JP2000096255A - Body of magnesium-containing metal treated with low electric resistance coating and its surface treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To impart corrosion resistance in the naked state, rust preventing property, adhesion and corrosion resistance of a coating film and low electric resistance by etching an Mg-containing metallic material subjecting it to high alkali treatment and forming a chemical conversion coating containing specified amounts of Ca, Mn and P and having a specified resistivity. SOLUTION: An Mg-containing metallic material is etched with an acid solution such as an about 0.5-10% phosphoric acid solution or a weak alkali solution such as an about 0.5-10% sodium pyrophosphate solution and it is treated with a high alkali solution such as an about 1-10%; NaOH solution. The treated metallic material is subjected to chemical conversion treatment with a solution of a chemical conversion treating agent containing about 1-20% Ca2+, about 1-4% Mn2+, about >=20% PO43+ and, optionally, about 0.02-2% oxidation treating agent to form a coating containing 1-500 mg/m2 Ca, 1-500 mg/m2 Mn and 1-1,000 mg/m2 P, having <=0.1 Ω.cm resistivity and effectively maintaining electromagnetic wave shielding property on the surface of the Mg-containing metallic material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a treated product having a coating having low corrosion resistance and low electric resistance on a magnesium-containing metal surface with bare corrosion resistance, rust prevention, coating film adhesion and coating corrosion resistance. About the method.

[0002]

2. Description of the Related Art In recent years, portable telephones, notebook personal computers, video cameras, and the like have been remarkably popularized. In order to solve this problem, it is required to take measures against the electromagnetic wave shielding property of the components of the housing. In addition, as a material for forming these housings, a material made of a magnesium alloy material has been widely used from the viewpoint of lightness, physical strength, and recyclability, instead of a material made of a plastic material.

[0003] This magnesium alloy material has the disadvantage of being highly corrosive. For this reason, it is common practice to form a film on the surface of a magnesium alloy by a method of performing a chemical conversion treatment with a chromium-based solution after a pretreatment with an alkali hydroxide solution, or by electroless nickel plating. However, the use of a chromium-based solution is highly harmful to the global environment, and it is desired to develop a treatment method using a non-chromium-based chemical conversion treatment agent.

[0004] Further, as a treatment method using a non-chromium-based chemical conversion treating agent for treating a magnesium alloy surface, a conventional method is as follows.
A method in which a high-temperature sodium hydroxide solution is brought into contact with the surface of a magnesium alloy (Japanese Patent Application Laid-Open No. 61-90776), a method of treating with a pyrophosphate solution and an alkali hydroxide solution (Japanese Patent Application Laid-Open No. 6-116740), Acid PH
A method of contacting an aqueous liquid containing phosphoric acid, manganese ions and an amine compound (JP-A-7-126858), an aqueous liquid containing phosphoric acid, calcium ions or aluminum ions and an amine compound under an acidic pH value. A contacting method (Japanese Patent Laid-Open No. 8-176842) and the like have been developed. However, none of these conventional methods using a non-chromium-based chemical conversion treatment agent can provide sufficient bare corrosion resistance of the formed film.

[0005]

The inventors of the present invention have conducted intensive studies on a non-chromium-based chemical conversion treating agent for treating the surface of a magnesium alloy.
According to the aqueous solution containing manganese ions and phosphate ions and further containing an oxidation promoter, the chemical conversion film obtained on the surface of the magnesium alloy by the chemical conversion treatment has a bare corrosion resistance, a rust prevention property, a paint adhesion property and a paint corrosion resistance. It has been found that excellent properties can be obtained for both sexes.

However, when the above-mentioned newly developed chemical conversion treatment solution is directly applied to the above-mentioned conventional treatment method used in the chemical conversion treatment step after pretreatment with an alkali hydroxide solution, formation of a film on the surface of the magnesium alloy. Thus, the electrical resistivity becomes a value of an electrical insulator exceeding 10 ⁶ Ω · cm. When a magnesium alloy having a film with such a high electrical resistivity is used as a constituent material of a housing of a mobile phone or the like, it is not possible to maintain sufficient shielding performance against electromagnetic waves generated.

In view of the above, the present invention provides a magnesium-containing metal material having a low electrical resistance that maintains a certain level of bare corrosion resistance, rust prevention, coating film adhesion and coating film corrosion resistance, and effectively maintains electromagnetic wave shielding properties. An object of the present invention is to provide a surface-treated product using a non-chromium-based chemical conversion treatment solution, which can form a chemical conversion film having resistivity, and a method for treating the same.

[0008]

Means for Solving the Problems In order to achieve the above-mentioned object, the present invention provides the following composition for a low electrical resistance coating of a magnesium-containing metal. That is, the chemical conversion coating on the surface of the magnesium-containing metal is 1 to 500 mg /
m ² calcium, 1 to 500 mg / m ² manganese and 1 to 1000 mg / m ² phosphorus, and an electrical resistivity of 0.1 Ω · cm or less.

By forming a chemical conversion film on the surface of the magnesium-containing metal material so as to contain the above-mentioned predetermined amounts of calcium, manganese and phosphorus, a certain bare corrosion resistance, rust prevention, coating film adhesion and coating film corrosion resistance are obtained. Obtained to maintain the properties. In particular, calcium and phosphorus are considered to contribute to the improvement of the bare corrosion resistance of the chemical conversion film, and manganese contributes to the improvement of the adhesion of the coating film. Further, by the electrical resistivity of the magnesium-containing metal surface is 0.1 Ω · cm or less,
Effective electromagnetic wave shielding properties of the constituent material can be maintained.

In other words, this electromagnetic wave shielding property is based on the principle that incident electromagnetic waves are absorbed by the low electrical resistivity of the chemical conversion film on the surface of the magnesium-containing metal material, and the absorbed electromagnetic wave energy is converted into heat and consumed. It is thought that it is based on.

In the present invention, the magnesium-containing metal includes magnesium itself, in addition to magnesium alloys such as Mg-Al-Zn alloy, Mg-Zn alloy and Mg-Al-Mn alloy. The magnesium-containing metal material includes not only the metal material itself but also a die-cast product material.

Next, a method for treating the magnesium-containing metal surface of the low electric resistance film according to the present invention which maintains the above-mentioned composition and performance is as follows.

First, in a first treatment method according to the present invention, a magnesium-containing metal material is subjected to a treatment with a high alkali solution after an etching treatment with an acid and / or a weak alkali solution, followed by a treatment with calcium ions and manganese. The method is characterized by including a step of performing a chemical conversion treatment using a chemical conversion treatment solution containing ions and phosphate ions and further including an oxidation treatment agent.

In the treatment method according to the present invention, the acid solution may be an aqueous solution of phosphoric acid, ammonium acid fluoride, nitric acid, sulfuric acid or the like, and the weak alkaline solution may be an aqueous solution of sodium pyrophosphate or the like. it can. The high alkali solution includes an aqueous solution of sodium hydroxide.

In this processing method, it is considered that the following effects occur. First, magnesium, aluminum, zinc, and the like contained in a magnesium-containing metal material are eluted by a chemical reaction with an acid or a weak alkali by an etching action in an acid and / or a weak alkali solution. At this time, for example, excessively generated powdery magnesium phosphate, aluminum phosphate, zinc phosphate, and other components eluted with magnesium, etc., are attached as smut. Then, the smut of this magnesium-containing metal material surface is
Most of them are dissolved and removed in a highly alkaline solution, but some of them remain. At this time, a part of the residual smut dissolves into magnesium hydroxide, which forms a passivation film on the surface of the magnesium-containing metal material, and the components of the residual smut, magnesium phosphate and aluminum phosphate, are removed. A mixed chemical conversion film is formed on the surface of the magnesium-containing metal material. These magnesium phosphate and aluminum phosphate are very small, and it is considered that their presence keeps the low electrical resistivity of the surface of the magnesium-containing metal material.

Therefore, in this treatment method, it is necessary to perform the etching treatment step using an acid or a weak alkali solution with a recipe suitable for the above-mentioned action. A preferable prescription in this etching treatment is, for example, that a phosphoric acid solution is a phosphoric acid aqueous solution having a concentration of 0.5 to 10% by weight, and immersion treatment is performed at room temperature for 10 seconds to 10 minutes. If the concentration of the phosphoric acid is less than 0.5% by weight or the treatment time is less than 10 seconds, the etching process is incomplete. If the etching treatment is incomplete, smut is not generated sufficiently, and a film having a small surface resistance cannot be obtained. Further, the formed film may be defective in bare corrosion resistance, film adhesion, and the like. If the concentration of the phosphoric acid exceeds 10% by weight or the processing time exceeds 10 minutes, the formed film becomes non-uniform and excessively remains after the film is formed. This causes a defect in film adhesion and the like.

The sodium pyrophosphate solution is prepared at a concentration of 0.5 to 10% by weight at a concentration of 50 to 60 ° C.
Under the temperature condition of 1 to 5 minutes. If the concentration of sodium pyrophosphate is less than 0.5% by weight or the treatment time is less than 1 minute, the etching becomes incomplete and causes poor corrosion resistance and poor adhesion of the formed film. And the amount of residual deposits described above becomes insufficient. For this reason, a film with low surface resistance cannot be obtained. If the concentration of sodium pyrophosphate exceeds 10% by weight or the processing time exceeds 10 minutes, the formed film becomes non-uniform.

In addition, the treatment with a highly alkaline solution exerts not only the degreasing treatment but also the action of neutralizing and removing the acid in the preceding step. A highly alkaline solution suitable for this effect is
For example, in the case of an aqueous solution of sodium hydroxide, it is preferable that the solution is immersed in 1 to 10% by weight under a heating condition of 50 to 60 ° C. for 1 to 5 minutes. If the concentration of the alkali is less than 1% by weight or the treatment time is less than 1 minute, the formation of the passivation film is not sufficient, and excess smut remains in the film, resulting in the bare corrosion resistance of the formed film. Becomes insufficient. On the other hand, if the alkali concentration exceeds 10% by weight or the treatment time exceeds 5 minutes, the amount of residual smut decreases, and it is insufficient to sufficiently reduce the electric resistance on the surface of the magnesium-containing metal material after the treatment. Become.

Next, in a second treatment method according to the present invention, a magnesium-containing metal material is treated with a fluoride solution after an etching treatment with an acid or weak alkali solution, and thereafter, with calcium ions and manganese ions. And a step of performing a chemical conversion treatment with a chemical conversion treatment solution containing an oxidation treatment agent.

The effect of the second treatment method is that magnesium is mainly eluted from the magnesium-containing metal material in an acid or weakly alkaline solution, and the excess component is reattached to the surface in a smut form. Most of the deposits are dissolved and removed in the fluoride solution in the next step, but a part thereof remains. It is considered that this contributes to a decrease in electric resistance on the surface of the magnesium-containing metal material as in the case of the first treatment method.

A preferable formulation suitable for such an action is the same as that of the first treatment method for an acid or weak alkali solution.

A preferred formulation for the hydrofluoric acid solution and the fluoride solution such as ammonium acid fluoride is to soak the solution in an aqueous solution concentration of 1 to 10% by weight for 1 to 10 minutes at room temperature. . If the hydrofluoric acid or ammonium ammonium fluoride concentration is less than 1% by weight or the treatment time is less than 1 minute, the etching treatment is incomplete. Further, the concentration of hydrofluoric acid or acidic aluminum fluoride exceeds 10% by weight, or
If the amount exceeds the limit, the formed film becomes non-uniform, the amount of residual deposits decreases, and the decrease in the electrical resistance on the surface of the magnesium-containing metal material becomes insufficient.

In the above-described first and second treatment methods, the etching treatment step using an acid or a weak alkaline bath solution is performed in such a manner that the material to be treated is a certain release agent on its surface, such as a magnesium alloy die-cast. Even in such a case, it becomes possible to obtain a chemical conversion film excellent in bare corrosion resistance and the like in the next chemical conversion treatment step.

Next, the chemical conversion treatment in each of the above-described treatment methods according to the present invention is performed by using calcium ions,
An aqueous solution containing manganese ions and phosphate ions and further containing an oxidation promoter is used as a chemical conversion treatment solution, and the magnesium-containing metal material can be immersed in a bath of the chemical conversion treatment solution.

In this chemical conversion treatment liquid, the calcium ions may be a mixture of one or more of calcium nitrate, calcium nitrite, calcium thiosulfate, calcium dihydrogen phosphate and the like. Further, the manganese ion can be obtained by mixing one or more of manganese carbonate, manganese nitrate, manganese hydrogen phosphate, manganese biphosphate, manganese borofluoride, and the like. Further, the phosphate ion may be formed by one or more of orthophosphoric acid, condensed phosphoric acid, phosphorous acid, hypophosphorous acid, and the like.

The preferred compounding amounts of each component of the chemical conversion treatment liquid are as follows. That is, calcium ion is 1 to
20% by weight, 1 to 4% by weight of manganese ion and 20% by weight or more of phosphate ion, and 0.02% of oxidation promoter
２2% by weight. When the amount of each of these components is within the above range, a chemical conversion film having good corrosion resistance and good adhesion to the coating film on the surface of the magnesium-containing metal material is stably and economically produced, and has a low electric resistance. It can be formed while maintaining the efficiency.

When calcium ions are insufficient,
When the corrosion resistance and coating film adhesion etc. decrease, and the manganese ion and phosphate ion are deficient, in addition to the decrease in coating film adhesion, white rust due to chlorine ions from the oxidation promoter is particularly increased. Cause it to occur.

Examples of the oxidation promoter include sodium chlorate, sodium hypochlorite and the like.
This oxidation promoter enhances the reactivity with the above-mentioned respective component ions during the chemical conversion treatment, and can provide a chemical conversion film having good bare corrosion resistance and the like. In addition, the preferred compounding amount of the oxidation promoter is to obtain a chemical conversion film having the above performance stably.
The ratio is in the range of 0.02 to 2.0% by weight.

It is preferable that the pH of the chemical conversion treatment solution containing the chemical conversion treatment solution is adjusted to 1.0 to 3.0. If the PH value is less than 1.0, the amount of etching becomes excessive during the chemical conversion treatment, causing a problem in the dimensional accuracy of the magnesium-containing metal material, and lowering the bare corrosion resistance. Also, if the PH value exceeds 3.0, the chemical conversion film deteriorates in performance such as bare corrosion resistance.

Further, the chemical conversion bath solution is used at 30 to 75 ° C.
Is preferably maintained at a temperature in the range of When the bath temperature is lower than 30 ° C., it takes a long time to form the chemical conversion film, which may cause a defect in the corrosion resistance of the chemical conversion film, such as naked corrosion resistance. When this temperature exceeds 75 ° C., performance such as bare corrosion resistance of the chemical conversion film deteriorates.

The time required for the chemical conversion treatment with the chemical conversion bath solution has a correlation with the bath solution temperature. That is,
If the bath temperature is less than 50 ° C, soak for 3 to 20 minutes. If the bath temperature is 50 ° C or higher, 0.5 to 1 minute.
It is preferable that the immersion condition is 0 minutes. If the bath temperature is less than 50 ° C. and the immersion time is short, the formation amount of the chemical conversion film becomes insufficient. If the bath temperature is 50 ° C. or higher and the immersion time is long, the formed film will be re-eluted and the performance such as bare corrosion resistance will be reduced. In addition, the film will cover the smut and the surface resistance will increase. There is.

The present invention is a processing method including the above-described processing steps, and it is preferable that a water-washing step is included after each of the above-described processing steps. According to the method, after washing with water, a drying treatment can be performed, and further a coating treatment can be performed. This coating treatment can be performed by undercoating an epoxy resin material by an electrodeposition coating or spray coating method, and then overcoating it with a melamine resin or the like.

[0033]

(Example 1) A magnesium alloy material (JIS H5303MD) by a thixomold method as a processing object
ID (ASTM AZ91D), 2 × 60 × 100m
m, prepared by Nippon Steel Corporation)
The steps of surface conditioning 1, water washing, surface conditioning 2, water washing, surface conditioning 3 and water washing with the treatment bath liquids of the working numbers 1 to 12 shown in Table 1 are sequentially performed by the immersion method under the treatment conditions shown in Table 2. Was.

[0034]

[Table 1]

[0035]

[Table 2]

The sodium hydroxide bath solution is as follows:
0.5% by weight of an anionic surfactant was blended. In addition, each of the other bath solutions contained a nonionic surfactant in an amount of 0.2% by weight.

Next, after the above-mentioned pretreatment, a chemical conversion treatment was carried out using a chemical conversion bath having the components shown in Table 3. The chemical conversion treatment was performed by immersing the object to be treated at a bath temperature of 70 ° C. for 2 minutes, 5 minutes, or 8 minutes.

[0038]

[Table 3]

Further, after washing with water and deionized water, 80
After drying by draining at 10 ° C. for 10 minutes, an epoxy resin coating film was formed to a thickness of 20 μm by a cationic electrodeposition coating method.

Implementation numbers 1 to 5 by such processing steps
Was repeated twice, and the average value thereof is shown in Tables 4 and 5 for the film properties on the surface of the magnesium alloy material.

[0041]

[Table 4]

[0042]

[Table 5]

Incidentally, the amount of element attachment was determined by a quantitative method using fluorescent X-rays. In addition, the electrical resistivity is Lorester MP (4 terminal 4 probe type) manufactured by Dia Instruments Co., Ltd.
Was measured. Further, the coating film corrosion resistance is determined by providing a cross-cut on the surface according to a conventional method and using this as a sample according to JISZ237.
The salt spray test (SST) according to 1 was performed for 720 hours,
It is a result of examining a peel width of a coating film. The adhesion of the coating film was determined according to JIS K5400 by dividing the sample surface into 100 parts by drawing a grid pattern on the surface of the sample, counting the number of grids remaining after tape-up, and judging according to the following criteria. That is, when the remaining number was 100, it was evaluated as 、, and otherwise, it was evaluated as ×.

According to the results shown in Table 4, the execution numbers 1 to
It can be seen that in each of the treatment steps of No. 4, the formed film is formed of one containing calcium, manganese and phosphorus in a predetermined amount or more.

Also, from the results of the film performance shown in Table 5, according to the processing steps of Examples 1 to 5, in any case, a low electric resistivity of 0.1 Ω · cm or less suitable for electromagnetic wave shielding. It can be seen that the film retains a certain standard in terms of maintaining the properties and the corrosion resistance of the formed film. In addition, in the case of the treatment steps of Examples 3 to 5, it can be seen that the prolongation of the chemical conversion treatment time further improves the corrosion resistance of the coating film, but sharply increases the electric resistance value. Therefore, in these treatment steps, the chemical conversion treatment time needs to be within 5 minutes.

Table 6 shows, as a comparative example, the film characteristics in the case of the processing steps of Examples 6 to 11.

[0047]

[Table 6]

From the results shown in Table 6, including the case where only the pre-treatment with the alkaline solution was performed (Example No. 7),
It can be seen that when these treatment steps are performed, the electrical resistivity of the magnesium alloy surface becomes a value of an electrical insulator far exceeding 0.1 Ω · cm. Also, in particular,
As in the case of the processing steps of execution numbers 6 and 11, the SST
(720 hours), a decrease in the corrosion resistance of the coating film is also confirmed.

Example 2 A magnesium alloy material (JIS H5303M) by a mold casting method as a processing object
For DID (ASTM AZ91D, a product distributed by the Magnesium Association of Japan), as pretreatment, surface conditioning 1, treatment with water, surface treatment 2, washing with water, surface treatment 3 with treatment numbers 13 to 25 shown in Table 7 Each step of the water washing was performed in order by the dipping method under the conditions shown in Table 8.

[0050]

[Table 7]

[0051]

[Table 8]

Incidentally, the sodium hydroxide bath solution is as follows:
0.5% by weight of an anionic surfactant was blended. In addition, each of the other bath solutions contained a nonionic surfactant in an amount of 0.2% by weight.

Next, after the above pretreatment, a chemical conversion treatment was carried out with a chemical conversion bath having the components shown in Table 3. Also,
This chemical conversion treatment was performed by immersing the object to be treated at 70 ° C. bath temperature for 2 minutes, 5 minutes or 8 minutes. Then, after further washing with water and deionized water,
Draining and drying were performed at 80 ° C. for 10 minutes, and thereafter, a resin coating film having a thickness of 20 to 30 μm was formed by acrylic resin coating.

The execution numbers 13 to 13 obtained by such processing steps
The treatment of No. 16 was repeated twice, and the average value was shown in Tables 9 and 10 as the film properties of the surface of the magnesium alloy material.

[0055]

[Table 9]

[0056]

[Table 10]

The method for measuring the element content, the method for measuring the electric resistivity, the method for measuring the corrosion resistance of the coating film, and the method for measuring the adhesion of the coating film are the same as those in Example 1.

According to the results shown in Table 9, the operation number 13
It can be seen that in any of the processing steps Nos. To 16, the formed film is formed of a material containing calcium, manganese and phosphorus for maintaining a predetermined amount.

Further, from the results of the film performance shown in Table 10, according to the processing steps of Examples Nos. 13 to 16, in any case, 0.1 Ω · c suitable for the electromagnetic wave shielding property was obtained.
It can be seen that the low resistivity of not more than m is maintained and that the coating film corrosion resistance of the formed film maintains a certain standard. Further, in the case of the treatment steps of Examples 15 and 16, it is understood that the chemical conversion treatment time is correlated with the electric resistance of the surface of the magnesium alloy material and the corrosion resistance of the coating film, as in the case of Example 1.

Tables 11 and 12 show the film properties in the case of the processing steps of Examples Nos. 17 to 25 as comparative examples.

[0061]

[Table 11]

[0062]

[Table 12]

From the results shown in Tables 11 and 12,
In the case of only pretreatment with an alkaline solution (execution number 17)
It can be seen that when these treatment steps are used, the electrical resistivity of the surface of the magnesium alloy material becomes an electrical insulator value far exceeding 0.1 Ω · cm.
In addition, in particular, as in the case of the processing steps Nos. 17 and 24, a decrease in the corrosion resistance of the coating film for SST (720 hours) is also confirmed.

(Test Example) The same magnesium alloy material as that in Example 1 was treated, and as a pretreatment, a degreasing treatment with a sodium hydroxide bath solution was performed at a concentration of 4% by weight and a liquid temperature of 55%.
After washing with water, the sample was immersed in a chemical conversion bath having the components shown in Table 13 and treated at 70 ° C. for 5 minutes. Thereafter, the resultant was washed with water, deionized water, drained and dried, and further, an epoxy resin film was formed to a thickness of 20 μm by a cationic electrodeposition coating method.

[0065]

[Table 13]

Table 14 shows the film properties of the surface of the magnesium alloy material by the treatments of Test Nos. 1 and 2 in such treatment steps.

[0067]

[Table 14]

From the results shown in Table 14, when either calcium or manganese is not contained as a composition element of the chemical conversion film, blisters are generated in the formed film, and good adhesion is observed in the coating film. It turns out that things cannot be obtained.

[0069]

As described above, since the present invention is constituted, the following effects are exhibited. First, according to the treated product of the present invention, a treated product of a formed film excellent in bare corrosion resistance, rust prevention, coating film adhesion and coating film corrosion resistance of a magnesium-containing metal material is provided as a material having a low electric resistance. Therefore, when this is a housing component material for a cellular phone, a personal computer, or the like, it can be used as a material that is lightweight, has high physical strength, and has excellent electromagnetic wave shielding properties.

Further, the treatment method according to the present invention uses a treatment bath solution for the conventional general pretreatment, and it is possible to obtain the above-mentioned treated product of the magnesium metal-containing material very easily and economically. it can.

Claims (3)

[Claims] 1. A chemical conversion coating on a surface of a magnesium-containing metal, comprising 1 to 500 mg / m ² of calcium, 1 to 50 mg / m ^2.
0 mg / m ² manganese and 1 to 1000 mg / m ²
A low-resistance treated film of a magnesium-containing metal, which contains phosphorus and has an electric resistivity of 0.1 Ω · cm or less. 2. A magnesium-containing metal material is subjected to an etching treatment with an acid and / or a weak alkali solution, followed by a treatment with a high alkali solution, followed by a calcium ion, a manganese ion and a phosphate ion, and further an oxidation treatment. A method for treating a magnesium-containing metal surface having a low electric resistance film, comprising a step of performing a chemical conversion treatment with a chemical conversion treatment solution containing a chemical agent. 3. A magnesium-containing metal material is subjected to a treatment with a fluoride solution after an etching treatment with an acid or a weak alkaline solution, and thereafter contains calcium ions, manganese ions and phosphate ions, and further contains an oxidizing agent. A method for treating a magnesium-containing metal surface having a low electrical resistance film, comprising a step of performing a chemical conversion treatment with a contained chemical conversion treatment solution.