A phosphorus-containing phenolic epoxy flame-retardant resin, a preparation method thereof, and a cured product of the phosphorus-containing phenolic epoxy flame-retardant resin

Abstract

The application provides a phosphorus-containing phenolic aldehyde epoxy flame-retardant resin, a preparation method of the phosphorus-containing phenolic aldehyde epoxy flame-retardant resin and a cured product of the phosphorus-containing phenolic aldehyde epoxy flame-retardant resin. The preparation method of the phosphorus-containing phenolic aldehyde epoxy flame-retardant resin is different from other methods of adding flame retardants by physical blending, and the method is fundamentally ensured to obtain high chemical flame retardancy by introducing phosphorus and a phenolic aldehyde resin flame-retardant structure without sacrificing mechanical properties. The low-viscosity phosphorus-containing phenolic aldehyde epoxy flame-retardant resin prepared by the method solves the problem that general phenolic aldehyde epoxy resins have too large viscosity and are not conducive to processing, and the resin is given a lower viscosity by using a special viscosity control means in a synthesis reaction stage of the phenolic aldehyde resin, and is more suitable for processing applications.

Description

Technical Field

[0001] This invention relates to the field of phenolic epoxy resin technology, and in particular to a phosphorus-containing phenolic epoxy flame retardant resin, its preparation method, and the cured product of the phosphorus-containing phenolic epoxy flame retardant resin. Background Technology

[0002] Since their advent, phenolic and epoxy resins have been widely used in various fields such as chemical engineering, electronics, machinery, aerospace, coatings, and adhesives, and are closely related to people's lives. However, with the development of science and technology and the improvement of application levels, traditional phenolic and epoxy resins can no longer meet the needs of most fields. Traditional epoxy resins have advantages such as good mechanical properties and excellent insulation properties, but they also have problems such as excessively high viscosity which is not conducive to processing and poor flame retardancy.

[0003] Given the current shortcomings of epoxy resins, it is necessary to improve them. Summary of the Invention

[0004] The purpose of this invention is to address the problems and shortcomings of existing technologies by providing a phosphorus-containing phenolic epoxy flame retardant resin, its preparation method, and a cured phosphorus-containing phenolic epoxy flame retardant resin. The phosphorus-containing phenolic epoxy flame retardant resin prepared by this method has excellent properties such as low viscosity and good flame retardancy. Moreover, the preparation method involved in this method is relatively simple and suitable for the application of process equipment materials in extreme environments.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This invention provides a method for preparing a phosphorus-containing phenolic epoxy flame-retardant resin, comprising the following steps:

[0007] Phenolic compounds and formaldehyde solution are mixed, a phosphorus-containing catalyst is added, and the mixture is refluxed in an acidic environment under an inert atmosphere to obtain phenolic resin.

[0008] Epichlorohydrin was added to phenolic resin, and the mixture was heated to a first temperature under an inert atmosphere and stirred to dissolve the phenolic resin. The mixture was then cooled to a second temperature, a catalyst was added, and the mixture was heated to a third temperature in an alkaline environment to carry out the reaction. After the reaction was completed, an extraction solvent was added, the mixture was separated, the organic phase was collected and distilled under reduced pressure to obtain phosphorus-containing phenolic epoxy flame retardant resin.

[0009] The phenolic compounds include at least one of phenol, o-methylphenol, and p-methylphenol.

[0010] Preferably, the phosphorus-containing catalyst includes at least one of phosphoric acid, metaphosphoric acid, hypophosphoric acid, and phosphorous acid.

[0011] Preferably, phenolic compounds and formaldehyde solution are mixed, a phosphorus-containing catalyst is added, the pH is adjusted to 1-2, and the mixture is refluxed under an inert atmosphere to obtain phenolic resin.

[0012] Preferably, the reflux reaction temperature is 100–105°C and the time is 10–15 min.

[0013] Preferably, the first temperature is 75-85°C, the second temperature is 65-75°C, and the third temperature is 70-80°C.

[0014] Preferably, the catalyst is a NaOH aqueous solution with a mass fraction of 20% to 30%;

[0015] The extraction solvent is acetone.

[0016] Preferably, the reaction is carried out at a third temperature. After the reaction is completed, an extraction solvent is added, the mixture is separated, the organic phase is collected and washed with water at 50-70°C until neutral, and then distilled under reduced pressure to obtain a phosphorus-containing phenolic epoxy flame retardant resin.

[0017] Preferably, the mass-to-volume ratio of phenolic compounds, phosphorus-containing catalysts, and formaldehyde solution is (20-30) g:(4-6) g:(28-40) mL;

[0018] The formaldehyde solution has a mass fraction of 37-40%.

[0019] The mass-to-volume ratio of phenolic compounds, epichlorohydrin, and NaOH aqueous solution is (20-30) g: (75-115) mL: (44-66) mL.

[0020] Secondly, the present invention also provides a phosphorus-containing phenolic epoxy flame retardant resin, which is prepared by the preparation method described above.

[0021] Thirdly, the present invention also provides a phosphorus-containing phenolic epoxy flame retardant resin cured product, wherein the phosphorus-containing phenolic epoxy flame retardant resin prepared by the above preparation method is mixed with an amine curing agent and then cured to obtain the phosphorus-containing phenolic epoxy flame retardant resin cured product.

[0022] The phosphorus-containing phenolic epoxy flame-retardant resin, its preparation method, and the cured phosphorus-containing phenolic epoxy flame-retardant resin of the present invention have the following advantages over the prior art:

[0023] 1. The preparation method of the phosphorus-containing phenolic epoxy flame-retardant resin of the present invention starts from the fundamental structure and differs from other methods that add flame retardants through physical blending. The method of the present invention, without sacrificing mechanical properties, fundamentally obtains high chemical flame retardancy by introducing the flame-retardant structure of phosphorus and phenolic resin. The low-viscosity phosphorus-containing phenolic epoxy flame-retardant resin prepared by the method of the present invention solves the problem that the viscosity of general phenolic epoxy resin is too high and not conducive to processing. A special viscosity control method is used in the epoxidation reaction stage to give it a lower viscosity, which is more suitable for processing applications. The preparation method of the present invention is different from the traditional synthesis method of phenolic epoxy resin based on epoxidation of phenolic resin. Starting from raw materials such as phenol, the preparation process is simple, the raw material utilization rate is high, and the post-processing process is convenient and reliable.

[0024] 2. The mechanical properties of the phosphorus-containing phenolic epoxy resin cured product of the present invention are basically the same as those of F-45 resin cured product and F-48 resin cured product in terms of tensile strength, flexural strength, flexural modulus and tensile modulus, with little difference. However, it is significantly better than F-45 and F-48 resin cured products in terms of elongation at break and especially impact strength. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 The image shows the infrared spectrum of the phosphorus-containing phenolic epoxy flame-retardant resin prepared in Example 1. Detailed Implementation

[0027] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0028] In the description of this invention, it should be understood that the orientation or positional relationship indicated by terms such as "above" is based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed when in use, or the orientation or positional relationship in which those skilled in the art are usually understood. It is only for the convenience of describing this invention and simplifying the description, and is not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0029] The order in which the embodiments are described below is not intended to limit the preferred order of the embodiments. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". Various embodiments of the invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any referenced number (fraction or integer) within the indicated range.

[0030] This application provides a method for preparing a phosphorus-containing phenolic epoxy flame-retardant resin, comprising the following steps:

[0031] S1. Phenolic compounds and formaldehyde solution are mixed, a phosphorus-containing catalyst is added, and the mixture is refluxed in an acidic environment under an inert atmosphere to obtain phenolic resin.

[0032] S2. Add epichlorohydrin to the phenolic resin, heat to the first temperature under an inert atmosphere, and stir to dissolve the phenolic resin; then cool to the second temperature, add a catalyst, and heat to the third temperature in an alkaline environment to carry out the reaction. After the reaction is completed, add an extraction solvent, separate the liquids, collect the organic phase and distill under reduced pressure to obtain phosphorus-containing phenolic epoxy flame retardant resin.

[0033] Phenolic compounds include at least one of phenol, o-methylphenol, and p-methylphenol.

[0034] The present invention discloses a method for preparing a phosphorus-containing phenolic epoxy flame-retardant resin. A phenolic compound and a formaldehyde solution are mixed, and a phosphorus-containing catalyst is added. The phenolic resin is then synthesized in an acidic environment. Subsequently, the phenolic resin undergoes an epoxidation reaction with epichlorohydrin (ECH) in an alkaline environment to obtain a low-viscosity phosphorus-containing phenolic epoxy flame-retardant resin. The phosphorus-containing phenolic epoxy flame-retardant resin prepared by this method exhibits excellent properties such as low viscosity and good flame retardancy. Furthermore, the preparation method is relatively simple and suitable for applications in process equipment materials used in extreme environments.

[0035] The present invention discloses a method for preparing phosphorus-containing phenolic epoxy flame-retardant resin. A linear phenolic resin is obtained using phenolic compounds and formaldehyde as raw materials under the action of a catalyst. Then, epichlorohydrin is used for epoxidation and viscosity control under the action of a catalyst to prepare a low-viscosity phosphorus-containing flame-retardant phenolic epoxy resin. This invention is the first to propose a method for preparing low-viscosity phosphorus-containing flame-retardant phenolic epoxy resin. The preparation process is simple, low-cost, and requires minimal post-processing. Its significant advantages include low viscosity of the phenolic epoxy resin prepared by this method and the introduction of phosphorus through phosphoric acid catalysis to enhance its flame-retardant properties.

[0036] In some embodiments, the phosphorus-containing catalyst includes at least one of phosphoric acid, metaphosphoric acid, hypophosphoric acid, and phosphorous acid.

[0037] In some embodiments, phenolic compounds and formaldehyde solution are mixed, a phosphorus-containing catalyst is added, the pH is adjusted to 1-2, and the mixture is refluxed under an inert atmosphere.

[0038] In some embodiments, the reflux reaction temperature is 100–105°C and the time is 10–20 min.

[0039] In some embodiments, the first temperature is 75–85°C, the second temperature is 65–75°C, and the third temperature is 70–80°C.

[0040] In some embodiments, the catalyst is an aqueous solution of NaOH with a mass fraction of 20% to 30%;

[0041] In some embodiments, the extraction solvent is acetone.

[0042] In some embodiments, the temperature is raised to a third temperature for the reaction. After the reaction is complete, an extraction solvent is added, the mixture is separated, the organic phase is collected and washed with water at 50–70°C until neutral, and the water is removed by vacuum distillation and the unreacted ECH and solvent are recovered to obtain a phosphorus-containing phenolic epoxy flame retardant resin.

[0043] In some embodiments, the mass-to-volume ratio of phenolic compounds, phosphorus-containing catalysts, and formaldehyde solution is (20-30) g:(4-6) g:(28-40) mL;

[0044] The formaldehyde solution has a mass fraction of 37-40%.

[0045] The mass-to-volume ratio of phenolic compounds, epichlorohydrin, and NaOH aqueous solution is (20-30) g: (75-115) mL: (44-66) mL.

[0046] In some embodiments, the inert atmosphere includes nitrogen, helium, neon, argon, etc.

[0047] In some embodiments, a method for preparing a phosphorus-containing phenolic epoxy flame-retardant resin includes the following steps:

[0048] S1. Preparation of phenolic resin: Phenol and formaldehyde were added to a three-necked flask at a molar ratio of 1:(0.8-0.9), and phosphoric acid catalyst was added dropwise. The pH of the system was adjusted to 1-2. A reflux condenser was added, and under an inert atmosphere, the mixture was stirred until the solution was homogeneous. The temperature was then raised to 100-105°C in stages, and the system was kept under reflux for 10-15 minutes. The flask was then removed from the heating device and stirred continuously. Room temperature distilled water was added and the mixture was washed several times until the pH of the system was 6-7. The aqueous layer was then removed to obtain phenolic resin.

[0049] S2. Preparation of phosphorus-containing phenolic epoxy flame-retardant resin: Epichlorohydrin (ECH) was added to the phenolic resin synthesized above. Using phenol as a reference, the molar ratio of phenol to ECH was maintained at 1:(4-5). Under an inert atmosphere, the temperature was raised to 75-85°C and stirred until the phenolic resin was completely dissolved. Then the temperature was lowered to 65-75°C, and a 20%-30% NaOH aqueous solution was added dropwise using a dropping funnel, maintaining the molar ratio of phenol to NaOH at 1:(1-2). The addition was completed within 10-30 minutes. After the NaOH aqueous solution was added, the temperature was raised to 70-80°C, and the reaction was continued for 1-4 hours. After heating was stopped and cooled to room temperature, the mixture was transferred to a separatory funnel, acetone was added for extraction, and after standing, the aqueous layer was separated (unreacted monomers and phosphoric acid were removed along with a portion of the aqueous layer). The organic phase was collected and washed several times with distilled water at 50–70 °C until the pH of the system was neutral. Then, it was subjected to vacuum distillation to remove water and recover unreacted ECH and solvent, yielding a phosphorus-containing phenolic epoxy flame retardant resin.

[0050] Furthermore, if the phenolic compound is phenol and the phosphorus-containing catalyst is phosphoric acid, the synthetic route for phenolic resin is as follows:

[0051]

[0052] Phenolic resin reacts with epichlorohydrin in the presence of NaOH aqueous solution as follows:

[0053]

[0054] Where n is a positive integer, for example, n is a positive integer such as 1, 2, 3, 4, 5, 10, 100, etc.

[0055] In the preparation process of the low-viscosity phosphorus-containing phenolic epoxy flame-retardant resin of the present invention, the phosphorus-containing catalyst used, such as phosphoric acid, will leave complex residues during the reaction (phosphoric acid forms complex bonds with phenolic resin). This residue is beneficial to the flame retardancy of the resin. The formation of the phenolic resin phosphoric acid complex is shown in the following reaction formula.

[0056]

[0057] The low-viscosity phosphorus-containing phenolic epoxy flame-retardant resin prepared by the method of this invention, starting from its fundamental structure, differs from other methods that add flame retardants through physical blending. This method, without sacrificing mechanical properties, fundamentally achieves high chemical flame retardancy by introducing the flame-retardant structure of phosphorus and phenolic resin. The low-viscosity phosphorus-containing phenolic epoxy flame-retardant resin prepared by this method solves the problem of excessive viscosity in general phenolic epoxy resins, which is detrimental to processing, and endows it with a lower viscosity, making it more suitable for processing applications. The preparation method of this invention differs from the traditional synthesis method of phenolic epoxy resins by epoxidation on the basis of phenolic resins. Starting from raw materials such as phenol, the preparation process is simple, the raw material utilization rate is high, and the post-processing process is convenient and reliable.

[0058] Based on the same inventive concept, the present invention also provides a phosphorus-containing phenolic epoxy flame retardant resin, which is prepared by the above-described preparation method.

[0059] Based on the same inventive concept, the present invention also provides a phosphorus-containing phenolic epoxy flame retardant resin cured product, which is obtained by mixing the phosphorus-containing phenolic epoxy flame retardant resin prepared by the above preparation method with an amine curing agent and then curing it to obtain the phosphorus-containing phenolic epoxy flame retardant resin cured product.

[0060] Specifically, amine curing agents include ethylenediamine, triethylenetetramine, tetraethylenepentamine, aniline, phenylenediamine, and polyethylene polyamine.

[0061] In some embodiments, 100 parts by weight of phosphorus-containing phenolic epoxy flame retardant resin are mixed with 15 to 20 parts by weight of amine curing agent, and after degassing, the mixture is poured into a polytetrafluoroethylene mold coated with a release agent and cured at room temperature (20 to 25°C) for 4 to 10 hours to obtain a cured phosphorus-containing phenolic epoxy flame retardant resin.

[0062] The following further illustrates the phosphorus-containing phenolic epoxy flame-retardant resin, its preparation method, and the cured product thereof using specific embodiments. This section further describes the invention in conjunction with specific embodiments, but should not be construed as limiting the invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in this invention are conventional reagents, methods, and equipment in the art.

[0063] Example 1

[0064] This embodiment provides a method for preparing a phosphorus-containing phenolic epoxy flame-retardant resin, including the following steps:

[0065] S1. Add 20g phenol and 28mL formaldehyde solution (40% by mass) to a three-necked flask, and add 4g phosphoric acid dropwise to adjust the pH of the system to 2. Stir under nitrogen protection and heat to 100℃, continue to reflux for 10min. After the reaction is complete, add room temperature (25℃) distilled water to wash several times until the system is neutral, and remove the water layer to obtain phenolic resin.

[0066] S2. Add 75 mL of epichlorohydrin (ECH) to the phenolic resin synthesized in S1. Heat to 75 °C under nitrogen protection and stir until the phenolic resin is completely dissolved. Then cool to 70 °C and add 44 mL of NaOH aqueous solution (20% by mass) dropwise using a dropping funnel, completing the addition within 30 min. After the NaOH aqueous solution is added, raise the temperature to 80 °C and continue the reaction for 2 h. After the reaction is complete, stop heating, cool to room temperature, transfer to a separatory funnel, add acetone for extraction, allow to stand, separate the aqueous layer, collect the organic phase, and wash the organic phase several times with distilled water at 60 °C until the system is neutral. Then perform vacuum distillation to remove water and recover unreacted ECH and solvent to obtain phosphorus-containing phenolic epoxy flame-retardant resin.

[0067] This embodiment also provides a phosphorus-containing phenolic epoxy flame retardant resin cured product, the preparation method of which includes: mixing 100 parts by weight of the phosphorus-containing phenolic epoxy flame retardant resin prepared in Example 1 with 18 parts by weight of an amine curing agent (specifically ethylenediamine), performing degassing treatment, pouring it into a polytetrafluoroethylene mold coated with a release agent, and curing at room temperature (25°C) for 8 hours to obtain the phosphorus-containing phenolic epoxy flame retardant resin cured product.

[0068] Example 2

[0069] This embodiment provides a method for preparing a phosphorus-containing phenolic epoxy flame-retardant resin, including the following steps:

[0070] S1. Add 30g phenol and 40mL formaldehyde solution (mass fraction 40%) to a three-necked flask, and add 6g phosphoric acid dropwise to adjust the pH of the system to 2. Stir under nitrogen protection and heat to 100℃, continue to reflux for 10min. After the reaction is complete, add room temperature (25℃) distilled water to wash several times until the system is neutral, and remove the water layer to obtain phenolic resin.

[0071] S2. Add 115 mL of epichlorohydrin (ECH) to the phenolic resin synthesized in S1. Heat to 75 °C under nitrogen protection and stir until the phenolic resin is completely dissolved. Then cool to 70 °C and add 66 mL of NaOH aqueous solution (20% by mass) dropwise using a dropping funnel, completing the addition within 30 min. After the NaOH aqueous solution is added, raise the temperature to 80 °C and continue the reaction for 2 h. After the reaction is complete, stop heating, cool to room temperature, transfer to a separatory funnel, add acetone for extraction, allow to stand, separate the aqueous layer, collect the organic phase, and wash the organic phase several times with distilled water at 60 °C until the system is neutral. Then perform vacuum distillation to remove water and recover unreacted ECH and solvent to obtain phosphorus-containing phenolic epoxy flame-retardant resin.

[0072] This embodiment also provides a phosphorus-containing phenolic epoxy flame retardant resin cured product, the preparation method of which includes: mixing 100 parts by weight of the phosphorus-containing phenolic epoxy flame retardant resin prepared in Example 2 with 18 parts by weight of an amine curing agent (specifically ethylenediamine), performing degassing treatment, pouring it into a polytetrafluoroethylene mold coated with a release agent, and curing at room temperature (25°C) for 8 hours to obtain the phosphorus-containing phenolic epoxy flame retardant resin cured product.

[0073] Comparative Example 1

[0074] This comparative example provides a method for preparing F-45 resin, including the following steps:

[0075] S1. Add 48g of bisphenol A and 28mL of formaldehyde solution (40% by mass) to a three-necked flask, and add 15 drops (0.75mL) of concentrated hydrochloric acid (37% by mass) dropwise to adjust the pH of the system to 2. Stir under nitrogen protection and heat to 100℃, and continue to reflux for 30min. After the reaction is complete, wash several times with distilled water at room temperature (25℃) until the system is neutral, and remove the water layer to obtain solid bisphenol type phenolic resin.

[0076] S2. Add 75 mL of epichlorohydrin (ECH) to the phenolic resin synthesized in S1. Heat to 75 °C under nitrogen protection and stir until the phenolic resin is completely dissolved. Then cool to 70 °C and add 44 mL of NaOH aqueous solution (20% by mass) dropwise using a dropping funnel, completing the addition within 30 min. After the NaOH aqueous solution is added, raise the temperature to 80 °C and continue the reaction for 2 h. After the reaction is complete, stop heating, cool to room temperature, transfer to a separatory funnel, add acetone for extraction, allow to stand, separate the aqueous layer, collect the organic phase, and wash the organic phase several times with distilled water at 60 °C until the system is neutral. Then perform vacuum distillation to remove water and recover unreacted ECH and solvent to obtain bisphenol A type phenolic epoxy resin with an average epoxy value of 0.45, i.e., F-45 resin.

[0077] Comparative Example 2

[0078] This comparative example provides a method for preparing F-48 resin, comprising the following steps:

[0079] S1. Add 48g of bisphenol A and 28mL of formaldehyde solution (40% by mass) to a three-necked flask, and add 4g of phosphoric acid dropwise to adjust the pH of the system to 2. Stir under nitrogen protection and heat to 100℃, and continue to reflux for 10min. After the reaction is complete, wash several times with room temperature (25℃) distilled water until the system is neutral and remove the water layer to obtain phosphorus-containing bisphenol type phenolic resin.

[0080] S2. Add 75 mL of epichlorohydrin (ECH) to the phenolic resin synthesized in S1. Heat to 75 °C under nitrogen protection and stir until the phenolic resin is completely dissolved. Then cool to 70 °C and add 44 mL of NaOH aqueous solution (20% by mass) dropwise using a dropping funnel, completing the addition within 30 min. After the NaOH aqueous solution is added, raise the temperature to 80 °C and continue the reaction for 2 h. After the reaction is complete, stop heating, cool to room temperature, transfer to a separatory funnel, add acetone for extraction, allow to stand, separate the aqueous layer, collect the organic phase, and wash the organic phase several times with distilled water at 60 °C until the system is neutral. Then perform vacuum distillation to remove water and recover unreacted ECH and solvent, obtaining a phosphorus-containing bisphenol A type phenolic epoxy resin with an average epoxy value of 0.48, which is designated as F-48 resin.

[0081] Comparative Example 3

[0082] This comparative example provides a method for preparing F-54 resin, comprising the following steps:

[0083] S1. Add 20g of phenol and 28mL of formaldehyde solution (40% by mass) to a three-necked flask, and add 15 drops (0.75mL) of concentrated hydrochloric acid (37% by mass) dropwise to adjust the pH of the system to 2. Stir under nitrogen protection and heat to 100℃, and continue to reflux for 30min. After the reaction is complete, wash several times with room temperature (25℃) distilled water until the system is neutral and remove the water layer to obtain hydrochloric acid catalyzed phenolic resin.

[0084] S2. Add 75 mL of epichlorohydrin (ECH) to the phenolic resin synthesized in S1. Heat to 75 °C under nitrogen protection and stir until the phenolic resin is completely dissolved. Then cool to 70 °C and add 44 mL of NaOH aqueous solution (20% by mass) dropwise using a dropping funnel, completing the addition within 30 min. After the NaOH aqueous solution is added, raise the temperature to 80 °C and continue the reaction for 2 h. After the reaction is complete, stop heating, cool to room temperature, transfer to a separatory funnel, add acetone for extraction, allow to stand, separate the aqueous layer, collect the organic phase, and wash the organic phase several times with distilled water at 60 °C until the system is neutral. Then perform vacuum distillation to remove water and recover unreacted ECH and solvent to obtain phenolic epoxy resin with an average epoxy value of 0.54, which is F-54 resin.

[0085] Performance testing

[0086] According to ICP-AES analysis, the phosphorus content of the phosphorus-containing phenolic epoxy flame retardant resin prepared in Example 1 was 54.0 mg / kg.

[0087] According to ICP-AES analysis, the phosphorus content of the phosphorus-containing phenolic epoxy flame retardant resin prepared in Example 2 was 52.8 mg / kg.

[0088] The infrared spectrum of the phosphorus-containing phenolic epoxy flame-retardant resin prepared in Example 1 is shown below. Figure 1 As shown.

[0089] Figure 1 593cm -1 The peak at 838 cm⁻¹ is the characteristic peak of in-plane bending vibration of COC. -1 The characteristic peak of the out-of-plane bending vibration of the H-substituted benzene ring at 914 cm⁻¹ is observed. -1 The peak at 1042 cm⁻¹ is a characteristic peak of the terminal epoxy group. -1 The peak at 1177–1243 cm⁻¹ is a characteristic peak of the stretching vibration of aliphatic ether CO. -1 The peak at 1504–1610 cm⁻¹ represents the stretching absorption vibration of COC in ethers. -1 The peak at this point is a characteristic absorption peak of the benzene ring. Analysis of the infrared spectrum indicates that the target compound was successfully prepared.

[0090] The viscosity of the phosphorus-containing phenolic epoxy flame retardant resins prepared in Examples 1 and 2 was measured using the standard method (GB / T22314-2008 Plastics, Epoxy Resins Viscosity Determination Method) at 0°C, 25°C, and 40°C using a rotational viscometer. Under the same conditions, the viscosity of F-45 resin, F-48 resin, and F-54 resin in Comparative Examples 1 and 3 was measured for comparison. The viscosity levels of the resins were compared, and the specific measurement results are shown in Table 1.

[0091] Table 1 - Viscosity Measurement Results

[0092]

[0093] As shown in the table above, regardless of the ambient temperature, the viscosity of the phosphorus-containing phenolic epoxy resins prepared in Examples 1-2 is significantly lower than that of F-45, F-48, and F-54 resins. Due to the structural characteristics of bisphenol A, F-45 resin has a very high viscosity, especially at 0°C, exhibiting a non-flowing, gel-like consistency. The viscosity of F-48 resin is only close to that of F-54 resin, but still significantly higher than that of the phosphorus-containing phenolic epoxy resins in Examples 1-2.

[0094] Specifically, phenol (C6H5OH) molecules contain only one phenolic hydroxyl group, have a short molecular chain, and low steric hindrance. During the reaction, it mainly condenses with formaldehyde through a single-site phenolic hydroxyl group to form linear phenolic resin. Due to the limited molecular chain growth, the basic molecular weight of the phenolic resin stage is relatively low, laying the foundation for its subsequent low viscosity characteristics. In contrast, bisphenol A ((CH3)2C(C6H4OH)2) contains two phenolic hydroxyl groups and has an isopropyl bridging structure. During the reaction, it condenses with formaldehyde through two-site phenolic hydroxyl groups, easily forming branched or cross-linked structures, leading to a significant increase in the molecular weight of the phenolic resin. High molecular weight resins exhibit stronger intermolecular forces and higher viscosity after epoxidation.

[0095] Cured products were prepared according to the methods in Examples 1 and 2, respectively. The dimensions of the cured product were 130.0 mm long × 6.5 mm wide × 3.2 mm thick. Cured products of epoxy resin F-45, epoxy resin F-48 and epoxy resin F-54 were prepared according to the same method. The dimensions of the cured product were 130.0 mm long × 6.5 mm wide × 3.2 mm thick. Specifically, the preparation method of bisphenol F type epoxy resin F-45 cured product was as follows: 100 parts by weight of epoxy resin F-45 was mixed with 18 parts by weight of amine curing agent (specifically ethylenediamine), and after degassing treatment, it was poured into a polytetrafluoroethylene mold coated with a release agent and cured at room temperature (25°C) for 8 hours to obtain F-45 resin cured product. The specific preparation method for bisphenol F type epoxy resin F-48 cured product is as follows: 100 parts by weight of epoxy resin F-48 are mixed with 18 parts by weight of an amine curing agent (specifically ethylenediamine), and after degassing, the mixture is poured into a polytetrafluoroethylene mold coated with a release agent and cured at room temperature (25℃) for 8 hours to obtain the F-48 cured product. The specific preparation method for bisphenol F type epoxy resin F-54 cured product is as follows: 100 parts by weight of epoxy resin F-54 are mixed with 18 parts by weight of an amine curing agent (specifically ethylenediamine), and after degassing, the mixture is poured into a polytetrafluoroethylene mold coated with a release agent and cured at room temperature (25℃) for 8 hours to obtain the epoxy resin F-54 cured product.

[0096] The limiting oxygen index of the phosphorus-containing phenolic epoxy flame retardant resin cured products, F-45 resin cured products, F-48 resin cured products and F-54 resin cured products in Examples 1 and 2 were tested using the standard method (GB / T 2406.1-2008 Test Method for Combustion Performance of Plastics - Oxygen Index Method). The limiting oxygen index was tested using an HC-2C model limiting oxygen index tester.

[0097] The standard method (GB / T 2408-2008 Determination of the flammability of plastics - horizontal and vertical methods) was used to test the flammability rating of the phosphorus-containing phenolic epoxy flame retardant resin cured products, as well as F-45, F-48, and F-54 cured products in Examples 1 and 2, respectively, using the vertical burning method. A CZF-4 vertical burning tester was used for the test.

[0098] The test results are shown in Table 2.

[0099] Table 2 - Test results of combustion performance of cured resin products

[0100]

[0101] As shown in Table 2 above, the cured product prepared by the low-viscosity phosphorus-containing phenolic epoxy flame-retardant resin using the method of this invention has a limiting oxygen index of 28%, classifying it as a flame-retardant material. Its vertical burning rating reaches V-0, and after two 10-second ablation treatments, the afterflame produced by the resin casting self-extinguishes within 10 seconds without dripping. In contrast, the F-54 resin cured product has a limiting oxygen index of 25% and a burning rating of V-1. The afterflame produced by the resin casting after two ablation treatments self-extinguishes within 37 seconds and 44 seconds respectively, with a longer self-extinguishing time than the phosphorus-containing phenolic epoxy resin. The F-48 resin cured product has a limiting oxygen index of 26% and a burning rating of V-1. After two ablation treatments, the afterflame of the resin casting self-extinguished within 42s and 50s respectively, with a longer self-extinguishing time compared to the phosphorus-containing phenolic epoxy resin. The resulting molten droplets could not ignite the underlying cotton wool. In contrast, the afterflame of the F-45 resin cured product after two 10-second ablation treatments self-extinguished within 56s and 58s respectively, and molten droplets capable of igniting the underlying cotton wool fell during both ablation processes. In conclusion, the introduction of phosphorus significantly improves the flame-retardant properties of the resin cured product.

[0102] Following the above method, the phosphorus-containing phenolic epoxy flame-retardant resin cured products of Examples 1-2, as well as F-54 resin cured products, F-48 resin cured products, and F-45 resin cured products were obtained respectively. The tensile strength, tensile modulus, elongation at break, flexural strength, flexural modulus, and impact strength of the resin cured products were tested according to GB / T 2567-2021 "Test Methods for Performance of Resin Castings". The results are shown in Table 3 below.

[0103] Table 3. Test results of mechanical properties of cured resin products

[0104]

[0105] As shown in Table 3 above, the mechanical properties of the phosphorus-containing phenolic epoxy resin cured products in Examples 1 and 2 are basically consistent with those of the F-45 and F-48 resin cured products in terms of tensile strength, tensile modulus, flexural strength, and flexural modulus, with little difference. However, they are significantly better than the F-45 and F-48 resin cured products in terms of elongation at break, especially impact strength.

[0106] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A process for the preparation of a phosphorus-containing phenolic novolac epoxy flame retardant resin, characterized in that, The method comprises the following steps: The phenolic compound, formaldehyde solution and phosphorus-containing catalyst are mixed, and then the mixture is refluxed in an inert atmosphere in an acidic environment to obtain a phenolic aldehyde resin. The phenolic aldehyde resin is added with epichlorohydrin, and then the mixture is stirred to dissolve the phenolic aldehyde resin when the temperature is increased to a first temperature in an inert atmosphere; then the temperature is decreased to a second temperature, a catalyst is added, and the mixture is reacted again when the temperature is increased to a third temperature in an alkaline environment; after the reaction is completed, an extraction solvent is added, and the organic phase is collected and distilled under reduced pressure to obtain the phosphorus-containing phenolic aldehyde epoxy flame-retardant resin. The phenolic compound comprises at least one of phenol, o-methylphenol and p-methylphenol. The phosphorus-containing catalyst is one of phosphoric acid, metaphosphoric acid, hypophosphorous acid and phosphorous acid.

2. The process for preparing phosphorus-containing phenolic epoxy flame-retardant resin according to claim 1, characterized in that, The phenolic compound, formaldehyde solution and phosphorus-containing catalyst are mixed, and then the mixture is refluxed in an inert atmosphere in an acidic environment to obtain a phenolic aldehyde resin.

3. The method according to claim 1, wherein the refluxing temperature is 100-105 DEG C, and the refluxing time is 10-15 min. The first temperature is 75-85 DEG C, the second temperature is 65-75 DEG C, and the third temperature is 70-80 DEG C.

4. The process for preparing phosphorus-containing phenolic epoxy flame retardant resin according to claim 1, characterized in that, The temperature is increased to the third temperature for reaction, and the reaction time is 1-4 h. The catalyst is a NaOH aqueous solution with a mass fraction of 20-30%.

5. The method for preparing the phosphorus-containing phenolic epoxy flame-retardant resin as described in claim 1, characterized in that, The extraction solvent is acetone. The temperature is increased to the third temperature for reaction, and then the extraction solvent is added after the reaction is completed; the mixture is separated, and the organic phase is collected and washed with water at 50-70 DEG C until neutral; and then the mixture is distilled under reduced pressure to obtain the phosphorus-containing phenolic aldehyde epoxy flame-retardant resin.

6. The process for preparing phosphorus-containing phenolic epoxy flame retardant resin according to claim 1, characterized in that, The mass / volume ratio of the phenolic compound, phosphorus-containing catalyst and formaldehyde solution is (20-30) g:(4-6) g:(28-40) mL.

7. The process for preparing phosphorus-containing phenolic epoxy flame retardant resin according to claim 5, wherein The mass fraction of the formaldehyde solution is 37-40%. The mass / volume ratio of the phenolic compound, epichlorohydrin and NaOH aqueous solution is (20-30) g:(75-115) mL:(44-66) mL. The phosphorus-containing phenolic aldehyde epoxy flame-retardant resin is prepared by using the preparation method according to any one of claims 1-7.

8. A phosphorus-containing phenolic epoxy flame-retardant resin characterized by comprising, The phosphorus-containing phenolic aldehyde epoxy flame-retardant resin is prepared by using the preparation method according to any one of claims 1-7.

9. A cured product of a phosphorus-containing phenolic epoxy flame-retardant resin, characterized by, The phosphorus-containing phenolic aldehyde epoxy flame-retardant resin is prepared by using the preparation method according to any one of claims 1-7.

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