JP2006219691A - Metal surface treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metal surface treatment method capable of forming a chemical film having excellent performance even when iron sludge is generated when performing the surface treatment of a metallic material containing an iron base material. <P>SOLUTION: The metal surface treatment method comprises a surface treatment step of bringing a metal surface treatment solution of pH 3.0-6.0 containing a specified amount of zirconium/titanium ions, fluoride ions and all fluorine into contact with the surface of the metallic material containing the iron base material, a pH reducing step of reducing pH of the metal surface treatment solution by 0.1-3.0 thereafter and dissolving zirconium/titanium contained in iron sludge generated in the metal surface treatment solution in the surface treatment step in the metal surface treatment solution, an iron sludge removing step of removing iron sludge from the metal surface treatment solution thereafter, and a collection and supply step of collecting the metal surface treatment solution with the iron sludge removed therefrom and supplying the solution to the surface treatment step while these steps are performed in a circulating manner. The concentration of the iron sludge in the metal surface treatment solution in the surface treatment step is maintained at ≤500 ppm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a metal surface treatment method.

As a method for depositing a surface treatment film having excellent corrosion resistance after coating on a metal surface, a zinc phosphate treatment method and a chromate treatment method are currently generally used. Among these, the zinc phosphate treatment method is a method in which a treatment liquid containing zinc phosphate is brought into contact with the metal surface, such as hot rolled steel sheets, cold rolled steel sheets, galvanized steel sheets, some aluminum alloys, etc. A film having excellent corrosion resistance can be deposited.
However, when the zinc phosphate treatment is performed, a large amount of sludge such as zinc phosphate and iron phosphate, which are byproducts of the reaction, is generated in the treatment liquid. The generation of sludge reduces the active ingredient concentration in the treatment liquid and adversely affects the corrosion resistance of the resulting film.
Moreover, if sludge adheres to the metal surface, the appearance after painting may deteriorate, or the sludge may adhere to the processing equipment and maintainability may deteriorate.
Furthermore, when sludge is generated, it is economically disadvantageous because it is necessary to discard the generated sludge or to replenish active ingredients having a reduced concentration in the treatment liquid.
Furthermore, depending on the type of aluminum alloy, the yarn rust resistance after coating cannot be sufficiently secured.

  On the other hand, it is possible to ensure sufficient coating performance for aluminum alloys by applying chromate treatment. However, chromate treatment containing harmful hexavalent chromium in the treatment liquid is avoided due to recent environmental regulations. In the direction. Therefore, various methods have been proposed as surface treatment methods that do not contain harmful components in the treatment liquid.

For example, Patent Document 1 contains a specific metal acetylacetonate and at least one compound selected from a water-soluble inorganic titanium compound and a water-soluble inorganic zirconium compound in a weight ratio of 1: 5000 to 5000: 1. A method for depositing a surface-treated film excellent in corrosion resistance and adhesion after coating with a metal surface treatment composition characterized by the above has been proposed. If this method is used, a magnesium alloy, zinc, and a galvanized alloy can be used in addition to an aluminum alloy as a metal material to be surface-treated.
However, with the technique described in Patent Document 1, it was impossible to deposit a surface treatment film on the surface of an iron-based material such as a cold-rolled steel sheet.

  On the other hand, Patent Document 2 proposes a method that can surface-treat iron-based materials in addition to aluminum-based materials. Specifically, it is a metal chemical conversion treatment method for treating a metal surface with a metal chemical conversion treatment agent containing zirconium ions and / or titanium ions and fluorine ions, wherein the metal chemical conversion treatment agent contains the zirconium ions. And / or the content of the titanium ion is 20 to 500 ppm on a mass basis, and the content of the fluorine ion is 6 times or more in molar ratio to the zirconium ion and / or the titanium ion, It is substantially free of phosphate ions, has a pH of 2 to 5, and the metal chemical conversion treatment method controls the iron ion concentration in the metal chemical conversion treatment agent being treated to 25 ppm or less. A metal chemical conversion treatment method has been proposed. The purpose of this method is to obtain a surface-treated film excellent in corrosion resistance and adhesion after coating on a metal surface such as iron, aluminum, zinc, etc., using a metal chemical conversion treatment agent that does not contain hexavalent chromium, which is a harmful component. It is said.

  Patent Document 3 also proposes a method capable of performing surface treatment on iron-based materials in addition to aluminum-based materials. Specifically, a water-based surface treatment liquid for surface-treating a metal material selected from iron-based material, zinc-based material, aluminum-based material and magnesium-based material individually or in combination of two or more thereof, One or more compounds selected from a zirconium compound and a titanium compound are contained as the metal element in an amount of 5 to 5000 ppm, free fluorine ions are contained in an amount of 0.1 to 100 ppm, and the pH is 2 to 6. Metal surface treatment liquids have been proposed.

JP 2000-199077 A JP 2004-43913 A JP 2004-190121 A

  However, as a result of intensive studies by the inventor, the following has been found. That is, in the method described in Patent Document 2, iron ions in the treatment liquid are generated by etching the iron-based material, and it is difficult to control the concentration to 25 ppm or less. In addition, a large-scale facility for removing iron ions is necessary, and a large running cost is required. Furthermore, when iron ions are removed to a concentration of 25 ppm or less, it is presumed that the active components in the treatment liquid are also removed, which may adversely affect the performance of the chemical conversion film.

In addition, when the treatment liquid described in Patent Document 3 is used, a surface treatment film having excellent corrosion resistance after coating is applied to various metal materials without considering the effect of accumulated iron ions because it is hardly affected by iron ions. It can be deposited.
However, in the metal surface treatment liquid described in Patent Document 3, when the amount of the metal to be treated containing iron is large, the eluted iron ions may be oxidized to precipitate iron sludge that is iron hydroxide. If iron sludge is deposited, the same problem as that described in Patent Document 2 may occur.

  Therefore, the present invention provides a metal surface treatment method for surface-treating a metal material containing an iron-based material, and is capable of forming a chemical conversion film having excellent performance even when iron sludge is generated. The purpose is to do.

  As a result of earnest research to achieve the above object, the present inventor contains 5-5000 ppm of ions of one or more metals selected from the group consisting of zirconium and titanium, and 0.1-100 ppm of fluoride ions. When the surface of a metal material is treated with a metal surface treatment solution having a total fluorine concentration of 100 to 50000 ppm and a pH of 3.0 to 6.0, the pH of the metal surface treatment solution is specified after the surface treatment step. By reducing the range, and then removing the iron sludge, the amount of the active ingredient in the metal surface treatment liquid that is taken out of the system can be reduced. As a result, even if the surface treatment is circulated, The inventors have found that it is possible to obtain a chemical conversion film having excellent performance, and have completed the present invention.

That is, the present invention provides the following (1) to (3).
(1) A metal surface treatment method for surface-treating a metal material containing an iron-based material,
PH 3.0-6, containing 5 to 5000 ppm of ions of one or more metals selected from the group consisting of zirconium and titanium, 0.1 to 100 ppm of fluoride ions, and a total fluorine concentration of 100 to 50000 ppm A surface treatment step of bringing a metal surface treatment solution of 0.0 into contact with the surface of the metal material;
After the surface treatment step, the pH of the metal surface treatment solution is lowered by 0.1 to 3.0, and the zirconium and titanium contained in the iron sludge generated in the metal surface treatment solution in the surface treatment step A pH lowering step of dissolving one or more metals selected from the group in the metal surface treatment liquid;
After the pH lowering step, an iron sludge removing step for removing the iron sludge from the metal surface treatment liquid;
After the iron sludge removal step, the metal surface treatment liquid from which the iron sludge has been removed is collected, and a recovery supply step for supplying the surface treatment step is circulated.
The metal surface treatment method which maintains the iron sludge density | concentration of the said metal surface treatment liquid in the said surface treatment process at 500 ppm or less.
(2) The metal surface treatment method according to (1), wherein a flocculant and / or an oxidizing agent is added to the metal surface treatment solution before or in the iron sludge removal step.
(3) The above metal material is an iron-based material, or a metal material composed of an iron-based material and one or more selected from the group consisting of a zinc-based material, an aluminum-based material, and a magnesium-based material ( The metal surface treatment method according to 1) or (2).

  According to the metal surface treatment method of the present invention, it is possible to form a chemical conversion film having excellent performance even when iron sludge is generated when a metal material containing an iron-based material is surface-treated.

Hereinafter, the metal surface treatment method of the present invention will be described in detail.
The metal surface treatment method of the present invention is a metal surface treatment method for treating a metal material containing an iron-based material.
The metal material used as the object of the metal surface treatment method of the present invention is not particularly limited as long as it is a metal material containing an iron-based material. For example, iron-based materials such as steel plates (for example, cold-rolled steel plates, hot-rolled steel plates, galvanized steel plates, alloy-plated steel plates); from the group consisting of iron-based materials, zinc-based materials, aluminum-based materials, and magnesium-based materials Examples thereof include metal materials composed of one or more selected.

  The metal surface treatment method of the present invention includes at least a surface treatment step, a pH lowering step, and an iron sludge removal step. Hereinafter, each step will be described.

<Surface treatment process>
The surface treatment step is a step of bringing a metal surface treatment solution described later into contact with the surface of the metal material described above.

The metal surface treatment liquid used in the surface treatment step contains 5-5000 ppm of one or more kinds of metal ions selected from the group consisting of zirconium and titanium, 0.1-100 ppm of fluoride ions, and total fluorine concentration Is a metal surface treatment solution having a pH of 3.0 to 6.0, which is 100 to 50,000 ppm.
Examples of the source of ions of one or more metals selected from the group consisting of zirconium and titanium include ZrCl ₄ , ZrOCl ₂ , Zr (SO ₄ ) ₂ , ZrOSO ₄ , Zr (NO ₃ ) ₄ as zirconium compounds. ZrO (NO ₃ ) ₂ , H ₂ ZrF ₆ , H ₂ ZrF ₆ salt, ZrO ₂ , ZrOBr ₂ , ZrF ₄ , and titanium compounds include TiCl ₄ , Ti (SO ₄ ) ₂ , TiOSO ₄ , Ti (NO ₃ ) ₄ , TiO (NO ₃ ) ₂ , TiO ₂ OC ₂ O ₄ , H ₂ TiF ₆ , a salt of H ₂ TiF ₆ , TiO ₂ and TiF ₄ may be mentioned. Of these, zirconium compounds are preferred.

Zirconium compounds and titanium compounds dissolve in acidic solutions and are relatively stable, but are unstable in alkaline solutions and readily precipitate as oxides or hydroxides of zirconium or titanium.
Here, since the metal surface treatment liquid used in the surface treatment step is an acidic solution, when it is brought into contact with the above-described metal material, a dissolution reaction of the metal material occurs. When the metal material is dissolved, the pH rises at the metal material interface, and an oxide and / or hydroxide of zirconium and / or titanium is deposited as a film on the surface of the metal material to form a film.

The concentration of ions of one or more metals selected from the group consisting of zirconium and titanium in the metal surface treatment solution (when both zirconium ions and titanium ions are contained, the total concentration) is 5 to 5000 ppm. Preferably, it is 20 to 3000 ppm.
As described above, the film formed by the metal surface treatment method of the present invention is an oxide and / or hydroxide of zirconium and / or titanium. When the concentration of ions of one or more metals selected from the group consisting of zirconium and titanium is 5 ppm or more, the concentration of the main component of the film is sufficiently high, so that a sufficient amount of adhesion to obtain corrosion resistance is practical. Can be obtained in processing time. Further, when the concentration of ions of one or more metals selected from the group consisting of zirconium and titanium is 5000 ppm or less, a sufficient amount of adhesion for obtaining corrosion resistance can be obtained economically advantageously.

Examples of the source of fluoride ions include HF, H ₂ ZrF ₆ , H ₂ ZrF ₆ salt, H ₂ TiF ₆ , H ₂ TiF ₆ salt, H ₂ SiF ₆ , H ₂ SiF ₆ salt, HBF ₄ , Fluorine compounds such as HBF ₄ salt, NaHF ₂ , KHF ₂ , NH ₄ HF ₂ , NaF, KF, NH ₄ F and the like.

The concentration of fluoride ions in the metal surface treatment liquid is preferably 0.1 to 100 ppm, and more preferably 20 to 70 ppm.
In the present invention, the fluoride ion concentration is the concentration of free fluorine ions (F ⁻ ) and can be measured using a commercially available ion electrode.
When the fluoride ion concentration is 100 ppm or less, the dissolution reaction of the metal material is sufficiently promoted. In addition, since ions of one or more kinds of metals selected from the group consisting of zirconium and titanium are stably present in the metal surface treatment liquid, they tend to precipitate as a film at the metal material interface.
When the fluoride ion concentration is 0.1 ppm or more, the stability and reactivity of the metal surface treatment solution are excellent. In the present invention, as described later, in the pH reduction step, the pH of the metal surface treatment solution is lowered to dissolve the insolubilized active ingredient in the iron sludge, but the fluoride ion concentration is 1 ppm or more. This effect becomes large.

  Fluoride ions have an action of promoting a dissolution reaction in an acidic solution for any of iron-based materials, zinc-based materials, aluminum-based materials, and magnesium-based materials. Further, fluoride ions have an effect of improving the stability of one or more metal ions selected from the group consisting of zirconium and titanium in the metal surface treatment solution. That is, fluoride ions increase the stability of the metal surface treatment liquid and also increase the reactivity with the metal material.

Since iron-based materials, zinc-based materials, aluminum-based materials, and magnesium-based materials have different reactivity, conventionally, it has been impossible to surface-treat two to four of these metal materials at the same time.
In the present invention, the balance between stability and reactivity of the metal surface treatment liquid can be freely changed by adjusting the fluoride ion concentration. Is possible.

  The metal surface treatment liquid used in the surface treatment step has a pH of 3.0 to 6.0, preferably a pH of 3.0 to 5.0. Within the above range, the balance between the dissolution of the metal material and the formation of the film is suitable.

The metal surface treatment liquid used in the surface treatment step has a total fluorine concentration of 100 to 50,000 ppm, preferably 200 to 10000 ppm, more preferably 250 to 2000 ppm.
In the present invention, the total fluorine concentration is the concentration of all fluorine contained in the metal surface treatment solution, and is measured according to JIS K0102 34-2.

In the metal surface treatment method of the present invention, in order to stably treat the metal over a long period of time, fluoride ions are supplied and the fluoride ion concentration is kept within a certain range in order to maintain the dissolved amount of the metal material at an optimum amount. Is preferred. In addition, in order to stably treat metal surfaces over a long period of time, metal ions such as iron ions, zinc ions, aluminum ions, and magnesium ions mixed from metal materials are stabilized. Preferably, ions are supplied and stabilized.
For these reasons, the metal surface treatment liquid used in the surface treatment step preferably contains a complex compound having fluorine. When the metal surface treatment liquid contains a complex compound having fluorine, when the fluoride ion concentration is lowered, fluorine existing as a complex compound is liberated, and the fluoride ion concentration is kept constant.
The content of the complex compound having fluorine in the metal surface treatment liquid is preferably such that the total fluorine concentration falls within the above range. When the total fluorine concentration is 100 ppm or more, even if a large amount of metal ions is mixed, it can be sufficiently stabilized. When the total fluorine concentration is 50000 ppm or less, sufficient stability can be obtained economically advantageously.

  The counter ion of the fluorine ion present as a complex compound is not particularly limited as long as it forms a complex compound with fluorine and maintains the fluoride ion concentration in the metal surface treatment liquid within a certain range. For example, calcium ion, magnesium ion, aluminum ion, and strontium ion can be mentioned.

  As described above, when the metal surface treatment liquid contains a complex compound having fluorine, the fluoride ions, in addition to the effect of improving the reactivity of the metal surface treatment liquid, remove the components eluted by the dissolution of the metal material. Responsible for long-term stability in the liquid.

In the case of zinc phosphate treatment, which is one of the prior arts, iron sludge is generated because, for example, iron ions eluted from an iron-based material form an insoluble salt with phosphoric acid.
On the other hand, in the present invention, the amount of iron sludge generated is very small because the free fluorine concentration is low and the elution amount of the metal material is small.
In particular, when the metal surface treatment liquid contains a complex compound having fluorine, when the fluoride ions in the metal surface treatment liquid are consumed in a long-term treatment, the fluorine ions present as the complex compound are By supplying free fluorine, fluoride ions are maintained in a certain range of concentration, so that metal ions such as iron ions, zinc ions, aluminum ions, magnesium ions, etc. that are mixed in a large amount by long-term treatment are stabilized. Thus, there is no adverse effect on chemical conversion.

The metal surface treatment liquid used in the surface treatment step can contain other components as long as the effects of the present invention are not impaired.
For example, metal ions other than zirconium and titanium, polymer compounds, activators, oxidizing agents, replenishers and the like can be mentioned.
Specifically, examples of metal ions other than zirconium and titanium include Hf, Si, Ag, Al, Cu, Fe, Mn, Mg, Ni, Co, and Zn.
The concentration of these metal ions in the metal surface treatment liquid is preferably 1 to 5000 ppm, and more preferably 1 to 3000 ppm.
Examples of the source of these metal ions include the metal oxides, hydroxides, chlorides, sulfates, nitrates, and carbonates.

As the polymer compound, a polymer compound commonly used for metal surface treatment can be used. For example, polyvinyl alcohol; poly (meth) acrylic acid; copolymer of acrylic acid and methacrylic acid; copolymer of ethylene and acrylic monomers such as (meth) acrylic acid and (meth) acrylate; ethylene And a copolymer of vinyl acetate; polyurethane; a cationic resin containing an amino group such as an amino-modified phenol resin, polyvinylamine, polyallylamine; a polyester resin; an epoxy resin.
The concentration of these polymer metal ions in the metal surface treatment liquid is preferably 0.1 to 1000 ppm, and more preferably 0.5 to 500 ppm.

The activator is not particularly limited, and at least one surfactant selected from the group consisting of a nonionic surfactant, an anionic surfactant and a cationic surfactant can be added.
The concentration of the activator in the metal surface treatment liquid is preferably 1 to 10000 ppm, and more preferably 10 to 5000 ppm.

Examples of the oxidizing agent include HClO ₃ , HBrO ₃ , HNO ₂ , HNO ₃ , HMnO ₄ , HVO ₃ , H ₂ O ₂ , H ₂ WO ₄ , and H ₂ MoO ₄ .
An addition amount of about 10 to 5000 ppm is sufficient for the concentration of the oxidizing agent in the metal surface treatment liquid.

  Further, in the metal surface treatment method of the present invention, a replenisher is preferably used in order to keep the active ingredient concentration constant. The replenisher is prepared with, for example, a concentrated composition containing, as main components, a component consumed by film formation and a component adhering to the object to be processed.

In the surface treatment step, the metal surface treatment liquid described above is brought into contact with the surface of the metal material described above.
The method of contacting is not particularly limited, and examples include immersion, roll coating, curtain flow coating, air spray, airless spray, bar coating, and brush coating.
Of these, immersion is preferred. The immersion can be performed using, for example, a metal surface treatment tank.

A film is formed on the surface of the metal material by the surface treatment process. Then, it is made to dry and the metal material which has a film | membrane on the surface can be obtained.
The drying method is not particularly limited, and examples thereof include hot air, far-infrared heating, direct fire, and induction heater.
The drying time is not particularly limited, but is usually set under industrially profitable conditions.

<PH lowering step>
After the surface treatment step described above, a pH lowering step is performed. The pH lowering step is selected from the group consisting of zirconium and titanium contained in the iron sludge generated in the metal surface treating solution in the surface treating step by reducing the pH of the metal surface treating solution by 0.1 to 3.0. This is a step of dissolving at least the seed metal in the metal surface treatment solution.

  In the surface treatment process, since the metal material containing the iron-based material is surface-treated with an acidic solution, as described above, iron sludge is generated even though it is extremely small. In the present invention, iron sludge is removed in an iron sludge removal step described later. In this step performed before that, one or more metals selected from the group consisting of zirconium and titanium contained in the iron sludge, etc. Only the active ingredient is dissolved by lowering the pH to dissolve the active ingredient. Thereby, it becomes possible to collect | recover an active ingredient in a metal surface treatment liquid, and to remove only the iron sludge with which iron content became relatively high as an unnecessary thing.

In the pH reduction step, the pH of the metal surface treatment solution is reduced by 0.1 to 3.0, preferably 0.2 to 2.0.
When the pH decrease is 0.1 or more, the amount of the active ingredient dissolved in the metal surface treatment liquid is sufficiently increased.
When the decrease in pH is 3.0 or less, dissolution of iron sludge in the metal surface treatment liquid can be suppressed, and iron sludge can be efficiently removed. In addition, when a part of iron sludge is dissolved due to a significant drop in pH, the dissolved iron sludge is treated with the metal surface treatment when the pH is raised in order to use the metal surface treatment liquid after removing the iron sludge again in the surface treatment process. Although it will precipitate again in a liquid, such a problem can also be suppressed as the fall of pH is 3.0 or less.

The method for lowering the pH is not particularly limited, and examples thereof include a method of adding an acidic substance.
Examples of acidic substances include inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, and phosphoric acid; formic acid, acetic acid, oxalic acid, adipic acid, stearic acid, maleic acid, succinic acid, tartaric acid, citric acid, apple Examples thereof include organic acids such as acid, lactic acid, fumaric acid, gluconic acid, phthalic acid, and succinic acid. Of these, nitric acid is preferred.
Further, the replenisher described above generally has a lower pH than the metal surface treatment liquid. Therefore, a replenisher can be used as the acidic substance.
These acidic substances can be used alone or in combination of two or more.

In this pH lowering step, one or more metals selected from the group consisting of zirconium and titanium contained in the iron sludge are dissolved in the metal surface treatment solution.
In addition, when the metal surface treatment liquid contains other active ingredients (for example, polymer compounds, metal ions other than zirconium and titanium), it is preferred that the present invention simultaneously dissolves such active ingredients in this step. This is one of the embodiments.

<Iron sludge removal process>
An iron sludge removal process is performed after the pH reduction process mentioned above. An iron sludge removal process is a process of removing iron sludge from a metal surface treatment liquid, and making the iron sludge density | concentration of a metal surface treatment liquid 500 ppm or less.

When the metal surface treatment liquid is used for a long time in the surface treatment process, the iron (II) ion concentration in the metal surface treatment liquid gradually increases due to dissolution of iron in the metal material. The metal surface treatment liquid used in the surface treatment step is not adversely affected by the chemical conversion even if the Fe (II) ion concentration is increased.
However, Fe (II) ions in the metal surface treatment liquid are oxidized to Fe (III) ions by an oxidation reaction. In the pH range of the metal surface treatment liquid used in the surface treatment step, Fe (III) ions are dissolved in a small amount, so iron hydroxide (Fe (OH) ₃ ) is generated from Fe (III) ions, and iron is removed. Insoluble matter (precipitate) contained is generated in the system. This is iron sludge.

As iron sludge accumulates, it adheres to the surface of the metal material and may cause deterioration of the appearance after painting. In addition, the generated iron sludge may adhere to the processing facility, and the maintainability may deteriorate.
Further, precipitation of iron hydroxide may reduce the concentration of the active ingredient in the metal surface treatment liquid, which may deteriorate the performance of the resulting film. This is considered to be because when the iron hydroxide is precipitated, the active ingredient co-deposits or the active ingredient is adsorbed on the iron hydroxide. The active ingredient is basically one or more metals selected from the group consisting of zirconium and titanium, but when a metal compound other than a polymer compound, zirconium and titanium is contained in the metal surface treatment liquid. These are also included.
Therefore, in this step, iron sludge is removed.

Although the method of removing iron sludge from a metal surface treatment liquid is not specifically limited, For example, the method of using a solid-liquid separator is mentioned.
The solid-liquid separator is not particularly limited. For example, a filtration / separation device using a bag filter, a paper filter or the like; a membrane separation device using a UF membrane, an MF membrane or the like; a centrifuge device;
These devices can be used alone, but can also be separated efficiently by combining two or more.

  In addition, it is one of preferred embodiments that preliminary separation is performed in a settling tank or the like before separation with a solid-liquid separation device. By preliminarily separating the liquid with a high iron sludge concentration, the solid-liquid separator and the iron sludge treatment facility can be reduced, or the flow rate of the metal surface treatment liquid sent to the solid-liquid separator can be reduced to lower the equipment load. Can be. As a result, the cost can be reduced.

  In addition, before performing separation or preliminary separation in a solid-liquid separation device, it is preferable to remove large dust (for example, lint) in the metal surface treatment liquid with a prefilter. The prefilter is not particularly limited, and a conventionally known prefilter can be used.

  In this step, in order to improve the efficiency of removing iron sludge, a flocculant and / or an oxidizing agent can be added as long as chemical conversion is not inhibited. Thereby, a solid-liquid separator and an iron sludge processing facility can be reduced, or the flow rate of the metal surface treatment liquid sent to the solid-liquid separator can be reduced to reduce the apparatus load. As a result, the cost can be reduced.

Examples of the flocculant include inorganic flocculants such as activated silicic acid, aluminum sulfate, polyaluminum chloride, ferrous sulfate, ferric chloride; polyacrylamide, polyethylene oxide, sodium polyacrylate, sodium alginate, polyalkyl Organic coagulants such as amino acrylate and polyaminomethyl acrylamide are listed.
Examples of the oxidizing agent include sodium nitrite, hydrogen peroxide, oxygen, and air.
These addition methods are not particularly limited, and can be performed according to a conventional method.

  The addition of the flocculant and / or the oxidizing agent can also be performed before this step.

  In this invention, although this process is required, since the quantity of the generated iron sludge is extremely small compared with the conventional method as mentioned above, a required installation and expense can be reduced.

The removed iron sludge can be discarded as it is.
Moreover, it can also process after reducing a moisture content with a dehydrator, a dryer, etc. When using a dehydrator or the like, the separated metal surface treatment liquid may be used in the surface treatment step. Iron sludge having a reduced moisture content can be discarded, but can also be used as a raw material for iron materials, concrete, ceramics, and the like.

<Recovery supply process>
A recovery supply process is performed after the iron sludge removal process mentioned above. The recovery supply step is a step of recovering the metal surface treatment liquid from which the iron sludge has been removed and supplying it to the surface treatment step described above.
That is, the metal surface treatment liquid from which the iron sludge has been removed in the iron sludge removal step is supplied to the surface treatment step and used for the surface treatment.

Since the metal surface treatment liquid used in the surface treatment process has a specific composition and pH as described above, before supplying the metal surface treatment liquid from which iron sludge has been removed to the surface treatment process as a whole. It is preferable that the composition and pH be adjusted. The same applies to the case where a metal surface treatment liquid separated from iron sludge by a dehydrator or the like is used.
Further, the composition and pH can be adjusted, for example, in a metal surface treatment tank after supplying the metal surface treatment liquid from which iron sludge has been removed to the surface treatment step. When performing in a metal surface treatment tank, a replenisher etc. are added so that it may become the specific composition and pH mentioned above.

The method for adjusting the pH is not particularly limited, and examples thereof include a method of adding an alkaline substance.
Examples of the alkaline substance include sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, ammonia, and triethanolamine.

In the metal surface treatment method of the present invention, the above-described surface treatment step, pH reduction step, iron sludge removal step, and recovery supply step are circulated in this order. In that case, the iron sludge density | concentration of the metal surface treatment liquid in a surface treatment process is maintained at 500 ppm or less, Preferably it is 300 ppm or less, More preferably, it is maintained at 200 ppm or less.
If it is within the above range, adverse effects caused by iron sludge can be suppressed.
In this invention, iron sludge density | concentration is solid content concentration of the insoluble matter containing iron in the metal surface treatment liquid measured according to JISK0102 14-1.

  In the metal surface treatment method of the present invention, steps other than the above steps can be appropriately performed.

  According to the metal surface treatment method of the present invention, a metal material containing an iron-based material, preferably selected from the group consisting of an iron-based material, or an iron-based material, a zinc-based material, an aluminum-based material, and a magnesium-based material. When a surface treatment is performed on a metal material composed of one or more kinds, a surface-treated film having excellent corrosion resistance after coating can be stably deposited over a long period of time.

  The metal material having a film formed by the metal surface treatment method of the present invention is used in a wide range of applications. For example, it is suitably used for an automobile body.

  The present invention will be specifically described below with reference to examples. However, the present invention is not limited to these.

1. Metal surface treatment (Example 1)
The following steps (a) to (f) were performed using the following metal surface treatment solution 1 using a 70 mm × 150 mm SPC (cold rolled steel sheet defined in JIS G3141) as a test plate.

<Metal surface treatment liquid 1>
Using hexafluorozirconic acid and magnesium nitrate, an aqueous solution having a zirconium ion concentration of 50 ppm and a magnesium ion concentration of 100 ppm was prepared. This aqueous solution was heated to 40 ° C. and held, then adjusted to pH 4.5 using a sodium hydroxide reagent and hydrofluoric acid, and a fluorine ion meter (IM-55G, manufactured by Toa Denpa Kogyo Co., Ltd.) The metal ion treatment solution 1 was obtained by adjusting the fluoride ion concentration measured in step 1 to 5 ppm. The total fluorine concentration in the obtained metal surface treatment solution 1 was 1000 ppm. The total fluorine concentration was measured according to JIS K0102 34-2 (hereinafter the same).

(A) Alkaline degreasing First, alkali degreasing was performed on the test plate. Alkaline degreasing is performed by diluting a degreasing agent (Fine Cleaner L4460 (registered trademark), manufactured by Nihon Parkerizing Co., Ltd.) with tap water to a concentration of 2% by mass, heating to 40 ° C., and then testing for 120 seconds. This was done by spraying the plate.

(B) Washing The test plate after alkaline degreasing was washed with water. Washing with water was performed by spraying water onto the test plate at room temperature for 30 seconds.

(C) Surface treatment The surface treatment was performed on the test plate after washing.
The surface treatment was performed using a metal surface treatment apparatus shown in FIG. A metal surface treatment apparatus 1 shown in FIG. 1 includes a metal surface treatment tank 10 containing 50 L of the metal surface treatment liquid, a pH adjustment tank 12, and a solid-liquid separation apparatus 14 including a sedimentation separation apparatus. ing.

In the metal surface treatment tank 10, one test plate after washing was immersed in the metal surface treatment solution for 120 seconds and then taken out (surface treatment step). In this surface treatment step, this operation was repeated to continuously immerse and take out 10,000 test plates. The processing efficiency was 20 sheets / h.
At that time, each component consumed by film formation and take-out (take-out amount: 2 mL / sheet) was replenished, and nitric acid or ammonia was added to keep the pH constant.

On the other hand, the metal surface treatment liquid used in the surface treatment step was sent from the metal surface treatment tank 10 to the pH adjustment tank 12. In the pH adjusting tank 12, nitric acid was added to the metal surface treatment solution to adjust the pH to 3.5 (pH lowering step).
Next, the pH-adjusted metal surface treatment liquid was sent from the pH adjustment tank 12 to the solid-liquid separator 14. In the solid-liquid separator 14, iron sludge in the metal surface treatment liquid was removed by sedimentation separation (iron sludge removal step).
Thereafter, the metal surface treatment liquid from which the iron sludge was removed was sent from the solid-liquid separation device 14 to the metal surface treatment tank 10 and used for the surface treatment process (recovery supply process).
Each of these steps was continuously performed by circulation during the processing of 10,000 test plates.

(D) Washing with water The test plate after the surface treatment was washed with water. Washing with water was performed by spraying water onto the test plate at room temperature for 30 seconds.

(E) Pure water washing The test plate after water washing was washed with pure water. The pure water washing was performed by spraying pure water on the test plate for 30 seconds at room temperature.

(F) Drying The test plate after pure water washing was dried. Drying was performed by placing the test plate in a hot air dryer heated to 90 ° C. for 5 minutes.

(Example 2)
Using the same test plate as used in Example 1 and the following metal surface treatment solution 2, the above steps (a) to (f) were performed according to the method of Example 1.
<Metal surface treatment liquid 2>
Using an aqueous hexafluorotitanate solution and strontium nitrate, an aqueous solution having a titanium ion concentration of 100 ppm and a strontium ion concentration of 500 ppm was prepared. After maintaining this aqueous solution at 40 ° C., the pH is adjusted to 5.0 using an aqueous ammonia solution and hydrofluoric acid, and the fluoride ion concentration measured with a fluorine ion meter is adjusted to 50 ppm. Thus, a metal surface treatment liquid 2 was obtained. The total fluorine concentration in the obtained metal surface treatment liquid 2 was 2000 ppm.

(Example 3)
Using the same test plate as used in Example 1 and the following metal surface treatment solution 3, the above steps (a) to (f) were performed according to the method of Example 1.
<Metal surface treatment liquid 3>
An aqueous solution having a zirconium ion concentration of 1000 ppm was prepared using zirconium oxynitrate and nitric acid. After maintaining this aqueous solution at 45 ° C., the pH is adjusted to 4.0 using an aqueous ammonia solution and hydrofluoric acid, and the fluoride ion concentration measured with a fluorine ion meter is adjusted to 10 ppm. Thus, a metal surface treatment liquid 3 was obtained. The total fluorine concentration in the obtained metal surface treatment liquid 3 was 9000 ppm.

(Comparative Example 1)
The steps (a) to (f) were performed according to the method of Example 1 using the same test plate as used in Example 1 and the following metal surface treatment solution 4.
<Metal surface treatment liquid 4>
An aqueous solution having a zirconium ion concentration of 50 ppm was prepared using zirconium nitrate. After maintaining this aqueous solution at 45 ° C., the pH is adjusted to 4.5 using an aqueous ammonia solution and hydrofluoric acid, and the fluoride ion concentration measured with a fluorine ion meter is adjusted to 70 ppm. A metal surface treatment solution 4 was obtained. The total fluorine concentration in the obtained metal surface treatment solution 4 was 90 ppm.

(Comparative Example 2)
Same as Example 1 except that the same test plate as used in Example 1 and the above-described metal surface treatment solution 1 were used and the pH after adjustment was adjusted to 1.5 in the pH reduction step of (c) above. The above steps (a) to (f) were performed by the method described above.

(Comparative Example 3)
Example 1 except that the pH was not adjusted by adding nitric acid in the pH adjusting tank 12 in the above (c), using the same test plate and the metal surface treatment liquid 1 used in Example 1. The above steps (a) to (f) were performed by the same method.

(Comparative Example 4)
Using the same test plate as used in Example 1 and the above-described metal surface treatment liquid 1, in the above (c), the pH was not adjusted by adding nitric acid in the pH adjusting tank 12, and the solid-liquid separator 14 was used. The above steps (a) to (f) were carried out in the same manner as in Example 1 except that the iron sludge was not settled and separated.

2. Evaluation of Metal Surface Treatment Liquid For the metal surface treatment liquid in the metal surface treatment tank 10 after treating 10,000 test plates, the iron sludge concentration and the zirconium ion concentration or titanium ion concentration and iron ion concentration after filtration were determined. It was measured.
The results are shown in Table 1.

3. Evaluation of the film About the test plates formed in Examples 1 to 3 and Comparative Examples 1 to 4 and having a film formed by the metal surface treatment, when one test plate was processed and 10000 test plates were processed The amount of film at the time of the measurement was measured.
The results are shown in Table 1. In the table, ○ indicates that the coating amount is an amount that does not affect the corrosion resistance and paint adhesion, ○ indicates that the coating amount may adversely affect the corrosion resistance and coating adhesion, and Δ indicates that the coating amount is corrosion resistance. In addition, the amount that had an adverse effect on the coating adhesion was marked as x.

  As is apparent from Table 1, according to the surface treatment method of the present invention (Examples 1 to 3), when a film was formed on a metal material containing an iron-based material, the corrosion resistance after coating of the film was excellent. It was possible to maintain the concentration of zirconium ions or titanium ions in the metal surface treatment solution, which is a suitable condition, within a suitable range during long-term treatment. Moreover, the iron sludge concentration could be suppressed within a range that does not adversely affect the appearance after coating and the maintainability of the apparatus. Furthermore, there was no effect on the coating amount due to the iron ion concentration.

On the other hand, when the total fluorine concentration of the metal surface treatment liquid used in the surface treatment step was too low (Comparative Example 1), the coating amount after the 10,000 sheet treatment was insufficient. This is presumably because the fluoride ion concentration in the metal surface treatment liquid decreased during the long-term treatment, etching of the metal surface was not performed, and the reactivity (chemical conversion) was lowered due to the influence of iron ions.
Moreover, when the grade of the fall of pH in a pH fall process was too large (comparative example 2), the zirconium ion density | concentration fell during the long-term process, and the iron sludge density | concentration rose. This is presumably because the iron sludge in the metal surface treatment solution was dissolved by greatly reducing the pH and could not be removed efficiently in the iron sludge removal step.
Further, when the pH was not lowered after the surface treatment step (Comparative Example 3), the zirconium ion concentration was lowered during the long-term treatment. This is considered to be because iron sludge is removed in the state containing zirconium.
In addition, when the pH was not lowered after the surface treatment step and the iron sludge was not removed (Comparative Example 4), the zirconium ion concentration decreased and the iron sludge concentration increased during the long-term treatment. did.

It is a schematic diagram of the metal surface treatment apparatus used in the Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Metal surface treatment apparatus 10 Metal surface treatment tank 12 pH adjustment tank 14 Solid-liquid separation apparatus

Claims (3)

A metal surface treatment method for treating a metal material including an iron-based material,
PH 3.0-6, containing 5 to 5000 ppm of ions of one or more metals selected from the group consisting of zirconium and titanium, 0.1 to 100 ppm of fluoride ions, and a total fluorine concentration of 100 to 50000 ppm A surface treatment step of bringing a metal surface treatment solution of 0.0 into contact with the surface of the metal material;
After the surface treatment step, the pH of the metal surface treatment solution is lowered by 0.1 to 3.0, and the zirconium and titanium contained in the iron sludge generated in the metal surface treatment solution in the surface treatment step A pH lowering step of dissolving one or more metals selected from the group in the metal surface treatment liquid;
After the pH lowering step, an iron sludge removing step for removing the iron sludge from the metal surface treatment liquid;
After the iron sludge removal step, the metal surface treatment liquid from which the iron sludge has been removed is collected, and a recovery supply step for supplying the surface treatment step is circulated.
The metal surface treatment method which maintains the iron sludge density | concentration of the said metal surface treatment liquid in the said surface treatment process at 500 ppm or less.   The metal surface treatment method according to claim 1, wherein a flocculant and / or an oxidizing agent is added to the metal surface treatment liquid before or in the iron sludge removal step.   The metal material is an iron-based material or a metal material composed of an iron-based material and one or more selected from the group consisting of a zinc-based material, an aluminum-based material, and a magnesium-based material. The metal surface treatment method as described in 2.

Images