Method for measuring the wax concentration of paint, coating method, and method for manufacturing surface-treated steel sheets.

Abstract

Provided are a method for measuring the wax concentration of a paint, a coating method, and a method for manufacturing a surface-treated steel sheet, which can measure the wax concentration contained in the paint at a point before applying the coating to the target material to be coated. 【Solution means】A solid content extraction step (step S101) of heating the paint to extract a solid containing wax, a wax extraction step (step S102) of immersing the solid in an organic solvent to obtain a wax extract, an analysis step (step S103) of analyzing the wax extract, and a calculation step (step S104) of calculating the wax concentration from the analysis results, and the heating conditions of the solid content extraction step satisfy the following. T W +20 ≦ T ≦ T W +70 90 ≦ t ≦ 150 T W +130 < T + t < T W +190 T is the heating temperature (°C), T W is the melting point of the wax (°C), and t is the heating time (minutes).

Description

[Technical Field]

[0001] This invention relates to a method for measuring the wax concentration of a paint, a coating method, and a method for manufacturing a surface-treated steel sheet. [Background technology]

[0002] For example, surface-treated steel sheets (hereinafter sometimes simply referred to as steel sheets) with a wax-containing coating applied to their surface are known. The amount of wax adhering to the steel sheet is an indicator that directly affects the workability of the steel sheet. Therefore, in order to determine whether the manufactured steel sheet meets the design-defined characteristics, there is a need for a technology that can easily and accurately measure the amount of wax adhering to the surface of the steel sheet.

[0003] Conventionally, a typical method for measuring the amount of wax adhering to the surface of a steel plate is to cut a test piece of a certain area from a steel plate coated with a wax-containing paint, and then measure the amount of wax adhering to the test piece by leaching it out (hereinafter referred to as the conventional method). In this conventional method, the test piece is immersed in an organic solvent to leach out the wax, and the amount of leached wax is measured optically. Examples of organic solvents include paint thinner, acetone, carbon tetrachloride, hexane, alcohols, and chloroform.

[0004] Another method for measuring the amount of wax adhering to the surface of a steel plate is disclosed in Patent Document 1. In the method disclosed in Patent Document 1, a metal strip is heat-treated at a specific temperature to remove the wax applied to the metal strip, and the amount of wax adhering is measured from the difference in carbon intensity of fluorescent X-rays of the metal strip before and after heat treatment. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2006-242579 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] In conventional methods, the evaluation of whether a steel sheet meets the design-defined characteristics is performed after a paint film is formed on the steel sheet. In other words, in conventional methods, it is not possible to evaluate whether the paint has a wax concentration that allows for the production of a steel sheet with the design-defined characteristics until after the steel sheet has been manufactured using the paint. Therefore, if the paint has a wax concentration that does not allow for the production of a steel sheet with the design-defined characteristics, the production yield of the steel sheet may deteriorate. The same situation applies to the method disclosed in Patent Document 1.

[0007] The present invention was made to solve the above problems and aims to provide a method for measuring the wax concentration of a paint, a coating method, and a method for manufacturing a surface-treated steel sheet, which can measure the wax concentration contained in the paint before it is applied to the material to be coated. [Means for solving the problem]

[0008] The means to solve the above problems are as follows: [1] A method for measuring the wax concentration of a paint, comprising: a solid content extraction step of heating a liquid paint containing wax to extract the solid content containing the wax as a solid from the paint; a wax extraction step of immersing the solid content in an organic solvent to extract the wax from the solid content to obtain a wax extract; an analysis step of performing a spectroscopic analysis of the wax extract; and a calculation step of calculating the wax concentration of the paint from the results of the spectroscopic analysis of the wax extract, wherein the heating conditions when heating the paint in the solid content extraction step satisfy the following equations (1), (2), and (3). T W +20≦T≦T W +70 ···(1) 90 ≤ t ≤ 150 ···(2) T W +130 <T+t<T W +190 ···(3) In the above formula, T is the heating temperature (°C), and T W is the melting point (°C) of the wax, and t is the heating time (minutes). [2] In the wax extraction step, the method for measuring the wax concentration of the paint according to [1], wherein either a plurality of cuts and a plurality of holes, or both a plurality of cuts and a plurality of holes are formed in the solid matter. [3] A coating method having a coating step of applying a paint to the surface of a target material to be coated to form a film, wherein the paint is a paint containing wax whose wax concentration is calculated using the method for measuring the wax concentration of the paint according to [1] or [2].[[]]Coating method. [4] The target material is any one of an unplated cold-rolled steel sheet, an unplated hot-rolled steel sheet, and a zinc-based plated steel sheet plated with zinc-based plating, according to the coating method of [3].[[]]Coating method. [5] A method for manufacturing a surface-treated steel sheet, wherein a paint containing wax is applied to the surface of a steel sheet by the coating method according to [3] to form a film, thereby manufacturing a surface-treated steel sheet. [6] A method for manufacturing a surface-treated steel sheet, wherein a paint containing wax is applied to the surface of a steel sheet by the coating method according to [4] to form a film, thereby manufacturing a surface-treated steel sheet.

Advantages of the Invention

[0009] According to the present invention, the wax concentration contained in the paint can be measured at a point before applying the coating to the target material to be coated.

Brief Description of the Drawings

[0010] [Figure 1] It is a flowchart for explaining the method for measuring the wax concentration of the paint according to the present embodiment. [Figure 2] It is a diagram for explaining the extraction of the solid content. [Figure 3] It is a diagram for explaining the extraction of wax. [Figure 4]This is a diagram for explaining a process of calculating the wax concentration of a paint to be measured by using the height of a peak specific to wax and a calibration curve. [Figure 5] This is a diagram showing an apparatus for manufacturing a surface-treated steel sheet. [Figure 6] This is a diagram collectively showing the heating conditions of the paints in Invention Examples 1 to 3 and Comparative Examples 1 to 6.

Mode for Carrying Out the Invention

[0011] In a method for measuring the wax concentration of a paint according to an embodiment of the present invention (hereinafter referred to as this embodiment), the paint for which the wax concentration is measured is applied to the surface of a steel sheet which is a material to be coated, and imparts characteristics determined in design to the surface of the steel sheet. In this embodiment, the steel sheet is referred to as a surface-treated steel sheet. Examples of the above-described characteristics include workability, corrosion resistance, chemical conversion treatability, and conductivity.

[0012] (Paint) As described above, the paint contains various components that impart characteristics to the steel sheet, and contains at least wax in order to improve the workability of the surface-treated steel sheet. The method for measuring the wax concentration of the paint according to this embodiment is a method for measuring the wax concentration contained in a liquid paint, and extracts a solid content containing wax contained in the paint as a solid by heating the paint. Then, the solid content is immersed in an organic solvent to extract wax from the solid content, and the wax concentration of the paint is determined by subjecting the extraction solution of the wax to spectroscopic analysis. This is because when measuring the wax concentration of a liquid paint, it is not preferable to measure the accurate wax concentration due to the influence of components other than wax in the paint.

[0013] (Material to be coated) The steel sheet to be coated will now be described. The steel sheet is not limited, but may be, for example, an unplated cold-rolled steel sheet, an unplated hot-rolled steel sheet, or a zinc-plated steel sheet. Examples of zinc-plated steel sheets include electro-zinc plated steel sheets, electro-zinc-nickel alloy plated steel sheets, and hot-dip galvanized steel sheets. The base steel sheet for the zinc-plated steel sheet may be either a hot-rolled steel sheet or a cold-rolled steel sheet. Furthermore, a steel sheet to be coated in this embodiment may also be an unplated cold-rolled steel sheet, an unplated hot-rolled steel sheet, or a zinc-plated steel sheet with a separate coating applied to its surface.

[0014] (Method for measuring the wax concentration of paint) Figure 1 is a flowchart illustrating the method for measuring the wax concentration of a paint according to this embodiment. In the example shown in Figure 1, first, a predetermined amount of the liquid paint 1 to be measured is taken, and the solid components contained in the paint 1 are extracted as solid matter (solid component extraction step, step S101). The paint 1 to be measured is the material to be coated, for example, the paint 1 before it is applied to a steel plate. Various components, including wax, contained in the paint 1 may be separated. If paint for wax concentration measurement is taken from paint in which the various components have separated, and the wax concentration of the paint is measured using this, there is a possibility that the accuracy of the measured wax concentration may be questionable. Therefore, when taking the paint 1, it is preferable to stir the paint 1 to uniformly disperse the various components, including wax. After stirring the paint 1, a predetermined amount of paint 1 to be used for measuring the wax concentration is taken and placed in a container 2 such as a glass container like a beaker or petri dish, or a dish made of folded aluminum foil. In this embodiment, the amount of liquid paint to be measured is not particularly limited. However, if the amount of paint sampled is too small, it may negatively affect the accuracy of the analysis. On the other hand, if the amount of paint sampled is too large, the time required for heating (described later) will be longer, which may reduce work efficiency. Therefore, in this embodiment, the amount of liquid paint sampled may be appropriately selected within the range of 3 to 10 ml.

[0015] The stirring method of Paint 1 is not limited, and Paint 1 to be measured may be stirred by a stirrer (not shown). The stirrer is not limited, and examples of the stirrer include a mixer and a stirrer. Alternatively, the Paint 1 to be measured may be stirred by applying vibration to Paint 1 by a vibration tester, or Paint 1 to be measured may be stirred by a sampler. The above-mentioned Paint 1 to be measured may be a new paint or the paint in a paint pan described later.

[0016] Heat the Paint 1 collected as described above under predetermined heating conditions to extract the solid content of the paint. FIG. 2 is a diagram for explaining the extraction of the solid content. As shown in FIG. 2, place the container 2 containing Paint 1 on the heater 3 and heat Paint 1 under predetermined heating conditions. Thereby, the liquid phase component of Paint 1 is evaporated or vaporized and removed. Thus, the solid content of Paint 1 is extracted as the solid matter 4. Examples of the heating conditions include the heating temperature and the heating time. Note that an oven may be used instead of the heater 3.

[0017] The heating temperature T (°C) and the heating time t (minutes) shall satisfy the following formulas (1) to (3). T W +20 ≤ T ≤ T W +70 ···(1) 90 ≤ t ≤ 150 ···(2) T W +130 < T + t < T W +190 ···(3) In the above formulas (1) and (3), T is the heating temperature (°C), and T W is the melting point (°C) of the wax to be measured. In formulas (2) and (3), t is the heating time (minutes). The melting point of the wax assumed in this embodiment is 75 to 90 °C, and in particular, a wax with a melting point of 78 to 83 °C is assumed.

[0018] In formula (1), when the heating temperature T is (T WIf the temperature is below (+20°C), it may not be possible to evaporate or vaporize the liquid phase components of paint 1 due to insufficient heat. Therefore, the heating temperature T should be (T W It is preferable that the temperature is above +20°C, (T W It is more preferable that the heating temperature T is (40°C or higher). W If the temperature exceeds (+70°C), the solid components of paint 1, i.e., the wax, may be overheated and deteriorate. If the wax deteriorates, it may not be possible to accurately measure the wax concentration. Therefore, the heating temperature T should be (T W It is preferable that the temperature is below +70°C, (T W It is more preferable that the temperature be below +50°C.

[0019] In formula (2), if the heating time t is less than 90 minutes, there is a possibility that the liquid phase components of the paint 1 that have not evaporated or vaporized will remain in the container 2 even after the heating time t has elapsed. To suppress the retention of liquid phase components in the container 2, the heating time t is preferably 90 minutes or more, and more preferably 120 minutes or more. Furthermore, if the heating time t exceeds 150 minutes, the solid matter 4, i.e., wax, will be heated even after the liquid phase components of the paint 1 have evaporated or vaporized. This may cause the wax to be overheated and deteriorate. If deterioration of the wax occurs, as mentioned above, it may not be possible to properly measure the wax concentration. For this reason, the heating time t is preferably 150 minutes or less, and more preferably 130 minutes or less. In addition, it is even more preferable that the heating temperature T is 120°C or higher and 125°C or lower, and the heating time t is 120 minutes or higher and 125 minutes or lower.

[0020] In equation (3), (T+t), which is the sum of the heating temperature T (°C) and the heating time t (minutes), is equal to (T W If the value is less than +130, it may not be possible to evaporate or vaporize the liquid phase components of the paint, or unevaporated or unvaporized liquid phase components of the paint may remain in the container. Therefore, (T+t) is (T W It needs to exceed +130), (T WIt is preferable that the temperature is 140°C or higher. On the other hand, the sum of the heating temperature T (°C) and the heating time t (minutes), (T+t), is (T W If the temperature is above +190, the solid components of the paint, i.e., the wax, may be overheated, making accurate measurement impossible. Therefore, (T+t) is (T W (T W It is preferable that it is less than or equal to +180.

[0021] From the viewpoint of promoting the evaporation or vaporization of the liquid phase components of paint 1, that is, to increase the surface area on which paint 1 is heated and the liquid phase components evaporate or vaporize, it is preferable that the container 2 described above be flat. When a flat container is used, when the heating of paint 1 under predetermined heating conditions is completed, the solid components of paint 1 are extracted as flat solids or thin film-like solids.

[0022] Next, wax is extracted from the solid matter 4 extracted in step S101 (wax extraction step, step S102). Figure 3 is a diagram illustrating the wax extraction. As shown in Figure 3, an organic solvent is placed in the container 2 in which the solid components of the paint 1 were extracted as solid matter 4, and the solid matter 4 is immersed in the organic solvent for a predetermined time (hereinafter referred to as immersion time) to dissolve the wax contained in the solid matter 4 into the organic solvent. When dissolving the wax contained in the solid matter 4 into the organic solvent, it is preferable to stir the organic solvent in the container 2 in order to promote the dissolution of the wax. After the predetermined immersion time has elapsed, the organic solvent is filtered. In this way, the organic solvent from which the wax has been dissolved and the residue are separated, and the filtrate, i.e., the organic solvent from which the wax has been dissolved, is collected in another container 5. Alternatively, instead of filtration, the organic solvent from which the wax has been dissolved and the residue may be separated by a centrifuge, and the supernatant of the organic solvent may be collected in another container 5. Examples of organic solvents include hexane and carbon tetrachloride. It is preferable to use carbon tetrachloride in order to elute wax from the solid material and suppress the elution of components other than wax.

[0023] The immersion time is preferably 3 hours or more and 12 hours or less. If the immersion time is less than 3 hours, the wax may not dissolve sufficiently into the organic solvent, which may adversely affect the accuracy of subsequent wax concentration measurements. Therefore, it is preferable to immerse the material for 3 hours or more. If the immersion time exceeds 12 hours, components other than wax may also dissolve into the organic solvent, which may adversely affect the accuracy of subsequent wax concentration measurements. It is more preferable that the immersion time be 6 hours or more and 12 hours or less in order to sufficiently dissolve the wax contained in the solid material 4 into the organic solvent and to suppress the dissolution of components other than wax. From the viewpoint of shortening the time required to measure the wax concentration, it is preferable that the immersion time be 6 hours or more and 7 hours or less.

[0024] Furthermore, in order to facilitate the penetration of organic solvents into the solid material 4 and promote the dissolution of wax, it is preferable to increase the specific surface area of ​​the solid material 4 by forming either multiple cuts or multiple holes, or both, in the solid material 4. When forming cuts in the solid material 4, it is preferable to form cuts both vertically and horizontally. Forming cuts both vertically and horizontally means forming cuts in the solid material 4 in a grid pattern, such that the line segments along the cuts intersect with each other.

[0025] The spacing between adjacent notches (hereinafter referred to as the notch pitch) is preferably 0.4 mm or more and 1.0 mm or less. From the viewpoint of increasing the specific surface area of ​​the solid material 4, narrowing the notch pitch is effective. However, the amount of wax eluted when the notch pitch is less than 0.4 mm is approximately the same as the amount of wax eluted when the notch pitch is 0.4 mm. This means that even when the notch pitch is less than 0.4 mm, the effect of eluting wax is almost saturated. Also, narrowing the notch pitch reduces work efficiency compared to when the notch pitch is wide. Conversely, when the notch pitch exceeds 1.0 mm, the specific surface area of ​​the solid material 4 does not increase easily, and the amount of wax eluted does not increase easily either. For this reason, from the viewpoint of specific surface area and work efficiency, the notch pitch is preferably 0.4 mm or more and 1.0 mm or less, and more preferably 0.4 mm or more and 0.7 mm or less.

[0026] Furthermore, since the cuts are formed to increase the specific surface area of ​​the solid material 4, their depth is not limited. Therefore, the specific surface area of ​​the solid material 4 may be increased by finely chopping and subdividing it. Also, when cuts are formed in the solid material 4 so as to intersect each other vertically and horizontally, it is preferable that the angle between the line segments along the intersecting cuts is between 45° and 90°. This is because, given the same number of cuts formed, the closer the angle between the line segments along the intersecting cuts is to 90°, the smaller the distance from each point of the solid material to the cut line becomes, which is advantageous for wax dissolution.

[0027] When forming multiple holes on the surface of the solid object 4, the spacing between adjacent holes is preferably, for example, 0.4 mm or more and 1.0 mm or less, and more preferably 0.7 mm or more and 1.0 mm or less. If the spacing between adjacent holes is less than 0.4 mm, the number of holes to be formed becomes excessive, so the spacing is preferably 0.4 mm or more, and more preferably 0.7 mm or more. If the spacing between adjacent holes exceeds 1.0 mm, the effect of increasing the specific surface area of ​​the solid object by forming the holes becomes small, so the spacing is preferably 1.0 mm or less. Furthermore, since the holes described above are formed to increase the specific surface area of ​​the solid object 4, similar to notches, their depth is not limited. Therefore, the holes described above may be through holes formed by penetrating the solid object 4. The holes or through holes described above may be formed by pins, or instead of pins, they may be formed using a fork-shaped tool having multiple pointed tips. The hole diameter is not particularly limited and may be, for example, 0.1 to 1.0 mm.

[0028] Returning to the explanation of Figure 1, the filtered organic solvent is analyzed following step S102 (analysis step, step S103). That is, spectroscopic analysis is performed on the organic solvent from which the wax has been eluted. Examples of spectroscopic analysis include infrared spectroscopy (hereinafter referred to as IR) and Fourier transform infrared spectroscopy (hereinafter referred to as FTIR). Compared with conventional IR, FTIR is highly sensitive and has a shorter measurement time, so in this embodiment, it is preferable to measure the wax concentration using FTIR rather than IR.

[0029] Next, the wax concentration of paint 1 is calculated based on the height of the wax-specific peak (calculation process, step S104). The process of calculating the wax concentration of paint 1 to be measured from the peak height of the wax-specific peak identified by FTIR will be explained. For example, several paints with known wax concentrations are prepared. Wax is extracted from each paint according to the method for measuring the wax concentration of paints shown in the flowchart in Figure 1, and FTIR analysis is performed on each wax extract. In this way, a calibration curve is created by determining the relationship between the peak height of the wax-specific peak and the corresponding wax concentration. Furthermore, for paint 1 to be measured whose wax concentration is unknown, wax is extracted according to the method for measuring the wax concentration of paints shown in the flowchart in Figure 1, and FTIR analysis is performed on the wax extract. The wax concentration of paint 1 to be measured whose wax concentration is unknown is calculated using the peak height of the wax-specific peak obtained by FTIR and the calibration curve. Figure 4 shows an example.

[0030] According to the method for measuring the wax concentration of a paint according to this embodiment, the wax concentration of a paint 1 whose wax concentration is unknown can be measured as described above. Therefore, the wax concentration of the paint 1 can be adjusted and maintained within a predetermined concentration range. In other words, the wax concentration of the paint 1 used in the manufacture of surface-treated steel sheets can be measured in advance before the manufacture of the surface-treated steel sheets and maintained within a predetermined concentration range. Therefore, it is possible to avoid situations in which surface-treated steel sheets are manufactured using paint 1 whose wax concentration is not within the predetermined concentration range, and the production yield of surface-treated steel sheets can be improved. Furthermore, surface-treated steel sheets coated with paint 1 can be manufactured continuously.

[0031] Here, a manufacturing apparatus for surface-treated steel sheets to which the method for measuring the wax concentration of the paint of this embodiment can be applied will be described. Figure 5 is a diagram showing a manufacturing apparatus for surface-treated steel sheets. The manufacturing apparatus shown in Figure 5 is a roll coater and has a paint pan 6, a circulation tank 7, and a roll unit 8. The paint pan 6 is equipment for storing the paint to be applied to the steel sheet S, which is the material to be coated. In the example shown in Figure 5, in order to apply paint to both sides of the steel sheet, the paint pans are provided on both sides of the steel sheet S in the transport direction of the steel sheet S (the vertical direction of the manufacturing apparatus shown in Figure 5). The circulation tank 7 is equipment for maintaining the amount of paint in the paint pan 6 at a predetermined storage amount and maintaining the component concentration in the paint at a nearly constant level. Therefore, as shown in Figure 5, each paint pan 6 and the circulation tank 7 are connected to each other via a liquid supply pipe 9 and a liquid return pipe 10. When the amount of paint stored in the paint pan 6 becomes low, or when a particular component becomes concentrated and the concentration of that component needs to be maintained within a predetermined concentration range, new paint is supplied to the circulation tank 7.

[0032] The roll unit 8 is equipment that picks up paint stored in the paint pan 6 and applies it to the steel plate S. In the example shown in Figure 5, the roll units are arranged on both sides of the steel plate S, allowing paint to be applied to both sides of the steel plate S. Each roll unit has an applicator roll 11, a pickup roll 12, and a doctor roll 13. The pickup roll 12 picks up paint stored in the paint pan 6. The applicator roll 11 applies the paint picked up by the pickup roll 12 to the steel plate S. The doctor roll 13 supports the pickup roll 12 and may also have a function to adjust the amount of paint picked up. The method of applying paint to the steel plate using the manufacturing apparatus shown in Figure 5 corresponds to the coating method of this embodiment. The process of applying paint to the steel plate using the manufacturing apparatus shown in Figure 5 corresponds to the coating process of this embodiment. Furthermore, the method of manufacturing a surface-treated steel plate by applying paint to the steel plate using the manufacturing apparatus shown in Figure 5 corresponds to the manufacturing method of a surface-treated steel plate of this embodiment.

[0033] The method for measuring the wax concentration of paint according to this embodiment can be applied to the manufacturing apparatus shown in Figure 5 when measuring the wax concentration of paint stored in the paint pan 6 and the circulation tank 7, and when measuring the wax concentration of new paint supplied to the circulation tank 7. By measuring the wax concentration of the paint according to this embodiment, the wax concentration of the paint applied to the steel sheet S can be adjusted and maintained within a predetermined concentration range. Therefore, it is possible to avoid manufacturing surface-treated steel sheets using paint whose wax concentration is not within the predetermined concentration range. In other words, the amount of wax adhering to the surface of the surface-treated steel sheet is the amount of wax adhering as determined by design, and the production yield of surface-treated steel sheets can be improved. As a result, surface-treated steel sheets coated with paint can be manufactured continuously.

[0034] Furthermore, multiple manufacturing devices as shown in Figure 5 may be installed in the direction of transport of the steel sheet S. This makes it possible to manufacture surface-treated steel sheets with multiple coatings formed on them. In addition, when forming multiple coatings on the surface of the steel sheet S, in order to ensure the processability of the surface-treated steel sheet, it is preferable that the paint forming the upper layer exposed to the outside is a paint containing wax whose wax concentration was calculated as described above. [Examples]

[0035] This section describes Example 1, in which the wax concentration of a paint was measured by changing the heating conditions of the paint, in the method for measuring the wax concentration of the paint according to this embodiment. Table 1 summarizes the heating conditions and evaluations of the paint in Invention Examples 1 to 3 and Comparative Examples 1 to 6. In Table 1, Table 2 (described later), and Table 3, "◎" means that the wax concentration in the paint could be measured, and "×" means that the wax concentration in the paint could not be measured. "△" means that although the wax concentration could be measured, components other than wax in the paint were also extracted. "+" attached to "◎" means that the wax concentration in the paint was measured well, and "-" attached to "◎" means that although the wax concentration in the paint could be measured, there is room for improvement. Figure 6 is a diagram summarizing the heating conditions of the paint in Invention Examples 1 to 3 and Comparative Examples 1 to 6.

[0036] [Table 1]

[0037] (Example of Invention 1) A liquid paint containing wax was stirred using a stirrer to uniformly disperse the various components, and 5 ml of the paint for wax concentration measurement was taken from the paint using a pipette.

[0038] The paint sample, collected using a pipette, was placed on a folded piece of aluminum foil and heated in an oven at 120°C for 120 minutes. After the heating time, the aluminum foil was removed from the oven and visually inspected to determine if the solid material on the foil was dry or had deteriorated. If the liquid phase component, i.e., liquid, was visible on the aluminum foil, it was determined that the solid material was not dry. If bubbles, bubble marks, or discoloration were present on the surface of the solid material, it was determined that the solid material had deteriorated.

[0039] The solid material, which was judged to be dry and undamaged, was placed in a beaker, and 20 ml of carbon tetrachloride was added to it. The solid material was then immersed in the carbon tetrachloride for 6 hours. The carbon tetrachloride was stirred during the immersion period. After 6 hours of immersion, the carbon tetrachloride from which the wax had eluted, i.e., the wax extract, was filtered and transferred to a flask. More carbon tetrachloride was added to the filtrate in the flask to adjust the volume to 25 ml. This volume-adjusted liquid sample was subjected to RTIR analysis.

[0040] In Invention Example 1, the subject was a paint containing a montan wax-based wax. The melting point of the wax in question was 80°C. In this example, the FTIR measurement was 2820-2900 cm⁻¹. -1 A peak characteristic of wax appears in the wavenumber region. The wax concentration of the paint was measured and quantified based on the peak height in that wavenumber region. Furthermore, in measuring and quantifying the wax concentration of the paint based on the peak height, a wax extract was prepared as described above for each of several paints for which the wax concentration was known, and subjected to FTIR analysis. Then, a calibration curve was created by organizing the relationship between the peak height obtained by FTIR analysis and the wax concentration corresponding to each peak height. Using this calibration curve and the peak height obtained by FTIR analysis in Invention Example 1, the wax concentration of the paint in Invention Example 1 was determined.

[0041] (Example of Invention 2) Invention Example 2 is an example in which the wax concentration of the paint was measured in the same manner as Invention Example 1, except that the heating temperature was 100°C and the heating time was 150 minutes.

[0042] (Example of Invention 3) Invention Example 3 is an example in which the wax concentration of a paint was measured in the same manner as Invention Example 1, except that the heating temperature was 150°C and the heating time was 90 minutes.

[0043] (Comparative Example 1) Comparative Example 1 is an example in which the wax concentration of the paint was measured in the same manner as in Invention Example 1, except that the heating temperature was 200°C and the heating time was 30 minutes.

[0044] (Comparative Example 2) Comparative Example 2 is an example in which the wax concentration of the paint was measured in the same manner as in Invention Example 1, except that the heating temperature was 120°C and the heating time was 150 minutes.

[0045] (Comparative Example 3) Comparative Example 3 is an example in which the wax concentration of the paint was measured in the same manner as in Invention Example 1, except that the heating temperature was 150°C and the heating time was 120 minutes.

[0046] (Comparative Example 4) Comparative Example 4 is an example in which the wax concentration of the paint was measured in the same manner as in Invention Example 1, except that the heating temperature was 120°C and the heating time was 90 minutes.

[0047] (Comparative Example 5) Comparative Example 5 is an example in which the wax concentration of the paint was measured in the same manner as in Invention Example 1, except that the heating temperature was 90°C and the heating time was 150 minutes.

[0048] (Comparative Example 6) Comparative Example 6 is an example in which the wax concentration of the paint was measured in the same manner as in Invention Example 1, except that the heating temperature was 90°C and the heating time was 80 minutes.

[0049] (Evaluation of Example 1) In all three invention examples, a completely dry solid was obtained. When the liquid samples from invention examples 1 to 3 were subjected to FTIR, measurement results with small variations in peak height and wax content were obtained in all cases. Furthermore, invention example 1 is preferable because the heating time can be shortened compared to invention example 2. Invention example 3 is preferable because the heating time can be shortened even further compared to invention example 1. However, in invention example 3, if the heating temperature in the oven rises above the set temperature, the solid may be overheated and deteriorate. Therefore, considering the stability of the heating conditions, invention example 1 is the most preferable of invention examples 1 to 3.

[0050] In Comparative Examples 1-3, it was observed that air bubbles were present on the surface of the solid material. This suggests that the solid material was overheated and altered, making it impossible to accurately measure the wax concentration.

[0051] In Comparative Examples 4 and 5, it was confirmed that liquid phase components were present on the aluminum foil along with the solid material. In other words, the solid material was not sufficiently dry. Therefore, when the solid material was immersed in carbon tetrachloride, the carbon tetrachloride became cloudy, and it was determined that accurate measurement of the wax concentration was not possible. In Comparative Example 6, it was confirmed that there was a larger amount of liquid phase components on the aluminum foil than in Comparative Examples 4 and 5. For the same reasons as in Comparative Examples 4 and 5, it was determined that accurate measurement of the wax concentration was not possible.

[0052] The heating conditions for the above-described examples 1 to 3 can be expressed as shown by the following equations (4) to (6). The conditions that satisfy all of the following equations (4) to (6) are shown as the shaded area (hatched area) in Figure 6. Here, the boundary line corresponding to equation (3) is outside the claims. As shown in Figure 6, it was found that when all of the following equations (4) to (6) are satisfied, the solid content of the paint can be obtained as a solid without altering it, and the wax concentration can be measured appropriately. Note that the following equations (4) to (6) are the same as the above-described equations (1) to (3). T W +20≦T≦T W +70 ···(4) 90 ≤ t ≤ 150 ···(5) T W +130 <T+t<T W +190 ···(6) [Examples]

[0053] In the method for measuring the wax concentration of paint according to this embodiment, Example 2 describes the effect of forming cuts in a solid when immersing a solid in carbon tetrachloride to dissolve the wax. Table 2 summarizes the evaluations of Invention Example 1, in which no cuts were formed in the solid, and Invention Example 4, in which cuts were formed in the solid.

[0054] [Table 2]

[0055] (Example of Invention 4) Invention Example 4 is an example in which cuts are made vertically and horizontally with a knife on the surface of a solid object with a cut pitch of 0.7 mm to 1.0 mm, and the intersection angle of the line segments along the intersecting cuts is 70 degrees to 90 degrees. In addition, the wax concentration of the paint is measured in the same manner as Invention Example 1.

[0056] (Evaluation of Example 2) In Invention Example 4, the variation in FTIR peak height was smaller than in Invention Example 1. This confirms that it is preferable to form vertical and horizontal cuts on the surface of the solid when immersing the solid in carbon tetrachloride.

[0057] Alternatively, instead of forming incisions, the specific surface area can also be increased by piercing the surface of the solid with a pin to create microscopic holes. For example, holes with a diameter of 0.3 mm can be formed across the entire surface of the solid. The spacing between adjacent holes can be set to between 0.8 mm and 1.0 mm. In this case, although not shown in Table 2, it was confirmed that the FTIR peak height and the variation in wax content were smaller than in Invention Example 1, similar to the case where incisions were formed. [Examples]

[0058] This section describes Example 3, which confirms the effect of immersion time in carbon tetrachloride on the method for measuring the wax concentration of paint according to this embodiment. Table 3 summarizes the immersion time and evaluation for Invention Example 5, Invention Example 6, Invention Example 7, and Comparative Example 7. During the immersion of the solid material in carbon tetrachloride, the carbon tetrachloride was stirred to promote the dissolution of wax.

[0059] [Table 3]

[0060] (Example of Invention 6) Invention Example 6 is an example in which the wax concentration of the paint was measured in the same manner as Invention Example 5, except that the immersion time was 3 hours.

[0061] (Example of Invention 7) Invention Example 7 is an example in which the wax concentration of the paint was measured in the same manner as Invention Example 5, except that the immersion time was 9 hours.

[0062] (Comparative Example 7) Comparative Example 7 is an example in which the wax concentration of the paint was measured in the same manner as in Invention Example 5, except that the immersion time was 12 hours.

[0063] (Evaluation of Example 3) In Invention Example 6, wax components remained in the beaker. The liquid sample, excluding this residual wax, was subjected to FTIR analysis. As a result, the peak height was smaller compared to Invention Example 5. This is thought to be due to incomplete elution of the wax into carbon tetrachloride, caused by the short immersion time.

[0064] In both Invention Example 5 and Invention Example 7, FTIR analysis revealed that a peak characteristic of wax appeared at a predetermined wavenumber, indicating that only the wax component was extracted. Invention Example 5 is preferable because it allows for a shorter immersion time compared to Invention Example 7. In Comparative Example 7, FTIR analysis revealed a peak characteristic of wax at a predetermined wavenumber, but peaks were also observed at other wavenumbers. This indicates that components other than wax were also extracted into the carbon tetrachloride, which is undesirable. [Explanation of Symbols]

[0065] 1 paint 2 containers 3 Heater 4. Solids 5 Other containers 6 Paint pan 7. Circulation tank 8 Roll Unit 9 Liquid supply pipe 10 Liquid return tube 11 Applicator Rolls 12 Pickup Roll 13. Dr. Roll S steel plate

Claims

1. A solid content extraction step involves heating a liquid paint containing wax to extract the solid content containing the wax as a solid from the paint, A wax extraction step involves immersing the solid in an organic solvent to extract the wax from the solid and obtain a wax extract, An analytical step of performing a spectroscopic analysis of the wax extract, The process includes a calculation step of calculating the wax concentration of the paint from the results of a spectroscopic analysis of the wax extract, A method for measuring the wax concentration of a paint, wherein the heating conditions when heating the paint in the solid content extraction step satisfy the following equations (1), (2), and (3). T Ｗ +20≦T≦T Ｗ +70 ・・・(1) 90 ≤ t ≤ 150 ... (2) T Ｗ +130<T+t<T Ｗ +190 ・・・(3) In the above formula, T is the heating temperature (°C), and T Ｗ θ is the melting point of the wax (°C), and t is the heating time (minutes).

2. The method for measuring the wax concentration of a paint according to claim 1, wherein the wax extraction step involves forming a plurality of incisions and / or holes, or both, in the solid material.

3. A coating method comprising a coating step of applying paint to the surface of a material to be coated to form a film, wherein the paint is a paint containing wax whose wax concentration is calculated using the method for measuring the wax concentration of paint described in claim 1 or claim 2.

4. The coating method according to claim 3, wherein the target material is any one of the following: an unplated cold-rolled steel sheet, an unplated hot-rolled steel sheet, and a zinc-plated steel sheet.

5. A method for manufacturing a surface-treated steel sheet, comprising applying a coating containing wax to the surface of a steel sheet by the coating method described in claim 3 to form a film, thereby manufacturing a surface-treated steel sheet.

6. A method for manufacturing a surface-treated steel sheet, comprising applying a coating containing wax to the surface of a steel sheet using the coating method described in claim 4 to form a film, thereby producing a surface-treated steel sheet.

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