Quaternary ammonium salt latent curing agent, single-component epoxy resin composition as well as preparation method and application of single-component epoxy resin composition

Abstract

The invention discloses a quaternary ammonium salt latent curing agent, a single-component epoxy resin composition as well as a preparation method and application of the single-component epoxy resin composition. The compound has a specific general formula (I) structure, and R is Si, O or S and is matched with a specific weak nucleophilic anion (such as PF). The curing agent can be pre-mixed with an alicyclic epoxy resin (such as a compound of a formula II / III) to form a single-component system which can be stably stored for at least 3 months at the temperature of less than or equal to 40 DEG C. When heated to 90-130 DEG C, the system can rapidly initiate polymerization of epoxy groups, and the curing efficiency is high. The invention successfully solves the industrial problem that the single-component storage stability and the medium-temperature curing activity of the cycloaliphatic epoxy resin in the prior art are difficult to consider at the same time, and has extremely high industrial application value.

Description

Technical Field

[0001] This invention relates to the field of polymer curing technology, specifically to a novel type of thermal cationic latent curing agent, a one-component epoxy resin composition containing the curing agent, and its application in curing alicyclic epoxy resins. Background Technology

[0002] Alicyclic epoxy resins are widely used in electronic packaging, composite materials, and optical adhesives due to their excellent weather resistance, high light transmittance, low viscosity, and good electrical insulation properties. However, a long-standing technical bottleneck exists in their thermosetting applications: common alicyclic epoxy resins (such as 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexylcarbamate, vinyl cyclohexene dioxide, and their derivatives) are extremely sensitive to cationic initiators.

[0003] Currently, the most commonly used thermo-cationic curing agents in industry, such as those based on sulfonium salts or iodonium salts (e.g., products from King Industries), face a dilemma in practical applications: On the one hand, low-temperature initiators like King Industries CXC-1612, while effectively initiating polymerization at lower temperatures (e.g., 80-120°C), have excessively high reactivity, reacting slowly with the resin at room temperature, making it impossible to pre-mix with the resin to form a single-component system. Users must perform two-component mixing before use, which is not only cumbersome and prone to curing defects due to uneven mixing, but also limits its application in automated production processes. On the other hand, latent initiators like King Industries CXC-1614, which can be stored as a single component with the resin, typically have excessively high initiation temperatures (>150°C), resulting in high curing energy consumption and long curing times. Furthermore, the high temperature may adversely affect the substrate, and problems such as low curing degree and darkening of the cured system's color also exist.

[0004] Therefore, there is an urgent need in the field to develop a new type of curing agent that must simultaneously meet two seemingly contradictory key properties: (1) it can be stored stably for a long time (at least 3 months) after being mixed with alicyclic epoxy resin at room temperature or slightly higher temperatures (e.g., ≤40°C), i.e., it has excellent latency; (2) it can rapidly and efficiently initiate resin curing under moderate heating conditions (e.g., 90-130°C), and the cured product has excellent properties. Summary of the Invention

[0005] The purpose of this invention is to overcome the aforementioned deficiencies of the prior art and provide a novel class of quaternary ammonium salt compounds as thermally cationic latent curing agents. This curing agent can be premixed with specific alicyclic epoxy resins to form a storage-stable single-component system, and rapidly initiates a curing reaction upon heating.

[0006] Another object of the present invention is to provide a one-component epoxy resin composition comprising the above-mentioned curing agent.

[0007] Another object of the present invention is to provide a method for preparing and curing the above-mentioned one-component epoxy resin composition.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows: In a first aspect, the present invention provides a quaternary ammonium salt compound as shown in general formula (I): Compound formula (Ⅰ); wherein R1 is selected from silicon (Si), oxygen (O) or sulfur (S) atoms; R2, R3, and R4 are each independently selected from C1-C10 alkyl, cycloalkyl, or aryl groups; It is selected from one of hexafluorophosphate (PF6⁻), tetrafluoroborate (BF4⁻), hexafluoroantimonate (SbF6⁻), hexafluoroarsenate (AsF6⁻), or trifluoromethanesulfonate (CF3SO3⁻).

[0009] Preferably, R2, R3, and R4 are methyl, ethyl, or phenyl. More preferably, The anions are PF6⁻ or SbF6⁻, which can endow compounds with better latency and thermal responsiveness.

[0010] In a second aspect, the present invention provides a one-component epoxy resin composition comprising: (A) At least one alicyclic epoxy compound; (B) A quaternary ammonium salt compound of formula (I) as described in the first aspect, used in an amount of 0.1% to 3.0% of the total mass of the composition; (C) Optional solvents, accelerators, toughening agents, fillers or other additives.

[0011] The alicyclic epoxy compounds are selected from compounds having the following structures (II) and / or (III) and mixtures thereof:

[0012] (Formula II, for example: 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexylcarbamate);

[0013] (Formula III, for example: vinylcyclohexene dioxide and its derivatives).

[0014] Thirdly, the present invention provides a method for preparing the quaternary ammonium salt compound described in the first aspect, comprising the following steps: The tertiary amine compound (NR2R3R4) is reacted with a haloalkane containing an R1-functional group (R1-CH2-Cl / Br) in an organic solvent to generate a quaternary ammonium salt halide intermediate. The quaternary ammonium halide intermediate is combined with a target anion. The metal salt or acid undergoes anion exchange reaction to obtain a quaternary ammonium salt compound of the target general formula (I).

[0015] Fourthly, the present invention provides a method for curing a one-component epoxy resin composition, comprising: heating the one-component epoxy resin composition of the second aspect above to a temperature of 80°C to 150°C and holding it for a certain time to allow it to fully cure.

[0016] The beneficial effects of this invention are as follows: Excellent storage stability: The quaternary ammonium salt curing agent of this invention has a unique molecular design (specific central atom R1 and a large weak nucleophilic anion). It exhibits extremely high chemical inertness at low temperatures (≤40℃). Experiments show that its mixture with alicyclic epoxy resin can be stably stored at 40℃ for more than 3 months with minimal viscosity change and no gelation.

[0017] Moderate curing temperature and high efficiency: When heated to above 90℃, this curing agent can rapidly decompose to generate active cationic species, efficiently initiating the ring-opening polymerization of epoxy groups. Differential scanning calorimetry (DSC) measurements show that its curing exothermic peak is typically between 100-120℃, achieving an ideal balance between low-temperature storage and rapid medium-temperature curing.

[0018] The cured product has excellent performance: the cured product obtained by using the curing agent of this invention has the advantages of light color, high transparency, high hardness, good adhesion and good heat resistance, which fully meet the requirements of high-end application fields.

[0019] Easy to use: It can be directly formulated into single-component products, which greatly simplifies the user's construction process, improves production efficiency and product consistency, and is especially suitable for assembly line operations and automated dispensing scenarios. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0021] Example 1: Preparation of (2-methoxybenzyl)-dimethyl(phenyl)-ammonium chloride 24.2 g (0.2 mol) of N,N-dimethylaniline, 31.3 g (0.2 mol) of o-methoxybenzyl chloride, and 130 g of dichloroethane were added to a 500 mL three-necked flask equipped with a stirrer, thermometer, and condenser. The mixture was heated to an internal temperature of 80 °C and stirred under reflux for 2 hours. After the reaction was complete, the solvent dichloroethane was removed by vacuum distillation to obtain a pale yellow viscous solid crude product. 300 g of n-heptane was added to the crude product, and the mixture was stirred at 25 °C for 2 hours. After filtration, the product was washed with a small amount of cold n-heptane and dried under vacuum to obtain 50.8 g of a white powdery solid product, with a yield of 91.4% and a melting point of 134 °C. This product is a quaternary ammonium salt halide intermediate.

[0022] Example 2: Preparation of (2-methoxybenzyl)-dimethyl(phenyl)-ammonium hexafluorophosphate 30.0 g (0.108 mol) of ammonium chloride salt prepared in Example 1 and 21.8 g (0.118 mol) of potassium hexafluorophosphate (KPF6) were placed in a three-necked flask, and 200 g of methanol was added. The mixture was stirred at 45 °C for 8 hours. After the reaction was complete, the mixture was cooled to room temperature, and the generated potassium chloride solid was removed by filtration. The clear filtrate was slowly added dropwise to 2000 g of ice water with stirring, and a white solid precipitated immediately. Stirring was continued for 1 hour, and the mixture was filtered. The solid was washed with deionized water until neutral, and dried under vacuum at 50 °C for 24 hours to obtain 33.5 g of white granular solid, with a yield of 80.1% and a melting point of 116 °C. The structure of the target product (Formula I, where R1=O, R2=R3=CH3, R4=C6H5) was confirmed by 1H NMR and mass spectrometry. =PF6⁻).

[0023] Example 3: Formulation and Performance Testing of One-Component Epoxy Resin Compositions Preparation of curing agent stock solution: Dissolve 10.0g of the curing agent prepared in Example 2 in 30.0g of propylene carbonate (PC) to obtain a clear and transparent curing agent solution A.

[0024] Preparation of a single-component resin composition: Take 100g of commercially available alicyclic epoxy resin (mainly compound II, brand name CER-170), add 2.0g of the above curing agent solution A (equivalent to 0.5% of the resin mass in solid content of curing agent), stir and mix evenly at room temperature to obtain a single-component epoxy resin composition B.

[0025] Storage stability test: Composition B was dispensed into sealed vials and stored in constant temperature ovens at 25°C, 40°C, and 60°C, respectively. Periodic samples were taken to test its viscosity (25°C, Brookfield rotational viscometer) and curing properties (DSC, heating rate 10°C / min). Simultaneously, resin composition C was prepared in the same proportion using a commercially available brand of alicyclic epoxy single-component curing agent requiring cold chain transportation (Comparative Example 1), and a parallel control test was conducted.

[0026] The test results are shown in the table below: sample Storage conditions Storage time Appearance and Flow Viscosity (cP, 25℃) DSC initial heat release temperature Tonset (°C) DSC peak temperature Tpeak (°C) Composition B of the present invention Initial preparation 0 days Transparent liquid, flows well 235 95.9 109.9 Store at 25℃ 90 days Transparent liquid, flows well 242 96.5 110.2 Store at 40℃ 90 days Transparent liquid, flows well 260 91.2 110.6 Store at 60℃ 60 days A transparent, slightly yellow liquid that is free-flowing. 253 92.1 111.4 Comparative Example 1 Composition C Initial preparation 0 days Transparent liquid, flows well 236 92.6 111.4 Store at 40℃ 30 days Complete gel solidification Unable to measure Unable to measure Unable to measure Conclusion: After storage at 40°C for 3 months, the viscosity of the curing agent system of this invention increased only slightly, while the DSC curing peak shape and temperature remained essentially unchanged, demonstrating excellent latent stability. In contrast, the comparative product completely failed under harsh conditions (40°C) in just 1 month, proving the significant progress of this invention.

[0027] Example 4: Performance Testing of Cured Products The composition B sample from Example 3, after being stored at 40°C for 90 days, was poured into a mold preheated to 100°C, cured at 110°C for 2 hours, and then post-cured at 130°C for 1 hour to obtain a transparent hard sample.

[0028] Performance tests were conducted on the product: Barcol hardness was 78; light transmittance (visible light) was >90%; glass transition temperature (Tg, DMA) was 125℃; and water absorption (immersion in water at 25℃ for 24 hours) was 0.35%. All properties met or exceeded the level of similar two-component system cured products.

[0029] Comparative Example 2: Using other anionic curing agents Following the method of Example 2, the anion exchange reagents were replaced with sodium tetrafluoroborate (NaBF4) and potassium trifluoromethanesulfonate (KCF3SO3), respectively, to prepare the corresponding quaternary ammonium salts. Single-component resins were prepared according to the method of Example 3 and stored at 40°C. The results showed that the viscosity of the BF4⁻ salt increased sharply after approximately 15 days and gelled after 30 days; the CF3SO3⁻ salt thickened significantly within 7 days. This demonstrates the crucial and unexpected role of the specific anion selected in this invention (such as PF6⁻) in achieving long-term latency.

Claims

1. A quaternary ammonium salt compound as shown in general formula (I), Compound formula (Ⅰ); in, R1 is selected from silicon (Si), oxygen (O), or sulfur (S) atoms; R2, R3, and R4 are each independently selected from C1-C10 alkyl, cycloalkyl, or aryl groups; It is selected from one of hexafluorophosphate (PF6⁻), tetrafluoroborate (BF4⁻), hexafluoroantimonate (SbF6⁻), hexafluoroarsenate (AsF6⁻), or trifluoromethanesulfonate (CF3SO3⁻).

2. The quaternary ammonium salt compound according to claim 1, characterized in that, R2, R3, and R4 are methyl, ethyl, or phenyl.

3. The quaternary ammonium salt compound according to claim 1 or 2, characterized in that, The It is either hexafluorophosphate (PF6⁻) or hexafluoroantimonate (SbF6⁻).

4. A one-component epoxy resin composition, characterized in that, Include: (A) At least one alicyclic epoxy compound; (B) The quaternary ammonium salt compound as described in any one of claims 1 to 3.

5. The one-component epoxy resin composition according to claim 4, characterized in that, The content of the quaternary ammonium salt compound (B) is from 0.1% to 3.0% of the total mass of the composition.

6. The one-component epoxy resin composition according to claim 4 or 5, characterized in that, The alicyclic epoxy compound (A) is selected from compounds having the following structures: (II) and / or (III) and mixtures thereof. and / or 7. A method for preparing the quaternary ammonium salt compound according to any one of claims 1 to 3, characterized in that, Includes the following steps: (1) A tertiary amine compound is subjected to a quaternization reaction with a haloalkane in an organic solvent to generate a quaternary ammonium salt halide intermediate, wherein the haloalkane has the structure R1-CH2-Z, wherein R1 is as defined in claim 1 and Z is a halogen; (2) The quaternary ammonium halide intermediate obtained in step (1) is reacted with a compound containing... The anion salt or acid undergoes anion exchange reaction to yield the quaternary ammonium salt compound, wherein... As defined in claim 1.

8. A method for curing a one-component epoxy resin composition as described in any one of claims 4 to 6, characterized in that, include: The composition is heated to a temperature of 80°C to 150°C for a curing reaction.

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