Evaluation method and film thickness control method for chemical conversion treated coatings

Abstract

This invention provides a method for evaluating a chemical conversion coating applied to a zinc-based plating. [Solution] An evaluation method characterized by contacting an analytical solution containing a metal element nobler than zinc with the surface of a zinc-plated member having a chemical conversion coating, and obtaining information regarding the thickness of the chemical conversion coating based on the change in appearance of the surface having the chemical conversion coating, wherein the analytical solution may contain copper, may be acidic, and it is preferable that the pH of the analytical solution is 2.0 to 4.0.

Description

Technical Field

[0005]

[0001] The present invention relates to an evaluation method for obtaining information on the film thickness of a chemical conversion coating film on zinc plating and zinc alloy plating (collectively referred to as "zinc-based plating" in the present disclosure), and a film thickness management method for a chemical conversion coating film using such a method.

Background Art

[0002] For a member applied with zinc-based plating (referred to as a "zinc-based plated member" in the present disclosure), a chemical conversion treatment is often performed to improve corrosion resistance and appearance, and a chemical conversion coating film is often provided on the zinc-based plating. The film thickness of the chemical conversion coating film provided on this zinc-based plated member varies depending on the treatment equipment, the concentration and pH of the treatment solution, the treatment time, the treatment temperature, and the like. Therefore, in order to stabilize the film thickness of the chemical conversion coating film, accurate management of the composition of the treatment solution and treatment conditions is required. In addition, the film thickness of the chemical conversion coating film may also be affected by the state of the zinc-based plating that is the base of the chemical conversion treatment.

[0003] When the film thickness of the chemical conversion coating film deviates excessively from a predetermined range, it may cause insufficient corrosion resistance and changes in appearance in the zinc-based plated member. When the degree of insufficient corrosion resistance and the degree of change in appearance are large, the zinc-based plated member after the chemical conversion treatment may become a defective product.

[0004] As a method for analyzing the film thickness of a chemical conversion coating film, there are a method of performing cross-sectional observation by TEM (transmission electron microscope), and a method of analyzing elements in the depth direction while sputtering the surface, such as XPS (X-ray photoelectron spectroscopy) and GD-OES (glow discharge optical emission surface analysis method) (for example, Patent Document 1, Patent Document 2).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

[0006] Measuring the film thickness of chemical conversion coatings using the above analysis method requires large-scale measuring equipment, including a vacuum pump. Furthermore, because the film thickness is at the tens to hundreds of nanometers level, the installation location must be prepared to maintain an appropriate measurement environment, including vibration and temperature. A preparation process to shape the test specimens to suit measurement by the measuring equipment is also essential. Moreover, as mentioned above, the film thickness of chemical conversion coatings is particularly thin, requiring advanced skills from the operator, such as identifying the measurement location on the test specimen.

[0007] In view of the current situation, the present invention provides a method for obtaining information regarding the thickness of a chemical conversion coating applied to a zinc-plated member without using a large-scale measuring device, and a method for managing the thickness of a chemical conversion coating using this method. [Means for solving the problem]

[0008] In order to solve the above problems, the inventors conducted research and obtained the following findings. Specifically, by dropping an analytical solution containing a metal element nobler than zinc onto a chemical conversion treatment film on a zinc-based plating, the chemical conversion treatment film dissolves, and the zinc-based plating covered by the chemical conversion treatment film comes into contact with the analytical solution. Through this contact, the component containing the noble metal element in the analytical solution chemically reacts with the zinc-based plating, resulting in the substitution deposition of the noble metal element onto the zinc plating.

[0009] Thus, for displacement precipitation to occur, the chemical conversion coating must be dissolved, and the amount of substance (precipitate) produced by displacement precipitation tends to increase in proportion to the increased contact time with the analytical solution. Therefore, the contact time between the analytical solution and the zinc-plated component, and the appearance of the zinc-plated component after contact, contain information about the thickness of the chemical conversion coating. Thus, by determining the time until displacement precipitation occurs and by checking the appearance of the precipitate using visual inspection or a spectrophotometer, the approximate thickness of the chemical conversion coating can be determined, and this can be used to manage the thickness of the chemical conversion coating in factories performing zinc-plated processes. Note that the properties of the analytical solution, such as pH, affect the time until displacement precipitation occurs and the amount of precipitate.

[0010] Based on the above findings, the completed present invention is as follows: (1) An evaluation method characterized by contacting an analytical solution containing a metal element nobler than zinc with the surface of a zinc-plated member having a chemical conversion coating, and obtaining information regarding the thickness of the chemical conversion coating based on the change in appearance of the surface having the chemical conversion coating. (2) The evaluation method according to (1) above, wherein the analytical solution contains copper element. (3) The evaluation method described in (1) above, wherein the analytical solution is acidic. (4) The evaluation method described in (1) above, wherein the pH of the analytical solution is 2.0 to 4.0. (5) The evaluation method described in (1) above for quantitatively or semi-quantitatively evaluating the change in appearance. (6) A method for controlling the thickness of a chemical conversion coating applied to a zinc-plated member, using any of the evaluation methods described in (1) to (5) above. [Effects of the Invention]

[0011] The present invention provides a simple method for evaluating the film thickness of a chemical conversion coating applied to a zinc-plated member. This makes it easier to manage the film thickness of the chemical conversion coating in factories performing zinc-plated processes, allowing for prompt countermeasures to be taken when defects occur due to insufficient or excessive film thickness. In other words, it improves the responsiveness to defects in the chemical conversion process, thereby reducing the occurrence of defective zinc-plated members. [Modes for carrying out the invention]

[0012] Embodiments of the present invention will be described below.

[0013] The analytical solution according to this embodiment contains one or more metal elements nobler than zinc (hereinafter also referred to as "analytical metal elements") in a form that can be dissolved in the analytical solution. Specific examples of analytical metal elements include gold, silver, copper, lead, nickel, cobalt, platinum, mercury, tin, vanadium, tungsten, molybdenum, and manganese.

[0014] The analytical solution according to this embodiment, upon contact with the surface of a zinc-plated member, dissolves the chemical conversion coating, that is, it dissolves the metal (including alloy) components contained in the chemical conversion coating into the analytical solution, and further dissolves the zinc contained in the zinc-plated coating, causing displacement deposition in which an insoluble substance containing the analytical metal element is deposited on the zinc-plated member. Hereinafter, this displacement-deposited insoluble substance will also be referred to as "analytical metal-containing precipitate." The analytical metal-containing precipitate generally consists mainly of the metal (including alloy) of the analytical metal element, but may also contain compounds containing the analytical metal element, such as hydroxides of the analytical metal element.

[0015] Considering the availability of the analytical metal element according to this embodiment, the stability of the solvent-soluble substance containing the analytical metal element (hereinafter also referred to as "analytical metal-containing solute") in the analytical solution (ability to maintain an appropriate state of dissolution), the safety of the analytical metal-containing solute and analytical metal-containing precipitates to the human body and the environment, and the ease of evaluating the appearance of analytical metal-containing precipitates formed on zinc-plated members, it is preferable to use copper as the analytical metal element. When the analytical metal element contains copper, analytical metal-containing precipitates are more likely to form when the analytical solution comes into contact with the zinc-plated member, thus reducing the time required for analysis and making it easier to evaluate changes in appearance.

[0016] The form of the metal-containing solute for analysis in the analytical solution is not limited, as long as it can produce metal-containing precipitates for analysis upon contact between the analytical solution and the zinc-plated component. For example, it may be a solvated ion such as a hydrated copper ion formed as a result of the inclusion of copper sulfate, a complex ion such as a hexachloroplatinate ion, or an oxygenate ion such as a tungstate ion or a molybdate ion (in this case, the metal-containing precipitate for analysis may include metal oxides or metal hydroxides).

[0017] The content of the metal-containing solute in the analytical solution, expressed in terms of the elemental content of the metal (unit: mol / L, hereinafter sometimes abbreviated as "metal content"), is set appropriately according to the type of metal-containing solute so that a metal-containing precipitate is formed within a predetermined time when the analytical solution comes into contact with the zinc-plated component.

[0018] As a non-limiting example, in some cases, the metal content is preferably 0.1 g / L or more and 10 g / L or less. When the metal content is excessively low, the substitution rate between the metal elements contained in the chemical conversion coating of the zinc-based plating member and the metal elements for analysis becomes slow, so it is difficult for metal-containing precipitates for analysis to occur, and there is a concern that it may be difficult to evaluate the appearance change by visual inspection or a spectrocolorimeter. When the metal content is excessively high, metal-containing precipitates for analysis are likely to occur excessively, and the generated metal-containing precipitates for analysis may fall off from the zinc-based plating. In this case, there is a concern that the accuracy of the appearance change evaluation may decrease. If the appearance evaluation becomes difficult or the accuracy decreases, it becomes difficult to appropriately obtain information on the thickness of the chemical conversion coating of the zinc-based plating member from the result of the appearance evaluation.

[0019] From the viewpoint of ease of evaluating the appearance change by visual inspection or a spectrocolorimeter, in some cases, the metal content is preferably 0.3 g / L or more and 7 g / L or less, and in more preferable cases, it is 0.5 g / L or more and 5 g / L or less.

[0020] The above analysis solution is adjusted to a pH at which the chemical conversion coating on the zinc-based plating can be dissolved, and the specific pH of the analysis solution is set based on the composition of the analysis solution and the like. Considering the solubility of metal elements nobler than zinc and the work safety, etc., the analysis solution according to the present embodiment is preferably acidic. Specifically, from the viewpoint of allowing the dissolution of the chemical conversion coating to proceed at an appropriate rate, the pH of the analysis solution may preferably be 1.0 to 6.0, more preferably 1.5 to 5.0, and particularly preferably 2.0 to 4.0.

[0021] For example, when the pH is relatively high, specifically in the vicinity of neutrality, the degree of dissolution of the chemical conversion coating by the analysis solution decreases, and in some cases, the chemical conversion coating may not be substantially dissolved. In such cases, it becomes difficult for the metal element for analysis to substitute and precipitate with the metal element contained in the chemical conversion coating, and there is concern that the time required for analysis may become longer. If the pH deviates excessively from the appropriate range, dissolution of the chemical conversion coating and precipitation of the metal-containing precipitate for analysis occur instantaneously regardless of the thickness of the chemical conversion coating, and it may be difficult to manage by methods such as visual inspection. Thus, when the pH setting in the analysis solution is excessively inappropriate, it becomes difficult to appropriately obtain information regarding the thickness of the chemical conversion coating of the zinc-based plating member from the results of the appearance evaluation.

[0022] Examples of the acid for adjusting the pH of the analysis solution include inorganic acids such as hydrochloric acid, nitric acid, sulfuric acid, and phosphoric acid, and organic acids such as citric acid, malic acid, acetic acid, and formic acid. Examples of the base for adjusting the pH of the analysis solution include inorganic bases such as sodium hydroxide, potassium hydroxide, and ammonia, and organic bases such as amines. The acid or base for adjusting the pH may be composed of only one type of acid or base, or may be composed of a plurality of types. In addition, the acid or base blended for adjusting the pH and the metal element for analysis may form a complex. In some cases, the stability of the analysis solution is improved by forming such a complex.

[0023] The solvent in the analysis solution is appropriately set according to the type of the metal-containing solute for analysis, and a typical solvent is water. When the solvent in the analysis solution is mainly composed of water, it may contain a polar solvent such as alcohol.

[0024] The specific method for the contact step, in which the analytical solution is brought into contact with a zinc-plated member having a chemical conversion coating to precipitate an analytical metal-containing precipitate, is arbitrary. The analytical solution may be directly dropped onto the surface of the zinc-plated member having the chemical conversion coating using a dropper or the like, or a reaction may be initiated by attaching filter paper or the like soaked in the analytical solution to the surface of the zinc-plated member having the chemical conversion coating, or the zinc-plated member having the chemical conversion coating may be immersed in the analytical solution.

[0025] Methods for evaluating changes in appearance of a zinc-plated component with a chemical conversion coating in contact with an analytical solution include visual inspection and evaluation using analytical instruments such as a spectrophotometer. When evaluating changes in appearance visually, it is possible to semi-quantitatively evaluate the changes in appearance by preparing comparison samples in advance and comparing them. When using analytical instruments, the changes in appearance can be quantitatively evaluated by extracting numerical data from the analysis results.

[0026] In the evaluation method according to this embodiment, information regarding the film thickness of the chemical conversion coating is obtained from the evaluation results of the above-mentioned changes in appearance. Information regarding the film thickness of the chemical conversion coating may also be obtained by quantitatively or semi-quantitatively evaluating the changes in appearance while keeping the conditions of the contact process (composition of the analytical solution, contact time, contact temperature, etc.) constant. Alternatively, information regarding the film thickness of the chemical conversion coating may be obtained using the conditions of the contact process as a variable. As a specific example of such an evaluation method, the contact time is used as a variable, and the time it takes for the appearance of the part of the zinc-plated member where the analytical metal-containing precipitate has formed to reach a predetermined state (for example, becoming the same color tone as a comparison sample) is measured, and information regarding the film thickness is obtained from this time.

[0027] In the method for controlling the film thickness of a chemical conversion coating according to this embodiment, the film thickness of the chemical conversion coating applied to a zinc-plated member is controlled using the evaluation method for changes in the appearance of the zinc-plated member described above. The evaluation items and criteria for controlling the film thickness are set as appropriate according to the evaluation method described above.

[0028] When evaluation is performed visually or using the analytical instruments described above, including comparison with a reference material, it is preferable to make the condition of the material being evaluated before the contact process as similar as possible to that of the reference material. Specifically, it is preferable that the surface condition of the material before zinc plating, the type of zinc plating bath, the type of chemical conversion treatment, and the treatment chemicals used are the same for both the material being evaluated and the reference material, and that the evaluation is performed according to a consistent standard. When comparing materials with different types of chemical conversion treatments and treatment chemicals, the appearance of the chemical conversion coating before the contact process may differ from the appearance of the reference material. In such cases, it may affect the visual evaluation or the measurement results of the analytical instruments described above.

[0029] Furthermore, if there are multiple components to be evaluated, it is preferable to use the same analytical solution. If the analytical metal-containing solute or pH in the analytical solution differs, the appearance of the substituted and precipitated analytical metal may differ. In such cases, it may affect visual evaluation and the measurement results of the analytical instruments mentioned above.

[0030] A method for manufacturing a zinc-plated member and a chemical conversion coating provided thereon according to one embodiment of the present invention comprises a plating step and a chemical conversion treatment step, which will be described below.

[0031] In the plating process, a zinc-based plating layer is formed on the substrate to obtain a zinc-plated member comprising the substrate and the zinc-based plating layer. The substrate is made of, for example, an iron-based material and is manufactured by rolling, casting, extrusion, etc., and its shape is created by machining such as rolling, cutting, and pressing, or by forming. The zinc-based plating layer may be formed by electroplating or by other methods.

[0032] The chemical conversion treatment process involves bringing a workpiece, which has a zinc-based plating layer formed on a substrate, into contact with a chemical conversion treatment solution, and then washing the workpiece to form a chemical conversion treatment film on it. Examples of methods for contacting the workpiece with the chemical conversion treatment solution include immersion in the chemical conversion treatment solution and spraying the chemical conversion treatment solution onto the workpiece. [Examples]

[0033] The effects of the present invention will be described below based on examples, but the present invention is not limited thereto.

[0034] The analysis targets 1 to 5 were prepared under the following conditions. (1) Base material: Iron-based material (steel plate measuring 100mm x 50mm, 0.8mm thick) (2) Zinc-based plating layer: Electro-zinc plating (Yuken Kogyo Co., Ltd. "Metas FZ-77A1 (primary brightener) / GC1 (secondary brightener)"), plating thickness 10 μm (3) Chemical treatment solution: "Metas YFA-CFA / CFB / HR" and "Metas YFA-M / 30HR" manufactured by Yuken Kogyo Co., Ltd. These chemicals were prepared at the concentrations listed in Table 1. (4) Chemical conversion treatment: The zinc-plated material was immersed in a chemical conversion treatment solution at 40°C for the treatment time shown in Table 1 (bubbling during immersion), then rinsed with water (rinsed with stagnant water followed by running water washing) and dried (80°C, 10 minutes).

[0035] The chemical treatment of the materials to be analyzed was carried out under the following conditions. [Table 1]

[0036] The film thickness of the chemical conversion coating on each component under analysis was measured from the surface in the depth direction using GD-OES (HORIBA's "GD-Profiler 2"). With GD-OES, the measurement results are expressed as the detection intensity (V) of each element contained in the coating and the detection time (seconds). Since the main component of all chemical conversion coatings in this example is Cr, the detection time (seconds) at which the detected Cr intensity was 10V or higher (a detection intensity that confirms the presence of sufficient Cr) was calculated, and the results are shown in Table 2.

[0037] When chemical conversion treatment solutions are applied under the same conditions of composition, pH, and temperature, the resulting chemical conversion coatings can be considered to be of the same quality. In GD-OES, the detection time is calculated by analyzing components detected while sputtering in the depth direction of the chemical conversion coating. Therefore, the detection time required to detect a specific component from a homogeneous chemical conversion coating can be considered to be proportional to the thickness of the chemical conversion coating. In other words, the results in Table 2 show that the chemical conversion coatings on analyzed members 1 to 3 are thicker in the order of member 1, 2, and 3, and that member 5 has a thicker chemical conversion coating than member 4 and 5.

[0038] [Table 2]

[0039] The analytical solutions were prepared under the conditions shown in Table 3 below.

[0040] [Table 3]

[0041] (Example 1) For each of the analyte components 1-3, 0.07 ml of analysis solution 1 or 2 was added dropwise using a dropper. After the adhesion time indicated in Table 4 below had elapsed, the added solution was wiped off, rinsed with running water, and then dried with a hairdryer. The appearance of the application area was evaluated visually and using the SCI-L value obtained with a spectrophotometer (Konica Minolta: CM-700D).

[0042] Visual evaluation was performed according to the following criteria. A: The entire dropper area is blackened. B: The area where the drop is placed is discolored but remains gray, or partially blackened. C: Almost no effect observed in the dripping area. The evaluation results are shown in Table 4 below.

[0043] [Table 4]

[0044] Table 2 shows that in the above test, the thickness of the chemical conversion coating increased in the order of 1, 2, and 3 for the analyzed components 1-3. As shown in Table 4, with the same adhesion time, the SCI-L value of the colorimeter tended to increase as the thickness of the chemical conversion coating of the analyzed components increased, and the change in appearance tended to be smaller in visual evaluation. A longer adhesion time tended to result in a smaller SCI-L value and a larger change in appearance.

[0045] (Example 2) For each of the analyte components 4-5, 0.07 ml of analysis solution 1 or 2 was added dropwise using a dropper. After the adhesion time indicated in Table 5 below had elapsed, the added solution was wiped off, rinsed with running water, and then dried with a hairdryer. The appearance of the application area was evaluated visually and using the SCI-L value obtained with a spectrophotometer (Konica Minolta: CM-700D).

[0046] Visual evaluation was performed according to the following criteria. A: The entire dropper area is blackened. B: The area where the drop is placed is discolored but remains gray, or partially blackened. C: Almost no effect observed in the dripping area. The evaluation results are shown in Table 5 below.

[0047] [Table 5]

[0048] From the results in Table 2, in the above test, the chemical conversion coating thickness was greater for analyzed component 5 than for analyzed component 4. As shown in Table 5, analyzed component 5, which had a thicker chemical conversion coating, tended to have a higher SCI-L value on the colorimeter at the same adhesion time, and also tended to show less change in appearance in visual evaluation. Longer adhesion times tended to result in lower SCI-L values ​​and greater changes in appearance in visual evaluation.

[0049] (Example 3) For each of the analyte components 4 and 5, 0.07 ml of analytical solution 3 was added dropwise using a dropper. After the adhesion time indicated in Table 6 had elapsed, the added solution was wiped off, the components were rinsed with running water, and then dried with a hairdryer. The appearance of the adhesion area was evaluated visually and using the SCI-L value obtained with a spectrophotometer (Konica Minolta: CM-700D).

[0050] Visual evaluation was performed according to the following criteria. A: The entire dropper area is blackened. B: The area where the drop is placed is discolored but remains gray, or partially blackened. C: Almost no effect observed in the drip area. The evaluation results are shown in Table 6 below.

[0051] [Table 6]

[0052] From the results in Table 2, comparing the analyzed components 4 and 5 in the above test, component 5 had a thicker chemical conversion coating. As shown in Table 6, at the same adhesion time, the thicker the chemical conversion coating of the analyzed component, the greater the SCI-L value of the colorimeter tended to be, and the smaller the change in appearance in visual evaluation was observed. The longer the adhesion time, the smaller the SCI-L value and the larger the change in appearance in visual evaluation tended to be.

[0053] (Example 4) 0.07 ml of analytical solution 4 was added dropwise to each of the target components 4 or 5 using a dropper. After the adhesion time indicated in Table 7 had elapsed, the added liquid was wiped off, rinsed with running water, and then dried. The appearance of the adhesion area was evaluated visually and using the SCI-L value measured with a spectrophotometer (Konica Minolta: CM-700D). Visual evaluation was performed according to the following criteria. A: The entire dropping area is covered with precipitate. B: The dropping area is partially covered with precipitates. The evaluation results are shown in Table 7 below.

[0054] [Table 7]

[0055] Comparing the analyzed components 4 and 5 in the above test, component 5 had a thicker chemical conversion coating. As shown in Table 7, at the same adhesion time, component 5, which had a thicker chemical conversion coating, tended to have a higher SCI-L value on the colorimeter, and visual evaluation also showed a tendency for smaller changes in appearance. Longer adhesion times tended to result in lower SCI-L values ​​and larger changes in appearance in visual evaluation.

Claims

1. An evaluation method characterized by contacting an acidic analytical solution containing a metal element nobler than zinc with the surface of a zinc-plated member having a chemical conversion coating, and obtaining information regarding the thickness of the chemical conversion coating based on the change in the appearance of the surface having the chemical conversion coating.

2. The evaluation method according to claim 1, wherein the analytical solution contains the element copper.

3. The evaluation method according to claim 1, wherein the pH of the analytical solution is 2.0 to 4.

0.

4. The evaluation method according to claim 1, which quantitatively or semi-quantitatively evaluates the aforementioned change in appearance.

5. A method for controlling the thickness of a chemical conversion coating applied to a zinc-plated member, using an evaluation method from any one of claims 1 to 4.

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