JPH0718021B2 - Method for controlling electric conductivity of phosphate chemical conversion treatment liquid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a phosphate chemical conversion treatment liquid used for forming a phosphate chemical conversion coating film such as zinc phosphate on the surface of a steel material. The present invention relates to a method of controlling electric conductivity.

[Conventional technology]

As a method relating to the phosphate chemical conversion treatment, for example, Japanese Patent Laid-Open No.
There is one disclosed in JP-A-60-43491.

This method uses a zinc phosphate chemical conversion treatment solution containing 5 g / l of Zn ²⁺ , 15 g / l of PO ₄ ³⁻ and 4.5 g / l of NO ₃ ⁻ at room temperature (0 ° C to 40 ° C).
Less than)).

On the other hand, in this method, the pH and redox potential (OR
Corresponding to the fluctuation of P), the main agent, the oxidation promoter (hereinafter referred to as an oxidizer), and the regulator (neutralizer) are supplied to the chemical conversion treatment liquid. That is, when the pH of the treatment liquid becomes higher than a predetermined value, the main agent (an acidic solution containing Zn ²⁺ , H ₃ PO ₄ , NO ₃ ^−, etc.) is supplied to the chemical conversion treatment liquid, and the pH value is kept at a predetermined value. When it becomes lower than the value (predetermined value (pH) ≧ predetermined value), a regulator (neutralizing agent) containing alkali is supplied to the chemical conversion treatment liquid,
Keep the pH of the chemical conversion treatment solution within a certain range. Further, the control of ORP, once ORP of the chemical conversion treatment liquid falls below a predetermined value, oxidizing agents ^- (free of NO ₂ and the like of the oxidizing agent) is supplied to the chemical conversion treatment solution, when a certain value or more, oxidation Stop the supply of agents,
It keeps the ORP of the chemical conversion treatment liquid within a certain range.

By controlling the above pH and ORP control within a certain range,
It causes an electrochemical general corrosion reaction on the surface of steel and forms a chemical conversion film on the surface.

[Problems to be solved by the invention]

In the above-mentioned JP-A-60-43491, the supply of the main agent to the chemical conversion treatment liquid is carried out by changing the pH as described above.

However, if the supply of the main agent is controlled only by the fluctuation of pH, the temperature change of the treatment liquid is large, the carry-in from the pre-treatment liquid to the treatment liquid, the carry-out of the treatment liquid is small, and the operating rate of the treatment equipment is lowered. , Zn ²⁺ , H ₂ in chemical conversion treatment liquid
PO ₄ ^-, NO ₃ ^- concentration of the reaction-participating material (main agent component) increases such, would cause the generation of Suraddji such Zn ₃ (PO _{4) 2} in the chemical conversion treatment liquid.

When sludge is generated in this manner, the formation of the phosphate conversion coating on the surface of the steel material tends to be insufficient.

[Means for solving problems]

In the present invention, as a result of earnest research in view of the above-mentioned points, the concentration of so-called main component of phosphate ion, oxo acid ion, and metal ion for forming a chemical conversion film in the chemical conversion treatment liquid is proportional to the electric conductivity in the chemical conversion treatment liquid. Paying attention to that, when the electrical conductivity of the chemical conversion treatment liquid is measured and the electrical conductivity exceeds a certain value,
The electrical conductivity of the chemical conversion treatment liquid is stopped by stopping the supply of the main agent, which is an acidic solution containing phosphate ions, oxoacid ions, and chemical conversion film forming metals, which regulates the upper limit of pH, to the chemical conversion treatment liquid. Is to be kept below a certain value.

In the present invention, the metal ion contained in the chemical conversion treatment liquid is at least one selected from the group consisting of zinc, manganese, calcium and magnesium. Further, nickel ions and cobalt ions may coexist with these.

Further, in the present invention, nitrate ions or chlorate ions are used as oxo acid ions, and these oxo acid ions play a role of assisting film formation by the metal ions. The nitrate ion is desirable.

In the present invention, the temperature of the chemical conversion treatment liquid is lower than 40 ° C, preferably 10 ° C to 35 ° C.

In the present invention, the pH of the chemical conversion treatment liquid is preferably 2.0 to 4.0, preferably pH 2.6 to 3.6. The pH is controlled by controlling the replenishment of the alkali-containing solution into the chemical conversion treatment solution. That is, when the pH of the chemical conversion treatment liquid reaches a certain value or less, an alkali, for example, caustic soda, caustic potash, sodium carbonate, etc., is supplied to the chemical conversion treatment solution containing a salt whose aqueous solution shows alkalinity, and the pH is more than a certain value. When the temperature reaches, the main agent containing phosphate ions, oxo acid ions, and metal ions is supplied into the chemical conversion treatment liquid.

In the present invention, the oxidation-reduction potential of the chemical conversion treatment liquid is 300 mV ~ 7
00mV (hydrogen standard electrode potential) is desirable. When the redox potential of the chemical conversion treatment liquid reaches a certain value or less, a solution containing an active oxidizing agent such as nitrite ion or hydrogen peroxide is supplied into the chemical conversion treatment liquid. Of course, when it reaches a certain value or more, the supply is stopped.

In the present invention, the value of the electric conductivity to be controlled in the chemical conversion treatment liquid varies depending on the treatment method, that is, the spray method, the immersion method, or the method of conveying the treated portion, that is, the hanger transfer method and the chain conveyor movement method. When the electrical conductivity of the chemical conversion treatment liquid exceeds the upper limit of the predetermined range, the concentration of the so-called main component of phosphate ions, oxoacid ions, and chemical conversion film-forming metal ions in the chemical conversion treatment liquid increases, and Even if the pH exceeds the upper limit value of the predetermined range, the main agent for returning the pH to the predetermined range is not supplied to the chemical conversion treatment solution because it easily causes generation. On the other hand, when the electrical conductivity of the chemical conversion treatment liquid is below the lower limit of the predetermined range, the concentration of the main agent component in the chemical conversion treatment liquid is naturally low, so that the main agent is supplied to the chemical conversion treatment liquid. .

The iron and steel materials used in the present invention include ordinary iron and steel, as well as surface-treated steel such as alloy steel and galvanized steel sheet.

In the present invention, as will be described later, when the redox potential of the chemical conversion treatment liquid exceeds the upper limit of the predetermined range, for example, FeSO
It is possible to lower the redox potential of the chemical conversion treatment liquid by adding an aqueous solution containing divalent iron ions such as ₄ , FeCl ₂ to the chemical conversion treatment liquid.

That is, if the component to be treated in the chemical conversion treatment liquid, that is, the state where the steel material is not subjected to the chemical conversion treatment is long, it takes time until the ORP of the chemical conversion treatment liquid decreases due to the start of the chemical conversion treatment of the treatment target component. Therefore, it is possible to avoid the problem that a good conversion coating cannot be obtained for the component to be processed in the initial stage of the conversion treatment.

[Action]

In the present invention, when the electrical conductivity of the chemical conversion treatment liquid exceeds a certain value, even if the main agent is supplied into the chemical conversion treatment liquid to control the upper limit of pH, the supply is forcibly stopped. It is a thing. As a result, the electrical conductivity of the chemical conversion treatment liquid does not exceed a certain value, so that the generation of sludge in the chemical conversion treatment liquid can be suppressed.

In the present invention, the electrical conductivity of the chemical conversion treatment liquid is controlled in a range of a certain value or less, in the chemical conversion treatment liquid, phosphate ions,
Since the total concentration of so-called soluble ionic components such as oxo acid ions and metal ions forming the chemical conversion film is controlled within a certain range, if the concentration is sufficient, the supply of the main agent that was being performed when the pH was raised is forcibly stopped. No problem,
Also, a slight increase in pH does not significantly affect the formation of the conversion coating.

〔The invention's effect〕

As described above, in the present invention, the electrical conductivity of the chemical conversion treatment liquid can be maintained within a range of a certain value or less, and therefore, practically suitable control of the chemical conversion treatment liquid is achieved.

〔Example〕

Hereinafter, description will be made with reference to examples. Although this embodiment is a spray method, it goes without saying that the present invention can also be applied to a dipping method.

As shown in the schematic diagram in Fig. 1, zinc ion 3.5 g / l, phosphate ion 16 g / l, nitrate ion 5.0 g / l, nickel ion 0.5
g / l, fluorine ion 50 ppm, the treatment tank for holding the chemical conversion treatment solution 1.0 m ³ containing sulfate ions 1.8 g / l, soluble iron ions 15~400ppm and nitrite ions 50 ppm, the solenoid valve 21
Via the main agent tank 2 to the main agent supply pipe 22, and via the solenoid valve 24 from the adjuster tank 7 to the adjuster supply pipe.
25 through the solenoid valve 31 and the oxidizer tank 3
The oxidant supply pipes 32 were connected to each other. Then, these solenoid valves 21, 31, 24 are connected by an electric circuit (not shown) that opens and closes with a pH meter 23 and a redox potential meter 33 immersed in the chemical conversion treatment solution, and when the pH becomes 3.46 or higher, the valve 21 is opened. Open and supply the main agent from the main agent tank 2 into the processing tank 1,
When is less than 3.46, close valve 21 and at the same time
The adjusting agent was supplied from the adjusting agent tank 7 into the treatment tank 1 at pH 3.43 or less, and the valve 24 was closed at pH 3.43 or more. On the other hand, the redox electrometer (silver chloride electrode) 33 is 210 mV
When it becomes below (in terms of silver chloride electrode potential), the solenoid valve 31 is opened, the oxidizing agent is supplied from the oxidizing agent tank 3 into the processing tank 1, and the solenoid valve 31 is closed when the redox potential meter 33 becomes 210 mV or more. did.

The above structure and control method are almost the same as the method of the above-mentioned Japanese Patent Laid-Open No. 60-43491. On the other hand, the redox potential is 260 mV
In the above case, the solenoid valve 34 is opened, and the adjusting agent, which is an aqueous solution of 10% ferrous sulfate, is supplied from the adjusting agent tank 8 to the processing tank 1, and the redox potential is 260 mV by the supply.
When the temperature falls below, the solenoid valve 34 is closed.

Also, used by the electric conductivity measuring device 43, when the conductivity is 17.7 ms or less, the valve 21 is opened to supply the main agent from the main agent tank 2 to the processing tank 1, and when the conductivity is 17.7 ms or more, the valve 21 is closed. I did it. In addition, if the conductivity is 18.3 ms or more, even if the pH in the processing tank 1 is 3.46 or more, the valve
21 was forcibly closed so that the supply of the main agent to the processing tank 1 was stopped. Further, a spray pipe 4 is provided on the side wall of the treatment tank 1, and a chemical conversion treatment liquid is sprayed onto the surface of the component W to be treated from a spray nozzle row 6 provided above the treatment tank 1 via a pump 5. I chose The sprayed chemical conversion treatment liquid is dropped into the treatment tank 1 and returned.

By the way, as the main agent for replenishment, the concentration of Zn ²⁺ , H ₃ PO ₄ , NO ₃ ⁻ , Ni ²⁺ , F ⁻ , which are the main ingredients of the chemical conversion treatment solution, is made about 25 times higher, and the supply rate is Is 50 ml / min. Also,
Supply 4% aqueous solution of NaNO ₂ as an oxidant, 5% aqueous solution of NaOH as a regulator in the tank 7, and 10% aqueous solution of FeSO ₄ as a regulator in the tank 8 at 50 ml / min. It is supplied at a speed into the processing tank 1.

As the object W to be processed, a stator (diameter 90 mm, thickness 27 mm), which is a magnetic clutch part for an automobile air conditioner, made by processing a steel product was used.

This processed part W is sprayed with 55 ° C alkaline aqueous solution for 2 minutes and degreased → washed with room temperature water for 1 minute → normal temperature (20-30 ° C)
1 minute spray washing → Preparene ZT made by Nihon Parkerizing Co., Ltd. dipping for 2 minutes with surface preparation liquid of 0.3% concentration → Chemical conversion treatment liquid at room temperature (average temperature 30-33 ° C) with the device in Fig. 1 Spray for 2 minutes and apply phosphate conversion coating → 1 minute spray cleaning with room temperature water → 1 minute spray cleaning with room temperature water → 30 seconds pure mist spray → Electropaint coating with Nippon Paint Power Top U-56 → Baked (180 ° C x 2 minutes).

Through the above steps, a phosphate chemical conversion film mainly containing zinc phosphate was formed on the surface of the component W to be treated, and an electrodeposition coating film was formed on this film.

In addition, the above-mentioned processing is performed by setting 60 parts W to be processed in one hanger and moving the hanger (bath in which the above-mentioned steps are performed) to the hanger every 2 minutes. Also,
The processing device shown in FIG. 1 processes 700 pieces for 1 hour and 8 times a day.
It was operated for an hour and the chemical conversion treatment liquid was automatically controlled.

FIG. 2 shows the electric conductivity state of the chemical conversion treatment liquid in the treatment tank 1 of the treatment apparatus of FIG. 1, and in the figure, A indicates the upper limit of the electric conductivity of the chemical conversion treatment liquid. An example is shown, and B is a comparative example in which the upper limit of the electric conductivity of the chemical conversion treatment liquid is not controlled. The comparative example is the same as the present example except that the upper limit of the electric conductivity of the chemical conversion treatment liquid is not controlled, and the other conditions are the same as those of the present example.

By the way, in the comparative example, (1) the upper limit of the electric conductivity of the chemical conversion treatment liquid is not controlled, (2) the temperature of the chemical conversion treatment is 30 to 33 ° C. on average, (3) chemical conversion treatment The operation rate of processing is about 50%, and spraying is performed for 4 hours a day. Since the parts to be processed are the hanger transfer system,
Due to factors such as less carry-on of the pretreatment liquid to the treatment tank (Fig. 1) and (4) less carry-out of the chemical conversion treatment liquid from the treatment tank due to the hanger transfer system, It can be seen that the electric conductivity of the chemical conversion treatment liquid increases with the passage of days. As a result, formation of sludge was recognized in the chemical conversion treatment liquid.

As understood from this comparative example, when some or all of the above-mentioned four conditions are overlapped, the electrical conductivity of the chemical conversion treatment liquid is controlled by the supply control of the main agent corresponding to the change in pH of the chemical conversion treatment liquid. Can not be controlled, in other words, it is difficult to control the total concentration of soluble ionic components in the chemical conversion treatment liquid.

On the other hand, in the case of this example (A in FIG. 2), except for the above (1) described in the comparative example, (2) to (4)
The conditions are the same as in the comparative example, but in this example, the supply of the main agent is stopped when the electrical conductivity of the chemical conversion treatment liquid exceeds the upper limit, so that the electrical conductivity can be maintained within a predetermined range. According to this example, the formation of sludge in the chemical conversion treatment liquid was extremely small.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of a processing apparatus used in the examples of the present invention, and FIG. 2 is a characteristic diagram showing the results of the presence or absence of electric conductivity control in the examples of the present invention and comparative examples. 1 ... Processing tank, 2 ... Main agent tank, 3 ... Oxidizing agent tank, 7 ... Adjusting agent tank, 8 ... Adjusting agent tank.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kentaro Sato 1-151-1 Nihonbashi, Chuo-ku, Tokyo Japan Parkerizing Co., Ltd. (72) Takahiro Onuki 1-1-15 Nihonbashi, Chuo-ku, Tokyo Japan Within Parkerizing Co., Ltd.

Claims (3)

[Claims] 1. A phosphate chemical compound containing a phosphate ion, an oxo acid ion, a metal ion for forming a chemical conversion film, and an oxidizing agent, and having a pH and a redox potential controlled within a predetermined range in a temperature range of less than 40 ° C. A method of contacting a steel material with a treatment liquid to form a phosphate conversion coating on the surface of the steel material, comprising measuring the electrical conductivity of the chemical treatment liquid, and the electrical conductivity of which exceeds a certain value. When, when the upper limit of the pH is regulated, the supply of the phosphoric acid, the oxoacid ion, and the main agent containing the chemical conversion film-forming metal to the chemical conversion treatment liquid is stopped, and the electricity of the chemical conversion treatment liquid is stopped. A method for controlling electric conductivity of a phosphate chemical conversion treatment liquid, characterized in that the electric conductivity is maintained below a certain value. 2. The control method according to claim 1, wherein when the pH of the chemical conversion treatment liquid exceeds an upper limit value of a predetermined range, the main agent is supplied to the chemical conversion treatment liquid to maintain a predetermined pH. When the lower limit value of the range is exceeded, a solution containing an alkali is supplied to the chemical conversion treatment liquid, and when the redox potential of the chemical conversion treatment liquid is lower than the lower limit value of the predetermined range, the oxidizing agent is the chemical conversion treatment. A material that is supplied to the liquid and reduces the redox potential when the oxidation-reduction potential exceeds the upper limit value of the predetermined range is supplied to the chemical conversion treatment liquid, and the electrical conductivity of the chemical conversion treatment liquid is the lower limit value of the predetermined range. When it is less than the above, the main agent is supplied to the chemical conversion treatment liquid, and when the electrical conductivity exceeds the upper limit value of the predetermined range, even if the pH exceeds the upper limit value of the predetermined range, the main agent Is not supplied to the chemical conversion treatment liquid Electrical conductivity control method of chemical conversion treatment solution. 3. The control method according to claim 1 or 2, wherein the chemical conversion treatment solution has a pH of 2.0 to 4.0, an oxidation-reduction potential of 300 mV to 800 mV (hydrogen standard electrode potential), and a temperature of Is a temperature range of less than 40 ° C. where active external heating is not performed, and a method for controlling electric conductivity of a phosphate chemical conversion treatment liquid.