CN109477235B - Method for forming cured electrophoretic coating film - Google Patents

Method for forming cured electrophoretic coating film Download PDF

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Publication number
CN109477235B
CN109477235B CN201780032487.3A CN201780032487A CN109477235B CN 109477235 B CN109477235 B CN 109477235B CN 201780032487 A CN201780032487 A CN 201780032487A CN 109477235 B CN109477235 B CN 109477235B
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electrophoretic coating
coating film
gloss
water
anionic
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CN109477235A (en
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金子敏雄
加纳裕久
西冈澄穗
青木胜
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Nippon Paint Industrial Coatings Co Ltd
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Nippon Paint Industrial Coatings Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
    • C09D5/44—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes for electrophoretic applications
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D13/00—Electrophoretic coating characterised by the process
    • C25D13/04—Electrophoretic coating characterised by the process with organic material
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D133/00—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Coating compositions based on derivatives of such polymers
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
    • C09D5/44—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes for electrophoretic applications
    • C09D5/4407—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes for electrophoretic applications with polymers obtained by polymerisation reactions involving only carbon-to-carbon unsaturated bonds
    • C09D5/4411—Homopolymers or copolymers of acrylates or methacrylates
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
    • C09D5/44—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes for electrophoretic applications
    • C09D5/448—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes for electrophoretic applications characterised by the additives used
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D7/00—Features of coating compositions, not provided for in group C09D5/00; Processes for incorporating ingredients in coating compositions
    • C09D7/40—Additives
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D13/00—Electrophoretic coating characterised by the process
    • C25D13/10—Electrophoretic coating characterised by the process characterised by the additives used
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D13/00—Electrophoretic coating characterised by the process
    • C25D13/22—Servicing or operating apparatus or multistep processes

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Abstract

The invention provides a method for forming a cured electrophoretic coating film with adjusted glossiness, such as a low-gloss coating film with low mirror surface glossiness or a matte coating film. The present invention provides a method for forming a cured electrophoretic coating film, comprising: an electrophoretic coating step of immersing a substrate in an anionic electrophoretic coating composition and applying a voltage to form an electrophoretic coating film; and a heat curing step of heat curing the electrophoretic coating film formed in the above-mentioned electrodeposition coating step to form a cured electrophoretic coating film; the anionic electrophoretic coating composition comprises an acrylic resin (A), a curing agent (B), a water-dispersible gloss adjuster (C) and a curing catalyst (D); the water-dispersible gloss adjuster (C) is a water dispersion of 1 or more waxes selected from natural waxes and polyolefin waxes; the wax constituting the water-dispersible gloss adjuster (C) has a softening point (Tm) of 100 ℃ or higher and a density of 0.91 to 1.10; the amount of the solid content of the water-dispersible gloss adjuster (C) contained in the anionic electrophoretic coating composition is 6 to 20 parts by mass per 100 parts by mass of the resin solid content of the anionic electrophoretic coating composition; the electrophoretic coating film formed in the electrophoretic coating step has a coating viscosity at 50 ℃ within a range of 10,000 to 100,000Pa · s.

Description

Method for forming cured electrophoretic coating film
Technical Field
The present invention relates to a method for forming a cured electrophoretic coating film using an anionic electrophoretic coating composition.
Background
The electrodeposition coating is a coating method in which a substrate is immersed in an electrodeposition coating composition and a voltage is applied thereto. This method can perform coating up to a fine part even in the case of a coated object having a complicated shape, and can automatically and continuously perform coating, and thus is widely used as an undercoating coating method for various coated objects. The electrodeposition coating composition includes 2 types of cationic electrodeposition coating compositions and anionic electrodeposition coating compositions. The cationic electrodeposition coating composition can generally form a cured electrodeposition coating film having more excellent rust prevention and corrosion resistance. On the other hand, an anionic electrophoresis composition is often used for an aluminum material. This is because an aluminum material can be provided with excellent corrosion resistance by first forming an anodic oxide film (anodic treatment film) by an anodic oxidation treatment and then performing anionic electrodeposition coating using an anionic electrodeposition composition.
In anionic electrophoresis coating, for example, in coating of an aluminum window frame, a coated object provided with a low-gloss coating film or a matte coating film having low specular gloss is generally capable of giving a quiet visual impression and also of giving a high-grade feeling, and therefore, in recent years, there has been an increasing demand for a coating method capable of forming such a coating film.
As a matte anionic electrophoretic coating composition, for example, Japanese patent laid-open publication No. 2002-188044 (patent document 1) describes an anionic matte electrophoretic coating composition comprising an acrylic resin (I), an alkoxysilyl group-containing emulsion polymer (II) and a crosslinking agent (III), wherein the alkoxysilyl group-containing emulsion polymer (II) is an emulsion polymer produced by emulsion polymerization in multistage using a polymerizable unsaturated monomer in the presence of water and an emulsifier, the polymerizable unsaturated monomer comprises the alkoxysilyl group-containing polymerizable unsaturated monomer in a proportion of 5 to 40% by weight based on the total weight of all monomers used in multistage, and the composition is characterized in that the compounding ratio of the acrylic resin (I), the alkoxysilyl group-containing emulsion polymer (II) and the crosslinking agent (III) is based on the total of the resin solids, (I) 20 to 70 wt%, (II) 5 to 40 wt%, and (III) 20 to 60 wt% (claim 1). Jp 2005-307161 a (patent document 2) describes an anionic electrophoretic paint comprising a core/shell type emulsion (a) which is an emulsion polymer produced by emulsion polymerization in multiple stages using a polymerizable unsaturated monomer in the presence of water and an emulsifier, an acrylic resin (B), and a curing agent (C), wherein the polymerizable unsaturated monomer contains an alkoxysilyl group-containing polymerizable unsaturated monomer in a proportion of 1 to 40 wt% based on the weight of the total monomers used in the multiple stages. However, the gloss of the cured electrophoretic coating film obtained from these anionic electrophoretic coating compositions varies greatly depending on the coating conditions and/or the shape of the object to be coated, and there is a problem that so-called uneven gloss occurs.
Jp-a-5-039445 (patent document 3) describes a method for forming a matte coating film, wherein a matte electrodeposition coating composition is diluted and electrophoresed, wherein the matte electrodeposition coating composition comprises (a) 5 to 50 wt% of a water-soluble fluorine-containing copolymer resin having a carboxyl group and a hydroxyl group, (B1) 5 to 60 wt% of a water-soluble or water-dispersible acrylic copolymer resin having an alkoxysilyl group, and (C) 20 to 60 wt% of a crosslinking agent (claim 1). The matte electrodeposition coating composition in patent document 3 is different from the method of the present invention in that (B1) a water-soluble or water-dispersible acrylic copolymer resin having an alkoxysilyl group is crosslinked to form an insoluble gel structure, and the insoluble gel particles give a matte effect.
Jp-a 8-113735 (patent document 4) describes a method for producing a resin composition for an electroless electrophoretic coating, which is characterized by adding an amino resin (E) to a copolymer (D) obtained by copolymerizing (a) a hydroxyalkyl group-containing ester monomer of an α, β -ethylenically unsaturated carboxylic acid, (B) an alkoxysilyl group-containing ester monomer of an α, β -ethylenically unsaturated carboxylic acid, and (c) a mixed monomer (B) of a copolymerizable vinyl group-containing monomer having no carboxyl group, in the presence of a water-soluble or water-dispersible vinyl copolymer (a) having a carboxyl group and a hydroxyl group in its side chain, mixing a wax (F) and partially neutralizing with an organic amine, and then adding water to prepare an emulsion (claim 1). However, when the resin composition for an electrodeposition coating obtained by the production method is used, the gloss of the obtained cured electrodeposition coating film may be greatly changed depending on the heat curing temperature, and a cured electrodeposition coating film having a desired gloss may not be obtained.
However, energy saving and CO reduction according to recent years2Further demands for reduction of environmental load such as emission amount require reduction of heat curing temperature in forming a coating film. On the other hand, lowering the heat curing temperature may lower the crosslinking density of the obtained cured electrophoretic coating film, and may lower the coating film properties such as hardness and corrosion resistance.
Documents of the prior art
Patent document
Patent document 1: japanese laid-open patent publication No. 2002-188044
Patent document 2: japanese patent laid-open publication No. 2005-307161
Patent document 3: japanese laid-open patent publication No. 5-039445
Patent document 4: japanese patent laid-open No. 8-113735.
Disclosure of Invention
Problems to be solved by the invention
The present invention has been made to solve the above conventional problems, and an object of the present invention is to provide a method for forming a cured electrophoretic coating film having an adjusted gloss level, such as a low-gloss coating film or a matte coating film having a low specular gloss.
Means for solving the problems
In order to solve the above problem, the present invention provides the following embodiments.
[1]
A method for forming a cured electrocoat film, comprising:
an electrophoretic coating step of immersing a substrate in an anionic electrophoretic coating composition and applying a voltage to form an electrophoretic coating film; and
a heat curing step of heat curing the electrophoretic coating film formed in the above-mentioned electrophoretic coating step to form a cured electrophoretic coating film;
the anionic electrophoretic coating composition comprises an acrylic resin (A), a curing agent (B), a water-dispersible gloss adjuster (C) and a curing catalyst (D);
the water-dispersible gloss adjuster (C) is a water dispersion of 1 or more waxes selected from natural waxes and polyolefin waxes;
the softening point (T) of the wax constituting the water-dispersible gloss adjuster (C)m) Is more than 100 ℃ and has a density of 0.91-1.10;
the amount of the solid content of the water-dispersible gloss adjuster (C) contained in the anionic electrophoretic coating composition is 6 to 20 parts by mass per 100 parts by mass of the resin solid content of the anionic electrophoretic coating composition;
the electrophoretic coating film formed in the electrophoretic coating step has a coating viscosity at 50 ℃ within a range of 10,000 to 100,000Pa · s.
[2]
The method according to the above, wherein the heating temperature (T) in the heating curing steph) Is 110 to 160 ℃.
[3]
The method, wherein the softening point (T)m) Is in the range of 100 to 140 ℃.
[4]
The method, wherein the viscosity of the electrophoretic coating film formed in the electrophoretic coating step is in the range of 1,000 to 10,000Pa · s at 80 ℃.
[5]
The method, wherein the acrylic resin (A) is an acrylic resin having a carboxyl group and a hydroxyl group,
the curing agent (B) is at least 1 selected from amino resin and blocked isocyanate compound.
[6]
The method, wherein the softening point (T)m) And heating temperature (T)h) A difference (DeltaT) of 10 ℃ to 50 ℃ inclusive, and Th＞Tm。
[7]
The method according to the above, wherein the cured electrophoretic coating film formed by the above-described forming method has a 60 ° specular gloss of 70 or less.
In the present specification, an uncured electrocoat before being heat-cured is referred to as an "electrocoat", and a coating film after being heat-cured is referred to as a "cured electrocoat" or simply a "cured coating film".
Effects of the invention
According to the method of the present invention, a cured electrophoretic coating film having an adjusted gloss such as a low-gloss coating film having a low specular gloss or a matte coating film can be obtained. The method of the present invention can provide a cured electrophoretic coating film having excellent final appearance without uneven gloss such as change in gloss due to change in heat curing temperature. In the method of the present invention, further, after the formation of the electrophoretic coating film, a cured electrophoretic coating film having good hardness can be obtained even in the case of heat curing under low-temperature curing conditions.
Detailed Description
The method for forming a cured electrophoretic coating film of the present invention comprises the steps of:
an electrophoretic coating step of immersing a substrate in an anionic electrophoretic coating composition and applying a voltage to form an electrophoretic coating film; and
and a heat curing step of heat curing the electrophoretic coating film formed in the above-mentioned electrodeposition coating step to form a cured electrophoretic coating film.
Hereinafter, the method of the present invention will be described in detail.
Coated article
The substrate to be coated in the forming method of the present invention is not particularly limited as long as it is a substrate having conductivity. Examples of the substrate include metal materials such as iron, stainless steel, aluminum, copper, zinc, tin, and alloys thereof, molded products of these metal materials, conductive plastics, and surface-treated products thereof. The metal material may be a base material subjected to plating treatment. In the present invention, examples of suitable substrates include iron substrates such as iron and stainless steel, and aluminum substrates such as aluminum and aluminum alloys.
Anionic electrophoretic coating composition
The anionic electrophoretic coating composition of the present invention comprises an acrylic resin (a), a curing agent (B), a water-dispersible gloss adjuster (C), and a curing catalyst (D).
Acrylic resin (A)
The acrylic resin (a) contained in the anionic electrophoretic coating composition is a coating film-forming resin. The acrylic resin (a) is preferably an acrylic resin having a carboxyl group and a hydroxyl group. Examples of the acrylic resin (A) include acrylic resins obtained by radical-polymerizing a carboxyl group-containing radical-polymerizable unsaturated monomer (a-1), a hydroxyl group-containing radical-polymerizable unsaturated monomer (a-2), and, if necessary, another radical-polymerizable unsaturated monomer (a-3).
The carboxyl group-containing radically polymerizable unsaturated monomer (a-1) is a compound having at least 1 carboxyl group and a polymerizable unsaturated bond in each of 1 molecule. Examples of the carboxyl group-containing radically polymerizable unsaturated monomer (a-1) include vinyl polymerizable α, β -unsaturated fatty acids such as (meth) acrylic acid, itaconic acid, maleic anhydride, fumaric acid, maleic acid monoester, itaconic acid monoester, crotonic acid, and citraconic acid, caprolactone-modified carboxyl group-containing (meth) acrylic monomers, and mixtures thereof. As the carboxyl group-containing radically polymerizable unsaturated monomer (a-1), at least 1 selected from acrylic acid and methacrylic acid is preferably used.
In the present specification, (meth) acrylic acid means acrylic acid or methacrylic acid.
The hydroxyl group-containing radically polymerizable unsaturated monomer (a-2) is a compound having at least 1 hydroxyl group and a polymerizable unsaturated bond in each of 1 molecule. Examples of the hydroxyl group-containing radically polymerizable unsaturated monomer (a-2) include hydroxyalkyl (meth) acrylates such as hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate and the like; (meth) acrylic acid (poly) alkylene glycol esters such as (meth) acrylic acid (poly) ethylene glycol ester and (meth) acrylic acid (poly) propylene glycol ester; and a reaction product of these hydroxyl group-containing acrylic monomers with a lactone compound such as β -propiolactone, dimethylpropanolide, butyrolactone, γ -valerolactone, γ -caprolactone, γ -octalactone, γ -dodecalactone, e-caprolactone or δ -caprolactone. Examples of the reaction product include commercially available products such as pregabalin (プラクセル) FM1 (trade name, caprolactone-modified (meth) acrylates, manufactured by xylonite chemical company), pregabalin FM2 (same left), pregabalin FM3 (same left), pregabalin FA1 (same left), pregabalin FA2 (same left), and pregabalin FA3 (same left).
The other radically polymerizable unsaturated monomer (a-3) is a monomer other than the above carboxyl group-containing radically polymerizable unsaturated monomer (a-1) and hydroxyl group-containing radically polymerizable unsaturated monomer (a-2), and is a compound having at least 1 radically polymerizable unsaturated bond in 1 molecule. Examples of the other radically polymerizable unsaturated monomer (a-3) include, for example, C of (meth) acrylic acid such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, lauryl (meth) acrylate, and cyclohexyl (meth) acrylate1-8Alkyl esters or C3-8A cycloalkyl ester; aromatic polymerizable monomers such as styrene, α -methylstyrene and vinyltoluene; (meth) acrylamides and derivatives thereof such as (meth) acrylamide, N-butoxymethyl (meth) acrylamide, and N-methylol (meth) acrylamide; (meth) acrylonitrile compounds; gamma- (meth) acryloxypropyltrimethoxysilane, gamma- (meth) acryloxypropylmethyldimethoxysilane, gamma- (meth) acryloxypropyltriethoxysilane, vinyltrimethyltrimethoxysilaneAlkoxysilyl group-containing polymerizable monomers such as oxysilanes.
As a method for radical copolymerization of the monomers (a-1), (a-2) and (a-3), a solution polymerization method, an emulsion polymerization method, etc. which are generally used by those skilled in the art can be used. In the production of the acrylic resin (A), it is preferable to use in the following range:
the carboxyl group-containing radical polymerizable unsaturated monomer (a-1) is preferably 3 to 30 mass%, more preferably 4 to 20 mass%, based on the total mass of the monomers;
the hydroxyl group-containing radically polymerizable unsaturated monomer (a-2) is preferably 3 to 40 mass%, more preferably 5 to 30 mass%, based on the total mass of the monomers; and
the other radical polymerizable unsaturated monomer (a-3) is preferably 30 to 90% by mass, more preferably 40 to 85% by mass, based on the total mass of the monomers.
The acid value of the acrylic resin (A) is preferably 15 to 150mgKOH/g, more preferably 40 to 80 mgKOH/g. When the acid value of the acrylic resin (A) is 15mgKOH/g or more, the water dispersibility of the resin is improved, and a uniform coating material can be produced. In addition, when the content of 150mgKOH/g or less is not more than 150mgKOH/g, there are advantages such as improvement in corrosion resistance, acid resistance and the like of the cured coating film.
The hydroxyl value of the acrylic resin (A) is preferably 30 to 200mgKOH/g, more preferably 50 to 150 mgKOH/g. When the hydroxyl value of the acrylic resin (A) is not less than Wie30mgKOH/g, the curing reaction is sufficiently caused, and the original film properties are obtained. When the amount of the hydroxyl group is less than 200mgKOH/g, unreacted hydroxyl groups do not remain in the coating film, and there is an advantage that corrosion resistance, acid resistance, and the like are not lowered.
In the present specification, the acid value and the hydroxyl value respectively represent a solid acid value and a solid hydroxyl value, and can be measured by the method described in JIS K0070.
The weight average molecular weight (Mw) of the acrylic resin (A) is preferably 5,000 to 100,000, more preferably 10,000 to 50,000. When the weight average molecular weight (Mw) of the acrylic resin (a) is 5000 or more, there are advantages such as improvement in coating performance such as corrosion resistance and acid resistance. In addition, in the case of 100,000 or less, there are advantages in that the fluidity of the electrophoretic coating film is improved, and a cured electrophoretic coating film having good coating film appearance is obtained.
In the present specification, the weight average molecular weight (Mw) is a value in terms of polystyrene measured by Gel Permeation Chromatography (GPC).
In the anionic electrophoretic coating composition of the present invention, the acrylic resin (a) is preferably used as a water-soluble or water-dispersible resin in which a carboxyl group is neutralized with an alkaline substance (for example, triethylamine, dimethylethanolamine, ammonia, etc.). In the neutralization of the acrylic resin (a), the neutralization rate is preferably 30 to 100%, more preferably 50 to 80%. When the neutralization degree is within the above range, the acrylic resin (a) can be dispersed well in the anionic electrophoretic coating composition.
In the anionic electrophoretic coating composition of the present invention, the content of the acrylic resin (a) is preferably 50 to 80% by mass based on 100% by mass of the total resin solid content of the acrylic resin (a) and the curing agent (B). When the amount is 50% by mass or more, chemical resistance such as acid resistance and alkali resistance and corrosion resistance are improved. In addition, in the case of 80% by mass or less, the electrophoretic coating film is sufficiently cured to obtain desired film properties.
The coating composition of the present invention may contain other coating film forming resins as necessary in addition to the above acrylic resin (a). Examples of the other coating film forming resin include polyester resin, urethane resin, epoxy resin, butadiene resin, phenol resin, xylene resin, and the like. From the viewpoint of improving the corrosion resistance of the cured electrophoretic coating film, an epoxy resin is preferable. In addition, the content in the case of using such another coating film forming resin is preferably less than 20% by mass, more preferably less than 10% by mass, relative to the resin solid content contained in the coating composition.
Curing agent (B)
The anionic electrophoretic coating composition of the present invention contains a curing agent (B). The curing agent (B) is preferably 1 or more selected from amino resins and blocked isocyanate compounds.
The amino resin is a condensate of an amino compound such as melamine, urea, or benzoguanamine and an aldehyde compound such as formaldehyde or acetaldehyde, which is modified with a lower alcohol such as methanol, ethanol, propanol, or butanol. Specific examples of such amino resins include a fully alkyl methyl/butyl mixed etherified melamine resin, a methylol methyl/butyl mixed etherified melamine resin, an imino methyl/butyl mixed etherified melamine resin, a fully alkyl methylated melamine resin, and an imino methylated melamine resin.
Commercially available amino resins can be used. Examples of commercially available products include fully alkyl methyl/butyl mixed etherified melamine resins such as semel (サイメル) 232, semel 232S, semel 235, semel 236, semel 238, semel 266, semel 267 and semel 285; methylol methyl/butyl mixed etherified melamine resins such as semel 272; imino methyl/butyl mixed etherified melamine resins such as semel 202, semel 207, semel 212, semel 253 and semel 254; fully alkyl methylated melamine resins such as semmel 300, semmel 301, semmel 303 and semmel 350; imide-type methylated melamine resins such as Semel 325, Semel 327, Semel 703, Semel 712, Semel 254, Semel 253, Semel 212 and Semel 1128 (manufactured by Oldenst (オルネクス) Japan Co., Ltd.), Uban (ユーバン) 20SE60 (manufactured by Mitsui chemical Co., Ltd., butyl etherified melamine resin) and the like.
As the blocked isocyanate compound, a blocked isocyanate compound obtained by reacting at least 1 selected from the following 1) to 3) with a blocking agent;
1) aliphatic diisocyanates such as trimethylene diisocyanate and hexamethylene diisocyanate, alicyclic diisocyanates such as isophorone diisocyanate, and the like,
2) Polyisocyanates having 2 or more functional groups obtained by reacting the above diisocyanates with polyhydric alcohols such as ethylene glycol, trimethylolpropane and pentaerythritol,
3) 3 mol of diisocyanate of the above 1) to obtain an isocyanurate bond-containing 3-functional isocyanate.
As the end-capping agent, there can be preferably used, for example, n-butanol, n-hexyl alcohol, 2-ethylhexanol, lauryl alcohol, phenol carbitol, methyl phenyl carbitol and other monohydric alkyl (or aromatic) alcohols; cellosolves such as ethylene glycol monohexyl ether and ethylene glycol mono 2-ethylhexyl ether; polyether type both-terminal glycols such as polyethylene glycol, polypropylene glycol, polytetramethylene ether glycol phenol, and the like; polyester type both-terminal polyols obtained from diols such as ethylene glycol, propylene glycol and 1, 4-butanediol and dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, suberic acid and sebacic acid; phenols such as p-tert-butylphenol and cresol; oximes such as dimethyl ketoxime, methyl ethyl ketoxime, methyl isobutyl ketoxime, methyl amyl ketoxime and cyclohexanone oxime; and lactams represented by epsilon-caprolactam and gamma-butyrolactam, and the like.
Specific examples of commercially available polyisocyanate compounds include Bayhydur (バイヒジュール) VPLS2186 (manufactured by Suzuki Bayer polyurethane Co., Ltd.).
As the curing agent (B), a mixture of the above amino resin and blocked isocyanate compound can be used. The curing agent (B) is preferably an amino resin, from the viewpoint of effectively obtaining the effects of the present invention.
In the anionic electrophoretic coating composition of the present invention, the content of the curing agent (B) is preferably 20 to 50% by mass based on 100% by mass of the total resin solid content of the acrylic resin (a) and the curing agent (B). When the amount is 20% by mass or more, the curing reaction proceeds sufficiently to obtain desired film properties. When the amount is 50% by mass or less, the adhesion and flexibility of the coating film are improved.
Water-dispersed gloss adjuster (C)
The anionic electrophoretic coating composition of the present invention contains a water-dispersible gloss adjuster (C). The water-dispersible gloss adjuster (C) is an aqueous dispersion of 1 or more waxes selected from natural waxes and polyolefin waxes. The wax is conditioned by a softening point (T)m) Is 100 ℃ or more and has a density of 0.91 to1.10.
Specific examples of the natural wax among the above waxes include wood wax, carnauba wax, petroleum-based microcrystalline wax, paraffin wax, mineral-based montan wax, and the like. Specific examples of the polyolefin wax include polyolefin waxes such as polyethylene, polypropylene, oxidized polyethylene, oxidized polypropylene, chlorinated polyethylene, and chlorinated polypropylene.
Examples of the method for producing the water dispersion of wax include:
a method in which the wax is dissolved in a hydrophilic organic solvent and then mechanically dispersed in an aqueous solvent;
a method of dispersing the wax in an aqueous solvent using a surfactant, a polymer emulsifier, or the like; and
a method in which the wax is reacted with an α, β -unsaturated carboxylic acid to introduce a carboxyl group, and then the introduced carboxyl group is neutralized with an organic amine or an inorganic base to emulsify and disperse the carboxyl group in an aqueous solvent.
In these production methods, polyethylene, polypropylene, oxidized polyethylene, oxidized polypropylene, and the like are preferably used as the wax.
In the present invention, the wax constituting the water-dispersed gloss adjuster (C) has a softening point (T)m) Is a substance with a temperature of more than 100 ℃. Softening point (T) of wax constituting the water-dispersed gloss adjuster (C)m) When the temperature is lower than 100 ℃, a sufficient gloss-controlling effect cannot be obtained. In addition, there is a defect that unevenness of gloss occurs in the cured electrophoretic coating film. Softening point (T) of wax constituting the water-dispersed gloss adjuster (C)m) Preferably in the range of 100 to 140 ℃.
Softening point (T) of wax constituting the water-dispersed gloss adjuster (C)m) Can be determined by: the wax constituting the water-dispersible gloss adjuster (C) was in a solid state before water-dispersing, and was determined by measuring the temperature at the time of softening by heating. Softening point (T) of wax constituting the water-dispersed gloss adjuster (C)m) Specifically, the state before water dispersion for preparing the water-dispersed gloss adjuster (C) can be usedThe wax of (2) is measured by a method in accordance with JIS K2207. In the above measurement, instead of the solid state before the water dispersion of the wax constituting the water dispersion type gloss adjuster (C), a wax in a solid state by evaporating the aqueous medium in the water dispersion type gloss adjuster (C) may be used.
In the present invention, the wax constituting the water-dispersed gloss adjuster (C) has a density of 0.91 to 1.10. The density of the wax constituting the water-dispersed gloss adjuster (C) is preferably in the range of 0.92 to 1.05. When the density of the wax constituting the water-dispersible gloss adjuster (C) is out of the above range, a defect may be generated in the appearance of the cured electrophoretic coating film in the obtained cured electrophoretic coating film.
The density of the wax constituting the water-dispersed gloss adjuster (C) can be measured by a method according to JIS K7112.
The water-dispersed gloss adjuster (C) is preferably an anionic dispersion type. The anionic electrophoretic coating composition obtained by using the water-dispersible gloss adjuster (C) as an anionic dispersion type has an advantage of improving coating stability.
As the water-dispersible gloss adjuster (C), a commercially available product can be used. Examples of commercially available products include HI-DISPER manufactured by Cellspack corporation(trade mark)AQUACER manufactured by SUSPENSION CHEMICAL JAPONICA CORPORATION(trade mark)Series sum AQUAMAT(trade mark)Chemipearl W manufactured by Mitsui chemical Co Ltd(trade mark)Arowbase (アローベース) series, manufactured by Ennikico Inc(trade mark)Series, etc.
In the present invention, the solid content of the water-dispersible gloss adjuster (C) contained in the anionic electrophoretic coating composition is 6 to 20 parts by mass with respect to 100 parts by mass of the resin solid content of the anionic electrophoretic coating composition. The solid content of the water-dispersible gloss adjuster (C) is preferably 7 to 20 parts by mass, more preferably 10 to 15 parts by mass. When the solid content of the water-dispersed gloss adjuster (C) is more than 20 parts by mass, the hardness of the obtained cured electrophoretic coating film may be lowered. When the solid content of the water-dispersed gloss adjuster (C) is less than 6 parts by mass, a sufficient gloss adjusting effect cannot be obtained.
In the present specification, the term "resin solid content of the anionic electrophoretic coating composition" refers to a resin solid content of a coating film-forming resin contained in the electrophoretic coating composition, and specifically refers to a resin solid content of the acrylic resin (a), the curing agent (B), and, if necessary, another coating film-forming resin.
Curing catalyst (D)
The anionic electrophoretic coating composition of the present invention contains a curing catalyst (D). Examples of the curing catalyst (D) include sulfonic acid catalysts such as n-butylbenzene sulfonic acid, pentylbenzene sulfonic acid, octylbenzene sulfonic acid, dodecylbenzene sulfonic acid, octadecylbenzene sulfonic acid, dibutylbenzene sulfonic acid, isopropylnaphthalene sulfonic acid, p-toluene sulfonic acid, dodecylnaphthalene sulfonic acid, dinonylnaphthalene disulfonic acid, and amine-neutralized products of these sulfonic acid catalysts; tin compound catalysts such as dioctyltin dilaurate, dioctyltin dibenzoate and dibutyltin dibenzoate.
The curing catalyst (D) is preferably the above sulfonic acid catalyst, and more preferably 1 or more selected from dodecylbenzenesulfonic acid, p-toluenesulfonic acid, dodecylnaphthalenesulfonic acid, dinonylnaphthalenesulfonic acid, and dinonylnaphthalenedisulfonic acid. In the anionic electrophoretic coating composition of the present invention, by using such a curing catalyst (D), the heating temperature in the heat curing step can be set to a heating condition of a relatively low temperature, for example, 100 to 160 ℃, preferably 110 to 160 ℃. Further, even when the heating temperature in the heating and curing step is a relatively low temperature heating condition as described above, there is an advantage that a cured electrophoretic coating film having excellent properties such as abrasion resistance can be formed.
The amount of the curing catalyst (D) contained in the anionic electrophoretic coating composition is preferably 0.05 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, and still more preferably 0.2 to 4 parts by mass, as the amount of the solid component of the curing catalyst (D), based on 100 parts by mass of the total solid components of the acrylic resin (a) and the crosslinking agent (B). When the amount is within the above range, a cured electrophoretic coating film having excellent properties such as scratch resistance can be formed.
Other ingredients, etc
The anionic electrophoretic coating composition in the present invention is an aqueous coating composition, and contains water as a main solvent. On the other hand, the anionic electrophoretic coating composition of the present invention may contain an organic solvent as necessary. Specific examples of the organic solvent include alcohols such as methanol, isopropanol, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, and methoxypropanol, ethers such as ethylene glycol monobutyl ether, propylene glycol monobutyl ether, and diethylene glycol monobutyl ether, ketones such as acetylacetone, esters such as ethylene glycol monoethyl ether acetate, and hexane. These organic solvents may be used alone in 1 kind, or may be used in combination in 2 kinds or more. However, the amount of the organic solvent is preferably as small as possible from the viewpoint of VOC emission control.
The anionic electrophoretic coating composition of the present invention may contain, as required, other additives known in the art, such as a colorant, a pigment, a film-forming aid, a drying retardation aid, a viscosity modifier, an antiseptic, a rust inhibitor, an antiseptic, a defoaming agent, a light stabilizer (e.g., hindered amine light stabilizer), an antioxidant, an ultraviolet absorber, and a pH modifier.
The anionic electrophoretic coating composition of the present invention may contain a pigment as necessary. The pigment is not particularly limited, and examples thereof include bulk pigments such as barium sulfate, talc, calcium carbonate, and barium sulfate; phosphomolybdate-based rust-preventive pigments such as aluminum zinc phosphomolybdate, and calcium phosphomolybdate, and molybdate-based rust-preventive pigments such as phosphate-based rust-preventive pigments; and coloring pigments generally used in the coating field, and the like.
Anionic pigment dispersion paste
When the pigment is contained in the anionic electrophoretic coating composition, the pigment is preferably prepared in advance in the form of a pigment dispersion paste from the viewpoint of ease of dispersion of the pigment. The anionic pigment dispersion paste can be prepared by dispersing a pigment in an anionic pigment dispersion resin.
As the anionic pigment-dispersing resin, for example, a modified acrylic resin prepared using an acrylic ester, acrylic acid, an azonitrile compound, or the like is preferably used.
The anionic pigment dispersion paste can be prepared by: the pigment dispersion liquid is prepared by mixing an anionic pigment dispersion resin, a pigment, an aqueous medium, and if necessary, a neutralizing base, and then dispersing the mixture by using a commonly used dispersing apparatus such as a ball mill or a sand mill until the particle diameter of the pigment in the mixture becomes a predetermined uniform particle diameter.
Examples of the neutralizing base include ammonia; organic amines such as diethylamine, ethylethanolamine, diethanolamine, monoethanolamine, monopropanolamine, isopropanolamine, ethylaminoethylamine, hydroxyethylamine, diethylenetriamine, and triethylamine; and alkaline compounds such as alkali metal hydroxides including sodium hydroxide and potassium hydroxide. Generally, the anionic pigment-dispersed paste is prepared so as to have a solid content of 35 to 70% by mass, preferably 40 to 65% by mass.
As the anionic pigment dispersion paste, commercially available anionic coloring paste can be used. Examples of commercially available products include WAJ-AAT-907 black, WAJ-AAT-825 violet, WAJ-AAT-731 blue (manufactured by Toyo chemical Co., Ltd.), Emakoru (エマコール) NS ochre 4622 (manufactured by Shanyang pigment Co., Ltd.).
Preparation of anionic electrophoretic coating composition
The anionic electrophoretic coating composition of the present invention can be prepared by dispersing the acrylic resin (a), the curing agent (B), the water-dispersible gloss adjuster (C), the curing catalyst (D), and, if necessary, an anionic pigment-dispersing paste in an aqueous medium. The aqueous medium is water or a mixture of water and the above-mentioned organic solvent. As the water, ion-exchanged water is preferably used. Here, the above-mentioned neutralizing base can be used as needed.
The amount of the neutralizing base is preferably at least 30%, preferably 50 to 120%, of the anionic group (carboxyl group) of the coating film-forming resin such as the acrylic resin (a). Further, the adjustment of the pH of the anionic electrophoretic coating composition may be performed using a neutralizing base. The pH of the anionic electrophoretic coating composition is preferably 7.0 to 9.0, more preferably 7.0 to 8.5.
Formation of cured electrophoretic coating film
The method of the invention comprises the following steps:
an electrophoretic coating step of immersing a substrate in an anionic electrophoretic coating composition and applying a voltage to form an electrophoretic coating film; and
and a heat curing step of heat curing the electrophoretic coating film formed in the above-mentioned electrodeposition coating step to form a cured electrophoretic coating film.
In this method, by using the anionic electrophoretic coating composition and setting the viscosity of the electrophoretic coating film formed in the electrophoretic coating step at 50 ℃ in the range of 10,000 to 100,000Pa · s, a cured electrophoretic coating film having an adjusted gloss such as a low gloss coating film having a low specular gloss or a matte coating film can be obtained, and the coating film is characterized by not being accompanied by defects such as a difference in gloss or a poor matte effect due to a difference in heating temperature.
The electrophoretic coating of the anionic electrophoretic coating composition is performed by immersing the object to be coated in the anionic electrophoretic coating composition as an anode and then applying a voltage of usually 1 to 400V between the object and the cathode. The coating temperature of the anionic electrophoretic coating composition at the time of electrophoretic coating is preferably 10 to 45 ℃, more preferably 15 to 30 ℃. The time for applying the voltage can be arbitrarily selected depending on the electrodeposition coating conditions, and may be, for example, 30 seconds to 5 minutes. By applying a voltage, an electrophoretic coating film is formed on the surface of the object to be coated. The formed electrophoretic coating film may be washed with water as necessary.
The method of the present invention is provided that the viscosity of the electrophoretic coating film formed in the above-mentioned electrophoretic coating step is within a range of 10,000 to 100,000Pa · s at 50 ℃. When the coating viscosity of the electrophoretic coating film at 50 ℃ is in the above range, the water-dispersible gloss adjuster (C) contained in the anionic electrophoretic coating composition of the present invention can satisfactorily exert a gloss adjusting function, and the gloss of the resulting cured electrophoretic coating film can be designed to be low (60 ° specular gloss of 70 or less).
In the present invention, the reason why the viscosity of the electrodeposition coating film is measured at 50 ℃ is as follows. The electrophoretic coating film is a coating film that is deposited on the surface of an object to be coated by applying a voltage. The electrocoat film is generally designed to be of higher viscosity (high Tg). Therefore, if the viscosity of the electrodeposition coating film is measured at a temperature of a conventional electrodeposition bath (e.g., 30 ℃), the viscosity is very high and sometimes cannot be measured. Therefore, it is difficult to measure the coating film viscosity of the electrodeposition coating film at 30 ℃. On the other hand, the deposited electrophoretic coating film generates heat flow by heating, and the viscosity temporarily decreases. Further, by further heating, a crosslinking reaction occurs in the coating film forming resin such as the acrylic resin (a) and the curing agent (B) contained in the electrophoretic coating film, and the viscosity of the coating film rapidly increases. Thereby, the electrophoretic coating film is cured to form a cured electrophoretic coating film. That is, the viscosity of the electrocoat film temporarily decreases by heating, and thereafter, the viscosity increases.
Further, Joule heat is generated during the electrodeposition coating, and the temperature rises to about 40 to 50 ℃ in the vicinity of the object to be coated. That is, the measurement of the viscosity at 50 ℃ can be said to reproduce the state of physical properties at the time of deposition of an electrophoretic coating film. From the above, the temperature of 50 ℃ is a temperature which is preferable for measuring the viscosity of the coating film in view of the above properties of the electrodeposition coating composition and is a temperature at which crosslinking of the coating film forming resin does not occur, that is, a temperature which is considered to be suitable for judging the properties at the time of deposition of the uncured electrodeposition coating film.
When the coating viscosity of the electrodeposition coating film at 50 ℃ is less than 10,000 pas, the thermal fluidity of the electrodeposition coating film deposited is improved, and therefore the gloss of the resulting cured electrodeposition coating film is increased. On the other hand, when the coating viscosity of the electrodeposition coating film at 50 ℃ is more than 100,000 pas, the fluidity of the resultant electrodeposition coating film is lowered, resulting in poor appearance of the cured coating film.
In the present invention, the viscosity of the electrophoretic coating film formed in the above-mentioned electrophoretic coating step is more preferably in the range of 1,000 to 10,000Pa · s at 80 ℃. By setting the coating viscosity of the electrophoretic coating film at 80 ℃ within the above range, the final appearance of the cured electrophoretic coating film can be made uniform while the gloss of the resulting cured electrophoretic coating film is designed to be low. The temperature of 80 ℃ may be referred to as a temperature immediately before the curing reaction of the acrylic resin (a) and the curing agent (B) contained in the electrodeposition coating film starts. By setting the coating viscosity at 80 ℃ of the electrophoretic coating film under such temperature conditions to the above range, a cured electrophoretic coating film having low gloss can be formed without excessively increasing the fluidity of the electrophoretic coating film by heating, and appearance defects of the cured electrophoretic coating film can be avoided.
The coating film viscosity at 50 ℃ and the coating film viscosity at 80 ℃ of the electrodeposition coating film can be measured in the following manner. First, electrophoretic coating was performed on a substrate for 180 seconds so that the film thickness became about 20 μm to form an electrophoretic coating film, and the electrophoretic coating film was washed with water to remove excess adhering electrophoretic coating composition. Next, after removing excess moisture adhering to the surface of the electrophoretic coating film, the coating film was immediately taken out without drying, and a sample was prepared. The viscosity of the coating film obtained in this manner can be measured at 50 ℃ and 80 ℃ by measuring the viscosity using a dynamic viscoelasticity measuring apparatus.
The electrophoretic coating film formed in the coating step is heated to be cured, thereby obtaining a cured electrophoretic coating film (heat curing step). In the method of the present invention, the heating temperature (T) in the heat curing steph) Preferably 110 to 160 ℃.
The above softening point (T)m) And heating temperature (T)h) The difference (. DELTA.T) is more preferably 10 ℃ to 50 ℃. With respect to the softening point (T)m) And heating temperature (T)h) More preferably
Th＞Tm(ii) a And
softening point (T)m) And heating temperature (T)h) The difference DeltaT is 10 ℃ or more and 50 ℃ or less.
Further, the Δ T is more preferably 10 ℃ or more and 30 ℃ or less.
By making the heating temperature (T) in the heat curing steph) Within the above range, and a softening point (T) of a wax constituting the water-dispersible gloss adjuster (C)m) Difference betweenWhen the amount is in an appropriate range, there is an advantage that the gloss of the obtained cured electrophoretic coating film can be favorably designed to be in a low range (60 ° specular gloss is 70 or less), and the occurrence of uneven gloss can be further suppressed.
The heating time of the electrodeposition coating film may be determined depending on the size of the substrate and the heating temperature (T)h) And the like as appropriate. The heating time is, for example, 5 to 60 minutes, preferably 10 to 30 minutes.
The thickness of the cured electrophoretic coating film formed by the method of the present invention is preferably 5 to 30 μm, and more preferably 10 to 25 μm.
The cured electrophoretic coating film formed by the method of the present invention more preferably has a 60 ° specular gloss of 70 or less. The 60 ° specular gloss is an index generally referred to as 60 ° gloss (Gs (60 °)), and is a value [ Gs (60 °) = ψ s/ψ os × 100(%) ] represented by a specular reflection light flux (ψ s) measured by irradiating a coating surface with light from a light source at an incident angle of 60 degrees and a ratio thereof with reference to the specular reflection light flux (ψ os) of a glass surface having a refractive index n =1.567 under the same condition, which is measured by the method according to JIS Z8741. The 60 degree specular gloss can be measured using a gloss meter such as Uni-Gross 60 (manufactured by コニカミノルタ Co., Ltd.).
By the method of the present invention, a cured electrophoretic coating film adjusted to a low gloss can be formed without causing uneven gloss. The effect of such a technique is not bound by theory, but it is considered that the softening point (T) of the wax constituting the water-dispersible gloss adjuster (C) contained in the anionic electrophoretic coating composition is controlledm) And the viscosity of the electrophoretic coating film at 50 ℃ is controlled to a specific range, and the change in the state of the coating film occurring during the heat curing of the electrophoretic coating film can be controlled, whereby the occurrence of uneven gloss can be suppressed in the process of forming a cured electrophoretic coating film having low gloss.
In the method of the present invention, there is an advantage that a coating film having sufficient coating film hardness can be formed even when the cured electrophoretic coating film is formed under conditions where the heating temperature in the heating and curing step is lower than that in the heating and curing step in the usual electrophoretic coating, for example, 100 to 160 ℃. This has an advantage that the environmental burden can be reduced in the coating step.
Examples
The present invention will be further specifically described with reference to the following examples, but the present invention is not limited thereto. In the examples, "parts" and "%" are based on mass unless otherwise specified.
Production example 1 production of acrylic resin (A)
Into a 2L reaction vessel equipped with a stirring device, a cooling tube, a nitrogen introduction tube, and a thermometer connected to a temperature controller, 700 parts of isopropyl alcohol was charged, and the mixture was heated to 80 ℃ under a nitrogen atmosphere. Into the reaction vessel, a mixed solution of 322 parts of Methyl Methacrylate (MMA), 140 parts of butyl acrylate (nBA), 140 parts of styrene (St), 84 parts of hydroxyethyl methacrylate (HEMA), 49 parts of Acrylic Acid (AA) and 7 parts of azoisobutyronitrile was uniformly dropped over 3 hours, and thereafter, the mixture was kept at 80 ℃ for 2 hours, thereby obtaining an acrylic resin (A) having an acid value of 55mgKOH/g, a hydroxyl value of 52mgKOH/g and a weight average molecular weight of 30,000.
EXAMPLE 1 preparation of anionic electrophoretic coating composition
328 parts (solid content concentration: 50%) of the acrylic resin (A) prepared in production example 1, 86 parts of melamine resin Semel 235 (solid content concentration: 100%) as a curing agent (B), and 11 parts of triethylamine were mixed and stirred, and 3.75 parts of dinonylnaphthalenesulfonic acid (curing catalyst (D)) and 71.4 parts of water-dispersible gloss control agent (C) were added and mixed, the amounts of which are shown in the following tables. The obtained mixture was diluted with ion-exchanged water to a solid content of 10% to obtain an anionic electrophoretic coating composition.
The amount of the water-dispersed gloss adjuster (C) described in the following table is a solid content part by mass relative to 100 parts by mass of the total resin solid content of the acrylic resin (a) and the curing agent (B) as the coating film forming resin.
Formation of cured electrophoretic coating
An SUS430 plate as a coating object is immersed in the obtained anionic electrophoretic coating composition, a direct current voltage of 80-200V is applied for 2.5 minutes, and electrophoretic coating is performed so that the cured film thickness reaches 20 μm, thereby forming an electrophoretic coating film. 3 of the coated sheets were prepared.
The coated sheet having the electrophoretic coating film was baked at heating temperatures (145 ℃, 165 ℃, 185 ℃, respectively) higher by 10 ℃, 30 ℃ and 50 ℃ than the softening point (Tm) of the water-dispersible gloss adjuster (C) used for preparing the anionic electrophoretic coating composition for 30 minutes, respectively, to obtain a coated sheet having a cured electrophoretic coating film.
Example 2 and comparative examples 1 to 5
In the preparation of the anionic electrophoretic coating composition, an anionic electrophoretic coating composition was prepared in the same manner as in example 1 except that the kind and amount of the water-dispersible gloss adjuster (C) and the amount of the curing catalyst (D) were changed as shown in the following table.
Using the obtained anionic electrophoretic coating composition, electrophoretic coating was performed in the same manner as in example 1 to obtain a coated sheet having a cured electrophoretic coating film.
Comparative example 6
An anionic electrophoretic coating composition was prepared in the same manner as in example 2, except that the water-dispersible gloss adjuster (C) was not used in the preparation of the anionic electrophoretic coating composition.
Using the obtained anionic electrophoretic coating composition, electrophoretic coating was carried out in the same manner as in example 1, and the coating plates were baked at 120 ℃, 140 ℃ and 160 ℃ for 30 minutes, respectively, to obtain cured electrophoretic coating films.
The coated sheets obtained in the above examples and comparative examples were evaluated by the following criteria. The evaluation results are shown in the following table.
Measurement of viscosity of electrophoretic coating film at 50 ℃ and 80 ℃ of electrophoretic coating film
Using the anionic electrodeposition coating compositions obtained in the examples and comparative examples, electrodeposition coating was performed on the substrate for 180 seconds so that the film thickness became about 20 μm, to form an electrodeposition coating film, and the electrodeposition coating film was washed with water to remove the excess electrodeposition coating composition. Subsequently, after removing water, the coating film was taken out immediately without drying to prepare a sample. The sample thus obtained was subjected to frequency dependence measurement of dynamic viscoelasticity under the set conditions of strain 0.5deg and frequency 0.02Hz using a rotary dynamic viscoelasticity measuring apparatus manufactured by Rheosol G-3000 UBM Co. The prepared sample was mounted, and the measurement temperature was maintained at 50 ℃. After the start of the measurement, the viscosity of the coating film was measured at a point when the electrophoretic coating film was uniformly spread in the cone plate. The coating film viscosity at 80 ℃ was measured in the same manner as described above, except that the measurement temperature was changed.
Evaluation of change in gloss due to change in heating temperature
Measurement of 60 ℃ specular gloss and evaluation of gloss
The 60 ℃ specular gloss of the coated sheet obtained above was measured using Uni-Gross 60 (manufactured by Konika Meinenda).
The case where the 60 ° specular gloss was 70 or less was evaluated as "o" which could be adjusted to the low gloss range, and the case where the specular gloss was more than 70 was evaluated as "x" which could not be adjusted to the low gloss range.
Difference in gloss due to change in heating temperature
The 60 ° specular gloss of each of the coated sheets heat-cured at the various heating temperatures was compared, and the difference between the gloss values was calculated by subtracting the minimum value from the maximum value of the 60 ° specular gloss, and evaluated by the following criteria.
O: the difference in gloss is 20 or less
X: the difference in gloss is greater than 20.
The larger the value of the difference is, the more likely the change in glossiness depending on the change in heating temperature is to occur. When the difference in gloss is more than 20, the difference in gloss can be clearly found even in visual evaluation.
When the change in gloss depending on the change in heating temperature is likely to occur, for example, when an electrophoretic coating film provided on a large-sized substrate or substrates having different thicknesses is heat-cured, there is a defect that the gloss is not uniform when the heating temperature is not uniform at each part of the substrate.
Evaluation of appearance of coating film
The cured electrophoretic coating film obtained by heating at a temperature of +30 ℃ of the softening point of the water-dispersed gloss adjuster (C) was visually evaluated based on the following criteria.
O: no appearance defects of the coating film such as stirring marks were observed
X: the coating film was found to have poor appearance such as a trace of stirring.
Stirring trace: it is considered that the coating film appearance is poor due to stirring of the electrodeposition coating composition at the time of formation of the electrodeposition coating film and observed as streaks on the cured electrodeposition coating film.
Evaluation of horizontal appearance unevenness
The electrodeposition coating compositions described in examples and comparative examples were used to perform electrodeposition coating by placing a substrate in a horizontal state in an electrodeposition coating composition in a non-stirred state. The obtained electrophoretic coating film was cured by heating at a temperature of +30 ℃ for 30 minutes, which is the softening point of the water-dispersed gloss adjuster (C). The appearance of the coating film after baking of the resulting coated plate was visually observed, and the difference in appearance between the upper surface and the lower surface was visually evaluated by the following criteria.
O: no difference was observed by visual observation, and the appearance was judged to be good.
X: visual observation revealed that the upper and lower surfaces had different degrees of extinction, and the appearance was judged to be defective.
Measurement of Pencil hardness
The pencil hardness of the cured electrophoretic coating film obtained by heating at a temperature of +30 ℃ the softening point of the water-dispersed gloss adjuster (C) was measured in accordance with JIS K5600-5-4. Specifically, a pencil (manufactured by Mitsubishi Pencil corporation: for the scratch hardness test of Japan paint inspection Association) was pressed and moved on the surface of the cured electrodeposition coating film so that the scratch angle reached 45 °, and the presence or absence of a flaw due to the lead of the pencil was visually observed.
For example, in the case of a test using a pencil with H, when no scratch occurs, it is judged that H or more. When the occurrence of the fine pits was visually confirmed in 1 out of 5 tests, it was judged as H. In addition, in the case where the dishing occurred 2 times or more in 5 times of the test, it was judged to be lower than H, and the evaluation was similarly performed in the first stage.
When the pencil hardness is less than F, it is judged that the hardness and scratch resistance are poor.
[ TABLE 1 ]
Figure DEST_PATH_IMAGE001
。
The water-dispersed gloss adjuster (C) used in the above examples and comparative examples is as follows.
(C1) Example 1, comparative examples 3 and 4: AQUAMAT208 manufactured by Daichchemistry Japan K.K. (solid content concentration (NV) = 35%; softening point (T)m) =135 ℃, density =1.00)
(C2) Example 2: ArowbaseSD-1010, U.S. Youngco (NV =20%, T)m=105 ℃, density =0.93)
(C3) Comparative example 1: ArowbaseSB-1010, U.S. Youngi (NV =25%, T)m=80 ℃, density =0.93)
(C4) Comparative example 2: chemipearl WP-100(NV =40%, T)m=148 ℃, density =0.90)
(C5) Comparative example 5: AQUACER531 (nonionic emulsion wax, NV =45%, T, manufactured by DaCHE Japan K.K.)mDensity =0.98) at 130 ℃.
As shown in the above evaluation results, the cured electrophoretic coating film formed using the anionic electrophoretic coating composition obtained in the examples exhibited little change in gloss due to a change in heating temperature, and was also visually confirmed to be not accompanied by appearance defects of the coating film.
Comparative example 1 is the constituent Water contentSoftening point (T) of wax of bulk gloss adjuster (C)m) Experimental examples below 100 ℃. In this case, the gloss of the resulting cured electrophoretic coating film is increased as a whole, and the difference in gloss due to a change in heating temperature is increased. Further, there is a defect that the hardness of the cured electrophoretic coating film becomes low.
Comparative example 2 is an experimental example in which the density of the wax constituting the water-dispersed gloss adjuster (C) is less than 0.91. In this case, the difference in glossiness due to the change in heating temperature becomes large. Further, occurrence of horizontal appearance unevenness was confirmed. The reason for this is considered to be that the wax constituting the water-dispersible gloss adjuster (C) has a low density, and thus the water-dispersible gloss adjuster (C) cannot be dispersed well in the anionic electrophoretic coating composition, and the water-dispersible gloss adjuster (C) does not exist uniformly on the upper and lower surfaces of the base material in the electrophoretic coating layer and the cured electrophoretic coating layer in the electrophoretic coating step and the heat curing step.
Comparative example 3 is an experimental example in which the amount of the water-dispersed gloss adjuster (C) is small. In this case, the gloss of the resulting cured electrophoretic coating film is increased as a whole, and the difference in gloss due to a change in heating temperature is increased. Further, the coating film was found to have an uneven appearance.
Comparative example 4 is an experimental example in which the amount of the water-dispersed gloss adjuster (C) is large. In this case, the value of the gloss becomes low, while the difference in gloss due to the change in heating temperature becomes large. Further, there is a defect that the hardness of the cured electrophoretic coating film becomes low.
Comparative example 5 is an experimental example in which the coating film viscosity at 50 ℃ of the electrodeposition coating film is less than 10,000. In this case, the difference in glossiness due to the change in heating temperature becomes large.
Comparative example 6 is an experimental example containing no water-dispersed gloss adjuster (C). At this time, the gloss of the cured electrodeposition coating film becomes very high.
Industrial applicability
According to the method of the present invention, there is an advantage in that a cured electrophoretic coating film with adjusted gloss such as a low gloss coating film with low specular gloss or a matte coating film can be formed without uneven gloss such as a change in gloss due to a change in heating temperature. In the method of the present invention, there is a further advantage in that, after the formation of the electrophoretic coating film, a cured electrophoretic coating film having good hardness can be obtained even in the case of heat curing under low-temperature curing conditions.

Claims (6)

1. A method for forming a cured electrocoat film, comprising:
an electrophoretic coating step of immersing a substrate in an anionic electrophoretic coating composition and applying a voltage to form an electrophoretic coating film; and
a heat curing step of heat curing the electrophoretic coating film formed in the electrophoretic coating step to form a cured electrophoretic coating film;
the anionic electrophoretic coating composition comprises an acrylic resin (A), a curing agent (B), a water-dispersible gloss adjuster (C) and a curing catalyst (D);
the acrylic resin (A) is an acrylic resin with carboxyl and hydroxyl;
the curing agent (B) is selected from 1 or more of amino resin and blocked isocyanate compound;
the water-dispersible gloss adjuster (C) is an aqueous dispersion of 1 or more waxes selected from natural waxes and polyolefin waxes;
the softening point (T) of the wax constituting the water-dispersed gloss adjuster (C)m) Is more than 100 ℃ and has a density of 0.91-1.10;
the anionic electrophoretic coating composition contains 6 to 20 parts by mass of a solid content of the water-dispersible gloss adjuster (C) per 100 parts by mass of a resin solid content of the anionic electrophoretic coating composition;
the electrophoretic coating film formed in the electrophoretic coating step has a coating viscosity at 50 ℃ within a range of 10,000 to 100,000Pa · s.
2. The method according to claim 1, wherein the heating temperature (T) in the heating and curing steph) Is 110 to 160 ℃.
3. Method according to claim 1 or 2, wherein the softening point (T)m) Is in the range of 100 to 140 ℃.
4. The method according to claim 1 or 2, wherein the electrocoating step forms an electrocoat film having a film viscosity at 80 ℃ in a range of 1,000 to 10,000 Pa-s.
5. Method according to claim 1 or 2, wherein the softening point (T)m) And heating temperature (T)h) A difference (DeltaT) of 10 ℃ to 50 ℃ inclusive, and Th＞Tm。
6. The method according to claim 1 or 2, wherein the cured electrocoat film formed by the forming method has a 60 ° specular gloss of 70 or less.
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