Preparation method and application of P-N synergistic halogen-free flame-retardant curing agent

Abstract

The invention belongs to the technical field of flame-retardant materials, and particularly relates to a preparation method of a P-N synergistic halogen-free flame-retardant curing agent and application of the P-N synergistic halogen-free flame-retardant curing agent in epoxy resin. Phosphorus oxychloride reacts with a phenolic compound containing an aldehyde group to obtain a polyaldehyde compound containing phospholipid, and then the polyaldehyde compound containing phospholipid reacts with N-methylethylenediamine to obtain a halogen-free flame-retardant curing agent containing phosphorus and nitrogen elements, and the halogen-free flame-retardant curing agent containing phosphorus and nitrogen elements is used for curing epoxy resin, so that the reaction type halogen-free flame-retardant epoxy resin material is prepared. Due to the synergistic effect of phosphorus and nitrogen elements, the material has excellent char forming performance and flame retardant property.

Description

Technical Field

[0001] The present invention belongs to the technical field of flame retardant materials, and particularly relates to a preparation method of a PN-synergistic halogen-free flame retardant curing agent and application thereof in epoxy resin. Background Art

[0002] Epoxy resin materials have strong chemical resistance, electrical insulation, good mechanical properties, high thermal stability, and low manufacturing costs. They are widely used in electronic and electrical materials such as integrated circuits, printed circuit boards, insulating packages, conductive adhesives, as well as chemical coatings and construction. However, as a polymer material, unmodified epoxy resin has a low limiting oxygen index value and is flammable, which greatly limits its application. Traditional epoxy resins are often modified by adding halogenated flame retardants such as tris(chloroethyl) phosphate, tris(2,3-dibromopropyl) phosphate, tetrabromobutane, and tetrabromobisphenol A to improve their flame retardancy. However, the introduction of halogenated flame retardants causes the material to produce more smoke, corrosive gases, and carcinogenic gases during combustion, which has a significant impact on the environment. Summary of the Invention

[0003] The present invention provides a PN synergistic halogen-free flame retardant curing agent and a preparation method thereof, which introduces phosphorus and nitrogen elements into the epoxy resin cross-linking network through chemical bonding to achieve molecular-level bonding between the flame retardant and the resin, while utilizing the PN synergistic effect to significantly improve the charring rate and flame retardant performance.

[0004] To achieve the above objectives, the specific technical solutions provided by the present invention are as follows:

[0005] The first aspect of the present invention is to provide a PN synergistic halogen-free flame retardant curing agent, the molecular structure of which is shown below:

[0006]

[0007] X1, X2, and X3 are independently selected from H or methoxy.

[0008] The second aspect of the present invention is to provide a method for preparing a PN-synergistic halogen-free flame retardant curing agent, comprising the following steps:

[0009] S1: dissolving an aldehyde-containing phenolic compound in an organic solvent, adding an acid-binding agent, and then dropwise adding phosphorus oxychloride into the reaction system to react to obtain a phospholipid-containing trialdehyde compound intermediate;

[0010] S2: The intermediate is subjected to an aldehyde-amine condensation reaction with N-methylethylenediamine in an organic solvent to obtain a PN synergistic halogen-free flame retardant.

[0011] In the above technical solution, in step S1, the aldehyde-containing phenolic compound is one or more of p-hydroxybenzaldehyde, vanillin or syringaldehyde, preferably vanillin.

[0012] In the above technical solution, in step S1, the organic solvent is one or more of tetrahydrofuran, chloroform, and dichloromethane, preferably dichloromethane.

[0013] In the above technical solution, in step S1, the molar ratio of the aldehyde-containing phenolic compound to phosphorus oxychloride is (3-5):1.

[0014] In the above technical solution, in step S1, the acid binding agent is one or more of sodium hydroxide, potassium carbonate, sodium carbonate, triethylamine, and pyridine, preferably triethylamine.

[0015] In the above technical solution, in step S1, the reaction temperature is 50-90° C., and the reaction time is 4-24 hours.

[0016] In the above technical solution, in step S2, the organic solvent is one or more of tetrahydrofuran, chloroform, and dichloromethane.

[0017] In the above technical solution, in step S2, the molar ratio of the intermediate to N-methylethylenediamine is 1:(3-5).

[0018] In the above technical solution, in step S2, the reaction temperature is 50-70° C., and the reaction time is 24-48 hours.

[0019] The third aspect of the present invention is to provide a reactive flame-retardant epoxy resin, comprising an epoxy resin prepolymer and the PN synergistic halogen-free flame-retardant curing agent according to claim 1, or the PN synergistic halogen-free flame-retardant curing agent prepared by the preparation method described above.

[0020] In the above technical solution, in the reactive flame-retardant epoxy resin, the mass ratio of the epoxy resin prepolymer to the PN-synergistic halogen-free flame-retardant curing agent is 100:(30-60).

[0021] In the above technical solution, the epoxy resin prepolymer is selected from one or more of glycidyl ether epoxy resins, glycidyl ester epoxy resins, glycidyl amine epoxy resins or alicyclic epoxy resins.

[0022] A fourth aspect of the present invention is to provide a method for preparing the flame retardant epoxy resin described above, comprising the following steps:

[0023] The PN-synergistic halogen-free flame retardant curing agent and the epoxy resin prepolymer are stirred until dissolved and then cured, and a reactive flame retardant epoxy resin material can be obtained after curing.

[0024] In the above technical solution, the PN synergistic halogen-free flame retardant curing agent and epoxy resin prepolymer are stirred evenly and poured into a mold, the mold is placed in a drying oven, and cured at 110°C, 130°C, 150°C, 170°C, and 190°C for 1 to 2 hours respectively, and the reactive flame retardant epoxy resin is obtained after cooling.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention provides a PN synergistic halogen-free flame retardant curing agent that can exert the synergistic flame retardant effect of phosphorus and nitrogen elements. The epoxy resin material prepared by applying the PN synergistic halogen-free flame retardant curing agent to epoxy resin has good flame retardant effect and good charring performance while maintaining high thermal stability. DETAILED DESCRIPTION

[0027] The following describes in detail a method for preparing a halogen-free flame-retardant basalt fiber-epoxy resin composite material of the present invention through five examples, but the protection scope of the present invention is not limited to these examples.

[0028] The present invention provides the following examples for further explanation, but does not limit the scope of protection of the claims of the present invention. The technical features of each embodiment of the present invention can be combined accordingly without conflict.

[0029] Example 1 (Synthesis of Curing Agent)

[0030] The preparation method of the PN synergistic halogen-free flame retardant curing agent of the present invention specifically comprises the following steps:

[0031] In step 1, 30.4 g of vanillin was placed in a round-bottom flask containing 70 mL of dichloromethane, and 20.2 g of triethylamine was added. The reaction system was then placed in an ice bath and 9.18 g of phosphorus oxychloride was added dropwise to the flask. The reaction solution was reacted at 80°C for 6 hours. Finally, the reaction solution was poured into n-hexane to precipitate the product, which was washed several times with cold methanol and then vacuum dried to obtain the target intermediate. The reaction equation is shown below:

[0032]

[0033] Step 2: Dissolve 10g of the intermediate and 4.44g of N-methylethylenediamine in dichloromethane and heat under reflux for 36 hours. The resulting crude product is evaporated and concentrated, reprecipitated with ethanol and ethyl acetate, and vacuum-dried at 40°C for 24 hours to obtain a PN-synergistic halogen-free flame retardant curing agent. The reaction equation is as follows:

[0034]

[0035] Example 2 (Preparation of flame retardant epoxy resin)

[0036] The method for preparing the reactive flame-retardant epoxy resin material of the present invention comprises the following steps:

[0037] After stirring 30 g of the PN synergistic halogen-free flame retardant curing agent prepared in Example 1 and 100 g of the epoxy resin prepolymer until homogeneous, the mixture was quickly poured into a preheated stainless steel mold. The mold was then placed in a blast drying oven and cured at 110°C, 130°C, 150°C, 170°C, and 190°C for 1 hour each. After cooling, a reactive flame retardant epoxy resin material was obtained.

[0038] Example 3

[0039] The method for preparing the flame retardant epoxy resin of the present invention comprises the following steps:

[0040] After stirring 33 g of the PN synergistic halogen-free flame retardant curing agent prepared in Example 1 and 100 g of the epoxy resin prepolymer until homogeneous, the mixture was quickly poured into a preheated stainless steel mold. The mold was then placed in a blast drying oven and cured at 110°C, 130°C, 150°C, 170°C, and 190°C for 1 hour each. After cooling, a reactive flame retardant epoxy resin material was obtained.

[0041] Example 4

[0042] The method for preparing the flame retardant epoxy resin of the present invention comprises the following steps:

[0043] After stirring 37 g of the PN synergistic halogen-free flame retardant curing agent prepared in Example 1 and 100 g of the epoxy resin prepolymer until homogeneous, the mixture was quickly poured into a preheated stainless steel mold. The mold was then placed in a blast drying oven and cured at 110°C, 130°C, 150°C, 170°C, and 190°C for 1 hour each. After cooling, a reactive flame retardant epoxy resin material was obtained.

[0044] Example 5

[0045] The method for preparing the flame retardant epoxy resin of the present invention comprises the following steps:

[0046] After stirring 40 g of the PN synergistic halogen-free flame retardant curing agent prepared in Example 1 and 100 g of the epoxy resin prepolymer until homogeneous, the mixture was quickly poured into a preheated stainless steel mold. The mold was then placed in a blast drying oven and cured at 110°C, 130°C, 150°C, 170°C, and 190°C for 1 hour each. After cooling, a reactive flame retardant epoxy resin material was obtained.

[0047] Example 6

[0048] The method for preparing the flame retardant epoxy resin of the present invention comprises the following steps:

[0049] After stirring 43 g of the PN synergistic halogen-free flame retardant curing agent prepared in Example 1 and 100 g of the epoxy resin prepolymer until homogeneous, the mixture was quickly poured into a preheated stainless steel mold. The mold was then placed in a blast drying oven and cured at 110°C, 130°C, 150°C, 170°C, and 190°C for 1 hour each. After cooling, a reactive flame retardant epoxy resin material was obtained.

[0050] Example 7

[0051] The method for preparing the flame retardant epoxy resin of the present invention comprises the following steps:

[0052] After stirring 47 g of the PN synergistic halogen-free flame retardant curing agent prepared in Example 1 and 100 g of the epoxy resin prepolymer until homogeneous, the mixture was quickly poured into a preheated stainless steel mold. The mold was then placed in a blast drying oven and cured at 110°C, 130°C, 150°C, 170°C, and 190°C for 1 hour each. After cooling, a reactive flame retardant epoxy resin material was obtained.

[0053] Example 8

[0054] The method for preparing the flame retardant epoxy resin of the present invention comprises the following steps:

[0055] 50 g of the PN synergistic halogen-free flame retardant curing agent prepared in Example 1 and 100 g of the epoxy resin prepolymer were stirred until homogeneous, and then quickly poured into a preheated stainless steel mold. The mold was then placed in a blast drying oven and cured at 110°C, 130°C, 150°C, 170°C, and 190°C for 1 hour each. After cooling, a reactive flame retardant epoxy resin material was obtained.

[0056] Example 9

[0057] The method for preparing the flame retardant epoxy resin of the present invention comprises the following steps:

[0058] After stirring 53 g of the PN synergistic halogen-free flame retardant curing agent prepared in Example 1 and 100 g of the epoxy resin prepolymer until homogeneous, the mixture was quickly poured into a preheated stainless steel mold. The mold was then placed in a blast drying oven and cured at 110°C, 130°C, 150°C, 170°C, and 190°C for 1 hour each. After cooling, a reactive flame retardant epoxy resin material was obtained.

[0059] Example 10

[0060] The method for preparing the flame retardant epoxy resin of the present invention comprises the following steps:

[0061] After stirring 57 g of the PN synergistic halogen-free flame retardant curing agent prepared in Example 1 and 100 g of the epoxy resin prepolymer until homogeneous, the mixture was quickly poured into a preheated stainless steel mold. The mold was then placed in a blast drying oven and cured at 110°C, 130°C, 150°C, 170°C, and 190°C for 1 hour each. After cooling, a reactive flame retardant epoxy resin material was obtained.

[0062] Comparative Example 1

[0063] 100g of epoxy resin prepolymer was mixed with 30g of a curing agent (4,4'-diaminodiphenylmethane) that did not contain phosphorus or nitrogen elements to form a uniform liquid. The mixture was quickly poured into a preheated stainless steel mold. The mold was then placed in a forced air drying oven and cured at 110°C, 130°C, 150°C, 170°C, and 190°C for 1 hour each. After cooling, the epoxy resin material was obtained for further comparative testing.

[0064] The flame retardant properties of the reactive flame retardant epoxy resin prepared by adding PN-synergistic halogen-free flame retardant curing agent in Example 2-10 and the epoxy resin in Comparative Example 1 were tested. The test data are shown in Table 1:

[0065] Table 1

[0066]

[0067] As can be seen from Table 1, the reactive flame retardant epoxy resin (Examples 2 to 10) prepared by adding a PN-synergistic halogen-free flame retardant curing agent can significantly improve the residual carbon rate of the epoxy resin material, and the limiting oxygen index and vertical combustion grade are also significantly improved. Among them, the residual carbon rate can reach more than 20%, the limiting oxygen index can reach more than 30%, and the combustion grade can reach V-0 level, indicating that the flame retardant-modified epoxy resin of the present invention can significantly improve the flame retardant properties of the epoxy resin.

[0068] The above embodiments are only intended to help understand the method and core concept of the present invention. It should be noted that, without departing from the principles of the present invention, a number of improvements and modifications may be made to the present invention by those skilled in the art, and such improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A PN synergistic halogen-free flame retardant curing agent, characterized in that: The chemical structure is shown below: X1, X2, and X3 are independently selected from H or methoxy.

2. The method for preparing the PN synergistic halogen-free flame retardant curing agent according to claim 1, characterized in that: The steps include: S1: dissolving an aldehyde-containing phenolic compound in an organic solvent, adding an acid-binding agent, and then dropwise adding phosphorus oxychloride into the reaction system to react to obtain a phospholipid-containing trialdehyde compound intermediate; S2: The intermediate is subjected to an aldehyde-amine condensation reaction with N-methylethylenediamine in an organic solvent to obtain a PN synergistic halogen-free flame retardant.

3. The method for preparing the PN synergistic halogen-free flame retardant curing agent according to claim 2, characterized in that: In step S1, the aldehyde-containing phenolic compound is selected from one or more of p-hydroxybenzaldehyde, vanillin, or syringaldehyde; the organic solvent is one or more of tetrahydrofuran, chloroform, and dichloromethane; the molar ratio of the aldehyde-containing phenolic compound to phosphorus oxychloride is (3-5):1; the acid-binding agent is one or more of sodium hydroxide, potassium carbonate, sodium carbonate, triethylamine, and pyridine; the reaction temperature is 50-90° C., and the reaction time is 4-24 hours.

4. The method for preparing the PN synergistic halogen-free flame retardant curing agent according to claim 2, characterized in that: In step S2, the organic solvent is one or more of tetrahydrofuran, chloroform, and dichloromethane; the molar ratio of the intermediate to N-methylethylenediamine is 1:(3-5); the reaction temperature is 50-70° C., and the reaction time is 24-48 hours.

5. A reactive flame retardant epoxy resin, characterized in that: It comprises an epoxy resin prepolymer and the PN synergistic halogen-free flame retardant curing agent described in claim 1, or the PN synergistic halogen-free flame retardant curing agent prepared by the preparation method described in claims 2 to 4.

6. The reactive flame retardant epoxy resin according to claim 5, characterized in that: The epoxy resin prepolymer is selected from one or more of glycidyl ether epoxy resin, glycidyl ester epoxy resin, glycidyl amine epoxy resin or alicyclic epoxy resin; in the flame retardant epoxy resin, the mass ratio of the epoxy resin prepolymer to the PN synergistic halogen-free flame retardant curing agent is 100:(30-60).

7. The method for preparing the reactive flame retardant epoxy resin according to claim 5 or 6, characterized in that: The method comprises the following steps: stirring a PN-synergistic halogen-free flame retardant curing agent and an epoxy resin prepolymer until dissolved, and then performing a curing treatment, and then preparing a reactive flame retardant epoxy resin material.

8. Use of the PN synergistic halogen-free flame retardant curing agent according to claim 1 or the PN synergistic halogen-free flame retardant curing agent prepared by the preparation method according to claims 2 to 4 in epoxy resin.

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