JPH06116741A - Coating pretreatment of aluminum metal or aluminum plated steel products - Google Patents

Abstract

PURPOSE:To provide the method for coating pretreatment of aluminum metals or aluminum plated steel products intended to improve water resistant secondary adhesion. CONSTITUTION:A zinc phosphate chemical conversion film is formed by a zinc phosphate chemical conversion treating liquid contg. a fluoride on the surfaces of the aluminum metals or aluminum plated steel products, the surfaces having the film are washed with hot water. As a result, the high effect of greatly improving the water resistant secondary adhesion without damaging the chemical conversion film is obtd. by the treatment simple to operate. In addition, the need for additional treatment stags and addition of chemicals is eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an aluminum-based metal or an aluminum-plated steel material, specifically, an aluminum plate, an aluminum alloy plate, a zinc-aluminum alloy-plated steel sheet, an aluminum die cast material (hereinafter referred to as an aluminum-based metal material The present invention relates to a pretreatment method for coating, which is particularly applicable to a pretreatment method for coating, which can remarkably improve the adhesion of a coating film after coating after treatment.

[0002]

2. Description of the Related Art Zinc phosphate chemical conversion treatment and chromate treatment are generally used as a pretreatment for coating an aluminum-based metal material, particularly as a coating base treatment. Among these, the zinc phosphate chemical conversion treatment is superior to the chromate treatment containing the harmful hexavalent chromium in the wastewater treatment of the treatment liquid, and simultaneously treats various metal materials such as cold-rolled steel sheets and galvanized steel sheets. It is advantageous in that it can be used, and is now widely used for automobile bodies and household electric appliances.

When an aluminum-based metal material is treated with a zinc phosphate-based chemical conversion treatment liquid to form a zinc phosphate-based chemical conversion coating on the surface of the aluminum-based metal material, a chemical conversion reaction proceeds, so that the presence of impurities on the surface of the aluminum-based metal material. It is necessary to remove the dynamic film, and an etching agent is used for the removal. A fluorine compound is usually used as an etching agent. When a zinc phosphate chemical conversion treatment is applied to an aluminum-based metal material, the aluminum ions eluted by etching hinder the chemical conversion reaction, resulting in a very short life of the treatment liquid. It has been extremely rare to apply it to metallic materials. Therefore, even if the coating is applied after the chemical conversion treatment, a high performance value is not often required for the coating performance.
Further, when a fluorine-based etching agent was used, the phosphate film had unevenness in uniformity because a method for controlling fluoride was not established.

However, after that, a method has been established in which an aluminum ion is removed out of the system as a co-deposited product by adding an additive to the treatment liquid (JP-A-2-277781).
No.), and by controlling the concentration of the fluorine compound in the etching agent in order to improve the variation in the uniformity of the phosphate film formed on aluminum, uniform etching is performed and the uniformity of the phosphate film is ensured. (JP-A-63-157879). By such a method, even in the zinc phosphate chemical conversion treatment of an aluminum-based metal material, a uniform chemical conversion film was obtained and continuous treatment became possible.

However, recently, a high degree of quality is required in pretreatment for coating such as automobile bodies, and not only the adhesiveness (primary adhesiveness) of the coating film when coated after forming the chemical conversion film, but also in the natural environment. The quality of the adhesiveness (secondary adhesiveness) of the coating film after a long time under high temperature, especially the secondary adhesiveness to moisture absorption (hereinafter referred to as water resistant secondary adhesiveness) is required. ing. However, the zinc phosphate-based chemical conversion coating film currently formed on the surface of an aluminum-based metal material does not have sufficient water-resistant secondary adhesion.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide an excellent water-resistant secondary surface on the surface of an aluminum-based metal or an aluminum-plated steel material. The purpose is to form a zinc phosphate-based chemical conversion film that also has adhesion.

[0007]

[Means for Solving the Problems] In order to solve the above-mentioned conventional problems, the present inventors first conducted a detailed investigation on the state of a zinc phosphate-based chemical conversion coating that was washed and dried after forming the chemical conversion coating. . As a result, it was discovered that eutectoids different from the composition of the film were present in the phosphate film. As a result of examining the correlation between the eutectoid and the water-resistant secondary adhesion, it was discovered that the more the eutectoid, the worse the water-resistant secondary adhesion.
When this co-deposited product was analyzed by fluorescent X-ray, fluorine (F) was detected, and further chemical analysis (atomic absorption analysis, etc.)
By this, Na and Al were detected. From the results of this analysis, it was inferred that the eutectoid was probably a complex fluoride compound such as Na ₃ AlF ₆ . These are considered to be present together with the crystals of the zinc phosphate-based conversion coating. The complex fluoride compound is generated when the surface of the aluminum-based metal material is etched by the fluorine-based etching agent, but these should be removed to the outside of the system by the addition treatment of the additive.
However, the fact that the complex fluoride-based compound exists together with the crystals of the zinc phosphate-based chemical conversion film means that the complex fluoride-based compound generated near the aluminum surface is in the crystals of the zinc phosphate-based chemical conversion film or crystal grains for some reason. It seems that it was adsorbed to the field and remained.

Therefore, the inventors of the present invention have earnestly studied to eliminate the factor of deterioration of the water-resistant secondary adhesiveness due to these fluoride-based eutectoid products. The method is a method of not depositing as a co-deposited material, or a method of removing the deposited co-deposited material.
Since no suitable method was found for the method of not depositing the co-deposited substance as described above, a method for removing the deposited co-deposited substance of was investigated.

Currently, the zinc phosphate chemical conversion coating on the surface of the aluminum metal material is washed with water at room temperature after the coating is formed. In this method, since the fluoride-based eutectoid remains, the water-resistant secondary adhesion is extremely poor. Therefore, in order to remove the eutectoids that are the cause of the deterioration of the water resistant secondary adhesion, an acid and alkali cleaning was tried. It was found that this method certainly removes the eutectoid, but has a drawback that the formed zinc phosphate-based chemical conversion coating is also damaged. Therefore, as a result of various studies on methods that do not damage the zinc phosphate-based chemical conversion coating, it was discovered that the eutectoid can be removed by washing with warm water without damaging the zinc phosphate-based chemical conversion coating, and the present invention was completed. .

That is, the present invention forms a zinc phosphate-based chemical conversion coating on the surface of an aluminum-based metal or an aluminum-plated steel material with a zinc phosphate-based chemical conversion treatment liquid containing a fluoride, and then the surface having the coating. The present invention provides a method for pretreatment of coating of an aluminum-based metal or an aluminum-based plated steel material, which comprises cleaning the material with warm water.

The structure of the present invention will be described in detail below. The basic treatment steps of the present invention include alkali degreasing, normal temperature water washing, zinc phosphate chemical conversion treatment, warm water washing, deionized water washing, and drying in this order on the surface of the aluminum-based metal or the aluminum-plated steel material, followed by coating treatment. Is a process step of applying. The greatest feature of the present invention is that the zinc phosphate-based chemical conversion coating film formed on the surface of the aluminum-based metal or the aluminum-based plated steel material is washed with warm water. Washing with warm water must be performed at least once, and the effect is not diminished if it is between the zinc phosphate chemical conversion treatment step and the coating treatment step (before drying). Further, each step may be processed in multiple stages. As a pre-step of the zinc phosphate-based chemical conversion treatment step, a surface adjusting step using a titanium colloid type surface adjusting agent may be provided for the purpose of refining the film crystals.

The washing conditions of the warm water washing are 40
It is necessary to carry out at least once for 20 seconds or more by a spraying method or a dipping method at a water temperature of not less than 0 ° C., and under these conditions, the eutectoid can be removed, and the remarkable effect of improving the water-resistant secondary adhesion can be obtained. If the water temperature is less than 40 ° C. or the treatment time is less than 20 seconds, the effect is not sufficient.
Further, it is particularly preferable to perform the treatment at 50 to 80 ° C. for 30 to 120 seconds.

As the treatment liquid in the zinc phosphate chemical conversion treatment step, an ordinary zinc phosphate chemical conversion treatment liquid is used. That is, zinc ion 0.4 to 2.5 g / L, nickel ion 0.3 to 3.0 g / L, phosphate ion 5 to 30 g / L
And 0.2 to 2.0 g of fluoride as fluorine (F)
It is preferable to contain / L. Zinc ions and phosphate ions are the supply sources of the film in the phosphate-based film formation, and if the zinc ion exceeds 2.5 g / L, a good film with excellent corrosion resistance after coating and adhesion to the coating film can be obtained. No, 0.
If it is less than 4 g / L, a dense and uniform film cannot be obtained. Phosphate ion is in the range of 5 to 30 g / L, and if it is less than 5 g / L, a good film cannot be obtained, and if it exceeds 30 g / Lwo, no further performance can be obtained, which is economically disadvantageous.

Nickel ions have the effect of refining the film crystals and the effect of improving the corrosion resistance after coating and the adhesion of the coating film as a result of reforming the coating crystal by incorporating nickel components into the coating film. Nickel ion is an additive metal component useful for coating performance, and 0.3 to 3.
0 g / L is added. If it is less than 0.3 g / L, the above-mentioned action cannot be sufficiently obtained, and if it exceeds 3.0 g / L, the effect is already saturated, which is economically disadvantageous.

As the fluorine component, one or more selected from fluoride ions and complex fluoride ions are added. The fluorine component is 0.2 as the amount of fluorine (F).
~ 2.0 g / L is required. If it is less than 0.2 g / L, the etching ability to the metal material is insufficient and sufficient chemical conversion cannot be obtained. If it exceeds 2.0 g / L, the metal material is The etching ability becomes excessive, which also hinders sufficient chemical conversion reaction.

The drying conditions after washing with warm water are the same as the conditions for ordinary pretreatment for coating. That is, the temperature is 80 to 150 ° C.
Therefore, the time is preferably 30 seconds or more. However, if the electrodeposition coating is applied thereon, the drying step can be omitted.

Further, the treatment method of the present invention has no adverse effect even when applied to a metal material other than the metal to be treated, specifically, a steel material mainly composed of a cold rolled steel sheet or a zinc-based plated steel sheet. Therefore, it can be applied to a composite molded body of the metal and another metal. At this time, when the composite molded body contains a steel material such as a cold rolled steel sheet, it is necessary to add a film formation accelerator to the zinc phosphate chemical conversion treatment liquid.

[0018]

The present inventors have found that the eutectoid is present together with the crystals of the zinc phosphate-based chemical conversion coating film formed on the surface of the aluminum-based metal or the aluminum-based plated steel material, and this eutectoid exhibits water-resistant secondary adhesion. It was discovered that there was an adverse effect, and a method of removing the eutectoid by washing with warm water was established.
The reason why eutectoids are removed by washing with warm water is not fully understood. The eutectoid seems to be a complex fluoride, but complex fluorides such as Na ₃ AlF ₆ are extremely insoluble in water at room temperature. It was totally unexpected that what was conventionally washed with water at room temperature and could not be removed at all could be removed with warm water at about 40 ° C. The fact that the eutectoid was able to be removed with warm water heated to about 20 ° C higher than before means that the solubility of the complex fluoride in water increases with the increase in temperature, and the active action of warm water causes the fluoride-based compound to dissolve. It is considered that the desorption reaction of the eutectoid was promoted.

[0019]

EXAMPLES Next, the effects of the present invention will be described with reference to some concrete examples of actual processing together with comparative examples. As the test plate, an aluminum alloy plate (J
IS-A5052) was used to form a film having a size of 70 × 150 mm, and the processing of the following Examples and Comparative Examples was performed. With respect to the treated test piece, the adhesion of the coating film after coating was evaluated by the water resistance secondary adhesion test and the corrosion resistance was evaluated by the salt water spray exposure test by the following methods.

-Treatment Step- (1) Degreasing [FC-L4460 (Nippon Parkerizing Alkaline Degreasing Agent)] 43 ° C 120 seconds Spray (2) Washing [tap water] Room temperature 30 seconds Spraying (3) Surface adjustment [PL- ZN (Titanium colloidal surface conditioner manufactured by Nippon Parkerizing Co., Ltd.)] (4) Zinc phosphate chemical conversion treatment (using four kinds of treatment liquids shown in Table 3) 43 ° C 120 seconds immersion (5) Rinsing [tap water] (Treatment conditions of Examples and Comparative Examples) (6) Rinse with deionized water [Deionized water (conductivity: 0.2 μS
/ Cm)] Room temperature 20 seconds Spray (7) Drain and dry 110 ° C 180 seconds (8) Electrodeposition coating [EL2000 (cationic electrodeposition coating manufactured by Kansai Paint Co.)] Bath temperature: 28 ° C, voltage: 250V, energization time: 180 Seconds,
Film thickness: 20μ Baking: 175 ° C, hold for 20 minutes (9) Intermediate coating [TP37 (Kansai Paint Co.)] Air spray coating, film thickness: 30μ, baking: 140 ° C
Hold for 30 minutes (10) Topcoat coating [Neo 6000 (manufactured by Kansai Paint Co.)] Air spray coating, film thickness: 40μ, baking: 140 ° C,
Hold for 30 minutes

-Measuring Method of Coating Weight- (1) Coating Weight of Treated Plate First, the weight of the treated plate after the chemical conversion treatment is measured (W1.
[G]). Next, the treated plate is immersed in a 5% chromic acid aqueous solution at room temperature for 5 minutes to remove the coating. The weight after peeling is measured (W2 [g]). And it calculated by the following formulas. Coating weight [g / m ² ] = (W1−W2) × 10000/210 (2) F adhesion amount The treated plate was cut into a size of 45 mmφ and measured by fluorescent X-ray spectroscopy.

-Coating adhesion test (water resistant secondary adhesion test)
-The coated plate produced by the treatment steps (1) to (10) is immersed in deionized water at 55 ° C for 240 hours, and immediately after the immersion, a sharp edged cutter is used to cut 100 mm of 2 mm square Gobang eyes. I put them individually. Tape peeling off eyebrow scratches, 1 /
The number of crevices separated by 2 or more was evaluated according to the criteria shown in Table 1.

-Corrosion resistance test (exposure test with salt water spray) -A cross-cut reaching a base material with a sharp cutter is put in a coated plate prepared by the processing steps (1) to (10), and when exposed outdoors, Brine spraying (5% saline) was performed twice a week. The test was conducted for 6 months, and the maximum bulge width on one side from the cross cut was measured and evaluated according to the criteria shown in Table 2.

From the results shown in Table 4, there is a correlation between the amount of eutectoid complex fluoride and the water-resistant secondary adhesion, and the larger the amount of eutectoid complex fluoride, the worse the water-resistant secondary adhesion.

As shown in Table 4, in Examples 1 to 7 in which the treatment liquids 1 to 4 were used and the washing conditions were also the warm water of the present invention, as shown in Table 4, sufficient coating weight was obtained and the warm water was used. Since the deposited amount of eutectoid fluoride after cleaning is also at a low level, both the water-resistant secondary adhesion after coating and the corrosion resistance are sufficiently satisfied.

On the other hand, in Comparative Examples 1 and 3, the washing temperature was below the lower limit of 40 ° C., and in Comparative Example 2, the washing time was below the lower limit of 20 seconds, and Comparative Example 4
Since both the washing temperature and washing time were below the lower limit,
In particular, the deterioration of the water resistant secondary adhesion was observed.

[0027]

The pretreatment method for coating of the present invention is characterized in that it is washed with warm water after the formation of the zinc phosphate type chemical conversion film. However, the chemical conversion film is damaged by such a simple operation. Without doing so, a large effect of significantly improving the water resistant secondary adhesion is provided. In addition, there is no need for additional treatment steps or addition of chemicals, which is a great advantage in practical use.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

[Table 3]

[0031]

[Table 4]

Claims (3)

[Claims] 1. A zinc phosphate-based chemical conversion coating is formed on a surface of an aluminum-based metal or aluminum-plated steel material with a zinc phosphate-based chemical conversion treatment liquid containing a fluoride, and the surface having the coating is heated with warm water. A pretreatment method for coating an aluminum-based metal or an aluminum-plated steel material, which is characterized in that it is washed with. 2. The coating of the aluminum-based metal or aluminum-plated steel according to claim 1, wherein the heating water is washed at a water temperature of 40 ° C. or higher at least once by a spray method or a dipping method for at least 20 seconds. Pretreatment method. 3. The aluminum-based metal or aluminum-based plated steel material according to claim 1, wherein the zinc phosphate-based chemical conversion treatment liquid contains 0.2 to 2.0 g / L of fluoride as the amount of fluorine (F). Processing method.