JPH07100872B2 - Chemical conversion treatment liquid for aluminum and aluminum alloys - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a novel aluminum and aluminum alloy chemical conversion treatment liquid which imparts excellent corrosion resistance and paint adhesion to the surface of aluminum and aluminum alloy before coating. With regard to this, for example, it is effectively applied to the surface of a lid material of a beverage can, that is, a can end material.

[Prior Art] Chemical conversion treatment liquids for aluminum and aluminum alloys can be roughly classified into chromate type and non-chromate type. Typical chromate types are chromate chromate treatment and phosphoric acid chromate treatment,
Chromate chromate treatment was put into practical use around 1950 and is still widely used for fin materials for heat exchangers. The chemical conversion treatment liquid contains chromic acid (CrO ₃ ) and hydrofluoric acid (HF) as main components, and further contains an accelerator.
A film containing valent chromium is formed. Phosphoric acid chromate chemical conversion treatment is disclosed in US Pat. No. 2,438,877, and the chemical conversion treatment liquid is chromic acid (CrO ₃ ) or phosphoric acid (H ₃ P
O ₄ ), hydrofluoric acid (HF), and the film formed is mainly composed of hydrated chromium phosphate (CrPO ₄ .4H ₂ O). Since this coating does not contain hexavalent chromium, it is still widely used as a coating base treatment for beverage cans and lid materials.

In addition to the chromate type treatment liquid described above, a non-chromate type liquid has been developed, and a representative invention thereof is the one disclosed in JP-A-52-131937. The disclosed processing solution is an acidic aqueous coating solution containing zirconium or titanium or mixtures thereof, phosphates and fluorides and having a pH of about 1.0-4.0. When a treatment is performed using the disclosed chemical conversion treatment liquid, a chemical conversion film containing zirconium or titanium oxide as a main component is formed on the aluminum surface. However, the non-chromate type treatment liquid has the advantage that it does not contain hexavalent chromium, but has the drawback that it is inferior in corrosion resistance and paint adhesion compared to the chromate type treatment liquid.

On the other hand, aluminum alloy plates or coils are painted and widely used as lid materials for beverage cans, that is, as can end materials, but they have undergone chemical conversion treatment to improve corrosion resistance and paint adhesion, and are used in most of Japan. In all cases, chromate phosphate treatment is used. In contrast, the non-chromate type chemical conversion treatment is inferior to the phosphoric acid chromate treatment in paint adhesion, and is currently only partially used in the United States. In the case of phosphoric acid chromate chemical conversion treatment for can end materials, phosphate ion is generally 10.0 to 40.0 g /
l, hexavalent chromium 2.0-4.0g / l and fluorine ion 0.7-1.5
It is treated with a treatment solution containing g / l. At present, vinyl chloride-based paints are mainly used for painting can end materials. That is, the can engineer is produced by a process in which an aluminum alloy coil or plate material is chromated with phosphoric acid, a vinyl chloride-based paint is applied, and then molding is performed.

[Problems to be Solved by the Invention]

The can end formed by using the aluminum alloy or coil treated in the conventional example, and the beverage can in which the beverage can is formed by the can main body filled with juice, beer, etc., is packed after the packing. It is sterilized under considerably severe conditions. In this sterilization step, water vapor permeates the coating film, and the permeated water vapor then condenses at the interface between the coating film and the chemical conversion film, which tends to cause a problem that the adhesion of the coating film is reduced. In fact, when a part of the can end is opened by the easy open method,
Since a defect (enamel feather) due to the peeling of the coating film may occur in the opening portion, the improvement of the coating adhesion is an important issue to be solved in the conventional example as a countermeasure.

[Means for Solving the Problems]

As a concrete means for solving the above-mentioned problems of the conventional example, the present invention provides a phosphate ion of 5.0 to 40.0 g / l and a hexavalent chromium ion of 1.0.
~ 4.0 g / l and fluoride ion 0.1 ~ 2.0 g / l, fluorosilicate ion 4.0 ~ 15.0 g / l or fluoroborate ion containing 0.5 ~ 3.0 g / l, pH to 1.0 ~ 3.0 The present invention provides a chemical conversion treatment liquid for aluminum and aluminum alloys, which imparts excellent corrosion resistance to the surface of aluminum or an aluminum alloy by the chemical conversion treatment liquid and forms a chemical conversion film having excellent paint adhesion. It is possible. That is, it is intended to provide a chemical conversion treatment liquid which imparts excellent corrosion resistance and paint adhesion to the surface of aluminum and aluminum alloy before coating.

[Description of composition and processing steps]

The chemical conversion treatment liquid of the present invention relates to an acidic treatment liquid containing fluorine complex ions, phosphate ions, hexavalent chromium and fluorine ions as essential components.

The fluorine complex ion is selected from fluorosilicate ion and fluoroborate ion. Fluorosilicic acid, fluoroboric acid and soluble salts thereof can be arbitrarily selected and used for containing the fluorine complex ion. In the case of fluorosilicate ion, the range of 4.0 to 15.0 g / l is preferable, and if it is less than 4.0 g / l, good paint adhesion is not limited. On the other hand, if it exceeds 15.0 g / l, etching will increase and the film will not be formed sufficiently.
In the case of fluoroborate ion, the range of 0.5 to 3.0 g / l is preferable, and if it is less than 0.5 g / l, good paint adhesion cannot be obtained. On the other hand, if it exceeds 3.0 g / l, the wastewater treatment becomes poor and there is an economic problem.

It is preferable to use phosphoric acid (H ₃ PO ₄ ) to contain phosphate ions. The content of phosphoric acid is preferably in the range of 5.0 to 40.0 g / l, and if it is less than 5.0 g / l, the amount of chromium phosphate in the formed film will be small and the coating adhesion will be poor. 40.0g / l
Even if it exceeds the above range, a good film is formed, but the cost of the treatment liquid becomes high, which is economically problematic.

Chromic acid (CrO ₃ ) is preferably used to contain hexavalent chromium. The content of chromic acid is preferably in the range of 1.0 to 4.0 g / l as hexavalent chromium ions, and if it is less than 1 g / l, the chemical conversion film is not sufficiently formed and the corrosion resistance is poor. Four.
If it exceeds 0 g / l, the treatment of wastewater of the treatment liquid becomes poor, and there are environmental and economic problems.

Fluoride ion is an important component that affects the film growth rate of the chemical conversion film. Hydrofluoric acid (HF), sodium fluoride (NaF), potassium fluoride (KF) and the like can be used to contain the fluoride ion. The fluorine ion concentration in the chemical conversion liquid was defined as follows. Ion electrode (fluorine
Using F-125, comparative HS-305DP Toa Denpa Kogyo KK and ion meter (IM-40S Toa Denpa Kogyo KK)
Chromic acid 5 g / l, phosphoric acid 15 g / l, and fixed amount of hydrofluoric acid (for example, 0.1 g / l, 1 g / l, 10 g / l) were adjusted to pH 2.0 with phosphoric acid or sodium hydroxide. The solution was used as a standard solution (fluoride ion concentration was defined as the total amount of fluorine in the added hydrofluoric acid) and calibrated. Then, the pH of the chemical conversion liquid was adjusted to 2.0 with phosphoric acid or sodium hydroxide and then measured with a fluorine ion meter, and the measured value was defined as the fluorine ion concentration.

The concentration of this fluorine ion is preferably in the range of 0.1 to 2.0 g / l, and if it is less than 0.1 g / l, the growth rate is too slow, and long-term treatment must be performed to obtain a sufficient chemical conversion film, resulting in poor productivity. There is a problem. On the contrary, if it exceeds 2.0 g / l, there is a problem that the growth rate becomes fast, the amount of film increases, and the appearance becomes opaque. Therefore, the concentration is preferably 0.1 to 2.0 g / l, particularly 0.4 to 1.0 g / l.

The pH of the chemical conversion treatment liquid is controlled in the range of 1.0 to 3.0, and an acid such as phosphoric acid, nitric acid or hydrochloric acid or sodium hydroxide, ammonium hydroxide or the like can be arbitrarily selected and used for adjusting the pH. If the pH is less than 1.0, etching will increase and it will be difficult to form a film. Conversely, if the pH exceeds 3.0, etching will be weak and a uniform film cannot be formed.

Next, a treatment process using the chemical conversion treatment liquid of the present invention will be described. The chemical conversion treatment liquid of the present invention can be used as a substitute for the chromate phosphate treatment liquid which is widely used at present. When the chemical conversion treatment of the present invention is performed on the surfaces of aluminum and aluminum alloys, the surface must first be cleaned, and as a cleaning method therefor, a treatment with an acid-based, alkali-based or solvent-based cleaning liquid or these Any combination of the above may be used. If necessary, the surfaces of aluminum and aluminum alloy may be washed and then further etched with acid or alkali. The treatment method using the liquid of the present invention may be either dipping or spraying, and the treatment temperature and the treatment time are factors that influence the amount of the chemical conversion film formed. The temperature of the processing solution is room temperature to 70 ℃
The range is from 35 to 55 ° C., and the treatment time is preferably from 1 to 90 seconds. The amount of the chemical conversion film is evaluated by the amount of chromium deposited as in the case of the chromate phosphate film. The amount of chromium deposited is preferably in the range of 5 to 50 mg / m ² , and is adjusted according to the degree of corrosion resistance required. The amount of chromium deposited can be controlled by appropriately adjusting the treatment temperature and the treatment time.

The chemical conversion film formed from the chemical conversion treatment liquid of the present invention is equivalent to the film formed in the phosphoric acid chromate treatment, and the chemical conversion film is mainly hydrated or chromium phosphate (CrPO ₄ .4H ₂ O)
Consists of.

〔Example〕

Several examples of the chemical conversion treatment liquid of the present invention will be given below, and their usefulness is shown in Table 1 in comparison with comparative examples.

The material is aluminum-magnesium alloy (JIS A508
2) was used. A small spray device was used for degreasing and chemical conversion treatment of this aluminum alloy. This small-sized spray device is designed to have the same spraying conditions as when sprayed in the continuous chemical conversion treatment line currently used in the chemical conversion treatment of the aluminum alloy coil. Painted for can ends (vinyl chloride type) on chemical-treated aluminum alloy sheets, coating thickness 12-14 μm
It was painted on and baked at 200 ° C for 10 minutes to obtain a test plate.
Further, the amount of chromium deposited on the chemical conversion film was measured using a fluorescent X-ray analyzer (Rigaku Denki Kogyo Model 3070F).

A salt spray test was conducted to evaluate the corrosion resistance. The salt spray test is based on JIS 2-2371 and is expressed as the time until blistering occurs in the coating film cross-cut portion of the test plate after coating. Therefore, the longer the time, the better the corrosion resistance. It is good if the spraying time is 2000 hours or more. For paint adhesion, the test plate after coating is cut into 5 x 150 mm strips and thermocompression bonded with a polyamide film to form a test piece, which is immersed in deionized boiling water for 3 hours and then peeled off by the 180 degree peel test method. Then, the peel strength at that time was evaluated. Therefore, the greater the peel strength, the better the paint adhesion. Generally, a width of 3.0 kgf / 5 mm is good. The enamel feather was evaluated according to the Alcoa method described in the lecture summary of the 73rd Autumn Meeting of the Japan Institute of Light Metals (p49). The evaluation was performed with the maximum width of the remaining coating film after peeling. Therefore, the smaller the remaining width of the coating film, the better the enamel feather. Generally, it is good if the residual width is 0.5 mm or less.

Example 1 An aluminum alloy was washed with a 4% heated aqueous solution (70 ° C.) of a commercially available strong alkaline degreasing agent (registered trademark Fine Cleaner 4418, manufactured by Nippon Parkerizing Co., Ltd.), and then washed with water to clean the surface, Chemical conversion treatment liquid 1 is heated to 50 ° C., sprayed for 5 seconds, then washed with tap water,
After further spraying with deionized water of 3,000,000 Ωcm or more for 10 seconds, it was dried in a hot air drying oven at 70 ° C for 5 minutes. After drying, coating was performed under the above conditions to evaluate corrosion resistance, paint adhesion, and enamel feather.

Chemical conversion treatment liquid 1 40% fluorosilicic acid _{(H 2 SiF 6) 18.8g /} l (SiF 6 2- 7.4g / l) 75% phosphoric acid _{(H 3 PO 4) 21.3g /} l (PO 4 3- 15.5g / l) Chromic acid (CrO ₃ ) 5.8g / l (Cr ⁶⁺ 3.0g / l) 20% Hydrofluoric acid (HF) 3.0g / l (F ^- 0.6g / l) pH 2.0] Ammonium hydroxide Example 2 After cleaning the aluminum alloy under the same conditions as in Example 1, the chemical conversion treatment liquid 2 was heated to 50 ° C. and sprayed for 5 seconds. After the treatment, the performance was evaluated by washing with water, drying and coating under the same conditions as in Example 1.

Chemical conversion treatment liquid 2 40% fluorosilicic acid (H ₂ SiF ₆ ) 12.5g / l (SiF ₆ ^2- 4.9g / l) 75% phosphoric acid (H ₃ PO ₄ ) 21.3g / l (PO ₄ ^3- 15.5g / l) Chromic acid (CrO ₃ ) 5.8g / l (Cr ⁶⁺ 3.0g / l) 20% Hydrofluoric acid (HF) 3.0g / l (F _- 0.6g / l) pH 2.0 (ammonium hydroxide Example 3 After cleaning the aluminum alloy under the same conditions as in Example 1, the chemical conversion treatment liquid 3 was heated to 50 ° C. and sprayed for 5 seconds. After the treatment, the performance was evaluated by washing with water, drying and coating under the same conditions as in Example 1.

Chemical conversion treatment solution 3 40% fluorosilicic acid _{(H 2 SiF 6) 18.8g /} l (SiF 6 2- 7.4g / l) 75% phosphoric acid _{(H 3 PO 4) 21.3g /} l (PO 4 3- 15.5g / l) Chromic acid (CrO ₃ ) 2.9g / l (Cr ⁶⁺ 1.5g / l) 20% Hydrofluoric acid (HF) 3.0g / l (F _- 0.6g / l) pH1.5 (adjusted with hydrochloric acid Example 4 After cleaning the aluminum alloy under the same conditions as in Example 1, the chemical conversion treatment liquid 4 was heated to 50 ° C. and sprayed for 5 seconds. After the treatment, the performance was evaluated by washing with water, drying and coating under the same conditions as in Example 1.

Chemical conversion treatment liquid 4 40% Fluorosilicic acid (H ₄ SiF ₆ ) 18.8g / l (SiF ₆ ^2- 7.4g / l) 75% Phosphoric acid (H ₃ PO ₄ ) 21.3g / l (PO ₄ ^3- 15.5g / l) Chromic acid (CrO ₃ ) 5.8g / l (Cr ⁶⁺ 3.0g / l) 20% Hydrofluoric acid (HF) 5.0g / l (F ^- 1.0g / l) pH 2.0 (sodium hydroxide Example 5 After cleaning the aluminum alloy under the same conditions as in Example 1, the chemical conversion treatment liquid 5 was heated to 50 ° C. and sprayed for 5 seconds. After the treatment, the performance was evaluated by washing with water, drying and coating under the same conditions as in Example 1.

Chemical conversion solution 5 fluoroborate _{(NaBF 4) 1.0g / l (} BF 4 - 0.8g / l) 75% phosphoric acid _{(H 3 PO 4) 21.3g /} l (PO 4 3- 15.5g / l) chromic acid (CrO ₃ ) 5.8g / l (Cr ⁶⁺ 3.0g / l) 20% Hydrofluoric acid (HF) 3.0g / l (F ^- 0.6g / l) pH2.0 (adjusted with ammonium hydroxide) Example 6 After cleaning the aluminum alloy under the same conditions as in Example 1, the chemical conversion treatment liquid 6 was heated to 50 ° C. and spray-treated for 5 seconds. After the treatment, the performance was evaluated by washing with water, drying and coating under the same conditions as in Example 1.

Chemical conversion solution 6 fluoroborate _{(NaBF 4) 2.0g / l (} BF 4 - 1.6g / l) 75% phosphoric acid _{(H 3 PO 4) 21.3g /} l (PO 4 3- 15.5g / l) chromic acid (CrO ₃ ) 5.8g / l (Cr ⁶⁺ 3.0g / l) 20% Hydrofluoric acid (HF) 3.0g / l (F ^- 0.6g / l) pH2.5 (adjusted with ammonium hydroxide) Example 7. After cleaning the aluminum alloy under the same conditions as in Example 1, the chemical conversion treatment liquid 1 was heated to 40 ° C. and spray-treated for 10 seconds. After the treatment, the performance was evaluated by washing with water, drying and coating under the same conditions as in Example 1.

Example 8 After cleaning an aluminum alloy under the same conditions as in Example 1, the chemical conversion treatment liquid 1 was heated to 50 ° C. and spray-treated for 10 seconds. After the treatment, the performance was evaluated by washing with water, drying and coating under the same conditions as in Example 1.

Comparative Example 1 After cleaning an aluminum alloy under the same conditions as in Example 1, the chemical conversion treatment liquid 7 was heated to 50 ° C. and sprayed for 5 seconds. After the treatment, the performance was evaluated by washing with water, drying and coating under the same conditions as in Example 1.

Chemical conversion treatment liquid 7 40% Fluorosilicic acid (H ₂ SiF ₆ ) 6.3g / l (SiF ₆ ^2- 2.5g / l) 75% Phosphoric acid (H ₃ PO ₄ ) 21.3g / l (PO ₄ ^3- 15.5g / l) Chromic acid (CrO ₃ ) 5.8g / l (Cr ⁶⁺ 3.0g / l) 20% Hydrofluoric acid (HF) 3.0g / l (F ^- 0.6g / l) pH 2.0 (ammonium hydroxide Comparative Example 2 After cleaning the aluminum alloy under the same conditions as in Example 1, the chemical conversion treatment liquid 8 was heated to 50 ° C. and sprayed for 5 seconds. After the treatment, the performance was evaluated by washing with water, drying and coating under the same conditions as in Example 1.

Chemical conversion solution 8 of 40% fluorosilicic acid _{(H 2 SiF 6) 40.0g /} l (SiF 6 2- 15.8g / l) 75% phosphoric acid _{(H 3 PO 4) 21.3g /} l (PO 4 3- 15.5g / l) Chromic acid (CrO ₃ ) 5.8g / l (Cr ⁶⁺ 3.0g / l) 20% Hydrofluoric acid (HF) 3.0g / l (F ^- 0.6g / l) pH 2.0 (ammonium hydroxide Comparative Example 3 After cleaning an aluminum alloy under the same conditions as in Example 1, a commercially available 5% aqueous solution of a phosphoric acid chromate agent (registered trademark Alchrome 702, manufactured by Nihon Parkerizing Co., Ltd.) was heated to 50 ° C. Sprayed for 5 seconds. After the treatment, the performance was evaluated by washing with water, drying and coating under the same conditions as in Example 1.

Comparative Example 4 After cleaning an aluminum alloy under the same conditions as in Example 1, a 2% aqueous solution of a commercially available non-chromating agent (registered trademark Palcoat K3761, manufactured by Nihon Parkerizing Co., Ltd.) was heated to 50 ° C. and sprayed for 30 seconds. . After the treatment, the performance was evaluated by washing with water, drying and coating under the same conditions as in Example 1.

As shown in Table 1, it can be understood that by using the chemical conversion treatment liquid of the present invention, excellent corrosion resistance and paint adhesion are obtained, and enamel feather is also excellent.

〔The invention's effect〕

As described above, the chemical conversion treatment liquid for aluminum and aluminum alloys according to the present invention has a phosphate ion of 5.0 to 40.
0g / l, hexavalent chromium ion 1.0-4.0g / l and fluorine ion 0.1-2.0g / l, fluorosilicate ion 4.0-15.0g / l
Or, containing 0.5 to 3.0 g / l of fluoroborate ion and having a pH of 1.0 to 3.0, in particular, by incorporating fluorosilicic acid or fluoroboric acid,
It has an excellent effect that a chemical conversion film having excellent corrosion resistance and paint adhesion can be formed on the surface of aluminum and aluminum alloy before coating.

Claims (1)

[Claims] 1. Phosphate ion 5.0 to 40.0 g / l, hexavalent chromium ion 1.0 to 4.0 g / l, fluorine ion 0.1 to 2.0 g / l, fluorosilicate ion 4.0 to 15.0 g / l or fluoroborate ion. Of 0.5 to 3.0 g / l and having a pH of 1.0 to 3.0. A chemical conversion treatment solution for aluminum and aluminum alloys.