Paint compositions with good adhesion to substrates

Abstract

The present invention provides a coating composition that exhibits excellent adhesion to a substrate and water resistance. It also provides a method for repairing damaged areas of an existing coating film formed on an article using the aforementioned coating composition. [Solution] A urethane coating composition comprising a hydroxyl group-containing component (a) and an isocyanate-containing component (b), wherein the hydroxyl group-containing component (a) comprises a hydroxyl group-containing (meth)acrylic component (a1), the hydroxyl group-containing (meth)acrylic component (a1) has a glass transition temperature of 85°C or less, a hydroxyl value (on a solid content basis) X of 10 mg KOH / g or more and 180 mg KOH / g or less, a number average molecular weight Y of 2,000 or more and 20,000 or less, and the ratio of X to Y, expressed as "X / Y × 100", is 0.10 or more and 5.00 or less.

Description

Technical Field

[0001] The present invention relates to a paint composition having good adhesion to a substrate.

Background Art

[0002] In recent years, the modes of painting have diversified, and the requirements for application to plastic substrates have increased. However, it has been pointed out that paints adhere poorly to plastic substrates with low surface free energy compared to substrates such as metals and glasses with high surface free energy. In particular, for olefin-based substrates such as polypropylene and polyethylene, and fluorine-based substrates such as polytetrafluoroethylene, whose surface free energy calculated by the extension of Fowkes' equation (Kitazaki-Hata theory) shown in Non-Patent Document 1 is less than 40 mJ / m 2 it is generally necessary to apply a dedicated primer or perform a surface treatment in order to adhere a paint to them. Although surface tension is shown in Non-Patent Document 1, here, in order to compare the magnitudes of the numerical values and discuss, it is replaced with surface free energy as an equivalent dimensional unit. Similarly hereinafter, discussions will be made in terms of surface free energy.

[0003] In Non-Patent Document 2, the adhesion mechanism of a chlorine-containing adhesion promoter to a polyolefin-based plastic material was elucidated, and using this mechanism, a non-chlorine adhesion promoter was studied, and three elements related to adhesion were disclosed. That is, first, the adhesion force of the adhesion promoter is developed by penetration into the plastic material and cohesive force; second, the adhesion force is improved by using an optimal penetration solvent and improving compatibility; third, in the acrylic homopolymer tested as a non-chlorine-based adhesion promoter, the permeability of a resin that satisfies both conditions of a specific solubility parameter and the molar volume of the acrylic side chain becomes high.

[0004] Furthermore, Non-Patent Document 3 investigates the adhesion of water-based coatings to plastic materials having various surface properties and discloses that the adhesion of the coating is good when the surface free energy of the coating is lower than the critical surface tension of the plastic material.

[0005] In actual paint design, it is necessary to consider not only the elements theoretically discussed in these non-patent documents, but also a variety of other factors such as the adhesion of the paint film to the plastic substrate, as well as the paint's pot life, storage stability, hardness, and weather resistance.

[0006] Patent Document 1 discloses a coating composition for plastics that provides excellent adhesion to plastic materials, stain resistance (resistance to oleic acid and lactic acid), and finish, even with a single coat. The coating composition for plastics contains a hydroxyl group-containing acrylic resin with a weight-average molecular weight of 3,000 to 20,000 and a hydroxyl value in the range of 100 to 200 mgKOH / g, a polyisocyanate compound, a curing catalyst, a silicone-based surface modifier, and a surface modifier that is essential for an acrylic-based surface modifier. Furthermore, from the viewpoint of stain resistance of the cured coating film, the coating composition is characterized in that, when applied to a dry film thickness of 30 ± 5 μm and cured by baking at 80°C for 20 minutes, the glass transition temperature of the cured coating film is 100°C or higher, and the intercrosslinking molecular weight of the cured coating film is 900 g / mol or less.

[0007] Patent Document 2 discloses a two-component polyurethane coating agent that can obtain a coating film with excellent adhesion, chemical resistance, and scratch resistance. The coating agent comprises a polyisocyanate component and a polyol component, wherein the polyisocyanate component comprises an aliphatic polyisocyanate, and the polyol component comprises an acrylic polyol, wherein the average hydroxyl value of the acrylic polyol is 60 mg KOH / g or more and 150 mg KOH / g or less, and the glass transition temperature of the acrylic polyol is 70°C or more and 100°C or less. Generally, lowering the average hydroxyl value of the polyol component improves adhesion, but tends to decrease chemical resistance and scratch resistance. Similarly, lowering the glass transition temperature of the polyol component improves adhesion and scratch resistance, but tends to decrease chemical resistance. However, the coating film obtained with the aforementioned coating agent has a good balance of adhesion, chemical resistance, and scratch resistance. The reason for this is discussed in the specification as follows. When the reaction between the polyisocyanate component and the polyol component (acrylic polyol) proceeds, a network is formed. However, if the glass transition temperature of the acrylic polyol is high, this network becomes rigid, and the movement of the acrylic polyol after the reaction is suppressed. As a result, the reactivity of the acrylic polyol decreases, and the number of functional groups that do not participate in the reaction increases (i.e., the number of acrylic polyols that do not form a network increases), resulting in the formation of a relatively loose network that is still rigid. Therefore, due to its rigidity, chemical resistance and scratch resistance are improved, and due to its loose network, adhesion is improved.

[0008] On the other hand, painting presents challenges such as the volatilization of diluting solvents during painting, energy consumption due to the use of drying ovens in the drying process of the paint film, and waste liquid treatment after painting. In light of recent global environmental issues and the need to improve the working environment, decorative films are attracting attention as an alternative to painting. In particular, as shown in Non-Patent Document 4, the three-dimensional decorative method called TOM (Three-Dimensional Overlay Method) has the characteristic of being able to handle large three-dimensional products regardless of the material of the substrate, and is therefore being applied to a wide range of fields such as automotive interior and exterior materials, home appliances, electronic materials, and building materials. Therefore, it is anticipated that in the future, there will be a need for repairs to automotive exterior materials that have decorative layers formed by decorative films. However, spot repair of damaged areas using decorative technology is difficult, and from a time and economic standpoint, it will be necessary to adopt methods using conventional repair paints. However, conventional repair paints may not be directly applicable to decorative films, which differ from paint films in terms of hardness and elongation. In particular, there are concerns regarding adhesion and finish.

[0009] For example, Non-Patent Document 5 discloses the "Technoloy®" series (manufactured by Sumitomo Chemical Co., Ltd., acrylic film). This series has a structure in which rubber-elastic particles are dispersed as island components relative to the sea components of the acrylic resin in order to improve brittleness while maintaining the excellent surface hardness of the acrylic resin. Therefore, depending on the type of film used as a decorative film, repair paint may not adhere sufficiently. Thus, identifying the type of film used as a decorative film and selecting the most suitable repair paint is a significant burden for painters. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2014-019714 [Patent Document 2] Japanese Patent Publication No. 2021-011544 [Non-patent literature]

[0011] [Non-Patent Document 1] Journal of the Adhesion Society of Japan, Vol. 8, pp. 131-140, 1972, "Extension of the Fowkes formula and evaluation of the surface tension of polymer solids" [Non-Patent Document 2] Research on Paints, No. 143, 2005, "Research on the mechanism of adhesion to plastic materials" [Non-Patent Document 3] DNT Coating Technical Report, No. 10, 2010, "Research on the adhesion of water-based paints to plastic materials with different surface properties" [Non-Patent Document 4] Journal of the Image Science Society of Japan, Vol. 48, No. 4, pp. 277-284, 2009, "Development and Application of Three-Dimensional Surface Decoration Technology (TOM Method)" [Non-Patent Document 5] Technical Journal, Sumitomo Chemical, 2006, "Development of High Value-Added Acrylic Film Technoloy (Registered Trademark)" [Overview of the project] [Problems that the invention aims to solve]

[0012] This invention has been made in view of the above background, and its main objective is to provide a coating composition that has excellent adhesion to a substrate and water resistance. It also aims to provide a method for repairing damaged areas of an existing coating film formed on an article using the coating composition. [Means for solving the problem]

[0013] As a result of diligent research to solve the aforementioned problems, the present inventors have found that a urethane coating composition containing a specific hydroxyl group-containing component (a) and an isocyanate-containing component (b) exhibits excellent adhesion to a substrate. In particular, they found that the contribution of the hydroxyl group-containing component (a) is dominant to the adhesion to the substrate compared to the contribution of the composition of the isocyanate-containing component (b). More specifically, it was found that the hydroxyl group-containing component (a) includes a hydroxyl group-containing (meth)acrylic component (a1), and that the hydroxyl group-containing (meth)acrylic component (a1) has an advantageous effect on adhesion to the substrate when all of the following conditions are met. First condition: The glass transition temperature must be 85°C or lower. Second condition: The hydroxyl value (based on solid content) X must be between 10 mg KOH / g and 180 mg KOH / g. Third condition: The number-average molecular weight Y must be between 2,000 and 20,000. Fourth condition: The ratio of X to Y, expressed as "X / Y × 100", must be between 0.10 and 5.00. [Effects of the Invention]

[0014] According to the present invention, a coating composition having good adhesion to a substrate can be obtained. Further, the coating composition can be applied to repair damaged portions of an existing coating film formed on an article. In addition, the substrate shall also include a decorative layer formed by a decorative film. Further, the coating composition can be applied to repair damaged portions of a decorated article (hereinafter simply abbreviated as "decorated article") to which a decorative film is attached.

Brief Description of the Drawings

[0015] [Figure 1] It is a cross-sectional view of a coating film showing one embodiment when directly coated on a substrate using the coating composition of the present invention. [Figure 2] It is a cross-sectional view of a repaired coating film showing one embodiment when repairing a shallow scratch on an existing coating film formed on an article using the coating composition of the present invention. [Figure 3] It is a cross-sectional view of a repaired coating film showing one embodiment when repairing a deep scratch on an existing coating film formed on an article using the coating composition of the present invention. [Figure 4] It is a cross-sectional view of a repaired coating film showing one embodiment when repairing a shallow scratch on a decorated article using the coating composition of the present invention. [Figure 5] It is a cross-sectional view of a repaired coating film showing one embodiment when repairing a deep scratch on a decorated article using the coating composition of the present invention.

[0016] In the present invention, damage that does not require filling unevenness with putty is defined as "shallow scratch", and damage that requires filling unevenness with putty is defined as "deep scratch". For example, as shown in FIG. 3, it is preferable to fill unevenness with putty for damage reaching the substrate of the article. Furthermore, in vehicle repair, especially partial repair, a technique called "blending paint" is used to prevent color differences between the repaired area and the surrounding unrepaired area, rather than painting the repaired area precisely. The repaired paint film in Figures 2-5 is shown on a curved surface, indicating that the aforementioned blending paint has been applied. Furthermore, although the decorative film is made up of multiple laminated films, Figures 4 and 5 do not go into detail about the layers or their structure, but simply show them as "decorated articles," and discuss them in different cases depending on the degree of damage to the decorated articles. [Modes for carrying out the invention]

[0017] The components used in the present invention will be described in detail below. Note that the raw materials exemplified in the following description are not intended to limit the composition of the present invention, and modifications may be made without departing from the spirit of the invention.

[0018] <Hydroxygroup-containing component (a)> The hydroxyl group-containing component (a) of the present invention comprises at least a hydroxyl group-containing (meth)acrylic component (a1). The hydroxyl group-containing (meth)acrylic component (a1) is characterized in that it has a glass transition temperature of 85°C or less, and its "X / Y × 100" (hereinafter defined as "hydroxyl group index"), which is expressed by the ratio of the hydroxyl value (on a solid content basis) X to the number average molecular weight Y, is 0.10 or more and 5.00 or less.

[0019] Here, the hydroxyl group index is an indicator representing the number of hydroxyl groups present per unit molecular weight. That is, the lower the hydroxyl group index, the fewer the number of hydroxyl groups per unit molecular weight, and the coarser the crosslinking due to the reaction with the isocyanate-containing component (b) described later. On the other hand, the higher the hydroxyl group index, the more hydroxyl groups there are per unit molecular weight, and the denser the crosslinking due to the reaction with the isocyanate-containing component (b) described later. Japanese Patent Publication No. 2014-019714, cited as Patent Document 1, specifies that a coating composition for plastics that can obtain a coating film with excellent adhesion to plastic materials, stain resistance (resistance to oleic acid and lactic acid), and finish, must have an intercrosslink molecular weight of the cured coating film below a certain value. Such intercrosslink molecular weight is calculated by evaluating the cured coating film with a dynamic viscoelasticity measuring device and applying a theoretical formula. On the other hand, the hydroxyl group index differs in that it is an index that shows the contribution of the hydroxyl group-containing component to the adhesion of the coating composition to the substrate. According to the present invention, it is possible to predict the adhesion to the substrate without causing a reaction between the hydroxyl group-containing (meth)acrylic component (a1) and the isocyanate-containing component (b), and is therefore not affected by reaction conditions such as reaction temperature and NCO / OH. Furthermore, Japanese Patent Publication No. 2021-011544, cited as Patent Document 2, discusses how the high glass transition temperature of acrylic polyols improves adhesion despite the rigidity of the network formed by the reaction with the polyisocyanate component. The aforementioned discussion suggests that a relatively loose network is formed as the amount of acrylic polyol that does not form a network increases, but this differs from the concept of the hydroxyl group index mentioned above.

[0020] Furthermore, the hydroxyl group-containing component (a) may also contain a hydroxyl group-containing (meth)acrylic component (a2) different from the hydroxyl group-containing (meth)acrylic component (a1), and other hydroxyl group-containing components (a3) ​​that are not (meth)acrylic components. However, it is preferable that the solid content of the hydroxyl group-containing (meth)acrylic component (a1) is 5 parts by weight or more, and more preferably 10 parts by weight or more, per 100 parts by weight of the total solid content of these hydroxyl group-containing components (a). Including the solid content of the hydroxyl group-containing (meth)acrylic component (a1) can improve adhesion to the substrate, and it is preferable that the solid content is 5 parts by weight or more, as this makes it easier to obtain stable adhesion.

[0021] Each of the components (a1) to (a3) ​​can be used individually, or two or more can be used in combination. Furthermore, there are no particular restrictions on the form of the hydroxyl group-containing component (a); it may be a solution or a dispersion. It may also be used in a solvent-free form. In addition, each of the other hydroxyl group-containing components (a), such as hydroxyl group-containing component (a3), may be a component of the coating film or an additive, and there are no restrictions on their formulation form.

[0022] <Hydroxyl group-containing (meth)acrylic component (a1)> The hydroxyl group-containing (meth)acrylic component (a1) in the present invention may be synthesized according to previously reported information, or a commercially available product may be used. When synthesized according to previously reported information, a (meth)acrylic monomer having a hydroxyl group is an essential component, and polymerizable unsaturated monomers having a carboxyl group and other polymerizable monomers can be used in combination.

[0023] There are no particular limitations on the hydroxyl group-containing (meth)acrylic monomer, but examples include esters of (meth)acrylic acid with polyhydric alcohols such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, glycerin mono(meth)acrylate, and glycerol di(meth)acrylate; lactone-modified (meth)acrylates obtained by ring-opening addition of ε-caprolactone to the ester; nitrogen-containing polymerizable unsaturated monomers such as N-hydroxymethyl (meth)acrylamide and N-hydroxyethyl (meth)acrylamide; allyl alcohol; and polyalkylene glycol mono(meth)acrylates such as polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, and polybutylene glycol mono(meth)acrylate. These can be used individually, but two or more can also be used in combination.

[0024] The polymerizable unsaturated monomer having a carboxyl group is not particularly limited, but examples include alkyl or cycloalkyl esters of (meth)acrylic acid such as methyl (meth)acrylate, n-butyl (meth)acrylate, iso-butyl (meth)acrylate, tert-butyl (meth)acrylate, hexyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, tert-butylcyclohexyl (meth)acrylate, isobornyl (meth)acrylate, adamantyl (meth)acrylate, acetoacetoxyethyl (meth)acrylate, etc.; acid components such as (meth)acrylic acid and maleic acid; (meth)acrylamide, N,N-dimethyl (meth) Examples include nitrogen-containing polymerizable unsaturated monomers such as acrylamide and diacetone acrylamide; polymerizable unsaturated monomers having epoxy groups such as glycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, and 3,4-epoxycyclohexylethyl (meth)acrylate; polymerizable unsaturated monomers having alkoxy groups such as alkoxy polyalkylene glycol mono(meth)acrylate, methoxypolyethylene glycol mono(meth)acrylate, and methoxypolybutylene glycol mono(meth)acrylate; and polyalkylene glycol di(meth)acrylate, such as polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, and polybutylene glycol di(meth)acrylate. These can be used individually, but two or more can also be used in combination.

[0025] Other polymerizable monomers are not particularly limited, but examples include aromatic polymerizable monomers having a vinyl group such as styrene, α-methylstyrene, and vinyltoluene; and polymerizable monomers having an alkoxysilyl group such as vinyltrimethoxysilane, vinyltriethoxysilane, γ-(meth)acryloyloxypropyltrimethoxysilane, and γ-(meth)acryloyloxypropyltriethoxysilane. These can be used individually, but two or more can also be used in combination.

[0026] The glass transition temperature of the hydroxyl group-containing (meth)acrylic component (a1) in the present invention is preferably 0°C or higher and 85°C or lower, and more preferably 10°C or higher and 70°C or lower. If the glass transition temperature is below 0°C, tack is likely to occur in the coating film. If the glass transition temperature exceeds 85°C, adhesion to the substrate may be insufficient.

[0027] The apparent glass transition temperature Tg (absolute temperature) of a copolymer can be calculated based on the following equation (1) (Fox's equation). 1 / Tg=W1 / Tg1+W2 / Tg2+W3 / Tg3+...+Wi / Tgi (1) Here, the subscripts 1, 2, 3, ...i represent the constituent monomer components, Wi is the weight fraction of constituent monomer component i, and Tgi represents the glass transition temperature (absolute temperature) of the homopolymer of constituent monomer component i.

[0028] In the present invention, the hydroxyl value (on a solid content basis) X of the hydroxyl group-containing (meth)acrylic component (a1) is preferably 10 mg KOH / g or more and 180 mg KOH / g or less, more preferably 15 mg KOH / g or more and 160 mg KOH / g or less, and even more preferably 15 mg KOH / g or more and 120 mg KOH / g or less. If the hydroxyl value (based on solid content) X is less than 10 mg KOH / g, the coating obtained by reaction with the isocyanate-containing component (b) described later will have fewer crosslinking sites per molecule, which may result in a deterioration of water resistance. If the hydroxyl value (based on solid content) X exceeds 180 mgKOH / g, the coating film obtained by reaction with the isocyanate-containing component (b) described later will have a large number of crosslinking sites per molecule, which may result in insufficient adhesion to the substrate.

[0029] In the present invention, the number-average molecular weight Y of the hydroxyl group-containing (meth)acrylic component (a1) is preferably 2,000 or more and 20,000 or less, and more preferably 2,500 or more and 15,000 or less. If the number-average molecular weight Y is less than 2,000, the coating obtained by the reaction with the isocyanate-containing component (b) described later may not have sufficient water resistance. If the number-average molecular weight Y exceeds 20,000, the compatibility with the isocyanate-containing component (b), described later, may deteriorate.

[0030] In this invention, the number-average molecular weight is the polystyrene-converted value obtained by GPC. For example, the measurement conditions in the example were: column temperature (Showa Denko K.K. KF-805L x 2) at 35°C, tetrahydrofuran (THF) as the eluent, flow rate at 1.0 mL / min, detection performed with an RI detector (differential refractometer), and sample concentration at 0.3 mass%.

[0031] In the present invention, the hydroxyl group index of the hydroxyl group-containing (meth)acrylic component (a1) is preferably 0.10 or more and 5.00 or less, and more preferably 0.25 or more and 3.50 or less. If the hydroxyl group index is less than 0.10 or greater than 5.00, adhesion to the substrate may be insufficient.

[0032] <Hydroxyl group-containing (meth)acrylic component (a2)> The hydroxyl group-containing (meth)acrylic component (a2) in the present invention is a different component from the hydroxyl group-containing (meth)acrylic component (a1). More specifically, it is a component having a glass transition temperature of over 85°C and / or a hydroxyl index of over 5.00. Similar to the hydroxyl group-containing (meth)acrylic component (a1), it may be synthesized according to previously reported methods or a commercially available product may be used.

[0033] In the present invention, the hydroxyl value (on a solid content basis) X of the hydroxyl group-containing (meth)acrylic component (a2) is preferably 40 mg KOH / g or more and 180 mg KOH / g or less, and more preferably 60 mg KOH / g or more and 170 mg KOH / g or less. If the hydroxyl value (based on solid content) X is less than 40 mgKOH / g, the coating obtained by reaction with the isocyanate-containing component (b) described later will have fewer crosslinking sites per molecule, which may result in a deterioration of water resistance. If the hydroxyl value (based on solid content) X exceeds 180 mgKOH / g, the coating film obtained by reaction with the isocyanate-containing component (b) described later will have a large number of crosslinking sites per molecule, which may result in insufficient adhesion to the substrate.

[0034] In the present invention, the number-average molecular weight Y of the hydroxyl group-containing (meth)acrylic component (a2) is preferably 2,000 or more and 20,000 or less. If the number-average molecular weight Y is less than 2,000, the coating obtained by the reaction with the isocyanate-containing component (b) described later may not have sufficient water resistance. If the number-average molecular weight Y exceeds 20,000, the compatibility with the isocyanate-containing component (b), described later, may deteriorate.

[0035] <Other hydroxyl group-containing components (a3)> The other hydroxyl group-containing component (a3) ​​in this invention is a hydroxyl group-containing component other than the (meth)acrylic component. It may be synthesized according to previously reported information, or a commercially available product may be used. There are no particular restrictions on such components, but examples include polyester polyols; polyether polyols; polycarbonate polyols; polyurethane polyols; and polyalkylene glycols such as polyethylene glycol, polypropylene glycol, and polybutylene glycol. Combinations of these, such as polyester polyurethane polyols, are also acceptable.

[0036] <Isocyanate-containing component (b)> The isocyanate-containing component (b) in the present invention is a component that can react with the hydroxyl group in the hydroxyl group-containing component (a), and is at least one selected from three types: aliphatic isocyanates, alicyclic isocyanates, and aromatic isocyanates. Furthermore, from the viewpoint of the water resistance of the coating film, it is preferable that the compound has two or more isocyanate groups in its molecule. These can be used individually, or two or more can be used in combination.

[0037] There are no particular restrictions on the aliphatic isocyanate, but examples include tetramethylene diisocyanate, pentamethylene diisocyanate, and hexamethylene diisocyanate (HDI). Examples of the aforementioned alicyclic isocyanates include 1,3-cyclopentane diisocyanate, 1,2-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, isophorone diisocyanate (IPDI), norbornane diisocyanate, and the like. Examples of the aforementioned aromatic isocyanates include 2,4- or 2,6-tolylene diisocyanate (TDI), xylylene diisocyanate (XDI), 4,4'-diphenylmethane diisocyanate (MDI), and the like. Furthermore, polymers such as biuret compounds, allophanate compounds, isocyanurate compounds, uretdione compounds, and adduct compounds can also be used. In addition, modified compounds can be used without departing from the spirit of the present invention, and they may be synthesized according to previously reported information or commercially available products may be used. However, if an isocyanate-containing component (b) with an extremely large molecular weight is used, the contribution of the isocyanate-containing component (b) to the cured coating film becomes large, and the indicator of adhesion to the substrate based on the hydroxyl group index of the hydroxyl group-containing component (a) may not function properly. In the present invention, a molecular weight of 2,000 or less is preferred, and a molecular weight of 1,000 or less is more preferred.

[0038] In the present invention, it is preferable to use an aliphatic polyisocyanate for the isocyanate-containing component (b). Aromatic polyisocyanates can also be used, but this is undesirable because the coating film tends to become rigid, raising concerns about reduced weather resistance. However, this does not preclude their use within limits where these disadvantages do not affect the outcome.

[0039] It is preferable to use a mixture of the hydroxyl group (OH) contained in the hydroxyl group-containing component (a) and the isocyanate group (NCO) contained in the isocyanate-containing component (b) in an equivalent ratio of NCO / OH in the range of 0.5 to 2.0. If the equivalent ratio NCO / OH is less than 0.5, sufficient coating hardness may not be achieved. If the equivalent ratio NCO / OH is greater than 2.0, the water resistance of the coating film may decrease.

[0040] <Other ingredients (c)> In the present invention, other components (c) may be included as needed. For example, it may contain additives commonly used in paints, such as dispersants, viscosity modifiers, surface modifiers, defoamers, UV absorbers, light stabilizers, catalysts, and silane coupling agents. It may also contain pigments, colorants, and matting agents. Furthermore, it can be diluted with a diluent solvent.

[0041] As for the pigments, conventionally known coloring pigments and extender pigments can be used without any particular restrictions. Depending on the desired color and coating performance, one or more types may be used in combination. Examples of coloring pigments include organic pigments such as anthraquinone, diketopyrrolopyrrole, quinacridone, perylene, dioxazine, benzimidazolon, isoindolinone, isoindoline, phthalocyanine, and surene pigments, as well as inorganic pigments such as yellow iron oxide, red iron oxide, azomethine copper complex, bismuth vanadate, titanium dioxide, silicon dioxide, zinc oxide, and carbon black. In addition, luminous pigments such as aluminum (including vapor-deposited aluminum), zinc, nickel, copper, silver, and their alloys; aluminum oxide, mica, and mica coated with metal oxides can also be used. Examples of extender pigments include inorganic pigments such as barium sulfate, 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 rust-preventive pigments include phosphate-based pigments such as zinc phosphate, calcium phosphate, and aluminum tripolyphosphate; phosphate-based pigments 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-exchange silica with cations such as calcium ions bonded by ion exchange; calcium silicate; mica-like iron oxide (MIO); and zinc powder.

[0042] <Paint composition> The paint composition in the present invention is preferably prepared by mixing liquid A containing the hydroxyl group-containing component (a) with liquid B containing at least the isocyanate-containing component (b), taking into consideration storage stability and pot life. Liquid A and liquid B can each be obtained by mixing them using known methods. Furthermore, in carrying out the present invention, liquid A and liquid B may each be the main component or the curing agent, or a third liquid may be added to create a multi-component paint composition.

[0043] <Painting Method> Liquid A and Liquid B can be mixed before use and applied using conventional painting methods. Examples include commonly used painting methods such as brushes, trowels, spatulas, rollers, air sprays, airless sprays, curtain flow coaters, roll coaters, and die coaters. Alternatively, the object to be painted can be finished by immersing it in the paint.

[0044] <Base material> The coating composition of the present invention exhibits good adhesion to various substrates, but its surface free energy, calculated by an extension of Fowkes' equation (Kitazaki-Hata theory), is 40 mJ / m². 2 Adhesion may be insufficient to olefin-based substrates such as polypropylene and polyethylene, and fluorine-based plastic substrates such as polytetrafluoroethylene, which have a viscosity of less than 1.5 mm. Therefore, it is preferable to apply a dedicated primer or surface treatment to such substrates. On the other hand, the coating composition in the present invention has a surface free energy of 40 mJ / m², calculated by an extension of Fowkes' equation (Kitazaki-Hata theory). 2 For plastic substrates meeting the above criteria, good adhesion is observed without the application of a special primer or surface treatment. Examples of such plastic substrates include polystyrene, acrylic, polyvinyl chloride, ABS, polycarbonate, urethane, polyester (including polyethylene terephthalate (PET)), polyamide, nylon, epoxy resin, phenolic resin, and fiber-reinforced plastics.

[0045] In addition to the plastic substrates mentioned above, the coating compositions of the present invention can also use metals, wood, wood-based materials, paper, glass, textile products, concrete, ceramic materials, and the like. Furthermore, composite materials of these materials can also be used. As the metal base material, for example, iron, copper, aluminum, etc., can be used. Alloys containing these metals can also be used. Furthermore, plated or surface-treated materials can also be used.

[0046] <Painting Process>

[0047] As one embodiment of the present invention, a case in which the paint composition of the present invention is applied to an ABS resin part will be described as an example. A painted article can be obtained by the following series of steps. [Step 1-1]: Step to prepare the base material. [Step 1-2]: A step of applying the coating composition of the present invention to the substrate to obtain a coating film. [Steps 1-3]: Steps to dry the coating film and obtain a painted article.

[0048] [Step 1-1]: Step to prepare the base material. First, prepare the ABS resin part to be used as the substrate to be coated. The ABS resin part can be used as is, but it is preferable to clean the surface by degreasing and washing. Alternatively, the surface may be polished before use. For polishing, for example, a manual method using sandpaper or a method using power tools such as a disc sander can be employed. After polishing, it is preferable to clean the coating surface by washing with water and degreasing. The same method can be used for the polishing-washing process below, and will simply be abbreviated as "polishing and washing".

[0049] [Step 1-2]: A step of applying the coating composition of the present invention to the substrate to obtain a coating film. Next, the paint composition of the present invention is applied to the substrate prepared in step 1-1 using an air spray gun to form a coating film with a dry film thickness of 10 to 100 μm, preferably 30 to 70 μm.

[0050] [Steps 1-3]: Steps to dry the coating film and obtain a painted article. Next, the coating obtained in steps 1-2 is dried. For example, it is dried at a temperature of 10-100°C, preferably 40-80°C, and a relative humidity of 5-90%, preferably 10-70%, for 10-180 minutes, preferably 20-120 minutes. Furthermore, a clear coating can be formed on top of the coating formed in steps 1-2. In this case, the clear coating can be applied after the coating formed in steps 1-2 has dried to the point where it is no longer fluid, and the two layers can be dried together as a multi-layer coating.

[0051] As another embodiment of the present invention, the repair of an existing coating film formed on an article will be described as an example. A repair coating film can be formed by the following series of steps. [Step 2-1]: The process of preparing and pre-treating the painted items to be repaired. [Step 2-2]: A step of applying the paint composition of the present invention to the damaged area to obtain a repair coating. [Step 2-3]: A step to dry the repair coating film and obtain a repaired painted article.

[0052] [Step 2-1]: The process of preparing and pre-treating the painted items to be repaired. First, prepare the painted item to be repaired. Since the damaged area to be repaired will have scratches and dents, sand and clean the area and its surroundings. If necessary, fill in any unevenness with putty, and then sand and clean again to make the surface uniform. When applying putty, it is preferable to apply a primer beforehand. Next, a primer or primer surfacer is applied and dried for 10 to 180 minutes at, for example, 10°C to 100°C to form a base coat layer. From the viewpoint of the finish of the repair coating film, it is preferable to polish and wash the base coat layer. If polishing and washing are performed, it is preferable that the dry film thickness after polishing and washing be 10 to 150 μm.

[0053] [Step 2-2]: A step of applying the paint composition of the present invention to the damaged area to obtain a repair coating. Next, the paint composition of the present invention is applied to the damaged area pretreated in step 2-1 to form a repair coating. This can be done in the same manner as in step 1-2.

[0054] [Step 2-3]: A step to dry the repair coating film and obtain a repaired painted article. Next, the repair coating obtained in step 2-2 is dried. This can be done in the same manner as in step 1-3.

[0055] As yet another embodiment of the present invention, the repair of a decorative article will be described as an example. A repair coating can be formed by the following series of steps. [Step 3-1]: The process of preparing and pre-treating the decorative item to be repaired. [Step 3-2]: A step of applying the paint composition of the present invention to the damaged area to obtain a repair coating. [Step 3-3]: A step to dry the repair coating film and obtain a repaired painted article.

[0056] [Step 3-1]: The process of preparing and pre-treating the decorative item to be repaired. First, prepare the decorative item to be repaired. Since the damaged area to be repaired has scratches and dents, polish and clean the area and its surroundings, and then apply a primer. Here, unlike in step 2-1, the constituent film of the decorative film is prone to stretching due to the heat and stress caused by polishing, so care must be taken to prevent the edges of the old film from becoming prominent. It is also preferable to apply a plastic primer. Fill in any unevenness with putty as needed, then sand and clean again to make the surface uniform. Next, a primer or primer surfacer is applied and dried for 10 to 180 minutes at, for example, 10°C to 100°C to form a base coat layer. From the viewpoint of the finish of the repair coating film, it is preferable to polish and wash the base coat layer. If polishing and washing are performed, it is preferable that the dry film thickness after polishing and washing be 10 to 150 μm. Here, in order to improve the sealing properties of the edges of the old film, a step of applying the coating composition of the present invention as a clear coating may be included.

[0057] [Step 3-2]: A step of applying the paint composition of the present invention to the damaged area to obtain a repair coating. The paint composition of the present invention is applied to the damaged area that has undergone the aforementioned pretreatment to form a repair coating. This can be done in the same manner as in steps 1-2.

[0058] [Step 3-3]: A step to dry the coating film and obtain a repaired painted article. The coating obtained in step 3-2 is dried. The repair coating is dried. This can be done in the same way as in step 1-3.

[0059] Although specific embodiments have been illustrated and described above, the present invention is not limited to these embodiments. Modifications may be made as appropriate depending on the embodiment. [Examples]

[0060] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0061] In the embodiments described below, unless otherwise specified, the following raw materials were used to produce the coating composition of the present invention. [Hydroxyl group-containing (meth)acrylic component (a1)] When synthesizing the hydroxyl group-containing (meth)acrylic component (a1), the raw materials shown in Table 1 below were used as constituent monomers. The glass transition temperatures of the homopolymers of each monomer were referenced from "Selection and Usage of Functional Monomers: Case Studies" (Publisher: Technical Information Association, Publication Date: July 31, 2017). For those not listed, the manufacturer's catalog values ​​were used.

[0062] [Table 1]

[0063] [Hydroxyl group-containing (meth)acrylic component (a2)] When synthesizing the hydroxyl group-containing (meth)acrylic component (a2), the raw materials shown in Table 1 were used as constituent monomers, similar to those used for the hydroxyl group-containing (meth)acrylic component (a1).

[0064] [Isocyanate-containing components (b)] • b-1: Duranate E405-70B (manufactured by Asahi Kasei Corporation, HDI adduct body) b-2: Duranate TPA-100 (manufactured by Asahi Kasei Corporation, isocyanurate derivative of HDI) b-3: Duranate 24A-100 (manufactured by Asahi Kasei Corporation, biuret form of HDI) • b-4: Duranate D201 (manufactured by Asahi Kasei Corporation, a bifunctional modified form of HDI) • b-5: Takenate D-140N (manufactured by Mitsui Chemicals, Inc., IPDI's trimethylolpropane adduct body) • b-6: Desmodule Z4470BA (manufactured by Sumika Covestro Urethane Co., Ltd., isocyanurate form of IPDI) • b-7: Stavio D-370N (manufactured by Mitsui Chemicals, Inc., isocyanurate derivative of 1,5-pentamethylene diisocyanate) Duranate, Takenate, Desumodo, and Stavio are all registered trademarks.

[0065] [Base material] (Acrylic film) • Technoloy S001G (manufactured by Sumitomo Chemical Co., Ltd., 125 μm; abbreviated as "Acrylic S001G" in the following table) • Acryprene HBS010P (manufactured by Mitsubishi Chemical Corporation, 75 μm; abbreviated as "Acrylic HBS010P" in the following table) (Urethane film) • Esmer URS PX98 (manufactured by Nippon Matai Co., Ltd., 50 μm, abbreviated as "Urethane PX98" in the table below) (PVC film) • Sumilight VSS-6702 (manufactured by Sumitomo Bakelite Co., Ltd., 60 μm, abbreviated as "PVC 6702" in the table below) (Polycarbonate film) • Panlite PC1151 (manufactured by Teijin Chemicals Ltd., 300 μm, abbreviated as "Polycarbonate PC1151" in the table below) (Easy-to-adhere PET film) • CosmoShine A4360 (manufactured by Toyobo Co., Ltd., 125 μm, abbreviated as "PET A4360" in the following table) Technoloy, Acryprene, Esmer, Sumilight, Panlight, and Cosmoshine are all registered trademarks.

[0066] <Preparation of hydroxyl group-containing (meth)acrylic component (a1)> (Synthesis Example 1) The hydroxyl group-containing (meth)acrylic component (a1) of the present invention was synthesized according to previously reported information. First, butyl acetate (56.9 parts by weight) was charged as a monomer into a reaction vessel equipped with a thermometer, stirrer, reflux tubing, dropping funnel, and nitrogen inlet tube, and refluxed. Next, 4-HBA (4.9 parts by weight), MMA (24.6 parts by weight), i-BMA (23.4 parts by weight), t-BMA (14.9 parts by weight), 2-EHA (15.6 parts by weight), CHMA (15.6 parts by weight), and AA (1.0 part by weight) were added dropwise over 4 hours as a polymerization initiator: Trigonox® BPIC-C75 (manufactured by Kayaku Nurion Co., Ltd., 5.2 parts by weight), followed by 4 hours of aging. After cooling, the solid content was adjusted to 50% with butyl acetate to obtain hydroxyl group-containing (meth)acrylic component a1-1.

[0067] (Synthesis examples 2-13, comparative synthesis examples 1-3) The synthesis was carried out in the same manner as in Synthesis Example 1, except for the change in composition shown in Table 2, yielding a1-2 to a1-13 as hydroxyl group-containing (meth)acrylic components (a1) and a2-1 to a2-3 as hydroxyl group-containing (meth)acrylic components (a2).

[0068] [Table 2]

[0069] Furthermore, Table 3 shows the results of calculating the solid content, glass transition temperature (Tg), hydroxyl value (based on solid content) X, number-average molecular weight Y, and hydroxyl index X / Y × 100 for the hydroxyl group-containing (meth)acrylic components (a1, a2) obtained in this manner.

[0070] [Table 3]

[0071] <Preparation of paint composition> As one embodiment, a method of preparation is shown in which solution A, which contains at least a hydroxyl group-containing component (a), and solution B, which contains at least an isocyanate-containing component (b), are mixed. [Liquid A] The hydroxyl group-containing component (a) and, if necessary, other components (c) were mixed and uniformly stirred using a disperser. A solid content of 30% to 70% is preferred. For example, a product designed with a solid content of 50% can be used. [Liquid B] The isocyanate-containing component (b) and, if necessary, other components (c) were mixed and uniformly stirred using a disperser. A solid content of 50% to 100% is preferred. For example, a product designed with a solid content of 70% can be used. Liquid A and Liquid B were mixed and uniformly stirred using a disperser so that the equivalent ratio of hydroxyl groups (OH) contained in the hydroxyl group-containing component (a) and isocyanate groups (NCO) contained in the isocyanate-containing component (b) (NCO / OH) was in the range of 0.5 to 2.0, thereby obtaining a paint composition. Here, an embodiment has been shown in which the invention is implemented as a two-component paint composition consisting of liquid A and liquid B. However, in implementing the present invention, liquid A and liquid B may be either the main component or the curing agent. Furthermore, a third liquid may be added to implement the invention as a multi-component paint composition.

[0072] <Evaluation Method> [Adhesion] To eliminate the contribution of additives in the paint composition to adhesion, the adhesion to the substrate was evaluated using test samples containing only a mixture of hydroxyl group-containing component (a) and isocyanate-containing component (b). The trend in adhesion to the substrate was similar regardless of the presence or absence of additives. The hydroxyl group-containing component (a) and the isocyanate-containing component (b) were uniformly stirred using a disperser to obtain a test sample, with an equivalent ratio of NCO / OH of 1.0. For each of the above-mentioned substrates, the test sample was applied using an applicator to achieve a dry film thickness of 50 μm, and the specimens were prepared by drying at 60°C for one day. For substrates with a film thickness of less than 100 μm, an unoriented polypropylene film (60 μm) was attached with adhesive as a reinforcing film to prevent deformation of the film during the drying process of the test samples. In accordance with JIS K 5600-5-6:1999, cuts were made on the surface of the coating of the test specimen using a utility knife to create 100 grid squares of 2 mm on each side. Test tape was then applied over the grid, and the remaining number of squares after the tape was quickly removed was evaluated according to the following criteria. ·Pass criteria ○: It is attached at a rate of 100 / 100. △: Adhering in 80 / 100 to 99 / 100. ×: Less than 80 / 100.

[0073] [water resistance] A paint composition was obtained according to the preparation method described above. The hydroxyl group-containing component (a) and the isocyanate-containing component (b) were mixed so that the equivalent ratio: NCO / OH was 1.0. Using an applicator, the material was applied to glass plates to achieve a dry film thickness of 50 μm, and the specimens were dried at 60°C for one day to prepare the test specimens. In accordance with JIS K 5600-6-1:2016, the test specimens were immersed in water at 20°C for 3 days, and the degree of blistering on the coating surface was visually assessed and evaluated according to the following criteria. ·Pass criteria ○: No swelling. △: Slight bulging present. ×: Has bulging.

[0074] (Example 1) Test samples were obtained using a1-1 as the hydroxyl group-containing component (a) and b-1 as the isocyanate-containing component (b), and their adhesion to various substrates was evaluated.

[0075] (Examples 2-13, Comparative Examples 1-3) The procedure was carried out in the same manner as in Example 1, except that the hydroxyl group-containing component (a) was changed to the component shown in Table 4.

[0076] [Table 4]

[0077] For urethane, PVC, polycarbonate, and easy-adhesion PET films, good adhesion was observed regardless of the glass transition temperature or hydroxyl index of the hydroxyl group-containing component (a). On the other hand, differences in adhesion were observed with respect to acrylic films depending on the glass transition temperature and hydroxyl index of the hydroxyl group-containing component (a). Here, differences in the tendency of adhesion were observed depending on the type of acrylic film, but in the case of a1, where the glass transition temperature of the hydroxyl group-containing component (a) is 85°C or lower and the hydroxyl index is between 0.10 and 5.00, good adhesion was observed regardless of the type of acrylic film.

[0078] (Examples 14-19) Next, a test sample was prepared in the same manner as in Example 1, except that the type of isocyanate-containing component (b) was changed as shown in Table 5, and "Acrylic S001G The adhesion to the film was evaluated.

[0079] [Table 5]

[0080] As shown in Table 5, the contribution of the hydroxyl group-containing component (a) is dominant to the adhesion to the substrate compared to the contribution of the composition of the isocyanate-containing component (b).

[0081] (Example 20) Next, the procedure was carried out in the same manner as in Example 1, except that a mixture of a1-1 and a2-1 was used as the hydroxyl group-containing component (a).

[0082] (Examples 21-31) The procedure was carried out in the same manner as in Example 1, except that the hydroxyl group-containing component (a) was a mixture of hydroxyl group-containing (meth)acrylic component (a1) and hydroxyl group-containing (meth)acrylic component (a2) in the weight ratio shown in Table 6.

[0083] [Table 6]

[0084] As shown in Table 6, the hydroxyl group-containing (meth)acrylic component (a2) alone sometimes exhibited poor adhesion to the acrylic film. However, when the hydroxyl group-containing (meth)acrylic component (a1) and the hydroxyl group-containing (meth)acrylic component (a2) were mixed in a weight ratio of 5:95, the adhesion to the acrylic film was partially improved. Furthermore, when mixed in a weight ratio of 10:90, the adhesion to the acrylic film was further improved.

[0085] (Example 32) Next, a1-1 (49.81 parts by weight) as the hydroxyl group-containing component (a), and other components (c) consisting of the dispersant DISPERBYK®-2000 (0.18 parts by weight), the pigment TIPAQUE® CR-95 (24.91 parts by weight), and butyl acetate (25.09 parts by weight) were mixed and uniformly stirred using a disperser to obtain solution A with a solid content of 50%. Using b-1 as the isocyanate-containing component (b) without dilution, solution B with a solid content of 70% was obtained. Liquids A and B were mixed so that the equivalent ratio of NCO / OH = 1.0, and the mixture was uniformly stirred using a disperser to obtain a paint composition. When the water resistance of the paint composition was evaluated, it received a rating of ○.

[0086] (Examples 33-47) The procedure was carried out in the same manner as in Example 32, except that the hydroxyl group-containing component (a) was changed to one of the components shown in Table 7.

[0087] [Table 7]

[0088] As shown in Table 7, the coating films formed by the coating compositions using the hydroxyl group-containing component (a) of the present invention all exhibited good water resistance. [Explanation of Symbols]

[0089] 1: Base material 2: Coating film formed by the coating composition of the present invention 3: Clear coating 4: Existing coating 5a: Shallow wound 5b: Shallow wound (scar) 6: Primer surfacer coating 7a: Deep wound 7b: Deep scar 8: Putty 9: Decorative items

Claims

1. A urethane coating composition comprising a hydroxyl group-containing component (a) and an isocyanate-containing component (b), The hydroxyl group-containing component (a) includes a hydroxyl group-containing (meth)acrylic component (a1), The hydroxyl group-containing (meth)acrylic component (a1) is The glass transition temperature is 85°C or lower. The hydroxyl value (based on solid content) X is 10 mg KOH / g or more and 180 mg KOH / g or less. The number-average molecular weight Y is between 2,000 and 20,000. The hydroxyl group index is between 0.10 and 5.

00. The hydroxyl group index is characterized by being an index obtained by "X / Y × 100" which is expressed by the ratio of X to Y. Urethane paint composition.

2. The hydroxyl group index is characterized to be 0.25 or more and 3.50 or less. The urethane coating composition according to claim 1.

3. The equivalent ratio of the hydroxyl group (OH) contained in the hydroxyl group-containing component (a) to the isocyanate group (NCO) contained in the isocyanate-containing component (b), namely NCO / OH, is 0.5 or more and 2.0 or less. The urethane coating composition according to claim 1.

4. The hydroxyl group-containing component (a) includes, in addition to the hydroxyl group-containing (meth)acrylic component (a1), a hydroxyl group-containing (meth)acrylic component (a2) that is different from the hydroxyl group-containing (meth)acrylic component (a1). The hydroxyl group-containing (meth)acrylic component (a2) is The above X is 40 mg KOH / g or more and 180 mg KOH / g or less, The above Y is 2,000 or more and 20,000 or less, The glass transition temperature is greater than 85°C, and / or the ratio of X to Y, "X / Y × 100", is greater than 5.

00. The solid content of the hydroxyl group-containing (meth)acrylic component (a1) is 10 parts by weight or more, relative to 100 parts by weight of the total solid content of the hydroxyl group-containing component (a). The urethane coating composition according to claim 1.

5. It is characterized by being used as a repair paint for damaged areas of existing coatings formed on articles. The urethane coating composition according to claim 1.

6. It is characterized by being used as a repair paint for damaged areas of decorative articles to which decorative films have been applied. The urethane coating composition according to claim 1.

7. At least the following steps: The process of preparing and pre-treating the painted items to be repaired. A step of applying the paint composition described in claim 5 to the area to be repaired to obtain a repair coating film, A step of drying the aforementioned repair coating to obtain a repaired painted article, A method for repairing and painting a painted article, characterized by including the following:

8. At least the following steps: The process of preparing and pre-treating the decorative article to be repaired, A step of applying the paint composition described in claim 6 to the area to be repaired to obtain a repair coating film, A step of drying the aforementioned repair coating to obtain a repaired painted article, A method for repairing and painting a decorative article, characterized by including the following:

9. Painted items to be repaired, The painted article comprises a painted and dried repair coating formed on the repair area, The repair coating is characterized in that the coating is made of the urethane coating composition described in claim 5 or 6. Repair and painting items.

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