CN109988287B

CN109988287B - Epoxy resin latent curing agent with high bonding strength and toughness and preparation method thereof

Info

Publication number: CN109988287B
Application number: CN201910302235.9A
Authority: CN
Inventors: 康富春; 唐增花; 刘海明
Original assignee: Guangdong Guyan Electronic Materials Co ltd
Current assignee: Guangdong Guyan Electronic Materials Co.,Ltd.
Priority date: 2019-04-16
Filing date: 2019-04-16
Publication date: 2021-10-22
Anticipated expiration: 2039-04-16
Also published as: CN109988287A

Abstract

The invention discloses an epoxy resin latent curing agent with high bonding strength and toughness and a preparation method thereof. The latent curing agent is prepared by carrying out amidation reaction on polyacrylate or polymethacrylate and alkyl imidazole or alkyl imidazole derivatives in a molar ratio of 1: 0.5-1.0 in the presence of a catalytic amount of an alkaline catalyst to obtain imidazole ring-containing polyamide. The polyamide is obtained by freezing at low temperature and pulverizing with jet mill. The compound of the latent curing agent and the epoxy resin can be stored for a long time and can cure the epoxy resin at a medium and low temperature, and a cured product has extremely high bonding strength and toughness.

Description

Epoxy resin latent curing agent with high bonding strength and toughness and preparation method thereof

Technical Field

The invention relates to an epoxy resin latent curing agent with high bonding strength and toughness and a preparation method thereof, in particular to a macromolecular latent curing agent obtained by grafting an imidazole compound onto a polymer chain, belonging to the technical field of organic synthesis.

Background

Imidazole compounds belong to traditional epoxy resin curing agents, and cured products of the imidazole compounds have heat resistance and insulation properties, so the imidazole compounds are widely applied to the field of electronic and electric appliances. However, the curing agent has a short pot life, cannot be used as a latent curing agent, and is too brittle as a cured product with an epoxy resin. The single-component epoxy resin adhesive is accurate in metering and convenient to use, and is particularly suitable for the industrial production of electronic appliances, so that imidazole compounds are generally modified into latent curing agents and are used for preparing the single-component adhesive. The currently marketed latent imidazole curatives still suffer from the drawbacks inherent in the original imidazole curatives: the cured product has high brittleness and poor bonding strength. If a toughening agent or plasticizer is added to the adhesive formulation, it will cause a decrease in heat resistance and adhesive strength.

To solve the above problems, CN101260185A reports a method of melt mixing hyperbranched polyester and imidazole-epoxy resin adduct, and attempts to solve the brittleness problem. However, the storage property of the compound with the epoxy resin is poor due to physical mixing, and the hyperbranched polyester is only used as an organic filler and has poor strength and toughness. We have attempted to graft imidazoles onto high molecular weight polymers to prepare latent curing agents that improve bond strength and provide toughness. The curing function of imidazole ring and the flexibility of polymer are combined together, thus fundamentally solving the problem that the cured product is brittle. The prior art has no report of the method.

Disclosure of Invention

The invention aims to provide a high-adhesion-strength and high-toughness latent epoxy resin curing agent, and a cured product obtained by mixing the epoxy resin latent epoxy resin curing agent with the epoxy resin has excellent adhesion strength and ultrahigh toughness so as to make up for the defects of a commercial product.

The technical scheme of the invention is as follows: a latent solidifying agent for epoxy resin with high adhesion strength and toughness is prepared from polyacrylate or polymethacrylate and alkyl imidazole or its derivative through amidation reaction in the presence of basic catalyst to obtain polyamide containing imidazole ring, low-temp freezing, and pulverizing.

The above-mentioned polyacrylates or polymethacrylates are saturated alkyl esters, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, 2-butyl, hexyl, octyl, isooctyl, cyclohexyl esters.

The alkyl imidazole is a saturated alkyl group or an aromatic group containing a hydrogen atom on the imidazole ring.

The above alkyl imidazole is imidazole, 2-methylimidazole, 2-ethylimidazole, 2-propylimidazole, 2-butylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole.

The alkyl imidazole derivative refers to that the N1 position is connected with an active group which can react with an ester group, and particularly refers to an alkyl group with an amino group.

The alkyl group with amino group refers to 2-aminoethyl, 3-aminopropyl and other straight-chain alkyl groups with amino group.

The molar ratio of the polymer monomer to the imidazole is 1: 0.5-1.0.

The above-mentioned basic catalyst refers to an inorganic base and a strongly basic organic base.

The inorganic base comprises alkali metal hydroxide and alkali metal hydride, and the organic base comprises alkali metal alkoxide and heterocyclic strong organic base DBU, DBN, DMAP and the like.

The amidation reaction refers to an acylation reaction between an alkyl imidazole or its derivative and an ester group, and is generally carried out by heating in the presence of a basic catalyst.

The product obtained converts it from a possibly rubbery state to a hard and brittle glassy state at low temperatures under refrigeration conditions and is therefore easy to pulverize.

The frozen hard and crisp solid is firstly primarily crushed by a mechanical crusher and then is subjected to impact crushing by a high-pressure airflow crusher. The high pressure air flow is freeze drying air flow to ensure no temperature rise and deliquescence during the crushing process.

The epoxy resin latent curing agent with high bonding strength and toughness is mainly prepared by a polymer grafting mode. Polyacrylates or polymethacrylates have excellent toughness and contain ester groups which can react with amino compounds by amidation to form strongly polar polyamides. The N1 site of the alkyl imidazole is secondary amine, the N1 site can be connected with alkylamine, and the alkyl imidazole and the ester group can be subjected to acylation reaction under the action of a basic catalyst to generate macromolecular polyamide with imidazole groups, so that imidazole rings of curable epoxy resin are introduced into a tough macromolecular chain, and the obtained imidazole curing agent does not react with the epoxy resin at normal temperature due to the high steric hindrance effect of the polymer, and is crosslinked only under heating, so that the imidazole curing agent has excellent latency. The invention combines the toughness and steric effect of the polymer, the strong polarity of the amide group and the curability of imidazole to prepare the latent curing agent of the epoxy resin with high bonding strength and toughness.

Detailed Description

The present invention is further illustrated in detail by the following examples, which are provided only for illustrating the present invention and are not intended to limit the scope of the present invention.

Example 1

86g of polymethyl acrylate, 82g of 2-methylimidazole and 2g of potassium hydroxide are placed in a three-neck flask, the three-neck flask is heated to 160 ℃ to be melted and stirred, and a by-product methanol generated in the reaction is distilled off. The reaction was continued until no methanol was distilled off, for about 8 hours. Pouring out the mixture while the mixture is hot, and airing the mixture to obtain a brown solid. Freezing overnight in a refrigerator, and pulverizing into micropowder with a mechanical pulverizer and a jet mill.

Example 2

142g of polybutyl acrylate, 110g of 2-ethyl-4-methylimidazole and 2g of potassium tert-butoxide are placed in a three-neck flask, heated to 160 ℃ for melting and stirred, and the butanol generated as a by-product in the reaction is evaporated. The reaction is continued until no butanol is distilled off, and the reaction time is about 6 hours. Pouring out the mixture while the mixture is hot, and airing the mixture to obtain a dark brown solid. Freezing overnight in a refrigerator, and pulverizing into micropowder with a mechanical pulverizer and a jet mill.

Example 3

100g of polymethyl methacrylate, 144g of 2-phenylimidazole and 2g of sodium methoxide are placed in a three-neck flask, heated to 180 ℃, and melted for reaction for 12 hours until no byproduct methanol is distilled off. Pouring out the mixture while the mixture is hot, and airing the mixture to obtain a light brown solid. Freezing overnight in a refrigerator, and pulverizing into micropowder with a mechanical pulverizer and a jet mill.

Example 4

100g of polymethyl methacrylate, 222g of 2-undecylimidazole and 2g of DMAP are placed in a three-neck flask, heated to 170 ℃, melted and reacted for 10 hours, and the generated byproduct methanol is evaporated to dryness. Pouring out the mixture while the mixture is hot, and airing the mixture to obtain a light brown solid. Freezing overnight in a refrigerator, and pulverizing into micropowder with a mechanical pulverizer and a jet mill.

Example 5

Putting 86g of polymethyl acrylate, 125g of 1- (2-aminoethyl) -2-methylimidazole and 2g of DMAP (dimethyl acetamide) in a three-neck flask, heating to 180 ℃, reacting for 3 hours, and evaporating to dryness to remove the generated byproduct methanol. Pouring out the mixture while the mixture is hot, and airing the mixture to obtain a brown solid. Freezing overnight in a refrigerator, and pulverizing into micropowder with a mechanical pulverizer and a jet mill.

Example 6

142g of polybutylmethacrylate, 139g of 1- (3-aminopropyl) -2-methylimidazole and 2g of DBU are placed in a three-neck flask, the temperature is heated to 180 ℃, the reaction is stirred for 8 hours, and the generated butanol is distilled out. Pouring out the mixture while the mixture is hot, and airing the mixture to obtain a brown solid. Freezing overnight in a refrigerator, and pulverizing into micropowder with a mechanical pulverizer and a jet mill.

The adhesive is prepared by the following formula in the following embodiments 1 to 6: 100 parts of liquid epoxy resin 828 (EEW 190), 20 parts of curing agent and 1 part of fumed silica. The results are as follows:

the properties of the cured products of examples 1 to 6 were compared with those of commercially available cured products as follows:

name of article	Example 1	Example 2	Example 3	Example 4	Example 5	Example 6	MC120D	8000K
									Adhesive Strength, MPA	265	292	278	306	320	325	138	130
Impact strength, KJ/m stand-by device	84	99	92	106	115	128	22	19

Wherein MC120D,8000K is available from solid research electronic materials, Inc. of Guangzhou city.

The results show that the high-adhesion-strength and high-toughness latent curing agent has the characteristics of good latency and high curing speed, and has the remarkable advantages that the adhesion strength of a cured product exceeds 300MPA and is more than 1 time higher than that of a commercially available product, and the impact strength exceeds 100 KJ/m and is 5 times higher than that of the commercially available product, so that the adhesion strength and the toughness are extremely excellent. The invention provides a production method of an epoxy resin latent curing agent with ultrahigh bonding strength and obdurability, and has wide market prospect.

Claims

1. A preparation method of epoxy resin latent curing agent with high bonding strength and toughness is characterized in that: the method comprises the following steps: placing polyacrylate or polymethacrylate, alkyl imidazole or alkyl imidazole derivatives and strong base in a three-neck flask, heating to 160-180 ℃ for melting and stirring, evaporating out by-products generated by the reaction until no by-products are distilled out, pouring out the materials while the materials are hot, airing to obtain brown solid, placing the brown solid in a refrigerator for freezing overnight, and then crushing the materials by using a machine and a jet mill to obtain the material;

the curing agent is prepared by carrying out amidation reaction on polyacrylate or polymethacrylate and alkyl imidazole or alkyl imidazole derivatives in proportion in the presence of an alkaline catalyst to prepare polyacrylamide or polymethacrylamide containing imidazole rings, freezing the polymer at low temperature, and crushing the polymer by using a mechanical and jet mill;

the polyacrylate or polymethacrylate is methyl ester, ethyl ester, propyl ester, isopropyl ester, butyl ester, isobutyl ester, 2-butyl ester, hexyl ester, octyl ester, isooctyl ester or cyclohexyl ester;

the alkyl imidazole is 2-methylimidazole, 2-ethylimidazole, 2-propylimidazole, 2-butylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 2-undecylimidazole or 2-heptadecylimidazole;

the alkyl imidazole derivative is an alkyl imidazole having an aminoalkyl group at the N1 position of the imidazole ring;

the low-temperature freezing refers to freezing below the glass transition temperature of the polymer;

the jet milling refers to high-pressure jet impact milling obtained by freeze drying;

the molar ratio of the monomer of the polyacrylate or the polymethacrylate to the alkyl imidazole or the alkyl imidazole derivative is 1:0.5 to 1.0.

2. The method for preparing the epoxy resin latent curing agent with high bonding strength and toughness as claimed in claim 1, wherein: the alkyl group having an amino group is a 2-aminoethyl group or a 3-aminopropyl group.

3. The method for preparing the epoxy resin latent curing agent with high bonding strength and toughness as claimed in claim 1, wherein: the basic catalyst comprises an inorganic base or a strong organic base; inorganic bases include alkali metal hydroxides, alkali metal hydrides; the strong organic base comprises alkoxide of alkali metal and heterocyclic strong organic base; the heterocyclic strong organic base comprises DBU, DBN or DMAP.

4. The method for preparing the epoxy resin latent curing agent with high bonding strength and toughness as claimed in claim 1, wherein: the amidation reaction refers to the reaction of alkyl imidazole or alkyl imidazole derivatives containing secondary amine or primary amine and polyacrylate or polymethacrylate to generate polyacrylamide or polymethacrylamide containing imidazole rings.