JPH0379438B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for forming a phosphate chemical coating such as zinc phosphate on the surface of a copper-based material. A method of forming a film is provided.

[Conventional technology]

Conventional chemical conversion treatments for steel materials include phosphate treatment and chromate treatment, which are frequently used for rust prevention or as a base treatment for painting. These phosphate treatments have been extensively studied both theoretically and industrially, and are almost technically established. On the other hand, as for chemical conversion treatment of copper-based materials, since copper itself is a chemically safe metal, there is no particularly effective method. The cuprous oxide method, which forms a cuprous oxide film on the surface of copper-based materials by treating for 10 minutes, and the cuprous oxide method, which forms a cuprous oxide film on the surface of copper-based materials, and the 3-day treatment at 100℃ or higher with an aqueous solution containing sodium hydroxide and potassium persulfate.
Copper oxide treatment and chromic acid treatment of black copper oxide method, which forms a cupric oxide film by treating for ~10 minutes, are known. There is also a method of galvanizing a copper-based material and then subjecting it to phosphate treatment.

[Problem that the invention seeks to solve]

Conventional chemical conversion treatment methods for copper-based materials have poor reactivity of the copper oxide film formed compared to chemical conversion treatment methods for steel materials, and are therefore unsuitable for pre-painting treatment. Furthermore, the processing method is cumbersome, so it is only used in extremely limited fields. This is due to the problem that copper-based materials cannot be treated with phosphates using the same method used to treat steel materials with phosphates, for reasons such as the ionization tendency of copper being smaller than that of hydrogen. be. Therefore, as a result of intensive research into the reactions that occur on the copper surface, the present inventor discovered a method of forming a phosphate-based chemical conversion film on the copper surface. The present invention provides a method for forming a chemical conversion film on the surface of a material.

[Means for solving problems]

In the method of forming a chemical conversion film on the surface of a copper-based material of the present invention, first, in a chemical conversion treatment bath 1, at least 2 g of phosphate ions are added, and Zn, Mn, Fe, Ca,
Contains at least 2g of metal ions consisting of at least one type of Mg, contains at least 1g of halogen ions excluding fluorine ions, and has a temperature of 20℃
Prepare a chemical conversion bath at ~40°C and a hydrogen ion concentration of PH0.5 to PH3.5.

By bringing this chemical conversion treatment bath into contact with a copper-based material, a film consisting of a phosphate and the copper halide is formed on the surface of the copper-based material.

[Detailed explanation of the structure of the invention]

The chemical conversion film forming method of the present invention is applied to copper-based materials made of copper and copper metal.

The chemical conversion treatment bath used in the chemical conversion film forming method of the present invention contains phosphate ions, metal ions, halogen ions, and an oxidizing agent. As in the case of chemical conversion treatment of steel surfaces, the metal ions contained in this chemical conversion treatment bath exist as dihydrogen phosphate compounds such as zinc, manganese, iron, calcium, and magnesium, which are stable in aqueous solution, and are expressed by the following formula: Metal ions whose solubility decreases can be used by the dehydrogenation reaction shown in (1).

xM(H ₂ PO ₄ )y→Mx(PO ₄ )y+2yH ⁺ ...(1) As the halogen ion, a cuprous salt of the halogen with a sufficiently small solubility product can be used, and chlorine, Bromine and iodine can be used.
Fluorine is difficult to use because its electronegativity is larger than that of oxygen, and its behavior in aqueous solutions is clearly different from that of other halogens, which have smaller electronegativity than oxygen.

Examples of oxidizing agents include hydrogen peroxide, nitrite ions, etc., which promote the dissolution of copper in an acidic solution and themselves perform a reduction reaction, as shown in formula (4) or (5).
Dichromate ion etc. can be used.

The components of the chemical conversion treatment bath used in the present invention are a main agent containing the above-mentioned metal ions, halogen ions, and phosphate ions (hereinafter referred to as the main agent component), and an auxiliary agent containing an oxidizing agent. The treatment bath is prepared by dissolving these main agents and auxiliary agents in water.

A chemical conversion film is formed on the surface of the copper-based material when the copper-based material comes into contact with the chemical conversion treatment bath formulated as described above, and the process will be explained step by step.

On the surface of the copper-based material that came into contact with the chemical conversion treatment bath,
An anode reaction (oxidation reaction such as metal dissolution) and a cathode reaction (reduction reaction) occur simultaneously.
First, the dissolution reaction of copper occurs, and the anodic reactions of the following formulas (2) and (3) and the cathode reactions by the oxidizing agent of the following formulas (4) and (5) occur, and the following formulas (4) or (5) occur. It is thought that copper dissolves in the chemical conversion treatment bath because the electrode potential of is higher than the electrode potential of equations (2) and (3).

Cu→Cu ⁺ +e ...(2) Cu ⁺ →Cu ²⁺ +e ...(3) H ₂ O ₂ +2H ⁺ +2e→2H ₂ O ...(4) NO ₂ ^- +2H ⁺ +e→H ₂ O+NO↑ ... …(5) In other words, the oxidizing agent in the acidic solution of the chemical conversion bath
Since the reactions in equations (4) and (5) consume electrons e, the reactions in equations (2) and (3) proceed, and copper dissolves. Next, regarding the film formation reaction, taking as an example the case where zinc is used as the metal ion and chlorine is used as the halogen ion, the film formation reaction occurs very close to the surface of the copper-based material.
The anodic reaction of equation (6) and the cathodic reaction of equation (7) occur, producing colloidal particles of zinc phosphate and cuprous chloride with a small solubility product, which coagulate on the surface of the copper-based material and form a film. It is thought that it forms.

3Zn ₂ ⁺ +2H ₂ PO ₄ ^- →Zn ₃ (PO ₄ ) ₂ ↓＋4H ⁺ ...(6) Cu ₂ ⁺ +Cl ^- +e→CuCl↓ ...(7) In the above chemical conversion film forming reaction, If the temperature is high, the dissociation reaction of phosphoric acid in formula (8) and the reactions in formulas (6) and (9) may proceed, generating hydrogen gas and producing sludge, which is not preferable.

H ₃ PO ₄ →H ⁺ +H ₂ PO ₄ ^- ...(8) 2H ⁺ +2e→H ₂ ↑ ...(9) Therefore, the temperature of the chemical conversion bath in the method of forming a chemical conversion film on the surface of a copper-based material of the present invention. The temperature is preferably 40°C or lower, and it is particularly desirable to maintain the temperature at 20 to 30°C.

In order for the film-forming reaction of these phosphates and cuprous halides to be adopted in a general production line, the reaction rate must be sufficiently high. In chemical reactions at electrodes, the factors that influence the reaction rate are the concentration of substances involved in the reaction, temperature, pressure, and electrode potential. Here, the higher the temperature, the higher the reaction rate, but in order to suppress the generation of hydrogen shown in equation (9), the lower the temperature is, the better. In the case of the immersion method, the pressure is usually constant at atmospheric pressure, but in the case of the spray method, it is better to have a higher pressure to some extent. Regarding the concentration of reactants, in the dissolution reaction, it is better to have a higher concentration of both the oxidizing agent such as hydrogen peroxide and hydrogen ions, and in the film forming reaction, it is necessary that the concentration of hydrogen ions is below a certain level. Regarding the electrode potential, it is necessary that the reaction potential of the oxidizing agent (cathode reaction potential) is larger (higher) than the dissolution reaction potential of copper (anode potential).

From the above, in order for the reaction to form a phosphate film on the surface of a copper-based material to proceed at a constant speed as an electrochemical reaction at 20°C to 30°C, (a) a material that dissolves at a sufficient rate at room temperature; It is necessary to create a combination of treatment baths, and (b) to maintain the concentration of the oxidizing agent and hydrogen ion concentration of the reaction-participating substances in a range that allows the formation of a phosphate film at room temperature.

In the chemical conversion film forming method of the present invention, the chemical conversion treatment bath 1
It is desirable that the chemical conversion treatment bath contains at least 2 g of phosphate ions, at least 2 g of metal ions such as zinc, and at least 1 g of halogen ions such as chlorine. ~PH3.5, the concentration of the oxidizing agent is 550 to 1000 mV in redox potential (silver chloride electrode potential),
Satisfies the conditions (a) and (b) above. In the method of the present invention, the temperature of the treatment bath is low and there is no temperature aid in dissolving the copper, so a high hydrogen ion concentration is required to drive the reaction. Therefore, the PH value of the treatment bath according to the present invention is in the range of PH0.5 to PH3.5.

In order to proceed with the copper dissolution reaction at the above hydrogen ion concentration (PH value), an oxidizing agent of a certain concentration or higher is required. In other words, the redox potential is the silver chloride electrode potential.
An oxidant concentration in the range of 550-1000 mV is required;
If it is lower than this range, film formation will be delayed or will not be formed at all. When it is higher than the above range, the excess oxidizing agent hardly contributes to the reaction, and the above range is sufficient.

In the chemical conversion film forming method of the present invention, as the film forming reaction progresses, the concentrations of the main component and the oxidizing agent decrease in the treatment bath, and as a result, the PH value and redox potential of the treatment bath change. Here, the change in PH is correlated with the change in the concentration of the main ingredient. In other words, as the main ingredient decreases, the PH of the treatment bath increases. Therefore, stable chemical conversion treatment can be performed by periodically or continuously measuring the PH of the treatment bath and replenishing the main ingredient when it reaches a certain value or higher.

The redox potential changes depending on the concentration of the oxidizing agent, as shown in FIG. 10, for example. Figure 10 shows the oxidizing agent concentration (horizontal axis) and the redox potential at the silver chloride electrode (vertical axis) in 180 processing baths containing 67 g of phosphate ions, 80 g of zinc ions, and 63 g of chloride ions. FIG. Here, 35% hydrogen peroxide aqueous solution was used as the oxidizing agent,
The temperature of the treatment bath is 20-30°C, and the pH is 1.4. 1st
It is clear from Figure 0 that when the concentration of the 35% hydrogen peroxide aqueous solution is in the range of 5 to 18 m/, the redox potential increases almost proportionally as the temperature increases.
In the method for forming a chemical conversion film of the present invention, the concentration range in which a film can be formed under the above conditions is part A in FIG. Therefore, the concentration can be determined by measuring the redox potential, and when the redox potential falls below a certain value (for example, 580 mV), it can be stabilized by replenishing an auxiliary agent containing 35% hydrogen peroxide. A chemical conversion treatment can be applied.

Both the PH value and the redox potential can be measured electrically, which is very simple and does not require complicated chemical analysis. Therefore, it becomes possible to automate the concentration management of the processing bath.

〔Effect of the invention〕

The chemical conversion film forming method of the present invention enables direct phosphate treatment of the surface of copper-based materials, which was previously considered impossible. Some halogenated 1st
A copper conversion coating is formed. It is clear that the chemical conversion coating is strong because the alternating current breakdown voltage is 200 V or more in the JIS-C-2110 short-time dielectric breakdown test method for solid insulating materials. Due to this feature, the method for forming a chemical conversion film of the present invention can be applied to, for example, copper enamelled electric wires.

Copper enamel electric wires have conventionally been manufactured by forming an organic coating made of synthetic resin directly on the copper surface, since it has not been possible to obtain a strong chemical conversion coating on the copper surface. However, the adhesion between the organic film and the copper was not good, and the film was frequently damaged when winding the wire into a coil. Therefore, by applying the chemical conversion film forming method of the present invention as a base treatment for copper enameled electric wires, great effects can be expected in improving the adhesion of the organic film, preventing damage to the organic film, and improving insulation resistance. In addition, similar to the effect of phosphate treatment of steel materials, it is also expected to be effective as a lubricating film during cold forging press processing.

In the chemical conversion film forming method of the present invention, the treatment bath
By measuring the PH value and redox potential, treatment baths can be easily managed. Further, the above measurement is a simple electrical measurement, and automatic management of the processing bath is also possible. Furthermore, since the treatment bath is carried out at a low temperature of 20 to 30°C, there is little self-decomposition reaction of the main ingredient and the oxidizing agent. Therefore, there is little loss of the main component and the oxidizing agent, allowing efficient use, and hardly any sludge is produced. Furthermore, since there is no need for heating, it is also advantageous from the point of view of energy saving.

〔Example〕

Examples will be explained below.

(First example) Chlorine ion 15g/, phosphate ion 40g/, zinc ion 25g/ and 35% hydrogen peroxide solution 20g/
Pour 800 ml of the treatment bath containing
A ring-shaped copper part for an automobile starter having a height of 20.5 mm was immersed in the above treatment bath at 25° C. for 3 minutes. Thereafter, it was washed with water and dried to form a chemical conversion film on the surface of the treated material.

When the obtained film was analyzed by fluorescent X-ray analysis, phosphorus, zinc, copper, chlorine, and impurity elements were qualitatively determined. This result was the same no matter where the film was taken, that is, the film was almost uniform. Figure 1 shows an electron micrograph of the film (×
1500). From the photograph, it is observed that the surface is covered with fine crystals. The size of this single crystal is approximately 1/3 to 1/5 the size of the crystal of the conventional zinc phosphate chemical conversion coating formed on the iron surface, and it can be seen that it is quite dense.

From the above analysis results, the obtained chemical conversion coating is considered to be a safe crystalline zinc phosphate chemical conversion coating.

(Second Example) FIG. 3 shows a schematic diagram of a treatment tank used in the chemical conversion film forming method of the present invention. Zinc ion 80g/,
Phosphate ion 67g/, chloride ion 63g/, and
Treatment bath containing 20g/35% hydrogen peroxide solution 0.18
A solenoid valve 21 is installed in the processing tank 1 that holds ^m3 .
A main agent supply pipe 22 was connected to the main agent tank 2 via the main agent tank 2, and an auxiliary agent supply pipe 25 was connected to the auxiliary agent tank 3 via the solenoid valve 24. Then, these solenoid valves 21 and 24 were immersed in a treatment bath.
A PH meter 23 and an oxidation-reduction potentiometer 33 are connected by an electric circuit (not shown) that opens and closes, and when the PH reaches 1.4 or more, the valve 21 opens and the main agent is supplied from the main agent tank 2 into the processing tank 1, and the PH reaches 1.4. If it becomes below, valve 2
1 was closed. On the other hand, the redox potential meter (silver chloride electrode) 33 is 600 mV (silver chloride electrode potential)
When the temperature was below 600 mV (silver chloride electrode potential), the solenoid valve 24 was opened, the auxiliary agent was supplied from the auxiliary agent tank 3 into the processing tank 1, and the solenoid valve 24 was closed when the oxidation-reduction potentiometer 33 reached 600 mV (silver chloride electrode potential) or higher.
The main ingredient for replenishment is zinc ion 320g/,
An acidic aqueous solution containing 280 g of phosphate ions and 200 g of chloride ions was used and was adjusted to be supplied from the main agent supply pipe 22 at a rate of 50 ml/min. A 35% aqueous hydrogen peroxide solution was used as the auxiliary agent for replenishment, and was adjusted to be supplied from the auxiliary agent supply pipe 25 at a rate of 50 ml/min. The material to be processed W is put into a barrel 4, and the barrel 4 is configured to rotate at a speed of 1 to 5 times per minute.

The material to be treated has an outer diameter of 40 mm and an inner diameter of 30 mm as shown in Figure 7.
A ring-shaped copper part for an automobile starter having a diameter of 20.5 mm and a height of 20.5 mm was used and subjected to chemical conversion treatment by the chemical conversion film forming method of the present invention using the apparatus schematically shown in FIG. In other words, in Fig. 4, 100 pieces per barrel are degreased with an alkaline aqueous solution at 55°C for 2 minutes in a degreasing tank A, and then degreased for 45 minutes in a hot water washing tank B.
Washed for 0.5 minutes with hot water at ℃, then washed with water at room temperature (20-30℃) for 0.5 minutes in cleaning tank C, then etched with acidic etching solution for 0.5 minutes at room temperature in etching layer D, and then washed. with room temperature water in a tank
It was washed for 0.5 minutes, then treated at 20 to 30°C for 3 minutes in the chemical conversion treatment tank shown in Figure 3 explained above, and then washed with room temperature water for 0.5 minutes in the washing tank.
Next, wash for 0.5 minutes with hot water at 70-80℃ in the washing tank.
Subsequently, it was dried in a drying oven at a temperature of 80 to 90°C for 2 minutes to form a chemical conversion film on the surface of the treated material.

The film formed by the chemical conversion film forming method of the present invention in the second embodiment is 5 to 10 g/m ² on the surface of the copper component.
The amount and film thickness were 10μ. Furthermore, chemical analysis of the ingredients was conducted to clarify the composition of the film, and it was found that the film was composed of 19% by weight of zinc, 19% by weight of chlorine, 33% by weight of copper, 10% by weight of phosphate ions, and 19% by weight of other substances. This ratio was the same no matter where the film was taken, ie, the film was almost uniform. FIG. 2 shows an electron micrograph of the film. Note that the magnification is 1500 times. In this photo, crystals like those in Figure 1 cannot be seen. Further, when this film was subjected to X-ray diffraction analysis, no large peak identifying zinc phosphate was observed. However, as mentioned above, zinc and phosphate ions were detected from the results of fluorescent X-ray and spectrophotometric analysis. In other words, it can be considered that the zinc phosphate in this film is in an amorphous state.

The following conclusions can be drawn from the above. That is,
The coating is considered to be a stable amorphous zinc phosphate chemical conversion coating consisting of 20% by weight of zinc phosphate, 52% by weight of cuprous chloride, and 28% by weight of water of crystallization.

In addition, in the chemical conversion treatment tank shown in Figure 4, 1200 pieces were processed per hour, a total of about 30,000 pieces, and all treatment bath management was done automatically. No abnormality was observed at all.

For reference, the memory of automatic control of the processing bath is shown in FIGS. 5 and 6. The PH adjustment system uses the BHC-76-6045 type PH electrode and HBR manufactured by Denki Kagaku Keiki Co., Ltd.
-92 type control recorder was used. Figure 5 schematically shows a part of the chart recorded by the PH recorder.
In FIG. 5, the horizontal axis shows time and the vertical axis shows PH value. The state in which the main agent is replenished when the pH is above 1.4 and the main agent is stopped when the pH falls below 1.4 is shown in Figure 5 A, and the material to be treated is not put into the processing bath. The condition is shown in Figure 5 (B), but when comparing parts (A) and (B) in Figure 5, there is almost no change in PH. This is clearly an effect of PH control.

The redox potential adjustment system is manufactured by Denki Kagaku Keiki Co., Ltd.
BHC-76-6026 type metal electrode (silver chloride electrode) and
An HBR-94 type control recorder was used. Silver chloride electrodes are commonly used, and conversion to hydrogen standard electrode potential is performed using equation (11).

E(NHE)=E(AgCl)+206−0.7(t−2.5)
...(11) E(NHE)...Hydrogen standard electrode potential (mV) E(AgCl)...Silver chloride electrode potential (mV) t...Temperature of processing bath (℃) In Figure 6, the horizontal axis is time , the vertical axis shows the redox potential (silver chloride electrode). In the figure, state C is a state in which the object to be processed is placed in the processing bath, and state D is a state in which no object is placed in the processing bath.
In both conditions C and D, the supply of the auxiliary agent is automatically controlled. In other words, when the redox potential is less than 600 mV (silver chloride electrode potential), supplement the auxiliary agent and raise the redox potential.
At 600 mV (silver chloride electrode potential) or higher, the supply of the auxiliary agent was stopped. As a result, the oxidation-reduction potential of the treatment bath was controlled within the range of 600±10 mV (silver chloride electrode potential).

[Test example]

In order to examine the effect of the film formed by the chemical conversion film forming method of the present invention, a ring-shaped copper part similar to that of the second embodiment was used, and a fourth
The chemical conversion treatment of the present invention is carried out in units 1 to 1 of the apparatus shown in the figure, and the drying step 2 is omitted, and a treatment bath mainly containing sodium stearate (Bondaryube 235 manufactured by Nippon Parkerizing Co., Ltd.) is applied in a metal bath. )
Metal soap treatment was performed at 80°C for 3 minutes using Approximately 30,000 ring-shaped copper parts of this example which had been subjected to the metal stamping process were subjected to cold forging press processing to produce the copper parts shown in FIG. 8. During this press working, the load applied to the press machine was measured, and the results are shown in FIG.

As a conventional example, a ring-shaped copper part shown in FIG. 7 having the same shape as the example was used. First, hot-dip galvanizing was applied, and then 5 g of zinc ions and 20 g of phosphate ions were applied.
g/, nitrate ion 10g/, fluoride ion 1.0
g/, treated at 80℃ for 1 minute in a conventional chemical conversion bath containing 0.5g/ of nickel ions, and then heated to 80-90℃.
A zinc phosphate chemical conversion film was formed on the surface of the ring-shaped copper part by drying it with hot air for 2 minutes. The chemical conversion-treated copper parts of this conventional example were subjected to a metal sieving process under the same conditions as in the second embodiment, and pressed in the same manner to produce about 30,000 parts as shown in FIG. During this press working, the load applied to the press machine was measured, and the results are shown in FIG.

As a comparative example, a ring-shaped copper part on which a chemical conversion film was formed by the chemical conversion film forming method of the present invention was pressed in the same manner as in the example and the conventional example, in the same manner as in the second example except that the metal stamping treatment was not performed. Processing was carried out and the load applied to the press machine was measured.
The results are shown in Figure 9.

The arrows shown in FIG. 9 indicate the width of variation in the load applied to the press machine when approximately 30,000 pieces were pressed. It is clear from FIG. 9 that in the example in which a copper part having a chemical conversion film was subjected to a metal soap treatment by the chemical conversion film forming method of the present invention, the conventional method was zinc plated, then treated with zinc phosphate, and then subjected to a metal soap treatment. Compared to the conventional example, the load on the press machine is only slightly increased, which is sufficient for practical use. It should be noted that if only the chemical conversion film formed by the chemical conversion film forming method of the present invention as a comparative example is applied, a large load is applied to the press machine, so it is desirable to perform a metal soap treatment.

As a result of the above, in the cold forging press working of copper-based materials, conventionally three steps of surface treatment were required, but by using the chemical conversion film forming method of the present invention, only two steps of surface treatment are required. , it becomes possible to significantly shorten the process.

[Brief explanation of drawings]

FIG. 1 is an electron micrograph showing the crystal structure of a chemical conversion film formed in an example of the present invention, FIG. 2 is an electron micrograph showing the crystal structure of another chemical conversion film formed in an example of the present invention, Fig. 3 is a schematic diagram of the chemical conversion treatment equipment used in the examples of the present invention, and Fig. 4 shows the cleaning,
A schematic diagram of a continuous processing system including a metal soap treatment and a chemical conversion treatment apparatus shown in FIG. 3, FIG. 5 is a part of a PH recorder chart of a processing liquid in an embodiment of the present invention, and FIG. 6 is a diagram of an embodiment of the present invention. 7 is a vertical cross-sectional view of the copper parts used in the example of the test example, the conventional example, and the comparative example, and FIG. 8 is the example of the test example, the conventional example. A vertical cross-sectional view of the copper parts after press working used in the examples and comparative examples, and Figure 9 shows the load applied to the machine during press working of the copper parts processed in the example of the test example, the conventional example, and the comparative example. Figure 10 is a diagram showing the relationship between 35% hydrogen peroxide concentration and redox potential (silver chloride electrode). 1... Processing tank, 2... Main agent tank, 3... Auxiliary agent tank, 4... Barrel, 23... PH meter, 33...
Oxidation-reduction potentiometer, W...Product to be treated.

Claims (1)

[Claims] 1. The chemical conversion bath 1 contains at least 2 g of phosphate ions, at least 2 g of metal ions consisting of at least one of Zn, Mn, Fe, Ca, and Mg, and contains no halogen ions except fluorine ions. Contains at least 1g, and the temperature is between 20℃ and 40℃ and the hydrogen ion concentration is PH.
Copper, characterized in that it is a chemical conversion treatment bath adjusted to pH 0.5 to 3.5, and the chemical conversion treatment bath is brought into contact with a copper-based material to form a film consisting of phosphate and copper halide on the surface of the copper-based material. A method of forming a chemical conversion film on the surface of system materials. 2. The method of forming a chemical conversion film on the surface of a copper-based material according to claim 1, wherein the oxidation-reduction potential of the chemical conversion treatment bath is in the range of 550 mV to 100 mV as a silver chloride electrode potential.