KR19990066876A - Background chemical treatment method for low lead ED - Google Patents

Abstract

An object of the present invention is to provide a pretreatment method for low lead electrodeposition coating containing no lead or containing only low concentration of lead.

As a solution for this, a zinc phosphate film is formed on the metal surface so that the corrosion resistance value by the AC impedance method is 2,500 Ωcm 2 or more, and the lead concentration in the electrodeposition bath is 300 ppm or less, preferably Chemical conversion treatment of the base metal, useful for substantially zero cationic electrodeposition coating, 0.5 to 1.5 g of zinc ions, 5 to 30 g of phosphate ions, and 0.1 to 4 g of nickel ions in 1 L of the chemical conversion solution There is a method of chemical conversion of a base metal, which is immersed in a chemical treatment solution containing 0.6 to 3 g of manganese ions, 0.05 g or more of fluorine ions, 5 to 20 ppm of copper ions, and a film formation accelerator.

Description

Background chemical treatment method for low lead ed

The present invention relates to a surface treatment method of a base metal to be electrodeposition coated. In particular, the present invention relates to a method for surface treatment of a base metal in the case of electrodeposition coating of a metal surface using an electrodeposition coating bath containing no lead or low lead content.

As a method of coating metals such as automobile bodies, cationic electrodeposition coating has been widely used in recent years. The main cationic electrodeposition coating composition generally contains a blocked polyisocyanate as an amino group-containing resin as an epoxy resin-based film-forming resin and a crosslinking agent. An antirust pigment is used for the purpose of maintaining the coating film durability after coating. As a rust preventive pigment, lead compounds, such as basic lead pigment, are mainly used. This paint composition has excellent rust resistance, while lead use, on the other hand, tends to be limited in terms of toxicity, and the electrodeposition coating bath should be free of lead in the future. On the other hand, in order to secure the adhesion and durability of the coating film, the surface of the metal (hereinafter abbreviated as base metal) to be electrodeposited prior to electrodeposition coating is pretreated with a chemical treatment solution as shown in FIG. 1. The chemical conversion treatment liquid usually contains zinc, manganese, nickel, fluoride, and the like, and a zinc phosphate film is formed on the surface of the base metal by this treatment.

Such chemical treatment solution is prescribed on the premise that lead is contained in the electrodeposition coating bath, and in the case of electrodeposition coating using an electrodeposition coating bath containing no lead or containing a predetermined concentration or more of lead, conventional chemical treatment Satisfactory coating film durability is not obtained with the liquid.

An object of the present invention is to provide a pretreatment method for low lead electrodeposition coating that does not contain lead or contains only lead at low concentrations.

1 is a process chart of chemical conversion treatment,

2 is an equivalent circuit of AC impedance,

* Explanation of symbols on the main parts of the drawings *

RΩ: resistance of the solution,

C _d : capacitance of the interface,

Z _f : Faraday impedance,

R _s : resistance component (polarization resistance) of Z _f ,

C _s : capacity component of Z _f ,

R _ct : Corrosion Resistance

The present invention is characterized in that a zinc phosphate film is formed on the metal surface such that the corrosion resistance value of the alternating current method is 2,500 Ωcm 2 or more. The chemical composition of the base metal useful for the cationic electrodeposition coating having a lead concentration of 300 ppm or less in the electrodeposition bath is provided. It is about a processing method.

In particular, the present invention relates to a method for chemically treating a base metal, which is useful for a cationic electrodeposition coating having a substantially zero lead concentration in an electrodeposition bath.

Specifically, the present invention provides 0.5 to 1.5 g of zinc ions, 5 to 30 g of phosphate ions, 0.1 to 4 g of nickel ions, 0.6 to 3 g of manganese ions and 0.05 g or more of fluorine ions in 1 L of the treatment liquid. In addition, the present invention relates to a chemical conversion treatment method for the base metal, which is immersed in a metal surface with a chemical conversion treatment solution containing 5 to 20 ppm of copper ions and a coating chemical accelerator as a main component.

By treating the base metal surface to be subjected to cationic electrodeposition coating by the chemical conversion treatment method of the present invention, it is possible to form an acidic zinc phosphate film having a corrosion resistance of 2,500 Ωcm 2 or more by the AC impedance method on the surface. By forming a film having such a corrosion resistance value, it is possible to form a coating film having excellent durability even when electrodeposition coating is carried out using a low lead cationic electrodeposition coating bath.

The chemical conversion treatment of the present invention provides a preferred method for treating the surface of the underlying metal to be treated prior to cationic electrodeposition coating that is substantially free of lead.

The electrodeposition coating composition which does not contain the lead made into this invention can illustrate the following, for example.

As a typical low lead electrodeposition coating composition, 40 to 95% by weight of a film-forming resin having an average molecular weight of 500 to 20,000 which can be diluted with water by acid neutralization, having both component (A) amino and hydroxyl groups, and (B A negative electrodeposition coating composition containing 5 to 60% by weight of a blocked polyisocyanate crosslinking agent can be exemplified.

The film-forming resin of component (A) may be diluted with water, for example, by an acid having an amino group (e.g., primary amino group, secondary amino group and tertiary amino group) and hydroxyl group (primary or secondary). The average molecular weight is 500 to 20,000 resins. In this case, the amount of the amino group is usually represented by an amine number, and is in the range of 30 to 150, preferably 45 to 80. Lack of amine titer lacks water dilution. The amount of hydroxyl group is represented by the primary hydroxyl value, and is 20 to 200, preferably 50 to 120. The hydroxyl group acts as a crosslinking point. In addition to the primary hydroxyl group, a secondary hydroxyl group, a primary amino group, and a secondary amino group are used as the crosslinkable reactor. Such a film-forming resin is generally formed by introducing an amino group into an epoxy resin, an epoxy-containing acrylic copolymer resin or a polyurethane resin.

Block isocyanate crosslinking agent (B) is generally used by blocking the isocyanate group of the polyfunctional isocyanate.

As the polyfunctional isocyanate, polyisocyanates having two or more isocyanate groups per molecule of aliphatic, alicyclic and / or aromatic are used. Specific examples thereof include tolylene diisocyanate, tolylene triisocyanate, 4,4'-diphenylmethane diisocyanate, isophorone diisocyanate (IPDI), xylylene diisocyanate (XDI), norbornene diisocyanate (NBDI), hexa Isomer or isomer mixture of methylene diisocyanate (HMDI), biphenyl tetra isocyanate, and / or naphthyl tetra isocyanate, and its hydrogenated substance, for example, dicyclohexyl methane diisocyanate, etc. are mentioned.

Blocking agents that can be used are well known in the art, and include aliphatic alcohols such as n-butanol, 2-ethylhexanol, ethylene glycol monobutyl ether and cyclohexanol; Phenols such as phenol, nitrophenol, cresol and nonylphenol; Oximes such as dimethyl keto oxime, methyl ethyl keto oxime and methyl isobutyl keto oxime; Lactams such as caprolactam.

Preparation of the cationic electrodeposition coating composition as described above, before or after the neutralization of the cationic electrodeposition resin, a metal compound and a crosslinking agent, if necessary, after neutralization, after neutralization, water oxidation or emulsification or cation The emulsification of the type electrodeposition resin is carried out by mixing a metal compound and, if necessary, a crosslinking agent. Neutralization can be performed with water-soluble organic acids, such as formic acid, acetic acid, lactic acid, propionic acid, citric acid, malic acid, tartaric acid, acrylic acid, and sulfamic acid, and inorganic acids, such as hydrochloric acid and phosphoric acid.

To the cationic electrodeposition coating composition of the present invention, a paint additive, for example, a coloring pigment, such as titanium white, carbon black, bencal, and the like, may be used as needed. Extender pigments such as talc, calcium carbonate, mica, clay, silica and the like; Anti-rust pigment, for example, a pollution-free rust preventive pigment, such as zinc phosphate and aluminum phosphate, basic lead silicate etc. are disperse | distributed to a pigment dispersion resin as needed, and it is used as a paste. Moreover, it can also contain a splash inhibitor, a solvent, a curable catalyst, etc.

Cationic electrodeposition coating is a well-known method. Generally, the electrodeposition coating composition is diluted with deionized water or the like so that the solid content concentration is about 5 to 40% by weight, preferably 15 to 25% by weight, and then the pH is 5.5 to 5.5. The electrodeposition bath formed by adjusting in the range of 8.0 can be normally adjusted to 15-35 degreeC of bath temperature, and can be performed using a to-be-coated object as a cathode on the conditions of 100-450V of load voltages.

Although the film thickness of the pigment formed by electrodeposition coating is not specifically limited, Generally, within the range of 5-60 micrometers, Preferably it is 10-40 micrometers based on a cured coating film. In addition, the print curing temperature of the coating film is generally appropriate to print at a time range of about 10 to 30 minutes at 100 to 200 ° C, preferably 160 to 180 ° C.

On the underlying metal surface treated by the chemical conversion treatment method of the present invention, a zinc phosphate film having a corrosion resistance of 2,500 Ωcm 2 or more by the alternating current impedance method of the metal surface is formed. The present inventors found that by forming a zinc phosphate film having an alternating current impedance in this range on a metal surface, even when no lead ions are contained in the cationic electrodeposition coating bath, a coating film having excellent durability is formed by electrodeposition coating.

The chemical conversion treatment method of the present invention is characterized in that an acidic zinc phosphate aqueous solution containing copper ions is used as the chemical conversion treatment agent.

Acidic zinc phosphate aqueous solution of the present invention is zinc ion 0.5 ~ 1.5 g / L, phosphate ion 5 ~ 30 g / L, nickel ion 0.1 ~ 4 g / L, manganese ion 0.6 ~ 3 g / L, fluorine ion 0.05 g / L As mentioned above, it contains a copper ion 5-20 ppm and a film formation accelerator as a main component.

The chemical conversion treatment liquid of the present invention contains 0.5 to 1.5 g / l of zinc ions, preferably 0.7 to 1.2 g / l, as an essential component. When the zinc ion is less than 0.5 g / l, a uniform phosphate film is not formed on the iron surface, and some blue color film is formed. In addition, if the content exceeds 1.5 g / L, a uniform phosphate film is formed, but the film on the iron-based surface is liable to form a leaf-shaped crystal such as that produced by spray treatment, and is not suitable as a base for cationic electrodeposition coating. , The concentration unit g / L means that the component is contained in g units in 1 L of the chemical conversion treatment liquid, hereinafter, the concentration unit g / L is used in the same sense).

Phosphate ions are contained in an amount of 5 to 30 g / l, preferably 10 to 20 g / l. When it is less than 5 g / l, it is easy to form a nonuniform film, and even if it exceeds 30 g / l, the effect more than this invention cannot be expected, and the amount of chemicals used increases and it is economically disadvantageous.

Nickel ions are contained 0.1 to 4 g / l, preferably 0.3 to 2 g / l. In the presence of manganese ions, nickel ions further improve chemical conversion film performance, and further improve adhesion and corrosion resistance after cationic electrodeposition coating. When the nickel ion is less than 0.1 g / l, the addition effect of the nickel ion does not appear, and when the nickel ion is more than 4 g / l, the zinc phosphate coating amount is lowered, which is not preferable because it shows a bad effect on the corrosion resistance.

Manganese ions contain 0.6 to 3 g / l, preferably 0.8 to 2 g / l. When it is less than 0.6 g / L, the manganese content in the film | membrane produced on a zinc type surface is small, and the base and coating film adhesiveness after cationic electrodeposition coating become inadequate. Even if it exceeds 3 g / L, the effect more than this invention cannot be expected, and it becomes economically disadvantageous.

The fluorine ion is 0.05 g / l or more, preferably 0.1 to 2 g / l. When it is less than 0.05 g / L, refinement of the phosphate film crystal, improvement of corrosion resistance after coating, and low temperature chemical conversion treatment cannot be achieved. Moreover, even if it contains an excess amount, the effect beyond this invention cannot be expected, and it is economically disadvantageous. Fluorine ions are preferably used as complex fluorine ions.

Copper ions are contained in 5 to 20 ppm, preferably 10 to 15 ppm. When it is less than 5 ppm, the coating film adhesion and the coating durability of the coating film are insufficient. On the other hand, when it exceeds 20 ppm, since the appearance changes, it is not preferable.

As film formation accelerator, 0.01 to 0.2 g / l of nitrite ion, preferably 0.04 to 0.15 g / l, 0.05 to 2 g / l of m-nitrobenzenesulfonic acid ion, preferably 0.1 to 1.5 g / l, hydrogen peroxide _{1 selected} from 0.5 to 5 g / l, preferably 1 to 4 g / l and hydroxylamine 0.1 to 5 g / l, preferably 0.5 to 2 g / l (in terms of 100% H ₂ O ₂ ) More than one species are used. If these accelerators do not reach the prescribed amount, sufficient film formation is impossible on the iron-based surface, yellow rust and the like occur, and when the amount exceeds the prescribed amount, it is easy to form a non-uniform film of blue color on the iron-based surface.

As a source of these main components, for example, zinc ions are zinc oxide, zinc carbonate, zinc nitrate, phosphate ions are phosphoric acid, zinc phosphate, manganese phosphate, etc., nickel ions are nickel carbonate, nickel nitrate, nickel chloride, nickel phosphate, etc. Manganese ions are manganese carbonate, manganese nitrate, manganese chloride, manganese phosphate, etc., fluorine ions are hydrofluoric acid, hydrofluoric acid, hydrofluoric acid silicon, metal salts thereof (e.g. zinc salt, nickel salt. The desired effect can not be achieved), and boron fluoride and / or silicon fluoride can be used as the complex fluorine ion source. Sodium nitrite, ammonium nitrite, sodium m-nitrobenzenesulfonate, hydrogen peroxide, hydroxylamine, etc. can be used as a film formation promoter.

The treatment liquid of the present invention may further contain nitrate ions and / or chlorate ions. Nitrate ions are used at a concentration of 1 to 10 g / l, preferably 2 to 8 g / l, and chlorate to 0.05 to 2 g / l, preferably 0.2 to 1.5 g / l. The source of nitrate may be sodium nitrate, ammonium nitrate, zinc nitrate, manganese nitrate, nickel nitrate, and the like. The source of chlorate ions may be sodium chlorate, ammonium chlorate, or the like.

The treatment temperature by the chemical conversion treatment liquid of the present invention may be 30 ~ 70 ℃, preferably 35 ~ 50 ℃. If the temperature is too low, the film formability is poor, requiring a long time treatment. If the temperature is too high, the balance of the treatment liquid is easily broken due to the decomposition of the film chemical accelerator and the occurrence of precipitation of the treatment liquid.

Immersion treatment time is 15 seconds or more, Preferably it is 30 to 120 second. If it is too short, the film which has a desired crystal | crystallization will not fully be formed. In addition, in the case of processing an object having a complicated shape, such as an automobile body, it is practically first immersed for at least 15 seconds, preferably 30 to 90 seconds, and then at least 2 seconds, preferably 5 to 45 seconds. Spray for seconds. In addition, in order to wipe off the sludge adhering at the time of immersion treatment, it is preferable to carry out a spray process for as long as possible. Therefore, the immersion process by this invention also includes the process aspect of this immersion process-spray process.

The present invention also relates to a thickening agent which provides a treatment liquid having the above-described configuration. This thickening agent comprises a zinc ion source, a phosphate ion source, a nickel ion source, a manganese ion source, a fluorine ion source, and a copper ion source by diluting the treatment liquid to 1 to 4% by weight / volume% to form a treatment liquid of the above constitution. It may contain in sufficient quantity. However, the sodium compound should not be contained at that time. This is because when manganese ions and / or fluorine ions and sodium ions coexist, precipitation forms and causes problems in preparation of the treatment liquid. Therefore, when using a sodium compound, it is necessary to add to a process bath in a separate liquid.

According to the present invention having the above-described configuration, a low temperature treatment of a coating film having both sufficient adhesion and corrosion resistance as a basis for the cationic electrodeposition coating is performed not only on the iron-based surface, but also on the zinc-based surface or a metal surface composed of both. It can be formed as.

The alternating current impedance of the chemically treated metal surface is described in Shintobu Sotojima, "Basic Electrochemistry" [Page 373; Published by Asakura Shoen (July 10, 1967)] and Akira Fujishima, Masuo Aizawa, “Electrochemical Measurements” [pages 219-222; Based on the principles described in Kiyoto Publishing (November 15, 1984), the following measurements can be made.

A metal plate to be measured was placed in a cell filled with a corrosion solution, the impedance was measured by sweeping the frequency, and the corrosion resistance value was calculated by an equivalent circuit analysis according to FIG. 2.

[Impedance measurement condition]

Frequency range: 100 KHz to 50 MHz

Applied voltage: 10 Ω against immersion potential

Corrosion solution: 5 wt% saline solution

Measuring area: 1 ㎠

Start of measurement: 30 minutes after immersion

Equivalent circuit: use the one shown in FIG.

Measuring instruments: Measuring instruments used in measuring devices are as follows.

1) Potential Starter: HA-501G (manufactured by Hoto Denko Co., Ltd.)

2) Frequency characteristic analyzer: S-5720 C (Neef Cairo Setbro)

3) AC impedance measurement software: HZ-1 AC (manufactured by Hoto Denko Co., Ltd.)

EXAMPLE

Hereinafter, the present invention will be described in detail by way of examples.

Examples 1 to 3

(I) chemical conversion of base metal

The 7 cm x 15 cm metal plate SPCC-SD (G 3141) degreased, water-washed, and surface-adjusted as in FIG. 1 was immersed in the chemical treatment solution of 42 degreeC shown in Table 1, and chemically processed. Immersion time was also described in liquid.

In the table, the standard phosphate chemical treatment liquid means that the following components are contained in 1 liter of the treatment liquid.

[Standard Phosphate Chemical Treatment]

Zinc ion 1.0 g / ℓ

Phosphate ions 15.0 g / ℓ

Nickel ion 1.0 g / ℓ

Manganese ion 0.6 g / ℓ

Nitrate ions 6.0 g / ℓ

Nitrite ion 0.14 g / ℓ

Silicon fluoride 1.0 g / ℓ

21.0 points total mountain

Yuri mountain 0.7 points

The chemically treated metal plate was again washed with water, purified water and dried to obtain a chemically treated metal plate as in FIG. 1.

Each process before and after the chemical conversion treatment as shown in FIG. 1 will be described below.

(a) degreasing

It was immersed for 2 minutes at 42 degreeC in the mixture of alkaline degreasing agent "Sapcleaner SD 250" (made by Nippon Paint, Inc.) A and B (concentration A in water 1.5 weight%, B adjusted to 0.7 weight%).

(b) water cleaning

Rinse for 15 seconds at room temperature using tap water.

(c) surface adjustment

It is immersed for 15 seconds at room temperature in the surface adjuster "Sapphire 5N-10" (made by Nippon Paint, concentration 0.1 weight%).

(d) water cleaning

Rinse for 15 seconds at room temperature using tap water.

(e) water purification

Immerse at room temperature for 15 seconds with ion-exchanged water.

(f) drying

It is dried for 10 minutes by hot air at 100 ° C.

(Ⅱ) AC Impedance Measurement of Chemically Treated Metal Plate

The chemical conversion treatment metal plate measured the AC impedance by the method described above.

(III) Cationic electrodeposition coating on chemically treated metal sheet

Synthesis Example 1 Synthesis of Gas Resin

A flask equipped with a stirrer, a cooler, a nitrogen introduction tube, a thermometer, and a dropping lot was prepared. 92 g of 2,4- / 2,6-tolylene diisocyanate (weight ratio = 8/2), 95 g of methyl isobutyl ketone, and 0.5 g of dibutyltin dilaurate were added to this flask, and 21 g of methanol was stirred with stirring. Was dropped further. Reaction started at room temperature and heated up to 60 degreeC by exotherm. Then, after continuing reaction for 30 minutes, 57 g of ethylene glycol mono-2-ethylhexyl ethers were dripped at the dropping lot, and 42 g of bisphenol A-propylene oxide 5 mol adducts were added again. The reaction was carried out mainly in the range of 60 ° C to 65 ° C, and continued until the isocyanate group disappeared while measuring the IR spectrum. Next, 365 g of epoxy resins of epoxy equivalent 188 synthesized with bisphenol A and epichlorohydrin were added, and the temperature was raised to 125 ° C. Thereafter, 1.0 g of benzyldimethylamine was added and reacted at 130 ° C until the epoxy equivalent was 410. Subsequently, when 87 g of bisphenol A was added to the reaction vessel and reacted at 120 ° C., the epoxy equivalent was 1190. After cooling, 11 g of diethanolamine, 24 g of N-methylethanolamine, and 25 g of ketimide (79 wt% methyl isobutyl ketone solution) of aminoethylethanolamine were added thereto, and the mixture was stirred at 110 ° C for 2 hours. Reacted for a while. Thereafter, the mixture was diluted with methyl isobutyl ketone until the nonvolatile content became 80%, and an oxazolidone ring-containing gas resin was obtained.

Synthesis Example 2 Synthesis of Blocked Isocyanate

A flask equipped with a stirrer, a cooler, a nitrogen introduction tube, a thermometer, and a dropping lot was prepared. To this flask was added 199 g of a trimer of hexamethylene diisocyanate (Colonate HX: manufactured by Nippon Polyurethane Co., Ltd.) and 11.3 g of ε-caprolactam. And the content in the flask was heated up to 80 degreeC, and it melt | dissolved uniformly. At this time, 32 g of methyl isobutyl ketone, 0.05 g of dibutyltin dilauryllate and 0.05 g of 1,8-diazabicyclo (5,4,0) -7-undecene were added. 78.3 g of methyl ethyl keto oxime was dripped at the dripping lot for 1 hour, paying attention to exotherm at the point which this was stirred, blowing nitrogen. The reaction was carried out until the isocyanate group disappeared in the IR spectrum to obtain a blocked isocyanate crosslinking agent.

Synthesis Example 3 Preparation of Pigment Dispersion Resin

A flask equipped with a stirrer, a cooler, a nitrogen introduction tube, a thermometer, and a dropping lot was prepared. 222.0 g of isophorone diisocyanate were added to this flask, and after diluting with 39.1 g of methyl isobutyl ketone, 0.2 g of dibutyltin dilaurylate was added. After heating up at 50 degreeC, 131.5 g of 2-ethylhexanols were dripped at the dropping lot for 2 hours at the point where nitrogen is bubbled and stirred. By moderately cooling, the reaction temperature during this time was kept at 50 degreeC. As a result, 2-ethylhexanol half-blocked isophorone diisocyanate was obtained (solid content 90%).

A flask equipped with a stirrer, a cooler, a nitrogen introduction tube, a thermometer, and a dropping lot was prepared. 376.0 g of EPON 828 (epoxy resin manufactured by SHERGAGAKU Co., Ltd.) and 114.0 g of bisphenol A were added to the flask, and the mixture was heated to 130 ° C. under a nitrogen atmosphere, and 0.75 g of dimethylbenzylamine was added to react the exotherm at 170 ° C. for 1 hour. The bisphenol-A epoxy resin which has an epoxy equivalent of 490g was obtained by doing this. Subsequently, after cooling to 140 degreeC, 198.4 g of said 2-ethylhexanol half-blocking isophorone diisocyanate were added, it was made to react at 140 degreeC for 1 hour, and 161.8 g of ethylene glycol monobutyl ether was added, and it reacted. The mixture was cooled to 100 ° C. To this, 366.0 g of thiodiethanol, 134.0 g of dimethylolpropionic acid, and 144.0 g of deionized water were added thereto, followed by reaction at 70 ° C to 75 ° C until an acid value of 0.241 was obtained, followed by dilution with 353.3 g of ethylene glycol monobutyl ether. A pigment dispersion resin having a sulfonation ratio of 82% was obtained (solid content 50%).

Synthesis Example 4 Preparation of Pigment Dispersion Paste

Carbon black, kaolin and titanium dioxide were dispersed in the pigment dispersion resin obtained in the synthesis example 3 by the following formulation, and it grind | pulverized with the sand mill, and obtained the pigment dispersion paste.

ingredient Parts by weight Pigment Dispersion Resin (50% Solid) 60 Carbon black 2 kaoline 15 Titanium dioxide 53 Deionized water 40

350 g (solid content) of the gas resin obtained in Synthesis Example 1 and 150 g (solid content) of the crosslinking agent obtained in Synthesis Example 2 were mixed, so that ethylene glycol mono-2-ethylhexyl ether was 3% (15 g) based on the solid content. Added. Then, glacial acetic acid was added to neutralize to a degree of neutralization of 40.5%, neutralized by addition of ion-exchanged water, and then methyl isobutyl ketone was removed under reduced pressure so that the solid content was 36.0%.

Into the emulsion thus obtained, 460.0 g of the pigment dispersion paste obtained in Synthesis Example 4, 2252.0 g of ion-exchanged water, and 1.0% by weight of dibutyltin oxide were added to the resin solid, and the electrodeposited solid was 20.0% by weight. The paint was prepared.

The lead-containing electrodeposition paint was prepared by using lead acetate in the lead-free electrodeposition paint bath and adding 1000 ppm as lead ions.

In the electrodeposition paint bath, the surface-treated cold rolled steel sheet was immersed as a cathode, electrodeposited to have a dry film thickness of 20 µ, and then cured for 160 ° C x 10 minutes to evaluate the coating film.

(Ⅳ) Evaluation of Durability of Electrodeposited Film

The durability of the obtained electrodeposition coating plate was tested by the following two methods.

(1) CCT test (cycle corrosion test)

After carving the crosscut (cutting cross hairs), 100 cycles of the cycle corrosion test (CCT) were performed, and after 100 cycles, the appearance was visually evaluated.

In addition, one cycle of the CCT was given the following environmental conditions:

Brine spray test (SST: 5% NaCl × 35 ℃) 2 hours

→ 2 hours under high temperature and humidity conditions (98% RH × 40 ℃)

→ 4 hours of drying condition (60 ℃)

(2) SDT Test (Saline Immersion Test)

The cut in the vertical direction was put in the test piece, and it was immersed in 5% saline at 40 degreeC for 240 hours, and the cut part was peeled off to evaluate peelability.

Table 1 shows the chemical composition treatment time, treatment time, corrosion resistance and corrosion resistance measurement results.

The criterion of the evaluation result of the CCT test and the SDT test in Table 1 was as follows.

CCT: ○ Maximum rust or expansion width on both sides 0 ~ 3 mm

× Maximum rust or inflation width on both sides 3 mm or more

SDT: ○ No Peel

△ peeling width 0 ~ 1 mm

× 1 mm or more peeling width

Comparative Example 1

A chemical conversion treatment and a cationic electrodeposition coating were carried out in the same manner as in Example 1 except that the standard phosphate chemical treatment solution was used as the chemical conversion treatment liquid, and the alternating current impedance of the chemical conversion metal plate and the corrosion resistance of the electrodeposition coating film were evaluated. The results are shown in Table 1.

Comparative Example 2

The chemical conversion treatment was carried out in the same manner as in Example 1 except that nickel ions were removed from the standard phosphate chemical treatment solution and 10 ppm copper ions were added instead. AC impedance and corrosion resistance of electrodeposition coating were evaluated. The results are shown in Table 1.

Example Treatment liquid composition Processing time (seconds) AC impedance (Ω㎠) of metal plate after acid phosphate treatment Durability of coating after electrodeposition coating CCT SDT With Pb none With Pb None ¹⁾ One Standardization Treatment Solution + Cu 5 ppm 120 2800 ○ ○ ○ ○ 2 Standardized Treatment Solution + Cu 10 ppm 120 2900 ○ ○ ○ ○ 3 Standardized Treatment Solution + Cu 20 ppm 120 3000 ○ ○ ○ ○ Comparative Example 1 Only standardized treatment liquid 120 1250 ○ × ○ × Comparative Example 2 Remove Ni from standardized treatment solution and add 10 ppm of Cu 120 2350 ○ × △ × 1) presence of lead in cationic electrodeposition coating bath

The metal converted by the method of the present invention can form a coating of high corrosion resistance on its surface. The metal plate having a coating film having a corrosion resistance value can form a coating film having excellent corrosion resistance even when the cationic electrodeposition coating is performed in an electrodeposition bath containing no lead or only a little lead. In addition, according to the chemical conversion treatment method of the present invention, chromium cleaning which is generally performed at the end of the chemical conversion treatment step is not required, and the use of heavy metals can be further reduced.

Claims (12)

A zinc phosphate coating is formed on a metal surface such that the corrosion resistance value of the alternating current method is 2,500 Ωcm 2 or more. The method for chemically treating a base metal useful for a cationic electrodeposition coating having a lead concentration of 300 ppm or less in an electrodeposition bath. The method according to claim 1, wherein the lead concentration in the electrodeposition bath is 100 ppm or less. The method according to claim 1, which is useful for cationic electrodeposition coating in which the lead concentration in the electrodeposition bath is substantially zero. The gallium ion is 0.5 to 1.5 g, the phosphate ion is 5 to 30 g, the nickel ion is 0.1 to 4 g, and the manganese ion is 0.6 to 3 in any one liter of the chemical conversion treatment liquid. g, a method of immersing a metal surface with a chemical conversion treatment solution containing 0.05 g or more of fluorine ions, 5 to 20 ppm of copper ions, and a coating chemical accelerator as a main component. The method of claim 4 wherein the fluorine ion is a complex fluorine ion. 6. A method according to claim 5, wherein complex fluorides are boron fluoride and / or silicon fluoride as the complex fluoride ion source. 5. The film forming accelerator according to claim 4, wherein the nitrite ion is 0.01 to 0.2 g / l, m-nitrobenzenesulfonate ion is 0.05 to 2 g / l, hydrogen peroxide 0.5 to 5 g / l and hydroxylamine 0.1 to 5 g / l. (All represent the concentration in the chemical conversion solution). The method according to claim 4, wherein the chemical conversion solution further contains 1 to 10 g of nitrate ions and 0.05 to 2 g of chlorate ions in 1 L. The method according to any one of claims 1 to 8, wherein the treatment temperature is 30 to 70 ° C. 10. The method according to any one of claims 1 to 9, wherein the dipping treatment is performed by first combining at least 15 dipping treatment followed by at least 2 spraying treatment. The method according to any one of claims 1 to 10, wherein the surface of the base metal has iron-based and zinc-based at the same time. The thickening agent for preparing the chemical conversion treatment liquid of Claim 4 or 8 by dilution with water.