JP2019019357A - Treatment method using de-zinc phosphate treatment agent containing cationic urethane resin and treated automobile component - Google Patents

Abstract

To provide a coating pretreatment method that is not limited in coating methods, has reduced environmental load, and can ensure excellent post-coating corrosion resistance for a hot-rolled steel plate.SOLUTION: The present invention provides a coating pretreatment method including treating a hot-rolled steel plate with a chemical conversion treatment agent to form a chemical coating. The chemical conversion treatment agent contains at least one selected from the group consisting of zirconium, titanium and hafnium (A), at least one selected from the group consisting of an amino group-containing silane coupling agent, its hydrolysate and its polymer (B), fluorine (C), and cationic urethane resin (D), with the content of (A) being a total of 20-600 mass ppm in terms of metal, and the pH being 3.5-5.5.SELECTED DRAWING: None

Description

  The present invention relates to a coating pretreatment method and a hot-rolled steel sheet.

  When cationic electrodeposition coating, powder coating or the like is applied to the surface of a metal material, chemical conversion treatment is usually performed for the purpose of improving properties such as corrosion resistance and coating film adhesion. The chromate treatment that has been used in the chemical conversion treatment from the viewpoint of further improving the adhesion and corrosion resistance of the coating film has recently been pointed out to be harmful to chromium, and it does not contain chromium. Development has been needed. As such chemical conversion treatment, treatment with zinc phosphate is widely performed.

  However, since the zinc phosphate-based treatment agent is a highly reactive treatment agent having a high concentration of metal ions and acid, the economical efficiency and workability in wastewater treatment are not good. Further, accompanying the metal surface treatment with the zinc phosphate-based treatment agent, water-insoluble salts are generated and precipitated as precipitates. Such precipitates are generally called sludge, and there is a problem of cost generation due to removal and disposal of such sludge. Moreover, since phosphate ion may give a load to the environment due to eutrophication, it requires labor in the treatment of waste liquid and is preferably not used. Furthermore, in the metal surface treatment with a zinc phosphate-based treatment agent, it is necessary to adjust the surface, and there is a problem that the process becomes long.

  Metal surface treatment agents composed of zirconium compounds are known as metal surface treatment agents other than such zinc phosphate-based treatment agents or chromate chemical conversion treatment agents. The metal surface treatment agent comprising such a zirconium compound has properties superior to the zinc phosphate chemical conversion treatment agent described above in that the generation of sludge is suppressed.

  However, the chemical conversion film obtained with a metal surface treatment agent comprising a zirconium compound has poor adhesion particularly with a coating film obtained by cationic electrodeposition coating, and is usually used as a pretreatment step for cationic electrodeposition coating. There were few. In such a metal surface treatment agent composed of a zirconium compound, improvement in adhesion and corrosion resistance are performed by using a component such as phosphate ion in combination. However, when phosphate ions are used in combination, the problem of eutrophication as described above occurs. Moreover, when processing an iron-type base material with such a metal surface treating agent, there existed a problem that sufficient adhesiveness of a coating film and corrosion resistance after coating were not obtained.

  A non-chromate metal surface treatment agent comprising a zirconium compound and an amino group-containing silane coupling agent is also known. However, such a non-chromate metal surface treatment agent is a coating type treatment agent for use in the field of coil coating, and the surface treatment using the non-chromate metal surface treatment agent cannot be washed with water after treatment and has a complicated shape. It was not supposed to be processed.

  In addition, it may be necessary to perform surface treatment of all metals in a single treatment on articles made of various metal materials such as automobile bodies and parts such as iron, zinc, and aluminum. There is a demand for the development of a coating pretreatment method that can perform chemical conversion treatment without any problem. On the other hand, it is also desired to develop a pretreatment method capable of performing chemical conversion treatment without causing the above-mentioned problems even in coatings other than cationic electrodeposition coating using powder coating, solvent coating, aqueous coating, and the like.

  In order to solve the above problem, 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. A coating pretreatment method is known in which an object to be treated is treated with a chemical conversion treatment agent to form a chemical conversion film (see, for example, Patent Document 1 described later).

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

Japanese Patent Application Laid-Open No. 2004-218070

  The present invention has been made in view of the above, and an object of the present invention is to provide a coating pretreatment method that has a low environmental burden and can ensure good post-coating corrosion resistance for hot-rolled steel sheets.

  The present invention is a pre-coating treatment method for treating a hot-rolled steel sheet with a chemical conversion treatment agent to form a chemical conversion film, wherein the chemical conversion treatment agent is at least one selected from the group consisting of zirconium, titanium, and hafnium (A). And 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 urethane resin (D), Content of said (A) is 20-600 mass ppm in total in conversion of a metal, and relates to the coating pre-processing method whose pH is 3.5-5.5.

  Moreover, the said (B) contains 5-1000 mass ppm in total with a solid content concentration, The said (D) contains 5-1000 mass ppm with a solid content concentration, The solid content mass of the said (B) with respect to said (D) The ratio ((B) / (D)) is preferably 0.005 to 200.

  The chemical conversion treatment agent may further contain 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. preferable.

  Moreover, this invention relates to the hot-rolled steel plate processed by the said coating pre-processing method.

  ADVANTAGE OF THE INVENTION According to this invention, the coating method is not limited, There is little load to an environment, and the coating pre-processing method which can ensure favorable post-painting corrosion resistance with respect to a hot-rolled steel plate can be provided.

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

The pre-painting treatment method according to the present embodiment forms a chemical conversion film on the surface of a hot-rolled steel sheet (hereinafter referred to as “hot-rolled steel sheet”) that is an object to be processed, and can ensure preferable post-coating corrosion resistance. It does not restrict | limit especially as a hot-rolled steel plate which is a to-be-processed object, It can apply to a wide range from a general hot-rolled steel plate to special steel. Such a processed hot-rolled steel sheet is widely used for automobile undercarriage parts and the like.
Since the hot-rolled steel sheet has an oxide film formed on the surface as described later, it is difficult to form a uniform chemical conversion film on the surface. However, the coating pretreatment method according to this embodiment can form a uniform chemical conversion film on the surface of a hot-rolled steel sheet. Therefore, good post-coating corrosion resistance of the treated hot-rolled steel sheet can be ensured.

The coating pretreatment method according to the present embodiment is a method of forming a chemical conversion film on the surface of a hot-rolled steel sheet with a chemical conversion treatment agent and treating the hot-rolled steel sheet.
The chemical conversion treatment agent according to this embodiment is selected from the group consisting of at least one (A) selected from the group consisting of zirconium, titanium, and hafnium, and an amino group-containing silane coupling agent, a hydrolyzate thereof, and a polymer thereof. At least 1 type (B), a fluorine (C), and a cationic urethane resin (D) are contained.
The chemical conversion treatment agent according to this embodiment is a chemical conversion treatment agent that does not substantially contain phosphate ions or harmful heavy metal ions, but a chemical conversion film having sufficient post-coating corrosion resistance on the surface of a hot-rolled steel sheet. Can be formed.

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

For example, when a surface treatment of a hot-rolled steel sheet is performed using a chemical conversion treatment agent containing zirconium, iron ions eluted in the chemical conversion treatment agent by metal dissolution reaction extract ZrF ₆ ²⁻ fluorine, It is considered that the zirconium hydroxide or oxide is generated by the increase in the interface pH, and this zirconium hydroxide or oxide is precipitated 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 immersion treatment of hot-rolled steel sheets having a complicated shape. In addition, when the surface treatment is performed using the chemical conversion treatment agent, a chemical conversion film firmly attached to the hot-rolled steel sheet is obtained by a chemical reaction, so that it can be washed with water after the treatment.

The zirconium source is not particularly limited, and examples thereof include alkali metal fluorozirconates such as K ₂ ZrF ₆ ; fluorozirconates such as (NH ₄ ) ₂ ZrF ₆ ; fluorozirconate acids such as H ₂ ZrF _6, etc. And soluble fluorozirconate, etc .; zirconium fluoride; zirconium oxide and the like.

The titanium source is not particularly limited. For example, alkali metal fluorotitanate, fluorotitanate such as (NH ₄ ) ₂ TiF ₆ ; soluble fluorotitanate such as fluorotitanate such as H ₂ TiF _6, etc .; titanium fluoride A titanium oxide can be mentioned.

The source of hafnium is not particularly limited, and examples thereof include fluorohafnate acids such as H ₂ HfF ₆ ; hafnium fluoride.
The at least one source selected from the group consisting of zirconium, titanium and hafnium is at least one selected from the group consisting of ZrF ₆ ²⁻ , TiF ₆ ²⁻ , and HfF ₆ ²⁻ due to high film forming ability. The compound which has is preferable.

  The total of at least one content selected from the group consisting of zirconium, titanium, and hafnium contained in the chemical conversion treating agent according to the present embodiment is in the range of a lower limit of 20 ppm by mass and an upper limit of 600 ppm by mass. If it is less than 20 ppm by mass, the resulting chemical conversion film has insufficient performance. If it exceeds 600 ppm by mass, no further effect can be expected, which is economically disadvantageous. The lower limit is more preferably 100 ppm by mass. The upper limit is more preferably 500 ppm by mass, and still more preferably 300 ppm by mass.

  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, the hydrolyzate thereof, and the polymer thereof acts on both the chemical conversion film and the coating film, the adhesion between them is improved.

  Such an effect is that the group that hydrolyzes to produce silanol is hydrolyzed and adsorbed on the surface of the metal substrate in a hydrogen bond manner, and the adhesion between the chemical conversion film and the metal substrate is caused by the action of the amino group. Presumed to be due to increase. As mentioned above, at least one (B) selected from the group consisting of the amino group-containing silane coupling agent, its hydrolyzate and its polymer contained in the chemical conversion film acts on both the metal substrate and the coating film. It is thought that it has the effect | action which improves mutual adhesiveness.

  The amino group-containing silane coupling agent is not particularly limited. For example, N-2 (aminoethyl) 3-aminopropylmethyldimethoxysilane, N-2 (aminoethyl) 3-aminopropyltrimethoxysilane, N-2 (Aminoethyl) 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N- (1,3-dimethyl-butylidene) propylamine, N- Well-known silane coupling agents such as phenyl-3-aminopropyltrimethoxysilane and N, N-bis [3- (trimethoxysilyl) propyl] ethylenediamine can be exemplified. Commercially available amino group-containing silane coupling agents such as KBM-602, KBM-603, KBE-603, KBM-903, KBE-9103, KBM-573 (manufactured by Shin-Etsu Chemical Co., Ltd.), XS1003 (Chisso Corporation) Etc.) can also be used.

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

  The polymer of the amino group-containing silane coupling agent is not particularly limited. For example, Silaace S-330 (γ-aminopropyltriethoxysilane; manufactured by Chisso Corporation), Silaace S-320 (N- (2-amino) Ethyl) -3-aminopropyltrimethoxysilane; manufactured by Chisso Corporation).

  In the chemical conversion treating agent according to the present embodiment, the total 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 is a lower limit of 5 mass in terms of solid content concentration. It is preferable to be within the range of ppm and an upper limit of 1000 mass ppm. If it is less than 5 mass ppm, sufficient coating film adhesion cannot be obtained. If it exceeds 1000 ppm by mass, no further effect can be expected, which is economically disadvantageous. The lower limit is more preferably 100 ppm by mass, and still more preferably 200 ppm by mass. The upper limit is more preferably 400 ppm by mass.

  Fluorine (C) plays a role as an etching agent for the substrate. The source of fluorine (C) is not particularly limited, and examples thereof include fluorides such as hydrofluoric acid, ammonium fluoride, boron fluoride acid, ammonium hydrogen fluoride, sodium fluoride, and sodium hydrogen fluoride. Can do. Examples of the complex fluoride include hexafluorosilicate, and specific examples thereof include hydrofluoric acid, zinc silicofluoride, manganese silicofluoride, magnesium silicofluoride, and hydrosilicofluoride. Examples thereof include nickel, iron silicohydrofluorate, and calcium silicohydrofluoride.

The cationic urethane resin (D) forms a uniform chemical conversion film on the surface of the hot-rolled steel sheet that is 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 an amino group, an ammonium base, a methylamino group, an ethylamino group, a dimethylamino group, a diethylamino group, Examples thereof include a trimethylamino group and a triethylamino group, and among them, a quaternary ammonium base is preferable.
Moreover, the polyol, isocyanate component, and polymerization method which comprise the urethane resin of cationic urethane resin (D) are not specifically limited, A conventionally well-known component and method are used.
Examples of the cationic urethane resin (D) include F2667D (Daiichi Kogyo Seiyaku Co., Ltd .: effective concentration 25%), Superflex 620 (Daiichi Kogyo Seiyaku Co., Ltd .: effective concentration 30%), Superflex 650 ( Commercial products such as those manufactured by Daiichi Kogyo Seiyaku Co., Ltd .: effective concentration 26%) can be used.

Although the cationic urethane resin (D) is not contained in the chemical conversion treatment agent, preferable effects such as post-coating corrosion resistance cannot be obtained. However, the amino group-containing silane coupling agent, its hydrolyzate and its polymer are obtained. When contained in the chemical conversion treatment agent together with at least one selected from the group consisting of (B), a uniform chemical conversion film is formed on the surface of the hot-rolled steel sheet, which is an object to be treated, and preferable anticorrosion properties after coating of the hot-rolled steel sheet Is secured.
Further, since the cationic urethane resin (D) does not undergo a competitive reaction with at least one selected from the group consisting of the amino group-containing silane coupling agent, a hydrolyzate thereof, and a polymer (B) thereof, It is preferably used without inhibiting the functions of the group-containing silane coupling agent, its hydrolyzate and its polymer (B).

  The compounding amount of the cationic urethane resin (D) in the chemical conversion treating agent according to the present embodiment is preferably in the range of a lower limit of 5 ppm by mass and an upper limit of 1000 ppm by mass in terms of solid content. If it is less than 5 mass ppm, sufficient coating film adhesion cannot be obtained. If it exceeds 1000 ppm by mass, no further effect can be expected, which is economically disadvantageous. The lower limit is more preferably 100 ppm by mass, and still more preferably 200 ppm by mass. The upper limit is more preferably 400 ppm by mass.

  In the chemical conversion treatment agent according to this embodiment, 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 mass ratio of the cationic urethane resin (D) ((B) / (D)) is preferably 0.005 to 200. By making mass ratio ((B) / (D)) into the said range, the preferable corrosion resistance of the hot-rolled steel plate in which the chemical conversion film was formed is obtained. The mass ratio ((B) / (D)) is more preferably 0.05 to 20, and further preferably 0.5 to 2.

  It is preferable that the chemical conversion treatment agent according to the present embodiment contains substantially no phosphate ions. The phrase “substantially free of phosphate ions” means that the phosphate ions are not included so much as to act as a component in the chemical conversion treatment agent, and the chemical conversion treatment agent used in the present embodiment is substantially phosphorus. Because it does not contain acid ions, it does not substantially use phosphorus, which causes environmental burdens, and sludge such as iron phosphate, zinc phosphate, etc. generated when using a zinc phosphate-based treatment agent Can be suppressed.

  In the chemical conversion treatment agent according to the present embodiment, the pH is in the range of the lower limit 3.5 and the upper limit 5.5. If it is less than 3.5, etching becomes excessive and a sufficient film cannot be formed. If it exceeds 5.5, etching becomes insufficient and a good film cannot be obtained. The lower limit is preferably 3.8 and more preferably 4.0. The upper limit is preferably 4.7, and more preferably 4.5. In order to adjust the pH of the chemical conversion treating agent according to this 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 this embodiment 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 as an adhesion and corrosion resistance imparting agent. It is preferable. By containing the adhesion and corrosion resistance imparting agent, a chemical conversion film having better adhesion and corrosion resistance can be obtained.

  The content of at least one selected from the group consisting of the magnesium ion, zinc ion, calcium ion, aluminum ion, gallium ion, indium ion and copper ion is within the range of the lower limit of 1 mass ppm and the upper limit of 5000 mass ppm. preferable. If the content is less than the lower limit, a sufficient effect cannot be obtained, which is not preferable. When the content exceeds the above upper limit, no further improvement in the effect is observed, which is economically disadvantageous, and the adhesion after coating may be reduced. The lower limit is more preferably 25 ppm by mass, and the upper limit is more preferably 3000 ppm by mass.

  The said chemical conversion treatment agent may use arbitrary components together as needed other than the said component. Examples of components that can be used include silica. By adding such components, it is possible to improve post-coating corrosion resistance.

<Pre-painting method>
The chemical conversion treatment in the coating pretreatment method according to the present embodiment is not particularly limited, and can be performed by bringing the chemical conversion treatment agent and the hot-rolled steel sheet surface into contact with each other under normal processing conditions. The treatment temperature in the chemical conversion treatment is preferably in the range of a lower limit of 20 ° C. and an upper limit of 70 ° C. The lower limit is more preferably 30 ° C, and the upper limit is more preferably 50 ° C. The chemical conversion time in the chemical conversion treatment is preferably in the range of a lower limit of 5 seconds and an upper limit of 1200 seconds. The lower limit is more preferably 30 seconds, and the 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, and a roll coating method.

In the pre-coating treatment method according to the present embodiment, before performing the chemical conversion treatment, the surface of the hot-rolled steel sheet is subjected to degreasing treatment, post-degreasing water washing treatment, and after the chemical conversion treatment, post-chemical conversion water washing treatment is performed. preferable.
The degreasing treatment is performed to remove oil and dirt adhering to the surface of the base material, and usually with a degreasing agent such as phosphorus-free and nitrogen-free degreasing cleaning liquid at about 30 to 55 ° C. for about several minutes. Immersion treatment is performed. If desired, a preliminary degreasing process can be performed before the degreasing process.

The post-degreasing rinsing treatment is performed by performing spraying once or more with a large amount of rinsing water in order to wash the degreaser after the degreasing treatment.
The post-chemical conversion water-washing treatment is performed once or more so as not to adversely affect the adhesion, corrosion resistance, and the like after the subsequent various coatings. In this case, it is appropriate that the final water washing is performed with pure water. In this post-chemical conversion water washing treatment, either spray water washing or immersion water washing may be used, and these methods may be combined for water washing.
After the post-chemical conversion water-washing treatment, it can be dried as necessary according to a known method, and thereafter various coatings can be performed.

  The coating pretreatment method according to the present embodiment does not have to perform the necessary surface adjustment treatment in the method of treating using a zinc phosphate-based chemical conversion treatment agent that has been practically used in the past. It is possible to carry out the chemical conversion treatment of the hot-rolled steel sheet with a small number of processes.

<Hot rolled steel sheet>
The hot-rolled steel sheet of the present embodiment has a chemical conversion film formed on at least one surface by the pre-coating treatment method according to the present embodiment.
The hot-rolled steel sheet according to this embodiment is not particularly limited, and can be applied to a wide range from a general hot-rolled steel sheet to a special steel.

Since a hot-rolled steel sheet is rolled in a temperature range exceeding 800 ° C., a thick oxide film (scale) of several μm to several tens μm is formed on the surface of the steel sheet. Such an oxide film may be used after being removed by a treatment such as pickling, but the oxide film may be generated again by a heat treatment such as quenching or tempering after processing such as pressing. In addition, since the oxide film itself has corrosion resistance, it is preferable to form a chemical conversion film on the oxide film by chemical conversion treatment.
Fine irregularities are formed on the surface of the oxide film formed on such a hot-rolled steel sheet, and the oxide film is porous with a large number of pores. For this reason, it is very difficult to form a uniform chemical conversion film on a hot-rolled steel sheet on which an oxide film is formed. When the chemical conversion film formed on the surface is non-uniform, a potential difference occurs between the coated part and the non-coated part, and a uniform electrodeposition coating film cannot be formed when electrodeposition coating is performed. Therefore, the conventional coating pretreatment method using a chemical conversion treatment agent composed of zirconium or the like cannot ensure post-coating corrosion resistance equivalent to that of a zinc phosphate chemical conversion treatment agent.
However, the hot-rolled steel sheet treated by the coating pretreatment method according to the present embodiment has a uniform chemical conversion film formed on the surface. A hot-rolled steel sheet on which such a uniform chemical conversion film is formed has preferable post-coating corrosion resistance.

  Although the mechanism by which such an effect is obtained is not certain, for example, due to the interaction between the cationic group of the cationic urethane resin (D) contained in the chemical conversion treatment agent and the surface of the steel sheet, the recesses and fineness of the oxide film can be obtained. It is considered that the pores are preferentially coated with the cationic urethane resin (D).

Conversion coating is formed on the hot-rolled steel sheet of the present embodiment, the lower limit 0.1 mg / m 2 in a total amount of metal coating weight is comprised chemical conversion treatment ^agent, in a range of the upper limit 500 mg / m ² preferable. 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 , no further effect is obtained, which is economically disadvantageous. The lower limit is more preferably 5 mg / m ² , and the upper limit is more preferably 200 mg / m ² .

  By performing laser processing, pressing, or the like on the hot-rolled steel sheet processed by the pre-painting method, a metal member molded according to various applications can be obtained. Or you may apply the said coating pre-processing method with respect to the hot-rolled steel plate previously shape-processed. Although it does not restrict | limit especially as a use of the metal member which concerns on this embodiment, A door, a bonnet, a roof, a hood, a fender, a trunk etc. are mentioned as a metal member for motor vehicles. Moreover, the metal member used for a motorcycle, a bus | bath, a bicycle etc. can also be mentioned. In the above applications where high post-coating corrosion resistance is required from the viewpoint of safety and aesthetics, a metal member made of a hot-rolled steel sheet treated by the pre-painting treatment method according to this embodiment is preferably used.

  The coating that can be performed on the hot-rolled steel sheet treated by the pre-painting treatment method according to the present embodiment is not particularly limited, and a conventionally known coating such as a cationic electrodeposition coating, a solvent coating, a water-based coating, or a powder coating. Painting using paint can be performed. For example, the cationic electrodeposition coating is not particularly limited, and a conventionally known cationic electrodeposition coating made of an aminated epoxy resin, an aminated acrylic resin, a sulfoniumated epoxy resin, or the like can be applied. Among them, the chemical conversion treatment agent is blended with at least one selected from the group consisting of an amino group-containing silane coupling agent, a hydrolyzate thereof, and a polymer thereof, thereby further improving the adhesion between the electrodeposition coating film and the conversion coating film. Therefore, a cationic electrodeposition paint made of a resin having a functional group showing reactivity or compatibility with an amino group is preferable.

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

  Next, the present invention will be described in more detail based on examples, but the present invention is not limited thereto. Unless otherwise specified, “ppm” in Examples and Comparative Examples indicates “mass ppm”.

<Example 1>
Using a commercially available hot-rolled steel sheet (SPH270, Nippon Test Panel Co., Ltd., 70 mm × 150 mm × 0.8 mm) as a base material, a coating pretreatment was performed under the following conditions.
(1) Pre-coating treatment Degreasing treatment: 2% by mass “Surf Cleaner 53” (Nippon Paint Surf Chemicals Co., Ltd., degreasing agent) was immersed at 40 ° C. for 2 minutes.
Washing with water after degreasing: spraying with tap water for 30 seconds.
Chemical conversion treatment: using KBM-603 (N-2 (aminoethyl) 3-aminopropyltrimethoxysilane: effective concentration 100%: manufactured by Shin-Etsu Chemical Co., Ltd.) as a zircon hydrofluoric acid and amino group-containing silane coupling agent Moreover, F2667D (Daiichi Kogyo Seiyaku Co., Ltd .: effective concentration 25%) is used as the cationic urethane resin, the zirconium (A) concentration is 100 mass ppm, and the amino group-containing silane coupling agent (B) concentration is as the solid content. A chemical conversion treatment agent having 100 mass ppm and a cationic urethane resin (D) concentration of 100 mass ppm was prepared. The pH was adjusted to 4 using sodium hydroxide. The temperature of the chemical conversion treatment agent was adjusted to 40 ° C., and the base material was immersed for 60 seconds. The coating amount at the initial stage of the treatment was 13.4 mg / m ² .

  Water treatment after chemical conversion: Sprayed with tap water for 30 seconds. Furthermore, it spray-processed for 10 second with ion-exchange water. Then, electrodeposition coating was performed in a wet state. The amount of film is included in the chemical conversion treatment agent using “ZSX Primus II” (X-ray analyzer manufactured by Rigaku Corporation) after drying the cold-rolled steel sheet after water washing treatment at 80 ° C. for 5 minutes in an electric drying furnace. The total amount of metal was analyzed.

(2) Coating After processing 1 m ² of cold-rolled steel sheet per liter of chemical conversion treatment agent, use “Powernics 310” (Cation Electrodeposition Paint manufactured by Nippon Paint Industrial Coatings Co., Ltd.) so that the dry film thickness becomes 20 μm. After electrodeposition coating, washing with water and baking at 170 ° C. for 20 minutes, a test plate was prepared.

<Examples 2 and 3>
A test plate was prepared in the same manner as in Example 1 except that a hot-rolled steel plate (SPH440, SPH590, manufactured by Nippon Test Panel Co., Ltd., 70 mm × 150 mm × 0.8 mm) was used as the substrate.

<Examples 4, 5, 8, 10, 19, 20>
A test plate was prepared in the same manner as in Example 1 except that the silane coupling agent (B) concentration and the cationic urethane resin (D) concentration were changed to the concentrations shown in Table 1, respectively.

<Examples 6 and 7>
As shown in Table 1, Superflex 620 (Daiichi Kogyo Seiyaku Co., Ltd .: effective concentration 30%) or Superflex 650 (Daiichi Kogyo Seiyaku Co., Ltd .: effective concentration 26%) is used as the cationic urethane resin (D). A test plate was prepared in the same manner as in Example 1 except that it was used.

<Examples 9, 11, and 12>
As shown in Table 1, zirconium (A) concentration is 100 mass ppm or 500 mass ppm, and silane coupling agent (B) is KBM-903 (3-aminopropyltrimethoxysilane: effective concentration 100%: Shin-Etsu Chemical Co., Ltd. Or XS1003 (N, N-bis [3- (trimethoxysilyl) propyl] ethylenediamine: effective concentration 50%: manufactured by Himi Corporation) or KBE-903 (3-aminopropyltriethoxysilane: effective concentration) 100%: Shin-Etsu Chemical Co., Ltd. was used, and the test plate was prepared in the same manner as in Example 1 except that the silane coupling agent (B) and the cationic urethane resin (D) had the concentrations shown in Table 1. Created.

<Examples 13 to 18>
Zirconium (A) concentration is set as shown in Table 1, zinc nitrate (Zn) is used as adhesion and corrosion resistance imparting material, and silane coupling agent (B) and cationic urethane resin (D) are shown in Table 1. A test plate was prepared in the same manner as in Example 1 except that the concentration was changed.

<Comparative Examples 1-5>
A test plate was prepared in the same manner as in Example 1 except that the silane coupling agent (B) and cationic urethane resin (D) concentrations and the hot-rolled steel plate as the substrate were as shown in Table 1.

<Reference Example 1>
As shown in Table 1, after degreasing and washing with water, surface adjustment was performed at room temperature for 30 seconds using Surffine GL1 (manufactured by Nippon Paint Surf Chemicals Co., Ltd.), and Surfdyne SD-5350 ( A test plate was obtained in the same manner as in Example 1 except that the chemical conversion treatment was performed by performing immersion treatment at 35 ° C. for 2 minutes using Nippon Paint Surf Chemicals Co., Ltd. It was.

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

[Secondary adhesion test (SDT)]
Two vertical and parallel cuts reaching the substrate were put in the obtained test plate, and then immersed in a 5% NaCl aqueous solution at 50 ° C. for 480 hours. Thereafter, the cut part was peeled off with tape, and the peeling of the paint was observed. The peeled state was evaluated according to the following evaluation criteria, and an evaluation of 2 or more was regarded as acceptable. The results are shown in Tables 1 and 2.
1: No peeling 2: Slight peeling 3: Peeling width 3 mm or more

[Salt spray test (SST)]
A crosscut reaching the substrate was put on the obtained test plate, and then a 5% NaCl aqueous solution was continuously sprayed for 240 hours in a salt spray tester maintained at 35 ° C. Thereafter, the swollen width from the cut portion was measured. A bulge width equal to or less than the bulge width in the zinc phosphate surface treatment agent shown in Reference Example 1 was regarded as acceptable. The results are shown in Tables 1 and 2.

[Composite cycle corrosion test (CCT)]
The obtained test plate was subjected to a combined cycle corrosion test after making a cross cut reaching the substrate. As the test method, 100 cycles of the combined test were carried out according to JASO M609-91. After the test, the swollen width from the cut portion was measured. A bulge width equal to or less than the bulge width in the zinc phosphate surface treatment agent shown in Reference Example 1 was regarded as acceptable. The results are shown in Tables 1 and 2.

From the comparison between Examples 1-20 and Comparative Examples 1-3, 5, the hot-rolled steel sheet treated with the chemical conversion treatment agent of Examples 1-20 is the chemical conversion treatment of Comparative Examples 1-3, 5. It was found that the secondary adhesiveness (SDT) was excellent as compared with the hot-rolled steel sheet treated with the agent. From this result, by performing the coating pretreatment of the hot-rolled steel sheet with 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. It was confirmed that the post-coating corrosion resistance can be imparted to the hot-rolled steel sheet.
Moreover, neither the hot-rolled steel plate processed with the chemical conversion treatment agent of Comparative Example 1 nor the hot-rolled steel plate processed with the chemical conversion treatment agent of Comparative Example 5 can obtain a preferable secondary adhesion (SDT). Therefore, in the case where the chemical conversion treatment agent does not contain at least one (B) selected from the group consisting of an amino group-containing silane coupling agent, a hydrolyzate thereof, and a polymer thereof, the inclusion of the cationic urethane resin (D) Even if the amount is increased, a preferable result is not obtained, and 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) It was confirmed that the pre-coating corrosion resistance preferred for the hot-rolled steel sheet can be imparted to the hot-rolled steel sheet by performing the pre-coating treatment of the hot-rolled steel sheet with the chemical conversion treatment agent.

  From the comparison with Examples 1-20 and Comparative Example 4, the hot-rolled steel sheet treated with the chemical conversion treatment agent of Examples 1-20 was treated with the chemical conversion treatment agent of Comparative Example 4. It was found that the results of the combined cycle corrosion test (CCT) were superior to those of the steel plate. From this result, it was confirmed that the pre-painting corrosion resistance can be imparted to the hot-rolled steel sheet by pre-coating the hot-rolled steel sheet with the chemical conversion treatment agent containing the cationic urethane resin (D).

  From a comparison between Examples 1-20 and Reference Example 1, the hot-rolled steel sheet treated with the chemical conversion treatment agent of Examples 1-20 is a hot-rolled steel sheet treated with the chemical conversion treatment agent of Reference Example 1. On the other hand, it was found that the results of the salt spray test (SST) and the combined cycle corrosion test (CCT) equivalent to or higher were obtained. From this result, according to the coating pretreatment method using the chemical conversion treatment agent of the present invention, the hot-rolled steel sheet has excellent post-coating corrosion resistance equivalent to or better than the conventional coating pretreatment method using a zinc phosphate-based treatment agent. It was confirmed that it could be granted.

Claims (4)

A pre-painting treatment method for treating a hot-rolled steel sheet with a chemical conversion treatment agent to form a chemical conversion film,
The chemical conversion treatment agent is at least one selected from the group consisting of zirconium, titanium and hafnium (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),
A cationic urethane resin (D),
Content of said (A) is 20-600 mass ppm in total in conversion of a metal,
A coating pretreatment method having a pH of 3.5 to 5.5. The total content of (B) is 5 to 1000 mass ppm in solid content concentration,
Containing (D) in a solid content concentration of 5-1000 mass ppm,
The coating pretreatment method according to claim 1, wherein the solid content mass ratio ((B) / (D)) of (B) to (D) is 0.005 to 200.   The said 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. 2. The coating pretreatment method according to 2.   A hot-rolled steel sheet processed by the coating pretreatment method according to claim 1.