JPS61183316A - Latent curing agent for one-component epoxy resin - Google Patents

Abstract

PURPOSE:To obtain an epoxy resin composition which is good in storage stability, low-temperature rapid curability and can give a cured product improved in transparency and water resistance, by using a specified hydrazide as a curing agent for the epoxy resin. CONSTITUTION:A latent curing agent comprising a hydrazide represented by formula I (wherein X is a residue derived by removing the two hydroxyl groups from a dihydric phenol and is a group of formula II or III). It is preferably that X in formula I is a residue derived from a dihydric phenol selected from among catechol, resorcinol and hydroquinone. The amount of the latent curing agent added is about 0.5-1.5 equivalent, in terms of equivalent of the epoxy groups in the epoxy resin. Said hydrazide compound can be readily obtained by the action of hydrazine hydrate on a diglycolate diester compound derived from 1mol of a dihydric phenol and 2mol of sodium monochloroacetate (formula IV, wherein X is the same as in formula I and R is an alkyl group).

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a latent curing agent for epoxy resins comprising a hydrazide compound.

(Problems to be solved by conventional techniques and inventions) Epoxy resins have excellent mechanical, electrical, and chemical hardening properties when cured using acid anhydride hardeners or amine hardeners. Because of this, it is used in an extremely wide range of applications such as electrical insulation materials, various molded products, adhesives, and paints. However, epoxy resin compositions containing amine compounds have poor storage stability, and epoxy resin compositions containing acid anhydride curing agents are relatively stable at room temperature, but on the other hand, they require considerably high temperatures during curing. It has the disadvantage of requiring long heating times. Therefore, it is common practice to shorten the curing time by using a curing accelerator such as a tertiary amine, a quaternary ammonium compound, or an organic metal complex salt. However, adding a curing accelerator improves curability;
This results in the disadvantage that storage stability is significantly impaired. Therefore, there is a strong demand for so-called latent curing agents that are stable at relatively low temperatures, do not gel, and quickly harden when heated. Particularly in the field of coatings, cured products that are colorless and provide transparency are desired due to both curing properties and color matching issues. By the way, some typical compounds that have been proposed as latent curing agents include dicyandiamide, dibasic acid hydrazide, boron trifluoride-amine adduct, guanamines, melamine, and the like. However, although dicyandiamide, dibasic acid hydrazide, and guanamine have excellent storage stability,
It has the drawback of requiring long-time curing at high temperatures of 150°C or higher, and boron trifluoride-amine adducts are highly hygroscopic, which adversely affects the properties of cured products. There are almost no known compounds that cure quickly at low temperatures and have excellent storage stability.

(Means for Solving the Problem) The present inventor has developed a product that has low temperature, fast curing properties, and storage stability.
As a result of intensive studies to develop a latent curing agent with excellent transparency and water resistance for cured products, we discovered that a hydrazide compound represented by the following general formula (A) is an excellent latent curing agent. , completed the invention.

H2NHN00CCH20-X-OCH2COONHN
H2(A) (However, X is a residue obtained by removing two hydroxyl groups from a dihydric phenol, or -@-1-@-, or -o-t
-e- group) The hydrazide compound represented by the above general formula (A) is, for example, a general formula HO-X-OH (where X is a dihydric phenol represented with the same meaning as above (e.g. catechol, resorcinol, hydroquinone, etc.). ), or bisphenol AD, or bisphenol A (hereinafter collectively referred to as dihydric phenols)), and a diglycolic acid diester compound (a) derived from 2 moles of sodium monochloroacetate, It can be easily obtained by reacting hydrazine hydrate with hydrazine hydrate.

R00CC1+2O-X-OCH2COOR' (
& ) (However, X has the same meaning as above, R represents an alkyl group) Diglycolic acid diester compound (a) is prepared by adding dihydric phenol [1 It can be produced and obtained in one step by heating and refluxing 2 moles of monochloroacetic acid methyl ester and 2 moles of monochloroacetic acid methyl ester in the presence of sodium ethoxide.

Diglycolic acid diester compound (a), which is an adduct of dihydric phenols and sodium monochloroacetate, is prepared by adding dihydric phenols and two times the molar amount of the phenols in a basic aqueous solution with sodium hydroxide. By heating and refluxing an equivalent amount or more of sodium monochloroacetate for several hours, a diglycolic acid sodium salt of dihydric phenols is obtained, and the sodium chloride is heated and refluxed for several hours in the presence of an acid catalyst such as hydrochloric acid in an ethanol solution. It is done by

In addition, from dihydric phenols and monochloroacetic acid methyl ester, monochloroacetic acid methyl ester in an amount of at least twice the molar equivalent of the phenols and sodium ethoxide in a twice molar equivalent are added to the dihydric phenol in a methanol solvent. , by heating under reflux for several hours.

The alcohol used for esterification of sodium diglycolic acid salt is not particularly limited, but aliphatic alcohols are usually used, and methanol and ethanol are practical.

Examples of acid catalysts that should be coexisting in the esterification include hydrochloric acid and sulfuric acid, but since the acid catalyst is consumed by the sodium diglycolic acid salt, it is necessary to use at least twice the molar equivalent of the sodium diglycolic acid salt. be done.

Furthermore, the monochloroacetic ester to be added to the dihydric phenol is not particularly limited, but alkyl esters are usually used, and methyl esters are practical.

The thus obtained diglycolic acid diester compound (a) of dihydric phenols is stirred at room temperature for several hours in a solvent such as methanol or ethanol with hydrazine hydrate in an amount of at least twice the mole of the adduct. After boiling or heating if necessary, remove excess hydrazine hydrate and the solvent, and recrystallize with an appropriate solvent such as methanol, ethanol, or water to obtain the desired hydrazide compound. It will be done.

Cured products of conventionally known dibasic acid hydrazides such as adipic acid hydrazide, sebacic acid hydrazide, and isophthalic acid hydrazide mixed with epoxy resin in a predetermined amount generally have poor water resistance.For example, adipic acid hydrazide has poor water resistance. , exhibits a water absorption of about 1% or more under boiling conditions for 1 hour.On the other hand, the latent curing agent for epoxy resin of the present invention has a cured product with a transparent appearance compared to the dibasic acid hydrazide described above. and under the same test conditions as above, 0°5
Not only does it exhibit water resistance within ~1.0%, but also the curing temperature,
It has the same or better performance in terms of closure during curing, transparency of the cured product, and storage stability.

The blending amount of the latent curing agent of the present invention is 0.00% as active hydrogen equivalent of the curing agent per 1 equivalent of epoxy group of the epoxy resin.
The range is 5 to 1.5 equivalents, preferably 0.7 to 1.2 equivalents.

Epoxy resins applicable to the hydrazide of the present invention include those containing one or more epoxy resins in one molecule, and include various well-known epoxy resins. For example, glycidyl ethers of polyhydric phenols, especially bisphenol A.
Examples include glycidyl ethers of , glycidyl ethers of bisphenol F, and polyglycidyl ethers of phenol formaldehyde resin.

Further, other curing agents, curing accelerators, and fillers may be added to the one-component epoxy resin composition of the present invention, if necessary.

Next, examples and comparative examples will show examples of synthesis of hydrazide compounds derived from dihydric phenols, and
The usefulness of this compound as a latent curing agent for epoxy resins will be explained, but the present invention is not limited to these Examples.

Example 1 Synthesis of hydroquinone diglycolic acid dihydrazide (1) 300 with reflux condenser, stirrer and dropping funnel
13.ml of sodium ethoxide in a three-necked flask.
Add 6 g (0.1 mol) and 100 ml of methanol,
11 g (0°1 mol) of hydroquinone, 21.8 g (0°2 mol) of methyl monochloroacetate, and 100 ml of methanol were added dropwise over about 1 hour, followed by heating under reflux for about 10 hours. The solvent was distilled off under reduced pressure, diluted sodium hydroxide solution was added, and the mixture was extracted with about 200 mJ of ethyl ether.

The extracted layer was washed with water, dried over magnesium sulfate, and the ether was distilled off under reduced pressure to obtain white crystals.

Recrystallization was performed in a solvent of 1:1 ethyl acetate and ethanol to obtain hydroquinone diglycolic acid ester 3.
．． 08g was obtained.

Add 2.84 g (0,013 mol) of hydroquinone diglycolic acid ester, 3.8 g (0,077 mol) of hydrazine hydrate, and 150 ml of methanol to a 200 ml Erlenmeyer flask, and heat at 50°C while stirring.
The reaction was carried out for about 2 hours. The generated white crystals were filtered under reduced pressure, washed with ether, and dried to obtain the desired product (1) 2.55
I got g.

The analytical values are shown below.

・Melting point 236-238℃ ・Elemental analysis value C (%) H (%) N (%) Measured value 47,40 5.78 22.04 Theoretical value (C
IOH14N4041. , te) 47.24 5.55
22.04 Example 2 Synthesis of 4.4″-ethylidene bisphenol diglycolic acid dihydrazide (IV)
214 g (1 mol) of bisphenol AD, manufactured by Mitsui Shell Petrochemicals Epoxy Co., Ltd., 20 g (0.5 mol) of sodium hydroxide, and 11 mol of water were added to a 13-hole flask and heated to reflux. 375 g (3 mol) of sodium monochloroacetate and 500 g of water were added while adding sodium hydroxide halfway to maintain the pH of the reaction solution at 10 or higher.
ml was added dropwise over about 10 hours. After heating under reflux for about 24 hours, the white solid produced was separated using a small centrifuge. After drying the obtained solid under reduced pressure,
It was dissolved in a solution of 1.51.36% ethanol and 0.51% hydrochloric acid, and heated under reflux for about 24 hours. The solvent was distilled off under reduced pressure,
Dilute aqueous sodium hydroxide was added to the reaction residue, and the mixture was extracted with ether.

The ether layer was washed and dried, and the ether was distilled off to obtain 220.6 g of 4,41-ethylidene bisphenol diglycolic acid diethyl ester in the form of an oil.

220. of diester in a 2I Erlenmeyer flask.
6 g and 1.51 g of ethanol were added, and while stirring using an electromagnetic stirrer, 173 g of hydrazine hydrate was added.
(3.4 mol) was added dropwise.

After the addition was completed, the mixture was stirred at about 50° C. for 3 hours. The obtained white precipitate was filtered, washed with ether, and dried under reduced pressure to obtain the target hydrazide compound (IV) at 200%.
I got 8g.

The analysis values are shown below.

・Melting point 168-169℃ ・Elemental analysis value C (%) H (%) N (%) Measured value 59
．． 97 6.21 17.56 Theoretical value (C18H22N
404) 60.32 6.19 17.86 Table 1 below shows the hydrazide compounds used in the present invention and their melting points.

Example 3 Curability, water resistance, and storage stability were evaluated using the blending ratios shown in Table 2.

1. Method for preparing samples for evaluation Using the compounding ratios shown in Table 2, each company's 4 yen samples were degassed and mixed under reduced pressure using a vacuum stirrer [manufactured by Ishikawa Factory] for 1 hour.

2. Evaluation of curability 2-1. Curing Temperature Using a gear oven, the temperature at which the sample was cured within 60 minutes was measured.

2-2. Appearance of cured product After heating at 150°C for 60 minutes, the cured product obtained by further curing at 160°C for 180 minutes was observed with the naked eye.

3. Evaluation of water resistance 1 g of the sample was poured into a mold with a diameter of 25 mm, heated at 150°C for 60 minutes, and further heated and cured at 160°C for 180 minutes. This cured product was taken out of the mold and boiled in boiling water at 100°C for 1 hour, and then the change in weight was measured.

4. Storage stability A sample was placed in a constant temperature bath at 40°C, and the number of days until fluidity disappeared was measured.

The results obtained are shown in Tables 3-6.

From the results in Tables 3 to 6 above, the hydrazide compound of the present invention is
It will be understood that the curability and storage stability are also good, and in particular the water resistance is far superior to known latent curing agents for epoxy resins, and the cured product is also transparent and tough.

Table 1 Table 2 (*) Results of bisphenol A diglycidyl ether type liquid epoxy resin made by Shell Oil Co., Ltd., 175-210 ton per epoxy Table 3 Curing temperature Table 4 Appearance of cured product Table 5 Water resistance Table 6 Storage Stability

Claims (3)

[Claims] (1) General formula (A) H_2NHNOOCCH_2O-X-OCH_2COO
NHNH_2(A) (However, X is 2 from dihydric phenol
Residues with hydroxyl groups removed, or ▲There are mathematical formulas, chemical formulas, tables, etc.▼, or ▲There are mathematical formulas, chemical formulas, tables, etc.▼. ) A latent curing agent for epoxy resins consisting of a hydrazide. (2) A latent curing agent for epoxy resins comprising a hydrazide according to claim (1), wherein X is a residue derived from a dihydric phenol selected from catechol, resorcinol, and hydroquinone. (3) X is a ▲ mathematical formula, chemical formula, table, etc. ▼ or ▲
There are mathematical formulas, chemical formulas, tables, etc. A latent curing agent for epoxy resins comprising a hydrazide according to claim (1), which is a ▼ group.