JP2002088137A - Low-temperature curing latent curable agent for epoxy resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a low-temperature curing latent curable agent for an epoxy resin, having high storage stability (latent ability) and low-temperature curability. SOLUTION: This low-temperature curing latent curable agent for an epoxy resin is characterized by comprising an epoxy resin adduct (C) of a compound A of the formula (R1 is a 2-18C straight-chain or branched-chain alkyl group; R2, R3, R4 and R5 are each the same or different and hydrogen, a 1-17C straight- chain or branched-chain alkyl group or aromatic group; n is an integer of 1-4; m is an integer of 1-4) to an epoxy resin (B) containing at least two epoxy groups.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-temperature curing latent curing agent for epoxy resin, a method for producing the same, an epoxy resin obtained by using the curing agent, and a compound contained in the curing agent.

[0002]

2. Description of the Related Art Latent curing agents for epoxy resins have reduced storage reactivity with epoxy resins and have storage stability.
Latent curing agents include dicyandiamide, amine adducts, urea-amine condensation systems with tertiary amine end groups,
Although imidazoles are known, these curing agents are 1
It had curability in a relatively high temperature range of 00 ° C. or higher. However, the number of plastic substrates to which heat cannot be applied is increasing, and a latent curing agent having low-temperature curability has been desired.

SUMMARY OF THE INVENTION An object of the present invention is to provide a low-temperature curing type latent curing agent for epoxy resins having high storage stability (latent) and low-temperature curability.

[0003]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that an epoxy resin adduct obtained by adding an epoxy resin to a specific compound has excellent latent properties and low-temperature curability. . The present invention has been made based on such findings. That is, the present invention provides a compound (A) represented by the following formula: (Wherein, R ₁ is a linear or branched alkyl group having 2 to 18 carbon atoms, and R ₂ , R ₃ , R ₄ and R ₅ are the same or different and are hydrogen, a linear chain having 1 to 17 carbon atoms. Or n is an integer of 1 to 4, m is an integer of 1 to 4) and an epoxy resin (B) having at least two epoxy groups. Provided is a low-temperature curing type latent curing agent for an epoxy resin, which comprises a resin adduct (C). Further, the present invention provides a method for producing the curing agent of the present invention, an epoxy resin obtained by using the curing agent of the present invention, and a compound usable for producing the curing agent of the present invention.

[0004]

BEST MODE FOR CARRYING OUT THE INVENTION The compound (A) of the present invention has the following formula: Indicated by R ₁ is a straight-chain or branched alkyl group having 2 to 18 carbon atoms, preferably a straight-chain or branched alkyl group having 4 to 12 such as butyl, isobutyl, hexyl, octyl, and n-nonyl. And particularly preferably an n-nonyl group. R ₂ , R ₃ , R ₄ and R ₅ are the same or different and are hydrogen, a linear or branched alkyl group having 1 to 17 carbon atoms, for example, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, and a butyl group. , An isobutyl group or an aromatic group, for example, a phenyl group or a benzyl group, preferably a combination of R ₂ and R ₃ and R ₄ and R ₅ is hydrogen and a linear or branched alkyl group having 1 to 4 carbon atoms, for example, It is a combination of a methyl group, an ethyl group, an n-propyl group, an isopropyl group, a butyl group, and an isobutyl group, and particularly preferably a combination of hydrogen and a methyl group. R ₂
And when the combination of R ₃ and R ₄ and R _{5 is} a combination of hydrogen and a linear or branched alkyl group having 1 to 4 carbon atoms, the alkyl groups may be the same or different;
2, 4 or 5 position of the imidazole ring, preferably 2 or 4
Position, particularly preferably at position 2. m is an integer of 1-4, preferably an integer of 1-2, and particularly preferably 1. n is an integer of 1-4, preferably an integer of 1-2, and particularly preferably 1. Particularly preferred are compounds represented by the following formula.

[0005] The compound (A) is prepared by the usual Mannich reaction,
For example, it can be produced by heating imidazole and an alkylphenol in the presence of an aldehyde according to the reaction described in British Patent No. 1288835. The imidazole used here is 2-
Methylimidazole, 4-methylimidazole, 2-
Methyl-4-ethylimidazole, 2-phenylimidazole, 2-undecylimidazole, 2-heptadecylimidazole and the like are mentioned. Preferred are 2-methylimidazole, 4-methylimidazole and 2-methyl-4-ethylimidazole, and particularly preferred is 2-methylimidazole.
Methyl imidazole. As the alkylphenol, cresol, p-isopropylphenol, p-
tert-butylphenol, p-sec-butylphenol, p-tert-amylphenol, p-ter
t-octylphenol, nonylphenol, dodecylphenol. Preferred are nonylphenol and dodecylphenol, and particularly preferred is nonylphenol. Examples of the aldehyde include formaldehyde, acetaldehyde, propionaldehyde, glyoxal aldehyde, and succinaldehyde. Preferred are formaldehyde, acetaldehyde and glyoxalaldehyde, and particularly preferred is formaldehyde. The reaction temperature is generally between 80 and 25
It is 0 degreeC, Preferably it is 100-200 degreeC, Especially preferably, it is 120-180 degreeC. In order to increase the efficiency of the reaction, it is preferable to collect the generated water.

The low-temperature curing type latent curing agent for an epoxy resin of the present invention is produced by adding an epoxy resin (B) to a compound (A). The method of adding the epoxy resin (B) to the compound (A) includes, for example, (1) a step of forming a solution of the compound (A), and (2) a step of adding the liquid epoxy resin (B) to the obtained solution. And adding an epoxy resin (B) to the compound (A). The epoxy resin (B) added to the compound (A) is
It is a resin having at least two epoxy groups in the molecule. The epoxy resin may be in any form of a monomer, an oligomer or a polymer, and its weight average molecular weight is generally 100 to 5000, preferably 200 to 300.
0, particularly preferably in the range of 300 to 1000. As the epoxy resin (B), glycidyl ether type,
Glycidyl ester type, glycidylamine type, alicyclic type,
Glycidylimine type, polyolefin oxide type, cycloolefin type, epoxy acetal type, polyglycidyl acrylate type, heterocyclic type and urethane-modified epoxy resin are exemplified, preferably glycidyl ether type and glycidyl ester type epoxy resin. Yes,
Particularly preferred is a glycidyl ether type epoxy resin. As a glycidyl ether type epoxy resin,
Bisphenol A type epoxy resin, bisphenol F
Type epoxy resin, novolak type epoxy resin, biphenyl ether type epoxy resin, diphenyl ether type epoxy resin, and polyfunctional type epoxy resin. Among these, bisphenol A type epoxy resin and bisphenol F type epoxy resin are preferable, and bisphenol A type epoxy resin is particularly preferable. The epoxy resin is, for example, a new epoxy resin, edited by Hiroshi Kakiuchi, 29 (198)
5) It may be produced according to the method described in Shokodo, but commercially available products can also be used. For example, a bisphenol A type epoxy resin commercially available under the trade name Epikote 828 (Yuka Kasper Epoxy Co., Ltd.) can be used.

The solvent used in step (1) needs to have a boiling point higher than the softening point of the adduct obtained.
MEK (methyl ethyl ketone), MIB
Ketone solvents such as K (methyl isobutyl ketone), ether solvents such as butyl cellosolve and ethyl cellosolve, alcohol solvents such as isopropanol, pentanol, hexanol and heptanol, benzene,
Aromatic solvents such as toluene and xylene, octane, aliphatic solvents such as pentane, hexane and heptane, TH
F and DMF, preferably toluene, xylene, hexane, heptane, hexanol, heptanol and DMF, particularly preferably DMF and xylol (industrial xylene). These solvents may be used alone or in combination. The concentration of the compound (A) in the solution is in the range of 10 to 100% by mass, preferably 30 to 80% by mass, particularly preferably 40 to 60% by mass.

From the viewpoint of improving the reactivity during the addition reaction, the epoxy resin (B) needs to be liquid at the following addition reaction temperature. When a solid epoxy resin is used at the reaction temperature, it is used after being dissolved in a solvent. As the solvent, those mentioned in the above step (1) can be used. Further, the solid epoxy resin (B) can be used as a suspension. The addition of the epoxy resin (B) to the solution obtained in the step (1) is carried out at 20 to 120 ° C, preferably 40 to 100 ° C, particularly preferably 60 to 80 ° C. The molar ratio of compound (A): epoxy resin (B) is
1: 0.3 to 1.0, preferably 1: 0.4 to 1.0, so that the resulting curing agent has sufficient latent and low temperature curability.
0.9, particularly preferably in the range of 1: 0.65 to 0.8. The additional mode is not necessarily limited to the theory. For example, the mode shown in the following scheme 1 can be considered, but is not limited to this.

[0009]

It is considered that the reaction with the epoxy resin involves an unshared electron pair of the nitrogen atom in the compound (A). Therefore, although Scheme 1 shows that only the nitrogen at the 3-position of the imidazole ring of the compound (A) participates in the reaction, the nitrogen atom bonded to the methylene group also participates in the addition reaction. Conceivable. However, since the nitrogen atom bonded to the methylene group is sterically hindered, the reactivity is considered to be lower than that of the nitrogen atom at the 3-position. It is considered that the addition reaction proceeds sufficiently within the range of the molar ratio of the compound (A) to the epoxy resin (B) before the addition reaction. Therefore, when the amount of the epoxy resin (B) is smaller than that of the compound (A), the unreacted compound (A) remains in the curing agent after the addition reaction. From the viewpoint of obtaining, it is preferable that the curing agent contains the compound (A). In this case, the molar ratio of the compound (A) to the epoxy resin adduct (C) in the curing agent obtained after the addition reaction depends on the molar ratio of the compound (A) to the epoxy resin (B) before the addition reaction. 0: 1.0 to 0.7: 0.3, preferably 0.1.
6: 0.4 to 0.1: 0.9, particularly preferably 0.3
5: 0.65 to 0.2: 0.8.

The hardener of the present invention is preferably pulverized by ordinary means and used from the viewpoint of curability. The average particle size of the pulverized curing agent is 40 μm or less, preferably 2 μm or less.
0 μm or less, particularly preferably 10 μm or less. A lower limit of 1 μm would be appropriate. For the pulverization, a usual pulverizer such as a pot mill and a jet mill can be used.

The curing agent of the present invention can be used as a low-temperature curing type latent curing agent in curing various epoxy resins. Further, by utilizing its low-temperature curability, it can be added to a conventional latent curing agent and used as a curing accelerator for accelerating curing. Epoxy resins that can be used for the curing include, but are not limited to, glycidyl ether type, glycidyl ester type, glycidylamine type and alicyclic epoxy resins. Examples of the glycidyl ether type epoxy resin include a bisphenol A type epoxy resin and a bisphenol F type epoxy resin. Therefore, the curing agent of the present invention can be used for curing the same epoxy resin as the epoxy resin used for its production. However, even in this case, from the viewpoint of obtaining excellent potential, compound (A)
Need not be used directly for curing the epoxy resin alone, but must be used for curing the epoxy resin after adding an epoxy resin to form a curing agent that suppresses the activity of the compound (A). Examples of the glycidyl ester type epoxy resin include a dimer acid modified epoxy resin and a phthalic acid diglycidyl ester resin. Examples of the glycidylamine type epoxy resin include a tetraglycidyldiaminophenylmethane resin and an N, N-diglycidylaniline resin. The alicyclic epoxy resin includes an alicyclic diepoxy acetal resin and an alicyclic diepoxy carboxylate resin. Among these, glycidyl ether type resins and glycidyl ester type resins are preferable, and glycidyl ether type resins are particularly preferable. Specifically, a bisphenol A-type glycidyl ether resin commercially available under the trade name Epikote 828 can be used.

The epoxy resin can be cured according to various curing methods known in the art, for example, at 80 to 120 ° C. for 30 to 60 minutes or 150 to 170 ° C.
By heating and curing for 10 to 30 minutes, but is not limited thereto. The amount of the curing agent of the present invention mixed with the epoxy resin varies depending on the type of the epoxy resin to be cured, the application, and the like, but is generally 1 to 100 parts by mass, preferably 1 to 100 parts by mass per 100 parts by mass of the epoxy resin. -50 parts by mass, particularly preferably 5-25 parts by mass. The curing temperature of the epoxy resin varies depending on the type of the epoxy resin to be cured, the application, etc., but the curing agent of the present invention can cure the epoxy resin at a lower temperature compared to the conventional latent curing agent. Therefore, generally 40 to 2
00 ° C, preferably 60 to 150 ° C, particularly preferably 8 ° C.
0-100 ° C.

The epoxy resin obtained by using the curing agent of the present invention can be used for various uses, for example, adhesives, sealing materials, laminating resins, paints, and curing accelerators. In particular, those having a higher glass transition temperature than epoxy resins obtained using a conventional latent curing agent can be preferably used for sealing materials and laminates because of their high heat resistance.

[0015]

The present invention will be described below with reference to examples.
The present invention is not limited to these examples.

Example 1 Preparation of compound (A) of the present invention Formalin 2.
0 mol and 2.0 mol of 2-methylimidazole,
The reaction was performed at 180 ° C. for 3 hours to obtain a compound represented by the following formula.

[0017]

The compound was subjected to GPC (gel permeation chromatography) (Showex GP, Showa Denko KK).
When the average molecular weight was measured by CRI-71),
Mw = 402 was shown. This was in good agreement with the theoretical molecular weight of the reactants.

Example 2 Production of low-temperature curing type latent curing agent of the present invention 1 mol of compound (A) produced in Example 1 was dissolved in xylene /
Dissolved in 363 ml of DMF solution (2: 1) (concentration of compound (A) in the solution: 50% by mass), and liquid epoxy resin (B) (Epikote828, bisphenol A type epoxy resin, weight average molecular weight: 380) 0.6 mol (Mole ratio of compound (A): epoxy resin (C) = 1: 0.
6) at 70 ° C., and then the xylene / DMF solution was distilled off under reduced pressure to obtain “curing agent I” containing the epoxy resin adduct (C). This epoxy resin adduct (C) was subjected to GPC (Showa Denko Corporation Shodex GPC RI-7).
When the average molecular weight was measured according to 1), Mw = 633 was shown. This value almost coincided with the theoretical molecular weight of the reactant. In addition, IR (JASCO Corporation FT / IR-23)
According to 0), absorption near 900 cm ^-1 had disappeared.
From this, it was confirmed that the oxirane ring of the epoxy resin was cleaved to cause an addition reaction. The molar ratio of the compound (A) to the epoxy resin adduct (C) in the obtained curing agent was estimated to be 0.4: 0.6.

Example 3 Production of an epoxy resin using the low-temperature curing type latent curing agent of the present invention and comparison of the glass transition point with an epoxy resin obtained using another curing agent produced in Example 2. Each one of a curing agent (curing agent I) and a comparative curing agent (curing agent II, curing agent III and curing agent IV)
The following epoxy resin was produced by mixing 0 parts by mass and 100 parts by mass of an epoxy resin (Epikote 828, bisphenol A type epoxy resin).

[0021]

^{* 1} Curing Agent II 1.0 mol of 2-methylimidazole was added to 200 parts of toluene.
dissolved in an epoxy resin (Epikote8).
28, bisphenol A type epoxy resin) 1.2 mol
Was added dropwise and reacted gently at 60 ° C. for 3 hours, and then toluene was distilled off under reduced pressure to obtain a curing agent II. ^{* 2} Curing agent III 2-phenylimidazole (1.0 mol) in toluene 20
0 ml, and the epoxy resin (EEW 250
(Product name: Epikote 834, manufactured by Yuka Shell Epoxy Co., Ltd., bisphenol A type epoxy resin) 0.6
5 mol was dripped and reacted gently at 60 ° C. for 3 hours.
Thereafter, toluene was distilled off under reduced pressure to obtain a curing agent III. ^{* 3} Hardener IV DICY (dicyandiamide)

The latency, curability and glass transition point (Tg) of each of the obtained epoxy resins were measured. Latency was evaluated by measuring the initial viscosity of the epoxy resin and the time until the viscosity doubled. Measurement of viscosity is based on JIS
The measurement was performed with a BH-type rotational viscometer (rotor No. 6, 10 rotations) according to K 6830. Low temperature curability was evaluated by measuring the gel time of the epoxy resin at various curing temperatures. Measurement of gel time is based on JIS K
Performed in accordance with 5909 (hot plate method). The glass transition point (Tg) is measured in accordance with JIS K 7121 using a differential scanning calorimeter (TG-DSC analyzer SSC 5200 manufactured by Seiko Instruments Inc.) (heating rate 10 ° C./min). Was. The measurement results are shown in the table below.

[0024]

Comparative Example 1
Compared with Examples 2 and 3, the epoxy resin using the curing agent of the present invention could be stored for as long as 4 months. Although the epoxy resin of Comparative Example 3 could be stored for a long time,
It did not show low temperature curability. Therefore, only by using the curing agent of the present invention, an epoxy resin having high potential and low-temperature curability could be obtained. Regarding the glass transition point of the cured epoxy resin,
The epoxy resin of the present invention showed a higher glass transition point than those of the comparative examples when cured at any of 50 ° C. and 170 ° C.

[0026]

The low-temperature curing type latent curing agent for epoxy resin according to the present invention has a high potential when mixed with a curing epoxy resin, and also has a low-temperature curing property. Therefore, it can be used for a substrate which cannot be applied with a high temperature, to which a conventional latent curing agent could not be applied. In addition, it is possible to contribute to a reduction in initial cost by improving productivity due to rapid curing of a conventional curing agent. Further, the epoxy resin having high heat resistance obtained by using the curing agent of the present invention can be used for a wide range of applications.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Katsutoshi Shiraishi 15 Suzukawa, Isehara City, Kanagawa Prefecture Isehara Industrial Park Sanwa Chemical Industry Co., Ltd. F term (reference) 4J036 AA01 AB14 AD08 AD15 AF01 AF06 AG03 AG07 AH07 AJ08 AJ17 AJ18 AK01 AK10 AK19 CB23 DA01 DA05 DC40 FB06 JA01 JA06 JA07 JA08 JA15

Claims (8)

[Claims] 1. A compound (A) represented by the following formula: (Wherein, R ₁ is a linear or branched alkyl group having 2 to 18 carbon atoms, and R ₂ , R ₃ , R ₄ and R ₅ are the same or different and are hydrogen, a linear chain having 1 to 17 carbon atoms. Or n is an integer of 1 to 4, m is an integer of 1 to 4) and an epoxy resin (B) having at least two epoxy groups. A low-temperature curing latent curing agent for an epoxy resin, comprising a resin adduct (C). 2. The low-temperature curing type latent curing agent for an epoxy resin according to claim 1, further comprising a compound (A). 3. The curing agent has a molar ratio of the compound (A) to the epoxy resin adduct (C) of 0.6: 0.4 to 0.4.
The low-temperature curing type latent curing agent for an epoxy resin according to claim 2, wherein the ratio is 1: 0.9. 4. The low-temperature curing type latent curing agent for an epoxy resin according to claim 1, wherein the epoxy resin (B) has a weight average molecular weight of 100 to 5,000. 5. A method for producing a low-temperature curing latent curing agent for an epoxy resin, comprising: forming a solution of the compound (A) according to claim 1;
And adding a liquid epoxy resin (B) to the solution of the compound (A) to add the epoxy resin (B) to the compound (A). 6. The compound (A): the epoxy resin (B) has a molar ratio of 1: 0.3 to 1.0.
The production method described in 1. 7. An epoxy resin obtained by using the low-temperature curing type latent curing agent for an epoxy resin according to claim 3. 8. A compound represented by the following formula: (Wherein, R ₁ is a linear or branched alkyl group having 2 to 18 carbon atoms, and R ₂ , R ₃ , R ₄ and R ₅ are the same or different and are hydrogen, a linear chain having 1 to 17 carbon atoms. Or a branched alkyl group or an aromatic group, n is an integer of 1 to 4, and m is an integer of 1 to 4.)