Microcapsule type epoxy resin latent curing accelerator taking modified starch as wall material and preparation method of microcapsule type epoxy resin latent curing accelerator

Abstract

The invention belongs to the technical field of epoxy resin latent curing accelerators, and discloses a microcapsule type epoxy resin latent curing accelerator taking modified starch as a wall material and a preparation method of the microcapsule type epoxy resin latent curing accelerator. Octenyl succinic anhydride cassava starch ester (OSAS) is used as a wall material, 2-methylimidazole (2-MI) is used as a core material, the microcapsule is prepared through a Pickering emulsion method, the microcapsule is applied to an epoxy resin (E51) / methylhexahydrophthalic anhydride (MHHPA) system for curing testing, and it is proved that the prepared microcapsule can play a role in promoting the E51 / MHHPA curing system and can be used for curing the epoxy resin (E51) / MHHPA curing system. Meanwhile, it is observed that the microcapsule can keep high fluidity of a system for more than 60 days at normal temperature, and meanwhile, the curing activity of the microcapsule at high temperature is kept.

Description

Technical Field

[0001] This invention belongs to the technical field of epoxy resin latent curing accelerators, and is based on the preparation of microcapsule-type latent curing accelerators using modified starch-stabilized Pickering emulsions. Specifically, it relates to a microcapsule-type epoxy resin latent curing accelerator with modified starch as the wall material and its preparation method. Background Technology

[0002] Epoxy resin (E51) is widely used in various fields due to its excellent thermal properties, superior chemical resistance, low curing shrinkage, and good adhesion and dimensional stability. In the electronic packaging industry, acid anhydrides are commonly used as curing agents because anhydride-cured epoxy resins exhibit better thermal and dielectric properties than those cured with amines and imidazoles. However, these epoxy compound systems have very high curing activation energies, resulting in very high curing temperatures. To lower the curing temperature and improve processability, accelerators are typically added to the epoxy system. Imidazole compounds are among the most commonly used accelerators. As epoxy curing accelerators, they can significantly reduce the curing temperature of thermosetting epoxy materials and increase the glass transition temperature (Tg), which is of great significance for epoxy resin products in the microelectronics packaging field.

[0003] Microencapsulation technology is widely used in food, pharmaceuticals, cosmetics, and other fields. Under certain conditions, it involves preparing membrane materials to form tiny capsules to encapsulate solids, liquids, and gases. This technology can control the release of substances and improve stability. Encapsulating imidazole curing accelerators in microcapsules is an effective method to ensure storage stability, extend shelf life, and maintain curing activity at high temperatures. Summary of the Invention

[0004] This invention provides a microcapsule-type epoxy resin latent curing accelerator with modified starch as the wall material, which is prepared by cross-coating 2-methylimidazole with octenyl succinic anhydride starch ester and aldehyde compound.

[0005] Furthermore, the mass ratio of the octenyl succinic anhydride starch ester to 2-methylimidazole is 2-5g:1g.

[0006] Furthermore, the octenyl succinic anhydride starch ester is prepared from tapioca starch and octenyl succinic anhydride.

[0007] Preferably, the ratio of cassava starch to octenyl succinic anhydride is 50g:3mL.

[0008] Furthermore, the aldehyde compound is glutaraldehyde.

[0009] Preferably, the aldehyde compound is a 3% glutaraldehyde fixative; the ratio of the amount of octenyl succinic anhydride starch ester, 2-methylimidazole and the 3% glutaraldehyde fixative is 2-5g:1g:3mL.

[0010] Furthermore, the preparation method of the microcapsule-type epoxy resin latent curing accelerator using modified starch as the wall material is as follows: a Pickering emulsion is prepared by using modified starch as a stabilizer, and then 2-MI is encapsulated to form microcapsules. First, starch is modified by wet process, and cassava starch is modified with OSA to obtain OSAS powder; then, OSAS is dissolved in deionized water as the aqueous phase, 2-MI is dissolved in CH2Cl2 solution, anhydrous ethanol is added as a solubilizer and emulsifier Span80 as the oil phase, glutaraldehyde is added as a crosslinking agent, and microcapsules are prepared by the Pickering emulsion-solvent evaporation method. Finally, the microcapsules are introduced into the E51 / MHHPA system, and the microcapsule accelerator gives the system excellent latency (storage period >60 days at room temperature) while maintaining curing activity at high temperature.

[0011] Furthermore, the preparation method of the microencapsulated epoxy resin latent curing accelerator includes the following steps: (1) Preparation of wet-process octenyl succinic anhydride starch ester (OSAS): Cassava starch was used as raw material, and the starch was modified by wet process: Cassava starch was dissolved in deionized water and stirred at a certain temperature. Then, the pH was adjusted with sodium hydroxide (NaOH) solution to form a starch suspension. A certain amount of octenyl succinic anhydride (OSA) was diluted with anhydrous ethanol to prepare an OSA solution. The OSA solution was slowly added to the starch suspension and stirred to react. After the reaction was completed, the sample was filtered, washed three times with deionized water and anhydrous ethanol respectively, and dried in an oven. After drying, it was ground into powder and passed through a 100-mesh sieve to obtain OSAS. (2) Preparation of microcapsules OSAS was dissolved in deionized water as the aqueous phase and stirred with an oil phase containing 2-MI (2-methylimidazole) to prepare a Pickering emulsion. Glutaraldehyde was then added to initiate a cross-linking reaction. After the reaction was complete, the mixture was poured into a separatory funnel and allowed to stand. After standing, the lower layer of microcapsules was collected, pre-frozen in a refrigerator, and then dried in a freeze dryer to obtain the microcapsule-type epoxy resin latent curing accelerator.

[0012] Furthermore, the ratio of cassava starch to octenyl succinic anhydride (OSA) is 50 g: 3 mL.

[0013] Furthermore, the stirring temperature is 40°C.

[0014] Furthermore, the pH value is 8-9.

[0015] Furthermore, the stirring reaction temperature is 40°C; the time is 1 hour.

[0016] Furthermore, the method for preparing the oil phase containing 2-MI is as follows: 2-methylimidazole is dissolved in CH2Cl2 solution (with anhydrous ethanol as a dissolving agent), and an emulsifier (such as Span80) is added to prepare the oil phase; wherein, the ratio of 2-methylimidazole to emulsifier is 1:0.01.

[0017] Preferably, the crosslinking reaction temperature is 50°C and the time is 2 hours.

[0018] Preferably, the volume ratio of CH2Cl2 to anhydrous ethanol in the CH2Cl2 solution is 10:1.

[0019] The application method of the microencapsulated epoxy resin latent curing accelerator prepared by the above method is as follows: The microencapsulated epoxy resin latent curing accelerator and the curing agent were mixed and pre-dispersed under magnetic stirring to obtain a dispersion. Then, the epoxy resin was mixed into the dispersion and stirred until homogeneous to obtain a uniform mixture. This mixture can be stored at room temperature for >60 days while maintaining its curing activity at high temperatures.

[0020] In the embodiments of this application, the curing agent is methyl hexahydrophthalic anhydride (MHHPA).

[0021] In the embodiments of this application, the epoxy resin is epoxy resin E51.

[0022] Furthermore, the mass of the microcapsule is 30% of the epoxy resin.

[0023] The beneficial effects of this invention are as follows: This invention provides a microencapsulated epoxy resin latent curing accelerator with modified starch as the wall material, which is prepared by cross-coating 2-methylimidazole with octenyl succinic anhydride starch ester and an aldehyde compound. Introducing this microencapsulated epoxy resin latent curing accelerator with modified starch as the wall material into an epoxy resin system (such as the E51 / MHHPA system) imparts excellent latency (room temperature storage time > 60 days) to the system while maintaining its curing activity at high temperatures. Attached Figure Description

[0024] Figure 1 The image shows a SEM image of the microcapsules from Example 1, with scale bars of 60 μm, 15 μm, and 3 μm. Figure 2 The 2-MI standard operating curve for Example 1; Figure 3 The infrared spectra of 2-MI and microcapsules in Example 1 are shown below. Figure 4The flowability of the resin systems of Application 2 and Comparative Application 2 at room temperature for 0–60 days (D) was measured. Detailed Implementation

[0025] Example 1

[0026] Weigh 50g of cassava starch (Nanjing Ganzhiyuan Co., Ltd.), dissolve it in 150mL of deionized water, and stir magnetically in a 40℃ water bath for 10 minutes to obtain a starch suspension. Adjust the pH of the starch solution to 8-9 with 3% NaOH solution. Measure 3mL of 98% OSA (octenyl succinic anhydride) solution and dilute it in 10mL of anhydrous ethanol. Slowly add the diluted OSA solution to the starch suspension using a dropper, and stir at 40℃ for 1 hour. After filtration, wash three times successively with deionized water and anhydrous ethanol. Dry in a 40℃ oven to constant weight, then grind and sieve before packaging for later use to obtain OSAS.

[0027] The total mass of OSAS and 2-MI (2-methylimidazole) was controlled to be 10 g. OSAS and 2-MI were weighed at a core-to-wall material mass ratio of 1:5. OSAS was dissolved in 90 mL of deionized water and stirred magnetically for 10 minutes to prepare the aqueous phase. 2-MI was dissolved in 10 mL of CH2Cl2 solution (with 1 mL of anhydrous ethanol as a dissolving agent). 1 mL of 1% Span80 was added as an emulsifier to prepare the oil phase. The oil phase was slowly added to the aqueous phase under high-speed homogenization at 10000 rpm for 5 minutes. The mixture was then transferred to a magnetic stirrer, and 3 mL of 3% glutaraldehyde fixative was added as a crosslinking agent. After reacting at 50°C for 2 hours, the mixture was separated by a separatory funnel. The lower layer of microcapsules was collected, pre-frozen, and then freeze-dried for 36 hours to obtain a microcapsule-type epoxy resin latent curing accelerator with an encapsulation rate of 61.60%.

[0028] Example 2 is the same as Example 1, except that the mass ratio of the core and wall materials used in the preparation of microcapsules in Example 2 is 1:2, and the resulting encapsulation rate is 26.17%.

[0029] Example 3 is the same as Example 1, except that the mass ratio of the core and wall materials in Example 3 to the microcapsules is 1:3, and the encapsulation rate is 31.63%.

[0030] Example 4 is the same as Example 1, except that the mass ratio of the core and wall materials in Example 4 to the microcapsule preparation is 1:4, and the encapsulation rate is 35.40%.

[0031] Example 5 is the same as Example 1, except that the temperature during microcapsule preparation in Example 5 is 30°C, and the encapsulation rate is 26.51%.

[0032] Example 6 is the same as Example 1, except that the temperature during microcapsule preparation in Example 6 is 40°C, and the encapsulation rate is 34.45%.

[0033] Example 7 is the same as Example 1, except that the temperature during microcapsule preparation in Example 7 is 60°C, and the encapsulation rate is 42.34%.

[0034] Comparative Example 1 is the same as Example 1, except that CH2Cl2 in Comparative Example 1 is replaced with the same molar amount of ethyl acetate. The encapsulation rate of the microcapsule-type epoxy resin latent curing accelerator prepared in Comparative Example 1 is lower than that in Example 1, at 40.23%, and its stability at room temperature is maintained for only 21 days.

[0035] Methods for determining microcapsule encapsulation efficiency: Determination of the measurement wavelength: A 50 mL solution of 2-MI standard was prepared using anhydrous ethanol as the solvent to serve as the working solution. Anhydrous ethanol was used as a blank control, and the working solution was scanned within the wavelength range of 190-650 nm. The 2-MI standard solution was diluted to concentration gradients of 25 mg / mL, 12 mg / mL, 6 mg / mL, and 3 mg / mL, and the absorbance was measured at the maximum absorption wavelength (295 nm) obtained in the previous scan. A standard working curve was plotted based on the relationship between absorption intensity and 2-MI concentration (e.g., ...). Figure 2 (As shown).

[0036] Determination of oil content on the surface of microcapsules: Accurately weigh 0.2 g of microcapsule sample, wash thoroughly with 50 mL of anhydrous ethanol, filter, and dilute the filtrate to 100 mL with anhydrous ethanol. Measure the absorbance of the solution at 295 nm wavelength, and calculate the 2-MI content adsorbed on the surface of the microcapsules using a standard curve.

[0037] Determination of total oil content in microcapsules: Dissolve 0.2 g of microcapsules in 1 mL of deionized water, add excess anhydrous sodium sulfate to remove water, extract 2-MI with anhydrous ethanol, filter, and dilute the filtrate to 100 mL with anhydrous ethanol. Measure the absorbance of this solution at 295 nm wavelength, and calculate the total 2-MI content in the microcapsules based on the standard curve.

[0038] Encapsulation efficiency = (1 - oil content on the surface of microcapsules / total oil content of capsules) × 100%

[0039] Application 1

[0040] 4.5 g of MHHPA and 1.5 g of the microencapsulated epoxy resin latent curing accelerator from Example 1 (the content of 2-MI in the microencapsulated epoxy resin latent curing accelerator is 2 wt% relative to the epoxy resin) were added to a beaker and stirred evenly with a magnetic stirrer; 5.0 g of epoxy resin E51 (epoxy value is 0.48) was added to the above beaker and stirred to form a homogeneous mixture. To prepare the epoxy thermosetting material, the mixture was degassed under vacuum for 0.5 hours and then poured into a mold; the mold was placed in an oven, and the mixture was cured for 2 hours at stages of increasing temperature (100°C, 130°C, and 150°C).

[0041] Comparative Application 1 is the same as Application 1, except that the microcapsule-type latent curing accelerator obtained in Example 1 was not added in Comparative Application 1.

[0042] Test results show that both the epoxy resin curing systems of Application 1 and Comparative Application 1 were successfully cured.

[0043] Application 2

[0044] 4.5 g of MHHPA and 1.5 g of the microencapsulated epoxy latent curing accelerator from Example 1 (the content of 2-MI in the microencapsulated epoxy latent curing accelerator is 2 wt% relative to the epoxy resin) were added to a beaker and stirred evenly with a magnetic stirrer; 5.0 g of epoxy resin E51 was added to the above beaker and stirred to form a homogeneous mixture. The epoxy thermosetting material was prepared, and after degassing the mixture under vacuum for 0.5 hours, it was poured into a centrifuge tube, and its flowability at room temperature was observed and recorded.

[0045] Comparison Application 2

[0046] Similarly, 4.5g MHHPA, 1.5g 2-MI and 5g epoxy resin E51 were mixed evenly, degassed together and poured into centrifuge tubes at the same time. Their flowability at room temperature was observed and recorded.

[0047] The test results for Application 2 and Comparison Application 2 are as follows: Figure 4 As shown, the microencapsulated epoxy resin latent curing accelerator system using application 2 exhibited good flowability, remaining fluid up to 30 days later. However, the 2-MI curing system showed poor flowability, with only one day remaining after a surface film had cured and the system could no longer flow.

[0048] Comparison Application 3

[0049] Comparative Application 3 is the same as Application 1, except that in the preparation of the microencapsulated epoxy resin latent curing accelerator in Comparative Application 3, modified silica (SiO2) is used instead of OSAS. The nano-silica is purchased from Aladdin, with an average particle size of 15±5 nm. It is a hydrophobically modified SiO2 obtained by modifying diphenyldimethoxysilane (DMDPS). The specific method is as follows: 2.00 g of nano-SiO2 is ultrasonically dispersed in 160 mL of 90% ethanol aqueous solution in a 200 mL beaker for 30 min. Simultaneously, DMDPS (0.06 g) is placed in a single-necked flask containing 10 mL of ethanol and 2 mL of ammonia and hydrolyzed under magnetic stirring at 50 °C for 30 min. Then, the obtained hydrolysis product is added dropwise to the ethanol dispersion of SiO2, and the reaction is carried out under magnetic stirring at 50 °C for 12 h. Afterwards, the product is centrifuged and washed three times with ethanol, and then dried at 40 °C for 8 h to obtain modified SiO2 nanoparticles. The obtained microcapsules were less fluid in the epoxy / anhydride system than those in Application 1, and lost their fluidity after 21 days. In contrast, the microcapsules in Example 1 prepared with OSAS had a room temperature storage life of more than 60 days, which greatly improved the storage performance.

[0050] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A microcapsule-type epoxy resin latent curing accelerator using modified starch as the wall material, characterized in that: It is prepared by cross-coating 2-methylimidazole with octenyl succinic anhydride starch ester and aldehyde compound; the mass ratio of octenyl succinic anhydride starch ester to 2-methylimidazole is 2-5:1; the octenyl succinic anhydride starch ester is obtained from cassava starch and octenyl succinic anhydride.

2. The microencapsulated epoxy resin latent curing accelerator with modified starch as the wall material as described in claim 1, characterized in that: The ratio of cassava starch to octenyl succinic anhydride is 50 g: 3 mL; the aldehyde compound is glutaraldehyde.

3. A method for preparing a microcapsule-type epoxy resin latent curing accelerator with modified starch as the wall material as described in claim 1 or 2, characterized in that, Includes the following steps: Step (1): Using cassava starch as raw material, the starch is modified by wet method: cassava starch is dissolved in deionized water and stirred, and then the pH of the solution is adjusted with sodium hydroxide solution to form a starch suspension; octenyl succinic anhydride is diluted with anhydrous ethanol to prepare OSA solution; OSA solution is added to starch suspension and stirred to react, and after the reaction is completed, it is filtered, washed, dried, ground into powder, and sieved to obtain octenyl succinic anhydride starch ester; Step (2): Dissolve the octenyl succinic anhydride starch ester obtained in step (1) in deionized water as the aqueous phase, and stir and mix it with the oil phase containing 2-methylimidazole to prepare a Pickering emulsion. Then, add glutaraldehyde to carry out a cross-linking reaction. After the reaction is completed, let it stand, collect the lower layer of microcapsules, freeze dry, and obtain the microcapsule-type epoxy resin latent curing accelerator with modified starch as the wall material.

4. The preparation method of the microcapsule-type epoxy resin latent curing accelerator with modified starch as the wall material as described in claim 3, characterized in that, The stirring temperature in step (1) is 40°C; And / or, the pH adjustment of the solution is: adjusting the pH value of the solution to 8-9; And / or, the stirring reaction temperature is 40°C and the time is 1 hour.

5. The preparation method of the microencapsulated epoxy resin latent curing accelerator with modified starch as the wall material as described in claim 3, characterized in that, The preparation method of the oil phase containing 2-methylimidazole in step (2) is as follows: 2-MI is dissolved in CH2Cl2 solution, and an emulsifier is added to mix and prepare the oil phase; the volume ratio of CH2Cl2 to anhydrous ethanol in the CH2Cl2 solution is 10:1; the amount ratio of 2-methylimidazole to emulsifier is 1:0.

01.

6. The preparation method of the microcapsule-type epoxy resin latent curing accelerator with modified starch as the wall material as described in claim 5, characterized in that, The emulsifier is Span80.

7. The preparation method of the microcapsule-type epoxy resin latent curing accelerator with modified starch as the wall material as described in claim 3, characterized in that, The cross-linking reaction in step (2) is carried out at a temperature of 50°C for 2 hours.

8. The application of a microencapsulated epoxy resin latent curing accelerator using modified starch as the wall material as described in claim 1 or 2, characterized in that: The microcapsule-type epoxy resin latent curing accelerator with modified starch as the wall material was mixed with the curing agent and pre-dispersed under magnetic stirring to obtain a dispersion; then the epoxy resin was mixed into the dispersion and stirred evenly.

9. The application as described in claim 8, characterized in that: The mass of the microcapsule-type epoxy resin latent curing accelerator with modified starch as the wall material is 30% of the epoxy resin.

10. The application as described in claim 8, characterized in that: The curing agent is methyl hexahydrophthalic anhydride; the epoxy resin is epoxy resin E51.

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