Method for preparing intrinsic black material from epoxy resin modified polyimide

Abstract

The invention belongs to the technical field of high polymer materials, and discloses a method for preparing an intrinsic black material from epoxy resin modified polyimide prepared from a bio-based material. Bio-based furfural and eugenol are used as monomers to synthesize a diphenol monomer, and then the diphenol monomer is epoxidized to prepare an epoxy monomer. And finally, adding the black epoxy resin into a commercial PAA acid solution prepared from ODA and BPDA for polycondensation to obtain an epoxy modified polyamide acid solution, and preparing the black epoxy resin / polyimide composite material by a thermal method. The epoxy monomer with high absorbance is introduced, the black composite material can be prepared only by adding a small amount, and the method is simple and efficient. The prepared black epoxy resin / polyimide composite material is excellent in shading performance and heat resistance and has wide application value in the fields of electronic industry, aerospace, instrument communication and the like.

Description

Technical Field

[0001] The present invention relates to the field of polymer materials, and particularly to a method for preparing an intrinsically black material by modifying polyimide with epoxy resin. Background Art

[0002] As a kind of high-performance polymer, polyimide (PI) has become a core material in fields such as aerospace, microelectronic packaging, and flexible displays due to its excellent high-temperature resistance (long-term use temperature > 300 °C), outstanding mechanical strength, chemical stability, and electrical insulation properties. However, charge transfer complexes (CTCs) generally exist in the molecular chains of traditional polyimides. This structure formed by the interaction between electron donors (such as amino groups) and acceptors (such as anhydrides) causes the material to have strong absorption in the visible light band (especially 400 - 600 nm), making it appear yellow or light brown. This characteristic limits its application in scenarios that require light shielding, electromagnetic shielding, or a dark appearance, such as the light shielding layer of optical sensors, black insulating films, and the casings of high-end electronic devices. Therefore, how to endow polyimide with intrinsic black characteristics through molecular design without relying on exogenous colorants has become an important research direction in the field of materials science.

[0003] To achieve the intrinsic blackening of polyimide, the epoxy resin modification technology has emerged. Its core mechanism lies in introducing epoxy resin into the polyimide system through chemical copolymerization or physical blending, and using the synergistic effect of the two to regulate the light absorption behavior of the material. Specifically, the epoxy groups of epoxy resin can react with the active groups (such as amino groups and hydroxyl groups) in the polyimide precursor (such as polyamic acid) to form a cross-linked network or an interpenetrating structure.

[0004] From the perspective of application requirements, intrinsically black polyimide materials exhibit irreplaceable advantages in many high-tech fields. In the microelectronics field, as integrated circuits develop towards high density and miniaturization, chip packaging materials need to have low light reflection characteristics to reduce signal interference. The introduction of traditional colorants (such as carbon black) may increase dielectric loss due to uneven dispersion, while the epoxy resin modification technology avoids this problem through molecular-level compounding. In the aerospace field, lightweight and high-temperature-resistant black coatings are crucial for the light shielding and thermal control performance of satellite optical instruments. Intrinsically black polyimide can meet the requirements without additional spraying processes. In addition, the development of electromagnetic shielding materials in 5G communication devices also benefits from this technology, because the darkening of materials is often accompanied by controllable adjustment of electrical conductivity. For example, by introducing a carbon nanotube / epoxy-PI composite system, the functions of electromagnetic wave absorption and visual concealment can be achieved simultaneously. Compared with the physical doping method, the intrinsic modification strategy has more advantages in maintaining the material's homogeneity, long-term stability, and processing performance.

[0005] Although the technology of epoxy resin modification has broad prospects, its practical application still faces multiple challenges. First of all, the balance problem between color depth and material properties needs to be solved urgently: excessive cross-linking can enhance light absorption, but it will lead to an increase in material brittleness and a decrease in thermal stability.

[0006] Generally speaking, the technology of preparing intrinsically black materials by modifying polyimide with epoxy resin embodies the advanced concept of "structure-property-function" integrated design of polymer materials. By regulating the molecular chain interaction and chemical structure, not only the color limitation of traditional materials has been broken through, but also the synergistic improvement of light shielding property, heat resistance and mechanical properties has been achieved. In the future, with the in-depth understanding of the chromogenic mechanism, the development of new epoxy monomers and the progress of green manufacturing processes, this technology is expected to be more widely applied in high-end electronic devices, intelligent sensing, national defense and military industries, etc., promoting the continuous development of high-performance polymer materials towards functionalization and intelligentization. This innovative path also provides an important reference for the research and development of other colored special engineering plastics. Summary of the Invention

[0007] In order to solve the deficiencies in the mechanical properties and dielectric properties of traditional black polyimide, a method of compounding a new type of epoxy resin with polyimide is adopted to solve this problem.

[0008] The technical solution of the present invention is as follows:

[0009] The structure of the epoxy resin monomer is as follows:

[0010] The above-mentioned monomer scheme includes the following steps:

[0011] (1) Put 15 g of eugenol into a 500 ml three-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a constant pressure dropping funnel. When the temperature is raised to 50 °C, add a 60% by mass aqueous sodium hydroxide solution (1.6 g), stir for a period of time, and then slowly and evenly drip 4.5 g of furfural (1 h) using the constant pressure dropping funnel. After the addition of raw materials is completed, raise the temperature to 60 °C and react for 9 h, then raise the temperature to 100 °C and react for 12 h. The final product is a black viscous liquid. Then add a large amount of chloroform and a small amount of hydrochloric acid for extraction until the lower aqueous phase is neutral, and then rotary evaporate the organic phase to obtain a yellowish-black block solid. Separate the solid by column chromatography, and the eluent is ethyl acetate: petroleum ether = 1:5. Collect the product and rotary evaporate to obtain a yellow solid powder.

[0012] (2) Heat the yellow solid powder obtained in step (1) and epichlorohydrin to 50 °C to obtain a clear liquid. Then add a catalyst and heat to 80 °C for ring-opening reaction for 5 - 7 h. After that, cool to 50 °C and add an aqueous sodium hydroxide solution, react for 2 - 3 h. After the reaction ends, cool to room temperature, filter out insoluble salts, and rotary evaporate to obtain the above product.

[0013] (3) Add ODA and BPDA in an equimolar ratio to a flask, add a certain amount of polar solvent, and stir at room temperature for 8 - 12 h to obtain an ODA / BPDA type PAA acid solution.

[0014] (4) Dissolve the prepared epoxy resin monomer in a polar solvent, add it to the stirring PAA acid solution in a certain proportion, and feed it in two batches. After adding, raise the temperature to 50 - 80 °C and stir and react for 8 - 24 h.

[0015] (5) Pour the prepared epoxy resin modified polyamic acid solution on a glass plate, scrape it flat with a 1000 - μm scraper, and cure it according to a certain curing procedure to finally obtain a 50 - 75 - μm black composite film.

[0016] The possible curing behaviors during the curing process are as follows:

[0017] (6) Immerse the cured composite film in an ultrasonic machine, heat and ultrasonicate for 30 min, then peel off the film, wash it with ethanol, and put it in an oven to dry at 80 °C for 24 h.

[0018] In the present invention, an epoxy compound is prepared, and then an epoxy resin / polyimide composite material is obtained by reacting the epoxy compound with a PAA acid solution. Eugenol and furfural used in the present invention can be extracted from natural plants in large quantities. At the same time, the preparation method is simple, the synthesis steps are few, and the finally prepared composite material has excellent light-shielding performance, high heat resistance and mechanical properties while ensuring.

[0019] Preferably, the catalyst selected in step (2) is TBAB or CTAB or TEABC.

[0020] Preferably, the final temperature of the temperature rise in step (4) is 70 °C.

[0021] Preferably, the polar solvents in steps (3) and (4) are DMAC and NMP.

[0022] Preferably, the addition amount of the epoxy monomer in step (4) is 5%, 10%, 15%, 20% of the carboxyl content of the polyamic acid solution.

[0023] Preferably, the reaction time in step (4) is 12 - 16 h.

[0024] Preferably, the curing procedure in step (5) is 80°C - 2h, 150°C - 2h, 240°C - 2h, 270°C - 2h.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] (1) The raw materials involved in the present invention are easily available and inexpensive.

[0027] (2) The entire reaction process is simple and does not require too harsh reaction conditions;

[0028] (3) Utilize the property of epoxy resin crosslinking into a network to modify polyimide, making it over-crosslink to form an interpenetrating structure, further enhancing its light-shielding ability. Compared with the traditional method, the black polyimide prepared by this method has more excellent performance and meets the requirements of commercialization. Description of the Drawings

[0029] Figure 1 It is the NMR spectrum of the diphenol resulting from the reaction of eugenol and furfural.

[0030] Figure 2 It is the NMR spectrum of the product EF-EP after epoxidation of the EF ring of the diphenol.

[0031] Figure 3 It is the infrared spectrum of the composites with different contents of the prepared epoxy resin.

[0032] Figure 4 It is the differential thermogravimetric analysis curve of the composites with different contents of the prepared epoxy resin.

[0033] Figure 5 It is the dynamic mechanical analysis curve of the composites with different contents of the prepared epoxy resin.

[0034] Figure 6 It is the ultraviolet absorption spectrum of the prepared composite material.

[0035] Figure 7 It is the physical display diagram. Specific Embodiment

[0036] The present invention will be further elaborated below in conjunction with the embodiments. These embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention fall within the scope claimed by the present invention.

[0037] Example 1

[0038] (1) 30 g of eugenol was placed into a 500 ml three-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a constant pressure dropping funnel. When the temperature was raised to 50 °C, an aqueous sodium hydroxide solution with a mass fraction of 40% (3.75 g) was added and stirred for a period of time. Then, 9.216 g of furfural was slowly and evenly added dropwise using the constant pressure dropping funnel over 1 h. After the addition of the raw materials was completed, the temperature was raised to 60 °C and the reaction was carried out for 4 - 8 h. Subsequently, the temperature was raised to 100 °C and the reaction was carried out for 3 - 6 h. The final product was a black viscous liquid. The obtained diphenol product was added to a large amount of ethyl acetate and a small amount of hydrochloric acid for extraction until the lower aqueous phase was neutral. Then, the organic phase was rotary evaporated to obtain a yellowish-black solid block, and this solid was separated by column chromatography with an eluent of ethyl acetate: petroleum ether at a ratio of 1:4. The product was collected and rotary evaporated to obtain a yellow solid powder.

[0039] (2) The yellow solid powder obtained above was heated with epichlorohydrin to 50 °C to obtain a clear liquid. Then, a catalyst was added and the reaction was carried out at 100 °C for ring-opening reaction for 5 - 7 h. Subsequently, the temperature was lowered to 60 °C and an aqueous sodium hydroxide solution was added, and the reaction was carried out for 2 - 3 h. After the reaction was completed, it was cooled to room temperature, and the salt substances were removed by filtration. The filtrate was diluted with ethyl acetate, and then loaded onto the column by the wet method. The target substance was obtained by column chromatography with an eluent of ethyl acetate: petroleum ether at a ratio of 1:3.

[0040] (3) Equimolar amounts of ODA and BPDA were added to a three-necked flask. Subsequently, a certain amount of NMP solution was added at a curing amount ratio of 15%, and the mixture was stirred and reacted for a period of time. Then, according to the carboxyl group content in the PAA acid solution, an epoxy resin monomer with a ratio of 5% was added, and the temperature was raised to 70 degrees Celsius and stirred and reacted for 15 h.

[0041] (4) The prepared epoxy resin-modified polyamic acid solution was poured on a glass plate and leveled with a 1000 µm scraper. Curing was carried out according to the curing program of 80 °C - 2 h, 150 °C - 2 h, 240 °C - 2 h, and 270 °C - 2 h.

[0042] (5) Through Figure 1 and Figure 2 nuclear magnetic analysis, it can be found that the preparation of EF-EP was successful.

[0043] (6) Through Figure 3 infrared spectrum, it can be found that the absorption peaks belonging to the epoxy functional group and the absorption peaks attributed to the terminal double bond disappeared at the position of 920 cm-1 wavelength. This indicates that during the curing process, crosslinking reaction occurred between the epoxy resin and the polyimide, and the reaction was very thorough.

[0044] (7) Through Figure 4It can be found from the differential thermal analysis diagram that as the addition amount of this epoxy resin increases, its char residue rate at 800 °C also increases continuously and is higher than that of single polyimide.

[0045] (8) Through Figure 5 It can be found from the dynamic thermodynamic analysis diagram that this composite material has excellent thermodynamic properties, and its glass transition temperature reaches above 290 °C, which is attributed to the increase in its crosslinking density.

[0046] (9) Through Figure 6 It can be found that by controlling the addition amount of epoxy resin, the prepared composite film has good absorption in the visible light region. When the addition amount is 5%, its cut-off wavelength is increased by 95 nm compared with the comparative sample. As the addition amount increases continuously, its cut-off wavelength continuously redshifts. When the addition amount is 20%, its cut-off wavelength reaches 630 nm. By comparing with the PAA acid solution and the film photo, it can be found that it corresponds to the presented black appearance.

[0047] Example 2

[0048] (1) Prepare epoxy monomers according to Example 1

[0049] (2) Add equimolar amounts of ODA and BPDA into a three-necked flask, then add a certain amount of NMP solution according to the curing amount of 15%, stir and react for a period of time. Then, according to the carboxyl group content in the PAA acid solution, add 10% of the epoxy resin monomer, heat to 70 °C, and stir and react for 15 h.

[0050] (3) Pour the prepared epoxy resin-modified polyamic acid solution onto a glass plate, scrape and level it with a 1000-μm scraper, and cure it according to the curing procedure of 80 °C - 2 h, 150 °C - 2 h, 240 °C - 2 h, 270 °C - 2 h.

[0051] Example 3

[0052] (1) Prepare epoxy monomers according to Example 1.

[0054] (3) Add equimolar amounts of ODA and BPDA into a three-necked flask, then add a certain amount of NMP solution according to the curing amount of 15%, stir and react for a period of time. Then, according to the carboxyl group content in the PAA acid solution, add 15% of the epoxy resin monomer, heat to 70 °C, and stir and react for 15 h.

[0055] (4) Pour the prepared epoxy resin-modified polyamic acid solution onto a glass plate, scrape and level it with a 1000-μm scraper, and cure it according to the curing procedure of 80 °C - 2 h, 150 °C - 2 h, 240 °C - 2 h, 270 °C - 2 h.

Claims

1. A method for preparing an intrinsically black material from epoxy resin modified polyimide, characterized in that, It includes the following steps: (1) Under nitrogen protection, mix eugenol, furfural and sodium hydroxide in a certain proportion, heat to 90 °C, react for a period of time, obtain a viscous liquid, add ethyl acetate and hydrochloric acid for extraction until the lower aqueous phase is neutral, and then rotary evaporate the organic phase to obtain a yellowish-black solid block. Separate this solid by recrystallization to obtain the product EF (5,5'-(furan-2-ylmethylene)bis(4-allyl-2-methoxyphenol)); (2) Under nitrogen protection, heat the above diphenol monomer EF, epichlorohydrin, and tetrabutylammonium bromide to carry out a ring-opening reaction for a period of time, then cool down and add sodium hydroxide to mix and carry out a ring-closing reaction for a period of time. Collect the epoxidized product EF-EP (2-(bis(2-allyl-4-methoxy-5-(oxiran-2-ylmethoxy)phenyl)methyl)furan) by column chromatography; (3) Add ODA / BPDA in an equimolar ratio to a flask, add a certain amount of polar solvent, and stir at room temperature for 8 - 12 h to obtain an ODA / BPDA type PAA acid solution; (4) Dissolve the prepared epoxy resin monomer in a polar solvent, add it to the stirring PAA acid solution in a certain proportion, feed it in two batches. After adding, raise the temperature to 50 - 80 °C and stir and react for 8 - 24 h; (5) Pour the prepared epoxy resin-modified polyamic acid solution on a glass plate, scrape and level it with a 1000 μm blade, and cure it according to a certain curing procedure to finally obtain a 50 - 75 μm black composite film.

2. The preparation method of the composite material according to claim 1, wherein The amount of epoxy resin added in step (4), the final temperature of the temperature rise, the stirring time, and the setting of the curing procedure in step (5).

3. The addition amount of the epoxy resin monomer in (4) according to claim 1 is 5 - 25% of the carboxyl group content in the PAA acid solution.

4. The final temperature of the temperature rise in (4) according to claim 1 is 50 - 80 °C.

5. The stirring time in (4) according to claim 1 is 8 - 24 h.

6. The curing procedure in (5) according to claim 1 is 80 °C - 2 h, 150 °C - 2 h, 240 °C - 2 h, 270 °C - 2 h.

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