JP2022084372A - Designable coating composition - Google Patents

Abstract

To provide a coating composition which can contribute to formation of a coated film having low glossiness and high weather resistance.SOLUTION: A coating composition contains at least a coated film-forming resin (A) and a crosslinking agent (B), in which an arithmetic average height (Ra) on the surface of a coated film obtained by curing the coating composition is 1.2 μm or more, and a development area ratio (Sdr) is 800% or more.SELECTED DRAWING: None

Description

INDUSTRIAL APPLICABILITY The present invention provides a coating film suitable for coating a substrate such as a steel plate with respect to a coating film having a uniform matte appearance and excellent designability and excellent weather resistance. ..

Painted steel sheets coated with cold-rolled steel sheets or plated steel sheets as the base material are also called pre-coated steel sheets (also called "PCM"), and are used for building materials such as shutters, shutters, doors, roofs and siding, and electricity for cooler outdoor units. It is used as an exterior material for equipment and various members such as interior materials. Usually, the pre-coated steel sheet is processed into a required product after the surface of the steel sheet is coated to form a coating film. Therefore, the coating film formed on the pre-coated steel sheet is required to have flexibility and high workability such that it does not crack or peel off during processing, for example, when the pre-coated steel sheet is bent. Moreover, since the pre-coated steel sheet constitutes the appearance of the above-mentioned member, the pre-coated steel sheet is required to have excellent designability. Further, the pre-coated steel sheet is required to have various properties such as wear resistance, scratch resistance, corrosion resistance, and weather resistance, depending on the intended use.

In recent years, in the field of pre-coated metal plates for building materials and equipment processing, there has been a demand for coated metal plates with better cosmetic properties, and topcoat paints and inorganic fine particles containing organic resin fine particles with a large particle size are being used. The market is for topcoat paints that are blended in large quantities, and matte coated metal plates that are coated with topcoat paints that are blended with amine compounds to form a uniform matte appearance by utilizing the difference in curing speed between the surface of the coating and the inside of the coating. It is out in.

In addition, there is an increasing demand for a low-gloss (matte) coating film appearance due to consumers' desire to upgrade, and various coating compositions and coating methods have been studied. For example, precoated steel sheets having low gloss by blending an extender pigment such as silica, calcium carbonate, and talc into a coating composition have been studied. However, these coating films have problems such as inferior processability and weather resistance.

For example, Patent Document 1 (Japanese Unexamined Patent Publication No. 2002-146280) describes a modified polyester resin (A), a polyester resin containing a hydroxyl group, or an acrylic resin as a coating composition for generating a coating film having a uniform matte appearance. (B) Invention of a coating composition containing a low-nuclear methylated melamine resin (C) and a mixture (D) of 1 equivalent of sulfonic acid and a secondary or tertiary amine having a boiling point of 30 ° C. or higher and 250 ° C. or lower. Is disclosed.

Japanese Unexamined Patent Publication No. 2002-146280

In the coating composition of Patent Document 1, although a coating film having a matte appearance with improved workability can be obtained, the weather resistance (fading property) of the coating film is particularly high in the hue region from medium to deep colors. There is room for improvement. In the present disclosure, the medium color and the deep color are defined by the lightness (L ^* value) of the coating film, and the lightness (L ^* value) is 3.2 of JIS K 5600-4-4 and JIS K 5600-. Calculated according to the description in 4-5. The brightness (L ^* value) can be measured with, for example, a spectrocolorimeter CM-M6 (manufactured by Konica Minolta) or the like. A paint color having a lightness (L ^* value) of less than 40 is defined as a dark color, and a paint color having a brightness (L * value) of 40 or more and less than 80 is defined as a medium color.
An object of the present disclosure is to provide a coating composition capable of contributing to the formation of a coating film having low gloss and high weather resistance.

To solve the above problems, the present disclosure provides the following aspects.
[1]
A coating composition containing at least a coating film-forming resin (A) and a cross-linking agent (B).
A coating composition having an arithmetic mean height (Ra) of 1.2 μm or more and a developed area ratio (Sdr) of 800% or more on the surface of a coating film obtained by curing the coating composition. ..
[2]
The coating composition according to [1], further comprising a sulfonic acid (C), an amine compound (D) and an aggregate (E).
[3]
The coating film-forming resin (A) is a resin having a hydroxyl group, and contains at least one selected from the group consisting of polyester resin, acrylic resin, urethane resin and modified products thereof, according to [1] or [2]. The described paint composition.
[4]
The coating composition according to any one of [1] to [3], wherein the cross-linking agent (B) contains at least one selected from the group consisting of a melamine resin and a urea resin.
[5]
The content of the cross-linking agent (B) is 5 parts by mass or more and 100 parts by mass or less as the resin solid content with respect to 100 parts by mass of the resin solid content of the coating film forming resin (A) [1] to [ 4] The coating composition according to any one of.
[6]
The content of the sulfonic acid (C) is 1.0 part by mass or more and 18.0 part by mass or less with respect to 100 parts by mass of the resin solid content of the coating film-forming resin (A), [2] to [ 5] The coating composition according to any one of.
[7]
The coating composition according to any one of [2] to [6], wherein the amine compound (D) is a secondary or tertiary amine having a boiling point of 50 ° C. or higher and 250 ° C. or lower.
[8]
The coating material according to any one of [2] to [7], wherein the neutralization rate of the acid group of the sulfonic acid (C) by the amine compound (D) is 300% or more and 3,000% or less. Composition.
[9]
The aggregate (E) is any of [2] to [8], which comprises at least one selected from the group consisting of acrylic resin particles, glass beads, acrylonitrile resin particles, urea resin particles, ceramic fibers and silica particles. The coating composition according to one.
[10]
The aggregate (E) contains at least one selected from the group consisting of acrylic resin particles, urea resin particles and silica particles.
The coating composition according to any one of [2] to [9], wherein the silica particles have a particle size of 1 μm or more and 20 μm or less.
[11]
A coated steel sheet having a coating film on the surface of a steel sheet and at least one of the steel sheets.
The coating film is formed of a coating composition containing at least a coating film forming resin (A) and a cross-linking agent (B).
The arithmetic mean height (Ra) on the surface of the coating film is 1.2 μm or more, and the developed area ratio (Sdr) is 800% or more.
A painted steel sheet characterized by being.
[12]
A coated steel sheet having a coating film on the surface of a steel sheet and at least one of the steel sheets.
The coating film is formed from the coating composition according to any one of [1] to [10].
The arithmetic mean height (Ra) on the surface of the coating film is 1.2 μm or more, and the developed area ratio (Sdr) is 800% or more.
A painted steel sheet characterized by being.
[13]
A coating step of applying the coating composition according to any one of [1] to [10] to an object to be coated, and drying and / or drying the coating composition after coating at a temperature of 150 ° C. or higher and 270 ° C. or lower. Including curing,
A method for manufacturing a coating film.

The coating composition of the present disclosure can contribute to the formation of a coating film having low gloss and high weather resistance.

Hereinafter, the coating composition of the present disclosure will be described.

The coating composition of the present disclosure contains at least a coating film forming resin (A) and a cross-linking agent (B).
The surface of the coating film obtained by curing the coating composition is characterized by having an arithmetic mean height (Ra) of 1.2 μm or more and a developed area ratio (Sdr) of 800% or more.
By using the coating composition of the present disclosure, the coating film obtained by curing the coating composition of the present disclosure has low gloss and good weather resistance. This should not be construed in a specific theory, but it can be thought of as follows. The coating film formed by the coating composition of the present disclosure has an uneven structure having a specific arithmetic mean height (Ra) and a developed area ratio (Sdr) on the surface thereof. Since the surface area of such a coating film increases, it is considered that the amount of ultraviolet rays received per unit area decreases, and as a result, deterioration of the coating film can be suppressed. Further, when the coating film formed from the coating composition of the present disclosure is used for a building member or the like, the time of irradiation with ultraviolet rays can be shortened, and as a result, deterioration of the coating film can be suppressed. It is considered that this is because the coating film has an uneven structure, so that the portion directly irradiated with the sun at one time is not directly irradiated with the sun at another time. Further, since the surface of the coating film has an uneven structure, diffused reflection of light occurs on the surface of the coating film, and as a result, the gloss of the coating film can be reduced, and the light is scattered to cause light to the inside of the coating film. It is considered that the incident can be suppressed and the deterioration from the inside of the coating film can be prevented.

The arithmetic mean height (also referred to as "Ra") is a parameter indicating the roughness of the surface of the coating film, and is the average of the absolute values of the height differences of each point with respect to the average surface of the surface of the coating film. show. When Ra is small, it means that the surface of the coating film is flatter, that is, a uniform matte appearance is not sufficiently formed. Ra is measured in accordance with JIS B 0601-2001, and can be measured by, for example, a surface roughness measuring machine HANDYSURF E-35B (manufactured by Tokyo Seimitsu Co., Ltd.).

Ra is 1.2 μm or more, preferably 2.5 μm or more. The upper limit of Ra is preferably 6 μm, more preferably 5 μm. When the obtained coating film has a uniform matte appearance, Ra is a value included in the above range.

The developed area ratio (also referred to as "Sdr") is the surface area (expanded area) that reflects the actual unevenness in the measurement area when measured based on ISO 25178, with respect to the area of the flat surface without unevenness in the measurement area. It is a parameter indicating how much it has increased, and is expressed by the following equation. It can be said that the smaller the Sdr is, the smoother the surface is, and the Sdr of a completely flat surface is 0%. Sdr can be measured by, for example, a laser microscope OPTELICS HYBRID C3 (manufactured by Lasertec).
Expanded area ratio (Sdr) = {(AB) / B} x 100 [%]
A: Surface area (expanded area) that reflects the actual unevenness in the measurement area
B: Area of a flat surface with no unevenness in the measurement area

Sdr is 800% or more, preferably 1,000% or more. The upper limit of Sdr is preferably 3,000%, more preferably 2,500%. When Sdr is within the above range, the resulting coating film has a uniform matte appearance.

On the surface of the coating film obtained by curing the coating composition of the present disclosure, Ra is 1.2 μm or more and Sdr is 800% or more, and this coating film has a more uniform matte appearance and is weather resistant. Excellent.

<Coating film forming resin (A)>
The coating film-forming resin (A) is not particularly limited as long as it has a functional group capable of reacting with the cross-linking agent (B) and has a coating film-forming ability.

Examples of the coating film-forming resin (A) include polyester resin and its modified product (urethane-modified polyester resin, epoxy-modified polyester resin, silicone-modified polyester resin, etc.); acrylic resin and its modified product (silicone-modified acrylic resin, etc.); Urethane resin and its modified products (ester-based urethane resin, ether-based urethane resin, carbonate-based urethane resin, epoxy-based urethane resin, etc.); ; Alchid resin and its modified product (urethane modified alkido resin, acrylic modified alkido resin, etc.); Resins such as fluororesin can be mentioned. Only one kind of these resins may be used alone, or two or more kinds thereof may be used in combination.

In one embodiment, the coating film forming resin (A) contains at least one selected from the group consisting of polyester resin, acrylic resin, urethane resin and modified products thereof. From the viewpoint of ease of forming a matte appearance and high weather resistance of the formed coating film, the coating film forming resin (A) is composed of a group consisting of polyester resin, acrylic resin, urethane resin and modified products thereof. It is preferable to include at least one selected.

In one embodiment, the coating film forming resin (A) may contain at least one selected from the group consisting of polyester resin, acrylic resin, and modified products thereof.

Preferably, the coating film-forming resin (A) is a resin having a hydroxyl group, and contains at least one selected from the group consisting of polyester resin, acrylic resin, urethane resin, and modified products thereof. From the viewpoint of processability and weather resistance of the coating film, a polyester resin having a hydroxyl group is preferable.

In one embodiment, the hydroxyl value (also referred to as “OHV”) of the coating film-forming resin (A) may be, for example, 5 mgKOH / g or more and 200 mgKOH / g or less, and 5 mgKOH / g or more and 150 mgKOH / g or less. There may be. By using such a coating film-forming resin (A), it is possible to obtain a coating film having an excellent coating film appearance and excellent weather resistance. In the present disclosure, the hydroxyl value is a value measured by a method based on JIS K 0070.
When the coating composition of the present disclosure contains a plurality of types of coating film-forming resin (A), it is preferable that the hydroxyl value of all the coating film-forming resin (A) is within the above range.
In another aspect, when the coating composition of the present disclosure contains a plurality of types of the coating film-forming resin (A), the average value of the hydroxyl values of the coating film-forming resin (A) may be included in the above range.

The coating film-forming resin (A) can have a number average molecular weight of 1,000 or more and 40,000 or less.
When the number average molecular weight is within such a range, it becomes easy to obtain a uniform matte appearance without a feeling of white blur. In the present disclosure, the number average molecular weight (Mn) is a value measured by gel permeation chromatography (GPC) and determined by polystyrene conversion.

The coating film-forming resin (A) has a resin solid content of 50 parts by mass with respect to a total of 100 parts by mass of the resin solids of the coating film-forming resin (A) and the cross-linking agent (B) in the coating composition of the present disclosure. It may be contained in an amount of 95 parts by mass or less. When the content of the coating film forming resin (A) is within the above range, a coating film having a uniform matte appearance can be obtained from the coating composition, and there is an advantage that the processability is also excellent.

(Polyester resin)
In one embodiment, the hydroxyl value of the polyester resin may be, for example, 5 mgKOH / g or more and 200 mgKOH / g or less, or 5 mgKOH / g or more and 150 mgKOH / g or less. When the hydroxyl value is within the above range, there is an advantage that the workability and weather resistance of the obtained coating film are excellent.

The number average molecular weight (Mn) of the polyester resin, for example, the hydroxyl group-containing polyester resin which is a modified product thereof, is preferably 1,000 or more and 40,000 or less, and more preferably 2,000 or more and 40,000 or less. It is preferable, and it is particularly preferable that it is 2,000 or more and 30,000 or less. In the present disclosure, unless otherwise specified, when the term "polyester resin" is simply used, it means that the polyester resin and at least one selected from the group consisting of modified products of the polyester resin are included.
When the polyester resin has such a number average molecular weight, the cross-linking reaction between the polyester resin and the cross-linking agent (B) proceeds sufficiently, and a coating film having high moisture resistance can be formed. Further, by having the polyester resin having a number average molecular weight as described above, it is possible to suppress the crosslink density of the formed coating film from becoming too high, and it is possible to form a coating film having a sufficient elongation rate, for example, sufficient. A coating film having bendability can be formed. Furthermore, by having the polyester resin having a number average molecular weight as described above, the coating composition of the present disclosure can have an appropriate viscosity and can be handled well.

The glass transition temperature (Tg) of the polyester resin is preferably −35 ° C. or higher and 110 ° C. or lower, for example, −30 ° C. or higher and 80 ° C. or lower, and −30 ° C. or higher and 60 ° C. or lower.
When the glass transition temperature (Tg) of the polyester resin is within the above range, the moisture permeability of the formed coating film does not become excessively high, and the moisture resistance of the coating film becomes sufficient.

The solid acid value of the polyester resin (including its modified product) is 0.1 mgKOH / g or more and 30 mgKOH / g or less, for example, 0.2 mgKOH / g or more and 30 mgKOH / g or less, and 0.3 mgKOH / g or more. It may be 30 mgKOH / g or less.
When the solid content acid value is in such a range, for example, hydrolysis resistance can be improved and a coating film having moisture resistance can be formed.

The polyester resin can be obtained by polycondensation of a polyhydric alcohol and a polybasic acid.
Specific examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, neopentyl glycol, 1,2-butanediol, 1,3-butanediol, and 2,3. -Butandiol or 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, hydrogenated bisphenol A, hydroxyalkylated bisphenol A, 1,4-cyclohexanedimethanol, 2,2-dimethyl- 3-Hydroxypropyl-2,2-dimethyl-3-hydroxypropionate (BASHPN), N, N-bis- (2-hydroxyethyl) dimethyl hydantin, polycaprolactone polyol, glycerin, sorbitol, annitol, trimethylolethane, Examples thereof include trimethylolpropane, trimethylolbutane, hexanetriol, pentaerythritol, dipentaerythritol, tris- (hydroxyethyl) isocyanate and the like. Only one type of polyhydric alcohol may be used alone, or two or more types may be used in combination.
Specific examples of the polybasic acid include, for example, phthalic acid, phthalic anhydride, tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrochloride phthalic acid, methyltetraphthalic acid, methyltetrahydrochloride phthalic acid, and hymic anhydride. Acid, trimellitic acid, trimellitic anhydride, pyromellitic acid, pyromellitic anhydride, isophthalic acid, terephthalic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, adipic acid, azelaic acid, sebacic acid, succinic acid , Dodecenyl succinic acid, lactic acid, dodecenyl succinic acid, dodecenyl anhydrous succinic acid, cyclohexane-1,4-dicarboxylic acid, endohydrate anhydride and the like. Only one type of polybasic acid may be used alone, or two or more types may be used in combination.

Examples of the modified polyester resin include modified polyester resins such as urethane-modified polyester resin, epoxy-modified polyester resin, acrylic-modified polyester resin, and silicone-modified polyester resin. For example, the urethane-modified polyester resin is a resin having polyester in the main chain and having its ends modified with isocyanate to be urethane-modified. For example, a silicone-modified polyester resin may be taken as an example of a polyester resin and an organic silicone (for example, an organic having a number average molecular weight of about 300 or more and 1,000 or less having ₃ -SiOCH groups and / or -SiOH groups as functional groups. It can be prepared by reacting with silicone). The amount of the organic silicone used is usually about 5 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the polyester resin. Further, taking a urethane-modified polyester resin as an example, this can be prepared by reacting the polyester resin with a polyisocyanate compound.
Commercially available products may be used as the polyester resin and the modified product of the hydroxyl group-containing polyester resin. Examples of commercially available products include Beckolite 46-118, Beckolite M-6205-50, Beckolite M-6401-52, Beckolite M-6402-50 (all manufactured by DIC Corporation), Byron 220, and Byron UR3500. Examples thereof include Byron UR5537, Byron UR8300, Byron UR4410, Byron GK13CS (all manufactured by Toyobo Corporation) and the like.

(acrylic resin)
In one embodiment, the hydroxyl value of the acrylic resin may be, for example, 5 mgKOH / g or more and 250 mgKOH / g or less, 5 mgKOH / g or more and 100 mgKOH / g or less, for example, 5 mgKOH / g or more and 70 mgKOH / g. It may be less than or equal to g.

The number average molecular weight (Mn) of the acrylic resin and its modified product is preferably 1,000 or more and 40,000 or less. In the present disclosure, unless otherwise specified, when the term "acrylic resin" is simply used, it means that it contains at least one selected from the group consisting of acrylic resin and modified products of acrylic resin.
When the acrylic resin has such a number average molecular weight, the cross-linking reaction between the acrylic resin and the cross-linking agent (B) proceeds sufficiently, and a coating film having high moisture resistance can be formed. Further, by using the acrylic resin having a number average molecular weight as described above, it is possible to suppress the crosslink density of the formed coating film from becoming too high, and it is possible to form a coating film having a sufficient elongation rate, for example, sufficient. A coating film having bendability can be formed. Furthermore, by using an acrylic resin having a number average molecular weight as described above, the coating composition of the present disclosure can have an appropriate viscosity and can be handled well.

The glass transition temperature (Tg) of the acrylic resin is preferably −35 ° C. or higher and 110 ° C. or lower, for example, −30 ° C. or higher and 80 ° C. or lower, and −30 ° C. or higher and 60 ° C. or lower.
When the glass transition temperature (Tg) of the acrylic resin is within the above range, the moisture permeability of the coating film does not become excessively high, and the moisture resistance of the coating film becomes sufficient.

The solid acid value of the acrylic resin (including its modified product) may be, for example, 0.1 mgKOH / g or more and 30 mgKOH / g or less.
When the solid content acid value is in such a range, for example, hydrolysis resistance can be improved and a coating film having moisture resistance can be formed.

The acrylic resin has a hydroxyl group such as hydroxymethyl (meth) acrylate, hydroxylethyl (meth) acrylate, hydroxylpropyl (meth) acrylate, hydroxybutyl (meth) acrylate, and N-methylolacrylamide (. From one or more monomers selected from (meth) acrylic monomers and lactone adducts thereof; (meth) acrylic acid; (meth) acrylic acid esters such as alkyl (meth) acrylic acid; (meth) acrylonitrile and the like. Acrylic resin can be mentioned. In addition to the structural units derived from the above-mentioned monomers, the acrylic resin can be used for other monomers (for example, carboxyl group-containing ethylenic monomers such as crotonic acid, itaconic acid, fumaric acid, and maleic acid, vinyl-based monomers such as styrene, etc.). It may contain the building blocks from which it is derived. In the present disclosure, (meth) acrylic acid represents acrylic acid or methacrylic acid.
Examples of the modified acrylic resin include modified acrylic resins such as silicone-modified acrylic resins. For example, taking a silicone-modified acrylic resin as an example, this can be prepared by reacting the acrylic resin with the organic silicone as described above. The amount of the organic silicone used is usually about 5 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the acrylic resin.

As the acrylic resin and its modified product, a commercially available product may be used. Examples of commercially available products include Acridic WSG-806 (manufactured by DIC Corporation), Cotax SA-105 (manufactured by Toray Fine Chemical Corporation), and the like.

(Urethane resin)
In one embodiment, the urethane resin has a hydroxyl group. In this embodiment, the hydroxyl value of the urethane resin may be, for example, 5 mgKOH / g or more and 250 mgKOH / g or less, 5 mgKOH / g or more and 100 mgKOH / g or less, for example, 5 mgKOH / g or more and 70 mgKOH / g. It may be less than or equal to g.

The number average molecular weight (Mn) of the urethane resin and the modified urethane resin is 1,000 or more and 30,000 or less, for example, 2,000 or more and 28,000 or less, and 2,500 or more and 25,000 or less. good. In one embodiment, the number average molecular weight (Mn) of the urethane resin and the modified urethane resin is 6,000 or more and 15,000 or less. Unless otherwise specified in the present disclosure, the term "urethane resin" simply means that it contains at least one selected from the group consisting of urethane resin and modified products of urethane resin.
When the urethane resin has such a number average molecular weight, it is possible to suppress the crosslink density of the formed coating film from becoming too high, and it is possible to form a coating film having a sufficient elongation rate, for example, sufficient bending workability. Can form a coating film having. Furthermore, by using the urethane resin having a number average molecular weight as described above, the coating composition of the present disclosure can have an appropriate viscosity and can be handled well.

In one embodiment, the glass transition temperature (Tg) of the urethane resin can be −30 ° C. or higher and 80 ° C. or lower, for example, −30 ° C. or higher and 60 ° C. or lower, and −30 ° C. or higher and 50 ° C. or lower. ..
When the glass transition temperature (Tg) of the urethane resin is within the above range, the moisture permeability of the coating film does not become excessively high, and the moisture resistance of the coating film becomes sufficient.

The solid acid value of the urethane resin (including its modified product) is 0.1 mgKOH / g or more and 30 mgKOH / g or less, for example, 0.2 mgKOH / g or more and 30 mgKOH / g or less, and 0.3 mgKOH / g or more. It may be 30 mgKOH / g or less.
When the solid content acid value is in such a range, for example, hydrolysis resistance can be improved and a coating film having moisture resistance can be formed.

Examples of the urethane resin include those obtained by reacting a polyol compound with a polyisocyanate compound and then further chain-extending with a chain extender.
The polyol compound is not particularly limited as long as it is a compound containing two or more hydroxyl groups per molecule, and for example, ethylene glycol, propylene glycol, diethylene glycol, 1,6-hexanediol, neopentyl glycol, and triethylene glycol. , Polyether polyols such as glycerin, trimethylolethane, trimethylolpropane, polycarbonate polyols, polyester polyols, bisphenol hydroxypropyl ethers, polyesteramide polyols, acrylic polyols, polyurethane polyols, or mixtures thereof.
The polyisocyanate compound is not particularly limited as long as it is a compound containing two or more isocyanate groups per molecule, and for example, an aliphatic isocyanate such as hexamethylene diisocyanate (HDI) and an alicyclic such as isophorone diisocyanate (IPDI). Examples thereof include aromatic diisocyanates such as group diisocyanate and tolylene diisocyanate (TDI), aromatic aliphatic diisocyanates such as diphenylmethane diisocyanate (MDI), and mixtures thereof.
The chain extender is not particularly limited as long as it is a compound containing one or more active hydrogens in the molecule, and water or an amine compound can be applied. Examples of the amine compound include aliphatic polyamines such as ethylenediamine, propylenediamine, hexamethylenediamine, diethylenetriamine, dipropylenetriamine, triethylenetetramine and tetraethylenepentamine, and aromatic polyamines such as tolylene diamine, xylylene diamine and diaminodiphenylmethane. , Alicyclic polyamines such as diaminocyclohexylmethane, piperazine, 2,5-dimethylpiperazine and isophoronediamine, hydrazines such as hydrazine, dihydrazide succinate, dihydrazide adipate, dihydrazide phthalate, hydroxyethyldiethylenetriamine, 2- [(2-Aminoethyl) amino] Examples thereof include alkanolamines such as ethanol and 3-aminopropanediol.

In one embodiment, an ester-based urethane resin, an ether-based urethane resin, and a carbonate-based urethane resin may be used as the urethane resin.

<Crosslinking agent (B)>
The cross-linking agent (B) reacts with the coating film-forming resin (A) to form a cured coating film.

Examples of the cross-linking agent (B) include a polyisocyanate compound; a blocked polyisocyanate compound (also referred to as “BI”) in which the isocyanate group of the polyisocyanate compound is blocked with an active hydrogen-containing compound; an amino resin; a phenol resin and the like. ..

The content (resin solid content) of the cross-linking agent (B) may be 5 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the resin solid content of the coating film forming resin (A). It may be 70 parts by mass or less, 10 parts by mass or more and 40 parts by mass or less, or 10 parts by mass or more and 30 parts by mass or less.
By containing the above-mentioned amount of the cross-linking agent (B), the cross-linking reaction between the coating film-forming resin (A) and the cross-linking agent (B) proceeds satisfactorily, the appearance of the obtained coating film becomes good, and a uniform matte appearance is obtained. Is obtained. In addition, the processability and corrosion resistance of the obtained coating film can be improved.

In one embodiment, the cross-linking agent (B) is an amino resin. The amino resin is excellent in cross-linking reactivity with the coating film-forming resin (A) even under a non-catalyst, and is preferable from the viewpoint of easy formation of a uniform matte appearance.

Examples of the amino resin include melamine resin and urea resin, and among these, melamine resin is preferable.
The amino resin (for example, melamine resin) has excellent cross-linking reactivity with the coating film forming resin (A), the appearance of the obtained coating film is particularly good, and a uniform matte appearance can be obtained. In addition, the processability and corrosion resistance of the obtained coating film can be improved.

"Melamine resin" generally means a thermosetting resin synthesized from melamine and aldehyde, and has a triazine nucleus and three reactive functional groups-NX ¹ X ² per triazine nucleus. ing. The melamine resin is a fully alkylated type containing -N (CH ₂ OR) ₂ [R indicates an alkyl group having 1 or more and 8 or less carbon atoms, the same applies hereinafter] as a reactive functional group; -N as a reactive functional group. Methylol group containing (CH ₂ OR) (CH ₂ OH); imino group containing -N (CH ₂ OR) (H) as reactive functional group; -N (CH ₂ OR) as reactive functional group Four types of methylol / imino group types containing (CH ₂ OH) and —N (CH ₂ OR) (H) or containing —N (CH ₂ OH) (H) can be exemplified.
Among the above melamine resins, it is preferable to use a completely alkylated melamine resin, and examples of such a resin include methylated melamine resin, butylated melamine resin, methyl and butyl mixed melamine resin, isobutylated melamine resin and the like. Among these, methylated melamine resin, butylated melamine resin, methyl and butyl mixed type melamine resin are preferable.

A commercially available product may be used as the melamine resin. Examples of commercially available products include Cymel 303, Cymel 254, Cymel 1170, Cymel 235, Cymel 238, Cymel 1123, Mycoat 715 (all manufactured by Dicel Ornex), Sumimar M-40S (manufactured by Sumitomo Chemicals), and Supermarket. Examples thereof include Beccamin J-820-60, Super Beccamin L-121-60, (all manufactured by DIC Corporation), Uban 20SE-60 (manufactured by Mitsui Chemicals, Inc.) and the like.
The above-mentioned melamine resin may be used alone or in combination of two or more. In some embodiments, the melamine resin and the polyisocyanate compound may be used in combination. Further, if necessary, a metal catalyst such as a tin compound or a titanium compound may be used.

The coating composition of the present disclosure may further include a sulfonic acid (C), an amine compound (D) and an aggregate (E).

<Sulfonic acid (C)>
The sulfonic acid (C) is a catalyst that promotes the reaction between the coating film-forming resin (A) and the cross-linking agent (B), and the reaction time can be shortened by adding the sulfonic acid (C). Further, the sulfonic acid (C) and the amine compound (D) can form a salt. The salt of the sulfonic acid (C) and the amine compound (D) has the effect of increasing the difference between the surface curing and the internal curing of the coating film formed from the coating composition, and as a result, the uniformity is high and white blurring occurs. It is possible to form a matte coating film with a small amount of.

The content of the sulfonic acid (C) is preferably 1.0 part by mass or more and 18.0 parts by mass or less, more preferably 2.0 parts by mass, with respect to 100 parts by mass of the resin solid content of the coating film forming resin (A). It may be 15.0 parts by mass or less, and may be, for example, 2.0 parts by mass or more and 9.0 parts by mass or less.
When the content of the sulfonic acid (C) is within the above range, there is an advantage that a matte coating film having high uniformity and less white blur can be obtained, and the obtained coating film has excellent chemical resistance. ..

Examples of the sulfonic acid include paratoluene sulfonic acid, dodecylbenzene sulfonic acid, dinonylnaphthalenedisulfonic acid, methanesulfonic acid, dinonylnaphthalenesulfonic acid and the like, and one of these may be used alone or 2 Seeds or more may be used together.

<Amine compound (D)>
The amine compound (D) is present to contribute to the neutralization of the sulfonic acid (C), and at least a part thereof may be present as a salt with the sulfonic acid (C) in the coating composition of the present disclosure. The amine compound (D) contributes to forming a uniform matte coating film.

The amine compound (D) is preferably a secondary or tertiary amine having a boiling point of 50 ° C. or higher and 250 ° C. or lower. The secondary or tertiary amine having a boiling point of 50 ° C. or higher and 250 ° C. or lower is not particularly limited, and for example, diethylamine, di-n-propylamine, diisopropylamine, diisobutylamine, di-n-butylamine, diamilamine, diallylamine, di. -Sec-butylamine, N-ethyl-1,2-dimethylpropylamine, N-methylhexylamine, di-n-octylamine, piperidine, 2-pipecholine, 3-pipecholine, 4-pipecholine, 2,4-lupetidine, 2,6-Lupetidine, 3,5-Lupetidine, 3-piperidinmethanol, triethylamine, tributylamine, triallylamine, N, N-dimethylethanolamine, N-methyldiallylamine, pyridine, N, N-dimethylallylamine, N-methyl Examples thereof include piperidine, 4-ethylpyridine, N-methylpiperazine, N-methylmorpholin and the like. These may be used alone or in combination of two or more. The amine compound (D) is more preferably a secondary or tertiary amine having a boiling point of 70 ° C. or higher and 220 ° C. or lower.

In one embodiment, the amine compound (D) is added to the coating composition of the present disclosure so that the neutralization rate of the acid group of the sulfonic acid (C) is preferably 300% or more, more preferably 320% or more. be able to. The amine compound (D) can be added so that the neutralization rate of the acid group of the sulfonic acid (C) is 3,000% or less, for example, 2,000% or less, specifically 1,600% or less. , More specifically, it can be added so as to be 1,500% or less, and more specifically, 550% or less. Here, the neutralization rate means the amount of the base of the amine compound (D) (mol%) with respect to the amount of the acid group of the sulfonic acid (C) of 100 mol%. The unit of the neutralization rate may be simply described as "%".
Although not limited to a specific theory, the neutralization rate in the above range causes the amine compound (D) to volatilize when the coating composition is baked, and at this time, the amine compound ( It is considered that the sulfonic acid (C) as a counter for the base of D) migrates to the surface layer of the formed film and is concentrated. By concentrating the sulfonic acid (C) on the surface layer in this way, the curing reaction on the surface layer is promoted, and as a result, the unevenness of the coating film surface is formed better, and the matte appearance coating film is easily formed. Conceivable.

The sulfonic acid (C) and the amine compound (D) may be blended in the coating composition as a mixture previously formed by mixing at 20 to 30 ° C. for 10 to 20 minutes. At this time, the mixture may contain a salt of the sulfonic acid (C) and the amine compound (D) (for example, a sulfonic acid obtained by blocking the sulfonic acid with a secondary or tertiary amine).
In another embodiment, a reaction product of the sulfonic acid (C) and the amine compound (D), for example, a commercially available blocked sulfonic acid compound in which the sulfonic acid is blocked with a secondary or tertiary amine is blended in the coating composition. You may. In this case, the amine compound (D) can be added together. Examples of commercially available blocked sulfonic acid compounds include dinonylnaphthalenedisulfonic acid, methanesulfonic acid, dinonylnaphthalenesulfonic acid, and amine-blocked compounds thereof.
Further, the sulfonic acid (C) and the amine compound (D) may be added to the coating composition and mixed at 20 to 30 ° C. for 10 to 20 minutes, for example.

When a salt of the sulfonic acid (C) and the amine compound (D) is added, the content of the salt is 1.0 in terms of sulfonic acid with respect to 100 parts by mass of the resin solid content of the coating film forming resin (A). It is preferably 23.0 parts by mass or more, and more preferably 2.0 parts by mass or more and 19.0 parts by mass or less.
In the present disclosure, when a compound such as a salt of the sulfonic acid (C) and the amine compound (D) is used, the content means an amount in terms of sulfonic acid.

In one embodiment, the content of the sulfonic acid (C) is 1 part by mass or more and 18 parts by mass or less with respect to 100 parts by mass of the resin solid content of the coating film-forming resin (A), and the amine (D). The neutralization rate of the above is preferably in the range of 300% or more and 3,000% or less, the content of the sulfonic acid (C) is 2 parts by mass or more and 15 parts by mass or less, and the amine (D) is neutralized. The rate is more preferably in the range of 320% or more and 2,000% or less, the content of the sulfonic acid (C) is 2 parts by mass or more and 15 parts by mass or less, and the neutralization rate of the amine (D) is 320. It is more preferably in the range of% or more and 1,500% or less. When the coating composition has the above-mentioned sulfonic acid (C) content and neutralization rate, the Ra and Sdr values on the surface of the formed coating film can be particularly good. Further, by using the coating composition as described above, a coating film having a matte appearance, low gloss and high weather resistance can be formed.

<Aggregate (E)>
By containing the aggregate (E), a matte coating film having high uniformity and less white blur can be stably developed in the coating film formed from the coating composition of the present disclosure.

The aggregate (E) may be added by 0.1 part by mass or more and 15 parts by mass or less with respect to 100 parts by mass of the resin solid content of the coating film forming resin (A) by adding 2 parts by mass or more and 12 parts by mass or less. May be good.
By adding the aggregate (E) in the above range, a uniform matte coating film can be developed particularly stably.

In one embodiment, the aggregate (E) comprises at least one selected from the group consisting of acrylic resin particles, glass beads, acrylonitrile resin particles, urea resin particles, ceramic fibers and silica particles, and includes acrylic resin particles and urea. It preferably contains at least one selected from the group consisting of resin particles and silica particles, and more preferably contains silica particles.
By including the aggregate (E) of this embodiment, a uniform matte coating film can be stably expressed in the coating film obtained from the coating composition of the present disclosure.

(Silica particles)
In one embodiment, the aggregate (E) is silica particles.
The average particle size of the silica particles may be preferably 1 μm or more and 20 μm or less, more preferably 2 μm or more and 17 μm or less, for example, 2 μm or more and 15 μm or less, and 2.5 μm or more and 15 μm or less. In the present disclosure, the average particle size of the aggregate (E) refers to the volume average particle size (D50) obtained by a normal measuring device using a laser scattering method, a diffraction method, or the like, and is, for example, a laser. The measurement can be performed using a diffraction type particle size distribution measuring device SALD-2300 (manufactured by Shimadzu Corporation) or the like.

The content of the silica particles may be 0.1 part by mass or more and 15 parts by mass or less with respect to 100 parts by mass of the resin solid content of the coating film forming resin (A), and may be 2 parts by mass or more and 12 parts by mass or less. There may be. When the content of the silica particles is within the above range, the obtained coating film can have a more uniform matte appearance.

The silica particles are not particularly limited, but may be produced by either a wet method or a dry method. Examples of the silica particles include silica particles whose surface is untreated, silica particles whose surface is treated with an organic substance, and organic solvent-dispersible colloidal silica.

Commercially available products may be used as the silica particles. Commercially available products include Siricia 710, Siricia 740, Siricia 550 (all manufactured by Fuji Silysia Chemical Ltd.), Mizukasil P-73 (manufactured by Mizusawa Industrial Chemical Ltd.), Nip Seal E-200A, and Nip Gel AZ-6A0 (all manufactured by Tosoh). (Silysia), GASIC HP270, GASIC HP395 (all manufactured by PQ Corporation) and the like can be mentioned.

(Acrylic resin particles)
In one embodiment, the aggregate (E) is acrylic resin particles.
The average particle size of the acrylic resin particles is preferably 1 μm or more and 20 μm or less, and may be, for example, 2 μm or more and 15 μm or less, 2.5 μm or more and 15 μm or less, or 5 μm or more and 10 μm or less.

The content of the acrylic resin particles may be 0.1 part by mass or more and 15 parts by mass or less with respect to 100 parts by mass of the resin solid content of the coating film forming resin (A), and is 2 parts by mass or more and 12 parts by mass or less. May be. When the content of the acrylic resin particles is within the above range, a uniform matte appearance can be formed.

Commercially available products may be used as the acrylic resin particles. Examples of commercially available products include Ganz Pearl GM-0801 (manufactured by Aica Kogyo Co., Ltd.).

(Urea resin particles)
In one embodiment, the aggregate (E) is urea resin particles.
The average particle size of the urea resin particles is preferably 1 μm or more and 20 μm or less, and may be, for example, 2 μm or more and 15 μm or less, and 2.5 μm or more and 15 μm or less.

The content of the urea resin particles may be 0.1 part by mass or more and 15 parts by mass or less with respect to 100 parts by mass of the resin solid content of the coating film forming resin (A), and is 2 parts by mass or more and 12 parts by mass or less. May be. When the content of the urea resin particles is within the above range, a more uniform matte appearance can be formed.

Commercially available products may be used as the urea resin particles. Examples of commercially available products include Pergopack M4 (manufactured by Lonza Japan) and the like.

In one embodiment, the sulfonic acid (C) is 1.0 part by mass or more and 18.0 part by mass or less (specifically, 2.0 part by mass) with respect to 100 parts by mass of the resin solid content of the coating film forming resin (A). (Parts or more and 9.0 parts by mass or less), the neutralization rate of the amine compound (D) is 300% or more and 3,000% or less (specifically, 300% or more and 1,500% or less, for example, 550% or less), bone. The material (E) may be added in an amount of 2 parts by mass or more and 12 parts by mass or less. In this embodiment, it is preferable to use sulfonic acid as the sulfonic acid (C), secondary or tertiary amine as the amine compound (D), and silica particles or acrylic resin particles as the aggregate (E). ..

<Other additives>
In the coating composition of the present disclosure, a thermoplastic resin can be further used in addition to the coating film forming resin (A).
Examples of the thermoplastic resin include chlorinated olefin resins such as chlorinated polyethylene and chlorinated polypropylene; homopolymers or copolymers containing vinyl chloride, vinyl acetate, vinylidene chloride and the like as monomer components; cellulose resins; acetal resins. Alexandre resin; Rubber chloride resin; Modified polypropylene resin (acid anhydride-modified polypropylene resin, etc.); Fluorine resin (for example, vinylidene fluoride resin, vinyl fluoride resin, copolymer of fluorinated olefin and vinyl ether, fluorination A copolymer of an olefin and a vinyl ester) and the like can be mentioned. As the thermoplastic resin, only one kind may be used alone, or two or more kinds may be used in combination.
By using the thermoplastic resin in combination, it is possible to obtain better coating film physical characteristics, for example, better coating film strength, elongation, etc. in the formed coating film.

The coating composition of the present disclosure may further contain other additives. Other additives include, for example, surface conditioners; extender pigments; coloring pigments, coloring agents such as dyes; waxes; heat-shielding pigments; brilliant pigments; solvents; ultraviolet absorbers (benzophenone-based ultraviolet absorbers, etc.); oxidation. Inhibitors (phenolic, sulfoid, hindered amine antioxidants, etc.); Plastics; Coupling agents (silane, titanium, zirconium couplings, etc.); Anti-sagging agents; Thickeners; Pigment dispersants; Pigment wetting agents; leveling agents; color separation inhibitors; precipitation inhibitors; antifoaming agents; antifreeze agents; emulsifiers; preservatives; antifungal agents; antibacterial agents; stabilizers and the like. These additives may be used alone or in combination of two or more.

As the surface conditioner, those well known to those skilled in the art for paints can be used.
Preferred surface conditioners include acrylic, silicone and fluorine-based surfactants. These may be used alone or in combination of two or more.
The matte appearance coating film is formed because the curing reaction of the surface layer portion of the coating film is fast, but the fluidity of the layer (also referred to as “lower layer portion”) existing on the inner surface side of the surface layer portion of the coating film is large. If it is too much, poor appearance such as circular gloss unevenness and cracked skin may occur. By adding a surface conditioner to the coating composition, the fluidity of the lower layer portion is suppressed to an appropriate state while maintaining the reaction temperature difference between the upper and lower layers of the coating film, and the appearance deterioration of the above coating film is suppressed and uniform. It can contribute to the formation of shrunken skin.
The content of the surface adjusting agent is, for example, 0.5 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the resin solid content of the coating film forming resin (A).
As the surface conditioner, for example, Disparon OX-70 (manufactured by Kusumoto Kasei Co., Ltd.) can be mentioned.

Examples of the extender pigment include calcium carbonate, barium sulfate, clay, talc, mica, glass fiber and the like. These may be used alone or in combination of two or more. In one embodiment, the content of the extender pigment is 1 part by mass or more and 40 parts by mass or less with respect to 100 parts by mass of the resin solid content of the coating film forming resin (A), for example, 10 parts by mass or more and 30 parts by mass or less. Is. When the amount of the extender pigment is within such a range, there is an advantageous effect such as improving the scratch resistance of the coating film.

Colored pigments include, for example, colored inorganic pigments such as titanium dioxide, carbon black, graphite, iron oxide, and cold dust; phthalocyanine blue, phthalocyanine green, quinacridone, perylene, anthrapyrimidine, carbazole violet, anthrapyridine, azoorange, and flavanthrone. Colored organic pigments such as yellow, isoindrin yellow, azo yellow, induthron blue, dibrom anzaslon red, perylene red, azo red, anthraquinone red; aluminum powder, alumina powder, bronze powder, copper powder, tin powder, zinc powder, Examples thereof include iron phosphate and atomized titanium. These may be used alone or in combination of two or more.

The heat-shielding pigment includes an inorganic heat-shielding pigment and / or an organic heat-shielding pigment.
Examples of the inorganic heat-shielding pigment include titanium oxide, magnesium oxide, barium oxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, indium oxide, sodium titanate, silicon oxide, nickel oxide, manganese oxide, and chromium oxide. Metal oxide pigments such as iron oxide, copper oxide, cerium oxide, aluminum oxide; iron oxide-manganese oxide, iron oxide-chromium oxide (for example, Daipiroxide Color Black # 9595 manufactured by Dainichi Seika Co., Ltd., Asahi Kasei Kogyo Co., Ltd. Black 6350), Iron Oxide-Cobalt Oxide-Chrome Oxide (eg, Dipiroxide Color Brown # 9290, Dipiroxide Color Black # 9590), Copper Oxide-Magnetic Oxide (eg, Dainichisei). Composite oxidation of manganese oxide-bismuth oxide (for example, Black6301 manufactured by Asahi Kasei Kogyo Co., Ltd.), manganese oxide-ittrium oxide (for example, Black6303 manufactured by Asahi Kasei Kogyo Co., Ltd.), etc. Material pigments; Metallic pigments such as aluminum, iron, magnesium, manganese, nickel, titanium, chromium and calcium; Further, alloy pigments such as iron-chromium, bismuth-manganese, iron-manganese and manganese-ittrium can be mentioned. These can be used alone or in combination of two or more.
Examples of the organic heat-shielding pigment include azo pigments, azomethine pigments, lake pigments, thioindigo pigments, and anthraquinone pigments (anthanthrone pigments, diaminoanthracinyl pigments, indanslon pigments, flavanthron pigments, and anthra. (Pyrimidine pigments, etc.), perylene pigments, perinone pigments, diketopyrrolopyrrole pigments, dioxazine pigments, phthalocyanine pigments, quiniphthalone pigments, quinacridone pigments, isoindolin pigments, isoindolinone pigments, etc. Be done. These can be used alone or in combination of two or more.
In the present disclosure, the heat-shielding pigment means light in the near-infrared wavelength range (wavelength: 780 nm to 2,500 nm) or light in the near-infrared wavelength range (wavelength: 780 nm to 2,500 nm). Indicates a pigment having a small absorption rate.

Examples of the brilliant pigment include aluminum foil, bronze foil, tin foil, gold leaf, silver foil, titanium metal foil, stainless steel foil, alloy foil such as nickel and copper, and foil pigment such as foil-like phthalocyanine blue. .. These may be used alone or in combination of two or more.

As the wax, waxes known to those skilled in the art for paints can be used, and examples thereof include microcrystallin, polyethylene, polypropylene, paraffin, carnauba and modified products thereof.

Examples of the solvent include water; ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol monobutyl ether, triethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, and the like. Glycol-based organic solvents such as dipropylene glycol monoethyl ether and propylene glycol monomethyl ether acetate; alcohol-based organic solvents such as methanol, ethanol, isopropyl alcohol and Solfit (manufactured by Claret); ether-based organic solvents such as dioxane and tetrahydrofuran; Ether-based organic solvents such as 3-methoxybutyl acetate, ethyl acetate, isopropyl acetate, butyl acetate; ketone-based organic solvents such as methyl ethyl ketone, acetone, methyl isobutyl ketone, cyclohexanone, isophorone; and N-methyl-2-pyrrolidone, toluene. , Pentan, iso-pentane, hexane, iso-hexane, cyclohexane, solvent naphtha, mineral spirit, T-SOL 100, T-SOL 150 (all are aromatic hydrocarbon solvents, manufactured by JXTG Energy Co., Ltd.) and the like. can. These may be used alone or in combination of two or more.

The coating composition of the present disclosure may be a water-based coating material or an organic solvent-based coating material.

<Preparation method of paint composition>
The method for preparing the coating composition of the present disclosure is not particularly limited. For example, it can be prepared by selecting and using a mixer such as a sand grind mill, a ball mill, a blender, a paint shaker or a disper, a disperser, a kneader and the like, and mixing each component.

(Applied material)
The object to be coated of the coating composition of the present disclosure is, for example, a galvanized steel sheet, a zinc-aluminum alloy-plated steel sheet, an aluminum alloy-plated steel sheet, or a hot-dip galvanized steel sheet manufactured by a melting method or an electrolytic method. Examples thereof include metal plates such as magnesium alloy plated steel plates, stainless steel plates, and cold-rolled steel plates. In addition to these steel plates or plated steel plates, metal plates such as aluminum plates (including aluminum alloy plates) can also be painted.
The metal plate is preferably surface-treated. Specifically, it is preferable that the metal plate is subjected to a chemical conversion treatment after being subjected to a pretreatment such as an alkaline degreasing treatment, a hot water washing treatment, and a water washing treatment. The chemical conversion treatment may be carried out by a known method, and examples thereof include chromate treatment, non-chromate treatment such as zinc phosphate treatment and the like. The surface treatment can be appropriately selected depending on the steel sheet to be used, but a treatment that does not contain heavy metals is preferable.

<Painted steel plate>
The coated steel sheet of the present disclosure has a steel sheet and a coating film formed from the coating composition of the present disclosure on at least one surface of the steel sheet. The coating composition contains at least a coating film-forming resin (A) and a cross-linking agent (B). On the surface of the coating film, the arithmetic mean height (Ra) is 1.2 μm or more, and the developed area ratio (Sdr) is 800% or more.

The film thickness of the coating film formed from the coating composition is 10 μm or more and 25 μm or less, and in one embodiment, the film thickness is 15 μm or more and 22 μm or less.

In one embodiment, the steel sheet has a coating film formed from the coating composition according to the present disclosure on one surface and a coating film formed from a known coating composition on the other surface. For example, the other surface may have a coating film formed from a known coating composition such as a coating composition containing an epoxy resin.

The coated steel sheet may have an undercoat coating film between the steel sheet and the coating film formed from the coating composition of the present disclosure.
The undercoat paint may be a conventionally known one, and examples thereof include a conventionally known non-chromium-based rust preventive paint.
By having the undercoat coating film, the adhesion and corrosion resistance of the coating film formed from the coating composition of the present disclosure can be enhanced.
In one embodiment, the film thickness of the undercoat coating film is 3 μm or more and 15 μm or less, for example, 5 μm or more and 10 μm or less.

<Manufacturing method of coating film>
The method for producing a coating film of the present disclosure is as follows.
It comprises a step of applying the coating composition of the present disclosure to an object to be coated, and drying and / or curing the coating composition at a temperature of 150 ° C. or higher and 270 ° C. or lower.

It is preferable to apply a chemical conversion treatment such as a phosphate treatment or a chromate treatment to the surface of the object to be coated as a coating base treatment, and then coat the coating composition on the chemical conversion treatment. By coating the coating composition of the present disclosure on the metal plate surface subjected to the chemical conversion treatment in this manner, the adhesion of the coating film to the metal plate surface is improved and the corrosion resistance is also improved. It is also possible to form an undercoat coating film (primer coating film) on the surface of a metal plate that has undergone chemical conversion treatment, and then coat the surface thereof.
The coating film made of the coating composition of the present invention can be formed by applying the coating composition to an object to be coated such as a steel plate and then performing a baking treatment for heating the object to be coated.
The coating composition can be applied to the object to be coated by using a bar coater, a roll coater, a roll curtain coater, a curtain flow coater, a die coater or a spray gun.
The baking method for heating the object to be coated after coating is not particularly limited, but the coating film may be baked by heating means such as hot air heating, infrared heating, induction heating, etc., and the resin may be crosslinked to obtain a cured coating film. can. The baking temperature (the maximum temperature reached by an object to be coated such as a steel sheet) is usually 180 ° C. or higher and 250 ° C. or lower, and the baking time is usually 10 seconds or longer and 200 seconds or lower.
The film thickness (dry film thickness) of the coating film obtained by using the coating composition of the present invention is usually 1 μm or more and 30 μm or less, and for example, in the case of a top coat film, it is preferably 10 μm or more and 25 μm or less.

Hereinafter, the present invention will be described in more detail with reference to Examples. The present invention is not limited to the following examples. In the examples, "parts" and "%" are based on mass unless otherwise specified.

[Coating film forming resin (A)]
As the coating film forming resins (A-1) to (A-6), those prepared as follows were used.

<Preparation of coating film forming resin (A-1)>
In a reaction vessel equipped with a thermometer, condenser and stirrer, 155 parts by mass of neopentyl glycol, 222 parts by mass of 1,6-hexanediol, 50 parts by mass of trimethylolpropane, 441 parts by mass of isophthalic acid, 132 parts by mass of adipic acid and 26 parts by mass of xylene is mixed, the temperature is gradually raised to 230 ° C. in a nitrogen stream, and while distilling off the generated water, the esterification amount reaches 126 parts by mass and the reaction product has a predetermined viscosity. The esterification reaction was carried out (step a1-1). Then, after lowering the temperature of the reaction vessel to 50 ° C., 90 parts by mass of xylene, 379 parts by mass of T-SOL150 and 87 parts by mass of propylene glycol monomethyl ether acetate were mixed (step a1-2) to form a coating resin (A). -1) (Polyester resin 1; solid content concentration: 60% by mass, number average molecular weight: 3,000, hydroxyl value: 55 mgKOH / g) was prepared.

<Preparation of coating film forming resin (A-2)>
The monomer composition of (step a1-1) was changed to 202 parts by mass of neopentyl glycol, 153 parts by mass of 1,6-hexanediol, 66 parts by mass of trimethylolpropane and 579 parts by mass of isophthalic acid (dehydrated amount: 122 parts by mass). The coating film forming resin (A-2) (polyester resin 2; solid content concentration: 60% by mass, number average molecular weight: 2, is the same as the preparation method of the coating film forming resin (A-1). 300, hydroxyl value: 70 mgKOH / g) was prepared.

<Preparation of coating film forming resin (A-3)>
87 parts by mass of xylene, 219 parts by mass of T-SOL150 and 292 parts by mass of propylene glycol monomethyl ether acetate were charged in a reaction vessel equipped with a thermometer, a condenser, a dropping funnel and a stirrer, and the temperature was raised to 130 ° C. under a nitrogen atmosphere. .. To this, a monomer solution consisting of 300 parts by mass of styrene, 61 parts by mass of methyl methacrylate, 510 parts by mass of n-butyl methacrylate, 116 parts by mass of hydroxyethyl methacrylate and 13 parts by mass of acrylic acid, and kayaester O (as an initiator). A starting agent solution consisting of 85 parts by mass of t-butylperoxy2-ethylhexanate (t-butylperoxy2-ethylhexanate) manufactured by Chemical Acid Axo and 92 parts by mass of xylene was added dropwise at a constant rate over 3 hours through a dropping funnel, and then the reaction temperature was adjusted. It was held at 130 ° C. for 30 minutes. Next, an initiator solution consisting of 10 parts by mass of kaya ester O and 40 parts by mass of xylene was added dropwise at a constant velocity in 30 minutes, and then the reaction product was held at 130 ° C. for 2 hours to form a coating resin (A-3). (Acrylic resin 1; solid content concentration: 60% by mass, number average molecular weight: 3,500, hydroxyl value: 45 mgKOH / g) was prepared.

<Preparation of coating film forming resin (A-4)>
The coating film-forming resin (except that the monomer composition was changed to 200 parts by mass of styrene, 382 parts by mass of methyl methacrylate, 282 parts by mass of n-butyl acrylate, 127 parts by mass of hydroxyethyl methacrylate and 9 parts by mass of acrylic acid. In the same manner as in the preparation method of A-3), a coating film-forming resin (A-4) (acrylic resin 2; solid content concentration: 60% by mass, number average molecular weight: 3,600, hydroxyl value: 50 mgKOH / g) was used. Prepared.

<Preparation of coating film forming resin (A-5)>
In a reaction vessel equipped with a thermometer, a condenser and a stirrer, 368 parts by mass of neopentyl glycol, 118 parts by mass of 1,6-hexanediol, 464 parts by mass of isophthalic acid, 51 parts by mass of adipic acid and 71 parts by mass of xylene are mixed. The esterification reaction was carried out until the dehydration amount reached 113 parts by mass and the reaction product had a predetermined viscosity while gradually raising the temperature to 230 ° C. in a nitrogen stream and distilling off the generated water (step). a5-1). Then, after lowering the temperature of the reaction vessel to 50 ° C., 117 parts by mass of hexamethylene diisocyanate, 0.5 part by mass of dibutyltin dilaurate, 456 parts by mass of xylene and 527 parts by mass of cyclohexanone were mixed and reacted at 110 ° C. The reaction was continued until the peak derived from the isocyanate group disappeared in IR (Shimadzu Fourier transform infrared spectrophotometer FTIR-8400S: manufactured by Shimadzu Corporation) (step a5-2), and the coating film forming resin (A-5) was used. (Polyurethane resin 1; solid content concentration: 50% by mass, number average molecular weight: 2,700, hydroxyl value: 42 mgKOH / g) was prepared.

<Preparation of coating film forming resin (A-6)>
The monomer composition of (step a5-1) was added to 314 parts by mass of neopentyl glycol, 193 parts by mass of 1,6-hexanediol and 493 parts by mass of isophthalic acid (dehydrated amount: 107 parts by mass), and to (step a5-2). Except for changing the added composition to 236 parts by mass of hexamethylene diisocyanate, 0.5 parts by mass of dibutyltin dilaurate, 494 parts by mass of xylene and 565 parts by mass of cyclohexanone, the same as the method for preparing the coating film forming resin (A-5). Similarly, a coating film-forming resin (A-6) (polyurethane resin 2; solid content concentration: 50% by mass, number average molecular weight: 4,400, hydroxyl value: 27 mgKOH / g) was prepared.

(Example 1)
[Preparation of paint composition 1]
83.4 parts by mass of coating film forming resin (A-1), 9.2 parts by mass of mixed solution of T-SOL 150 / Solfit = 1/1 (mass ratio) as solvent, black 6350 50.1 as coloring pigment The parts by mass were stirred and mixed with a disper to obtain a mixture.
Next, in a desktop SG mill 1500W type disperser (manufactured by Ohira System Co., Ltd.), the total amount of the obtained mixture and 100 parts by mass of glass beads (the same amount as the total mass of the pigment dispersion paint (or the amount corresponding to 1.5 times)). ) Was added, and pigment dispersion was carried out until the particle size of Black 6350 became 10 μm or less to prepare a pigment-dispersed paint.
Further, with respect to 142.7 parts by mass of this pigment dispersion coating material, 15.0 parts by mass of the cross-linking agent (B-1), 2.4 parts by mass of the sulfonic acid (C-1), and the amine compound (D-1) 4. 0 parts by mass, 5.0 parts by mass of aggregate (E-1) and 1.12 parts by mass of Disparon OX-70 as a surface conditioner were stirred and mixed with a disper to obtain a coating composition. The amine compound (D-1) was added so that the neutralization rate of the sulfonic acid (C-1) was 540%.
The obtained paint composition was subjected to Ford Cup No. Diluting with a mixed solution of T-SOL 150 / cyclohexanone = 1/1 so as to be 100 seconds (25 ° C.) at 4 was obtained to obtain a coating composition 1.

[Manufacturing of painted steel sheets]
After alkaline degreasing a hot-dip galvanized steel sheet with a thickness of 0.4 mm, a phosphoric acid treatment agent Surfcoat EC2310 (manufactured by Nippon Paint Surf Chemicals Co., Ltd.) was applied to the front and back surfaces of the steel sheet for chemical conversion treatment and dried. ..
Next, on the back surface of the obtained steel sheet, Super Rack R-90 (epoxy resin paint manufactured by Nippon Paint Industrial Coatings Co., Ltd.) was applied as a back surface undercoat paint, and a bar coater was applied so that the dry film thickness was 5 μm. It was painted using and baked for 60 seconds under the condition that the maximum temperature reached by the material was 230 ° C. to form a back surface coating film.
As an undercoat paint, a flexible coat 612WW iodine primer (polyester resin primer manufactured by Nippon Paint Industrial Coatings Co., Ltd.) was applied using a bar coater so that the dry film thickness was 5 μm, and the maximum temperature reached by the material was 215 ° C. Baking was performed for 25 seconds under the above conditions to form an undercoat coating film.
Then, the coating composition 1 obtained above is coated with a bar coater so that the dry coating film has a thickness of 22 μm, and baked for 25 seconds under the condition that the maximum temperature of the material reaches 220 ° C., and the surface top coating film is applied. Was formed, and a painted steel plate was obtained. The brightness (L ^* value) of the obtained coating film was 23.4.

(Examples 2 to 30, Comparative Examples 1 to 8)
The paint compositions 2 to 30 and the paint compositions 34 to 41 were prepared in the same manner as in Example 1 except that the types and amounts of each component were changed as shown in Tables 1A to 1H. Using the obtained coating composition, a coated steel sheet was formed in the same manner as in the production of the coated steel sheet of Example 1. The brightness (L ^* value) of the obtained coating films was in the range of 22.5 to 24.9 (dark color).

(Example 31)
The pigment type and amount were changed to 1.2 parts by mass of black 6350, 1.6 parts by mass of type CR-97, 42.7 parts by mass of TAROX synthetic iron oxide HY-100, and 1.5 parts by mass of TODA COLOR KN-V. Except for the above, the coating composition 31 was prepared in the same manner as in Example 1. Using the obtained coating composition 31, a coated steel sheet was formed in the same manner as in the production of the coated steel sheet of Example 1. The brightness (L ^* value) of the obtained coating film was 51.6 (medium coloring).

(Example 32)
The pigment type and amount were changed to 18.6 parts by mass of COLOR BLACK FW200 BEADS, 10.4 parts by mass of Typake CR-97, 2.6 parts by mass of TODA COLOR KN-V, and 6.3 parts by mass of LIONOL BLUE SPG-8. Except for the above, the coating composition 32 was prepared in the same manner as in Example 1. Using the obtained coating composition 32, a coated steel sheet was formed in the same manner as in the production of the coated steel sheet of Example 1. The brightness (L ^* value) of the obtained coating film was 18.2 (deep color).

(Example 33)
The pigment type and amount were changed to 19.7 parts by mass of black 6350, 70.3 parts by mass of typake CR-97, 4.6 parts by mass of TAROX synthetic iron oxide HY-100, and 0.1 parts by mass of TODA COLOR KN-V. Except for the above, the coating composition 33 was prepared in the same manner as in Example 1. Using the obtained coating composition 33, a coated steel sheet was formed in the same manner as in the production of the coated steel sheet of Example 1. The brightness (L ^* value) of the obtained coating film was 54.7 (medium coloring).

The components shown in the table below used in Examples and Comparative Examples are as follows.
[Crosslinking agent (B)]
(B-1) Cymel 303 (manufactured by Ornex Japan), methylated melamine resin; solid content concentration: 100% by mass
(B-2) Super Beccamin L-155-70 (manufactured by DIC Corporation), butylated melamine resin; solid content concentration: 70% by mass
(B-3) Amidia G-1850 (manufactured by DIC), urea resin; solid content concentration: 60% by mass
[Sulfonic acid (C)]
(C-1) Dodecylbenzene sulfonic acid (manufactured by Kao Chemical Co., Ltd.)
(C-2) P-toluenesulfonic acid (manufactured by Gangnam Kako Co., Ltd.)
[Neutralizing amine (D)]
(D-1) Triethylamine, tertiary amine; boiling point: 90 ° C.
(D-2) Diisopropylamine, secondary amine; boiling point: 84 ° C.
(D-3) Diethanolamine, secondary amine; boiling point: 268 ° C.
[Aggregate (E)]
(E-1) Nip seal E-200A (manufactured by Tosoh Silica), silica fine particles; average particle size: 3 μm
(E-2) Nip gel AZ-6A0 (manufactured by Tosoh Silica), silica fine particles; average particle size: 6 μm
(E-3) GAIR HP270 (manufactured by PQ Corporation), silica fine particles; average particle size: 9 μm
(E-4) GAIR HP395 (manufactured by PQ Corporation), silica fine particles; average particle size: 14 μm
(E-5) Ganzpearl GM-0801 (manufactured by Aica Kogyo Co., Ltd.), acrylic resin fine particles; average particle size: 8 μm
(E-6) Pergopack M4 (manufactured by Lonza Japan), urea resin particles; particle size: 4 μm
(E-7) Ganzpearl GM-2801 (manufactured by Aica Kogyo Co., Ltd.), acrylic resin fine particles; average particle size: 28 μm
[others]
Surface conditioner:
・ Disparon OX-70 (manufactured by Kusumoto Kasei Co., Ltd.), acrylic surface conditioner; solid content concentration: 30% by mass
Pigment:
・ Black 6350 (manufactured by Asahi Kasei Kogyo Co., Ltd.), Chromium iron oxide ・ COLOR BLACK FW200 BEADS (manufactured by Orion Engineered Carbons), Carbon Black Typake CR-97 (manufactured by Ishihara Sangyo Co., Ltd.), Titanium dioxide ・ TAROX synthesis Iron oxide HY-100 (manufactured by Titanium Industry Co., Ltd.), yellow iron oxide / TODA COLOR KN-V (manufactured by Toda Pigment Co., Ltd.), ferric oxide / LIONOL BLUE SPG-8 (manufactured by Toyo Color Co., Ltd.), copper phthalocyanine solvent:
-T-SOL 150 (manufactured by JXTG Energy Co., Ltd.), aromatic solvent-Solfit (manufactured by Kuraray), alcohol-based solvent-cyclohexanone (manufactured by Shoei Chemical Industry Co., Ltd.), ketone solvent

[Evaluation item]
The evaluation results in the table are evaluated as follows.

1) Arithmetic mean height (Ra)
The arithmetic mean height (Ra) of the coating film surface obtained in Examples and Comparative Examples is based on JIS B 0601-2001 using a surface roughness measuring machine HANDYSURF E-35B (manufactured by Tokyo Seimitsu Co., Ltd.). It was measured.

2) Expanded area ratio (Sdr)
The developed area ratio (Sdr) of the coating film surface obtained in Examples and Comparative Examples was measured using a laser microscope OPTELICS HYBRID C3 (manufactured by Lasertec, magnification: 50 times) in accordance with ISO 25178.

3) Appearance of coating film The appearance of the coating film obtained in Examples and Comparative Examples was visually observed, and the degree of matte appearance of the coating film was evaluated according to the following criteria.
⊚: The entire coating film has a uniform and clearly matte appearance.
◯: A matte appearance is formed, but a small part is uneven and / or unclear.
Δ: A matte appearance is formed, but is partially non-uniform and / or unclear.
X: A matte appearance is formed, but is significantly non-uniform and / or unclear.
XX: No matte appearance is formed.

4) Glossiness The 60 ° glossiness of the coating film obtained in Examples and Comparative Examples was measured to JIS K 5600-4-7 (mirror glossiness) using a gloss meter VG 7000 (manufactured by Nippon Denshoku Kogyo Co., Ltd.). Measured in compliance. The glossiness was evaluated according to the following criteria.
⊚: Glossiness is 1.0 or less 〇: Glossiness is more than 1.0 and 1.5 or less Δ: Glossiness is more than 1.5 and 2.5 or less ×: Glossiness is more than 2.5

5) Accelerated weathering resistance For the coated steel sheets obtained in Examples and Comparative Examples, use Sunshine Weather Meter S80 (manufactured by Suga Test Instruments Co., Ltd.), which is a sunshine carbon arc lamp type accelerated weathering resistance tester specified in JIS B 7753. , 2,000 hours and 5,000 hours of accelerated weathering tests were performed. The operating conditions are as follows.
Irradiance: 255 W / m ²
Black panel temperature: 63 ° C
Water injection time: 18 minutes out of 120 minutes The appearance of each coated steel sheet after the accelerated weather resistance test was evaluated using a color difference meter SM-T45 (manufactured by Suga Test Instruments Co., Ltd.). The evaluation criteria are as follows, and 〇 or higher was regarded as acceptable.
⊚: Color difference (ΔE) is 1.0 or less 〇: ΔE is more than 1.0 and 2.0 or less ×: ΔE is more than 2.0 and 5.0 or less × ×: ΔE is more than 5.0

As shown in Examples 1 to 33, when the Ra and Sdr values of the formed coating film are included in a specific range, the formed coating film has a low gloss and a uniform matte appearance and is promoted. It was confirmed in the weather resistance test that it had good weather resistance with little discoloration and fading.
On the other hand, as shown in the coating compositions of Comparative Examples 1 to 8, when Ra and / or Sdr of the formed coating film is out of a specific range, the formed coating film has low gloss and / or uniform. The result was that the appearance was not matte, or the discoloration and fading were large in the accelerated weather resistance test, and the weather resistance was inferior.

According to the coating composition of the present disclosure, it is possible to form a coating film having low gloss and high weather resistance. Further, since it has low gloss, it is possible to form a coating film having excellent designability, high uniformity, and a matte appearance with less white blur.

Claims (13)

A coating composition containing at least a coating film-forming resin (A) and a cross-linking agent (B).
A coating composition having an arithmetic mean height (Ra) of 1.2 μm or more and a developed area ratio (Sdr) of 800% or more on the surface of a coating film obtained by curing the coating composition. .. The coating composition according to claim 1, further comprising a sulfonic acid (C), an amine compound (D) and an aggregate (E). The coating film forming resin (A) is a resin having a hydroxyl group, and comprises at least one selected from the group consisting of polyester resin, acrylic resin, urethane resin and modified products thereof, according to claim 1 or 2. Paint composition. The coating composition according to any one of claims 1 to 3, wherein the cross-linking agent (B) contains at least one selected from the group consisting of a melamine resin and a urea resin. The content of the cross-linking agent (B) is 5 parts by mass or more and 100 parts by mass or less as the resin solid content with respect to 100 parts by mass of the resin solid content of the coating film forming resin (A), claims 1 to 4. The coating composition according to any one of the above items. The content of the sulfonic acid (C) is 1.0 part by mass or more and 18.0 part by mass or less with respect to 100 parts by mass of the resin solid content of the coating film-forming resin (A), claims 2 to 5. The coating composition according to any one of the above items. The coating composition according to any one of claims 2 to 6, wherein the amine compound (D) is a secondary or tertiary amine having a boiling point of 50 ° C. or higher and 250 ° C. or lower. The coating composition according to any one of claims 2 to 7, wherein the neutralization rate of the acid group of the sulfonic acid (C) by the amine compound (D) is 300% or more and 3,000% or less. .. Any one of claims 2 to 8, wherein the aggregate (E) contains at least one selected from the group consisting of acrylic resin particles, glass beads, acrylonitrile resin particles, urea resin particles, ceramic fibers and silica particles. The coating composition according to the section. The aggregate (E) contains at least one selected from the group consisting of acrylic resin particles, urea resin particles and silica particles.
The coating composition according to any one of claims 2 to 9, wherein the silica particles have a particle size of 1 μm or more and 20 μm or less. A coated steel sheet having a coating film on the surface of a steel sheet and at least one of the steel sheets.
The coating film is formed of a coating composition containing at least a coating film forming resin (A) and a cross-linking agent (B).
The arithmetic mean height (Ra) on the surface of the coating film is 1.2 μm or more, and the developed area ratio (Sdr) is 800% or more.
A painted steel sheet characterized by being. A coated steel sheet having a coating film on the surface of a steel sheet and at least one of the steel sheets.
The coating film is formed from the coating composition according to any one of claims 1 to 10.
The arithmetic mean height (Ra) on the surface of the coating film is 1.2 μm or more, and the developed area ratio (Sdr) is 800% or more.
A painted steel sheet characterized by being. A coating step of applying the coating composition according to any one of claims 1 to 10 to an object to be coated, and drying and / or curing the coating composition after coating at a temperature of 150 ° C. or higher and 270 ° C. or lower. Including that
A method for manufacturing a coating film.