction and accumulating can occur. Therefore, when plating is carried out for a long time in continuous process, only the concentration of the ferrous ion participating in the plating reaction is sharply reduced, and the concentration of ferric ion increases, so the plating efficiency can be reduced, so that the plating amount of the target level can not be obtained, and burning occurs, causing the plating quality to be reduced, so the solution must be regularly replaced, and the waste of raw materials becomes extremely serious.

[0041] The present inventors, in order to solve the above-mentioned problems, realized through research that when a constant level of ferric ions is included in an iron electroplating solution, the oxidation of ferrous ions to form ferric ions in the anode is suppressed, and the reaction of reducing ferric ions to ferrous ions in the cathode is accelerated, so that ferric ions can be used as an iron electroplating raw material, and since the pH and the concentration of ferric iron change little, the state of the solution does not change greatly in the continuous electroplating process, so that the plating efficiency can be stably ensured even in long-term use, and when amino acids or amino acid polymers are used as chelating agents in the electrolytic solution for iron electroplating, the generation of sludge caused by the generation of ferric iron is suppressed, and high plating efficiency can be obtained, thereby completing the present invention.

[0042] That is, according to a preferred embodiment of the present invention, oxidation of ferrous iron to ferric iron to form sludge is suppressed, while ferric iron ions are reused as a raw material for iron plating, thereby suppressing deterioration of the solution and maintaining a certain plating efficiency.

[0043] According to one aspect of the present invention, there is provided an iron electroplating solution, comprising: iron ions including ferrous ions and ferric ions; a complexing agent; and inevitable impurities, wherein the content of the ferric ions in the iron ions is 5-60% by weight. The inevitable impurities in the present invention, for example, represent alloy components such as manganese and silicon dissolved in a substrate steel sheet or components contained in a solution raw material.

[0044] According to a preferred embodiment of the present invention, the iron plating solution comprises ferrous ions and ferric ions. In order to obtain high plating efficiency, it may be advantageous to only comprise ferrous ions, but when only comprising ferrous ions, the solution deteriorates and the plating efficiency is sharply reduced, thus causing quality deviation in a continuous electroplating process, and is therefore not preferred.

[0045] Thus, in the present invention, the content of ferric iron in the iron ion is preferably 5-60% by weight, more preferably 5-40% by weight. When the content of the ferric iron is less than 5%, the speed at which ferric iron is reduced to ferrous iron in the cathode is less than the speed at which ferrous iron is oxidized to ferric iron in the anode, so the concentration of ferric iron rises sharply, and the coating efficiency continues to decrease while pH is sharply reduced. On the other hand, when the concentration of ferric iron ions exceeds 60%, the reaction amount at which ferric iron is reduced to ferrous iron in the cathode is greatly increased compared with the reaction amount at which ferrous iron is reduced and metallic iron is precipitated, so the coating efficiency is reduced, and the coating quality can be reduced. Therefore, considering the devices and process characteristics such as the amount of solution lost by sticking to the band and the concentration change rate caused by evaporation, the content of the ferric iron in the iron ion is preferably 5-60% by weight.

[0046] In addition, in order to prepare a solution containing ferrous ions, a method of dissolving pure metallic iron, iron oxide or iron hydroxide in high concentration sulfuric acid or mixing and dissolving ferrous sulfate and ferric sulfate, etc. can be used, but it is not limited to the above raw materials and methods.

[0047] In addition, in order to prepare an iron plating solution containing trivalent iron ions, a sulfate-based plating solution (electrolyte) containing trivalent iron can be prepared by mixing and dissolving sulfates, iron oxides, iron hydroxides, etc. containing trivalent iron, or by adding an oxidant such as hydrogen peroxide or injecting air for oxidation after preparing a sulfate-based electrolyte containing only ferrous iron, or by applying an anode for electro-oxidation, without being limited thereto.

[0048] The concentration of the iron ions is preferably 1-80 g per liter of the iron electroplating solution, more preferably 10-50 g per liter of the iron electroplating solution. When the concentration of the iron ions is less than 1 g / L, there is a problem of a sharp decrease in plating efficiency and plating quality, but when the concentration of the iron ions exceeds 80 g / L, precipitation may occur due to the solubility, and in the continuous plating process, the loss of raw materials increases due to the loss of solution, so it is not economical.

[0049] The iron electroplating solution of the present invention contains a complexing agent, contains a large amount of trivalent iron and does not generate sludge. In order to maintain high plating efficiency, amino acids or amino acid polymers are preferably used as complexing agents.

[0050] Amino acids refer to organic molecules formed by the bonding of carboxyl groups (-COOH) and amine groups (-NH2), and amino acid polymers refer to organic molecules formed by the polymerization of two or more amino acids. Amino acid polymers exhibit complexing agent properties similar to those of amino acids. Therefore, in the following description, amino acids and amino acid polymers are collectively referred to as amino acids.

[0051] When amino acids are dissolved in neutral water, the amine combines with hydrogen ions to become positively charged, and the carboxyl group dissociates hydrogen ions to become negatively charged, so the amino acid molecules remain neutrally charged. When the solution is acidified, the carboxyl group combines with hydrogen ions again to become neutrally charged, and the amine becomes positively charged, so the amino acid molecules form cations. That is, amino acids form neutral charges or cations in weakly acidic aqueous solutions.

[0052] When amino acids are added to an acidic electrolyte containing iron ions, they are complexed with ferrous ions and ferric ions, and the iron ions complexed with amino acids also remain in a cationic state in the complexed state. Therefore, conventional complexing agents with multiple carboxyl groups exhibit electrically opposite characteristics compared to the case of being negatively charged in a weakly acidic aqueous solution.

[0053] In addition, compared with complexing agents containing multiple carboxyl groups such as citric acid and EDTA, amino acids form fewer bonds with iron ions and have weaker binding force, but their binding force with ferric ions that produce sludge is strong enough, so precipitation caused by ferric ions can be prevented. In addition, since ferric ions can remain cationic even when complexed, ferric ions are easily transferred to the cathode and reduced to ferrous ions, so they can participate in the plating reaction, but the movement to the anode is inhibited, and the formation rate of ferric ions slows down. Therefore, even if long-term continuous plating is performed, the concentration of ferric ions is maintained at a certain level, and a certain plating efficiency is maintained, and there is no need to replace the electrolyte.

[0054] In addition, in the continuous electroplating process, when the iron ions in the solution are consumed by plating, the solution is acidified, and even if the same amount of iron ions are precipitated, the pH change of the solution containing trivalent ferrous ions is reduced compared with the solution containing only ferrous ions. When the pH increases, a part of the trivalent ferrous ions combines with the hydroxide ions, and when the pH decreases, the hydroxide ions are separated and neutralized. Therefore, the solution containing trivalent ferrous ions slows down the pH change in the absence of a separate pH buffer, thereby playing the role of a pH buffer, so that a certain electroplating efficiency can be maintained in the continuous electroplating process.

[0055] Therefore, sludge can be prevented by using amino acids as chelating agents, ferrous ions and ferric ions can be used as plating raw materials, and when ferrous ions and ferric ions are mixed, the pH change of the solution is slowed down and the accumulation of ferric ions is easily prevented, so a certain electroplating efficiency and plating quality can be maintained in the continuous electroplating process.

[0056] In addition, the complexing agent is preferably added in an amount of 1:0.05 to 2.0 with a molar concentration ratio of the iron ion and the complexing agent, more preferably in an amount of 1:0.5 to 1.0. When the addition of the complexing agent is less than 0.05, the excessive ferric iron ion contained cannot be suppressed to be combined with hydroxide ions or oxygen to form sludge, even if ferric iron is not included, the plating efficiency is greatly reduced, and then burning is caused, resulting in a deterioration in plating quality. On the other hand, even if the addition of the complexing agent exceeds 2.0, the effect and plating quality of the sludge are suppressed, but due to the rise in overvoltage, the plating efficiency is reduced, and compared with the raw material containing iron ions such as iron sulfate, an excessive relatively high-priced amino acid is unnecessarily included, so the cost of raw materials increases, resulting in uneconomical.

[0057] The complexing agent is preferably one or more selected from amino acids or amino acid polymers, for example, one or more selected from alanine, glycine, serine, threonine, arginine, glutamine, glutamic acid and glycylglycine.

[0058] According to a preferred embodiment of the present invention, the pH of the iron electroplating solution is preferably 1.2 to 6.0, more preferably 2 to 4. When the pH is less than 1.2, the reduction reaction of hydrogen ions increases sharply, and the electroplating efficiency decreases sharply. On the other hand, when the pH exceeds 6, ferrous ions also form sludge, and it is difficult to keep the solution clean even if a large amount of complexing agents are contained. In addition, when the pH is 4 to 6, although the solution itself can be kept clean when not electroplating, sludge may be temporarily generated and turbid in the process of applying electricity to carry out plating. Therefore, it is more preferred that the pH is adjusted to 2 to 4 to prevent the formation of sludge while maintaining a high plating efficiency. In addition, the pH adjustment can use an acidic solution and an alkaline solution comprising sulfuric acid, sodium hydroxide, potassium hydroxide, ammonia, etc., and is not limited thereto.

[0059] According to a preferred embodiment of the present invention, the iron plating solution may further include a conductive aid (wherein 0 is excluded) of less than 200 g per liter of iron plating solution as required. For example, when the concentration of iron ions is low and pH is high and high current operation is required, a conductive aid may be used to reduce the plating voltage. However, when the concentration of iron ions exceeds 200 g / L, the conductivity will not increase significantly, the specific gravity of the solution increases, which is unfavorable for solution circulation, and precipitation may occur at low temperatures, so it is preferred to use an amount of less than 200 g per liter of iron plating solution.

[0060] The type of the conductive auxiliary agent is not particularly limited, but for example, one or more selected from sodium sulfate, potassium sulfate, and ammonium sulfate may be used.

[0061] In addition, according to another aspect of the present invention, there is provided an iron-plated steel sheet plated with the iron electroplating solution. Preferably, when the iron electroplating solution is used at a temperature below 80°C and a current of 0.5-150A / dm 2 When electroplating is carried out at a current density of , an iron-plated steel sheet can be obtained which can maintain high electroplating efficiency and form a high-quality iron-plated layer without generating sludge.

[0062] The present invention will be described in more detail below through specific embodiments. The following examples are merely examples to help understand the present invention, and the scope of the present invention is not limited thereto. DETAILED DESCRIPTION

[0063] Example

[0064] In order to prepare the iron plating solution, ferrous sulfate and ferric sulfate are used. As the complexing agent, one of amino acids is selected, and the concentration of the complexing agent is dissolved by weight calculated by molar concentration ratio according to the concentration of iron ions.

[0065] The pH of the solution is adjusted using sulfuric acid or sodium hydroxide. The order of solution preparation is to dissolve the complexing agent, conductive aid, etc. in pure water first and then add ferric sulfate. If ferric sulfate is dissolved first, sludge will be generated during the dissolution process, and even if the complexing agent is added later, the sludge will not be dissolved well. Therefore, it is preferred to add ferric sulfate after the complexing agent is completely dissolved.

[0066] When a solution having a pH of 4 or higher is prepared, it is neutralized with sodium hydroxide, and the precipitate temporarily generated in the process is completely dissolved by stirring for a sufficient time. The prepared plating solution is heated to 50°C.

[0067] Copper plates and cold-rolled steel plates were used as the base metals. The surface of the base metal was washed with alcohol, degreased under normal alkaline degreasing conditions, dipped in a 1-5% sulfuric acid solution and pickled for about 10 seconds, and then washed with pure water before plating.

[0068] An insoluble metal plate coated with IrO2 was used as the anode, and the area to be plated was the same as that of the anode plate. Table 1 shows the results of plating using the plating solutions prepared respectively.

[0069] In addition, for the iron plating solution of the present invention, taking into account the plating efficiency after preparing the solution, whether sludge is generated, and being designed to be used for a long time in a continuous process, a total of 3 steps are performed for plating after preparing each solution to determine the electroplating efficiency and sludge generation during solution modification. For example, in the continuous process, iron ions are consumed in excess of a certain amount, resulting in a decrease in pH, and a large amount of ferrous ions are oxidized to trivalent iron, etc.

[0070] Specifically, in step 1, each solution is prepared and heated, and a rectifier is connected to the substrate metal and the anode plate, and then the current density and the plating time are controlled, so as to manufacture the plating test piece in the initial plating solution. The substrate metal uses a copper plate and a cold-rolled steel plate, and the plating efficiency is measured by the result of plating on the copper plate, and the plating adhesion is evaluated by the result of plating on the cold-rolled steel plate. In order to measure the electroplating efficiency, the coating of the test piece plated on the copper plate is dissolved with a hydrochloric acid solution, and the total amount of the iron component in the solution is measured to calculate the plating amount, which is expressed as the initial plating efficiency.

[0071] In step 2, in order to confirm the change in the characteristics of the solution during long-term electroplating with the above solution, the total current that can precipitate 10% of the total amount of iron ions contained in the plating solution is calculated, and the current is continuously applied, and the substrate metal is regularly replaced when necessary.

[0072] In step 3, a plating test piece is prepared by the same method as step 1 using the solution modified by long-term application of electric current, and the plating quality and post-plating efficiency are measured.

[0073] The surface shape of the iron-plated layer obtained using a cold-rolled steel sheet as the base metal was analyzed using a scanning electron microscope, and the surface of the plated test piece was visually checked with a tape to see if the plating layer had fallen off. The plating adhesion level is shown in Table 1, and the evaluation criteria are as follows.

[0074] ○: The level of the fallen powder cannot be confirmed visually at all

[0075] △: The level at which the coating can be visually confirmed to have fallen off in the form of powder

[0076] ×: Level where the plating peels off or falls off in large quantities in the form of powder

[0077] [Table 1]

[0078]

[0079] The results of using glutamine, one of the amino acids, as a complexing agent according to the concentration of iron ions are shown in Examples 1 to 4 and Comparative Example 1. The concentration of glutamine is 0.5 times the concentration of iron ions in terms of molar concentration ratio, and the pH is adjusted to 2 to 4. The plating current density is 10-50 A / dm depending on the concentration of iron ions in the solution. 2 Plating is performed. As shown in Examples 1 to 4, when the concentration of iron ions is 1 g / L or more, the plating adhesion is good, sludge is not generated due to long-term use, and the plating efficiency tends to increase as the iron concentration increases. However, as shown in Comparative Example 1, when the concentration of iron ions is very low, the limiting current density of the iron plating reaction is low, so the plating efficiency is low, a large amount of hydroxide is mixed into the plating layer, a black plating layer is formed, and the adhesion becomes poor.

[0080] Figure 1 The plating solution of Example 3 is shown in FIG. 2 The initial scanning electron microscope photo of the test piece plated with a current density of 0.7 seconds. The iron plating starts to grow in the form of spherical iron metal particles in the early stage. Figure 2 The later scanning electron microscope photos of the test piece are shown. When the plating time is increased, the plating structure gradually becomes dense, such as Figure 2 As shown, when the plating time is 2.0 seconds or longer, a dense plating layer is formed.

[0081] With reference to the results of Example 5 to Example 7 and Comparative Example 2 and Comparative Example 3, as the ratio of ferric iron in the whole iron ion increases, the initial plating efficiency has a tendency to gradually decrease. However, as the ratio of ferric iron increases, when 10% of the total amount of the iron ion that can be plated is applied and modified, the plating efficiency increases instead. In particular, as shown in Comparative Example 2, when the content of ferric iron in the initial solution is less than 5%, the plating efficiency in the long-term solution is sharply reduced instead, so it is difficult to maintain a constant plating efficiency in a continuous process. In addition, when the concentration of ferric iron exceeds 60%, compared with the initial solution, the plating efficiency in the modified solution increases slightly, but the plating efficiency of the initial solution and the later solution is relatively low, and the coating easily falls off, so the plating quality is reduced.

[0082] Examples 8 to 11 and Comparative Example 4 use glutamine as a complexing agent, and show the plating efficiency and whether sludge is generated according to the content of the complexing agent. As in Comparative Example 4, when the concentration of the complexing agent relative to the molar concentration of iron is 0.01 or less, the plating efficiency is reduced, sludge is easily generated during the plating process, and it is difficult to perform electroplating stably, such as the plating layer also falling off, etc., but when the concentration of the complexing agent relative to the molar concentration of iron is 0.05 or more, the plating efficiency is high and sludge is not generated.

[0083] The results of measuring the plating efficiency using glycylglycine, an amino acid polymer, as a complexing agent are shown in Examples 12 to 16. The plating efficiency was good in both the initial and fully modified solutions, and no sludge was generated.

[0084] In Example 17 and Example 18 and Comparative Examples 5 and 6, electroplating is performed by adjusting the pH of the iron plating solution to 1 to 6. As in Comparative Example 5, the iron plating solution with a pH less than 1.2 is very stable and can maintain cleanliness, but the plating efficiency is too low. However, when the pH is above 1.2, the plating efficiency will gradually increase as the pH increases. When the pH exceeds 4, the cleanliness of the solution is maintained during the period when no plating is performed, but a small amount of precipitate is produced during the continuous plating process, and most of it is dissolved during stirring. However, when the pH exceeds 5, the precipitate produced during the plating process cannot be naturally redissolved even if stirred, and the coating easily falls off, so the plating efficiency is reduced instead.

[0085] In order to be applicable in industry, the current density needs to be adjusted as needed, so the wider the range of operable current density, the better. In Examples 19 to 23, the current density is adjusted to 0.5-150 A / dm 2 The plating efficiency is measured by changing the current density between 100A / dm and 200A / dm. The lower the current density, the more hydrogen is generated and the side reaction of reducing ferric ions to ferrous ions increases compared to the current consumed by plating, thus showing a tendency of decreasing plating efficiency. In addition, as the current density increases to 100A / dm 2 , the plating efficiency increases significantly, when the current density exceeds this range and increases to 150A / dm 2 When the plating efficiency is slightly reduced, the plating efficiency is still high while the plating quality is good and no sludge is generated.

[0086] In Example 24, alanine as an amino acid was used as a complexing agent, and in Comparative Examples 7 and 8, solutions prepared by using citric acid and gluconic acid, which only have carboxyl groups in the molecule, as complexing agents were used for electroplating. In the solution using alanine, the initial and later plating efficiencies of a level similar to that of the case where glutamine as an amino acid or glycylglycine as an amino acid polymer was used as a complexing agent were obtained, and no sludge was generated during the plating process. However, when citric acid and gluconic acid were used as complexing agents, although no sludge was generated, the initial plating efficiency was very low, and the coating easily fell off, so good plating quality could not be obtained, and the plating efficiency was sharply reduced in the solution used for a long time.

[0087] Figure 3 , which is a photograph of a test piece plated with the solution of Comparative Example 7 using citric acid as a complexing agent, observed by scanning electron microscopy. Figure 1 and Figure 2 The plating structure obtained in the iron plating solution containing citric acid is different from that of the iron plating solution. The plating structure is plated with very fine and coarse particles and contains a very large amount of hydroxide in the plating layer.

[0088] According to the above results, unlike plating solutions using commonly used carboxylic acid complexing agents as complexing agents, solutions containing amino acids or amino acid polymers as complexing agents prevent the mixing of hydroxides and inhibit combustion, thereby obtaining high-quality plating layers, and the electroplating efficiency is high. The plating efficiency is maintained even after long-term use, and the generation of sludge is inhibited, so it is expected that high-speed continuous operation can be achieved.

[0089] The embodiments of the present invention are described in detail above, but the scope of rights of the present invention is not limited thereto, and various modifications and variations can be made without departing from the technical concept of the present invention described in the claims, which is obvious to those skilled in the art.

Claims

1. An iron electroplating solution comprising: iron ions including ferrous ions and ferric ions; a complexing agent; and unavoidable impurities, in, The content of trivalent iron ions in the iron ions is 5-60% by weight. The complexing agent is one or more selected from amino acids and amino acid polymers, The molar concentration ratio of the iron ion to the complexing agent is 1:0.05 to 2.0, The pH of the iron electroplating solution is 1.2 to 4.

0.

2. The iron electroplating solution according to claim 1, characterized in that The concentration of the iron ions is 1-80 g per 1 liter of the iron electroplating solution.

3. The iron electroplating solution according to claim 1, characterized in that The complexing agent is one or more selected from alanine, glycine, serine, threonine, arginine, glutamine, glutamic acid and glycylglycine.

4. The iron electroplating solution according to claim 1, characterized in that The iron electroplating solution further includes 200 g or less and excluding 0 g of a conductive auxiliary agent per 1 liter of the iron electroplating solution.

5. The iron electroplating solution according to claim 4, characterized in that The conductive auxiliary agent is one or more selected from sodium sulfate, potassium sulfate and ammonium sulfate. 6 . A plated steel sheet, which is plated with the iron electroplating solution according to claim 1 .

Images