JP7498587B2 - Thermal Latent Polymerization Initiator - Google Patents

Description

The present invention relates to a thermal latent polymerization initiator that is difficult to initiate curing at room temperature but can cure a cationic curable compound at a lower temperature, a cationic curable resin composition containing the thermal latent polymerization initiator, and a method for curing a cationic curable compound using the thermal latent polymerization initiator.

Cationic polymerization is an ionic polymerization in which the active species, which are the initiating and propagating species, are cations. For example, in the cationic polymerization of vinyl monomers, the π bond of the vinyl monomer attacks the electrophilic cationic curing catalyst to generate a new cation. This cation is then attacked by the π bond of another vinyl monomer. This reaction occurs continuously to grow the polymer chain, but the polymer growth is hindered by β-proton elimination and other factors. Living cationic polymerization, an ideal polymerization system consisting only of initiation and propagation reactions, has also been developed, in which β-proton elimination and other factors are suppressed by designing the initiation system. In addition, cationic ring-opening polymerization of epoxides, which is initiated by the attack of the cationic curing catalyst by the lone electron pair of an oxygen atom, is also one of the major cationic polymerizations.

Compared with radical polymerization, cationic polymerization has the advantage that curing inhibition by oxygen does not occur and that shrinkage during curing is small, and various applications of cationic polymerization are being considered. For example, Patent Document 1 discloses a cationic curable resin composition that is excellent in heat resistance, moist heat resistance, low water absorption, UV radiation resistance, etc., and can produce molded products useful for optical components, etc., and that contains a cationic curable compound and a cationic curing catalyst consisting of a specific Lewis acid and a Lewis base. Patent Document 2 discloses a lamination resin composition for forming a light selective transmission filter, an image sensor, etc., and contains an oxirane ring-containing compound, a solvent, a cationic curing catalyst, and a nitrogen-containing compound having a boiling point of 120°C or higher.

As a cationic curing catalyst, a compound with excellent cationic polymerization promotion activity is naturally preferable. However, a cationic curing catalyst with excellent catalytic activity immediately starts curing the cationic curable compound, so it is difficult to distribute it as an uncured composition product together with the cationic curable compound. Also, in actual manufacturing sites, compositions containing cationic curable compounds and cationic curing catalysts are produced in large quantities, and curing and molding are sometimes carried out the next day or later. In such cases, if curing begins immediately upon mixing the cationic curable compound and the cationic curing catalyst, molding becomes difficult. Therefore, a thermally latent polymerization initiator has been developed that does not show catalytic activity at room temperature in a mixture with a cationic curable compound, but shows catalytic activity when heated.

For example, Patent Document 3 discloses a thermal latent polymerization initiator that contains 2,2,6,6-tetramethylpiperidine or a derivative thereof and tris(pentafluorophenyl)borane in a specified molar ratio.

International Publication No. 2012/060449 JP 2015-152861 A Patent No. 5579859

As described above, thermal latent polymerization initiators containing cationic curable compounds have already been developed.
Although it is obvious that the thermal latent polymerization initiator is difficult to start curing at room temperature, if the peak top temperature for curing is low, low temperature curing is possible, so that the heating energy for curing can be reduced. In addition, curing treatment is possible even in a state where it is combined with a material with low heat resistance, which is very advantageous industrially.
Therefore, an object of the present invention is to provide a thermal latent polymerization initiator which is difficult to initiate curing at room temperature but is capable of low-temperature curing, a cationic curable resin composition containing the thermal latent polymerization initiator, and a method for curing a cationic curable compound using the thermal latent polymerization initiator.

The present inventors have conducted extensive research to solve the above problems, and have found that an excellent thermally latent polymerization initiator can be obtained by using a nucleophilic nitrogen-containing compound as a compound that imparts thermal latency to a compound having cationic curing catalytic ability and by appropriately defining the molar ratio of the nucleophilic nitrogen atom contained in the nucleophilic nitrogen-containing compound to the cationic curing catalytic compound, thereby completing the present invention.
The present invention will now be described.

［式中、
Ｆはフルオロ基を示し、
Ｒは置換基を有していてもよい炭化水素基を示し、
ｌは、１以上、５以下の整数を示し、
ｍは１以上の整数を示し、
ｎは０以上の整数を示し、
ｍ＋ｎ＝３であり、
ｎが２以上の整数である場合、２以上のＲは互いに同一であっても異なっていてもよい。］
前記式（Ｉ）で表される化合物に対する前記求核性窒素含有化合物に含まれる求核性窒素原子のモル比が２以上であることを特徴とする熱潜在性重合開始剤。
［２］ 前記モル比が１０以下である前記［１］に記載の熱潜在性重合開始剤。
［３］ 前記求核性窒素含有化合物がアンモニアである前記［１］または［２］に記載の熱潜在性重合開始剤。
［４］ 前記式（Ｉ）で表される化合物がトリス（ペンタフルオロフェニル）ボランである前記［１］～［３］のいずれかに記載の熱潜在性重合開始剤。
［５］ 前記［１］～［４］のいずれかに記載の熱潜在性重合開始剤、およびカチオン硬化性化合物を含有することを特徴とするカチオン硬化性樹脂組成物。
［６］ 前記カチオン硬化性化合物がエポキシ化合物である前記［５］に記載のカチオン硬化性樹脂組成物。
［７］ 前記カチオン硬化性化合物１００質量部に対して、前記［１］～［４］のいずれかに記載の熱潜在性重合開始剤を０．０１質量部以上、１０質量部以下含有する前記［５］または［６］に記載のカチオン硬化性樹脂組成物。
［８］ カチオン硬化性化合物を硬化する方法であって、
前記［１］～［４］のいずれかに記載の熱潜在性重合開始剤と前記カチオン硬化性化合物を混合してカチオン硬化性樹脂組成物を得る工程、および、
前記カチオン硬化性樹脂組成物を５０℃以上に加熱する工程を含むことを特徴とする方法。 [1] A compound represented by the following formula (I) and a nucleophilic nitrogen-containing compound,

[Wherein,
F represents a fluoro group;
R represents a hydrocarbon group which may have a substituent;
l represents an integer of 1 to 5,
m represents an integer of 1 or more;
n represents an integer of 0 or more;
m+n=3,
When n is an integer of 2 or more, two or more R may be the same or different.
A thermal latent polymerization initiator, characterized in that the molar ratio of nucleophilic nitrogen atoms contained in the nucleophilic nitrogen-containing compound to the compound represented by formula (I) is 2 or more.
[2] The thermal latent polymerization initiator according to [1], wherein the molar ratio is 10 or less.
[3] The thermal latent polymerization initiator according to [1] or [2], wherein the nucleophilic nitrogen-containing compound is ammonia.
[4] The thermal latent polymerization initiator according to any one of [1] to [3], wherein the compound represented by formula (I) is tris(pentafluorophenyl)borane.
[5] A cationically curable resin composition comprising the thermal latent polymerization initiator according to any one of [1] to [4] above, and a cationically curable compound.
[6] The cationically curable resin composition according to [5], wherein the cationically curable compound is an epoxy compound.
[7] The cationically curable resin composition according to the above [5] or [6], containing 0.01 parts by mass or more and 10 parts by mass or less of the thermal latent polymerization initiator according to any one of the above [1] to [4] relative to 100 parts by mass of the cationically curable compound.
[8] A method for curing a cationically curable compound, comprising the steps of:
A step of mixing the thermal latent polymerization initiator according to any one of [1] to [4] above with the cationic curable compound to obtain a cationic curable resin composition; and
The method comprises the step of heating the cationically curable resin composition to 50° C. or higher.

The thermal latent polymerization initiator according to the present invention is difficult to start curing at room temperature, but can cure a cationic curable compound at a lower temperature. As a result, it is possible to reduce the heating energy required for curing the cationic curable compound, and the curing process is possible even when combined with a material with low heat resistance. The thermal latent polymerization initiator according to the present invention contains a cationic curing catalyst containing a boron atom and a nucleophilic nitrogen-containing compound, and by optimizing the molar ratio of these compounds, it has been possible to successfully obtain a molded product free of defects such as air bubbles. The molded product obtained by curing a cationic curable compound with the thermal latent polymerization initiator according to the present invention was colorless and the curing reaction was fully completed. Therefore, the present invention is very useful industrially as a technology that can efficiently cure and mold a cationic curable resin composition at a low temperature.

The thermal latent polymerization initiator according to the present invention contains a compound represented by formula (I) (hereinafter referred to as "compound (I)") and a nucleophilic nitrogen-containing compound.

Compound (I) is a compound that functions as a cationic curing catalyst that accelerates curing by undergoing nucleophilic attack by a cationic curable compound or its oligomer, since the boron atom is electron deficient due to electrons being attracted by the fluorophenyl group.

The hydrocarbon group R is not particularly limited as long as it does not impair the catalytic activity of compound (I), and examples thereof include a _C1-6 alkyl group, a _C2-6 alkenyl group, a _C2-6 alkynyl group, a _C6-12 aryl group, and a _C6-12 aryl- _C1-6 alkyl group. The term " _C1-6 alkyl group" refers to a linear or branched monovalent saturated aliphatic hydrocarbon group having 1 to 6 carbon atoms, and examples thereof include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, s-butyl, t-butyl, n-pentyl, and n-hexyl. A _C1-4 alkyl group is preferred, a _C1-2 alkyl group is more preferred, and methyl is most preferred.

The term " _C2-6 alkenyl group" refers to a straight-chain or branched-chain monovalent unsaturated aliphatic hydrocarbon group having 2 to 6 carbon atoms and at least one carbon-carbon double bond. Examples include ethenyl (vinyl), 1-propenyl, 2-propenyl (allyl), isopropenyl, 2-butenyl, 3-butenyl, isobutenyl, pentenyl, hexenyl, etc. A _C2-4 alkenyl group is preferred, and ethenyl (vinyl) or 2-propenyl (allyl) is more preferred.

The term " _C2-6 alkynyl group" refers to a straight-chain or branched-chain monovalent unsaturated aliphatic hydrocarbon group having 2 to 6 carbon atoms and having at least one carbon-carbon triple bond. Examples include ethynyl, 1-propynyl, 2-propynyl, 2-butynyl, 3-butynyl, pentynyl, hexynyl, etc. A _C2-4 alkynyl group is preferred, and a _C2-3 alkynyl group is more preferred.

The term "C _6-12 aryl group" refers to a monovalent aromatic hydrocarbon group having 6 or more carbon atoms and no more than 12 carbon atoms. Examples include phenyl, naphthyl, indenyl, biphenyl, etc., and preferably phenyl.

The "C _6-12 aryl-C _1-6 alkyl group" is a C _1-6 alkyl group substituted with a C _6-12 aryl group, and examples thereof include benzyl.

The hydrocarbon group R may have a substituent. The substituent α of an aliphatic hydrocarbon such as a C _1-6 alkyl group, a C _2-6 alkenyl group, a C _2-6 alkynyl group, and a C _1-6 alkyl group in a C _6-12 aryl-C _1-6 alkyl group is not particularly limited, and examples thereof include substituents selected from a C _1-6 alkoxy group, a C _1-6 alkoxy-carbonyl group, a hydroxyl group, a formyl group, a carboxy group, an amino group, a halogeno group, a cyano group, and a nitro group, and the substituent β of an aromatic hydrocarbon such as a C _6-12 aryl group, and a C _6-12 aryl group in a C _6-12 aryl-C _1-6 alkyl group includes substituents selected from a C _1-6 alkyl group, a C _1-6 alkoxy group, a C _1-6 alkoxy-carbonyl group, a hydroxyl group, a formyl group, a carboxy group, an amino group, a halogeno group, a cyano group, and a nitro group.

When the hydrocarbon group R has a substituent, the number of the substituents is not particularly limited as long as the substituents are substitutable, but can be, for example, 1 or more and 5 or less. When the number of the substituents is 2 or more, the 2 or more substituents may be the same or different.

From the reaction mechanism of compound (I), it is preferable that the number of fluoro groups on the phenyl group is large, and it is also preferable that the number of fluorophenyl groups is large, while the number of R groups is small. Therefore, in formula (I), l is preferably 2 or more, 3 or more, or 4 or more, and more preferably 5, m is preferably 2 or more, and preferably 3, and n is preferably 2 or less, or 1 or less, and more preferably 0. From this perspective, tris(pentafluorophenyl)borane (TPB) is suitable as compound (I).

In the present invention, the nucleophilic nitrogen-containing compound is thought to inhibit the catalytic activity of compound (I) at room temperature by coordinating the lone electron pair of the nucleophilic nitrogen atom contained in the nucleophilic nitrogen-containing compound to the boron atom of compound (I), while it is thought to separate from compound (I) under heating to activate the catalytic activity of compound (I).

Nucleophilic nitrogen-containing compounds are compounds in which the nucleophilic nitrogen atom can regulate the catalytic activity of compound (I) through the above-mentioned mechanism of action, and do not include compounds in which the nitrogen atom is not nucleophilic due to steric hindrance or is only a non-nucleophilic nitrogen atom with low nucleophilicity, such as N,N-diisopropylethylamine and diazabicycloundecene. In addition, compounds containing nitrogen atoms do not include compounds that contain only nitrogen atoms that are not nucleophilic, such as amide groups or general imino groups.

Examples of the nucleophilic nitrogen-containing compound include ammonia, mono-C _1-6 alkylamines such as monomethylamine, monoethylamine, monoisopropylamine, monobutylamine, etc., di-C _1-6 alkylamines such as dimethylamine, diethylamine, diisopropylamine, methylethylamine, etc., and polyvalent amines such as ethylenediamine, etc. From the viewpoint of being easily removed from the cured product, a nucleophilic nitrogen-containing compound having a lower boiling point is preferred, specifically, ammonia and/or a mono-C _1-6 alkylamine is preferred, and ammonia is more preferred.

In the thermal latent polymerization initiator according to the present invention, the molar ratio of the nucleophilic nitrogen atom contained in the nucleophilic nitrogen-containing compound to compound (I) is 2 or more. As described above, at room temperature, it is considered that the lone electron pair of the nucleophilic nitrogen atom contained in the nucleophilic nitrogen-containing compound is coordinated to the boron atom of compound (I), thereby suppressing the catalytic activity of compound (I). Therefore, the nucleophilic nitrogen atom here is one whose lone electron pair can be coordinated to an electrophilic group and exhibits basicity according to the Lewis definition. Thus, for example, N-methylimidazole contains two nitrogen atoms, but has only one amino group that exhibits basicity and can be said to be a monovalent base, so the number of amino groups taken into account in calculating the molar ratio is one per molecule.

When the molar ratio is 2 or more, the thermal latent polymerization initiator of the present invention does not start curing at room temperature, and the higher the molar ratio, the higher the curing initiation temperature. Therefore, the molar ratio is preferably 2.2 or more or 2.5 or more, and more preferably 3 or more.

On the other hand, if the molar ratio is too high, curing may not start or bubbles may occur when the nucleophilic nitrogen-containing compound is removed from the cured product by heating. However, if the molar ratio is 10 or less, curing starts more reliably and the generation of bubbles can be suppressed. The molar ratio is preferably 8 or less, and more preferably 6 or less.

When at least one of compound (I) or the nucleophilic nitrogen-containing compound is liquid at room temperature, the thermal latent polymerization initiator may be prepared by simply mixing compound (I) and the nucleophilic nitrogen-containing compound. When both compound (I) and the nucleophilic nitrogen-containing compound are solid at room temperature, it is preferable to prepare the thermal latent polymerization initiator by mixing compound (I) and the nucleophilic nitrogen-containing compound in a solvent. The solvent used is not particularly limited as long as it does not inhibit the formation of a complex between compound (I) and a nucleophilic nitrogen-containing compound and can dissolve them appropriately. For example, aromatic hydrocarbon solvents such as toluene; aliphatic hydrocarbon solvents such as n-hexane; ketone-based solvents such as acetone and methyl ethyl ketone; alcohol-based solvents such as methanol, ethanol, and isopropanol; ether-based solvents such as tetrahydrofuran; ester-based solvents such as ethyl acetate; nitrile-based solvents such as acetonitrile; halogenated hydrocarbon solvents such as chloroform; amide-based solvents such as dimethylformamide; sulfoxide-based solvents such as dimethyl sulfoxide; lactone-based solvents such as γ-butyrolactone; carbonate-based solvents such as ethylene carbonate, and mixed solvents of two or more of these can be used.

The cationic curable resin composition according to the present invention contains the above-mentioned thermal latent polymerization initiator and a cationic curable compound.

A cationic curing compound is a compound that uses a Lewis acid, compound (I), as a polymerization initiator, has a functional group that generates a cation by attacking compound (I), and when the generated cation is attacked by the same functional group of another molecule, the polymer chain extends and the compound hardens.

Examples of cationic curable compounds include cyclic ethers such as epoxy compounds; cyclic sulfides; cyclic amines; styrenes such as isobutene, vinyl ether, and α-methylstyrene; vinyl monomers such as vinylcarbazole, cyclopentadiene, norbornadiene, indene, tetrahydroindene, and β-pinene; cyclic acetals such as 1,3-dioxolane, 1,3,5-trioxane, bicycloorthoesters, and spiroorthocarbonates; cyclic iminoethers such as 2-oxazoline; and lactones such as β-propiolactone, δ-valerolactone, and ε-caprolactone.

The amounts of the cationic curable compound and the thermal latent polymerization initiator may be adjusted as appropriate. For example, the ratio of the thermal latent polymerization initiator to 100 parts by mass of the cationic curable compound, particularly the ratio of the total mass of compound (I) and the nucleophilic nitrogen-containing compound, may be 0.01 parts by mass or more and 10 parts by mass or less. If the ratio is within the range, the curing of the cationic curable compound can be more effectively promoted. The ratio is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and is preferably 5 parts by mass or less, and more preferably 2 parts by mass or less.

In cases where the cationic curable compound is liquid at room temperature, the cationic curable resin composition of the present invention may be prepared by simply mixing the heat latent polymerization initiator and the cationic curable compound. However, in cases where both the heat latent polymerization initiator and the cationic curable compound are solid at room temperature, it is preferable to use a solvent.

The solvent used in the cationic curable resin composition is not particularly limited as long as it can adequately dissolve the thermal latent polymerization initiator and the cationic curable compound and does not inhibit curing. Examples of the solvent include aromatic hydrocarbon solvents such as toluene; aliphatic hydrocarbon solvents such as n-hexane; ketone-based solvents such as acetone and methyl ethyl ketone; alcohol-based solvents such as methanol, ethanol, and isopropanol; ether-based solvents such as tetrahydrofuran; ester-based solvents such as ethyl acetate; nitrile-based solvents such as acetonitrile; halogenated hydrocarbon solvents such as chloroform; amide-based solvents such as dimethylformamide; sulfoxide-based solvents such as dimethyl sulfoxide; lactone-based solvents such as γ-butyrolactone; carbonate-based solvents such as ethylene carbonate; and mixed solvents of two or more of these.

In addition to the thermal latent polymerization initiator and the cationic curable compound, the cationic curable resin composition may contain general additives. Examples of such additives include antistatic agents, flame retardants, antibacterial agents, antioxidants, and pigments.

The curing start temperature of the cationic curable resin composition is preferably 50°C or higher. Since the maximum temperature in most countries is below 50°C, if the curing start temperature is 50°C or higher, the cationic curable resin composition will not cure at room temperature. On the other hand, if the curing start temperature is too high, the amount of energy required for curing will increase, so the curing start temperature is preferably 90°C or lower. The curing start temperature is preferably 55°C or higher, more preferably 60°C or higher, and is preferably 85°C or lower, more preferably 80°C or lower.

When the cationic curable resin composition is subjected to differential scanning calorimetry (DSC), the curing proceeds as the heating temperature is raised after the curing start temperature, and the amount of heat generated increases accordingly, but the amount of heat generated reaches a peak at a certain temperature, after which the amount of heat generated decreases. The lower the temperature corresponding to the peak top of the amount of heat generated, the smaller the total amount of energy required for heating for curing, and the curing can be completed with a smaller amount of energy. The heat generation peak top temperature is preferably 70°C or higher and 120°C or lower. If the heat generation peak top temperature is 70°C or higher, the curing start temperature can be more reliably above room temperature, and if it is 120°C or lower, the amount of curing energy can be further suppressed. The heat generation peak top temperature is preferably 75°C or higher, more preferably 80°C or higher, and more preferably 110°C or lower, and more preferably 100°C or lower.

The method for curing a cationic curable compound according to the present invention includes a step of mixing the heat latent polymerization initiator and the cationic curable compound to obtain a cationic curable resin composition, and a step of heating the cationic curable resin composition to 50°C or higher. As described above, the cationic curable resin composition can be easily prepared by simply mixing the heat latent polymerization initiator and the cationic curable compound.

The heating temperature for curing the cationic curable resin composition is equal to or higher than the curing start temperature of the cationic curable resin composition, and is preferably equal to or higher than 50°C. The heating temperature is more preferably equal to or higher than 60°C or 70°C, and even more preferably equal to or higher than 80°C or 90°C. If the heating temperature is equal to or higher than the curing start temperature, curing is considered to proceed, but if the heating temperature is low, the curing time will be long, so the heating temperature is preferably equal to or lower than (the heat generation peak top temperature of the cationic curable resin composition + 50°C), more preferably equal to or lower than (the heat generation peak top temperature of the cationic curable resin composition + 20°C), and even more preferably equal to or lower than (the heat generation peak top temperature of the cationic curable resin composition + 10°C).

The thermal latent polymerization initiator according to the present invention can cure cationic curable compounds at lower temperatures, and can therefore be used, for example, as an adhesive component for bonding materials with low heat resistance, or can be used in a batch mounting process in which components are mounted and then heat-treated as a unit before assembly. Specific applications include films, lenses, covers, protective plates, support materials, binders for functional materials, coating materials, insulating materials, adhesives, and other optical and electronic components.

The present invention will be explained in more detail below with reference to examples. However, the present invention is not limited to the following examples, and it is of course possible to carry out the invention with appropriate modifications within the scope of the above and below-mentioned aims, and all such modifications are included in the technical scope of the present invention.

Example 1: Production of thermal latent polymerization initiator To tris(pentafluorophenyl)borane (hereinafter, abbreviated as "TPB") (0.906 g, 1.770 mmol), a 2 mol/L ammonia-2-propanol solution (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) (containing 2.084 g, 5.309 mmol of ammonia) was added, and the mixture was stirred for 1 hour until the TPB was dissolved.

Example 2: Preparation of a thermally latent polymerization initiator To TPB (0.906 g, 1.770 mmol), a 2 mol/L ammonia-ethanol solution (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) (containing 2.642 g, 6.689 mmol of ammonia) was added, and the mixture was stirred for 1 hour until the TPB was dissolved.

Example 3: Production of a thermally latent polymerization initiator To TPB (0.906 g, 1.770 mmol), a 2 mol/L ammonia-2-propanol solution (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) (containing 4.170 g, 10.624 mmol of ammonia) was added, and the mixture was stirred for 1 hour until the TPB was dissolved.

Comparative Example 1: Production of a thermal latent polymerization initiator To TPB (10.556 g, 20.617 mmol), 2,2,6,6-tetramethyl-4-piperidine ester of 1,2,3,4-butanetetracarboxylic acid ("ADK STAB LA57", manufactured by ADEKA CORPORATION, chemical structure shown below) (4.200 g, 5.309 mmol) and propylene carbonate (14.000 g) were added, and the mixture was stirred for 1 hour until dissolved.

Comparative Example 2: Production of a thermally latent polymerization initiator To TPB (0.906 g, 1.770 mmol), a 2 mol/L ammonia-2-propanol solution (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) (containing 1.292 g, 3.292 mmol of ammonia) was added, and the mixture was stirred for 1 hour until the TPB was dissolved.

The N-compounds used to impart thermal latency to TPB in Examples 1 to 3 and Comparative Examples 1 and 2, the molar ratio of nucleophilic nitrogen to boron (N/B), and the TPB concentrations in the solvent and initiator are shown in Table 1. Note that "%" in the table indicates mass %.

Test Example 1: Stability test (1) Preparation of resin compositions Resin compositions 1 to 5 were prepared by uniformly mixing 1 part by mass of the thermal latent polymerization initiator of Examples 1 to 3 or Comparative Examples 1 and 2 with 100 parts by mass of 3',4'-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate ("Celloxide 2021P" manufactured by Daicel Corporation), which is a bifunctional alicyclic epoxy compound.

(2) Stability Test The viscosity of the above resin compositions 1 to 5 was measured at a measurement temperature of 25° C. using an E-type viscometer. Then, each resin composition was stored at 25° C., and the viscosity was measured in the same manner after 1 day and 4 days. The results are shown in Table 2.

As shown in the results in Table 2, the resin composition 4 containing a hindered amine in the polymerization initiator (Comparative Example 1) had relatively poor stability. The reason for this is considered to be that the coordination power of the hindered amine with respect to TPB was small, and the polymerization catalytic activity of TPB could not be suppressed.
Resin composition 5 containing the polymerization initiator (Comparative Example 2) was stable at first, but after 4 days, its stability was found to have decreased. This is thought to be because the molar ratio of nucleophilic nitrogen to boron (N/B) was as small as 1.86, and therefore ammonia was unable to sufficiently suppress the polymerization catalytic activity of TPB.
In contrast, resin compositions 1 to 3 containing polymerization initiators (Examples 1 to 3) with a large molar ratio of nucleophilic nitrogen to boron (N/B) did not show any significant change in viscosity even four days after production, demonstrating that they have excellent room temperature stability.

Test Example 2: Differential Scanning Calorimetry (DSC)
12 mg of each resin composition prepared in Test Example 1 was weighed out and subjected to differential scanning calorimetry at a measurement temperature range of 30 to 300°C, a heating rate of 10°C/min, and a nitrogen flow rate of 20 mL/min. The uncured region of 30 to 40°C was taken as the baseline, and the temperature at which heat generation began and moved away from the linear extension of the baseline was taken as the curing initiation temperature. The temperature at which the intensity was highest among the exothermic peaks was read as the peak top. The results are shown in Table 3.

As shown in the results in Table 3, Resin composition 4 containing a hindered amine in the polymerization initiator (Comparative Example 1) started curing at a relatively low temperature, but had a high peak top temperature. The reason for this may be that although the molar ratio of nucleophilic nitrogen to boron (N/B) was small at 1.03, the energy required to dissociate the hindered amine once coordinated to TPB from the TPB was large.
Moreover, resin composition 5 containing a polymerization initiator (Comparative Example 2) started curing at 40° C. Even in Japan, the temperature can exceed 40° C., so this is not stable.
In contrast, resin compositions 1 to 3 containing polymerization initiators having a large molar ratio of nucleophilic nitrogen to boron (N/B) (Examples 1 to 3) started curing at temperatures above 60°C, and therefore it can be said that they are difficult to cure at room temperature. However, both the curing initiation temperature and the peak top temperature were relatively low, indicating that less energy was required for curing.

Test Example 3: Molding Evaluation A 4 mm thick silicone rubber sheet with a 10 mm x 10 mm hole was attached to a glass plate and placed on a hot plate. The holes in the silicone rubber sheet were filled with each of the resin compositions prepared in Test Example 1 and covered with a glass plate. After heating at 80°C for 10 minutes on the hot plate, the glass and silicone rubber sheet were removed to obtain a cured product, and the appearance was observed. The results are shown in Table 4.

As shown in the results in Table 4, resin composition 4 containing a hindered amine in the polymerization initiator (Comparative Example 1) did not cure under the above size and heating conditions. This result is consistent with the result of Test Example 2, in which the peak top temperature was high. In addition, since the hindered amine used has a large molecular weight, it is considered that it does not cause bubbles.
Resin composition 5 containing the polymerization initiator (Comparative Example 2) was cured under the above size and heating conditions, and no bubbles were generated. Although ammonia, which has a low boiling point, was used as the amine, no bubbles were generated, probably because the relative amount of nucleophilic nitrogen to boron was small.
Resin compositions 1 to 3 containing the polymerization initiators (Examples 1 to 3) were also cured under the above size and heating conditions, and no bubbles were formed, despite the relative amount of nucleophilic nitrogen to boron being high.
In contrast, since the molar ratio of nucleophilic nitrogen to boron (N/B) is large and curing begins at above 60°C, it can be said that it is difficult to cure at room temperature. However, both the curing initiation temperature and the peak top temperature can be said to be relatively low, which shows that only a small amount of energy is required for curing.

These results demonstrate that the polymerization initiator of the present invention is an excellent thermally latent initiator that combines thermal latency and low-temperature curing properties.

Claims (8)

1. A method for curing a cationically curable compound, comprising the steps of:
A step of mixing a thermal latent polymerization initiator and the cationic curable compound to obtain a cationic curable resin composition; and
The method includes the step of heating the cationic curable resin composition to 50° C. or more and 110° C. or less,
The thermal latent polymerization initiator comprises a compound represented by the following formula (I) and a nucleophilic nitrogen-containing compound,

[Wherein,
F represents a fluoro group;
R represents a hydrocarbon group which may have a substituent;
l represents an integer of 1 to 5,
m represents an integer of 1 or more;
n represents an integer of 0 or more;
m+n=3,
When n is an integer of 2 or more, two or more R may be the same or different.
the molar ratio of the nucleophilic nitrogen atom contained in the nucleophilic nitrogen-containing compound to the compound represented by formula (I) is 2 or more and 10 or less;
The method according to claim 1, wherein the nucleophilic nitrogen-containing compound is ammonia, a mono C _1-6 alkylamine, a di C _1-6 alkylamine or an ethylenediamine . The method of claim 1, wherein the molar ratio is 8 or less. The method according to claim 1 or 2, wherein the nucleophilic nitrogen-containing compound is ammonia. The method according to any one of claims 1 to 3, wherein the compound represented by formula (I) is tris(pentafluorophenyl)borane. The method according to any one of claims 1 to 4, wherein the cationic curable resin composition further contains a solvent. The method according to any one of claims 1 to 5, wherein the cationic curable compound is an epoxy compound. The method according to any one of claims 1 to 6, wherein the cationic curable resin composition contains 0.01 parts by mass or more and 10 parts by mass or less of the thermal latent polymerization initiator per 100 parts by mass of the cationic curable compound. The method according to any one of claims 1 to 7, wherein the cationically curable resin composition further contains one or more additives selected from an antistatic agent, a flame retardant, an antibacterial agent, an antioxidant, and a pigment.