JPH01191785A - Phosphating method and processing solution - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial application field]

The present invention is applicable to metal surfaces such as steel, various galvanized steel sheets (
Pre-painting treatment, especially on the surface of steel sheets such as electrogalvanized steel sheets, hot-dip galvanized steel sheets, alloyed galvanized steel sheets, l: e-Zn-plated steel sheets, Al-Zn-plated steel sheets, etc.) or these alone or in combination. The present invention relates to a phosphate chemical conversion treatment method for forming a chemical conversion film containing Ni and Mn as a pretreatment for cationic electrodeposition coating, and a treatment liquid used in the method.

[Prior art]

Conventionally, as a treatment liquid used for this type of phosphorus M chloride treatment, the one disclosed in Japanese Patent Application Laid-Open No. 60-50175 is well known. This well-known treatment liquid is a technique invented for the purpose of improving water-resistant secondary adhesion by adding Mn.

[Problem to be solved by the invention]

The treatment liquid of the conventional example has a particularly specified concentration ratio of Ni and Mn, and is intended to improve the water-resistant secondary adhesion. is not considered at all. Regarding this salt water corrosion resistance, in most of the conventional inventions, there was a problem in that the performance was significantly deteriorated compared to those without the addition of Mn. In particular, many zinc phosphate treatments on galvanized steel sheets have poor salt water corrosion resistance, but these cannot be determined solely by the composition of the phosphate chemical treatment solution. In other words, even if the water resistant secondary adhesion is improved, the original purpose of corrosion resistance is natural! It has been found that this material is ineffective in terms of corrosion resistance and salt water corrosion resistance, and there is a major problem in improving its inherent corrosion resistance. Furthermore, in the treatment liquid of the conventional example, even if it is carried out within a range of concentration ratios of Ni and Mn, a highly corrosion-resistant film cannot be obtained over the entire range of concentration ratios. In other words, since the optimal treatment conditions for this type of phosphate coating differ depending on the material, the quality of the coating can be determined by individually measuring the corrosion resistance after coating, depending on the composition liquid, treatment method, or type of paint. The reality is that there are variations in these individual measurements, and there is also the troublesome issue of having to conduct multiple tests over multiple ranges and make measurements.

[Means to solve the problem]

As a specific means for solving the problems of the conventional example,
In the present invention, when carrying out a chemical conversion treatment using a treatment solution containing at least Zn, PO4, and F ions and to which Ni and Mn ions are added, a test piece that has been previously chemically treated using the same treatment solution is subjected to a constant current pulse. A phosphate chemical conversion treatment method, characterized in that the optimum conditions for a chemical conversion film are measured by a measuring means, and the amounts of Ni and Mn ions added are controlled based on the data obtained by the measurement, and Ni in the treatment solution. and the content of Mn ions is Mn/Ni<0.5 (weight ratio), the time from the Zn deposition potential to the hydrogen generation potential by constant current pulse measurement means is 2.5 sec or less, and the Ni content rate 1.0-4. Owt%
, Mn content 2.0-4. Owt%, and furthermore, in the chemically converted film, by specifying that at least 10% of the Ni component in the phosphate chemical conversion film remains at the interface with the material. It is possible to improve the natural exposure corrosion resistance and salt water corrosion resistance of steel and various galvanized steel sheets. In particular, in order to solve the problem of severe blistering after painting in salt water or high humidity environments, galvanized steel sheets are processed using constant-fa current pulse measuring means that can measure the state of corrosion. The phosphate film deposited for each solution is modified to the best possible quality, and Ni is deposited on the substrate interface of the borosidi (pores) formed, even under the following circumstances. It is possible to form a chemical conversion film that exhibits high corrosion resistance.

【Example】

Next, the present invention will be explained in more detail. First, the constant current pulse measuring means used in the present invention will be explained. FIG. 1 shows a schematic diagram of a constant current pulse measuring device.
In the figure, 1 is a glass cell, the bottom of which is partially open, and a test plate 2 is placed facing the opening.
The test plate 2 is sandwiched between rubber gaskets 3 and 4 to prevent water from leaking around it, and the test plate is held together with the rubber gasket by a holding plate 5. A counter electrode 6 is inserted into the glass cell. At the same time, a salt bridge 7 is inserted therethrough, and this salt bridge 7 is also provided in the reference electrolytic cell 8 so that current can be passed between them. A predetermined amount of a 5% NaCJ electrolyte 9 is stored in the glass cell 1 and the reference electrolytic cell 8, and a reference electrode 10 is provided in the reference electrolytic cell 8 to measure the reference potential. A galvanostat 11 that supplies a constant pulse current to each electrode and test plate arranged in this way is electrically connected to each of them, and a recorder 12 for recording measurement results is connected to the galvanostat. It is. In addition, 13 is a stopper. When measuring the chemical conversion coating on the test plate 2 using such a device, the test plate is used that has a chemical conversion coating formed on its surface by the method used depending on the treatment solution used. For example, the test plate is exposed to NaOH at pH 1.25.
It is immersed in an aqueous solution for 30 minutes, washed with water, air-dried, and then subjected to measurement. By immersing it in the NaOH aqueous solution in this way,
The porosity of the film expands, resulting in a situation similar to cathodic corrosion under the paint film. Then, the corrosion rate of the film is measured using constant current pulse measuring means. The measurement conditions are as follows. Spoon 11 Electrolyte: 5% NaCj! Temperature: 20°C Interelectrode path l11i: 11 Electrode area: 1.5Qlφ (1,77aJ) Chemical conversion treatment on EG plate (cathode) Reference electrode: Silver/silver chloride counter electrode: Platinum (anode) Constant current: 1,5 mA, On time 30
sec. off time 30SeC. When the chemical conversion coating on the test plate set in the glass cell 1 was measured under the above conditions, the graph shown in FIG. 2 was obtained. In the same graph, t is ff1l (plating corrosion rate) at the time of measurement, Vz is the Zn deposition potential, and VH is the hydrogen generation potential, and the performance of the film can be determined by measuring the time between vZ and VH. . In other words, t indicates the time for Zn eluted from the porosity of the phosphate film to precipitate again during the standing time after being immersed in the electrolytic solution, so since it is a constant current, it is proportional to the amount of dissolved Zn. do. To explain this point in more detail, the amount of Zn dissolved within 30 seconds after the test plate comes into contact with the electrolytic solution is measured. For example, Ni is mixed into the phosphate film added to the processing solution, but some percentage of it is precipitated as Ni0 in the porosity of the phosphate film and forms fine crystals of the phosphate film. At the same time, the cathode polarization of the porosity area is controlled. Therefore, the more Ni0 is precipitated in the porosity portion, the more the base metal is eluted, and the length becomes shorter as measured by the constant current pulse measurement means. In other words, it shows that it is not easily corroded. If there is too much Mn, it becomes difficult for this Ni to be included in the film, so
Corrosion resistance deteriorates. However, since it chemically stabilizes a small amount of Mn1 phosphate film and controls the expansion of porosity, it improves corrosion resistance. From this, the constant current pulse measuring means is suitable for evaluating the corrosion resistance of the phosphate film, and therefore the optimum film properties can be determined. According to research results, at least 10% or more of Ni in the film should be precipitated at the material interface, and furthermore, Ni in the film should be about 1% to 4% of the phosphate film crystals.
%, and Mn is about 2% to 4%.
It is desirable that it be contained. In order to obtain such a phosphate film, the Mn/Niff1ff in the phosphate treatment solution must be
It has been found that it is desirable that the i ratio is 0.5 or less. That is, in measuring the amount of corrosion using a constant current pulse measuring means, the material is first immersed in an aqueous solution of a predetermined pH so that the corrosion under the coating film is obtained, and the time period is 30 minutes to 12 hours. Next, the salt water resistance is evaluated by immersing it in 5% NaCj, but any corrosive solution suitable for the corrosive environment may be used. Electricity is first applied after dipping for a predetermined period of time (approximately 30 seconds); however, if the dipping time is too short, the amount of metal corrosion on the substrate will be small, resulting in measurement errors; on the other hand, if the dipping time is not too long, the eluted metal ions will reach the surface of the substrate. It also spreads offshore, which also causes errors. Next, when current is applied at a constant current of 1°sm A/aJ, the Zn deposition potential becomes vZ and the eluted Zn ions are plated, and when the eluted 7n ions disappear, N2 is generated, that is, hydrogen generation potential (VH) Changes to This VZ
The time t until -VH becomes the time for Zn electrodeposition m, that is, the time for Zn elution, so that minute TI4 erosion of Zn can be accurately measured. Even if there is a lot of Ni in the phosphate film, if there is little Ni precipitated in the porosity portion, t will be long, so at least 10% or more needs to be Ni precipitated at the interface. As the porosity increases, m of the interface Ni also increases, but since the area of the porosity increases, t becomes longer, which is not preferable. Even if there are no phosphate crystals on the metal surface and it is covered only with a N: film, the coating performance will decrease, so the Ni1l in the film is 1.
．． O10-4.0% is desirable. Mn is 2.0 to 4.0
%, t becomes shorter and thicker, but this content range is useful for increasing the alkali resistance of the phosphoric acid film, and if it exceeds this range, t becomes longer. This is because the Ni content in the film decreases. Therefore, t is 3 seconds or less, preferably 2.5 seconds or less. In order to form such a phosphate film, it is necessary to maintain Mn/N i in the phosphate treatment solution to 0.5 or less. Mn is 0.5 to 1.4 g/l 1'atte, and since its amount varies depending on the grade of the material, it cannot be determined for boat fishing, so it is determined by measurement using constant current pulse measuring means. There are characteristics. For example, when examining the effect of the concentration of Ni in the treatment solution for phosphate conversion coatings, the graph in FIG. 3 shows the results. In this case, looking at the corrosion rate of the film formed when the Mn in the treatment solution is 0.99/J, the Ni concentration corresponding to the range of 2.5 seconds is approximately 2.3 to 4.59/fJ. in range. In other words, when the amount of Mn in the treatment liquid is specified, the amount of Ni under optimal conditions is inevitably determined. This determined range is an extremely narrow range, and a good film cannot be formed even if this range is exceeded in any direction. Furthermore, when the effect of the concentration of Ni in the treatment liquid was investigated, the graph in FIG. 4 shows the results. In this case, Ni in the treatment solution is 3.
Looking at the corrosion rate of the film formed at 0g/ρ, 2
．． The Mn concentration corresponding to the 5 second range is approximately 0.5 to 1.2 g.
/j range. This determined range is also an extremely narrow range, and a good film cannot be formed even if this range is exceeded in any direction. Further, the preferable range of the above-mentioned components is such that when the amount of one of the components is specified, the amount of the other component is calculated, and both of these are determined within a narrow range. The determination of the above range also differs depending on the material. Examples are shown in the table below. Next, preferred experimental examples when implementing the method of the present invention are shown below. Experimental example 1 Material Silver zinc (electrogalvanized steel sheet - Nippon Steel II) Chemical process ■Degreasing Fine cleaner 14410 20g/fl
(Manufactured by Nippon Parriki Rising Co., Ltd.) Spray 1 minute, dip 2 minutes ■ Wash with water Spray 30 seconds Room temperature 0 surface adjustment Brebaren 4040 ■ Chemical 43℃ dip 2 minutes ■ Wash with water Spray 30 seconds Room temperature ■ Deionized water wash Spray 30 seconds Room temperature ■ Air dry painting Cationic electrodeposition coating (Nileclone 9400 manufactured by Kansai Paint Co., Ltd.) 20 μm coating thickness After that, medium and top coatings were applied. The composition of the treatment liquid used for chemical formation in (①) above is: Zn ion 1.29/JMn ion
0.9g/JNi ion 3.
0g/j! Silicofluoride ion (as F) 0.7g/j Fluoride ion 0.2g/j phosphate ion
15g/41 NO2 ion 0.059/JNO3 ion 3.0g/j! The gold content of Mn and Ni in the film components formed on the test piece treated with the same treatment solution was 0.09 g of Mn/0.08 g of Ni/TIt,
The content of Mn and Ni in the film component is Mn
2.9wt%Ni2
．． It was 8wt%. As a result of measuring this test piece using a constant current pulse measuring means, t was approximately 2°5.
It was less than sec. The results of alkali resistance and mixed salt water immersion tests showed good results. In addition, although the composition of Ni and Mn was explained in the said Example, it is not limited to this, For example, the compounding ratio of Ni and CalMG or Sr etc. can be similarly carried out.

【Effect of the invention】

As explained above, the phosphate film formed by the phosphate chemical conversion treatment method and treatment solution of the present invention has the effect of most effectively controlling under-film corrosion, and has high corrosion resistance. This has an excellent effect in that it solves the serious problem of the conventional method, which has good second-class water resistance but is inferior in natural exposure and salt water corrosion resistance. Further, the present invention not only allows the corrosion resistance of a phosphate film to be determined, but also has the excellent effect of forming an appropriate phosphate film in accordance with the surface condition of the material. Furthermore, according to the present invention, the optimal phosphate film and its treatment method can be selected without conducting numerous and troublesome corrosion tests, so that the treatment solution for forming the optimal phosphate film for each material can be selected. It also has various excellent effects such as being able to determine the composition.

[Brief explanation of the drawing]

FIG. 1 is a schematic side view of a device used for constant current pulse measurement applied to the method of the present invention, and FIG. 2 is a graph showing the corrosion and precipitation state of Zn in a chemical conversion coating measured by the same device. FIG. 3 is a graph showing the effect of Ni at 11 degrees in the treatment liquid with Mn specified, and FIG. 4 is a graph showing the effect of Mnm degree in the treatment liquid with Ni specified. 1...Glass cell 2...Test plate 3
．． 4...Rubber gasket 5...Press plate 6...
...Opposite 7...Shiobashi 8...
... Reference electrolytic cell 9 ... Electrolyte 10 ...
... Reference electrode 11 ... Galvanostat 12 ... Recorder 13 ... Stopper 1 diagram

Claims (5)

[Claims] (1) Contains at least Zn, PO_4 and F ions,
When carrying out chemical conversion treatment using a treatment solution to which Ni and Mn ions have been added, the optimum conditions for the chemical conversion coating are measured using a constant current pulse measuring means on a test piece that has been previously chemically treated using the same treatment solution. A phosphate chemical conversion treatment method characterized in that the amounts of Ni and Mn ions added are controlled based on data obtained by. (2) The content of Ni and Mn ions in the processing solution is Mn/N
i<0.5 (weight ratio), and the time from the Zn deposition potential to the hydrogen generation potential by constant current pulse measuring means is 2.5 s.
The phosphate chemical conversion treatment method according to claim 1, wherein the phosphate chemical conversion treatment method is less than or equal to ec. (3) Ni content in chemical conversion coating 1.0 to 4.0wt
%, and the Mn content is 2.0 to 4.0 wt%. (4) The phosphate chemical conversion treatment method according to claim 1 or 2, wherein in the chemically converted film, at least 10% of the Ni component in the phosphate chemical film remains at the interface with the material. (5) Zn ion 0.5-1.5g/l, Mn ion 0
．． 5-1.2g/l, Ni ion 2.3-4.5g/l
, fluoride ion or chain fluoride ion is F and 0.
1 to 2 g/l, 5 to 30 g/l of phosphate ions, and a film formation accelerator, and the difference from the metal deposition potential to the hydrogen generation potential by constant current pulse measuring means of the phosphate chemical conversion film to be chemically formed. Phosphate chemical treatment solution adjusted so that the time is 2.5 seconds or less.