Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/10—Electroplating with more than one layer of the same or of different metals
  • C25D5/12—Electroplating with more than one layer of the same or of different metals at least one layer being of nickel or chromium
  • C25D5/14—Electroplating with more than one layer of the same or of different metals at least one layer being of nickel or chromium two or more layers being of nickel or chromium, e.g. duplex or triplex layers
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/16—Electroplating with layers of varying thickness
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/18—Electroplating using modulated, pulsed or reversing current
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/34—Pretreatment of metallic surfaces to be electroplated
  • C25D5/36—Pretreatment of metallic surfaces to be electroplated of iron or steel

Definitions

• Sn-plated steel sheet has excellent corrosion resistance, weldability, and workability, and is easy to manufacture, so it has been used for over 200 years as a material for various metal cans such as beverage cans, food cans, pail cans, and 18-liter cans.
• Tin-free steel sheet is a surface-treated steel sheet in which a metallic chromium layer and a chromium oxide layer are formed on the surface of the steel sheet, and is typically produced by electrolyzing the steel sheet in an electrolyte containing hexavalent chromium (Patent Documents 1 to 3). Due to its excellent corrosion resistance, tin-free steel sheet is now extremely commonly used as a steel sheet for containers, replacing tinplate. However, because typical tin-free steel sheet has an insulating chromium oxide layer on the surface, it has poor weldability.
• Patent Documents 4 and 5 a type of tin-free steel sheet with excellent weldability is known, in which granular protrusions are formed on the surface of the steel sheet by performing anodic electrolysis between multiple cathodic electrolysis treatments during electrochromic chromium plating.
• a surface treatment layer is formed by electrolysis in an electrolyte containing a trivalent chromium compound such as basic chromium sulfate.
• Patent Documents 6, 7, and 8 make it possible to form a surface treatment layer without using hexavalent chromium. Furthermore, Patent Documents 6, 7, and 8 also show that these methods can produce surface-treated steel sheets with excellent film corrosion resistance and paint corrosion resistance.
• the present invention was made in consideration of the above-mentioned circumstances, and its purpose is to provide a surface-treated steel sheet that can be produced without using hexavalent chromium and that has excellent film corrosion resistance, paint corrosion resistance, and weldability.
• the inventors of the present invention have discovered that in a surface-treated steel sheet having a chromium-containing layer disposed on at least one surface of the steel sheet, by controlling the outermost surface structure of the chromium-containing layer and the atomic ratio of C to Cr in the chromium-containing layer, it is possible to obtain a surface-treated steel sheet with excellent film corrosion resistance, paint corrosion resistance, and weldability.
• the present invention was completed based on the above findings.
• the gist of the present invention is as follows:
• a steel plate A surface-treated steel sheet comprising a chromium-containing layer disposed on at least one surface of the steel sheet, Granular protrusions are present on the outermost surface of the chromium-containing layer, and in a zero-order persistence diagram created from a distribution image of the granular protrusions,
• the minimum birth size is -20 nm or more and less than -2 nm
• the maximum Death size is 15 nm or less
• the number of data points having a death size of 0.5 nm or more and 15 nm or less is 0.01/ nm2 or more and less than 0.10/ nm2
• the chromium-containing layer has an atomic ratio of C to Cr of 0.2% or more and 50.0% or less.
• mass % C: 0.0001 to 0.13%, Si: 0 to 0.020%, P: 0 to 0.020%, S: 0 to 0.030%, Al: 0 to 0.20%, and N: 0 to 0.040%, and optionally further containing, in mass%, Mn: 0.01-0.60%, Cu: 0 to 0.20%, Ni: 0 to 0.15%, Cr: 0 to 0.10%, Mo: 0 to 0.05%, Ti: 0 to 0.020%, Nb: 0 to 0.020%, B: 0 to 0.020%, Ca: 0-0.020%, Contains at least one selected from the group consisting of Sn: 0 to 0.020% and Sb: 0 to 0.020%, It is preferable to use a steel sheet having a composition with the balance consisting of Fe and unavoidable impurities. Of the above composition, the lower the content of Si, P, S, Al, and N, the more preferable it is. Mn,
• the surface-treated steel sheet is painted or laminated with a film
• the surface-treated steel sheet is immersed in the agent until the paint or film peels off, then rinsed with running water and dried before observation.
• the agent is selected to match the paint or film; for example, sulfuric acid or hydrogen peroxide can be used.
• the immersion temperature is adjusted appropriately depending on the type of agent, etc.
• Figure 4 shows a specific example of the calculation used to create a zero-order persistence diagram from the distance distribution shown in Figure 3.
• the space is filled from -18 nm, which is the minimum value of the distance distribution in Figure 3.
• Figure 5 shows a schematic diagram of the zeroth-order persistence diagram obtained by the above calculation.
• Figure 5 is a contour plot in which the number of data points (number of plots) is represented by shades of black and white. In this way, a corresponding zeroth-order persistence diagram can be obtained from a single SEM image.
• birth size is -30 nm and the death size is 50 nm, this means that a different granular protrusion exists at a position approximately 100 nm away from a granular protrusion with a diameter of 60 nm. Furthermore, combining and simultaneously analyzing birth size and death size enables more detailed data analysis.
• the minimum birth size is -20 nm or more, preferably -17 nm or more, and more preferably -15 nm or more.
• the minimum birth size is less than -2 nm, and preferably less than -5 nm.
• the number of data points with a death size of 0.5 nm to 15 nm is 0.01/ nm2 or more. Because weldability is better in welding with high pressure, a death size of 0.02/nm2 or more is preferable, and 0.03/nm2 or more is more preferable. On the other hand, even if the number of granular protrusions is excessive, weldability actually deteriorates in welding with high pressure. Therefore, the number of data points with a death size of 0.5 nm to 15 nm is less than 0.10/ nm2 , preferably less than 0.08/ nm2 . The number of data points is calculated as a ratio (number density) of the area of the observation region of the distribution image of the granular protrusions.
• a surface-treated steel sheet having the above-described properties can be produced by the method described below.
• a method for producing a surface-treated steel sheet according to a preferred embodiment of the present invention is a method for producing a surface-treated steel sheet comprising a steel sheet and a chromium-containing layer disposed on at least one surface of the steel sheet, the method comprising: an electrolyte solution preparation step of preparing an electrolyte solution containing trivalent chromium ions; a coating formation step of forming the chromium-containing layer, In the electrolyte solution preparation step, a trivalent chromium ion source, a carboxylic acid compound, and water are mixed; The electrolyte solution is prepared by adjusting the pH to 4.0 to 7.0 and the temperature to 40 to 70°C.
• the steel sheet is subjected to cathodic electrolysis C1, anodic electrolysis A1, and cathodic electrolysis C2 in this order using the electrolytic solution,
• the electricity density of the anodic electrolysis treatment A1 is 0.50 C/dm 2 or more and 20.00 C/dm 2 or less
• the electricity density of the cathodic electrolytic treatment C2 is 1.0 C/ dm2 or more and 150.0 C/dm2 or less .
• the production method includes the following steps (1) and (2). Each step will be described below. (1) An electrolyte preparation step for preparing an electrolyte containing trivalent chromium ions; (2) A film formation step for forming a chromium-containing layer.
• Electrolytic solution preparation process (i) Mixing In the electrolytic solution preparation step, first, a trivalent chromium ion source, a carboxylic acid compound, and water are mixed to prepare an aqueous solution.
• any compound capable of supplying trivalent chromium ions can be used as the trivalent chromium ion source.
• at least one selected from the group consisting of chromium chloride, chromium sulfate, and chromium nitrate can be used as the trivalent chromium ion source.
• the content of the trivalent chromium ion source in the aqueous solution is not particularly limited, but is preferably 3 g/L or more, and more preferably 5 g/L or more, calculated as trivalent chromium ions.
• the content of the trivalent chromium ion source is preferably 50 g/L or less, and more preferably 40 g/L or less.
• BluCr (registered trademark) TFS A from Atotech can be used as the trivalent chromium ion source.
• the charge density of the cathodic electrolysis treatment C1 is not particularly limited. However, the amount of chromium deposited in the chromium-containing layer can be controlled by the charge density of the cathodic electrolysis treatment C1. Therefore, the charge density is preferably 5.0 C/dm2 or more , more preferably 10.0 C/dm2 or more . For the same reason, the charge density is preferably 200.0 C/dm2 or less , more preferably 180.0 C/dm2 or less .
• the current density and current application time of the cathodic electrolysis treatment C1 are not particularly limited and can be appropriately set to achieve the desired value of the electricity density, which is expressed as the product of the current density (unit: A/dm 2 ) and the current application time (unit: sec.) of the electrolysis treatment.
• the temperature of the electrolyte when performing cathodic electrolysis C1 is not particularly limited, but in order to efficiently form a chromium-containing layer, it is preferable to set the temperature in the range of 40°C or higher and 70°C or lower. From the perspective of stably producing the above-mentioned surface-treated steel sheet, it is preferable to monitor the temperature of the electrolyte during cathodic electrolysis C1 and maintain it in the above temperature range.
• the concentration of the electrolyte constantly changes due to factors such as the formation of a chromium-containing layer on the steel sheet, the introduction and removal of the solution, and the evaporation of water.
• the change in concentration of the electrolyte in cathodic electrolysis C1 varies depending on the equipment configuration and manufacturing conditions. Therefore, from the perspective of more stable production of surface-treated steel sheets, it is preferable to monitor the concentrations of the components contained in the electrolyte in cathodic electrolysis C1 and maintain them within the concentration ranges described above.
• Anodic electrolysis treatment A1 Next, the steel sheet subjected to cathodic electrolysis C1 is subjected to anodic electrolysis A1 using the electrolytic solution.
• the chromium-containing layer formed by cathodic electrolysis C1 is dissolved, forming a generation site for granular precipitates of metallic chromium and chromium compounds in cathodic electrolysis C2.
• the granular precipitates of metallic chromium and chromium compounds may be simply referred to as granular chromium.
• trivalent chromium is oxidized to hexavalent chromium on the steel sheet surface.
• the charge density exceeds 20.00 C/ dm2 , the oxidation reaction of trivalent chromium may proceed locally on the steel sheet surface, increasing the hexavalent chromium concentration, destabilizing the electrolyte, and possibly resulting in excessive chromium oxide deposition. Therefore, the charge density is 20.00 C/dm2 or less, preferably 18.00 C/dm2 or less , and more preferably 16.00 C/dm2 or less .
• the current density and current application time for the anodic electrolysis treatment A1 are not particularly limited and can be set appropriately to achieve the desired electrical charge density.
• the temperature of the electrolyte when performing anodic electrolysis treatment A1 is not particularly limited, and the preferred embodiment is the same as that for cathodic electrolysis treatment C1. From the perspective of stably producing the above-mentioned surface-treated steel sheet and more reliably suppressing an increase in the hexavalent chromium concentration, it is preferable to monitor the temperature of the electrolyte during anodic electrolysis treatment A1 and maintain it within the above temperature range.
• the pH of the electrolyte when performing anodic electrolysis A1 is not particularly limited, and the preferred embodiment is the same as that for cathodic electrolysis C1. From the perspective of stably producing the above-mentioned surface-treated steel sheet and more reliably suppressing an increase in the hexavalent chromium concentration, it is preferable to monitor the pH of the electrolyte during anodic electrolysis A1 and maintain it within the above pH range.
• the steel sheet that has been subjected to the anodic electrolysis treatment A1 is subjected to cathodic electrolysis treatment C2 using the electrolytic solution described above.
• cathodic electrolysis treatment C2 a chromium-containing layer can be formed on the steel sheet, and particulate chromium can be precipitated starting from the above-mentioned generation sites.
• the charge density of the cathodic electrolytic treatment C2 is less than 1.0 C/ dm2 , granular chromium may not be sufficiently precipitated, resulting in an excessively small maximum Death size in the finally obtained surface-treated steel sheet. Furthermore, the number of data points having a Death size of 0.5 nm or more and 15 nm or less may be excessively small. Therefore, the charge density is 1.0 C/dm2 or more , preferably 3.0 C/ dm2 or more, and more preferably 5.0 C/dm2 or more .
• the charge density is 150.0 C/dm2 or less, preferably 120.0 C/dm2 or less , and more preferably 100.0 C/ dm2 or less.
• the current density and current application time for the cathodic electrolysis treatment C2 are not particularly limited and can be set appropriately to achieve the desired electrical charge density.
• the temperature of the electrolyte when performing cathodic electrolysis treatment C2 is not particularly limited, and the preferred embodiment is the same as that of cathodic electrolysis treatment C1. From the same perspective as for cathodic electrolysis treatment C1, it is preferable to monitor the temperature of the electrolyte during cathodic electrolysis treatment C2 and maintain it within the above temperature range.
• the pH of the electrolyte when performing cathodic electrolysis treatment C2 is not particularly limited, and the preferred embodiment is the same as that of cathodic electrolysis treatment C1. From the same perspective as for cathodic electrolysis treatment C1, it is preferable to monitor the pH of the electrolyte in cathodic electrolysis treatment C2 and maintain it within the above pH range.
• cathodic electrolysis treatment C2 there are no particular restrictions on the type of electrode used when performing cathodic electrolysis treatment C2, and the preferred embodiment is the same as for cathodic electrolysis treatment C1.
• cathodic electrolysis treatment C1 From the same perspective as in cathodic electrolysis treatment C1, it is preferable to monitor the concentrations of the components contained in the electrolyte in cathodic electrolysis treatment C2 and maintain them within the concentration ranges described above.
• the steel sheet after cathodic electrolysis C2 may be subjected to anodic electrolysis A2 using the above-mentioned electrolytic solution.
• anodic electrolysis A2 the chromium-containing layer formed by cathodic electrolysis C2 is dissolved, and a site for generating particulate deposits of metallic chromium and chromium compounds in cathodic electrolysis C3 is formed.
• trivalent chromium is oxidized to hexavalent chromium on the steel sheet surface as in anodic electrolysis A1.
• the hexavalent chromium is immediately reduced to trivalent chromium, so that in practice, no hexavalent chromium is present in the electrolytic solution.
• the electricity density of the anodic electrolysis treatment A2 is less than 0.50 C/ dm2 , the chromium oxide will not dissolve sufficiently. Therefore, the electricity density is preferably 0.50 C/dm2 or more .
• the electricity density exceeds 20.00 C/ dm2 , the oxidation reaction of trivalent chromium will proceed locally on the steel sheet surface, increasing the hexavalent chromium concentration and making the electrolyte unstable.
• the chromium-containing layer may dissolve, resulting in an arithmetic mean roughness of less than 1.30 nm. Therefore, the electricity density is preferably 20.00 C/dm2 or less .
• the current density and current application time for the anodic electrolysis treatment A2 are not particularly limited and can be set appropriately to achieve the desired electrical charge density.
• the temperature of the electrolyte when performing anodic electrolysis treatment A2 is not particularly limited, and the preferred embodiment is the same as that for cathodic electrolysis treatment C1. From the perspective of stably producing the above-mentioned surface-treated steel sheet and more reliably suppressing an increase in the hexavalent chromium concentration, it is preferable to monitor the temperature of the electrolyte during anodic electrolysis treatment A2 and maintain it within the above temperature range.
• the pH of the electrolyte when performing anodic electrolysis A2 is not particularly limited, and the preferred embodiment is the same as that for cathodic electrolysis C1. From the perspective of stably producing the above-mentioned surface-treated steel sheet and more reliably suppressing an increase in the hexavalent chromium concentration, it is preferable to monitor the pH of the electrolyte during anodic electrolysis A2 and maintain it within the above pH range.
• the steel sheet after the anodic electrolysis treatment A2 may be subjected to cathodic electrolysis treatment C3 using the electrolytic solution.
• cathodic electrolysis treatment C3 it is possible to densely precipitate granular chromium starting from the above-mentioned generation sites, and it is possible to reduce the above-mentioned maximum Death size.
• the electricity density of the cathodic electrolytic treatment C3 is less than 1.0 C/ dm2 , the granular chromium will not be sufficiently precipitated. Therefore, the electricity density is preferably 1.0 C/ dm2 or more. On the other hand, if the electricity density exceeds 150.0 C/ dm2 , the granular chromium will become excessively coarse, and as a result, the number of data points in the finally obtained surface-treated steel sheet may become excessively large. Therefore, the electricity density is preferably 150.0 C/dm2 or less .
• the current density and current application time for the cathodic electrolysis treatment C3 are not particularly limited and can be set appropriately to achieve the desired electrical charge density.
• the temperature of the electrolyte when performing cathodic electrolysis treatment C3 is not particularly limited, and the preferred embodiment is the same as that of cathodic electrolysis treatment C2. From the same perspective as for cathodic electrolysis treatment C1, it is preferable to monitor the temperature of the electrolyte in cathodic electrolysis treatment C3 and maintain it within the above temperature range.
• the pH of the electrolyte when performing cathodic electrolysis treatment C3 is not particularly limited, and the preferred embodiment is the same as that of cathodic electrolysis treatment C1. From the same perspective as for cathodic electrolysis treatment C1, it is preferable to monitor the pH of the electrolyte in cathodic electrolysis treatment C3 and maintain it within the above pH range.
• cathodic electrolysis treatment C3 there are no particular restrictions on the type of electrode used when performing cathodic electrolysis treatment C3, and the preferred embodiment is the same as for cathodic electrolysis treatment C1.
• cathodic electrolysis treatment C1 From the same perspective as in cathodic electrolysis treatment C1, it is preferable to monitor the concentrations of the components contained in the electrolyte in cathodic electrolysis treatment C3 and maintain them within the concentration ranges described above.
• the surface-treated steel sheet is preferably washed with water at least once, which makes it possible to remove the electrolytic solution remaining on the surface of the steel sheet.
• the water washing can be carried out by any method without particular limitations.
• a water washing tank can be provided downstream of the immersion tank used for the immersion treatment, and the steel sheet can be continuously immersed in water after immersion.
• the steel sheet can be washed by spraying water onto it after immersion.
• the water used for the rinsing is not particularly limited, but it is preferable to use at least one of reverse osmosis water (RO water), ion-exchanged water, and distilled water.
• the electrical conductivity of the water used for the rinsing is not particularly limited, but it is preferably 100 ⁇ S/m or less, more preferably 50 ⁇ S/m or less, and even more preferably 30 ⁇ S/m or less.
• the temperature of the water used for the washing is not particularly limited and may be any temperature. However, an excessively high temperature places an excessive burden on the washing equipment, so the temperature of the water used for washing is preferably 95°C or less. On the other hand, the lower limit of the temperature of the water used for washing is not particularly limited, but it is preferably 0°C or higher. The temperature of the water used for the washing may be room temperature.
• drying may be carried out as desired.
• a conventional dryer or electric oven drying method can be used.
• the temperature during the drying process be 100°C or less.
• the temperature during the drying process is no particular lower limit, but it is usually around room temperature.
• the steel sheet Prior to the film forming step, the steel sheet may be optionally subjected to a pretreatment, which is preferably at least one of degreasing, pickling, and water washing.
• a pretreatment which is preferably at least one of degreasing, pickling, and water washing.
• Degreasing allows the removal of rolling oil, rust-preventive oil, and other substances adhering to the steel sheet. There are no particular restrictions on the degreasing method, and it can be carried out by any method. After degreasing, it is preferable to rinse the steel sheet with water to remove the degreasing treatment liquid adhering to the surface.
• the natural oxide film present on the surface of the steel sheet can be removed, allowing for the effective formation of a chromium-containing layer in the subsequent film formation process.
• the pickling can be performed by any method without any particular restrictions. After the pickling, it is preferable to rinse the steel sheet with water to remove any pickling solution adhering to the surface.
• the uses of the surface-treated steel sheet of the present invention are not particularly limited, but it is particularly suitable as a surface-treated steel sheet for containers used in the manufacture of various containers such as food cans, beverage cans, pail cans, and 18-liter cans.
• electrolyte preparation process First, electrolyte solutions having compositions A to G shown in Table 1 were prepared under the conditions shown in Table 1. That is, each component shown in Table 1 was mixed with water to prepare an aqueous solution, and then the aqueous solution was adjusted to the pH and temperature shown in Table 1. Note that electrolyte solution G corresponds to the electrolyte solution used in the examples of Patent Document 6. Ammonia water was used to increase the pH in all cases, and sulfuric acid was used for electrolyte solutions A, B, and G, hydrochloric acid for electrolyte solutions C and D, and nitric acid for electrolyte solutions E and F to decrease the pH.
• the steel sheet used was a cold-rolled steel sheet. More specifically, a steel sheet for cans (T4 base sheet) having a thickness of 0.17 mm was used.
• the steel sheet was pretreated by electrolytic degreasing, water washing, pickling by immersion in dilute sulfuric acid, and water washing, in that order.
• cathodic electrolysis C1 anodic electrolysis A1
• cathodic electrolysis C2 cathodic electrolysis C2
• cathodic electrolysis C3 cathodic electrolysis C3 in this order as additional electrolysis treatments.
• the conditions for anodic electrolysis A2 were a current density of 2 A/dm 2 , electrolysis time of 0.80 sec, and electricity density of 1.60 C/dm 2.
• the conditions for cathodic electrolysis C3 were a current density of 40 A/dm 2 , electrolysis time of 1.2 sec, and electricity density of 48.0 C/dm 2.
• the electrolytic solution during each electrolysis treatment was maintained at the pH and temperature shown in Table 1.
• An insoluble electrode having iridium oxide coated on a Ti substrate was used as the electrode for each electrolysis treatment.
• the specimen was washed with water having an electrical conductivity of 100 ⁇ S/m or less and then dried at room temperature using a blower. Note that when the electrolysis was performed using electrolytic solution G, the stability of the electrolytic solution was reduced, and a significant chromium-containing layer could not be formed due to the generation of precipitation and hexavalent chromium, so subsequent measurements and evaluations were not performed.
• the amount of chromium deposited per side of the chromium-containing layer and the amount of chromium oxide deposited per side of the steel sheet were measured using the method described above. Furthermore, for each of the obtained surface-treated steel sheets, the atomic ratio of C to Cr in the chromium-containing layer was measured using the method described above. Furthermore, a zero-order persistence diagram was created using the method described above from the distribution image of granular protrusions on the outermost surface of the chromium-containing layer, and the minimum birth size, maximum death size, and the number of data points where the death size was between 0.5 nm and 15 nm were determined. The measurement results are shown in Table 3.
• Laminated steel sheets were produced by laminating an isophthalic acid copolymerized polyethylene terephthalate film with a stretch ratio of 3.1 x 3.1, a thickness of 25 ⁇ m, a copolymerization ratio of 12 mol%, and a melting point of 224°C on both sides of the resulting surface-treated steel sheet.
• the lamination was carried out under conditions that resulted in a crystallinity of the resin film of 10% or less, specifically, a steel sheet feed speed of 40 m/min, a rubber roll nip length of 17 mm, and a time from pressing to water cooling of 1 sec.
• the crystallinity of the resin film was determined using the density gradient tube method in accordance with JIS K7112.
• the nip length refers to the length in the conveying direction of the area where the rubber roll and steel sheet come into contact.
• painted steel plates were prepared as samples to be used to evaluate the paint corrosion resistance using the following procedure.
• An epoxy phenol-based paint was applied to the surface of the obtained surface-treated steel sheet, and baked at 210°C for 10 minutes to prepare a painted steel sheet.
• the coating weight of the paint was 50 mg/ dm2 .
• Film corrosion resistance was evaluated using the following four criteria: film peel width (total width extending from the cut) was measured at four random locations on the crosscut of the laminated steel sheet, and the average of the four values was calculated and considered to be the corrosion width. Paint corrosion resistance was evaluated using the following four criteria: film peel width (total width extending from the cut) was measured at four random locations on the crosscut of the coated steel sheet, and the average of the four values was calculated and considered to be the corrosion width. Film corrosion resistance and paint corrosion resistance were evaluated using the following four criteria: In practice, a rating of 1 to 3 can be said to be excellent in corrosion resistance.

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  • 2025-02-20 WO PCT/JP2025/005948 patent/WO2025204350A1/ja active Pending
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