JP2002146596A - Pretreatment method for coating and formed article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pretreatment method for electrodeposition coating for a metallic molding by which, in electrodeposition coating, the surface of a coating film is made uniform, and its good appearance can be obtained. SOLUTION: In this pretreatment method for coating, a galvanized steel sheet coated with a phosphate film with a film amount of 0.1 to 2 g/m2 is molded, and the above molding is subjected to phosphate film conversion treatment and water washing after the chemical conversion. The pH of the water washing solution in the water washing after the chemical conversion is controlled to the range of 4 to 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pretreatment method for coating a metal molded product, and more particularly, to an electrodeposition coating of a metal molded product having a zinc-plated steel sheet coated with a zinc phosphate film as a sheet metal structure. It relates to a pretreatment method.

[0002]

2. Description of the Related Art In general, a metal molding of an automobile or the like is inspected by an automobile maker or the like to form an electro-galvanized steel sheet on an automobile body, press-weld, and grind an uneven portion of the body with a grindstone. Electrodeposition coating is performed after a series of pre-coating processing steps of degreasing, water washing, surface conditioning, zinc phosphate film chemical conversion treatment, and water washing after chemical conversion are performed.

[0003] Conventionally, electrogalvanized steel sheets carried into an automobile manufacturer have been subjected to treatments such as lubricating oil application and winding in order to maintain good formability. However, in recent years, from the viewpoint of preventing the oxidization of electrogalvanized steel sheet over time and improving the press formability,
Electrogalvanized plated steel sheets that have been coated with a zinc phosphate film in advance have come to be carried in.

Japanese Patent Application Laid-Open No. 8-67989 discloses that one surface of a zinc-based plated steel sheet has an adhesion amount of 0.05 to 0.5 g / m 2.
^A rustproof steel sheet for automobiles is disclosed in which a phosphate crystal film consisting of ² is dispersed and a phosphate film having an adhesion amount of 0.5 to 3.0 g / m ² is formed on the other surface. . this is,
The surface on which the phosphate film having an adhesion amount of 0.5 to 3.0 g / m ² was formed was used as the surface to be the mating portion, and the adhesion amount of 0.05 to 0.3 g / m ² was used.
By providing the surface on which the phosphate crystal film of 5 g / m ² is dispersed and present as the surface of the vehicle body, a rust-proof steel sheet excellent in corrosion resistance, paintability and weldability at the joint is provided. is there.

[0005] However, after the forming and press welding, when a forming inspection such as grinding an uneven portion of the vehicle body with a grindstone is performed, the electrogalvanized steel sheet previously coated with a zinc phosphate film is subjected to a pre-coating treatment. When electrodeposition coating is performed, a large difference in electric resistance occurs between the part shaved with the grindstone and the part not shaved, the electrodeposited coating surface becomes uneven, and the coating film appearance is inferior There was a problem. Although the portion that was cut off with the grindstone was repaired by the formation of a new zinc phosphate film in the pre-coating process, it did not completely eliminate the non-uniformity in electrical resistance. In particular, when a portion cut off with a grindstone after electrodeposition coating becomes a concave scar, it is difficult to repair that portion and the scratch is conspicuous.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrodeposition method for a metal molded article coated with a phosphate film, which has a uniform surface and a good appearance when subjected to electrodeposition coating. An object of the present invention is to provide a method for pre-coating.

[0007]

According to the present invention, a coating amount of 0.1
Since a zinc-based plated steel sheet coated with a phosphate film of up to ² g / m ² is formed, and the above-mentioned formed article is processed by a processing step including a step of subjecting the formed article to a phosphate film conversion treatment and a step of washing with water after the formation, It is a pretreatment method for coating, wherein the pH of the rinsing liquid in the post-chemical conversion rinsing is controlled in the range of 4 to 7. Less than,
The present invention will be described in detail.

[0008] The present inventors have suggested that the pH of the washing solution used in the washing step after chemical conversion is usually about 3 because of the carry-in of the phosphate film chemical conversion treatment which is the preceding step. In some cases, the phosphate film has a large weight loss, which dissolves the acid in the phosphate film.Therefore, the difference in the thickness of the phosphate film between the portion ground by the grindstone and the other portion is large. It was found that the surface of the coating film after coating became uneven. On the other hand, when the pH of the washing liquid used in the washing step after chemical conversion is controlled to be near neutral pH 4 to 7, acid dissolution of the phosphate film is suppressed, and the portion cut off by the grindstone is removed. The present inventors have found that the difference in the thickness of the phosphate film from the unsharpened portion is small, and that the surface of the coated film becomes uniform even when electrodeposition coating is performed, and the present invention has been completed.

That is, in the coating pretreatment method of the present invention,
The pH of the rinsing liquid in the rinsing after chemical formation is controlled in the range of 4 to 7. If the pH is less than 4, the phosphate film undergoes a large amount of acid dissolution due to the dissolution of the phosphate film, so that the difference in the thickness of the phosphate film between the portion that has been ground with the grinding stone and the portion that has not been ground becomes large. The coating film surface becomes non-uniform when applied. Even if the pH exceeds 7, there is no more effect than obtained within the above range, and the amount of the basic compound added to control the pH to exceed 7 increases, which is uneconomical. Preferably, the pH is in the range of 5 to 7, more preferably, pH
It is in the range of 5.5 to 6.5.

[0010] As described above, the washing liquid in the above-mentioned washing after the chemical conversion is usually about pH 3, but it is preferably pH 4 to 4.
In order to control the pH in the range of 7, the object to be treated to which the chemical conversion liquid adheres is washed with a large amount of clean water by a method such as immersion or spraying, and the pH of the washing water in contact with the object is controlled to 4 to 7. How to do
Alternatively, a method in which a basic compound or an aqueous solution thereof is added to the above aqueous solution to control the pH of the washing solution to 4 to 7 is preferable. The basic compound or an aqueous solution thereof is not particularly limited, and examples thereof include sodium hydroxide, potassium hydroxide and their aqueous solutions, and aqueous ammonia. In the method in which the addition of a basic compound or the like is unnecessary, in order to control the pH of the solution in the washing tank to 4 to 7, a part or all of the object to be treated is washed with clean water immediately after the chemical conversion step, and the treatment is performed. A method of discarding water as it is, without using it as feed raw water in the next washing step, may be employed.

A pretreatment method for coating according to the present invention comprises a step of forming a zinc-based plated steel sheet coated with a phosphate film, subjecting the formed article to a phosphate film conversion treatment, and a step of rinsing after the formation. The processing is performed by The base steel sheet used for the galvanized steel sheet is not particularly limited. For example, mild steel sheet, high-strength steel sheet, deep drawn steel sheet, corrosion-resistant steel sheet, steel sheet subjected to a surface modification treatment, which is a normal steel sheet for automobiles, etc. Can be mentioned. The zinc-based plating applied to both surfaces of the steel sheet is performed according to a conventional method, and may be either hot-dip plating or electroplating. The type of the plating film is not particularly limited, either. For example, zinc plating; alloy plating of zinc-iron, zinc-nickel, zinc-chromium, zinc-manganese, etc .; dispersion plating of zinc-SiO ₂ , zinc Cr ₂ O _3, etc. Can be mentioned.

If necessary, the zinc-based plated steel sheet can be previously subjected to degreasing with an alkali degreasing cleaning solution, a phosphorus-free / nitrogen-free degreasing cleaning solution, subsequent cleaning, and surface conditioning. For the above degreasing, subsequent cleaning and surface conditioning,
This can be done according to conventional methods. Next, a phosphate film conversion treatment [1] is performed. The above-mentioned phosphating solution contains normal zinc phosphate as a main component, and as a cation component, other than zinc, Ni ²⁺ , Mg ²⁺ , Co ²⁺ ,
Cu ²⁺ , Mn ²⁺ , Ca ⁺ , Na ²⁺ , Fe ²⁺ , NH ₄ ⁺ ,
H ⁺ , as anion components, PO ₄ ³⁻ , NO ₃ ⁻ , NO _{2
^{-, F -, SiF 6 2-}} , ClO 3 -, may be included SO ₄ ^2-like. In addition, some organic acids and the like can be included.

The amount of the zinc phosphate film formed by the phosphate film conversion treatment [1] is 0.1 to ² g / m ² .
If the amount is less than 0.1 g / m ² , the amount of the film is small, so that press formability and rust prevention are insufficient. If it exceeds ² g / m ² , the weldability will be insufficient. Preferably, 1-2 g / m
² In addition, the surface of the zinc-plated steel sheet to be joined is required to have corrosion resistance.
Is preferably to 1.5 g / m ^2.

The zinc-coated steel sheet subjected to the above-mentioned phosphate film conversion treatment [1] is formed into a target molded product, press-welded, and subjected to a molding inspection such as grinding an uneven portion of the molded product with a grindstone. Will be The molded product is then degreased, washed with water, surface-adjusted, phosphate film chemical conversion treatment [2], washed with water after chemical conversion, and further dried if necessary, and then subjected to electrodeposition coating.

The degreasing, water washing, surface conditioning, and phosphate film conversion treatment [2] performed after the above-described forming may be the same conditions as those performed on the zinc-based plated steel sheet before the forming. However, while the above-mentioned phosphate film conversion treatment [1] is performed in order to secure the performance at the time of forming such as rust prevention, press formability and weldability and before forming, the above-mentioned phosphate film conversion treatment is performed. The chemical conversion treatment [2] is preferably performed for a longer time in the phosphate film chemical conversion treatment [2] from the difference that the chemical conversion treatment [2] is performed in order to ensure high corrosion resistance as a molded product after coating. Although the treatment time depends on the concentration of the chemical conversion treatment solution and the treatment temperature, it is usually 1 to 30 seconds in the phosphate film chemical conversion treatment [1], and 30 seconds to 5 seconds in the phosphate film chemical conversion treatment [2]. Minutes.

After the above-mentioned phosphate film chemical conversion treatment [2] is performed, water washing is performed after chemical conversion. In the present invention, it is necessary to control the pH of the washing solution within the range of 4 to 7. In the above-mentioned post-chemical water washing, either spray water washing or immersion water washing may be used, and water washing can be performed by combining these methods.However, if the water washing after chemical formation is insufficient, the appearance of the coating film and the like in the subsequent electrodeposition coating is reduced. It is preferable to perform several-stage water washing because of adverse effects, and it is appropriate to perform final water washing with pure water. In the case of several-stage washing, it is necessary to control the pH of any of the washing waters in the range of 4 to 7. In the present invention, since it is necessary to constantly control the pH within the range of 4 to 7, an automatic control method in which a part of the washing water is periodically sampled is preferable. After the above-mentioned post-formation water washing, it is dried if necessary according to a known method, and thereafter, electrodeposition coating can be performed.

The coating pretreatment method of the present invention is excellent in rust prevention, press formability and weldability since the amount of the zinc phosphate coating on the pre-treated steel sheet is 0.1 to ² g / m ^2. ,
Since the pH of the rinsing liquid in the rinsing after chemical conversion is controlled in the range of 4 to 7, the thickness of the electrodeposited film after the electrodeposition coating is uniform, and a concave scar is less likely to be generated on the surface.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The above-mentioned phosphate film chemical conversion treatment [2]
After chemical conversion, water washing is usually performed in a combination of multi-stage spray cleaning and immersion cleaning for effective cleaning, and the final cleaning is performed with pure water. From the viewpoint of reduction of the amount, the liquid after each treatment is used as washing water in the washing step in the preceding stage.

FIG. 1 is a flow sheet for controlling the pH of the post-chemical water washing tank. In this, water washing is performed after chemical formation in the order of spray water washing, immersion water washing, and spray water washing. First, the molded product
The spray rinsing is performed by the immersion spray 1, and the rinsing liquid in the immersion rinsing tank 2 is supplied via the spray pump 3 as a pre-treatment liquid. Next, the molded product is immersed in the immersion rinsing tank 2 to effectively clean the interior of the molded product and the bag structure. The pH of the immersion washing tank 2 is set via a pH meter 4.
The controller 5 is connected. The pH controller 5 monitors the pH of the rinsing liquid in the immersion rinsing tank 2 to be in the range of 4 to 7, and a basic aqueous solution is appropriately added to the immersion rinsing tank 2 from the chemical tank 6 by the chemical pump 7. Spray pump ON for spray pump 3-
An OFF signal is issued. Thereafter, the molded product is subjected to spray rinsing with the outlet spray 8, and the post-treatment liquid is supplied to the immersion rinsing tank 2. Note that pure water can be used as the washing liquid used in the outlet spray 8.
By the method of automatically controlling the pH as shown in FIG.
The pH of the washing water in the washing after chemical formation is kept constant, and
In the case of several-stage washing, any of the washing water can be controlled in a pH range of 4 to 7.

[0020]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. Example 1 (1) Pre-coating treatment Commercially available electrogalvanized steel sheet (Gin coat manufactured by Nippon Steel Corporation, untreated; basis weight 30/30; 0.07 cm × 7 cm)
× 15 cm) was subjected to a pre-coating treatment under the following process conditions. Among them, in the chemical conversion treatment step, as shown in Table 1, treatments a to d in which the contact time was changed were performed. Degreasing: Surf Cleaner SD280MZ treatment (degreasing agent manufactured by Nippon Paint Co., Ltd.) Flow immersion at 40 ° C. for 120 seconds Rinse with water: Tap water Running water washing for 10 seconds Wetted Surface adjustment: Surf Fine 5MZ-1 (Nippon Paint Co., Ltd. surface conditioning agent) 20 ° C. 10 Fluid immersion in seconds Chemical treatment: Surfdyne SD2500MZL (Chemical treatment agent manufactured by Nippon Paint Co., Ltd.) 40 ° C Fluid immersion Water washing: Pure water Flowing water washing 10 seconds Liquid contact The weight of the galvanized steel sheet after each of the above treatments a to d The galvanized steel sheet after the treatment is immersed in a 5% by weight solution of chromic anhydride at 20 to 25 ° C. for 5 minutes to dissolve the pre-coating, washed with water and then dried, and the weight difference is measured. Table 1 shows the film amount converted to
It was shown to.

[0021]

[Table 1]

(2) Pre-coating treatment The above-mentioned four types of pre-coating-treated electrogalvanized steel sheets were scratched with linear grindstones. This assumes a molding inspection after the actual molding of the vehicle body. After that, it was processed under the following pre-painting process conditions assuming an automotive pre-painting line. Degreasing: The same method as the degreasing step in the pre-coating treatment (1) First rinsing: Flowing water washing with a 10-fold diluted solution of the degreaser
10 seconds wet contact 2nd water washing: Fluid water washing with 100 times diluted solution of the above degreasing solution 40 ° C 120 seconds flowing immersion Surface adjustment: Same method as the surface adjustment step in pre-coating treatment (1) Chemical conversion treatment: Pre-coating treatment The same method as in the chemical conversion treatment step in (1), except that the liquid contact condition is constant immersion at 40 ° C. for 120 seconds. After the chemical formation, the third washing: pH 6.0 with sodium hydroxide.
After 10 seconds of chemical contact with water, the fourth washing with sodium hydroxide: pH 6.0 with sodium hydroxide.
10 seconds of pure water 5th rinse: running water with pure water for 10 seconds

(3) Cationic electrodeposition coating The pre-treated steel sheet subjected to the above-mentioned coating pretreatment (2) was electrodeposited. Coating conditions: Powertop V-20 (Cation-type electrodeposition coating made by our company) 200V × 30 seconds pressure increase Paint liquid temperature 32 ° C. Pre-coating treated steel plate after pre-coating treatment (2) and pre-coating treatment (1) Measure the difference in weight of the galvanized steel sheet,
The value converted per unit area is shown in Table 2 as the amount of film after water washing.

[0024]Evaluation  1. For electrogalvanized steel sheet that has been pre-coated (1)
Then, the weldability and formability were evaluated as follows.
Was. The results are shown in Table 1.Weldability  A Cu-Cr alloy electrode tip with a tip diameter of 4.5 mm (CF
), And welding was performed under the following conditions. Squeeze time: 30 cycles Welding time: 13 cycles Holding time: 2 cycles Pressure: 250 kgf Under these conditions, the welding current is changed in 0.3 kA steps,
Nugget diameter (4 x (plate thickness)^1/2 ) Minimum current that can form
Range between the current value and the current value generated by dust (appropriate current range)
I asked. An appropriate current range of 1 kA or more was evaluated as good.
Was.

[0025]Formability  The coefficient of kinetic friction due to flat plate drawing was evaluated. 30mm width
Anti-corrosion oil (Knox Last 53 manufactured by Parker Kosan)
0) is 1.5 g / m^Two Apply oil and press load 500kgf
And withdraw at a speed of 200 mm / min.
The dynamic friction coefficient was calculated. Good when the dynamic friction coefficient is 0.12 or less
We evaluated as good. 2. Electrogalvanized steel with cationic electrodeposition coating (3)
Visually check the coating uniformity of the plate including the whetstone scar
Was evaluated. The results are shown in Table 2.

Comparative Example 1 In the pre-coating treatment (2), the same treatment as in Example 1 was performed, except that the pH control with sodium hydroxide was not performed in the third washing after the formation and the fourth washing after the formation. The pH at this time was 3.8. The results are shown in Table 2.

[0027]

[Table 2]

Example 2 In the same manner as in Example 1 except that the pH of the third washing and the fourth washing after chemical conversion were changed as shown in Table 3 in the pre-coating treatment (2) of Example 1, And processed. The pH of the washing solution was adjusted using sodium hydroxide or phosphoric acid. Table 3 shows the evaluation results of the coating uniformity visually.

[0029]

[Table 3]

From the results shown in Tables 2 and 3, when the pH of the washing solution was controlled at 4 to 7, the surface of the coating film which had been electrodeposited was uniform even at the whetstone scar portion. on the other hand,
Comparative Example 1 in which pH control was not performed and the pH of the washing solution was 4
If it is less than 1, the surface of the electrodeposition coating film was concave at the whetstone scar and was not uniform.

[0031]

The coating pretreatment method of the present invention has the above-mentioned structure, so that the surface of the electrodeposition film after the electrodeposition coating is uniform can be obtained.

[Brief description of the drawings]

FIG. 1 is an example of a pH control flow sheet for a post-chemical water washing tank.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Inlet spray 2 Immersion water washing tank 3 Spray pump 4 pH meter 5 pH controller 6 Chemical tank 7 Chemical pump 8 Outlet spray

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Fumihisa Kishimoto 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd. (72) Toshihiro Yoshida 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd. (72) Inventor Seiwa Ishizuka 1 Fujimachi, Hirohata-ku, Himeji City, Hyogo Prefecture Nippon Steel Hirohata Works, Ltd. (72) Inventor Hiroshi Nakamura 1 Fujimachi, Hirohata-ku, Himeji City, Hyogo Prefecture Nippon Steel Hirohata Corporation Inside the steelworks (72) Inventor Kimitaka Hayashi 1 Fuji-cho, Hirohata-ku, Himeji-shi, Hyogo Nippon Steel Corporation Hirohata Works (72) Inventor Tamotsu Sokata 19-17 Ikedanakamachi, Neyagawa-shi, Osaka Nippon Paint Inside (72) Inventor Akira Iino 19-17 Ikedanakacho, Neyagawa-shi, Osaka Japan Paint Co., Ltd. (72) Inventor Shigeaki Hiura Ikedanakacho, Neyagawa-shi, Osaka No.19-17 Nippon Paint Co., Ltd. F term (reference) 4D075 BB65Z BB75Y BB99Z CA33 CA48 DA06 DA23 DB05 DC11 4K044 AA02 BA10 BA17 BB04 BC02 BC04 BC08 CA11 CA16 CA18 CA64

Claims (3)

[Claims] 1. A step of forming a zinc-plated steel sheet coated with a phosphate film having a coating amount of 0.1 to ² g / m ² , a step of subjecting the formed article to a phosphate film chemical conversion treatment, and a step of washing with water after the chemical conversion. A pre-coating treatment method comprising performing the treatment by a treatment step comprising: controlling the pH of the washing liquid in the post-chemical formation washing in a range of 4 to 7. 2. The pre-coating method according to claim 1, wherein the pH of the aqueous solution is controlled in the range of 4 to 7 by adding a basic compound or an aqueous solution thereof to the washing liquid in the post-chemical water washing. 3. A molded article treated by the coating pretreatment method according to claim 1.