Active energy ray-curable coating composition for metal substrates, laminate, molded member, and method for producing same

Abstract

To provide an active energy ray-curable coating composition for a metal substrate which achieves all of high hardness, high processing and high weather resistance and a laminate and a molding processing member using the same and further to provide an active energy ray-curable coating composition for a metal substrate having good coating film properties and good storage stability even when an ultraviolet absorber is used.SOLUTION: There are provided: an active energy ray-curable coating composition for a metal substrate which comprises a urethane (meth)acrylate (A), a multifunctional (meth)acrylate monomer (B) having an isocyanurate skeleton, a radical polymerizable monofunctional monomer (C), an ultraviolet absorber (D) and a light stabilizing agent (E), in which the radical polymerizable monofunctional monomer (C) includes a radical polymerizable monofunctional monomer (C-1) having an alicyclic structure and a radical polymerizable monofunctional monomer (C-2) having a heterocyclic ring structure; and a laminate and a molding processing member using the same.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an active energy ray-curable coating composition for metal substrates, a laminate, a molded member, and a method for producing the same. [Background technology]

[0002] Generally, there are two methods for painting metal substrates: a post-coat method, in which painting is done after the product is formed, and a pre-coat method, in which painting is done before the product is formed. Here, metal substrates painted using the pre-coat method are called PCM (pre-coated metal), and the paint used for them is called PCM paint.

[0003] The post-coating method involves painting metal substrates after they have been processed into products or parts, so a painting system tailored to the shape and size of the object to be painted is required.On the other hand, the pre-coating method involves coating metal substrates in the form of plates, so continuous operation at very high speeds is possible, and film thickness can be easily controlled, making it possible to form a very uniform film.

[0004] However, because PCMs are processed after painting, they must not only have the hardness and durability required for their primary applications in building materials and home appliances, but also be processable enough to withstand the various molding processes carried out in the manufacturing process.In addition, they must also have excellent aesthetic appeal.

[0005] Conventional solvent-dried coating compositions have poor productivity due to the time required for drying the solvent, and also have environmental impact issues such as the generation of VOCs (volatile organic compounds) and CO2 emissions, so coating compositions that are cured with active energy rays such as electron beams and ultraviolet rays have come into use. These active energy ray-curable coating compositions generally can be used without solvent and can be cured in a short time with little energy, and therefore have excellent properties from the perspectives of improving productivity and reducing the environmental impact.

[0006] Many PCMs require high weather resistance. Especially when used as building materials, outdoor weather resistance of more than ten years is often required. A known method for improving weather resistance is to incorporate additives such as ultraviolet absorbers and light stabilizers. However, since many of these additives are poorly soluble in acrylate monomers, they may precipitate during storage in solventless coating compositions, making it difficult to increase their addition amounts. Furthermore, ultraviolet absorbers and light stabilizers absorb and / or reflect active energy rays such as ultraviolet rays. This can reduce the curability of active energy ray-curable coating compositions and reduce coating film properties such as water resistance, chemical resistance, and hardness.

[0007] Patent Document 1 proposes an active energy ray-curable resin composition containing a (meth)acrylic polymer, a urethane (meth)acrylate having 1 to 4 (meth)acryloyl groups, a monomer having one or more (meth)acryloyl groups, and a photopolymerization initiator, wherein the solvent content is 1 mass% or less of the total amount of the active energy ray-curable resin composition. Patent Document 2 also proposes a coating film formation method in which a coating composition containing a urethane (meth)acrylate having a weight-average molecular weight of 550 or more but less than 10,000 and having two or more (meth)acryloyl groups per molecule, a polymerizable unsaturated compound having a weight-average molecular weight of 200 or more but less than 550 and having two or more polymerizable unsaturated groups per molecule, and a polymerization initiator is applied to a substrate under conditions in which the temperature reaches 28 to 70°C, and then cured. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent Publication No. 2022-131646 [Patent Document 2] Patent Publication No. 2017-177058 Summary of the Invention [Problem to be solved by the invention]

[0009] However, while the coating agent for pre-coated metals described in Patent Document 1 achieves both high hardness and high processability, there is no mention of weather resistance. Adding UV absorbers or light stabilizers to improve weather resistance may result in a deterioration in the physical properties of the cured coating film, or there is a concern that the UV absorbers may precipitate during storage. Furthermore, Patent Document 2 discloses a method for forming a coating film using a coating composition with good adhesion and pencil hardness, but there is no mention of the processability or weather resistance of the coating film or the storage stability of the coating.

[0010] An object of the present invention is to provide an active energy ray-curable coating composition that achieves all of high hardness, high processability, and high weather resistance, and a coated article and a molded member using the same. Another object of the present invention is to provide an active energy ray-curable coating composition for metal substrates that exhibits good coating film properties even when an ultraviolet absorber is used, and that does not precipitate during storage, resulting in good storage stability.

[0011] As a result of extensive research into solving the above problems, the present inventors have found that the above problems can be solved by the active energy ray-curable coating composition for metal substrates shown below, and have thus completed the present invention.

[0012] That is, the present invention is [1] The present invention relates to an active energy ray-curable coating composition for metal substrates, which comprises a urethane (meth)acrylate (A), a polyfunctional (meth)acrylate monomer (B) having an isocyanurate skeleton (excluding the urethane (meth)acrylate (A)), a radical polymerizable monofunctional monomer (C) (excluding the urethane (meth)acrylate (A)), an ultraviolet absorber (D), and a light stabilizer (E), wherein the radical polymerizable monofunctional monomer (C) comprises a radical polymerizable monofunctional monomer (C-1) having an alicyclic structure and a radical polymerizable monofunctional monomer (C-2) having a heterocyclic structure.

[0013] The present invention also provides [2] The present invention relates to an active energy ray-curable coating composition for metal substrates according to the above [1], wherein the content ratio (mass ratio) of the radical polymerizable monofunctional monomer (C-1) having an alicyclic structure to the radical polymerizable monofunctional monomer (C-2) having a heterocyclic structure is 20 / 80 to 70 / 30.

[0014] The present invention also provides [3] The active energy ray-curable coating composition for metal substrates according to [1] or [2], wherein the content of the solvent is 3 mass % or less based on the total amount of the active energy ray-curable coating composition for metal substrates.

[0015] The present invention also provides [4] The active energy ray-curable coating composition for metal substrates according to any one of [1] to [3], wherein the content of the photopolymerization initiator is 0.5 mass % or less based on the total amount of the active energy ray-curable coating composition for metal substrates.

[0016] The present invention also provides [5] The present invention relates to an active energy ray-curable coating composition for metal substrates according to any one of [1] to [4] above, which is for use in pre-coating metals.

[0017] The present invention also provides [6] A laminate having a cured layer of the active energy ray-curable coating composition for metal substrates according to any one of [1] to [5] above on a metal substrate.

[0018] The present invention also provides [7] The present invention relates to a method for producing a laminate, which comprises applying the active energy ray-curable coating composition for metal substrates according to any one of the above [1] to [5] to a metal substrate and curing the composition with active energy rays.

[0019] The present invention also provides [8] A molded member using the laminate described in [6] above.

[0020] The present invention also provides [9] A method for producing a molded member, comprising applying the active energy ray-curable coating composition for metal substrates according to any one of [1] to [5] to a metal substrate, curing the composition with active energy rays, and molding the metal substrate. [Effects of the Invention]

[0021] The present invention can provide an active energy ray-curable coating composition that achieves all of high hardness, high processability, and high weather resistance, as well as a laminate and a molded product using the same. The present invention also can provide an active energy ray-curable coating composition for metal substrates that exhibits good coating film properties even when an ultraviolet absorber is used, and that exhibits good storage stability without causing precipitation of the ultraviolet absorber during storage. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, embodiments of the present invention will be described in detail. Note that the present invention is not limited to the following embodiments, and various modifications can be made within the scope of the present invention.

[0023] In the following description, (meth)acrylate, (meth)acryloyl, and (meth)acrylic mean methacrylate and / or acrylate, methacryloyl and / or acryloyl, and methacrylic and / or acrylic, respectively.

[0024] In the following description, the "number of functional groups" refers to the number of radically polymerizable groups, such as acryloyl groups, methacryloyl groups, and other reactive unsaturated groups, that a resin or compound has in one molecule.

[0025] In this specification, the binder composition refers to the components constituting the binder, excluding colorants, UV absorbers, light stabilizers, and other additives from the paint. Specifically, it refers to a mixture containing the urethane (meth)acrylate (A), the polyfunctional (meth)acrylate monomer (B) having an isocyanurate skeleton, the radically polymerizable monofunctional monomer (C), other compounds having radically polymerizable groups, and an inert resin.

[0026] Components that are or can be contained in the active energy ray-curable coating composition of this embodiment (hereinafter also simply referred to as "coating") will be described below.

[0027] <Urethane (meth)acrylate (A)> The urethane (meth)acrylate (A) contained in the active energy ray-curable coating composition of the present invention is not particularly limited, and may be any (meth)acrylate having a urethane bond. By including the urethane (meth)acrylate (A), the coating material of the present invention exhibits a good balance between coating film hardness and processability, and also exhibits good adhesion. Examples of the urethane (meth)acrylate (A) include oligomers obtained by reacting a polyisocyanate compound, a polyol compound, and a hydroxyl group-containing (meth)acrylate; and oligomers obtained by reacting a polyisocyanate compound and a hydroxyl group-containing (meth)acrylate. Examples of commercially available products include EBECRYL4858 (bifunctional), EBECRYL8311, EBECRYL8402 (bifunctional), EBECRYL8701 (trifunctional), EBECRYL9260 (trifunctional), EBECRYL8606 (tetrafunctional), and EBECRYL8301R (hexafunctional), manufactured by Daicel Allnex Corporation, and CN8888NS (bifunctional), CN8898NS (bifunctional), CN8881NS (bifunctional), CN964NS (bifunctional), and CN9013NS (ninafunctional), manufactured by Sartomer Corporation.

[0028] The urethane (meth)acrylate (A) is preferably an aliphatic urethane (meth)acrylate. The aliphatic urethane (meth)acrylate refers to a urethane (meth)acrylate in which the polyol component and the isocyanate component constituting it are both aliphatic and which does not have an aromatic ring in the molecule. The aliphatic urethane (meth)acrylate is preferred from the viewpoints of being easily imparted with adhesion, excellent processability, and excellent weather resistance.

[0029] The number of functional groups in the urethane (meth)acrylate (A) is preferably 2 to 4, and more preferably 2 to 3. If the number of functional groups is equal to or greater than the above-mentioned lower limit, the hardness of the coating film increases, and if it is equal to or less than the above-mentioned upper limit, the hardness of the coating film does not become too high and processability is improved. Furthermore, the content of the urethane (meth)acrylate (A) is preferably 5 to 40 mass%, more preferably 10 to 35 mass%, and even more preferably 15 to 30 mass%, based on the total amount of the binder composition. Having the content of the urethane (meth)acrylate (A) within the above range ensures a good balance between the hardness and processability of the coating film.

[0030] <Polyfunctional (meth)acrylate monomer (B) having an isocyanurate skeleton> The polyfunctional (meth)acrylate monomer (B) having an isocyanurate skeleton is a (meth)acrylate other than the urethane (meth)acrylate (A) and has an isocyanurate group and a (meth)acryloyl group. By including this monomer (B), the coating material of the present invention can ensure good processability while improving the coating film hardness. Examples include bis((meth)acryloxymethyl)hydroxymethyl isocyanurate, bis((meth)acryloxyethyl)hydroxyethyl isocyanurate, tris((meth)acryloxymethyl)isocyanurate, tris((meth)acryloxyethyl)isocyanurate, methoxylated isocyanuric acid triacrylate, ethoxylated isocyanuric acid triacrylate, caprolactone-modified di((meth)acryloxymethyl)isocyanurate, and caprolactone-modified tris((meth)acryloxyethyl)isocyanurate. Among these, it is preferable that the monomer (B) has a structure modified with a polylactone, because this provides excellent processability for the coated article obtained using the coating composition. Specific examples of such a structure include caprolactone-modified di((meth)acryloxymethyl)isocyanurate and caprolactone-modified tris((meth)acryloxyethyl)isocyanurate. Commercially available products include Aronix M-313, Aronix M-315, Aronix M-327 (manufactured by Toagosei Co., Ltd.), A-9300, A-9300-1CL (manufactured by Shin-Nakamura Chemical Co., Ltd.), SR368 (manufactured by Sartomer Inc.), etc. These acrylate monomers can be used alone or in combination of two or more.

[0031] The content of the polyfunctional (meth)acrylate monomer (B) having an isocyanurate skeleton is preferably 5 to 30 mass %, more preferably 10 to 25 mass %, and even more preferably 10 to 20 mass %, based on the total amount of the binder composition. When the content of the polyfunctional (meth)acrylate monomer (B) having an isocyanurate skeleton is 5 mass % or more, the coated article obtained using the coating composition has a coating film hardness more suitable for PCM applications. Furthermore, when the content of the polyfunctional (meth)acrylate monomer (B) having an isocyanurate skeleton is 30 mass % or less, the coated article obtained using the coating composition has good processability.

[0032] <Radical polymerizable monofunctional monomer (C)> The coating composition of the present invention contains a radically polymerizable monofunctional monomer (C). The radically polymerizable monofunctional monomer (C) is a radically polymerizable monomer other than the urethane (meth)acrylate (A), has only one radically polymerizable group, and polymerizes upon irradiation with active energy rays. The radically polymerizable monofunctional monomer (C) has the effect of significantly reducing the viscosity of the coating composition, thereby improving the adhesion and smoothness of the cured coating film.

[0033] The radical polymerizable monofunctional monomer (C) includes a radical polymerizable monofunctional monomer (C-1) having an alicyclic structure and a radical polymerizable monofunctional monomer (C-2) having a heterocyclic structure. The radical polymerizable monofunctional monomer (C-1) having an alicyclic structure is a radical polymerizable monofunctional monomer having a ring structure composed only of carbon in the compound, which easily dissolves UV absorbers and improves the storage stability of the paint. The radical polymerizable monofunctional monomer (C-2) having a heterocyclic structure is a radical polymerizable monofunctional monomer having a ring structure composed of at least two different elements, which has higher coating film hardness and heat resistance. The present invention improves weather resistance through the synergistic effect of the monomer (C-1) and the monomer (C-2), and can achieve both coating film hardness, processability, and storage stability.

[0034] As the radical polymerizable monofunctional monomer (C-1) having an alicyclic structure, for example, 3,3,5-trimethylcyclohexyl acrylate, hexahydrophthalic acid ethyl (meth)acrylate, hexahydrophthalic acid propyl (meth)acrylate, cyclohexyl acrylate, t-butylcyclohexyl (meth)acrylate, dicyclopentenyl oxyethyl (meth)acrylate, dicyclopentanyl acrylate, dicyclopentenyl acrylate, isobornyl acrylate, vinylcyclohexane, etc. Among them, from the viewpoint of excellent solubility of ultraviolet absorber, it is preferable to have a condensed ring structure.As such specific examples, isobornyl acrylate, dicyclopentanyl acrylate are preferred.

[0035] Examples of radically polymerizable monofunctional monomers (C-2) having a heterocyclic structure include tetramethylpiperidyl methacrylate, (2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl acrylate, (cyclohexanespiro-2-(1,3-dioxolan-4-yl))methyl acrylate, acryloylmorpholine, cyclic trimethylolpropane formal acrylate, tetrahydrofurfuryl acrylate, acrylic acid polymer esters of tetrahydrofurfuryl alcohol, N-vinylcaprolactam, and N-vinylpyrrolidone. Among these, those having a glass transition temperature (Tg) of 0°C or higher are preferred. Specific examples include acryloylmorpholine (Tg = 145°C) and cyclic trimethylolpropane formal acrylate (Tg = 27°C). The glass transition temperature of component (C-2) can be measured using a differential scanning calorimeter (DSC).

[0036] The content of the radically polymerizable monofunctional monomer (C-1) having an alicyclic structure is preferably 10 to 45% by mass, more preferably 20 to 40% by mass, based on the total amount of the binder composition. The content of component (C-1) within the above range provides a good balance between the solubility of the UV absorber and the hardness of the coating film. The content of the radically polymerizable monofunctional monomer (C-2) having a heterocyclic structure is preferably 25 to 40% by mass, more preferably 15 to 30% by mass, based on the total amount of the binder composition. The content of component (C-2) within the above range provides a good balance between weather resistance and the hardness of the coating film.

[0037] The content ratio (mass ratio) of the radical polymerizable monofunctional monomer (C-1) having an alicyclic structure to the radical polymerizable monofunctional monomer (C-2) having a heterocyclic structure is preferably 20 / 80 to 70 / 30, more preferably 25 / 75 to 60 / 40. When the content ratio of component (C-1) to component (C-2) is within the above range, good coating hardness and weather resistance can be maintained while ensuring the solubility of the ultraviolet absorber.

[0038] <Ultraviolet absorber (D)> Examples of the ultraviolet absorber (D) include organic ultraviolet absorbers such as salicylic acid-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, triazine-based ultraviolet absorbers, and cyanoacrylate-based ultraviolet absorbers, as well as inorganic ultraviolet absorbers made of fine particles of zinc oxide, titanium oxide, or cerium oxide. Among these, benzotriazole-based ultraviolet absorbers and triazine-based ultraviolet absorbers are more preferred because they have high ultraviolet absorption ability and are resistant to deterioration even when exposed to high energy such as ultraviolet light.

[0039] Specific examples of benzotriazole-based ultraviolet absorbers include 2-(2-hydroxy-5-methylphenyl)benzotriazole, 2-(2-hydroxy-3,5-di-tert-amylphenyl)benzotriazole, and 3-[3-(benzotriazol-2-yl)-5-tert-butyl-4-hydroxyphenyl]propionic acid ester of polyethylene glycol. Specific examples of triazine-based ultraviolet absorbers include 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[(hexyl)oxy]phenol, 1,3,5-triazine-2,4,6(1H,3H,5H)-trione, and 1,3,5-tri[[3,5-bis-(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]. Commercially available products include "ADEKA STAB LA-F70" and "ADEKA STAB LA-40" manufactured by ADEKA Corporation, and "Tinuvin 405" and "Tinuvin 479" manufactured by BASF Japan Ltd.

[0040] <Light stabilizer (E)> Examples of the light stabilizer (E) include hindered amine light stabilizers (HALS), phenolic antioxidants, phosphorus-based antioxidants, and sulfur-based antioxidants. Among them, HALS is more preferred because of its high thermal stability and excellent radical scavenging ability. Specific examples of HALS include 2-(3,5-di-tert-butyl-4-hydroxybenzyl)-2'-n-butylmalonic acid bis(1,2,2,6,6-pentamethyl-4-piperidyl), bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate, bis(1,2,2,6,6-pentamethyl-4-piperidinyl)sebacate, and methyl(1,2,2,6,6-pentamethyl-4-piperidinyl)sebacate. ester, 2,4-bis[N-butyl-N-(1-cyclohexyloxy-2,2,6,6-tetramethylpiperidin-4-yl)amino]-6-(2-hydroxyethylamine)-1,3,5-triazine), tetrakis(2,2,6,6-tetramethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate, 1,2,2,6,6-pentamethyl-4-piperidinyl methacrylate, and the like. Commercially available products include "ADEKA STAB LA-72" and "ADEKA STAB LA-82" manufactured by ADEKA Corporation, and "Tinuvin 123" and "Tinuvin 249" manufactured by BASF Japan Ltd.

[0041] These ultraviolet absorbers (D) and light stabilizers (E) may be added to the composition in any amount, but from the viewpoint of solubility in the coating, their total content is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less, based on the total amount of the binder composition. Furthermore, the content of ultraviolet absorber (D) is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 8% by mass or less, based on the total amount of the binder composition. The content of light stabilizer (E) is preferably 7% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less, based on the total amount of the binder composition. By having the contents of ultraviolet absorber (D) and light stabilizer (E) within the above ranges, good weather resistance can be achieved while ensuring coating film hardness and storage stability of the coating.

[0042] In addition to the urethane (meth)acrylate (A), the polyfunctional (meth)acrylate monomer (B) having an isocyanurate skeleton, the radically polymerizable monofunctional monomer (C), the ultraviolet absorber (D), and the light stabilizer (E), other radically polymerizable monomers / oligomers and inert resins may also be contained. The amount of the other radically polymerizable monomers / oligomers and inert resins is not particularly limited, but is preferably 30% by mass or less of the binder composition.

[0043] [Additives] The active energy ray-curable coating composition of the present invention may contain known additives as appropriate, such as colorants, sensitizers, polymerization initiators, fluorescent brighteners, curing agents, coupling agents, plasticizers, leveling agents, surface conditioners, antifoaming agents, substrate wetting agents, antistatic agents, extender pigments, and pigment dispersants.

[0044] [Coloring agent] As the colorant, at least one of a pigment and a dye can be used. From the viewpoint of weather resistance, a pigment is preferred. There are no particular limitations on the pigment, and any known pigment can be used. Either an inorganic pigment or an organic pigment can be used. One type of pigment can be used alone, or two or more types can be used in combination.

[0045] Examples of the inorganic pigments include ultramarine, titanium dioxide, iron oxides, composite oxides, and carbon blacks.

[0046] Examples of the organic pigment include phthalocyanine pigments, azo pigments, quinacridone pigments, diketopyrrolopyrrole pigments, and quinophthalone pigments.

[0047] The content of the pigment is adjusted appropriately depending on the type and purpose. For example, the content of the pigment in the coating composition is preferably 3% by mass or more. Also, the content of the pigment in the coating composition is preferably 60% by mass or less. By keeping the content of the pigment within the above range, the coating composition can ensure dispersion stability while exhibiting sufficient hiding power.

[0048] [solvent] The active energy ray-curable coating composition of the present invention preferably contains substantially no organic solvents or water. "Substantially no" means 3% or less, more preferably 1% or less, of the total mass of the active energy ray-curable coating composition. The absence of solvents eliminates the need for a drying step by heating, resulting in excellent productivity. Another advantage is that environmental impacts such as VOC generation and CO2 emissions can be reduced.

[0049] [Photopolymerization initiator] The photopolymerization initiator is not particularly limited, and known photopolymerization initiators can be used as appropriate. When the active energy ray-curable coating composition for metal substrates of the present invention is cured by ultraviolet light, it is necessary to contain a photopolymerization initiator. The content of the photopolymerization initiator is not particularly limited. For example, the content of the photopolymerization initiator in the coating composition is preferably 2 to 15 mass %, more preferably 3 to 10 mass %. When the content of the photopolymerization initiator is within the above range, the coating composition is easily cured sufficiently even when cured by ultraviolet light. When the active energy ray-curable coating composition for metal substrates of the present invention is cured by electron beams, it is preferable that the composition does not contain a photopolymerization initiator. For example, the content of the photopolymerization initiator is preferably 0.5 mass % or less, more preferably 0.1 mass % or less, based on the total amount of the coating composition.

[0050] [viscosity] The viscosity of the active energy ray-curable coating composition of the present invention is not particularly limited and can be appropriately set depending on the coating method. For example, in the case of coating using a roll coater, the viscosity at 25°C is preferably 100 to 2000 mPa·s, more preferably 200 to 1000 mPa·s, and most preferably 200 to 500 mPa·s. When the viscosity at 25°C is within the above range, excellent coating suitability is achieved. The viscosity is measured using a viscoelasticity measuring device (Discovery HR-2, manufactured by TA Instruments Japan) with a cone diameter of 20 mm, a cone angle of 1 degree, a temperature of 25°C, and a shear rate of 0.1 sec -1 After 60 seconds, the shear rate was increased to 100 sec -1 When the shear rate reaches 100 sec -1 This refers to the measurement value at the time.

[0051] [Base material] Metal substrates are particularly suitable as substrates to which the coating material of the present invention is applied. Specific examples of metal substrates include galvanized steel sheets, aluminum sheets, tin-free steel (TFS) sheets, tin plates, galvanized sheets, stainless steel sheets, copper sheets, and brass sheets. Alternatively, metal substrates having a base coat layer, a primer layer, or the like formed on these metal sheets are preferred. Furthermore, they may be laminated with a resin film. For example, when used as a building material, hardness and weather resistance are particularly required, and steel substrates such as Galvanized Steel Sheets (registered trademark) and stainless steel sheets are more preferred.

[0052] [Coating method] The active energy ray-curable coating composition of the present invention can be applied by known methods such as gravure coating, gravure reverse coating, gravure offset coating, spin coating, roll coating, reverse roll coating, curtain coating, kiss coating, dip coating, silk screen coating, wire bar coating, flow coating, comma coating, etc. Among these, roll coating and reverse roll coating are more preferred in terms of being particularly suitable for precoat coating, which requires sufficient hardness and processability after coating and curing, and which are highly productive.

[0053] [Curing method] The method for curing the active energy ray-curable coating composition of the present invention is not particularly limited, and known methods can be used. For example, the composition can be cured by irradiation with α-rays, γ-rays, electron beams, X-rays, ultraviolet rays, visible light, infrared rays, etc. Among these, ultraviolet rays and electron beams are preferred, and electron beams are more preferred.

[0054] When cured with electron beams, the curing is not inhibited by the blocking of ultraviolet rays, etc., which occurs with high pigment concentrations or the incorporation of ultraviolet absorbers. Furthermore, because no initiator is required, there is no shortening of the paint pot life or degradation of coating film performance due to initiator decomposition products after curing, and the effects of the present invention, such as improved coating film hardness, processability, and weather resistance, can be maximized.

[0055] Curing with electron beams is preferably carried out by irradiating with electron beams at an acceleration voltage of 10 to 500 kV, particularly 30 to 200 kV. When curing is carried out with electron beams at an acceleration voltage of 30 to 200 kV, the effect of the present invention of improving the hardness and processability of the coating film can be maximized. If the acceleration voltage is too high, it becomes difficult to balance the hardness and processability of the resulting coating film. The preferred irradiation dose is about 10 kGy to 200 kGy, and more preferably 30 kGy to 200 kGy. If the irradiation dose is too low, curing will be insufficient, and if it is too high, the processability of the coating film will be impaired.

[0056] [Laminate] The active energy ray-curable coating composition of the present invention is applied to a substrate, and then cured by irradiation with active energy rays to obtain a laminate. The coating thickness of the active energy ray-curable coating composition is usually preferably 1 to 50 μm, and more preferably 10 to 20 μm. The laminate can be suitably used as a precoated metal.

[0057] [Molded processed parts] The laminate of the present invention has excellent processability and is not particularly limited in the processing method, and can be suitably used, for example, as a molded and processed member for building materials, home electric appliances, etc. [Example]

[0058] The present invention will be described in detail below with reference to examples, but the following examples are not intended to limit the scope of the present invention in any way.

[0059] [Preparation of active energy ray-curable coating composition: Example 1] According to the formulation shown in Table 1, each raw material was mixed at room temperature by stirring with a disperser (3000 rpm) to prepare an active energy ray-curable coating composition. The resulting coating composition was evaluated for processability, coating film hardness and weather resistance, long-term weather resistance, and storage stability using the following evaluation methods. The results are shown in Table 1.

[0060] [Preparation of active energy ray-curable coating compositions: Examples 2 to 32, Comparative Examples 1 to 6] Examples 2 to 32 and Comparative Examples 1 to 6 were obtained in the same manner as Example 1, except that the raw materials and amounts shown in Tables 1 and 2 were changed. The numbers in Tables 1 and 2 indicate the blending amounts (% by mass).

[0061] [Laminate manufacturing method] The obtained active energy ray-curable coating composition was applied to a substrate, Galvalume Steel Plate (registered trademark) (Yodogawa Steel Works, Yodo GL Eco Green, thickness 0.27 mm) using a bar coater #14 (coating thickness approximately 20 μm).The coating composition was then cured by irradiating it with electron beams using an electron beam irradiation device i-Compact EB (Iwasaki Electric Co., Ltd., acceleration voltage 90 kV, exposure dose 100 kGy) to produce a laminate.

[0062] [Workability] The workability was evaluated by a 180° bending test using a DuPont impact tester. Ten steel substrate sheets were sandwiched between the test pieces, with the cured coating facing outward, and the inside of the bent section was sandwiched between them. A 1 kg load was dropped from a height of 50 cm onto the test piece, bending the coated piece 180° to obtain a processed product. The presence or absence of cracks in the bent section of the processed product was visually inspected, and the workability was evaluated as follows: 〔evaluation〕 A: No cracks were found. B: Only very small cracks were observed. C: Only minor cracks were observed. D: Large cracks were observed. The evaluations for practical use are A, B, and C.

[0063] [Coating film hardness] The coating hardness was evaluated by pencil hardness in accordance with JIS K5600-5-4. A scratch test was performed by applying pencils of various hardness to the surface of the cured coating at a 45° angle and applying a load of 750 g, and the hardness of the hardest pencil that did not scratch was evaluated. 〔evaluation〕 A: Hardness H and no scratches were found. B: Hardness F and no scratches were found. C: No scratches were observed at hardness HB. D: Scratches were confirmed at hardness HB. The evaluations for practical use are A, B, and C.

[0064] [Weather resistance] Weather resistance was evaluated using a xenon lamp (product name "Q-SUN Xe-1", manufactured by Q-Lab) at 120W / m 2 The test pieces were repeatedly subjected to an irradiation process in which ultraviolet light was irradiated for 102 minutes under irradiation conditions with a black panel temperature of 63°C, and a shower process in which water was sprayed for 18 minutes while irradiating with ultraviolet light under the same irradiation conditions, and the surface condition of the test pieces was evaluated after 700 hours had passed. 〔evaluation〕 A: No abnormalities B: A very small amount of surface abnormality occurs C: Minor surface abnormalities D: A large amount of surface abnormalities occurs The evaluations for practical use are A, B, and C.

[0065] [Long-term weather resistance] Long-term weather resistance was evaluated using a xenon lamp (product name "Q-SUN Xe-1", manufactured by Q-Lab) at 120W / m 2 The test pieces were repeatedly subjected to an irradiation process in which they were irradiated with ultraviolet light for 102 minutes under irradiation conditions with a black panel temperature of 63°C, and a shower process in which they were sprayed with water for 18 minutes while irradiating with ultraviolet light under the same irradiation conditions, and the surface condition of the test pieces was evaluated after 2,100 hours had passed. 〔evaluation〕 A: No abnormalities B: A very small amount of surface abnormality occurs C: Minor surface abnormalities D: A large amount of surface abnormalities occurs The evaluations for practical use are A, B, and C.

[0066] [Storage stability] After the paint was prepared, it was left to stand at room temperature for one week, and then visually inspected to see if any precipitates formed in the paint, and the storage stability was evaluated as follows. 〔evaluation〕 A: No precipitates. B: Only a very small amount of precipitate was observed. C: Only a small amount of precipitate was observed. D: Clear precipitates were observed. The evaluations for practical use are A, B, and C.

[0067] [Table 1]

[0068] [Table 2]

[0069] The information for each raw material in Table 1 is as follows: EBECRYL8402: Aliphatic urethane acrylate (bifunctional), manufactured by Daicel Allnex Co., Ltd. EBECRYL8701: Aliphatic urethane acrylate (trifunctional), manufactured by Daicel Allnex Co., Ltd. EBECRYL8301R: Aliphatic urethane acrylate (hexafunctional), manufactured by Daicel Allnex Co., Ltd. Miramar M370: Tris (2-hydroxyethyl) isocyanurate triacrylate, manufactured by MIWON Aronix M327: ε-caprolactone-modified tris(2-hydroxyethyl isocyanurate) triacrylate, manufactured by Toagosei Co., Ltd. IBXA: Isobornyl acrylate, manufactured by Osaka Organic Chemical Industry Co., Ltd. FA513AS: Dicyclopentanyl acrylate, manufactured by Resonac Viscoat 196: 3,3,5-trimethylcyclohexyl acrylate, manufactured by Osaka Organic Chemical Industry Co., Ltd. ACMO: Acryloylmorpholine, manufactured by KJ Chemicals Viscoat 200: Cyclic trimethylolpropane formal acrylate, manufactured by Osaka Organic Chemical Industry Co., Ltd. Viscoat 150: Tetrahydrofurfuryl acrylate, manufactured by Osaka Organic Chemical Industry Co., Ltd. Light acrylate HPP-A: Hydroxypivalic acid neopentyl glycol diacrylate, manufactured by Kyoeisha Chemical Co., Ltd. Light Acrylate LA: Lauryl acrylate, manufactured by Kyoeisha Chemical Co., Ltd. Adeka STAB LA-F70: 6,6',6''-(1,3,5-triazine-2,4,6-triyl)tris[3-(hexyloxy)-2-methylphenol], manufactured by ADEKA Corporation Adekastab LA-46: 2-ethylhexanoate = 2-[3-hydroxy-4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenoxy]ethyl, manufactured by ADEKA Corporation Tinuvin 479: Hydroxyphenyltriazine UV absorber, manufactured by BYK MT-700HD: Fine particle titanium dioxide (average primary particle size 50 nm), manufactured by Teika Co., Ltd. Tinuvin 400: 2-[4,6-bis(2,4-dimethylphenyl)-s-triazin-2-yl]5-[2-hydroxy-3-(dodecyloxy)propoxy]phenol, manufactured by BYK RUVA-93: 2-[2-hydroxy-5-[2-(methacryloyloxy)ethyl]phenyl]-2H-benzotriazole, manufactured by Otsuka Chemical Co., Ltd. ADK STAB LA-72: Bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, manufactured by ADEKA Corporation Tinuvin 292: bis(1,2,2,6,6-pentamethyl-4-piperidinyl) decanedioate, manufactured by BYK Adekastab AO-20: Tris(3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate, manufactured by ADEKA Corporation CR58-2: Titanium oxide, manufactured by Ishihara Sangyo Kaisha DisperBYK111: Copolymer containing acid groups, manufactured by BYK

[0070] As is clear from the results in Tables 1 and 2, in Examples 1 to 32, which used the active energy ray-curable coating composition of the present invention, the resulting cured coating films achieved all of high hardness, excellent processability, and excellent weather resistance, and the coating compositions had good storage stability. On the other hand, in Comparative Examples 1 to 6, one or more of coating film hardness, processability, weather resistance, long-term weather resistance, and storage stability were insufficient.

Claims

1. An active energy ray-curable coating composition for metal substrates, comprising a urethane (meth)acrylate (A), a polyfunctional (meth)acrylate monomer (B) having an isocyanurate skeleton (excluding the urethane (meth)acrylate (A)), a radical polymerizable monofunctional monomer (C) (excluding the urethane (meth)acrylate (A)), an ultraviolet absorber (D), and a light stabilizer (E), wherein the radical polymerizable monofunctional monomer (C) comprises a radical polymerizable monofunctional monomer (C-1) having an alicyclic structure and a radical polymerizable monofunctional monomer (C-2) having a heterocyclic structure; an active energy ray-curable coating composition for metal substrates, the content of a solvent being 3 mass% or less based on the total amount of the active energy ray-curable coating composition for metal substrates, and the viscosity at 25°C being 100 to 2000 mPa·s.

2. 2. The active energy ray-curable coating composition for metal substrates according to claim 1, wherein the content ratio (mass ratio) of the radical polymerizable monofunctional monomer (C-1) having an alicyclic structure to the radical polymerizable monofunctional monomer (C-2) having a heterocyclic structure is 20 / 80 to 70 / 30.

3. An active energy ray-curable coating composition for metal substrates as described in claim 1, wherein the content of the urethane (meth)acrylate (A) is 5 to 40 mass% based on the total amount of the binder composition.

4. An active energy ray curable coating composition for metal substrates as described in claim 1, used for roll coater coating.

5. 2. The active energy ray-curable coating composition for metal substrates according to claim 1, wherein the content of the photopolymerization initiator is 0.5 mass % or less based on the total amount of the active energy ray-curable coating composition for metal substrates.

6. The active energy ray-curable coating composition for metal substrates according to claim 1, which is for use in pre-coating metal.

7. A laminate having a cured layer of the active energy ray-curable coating composition according to any one of claims 1 to 6 on a metal substrate.

8. A method for producing a laminate, comprising applying the active energy ray-curable coating composition according to any one of claims 1 to 6 to a metal substrate and curing the composition with active energy rays.

9. A molded member using the laminate according to claim 7.

10. A method for producing a molded member, comprising applying the active energy ray-curable coating composition according to any one of claims 1 to 6 to a metal substrate, curing the composition with active energy rays, and molding the composition.

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