JP4142616B2 - Preparation method of surface treatment liquid - Google Patents

Description

The present invention shows a material made of a metal-based material (metal, alloy, or plating. Examples of the material made of plating include zinc plating and zinc alloy plating). It is related with the preparation method of the surface treatment liquid obtained.

Zinc plating or zinc alloy plating (hereinafter referred to as zinc-based plating) is widely used as a surface treatment method for metal-based materials using sacrificial corrosion protection of zinc. This zinc-based plating has good anticorrosion properties, but has the disadvantage that the coating dissolves in a relatively short period of time and the corrosion resistance deteriorates, so that the corrosion resistance can be maintained over a long period of time. Generally, chromate treatment is performed later.
The coating type, reaction type, and electrolytic type are known for chromate treatment, and all of them use the repair of the chromate film by reducing hexavalent chromium ions to maintain good corrosion resistance. Includes soluble hexavalent chromium.

Hexavalent chromium is indispensable for the self-healing property of the chromate film, but has the potential to cause environmental pollution to the natural environment due to its toxicity. For example, the environmental standard value in the Water Pollution Control Law is also set as very low as 0.05 ppm, and it is considered preferable to eliminate hexavalent chromium from the film as much as possible. Moreover, since hexavalent chromium has carcinogenicity, the smaller the elution of hexavalent chromium, the better.
For these reasons, a trivalent chromium chromate method has been proposed as a film forming method that does not use hexavalent chromium without impairing the rust preventive ability of conventional chromate films.

Patent Document 1 proposes a trivalent chromium chromate solution in which an organic acid having an anion faster than the ligand substitution rate of a fluoro complex is added as a chelating agent. The chromate liquid of Patent Document 1 is used for a chromate liquid composed only of trivalent chromium without using hexavalent chromium, and can form a film having a better rust preventive ability than conventional trivalent chromium chromate films. It is possible.
JP 2004-3019 A

Trivalent chromium chromate solution in Patent Document 1, without the addition of reagents hexavalent chromium during vatting. However, a trivalent chromium compound is added, and hexavalent chromium ions are always mixed in the trivalent chromium compound as impurities at the pharmaceutical stage. In particular, industrial chemicals tend to contain more impurities than test reagents, and even in test reagents, trivalent chromium compounds contain trace amounts of hexavalent chromium ions. Therefore, there is a possibility that hexavalent chromium is also mixed in the surface treatment film formed using the trivalent chromium chromate solution of Patent Document 1.
Since hexavalent chromium contained in the surface treatment film is soluble in water, there is a high possibility of elution out of the film as water-soluble hexavalent chromium ions. Hexavalent chromium ions may affect the natural environment and the human body, and there has been a need for a lower concentration of elution from the film than before.

An object of this invention is to provide the adjustment method of the surface treatment liquid which can solve such a problem.
The present invention provides a surface treatment solution having a hexavalent chromium ion concentration lower than that of a conventional method for preparing a trivalent chromium chromate solution by adding a reducing agent that reduces hexavalent chromium ions to trivalent chromium ions in the building bath stage. It is an object of the present invention to provide a method for preparing a surface treatment solution capable of obtaining the above.

In order to achieve the above object, the present invention takes the following means for the method of adjusting the surface treatment liquid. That is,
To an aqueous solution of a trivalent chromium compound containing 21.5 to 121 ppm of hexavalent chromium ions as impurities, Li, Be, Na, Mg, K, Ca, Al, Si, Ti, V, Mn, Fe, Co, Ni, Cu Zn, Sr, Zr, Nb, Mo, Pd, Ag, Sn, Ba, Ta, W, Pt, Au, Bi, Ce one or more cations selected from metal ions or ammonium ions, This hexavalent chromium is divided before and after the addition of a supporting salt composed of one or more anions selected from halogen ions, sulfate ions, nitrate ions, phosphate ions, carboxylate ions, dicarboxylate ions or oxycarboxylate ions. Ions are reduced to trivalent chromium ions, sodium bisulfite, sodium sulfite, sodium metabisulfite, sulfur dioxide or phosphorous acid A reducing agent composed of one or more sulfur oxides or phosphorous oxides selected from the above, the temperature of the surface treatment liquid is set to 60 to 90 ° C. after the addition of the reducing agent, and the total amount of the reducing agent added is When it is assumed that the reaction has occurred 100%, a reduction reaction is carried out by adding 2.0 times the theoretically required hexavalent chromium ion concentration, and the hexavalent chromium ion concentration is 10 ppm or less. This you reduced, it is possible to hexavalent chromium ion concentration compared to the process for the preparation of conventional trivalent chromium chromate solution to obtain a low surface treatment liquid. Moreover, compared with the case where other reducing agents are used, the concentration of hexavalent chromium ions contained in the surface treatment liquid can be lowered.

By the method for adjusting a surface treatment liquid of the present invention, a surface treatment liquid having a lower hexavalent chromium ion concentration than that of a conventional method for adjusting a trivalent chromium chromate liquid can be obtained.

The surface treatment liquid of the present invention is a support mainly containing trivalent chromium ions generated by water-soluble trivalent chromium compounds, hexavalent chromium ions contained in trace amounts as impurities of the trivalent chromium compounds, and metals other than chromium. It is an aqueous solution containing a salt and is used to form a surface treatment film (so-called chromate film) having a high anticorrosion property on the surface of a metal-based material.
Examples of the metallic material include steel materials, metals such as zinc, nickel, aluminum, copper, and tin, alloy materials such as stainless steel and brass, and plating films applied to these metal materials. Since the corrosion resistance of the plating film can be stabilized for a long time, it is particularly suitable for the surface of zinc or zinc-based alloy plating film.

The trivalent chromium compound is a salt that is soluble in the surface treatment solution and has strong mineral acid ions as anions. In particular, chromium (III) chloride, chromium (III) sulfate, chromium nitrate ( III) is preferably used. The trivalent chromium compound is added in an aqueous solution so that the trivalent chromium ion concentration is 0.1 to 20 g / l, preferably 1 to 10 g / l. By setting the trivalent chromium ion concentration to 0.1 to 20 g / l, the surface treatment film can be formed at a good film forming speed.
The hexavalent chromium ion is contained as an impurity in the trivalent chromium compound, and is ionized and present in an aqueous solution of the trivalent chromium compound or a surface treatment liquid prepared using the aqueous solution. When measured using capillary electrophoresis or the like, it becomes about 300 ppm. The hexavalent chromium ions are reduced from hexavalent chromium ions to trivalent chromium ions by adding a reducing agent in the building bath stage, whereby the amount of hexavalent chromium ions taken into the film can be reduced and eluted from the film. The effect of valent chromium ions on the natural environment and human body can be reduced. Moreover, by adding the reducing agent at the building bath stage, hexavalent chromium ions having strong oxidizing power can be selectively reduced, and the concentration of hexavalent chromium ions can be reduced preferentially.

The concentration of the hexavalent chromium ion is limited to 20 ppm or less, preferably 10 ppm or less, by the addition of a reducing agent in the building bath stage. By suppressing the concentration to 20 ppm or less, the amount of hexavalent chromium ions taken into the surface treatment film can be reduced as compared with the conventional trivalent chromium chromate method.
The reducing agent may be a sulfur oxide or phosphorous oxide such as sodium bisulfite, sodium sulfite, sodium metabisulfite, sulfur dioxide, phosphorous acid, etc., particularly sodium bisulfite, sodium sulfite, sodium metabisulfite. Can be suitably used. By using sodium bisulfite, sodium sulfite, or sodium metabisulfite, hexavalent chromium ions contained in a small amount (about 300 ppm) in the surface treatment solution can be reduced to trivalent chromium ions in a high yield. The hexavalent chromium ion concentration in the treatment liquid can be reduced to a lower concentration than other reducing agents.

The support salt is mainly composed of a cation mainly composed of metal ions and an anion generated by dissociation of an acid such as an inorganic acid or an organic acid, and a plurality of types of support salts can be used in combination.
The cations include Li, Be, Na, Mg, K, Ca, Al, Si, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Sr, Zr, Nb, Mo, Pd, Ag, Sn, One or more selected from metal ions or ammonium ions of each valence of Ba, Ta, W, Pt, Au, Bi or Ce can be used, and the cation is added in a total cation addition amount of 100 g / l or less, preferably It is added in the range of 50 g / l or less. In addition, although it is more preferable to add the said cation, the case where the said cation is not added is also considered. By adding the cation in the range of 100 g / l or less, the corrosion product of the base metal (in the case where the metal-based material is plating and the base metal on which the plating film is formed) is stabilized. Or the film can be densified, and the durability of the corrosion resistance can be increased.

The anion is an inorganic acid ion or an organic acid ion, and one or more of these anions are added in a total anion addition amount of 300 g / l or less, preferably 100 g / l or less.
Examples of the inorganic acid ions include halogen ions such as chlorine ions, fluorine ions, bromine ions, chlorate ions, perchlorate ions, chlorite ions, hypochlorite ions, sulfate ions, sulfite ions, nitrate ions, Examples include nitrate ion, phosphate ion (orthophosphate ion), polyphosphate ion, metaphosphate ion, pyrophosphate ion or ultraphosphate ion, especially halogen ion, sulfate ion, nitrate ion or phosphate ion (orthophosphate ion) ) Is preferably used.

Examples of organic acid ions include monocarboxylic acid ions such as acetate ions, dicarboxylic acid ions such as tartrate ions, tricarboxylic acid ions, and hydroxycarboxylic acid ions. Particularly, oxalate ions, malonate ions, succinate ions, Glutarate ion, adipate ion, pimelate ion, suberate ion, azelate ion, sebacate ion, maleate ion, phthalate ion, terephthalate ion, tartaric acid ion, citrate ion, malate ion, ascorbate ion Etc. can be used suitably.
These supporting salts function as a ligand (ligand) to form a complex with chromium ions in an aqueous solution, and have an effect of increasing the reactivity of trivalent chromium on the material surface.

The surface treatment liquid of the present invention can be used by diluting or mixing at the time of surface treatment and adjusting the concentration. By diluting or mixing, the stability of the liquid is improved and long-term storage is possible, and the transportation cost can be reduced by weight reduction and the storage space can be reduced by reducing the volume.
As shown in FIG. 1, the surface treatment method using the surface treatment liquid of the present invention cleans or sensitizes the surface of the metal-based material to be treated in the pretreatment step, and each chemical in the preparation step. The surface treatment liquid is set to a predetermined liquid composition, pH, and bath temperature, a surface treatment film is formed using the surface treatment liquid in the chemical conversion step, and then the surface treatment film is obtained by washing and drying. Is.

The pretreatment step is a step composed of water washing, acid washing treatment, heat treatment, flash treatment, and activation treatment, and these treatments can be used in combination according to the surface state and material of the object to be treated. .
The acid cleaning treatment is a treatment for removing dirt such as contaminants and oils and fats adhering to the surface of an object to be treated using a treatment liquid in which nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid or carboxylic acid or a combination of these acids is combined. The heat treatment is preferably a process for removing a gas component such as hydrogen gas contained in a metal-based material or a plating film, and particularly the object to be processed having a plating film. It is preferable to use for.

Further, the flash treatment is a washing treatment with an alkaline solution, and is performed to improve the adhesion with the base, and the activation treatment is performed with nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid or carboxylic acid or these acids. Using the combined treatment liquid, metal oxides and the like formed on the surface of the object to be treated are removed to promote good formation of the surface treatment film and to obtain good adhesion.
In the pretreatment step, a combination of treatments to be performed can be changed depending on the surface state and material of the workpiece. For example, an object to be processed having a clean surface that does not have processing oil or contamination on the surface may be washed only with water, but the activation treatment is applied to an object to be processed such as aluminum that is likely to be in a passive state. Is preferred.

In the preparation method of the surface treatment liquid of the present invention, an aqueous solution of a trivalent chromium compound containing trivalent chromium ions and hexavalent chromium ions generated by dissociation of the trivalent chromium compound in the preparation bath stage of the preparation step, The reducing agent that reduces dissolved hexavalent chromium ions to trivalent chromium ions is added to lower the concentration of dissolved hexavalent chromium ions, and then the addition of supporting salt and adjustment of pH and bath temperature are performed. Part of the preparation process included.
In the method for preparing the surface treatment liquid, a reduction reaction of the reducing agent is used. Since this reduction reaction is an exothermic reaction, cooling is performed on the aqueous solution of the trivalent chromium compound in order to improve the reaction rate. However, since the reaction yield decreases when the temperature is too low, the bath temperature to which the reducing agent is added is preferably 60 to 90 ° C. By maintaining the bath temperature at 60 to 90 ° C., it is possible to efficiently reduce the hexavalent chromium ion concentration.

Further, when it is assumed that the reaction has occurred 100%, the reducing agent is added so that the concentration of the reducing agent is 1.0 to 2.0 times the theoretically required hexavalent chromium ion concentration. Is preferred. By adding the reducing agent to a concentration of 1.0 to 2.0 times, it is possible to minimize the reducing agent to be used, and to reduce the concentration of unreacted hexavalent chromium. Become.
Furthermore, it is preferable not to add a large amount of the reducing agent at a time in order to avoid sudden heat generation, but to add a small amount continuously, and to add a reducing agent so as to balance the heat generation amount and the heat absorption amount by cooling, If too much time is added to the addition of the reducing agent, the productivity deteriorates. Therefore, it is preferable to add the reducing agent separately before and after the addition of the supporting salt. By adding the reducing agent separately in this way, it is possible to prevent a decrease in the reaction rate due to heat generation, and it is possible to reduce hexavalent chromium ions that may be contained in the supporting salt and reduce the concentration.

Next, the supporting salt is added to an aqueous solution of a trivalent chromium compound, and an inorganic acid or acetic acid such as hydrochloric acid, nitric acid, sulfuric acid or the like is used so that the pH becomes 0.5 to 5.0, preferably 1.5 to 3.5. A surface treatment solution is obtained by appropriately adding an organic acid or a salt thereof such as a bath temperature of 10 to 70 ° C., preferably 20 to 50 ° C.
The chemical conversion step is a step of forming a surface treatment film on the object to be treated. The surface treatment film is formed by immersing the object to be treated for 5 to 120 seconds, preferably 10 to 90 seconds.
In addition, after forming the surface treatment film, a liquid composition containing silicon or a silicon-based resin is applied on the surface treatment film, or a resin containing a fine particle such as polytetrafluoroethylene, wax, or these resins are included. A liquid composition such as a coating agent may be applied to form a surface protective film having wear resistance and water repellency on the surface. Further, a pigment or a dye may be applied to be colored or the corrosion resistance may be further improved. As a result, a protective film having decorativeness and wear resistance can be obtained.

The protective film is composed of the surface-treated film, or a surface-treated film and a surface protective film formed on the surface, and the surface-treated film is formed by trivalent chromium ions generated by water-soluble trivalent chromium compounds; The surface of the metallic material is brought into contact with a surface treatment solution containing a supporting salt, hexavalent chromium ions contained as impurities in the trivalent chromium compound, and a reducing agent that reduces the hexavalent chromium ions to trivalent chromium ions. It is formed by that.
The surface treatment film is formed in the chemical conversion step using the surface treatment solution, so that the concentration of hexavalent chromium contained in the total weight of the film is suppressed to 0.2 ppm or less, and the hexavalent that is eluted. The chromium ion concentration can be lowered, and the burden on the human body and the natural environment can be reduced.

Further, the surface treatment film does not vary in the concentration distribution of hexavalent chromium contained in the film by using the surface treatment solution, and the concentration distribution of hexavalent chromium in the film is perpendicular to the depth direction. A uniform film having a surface concentration of 0.2 μg / cm ² or less can be obtained for any surface distribution. Thereby, the hexavalent chromium ion concentration to elute can be stably maintained at a low concentration.
The present invention will be described in more detail with reference to examples and comparative examples, but the contents of the present invention are not limited to the examples.

  In order to show the effect of the preparation method of the surface treatment liquid of the present invention on the reduction of the hexavalent chromium ion concentration in the surface treatment liquid, as shown in Table 1, a trivalent chromium compound, a supporting salt, a dye, a stabilizer, etc. 7 types of surface treatment liquids that are prepared without adding a reducing agent, and 7 types of surface treatments that have the same composition as the 7 types of surface treatment liquids but are prepared by addition of a reducing agent A liquid was also prepared. The dissolved hexavalent chromium ion concentration of the obtained surface treatment liquid was analyzed, and to what extent the adjustment method of the present invention reduced the hexavalent chromium ion concentration in each surface treatment liquid having different liquid compositions. The hexavalent chromium ion concentration was analyzed by measuring the filtrate from which trivalent chromium ions were removed by precipitation filtration by capillary electrophoresis, absorptiometry using ICP, diphenylcarbazide or the like. The reagents used in the preparation of Table 1 are all trivalent chromium compound reagents.

  Liquid composition No. 1-7 and liquid composition No.1. Comparing 8-14, the reduction of the hexavalent chromium ion concentration is larger than the reduction of the trivalent chromium ion concentration by adding the reducing agent at the preparation stage. It turns out that it is reduce | restored to trivalent chromium ion. Moreover, liquid composition No. to which no supporting salt or the like is added. 1-4 and No.1. No. 8-11 and liquid composition No. to which supporting salt etc. are added. 5-7 and no. Compared with 12-14, both have reduced hexavalent chromium ion concentration, and even if the supporting salt is added, the effect of reducing hexavalent chromium ions by the addition in the reducing agent preparation stage is not hindered. I understand.

Next, based on the basic liquid composition of A to J, those in which the reducing agent was added in the preparation stage are shown in Table 2 as Examples 1 to 10, and those in which the reducing agent was not added in the preparation stage are shown in Table 3. Are shown as Comparative Examples 1-10. Further, Table 2 shows that using a sodium nitrite sulfate as the reducing agent as Examples 1-10. The basic liquid composition is adjusted by changing the kind of the trivalent chromium compound and the supporting salt, and is adjusted so that complex ions obtained in the surface treatment liquid are different.
Moreover, using the surface treatment liquid having these liquid compositions, a film was formed under the various treatment conditions shown in Tables 2 and 3 with the galvanized product as the product to be treated. The valence chromium concentration was measured to evaluate the performance. Incidentally, the corrosion resistance is the time until a white corrosion product is first formed in an SST (salt spray) test specified in JIS. The hexavalent chromium concentration in the film was determined using ICP of the filtrate.

  In Example 1, sodium bisulfite was added to the basic liquid composition A for reduction treatment. Similarly, compared with Comparative Example 1 using the basic liquid composition A, the hexavalent chromium concentration was 32.5 ppm to 5%. Reduced to 5 ppm. As a result of film formation by immersing in a surface treatment solution having a pH of 2.2 and a bath temperature of 30 ° C. for 20 seconds, the appearance and corrosion resistance of the film are the same as in Comparative Example 1, but hexavalent chromium in the film The concentration is reduced from 0.220 ppm to 0.045 ppm.

In Examples 2 to 10, sodium bisulfite was added to the basic liquid compositions B to J for reduction treatment. Compared to Comparative Examples 2 to 10 using the same liquid composition, the hexavalent chromium concentrations were respectively lower. It is greatly reduced. As a result of film formation, the appearance and corrosion resistance are equivalent to those of Comparative Examples 2 to 10, but the hexavalent chromium concentration in the film is reduced.
When comparing Examples 1 to 10 and Comparative Examples 1 to 10, each example in which a reducing agent was added at the preparation stage reduced the hexavalent chromium ion concentration in the surface treatment solution without losing the appearance and corrosion resistance. It can be seen that the hexavalent chromium concentration taken into the formed film can be reduced.

Comparative example

The ratio Comparative Examples 1 to 10 are those used in the surface treatment liquid to prepare a basic liquid composition A~J without reduction, although the corrosion resistance and appearance as compared with Examples 1 to 10 equivalent, surface The hexavalent chromium concentration in the treatment liquid and the hexavalent chromium concentration in the film are high.

It is a block diagram which shows the surface treatment process of this invention.

Claims (1)

To an aqueous solution of a trivalent chromium compound containing 21.5 to 121 ppm of hexavalent chromium ions as impurities, Li, Be, Na, Mg, K, Ca, Al, Si, Ti, V, Mn, Fe, Co, Ni, Cu Zn, Sr, Zr, Nb, Mo, Pd, Ag, Sn, Ba, Ta, W, Pt, Au, Bi, Ce one or more cations selected from metal ions or ammonium ions, This hexavalent chromium is divided before and after the addition of a supporting salt composed of one or more anions selected from halogen ions, sulfate ions, nitrate ions, phosphate ions, carboxylate ions, dicarboxylate ions or oxycarboxylate ions. Ions are reduced to trivalent chromium ions, sodium bisulfite, sodium sulfite, sodium metabisulfite, sulfur dioxide or phosphorous acid A reducing agent composed of one or more sulfur oxides or phosphorous oxides selected from the above, the temperature of the surface treatment liquid is set to 60 to 90 ° C. after the addition of the reducing agent, and the total amount of the reducing agent added is When it is assumed that the reaction has occurred 100%, a reduction reaction is carried out by adding 2.0 times the theoretically required hexavalent chromium ion concentration, and the hexavalent chromium ion concentration is 10 ppm or less. process for the preparation of the surface treatment liquid to reduce to said Rukoto to.

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