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

Abstract

An object of the present invention is to provide an active energy ray-curable coating composition for metal substrates that provides a cured coating film with good hardness, processability, and weather resistance, as well as a laminate 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 provides good coating film properties even when an ultraviolet absorber is used, does not cause precipitation of the ultraviolet absorber during storage, and has good storage stability. [Solution] An active energy ray-curable coating composition for metal substrates, comprising a binder component (A) and an ultraviolet absorber (B), wherein the binder component (A) comprises a urethane (meth)acrylate (A-1), a radical-polymerizable monofunctional monomer (A-2) having an alicyclic structure, and a radical-polymerizable monofunctional monomer (A-3) having a heterocyclic structure and a homopolymer glass transition temperature (Tg) of 20°C or higher; and a coating laminate using the same.

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 coating the metal substrate after it has been processed into a product or part, so a coating system suited to the shape and size of the object to be coated is required.On the other hand, the pre-coating method involves coating a plate-shaped metal substrate, so roll coating is widely used, allowing for continuous operation at very high speeds.

[0004] However, because PCMs are processed after painting, they must not only have the hardness and various resistances required for their main 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 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. In particular, 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. Commonly used 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. Furthermore, since many of these additives are poorly soluble in acrylate monomers, they may precipitate during storage in solvent-free active energy ray-curable coating compositions, making it difficult to increase their addition amounts.

[0007] Patent Document 1 discloses an active energy ray-curable resin composition comprising 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. Patent Document 2 also discloses an active energy ray-curable coating composition for metal substrates, which contains a urethane (meth)acrylate having a weight-average molecular weight of 1,000 to 60,000, a compound having a hydrophilic group and one ethylenically unsaturated group, a compound having a cyclic hydrocarbon group and one ethylenically unsaturated group but no hydrophilic group, and a compound having two or more (meth)acryloyl groups. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent Publication No. 2022-131646 [Patent Document 2] Patent No. 5935668 Summary of the Invention [Problem to be solved by the invention]

[0009] However, while the active energy ray-curable coating agent described in Patent Document 1 provides good coating film hardness and processability, there is no mention of weather resistance. Adding an ultraviolet absorber or the like to improve weather resistance may result in a decrease in coating film physical properties after curing, or there is a concern that the ultraviolet absorber may precipitate during storage. Furthermore, Patent Document 2 discloses an active energy ray-curable coating composition for metal substrates that has good adhesion and solvent resistance, but there is no mention of coating film physical properties or weather resistance.

[0010] An object of the present invention is to provide an active energy ray-curable coating composition for metal substrates that provides a cured coating film with good hardness, processability, and weather resistance, as well as a laminate 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 provides good coating film properties even when an ultraviolet absorber is used, and that has good storage stability without causing precipitation of the ultraviolet absorber during storage.

[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] An active energy ray-curable coating composition for metal substrates, comprising a binder component (A) and an ultraviolet absorber (B), The binder component (A) is a urethane (meth)acrylate (A-1); a radical polymerizable monofunctional monomer (A-2) having an alicyclic structure; a radical polymerizable monofunctional monomer (A-3) having a heterocyclic structure and a homopolymer glass transition temperature (Tg) of 20°C or higher; An active energy ray-curable coating composition for metal substrates, comprising:

[0013] [2] The active energy ray-curable coating composition for metal substrates according to [1], wherein the content ratio (mass ratio) of the radical polymerizable monofunctional monomer (A-2) having an alicyclic structure to the radical polymerizable monofunctional monomer (A-3) having a heterocyclic structure and having a homopolymer glass transition temperature (Tg) of 20°C or higher is 30 / 70 to 80 / 20.

[0014] [3] The active energy ray-curable coating composition for metal substrates according to [1] or [2], wherein the content of the radical polymerizable monofunctional monomer (A-2) having an alicyclic structure is 15 to 45 mass% based on the total amount of the binder component (A).

[0015] [4] The active energy ray-curable coating composition for metal substrates according to any one of [1] to [3], wherein the content of the radical polymerizable monofunctional monomer (A-3) having a heterocyclic structure and a homopolymer glass transition temperature (Tg) of 20°C or higher is 10 to 40 mass% based on the total amount of the binder component (A).

[0016] [5] The active energy ray-curable coating composition for metal substrates according to any one of [1] to [4], wherein the content of the urethane (meth)acrylate (A-1) is 15 to 45 mass% based on the total amount of the binder component (A).

[0017] [6] The active energy ray-curable coating composition for metal substrates according to any one of [1] to [5], 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.

[0018] [7] The active energy ray-curable coating composition for metal substrates according to any one of [1] to [6], 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.

[0019] [8] The active energy ray-curable coating composition for metal substrates according to any one of [1] to [7] above, which is for use on pre-coated metal.

[0020] [9] A laminate having, on a metal substrate, a cured coating film of the active energy ray-curable coating composition for metal substrates according to any one of [1] to [8] above.

[0021]

[10] A molded product using the laminate described in [9] above.

[0022]

[11] A method for producing a laminate, comprising applying the active energy ray-curable coating composition for metal substrates according to any one of [1] to [8] above to a metal substrate with a roll coater, and curing the composition with active energy rays.

[0023]

[12] A method for producing a molded product, comprising applying the active energy ray-curable coating composition for metal substrates according to any one of [1] to [8] above to a metal substrate using a roll coater, curing the composition with active energy rays, and molding the composition. [Effects of the Invention]

[0024] The present invention can provide an active energy ray-curable coating composition for metal substrates that provides a cured coating film with good hardness, processability, and weather resistance, as well as a laminate and a molded member using the same. The present invention also can provide an active energy ray-curable coating composition for metal substrates that provides good coating film properties even when an ultraviolet absorber is used, and that has good storage stability without causing precipitation of the ultraviolet absorber during storage. DETAILED DESCRIPTION OF THE INVENTION

[0025] 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.

[0026] 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.

[0027] In the following description, the "number of functional groups" refers to the number of radically polymerizable functional groups, such as acryloyl groups, methacryloyl groups, vinyl groups, and other ethylenically unsaturated groups, that a resin or compound has in one molecule.

[0028] In this specification, the binder component (A) refers to the vehicle remaining in the coating composition excluding the pigment, UV absorber, light stabilizer, and other additives. Specifically, it refers to a mixture containing a urethane (meth)acrylate (A-1), a radically polymerizable monofunctional monomer (A-2) having an alicyclic structure, a radically polymerizable monofunctional monomer (A-3) having a heterocyclic structure and a homopolymer glass transition temperature (Tg) of 20°C or higher, other compounds having radically polymerizable groups, and an inert resin.

[0029] As used herein, the term "homopolymer glass transition temperature (Tg)" refers to the temperature at which a polymer made of a single monomer changes from a glassy state to a rubbery state when heated, and is measured, for example, by a differential scanning calorimeter (DSC) or a thermomechanical analyzer (TMA).

[0030] Hereinafter, the components that are or can be contained in the active energy ray-curable coating composition for metal substrates of this embodiment (hereinafter also simply referred to as "coating") will be described.

[0031] [Binder component (A)] <Urethane (meth)acrylate (A-1)> The urethane (meth)acrylate (A-1) is not particularly limited, and may be any (meth)acrylate having a urethane bond. By including the urethane (meth)acrylate (A-1), the coating material of the present invention has a good balance between coating film hardness and processability, and also has good adhesion. Examples of the urethane (meth)acrylate (A-1) 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. Commercially available products include, for example, Daicel Allnex's EBECRYL4858 (bifunctional), EBECRYL8311 (trifunctional), EBECRYL8402 (bifunctional), EBECRYL8701 (trifunctional), EBECRYL9260 (trifunctional), EBECRYL8606 (tetrafunctional), and EBECRYL8301R (hexafunctional); Sartomer's CN8888NS (bifunctional), CN8898NS (bifunctional), CN8881NS (bifunctional), CN964NS (bifunctional), and CN9013NS (9 functional); and MIWON's Miramer PU320 (trifunctional), Miramer PU340 (trifunctional), and Miramer PU5000 (hexafunctional).

[0032] The urethane (meth)acrylate (A-1) 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.

[0033] The number of functional groups in the urethane (meth)acrylate (A-1) is preferably 2 to 4, and more preferably 2 to 3. If the number of functional groups is equal to or greater than the lower limit, the hardness of the coating film increases, and if the number of functional groups is equal to or less than the 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-1) is preferably 15 to 45 mass%, more preferably 20 to 40 mass%, and even more preferably 25 to 35 mass%, based on the total amount of the binder component (A). When the content of the urethane (meth)acrylate (A-1) is within the above range, a good balance between the hardness and processability of the coating film is achieved.

[0034] <Radical polymerizable monofunctional monomer having an alicyclic structure (A-2)> In the radical polymerizable monofunctional monomer (A-2) having an alicyclic structure (hereinafter also referred to as "component (A-2)"), the alicyclic structure is a non-aromatic ring structure composed only of carbon. By including the radical polymerizable monofunctional monomer (A-2) having an alicyclic structure, the coating material of the present invention has excellent weather resistance and easily dissolves ultraviolet absorbers.

[0035] The radically polymerizable monofunctional monomer (A-2) having an alicyclic structure is not particularly limited, and examples include 3,3,5-trimethylcyclohexyl (meth)acrylate, hexahydrophthalic acid ethyl (meth)acrylate, hexahydrophthalic acid propyl (meth)acrylate, cyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, isobornyl (meth)acrylate, etc. From the viewpoint of providing a coating film with good weather resistance and high hardness, the homopolymer glass transition temperature (Tg) of component (A-2) is preferably 10°C or higher, more preferably 40°C or higher, and even more preferably 70°C or higher.

[0036] Component (A-2) preferably has a fused ring structure because it provides excellent solubility for the UV absorber. Specific examples include isobornyl acrylate (Tg = 97°C) and dicyclopentanyl acrylate (Tg = 120°C).

[0037] The content of component (A-2) is preferably 15 to 45 mass %, more preferably 20 to 40 mass %, and even more preferably 25 to 35 mass %, based on the total amount of binder component (A). When the content of component (A-2) is within the above range, a good balance between the solubility of the ultraviolet absorber and the coating hardness is achieved.

[0038] <Radically polymerizable monofunctional monomer (A-3) having a heterocyclic structure and a homopolymer glass transition temperature (Tg) of 20°C or higher> In the radically polymerizable monofunctional monomer (A-3) (hereinafter also referred to as "component (A-3)") having a heterocyclic structure and a homopolymer glass transition temperature (Tg) of 20°C or higher, the heterocyclic structure is a ring structure composed of at least two different elements. By including component (A-3), the coating material of the present invention has high coating film hardness and excellent heat resistance.

[0039] The radically polymerizable monofunctional monomer (A-3) having a heterocyclic structure and a homopolymer glass transition temperature (Tg) of 20°C or higher is not particularly limited, and examples thereof include glycerin carbonate acrylate, 4-cyclohexene-1,2-dicarboximide-N-ethyl acrylate, 2-(cyclohexane-1,2-dicarboximide)ethyl acrylate, acryloylmorpholine, cyclic trimethylolpropane formal acrylate, N-vinylcaprolactam, N-vinylpyrrolidone, etc. From the viewpoint of providing a coating film with good weather resistance and high hardness, the homopolymer glass transition temperature (Tg) of component (A-3) is preferably 50°C or higher, and more preferably 80°C or higher.

[0040] From the viewpoint of excellent coating hardness, it is preferable that component (A-3) contains nitrogen in the heterocycle, and specific examples thereof include acryloylmorpholine (Tg = 145°C) and N-vinylcaprolactam (Tg = 90°C).

[0041] The content of component (A-3) is preferably 10 to 40 mass %, more preferably 15 to 35 mass %, and even more preferably 20 to 30 mass %, based on the total amount of binder component (A). When the content of component (A-3) is within the above range, a good balance between weather resistance and coating hardness is achieved.

[0042] The content ratio (mass ratio) of component (A-2) to component (A-3) is preferably 30 / 70 to 80 / 20, more preferably 40 / 60 to 70 / 30, and even more preferably 45 / 55 to 65 / 35. When the content ratio of component (A-2) to component (A-3) is within the above range, good coating hardness can be maintained while ensuring the solubility of the ultraviolet absorber.

[0043] The binder component (A) may contain other radical polymerizable monomers and / or oligomers in addition to the above (A-1), (A-2), and (A-3). The amount of other radical polymerizable monomers and / or oligomers is not particularly limited, but is preferably 40 mass% or less based on the total amount of the binder component (A). The binder component (A) may also contain an inert resin, etc.

[0044] [Additives] <Ultraviolet absorber (B)> Examples of the ultraviolet absorber (B) 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.

[0045] 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.

[0046] The ultraviolet absorber (B) may be added to the coating material in any amount, but from the viewpoints of solubility in the coating material and coating film strength, it is preferably added in an amount of 3 to 15 mass %, more preferably 5 to 10 mass %, based on the total amount of the binder component (A).

[0047] The active energy ray-curable coating composition for metal substrates of the present invention may contain, in addition to the ultraviolet absorber (B), known additives as appropriate, such as light stabilizers, pigments, dyes, sensitizers, polymerization initiators, fluorescent brighteners, curing agents, coupling agents, plasticizers, surface conditioners, antifoaming agents, substrate wetting agents, antistatic agents, extender pigments, and pigment dispersants.

[0048] Examples of light stabilizers 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.

[0049] The content of the light stabilizer 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 component (A).

[0050] The pigment is not particularly limited, and any known pigment can be used, and 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.

[0051] Examples of the inorganic pigments include ultramarine, titanium dioxide, iron oxides, composite oxide pigments, and carbon blacks.

[0052] Examples of the organic pigment include phthalocyanine pigments, azo pigments, quinacridone pigments, diketopyrrolopyrrole pigments, and quinophthalone pigments.

[0053] The content of the pigment is adjusted appropriately depending on the type and purpose. For example, the content of the pigment is preferably 3% by mass or more based on the total amount of the coating composition. Also, the content of the pigment is preferably 60% by mass or less based on the total amount of the coating composition. By keeping the content of the pigment within the above range, the coating composition can ensure dispersion stability while exhibiting sufficient hiding power.

[0054] [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. When the active energy ray-curable coating composition for metal substrates of the present invention is cured by electron beams, it is preferable that it 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.

[0055] [solvent] The active energy ray-curable coating composition for metal substrates 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 amount of the active energy ray-curable coating composition for metal substrates. 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.

[0056] [viscosity] The viscosity of the active energy ray-curable coating composition for metal substrates of the present invention is not particularly limited and can be appropriately set depending on the coating method. For example, when coating is performed using a roll coater, which is preferably used in the production of PCM, 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. A viscosity at 25°C within the above range provides excellent coating and printing suitability. Viscosity is measured, for example, 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 It can be calculated from the measured value at time.

[0057] [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 sheet substrates such as galvanized steel sheets and zinc-plated steel sheets are more preferred.

[0058] [Coating method] The active energy ray-curable coating composition for metal substrates 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, 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.

[0059] [Curing method] The method for curing the active energy ray-curable coating composition for metal substrates of the present invention is not particularly limited, and known methods can be used. For example, curing can be achieved 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.

[0060] The coating composition of the present invention exhibits the effects of the present invention, namely, improved hardness, processability and weather resistance of the coating film, even when cured by ultraviolet light. When the coating composition of the present invention is cured by electron beam irradiation, it is not inhibited by UV light blocking, which can occur with high pigment concentrations or the incorporation of UV absorbers. Furthermore, because no initiator is required, the pot life of the coating is not shortened and there is no deterioration in coating film performance due to initiator decomposition products after curing. Therefore, the effects of the present invention, such as improved coating film hardness, processability, and weather resistance, can be maximized.

[0061] 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 decrease.

[0062] [Laminate] The active energy ray-curable coating composition for metal substrates of the present invention is applied to a substrate, and then cured by irradiating with active energy rays to obtain a laminate having a cured coating film on the metal substrate. The coating thickness of the active energy ray-curable coating composition for metal substrates is usually preferably 1 to 50 μm, and more preferably 10 to 20 μm. The laminate can be suitably used as a precoated metal.

[0063] [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]

[0064] 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.

[0065] [Preparation of active energy ray-curable coating composition for metal substrates: Example 1] According to the formulation shown in Table 1, the raw materials were mixed at room temperature by stirring with a disperser (3000 rpm) to prepare an active energy ray-curable coating composition for metal substrates. The resulting coating composition was evaluated for storage stability, processability, coating film hardness, and weather resistance using the following evaluation methods. The results are shown in Table 1.

[0066] [Preparation of active energy ray-curable coating compositions for metal substrates: Examples 2 to 26, Comparative Examples 1 to 7] Examples 2 to 26 and Comparative Examples 1 to 7 were obtained in the same manner as Example 1, except that the raw materials and amounts shown in Table 1 were changed. The numbers in Tables 1 and 2 indicate the blend amounts (mass %).

[0067] [Laminate manufacturing method] The obtained active energy ray-curable coating composition for metal substrates was applied to a substrate, Galvalume steel plate (registered trademark, Yodogawa Steel Works, Yodo GL Eco Green, thickness 0.27 mm) using a reverse roll coater to a coating thickness of 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.

[0068] [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.

[0069] [Workability] The workability was evaluated by a 180° bending test to evaluate bending resistance. A test piece was sandwiched between 10 steel substrate sheets, with the cured coating facing outward, and the inside of the bent portion was bent by 180° by dropping a 1 kg load on the test piece from a height of 50 cm. The bent portion of the processed piece was visually evaluated for the presence or absence of cracks. 〔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.

[0070] [Coating film hardness] The hardness of the coating was evaluated by measuring 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 found at hardness HB. D: Scratches were confirmed at hardness HB. The evaluations for practical use are A, B, and C.

[0071] [Weather resistance] Weather resistance was evaluated using a xenon weather resistance tester (product name "Q-SUN Xe-1", manufactured by Q-Lab) at 120W / m 2 The test pieces were repeatedly exposed to UV light for 102 minutes at a black panel temperature of 63°C, followed by a shower process in which water was sprayed onto the test pieces for 18 minutes while irradiating with UV light under the same conditions. The surface condition of the test pieces was evaluated after 700 hours. 〔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.

[0072] [Table 1]

[0073] [Table 2]

[0074] The information on each raw material in Tables 1 and 2 is as follows: EBECRYL8402: Difunctional aliphatic urethane acrylate (Daicel Allnex) EBECRYL8701: Trifunctional aliphatic urethane acrylate (Daicel Allnex) MIRAMER PU5000: Hexafunctional aliphatic urethane acrylate (MIWON) IBXA: Isobornyl acrylate (Osaka Organic Chemical Industry Co., Ltd.) Viscoat 196: 3,3,5-trimethylcyclohexyl acrylate (Osaka Organic Chemical Industry Co., Ltd.) Viscoat 155: Cyclohexyl acrylate (Osaka Organic Chemical Industry Co., Ltd.) ACMO: Acryloylmorpholine (KJ Chemicals) Aronix M-140: N-acryloyloxyethyl hexahydrophthalimide (Toagosei Co., Ltd.) Viscoat 200: Cyclic trimethylolpropane formal acrylate (Osaka Organic Chemical Industry Co., Ltd.) Iupimer UV SA1002: Tricyclodecane dimethanol diacrylate (Mitsubishi Chemical Corporation) Light Acrylate HPP-A: Hydroxypivalic acid neopentyl glycol diacrylate (Kyoeisha Chemical Co., Ltd.) Viscoat 150: Tetrahydrofurfuryl acrylate (Osaka Organic Chemical Industry Co., Ltd.) Adekastab LA-46: 2-ethylhexanoate = 2-[3-hydroxy-4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenoxy]ethyl (ADEKA Corporation) Tinuvin 479: Hydroxyphenyltriazine UV absorber (BYK) (Structure not disclosed) RUVA-93: 2-[2-hydroxy-5-[2-(methacryloyloxy)ethyl]phenyl]-2H-benzotriazole (Otsuka Chemical Co., Ltd.) ADK STAB LA-72: Bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate (ADEKA Corporation) Typaque CR-90: Rutile titanium dioxide (Ishihara Sangyo Co., Ltd.) DisperBYK111: Copolymer containing acid groups (BYK)

[0075] As is clear from the results in Tables 1 and 2, in Examples 1 to 26, which used the active energy ray-curable coating composition for metal substrates of the present invention, the obtained cured coating films were good in all of hardness, processability, and weather resistance, and the coating compositions had good storage stability. On the other hand, in Comparative Examples 1 to 7, one or more of hardness, processability, weather resistance, and storage stability were insufficient.

Claims

1. An active energy ray-curable coating composition for metal substrates, comprising a binder component (A) and an ultraviolet absorber (B), The binder component (A) is urethane (meth)acrylate (A-1); a radical polymerizable monofunctional monomer (A-2) having an alicyclic structure; and a radically polymerizable monofunctional monomer (A-3) having a heterocyclic structure and a homopolymer glass transition temperature (Tg) of 20°C or higher, 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 (A-2) having an alicyclic structure to the radical polymerizable monofunctional monomer (A-3) having a heterocyclic structure and having a homopolymer glass transition temperature (Tg) of 20°C or higher is 30 / 70 to 80 / 20.

3. The active energy ray-curable coating composition for metal substrates according to claim 1, wherein the content of the radical polymerizable monofunctional monomer (A-2) having an alicyclic structure is 15 to 45 mass% based on the total amount of the binder component (A).

4. 2. The active energy ray-curable coating composition for metal substrates according to claim 1, wherein the content of the radically polymerizable monofunctional monomer (A-3) having a heterocyclic structure and a homopolymer glass transition temperature (Tg) of 20°C or higher is 10 to 40 mass% based on the total amount of the binder component (A).

5. The active energy ray-curable coating composition for metal substrates according to claim 1, wherein the content of the urethane (meth)acrylate (A-1) is 15 to 45 mass% based on the total amount of the binder component (A).

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

7. 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.

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

9. A laminate having a cured coating film of the active energy ray-curable coating composition for metal substrates according to any one of claims 1 to 8 on a metal substrate.

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

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

12. A method for producing a molded member, comprising applying the active energy ray-curable coating composition for metal substrates according to any one of claims 1 to 8 to a metal substrate with a roll coater, curing the composition with active energy rays, and molding the composition.

Images