SURFACE TREATMENT AGENT, SURFACE-TREATED METAL, AND SURFACE TREATMENT METHOD

Description

This application is based on and claims the benefit of priority from Japanese Patent Application No. 2024-138497, filed on 20 Aug. 2024, the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present disclosure relates to a surface treatment agent, a surface-treated metal, and a surface treatment method.

Related Art

Conventionally, when cationic electrodeposition coating or powder coating is applied to the surface of a metal substrate, the surface of the metal substrate is subjected to a surface treatment in advance for the purpose of improving corrosion resistance, coating film adhesion, and the like. In recent years, surface treatment (chemical conversion treatment) using zinc phosphate, which does not contain chromium, has been widely performed.

The chemical conversion treatment using zinc phosphate has issues that, due to the high reactivity of the treatment agent, wastewater treatment is difficult, sludge is generated, and the environmental load is large. Thus, a chemical conversion treatment agent including at least one selected from the group consisting of zirconium, titanium, and hafnium, fluorine, and a water-soluble resin has been proposed (for example, see Japanese Unexamined Patent Application, Publication No. 2004-218074).

The technique disclosed in Japanese Unexamined Patent Application, Publication No. 2004-218074 can perform good chemical conversion treatment on metals such as iron, zinc, and aluminum. However, there was still room for improvement in corrosion resistance obtained after coating such as cationic electrodeposition coating or powder coating. Therefore, a chemical conversion treatment agent having improved corrosion resistance has been proposed (see Japanese Patent No. 7052137).

• Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2004-218074
• Patent Document 2: Japanese Patent No. 7052137

SUMMARY OF THE INVENTION

Further improvement in adhesion to a coating film has been demanded for the technique disclosed in Japanese Patent No. 7052137.

The present disclosure has been made in view of the above, and an object of the present disclosure is to provide a surface treatment agent capable of improving adhesion to a coating film.

A first aspect of the present disclosure relates to a surface treatment agent including: at least one metal component (A) selected from the group consisting of zirconium, titanium, and hafnium; and an alkyldiallylamine polymer (C). The metal component (A) has a content of 10 to 10000 ppm by mass in terms of metal element with respect to a total mass of the surface treatment agent. The alkyldiallylamine polymer (C) includes at least one of a segment having a heterocyclic structure represented by the following formula (1a) or a segment having a heterocyclic structure represented by the following formula (1b):

where R¹ in the above formulas (1a) and (1b) represents an alkyl group or an aralkyl group.

In a second aspect of the present disclosure according to the first aspect, the alkyldiallylamine polymer (C) has a weight average molecular weight of 500 to 500,000 and a content of 25 to 5,000 ppm by mass in terms of resin solid content concentration with respect to the total mass of the surface treatment agent.

In a third aspect of the present disclosure according to the first or second aspect, the surface treatment agent further includes at least one metal component selected from the group consisting of aluminum, copper, and zinc.

In a fourth aspect of the present disclosure according to any one of the first to third aspects, the surface treatment agent has a pH of 2.0 to 6.0.

In a fifth aspect of the present disclosure according to any one of the first to fourth aspects, the alkyldiallylamine polymer (C) has a content ratio of a sum of the segment having a heterocyclic structure represented by the above formula (1a) and the segment having a heterocyclic structure represented by the above formula (1b) of 25 mol % or more and 100 mol % or less with respect to all segments included in the alkyldiallylamine polymer (C).

In a sixth aspect of the present disclosure according to any one of the first to fifth aspects, the surface treatment agent further includes fluorine (B), and the fluorine (B) has a concentration of 10 to 12,500 ppm by mass in terms of fluorine element with respect to the total mass of the surface treatment agent.

A seventh aspect of the present disclosure relates to a surface-treated metal having a surface on which a surface treatment film is formed by the surface treatment agent according to any one of the first to sixth aspects.

In an eighth aspect of the present disclosure according to the seventh aspect, the surface treatment film has a content of the metal component (A) of 5 to 500 mg/m² in terms of metal element.

A ninth aspect of the present disclosure relates to a surface treatment method including forming a surface treatment film by treating a surface of an object to be coated with the surface treatment agent according to any one of the first to sixth aspects.

In a tenth aspect of the present disclosure according to the ninth aspect, the surface treatment method further includes forming an electrodeposited coating film by subjecting the object to be coated having the surface treatment film formed thereon to electrodeposition coating.

According to the present disclosure, it is possible to provide a surface treatment agent capable of improving adhesion to a coating film.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, an embodiment of the present disclosure will be described. The present disclosure is not limited to the following description of the embodiment.

<Surface Treatment Agent>

The surface treatment agent according to the present embodiment can form, on the surface of a metal substrate, a surface treatment film that provides favorable corrosion resistance after coating. The metal substrate on which the surface treatment film has been formed and coated is not particularly limited, and can be used in various applications such as automobile bodies and automobile parts. Examples of the coating include cationic electrodeposition coating, powder coating, aqueous coating, and solvent coating.

The surface treatment agent according to the present embodiment includes at least one metal component (A) selected from the group consisting of zirconium, titanium, and hafnium, and an alkyldiallylamine polymer (C). Optionally, fluorine (B) may be further included.

(Metal Component (A))

The metal component (A) is a surface treatment film-forming component. By forming a surface treatment film containing at least one metal component (A) selected from the group consisting of zirconium, titanium, and hafnium on a metal substrate, the corrosion resistance and wear resistance of the metal substrate can be improved, and the adhesion to a coating film such as an electrodeposited coating film can be improved.

The source of the zirconium is not particularly limited, and examples thereof include an alkali metal fluorozirconate such as K₂ZrF₆, zircon hydrofluoric acid (H₂ZrF₆), ammonium hexafluorozirconate ((NH₄)₂ZrF₆), zirconium ammonium carbonate ((NH₄)₂ZrO(CO₃)₂), tetraalkylammonium-modified zirconium, zirconium fluoride, and zirconium oxide.

The source of the titanium is not particularly limited, and examples thereof include alkali metal fluorotitanate; fluorotitanates such as (NH₄)₂TiF₆, and soluble fluorotitanate acid such as H₂TiF₆; titanium fluoride; and titanium oxide.

The source of the hafnium is not particularly limited, and examples thereof include fluorohafnate acid such as H₂HfF₆, and hafnium fluoride.

The content of the metal component (A) is 10 to 10000 ppm by mass in terms of metal element with respect to the total mass of the surface treatment agent (the total mass including the solid content and volatile content of the surface treatment agent; the same applies below). When the content of the metal component (A) is less than 10 ppm, sufficient performance of the resulting surface treatment film cannot be obtained. When the content of the metal component (A) exceeds 10000 ppm by mass, no further effect can be obtained, which is economically disadvantageous. From the above viewpoint, the content of the metal component (A) is preferably 50 to 2000 ppm by mass, more preferably 100 to 1000 ppm in terms of metal element.

(Fluorine (B))

The fluorine (B) has a function of etching the surface of the metal substrate. The source of the fluorine is not particularly limited, and examples thereof include fluorides such as hydrofluoric acid, ammonium fluoride, boric acid fluoride, ammonium hydrogen fluoride, sodium fluoride, and sodium hydrogen fluoride. Examples of complex fluoride include hexafluorosilicates, and specific examples thereof include hydrosilicofluoric acid, zinc hydrosilicofluoric acid, manganese hydrosilicofluoric acid, magnesium hydrosilicofluoric acid, nickel hydrosilicofluoric acid, iron hydrosilicofluoric acid, and calcium hydrosilicofluoric acid. A fluorine-containing compound such as an alkali metal fluorozirconate exemplified as a source of the metal component (A) is a source of the metal component (A) and may also be a source of the fluorine (B).

The concentration of the fluorine (B) is preferably 10 to 12500 ppm by mass in terms of fluorine element with respect to the total mass of the surface treatment agent. When the concentration of the fluorine (B) is less than 10 ppm by mass, etching is insufficient and a satisfactory surface treatment film cannot be obtained. When the concentration of the fluorine (B) exceeds 12500 ppm by mass, etching becomes excessive and a surface treatment film cannot be sufficiently formed. From the above viewpoint, the concentration of the fluorine (B) is more preferably 125 to 1250 ppm by mass. The concentration of the fluorine (B) can be measured by quantitative analysis using ion chromatography, for example.

(Alkyldiallylamine Polymer (C))

The alkyldiallylamine polymer (C) is a polymer including at least a segment derived from alkyldiallylamine (hereinafter, may be referred to as an “alkyldiallylamine segment”). The alkyldiallylamine segment may be in a quaternized form. The alkyldiallylamine polymer (C) may include only alkyldiallylamine segments in its structure or may include segments other than the alkyldiallylamine segments. Each of the segments may independently have a counterion. The alkyldiallylamine polymer (C) may be a homopolymer or a copolymer.

[Alkyldiallylamine Segment]

The alkyldiallylamine segment has a heterocyclic structure represented by the following formula (1a) or (1b):

In the above formulas (1a) and (1b), R¹ represents an alkyl group or an aralkyl group. Examples of the alkyl group include an unsubstituted alkyl group having 1 or more and 10 or less carbon atoms, and more preferably an unsubstituted alkyl group having 1 or more and 6 or less carbon atoms. Specific examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, and a hexyl group. The aralkyl group is preferably an aralkyl group having 7 or more and 11 or less carbon atoms. Examples of the aralkyl group having 7 to 11 carbon atoms include a benzyl group, a phenylethyl group, a phenylpropyl group, a phenylbutyl group, and a naphthylmethyl group.

The alkyldiallylamine polymer (C) is preferably an acid addition salt having an anionic counterion to an ammonium cation. The dissociation constant pKa of the acid forming the acid addition salt is preferably in the range of −3.7 to 4.8. In the present specification, the dissociation constant pKa of the acid means a numerical value at a temperature of 25° C. when the solvent is water. The alkyldiallylamine segment constituting the alkyldiallylamine polymer (C) as the acid addition salt is represented by, for example, the following general formulas (1c) and (1d).

In the above formulas (1c) and (1d), R² represents an alkyl group or an aralkyl group, R³ represents hydrogen, an alkyl group, or an aralkyl group, and D-represents a monovalent anion.

The anionic counterion is not particularly limited, and may be for example, a monovalent anion, and examples thereof include a carboxylic acid ion such as a formate ion, an acetate ion, and a benzoate ion, a chloride ion, a sulfate ion, a sulfamate ion, and a nitrate ion. Examples of the acid forming the acid addition salt include organic acids such as formic acid, acetic acid, and benzoic acid, as well as inorganic acids such as hydrochloric acid, sulfuric acid, sulfamic acid, and nitric acid.

The content ratio of the alkyldiallylamine segment is preferably 25 mol % or more and 100 mol % or less with respect to all segments of the alkyldiallylamine polymer (C). When the content ratio of the alkyldiallylamine segment is within the range described above, the adhesion of the formed surface treatment film to the coating film can be improved. From the above viewpoint, the above content ratio is more preferably 50 mol % or more and 100 mol % or less.

[Other Segments]

The segments other than the alkyldiallylamine segments included in the alkyldiallylamine polymer (C) are not particularly limited, and examples thereof include a segment derived from allylamine, a segment derived from sulfur dioxide (sulfonyl group); or a segment derived from an unsaturated compound having a hydroxy group such as 2-hydroxyethyl (meth)acrylate; a segment derived from a (meth)acrylic monomer having a primary amino group; a segment derived from N, N-dialkylaminoalkyl (meth)acrylate and a salt or quaternary compound thereof, N, N-dialkylaminoalkyl (meth)acrylamide and a salt or quaternary compound thereof, vinylimidazole and a salt or quaternary compound thereof, vinylpyridine and a salt or quaternary compound thereof, N-alkylallylamine and a salt thereof, N, N-dialkylallylamine and a salt thereof, N-alkyldiallylamine and a salt or quaternary compound thereof, or the like; and a segment derived from an alkyl ester of (meth)acrylate such as methyl (meth)acrylate and ethyl (meth)acrylate, a vinyl carboxylate such as vinyl acetate and vinyl propionate, an unsaturated acid, or the like.

The segment derived from allylamine has, for example, a structure represented by the following formula (2).

The segment derived from allylamine may have the same anionic counterion as that of the above alkyldiallylamine segment.

Examples of the (meth)acrylic monomer having a primary amino group include acrylamide, methacrylamide, aminomethyl (meth)acrylate, aminoethyl (meth)acrylate, aminopropyl (meth)acrylate, aminobutyl (meth)acrylate, aminopentyl (meth)acrylate, and aminohexyl (meth)acrylate.

The weight average molecular weight of the alkyldiallylamine polymer (C) is preferably 500 to 500,000. When the weight average molecular weight is less than 500, sufficient adhesion of the surface treatment film cannot be obtained. When the weight average molecular weight exceeds 500,000, the formation of a surface treatment film may be inhibited. From the above viewpoint, the weight average molecular weight of the alkyldiallylamine polymer (C) is preferably 5,000 to 100,000.

The weight average molecular weight of the alkyldiallylamine polymer (C) can be measured, for example, by gel permeation chromatography (GPC). For example, a Hitachi L-6000 type high-performance liquid chromatograph can be used as a measuring instrument. Hitachi L-6000 can be used as an eluent flow pump. A Shodex RI SE-61 differential refractive index detector can be used as a detector. Asahipak aqueous gel filtration types GS-220HQ (exclusion limit molecular weight: 3000) and GS-620HQ (exclusion limit molecular weight: 2000000) which are connected can be used as a column. An example of the GPC measurement method is described below. The sample is adjusted to a concentration of 0.5 g/100 ml with an eluent, and 20 μl of the sample is used. As the eluent, 0.4 mol/L sodium chloride aqueous solution is used. The measurement is carried out with a column temperature of 30° C. and a flow rate of 1.0 ml/min. A calibration curve is determined using polyethylene glycol with a molecular weight of 106, 194, 440, 600, 1470, 4100, 7100, 10300, 12600, 23000, or the like as a standard sample. The weight average molecular weight (Mw) of the polymer is determined based on the calibration curve.

The content of the alkyldiallylamine polymer (C) is preferably 25 to 5,000 ppm by mass in terms of the resin solid content concentration with respect to the total mass of the surface treatment agent. When the content is less than 25 ppm by mass, sufficient adhesion of the surface treatment film cannot be obtained. When the content is more than 5,000 ppm by mass, the formation of the surface treatment film may be inhibited. From the above viewpoint, the content of the alkyldiallylamine polymer (C) is more preferably 50 to 2,500 ppm by mass, and still more preferably 50 to 600 ppm by mass in terms of the resin solid content concentration.

The alkyldiallylamine polymer (C) may be modified to the extent that the object of the present invention is not impaired. For example, a part of the amino group of the alkyldiallylamine polymer (C) may be modified by a method such as acetylation, or may be cross-linked with a cross-linking agent to such an extent that solubility is not affected.

The method for preparing the alkyldiallylamine polymer (C) is not particularly limited, and examples thereof include a method in which a mixture of monomers obtained by mixing alkyldiallylamine, and other components as necessary is radically polymerized in a suitable solvent in the presence of a radical polymerization initiator. As the polymerization conditions, conditions known to those skilled in the art can be selected as appropriate.

(Other Polymers)

The surface treatment agent according to the present embodiment may include polymers other than the alkyldiallylamine polymer (C). Examples of the polymers other than the alkyldiallylamine polymer (C) include polymer components such as diallylamine polymers other than the alkyldiallylamine polymer (C), polyallylamine resins, polyvinylamine resins, polydiallylamine resins, urethane resins, acrylic resins, polyester resins, and natural polymer derivatives such as chitin/chitosan derivatives and cellulose derivatives. When the surface treatment agent of the present embodiment includes polymers other than the alkyldiallylamine polymer (C), the solid content mass of the alkyldiallylamine polymer (C) is preferably 80% by mass or more, more preferably 90% by mass or more, and still more preferably 95% by mass or more with respect to the total solid content mass of all polymers.

(Other Components)

The surface treatment agent according to the present embodiment preferably further includes a silane coupling agent. By including the silane coupling agent in the surface treatment agent, the adhesion of the surface treatment film to the coating film can be further improved. The silane coupling agent is not particularly limited, and is preferably, for example, one or more silane coupling agents selected from the group consisting of an amino group-containing silane coupling agent, an epoxy group-containing silane coupling agent, a hydrolysate of an amino group-containing silane coupling agent, a hydrolysate of an epoxy group-containing silane coupling agent, a polymer of an amino group-containing silane coupling agent, and a polymer of an epoxy group-containing silane coupling agent.

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, and 3-triethoxysilyl-N-(1,3-dimethyl-butylidene) propylamine, N-phenyl-3-aminopropyltrimethoxysilane, and N, N-bis [3-(trimethoxysilyl) propyl]ethylenediamine. Commercially available amino group-containing silane coupling agents such as KBM-602, KBM-603, KBE-603, KBM-903, KBE-9103, and KBM-573 (manufactured by Shin-Etsu Chemical Co., Ltd.) can also be used.

The hydrolysate of the amino group-containing silane coupling agent can be produced by a conventionally known method, for example, a method in which the amino group-containing silane coupling agent is dissolved in ion-exchanged water and adjusted to be acidic with any acid. As the hydrolysate of the amino group-containing silane coupling agent, a commercially available product such as KBP-90 (manufactured by Shin-Etsu Chemical Co., Ltd.: 32% active ingredient) can also be used.

The epoxy group-containing silane coupling agent is not particularly limited, and examples thereof include 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyldiethylethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, and 5,6-epoxyhexyltriethoxysilane. Commercially available products such as “KBM-403”, “KBE-403”, “KBE-402”, and “KBM-303” (manufactured by Shin-Etsu Chemical Co., Ltd.) can also be used.

The surface treatment agent according to the present embodiment may include components other than those described above. For example, it is preferable that the surface treatment agent further includes at least one metal component selected from the group consisting of aluminum, copper, and zinc as a surface treatment film-forming component. Accordingly, the corrosion resistance of the metal substrate on which the surface treatment film is formed can be further improved. In addition to those described above, at least one metal component selected from the group consisting of magnesium, calcium, gallium, and indium may be contained as a surface treatment film-forming component. Also, metal components such as manganese, iron, cobalt, nickel, and chromium may be contained. The sources of the film-forming components are not particularly limited, and examples thereof include oxides, hydroxides, fluorides, chlorides, sulfates, nitrates, borates, carbonates, and organic acid salts, of each metal. The metal components of the film-forming components may be contained in the surface treatment agent as components eluted from the metal substrate to be surface-treated in a surface treatment bath.

The surface treatment agent according to the present embodiment may contain an oxidizing agent. For example, it is preferable that the surface treatment agent further contains at least one oxidizing agent selected from the group consisting of nitric acid and nitrous acid as a surface treatment film-forming component. This promotes the formation of the surface treatment film, and can further improve the corrosion resistance of the metal substrate. Examples of the oxidizing agent include an inorganic acid or a salt thereof. It is considered that an inorganic acid or a salt thereof promotes the reaction of forming the surface treatment film as the oxidizing agent. Examples of the inorganic acid include nitric acid, nitrous acid, hydrochloric acid, bromic acid, chloric acid, hydrogen peroxide, HMnO₄, and HVO₃. The surface treatment agent may contain sulfonic acid group-containing compounds or salts thereof as oxidizing agents.

The surface treatment agent according to the present embodiment preferably contains substantially no phosphate ions. In the present specification, “contains substantially no phosphate ions” means that phosphate ions are not contained to such an extent that they act as a component in the surface treatment agent. Since the surface treatment agent according to the present embodiment does not substantially contain phosphate ions, phosphorus, which causes environmental load, is not substantially used. In addition, it is possible to suppress the generation of sludge such as iron phosphate and zinc phosphate, which are generated when using a zinc phosphate treatment agent.

(pH)

The surface treatment agent preferably has a pH of 2.0 to 6.0. When the pH is less than 2.0, etching becomes excessive, and a surface treatment film cannot be sufficiently formed. When the pH exceeds 6.0, etching is insufficient, and a good surface treatment film cannot be obtained. From the above viewpoint, the pH is more preferably 2.0 to 5.5, and still more preferably 3.0 to 4.5. In order to adjust the pH of the surface treatment agent, acidic compounds such as nitric acid and sulfuric acid and basic compounds such as sodium hydroxide, potassium hydroxide, and ammonia can be used.

<Surface-Treated Metal>

The surface-treated metal includes a surface treatment film obtained by curing the surface treatment agent according to the present embodiment on the surface of a metal substrate that is an object to be coated. The surface-treated metal according to the present embodiment has not only excellent adhesion between the surface treatment film and the metal substrate as well as corrosion resistance, but also excellent adhesion between a coating film and the surface treatment film as well as corrosion resistance when the coating film such as an electrodeposited coating film is further formed on the surface treatment film. The metal substrate is not particularly limited, and examples thereof include an iron-based substrate, an aluminum-based substrate, a zinc-based substrate, and a magnesium-based substrate. Here, the iron-based substrate, the aluminum-based substrate, the zinc-based substrate, and the magnesium-based substrate respectively mean an iron-based substrate composed of iron and/or an alloy thereof, an aluminum-based substrate composed of aluminum and/or an alloy thereof, a zinc-based substrate composed of zinc and/or an alloy thereof, and a magnesium-based substrate composed of magnesium and/or an alloy thereof. The metal substrate may be composed of a plurality of metal substrates selected from among an iron-based substrate, an aluminum-based substrate, and a zinc-based substrate.

In the surface-treated metal according to the present embodiment, the content of the metal component (A) in the surface treatment film formed by the surface treatment agent is preferably 5 to 500 mg/m² in terms of metal element. When the content of the metal component (A) is less than 5 mg/m², a uniform surface treatment film cannot be obtained. When the content of the metal component (A) exceeds 500 mg/m², no further effect can be obtained, which is economically disadvantageous. The content of the metal component (A) is more preferably 5 to 200 mg/m². In the surface treatment film formed by the surface treatment agent, C/A, which is the ratio of the content of carbon to the content of the metal component (A), is preferably 7 to 25%.

The surface-treated metal having the surface treatment film obtained by curing the surface treatment agent of the present embodiment is formed by causing a polymerization reaction or the like of components contained in the surface treatment agent. Thus, the structure of the resulting polymer becomes complex, making it impossible or essentially impractical to directly specify the surface treatment film by its structure. That is, there are circumstances where it is impossible or impractical to directly specify the surface-treated metal of the present embodiment by its structure or characteristics (impossible or impractical circumstances).

<Surface Treatment Method>

The surface treatment method for treating the surface of the metal substrate using the surface treatment agent according to the present embodiment may include a surface treatment film forming step and an electrodeposited coating film forming step.

(Surface Treatment Film Forming Step)

The surface treatment film forming step is a step of forming a surface treatment film on the surface of the metal substrate to produce a surface-treated metal. The surface treatment film forming step is performed by bringing the surface treatment agent into contact with the surface of the metal substrate. The contact method is not particularly limited, and examples thereof include an immersion method, a spray method, and a roll coating method. The treatment temperature in the surface treatment film forming step may be in the range of 15 to 70° C., and is preferably in the range of 30 to 50° C. The treatment time in the surface treatment film forming step may be in the range of 5 to 1200 seconds, and is preferably in the range of 30 to 120 seconds.

(Electrodeposited Coating Film Forming Step)

In the electrodeposited coating film forming step, the surface-treated metal produced in the surface treatment film forming step is subjected to electrodeposition coating to form an electrodeposited coating film on the surface. The electrodeposition coating is not particularly limited, and, for example, it is possible to use cationic electrodeposition coating. The cationic electrodeposition paint used for the cationic electrodeposition coating is not particularly limited, and it is possible to use a conventionally known cationic electrodeposition paint made of an aminated epoxy resin, an aminated acrylic resin, an epoxy resin in a sulfonium form, or the like. The electrodeposition coating method using the electrodeposition paint is not particularly limited, and a known electrodeposition coating method can be applied.

(Other Steps)

In the surface treatment method according to the present embodiment, a degreasing treatment step and a post-degreasing water-rinsing treatment step may be performed before the surface treatment film forming step. Another surface treatment step may be performed after the post-degreasing water-rinsing treatment step and before the surface treatment film forming step, and a post-surface treatment water-rinsing treatment step may be performed after the surface treatment film forming step and before the electrodeposited coating film forming step.

The degreasing treatment step is performed by performing an immersion treatment at, for example, 30 to 55° C. for about several minutes with a degreasing agent such as a phosphorus-free/nitrogen-free degreasing cleaning liquid. A preliminary degreasing treatment may be performed before the degreasing treatment step.

In the post-degreasing water-rinsing treatment step, the degreasing agent is rinsed with water after the degreasing treatment, in which the degreasing agent is sprayed with a large amount of rinse water once or several times.

The post-surface treatment water-rinsing treatment step is performed by performing one or more spray treatments or immersion water-rinsing within a range that does not affect adhesion and corrosion resistance after coating. The final water-rinsing treatment is preferably performed with ion-exchanged water or pure water. After the post-surface treatment water-rinsing treatment step, a step of drying the surface-treated metal may be provided as necessary.

In the above embodiment, the surface treatment method for treating the surface of the metal substrate includes the electrodeposited coating film forming step. The surface treatment method of the present invention may include, instead of the electrodeposited coating film forming step, a step of performing any of powder coating, aqueous coating, and solvent coating on the object to be coated on which the surface treatment film has been formed. The step of performing powder coating, aqueous coating, or solvent coating is not particularly limited, and a conventionally known method can be used. The surface treatment agent according to the present embodiment can impart corrosion resistance equivalent to that imparted to an electrodeposited coating film, to a coating film formed by powder coating, aqueous coating, or solvent coating.

EXAMPLES

Hereinafter, the content of the present disclosure will be described in more detail based on Examples. The content of the present disclosure is not limited to the following Examples.

Example 1

A commercially available cold-rolled steel sheet (SPCC-SD, manufactured by Nippon Testpanel Co., Ltd., 70 mm×150 mm×0.8 mm) was used as the metal substrate, and subjected to surface treatment under the following conditions.

As the degreasing treatment step, the substrate was immersed in 2% by mass of “SURFCLEANER 53” (degreasing agent, manufactured by Nippon Paint Surf Chemicals, Co., Ltd.) at 40° C. for 2 minutes. As the post-degreasing water-rinsing treatment step, the substrate was sprayed with tap water for 30 seconds. As the surface treatment step, the surface treatment agent was prepared using zircon hydrofluoric acid, alkyldiallylamine polymer (alkyldiallylamine segment: 100 mol %, molecular weight 20000, hydrochloric acid (pKa-3.7) salt), and zinc nitrate hexahydrate (Zn(NO₃)₂·6H₂O) such that the content of Zr was 100 ppm by mass in terms of metal element, the fluorine concentration was 125 ppm by mass, the content of the alkyldiallylamine polymer was 150 ppm by mass in terms of resin solid content concentration, the content of Al was 50 ppm by mass, and the content of Zn was 500 ppm by mass as shown in Table 1. The pH was adjusted to 4.2 using sodium hydroxide. The temperature of the surface treatment agent was adjusted to 40° C., and the metal substrate was immersed in the surface treatment agent for 120 seconds.

As the post-surface treatment water-rinsing treatment step, the substrate was sprayed with tap water for 30 seconds. Furthermore, the substrate was sprayed with ion-exchanged water for 30 seconds. Subsequently, as the drying treatment, the substrate was dried in an electric drying furnace at 80° C. for 5 minutes. The content (mg/m²) of Zr as the metal component (A) and the content (mg/m²) of C derived from the alkyldiallylamine polymer in the surface treatment film were measured using “ZSX Primus II” (X-ray analyzer manufactured by Rigaku Corporation). The results were presented in Table 2. In Table 2, the “Zr film amount” indicates the content of zirconium as the metal component (A) in the surface treatment film, and the “C film amount” indicates the content of carbon in the surface treatment film.

As the electrodeposited coating film forming step, the substrate was subjected to electrodeposition coating so as to have a dried film thickness of 20 μm using “POWERNICS 310” (cationic electrodeposition paint manufactured by NIPPON PAINT AUTOMOTIVE COATINGS CO., LTD.), then rinsed with water, and then the coating film was baked by heating at 170° C. for 20 minutes to prepare a test plate of Example 1.

OTHER EXAMPLES AND COMPARATIVE EXAMPLES

Each of the test plates of other Examples and Comparative Examples was prepared in the same manner as in Example 1, except that the composition of the surface treatment agent in the surface treatment step was as shown in Table 1, and that the metal substrate or the treatment temperature was as shown in Table 2. Aluminum nitrate nonahydrate was used as an aluminum component, zinc nitrate hexahydrate was used as a zinc (Zn) component, copper nitrate trihydrate was used as a copper (Cu) component, and the surface treatment agent was prepared such that the contents of Al and Cu became the concentrations shown in Table 1. In Examples 15 to 18, two types of resins (polymers) were used in combination. The mixture of two types of resins in Examples 15 to 17 was the combination of PAS-M-1:PAA-D19HCl shown below, with Example 15 being 1:3, Example 16 being 1:1, and Example 17 being 3:1 (all in ppm by mass ratio). Example 18 was the combination of PAS-M-1:PAS-21CL of 1:1 (in ppm by mass ratio). In Example 19, PAS-M-1 and a silane coupling agent were used in combination, and in Example 20, surface treatment was performed at a low temperature. The concentration (ppm by mass) of each component shown in Table 1 means the concentration of each component with respect to the total mass of the surface treatment agent. In Table 1, the “alkyldiallylamine polymer (C)” is abbreviated as “polymer (C)”. Details of the symbols (abbreviations) shown in Tables 1 and 2 are shown below.

(Alkyldiallylamine Polymer (C))

Hereinafter, the following items, unless otherwise noted, were manufactured by Nittobo Medical Co., Ltd. Mw means a weight average molecular weight.

• • PAS-M-1: methyldiallylamine hydrochloride polymer (Mw: 20,000)
  • PAS-M-1L: methyldiallylamine hydrochloride polymer (Mw: 5,000)
  • PAS-M-1A: methyl diallylamine acetate polymer (Mw: 20,000)
  • PAS-22SA-40: methyl diallylamine amide sulfate polymer (Mw: 15,000)
  • PAS-2201Cl: methyldiallylamine hydrochloride-sulfur dioxide copolymer (Mw: 3,000)

(Other Components)

• • PAA-D19HCl: allylamine hydrochloride-diallylamine hydrochloride copolymer (Mw: 40,000, Segment Ratio: allylamine segment 5%, diallylamine segment (R¹ in the above formula (1a) is a hydrogen atom) 95%).
  • PAS-21CL: diallylamine hydrochloride polymer (Mw: 20,000), a polymer having diallylamine segments in which R¹ in the above formula (1a) is a hydrogen atom.
  • KBM-603: N-2 (aminoethyl) 3-aminopropyltrimethoxysilane manufactured by Shin-Etsu Chemical Co., Ltd.
  • Al: aluminum nitrate nonahydrate (manufactured by FUJIFILM Wako Pure Chemical Corporation)
  • Zn: zinc (II) nitrate hexahydrate (manufactured by FUJIFILM Wako Pure Chemical Corporation)
  • Cu: copper (II) nitrate trihydrate (manufactured by FUJIFILM Wako Pure Chemical Corporation)

(Substrate)

• • SPC: cold-rolled steel sheet (SPCC-SD, manufactured by Nippon Testpanel Co., Ltd., 70 mm×150 mm×0.8 mm)
  • GA: alloyed hot-dip galvanized steel sheet (SCGA270D, manufactured by Nippon Testpanel Co., Ltd., 70 mm×150 mm×0.8 mm)
  • GI: hot-dip galvanized steel sheet (GC090190AB, manufactured by Etalon, 70 mm×150 mm×0.8 mm)
  • Al: aluminum alloy (6K₂₁, manufactured by Kobe Steel, Ltd., 70 mm×150 mm×0.8 mm)

The pKa of acetic acid, which is an acid forming an acid addition salt, is 4.8, and the pKa of sulfamic acid is 1.0.

[Adhesion Test 1]

Each of the test plates of the Examples and Comparative Examples was cut into a grid of 10×10 squares with a width of 1 mm so as to reach the base metal. Thereafter, a Cellotape (registered trademark) peeling test was carried out on the grid-cut surface of the electrodeposited coating film to measure the peeling rate of the coating film. Evaluation was carried out according to the following criteria, and 4 or more was judged to be acceptable. The results are shown in Table 2.

(Evaluation Criteria)

• • 5: peeled off squares 0/100
  • 4: peeled off squares 1/100 to 5/100
  • 3: peeled off squares 6/100 to 10/100
  • 2: peeled off squares 11/100 to 50/100
  • 1: peeled off squares 50/100 to 100/100

[Adhesion Test 2]

The test plates of the Examples and Comparative Examples were immersed in pure water at 40° C. for 240 hours. Excess moisture in the test plates was then wiped off with cloth. Then, each of the test plates was cut into a grid of 10×10 squares with a width of 1 mm so as to reach the base metal. Thereafter, a Cellotape (registered trademark) peeling test was carried out on the grid-cut surface of the electrodeposited coating film to measure the peeling rate of the coating film. Evaluation was carried out according to the same criteria as described above, and 4 or more was judged to be acceptable. The results are shown in Table 2.

TABLE 1
						Weight
						Average
						Molecular
		Zr	Fluorine		Counterion	Weight (Mw)	Alkyldiallylamine
		Concentration	Concentration	Polymer	to Polymer	of Polymer	Segment
		(ppm by mass)	(ppm by mass)	(C)	(C)	(C) (Mw)	(mol %)
Example	1	100	125	PAS-M-1	Hydrochloric	20000	100
					acid
	2	200	250	PAS-M-1	Hydrochloric	20000	100
					acid
	3	300	375	PAS-M-1	Hydrochloric	20000	100
					acid
	4	500	625	PAS-M-1	Hydrochloric	20000	100
					acid
	5	200	250	PAS-M-1L	Hydrochloric	5000	100
					acid
	6	200	250	PAS-M-1A	Acetic acid	20000	100
	7	200	250	PAS-22SA-40	Sulfuric acid	15000	100
	8	200	250	PAS-M-1	Hydrochloric	20000	100
					acid
	9	200	250	PAS-M-1	Hydrochloric	20000	100
					acid
	10	200	250	PAS-M-1	Hydrochloric	20000	100
					acid
	11	200	250	PAS-M-1	Hydrochloric	20000	100
					acid
	12	1000	1250	PAS-M-1	Hydrochloric	20000	100
					acid
	13	200	250	PAS-M-1	Hydrochloric	20000	100
					acid
	14	200	250	PAS-2201C1	Hydrochloric	3000	50
					acid
	15	300	250	PAS-M-1	Hydrochloric	20000	100
					acid
	16	300	250	PAS-M-1	Hydrochloric	20000	100
					acid
	17	300	250	PAS-M-1	Hydrochloric	20000	100
					acid
	18	300	250	PAS-M-1	Hydrochloric	20000	100
					acid
	19	300	250	PAS-M-1	Hydrochloric	20000	100
					acid
	20	300	250	PAS-M-1	Hydrochloric	20000	100
					acid
Comparative	1	200	250	—	—	—	—
Example	2	450	563	—	—	—	—
	3	200	250	—	—	—	—

			Solid Content	Other Component
			Concentration	& Solid Content	Al	Zn	Cu
			of Polymer (C)	Concentration	Concentration	Concentration	concentration
			(ppm by mass)	(ppm by mass)	(ppm by mass)	(ppm by mass)	(ppm by mass)
	Example	1	150	—	50	500	0
		2	100	—	50	500	0
		3	50	—	50	500	0
		4	30	—	50	500	0
		5	100	—	50	500	0
		6	100	—	50	500	0
		7	100	—	50	500	0
		8	100	—	50	500	0
		9	100	—	50	500	0
		10	100	—	50	500	0
		11	2500	—	50	500	0
		12	100	—	50	500	0
		13	100	—	50	500	100
		14	100	—	50	500	0
		15	25	PAA-D19HCl	50	500	0
				(75)
		16	50	PAA-D19HCl	50	500	0
				(50)
		17	75	PAA-D19HCl	50	500	0
				(25)
		18	50	PAS-21CL (50)	50	500	0
		19	100	KBM-603 (100)	50	500	0
		20	100	—	50	500	0
	Comparative	1	0		50	500	0
	Example	2	0	KBM-603 (100)	50	500	0
		3	0	PAS-21CL (100)	50	500	0

	TABLE 2
	Treatment		Evaluation

Temperature

Film Amount

Adhesion

Adhesion

	Substrate	(° C.)	Zr	C	1	2

Example	1	SPC	40	25.4	3.2	5	5
	2	SPC	40	30.8	3.7	5	5
	3	SPC	40	36.9	4.0	5	5
	4	SPC	40	45.6	3.5	5	5
	5	SPC	40	43.2	5.7	5	5
	6	SPC	40	37.9	5.4	5	5
	7	SPC	40	39.4	4.3	5	5
	8	GA	40	30.1	5.0	5	5
	9	Al	40	42.5	4.2	5	5
	10	GI	40	65.9	5.1	5	5
	11	SPC	40	35.6	4.0	5	5
	12	SPC	40	30.9	4.0	5	5
	13	SPC	40	80.7	6.1	5	5
	14	SPC	40	16.9	3.8	5	5
	15	SPC	40	36.5	6.3	5	5
	16	SPC	40	26.3	5.4	5	5
	17	SPC	40	28.5	6.3	5	5
	18	SPC	40	25.3	5.6	5	5
	19	SPC	40	25.9	4.0	5	5
	20	SPC	25	27.7	3.3	5	5
Comparative	1	SPC	40	58.7	3.1	2	1
Example	2	SPC	40	65.4	6.4	2	3
	3	SPC	40	30.8	7.5	3	3

From the results of Tables 1 and 2, it was confirmed that the surface treatment agent according to each of the Examples provided favorable adhesion after coating compared to the surface treatment agents according to the Comparative Examples.