JP5231377B2 - Method of coating iron-based substrate with powder coating - Google Patents

Description

  The present invention relates to a method for coating an iron-based substrate with a powder coating film.

As powder coatings, epoxy resins, acrylic resins, polyester resins, etc. are used as main binders, and if necessary, curing agents such as polycarboxylic acids, melamine resins and blocked isocyanates are widely known. It is used in many fields such as home appliances, automobiles, and building materials. Among them, the powder coating composition mainly composed of the thermosetting resin composition is required to be baked at a certain temperature or higher, usually 180 ° C. or higher.
Such high-temperature baking requires a large amount of energy, and therefore is not environmentally preferable.
In order to solve this problem, Japanese Patent Application Laid-Open No. 2001-294805 discloses a β-hydroxyalkylamide curing agent represented by the following formula and a resin solid content acid value of 10 to 100, and a softening point of 80 to 150 ° C. A powder coating composition containing particles mainly composed of a polyester resin, wherein the particles have a volume average particle diameter of 5 to 30 μm, the equivalent number of hydroxyl groups of the curing agent and the carboxyl groups of the polyester resin The powder coating composition whose ratio with the number of equivalents is 0.4 to 1.3:

(Wherein R ¹ is a hydrogen atom, a methyl group or an ethyl group, R ² is a hydrogen atom, an alkyl group having 1 to 5 carbon atoms or HOCH (R ¹ ) CH ₂ —, and A is a divalent hydrocarbon. Represents the group).
By using this powder coating composition, it is possible to form a coating film with excellent low-temperature curability and high appearance, but for coating an iron-based substrate, water resistance, light resistance, heat resistance, etc. In view of obtaining a powder coating film having excellent secondary physical properties, there was still room for improvement.

  An iron-based substrate to be coated with a powder coating is usually subjected to chemical conversion treatment for the purpose of improving performances such as corrosion resistance and coating film adhesion before coating with the powder coating. A chemical conversion treatment method that can improve adhesion and corrosion resistance of the coating film, does not use chrome, which is a harmful metal, and does not rely on a zinc phosphate-based treatment agent that is problematic in terms of economy and workability in wastewater treatment. As a method, a method using a metal surface treatment agent composed of a zirconium compound is known (for example, Patent Document 2).

JP 2001-294805 A Japanese Patent Application Laid-Open No. 2004-218070

  In view of the above background, the present invention is a method for coating an iron-based substrate with a powder coating, which can be baked at a low temperature, and has water resistance, light resistance, and An object of the present invention is to provide a method for obtaining a powder coating film that is excellent in secondary physical properties including a performance evaluation test in which addition to a coating film such as heat resistance is increased.

One aspect of the present invention is a method of coating an iron-based substrate,
The surface of the iron-based substrate
(A) at least one selected from zirconium, titanium, and hafnium,
(B) by treating with a chemical conversion treatment agent containing fluorine and (c) an amino-functional compound;
Step A for forming the chemical conversion treatment layer,
On the chemical conversion treatment layer, a polyester resin having an acid value of 30 to 70 mgKOH / g, and a general formula I
(Wherein R ¹ represents a hydrogen atom, a methyl group or an ethyl group, R ² represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms or HO—CH (R ¹ ) —CH ₂ —, and A represents 2 A step B of applying a powder coating composition containing a β-hydroxyalkylamide curing agent represented by the following formula: and a step C of baking and curing the powder coating composition;
It is the method characterized by having.

In the step C, the powder coating composition is preferably baked and cured at a temperature of 130 ° C. to 160 ° C.
Said amino-functional compound is preferably
An amino-functional silane coupling agent, a hydrolyzate thereof, and a condensate thereof,
Polyallylamine,
It is at least one selected from amine-modified epoxy resins and amine-modified phenol resins.
The content of the amino functional compound in the chemical conversion treatment agent is preferably in the range of 5 to 5000 ppm based on the total mass of the chemical conversion treatment agent.
The pH of the chemical conversion treatment agent is preferably 2.5 to 5.0.
The polyester resin preferably has a weight average molecular weight of 1,000 to 150,000.
The iron-based substrate is preferably at least one selected from the group consisting of a cold-rolled steel plate, an electrogalvanized steel plate, a hot-dip galvanized steel plate, tinplate, and stainless steel.
The mass ratio of the β-hydroxyalkylamide curing agent and the polyester resin in the powder composition is preferably 3/97 to 10/90.
The volume average particle diameter of the powder coating composition is preferably 20 to 40 μm.

  Another aspect of the present invention is an iron-based substrate coated by the above method.

  Another aspect of the present invention is an article containing an iron-based substrate coated by the above method.

  In the present specification, unless otherwise indicated, ppm means mg / kg.

According to the method of coating an iron-based substrate of the present invention, a powder coating film that can be baked at a low temperature and has excellent secondary physical properties such as water resistance, light resistance, and heat resistance. Is obtained.
Further, the iron-based substrate coated with the “method of coating an iron-based substrate” of the present invention, and an article containing the iron-based substrate, the coating film has water resistance, light resistance, heat resistance, etc. Excellent secondary physical properties.

  Hereinafter, the present invention will be described in detail.

Hereinafter, a method for coating the metal of the present invention (specifically, an iron-based substrate) will be described in detail.
<Process A>
The method of coating the iron-based substrate of the present invention includes:
The surface of the iron-based substrate
(A) at least one selected from zirconium, titanium, and hafnium,
(B) by treating with a chemical conversion treatment agent containing fluorine and (c) an amino-functional compound;
Step A for forming the chemical conversion treatment layer,
Have

  “At least one selected from zirconium, titanium, and hafnium” used in the chemical conversion treatment agent is a chemical conversion film (oxide film) forming component, and the substrate is at least selected from the group consisting of zirconium, titanium, and hafnium. By forming the chemical conversion film containing one kind, the corrosion resistance and wear resistance of the base material can be improved, and the adhesion to the coating film can be further improved.

For example, in the case of a chemical conversion treatment agent containing zirconium, zirconium in the chemical conversion treatment agent forms a complex with fluorine. When the surface treatment of the iron-based substrate is carried out using the chemical conversion treatment agent, the metal ions eluted in the chemical conversion treatment agent by the metal dissolution reaction extract the fluorine of ZrF ₆ ^2- , and the interface pH rises. Thus, it is considered that a zirconium hydroxide or oxide is generated, and this zirconium hydroxide or oxide is deposited on the surface of the substrate. However, the present invention is not limited to the one having this mechanism. When a surface treatment is performed using the chemical conversion treatment agent, a chemical conversion film firmly attached to the object to be treated is obtained by a chemical reaction, and thus water washing can be performed after the treatment.

The zirconium source is not particularly limited, and examples thereof include soluble fluorozirconates such as K ₂ ZrF ₆ , (NH ₄ ) ₂ ZrF ₆ , H ₂ ZrF _6, and other salts of fluorozirconate and salts thereof; Zirconium oxide; zirconium oxide and the like can be mentioned.

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 hafnium supply source 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 content of “at least one selected from the group consisting of zirconium, titanium, and hafnium” contained in the chemical conversion treatment agent is within a range of a lower limit of 20 ppm and an upper limit of 10000 ppm in terms of metal, based on the total mass of the chemical conversion treatment agent. Preferably there is. When the content is less than the lower limit, the performance of the chemical conversion film may be insufficient. On the other hand, when the content exceeds the upper limit, a further effect may not be expected, which may be economically disadvantageous. There is. The lower limit is more preferably 50 ppm, and the upper limit is more preferably 2000 ppm. The lower limit is more preferably 150 ppm, and the upper limit is more preferably 500 ppm.

  Fluorine contained in the chemical conversion treatment agent serves as an etching agent for the substrate. The fluorine supply source is not particularly limited. For example, fluorine may be derived from the above-described fluorine-containing compounds as a zirconium source, a titanium source, and a hafnium source. In addition, as a supply source of fluorine, fluorides such as hydrofluoric acid, ammonium fluoride, boron fluoride acid, ammonium hydrogen fluoride, sodium fluoride, sodium hydrogen fluoride; and hexafluorosilicate (Eg, hydrofluoric acid, zinc silicofluoride, manganese silicofluoride, magnesium silicofluoride, nickel silicofluoride, iron silicofluoride, calcium silicofluoride), etc. Can also be mentioned.

  The fluorine ion content (free fluorine) contained in the chemical conversion treatment agent varies depending on the pH of the chemical conversion treatment agent, etc., but is within the range of a lower limit of 20 ppm and an upper limit of 10,000 ppm based on the total mass of the chemical conversion treatment agent. Is preferred. The lower limit is more preferably 50 ppm, and the upper limit is more preferably 2000 ppm. The lower limit is more preferably 150 ppm, and the upper limit is more preferably 700 ppm. The fluorine ion content can be measured with a fluorine ion meter.

  The amino functional compound contained in the chemical conversion treatment agent is a compound having at least one (preferably two or more) amino functional group in the molecule. The amino functional compound is presumed to improve the adhesion between the chemical conversion film and the coating film formed from the powder coating composition. However, the present invention is not limited to the one having this mechanism.

The amino functional compound is not particularly limited, but preferably
An amino-functional silane coupling agent, a hydrolyzate thereof, and a condensate thereof,
Polyallylamine,
Examples include amine-modified epoxy resins and amine-modified phenol resins.

  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.

  The condensate 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) A commercially available product such as ethyl) -3-aminopropyltrimethoxysilane (manufactured by Chisso Corporation) can be hydrolyzed and condensed by a known method. Commercially available products such as KBP-90 (manufactured by Shin-Etsu Chemical Co., Ltd .: active ingredient 32%) can also be used as the condensate.

The polyallylamine is a water-soluble resin having a structural unit represented by the following formula (1). Preferably, the polyallylamine is a water-soluble resin composed only of a structural unit represented by the following formula (1).

For example, PAA series (Nittobo Co., Ltd.) can be used as the polyallylamine.
Among them, PAA10C (polyallylamine resin, molecular weight 15000, Nittobo Co., Ltd.) is preferable.

The amine-modified epoxy resin is not particularly limited as long as it is an epoxy skeleton resin having an amino group. The epoxy resin is not particularly limited. For example, bisphenol A type epoxy resin, bisphenol F type epoxy resin, hydrogenated bisphenol A type epoxy resin, hydrogenated bisphenol F type epoxy resin, bisphenol A propylene oxide addition type epoxy resin, bisphenol F propylene oxide addition type epoxy resin, novolak type epoxy resin, etc. can be mentioned. Among these, bisphenol F type epoxy resin is preferable, and bisphenol F epichlorohydrin type epoxy resin is more preferable. The amino group is not particularly limited, and examples thereof include -NH ₂ group, monoalkylamino group, dialkylamino group, monohydroxyamino group, dihydroxyamino group, and other compounds having primary to tertiary amines. Can do. The reaction for introducing an amino group into the epoxy resin forming the skeleton is not particularly limited, and examples thereof include a usual method such as a method of mixing an epoxy resin and an amine compound in a solvent.

The amine-modified phenol resin is not particularly limited as long as it is a phenol skeleton resin having an amino group. For example, NPK series (Sumitomo Bakelite) can be used, and Sumilite Resin-NPK-261 (Amine-modified phenolic resin, Sumitomo Bakelite) is preferably used.
The said amino functional compound may be used independently and may be used in combination of 2 or more type.

  The content of the amino functional compound in the chemical conversion treatment agent is preferably in the range of a lower limit of 5 ppm and an upper limit of 5000 ppm based on the total mass of the chemical conversion treatment agent. If it is less than 5 ppm, there is a possibility that a film having sufficient coating film adhesion cannot be obtained. If it exceeds 5000 ppm, no further effect can be expected, which may be disadvantageous economically. The lower limit is more preferably 10 ppm and even more preferably 50 ppm. The upper limit is more preferably 1000 ppm and even more preferably 500 ppm.

  It is preferable that the chemical conversion treatment agent is substantially free of phosphate ions. “Substantially free of phosphate ions” means that phosphate ions are not included to the extent that they act as components in the chemical conversion treatment agent. Since the chemical conversion treatment agent used in the present invention does not substantially contain phosphate ions, it does not substantially use phosphorus that causes environmental burdens, and a zinc phosphate-based treatment agent is used. Generation | occurrence | production of sludge like iron phosphate, zinc phosphate, etc. which generate | occur | produce can be suppressed.

  The chemical conversion treatment agent preferably has a pH in the range of a lower limit of 2.5 and an upper limit of 5.0. If the pH is less than the lower limit, etching may be excessive and sufficient film formation may not be possible. On the other hand, if the pH exceeds the upper limit, etching may be insufficient and a good film may not be obtained. The lower limit is more preferably 3.0, and the upper limit is more preferably 4.5. 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.

  The chemical conversion treatment agent may further contain at least one selected from the group consisting of magnesium ion, zinc ion, calcium ion, aluminum ion, gallium ion, indium ion, tin ion and copper ion as an adhesion and corrosion resistance imparting agent. 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 magnesium ion, zinc ion, calcium ion, aluminum ion, gallium ion, indium ion and copper ion in the chemical conversion treatment agent is based on the total mass of the chemical conversion treatment agent. It is preferable to be within a range of 1 ppm and an upper limit of 5000 ppm. If the content is less than the lower limit, a sufficient effect may not be obtained. When the content exceeds the upper limit, no further improvement in the effect is observed, which may be disadvantageous economically, and adhesion after coating may be deteriorated. The lower limit is more preferably 25 ppm, and the upper limit is more preferably 3000 ppm.

  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.

  The chemical conversion treatment in Step A of the present invention is not particularly limited, and can be performed by bringing a chemical conversion treatment agent into contact with the metal surface 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 treatment time in the chemical conversion treatment is preferably in the range of a lower limit of 5 seconds and an upper limit of 20 minutes. The lower limit is more preferably 30 seconds, and the upper limit is more preferably 2 minutes. 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 chemical conversion treatment in step A of the present invention, before the chemical conversion treatment, the surface of the iron-based substrate may be subjected to a degreasing treatment and a degreasing water washing treatment. After the chemical conversion treatment, a post-chemical conversion water washing treatment may or may not be performed.
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 may be performed as necessary. If desired, a preliminary degreasing process may be performed before the degreasing process.

The post-degreasing rinsing treatment can be performed by spraying once or more with a large amount of rinsing water in order to wash the degreasing agent after degreasing.
The post-chemical conversion rinsing treatment is preferably carried out 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, the powder coating composition of Step B, which will be described later, is applied after drying according to a known method.

  As an iron-type base material coat | covered by the method of this invention, it consists of a SPCC steel plate (cold rolled steel plate), a SECC bonde steel plate (electrogalvanized steel plate), SGCC (hot dip galvanized steel plate), SPTE (tinplate), stainless steel. Examples include materials selected from the group. As the stainless steel, SUS304, SUS304L, SUS303, SUS316, SUS316L, or the like may be used.

  The pretreatment of the iron-based substrate is not particularly limited. That is, as the iron-based substrate, galvanized steel sheet, zinc-nickel plated steel sheet, zinc-iron plated steel sheet, zinc-chromium plated steel sheet, zinc-aluminum plated steel sheet, zinc-titanium plated steel sheet, zinc-magnesium plated steel sheet, Examples thereof include zinc-based electroplating such as zinc-manganese-plated steel plate, hot-dip plating, zinc-plated alloy-plated steel plate such as vapor-deposited steel plate, and the like.

Conversion coating obtained by painting pretreatment method of the present invention, the lower limit 0.1 mg / ^{m 2} in a total amount of metal (zirconium, titanium, hafnium) the coating weight is comprised chemical conversion treatment agent, the range of the upper limit 500 mg / ^{m 2} It is preferable to be within. If the total amount is less than the lower limit, a uniform chemical conversion film may not be obtained. On the other hand, if the total amount exceeds the above upper limit, no further effect is obtained, which may be disadvantageous economically. The lower limit is more preferably 5 mg / m ² , and the upper limit is more preferably 200 mg / m ² .

<Process B>
The method of coating the iron-based substrate of the present invention comprises a polyester resin having an acid value of 30 to 70 mgKOH / g on the chemical conversion treatment layer formed in the step A, and a general formula I

(Wherein R ¹ represents a hydrogen atom, a methyl group or an ethyl group, R ² represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms or HO—CH (R ¹ ) —CH ₂ —, and A represents 2 And a step B of applying a powder coating composition containing a β-hydroxyalkylamide curing agent represented by the formula:

The polyester resin has an acid value of 30 to 70 mgKOH / g.
In the present specification, the acid value of the polyester resin means the number of mg (mg KOH / g) of potassium hydroxide necessary for neutralization of 1 g of the nonvolatile content of the polyester resin.
In this specification, the acid value of a polyester resin can be determined by the method based on JISK0070.
When the acid value is outside the above range, the curability and corrosion resistance of the coating film may be reduced.

The softening point of the polyester resin is preferably 80 to 150 ° C, and more preferably 90 to 130 ° C. When the said softening point is lower than 80 degreeC, there exists a possibility that blocking resistance may fall, and when higher than 150 degreeC, there exists a possibility that the smoothness of the coating film obtained may fall.
On the other hand, the weight average molecular weight of the polyester resin is preferably 1000 to 150,000, more preferably 3000 to 70000, and still more preferably 4000 to 50000. If the weight average molecular weight is too small, the performance and physical properties of the resulting coating film may be reduced. On the other hand, if the weight average molecular weight is too large, the smoothness and appearance of the resulting coating film will be reduced. There is a fear.
In the present specification, the softening point of the polyester resin can be determined by a method according to JIS K 2207. In the present specification, the weight average molecular weight and the number average molecular weight can be determined by gel permeation chromatography (GPC) using polystyrene as a standard substance.

  The polyester resin may be a composite of two or more polyester resins. In that case, the above-mentioned physical property values and characteristic values mean values of the entire composite.

  Such a polyester resin can be obtained by subjecting an acid component mainly containing a polyvalent carboxylic acid and an alcohol component mainly containing a polyhydric alcohol to polycondensation by an ordinary method. By selecting the respective components and the conditions for condensation polymerization, a polyester resin having the above physical property values and special values can be obtained. Here, “mainly” means occupying 70 mol% or more of the whole.

  The acid component is not particularly limited, and examples thereof include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, trimellitic acid and anhydrides thereof, 2,6-naphthalenedicarboxylic acid, and 2,7-naphthalenedicarboxylic acid. Examples thereof include acids and anhydrides thereof, succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, saturated aliphatic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, and anhydrides thereof. In addition, lactones such as γ-butyrolactone and ε-caprolactone, and corresponding hydroxycarboxylic acids, aromatic oxymonocarboxylic acids such as p-oxyethoxybenzoic acid, and the like can be mentioned. Two or more acid components may be used. Of these, isophthalic acid and terephthalic acid are preferable in terms of durability, physical properties, and cost. The proportion of terephthalic acid and isophthalic acid in the total acid component is 70 mol% or more, preferably 75 mol% or more, particularly preferably 80 mol% or more. Here, “the total proportion of terephthalic acid and isophthalic acid as the acid component is 70 mol% or more” means that these are used as the main raw material. About the upper limit of terephthalic acid and isophthalic acid content, it is good also considering the whole quantity of the acid component used for preparation of a polyester resin as a terephthalic acid and / or isophthalic acid. Further, when particularly improving weather resistance, the proportion of isophthalic acid in the total acid component is 70 mol% or more, preferably 80 mol% or more, particularly preferably 90 mol% or more. Here, “the proportion of isophthalic acid in the total acid component is 70 mol% or more” means that isophthalic acid is used as a main raw material.

  The alcohol component is not particularly limited. For example, ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,5-hexanediol, diethylene glycol, triethylene glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, bisphenol A alkylene oxide adduct, bisphenol S alkylene oxide adduct, 1,2-propanediol, neopentyl glycol, 1,2-butanediol, 1,3 -Butanediol, 1,2-pentanediol, 2,3-pentanediol, 1,4-pentanediol, 1,4-hexanediol, 2,5-hexanediol, 3-methyl-1,5-pentanediol, 1,2-dodecanediol, 1 Diols of 2 octadecanediol etc., trimethylol propane, glycerine, may be mentioned polyhydric alcohols such trivalent or more such as pentaerythritol and the like. Two or more alcohol components may be used.

The β-hydroxyalkylamide curing agent has the general formula I

(Wherein R ¹ represents a hydrogen atom, a methyl group or an ethyl group, R ² represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms or HO—CH (R ¹ ) —CH ₂ —, and A represents 2 Represents a valent hydrocarbon group.
In the formula, R ¹ is a hydrogen atom or a methyl group, R ² is HOCH (R ¹ ) CH ₂ —, and A is an alkylene group having 2 to 10 (more preferably 4 to 8) carbon atoms. Is preferred.
The curing agent is a known synthesis method, specifically, for example, a carboxylic acid and / or a carboxylic acid ester and β-hydroxyalkylamine are reacted in the presence of an alkoxide catalyst such as sodium or potassium. Can be obtained.
Examples of the carboxylic acid and carboxylic acid ester used here include succinic acid, adipic acid, glutaric acid, dimethyl succinate, diethyl succinate, and dimethyl adipate.
Examples of β-hydroxyalkylamine include N-methylethanolamine, diethanolamine, N-methylpropanolamine and the like.
Moreover, the β-hydroxyalkylamide curing agent represented by the general formula I is also available as a commercial product. Such a β-hydroxyalkylamide curing agent has, for example, the following chemical structure:

Examples include Primid XL552 (EMS-PRIMD).

  The powder coating composition used in the method of the present invention contains the β-hydroxyalkylamide curing agent and the carboxylic acid-containing polyester resin as main components. Here, “as the main component” means, for example, a total of the content of the β-hydroxyalkylamide curing agent and the content of the carboxylic acid-containing polyester resin with respect to the entire powder coating composition is 80% by mass or more. It means that.

  The mass ratio of the content of the curing agent to the content of the polyester resin in the powder composition is preferably 3/97 to 10/90. Outside this range, the curability of the coating film may be insufficient.

  The ratio of the number of equivalents of the hydroxyl group of the curing agent to the number of equivalents of the polyester resin carboxyl group is preferably 0.4 to 1.3. Outside this range, the curability of the coating film may be insufficient.

  The volume average particle diameter of the particles of the powder composition is preferably 20 to 40 μm. When the volume average particle size is less than 20 μm, the transportability of the powder coating material is lowered, which may cause a problem in coating workability and may cause a reduction in coating efficiency. On the contrary, when the average volume particle diameter exceeds 40 μm, the smoothness of the coating film is lowered, and the appearance of the coating film may be deteriorated. The volume average particle diameter is more preferably 20 to 30 μm. In addition, the said volume average particle diameter can be measured with a particle size analyzer (for example, Nikkiso Co., Ltd. make, Microtrac HRA X-100).

  Furthermore, in order to form a uniform coating film on the object having a complicated shape having a non-planar part, the ratio of particles having a particle diameter of 1/5 or less of the volume average particle diameter is 5% by mass or less. It is preferable to contain.

  The powder coating composition used in the method of the present invention preferably has a minimum melt viscosity of 60 to 2000 poise. If the minimum melt viscosity is too high, a coating film having a good appearance may not be obtained. If the minimum melt viscosity is too high, the effect of the above particle diameter may be reduced, and the melted coating film may have a sagging property ( Sagging property may be worsened.

Here, the minimum melt viscosity is the viscosity obtained by the following measurement:
The coating is heated at a rate of 10 ° C. per minute until the target temperature is reached, and then the melt viscosity of the coating is measured over time under the condition of maintaining the target temperature. Find the lowest viscosity and use it as the lowest melt viscosity.

  For the measurement of the minimum melt viscosity, it is preferable to use a complex viscosity by dynamic viscoelasticity measurement.

The powder coating composition used in the method of the present invention may contain a surface conditioner if desired. Examples of such surface conditioners include alkyl esters of (meth) acrylic acid such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and lauryl (meth) acrylate. Obtained from one or more kinds of raw materials, having an SP value of 9.0 or less, a number average molecular weight of 300 to 50000, preferably 1000 to 30000, and a glass transition temperature of less than 20 ° C., preferably An acrylic resin having a temperature of 0 ° C. or lower is preferably used.
When the SP value is too high, if it exceeds 9.0, it will approximate the SP value of the polyester resin, so that the polyester resin is in the process of melting the applied powder paint and forming a coating film. This is because it is difficult to positively move to the surface of the coating film, and as a result, it cannot be considered to contribute to improvement of the flow property on the surface of the coating film.

  Here, the SP value refers to a solubility parameter, which is described in detail in the literature (SUH, CLARKE, JPSA-1, 5, 1671-1681 (1967)), and its measuring method. Is a method well known to those skilled in the art, such as the turbidity method.

  On the other hand, when the glass transition temperature (Tg) exceeds 20 ° C., there is a possibility that a good appearance of the coating film cannot be obtained. And if the number average molecular weight is less than 300, even if it moves on the surface of the coating film, the effect of contributing to the flow property becomes small, and if it exceeds 50,000, it may be difficult to move on the surface of the coating film. is there.

  The amount of the acrylic resin as the surface conditioner in the powder coating composition used in the method of the present invention is 0.01 to 5 parts by mass with respect to 100 parts by mass in total of the curing agent and the polyester resin. Preferably, it is 0.05-3 mass parts, More preferably, it is 0.1-2 mass parts. If the amount of the acrylic resin is too small, the surface cannot be adjusted sufficiently and the probability of appearance failure is increased. On the other hand, if the amount of the acrylic resin is too large, the blocking property of the paint may be lowered.

  The powder coating composition used in the present invention may further contain inorganic fine particles or organic fine particles as a fluidity imparting agent. This is because inclusion of such fine particles can further improve transportability and blocking performance.

  Examples of the inorganic fine particles include hydrophobic silica, hydrophilic silica, aluminum oxide, and titanium oxide. Examples of commercially available inorganic fine particles include AEROSIL 130, AEROSIL 200, AEROSIL 300, AEROSIL R-972, AEROSIL R-812, AEROSIL R-812S, titanium dioxide T-805, titanium dioxide P-25, Aluminum Oxide C ( Nippon Aerosil Co., Ltd.), Carplex FPS-1 (Shionogi Pharmaceutical Co., Ltd.) and the like can be exemplified. The added amount of the inorganic particles is preferably 0.05 to 2 parts by mass with respect to 100 parts by mass of the entire powder coating composition, from the viewpoint of the effect to be imparted and the smoothness of the coating film and the coating efficiency. More preferably, it is 0.1-1 mass part. If the added amount is too small, the effect is reduced, and if the added amount is too large, the smoothness of the coating film may be lowered, or glossiness may occur.

  On the other hand, as the organic fine particles, non-crosslinked organic resin particles having a particle diameter of 0.001 to 0.5 μm, preferably 0.01 to 0.5 μm, or a particle diameter of 0.01 to 2 μm, preferably Is preferably a crosslinked organic resin particle of 0.01 to 1 μm. Examples of the organic resin include a vinyl resin, an acrylic resin, an epoxy resin, and a polyester resin. An acrylic resin is preferable because it can be easily produced industrially.

  The non-crosslinked organic resin particles are obtained by directly producing, for example, emulsion polymerization or suspension polymerization, or by producing a resin by solution polymerization or bulk polymerization, and pulverizing and classifying the resin. The glass transition temperature (Tg) of the non-crosslinked organic resin particles is 50 to 150 ° C., preferably 70 to 120 ° C. When non-crosslinked organic resin particles are used, when heat is applied to the powder coating, the organic resin fine particles themselves flow to obtain a coating film having an excellent appearance. If the Tg is less than 50 ° C., it is difficult to ensure sufficient anti-blocking performance of the powder coating during storage and transportation, while those having a Tg exceeding 150 ° C. are not very practical. The average particle diameter of the non-crosslinked organic resin fine particles is 0.001 to 0.5 μm, preferably 0.01 to 0.5 μm. Moreover, the addition amount is 0.05-35 mass parts with respect to 100 mass parts of the said whole powder coating materials, Preferably it is about 0.1-10 mass parts. This is because the average particle size of the non-crosslinked organic resin fine particles is proportional to the amount added, and the lower limit of the particle size is about 0.001 μm because of the ease of industrial production of the organic resin fine particles. The amount of addition of about 0.05% by mass is necessary for the manifestation of the effect due to the addition of particles, and the amount of addition of resin fine particles necessary for imparting blocking resistance increases as the particle size increases. When the particle size exceeds 0.5μ, the fluidity of the powder coating is deteriorated, and when the powder coating is applied by the coating gun, the powder coating particles adhere to the tip of the coating gun and tend to aggregate. As the invention object of obtaining a high-appearance coating film is difficult to achieve due to scattering of the coating film, the particle size is limited to a maximum of 0.5μ. Must be up to about 35% by mass It is based on the findings of that.

  Examples of monomers used in the production of non-crosslinked acrylic resins include acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, 2-hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxy Butyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, acrylic amide, methacrylic acid amide, acrylonitrile, methacrylonitrile, methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, 2- Examples include ethylhexyl (meth) acrylate and styrene.

  The crosslinked organic resin particles are fine particles of an organic resin having a three-dimensional structure, and are not substantially dissolved in a solvent and do not melt by heating at a baking temperature.

  The crosslinked organic resin particles are obtained by producing a resin by solution polymerization, bulk polymerization, or the like, and pulverizing and classifying the resin, but are obtained by directly producing by emulsion polymerization or suspension polymerization. Or obtained by performing a crosslinking reaction after the formation of non-crosslinked organic resin particles.

  The crosslinked organic resin fine particles preferably have an average particle diameter of 0.01 to 2 μm. If the average particle diameter exceeds 2 μm, the coating tends to be rough at the time of coating, whereas if the average particle diameter is less than 0.01 μm, it is not very effective. The amount is preferably 0.05 to 10 parts by mass (more preferably 0.1 to 5 parts by mass) with respect to 100 parts by mass of the whole powder coating material. If this amount is too small, the effect of improving blocking resistance may not be obtained. Conversely, if this amount is too large, the appearance may deteriorate.

  The crosslinked organic resin fine particles are preferably obtained from a vinyl resin, an acrylic resin, an epoxy resin, a polyester resin, etc., like the non-crosslinked organic resin particles, but among them, the acrylic resin is industrially produced. It is preferable because it is easy.

  The crosslinked organic resin particles obtained from this acrylic resin can be obtained, for example, from a mixture of 1% by mass or more of a crosslinkable acrylic monomer and other monomers. The crosslinkable acrylic monomer is a monomer having at least two radical polymerizable unsaturated groups in the molecule, or at least two monomers each having a functional group capable of reacting with each other and a radical polymerizable unsaturated group. Means. If the amount of the cross-linkable acrylic monomer is less than 1% by mass, a sufficient cross-linked structure cannot be obtained, and the powder paint may partially dissolve and swell during baking, which may reduce the smoothness of the coating film. is there.

  Examples of the monomer having at least two radical polymerizable unsaturated groups in the molecule include a polymerizable unsaturated monocarboxylic acid ester of a polyhydric alcohol, a polymerizable unsaturated alcohol ester of a polybasic acid, and two or more monomers. An aromatic compound substituted with a vinyl group can be used. Examples thereof include ethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, trimethylolpropane tri (meth) ) Acrylate, 1,4-butanediol (meth) acrylate, neopentyl glycol di (meth) acrylate, 1,6-hexaneol di (meth) acrylate, pentaerythritol di (meth) acrylate, pentaerythritol tetra (meth) acrylate Glycerol di (meth) acrylate, 1,1,1-trishydroxymethylethane di (meth) acrylate, triallyl cyanurate, triallyl isocyanurate, triallyl trimellitate, diary Terephthalate, there diallyl phthalate, allyl (meth) acrylate and divinyl benzene and the like.

  Examples of combinations of monomers having two radically polymerizable unsaturated groups each carrying a functional group capable of reacting with each other include epoxy group-containing ethylenically unsaturated monomers such as glycidyl acrylate and glycidyl methacrylate, and acrylic acid And ethylenically unsaturated monomers containing carboxyl groups such as methacrylic acid and crotonic acid. Other combinations of functional groups that can react with each other include amino groups and carboxylic acid groups, epoxy groups and carboxylic acids, or anhydrides thereof. It is included.

  As said other monomer, the monomer currently used for manufacture of the said non-crosslinked acrylic resin can be mentioned.

  The powder coating composition used in the present invention may contain a pigment and an additive as necessary.

  The type of the pigment is not particularly limited. Specifically, titanium dioxide, bengara, yellow iron oxide, carbon black, phthalocyanine blue, phthalocyanine green, quinacridone pigments, azo pigments and other colored pigments, metallic pigments of each color, Examples include pearl pigments of various colors, metal powders and those subjected to surface treatment, extender pigments such as talc, silica, calcium carbonate, and precipitated barium sulfate. In order to reduce gloss, it is preferable to include an inorganic matting agent such as talc, silica, calcium carbonate, barium sulfate, feldspar, and wollastonite, or an organic matting agent composed of organic fine particles. The volume average particle diameter of the matting agent is preferably 3 to 30 μm.

  Examples of the additive include a charge control agent, a plasticizer, an ultraviolet absorber, an antioxidant, and a wax inhibitor. About these, what is normally used for the powder coating material can be used.

  Next, the manufacturing method of the powder coating composition used by this invention is demonstrated. That is, it is used in the present invention by particles having a specific particle diameter obtained as a main component of the above-mentioned polyester resin composition having the above-mentioned β-hydroxyalkylamide curing agent and a specific range of acid value and softening point. A powder coating composition is obtained. Furthermore, it can be obtained by adding fine particles having a smaller particle diameter as a fluidity imparting agent than the particle diameter of the particles.

  First, the β-hydroxyalkylamide curing agent and the polyester resin composition, which are the main constituents of the particles, and a predetermined amount of the surface conditioner, pigment, and other additives, if necessary, are mixed. Mix evenly with a machine. As the mixer, a general mixer such as a Henschel mixer, a ball mill, or a Banbury mixer is used.

  Next, the obtained mixture is melt-kneaded. Here, the mixture is heated and melted by a kneader such as an extruder or a hot roll. Next, the pellets obtained in this melt-kneading step are pulverized using a pulverizer such as an atomizer or a jet mill. In addition, after the above components are melt-kneaded and mixed, the resulting mixture can be directly obtained as powder particles by spray drying. The volume average particle size of the powder coating composition used in the present invention thus obtained is preferably 20 to 40 μm, and classification is carried out to adjust the particle size distribution by removing large particles and fine particles. It is preferable to use the particles after

  The particles thus obtained can be used as a powder coating as they are, but may also be a powder coating containing the fine particles.

  The fine particles may be added before pulverization of the pellet, or may be added to the pulverized or classified particles and stirred and mixed by a mixer such as a super mixer. By such an addition method, it is considered that the fine particles are usually present in the powder paint in a state of adhering to the surface of the particles and a state of being slightly embedded in the surface of the particles.

  The powder coating composition used in the present invention can be applied to an object to be coated and then heated to obtain a coating film. The material to be coated is not particularly limited, and specific examples include iron plates, steel plates, aluminum plates and the like, and surface treated products thereof.

  The method for applying is not particularly limited, and methods well known by those skilled in the art such as spray coating method, electrostatic powder coating method, fluidized dipping method, etc. can be used. An electrostatic powder coating method is preferably used.

  Although the coating film thickness at the time of apply | coating the powder coating composition used by this invention is not specifically limited, It can set to 20-100 micrometers.

<Process C>
The method for coating an iron-based substrate of the present invention further includes a step C for baking and curing the powder coating composition applied in the step B.
The powder coating composition can be baked using conditions and equipment normally used for baking the powder coating composition. Furthermore, in the method of coating the iron-based substrate of the present invention, the powder coating composition can be suitably baked even at a temperature lower than the baking temperature of a normal powder coating composition. From the viewpoint of reducing energy required for baking, a lower baking temperature is preferable.
However, if the baking temperature is too low, secondary physical properties such as good water resistance, light resistance, and heat resistance may not be obtained. It tends to be difficult to obtain a film. This can be expected to maintain the smoothness of the coating film finally obtained by melting the resin component before the uncured coating film adhered to the object undergoes a curing reaction, but does not contain a solvent. This is because it is difficult to impart meltability with a solvent in an uncured coating film derived from a powder paint. In order to solve the problem, a method of lowering the molecular weight or glass transition temperature of the resin component used in the powder coating can be considered. If these values are too low, storage of the powder coating containing the resin is possible. Stability is reduced. For this reason, ensuring low-temperature curability and ensuring the storage stability of the powder coating are often contradictory events, and slightly lowering the baking temperature is a major technical issue.
In the present invention, as a result of paying attention to the chemical conversion treatment in order to solve the above-mentioned problems, the inventors have succeeded in further lowering the lower limit of the baking temperature of the powder coating material known so far. Specifically, the baking temperature is preferably 130 ° C to 160 ° C, more preferably 130 ° C to 145 ° C. In particular, if the baking temperature is 130 ° C. to 145 ° C., the powder coating composition can be baked using an ordinary solvent-based coating oven.
According to the method of coating an iron-based substrate of the present invention, a coating film having secondary physical properties such as good water resistance, light resistance, and heat resistance can be obtained even at a baking temperature lower than usual. As described above, even if baking is performed at a temperature considerably lower than the baking temperature of powder coatings known so far in the present application, coatings represented by good water resistance, weather resistance, heat resistance, coating film appearance, etc. The membrane performance could be secured. The reason for this is not clear, but any of the components (a) to (c) contained in the chemical conversion treatment agent on the surface of the metal substrate is a catalyst for the curing reaction of the powder coating used in the step B. It is possible that there was an effect. In addition, it is considered that some effect of promoting adhesion between the surface of the coating formed by the chemical conversion treatment and the lower surface of the coating formed from the powder coating was obtained.
Although baking time can be suitably adjusted with baking temperature, it is 10 to 120 minutes normally, Preferably it is 15 to 60 minutes.

  Preferably, the preferred items detailed above are used in combination with other suitable items.

  The iron-based substrate coated with the “method for coating an iron-based substrate” of the present invention is also an embodiment of the present invention, and an article containing the iron-based substrate is also an embodiment of the present invention. is there.

  EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited only to these examples.

<Examples 1 to 21 and Comparative Examples 1 to 9>
[Manufacture of powder coatings]
(Powder paint 1)
100 parts by mass of CRYLCOAT 2617-3 (polyester resin manufactured by Daicel-Cytec, acid value 33, glass transition temperature 62 ° C.)
Fine Dick A241 (Dainippon Ink Chemical Co., Ltd., epoxy group-containing vinyl polymer, epoxy equivalent 600, softening point 109 ° C.)
Epototo YD-014 (manufactured by Toto Kasei Co., Ltd., epoxy resin, epoxy equivalent 950), 5 parts by mass,
5 parts by mass of Primid XL552 (β-hydroxyalkylamide curing agent, hydroxyl group equivalent 84, manufactured by EMS-PRIMD),
0.5 parts by mass of acronal 4F (manufactured by BASF, acrylic polymer, surface conditioner having Tg of −55 ° C., solubility parameter SP of 9.3, number average molecular weight of 16500),
1 part by weight of benzoin,
Using 65 parts by mass of Typeke CR-90 (Ishihara Sangyo Co., Ltd., rutile-type titanium dioxide pigment) as a raw material, the mixture is mixed for about 3 minutes using a super mixer (manufactured by Nippon Spindle Co., Ltd.) Melt-kneaded at about 110 ° C.
Thereafter, the obtained melt-kneaded product was cooled to room temperature, and then pulverized using a pulverizer atomizer (Fuji Powdal Co., Ltd.). The resulting powder was used as an air classifier DS-2 (Nippon Pneumatic Industry). And the fine particles and coarse particles are removed, so that the content of the powder having a volume average particle diameter of 25 μm and a particle diameter of 1/5 or less of the volume average particle diameter is 2% by mass. A powder coating was obtained.

(Powder paint 2)
The powder paint is the same as the powder paint 1 except that CRYLCOAT 4420-0 (a polyester resin manufactured by Daicel-Cytec, acid value 50, glass transition temperature 64 ° C.) is used instead of CRYLCOAT 2617-3. 2 was created.

(Powder paint 3)
The powder paint is the same as the powder paint 1 except that CRYLCOAT 2621-2 (Daicel Cytec polyester resin, acid value 70, glass transition store temperature 62 ° C.) is used instead of CRYLCOAT 2617-3. 3 was created.

(Powder paint 4)
Fine Dick M8020 (Dainippon Ink & Chemicals, hydroxyl polyester resin, hydroxyl value 30, weight average molecular weight is 18000) 85 parts by mass and Vestagon B-1530 (Degussa Huls, block isocyanate curing agent) 15 parts by mass ,
0.5 parts by mass of acronal 4F,
1 part by weight of benzoin,
50 parts by mass of Taipek CR-90,
Using 35 parts by mass of precipitated barium sulfate 100 as a raw material, mixing is carried out for about 3 minutes using a mixer super mixer (manufactured by Nihon Spindle Co., Ltd.), and further at about 110 ° C. using a melt kneader Kneader (made by Busus) Melt kneaded. Thereafter, the obtained melt-kneaded product was cooled to room temperature, and then pulverized using a pulverizer atomizer (Fuji Powdal Co., Ltd.). The resulting powder was used as an air classifier DS-2 (Nippon Pneumatic Industry). And the fine particles and coarse particles are removed, so that the content of the powder having a volume average particle diameter of 25 μm and a particle diameter of 1/5 or less of the volume average particle diameter is 2% by mass. A powder coating was obtained.

[Production of amine-modified epoxy resin (amino functional compound)]
(AME-I)
AME-I was produced by the following method.
386 parts by mass of liquid epoxy resin DER-331 (bisphenol A type epoxy resin manufactured by Dow Chemical Co., Ltd.), 114 parts by mass of bisphenol A, propylene glycol monomethyl, in a reaction vessel equipped with a stirrer, a cooler, a temperature controller, a nitrogen introduction tube, and a dropping funnel After charging 56 parts by mass of ether and 0.06 parts by mass of 2-ethyl-4-methylimidazole to obtain a composition having a solid concentration of 90% by mass, the reactor was heated to 145 ° C. while being purged with nitrogen gas. A bisphenol A type epoxy resin composition having an epoxy equivalent of 500 and a number average molecular weight of 1000 was synthesized by incubating for 3 hours. 69 parts by mass of propylene glycol monomethyl ether was added to the obtained bisphenol A type epoxy resin composition to obtain a bisphenol A type epoxy resin composition having a solid content concentration of 80% by mass and cooled to 90 ° C.
Next, 625 parts by mass of the bisphenol A type epoxy resin composition cooled to 90 ° C. (500 parts by mass as a solid content), aminoethylethanolamine MIBK block (aminoethylethanolamine blockade), 236 parts by mass It was added so that 1 equivalent of amine (excluding amine blocked with methyl isobutyl ketone) was equivalent to 1 equivalent of epoxy. Further, after adding 119 parts by mass of propylene glycol monomethyl ether so that the solid content concentration becomes 70% by mass, the temperature of the composition is adjusted to 115 ° C. and kept for 1 hour to react, and then cooled to 100 ° C. by standing. Then, an epoxy resin to which monoketimine (aminoethylethanolamine MIBK block) was added was synthesized.
Next, while stirring a container containing 66 parts by mass of 90% by mass acetic acid and 322 parts by mass of pure water with a chemistor, 970 was added to the epoxy resin to which the obtained monoketimine (aminoethylethanolamine MIBK block) was added. A mass part was dropped to synthesize a resin composition having a solid content concentration of 50% by mass and a neutralization rate of 50%, and further pure water was added dropwise to obtain a soluble epoxy resin solution AME-I having a solid content concentration of 10% by mass. Prepared (—NH ₂ and / or —NH ₃ ⁺ about 0.2 mol / 100 g resin).

(AME-II)
AME-II was produced by the following method.
30 parts of diethanolamine and 110 parts of cellosolve acetate were added to 190 parts by mass of bisphenol F epichlorohydrin type epoxy compound having an epoxy equivalent of 190, and reacted at 100 ° C. for 2 hours to obtain an amino group-containing water-soluble epoxy compound AME-II having a nonvolatile content of 70%. Obtained.

[Chemical conversion treatment]
Using a commercially available cold-rolled steel sheet (SPCC-SD, manufactured by Nippon Test Panel Co., Ltd., 70 mm × 150 mm × 0.8 mm) as a base material, chemical conversion treatment was performed under the conditions described below and in Table 1.
In Table 1, APS is KBM-603 (N-2 (aminoethyl) 3-aminopropyltrimethoxysilane, effective concentration 100%, manufactured by Shin-Etsu Chemical Co., Ltd.),
PAA10C is PAA10C (polyallylamine resin, molecular weight 15000, Nittobo Co., Ltd.)
AME-I is AME-I (amine-modified epoxy resin) whose production method is described above.
AME-II indicates AME-II (amine-modified epoxy resin) whose production method is described above, and NPK-261 indicates Sumilite resin-NPK-261 (amine-modified phenol resin, Sumitomo Bakelite).
In Table 1, FF represents the fluorine ion concentration.
(A) Chemical conversion treatment (zirconium treatment): Examples 1 to 21 and Comparative Examples 2 to 3
Degreasing treatment: A 2 mass% aqueous solution of “Surf Cleaner 53” (a degreasing agent manufactured by Nippon Paint Co., Ltd.) was sprayed at 40 ° C. for 2 minutes.
Washing with water after degreasing: spraying with tap water for 30 seconds.
Chemical conversion treatment: The substrate was sprayed for 60 seconds using each chemical conversion solution adjusted to the conditions shown in Table 1.
Chemical conversion solution: Zircon hydrofluoric acid and an adhesion promoter (amino functional compound) shown in Table 1 were dissolved in tap water to prepare each chemical conversion solution. In the case of a chemical conversion treatment solution using KBM-603, after dissolving KBM-603 in tap water so as to have a concentration of 5% by mass, the mixture is stirred at room temperature for 3 hours to obtain a hydrolysis and condensate. Using. The pH of the chemical conversion solution was adjusted using sodium hydroxide. The total fluorine of the chemical conversion treatment liquid was adjusted using acidic sodium fluoride.
Washing treatment after chemical conversion: 30 seconds immersion treatment with tap water. Furthermore, it spray-processed for 10 second with ion-exchange water. Then, after air-drying at room temperature, powder coating was performed.
The coating amount is included in the chemical conversion treatment agent using “XRF1700” (Shimadzu X-ray fluorescence analyzer) after the cold-rolled steel sheet after the water washing treatment is dried at 80 ° C. for 5 minutes in an electric drying furnace. The total amount of metals analyzed.
(B) Chemical conversion treatment (zinc phosphate treatment): Comparative examples 1, 4 to 9
Using commercially available cold-rolled steel plate (SPCC-SD, manufactured by Nippon Test Panel Co., Ltd., 70 mm × 150 mm × 0.8 mm) as a base material, using Surffine 5N-8M (manufactured by Nippon Paint Co., Ltd.) after degreasing and washing treatment. Surface adjustment was performed at room temperature for 30 seconds, and it was carried out except that chemical conversion treatment was performed by performing a spray treatment at 35 ° C. for 2 minutes using Surfdyne SD-5350 (a zinc phosphate chemical conversion treatment agent manufactured by Nippon Paint Co., Ltd.). A test plate was obtained in the same manner as in Example 1.

[Application and baking of powder paint]
The powder coating was applied and baked on the substrate subjected to chemical conversion treatment under the conditions shown in Table 1.
The powder coating was applied to a surface-treated (30 cm × 40 cm) substrate with an applied voltage of 80 kV using a corona discharge electrostatic powder coating machine (trade name “MXR-100VT-mini” manufactured by Asahi Sunac Corporation). A coated plate was prepared by painting and then baking under the conditions described in Table 1.
In Table 1, AV represents an acid value, and OHV represents a hydroxyl value. In addition, in this specification, a hydroxyl value means the hydroxyl value calculated | required by the method as described in JISK0070.

[test]
The obtained coated plate (test piece) was tested and evaluated according to the following designated evaluation method. The results are shown in Table 1.
(1) Impact test The presence or absence of cracking or peeling of the coating film was examined under the following conditions using a DuPont system conforming to JIS K5400 8.3.2. A case where no cracking or peeling was observed on the coating film was accepted.
Weight: 500g
Shooting mold and cradle size: 1/2 inch Fall distance: 30cm
(2) Salt water spray test After putting the crosscut which reaches to a base material to the obtained test board, 5% NaCl aqueous solution was sprayed continuously for 500 hours in the salt spray test device kept at 35 ° C. Then, the swelling width (one-side rust width) from the cut part was measured.
(3) Water resistance test Each test piece was immersed in warm water at 40 ° C. for 500 hours and then left for 24 hours, and then 10 vertical and horizontal cuts were made in the coating film of each test piece at intervals of 1 mm with a cutter. The cellophane tape was affixed and peeled off, and the remaining squares out of 100 squares were counted.
(4) Moisture resistance test The test plate was left in a constant temperature and humidity tester (humidity 95%, temperature 50 ° C) for 240 hours. Next, after leaving the test plate in the atmosphere for 1 hour, the test piece was cut into 10 coats at 1 mm intervals in the coating film of each test piece, and cellophane tape was affixed and peeled off. The remaining eyes were counted among the more eyes.

Claims (11)

A method for coating an iron-based substrate,
The surface of the iron-based substrate
(A) at least one selected from zirconium, titanium, and hafnium,
(B) by treating with a chemical conversion treatment agent containing fluorine and (c) an amino-functional compound;
Step A for forming the chemical conversion treatment layer,
On the chemical conversion treatment layer,
A polyester resin having an acid value of 30 to 70 mg KOH / g, and a general formula I

(Wherein R ¹ represents a hydrogen atom, a methyl group or an ethyl group, R ² represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms or HO—CH (R ¹ ) —CH ₂ —, and A represents 2 A step B of applying a powder coating composition containing a β-hydroxyalkylamide curing agent represented by the following formula: and a step C of baking and curing the powder coating composition;
A method characterized by comprising: The method according to claim 1, wherein in the step C, the powder coating composition is baked and cured at a temperature of 130C to 160C. The amino-functional compound is
An amino-functional silane coupling agent, a hydrolyzate thereof, and a condensate thereof,
Polyallylamine,
The method according to claim 1 or 2, wherein the method is at least one selected from an amine-modified epoxy resin and an amine-modified phenol resin. The content of the amino-functional compound in the chemical conversion treatment agent is within a range of 5 to 5000 ppm based on the total mass of the chemical conversion treatment agent, according to any one of claims 1 to 3. the method of. The method according to any one of claims 1 to 4, wherein the chemical conversion treatment agent has a pH of 2.5 to 5.0. The method according to any one of claims 1 to 5, wherein the polyester resin has a weight average molecular weight of 1,000 to 150,000. The iron-based substrate is at least one selected from the group consisting of a cold-rolled steel plate, an electrogalvanized steel plate, a hot-dip galvanized steel plate, tinplate, and stainless steel. The method according to claim 1. 8. The mass ratio of the β-hydroxyalkylamide curing agent and the polyester resin in the powder composition is 3/97 to 10/90, 9. The method described in 1. The method according to claim 1, wherein the powder coating composition has a volume average particle size of 20 to 40 μm. The iron-type base material coat | covered with the method of any one of Claims 1-9. An article containing an iron-based substrate coated by the method according to any one of claims 1 to 9.