Method for improving the low-temperature curing properties of a curing agent composition, a resin composition, a resin film, a laminate, and a curing agent composition.

Abstract

To provide a curing agent composition that exhibits excellent storage stability and low-temperature curing properties. [Solution] A curing agent composition comprising a blocked polyisocyanate (B) and a melamine resin (M), wherein the blocked polyisocyanate (B) is a blocked polyisocyanate derived from a polyisocyanate and a blocking agent containing a malonic acid ester, and includes a constituent unit represented by general formula (I), and the total mass of solids contained in the blocked polyisocyanate (B) is 8 parts by mass or more and 100 parts by mass or less, relative to 100 parts by mass of the total mass of solids contained in the melamine resin (M). [C1] TIFF2026067517000015.tif31170

Description

[Technical Field]

[0001] The present invention relates to a curing agent composition, a resin composition, a resin film, a laminate, and a method for improving the low-temperature curing properties of a curing agent composition. [Background technology]

[0002] Conventionally, polyurethane resin paints have excellent abrasion resistance, chemical resistance, and stain resistance. In particular, polyurethane resin paints using polyisocyanates obtained from aliphatic or alicyclic diisocyanates have even better weather resistance, and demand for them is increasing. However, polyurethane resin paints are generally two-component, making them extremely inconvenient to use. Specifically, ordinary polyurethane resin paints consist of two components, polyol and polyisocyanate, and the polyol and polyisocyanate must be stored separately and mixed at the time of painting. Furthermore, once the two are mixed, the paint gels in a short time and becomes unusable. Due to these problems, polyurethane resin paints are extremely difficult to use in automated painting in fields such as automotive painting or electrocoating. In addition, since isocyanates react readily with water, they cannot be used in water-based paints such as electrodeposition paints. Moreover, when using paints containing isocyanates, thorough cleaning of the painting machine and painting tank is required after work, which significantly reduces work efficiency.

[0003] To address the aforementioned challenges, it has been proposed to use blocked polyisocyanates, in which all active isocyanate groups are blocked with a blocking agent. These blocked polyisocyanates do not react with polyols at room temperature. However, heating causes the blocking agent to dissociate, regenerating the active isocyanate groups, which then react with the polyol to cause a crosslinking reaction, thus overcoming the aforementioned challenges. Consequently, numerous blocking agents have been investigated, with phenol and methyl ethyl ketoxime being typical examples.

[0004] However, when using blocked polyisocyanates with these blocking agents, a high curing temperature of 140°C or higher is generally required. This high curing temperature is not only energy-intensive but also necessitates heat resistance in the substrate, limiting its applications.

[0005] On the other hand, research is being conducted on block polyisocyanates using active methylene compounds such as acetoacetate esters and malonic acid diesters as low-temperature curing type block polyisocyanates (see, for example, Patent Document 1). Among these, technologies for further low-temperature curing are being continuously investigated. For example, Patent Documents 2 and 3 propose block polyisocyanate compositions that cure at low temperatures. Furthermore, it is generally known that melamine-based compounds are used as curing agents to achieve coating hardness (see, for example, Patent Document 4). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 3547197 [Patent Document 2] International Publication No. 2019 / 065890 [Patent Document 3] Patent No. 5855091 [Patent Document 4] Japanese Patent Application Publication No. 11-228904 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, in curing agent compositions using active methylene compounds or melamine compounds, there is room for improvement in terms of both low-temperature curing properties and storage stability.

[0008] The present invention has been made in view of the above circumstances, and provides a curing agent composition excellent in both low-temperature curability and storage stability, a resin composition, a resin film, and a laminate using the curing agent composition, and a method for improving the low-temperature curability of a curable composition.

Means for Solving the Problems

[0009] That is, the present invention includes the following aspects. (1) A curing agent composition containing a blocked polyisocyanate (B) and a melamine resin (M), wherein the blocked polyisocyanate (B) is derived from a polyisocyanate and a blocking agent containing a malonic ester, and is a blocked polyisocyanate containing a structural unit represented by the following general formula (I), and the total mass of the solid content contained in the blocked polyisocyanate (B) with respect to 100 parts by mass of the total mass of the solid content contained in the melamine resin (M) is 8 parts by mass or more and 100 parts by mass or less.

[0010]

Chemical formula

[0011] (In the general formula (I), R

[0012] , R 12 and R 13 are each independently an alkyl group which may contain one or more substituents selected from the group consisting of a hydroxy group and an amino group. The total number of carbon atoms of the R 11 , the R 12 and the R 13 is 3 or more and 20 or less. R 14 , R 15 and R 16 are each independently a hydrogen atom or an alkyl group which may contain one or more substituents selected from the group consisting of a hydroxy group and an amino group. The wavy line represents a bond.)

[0012] (2) The curing agent composition according to (1), wherein the structure represented by the general formula (I) includes a structure represented by the following general formula (I-1).

[0013] [ka]

[0014] (In general formula (I-1), R 111 , R 112 and R 113 Each of these is an alkyl group which may independently contain one or more substituents selected from the group consisting of hydroxyl groups and amino groups. 111 , the R 112 and R 113 The total number of carbon atoms is between 3 and 20. 114 and R 115 Each of these alkyl groups may independently contain a hydrogen atom or one or more substituents selected from the group consisting of a hydroxyl group and an amino group. (The wavy lines represent bonds.)

[0015] (3) The above R 11 , the R 12 and R 13 Each of these is independently an unsubstituted alkyl group, and The aforementioned R 14 , the R 15 and R 16 The curing agent composition according to (1), wherein each is independently a hydrogen atom or an unsubstituted alkyl group. (4) The curing agent composition according to any one of (1) to (3), wherein the polyisocyanate is a polyisocyanate derived from one or more diisocyanates selected from the group consisting of aliphatic diisocyanates and alicyclic diisocyanates. (5) The curing agent composition according to any one of (1) to (4), wherein the average number of isocyanate groups of the polyisocyanate is 3.5 or more. (6) A resin composition comprising the curing agent composition described in any one of (1) to (5) and a polyvalent hydroxy compound. (7) A resin film obtained by curing the resin composition described in (6). (8) A laminate comprising one or more layers of the resin film described in (7) on a substrate, A laminate in which the thickness of each layer of the resin film is 1 μm or more and 50 μm or less. (9) A method for improving the low-temperature curing properties of a curing agent composition, comprising: a curing agent composition manufacturing step of mixing a melamine resin (M) and a blocked polyisocyanate (B); a resin composition manufacturing step of mixing the curing agent composition with a polyvalent hydroxy compound after the curing agent composition manufacturing step; and a curing step of curing the resin composition obtained in the resin composition manufacturing step to obtain a resin film, wherein the blocked polyisocyanate (B) is a blocked polyisocyanate derived from a polyisocyanate and a blocking agent containing a malonic acid ester, and contains a constituent unit represented by the following general formula (I), and the total mass of solids contained in the blocked polyisocyanate (B) is 8 parts by mass or more and 100 parts by mass or less, relative to 100 parts by mass of the total mass of solids contained in the melamine resin (M).

[0016] [ka]

[0017] (In general formula (I), R 11 , R 12 and R 13 Each of these is an alkyl group which may independently contain one or more substituents selected from the group consisting of hydroxyl groups and amino groups. 11 , the R 12 and R 13 The total number of carbon atoms is between 3 and 20. 14 , R 15 and R 16 Each of these alkyl groups may independently contain a hydrogen atom or one or more substituents selected from the group consisting of a hydroxyl group and an amino group. (The wavy lines represent bonds.) [Effects of the Invention]

[0018] According to the curing agent composition of the above embodiment, a curing agent composition that is excellent in both low-temperature curability and storage stability can be provided. According to the resin composition of the above embodiment, a resin composition comprising the curing agent composition that is excellent in low-temperature curability can be provided. According to the resin film of the above embodiment, a resin film obtained by curing the resin composition can be provided. According to the laminate of the above embodiment, a laminate comprising the resin film can be provided. According to the method for improving the low-temperature curability of the curing agent composition of the above embodiment, a method for providing a curing agent composition with excellent low-temperature curability can be provided. [Modes for carrying out the invention]

[0019] The following describes in detail embodiments for carrying out the present invention (hereinafter referred to as "this embodiment"). However, the present invention is not limited to the following embodiments. The present invention can be implemented with appropriate modifications within the scope of its gist.

[0020] In this specification, "polyol" means a compound having two or more hydroxyl groups (-OH). In this specification, "polyisocyanate" means a reaction product in which multiple monomer compounds having one or more isocyanate groups (-NCO) are bonded together. In this specification, "constituent unit" means a structure in a polyisocyanate or blocked polyisocyanate that originates from a single monomer molecule. For example, a constituent unit derived from malonic acid ester refers to a structure in a blocked polyisocyanate that originates from a single molecule of malonic acid ester. A constituent unit may be a unit directly formed by a (co)polymerization reaction of monomers, or it may be a unit in which a part of the (co)polymer has been converted to another structure by processing.

[0021] <Curing agent composition> The curing agent composition of this embodiment comprises a blocked polyisocyanate (B) and a melamine resin (M), wherein the total mass of solids contained in the blocked polyisocyanate (B) is 8 parts by mass or more and 100 parts by mass or less, relative to 100 parts by mass of the total mass of solids contained in the melamine resin (M). The aforementioned blocked polyisocyanate (B) is derived from a polyisocyanate and a blocking agent containing a malonic acid ester, and comprises a constituent unit represented by the following general formula (I).

[0022] [ka]

[0023] (In general formula (I), R 11 , R 12 and R 13 Each of these is an alkyl group which may independently contain one or more substituents selected from the group consisting of hydroxyl groups and amino groups. 11 , the R 12 and R 13 The total number of carbon atoms is between 3 and 20. 14 , R 15 and R 16 Each of these alkyl groups may independently contain a hydrogen atom or one or more substituents selected from the group consisting of a hydroxyl group and an amino group. (The wavy lines represent bonds.)

[0024] The curing agent composition of this embodiment, having the above configuration, exhibits excellent low-temperature curing properties and storage stability.

[0025] In this specification, "low-temperature curability" is evaluated by the method described in [Evaluation 1] in the examples described later. In the present invention, "excellent low-temperature curability" means that the curing reaction proceeds sufficiently even under low heating conditions of 100°C or below. Generally, melamine resins do not cure at temperatures below 100°C. On the other hand, as shown in the examples described later, the curing agent composition of this embodiment allows the curing reaction to proceed sufficiently even under heating conditions of 80°C, even when containing melamine resin (M).

[0026] Next, each component of the curing agent composition of this embodiment will be described in detail below.

[0027] Blocked polyisocyanate (B) Blocked polyisocyanate (B) is a reaction product of polyisocyanate and a blocking agent containing malonic acid ester. That is, in blocked polyisocyanate (B), at least some, preferably all, of the isocyanate groups in the polyisocyanate are blocked with a blocking agent containing malonic acid ester.

[0028] [Constituent Unit (I)] Blocked polyisocyanates (B) contain a constituent unit (I) within their molecule. Constituent unit (I) is a structure formed when the isocyanate group of the polyisocyanate is blocked by a malonic acid ester.

[0029] [ka]

[0030] (In general formula (I), R 11 , R 12 and R 13 Each of these is an alkyl group which may independently contain one or more substituents selected from the group consisting of hydroxyl groups and amino groups. 11 , the R 12 and R 13 The total number of carbon atoms is between 3 and 20. 14 , R 15 and R 16 Each of these alkyl groups may independently contain a hydrogen atom or one or more substituents selected from the group consisting of a hydroxyl group and an amino group. (The wavy lines represent bonds.)

[0031] (R 11 , R 12 , R 13 , R 14 , R 15 and R 16 ) R 11 , R 12 , R 13 , R 14 , R 15 and R 16 The number of carbon atoms in the alkyl group is preferably 1 to 20, more preferably 1 to 8, even more preferably 1 to 6, and particularly preferably 1 to 4.

[0032] Examples of alkyl groups without substituents include methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, tert-butyl group, sec-butyl group, isobutyl group, n-pentyl group, isopentyl group, neopentyl group, tert-pentyl group, 1-methylbutyl group, n-hexyl group, 2-methylpentyl group, 3-methylpentyl group, 2,2-dimethylbutyl group, 2,3-dimethylbutyl group, n-heptyl group, 2-methylhexyl group, 3-methylhexyl group, 2,2-dimethylpentyl group, 2,3-dimethylpentyl group, 2,4-dimethylpentyl group, 3,3-dimethylpentyl group, 3-ethylpentyl group, 2,2,3-trimethylbutyl group, n-octyl group, isooctyl group, 2-ethylhexyl group, nonyl group, decyl group, and the like.

[0033] In one embodiment of the present invention, R 11 , R 12 , R 13 , R 14 , R 15 and R 16 These are, independently, alkyl groups having a hydroxyl group as a substituent, or alkyl groups having an amino group as a substituent.

[0034] Examples of alkyl groups containing a hydroxyl group as a substituent include hydroxymethyl, hydroxyethyl, and hydroxypropyl groups.

[0035] Examples of alkyl groups containing an amino group as a substituent include aminomethyl, aminoethyl, aminopropyl, and aminobutyl groups.

[0036] Examples of alkyl groups containing hydroxyl and amino groups as substituents include hydroxyaminomethyl, hydroxyaminoethyl, and hydroxyaminopropyl groups.

[0037] R 11 , R 12 and R 13 The total number of carbon atoms is 3 to 20, preferably 4 to 20, more preferably 4 to 12, even more preferably 4 to 9, and particularly preferably 4 to 6. R 11 , R 12 and R 13 If the total number of carbon atoms is above the lower limit, the hardness of the resin film can be achieved. On the other hand, if it is below the upper limit, curability at low temperatures of 100°C or below can be achieved. Furthermore, from the viewpoint of improving chemical resistance when used as a resin film, R 11 , R 12 and R 13 The most preferable total number of carbon atoms is 4.

[0038] Among them, R 11 , R 12 , R 13 , R 14 , R 15 and R 16 The alkyl group in is preferably an unsubstituted alkyl group, and more preferably an unsubstituted alkyl group having 1 to 4 carbon atoms.

[0039] From the perspective of further improving low-temperature curing properties, R 11 , R 12 and R 13 Each of these groups is preferably an unsubstituted alkyl group, more preferably an unsubstituted alkyl group having 1 to 4 carbon atoms, and even more preferably a methyl group or an ethyl group. R 11 , R 12 and R 13 Preferably, at least one of them is an ethyl group.

[0040] R 14 、R 15 and R 16 are each independently preferably a hydrogen atom or an unsubstituted alkyl group, more preferably a hydrogen atom or an unsubstituted alkyl group having 1 to 4 carbon atoms, and even more preferably a hydrogen atom, a methyl group or an ethyl group.

[0041] R 14 、R 15 and R 16 Of these, at least one is preferably a hydrogen atom, and more preferably only one is a hydrogen atom. R 14 、R 15 and R 16 By having at least one of these be a hydrogen atom, both low-temperature curability and storage stability are excellent. That is, as the structural unit (I), it is more preferable to include a structural unit represented by the following general formula (I-1) (hereinafter, may be referred to as "structural unit (I-1)").

[0042] <00管理0377>

Chemical formula

[0043] (In the general formula (I-1), R 111 、R<00管理0100>and R<00管理0101>are the same as R<00管理0102>、R​​​​​​​​​​​​​​​​​​​​​The total number of carbon atoms is 3 to 20, preferably 4 to 20, more preferably 4 to 12, even more preferably 4 to 9, and particularly preferably 4 to 6. R 111 , R 112 and R 113 If the total number of carbon atoms is above the lower limit, the hardness of the resin film can be achieved. On the other hand, if it is below the upper limit, low-temperature curing properties can be achieved. Furthermore, from the viewpoint of solvent resistance when formed into a resin film, R 111 , R 112 and R 113 The most preferable total number of carbon atoms is 4.

[0045] Among them, R 111 , R 112 and R 113 , R 114 and R 115 The alkyl group in is preferably an unsubstituted alkyl group, and more preferably an unsubstituted alkyl group having 1 to 4 carbon atoms.

[0046] R 111 , R 112 and R 113 In terms of hardness and curability at low temperatures when formed into a resin film, it is preferable that the group be an unsubstituted alkyl group, more preferably an unsubstituted alkyl group having 1 to 4 carbon atoms, and even more preferably a methyl group or an ethyl group, as these factors improve the hardness and curability at low temperatures when formed into a resin film. R 111 , R 112 and R 113 Preferably, at least one of them is an ethyl group.

[0047] R 114 and R 115 Each of these is preferably a hydrogen atom or an unsubstituted alkyl group, more preferably a hydrogen atom or an unsubstituted alkyl group having 1 to 4 carbon atoms, and even more preferably a hydrogen atom, a methyl group, or an ethyl group.

[0048] The content of constituent unit (I-1) relative to the total molar amount of constituent unit (I) (constituent unit (I-1) / constituent unit (I)) is preferably 10 mol% or more, more preferably 30 mol% or more, even more preferably 50 mol% or more, even more preferably 80 mol% or more, and particularly preferably 90 mol% or more. A content of constituent unit (I-1) above the above lower limit results in better low-temperature curing properties. On the other hand, the upper limit of the content of constituent unit (I-1) can be, for example, 100 mol% of the total molar amount of structure (I), meaning that all constituent unit (I) can be constituent unit (I-1), 95 mol%, or 90 mol% of the total molar amount of constituent unit (I). The content of constituent unit (I-1) relative to the total molar amount of constituent unit (I) (constituent unit (I-1) / constituent unit (I)) is, for example, for a curing agent composition. 13 By measuring the composition ratio of constituent unit (I-1) to constituent unit (I) using 1C-NMR, the molar ratio of constituent unit (I-1) to constituent unit (I) can be calculated.

[0049] [Constituent Unit (II)] It is preferable that the blocked polyisocyanate (B) further contains, in addition to the above-mentioned constituent unit (I), a constituent unit represented by the following general formula (II) (hereinafter sometimes referred to as "constituent unit (II)").

[0050] [ka] (In general formula (II), R 21 , R 22 , R 23 and R 24 These are the R values ​​mentioned above, respectively. 15 and R 16 It is the same as above. The wavy lines represent binding sites, indicating the binding sites with the residues of the polyisocyanate excluding the isocyanate group.

[0051] (R 21 , R 22 , R23 and R 24 ) R 21 , R 22 , R 23 and R 24 As for the resin film, hydrogen atoms or unsubstituted alkyl groups having 1 to 4 carbon atoms are preferred, and hydrogen atoms, methyl groups, or ethyl groups are more preferred, as they exhibit excellent hardness. Furthermore, R is preferred because it exhibits excellent low-temperature curing properties. 21 , R 22 , R 23 and R 24 A methyl group or, more preferably, an ethyl group.

[0052] R 21 , R 22 , R 23 and R 24 If all of them are methyl groups, then both ester moieties of the malonic acid ester of constituent unit (II) become isopropyl groups. Also, R 21 and R 22 Either one of them is a hydrogen atom, and the other is a methyl group, and R 23 and R 24 If one of them is a hydrogen atom and the other is a methyl group, then both ester sites of the malonic acid ester of constituent unit (II) become ethyl groups.

[0053] Among them, R 21 , R 22 , R 23 and R 24 It is particularly preferable that all of them are methyl groups, that is, that both ester moieties of the malonic acid ester of constituent unit (II) are isopropyl groups.

[0054] The molar ratio of constituent unit (II) to constituent unit (I) (constituent unit (II) / constituent unit (I)) is preferably 4 / 96 or more and 96 / 4 or less, more preferably 5 / 95 or more and 95 / 5 or less, even more preferably 7 / 93 or more and 93 / 7 or less, even more preferably 10 / 90 or more and 90 / 10 or less, even more preferably 20 / 80 or more and 85 / 15 or less, even more preferably 30 / 70 or more and 85 / 15 or less, particularly preferably 35 / 65 or more and 85 / 15 or less, and most preferably 50 / 50 or more and 70 / 30 or less. Having the constituent unit (II) / constituent unit (I) ratio above the lower limit can result in better hardness when formed into a resin film. Also, having it below the upper limit can result in better low-temperature curability. The molar ratio of constituent unit (II) to constituent unit (I) is, for example, when preparing a curing agent composition. 1 H-NMR and 13 It can be calculated by measuring the composition ratio of constituent unit (II) to constituent unit (I) using 1C-NMR.

[0055] [Polyisocyanate] Polyisocyanates are reaction products obtained by reacting multiple monomer compounds having one or more isocyanate groups (-NCO) (hereinafter sometimes referred to as "isocyanate monomers").

[0056] Polyisocyanates can have one or more functional groups selected from the group consisting of allophanate groups, uretdione groups, iminooxadiazinedione groups, isocyanurate groups, urethane groups, and biuret groups. Among these, having isocyanurate groups is preferable because it provides excellent weather resistance.

[0057] The isocyanate monomer is preferably one having 4 to 30 carbon atoms. Specific examples of isocyanate monomers include the following. These isocyanate monomers may be used individually or in combination of two or more. (1) Aromatic diisocyanates such as diphenylmethane-4,4'-diisocyanate (MDI), 1,5-naphthalene diisocyanate, tolylene diisocyanate (TDI), and xylylene diisocyanate, m-tetramethylxylylene diisocyanate (TMXDI). (2) Aliphatic diisocyanates such as 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate (hereinafter sometimes referred to as "HDI"), 2,2,4-trimethyl-1,6-diisocyanatohexane, 2,4,4-trimethyl-1,6-hexamethylene diisocyanate, 2-methylpentane-1,5-diisocyanate (MPDI), and lysine diisocyanate (hereinafter sometimes referred to as "LDI"). (3) Alicyclic diisocyanates such as isophorone diisocyanate (hereinafter sometimes referred to as "IPDI"), 1,3-bis(diisocyanate methyl)cyclohexane, 4,4'-dicyclohexylmethane diisocyanate, diisocyanate norbornane, and di(isocyanate methyl)norbornane. (4) Triisocyanates such as 4-isocyanate methyl-1,8-octamethylene diisocyanate (hereinafter sometimes referred to as "NTI"), 1,3,6-hexamethylene triisocyanate (hereinafter sometimes referred to as "HTI"), bis(2-isocyanatoethyl)2-isocyanatoglutarate (hereinafter sometimes referred to as "GTI"), and lysine triisocyanate (hereinafter sometimes referred to as "LTI").

[0058] In particular, due to their excellent weather resistance, one or more diisocyanates selected from the group consisting of aliphatic diisocyanates and alicyclic diisocyanates are preferred as the isocyanate monomer. Furthermore, HDI or IPDI are more preferred as the isocyanate monomer due to their ease of industrial availability. Moreover, HDI is even more preferred as the isocyanate monomer from the viewpoint of reducing the viscosity of the block polyisocyanate component.

[0059] Furthermore, as the isocyanate monomer used in the production of polyisocyanates, either aliphatic diisocyanates or alicyclic diisocyanates may be used alone, or they may be used in combination. In particular, it is preferable to use a combination of aliphatic diisocyanates and alicyclic diisocyanates, and it is more preferable to use HDI and IPDI. By using aliphatic diisocyanates and alicyclic diisocyanates, the toughness and hardness of the resin film can be further improved.

[0060] (Polyol) It is preferable that the polyisocyanate is derived from the diisocyanate monomer described above and a polyol having an average number of hydroxyl functional groups of 3.0 or more and 8.0 or less. This allows for a larger average number of isocyanate groups in the resulting polyisocyanate. In this polyisocyanate, urethane groups are formed by the reaction of the hydroxyl groups of the polyol with the isocyanate groups of the diisocyanate monomer.

[0061] The average number of hydroxyl groups in a polyol is preferably 3.0 to 8.0, more preferably 3 to 6, even more preferably 3 to 5, and particularly preferably 3 or 4. Here, the average number of hydroxyl groups in a polyol refers to the number of hydroxyl groups present in one polyol molecule.

[0062] As for the number-average molecular weight of the polyol, from the viewpoint of improving coating hardness and strength, it is preferably 100 to 1000, preferably 100 to 900, more preferably 100 to 600, even more preferably 100 to 570, even more preferably 100 to 500, even more preferably 100 to 400, particularly preferably 100 to 350, and most preferably 100 to 250. By having the number-average molecular weight of the polyol within the above range, the curing agent composition exhibits superior low-temperature curing properties, and particularly superior hardness and strength. The number-average molecular weight Mn of the polyol is, for example, the number-average molecular weight of polystyrene measured by GPC.

[0063] Examples of such polyols include trimethylolpropane, glycerol, and polycaprolactone polyols derived from trivalent or higher polyhydric alcohols and ε-caprolactone.

[0064] Commercially available polycaprolactone polyols include Daicel's "Praxel 303" (number average molecular weight 300), "Praxel 305" (number average molecular weight 550), "Praxel 308" (number average molecular weight 850), and "Praxel 309" (number average molecular weight 900).

[0065] (Method for producing polyisocyanates) The method for producing polyisocyanate is described in detail below. Polyisocyanates can be obtained, for example, by simultaneously producing allophanate reactions to form allophanate groups, uretdione reactions to form uretdione groups, iminooxadiadindione reactions to form iminooxadiadindione groups, isocyanurate reactions to form isocyanurate groups, urethane reactions to form urethane groups, and biuret reactions to form biuret groups in the presence of an excess of isocyanate monomer, and then removing the unreacted isocyanate monomer after the reaction is complete. In other words, the polyisocyanate obtained by the above reaction is a reaction product in which multiple isocyanate monomers are bonded together and which has one or more groups selected from the group consisting of allophanate groups, uretdione groups, iminooxadiadindione groups, isocyanurate groups, urethane groups, and biuret groups. Alternatively, the above reactions may be carried out separately, and the resulting polyisocyanates may be mixed in a specific ratio. From the standpoint of ease of production, it is preferable to perform the above reaction in one step to obtain polyisocyanate; however, from the viewpoint of freely adjusting the molar ratio of each functional group, it is preferable to produce them separately and then mix them.

[0066] The allophanate reaction, uretdione reaction, iminooxadiazinedione reaction, isocyanurate reaction, urethane reaction, and biuret reaction described above may be carried out sequentially, or some of them may be carried out in parallel. After the reaction is complete, unreacted isocyanate monomers can be removed from the reaction solution by thin-film distillation, extraction, or other methods to obtain polyisocyanate.

[0067] Furthermore, antioxidants or UV absorbers may be added to the obtained polyisocyanate, for example, to suppress discoloration during storage. Examples of antioxidants include hindered phenols such as 2,6-di-tert-butyl-p-cresol. Examples of ultraviolet absorbers include benzotriazole and benzophenone. These antioxidants and ultraviolet absorbers may be used individually or in combination of two or more. The amount of these added is preferably 10 ppm by mass or more and 500 ppm by mass relative to the mass of the polyisocyanate.

[0068] (Average number of isocyanate groups in polyisocyanates) The average number of isocyanate groups in the polyisocyanate is preferably 2 or more, in order to enhance low-temperature curability. Furthermore, from the viewpoint of achieving both low-temperature curability and compatibility with polyvalent hydroxy compounds, a value of 3.0 to 20.0 is more preferable, 3.2 to 10.0 is even more preferable, 3.4 to 8.0 is particularly preferable, and 3.5 to 6.0 is most preferable. The average number of isocyanate functional groups in a polyisocyanate can be measured using the method described in the examples below.

[0069] (hydrophilic compound) Alternatively, a hydrophilic compound-modified polyisocyanate may be used, in which a portion of the polyisocyanate is modified with a hydrophilic compound.

[0070] Examples of hydrophilic compounds include nonionic hydrophilic compounds, anionic hydrophilic compounds, and cationic hydrophilic compounds. These hydrophilic compounds may be used individually or in combination of two or more types.

[0071] Examples of nonionic hydrophilic compounds include monoalcohols and compounds obtained by adding ethylene oxide to the hydroxyl group of an alcohol. Examples of monoalcohols include methanol, ethanol, and butanol. Examples of compounds obtained by adding ethylene oxide to the hydroxyl group of an alcohol include ethylene glycol, diethylene glycol, and polyethylene glycol. These nonionic hydrophilic compounds also possess active hydrogen groups that react with isocyanate groups.

[0072] Among nonionic hydrophilic compounds, polyethylene glycol monoalkyl ethers, obtained by adding ethylene oxide to the hydroxyl group of a monoalcohol, are preferred because they can improve the water dispersibility of the curing agent composition with a small amount of use.

[0073] The number of ethylene oxide atoms added to the compound is preferably 4 to 30, and more preferably 4 to 25. When the number of ethylene oxide atoms is above the lower limit, the curing agent composition tends to be more effectively given water dispersibility, and when the number of ethylene oxide atoms is below the upper limit, precipitates of the curing agent composition tend to be less likely to occur during low-temperature storage.

[0074] Specifically, examples of cationic hydrophilic compounds include compounds having both a cationic hydrophilic group and an active hydrogen group. Alternatively, a hydrophilic compound may be formed by combining a compound having an active hydrogen group, such as a glycidyl group, with a compound having a cationic hydrophilic group, such as a sulfide or phosphine. In this case, a compound having an isocyanate group and a compound having an active hydrogen group are reacted beforehand to add a functional group such as a glycidyl group, and then the compound such as a sulfide or phosphine is reacted. From the viewpoint of ease of production, compounds having both a cationic hydrophilic group and an active hydrogen group are preferred.

[0075] Examples of anionic hydrophilic compounds include compounds that possess both an anionic group and an active hydrogen group, and more specifically, compounds in which the carboxyl group of a monohydroxycarboxylic acid or polyhydroxycarboxylic acid is the anionic group.

[0076] [Blocking agent] The blocking agent contains a malonic acid ester. There are no particular limitations on the malonic acid ester, but a malonic acid ester having a primary alkyl group, a malonic acid ester having a secondary alkyl group, or a malonic acid ester having a tertiary alkyl group is preferred, and a malonic acid ester having a secondary alkyl group or a malonic acid ester having a tertiary alkyl group is more preferred. The blocking agent may contain one of each of the malonic acid ester having a secondary alkyl group, a malonic acid ester having a primary alkyl group, and a malonic acid ester having a tertiary alkyl group, or it may contain a combination of two or more.

[0077] There are no particular limitations on malonic acid esters having a primary alkyl group, but examples include dimethyl malonate, diethyl malonate, dipropyl malonate, dibutyl malonate, dicyclohexyl malonate, and diphenyl malonate. Among these, diethyl malonate is preferred as the malonic acid ester having a primary alkyl group.

[0078] There are no particular limitations on malonic acid esters having a secondary alkyl group, but examples include di-sec-butyl malonate, diisopropyl malonate, and isopropylethyl malonate. Among these, diisopropyl malonate is preferred as the malonic acid ester having a secondary alkyl group.

[0079] Examples of malonic acid esters having a tertiary alkyl group include, but are not limited to, di-tert-butyl malonate, di(2-methyl-2-butyl) malonate, di(2-methyl-2-pentyl) malonate, (tert-butyl) ethyl malonate, (2-methyl-2-butyl) ethyl malonate, (2-methyl-2-butyl) isopropyl malonate, (2-methyl-2-pentyl) ethyl malonate, (2-methyl-2-pentyl) isopropyl malonate, and (2-methyl-2-pentyl) hexyl isopropyl malonate. Among these, di(2-methyl-2-butyl) malonate, di(2-methyl-2-pentyl) malonate, isopropyl (2-methyl-2-butyl) malonate, ethyl (2-methyl-2-pentyl) malonate, or isopropyl (2-methyl-2-pentyl) malonate is preferred, ethyl (2-methyl-2-butyl) malonate, isopropyl (2-methyl-2-butyl) malonate, ethyl (2-methyl-2-pentyl) malonate, or hexyl isopropyl (2-methyl-2-pentyl) malonate is more preferred, and di-tert-butyl malonate, isopropyl (2-methyl-2-butyl) malonate, or isopropyl (2-methyl-2-pentyl) malonate is even more preferred. The malonic acid ester having a tertiary alkyl group may be a commercially available product, or it may be synthesized using the method described in Reference 1 (Japanese Patent Publication No. 11-130728).

[0080] In the production of blocked polyisocyanate (B), the content of the malonic acid ester having a secondary alkyl group and the malonic acid ester having a tertiary alkyl group, relative to the total molar amount of the blocking agent, is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 90 mol% or more, particularly preferably 95 mol% or more, and most preferably 100 mol%. By keeping the content of malonic acid esters having a secondary alkyl group and malonic acid esters having a tertiary alkyl group within the above range, low-temperature curability can be further improved.

[0081] (Other blocking agents) The blocking agent used in the production of blocked polyisocyanate (B) may also include other blocking agents in addition to malonic acid ester, as long as they do not interfere with the effects achieved by the curing agent composition of this embodiment.

[0082] Other blocking agents include 1) alcohol compounds, 2) alkylphenol compounds, 3) phenol compounds, 4) active methylene compounds other than malonic acid esters, 5) mercaptan compounds, 6) acid amide compounds, 7) acid imide compounds, 8) imidazole compounds, 9) urea compounds, 10) oxime compounds, 11) amine compounds, 12) imide compounds, 13) bisulfites, 14) pyrazole compounds, and 15) triazole compounds. More specifically, the following are examples of blocking agents.

[0083] [Method for producing blocked polyisocyanate (B)] Blocked polyisocyanate (B) is obtained by reacting the above polyisocyanate (or hydrophilic compound-modified polyisocyanate) with the above blocking agent.

[0084] When using hydrophilic compound-modified polyisocyanate as the polyisocyanate, the reaction between the polyisocyanate and the hydrophilic compound, and the reaction between the polyisocyanate and the blocking agent can be carried out simultaneously, or the second and subsequent reactions can be carried out after either reaction has been carried out first. In particular, it is preferable to carry out the reaction between the polyisocyanate and the hydrophilic compound first to obtain a hydrophilic compound-modified polyisocyanate modified by the hydrophilic compound, and then carry out the reaction between the obtained hydrophilic compound-modified polyisocyanate and the blocking agent.

[0085] The reaction between polyisocyanate and hydrophilic compound may use organometallic salts, tertiary amine compounds, or alkali metal alkoxides as catalysts. Examples of metals constituting the organometallic salts include tin, zinc, and lead. Examples of alkali metals include sodium.

[0086] The reaction temperature between polyisocyanate and hydrophilic compound is preferably between -20°C and 150°C, and more preferably between 30°C and 130°C. A reaction temperature above the lower limit tends to result in higher reactivity. Conversely, a reaction temperature below the upper limit tends to more effectively suppress side reactions.

[0087] It is preferable to completely react the hydrophilic compound with the polyisocyanate so that no unreacted residue remains. By preventing any unreacted residue, the water dispersion stability and low-temperature curing properties of the curing agent composition tend to be less likely to deteriorate.

[0088] The blocking reaction between polyisocyanate (or hydrophilic compound-modified polyisocyanate) and a blocking agent is not particularly limited, but two methods are described below. 1) A method of reacting the above-mentioned polyisocyanate with a blocking agent containing malonic acid ester. 2) A method of reacting the above-mentioned polyisocyanate with a blocking agent containing a malonic acid ester, adding an alcohol having a chain alkyl group to the resulting reaction product, and introducing an alkyl group derived from the alcohol by transesterification of the terminal ester portion of the reaction product.

[0089] Of the two methods described above, method 2) is preferred, considering the ease of the process and the ease of controlling the molar ratio of constituent unit (II) to constituent unit (I).

[0090] The blocking reaction between polyisocyanate and a blocking agent can be carried out with or without the presence of a solvent, yielding blocked polyisocyanate.

[0091] Furthermore, the blocking agent may consist of one type of malonic acid ester, or a combination of two or more types.

[0092] The amount of blocking agent added is usually 80 mol% to 200 mol% relative to the total molar amount of isocyanate groups, and preferably 90 mol% to 150 mol%.

[0093] Furthermore, when using malonic acid esters having a secondary alkyl group and malonic acid esters having a tertiary alkyl group in the added blocking agent, the molar ratio of malonic acid ester having a secondary alkyl group to malonic acid ester having a tertiary alkyl group (malonic acid ester having a secondary alkyl group / malonic acid ester having a tertiary alkyl group) is preferably greater than 5 / 95 and less than 95 / 5, more preferably 7 / 93 to 93 / 7, even more preferably 10 / 90 to 93 / 7, particularly preferably 20 / 80 to 93 / 7, and most preferably 30 / 70 to 93 / 7. A molar ratio above the lower limit of the above can result in good hardness when formed into a resin film. Also, a molar ratio below the upper limit of the above can result in good low-temperature curability.

[0094] When using a solvent during the blocking reaction, it is sufficient to use a solvent that is inert to the isocyanate group. When a solvent is used, the content of non-volatile components per 100 parts by mass of the curing agent composition is usually 10 parts by mass or more and 95 parts by mass or less, preferably 20 parts by mass or more and 80 parts by mass or less, and more preferably 30 parts by mass or more and 75 parts by mass or less.

[0095] In the blocking reaction, organometallic salts such as tin, zinc, and lead, tertiary amine compounds, and alkali metal alkoxides such as sodium may be used as catalysts. The amount of catalyst added varies depending on the temperature of the blocking reaction, etc., but is usually 0.05 parts by mass or more and 1.5 parts by mass or less per 100 parts by mass of polyisocyanate, and preferably 0.1 parts by mass or more and 1.0 part by mass or less.

[0096] The blocking reaction can generally be carried out at temperatures between -20°C and 150°C, preferably between 0°C and 100°C, and more preferably between 10°C and 80°C. A temperature above the lower limit of the blocking reaction allows for a higher reaction rate. Furthermore, a temperature below the upper limit of the blocking reaction allows for greater suppression of side reactions.

[0097] After the blocking reaction, neutralization treatment may be performed by adding an acidic compound or the like. The acidic compound may be an inorganic acid or an organic acid. Examples of inorganic acids include hydrochloric acid, phosphorous acid, and phosphoric acid. Examples of organic acids include methanesulfonic acid, p-toluenesulfonic acid, dioctyl phthalate, and dibutyl phthalate.

[0098] When manufactured by the method described in (2) above, a transesterification reaction is carried out following the blocking reaction. 2) The alcohols having a chain alkyl group used in the transesterification reaction are preferably monoalcohols, including primary monoalcohols such as methanol, ethanol, propanol, butanol, hexanol, and 2-ethylhexanol; secondary monoalcohols such as isopropanol, 2-butanol, 2-pentanol, and 2-hexanol; and tertiary monoalcohols such as tert-butanol, 2-methyl-2-butanol, 2-methyl-2-pentanol, 2-methyl-2-hexanol, 2-methyl-2-heptanol, 2-methyl-2-octanol, 3-methyl-3-pentanol, 3-ethyl-3-hexanol, and 3-ethyl-3-octanol.

[0099] Furthermore, the linear alkyl group of the alcohol may be the same as that of the malonic acid ester, or it may be a different linear alkyl group. When the alcohol has a different linear alkyl group than that of the malonic acid ester, it is preferable to use a monoalcohol having a linear alkyl group with a different number of alkyl substitutions than that of the malonic acid ester. Specifically, when a malonic acid ester having a secondary alkyl group is used alone as a blocking agent, a monoalcohol having a tertiary alkyl group can be used.

[0100] When producing by method 2), it is preferable to remove any residual alcohol produced or added during or after the transesterification reaction by distillation under normal or reduced pressure. In particular, in order to efficiently carry out the transesterification reaction, it is preferable to remove the alcohol generated during the transesterification reaction by performing operations such as distillation. In this case, in order to efficiently remove the alcohol component generated by the exchange reaction, it is even more preferable that the added alcohol component has a boiling point higher than that of the generated alcohol component.

[0101] Transesterification reactions can generally be carried out at temperatures between 0°C and 150°C. In particular, it is preferable to carry out the transesterification reaction at temperatures between 30°C and 120°C, and more preferably at temperatures between 50°C and 100°C. A temperature above the lower limit of the transesterification reaction allows for a higher reaction rate. Furthermore, a temperature below the upper limit of the transesterification reaction allows for greater suppression of side reactions.

[0102] The alcohol content in the curing agent composition is preferably 0.05 parts by mass or more and 41 parts by mass or less, more preferably 0.1 parts by mass or more and 30 parts by mass or less, and even more preferably 0.5 parts by mass or more and 10 parts by mass or less, per 100 parts by mass of solids of the curing agent composition. A minimum alcohol content above the lower limit ensures good storage stability of the curing agent composition. Furthermore, a minimum alcohol content below the upper limit prevents the viscosity from increasing significantly when compounded with the resin composition. Note that "alcohol content in the curing agent composition" here refers to the amount of alcohol remaining in the curing agent composition as a single compound.

[0103] ≪Melamine resin (M)≫ Melamine resin (M) generally refers to a thermosetting resin synthesized from melamine and aldehyde, with three reactive functional groups (-NX) in one triazine core molecule. 1 X 2 It holds.

[0104] Examples of melamine resin (M) include four types: a fully alkyl type containing -N-(CH2OR)2 [where R is an alkyl group, the same applies hereafter] as a reactive functional group; a methylol group type containing -N-(CH2OR)(CH2OH) as a reactive functional group; an imino group type containing -N-(CH2OR)(H) as a reactive functional group; and a methylol / imino group type containing both -N-(CH2OR)(CH2OH) and -N-(CH2OR)(H), or containing -N-(CH2OH)(H).

[0105] As the melamine resin (M), a partially methylolated melamine resin or a fully methylolated melamine resin obtained by the reaction of a melamine component with an aldehyde component can be used. Examples of aldehyde components include formaldehyde, paraformaldehyde, acetaldehyde, and benzaldehyde.

[0106] Furthermore, a methylolated melamine resin can also be used in which the methylol groups have been partially or completely etherified with a suitable alcohol. Examples of alcohols used for etherification include methyl alcohol, ethyl alcohol, n-propyl alcohol, iso-propyl alcohol, n-butyl alcohol, iso-butyl alcohol, 2-ethyl-1-butanol, and 2-ethyl-1-hexanol.

[0107] The melamine resin (M) is preferably a methyl etherified melamine resin in which the methylol groups of a partially or completely methylolated melamine resin are partially or completely etherified with methyl alcohol, a butyl etherified melamine resin in which the methylol groups of a partially or completely methylolated melamine resin are partially or completely etherified with butyl alcohol, or a methyl-butyl mixed etherified melamine resin in which the methylol groups of a partially or completely methylolated melamine resin are partially or completely etherified with methyl alcohol and butyl alcohol, with the methyl-butyl mixed etherified melamine resin being more preferred.

[0108] The weight-average molecular weight of the melamine resin is preferably 400 to 6,000, more preferably 500 to 4,000, and even more preferably 600 to 3,000. The weight-average molecular weight of melamine resin is the weight-average molecular weight based on polystyrene, measured by gel permeation chromatography (GPC).

[0109] Commercially available melamine resin can be used. Examples of commercially available product names include: "Cymel 202", "Cymel 203", "Cymel 204", "Cymel 211", "Cymel 212", "Cymel 238", "Cymel 251", "Cymel 253", "Cymel 254", "Cymel 303", "Cymel 323", "Cymel 324", "Cymel 325", "Cymel 327", "Cymel 350", "Cymel 370", "Cymel 380", "Cymel 385", "Cymel 1156", "Cymel 1158", "Cymel 1116", and "Cymel 11 Examples include "30" (manufactured by Ornex Japan Co., Ltd.), "Regimin 735", "Regimin 740", "Regimin 741", "Regimin 745", "Regimin 746", and "Regimin 747" (manufactured by Monsanto); "Uban 120", "Uban 20HS", "Uban 20SE", "Uban 2021", "Uban 2028", and "Uban 28-60" (manufactured by Mitsui Chemicals, Inc.); and "Sumimar M55", "Sumimar M30W", and "Sumimar M50W" (manufactured by Sumitomo Chemical Co., Ltd.).

[0110] In the curing agent composition of this embodiment, the total mass of solids contained in the blocked polyisocyanate (B) is preferably 12 parts by mass or more, more preferably 14 parts by mass or more, even more preferably 20 parts by mass or more, and particularly preferably 30 parts by mass or more, based on 100 parts by mass of the total mass of solids contained in the melamine resin (M). Furthermore, the total mass of solids contained in the blocked polyisocyanate (B) is preferably 92 parts by mass or less, more preferably 88 parts by mass or less, even more preferably 82 parts by mass or less, and particularly preferably 80 parts by mass or less, based on 100 parts by mass of the total mass of solids contained in the melamine resin (M). The above upper and lower limits for the total mass of solids contained in block polyisocyanate (B) relative to 100 parts by mass of total solids contained in melamine resin (M) can be arbitrarily combined. For example, 12 parts by mass or more and 80 parts by mass or less, 14 parts by mass or more and 80 parts by mass or less, 20 parts by mass or more and 90 parts by mass or less, 30 parts by mass or more and 80 parts by mass or less, etc. The total mass of solids contained in block polyisocyanate (B) is within the above numerical range, resulting in excellent low-temperature curability and storage stability. In this embodiment, the "solid content" contained in the curing agent composition refers to non-volatile components excluding substances that can volatilize during the formation of the resin film, etc.

[0111] <<Other components>> In addition to the block polyisocyanate (B) and the melamine resin (M) described above, the curing agent composition of this embodiment may further contain other components such as resins, surface modifiers, and solvents.

[0112] Examples of resins include polyethylene resin, polypropylene resin, acrylonitrile-butadiene-styrene (ABS) resin, polyamide resin, acrylic resin, vinylidene chloride resin, polycarbonate resin, polyurethane resin, and epoxy resin.

[0113] The surface modifier is not particularly limited, but examples include silicone-based and acrylic-based agents.

[0114] The surface modifier content is preferably 0.05% by mass or more and 5% by mass or less relative to the solid content of the curing agent composition. A surface modifier content above the lower limit of the above value results in excellent appearance when formed into a resin film. Furthermore, by keeping the surface conditioning agent content below the above upper limit, the resin film exhibits better resistance to repellency, recoating properties, and stain resistance.

[0115] Commercially available silicone-based surface modifiers can be used, such as BYK-300, BYK-302, BYK-306, BYK-307, BYK-310, BYK-313, BYK-315N, BYK-320, BYK-322, BYK-323, BYK-325, BYK-326, BYK-330, BYK-331, BYK-333, BYK-342, B YK-346, BYK-370, BYK-375, BYK-377, BYK-378, BYK-3760 (manufactured by BYK); Disparon 1711EF, Disparon 1761, Disparon LS-001, Disparon LS-050, Disparon LS-280, Disparon LS-460, Disparon LS-480 (manufactured by Kusumoto Kasei Co., Ltd.); Tego Examples include Flow 425, Tego Glide 100, Tego Glide 110, Tego Glide 130, Tego Glide 406, Tego Glide 420, Tego Glide 432, Tego Glide 435, Tego Glide 440, Tego Glide 450, Tego Glide 482, Tego Glide 485, Tego Glide ZG400, Tego wet KL245, Tego wet 250, Tego wet 260, Tego wet 265, Tego wet 270, and Tego wet 280 (manufactured by Evonik Tego Chemie). These may be used individually or in combination of two or more types.

[0116] Examples of commercially available acrylic surface modifiers include BYK-350, BYK-354, BYK-355, BYK-356, BYK-358N, BYK-361N, BYK-392, BYK-394, BYK-3441 (manufactured by BYK Corporation); Disparon LF-1983, Disparon LF-1984, LF-1985, Disparon UVX-35, Disparon UVX-36 (manufactured by Kusumoto Kasei Co., Ltd.); Tego Flow 300, Tego Flow 370, Tego Flow ATF2, and Tego Flow ZFS460. These may be used individually or in combination of two or more.

[0117] Other types of surface modifiers not listed above can be commercially available, including BYK-399, BYK-3440, BYK-3550, BYK-3560, BYK-3565, BYK-SILCLEAN 3700, BYK-SILCLEAN 3701, BYKETOL-OK (manufactured by BYK); Disparon UVX-272, Disparon UVX-2285, Disparon LHP-810, Disparon NSH-8430HF, Disparon LHP-90, Disparon LHP-91, and Disparon LHP-95, Disparon LHP-96 (manufactured by Kusumoto Kasei Co., Ltd.). These may be used individually or in combination of two or more types.

[0118] The solvents include 1-methylpyrrolidone, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, dipropylene glycol monomethyl ether, propylene glycol monomethyl ether, 3-methoxy-3-methyl-1-butanol, ethylene glycol diethyl ether, diethylene glycol diethyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dipropylene glycol dimethyl ether (DPDM), propylene glycol dimethyl ether, methyl ethyl ketone, acetone, and Examples of solvents include ethyl isobutyl ketone, propylene glycol monomethyl ether acetate, ethanol, methanol, iso-propanol, 1-propanol, iso-butanol, 1-butanol, tert-butanol, 2-ethylhexanol, cyclohexanol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,4-butanediol, 1,3-butanediol, ethyl acetate, isopropyl acetate, butyl acetate, toluene, xylene, pentane, iso-pentane, hexane, iso-hexane, cyclohexane, solvent naphtha, and mineral spirits. These solvents may be used individually or in combination of two or more. From the viewpoint of dispersibility in water, solvents with a solubility in water of 5% by mass or more are preferred, and specifically, DPDM is preferred.

[0119] (Method for manufacturing the curing agent composition) The curing agent composition is not particularly limited, but for example, it can be obtained by mixing the above-mentioned blocked isocyanate (B) and melamine resin (M) such that the solid content of blocked polyisocyanate (B) is 8 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the solid content of melamine resin (M). Melamine resin (M) may be added during or after the blocking reaction. The temperature at which the above-mentioned blocked isocyanate (B) and melamine resin (M) are mixed is not particularly limited, but is preferably between 20°C and 100°C. A reaction temperature above the lower limit tends to result in higher hardness. Conversely, a reaction temperature below the upper limit tends to more effectively suppress side reactions.

[0120] <Resin composition> The resin composition of this embodiment comprises the curing agent composition described above and a polyvalent hydroxy compound. The resin composition of this embodiment can also be described as a one-component resin composition comprising a curing agent component and a main component.

[0121] The resin composition of this embodiment, by containing the curing agent composition described above, exhibits excellent low-temperature curing properties.

[0122] The components of the resin composition of this embodiment will be described in detail below.

[0123] <<Polyvalent hydroxy compounds>> In this specification, "polyvalent hydroxy compound" means a compound having at least two hydroxyl groups in one molecule, and is also called a "polyol."

[0124] Specific examples of the polyhydric hydroxy compounds include aliphatic hydrocarbon polyols, polyether polyols, polyester polyols, epoxy resins, fluorine-containing polyols, and acrylic polyols. Among these, polyester polyols, fluorine-containing polyols, or acrylic polyols are preferred as polyhydric hydroxy compounds.

[0125] [Hydroxyl value and acid value of polyhydric hydroxy compounds] The hydroxyl value of the polyvalent hydroxy compound contained in the resin composition of this embodiment is preferably 5 mg KOH / g or more and 300 mg KOH / g or less, more preferably 10 mg KOH / g or more and 280 mg KOH / g or less, and even more preferably 30 mg KOH / g or more and 250 mg KOH / g or less. By having the hydroxyl value of the polyvalent hydroxy compound within the above range, a resin film with superior physical properties such as tensile strength can be obtained. Specifically, by having the hydroxyl groups of the polyvalent hydroxy compound above the lower limit, the crosslinking density of the urethane due to the reaction with the polyisocyanate is increased, making it easier for the urethane bond to function. On the other hand, by having the hydroxyl groups of the polyvalent hydroxy compound below the upper limit, the crosslinking density does not increase too much, resulting in better mechanical properties of the resin film. The hydroxyl value of the polyvalent hydroxy compound is measured, for example, by potentiometric titration and calculated as a value relative to the solid content in the polyvalent hydroxy compound.

[0126] [Glass transition temperature (Tg) of polyvalent hydroxy compounds] The glass transition temperature (Tg) of the polyvalent hydroxy compound contained in the resin composition of this embodiment is preferably 0°C to 100°C, more preferably 0°C to 90°C, even more preferably 0°C to 80°C, and particularly preferably 5°C to 70°C. A glass transition temperature of the polyvalent hydroxy compound within the above range results in a resin film with superior tensile strength. The glass transition temperature of the polyvalent hydroxy compound can be measured, for example, using a differential scanning calorimetry (DSC) analyzer.

[0127] [Weight-average molecular weight (Mw) of polyhydric hydroxy compounds] The weight-average molecular weight Mw of polyvalent hydroxy compounds is 5.0 × 10⁻⁶. 3 The above 2.0 × 10 5 The following is preferable: 5.0 × 10 3 The above 1.5 × 10 5 The following is more preferable: 5.0 × 10 3 The above 1.0 × 10 5The following is even more preferable: When the weight-average molecular weight Mw of the polyvalent hydroxy compound is within the above range, a resin film with superior physical properties such as tensile strength can be obtained. The weight-average molecular weight Mw of the polyvalent hydroxy compound is the weight-average molecular weight based on polystyrene, measured by gel permeation chromatography (GPC).

[0128] [NCO / OH] The molar equivalent ratio (NCO / OH) of the isocyanate groups of the curing agent composition to the hydroxyl groups of the polyvalent hydroxy compound contained in the resin composition of this embodiment is determined by the required physical properties of the resin film, but is usually between 0.01 and 10.00. In particular, the molar equivalent ratio (NCO / OH) is preferably between 0.10 and 5.00, more preferably between 0.20 and 3.00, and even more preferably between 0.25 and 2.00.

[0129] <<Other additives>> The resin composition of this embodiment may further contain other additives. Other additives include curing agents, curing catalysts, solvents, pigments (extender pigments, coloring pigments, metallic pigments, etc.) that can react with the crosslinking functional groups in polyvalent hydroxy compounds, UV absorbers, light stabilizers, radical stabilizers, anti-yellowing agents to suppress discoloration during the baking process, coating surface modifiers, flow modifiers, pigment dispersants, defoamers, thickeners, and film-forming aids.

[0130] (Method for manufacturing resin compositions) The resin composition of this embodiment can be used in both solvent-based and water-based systems.

[0131] When producing an aqueous resin composition, first, a polyvalent hydroxy compound or its aqueous dispersion or aqueous solution is added, as needed, to which additives such as a curing agent, curing catalyst, solvent, pigments (extender pigments, coloring pigments, metallic pigments, etc.), ultraviolet absorber, light stabilizer, radical stabilizer, anti-yellowing agent to suppress discoloration during the baking process, coating surface modifier, flow modifier, pigment dispersant, defoamer, thickener, and film-forming aid are added. Next, the curing agent composition or its aqueous dispersion is added as a curing agent, and water or solvent is further added as needed to adjust the viscosity. Finally, the mixture is forcibly stirred using a stirring device to obtain an aqueous resin composition.

[0132] When manufacturing a solvent-based resin composition, first, a polyvalent hydroxy compound or its solvent dilution is mixed with additives such as a curing agent, curing catalyst, solvent, pigments (extender pigments, coloring pigments, metallic pigments, etc.) that can react with the crosslinkable functional group in the polyvalent hydroxy compound, UV absorber, light stabilizer, radical stabilizer, anti-yellowing agent to suppress discoloration during the baking process, coating surface modifier, flow modifier, pigment dispersant, defoamer, thickener, and film-forming aid. Next, the curing agent composition is added as a curing agent, and if necessary, a solvent is further added to adjust the viscosity. Finally, the mixture is stirred by hand or using a stirring device such as a mixer to obtain the solvent-based resin composition.

[0133] <Resin film> The resin film of this embodiment is obtained by curing the above-mentioned resin composition.

[0134] The resin film of this embodiment is obtained by coating the above-mentioned resin composition onto a substrate using known methods such as roll coating, curtain flow coating, spray coating, bell coating, and electrostatic coating, and then curing it by heating.

[0135] From the viewpoint of energy saving and the heat resistance of the substrate, the heating temperature is preferably 70°C to 120°C, more preferably 70°C to 110°C, and even more preferably 75°C to 100°C.

[0136] From the viewpoint of energy saving and the heat resistance of the base material, the heating time is preferably 1 minute or more and 60 minutes or less, and more preferably 2 minutes or more and 40 minutes or less.

[0137] The substrate is not particularly limited and includes the exterior panels of automobile bodies such as passenger cars, trucks, motorcycles, and buses; automobile parts such as bumpers; the exterior panels of household electrical appliances such as mobile phones and audio equipment; and various films. Among these, the exterior panels of automobile bodies or automobile parts are preferred.

[0138] The material of the base material is not particularly limited and includes metal materials such as iron, aluminum, brass, copper, tinplate, stainless steel, galvanized steel, and zinc alloy (Zn-Al, Zn-Ni, Zn-Fe, etc.) plated steel; resins such as polyethylene resin, polypropylene resin, acrylonitrile-butadiene-styrene (ABS) resin, polyamide resin, acrylic resin, vinylidene chloride resin, polycarbonate resin, polyurethane resin, epoxy resin, and various FRP plastic materials; inorganic materials such as glass, cement, and concrete; wood; and fibrous materials such as paper and cloth. Among these, metal materials or plastic materials are preferred.

[0139] The substrate may be the surface of the metal material described above, or the metal surface of a car body or the like molded from the metal material, that has been subjected to surface treatment such as phosphate treatment, chromate treatment, or composite oxide treatment, and may also have a coating film formed thereon. The substrate on which the coating film is formed may be one on which a surface treatment has been applied as necessary, and an undercoat coating film has been formed thereon, for example, a car body on which an undercoat coating film has been formed by electrodeposition paint. The substrate may be the surface of the plastic material described above, or the plastic surface of an automobile part or the like molded from the metal material, that has been subjected to a desired surface treatment. Furthermore, the substrate may be a combination of plastic material and metal material.

[0140] Because the resin film of this embodiment exhibits excellent low-temperature curing properties, it is suitable for use in products in various fields where energy conservation is required, and as a coating for materials with low heat resistance.

[0141] <Laminate> The laminate of this embodiment is formed by laminating one or more layers of the above-mentioned resin film on a substrate. The thickness of each layer of the resin film is between 1 μm and 50 μm.

[0142] The laminate of this embodiment may contain two or more layers of the above-mentioned resin film having the same composition, or it may contain two or more layers of the above-mentioned resin film having different compositions.

[0143] Furthermore, the same materials as those exemplified in the "resin film" section above can be used as the base material.

[0144] The laminate of this embodiment is obtained by applying the above resin composition to a substrate using known methods such as roll coating, curtain flow coating, spray coating, bell coating, and electrostatic coating, and then heating and curing each layer, or by heating and curing all layers together after coating.

[0145] In addition to the substrate and the resin film, the laminate of this embodiment may include layers made of other known components, such as a primer layer, an adhesive layer, or a decorative layer.

[0146] <Method for improving the low-temperature curing properties of a curing agent composition> One aspect of the present invention is a method for improving the low-temperature curing properties of a curing agent composition. According to the present invention, the low-temperature curing properties of a curing agent composition containing a melamine resin that does not cure at temperatures below 100°C can be improved. According to one aspect of the present invention, by using a curing agent composition obtained by mixing a melamine resin (M) and a specific block polyisocyanate (B) in a specific ratio, reactivity is improved, and the low-temperature curing properties of the curing agent composition containing the melamine resin can be improved.

[0147] The method for improving the low-temperature curing properties of the curing agent composition of this embodiment (hereinafter also simply referred to as "the method for improving the low-temperature curing properties of this embodiment") comprises a curing agent composition manufacturing step of mixing a melamine resin (M) and a blocked polyisocyanate (B); a resin composition manufacturing step of mixing the curing agent composition with a polyvalent hydroxy compound after the curing agent composition manufacturing step; and a curing step of curing the resin composition obtained in the resin composition manufacturing step to obtain a resin film, wherein the blocked polyisocyanate (B) is a blocked polyisocyanate derived from a polyisocyanate and a blocking agent containing a malonic acid ester, and includes a constituent unit represented by the following general formula (I). The total mass of solids contained in the block polyisocyanate (B) is 8 parts by mass or more and 100 parts by mass or less, relative to 100 parts by mass of the total mass of solids contained in the melamine resin (M).

[0148] [ka]

[0149] (In general formula (I), R 11 , R 12 and R 13 Each of these is an alkyl group which may independently contain one or more substituents selected from the group consisting of hydroxyl groups and amino groups. 11 , the R 12 and R 13 The total number of carbon atoms is between 3 and 20. 14 , R 15 and R 16 Each of these alkyl groups may independently contain a hydrogen atom or one or more substituents selected from the group consisting of a hydroxyl group and an amino group. (The wavy lines represent bonds.)

[0150] The process for manufacturing the curing agent composition in the method for improving low-temperature curability of this embodiment is the same as the process described in the above-mentioned <Curing Agent Composition> (Method for Manufacturing the Curing Agent Composition). The melamine resin (M) and blocked polyisocyanate (B) mixed in the curing agent composition manufacturing process are the same as the blocked polyisocyanate (B) and melamine resin (M) in the curing agent composition described above.

[0151] The resin composition manufacturing process in the method for improving low-temperature curability of this embodiment is the same as the process described in the above-mentioned method for manufacturing the resin composition.

[0152] The curing step in the method for improving low-temperature curability in this embodiment is the same as the curing step in the <resin film> described above. The heating temperature and heating time in the curing process are the same as those for the <resin film> described above. [Examples]

[0153] The embodiment will be described in more detail below based on examples and comparative examples, but the embodiment is not limited in any way by the following examples.

[0154] <Test Items> The polyisocyanate P-1 and blocked polyisocyanate (B) obtained in the synthesis example, as well as the curing agent compositions obtained in the examples and comparative examples, were subjected to measurement and evaluation of their physical properties according to the methods described below.

[0155] [Physical Properties 1] (Isocyanate group (NCO) content) To measure the NCO content of polyisocyanates, polyisocyanates before blocking with a blocking agent were used as the sample. First, 2 g to 3 g of the sample was accurately weighed into a flask (Wg). Next, 20 mL of toluene was added and the sample was dissolved. Then, 20 mL of a 2 N di-n-butylamine toluene solution was added and mixed, and the mixture was left at room temperature for 15 minutes. Next, 70 mL of isopropyl alcohol was added and mixed. This solution was then titrated with a 1 N hydrochloric acid solution (factor F) on an indicator. The obtained titration value was defined as V2 mL. Next, the titration value obtained without the polyisocyanate sample was defined as V1 mL. Then, the isocyanate group (NCO) content (mass%) of the polyisocyanate was calculated using the following formula.

[0156] Isocyanate group (NCO) content (mass%) = (V1-V2) × F × 42 / (W × 1000) × 100

[0157] Furthermore, the effective NCO content of blocked isocyanate (B) was calculated using the following formula.

[0158] Effective NCO content [mass%] = {100 × (mass of isocyanate groups in the solid content of the polyisocyanate used in the blocking reaction)} / (mass of blocked polyisocyanate (B) after the blocking reaction)

[0159] [Physical Properties 2] (Number-average molecular weight and weight-average molecular weight) The number-average molecular weight and weight-average molecular weight are those measured using gel permeation chromatography (GPC) with the following apparatus, based on polystyrene. To measure the number-average molecular weight of polyisocyanates, polyisocyanates were used as the sample before blocking with a blocking agent. For weight-average molecular weight, block polyisocyanate (B) was used directly as the measurement sample. The measurement conditions are shown below.

[0160] (Measurement conditions) Equipment: HLC-802A, manufactured by Tosoh Corporation Column: Tosoh Corporation, G1000HXL x 1 G2000HXL x 1 G3000HXL x 1 Carrier: Tetrahydrofuran Detection method: Differential refractometer

[0161] [Physical Properties 3] (Average number of isocyanate groups) The average number of isocyanate groups (average number of NCO groups) of the polyisocyanate was determined by the following formula. In the formula, "Mn" is the number-average molecular weight of the polyisocyanate, and the value measured in "Physical Properties 2" above was used. "NCO content" is the isocyanate group content of the polyisocyanate measured before blocking with the blocking agent, and the value calculated in "Physical Properties 1" above was used.

[0162] Average number of isocyanate groups = (Mn × NCO content × 0.01) / 42

[0163] [Physical Properties 4] (Solid content of block polyisocyanate (B)) The solid content of block polyisocyanate (B) was determined as follows: First, an aluminum dish with a base diameter of 38 mm was accurately weighed. Next, approximately 1 g of the block polyisocyanate (B) produced in the examples and comparative examples was placed on the aluminum dish and accurately weighed (W1). Next, the block polyisocyanate (B) was adjusted to a uniform thickness. Next, the block polyisocyanate (B) on the aluminum dish was kept in an oven at 105°C for 1 hour. After the aluminum dish had returned to room temperature, the block polyisocyanate (B) remaining on the aluminum dish was accurately weighed (W2). Next, the solid content (mass%) of the block polyisocyanate (B) was calculated using the following formula.

[0164] Solid content (mass%) of block polyisocyanate (B) = W2 / W1 × 100

[0165] [Physical Properties 5] (Content (moles) of constituent unit (I)) The content of constituent unit (I) in block polyisocyanate (B) is determined under the following conditions: 13 The result was calculated using 1C-NMR.

[0166] (Measurement conditions) Device: JEOL “JEOL-ECZ500(SC)” (product name) Solvent: Deuterated chloroform Total number of times: 5120 Sample concentration: 50 wt / vol% Chemical shift standard: Deuterated chloroform was set at 77.0 ppm.

[0167] [Physical Properties 6] (Content of constituent unit (I-1) relative to the total molar amount of constituent unit (I)) The content (mol%) of constituent unit (I-1) relative to the total molar amount of constituent unit (I) in block polyisocyanate (B) was calculated using the method shown below.

[0168] Specifically, using JEOL's "JEOL-ECZ500(SC)" (product name), 13 By measuring with 1C-NMR, the total molar amount of constituent unit (I) (including constituent unit (I-1)) and the molar amount of constituent unit (I-1) were calculated, and their molar ratio was determined.

[0169] (Measurement conditions) Device: JEOL “JEOL-ECZ500(SC)” (product name) Solvent: Deuterated chloroform Total number of times: 5120 Sample concentration: 50 wt / vol% Chemical shift standard: Deuterated chloroform was set at 77.0 ppm.

[0170] [Physical Properties 7] (Molar ratio of constituent unit (II) / constituent unit (I)) The molar ratio of constituent unit (II) to constituent unit (I) (constituent unit (II) / constituent unit (I)) is obtained by evaporating the block polyisocyanate (B) at a temperature of 50°C or lower using an evaporator to remove the solvent and other components, and then drying under reduced pressure.13 The molar ratio of constitutional unit (II) to constitutional unit (I) was calculated by measuring the composition ratio of constitutional unit (II) to constitutional unit (I) by ¹³C-NMR.

[0171] (Measurement conditions) Apparatus: "JEOL-ECZ500(SC)" (trade name) manufactured by JEOL Ltd. Solvent: Deuterated chloroform Number of integrations: 5120 times Sample concentration: 50 wt / vol% Chemical shift reference: Deuterated chloroform was set to 77.0 ppm.

[0172] [Preparation of resin composition] An acrylic polyol (manufactured by allnex, "Setalux® 1767" (trade name), hydroxyl value 150 mgKOH / resin g, solid content 65 mass%) and each curing agent composition were blended so that the mass ratio per solid content was 60:40. Further, butyl acetate was blended and adjusted to a solid content of 40 mass% to obtain a resin composition.

[0173] [Evaluation 1] (Low-temperature curability) The resin composition obtained in the above "Preparation of resin composition" was coated on a polypropylene (PP) plate to a dry film thickness of 40 μm, and then heat-dried at 80 °C for 30 minutes to obtain a resin film. The percentage (mass%) of the value obtained by dividing the mass of the undissolved portion when the obtained resin film was immersed in acetone at 23 °C for 24 hours by the mass before immersion was determined as the gel fraction. Using the calculated gel fraction, the low-temperature curability was evaluated according to the following evaluation criteria. The larger the gel fraction, the better the low-temperature curability (evaluation results A, B), and the smaller the gel fraction, the poorer the low-temperature curability (evaluation result C). A: 80 mass% or more B: 70% or more and less than 80 mass% C: Less than 70 mass%

[0174] [Evaluation 2] (Storage stability) The storage stability was evaluated by measuring the pH before and after storing the above resin composition under predetermined conditions and using the change value from the pH immediately after blending. Specifically, for the obtained resin composition, the pH after storing in a 20 mL glass bottle at 40 °C for 10 days was measured, and the change value (absolute value) from the pH immediately after blending was evaluated according to the following criteria. The smaller the change value, the better the storage stability (evaluation results A, B), and the larger the change value, the worse (evaluation results C, D). A: Less than 0.2 B: 0.2 or more and less than 0.4 C: 0.4 or more and less than 0.6 D: 0.6 or more

[0175] <Synthesis of Polyisocyanate P-1> [Synthesis Example 1] Into a four-necked flask equipped with a thermometer, stirring blades, and a reflux condenser, under a nitrogen stream, 100 parts by mass of HDI and 5.3 parts by mass of a polyester polyol (polycaprolactone triol) derived from a trivalent alcohol and ε-caprolactone (manufactured by Daicel Chemical Industries, Ltd., "Placcel 303" (trade name), average functionality: 3, number average molecular weight 300) were charged, and the temperature inside the reactor was maintained at 89 °C for 1 hour with stirring to carry out a urethanization reaction. Then, the temperature inside the reactor was maintained at 63 °C, and tetramethylammonium caprylate, an isocyanuration catalyst, was added. Phosphoric acid was added to stop the reaction when the yield reached 52% by mass. After filtering the reaction solution, unreacted HDI was removed using a thin-film evaporator to obtain an isocyanurate-type polyisocyanate (hereinafter sometimes referred to as "polyisocyanate P-1").

[0176] The NCO content of the obtained polyisocyanate P-1 was 18.6% by mass, the number average molecular weight was 1220, and the average number of isocyanate groups was 5.4. Also, for the obtained polyisocyanate P-1 1 1H-NMR analysis was performed to confirm the presence of isocyanurate groups.

[0177] <Production of Block Polyisocyanate (B)> [Synthesis Example 2] In a four-necked flask equipped with a thermometer, stirring blades, and reflux condenser, 100 parts by mass of polyisocyanate P-1 obtained in Synthesis Example 1, 70 mol% of diisopropyl malonate relative to 100 mol% of NCO groups, and 30 mol% of (2-methyl-2-butyl)isopropyl malonate relative to 100 mol% of NCO groups were charged under a nitrogen stream. Dipropylene glycol dimethyl ether (DPDM) was then added to prepare a solution with a solid content of 60% by mass. Next, while stirring, 0.8 parts by mass of methanol solution containing sodium methylate (28% by mass relative to the total mass of the solution) was added dropwise. The external bath was then adjusted to a solution temperature of 55°C, and the blocking reaction was carried out at 55°C for 5 hours to obtain a block polyisocyanate (B) containing a solid content of 60% by mass.

[0178] The composition and physical properties of the obtained block polyisocyanate (B)-containing liquid are shown in Table 1 below.

[0179] [Table 1]

[0180] <Manufacturing of curing agent composition> [Examples 1-4, Comparative Examples 1-2] A water-based acrylic emulsion (YACL3, manufactured by Asahi Kasei Corporation) and melamine resin (product name "Cymel 325", manufactured by Allnex, solids content 80% by mass) were mixed at 800 rpm for 10 minutes to obtain the solids content (parts by mass) shown in Table 2 below. Next, the block polyisocyanate (B) obtained in Synthesis Example 2 was added to obtain the solids content (parts by mass) shown in Table 2 below, and a surface modifier (product name "BYK346") and deionized water were added to obtain the parts by mass shown in Table 2 below, and the mixture was mixed at 800 rpm for 10 minutes to obtain the desired curing agent composition.

[0181] [Examples 5-8, Comparative Examples 3-4] A water-based acrylic emulsion (YACL3, manufactured by Asahi Kasei Corporation) and melamine resin (product name "Cymel 327", manufactured by Allnex, solids content 90% by mass) were mixed at 800 rpm for 10 minutes to obtain the solids content (parts by mass) shown in Table 3 below. Next, the block polyisocyanate (B) obtained in Synthesis Example 2 was added to obtain the solids content (parts by mass) shown in Table 3 below, and a surface modifier (product name "BYK346") and deionized water were added to obtain the parts by mass shown in Table 3 below, and the mixture was mixed at 800 rpm for 10 minutes to obtain the desired curing agent composition.

[0182] The low-temperature curing properties and storage stability of the obtained curing agent composition were evaluated. The results are shown in Tables 2 and 3 below. In Tables 2 and 3, "total mass of (B) relative to (M)" means the total mass of solids contained in block polyisocyanate (B) relative to 100 parts by mass of the total mass of solids contained in melamine resin (M).

[0183] [Table 2]

[0184] [Table 3]

[0185] As shown in Tables 2 and 3 above, a curing agent composition in which the total mass of solids contained in block polyisocyanate (B) is 8 to 100 parts by mass relative to 100 parts by mass of the total mass of solids contained in melamine resin (M) was confirmed to have good low-temperature curing properties and storage stability. On the other hand, as shown in Tables 2 and 3 above, curing agent compositions in which the total mass of solids contained in block polyisocyanate (B) is less than 8 parts by mass per 100 parts by mass of total solids contained in melamine resin (M) exhibited poor low-temperature curing properties, making it difficult to achieve both low-temperature curing and storage stability.

[0186] Also, as shown in Table 2 above, in comparison between the curing agent composition (Example 2) in which the total mass of the solid content contained in the blocked polyisocyanate (B) is 15 parts by mass with respect to 100 parts by mass of the total mass of the solid content contained in the melamine resin (M), and the curing agent composition (Example 1) in which the total mass of the solid content contained in the blocked polyisocyanate (B) is 10 parts by mass with respect to 100 parts by mass of the total mass of the solid content contained in the melamine resin (M), the curing agent composition of Example 2 showed a tendency of better low-temperature curability.

[0187] Also, as shown in Table 2 above, in comparison between the curing agent composition (Example 3) in which the total mass of the solid content contained in the blocked polyisocyanate (B) is 31 parts by mass with respect to 100 parts by mass of the total mass of the solid content contained in the melamine resin (M), and the curing agent composition (Example 4) in which the total mass of the solid content contained in the blocked polyisocyanate (B) is 92 parts by mass with respect to 100 parts by mass of the total mass of the solid content contained in the melamine resin (M), the curing agent composition of Example 3 showed a tendency of better storage stability.

[0188] Also, as shown in Table 3 above, in comparison between the curing agent composition (Example 6) in which the total mass of the solid content contained in the blocked polyisocyanate (B) is 14 parts by mass with respect to 100 parts by mass of the total mass of the solid content contained in the melamine resin (M), and the curing agent composition (Example 5) in which the total mass of the solid content contained in the blocked polyisocyanate (B) is 8 parts by mass with respect to 100 parts by mass of the total mass of the solid content contained in the melamine resin (M), the curing agent composition of Example 6 showed a tendency of better low-temperature curability.

[0189] Also, as shown in Table 3 above, in comparison between the curing agent composition (Example 7) in which the total mass of the solid content contained in the blocked polyisocyanate (B) is 27 parts by mass with respect to 100 parts by mass of the total mass of the solid content contained in the melamine resin (M), and the curing agent composition (Example 8) in which the total mass of the solid content contained in the blocked polyisocyanate (B) is 82 parts by mass with respect to 100 parts by mass of the total mass of the solid content contained in the melamine resin (M), the curing agent composition of Example 7 showed a tendency of better storage stability.

Claims

1. A curing agent composition comprising a blocked polyisocyanate (B) and a melamine resin (M), The aforementioned blocked polyisocyanate (B) is a blocked polyisocyanate derived from a polyisocyanate and a blocking agent containing a malonic acid ester, and contains a constituent unit represented by the following general formula (I). A curing agent composition wherein the total mass of solids contained in the block polyisocyanate (B) is 8 parts by mass or more and 100 parts by mass or less, relative to 100 parts by mass of the total mass of solids contained in the melamine resin (M). 【Chemistry 1】 (In general formula (I), R １１ , R １２ and R １３ are each independently an alkyl group which may contain one or more substituents selected from the group consisting of a hydroxy group and an amino group. The total number of carbon atoms of the R １１ , the R １２ and the R １３ is 3 or more and 20 or less. R １４ , R １５ and R １６ are each independently a hydrogen atom or an alkyl group which may contain one or more substituents selected from the group consisting of a hydroxy group and an amino group. The wavy line represents a bond.)

2. The curing agent composition according to claim 1, wherein the structure represented by the general formula (I) includes the structure represented by the following general formula (I-1). 【Chemistry 2】 (In general formula (I-1), R １１１ , R １１２ and R １１３ Each of these is an alkyl group which may independently contain one or more substituents selected from the group consisting of hydroxyl groups and amino groups. １１１ , the R １１２ and R １１３ The total number of carbon atoms is between 3 and 20. １１４ and R １１５ Each of these is an alkyl group that may independently contain one or more substituents selected from the group consisting of a hydrogen atom, a hydroxyl group, and an amino group. (The wavy lines represent bonding bonds.)

3. The aforementioned R １１ , the R １２ and R １３ Each of these is independently an unsubstituted alkyl group, and The aforementioned R １４ , the R １５ and R １６ The curing agent composition according to claim 1, wherein each is independently a hydrogen atom or an unsubstituted alkyl group.

4. The curing agent composition according to claim 1 or 2, wherein the polyisocyanate is a polyisocyanate derived from one or more diisocyanates selected from the group consisting of aliphatic diisocyanates and alicyclic diisocyanates.

5. The curing agent composition according to claim 1 or 2, wherein the average number of isocyanate groups of the polyisocyanate is 3.5 or more.

6. A resin composition comprising the curing agent composition according to claim 1 or 2 and a polyvalent hydroxy compound.

7. A resin film obtained by curing the resin composition according to claim 6.

8. A laminate comprising one or more layers of the resin film described in claim 7 on a substrate, A laminate in which the thickness of each layer of the resin film is 1 μm or more and 50 μm or less.

9. A method for improving the low-temperature curing properties of a curing agent composition, A curing agent composition manufacturing process involves mixing melamine resin (M) and block polyisocyanate (B) to obtain a curing agent composition, A resin composition manufacturing step is performed, in which the curing agent composition is mixed with a polyhydric hydroxy compound after the curing agent composition manufacturing step to obtain a resin composition, A curing step is performed to obtain a resin film by curing the resin composition obtained in the resin composition manufacturing step, Includes, The aforementioned blocked polyisocyanate (B) is a blocked polyisocyanate derived from a polyisocyanate and a blocking agent containing a malonic acid ester, and contains a constituent unit represented by the following general formula (I). A method wherein the total mass of solids contained in the block polyisocyanate (B) is 8 parts by mass or more and 100 parts by mass or less, relative to 100 parts by mass of the total mass of solids contained in the melamine resin (M). 【Transformation 3】 (In general formula (I), R １１ , R １２ and R １３ Each of these is an alkyl group which may independently contain one or more substituents selected from the group consisting of hydroxyl groups and amino groups. １１ , the R １２ and R １３ The total number of carbon atoms is between 3 and 20. １４ , R １５ and R １６ Each of these is an alkyl group that may independently contain one or more substituents selected from the group consisting of a hydrogen atom, a hydroxyl group, and an amino group. (The wavy lines represent bonding bonds.)

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