JP7729641B2 - Zinc phosphate coating conversion agent for pretreatment of cathodic electrodeposition coating - Google Patents

Description

The present invention relates to a zinc phosphate conversion agent used in spray conversion coating, a pretreatment for cationic electrodeposition coating.

Metal products are generally painted to prevent rust or to enhance their appearance. Before painting, the metal product is degreased and treated with zinc phosphate as a pretreatment to remove grease, dirt, and rust from the metal product, thereby strengthening the adhesion between the paint film and the base material and increasing the corrosion resistance of the paint film.

Painting methods include spray gun painting and dipping. Currently, when corrosion resistance is required, electrodeposition painting, especially cationic electrodeposition painting, is widely used because it provides high corrosion resistance, good adhesion, and coating performance, and is highly productive and suitable for mass production.

When carrying out cathodic electrodeposition coating, zinc phosphate treatment as a pretreatment is essential to fully demonstrate the coating performance. Two types of zinc phosphate coatings are generally known as components of the zinc phosphate coatings formed on the surface of steel products: hopeite, represented by the following formula (1), and phosphophyllite, represented by formula (2). Hopeite and phosphophyllite have different characteristics, with phosphophyllite having better alkali resistance than hopeite.
Zn ₃ (PO ₄ ) _{2.4H 2} O (1)
Zn ₂ M(PO ₄ ) _{2.4H 2} O (2)
(M=metal such as Fe, Ni, Mn, etc.)

When cationic electrodeposition coating is performed after zinc phosphate conversion coating, the quality of the zinc phosphate coating has a significant impact on the corrosion resistance of the coating; if there is little iron, manganese, or nickel other than zinc in the zinc phosphate coating represented by formula (2), the corrosion resistance of the coating tends to decrease. Furthermore, if the weight of the zinc phosphate coating is too large, the corrosion resistance and adhesion of the coating will decrease.

During cationic electrodeposition coating, the pH at the interface rises to around 12 (alkaline) during electrodeposition coating. Therefore, if there is a large amount of hopeite, as shown in formula (1), the zinc phosphate film will dissolve, and this dissolution will reduce the adhesion between the coating and the zinc phosphate film, which in turn reduces the corrosion resistance of the coating.

Phosphophyllite, as expressed by formula (2), is alkali-resistant and does not easily dissolve when the pH at the interface rises during electrodeposition coating. Phosphophyllite itself is also corrosion-resistant. Therefore, during electrodeposition coating, the greater the proportion of phosphophyllite in the zinc phosphate coating, the less the zinc phosphate coating dissolves, improving the corrosion resistance of the coating.

The ratio of hopeite to phosphophyllite in a zinc phosphate coating is called the P ratio, and where P is the amount of phosphophyllite present and H is the amount of hopeite present, the P ratio is expressed as {P ÷ (P + H)} × 100.

Zinc phosphate coating methods can be broadly divided into spray coating conversion treatment, in which chemicals are sprayed onto the metal product, and immersion coating conversion treatment, in which the metal product is immersed in chemicals. In spray coating conversion treatment, chemicals are showered onto the metal product, and a zinc phosphate coating is produced by a chemical reaction between the chemicals and the surface of the metal product. In immersion coating conversion treatment, a zinc phosphate coating is similarly produced by a chemical reaction between the chemicals and the surface of the metal product.

JP 10-168580 Public Relations JP Patent Publication No. Hei 6-57443 JP 4-6281 Public Relations

When comparing the P ratio of zinc phosphate coatings produced by spray coating chemical conversion treatment with that of zinc phosphate coatings produced by immersion coating chemical conversion treatment, the P ratio of zinc phosphate coatings produced by spray coating chemical conversion treatment tends to be lower, generally due to differences in contact time and contact speed with the chemicals. Generally, the P ratio of zinc phosphate coatings produced by spray coating chemical conversion treatment is 60-70%, while the P ratio of coatings produced by immersion coating chemical conversion treatment is 80-95%.

With conventional technology, when zinc phosphate treatment was performed as a spray coating chemical conversion treatment as a pretreatment for cationic electrodeposition coating, it was difficult to produce a zinc phosphate coating with a sufficiently high P ratio.

The present invention was made in consideration of the above-mentioned problems, and aims to provide a zinc phosphate conversion agent that can produce, through spray conversion coating, a zinc phosphate coating with a high P ratio equivalent to that of zinc phosphate coatings produced through immersion conversion coating.

The inventors conducted extensive research to achieve the above-mentioned objectives and discovered that by adjusting the concentrations of calcium ions and nickel ions contained in the zinc phosphate conversion agent to within a specified range, the P ratio of the zinc phosphate coating produced by spray conversion coating becomes comparable to the P ratio of the zinc phosphate coating produced by immersion conversion coating.

The present invention was made based on this finding and has the following configuration.

(Configuration 1)
A zinc phosphate coating conversion agent used in spray coating conversion treatment, which is a pretreatment for cationic electrodeposition coating,
zinc ions, calcium ions, nickel ions, zinc ions, phosphate ions, and nitrate ions;
The concentration of calcium ions ranges from 1000 mg/L to 2000 mg/L;
A zinc phosphate coating conversion agent having a nickel ion concentration ranging from 1000 mg/L to 2000 mg/L.

(Configuration 2)
2. The zinc phosphate coating chemical conversion agent according to claim 1, wherein the calcium ion source is at least one selected from the group consisting of tricalcium phosphate, calcium glycerophosphate, calcium hydroxide, and calcium chloride.

(Configuration 3)
3. The zinc phosphate coating conversion agent according to claim 1, wherein the source of nickel ions is at least one selected from the group consisting of nickel nitrate and nickel carbonate.

(Configuration 4)
4. The zinc phosphate coating conversion agent of any one of claims 1 to 3, wherein the zinc ion concentration is in the range of 1500 mg/L to 2500 mg/L.

(Configuration 5)
5. The zinc phosphate coating conversion agent according to any one of claims 1 to 4, wherein the concentration of phosphate ions is in the range of 15,000 mg/L to 18,000 mg/L.

(Configuration 6)
6. The zinc phosphate coating conversion agent according to any one of claims 1 to 5, wherein the concentration of nitrate ions is in the range of 5,000 mg/L to 12,000 mg/L.

(Configuration 7)
7. The zinc phosphate conversion agent of any one of claims 1 to 6, further comprising manganese ions at a concentration ranging from 200 mg/L to 500 mg/L.

(Configuration 8)
8. The zinc phosphate coating conversion agent according to any one of claims 1 to 7, further comprising sodium ions at a concentration of 5000 mg/L or less.

As described above, the zinc phosphate conversion agent of the present invention contains zinc ions, calcium ions, nickel ions, zinc ions, phosphate ions, and nitrate ions, with the calcium ion concentration ranging from 1000 mg/L to 2000 mg/L and the nickel ion concentration ranging from 1000 mg/L to 2000 mg/L. Therefore, spray conversion coating can produce a zinc phosphate coating with a high P ratio equivalent to that of zinc phosphate coatings produced by immersion conversion coating. Therefore, spray conversion coating of metal products with the zinc phosphate conversion agent of the present invention can provide a base suitable for cationic electrodeposition coating, and a highly corrosion-resistant coating with corrosion resistance equivalent to that produced by immersion conversion coating can be obtained.

1 shows an electron microscope photograph of the surface of a test plate spray-coated with the zinc phosphate conversion solution of Example 1-5. 1 shows an electron microscope photograph of the surface of a test plate spray-coated with the zinc phosphate conversion solution of Comparative Example 1-7. 1 shows an electron microscope photograph of the surface of a test plate subjected to immersion chemical conversion treatment using the zinc phosphate chemical conversion solution of Reference Example.

The following describes in detail the embodiments of the present invention. Note that the following embodiments are merely examples of how the present invention can be realized, and are not intended to limit the scope of the present invention.

A. Zinc Phosphate Coating Conversion Agent The zinc phosphate coating conversion agent of this embodiment is an aqueous solution containing metal ions and an acid component.

1. Metal Ions Metal ions include zinc ions, calcium ions, and nickel ions. Other metal ions such as manganese ions and sodium ions may also be included.

Experience has shown that the zinc ion concentration in the zinc phosphate coating conversion agent should preferably be in the range of 1500 mg/L to 2500 mg/L. If the zinc ion concentration is less than 1500 mg/L, the conversion reaction will not proceed, and if the zinc ion concentration is more than 2500 mg/L, the corrosion resistance of the coating formed by cationic electrodeposition coating will decrease.

In the zinc phosphate coating conversion agent, the concentration of calcium ions is in the range of 1000 mg/L to 2000 mg/L, preferably in the range of 1200 mg/L to 1500 mg/L.
In the zinc phosphate coating conversion agent, the concentration of nickel ions is in the range of 1000 mg/L to 2000 mg/L, preferably in the range of 1200 mg/L to 1500 mg/L.
Calcium ions and nickel ions function to suppress the chemical reaction. When the concentrations of both calcium ions and nickel ions are in the range of 1000 mg/L to 2000 mg/L, it is believed that the chemical reaction is appropriately suppressed and good film crystals are obtained. When the concentration of at least one of calcium ions and nickel ions is less than 1000 mg/L, it is believed that the chemical reaction is not appropriately suppressed and good film crystals are not obtained. When the concentration of at least one of calcium ions and nickel ions exceeds 2000 mg/L, it is believed that the chemical reaction is excessively suppressed and good film crystals are not obtained.

When manganese ions are contained in the zinc phosphate coating conversion agent, experience has shown that the manganese ion concentration should preferably be in the range of 200 mg/L to 500 mg/L. If the manganese ion concentration is less than 200 mg/L, the corrosion resistance of the coating formed by cationic electrodeposition coating will decrease, and if the manganese ion concentration is more than 500 mg/L, the conversion reaction may be inhibited.

When sodium ions are contained in the zinc phosphate coating agent, the sodium ion concentration is preferably 5000 mg/L or less. If the sodium ion concentration exceeds 5000 mg/L, it may not be possible to maintain a stable zinc ion concentration.

Examples of sources of zinc ions include zinc oxide and zinc carbonate.
Examples of calcium ion sources include tricalcium phosphate, calcium glycerophosphate, calcium hydroxide, calcium chloride, and calcium oxide.
Examples of sources of nickel ions include nickel nitrate and nickel carbonate.

Examples of sources of manganese ions include manganese phosphate, manganese nitrate, and manganese carbonate.
An example of a source of sodium ions is sodium hydroxide.

2. Acid Component The acid component contains phosphate ions and nitrate ions. Other acid components may include ions containing fluorine atoms and nitrite ions.

The phosphate ion concentration in the zinc phosphate coating conversion agent is preferably in the range of 15,000 mg/L to 18,000 mg/L. A phosphate ion concentration in this range maintains normal conversion properties and stabilizes each component.

The concentration of nitrate ions in the zinc phosphate coating conversion agent is preferably in the range of 5,000 mg/L to 12,000 mg/L. When the nitrate ion concentration is in this range, normal conversion properties can be maintained and each component is stabilized.

When the zinc phosphate coating conversion agent contains ions containing fluorine atoms, the concentration of the ions containing fluorine atoms is preferably in the range of 500 mg/L to 1200 mg/L. This is because a concentration of ions containing fluorine atoms in this range maintains normal conversion properties and stabilizes each component.

When nitrite ions are contained in the zinc phosphate coating conversion agent, the concentration of nitrite ions is preferably in the range of 400 mg/L to 700 mg/L. This is because normal conversion properties can be maintained when the nitrite ion concentration is in this range. If the nitrite ion concentration is less than 400 mg/L, the conversion reaction will not proceed, and rust may form, resulting in poor conversion. If the nitrite ion concentration is more than 700 mg/L, temper color may appear on the surface of the metal product, and normal conversion may not occur.

Phosphate ion sources include phosphoric acid (orthophosphoric acid).
An example of a source of nitrate ions is nitric acid.

Examples of sources of ions containing fluorine atoms include hydrofluoric acid, fluoroboric acid, and hydrofluosilicic acid.
Sources of nitrite ions include sodium nitrite.

B. Effects The zinc phosphate conversion agent of this embodiment contains zinc ions, calcium ions, nickel ions, zinc ions, phosphate ions, and nitrate ions, with the calcium ion concentration ranging from 1000 mg/L to 2000 mg/L and the nickel ion concentration ranging from 1000 mg/L to 2000 mg/L. Therefore, a zinc phosphate coating with a high P ratio equivalent to that of a zinc phosphate coating produced by a dip-coating chemical conversion treatment can be produced by spray-coating chemical conversion treatment. Therefore, by spray-coating a metal product with the zinc phosphate conversion agent of this embodiment, a substrate suitable for cationic electrodeposition coating can be obtained, and a highly corrosion-resistant coating film with corrosion resistance equivalent to that produced by a dip-coating chemical conversion treatment can be obtained. Furthermore, because a zinc phosphate coating with a P ratio equivalent to that of a zinc phosphate coating produced by a dip-coating chemical conversion treatment can be produced by spray-coating chemical conversion treatment, there is no need to convert the equipment used for spray-coating chemical conversion treatment to that used for dip-coating chemical conversion treatment.

The present invention will be explained in more detail below based on examples and comparative examples. Note that the following examples are merely examples of the present invention and are not intended to limit the scope of the present invention.

The materials used in the examples and comparative examples are as follows.
(a) Metal Ions Tribasic calcium phosphate (manufactured by Yoneyama Chemical Industry Co., Ltd.) was used as a source of calcium ions.
Nickel nitrate (manufactured by Junsei Chemical Co., Ltd.) was used as a source of nickel ions.
Zinc oxide (manufactured by Wako Pure Chemical Industries, Ltd.) was used as a source of zinc ions.
Manganese carbonate (manufactured by Wako Pure Chemical Industries, Ltd.) was used as a source of manganese ions.
Sodium hydroxide (manufactured by Kanto Chemical Co., Ltd.) was used as a source of sodium ions.

(b) Acid Component Phosphoric acid (manufactured by Kanto Chemical Co., Ltd.) was used as a source of phosphate ions.
Nitric acid (manufactured by UBE) was used as a source of nitrate ions.
As a source of ions containing fluorine atoms, fluoroboric acid (manufactured by Stella Chemifa Co., Ltd.) was used.
Sodium nitrite (manufactured by Kanto Chemical Co., Ltd.) was used as a source of nitrite ions.

The properties of the zinc phosphate coating conversion agents of the Examples, Comparative Examples, and Reference Examples are shown in Table 1. In the descriptions of the Examples, Comparative Examples, and Reference Examples, the concentration of each ion is a value based on the entire zinc phosphate coating conversion agent.

Example 1.
The zinc phosphate conversion solution of Example 1 was prepared as follows.
Phosphoric acid and nitric acid were added to water. Zinc oxide, manganese carbonate, tricalcium phosphate, nickel nitrate, and fluoroboric acid were added to the resulting aqueous solution. Furthermore, the free acidity was adjusted to 0.3 pt with sodium hydroxide to optimize the conversion properties, and sodium nitrite was added to appropriately promote the conversion reaction, resulting in the desired zinc phosphate conversion solution.

The resulting zinc phosphate coating solution had a phosphate ion concentration of 16,500 mg/L (a calculated value based on the amount of each material used (hereinafter simply referred to as "calculated value")), a nitrate ion concentration of 12,000 mg/L (calculated value), a zinc ion concentration of 1,500 mg/L (calculated value), a manganese ion concentration of 400 mg/L (calculated value), a calcium ion concentration of 1,200 mg/L (calculated value), a nickel ion concentration of 1,200 mg/L (calculated value), a tetrafluoroborate ion concentration of 700 mg/L (calculated value), a sodium ion concentration of 4,500 mg/L (calculated value), and a nitrite ion concentration of 600 mg/L (calculated value). Furthermore, in the descriptions of the examples, comparative examples, and reference examples, the concentrations of each ion are calculated based on the amount of each material used.

Example 2.
In the same manner as in Example 1, a zinc phosphate conversion solution was prepared.
The resulting zinc phosphate coating solution had a phosphate ion concentration of 16,500 mg/L, a nitrate ion concentration of 10,000 mg/L, a zinc ion concentration of 1,500 mg/L, a manganese ion concentration of 400 mg/L, a calcium ion concentration of 1,200 mg/L, a nickel ion concentration of 1,500 mg/L, a tetrafluoroborate ion concentration of 700 mg/L, a sodium ion concentration of 4,500 mg/L, and a nitrite ion concentration of 600 mg/L.

Example 3.
In the same manner as in Example 1, a zinc phosphate conversion solution was prepared.
In the obtained zinc phosphate coating chemical solution, the phosphate ion concentration was 16,500 mg/L, the nitrate ion concentration was 10,000 mg/L, the zinc ion concentration was 1,500 mg/L, the manganese ion concentration was 400 mg/L, the calcium ion concentration was 1,200 mg/L, the nickel ion concentration was 1,900 mg/L, the tetrafluoroborate ion concentration was 700 mg/L, the sodium ion concentration was 4,500 mg/L, and the nitrite ion concentration was 600 mg/L.

Example 4.
In the same manner as in Example 1, a zinc phosphate conversion solution was prepared.
In the obtained zinc phosphate coating chemical solution, the phosphate ion concentration was 16,500 mg/L, the nitrate ion concentration was 10,000 mg/L, the zinc ion concentration was 1,500 mg/L, the manganese ion concentration was 400 mg/L, the calcium ion concentration was 1,900 mg/L, the nickel ion concentration was 1,200 mg/L, the tetrafluoroborate ion concentration was 700 mg/L, the sodium ion concentration was 4,500 mg/L, and the nitrite ion concentration was 600 mg/L.

Example 5.
In the same manner as in Example 1, a zinc phosphate conversion solution was prepared.
In the obtained zinc phosphate coating chemical solution, the phosphate ion concentration was 16,500 mg/L, the nitrate ion concentration was 10,000 mg/L, the zinc ion concentration was 1,500 mg/L, the manganese ion concentration was 400 mg/L, the calcium ion concentration was 1,900 mg/L, the nickel ion concentration was 1,900 mg/L, the tetrafluoroborate ion concentration was 700 mg/L, the sodium ion concentration was 4,000 mg/L, and the nitrite ion concentration was 600 mg/L.

Comparative Example 1.
In Comparative Example 1, a zinc phosphate coating solution was produced in the same manner as in Example 1, except that tricalcium phosphate was not used.
In the obtained zinc phosphate coating chemical solution, the phosphate ion concentration was 16,000 mg/L, the nitrate ion concentration was 10,000 mg/L, the zinc ion concentration was 1,500 mg/L, the manganese ion concentration was 400 mg/L, the calcium ion concentration was 0 mg/L, the nickel ion concentration was 400 mg/L, the tetrafluoroborate ion concentration was 700 mg/L, the sodium ion concentration was 5,500 mg/L, and the nitrite ion concentration was 600 mg/L.

Comparative Example 2.
In the same manner as in Example 1, a zinc phosphate conversion solution was prepared.
In the obtained zinc phosphate coating chemical solution, the phosphate ion concentration was 16,500 mg/L, the nitrate ion concentration was 10,000 mg/L, the zinc ion concentration was 1,500 mg/L, the manganese ion concentration was 400 mg/L, the calcium ion concentration was 1,200 mg/L, the nickel ion concentration was 500 mg/L, the tetrafluoroborate ion concentration was 700 mg/L, the sodium ion concentration was 4,500 mg/L, and the nitrite ion concentration was 600 mg/L.

Comparative Example 3.
In the same manner as in Example 1, a zinc phosphate conversion solution was prepared.
The resulting zinc phosphate coating solution had a phosphate ion concentration of 16,500 mg/L, a nitrate ion concentration of 10,000 mg/L, a zinc ion concentration of 1,500 mg/L, a manganese ion concentration of 400 mg/L, a calcium ion concentration of 1,200 mg/L, a nickel ion concentration of 3,000 mg/L, a tetrafluoroborate ion concentration of 700 mg/L, a sodium ion concentration of 4,000 mg/L, and a nitrite ion concentration of 600 mg/L.

Comparative Example 4.
In the same manner as in Example 1, a zinc phosphate conversion solution was prepared.
In the obtained zinc phosphate coating chemical solution, the phosphate ion concentration was 16,500 mg/L, the nitrate ion concentration was 10,000 mg/L, the zinc ion concentration was 1,500 mg/L, the manganese ion concentration was 400 mg/L, the calcium ion concentration was 500 mg/L, the nickel ion concentration was 1,200 mg/L, the tetrafluoroborate ion concentration was 700 mg/L, the sodium ion concentration was 4,500 mg/L, and the nitrite ion concentration was 600 mg/L.

Comparative Example 5.
In the same manner as in Example 1, a zinc phosphate conversion solution was prepared.
In the obtained zinc phosphate coating chemical solution, the phosphate ion concentration was 16,500 mg/L, the nitrate ion concentration was 10,000 mg/L, the zinc ion concentration was 1,500 mg/L, the manganese ion concentration was 400 mg/L, the calcium ion concentration was 3,000 mg/L, the nickel ion concentration was 1,200 mg/L, the tetrafluoroborate ion concentration was 700 mg/L, the sodium ion concentration was 4,000 mg/L, and the nitrite ion concentration was 600 mg/L.

Comparative Example 6.
In the same manner as in Example 1, a zinc phosphate conversion solution was prepared.
In the obtained zinc phosphate coating chemical solution, the phosphate ion concentration was 16,500 mg/L, the nitrate ion concentration was 10,000 mg/L, the zinc ion concentration was 1,500 mg/L, the manganese ion concentration was 400 mg/L, the calcium ion concentration was 500 mg/L, the nickel ion concentration was 500 mg/L, the tetrafluoroborate ion concentration was 700 mg/L, the sodium ion concentration was 4,500 mg/L, and the nitrite ion concentration was 600 mg/L.

Comparative Example 7.
In the same manner as in Example 1, a zinc phosphate conversion solution was prepared.
In the obtained zinc phosphate coating chemical solution, the phosphate ion concentration was 16,500 mg/L, the nitrate ion concentration was 10,000 mg/L, the zinc ion concentration was 1,500 mg/L, the manganese ion concentration was 400 mg/L, the calcium ion concentration was 3,000 mg/L, the nickel ion concentration was 3,000 mg/L, the tetrafluoroborate ion concentration was 700 mg/L, the sodium ion concentration was 3,500 mg/L, and the nitrite ion concentration was 600 mg/L.

Reference Example: A reference example is a commercially available immersion zinc phosphate coating conversion solution, Chemicoat No. 5700M (manufactured by Chemicoat Co., Ltd.).

In the zinc phosphate coating solution of the reference example, the phosphate ion concentration is 15,000 mg/L, the nitrate ion concentration is 8,000 mg/L, the zinc ion concentration is 1,500 mg/L, the manganese ion concentration is 400 mg/L, the calcium ion concentration is 0 mg/L, the nickel ion concentration is 400 mg/L, the tetrafluoroborate ion concentration is 700 mg/L, the sodium ion concentration is 5,000 mg/L, and the nitrite ion concentration is 600 mg/L.

<Spray film conversion treatment>
Test plates (cold rolled steel plates (SPCC-SD) manufactured by Nippon Test Panel Co., Ltd.) were spray-coated with the zinc phosphate conversion coating solutions of Examples 1-5 and Comparative Examples 1-7.

The spray coating conversion treatment was carried out in the following manner.
The degreased and water-washed test plates were immersed in 0.2% Chemicoat No. S-2 (manufactured by Chemicoat Co., Ltd.) for 30 seconds to condition the surface. The zinc phosphate coating conversion solutions of Examples 1-5 and Comparative Examples 1-7 were sprayed onto the surface-conditioned test plates at 40°C for 2 minutes. After spraying, the test plates were washed with water and then dried at 100°C for 5 minutes.
When spraying zinc phosphate conversion solution, it is stored in a liquid tank and sent out using a pump, etc. A nozzle is attached to the destination, allowing the zinc phosphate conversion solution to efficiently come into contact with the test plate. After contact, the solution returns to the liquid tank and is circulated for reuse.

<Immersion chemical conversion coating>
A test plate (a cold-rolled steel plate (SPCC-SD) manufactured by Nippon Test Panel Co., Ltd.) was subjected to a dip coating conversion treatment using the zinc phosphate coating conversion solution of the reference example.

The dip coating chemical conversion treatment was carried out in the following manner.
The degreased and water-washed test plate was immersed in 0.2% Chemicoat No. S-2 for 30 seconds to condition the surface. The surface-conditioned test plate was then immersed in the zinc phosphate coating solution of the Reference Example at 40°C for 2 minutes. After immersion, the test plate was washed with water and then dried at 100°C for 5 minutes.

<Electron microscope photography>
The chemically treated test plate was photographed using an electron microscope (TM-3030Plus, manufactured by Hitachi High-Technologies Corporation) at a magnification of 1000 times.

Figure 1 shows an electron microscope photograph of the surface of a test plate that was spray-coated using the zinc phosphate conversion solution of Example 1-5, Figure 2 shows an electron microscope photograph of the surface of a test plate that was spray-coated using the zinc phosphate conversion solution of Comparative Example 1-7, and Figure 3 shows an electron microscope photograph of the surface of a test plate that was immersion-coated using the zinc phosphate conversion solution of the Reference Example.

From the electron microscope photograph of FIG. 1, it can be seen that the zinc phosphate coating formed using the zinc phosphate coating conversion solution of Example 1-5 is composed of uniform and dense crystals.
From the electron microscope photograph of FIG. 2, it can be seen that the zinc phosphate coating formed using the zinc phosphate coating conversion solution of Comparative Example 1-7 is composed of needle-like crystals, with gaps existing between the crystals.
From the electron microscope photograph of FIG. 3, it can be seen that the zinc phosphate coating formed using the zinc phosphate coating conversion solution of the Reference Example is composed of uniform and dense crystals.

<Measurement of P ratio>
The P ratios of the zinc phosphate coatings formed using the zinc phosphate coating solution of Example 1-5, the zinc phosphate coating solution of Comparative Example 1-7, and the zinc phosphate coating solution of Reference Example were measured.

The P ratio was measured as follows.
The chemically treated test plate was placed in an X-ray diffractometer (Rigaku Corporation, RINT2500HLB) and the zinc phosphate coating was irradiated with X-rays. From the X-ray diffraction results, the X-ray intensity of hopite (H) and the X-ray intensity of phosphophyllite (P) were measured, and the P ratio = {P ÷ (P + H)} × 100 was calculated.
As shown in Table 1, the P ratio of the zinc phosphate coating film formed using the zinc phosphate coating conversion solution of Example 1-5 was higher than the P ratio of the zinc phosphate coating film formed using the zinc phosphate coating conversion solution of Comparative Example 1-7, and was comparable to the P ratio of the zinc phosphate coating film formed using the zinc phosphate coating conversion solution of the Reference Example.

<Electrodeposition coating>
The chemically treated test panels were subjected to cathodic electrodeposition coating.
The cathodic electrodeposition coating was carried out as follows.

The chemically treated test panel was immersed in paint (Kansai Paint, product name KG530), and a voltage of 250 V was applied between the electrodes for 4 minutes to form a coating film on the surface of the chemically treated test panel. After the coating film was formed, it was baked at 220°C for 20 minutes.

<Primary Adhesion Test>
The electrodeposition coated test plates were subjected to a primary adhesion test based on JIS K5600-5-6.

The primary adhesion test was carried out as follows.
One hundred 1 mm squares were formed on an electrodeposition-coated test plate, and cellophane tape was pressed against the 100 squares. The cellophane tape was quickly peeled off and the state of peeling of the coating film was observed. The number of squares where the coating film was not peeled off was counted. The greater the number of squares where the coating film was not peeled off, the better the evaluation of adhesion performance.

As shown in Table 1, when the test plate was pretreated with any of the zinc phosphate coating solutions of Example 1-5, Comparative Example 1-7, and Reference Example, the primary adhesion test result was 100/100 (i.e., no peeling of the coating occurred from any of the 100 squares), indicating good coating adhesion.

<Saltwater hot water immersion test>
The electrodeposition coated test plates were subjected to a hot salt water immersion test.

The hot salt water immersion test was carried out as follows.
A cross-cut was made in the coated test panel, reaching both the coating and the substrate. The test panel with the cross-cut was immersed in a 5% aqueous sodium chloride solution heated to 50°C for 240 hours. After rinsing with water, cellophane tape was pressed along the cross-cut. The cellophane tape was quickly peeled off and the state of peeling of the coating film was observed. The narrower the width of the peeled coating, the better the corrosion resistance was evaluated.
In Table 1, a peeled width of the coating film of 1 mm or less is given an A rating, a peeled width of more than 1 mm but less than 3 mm is given a B rating, and a peeled width of 3 mm or more is given a C rating.

As shown in Table 1, when the test plate was pretreated (spray coating chemical treatment) with the zinc phosphate coating solution of Example 1-5, the result of the saltwater hot water immersion resistance test was rated A. When the test plate was pretreated (spray coating chemical treatment) with the zinc phosphate coating solution of Comparative Example 1-7, the result of the saltwater hot water immersion resistance test was rated B or C. When the test plate was pretreated (immersion coating chemical treatment) with the zinc phosphate coating solution of the Reference Example, the result of the saltwater hot water immersion resistance test was rated A. When the test plate was pretreated (spray coating chemical treatment) with the zinc phosphate coating solution of Example 1-5, a coating film with saltwater hot water immersion resistance comparable to that formed when the test plate was pretreated (immersion coating chemical treatment) with the zinc phosphate coating solution of the Reference Example was formed.

<Salt spray resistance test>
The electrodeposition coated test plates were subjected to a salt spray resistance test based on the neutral salt spray test method described in JIS Z2371.

The salt spray resistance test was carried out as follows.
A cross-cut was made in the painted test panel, reaching the paint and the substrate. The test panel with the cross-cut was subjected to a salt spray resistance test for 1000 hours based on the neutral salt spray test method described in JIS Z2371. After rinsing with water, cellophane tape was pressed along the cross-cut. The cellophane tape was quickly peeled off and the peeling state of the coating film was observed. The narrower the width of the peeled coating, the better the corrosion resistance was evaluated.
In Table 1, a peeled width of the coating film of 1 mm or less is given an A rating, a peeled width of more than 1 mm but less than 3 mm is given a B rating, and a peeled width of 3 mm or more is given a C rating.

As shown in Table 1, when the test plate was pretreated (spray coating conversion treatment) with the zinc phosphate coating solution of Example 1-5, the salt spray resistance test result was rated A. When the test plate was pretreated (spray coating conversion treatment) with the zinc phosphate coating solution of Comparative Example 1-7, the salt spray resistance test result was rated B or C. When the test plate was pretreated (immersion coating conversion treatment) with the zinc phosphate coating solution of the Reference Example, the salt spray resistance test result was rated A. When the test plate was pretreated (spray coating conversion treatment) with the zinc phosphate coating solution of Example 1-5, a coating film with salt spray resistance comparable to that formed when the test plate was pretreated (immersion coating conversion treatment) with the zinc phosphate coating solution of the Reference Example was formed.

In the zinc phosphate coating solution of Examples 1-5, the calcium ion concentration ranged from 1000 mg/L to 2000 mg/L, and the nickel ion concentration ranged from 1000 mg/L to 2000 mg/L. The P ratio of the zinc phosphate coating produced by spray-coating with the zinc phosphate coating solution of Examples 1-5 was comparable to the P ratio of the zinc phosphate coating produced by immersion-coating with the zinc phosphate coating solution of the Reference Example. Therefore, when the test plate was pretreated (spray-coating) with the zinc phosphate coating solution of Examples 1-5, a highly corrosion-resistant coating was obtained with corrosion resistance equivalent to that of the test plate pretreated (immersion-coating) with the zinc phosphate coating solution of the Reference Example. Furthermore, the coating produced when the test plate was pretreated (spray-coating) with the zinc phosphate coating solution of Examples 1-5 had high adhesion.

As mentioned above, the present invention has been described in detail based on the embodiments and examples, but the present invention is not limited to these. It is clear that a person with ordinary skill in the relevant field can make modifications and improvements within the technical spirit of the present invention.

Claims (9)

A zinc phosphate coating conversion agent used in spray coating conversion treatment, which is a pretreatment for cationic electrodeposition coating,
containing calcium ions, nickel ions, zinc ions, phosphate ions, and nitrate ions;
The concentration of calcium ions ranges from 1000 mg/L to 2000 mg/L;
A zinc phosphate coating conversion agent having a nickel ion concentration ranging from 1000 mg/L to 2000 mg/L. The zinc phosphate coating conversion agent according to claim 1, wherein the calcium ion source is at least one selected from the group consisting of calcium triphosphate, calcium glycerophosphate, calcium hydroxide, and calcium chloride. The zinc phosphate coating conversion agent according to claim 1, wherein the source of nickel ions is at least one selected from the group consisting of nickel nitrate and nickel carbonate. The zinc phosphate coating conversion agent according to claim 1, wherein the zinc ion concentration is in the range of 1500 mg/L to 2500 mg/L. The zinc phosphate coating conversion agent according to claim 1, wherein the concentration of phosphate ions is in the range of 15,000 mg/L to 18,000 mg/L. The zinc phosphate coating conversion agent according to claim 1, wherein the concentration of nitrate ions is in the range of 5,000 mg/L to 12,000 mg/L. A zinc phosphate coating conversion agent used in spray coating conversion treatment, which is a pretreatment for cationic electrodeposition coating,
containing calcium ions, nickel ions, zinc ions, phosphate ions, and nitrate ions;
The concentration of calcium ions ranges from 1000 mg/L to 2000 mg/L;
The concentration of nickel ions ranges from 1000 mg/L to 2000 mg/L;
A zinc phosphate coating conversion agent further comprising manganese ions at a concentration ranging from 200 mg/L to 500 mg/L. A zinc phosphate coating conversion agent used in spray coating conversion treatment, which is a pretreatment for cationic electrodeposition coating,
containing calcium ions, nickel ions, zinc ions, phosphate ions, and nitrate ions;
The concentration of calcium ions ranges from 1000 mg/L to 2000 mg/L;
The concentration of nickel ions ranges from 1000 mg/L to 2000 mg/L;
A zinc phosphate coating conversion agent further comprising sodium ions at a concentration of 5000 mg/L or less. 9. The zinc phosphate coating chemical agent according to claim 1, wherein the content of phosphophyllite in the zinc phosphate coating formed by spray coating chemical treatment with the zinc phosphate coating chemical agent is P and the content of hopite is H, and the content (%) of phosphophyllite calculated by {P÷(P+H)}×100 is 90% or more.