US20090078340A1

US20090078340A1 - Method of chemical treatment and chemically treated member

Info

Publication number: US20090078340A1
Application number: US11/919,454
Authority: US
Inventors: Katsutoshi Ando; Yasuhito Murai; Kazuhiro Makino; Shinya Nishida; Masanobu Futsuhara; Toshiaki Shimakura
Original assignee: Honda Motor Co Ltd; Nippon Paint Co Ltd
Current assignee: Honda Motor Co Ltd; Nippon Paint Co Ltd
Priority date: 2005-04-28
Filing date: 2006-04-27
Publication date: 2009-03-26
Also published as: WO2006118218A1; CN101163820A; GB2440863A; JPWO2006118218A1; GB0722061D0; CA2606171A1

Abstract

A chemical treatment method in which an object to be treated is treated with a chemical treating agent to form a chemical conversion coating, in which the object to be treated has at least one aluminum-plated steel sheet and at least one member selected from the group consisting of cold-rolled steel sheets, zinc-plated steel sheets, and aluminum sheets and the chemical treating agent is one which has zirconium, fluorine, and an aminated silane coupling agent and in which the zirconium content is 100-700 ppm in terms of metal amount and the fluorine/zirconium ratio is 3.5-7.0 by mole. A sufficient coating amount can be ensured on the surface of a zinc deposit, cold-rolled steel sheet, zinc-plated steel sheet, aluminum-plated steel sheet, or the like and a chemical conversion coating having sufficient base-hiding properties and sufficient adhesion can be formed.

Description

TECHNICAL FIELD

The present invention relates to a method of a chemical conversion treatment, and more specifically, relates to a method of a chemical conversion treatment suited for pretreatment prior to painting of general industrial products, particularly automotive bodies, and a member subjected to a chemical conversion treatment obtained by the method of the chemical conversion treatment.

BACKGROUND ART

Conventionally, automotive bodies are configured with bases of soft steel plates such as unprocessed iron materials and galvanized steel plate, and aluminum and the like. Exemplary surface treatment technique for these items includes treatment with zinc phosphate, in which a zinc phosphate coating film is deposited on a material surface, thereby ensuring the corrosion resistance and adhesiveness of the painting. (See, Patent Document 1).
However, recently a broad range of materials have been used for automotive bodies in order to achieve lower weight bodies. In particular, the application of high-tensile steel plates has been rapidly increasing. Desired characteristics for steel plates such as strength, elongation and the like vary depending on which part of the automotive body they are applied. For example, with respect to strength, there are a variety of classes, i.e., from 270 MPa class to 1500 MPa class or greater. Among these, steel plates having strength of 440 MPa or greater are referred to as high-tensile steel plates, while those having strength of less than 440 MPa are referred to as soft steel plates, in general.
With such a broad range of steel plates, steel plate alloy composition and production methods varies depending on the required characteristics. Particularly, as the amount of Si component increases, etchability of the material surface deteriorates, leading to non-uniformity of the deposition of the zinc phosphate coating film when treated with a conventional zinc phosphate coating technique. Thus, it is not easy to ensure the corrosion resistance and adhesiveness of the coated film. Furthermore, in ultra high-tensile steel plates having a strength exceeding 1000 MPa, accuracy of the size attained in forming is inferior according to common cold stamping production methods. Therefore, hot hardening such as induction hardening is carried out after the formation, or a hot stamping production method is employed in which heating is conducted during forming. Thus, it becomes more difficult to ensure the adhesiveness and corrosion resistance of the coated film. Particularly, in hot stamping production methods, the material surface is oxidized by thermal history when the unprocessed iron material is used, thereby failing to achieve the corrosion resistance and adhesiveness of the coated film. In order to achieve satisfactory corrosion resistance and adhesiveness, elimination of the oxide scale by shot blasting is a prerequisite, thus leading to economical disadvantages. Hence, as a procedure for preventing surface oxidation in hot stamping, aluminum coated steel plates have been extensively used.
According to a feature of the aluminum coated steel plates, heating during formation results in diffusion of the coated component on the iron basis metal, whereby the AlFe alloy is produced. Since this AlFe alloy is stable, high corrosion resistance is exhibited. In contrast, because no common zinc phosphate coating film is formed what so ever, sufficient adhesiveness of the coated film cannot be achieved. This is based on resistance to etching because of the stability irrespective of the requirement of continuous electron donation by etching of the material for deposition of the crystalline zinc phosphate coating film.
Accordingly, a novel surface treatment technique for deposition of an amorphous coating film has been desired which enables a metal product to be coated by electron donation with slight etching of the material. For example, a surface treatment technique based on a zircon coating film is exemplified, which was proposed also as a surface treatment method of automotive bodies (see, Patent Document 2). Moreover, in light of environmental protection, and discharge of sludge being a drawback of the zinc phosphate coating film, techniques utilizing a zircon coating film have been established as a surface treatment method of automotive bodies, and thus an improvement of the adhesiveness of paint by adding a resin component, and providing a rust-preventive property through the addition of a metal component have been attempted (see, Patent Documents 3 to 5).
Patent Document 1: Japanese Unexamined Patent Application Publication No. 1998-204649
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2003-334490
Patent Document 3: Pamphlet of WO 2002/103080
Patent Document 4: Japanese Unexamined Patent Application Publication No. 2004-218070
Patent Document 5: Japanese Unexamined Patent Application Publication No. 2004-218075

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

According to a zircon coating film-based surface treatment technique, the amount of zircon coating film is likely to be lower on an aluminum coated steel plate obtained by a hot stamping production method compared to the amount of zircon coating film obtained on either an unprocessed iron material or a galvanized steel plate, both of which are obtained by a hot stamping production method. Accordingly, conventional zircon coating film-based surface treatment techniques cannot yield a coated film having sufficient adhesiveness.
As previously described, a method of a chemical conversion treatment which can ensure a sufficient amount of coating film, and can simultaneously form coating films of the chemical conversion treatment that can achieve sufficient basis metal concealment and coated film adhesiveness on any of a zinc-coated material, a cold-rolled steel plate material, a galvanized steel plate material and an aluminum coated steel plate material has not been hitherto established. Therefore, establishment of such a method of the chemical conversion treatment is very advantageous for automotive bodies, automobile parts and the like configured with these materials.
The present invention was made in order to solve the aforementioned problems, and an object of the invention is to provide a method of a chemical conversion treatment which can ensure a sufficient amount of the coating film, and can simultaneously form a coating film of the chemical conversion treatment that can achieve sufficient basis metal concealment and coated film adhesiveness on the surface of a zinc coating, a cold-rolled steel plate, a galvanized steel plate, an aluminum coated steel plate and the like, and a member subjected to a chemical conversion treatment obtained by this method of the chemical conversion treatment.

Means for Solving the Problems

The present inventors undertook a detailed investigation in view of the aforementioned problems, and consequently discovered that the problems can be solved by a chemical conversion treatment agent including zirconium, fluorine, and an amino group-containing a silane coupling agent through specifying the ratio of these components. Accordingly, the present invention was accomplished. More specifically, the present invention provides the following.
In a first aspect of the present invention, a method of a chemical conversion treatment for forming a chemical conversion coating film including treating an object with a chemical conversion treatment agent is provided, wherein the object includes at least one aluminum coated steel plate, and at least one selected from the group consisting of a cold-rolled steel plate, a galvanized steel plate, and an aluminum plate; the chemical conversion treatment agent contains zirconium, fluorine, and an amino group-containing silane coupling agent; the content of zirconium with respect to the metal content in the chemical conversion treatment agent is no less than 100 ppm and no greater than 700 ppm; and the molar ratio of fluorine to zirconium is no less than 3.5 and no greater than 7.0.
In a second aspect of the present invention, the method of a chemical conversion treatment according to the first aspect is provided, wherein the content of the amino group-containing silane coupling agent in the chemical conversion treatment agent is no less than 50 ppm and no greater than 500 ppm based on the solid content.
In a third aspect of the present invention, the method of a chemical conversion treatment according to either the first or second aspect is provided, wherein the pH of the chemical conversion treatment agent is no less than 2.6 and no greater than 4.5.
In a fourth aspect of the present invention, the method of a chemical conversion treatment according to any one of the first to third aspects is provided, wherein the chemical conversion treatment agent further contains at least one agent for imparting adhesiveness and corrosion resistance selected from the group consisting of a magnesium ion, a zinc ion, a calcium ion, an aluminum ion, a gallium ion, an indium ion, and a copper ion.
In a fifth aspect of the present invention, the method of a chemical conversion treatment according to any one of the first to fourth aspects is provided, wherein the object is a member for an automotive body, and an automotive body.
In a sixth aspect of the present invention, a member subjected to a chemical conversion treatment is provided, including a conversion coating film formed by the method of the chemical conversion treatment according to any one of the first to fifth aspects.

EFFECTS OF THE INVENTION

According to the method of a chemical conversion treatment of the present invention, a method of a chemical conversion treatment which can ensure a sufficient amount of the coating film, and can simultaneously form coating films of the chemical conversion treatment that can achieve sufficient basis metal concealment and coated film adhesiveness on the surface of not only a zinc coating, a cold-rolled steel plate, a galvanized steel plate, but also an aluminum coated steel plate and the like, and a member subjected to a chemical conversion treatment obtained by this method of the chemical conversion treatment can be provided. Thus, the variety of aluminum coated steel plates that can be used for automotive bodies can be increased. Moreover, also on the edge part of the basis metal, the coating film can be readily formed, and thus prevent the generation of rust which has been a concern on parts where the basis iron metal is exposed due to cracking of the coating in the course of formation, scratches, and the like.

PREFERRED MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be explained.

Chemical Conversion Treatment Agent

The present invention is directed to a method of a chemical conversion treatment for forming a chemical conversion coating film including treating an object with a chemical conversion treatment agent, wherein the chemical conversion treatment agent contains zirconium, fluorine, and an amino group-containing silane coupling agent.

Zirconium Component

Zirconium included in the chemical conversion treatment agent is a component for forming the conversion coating film. Formation of the conversion coating film containing zirconium on the object enables improvement of the corrosion resistance and abrasion resistance of the base material, and further increase the adhesiveness with the coated film.
When the surface treatment of the object is conducted with the chemical conversion treatment agent containing zirconium for use in the present invention, the solubilizing reaction of the metal that constitutes the object results in production of a hydroxide or an oxide of zirconium because a metal ion eluted into the chemical conversion treatment agent draws fluorine of ZrF₆ ²⁻, and because the pH at the boundary is elevated. Accordingly, this hydroxide or oxide of zirconium is considered to be deposited on the surface of the object. Since the chemical conversion treatment agent used in the present invention is a reactive chemical conversion treatment agent, it can also be used when immersing an object having a complicated shape. Furthermore, since the conversion coating film rigidly adhered to the object can be attained by a chemical reaction, washing with water can be also conducted after the treatment.
The source of zirconium is not particularly limited, and examples thereof include alkali metal fluorozirconates such as K₂ZrF₆, fluorozirconates such as (NH₄)₂ZrF₆, soluble fluorozirconates such as fluorozirconate acids such as H₂ZrF₆, zirconium fluoride, zirconium oxide, zirconyl nitrate, and zirconium carbonate and the like.

Content of Zirconium

The content of zirconium included in the chemical conversion treatment agent used in the present invention falls within a range of no less than 100 ppm and no greater than 700 ppm expressed with respect to the metal content. When the content is less than 100 ppm, a sufficient amount of the coating film cannot be attained on the aluminum coated steel plate. In contrast, when the content exceeds 700 ppm, an economical disadvantage results because a much greater effect cannot be expected. Preferably, the content is no less than 150 ppm and no greater than 550 ppm.

Fluorine Component

Fluorine included in the chemical conversion treatment agent used in the present invention plays a role as an etching agent of the object. Although the source of fluorine is not particularly limited, examples thereof include fluorides such as hydrofluoric acid, ammonium fluoride, fluoborate, ammonium hydrogen fluoride, sodium fluoride, and sodium hydrogen fluoride. Furthermore, a complex fluoride can be also used as the source, and examples thereof include hexafluorosilicic acid salts, specifically, hydrofluosilicic acid, zinc hydrofluosilicicate, manganese hydrofluosilicate, magnesium hydrofluosilicate, nickel hydrofluosilicate, iron hydrofluosilicate, calcium hydrofluosilicate, and the like.

Content of Fluorine Component

With respect to the content of fluorine included in the chemical conversion treatment agent used in the present invention, the molar ratio of fluorine to zirconium falls within a range of no less than 3.5 and no greater than 7.0. When the molar ratio of fluorine to zirconium is lower than 3.5, precipitation may be result as the solution becomes unstable. In contrast, when the ratio is higher than 7.0 sufficient formation of the coating film is not achieved due to reduction in the etching force. The ratio is preferably, no less than 4.5 and no greater than 6.5, and more preferably no less than 5.0 and no greater than 6.0.

Amino Group-Containing Silane Coupling Agent

The amino group-containing silane coupling agent included in the chemical conversion treatment agent used in the present invention is a compound, which has at least one alkyl chain in the molecule, wherein the at least one alkyl chain has at least one amino group, and which includes an alkoxy group or halogen (predominantly chlorine) as a functional group or an element that binds to a dangling bond of silicon. Since the amino group-containing silane coupling agent acts on both of the conversion coating film and the coated film formed later, adhesiveness of both films can be improved.
Such an effect is speculated to be caused because silanol produced by hydrolysis of the alkoxy group is covalently adsorbed on the surface of the object, or on the surface of the zirconium coating film.
In addition, since the amino group-containing silane coupling agent included in the conversion coating film acts not only on the object but also on the coated film formed later, it is believed to serve in improving their adhesiveness with one another. In particular, the amino group-containing silane coupling agent can exhibit an effect to improve the adhesiveness to the coated film formed with paint for cation electrodeposition.
The amino group-containing silane coupling agent is not particularly limited, and examples thereof include known silane coupling agents such as N-2(aminoethyl)3-aminopropylmethyldimethoxysilane, N-2(aminoethyl)3-aminopropyltrimethoxysilane, N-2(aminoethyl)3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, N,N-bis[3-(trimethoxysilyl)propyl]ethylenediamine, and 3-aminopropyltrichlorosilane and the like. Moreover, KBM-602, KBM-603, KBE-603, KBM-903, KBE-9103, KBM-573 (manufactured by Shin-Etsu Chemical Co., Ltd.), XS1003 (manufactured by Chisso Corporation) and the like which have been commercially available as amino group-containing silane coupling agents can be also used intact. Among these, N-2(aminoethyl)3-aminopropyltriethoxysilane (APS-L), N-2(aminoethyl)3-aminopropyltrimethoxysilane (APS-L), 3-aminopropyltriethoxysilane (APS-S), and 3-aminopropyltrimethoxysilane are preferred.

Content of Amino Group-Containing Silane Coupling Agent

The content of the amino group-containing silane coupling agent included in the chemical conversion treatment agent used in the present invention falls within a range of preferably no less than 50 ppm and no greater than 500 ppm based on the solid content. When the content is less than 50 ppm, sufficient adhesiveness of the coated film may not be achieved. In contrast, when the content exceeds 500 ppm, an economical disadvantage results because a much greater effect cannot be expected. The content falls within a range of more preferably no less than 100 ppm and no greater than 300 ppm, and more preferably no less than 150 ppm and no greater than 250 ppm.

pH of Chemical Conversion Treatment Agent

The pH of the chemical conversion treatment agent used in the present invention is preferably no less than 2.6 and no greater than 4.5. When the pH is lower than 2.6, sufficient formation of the coating film may not be achieved due to excessive etching, or the resulting non-uniform coating film may adversely affect the appearance of coated paint. In contrast, when the pH is higher than 4.5, the etching may become insufficient, thereby leading to failure in obtaining a favorable coating film. The pH falls within a range of more preferably no less than 3.0 and no greater than 4.2, and still more preferably no less than 3.2 and no greater than 4.0.
The pH of the chemical conversion treatment agent can be adjusted using an acidic compound such as nitric acid or sulfuric acid, and a basic compound such as sodium hydroxide, potassium hydroxide or ammonia.

Agent for Imparting Adhesiveness and Corrosion Resistance

It is preferred that the chemical conversion treatment agent used in the present invention further includes at least one agent for imparting adhesiveness and corrosion resistance selected from the group consisting of an iron ion, a magnesium ion, a zinc ion, a calcium ion, an aluminum ion, a gallium ion, an indium ion, and a copper ion. In the present invention, the conversion coating film having more favorable adhesiveness and corrosion resistance can be obtained by including the agent for imparting adhesiveness and corrosion resistance.

Content of Agent for Imparting Adhesiveness and Corrosion Resistance

The content of the agent for imparting adhesiveness and corrosion resistance optionally added to the chemical conversion treatment agent used in the present invention preferably falls within a range of no less than 1 ppm and no greater than 5000 ppm. When the content is less than 1 ppm a sufficient effect of imparting the adhesiveness and corrosion resistance cannot be achieved. In contrast, when the content exceeds 5000 ppm an economical disadvantage results because any additional effect cannot be found, otherwise, the adhesiveness following painting may deteriorate. The content falls within a range of more preferably no less than 25 ppm and no greater than 1000 ppm.

Other Component

In the chemical conversion treatment agent used in the present invention, other optional component may be included in combination as needed in addition to the aforementioned components. An exemplary component that can be used is silica and the like. By adding such a component, an improvement in the corrosion resistance after painting is achieved.
Furthermore, it is preferred that the chemical conversion treatment agent is an agent not substantially containing a phosphate ion. The term “not substantially containing a phosphate ion” means that a phosphate ion is not included in an amount to exhibit an action as a component in the chemical conversion treatment agent. By using the chemical conversion treatment agent not substantially containing a phosphate ion, use of phosphorus which is responsible for environmental burden can be avoided, and generation of sludge such as iron phosphate, and zinc phosphate can be prevented which may be produced in use of the zinc phosphate-based treatment agent.

Method of Chemical Conversion Treatment

The method of the chemical conversion treatment of the present invention is not particularly limited, and can be performed under a common treatment condition by bringing the chemical conversion treatment agent into contact with the surface of the object. Examples of the method include a dipping method, a spraying method, a roll coating method and the like.

Condition of Chemical Conversion Treatment

The treatment temperature in the chemical conversion treatment falls within a range of preferably no less than 20° C. and no greater than 70° C. More preferably, it falls within a range of no less than 30° C. and no greater than 50° C. When the temperature is less than 20° C. sufficient formation of the coating film may not be achieved, and adjustment of the temperature is necessary in summer. Also, when the temperature is greater than 70° C. an economical disadvantage results since no additional effect is particularly exhibited. It is preferred that the duration of the chemical conversion treatment fall within a range of no less than 5 sec and no greater than 1100 sec. More preferably, the duration falls within a range of no less than 30 sec and no greater than 120 sec. When the duration is less than 5 sec a sufficient amount of the coating film cannot be achieved. When the duration is greater than 1100 sec an additional effect is not exhibited with a further increase in the amount of coated film.
In the method of the chemical conversion treatment of the present invention, surface conditioning treatment may not be conducted as in conventionally practiced treatment with a zinc phosphate-based chemical conversion treatment agent. Thus, the chemical conversion treatment of the object can be conducted with fewer steps.

Object

Examples of the object which may be used in the method of the chemical conversion treatment of the present invention include iron-based base materials, aluminum-based base materials, and zinc-based base materials and the like. The iron, aluminum, and zinc-based base materials mean iron-based base material constituted with iron and/or an alloy thereof, aluminum base materials constituted with aluminum and/or an alloy thereof, and zinc-based base materials constituted with zinc and/or an alloy thereof.
Particularly, in the present invention, a sufficient amount of the zircon coating film can be achieved on the aluminum coated steel plates after the hot stamping, which had conventionally involved problems, and sufficient paint adhesiveness can be achieved even on an aluminum coated steel plate.
Moreover, the method of the chemical conversion treatment of the present invention can be simultaneously applied to an object constituted with multiple metal base materials among an iron-based base material, an aluminum-based base material, and a zinc-based base material. The automotive bodies, the automobile parts, and the like are configured with items constituted with various metal materials such as iron, zinc, aluminum and the like. Therefore, there may be the case in which the surface treatment therefor must be conducted on all materials by a single treatment. However, according to the method of the chemical conversion treatment of the present invention, the chemical conversion treatment can be achieved on all the materials without problem in a single operation.
The iron-based base materials used as the object of the present invention are not particularly limited, and examples thereof include cold-rolled steel plates and hot-rolled steel plates. The aluminum-based base materials are also not particularly limited, and examples thereof include 5000 series aluminum alloy, 6000 series aluminum alloy, and aluminum-coated steel plates treated by aluminum-based electroplating, hot dipping, or vapor deposition plating. Furthermore, zinc-based base materials are also not particularly limited, and examples thereof include zinc or zinc-based alloy coated steel plates treated by zinc-based electroplating, hot dipping, or vapor deposition plating, such as galvanized steel plate, zinc-nickel coated steel plate, zinc-iron coated steel plate, zinc-chromium coated steel plate, zinc-aluminum coated steel plate, zinc-titanium coated steel plate, zinc-magnesium coated steel plate, and zinc-manganese coated steel plate. In the present invention, iron, aluminum and zinc-based base materials can be simultaneously subjected to the chemical conversion treatment.

Average Amount of Coating Film of Conversion Coating Film

Average amount of the coating film of the conversion coating film obtained by the method of the chemical conversion treatment of the present invention preferably falls within a range of no less than 0.1 mg/m²and no greater than 500 mg/m²based on the total amount of the metal included in the chemical conversion treatment agent. An average amount of less than 0.1 mg/m²is not preferred because a uniform conversion coating film cannot be obtained, and hence favorable adhesiveness may not be achieved. In contrast, an average amount exceeding 500 mg/m²is economically disadvantageous since any greater effect cannot be exhibited. More preferably, the average amount falls within a range of no less than 5 mg/m²and no greater than 150 mg/m².
In the method of the chemical conversion treatment of the present invention, a sufficient amount of the zircon coating film can be achieved also on the aluminum coated steel plates after the hot stamping, which had conventionally involved problems, and sufficient paint adhesiveness can be achieved even on the aluminum coated steel plates. Thus, also in the case in which the chemical conversion treatment is simultaneously applied to the object constituted with multiple metal base materials including an aluminum coated steel plate, sufficient paint adhesiveness can be achieved. According to the method of the chemical conversion treatment of the present invention, the average amount of the conversion coating film of no less than 10 mg/m²can be achieved also on the aluminum coated steel plates.

Coated Film Formed Later

As the coated film formed on the conversion coating film after the formation of the conversion coating film by the method of the chemical conversion treatment of the present invention, coated films formed with a conventionally known paint such as a cation electrodeposition paint, a solvent paint, an aqueous paint, a powder paint or the like may be exemplified. Examples of the cation electrodeposition paint include conventionally known cation electrodeposition paints such as aminated epoxy resins, aminated acrylic resins, sulfonium epoxy resins and the like. Among these, because adhesiveness of the conversion coating film with the electrodeposition coated film can be further improved due to the action of the amino group-containing silane coupling agent included in the chemical conversion treatment agent, cation electrodeposition paints including a resin that has a functional group exhibiting reactivity or compatibility with the amino group are preferred.

Pretreatment of Object

It is preferred that the object of the present invention is subjected to a degreasing treatment followed by a water washing treatment before conducting the aforementioned chemical conversion treatment. The degreasing treatment is conducted in order to remove oil and stains adhered to the surface of the object. In usual cases, immersion treatment is conducted for several minutes at a temperature from 30° C. to 55° C. using a degreasing agent such as a phosphate-free and nitrogen-free degreasing detergent. If desired, preliminary degreasing treatment may be conducted before the degreasing treatment. Furthermore, a water washing treatment following the degreasing treatment is conducted for washing away the degreasing agent, at least once by a spray treatment with a large amount of washing water.

Post-Treatment of Object

The member subjected to the chemical conversion treatment having the conversion coating film formed by the method of the chemical conversion treatment of the present invention is preferably subjected to water washing treatment before the formation of the coated film to be conducted later. The water washing treatment following the chemical conversion treatment is conducted at least once so as not to adversely affect adhesiveness, corrosion resistance and the like after completing the following various types of painting. In this case, it is suitable to conduct the final water washing with pure water. The water washing treatment following the chemical conversion treatment may be either spray water washing or immersion water washing, and combination of these is also acceptable for the water washing. After conducting the water washing treatment following the chemical conversion treatment, the object is dried according to a known method as needed, and thereafter, the coated film is formed with various types of painting.

EXAMPLES

Next, the present invention will be explained more specifically by way of Examples and Comparative Examples, but the present invention is not limited only to these Examples. The amount to be blended is represented by parts by weight unless specifically stated otherwise.

Example 1

A commercially available cold-rolled steel plate (SPCC-SD, manufactured by Nippon Testpanel Co., Ltd., 70 mm×150 mm×0.8 mm), a high-tensile steel plate (JSC780T, manufactured by Nippon Steel Corporation, 70 mm×150 mm×0.8 mm), and an aluminum coated steel plate (USIBOR1500P, manufactured by ARCELOR S. A., 70 mm×150 mm×2.3 mm) were provided as the object.

Pretreatment of Object Before Chemical Conversion Treatment

Degreasing Treatment

Using 1.6% by weight of EC90 (degreasing agent, manufactured by Nippon Paint Co., Ltd.), an immersion treatment was conducted at 42° C. for 2 min.

Water Washing Treatment

After conducting the degreasing treatment, the object was subjected to immersion washing with a water washing bath. Thereafter, spray washing was carried out with tap water for about 30 sec.

Chemical Conversion Treatment

Using zirconyl nitrate (manufactured by Nippon Light Metal Co., Ltd.) as the zirconium source, and KBE-903 (APS-S) (aminopropyltriethoxysilane: effective concentration: 100%, manufactured by Shin-Etsu Chemical Co., Ltd.) as the amino group-containing silane coupling agent, the chemical conversion treatment agent having a zirconium content of 500 ppm, a fluorine content of 416 ppm (molar ratio=416×91.2/500×19.0=4.0), and the amino group-containing silane coupling agent content of 100 ppm based on the solid content was prepared including 100 ppm of a magnesium ion, and 500 ppm of a zinc ion, as the agent for imparting adhesiveness and corrosion resistance. Furthermore, the pH was adjusted to give 2.8 with a 10% aqueous sodium hydroxide solution. The temperature of the chemical conversion treatment agent was adjusted to 40° C., and thereafter, the object was subjected to the immersion treatment for 60 sec.

Measurement of Amount of Coating Film

The amount of the coating film following the chemical conversion treatment was determined on each steel plate. With respect to the amount of the coating film, the amount of Zr (mg/m²) and the amount of Si (mg/m²) included in the coating film of the chemical conversion treatment were measured using a fluorescent X-ray analyzer XRF-1700 (an apparatus for fluorescent X-ray analysis, manufactured by Shimadzu Corporation). The results are shown in Table 1.

Water Washing Treatment Following the Chemical Conversion Treatment

On each steel plate subjected to the chemical conversion treatment a spray treatment with tap water was conducted for 30 sec. Subsequently, the spray treatment was conducted with ion exchanged water for 30 sec.

Electrodeposition Painting

Electrodeposition painting was carried out on each of the steel plates while in a wet state resulting from the water washing treatment that followed the chemical conversion treatment. The electrodeposition painting was performed using PN150 (cation electrodeposition paint, manufactured by Nippon Paint Co., Ltd.) so as to give a dry film thickness of 20 μm. After forming the coated film by electrodeposition painting, each steel plate was washed with water. Then, baking was conducted at 170° C. for 20 min to obtain a test plate.

Secondary Adhesiveness Test (SDT)

Thus resulting test plate was incised to provide two parallel cut lines that run longitudinally, with the depth to reach to the basis metal. Then, immersion in a 5% aqueous NaCl solution was carried out at 55° C. for 240 hrs. Thereafter, a tape was attached at the location of the cut and then peeled, and the stripped state of the paint was observed. Depending on the size of the maximum stripped width, the following evaluation was made. The results are shown in Table 1.
A: Less than 1 mm
B: 1 mm to 2 mm
C: 2 mm to 3 mm
D: Greater than 3 mm

Complex Cycle Test (CCT)

Thus resulting test plate was incised to provide parallel cuts that run longitudinally, with the depth to reach to the basis metal. Then, a 5% aqueous NaCl solution was continuously sprayed for 2 hrs in a salt spray test unit maintained at 35° C. Then, the test plate was dried at 60° C. and a humidity of 20 to 30% for 4 hrs, followed by keeping under a humid condition at 50° C. and a humidity of 95% or higher for 2 hrs. Such a sequence of procedures was defined as one cycle, and 100 cycles were carried out. After carrying out 100 cycles, the width bulged from the cut part was measured. Depending on the size of the maximum bulged width, the following evaluation was made. The results are shown in Table 1.
A: Less than 3 mm
B: 3 mm to 4 mm
C: 4 mm to 5 mm
D: Greater than 5 mm

Example 2

A similar operation to Example 1 was performed except that the fluorine content was 570 ppm (molar ratio=570×91.2/500×19.0=5.5); KBM-603 (APS-L) (N-(2-aminoethyl)-3-aminopropyltriethoxysilane, effective concentration: 100%, manufactured by Shin-Etsu Chemical Co., Ltd.) was used as the amino group-containing silane coupling agent at 100 ppm based on the solid content; and the pH was adjusted to 3.5 to obtain a test plate. The evaluation results of the resulting test plate are shown in Table 1.

Example 3

A similar operation to Example 1 was performed except that the fluorine content was 574 ppm (molar ratio=574×91.2/500×19.0=5.5); KBM-603 (APS-L) (N-(2-aminoethyl)-3-aminopropyltriethoxysilane, effective concentration: 100%, manufactured by Shin-Etsu Chemical Co., Ltd.) was used as the amino group-containing silane coupling agent at 200 ppm based on the solid content; and the pH was adjusted to 3.5 to obtain a test plate. The evaluation results of the resulting test plate are shown in Table 1.

Example 4

A similar operation to Example 1 was performed except that the zirconium content was 200 ppm, and the fluorine content was 210 ppm (molar ratio=210×91.2/200×19.0=5.0); and the pH was adjusted to 3.5 to obtain a test plate. The evaluation results of the resulting test plate are shown in Table 1.

Example 5

A similar operation to Example 1 was performed except that the zirconium content was 200 ppm, and the fluorine content was 210 ppm (molar ratio=210×91.2/200×19.0=5.0); the amino group-containing silane coupling agent was not used; and the pH was adjusted to 3.5 to obtain a test plate. The evaluation results of the resulting test plate are shown in Table 1.

Example 6

A similar operation to Example 1 was performed except that the fluorine content was 626 ppm (molar ratio=626×91.2/500×19.0=6.0); KBM-603 (APS-L) (N-(2-aminoethyl)-3-aminopropyltriethoxysilane, effective concentration: 100%, manufactured by Shin-Etsu Chemical Co., Ltd.) was used as the amino group-containing silane coupling agent at 250 ppm based on the solid content; a zinc ion was used at 500 ppm as the agent for imparting adhesiveness and corrosion resistance; and the pH was adjusted to 3.5 to obtain a test plate. The evaluation results of the resulting test plate are shown in Table 1.

Comparative Example 1

A similar operation to Example 1 was performed except that the chemical conversion treatment was changed to a treatment with zinc phosphate as described below to obtain a test plate. The evaluation results of the resulting test plate are shown in Table 1.
Treatment with Zinc Phosphate
Surface conditioning of each object subjected to the degreasing treatment and water washing treatment was carried out using 0.3% GL1 (surface conditioning agent, manufactured by Nippon Paint Co., Ltd.) by immersion at room temperature for 30 sec. Thereafter, Surfdyne SD-6800 (zinc phosphate-based chemical conversion treatment agent, manufactured by Nippon Paint Co., Ltd.) was used to conduct the immersion treatment at 42° C. for 2 min.

Comparative Example 2

A similar operation to Example 1 was performed except that the zirconium content was 100 ppm, and the fluorine content was 250 ppm (molar ratio=250×91.2/100×19.0=12.0); and the pH was adjusted to 3.5 to obtain a test plate. The evaluation results are shown in Table 1.

Comparative Example 3

A similar operation to Example 2 was performed except that the fluorine content was 940 ppm (molar ratio=940×91.2/500×19.0=9.0); KBM-603 (APS-L) (N-(2-aminoethyl)-3-aminopropyltriethoxysilane, effective concentration: 100%, manufactured by Shin-Etsu Chemical Co., Ltd.) was used as the amino group-containing silane coupling agent at 250 ppm based on the solid content; the agent for imparting adhesiveness and corrosion resistance was not used; and the pH was adjusted to 3.5 to obtain a test plate. The evaluation results are shown in Table 1.

	TABLE 1

	Composition of Chemical Conversion Bath		CCT

	Zr	F	APS-S	APS-L	Mg	Zn		Base	60	SDT
Examples	ppm	ppm	ppm	ppm	ppm	ppm	pH	Material	Cycles	240 h

Example	500	416	100	—	100	500	2.8	SPC	A	A
1								780T	A	A
								Al/Fe	A	A
Example	500	570	—	100	100	500	3.5	SPC	A	A
2								780T	A	A
								Al/Fe	A	A
Example	500	574	—	200	100	500	3.5	SPC	A	A
3								780T	A	A
								Al/Fe	A	A
Example	200	210	100	—	100	500	3.5	SPC	A	A
4								780T	A	A
								Al/Fe	A	A
Example	200	210	—	—	100	500	3.5	SPC	A	A
5								780T	A	A
								Al/Fe	A	A
Example	500	626	—	250	—	500	3.5	SPC	A	A
6								780T	A	A
								Al/Fe	A	A

Comparative	Treatment with Zinc Phosphate	3.5	SPC	A	B
Example			780T	A	B
1			Al/Fe	A	C

Comparative	100	250	100	—	100	500	3.5	SPC	A	B
Example								780T	C	B
2								Al/Fe	A	C
Comparative	500	940	—	250	—	—	3.5	SPC	A	B
Example								780T	C	B
3								Al/Fe	A	C

APS-S: NH₂(CH₂)₃Si(OC₂H₅)₃
APS-L: NH₂(CH₂)₂NH(CH₂)₃Si(OC₂H₅)₃

INDUSTRIAL APPLICABILITY

The member subjected to the chemical conversion treatment obtained according to the present invention can ensure a sufficient amount of the coating film also on the aluminum coated steel plate, and a sufficient amount of the coating film of the chemical conversion treatment can be simultaneously formed on various types of objects. In addition, sufficient corrosion resistance can be achieved. Therefore, it is preferably used in a field of outside plates of vehicles such as automotive bodies, bodies of two-wheeled vehicles before painting, various types of parts, outer surfaces of vessels, coil coatings, and the like, which will subsequently be subjected to painting.

Claims

1-6. (canceled)

7. A method of a chemical conversion treatment for forming a chemical conversion coating film comprising treating an object with a chemical conversion treatment agent, wherein

the object includes at least one aluminum coated steel plate, and at least one selected from the group consisting of a cold-rolled steel plate, a galvanized steel plate, and an aluminum plate;

the chemical conversion treatment agent comprises zirconium, fluorine, and an amino group-containing silane coupling agent;

the content of zirconium with respect to metal content in the chemical conversion treatment agent is no less than 100 ppm and no greater than 700 ppm; and

the molar ratio of fluorine to zirconium is no less than 3.5 and no greater than 7.0.

8. The method of a chemical conversion treatment according to claim 7 wherein the content of the amino group-containing silane coupling agent in the chemical conversion treatment agent is no less than 50 ppm and no greater than 500 ppm with respect to the solid content.

9. The method of a chemical conversion treatment according to claim 7 wherein the pH of the chemical conversion treatment agent is no less than 2.6 and no greater than 4.5.

10. The method of a chemical conversion treatment according to claim 8 wherein the pH of the chemical conversion treatment agent is no less than 2.6 and no greater than 4.5.

11. The method of a chemical conversion treatment according to claim 7 wherein the chemical conversion treatment agent further comprises at least one agent for imparting adhesiveness and corrosion resistance selected from the group consisting of a magnesium ion, a zinc ion, a calcium ion, an aluminum ion, a gallium ion, an indium ion, and a copper ion.

12. The method of a chemical conversion treatment according to claim 7 wherein the object is a member for an automotive body, and an automotive body.

13. A member subjected to a chemical conversion treatment comprising a conversion coating film formed by the method of the chemical conversion treatment according to claim 7.