CN113597455A - Coating composition and coated metal sheet - Google Patents

Coating composition and coated metal sheet Download PDF

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Publication number
CN113597455A
CN113597455A CN201980094187.7A CN201980094187A CN113597455A CN 113597455 A CN113597455 A CN 113597455A CN 201980094187 A CN201980094187 A CN 201980094187A CN 113597455 A CN113597455 A CN 113597455A
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mass
parts
coating composition
resin
content
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CN113597455B (en
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藤本泰载
山口裕树
高冈真司
尾和克美
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Nippon Steel Corp
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Nippon Steel and Sumitomo Metal Corp
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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
    • C09D201/00—Coating compositions based on unspecified macromolecular compounds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
    • B05D7/14—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials to metal, e.g. car bodies
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B15/00—Layered products comprising a layer of metal
    • B32B15/04—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material
    • B32B15/08—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/34—Silicon-containing compounds
    • C08K3/36—Silica
    • 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
    • C09D163/00—Coating compositions based on epoxy resins; Coating compositions based on derivatives of epoxy resins
    • 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
    • C09D175/00—Coating compositions based on polyureas or polyurethanes; Coating compositions based on derivatives of such polymers
    • C09D175/04—Polyurethanes
    • 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
    • C09D179/00—Coating compositions based on macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing nitrogen, with or without oxygen, or carbon only, not provided for in groups C09D161/00 - C09D177/00
    • 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
    • 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
    • C09D5/002—Priming paints
    • 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
    • C09D5/08—Anti-corrosive paints
    • 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
    • C09D7/60—Additives non-macromolecular
    • C09D7/61—Additives non-macromolecular inorganic
    • 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
    • C09D7/60—Additives non-macromolecular
    • C09D7/63—Additives non-macromolecular organic

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  • Chemical & Material Sciences (AREA)
  • Wood Science & Technology (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Organic Chemistry (AREA)
  • Materials Engineering (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Inorganic Chemistry (AREA)
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  • Polymers & Plastics (AREA)
  • Health & Medical Sciences (AREA)
  • Paints Or Removers (AREA)
  • Laminated Bodies (AREA)

Abstract

The coating composition of the present invention comprises a nonionic water-dispersible resin (a), a phosphoric acid-modified epoxy resin (b), a melamine compound (c), a silane coupling agent (d), and silica particles (e) ion-exchanged with a metal having a valence of 2. The content of the nonionic water-dispersible resin (a) is 60 to 94.5 parts by mass, the content of the phosphoric acid-modified epoxy resin (b) is 5 to 39.5 parts by mass, the content of the melamine compound (c) is 0.5 to 10 parts by mass, and the content of the silane coupling agent (d) is 0.3 to 5 parts by mass, based on 100 parts by mass of the total of the components (a), (b), and (c).

Description

Coating composition and coated metal sheet
Technical Field
The present invention relates to a coating composition and a coated metal sheet.
Background
Coated metal sheets are generally produced by applying a paint to the surface of a metal sheet such as a plated steel sheet. As the coating material, a water-based coating material may be used instead of the solvent-based coating material from the viewpoint of reducing the environmental load.
As such an aqueous coating material, a coating composition containing an epoxy resin dispersion, an acrylic resin emulsion, and a rust preventive pigment such as calcium phosphomolybdate has been proposed (for example, see patent document 1).
Documents of the prior art
Patent document
Patent document 1: japanese patent laid-open No. 2014-196426.
Disclosure of Invention
Problems to be solved by the invention
However, a coated metal sheet having a coating film obtained from the coating composition of patent document 1 has the following problems: when the coating film is stored for a certain period of time under high-temperature and high-humidity conditions, moisture in the environment is likely to penetrate into the coating film, and the coating film is likely to swell (see fig. 1A described later). Further, it is desired that the coating composition has a small increase in viscosity during storage and has good storage stability.
The present invention has been made in view of the above circumstances, and an object thereof is to provide a coating composition and a coated metal sheet which have good storage stability and can suppress the swelling of a coating film under high-temperature and high-humidity conditions.
Means for solving the problems
The present invention relates to the following coating composition and coated metal sheet.
The coating composition comprises a nonionic water-dispersible resin (a), a phosphoric acid-modified epoxy resin (b), a melamine compound (c), a silane coupling agent (d), 2-valent metal ion-exchanged silica particles (e), and water, wherein the content of the nonionic water-dispersible resin (a) is 60-94.5 parts by mass, the content of the phosphoric acid-modified epoxy resin (b) is 5-39.5 parts by mass, the content of the melamine compound (c) is 0.5-10 parts by mass, and the content of the silane coupling agent (d) is 0.3-5 parts by mass, based on 100 parts by mass of the total of the nonionic water-dispersible resin (a), the phosphoric acid-modified epoxy resin (b), and the melamine compound (c).
The coated metal sheet of the present invention comprises a metal sheet and an undercoat layer disposed on the metal sheet, wherein the undercoat layer is composed of a cured product of the coating composition of the present invention.
Effects of the invention
The present invention can provide a coating composition and a coated metal sheet which have good storage stability and can suppress the swelling of a coating film under high-temperature and high-humidity conditions.
Drawings
Fig. 1A to 1C are photographs showing the surface of a coating film after storage under high-temperature and high-humidity conditions.
Detailed Description
A cured product of the coating composition (aqueous coating composition) of the present invention containing the nonionic water-dispersible resin (a), the phosphoric acid-modified epoxy resin (b), the melamine compound (c), the silane coupling agent (d), the 2-valent metal ion-exchanged silica particles (e), and water at a predetermined ratio can have high moisture resistance. The reason is not clear, but is presumed as follows.
Fig. 1A to 1C are photographs showing the surface of a coating film after storage under high-temperature and high-humidity conditions. Among them, fig. 1A is an observation result of a comparative coating film 1 (a coating film containing only the component (a), fig. 1B is an observation result of a comparative coating film 2 (a coating film containing the components (B), (C), and (d)) added to the component (a)), and fig. 1C is an observation result of a coating film of the present invention (a coating film containing the component (e) added to the components (a), (B), (C), and (d)).
First, the present inventors have found that the moisture resistance of a coating film can be improved by adding components (B), (c), and (d) (crosslinking components) to component (a) (see fig. 1B). Further, the inventors of the present invention have studied whether the moisture resistance of the coating film can be further improved by further adding a rust-preventive component in addition to the components (b), (c) and (d). As a result, it was found that the moisture resistance of the obtained coating film can be significantly improved by adding "silica particles (e) exchanged with a 2-valent metal ion" as a rust-preventive component (see fig. 1C).
Further, these studies revealed that the more the metal ion-exchanged silica has a moderately high activity and a large amount of metal ions (released into water), the higher the effect of improving the moisture resistance of the coating film. Further, it is found that the more highly moisture-resistant coating film, the more likely the viscosity of the composition containing the components (b), (c) and (d) increases with time, that is, the more likely the crosslinking reaction between the component (b) and the component (c) occurs.
That is, it is considered that in the coating composition of the present invention, metal ions are easily eluted appropriately from the "silica particles (e) exchanged with a metal ion having a valence of 2"; since the activity of the metal ions is appropriately high, the eluted metal ions promote a crosslinking reaction between the phosphoric acid-modified epoxy resin (b) and the melamine compound (c), a crosslinking reaction between the silane coupling agent (d) and a functional group on the surface of the silica particle (e), or a crosslinking reaction between the silane coupling agent (d) and the melamine compound (c) (the eluted metal ions function as a catalyst). For the above reasons, it is considered that the crosslinking reaction is easily highly advanced, and a cured product having a high crosslinking density can be obtained, and therefore, high moisture resistance can be obtained.
On the other hand, the storage stability of a coating composition in which a crosslinking reaction is likely to occur tends to be low. On the other hand, by adjusting the quantitative ratio of the components (a), (b), (c), and (d) and preferably further selecting the type of the component (e), the storage stability can be improved without adversely affecting the moisture resistance of the cured product.
That is, the coating composition of the present invention comprises a nonionic water-dispersible resin (a), a phosphoric acid-modified epoxy resin (b), a melamine compound (c), a silane coupling agent (d), silica particles (e) ion-exchanged with a metal having a valence of 2, and water, and the content of each of the components (a), (b), and (c) is adjusted to be within a predetermined range with respect to 100 parts by mass of the total of the components (a), (b), and (c). The coating composition of the present invention will be specifically described below.
1. Coating composition
The coating composition of the present invention comprises a nonionic water-dispersible resin (a), a phosphoric acid-modified epoxy resin (b), a melamine compound (c), a silane coupling agent (d), silica particles (e) ion-exchanged with a metal having a valence of 2, and water.
1-1. nonionic Water-dispersible resin (a)
The nonionic water-dispersible resin (a) is a water-dispersible resin having a nonionic hydrophilic group and no ionic functional group. The nonionic hydrophilic group may be a hydroxyl group, an amide group, a polyoxyalkylene group (e.g., polyoxyethylene group), or the like. Among them, the nonionic hydrophilic group is preferably a polyoxyethylene group from the viewpoint of improving the storage stability of the coating composition.
Examples of the nonionic water-dispersible resin (a) include nonionic urethane resins, nonionic acrylic resins, nonionic epoxy resins, and nonionic polyester resins. These resins may be obtained by polymerizing monomers or stirring the resins in the presence of a nonionic surfactant (or a dispersant having a nonionic hydrophilic group such as a polyoxyalkylene group and a reactive group), or may be obtained by polymerizing monomer components including a monomer having a nonionic hydrophilic group.
The nonionic urethane resin may be, for example, a polymer obtained by reacting a polyol component containing a polyol having a nonionic hydrophilic group (for example, a hydroxyl group) with a polyisocyanate component.
Examples of the polyisocyanate component include: polyisocyanates having an alicyclic structure such as cyclohexane diisocyanate, dicyclohexylmethane diisocyanate, and isophorone diisocyanate; aromatic polyisocyanates such as 4,4 '-diphenylmethane diisocyanate, 2, 4' -diphenylmethane diisocyanate, phenylene diisocyanate, and toluene diisocyanate; aliphatic polyisocyanates such as hexamethylene diisocyanate and lysine diisocyanate.
Examples of the polyol having a nonionic hydrophilic group include a 3-or more-membered polyol (when the nonionic hydrophilic group is a hydroxyl group), polyoxyethylene glycol, and a compound having a polyoxyethylene group and at least 2 hydroxyl groups (when the nonionic hydrophilic group is a polyoxyethylene group).
The polyol component may further contain other polyols than the above. Examples of the other polyhydric alcohols include aliphatic polyhydric alcohols such as ethylene glycol, propylene glycol, 1, 4-butanediol, 1, 6-hexanediol, trimethylolpropane, and glycerin; polyether polyols such as polyethylene glycol and polypropylene glycol; polyester polyols obtained from dicarboxylic acids such as adipic acid, sebacic acid, phthalic acid, and isophthalic acid, and diols.
The nonionic acrylic resin may be, for example, a copolymer of (meth) acrylate and a polymerizable unsaturated monomer having a nonionic hydrophilic group. Examples of the polymerizable unsaturated monomer having a nonionic hydrophilic group include hydroxyl group-containing (meth) acrylates, (meth) acrylamides, polymerizable unsaturated monomers having a polyoxyalkylene group, and the like.
The nonionic polyester resin may be, for example, a polycondensate of a polyol component containing a polyol having a nonionic hydrophilic group and a polycarboxylic acid. The same polyols as described above can be used as the polyol having a nonionic hydrophilic group. Examples of the polycarboxylic acid include aliphatic polycarboxylic acids such as adipic acid, sebacic acid and butanetricarboxylic acid, and aromatic polycarboxylic acids such as terephthalic acid and trimellitic acid.
Examples of the nonionic epoxy resin include: a resin obtained by stirring an epoxy resin in the presence of a polyoxyalkylene compound having a functional group (amino group, epoxy group) reactive with an epoxy group and a polyoxyalkylene group; and resins obtained by reacting a compound having 2 or more epoxy groups with polyethylene glycol or a monoester thereof.
Among them, nonionic acrylic resins and nonionic urethane resins are preferable from the viewpoint of improving storage stability. In addition, from the viewpoint of easily improving the moisture resistance of the obtained coating film, nonionic epoxy resins and nonionic urethane resins are preferable. That is, a nonionic urethane resin is particularly preferable from the viewpoint of good storage stability, easy improvement of moisture resistance of the coating film, and excellent adhesion of the coating film.
The weight average molecular weight of the nonionic water-dispersible resin (a) is not particularly limited, and is preferably 50000 to 1000000, for example. If the weight average molecular weight of the nonionic water-dispersible resin (a) is 50000 or more, sufficient strength or flexibility is easily imparted to the obtained coating film, and if it is 1000000 or less, an increase in viscosity of the coating composition is easily suppressed, and adverse influence on coatability is hardly exerted.
The weight average molecular weight can be calculated from the molecular weight of standard polystyrene based on the chromatogram determined by gel permeation chromatography according to JIS K0124-2011.
Preferably, the content of the nonionic water-dispersible resin (a) is 60 to 94.5 parts by mass based on 100 parts by mass of the total of the components (a), (b) and (c). If the content of the nonionic water-dispersible resin (a) is 60 parts by mass or more, the nonionic water-dispersible resin (a) is less likely to be accelerated by the metal ions eluted from the silica particles (e) exchanged with the 2-valent metal ions than, for example, the phosphoric acid-modified epoxy resin (b), and therefore, the storage stability of the coating composition is easily improved. If the content of the nonionic water-dispersible resin (a) is 94.5 parts by mass or less, the resultant coating film is less likely to have adverse effects on moisture resistance, adhesion, and corrosion resistance. From the same viewpoint, the content of the nonionic water-dispersible resin (a) is more preferably 70 to 89 parts by mass, and still more preferably 70 to 85 parts by mass, based on 100 parts by mass of the total of the components (a), (b) and (c).
1-2 phosphoric acid modified epoxy resin (b)
The phosphoric acid-modified epoxy resin (b) can improve the adhesion between the coating film and the metal plate and the moisture resistance. The phosphoric acid-modified epoxy resin (b) is a resin obtained by reacting an epoxy resin with a compound having a phosphoric acid bond, and can be formed into an emulsion by neutralization with a base such as a volatile amine.
The epoxy resin to be a raw material is not particularly limited, and examples thereof include: bisphenol epoxy resins such as bisphenol a epoxy resin and bisphenol F epoxy resin; biphenyl type epoxy resin; a novolac type epoxy resin; naphthalene type epoxy resins; alicyclic epoxy resins obtained from cyclohexane dimethanol, hydrogenated bisphenol A, and the like. Among them, bisphenol a type epoxy resins are preferred from the viewpoint of adhesion and corrosion resistance.
The weight average molecular weight of the epoxy resin is preferably 800-50000. If the weight average molecular weight of the epoxy resin is 800 or more, sufficient flexibility is easily imparted to the obtained coating film, and if it is 50000 or less, increase in viscosity of the coating composition is easily suppressed, and adverse effect on coatability is hardly exerted.
The compound having a phosphate bond is not particularly limited, and examples thereof include: phosphoric acids such as metaphosphoric acid, orthophosphoric acid and pyrophosphoric acid; phosphoric acid esters such as diethyl phosphate, dibutyl phosphate, and dioctyl phosphate.
Preferably, the amount (modification amount) of the compound having a phosphoric acid bond reacted with the epoxy resin is the following amount: the number of moles of the phosphate group in the compound having a phosphate bond is, for example, 0.1 to 1.5 moles per 1 mole of the epoxy group in the epoxy resin.
Examples of the volatile amine used for neutralization include triethylamine and the like.
Preferably, the content of the phosphoric acid-modified epoxy resin (b) is 5 to 39.5 parts by mass with respect to 100 parts by mass of the total of the components (a), (b) and (c). If the content of the phosphoric acid-modified epoxy resin (b) is 5 parts by mass or more, a cured product having a high crosslinking density can be formed by a crosslinking reaction with the melamine compound (c), and therefore, the adhesion between the coating film and the metal plate and the moisture resistance are easily improved, and if it is 39.5 parts by mass or less, an increase in viscosity due to a crosslinking reaction with the melamine compound (c) or the like is less likely to occur during storage, and therefore, the storage stability of the coating composition is less likely to be adversely affected. From the same viewpoint, the content of the phosphoric acid-modified epoxy resin (b) is more preferably 10 to 29 parts by mass, and still more preferably 15 to 25 parts by mass, based on 100 parts by mass of the total of the components (a), (b) and (c).
From the same viewpoint as above, the content of the phosphoric acid-modified epoxy resin (b) is preferably 5 to 40 parts by mass, more preferably 10 to 30 parts by mass, and still more preferably 15 to 30 parts by mass, based on 100 parts by mass of the total of the nonionic water-dispersible resin (a) and the phosphoric acid-modified epoxy resin (b).
1-3. Melamine Compound (c)
The melamine compound (c) can function as a curing agent for the phosphoric acid-modified epoxy resin (b). Thus, the cured product of the coating composition can have good moisture resistance and corrosion resistance (particularly moisture resistance).
The kind of the melamine compound (c) is not particularly limited, and a known melamine curing agent can be used as the melamine compound (c). Examples of the melamine compound (c) include: methylolated melamine compounds obtained by reacting melamine with an aldehyde, and melamine compounds obtained by etherification of at least a part of the methylol groups with an alcohol (for example, 1-membered alcohol such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, 2-ethylbutanol, 2-ethylhexanol).
Examples of methylolated melamine compounds include trimethylolmelamine, hexamethylolmelamine, tributylmelamine, hexabutylmelamine. Examples of the etherate of the methylolated melamine compound include methoxymethylmelamine (e.g., hexamethoxymethylmelamine, etc.), ethoxymethylmelamine, ethoxybutylmelamine, butoxybutylmelamine.
Among them, from the viewpoint of easily improving the storage stability of the coating composition, it is preferable to use a melamine compound obtained by etherifying at least a part of the methylol groups of a methylolated melamine compound with a 1-membered alcohol having 1 to 4 carbon atoms.
Preferably, the content of the melamine compound (c) is 0.5 to 10 parts by mass relative to 100 parts by mass of the total of the components (a), (b) and (c). When the content of the melamine compound (c) is 0.5 parts by mass or more, the phosphoric acid-modified epoxy resin (b) is easily crosslinked sufficiently, and therefore, the adhesion between the coating film and the metal plate, the moisture resistance, and the corrosion resistance are easily improved, and when it is 10 parts by mass or less, the viscosity increase due to the crosslinking reaction of the phosphoric acid-modified epoxy resin (b) is less likely to occur during storage, and therefore, the storage stability is less likely to be adversely affected. From the same viewpoint, the content of the melamine compound (c) is more preferably 1 to 8 parts by mass, and still more preferably 3 to 8 parts by mass, based on 100 parts by mass of the total of the components (a), (b) and (c).
1-4. silane coupling agent (d)
The silane coupling agent (d) can improve the adhesion between the coating film and the metal plate. The silane coupling agent (d) can further improve the moisture resistance and adhesion of the obtained coating film by performing a crosslinking reaction with the functional groups on the surfaces of the silica particles (e) ion-exchanged with a metal having a valence of 2, which will be described later.
The silane coupling agent (d) is a compound having an alkoxy group or the like which provides a silanol group (Si — OH) by hydrolysis and an organic group such as an epoxy group, a vinyl group, an amino group, a mercapto group, or an alkyl group in the molecule.
Examples of the silane coupling agent (d) include epoxy-based silane coupling agents having an epoxy group in the molecule, such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltripropoxysilane, 3-glycidoxypropyltributoxysilane, 3-glycidoxypropyltriphenoxysilane, 2- (3, 4-epoxycyclohexyl) ethyltrimethoxysilane; vinyl silane coupling agents having a vinyl group in the molecule, such as vinyltrimethoxysilane and vinylmethoxysilane; amine-based silane coupling agents having amino groups in the molecule, such as aminomethyl trimethoxysilane, aminomethyl triethoxysilane, aminomethyl tripropoxysilane, aminomethyl tributoxysilane, aminomethyl triphenoxysilane, aminoethyl trimethoxysilane, and γ -aminopropyltrimethoxysilane; mercapto silane coupling agents having mercapto groups in the molecule, such as mercaptomethyltrimethoxysilane, mercaptomethyltriethoxysilane, mercaptomethyltripropoxysilane, mercaptomethyltributoxysilane, mercaptomethyltriphenoxysilane, and γ -mercaptopropylmethyldiethoxysilane. Among them, epoxy silane coupling agents are preferable from the viewpoints of good affinity with the phosphoric acid-modified epoxy resin (b), capability of performing a crosslinking reaction with the melamine compound (c), and easiness of obtaining a cured product having high moisture resistance.
Preferably, the content of the silane coupling agent (d) is 0.3 to 5 parts by mass with respect to 100 parts by mass of the total of the components (a), (b) and (c). When the content of the silane coupling agent (d) is 0.3 parts by mass or more, the adhesion between the coating film and the metal plate, the moisture resistance and the corrosion resistance are easily improved, and when the content is 5 parts by mass or less, the storage stability of the coating composition is hardly adversely affected. From the same viewpoint, the content of the silane coupling agent (d) is more preferably 1 to 4 parts by mass, and still more preferably 1.5 to 3 parts by mass, relative to 100 parts by mass of the total of the components (a), (b) and (c).
1-5 silica particles (e) exchanged with a metal ion of valency 2
The silica particles (e) exchanged with the metal ions having a valence of 2 are silica particles in which at least a part of the hydroxyl groups on the surface of the silica particles is replaced with the metal ions having a valence of 2 by ion exchange. The silica particles (e) exchanged with the 2-valent metal ion can improve the moisture resistance and corrosion resistance of the coating film.
The silica particles (e) exchanged with a 2-valent metal ion are not particularly limited, and examples thereof include calcium (Ca) -exchanged silica, magnesium (Mg) -exchanged silica, strontium (Sr) -exchanged silica, and manganese (Mn) -exchanged silica. Among these, silica particles ion-exchanged with an alkaline earth metal having a valence of 2 are preferable, and calcium (Ca) -exchanged silica and magnesium (Mg) -exchanged silica are preferable from the viewpoint of easily providing a coating film having good moisture resistance and corrosion resistance, and magnesium (Mg) -exchanged silica is more preferable from the viewpoint of easily improving storage stability.
The average particle diameter of the silica particles (e) exchanged with the 2-valent metal ion is not particularly limited, and may be, for example, 1 to 5 μm. The average particle diameter of the silica particles (e) exchanged with the 2-valent metal ions can be measured as a median particle diameter in a volume distribution obtained by a laser diffraction/scattering method, for example.
The amount of metal ion exchange in the silica particles (e) exchanged with a metal ion having a valence of 2 is not particularly limited, and may be, for example, 4 to 8% by mass relative to the silica carrier (containing no metal ion). If the amount of metal ion exchange is not less than a certain amount, the amount of metal ion elution is likely to be increased (although it depends on the type of metal ion), and the crosslinking reaction between the phosphoric acid-modified epoxy resin (b) and the melamine compound (c) is likely to be accelerated.
The amount of metal ion exchange can be determined, for example, from the charge ratio of the raw materials in the production of the metal ion-exchanged silica. The measurement can also be obtained by the following method.
1) A certain amount of silica particles (e) ion-exchanged with a metal having a valence of 2 was added to a 1 mass% aqueous solution of sodium chloride, and the mixture was sufficiently stirred at 23 ℃ for 30 minutes.
2) The amount of the 2-valent metal ion (mass% relative to the silica carrier) contained in the stirred aqueous solution was measured by ion chromatography as the amount of metal ion exchange.
The elution amount of the metal ions in the coating composition can be adjusted by, for example, the amount of metal ions exchanged in the silica particles (e) exchanged with the metal ions having a valence of 2, the kind of the metal ions, the production conditions of the metal ion-exchanged silica, and the like. In order to moderately increase the elution amount of the metal ions, for example, it is preferable to moderately increase the metal ion exchange amount, or to select 2-valent alkaline earth metal ions as the metal ions.
Preferably, the content of the 2-valent metal ion-exchanged silica particles (e) is 5 to 70 parts by mass relative to 100 parts by mass of the total of the components (a), (b) and (c). When the content of the 2-valent metal ion-exchanged silica particles (e) is 5 parts by mass or more, the crosslinking reaction of the component (b) and the component (c) is easily sufficiently promoted, and hence the adhesion between the coating film and the metal plate, the moisture resistance, and the corrosion resistance (particularly, the moisture resistance) are easily improved, and when it is 70 parts by mass or less, the increase in viscosity due to the crosslinking reaction of the component (b) and the component (c) is hardly caused during storage, and therefore the storage stability of the coating composition is hardly adversely affected. From the same viewpoint, the content of the 2-valent metal ion-exchanged silica particles (e) is more preferably 7.5 to 55 parts by mass, and still more preferably 15 to 45 parts by mass, relative to 100 parts by mass of the total of the components (a), (b), and (c).
1-6. other ingredients
The coating composition of the present invention may further contain other components than the components (a) to (e) and water, as necessary. Examples of other ingredients include: water-soluble organic solvents (for example, alcohols such as methanol, ethanol and n-propanol; ketones such as acetone and methyl ethyl ketone; polyalkylene glycols such as ethylene glycol, diethylene glycol and propylene glycol), emulsifiers (nonionic surfactants, for example, polyoxyethylene alkyl ethers, polyoxyalkylene alkyl ethers, polyoxyethylene derivatives, sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters, polyoxyethylene fatty acid esters, etc.); (e) rust inhibitors other than the above (e.g., zinc phosphate, zinc phosphite, magnesium zinc phosphate, magnesium phosphite, silica, zirconium phosphate, 2-aluminum tripolyphosphate, zinc oxide, zinc phosphomolybdate, barium metaborate, and strontium chromate); pH regulator (bases such as triethylamine, triethanolamine, sodium hydroxide, sodium carbonate and potassium carbonate, acids such as hydrochloric acid, acetic acid and citric acid); film-forming aids (water-soluble organic solvents with boiling points of 150-250 ℃ such as butyl cellosolve, TEXANOL, carbitol and the like); and pigments (coloring pigments such as titanium oxide, carbon black, chromium oxide, iron oxide, and red iron oxide, and extender pigments such as barium sulfate, titanium oxide, silica, and calcium carbonate).
The total content of the other components (excluding the water-soluble organic solvent) may be 10 parts by mass or less with respect to 100 parts by mass of the total of the components (a), (b), and (c).
The coating composition of the present invention can be obtained by any method. For example, the coating composition of the present invention can be obtained by mixing the components (a) to (e), water, and if necessary, other components such as an emulsifier. The components (a) and (b) may be used in the form of an aqueous dispersion. That is, the coating composition of the present invention can also be obtained by mixing the components (c) to (e) and, if necessary, other components in an aqueous dispersion of the components (a) and (b).
The coating composition of the present invention has high storage stability and can provide a coating film having high moisture resistance. Therefore, the coating composition is preferably used as a coating composition for a base coat layer of a metal plate.
2. Coated metal plate
The coated metal sheet of the present invention has a metal sheet and an undercoat layer disposed thereon.
2-1. Metal plate
The metal plate to be the original coated plate can be appropriately selected according to the application of the coated metal plate. Examples of the metal plate include: galvanized steel sheets, Zn — Al alloy-plated steel sheets, Zn — Al — Mg alloy-plated steel sheets, aluminum-plated steel sheets, and the like; cold-rolled steel sheet, stainless steel sheet (containing austenite system,Martensite, ferrite-martensite dual phase) steel sheets; an aluminum plate; aluminum alloy plate; and a copper plate. Among these, the metal sheet is preferably a plated steel sheet, and more preferably a hot-dip plated steel sheet, from the viewpoint of improving corrosion resistance. The plating adhesion amount of the plated steel sheet is not particularly limited, and may be, for example, 30 to 500g/m2。
The thickness of the metal plate is not particularly limited, and may be set according to the application and workability, and is preferably 0.1 to 2mm, for example.
From the viewpoint of improving the corrosion resistance and coating film adhesion of the coated metal sheet, the surface of the metal sheet may be subjected to chemical conversion treatment. The kind of the chemical conversion treatment is not particularly limited, and examples thereof include chromate treatment, chromium-free treatment, and phosphate treatment.
The chemical conversion treatment can be carried out by a known method. For example, the chemical conversion treatment solution may be applied to the surface of the steel sheet by a method such as roll coating, spin coating, or spray coating, and dried without washing with water. The drying temperature and drying time are not particularly limited as long as the moisture can be evaporated. From the viewpoint of productivity, the drying temperature is preferably in the range of 60 to 150 ℃ and the drying time is preferably in the range of 2 to 10 seconds. The amount of the chemical conversion coating deposited is not particularly limited, and may be within a range that effectively contributes to the improvement of corrosion resistance and coating film adhesion. For example, in the case of a chromate film, the amount of Cr deposited is 5 to 100mg/m in terms of total Cr2The amount of adhesion can be adjusted. In addition, in the case of a chromium-free coating, the amount of the coating is 10 to 500mg/m in the case of a Ti-Mo composite coating2In the case of a fluoric acid coating, the amount of fluorine deposited or the amount of total metal deposited is 3 to 100mg/m2The amount of adhesion may be adjusted within the range of (3). In addition, in the case of a phosphate coating, the amount of the phosphate coating is 5 to 500mg/m2The amount of adhesion can be adjusted.
2-2. base coat
The undercoat layer can improve not only the adhesion between the top layer disposed thereon and the metal plate but also the moisture resistance and corrosion resistance of the resulting coated metal plate. The undercoat layer is composed of a cured product of the coating composition of the present invention.
The thickness of the primer layer is preferably 1 to 10 μm. When the thickness of the primer layer is 1 μm or more, the adhesion between the metal plate and the top layer is easily improved, and sufficient moisture resistance and corrosion resistance are easily obtained. If the thickness of the primer layer is 10 μm or less, the appearance and workability of the coated metal sheet are less likely to be adversely affected. From the above viewpoint, the thickness of the undercoat layer is more preferably 2 to 7 μm.
2-3. top layer
The coated metal sheet of the present invention preferably further has one or more coating films disposed on the undercoat layer.
The top layer on the surface, i.e., the uppermost layer, of the one or more coating films may be composed of a resin composition containing a thermoplastic resin.
The kind of the thermoplastic resin can be appropriately set according to the use of the coated metal sheet. Examples of the thermoplastic resin include acrylic resins, polyesters, fluororesins, acrylic-styrene resins, silicone resins. The resin may contain only 1 kind of the above resin, or may contain 2 or more kinds.
Alternatively, the top layer may be composed of a cured product of a resin composition containing a resin having a functional group reactive with a curing agent (curable resin) and a curing agent.
Examples of the curable resin include curable polyesters such as oil-free polyester resins (hydroxyl group-containing polyester resins), curable acrylic resins such as hydroxyl group-containing acrylic resins, epoxy resins, phenol resins, urea resins, melamine resins, benzoguanamine resins, and urethane-, silicone-or epoxy-modified products of these resins.
The curing agent may be appropriately selected depending on the type of the curable resin, the baking conditions of the top layer, and the like. Examples of the curing agent such as a curable resin having a hydroxyl group include melamine compounds and isocyanate compounds, for example. As the melamine compound, the same melamine compounds as described above can be used. Examples of the isocyanate compound include aliphatic isocyanate compounds such as Hexamethylene Diisocyanate (HDI); alicyclic isocyanate compounds such as norbornene diisocyanate (NBDI), isophorone diisocyanate (IPDI), cyclohexane diisocyanate, and dicyclohexylmethane diisocyanate; aromatic isocyanate compounds such as methylene diphenyl diisocyanate (MDI), Toluene Diisocyanate (TDI), and Xylylene Diisocyanate (XDI).
These resin compositions may further contain other components such as a coloring pigment and an extender pigment within the range that achieves the effects of the present invention. As the coloring pigment and the extender pigment, the same coloring pigment and extender pigment as those which can be contained in the aforementioned undercoat layer can be used.
The thickness of the top layer also depends on the desired properties, for example preferably 2 to 40 μm. When the thickness of the top layer is 2 μm or more, desired design properties are easily obtained, and when it is 40 μm or less, the appearance and processability are not easily adversely affected. From the above viewpoint, the thickness of the top layer is more preferably 5 to 30 μm.
One or more coating films may further have other layers such as an intermediate layer.
For example, the intermediate layer may be disposed on the surface of the primer layer, that is, between the primer layer and the top layer, in order to improve the design of the coated metal sheet by a synergistic effect in appearance between the intermediate layer and the top layer.
The intermediate layer may be formed of a resin composition containing a thermoplastic resin or a cured product of a resin composition containing a curable resin and a curing agent, as described above. These resin compositions may further contain other components as required. The same components as those listed as the components of the resin compositions constituting the undercoat layer and the top layer may be used as the components contained in the intermediate layer depending on the application of the coated metal sheet.
The thickness of the intermediate layer is preferably a constant value or more from the viewpoint of easily obtaining a desired effect, and is preferably a constant value or less from the viewpoint of not affecting the appearance of the coated metal sheet. The thickness of the intermediate layer may be, for example, 5 to 30 μm, from the viewpoint of obtaining a desired effect of improving the design property.
3. Method for manufacturing coated metal plate
The coated metal sheet of the present invention can be produced by any method. Preferably, the method for producing a coated metal sheet of the present invention includes, for example, the step 1) of applying the coating composition of the present invention on a metal sheet as a coating original sheet, and then drying and curing the coating composition to form an undercoat layer, and further includes the step 2) of forming one or more coating films on the undercoat layer.
Concerning the step 1)
The coating composition of the present invention is applied to a metal plate.
The method of applying the coating composition is not particularly limited, and examples thereof include roll coating method, roll curtain coating method, flow coating method, curtain flow method and spray coating method.
Then, the coating composition applied to the surface of the metal plate is dried and baked (cured), to form an undercoat layer.
The baking temperature may be a temperature at which the resin component can be melted and/or cured, and may be, for example, 70 to 250 ℃.
Concerning the step 2)
One or more coating films are formed on the obtained primer layer. For example, a top coating composition is applied over a base coat.
In addition to the aforementioned ingredients, the top coat coating composition may also contain a solvent. The solvent is not particularly limited as long as it can dissolve the curable resin, and examples thereof include aprotic polar solvents such as N-methyl-2-pyrrolidone (NMP), N-Dimethylformamide (DMF), N-dimethylacetamide (DMAc), N-Dimethylimidazolidinone (DMI), and methyl isobutyl ketone (MIBK); ethers such as diethylene glycol dimethyl ether (DMDG) and diethylene glycol Diethyl Ether (DEDG); halogenated aliphatic hydrocarbons such as methylene chloride and carbon tetrachloride; hydrocarbons such as xylene; and alcohols.
The method of applying the top coating composition may be the same as described above.
Next, the coated top layer coating composition is dried and baked (cured) to form a top layer. The baking temperature may be a temperature at which the cured resin can be melted and/or cured, and may be, for example, 200 to 260 ℃.
[ examples ]
The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.
1. Material for coating composition
< aqueous Dispersion of nonionic Water-dispersible resin (a) >
Aqueous dispersion of resin a: an aqueous dispersion of a nonionic urethane resin, HUX-841 manufactured by ADEKA corporation (32% by mass as a solid content, urethane resin having a polyoxyethylene group as a nonionic hydrophilic group)
Aqueous dispersion of resin B: aqueous dispersion of nonionic acrylic resin DXA.4081 (acrylic resin having polyoxyethylene group as nonionic hydrophilic group, solid content 50 mass%) manufactured by NAOBIZHI CHEMICAL CORPORATION
Aqueous dispersion of resin C: an aqueous dispersion of a nonionic epoxy resin, Yukraesin NE316 (45% by mass in solid content, epoxy resin having a hydroxyl group as a nonionic hydrophilic group) manufactured by Gemura oil chemical Co., Ltd
Aqueous dispersion of resin D: an aqueous dispersion of an anionic urethane resin, SUPERFLEX 170 (33% by mass solid content, urethane resin having a carboxyl group as an anionic hydrophilic group), manufactured by first Industrial pharmaceutical Co., Ltd
< aqueous Dispersion of phosphoric acid-modified epoxy resin (b) >
60g of orthophosphoric acid and 280g of propylene glycol monomethyl ether were charged, 850g of bisphenol A type epoxy resin (JeR 1055, molecular weight 1600, epoxy equivalent: 800 to 900g/eq, manufactured by Mitsubishi chemical corporation) was slowly added, and the mixture was reacted at 80 ℃ for 2 hours. After the reaction was completed, 120g of triethylamine and 1950g of water were added to the reaction solution to obtain an aqueous dispersion of a phosphoric acid-modified epoxy resin (average particle size: 0.11 μm) having a solid content of 28 mass%.
< Melamine Compound (c) >
Hexamethoxymethyl melamine (CYMEL 303, Mitsui Cytec Co., Ltd.)
< silane coupling agent (d) >
Glycidoxypropylmethyldiethoxysilane (KBM-403, product of shin-Etsu Silicone Co., Ltd.)
< Metal ion-exchanged silica >
Mg-exchanged silica: sylomask 52M (average particle diameter 2.7 μ M, metal ion exchange amount 6 mass%)
Ca-exchanged silica: sylomask 52 (average particle diameter 2.7 μm, metal ion exchange amount 6 mass%)
Sr-exchanged silica: prepared according to manufacturing example 1. The amount of metal ion exchange was set to 6 mass%.
Production example 1
To 10000 parts by mass of a strontium chloride aqueous solution having a concentration of 5% by mass, 10 parts by mass of silica (SYLYSIA 710, manufactured by Fuji Silysia Chemical corporation) was added. After stirring and mixing for 5 hours, the mixture was filtered, and the solid content was taken out, washed with water thoroughly and dried to obtain strontium ion-exchanged silica.
Mn-exchanged silica: prepared according to manufacturing example 2.
Production example 2
Manganese ion-exchanged silica was obtained in the same manner as in production example 1, except that strontium chloride was changed to manganese chloride. The amount of metal ion exchange was 6% by mass.
Li-exchanged silica: prepared according to manufacturing example 3.
(production example 3)
Lithium ion-exchanged silica was obtained in the same manner as in production example 1, except that strontium chloride was changed to lithium hydroxide. The amount of metal ion exchange was 6% by mass.
Al-exchanged silica: prepared according to manufacturing example 4.
Production example 4
An aluminum ion-exchanged silica was obtained in the same manner as in production example 1, except that strontium chloride was changed to aluminum chloride. The amount of metal ion exchange was 6% by mass.
< Un-exchanged silica >
Silica (no ion exchange): SYLYSIA710 (average particle size 2.7 μm) manufactured by Fuji Silysia Chemical Co., Ltd
2. Coating composition
< coating compositions 1 to 39>
A coating composition was obtained by mixing an aqueous dispersion of a nonionic water-dispersible resin (a), an aqueous dispersion of a phosphoric acid-modified epoxy resin (b), a melamine compound (c), a silane coupling agent (d), and metal ion-exchanged silica or non-exchanged silica so as to have a solid content composition shown in table 1 or table 2.
The compositions of the coating compositions 1 to 24 are shown in table 1; the compositions of the coating compositions 25 to 39 are shown in Table 2.
Figure BDA0003263611500000171
Figure BDA0003263611500000181
3. Production and evaluation of coated Metal sheet
< production of coated Metal plates 1 to 39>
(1) Preparation of Metal sheet (coated original plate)
A cold-rolled steel sheet having a thickness of 0.5mm was prepared. The steel sheet was introduced into a plating bath of 55 mass% Al-45 mass% Zn alloy, and plating layers of 55 mass% Al-45 mass% Zn alloy were formed on both surfaces of the cold-rolled steel sheet. Next, the obtained steel sheet was cooled from the molten state to 130 ℃ at a rate of 25 ℃/sec, and then cooled to room temperature (25 ℃) by water cooling (water quenching), to obtain a plated steel sheet. The plating adhesion amount on one surface of the obtained plated steel sheet was 80g/m2。
The surface of the resulting plated steel sheet was coated with a chromium-free chemical conversion treatment solution by a bar coater and then driedDrying to form a chemical conversion coating. As the chromium-free chemical conversion treatment liquid, fluorotitanic acid (H) was used2TiF6): 0.1mol/L and fluorozirconic acid (H)2ZrF6): 0.1mol/L of the mixed solution. The amount of the chemical conversion coating was 3.5mg/m in terms of the total metal elements of Ti and Zr2。
(2) Formation of the primer layer
The coating compositions shown in Table 1 or Table 2 were applied to the obtained chemical conversion coating film by a bar coater, and then baked under conditions of a maximum plate temperature of 150 ℃ and a drying time of 30 seconds to form a primer layer having a thickness of 5 μm.
(3) Formation of the Top layer
(preparation of Top-coating composition)
To a polyester clear coat (NippeSeupercoat 250HQ manufactured by Nippon Paint Industrial Coatings, oil-free curable polyester resin, coating material containing a melamine curing agent), 5 parts by mass of a phthalocyanine blue pigment (Chromofine4927, manufactured by Daiday Kogyo Co., Ltd.) and 3 parts by mass of titanium oxide (TIPAQUE WHITE, R-930, manufactured by Shikyo Co., Ltd.) were added and mixed with respect to 100 parts by mass of the solid content of the resin, and the mixture was uniformly dispersed to obtain a top coat composition.
Next, the top coating composition prepared above was applied to the obtained base coat layer by a bar coater, and then, the resultant was baked under conditions of a maximum plate temperature of 220 ℃ and a drying time of 40 seconds to form a top layer having a film thickness of 15 μm, thereby obtaining a coated metal plate.
(4) Evaluation of
The storage stability of the coating composition used for producing the coated metal sheet was evaluated by the following method.
(storage stability)
The ford cup viscosity (seconds) of the obtained coating composition was measured immediately after the preparation and after the storage at 40 ℃ for 30 days in an atmosphere of 30% Rh. The measurements were carried out at 20 ℃ in accordance with ASTM D1200, ISO2431, using a No.4 Ford cup. Then, the storage stability was evaluated based on the following criteria.
Very good: the rise of viscosity is less than 5 seconds
O: the increase in viscosity was 5 seconds or more and 30 seconds or less
And (delta): the increase of viscosity is more than 30 seconds
X: coating gelation
The top layer of the resulting coated metal sheet was evaluated for adhesion, moisture resistance, and corrosion resistance by the following methods.
(Adhesivity)
On the surface of the top layer of the coated metal plate, 100 squares of cuts were formed by cutting lines at intervals of 1 mm. The tape was attached to the formed cut portion, and the tape was peeled off, and then the peel area of the cut portion was obtained. Then, the adhesion of the interface between the metal plate and the undercoat layer was evaluated according to the following criteria.
Very good: 0% of peeled area (No peeling)
O: a peeling area of more than 0% and 10% or less
And (delta): a peeling area of more than 10% and 20% or less
X: the stripping area is more than 20 percent
If the value is not less than Δ, the result is judged to be good.
(moisture resistance)
The coated metal plate was exposed to a humid environment (50 ℃, 95% Rh) for 1000 hours. Then, the area ratio of the occurrence of swelling at the flat portion of the top layer was measured. Then, the moisture resistance was evaluated according to the following criteria.
Very good: expansion incidence 0% (no expansion)
Good: the expansion incidence rate is more than 0 percent and less than 5 percent
And (delta): the expansion incidence rate is more than 5 percent and less than 20 percent
X: the expansion incidence rate is more than 20 percent
If the value is not less than Δ, the result is judged to be good.
(Corrosion resistance)
The coated metal sheet was subjected to 120 cycles of 1 cycle of spraying 5% brine for 1 hour, drying for 4 hours (60 ℃, 30% Rh), and wetting for 3 hours (50 ℃, 95% Rh) so as to reach the plating layer of the plated steel sheet with a knife to form X-shaped cross-cut scratches. Then, the maximum expansion width of the cross-hatched portion after the test was measured. The maximum expansion width indicates the maximum width of the depth of invasion of expansion from the cross-hatched portion. Then, the corrosion resistance was evaluated according to the following criteria.
Very good: maximum expansion amplitude of 2mm or less
O: the maximum expansion amplitude is more than 2mm and less than 4mm
And (delta): the maximum expansion amplitude is more than 4mm and less than 5mm
X: maximum expansion amplitude exceeding 5mm
If the value is not less than Δ, the result is judged to be good.
The evaluation results of the coating compositions 1 to 24 and the coated metal sheets 1 to 24 are shown in Table 3, and the evaluation results of the coating compositions 25 to 39 and the coated metal sheets 25 to 39 are shown in Table 4.
[ Table 3]
Figure BDA0003263611500000211
Figure BDA0003263611500000221
[ Table 4]
Figure BDA0003263611500000222
As shown in tables 3 and 4, it is understood that the coating compositions 1 to 27 all have good storage stability, and the obtained coated metal sheets 1 to 27 have good moisture resistance.
In particular, it is found that by setting the content of the 2-valent metal ion-exchanged silica (e) to 7.5 to 50 parts by mass relative to 100 parts by mass of the total of the components (a), (b) and (c), both the storage stability and the moisture resistance can be more enhanced (comparison of the coated metal plates 11 to 15, 18, 25 and 26).
Further, it is found that, among the 2-valent metal ion-exchanged silica (e), particularly, Mg-exchanged silica, even if the content thereof is large, the coating composition containing the Mg-exchanged silica can maintain good storage stability (comparison of the coating compositions 18 to 21).
On the other hand, it is found that the coated metal plates 30, 33 and 38 having an excessive amount of the components (b), (c) and (d) have good moisture resistance, but the storage stability of the coating composition is low.
It is also found that the coating compositions 29, 31, 32 and 37 having too small amounts of the components (b), (c) and (d) all have good storage stability, but the coated metal sheets have low moisture resistance. Further, it is found that the coating compositions 34 to 36 containing no metal ion-exchanged silica having a valence of 2 as the component (e) or using metal ion-exchanged silica other than the component (e) are excellent in storage stability, but the coated metal sheet has low moisture resistance.
Further, it is found that if the component (a) is an anionic water-dispersible resin, the storage stability is lowered (comparison between the coating compositions 18 and 39). This is considered to be because the anionic water-dispersible resin (a) reacts with eluted metal ions.
The present application claims priority based on japanese patent application No. 2019-060717, filed on 27/3/2019. The contents described in the specification and drawings of this application are all incorporated in the specification of this application.
Industrial applicability
The present invention can provide a coating composition and a coated metal sheet which have good storage stability and can suppress the swelling of a coating film under high-temperature and high-humidity conditions.

Claims (7)

1. A coating composition characterized in that,
comprising a nonionic water-dispersible resin (a), a phosphoric acid-modified epoxy resin (b), a melamine compound (c), a silane coupling agent (d), silica particles (e) ion-exchanged with a metal having a valence of 2, and water,
the content of the nonionic water-dispersible resin (a) is 60 to 94.5 parts by mass, the content of the phosphoric acid-modified epoxy resin (b) is 5 to 39.5 parts by mass, the content of the melamine compound (c) is 0.5 to 10 parts by mass, and the content of the silane coupling agent (d) is 0.3 to 5 parts by mass, based on 100 parts by mass of the total of the nonionic water-dispersible resin (a), the phosphoric acid-modified epoxy resin (b), and the melamine compound (c).
2. The coating composition of claim 1,
the content of the 2-valent metal ion-exchanged silica particles (e) is 7.5 to 55 parts by mass per 100 parts by mass of the total of the nonionic water-dispersible resin (a), the phosphoric acid-modified epoxy resin (b), and the melamine compound (c).
3. The coating composition of claim 1 or 2,
the silica particles (e) exchanged with a metal ion having a valence of 2 are magnesium-exchanged silica.
4. The coating composition according to any one of claims 1 to 3,
the nonionic water-dispersible resin (a) is a nonionic urethane resin.
5. A coated metal sheet, characterized in that,
comprising a metal plate and an undercoat layer disposed on the metal plate,
the primer layer is composed of a cured product of the coating composition according to any one of claims 1 to 4.
6. The coated metal sheet according to claim 5,
the metal plate is a plated steel plate.
7. The coated metal sheet according to claim 5 or 6,
and at least one coating film disposed on the primer layer.
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