Multi-layer coating

Abstract

Provided is a multilayer coating film having at least two layers, a coating film 2 and a polyurea coating film 1, which can avoid yellowing caused by migration of a free amine component contained in the coating film 2 to the polyurea coating film 1. [Solution] A coating composition containing at least three components: component (a) that contains an amino group and is reactive with an isocyanate group, polyisocyanate (b), and ultraviolet absorber (UVA) (d), wherein the mixing ratio of benzotriazole-based ultraviolet absorber (UVA) (d1) is 20 parts by weight or less per 100 parts by weight of the total amount of ultraviolet absorber (UVA) (d). The polyurea coating film 1 formed by the coating film 1 forms a multilayer coating film together with the coating film 2, and does not yellow even when heated and dried at a temperature of 40°C or higher.

Description

[Technical Field]

[0001] The present invention relates to a multi-layer coating film. [Background technology]

[0002] Polyurethane coatings obtained by reacting polyol compositions with polyisocyanate compositions have excellent adhesion to a variety of substrates. They also have excellent hardness, impact resistance, and abrasion resistance, while also possessing elasticity and flexibility, making them suitable for a wide range of applications, including civil engineering and construction, industrial applications, and automotive applications.

[0003] In recent years, the use of polyurea coatings, which are tougher and have higher chemical resistance, has been seen. These polyurea coatings are obtained by the reaction of a polyamine composition with a polyisocyanate composition. Their most notable feature is the high reactivity between the amino groups in the polyamine composition and the isocyanate groups in the polyisocyanate composition, allowing the curing reaction to proceed very quickly even at room temperature.

[0004] However, there are also drawbacks to its high reactivity. For example, due to its short pot life, a dedicated coating tool is required to apply the A-liquid containing the polyamine composition and the B-liquid containing the polyisocyanate composition by collision mixing with a spray gun. Also, the joints of the coatings may not be uniformly finished.

[0005] To address these issues, Patent Document 1 discloses a coating composition with a good pot life, which contains a base agent (I) having a polyamine compound (A) and a curing agent (II) having a polyisocyanate compound (B). At least one of the base agent (I) and the curing agent (II) contains a pigment (C), the polyamine compound (A) contains an aspartic acid ester amine (A1), and the polyisocyanate compound (B) contains an allophanate group-containing polyisocyanate compound (B1). The above-mentioned configuration indicates that application can be performed using ordinary application methods, not just with specialized application tools that apply by collision mixing. The following considerations are given in the specification as to why the pot life is good. The reaction between the polyamine compound (A) and the polyisocyanate compound (B) is thought to involve a nucleophilic reaction of the amino group with the carbon atom of the isocyanate group. Therefore, it is thought that suppressing this reaction can improve the pot life. In the aspartic acid ester amine (A1), the secondary amino group has a -CH(COOR) group. 2 )-CH2-COOR 2 are bonded (where R 2 are independent of each other, C 1-20 (represents a hydrocarbon group). Therefore, it is thought that the secondary amino group is affected by steric hindrance caused by such a group, and the nucleophilic reaction with the isocyanate group may be suppressed.

[0006] Patent Document 2 discloses a coating composition comprising (A) at least one polyaspartic acid ester, (B) at least one polyisocyanate crosslinking agent having a free isocyanate group, and (C) at least one compound having at least one epoxy group and at least one alkoxysilane group. In this disclosure, the coating compositions are indicated to be particularly for use in vehicle refinish paints as primer layers, primer surfacer layers, pigmented topcoat layers or clear coat layers.

[0007] On the other hand, one drawback of using polyurea coatings is that components containing aspartic acid esters tend to yellow during storage. Patent Document 3 discloses that adding a specific antioxidant to the component containing polyaspartic acid ester in a two-component clear coating can suppress yellowing during storage at room temperature or at high temperatures (e.g., 50°C).

[0008] Furthermore, Patent Document 4 points out three methods for suppressing yellowing. First, as is commonly done in two-component coatings, the isocyanate-reactive component (A) containing the polyaspartic acid ester and the polyisocyanate (B) are separated into two separate containers C1 and C2, with the container C1 containing the isocyanate-reactive component (A) containing the polyaspartic acid ester and the container C2 containing the polyisocyanate (B). Second, a container C3 is provided separate from the containers C1 and C2 to prevent contact with the specific solvent during storage. As a specific preferred embodiment, the container C3 is shown to be separated so as to contain a specific solvent (S1) and, optionally, a specific solvent (S2). Third, there is a method for avoiding a combination of a specific ultraviolet absorber (UVA) and / or hindered amine light stabilizer (HALS). A specific preferred embodiment is shown in which the UVA and / or HALS are contained in the container C3. Furthermore, a particularly preferred embodiment is shown in which 2-(2-hydroxyphenyl)-benzotriazole is used as the UVA and a mixture of bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate and methyl 1,2,2,6,6-pentamethyl-4-piperidylsebacate is used as the HALS.

[0009] Patent Document 5 discloses a polyurea coating composition containing the reaction product of an isocyanate-functional component (A) and an isocyanate-reactive component (B) containing a polyaspartic acid ester. While the specification mentions that the composition may contain UV absorbers and light stabilizers, it does not specify the types of these additives. In the examples, Tinuvin® 1130, a benzotriazole-based UV absorber, is used. Furthermore, the coating composition is sprayed directly onto various metal steel plates, and the coating composition is used to evaluate its physical properties. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Patent No. 7281591 [Patent Document 2] WO2014 / 138052A1 Brochure [Patent Document 3] Publication EP2829562A1 [Patent Document 4] Special Publication No. 2023-516416 [Patent Document 5] Special Publication No. 2013-523972

[0011] However, the present inventors conducted further studies based on the contents of the above prior art documents and found that in a multi-layer coating film having at least two layers, coating film 2 and polyurea coating film 1, yellowing may occur in the polyurea coating film 1 under specific conditions. Although the above prior art documents describe yellowing of paints during storage, they do not disclose yellowing in multi-layer coating films having a specific coating film configuration. Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention has been made in view of the above background, and aims to provide a multilayer coating film having at least two layers, a coating film 2 and a polyurea coating film 1. Specifically, the present invention aims to provide a multilayer coating film that can avoid yellowing caused by migration of free amine components contained in the coating film 2 to the polyurea coating film 1. Here, "free" refers to a state in which the amine component is not bound to the components constituting the coating film via a covalent bond. The free amine component contained in the coating film 2 can move within the coating film during the drying process. In addition, in the case of a multi-layer coating film, the free amine component may migrate between different coating films. Although the mechanism of yellowing is not clear, it is thought that under certain conditions, the free amine component reaches the polyurea coating film 1, interacts with the components contained in the polyurea coating film 1, and causes yellowing. One embodiment of such a multilayer coating film is a multilayer coating film for vehicles, in which, for example, the coating film 2 is an aqueous colored base coating film to which an amine component is added as a pH adjuster, and the polyurea coating film 1 is a clear coating film formed as the outermost layer. [Means for solving the problem]

[0013] As a result of intensive research to solve the above-mentioned problems, the present inventors have found that in a multilayer coating film having at least two layers, coating film 2 and polyurea coating film 1, yellowing occurs in said polyurea coating film 1 when at least the following four conditions are all satisfied: Here, said polyurea coating film 1 is a coating film formed by applying paint 1, and said paint 1 is a coating composition containing at least three components: component (a) containing an amino group and reactive with an isocyanate group, polyisocyanate (b), and ultraviolet absorber (hereinafter sometimes abbreviated as UVA) (d). Below, the above-exemplified embodiment will be explained.

[0014] <Conditions for yellowing of polyurea coating 1> [First condition] The polyurea coating film 1 contains a constituent derived from a polyaspartic acid ester (a1) as the component (a) that contains an amino group and is reactive with an isocyanate group. [Second condition] The UVA (d) in the polyurea coating film 1 contains a benzotriazole-based UVA (d1) as a main component. In this invention, "as a main component" means that it is included as an essential component. However, even if a benzotriazole-based UVA (d1) is added as an auxiliary component, this does not fall under the second condition. Specifically, the addition of 20% by weight or less of the total amount of UVA (d) does not fall under the category of "addition as a main component." [Third condition] The coating film 2 contains a free amine component (x). [Fourth condition] After a multilayer coating film having at least two layers, the coating film 2 and the polyurea coating film 1, is formed, the multilayer coating film is dried by heating at a temperature of 40°C or higher in the state in which the free amine component (x) is present in the multilayer coating film.

[0015] The present invention has been accomplished by avoiding at least one of these conditions. However, the polyaspartic acid ester (a1) is an essential component for forming urea bonds while ensuring the pot life of the coating material 1. Note that, under specific limited conditions, such as using a dedicated coating tool, it is possible to avoid the first condition, but this would result in problems such as limited applications and high costs for installing the equipment.

[0016] Furthermore, while recent environmental concerns have led to the shift to water-based paints, in order to shorten the painting process, rather than thoroughly drying or curing each coating film and proceeding with each coating step, it is preferable to proceed to the next coating step in a dry or semi-cured state to the extent that fluidity does not occur, and then heat-dry the entire coating together to finish. Given this background, although the curing reaction of the polyurea coating film 1 itself proceeds even at room temperature, there is a possibility that it will be heat-dried as a multi-layer coating. While a multi-layer coating can be finished by drying at room temperature, a long drying time is required, which creates the problem of securing a drying space. On the other hand, even if a finished product is dried at room temperature, placing a coated article with a multi-layer coating formed on it outdoors can easily reach temperatures of around 40 to 60°C due to the influence of sunlight. Therefore, in reality, it is difficult to avoid the fourth condition.

[0017] Furthermore, for example, in the aqueous coating film formed by applying an aqueous paint to which an amine component has been added as a pH adjuster, free amine component (x) may be present. If the coating film 2 is formed using, for example, a solvent-based acrylic urethane paint that does not contain such a pH adjuster, it is possible to avoid the third condition, but this would go against the trend toward environmental friendliness. In view of the above, it is preferable to avoid at least one condition selected from the second condition, the third condition, and the fourth condition, and among these, it is particularly preferable to avoid the second condition. [Effects of the Invention]

[0018] According to one embodiment of the multilayer coating film for vehicles of the present invention, yellowing of the polyurea coating film 1 used as the clear coating film can be suppressed by avoiding certain conditions. In the previous problem, one embodiment of the conditions under which yellowing occurs was explained as an example, but the present invention is not limited to the above example, and yellowing of the polyurea coating film 1 can be suppressed by a similar mechanism. DETAILED DESCRIPTION OF THE INVENTION

[0019] Each component used in the present invention will be described in detail below. Note that the raw materials exemplified in the following description do not limit the constitution of the present invention, and may be changed within the scope of the present invention.

[0020] <Polyurea coating film 1> The polyurea coating film 1 in the present invention is formed by applying a coating material 1. Here, the coating material 1 is a coating composition containing three components: a component (a) that contains at least an amino group and is reactive with an isocyanate group, a polyisocyanate (b), and a UVA (d). Since the reaction between amino groups and isocyanate groups proceeds very rapidly, it is preferable to prepare the coating material 1 by mixing liquid A containing at least the component (a) that contains the amino group and is reactive with the isocyanate group and liquid B containing at least the polyisocyanate (b) immediately before application. In carrying out the present invention, either the liquid A or the liquid B may be the main agent or the curing agent, and a third liquid may be added.

[0021] <Component (a) that contains an amino group and is reactive with an isocyanate group> The component (a) in the present invention that contains an amino group and is reactive with an isocyanate group has at least one amino group in the molecule and is reactive with the isocyanate group contained in the polyisocyanate (b) described below. To ensure the pot life of the coating material 1, it is preferable to contain a polyaspartic acid ester (a1). It may also contain a polyamine (a2) that is different from the polyaspartic acid ester (a1) and has two or more primary or secondary amino groups in the molecule. Furthermore, it may contain an amine compound (a3) ​​that has only one amino group in the molecule, provided that this does not deviate from the spirit of the present invention.

[0022] <Polyaspartic acid ester (a1)> The chemical structure of the polyaspartic acid ester (a1) is shown in Chemical Formula 1 below. The polyaspartic acid ester (a1) can be synthesized according to a previously reported method, but a commercially available product may also be used. For example, it is available as the Desmophen (registered trademark) NH series from Sumika Covestro Urethane Co., Ltd.

[0023] [ka] (Here, X is an n-valent organic group which is inert to isocyanate groups and is obtained by removing n primary amino groups from a polyamine containing the primary amino groups. Preferably, X is any one of an aliphatic hydrocarbon, an alicyclic hydrocarbon, and an aromatic hydrocarbon, and may be linear or branched. R1 and R2 are the same or different organic groups which are inert to isocyanate groups. n is an integer of 2 or greater.)

[0024] The reason why the polyurea coating using the polyaspartic acid ester (a1) can ensure a sufficient pot life has been previously reported. To adjust the pot life, the polyaspartic acid ester (a1) may be used singly or in combination of two or more. From the viewpoint of suppressing yellowing of the polyurea coating film, the organic group X in the "Chemical Formula 1" is preferably an aliphatic hydrocarbon or an alicyclic hydrocarbon. However, this does not exclude the use of an aromatic hydrocarbon as the organic group X, as long as yellowing can be suppressed to the extent required for the intended use of the target product.

[0025] In the present invention, the polyaspartic acid ester (a1) can have an amine equivalent of 200 or more and 500 or less. A more preferred amine equivalent is 200 or more and 300 or less. By using an amine equivalent in this range, the reaction rate with the polyisocyanate (b) can be adjusted to ensure an appropriate pot life. Furthermore, the water resistance and hardness of the resulting polyurea coating film 1 can be improved.

[0026] The amount of the polyaspartic acid ester (a1) can be 80% by weight or more and 100% by weight or less of the total amount of the component (a) that contains an amino group and is reactive with an isocyanate group, taking into consideration the pot life of the coating material 1 and the physical properties of the polyurea coating film 1. It can be more preferably 90% by weight or more and 100% by weight or less.

[0027] <Polyamine (a2)> The polyamine (a2) in the present invention is different from the polyaspartic acid ester (a1) and has two or more primary or secondary amino groups in the molecule. That is, it is either a polyamine having only two or more primary amino groups in the molecule, a polyamine having only two or more secondary amino groups, or a polyamine having one or more primary amino groups and one or more secondary amino groups. If it has such a configuration, it may further have a tertiary amino group. The polyamine (a2) contains at least one selected from aliphatic polyamines and alicyclic polyamines. Aromatic polyamines are preferably not used because they may cause yellowing of the coating film. However, this does not exclude the use of aromatic polyamines to the extent that yellowing can be suppressed.

[0028] Examples of the aliphatic polyamines include primary polyamines having an alkylene skeleton, such as ethylenediamine, 1,3-propanediamine, 1,4-butanediamine, 1,5-pentanediamine, 1,6-hexanediamine, and 1,8-octanediamine; secondary polyamines having an alkylene skeleton, such as N,N'-dimethylethylenediamine, N,N'-dimethyl-1,3-diaminopropane, N,N'-dimethyl-1,2-diaminobutane, N,N'-dimethyl-1,4-diaminobutane, N,N'-dimethyl-1,5-diaminopentane, and N,N'-dimethyl-1,6-diaminohexane; mixed primary and secondary polyamines having an alkylene skeleton, such as diethylenetriamine and triethylenetetramine; and structural isomers thereof. Also included are amine-terminated polyethers such as bis(3-aminopropyl) ether, 1,2-bis(3-aminopropoxy)ethane, 1,3-bis(3-aminopropoxy)-2,2'-dimethylpropane, and bis(2-aminopropyl)polypropylene glycol.

[0029] Examples of the alicyclic polyamines include 1,3-bisaminocyclohexane, 1,3-bisaminomethylcyclohexane, 1,3-bisaminoethylcyclohexane, hydrogenated 4,4'-diaminodiphenylmethane, isophoronediamine, piperazine, and the like; and structural isomers thereof.

[0030] Examples of the aromatic polyamines include p-phenylenediamine, 2,4-tolylenediamine, m-aminobenzylamine, m-xylylenediamine, p-xylylenediamine, 1,5-naphthalenediamine, 4,4'-diaminodiphenylmethane, and the like; and structural isomers thereof.

[0031] <Amine compound (a3)> The amine compound (a3) ​​in the present invention has only one amino group in the molecule, and examples thereof include di-n-butylamine, diisobutylamine, di-n-octylamine, and di(2-ethylhexyl)amine.

[0032] <Polyisocyanate (b)> The polyisocyanate (b) in the present invention is at least one selected from the group consisting of aliphatic isocyanates, alicyclic isocyanates, and aromatic isocyanates, and may be used alone or in combination of two or more thereof.

[0033] Examples of the aliphatic isocyanate include tetramethylene diisocyanate, pentamethylene diisocyanate, and hexamethylene diisocyanate (HDI). Examples of the alicyclic isocyanate include 1,3-cyclopentane diisocyanate, 1,2-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, isophorone diisocyanate (IPDI), and norbornane diisocyanate. Examples of the aromatic isocyanate include 2,4- or 2,6-tolylene diisocyanate (TDI), xylylene diisocyanate (XDI), and 4,4'-diphenylmethane diisocyanate (MDI). Furthermore, polymers such as biuret, allophanate, isocyanurate, uretdione and adduct thereof can also be used. Furthermore, modified products can also be used within the scope of the present invention.

[0034] In the present invention, it is preferable to use at least one polyisocyanate compound (b) selected from aliphatic isocyanates and alicyclic isocyanates. In addition, in consideration of the pot life of the coating material and the physical properties of the resulting coating film, it is preferable to use an isocyanurate of hexamethylene diisocyanate (hereinafter sometimes abbreviated as HDI) and / or an isocyanurate of isophorone diisocyanate (hereinafter sometimes abbreviated as IPDI). In general, aromatic isocyanates have higher reactivity than aliphatic isocyanates because the electrophilicity of the isocyanate carbon is increased by the resonance structure. Therefore, the reaction rate for forming urea bonds can be adjusted by appropriately selecting the polyisocyanate compound (b) as described above. However, aromatic isocyanates are preferably not used because they may cause yellowing of the coating film. However, this does not exclude the use of aromatic polyamines as long as they can suppress yellowing to the extent required by the intended use of the target product.

[0035] <Hydroxyl group-containing component (c)> A hydroxyl group-containing component (c) may be included as another resin component within the scope of the present invention. The inclusion of the hydroxyl group-containing component (c) can improve the weather resistance and water resistance of the polyurea coating film 1. In addition, viscosity adjustment during application becomes easier, allowing adjustment of the coating film appearance.

[0036] Examples of the hydroxyl group-containing component (c) include glycerin, polyethylene glycol, polypropylene glycol, polycaprolactone triol, epoxy polyol, acrylic polyol, polyurethane polyol, polyester polyol, polycarbonate polyol, polyether polyol, etc. These can be used alone or in combination of two or more.

[0037] In consideration of the storage stability of the paint, the hydroxyl group-containing component (c) can be mixed with the liquid A, avoiding mixing with the liquid B. In addition to the liquids A and B, a third liquid can be added to form a multi-liquid paint.

[0038] The amino group (NH) contained in the component (a) containing an amino group and reactive with an isocyanate group, the isocyanate group (NCO) contained in the polyisocyanate (b), and the hydroxyl group (OH) contained in the hydroxyl group-containing component (c) are preferably mixed in an equivalent ratio (NH + OH) / NCO of 0.65 to 1.20, more preferably 0.75 to 1.20, and even more preferably 0.80 to 1.10. If the equivalent ratio (NH+OH) / NCO is less than 0.65, the water resistance of the resulting polyurea coating film 1 may be reduced. If the equivalent ratio (NH+OH) / NCO is greater than 1.20, the resulting polyurea coating film 1 may be yellowed. Furthermore, insufficient curing may result in insufficient coating film hardness, or tackiness may remain.

[0039] The indentation hardness of the polyurea coating film 1 can be set depending on the application. The indentation hardness can be measured, for example, using a microindentation hardness tester ENT-NEXUS (manufactured by Elionix Co., Ltd.) under the following conditions (the test method complies with ISO 14577-1 / JIS Z 2255). <Test conditions> - A single film of polyurea coating 1 with a dry thickness of 60 μm was produced on a tin plate. Start load: 0mN, End load: 30mN -Start load when unloading: 30mN, end load: 0mN Indentation depth: 1,000 nm

[0040] In one embodiment, when toughness of the polyurea coating film 1 is required, the indentation hardness is set to 180 N / mm 2 More than 260N / mm 2 It is preferable to set it below 200N / mm 2 More than 240N / mm 2 It is more preferable to set the indentation hardness to 260 N / mm 2 If it is larger than this, there is a risk that the polyurethane coating film 1 may suffer from poor appearance such as cracks. In another embodiment, when flexibility or conformability of the polyurea coating film 1 is required, the indentation hardness is set to 100 N / mm 2 More than 180N / mm 2 It is preferable to set it to less than 120N / mm 2 More than 160N / mm 2 It is more preferable to set the indentation hardness to 100 N / mm or less. 2 If it is smaller, the blocking resistance of the polyurea coating film 1 may deteriorate. Although specific embodiments have been illustrated and described above, the present invention is not limited to these embodiments.

[0041] When two polyurea coating films 1 with different indentation hardnesses were prepared and compared, the smaller the indentation hardness value, the less likely yellowing occurred. The smaller the indentation hardness value, the lower the crosslink density of the coating film tends to be, and the more likely the free amine component (x) that has migrated to the polyurea coating film 1 is to be released outside the coating film. This is thought to be because the free amine component (x) is less likely to interact with the components contained in the polyurea coating film 1. However, a more detailed discussion will require consideration of the reaction kinetics of the crosslinking reaction of the polyurea coating film 1.

[0042] <Ultraviolet absorber (UVA) (d)> The UVA (d) in the present invention includes at least a benzotriazole-based UVA (d1) and / or a hydroxyphenyltriazine-based UVA (d2). However, when the benzotriazole-based UVA (d1) is contained in the polyurea coating film 1, yellowing of the polyurea coating film 1 may occur when the polyurea coating film 1 is combined with the coating film 2. The mechanism of yellowing is unclear, but it is thought that the yellowing may be caused by the free amine component (x) contained in the coating film 2 migrating to the polyurea coating film 1 during the coating film drying process under certain conditions. Therefore, in the present invention, it is preferable not to use benzotriazole-based UVA (d1) as an essential component. However, this does not exclude the use of benzotriazole-based UVA (d1) to the extent that yellowing can be suppressed, and the amount added can be adjusted taking into account the physical properties of the coating film, such as weather resistance. Specifically, benzotriazole-based UVA (d1) can be added as an auxiliary component, more specifically, it can be added in an amount of 20 wt% or less based on the total amount of UVA (d). UVA (d3) other than the benzotriazole-based UVA (d1) and the hydroxyphenyltriazine-based UVA (d2) can also be used in combination. If the benzotriazole-based UVA (d1) is 20% by weight or less of the total amount of UVA (d), the contribution of the hydroxyphenyltriazine-based UVA (d2) and other UVA (d3) is large, and the product can be used at an acceptable level of yellowing. On the other hand, if the benzotriazole-based UVA (d1) exceeds 20% by weight of the total amount of UVA (d), the contribution of the benzotriazole-based UVA (d1) increases dramatically. Yellowing becomes particularly noticeable after weather resistance testing.

[0043] <Other ingredients (e)> In the present invention, other components (e) may further be contained as required. For example, the composition may contain additives commonly used in paints, such as dispersants, viscosity modifiers, surface modifiers, antifoaming agents, light stabilizers (hereinafter sometimes abbreviated as HALS), catalysts, silane coupling agents, reaction accelerators, and reaction retarders. It may also contain pigments, colorants, and matting agents. It may also contain antioxidants to enhance storage stability. If necessary, it may be diluted with an organic solvent.

[0044] As the pigment, any conventionally known color pigment, extender pigment, or anti-rust pigment can be used without any particular limitation. These pigments can be used alone or in combination of two or more types depending on the desired color and coating film performance. Examples of color pigments include organic pigments such as anthraquinones, diketopyrrolopyrroles, quinacridones, perylenes, dioxazines, benzimidazolones, isoindolinones, isoindolines, phthalocyanines, and threnes, and inorganic pigments such as yellow iron oxide, red iron oxide, azomethine copper complexes, bismuth vanadate, titanium oxide, silicon oxide, zinc oxide, and carbon black. Luster pigments such as aluminum (including vapor-deposited aluminum), zinc, nickel, copper, silver, and alloys thereof; aluminum oxide, mica, and mica surface-coated with a metal oxide can also be used. Examples of extender pigments include inorganic pigments such as barium sulfate, calcium carbonate, barium carbonate, calcium carbonate, magnesium oxide, magnesium carbonate, magnesium hydroxide, barium titanate, calcium hydroxide, calcium sulfite, calcium sulfate, calcium oxide, calcium silicate, silica, zeolite, talc, kaolin, and clay. Examples of anti-rust pigments include phosphate-based pigments such as zinc phosphate, calcium phosphate, and aluminum tripolyphosphate; phosphites such as zinc phosphite, calcium phosphite, and aluminum phosphite; molybdate-based pigments such as zinc molybdate and calcium molybdate; metaborate-based pigments such as zinc metaborate, calcium metaborate, and barium metaborate; ion-exchanged silica in which cations such as calcium ions are bonded by ion exchange; calcium silicate; micaceous iron oxide (MIO); and zinc powder.

[0045] As the antioxidant, a hindered phenol-based compound or a phosphite-based compound can be used. Examples of hindered phenol antioxidants include 2,4-dimethyl-6-tert-butylphenol, 4,4'-methylenebis(2,6-di-tert-butylphenol), 3,5-di-tert-butyl-4-hydroxytoluene, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and ethylenebis(oxyethylene)bis[3-(5-tert-butyl-4-hydroxy-m-toluyl)propionate]. Examples of the phosphite-based antioxidants include tributyl phosphite, tris(2-ethylhexyl) phosphite, tridecyl phosphite, triphenyl phosphite, and tris(2,4-di-tert-butylphenyl) phosphite. Among these, it is preferable to use a phosphite-based antioxidant from the viewpoint of preventing yellowing during storage of the paint.

[0046] The other component (e) can be added to the solution A and / or the solution B within the scope of the present invention.

[0047] In one embodiment, the liquid A contains a surface conditioner, HALS, an antioxidant, and an organic solvent, while the liquid B contains a silane coupling agent and an organic solvent.

[0048] In another embodiment, the liquid A contains a dispersant, a surface conditioner, a HALS, an antioxidant, a pigment, and an organic solvent, and the liquid B contains an organic solvent.

[0049] In another embodiment, the liquid A contains HALS, an antioxidant, a silane coupling agent, and an organic solvent, and the liquid B contains an organic solvent.

[0050] Although specific embodiments have been illustrated and described above, the present invention is not limited to these embodiments.

[0051] <Coating film 2> The coating film 2 in the present invention is a coating film containing at least a free amine component (x). Here, the amine component (x) is a component different from the polyaspartic acid ester (a1). The term "free" refers to a state in which the amine component (x) is not bonded to any of the components constituting the coating film via a covalent bond. The presence of the free amine component (x) allows it to migrate within the coating film during the drying process. Furthermore, in the case of a multi-layer coating film, it may migrate between coating films. The free amine component (x) may be present in the coating film 2, for example, when it is used as a pH adjuster for a water-based coating film, or when an excess of amine curing agent is present in an epoxy / amine curing system.

[0052] In the present invention, the amine component (x) is characterized in that it has an amine equivalent of less than 200, from the viewpoint of allowing the amine component (x) to move in the coating film. Examples of such amine components (x) include ammonia; alkyleneamines such as ethylenediamine, diethylenetriamine, and triethylenetetramine; and aminoalcohols such as N-(2-aminoethyl)ethanolamine, N-methylethanolamine, N,N-dimethylethanolamine, and N-methyldiethanolamine.

[0053] <Other coatings> In the present invention, in addition to the polyurea coating film 1 and the coating film 2, other coating films may be included. Examples of other coating films include a primer coating film, a surfacer coating film, a base coating film, and a clear coating film. A putty layer may be provided for coating film repair. In addition, a printed layer or a decorative layer such as vapor deposition or plating may be provided. Specific embodiments will be exemplified and explained below, but the present invention is not limited to these embodiments.

[0054] One embodiment of the present invention is a multi-layer coating film formed on an aluminum substrate, with a primer coating film as coating film 2 and a clear coating film formed thereon as polyurethane coating film 1. In this way, no other coating film may be provided.

[0055] In another embodiment, a multi-layer coating film is formed on a polypropylene bumper, with a primer coating film and a surfacer coating film as other coating films, and on top of that, a colored base coating film as coating film 2 and a clear coating film as polyurethane coating film 1 as the outermost layer.

[0056] In yet another embodiment, a multilayer coating film is formed on a fiber-reinforced plastic substrate, with a primer coating film as coating film 2, a surfacer coating film as another coating film on top of that, and a colored base coating film as polyurethane coating film 1 as the outermost layer.

[0057] <Method of manufacturing the coating composition> In consideration of storage stability and pot life, the coating composition of the present invention is preferably prepared by mixing a liquid A containing at least the component (a) that contains an amino group and is reactive with an isocyanate group with a liquid B containing at least the polyisocyanate (b). The liquids A and B can be obtained by mixing them using known methods. Furthermore, a third liquid may be added in addition to the liquid A and the liquid B to form a multi-liquid coating composition.

[0058] <Painting method> The liquids A and B can be mixed before use and applied by a common coating method, such as brush, roller, air spray, airless spray, curtain flow coater, roll coater, or die coater. Alternatively, the object to be coated can be immersed in the paint to finish the coating.

[0059] There are no particular limitations on the substrate used as the object to be coated, and examples thereof include metals and plastics. Also, composite materials of these materials can be used. Wood, wood-based materials, paper, glass, textile products, concrete, ceramic materials, and the like can also be used. Examples of metal substrates that can be used include iron, copper, and aluminum. Also, alloys containing these metals can be used. Furthermore, plated or surface-treated substrates can also be used. Examples of plastic substrates include polypropylene resin, polycarbonate resin, fiber-reinforced resin, ABS resin, vinyl chloride resin, urethane resin, polyester resin, polystyrene resin, polyamide resin, etc. Furthermore, these plastic substrates coated with a primer can also be used.

[0060] <Painting process> As an embodiment of the present invention, a method for forming a multi-layer coating film for a vehicle will be described as an example, but modifications may be made as appropriate depending on the embodiment. A multi-layer coating film can be formed by the following series of steps. [Step 1]: Preparing the base material [Step 2]: A step of forming a water-based colored base coating film as coating film 2 [Step 3]: Step of forming a clear coating film as the polyurea coating film 1 [Step 4]: The multi-layer coating is dried together to finish the finish.

[0061] [Step 1]: Preparing the base material First, a substrate to be used as a coating object is prepared. The substrate can be used as is, but it is preferable to clean the surface by degreasing with a solvent or washing. A primer layer or a primer surfacer layer may also be formed on the substrate.

[0062] [Step 2]: A step of forming a water-based colored base coating film as coating film 2 Next, an aqueous colored base coating film is applied as coating film 2 to at least a portion of the substrate prepared in step 1 using an air spray gun so that the dry film thickness is 10 to 100 μm, preferably 10 to 50 μm. The aqueous colored base coating film can be completely freed of volatile components or completely cured, but flash-off is preferred from the viewpoint of reducing the energy consumption required for drying. Here, flash-off refers to a process of volatilizing most of the volatile components contained in the aqueous colored base coating film applied to the substrate surface before proceeding to the next coating step. Flash-off is typically carried out for 30 seconds to 30 minutes at a temperature ranging from 5 to 120°C, preferably from 5 to 45°C, and a relative humidity of 10 to 100%, preferably from 40 to 70%. The coating is fluid immediately after application, but flash-off eliminates the fluidity, resulting in a uniform coating that can be moved on to the next coating step. Furthermore, the drying step described below allows the multi-layer coating to be finished all at once.

[0063] [Step 3]: Step of forming a clear coating film as the polyurea coating film 1 Next, a clear coating film is applied as a polyurethane coating film 1 using an air spray gun so that the dry film thickness is 30 to 100 μm, preferably 50 to 70 μm. It should be noted that another coating film may be provided between the coating film 2 and the polyurethane coating film 1.

[0064] [Step 4]: The multi-layer coating is dried together to finish the finish. The multilayer coating films obtained in steps 1 to 3 can be dried together to finish the coating, for example, at a temperature of 5 to 120°C, preferably 5 to 45°C, and a relative humidity of 10 to 100%, preferably 40 to 70%, for 30 to 90 minutes, preferably 30 to 60 minutes.

[0065] <Causes of yellowing and how to avoid them> The present inventors have found that yellowing of the polyurea coating film 1 occurs when at least the following four conditions are all satisfied in the configuration of the multilayer coating film. [First condition] The polyurea coating film 1 contains a constituent derived from a polyaspartic acid ester (a1) as the component (a) that contains an amino group and is reactive with an isocyanate group. [Second condition] The UVA (d) in the polyurea coating film 1 contains a benzotriazole-based UVA (d1) as a main component. In this invention, "as a main component" means that it is included as an essential component. Addition as an auxiliary component is not considered to be included. Specifically, addition of 20% by weight or less of the total amount of UVA(d) is not considered to be added "as a main component." [Third condition] The coating film 2 contains a free amine component (x). [Fourth condition] After a multilayer coating film having at least two layers, the coating film 2 and the polyurea coating film 1, is formed, the multilayer coating film is dried by heating at a temperature of 40°C or higher in the state in which the free amine component (x) is present in the multilayer coating film.

[0066] The mechanism of yellowing is unclear, but to explain it using an example of a coating process, it is thought that the free amine component (x) contained in the aqueous colored base coating film (coating film 2) migrates to the polyurea coating film 1 during the drying stage in step 4. It is also thought that this migration is accelerated by heat drying. It is thought that the yellowing of the polyurea coating film 1 occurs as a result of interaction with the components contained in the polyurea coating film 1.

[0067] For example, Japanese Patent No. 5019325 discloses that an ultraviolet absorber having a phenolic hydroxyl group is colored by alkali or metal ions. Specifically, the following is described: The phenolic hydroxyl group of UV absorbers undergoes a deprotonation reaction in the presence of alkali to form a phenolate anion. This deprotonation shifts the absorption wavelength to longer wavelengths, and the absorbance also increases in the visible light region. This results in a coloration known as yellowing.

[0068] In the present application, too, the mechanism described in the above-mentioned Japanese Patent No. 5019325 is believed to contribute to yellowing, but there are some points that cannot be fully explained, and in reality, various factors are thought to be influential. Strictly speaking, for example, the structure and film thickness of the multilayer coating film, drying conditions, etc. are included. In addition, the crosslinking density of the polyurea coating film 1 and the speed of the crosslinking reaction are also thought to have an influence, and more strictly, a detailed discussion is needed taking into account reaction kinetics. Considering the mechanism described in Japanese Patent Publication No. 5019325, the chemical structure of UVA (d) is also thought to be a factor contributing to the yellowing of the polyurea coating film 1. Even if a phenolic hydroxyl group is present, the degree of deprotonation of the phenolic hydroxyl group is affected by changes in electron density due to the influence of other substituents attached to the aromatic ring. The degree of deprotonation of the phenolic hydroxyl group is also affected by steric hindrance around the phenolic hydroxyl group. Based on these points, it is presumed that if the amount of benzotriazole-based UVA (d1) is 20 wt% or less of the total amount of UVA (d), the contribution of hydroxyphenyltriazine-based UVA (d2) and other UVA (d3) is significant, and the polyurea coating film 1 can be used with acceptable levels of yellowing. In any case, it is believed that yellowing occurs at least when the free amine component (x) is present in the multilayer coating film and interacts with a component contained in the polyurea coating film 1. In other words, it is believed that yellowing occurs when at least all of the four conditions 1 to 4 are satisfied. On the other hand, yellowing was suppressed when the aqueous colored base coating film was dried, for example, at 40°C for 5 days in step 2. Yellowing was also suppressed when the film was finished by drying at room temperature (for example, 20°C) without heating in step 4. However, yellowing occurred when the film was subsequently heated, for example, at 60°C for 1 day, which indicates that there is a potential for yellowing.

[0069] By avoiding at least one of the above four conditions, yellowing of the polyurea coating film 1 can be suppressed. However, the polyaspartic acid ester (a1) is an essential component to ensure the pot life of the coating material 1. Therefore, it is preferable to avoid at least one of the second, third, and fourth conditions. On the other hand, yellowing can be suppressed by heat-drying the aqueous colored base coating (coating 2) before proceeding to the next process, but this is not desirable from the perspective of energy consumption. Also, yellowing can be suppressed by not finishing with heat drying, but as mentioned above, the possibility of potential yellowing cannot be eliminated. For example, if a coated product is placed outdoors, the temperature can easily reach 40 to 60°C, which may cause yellowing in the future. From the above, it is particularly preferable to avoid the second condition, that is, not to include benzotriazole-based UVA (d1) as the main component, that is, to design it so that its content is 20% by weight or less of the total amount of UVA (d). [Example]

[0070] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0071] In the examples below, unless otherwise specified, the following raw materials were used to prepare Paint 1. "Desmophen," "Jeffamine," "Duranate," "Desmodur," and "Tinuvin" are all registered trademarks. <Raw materials used in preparing paint 1> [Polyaspartic acid ester (a1)] Desmophen NH1220 (manufactured by Sumika Covestro Urethane Co., Ltd., amine equivalent: 234) Desmophen NH1420 (manufactured by Sumika Covestro Urethane Co., Ltd., amine equivalent: 276) [Polyamine (a2)] Jeffamine D-2000 (Huntsman, amine equivalent: 1,000) [Polyisocyanate (b)] Duranate TLA-100 (Asahi Kasei Corporation, HDI isocyanurate, isocyanate equivalent: 180) Desmodur Ultra Z4470 BA (manufactured by Sumika Covestro Urethane Co., Ltd., isocyanurate of IPDI, isocyanate equivalent: 360) [Hydroxyl group-containing component (c)] Acrylic urethane resin (synthesized according to a previous report. Solid content: 60%, glass transition temperature: 60°C, hydroxyl group equivalent (solid content): 510) [Benzotriazole-based UVA (d1)] Tinuvin 1130 (manufactured by BASF) Tinuvin 384-2 (BASF) [Hydroxyphenyltriazine UVA (d2)] Tinuvin 400 (BASF) Tinuvin 405 (BASF) Tinuvin 479 (BASF) [Other ingredients (e)] Tinuvin 292 (BASF, HALS) JP-308E (Johoku Chemical Industry Co., Ltd., phosphite ester antioxidant)

[0072] The following paint was used to form the coating film 2. "Neo Water Base" is a registered trademark. <Paint used to form coating film 2> 979-1204 (Rock Paint Co., Ltd., Neo Waterbase HG White, water-based color base paint) 979-4006 (Rock Paint Co., Ltd., Neo Water-Based Snow Medium Metallic, water-based colored base paint)

[0073] <How to prepare paint 1> [Liquid A] The component (a) containing an amino group and reactive with an isocyanate group, the ultraviolet absorber (UVA) (d), and optionally the hydroxyl group-containing component (c) and other components (e) were mixed and stirred uniformly using a disperser. The solid content is preferably 30% to 70%. In one embodiment, a solid content of 47% can be used. [Liquid B] Polyisocyanate (b) and, if necessary, other components (e) were mixed and stirred uniformly using a disperser. The solid content is preferably 50% or more and 100% or less. In one embodiment, a mixture designed for a solid content of 70% can be used.

[0074] Liquid A and Liquid B were mixed and uniformly stirred using a disper so that the equivalent ratio (NH+OH) / NCO of the amino group (NH) contained in the component (a) that contains an amino group and is reactive with an isocyanate group, the isocyanate group (NCO) contained in the polyisocyanate (b), and the hydroxyl group (OH) contained in the hydroxyl group-containing component (c) was in the range of 0.65 to 1.20. In one embodiment, the liquid A and the liquid B are mixed in a weight ratio of 2:1 to prepare paint 1 with a spray solid content of 55%. The present invention is not limited to the above embodiment, and in consideration of storage stability and handling, the solid contents of liquids A and B can be adjusted using a dilution solvent to change the blending ratio to 5:1, 3:1, 1:1, etc. However, in order to keep the equivalent ratio (NH + OH) / NCO in the range of 0.65 to 1.20, it is preferable to adjust the solid weight ratio of liquids A and B to be in the range of 2:1 to 1:2. The viscosity of the paint 1 is preferably 8 to 15 seconds, more preferably 9 to 11 seconds, immediately after preparation, when a viscosity cup NK-2 (manufactured by Anest Iwata Corp.) is immersed in the paint 1 at a temperature of 20°C and a relative humidity of 50%, the time from the moment the cup is immersed in the paint 1 to the moment the cup is lifted up until the paint in the cup runs out is measured.

[0075] <How to prepare the test plate> A cationic electrodeposited plate (manufactured by Asahi B-Techno Co., Ltd., substrate: SPCC-SD) was coated with 202-6940 / 202-0110 (manufactured by Rock Paint Co., Ltd., Rock Plasf Climax (medium gray), primer surfacer) using an air spray gun to a dry film thickness of 100 to 150 μm, and then dried at 20°C for one day. From the perspective of the finish quality of the multilayer coating film, the primer surfacer layer can be polished. Polishing can be performed manually using sandpaper, or by using a power tool such as a disc sander. When polishing, it is preferable to polish the dry film thickness after polishing to 50 to 120 μm. After polishing, it is preferable to clean the coating surface by rinsing with water or degreasing with a solvent. Next, using an air spray gun, paint 2 was applied to a dry film thickness of 20 to 30 μm to form paint film 2. After flashing off for 15 minutes, paint 1 was applied using an air spray gun to a dry film thickness of 50 to 70 μm to form polyurea paint film 1. The multilayer paint film thus obtained was dried at 60°C for 3 days to prepare a test panel.

[0076] <Evaluation method> [Evaluation method for color difference Δb*] After forming the polyurea coating film 1, the b* value was measured at the point when the film was dried at 20°C for 1 hour, with the initial value being the value. Unless otherwise specified, the b* value was also measured in the same manner after drying at 60°C for 3 days, and the difference Δb* between the values ​​was calculated. A spectrophotometer (CM-26dG, manufactured by Konica Minolta, Inc.) was used for color measurement. A D65 light source was used, the viewing angle was set to 10°, and measurements were performed using the SCI method. The degree of yellowing was evaluated from the Δb* value using the following criteria. ○: Δb* is less than 0.5 ○△: Δb* is 0.5 or more and less than 1.0 △: Δb* is 1.0 or more and less than 1.5 ×: Δb* is 1.5 or more

[0077] [Pot life of paint 1] In the present invention, the pot life was defined as the time required for the viscosity of paint 1 to reach a certain standard after preparation. Specifically, at a temperature of 20°C and a relative humidity of 50%, a viscosity cup NK-2 (manufactured by Anest Iwata Corporation) was immersed in paint 1 to fill the cup, and the time from the moment the cup was lifted out to the time the paint in the cup was gone was measured. The time required for the measured time to reach 20 seconds or more was defined as the pot life. Evaluation was based on the following criteria. 〇: Pot life is 30 minutes or more ×: Pot life is less than 30 minutes

[0078] [Storage stability of paint 1] Paint 1 was left to stand at 40°C for 3 months, and the degree of yellowing (visually determined), viscosity change, and reactivity (change in pot life before and after storage) were comprehensively evaluated according to the following criteria. ○: No significant changes in any of the items. ×: There is a clear change in at least one item.

[0079] [Weather resistance of multi-layer coating] In accordance with JIS K 5600-7-7:2008, a super xenon weather meter (SX75, manufactured by Suga Test Instruments Co., Ltd., irradiation intensity: 180 W / m 2 Using a black panel thermometer, accelerated weather resistance tests were conducted at 61-65°C with a cycle of 18 minutes of wetting and 102 minutes of drying. The b* value at the beginning of the test was taken as the initial value, and the difference between the b* value after 2000 hours, Δb*, was calculated. The degree of yellowing was evaluated based on the Δb* value using the following criteria. ○: Δb* is less than 0.5 ○△: Δb* is 0.5 or more and less than 1.0 △: Δb* is 1.0 or more and less than 1.5 ×: Δb* is 1.5 or more

[0080] <Preliminary Consideration> As a preliminary study, we divided the cases into those with and without the following four conditions. [First condition] The polyurea coating film 1 contains a constituent component derived from the polyaspartic acid ester (a1). [Second condition] The UVA (d) in the polyurea coating film 1 contains a benzotriazole-based UVA (d1) as a main component. In the present invention, "as a main component" means that it is contained as an essential component. Addition as an auxiliary component, specifically, addition of 20% by weight or less of the total amount of ultraviolet absorber (UVA) (d), does not fall under the category of addition "as a main component." [Third condition] The coating film 2 contains a free amine component (x). [Fourth condition] After a multilayer coating film having at least two layers, the coating film 2 and the polyurea coating film 1, is formed, the multilayer coating film is dried by heating at a temperature of 40°C or higher in the presence of the free amine component (x) in the multilayer coating film.

[0081] (Comparative Reference Example 1) 202-6940 / 202-0110 (Rock Paint Co., Ltd., Rock Plassaf Climax (medium gray), primer surfacer) was applied to a cationic electrodeposited plate (manufactured by Asahi B-Techno Co., Ltd., substrate: SPCC-SD) using an air spray gun so that the dry film thickness was 120 μm, and the coating was dried at 20°C for 1 day. The coating surface was polished using a disc sander so that the film thickness was 80 μm, and the coating surface was cleaned by solvent degreasing. Next, using an air spray gun, 979-1204 was applied as the aqueous base paint for Paint 2 to a dry film thickness of 25 μm, forming Paint Film 2. After flashing off for 15 minutes, an air spray gun was used to apply a paint having the composition described in Comparative Example 1 below as Paint 1 to a dry film thickness of 50 μm, forming Polyurea Coating Film 1. The multilayer coating film thus obtained was dried at 60° C. for 1 day.

[0082] (Reference example 1) A multilayer coating film was formed in the same manner as in Comparative Reference Example 1, except that 149-6250 / 149-6120 (Ecorock (registered trademark) Hyper Clear LW, solvent-based acrylic urethane clear coating, manufactured by Rock Paint Co., Ltd.) was used as coating material 1. This clear coating material was not a polyurea coating film, and did not contain any constituents derived from the polyaspartic acid ester (a1).

[0083] (Reference example 2) A multi-layer coating film was formed in the same manner as in Comparative Reference Example 1, except that a coating having the composition described in Example 1 below was applied as Coating 1. Coating 1 used here does not contain a benzotriazole-based UVA (d1).

[0084] (Reference example 3) A multi-layer coating film was formed in the same manner as in Comparative Reference Example 1, except that Coating Film 2 was formed using 077-0204 (Protouch (registered trademark) White, solvent-based colored base paint, manufactured by Rock Paint Co., Ltd.). This coating film did not contain any free amine component (x).

[0085] (Reference example 4) A multi-layer coating film was formed in the same manner as in Comparative Reference Example 1, except that the multi-layer coating film was dried at 20°C for 7 days.

[0086] [Table 1]

[0087] As shown in Table 1, Comparative Reference Example 1, which satisfied all four conditions, had a Δb* value of more than 1.5, and significant yellowing was confirmed. On the other hand, Reference Examples 1 to 4 did not satisfy any of the four conditions, and therefore yellowing was suppressed. However, in Reference Example 3, when the obtained multi-layer coating film was dried at 20°C for 7 days and then further dried at 60°C for 1 day, Δb* became 1.18.

[0088] Example 1 202-6940 / 202-0110 (Rock Paint Co., Ltd., Rock Plassaf Climax (medium gray), primer surfacer) was applied to a cationic electrodeposited plate (manufactured by Asahi B-Techno Co., Ltd., substrate: SPCC-SD) using an air spray gun so that the dry film thickness was 120 μm, and the coating was dried at 20°C for 1 day. The coating surface was polished using a disc sander so that the film thickness was 80 μm, and the coating surface was cleaned by solvent degreasing. Next, 979-1204 was applied as the aqueous base paint for Paint 2 to a dry film thickness of 25 μm to form Paint Film 2. After flashing off for 15 minutes, Paint 1 prepared as described below was applied using an air spray gun to a dry film thickness of 50 μm to form Polyurea Coating Film 1. The multi-layer coating film thus obtained was dried at 60°C for 3 days.

[0089] Paint 1 was prepared according to the following procedure. As component (a) having an amino group and reactive with isocyanate groups, 42.00 parts by weight of Desmophen NH1420 was used; as component (c) containing a hydroxyl group, 2.00 parts by weight of an acrylic urethane resin synthesized according to a previously reported method was used; as component (d2) containing a hydroxyl group, 1.00 parts by weight of Tinuvin 400 was used as a hydroxyphenyltriazine-based UVA; as other components (e), 1.00 parts by weight of Tinuvin 292 (HALS) and 1.00 parts by weight of JP-308E (a phosphite ester-based antioxidant); and a solvent was added to adjust the solids content to 47%, and the mixture was stirred and mixed using a disper to obtain liquid A. As polyisocyanate (b), 26.25 parts by weight of Duranate TLA-100, 8.75 parts by weight of Desmodur Ultra Z4470 BA, and a solvent were added so that the solid content was 70%, and the mixture was stirred and mixed using a disper to obtain liquid B. The liquid A and the liquid B were mixed in a weight ratio of 2:1 to prepare paint 1 with a spray solid content of 55%.

[0090] The pot life and storage stability of the paint 1 were both rated as good. After the multi-layer coating film was formed, the Δb* before and after drying at 60°C for 3 days was less than 0.5, also rated as good. Furthermore, the Δb* before and after the weather resistance test was also less than 0.5, also rated as good.

[0091] (Examples 2 to 11, Comparative Examples 1 to 5) The test was carried out in the same manner as in Example 1, except that the composition of Paint 1 was changed to the composition shown in Tables 2 and 3.

[0092] [Table 2]

[0093] [Table 3]

[0094] In Examples 2 and 3, Tinuvin 405 and Tinuvin 479 were used as hydroxyphenyltriazine UVAs (d2), respectively. In both cases, the same results as in Example 1 were obtained. On the other hand, in Comparative Examples 1 and 2, Tinuvin 1130 and Tinuvin 384-2 were used as benzotriazole-based UVAs (d1), respectively, and yellowing occurred when the multilayer coating film was dried at 60°C for 3 days. On the other hand, in Comparative Example 3, when UVA(d) was not added, yellowing did not occur after the multilayer coating film was heated and dried at 60°C, but yellowing occurred before and after the weather resistance test.

[0095] In Examples 4 to 5 and Comparative Examples 4 to 5, a combined system of benzotriazole-based UVA (d1) and hydroxyphenyltriazine-based UVA (d2) was investigated based on Example 1. The contribution of benzotriazole-based UVA (d1) to yellowing was greater, and this became particularly noticeable when the mixing ratio of benzotriazole-based UVA (d1) to the total amount of UVA (d) exceeded 20% by weight.

[0096] In Examples 6 to 8, the equivalent ratio (NH+OH) / NCO was fixed at about 0.85, and the composition of Solution A was varied for investigation. In all cases, the same results as in Example 1 were obtained.

[0097] In Examples 9 to 11, the ratio of the isocyanurate of HDI and the isocyanurate of IPDI contained in Solution B was changed based on Example 1. By changing the ratio, the equivalent ratio (NH + OH) / NCO was changed to 0.85 to 1.07, and within this range, the same results as in Example 1 were obtained.

[0098] (Examples 12 to 15, Comparative Examples 6 to 8) The test was carried out in the same manner as in Example 1, except that the combination of paint 1 and paint 2 was changed as shown in Table 4.

[0099] [Table 4]

[0100] In Examples 12 and 13, the paint composition described in Example 1 was used as Paint 1, and 979-4006 and WB01 Chromax Pro White HS (aqueous colored base paint manufactured by Axalta Coating Systems) were used as Paint 2, respectively, and the results were similar to those of Example 1. In addition, in Examples 14 and 15, the same investigations as in Examples 12 and 13 were carried out except that the coating composition described in Example 7 was used as coating material 1, and the results were the same as in Example 1. On the other hand, in Comparative Examples 6 to 8, the same study was carried out as in Examples 12 and 13, except that Chromax CC6750 Ultra Performance Energy System Clear (manufactured by Axalta Coating Systems, room temperature drying clear) was used as paint 1. When the multi-layer coating film was formed by heat drying, significant yellowing occurred. "Chromax" is a registered trademark.

Claims

1. A method for inhibiting yellowing of a coating film, which inhibits yellowing of the polyurea coating film 1 when forming a multi-layer coating film by performing at least two steps, a step of forming a coating film 2 and a step of forming a polyurea coating film 1, identifying the amine component; The step of forming the polyurethane coating film 1 is a step of applying a paint 1, The coating material 1 is a coating material composition containing at least three components: a component (a) containing an amino group and reactive with an isocyanate group, a polyisocyanate (b), and an ultraviolet absorber (UVA) (d), and the ultraviolet absorber (UVA) (d) contains at least a benzotriazole-based ultraviolet absorber (UVA) (d1) and / or a hydroxyphenyltriazine-based ultraviolet absorber (UVA) (d2); the mixing ratio of the benzotriazole-based ultraviolet absorber (UVA) (d1) is 20 parts by weight or less relative to 100 parts by weight of the total amount of the ultraviolet absorber (UVA) (d); The component (a) containing an amino group and reactive with an isocyanate group includes a polyaspartic acid ester (a1) represented by the following Chemical Formula 1, 【Chemistry 1】 (Here, X is an n-valent organic group which is inert to isocyanate groups and is obtained by removing n primary amino groups from a polyamine containing the primary amino groups. R1 and R2 are the same or different organic groups which are inert to isocyanate groups. n is an integer of 2 or more.) The step of forming the coating film 2 is a step of applying a paint 2, the coating material 2 contains an amine component (x) that is different from the polyaspartic acid ester (a1) and has an amine equivalent of less than 200; the amine component (x) is not bonded to any component constituting the coating film 2 via a covalent bond, The step of checking the amine component is characterized in that the presence or absence of the amine component (x) is checked, and the coating material 1 is recommended to be applied in the step of forming the polyurea coating film 1. A method for preventing yellowing of coating films.

2. The component (a) containing an amino group and reactive with an isocyanate group contains 80% by weight or more of the polyaspartic acid ester (a1). The method for inhibiting yellowing of a coating film according to claim 1.

3. The polyaspartic acid ester (a1) has an amine equivalent of 200 or more and 300 or less. The method for inhibiting yellowing of a coating film according to claim 1.

4. In the above "Chemical Formula 1," X is any one of an aliphatic hydrocarbon, an alicyclic hydrocarbon, and an aromatic hydrocarbon. The method for inhibiting yellowing of a coating film according to claim 1.

5. The polyisocyanate (b) contains at least an isocyanurate of hexamethylene diisocyanate (HDI) and / or an isocyanurate of isophorone diisocyanate (IPDI). The method for inhibiting yellowing of a coating film according to claim 1.

6. The coating film 1 contains at least one component selected from a pigment, a colorant, and a matting agent. The method for inhibiting yellowing of a coating film according to claim 1.

7. The coating film 1 is a clear coating film, and the coating film 2 is a colored base coating film. The method for inhibiting yellowing of a coating film according to claim 1.

8. The paint 1 contains a phosphite ester-based antioxidant. The method for inhibiting yellowing of a coating film according to claim 1.

9. At least the following four steps: (1) Step of confirming amine components (2) forming the coating film 2; (3) a step of forming the polyurethane coating film 1; (4) a step of drying the multi-layer coating film together to finish it; 2. The method for inhibiting yellowing of a coating film according to claim 1, comprising:

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