JP2002180267A - Treatment method for preventing elution of lead from lead-containing copper alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for preventing such a phenomenon that lead elutes from a metal piece for water supply pipe of a water feed apparatus made of a lead-containing copper alloy material into the water in use. SOLUTION: In the method for preventing the elution of lead into water, as pretreatment, the surface of a metal piece for water feed made of a lead- containing copper alloy material is cleaned with an alkaline degreasing solution containing caustic soda and a surfactant. After being plated by an ordinary nickel-chromium plating process, the metal piece is dipped into a chromium- containing chromate treatment solution containing an aromatic heterocyclic compound such as benzotriazole, or an aqueous solution of phosphoric acid and phosphate, or an acidic solution, or an alkaline solution, or a neutral solution so that a firm film is deposited on the surface.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lead-containing copper alloy for preventing lead from eluting into tap water from parts such as a flush fitting made of lead-containing copper alloy. To prevent the elution of lead from components. 2. Description of the Related Art Water supply / distribution fittings are manufactured through a process such as cutting a copper alloy casting or a copper alloy rod and a tube.
For the purpose of improving the workability at the time of cutting, these copper alloys usually contain several% (eg, BC-6 about 5%, free-cutting brass 2-3%)
Lead is added. [0003] Lead added to a copper alloy does not form a solid solution called a mixed crystal like a general alloy material,
It is said that compounds such as lead and oxides of lead are present in particulate form and, in the case of castings, collect on the surface of the alloy. This phenomenon is believed to be due to the specific gravity difference. [0004] Therefore, from the water supply and distribution metal fittings made of lead-containing copper alloy, it is inevitable that lead is eluted into water by passing water through the metal fittings. As a result, elution of lead from water taps became a problem. [0005] However, a copper alloy material to which lead is not added is difficult to cut and is not suitable for those requiring detailed processing such as faucet fittings. Is used. In order to solve these problems, there is a method in which a lead-containing copper alloy component is immersed in a strong alkaline solution and subjected to a slight etching treatment to elute lead and lead oxide near the surface of the alloy material. It is difficult to completely prevent the elution of lead. According to the present invention, a water-supplying metal fitting made of a copper alloy containing lead and having good workability is immersed in a treatment liquid to form a strong film on the surface of the copper alloy. It is intended to provide a method for preventing elution in water at times. SUMMARY OF THE INVENTION The present invention provides a water-supply fitting made of a lead-containing copper alloy, which is washed with an alkaline degreaser or the like as a pretreatment, plated in a usual plating step, and then treated with various benzotriazole compounds. Chromium compound containing an aromatic heterocyclic compound such as an aromatic heterocyclic compound such as benzothiazole and a salt thereof or a chromium compound-free acid solution or a chromium compound-free acid solution or an alkaline solution or a neutral solution, and copper It forms a strong film on the surface of the alloy to prevent the elution of lead. [0009] The organic compound which has the possibility of protecting the surface by forming a film by bonding with copper ranges from a long-chain aliphatic sulfide to a benzene derivative containing nitrogen or sulfur. There are many up to. A well-known heterocyclic compound formed by bonding nitrogen and copper having an unshared electron pair is copper phthalocyanine, which forms a strong film which is not easily attacked by water or a solvent, and has a high adhesion. One of the best is benzotriazole. The structure of the coating is described in Cotton, J. et al. B ^*
Clarifies the structure as follows. a) In the case of cuprous salt b) In the case of cupric salt Normally, copper is cupric when in the air, and is considered to form a strong film by bonding in a network as shown in b). The inventor paid attention to this point, and came up with the idea of forming a film of a compound of copper and benzotriazole by immersing it in a treatment solution containing benzotriazole and preventing elution of lead. Relatively similar to the structure of benzotriazole, 2-mercaptobenzimidazole, 1
-Hydrobenzimidazole, benzimidazole, guanine, adenine, etc. These compounds are also found to form compounds with copper and nitrogen having an unshared electron pair, but lead is not as strong as benzotriazole because its film is not as strong. Is slightly eluted. In addition, in addition to the above-mentioned similar compound, 2-mercaptobenzothiazole (C ₇ H ₅
NS ₂ ) and salts thereof, which are known to react with copper to form a strong protective film like benzotriazole, and are very effective in preventing lead elution according to the present purpose. Confirmed by experiment. However, this substance is not practical because it is poorly soluble in water, is susceptible to oxidizing acids such as chromic acid and sulfuric acid, and is selected as a target substance as a carcinogen for humans. [0014] The bond between benzotriazole and copper is fairly strong, and empirically, by packaging copper products in rust-proof paper impregnated with about 2% benzotriazole, it is useful for long-term copper rust prevention. Are known. It has also been found that contact resistance does not change over a long period of time when electrical components made of copper alloy are treated with benzotriazole vapor. The inventors have inferred from these facts that a liquid containing benzotriazole, whether acidic, alkaline or neutral, forms a film by reaction with copper. In fact, it has been found that, when various aqueous solutions containing benzotriazole containing different liquid properties are prepared and immersion-treated with a lead-containing copper alloy, there is a large difference in the degree of elution of lead as compared with those not containing. For corrosion protection of metals, there has been a method of forming a film having excellent corrosion resistance by chromate treatment, which is widely used as a post-treatment of zinc or cadmium plating or as a corrosion treatment of aluminum and its alloy materials. . This chromate treatment is considered to be somewhat effective for brass, although the formation of a protective film on copper and other alloys is weak. Then, the lead-containing copper alloy was subjected to a chromate treatment to examine whether or not lead was eluted. The amount of lead eluted was considerably smaller than that of the untreated lead alloy. When benzotriazole is added to this chromate solution, elution of lead is almost eliminated. That is, it is evidence that a chemical conversion coating composed of copper and benzotriazole or a mixed coating of benzotriazole and chromium is much stronger than a chromium coating in preventing lead elution. Next, three compounds, guanine, benzimidazole and adenine, having a structure similar to that of benzotriazole were examined. Each of them was found to have an effect of preventing lead elution, but all were as effective as benzotriazole. I couldn't. When 2-mercaptobenzothiazole and a salt thereof were added to a chromate solution containing chromic acid and examined, a considerable effect was observed, but it was found that the solution turned brown and clearly decomposed. Was. The same change was confirmed in the combination and mixing with a commercially available chromating agent for zinc. This is the same tendency for benzotriazole, and mixing with high concentration of chromic anhydride or pumping in of chromic acid from the previous step hastens the oxidative decomposition, so that it is necessary to minimize it. According to experiments, it is desirable that the control standard be approximately 10 g / l or less. As described above, even if the solution containing benzotriazole is acidic, alkaline or even neutral, it forms a chemical conversion film with copper, which is effective in preventing the elution of lead. The effect can be seen even when the acid solution is added and used in combination. Regarding the acidity, the effect of chromic acid is that benzotriazole is decomposed depending on its concentration, but the effect of preventing lead elution of the film is remarkably recognized. . Phosphoric acid and an acid having a phosphoric acid group as the acidic liquid,
Sulfuric acid and acid having a sulfuric acid group, hydrochloric acid and acid having a hydrochloric acid group, glycolic acid and organic acids (for example, oxalic acid, citric acid,
Malic acid) is also effective. As the alkaline liquid, strong basic acids, phosphates, carbonates, silicates and the like are also effective. As the neutral liquid, various neutral salts, benzotriazole solvents and combinations thereof are also conceivable. Next, phosphoric acid, unlike sulfuric acid and hydrochloric acid, has a low risk of attacking metals and is therefore relatively safe even at a high concentration. According to reconnaissance tests, the concentration is 10 g / l
Is less effective, and a solution containing benzotriazole at a concentration of 50 g / l or more has a great effect in preventing the elution of lead.
This leads to much less lead elution than chromic acid. In the case of an acid solution, the concentration is limited by itself in consideration of the acid corrosion of the material.
Even at a concentration of about 150 g / l, there is little effect on the material. When the temperature is increased, the reaction becomes faster and stronger, but at room temperature, 5 minutes is sufficient. When chromic acid is used, chromium is not eluted at all, and stricter regulations may be considered in the future from the viewpoints of pollution and health and safety. However, phosphoric acid has few such problems. In the case of alkaline, a film of benzotriazole is formed, but the amount of lead eluted is large because it is weaker than acidic. In the case of neutral, a slightly better result was obtained than in the case of alkaline, but the amount of lead eluted was also larger than in the case of acid. It is considered that the reason for this is that in the case of an acid, the metal surface is activated by the acid. Next, the present invention will be described specifically with reference to examples, but the present invention is not limited to these examples. Example 1 The following lead-containing copper alloy was used in the example. JIS H3250 (C3604) Free-cutting brass round bar cut product (Cu: 57.0 to 61.0, Pb: 1.8 to
3.7, Fe: 0.5 or less, Sn: 0.7 or less, Zn:
(Remainder, unit%) As the treatment liquid, an aqueous solution having the following composition was used. A: sodium dichromate 30 g / l, sulfuric acid 6 g / l, benzotriazole 5 g / l B: sulfuric acid 6 g / l, benzotriazole 5 g / l C: phosphoric acid 50 g / l, benzotriazole 5 g / l D: phosphoric acid 50 g / l E: phosphoric acid 100 g / l, benzotriazole 10 g / l F: sodium hydroxide 2.5 g / l, benzotriazole 5 g / l G: ethyl alcohol 15 g / l, benzotriazole 5 g / l Test sample material: Free-cutting brass C3604BD, faucet fittings; approx. 33
g, surface area: 44.0 cm ² Lead elution prevention test-1 The sample was immersed in an alkaline degreasing agent aqueous solution (50 g / l) containing caustic soda and a surfactant at 50 ° C. for 10 minutes, and was placed on the surface of the sample. Remove the attached fats and oils and clean the sample surface. This is added to the above treatment liquids A to G at 50 ° C.
For 2 minutes and then washed with water and dried. Lead dissolution test-1 A sample which was immersed in the treatment solution of A to G was subjected to a lead dissolution test to determine the effect. For comparison, an untreated sample (only the degreasing treatment) was also subjected to lead elution. In order to elute lead in a short time,
As an acceleration test, a 0.01% acetic acid aqueous solution was used. The elution conditions are as follows. 0.01% acetic acid aqueous solution: 20
0 ml, temperature: room temperature, immersion time: 5 minutes Lead elution test result-1 A sample treated to prevent lead elution with the above-mentioned treatment liquids A to G was used.
It was immersed in 200 ml of a 0.01% acetic acid aqueous solution at room temperature for 5 minutes, and the amount of eluted lead was measured. The results of the treatment with the treatment liquids A to G show that the amount of lead eluted is greatly reduced as compared with the untreated one. Comparing these results, A has a considerable effect, but does not reach DE. The amount of lead eluted is related to the concentration of phosphoric acid and benzotriazole. According to this example, the concentration of phosphoric acid is 50 g / l or more and benzotriazole is 10 g.
It seems that a processing solution of about / l is practical. Lead dissolution test-2 Since most of the water supply fittings are actually used for general tap water, a lead dissolution test was performed using city tap water. Lead Elution Test Result-2 A sample treated to prevent lead elution with the above treatment liquids A to G was immersed in 200 ml of Nagoya city tap water to measure the amount of lead eluted. Compared to the 0.01% acetic acid aqueous solution, the elution amount of lead was extremely small, and no lead was detected from the samples treated for A to E. Example 2 The treatment solution containing benzotriazole had a considerable effect on preventing the elution of lead. Next, about three kinds of the above-mentioned compounds having similar chemical structures to benzotriazole, an acid aqueous solution is used as a treatment liquid, and comparison is made with Example-1. The compound used was guanine,
They are three compounds of benzimidazole and adenine. These structures are similar to benzotriazole, but are all diazole compounds. Example 3 The same test sample as in Example 1 was used. As the treatment liquid, an aqueous solution having the following composition was used. H: sulfuric acid 6 g / l, guanine 10 g / l I: sulfuric acid 6 g / l, benzimidazole 10 g / l J: sulfuric acid 6 g / l, adenine 10 g / l This was performed in the same manner as in Prevention treatment-1.
This was immersed in the above treatment liquids H to J at 50 ° C. for 2 minutes, washed with water and dried. Lead Elution Test-3 A sample treated to prevent lead elution with the treatment solutions of H to J was used in Example-1.
In the same manner as in the above, it was immersed in a 0.01% acetic acid aqueous solution, and the amount of lead eluted was measured. Lead elution test result-3 Compared with the benzotriazole of Example 1, the amount of lead eluted was considerably larger, but was reduced to about 1/10 of that of the untreated sample. This seems to be due to the fact that the film strength with copper is weaker than that of benzotriazole or the film is dissolved in water. That is, it is presumed that a strong film like triazole is hardly formed with diazole. However, when this is immersed in tap water, the amount eluted in tap water is estimated to be about 20 to 25 ppb under the same conditions, as estimated from the elution test result-2 described above.

Claims (1)

Claims 1. To remove metal film made of lead-containing copper alloy (mostly used for water supply equipment of a water supply device) as a cleaning treatment to remove an oil film or the like on the surface, a caustic alkaline degreasing agent is used. A method for preventing lead elution by immersing in a solution containing an aromatic heterocyclic compound such as benzotriazole, various benzotriazole compounds, and benzothiazole and its salts after cleaning the surface by immersion or electrolytic treatment. 2. An aromatic heterocyclic compound such as benzotriazole, various compounds such as benzotriazole, and various compounds such as benzothiazole and a salt thereof, on the product after nickel and chromium plating according to claim 1. Of leaching of lead by immersion treatment in acidic, alkaline or neutral solution containing aromatic heterocyclic compound such as