Method for producing multilayer coating film

Abstract

The purpose of the present invention is to provide a method for producing a multilayer coating film, whereby a multilayer coating film having a smooth appearance can be achieved even when wet-on-wet coating is performed using an aqueous coating composition as an undercoat coating composition. 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 being an aqueous coating composition containing an aqueous main agent (I) and an aqueous curing agent (II), the aqueous main agent (I) containing an aqueous dispersion of an epoxy resin (A), the aqueous curing agent (II) containing a polyamine compound (B), and the aqueous curing agent (II) containing a polyamine compound (B). At least one of the aqueous main agent (I) and the aqueous curing agent (II) contains a particulate material (D), and the content of the particulate material (D) is more than 120 parts by mass and 380 parts by mass or less relative to 100 parts by mass of a resin solid component contained in the aqueous coating composition.

Description

Technical Field

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

[0002] In recent years, awareness of reducing environmental burdens has increased, leading to a demand for environmentally friendly products. In the coatings field, for example, there is a demand for reducing the amount of organic solvents used. This demand can be met by using aqueous coating compositions that use water as a solvent. In the coatings field used in industrial machinery and construction machinery, there is also a growing demand for switching to aqueous coating compositions.

[0003] Industrial and construction machinery are typically large and can withstand heavy loads, and therefore typically have thicker substrates (steel plates) than, for example, automobile bodies. Consequently, when coating such industrial and construction machinery, the high heat capacity of the coating material can lead to insufficient heat transfer to the coating in the heating furnace. Therefore, when coating such coating materials, room-temperature film-forming coating compositions are selected that can form a coating film even at room temperature, eliminating the need for high-temperature heating steps.

[0004] Industrial machinery and construction machinery are often used in harsh physical environments. Therefore, the coatings that protect their surfaces are typically required to have both excellent corrosion resistance and excellent weather resistance. Methods for forming coatings that satisfy both corrosion resistance and weather resistance include using a coating composition with excellent corrosion resistance as a basecoat and then applying a topcoat with excellent weather resistance to form a multilayer coating.

[0005] For example, Patent Document 1 describes a method for forming a thick-film anticorrosion coating, characterized in that a weak-solvent-type high-solid modified epoxy resin coating is applied as a bottom layer, followed by an upper layer of a weak-solvent-type high-solid polyurethane resin coating, wherein the weak-solvent-type high-solid modified epoxy resin coating comprises a binder resin component consisting of 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 consisting of a polyol resin having a hydroxyl value of 10 to 100 mgKOH / g and a polyisocyanate compound.

[0006] This method describes a method in which a single undercoat and a single topcoat are applied, achieving an anticorrosion effect equivalent to that achieved by conventional multilayer coating. However, this method involves applying the topcoat after the undercoat has been applied and then drying at room temperature for 24 hours. This method requires a long time to form the multilayer coating film, resulting in poor coating efficiency (also known as coating workability).

[0007] In recent years, a wet-on-wet coating method (also known as two-coat-one-bake) has attracted much attention from the perspective of shortening the coating process. This coating method is a coating method that can shorten the coating process by applying a base coating composition and then applying an overcoat coating composition without drying the base coating composition. Thereafter, both coating films are dried simultaneously.

[0008] Regarding wet-on-wet coating, Patent Document 2 studies the following multi-layer coating film formation method, 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.

[0009] Patent document 3 studies the following: in 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 body pigment content in the primer coating film and the top coating film.

[0010] 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; as an overcoat coating composition, a composition comprising an acrylic resin, an isocyanate compound and a surface conditioner is used; and the difference in surface tension between the undercoat coating composition and the overcoat coating composition is set to 2 to 8 mN / m, etc.

[0011] Patent Document 5 describes that a composition comprising an epoxy resin, an anti-rust pigment, a coloring pigment, and an extender pigment is used as a primer coating composition, and a composition comprising an acrylic resin and an active methylene-blocked polyisocyanate compound is used as a top coating composition, wherein 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, for example.

[0012] Prior art literature

[0013] Patent Literature

[0014] Patent Document 1: Japanese Patent Application Laid-Open No. 2010-188239

[0015] Patent Document 2: Japanese Patent Application Laid-Open No. 2020-192516

[0016] Patent Document 3: Japanese Patent Application Laid-Open No. 2021-160120

[0017] Patent Document 4: International Publication No. 2013 / 024784

[0018] Patent Document 5: Japanese Patent Application Publication No. 2018-008205 Summary of the Invention

[0019] Problems to be solved by the invention

[0020] Here, when the bottom coating composition and the top coating composition are wet-on-wet applied, there is a problem that the following undesirable conditions are easily caused: the coating composition mixes with each other between the layers of the two undried coating films (also referred to as mixed layers), and the appearance of the multilayer coating film obtained after drying deteriorates. This problem is particularly evident when using a water-based coating composition as the bottom coating composition. Especially when industrial machinery and construction machinery are coated objects, the coating film thickness is large compared with automobile bodies, and, as described above, a normal temperature coating film forming coating composition is selected. Therefore, existing known coating compositions are all solvent-based coating compositions that use a solvent as a dispersion medium. Regarding the situation of wet-on-wet application using a water-based coating composition, it cannot be said that sufficient research has been carried out. Especially in wet-on-wet application, the coating films of the two layers are dried simultaneously, so when drying and / or curing, the appearance of the coating film easily deteriorates.

[0021] An object of the present disclosure is to provide a method for producing a multilayer coating film that can achieve a multilayer coating film having a smooth appearance even when an aqueous coating composition is used as an undercoat coating composition and wet-on-wet coating is performed.

[0022] Means used to solve problems

[0023] The present disclosure includes the following technical solutions.

[0024] [1] A method for producing a multilayer coating film, comprising:

[0025] a primer coating film forming step of applying a primer coating composition on the object to be coated to form a primer coating film;

[0026] 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

[0027] A drying step in which the bottom coating film and the top coating film are dried simultaneously to form a multilayer coating film.

[0028] 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).

[0029] The aqueous main agent (I) comprises an aqueous dispersion of the epoxy resin (A),

[0030] The aforementioned water-based curing agent (II) comprises a polyamine compound (B),

[0031] At least one of the aqueous main agent (I) and the aqueous curing agent (II) contains a particulate material (D),

[0032] The content of the particulate material (D) is more than 120 parts by mass and not more than 380 parts by mass relative to 100 parts by mass of the resin solid content contained in the aqueous coating composition.

[0033] [2] The production method according to [1], wherein the polyamine compound (B) comprises at least one selected from aliphatic polyamines, alicyclic polyamines, aromatic polyamines, polyoxyalkylene-containing polyamines, polyoxyalkylene-containing aromatic polyamines, and polyamide-amine compounds.

[0034] [3] The production method according to [1] or [2], wherein the polyamine compound (B) contains at least one selected from alicyclic polyamines, aromatic polyamines, aromatic polyamines containing polyoxyalkylene groups, and polyamidoamines.

[0035] [4] The method for producing a multilayer coating film according to any one of [1] to [3], wherein the epoxy equivalent of the epoxy resin (A) is 100 g / eq or more and 5,000 g / eq or less.

[0036] [5] The method for producing a multilayer coating film according to any one of [1] to [4], wherein the active hydrogen equivalent of the polyamine compound (B) is 10 g / eq or more and 1,000 g / eq or less.

[0037] [6] The method for producing a multilayer coating film 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 0.3 or more and 2.0 or less.

[0038] [7] The method for producing a multilayer coating film according to any one of [1] to [6], wherein the internal stress of the undercoat film formed from the undercoat composition is 0.09 MPa or more and 0.50 MPa or less.

[0039] [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),

[0040] The main agent (III) comprises a film-forming resin,

[0041] The coating film forming resin has a hydroxyl group,

[0042] The curing agent (IV) contains a polyisocyanate compound.

[0043] Effects of the Invention

[0044] According to the method for producing a multilayer coating film disclosed herein, even when wet-on-wet coating is performed using an aqueous coating composition as an undercoat coating composition, a multilayer coating film having a smooth appearance can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a schematic diagram showing a method for measuring internal stress. DETAILED DESCRIPTION

[0046] The method for producing a multilayer coating film disclosed herein comprises:

[0047] a primer coating film forming step of applying a primer coating composition on the object to be coated to form a primer coating film;

[0048] 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

[0049] A drying step in which the bottom coating film and the top coating film are dried simultaneously to form a multilayer coating film.

[0050] 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).

[0051] The aqueous main agent (I) comprises an aqueous dispersion of the epoxy resin (A),

[0052] The aforementioned water-based curing agent (II) comprises a polyamine compound (B),

[0053] At least one of the aqueous main agent (I) and the aqueous curing agent (II) contains a particulate material (D), and the content of the particulate material (D) is greater than 120 parts by mass and less than 380 parts by mass relative to 100 parts by mass of the resin solid content contained in the aqueous coating composition.

[0054] According to the method for producing a multilayer coating film disclosed herein, even when wet-on-wet coating is performed using an aqueous coating composition as an undercoat coating composition, a multilayer coating film having a smooth appearance can be achieved.

[0055] The present disclosure is not bound by a specific theory, but according to the research of the present inventors, it is believed that the reason why a multilayer coating film with a smooth appearance can be achieved by the manufacturing method of the multilayer coating film disclosed herein is as follows. The present inventors have studied the formation process of the multilayer coating film during wet-on-wet coating, and focused on the state of the stage after the coating composition is applied and before drying. It can be considered that: in this stage, both the lower coating film and the upper coating film are in a wet state, and the interfaces of the uncured lower coating film and the upper coating film are mixed with each other to a certain extent. It is believed that the lower coating film contains a water-based main agent and a water-based curing agent, and shrinks when it is dried, thereby generating internal stress. As mentioned above, it is believed that in the stage before drying, the lower coating film and the upper coating film are both in a wet state, and the interfaces are mixed with each other. Therefore, the internal stress generated when the lower coating film is dried and formed into a coating film will also be conducted to the upper coating film. Therefore, it is believed that as the lower coating film shrinks during curing, the upper coating film will also shrink, which will be apparent in the form of deterioration of the appearance of the multilayer coating film.

[0056] The present inventors, motivated by the desire to suppress the cure shrinkage of the undercoat film in order to improve the appearance of the multilayer coating film, investigated the use of a specified amount of particulate material in the undercoat coating composition. They found that while cure progresses, cure shrinkage is suppressed, and further, the miscibility of the undercoat and overcoat films is appropriately maintained. This allows for the production of a multilayer coating film with a superior appearance without compromising wet-on-wet coating properties.

[0057] In the present disclosure, a film obtained after application of the coating composition and before drying and curing is referred to as a coating film, and a film obtained after drying and curing is referred to as a coating film.

[0058] (Undercoat film forming step)

[0059] 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.

[0060] The coating method of the undercoat composition is not particularly limited, and examples thereof include commonly used coating methods such as dipping, brushing, roller, roller coater, air spray, airless spray, curtain coater, roller curtain coater, and die coater. In the aforementioned spray coating, a two-component mixing gun may be used as needed. These can be appropriately selected depending on the object to be coated.

[0061] The application of the above-mentioned undercoat coating composition can be carried out in a manner that the dry film thickness of the undercoat coating film (hereinafter, the "dry film of the coating film" will also be referred to as the "coating film", and the "dry film thickness of the coating film" will be 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 carried out 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 a thick film. In addition, by setting the undercoat coating film to be 10 μm or more, it is easy to fully protect the substrate, and by setting it to be 100 μm or less, it is easy to suppress the occurrence of defects such as pores in the multilayer coating film.

[0062] Examples of the coated substrate include metal substrates such as iron, zinc, tin, copper, titanium, tin-plated iron, and galvanized iron. These metal substrates may be plated with zinc, copper, chromium, or the like, and may also be surface treated with a surface treatment agent such as chromic acid, zinc phosphate, or zirconium salts.

[0063] The method for producing the multilayer coating film disclosed herein 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 handling machinery, machinery for foundation engineering (diesel hammers, hydraulic hammers, etc.), machinery for tunnel engineering (borrowing 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; and other coated objects with large heat capacity that are not easily heated even when heated. The method for producing the multilayer coating film disclosed herein can be suitably used for coating construction machinery or industrial machinery that are coated objects with large heat capacity and are not easily heated even when heated.

[0064] (Top coating film forming step)

[0065] In the top coating film forming step, the top coating composition is applied wet-on-wet onto the bottom coating film to form the top coating film, thereby forming the undried top coating film on the undried bottom coating film.

[0066] Typically, wet-on-wet coating includes a coating method in which an undried top coating film is formed on an undried bottom coating film, and the undried bottom coating film and the undried top coating film are dried simultaneously to form a multilayer coating film. Wet-on-wet coating can shorten the coating process, and since there is no need to dry the bottom coating film, energy efficiency is good. Furthermore, in the method for producing the multilayer coating film of the present disclosure, the bottom coating composition described below is used. Therefore, even when wet-on-wet coating is performed using an aqueous coating composition as the bottom coating composition, a multilayer coating film having a smooth surface can be produced.

[0067] 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 being "dry to the touch" as defined in JIS K 5600-1-1. For example, it can be confirmed by lightly touching the center of the coated surface with a fingertip and whether the fingertip is dirty.

[0068] From the perspective of work efficiency, the interval between forming the undercoat film and applying the topcoat composition (hereinafter also referred to as "coating interval" or "interval") may be greater than 0 minutes and may be 1 to 60 minutes, 1 to 30 minutes, or 1 to 15 minutes. Using the multilayer coating film forming method disclosed herein, a multilayer coating film having excellent coating appearance can be obtained even when the topcoat composition is applied while the undercoat film is barely dried. The temperature between intervals may be, for example, 0°C or higher and lower than 40°C, or 5°C or higher and lower than 35°C.

[0069] In addition, after forming the base coating film and before applying the top coating composition, the base coating film can also 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 top coating can be applied when the base coating film is semi-dried.

[0070] The coating method for applying the coating composition is not particularly limited, and examples thereof include commonly used coating methods such as dipping, brushing, roller, roller coater, air spray, airless spray, curtain coater, roller curtain coater, and die coater. For the aforementioned spray coating, a two-component mixing gun may be used as needed. These can be appropriately selected depending on the object to be coated.

[0071] The application of the above-mentioned top coating composition can be carried out in a manner such that the dry film thickness of the top coating film (hereinafter also referred to as "the film thickness of the top coating film") becomes 10 to 100 μm, preferably 20 to 80 μm. In one embodiment, the application of the above-mentioned top coating composition can be carried out in a manner such that the film thickness of the top coating film becomes 30 to 70 μm, and further becomes 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 the coating is applied as a thick film. In addition, by setting the film thickness of the top coating film to 10 μm or more, it is easy to improve the shielding property of the bottom coating film, and by setting it to 100 μm or less, it is easy to suppress the occurrence of defects such as pores in the multilayer coating film.

[0072] (Drying process)

[0073] In the drying step, the undercoat coating film and the topcoat coating film are dried simultaneously, thereby forming a multilayer coating film.

[0074] The drying temperature is preferably 5 to 100° C., and further 15 to 80° C. In one embodiment, the drying temperature can be 5 to 35° C., and the drying time can be 1 to 10 days. In another embodiment, the drying temperature can be, for example, 50 to 100° C., and further 60 to 80° C., and the drying time in this case can be 15 to 60 minutes. Furthermore, in another embodiment, after drying at 5 to 35° C. (room temperature drying) for 15 to 60 minutes, drying at 50 to 100° C. (preferably 60 to 80° C.) (forced drying) for 15 to 60 minutes can be performed.

[0075] (Mid-coat film forming process)

[0076] The method for manufacturing a multi-layer coating film disclosed herein may further include: applying a mid-coat coating composition on an undried bottom coating film by wet-on-wet application to form an undried mid-coat coating film, and may further include: applying a mid-coat coating composition on the aforementioned undried bottom coating film by further wet-on-wet application to form an undried mid-coat coating film.

[0077] The interval from forming the undercoat film to applying the midcoat composition and the interval from forming the midcoat film to further applying the midcoat composition can be appropriately applied using the conditions described above as the interval from forming the undercoat film to applying the topcoat composition.

[0078] As the coating method of the mid-coat coating composition, the method described above as the coating method of the top coating composition can be appropriately used. In addition, when applying the mid-coat coating composition, the dry film thickness of the mid-coat coating film (hereinafter also referred to as "film thickness of the mid-coat coating film") can be applied in a manner that reaches the range described above as the dry film thickness of the top coating film.

[0079] 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 well 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 an extender pigment can be appropriately used.

[0080] When the method for producing a multi-layer coating film includes a mid-coat film forming step, the bottom coating film in the top coating film forming step may be understood as the bottom coating film. Furthermore, when the method for producing a multi-layer coating film includes a mid-coat film forming step, wet-on-wet coating also includes a coating method in which an undried bottom coating film and a top coating film are formed on an undried bottom coating film, and the undried bottom coating film, the undried mid-coat coating film, and the undried top coating film are all dried simultaneously to produce a multi-layer coating film.

[0081] A coating method comprising forming an undried mid-coat film on an undried bottom-coat film, drying the undried bottom-coat film and the undried mid-coat 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;

[0082] A coating method in which an undried undercoat film is dried to form an undercoat film, an undried midcoat film and an undried topcoat film are formed on the undercoat film, and the undried midcoat film and the undried topcoat film are dried simultaneously to form a multilayer coating film.

[0083] (Undercoat coating composition)

[0084] The base coating composition is a two-component curable water-based coating composition comprising a water-based base (I) and a water-based curing agent (II). The water-based base (I) and the water-based curing agent (II) are stored separately and mixed immediately before coating to provide the mixture for coating.

[0085] Water-based coating compositions use water as a dispersion medium, and compared with the solvent-based coating compositions using a solvent as a dispersion medium, the drying speed of the dispersion medium is low. Especially, in wet-on-wet coating, when the bottom coating composition is a water-based coating composition, compared with the situation 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 herein, 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.

[0086] 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). Furthermore, at least one of the aqueous main agent (I) and the aqueous curing agent (II) may comprise a particulate material (D), and at least one of the aqueous main agent (I) and the aqueous curing agent (II) may further comprise an organic solvent (C) and / or a viscosity modifier (E), as needed.

[0087] (A) Epoxy resin aqueous dispersion

[0088] The epoxy resin aqueous dispersion (A) contained in the aqueous main component (I) is a component in which epoxy resin is dispersed in water.

[0089] Epoxy resins preferably have an average of at least two epoxy groups per molecule. The epoxy equivalent weight of the epoxy resin can be from 100 g / eq to 5,000 g / eq, from 100 g / eq to 3,000 g / eq, or from 150 g / eq to 1,000 g / eq. By keeping the epoxy equivalent weight within this range, the water dispersion stability of the epoxy resin can be ensured, the coating workability of the resulting coating composition can be improved, and the film-forming properties of the resulting multilayer coating film can be improved in appearance.

[0090] In addition, the epoxy equivalent in this disclosure means solid content epoxy equivalent, and can be measured by the method based on JIS K7236.

[0091] The epoxy resin may be saturated or unsaturated, and may be any of aliphatic, alicyclic, aromatic, and heterocyclic types. It may have a hydroxyl group and may be a modified product modified with an aliphatic polyol compound.

[0092] The epoxy resin is preferably a polyglycidyl ether epoxy resin having a backbone based on polyphenols, hydrogenated products of polyphenols, polyols, and / or novolac phenol. The backbone preferably includes a backbone based on polyols and / or phenols, and preferably includes a backbone based on diols.

[0093] 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 aforementioned compounds.

[0094] As the hydrogenation products of the aforementioned polyphenols, hydrogenation products of the aforementioned compounds can be cited.

[0095] The polyols are not particularly limited, and examples thereof include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol (n=4-35), 1,2-propylene glycol, polypropylene glycol (n=2-15), 1,3-propylene glycol, 1,4-butylene glycol, 1,5-pentanediol, 1,6-hexanediol, 1,2,6-hexanetriol, glycerin, neopentyl glycol, trimethylolethane, and trimethylolpropane. Among the above compounds, polypropylene glycol (n=8-10) is particularly preferred.

[0096] As epoxy resins, polyglycidyl esters obtained by reacting a polycarboxylic acid with epichlorohydrin or a derivative thereof may also be used. The polycarboxylic acid is not particularly limited, 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-naphthalenedicarboxylic acid, and dimerized linolenic acid. Among these, diglycidyl adipate, diglycidyl phthalate, and diglycidyl hexahydrophthalate are preferred.

[0097] Among the aforementioned epoxy resins, bisphenol-type epoxy resins such as bisphenol A-type epoxy resin and bisphenol F-type epoxy resin are preferred.

[0098] The epoxy resin may be a polyol-modified epoxy resin obtained by reacting an aliphatic polyol compound with an epoxy resin, as needed. The polyol-modified epoxy resin can be prepared by condensing the epoxy resin and the aliphatic polyol compound. The mass ratio of the epoxy resin to the aliphatic polyol compound (mass of epoxy resin:mass of aliphatic polyol compound) in the condensation reaction is preferably in the range of 95:5 to 5:95. Polyol-modified epoxy resins have the advantage of being well-dispersible in water.

[0099] 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 its molecule.

[0100] 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 more preferred. As the aforementioned polyalkylene glycol, a polyalkylene glycol having an alkylene group with a carbon number of 4 or less is preferred, and examples thereof include polyethylene glycol, polypropylene glycol, polybutylene glycol, and block copolymers of ethylene oxide and propylene oxide. In addition, mixtures and copolymers of the aforementioned polyalkylene glycols may also be used. In addition, end-capping may be performed partially using monohydric alcohols, etc. The aforementioned polyalkylene glycol may partially have a branched structure, and is more preferably a straight-chain polyalkylene glycol.

[0101] The aforementioned aliphatic polyol compound may be a mixture of the aforementioned polyether polyol (especially polyalkylene glycol) and other aliphatic polyols. Examples of the aforementioned other aliphatic polyols include aliphatic polyester polyols, aliphatic polycarbonate polyols, aliphatic polyamide polyols, and aliphatic polyurethane polyols, with aliphatic polyester polyols being 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, and more preferably 90% by mass or more and 100% by mass or less.

[0102] 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.

[0103] The condensation reaction is preferably carried out at a ratio such that the ratio z(OH):z(EP) of the hydroxyl equivalent of the aliphatic polyol compound to the epoxy equivalent of the epoxy resin is 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 carrying out the reaction within the above range, there is an advantage in 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.

[0104] The epoxy resin contained in the epoxy resin aqueous dispersion (A) preferably comprises a polyol-modified bisphenol-type epoxy resin such as a polyol-modified bisphenol A epoxy resin or a polyol-modified bisphenol F epoxy resin. These polyol-modified bisphenol-type epoxy resins have the advantages of having suitable water dispersibility and improving the physical properties of the resulting multilayer coating film. As another embodiment, for example, the aforementioned polyol-modified epoxy resin (preferably a polyol-modified bisphenol-type epoxy resin) and a bisphenol-type epoxy resin (a bisphenol-type epoxy resin not modified by a polyol) can be used in combination.

[0105] The number average molecular weight of the epoxy resin is preferably 200 to 20,000, more preferably 300 to 10,000. Within this range, there is an advantage in ensuring 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.

[0106] In addition, in this disclosure, the number average molecular weight is a polystyrene conversion value based on gel permeation chromatography (GPC).

[0107] The epoxy resin aqueous dispersion (A) can be prepared by conducting a synthesis reaction of an epoxy resin (polyol-modified epoxy resin) in the absence of a solvent or in the presence of a suitable organic solvent, then adding the resulting mixture dropwise to water and mixing. Excess solvent can be removed as needed to produce an aqueous dispersion. A dispersant such as a surfactant can be used, if necessary, when dispersing the epoxy resin in water.

[0108] As the epoxy resin aqueous dispersion (A), commercially available products may be used, such as the BECKOPOX series (manufactured by Ornex Japan Co., Ltd.), the jER series (manufactured by Mitsubishi Chemical Corporation), and the ADEKA Resin EM series (manufactured by ADEKA Corporation).

[0109] The aforementioned epoxy resin aqueous dispersions may be used alone or in combination of two or more.

[0110] The aforementioned water-based main agent (I) may include other resin components as needed on the basis of including epoxy resin aqueous dispersion (A). As other resin components, for example, polyurethane resin aqueous dispersion, polyester resin aqueous dispersion, acrylic resin aqueous dispersion etc. can be listed. As the preferred resin component when also including other resin components, from the viewpoints such as compatibility with 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 with the amount of each performance of the aforementioned water-based coating composition and each performance of the obtained multilayer coating film as a condition.

[0111] 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).

[0112] It should be noted that in the present disclosure, the "resin solid content" of the base coating composition refers to: the total amount of solid content of the resin components that can be contained in the water-based main agent (I) and the water-based curing agent (II), specifically refers to: the solid content of the epoxy resin (A) and the solid content of the resin that can be contained in the coating film-forming resin such as the polyurethane resin aqueous dispersion, polyester aqueous dispersion, acrylic resin aqueous dispersion added as desired, and the total amount of the solid content of the polyamine compound (B) described later.

[0113] The amount of the resin solid content in the undercoat composition may be preferably 10 parts by mass or more and 80 parts by mass or less, more preferably 15 parts by mass or more and 70 parts by mass or less, based on 100 parts by mass of the total solid content contained in the undercoat composition.

[0114] In the present disclosure, the solid content refers to the heating residue after drying at 105° C. for 1 hour.

[0115] (B) Polyamine compounds

[0116] The polyamine compound (B) may be any compound having two or more amino groups in one molecule.

[0117] 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.

[0118] Examples of the aliphatic amine include alkylene polyamines, polyalkylene polyamines, and other aliphatic amines.

[0119] Examples of alkylene polyamines include H2N-(R 1 -NH) n -H(where R 1 represents 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; and n represents an integer of 1 to 5. ) and the like.

[0120] More specific examples include methylenediamine, ethylenediamine, 1,2-diaminopropane, 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, 1,3-diaminopentane, neopentanediamine, 1,6-diaminohexane (hexamethylenediamine), 2-methyl-1,5-pentanediamine, 1,7-diaminoheptane, methylhexamethylenediamine, 1,8-diaminooctane, 1,9-diaminononane, and 1,10-diaminodecane.

[0121] Examples of the polyalkylene polyamine include diethylenetriamine, bis(3-aminopropylamine), triethylenetetramine, N,N-bis(3-aminopropyl)ethylenediamine, tetraethylenepentamine, pentaethylenehexamine, and hexamethylenetetramine.

[0122] 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.

[0123] Examples of the alicyclic polyamine include 1,4-cyclohexanediamine, 4,4'-methylenebiscyclohexylamine, 4,4'-isopropylidenebiscyclohexylamine, norbornanediamine, bis(aminomethyl)cyclohexane, diaminodicyclohexylmethane, isophoronediamine, menthanediamine (MDA), and 1,4-bis(3-aminopropyl)piperazine.

[0124] 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 specific examples include 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, and bis(aminoethyl)naphthalene.

[0125] Polyamines containing polyoxyalkylene groups are polyamine compounds having polyoxyalkylene chains, and are compounds that do not fall under the "polyoxyalkylene-containing aromatic polyamines" described below, that is, compounds that do not have aromatic groups. Examples of the polyoxyalkylene chains contained in polyamines containing polyoxyalkylene groups include polyoxyethylene chains, polyoxypropylene chains, poly(oxyethylene-oxypropylene) chains, and poly(oxytetramethylene) chains.

[0126] 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 are also referred to as polyoxyalkylene group-containing aliphatic polyamines.

[0127] 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 or pentaerythritol with an alkylene oxide such as ethylene oxide and / or propylene oxide into amino groups.

[0128] The molecular weight of the polyamine containing polyoxyalkylene groups is preferably 100 to 5,000, more preferably 120 to 3,000, and even more preferably 120 to 500. A molecular weight within this range has the advantage of improving the appearance of the resulting coating film. If the molecular formula of the polyamine compound is known, the molecular weight can be calculated based on the molecular formula. If the number of repeating oxyalkylene units in the polyoxyalkylene chain is not a natural number, the molecular weight may be a number average molecular weight.

[0129] As the polyamine containing polyoxyalkylene groups, commercially available products can be used, and examples of commercially available products include polyoxyalkylene group-containing aliphatic polyamines such as Jeffamine M-600, Jeffamine M-1000, Jeffamine D-230, Jeffamine D-2000, Jeffamine EDR-148, Jeffamine T-403, and Jeffamine T-3000 (all manufactured by Huntersman Advanced Materials).

[0130] 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.

[0131] Examples of the polyoxyalkylene group-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 then introducing an amino group-containing aromatic compound.

[0132] As the aromatic polyamine containing a polyoxyalkylene group, a commercially available product can be used. Examples of the commercially available product include the Erasmer series (manufactured by KUMIAI Chemical Co., Ltd.).

[0133] The polyamidoamine compound used in the production method of the present disclosure is not particularly limited as long as it has a polyamide structure and at least two active hydrogen atoms in the molecule. In this specification, active hydrogen refers to hydrogen atoms bonded to nitrogen atoms of amino groups in polyamidoamine compounds and polyamine compounds.

[0134] The polyamide amine compound used as the polyamide amine compound can be produced by conventional methods, for example, by a condensation reaction of a polyamine compound and a polycarboxylic acid compound. In this case, the active hydrogen content of the resulting polyamide amine compound can be adjusted by adjusting the ratio of the polyamine compound to the polycarboxylic acid compound used in the reaction.

[0135] The polyamine compound used to produce the polyamidoamine compound is not particularly limited 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.

[0136] The polycarboxylic acid compound used for producing the polyamidoamine compound is not particularly limited as long as it has at least two carboxyl groups in the molecule, but is preferably a dicarboxylic acid such as an aliphatic dicarboxylic acid and a dimer acid.

[0137] 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.

[0138] In addition to the polyamidoamine compound, the polyamidoamine compound may also contain water or an aqueous solvent. Examples of the aqueous solvent include 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, and 1-propoxy-2-propanol; and aprotic polar solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone. These solvents may be used alone or in combination of two or more. Among the aforementioned, the polyamidoamine compound preferably contains water.

[0139] 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).

[0140] As the polyamidoamine compound, commercially available polyamidoamine compounds may also be used. Examples of such polyamidoamine compounds include Aradur 3986, Aradur 38-1 (manufactured by HUNTSMAN), 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.

[0141] The aforementioned polyamine compound (B) can be used alone or in combination of two or more. In one embodiment, the aforementioned 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, and more preferably comprises at least one selected from alicyclic polyamines, aromatic polyamines, aromatic polyamines containing polyoxyalkylene groups, and polyamide amine compounds. Alicyclic polyamines, aromatic polyamines, and aromatic polyamines containing polyoxyalkylene groups have a cyclic structure in their molecules, and polyamide amine compounds have a fluffy structure. Therefore, due to the steric hindrance of these polyamine compounds, the curing shrinkage of the bottom coating film is suppressed, the internal stress becomes smaller, and the appearance of the resulting multilayer coating film becomes good.

[0142] The aforementioned aqueous curing agent (II) only needs to contain the polyamine compound (B). 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-exchanged water, pure water, surface water, industrial water, etc.), and mixtures of water and water-miscible organic solvents 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 examples thereof include alcohols such as isopropyl alcohol; glycol ethers, etc.

[0143] 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. In addition, a surfactant, a dispersing resin, etc. can be used in combination in the dispersion of the polyamine compound (B) as needed.

[0144] As one method of dispersing the polyamine compound (B), there is mentioned a method of preparing a polyamine compound aqueous dispersion by mixing the polyamine compound (B) and a surfactant in an aqueous solvent.

[0145] The surfactant preferably includes at least one of an anionic surfactant and a nonionic surfactant. 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.

[0146] Phosphate ester surfactants, one type of anionic surfactant, are surfactants having a phosphoric acid group as an anionic group. Examples of phosphate ester surfactants include polyoxyalkylene alkyl ether phosphates, polyoxyalkylene alkylphenyl ether phosphates, and salts thereof, such as ammonium salts, lithium salts, sodium salts, and potassium salts.

[0147] Commercially available products may be used as the phosphate ester and its salt, and examples of the commercially available products include DISPARLON PW-36, DISPARLON AQ-330 (manufactured by Kusumoto Chemicals Co., Ltd.), DISPERBYK-103, DISPERBYK-111, and DISPERBYK-145 (manufactured by Bicchemie Japan Co., Ltd.).

[0148] 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, hexanoic acid, heptanoic acid, octanoic acid, 2-ethylhexanoic acid, nonanoic acid, decanoic 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, undecenoic acid, myristoleic acid, palmitoleic acid, 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, mead acid, and eicosatrienoic acid; and octadecanoic acid. Tetraunsaturated fatty acids such as tetraenoic acid, arachidonic acid, eicosatetraenoic acid, and adrenic acid; pentaunsaturated fatty acids such as octadecapentanoic 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, and potassium salts.

[0149] As the carboxylic acid-based surfactant, a commercially available product can be used, and can be obtained from, for example, Kishida Chemical Co., Ltd., Tokyo Chemical Industry Co., Ltd., Nippon Seika Co., Ltd., and the like.

[0150] Sulfonic acid-type surfactants, one type of anionic surfactant, are surfactants having a sulfonic acid group as an anionic group. Examples of surfactants having a sulfonic acid group include alkylbenzenesulfonic acid, alkyldiphenyletherdisulfonic acid, perfluoroalkoxybenzenesulfonic acid, alkylsulfonic acid, alkylnaphthalenesulfonic acid, sulfosuccinic acid, N-acylsulfonic acid, polyoxyethylene alkylphenyl ether sulfate, alkylsulfuric acid, alkylethersulfuric acid, and alkylamidesulfuric acid; and salts thereof, such as ammonium salts, lithium salts, sodium salts, and potassium salts.

[0151] As the surfactant having a sulfonic acid group, commercially available products can be used. Examples of commercially available products include Perex SS-H, Neoprex G-25 (manufactured by Kao Corporation), Repolan PB-800 (manufactured by Lion Corporation), Teika Pawar L128 (manufactured by Teika Co., Ltd.), Niucol 565SNC, Niucol 707SF (manufactured by Nippon Emulsifier Co., Ltd.), and Aqualon KH-10 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.).

[0152] Sulfate ester surfactants, one type of anionic surfactant, are surfactants having a sulfate group as an anionic group. Examples of sulfate ester surfactants include fatty acid sulfates, alkyl sulfates, alkyl ether sulfates, and amide ether sulfates. Commercially available surfactants having a sulfate group can be used.

[0153] Examples of the nonionic surfactant include at least one selected from polyoxyalkylene glycol fatty acid esters, polyoxyalkylene glycol fatty acid esters, and polyoxyalkylene alkyl ethers. Commercially available nonionic surfactants may also be used. Examples of commercially available nonionic surfactants include the Genapol series, Genagen series (manufactured by Clariant Japan Co., Ltd.), the Noigen series (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and the Niucol N700 series (manufactured by Nippon Emulsifier Co., Ltd.).

[0154] The 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 both may be used in combination.

[0155] The temperature and dispersion conditions in the above-mentioned dispersion preparation step can be appropriately selected within the ranges generally performed by those skilled in the art.

[0156] 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 adjusting 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 is improved, and the water resistance of the obtained multilayer coating film is improved.

[0157] The content of the polyamine compound (B) in the aqueous dispersion of the polyamine compound (B) can be appropriately selected depending on the structure and molecular weight of the polyamine compound (B), and is preferably, for example, from 30% to 90% by mass, and more preferably from 40% to 80% by mass. Within the aforementioned range, there is the advantage of improving the dispersion stability of the mixture containing the aqueous main agent (I) and the aqueous curing agent (II).

[0158] In the aqueous dispersion of the polyamine compound (B), the average particle size of the aqueous dispersion (the dispersed polyamine compound (B)) is preferably 100 to 1,000 nm, more preferably 100 to 300 nm. By setting the average particle size of the aqueous dispersion within this range, there are advantages such as improved dispersion stability of the mixture comprising the aqueous main agent (I) and the aqueous curing agent (II). Furthermore, there are advantages such as ensuring better reactivity between the aqueous epoxy resin dispersion (A) and the polyamine compound (B), resulting in an improved appearance of the resulting multilayer coating film.

[0159] In addition, in this disclosure, the average particle diameter of the aqueous dispersion refers to the average particle diameter determined by the 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.

[0160] The active hydrogen equivalent of the polyamine compound is preferably 10 g / eq or more and 1,000 g / eq or less, more preferably 20 g / eq or more and 900 g / eq or less, and even more preferably 35 g / eq or more and 800 g / eq or less.

[0161] In addition, in this disclosure, the active hydrogen equivalent of a polyamine compound means the active hydrogen equivalent of a solid content, and it can be measured by the method based on JIS K 7237:1995.

[0162] 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 0.3 or more and 2.0 or less, more preferably 0.4 or more and 1.5 or less, and even more preferably 0.5 or more and 1.0 or less. Within this range, there is the advantage of ensuring better reactivity between the aqueous epoxy resin dispersion (A) and the polyamine compound (B), and improving the adhesion between the multilayer coating film obtained from the undercoat composition and the coated object.

[0163] The active hydrogen equivalent when two or more polyamine compounds are used in combination can be calculated using the following formula. That is, when the active hydrogen equivalent of the polyamine compound obtained by mixing M parts by mass (solid content) of a polyamine compound (B1) having an active hydrogen equivalent of H1 with N parts by mass (solid content) of a polyamine compound (B2) having an active hydrogen equivalent of H2 is Z, Z is calculated according to the following formula.

[0164] Z=[(M+N)×H1×H2] / (M×H2+N×H1)

[0165] (C) Organic solvents

[0166] As the organic solvent (C), any organic solvent used in the coating field can be used. While not being bound by any particular theory, the organic solvent (C) has a different polarity and boiling point than water. Therefore, by using an organic solvent (C), the drying properties of the undercoat coating film can be controlled. In addition, the organic solvent (C) can function as a diluent. In one embodiment, the organic solvent (C) can be used to accelerate the drying of the undercoat coating film.

[0167] 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; and amide solvents such as N-methylpyrrolidone.

[0168] 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 adjusting the relative evaporation rate within the aforementioned range, there are advantages in improving the drying properties of the resulting coating composition and the appearance of the resulting multilayer coating film. Preferred organic solvents having a relative evaporation rate of 0.5 to 6 include 2-methoxypropanol (propylene glycol monomethyl ether), ethanol, and isopropyl alcohol.

[0169] 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 of n-butyl acetate is set to 1.

[0170] When the organic solvent (C) is used, the content of the organic solvent (C) in the undercoat composition is preferably 0.1 to 25 mass %, more preferably 0.5 to 20 mass %, and even more preferably 1 to 18 mass %.

[0171] It should be noted that the content of the organic solvent (C) in the aforementioned base 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 base coating composition (the total amount of the aqueous main agent (I) and the aqueous curing agent (II)).

[0172] When the organic solvent (C1) is used, in one embodiment, the content of the organic solvent (C1) in the organic solvent (C) is preferably 100% by mass, and in another embodiment, it is preferably 10 to 80% by mass, more preferably 30 to 75% by mass.

[0173] When the organic solvent (C) is used, the organic solvent (C) may be contained in either the aqueous main agent (I) or the aqueous curing agent (II), but is preferably contained in both the aqueous main agent (I) and the aqueous curing agent (II).

[0174] 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 1.5 to 10% by mass.

[0175] 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 35% by mass.

[0176] When the content of the organic solvent (C) is within the above range, there are advantages in that the drying properties of the resulting coating composition are improved, and the appearance of the resulting multilayer coating film is improved.

[0177] The organic solvent (C) may be contained in either the aqueous base (I) or the aqueous curing agent (II). In one embodiment, the organic solvent (C) may be contained only in the aqueous base (I). In another embodiment, the organic solvent (C) may be contained only in the aqueous curing agent (II). In yet another embodiment, the organic solvent (C) may be contained in both the aqueous base (I) and the aqueous curing agent (II).

[0178] (D) Granular materials

[0179] The particulate material (D) is a granular material that does not substantially change in volume in the aqueous coating composition and the multilayer coating film. The material can be either an inorganic material or an organic material, preferably an inorganic material. The inclusion of the particulate material (D) allows for a multilayer coating film having a good appearance.

[0180] The granular material (D) preferably contains one or more selected from the group consisting of a rust-proof pigment (D1), an extender pigment (D2), a coloring pigment (D3), and a filler (D4).

[0181] Examples of the rust-preventive pigment (D1) include iron phosphate, aluminum phosphate, calcium phosphate, aluminum tripolyphosphate, aluminum phosphomolybdate, and aluminum zinc phosphomolybdate.

[0182] The content of the rust-preventive pigment (D1) is preferably from 0 to 250 parts by mass based on 100 parts by mass of the resin solid content of the undercoat coating composition. In one embodiment, it is more preferably from 5 to 200 parts by mass, further preferably from 10 to 150 parts by mass, even more preferably from 20 to 100 parts by mass, and in another embodiment, it is more preferably from 0 parts by mass.

[0183] Examples of the extender pigment (D2) include kaolin, talc, aluminum silicate, calcium silicate, calcium carbonate, mica, and clay.

[0184] The content of the extender pigment (D2) is preferably 0 parts by mass or more and 200 parts by mass or less relative to 100 parts by mass of the resin solid content of the undercoat coating composition. In one embodiment, it is more preferably 1 part by mass or more and 150 parts by mass or less, further preferably 5 parts by mass or more and 100 parts by mass or less, and in another embodiment, it is more preferably 0 parts by mass.

[0185] Examples of the coloring pigment (D3) include organic coloring pigments such as azo chelate pigments, insoluble azo pigments, condensed azo pigments, phthalocyanine pigments, indigo pigments, perylene pigments, perylene pigments, dioxane pigments, quinacridone pigments, isoindolinone pigments, isoindolinone pigments, diketopyrrolopyrrole pigments, and metal complex pigments; and inorganic coloring pigments such as chrome yellow, iron oxide yellow, iron oxide red, carbon black, and titanium dioxide.

[0186] The content of the coloring pigment (D3) is preferably 10 parts by mass or more and 200 parts by mass or less relative to 100 parts by mass of the resin solid content of the undercoat coating composition. In one embodiment, it is more preferably 15 parts by mass or more and 170 parts by mass or less, further preferably 15 parts by mass or more and 150 parts by mass or less, further preferably 15 parts by mass or more and 110 parts by mass or less, and in another embodiment, it is more preferably 0 parts by mass.

[0187] (D4) Filler

[0188] The filler (D4) may include an inorganic filler.

[0189] Examples of the inorganic filler include inorganic fillers other than the above-mentioned extender pigments, such as glass, silica, colloidal silica, barium sulfate, alumina, bentonite, etc. The inorganic filler may be used alone or in combination of two or more.

[0190] In one embodiment, the filler (D4) accounts for preferably 0% by mass or more and 150% by mass or less, more preferably 0% by mass or more and 70% by mass or less, and further preferably 0% by mass or more and 50% by mass or less, in a total of 100 parts by mass of the granular material (D). In another embodiment, the filler (D4) accounts for preferably 10% by mass or more and 150% by mass or less, more preferably 15% by mass or more and 120% by mass or less, and further preferably 20% by mass or more and 110% by mass or less, in a total of 100 parts by mass of the granular material (D).

[0191] The total content of the rust-preventive pigment (D1), the extender pigment (D2), the coloring pigment (D3), and the filler (D4) is preferably 90% by mass or more and 100% by mass or less, and more preferably 95% by mass or more and 100% by mass or less, based on 100 parts by mass of the total of the granular material (D).

[0192] The aforementioned granular material (D) may further contain other granular materials (D5) in addition to the anti-rust pigment (D1), the extender pigment (D2), the coloring pigment (D3) and the filler (D4).

[0193] The granular material (D) may be used alone or in combination of two or more.

[0194] The content of the particulate material (D) is preferably greater than 120 parts by mass and less than 380 parts by mass, more preferably greater than 125 parts by mass and less than 350 parts by mass, further preferably greater than 130 parts by mass and less than 300 parts by mass, and even more preferably greater than 130 parts by mass and less than 250 parts by mass, relative to a total of 100 parts by mass of the resin solids content of the base coating composition. By adjusting the content of the particulate material (D) within the aforementioned range, a multilayer coating film having a good appearance can be obtained.

[0195] The true density of the granular material (D) is preferably 0.8 g / cm 3 Above and 12g / cm 3 Below, more preferably 1g / cm 3 Above and 10g / cm 3 Below, more preferably 1.1 g / cm 3 Above 9g / cm 3 If the true density of the granular material (D) is within the above range, a multilayer coating film with good appearance can be obtained. It should be noted that, in the present disclosure, the true density of the granular material refers to the density calculated based on the volume of the granular material itself (the volume after deducting the gap portion from the volume of the container when the granular material is filled into a container of a specified volume). The true density of the granular material (D) can be measured using a Gay-Lussac pycnometer (density meter) and by a method based on JIS K 0061.

[0196] The average particle size of the granular material (D) is preferably 50 nm or more and 30 μm or less, more preferably 80 nm or more and 20 μm or less, and even more preferably 100 nm or more and 10 μm or less.

[0197] In the present disclosure, the average particle size of the granular material (D) refers to the average particle size (D50) obtained by using a conventional measuring instrument such as a laser scattering method or a diffraction method, and can be measured using, for example, a laser diffraction particle size distribution analyzer SALD-2300 (manufactured by Shimadzu Corporation).

[0198] The particulate material (D) may be contained in either the aqueous main agent (I) or the aqueous curing agent (II), but is preferably contained in the aqueous main agent (I).

[0199] The internal stress of the undercoat film formed from the undercoat composition is preferably 0.09 MPa to 0.50 MPa, more preferably 0.17 MPa to 0.42 MPa, and even more preferably 0.27 MPa to 0.35 MPa.

[0200] In the present disclosure, the internal stress of the undercoat film formed from the undercoat composition can be measured by the "Inoue and Kobatake method" (Sato Kozo; Polymer Processing, 42(11), 557 (1993)).

[0201] Specifically, a primer coating composition was first applied to a 100 μm thick short strip of PET film so that the dry coating thickness reached h1, thereby obtaining a PET film having a coating film. Next, knife-shaped supports were arranged at intervals of 70 mm, and the aforementioned PET film having a coating film was placed on the knife-shaped supports. Furthermore, the temperature was raised to 60°C and maintained at 60°C for 60 minutes to cure the coating film, thereby obtaining a coating film. Thereafter, the film was cooled to 20°C over 5 minutes, and the deflection (δ) of the PET film at 20°C was measured. Based on the measured values, the internal stress was calculated according to the following formula.

[0202] S=1 / 6h1(h1+h2)×E2h2 3 / (1-ν2 2 )×1 / ρ

[0203] [Where,

[0204] S: internal stress

[0205] h1: thickness of the coating

[0206] h2: thickness of PET film

[0207] E2: elastic modulus of PET film

[0208] ν2: Poisson's ratio of PET film

[0209] ρ: radius of curvature [ρ = L 2 / 8δ (where L is the distance between blade supports (70 mm) and δ is the deflection)

[0210] <Preparation of Undercoat Composition>

[0211] The aqueous main agent (I) and aqueous curing agent (II) of the above-mentioned base coating composition can be prepared by mixing the aforementioned components separately using methods known to those skilled in the art. The coating composition can be prepared using methods commonly used by those skilled in the art. For example, kneading and mixing using a kneader or roller, or dispersion and mixing using a sand mill or disperser, etc., can be used.

[0212] The above-mentioned bottom coating composition can include other components according to purpose and use on the basis of including the above-mentioned components. As other components, for example, organic solvents, resin components, dispersants, curing catalysts, viscosity modifiers, 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 resulting multilayer coating film.

[0213] Regarding the timing for mixing the aqueous main agent (I) and aqueous curing agent (II) in the above-mentioned base coating composition, the aqueous main agent (I) and aqueous curing agent (II) can be mixed before use and applied using a conventional coating method. Alternatively, coating can be performed by using a two-component mixing gun, where various liquids are fed to the gun and mixed at the front end of the gun.

[0214] (Top coating composition)

[0215] The topcoat composition is not particularly limited, but preferably a two-component curable coating composition comprising a base agent (III) and a curing agent (VI) is used. The base agent (III) and the curing agent (VI) are stored separately and mixed immediately before coating to provide the mixture for coating.

[0216] In one embodiment, the main agent (III) comprises a film-forming resin having hydroxyl groups, and the curing agent (VI) comprises a polyisocyanate compound. The hydroxyl groups of the film-forming resin react with the isocyanate groups of the polyisocyanate compound to form urethane bonds, thereby curing the top coating film.

[0217] The top coating composition may be an aqueous coating composition using water as a dispersion medium, or a solvent-based coating composition using a solvent as a dispersion medium.

[0218] (Water-based topcoat composition)

[0219] The aforementioned water-based top 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 film-forming resin having a hydroxyl group, and the water-based curing agent (VIa) preferably comprises a polyisocyanate compound.

[0220] 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.

[0221] Acrylic resin aqueous dispersion (Fa)

[0222] The acrylic resin contained in the acrylic resin aqueous dispersion (Fa) is a polymer of a monomer mixture containing ethylenically unsaturated monomers and has hydroxyl groups. By including the acrylic resin aqueous dispersion (Fa) in the aqueous main agent (IIIa), the multilayer coating film can be endowed with excellent coating properties such as adhesion and water resistance. Furthermore, a multilayer coating film having a smooth surface can be formed, for example, a multilayer coating film having excellent surface smoothness can be formed.

[0223] Examples of the ethylenically unsaturated monomer include hydroxyl group-containing monomers, carboxyl group-containing monomers, and other monomers.

[0224] Examples of the hydroxyl group-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; polyalkylene glycol monoesters of (meth)acrylate 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 ε-caprolactone-modified (meth)acrylates include Placcel FA-1, Placcel FA-2, Placcel FA-3, Placcel FA-4, Placcel FA-5, Placcel FM-1, Placcel FM-2, Placcel FM-3, Placcel FM-4, and Placcel FM-5, all manufactured by Daicel Chemical Industries, Ltd. In this specification, (meth)acrylic acid refers to both acrylic acid and methacrylic acid.

[0225] 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.

[0226] Examples of other monomers used in the acrylic resin aqueous dispersion (Fa) include styrene-based 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.

[0227] The above-mentioned ethylenically unsaturated monomers may be used alone or in combination of two or more.

[0228] The hydroxyl value of the acrylic resin aqueous dispersion (Fa) is preferably 40 to 200 mgKOH / g, more preferably 50 to 200 mgKOH / g. A hydroxyl value of 40 mgKOH / g or greater improves reactivity with the water-dispersible polyisocyanate (Ga), making it easier to maintain the physical strength of the resulting multilayer coating film. Furthermore, a hydroxyl value of 200 mgKOH / g or less makes it easier to maintain the water resistance of the resulting multilayer coating film.

[0229] The acid value of the acrylic resin aqueous dispersion (Fa) is preferably 2 to 150 mgKOH / g, more preferably 2 to 100 mgKOH / g. By setting the acid value within the above range, the physical strength of the obtained multilayer coating film can be easily maintained.

[0230] 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.

[0231] 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. A number average molecular weight of 1,000 or greater facilitates maintaining the physical strength of the resulting multilayer coating film, while a number average molecular weight of 100,000 or less facilitates maintaining the smoothness of the resulting multilayer coating film.

[0232] 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, adding the resulting polymer dropwise to water for mixing, and removing excess solvent as needed.

[0233] During the polymerization reaction, a polymerization initiator may be used. 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.

[0234] The polymerization temperature can be, for example, 80 to 140°C, and the polymerization time can be appropriately adjusted depending on the polymerization temperature and 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, if necessary, a polymerization initiator to a heated polymerization solvent. The polymerization solvent is not particularly limited, but preferably has a boiling point of approximately 60 to 250°C.

[0235] 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.

[0236] A neutralizing agent can 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 excellent water dispersibility to the acrylic resin. The neutralizing agent is not particularly limited, and examples thereof include 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. These neutralizing agents can be used alone or in combination of two or more.

[0237] The acrylic resin aqueous dispersion (Fa) can be prepared by mixing water with an acrylic resin that has been neutralized as needed, or by mixing the acrylic resin in water. In the preparation of the acrylic resin aqueous dispersion (Fa), excess organic solvent may be removed before adding a neutralizing agent or after water dispersion, as needed.

[0238] As the acrylic resin aqueous dispersion (Fa), a commercially available product can be used. Examples of the commercially available product include, but are not particularly limited to, MACRYNAL series products such as MACRYNAL VSM6299 / 42WA (manufactured by Surface Specialties); BAYHYDROL series products such as BAYHYDROL XP2470 (manufactured by Bayer AG); BAYNOCK series products such as BAYNOCK WD-551 (manufactured by DIC Corporation); and NeoCryl series products such as NeoCryl XK-555 (manufactured by DSM Corporation).

[0239] Water-dispersible polyisocyanate (Ga)

[0240] The water-dispersible polyisocyanate (Ga) is a water-dispersible compound having two or more isocyanate groups per molecule. It refers to a polyisocyanate compound that disperses without separation when added to an aqueous medium. The water-dispersible polyisocyanate (Ga) may be modified with a hydrophilic compound having a hydrophilic group, as needed. The hydrophilic group may be either an ionic or nonionic hydrophilic group.

[0241] Examples of the water-dispersible polyisocyanate (Ga) include aromatic diisocyanates such as toluene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), and m-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 forms, isocyanurate forms, and trimethylolpropane (TMP) adducts of these aromatic diisocyanates, aliphatic diisocyanates, and alicyclic polyisocyanates. These water-dispersible polyisocyanates (Ga) may be used alone or in combination of two or more.

[0242] In addition, in this disclosure, "alicyclic" means having an alicyclic structure in the molecule.

[0243] 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 are less reactive than aromatic polyisocyanates and can suppress side reactions with aqueous media such as water.

[0244] In the 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 within a single polyisocyanate compound. Since the polymer polyisocyanate compound is trifunctional or higher, 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.

[0245] In the aqueous top coating composition, the molar ratio (NCO / OH) of the isocyanate groups of the water-dispersible polyisocyanate (Ga) to the hydroxyl groups of the acrylic resin aqueous dispersion (Fa) is preferably 0.5 to 3.0, more preferably 0.8 to 2.0. By adjusting the molar ratio (NCO / OH) within this range, the curing reactivity of the aqueous top coating composition can be advantageously maintained within a favorable range.

[0246] The aqueous main agent (IIIa) and the aqueous curing agent (IVa) contain water as a dispersion medium. As the water, ion-exchanged water, distilled water, etc. can be used.

[0247] In 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, propyl alcohol, isopropyl alcohol, 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.

[0248] 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% by mass to 100% by mass, or 70% by mass to 100% by mass.

[0249] Other ingredients

[0250] The aforementioned water-based top coating composition may further comprise, in addition to the aforementioned components, other components such as pigments, resin particles, resin components, dispersants, curing catalysts, tackifiers, film-forming aids, and additives commonly used in coating compositions (e.g., ultraviolet absorbers, light stabilizers, antioxidants, defoamers, surface conditioners, anti-pinhole agents, rust inhibitors, etc.), depending on the purpose and use. These components may be contained in either the water-based main agent (IIIa) or the water-based curing agent (IVa).

[0251] (Solvent-based top coating composition)

[0252] The solvent-based topcoat coating composition is preferably a two-component curable coating composition comprising a base (IIIb) as the base (III) and a curing agent (IVb) as the curing agent (IV). The base (IVb) preferably comprises an acrylic resin (Fb) as the coating film-forming resin, and the curing agent (IVb) preferably comprises a polyisocyanate compound (Gb). Furthermore, the base (IIIb) and / or the curing agent (IVb) may contain an extender pigment and a viscosity modifier.

[0253] Acrylic resin (Fb)

[0254] The acrylic resin (Fb) is a polymer of a monomer mixture containing ethylenically unsaturated monomers and has hydroxyl groups. The inclusion of the acrylic resin (Fb) in the main component (IIIb) improves adhesion of the top coating film to the bottom coating film, and allows the multilayer coating film to have excellent coating properties such as water resistance. Furthermore, a multilayer coating film having a smooth surface can be formed, enabling, for example, a multilayer coating film with excellent surface smoothness.

[0255] Examples of the ethylenically unsaturated monomer include hydroxyl group-containing monomers and other monomers.

[0256] 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.

[0257] 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)acrylamides such as aminoethyl (meth)acrylamide, dimethylaminomethyl (meth)acrylamide, and methylaminopropyl (meth)acrylamide; vinyl cyanide 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.

[0258] The above-mentioned ethylenically unsaturated monomers may be used alone or in combination of two or more.

[0259] As other monomers used in the acrylic resin (Fb), the aforementioned alkyl (meth)acrylates and the aforementioned 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, and the like are more preferred.

[0260] The acrylic resin (Fb) preferably has a hydroxyl value of 40 to 200 mgKOH / g, more preferably 50 to 200 mgKOH / g. By setting the solid content hydroxyl value within the above range, it can react appropriately with the polyisocyanate compound (Gb) described below, and desired coating properties can be obtained.

[0261] The acid value of the acrylic resin (Fb) is preferably 2 to 150 mgKOH / g, more preferably 5 to 30 mgKOH / g. By keeping the acid value within this range, desired coating properties can be achieved. The solid content acid value of the acrylic resin (Fb) is more preferably 5 to 30 mgKOH / g.

[0262] 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 even more preferably 3,500 to 12,000. A number average molecular weight of 3,000 or greater for the acrylic resin (Fb) improves the drying properties of the coating composition, prevents dust from scattering in the coating room due to the stickiness of the coating composition, maintains a good coating environment, and improves the physical properties of the resulting multilayer coating film. Furthermore, a number average molecular weight of 20,000 or less for the acrylic resin (Fb) improves the gloss of the multilayer coating film.

[0263] The acrylic resin (Fb) can be produced by polymerizing the monomer mixture in the absence of a solvent or in the presence of a suitable organic solvent. Examples of polymerization methods include free radical polymerization, which can be carried out using a free radical polymerization initiator. Specifically, these methods include bulk polymerization, solution polymerization, and a bulk-suspension two-stage polymerization method in which bulk polymerization is followed by suspension polymerization. Among these, solution polymerization is particularly preferred, and examples include methods in which the monomer mixture is heated at a temperature of, for example, 80 to 200° C. while stirring in the presence of a free radical polymerization initiator.

[0264] As the acrylic resin (Fb), commercially available products can be used. Examples of the commercially available products include, but are not particularly limited to, Acrylic series products such as Acrylic A-428 (manufactured by DIC Corporation), Daiyanal series products such as Daiyanal LC-2657 (manufactured by Mitsubishi Chemical Corporation), and Hitaloid series products (manufactured by Showa Denko Materials Co., Ltd.).

[0265] The coating film forming resin may contain, in addition to the acrylic resin (Fb), a polyester resin, an epoxy resin, etc. as needed.

[0266] From the perspective of film water resistance and finishing properties, 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. In one embodiment, it is 50% by mass or more and 90% by mass or less. In another embodiment, it is 90% by mass or more and 100% by mass or less. By including the acrylic resin in this range, a multilayer coating film with better drying properties can be formed on the coated object by wet-on-wet coating.

[0267] In the present disclosure, the “solid content of the coating film forming resin” refers to the total amount of the solid content of the acrylic resin, the solid content of the epoxy resin, and the solid content of other resins that may be contained in the coating film forming resin.

[0268] Polyisocyanate compound (Gb)

[0269] The polyisocyanate compound (Gb) refers to a compound having two or more isocyanate groups in one molecule.

[0270] Examples of the polyisocyanate compound (Gb) include aliphatic diisocyanates, alicyclic diisocyanates, aromatic diisocyanates, and polymers of aliphatic diisocyanates, alicyclic diisocyanates, and aromatic diisocyanates. The polyisocyanate compound (Gb) may be a so-called asymmetric compound. The polyisocyanate compound (Gb) preferably has 5 to 24 carbon atoms, more preferably 6 to 18 carbon atoms.

[0271] 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.

[0272] Examples of the alicyclic diisocyanate include cyclohexane diisocyanate, isophorone diisocyanate (IPDI), and dicyclohexylmethane diisocyanate.

[0273] 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.

[0274] Examples of the polymer include a biuret form, an isocyanurate form, and a trimethylolpropane (TMP) adduct.

[0275] The polyisocyanate compound (Gb) may be used alone or in combination of two or more.

[0276] The polyisocyanate compound (Gb) preferably contains at least an isocyanurate of the aliphatic diisocyanate, alicyclic diisocyanate, or aromatic diisocyanate, and preferably contains an isocyanurate of the aliphatic diisocyanate. When the polyisocyanate compound (Gb) contains such an isocyanurate, the content of the isocyanurate in the polyisocyanate compound (Gb) is preferably 60% by mass or more.

[0277] In the solvent-based top-coat coating composition, the molar ratio (NCO / OH) of the isocyanate groups of the polyisocyanate compound (Gb) to the hydroxyl groups of the coating film-forming resin is preferably within a range of 0.5 to 2.0, more preferably 0.8 to 1.6. By maintaining the molar ratio (NCO / OH) within this range, the solvent-based top-coat coating composition is sufficiently cured, and desired coating film properties can be obtained.

[0278] In one embodiment, an extender pigment and a viscosity modifier 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.

[0279] 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, Suzorite Mica, and Kuralite Mica.

[0280] 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. These extenders can be used alone or in combination.

[0281] 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.

[0282] By using the extender pigment and the viscosity modifier in combination, the viscosity and viscosity behavior of the top coating composition, such as viscosity recovery, can be appropriately adjusted, and appropriate leveling and flow properties can be imparted.

[0283] As the viscosity adjuster, any of the compounds described as the viscosity adjusters used in the above-mentioned undercoat coating composition can be used.

[0284] The viscosity modifier is preferably in a range 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, relative to 100 parts by mass of the coating film-forming resin.

[0285] For example, when the total solid content of the aforementioned film-forming resin, curing agent (IVb), extender 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%.

[0286] In the solvent-based topcoat coating composition, the base agent (IIIb) and the curing agent (IVb) contain an organic solvent as a dispersion medium. Examples of the organic solvent include solvents commonly used in solvent-based coatings, such as 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, and naphtha. In particular, coating design can be achieved without using organic solvents, such as xylene, whose usage is subject to legal restrictions under the Regulations for the Prevention of Damage from Specified Chemical Substances (Regulations).

[0287] Other ingredients, etc.

[0288] The solvent-based coating composition may contain various known additives as needed. As various additives, additives used in coating compositions may be appropriately used, and examples thereof include pigments such as coloring pigments and rust-proof pigments, anti-drifting / anti-settling agents, curing catalysts (organometallic catalysts), anti-color separation agents, dispersants, defoaming / anti-cratering agents, thickeners, leveling agents, matting agents, ultraviolet absorbers, antioxidants, plasticizers, film-forming aids, organic solvents, and the like. The blending amounts of these components may be appropriately adjusted within a range that does not impair the effects of the present disclosure.

[0289] Example

[0290] The present disclosure will be described in more detail with reference to the following examples, but the present disclosure is not limited thereto.

[0291] <Manufacturing Example 1> Manufacturing Example of Primer Coating Composition

[0292] <Preparation Example of Pigment Dispersion Paste for Undercoat Coating Composition>

[0293] In a dispersion container, 38.00 parts by mass of BECKOPOX EP386W / 52WA as the epoxy resin aqueous dispersion (A-1), 21.79 parts by mass of ion-exchanged water, 2.00 parts by mass of IPA as the organic solvent (C-1), 0.45 parts by mass of BYK-011 as a defoamer, 1.90 parts by mass of BYK-2015 as a dispersant, 5.70 parts by mass of LF BOUSEI ZP-DL as a pigment of the particulate material (D1-1), 6.80 parts by mass of SSS talc as the particulate material (D2-1), 1.80 parts by mass of LOMON Titanium Dioxide R-9962 as the particulate material (D3-1), and 0.50 parts by mass of TAROX synthetic iron oxide LL-XLO as the particulate material (D3-2) were premixed using a disperser. Thereafter, a dispersion treatment was performed using an SG mill (dispersion medium: glass beads) at 1,500 rpm until the dispersed particle size of the pigment became 20 μm or less, thereby obtaining a pigment dispersion paste 1 for an undercoat coating composition.

[0294] <Preparation Example of Undercoat Composition>

[0295] (Water-based main agent for base coating composition)

[0296] 198.94 parts by mass of a pigment dispersion paste for an undercoat composition and 1.06 parts by mass of Surfynol 440 as a surface conditioner were mixed and stirred using a disperser to obtain an aqueous base agent 1 for an undercoat composition. Aqueous base agents 2 to 37 for undercoat compositions were obtained by the same procedure except that the components and amounts shown in Tables 1 to 4 were used in place of the aforementioned components.

[0297] (Water-based curing agent for base coating composition)

[0298] 10.84 parts by mass of LUCKAMIDE WN-720Z as a polyamine compound (B1-1), 5.50 parts by mass of IPA as an organic solvent (C1-1), and 0.25 parts by mass of ion-exchanged water were mixed and stirred using a disperser to obtain aqueous curing agent 1. Aqueous curing agents 2 to 6 were obtained by the same procedure except that the components and amounts shown in Tables 1 to 4 were used in place of the aforementioned components.

[0299] (Details of Materials Used in Undercoat Composition)

[0300] Epoxy resin aqueous dispersion (A)

[0301] (A-1) BECKOPOX EP 386w / 52WA (manufactured by Allnex, bisphenol A type epoxy resin dispersion), epoxy equivalent: 520 g / eq, solid content: 52% by mass

[0302] (A-2)

[0303] EM-0427WC (manufactured by Adeka Corporation, bisphenol A type epoxy resin aqueous dispersion), epoxy equivalent: 230 g / eq, solid content: 50% by mass

[0304] (A-3) BECKOPOX EP 2307W / 45WAMP (manufactured by Allnex, bisphenol A epoxy resin dispersion), epoxy equivalent: 1,980 g / eq, solid content: 45% by mass

[0305] Polyamine compound (B)

[0306] (B1-1) LUCKAMIDE WN-720Z (manufactured by DIC Corporation, polyamine compound), active hydrogen equivalent: 177 g / eq, solid content concentration: 50 mass %

[0307] (B1-2) B-5115 (manufactured by Daito Sangyo Co., Ltd., polyamine compound), active hydrogen equivalent: 39 g / eq, solid content concentration: 100 mass%

[0308] (B1-3) J-1033 (manufactured by Daito Sangyo Co., Ltd., polyamine compound), active hydrogen equivalent: 60 g / eq, solid content concentration: 100 mass%

[0309] (B-4) Aradur 3986 (manufactured by HUNTSMAN Advanced Materials, aqueous dispersion of a polyamide-amine compound), active hydrogen equivalent: 415 g / eq, solid content concentration: 40 mass %

[0310] Organic solvent (C)

[0311] (C1-1) IPA (manufactured by Shoei Chemical Co., Ltd., isopropyl alcohol), evaporation rate: 1.5

[0312] (C1-2) Ethanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), evaporation rate: 1.54

[0313] (C1-3) PGM (Dawanoul PM glycol ether, manufactured by Daw Kemikal Co., Ltd., propylene glycol monomethyl ether), evaporation rate: 0.71

[0314] Granular material (D)

[0315] (D1-1) LF Bousei ZP-DL (manufactured by Kikuchikara Co., Ltd., zinc phosphate-based anti-rust pigment), true density: 4.0 g / cm 3

[0316] (D1-2) CLF-102 (manufactured by Guangxi Chemical Industry Research Institute, aluminum tripolyphosphate-based anti-rust pigment), true density: 2.6 g / cm 3

[0317] (D2-1) SSS talc (manufactured by Nippon Talc Co., Ltd.), true density: 2.9 g / cm 3

[0318] (D2-2) NC clay (Kaolin, manufactured by Inamori Mining Co., Ltd.), true density: 2.7 g / cm 3

[0319] (D3-1) LOMON Titanium Dioxide R-996 (manufactured by SICHUAN LOMON TITANIUM INDUSTRY, titanium dioxide), true density: 4.1 g / cm 3

[0320] (D3-2) TAROX synthetic iron oxide LL-XLO (manufactured by Titanium Industry Co., Ltd., iron oxide yellow), true density: 5.24 g / cm 3

[0321] (D3-3) Carbon MA-100 (manufactured by Mitsubishi Chemical Corporation, carbon black), true density: 2.25 g / cm 3

[0322] (D4-1) CRYSTALITE VX-S2 (manufactured by Ronson Co., Ltd., high-purity crystalline quartz filler), true density: 1.8 g / cm 3

[0323] (D4-2) Precipitated barium sulfate PS07 (manufactured by Guangxi Xiangzhou Lianzhuang Chemical Co., Ltd., precipitated barium sulfate), true density: 4.5 g / cm 3

[0324] Others (Materials for base coating compositions)

[0325] BYK-011 (manufactured by Big Kemi Japan Co., Ltd., defoaming agent), solid content concentration: 30% by mass

[0326] BYK-2015 (dispersant, manufactured by Big Kemi Japan Co., Ltd.), solid content concentration: 40% by mass

[0327] Surfynol 440 (surface conditioner, manufactured by Ebony Jack Co., Ltd.), solid content concentration: 100% by mass

[0328] <Manufacturing Example 2> Preparation Example of Water-Based Top Coating Composition

[0329] <Preparation Example of Pigment Dispersion Paste for Water-Based Top Coating Composition>

[0330] (Pigment dispersion paste for aqueous top coating composition)

[0331] Using a disperser, 23.4 parts by mass of ion-exchanged water, 0.5 parts by mass of BYK-420 as a viscosity modifier, 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. The mixture was then dispersed using an SG mill (dispersion medium: glass beads) at 1,500 rpm until the coarse particles of the pigment were 15 μm or less, yielding a pigment-dispersed paste 1 for an aqueous top coating composition.

[0332] <Preparation of Water-Based Top Coating Composition>

[0333] (Water-based main agent 1 of water-based top coating composition)

[0334] 56.0 parts by mass of Setaqua 65155 as an acrylic resin aqueous dispersion, 5.0 parts by mass of Solvesso 1005.0 parts by mass of an organic solvent, 2.0 parts by mass of butyl cellosolve, 2.0 parts by mass of ion-exchanged 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.

[0335] (Curing agent 1 for water-based top coating composition)

[0336] 8.10 parts by mass of Duranet TPA-100 and 2.20 parts by mass of Bio-Dure 401-60, which are water-dispersible polyisocyanates, were mixed and stirred using a disperser to obtain a curing agent 1 for an aqueous top coating composition.

[0337] <Production Example 3>

[0338] <Preparation Example of Water-Based Top Coating Composition 2>

[0339] (Main agent 2 for water-based top coating composition)

[0340] 27.3 parts by mass of BANOC WD-5512 as an aqueous dispersion of an acrylic resin and 10.0 parts by mass of AQUATIX-8421 as an aqueous dispersion of a polyolefin wax were mixed and stirred using a disperser to obtain a main agent 2 for an aqueous top coating composition.

[0341] (Top coat with water-based curing agent 2)

[0342] 69.5 parts by mass of Bio-Dure 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.

[0343] (Details of Materials for Preparing the Water-Based Top Coating Composition)

[0344] Setaqua 6515 (manufactured by Allnex, polyol acrylic aqueous dispersion), hydroxyl value: 109 mgKOH / g, solid content: 45% by mass

[0345] Bandok 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: 44% by mass)

[0346] Duranet TPA-100 (manufactured by Asahi Kasei Corporation, isocyanurate-type hexamethylene diisocyanate (HDI)), NCO content: 23.1% by mass, solid content: 100% by mass

[0347] Bio-Diure 401-60 (manufactured by Sumika Bio-Wulite Co., Ltd., hydrophilic modified isophorone diisocyanate), NCO content: 13.3% by mass, solid content concentration: 60% by mass

[0348] Bio-Diure 304 (manufactured by Sumika Bio-Wuletan Co., Ltd.), nonionic modified polyisocyanate (an allophanate-modified polyisocyanate obtained by introducing allophanate groups into isocyanate chains by further adding HDI trimer to urethane groups generated by adding a hydrophilic polyether to HDI trimer, having a nonionic hydrophilic group), solid content concentration: 100% by mass

[0349] AQUATIX-8421 (manufactured by BYK, polyolefin wax aqueous dispersion, active ingredient concentration: 20% by mass)

[0350] Solvesso 100 (manufactured by Shoei Chemical Industry Co., Ltd., organic solvent)

[0351] Butyl cellosolve (made by Sankyo Chemical Co., Ltd., organic solvent)

[0352] 2-Butoxyethyl acetate (manufactured by Kanto Chemical Co., Ltd., organic solvent)

[0353] (Details of Materials for Water-Based Top Coating Composition)

[0354] BYK-420 (manufactured by Big Kemi Japan Co., Ltd., viscosity regulator), solid content concentration: 52% by mass)

[0355] BYK-2015 (dispersant, manufactured by Big Kemi Japan Co., Ltd.), solid content concentration: 40% by mass

[0356] Surfynol 440 (surface conditioner, manufactured by Ebony Jack Co., Ltd.), solid content concentration: 100% by mass

[0357] TI-PURE R-960 (manufactured by Dupont, titanium oxide)

[0358] <Preparation of Test Specimen with Multilayer Coating Film>

[0359] (Example 1)

[0360] A JIS G 3141 (SPCC-SB) cold-rolled steel sheet measuring 0.8 × 70 × 150 mm was degreased with xylene. Next, the undercoat composition obtained in the aforementioned manufacturing example was mixed with 1100.0 parts by mass of the aqueous base agent and 116.60 parts by mass of the aqueous curing agent for the undercoat composition using a disperser (undercoat (1)). The mixture was then applied to the steel sheet using air spraying to a dry film thickness of 45 μm, thereby forming an undried undercoat coating film.

[0361] It should be noted that the undercoat (1) is compounded in such a manner that the ratio of the active hydrogen equivalent of the polyamine compound in the aqueous curing agent 1 of the undercoat coating composition to the epoxy equivalent of the epoxy resin as the coating film-forming resin in the aqueous main agent 1 of the undercoat coating composition (active hydrogen equivalent / epoxy equivalent) becomes 0.8.

[0362] Next, at room temperature (25°C), after an interval of 7 minutes, while the above-mentioned undercoat coating film is not dried, a disperser is used on the surface of the above-mentioned undercoat coating film so that the molar ratio (NCO / OH) of the isocyanate group of the polyisocyanate compound in the curing agent 1 for the aqueous top coating composition obtained in the above-mentioned manufacturing example and the hydroxyl group of the acrylic resin as the coating film-forming resin in the main agent 1 for the aqueous top coating composition becomes 1.0 (top coating (1)), and wet-on-wet coating is performed using air spraying so that the dry film thickness becomes 45 μm to form an undried top coating film.

[0363] After leaving it at room temperature (25° C.) for 10 minutes, it was dried at 60° C. for 60 minutes (forced drying) to obtain a test piece having a multilayer coating film with a dry film thickness of 90 μm.

[0364] <Examples 2 to 42 and Comparative Examples 1 to 3>

[0365] A bottom coating composition and a top coating composition were produced in the same manner as in Production Example 1 except that the types and / or amounts of the components were changed to the amounts shown in Tables 1 to 4. It should be noted that, as an aqueous top coating composition, in Example 42, the isocyanate group of the polyisocyanate compound in the aqueous top coating composition curing agent 2 obtained in the aforementioned Production Example and the hydroxyl group of the acrylic resin as the coating film-forming resin in the aqueous top coating composition main agent 2 were mixed using a disperser in such a manner that the molar ratio (NCO / OH) was 1.0 (top coating (2)).

[0366] A test piece having a multilayer coating film was obtained in the same manner as in Example 1 except that the above-mentioned undercoat coating composition and the above-mentioned topcoat coating composition were used to form a coating film under the conditions (combinations of coating compositions) shown in Tables 1 to 4.

[0367] <Reference example>

[0368] The reference example is an example in which, instead of applying the bottom coating (1) and the top coating (1) wet-on-wet in Example 1, a bottom coating (44) is used, applied, forced to dry, and then the top coating (1) is applied thereon, which is further forced to dry. That is, Comparative Example 3 is an example in which a multilayer coating film is formed by the conventional method (two coats, two bakes).

[0369] That is, after applying the bottom coating (44) in the same manner as in Example 1, the bottom coating (44) was dried at room temperature (25°C) for 60 minutes after a 7-minute interval (forced drying) at 60°C. Thereafter, after a 30-minute interval at room temperature (25°C), the top coating (1) was applied in the same manner as in Example 1, and the bottom coating (44) was dried at room temperature (25°C) for 10 minutes after a 10-minute interval (forced drying) at 60°C to obtain a test piece having a multilayer coating film with a dry film thickness of 90 μm.

[0370] <Evaluation Items>

[0371] 1) Coating appearance (visual inspection)

[0372] The appearance of the multilayer coating films obtained in Examples and Comparative Examples was visually observed and evaluated according to the following criteria: 3 points or more was considered acceptable.

[0373] 5 points: The coating surface is smooth, no round objects (concavities and convexities) are observed, and when the coating film is illuminated with a fluorescent light, its image can be clearly recognized.

[0374] 4 points: Slightly round objects (concaves and convexities) exist on the coating surface, but when the coating film is illuminated with a fluorescent light, the image thereof can be roughly clearly recognized.

[0375] 3 points: There are circular objects (concaves and convexities) on the coating surface, but their images can be recognized when the coating film is illuminated with a fluorescent light.

[0376] 2 points: There are circular objects (concaves and convexities) on the coating surface. When the coating film is illuminated with fluorescent light, the image is slightly blurred but can be recognized.

[0377] 1 point: The coating film has many circular objects (concaves and convexities). When the coating film is illuminated with a fluorescent light, the image is blurred and almost unrecognizable.

[0378] 2) Coating appearance (gloss values at 20° and 60°)

[0379] 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 micro-TRI-gloss (manufactured by BYK) and evaluated according to the following criteria: 3 points or higher was considered acceptable.

[0380] 20° gloss value

[0381] 5 points: 70 or above

[0382] 4 points: 65 or above and less than 70

[0383] 3 points: 60 or above and less than 65

[0384] 2 points: 55 or above and less than 60

[0385] 1 point: less than 55

[0386] 60° gloss value

[0387] 5 points: 85 or above

[0388] 4 points: 80 or above and less than 85

[0389] 3 points: 75 or above and less than 80

[0390] 2 points: 70 or above and less than 75

[0391] 1 point: less than 70

[0392] 3) Internal stress

[0393] The internal stress (S) of the base coating film at 20°C based on the method of Inoue and Kobata was calculated by Figure 1 The deformation amounts of the undercoat film and the PET film were measured by the bimetallic method schematically shown in , and calculated according to the following formula (Sato Hirozo; Polymer Processing, 42(11), 557(1993)).

[0394] Specifically, the undercoat composition was first applied to a 100 μm thick short strip of PET film so that the dry film thickness of the undercoat film became 40 μm (h1), thereby obtaining a PET film having a coating film. Figure 1 The PET film with the coating film was placed on the knife-edge support (indicated by the triangle mark in the figure) at intervals of 70 mm. Next, the temperature was raised to 60°C over 3 minutes and maintained at 60°C for 60 minutes to cure the coating film, thereby forming a coating film. The film was then cooled to 20°C over 5 minutes. The deflection (δ) of the PET film at 20°C was measured, and the internal stress was calculated using the following formula based on the measured values.

[0395] S=1 / 6h1(h1+h2)×E2h2 3 / (1-ν2 2 )×1 / ρ

[0396] Where,

[0397] S: internal stress (Pa)

[0398] h1: Dry film thickness of the coating (40 μm = 40 × 10 -6 m)

[0399] h2: Thickness of PET film (100 μm = 100 × 10 -6 m)

[0400] E2: Elastic modulus of PET film (2.45 GPa = 2.45 × 10 9 Pa)

[0401] ν2: Poisson's ratio of PET film (0.4)

[0402] ρ: radius of curvature [ρ = L 2 / 8δ(where L is the distance between blade supports (70 mm = 70 × 10 -3 m), δ: deformation variable)].

[0403] 4) Adhesion

[0404] For the multilayer coating of the test piece obtained in the embodiment and the comparative example, 11 scratches were made in the vertical and horizontal directions at intervals of 1 mm using a cutter until the depth of the steel plate to be coated was reached, and a transparent tape (registered trademark) (manufactured by Nichiban Co., Ltd.) was pasted thereon and peeled off, and the number of remaining grids among 100 grids was counted (checkerboard test). It should be noted that 100 / 100 represents the case where the peeling area of the coating is 0%, for example, 90 / 100 represents the case where the peeling area of the coating is 10%, and 50 / 100 represents the case where the peeling area of the coating is 50%. 95 / 100 was set as qualified. It should be noted that when the evaluation is 94 / 100 or less, obvious problems arise in terms of practicality.

[0405] [Table 1]

[0406]

[0407] [Table 2]

[0408]

[0409] [Table 3]

[0410]

[0411] [Table 4]

[0412]

[0413] Examples 1 to 42 are examples of the present invention. Even when wet-on-wet coating is performed using an aqueous coating composition as an undercoat coating composition, a multilayer coating film having a smooth appearance can be obtained.

[0414] Comparative Example 1 is an example in which the content of the particulate material (D) does not satisfy 120 parts by mass, and the appearance of the obtained multilayer coating film is not sufficiently satisfactory.

[0415] Comparative Example 2 is an example in which the content of the particulate material (D) exceeded 380 parts by mass, and the resulting multilayer coating film did not exhibit sufficiently satisfactory adhesion to the coated object.

[0416] Comparative Example 3 is an example in which the particulate material (D) was not contained, and the appearance of the obtained multi-layer coating film was not sufficiently satisfactory.

[0417] The reference example is an example of forming a multilayer coating film using the same basecoat and topcoat as Comparative Example 3 (an example without particulate material (D)), without wet-on-wet coating, but using a conventional method (two coats, two bakes). In this case, even without the presence of particulate material (D), a multilayer coating film with a smooth appearance was obtained.

Claims

1. A method for producing a multilayer coating film, comprising: a primer coating film forming step of applying a primer coating composition on the object to be coated to form a primer 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; and A drying step of drying the bottom coating film and the top 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 a particulate material (D), The content of the particulate material (D) is more than 120 parts by mass and less than or equal to 380 parts by mass relative to 100 parts by mass of the resin solid content contained in the aqueous coating composition.

2. The manufacturing method according to claim 1, wherein The polyamine compound (B) includes at least one selected from aliphatic polyamines, alicyclic polyamines, aromatic polyamines, polyoxyalkylene-containing polyamines, polyoxyalkylene-containing aromatic polyamines, and polyamidoamine compounds.

3. The manufacturing method according to claim 1, wherein The polyamine compound (B) contains at least one selected from the group consisting of alicyclic polyamines, aromatic polyamines, polyoxyalkylene group-containing aromatic polyamines, and polyamidoamines.

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

5. The method for producing a multilayer coating film according to claim 1, wherein The active hydrogen equivalent of the polyamine compound (B) is 10 g / eq or more and 1,000 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 0.3 or more and 2.0 or less.

7. The method for producing a multilayer coating film according to claim 1, wherein An undercoat coating film formed from the undercoat coating composition has an internal stress of 0.09 MPa or more and 0.50 MPa or less.

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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