JPH0340120B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for producing a single-sided electrical Pb-Sn alloy plated steel sheet whose non-plated iron surface has excellent phosphating properties and coating performance. (Conventional technology, problems) Pb-Sn alloy electroplated steel sheet is disclosed in Japanese Patent Application Laid-Open No. 54-66338.
However, recently, single-sided steel sheets have been used as steel sheets for fuel containers for automobiles and motorcycles.
There is a demand for the development of Pb-Sn alloy plated steel sheets. The inner surface of the fuel container is a plating layer of a Pb-Sn alloy that has excellent corrosion resistance against fuels such as gasoline, and the outer surface of the fuel container is in high demand for materials for fuel containers that can be coated with corrosion protection and decorative coating. . This Pb-Sn alloy single-sided plated steel sheet is generally produced by cathodic electrolytic treatment in which electricity is applied to an electrode placed opposite the single-sided plated side of the steel strip in an aqueous solution containing Pb ⁺² ions and Sn ⁺² ions. Manufactured in However, on the non-plated surface, there is a very small amount of
Pb and Sn metals are deposited no matter how devised the electrolytic method is. That is, unless a complicated method such as applying an electrolyte adhesion inhibitor to the non-plated surface is applied, there is a method that prevents the electrolytic current from flowing to the non-plated surface, for example, by making the width of the electrode narrower than the width of the steel strip. Alternatively, even if a method is used in which dummy cathodes are provided close to both ends of ^{the steel} strip ^, very small amounts of Pb are
- It is inevitable that Pb-Sn alloy will adhere due to Sn alloy plating. When a very small amount of Pb-Sn alloy is deposited on the unplated surface in this way, the first
As shown in the figure, the phosphoric acid treatment properties of the paint base treatment are significantly inhibited. As a result, the performance after painting, especially the adhesion of the paint over time after being exposed to a corrosive environment for a long time, the corrosion resistance after painting, etc. deteriorate significantly. Therefore, the present invention solves these problems and provides a method for producing a single-sided electrical Pb-Sn alloy plated steel sheet having a non-plated side that is excellent in phosphate treatment and painting performance. The purpose is to (Means for Solving the Problems) The gist of the present invention is to apply electricity to a cathode by applying current from an electrode provided opposite to one side of a steel strip in an aqueous solution containing Pb ²⁺ ions and Sn ²⁺ ions as main components. Electrolytic treatment is applied to produce a single-sided electric Pb-Sn alloy plated steel sheet, and after washing with water, it contains 1 to 100 g of citric acid, tartaric acid, citric acid, formic acid and/or one or more of these salts. An anodic electrolytic treatment is carried out for 0.5 to 10 seconds at a current density of 0.1 to 30 A/dm ² in an aqueous solution containing divalent or trivalent metal ions, and then an anodic electrolytic treatment is performed in an aqueous solution containing divalent or trivalent metal ions.
Pressurize a suspension of phosphate with a pH of 3 to 8 at 100g/
A method for manufacturing a single-sided electrolytic lead-tin alloy plated steel sheet with a non-plated surface that has excellent coating performance, characterized by spraying treatment at 0.5 to 5 Kg/ ^cm2 for 1 to 10 seconds, and Pb ²⁺ ion and Sn ^One- sided electrical Pb-
Manufacture Sn-based alloy plated steel sheets, and after washing with water,
g/ of citric acid, tartaric acid, succinic acid, formic acid and/or
Or an anodic electrolysis treatment is performed for 0.5 to 10 seconds at a current density of 0.1 to 30 A/dm ² in an aqueous solution containing one or more of these salts, and then Ni, Co, Ni-
Co alloy, Ni-P, Co-P, Fe-P, or Ni,
These metals or alloys are applied to the non-plated surface by cathodic electrolysis in an aqueous solution of phosphate containing an alloy consisting of two or more of Co or Fe metals and P.
This is a method for manufacturing a single-sided electrolytic lead-tin alloy plated steel sheet with a non-plated surface that has excellent coating performance and is characterized by adhesion of mg/ ^m2 . (Function) The details of the present invention will be explained below. In the present invention, the plated original plate is used in the normal steelmaking process,
A cold-rolled steel sheet manufactured through a rolling process, annealing process, etc. is used, and it is also subjected to pre-treatments such as degreasing and pickling in the normal manufacturing process of surface-treated steel sheets, and is then cleaned and activated. After that, Pb-Sn was applied to only one side of the steel strip.
Alloy plating treatment is applied. Single-sided electrolytic Pb-Sn alloy plating of a steel strip is usually performed by using a well-known aqueous solution containing Pb ²⁺ ions and Sn ²⁺ ions as the main components as an electrolytic plating bath, and plating only one side of the steel strip. Electricity is applied from the provided electrode, and a Pb-Sn alloy coating layer is applied to only one side of the steel strip. The electrolytic plating bath composition, electrolytic plating conditions, etc. of this Pb-Sn alloy are not specified in any way, and any commonly used method may be used.
For example, the electrode used in single-sided electric Pb-Sn alloy plating may be either a soluble electrode using a Pb-Sn alloy or an insoluble electrode such as a Ti plate coated with platinum. In addition, for the electrolytic plating bath composition, an aqueous solution containing Pb ⁺² and Sn ⁺² ions corresponding to the alloy composition of Pb and Sn, such as a borofluoride bath, a phenolsulfonic acid bath, and a citric acid bath, is used. It will be done. An example is shown below. ( _a ) Example of electrolytic conditions using a borofluoride bath for the purpose of Pb _{- 8} %Sn alloy plating composition ₄ ) ₂ 40g/ H ₃ BO ₃ 25g/ Γ current density 40A/dm ² Γ electrolysis temperature 50℃ (b) Electrolysis conditions using a phenolsulfonic acid bath for the purpose of Pb-12%Sn alloy plating composition Example: Γ electrolytic bath composition PbO 47g / SnO 8g / phenolsulfonic acid 200g / organic additive 5g / Γ current density 5A/dm ² Γ electrolysis temperature 50℃ In this way, it corresponds to the required alloy composition of Pb and Sn. Using an electrolytic plating bath containing an aqueous solution containing Pb ⁺² ions and Sn ⁺² ions, Pb− is applied to only one side of the steel strip with an electrolytic amount corresponding to the required plating thickness.
Perform Sn-based alloy plating treatment and then wash with water. As mentioned above, the plated and iron surfaces of the single-sided Pb-Sn alloy-plated steel sheet manufactured in this way are non-conductive because a trace amount of Pb-Sn alloy adheres to them, deteriorating phosphating properties and painting performance. Remove trace amounts of Pb-Sn alloy attached to the plating surface. For the purpose of the present invention, Pb, Sn, Pb-Sn alloy, etc. attached to the non-plated surface significantly inhibits the formation of a phosphate crystal film whose main component is zinc phosphate, so its removal is an extremely important process. It is carried out under the following conditions. However, a trace amount of material adhered to the unplated surface
In the removal work (operation) of Pb-Sn alloy, other
It is necessary to prevent the Pb-Sn alloy plating surface from dissolving or being damaged, resulting in deterioration of corrosion resistance and discoloration of the plating appearance. As a result of various studies from this point of view, we found that citric acid, tartaric acid, citric acid, formic acid and/or
Or, if an anodic electrolytic treatment is performed in which an electrode is placed only on the side facing the non-plated surface and electricity is applied in an aqueous solution containing one or more of these salts,
It was found that trace amounts of Pb-Sn alloy deposits attached to non-plated surfaces could be removed without impairing the corrosion resistance of the plated surfaces. In other words, the anodic electrolytic treatment in the above treatment bath easily removes trace amounts of Pb-Sn alloy deposits adhering to the non-plated surface, dissolves the Pb-Sn alloy plated surface,
There is almost no deterioration in corrosion resistance or appearance due to damage. Furthermore, in order to obtain this effect, the following processing conditions are used. That is, an aqueous solution consisting of one or more of citric acid, tartaric acid, succinic acid, formic acid, and salts thereof is used, and the concentration thereof is in the range of 1 g/~1000 g/, preferably 5 g/~50 g/. If the concentration is less than 1g/, Pb-Sn adheres to the non-plated surface.
It is difficult to remove deposits from the Pb-Sn alloy, and if the concentration exceeds 100g/, it will dissolve the Pb-Sn alloy plating layer on other plating surfaces, deteriorating the corrosion resistance and deteriorating the appearance due to discoloration. do. In addition, as the salts of citric acid, tartaric acid, succinic acid, and formic acid used in the present invention, Na salts, K salts, and ammonium salts are used. The conditions for the anodic electrolytic treatment of the non-plated surface were: current density: 0.1 A/dm ² to 30 A/dm ² , electrolytic treatment time;
Specify 0.5 to 10 seconds. If the current density is less than 0.1 A/dm ² , it takes too much time to remove the Pb-Sn alloy deposits on the non-plated surface, causing damage to the Pb-Sn alloy layer on the plated surface. Furthermore, if the current density exceeds 30A/ ^dm2 , the removal effect will be saturated and the electrolytic voltage applied between the electrode and the steel strip will increase, which not only increases electricity costs but also causes oxidation of Fe. Undesirable. Also, the preferred current density is 0.5~
It is in the range of 5A/ ^dm2 . Moreover, the electrolytic treatment time is 0.5 to 10 seconds. If it takes less than 0.5 seconds, it will be difficult to uniformly remove the Pb-Sn alloy deposits on the non-plated surface, and if it takes more than 10 seconds, it will dissolve and damage the Pb-Sn alloy plating layer on the plated surface, resulting in deterioration of corrosion resistance and discoloration of the appearance. Deterioration such as this becomes more likely to occur. Therefore, the processing time is 0.5 seconds to 10 seconds, preferably 1 second to 5 seconds. Next, there are no particular regulations regarding the temperature, pH, etc. of the treatment bath, but the treatment temperature is 20 to 80℃, and the pH is
1.5-11 is preferred. If the processing temperature is less than 20℃,
The removal speed is slow, the processing time is too long, and if the processing temperature exceeds 80℃, fumes and mist are generated in the processing bath, which is not favorable for the working environment.
The Pb-Sn alloy plating layer on the plating surface is also prone to discoloration. Regarding pH, if it is less than 1.5, it has little effect on removing deposits of Pb-Sn alloy attached to the non-plated surface, but it discolors the Pb-Sn alloy plating layer on the plated surface. On the other hand, if the pH exceeds 11, it will have little effect on the removal work, but the plating surface will be damaged.
There is a tendency for the Pb-Sn alloy plating layer to dissolve and be damaged, which is unfavorable in terms of corrosion resistance and surface discoloration. Using the above processing conditions and methods, the non-plated surface can be
After removing the Pb-Sn alloy deposits, wash with water. However, when the unplated surface is an iron surface, the Pb-Sn alloy deposits that inhibit the formation of phosphate crystals are removed, but the deposits necessary for the formation of microcells necessary for the formation of phosphate crystals are No oxide film exists. Therefore, the phosphate crystals become coarse and the corrosion resistance after coating deteriorates. Therefore, in the present invention, in order to ensure the phosphatability and post-painting performance of the non-plated surface, Pb-Sn related alloy deposits attached to the non-plated surface are removed,
Next, after washing with water or brushing, a phosphate crystal nucleation promotion treatment is performed. In other words, the formation of phosphate crystals on the steel plate surface is generally considered as follows. The main component of the phosphate treatment solution is acidic zinc phosphate (Zn(H ₂ PO ₄ ) ₂ ), and So (1)
Equilibrium as shown in Eq. 3Zn ₂ ⁺ +2H ₂ PO ₄ ^2- Zn ₃ (PO ₄ ) ₂ +4H ⁺ ...(1) When a steel plate is immersed in this solution, the following dissolution reaction occurs on the surface of the steel plate. Fe+2H ⁺ →Fe ²⁺ +H ₂ ...(2) When this dissolution is viewed microscopically, a couple reaction (microcell) is formed in which Fe ²⁺ is generated at the local anode and H ₂ is generated at the local cathode. At the local cathode, due to the consumption of H ⁺ ions, (1)
The equilibrium of the equation is broken, the reaction proceeds to the right, and as the pH increases, crystals of sparingly soluble Zn ₃ (PO ₄ ) ₂ (hopite, Zn ₃
(PO ₄ ) ₂・4H ₂ O) precipitates out. However, although the main component of the film is hopeite, some of the Fe ²⁺ present at the interface is replaced with Zn (Zn ₃ Fe (PO ₄ ) ₂ .4H ₂ O).
(phosphophyllite) is also formed in small amounts. As described above, phosphate crystals are deposited on the steel plate at the local cathode part of the iron, and a film is formed over the entire surface while changing the positions of the cathode and anode sequentially over time. Therefore, the precipitation reaction of phosphate crystals is an electrochemical reaction that depends on the properties of the steel surface, and a dense phosphate film is formed when a large number of microcells are formed on the surface of the steel sheet. The invisible oxide film on the surface of the steel sheet has a large influence on the formation of microcells, and the thickness of the oxide film significantly influences the formation of crystal nuclei and the size of the crystal nuclei formed. To this end, on the steel sheet surface from which the oxide film has been removed, the active source for microcell formation disappears because the oxide film is removed, and the number of crystal nuclei generated decreases, as well as coarse phosphate crystals. tend not to be generated. This tendency is similar to the unplated surface of single-sided electric Pb-Sn alloy plated steel sheets, which produces uniform and dense phosphate crystal nuclei, which in turn affects the performance after coating, especially the adhesion and corrosion resistance after aging. In order to improve this, it is desirable to take measures to enable the formation of a large number of microcells instead of oxide films on the iron surface. As a countermeasure against this, as a result of various studies, we decided to spray the unplated surface of the steel strip with a suspension containing an insoluble phosphate of a divalent or trivalent metal, particularly preferably with a suspension of zinc phosphate. It has been found that it is preferable to provide an active source that forms a large number of microcells instead of an oxide film. These are then It became the source of phosphate crystal nucleus generation, which significantly promoted the generation of phosphate crystal nuclei, produced uniform and dense phosphate crystals, and significantly improved the performance after painting. In this phosphate suspension spraying treatment, 10 to 100 g of Zn ₃ (PO ₄ ) _{2.5H 2} O etc. (preferably 20 A suspension of pH 3 to 8 (preferably PH 4 to 7) prepared by colloidally suspending ~50g/) in an aqueous solution whose pH has been adjusted with phosphoric acid is heated to a pressure of 0.5 to 5Kg/.
cm ² (preferably 1.5-3.5Kg/cm ² ) pressure at room temperature ~
Spray at 60°C for 1 to 10 seconds (preferably 2 to 5 seconds). In this case, the phosphate suspension was mixed with 10%
Although a concentration of more than 100 g/g is required, the effect reaches a saturation range at an excessive concentration of more than 100 g/1.
Therefore, the concentration of the phosphate suspension is between 10 and 100 g/
And so. In addition, the pH of the phosphate suspension is limited to a range in which phosphate crystal nuclei are likely to be generated; if the pH is less than 3, the formation of crystal nuclei is inhibited by the dissolution of Fe;
When the pH exceeds 8, Fe becomes passivated and the generation of crystal nuclei is hindered. The pressure at which the phosphate suspension thus adjusted is sprayed onto the steel plate is necessary to uniformly generate phosphate crystal nuclei, and is 0.5
If it is less than Kg/ ^cm2 , the distribution of crystal nuclei will be uneven, and 5
When the pressure exceeds Kg/cm ² , the pressure is too strong and it becomes difficult to generate crystal nuclei. The spraying time at this time is within the range necessary to generate dense and fine phosphate crystal nuclei.If the spraying time is short, less than 1 second, the crystal nuclei will be scattered, and if the spraying time is longer than 10 seconds, the crystal nuclei will be scattered. However, there is a problem in that they form coarse crystal nuclei and impair decorative coating properties. For suspensions, Cu ₃ (PO ₄ ) ₂ , Mg ₃
(PO ₄ ) ₂ , Mn ₃ (PO ₄ ) ₂ , Fe(PO ₄ ), or other insoluble phosphates suspended in water are used. Similarly, as a method to form microcells instead of an oxide film, Ni, Co, Ni-Co alloy, Ni-P, which is less soluble in phosphate aqueous solution than Fe, can be coated on the surface of the steel sheet.
Co-P, Fe-P, or an alloy consisting of two or more of Ni, Co, or Fe metals and P is forcibly deposited discontinuously to promote the local dissolution reaction of Fe. It can also serve as an active source for forming a large number of microcells instead of an oxide film. These metals or alloys can be easily applied to the surface of a steel sheet by cathodic electrolyzing only the unplated surface of the steel strip in an aqueous solution containing the ions described above. However, the precipitation form by electrodeposition requires the presence of a large number of discontinuous precipitation nuclei;
The amount of adhesion is in the range of 3 to 30 mg/m ² . If the amount of deposition is less than 3 mg/m ² , the electrodeposit becomes a cathode, and the steel plate surface becomes an anode, resulting in little reaction promotion effect and insufficient effect on the uniform and dense formation of phosphate crystal nuclei. In addition, if the amount of the deposit exceeds 30mg/ ^m2 , the electrodeposit will continue to precipitate, making it difficult for the anode dissolution reaction to occur on the steel plate surface, reducing the microcell generation effect, and forming a uniformly dense phosphate. Crystal formation is inhibited. These deposits therefore range from 3 to 30 mg/m ² , preferably from 5 to 15 mg/m ² . As described above, in the production of single-sided electrical Pb-Sn alloy plated steel sheets, trace amounts of Pb-Sn alloy deposits on the non-plated surface have a negative effect on phosphating properties and coating performance. By removing it without deteriorating the performance of the plated surface, and at the same time further promoting the formation of phosphate crystals,
Due to these combined effects, a single-sided electrical Pb-Sn alloy plated steel sheet with excellent phosphating properties and coating performance can be obtained. In the present invention, the alloy composition of the Pb-Sn alloy plating is not particularly restricted, and may be Pb as the main component and 1 to 50% Sn, or in addition Sb,
Applicable to products with small amounts of alloying elements such as Ni and Co added. (Example) Cold-rolled steel strip was degreased in a 3% sodium orthosilicate aqueous solution, surface cleaned by cathodic electrolytic pickling with a 7.5% H ₂ SO ₄ aqueous solution, and a predetermined alloy composition and adhesion amount were achieved after activation treatment. Pb-Sn alloy plating was carried out on one side, and after plating, the surface was washed with water, and as shown in Table 1, a trace amount of the non-plated surface was removed by the method of the present invention.
Pb-Sn alloy deposits were removed by anodic electrolytic treatment, followed by phosphate treatment, and performance evaluation tests were conducted. As shown in Table 1, the intended performance improvement effect was extremely large. In order to manufacture the single-sided electric Pb-Sn alloy plated steel strip of the present invention, a soluble electrode having the same composition as the target alloy composition is applied to one side of the steel strip in an electrolytic treatment bath at a distance of 20 mm from both ends of the steel strip. At the same time, dummy cathodes were installed approximately parallel to the steel strip and approximately 7.5 mm apart from both ends to prevent the electrolytic current from going around to the non-plated side as much as possible. did. Next, the performance of the single-sided Pb-Sn alloy plated steel sheet manufactured by the method of the present invention was evaluated using the test method and evaluation criteria shown below. Γ Evaluation test method and evaluation criteria 1 Evaluation test method and evaluation criteria for non-plated surface (1) Phosphate treatment method Appearance after phosphate treatment using a full dip type phosphate treatment bath The formation of phosphoric acid crystals was observed using a scanning electron microscope (1500x magnification) and judged based on the following evaluation criteria. ◎……Produces uniformly dense phosphate crystals with a uniform appearance. ○...The appearance is uniform, but the phosphate crystals are somewhat coarse. △... Even in the appearance and microscopic observation using a scanning electron microscope, phosphate crystals were partially formed in areas where no phosphate crystals were formed (spot areas). ×...Appearance shows that there are some areas where phosphate crystals are not clearly formed. (2) Adhesion after painting: Apply 20μ cationic electrodeposition coating, then apply intermediate coating.
Spray coat 35μ and topcoat 30μ respectively.
Painted with 3 coats of 85μ. The test materials were each placed in distilled water at 50℃ for 240 hours.
After soaking for 480 hours, immediately dry and cut into 2mm x 2
100 mm-sized base grids were created, and the adhesion was evaluated by peeling off cellophane tape (registered trademark). ◎...There is almost no peeling of the paint film, and the adhesion is extremely good. ○... Peeling of the paint film is clearly observed, but the peeled area is small at about 5% or less, and the paint film adhesion is quite good. Δ...The peeled area of the paint film was 5 to 20%, and the adhesion of the paint film was quite poor. ×...The peeled area of the paint film is 20% or more, and the paint film adhesion is extremely poor. (3) Corrosion resistance after coating A cationic electrodeposition coating was applied to a thickness of 20 μm, scratches reaching the base metal were made, and the corrosion resistance of the sub-defects in the coating was evaluated by a salt spray test. The evaluation is based on a salt spray test.
After 30 days (720 hours), evaluation was made based on the following criteria, taking into account the appearance of blisters from the scratch area and the occurrence of blisters on other flat areas. ◎...The maximum blistering width on one side of the scratched part is 1.5 mm or less, and the number of blisters on the flat part is less than 5. ○...The maximum blistering width on one side of the scratched part is 3 mm or less, and the number of blisters on the flat part is less than 10. △...The maximum blistering width on one side of the scratched part is 3 mm or less, or the number of blisters on the flat part is less than 20. ×... The maximum blister width on one side of the scratched part is 3 mm or more, or the number of blisters on the flat part is 20 or more. 2 Performance evaluation test method and performance of plating surface (1) Surface appearance Visually observe the Pb-Sn alloy plating surface.
The appearance was evaluated using the following evaluation criteria. ◎……Uniform appearance with no discoloration on the surface. ○...Slight discoloration occurs on the surface, but uniform appearance. △...Slight discoloration occurred on the surface, and slight unevenness occurred in some areas. ×...Surface discoloration is significant and the appearance is uneven. (2) Corrosion resistance The occurrence of red rust after 72 hours of the salt spray test was evaluated using 300 squares of 10 x 10 mm, and the squares in which red rust had occurred were expressed as a percentage, based on the following evaluation criteria. Ivy. ◎……Red rust occurrence rate is less than 10%. ○…Red rust occurrence rate is less than 20%. △……Red rust occurrence rate is less than 40%. ×……Red rust occurrence rate is 40% or more.

【table】

【table】 [Brief explanation of drawings]

FIG. 1 is a diagram showing the trace amount of Pb-Sn alloy deposited on the non-plated surface of a single-sided electrical Pb-Sn alloy-plated steel sheet (an example of 12% Sn) and the phosphate treatment properties. *Evaluation criteria: Using an immersion type phosphate treatment bath, the amount of Pb-Sn alloy deposited on the unplated surface and the state of phosphate crystal formation after phosphate treatment were measured using a scanning electron microscope (1500x magnification). Judgment. ◎……Phosphate crystals are formed uniformly and densely. ○...Phosphate crystals are somewhat coarse, but formed relatively uniformly. △... Generation of phosphate crystal nuclei is observed, but it is quite rough. x... Generation of phosphate crystal nuclei is hardly observed.

Claims (1)

[Claims] 1. ^{One -} sided electrolytic Pb-
Manufacture Sn-based alloy plated steel sheets, and after washing with water,
g/ of citric acid, tartaric acid, succinic acid, formic acid and/or
Or an anodic electrolytic treatment is performed for 0.5 to 10 seconds at a current density of 0.1 to 30 A/dm ² in an aqueous solution containing one or more of these salts, and then the salt containing divalent or trivalent metal ions is treated. PH3 at concentration 10-100g/
A single-sided electrolytic lead-tin alloy plated steel sheet with a non-plated surface and excellent painting performance, characterized by spraying a suspension of phosphates of ~8 at a pressure of 0.5 to 5 Kg/ ^cm2 for 1 to 10 seconds. manufacturing method. 2 ^{One- sided} electrolytic Pb-
Manufacture Sn-based alloy plated steel sheets, and after washing with water,
g/ of citric acid, tartaric acid, succinic acid, formic acid and/or
Or an anodic electrolysis treatment is performed for 0.5 to 10 seconds at a current density of 0.1 to 30 A/dm ² in an aqueous solution containing one or more of these salts, and then Ni, Co, Ni-
Co alloy, Ni-P, Co-P, Fe-P, or Ni,
These metals or alloys are applied to the non-plated surface by cathodic electrolysis in an aqueous solution of phosphate containing an alloy consisting of two or more of Co or Fe metals and P.
A method for producing a single-sided electrolytic lead-tin alloy plated steel sheet having a non-plated surface with excellent coating performance, characterized by adhesion of mg/ ^m2 .