CN110869535A - Treatment method using zinc dephosphorylating treatment agent comprising cationic polyurethane resin and treated automobile part - Google Patents

Abstract

The invention provides a pre-coating treatment method which is not limited by a coating method, has little burden on the environment and can ensure good corrosion resistance after coating on a hot-rolled steel plate. A pretreatment method for coating, which is a pretreatment method for coating for treating a hot-rolled steel sheet with a chemical conversion agent to form a chemical conversion coating, wherein the chemical conversion agent comprises: at least one (A) selected from the group consisting of zirconium, titanium and hafnium; at least one (B) selected from the group consisting of amino group-containing silane coupling agents, hydrolysates thereof, and polymers thereof; fluorine (C); and a cationic urethane resin (D) and (A), the content of (D) and (A) being 20 to 600 ppm by mass in terms of metal, the pH of the chemical conversion treatment agent being 3.5 to 5.5.

Description

Treatment method and treated automobile part using zinc dephosphorization treatment agent containing cationic polyurethane resin

technical field

The invention relates to a pre-coating treatment method and a hot-rolled steel sheet.

Background technique

When performing cationic electrodeposition coating, powder coating, etc. on the surface of a metal material, chemical conversion treatment is generally performed in order to improve properties such as corrosion resistance and coating film adhesion. From the viewpoint of being able to further improve the adhesion and corrosion resistance of the coating film, the harmfulness of chromium has been pointed out in recent years for the chromate treatment that has been used for chemical conversion treatment, and it is necessary to develop a chemical conversion treatment agent that does not contain chromium. As such a chemical conversion treatment, treatment using zinc phosphate is widely performed.

However, the zinc phosphate-based treatment agent is a treatment agent with high metal ion and acid concentration and very strong reactivity, and therefore, the economical efficiency and workability at the time of wastewater treatment are not good. Furthermore, along with the metal surface treatment using a zinc phosphate-based treatment agent, water-insoluble salts are generated and precipitated as precipitates. Such a sediment is generally referred to as a sludge, and there are problems such as a cost of removing and discarding such a sludge. In addition, since phosphate ions may impose a burden on the environment due to eutrophication, labor is required for waste liquid treatment, and it is preferable not to use them. Furthermore, when metal surface treatment is performed using a zinc phosphate-based treatment agent, surface conditioning is required, and there is a problem that the process becomes longer.

As metal surface treatment agents other than such zinc phosphate-based treatment agents or chromate treatment agents, metal surface treatment agents composed of zirconium compounds are known. From the viewpoint of suppressing the generation of sludge, such a metal surface treatment agent composed of a zirconium compound has excellent properties compared with the above-mentioned zinc phosphate-based chemical conversion treatment agent.

However, the chemical conversion film obtained by using the metal surface treating agent composed of a zirconium compound has poor adhesion to the coating film obtained by cationic electrodeposition coating, and is rarely used as a pretreatment step for cationic electrodeposition coating. In such a metal surface treatment agent composed of a zirconium compound, by combining components such as phosphate ions, adhesion improvement and corrosion resistance are improved. However, when a phosphate ion is used together, the problem of eutrophication as mentioned above arises. In addition, when an iron-based base material is treated with such a metal surface treatment agent, there is a problem that sufficient coating film adhesion and corrosion resistance after coating cannot be obtained.

Also known are non-chromate metal surface treatment agents composed of a zirconium compound and an amino group-containing silane coupling agent. However, this non-chromate metal surface treatment agent is a so-called coating-type treatment agent for use in the field of coil coatings, and the surface treatment using this non-chromate metal surface treatment agent cannot be washed with water after treatment, and further, It is also not suitable for processed objects with complex shapes.

Furthermore, it is sometimes necessary to carry out surface treatment of all metals in a single treatment for articles made of various metal materials such as iron, zinc, and aluminum, such as automobile bodies and parts. A pre-coating treatment method that implements chemical conversion treatment. On the other hand, also in coating other than cationic electrodeposition coating using powder coatings, solvent coatings, water-based coatings, etc., it is desired to develop a chemical conversion treatment without causing the above-mentioned problems. preprocessing method.

In order to solve the above-mentioned problems, there is known a pre-painting method for forming a chemical film by treating an object to be treated with a chemical conversion treatment agent containing at least one selected from the group consisting of zirconium, titanium, and hafnium, Fluorine, and at least one selected from the group consisting of an amino group-containing silane coupling agent, a hydrolyzate thereof, and a polymer thereof (for example, refer to Patent Document 1 described later).

According to the above-described pre-coating treatment method, the coating method is not limited, and the same adhesion and post-coating corrosion resistance as when a zinc phosphate-based chemical conversion treatment agent is used can be obtained. However, when it is applied to a hot-rolled steel sheet having an oxide film formed on the surface, which is used for chassis parts of automobiles, etc., it is difficult to ensure sufficient corrosion resistance after painting.

prior art literature

Patent Literature

Patent Document 1: Japanese Patent Laid-Open No. 2004-218070

SUMMARY OF THE INVENTION

The problem to be solved by the invention

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a pre-coating treatment method that can ensure good post-coating corrosion resistance for a hot-rolled steel sheet with less burden on the environment.

methods for solving problems

The present invention relates to a pre-coating treatment method, which is a pre-coating treatment method for forming a chemical film by treating a hot-rolled steel sheet with a chemical conversion treatment agent, wherein the chemical conversion treatment agent contains: a compound selected from the group consisting of zirconium, titanium and hafnium. at least one (A); at least one (B) selected from the group consisting of an amino group-containing silane coupling agent, a hydrolyzate thereof, and a polymer thereof; fluorine (C); and a cationic polyurethane resin (D), The content of the above-mentioned (A) is 20 to 600 mass ppm in total in terms of metal, and the pH of the above-mentioned chemical conversion treatment agent is 3.5 to 5.5.

In addition, the above-mentioned (B) is contained in a total of 5 to 1000 mass ppm in terms of solid content concentration, and 5 to 1000 mass ppm of above-mentioned (D) is contained in terms of solid content concentration, and the above-mentioned (B) is relative to the above-mentioned solid content of (D). The mass ratio ((B)/(D)) is preferably 0.005 to 200.

In addition, it is preferable that the above-mentioned chemical conversion treatment agent further contains at least one adhesion and corrosion resistance imparting agent selected from the group consisting of magnesium ions, zinc ions, calcium ions, aluminum ions, gallium ions, indium ions, and copper ions.

In addition, the present invention relates to a hot-rolled steel sheet treated by the above-described pre-coating treatment method.

Invention effect

According to the present invention, it is possible to provide a pre-coating treatment method which is not limited by the coating method, has a small burden on the environment, and can ensure good corrosion resistance after coating on a hot-rolled steel sheet.

Detailed ways

Hereinafter, embodiments of the present invention will be described. In addition, this invention is not limited to the following embodiment.

The pre-coating treatment method according to the present embodiment forms a chemical film on the surface of a hot-rolled steel sheet (hereinafter, referred to as "hot-rolled steel sheet") as a workpiece, and can secure ideal corrosion resistance after coating. The hot-rolled steel sheet to be processed is not particularly limited, and can be applied to a wide range from general hot-rolled steel sheets to special steels. Such treated hot-rolled steel sheets are widely used for chassis parts of automobiles and the like.

Since the oxide film is formed on the surface of the hot-rolled steel sheet as will be described later, it is difficult to form a uniform chemical conversion film on the surface. However, the pre-coating treatment method according to the present embodiment can form a uniform chemical conversion film on the surface of the hot-rolled steel sheet. Therefore, good corrosion resistance after coating of the treated hot-rolled steel sheet can be ensured.

The pre-coating treatment method according to the present embodiment is a method of treating the hot-rolled steel sheet by forming a chemical conversion film on the surface of the hot-rolled steel sheet using a chemical conversion treatment agent.

The chemical conversion treatment agent according to the present embodiment contains at least one (A) selected from the group consisting of zirconium, titanium, and hafnium, and selected from the group consisting of an amino group-containing silane coupling agent, a hydrolyzate thereof, and a polymer thereof At least one of (B), fluorine (C), and a cationic polyurethane resin (D).

The chemical conversion treatment agent according to the present embodiment is substantially free of phosphate ions and harmful heavy metal ions, but can form a chemical conversion film having sufficient corrosion resistance after painting even on the surface of a hot-rolled steel sheet.

At least one (A) selected from the group consisting of zirconium, titanium and hafnium is a chemical conversion film forming component, and by forming a chemical conversion film containing at least one selected from the group consisting of zirconium, titanium and hafnium on the substrate, As a result, the corrosion resistance and wear resistance of the base material can be improved, and the adhesion with the coating film can be further improved.

For example, when the surface treatment of a hot-rolled steel sheet is performed using a chemical conversion treatment agent containing zirconium, the fluorine of ZrF ₆ ^2- is attracted by iron ions eluted in the chemical conversion treatment agent due to the dissolution reaction of the metal, and the pH of the interface increases. As a result, zirconium hydroxide or oxide is generated, and it is considered that the zirconium hydroxide or oxide precipitates on the surface of the substrate. As described above, since the chemical conversion treatment agent in the present embodiment is a reactive chemical conversion treatment agent, it can also be used for the dipping treatment of a hot-rolled steel sheet having a complicated shape. In addition, when the surface treatment is performed using the above-mentioned chemical conversion treatment agent, a chemical conversion film firmly adhered to the hot-rolled steel sheet due to a chemical reaction can be obtained, and therefore, water washing may be performed after the treatment.

The supply source of the zirconium is not particularly limited, and examples thereof include alkali metal fluorozirconates such as K ₂ ZrF _{6 ;} fluoro zirconates such as (NH ₄ ) ₂ ZrF ₆ and the like _; Zirconate, etc.; zirconium fluoride; zirconium oxide, etc.

The supply source of titanium is not particularly limited, and examples include alkali metal fluorotitanates, fluorotitanates such as (NH ₄ ) ₂ TiF ₆ , etc.; soluble fluoro titanates such as fluoro titanates such as H ₂ TiF ₆ , and the like; Titanium fluoride; titanium oxide, etc.

The supply source of the hafnium is not particularly limited, and examples thereof include fluorohafnium acid such as H ₂ HfF ₆ , and hafnium fluoride. As the supply source of at least one selected from the group consisting of zirconium, titanium, and hafnium, it is preferable to have a material selected from the group consisting of ZrF ₆ ^2- , TiF ₆ ^2- , and HfF ₆ ^2- from the viewpoint of high film forming ability. at least one compound of the group.

The total content of at least one selected from the group consisting of zirconium, titanium, and hafnium contained in the chemical conversion treatment agent according to the present embodiment is within the range of a lower limit of 20 mass ppm and an upper limit of 600 mass ppm in terms of metal. If it is less than 20 mass ppm, the performance of the obtained chemical conversion film is insufficient, and if it exceeds 600 mass ppm, further effects cannot be expected, which is economically disadvantageous. The above lower limit is more preferably 100 mass ppm. The said upper limit is more preferably 500 mass ppm, and still more preferably 300 mass ppm.

At least one (B) selected from the group consisting of an amino group-containing silane coupling agent, a hydrolyzate thereof, and a polymer thereof is a compound having at least one amino group in the molecule and having a siloxane bond. When at least one (B) selected from the group consisting of the amino group-containing silane coupling agent, its hydrolyzate, and its polymer acts on both the chemical conversion film and the coating film, the adhesiveness of both improves.

This effect is presumed to be due to hydrolysis of silanol-producing groups to hydrolyze and hydrogen bond adsorption to the surface of the metal substrate, and improvement of the adhesiveness between the chemical conversion film and the metal substrate due to the action of the amino group. It is considered that at least one (B) selected from the group consisting of an amino group-containing silane coupling agent, a hydrolyzate thereof, and a polymer thereof contained in the chemical-forming film as described above passes through both the metal substrate and the coating film. It has the effect of improving mutual adhesion.

The above-mentioned amino group-containing silane coupling agent is not particularly limited, and examples thereof include N-2(aminoethyl)3-aminopropylmethyldimethoxysilane, N-2(aminoethyl)3-aminopropyl Trimethoxysilane, N-2(aminoethyl)3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilane Alkylsilyl-N-(1,3-dimethyl-butylene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, N,N-bis[3-(trimethoxysilane) (yl)propyl]ethylenediamine and other known silane coupling agents and the like. Commercially available amino group-containing silane coupling agents KBM-602, KBM-603, KBE-603, KBM-903, KBE-9103, KBM-573 (the above are manufactured by Shin-Etsu Chemical Co., Ltd.), XS1003 can also be used (made by Chisso Co., Ltd.), etc.

The hydrolyzate of the above-mentioned amino group-containing silane coupling agent can be produced by a conventionally known method, for example, a method of dissolving the above-mentioned amino group-containing silane coupling agent in ion-exchanged water and adjusting it to be acidic with an arbitrary acid. As the hydrolyzate of the above-mentioned amino group-containing silane coupling agent, commercially available products such as KBP-90 (manufactured by Shin-Etsu Chemical Co., Ltd.: active ingredient 32%) can also be used.

The polymer of the amino group-containing silane coupling agent is not particularly limited, and examples thereof include SILA ACE S-330 (γ-aminopropyltriethoxysilane; manufactured by Chisso Co., Ltd.), SILA ACE S-320 (N -(2-aminoethyl)-3-aminopropyltrimethoxysilane; manufactured by Chisso Co., Ltd.) and other commercially available products.

The total compounding amount of at least one (B) selected from the group consisting of an amino group-containing silane coupling agent, a hydrolyzate thereof, and a polymer thereof in the chemical conversion treatment agent according to the present embodiment is preferably the lower limit in terms of solid content concentration Within the range of 5 mass ppm and the upper limit of 1000 mass ppm. If it is less than 5 mass ppm, sufficient coating film adhesiveness cannot be obtained. If it exceeds 1000 mass ppm, further effects cannot be expected, which is economically disadvantageous. The said lower limit is more preferably 100 mass ppm, and still more preferably 200 mass ppm. The above upper limit is more preferably 400 mass ppm.

Fluorine (C) functions as an etchant for the substrate. The supply source of fluorine (C) is not particularly limited, and examples thereof include fluorides such as hydrofluoric acid, ammonium fluoride, fluoroboric acid, ammonium hydrogen fluoride, sodium fluoride, and sodium hydrogen fluoride. In addition, examples of the complex fluoride include hexafluorosilicate, and specific examples thereof include fluorosilicic acid, zinc fluorosilicate, manganese fluorosilicate, magnesium fluorosilicate, nickel fluorosilicate, and fluorosilicic acid. Iron, calcium fluorosilicate, etc.

The cationic urethane resin (D) forms a uniform chemical film on the surface of the hot-rolled steel sheet as the object to be processed. The cationic urethane resin (D) is a urethane resin having a cationic functional group, and examples of the cationic functional group include amino groups, ammonium salt groups, methylamino groups, ethylamino groups, dimethylamino groups, diethylamino groups, and trimethylamino groups. amino group, triethylamino group, etc., among which quaternary ammonium salt group is preferred.

In addition, the polyol, isocyanate component and polymerization method of the polyurethane resin constituting the cationic polyurethane resin (D) are not particularly limited, and conventionally known components and methods can be used.

As the cationic polyurethane resin (D), for example, F2667D (manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.: effective concentration 25%), SUPERFLEX 620 (manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.: effective concentration 30%), SUPERFLEX 650 (Daiichi Kogyo Co., Ltd.: effective concentration) can be used. Pharmaceutical Co., Ltd.: effective concentration 26%) and other commercially available products.

If the cationic urethane resin (D) is contained only in the chemical conversion treatment agent, the desired effects such as corrosion resistance after painting cannot be obtained. At least one (B) of the group consisting of polymers is contained in the chemical conversion treatment agent, and a uniform chemical conversion film can be formed on the surface of the hot-rolled steel sheet as a to-be-processed object, thereby ensuring ideal post-coating corrosion resistance of the hot-rolled steel sheet sex.

In addition, since the cationic polyurethane resin (D) does not undergo a competitive reaction with at least one selected from the group consisting of the above-mentioned amino group-containing silane coupling agent, its hydrolyzate, and its polymer (B), it is preferably not hindered It is used when the function of the amino group-containing silane coupling agent, its hydrolyzate, and its polymer (B).

It is preferable that the compounding quantity of the cationic polyurethane resin (D) in the chemical conversion treatment agent which concerns on this embodiment exists in the range of a minimum of 5 mass ppm and an upper limit of 1000 mass ppm in solid content concentration. If it is less than 5 mass ppm, sufficient coating film adhesiveness cannot be obtained. If it exceeds 1000 mass ppm, further effects cannot be expected, which is economically disadvantageous. The said lower limit is more preferably 100 mass ppm, and still more preferably 200 mass ppm. The above upper limit is more preferably 400 mass ppm.

In the chemical conversion treatment agent according to the present embodiment, the mass ratio of at least one (B) selected from the group consisting of an amino group-containing silane coupling agent, a hydrolyzate thereof, and a polymer thereof to the cationic urethane resin (D) ((B)/(D)) is preferably 0.005 to 200. By setting the mass ratio ((B)/(D)) to be in the above-mentioned range, ideal corrosion resistance of the hot-rolled steel sheet on which the chemical conversion film is formed can be obtained. The mass ratio ((B)/(D)) is more preferably 0.05 to 20, and even more preferably 0.5 to 2.

The chemical conversion treatment agent according to the present embodiment preferably does not substantially contain phosphate ions. Not substantially containing phosphate ions means that the phosphate ions contained are not enough to act as components in the chemical conversion treatment agent. Since the chemical conversion treatment agent used in this embodiment does not substantially contain phosphate ions, it does not substantially use phosphate ions. Phosphorus, which causes an environmental burden, can suppress the generation of sludge such as iron phosphate, zinc phosphate, etc., which are generated when a zinc phosphate-based treatment agent is used.

The pH of the chemical conversion treatment agent according to the present embodiment is within the range of the lower limit of 3.5 and the upper limit of 5.5. If it is less than 3.5, a sufficient film cannot be formed due to excessive etching. If it exceeds 5.5, etching will become insufficient, and a favorable coating will not be obtained. The said lower limit becomes like this. Preferably it is 3.8, More preferably, it is 4.0. The upper limit is preferably 4.7, and more preferably 4.5. In order to adjust the pH of the chemical conversion treatment agent according to the present embodiment, acidic compounds such as nitric acid and sulfuric acid, and basic compounds such as sodium hydroxide, potassium hydroxide, and ammonia can be used.

The chemical conversion treatment agent according to the present embodiment preferably further contains at least one selected from the group consisting of magnesium ions, zinc ions, calcium ions, aluminum ions, gallium ions, indium ions, and copper ions for imparting adhesion and corrosion resistance. agent. By containing the above-mentioned adhesiveness and corrosion resistance imparting agent, a chemical conversion film having more favorable adhesiveness and corrosion resistance can be obtained.

The content of at least one selected from the group consisting of magnesium ions, zinc ions, calcium ions, aluminum ions, gallium ions, indium ions, and copper ions is preferably within a range of 1 mass ppm as a lower limit and 5000 mass ppm as an upper limit. If the above-mentioned content is less than the above-mentioned lower limit, a sufficient effect cannot be obtained, which is not preferable. If the above-mentioned content exceeds the above-mentioned upper limit, further improvement of the effect cannot be observed, which is economically disadvantageous, and the adhesiveness after painting may also decrease. The said lower limit is more preferably 25 mass ppm, and the said upper limit is more preferably 3000 mass ppm.

In addition to the above-mentioned components, the above-mentioned chemical conversion treatment agent may use arbitrary components in combination as necessary. Silica etc. are mentioned as a component which can be used. By adding such a component, the corrosion resistance after painting can be improved.

＜Pre-painting treatment method＞

The chemical conversion treatment in the coating pre-treatment method according to the present embodiment is not particularly limited, and can be performed by bringing a chemical conversion treatment agent into contact with the surface of the hot-rolled steel sheet under normal processing conditions. The treatment temperature in the above-mentioned chemical conversion treatment is preferably within a range of 20°C as the lower limit and 70°C as the upper limit. The above lower limit is more preferably 30°C, and the above upper limit is more preferably 50°C. The chemical conversion time in the above-mentioned chemical conversion treatment is preferably within the range of the lower limit of 5 seconds and the upper limit of 1200 seconds. The above-mentioned lower limit is more preferably 30 seconds, and the above-mentioned upper limit is more preferably 120 seconds. The chemical conversion treatment method is not particularly limited, and examples thereof include a dipping method, a spray method, a roll coating method, and the like.

In the coating pre-treatment method according to the present embodiment, it is preferable that the surface of the hot-rolled steel sheet is subjected to degreasing treatment and post-degreasing water washing treatment before the above-mentioned chemical conversion treatment, and that the post-chemical conversion treatment is carried out after the above-mentioned chemical conversion treatment.

The above-mentioned degreasing treatment is a step performed to remove oil and stains adhering to the surface of the substrate, and is usually immersed at 30 to 55° C. for several minutes using a degreasing agent such as a phosphorus-free and nitrogen-free degreasing cleaning solution. If necessary, a pre-degreasing treatment may be performed before the degreasing treatment.

The above-mentioned post-degreasing water washing treatment is a treatment performed by performing one or more spray treatments using a large amount of washing water in order to wash the degreasing agent after the degreasing treatment.

The above-mentioned post-chemical washing treatment is performed one or more times so as not to adversely affect the adhesion, corrosion resistance, etc. after various subsequent coatings. In this case, the final water washing is suitably performed with pure water. In this post-chemical washing treatment, either spray washing or immersion washing may be used, and these methods may be combined for washing.

After the above-mentioned post-chemical washing treatment, drying can be carried out according to known methods as necessary, and then various kinds of coating can be carried out.

The pre-coating treatment method according to the present embodiment can eliminate the need for surface conditioning treatment required in the conventionally practical method of treatment using a zinc phosphate-based chemical conversion treatment agent, so that hot-rolled steel sheets can be hot-rolled with fewer steps. chemical processing.

＜Hot rolled steel plate＞

The hot-rolled steel sheet of the present embodiment has a chemical conversion film formed on at least one surface thereof by the pre-coating treatment method according to the present embodiment.

The hot-rolled steel sheet according to the present embodiment is not particularly limited, and can be applied to a wide range from general hot-rolled steel sheets to special steels.

Since the hot-rolled steel sheet is rolled in a temperature range exceeding 800° C., a scale of several μm to several tens of μm is formed on the surface of the steel sheet. Such oxide films are sometimes used after being removed by a treatment such as pickling, and oxide films are sometimes regenerated by heat treatment such as quenching and tempering after pressing or other processing. In addition, since the oxide film itself has corrosion resistance, it is preferable to use chemical conversion treatment in the oxide film. A chemical film is formed on the oxide film.

On the surface of the oxide film formed on such a hot-rolled steel sheet, fine irregularities are formed, and the oxide film further becomes a porous shape having many pores. Therefore, it is very difficult to form a uniform chemical conversion film on the hot-rolled steel sheet on which the oxide film is formed. When the chemical conversion film formed on the surface is non-uniform, a potential difference occurs between the coated portion and the uncoated portion, and a uniform electrodeposition coating film cannot be formed during electrodeposition coating. Therefore, in the conventional pre-painting treatment method using a chemical conversion treatment agent composed of zirconium or the like, it was not possible to ensure post-painting corrosion resistance equivalent to that of a zinc phosphate-based chemical conversion treatment agent.

However, the hot-rolled steel sheet treated by the pre-coating treatment method according to the present embodiment has a uniform chemical conversion film formed on the surface. The hot-rolled steel sheet on which such a uniform chemical film is formed has ideal corrosion resistance after painting.

The mechanism for obtaining such an effect is not clear, but the reason is thought to be as follows. For example, the interaction between the cationic groups of the cationic polyurethane resin (D) contained in the chemical conversion treatment agent and the surface of the steel sheet causes the concave parts and fine particles of the oxide film to be formed. The pores are preferentially covered with the cationic polyurethane resin (D).

In the chemical conversion film formed on the surface of the hot-rolled steel sheet of the present embodiment, the amount of the film is preferably within the range of a lower limit of 0.1 mg/m ² and an upper limit of 500 mg/m ² in terms of the total amount of metals contained in the chemical conversion treatment agent. If it is less than 0.1 mg/m ² , a uniform chemical conversion film cannot be obtained, which is not preferable. If it exceeds 500 mg/m ² , further effects cannot be obtained, which is economically disadvantageous. The above-mentioned lower limit is more preferably 5 mg/m ² , and the above-mentioned upper limit is more preferably 200 mg/m ² .

Laser processing, press processing, etc. are performed on the hot-rolled steel sheet processed by the above-described pre-coating treatment method to obtain metal members which have been shaped according to various applications. Alternatively, the above-described pre-coating treatment method may be applied to a preformed hot-rolled steel sheet. The application of the metal member according to the present embodiment is not particularly limited, but examples of the metal member for automobiles include doors, hoods, roofs, hoods, fenders, trunks, and the like. In addition, metal members used for motorcycles, buses, bicycles, and the like can also be used. From the viewpoints of safety and aesthetics, in the above-mentioned applications requiring high corrosion resistance after painting, it is preferable to use a metal member composed of a hot-rolled steel sheet treated by the pre-painting treatment method according to the present embodiment. .

The coating that can be applied to the hot-rolled steel sheet treated by the pre-coating treatment method according to the present embodiment is not particularly limited, and conventionally known cationic electrodeposition paints, solvent paints, water-based paints, and powder paints can be used. paint for painting. For example, the above-mentioned cationic electrodeposition paint is not particularly limited, and conventionally known cationic electrodeposition paints composed of aminoated epoxy resins, aminoated acrylic resins, sulfonated epoxy resins, and the like can be applied. In particular, since at least one selected from the group consisting of an amino group-containing silane coupling agent, a hydrolyzate thereof, and a polymer thereof is blended in the chemical conversion treatment agent, in order to further improve the adhesion between the electrodeposited coating film and the chemical conversion film , preferably a cationic electrodeposition coating composed of a resin having a functional group showing reactivity or compatibility with an amino group.

The present invention is not limited to the above-described embodiments, and modifications, improvements, and the like within a range that can achieve the object of the present invention are also included in the present invention.

Example

Next, the present invention will be described in further detail based on examples, but the present invention is not limited thereto. In addition, unless otherwise indicated, "ppm" described in an Example and a comparative example means "mass ppm".

<Example 1>

A commercially available hot-rolled steel sheet (SPH270, manufactured by Japan Testpanel Co., Ltd., 70 mm×150 mm×0.8 mm) was used as a base material, and pre-coating treatment was performed under the following conditions.

(1) Pre-coating treatment

Degreasing treatment: Immersion treatment was performed at 40° C. for 2 minutes with 2% by mass of “SURF CLEANER 53” (a degreasing agent manufactured by Japan Paint Surf Chemicals Co., Ltd.).

Water washing treatment after degreasing: spray treatment with tap water for 30 seconds.

Chemical conversion treatment: Using fluorozirconic acid and KBM-603 (N-2(aminoethyl)3-aminopropyltrimethoxysilane as an amino group-containing silane coupling agent: 100% effective concentration: manufactured by Shin-Etsu Chemical Co., Ltd. ), and F2667D (manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.: effective concentration 25%), which is a cationic polyurethane resin, was used to prepare a silane coupling agent (B ) A chemical conversion treatment agent having a concentration of 100 mass ppm and a cationic polyurethane resin (D) concentration of 100 mass ppm. The pH was adjusted to 4 using sodium hydroxide. The temperature of the chemical conversion treatment agent was adjusted to 40° C., and the substrate was immersed for 60 seconds. The amount of the film in the initial stage of the treatment was 13.4 mg/m ² .

Water washing treatment after formation: spray treatment with tap water for 30 seconds. Further, spray treatment was performed with ion-exchanged water for 10 seconds. Then, electrodeposition coating is performed in a wet state. Regarding the amount of film, the cold-rolled steel sheet after the water washing treatment was dried in an electric drying furnace at 80°C for 5 minutes, and then "ZSX Primus II" (X-ray analyzer manufactured by Rigaku Co., Ltd.) was used as the chemical conversion treatment agent. The total amount of metals was analyzed.

(2) Painting

After treating 1 m ² of cold-rolled steel sheet per 1 L of chemical conversion treatment agent, electrodeposition was performed so that the dry film thickness would be 20 μm using “POWERNICS 310” (cationic electrodeposition paint manufactured by Nippon Paint Industrial Coatings). After painting, washing with water, heating at 170° C. for 20 minutes, and sintering, to prepare a test panel.

<Example 2, 3>

A test panel was produced in the same manner as in Example 1, except that a hot-rolled steel sheet (SPH440, SPH590, manufactured by Nippon Testpanel Co., Ltd., 70 mm×150 mm×0.8 mm) was used as a base material.

<Examples 4, 5, 8, 10, 19, 20>

A test panel was produced in the same manner as in Example 1, except that the concentration of the silane coupling agent (B) and the concentration of the cationic urethane resin (D) were respectively the concentrations shown in Table 1.

<Example 6, 7>

As shown in Table 1, SUPERFLEX 620 (manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.: effective concentration 30%) or SUPERFLEX 650 (manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.: effective concentration 26%) was used as the cationic polyurethane resin (D), except Other than that, it carried out similarly to Example 1, and produced the test plate.

<Examples 9, 11, 12>

As shown in Table 1, the concentration of zirconium (A) was set to 100 mass ppm or 500 mass ppm, and KBM-903 (3-aminopropyltrimethoxysilane: effective concentration 100%: manufactured by Shin-Etsu Chemical Co., Ltd.) or XS1003 (N,N-bis[3-(trimethoxysilyl)propyl]ethylenediamine: effective concentration 50%: manufactured by Nippon-American Shoji Co., Ltd.) or KBE-903 (3-aminopropyltriethoxy Silane: effective concentration 100%: manufactured by Shin-Etsu Chemical Co., Ltd.) As the silane coupling agent (B), the silane coupling agent (B) and the cationic urethane resin (D) were set to the concentrations shown in Table 1, except Other than that, it carried out similarly to Example 1, and produced the test plate.

<Examples 13 to 18>

The zirconium (A) concentrations were respectively the concentrations shown in Table 1, zinc nitrate (Zn) was used as the adhesion and corrosion resistance imparting material, and the silane coupling agent (B) and the cationic urethane resin (D) were used. A test plate was produced in the same manner as in Example 1, except that it was the concentration shown in Table 1.

<Comparative Examples 1 to 5>

Except that the concentration of the silane coupling agent (B) and the cationic urethane resin (D) and the hot-rolled steel sheet as the base material are shown in Table 1, a test panel was produced in the same manner as in Example 1.

<Reference Example 1>

As shown in Table 1, after degreasing and washing with water, surface conditioning was performed at room temperature for 30 seconds using SURFFINE GL1 (manufactured by Japan Paint Surfchemals Co., Ltd.) ) in place of the above-mentioned chemical conversion treatment agent, except that the chemical conversion treatment was performed by dipping at 35° C. for 2 minutes, it was carried out in the same manner as in Example 1 to obtain a test plate.

The following evaluation tests were performed using the test panels of Examples 1 to 20, Comparative Examples 1 to 5, and Reference Example 1 obtained as described above.

[Secondary Adhesion Test (SDT)]

The obtained test plate was dipped in a 5% NaCl aqueous solution at 50° C. for 480 hours after two longitudinal parallel cutting lines reaching the substrate were drawn. Then, tape peeling was performed on the cut portion, and peeling of the paint was observed. The peeling state was evaluated according to the following evaluation criteria, and the evaluation 2 or more was made pass. The results are shown in Tables 1 and 2.

1: No peeling

2: Slight peeling

3: The peeling width is more than 3mm

[Salt Spray Test (SST)]

After a cross-cut line up to the substrate was drawn on the obtained test plate, a 5% NaCl aqueous solution was continuously sprayed for 240 hours in a saline spray tester maintained at 35°C. Then, the swelling width from the cut portion was measured. The above-mentioned swelling width was equal to or less than the swelling width in the zinc phosphate-based surface treatment agent shown in Reference Example 1, and was regarded as acceptable. The results are shown in Tables 1 and 2.

[Combined Cyclic Corrosion Test (CCT)]

The composite cyclic corrosion test was carried out after a cross-cut line up to the substrate was drawn on the obtained test panel. Regarding the test method, the composite test was carried out for 100 cycles according to the regulations of JASO M609-91. After the test, the swelling width from the cut portion was measured. The above-mentioned swelling width was equal to or less than the swelling width in the zinc phosphate-based surface treatment agent shown in Reference Example 1, and was regarded as acceptable. The results are shown in Tables 1 and 2.

[Table 1]

From the comparison of Examples 1 to 20 with Comparative Examples 1 to 3 and 5, it can be seen that the hot-rolled steel sheets treated with the chemical conversion treatment agents of Examples 1 to 20 were treated with the chemical conversion treatment agents of Comparative Examples 1 to 3 and 5. Compared with the treated hot-rolled steel sheet, the secondary adhesion (SDT) is excellent. From this result, it was confirmed that the pre-coating treatment of the hot-rolled steel sheet was carried out by using a chemical conversion treatment agent containing at least one (B) selected from the group consisting of an amino group-containing silane coupling agent, a hydrolyzate thereof, and a polymer thereof. , which can impart ideal post-coating corrosion resistance to hot-rolled steel sheets.

In addition, since the hot-rolled steel sheet treated with the chemical conversion treatment agent of Comparative Example 1 and the hot-rolled steel sheet treated with the chemical conversion treatment agent of Comparative Example 5 could not obtain satisfactory secondary adhesion (SDT), the desired secondary adhesion (SDT) was not obtained. It was confirmed that when at least one (B) selected from the group consisting of an amino group-containing silane coupling agent, a hydrolyzate thereof, and a polymer thereof is not contained in the chemical conversion treatment agent, even if the cationic urethane resin (D) is added ) content is not satisfactory, by using at least one (B) selected from the group consisting of an amino group-containing silane coupling agent, a hydrolyzate thereof, and a polymer thereof and a cationic urethane resin (D) The chemical conversion treatment agent used in combination can be used for pre-coating treatment of hot-rolled steel sheets, and can impart ideal post-coating corrosion resistance to hot-rolled steel sheets.

From the comparison between Examples 1 to 20 and Comparative Example 4, it can be seen that the hot-rolled steel sheets treated with the chemical conversion treatment agents of Examples 1 to 20 are less than the hot-rolled steel sheets treated with the chemical conversion treatment agents of Comparative Example 4. The results of the combined cyclic corrosion test (CCT) were excellent. From this result, it was confirmed that by pre-coating the hot-rolled steel sheet with the chemical conversion treatment agent containing the cationic urethane resin (D), the hot-rolled steel sheet can be provided with ideal post-coating corrosion resistance.

From the comparison between Examples 1 to 20 and Reference Example 1, it can be seen that the hot-rolled steel sheets treated with the chemical conversion treatment agents of Examples 1 to 20 are equivalent to those treated with the chemical conversion treatment agents of Reference Example 1. The results of the above salt spray test (SST) and combined cyclic corrosion test (CCT). From this result, it was confirmed that, according to the pre-coating treatment method using the chemical conversion treatment agent of the present invention, it was possible to provide a hot-rolled steel sheet with an excellent coating equal to or higher than that of the conventional pre-coating treatment method using a zinc phosphate-based treatment agent. Corrosion resistance after installation.

Claims (4)

1. A method of pretreatment before coating for treating a hot-rolled steel sheet with a chemical conversion agent to form a chemical conversion coating,

the chemical conversion treatment agent comprises: at least one (A) selected from the group consisting of zirconium, titanium and hafnium; at least one (B) selected from the group consisting of amino group-containing silane coupling agents, hydrolysates thereof, and polymers thereof; fluorine (C); and a cationic urethane resin (D),

the content of (A) is 20 to 600 mass ppm in terms of metal,

the pH value of the chemical conversion treatment agent is 3.5-5.5.

2. The pretreatment for coating according to claim 1, wherein the total amount of the (B) is 5 to 1000 mass ppm in terms of solid content,

the amount of the (D) is 5 to 1000 mass ppm in terms of solid content,

the mass ratio of the solid component of (B) to the solid component of (D), (B)/(D), is 0.005 to 200.

3. The pretreatment before coating treatment method according to claim 1 or 2, wherein the chemical conversion treatment agent further contains at least one of an adhesion and corrosion resistance imparting agent selected from the group consisting of magnesium ions, zinc ions, calcium ions, aluminum ions, gallium ions, indium ions, and copper ions.

4. A hot-rolled steel sheet treated by the pretreatment for painting described in any one of claims 1 to 3.