A flame retardant for improving the impact resistance of epoxy resin and its preparation method

Abstract

The present invention discloses a flame retardant for improving the impact resistance of epoxy resin and a preparation method thereof. The preparation raw materials include polyetheramine, phosphorus-containing flame retardant (DOPO), diisocyanate and epoxy resin. The method for preparing this additive only requires two-step reactions: reacting DOPO, polyetheramine and diisocyanate under certain conditions and then pre-polymerizing with epoxy resin, and the product is obtained as an orange-yellow liquid after vacuum distillation. This compound grafts the phosphorus-containing flame retardant and polyurea onto the epoxy resin matrix by using the isocyanate group and urea bond in the polyurea, and can effectively endow the flame retardant performance of DOPO and the mechanical properties of polyurea to the epoxy resin matrix, thereby improving the flame retardancy and mechanical properties of the epoxy resin;

Description

Technical Field

[0001] The present invention relates to a bifunctional additive and a preparation method thereof, in particular to a flame retardant capable of improving the impact resistance of epoxy resin and a preparation method thereof. Background Art

[0002] Epoxy resin (EP), as a very important thermosetting resin in life, has excellent chemical resistance, adhesion performance, mechanical properties, etc., and can be used as coatings, adhesives and molding materials, and is widely used in many fields. However, after curing, epoxy resin has a high crosslinking density and internal stress, and is brittle when cured without adding other additives, with disadvantages such as poor impact resistance, peel resistance, crack resistance and hygrothermal resistance. Moreover, conventional epoxy resins and their composites usually have high flammability, which poses a great safety hazard, and flammability is also a problem of most polymer materials. Due to the flammable nature of epoxy resin, its application scope is greatly limited. Therefore, the research on the mechanical properties and flame retardant properties of epoxy resin is of great significance for expanding its application in the fields of electronics, electrical and aerospace.

[0003] The research on the flame retardancy of epoxy resin is increasingly tending to halogen-free flame retardants. Replacing halogen with other flame retardant elements and developing high-efficiency, low-toxicity, low-smoke halogen-free environmentally friendly flame retardants and new flame retardant epoxy resin materials have become the research hotspots of domestic and foreign scholars. Among them, phosphorus and nitrogen compounds, as a new type of flame retardant, have attracted much attention due to their advantages of improving the flame retardancy, thermal stability and organic solubility of epoxy resin, and having little impact on the mechanical properties of the matrix material.

[0004] Polyurea is an elastomer material formed by the reaction of isocyanate and amino compounds. Polyurea elastomer has the advantages of coatings and plastics, as well as the characteristics of fiberglass and rubber, and has extremely excellent physical and chemical properties, and is applied in building waterproofing, marine anti-corrosion, automotive coatings, etc. In addition, due to its unique impact and explosion resistance performance, polyurea elastomer has become one of the important materials for achieving lightweight protection in recent years. After strict testing of the polyurea coating, it is found that its explosion resistance performance is very excellent, and it has excellent impact resistance and extremely strong tensile strength, which keeps the operation of equipment and systems in the best state and extends the service life of equipment. In the military field, the product has extremely strong characteristics such as personnel protection, anti-terrorism and anti-explosion, and strengthening the structure. Summary of the Invention

[0005] The object of the present invention is to provide a flame retardant for improving the impact resistance of epoxy resin and a preparation method thereof. In the present invention, epoxy resin and DOPO are grafted onto the polyurea chain segment, so that the prepolymer not only has excellent mechanical properties of polyurea, but also contains two flame retardant elements, phosphorus and nitrogen. The bifunctional additive provided by the present invention has the characteristics of high flame retardancy efficiency, halogen-free, low smoke and low toxicity, which conforms to the concept of protecting the ecological environment by people today.

[0006] The technical solution of the present invention is as follows:

[0007] A bifunctional additive having the following structure:

[0008]

[0009] Wherein,

[0010] n is any natural number from 0 to 999;

[0011] R is a bisphenol A epoxy resin E51 group, and the structural formula is as follows:

[0012]

[0013] Wherein, the * position is the connection site, and m is any natural number from 0 to 999.

[0014] The preparation method of the bifunctional additive described in the present invention is:

[0015] (1) Mix MDI (diphenylmethane-4,4'-diisocyanate) with a solvent to obtain an MDI solution; mix polyetheramine with a solvent to obtain a polyetheramine solution; mix DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide), triethylamine and a solvent to obtain a DOPO solution;

[0016] The solvent is toluene, ethylene glycol or N,N-dimethylformamide (DMF);

[0017] (2) Under N2 protection, drop the DOPO solution into the MDI solution, react at 20-100 °C for 0.5-3 h, then drop the polyetheramine solution, and react at 40-150 °C for 1-3 h to obtain an intermediate product A (without purification, directly used for the next step of reaction);

[0018] Wherein, the molar ratio of MDI, DOPO and polyetheramine in the feed is 2:2:1-4:4:1;

[0019] The mass ratio of triethylamine to DOPO in the DOPO solution is 1:25-45;

[0020] (3) Preheat bisphenol A epoxy resin E51 to 80 - 120 °C, then add intermediate product A, keep the temperature for reaction for 2 - 6 h, and after removing the solvent by vacuum distillation, obtain the final product, a bifunctional auxiliary agent;

[0021] Among them, the molar ratio of bisphenol A epoxy resin E51 to intermediate product A in the feed is 6:1 - 20:1;

[0022] The synthesis route is as follows:

[0023]

[0024] The principle of the present invention lies in:

[0025] The main chain of the bifunctional auxiliary agent molecule is small - molecule polyurea. DOPO is introduced at both ends of the main chain to synthesize intermediate product A, and then the epoxy resin is grafted onto the molecular chain by the reaction of the active hydrogen atoms of the urea bonds in the small - molecule polyurea with the epoxy groups in the epoxy resin. Since the reaction conditions between the secondary amine in the urea bond and the epoxy group are relatively harsh, in order to prevent the flame retardant from affecting the curing conditions of the epoxy resin and the epoxy resin from being cured by intermediate product A during the reaction, an excessive amount of epoxy resin is used to graft with the small - molecule polyurea to reduce the later curing conditions, and finally a flame retardant that can improve the impact resistance of the epoxy resin is synthesized.

[0026] The bifunctional auxiliary agent of the present invention can be used to prepare flame - retardant epoxy resin. The prepared epoxy resin can exhibit good flame - retardant properties. On the other hand, the cured epoxy resin also exhibits good mechanical properties.

[0027] The beneficial effects of the present invention are mainly reflected in:

[0028] The present invention uses small - molecule polyurea as the main chain, introduces a phosphorus - containing compound on the polyurea molecular chain and grafts the epoxy resin to prepare an auxiliary agent. Using the bifunctional auxiliary agent prepared by the present invention can not only improve the flame - retardant properties of the epoxy resin, but also reduce the cross - linking density and internal stress of the epoxy resin by introducing urea bonds and ether bonds into the epoxy resin structure system, thereby improving its mechanical properties. Specific embodiments

[0029] The present invention will be further described below through specific examples, but the protection scope of the present invention is not limited thereto.

[0030] Example 1:

[0031] The preparation method of the bifunctional epoxy resin auxiliary agent in this example includes the following steps:

[0032] (1) Preparation of Intermediate A: Under the protection of N2, 5 g of MDI and 10 ml of toluene solvent were loaded into a 250-ml round-bottom flask equipped with a condenser and mechanically mixed for 5 min. Then, 4.3 g of DOPO, 0.1 g of triethylamine, and 20 ml of toluene were mixed and added to the flask at a rate of 1 drop per second at 25 °C and mixed for 60 min. Next, 1.9 g of polyetheramine (Exploration Platform, Adamas, D-230) and 10 ml of toluene were mixed and added dropwise to the round-bottom flask at a rate of 1 drop per 3 seconds and stirred for 30 min. Then, the temperature was raised to 60 °C and reacted for 180 min to obtain Intermediate A;

[0033] (2) Bifunctional epoxy resin additive: 90 g of epoxy resin (Wuxi Resin Factory, epoxy equivalent - 188) was preheated to 120 °C, and then the above Intermediate A was added to the epoxy resin and stirred at this temperature for 3 h. After that, the final product was obtained through vacuum distillation.

[0034] Example 2:

[0035] The preparation method of the bifunctional epoxy resin additive in this example includes the following steps:

[0036] (1) Preparation of Intermediate A: Under the protection of N2, 10 g of MDI and 40 ml of DMF solvent were loaded into a 500-ml round-bottom flask equipped with a condenser and mechanically mixed for 5 min. Then, 8.6 g of DOPO, 0.3 g of triethylamine, and 40 ml of DMF were mixed and added to the flask at a rate of 1 drop per second at 25 °C and mixed for 60 min. 3.8 g of polyetheramine and 40 ml of DMF were mixed and added dropwise to the round-bottom flask at a rate of 1 drop per 3 seconds and stirred for 30 min. Then, the temperature was raised to 80 °C and reacted for 180 min to obtain Intermediate A;

[0037] (2) Bifunctional epoxy resin additive: 90 g of epoxy resin was preheated to 120 °C, and then the above Intermediate A was added to the epoxy resin and stirred at this temperature for 3 h. After that, the final product was obtained through vacuum distillation.

[0038] Example 3:

[0039] Application of the bifunctional epoxy resin additive prepared in Example 1

[0040] The specific method of the above application is as follows: The epoxy resin and the bifunctional epoxy resin additive were mixed at 80 °C to obtain a homogeneous solution; then, the curing agent diethylenetriamine was added to the above mixture and continuously stirred until completely mixed; the mixed system was degassed under vacuum, and then sprayed and poured into a mold, and left to stand at room temperature for 24 h until the epoxy resin was completely cured.

[0041] In this experimental example, the dosage ratios of the raw materials are shown in Table 1 below. For the convenience of distinction and understanding, the bifunctional epoxy resin additive prepared in Example 1 is represented by the symbol "M".

[0042] Table 1 Raw material composition and dosage (parts by weight) during the application of the bifunctional additive

[0043] 1# 2# 3# 4# 5# 6# E51 0 20 40 60 80 100 M 100 80 60 40 20 0

[0044] Performance tests were carried out on each sample prepared in Example 3. The test standards were: GB / T 2406-1993 Limiting Oxygen Index Test, GB / T 1732 Impact Resistance Test, and GB / T 6739 Pencil Hardness Test. The test results are shown in Table 2 below.

[0045] Table 2 Performance test results of each sample prepared in Example 3

[0046] 1# 2# 3# 4# 5# 6# LOI / % 27 25 25 23 21 20 Pencil hardness 5H 5H 5H 5H 5H 5H Impact resistance / cm 48 46 >50 42 15 15

[0047] It can be seen from the data in Table 2 that without sacrificing hardness, both the flame retardant performance and the impact resistance performance have been improved. In particular, the improvement in impact resistance is the most obvious. Without other additives, the impact resistance of the epoxy resin has increased by nearly 300%, and the limiting oxygen index also increases with the increase in the additive content.

Claims

1. A flame retardant that can improve the impact resistance of epoxy resin, and the flame retardant has the following structure: Among them, n is any natural number from 0 to 999; R is a bisphenol A epoxy resin E51 group, and the structural formula is as follows: Among them, the * position is the connection site, and m is any natural number from 0 to 999.

2. The preparation method of the flame retardant capable of improving the impact resistance of epoxy resin according to claim 1, characterized in that, The preparation method is as follows: (1) Mix MDI with a solvent to obtain an MDI solution; mix polyetheramine with a solvent to obtain a polyetheramine solution; mix DOPO, triethylamine and a solvent to obtain a DOPO solution; (2) Under N2 protection, drop the DOPO solution into the MDI solution, react at 20-100 °C for 0.5-3 h, then drop the polyetheramine solution, and react at 40-150 °C for 1-3 h to obtain intermediate product A; (3) Preheat bisphenol A epoxy resin E51 to 80-120 °C, then add intermediate product A, keep the temperature and react for 2-6 h, and remove the solvent by vacuum distillation to obtain the final product, a flame retardant that can improve the impact resistance of epoxy resin; The synthesis route is as follows:

3. The preparation method according to claim 2, characterized in that, In step (1), the solvent is toluene, ethylene glycol or N,N-dimethylformamide.

4. The preparation method according to claim 2, characterized in that, In step (2), the molar ratio of MDI, DOPO, and polyetheramine is 2:2:1-4:4:1; the mass ratio of triethylamine to DOPO in the DOPO solution is 1:25-45.

5. The preparation method according to claim 2, characterized in that, In step (3), the molar ratio of bisphenol A epoxy resin E51 to intermediate product A is 6:1-20:1.

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