Method for producing multilayer coating film

Abstract

The purpose of the present invention is to provide a method for producing a multilayer coating film, which uses an aqueous coating composition as an undercoat coating composition, and which makes it possible to achieve a multilayer coating film having a smooth appearance even during wet-on-wet coating. A method for producing a multilayer coating film according to the present disclosure comprises: a lower coating film formation step for forming a lower coating film by applying a lower coating composition on an object to be coated; a top coat coating film formation step for forming a top coat coating film by applying a top coat coating composition on the bottom coat coating film by wet-on-wet; and a drying step for simultaneously drying the undercoat coating film and the overcoat coating film to form a multilayer coating film, the undercoat coating composition comprising an aqueous main agent (I) and an aqueous curing agent (II), the aqueous main agent (I) comprising an aqueous dispersion of an epoxy resin (A), the aqueous curing agent (II) comprising a polyamine compound (B), and the aqueous main agent (I) comprising an aqueous dispersion of an epoxy resin (A), and the aqueous curing agent (II) comprising a polyamine compound (B). The aqueous main agent (I) and / or the aqueous curing agent (II) contains an organic solvent (C), and the polyamine compound (B) contains a polyamine compound (B1) having an active hydrogen equivalent of 100-200 g / eq inclusive and a polyamine compound (B2) having an active hydrogen equivalent of 300-900 g / eq inclusive.

Description

Technical Field

[0001] The present application relates to a method for producing a multilayer coating film. Background Art

[0002] In recent years, the awareness of reducing environmental burden has increased, and environmentally friendly products have been sought. In the field of coatings, for example, it is required to reduce the amount of organic solvents used, and this requirement can be met by using water-based coating compositions using water as a solvent. In the field of coatings used in industrial machinery and construction machinery, conversion to water-based coating compositions is also increasingly sought.

[0003] Industrial machinery and construction machinery are usually large and can withstand high loads, and therefore have the characteristic that the base material (steel plate) is thicker than that of automobile bodies. Therefore, when such industrial machinery and construction machinery are coated objects, there is a problem that the heat capacity of the coated objects is large and the heat is not fully transferred to the coated objects in the heating furnace. Therefore, when coating such coated objects, a room temperature coating film forming coating composition is selected that can form a coating film even at room temperature without requiring a high temperature heating process.

[0004] A multilayer coating is usually provided on the surface of a coated object such as industrial machinery and construction machinery, and the multilayer coating sequentially forms a plurality of coatings having various functions. As an example of a method for forming a coating satisfying both corrosion resistance and weather resistance, a method of using a coating composition with excellent corrosion resistance as a bottom coating composition and then using a top coating composition with excellent weather resistance can be considered. For example, Patent Document 1 describes a method for forming a thick film type anticorrosive coating, characterized in that a weak solvent type high solid modified epoxy resin coating is applied as a bottom coating, and then a weak solvent type high solid polyurethane resin coating is applied as a top coating, wherein the weak solvent type high solid modified epoxy resin coating comprises a binder resin component formed by a modified epoxy resin having an epoxy equivalent of 400 to 2,000 g / eq based on the total mass of the binder resin component, an amine resin, and a reactive diluent, and the weak solvent type high solid polyurethane resin coating comprises a binder resin component formed by a polyol resin having a hydroxyl value of 10 to 100 mgKOH / g and a polyisocyanate compound.

[0005] It is described that according to this method, the same anti-corrosion effect as that achieved by conventional multi-layer coating of each layer can be obtained by applying the bottom coating and the top coating once each. However, this method requires a long time in the process of forming the multi-layer coating film, because the efficiency of the coating process (also called coating operability) is poor.

[0006] From the perspective of improving the efficiency of the coating process, a coating method called wet-on-wet has attracted much attention in recent years. This coating method is a coating method in which after applying the undercoat coating composition, the overcoat coating composition is applied without drying the undercoat coating composition, and then the two coating films are dried simultaneously, thereby shortening the coating process.

[0007] Regarding wet-on-wet coating, Patent Document 2 studies a method for forming a multilayer coating film, which includes: applying an undercoat coating composition containing an epoxy resin, an alicyclic hydrocarbon resin and a polyisocyanate compound on a coated object to form an uncured undercoat coating film, and applying an overcoat coating matrix coating composition containing an acrylic resin and a polyisocyanate compound on the uncured undercoat coating film.

[0008] Patent document 3 studies the following: for a laminated coating having a primer coating film comprising a reaction product of an epoxy resin and a pigment and a top coating film formed on the primer coating film and comprising a reaction product of an acrylic resin, a blocked isocyanate compound and a pigment, adjusting the pigment content and the content of the physical pigment in the primer coating film and the top coating film.

[0009] Patent document 4 states that: as an undercoat coating composition, a composition comprising an acrylic resin, an epoxy resin, an isocyanate compound and a surface conditioner is used, and as an overcoat coating composition, a composition comprising an acrylic resin, an isocyanate compound and a surface conditioner is used, and the surface tension difference between the undercoat coating composition and the overcoat coating composition is set to 2 to 8 mN / m, etc.

[0010] Patent document 5 states that: as a primer coating composition, a composition comprising an epoxy resin, an anti-rust pigment, a coloring pigment and a body pigment is used, and as a top coating composition, a composition comprising an acrylic resin and an active methylene-blocked polyisocyanate compound is used, and the ratio of the acrylic resin to the active methylene-blocked polyisocyanate compound (acrylic resin / active methylene-blocked polyisocyanate) is set to 60 / 40 to 80 / 20, etc.

[0011] Prior art literature

[0012] Patent Literature

[0013] Patent Document 1: Japanese Patent Application Publication No. 2010-188239

[0014] Patent Document 2: Japanese Patent Application Publication No. 2020-192516

[0015] Patent Document 3: Japanese Patent Application Publication No. 2021-160120

[0016] Patent Document 4: International Publication No. 2013 / 024784

[0017] Patent Document 5: Japanese Patent Application Publication No. 2018-008205 Summary of the invention

[0018] Problems to be solved by the invention

[0019] Here, when the bottom coating composition and the top coating composition are wet-on-wet coated, there is a problem that the coating composition is easily mixed (also called mixed layer) between the layers of the two undried coating films, and the appearance of the multilayer coating film obtained after drying deteriorates. This problem is particularly obvious when using an aqueous coating composition as the bottom coating composition. Therefore, especially in the case of industrial machinery and construction machinery as the coated object, the coating film thickness is large compared with the automobile body, etc., and the normal temperature coating film forming coating composition is selected as above. Therefore, the coating compositions known in the past are all solvent-based coating compositions using a solvent as a dispersion medium. It cannot be said that sufficient research has been conducted on the case of wet-on-wet coating using an aqueous coating composition.

[0020] An object of the present disclosure is to provide a method for producing a multilayer coating film, which can realize a multilayer coating film having a smooth appearance even in wet-on-wet coating by using an aqueous coating composition as an undercoat coating composition.

[0021] Means for solving problems

[0022] The present disclosure includes the following aspects.

[0023] [1] A method for producing a multilayer coating film, comprising:

[0024] a bottom coating film forming step of applying a bottom coating composition on the object to be coated to form a bottom coating film;

[0025] an upper coating film forming step of applying an upper coating composition on the lower coating film by wet-on-wet coating to form an upper coating film; and

[0026] a drying step of drying the lower coating film and the upper coating film simultaneously to form a multilayer coating film,

[0027] The above-mentioned bottom coating composition is a water-based coating composition comprising a water-based main agent (I) and a water-based curing agent (II).

[0028] The aqueous main agent (I) comprises an aqueous dispersion of an epoxy resin (A),

[0029] The aforementioned water-based curing agent (II) comprises a polyamine compound (B),

[0030] At least one of the aqueous main agent (I) and the aqueous curing agent (II) contains an organic solvent (C),

[0031] The polyamine compound (B) includes a polyamine compound (B1) having an active hydrogen equivalent of 100 g / eq or more and 200 g / eq or less and a polyamine compound (B2) having an active hydrogen equivalent of 300 g / eq or more and 900 g / eq or less.

[0032] [2] The method for producing a multilayer coating film according to [1], wherein the content of the polyamine compound (B1) in the total of the polyamine compound (B1) and the polyamine compound (B2) is 10% by mass or more and 90% by mass or less.

[0033] [3] The production method according to [1] or [2], wherein the polyamine compound (B1) and the polyamine compound (B2) each contain at least one selected from aliphatic polyamines, alicyclic polyamines, aromatic polyamines, polyamines containing polyoxyalkylene groups, aromatic polyamines containing polyoxyalkylene groups and polyamide amine compounds.

[0034] [4] The method for producing a multilayer coating film according to any one of [1] to [3], wherein at least one of the aqueous main agent (I) and the aqueous curing agent (II) further contains a curing catalyst (E).

[0035] [5] The method for producing a multilayer coating film according to any one of [1] to [4], wherein the epoxy equivalent of the epoxy resin (A) is 100 g / eq or more and 5,000 g / eq or less.

[0036] [6] The method for producing a multilayer coating according to any one of [1] to [5], wherein the ratio of the active hydrogen equivalent of the polyamine compound (B) to the epoxy equivalent contained in the epoxy resin (A) (active hydrogen equivalent / epoxy equivalent) is 0.2 or more and 1.0 or less.

[0037] [7] The method for producing a multilayer coating film according to any one of [1] to [6], wherein at least one of the aqueous main agent (I) and the aqueous curing agent (II) further contains a viscosity modifier (D).

[0038] [8] The method for producing a multilayer coating film according to any one of [1] to [7], wherein the top coating composition is a coating composition comprising a main agent (III) and a curing agent (IV),

[0039] The main agent (III) comprises a coating film forming resin,

[0040] The coating film forming resin has a hydroxyl group,

[0041] The curing agent (IV) contains a polyisocyanate compound.

[0042] Effects of the Invention

[0043] According to the method for producing a multilayer coating film of the present disclosure, a multilayer coating film having a smooth appearance can be achieved even when wet-on-wet coating is performed by using an aqueous coating composition as an undercoat coating composition. DETAILED DESCRIPTION

[0044] The method for producing a multilayer coating film disclosed herein comprises:

[0045] a bottom coating film forming step of applying a bottom coating composition on the object to be coated to form a bottom coating film;

[0046] an upper coating film forming step of applying an upper coating composition on the lower coating film by wet-on-wet coating to form an upper coating film; and

[0047] a drying step of drying the lower coating film and the upper coating film simultaneously to form a multilayer coating film,

[0048] The above-mentioned bottom coating composition is a water-based coating composition comprising a water-based main agent (I) and a water-based curing agent (II).

[0049] The aqueous main agent (I) comprises an aqueous dispersion of an epoxy resin (A),

[0050] The aforementioned water-based curing agent (II) comprises a polyamine compound (B),

[0051] The aforementioned aqueous main agent (I) and / or the aforementioned aqueous curing agent (II) contain an organic solvent (C),

[0052] The polyamine compound (B) includes a polyamine compound (B1) having an active hydrogen equivalent of 100 g / eq or more and 200 g / eq or less and a polyamine compound (B2) having an active hydrogen equivalent of 300 g / eq or more and 900 g / eq or less.

[0053] According to the method for producing a multilayer coating film of the present disclosure, a multilayer coating film having a smooth appearance can be achieved even when wet-on-wet coating is performed by using an aqueous coating composition as an undercoat coating composition.

[0054] Although not bound by a specific theory, according to the research of the present inventors, as the cause of poor appearance (poor smoothness) in the wet-on-wet coating system, it can be considered that: when forming the upper coating film, the amine compound used as the curing agent of the lower coating composition is transferred from the lower coating composition (lower coating film) to the upper coating composition (upper coating film). Therefore, the present inventors studied: in order to inhibit the transfer of the amine compound, the viscosity of the lower coating film is increased during the period (interval) from the formation of the lower coating film to the application of the upper coating film, and the curing reaction of the epoxy resin and the water-based curing agent in the lower coating film is promoted. And it is found that: by combining two amine compounds with a specific active hydrogen equivalent as amine compounds, the viscosity of the lower coating film can be increased, and the curing reaction of the epoxy resin and the water-based curing agent is promoted, thereby completing the manufacturing method of the multilayer coating film described in the present disclosure.

[0055] In the present disclosure, a film after coating of the coating composition and before drying to curing is referred to as a coating film, and a film after drying to curing is referred to as a coating film.

[0056] (Undercoat coating film forming step)

[0057] In the above-mentioned undercoat coating film forming step, an undercoat coating composition is applied to the object to be coated, thereby forming an undercoat coating film.

[0058] The coating method of the undercoat coating composition is not particularly limited, and commonly used coating methods such as dipping, brushing, roller, roller coater, air spray, airless spray, curtain coater, roller curtain coater, die coater, etc. can be listed. In the aforementioned spraying, a two-component mixing gun can be used as needed. They can be appropriately selected according to the object to be coated.

[0059] The application of the above-mentioned undercoat coating composition can be implemented in a manner that the dry film thickness of the undercoat coating film (hereinafter, "the dry film of the coating film" is also referred to as "the coating film", and "the dry film thickness of the coating film" is referred to as "the film thickness of the coating film") is 10 to 100 μm, preferably 15 to 70 μm. In one embodiment, the application of the above-mentioned undercoat coating composition can be implemented in a manner that the film thickness of the undercoat coating film is 30 to 70 μm, and further 40 to 60 μm. By using the undercoat coating composition described later, a smooth and defect-free multilayer coating film can be obtained even when the coating is applied as a thick film. In addition, by setting the undercoat coating film to be more than 10 μm, it is easy to fully protect the substrate, and by setting it to be less than 100 μm, it is easy to suppress the occurrence of pinholes and other undesirable conditions in the multilayer coating film.

[0060] Examples of the coated object include metal substrates such as iron, zinc, tin, copper, titanium, tinplate, galvanized iron, etc. These metal substrates may be plated with zinc, copper, chromium, etc., or may be surface treated with a surface treatment agent such as chromic acid, zinc phosphate, or zirconium salt.

[0061] The method for manufacturing the multilayer coating film disclosed in the present invention can also be suitably used for coated objects with large heat capacity, such as metal substrates, which are difficult to fully conduct heat in a heating furnace. As such coated objects, specifically, there can be cited construction machinery (such as bulldozers, scrapers, hydraulic excavators, excavators, handling machinery (trucks, trailers, etc.), cranes / cargo loading and unloading machinery, machinery for foundation engineering (diesel hammers, hydraulic hammers, etc.), machinery for tunnel engineering (boring machines, etc.), rollers, etc.); industrial machinery such as weak current / heavy current machines for general industrial use, agricultural machinery, steel furniture, working machinery and large vehicles; other coated objects with large heat capacity that are not easy to heat up even if heated, etc. The method for manufacturing the multilayer coating film disclosed in the present invention can be suitably used for coating construction machinery or industrial machinery that are coated objects with large heat capacity and are not easy to heat up even if heated.

[0062] (Top coating film forming step)

[0063] In the top coating film forming step, the top coating composition is applied wet-on-wet on the bottom coating film to form the top coating film, thereby forming a state where the undried top coating film is formed on the undried bottom coating film.

[0064] Representatively, wet-on-wet includes the following coating method: forming an undried upper coating film on an undried lower coating film, and drying the undried lower coating film and the undried upper coating film at the same time to form a multilayer coating film. The coating process can be shortened by wet-on-wet coating, and in addition, it is not necessary to dry the lower coating film, so the energy efficiency is good. In addition, in the manufacturing method of the multilayer coating film disclosed in the present invention, the lower coating composition described later is used, so even when wet-on-wet coating is implemented using an aqueous coating composition as the lower coating composition, a multilayer coating film with a smooth surface can be manufactured.

[0065] In one embodiment, the film coated with the base coating composition, the top coating composition and the mid-coat coating composition described later is not dry, which means that it has not reached the state of "dry to touch" as specified in JIS K5600-1-1. For example, it can be confirmed by lightly touching the center of the coated surface with a fingertip and whether the fingertip is dirty.

[0066] From the viewpoint of work efficiency, the interval from the formation of the lower coating film to the application of the upper coating composition (hereinafter also referred to as "coating interval", "interval") is more than 0 minutes, and can be 1 to 60 minutes, 1 to 30 minutes, or 1 to 15 minutes. If the multilayer coating film forming method disclosed in the present invention is used, even if the upper coating composition is applied when the lower coating film is almost not dried, a multilayer coating film with excellent coating film appearance can be obtained. The temperature between the intervals can be, for example, above 0°C and below 40°C, or above 5°C and below 35°C.

[0067] In addition, after forming the undercoat film and before applying the topcoat coating composition, the undercoat film can be pre-dried at a temperature exceeding normal room temperature (for example, 40 to 100°C, more preferably 40 to 80°C) for about 1 minute to 10 minutes, and the topcoat coating can be applied when the undercoat film is semi-dried.

[0068] The coating method of the coating composition is not particularly limited, and commonly used coating methods such as dipping, brushing, roller, roller coater, air spray, airless spray, curtain coater, roller curtain coater, die coater, etc. can be listed. In the aforementioned spraying, a two-component mixing gun can be used as needed. These can be appropriately selected according to the object to be coated.

[0069] The coating of the above-mentioned top coating composition can be implemented in a manner that the dry film thickness of the top coating film (hereinafter also referred to as "the film thickness of the top coating film") is 10 to 100 μm, preferably 20 to 80 μm. In one embodiment, the coating of the above-mentioned top coating composition can be implemented in a manner that the film thickness of the top coating film is 30 to 70 μm, and further 40 to 60 μm. By using the top coating composition and the bottom coating composition described later, a smooth and defect-free multilayer coating film can be obtained even when a thick film is coated. In addition, by setting the film thickness of the top coating film to more than 10 μm, it is easy to improve the shielding property of the bottom coating film, and by setting it to less than 100 μm, it is easy to suppress the occurrence of pinholes and other undesirable conditions in the multilayer coating film.

[0070] (Drying process)

[0071] In the drying step, the undercoat coating film and the topcoat coating film are dried simultaneously, thereby forming a multilayer coating film.

[0072] In one embodiment, the drying temperature may be 5 to 35° C. and the drying time may be 1 to 10 days. In another embodiment, the drying temperature may be, for example, 50 to 100° C., or further 60 to 80° C., and the drying time may be 15 to 60 minutes.

[0073] (Mid-coat film forming process)

[0074] The manufacturing method of the multi-layer coating film disclosed in the present invention may also include: a process of applying a mid-coat coating composition on an undried undercoat coating film by wet-on-wet to form an undried mid-coat coating film, and may also include: a process of further applying a mid-coat coating composition on the aforementioned undried mid-coat coating film by wet-on-wet to form an undried mid-coat coating film.

[0075] The interval from forming the undercoat film to applying the intermediate coating composition and the interval from forming the intermediate coating film to further applying the intermediate coating composition can be appropriately used as the conditions described above as the interval from forming the undercoat film to applying the top coating composition.

[0076] As the coating method of the midcoat coating composition, the method described above as the coating method of the topcoat coating composition can be appropriately used. In addition, when the midcoat coating composition is applied, the dry film thickness of the midcoat coating film (hereinafter also referred to as "the film thickness of the midcoat coating film") can be applied in a manner that becomes the aforementioned range according to the dry film thickness of the topcoat coating film.

[0077] The mid-coat coating composition is not particularly limited and may be any of an aqueous coating composition and a solvent-based coating composition. A coating composition known to those skilled in the art as a mid-coat coating composition containing a film-forming resin, a curing agent, an organic and / or inorganic coloring pigment and / or a body pigment, etc. may be appropriately used.

[0078] When the method for manufacturing a multi-layer coating film includes a middle coating film forming step, in the top coating film forming step, the bottom coating film can be understood as the middle coating film. In addition, when the method for manufacturing a multi-layer coating film includes a middle coating film forming step, wet-on-wet also includes the following coating method: forming an undried middle coating film and a top coating film on an undried bottom coating film, and drying the undried bottom coating film, the undried middle coating film, and the undried top coating film at the same time to form a multi-layer coating film;

[0079] A coating method comprising forming an undried mid-coat coating film on an undried bottom coating film, drying the undried bottom coating film and the undried mid-coat coating film simultaneously to form a preliminary multi-layer coating film, forming an upper coating film on the preliminary multi-layer coating film, and drying the upper coating film to form a multi-layer coating film;

[0080] A coating method in which an undried undercoat coating film is dried to form an undercoat coating film, an undried intermediate coating film and an undried top coating film are formed on the undercoat coating film, and the undried intermediate coating film and the undried top coating film are dried simultaneously to form a multilayer coating film.

[0081] (Undercoat coating composition)

[0082] The above-mentioned base coating composition is a two-component curable water-based coating composition comprising a water-based main agent (I) and a water-based curing agent (II). The water-based main agent (I) and the water-based curing agent (II) are stored separately, mixed just before coating, and provided for coating in the form of a mixture.

[0083] The aqueous coating composition uses water as a dispersion medium, and the drying speed of the dispersion medium is low compared with the solvent-based coating composition using a solvent as a dispersion medium. Especially, in wet-on-wet coating, when the bottom coating composition is an aqueous coating composition, compared with the case of using a solvent-based coating composition, the tendency of mixing (mixed layer) between the undried bottom coating film and the undried top coating film is obvious. However, in the manufacture method of the multilayer coating film disclosed in the present invention, a specific bottom coating composition is used, therefore, the mixed layer can be suppressed, and a multilayer coating film with a smooth surface can be formed.

[0084] The aqueous main agent (I) comprises an aqueous dispersion of an epoxy resin (A), and the aqueous curing agent (II) comprises a polyamine compound (B). In addition, at least one of the aqueous main agent (I) and the aqueous curing agent (II) may comprise an organic solvent (C) or a viscosity modifier (D).

[0085] (A) Epoxy resin aqueous dispersion

[0086] The epoxy resin aqueous dispersion (A) contained in the aqueous main agent (I) is a component in which an epoxy resin is dispersed in water.

[0087] The epoxy resin preferably has at least two epoxy groups on average in one molecule. The epoxy equivalent of the epoxy resin may be 100 g / eq or more and 5,000 g / eq or less, 100 g / eq or more and 3,000 g / eq or less, or 150 g / eq or more and 1,000 g / eq or less. By making the epoxy equivalent within such a range, the water dispersion stability of the epoxy resin, the coating workability of the obtained coating composition, and the film-forming property of the obtained multilayer coating film can be ensured, and the coating film appearance is good.

[0088] In addition, the epoxy equivalent in this disclosure means solid content epoxy equivalent, and can be measured by the method based on JIS K7236.

[0089] The epoxy resin may be saturated or unsaturated, and may be any of aliphatic, alicyclic, aromatic, and heterocyclic. It may have a hydroxyl group, and may be a modified product modified with an aliphatic polyol compound.

[0090] The epoxy resin is preferably a polyglycidyl ether epoxy resin having a skeleton based on polyphenols, hydrogenated products of polyphenols, polyols and / or novolac phenol. The skeleton preferably includes a skeleton based on polyols and / or phenols, and preferably includes a skeleton based on diols.

[0091] Examples of the polyphenols include resorcinol, hydroquinone, 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), an isomer mixture of dihydroxydiphenylmethane (bisphenol F), tetrabromobisphenol A, 4,4'-dihydroxydiphenylcyclohexane, 2,2-bis(4-hydroxy-3-methylphenyl)propane, 4,4'-dihydroxybiphenyl, 4,4'-dihydroxybenzophenone, 1,1-bis(4-hydroxyphenyl)ethane, 2,2-bis[4-(2'-hydroxypropoxy)phenyl]propane, 1,1-bis(4-hydroxyphenyl)isobutane, 2,2-bis(4-hydroxy-3-tert-butylphenyl)propane, bis(2-hydroxynaphthyl)methane, 1,5-dihydroxynaphthalene, tris(4-hydroxyphenyl)methane, bis(4-hydroxyphenyl)ether, bis(4-hydroxyphenyl)sulfone, and halides of the above compounds.

[0092] As the hydrogenation products of the aforementioned polyphenols, hydrogenation products of the aforementioned compounds can be mentioned.

[0093] The polyols are not particularly limited, and examples thereof include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol (n=4 to 35), 1,2-propylene glycol, polypropylene glycol (n=2 to 15), 1,3-propylene glycol, 1,4-butylene glycol, 1,5-pentanediol, 1,6-hexanediol, 1,2,6-hexanetriol, glycerol, neopentyl glycol, trimethylolethane, and trimethylolpropane. Among the above compounds, polypropylene glycol (n=8 to 10) is particularly preferred.

[0094] As epoxy resin, polyglycidyl esters obtained by reaction of polycarboxylic acid with epichlorohydrin or its derivatives may also be used. As the polycarboxylic acid, there is no particular limitation, and examples thereof include aliphatic, alicyclic or aromatic polycarboxylic acids, such as oxalic acid, succinic acid, adipic acid, glutaric acid, phthalic acid, terephthalic acid, hexahydrophthalic acid, 2,6-naphthalene dicarboxylic acid and dimerized linolenic acid. Among them, diglycidyl adipic acid, diglycidyl phthalate and diglycidyl hexahydrophthalate are preferred.

[0095] Among the above-mentioned epoxy resins, bisphenol-type epoxy resins such as bisphenol A-type epoxy resin and bisphenol F-type epoxy resin are preferred.

[0096] The epoxy resin may be a polyol-modified epoxy resin obtained by reacting an aliphatic polyol compound with an epoxy resin as required. The polyol-modified epoxy resin may be prepared by condensing the epoxy resin and the aliphatic polyol compound. The mass ratio of the epoxy resin to the aliphatic polyol compound in the condensation reaction (mass of the epoxy resin: mass of the aliphatic polyol compound) is preferably in the range of 95:5 to 5:95. The polyol-modified epoxy resin has the advantage of having good water dispersibility.

[0097] It should be noted that, in the present disclosure, an aliphatic polyol compound refers to a polyol compound that does not contain an aromatic hydrocarbon group in the molecule.

[0098] As the aforementioned aliphatic polyol compound, there is no particular limitation, and examples thereof include aliphatic polyether polyols, aliphatic polyester polyols, aliphatic polycarbonate polyols, aliphatic polyurethane polyols, etc., among which polyether polyols are preferred, and polyalkylene glycols are further preferred. As the aforementioned polyalkylene glycol, a polyalkylene glycol having an alkylene group with a carbon number of 4 or less is preferred, and block copolymers of polyethylene glycol, polypropylene glycol, polybutylene glycol, ethylene oxide and propylene oxide, etc. can be listed. In addition, mixtures and copolymers of the aforementioned polyalkylene glycols can also be used. In addition, end capping can be performed partially using monohydric alcohols, etc. The aforementioned polyalkylene glycol can partially have a branched structure, and is more preferably a straight-chain polyalkylene glycol.

[0099] The aforementioned aliphatic polyol compound may be a mixture of the aforementioned polyether polyol (especially polyalkylene glycol) and other aliphatic polyols. As the aforementioned other aliphatic polyols, aliphatic polyester polyols, aliphatic polycarbonate polyols, aliphatic polyamide polyols, aliphatic polyurethane polyols, etc. may be cited, and aliphatic polyester polyols are particularly preferred. The content of the polyether polyol in the aliphatic polyol compound is preferably 70% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less.

[0100] Examples of the aforementioned other aliphatic polyols include aliphatic polyester polyols of aliphatic dicarboxylic acids and aliphatic diols; compounds obtained by condensation reaction of a compound selected from dicarboxylic acids having 3 to 40 carbon atoms, diols having 2 to 20 carbon atoms, primary diamines having 2 to 40 carbon atoms, polyalkylene polyamine compounds, or amino alcohols; and the like.

[0101] The condensation reaction is preferably carried out at a ratio of z(OH):z(EP) of the hydroxyl equivalent of the aliphatic polyol compound to the epoxy equivalent of the epoxy resin of 1:3.6 to 1:10. The z(OH):z(EP) is more preferably in the range of 1:4 to 1:9, and further preferably in the range of 1:4.5 to 1:8. By reacting in the above range, there is an advantage that good water dispersibility can be obtained. The epoxy equivalent of the modified epoxy resin (polyol-modified epoxy resin) is preferably 100 g / eq or more and 10,000 g / eq or less, more preferably 150 g / eq or more and 5,000 g / eq or less, and further preferably 200 g / eq or more and 2,000 g / eq or less.

[0102] The epoxy resin contained in the epoxy resin aqueous dispersion (A) preferably includes polyol-modified bisphenol-type epoxy resins such as polyol-modified bisphenol A epoxy resin and polyol-modified bisphenol F epoxy resin. These polyol-modified bisphenol-type epoxy resins have the advantages of having suitable water dispersibility and good physical properties of the obtained multilayer coating film. As another embodiment, for example, the aforementioned polyol-modified epoxy resin (preferably including a polyol-modified bisphenol-type epoxy resin) and a bisphenol-type epoxy resin (a bisphenol-type epoxy resin without polyol modification) can be used in combination.

[0103] The number average molecular weight of the epoxy resin is preferably 200 to 20,000, more preferably 300 to 10,000. Within such a range, there is an advantage that the water dispersion stability of the epoxy resin, the coating workability of the resulting coating composition, and the film-forming properties of the resulting multilayer coating film can be ensured.

[0104] In addition, in this disclosure, the number average molecular weight is a polystyrene conversion value based on gel permeation chromatography (GPC).

[0105] The preparation of the epoxy resin aqueous dispersion (A) can be carried out by performing a synthesis reaction of the epoxy resin (polyol-modified epoxy resin) in the absence of a solvent or in the presence of an appropriate organic solvent, then dropping the mixture into water and mixing it, and removing excess solvent as needed to prepare an aqueous dispersion. When dispersing the epoxy resin in water, a dispersant such as a surfactant can be used as needed.

[0106] As the epoxy resin aqueous dispersion (A), a commercially available product may be used, and examples of the commercially available product include BECKOPOX series (manufactured by Olunex Japan Co., Ltd.), jER series (manufactured by Mitsubishi Chemical Corporation), and ADEKA Resin EM series (manufactured by ADEKA Corporation).

[0107] The above-mentioned epoxy resin aqueous dispersions may be used alone or in combination of two or more.

[0108] The aforementioned water-based main agent (I) may include other resin components as required on the basis of including the epoxy resin aqueous dispersion (A). As other resin components, for example, polyurethane resin aqueous dispersion, polyester resin aqueous dispersion, acrylic resin aqueous dispersion, etc. may be listed. As the preferred resin component when also including other resin components, from the viewpoints of compatibility with the epoxy resin aqueous dispersion (A), polyurethane resin aqueous dispersion is preferably used. The preferred amount when the aforementioned water-based main agent (I) also includes other resin components such as polyurethane resin aqueous dispersion is based on the amount of each performance of the aforementioned water-based coating composition and each performance of the obtained multilayer coating film, etc. as a condition.

[0109] When the aqueous main agent (I) further comprises a polyurethane resin aqueous dispersion in addition to the epoxy resin aqueous dispersion (A), the content of the polyurethane resin aqueous dispersion is preferably 0.5 to 20 parts by mass based on the resin solid content per 100 parts by mass of the resin solid content of the epoxy resin aqueous dispersion (A).

[0110] It should be noted that in the present disclosure, the "resin solid content" of the base coating composition refers to the total amount of the solid content of the epoxy resin (A) and the solid content of the polyurethane resin aqueous dispersion, polyester aqueous dispersion, acrylic resin aqueous dispersion added as desired and the solid content of other resins that may be contained in the coating film forming resin.

[0111] (B) Polyamine compounds

[0112] The polyamine compound (B) may be a compound having two or more amino groups in one molecule. The polyamine compound disclosed herein includes a polyamine compound (B1) having an active hydrogen equivalent of 100 g / eq or more and 200 g / eq or less and a polyamine compound (B2) having an active hydrogen equivalent of 300 g / eq or more and 900 g / eq or less.

[0113] In addition, in this disclosure, the active hydrogen equivalent of a polyamine compound means a solid content active hydrogen equivalent, and it can be measured by the method based on JIS K 7237:1995.

[0114] The active hydrogen equivalent of the polyamine compound (B1) is preferably 110 g / eq or more and 160 g / eq or less. When the active hydrogen equivalent of the polyamine compound (B1) is less than 100 g / eq, the appearance of the obtained multilayer coating film is reduced. In addition, when it exceeds 200 g / eq, the appearance of the obtained multilayer coating film becomes poor. Although it should not be construed in a restrictive manner by a specific theory, it can be considered that: when the active hydrogen equivalent is outside the aforementioned range, the curing reaction rate is reduced.

[0115] The active hydrogen equivalent of the polyamine compound (B2) is preferably 300 g / eq or more and 800 g / eq or less, and more preferably 300 g / eq or more and 500 g / eq or less. When the active hydrogen equivalent of the polyamine compound (B2) is less than 300 g / eq, the appearance of the obtained multilayer coating film is deteriorated. When it exceeds 900 g / eq, the coating viscosity of the obtained coating composition is increased, and the coating workability is deteriorated.

[0116] The content of the polyamine compound (B1) in the total of the polyamine compound (B1) and the polyamine compound (B2) is preferably 10% by mass or more and 90% by mass or less, more preferably 20% by mass or more and 85% by mass or less, further preferably 30% by mass or more and 80% by mass or less, and further preferably 55% by mass or more and 75% by mass or less. By being within the above range, there are the following advantages: good reactivity with the epoxy resin aqueous dispersion (A) is ensured, and intermixing of the undried lower coating film and the undried upper coating film is suppressed, so that the appearance of the obtained multilayer coating film becomes good.

[0117] In the polyamine compound (B), the total content of the polyamine compound (B1) and the polyamine compound (B2) is preferably 50% by mass or more and 100% by mass or less, more preferably 80% by mass or more and 100% by mass or less, and further preferably 90% by mass or more and 100% by mass or less.

[0118] In addition, content of the polyamine compound in this indication is content based on solid content.

[0119] The aforementioned polyamine compound (B) may contain a polyamine compound other than the aforementioned polyamine compound (B1) and the polyamine compound (B2), that is, a polyamine compound having an active hydrogen equivalent of less than 100 g / eq, a polyamine compound having an active hydrogen equivalent of more than 200 g / eq and less than 300 g / eq, and a polyamine compound having an active hydrogen equivalent of more than 900 g / eq, within a range that does not affect the performance of the coating composition and the obtained multilayer coating film.

[0120] Examples of the polyamine compound (B) include aliphatic polyamines, alicyclic polyamines, aromatic polyamines, polyoxyalkylene group-containing polyamines, polyoxyalkylene group-containing aromatic polyamines, and polyamidoamine compounds.

[0121] Examples of the aliphatic amine include alkylene polyamines, polyalkylene polyamines, and other aliphatic amines.

[0122] Examples of the alkylene polyamines include H2N-R 1 -NH2(where R 1A polyamine compound represented by a divalent hydrocarbon group having 1 to 12 carbon atoms which is optionally substituted with one or more hydrocarbon groups having 1 to 10 carbon atoms.

[0123] More specifically, methylenediamine, ethylenediamine, 1,2-diaminopropane, 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane, 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane, 1,10-diaminodecane, etc. are mentioned.

[0124] Examples of the polyalkylene polyamine include diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, and hexamethylenetetramine.

[0125] Examples of other aliphatic amines include tetrakis(aminomethyl)methane, tetrakis(2-aminoethylaminomethyl)methane, 1,3-bis(2′-aminoethylamino)propane, triethylene-bis(trimethylene)hexamine, bis(3-aminoethyl)amine, and bishexamethylenetriamine.

[0126] Examples of the alicyclic polyamine include 1,4-cyclohexanediamine, 4,4′-methylenebiscyclohexylamine, 4,4′-isopropylidenebiscyclohexylamine, norbornanediamine, bis(aminomethyl)cyclohexane, diaminodicyclohexylmethane, isophoronediamine, and menthanediamine (MDA).

[0127] Examples of the aromatic polyamine include bis(aminoalkyl)benzene, bis(aminoalkyl)naphthalene, aromatic polyamine compounds having two or more primary amino groups bonded to a benzene ring, and other aromatic polyamine compounds. The aromatic polyamine is not particularly limited, and more specifically, bis(cyanoethyl)diethylenetriamine, o-xylylenediamine, m-xylylenediamine (MXDA), p-xylylenediamine, phenylenediamine, naphthalenediamine, diaminodiphenylmethane, diaminodiethylphenylmethane, 2,2-bis(4-aminophenyl)propane, 4,4'-diaminodiphenyl ether, 4,4'-diaminobenzophenone, 4,4'-diaminodiphenyl sulfone, 2,2'-dimethyl-4,4'-diaminodiphenylmethane, 2,4'-diaminobiphenyl, 2,3'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl, bis(aminomethyl)naphthalene, bis(aminoethyl)naphthalene, and the like are exemplified.

[0128] The polyamine containing polyoxyalkylene groups is a polyamine compound having a polyoxyalkylene chain, and refers to a compound that does not belong to the "aromatic polyamine containing polyoxyalkylene groups" shown below, that is, a compound that does not have an aromatic group. Examples of the polyoxyalkylene chain possessed by the polyamine containing polyoxyalkylene groups include polyoxyethylene chains, polyoxypropylene chains, poly(oxyethylene-oxypropylene) chains, and poly(oxytetramethylene) chains.

[0129] Examples of polyoxyalkylene group-containing polyamines include polyoxyalkylene diamines such as polyoxyethylene diamine, polyoxypropylene diamine, and poly(oxyethylene-oxypropylene) diamine. These are compounds in which polyoxyalkylene groups are introduced into aliphatic polyamines, and may also be referred to as polyoxyalkylene group-containing aliphatic polyamines.

[0130] Examples of other polyoxyalkylene-containing polyamines include polyamines obtained by converting two or more hydroxyl groups of a compound obtained by reacting a polyol such as trimethylolpropane and pentaerythritol with an alkylene oxide such as ethylene oxide and / or propylene oxide into amino groups.

[0131] The molecular weight of the polyamine containing polyoxyalkylene is preferably 200 to 5,000, more preferably 600 to 3,000. By making the molecular weight within the above range, there is an advantage that the appearance of the obtained coating film becomes good. When the molecular formula of the polyamine compound is known, the molecular weight can be calculated according to the molecular formula. In addition, when the number of repeating units of the oxyalkylene in the polyoxyalkylene chain is not a natural number, the molecular weight can be a number average molecular weight.

[0132] As the polyamine containing a polyoxyalkylene group, a commercially available product can be used. Examples of the commercially available product include polyoxyalkylene group-containing aliphatic polyamines such as the JEFFAMINE series (manufactured by HUNTSMAN).

[0133] The polyoxyalkylene group-containing aromatic polyamine is a polyamine compound having a polyoxyalkylene chain and an aromatic group. Specific examples of the polyoxyalkylene chain are the same as those described above.

[0134] Examples of the polyoxyalkylene-containing aromatic polyamine include polyamines obtained by introducing alkylene oxides such as ethylene oxide, propylene oxide and / or tetramethylene oxide into polyols such as glycol, trimethylolpropane and pentaerythritol, and introducing an amino group-containing aromatic compound.

[0135] As the polyoxyalkylene group-containing aromatic polyamine, a commercially available product can be used. Examples of the commercially available product include the Erasmer series (manufactured by KUMIAI Chemical Co., Ltd.).

[0136] The polyamidoamine compound used in the production method of the present disclosure is not particularly limited as long as it has a polyamide structure in the molecule and has at least two active hydrogen atoms. In the present specification, active hydrogen refers to hydrogen bonded to the nitrogen atom of the amino group in the polyamidoamine compound and the polyamine compound.

[0137] The polyamide amine compound used as the polyamide amine compound can be prepared by a conventional method, for example, by a condensation reaction of a polyamine compound and a polycarboxylic acid compound. In this case, the amount of active hydrogen in the obtained polyamide amine compound can be adjusted by adjusting the ratio of the polyamine compound to the polycarboxylic acid compound used in the reaction.

[0138] As the polyamine compound used to make the polyamidoamine compound, there is no particular limitation as long as it is a compound having at least two amino groups in the molecule, and at least one selected from aliphatic chain polyamines, aliphatic cyclic polyamines and aromatic polyamines can be used. As the aliphatic chain polyamine, polyalkylene polyamines such as diethylenetriamine, triethylenetetramine and tetraethylenepentamine can also be suitably used.

[0139] The polycarboxylic acid compound used for producing the polyamidoamine compound is not particularly limited as long as it is a compound having at least two carboxyl groups in the molecule, but dicarboxylic acids such as aliphatic dicarboxylic acids and dimer acids are preferred.

[0140] In the production of the polyamidoamine compound, in addition to the polyamine compound and the polycarboxylic acid compound, an aminocarboxylic acid compound, a polyol compound, a lactam compound, etc. may be reacted as appropriate to produce a modified polyamidoamine compound.

[0141] In addition to the polyamide amine compound, the polyamide amine compound may also contain water or an aqueous solvent. As the aqueous solvent, protic polar solvents such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methoxyethanol, 2-ethoxyethanol, 2-propoxyethanol, 2-butoxyethanol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, 1-propoxy-2-propanol, etc.; non-protic polar solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, etc., which can be used alone or in combination of two or more. Among the above, the polyamide amine compound preferably contains water.

[0142] The solid content concentration of the polyamidoamine compound is preferably 20% by mass or more and 90% by mass or less in the polyamine compound (B).

[0143] As the polyamide amine compound, a commercially available polyamide amine compound may also be used. Examples of the polyamide amine compound include Aradur 3986, Aradur 38-1 (manufactured by HUNTSMAN Advanced Materials), EPIKURE Curing Agent 8535-W-50, and EPIKURE Curing Agent 8530-W-75 (manufactured by HEXION), and these may be used alone or in combination of two or more.

[0144] The polyamine compound (B) may be used alone or in combination of two or more thereof. In one embodiment, the polyamine compound (B) preferably comprises at least one selected from aliphatic polyamines, alicyclic polyamines, aromatic polyamines, polyamines containing polyoxyalkylene groups, aromatic polyamines containing polyoxyalkylene groups, and polyamide amine compounds.

[0145] The aforementioned aqueous curing agent (II) only needs to contain the polyamine compound (B), and in one embodiment, it can be an aqueous dispersion of the polyamine compound (B). The aqueous dispersion of the polyamine compound (B) can be prepared by dispersing the aforementioned polyamine compound (B) in an aqueous solvent. As aqueous solvents, water (ion exchange water, pure water, surface water, industrial water, etc.), and mixtures of water and water-miscible organic solvents, etc. can be listed. As water-miscible organic solvents, solvents that do not react with the epoxy resin (A) and the polyamine compound (B) can be used, and alcohols such as isopropyl alcohol; glycol ethers, etc. can be listed.

[0146] As a method for dispersing the polyamine compound (B) in an aqueous solvent, when the polyamine compound (B) has a hydrophilic group, the polyamine compound (B) can be dispersed by adding it to water and stirring it. In addition, in the dispersion of the polyamine compound (B), a surfactant, a dispersing resin, etc. can be used in combination as needed.

[0147] As one method of dispersing the polyamine compound (B), there is mentioned a method of preparing a polyamine compound water dispersion by mixing the polyamine compound (B) and a surfactant in an aqueous solvent.

[0148] The surfactant preferably includes at least one of anionic surfactants and nonionic surfactants. Furthermore, the anionic surfactant is preferably at least one selected from phosphate surfactants, carboxylic acid surfactants, sulfonic acid surfactants and sulfate surfactants. The nonionic surfactant is preferably at least one selected from polyoxyalkylene glycol fatty acid esters, polyalkylene glycol fatty acid esters and polyoxyalkylene alkyl ethers.

[0149] Phosphate ester surfactants, which are one type of anionic surfactants, are surfactants having a phosphoric acid group as an anionic group. Examples of phosphate ester surfactants, for example, surfactants having a phosphoric acid group include polyoxyalkylene alkyl ether phosphoric acid esters, polyoxyalkylene alkylphenyl ether phosphoric acid esters, and salts thereof, such as ammonium salts, lithium salts, sodium salts, potassium salts, and the like.

[0150] As the phosphate ester and its salt, commercially available products may be used, and examples of commercially available products include DISPARLO NPW-36, DISPARLON AQ-330 (manufactured by Kusumoto Chemicals Co., Ltd.), DISPERBYK-103, DISPERBYK-111, and DISPERBYK-145 (manufactured by Bicchemie Japan Co., Ltd.).

[0151] Carboxylic acid-type surfactants, which are one type of anionic surfactants, are surfactants having a carboxylic acid group as an anionic group. Examples of carboxylic acid-type surfactants include saturated fatty acids such as propionic acid, butyric acid, valeric acid, caproic acid, heptanoic acid, caprylic acid, 2-ethylhexanoic acid, nonanoic acid, capric acid, lauric acid, myristic acid, palmitic acid, heptadecanoic acid, stearic acid, isostearic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid, montanic acid, melissic acid, and 12-hydroxystearic acid; monounsaturated fatty acids such as crotonic acid, undecylenic acid, myristoleic acid, palmitoleic acid, cis-6-hexadecenoic acid, oleic acid, elaidic acid, vaccenic acid, gadoleic acid, erucic acid, and nervonic acid; diunsaturated fatty acids such as linoleic acid, eicosadienoic acid, and docosadienoic acid; triunsaturated fatty acids such as linolenic acid, pinolenic acid, eleostearic acid, melissic acid, and eicosatrienoic acid; Tetraunsaturated fatty acids such as octadecanoic acid, arachidonic acid, eicosatetraenoic acid, and adrenic acid; pentaunsaturated fatty acids such as octadecapentaenoic acid, eicosapentaenoic acid, docosapentaenoic acid, oleic acid, and tetracosapentaenoic acid; hexaunsaturated fatty acids such as docosahexaenoic acid and tetracosahexaenoic acid; vegetable oil derivatives and mixed fatty acids such as castor oil fatty acid, coconut oil fatty acid, linseed oil fatty acid, bran fatty acid, rice bran oil fatty acid, soybean fatty acid, safflower fatty acid, tall oil fatty acid, and dehydrated castor oil fatty acid; dicarboxylic acids such as sebacic acid, adipic acid, and dimer acid; aromatic carboxylic acids such as benzoic acid, salicylic acid, and cinnamic acid; and salts thereof, such as ammonium salts, lithium salts, sodium salts, potassium salts, and the like.

[0152] As the carboxylic acid type surfactant, a commercially available product can be used, and it can be obtained from, for example, Kishida Chemical Co., Ltd., Tokyo Chemical Industry Co., Ltd., Nippon Seika Co., Ltd., and the like.

[0153] Sulfonic acid type surfactants, which are one type of anionic surfactants, are surfactants having a sulfonic acid group as an anionic group. Examples of surfactants having a sulfonic acid group include the following:

[0154] Alkylbenzenesulfonic acid, alkyldiphenyletherdisulfonic acid, perfluoroalkoxybenzenesulfonic acid, alkylsulfonic acid, alkylnaphthalenesulfonic acid, sulfosuccinic acid, N-acylsulfonic acid, polyoxyethylene alkylphenyl ether sulfate, alkylsulfuric acid, alkylethersulfuric acid, alkylamidesulfuric acid, etc.; and salts thereof, such as ammonium salts, lithium salts, sodium salts, potassium salts, etc.

[0155] As the surfactant having a sulfonic acid group, commercially available products can be used. Examples of commercially available products include Perex SS-H, Neoperex G-25 (manufactured by Kao Corporation), Lipolan PB-800 (manufactured by Lion Corporation), Teika Pawl L128 (manufactured by Teika Co., Ltd.), Nycore 565SNC, Nycore 707SF (manufactured by Nippon Emulsifier Co., Ltd.), and Aqualon KH-10 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.).

[0156] Sulfate ester surfactants, which are one type of anionic surfactants, are surfactants having a sulfate group as an anionic group. Examples of sulfate ester surfactants include fatty acid sulfate ester salts, alkyl sulfate ester salts, alkyl ether sulfate ester salts, and amide ether sulfate ester salts. Commercially available products can be used as the surfactants having a sulfate group.

[0157] As the nonionic surfactant, for example, at least one selected from polyoxyalkylene glycol fatty acid esters, polyoxyalkylene glycol fatty acid esters and polyoxyalkylene alkyl ethers can be cited. As the nonionic surfactant, commercially available products can also be used. As commercially available products, for example, Genapol series, Genagen series (manufactured by Clariant Japan Co., Ltd.), Noigen series (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), Niucore N700 series (manufactured by Nippon Emulsifier Co., Ltd.), etc. can be cited.

[0158] The above-mentioned surfactants may be used alone or in combination of two or more. For example, only anionic surfactants may be used, only nonionic surfactants may be used, or anionic surfactants and nonionic surfactants may be used in combination.

[0159] The temperature and dispersion conditions in the above-mentioned dispersion preparation step can be appropriately selected within the ranges usually performed by those skilled in the art.

[0160] When a surfactant is used, the content of the surfactant in the aqueous dispersion of the polyamine compound (B) is preferably 0.01 parts by mass or more and 20 parts by mass or less relative to 100 parts by mass of the polyamine compound (B). By making the content of the surfactant within the aforementioned range, there is an advantage that the water dispersibility of the aqueous dispersion of the polyamine compound (B) obtained becomes good, and the water resistance of the obtained multilayer coating film, etc.

[0161] The content of the polyamine compound (B) contained in the aqueous dispersion of the polyamine compound (B) can be appropriately selected according to the structure and molecular weight of the polyamine compound (B), for example, preferably 30% by mass or more and 90% by mass or less, more preferably 40% by mass or more and 80% by mass or less. By being within the above range, there is an advantage of improving the dispersion stability of the mixture mixed with the above aqueous main agent (I) and the above aqueous curing agent (II).

[0162] In the aqueous dispersion of the polyamine compound (B), the average particle size of the aqueous dispersion (dispersed polyamine compound (B)) is preferably 100 to 1,000 nm, more preferably 100 to 300 nm. By making the average particle size of the aqueous dispersion within the above range, there is an advantage of improving the dispersion stability of the mixture containing the aqueous main agent (I) and the aqueous curing agent (II). In addition, there is an advantage of ensuring better reactivity between the epoxy resin aqueous dispersion (A) and the polyamine compound (B), and improving the appearance of the obtained multilayer coating film.

[0163] In addition, in this disclosure, the average particle diameter of the water dispersion means an average particle diameter 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.

[0164] The ratio of the active hydrogen equivalent of the polyamine compound (B) to the epoxy equivalent of the epoxy resin (A) (active hydrogen equivalent / epoxy equivalent) is preferably 0.2 to 1.0, more preferably 0.4 to 1.0, and even more preferably 0.5 to 0.9.

[0165] By being within the above range, there is an advantage that better reactivity between the epoxy resin aqueous dispersion (A) and the polyamine compound (B) is ensured, and a multilayer coating film obtained from the undercoat coating composition exhibits a good appearance.

[0166] It should be noted that the active hydrogen equivalent when two or more polyamine compounds are used in combination can be calculated by the following calculation formula. That is, when the active hydrogen equivalent of the polyamine compound obtained by mixing M parts by mass (solid content parts by mass) of the polyamine compound (B1) having an active hydrogen equivalent of H1 and N parts by mass (solid content parts by mass) of the polyamine compound (B2) having an active hydrogen equivalent of H2 is set to Z, Z is calculated according to the following formula.

[0167] Z=[(M+N)×H1×H2] / (M×H2+N×H1)

[0168] (C) Organic solvents

[0169] As the organic solvent (C), an organic solvent used in the field of coatings can be used. Although not bound by a specific theory, the organic solvent (C) has a polarity and boiling point different from water. Therefore, by using the organic solvent (C), the dryness of the bottom coating film can be controlled. In addition, the organic solvent (C) can act as a diluent. In one embodiment, the organic solvent (C) can be used to accelerate the drying of the bottom coating film.

[0170] The organic solvent (C) is not particularly limited, and examples thereof include aromatic hydrocarbon solvents such as xylene and toluene; ether solvents such as dipropylene glycol dimethyl ether, ethylene glycol monobutyl ether, 2-methoxypropanol (propylene glycol monomethyl ether), diethylene glycol monobutyl ether, butyl diglycol, 2-butoxypropanol, methyl ether acetate, propylene glycol monomethyl ether acetate, tetrahydrofuran, and dioxane; alcohol solvents such as ethanol, methanol, propanol, isopropanol, 2-butanol, and tert-butanol; glycol solvents such as ethylene glycol and propylene glycol; amide solvents such as N-methylpyrrolidone, and the like.

[0171] The organic solvent (C) preferably includes an organic solvent (C1) having a relative evaporation rate of 0.5 to 6 when n-butyl acetate is set to 1. The relative evaporation rate of the organic solvent (C1) is preferably 1 to 5, more preferably 1 to 2. By making the relative evaporation rate within the aforementioned range, there are advantages that the drying property of the obtained coating composition becomes good and the appearance of the obtained multilayer coating film becomes good. As the organic solvent having a relative evaporation rate of 0.5 to 6, 2-methoxypropanol (propylene glycol monomethyl ether), ethanol, and isopropanol are preferred.

[0172] In the present disclosure, the evaporation rate of the organic solvent (C) is a value measured according to the test method specified in ASTM D3539-87 (2004) of the American Society for Testing and Materials, and represents a converted value when the evaporation rate value of n-butyl acetate is set to 1.

[0173] When the organic solvent (C) is used, the content of the organic solvent (C) in the undercoat composition is preferably 0.1 to 25% by mass, more preferably 0.5 to 20% by mass, and even more preferably 1 to 18% by mass.

[0174] It should be noted that the content of the organic solvent (C) in the aforementioned undercoat coating composition is the value obtained by dividing the total amount (mass parts) of the organic solvent (C) contained in the aqueous main agent (I) and the aqueous curing agent (II) by the amount (mass parts) of the undercoat coating composition (the total amount of the aqueous main agent (I) and the aqueous curing agent (II)).

[0175] When the organic solvent (C1) is used, the content of the organic solvent (C1) in the organic solvent (C) may be 100% by mass, preferably 10 to 80% by mass, and more preferably 30 to 75% by mass.

[0176] When the organic solvent (C) is used, the organic solvent (C) may be contained in any one of the aqueous main agent (I) and the aqueous curing agent (II), but is preferably contained in both the aqueous main agent (I) and the aqueous curing agent (II).

[0177] The content of the organic solvent (C) in the aqueous main agent (I) is preferably 0.1 to 20% by mass, more preferably 0.5 to 15% by mass, and even more preferably 3 to 10% by mass.

[0178] The content of the organic solvent (C) in the aqueous curing agent (II) is preferably 0.1% by mass to 50% by mass, more preferably 1% by mass to 40% by mass, and even more preferably 5% by mass to 30% by mass.

[0179] When the content of the organic solvent (C) is within the above range, there are advantages in that the drying properties of the obtained coating composition become good and the appearance of the obtained multilayer coating film becomes good.

[0180] (D) Viscosity regulator

[0181] The viscosity modifier has the function of increasing the viscosity by utilizing the interaction between molecules, swelling of the material, and the like.

[0182] As the aforementioned viscosity regulator, a known viscosity regulator can be used, and viscosity regulators such as carbamate viscosity regulators, urea viscosity regulators, polyacrylic acid viscosity regulators, polyamide viscosity regulators, cellulose viscosity regulators, clay minerals such as bentonite, etc. can be used. Among them, carbamate viscosity regulators and / or urea viscosity regulators are more preferred. By using the aforementioned viscosity regulator, there are advantages such as being able to appropriately adjust the viscosity of the resulting coating composition, being able to improve the coating workability of the resulting coating composition, and improving the appearance of the resulting multilayer coating film.

[0183] Examples of the urethane viscosity modifier include compounds having a urethane bond and a polyether chain in the molecule and a hydrophobic group at the terminal, such as polyether polyol urethane prepolymers, urethane-modified polyether viscosity modifiers, etc. These are known to effectively exhibit a thickening effect by associating urethane bonds with each other in an aqueous medium.

[0184] As the urethane viscosity modifier, commercial products can be used, such as ADEKANOLE UH-814N, UH-752, UH-750, UH-420, and UH-462 (manufactured by ADEKA Corporation); SN Scaler 621N and SN Scaler 623N (manufactured by Sannopoulos Co., Ltd.); and RHEOLATE 244 and 278 (manufactured by Elameans Corporation).

[0185] Examples of the urea-based viscosity modifier include compounds obtained by reacting a monoisocyanate or diisocyanate compound with a primary polyamine or a secondary polyamine. Commercially available products may be used as the urea-based viscosity modifier. Examples of commercially available products include BYK-410, BYK-411, BYK-415, BYK-420, BYK-425, and BYK-428.

[0186] The above-mentioned viscosity adjusters may be used alone or in combination of two or more.

[0187] The content of the viscosity modifier is preferably 0.01 to 20 parts by mass, more preferably 0.05 to 10 parts by mass, and even more preferably 0.1 to 5 parts by mass, based on 100 parts by mass of the resin solid content.

[0188] When the content of the viscosity modifier (D) is within the above range, there is an advantage that the viscosity of the resulting coating composition can be appropriately adjusted, and the coating workability of the resulting coating composition and the appearance of the resulting multilayer coating film can be improved.

[0189] The viscosity adjuster (D) may be contained in any one of the aqueous main agent (I) and the aqueous curing agent (II), but is preferably contained in the aqueous main agent (I).

[0190] (E) Curing catalyst

[0191] The undercoat coating composition preferably includes a curing catalyst. The curing catalyst can be any compound that can promote the crosslinking reaction between the epoxy resin (A) contained in the water-based main agent (I) and the water-based curing agent (II). As the curing catalyst (E), an amine-based curing catalyst is preferred. As the amine-based curing catalyst, an imidazole compound, a tertiary amine or its salt, a phosphine compound, etc. are preferred, and a tertiary amine is particularly preferred. By including the aforementioned curing catalyst, there is an advantage that a better reactivity of the epoxy resin aqueous dispersion (A) and the polyamine compound (B) can be ensured, and the appearance of the resulting multilayer coating becomes good.

[0192] Examples of the amine curing catalyst include triethylenediamine, 2-methyltriethylenediamine, quinuclidine, 2-methylquinuclidine, N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetramethylpropylenediamine, N,N,N',N",N"-pentamethyldiethylenetriamine, N,N,N',N",N"-pentamethyl-(3-aminopropyl)ethylenediamine, N,N,N',N",N"-pentamethyldipropylenetriamine, N,N,N',N'-pentamethyl-(3-aminopropyl)ethylenediamine, N,N,N',N",N"-pentamethyldipropylenetriamine, N,N,N',N'-pentamethyl-(3-aminopropyl)ethylenediamine, N,N,N',N",N"-pentamethyldipropylenetriamine, N,N,N',N'-pentamethyldipropylenetriamine, N,N,N',N'-pentamethyldiethylene ... -Tetramethylhexamethylenediamine, bis(2-dimethylaminoethyl) ether, triethylamine, tributylamine, dimethylethanolamine, dimethylisopropanolamine, dimethylaminoethoxyethanol, triethanolamine, quinoline, N,N-dimethyl-N'-(2-hydroxyethyl)ethylenediamine, N,N-dimethyl-N'-(2-hydroxyethyl)propanediamine, bis(dimethylaminopropyl)amine, bis(dimethylaminopropyl)isopropanolamine, N,N-dimethylbenzylamine, 3-aminopropyldimethyl 3-quinuclidine, N,N,N',N'-tetramethylguanidine, 1,3,5-tris(N,N-dimethylaminopropyl)hexahydro-S-triazine, 1,8-diazabicyclo[5.4.0]undecene-7, 1,5-diazabicyclo[4.3.0]nonene-5, N-methyl-N'-(2-dimethylaminoethyl)piperazine, N,N'-dimethylpiperazine, dimethylcyclohexylamine, N-methylmorpholine, N-ethylmorpholine, 1-methylimidazole, 1,2-dimethoxy-1-nitropropene, Tertiary amines such as methylimidazole, 1-isobutyl-2-methylimidazole, 1-dimethylaminopropylimidazole, N,N-dimethylhexanolamine, N-methyl-N'-(2-hydroxyethyl)piperazine, 1-(2-hydroxyethyl)imidazole, 1-(2-hydroxypropyl)imidazole, 1-(2-hydroxyethyl)-2-methylimidazole, and 1-(2-hydroxypropyl)-2-methylimidazole, and compounds obtained by making amine salts of these tertiary amines with phenol, octanoic acid, quaternary tetraphenylborate, etc.

[0193] Among them, N,N-dimethylbenzylamine and 3-aminopropyldimethylamine are preferred, and 3-aminopropyldimethylamine is particularly preferred.

[0194] As the curing catalyst (E), these compounds may be used alone or in combination of two or more.

[0195] In one embodiment, the content of the curing catalyst (E) is preferably 0 mass parts or more and 5 mass parts or less, more preferably 0 mass parts or more and 3 mass parts or less, relative to the total of 100 mass parts of the resin solids of the coating film forming resin (A) and the solids of the polyamine compound (B). In other embodiments, the content of the curing catalyst (E) is preferably 0.2 mass parts or more and 5 mass parts or less, more preferably 0.8 mass parts or more and 3 mass parts or less, relative to the total of 100 mass parts of the resin solids of the coating film forming resin (A) and the solids of the polyamine compound (B). By making the content of the curing catalyst (E) within the above range, there is an advantage that the curing reactivity of the obtained coating composition can be appropriately adjusted and the coating workability of the obtained coating composition and the appearance of the obtained multilayer coating film can be good.

[0196] <Preparation of Undercoat Coating Composition>

[0197] The aqueous main agent (I) and aqueous curing agent (II) of the above-mentioned bottom coating composition can be prepared by mixing the above-mentioned various components respectively using methods known to those skilled in the art. The coating composition can be prepared by methods commonly used by those skilled in the art. For example, a kneading and mixing method using a kneader or a roller, or a dispersion and mixing method using a sand mill or a disperser can be used.

[0198] The above-mentioned coating composition can include other components according to the purpose and purpose on the basis of including the above-mentioned components. As other components, for example, organic solvents, pigments, resin particles, resin components, dispersants, curing catalysts, tackifiers, film-making aids, and additives commonly used in coating compositions (such as ultraviolet light absorbers, light stabilizers, antioxidants, defoamers, surface conditioners, anti-pinhole agents, rust inhibitors, etc.) can be listed. These components can be added to the main agent and / or curing agent in a manner that does not damage the various physical properties of the coating composition of the present disclosure and / or the obtained multilayer coating film.

[0199] Regarding the timing of mixing the water-based main agent (I) and the water-based curing agent (II) in the above-mentioned bottom coating composition, the water-based main agent (I) and the water-based curing agent (II) can be mixed before use and applied using a common coating method. Alternatively, the coating can be applied by using a two-component mixing gun to transport various liquids to the gun and mixing them at the front end of the gun.

[0200] (Top coating composition)

[0201] The top coating composition is not particularly limited, but preferably a two-component curing coating composition comprising a main agent (III) and a curing agent (VI) is used. The main agent (III) and the curing agent (VI) are stored separately, mixed just before coating, and provided for coating in the form of a mixture.

[0202] In one embodiment, the main agent (III) comprises a film-forming resin having a hydroxyl group, and the curing agent (VI) comprises a polyisocyanate compound. The hydroxyl group of the film-forming resin reacts with the isocyanate group of the polyisocyanate compound to form a urethane bond, thereby curing the top coating film.

[0203] The top coating composition may be an aqueous coating composition using water as a dispersion medium, or may be a solvent-based coating composition using a solvent as a dispersion medium.

[0204] (Water-based top coating composition)

[0205] The aforementioned water-based topcoat coating composition is preferably a two-component curable coating composition comprising a water-based main agent (IIIa) as the main agent (III) and a water-based curing agent (VIa) as the curing agent (VI). The water-based main agent (IIIa) preferably comprises a coating film-forming resin having a hydroxyl group, and the water-based curing agent (VIa) preferably comprises a polyisocyanate compound.

[0206] In one embodiment, the aqueous main agent (IIIa) contains an acrylic resin aqueous dispersion (Fa) as a coating film-forming resin, and the aqueous curing agent (VIa) contains a water-dispersible polyisocyanate (Ga) as a polyisocyanate compound.

[0207] Acrylic resin aqueous dispersion (Fa)

[0208] The acrylic resin contained in the acrylic resin aqueous dispersion (Fa) is a polymer of a monomer mixture containing ethylenically unsaturated monomers, and has a hydroxyl group. By making the aforementioned main agent (IIIa) contain the acrylic resin aqueous dispersion (Fa), it is possible to impart good coating properties such as adhesion and water resistance to the multilayer coating film. In addition, a multilayer coating film with a smooth surface shape can be formed, and for example, a multilayer coating film with excellent surface smoothness can be formed.

[0209] Examples of the ethylenically unsaturated monomer include hydroxyl group-containing monomers, carboxyl group-containing monomers, and other monomers.

[0210] Examples of the hydroxyl-containing monomer include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2,3-dihydroxybutyl (meth)acrylate; (meth)acrylate polyalkylene glycol monoesters such as polyethylene glycol mono(meth)acrylate; and ε-caprolactone-modified products of the aforementioned hydroxyalkyl (meth)acrylates and the aforementioned polyalkylene glycol monoesters of (meth)acrylate (also referred to as "ε-caprolactone-modified (meth)acrylate"). Specific examples of the ε-caprolactone-modified (meth)acrylate include Pluckcell FA-1, Pluckcell FA-2, Pluckcell FA-3, Pluckcell FA-4, Pluckcell FA-5, Pluckcell FM-1, Pluckcell FM-2, Pluckcell FM-3, Pluckcell FM-4, and Pluckcell FM-5 manufactured by Daicel Chemical Industries, Ltd. It should be noted that in this specification, (meth)acrylic acid refers to acrylic acid and methacrylic acid.

[0211] Examples of carboxyl group-containing monomers include monocarboxylic acids such as (meth)acrylic acid, 2-ethylacrylic acid, and crotonic acid; dicarboxylic acids such as maleic acid, fumaric acid, and itaconic acid; and dicarboxylic acid monoesters such as ethyl maleate, butyl maleate, ethyl itaconate, and butyl itaconate. Preferred carboxyl group-containing ethylenically unsaturated monomers include acrylic acid and methacrylic acid.

[0212] Other monomers used in the acrylic resin aqueous dispersion (Fa) include, for example, styrene monomers such as styrene, α-methylstyrene, and vinyltoluene; alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-, iso-, and tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and lauryl (meth)acrylate; and amides such as (meth)acrylamide.

[0213] The above-mentioned ethylenically unsaturated monomers may be used alone or in combination of two or more.

[0214] The hydroxyl value of the acrylic resin aqueous dispersion (Fa) is preferably 40 to 200 mgKOH / g, more preferably 50 to 200 mgKOH / g. By setting the hydroxyl value to 40 mgKOH / g or more, the reactivity with the water-dispersible polyisocyanate (Ga) is good, and the physical strength of the obtained multilayer coating film is easily maintained. In addition, by setting the hydroxyl value to 200 mgKOH / g or less, the water resistance of the obtained multilayer coating film is easily maintained.

[0215] The acid value of the acrylic resin aqueous dispersion (Fa) is preferably 2 to 150 mgKOH / g, more preferably 2 to 100 mgKOH / g. When the acid value is within the above range, the physical strength of the obtained multilayer coating film can be easily maintained.

[0216] In addition, in this specification, both the acid value and the hydroxyl value show the value converted into solid content, and are the values ​​measured by the method based on JIS K 0070.

[0217] The number average molecular weight of the acrylic resin aqueous dispersion (Fa) is preferably 1,000 to 100,000, more preferably 1,000 to 50,000. When the number average molecular weight is 1,000 or more, the physical strength of the obtained multilayer coating film can be easily maintained, and when the number average molecular weight is 100,000 or less, the smoothness of the obtained multilayer coating film can be easily maintained.

[0218] The acrylic resin aqueous dispersion (Fa) can be prepared by polymerizing the aforementioned monomer mixture in the absence of a solvent or in the presence of an appropriate organic solvent, dropping the obtained polymer into water, mixing the polymer, and removing excess solvent as necessary.

[0219] During the polymerization reaction, a polymerization initiator may be used, and a free radical polymerization initiator may be used as the polymerization initiator. Specific examples of the polymerization initiator include organic peroxides such as benzoyl peroxide, tert-butyl peroxide, and cumene hydroperoxide; and organic azo compounds such as azobiscyanovaleric acid and azoisobutyronitrile.

[0220] The polymerization temperature can be, for example, 80 to 140° C., and the polymerization time can be appropriately adjusted according to the polymerization temperature and the reaction scale, and can be, for example, 1 to 8 hours. The polymerization reaction can be carried out, for example, by dropwise adding the monomer mixture and a polymerization initiator used as required to a heated polymerization solvent. The polymerization solvent is not particularly limited, and preferably has a boiling point of about 60 to 250° C.

[0221] Examples of polymerization solvents that can be suitably used include water-insoluble organic solvents such as butyl acetate, xylene, toluene, methyl isobutyl ketone, propylene glycol, dipropylene glycol dimethyl ether, and methyl ether acetate; and water-soluble organic solvents such as tetrahydrofuran, ethanol, methanol, propanol, isopropanol, 2-butanol, tert-butanol, dioxane, methyl ethyl ketone, ethylene glycol, ethylene glycol monobutyl ether, 2-methoxypropanol, 2-butoxypropanol, diethylene glycol monobutyl ether, butyl diglycol, N-methylpyrrolidone, ethylene carbonate, and propylene carbonate.

[0222] A neutralizing agent may be added to the acrylic resin obtained by polymerization to neutralize at least a portion of the acid groups contained in the acrylic resin. This process can impart good water dispersibility to the acrylic resin. The neutralizing agent is not particularly limited, and organic amines such as monomethylamine, dimethylamine, trimethylamine, triethylamine, diisopropylamine, monoethanolamine, diethanolamine, and dimethylethanolamine; and inorganic bases such as sodium hydroxide, potassium hydroxide, and lithium hydroxide may be used. These neutralizing agents may be used alone or in combination of two or more.

[0223] The acrylic resin aqueous dispersion (Fa) can be prepared by mixing water with the acrylic resin neutralized as required or by mixing the acrylic resin in water. In the preparation of the acrylic resin aqueous dispersion (Fa), the excess organic solvent may be removed before adding the neutralizing agent or after water dispersion as required.

[0224] As the acrylic resin aqueous dispersion (Fa), commercially available products can be used. Commercially available products are not particularly limited, and examples thereof include MACRYNAL series such as MACRYNAL VSM6299 / 42WA (manufactured by Surface Specialties); BAYHYDROL series such as BAYHYDROL XP2470 (manufactured by Bayer AG); BAYNOCK series such as BAYNOCK WD-551 (manufactured by DIC); NeoCryl series such as NeoCryl XK-555 (manufactured by DSM); and the like.

[0225] Water dispersible polyisocyanate (Ga)

[0226] The water-dispersible polyisocyanate (Ga) is a water-dispersible compound having two or more isocyanate groups in one molecule, and refers to a polyisocyanate compound that can be dispersed without separation when added to an aqueous medium. The water-dispersible polyisocyanate (Ga) may be a substance modified with a hydrophilic compound having a hydrophilic group as required. The hydrophilic group may be an ionic hydrophilic group or a nonionic hydrophilic group.

[0227] As the water-dispersible polyisocyanate (Ga), there can be cited aromatic diisocyanates such as toluene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), and meta-xylylene diisocyanate (MXDI); aliphatic diisocyanates such as trimethylene diisocyanate, tetramethylene diisocyanate, and hexamethylene diisocyanate (HDI); alicyclic polyisocyanates such as cyclohexane diisocyanate, dicyclohexylmethane diisocyanate, and isophorone diisocyanate (IPDI); and polymers such as biuret bodies, isocyanurate bodies, and trimethylolpropane (TMP) adducts of the aromatic diisocyanate, aliphatic diisocyanate, and alicyclic polyisocyanate. These water-dispersible polyisocyanates (Ga) can be used alone or in combination of two or more.

[0228] In addition, in this disclosure, "alicyclic" means having an alicyclic structure in the molecule.

[0229] The water-dispersible polyisocyanate (Ga) is preferably an aliphatic diisocyanate and / or an alicyclic polyisocyanate, more preferably hexamethylene diisocyanate (HDI) and / or isophorone diisocyanate (IPDI). Aliphatic diisocyanates and alicyclic polyisocyanates have lower reactivity than aromatic polyisocyanates and can inhibit side reactions with aqueous media such as water.

[0230] In the aforementioned water-dispersible polyisocyanate (Ga), the polyisocyanate groups may be modified, and a cross-linked structure based on multiple isocyanate groups may exist between multiple polyisocyanate compounds or in a single polyisocyanate compound. The aforementioned polymer polyisocyanate compound is trifunctional or higher, and therefore, at least one of the multiple isocyanate groups may be modified, and at least two isocyanate groups may contribute to the formation of a cross-linked structure.

[0231] In the above-mentioned water-based top coating composition, the molar ratio (NCO / OH) of the isocyanate group of the water-dispersible polyisocyanate (Ga) to the hydroxyl group of the acrylic resin aqueous dispersion (Fa) is preferably 0.5 to 3.0, and more preferably 0.8 to 2.0. By making the above-mentioned molar ratio (NCO / OH) within this range, there is an advantage that the curing reactivity of the water-based top coating composition can be ensured to be within a good range.

[0232] The aqueous main agent (IIIa) and the aqueous curing agent (IVa) contain water as a dispersion medium. As the water, ion exchange water, distilled water, etc. can be used.

[0233] In the aforementioned water-based coating composition, water-based main agent (IIIa) and / or water-based curing agent (IVa) can include organic solvent as required. As organic solvent, for example butyl acetate, dimethylbenzene, toluene, methyl isobutyl ketone, propylene glycol, dipropylene glycol dimethyl ether, methyl ether acetate, tetrahydrofuran, ethanol, methanol, propanol, isopropanol, 2-butanol, the tert-butyl alcohol, dioxane, methyl ethyl ketone, ethylene glycol, ethylene glycol monobutyl ether, ethylene glycol monobutyl ether acetate (butyl acetate cellosolve), propylene glycol monomethyl ether acetate, 2-methoxy propanol, 2-butoxy propanol, diethylene glycol monobutyl ether, butyl diglycol, N-methyl pyrrolidone, ethylene carbonate and propylene carbonate etc. can be listed. These organic solvents can be the organic solvent used in the preparation of acrylic resin aqueous dispersion (Fa), water-dispersible polyisocyanate (Ga) etc., or can be the solvent added separately in the preparation of water-based coating composition.

[0234] In the aqueous main agent (IIIa) and the aqueous curing agent (IVa), the content of water in the total of water and the organic solvent may be, for example, 50 mass % to 100 mass % or 70 mass % to 100 mass %.

[0235] Other ingredients

[0236] The aforementioned water-based top coating composition may further include pigments, resin particles, resin components, dispersants, curing catalysts, tackifiers, film-forming aids, additives commonly used in coating compositions (e.g., ultraviolet absorbers, light stabilizers, antioxidants, defoamers, surface conditioners, anti-pinhole agents, rust inhibitors, etc.) and other components according to the purpose and use. These components may be included in either the water-based main agent (IIIa) or the water-based curing agent (IVa).

[0237] (Solvent-based top coating composition)

[0238] The solvent-based coating composition is preferably a two-component curable coating composition comprising a main agent (IIIb) as the main agent (III) and a curing agent (IVb) as the curing agent (IV). The main agent (IVb) preferably comprises an acrylic resin (Fb) as a coating film-forming resin, and the curing agent (IVb) preferably comprises a polyisocyanate compound (Gb). In addition, the main agent (IIIb) and / or the curing agent (IVb) may comprise an extender pigment and a viscosity modifier.

[0239] Acrylic resin (Fb)

[0240] The acrylic resin (Fb) is a polymer of a monomer mixture containing ethylenically unsaturated monomers, and has a hydroxyl group. By making the main agent (IIIb) contain the acrylic resin (Fb), it is possible to impart adhesion of the top coating film to the bottom coating film, and to impart good coating film properties such as water resistance to the multilayer coating film. In addition, a multilayer coating film with a smooth surface shape can be formed, and for example, a multilayer coating film with excellent surface smoothness can be formed.

[0241] Examples of the ethylenically unsaturated monomer include hydroxyl group-containing monomers and other monomers.

[0242] Examples of the hydroxyl group-containing monomer include the aforementioned hydroxyalkyl (meth)acrylates, the aforementioned polyalkylene glycol monoester (meth)acrylates, and the aforementioned ε-caprolactone-modified (meth)acrylates.

[0243] Other monomers used in the acrylic resin (Fb) include the aforementioned carboxyl group-containing monomers; the aforementioned alkyl (meth)acrylates; alicyclic (meth)acrylic monomers such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, tricyclodecyl (meth)acrylate, and adamantyl (meth)acrylate; amino group-containing (meth)acrylates such as aminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, and butylaminoethyl (meth)acrylate; amide group-containing monomers such as (meth)acrylamide, N-hydroxymethyl (meth)acrylamide, methoxybutyl (meth)acrylamide, and diacetone (meth)acrylamide; amino group-containing (meth)acrylamide such as aminoethyl (meth)acrylamide, dimethylaminomethyl (meth)acrylamide, and methylaminopropyl (meth)acrylamide; cyanide vinyl monomers such as (meth)acrylonitrile and α-chloroacrylonitrile; saturated aliphatic carboxylic acid vinyl ester monomers such as vinyl acetate and vinyl propionate; the aforementioned styrene monomers, etc.

[0244] The above-mentioned ethylenically unsaturated monomers may be used alone or in combination of two or more.

[0245] As other monomers used in the acrylic resin (Fb), the alkyl (meth)acrylates and the alicyclic (meth)acrylic monomers are preferred, and acrylic acid, methacrylic acid, methyl (meth)acrylate, ethyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, cyclohexyl (meth)acrylate, etc. are more preferred.

[0246] The acrylic resin (Fb) preferably has a hydroxyl value of 40 to 200 mgKOH / g, more preferably 50 to 200 mgKOH / g. When the solid content hydroxyl value is within the above range, it can react appropriately with the polyisocyanate compound (Gb) described below, and desired coating properties can be obtained.

[0247] The acid value of the acrylic resin (Fb) is preferably 2 to 150 mgKOH / g, more preferably 5 to 30 mgKOH / g. By setting the acid value within the above range, desired coating properties can be obtained. The solid content acid value of the acrylic resin (Fb) is more preferably 5 to 30 mgKOH / g.

[0248] The number average molecular weight of the acrylic resin (Fb) is preferably 3,000 to 20,000, more preferably 3,500 to 15,000, and further preferably 3,500 to 12,000. By making the number average molecular weight of the acrylic resin (Fb) 3,000 or more, the drying property of the coating composition can be improved, the adhesion of dust caused by the stickiness of the coating composition scattered in the coating room can be prevented, a good coating environment can be maintained, and the coating properties of the obtained multilayer coating film can be improved. In addition, by making the number average molecular weight of the acrylic resin (Fb) 20,000 or less, the gloss of the multilayer coating film can be improved.

[0249] The acrylic resin (Fb) can be produced by polymerizing the aforementioned monomer mixture in the absence of a solvent or in the presence of an appropriate organic solvent. As a polymerization method, for example, a free radical polymerization method can be listed, and the free radical polymerization method can be implemented using a free radical polymerization initiator. Specifically, it can be a bulk polymerization method, a solution polymerization method, a bulk-suspension two-stage polymerization method in which suspension polymerization is performed after bulk polymerization, etc. Among these, a solution polymerization method is particularly preferred, and for example, a method in which the aforementioned monomer mixture is heated while stirring at a temperature of, for example, 80 to 200° C. in the presence of a free radical polymerization initiator can be listed.

[0250] As the acrylic resin (Fb), commercially available products can be used. The commercially available products are not particularly limited, and examples thereof include Acrylic series such as Acrylic A-428 (manufactured by DIC Corporation), Diyanal series such as Diyanal LC-2657 (manufactured by Mitsubishi Chemical Corporation), and Hitaloid series (manufactured by Showa Denko Materials Co., Ltd.).

[0251] The coating film forming resin may contain a polyester resin, an epoxy resin, etc. as necessary in addition to the acrylic resin (Fb).

[0252] From the viewpoint of film water resistance and finishing properties, the content of the solid content of the acrylic resin (Fb) in 100% by mass of the solid content of the film-forming resin is preferably 40% by mass or more and 100% by mass or less, more preferably 50% by mass or more and 100% by mass or less, and in one embodiment, 50% by mass or more and 90% by mass or less. In another embodiment, 90% by mass or more and 100% by mass or less. By including the acrylic resin in such a range, a multilayer coating film with better drying properties can be formed on the coated object by wet-on-wet coating.

[0253] It should be noted that in the present disclosure, “solid content of coating film forming resin” refers to the total amount of solid content of epoxy resin and solid content of other resins that may be contained in the coating film forming resin in addition to the solid content of acrylic resin.

[0254] Polyisocyanate compound (Gb)

[0255] The polyisocyanate compound (Gb) refers to a compound having two or more isocyanate groups in one molecule.

[0256] Examples of the polyisocyanate compound (Gb) include aliphatic diisocyanates; alicyclic diisocyanates; aromatic diisocyanates; polymers of aliphatic diisocyanates, alicyclic diisocyanates, and aromatic diisocyanates. The polyisocyanate compound (Gb) may be a so-called asymmetric compound. The number of carbon atoms contained in the polyisocyanate compound (Gb) is preferably 5 to 24, more preferably 6 to 18.

[0257] Examples of the aliphatic diisocyanate include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexane diisocyanate, undecane diisocyanate-(1,11), lysine ester diisocyanate, diethylene glycol diisocyanate, dipropylene glycol diisocyanate, triethylene glycol diisocyanate, and thiodipropyl diisocyanate.

[0258] Examples of the alicyclic diisocyanate include cyclohexane diisocyanate, isophorone diisocyanate (IPDI), and dicyclohexylmethane diisocyanate.

[0259] Examples of the aromatic diisocyanate include 1,5-dimethyl-2,4-bis(isocyanatomethyl)benzene, 1,5-trimethyl-2,4-bis(ω-isocyanatoethyl)benzene, 1,3,5-trimethyl-2,4-bis(isocyanatomethyl)benzene, 1,3,5-triethyl-2,4-bis(isocyanatomethyl)benzene, 2,4- and / or 2,6-toluene diisocyanate, 4,4′-diphenylmethane diisocyanate, and 1,4-diisocyanatoisopropylbenzene.

[0260] Examples of the polymer include a biuret form, an isocyanurate form, and a trimethylolpropane (TMP) adduct.

[0261] The polyisocyanate compound (Gb) may be used alone or in combination of two or more.

[0262] The polyisocyanate compound (Gb) preferably contains at least the isocyanurate of the aliphatic diisocyanate, alicyclic diisocyanate, and aromatic diisocyanate, and preferably contains the isocyanurate of the aliphatic diisocyanate. When the polyisocyanate compound (Gb) contains the isocyanurate, the content of the isocyanurate in the polyisocyanate compound (Gb) is preferably 60% by mass or more.

[0263] In the above-mentioned solvent-based top coating composition, the molar ratio (NCO / OH) of the isocyanate group of the polyisocyanate compound (Gb) to the hydroxyl group of the coating film forming resin is preferably in the range of 0.5 to 2.0, and more preferably 0.8 to 1.6. By making the above-mentioned molar ratio (NCO / OH) in this range, the solvent-based top coating composition is fully cured and the desired coating film properties can be obtained.

[0264] In one embodiment, an extender pigment and a viscosity adjuster may be used in combination with the acrylic resin (Fb). This combination can further improve the drying properties of the coating and improve the appearance of the coating film.

[0265] Examples of the extender pigment include talc, clay, calcium carbonate, magnesium carbonate, barium sulfate, silicic acid, silicates, alumina hydrate, calcium sulfate, gypsum, micaceous iron oxide (MIO), glass flakes, sulphuric acid, and clay.

[0266] In one embodiment, the extender pigment is selected from calcium carbonate, barium sulfate, and talc. For example, heavy calcium carbonate, light calcium carbonate, precipitated barium sulfate, and surface-treated talc can be used. Such extender pigments can be used alone or in combination.

[0267] The amount of the extender pigment is preferably 0 parts by mass or more and 100 parts by mass or less, and more preferably 0 parts by mass or more and 50 parts by mass or less, based on 100 parts by mass of the coating film-forming resin.

[0268] By using the extender pigment and the viscosity adjuster in combination, the viscosity and viscosity behavior of the top coating composition, such as viscosity recovery, can be appropriately adjusted, and appropriate leveling properties and flow properties can be imparted.

[0269] As the viscosity adjuster, any of the compounds described as the viscosity adjuster used in the above-mentioned undercoat coating composition can be used.

[0270] The viscosity modifier is preferably in an amount of 0.01 to 20 parts by mass, more preferably 0.05 to 10 parts by mass, and even more preferably 0.1 to 5 parts by mass, based on 100 parts by mass of the coating film-forming resin.

[0271] For example, when the total solid content of the aforementioned film-forming resin, curing agent (IVb), body pigment and viscosity regulator is set to 100 mass%, the solid content of the film-forming resin (Fb) is preferably greater than 20 mass% and less than 80 mass%, more preferably greater than 30 mass% and less than 60 mass%, and in one embodiment, greater than 35 mass% and less than 55 mass%.

[0272] In the above-mentioned solvent-based top coating composition, the main agent (IIIb) and the curing agent (IVb) contain an organic solvent as a dispersion medium. As the organic solvent, a solvent commonly used in solvent-based coatings may be contained, and examples thereof include methyl ethyl ketone, cyclohexanone, Solvesso 100 (manufactured by Exxon Chemical Company), methoxybutyl acetate, cellosolve acetate, butyl cellosolve acetate, methyl acetate, ethyl acetate, butyl acetate, petroleum ether, naphtha, etc. In particular, even if an organic solvent such as xylene, which is subject to legal restrictions under the Regulations for the Prevention of Damage to Specified Chemical Substances (Special Regulations) due to its use amount, is not selected, coating design can be performed.

[0273] Other ingredients

[0274] The above-mentioned solvent-based coating composition may include known various additives as required. As various additives, the additives used in the coating composition may be appropriately used, and for example, pigments such as coloring pigments, rust-proof pigments, anti-flowing / anti-settling agents, curing catalysts (organic metal catalysts), anti-color separation agents, dispersants, defoaming / anti-pinhole agents, thickeners, leveling agents, matting agents, ultraviolet light absorbers, antioxidants, plasticizers, film-making aids, organic solvents, etc. may be listed. The blending amount of these components may be appropriately adjusted in the range that does not damage the effects of the present disclosure.

[0275] Example

[0276] The present disclosure will be described in more detail with reference to the following examples, but the present disclosure is not limited thereto.

[0277] <Manufacturing Example 1> Manufacturing Example of Primer Coating Composition

[0278] <Preparation Example of Pigment Dispersion Paste for Undercoat Coating Composition>

[0279] Using a disperser, 19.3 parts by mass of ion exchange water, 0.4 parts by mass of BYK-011 as a defoamer, 5.0 parts by mass of BYK-2015 as a dispersant, 0.2 parts by mass of BENTONE LT, 9.3 parts by mass of LOMON Titanium Dioxide R-996 as a pigment, 6.0 parts by mass of LF BOUSEI ZP-DL, 12.0 parts by mass of SSS talc, 6.0 parts by mass of TAROX synthetic iron oxide LL-XLO, and 3.2 parts by mass of precipitated barium sulfate PS07 were premixed in a dispersion container. Thereafter, a dispersion treatment was performed at 1,500 rpm using an SG mill (dispersion medium: glass beads) until the coarse particles of the pigment were 25 μm or less, thereby obtaining a pigment dispersion paste 1 for an undercoat coating composition.

[0280] <Preparation Example of Undercoat Coating Composition>

[0281] (Water-based main agent for base coating composition)

[0282] 36.1 parts by mass of EM-101-50 (A-1) as an epoxy resin aqueous dispersion (A), 2.0 parts by mass of Davanol PM glycol ether as an organic solvent (C) and 161.4 parts by mass of a pigment dispersion paste for an undercoat coating composition were mixed and stirred using a disperser to obtain an aqueous main agent 1 for an undercoat coating composition. In addition, aqueous main agents 2 to 15 for undercoat coating compositions were obtained in the same manner except that the components and amounts shown in Tables 1A to 1J were used instead of the aforementioned components.

[0283] (Water-based curing agent for base coating composition)

[0284] 2.15 parts by mass of Aradur 38-1 as a polyamine compound (B1-1), 8.58 parts by mass of Aradur 3986 as a polyamine compound (B2-1), 0.71 parts by mass of Davanol PM glycol ether as an organic solvent (C1-3), and 2.64 parts by mass of IPA as an organic solvent (C1-1) were mixed and stirred using a disperser to obtain an aqueous curing agent 1. In addition, aqueous curing agents 2 to 24 were obtained in the same manner except that the components and amounts shown in Tables 1A to 1J were used instead of the above components.

[0285] (Details of Materials Used in Undercoat Coating Composition)

[0286] Epoxy resin aqueous dispersion (A)

[0287] (A-1) EM-101-50 (manufactured by Adeka Corporation, bisphenol A type epoxy resin aqueous dispersion), epoxy equivalent: 505 g / eq, solid content concentration: 47 mass %

[0288] (A-2) BECKOPOX EP 147w (manufactured by Allnex, bisphenol A / F type epoxy resin emulsifiable in water), epoxy equivalent: 194 g / eq, solid content concentration: 100 mass %

[0289] (A-3) BECKOPOX EP 2307W / 45WAMP (manufactured by Allnex, bisphenol A type epoxy resin dispersion), epoxy equivalent: 1,980 g / eq, solid content concentration: 45 mass %

[0290] Polyamine compound (B)

[0291] (B1-1) Aradur 38-1 (manufactured by HUNTSMANA Advanced Materials Co., Ltd., polyamide amine compound aqueous dispersion), active hydrogen equivalent: 150 g / eq, solid content concentration: 80 mass %

[0292] (B1-2) EPIKURE Curing Agent 8535-W-50 (manufactured by HEXION, polyamide amine compound aqueous dispersion), active hydrogen equivalent: 102 g / eq, solid content concentration: 50 mass %

[0293] (B1-3) BECKOCURE EH623w / 80WA (manufactured by Allnex, polyamine compound aqueous dispersion), active hydrogen equivalent: 200 g / eq, solid content concentration: 80 mass %

[0294] (B2-1) Aradur 3986 (manufactured by HUNTSMANA Advanced Materials, aqueous dispersion of polyamide amine compound), active hydrogen equivalent: 415 g / eq, solid content concentration: 40 mass %

[0295] (B2-2) EPILINK 701 (manufactured by Evonik, polyamine compound aqueous dispersion), active hydrogen equivalent: 300 g / eq, solid content concentration: 55 mass %

[0296] (B2-3) BECKOCURE EH2100w / 44WA (manufactured by Allnex, polyamine compound aqueous dispersion), active hydrogen equivalent: 570 g / eq, solid content concentration: 44 mass %

[0297] (b-1) EPIKURE Curing Agent 8530-W-75 (manufactured by HEXION, polyamide amine compound aqueous dispersion), active hydrogen equivalent: 90 g / eq, solid content concentration: 75 mass %

[0298] (b-2) Aradur 3985 (manufactured by HUNTSMAN Advanced Materials Co., Ltd., polyamide amine compound aqueous dispersion), active hydrogen equivalent: 265 g / eq, solid content concentration: 55 mass %

[0299] (b-3) BECKOCURE EH2260w / 41WA (manufactured by Allnex, aqueous dispersion of polyamine compound), active hydrogen equivalent: 1,000 g / eq, solid content concentration: 41 mass %

[0300] Organic solvent (C)

[0301] (C1-1) IPA (manufactured by Shoei Chemical Co., Ltd., isopropyl alcohol), evaporation rate: 1.5

[0302] (C1-2) Ethanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), evaporation rate: 1.54

[0303] (C1-3) PGM (Dawanool PM glycol ether, manufactured by Dai Chemical Co., Ltd., propylene glycol monomethyl ether), evaporation rate: 0.71

[0304] Viscosity modifier (D)

[0305] (D-1) BYK-420 (manufactured by BYK, modified urea-based adhesive), solid content concentration: 52% by mass

[0306] (D-2) SN Siquener 660T (manufactured by Sannopou Co., Ltd., urethane-modified polyether), solid content concentration: 20 mass %

[0307] Curing catalyst (E)

[0308] (E-1) Kao Life No. 20 (manufactured by Kao Corporation, dimethylbenzylamine), active ingredient concentration: 100% by mass

[0309] (E-2) DMP-30 (manufactured by Kanto Chemical Co., Ltd., 2,4,6-tris(dimethylaminomethyl)phenol), active ingredient concentration: 100% by mass

[0310] Others (materials for preparing pigment dispersion paste for undercoat coating composition)

[0311] BYK-011 (manufactured by Big Chemie Jampan Co., Ltd., defoaming agent), solid content concentration: 30% by mass

[0312] BYK-2015 (manufactured by Big Chemie Jampan Co., Ltd., dispersant), solid content concentration: 40% by mass

[0313] pigment

[0314] LOMON Titanium Dioxide R-996 (manufactured by SICHUAN LOMON TITANIUM INDUSTRY, titanium dioxide)

[0315] ·LF ボウセイZP-DL (manufactured by Kuraru Co., Ltd., zinc phosphate anti-rust pigment)

[0316] ·SSS talc (manufactured by Nippon Talc Co., Ltd., talc)

[0317] ·TAROX synthetic iron oxide LL-XLO (manufactured by Titanium Industry Co., Ltd., yellow iron oxide)

[0318] ·Precipitated barium sulfate PS07 (manufactured by Guangxi Xiangzhou Lianzhuang Chemical Co., Ltd., Precipitated barium sulfate)

[0319] <Manufacturing Example 2> Preparation Example of Water-Based Top Coating Composition

[0320] <Preparation Example of Pigment Dispersion Paste for Water-Based Top Coating Composition>

[0321] (Pigment dispersion paste for aqueous top coating composition)

[0322] Using a disperser, 23.4 parts by mass of ion exchange water, 0.5 parts by mass of BYK-420 as a viscosity agent, 5.6 parts by mass of BYK-2015 as a dispersant, 2.0 parts by mass of Surfynol 440 as a defoamer, and 70 parts by mass of TI-PURE R-960 as a pigment were premixed in a dispersion container. Thereafter, a dispersion treatment was performed at 1,500 rpm using an SG mill (dispersion medium: glass beads) until the coarse particles of the pigment reached 25 μm or less, thereby obtaining a pigment dispersion paste 1 for an aqueous top coating composition.

[0323] <Preparation of water-based top coating composition>

[0324] (Water-based main agent 1 of water-based top coating composition)

[0325] 56.0 parts by mass of Setaqua 65155 as an acrylic resin aqueous dispersion, 5.0 parts by mass of Solvesso 100 as an organic solvent, 2.0 parts by mass of butyl cellosolve, 2.0 parts by mass of ion exchange water, and 1103.5 parts by mass of a pigment dispersion paste for an aqueous top coating were mixed and stirred using a disperser to obtain a main agent 1 for an aqueous top coating composition.

[0326] (Curing agent 1 for water-based top coating composition)

[0327] 8.10 parts by mass of Dulanet TPA-100 and 2.20 parts by mass of Bio-Dure 401-60 as water-dispersible polyisocyanate were mixed and stirred using a disperser to obtain a curing agent 1 for an aqueous top coating composition.

[0328] <Production Example 3>

[0329] <Preparation Example of Water-Based Top Coating Composition 2>

[0330] (Main agent 2 for water-based top coating composition)

[0331] 27.3 parts by mass of Vanok WD-5512 as an acrylic resin aqueous dispersion and 10.0 parts by mass of AQUATIX-8421 as a polyolefin wax aqueous dispersion were mixed and stirred using a disperser to obtain a main agent 2 for an aqueous top coating composition.

[0332] (Top coat with water-based curing agent 2)

[0333] 69.5 parts by mass of Biohidure 304 as a water-dispersible polyisocyanate and 35.3 parts by mass of 2-butoxyethyl acetate as an organic solvent were mixed and stirred using a disperser to obtain a curing agent 2 for a water-based top coating material.

[0334] (Details of Materials for Preparing the Aqueous Top Coating Composition)

[0335] Setaqua 6515 (manufactured by Allnex, polyol acrylic aqueous dispersion), hydroxyl value: 109 mgKOH / g, solid content concentration: 45% by mass

[0336] Vanok WD-551 (manufactured by DIC Corporation, acrylic dispersion, acid value: 8.5 mgKOH / g, hydroxyl value: 100 mgKOH / g, number average molecular weight: 4,600, solid content concentration: 44% by mass)

[0337] Dulanet TPA-100 (manufactured by Asahi Kasei Corporation, isocyanurate-type hexamethylene diisocyanate (HDI)), NCO content: 23.1% by mass, solid content concentration: 100% by mass

[0338] · Biohydride 401-60 (manufactured by Sumika Biohydriden Co., Ltd., hydrophilic modified isophorone diisocyanate), NCO content: 13.3% by mass, solid content concentration: 60% by mass

[0339] · Biohydride 304 (manufactured by Sumika Biohydride Co., Ltd., nonionic modified polyisocyanate (a substance obtained by introducing allophanate groups into isocyanate chains by further adding HDI trimer to urethane groups generated by adding hydrophilic polyether to HDI trimer, which has a nonionic hydrophilic group and further introduces allophanate groups into isocyanate chains), solid content concentration: 100% by mass

[0340] AQUATIX-8421 (manufactured by BYK, polyolefin wax aqueous dispersion, active ingredient concentration: 20% by mass)

[0341] ·Solvesso 100 (manufactured by Shoei Chemical Industry Co., Ltd., organic solvent)

[0342] ・Butyl cellosolve (made by Sankyo Chemical Co., Ltd., organic solvent)

[0343] · 2-Butoxyethyl acetate (manufactured by Kanto Chemical Co., Ltd., organic solvent)

[0344] (Details of Materials for Pigment Dispersion Paste for Water-Based Top Coating Composition)

[0345] BYK-420 (manufactured by Big Chemie Jampan Co., Ltd., viscosity regulator), solid content concentration: 52% by mass)

[0346] BYK-2015 (manufactured by Big Chemie Jampan Co., Ltd., dispersant), solid content concentration: 40% by mass

[0347] Surfynol 440 (manufactured by Nissin Chemical Industry Co., Ltd., defoaming agent), solid content concentration: 100% by mass

[0348] TI-PURE R-960 (manufactured by Dupont, titanium oxide)

[0349] <Formation of Multilayer Coating Film>

[0350] (Example 1)

[0351] The degreasing of a cold-rolled steel sheet of JIS G 3141 (SPCC-SB) with dimensions of 0.8×70×150 mm was carried out using xylene. Subsequently, the polyamine compound in the aqueous curing agent 1 and the epoxy equivalent group of the film-forming resin, i.e., epoxy resin, in the aqueous base agent 1 of the undercoat coating composition obtained in the above-mentioned production example were mixed using a disperser in such a manner that the ratio of the active hydrogen equivalent to the epoxy equivalent (active hydrogen equivalent / epoxy equivalent) became 0.59 (undercoat (1)), and the mixture was applied onto the above-mentioned steel sheet by air spraying so that the dry film thickness became 45 μm, thereby forming an undried undercoat coating film.

[0352] Subsequently, at room temperature (25 °C) with an interval of 7 minutes, in the state where the above-mentioned undercoat coating film was undried, using a disperser, the surface of the above-mentioned undercoat coating film was mixed in such a manner that the molar ratio of the isocyanate group of the polyisocyanate compound in the aqueous topcoat coating composition curing agent 1 obtained in the above-mentioned production example to the hydroxyl group of the film-forming resin, i.e., acrylic resin, in the aqueous topcoat coating composition base agent 1 became 1.58 (topcoat (1)), and wet-on-wet coating was carried out by air spraying so that the dry film thickness became 45 μm, thereby forming an undried topcoat coating film.

[0353] After standing at room temperature (25 °C) for 20 minutes, it was dried at 60 °C for 60 minutes (forced drying) to obtain a multilayer coating film with a dry film thickness of 90 μm.

[0354] <Examples 2 to 39 and Comparative Examples 1 to 7>

[0355] The types and / or amounts of the respective components were changed to the amounts shown in Tables 1A to 1J, and except for this, the same operations as in Production Example 1 were carried out to produce an undercoat coating composition and a topcoat coating composition. It should be noted that as the aqueous topcoat coating composition, in Example 26, the polyisocyanate compound in the aqueous topcoat coating composition curing agent 2 obtained in the above-mentioned production example and the hydroxyl group of the film-forming resin, i.e., acrylic resin, in the aqueous topcoat coating composition base agent 2 were mixed using a disperser in such a manner that the molar ratio of NCO / OH became 1.58 (topcoat (2)). In addition, as the solvent-based topcoat coating composition, in Example 27, Nippe Uretopp Eco (manufactured by Nippon Paint Industrial Coatings Co., Ltd., solvent-based two-component urethane-based coating) (topcoat (3)) was used, and in Example 28, Nippe Mighty Rack (10:1) (manufactured by Nippon Paint Industrial Coatings Co., Ltd., solvent-based two-component urethane-based coating) (topcoat (4)) was used.

[0356] In addition, a multilayer coating film was obtained in the same manner as in Example 1 except that the coating film was formed under the coating conditions shown in Tables 1A to 1J.

[0357] <Evaluation Items>

[0358] 1) Coating appearance (visual inspection)

[0359] The appearance of the multilayer coating films obtained in Examples and Comparative Examples was visually observed and evaluated based on the following criteria: 3 points or more was considered acceptable.

[0360] 7 points: The coating surface is smooth and no spherical objects (concavities and convexities) are confirmed. When the coating film is irradiated with a fluorescent light, its image can be clearly recognized.

[0361] 6 points: There are very few spherical objects (concavities and convexities) on the coating surface, but when the coating film is irradiated with a fluorescent light, the image can be clearly recognized.

[0362] 5 points: Spherical objects (concavities and convexities) are slightly present on the coating surface, but when the coating film is illuminated with a fluorescent light, the image thereof can be roughly clearly recognized.

[0363] 4 points: Spherical objects (concavities and convexities) exist on the coating surface, but their images can be recognized when the coating film is irradiated with a fluorescent light.

[0364] 3 points: There are spherical objects (concavities and convexities) on the coating surface. When the coating film is irradiated with a fluorescent light, the image is slightly blurred, but can be recognized.

[0365] 2 points: There are many spherical objects (concavities and convexities) in the coating film, and when the coating film is irradiated with a fluorescent light, the image is blurred and difficult to recognize.

[0366] 1 point: There are many spherical objects (concaves and convexities) on the coating film, and the image thereof is hardly recognizable when the coating film is irradiated with a fluorescent light.

[0367] 2) Coating appearance (WaveScan: du value)

[0368] The appearance of the multilayer coating films obtained in Examples and Comparative Examples was measured for dullness (du value) using Wave-Scan II (manufactured by BYK Gardner) (measurement wavelength: 100 μm or less) and evaluated according to the following criteria. 3 points or more was considered acceptable.

[0369] Here, the du value measured by the aforementioned device is a value related to scattered light caused by structures less than 100 μm (ultra-high frequency concavities and convexities). The smaller the du value, the smaller the absolute amount of structures less than 100 μm (ultra-high frequency concavities and convexities), that is, the higher the surface smoothness. It should be noted that the angle of incident light (the angle between the normal direction of the surface of the measurement object and the incident light) when measuring the du value is 20 degrees.

[0370] 7 points: du value is less than 20

[0371] 6 points: du value is greater than 20 and less than 25

[0372] 5 points: du value is 25 or more and less than 30

[0373] 4 points: du value is 30 or more and less than 35

[0374] 3 points: du value is 35 or more and less than 40

[0375] 2 points: du value is 40 or more and less than 45

[0376] 1 point: du value is 45 or above

[0377] 3) Film appearance (gloss values ​​at 20° and 60°)

[0378] The gloss values ​​(20° and 60° gloss values) of the multilayer coating films obtained in Examples and Comparative Examples were measured using a gloss meter GM-268A (manufactured by Konica Minolta Co., Ltd.) and evaluated based on the following criteria. 3 points or more were considered acceptable.

[0379] 20° gloss value

[0380] 7 points: 80 or above

[0381] 6 points: 78 or more and less than 80

[0382] 5 points: 75 or above and less than 78

[0383] 4 points: 73 or more and less than 75

[0384] 3 points: 70 or above and less than 73

[0385] 2 points: 68 or more and less than 70

[0386] 1 point: less than 68

[0387] 60° gloss value

[0388] 7 points: 90 or above

[0389] 6 points: 88 or above and less than 90

[0390] 5 points: 85 or above and less than 88

[0391] 4 points: 83 or above and less than 85

[0392] 3 points: 80 or above and less than 83

[0393] 2 points: 78 or more and less than 80

[0394] 1 point: less than 78

[0395]

Table 1A

[0396]

[0397]

Table 1B

[0398]

[0399]

Table 1C

[0400]

[0401]

Table 1D

[0402]

[0403]

Table 1E

[0404]

[0405]

Table 1F

[0406]

[0407]

Table 1G

[0408]

[0409]

Table 1H

[0410]

[0411]

Table 1I

[0412]

[0413]

Table 1J

[0414]

[0415] Examples 1 to 39 are examples of the present invention, which use an aqueous coating composition as an undercoat coating composition and can obtain a multilayer coating film having a smooth appearance even in the case of wet-on-wet coating.

[0416] Comparative Examples 1, 2, and 6 are examples in which the polyamine compound (B1) was not used, and the appearance of the obtained multilayer coating films was not sufficiently satisfactory.

[0417] Comparative Examples 3 to 5 are examples in which the polyamine compound (B2) was not used. In these cases, the appearance of the obtained multilayer coating films was also not sufficiently satisfactory.

[0418] Comparative Example 7 is an example in which the organic solvent (C) was not used, and the appearance of the obtained multilayer coating film was not sufficiently satisfactory.

Claims

1. A method for producing a multilayer coating, comprising: a bottom coating film forming step of applying a bottom coating composition on the object to be coated to form a bottom coating film; an upper coating film forming step of applying an upper coating composition on the lower coating film by wet-on-wet coating to form an upper coating film; as well as a drying step of drying the lower coating film and the upper coating film simultaneously to form a multilayer coating film, The bottom coating composition is a water-based coating composition comprising a water-based main agent (I) and a water-based curing agent (II), The aqueous main agent (I) comprises an aqueous dispersion of an epoxy resin (A), The water-based curing agent (II) comprises a polyamine compound (B), At least one of the aqueous main agent (I) and the aqueous curing agent (II) contains an organic solvent (C), The polyamine compound (B) includes a polyamine compound (B1) having an active hydrogen equivalent of 100 g / eq or more and 200 g / eq or less and a polyamine compound (B2) having an active hydrogen equivalent of 300 g / eq or more and 900 g / eq or less.

2. The method for producing a multilayer coating film according to claim 1, wherein: The content of the polyamine compound (B1) in the total of the polyamine compound (B1) and the polyamine compound (B2) is 10% by mass or more and 90% by mass or less.

3. The manufacturing method according to claim 1 or 2, wherein: The polyamine compound (B1) and the polyamine compound (B2) each contain at least one selected from aliphatic polyamines, alicyclic polyamines, aromatic polyamines, polyoxyalkylene-containing polyamines, polyoxyalkylene-containing aromatic polyamines, and polyamidoamine compounds.

4. The method for producing a multilayer coating film according to any one of claims 1 to 3, wherein At least one of the aqueous main agent (I) and the aqueous curing agent (II) further contains a curing catalyst (E).

5. The method for producing a multilayer coating film according to any one of claims 1 to 4, wherein The epoxy equivalent of the epoxy resin (A) is 100 g / eq or more and 5,000 g / eq or less.

6. The method for producing a multilayer coating film according to any one of claims 1 to 5, wherein: The ratio of the active hydrogen equivalent of the polyamine compound (B) to the epoxy equivalent contained in the epoxy resin (A) (active hydrogen equivalent / epoxy equivalent) is 0.2 or more and 1.0 or less.

7. The method for producing a multilayer coating film according to any one of claims 1 to 6, wherein: At least one of the aqueous main agent (I) and the aqueous curing agent (II) further includes a viscosity regulator (D).

8. The method for producing a multilayer coating film according to any one of claims 1 to 7, wherein: The top coating composition is a coating composition comprising a main agent (III) and a curing agent (IV), The main agent (III) comprises a coating film forming resin, The coating film forming resin has a hydroxyl group, The curing agent (IV) contains a polyisocyanate compound.

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