Photocurable resin composition, vehicle paint, coating film forming method, and coated article

Abstract

To provide a photocurable resin composition which is excellent in a filling effect and can conceal irregularities on a surface of a coated article.SOLUTION: A photocurable resin composition contains: a photocurable component (A) that is polyfunctional acrylate having four or more (meth)acrylate groups; a hydroxyl group-containing acrylic resin (B-1) having a weight average molecular weight of 3,000-8,000; a hydroxyl group-containing acrylic resin (B-2) having a weight average molecular weight of 10,000-30,000; a particle component (C); polyisocyanate (D); and a photopolymerization initiator (E), wherein with respect to 100 mass% of the total amount of the photocurable component (A), the acrylic resin (B-1), the acrylic resin (B-2), the particle component (C), and the photopolymerization initiator (E), a blending ratio of the polyisocyanate (D) is 10-100 mass%.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a photocurable resin composition, a vehicle paint, a coating film forming method, and a coated article.

Background Art

[0002] When painting a material having unevenness on its surface, the convex portions are concealed by increasing the film thickness or polished smooth with sandpaper or the like before painting, and the concave portions are treated by filling pinholes with putty or the like, applying putty to make the surface smooth, and the like. However, such pretreatment not only reduces productivity, but also causes problems such as an increase in volatile organic compounds (hereinafter referred to as VOC) due to an increase in the amount of paint used. Further, when the cause of the concave portion is a pinhole generated by air enclosed in the material, it is difficult to completely fill all of the pinholes with putty before painting, and air may remain in the pinholes. If painting and baking are performed with air remaining in the pinholes, there is a problem that coating defects such as the liquid paint after painting being sucked into the pinholes or the air in the pinholes expanding during baking and damaging the coating film may occur.

[0003] Fiber-reinforced plastic materials (hereinafter referred to as FRP materials) are lightweight while having excellent properties such as strength, rigidity, and dimensional stability compared to iron, aluminum, etc. In automotive vehicle members, it is being widely considered for use as a material that contributes to improved fuel efficiency through weight reduction. However, it has only been applied to some vehicle members such as automotive lamp reflectors and spoilers. Since FRP materials are formed by kneading multiple materials, they are prone to unevenness. The unevenness here includes segregation unevenness caused by insufficient mixing of fibers where the fibers appear on the surface of the material, protrusions caused by the protrusion of single fibers, and pinholes where air bubbles mixed during fiber mixing appear on the surface and become concave. Also, completely encapsulated air bubbles are difficult to detect initially and can break the material or coating film during baking, making it difficult to predict the occurrence location and take preventive measures in advance. Thus, since FRP materials are prone to coating defects, productivity is poor, and they have only been applied to some parts such as high-class cars and racing cars. Therefore, in order to increase the number of members using FRP materials with excellent characteristics, the development of putty paints with an excellent plugging effect for suppressing coating defects has been demanded.

[0004] Patent Document 1 discloses a coating method in which a two-component urethane paint containing (a) a mixed polyol of an acrylic polyol having a hydroxyl value of 15 to 25 and an acrylic polyol having a hydroxyl value of 35 to 45, and (b) a mixture of xylylene diisocyanate-based polyisocyanates having different isocyanate group contents is brought into contact with an atmosphere containing tertiary amine vapor and cured. However, such a coating method has disadvantages in terms of safety, environmental load, and cost, such as large equipment for contacting with dangerous tertiary amine vapor and wastewater treatment, in addition to the conventional baking process.

[0005] Patent Document 2 discloses a photocurable resin composition containing a urethane (meth)acrylate having six or more (meth)acryloyl groups, a hydroxyl group-containing acrylic resin (B) having a hydroxyl value of 10 to 200 mgKOH / g, and a polyisocyanate (C). However, this photocurable resin composition has not been studied as a putty for suppressing coating defects. Further, no detailed limitation has been made on the hydroxyl group-containing acrylic resin (B).

[0006] In addition, when irradiating a conventional photocurable resin composition with light, a light source having a wide wavelength range that can be irradiated, such as a mercury lamp or an electrodeless lamp, is used. However, these light sources have disadvantages in terms of equipment, such as being large-sized, requiring air conditioning equipment due to generating high heat, and requiring an exhaust duct up to the outdoors due to generating ozone. Further, since mercury is used, there are also problems regarding the environment and the safety of workers. In addition, since infrared rays are also irradiated, the burden on workers is large. Therefore, the development of a photocurable resin composition that can use a light source that is smaller, has excellent versatility, and improves problems such as safety and power saving has been desired.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] In view of the above, the present invention relates to a photocurable resin composition having an excellent plugging effect. Further, when using the above photocurable resin composition as a putty, it is possible to suppress coating defects of topcoating paints such as colored paints and clear paints and improve the coating appearance. Further, since it also has excellent adhesion to the topcoating paint, a multilayer coating film excellent in strength, durability, etc. can be obtained.

Means for Solving the Problem

[0009] The present invention relates to a laminated film having a cured coating film, a base coating film, and a clear coating film formed of a photocurable resin composition in this order. Manufacturing method wherein The photocurable resin composition is a photocurable component (A) which is a polyfunctional acrylate having 4 or more (meth)acrylate groups, a hydroxyl group-containing acrylic resin (B-1) having a weight average molecular weight in the range of 3000 to 8000, a hydroxyl group-containing acrylic resin (B-2) having a weight average molecular weight in the range of 10000 to 30000, a particle component (C), a polyisocyanate (D), and a photopolymerization initiator (E), The blending ratio of the polyisocyanate (D) is 10 to 100% by mass with respect to 100% by mass of the total amount of the photocurable component (A), the acrylic resin (B-1), the acrylic resin (B-2), the particle component (C), and the photopolymerization initiator (E). , Step (1) of applying the above photocurable resin composition onto an object to be coated and Step (2) of irradiating the coating film obtained in Step (1) with a single-wavelength light source having a wavelength range of 350 to 450 nm, Furthermore, a method for manufacturing a laminated film, characterized by having a step of performing base coating and clear coating and then heat curing relates to.

Effects of the Invention

[0011] Since the photocurable resin composition of the present invention has an excellent blocking effect, it can conceal the unevenness on the surface of the object to be coated. Furthermore, the effect of suppressing subsequent coating defects can also be obtained.

Brief Description of the Drawings

[0012]

Figure 1

Embodiments for Carrying Out the Invention

[0013] The present invention relates to a photocurable resin composition comprising a photocuring component (A) which is a polyfunctional acrylate having 4 or more (meth)acrylate groups, a hydroxyl group-containing acrylic resin (B-1) having a weight average molecular weight in the range of 3000 to 8000, a hydroxyl group-containing acrylic resin (B-2) having a weight average molecular weight in the range of 10,000 to 30,000, a particle component (C), a polyisocyanate (D) and a photopolymerization initiator (E).

[0014] The photocurable resin composition of the present invention is particularly preferably used by directly applying it onto a resin substrate having many surface irregularities such as FRP, and may also be used on a substrate with pinholes filled with putty or a substrate sanded to polish the convex portions.

[0015] Since the above photocurable resin composition contains a high molecular weight hydroxyl group-containing acrylic resin (B-2) and a particle component (C), after coating, the fluidity of the liquid paint is controlled, and the occurrence of concave defects generated by flowing into segregation dents and pinholes on the substrate can be reduced. In addition, the high molecular weight hydroxyl group-containing acrylic resin (B-2) can improve the dimensional stability and the adhesion to the substrate and the topcoat paint by reducing the influence such as shrinkage due to thermosetting with the polyisocyanate (D) by designing the hydroxyl value to be low.

[0016] Furthermore, since the above photocurable resin composition contains a photocuring component (A) and a low molecular weight hydroxyl group-containing acrylic resin (B-1), a coating film having a high crosslink density on the surface can be formed by UV curing, and a coating film having a high crosslink density inside the coating film can be formed by thermosetting. Therefore, coating defects such as air expansion in pinholes and damage to the coating film after coating the topcoat paint can be reduced. In addition, since the above photocurable resin composition contains a photocuring component (A) and a low-molecular-weight hydroxyl group-containing acrylic resin (B-1), even when the coating film thickness becomes thick, for example, when hiding convex portions and UV light does not reach sufficiently inside, the crosslinking density on the surface by UV curing and the crosslinking density inside by thermal curing are maintained. Therefore, coating defects such as air expanding from the inside and damaging the coating film can be reduced at various film thicknesses. Such a curing method using both UV curing and thermal curing is effective not only for FRP substrates but also for members such as three-dimensional shaped objects that cannot be coated with a uniform coating film over the entire surface.

[0017] The photocurable resin composition of the present invention contains a high-molecular-weight hydroxyl group-containing acrylic resin (B-2) and a particle component (C), whereby the viscosity immediately after coating is controlled, and a highly smooth coating film that is not sucked into the recesses can be obtained. In addition, a coating film having good adhesion to the substrate and the topcoat paint can be obtained by a thermal reaction with a polyisocyanate (D). Further, by the photocuring reaction of the photocuring component (A) and the thermal curing of the low-molecular-weight hydroxyl group-containing acrylic resin (B-1) and the polyisocyanate (D), a coating film having a high crosslinking density can be obtained at various film thicknesses, hiding the convex portions and suppressing the expansion of the air remaining in the unevenness, and maintaining the smooth state of the overall coating film coated with the topcoat paint. Therefore, the photocurable resin composition of the present invention is suitably used for an object to be coated having unevenness, and particularly has excellent performance as a putty.

[0018] The photocurable resin composition of the present invention further contains a photoinitiator (E). Since the above photoinitiator (E) is contained, photocuring can be suitably performed only by irradiating with a single-wavelength light source. Since photocuring at a single wavelength is possible, for example, a small and highly versatile light source such as a UV-LED lamp can be used. Hereinafter, the present invention will be described in detail.

[0019] Photocurable component (A) The photocurable resin composition of the present invention contains a polyfunctional acrylate having 4 or more (meth) acrylate groups as the photocuring component (A). The polyfunctional (meth)acrylate having 4 or more (meth)acrylate groups has good polymerization activity when irradiated with active energy rays. By including the polyfunctional (meth)acrylate having 4 or more (meth)acrylate groups in the photocurable resin composition, there is an advantage that a coating film having a high crosslink density on the surface can be obtained.

[0020] The above polyfunctional (meth)acrylate can be prepared by subjecting a polyhydric alcohol and (meth)acrylate to a dealcoholization reaction. Specific examples of the polyfunctional (meth)acrylate include, for example, tetrafunctional (meth)acrylates such as pentaerythritol tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, tripentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate; pentafunctional (meth)acrylates such as dipentaerythritol penta(meth)acrylate, tripentaerythritol penta(meth)acrylate; hexafunctional (meth)acrylates such as dipentaerythritol hexa(meth)acrylate, tripentaerythritol hexa(meth)acrylate; hepta- or higher-functional (meth)acrylates such as tripentaerythritol hepta(meth)acrylate, tripentaerythritol octa(meth)acrylate; and the like.

[0021] The polyfunctional (meth)acrylate used in the present invention is not particularly limited in molecular weight, but preferably has a molecular weight of 3000 or less. That is, it is not a polymer, and it is preferably a compound having a relatively low molecular weight. Such a molecular weight is a value calculated from the chemical structural formula of the polyfunctional (meth)acrylate. These polyfunctional (meth)acrylates may be used alone or in combination of two or more. Further, the photocurable resin composition of the present invention may be a composition in which other photocurable compounds are used in combination.

[0022] The blending ratio of the photocurable component (A) contained in the above photocurable resin composition is preferably 6% by mass or more and 54% by mass or less, more preferably 20% by mass or more and 40% by mass or less, based on 100% by mass of the total amount of the photocurable component (A), the hydroxyl group-containing acrylic resin (B-1), the hydroxyl group-containing acrylic resin (B-2), and the particle component (C). When the blending ratio of the above photocurable component (A) is 6% by mass or more, the crosslinking density on the surface of the obtained coating film can be improved. Further, when it is 54% by mass or less, there is an advantage that excessive curing shrinkage can be reduced, and the adhesion between the substrate and the topcoat paint can be kept good.

[0023] Hydroxyl group-containing acrylic resin (B-1) The hydroxyl group-containing acrylic resin (B-1) is a low molecular weight hydroxyl group-containing acrylic resin having a weight average molecular weight in the range of 3000 to 8000. In the present invention, it is an important requirement to use the low molecular weight hydroxyl group-containing acrylic resin (B-1) and the high molecular weight hydroxyl group-containing acrylic resin (B-2) described later in combination. That is, by using these two kinds of hydroxyl group-containing acrylic resins in combination, a good plugging effect and sufficient coating film strength as a pattern coating film can be imparted.

[0024] When the weight average molecular weight is in the range of 3000 to 8000, when coating and heat curing are performed thereon, the crosslinking of the hydroxyl group-containing acrylic resin (B-1) proceeds, and a cured coating film having a high crosslinking density can be formed. The weight average molecular weight is preferably 4000 or more, more preferably 6000 or more.

[0025] The weight average molecular weight in this specification is a value measured by gel permeation chromatography using HLC-8200 manufactured by Tosoh Corporation. The measurement conditions are as follows. Three columns of TSgel Super Multipore HZ-M Developing solvent Tetrahydrofuran Column injection port oven at 40 °C Flow rate: 0.35 ml Detector: RI Standard polystyrene, PS oligomer kit manufactured by Tosoh Corporation

[0026] In the present invention, the "acrylic resin" refers to a polymer obtained by polymerizing a monomer composition containing at least one monomer among acrylic acid and its esters, methacrylic acid and its esters.

[0027] The hydroxyl group-containing acrylic resin (B-1) according to the present invention can be constituted. As a suitable monomer composition satisfying the above conditions, for example, hydroxyethyl acrylate, hydroxybutyl acrylate, etc., which are hydroxy-containing acrylic esters; 2-hydroxyethyl methacrylate, 4-hydroxybutyl methacrylate, etc., which are hydroxy-containing methacrylic esters; at least one of them, and further, if necessary, acrylic acid; acrylic acid esters such as methyl acrylate, butyl acrylate, isobutyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, isobornyl acrylate; methacrylic acid; methacrylic acid esters such as methyl methacrylate, butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, isobornyl methacrylate; ethylenically unsaturated monomers having an aromatic ring such as styrene; etc. A composition containing at least one of them can be mentioned. The composition of the monomer composition may be appropriately adjusted according to various physical properties required for the hydroxyl group-containing acrylic resin (B-1).

[0028] The monomer composition can be polymerized using a solvent such as butyl acetate. Also, the type of solvent, the concentration of the monomer composition during polymerization, or the type, amount, polymerization temperature, polymerization time, etc. of the polymerization initiator can be appropriately adjusted according to various physical properties required for the hydroxyl group-containing acrylic resin (B-1). Therefore, the production method of the hydroxyl group-containing acrylic resin (B-1) is not particularly limited, and a commercially available hydroxyl group-containing acrylic resin (B-1) may be used.

[0029] The above hydroxyl group-containing acrylic resin (B-1) preferably has a hydroxyl value (OHV) in the range of 120 to 200 mgKOH / g. By setting the hydroxyl value within such a range, it is preferable in that a good crosslinking density can be imparted to the coating film. The lower limit of the above hydroxyl value is more preferably 150 mgKOH / g. The upper limit of the above hydroxyl value is more preferably 170 mgKOH / g. In addition, the hydroxyl value can be determined by a neutralization titration method using an aqueous potassium hydroxide solution described in JIS K 0070.

[0030] The blending ratio of the hydroxyl group-containing acrylic resin (B-1) is preferably 4% by mass or more and 36% by mass or less, more preferably 10% by mass or more and 30% by mass or less, based on 100% by mass of the total amount of the photocuring component (A), the hydroxyl group-containing acrylic resin (B-1), the hydroxyl group-containing acrylic resin (B-2), and the particle component (C).

[0031] The glass transition temperature of the above hydroxyl group-containing acrylic resin (B-1) is preferably -15°C or higher and 45°C or lower, more preferably 0°C or higher and 30°C or lower. By having the glass transition temperature within such a range, the coating film can have a high crosslinking density and elasticity. The glass transition temperature in this specification uses the value measured by the following process with a differential scanning calorimeter (DSC) (thermal analyzer SSC5200 (manufactured by Seiko Instruments Inc.)). Specifically, in the process of heating from 20°C to 150°C at a heating rate of 10°C / min (Process 1), the process of cooling from 150°C to -50°C at a cooling rate of 10°C / min (Process 2), and the process of heating from -50°C to 150°C at a heating rate of 10°C / min (Process 3), the value obtained from the chart during the heating in Process 3 was used as the glass transition temperature. That is, the temperature indicated by the arrow in the chart shown in Figure 1 was taken as Tg (glass transition temperature).

[0032] The solid content acid value (AV) of the above-mentioned hydroxyl group-containing acrylic resin (B-1) is preferably 0.5 mgKOH / g or more and 15 mgKOH / g or less, and more preferably 2 mgKOH / g or more and 10 mgKOH / g or less. When the acid value of the above-mentioned hydroxyl group-containing acrylic resin (B-1) is within such a range, the adhesion to the substrate and the topcoat paint can be improved.

[0033] Hydroxyl group-containing acrylic resin (B-2) The hydroxyl group-containing acrylic resin (B-2) is a high molecular weight hydroxyl group-containing acrylic resin having a weight average molecular weight in the range of 10,000 to 30,000. When the above-mentioned weight average molecular weight is within the range of 10,000 to 30,000, the viscosity of the photocurable resin composition of the present invention can be controlled, so that a good plugging effect can be imparted. The above-mentioned weight average molecular weight is preferably 13,000 or more and preferably 23,000 or less.

[0034] The suitable monomer composition capable of constituting the above-mentioned hydroxyl group-containing acrylic resin (B-2) and satisfying the above conditions is not particularly limited, and those described for the above-mentioned hydroxyl group-containing acrylic resin (B-1) can be used.

[0035] The hydroxyl group-containing acrylic resin (B-2) preferably has a hydroxyl value (OHV) in the range of 5 to 70 mgKOH / g. When the hydroxyl value is within such a range, the curing shrinkage during thermosetting can be reduced, and a coating film with good dimensional stability and excellent adhesion can be obtained. The above-mentioned hydroxyl value is more preferably 20 to 55 mgKOH / g.

[0036] The glass transition temperature of the above-mentioned hydroxyl group-containing acrylic resin (B-2) is preferably 40°C or more and 100°C or less, and more preferably 50°C or more and 80°C or less. When the glass transition temperature is within such a range, the coating film can have particularly excellent adhesion to the substrate.

[0037] The solid content acid value (AV) of the above-mentioned hydroxyl group-containing acrylic resin (B-2) is preferably 0.5 mgKOH / g or more and 30 mgKOH / g or less, more preferably 2 mgKOH / g or more and 10 mgKOH / g or less. When the acid value of the above-mentioned hydroxyl group-containing acrylic resin (B-2) is within such a range, the coating film can obtain particularly excellent adhesion to the substrate.

[0038] The blending ratio of the hydroxyl group-containing acrylic resin (B-2) is preferably 4% by mass or more and 36% by mass or less, more preferably 10% by mass or more and 30% by mass or less, based on 100% by mass of the total amount of the photocuring component (A), the hydroxyl group-containing acrylic resin (B-1), the hydroxyl group-containing acrylic resin (B-2), and the particle component (C).

[0039] The SP values of the above-mentioned hydroxyl group-containing acrylic resins (B-1) and (B-2) are not particularly limited, but preferably the difference is less than 1. When the difference in SP values is less than 1, the compatibility of the hydroxyl group-containing acrylic resins (B-1) and (B-2) is high, so a coating film with high uniformity can be formed, and thus a coating film with excellent physical properties can be formed, which is preferable. The difference in the above-mentioned SP values is more preferably less than 0.5. In this specification, the SP value means the SP value by the turbidity method. The above-mentioned SP value is an abbreviation of solubility parameter and is a measure of solubility. The larger the SP value, the higher the polarity, and conversely, the smaller the SP value, the lower the polarity.

[0040] Particle component (C) The photocurable resin composition of the present invention further contains a particle component (C). By containing the above-mentioned particle component (C), the viscosity of the paint can be controlled, and a film can be formed by ensuring a sufficient thickness to conceal unevenness. In addition, it becomes difficult for the liquid paint composition to enter the recesses and pinholes on the surface of the object to be coated immediately after coating, and a good blocking effect can be obtained.

[0041] The above-mentioned particulate component (C) is not particularly limited as long as it is usually blended in a resin composition, but preferably has an average particle diameter of 20 μm or less. When the average particle diameter is 20 μm or less, a better plugging effect can be expected. More preferably, the above-mentioned average particle diameter is 10 μm or less. The above-mentioned average particle diameter represents D50 measured using a laser diffraction particle size distribution analyzer.

[0042] The above-mentioned particulate component (C) may be inorganic substance particles or organic polymer particles. Examples of the above-mentioned inorganic substance particles include natural or synthetic mica, barium sulfate, aluminum powder, aluminum flakes, iron oxide, kaolin clay, talc, silica fine powder, and titanium oxide. Examples of the silica fine powder include wet silica, dry silica, colloidal silica, etc.

[0043] Examples of the above-mentioned organic polymer particles include fluororesins such as polytetrafluoroethylene, polyethylene, polypropylene, silicone, cellulose, urethane, nylon, polyester, phenol resin, acrylic resin, amino resin, polyamide resin, and modified resins thereof.

[0044] As the particulate component (C), it is preferably at least one selected from among talc, silica, and kaolin clay. Also, two or more thereof may be used in combination.

[0045] The blending ratio of the above-mentioned particulate component (C) is preferably 6% by mass or more and 54% by mass or less, more preferably 25% by mass or more and 45% by mass or less, based on 100% by mass of the total amount of the photocuring component (A), the hydroxyl group-containing acrylic resin (B-1), the hydroxyl group-containing acrylic resin (B-2), and the particulate component (C). When the blending ratio is less than 6% by mass, the fluidity of the coating liquid may increase and flow into pinholes, impairing the smoothness of the coating film surface. On the other hand, when an amount exceeding 54% by mass is blended, the fluidity may decrease, impairing the smoothness of the coating film surface, and the hue and smoothness of the topcoat paint may deteriorate.

[0046] Polyisocyanate (D) The photocurable resin composition of the present invention further contains a polyisocyanate (D). By blending the above polyisocyanate (D), when thermosetting the coating film formed thereon, a crosslinked structure is formed with the above hydroxyl group-containing acrylic resins (B-1) and (B-2), the coating film strength can be increased, and further coating defects can be suppressed. In addition, the adhesion to the coating film layer formed thereon can be increased, and the strength as a multilayer coating film can also be increased.

[0047] The blending ratio of the above polyisocyanate (D) is 10 to 100% by mass based on 100% by mass of the total amount of the photocuring component (A), the hydroxyl group-containing acrylic resins (B-1) and (B-2), the particle component (C), and the photopolymerization initiator (E). If the blending ratio is less than 10% by mass, the crosslinking density of the coating film becomes low, and the coating film may not be able to follow the expansion of the air contained in the pinholes, resulting in poor appearance of the topcoat paint. On the other hand, if the amount exceeds 100% by mass, the total amount of the hydroxyl group-containing acrylic resin (B-2) and the particle component (C) becomes low, so that the fluidity of the coating liquid becomes high, and it may flow into the pinholes and impair the smoothness of the coating film surface.

[0048] The above polyisocyanate (D) is not particularly limited as long as it is a compound having two or more isocyanate groups. For example, aromatic ones such as tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate, and metaxylylene diisocyanate; aliphatic ones such as hexamethylene diisocyanate; alicyclic ones such as isophorone diisocyanate; its monomers and multimers such as its burette type, nurate type, and adduct type can be mentioned.

[0049] Examples of commercially available products of the above polyisocyanate (D) include Duranate 24A-90PX (NCO: 23.6%, trade name, manufactured by Asahi Kasei Corporation), Sumidule N-3200-90M (trade name, manufactured by Sumitomo Bayer Urethane Co., Ltd.), Takenate D165N-90X (trade name, manufactured by Mitsui Chemicals, Inc.), Sumidule N-3300, Sumidule N-3500 (both trade names, manufactured by Sumitomo Bayer Urethane Co., Ltd.), Duranate THA-100 (trade name, manufactured by Asahi Kasei Corporation), and the like. Further, blocked isocyanates obtained by blocking these can also be used as necessary.

[0050] Photopolymerization initiator (E) The photocurable resin composition of the present invention further contains a photopolymerization initiator (E). The photopolymerization initiator (E) is a compound that initiates the polymerization of the acryloyl group of the acrylate compound of the photocuring component (A) by cleavage within the molecule by active energy rays such as light. Examples of the photopolymerization initiator (E) include carbonyl compounds such as benzoin, benzoin monomethyl ether, benzoin isopropyl ether, acetoin, benzophenone, p-methoxybenzophenone, diethoxyacetophenone, benzyldimethyl ketal, 2,2-diethoxyacetophenone, 1-hydroxycyclohexyl phenyl ketone, methyl phenyl glyoxylate, ethyl phenyl glyoxylate, 2-hydroxy-2-methyl-1-phenylpropan-1-one, etc.; acylphosphine oxide-based compounds such as 2,4,6-trimethylbenzoyl diphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, etc.; sulfur compounds such as tetramethylthiuram monosulfide, tetramethylthiuram disulfide, etc. These can be used alone or in combination of two or more.

[0051] Among the above, acylphosphine oxide-based compounds having a maximum absorption wavelength in the region of 360 nm or more and 410 nm or less are particularly preferred. The above-mentioned photoinitiator (E) is preferably 0.5 to 20% by mass, more preferably 5 to 15% by mass, in the solid content of the photocurable resin composition. By using it within this range, a cured coating film can be favorably formed.

[0052] The above-mentioned photocurable resin composition may further contain ordinary additives used in paints. Examples of the above-mentioned ordinary additives include known additives such as coloring pigments, moisture-resistant pigments, other resins, dispersants, anti-settling agents, organic solvents, defoaming agents, thickeners, rust preventives, ultraviolet absorbers, antioxidants, hindered amines, surface modifiers, and the like.

[0053] The photocurable resin composition of the present invention preferably has its viscosity adjusted to exhibit a high blocking effect, and the thixotropy value of the paint to be applied is preferably 3 or more and 9 or less. When the thixotropy value of the paint is less than 3, the fluidity of the paint is high and it may flow into pinholes, impairing the smoothness of the coating film surface. When the thixotropy value of the paint exceeds 9, the fluidity of the paint is low and the surface of the paint after application is not smoothed, thus impairing the smoothness, hue, and appearance of the topcoat paint. The thixotropy value in this specification is a value measured using a TVB-22L BL type viscometer manufactured by Toyo Seiki Co., Ltd. For the measurement method and the calculation method of the thixotropy value, the paint is adjusted to a liquid temperature of 20°C, a measuring rotor is attached to the BL type viscometer, and the viscosities at a rotor rotation speed of 60 revolutions per minute and 6 revolutions per minute are measured. The calculation method of thixotropy is obtained by the following formula. Thixotropy value = (viscosity value at 60 revolutions per minute) / (viscosity value at 6 revolutions per minute)

[0054] The photocurable resin composition of the present invention can be particularly suitably used as a putty for a material having irregularities on its surface. Hereinafter, the use as a putty will be described in detail. The material having irregularities on the surface is not particularly limited, and examples thereof include FRP materials in which fibers such as glass, carbon, Kevlar, polymer polyethylene, boron, and zylon are combined. Further, even in resins with high water absorption, defects due to evaporation of water during thermosetting can be prevented, so it can also be applied to materials such as nylon, ABS, ASA, PET, PBT-PET, PMMA, and polycarbonate. These materials are widely used for automotive reflectors such as headlamps, tail lamps, and side lamps, vehicle members such as spoilers, etc. Therefore, the photocurable resin composition of the present invention can be suitably used as a vehicle paint. Such a vehicle paint is also one of the present inventions.

[0055] The coating method of the photocurable resin composition of the present invention is not particularly limited. For example, after washing an FRP molded product with an aqueous cleaning agent, the above photocurable resin composition can be coated on the surface of the molded product, and then irradiated with ultraviolet rays to form a coating film. Further, after coating, in order to remove the solvent remaining in the paint, air drying or a desolventizing step may be added before UV irradiation for shortening the process.

[0056] The above coating is not particularly limited and can be performed by known methods such as air spray coating, electrostatic coating, and dip coating. In the above coating, it is preferably performed so that the dry film thickness becomes 10 to 70 μm, and before the above ultraviolet irradiation, it is preferably air dried or preheated at normal temperature to 100 ° C. for 5 to 25 minutes, preferably 5 to 20 minutes, to evaporate the solvent. When the temperature of the above preheating exceeds 100 ° C., there is no influence on the performance, but it is economically disadvantageous.

[0057] The above ultraviolet irradiation is preferably performed under conditions of about 500 to 5000 mJ / cm 2 The photocurable resin composition of the present invention can be cured by the above ultraviolet irradiation. In the above ultraviolet irradiation, active energy rays such as high-pressure mercury lamps, metal halide lamps, xenon lamps, UV-LED lamps, and electron beams usually used in the art can be used.

[0058] In particular, since the photocurable resin composition of the present invention contains a photoinitiator (E), photocuring can be suitably performed using a single-wavelength light source. For example, when an acylphosphine oxide compound having a maximum absorption wavelength in the region of 360 nm or more and 410 nm or less as described above is used as the photoinitiator (E), it is preferable to perform ultraviolet irradiation using a UV-LED lamp having a wavelength range of 350 to 450 nm. The above UV-LED lamp is easy to handle among the above ultraviolet irradiation devices, and can be easily installed in places where conventional installation was difficult, such as a handy type, a type that can be moved by a trolley, or a type arranged linearly, and has excellent workability. In addition, since it does not generate ozone, an exhaust duct is not required, and since it generates little heat, air conditioning equipment can be reduced. Therefore, it is a very preferable light source in terms of equipment. Furthermore, by using a UV-LED lamp, the radiation of heat rays emitted from the UV-LED to the material can be minimized, so that deformation due to heat of the material, which is usually a problem, can be prevented, and the occurrence of defective products can be prevented. At the same time, since the emission of heat rays from the UV-LED is extremely small, disasters such as physical damage and burns to workers due to heat rays can be avoided, and the safety of workers during construction can be improved at each stage. Of course, conventional conveyor-type or robot-type UV-LED lamps also have advantages in workability and safety.

[0059] The present invention also relates to a method for forming a coating film, which comprises a step (1) of applying the above photocurable resin composition onto an object to be coated and a step (2) of irradiating the coating film obtained in step (1) with a single wavelength. Furthermore, a coated article having a cured coating film obtained by curing the photocurable resin composition of the present invention is also one of the present inventions.

[0060] After the photocurable resin composition of the present invention is cured by energy rays, it is preferable to further apply a topcoat such as a base paint or a clear paint. In addition, primer coating may be performed as necessary before applying the above topcoat. The above primer coating is not particularly limited, and for example, a known primer for plastics may be applied.

[0061] It is preferable that after the photocurable resin composition of the present invention is irradiated with UV to cure the surface after coating, base coating, clear coating and, if necessary, a second putty coating are performed. Heat curing may be performed for each coating of the second putty paint, base paint, and clear paint, or may be performed after coating the second putty paint, base paint, and clear paint from the viewpoint of productivity. Further, in order to enhance the color development of the base paint, heat curing of the putty paint may be performed. By performing coating in such a manner, since a certain strength is imparted to the coating film of the photocurable resin composition, it is possible to significantly reduce appearance defects caused by the expansion of gas remaining in the unevenness during heating.

[0062] The above base coating and clear coating are not particularly limited, and for example, they can be performed by applying a clear coating to a known solvent-based base paint and an aqueous base paint and then heat curing.

[0063] The method for applying the above topcoat paint composition is not particularly limited, and for example, air spray coating, airless spray coating, bell coating, or the like can be employed.

[0064] The baking temperature of the above topcoat paint composition is preferably, for example, 70 to 130 °C in view of the balance between rapid curing and prevention of deformation of the FRP molded article. More preferably, it is 80 to 120 °C. The baking time is usually 10 to 60 minutes, preferably 15 to 50 minutes, and more preferably 20 to 40 minutes. If the baking time is less than 10 minutes, the curing of the coating film is insufficient, and the performance such as water resistance and solvent resistance of the cured coating film deteriorates. On the other hand, if the baking time exceeds 60 minutes, overcuring occurs, resulting in a decrease in adhesion in recoating, etc., the total time of the painting process becomes long, and the energy cost increases. Note that this baking time means the time during which the surface of the substrate actually continues to maintain the target baking temperature. More specifically, it does not consider the time until the target baking temperature is reached, but means the time when the target temperature is reached and the temperature is continuously maintained.

[0065] Examples of the heating device used for simultaneously baking the uncured film of the paint include drying ovens that utilize heating sources such as hot air, electricity, gas, and infrared rays. Using a drying oven that combines two or more of these heating sources is preferable because the drying time is shortened.

[0066] The photocurable resin composition of the present invention can be particularly preferably used as a vehicle paint. Specific examples of the vehicle include various automotive parts such as FRP automotive bodies and spoilers.

Examples

[0067] Hereinafter, the present invention will be described with reference to examples. In the examples, “%” and “parts” in the mixing ratio mean “mass %” and “parts by mass” unless otherwise specified. The present invention is not limited to the examples described below.

[0068] Production Example 1 Synthesis of Hydroxyl Group-Containing Acrylic Resin 1-(1) 100 parts of butyl acetate was charged into a four-necked flask equipped with a heating device, a stirring device, a thermometer, a reflux condenser, a nitrogen inlet tube, and a dropping device, and the temperature was raised to 120 °C while stirring and introducing nitrogen. Next, a mixed solution of 9.9 parts of styrene, 54.3 parts of 2-ethylhexyl methacrylate, 34.8 parts of 2-hydroxyethyl methacrylate, 1.0 part of methacrylic acid, and 10 parts of Kayester-O as a polymerization initiator was dropped from the dropping device over 3 hours. Next, stirring was continued for 120 minutes to complete the reaction, and the target hydroxyl group-containing acrylic resin 1-(1) was obtained (resin solid content 50%). The blending amounts and physical properties of the hydroxyl group-containing acrylic resin 1-(1) are shown in Table 1.

[0069] Production Examples 2 to 10 Production of Acrylic Resins 1-(2) to 1-(10) Using the same equipment as that used in the synthesis of the hydroxyl group-containing acrylic resin 1-(1), except that the solvent, monomer, initiator, and polymerization temperature were changed to the blending amounts described in Table 1, the same synthesis procedure and operations as those of the hydroxyl group-containing acrylic resin 1-(1) were carried out, and the hydroxyl group-containing acrylic resins 1-(2) to 1-(10) described in Table 1 were obtained. The physical properties are also shown in Table 1.

[0070] (Hydroxyl value (OHV)) The hydroxyl value was determined by a neutralization titration method using an aqueous potassium hydroxide solution described in JIS K 0070.

[0071] (Weight average molecular weight) The weight average molecular weight (Mw) is a value measured by GPC (gel permeation chromatography) and is the weight average molecular weight in terms of polystyrene.

[0072] (Solubility parameter (SP value)) The solubility parameter (SP value) was actually measured by the method described in this specification.

[0073] (Glass transition temperature (Tg)) The glass transition temperature (Tg) was measured using a DSC (Differential Scanning Calorimeter) manufactured by Seiko Instruments Inc.

[0074]

Table 1

[0075] Production Examples 11 to 20 Production of Acrylic Resins 1-(11) to 1-(20) Using the same equipment as that used in the synthesis of the acid group-containing acrylic resin 1-(1), except for changing the solvent, monomer, initiator, and polymerization temperature to the compounding amounts shown in Table 1, the same synthesis procedure and operations as those for the hydroxyl group-containing acrylic resin 1-(1) were carried out to obtain the hydroxyl group-containing acrylic resins 1-(11) to 1-(20) shown in Table 2. The physical properties are also shown in Table 2.

[0076]

Table 2

[0077] Production Examples 21 to 29 Production of Acrylic Resins 2-(1) to 2-(9) Using the same equipment as that used in the synthesis of the hydroxyl group-containing acrylic resin 1-(1), except for changing the solvent, monomer, initiator, and polymerization temperature to the compounding amounts shown in Table 3, the same synthesis procedure and operations as those for the synthesis of the hydroxyl group-containing acrylic resin 1-(1) were carried out to obtain the hydroxyl group-containing acrylic resins 2-(1) to 2-(9) shown in Table 3. The physical properties are also shown in Table 3.

[0078]

Table 3

[0079] Production Examples 30 - 40 Production of Acrylic Resins 2-(10) - 2-(18) Using the same equipment as that used in the synthesis of the hydroxyl - group - containing acrylic resin 1-(1), except for changing the solvent, monomer, initiator, and polymerization temperature to the compounding amounts shown in Table 1, the same synthetic procedure and operations as those for the hydroxyl - group - containing acrylic resin 1-(1) were carried out to obtain the hydroxyl - group - containing acrylic resins 2-(10) - 2-(18) shown in Table 4. The physical properties are also shown in Table 4.

[0080]

Table 4

[0081] Photocurable component (A) The photocurable component (A) used is as follows. Pentaerythritol tetraacrylate (manufactured by Sartomer Co., Ltd.: SR295) Ditrimethylolpropane tetraacrylate (manufactured by Sartomer Co., Ltd.: SR355) Dipentaerythritol hexaacrylate (manufactured by Sartomer Co., Ltd.: DPHA)

[0082] Particle component (C) As the particulate component (C), silica paste 1 was prepared and used as follows. (Manufacturing method of acrylic resin 3) Into a four-necked flask equipped with a heating device, a stirring device, a thermometer, a reflux condenser, a nitrogen inlet tube, and a dropping device, 22 parts of toluene and 44 parts of methyl isobutyl ketone were charged, and the temperature was raised to 120 °C while stirring and introducing nitrogen. Next, from the dropping device, a mixed solution of 7.6 parts of methyl methacrylate, 52.3 parts of butyl acrylate, 15.9 parts of butyl methacrylate, 23.2 parts of 2-hydroxyethyl methacrylate, 1.0 part of methacrylic acid, and 0.08 part of Kayacel - O as a polymerization initiator was added dropwise over 3 hours. Then, stirring was continued for 120 minutes to complete the reaction, and the target acrylic resin 3 was obtained (resin solid content 60%). The molecular weight (MW) of the obtained acrylic resin 3 was 49000, the SP was 10.6, and the Tg was -14. (Method for preparing silica paste 1) 54 parts of acrylic resin 3, 10 parts of toluene, 10 parts of methyl isobutyl ketone, and 10 parts of SIPERNAT 22LS (trade name, manufactured by Nippon Aerosil Co., Ltd.) were charged into a bead mill disperser and dispersed with 2 mm zirconium beads. To this dispersion solution, a mixed solution of 1.2 parts of Disparlon 6901 - 20X (trade name, manufactured by Kusumoto Chemicals, Ltd.), 3.8 parts of xylene, 0.7 part of ethanol, and 0.3 part of methanol was added. Then, 5 parts of toluene and 5 parts of methyl isobutyl ketone were added and diluted to obtain silica paste 1. The obtained silica paste 1 had a viscosity of 60 KU and a particle size of 10 μm or less. The other particulate components are as follows.

[0083]

Table 5

[0084] Polyisocyanate (D) The polyisocyanate (D) used is as follows. TPA - 100 (isocyanurate type): hexamethylene isocyanurate manufactured by Asahi Kasei Corporation 24A - 100 (biuret type): hexamethylene diisocyanate manufactured by Asahi Kasei Corporation P301-75E (adduct type): Hexamethylene isocyanurate manufactured by Asahi Kasei Corporation

[0085] Photopolymerization initiator (E) The photoinitiator (E) used is as follows. Benzophenone (trade name Benzophenone: manufactured by Degussa) Methyl phenylglyoxylate (trade name Omnirad MBF: manufactured by IGM RESINS)

[0086] Example 1 Into a container equipped with a stirrer, each component shown in Table 6 was put, and while stirring, MEK in an amount such that the final paint had an NV of 30% was added, and the mixture was stirred for 30 minutes to obtain a photocurable resin composition. The obtained photocurable resin composition was spray-coated so that the dry film thickness became 35 μm, and heated at 80 °C for 5 minutes in a hot air drying oven to remove the solvent. Next, using a UV-LED lamp (manufactured by Eye Graphics, UV-LED handy device (UV-LED365)), irradiation was performed at a height of 6 cm for 15 seconds to obtain a cured coating film. Here, the light amount in the ultraviolet irradiation was measured using an Eye ultraviolet integrated illuminance meter UV METER UVPF-A2 (light receiving part 365 nm) manufactured by Eye Graphics.

[0087] Examples 2 to 129, Comparative Examples 1 to 24 Except that the formulation was changed to that described in Tables 6 to 20, the coating films of Examples 2 to 129 and Comparative Examples 1 to 24 were formed in the same manner as in Example 1 to obtain final coated plates.

[0088] Example 130 Into a container equipped with a stirrer, each component shown in Table 19 was put, and while stirring, MEK in an amount such that the final paint had an NV of 30% was added, and the mixture was stirred for 30 minutes to obtain a photopolymerizable resin composition. The obtained photopolymerizable resin composition was spray-coated so that the dry film thickness was 35 μm, and heated at 80 °C for 5 minutes in a hot air drying furnace to remove the solvent. Next, using a UV-LED lamp (manufactured by Eye Graphics Co., Ltd., UV-LED handy device (UV-LED365)), irradiation was performed at a height of 6 cm for a specified time to obtain a cured coating film. Here, the light amount in the ultraviolet irradiation was measured using an Eye ultraviolet integrated illuminometer UV METER UVPF-A2 (light receiving part 365 nm) manufactured by Eye Graphics Co., Ltd.

[0089] Examples 131 to 165, Comparative Examples 25 to 33 Except for changing the formulation described in Tables 21 to 25 and the irradiation time of the UV-LED lamp, coating films of Examples 131 to 165 and Comparative Examples 25 to 33 were formed in the same manner as in Example 130 to obtain final coated plates.

[0090] Formation of laminate film 1 (without primer layer) After coating and curing the putty paints of the above Examples and Comparative Examples, a laminate film was formed by the following method. After coating and curing the putty paints of the above Examples and Comparative Examples, a solvent-based base paint composition (manufactured by Nippon Paint Automotive Coatings Co., Ltd.: R-160) was coated so that the dry film thickness was 15 μm, and subsequently, a clear paint composition (manufactured by Nippon Paint Automotive Coatings Co., Ltd.: R-2830) was coated so that the dry film thickness was 25 μm. After completion of the coating, the sample was allowed to stand for 10 minutes and then heat-cured at 80 °C for 30 minutes to obtain a test piece having a multilayer coating film.

[0091] Formation of laminate film 2 (with primer layer) After coating and curing the putty paints of the above Examples and Comparative Examples, a laminate film was formed by the following method. After applying and curing the patent paints of the above Examples and Comparative Examples, a solvent-based primer paint composition (manufactured by Nippon Paint Automotive Coatings Co., Ltd.: R-241) was further applied so that the dry film thickness became 20 μm. After completion of the application, the coating was allowed to stand for 10 minutes and then heat-cured at 80°C for 30 minutes. Thereafter, a solvent-based base paint composition (manufactured by Nippon Paint Automotive Coatings Co., Ltd.: R-160) was applied so that the dry film thickness became 15 μm, and subsequently, a clear paint composition (manufactured by Nippon Paint Automotive Coatings Co., Ltd.: R-2830) was applied so that the dry film thickness became 25 μm. After completion of the application, the coating was allowed to stand for 10 minutes and then heat-cured at 80°C for 30 minutes to obtain a test piece having a multilayer coating film.

[0092] [Effect of Sealing Function (Evaluation on Cured Film of Photo-Curable Resin Composition)] ·Sealing effect that suppresses and conceals the inflow of paint into the recesses and pinholes on the FRP material The photo-curable resin composition was applied to the FRP material and cured by UV. On the evaluation plate, when the recesses and pinholes of the FRP material were concealed on the coating film surface and no defects were visually observed, it was rated as ◎; when slight recesses or pinholes were recognized, it was rated as ○; when either the recess or the pinhole was not concealed, it was rated as △; when the recesses and pinholes were not concealed, it was rated as ×. ◎: When the recesses and pinholes of the FRP material are concealed and no defects are visually observed ○: When slight recesses or pinholes are recognized △: When either the recess or the pinhole is not concealed ×: When the recesses and pinholes are not concealed

[0093] [Effect of Sealing Function (Evaluation on Multilayer Film)] ·Sealing effect that suppresses the air expansion encapsulated in the FRP material On the evaluation board with the laminated film 1 or 2 formed on the FRP material, when there are no defects formed by the rupture of bubbles on the coating film surface, it is rated as ◎; when there is a slight swelling of the coating film but no defects due to rupture, it is rated as ○; when there are many swellings in the coating film but no defects due to rupture, it is rated as △; when there are many swellings in the coating film and many defects due to rupture, it is rated as ×. ◎: When there are no defects formed by the rupture of bubbles on the coating film surface ○: When there is a slight swelling of the coating film but no defects due to rupture △: When there are many swellings in the coating film but no defects due to rupture ×: When there are swellings in the coating film and many defects due to rupture

[0094] [Adhesion of laminated film] On the evaluation board with the laminated film 1 or 2 formed on the FRP material, 100 base meshes were made at 2 m intervals on the surface of the test piece with a single-edge razor, and then cellophane adhesive tape (JIS Z 1522) was sufficiently pressure-bonded thereon and quickly peeled off in the 90° direction. The peeling state of the coating film was evaluated by the number of base meshes of the remaining coating film. When 100 are left intact, it is rated as ○; when 60 - 99 remain, it is rated as △; when less than 60 remain, it is rated as ×. [Adhesion of coating film] ○: When 100 are left intact △: When 60 - 99 remain ×: When less than 60 remain

[0095] [Hot water resistance test] The test piece prepared in the same way as the above initial adhesion evaluation was immersed in warm water at 40 °C for 240 hours, pulled out from the water, dried at room temperature for 1 hour, and then the adhesion to the base material was examined in the same way as the initial adhesion evaluation. [Adhesion after hot water resistance test] ○: When 100 are left intact △: When 60 - 99 remain ×: When less than 60 remain

[0096]

Table 6

[0097]

Table 7

[0098]

Table 8

[0099]

Table 9

[0100]

Table 10

[0101]

Table 11

[0102]

Table 12

[0103]

Table 13

[0104]

Table 14

[0105]

Table 15

[0106]

Table 16

[0107]

Table 17

[0108]

Table 18

[0109]

Table 19

[0110]

Table 20

[0111]

Table 21

[0112]

Table 22

[0113]

Table 23

[0114]

Table 24

[0115]

Table 25

[0116] From the results of the above-described respective examples, it is clear that the photocurable resin composition of the present invention can achieve coatability and good coating film physical properties.

Industrial Applicability

[0117] The photocurable resin composition of the present invention can be suitably used as a resin composition to be directly applied onto a resin member having unevenness on its surface.

Claims

【Claim 1】 A method for manufacturing a laminated film having a cured coating film, a base coating film, and a clear coating film formed of a photocurable resin composition in this order, wherein the photocurable resin composition is a photocurable component (A) which is a polyfunctional acrylate having 4 or more (meth)acrylate groups, a hydroxyl group-containing acrylic resin (B-1) having a weight average molecular weight in the range of 3000 to 8000, a hydroxyl group-containing acrylic resin (B-2) having a weight average molecular weight in the range of 10000 to 30000, a particle component (C), a polyisocyanate (D), and a photopolymerization initiator (E), the blending ratio of the polyisocyanate (D) is 10 to 100% by mass with respect to 100% by mass of the total amount of the photocurable component (A), the acrylic resin (B-1), the acrylic resin (B-2), the particle component (C), and the photopolymerization initiator (E), a step (1) of applying the photocurable resin composition onto an object to be coated, and a step (2) of irradiating the coating film obtained in step (1) with a single-wavelength light source having a wavelength range of 350 to 450 nm, further comprising a step of performing base coating and clear coating and heat curing. A method for manufacturing a laminated film characterized by this.

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