Blocked isocyanate composition, curing agent and powder coating composition containing the same, and coating film made of cured product of the powder coating composition

Abstract

To provide a blocked isocyanate composition which gives a powder coating composition excellent in low-temperature curability.SOLUTION: There is provided a blocked isocyanate composition comprising a blocked product of a polyisocyanate composition, wherein the polyisocyanate composition comprises a butane diisocyanate derivative having isocyanate groups. The blocked product of the polyisocyanate composition comprises blocked compounds in which at least a part of the isocyanate groups of butane diisocyanate derivative is blocked by a blocking agent. At least a part of the butane diisocyanate derivative having isocyanate groups has isocyanurate groups. The molar ratio of the isocyanurate group to the total number of moles of isocyanurate groups, uretdione groups, iminooxadiazinedione groups, urethane groups, allophanate groups, urea groups and biuret groups in the composition is 35 to 100 mol%.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to a blocked isocyanate composition, a curing agent and a powder coating composition containing the same, and a coating film comprising a cured product of the powder coating composition. [Background technology]

[0002] Powder coating compositions contain a powder-like base agent and a curing agent, and are easy to recover and reuse, and do not use organic solvents, so that there is an increasing demand for them as environmentally friendly coatings. As such powder coating compositions, there are known powder coating compositions containing a hydroxyl group-containing compound such as a polyol as a base agent and a powder-like blocked isocyanate as a curing agent, and the powder coating composition is cured by heating the powder coating composition attached to the surface of a substrate to remove the blocking agent of the blocked isocyanate and react the isocyanate with the polyol, thereby forming a coating film on the substrate.

[0003] As a blocked isocyanate used in such a powder coating composition, for example, blocked IPDI in which the isocyanate group of an isocyanurate of isophorone diisocyanate (IPDI) is blocked with a blocking agent such as oxime, lactam, etc. However, powder coating compositions containing this blocked IPDI have a problem in that they have a high curing initiation temperature.

[0004] Therefore, JP 2022-54868 A (Patent Document 1) proposes a powder coating composition having excellent low-temperature curing properties, which contains a blocked isocyanate in which the isocyanate group of a triisocyanate compound having a specific structure is blocked with an amine compound or an alcohol-based compound. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2022-54868 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of one aspect of the present disclosure is to provide a blocked isocyanate composition and a curing agent capable of obtaining a powder coating composition having excellent low-temperature curing properties. Another object of the present disclosure is to provide a powder coating composition having excellent low-temperature curing properties. Still another object of the present disclosure is to provide a coating film obtained from the powder coating composition. [Means for solving the problem]

[0007] The present disclosure provides the following aspects. [1] A blocked isocyanate composition comprising a blocked polyisocyanate composition, The polyisocyanate composition contains a butane diisocyanate derivative having an isocyanate group, The blocked product of the polyisocyanate composition includes a product in which at least a part of the isocyanate groups of the butane diisocyanate derivative is blocked with a blocking agent, At least a part of the butane diisocyanate derivative having an isocyanate group has an isocyanurate group, The following formula (1): X=(A / (A+B+C+D+E+F+G))×100 (1) (In the formula (1), A, B, C, D, E, F, and G respectively represent the contents of the isocyanurate group, the uretdione group, the iminooxadiazinedione group, the urethane group, the allophanate group, the urea group, and the biuret group in the blocked isocyanate composition.) The molar ratio X of the isocyanurate group in the blocked isocyanate composition is 30 to 100 mol %, The blocked isocyanate composition, wherein the blocking agent is at least one selected from the group consisting of pyrazole-based compounds, imidazole-based compounds, oxime-based compounds, triazole-based compounds, active methylene-based compounds, and amine-based compounds. [2] The blocked isocyanate composition according to [1], wherein the blocking agent is at least one selected from the group consisting of pyrazole-based compounds having a melting point of 70°C or higher, imidazole-based compounds having a melting point of 95°C or higher, and amine-based compounds having a melting point of -70°C or higher. [3] The blocked isocyanate composition according to [1] or [2], wherein the molar ratio X of the isocyanurate group is 60 to 100 mol %. [4] A curing agent comprising the blocked isocyanate composition according to any one of [1] to [3]. [5] A powder coating composition comprising a compound having two or more active hydrogen-containing groups in one molecule and the curing agent described in [4]. [6] A coating film comprising a cured product of the powder coating composition described in [5]. Effect of the Invention

[0008] According to one aspect of the present disclosure, it is possible to provide a blocked isocyanate composition and a curing agent capable of obtaining a powder coating composition having excellent low-temperature curing properties. According to another aspect of the present disclosure, it is possible to provide a powder coating composition having excellent low-temperature curing properties. Furthermore, according to another aspect of the present disclosure, it is possible to provide a coating film obtained from the powder coating composition. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, the embodiments of the present disclosure will be described in detail. In this specification, a numerical range indicated with "~" indicates a range including the numerical values ​​before and after "~" as the minimum and maximum values, respectively. The minimum or maximum value of a numerical range indicated with "~" can be arbitrarily combined with the maximum or minimum value of another numerical range indicated with "~". In addition, the upper and lower limit values ​​individually indicated can also be arbitrarily combined.

[0010] <Blocked isocyanate composition and curing agent> A blocked isocyanate composition according to one embodiment of the present disclosure is a blocked isocyanate composition comprising a blocked product of a polyisocyanate composition, the polyisocyanate composition comprising a butane diisocyanate derivative having an isocyanate group, the blocked product of the polyisocyanate composition comprising at least a portion of the isocyanate groups of the butane diisocyanate derivative blocked with a blocking agent, at least a portion of the butane diisocyanate derivative having an isocyanate group has an isocyanurate group, and the blocked isocyanate composition is represented by the following formula (1): X=(A / (A+B+C+D+E+F+G))×100 (1) (In the formula (1), A, B, C, D, E, F, and G respectively represent the contents of the isocyanurate group, the uretdione group, the iminooxadiazinedione group, the urethane group, the allophanate group, the urea group, and the biuret group in the blocked isocyanate composition.) The blocked isocyanate composition has a molar ratio X of isocyanurate groups of 30 to 100 mol %, and the blocking agent is at least one selected from the group consisting of pyrazole compounds, imidazole compounds, oxime compounds, triazole compounds, active methylene compounds and amine compounds. By using this blocked isocyanate composition as a curing agent, a powder coating composition having excellent low-temperature curing properties can be obtained.

[0011] (Butane diisocyanate derivatives having isocyanate groups) The butane diisocyanate derivative having an isocyanate group (hereinafter sometimes abbreviated as "NCO group") (hereinafter sometimes abbreviated as "NCO group-containing BDI derivative") is a compound derived from butane diisocyanate (hereinafter sometimes abbreviated as "BDI"), and includes, in addition to BDI multimers such as dimers and trimers of the BDI having structural units (e.g., isocyanurate groups [formula (A) below], urethodione groups [formula (B) below], and iminooxadiazinedione groups [formula (C) below]) formed by a reaction (intermolecular reaction) between the NCO groups of the BDI, a urethane group [formula (D) below] formed by a reaction between the NCO group of the BDI and a hydroxyl group of a hydroxyl group-containing compound. and a compound having an allophanate group [formula (E)] formed by a reaction between an NCO group of the BDI and a urethane group of a urethane group-containing compound (hereinafter sometimes abbreviated as an allophanate group-containing compound). A compound having a urea group [formula (F)] formed by a reaction between an NCO group of the BDI and an amino group of an amino group-containing compound (hereinafter sometimes abbreviated as a urea group-containing compound). A compound having a biuret group [formula (G)] formed by a reaction between an NCO group of the BDI and a urea group of a urea group-containing compound (hereinafter sometimes abbreviated as a biuret group-containing compound).

[0012] [ka]

[0013] Examples of the BDI include 1,2-butane diisocyanate (1,2-BDI), 1,3-butane diisocyanate (1,3-BDI), 1,4-butane diisocyanate (1,4-BDI), and 2,3-butane diisocyanate (2,3-BDI). These BDIs may be used alone or in combination of two or more. Among these BDIs, 1,4-BDI is preferred from the viewpoint of high reactivity of the NCO group bonded to the primary carbon, and BDI used as a raw material for the NCO group-containing BDI derivative preferably contains 90% by mass or more (more preferably 95% by mass or more, and even more preferably 100% by mass) of 1,4-BDI.

[0014] Examples of the BDI polymer having a structural unit formed by a reaction between the NCO groups of the BDI include the compound having the isocyanurate group (isocyanurate compound), the compound having the uretdione group (uretdione compound), and the compound having the iminooxadiazinedione group (iminooxadiazinedione compound).

[0015] The isocyanurate of BDI may contain at least one isocyanurate group in one molecule, and may contain two or more. Examples of the isocyanurate of BDI containing one isocyanurate group in one molecule include a BDI trimer, as well as a compound (tetramer or higher) in which the NCO group of the BDI trimer further reacts with another BDI molecule or another NCO group-containing BDI derivative molecule to polymerize without forming the isocyanurate group. Examples of the isocyanurate of BDI containing two or more isocyanurate groups in one molecule include a compound (pentamer or more) in which one of the NCO groups of the isocyanurate of BDI containing at least one isocyanurate group in one molecule reacts (cyclopolymerization) with the NCO group of two other BDI molecules or two other NCO group-containing BDI derivative molecules to further form one isocyanurate group, a compound (hexamer or more) in which the NCO groups of the isocyanurate of BDI containing at least one isocyanurate group in one molecule are bonded together (intermolecular bond), and a compound (seven or more) in which two of the NCO groups of the isocyanurate of BDI containing at least one isocyanurate group in one molecule react (cyclopolymerization) with the NCO group of two other BDI molecules or two other NCO group-containing BDI derivative molecules to further form two isocyanurate groups.

[0016] In addition, the isocyanurate compound of BDI may further contain an NCO derivative group other than the isocyanurate group formed by a reaction between the NCO groups (e.g., the uretdione group, the iminooxadiazinedione group, etc.) formed by a reaction between the NCO groups and another functional group (e.g., a hydroxyl group, a urethane group, an amino group, a urea group, etc.) (e.g., a urethane group formed by a reaction between the NCO group and a hydroxyl group, an allophanate group formed by a reaction between the NCO group and a urethane group, a urea group formed by a reaction between the NCO group and an amino group, a biuret group formed by a reaction between the NCO group and a urea group, etc.). Therefore, in the present disclosure, the isocyanurate derivative of BDI includes not only compounds having only the isocyanurate group as a structural unit derived from the NCO group, but also compounds having the isocyanurate group and at least one other NCO-derived group selected from the group consisting of the uretdione group, the iminooxadiazinedione group, the urethane group, the allophanate group, the urea group, and the biuret group (that is, in the present disclosure, all NCO group-containing BDI derivatives having an isocyanurate group are classified as the isocyanurate derivative of BDI, and the uretdione and iminooxadiazinedione derivatives of BDI, the urethane group-containing compounds, the allophanate group-containing compounds, the urea group-containing compounds, and the biuret group-containing compounds are all considered to be NCO group-containing BDI derivatives not containing an isocyanurate group).

[0017] (Polyisocyanate composition) The polyisocyanate composition contains the NCO group-containing BDI derivative, and at least a part of the NCO group-containing BDI derivative has an isocyanurate group. That is, the polyisocyanate composition contains the NCO group-containing BDI derivative that contains at least the isocyanurate body of the BDI (including the compound having the isocyanurate group and the other NCO-derived group), and the NCO group-containing BDI derivative may further contain other NCO group-containing BDI derivatives (NCO group-containing BDI derivatives not having an isocyanurate group) other than the isocyanurate body, such as the uretdione body of the BDI, the iminooxadiazinedione body of the BDI, the urethane group-containing compound, the allophanate group-containing compound, the urea group-containing compound, the biuret group-containing compound, etc., but it is preferable to contain only the isocyanurate body of the BDI.

[0018] In such a polyisocyanate composition, the content of the NCO group-containing BDI derivative (the total content of the isocyanurate of BDI and the other NCO group-containing BDI derivatives other than the isocyanurate) is, from the viewpoints of obtaining a solid (powdered) blocked isocyanate composition and suppressing odors due to low molecular weight components such as BDI, preferably 95 mass % or more, more preferably 99 mass % or more, and even more preferably 100 mass %, based on the total mass of the solids in the polyisocyanate composition.

[0019] In addition, in the polyisocyanate composition, from the viewpoint of increasing the number of NCO groups used in curing the powder coating composition, the NCO content is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 25% by mass or more, based on the total mass of the solid content in the polyisocyanate composition. In addition, from the viewpoint of reducing the content of low molecular weight components such as BDI and suppressing odor, the upper limit of the NCO content is preferably 36% by mass or less, more preferably 33% by mass or less, and even more preferably 30% by mass or less, based on the total mass of the solid content in the polyisocyanate composition.

[0020] (Method for producing polyisocyanate composition) The polyisocyanate composition containing the NCO group-containing BDI derivative containing at least the isocyanurate of BDI can be produced by an isocyanuration reaction of the BDI. For example, the isocyanurate of BDI can be produced by reacting the isocyanate groups of the BDI with each other in the presence of a known isocyanuration catalyst.

[0021] Examples of the isocyanurate catalyst include quaternary onium salts, metal carboxylates, and aminosilyl group-containing compounds. These isocyanurate catalysts may be used alone or in combination of two or more. Among these isocyanurate catalysts, from the viewpoint of suppressing the production of high molecular weight substances, aminosilyl group-containing compounds such as aminosilane and silylurea are preferred, disilazanes such as hexamethyldisilazane and heptamethyldisilazane are more preferred, and hexamethyldisilazane is even more preferred.

[0022] The amount of the isocyanurate catalyst used is preferably 0.01 to 10 parts by mass, and more preferably 0.1 to 3 parts by mass, relative to 100 parts by mass of the charged amount of the BDI. As the amount of the isocyanurate catalyst used increases, the isocyanurate reaction proceeds more selectively than other reactions such as the uretdione reaction and the biuret reaction.

[0023] The reaction temperature of the isocyanurate-forming reaction of BDI is preferably 80 to 180° C., more preferably 100 to 160° C., from the viewpoint of being able to shorten the reaction time and to suppress coloration of the resulting polyisocyanate composition. The reaction time of the isocyanurate-forming reaction of BDI is preferably 0.5 to 6 hours, more preferably 1 to 5 hours, from the viewpoint of being able to suppress coloration of the resulting polyisocyanate composition.

[0024] The isocyanuration reaction of BDI may be terminated by adding a reaction terminator for the purpose of suppressing the generation of high molecular weight substances. The reaction terminator is a compound that deactivates the isocyanuration catalyst, and examples of the reaction terminator include water and hydroxyl group-containing compounds, and alcohols are preferred. These reaction terminators may be used alone or in combination of two or more.

[0025] The amount of the reaction terminator to be added varies depending on the type of the reaction terminator and the type of the isocyanurate catalyst used, but for example, it is preferably 0.1 to 3.5 equivalents, more preferably 0.8 to 2.5 equivalents, relative to 1 equivalent of the isocyanurate catalyst. By setting the amount of the reaction terminator to be added to the lower limit or more, the storage stability of the resulting polyisocyanate composition is improved. In addition, by setting the amount of the reaction terminator to be added to the upper limit or less, the reaction between the reaction terminator and the BDI is suppressed, and the decrease in the isocyanate group content can be suppressed.

[0026] The isocyanuration reaction of BDI is preferably carried out under an inert gas atmosphere such as nitrogen or argon. The isocyanuration reaction of BDI may be carried out in the presence or absence of an organic solvent. When the isocyanuration reaction of BDI is carried out in the presence of an organic solvent, it is preferable to use an organic solvent that does not affect the reaction and has a boiling point equal to or higher than the reaction temperature. Examples of such organic solvents include aliphatic hydrocarbons such as octane, alicyclic hydrocarbons such as cyclohexane and methylcyclohexane, ketones such as methyl isobutyl ketone and cyclohexanone, esters such as butyl acetate and isobutyl acetate, glycol ether esters such as ethylene glycol ethyl ether acetate, propylene glycol monomethyl ether acetate, 3-methyl-3-methoxybutyl acetate, and ethyl-3-ethoxypropionate, ethers such as dioxane, halogenated hydrocarbons such as methylene iodide and monochlorobenzene, and polar aprotic solvents such as N-methylpyrrolidone, dimethylformamide, dimethylacetamide, dimethylsulfoxide, and hexamethylphosphonylamide. These organic solvents may be used alone or in combination of two or more.

[0027] In the isocyanurate reaction of BDI, it is preferable to remove unreacted BDI (free BDI) from the reaction solution containing the obtained polyisocyanate composition after the reaction is completed. This suppresses odor caused by BDI. In addition, by removing free BDI so that the residual content of free BDI is 5 mass% or less, odor caused by BDI is suppressed and a decrease in storage stability of the obtained polyisocyanate composition is suppressed. Examples of methods for removing free BDI include a removal method by thin film distillation at 90 to 130°C under a high vacuum of 10 to 100 Pa, and an extraction method using an organic solvent.

[0028] (Blocked isocyanate composition) The blocked isocyanate composition of one embodiment of the present disclosure comprises a blocked product of the polyisocyanate composition, and the blocked product of the polyisocyanate composition comprises the NCO group-containing BDI derivative in which at least a portion of the NCO groups therein are blocked with a blocking agent (hereinafter, sometimes abbreviated as "blocked product of the NCO group-containing BDI derivative").

[0029] In such a blocked isocyanate composition, the content of the blocked product of the NCO group-containing BDI derivative (the total content of the blocked product of the isocyanurate of BDI and the blocked product of the other NCO group-containing BDI derivative other than the isocyanurate) is preferably 95 mass % or more, more preferably 99 mass % or more, and even more preferably 100 mass %, based on the total mass of the solid content in the blocked isocyanate composition, from the viewpoints of obtaining a solid (powdered) blocked isocyanate composition and suppressing odor due to low molecular weight components such as BDI.

[0030] The blocking agent is at least one selected from the group consisting of pyrazole compounds, imidazole compounds, oxime compounds, triazole compounds, active methylene compounds, and amine compounds. Examples of the pyrazole compounds include 3,5-dimethylpyrazole, 3-phenylpyrazole, 3-methylpyrazole, and pyrazole. Examples of the imidazole compounds include 2-isopropylimidazole, 2-phenylimidazole, 2-ethylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, and imidazole. Examples of the oxime compounds include cyclohexanone oxime, cyclopentanone oxime, acetoxime, methylethylketoxime, formaldoxime, and acetaldoxime. Examples of the triazole compounds include 1,2,4-triazole, 1,2,3-triazole, 3,5-dimethyl-1,2,4-triazole, and benzotriazole. Examples of the active methylene compounds include diethyl malonate, dimethyl malonate, diisopropyl malonate, di-tert-butyl malonate, methyl acetoacetate, ethyl acetoacetate, and acetylacetone. Examples of the amine compounds include diisopropylamine, 2-ethylhexylamine, cyclohexylamine, aniline, carbazole, piperidine, and benzylamine. Among these blocking agents, from the viewpoint of improving the blocking resistance of the blocked isocyanate composition, pyrazole compounds (3,5-dimethylpyrazole, 3-phenylpyrazole, etc.) having a melting point of 70° C. or more, imidazole compounds (2-isopropylimidazole, 2-phenylimidazole, etc.) having a melting point of 95° C. or more, and amine compounds (cyclohexylamine, diisopropylamine, etc.) having a melting point of −70° C. or more are preferred.

[0031] In the blocked isocyanate composition, a compound represented by the following formula (1): X=(A / (A+B+C+D+E+F+G))×100 (1) (In the formula (1), A, B, C, D, E, F, and G respectively represent the contents of the isocyanurate group, the uretdione group, the iminooxadiazinedione group, the urethane group, the allophanate group, the urea group, and the biuret group in the blocked isocyanate composition.) The molar ratio X of the isocyanurate group in the blocked isocyanate composition is 30 to 100 mol%. By setting the molar ratio X of the isocyanurate group to the lower limit or more, a solid (powdered) blocked isocyanate composition can be obtained. In addition, the lower limit of the molar ratio X of the isocyanurate group is preferably 50 mol% or more, more preferably 55 mol% or more, and even more preferably 60 mol% or more, from the viewpoint of improving the blocking resistance of the blocked isocyanate composition.

[0032] The molar ratio X of the isocyanurate group [unit: mol %] is calculated by taking the signal of the carbon atom of chloroform as the chemical shift reference (77.16 ppm) for the polyisocyanate composition before blocking containing the NCO group-containing BDI derivative, 13 The C-NMR spectrum was measured and 13 Based on the C-NMR spectrum, the signal areas (contents of each functional group) of carbon atoms corresponding to an isocyanurate group, a uretdione group, an iminooxadiazinedione group, a urethane group, an allophanate group, a urea group, and a biuret group were determined, and the signal areas (contents of each functional group) of carbon atoms corresponding to an isocyanurate group, a urea group, and a biuret group were calculated based on the C-NMR spectrum, and the signal areas (contents of each functional group) of X = (A / (A+B+C+D+E+F+G)) × 100 The calculation was made as follows. In the above formula, A to G are A: Isocyanurate group content = signal area around 148.7 ppm / 3 B: Uretdione group content = signal area around 157.4 ppm / 2 C: Iminooxadiazinedione group content = signal area around 139.3 ppm / 1 D: Urethane group content = signal area around 156.6 ppm / 1 E: Allophanate group content = signal area around 153.5 ppm / 1 F: Urea group content = signal area around 157.5 ppm / 1 G: Biuret group content = signal area around 156.1 ppm / 2 Shows.

[0033] In addition, from the viewpoint of reducing the amount of free blocking agent remaining in the coating film, the blocked isocyanate composition has an available NCO content of preferably 5% by mass or more, more preferably 8% by mass or more, and even more preferably 10% by mass or more, based on the total mass of the solid contents in the blocked isocyanate composition. From the viewpoint of reducing the content of low molecular weight components such as BDI and suppressing odor, the upper limit of the available NCO content is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less, based on the total mass of the solid contents in the blocked isocyanate composition.

[0034] Furthermore, from the viewpoint of improving the blocking resistance of the blocked isocyanate composition, the melting point is preferably 60° C. or higher, more preferably 80° C. or higher, and even more preferably 100° C. or higher. Moreover, from the viewpoint of improving the film-formability of the coating film, the upper limit of the melting point of the blocked isocyanate composition is preferably 170° C. or lower, more preferably 150° C. or lower, and even more preferably 140° C. or lower.

[0035] (Method for producing blocked isocyanate composition) The blocked isocyanate composition can be produced by reacting at least a portion of the NCO groups of the NCO group-containing BDI derivative in the polyisocyanate composition with the blocking agent.

[0036] The amount of the blocking agent added is preferably 0.5 to 1.5 equivalents, and more preferably 0.8 to 1.2 equivalents, per mole of NCO groups in the polyisocyanate composition, from the viewpoint of improving the storage stability of the blocked isocyanate composition.

[0037] The reaction temperature of the reaction between the NCO group and the blocking agent is preferably 10 to 100° C., more preferably 20 to 80° C., from the viewpoint of suppressing side reactions between the NCO groups. The reaction time of the reaction between the NCO group and the blocking agent is preferably 0.1 to 5 hours, more preferably 0.5 to 3 hours, from the viewpoint of preventing coloration of the blocked isocyanate composition.

[0038] The reaction between the NCO group and the blocking agent is preferably carried out under an inert gas atmosphere such as nitrogen or argon. The reaction between the NCO group and the blocking agent may also be carried out in an organic solvent. Examples of the organic solvent include aliphatic hydrocarbons such as octane, alicyclic hydrocarbons such as cyclohexane and methylcyclohexane, ketones such as methyl isobutyl ketone and cyclohexanone, esters such as ethyl acetate, butyl acetate, and isobutyl acetate, glycol ether esters such as ethylene glycol ethyl ether acetate, propylene glycol monomethyl ether acetate, 3-methyl-3-methoxybutyl acetate, and ethyl-3-ethoxypropionate, ethers such as dioxane, halogenated hydrocarbons such as methylene iodide and monochlorobenzene, and polar aprotic solvents such as N-methylpyrrolidone, dimethylformamide, dimethylacetamide, dimethylsulfoxide, and hexamethylphosphonylamide. These organic solvents may be used alone or in combination of two or more.

[0039] (hardening agent) The curing agent according to one embodiment of the present disclosure contains the blocked isocyanate composition. The curing agent may be dissolved in a solvent before use, but it is preferable to use the blocked isocyanate composition as a curing agent for a powder coating composition, since the blocked isocyanate composition is in a solid (powder) form and a powder coating composition having excellent low-temperature curing properties can be obtained.

[0040] <Powder coating composition and coating film> The powder coating composition of another embodiment of the present disclosure contains a powdered compound (active hydrogen group-containing compound) having two or more groups (active hydrogen groups) having active hydrogen in one molecule, and the curing agent. The powder coating composition has excellent low-temperature curing properties, so it can be cured at a low heating temperature. In addition, the coating film of another embodiment of the present disclosure is made of a cured product of the powder coating composition.

[0041] Examples of the active hydrogen group include a hydroxyl group, an amino group, etc. Examples of the active hydrogen group-containing compound include a powdered polyol, a powdered polyamine, a powdered amino alcohol, etc.

[0042] The polyol is not particularly limited as long as it is in powder form, and examples thereof include polyester polyol, polyether polyol, polycarbonate polyol, polyolefin polyol, acrylic polyol, silicone polyol, castor oil polyol, fluorine polyol, ester exchange product of two or more kinds of polyols, hydroxyl group-terminated prepolymers obtained by urethane reaction with polyisocyanate, etc. These polyols may be used alone or in combination of two or more kinds.

[0043] The polyamine is not particularly limited as long as it is in powder form, and examples thereof include tetramethylenediamine, hexamethylenediamine, cyclohexanediamine, phenylenediamine, bis(hexamethylene)triamine, diaminobenzidine, etc. These polyamines may be used alone or in combination of two or more kinds.

[0044] In the powder coating composition, the compounding ratio of the active hydrogen group-containing compound and the curing agent is not particularly limited, but the equivalent ratio (active hydrogen group: NCO group) between the active hydrogen group of the active hydrogen group-containing compound and the NCO group of the curing agent (NCO group calculated from the effective NCO content of the blocked isocyanate composition) is preferably 1:0.5 to 1:2, more preferably 1:0.8 to 1:1.2. When the equivalent ratio of the active hydrogen group and the NCO group is equal to or higher than the lower limit, the active hydrogen group does not become too excessive, so the adhesion of the coating film tends to be further improved, and the decrease in crosslink density is suppressed, and the durability and mechanical strength of the coating film tend to be further improved. When the equivalent ratio of the active hydrogen group and the NCO group is equal to or lower than the upper limit, the NCO group does not become too excessive, so the reaction with moisture in the air is suppressed, so the swelling of the coating film is further reduced, and the associated decrease in adhesion of the coating film tends to be further suppressed.

[0045] The powder coating composition may contain various additives, such as antioxidants such as 2,6-di-tert-butyl-4-methylphenol, ultraviolet absorbers, pigments, dyes, solvents, flame retardants, hydrolysis inhibitors, lubricants, plasticizers, fillers, antistatic agents, dispersants, catalysts, storage stabilizers, surfactants, and leveling agents, as required.

[0046] The coating film can be formed by applying the powder coating composition onto an adherend and curing it by heating. The material of the adherend is not particularly limited, and examples thereof include metals such as stainless steel, phosphate-treated steel, galvanized steel, iron, copper, aluminum, and brass, and glass.

[0047] The heating temperature of the powder coating composition is preferably 80 to 180° C., more preferably 100 to 160° C. The powder coating composition has excellent low-temperature curing properties, and can be cured at a heating temperature within the above range. The heating time of the powder coating composition is not particularly limited, but is preferably 0.1 to 4 hours, more preferably 0.5 to 2 hours. EXAMPLES

[0048] The present disclosure will be described in more detail below with reference to examples and comparative examples, but the present disclosure is not limited to the following examples. The blocking agents used in the examples and comparative examples are shown in Table 1.

[0049] [Table 1]

[0050] In addition, the physical properties of the polyisocyanate composition, the blocking agent, the blocked isocyanate composition, the powder coating composition and the coating film were measured and the characteristics were evaluated according to the following methods.

[0051] <NCO content of polyisocyanate composition> The NCO content of the polyisocyanate composition was determined by reacting the polyisocyanate composition with a secondary amine and then back titrating the unreacted secondary amine with hydrochloric acid.

[0052] <Mole ratio of isocyanurate groups> The polyisocyanate composition before blocking was dissolved in deuterated chloroform containing 0.2% by mass of tetramethylsilane to prepare a measurement sample with a concentration of 0.2 g / ml. 13 The carbon atom signal of chloroform was used as the chemical shift reference (77.16 ppm) by C-NMR under the conditions of a resonance frequency of 100 MHz and an accumulation number of 1024. 13 The C-NMR spectrum was measured to determine the signal areas of the carbon atoms corresponding to the isocyanurate group, the uretdione group, the iminooxadiazinedione group, the urethane group, the allophanate group, the urea group, and the biuret group (the content of each functional group). The molar ratio X of the isocyanurate group [unit: mol %] was calculated using the following formula: X = (A / (A+B+C+D+E+F+G)) × 100 The calculation was made as follows. In the above formula, A to G are A: Isocyanurate group content = signal area around 148.7 ppm / 3 B: Uretdione group content = signal area around 157.4 ppm / 2 C: Iminooxadiazinedione group content = signal area around 139.3 ppm / 1 D: Urethane group content = signal area around 156.6 ppm / 1 E: Allophanate group content = signal area around 153.5 ppm / 1 F: Urea group content = signal area around 157.5 ppm / 1 G: Biuret group content = signal area around 156.1 ppm / 2 Shows.

[0053] <Melting point of blocking agent> The melting point of the blocking agent was determined from the peak top temperature of the endothermic peak observed by differential scanning calorimetry (DSC) using a differential scanning calorimeter (manufactured by PerkinElmer, product name: DSC8500). The endothermic peak was the one observed when the blocking agent was once heated and dissolved, cooled to below the melting point, and then heated again. For example, in the case of 3,5-dimethylpyrazole, the material was heated from 23°C to 130°C at a heating rate of 10°C / min, held at 130°C for 2 minutes, cooled to 50°C at a heating rate of 10°C / min, and then heated to 130°C at a heating rate of 10°C / min. The peak top temperature of the endothermic peak observed during this heating was taken as the melting point.

[0054] <Available NCO content of blocked isocyanate composition> The available NCO content of the blocked isocyanate composition is calculated by the following formula: Available NCO content [unit: mass%] = (content of polyisocyanate composition) × (NCO content of polyisocyanate composition) / (total mass of blocked isocyanate composition) The calculation was made as follows.

[0055] <Melting point of blocked isocyanate composition> The blocked isocyanate composition was spread on a steel plate (JIS G3141, manufactured by Paltec Co., Ltd., product name: SPCC-SB) to a thickness of about 500 μm, and the steel plate was placed on a hot plate (manufactured by Tokyo Glass Instruments Co., Ltd., product name: FHP-380AL) and heated at a predetermined temperature for 5 minutes, after which the appearance of the blocked isocyanate composition was observed. This appearance observation was performed on the blocked isocyanate composition heated at various temperatures, and the temperature at which the blocked isocyanate composition completely melted was taken as the melting point.

[0056] <Blocking resistance of blocked isocyanate composition> The blocked isocyanate composition powder was classified using a sieve with a mesh size of 106 μm (manufactured by Tokyo Screen Co., Ltd.), and the blocked isocyanate composition powder that passed through the sieve was placed in a cylindrical glass container with an inner diameter of 20 mm and allowed to stand for 7 days in an oven at 40° C. The cylindrical container was removed from the oven, and the blocked isocyanate composition powder in the cylindrical container was classified using a sieve with a mesh size of 106 μm (manufactured by Tokyo Screen Co., Ltd.), and the mass of the blocked isocyanate composition powder that passed through the sieve was measured and calculated using the following formula: Passage rate of blocked isocyanate composition powder [unit: %] = mass of blocked isocyanate composition powder passed through sieve / total mass of blocked isocyanate composition powder passed through sieve × 100 The passing rate of the blocked isocyanate composition powder was calculated by the above formula, and the blocking resistance of the blocked isocyanate composition was evaluated according to the following criteria. A higher passing rate means better blocking resistance. A: Passage rate = 90~100%. B: Passage rate = 70~89%. C: Passage rate = 0~69%. D: The blocked isocyanate composition is liquid at room temperature, making evaluation difficult.

[0057] [Synthesis of polyisocyanate composition] A synthesis example of a polyisocyanate composition used in producing the blocked isocyanate composition of the present embodiment will be specifically described below, but the polyisocyanate composition used in producing the blocked isocyanate composition according to one embodiment of the present disclosure is not limited to the one obtained in the synthesis example below.

[0058] (Synthesis Example 1) A 1L four-neck flask equipped with a stirrer, a thermometer, a cooling tube, and a nitrogen gas inlet tube was charged with 800 g of 1,4-butane diisocyanate (1,4-BDI, NCO content: 60.0% by mass) and heated to 100 ° C., to which 8.0 g of hexamethyldisilazane, an isocyanurate catalyst, was added, and the mixture was heated to 120 ° C. and stirred for 1.7 hours to carry out an isocyanurate reaction. The mixture was then cooled to 50 ° C. in a water bath, and 4.8 g of ethanol, a reaction terminator, was added, and the termination reaction was carried out at 50 ° C. for 0.5 hours. After cooling the resulting reaction solution, excess 1,4-BDI was removed by thin-film distillation (conditions: 110 ° C., 0.04 kPa) to obtain a polyisocyanate composition P-1 consisting of a 1,4-BDI derivative containing an isocyanurate of 1,4-BDI (yield: 96 g). The resulting polyisocyanate composition had an NCO content of 26.7 mass % and a molar ratio of isocyanurate groups of 88 mol %.

[0059] (Synthesis Example 2) A 1L four-neck flask equipped with a stirrer, a thermometer, a cooling tube, and a nitrogen gas inlet tube was charged with 800 g of 1,4-butane diisocyanate (1,4-BDI, NCO content: 60.0% by mass) and heated to 120°C, to which 3.2 g of heptamethyldisilazane, an isocyanurate catalyst, was added, and the mixture was heated to 150°C and stirred for 2.1 hours to carry out an isocyanurate reaction. The mixture was then cooled to 50°C in a water bath, and 1.8 g of ethanol, a reaction terminator, was added, and the termination reaction was carried out at 50°C for 0.5 hours. After cooling the resulting reaction solution, excess 1,4-BDI was removed by thin-film distillation (conditions: 110°C, 0.04 kPa) to obtain a polyisocyanate composition P-2 consisting of a 1,4-BDI derivative containing an isocyanurate of 1,4-BDI (yield: 192 g). The resulting polyisocyanate composition had an NCO content of 27.8 mass % and a molar ratio of isocyanurate groups of 77 mol %.

[0060] (Synthesis Example 3) In a 1L four-neck flask equipped with a stirrer, a thermometer, a cooling tube, and a nitrogen gas inlet tube, 800 g of 1,4-butane diisocyanate (1,4-BDI, NCO content: 60.0% by mass) was charged, heated to 150 ° C., and stirred for 3 hours. 4.8 g of hexamethyldisilazane, an isocyanurate catalyst, was added to this, and the mixture was stirred for 3.4 hours to carry out an isocyanurate reaction. Thereafter, the temperature was lowered to 50 ° C. in a water bath, 2.9 g of ethanol, a reaction terminator, was added, and the termination reaction was carried out at 50 ° C. for 0.5 hours. After cooling the resulting reaction solution, excess 1,4-BDI was removed by thin-film distillation (conditions: 110 ° C., 0.04 kPa) to obtain a polyisocyanate composition P-3 consisting of a 1,4-BDI derivative containing an isocyanurate of 1,4-BDI (yield: 160 g). The resulting polyisocyanate composition had an NCO content of 27.3 mass % and a molar ratio of isocyanurate groups of 56 mol %.

[0061] (Synthesis Example 4) A 1L four-neck flask equipped with a stirrer, a thermometer, a cooling tube, and a nitrogen gas inlet tube was charged with 800 g of 1,4-butane diisocyanate (1,4-BDI, NCO content: 60.0% by mass) and heated to 120°C, to which 0.8 g of hexamethyldisilazane, an isocyanurate catalyst, was added, and the mixture was heated to 140°C and stirred for 6 hours to carry out an isocyanurate reaction. The mixture was then cooled to 50°C in a water bath, and 0.5 g of ethanol, a reaction terminator, was added, and the termination reaction was carried out at 50°C for 0.5 hours. After cooling the resulting reaction solution, excess 1,4-BDI was removed by thin-film distillation (conditions: 110°C, 0.04 kPa) to obtain a polyisocyanate composition P-4 consisting of a 1,4-BDI derivative containing an isocyanurate of 1,4-BDI (yield: 83 g). The resulting polyisocyanate composition had an NCO content of 28.4 mass % and a molar ratio of isocyanurate groups of 23 mol %.

[0062] [Synthesis of blocked isocyanate composition] Example 1 20 g of polyisocyanate composition P-1 (NCO content = 26.7%) and 14 g of ethyl acetate (concentration = 70 NV%) were charged into a 100 ml three-neck flask equipped with a stirrer, a thermometer, and a nitrogen gas inlet tube, and 12 g (1 equivalent to the number of moles of NCO group) of 3,5-dimethylpyrazole (DMP, melting point: 108 ° C.) as a blocking agent was added thereto, and the mixture was heated to 50 ° C. and stirred for 1 hour. The ethyl acetate in the resulting reaction solution was distilled off under reduced pressure using an evaporator. The resulting solid was washed with 50 g of n-hexane to obtain a blocked isocyanate composition powder (yield: 32 g). The properties of this blocked isocyanate composition powder are shown in Table 2.

[0063] (Examples 2 to 16 and Comparative Examples 1 to 6) A blocked isocyanate composition powder was obtained in the same manner as in Example 1, except that the types of polyisocyanate composition and blocking agent shown in Table 2 were used. The properties of this blocked isocyanate composition powder are shown in Table 2. In Table 2, "IPDIT" represents isophorone diisocyanate-based polyisocyanate (manufactured by Evonik, product name: VESTANAT T1890 / 100) and "HXLV" represents 1,6-diisocyanatohexane-based polyisocyanate (manufactured by Tosoh Corporation, product name: Coronate HXLV).

[0064] <Stability of powder coating composition> The blocked isocyanate composition powder and powder polyester polyol (manufactured by Japan U-Pica Co., Ltd., product name: U-Pica Coat GV-740, hydroxyl value: 49 mg KOH / g resin) obtained in Examples 1 to 16 and Comparative Examples 1 to 6 were classified using a sieve with a mesh size of 106 μm (manufactured by Tokyo Screen Co., Ltd.), and the powder polyol and the blocked isocyanate composition powder that passed through the sieve were mixed so that the equivalent ratio of the hydroxyl group and the isocyanate group calculated from the effective NCO content was 1:1 to prepare a powder coating composition. This powder coating composition was placed in a glass cylindrical container with an inner diameter of 20 mm and allowed to stand at 23° C. for 5 hours. The powder coating composition after standing was classified using a sieve with a mesh size of 106 μm (manufactured by Tokyo Screen Co., Ltd.), and the mass of the powder coating composition that passed through the sieve was measured and calculated using the following formula: Passage rate of powder coating composition [unit: %] = mass of powder coating composition passed through sieve / total mass of powder coating composition passed through sieve × 100 The passing rate of the powder coating composition was calculated by the above, and the stability of the powder coating composition was evaluated according to the following criteria. The results are shown in Table 2. A higher passing rate means better stability. A: Passage rate = 90~100%. B: Passage rate = 70~89%. C: Passage rate = 0~69%. D: The blocked isocyanate composition is liquid at room temperature, making it difficult to prepare a powder coating.

[0065] <Curing initiation temperature of powder coating composition> The blocked isocyanate composition powder obtained in Examples 1 to 16 and Comparative Examples 1 to 6 and powder polyester polyol (manufactured by Japan U-Pica Co., Ltd., product name: U-Pica Coat GV-740, hydroxyl value: 49 mg KOH / g resin) were mixed so that the equivalent ratio of hydroxyl groups to isocyanate groups calculated from the effective NCO content was 1:1 to prepare a powder coating composition. This powder coating composition was spread on a steel plate (JIS G3141, manufactured by Paltec Co., Ltd., product name: SPCC-SB) to a thickness of about 500 μm, and the steel plate was placed on a hot plate (manufactured by Tokyo Glass Instruments Co., Ltd., product name: FHP-380AL), and the powder coating composition was cured by heating at a predetermined temperature for 30 minutes to prepare a coating film. This coating film was prepared at various heating temperatures, and a rubbing test was performed on each of the obtained coating films using methyl ethyl ketone, and the heating temperature at which the coating film did not completely dissolve after 100 rubbings was determined as the curing initiation temperature. The results are shown in Table 2.

[0066] [Table 2]

[0067] As described above, by using a curing agent containing the blocked isocyanate composition according to one embodiment of the present disclosure, a powder coating composition having excellent low-temperature curing properties can be obtained. Therefore, by using a powder coating composition containing the blocked isocyanate composition according to one embodiment of the present disclosure as a curing agent, it becomes possible to form a coating film by heating at a low temperature.

Claims

1. A blocked isocyanate composition comprising a blocked polyisocyanate composition, The polyisocyanate composition contains a butane diisocyanate derivative having an isocyanate group, The blocked product of the polyisocyanate composition includes a product in which at least a part of the isocyanate groups of the butane diisocyanate derivative is blocked with a blocking agent, At least a part of the butane diisocyanate derivative having an isocyanate group has an isocyanurate group, The following formula (1): X=(A / (A+B+C+D+E+F+G))×100 (1) In the formula (1), A, B, C, D, E, F, and G respectively represent the contents of the isocyanurate group, the uretdione group, the iminooxadiazinedione group, the urethane group, the allophanate group, the urea group, and the biuret group in the blocked isocyanate composition. The molar ratio X of the isocyanurate group in the blocked isocyanate composition is 30 to 100 mol %, The blocked isocyanate composition, wherein the blocking agent is at least one selected from the group consisting of pyrazole-based compounds, imidazole-based compounds, oxime-based compounds, triazole-based compounds, active methylene-based compounds, and amine-based compounds.

2. The blocked isocyanate composition according to claim 1, wherein the blocking agent is at least one selected from the group consisting of pyrazole-based compounds having a melting point of 70° C. or higher, imidazole-based compounds having a melting point of 95° C. or higher, and amine-based compounds having a melting point of −70° C. or higher.

3. The blocked isocyanate composition according to claim 1, wherein the molar ratio X of the isocyanurate groups is 60 to 100 mol %.

4. A curing agent comprising the blocked isocyanate composition according to any one of claims 1 to 3.

5. 5. A powder coating composition comprising a compound having two or more active hydrogen-containing groups in one molecule and the curing agent according to claim 4.

6. A coating film comprising a cured product of the powder coating composition according to claim 5.

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