JPH0357192B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for chemically forming a zinc phosphate film on an iron-based material, which can form a zinc phosphate film on the surface of an iron-based material even with a chemical conversion solution at room temperature. [Prior art] Conventionally, iron-based materials have been treated with an acidic zinc phosphate-based film conversion solution containing nitrite ions to form a crystalline zinc phosphate-based film, thereby improving the corrosion resistance and corrosion resistance of the surface of iron-based materials. It is well known that it plays an important industrial role in improving paint adhesion. By heating this zinc phosphate-based coating chemical solution, the main component, primary zinc phosphate, becomes Zn(H ₂ PO ₄ ) ₂ ZnHPO ₄ +H ₃ PO ₄ …(1) 3ZnHPO ₄ Zn _{3 4} ) ₂ + H ₃ PO ₄ …(2) dissociates and reaches equilibrium at a certain point. When an iron-based material is immersed in the liquid in this state, iron is dissolved in the liquid due to the reaction 2H ₃ PO ₄ +Fe→ Fe(H ₂ PO ₄ ) ₂ +H ₂ ...(3), and the interaction between the iron-based material surface and the liquid occurs. As the PH of the liquid at the interface increases (the degree of free phosphoric acid decreases), the dissociation of formulas (1) and (2) proceeds from left to right and insoluble secondary or tertiary zinc phosphate is generated. Precipitates as crystals on the surface of iron-based materials,
It is said to be a zinc phosphate-based film. In this way, it is necessary to heat the chemical solution to chemically form a zinc phosphate film on the surface of iron-based materials, and when it is used as a base for painting, it is usually heated to 40 to 85 degrees Celsius. . However, recently there has been a demand for energy saving, and research has begun on a zinc phosphate-based film formation method that can form a film without heating the chemical solution.
Nothing that can meet this demand has yet appeared. [Object of the Invention] The present invention provides a phosphor that can form a good zinc phosphate film on the surface of an iron material by various treatment methods even with a zinc phosphate film conversion solution at room temperature (35°C or lower). The purpose of the present invention is to provide a zinc oxide film formation method. [Structure of the invention] The present invention has been made to achieve the above object,
Iron-based materials are treated with a room-temperature zinc phosphate coating conversion solution that contains 10 ppm or more of trivalent iron ions as a conversion accelerator in the presence of nitrite ions, and maintains a specific pH. A method for chemically forming a zinc phosphate film on an iron-based material, characterized in that a zinc phosphate film is chemically formed on the surface of the iron-based material, the method comprising:
By containing a specific amount of valent iron ions and changing the pH according to the zinc ion concentration in the chemical solution, a good zinc phosphate film can be formed on the surface of iron-based materials without heating the chemical solution. It can be done. The presence of nitrite ions can be confirmed by adding sodium sulfamate to the zinc phosphate coating solution.
It is produced by the generation of _N2 gas. In addition, the method for measuring trivalent iron ion concentration is as follows: Collect an appropriate amount of chemical solution → add 1% oxine acetic acid solution → add 2N ammonium acetate to pH 2.8 to 3.2.
→ add chloroform and shake → filter and dehydrate the separated chloroform layer through a filter paper containing anhydrous sodium sulfate → quantify the trivalent iron ion concentration by absorbance measurement. I can do it. The amount of trivalent iron ions to be contained in the zinc phosphate coating chemical solution is less than 9 ppm, which is somewhat insufficient to achieve the object of the present invention, and it is preferable to contain it to a saturated state of 10 ppm or more, preferably 40 ppm or more. A film can be formed. In order to contain trivalent iron ions in the zinc phosphate coating solution, steel wool or other iron-based materials are immersed in the zinc phosphate coating solution to generate trivalent iron ions, or easily soluble trivalent iron salts, e.g.
Fe (NO ₃ ) ₃・9H ₂ O, FeCl ₃・6H ₂ O, Fe ₂ (SO ₄ ) ₃・
xH ₂ O etc. are added to the zinc phosphate coating chemical solution.
Valence iron ions may also be generated. Further, iron ions eluted during the process of treating iron-based materials with a zinc phosphate-based coating solution at room temperature are also used as trivalent iron ions. In short, when treating iron-based materials, it is important that the zinc phosphate-based coating solution contains trivalent iron ions. The pH of the zinc phosphate coating solution depends on the concentration of zinc ions in the solution, and is preferably in the range of 15-x/3≧y>11-x/3. Here, y represents the PH value of the zinc phosphate-based film forming solution, and x represents the value of the zinc ion concentration (g/) in the zinc phosphate-based film forming solution. If y is larger than 15-x/3, it is difficult to maintain the zinc ion concentration in the chemical solution, and 11
If the value is smaller than -x/3, defective film formation is likely to occur. Table 1 shows an example of the results of an experiment conducted using the normal temperature immersion method while varying the zinc ion concentration and pH in a zinc phosphate film conversion solution containing 50 ppm of trivalent iron ions.

[Table] × Poor film formation △ Precipitate formed in the chemical solution
The total acidity of the zinc phosphate coating chemical solution containing 50 ppm (sample 10 ml, titrant N/10 NaOH, indicator phenolphthalein) is 4 points in Figure A.
Figure B is 5 points, Figure C is 25 points, Figure D is 30 points.
It is a micrograph showing the crystal structure of the film when the points are changed. As you will see,
Coarse crystals are precipitated when the total acidity is 4 points (Figure A), but dense crystals are precipitated when the total acidity is 5 to 30 points (Figures B to D). It can be seen that if the value is 5 points or more, a good zinc phosphate-based film is formed. Therefore, the total acidity of the chemical conversion liquid of the present invention can be used for chemical conversion treatment in the range of 5 to 30 points, but preferably 7 to 20 points, and if it exceeds 30 points, the consumption of the liquid increases and it is not economical. Not only is this undesirable, but the washing water in the next washing step is significantly contaminated, and the amount of water supplied becomes large, making wastewater treatment complicated. FIG. 2 is a graph showing the relationship between the stable amount of trivalent iron ions in the zinc phosphate coating solution and temperature. As is clear from this graph, the conventional humidifying type zinc phosphate coating chemical solution has a
It is impossible to maintain the above trivalent iron ions in the liquid. For example, in Japanese Patent Application Laid-Open No. 55-31144, iron is contained in an amount of 10 to 200 mg/(ppm), but for the above reasons, iron hydroxide is added intermittently or continuously. ing. Furthermore, in this publication, iron hydroxide is added to prevent the reaction of equations (1) and (2) from proceeding and the tertiary zinc phosphate to re-precipitate in the bath. However, this is caused by the heating of the bath,
In the case of the present application, since it is a room temperature type, such reprecipitation phenomenon hardly occurs. Therefore, trivalent iron ions are not included to prevent re-precipitation of tertiary zinc phosphate. The most common treatment method using these chemical liquids is the spray method for painting home appliances, agricultural machinery, steel furniture, etc.; however, for car bodies, the dip method, dip, spray method, etc. There are various methods such as spray, dip method, half-dip method, and intermittent spray method. Furthermore, when applied to coating agents for plastic working such as cold forging of automobile parts and bicycle parts, the dip method is the mainstream. The method for chemically forming a phosphate film according to the present invention can be applied to any of these treatment methods. In addition, there is no problem in applying the present invention to surface chemical conversion treatment using an in-line method for wire rods or a cell method for galvanized steel plates. Example 1 A cold-rolled steel sheet was degreased with alkali, washed with water, and subjected to surface conditioning (Percolene Z treatment...manufactured by Nippon Parkerizing Co., Ltd.), and then treated with a zinc phosphate-based coating chemical solution having the following composition: Zn 3.0g/PO ₄ 7.7g/NO ₃ 1.9g/ Ni 0.1g/ NO ₂ (Added NaNO ₂ ) 0.1g/ Total acidity 12 points PH 3.3 with 10ppm of trivalent iron ion [Fe(NO ₃ ) ₃・9H ₂ O]
After adding and spraying for 2 minutes, washing with water and drying, the appearance was evaluated. Then, epoxy solvent paint EP-1000 (manufactured by Kansai Paint Co., Ltd.) was applied to a thickness of 15 to 20 μm, and the paint was heated at 150℃ for 5 minutes.
Baked and dried for a minute, scratched the painted surface with a cutter knife, conducted a salt spray test according to JIS-Z-2371 for 500 hours, and peeled off the painted surface with cellophane tape.
Table 2 shows the results of measuring the width of the coating film peeled from the scratched area. Example 2 The same cold-rolled steel sheet as in Example 1 was pretreated in the same way and treated with the same zinc phosphate-based film conversion solution,
This is an example when 50 ppm of trivalent iron ions are added. Cold rolled steel sheets were treated under the same conditions as in Example 1 and the same tests were conducted. Table 2 shows the results.

[Table] The general zinc phosphate coating chemical solution used in the present invention includes organic chelating agents such as citric acid, chlorates, oxygen salts such as hydrogen peroxide, nickel, manganese, cobalt, etc. Also includes those containing metal salts. Example 3 Cold-rolled steel sheets were pretreated in the same way as in Example 2, and treated with the same zinc phosphate-based film conversion solution using various treatment methods. Table 3 shows that chemical conversion treatment is possible with any method. This shows that.

[Effect]

In the present invention, trivalent iron ions in the zinc phosphate-based film conversion solution do not contribute as a film component like zinc ions, which are the main component of the chemical solution, but rather as a conversion accelerator. If the pH of the chemical solution is maintained within an appropriate range according to the zinc ion concentration in the zinc oxide film forming solution, these trivalent iron ions will effectively work on the film forming reaction at room temperature, and zinc phosphate will be removed by conventional heating. Demonstrates chemical conversion properties equivalent to those of the system film conversion method. [Effects of the Invention] As explained above, in the present invention, trivalent iron ions are added as a conversion accelerator in the presence of nitrite ions to the zinc phosphate film conversion solution that is commonly used.
By containing 10ppm or more and maintaining the chemical conversion solution at a specific pH depending on the zinc ion concentration in the chemical conversion solution, chemical conversion treatment can be performed at room temperature (below 35℃), and heating means are not required. Therefore, excellent effects can be achieved in that the amount of heat can be saved and heating equipment can be omitted. Moreover, not only does it become unnecessary to control the temperature of the chemical liquid, but since there is no heating, it also has the excellent effect of eliminating inconveniences such as occurrence of yellow rust due to drying of the treated product. Furthermore, the decomposition of nitrite ions in the chemical liquid due to heating can be prevented, making it economically superior from the viewpoint of component management and consumption of the chemical liquid. In addition, since the treatment method can be adapted to various methods, heating pipes are no longer required in the equipment, tank capacity can be reduced, and the sludge generated during phosphate treatment firmly adheres to the heating pipes, preventing heating. Maintenance problems that reduce efficiency are resolved. Furthermore, the spray method has many advantages, such as eliminating the problem of nozzle clogging.

[Brief explanation of drawings]

FIGS. 1A, B, C, and D are micrographs showing the crystal structure of a zinc phosphate film magnified 250 times to show the characteristics of the film processed according to the present invention.
Diagram A is a crystal structure with a total acidity of 4 points, diagram B is a crystal structure with a total acidity of 5 points, and diagram C is a crystal structure with a total acidity of 25 points.
Figure 2 is a graph showing the relationship between the stable amount of trivalent iron ions in a zinc phosphate coating chemical solution and temperature. It is.

Claims (1)

[Claims] 1 Zinc phosphate film chemical formation at room temperature with the essential conditions of containing 10 ppm or more of trivalent iron ions as a chemical conversion accelerator in the presence of nitrite ions and maintaining the pH within the range of the following formula. A method for chemically forming a zinc phosphate film on iron-based materials, which is characterized by treating the iron-based material with a liquid to chemically form a zinc phosphate film on the surface thereof. 15-x/3≧y>11-x/3 y: PH value of zinc phosphate-based film forming solution x: Value of zinc ion concentration (g/) in zinc phosphate-based film forming solution. 2. The film forming solution as set forth in item 1 above is characterized in that the treatment method is one of the following methods: spray method, dip method, spray, dip method, half dip method, dip spray method, and intermittent spray method. Zinc phosphate film conversion method.