A modified epoxy resin with high flame retardancy performance and its preparation method

Abstract

The present invention belongs to the technical field of polymer flame retardants, and particularly relates to a modified epoxy resin with high flame retardancy and a preparation method thereof. The modified epoxy resin is made from the following components in parts by weight: 100 parts of epoxy resin, 3 - 40 parts of flame retardant, 0.1 - 2 parts of accelerator, and 0.5 - 30 parts of auxiliary curing agent; the flame retardant is a derivative of diphenylphosphine oxide formed by the reaction of diphenylphosphine oxide with a ketone compound, having a P-C-OH structure; the epoxy resin, the prepared flame retardant, the accelerator, and the auxiliary curing agent are mixed evenly at a certain temperature for reaction, curing, and demolding after cooling to obtain a modified epoxy resin with high flame retardancy, which can self-extinguish within a short time, and the shortest self-extinguishing time is 2.1 s. The derivative of diphenylphosphine oxide can promote the carbonization of epoxy resin, and the limiting oxygen index values of the modified flame-retardant epoxy resin are all greater than 30%.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer flame retardants, and particularly relates to a modified epoxy resin with high flame retardancy and a preparation method thereof. Background Art

[0002] Epoxy resins are a type of thermosetting polymer. Due to their good mechanical properties, chemical resistance (resistance to acids, alkalis, and solvents, etc.), heat resistance, and electrical insulation properties, they are often used as adhesives, composites, and coatings, etc., and are widely applied in multiple industrial fields. The main constituent elements of epoxy resins are three elements: C, H, and O. Unmodified epoxy resins are flammable, with a limiting oxygen index of about 23%, and no rating in vertical burning UL-94. They can continue to burn in air. When burning, they release a large amount of heat, a large amount of soot, and harmful gases, posing potential safety hazards to people's lives and property as well as the ecological environment.

[0003] Reactive phosphorus-based flame retardants are commonly used as additives for epoxy resins. Commonly used reactive phosphorus-based flame retardants include DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) and DPO (diphenylphosphine oxide), etc. DPO-based flame retardants have advantages such as higher phosphorus content and better mechanical properties than DOPO-based flame retardants, effectively improving the flame retardancy of the matrix. At present, many derivatives of DOPO have been developed for the flame retardant application of epoxy resins (CN201911296249.0, CN201610606516.X, CN201810235375.4), but their synthesis process is often complex, and the raw materials used in the synthesis are also restricted by cost and environmental protection. Generally speaking, the synthesis process of DOPO derivatives requires the addition of external solvents and has cumbersome synthesis steps (US9399712B2). Moreover, the flame retardancy and curing ability in epoxy resins modified by such flame retardants cannot be satisfied simultaneously. Therefore, how to develop a new type of flame retardant with a simple synthesis process, low production cost, high flame retardancy efficiency, and a curing effect has become the focus of this technical field. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a modified epoxy resin with high flame retardancy and a preparation method thereof. The technical solution adopted is as follows:

[0005] A modified epoxy resin with high flame retardancy is made from the following components in parts by weight: 100 parts of epoxy resin, 3 - 40 parts of flame retardant, 0.1 - 2 parts of accelerator, and 0.5 - 30 parts of auxiliary curing agent; wherein, the flame retardant is a derivative of diphenylphosphine oxide formed by the reaction of diphenylphosphine oxide with a ketone compound, having a P-C-OH structure, and its structural formula is:

[0006]

[0007] Among them, the R1 group is any one of —H, —C n H 2n+1 alkyl, and —Ph phenyl, the R2 group is any one of —H, —C n H 2n+1 alkyl, and —Ph phenyl, and n is a natural number; if R1 or R2 is phenyl, the substituents on the benzene ring are not limited.

[0008] Preferably, the promoter is any one of triphenylphosphine, phenol, resorcinol, m-cresol, triethylamine, and triethanolamine.

[0009] Preferably, the auxiliary curing agent is any one of 4,4'-diaminodiphenyl sulfone, 4,4'-sulfonyldianiline, 4-aminophenyl sulfone, bis(4-aminophenyl) sulfone, 4-aminophenyl sulfone, ethylenediamine, m-phenylenediamine, phthalic anhydride, and dicyandiamide.

[0010] Preferably, the epoxy resin is any one of bisphenol A epoxy resin, bisphenol F epoxy resin, phenolic epoxy resin, and bisphenol S epoxy resin.

[0011] Preferably, the ketone compound is any one of acetone, acetophenone, and methyl ethyl ketone.

[0012] The preparation method of the above-mentioned modified epoxy resin with high flame retardancy specifically includes the following steps:

[0013] Mix diphenylphosphine oxide with a ketone compound, and carry out a synthesis reaction under the protection of an inert gas. The synthesis temperature is 0-80 °C, the reaction time is 3-12 h, to obtain a precipitate. Filter by suction, wash, and then dry for 3 h; grind it into a powder with an agate mortar to obtain a flame retardant;

[0014] Or mix diphenylphosphine oxide with a ketone compound in an organic solvent, and carry out a synthesis reaction under the protection of an inert gas. The synthesis temperature is 0-80 °C, the reaction time is 3-12 h, to obtain a precipitate. Filter by suction, wash, and then dry for 3 h; grind it into a powder with an agate mortar to obtain a flame retardant;

[0015] Step 2. Prepare a modified epoxy resin with high flame retardancy

[0016] A certain weight portion of epoxy resin, the flame retardant prepared in Step 1, a promoter, and a co-curing agent are mixed evenly at a certain temperature for a preparation reaction; after the preparation is completed, bubbles are removed under vacuum and then poured into a preheated mold, cured at 90 - 130 °C for 1 - 5 h, and then cured at 140 - 180 °C for another 1 - 5 h; after cooling, demolding is carried out to obtain a modified epoxy resin with high flame retardant performance. The types of substituents R1 and R2 of the derivative of diphenylphosphine oxide can adjust the activity of H on C-OH participating in the curing, thereby regulating the curing effect of the diphenylphosphine oxide derivative on the epoxy resin.

[0017] Preferably, the ketone compound reacts with diphenylphosphine oxide in a molar ratio of not less than 1:1.

[0018] Preferably, the molar ratio of the ketone compound to diphenylphosphine oxide is 6 - 10:1.

[0019] Preferably, in the said Step 1, the organic solvent is any one of ethyl acetate, toluene, and ethanol.

[0020] Preferably, in the said Step 2, the preparation temperature is 120 - 180 °C and the reaction time is 1 - 5 h.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] The derivative of diphenylphosphine oxide involved in the present invention adopts a direct synthesis method, and the obtained product has a high yield, high purity, and the product does not need to be purified.

[0023] During combustion, the derivative of diphenylphosphine oxide can promote the carbonization of the epoxy resin, enabling the modified epoxy resin to self-extinguish within a short time. The modified phosphorus-containing epoxy resin can self-extinguish within a very short time, and the limiting oxygen index value of the modified flame retardant epoxy resin is greater than 30%. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is the vertical combustion diagram of the modified epoxy resin EP1 - DA2 - a sample prepared in Example 3 of the present invention;

[0025] Figure 2 It is the comparison diagram of the CCT test residual carbon of the modified epoxy resin EP1 - DA2 - a sample prepared in Example 3 of the present invention and the pure epoxy resin. DETAILED DESCRIPTION OF THE INVENTION

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings, embodiments, and tables. The accompanying drawings are only for illustrative purposes; obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts belong to the scope of protection of the present invention.

[0027] Example 1

[0028] Mix diphenylphosphine oxide and acetophenone in a molar ratio of 1:8, react at 55 °C under N2 gas protection for 10 h to obtain a precipitate. Filter by suction, wash and then dry for 3 h. Grind to obtain the flame retardant DA1-a.

[0029] Mix 100 parts of epoxy resin E-44, 9 parts of DA1-a, 0.27 part of triphenylphosphine PPh3, and 24 parts of diaminodiphenylsulfone evenly at 160 °C for a preparation reaction. The reaction time is 4 hours. After removing bubbles under vacuum, pour it into a preheated mold, cure at 120 °C for 2 h, and cure at 170 °C for 2 h. Demold after cooling to obtain epoxy resin EP1-DA1-a modified with DA1-a and having high flame retardancy. The flame retardancy of the obtained modified epoxy resin is shown in Table 1.

[0030] Example 2

[0031] Mix diphenylphosphine oxide and acetophenone in a molar ratio of 1:8 in 60 ml of ethyl acetate, react at 55 °C under N2 gas protection for 8 h to obtain a precipitate. Filter by suction, wash and then dry for 3 h. Grind to obtain the flame retardant DA1-b.

[0032] Mix 100 parts of epoxy resin E-20, 4 parts of DA1-b, 0.12 part of triphenylphosphine PPh3, and 13 parts of diaminodiphenylsulfone evenly by mechanical stirring at 160 °C. The stirring time is 4 hours. After removing bubbles under vacuum, pour it into a preheated mold, cure at 120 °C for 2 h, and cure at 170 °C for 2 h. Demold after cooling to obtain epoxy resin EP2-DA1-b modified with DA1-b and having high flame retardancy. The flame retardancy of the obtained modified epoxy resin is shown in Table 1.

[0033] Example 3

[0034] Mix diphenylphosphine oxide and acetone in a molar ratio of 1:7, react at 25 °C under N2 gas protection for 6 h to obtain a precipitate. Filter by suction, wash and then dry for 3 h. Grind to obtain the flame retardant DA2-a.

[0035] 100 parts of epoxy resin E-44, 8 parts of DA2-a, 0.24 parts of triphenylphosphine PPh3, and 25 parts of diaminodiphenyl sulfone were mechanically stirred evenly at 170 °C for the preparation reaction. The stirring time was 4 hours. After removing bubbles under vacuum, it was poured into a preheated mold and cured at 120 °C for 2 hours and then at 160 °C for 2 hours. After cooling, it was demolded to obtain epoxy resin EP1-DA2-a modified with DA2-a and having high flame retardancy. The flame retardancy of the obtained modified epoxy resin is shown in Table 1.

[0036] Example 4

[0037] Diphenylphosphine oxide and acetone were mixed at a molar ratio of 1:6 in 40 ml of ethyl acetate. Under the protection of N2 gas at 25 °C, the reaction was carried out for 6 hours to obtain a precipitate. It was filtered by suction, washed, and then dried for 3 hours. After grinding, the flame retardant DA2-b was obtained.

[0038] 100 parts of epoxy resin E-51, 9.3 parts of DA2-b, 0.21 parts of triethylamine, and 29 parts of diaminodiphenyl sulfone were mechanically stirred evenly at 170 °C. After removing bubbles under vacuum, it was poured into a preheated mold and cured at 120 °C for 2 hours and then at 160 °C for 2 hours. After cooling, it was demolded to obtain epoxy resin EP3-DA2-b modified with DA2-b and having high flame retardancy. The flame retardancy of the obtained modified epoxy resin is shown in Table 1.

[0039] Example 5

[0040] Diphenylphosphine oxide and formaldehyde were mixed at a molar ratio of 1:6. Under the protection of N2 gas at 65 °C, the reaction was carried out for 6 hours to obtain a white precipitate. It was filtered by suction, washed, and then dried for 3 hours. After grinding, the flame retardant DA3-a was obtained.

[0041] 100 parts of bisphenol F-type epoxy resin, 7 parts of DA3-a, 0.18 parts of triethylamine, and 16 parts of 4-aminobenzenesulfone were mechanically stirred evenly at 160 °C. After removing bubbles under vacuum, it was poured into a preheated mold and cured at 130 °C for 2 hours and then at 180 °C for 2 hours. After cooling, it was demolded to obtain epoxy resin EP4-DA3-a modified with DA3-a and having high flame retardancy. The flame retardancy of the obtained modified epoxy resin is shown in Table 1.

[0042] Example 6

[0043] Diphenylphosphine oxide and methyl ethyl ketone were mixed at a molar ratio of 1:7. Under the protection of N2 gas at 35 °C, the reaction was carried out for 6 hours to obtain a precipitate. It was filtered by suction, washed, and then dried for 2 hours. After grinding, the flame retardant DA4-a was obtained.

[0044] Mix 100 parts of epoxy resin E-44, 9 parts of DA4-a, 0.27 part of triphenylphosphine PPh3, and 26 parts of 4-aminophenyl sulfone evenly by mechanical stirring at 170 °C. After removing air bubbles under vacuum, pour the mixture into a preheated mold, cure at 120 °C for 2 h, and then cure at 155 °C for 2 h. Demold after cooling to obtain DA4-a modified epoxy resin EP1-DA4-a with high flame retardancy. The flame retardancy of the obtained modified epoxy resin is shown in Table 1.

[0045] Example 7

[0046] Mix diphenylphosphine oxide and methyl ethyl ketone in a molar ratio of 1:7 and dissolve them in 50 ml of toluene. React for 6 h at 35 °C under N2 gas protection to obtain a precipitate. Filter by suction, wash, and then dry for 2 h. Grind to obtain the flame retardant DA4-b.

[0047] Mix 100 parts of epoxy resin E-20, 5 parts of DA4-b, 0.15 part of triethylamine, and 24 parts of diaminodiphenyl sulfone evenly by mechanical stirring at 170 °C. After removing air bubbles under vacuum, pour the mixture into a preheated mold, cure at 120 °C for 2 h, and then cure at 165 °C for 2 h. Demold after cooling to obtain DA4-b modified epoxy resin EP2-DA4-b with high flame retardancy. The flame retardancy of the obtained modified epoxy resin is shown in Table 1.

[0048] Example 8

[0049] Mix diphenylphosphine oxide and methyl ethyl ketone in a molar ratio of 1:7 and dissolve them in 60 ml of ethyl acetate. React for 6 h at 35 °C under N2 gas protection to obtain a precipitate. Filter by suction, wash, and then dry for 2 h. Grind to obtain the flame retardant DA4-c.

[0050] Mix 100 parts of epoxy resin E-51, 10 parts of DA4-c, 0.36 part of triethylamine, and 24 parts of diaminodiphenyl sulfone evenly by mechanical stirring at 170 °C. After removing air bubbles under vacuum, pour the mixture into a preheated mold, cure at 120 °C for 2 h, and then cure at 160 °C for 2 h. Demold after cooling to obtain DA4-c modified epoxy resin EP3-DA4-c with high flame retardancy. The flame retardancy of the obtained modified epoxy resin is shown in Table 1.

[0051] Table 1 is a data table of the flame retardancy of the products prepared in each example. The data are as follows:

[0052] Flame Retardancy of Samples in Each Example of Table 1

[0053]

[0054] The testing methods involved in the present invention, namely the cone calorimeter test (CCT), the vertical burning test (UL-94), and the limiting oxygen index test (LOI), are carried out in accordance with the ISO4589-2017 standard. Table 1 presents the afterflame time, vertical burning rating, and limiting oxygen index of the products prepared in 8 examples.

[0055] As can be seen from the table, the performance of the product obtained in Example 5 is poorer than that of the products obtained in other examples. The raw materials used in Example 5 are diphenylphosphine oxide and formaldehyde, without using ketone compounds, while other examples all involve the reaction of diphenylphosphine oxide and ketone compounds. Example 5 can be used as a comparative example for other examples.

[0056] In the diphenylphosphine oxide derivatives of the present invention, the H on the P-C-OH group in the molecular structure has a curing effect. The -OH in DA3-a synthesized in Example 5 belongs to primary alcohol, while the -OH in the products synthesized in other examples are all tertiary alcohols. Generally, the reactivity order of epoxy groups with alcohols is: primary alcohol > secondary alcohol > tertiary alcohol. Compared with primary and secondary alcohols, the curing reaction temperature of tertiary alcohol with epoxy resin exceeds 200 °C, but epoxy resin will decompose at higher temperatures. The chemical structures of the products prepared in the present invention are all tertiary alcohols (such as DA2-a, DA4-a), but due to the influence of P-C, C-R1, and C-R2 chemical bonds, the H on the tertiary alcohol structure has certain curing activity, and can be cured at about 150 °C, connecting with epoxy resin by covalent bonds, so that the flame retardant is more evenly dispersed in the polymer, thus achieving flame retardant effect even at low phosphorus content. Therefore, this molecular structure is used for the curing and flame retardancy of epoxy resin.

[0057] During combustion, the derivatives of diphenylphosphine oxide can promote the carbonization of epoxy resin, enabling the modified phosphorus-containing epoxy resin to self-extinguish within a short time. The vertical burning ratings of the modified flame retardant epoxy resins added with derivatives of diphenylphosphine oxide all reach the V-0 grade. Under the national standard of t1 + t2 < 10 s, the modified epoxy resin can self-extinguish at t1 + t2 = 4.2 s (the product prepared in Example 1), and the shortest self-extinguishing time is t1 + t2 = 2.1 s (the product prepared in Example 3). Moreover, the limiting oxygen index values of the modified epoxy resins are all greater than 30%.

[0058] As Figure 1 shown, the state diagrams of the vertical burning conditions of the product EP1-DA2-a obtained in Example 3 at 0 s, 0.5 s, 1 s, 1.6 s, and 2.1 s after ignition are respectively shown from left to right. EP1-DA2-a can self-extinguish 2.1 s after the flame is removed after continuous ignition for 10 s, indicating that the epoxy resin added with the flame retardant DA2-a has excellent flame retardant performance.

[0059] As Figure 2As shown, by comparing the top view and front view of the char residues after cone calorimeter tests of pure epoxy resin (a), (c) and EP1-DA2-a (b), (d) prepared in Example 3, it can be clearly seen that the amount of char residue after the combustion of EP1-DA2-a increases, the char layer expands significantly, and it has an obvious solid-phase flame retardant effect.

[0060] The E-44 type epoxy resin, E-20 type epoxy resin, bisphenol F type epoxy resin used in the present invention are from Zhenjiang Danbao Resin Co., Ltd. Diphenylphosphine oxide is from Qingdao Fusilin Chemical Technology Co., Ltd. 4,4'-Diaminodiphenylsulfone and 4-aminophenylsulfone are from Aladdin Reagent (Shanghai) Co., Ltd. Acetone, ethyl acetate, and toluene are from Chengdu Kelong Chemical Co., Ltd. Acetophenone is from Aladdin Reagent (Shanghai) Co., Ltd. Formaldehyde is from Shanghai Macklin Biochemical Technology Co., Ltd. Triethylamine is from Aladdin Reagent (Shanghai) Co., Ltd. Other methods not mentioned adopt the prior art.

[0061] Those of ordinary skill in the art will realize that the embodiments shown here are for helping readers understand the principles of the present invention, and it should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those of ordinary skill in the art can make various other transformations in other aspects without departing from the essence of the present invention according to the technical revelations disclosed in the present invention, and still fall within the protection scope of the present invention.

Claims

1. A preparation method of a modified epoxy resin with high flame retardancy performance, characterized in that, It is made from the following components by weight: 100 parts of epoxy resin, 3 - 40 parts of flame retardant, 0.1 - 2 parts of accelerator, and 0.5 - 30 parts of auxiliary curing agent; wherein, the flame retardant is a derivative of diphenylphosphine oxide formed by the reaction of diphenylphosphine oxide with a ketone compound, having a P-C-OH structure, and its structural formula is: Among them, the R1 group is any one of —H, —C n H 2n+1 alkyl, and —Ph phenyl, the R2 group is one of —H, —C n H 2n+1 alkyl, and —Ph phenyl, n is a natural number; if R1 or R2 is phenyl, the substituents on the benzene ring are not limited; The preparation method includes the following steps: Step 1. Prepare the flame retardant Mix diphenylphosphine oxide with a ketone compound, and carry out a synthesis reaction under the protection of an inert gas. The synthesis temperature is 0 - 80 °C, the reaction time is 3 - 12 h, to obtain a precipitate. Filter by suction, wash, and then dry for 3 h; grind it into a powder with an agate mortar to obtain the flame retardant; wherein, the molar ratio of the ketone compound to diphenylphosphine oxide is 6 - 10:1; Step 2. Prepare the modified epoxy resin with high flame retardancy Mix a certain weight of epoxy resin, the flame retardant prepared in Step 1, accelerator, and auxiliary curing agent evenly at a certain temperature for a preparation reaction; after preparation, remove the bubbles under vacuum and pour it into a preheated mold, cure at 90 - 130 °C for 1 - 5 h, and then cure at 140 - 180 °C for 1 - 5 h; demold after cooling to obtain the modified epoxy resin with high flame retardancy.

2. The preparation method of a modified epoxy resin with high flame retardancy according to claim 1, characterized in that, The accelerator is any one of triphenylphosphine, phenol, resorcinol, m-cresol, triethylamine, and triethanolamine.

3. The preparation method of a modified epoxy resin with high flame retardancy according to claim 1, characterized in that, The auxiliary curing agent is any one of 4,4'-diaminodiphenyl sulfone, 4,4'-sulfonyldianiline, ethylenediamine, m-phenylenediamine, phthalic anhydride, and dicyandiamide.

4. The preparation method of a modified epoxy resin with high flame retardancy according to claim 1, characterized in that, The epoxy resin is any one of bisphenol A epoxy resin, bisphenol F epoxy resin, phenolic epoxy resin, and bisphenol S epoxy resin.

5. The preparation method of a modified epoxy resin with high flame retardancy according to claim 1, characterized in that, The ketone compound is any one of acetone, acetophenone, and methyl ethyl ketone.

6. The preparation method of a modified epoxy resin with high flame retardancy according to claim 1, characterized in that, In Step 2, the preparation temperature is 120 - 180 °C, and the reaction time is 4 h.

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