AU2022291046A1

AU2022291046A1 - Aqueous coating composition, coating film, and method for producing coating film

Info

Publication number: AU2022291046A1
Application number: AU2022291046A
Authority: AU
Inventors: Kensaku AZECHI; Mitsutaka NAMBO; Kenichi SHIMAMURA
Original assignee: Nippon Paint Ind Coatings Co Ltd; Nippon Paint Industrial Coatings Co Ltd
Current assignee: Nippon Paint Industrial Coatings Co Ltd
Priority date: 2021-06-10
Filing date: 2022-04-22
Publication date: 2023-10-26
Also published as: TW202302673A; JP2022189126A; KR20240018566A; WO2022259774A1; CN117440996A; JP7101294B1

Abstract

The present invention addresses the problem of providing an aqueous coating composition which, although of a one-pack type, has excellent storage stability and which can form coating films satisfactory in terms of processability including bendability and of crack resistance and scratch resistance during processing. This aqueous coating composition comprises a film-forming resin (A), a crosslinking agent (B), a sulfonic acid compound (C), and an amine compound (D), wherein the film-forming resin (A) includes an acrylic resin (A1), the film-forming resin (A) has a hydroxyl value of 5-35 mgKOH/g, the crosslinking agent (B) includes a fully alkylated melamine resin (B1), and the degree of neutralization of the acid groups of the sulfonic acid compound (C) with the amine compound (D) is 100-1,300% by mole.

Description

DESCRIPTION TITLE OF INVENTION: AQUEOUS COATING COMPOSITION, COATING FILM, AND METHOD FOR PRODUCING COATING FILM TECHNICAL FIELD

[0001]

The present disclosure relates to an aqueous coating composition, a coating

film, and a method for producing a coating film.

BACKGROUND ART

[0002]

Coated steel sheets which are obtained by applying coating to metal substrates

such as a cold-rolled steel sheet and a plated steel sheet and then subjected to forming

processing are also referred to as precoated steel sheets (hereinafter, also referred to as

"PCM"), and are used for such applications as construction members such as a shutter,

a ceiling, a door, a roof, or siding; exterior materials of electrical equipment such as

outdoor units of air conditioners; and interior materials. The precoated steel sheet is

usually manufactured by applying a coating composition to a surface of the metal

substrate and performing heating (baking) at 200 to 270°C for 30 to 60 seconds, for

example, to form a coating film, and the precoated steel sheet is then subjected to

molding processing. For this reason, the coating film of the precoated steel sheet is

required to have processability as much as cracking or peeling does not occur during

processing, and hardness as much as scratches or depressions do not occur.

[0003]

Coating compositions comprise a one-pack type coating composition in which

a main agent comprising a coating film-forming resin and a curing agent comprising a crosslinking agent coexist in the same system, and a two-pack type coating composition whose main agent and curing agent are separately stored and mixed at the time of use.

Among these, the two-pack type coating composition is superior in storage stability to

the one-pack type coating composition as the main agent and the curing agent of the

two-pack type coating composition are not mixed until immediately before use.

However, a two-pack type coating composition sometimes has a problem in

handleability or coating workability, for example, it is required to mix a main agent and

a curing agent at prescribed proportions and stir them to render them uniform at the time

of use or the time for which the two-pack type coating composition can be used is

limited. Therefore, a one-pack type coating composition is demanded.

[0004]

In recent years, the awareness of environmental load reduction has increased,

and replacement with environmentally friendly products has been required. In the

field of coating materials as well, it is required, for example, to reduce the amount of

use of a volatile organic compound (VOC), and such a requirement can be satisfied by

using an aqueous coating composition. That is, in the market, the need for a one-pack

type aqueous coating composition has been significantly increased.

[0005]

Various one-pack type aqueous coating compositions have been proposed, and

for example, in an aqueous coating composition comprising an acrylic copolymer

containing a hydroxy group and a carboxyl group, an aqueous amino resin, an amine

compound, and a hydrophilic organic solvent, it has been proposed to neutralize

carboxyl groups contained in the acrylic copolymer containing a hydroxy group and a

carboxyl group with the amine compound (Patent Literature 1). Besides, in a

water-soluble acrylic coating composition comprising a copolymer composed of a hydroxy group-containing (meth)acrylic acid ester, a carboxyl group-containing vinyl monomer, a long-chain alkyl group-containing (meth)acrylic acid ester and a vinyl monomer, a water-soluble amino resin and an aqueous medium, it has been proposed to neutralize carboxyl groups of an acrylic copolymer containing a hydroxy group and a carboxyl group using an amine compound (Patent Literature 2). Furthermore, in an aqueous coating composition for metal covering comprising an acrylic resin containing a hydroxy group and a carboxyl group and having a glass transition point in the range of

-10°C to 80°C, an acrylic resin containing a hydroxy group and a carboxyl group and

having a glass transition point in the range of -50 to 20°C, an aqueous amino resin, a

basic compound, and an aqueous medium, it has been proposed to neutralize carboxyl

groups of the acrylic resin containing a hydroxy group and a carboxyl group with the

basic compound (Patent Literature 3). In addition, Patent Literature 4 proposes an

aqueous coating composition comprising an aqueous resin, a melamine resin, and a

phosphate catalyst as a weak acid catalyst, and proposes neutralizing an aqueous resin

using a basic compound (Patent Literature 4).

CITATIONS LIST PATENT LITERATURES

[0006]

Patent Literature 1: JP-A-2001-323207

Patent Literature 2: JP-A-2001-240624

Patent Literature 3: JP-A-2000-017225

Patent Literature 4: JP-A-2015-174958

SUMMARY OF INVENTION TECHNICAL PROBLEMS

[0007]

However, with coating films formed of the coating compositions described in

Patent Literature 1 to 4, the processability (adhesion and crack resistance) and scratch

resistance of precoated steel sheets obtained are not sufficiently satisfactory.

[0008]

Furthermore, since in a one-pack type coating composition, a main agent and a

curing agent coexist in the same system, this type of coating composition has a trade-off

relationship as follows: the storage stability of the coating composition decreases when

the reactivity of the main agent and the curing agent is improved for the purpose of

improving the coating film properties, whereas the coating film properties deteriorate

when the reactivity is reduced for the purpose of improving the storage stability of the

coating composition. Therefore, it has been very difficult to achieve both storage

stability and coating film properties with a one-pack type coating composition.

[0009]

The present inventors have conducted intensive studies in order to solve such

problems, and have found that high storage stability can be achieved even in a one-pack

type composition by using a fully-alkylated melamine resin as a crosslinking agent and

also using a sulfonic acid compound and an amine compound such that a specific

neutralization ratio is achieved, and further, good coating film properties (in particular,

processability (adhesion and crack resistance) and scratch resistance) can be exhibited

even when coating is performed under high temperature and short time conditions

peculiar to a precoated steel sheet, and have accomplished the aqueous coating

composition and the method for producing a coating film according to the present

disclosure.

[0010]

A challenge of the present disclosure is to provide an aqueous coating

composition which is superior in storage stability even in a one-pack type and can form

a coating film having good processability such as bending and good crack resistance

and good scratch resistance during processing.

SOLUTIONS TO PROBLEMS

[0011]

The present disclosure provides the following aspects.

[1]

An aqueous coating composition comprising a coating film-forming resin (A),

a crosslinking agent (B), a sulfonic acid compound (C), and an amine compound (D),

wherein the coating film-forming resin (A) comprises an acrylic resin (Al),

the coating film-forming resin (A) has a hydroxyl value of 5 mg KOH/g or

more and 35 mg KOH/g or less,

the crosslinking agent (B) comprises a fully-alkylated melamine resin (B1), and

a molar neutralization ratio of an acid group of the sulfonic acid compound (C)

by the amine compound (D) is 100% or more and 1,300% or less.

[2] The aqueous coating composition according to [1], wherein the coating

film-forming resin (A) has a weight average molecular weight of 100,000 or more.

[3] The aqueous coating composition according to [1] or [2], wherein at a

temperature of 23°C, a shear viscosity measured at a shear rate of 0.01 s-1 is 30,000

mPa-s or less, a shear viscosity measured at a shear rate of 10 s-1 is 800 mPa-s or less,

and a shear viscosity measured at a shear rate of 1,000 s-' is 150 mPa-s or more.

[4] The aqueous coating composition according to any one of [1] to [3], further

comprising an organic solvent (El).

[5] The aqueous coating composition according to any one of [1] to [4], which

is for coil coating.

[6] A method for producing a coating film, comprising:

a step of applying the aqueous coating composition according to any one of [1]

to [5] to an article to be coated to form an applied film; and

a step of drying and/or curing the applied film under the condition that the

maximum ultimate temperature is 180°C or higher and the drying and/or curing time is

120 seconds or less to form a coating film.

ADVANTAGEOUS EFFECTS OF INVENTION

[0012]

By the present disclosure, there is provided an aqueous coating composition

which is superior in storage stability even in a one-pack type and can form a coating

film having good processability such as bending and good crack resistance and good

scratch resistance during processing.

DESCRIPTION OF EMBODIMENTS

[0013]

The aqueous coating composition of the present disclosure comprises a coating

film-forming resin (A), a crosslinking agent (B), a sulfonic acid compound (C), and an

amine compound (D).

[0014]

The coating film-forming resin (A) comprises an acrylic resin (Al). The

acrylic resin (A1) represents a polymer having a unit derived from a monomer having a

(meth)acryloyl group, and can be prepared by polymerizing a monomer mixture containing a monomer having an ethylenically unsaturated bond. In the present description, (meth)acrylic acid represents acrylic acid or methacrylic acid.

[0015]

Examples of the monomer having an ethylenically unsaturated bond comprise

unsaturated carboxylic acids such as (meth)acrylic acid, crotonic acid, isocrotonic acid,

2-propenoic acid, ethacrylic acid, propylacrylic acid, and isopropylacrylic acid;

unsaturated polycarboxylic acids (including anhydrides thereof) such as maleic acid,

fumaric acid, and itaconic acid; monoalkyl esters of unsaturated polycarboxylic acids

such as ethyl maleate, butyl maleate, ethyl fumarate, butyl fumarate, ethyl itaconate, and

butyl itaconate; alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl

(meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate,

t-butyl (meth)acrylate, n-pentyl (meth)acrylate, neopentyl (meth)acrylate, isopentyl

(meth)acrylate, sec-pentyl (meth)acrylate, 3-pentyl (meth)acrylate, hexyl (meth)acrylate,

heptyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl

(meth)acrylate, decyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate,

and stearyl (meth)acrylate; (meth)acrylate esters having an alicyclic hydrocarbon group

such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate,

tricyclodecyl (meth)acrylate, and adamantyl (meth)acrylate; hydroxyalkyl

(meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate,

and 4-hydroxybutyl (meth)acrylate; (meth)acrylate esters having a hydroxy group such

as lactone adducts thereof (the lactone comprises s-caprolactone, etc.); monomers

having an organosilyl group such as y-(meth)acryloxypropyltrimethoxysilane,

y-(meth)acryloxypropylmethyldimethoxysilane, y-(meth)acryloxypropyltriethoxysilane,

y-(meth)acryloxypropylmethyldiethoxysilane, vinyltrimethoxysilane,

vinylmethyldimethoxysilane, vinyltriethoxysilane, and vinylmethylditoxysilane; monomers having a sulfonic acid group such as a-vinylbenzenesulfonic acid, p-(meth)acrylamidopropanesulfonic acid, and t-butyl(meth)acrylamidosulfonic acid; monomers having a phosphoric acid group such as phosphate monoesters of the above-mentioned (meth)acrylate esters having a hydroxy group; (meth)acrylamide monomers such as (meth)acrylamide, N-methylol(meth)acrylamide, methoxybutyl(meth)acrylamide, and diacetone (meth)acrylamide; (meth)acrylamide monomers having an amino group such as aminoethyl(meth)acrylamide, dimethylaminoethyl(meth)acrylamide, and methylaminopropyl (meth)acrylamide;

(meth)acrylate esters having an epoxy group (oxiranyl group) such as glycidyl

(meth)acrylate; (meth)acrylonitrile monomers such as (meth)acrylonitrile and

c-chloro(meth)acrylonitrile; vinyl carboxylates such as vinyl acetate and vinyl

propionate; styrene-based monomers such as styrene, a-methylstyrene, C-methylstyrene

dimer, vinyltoluene, and divinylbenzene; carbonyl group monomer; and crosslinkable

monomers such as polyfunctional vinyl monomers other than those recited above.

As to the monomer having an ethylenically unsaturated bond described above,

only one monomer may be used, or two or more of themr may be used in combination.

[0016]

The acrylic resin (Al) has a hydroxy group. Due to the hydroxy group in the

acrylic resin (Al), a crosslinking reaction occurs between the hydroxy group and a

reactive group of the crosslinking agent, to cure a coating film. In order for the acrylic

resin (Al) to have a hydroxy group, it is beneficial to use a (meth)acrylate ester having

a hydroxy group as the monomer having an ethylenically unsaturated bond when

forming a polymer.

[0017]

The hydroxyl value of the acrylic resin (Al) having a hydroxy group is

preferably 5 mg KOH/g or more, more preferably 7 mg KOH/g or more, and still more

preferably 10 mg KOH/g or more, and preferably 50 mg KOH/g or less, more

preferably 35 mg KOH/g or less, still more preferably 30 mg KOH/g or less, further

preferably 25 mg KOH/g or less. Within the above range, there is an advantage that a

coating film having good processability (adhesion and crack resistance) can be obtained.

[0018]

In the (meth)acrylate ester having a hydroxy group, the number of the carbon

atoms in the group bonded to the (meth)acryloyl group is preferably 1 to 3, and more

preferably 2. Containing a (meth)acrylate ester which has a hydroxy group and in

which the group bonded to the (meth)acryloyl group has 1 to 3 carbon atoms offers an

advantage that a coating film superior in scratch resistance can be obtained. The

content of the (meth)acrylate ester having a hydroxy group in which the group bonded

to the (meth)acryloyl group has 1 to 3 carbon atoms in all the (meth)acrylate ester

having a hydroxy group is preferably 70% by mass or more, more preferably 80% by

mass or more, and the upper limit is 100% by mass.

[0019]

The weight average molecular weight of the acrylic resin (Al) is, for example,

,000 or more, preferably 100,000 or more, and more preferably 150,000 or more, and

is, for example, 10,000,000 or less, and preferably 2,000,000 or less. The larger the

weight average molecular weight of the acrylic resin (Al) is, the better the scratch

resistance is, and there is an advantage that a coating film superior in processability can

be obtained.

[0020]

In the present description, the weight average molecular weight is a

polystyrene-equivalent value determined by gel permeation chromatography (GPC).

[0021]

The acrylic resin (Al) preferably has an acid group. When the acrylic resin

(A1) has an acid group, dispersibility in an aqueous medium (E) described later can be

imparted.

In order for the acrylic resin (A1) to have an acid group, it is beneficial to

merely use, as the monomer having an ethylenically unsaturated bond when forming a

polymer, a monomer having an acid group such as an unsaturated monocarboxylic acid,

an unsaturated polycarboxylic acid, a monoalkyl ester of an unsaturated polycarboxylic

acid, a monomer having a sulfonic acid group, or a monomer having a phosphoric acid

group.

[0022]

As the monomer having an acid group, an unsaturated monocarboxylic acid, an

unsaturated polycarboxylic acid, and a monoalkyl ester of an unsaturated

polycarboxylic acid are preferable, an unsaturated monocarboxylic acid and an

unsaturated polycarboxylic acid are more preferable, an unsaturated monocarboxylic

acid is still more preferable, and (meth)acrylic acid is particularly preferable.

[0023]

The acid value of the acrylic resin (Al) is preferably 5 mg KOH/g or more, and

is preferably 50 mg KOH/g or less, and more preferably 30 mg KOH/g or less. Within

the above range, there is an advantage that the acrylic resin (Al) can be stably dispersed

in the aqueous medium (E).

[0024]

In the present description, the acid value and the hydroxyl value of the acrylic

resin (A1) represent a solid acid value and a solid hydroxyl value, respectively, and can

be measured in accordance with JIS K 0070: 1999.

[0025]

The glass transition temperature (Tg) of the acrylic resin (Al) is preferably

-70°C or higher, more preferably 0°C or higher, still more preferably 10°C or higher,

and further preferably 15°C or higher, and is preferably 95°C or lower, more preferably

°C or lower, still more preferably 85°C or lower, and further preferably 80°C or lower.

Within the above range, there is an advantage that a coating film superior in coating

film processability and scratch resistance can be obtained.

[0026]

The glass transition temperature can be calculated as the reciprocal of the sum

of respective quotients obtained by dividing the mass fraction of each monomer

constituting the acrylic resin (Al) by the Tg (K: Kelvin) value of the homopolymer

derived from each monomer.

More specifically, in the present description, the glass transition temperature

(Tg) can be calculated using the Fox equation (T. G. Fox; Bull. Am. Phys. Soc., 1 (3),

123 (1956)).

For example, when the resin is a polymer of a plurality of monomers

(monomer A, monomer B, ... monomer N), a Tg represented by the following general

formula is defined as Tg of the resin,

1/Tg = wa/Tga + wb/Tgb+... + wn/Tgn

where:

Tga: glass transition temperature (K) of homopolymer of monomer A, wa:

mass fraction of monomer A,

Tgb: glass transition temperature (K) of homopolymer of monomer B, wb:

mass fraction of monomer B,

Tgn: glass transition temperature (K) of homopolymer of monomer N, wn:

mass fraction of monomer N, and

wa + wb + wn = 1.

[0027]

Among the monomers forming the acrylic resin (Al), the monomer having an

ethylenically unsaturated bond preferably contains an alkyl (meth)acrylate, and more

preferably contains an alkyl (meth)acrylate having an alkyl group having 1 to 6, more

preferably 1 to 4 carbon atoms. Use of a monomer within the above range offers an

advantage that a resulting coating film is superior in scratch resistance. The content of

the alkyl (meth)acrylate having an alkyl group having 1 to 6 carbon atoms is preferably

% by mass or more, more preferably 30% by mass or more, and still more preferably

% by mass or more, and preferably 95% by mass or less, more preferably 85% by

mass or less, and still more preferably 80% by mass or less in all the alkyl

(meth)acrylate.

[0028]

From the viewpoint of weather resistance, the content of the styrene-based

monomer in all the monomers contained in the acrylic resin (A1) is preferably 10% by

mass or less, more preferably 5% by mass or less, and still more preferably 3% by mass

or less, and the lower limit is 0% by mass.

[0029]

When the acrylic resin (Al) has an acid group, the aqueous coating

composition may contain a basic compound. When the aqueous coating composition

contains a basic compound, a part or all of the acid groups are neutralized, and dispersibility in water can be favorably imparted to the acrylic resin. As the basic compound, for example, ammonia, an amine compound, or an alkali metal can be used.

In addition, a part of the amine compound (D) described later may be used as the basic

compound.

In addition, dispersibility in water may be imparted to the acrylic resin using a

publicly-known anionic and/or nonionic surfactant.

[0030]

The content of the acrylic resin (Al) in the coating film-forming resin (A) is

preferably 5% by mass or more, more preferably 10% by mass or more, and still more

preferably 15% by mass or more, and the upper limit is 100% by mass.

[0031]

The acrylic resin (Al) is preferably an aqueous resin, and may be a

water-soluble resin that can be dissolved in the aqueous medium (E) or may be a

water-dispersible resin that can be dispersed in the aqueous medium (E) such as a

colloidal dispersion type or an emulsion type (emulsion polymerization type, forced

emulsification type). The acrylic resin (A1) is preferably a water-dispersible resin,

more preferably an emulsion type water-dispersible resin, and particularly preferably an

emulsion type water-dispersible resin obtained through emulsion polymerization.

When the acrylic resin (Al).has an acid group and/or a hydroxy group and/or coexists

with an emulsifier, an aqueous resin can be obtained.

[0032]

When the acrylic resin (Al) is an emulsion type water-dispersible resin, the

average particle size of the emulsion particles is preferably 500 nm or less, more

preferably 300 nm or less, and still more preferably 200 nm or less, and may be, for

example, 10nmormore,30nm ormore,or50nmormore. Within the above range, there is an advantage that the emulsion particles and the coating composition containing the emulsion particles have good storage stability. The average particle size as referred to herein is an average particle size determined by a dynamic light scattering method, and specifically, it can be measured using an electrophoretic light scattering photometer

ELSZ Series (manufactured by Otsuka Electronics Co., Ltd.) or the like.

[0033]

The minimum filming temperature (MFT) of the acrylic resin (A1) is

preferably 50°C or higher, more preferably 60°C or higher, and still more preferably

°C or higher, and may be, for example, 200°C or lower, 150°C or lower, or 120°C or

lower. Within the above range, there is an advantage that scratch resistance of a

resulting coating film is improved and blocking between coating films is inhibited. In

the present description, the minimum filming temperature means the minimum

temperature at which a uniform film without cracks is formed when the emulsion type

water-dispersible resin is dried, and can be measured in accordance with JIS K 6828-2:

2003.

[0034]

When the acrylic resin (Al) is an emulsion type water-dispersible resin, the

emulsion may be an emulsion in which multilayer structure particles composed of a

core part and a shell part are dispersed.

[0035]

The multilayer structure particle can be prepared by, for example, the method

described in JP-A-2002-012816.

[0036]

The acrylic resin (A1) can be produced by polymerizing the monomer having

an ethylenically unsaturated bond described above, and the polymerization reaction can be carried out, for example, by heating the monomer having an ethylenically unsaturated bond with stirring in a part of or all the aqueous medium (E). The polymerization reaction is preferably an emulsion polymerization reaction. In the polymerization reaction, it is preferable to allow a polymerization initiator to coexist, and it is preferable to allow an emulsifier to coexist, as necessary. The reaction temperature is preferably, for example, 30 to 100°C, and the reaction time is preferably, for example, 1 to 10 hours.

[0037]

As the polymerization initiator, a radical polymerization initiator is preferable.

As a water-soluble free radical polymerization initiator, persulfate salts such as

potassium persulfate, sodium persulfate, and ammonium persulfate can be used. In

addition, a redox initiator containing a combination of an oxidizing agent such as

potassium persulfate, sodium persulfate, ammonium persulfate, and hydrogen peroxide

and a reducing agent such as sodium bisulfite, sodium thiosulfate, Rongalite, and

ascorbic acid can be used. These radical polymerization initiators may be dissolved in

a part or all of the aqueous medium (E) and used in the form of an aqueous solution.

[0038]

As the emulsifier, an anion or nonionic emulsifier having a hydrophobic moiety

such as a hydrocarbon group having 6 or more carbon atoms and a hydrophilic moiety

such as a carboxylate salt, a sulfonate salt or a sulfate salt partial ester in the same

molecule can be used. Examples of the anionic emulsifier comprise an alkali metal

salt or ammonium salt of a halfester of sulfuric acid with an alkylphenol or higher

alcohol; an alkali metal salt or ammonium salt of an alkyl- or allyl-sulfonate; an alkali

metal salt or ammonium salt of a halfester of sulfuric acid with a polyoxyethylene

alkylphenyl ether, polyoxyethylene alkyl ether or polyoxyethylene allyl ether; and various anionic reactive emulsifiers having an acryl-, methacryl-, propenyl-, allyl-, allyl ether-, or maleic acid-based group and an ethylenically unsaturated bond.

Examples of the nonionic emulsifier comprise polyoxyalkylene ethers such as

polyoxyethylene alkyl phenyl ether, polyoxyethylene alkyl ether, and polyoxyethylene

allyl ether; and various nonionic reactive emulsifiers having an acryl-, methacryl-,

propenyl-, allyl-, allyl ether-, or maleic acid-based group and an ethylenically

unsaturated bond.

[0039]

Moreover, in polymerization (preferably, emulsion polymerization), the

combined use of an auxiliary agent (a chain transfer agent) for molecular weight

adjustment such as mercaptan compounds and lower alcohols is preferable in many

cases from the viewpoint of promoting polymerization (preferably, emulsion

polymerization) and from the viewpoint of promoting smooth and uniform formation of

a coating film to improve the adhesion to an article to be coated, and it is appropriately

carried out according to the situation.

[0040]

When emulsion polymerization is carried out, there can be used any emulsion

polymerization method, such as a conventional single-stage continuous uniform

dropwise monomer addition method; a core-shell polymerization method that is a

multi-stage monomer feeding method; and a power feed polymerization method

wherein formulation of the monomers to be fed is continuously altered during

polymerization.

[0041]

The acrylic resin (Al) may be processed in advance into an aqueous solution or

aqueous dispersion containing the acrylic resin (Al) and a part of the aqueous medium

(E) described later, and then used in the preparation of an aqueous coating composition.

The aqueous solution or aqueous dispersion may further contain the emulsifier.

[0042]

As the acrylic resin (Al), a commercially available product may be used. A

single acrylic resin (Al) may be used, or two or more of them may be used in

combination.

[0043]

The coating film-forming resin (A) may comprise another resin (A2) in

addition to the acrylic resin (Al).

[0044]

Examples of the other resin (A2) comprise a hydroxy group-free acrylic resin, a

urethane resin, a vinyl acetate resin, a fluororesin, and a vinyl chloride resin, each of

which is preferably an aqueous resin, more preferably a water-dispersible resin, and still

more preferably an emulsion type water-dispersible resin. The other resin (A2) may be

processed in advance into an aqueous solution or aqueous dispersion containing the

resin (A2) and a part of the aqueous medium (E), and then used in the preparation of an

aqueous coating composition. The aqueous solution or aqueous dispersion may

contain an emulsifier.

[0045]

The hydroxy group-free acrylic resin represents a polymer having a unit

derived from a monomer having a (meth)acryloyl group, and can be prepared by

polymerizing a mixture of monomers having no hydroxy group among the monomers

having an ethylenically unsaturated bond.

[0046]

The weight average molecular weight of the hydroxy group-free acrylic resin is

preferably 50,000 or more, more preferably 100,000 or more, still more preferably

150,000 or more, and preferably 10,000,000 or less, more preferably 2,000,000 or less,

and still more preferably 500,000 or less. Within the above range, there is an

advantage that the processability of a resulting coating film is improved.

[0047]

The glass transition temperature of the hydroxy group-free acrylic resin is

preferably 80°C or lower, more preferably 60°C or lower, and still more preferably

0 C or lower, and is preferably 200 C or higher, more preferably 30°C or higher, and

still more preferably 40°C or higher. Within the above range, there is an advantage

that scratch resistance is improved.

[0048]

The minimum filming temperature (MFT) of the acrylic resin is preferably

°C or higher, more preferably 60 0 C or higher, and still more preferably 70°C or

higher, and may be, for example, 200°C or lower, 1500 C or lower, or 1200 C or lower.

Within the above range, there is an advantage that scratch resistance of a resulting

coating film is improved and blocking between coating films is inhibited.

[0049]

The hydroxy group-free acrylic resin preferably has an acid group. The acid

value of the hydroxy group-free acrylic resin is preferably 5 mg KOH/g or more, and is

preferably 50 mg KOH/g or less, and more preferably 30 mg KOH/g or less.

[0050]

When the hydroxy group-free acrylic resin is contained, the content thereof is

preferably 20% by mass or more, and more preferably 30% by mass or more, and is preferably 90% by mass or less, and more preferably 85% by mass or less in the total of the acrylic resin (Al) and the hydroxy group-free acrylic resin.

[0051]

The hydroxyl value of the coating film-forming resin (A) is 5 mg KOH/g or

more, preferably 7 mg KOH/g or more, and more preferably 10 mg KOH/g or more,

and is 35 mg KOH/g or less, preferably 30 mg KOH/g or less, and more preferably 25

mg KOH/g or less. Within the above range, there is an advantage that a coating film

having good processability and scratch resistance can be obtained.

[0052]

The acid value of the coating film-forming resin (A) is preferably 5 mg KOH/g

or more, and is preferably 50 mg KOH/g or less, and more preferably 30 mg KOH/g or

less. Within the above range, there is an advantage that the coating film-forming resin

(A) can be stably dispersed in the aqueous medium (E).

[0053]

The weight average molecular weight of the coating film-forming resin (A) is,

for example, 50,000 or more, preferably 100,000 or more, and more preferably 150,000

or more, and is, for example, 10,000,000 or less, and preferably 2,000,000 or less.

Within the above range, there is an advantage that a coating film having good

processability can be obtained.

[0054]

The glass transition temperature (Tg) of the coating film-forming resin (A) is

preferably -70°C or higher, more preferably 20°C or higher, still more preferably 25°C

or higher, and further preferably 30°C or higher and is preferably 95°C or lower, more

preferably 70°C or lower, still more preferably 60°C or lower, and further preferably

°C or lower. Within the above range, there is an advantage that a coating film

superior in coating film processability and scratch resistance can be obtained.

[0055]

As the coating film-forming resin (A), one resin may be used, or two or more

resins may be used in combination. When two or more resins as the coating

film-forming resin (A) are contained, each parameter of the coating film-forming resin

(A), except for the glass transition temperature, may be calculated as a weighted

average value on the basis of the parameter and the content of each resin. The glass

transition temperature may be calculated as the reciprocal of the sum of values obtained

by dividing the mass-based content of each coating film-forming resin by the glass

transition temperature (K: Kelvin value).

[0056]

The content of the coating film-forming resin (A) is preferably 50 parts by

mass or more, more preferably 70 parts by mass or more, and still more preferably 80

parts by mass or more, and is preferably 100 parts by mass or less, more preferably 95

parts by mass or less, and still more preferably 90 parts by mass or less based on 100

parts by mass of the solid of the aqueous coating composition. In the present

description, the content of the coating film-forming resin (A) represents the content of

only the solid.

[0057]

In the present description, the solid of the aqueous coating composition

represents a portion obtained by excluding the aqueous medium (E) from the entire

aqueous coating composition.

[0058]

The crosslinking agent (B) is a compound having, in one molecule, two or

more groups capable of reacting with a hydroxy group contained in the coating

film-forming resin (A), and can form a coating film through a crosslinking reaction with

the coating film-forming resin (A). The crosslinking agent (B) comprises an amino

resin, and examples of the amino resin comprise a melamine resin, a urea resin, and

benzoguanamine. From the viewpoint of the storage stability of a resulting coating

composition and various physical properties (processability and scratch resistance) of a

resulting coating film, the amino resin preferably comprises a melamine resin.

[0059]

The melamine resin is a thermally curable resin synthesized from melamine

and an aldehyde, and is preferably a compound having three reactive functional groups

represented by the following formula as reactive functional groups in one molecule of

the triazine nucleus, or a polycondensate thereof,

-NX1X2

wherein X 1 and X 2 each independently represent a hydrogen atom, a methylol

group, or -CH 2-OR';

R 1 represents an alkyl group having 1 to 8 carbon atoms, preferably a linear or

branched alkyl group having 1 to 8 carbon atoms; and

when a plurality of -CH 2-OR 1 units is contained in the same molecule, a

plurality of R's may be the same or different.

[0060]

Examples of the melamine resin comprise the following four types: a

fully-alkylated containing only -N(CH2OR) 2 as reactive functional; a methylol group

type containing -N-(CH 2 OR)(CH 2 OH) as a reactive functional group; an imino group

type containing -N-(CH20R)(H) as a reactive functional group; and a methylol/imino group type containing -N-(CH 2OR')(CH2OH) and -N-(CH 2OR')(H) or containing

-N-(CH2OH)(H) as reactive functional groups. R1 is preferably an alkyl group having

1 to 4 carbon atoms, and is preferably a methyl group, a n-butyl group, or an isobutyl

group.

[0061]

In the present disclosure, among the melamine resins, it is preferable that a

fully-alkylated melamine resin (B1), which is a compound in which both X1 and X 2 are

-CH2-OR, or a polycondensate thereof is contained, and examples of such a resin

comprise a methylated melamine resin, a butylated melamine resin, and an isobutylated

melamine resin. Containing the fully-alkylated melamine resin offers an advantage

that the storage stability of a resulting coating composition is good and the reactivity

with the acrylic resin (Al) at a high temperature in the presence of a catalyst is good.

[0062]

The degree of polymerization in the fully-alkylated melamine resin (B1) is 1 or

more, preferably 1.2 or more, and more preferably 1.5 or more, and is preferably 10 or

less, more preferably 5 or less, and further preferably 3 or less.

[0063]

The number average molecular weight of the fully-alkylated melamine resin

(B1) is preferably 300 or more, and is preferably 2,000 or less, more preferably 1,300 or

less, still more preferably 1,000 or less, and particularly preferably 800 or less.

In the present description, the number average molecular weight is a

polystyrene-equivalent value determined by gel permeation chromatography (GPC).

[0064]

As the fully-alkylated melamine resin (B1), a commercially available product

can be used, and examples thereof comprise CYMEL 303, CYMEL 325, CYMEL 350,

CYMEL 370, MYCOAT 715 (all are methylated melamine resins, manufactured by

Allnex Japan Inc.), CYMEL 202, CYMEL 235, CYMEL 254, CYMEL 1123, CYMEL

1128, CYMEL 1170, MYCOAT 212 (all are methylated-butylated mixed melamine

resins, manufactured by Allnex Japan Inc.), SUMIMAL M-40S (methylated melamine

resin, manufactured by Sumitomo Chemical Co., Ltd.), AMIDIR J-820-60 and AMIDIR

L-127-60 (all are butylated melamine resins, manufactured by DIC Corporation).

These may be used singly, or two or more of them may be used in combination.

[0065]

The content of the fully-alkylated melamine resin (B1) in the crosslinking

agent (B) is preferably 80% by mass or more, more preferably 90% by mass or more,

and still more preferably 95% by mass or more, and the upper limit is 100% by mass.

[0066]

The crosslinking agent (B) may comprise another crosslinking agent (B2) in

addition to the fully-alkylated melamine resin (B1). Examples of the other

crosslinking agent (B2) comprise melamine resins other than the fully-alkylated

melamine resin (B1) and amino resins such as urea resins and benzoguanamine resins.

The amino resins have high reactivity with the coating film-forming resin (A), and a

resulting coating film has good appearance and moisture resistance.

[0067]

As the crosslinking agent (B), one crosslinking agent may be used, or two or

more crosslinking agents may be used in combination.

[0068]

The ratio of the content of the crosslinking agent (B) to the content of the

coating film-forming resin (A), (B)/(A) on mass basis, is preferably 5/95, more

preferably 10/90 or more, and is preferably 30/70 or less, and more preferably 20/80 or less. Within the above range, there is an advantage that a resulting coating film have good processability and scratch resistance.

[0069]

The sulfonic acid compound (C) can act as a catalyst that promotes the reaction

between the coating film-forming resin (A) and the crosslinking agent (B). Therefore,

there is an advantage that high reactivity can be imparted to a resulting coating

composition.

[0070]

The sulfonic acid compound (C) may be either a monosulfonic acid compound

or a polysulfonic acid compound. Examples of the sulfonic acid compound comprise

aliphatic sulfonic acids such as methanesulfonic acid; and aromatic sulfonic acids such

as paratoluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic

acid, and dinonylnaphthalenedisulfonic acid. As the sulfonic acid compound (C), only

one sulfonic acid compound may be used, or two or more sulfonic acid compounds may

be used in combination.

[0071]

The content of the sulfonic acid compound (C) is preferably 0.1 parts by mass

or more, and more preferably 0.5 parts by mass or more, and is preferably 5 parts by

mass or less, and more preferably 3 parts by mass or less based on 100 parts by mass of

the coating film-forming resin (A). When the content of the sulfonic acid compound

(C) is within the above range, a coating film having good processability (adhesion and

crack resistance) and scratch resistance in a precoated steel sheet can be formed.

[0072]

The amine compound (D) has an action of neutralizing the sulfonic acid

compound (C), and when the amine compound (D) coexists with the sulfonic acid

compound (C) such that a specific neutralization ratio is achieved, there is an advantage

that both the stability of the aqueous coating composition at the time of storage (for

example, at 15 to 50°C) and high reactivity at the time of heat drying and curing after

coating can be achieved. The amine compound (D) may exist with a part thereof

forming a salt with the sulfonic acid compound (C).

[0073]

The amine compound (D) is a compound having one or more amino groups,

and is preferably a secondary or tertiary amine compound.

[0074]

The substituent on a nitrogen atom of the amine compound is preferably a

saturated or unsaturated aliphatic hydrocarbon group, and the hydrogen atoms contained

in the saturated or unsaturated aliphatic hydrocarbon group may be each independently

replaced by -COOH, -OH, or the like, and -CH 2 - contained in the saturated or

unsaturated aliphatic hydrocarbon group may be replaced by -0-. Substituents on a

nitrogen atom of the amine compound may be bonded to each other to form a ring

containing the nitrogen atom.

[0075]

Examples of the amine compound (D) comprise secondary aliphatic amine

compounds such as diethylamine, di-n-propylamine, diisopropylamine, diisobutylamine,

di-n-butylamine, di-sec-butylamine, diamylamine, N-ethyl-1,2-dimethylpropylamine,

N-methylhexylamine, di-n-octylamine, and diallylamine; tertiary aliphatic amine

compounds such as triethylamine, tributylamine, triallylamine,

N,N-dimethylethanolamine, N-methyldiallylamine, and N,N-dimethylallylamine; secondary cyclic amine compounds such as piperidine, 2-pipecoline, 3-pipecoline,

4-pipecoline, 2,4-lupetidine, 2,6-lupetidine, 3,5-lupetidine, and 3-piperidinemethanol;

tertiary cyclic amine compounds such as N-methylpiperidine, N-methylpiperazine, and

N-methylmorpholine; and amine compounds which are aromatic compounds such as

pyridine and 4-ethylpyridine.

[0076]

The boiling point of the amine compound (D) is preferably 50°C or higher,

more preferably 70°C or higher, and still more preferably 100°C or higher, and is

preferably 250°C or lower, and more preferably 220°C or lower. Within the above

range, there is an advantage that the storage stability of the aqueous coating

composition can be further improved.

[0077]

The content of the amine compound (D) is in a range such that a neutralization

ratio of the sulfonic acid compound (C) by the amine compound (D), that is, a molar

neutralization ratio determined by the following formula is 100% or more and 1,300%

or less.

Neutralization ratio (%)= [(base value of amine compound (D) x number of

moles of amine compound (D))/(acid value of sulfonic acid compound (C) x number of

moles of sulfonic acid compound (C))] x 100

[0078]

The neutralization ratio is preferably 200% or more, and more preferably 300%

or more, and may be, for example, 1,300% or less, 1,100% or less, 1,000% or less,

900% or less, or 800% or less. Although it should not be construed as being limited to

a specific theory, it is considered that when being within the above range, the amine

compound (D) blocks the sulfonic acid group of the sulfonic acid compound (C) at the time of storage (for example, at 15 to 30C) and inhibits the catalytic action, so that the storage stability can be improved, and the block is removed at the time of heat drying/curing (for example, at 180°C or higher) after coating, so that the sulfonic acid compound (C) can exhibit a function as a catalyst.

[0079]

It is known that the fully-alkylated melamine resin (B1) has lower reactivity

than a melamine resin generally used as a crosslinking agent, such as an imino

group-type melamine resin or a methylol group-type melamine resin. However, as a

result of studies by the present inventors, it has been found that the reactivity of the

fully-alkylated melamine resin (B1) is low in the case of a low-temperature reaction (for

example, at 60 to 80°C), and the reactivity at a high temperature is high when the

fully-alkylated melamine resin (B1), the sulfonic acid compound (C), and the amine

compound (D) are used such that the above-mentioned neutralization ratios are achieved.

When the fully-alkylated melamine resin (B1), the sulfonic acid compound (D), the

amine compound (D), and the neutralization ratio are combined, an aqueous coating

composition having good storage stability and particularly suitable for coating at a high

temperature in a short time can be obtained and the crosslinking density can be

increased, and therefore, there is an advantage that a coating film having superior

coating film processability (adhesion and crack resistance) can be obtained.

[0080]

The sulfonic acid compound (C) and the amine compound (D) may be directly

used for preparing an aqueous coating composition, or may be used for preparing an

aqueous coating composition as a mixture obtained by mixing them in advance. At

this time, in the mixture, the sulfonic acid compound (C) and a part or all of the amine

compound (D) may have formed a salt (for example, a salt in which the sulfonic acid group contained in the sulfonic acid compound (C) is blocked by the amino group contained in the amine compound (D)), or a salt of the sulfonic acid compound (C) and a part or all of the amine compound (D) may be formed and then blended in the coating composition. Examples of the salt of the sulfonic acid compound (C) and a part or all of the amine compound (D) comprise aliphatic sulfonic acids such as methanesulfonic acid; and aromatic sulfonic acids such as dinonylnaphthalenedisulfonic acid and dinonylnaphthalenesulfonic acid, and amine blocks thereof. As the salt of the sulfonic acid compound (C) and a part or all of the amine compound (D), a commercially available product may also be used.

[0081]

In one embodiment, it is preferable that the content of the sulfonic acid

compound (C) is 1 part by mass or more and 5 parts by mass or less based on 100 parts

by mass of the coating film-forming resin (A) and the neutralization ratio is 100% or

more and 1,300% or less; it is more preferable that the content of the sulfonic acid

compound (C) is 0.1 parts by mass or more and 5 parts by mass or less based on 100

parts by mass of the coating film-forming resin (A) and the neutralization ratio is 200%

or more and 1,000% or less; and it is still more preferable that the content of the

sulfonic acid compound (C) is 2 parts by mass or more and 9 parts by mass or less

based on 100 parts by mass of the coating film-forming resin (A) and the neutralization

ratio is 300% or more and 900% or less. When the coating composition has the

amounts of the sulfonic acid compound (C) and the amine compound (D) and the

neutralization ratio as described above, the storage stability at a low temperature

(storage temperature, for example, 15 to 30C) is high and the reactivity at a high

temperature is further enhanced, and the processability (adhesion and crack resistance)

and scratch resistance of a resulting coating film are further improved.

[0082]

The total content of the coating film-forming resin (A), the crosslinking agent

(B), the sulfonic acid compound (C), and the amine compound (D) in the solid content

of the aqueous coating composition is, for example, preferably 50% by mass or more,

more preferably 70% by mass or more, and still more preferably 80% by mass or more,

and the upper limit is 100% by mass or less.

[0083]

The aqueous coating composition comprises an aqueous medium (E). The

aqueous medium (E) is preferably water, an organic solvent (El), or a mixture of water

and an organic solvent (El).

[0084]

The organic solvent (El) is preferably a hydrophilic organic solvent, and

examples thereof comprise an organic solvent having a solubility in water of 0.1g/100 g

H20 or more at 25°C. Examples of such an organic solvent comprise glycol-based

solvents such as ethylene glycol, propylene glycol, butanediol, pentanediol, diethylene

glycol, dipropylene glycol, and triethylene glycol; glycol ether-based solvents such as

ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol monobutyl ether,

diethylene glycol monobutyl ether acetate, triethylene glycol monoethyl ether,

propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene

glycol monopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol

monoethyl ether, and propylene glycol monomethyl ether acetate; alcohol-based

solvents such as methanol, ethanol, isopropyl alcohol, and benzyl alcohol; cyclic

ether-based solvents such as dioxane and tetrahydrofuran; alcohol ester-based solvents

such as 2,2,4-trimethylpentane-1,3-diol monoisobutyrate; ketone-based solvents such as acetone; and N-methyl-2 pyrrolidone. Using such an organic solvent offers an advantage that a resulting coating composition has good wettability with a substrate.

[0085]

In one embodiment, the boiling point of the organic solvent (El) is preferably

150°C or higher, and more preferably 180°C or higher, and is preferably 300°C or lower,

and more preferably 250°C or lower. Examples of such an organic solvent comprise

glycol-based solvents such as propylene glycol (1,2-propanediol), 1,4-butanediol,

1,5-pentanediol, diethylene glycol, and dipropylene glycol, and diethylene glycol is

particularly preferable. These may be used singly, or two or more of them may be

used.

[0086]

The solubility in water of the organic solvent (El) is preferably 0.1 g/100 g

H2 0 or more, more preferably 1 g/100 g H 2 0 or more, and still more preferably 5 g/100

gH 20ormoreat25°C. The organic solvent (El) maybe freely miscible with water.

[0087]

The content of the organic solvent (El) in the aqueous medium (E) is 3% by

mass or more, preferably 4% by mass or more, and more preferably 5% by mass or

more, and is preferably 30% by mass or less, more preferably 20% by mass or less, and

still more preferably 10% by mass or less. Within the above range, there is an

advantage that the load on the environment can be reduced and the storage stability of

the coating composition, the wettability to a substrate, and the appearance of a resulting

coating film are good.

[0088]

The content of the aqueous medium (E) is preferably 40% by mass or more,

more preferably 50% by mass or more, and still more preferably 55% by mass or more, and is preferably 90% by mass or less, more preferably 80% by mass or less, and still more preferably 85% by mass or less.

[0089]

The aqueous coating composition may comprise an organic solvent other than

the aqueous medium (E), as necessary. Examples of the organic solvent other than (E)

comprise diethylene glycol dibutyl ether and 2,2,4-trimethyl-1,3-pentanediol

monoisobutyrate (Texanol). The boiling point of the organic solvent other than (E) is

preferably 150°C or higher, and more preferably 180°C or higher, and is preferably

300°C or lower, and more preferably 250°C or lower.

[0090]

The aqueous coating composition may further comprise other additives, as

necessary. Examples of such other additives comprise extender pigments; colorants

such as coloring pigments and dyes; heat shielding pigments; luster pigment; aggregates

(resin particles, silica particles, and the like); waxes; solvents other than those described

above; ultraviolet absorbers (benzophenone-based ultraviolet absorbers, and the like);

antioxidants (phenolic, sulfide-based, and hindered amine-based antioxidants, and the

like); plasticizers; coupling agents (silane-based, titanium-based, zirconium-based

coupling agents, and the like); anti-sagging agents; viscosity modifiers; pigment

dispersing agents; pigment wetting agents; surface conditioning agents (silicone-based,

organic polymer-based, and the like); leveling agents; anti-flooding agents; suspending

agents; anti-settling agents; anti-foaming agents; surfactants; anti-freezing agents;

emulsifiers; rust inhibitors; preservatives; antifungal agents; antibacterial agents; and

stabilizers. These additives may be used singly, or two or more of them may be used

in combination.

[0091]

Examples of the viscosity modifier (F) comprise an associative viscosity

modifier utilizing a bonding force (interaction) of a hydrophilic group (moiety) or a

hydrophobic group (moiety); and a thickening-type viscosity modifier comprise

viscosity increasing type viscosity modifiers utilizing solubilizing/thickening action of a

polymer. The associative viscosity modifier comprises a hydrophilic associative

viscosity modifier in which a hydrogen bond is formed between viscosity modifiers or

with a base resin and the bonding force (interaction) is utilized, and a hydrophobic

associative viscosity modifier in which the interaction between hydrophobic groups

(moieties) in the molecule is utilized. Examples of the associative viscosity modifier

comprise an alkali-thickening-type viscosity modifier in which the

solubilizing/thickening action of a polymer by alkali is utilized.

[0092]

Examples of the hydrophilic associative viscosity modifier comprise a

polyamide type viscosity modifier. The polyamide-type viscosity modifier to be used

may be a commercially available product, and examples thereof comprise (the following

are all trade names) BYK-430, BYK-431 (manufactured by BYK-Chemie GmbH),

DISPARLON AQ-580, DISPARLON AQ-600, DISPARLON AQ-607 (manufactured by

Kusumoto Chemicals, Ltd.), THIXOL W-300 and THIXOL W-400LP (manufactured by

Kyoeisha Chemical Co., Ltd.).

[0093]

The hydrophobic associative viscosity modifier to be used may be a

commercially available product, and examples thereof comprise ADEKA NOL UH-420,

ADEKA NOL UH-462, ADEKA NOL UH-472, ADEKA NOL UH-526, UH-540,

ADEKA NOL UH-814N (manufactured by ADEKA Corporation), PRIMAL RH-1020,

PRIMAL RM-2020 (manufactured by The Dow Chemical Company),

SN-THICKENER 612, SN-THICKENER 621, and NOPALL 700N (manufactured by

San Nopco Ltd.).

[0094]

Examples of the alkali thickening-type viscosity modifier comprise viscose,

methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, sodium polyacrylate,

polyvinyl alcohol, and carboxymethyl cellulose. In addition, a commercially available

product may be used, and examples thereof comprise cellulose-based viscosity

modifiers such as TYLOSE MH and TYLOSE H (manufactured by Merck); PRIMAL

ASE-60, PRIMAL TT-615, PRIMAL RM-5 (manufactured by The Dow Chemical

Company), and Ukarpolyfove (manufactured by Union Carbide Corporation).

These may be used singly, or two or more of them may be used in combination.

[0095]

The viscosity modifier (F) is preferably an associative viscosity modifier.

Containing the associative viscosity modifier offers an advantage that coating

workability with a roll coater (roll coater coatability) is improved. Specifically, the

viscosity of the coating composition can be Newtonian at a high shear rate. In addition,

more preferably, using the hydrophobic associative viscosity modifier in combination

offers an advantage that physical properties such as water resistance of a resulting

coating film can be improved.

[0096]

The content of the viscosity modifier (F) contained in the aqueous coating

composition of the present disclosure is preferably 0.01 to 20 parts by mass, and more

preferably 0.1 to 10 parts by mass, based on 100 parts by mass of the total solid content

of the coating film-forming resin (A) and the crosslinking agent (B). When the amount of the viscosity modifier (F) is within such a range, there is an advantage that coating workability with a roll coater (roll coater coatability) and appearance and water resistance of a resulting coating film are improved.

[0097]

Examples of the extender pigment comprise calcium carbonate, barium sulfate,

clay, talc, mica, and glass fiber. These may be used singly, or two or more of them

may be used in combination.

[0098]

In one embodiment, the amount of the extender pigment is preferably 1 part by

mass or more and 40 parts by mass or less, and more preferably 10 parts by mass or

more and 30 parts by mass or less based on 100 parts by mass of the total solid content

of the coating film-forming resin (A) and the curing agent (B). When the amount of

the extender pigment is within such a range, the scratch resistance of a coating film is

likely to be improved.

[0099]

Examples of the coloring pigment comprise coloring inorganic pigments such

as titanium dioxide, carbon black, graphite, iron oxide, and coal dust; coloring organic

pigments such as phthalocyanine blue, phthalocyanine green, quinacridone, perylene,

anthrapyrimidine, carbazole violet, anthrapyridine, azo orange, flavanthrone yellow,

isoindoline yellow, azo yellow, indanthrone blue, dibromanzathrone red, perylene red,

azo red, and anthraquinone red; aluminum powder, alumina powder, bronze powder,

copper powder, tin powder, zinc powder, iron phosphide, and atomized titanium.

These may be used singly, or two or more of them may be used in combination.

[0100]

The heat shielding pigment refers to a pigment which does not absorb light in a

near-infrared wavelength range (wavelength: 780 nmto 2,500 nm) or has a small light

absorptance in a near-infrared wavelength range (wavelength: 780 nm to 2,500 nm).

The heat shielding pigment is not particularly limited, and the following inorganic heat

shielding pigment and organic heat shielding pigment can be used.

[0101]

Examples of the inorganic heat shielding pigment comprise metal oxide-based

pigments such as titanium oxide, magnesium oxide, barium oxide, calcium oxide, zinc

oxide, zirconium oxide, yttrium oxide, indium oxide, sodium titanate, silicon oxide,

nickel oxide, manganese oxide, chromium oxide, iron oxide, copper oxide, cerium

oxide, and aluminum oxide; complex oxide pigments such as iron oxide-manganese

oxide, iron oxide-chromium oxide (for example, DAIPYROXIDE Color Black #9595

manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd. and Black 6350

manufactured by Asahikasei Kogyo Co., Ltd.), iron oxide-cobalt oxide-chromium oxide

(for example, DAIPYROXIDE Color Brown #9290 and DAIPYROXIDE Color Black

#9590 manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.), copper

oxide-magnesium oxide (for example, DAIPYROXIDE Color Black #9598

manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.), manganese

oxide-bismuth oxide (for example, Black 6301 manufactured by Asahikasei Kogyo Co.,

Ltd.), and manganese oxide-yttrium oxide (for example, Black 6303 manufactured by

Asahikasei Kogyo Co., Ltd.); metallic pigments such as silicon, aluminum, iron,

magnesium, manganese, nickel, titanium, chromium, and calcium; and alloy-based

pigments such as iron-chromium, bismuth-manganese, iron-manganese, and

manganese-yttrium. These may be used singly, or two or more of them may be used in

combination.

[0102]

Examples of the organic heat shielding pigment comprise azo pigments,

azomethine pigments, lake pigments, thioindigo pigments, anthraquinone pigments

(anthanthrone pigments, diaminoanthraquinonyl pigments, indanthrone pigments,

flavanthrone pigments, anthrapyrimidine pigments, etc.), perylene pigments, perinone

pigments, diketopyrrolopyrrole pigments, dioxazine pigments, phthalocyanine pigments,

quinophthalone pigments, quinacridone pigments, isoindoline pigments, and

isoindolinone pigments. These may be used singly, or two or more of them may be

used in combination.

[0103]

Examples of the luster pigments comprise foil pigments such as aluminum foil,

bronze foil, tin foil, gold foil, silver foil, titanium metal foil, stainless steel foil, alloy

foil of nickel and copper, and the like, and foil-like phthalocyanine blue. These may

be used singly, or two or more of them may be used in combination.

[0104]

As the wax, waxes known to those skilled in the art for coating materials can

be used, and examples thereof comprise microcrystalline, polyethylene, polypropylene,

paraffin, carnauba wax, and modified products thereof. These may be used singly, or

two or more of them may be used in combination.

[0105]

The shear viscosity of the aqueous coating composition is preferably 30,000

mPa-s or less, more preferably 20,000 mPa-s or less, and still more preferably 10,000

mPa-s or less, and is preferably 3,000 mPa-s or more, more preferably 4,000 mPa-s or

more, and still more preferably 5,000 mPa-s or more when measured at a shear rate of

0.01 s-1 at a temperature of 23°C. When measured at a shear rate of 10 s-1, the shear viscosity is preferably 800 mPa-s or less, more preferably 700 mPa-s or less, and still more preferably 600 mPa-s or less, and is preferably 300 mPa-s or more, more preferably 400 mPa-s or more, and still more preferably 500 mPa-s or more. When measured at a shear rate of 1,000 s-, the shear viscosity is preferably 1,000 mPa-s or less, more preferably 150 mPa-s or more, and is preferably 500 mPa-s or less. Within the above range, the viscosity is suitable for the pickup property of the coating material at the time of roll coater coating.

The shear viscosity can be, for example, a value measured immediately after

preparation of the coating composition.

The shear viscosity can be measured using a rotary viscometer, and can be

measured using, for example, a stress control type rheometer MCR301 (manufactured

by Anton Paar GmbH) or the like.

[0106]

The method for preparing the aqueous coating composition of the present

disclosure is not particularly limited, and the aqueous coating composition can be

prepared by mixing the respective components. For example, mixing can be

performed using a mixer disperser such as a roller mill, a ball mill, a bead mill, a pebble

mill, a sand grinding mill, a pot mill, a paint shaker, or a disper, a kneader, or the like.

[0107]

A coating film formed from the aqueous coating composition and a method for

producing the coating film are also comprised in the technical scope of the present

disclosure.

[0108]

Examples of the article to be coated (substrate) to which the aqueous coating

composition of the present disclosure is applied comprise galvanized steel sheets,

zinc-aluminum alloy plated steel sheets, aluminum alloy plated steel sheets, hot-dip

zinc-aluminum-magnesium alloy plated steel sheets, stainless steel sheets, and cold

rolled steel sheets produced by a melting method, an electrolytic method, or the like.

In addition to these steel plates or plated steel plates, a metal plate such as an aluminum

plate (including an aluminum alloy plate) can also be used as a coating target.

[0109]

The article to be coated is preferably surface-treated. Specifically, the article

to be coated is preferably subjected to chemical conversion treatment after being

subjected to pretreatment such as alkali degreasing treatment, hot water washing

treatment, or water washing treatment. The surface treatment may be carried out by a

publicly-known method, and examples thereof comprise chromate treatment and

non-chromate treatment such as zinc phosphate treatment. While the surface treatment

may be appropriately selected depending on the steel sheet to be used, treatment free of

heavy metals is preferable. By applying the coating composition of the present

disclosure to an article to be coated subjected to chemical conversion treatment as

described above, adhesion of a coating film to a metal plate surface is improved and

corrosion resistance is also improved. It is also possible to form an undercoat coating

film (primer coating film) on the metal plate surface subjected to the chemical

conversion treatment and then apply the coating composition to the undercoat coating

film. The thickness of the undercoat coating film is preferably 3 tm or more, and

more preferably 5 pm or more, and is preferably 15 pm or less, and more preferably 10

pm or less.

[0110]

The method for producing a coating film of the present disclosure comprises:

a step of applying the aqueous coating composition of the present disclosure to

an article to be coated to form an applied film; and

a step of drying and/or curing the applied film under the condition that the

120 seconds or less to form a coating film.

[0111]

The method for applying the aqueous coating composition of the present

disclosure to an article to be coated is not particularly limited, and conventionally

known methods such as a roll coater method, an airless spray method, an electrostatic

spray method, and a curtain flow coater method can be employed. A roll coater

method and a curtain flow coater method are preferable, and a roll coater method is

more preferable.

[0112]

The maximum ultimate temperature is preferably 200 seconds or more, and

may be, for example, 280 seconds or less, 270 seconds or less, or 250 seconds or less.

The drying and/or curing time is 120 seconds or less, and may be 60 seconds or less, 30

seconds or less, 10 seconds or less, or 6 seconds or less, and is preferably 1 second or

more.

[0113]

The method for drying and/or curing the applied film is not particularly limited,

but heating means such as hot air heating, infrared ray heating, or induction heating can

be used.

[0114]

The film thickness (dry film thickness) of the coating film after drying and/or

curing is preferably 1 m or more, more preferably 5 m or more, and preferably 30 pm

or less, more preferably 25 pm or less.

[0115]

A laminate including the article to be coated and the coating film formed on the

article is also comprised in the technical scope of the present disclosure.

[0116]

When the article to be coated has the coating film on one surface, the article to

be coated may further have a coating film formed from a publicly-known coating

composition, such as a coating composition containing an epoxy resin, on the other

surface.

[0117]

The aqueous coating composition of the present disclosure can afford a coating

film having high curability and good coating film properties (processability such as

adhesion and crack resistance, and scratch resistance) even when coating is performed

under conditions with a higher temperature and a shorter time than those usually

employed as coating conditions for metal substrates (for example, drying/curing

temperature: 60 to 80°C, drying/curing time: 30 minutes to 1 hour).

[0118]

The aqueous coating composition of the present disclosure has high storage

stability, and a coating film obtained therefrom is hardly peeled off from an article to be

coated and has good adhesion even during processing such as bending, and also has

controlled generation of cracks, good crack resistance, and superior scratch resistance.

Therefore, the aqueous coating composition of the present disclosure can be suitably

used for coating metal, particularly precoating.

EXAMPLES

[0119]

The present disclosure will be described more specifically with reference to the

following examples, but the present invention is not limited to them. In the examples,

"parts" and "%" are on a mass basis unless otherwise indicated.

[0120]

0.6 parts by mass of PELEX SS-H (surfactant, manufactured by Kao

Corporation) was dissolved in 60 parts by mass of ion-exchanged water. A monomer

mixture containing 53.0 parts by mass of methyl methacrylate, 39.2 parts by mass of

n-butyl acrylate, 5.8 parts by mass of 2-hydroxyethyl methacrylate, and 2.0 parts by

mass of methacrylic acid was added thereto, followed by stirring, and thus 150.5 parts

by mass of a monomer pre-emulsion was prepared. Separately, 1.0 parts by mass of

ammonium persulfate as an initiator was dissolved in 20 parts by mass of

ion-exchanged water to prepare an aqueous initiator solution.

[0121]

A reaction vessel equipped with a thermometer, a condenser, and a stirrer was

charged with 40 parts by mass of ion-exchanged water and 0.4 parts by mass of PELEX

SS-H, and the mixture was heated to 80°C under a nitrogen atmosphere. The aqueous

initiator solution was added dropwise thereto over 180 minutes while maintaining the

temperature at 80°C, and after 10 minutes from the start of the dropwise addition, the

monomer pre-emulsion was added dropwise through another port of the reaction vessel

over 150 minutes and emulsion polymerization was carried out. After completion of

the dropwise addition of the aqueous initiator solution, the mixture was further heated

and stirred at 80°C for 60 minutes and then cooled to room temperature, and 2.10 parts by mass of dimethylethanolamine was added thereto, and thus an acrylic emulsion

(solid concentration: 45% by mass) in which coating film-forming resin (A-1) was

dispersed in an aqueous medium was prepared.

[0122]

Coating film-forming resins (A-2) to (A-li) were prepared in the same manner

as described above except that the type and the amount of a monomer and the amount of

the initiator were changed as given in Table 1. The characteristic values such as the

hydroxyl value in each coating film-forming resin are given in Table 1.

[0123]

Details of the respective components given in the following tables used in

Examples and Comparative Examples are as follows.

Coating film-forming resin (A)

(A-12) VYLONAL MD-2000 (polyester resin emulsion manufactured by

Toyobo Co., Ltd.); hydroxyl value: 6 mg KOH/g, acid value: 2 mg KOH/g, weight

average molecular weight: 30,000, glass transition temperature: 67°C, minimum filming

temperature: 48°C, average particle size: 125 nm, solid concentration: 40% by mass

Crosslinking agent (B)

(B-1) CYMEL 303 (fully-alkylated methylated melamine resin, manufactured

by Allnex Japan Inc.); solid concentration: 100% by mass, number average molecular

weight: 455

(B-2) CYMEL 300 (fully-alkylated methylated melamine resin, manufactured

weight: 390

Other crosslinking agents

(b-1) CYMEL 327 (imino group-type methylated melamine resin,

manufactured by Allnex Japan Inc.); solid concentration: 90% by mass, number average

molecular weight: 470

(b-2) MYCOAT 508 (imino group-type butylated melamine resin,

manufactured by Allnex Japan Inc.); solid concentration: 80% by mass, number average

molecular weight: 1,500

Sulfonic acid compound (C)

(C-1) AC400S (dodecylbenzenesulfonic acid, manufactured by TAYCA Co.,

Ltd.); solid concentration: 25% by mass

(C-2) AC700 (paratoluenesulfonic acid, manufactured by TAYCA Co., Ltd.);

solid concentration: 25% by mass

(C-3) Nacure-1051 (dinonylnaphthalenesulfonic acid, manufactured by

Kusumoto Chemicals, Ltd.); solid concentration: 51% by mass

Other acid compounds

(c-1) Cycat 296 (phosphoric acid compound, manufactured by Allnex Japan

Inc.); solid concentration: 50% by mass

Amine compound (D)

(D-1) DMEA (dimethylethanolamine, manufactured by Mitsubishi Gas

Chemical Co., Inc.); boiling point: 134°C

(D-2) AMP (2-amino-2-methyl-1-propanol, manufactured by Kokusan

Chemical Co., Ltd.); boiling point: 165°C

(D-3) TEA (triethylamine, manufactured by Mitsubishi Gas Chemical Co.,

Inc.); boiling point: 90°C

Aqueous medium (E)

(El-1) Diethylene glycol (manufactured by Nippon Shokubai Co., Ltd.);

boiling point: 244°C, solubility in water: infinite (freely miscible with water)

(El-2) Propylene glycol (manufactured by Sankyo Chemical Co., Ltd.); boiling

point: 187°C, solubility in water: infinite (freely miscible with water)

(El-3) Dipropylene glycol (manufactured by Showa Chemicals Co., Ltd.);

boiling point: 232°C, solubility in water: infinite (freely miscible with water)

(E1-4) 1,4-Butanediol (manufactured by Sankyo Chemical Co., Ltd.); boiling

point: 228°C, solubility in water: infinite (freely miscible with water)

(El-5) 1,5-Pentanediol (manufactured by Ube Industries, Ltd.); boiling point:

242°C, solubility in water: infinite (freely miscible with water)

Viscosity modifier (F)

(F-1) SN-THICKENER 612 (polyether urethane-based hydrophobic

associative viscosity modifier, manufactured by San Nopco Ltd.); solid concentration:

% by mass

(F-2) SN-THICKENER 621 (polyether urethane-based hydrophobic

% by mass

(F-3) ADEKA NOL UH-526 (polyether urethane-based hydrophobic

associative viscosity modifier, manufactured by ADEKA Corporation); solid

concentration: 30% by mass

(F-4) PRIMAL RM-202ONPR (polyether urethane-based hydrophobic

associative viscosity modifier, manufactured by The Dow Chemical Company); solid

concentration: 20% by mass

(F-5) PRIMAL ASE-60 (polyacrylate ester emulsion-based alkali swelling type

viscosity control agent, manufactured by The Dow Chemical Company); solid

concentration: 28% by mass

[0124]

1.63 parts by mass of DISPERBYK-190 (manufactured by BYK-Chemie

GmbH) as a dispersant, 0.25 parts by mass of dimethylethanolamine, 0.05 parts by mass

of SN-477T (manufactured by San Nopco Ltd.) as a defoaming agent, 32.9 parts by

mass of ion-exchanged water, and 65.2 parts by mass of titanium dioxide (Ti-Pure

R-706, manufactured by DuPont) as a pigment were preliminarily mixed, and then

dispersed at 1,600 rpm using an SG mill (dispersion medium: glass beads) until the

maximum particle size of coarse pigment particles reached 5 pm, thereby affording a

pigment dispersion paste.

[0125]

55.1 parts by mass of the pigment dispersion paste obtained in the production

example, 80.0 parts by mass of the coating film-forming resin (A-1) obtained in the

production example, 20.0 parts by mass of the coating film-forming resin (A-8), and

17.6 parts by mass of CYMEL 303 as the crosslinking agent (B-1) were mixed, and then

5.4 parts by mass of diethylene glycol (El-1) and 5.4 parts by mass of propylene glycol

(El-2) as aqueous media were mixed and stirred. Next, 1.2 parts by mass of

dodecylbenzenesulfonic acid as the sulfonic acid compound (C-1) and 1.9 parts by mass

of dimethylethanolamine as the amine compound (D-1) were stirred with a disper, and

further, 0.2 parts by mass of SN-THICKENER 612 as the viscosity modifier (F -1) was

mixed with stirring, affording coating composition 1.

[0126]

(Coating compositions 2 to 45, Comparative Examples 1 to 10)

Coating compositions were prepared in the same manner as in the coating

composition 1 except that the type and amount of the respective components were

changed as given in Tables 2 to 7.

[0127]

A 0.4 mm-thick hot dip galvanized steel sheet was alkali-degreased, and then

subjected to non-chromium chemical conversion treatment by applying a phosphoric

acid treatment agent, SURFCOAT EC2310 (manufactured by Nippon Paint Surf

Chemicals Co., Ltd.) to the front and back surfaces of the steel sheet, followed by

drying.

Next, the coating composition 1 obtained in the production example was

applied to the front surface of the steel sheet using a bar coater such that a resulting dry

coating film had a thickness of 18 m, and baking was performed for 30 seconds under

the condition with a maximum ultimate material temperature of 230°C to form a surface

coating film, thereby affording a coated steel sheet.

[0128]

1) Measurement of shear viscosity

The shear viscosity of each of the coating compositions obtained in Examples

and Comparative Examples was measured at shear rates of 0.1 s-1, 10 s-1, and 1,000 s-1

using a stress-controlled rheometer MCR301 (manufactured by Anton Paar GmbH, jig:

mm parallel plate, gap: 0.5 mm). The measurement temperature was adjusted to

23 0 C.

[0129]

2) Storage stability

Evaluation was performed using a Ford Cup No. 4 (manufactured by Ueshima

Seisakusho Co., Ltd.) in accordance with the method specified in JIS K 5600 2-2 (flow

cup method).

Ion-exchanged water was added to each of thecoating compositions obtained

in Examples and Comparative Examples to adjust the viscosity to 60 ±10 seconds

(initial viscosity (sec)). Specifically, the initial viscosity was a viscosity measured

immediately after dilution with the ion-exchanged water and stirring at 1,000 rpm for 3

minutes using a disper. The temperature of the coating material was adjusted to 25°C.

[0130]

The coating composition adjusted to the initial viscosity (60 ±10 seconds

(25°C)) was put in a 1/5 can up to a volume of 80 to 90%, sealed, and then left at rest in

a thermostatic chamber at 40°C. Thereafter, the sample was taken out after 14 days

(two weeks), and the viscosity was measured in the same manner as described above

(viscosity over time (sec)).

The change rate of the viscosity over time relative to the initial viscosity was

calculated by the following formula, and the storage stability was evaluated according

to the following criteria. The rating of 0 or higher was regarded as acceptable.

Viscosity change rate (%)= viscosity over time (sec)/initial viscosity (sec) x

100

G: The viscosity change rate is 0% or more and less than 30%.

0: The viscosity change rate is 30% or more and less than 50%.

A: The viscosity change rate is 50% or more and less than 100%.

X: The viscosity change rate is 100% or more.

[0131]

) Coating workability (roll coater coatability)

Each of the coating compositions obtained in Examples and Comparative

Examples was applied to an article to be coated under the following conditions using a

small test coater (manufactured by N.K. TEC Co., Ltd.) equipped with three rolls

(backup roll, application roll, pickup roll), and the roll coater coatability was evaluated

according to the following criteria. The rating of 0 or higher was regarded as

acceptable. The test conditions were a room temperature of 23°C and a humidity of 60

RH%.

• Article to be coated: GL steel sheet having a size of 300 mm x 2,000 mm x

0.35 mm (manufactured by Nippon Steel Coated Sheet Corporation)

• Coating conditions:

• Line speed: 50 m/min

• Peripheral speed of roll: application roll: 65 m/min (line speed ratio:

130%), pickup roll: 20 m/min (line speed ratio: 40%)

• Backup roll pressure: 60 kgf 2 • Reference applied amount: the mass of dry coating film is 28 g/m

•Baking conditions: for 30 seconds under the condition that the maximum

ultimate material temperature of the article to be coated is 230°C

0: The coating composition can be uniformly applied to the entire surface at

the reference applied amount.

0: The coating composition can be uniformly applied to the entire surface, but

the applied amount is 20 to 28 g/m 2 .

A: The coating composition can be uniformly applied to the entire surface, but

the applied amount is less than 20 g/m 2 , and the film thickness is uneven.

X: An uncoated portion is generated, and the entire surface cannot be coated.

[0132]

In the roll coater, the coating material is wound up by a pickup roll, transferred

to an application roll, further transferred to a backup roll, and applied to an article to be

coated. When the coating material is appropriately wound up by the pickup roll and

the transfer of the coating material to the backup roll is appropriately performed by the

application roll and the backup roll pressure, the coating material is uniformly applied

to the article to be coated. However, when only a small amount of the coating material

is wound up by the pickup roll, unevenness occurs at the time of transfer between rolls,

and the coating material is not uniformly applied to the article to be coated.

[0133]

4) Processability (adhesion)

Each of the coated steel sheets obtained in Examples and Comparative

Examples was cut into a size of 5 cm x 3 cm, and subjected to preliminary bending

using a seaming machine (manufactured by Ueshima Seisakusho Co., Ltd.) such that the

coating film surface was on the front side. Two steel sheets having the same thickness

(0.4 mm) were sandwiched between the test pieces, and bent with a pressing machine

(manufactured by Kyoritsu Kogyo Co., Ltd.). Cellophane tape (registered trademark)

(LP-24, manufactured by Nichiban Co., Ltd.) was brought into close contact with the

processed portion of the coated steel sheet, and peeled off at once to evaluate the

adhesion of the processed portion coating film. The appearance of the portion peeled

off with the tape was evaluated according to the following criteria. Score 4 or more

was regarded as acceptable.

5: The metal base is not found in the tape peeled portion.

4: The metal base was found in less than 20% (more than 0%) of the area of the

tape peeled portion.

3: The metal base is found in 20% or more and less than 50% of the area of the

tape peeled portion.

2: The metal base is found in 50% or more and less than 80% of the area of the

tape peeled portion.

1: The metal base is found in 80% or more of the area of the tape peeled

portion.

[0134]

) Processability (crack resistance)

Each of the coated steel sheets obtained in Examples and Comparative

coating film surface was on the front side. Five steel sheets having the same thickness

(manufactured by Kyoritsu Kogyo Co., Ltd.). The state (cracks) of the coating film of

the processed portion was observed with a loupe of 15 magnifications, and the

processability was evaluated according to the following criteria. Score 4 or more was

regarded as acceptable. The test conditions were a temperature of 23°C and a

humidity of 60 RH%.

5: No crack was observed in the processed portion.

4: Cracks are observed in (more than 0% and) less than 20% of the area of the

processed portion.

3: Cracks are observed in 20% or more and less than 50% of the area of the

processed portion.

2: Cracks are observed in 50% or more and less than 80% of the area of the

processed portion.

1: Cracks are observed in 80% or more of the area of the processed portion.

[0135]

6) Scratch resistance

Using a continuous loading scratching intensity tester TYPE: 18/18L

(manufactured by Shinto Scientific Co., Ltd.), a diamond needle (R-processed conical

scratch needle, diameter: 0.4 mm) subjected to R processing to R 0.4 mm was applied to

the coating film surface of each of the coated steel sheets obtained in Examples and

Comparative Examples, and the coated steel sheet was rubbed once at a speed of 300

mm/min and a moving width of 10 cmunder a load. The weight of the load with

which the coating film surface was scratched and the exposure of the base could be

confirmed was evaluated according to the following criteria. The rating of 0 or higher

was regarded as acceptable. The load was applied with increase at 500 gf intervals,

and the test conditions were a temperature of 23°C and a humidity of 60 RH%.

G: The base is not exposed even when the load exceeds 3,000 g.

0: The base is exposed at a load of more than 2,000 and 3,000 g or less.

A: The base is exposed at a load of more than 1,000 g and 2,000 g or less.

X: The base is exposed at a load of 1,000 g or less.

[0136]

[Table 1] Acrylic resin (A) (A-1) I(A-2) I(A-3) I(A-4) I(A-5) (A-6) Methyl methacrylate 53.0 48.3 78.9 74.4 76.2 82.6 Type and blending n-Butyl acrylate 39.2 38.1 13.3 12.0 0.0 14.2 amount of monomer 2-Ethylhexyl acrylate 10.2 having ethylenically unsaturated bond 2-Hydroxyethyl methacrylate 5.8 11.6 5.8 11.6 11.6 1.2 Methacrylic acid 2.0 2.0 2.0 2.0 2.0 2.0 Polymerization initiator Ammonium persulfate 1.0 1.0 1.0 1.0 1.0 1.0 Total amount (parts by mass) of monomers having 100.0 100.0 100.0 100.0 100.0 100.0 ethylenically unsaturated bond I Solid concentration (% by mass) 45.0 45.0 45.0 45.0 45.0 45.0 Hydroxyl value (mg KOH/g) 25 50 25 50 50 5 Acid value (mg KOH/g) 13 13 13 13 13 13 Weight average molecular weight 130,000 145,000 138,000 150,000 140,000 140,000 Glass transition temperature (°C) 20 20 70 70 70 70 Minimum filming temperature (°C) 50 50 80 80 65 65 Average particle size (nm) 130 125 115 140 120 120 Acrylic resin (A) (A-7) (A-8) (A-9) (A-10) (A-11) Methyl methacrylate 75.7 57.6 83.5 57.6 74.4 Type and blending - n-Butyl acrylate 11.8 40.4 14.5 40.4 12.0 amount of monomer 2-Ethylhexyl acrylate having ethylenically unsaturated bond 2-Hydroxyethyl methacrylate 11.6 11.6 Methacrylic acid 0.9 2.0 2.0 2.0 2.0 Polymerization initiator Ammonium persulfate 1.0 1.0 1.0 3.0 3.0 Total amount (parts by mass) of monomers having 100.0 100.0 100.0 100.0 100.0 ethylenically unsaturated bond Solid concentration (% by mass) 45.0 45.0 45.0 45.0 45.0 Hydroxyl value (mg KOH/g) 50 0 0 0 50 Acid value (mg KOH/g) 6 13 13 13 13 Weight average molecular weight 135,000 150,000 145,000 50,000 45,000 Glass transition temperature (°C) 70 20 70 20 70 Minimum filming temperature (°C) 80 45 85 30 60 Average particle size (nm) 110 130 120 130 140

[0137]

[Table 2] Example Example Example Example Example Example Example Example Example Example 1 2 3 4 5 6 7 8 9 10 (A-1) 44.4 111.0 222.0 (A-2) 44.0 111.0 133.0 (A-3) 111.0 (A-4) 44.0 111.0 (A-5) 44.0 Coating film-forming (A-6) resin (A) (A-7) (A-8) 178.0 111.0 178.0 111.0 178.0 178.0 111.0 111.0 89.0 (A-9) (A-10) (A-Il) (A-12) (B-1) 17.6 17.6 17.6 17.6 17.6 17.6 17.6 17.6 17.6 17.6 Crosslinkingagent(D) (B-2) Other crosslinking (b-1) agents (b-2) (C-1) 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 Sulfonic acid (C-2) compound (C) (C-2) (C-3) Other acid compounds (c-1) (D-1) 1.9 1.9 1.9 1.9 1.9 1.9 1.9 1.9 1.9 1.9 Amine compound (D) (D-2) (D-3) (El-1) 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 (El-2) 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 Organic solvent (El) (EI-3) (El-4) (EI-5) (F-1) 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 (F-2) Viscosity modifier (F) (F-3) (F-4) (F-5) Hydroxylvalue(mgKOH/g)of(A) 5.0 12.5 10.0 12.5 10.0 10.0 25.0 25.0 30.0 25.0 Weight average molecular weight of(A) 146,000 140,000 149,000 144,000 150,000 148,000 150,000 147,500 147,000 130,000 Glasstransitiontemperature(°C)of(A) 20.0 20.0 20.0 43.0 28.7 28.7 43.0 20.0 20.0 20.0 Massratioof(B)to(A),(B)/(A) 15/85 15/85 15/85 15/85 15/85 15/85 15/85 15/85 15/85 15/85 Amount(partsbymass)of(C)basedon 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 100 parts by mass of solid content of (A) Neutralizationrate(%) of(C) by (D) 600 600 600 600 600 600 600 600 600 600 Shear rate 21,000 25,000 19,000 22,000 21,000 18,500 19,000 18,000 20,500 22,500 Shear viscosity Shear rate (mPa-s)ofcoating 10(S ) 380 450 520 600 500 360 450 550 600 550 composition oS) composite S180 200 250 220 250 280 250 290 300 250

Storage stability Rate ofchange of viscosity G 0 0 0 D 0 0 a0 Coating workability Rollcoater coatability 0 O O O O O O Processability 5 5 5 4 5 4 5 5 5 5 Coating film (adhesion) performance Processability 5 5 5 4 5 5 4 5 4 5 evaluation (crack resistance) Scratch resistance 0 0 0 0 0 0 0 0 0

[0138]

[Table 3] Example Example Example Example Example Example Example Example Example Example I 11 1 12 13 14 15 16 17 18 19 20 (A-1) (A-2) (A-3) (A-4) 133.0 44.0 44.0 44.0 44.0 44.0 44.0 44.0 (A-5) Coating film-forning (A-6) 222.0 resin (A) (A-7) 222.0 (A-8) 89.0 178.0 178.0 178.0 178.0 178.0 178.0 178.0 (A-9) (A-10) (A-li) (A-12) roslinking agent (B) (B-1) 17.6 17.6 17.6 17.6 17.6 17.6 11.1 25.0 8.8 (B-2) 17.6 8.8 Other crosslinking (b-1) agents (b-2) (C-1) 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 Sulfonicacid (C-2) compound (C) (C3 (C.-3) Other acid compounds (c-1) (D-1) 1.9 1.9 1.9 0.3 3.2 4.2 1.9 1.9 1.9 1.9 Amine compound (D) (D-2) (d-1) (El-1) 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 (EI-2) 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 Organic solvent (El) (EI-3) (El-4) (EI-5) (F-1) 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 (F-2) Viscosity modifier (F) (F-3) (F-4) (F-5) Hydroxylvalue(mgKOH/g)of(A) 5.0 25.0 35.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 Weightaveragemolecularweightof(A) 140,000 135,000 150,000 150,000 150,000 150,000 150,000 150,000 150,000 150,000 Glaasstransitiontemperature(°C)of(A) 20.0 20.0 48.0 28.7 28.7 28.7 28.7 28.7 28.7 28.7 Massratioof(B)to(A),(B)/(A) 15/85 15/85 15/85 15/85 15/85 15/85 10/90 20/80 15/85 15/85 Amount(partsbymass)of(C)basedon 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 100 parts by mass of solid content of (A) Neutralizationrate(%)of(C)by(D) 600 600 600 100 1,000 1,300 600 600 600 600 Shear ra : 23,000 22,500 25,000 22,000 21,500 23,000 24,000 28,000 22,000 20,000 Shearviscosity Shear rate (mPa-s)ofcoating 10(a-) 480 550 650 600 550 450 500 650 450 550 composition Shearrate: 230 210 270 210 180 200 220 280 200 230 1,000(a'1)I

Storage stability Rate ofchange of 0 0 0 0 0 0 0 0 0 viscosityII

Coating workability Rollcoater coatahility 0 O O o 0 0 0 0 0 0 Processability 5 4 5 5 5 5 4 5 4 4 Coating film (adhesion) performance Processability 5 5 4 5 5 5 5 4 4 4 evaluation (crack resistance) Scratch resistance 0 0 0 0 1 0 0 0 o 0

[0139]

[Table 4] Example Example Example Example Example Example Example Example Example Example 21 22 23 24 25 26 27 28 29 30 (A-1) (A-2) (A-3) (A-4) 44.0 44.0 44.0 44.0 44.0 44.0 44.0 44.0 44.0 44.0 (A-5) Coating film-forming (A-6) resin (A) (A-7) (A-8) 178.0 178.0 178.0 178.0 178.0 178.0 178.0 178.0 178.0 178.0 (A-9) (A-10) (A-Il) (A-12) agent(B) (B-1) 17.6 17.6 17.6 17.6 17.6 17.6 17.6 17.6 17.6 17.6 rosalinlingn (B-2) Other crosslinking (b-1) agents (b-2) 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 Sulfonicacid (C-1) compound (C) (C-2) 1.2 (C-3) 1.2 Other acid compounds (c-1) (D-1) 3.7 1.4 1.9 1.9 1.9 1.9 1.9 1.9 1.9 Amine compound (D) (D-2) 1.9 (d-1) (El-I) 5.4 5.4 5.4 5.4 5.4 5.4 2.7 5.4 5.4 5.4 (El-2) 5.4 5.4 5.4 2.7 5.4 5.4 5.4 Organic solvent (El) (EI-3) 5.4 (EI-4) 5.4 (EI-5) 5.4 (F-1) 0.2 0.2 0.2 0.2 0.2 0.2 0.2 (F-2) 0.4 Viscosity modifier (F) (F-3) 0.8 (F-4) 1.0 (F-5) Hydroxylvalue(mgKOH/g)of(A) 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 Weight average molecular weight of(A) 150,000 150,000 150,000 150,000 150,000 150,000 150,000 150,000 150,000 150,000 Glasstransitiontemperature(°C)of(A) 28.7 28.7 28.7 28.7 28.7 28.7 28.7 28.7 28.7 28.7 Massratioof(B)to(A),(B)/(A) 15/85 15/85 15/85 15/85 15/85 15/85 15/85 15/85 15/85 15/85 Amount(partsbymass)of(C)basedon 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 100 parts by mass of solid content of (A) Neutralizationrate(%)of(C)by(D) 600 600 600 600 600 600 600 600 600 600 Shearmte: 19,000 16,500 17,000 19,000 25,000 21,500 12,000 18,000 12,000 13,000 Shear viscosity Shear rate (mPa-s)ofcoating 10(s-') 450 350 450 350 450 480 300 500 400 350 composition Shearmte, 250 160 200 160 180 200 170 200 160 170 1,000(a-')II

Storage stability Rate ofchange of E 0 0 D D 0 0 0 0 0 viscosity Coating workability Rollcoater A A A O 0 G A 0 A A coatabilityII Processability 5 5 4 5 4 5 4 4 4 4 Coating film (adhesion) performance Processability 5 4 4 5 5 4 4 4 4 4 evaluation (crack resistance) Scratchresistance 0 0 0 0 0 0 0 0 0 0

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[Table 5] Example Example Example Example Example Example Example Example Example Example 31 32 33 34 35 36 37 38 39 40 (A-1) (A-2) (A-3) (A-4) 44.0 44.0 44.0 44.0 44.0 44.0 44.0 (A-5) 222.0 Coating film-forming (A-6) resin (A) (A-7) (A-8) 178.0 178.0 178.0 178.0 178.0 178.0 178.0 (A-9) (A-10) 44.0 (A-lI) 178.0 (A-12) 250.0 agent(B) (B-1) 17.6 17.6 30.0 17.6 17.6 17.6 40.0 21.8 21.8 21.8 Crosslinking a(B-2)

Other crosslinking (b-1) agents (b-2) (C-1) 1.2 1.2 1.3 1.2 1.2 1.2 1.4 0.01 7.2 1.2 Sulfonic acid (C-2) compound (C) (C-2) (C-3) Other acid compounds (c-1) (D-1) 1.9 2.1 1.9 1.9 1.9 2.3 0.002 11.8 1.9 Amine compound (D) (D-2) (D-3) 2.2 (El-1) 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 10.8 (EI-2) 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 Organic solvent (El) (El-3) (El-4) (E1-5) (F-1) 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 (F-2) Viscosity modifier (F) (F-3) (F-4) (F-5) 0.5 Hydroxylvalue(mgKOH/g)of(A) 10.0 10.0 10.0 10.0 10.0 6.0 10.0 10.0 10.0 10.0 Weightaveragemolecularweightof(A) 150,000 150,000 150,000 49,000 150,000 30,000 150,000 150,000 150,000 150,000 Glasstransitiontemperature(°C)of(A) 28.7 28.7 28.7 28.7 70.0 67.0 28.7 28.7 28.7 28.7 Massratioof(B)to(A),(B)/(A) 15/85 15/85 30/70 15/85 15/85 15/85 60/40 15/85 15/85 15/85 Amount(partsbymass)of(C)basedon 1.0 1.0 1.0 1.0 1.0 1.0 1.0 0.05 6.0 1.0 100 parts by mass ofsolid content of(A) Neutralizationrate(%)of(C)by(D) 600 600 600 600 600 600 600 600 600 600 Shear raty 35,000 19,000 24,000 23,000 22,000 12,000 23,000 22,000 23,000 21,000 Shear viscosity Shart (mPa-s)ofcoating 0 srate 600 580 550 320 450 900 600 500 550 500 composition 0s'I Shearrate, 130 160 250 220 200 400 250 200 230 1 220 1,000 (g- )I

Storage stability Rate ofchange of viscosity Coating workability Rollcoater coatability A 0 A 0 0 A O 0 0 0

Processability 5 4 5 3 5 4 5 5 5 5 Coating film (adhesion) performance Processability 4 4 3 4 4 3 3 5 5 5 evaluation (crack resistance) Scratch resistance 0 A 0 0 A A 0 A 0 0

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[Table 6] Example Example Example Example Example 41 42 43 44 45 (A-1) (A-2) (A-3) (A-4) 44.0 44.0 44.0 44.0 44.0 (A-5) Coating film-forming (A-6) resin (A) (A-7) (A-8) 178.0 178.0 178.0 178.0 178.0 (A-9) (A-10) (A-li) (A-12) agent(B (B-1) 21.8 21.8 21.8 21.8 21.8 slinking g (D) (B-2) Other crosslinking (b-1) agents (b-2) (C-1) 1.2 1.2 1.2 1.2 1.2 Sulfonic acid (C-2) compound (C) (C-2) (C-3) Other acid compounds (c-1) (D-1) 1.9 1.9 1.9 1.9 1.9 Amine compound (D) (D-2) (D-3) (EI-1) 0.0 5.4 5.4 5.4 (EI-2) 10.8 0.0 5.4 5.4 5.4 Organic solvent (El) (EI-3) (EI-4) (EI-5) (F-1) 0.2 0.2 0.0 0.1 0.4 (F-2) Viscosity modifier (F) (F-3) (F-4) (F-5) Hydroxyl value (mg KOH/g) of (A) 10.0 10.0 10.0 10.0 10.0 Weight average molecular weight of(A) 150,000 150,000 150,000 150,000 150,000 Glass transition temperature (°C) of(A) 28.7 28.7 28.7 28.7 28.7 Mass ratio of(B) to (A), (B)/(A) 15/85 15/85 15/85 15/85 15/85 Amount (parts by mass) of (C) based on 1.0 1.0 1.0 1.0 1.0 100 parts by mass ofsolid content of(A) Neutralization rate (%) of (C) by (D) 600 600 600 600 600 Shear rate: 22,000 21,000 13,000 17,000 45,000 Shear viscosity Shearrate) (mPa-s)ofcoating 10sae 380 450 250 350 900 composition 1( Shearrate: 230 220 100 140 300 1,000(s-') Storage stability Rate ofchange of 0 A 0 0 A viscosity Coating workability Rollcoater A A A 0 coatahility Processability 5 5 3 4 5 Coating film (adhesion) performance Processability 4 4 5 5 5 evaluation (crack resistance) Scratchresistance 0 A 0 0 0

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[Table 7] Comparative Comparative Comparative Comparative Comparative Comparative Comparative Comparatie Comparative Comparative Example 1 Example 2 Example 3 Example 4 Example 5 Example6 Example 7 Example 8 Example 9 Example 10 (A-1) (A-2) 178.0 222.0 (A-3) (A-4) 44.0 44.0 44.0 44.0 44.0 20.0 (A-5) Coating (A-6) film-forming resi (A-7 (A7) (A) (A-8) 222.0 44.0 178.0 170.0 170.0 178.0 178.0 178.0 (A-9) 222.0 (A-10) (A-Il1) (A-12) Crosslinking aged (B-1) 17.6 17.6 17.6 17.6 17.6 17.6 17.6 17.6 (B) (B-2) Other crosslinking (b-1) 17.6 agents (b-2) 17.6

Salfonicacid (C-I) 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 compound (C) (C-2) (C-3) Otheracid (c-1) 1.2 compounds (cI1. (D-I) 1.9 1.9 1.9 1.9 0.0 0.2 4.8 1.9 1.9 2.0 ec(m pou< (D-2) (d- 1) (El-1) 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 Organicsolvent (E1-2) 5.4 (El) (E1-3) (EI-4) (EI-5) (F-1) 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 . t . (F-2) viscosityy modiie (F-3) (F-4) (F-5) Hydroxylvalue(mgKOH/g)of(A) 0 0 40 50 10 10 10 10 10 10 Weight average molecular weight of 150,000 145,000 146,000 145,000 150,000 150,000 150,000 150,000 150,000 150,000 (A) Glass transition temperature (C) of 20.0 70.0 20.0 20.0 28.7 28.7 28.7 28.7 28.7 28.7 (A)I Mass ratio of(B) to (A), (B)/(A) 15/85 15/85 15/85 15/85 15/85 I5/85 15/85 15/85 15/85 15/85 Amount (parts by mass) of(C) based on100partsbymassofsolidcontent 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 of(A) Neutralizationrate(%)of(C)by(D) 600 600 600 600 0 50 1,500 600 600 600 Shear rae: 18,000 20,000 17,000 19,000 18,000 16,000 22,000 14,000 16,000 17,000 Shear viscosity Shearrate: (mPa-s)ofcoating 10 (Sr) 500 500 600 500 550 450 530 580 400 430 composition Shearrate: 210 240 230 200 210 190 200 250 210 180 ___________ 1,000(s-1)

Storage stability ate change 0 A A 0 A

Coating Roll copter 0A workahility oOtability Processability 5 4 3 1 5 5 2 3 4 Coating film (adhesion) performance Processability 5 1 2 1 5 5 5 4 2 4 evaluation (crack resistance) Scratch resistance X X X 0 0 0 x

[0143]

Examples 1 to 45 are examples of the present disclosure, and were high in

storage stability, superior in processability, and good in scratch resistance.

[0144]

Comparative Examples 1 and 2 are examples in which the hydroxyl value of

the acrylic resin (Al) was less than 5 mg KOH/g, and were poor in scratch resistance.

Comparative Examples 3 and 4 are examples in which the hydroxyl value of the acrylic

resin (Al) exceeded 35 mg KOH/g, and were poor in storage stability and processability.

Comparative Examples 5 and 6 are examples in which the neutralization ratio of the

sulfonic acid compound (C) by the amine compound (D) was less than 100%, and were

poor in storage stability. Comparative Example 7 was an example in which the

neutralization ratio of the sulfonic acid compound (D) by the amine compound (D)

exceeded 1,300%, and was poor in storage stability. Comparative Examples 8 and 9

were examples not containing the fully-alkylated melamine resin (B1) as the

crosslinking agent (B), and were poor inprocessability. Comparative Example 10 was

an example not containing the sulfonic acid compound (C) and using a phosphoric acid

compound, and was poor in storage stability and scratch resistance.

Claims

1. An aqueous coating composition comprising a coating film-forming resin (A),

wherein the coating film-forming resin (A) comprises an acrylic resin (Al)

having a hydroxy group,

the coating film-forming resin (A) has a hydroxyl value of 5 mg KOH/g or

more and 35 mg KOH/g or less,

the crosslinking agent (B) comprises a fully-alkylated melamine resin (B1), and

a molar neutralization ratio of an acid group of the sulfonic acid compound (C)

by the amine compound (D) is 100% or more and 1,300% or less.

2. The aqueous coating composition according to claim 1, wherein the coating

film-forming resin (A1) has a weight average molecular weight of 100,000 or more.

3. The aqueous coating composition according to claim 1 or 2, wherein at a

temperature of 23°C, a shear viscosity measured at a shear rate of 0.01 s-' is 30,000

mPa-s or less, a shear viscosity measured at a shear rate of 10 s-' is 800 mPa-s or less,

and a shear viscosity measured at a shear rate of 1,000 s 1 is 150 mPa-s or more.

4. The aqueous coating composition according to any one of claims 1 to 3, further

comprising an organic solvent (El).

5. The aqueous coating composition according to any one of claims 1 to 4, the

aqueous coating composition being for coil coating.

6. A method for producing a coating film, comprising:

a step of applying the aqueous coating composition according to any one of

claims 1 to 5 to an article to be coated to form an applied film; and a step of drying and/or curing the applied film under a condition that the maximum ultimate temperature is 180°C or higher and a drying and/or curing time is

120 seconds or less to form a coating film.