Modified blocked polyisocyanate, coating composition, coating layer and method for forming coating layer

Abstract

To provide a novel coating composition with superior curability and a modified blocked polyisocyanate for use in the coating composition.SOLUTION: The present invention provides a modified blocked polyisocyanate which is a blocked polyisocyanate modified with a cyclic amino alcohol represented by formula (I).SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to modified blocked polyisocyanates, coating compositions, coatings, and methods for forming coatings. [Background technology]

[0002] Polyisocyanates have been known as curing agents used in paints, etc. For example, polyurethane resin paints that combine polyols and polyisocyanates are known to have very good abrasion resistance, chemical resistance, and stain resistance.

[0003] Paints using polyisocyanate as a curing agent are generally two-liquid compositions, in which the base agent (e.g., polyol) and polyisocyanate are stored separately and mixed when used for painting. However, once mixed, the paint hardens in a short time, so the pot life is short, and there are problems with workability when painting. In addition, since polyisocyanate easily reacts with water, it was impossible to use the above-mentioned paint in water-based paints such as electrodeposition paints.

[0004] As a method for dealing with these problems, a method is known in which polyisocyanate is inactivated by reacting it with a blocking agent. The blocked polyisocyanate obtained by this method does not react with the base agent (polyol, etc.) at room temperature, but when heated, the blocking agent dissociates, regenerating the isocyanate group, which then reacts with the base agent to form a crosslink. Therefore, according to the above method, the pot life is not limited, and it is possible to mix the base agent and the curing agent in advance to form a paint, and it is also possible to apply polyisocyanate to water-based paints.

[0005] In paints that use blocked polyisocyanate as a curing agent, catalysts (blocking agent dissociation catalysts) such as quaternary ammonium salts are sometimes used to reduce the thermal energy required to dissociate the blocking agent (see Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2014-084426 A Summary of the Invention [Problem to be solved by the invention]

[0007] Conventionally, paints have been baked at high temperatures of 150°C or higher, but in recent years, there has been a demand for curing paint films at lower temperatures (for example, at temperatures of 140°C or lower) than conventionally in order to reduce costs and carbon dioxide emissions during baking coating, and to suppress deterioration of the coated object due to heat. Therefore, it is also important that the paint composition has good curability, that is, that a paint film with good hardness and gel fraction can be formed when the paint composition is baked at a lower temperature than conventionally. In this regard, the above-mentioned quaternary ammonium salt improves the curability of the paint composition containing the blocked polyisocyanate, and makes it possible to cure the paint film even at a temperature of 140°C or lower. On the other hand, there is little known about a method for obtaining a paint composition with excellent curability without adding a blocking agent dissociation catalyst such as a quaternary ammonium salt.

[0008] Some aspects of the present disclosure have an object to provide a novel coating composition having excellent curing properties and a modified blocked polyisocyanate for use in the coating composition. [Means for solving the problem]

[0009] As a result of the investigations by the inventors of the present disclosure, it has become clear that by using a blocked polyisocyanate modified with a cyclic amino alcohol having a specific structure (modified blocked polyisocyanate), a coating composition having excellent curability can be obtained without adding a blocking agent dissociation catalyst. The present disclosure has been made based on the findings of the above inventors.

[0010] The present disclosure provides at least the following [1] to [6].

[0011] [1] A modified blocked polyisocyanate which is a blocked polyisocyanate modified with a cyclic amino alcohol represented by the following formula (I): [ka] [In formula (I), R 1 ~R 5 each independently represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms, a and b each independently represent 0 or 1, and a+b represents 1.]

[0012] [2] The modified blocked polyisocyanate according to [1], which contains a structure derived from an aliphatic polyisocyanate having 4 to 6 carbon atoms or a derivative thereof.

[0013] [3] The modified blocked polyisocyanate according to [1] or [2], which has at least one group selected from the group consisting of an isocyanate group blocked with an oxime-based blocking agent, an isocyanate group blocked with a pyrazole-based blocking agent, and an isocyanate group blocked with an imidazole-based blocking agent.

[0014] [4] A coating composition comprising a base agent and a curing agent, A coating composition, wherein the curing agent comprises the modified blocked polyisocyanate according to any one of [1] to [3].

[0015] [5] A coating film formed from the coating composition described in [4].

[0016] [6] A method for forming a coating film, comprising the steps of applying the coating composition according to [4] to a substrate and heating the composition at 120 to 140°C to cure the composition. Effect of the Invention

[0017] According to some aspects of the present disclosure, it is possible to provide a novel coating composition having excellent curing properties and a modified blocked polyisocyanate used in the coating composition. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, exemplary embodiments of the present disclosure will be described. However, the present disclosure is not limited to the following embodiments. In this specification, a numerical range indicated using "~" indicates a range including the numerical values ​​before and after "~" as the minimum and maximum values, respectively. In addition, unless specifically stated otherwise, the units of the numerical values ​​before and after "~" are the same. In addition, the upper limit and lower limit values ​​individually stated can be combined in any combination.

[0019] <Modified blocked polyisocyanate> The modified blocked polyisocyanate according to one embodiment of the present disclosure is a blocked polyisocyanate modified with a cyclic amino alcohol represented by the following formula (I) (hereinafter also referred to as "cyclic amino alcohol (I)"). [ka]

[0020] In formula (I), R 1 ~R 5 each independently represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms, a and b each independently represent 0 or 1, and a+b represents 1. 1 ~R 5 may be the same or different from each other.

[0021] The modified blocked polyisocyanate can provide a novel coating composition with excellent curability. That is, the modified blocked polyisocyanate can provide a coating composition capable of forming a coating film with good hardness and gel fraction even when baked at a temperature of 140° C. or less (for example, 120 to 140° C.). In addition, since the modified blocked polyisocyanate itself can function as a blocking agent dissociation catalyst, it can dissociate the blocking agent by heating to generate isocyanate groups (free isocyanate groups) even in the absence of a blocking agent dissociation catalyst. Therefore, the modified blocked polyisocyanate can provide a coating composition that is less likely to cause coloring of the coating film due to blocking agent dissociation catalysts such as quaternary ammonium salts.

[0022] The modified blocked polyisocyanate has, for example, a structure derived from an unblocked polyisocyanate, an isocyanate group blocked with a blocking agent (hereinafter also referred to as a "blocked isocyanate group"), and an isocyanate group modified with a cyclic amino alcohol (I) (hereinafter also referred to as a "modified isocyanate group").

[0023] (Unblocked Polyisocyanate) The unblocked polyisocyanate is a polyisocyanate that does not have the above-mentioned blocked isocyanate group. The unblocked polyisocyanate has a plurality of isocyanate groups (free isocyanate groups). Examples of the unblocked polyisocyanate include aromatic polyisocyanates, aliphatic polyisocyanates, alicyclic polyisocyanates, and polyisocyanate derivatives thereof. Examples of the derivatives include isocyanurates, allophanates, biuret compounds, and the like.

[0024] From the viewpoint of improving the yellowing resistance of the cured coating film, the unblocked polyisocyanate is preferably one that does not have an aromatic ring, that is, a non-aromatic polyisocyanate. Examples of non-aromatic polyisocyanates include aliphatic polyisocyanates such as hexamethylene diisocyanate, tetramethylene diisocyanate, 2-methyl-pentane-1,5-diisocyanate, 3-methyl-pentane-1,5-diisocyanate, lysine triisocyanate, and trioxyethylene diisocyanate; alicyclic polyisocyanates such as isophorone diisocyanate, cyclohexyl diisocyanate, hydrogenated diphenylmethane diisocyanate, norbornane diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated xylene diisocyanate, and hydrogenated tetramethylxylene diisocyanate, and derivatives thereof.

[0025] From the viewpoint of easily obtaining a coating composition having excellent curability, the unblocked polyisocyanate preferably contains an aliphatic polyisocyanate having 4 to 6 carbon atoms or a derivative thereof, and more preferably contains hexamethylene diisocyanate or a derivative thereof. In other words, the modified blocked polyisocyanate preferably has a structure derived from an aliphatic polyisocyanate having 4 to 6 carbon atoms or a derivative thereof, and more preferably has a structure derived from hexamethylene diisocyanate or a derivative thereof. As the derivative of hexamethylene diisocyanate, at least one selected from the group consisting of an isocyanurate, an allophanate, and a biuret is preferably used, and an isocyanurate is more preferably used. When the unblocked polyisocyanate contains an isocyanurate, from the viewpoint of further improving the hardness of the coating film, the content of the isocyanurate trimer (isocyanurate trimer content) based on the total mass of the unblocked polyisocyanate is preferably 50% by mass or more, and the content of the isocyanurate group (isocyanurate group content) relative to the total (100 mol%) of the isocyanurate group and allophanate group in the unblocked polyisocyanate is preferably more than 80 mol%. The upper limit of the isocyanurate trimer content may be 80% by mass, and the upper limit of the isocyanurate group content may be 99 mol%.

[0026] (Blocked isocyanate group) The blocked isocyanate group is an isocyanate group blocked with a blocking agent and has a structure derived from the blocking agent. In other words, the blocked isocyanate group can be defined as a group formed by the reaction between the blocking agent and an isocyanate group.

[0027] Examples of blocking agents include alcohol-based blocking agents such as methanol, ethanol, n-butanol, isobutanol, 2-ethylhexanol, butyl cellosolve, propylene glycol monomethyl ether, ethylene glycol, and benzyl alcohol; phenol-based blocking agents such as phenol, cresol, ethylphenol, butylphenol, and 2-hydroxypyridine; lactam-based blocking agents such as ε-caprolactam, δ-valerolactam, and γ-butyrolactam; oxime-based blocking agents such as formaldoxime, acetaldoxime, acetoneoxime, methylethylketoxime, methylisobutylketoxime, and cyclohexanoneoxime; imidazole, 2-methylimidazole, 4-methylimidazole, 2,4-dimethylimidazole, and the like. Examples of the blocking agent include imidazole, 2-ethylimidazole, 2-propylimidazole, 2-isopropylimidazole, 4-methyl-2-propylimidazole, 2-phenylimidazole, 4-phenylimidazole, 5-phenylimidazole, 2-methyl-4-phenylimidazole, 2-ethyl-4-methylimidazole, 2-undecylimidazole, and 2-heptadecylimidazole; pyrazole blocking agents such as 3,5-dimethylpyrazole, 3-methylpyrazole, and pyrazole; amine blocking agents such as diphenylamine, diisopropylamine, and isopropylethylamine; and triazole blocking agents such as triazole, 1,2,4-triazole, and 3,5-dimethyl-1,2,4-triazole. From the viewpoint of storage stability, oxime blocking agents are preferred, and methyl ethyl ketoxime is more preferred. From the viewpoint of curability, pyrazole blocking agents are preferred, and 3,5-dimethylpyrazole is more preferred. From the viewpoint of suppressing coloration of the coating film, oxime-based blocking agents and pyrazole-based blocking agents are preferred. From the viewpoint of obtaining a coating composition with superior curability, pyrazole-based blocking agents and imidazole-based blocking agents are preferred, and 3,5-dimethylpyrazole, 2-phenylimidazole and 2-ethyl-4-methylimidazole are more preferred.

[0028] From the above viewpoint, in one embodiment, it is preferable that the modified blocked polyisocyanate has at least one group selected from the group consisting of an isocyanate group blocked with an oxime-based blocking agent, an isocyanate group blocked with a pyrazole-based blocking agent, and an isocyanate group blocked with an imidazole-based blocking agent.

[0029] (Modified isocyanate group) The modified isocyanate group is an isocyanate group modified with a cyclic amino alcohol (I). The modified isocyanate group can also be described as a group formed by the reaction of the cyclic amino alcohol (I) with an isocyanate group. The modified isocyanate group has, for example, a structure represented by the following formula (Ia). [ka]

[0030] R in formula (Ia) 1 ~R 5 and a and b are R 1 ~R 5 , and has the same meaning as a and b, and * represents a bond.

[0031] R 1 ~R 5 Examples of the alkyl group having 1 to 4 carbon atoms represented by the formula (I) include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, an s-butyl group, and a t-butyl group. 1 ~R 5 Examples of the alkoxy group having 1 to 4 carbon atoms represented by the formula (I) include a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxy group, an s-butoxy group, and a t-butoxy group.

[0032] From the viewpoint of further improving the curability, R 1 is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms, and R 2 ~R 4 are each independently a hydrogen atom or a methyl group, R 5is preferably a hydrogen atom, and R 1 ~R 4 are each independently a hydrogen atom or a methyl group, R 5 is more preferably a hydrogen atom, and R 1 ~R 5 It is more preferable that all of are hydrogen atoms.

[0033] Preferred specific examples of the cyclic amino alcohol (I) include compounds represented by the following formulas 1 to 24. [ka]

[0034] The content of the modified isocyanate group may be 0.1 to 30 mass%, 0.5 to 20 mass%, or 1 to 10 mass%, based on the total mass of the compound obtained by dissociating the blocking agent from the modified blocked polyisocyanate.

[0035] The modified blocked polyisocyanate may have a free isocyanate group, but from the viewpoint of storage stability, it is preferable that the modified blocked polyisocyanate does not have a free isocyanate group. For example, all of the effective isocyanate groups in the modified blocked polyisocyanate may be blocked isocyanate groups. Here, the effective isocyanate group means both a free isocyanate group and a blocked isocyanate group.

[0036] The effective isocyanate group content of the modified blocked polyisocyanate (hereinafter referred to as "effective NCO content") may be 4 to 28 mass%, 5 to 25 mass%, or 6 to 22 mass% from the viewpoint of further enhancing the curability of the coating material. Here, the effective NCO content is the isocyanate group present in the modified blocked polyisocyanate that can participate in a crosslinking reaction, expressed in mass%. The effective NCO content can be rephrased as the content (free NCO content) of the free isocyanate group in the compound obtained by dissociating the blocking agent from the modified blocked polyisocyanate relative to the total mass of the modified blocked polyisocyanate. The free NCO content can be determined by reacting the isocyanate group in the measurement sample (the compound obtained by dissociating the blocking agent from the modified blocked polyisocyanate) with an excess of secondary amine, and then back titrating the unreacted secondary amine with hydrochloric acid.

[0037] The weight average molecular weight of the modified blocked polyisocyanate may be, for example, 600 to 4000. When the weight average molecular weight of the modified blocked polyisocyanate is within such a range, the curability tends to be further improved. From the same viewpoint, the weight average molecular weight of the modified blocked polyisocyanate may be 700 or more or 800 or more, and 3500 or less or 3000 or less. The weight average molecular weight in this specification is a standard polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0038] The modified blocked polyisocyanate can be obtained, for example, by reacting a polyisocyanate having a free isocyanate group, such as an unblocked polyisocyanate, with a blocking agent and a cyclic amino alcohol (I). That is, the modified blocked polyisocyanate can be a reaction product of a polyisocyanate having a free isocyanate group, a blocking agent and a cyclic amino alcohol (I). The polyisocyanate having a free isocyanate group, the blocking agent and the cyclic amino alcohol (I) may each be used alone or in combination of two or more. However, from the viewpoint of improving the yellowing resistance of the cured coating film, it is preferable not to use an aromatic polyisocyanate as the polyisocyanate having a free isocyanate group.

[0039] The order in which the polyisocyanate having a free isocyanate group, the blocking agent, and the cyclic aminoalcohol (I) are reacted is not particularly limited. It is preferable to react the polyisocyanate having a free isocyanate group with the cyclic aminoalcohol (I) to obtain an isocyanate group-terminated precursor, and then react the obtained isocyanate group-terminated precursor with the blocking agent.

[0040] The reaction between the polyisocyanate having a free isocyanate group and the cyclic amino alcohol (I) may be carried out, for example, in the presence of a solvent. As the solvent, aromatic solvents such as toluene and xylene, ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, ester solvents such as ethyl acetate and butyl acetate, and glycol ether solvents such as ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, and diethylene glycol diethyl ether can be used. The reaction temperature may be 20 to 200°C. The reaction time may be, for example, 1 to 10 hours. The above reaction proceeds even without a catalyst, but the reaction can also be accelerated by using a known urethane reaction catalyst.

[0041] The reaction between the isocyanate-terminated precursor and the blocking agent can be carried out according to the reaction conditions of a normal blocking reaction. The reaction between the isocyanate-terminated precursor and the blocking agent can be carried out at room temperature or with heating. Regardless of whether or not heating is carried out, the temperature of the reaction liquid can be, for example, 20 to 200°C.

[0042] The amount of polyisocyanate, blocking agent and cyclic amino alcohol (I) used may be adjusted so that the content of modified isocyanate groups falls within the above range. For example, in the above method, 0.1 to 60 mol% of cyclic amino alcohol (I) may be used based on the total number of moles of free isocyanate groups in the polyisocyanate before blocking. When polyisocyanate and blocking agent are reacted before modification with cyclic amino alcohol, 40 to 99 mol% of blocking agent may be used based on the total number of moles of free isocyanate groups in the polyisocyanate before blocking, and 0.1 to 60 mol% of cyclic amino alcohol (I) may be used based on the total number of moles of free isocyanate groups in the obtained blocked polyisocyanate.

[0043] The modified blocked polyisocyanate may be a compound derived from a reaction product of a polyisocyanate having a free isocyanate group, a blocking agent, and a cyclic amino alcohol (I). The modified blocked polyisocyanate may be, for example, a compound obtained by reacting a reaction product of a polyisocyanate having a free isocyanate group, a blocking agent, and a cyclic amino alcohol (I) with a compound capable of reacting with the free isocyanate group in the reaction product (e.g., an active hydrogen group-containing compound, etc.).

[0044] The modified blocked polyisocyanate described above is preferably used as a curing agent for a coating composition. That is, another embodiment of the present disclosure is a curing agent for a coating material, comprising the modified blocked polyisocyanate. The curing agent for the coating material may contain a blocking agent dissociation catalyst, but from the viewpoint of suppressing coloration of the coating film, it is preferable that the curing agent does not contain a quaternary ammonium salt.

[0045] <Paint composition> A coating composition according to another embodiment of the present disclosure comprises a base agent and a curing agent, and the curing agent comprises the modified blocked polyisocyanate according to the above embodiment.

[0046] The coating composition contains the modified blocked polyisocyanate of the embodiment, and therefore has excellent curing properties. Therefore, the coating composition can form a coating film having good hardness and gel fraction even when baked at a lower temperature than conventional (for example, at a temperature of 140°C or lower). In addition, the coating composition can easily form a coating film with reduced coloring by adjusting the amount of the quaternary ammonium salt.

[0047] (Main ingredient) The base agent contains, for example, an active hydrogen group-containing compound. Examples of the active hydrogen group include a hydroxy group and an amino group. The active hydrogen group-containing compound has an average number of functional groups (average number of active hydrogen groups) of 2 or more, preferably 2 to 50. Examples of active hydrogen-containing compounds having such an average number of functional groups include polyols, polyamines, and amino alcohols. In particular, when the base agent contains a polyol as the active hydrogen group-containing compound, it is easy to obtain better curing properties and a coating film with less coloring.

[0048] The number average molecular weight of the active hydrogen group-containing compound is, for example, 500 to 20,000, and preferably 500 to 10,000. Examples of active hydrogen group-containing compounds having such a number average molecular weight include polyurethane resins, polyamide resins, saturated or unsaturated polyester resins, alkyd resins modified with saturated or unsaturated fatty acids, acrylic resins, fluororesins, epoxy resins, and cellulose resins (all of which are resins having active hydrogen groups). Furthermore, in consideration of the coating film performance such as gloss, body feel, hardness, durability, flexibility, and drying property, and cost, saturated or unsaturated polyester resins, alkyd resins modified with saturated or unsaturated fatty acids, and acrylic resins are preferred.

[0049] The active hydrogen group-containing compound may be used alone or in combination of two or more kinds.

[0050] (hardening agent) The curing agent includes the modified blocked polyisocyanate of the above embodiment. The modified blocked polyisocyanate may be used alone or in combination of two or more. For example, two or more modified blocked polyisocyanates derived from different types of unblocked polyisocyanates may be used in combination. The curing agent may further include an isocyanate compound (a compound having an isocyanate group) other than the modified blocked polyisocyanate of the above embodiment. The content of the isocyanate compound may be 0 to 40 mass%, 0 to 20 mass%, or 0 to 10 mass%, based on the total mass of the isocyanate compounds in the curing agent.

[0051] The blending ratio of the base agent and the curing agent in the coating composition may be adjusted based on the ratio of the total amount of effective isocyanate groups in the curing agent to the total amount of active hydrogen groups in the base agent. The ratio of the total amount of effective isocyanate groups in the curing agent to the total amount of active hydrogen groups in the base agent is preferably 1 / 9 to 9 / 1, more preferably 2 / 8 to 8 / 2, in molar ratio. When the molar ratio is within the above range, better curability can be obtained.

[0052] The coating composition may further contain, as other components, additives such as pigments, dispersion stabilizers, viscosity modifiers, leveling agents, antigelling agents, light stabilizers, antioxidants, ultraviolet absorbers, heat resistance improvers, inorganic and organic fillers, plasticizers, lubricants, antistatic agents, reinforcing materials, catalysts, etc. These components may be contained in the base agent or the curing agent.

[0053] The coating composition may contain a solvent as another component. Examples of the solvent include benzene, toluene, xylene, cyclohexane, acetone, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, n-butyl acetate, cellosolve acetate, propylene glycol monomethyl ether acetate, diethylene glycol dimethyl ether, and 1,4-dioxane. These solvents may be used alone or in combination of two or more. The content of the solvent may be 0 to 95% by mass, 5 to 90% by mass, or 10 to 80% by mass based on the total mass of the coating composition.

[0054] The coating composition may contain an unblocked polyisocyanate (e.g., a polyisocyanate remaining as an unreacted substance) or may contain a blocking agent (e.g., a blocking agent remaining as an unreacted substance). The content of the unblocked polyisocyanate contained in the coating composition may be 5% by mass or less, or may be 0% by mass, based on the total solid content of the coating composition. The content of the blocking agent contained in the coating composition may be 5% by mass or less, or may be 0% by mass, based on the total solid content of the coating composition.

[0055] The coating composition may be a one-liquid type composition in which all of the components are contained in one liquid, or a multi-liquid type composition in which the components are present separately in multiple liquids. The multi-liquid type coating composition may comprise a first liquid containing a base agent and a second liquid containing a curing agent.

[0056] The coating composition can be used as an automotive topcoat paint, anti-chipping paint, electrodeposition paint, paint for automotive parts, paint for automotive repair, pre-coated metal and rust-proof steel plate for metal products such as home appliances and office equipment, paint for building materials, paint for plastics, adhesive, adhesion promoter, sealant, etc.

[0057] <Coating film and coating film formation method> Another embodiment of the present disclosure is a coating film formed from the coating composition of the above embodiment. Also, another embodiment of the present disclosure is a method for forming a coating film, comprising the steps of applying the coating composition of the above embodiment to a substrate and curing the coating film (uncured coating film) made of the coating composition.

[0058] The coating film may be an uncured coating film made of the coating composition of the above embodiment, or may be a coating film (cured coating film) formed by curing the uncured coating film. The thickness of the coating film is, for example, 5 to 40 μm. The coating film may be a thin film with a thickness of less than 20 μm.

[0059] The coating composition may be applied by a known method such as roll coating, curtain flow coating, spray coating, electrostatic coating, bell coating, electrodeposition coating, etc. The amount of coating composition to be applied, the thickness of the coating film, etc. may be appropriately determined depending on the material of the surface to be coated, etc.

[0060] The coating film (uncured coating film) made of the coating composition may be cured by heating the coating film. The heating temperature (baking temperature) may be, for example, 200° C. or lower, and the heating time (baking time) may be, for example, 10 to 180 minutes. Conventionally, baking of coating compositions has been carried out at high temperatures of 150° C. or higher, but according to the coating composition of the present embodiment, a good cured coating film can be obtained even when baking is carried out at 140° C. or lower (for example, 120 to 140° C.).

[0061] Examples of the substrate include molded articles made of materials such as stainless steel, phosphate-treated steel, zinc-coated steel, iron, copper, aluminum, brass, glass, acrylic polyol, polycarbonate resin, polyethylene terephthalate resin, polyethylene naphthalate resin, polybutylene phthalate resin, polystyrene resin, AS resin, ABS resin, polycarbonate-ABS resin, 6-nylon resin, 6,6-nylon resin, MXD6 nylon resin, polyvinyl chloride resin, polyvinyl alcohol resin, polyurethane resin, phenol resin, melamine resin, polyacetal resin, chlorinated polyolefin resin, polyolefin resin, polyamide resin, polyether ether ketone resin, polyphenylene sulfide resin, NBR resin, chloroprene resin, SBR resin, and SEBS resin, and surface-treated articles of the molded articles. The surface-treated article may be a molded article (surface-treated molded article) made of an olefin resin such as polyethylene or polypropylene that has been subjected to a surface treatment such as a corona discharge treatment. EXAMPLES

[0062] The contents of the present disclosure will be described in more detail below using examples, comparative examples, and reference examples, but the present disclosure is not limited to the following examples.

[0063] <Synthesis Example 1: Synthesis of Polyisocyanate A-1> In a four-neck flask equipped with a stirrer, a thermometer, a heating device, a nitrogen seal tube, and a cooling tube, 995 g of hexamethylene diisocyanate (hereinafter referred to as HDI), 5.0 g of 1,3-butanediol (manufactured by Tokyo Chemical Industry Co., Ltd.), and 0.3 g of phenol (manufactured by Tokyo Chemical Industry Co., Ltd.) were charged, and a urethane reaction was carried out at 80 ° C. for 2 hours under a nitrogen stream. Then, 0.04 g of potassium 2-ethylhexanoate (manufactured by Tokyo Chemical Industry Co., Ltd.), which is an isocyanurate catalyst, was added, and an isocyanurate reaction was carried out at 70 ° C. for 2 hours. After the NCO content reached 40.0 mass%, 0.15 g of JP-508 (manufactured by Johoku Chemical Industry Co., Ltd.) was added, a termination reaction was carried out, and the reaction liquid was cooled to room temperature. This reaction liquid was subjected to thin-film distillation at a temperature of 130 ° C. and a pressure of 0.04 kPa to remove unreacted HDI, and a purified polyisocyanate A-1 was obtained. The NCO content of Polyisocyanate A-1 was 21.8% by mass, and the viscosity at 25°C was approximately 2,500 mPa·s.

[0064] ( 1 H-NMR: Measurement of isocyanurate group content) Polyisocyanate A-1 1 H-NMR measurement was carried out to determine the isocyanurate group content (the content of isocyanurate groups relative to the total of isocyanurate groups and allophanate groups (100 mol%)). Specifically, the isocyanurate group content was calculated from the area of ​​the signal of the hydrogen atom of the methylene group adjacent to the nitrogen atom of the isocyanurate group at around 3.7 ppm and the signal of the hydrogen atom bonded to the nitrogen atom of the allophanate group at around 8.5 ppm. The isocyanurate group content was 89 mol%. 1 H-NMR measurements were performed under the following conditions. [Measurement conditions] (1) Measuring device: ECX400M (manufactured by JEOL Ltd., 1 H-NMR) (2) Measurement temperature: 23℃ (3) Sample concentration: 0.1 g / 1 ml (4) Number of times accumulated: 16 (5) Relaxation time: 5 seconds (6) Solvent: Deuterium dimethyl sulfoxide (7) Chemical shift standard: hydrogen atom signal of methyl group in deuterium dimethyl sulfoxide (2.5 ppm)

[0065] <Example 1> (Preparation of Modified Blocked Polyisocyanate Composition) In a four-neck flask equipped with a stirrer, a thermometer, a heating device, a nitrogen seal tube, and a cooling tube, 510 g of polyisocyanate A-1 and 27 g of RZETA (manufactured by Tosoh Corporation, 1,4-diazabicyclo[2,2,2]octane-2-methanol, "RZETA" is a registered trademark (hereinafter the same)) were charged, and the flask was replaced with nitrogen. The flask was heated to a reaction temperature of 80°C while stirring, and reacted at the same temperature for 2 hours. 250 g of butyl acetate (manufactured by Kishida Chemical Co., Ltd.) was charged into the resulting reaction liquid and stirred for 30 minutes, after which 213 g of methyl ethyl ketoxime (manufactured by Ube Industries, "MEKO" in the table) was charged in three separate portions so that the temperature did not exceed 80°C. Then, the reaction was carried out at 70°C for 2 hours, and the infrared absorption spectrum (IR measurement) showed a peak of NCO group (2270 cm -1 When the solids concentration (content of modified blocked polyisocyanate) disappeared, the mixture was cooled to room temperature to obtain a composition containing modified blocked polyisocyanate (hereinafter referred to as "modified blocked polyisocyanate composition (1)"). The solids concentration of the composition (content of modified blocked polyisocyanate) was 75 mass%, and the weight average molecular weight of the modified blocked polyisocyanate was 1537 g / mol. The weight average molecular weight in this example is the weight average molecular weight in terms of standard polystyrene, and was determined by GPC measurement under the following conditions. [Measurement conditions] (1) Measuring device: HLC-8420 (manufactured by Tosoh Corporation) (2) Column: TSKgel (Tosoh Corporation) G3000H-XL, G2000H-XL, G1000H-XL, one of each connected in series (3) Carrier: Tetrahydrofuran (4) Detection method: Differential refractive index detector

[0066] (Preparation of Coating Composition) A coating composition of Example 1 was prepared by mixing 52 g of ACRYDIC A-801 (trade name, manufactured by DIC Corporation, acrylic polyol, solid content concentration: 50 mass%, hydroxyl value: 50 mgKOH / g), 19 g of the modified blocked polyisocyanate composition (1), and 29 g of butyl acetate.

[0067] (Cure Evaluation) [Martens hardness measurement] The coating composition prepared above was applied to a color steel plate (white) so that the thickness before drying was 100 μm. The resulting coating film was left at room temperature for 60 minutes, and then baked by heating for 20 minutes in a thermostatic chamber at 130° C. The indentation strength of the coating film after baking (cured coating film) was measured under the following conditions in accordance with ISO 14577. The results are shown in Table 1. 〔conditions〕 Test equipment: Fischerscope HM2000 (manufactured by Fisher Instruments) Indenter: Vickers diamond Test load: 5mN Test temperature: 25℃

[0068] [Gel fraction measurement] The coating composition prepared above was applied to a release paper so that the thickness before drying was 200 μm. The obtained coating film was left at room temperature for 60 minutes, and then baked by heating in a thermostatic chamber at 130° C. for 20 minutes. The baked coating film (cured coating film) was immersed in methyl ethyl ketone at room temperature for 24 hours to determine the gel fraction. The gel fraction was calculated from the following formula. The results are shown in Table 1. Gel fraction (unit: mass%) = mass of coating film after immersion (mass of undissolved part) / mass of coating film before immersion × 100

[0069] (Evaluation of the coloring of the coating film) The coating composition prepared above was applied to a color steel plate (white) so that the thickness before drying was 100 μm. The obtained coating film was left at room temperature for 60 minutes, and then baked by heating for 60 minutes in a thermostatic chamber at 160 ° C. The b* value of the coating film (cured coating film) after baking was measured according to the CIE Lab standard using a BYK-GARDNER colorimeter (product name: SPECTRO2GUIDE) to evaluate the coloring degree of the coating film. The results are shown in Table 1.

[0070] <Example 2> (Preparation of Modified Blocked Polyisocyanate Composition) In a four-neck flask equipped with a stirrer, thermometer, heating device, nitrogen seal tube, and cooling tube, 494 g of polyisocyanate A-1 and 26 g of RZETA were charged, the atmosphere in the flask was replaced with nitrogen, and the reaction temperature was heated to 80°C while stirring, and the reaction was carried out at the same temperature for 2 hours. 250 g of butyl acetate was charged into the resulting reaction liquid and stirred for 30 minutes, after which 230 g of 3,5-dimethylpyrazole (manufactured by Tokyo Chemical Industry Co., Ltd., "DMP" in the table) was charged in three separate portions so that the temperature did not exceed 80°C. The reaction was then carried out at 70°C for 2 hours, and the infrared absorption spectrum (IR measurement) showed a peak of the NCO group (2270 cm -1 When the solids concentration (content of the modified blocked polyisocyanate) disappeared, the mixture was cooled to room temperature to obtain a composition containing the modified blocked polyisocyanate (hereinafter referred to as "modified blocked polyisocyanate composition (2)"). The solids concentration of the composition (content of the modified blocked polyisocyanate) was 75 mass%, and the weight average molecular weight of the modified blocked polyisocyanate was 1622 g / mol.

[0071] (Preparation of Coating Composition) The coating composition of Example 2 was prepared by mixing 51 g of ACRYDIC A-801, 19 g of the modified blocked polyisocyanate composition (2), and 30 g of butyl acetate.

[0072] (evaluation) The curability of the coating composition prepared above and the coloring degree of the coating film made of the coating composition were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0073] <Example 3> (Preparation of Modified Blocked Polyisocyanate Composition) In a four-neck flask equipped with a stirrer, thermometer, heating device, nitrogen seal tube, and cooling tube, 429 g of polyisocyanate A-1 and 23 g of RZETA were charged, the atmosphere in the flask was replaced with nitrogen, and the reaction temperature was heated to 80°C while stirring, and the reaction was carried out at the same temperature for 2 hours. 250 g of butyl acetate was charged into the resulting reaction liquid and stirred for 30 minutes, after which 300 g of 2-phenylimidazole (manufactured by Tokyo Chemical Industry Co., Ltd., "2-PI" in the table) was charged in three separate portions so that the temperature did not exceed 80°C. The reaction was then carried out at 70°C for 2 hours, and the infrared absorption spectrum (IR measurement) showed a peak of the NCO group (2270 cm -1 When the solids concentration (content of the modified blocked polyisocyanate) disappeared, the mixture was cooled to room temperature to obtain a composition containing the modified blocked polyisocyanate (hereinafter referred to as "modified blocked polyisocyanate composition (3)"). The solids concentration of the composition (content of the modified blocked polyisocyanate) was 75 mass%, and the weight average molecular weight of the modified blocked polyisocyanate was 2075 g / mol.

[0074] (Preparation of Coating Composition) The coating composition of Example 3 was prepared by mixing 49 g of ACRYDIC A-801, 21 g of the modified blocked polyisocyanate composition (3), and 30 g of butyl acetate.

[0075] (evaluation) The curability of the coating composition prepared above and the coloring degree of the coating film made of the coating composition were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0076] <Example 4> (Preparation of Modified Blocked Polyisocyanate Composition) In a four-neck flask equipped with a stirrer, thermometer, heating device, nitrogen seal tube, and cooling tube, 473 g of polyisocyanate A-1 and 25 g of RZETA were charged, the atmosphere in the flask was replaced with nitrogen, and the reaction was heated to a reaction temperature of 80°C while stirring, and allowed to react at the same temperature for 2 hours. 250 g of butyl acetate was charged into the resulting reaction liquid and stirred for 30 minutes, after which 252 g of 2-ethyl 4-methylimidazole (manufactured by Tokyo Chemical Industry Co., Ltd., "2E4MZ" in the table) was charged in three separate portions so that the temperature did not exceed 80°C. The reaction was then allowed to proceed for 2 hours at 70°C, and the infrared absorption spectrum (IR measurement) showed a peak of the NCO group (2270 cm -1 When the solids concentration (content of the modified blocked polyisocyanate) disappeared, the mixture was cooled to room temperature to obtain a composition containing the modified blocked polyisocyanate (hereinafter referred to as "modified blocked polyisocyanate composition (4)"). The solids concentration of the composition (content of the modified blocked polyisocyanate) was 75 mass%, and the weight average molecular weight of the modified blocked polyisocyanate was 1754 g / mol.

[0077] (Preparation of Coating Composition) The coating composition of Example 4 was prepared by mixing 50 g of ACRYDIC A-801, 20 g of the modified blocked polyisocyanate composition (4), and 30 g of butyl acetate.

[0078] (evaluation) The curability of the coating composition prepared above and the coloring degree of the coating film made of the coating composition were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0079] <Comparative Example 1> A composition containing a non-modified blocked polyisocyanate (hereinafter referred to as "non-modified blocked polyisocyanate composition (1)") was obtained in the same manner as in Example 1, except that RZETA was not used. The solids concentration of the composition (content of non-modified blocked polyisocyanate) was 75 mass%, and the weight average molecular weight of the non-modified blocked polyisocyanate was 1401 g / mol. Next, a coating composition was prepared in the same manner as in Example 1, except that non-modified blocked polyisocyanate (1) was used instead of modified blocked polyisocyanate composition (1). Next, the curability of the obtained coating composition and the coloring degree of the coating film made of the coating composition were evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0080] <Comparative Example 2> A composition containing a modified blocked polyisocyanate (hereinafter referred to as "modified blocked polyisocyanate composition (5)") was obtained in the same manner as in Example 1, except that Kao Raiser No. 25 (manufactured by Kao Corporation, 6-(dimethylamino)-1-hexanol, "Kao Raiser" is a registered trademark) was used instead of RZETA. The solid content concentration of the composition (content of modified blocked polyisocyanate) was 75 mass%, and the weight average molecular weight of the modified blocked polyisocyanate was 1540 g / mol. Next, a coating composition was prepared in the same manner as in Example 1, except that the modified blocked polyisocyanate composition (5) was used instead of the modified blocked polyisocyanate composition (1). Next, the curability of the obtained coating composition and the coloring degree of the coating film made of the coating composition were evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0081] <Comparative Example 3> A coating composition was prepared in the same manner as in Example 1, except that the unmodified blocked polyisocyanate composition (1) prepared in Comparative Example 1 was used instead of the modified blocked polyisocyanate composition (1), and RZETA was added as a blocking agent dissociation catalyst in an amount of 5 g per 100 g of polyisocyanate A-1. Next, the curability of the obtained coating composition and the coloring degree of the coating film made of the coating composition were evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0082] <Reference example 1> A coating composition was prepared in the same manner as in Example 1, except that the unmodified blocked polyisocyanate composition (1) prepared in Comparative Example 1 was used instead of the modified blocked polyisocyanate composition (1), and trimethyloctylammonium methyl carbonate (manufactured by Tosoh Corporation) was added as a blocking agent dissociation catalyst in an amount of 5 g per 100 g of polyisocyanate A-1. The curability of the resulting coating composition and the coloring degree of the coating film made of the coating composition were then evaluated in the same manner as in Example 1. The results are shown in Table 3.

[0083] [Table 1]

[0084] [Table 2]

[0085] [Table 3]

Claims

1. A modified blocked polyisocyanate which is a blocked polyisocyanate modified with a cyclic amino alcohol represented by the following formula (I): 【Chemistry 1】 [In formula (I), R １ ~R ５ each independently represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms, a and b each independently represent 0 or 1, and a+b represents 1.

2. The modified blocked polyisocyanate according to claim 1, which contains a structure derived from an aliphatic polyisocyanate having 4 to 6 carbon atoms or a derivative thereof.

3. The modified blocked polyisocyanate according to claim 1, which has at least one group selected from the group consisting of an isocyanate group blocked with an oxime-based blocking agent, an isocyanate group blocked with a pyrazole-based blocking agent, and an isocyanate group blocked with an imidazole-based blocking agent.

4. A coating composition comprising a base agent and a curing agent, A coating composition, wherein the curing agent comprises the modified blocked polyisocyanate according to any one of claims 1 to 3.

5. A coating film formed from the coating composition according to claim 4.

6. A method for forming a coating film, comprising the steps of applying the coating composition according to claim 4 to an object to be coated and heating the composition at 120 to 140°C to cure the composition.

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