Post-treatment solution for plated films and method for treating plated films

Abstract

To provide a post-treatment solution that imparts excellent corrosion resistance to a trivalent chromium plating film and suppresses color changes on the surface of the treated object, and a method for treating a trivalent chromium plating film. [Solution] A post-treatment solution for trivalent chromium plating containing an oxidizing agent, phosphate ions, and an ionic surfactant. A method for treating a trivalent chromium plating by using the post-treatment solution on the trivalent chromium plating. The post-treatment solution preferably has a pH of less than 8.0.

Description

[Technical Field]

[0001] The present invention relates to a post-treatment solution for trivalent chromium plating films and a method for treating trivalent chromium plating films. [Background technology]

[0002] Chromium plating and chromate treatment have traditionally been used as surface treatment methods for various parts, including those for household and automotive use. In particular, hexavalent chromium plating and hexavalent chromate treatment provide not only good decorative properties but also excellent corrosion resistance to the outer surface. In recent years, from the perspective of safety and hygiene, plating and surface treatment technologies using trivalent chromium instead of hexavalent chromium are also being investigated.

[0003] However, since trivalent chromium coatings generally tend to have inferior corrosion resistance compared to hexavalent chromium coatings, electrolytic chromate treatment (post-treatment) using hexavalent chromium is performed on trivalent chromium plating films, meaning the entire process is not hexavalent chromium-free. In addition, electrolytic chromate treatment can sometimes cause significant changes in the color tone of the treated surface.

[0004] Therefore, there is a need for a treatment technology that can provide excellent corrosion resistance without using hexavalent chromium, and that does not cause significant color changes on the surface of the treated object, and research into such technologies is ongoing.

[0005] For example, Patent Document 1 discloses a method for forming a phosphate film on a plating film made of trivalent chromium, etc., and further treating the film with an oxidizing agent such as hydrogen peroxide or nitric acid. Patent Document 2 discloses a rust inhibitor containing a phosphate, an oxidizing agent, and a nonionic surfactant. Furthermore, Patent Document 3 discloses a cathode electrolytic treatment solution for trivalent chromium plating films, mainly consisting of a specific amount of hydrogen peroxide and a phosphorus compound, and optionally containing an organic acid buffer. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 7-258882 [Patent Document 2] Japanese Patent Publication No. 2005-97701 [Patent Document 3] Patent No. 7356769 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, in the treatment method disclosed in Patent Document 1, for example, satisfactory corrosion resistance is often not achieved unless the surface of the workpiece is further coated or otherwise treated. Even with the treatment methods described in Patent Documents 2 and 3, it is difficult to obtain sufficient corrosion resistance. Furthermore, in these conventional methods, if the pH of the treatment solution deviates slightly from the recommended range, hexavalent chromium may leach into the treatment solution.

[0008] The present invention aims to provide a post-treatment solution for trivalent chromium plating films and a method for treating trivalent chromium plating films that imparts excellent corrosion resistance to the trivalent chromium plating film and is less likely to cause significant color changes on the surface of the treated object, in order to solve the above-mentioned problems. [Means for solving the problem]

[0009] As a result of diligent research to solve the above-mentioned problems, the present inventors have discovered that by adding a specific surfactant to a treatment solution containing an oxidizing agent and phosphate ions, a post-treatment solution can be obtained that imparts excellent corrosion resistance to the treated object while hardly altering the appearance of the treated object's surface, thus completing the present invention.

[0010] In other words, the present invention provides the following (1) to (4). (1) Contains an oxidizing agent, phosphate ions, and an ionic surfactant, A post-treatment solution for trivalent chromium plating films. (2) The post-treatment solution from (1) above, with a pH of less than 8.0. (3) The post-treatment liquid according to (1) or (2) above, wherein the oxidizing agent contains one or more chemical species selected from peroxides, persulfuric acid, persulfates, peroxonitric acid, peroxonitrates, peroxocarbonates, peroxoborates, peroxophosphates, peroxy acids, peroxy acid salts, chlorates, bromates, iodates, nitrates, nitrites, and permanganates. (4) A method for treating a trivalent chromium plating film, which comprises treating the trivalent chromium plating film with the post-treatment liquid according to any one of (1) to (3) above.

Advantages of the Invention

[0011] According to the post-treatment liquid and the treatment method for a trivalent chromium plating film of the present invention, excellent corrosion resistance can be imparted without causing a large change in the color tone of the surface of the object to be treated.

Brief Description of the Drawings

[0012] [Figure 1] It is a photograph of the appearance after subjecting a trivalent chromium plating film treated with the post-treatment liquid according to an embodiment of the present invention to a CASS test. [Figure 2] It is a photograph of the appearance after subjecting a trivalent chromium plating film not treated with the post-treatment liquid to a CASS test. [Figure 3] It is a photograph of the appearance after subjecting a trivalent chromium plating film subjected to a conventional electrolytic chromate treatment to a CASS test. [Figure 4] It is a photograph of the appearance after subjecting a trivalent chromium plating film cathodically electrolyzed with the post-treatment liquid according to an embodiment of the present invention to a CASS test.

Modes for Carrying Out the Invention

[0013] Hereinafter, the present invention will be described in detail based on embodiments, but the present invention is not limited to these embodiments.

[0014] ≪Post-treatment Liquid for Trivalent Chromium Plating Film≫ The post-treatment solution of this embodiment is a post-treatment solution used for post-treatment applied to the surface of a trivalent chromium plating film on a part or the like on which a trivalent chromium plating film has been formed.

[0015] Specifically, the post-treatment solution is a post-treatment solution for trivalent chromium plating films that contains an oxidizing agent, phosphate ions, and an ionic surfactant. This post-treatment solution can be obtained, for example, by dissolving or dispersing a conventionally known oxidizing agent, phosphoric acid and / or phosphate, and an ionic surfactant in an aqueous solvent.

[0016] <Oxidizing agent> There are no particular restrictions on the oxidizing agent, and various known ones can be used. For example, one or more chemical species selected from peroxides, persulfuric acid, persulfate, peroxonitrate, peroxonitrate, peroxocarbonate, peroxoborate, peroxophosphate, peroxy acid, peroxyate, chlorate, bromate, iodate, nitrate, nitrite, and permanganate can be used, but are not limited to these. Note that persulfuric acid is sometimes called peroxosulfuric acid, peroxocarbonate is sometimes called percarbonate, and peroxy acid is sometimes called percarboxylic acid.

[0017] The oxidizing agent may also be a mixture or adduct of several of the compounds mentioned above. For example, in addition to Na2C2O6, adducts such as Na2CO3·H2O2·0.5H2O, Na2CO4·H2O2, and 2Na2CO3·3H2O2 are known as sodium salts of peroxocarbonate, and any of these, or mixtures thereof, can be used.

[0018] In the post-treatment solution of this embodiment, it is preferable that the oxidizing agent contains a peroxide. Using the post-treatment solution of this embodiment containing a peroxide makes it easier to achieve superior corrosion resistance and to suppress discoloration of the treated object's appearance.

[0019] Here, peroxide refers to a substance that contains or can generate hydrogen peroxide (H2O2), and in addition to hydrogen peroxide, peroxide ions O2 2-It includes compounds containing, for example, hydrogen peroxide, lithium peroxide, sodium peroxide, potassium peroxide, magnesium peroxide, calcium peroxide, strontium peroxide, barium peroxide, etc., but is not limited thereto. In addition, adduct-type percarbonates such as the above-mentioned Na2CO3·H2O2·0.5H2O, Na2CO4·H2O2, 2Na2CO3·3H2O2 are included in peroxides.

[0020] There is no particular limitation on the concentration of the above oxidizing agent in the post-treatment liquid of this embodiment, and it can be appropriately selected according to the type of the oxidizing agent used, the type of the object to be treated, etc. For example, it may be about 1 to 100 g / L, particularly about 3 to 20 g / L.

[0021] <Phosphate ion> The phosphate ion is not particularly limited. For example, orthophosphate ion (PO4 3- ), metaphosphate ion (P2O6 4- ), phosphite ion (HPO3 2- ), hypophosphite ion (H2PO3 - ), pyrophosphate ion (P2O7 4- ), trimetaphosphate ion (P3O9 3- ), tetrametaphosphate ion (P4O 12 4- ), pyrophosphite ion (H2P2O5 2- ), and furthermore polymetaphosphite ions, etc. can be mentioned, but are not limited thereto. A plurality of phosphate ions may coexist.

[0022] The phosphate ion can be obtained by dissolving a conventionally known phosphoric acid and its salt in an aqueous solvent. Examples of phosphates include alkali metal salts, alkaline earth metal salts, ammonium salts, etc., such as sodium phosphate, potassium phosphate, ammonium phosphate, sodium hydrogen phosphate, potassium hydrogen phosphate, ammonium hydrogen phosphate, etc., but are not limited thereto. Among them, trisodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, magnesium phosphate, magnesium hydrogen phosphate, etc. are preferable.

[0023] There are no particular restrictions on the concentration of phosphate ions in the post-treatment solution of this embodiment, and it can be appropriately selected depending on the oxidizing agent used, the type of material to be treated, etc. For example, it may be 1 to 500 g / L, and especially 10 to 100 g / L.

[0024] <Ionic surfactants> The post-treatment solution for trivalent chromium plating in this embodiment is characterized by containing an ionic surfactant along with an oxidizing agent and phosphate ions. As shown in the examples described later, the inclusion of an ionic surfactant in the post-treatment solution makes it possible to impart excellent corrosion resistance to the workpiece.

[0025] There are no particular restrictions on ionic surfactants; anionic surfactants, cationic surfactants, and amphoteric surfactants can all be used. It is also possible to use multiple types of ionic surfactants in combination.

[0026] [Anionic surfactants] There are no particular restrictions on the anionic surfactant, and conventionally known surfactants can be used. For example, carboxylates such as long-chain fatty acid salts, alkyl hydroxy ether carboxylates, polyoxyethylene alkyl ether carboxylates, and poly(meth)acrylic acid; sulfonates such as long-chain aliphatic sulfonates and alkylbenzene sulfonates; sulfate esters such as sulfate esters of higher alcohols and sulfate esters of higher alcohol ethylene oxide adducts; phosphate esters such as phosphate esters of higher alcohols and phosphate esters of higher alcohol ethylene oxide adducts; and also alkanoyl methyl taulide and carboxylic acid / sulfonates, but are not limited to these. Multiple types of anionic surfactants can also be used in combination.

[0027] More specifically, examples include sodium, potassium, and ammonium salts of fatty acids such as lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, palm fatty acid, coconut fatty acid, olive fatty acid, poly(meth)acrylic acid, and polycarboxylic acid; sodium, potassium, and ammonium salts of lauryl sulfonic acid, dodecylbenzenesulfonic acid, sulfosuccinic acid, and cocoyl isethionic acid; sodium, potassium, and ammonium salts of sulfate esters such as octyl sulfate, 2-ethylhexyl sulfate, decyl sulfate, lauryl sulfate, laureth sulfate, polyoxyethylene alkyl ether sulfate, and polyoxyethylene alkylphenyl ether sulfate; and sodium, potassium, and ammonium salts of oleyl phosphate and polyoxyethylene alkylphenyl ether phosphate ester.

[0028] There are no particular restrictions on the molecular weight of these anionic surfactants; for example, those with a mass-average molecular weight of 100 to 100,000, and especially those with a mass-average molecular weight of around 200 to 70,000, can be used.

[0029] [Cationic surfactants] There are no particular restrictions on the cationic surfactant, and conventionally known surfactants can be used. For example, ammonium (NH4) in the narrow sense. + Examples of ammonium salts include, but are not limited to, salts such as monoalkylammonium salts, dialkylammonium salts, tetraalkylammonium salts, pyridinium salts, fatty acid amide type quaternary ammonium salts, as well as monoalkyl ether type, dialkyl ester type, and benzalkonium type ammonium salts, and amine salts which are neutralized products of higher alkylamines, higher alkylamine ethylene oxide adducts, ethanolamine, etc., as well as amine salts such as fatty acid ester amine salts, fatty acid amide amine salts, and urea condensation amine salts. Multiple types of cationic surfactants can also be used in combination.

[0030] Polyalkyleneimines can also be used as surfactants. Typical examples of polyalkyleneimines include, but are not limited to, linear polyethyleneimines, branched polyethyleneimines, and cyclic polyethyleneimines.

[0031] More specifically, examples include lauryltrimethylammonium chloride, cetyltrimethylammonium chloride, stearyltrimethylammonium chloride, stearylbenzyldimethylammonium chloride, dicocodimonium chloride, benzalkonium chloride, benzethonium chloride, linear polyethyleneimine, branched polyethyleneimine, dicocoylethylhydroxyethylmonium methosulfate, distearoylethylhydroxyethylmonium methosulfate, stearamidopropyldimethylamine, behenamidopropyldimethylamine, and the like.

[0032] There are no particular restrictions on the molecular weight of these cationic surfactants; for example, those with a mass-average molecular weight of 100 to 100,000, and especially those with a mass-average molecular weight of around 200 to 70,000, can be used.

[0033] [Amphoteric surfactants] There are no particular restrictions on the amphoteric surfactant used; conventionally known surfactants can be used. Examples include, but are not limited to, amino acid type and betaine type carboxylate type amphoteric surfactants, sulfate ester type amphoteric surfactants, sulfonate type amphoteric surfactants, and phosphate ester type amphoteric surfactants. Multiple types of amphoteric surfactants can also be used in combination.

[0034] More specifically, examples include sodium cocoamphoacetate, sodium lauroamphoacetate, disodium cocoamphodiacetate, cocamidopropyl betaine, lauramidopropyl betaine, myristamidopropyl betaine, palm kernel fatty acid amidopropyl betaine, lauryl betaine, cocobetaine, lauryl hydroxysultaine, lauramidopropyl hydroxysultaine, cocamidopropyl hydroxysultaine, lauramine oxide, lauramidopropylamine oxide, lecithin, lysolecithin, and the like.

[0035] There are no particular restrictions on the molecular weight of these amphoteric surfactants; for example, those with a mass-average molecular weight of 100 to 100,000, and especially those with a mass-average molecular weight of around 200 to 70,000, can be used.

[0036] [Amount of ionic surfactant] There are no particular restrictions on the concentration of the ionic surfactant in the post-treatment solution of this embodiment, and it can be appropriately selected depending on the oxidizing agent used, the type of material to be treated, etc. For example, it may be 0.01 to 20 g / L, and especially 0.05 to 5 g / L.

[0037] <pH of post-treatment solution> There are no particular restrictions on the pH of the post-treatment solution. However, the pH of the post-treatment solution is preferably in the neutral to acidic range, for example, less than 8.0, more preferably between 2.0 and 7.5, and even more preferably between 3.0 and 6.0. A pH of less than 8.0 in the post-treatment solution makes it easier to suppress the elution of hexavalent chromium.

[0038] The pH of the post-treatment solution can be adjusted by selecting the components used, particularly the type of oxidizing agent and phosphoric acid (salt). For example, a low pH can be achieved by using a large amount of phosphoric acid as a source of phosphate ions, while a high pH can be achieved by using a large amount of trisodium phosphate, etc. Furthermore, the pH may be adjusted by adding acids such as hydrochloric acid, sulfuric acid, nitric acid, and formic acid, bases such as caustic alkali and ammonia water, or even buffering agents.

[0039] <Other additives> The post-treatment solution of this embodiment may contain components other than the oxidizing agent, phosphate ions, and ionic surfactants mentioned above, as well as optional pH adjusters such as acids, bases, and buffers, in amounts of approximately 50 g / L or less, for example, 0.1 to 10 g / L. Examples of additives include hydrogen peroxide decomposition inhibitors such as magnesium sulfate and magnesium phosphate, conductivity imparting agents including conductive salts, hydrogen generation inhibitors, dispersants, dispersion aids, brighteners, antioxidants, viscosity modifiers, wetting agents, dyes, and nonionic surfactants such as polyalkylene glycol compounds.

[0040] <Preparation of post-treatment solution> The post-treatment solution for trivalent chromium plating films in this embodiment can be prepared by dissolving or dispersing the above-mentioned oxidizing agent, phosphate ions, and ionic surfactant, as well as other optional additives, in, for example, an aqueous solvent. There are no particular restrictions on the mixing order of the components. Water is preferred as the aqueous solvent. In addition, as described above, multiple types of the same surfactants can be used in combination as anionic surfactants, cationic surfactants, and amphoteric surfactants.

[0041] <Characteristics of the post-treatment solution according to this embodiment> The post-treatment solution for trivalent chromium plating films of this embodiment provides excellent corrosion resistance to the trivalent chromium plating film while being hexavalent chromium-free, and suppresses color changes on the surface of the treated object. It also has the advantage of making it difficult for hexavalent chromium to leach from the treated object. Therefore, by utilizing the post-treatment solution of this embodiment, chromium-plated products with a good appearance can be easily manufactured without safety and hygiene problems. The post-treatment solution of this embodiment requires less safety and hygiene measures and does not require expensive raw materials, so it can contribute to further simplification and cost reduction of the manufacturing process.

[0042] Although this invention is not limited by any particular theory, one possible reason why the post-treatment solution of this embodiment exhibits excellent corrosion resistance is that the coexistence of ionic surfactants improves the compatibility between the surface of the workpiece and the oxidizing agent and phosphate ions. For example, the ions in the surfactant ionically interact with both the surface of the trivalent chromium plating film and the phosphate ions and oxidizing agent, which may result in the trivalent chromium plating film being treated more uniformly, while the progression of local oxidation is suppressed, leading to excellent corrosion resistance. Furthermore, since it does not need to contain transition metal ions like chromate treatment solutions, it is thought that it is less likely to change the color tone of the surface of the workpiece.

[0043] ≪Treatment method for trivalent chromium plating≫ The method for treating a trivalent chromium plating film according to this embodiment is characterized by treating the trivalent chromium plating film using the post-treatment solution described above. Specifically, the trivalent chromium plating film can be treated by bringing the workpiece into contact with the post-treatment solution, for example, by immersing it in the post-treatment solution. Alternatively, the workpiece can be treated by pouring the post-treatment solution over the surface of the trivalent chromium plating film. Or, the trivalent chromium plating film may be treated by applying an electric current to the workpiece, an electrolytic treatment, for example, a cathode electrolytic treatment. Among these methods, immersion treatment is preferred because it is easy to operate and there is no variation in treatment due to the current density distribution.

[0044] <Immersion Treatment Conditions> There are no particular restrictions on the conditions for the immersion treatment, and any conditions can be set depending on the composition of the post-treatment solution used and the type of workpiece. For example, the trivalent chromium plating film may be treated by immersing the workpiece in a post-treatment solution at a liquid temperature of 25 to 60°C, particularly 30 to 50°C, for 15 seconds to 10 minutes, particularly 30 seconds to 5 minutes. If the liquid temperature is below 25°C, the treatment may take longer, and if the immersion time is less than 15 seconds, the treatment may be insufficient, making it difficult to achieve good corrosion resistance. On the other hand, if the liquid temperature exceeds 60°C, it may lead to increased costs for maintaining the liquid temperature and deterioration of the working environment due to the volatilization of the oxidizing agent. The amount of post-treatment solution (immersion solution) used during immersion is preferably 5 to 200 times, particularly 10 to 100 times, by volume relative to the workpiece. In addition, during the immersion treatment, the treatment solution may be stirred by an agitator or air, or the workpiece may be oscillated by an agitator.

[0045] <Electrolytic treatment conditions> The conditions for electrolytic treatment are not particularly limited, and normal electrolytic treatment conditions can be used. For example, the liquid temperature can be set to 25-60°C, especially 30-50°C, and the cathode current density to 0.01-5 A / dm². 2 Degree, especially 0.01~1A / dm 2 The electrolytic treatment should ideally last 30 seconds to 20 minutes, particularly 5 to 10 minutes. During the electrolytic treatment, it is preferable to stir the treatment solution and agitate the workpiece. From the viewpoint of suppressing hexavalent chromium, a titanium anode coated with iridium oxide is preferred for use.

[0046] <Object to be processed> The workpiece to which the processing method of this embodiment is applied can be any article that has a trivalent chromium plating film. For example, it can be applied to a variety of articles, such as household goods including plumbing fixtures such as faucets and shower heads, building components such as doorknobs and handrails, automobile parts such as front grilles, emblems and interior parts for automobiles, and electrical and electronic equipment components such as buttons used in mobile phones. There are no particular restrictions on the shape, size, or material as long as it has a trivalent chromium plating film. For example, it is possible to use materials that have been subjected to electroless plating or metal vapor deposition followed by trivalent chromium plating, as well as various metal materials and conductive ceramic materials.

[0047] Prior to contacting the workpiece with the post-treatment solution, the workpiece may be subjected to surface cleaning, alkaline degreasing, etching, etc. Furthermore, it is preferable to wash the workpiece with water or the like and dry it after contact with the post-treatment solution.

[0048] The method for treating trivalent chromium plating films according to this embodiment provides excellent corrosion resistance to the trivalent chromium plating film while being hexavalent chromium-free, and suppresses color changes on the surface of the treated object. It also has the advantage of making it difficult for hexavalent chromium to leach from the treated object. Therefore, it is particularly useful when improving the corrosion resistance of articles where safety and hygiene are required. Furthermore, the treatment method of this embodiment does not require expensive equipment and can be performed simply, making it beneficial from the standpoint of reducing costs and working time. [Examples]

[0049] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0050] [Example 1] (Preparation of post-treatment solution) To 1 liter of water, 8 mL of 35% hydrogen peroxide as an oxidizing agent, 80 g of sodium dihydrogen phosphate, 5 g of magnesium phosphate, and 0.1 g of sodium 2-ethylhexyl sulfate as an anionic surfactant were added and stirred to prepare a post-treatment solution for trivalent chromium plating. The pH of the resulting post-treatment solution was 4.0.

[0051] (Immersion treatment) As the material to be treated, a plate-shaped sample (60 × 100 × 0.4 mm) was prepared, consisting of a brass plate coated with nickel plating (film thickness 10 μm) and trivalent chromium plating (film thickness 0.10 μm). This sample was immersed in the above-mentioned post-treatment solution, maintained at 40°C, for 60 seconds while being agitated with 0.5 L / min of air. The sample was then removed, washed with water, and dried to obtain the treated sample, which was then subjected to the following evaluation test.

[0052] (Evaluation of color changes) For the surface of the trivalent chromium plating film of the treated sample, a colorimeter was used in accordance with JIS Z 8729, L * a * b * The chromaticity of the color system was measured. The same measurement was performed on the surface of an untreated trivalent chromium-plated film. This was subtracted from the chromaticity values ​​of the treated samples to calculate the change in chromaticity and evaluate the degree of change in color tone. The measurement results are shown in Table 1 below.

[0053] (Evaluation of corrosion resistance) Corrosion resistance was evaluated by the CASS test in accordance with JIS H8502. An aqueous solution containing 50±5 g / L of sodium chloride and 0.26±0.02 g / L of cupric chloride (CuCl2·2H2O), with the pH adjusted to 3.0-3.2 with acetic acid, was sprayed onto the sample for 80 hours under the following conditions. A photograph of the treated sample after spraying is shown in Figure 1, and the rating number (RN) is shown in Table 1 below. ·Spray amount: 1.5±0.5ml / 80cm 2 / h • Temperature inside the test chamber: 50±2℃ • Saltwater tank temperature: 50±2℃ • Air saturator temperature: 63±2℃ • Compressed air pressure: 70~167kPa

[0054] [Contrastive example] The same trivalent chromium-plated sample used in Example 1 was evaluated for RN in the same manner as in Example 1, without treatment with the post-treatment solution (untreated). The evaluation results are shown in Table 1 below. A photograph of the sample's appearance after the CASS test is shown in Figure 2.

[0055] [Example 2] The same procedure as in Example 1 was followed, except that a cationic polyethyleneimine (linear, molecular weight 70,000) was used as the surfactant. The results of the chromaticity change and RN evaluation are shown in Table 1 below.

[0056] [Comparative Example 1] The same procedure as in Example 1 was followed, except that nonionic ethylene glycol was used as the surfactant. The evaluation results for chromaticity change and RN are shown in Table 1 below.

[0057] [Example 3] The same procedure as in Example 1 was followed, except that an anionic polyacrylic acid (molecular weight 5000) was used as the surfactant. The results of the chromaticity change and RN evaluation are shown in Table 1 below.

[0058] [Comparative Example 2] To 1 liter of water, 100 mL of ECR-500 (manufactured by JCU Corporation) was added and stirred to prepare an electrolytic chromate treatment solution using anhydrous chromic acid. The pH of the resulting treatment solution was 4.0. This treatment solution was maintained at 40°C, and the same trivalent chromium plated sample used in Example 1 was immersed in it to a temperature of 0.1 A / dm². 2 A 1-minute cathode electrolytic treatment was performed. The evaluation results are shown in Table 1 below. A photograph of the sample's appearance after the CASS test is shown in Figure 3.

[0059] [Table 1]

[0060] In Examples 1-3, which were treated with immersion in a post-treatment solution containing an ionic surfactant, the RN values ​​after the CASS test were high (Table 1), and almost no surface corrosion was observed (Figure 1: the difference from the CASS test results of the control example shown in Figure 2 is clear), demonstrating excellent corrosion resistance. Furthermore, the change in color tone due to the treatment was also small.

[0061] On the other hand, in Comparative Example 1, which used a post-treatment solution containing a nonionic surfactant, the color change after treatment was small, but the RN value was the same as the untreated control sample, indicating insufficient corrosion resistance. Furthermore, in the sample of Comparative Example 2, which underwent conventional electrolytic chromate treatment, the corrosion resistance was sufficient, but the color change was significant (Figure 3).

[0062] [Examples 4-5] The same procedure as in Example 1 was followed, except that a cationic benzethonium chloride (Example 4) or an anionic polycarboxylic acid copolymer (Example 5) was used as the surfactant. The results of the chromaticity change and RN evaluation are shown in Table 2 below.

[0063] [Comparative Example 3] The same procedure as in Example 1 was followed, except that a nonionic polyvinylpyrrolidone (molecular weight 10,000) was used as the surfactant. The results of the chromaticity change and RN evaluation are shown in Table 2 below.

[0064] [Example 6] The procedure was the same as in Example 5, except that 10.0 g of sodium percarbonate (2Na2CO3·3H2O2) was used as the oxidizing agent instead of hydrogen peroxide. The results of the chromaticity change and RN evaluation are shown in Table 2 below.

[0065] [Example 7] The same trivalent chromium plated sample used in Example 1 was immersed in the same treatment solution used in Example 6, at a rate of 0.1 A / dm 2Cathodic electrolysis was performed on the sample for 8 minutes. The chromaticity change and RN of the treated sample were evaluated in the same manner as in Example 1. The evaluation results are shown in Table 2 below. A photograph of the appearance of the sample after the CASS test is shown in Figure 4.

[0066] [Table 2]

[0067] In Examples 4-6, which used post-treatment solutions containing different types of ionic surfactants or oxidizing agents than those used in Example 1, excellent corrosion resistance was observed, similar to Examples 1-3, and the change in color due to the treatment was minimal. Similarly, in Example 7, which underwent cathodic electrolysis, excellent corrosion resistance was also observed (Figure 4: the difference from, for example, Figure 2 is clear), and the change in color due to the treatment was minimal.

[0068] On the other hand, in Comparative Example 3, which used a post-treatment solution containing a nonionic surfactant, the corrosion resistance was not sufficient, and the color change was greater compared to Examples 4-6.

[0069] [Examples 8-13] The trivalent chromium plating film was post-treated in the same manner as in Example 1, except that the pH was adjusted to 3.0-10.0 by adding phosphoric acid or sodium hydroxide to the post-treatment solution. The post-treated samples were subjected to a pack test based on the color development principle of the diphenylcarbazide spectrophotometric method according to JIS K 0102 65.2.1, and the concentration of hexavalent chromium eluted into water was measured. The test results are shown in Table 3 below.

[0070] [Table 3]

[0071] Table 3 shows that post-treatment solutions containing an oxidizing agent, phosphate ions, and an ionic surfactant can suppress the elution of hexavalent chromium from treated samples over a wide pH range of 3.0 to 10.0. In particular, lowering the pH of the post-treatment solution to below 8.0 allowed for more reliable suppression of hexavalent chromium elution.

Claims

1. Contains an oxidizing agent, phosphate ions, and an ionic surfactant. A post-treatment solution for trivalent chromium plating films.

2. The pH is less than 8.

0. The post-treatment liquid according to claim 1.

3. The oxidizing agent comprises one or more chemical species selected from peroxides, persulfuric acid, persulfates, peroxonitrates, peroxonitrates, peroxocarbonates, peroxoborates, peroxophosphates, peroxy acids, peroxyates, chlorates, bromates, iodates, nitrates, nitrites, and permanganates. The post-treatment liquid according to claim 1 or 2.

4. The trivalent chromium plating film is treated with the post-treatment solution described in claim 1 or 2. A method for treating trivalent chromium plating films.

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