A bio-based flame-retardant polyurethane pouring sealant and a preparation method thereof

Abstract

The present application relates to the field of bio-based flame-retardant materials, and more particularly to a bio-based flame-retardant polyurethane pouring sealant and a preparation method thereof. The bio-based flame-retardant polyurethane pouring sealant is composed of an A component containing a phosphorus acid bis(tolyl) monococoyl ester bio-based flame retardant and a B component containing castor oil and modified soybean oil polyol. The flame retardant has high phosphorus content, good char-forming structure and high bio-based content by regulating the ratio of tolyl and cocoyl, and has excellent flame-retardant efficiency. The A and B components are prepared by vacuum dehydration and mixing, respectively, and the ratio can be adjusted, and the construction is simple. The present application uses low epoxy value epoxy soybean oil with an epoxy value of 2.0±0.5%, which significantly improves the long-term stability and the wet heat aging electrical insulation performance of the system without reducing the flame-retardant grade. The product after curing has V0 level flame-retardant performance, low water absorption, high adhesive strength, excellent mechanical properties, green environmental protection, low toxicity and low migration, and is suitable for circuit board and other electronic device pouring protection.

Description

Technical Field

[0001] This invention relates to the field of bio-based flame retardant materials, and more specifically to a bio-based flame retardant polyurethane potting compound and its preparation method. Background Technology

[0002] Polyurethane potting compounds, due to their excellent adhesion, weather resistance, electrical insulation, and curing properties, are widely used in the encapsulation and protection of electronic circuit boards and electrical components, effectively providing moisture protection, dustproofing, insulation, and mechanical protection. Under the requirements of electronic and electrical safety, potting compounds must possess good flame-retardant properties. Traditional polyurethane potting compounds often add petrochemical-based flame retardants such as tricresyl phosphate (TCP) to meet flame-retardant standards. However, these flame retardants pose a neurotoxicity risk, and their raw materials rely on non-renewable petrochemical resources, which is inconsistent with current environmental protection trends.

[0003] Existing bio-based flame-retardant polyurethane materials are mostly modified with biomass raw materials such as cashew nut shell powder and castor oil. Although this can improve the environmental friendliness of the materials, cashew nut shell powder-based phosphate flame retardants have problems such as simple structure, low phosphorus content, and insufficient char formation. Some products are prone to defects such as failing to meet flame retardant standards, high migration, and poor compatibility with polyurethane matrix. At the same time, traditional epoxy soybean oil plasticizers have high epoxy values, which will lead to a decrease in the long-term stability of potting compounds. After high temperature and high humidity aging, the resistivity will decrease significantly, making it difficult to meet the long-term reliable protection requirements of electronic devices.

[0004] Currently, there is a lack of polyurethane potting compounds on the market that combine high bio-based content, high efficiency in flame retardancy, low toxicity and environmental friendliness, and long-term stability. The structural design and formulation system of bio-based flame retardants still need to be optimized to solve the balance between flame retardant performance, bio-based content, processing stability and durability, and promote the large-scale application of bio-based flame-retardant polyurethane potting compounds in the electronics and electrical fields. Summary of the Invention

[0005] To address the aforementioned technical problems, the first aspect of this invention provides a bio-based flame-retardant polyurethane potting compound, comprising component A and component B, wherein the raw materials for preparing component A include isocyanate and bio-based flame retardant; and the raw materials for preparing component B include bio-based polyol, plasticizer, catalyst, and defoamer.

[0006] As an feasible example, the raw materials for preparing the bio-based flame retardant include phosphorus oxychloride, cresol, and cashew nut shell powder.

[0007] As an implementable example, the mass ratio of component A to component B is 1:(1-5).

[0008] As an example of implementation, the raw materials for component A also include plasticizers.

[0009] This invention defines a two-component (A and B) system for bio-based flame-retardant polyurethane potting compound. Component A contains isocyanate and a bio-based flame retardant, while component B contains a bio-based polyol, plasticizer, catalyst, and defoamer. The bio-based flame retardant is specifically derived from phosphorus oxychloride, cresol, and cashew nut shell powder. This allows for the construction of a stable and clearly defined polyurethane potting compound system, enabling separate storage of the two components, avoiding pre-reaction, and ensuring product storage and application stability. Furthermore, the use of biomass as the primary raw material enhances the environmental friendliness of the formulation and the controllability of the flame retardant structure. By limiting the mass ratio of components A to B to 1:(1-5), the ratio of functional groups in the curing reaction can be precisely controlled, ensuring complete curing of the potting compound and balanced mechanical and adhesive properties. Combined with the synergistic flame-retardant effect of the phosphorus-aromatic rings of the bio-based flame retardant and the stabilizing effect of low-epoxy value epoxidized soybean oil, the final result is a comprehensive effect of V-0 flame retardancy, low water absorption, low toxicity and low migration, and excellent resistivity maintenance after high-temperature and high-humidity aging. This also meets the requirements for industrial potting processability and long-term protection of electronic devices.

[0010] As an implementable example, the preparation method of the bio-based flame retardant includes the following steps: S1. Add phosphorus oxychloride to the reactor and cool it to 10-15℃ (lower temperature is more conducive to controlling the monosubstitution reaction). S2. Add cresol dropwise. After the addition is complete, keep the reaction at 20-30℃ for 1-2 hours. During the reaction, maintain a pressure of -0.01~-0.08MPa and remove the byproduct HCl under negative pressure. After the reaction is complete, cresoloxyphosphoryl dichloride is obtained. S3. Add the mixture of cashew phenol and cresol dropwise, and keep the reaction at 20-30℃ for 1-2 hours. During the reaction, maintain a pressure of -0.01~-0.08MPa to remove the byproduct HCl under negative pressure. After the reaction is completed, remove the low-boiling substances by vacuum distillation to obtain the bio-based flame retardant bis(tolyl) cashew phenol ester.

[0011] In this invention, the structural formula of cresoloxyphosphoryl dichloride is (CH3C6H4O)P(O)Cl2; the structural formula of bis(tolyl)-cashew phenolic ester phosphate is (CH3C6H4O)2P(O)(O-C6H4-C 15 H 29 ).

[0012] This invention employs a process design involving stepwise low-temperature dropwise addition, segmented temperature-controlled reaction, negative pressure HCl removal, and vacuum distillation post-treatment. This precise control of the substitution sequence and reaction extent ensures the formation of high-purity bis(tolyl)-cashew phenol ester, avoiding side reactions and impurity generation. The low-temperature feeding in step S1 and the temperature-controlled holding in step S2 stably generate the cresoloxyphosphoryl dichloro intermediate. Negative pressure HCl removal promotes the forward reaction and increases the conversion rate. The dropwise addition of cashew phenol and secondary temperature holding in step S3 ensure complete substitution of the intermediate, while vacuum distillation removes low-boiling substances and residual impurities, ultimately yielding a bio-based flame retardant with a well-defined structure and excellent flame retardant and thermal stability.

[0013] As an implementable example, the molar ratio of phosphorus oxychloride and cresol (cresol being a mixture of o-cresol, m-cresol, and p-cresol) is 1:(2-2.05); more preferably, the molar ratio is 1:2.

[0014] This invention sets the theoretical molar ratio of phosphorus oxychloride to mixed cresols at 1:2. In the actual reaction, phosphorus oxychloride and cresols are controlled to undergo the first-step substitution reaction at a 1:1 ratio. This ensures the precise generation of the bis(tolyl)-carbonyl dichloro intermediate, avoiding tri- or mono-substituted byproducts and guaranteeing that the flame retardant's main chain structure is bis(tolyl)-cainol phosphate. The remaining molar of cresol does not participate in the first-step reaction but reacts with cashew phenols in the subsequent reaction, participating in system equilibrium. This stabilizes the reaction environment, suppresses side reactions, and improves the selectivity and purity of the target product. This feeding ratio design allows for strict control of the number and type of substituents on the phosphorus atoms, ensuring that the final flame retardant has a moderate phosphorus content, a stable aromatic ring char structure, and a high bio-based content. Simultaneously, it avoids the formation of triphenyl phosphate impurities, enabling the flame retardant to exhibit excellent flame retardancy, compatibility, and low migration in polyurethane potting compounds, meeting the environmental and safety requirements of electronic potting materials.

[0015] As an implementable example, the molar ratio of cresoloxyphosphoryl dichloride and cashew phenol is 1:(1-1.05).

[0016] This invention sets the molar ratio of cresoloxyphosphoryl dichloride to cashew phenol to 1:(1-1.05), resulting in a slight excess of cashew phenol. This ensures complete reaction of the phosphoryl dichloride intermediate, improving the purity and yield of the target bio-based flame retardant. The slight excess of cashew phenol allows for sufficient substitution of the P-Cl bonds in cresoloxyphosphoryl dichloride, avoiding residual active chlorine atoms and preventing subsequent side reactions in the polyurethane system that could affect curing and electrical properties. Simultaneously, it reduces problems such as hydrolysis, discoloration, and decreased stability caused by unreacted intermediates, resulting in a more regular flame retardant structure and more stable phosphorus content, ultimately ensuring the flame retardancy, insulation, and long-term reliability of the potting compound.

[0017] As an implementable example, the isocyanate includes one or more of MDI (4,4'-diphenylmethane diisocyanate), MDI derivatives, TDI (toluene diisocyanate), HDI (hexamethylene diisocyanate), IPDI (isophorone diisocyanate), or hydrogenated MDI.

[0018] Furthermore, the isocyanate is MDI, and the MDI is liquefied MDI.

[0019] As an implementable example, the plasticizer includes one or more of DOA (dioctyl adipate), DINP (diisononyl phthalate), DPHP (di(2-propylheptyl) phthalate), and epoxidized soybean oil.

[0020] Furthermore, the epoxy value of the epoxidized soybean oil is 1-7%.

[0021] Furthermore, the epoxy value of the epoxidized soybean oil is 2.0 ± 0.5%.

[0022] This invention uses customized low-epoxy-value epoxidized soybean oil with an epoxy value of 2.0±0.5%, the core function of which is to ensure that the UL (Usage Limiting) is not affected. 94 flame retardant rating, can stably reach V Under the premise of Grade 0, the lower epoxy content reduces side reactions, post-crosslinking and thermo-oxidative aging tendencies, making the system more stable for long-term use. At the same time, it can still maintain a higher volume resistivity after aging for 500 hours at 85℃ and 85%RH, significantly improving the electrical insulation reliability of the potting compound. It also retains the advantages of epoxy soybean oil plasticizer, low toxicity, bio-based environmental protection, good compatibility and reduced risk of small molecule migration.

[0023] As an implementable example, the catalyst comprises at least one of dibutyltin dilaurate, dibutyltin diacetate, stannous octanoate, bismuth neodecanoate, bismuth octanoate, bismuth isooctanoate, bismuth naphthenate, bismuth laurate, zinc octanoate, zinc isooctanoate, zinc neodecanoate, zinc naphthenate, or zinc laurate.

[0024] As an feasible example, the bio-based polyols include one or more of castor oil, modified castor oil polyols, modified soybean oil polyols, modified cashew nut shell oil polyols, and modified palm oil polyols.

[0025] A second aspect of this invention provides a method for preparing a bio-based flame-retardant polyurethane potting compound, comprising the following steps: The plasticizer and bio-based flame retardant are mixed, heated to 100-120℃, then dehydrated under vacuum at -0.09~-0.095MPa, then cooled to below 60℃, isocyanate is added, stirred evenly, cooled, filtered and discharged to obtain component A; Bio-based polyols and plasticizers are mixed, heated to 100-120℃, then dehydrated under vacuum at -0.09~-0.095MPa, and then cooled to below 60℃. Defoamer and catalyst are added, stirred evenly, cooled, filtered, and discharged to obtain component B.

[0026] Beneficial effects (I) This invention uses castor oil and modified soybean oil polyols as bio-based polyol components, combined with a self-synthesized bis(tolyl)-cashew phenolic ester bio-based flame retardant. It extensively uses renewable biomass raw materials to replace petrochemical raw materials, significantly increasing the overall bio-based carbon content of the potting compound, aligning with the trend of green and low-carbon development. Compared to the traditional flame retardant TCP, this invention's bio-based flame retardant replaces part of the petrochemical cresol with cashew phenol, eliminating the inherent neurotoxicity risk of TCP from the source, while retaining highly efficient flame retardant properties. This makes the potting compound safer and more environmentally friendly during use, suitable for electronic and electrical potting scenarios with strict environmental and toxicity requirements.

[0027] (II) This invention, through precise control of the toluene-to-cashnutyl group ratio, enables the bio-based flame retardant to possess a moderate phosphorus content and a good aromatic char structure, resulting in significantly superior flame retardant efficiency compared to similar cashewylyl phenolic ester flame retardants such as toluene-based bis-cashnutyl ester and tri-cashnutyl ester. The potting compound has been tested and shows stable performance at V... Rating 0, with flame retardant effect comparable to traditional TCP flame retardant systems, while avoiding the formation of triphenyl phosphate impurities, resulting in higher product purity, better char formation and thermal stability, providing reliable fire protection for electronic components such as circuit boards.

[0028] (III) This invention uses a customized low-epoxy-value epoxy soybean oil with an epoxy value of 2.0±0.5%. Without affecting flame retardant performance, it significantly reduces system side reactions and post-crosslinking tendencies, effectively inhibiting thermo-oxidative aging. After aging for 500 hours at 85℃ and 85%RH (double 85%), the potting compound exhibits high volume resistivity retention and electrical insulation reliability far superior to conventional 6.0% epoxy-value epoxy soybean oil systems. Long-term use results in slow resistance decay, ensuring stable operation of electronic devices in humid and hot environments and extending product lifespan.

[0029] (iv) The bio-based flame retardant of this invention has good compatibility with the polyurethane system, which can significantly improve the tensile strength, elongation at break and shear strength of the potting compound, enhance the toughness of the material and reduce brittleness. After curing, the adhesive layer firmly adheres to electronic components, circuit boards and common substrates, with strong interfacial bonding force, and is not prone to problems such as delamination and cracking. At the same time, it has a lower water absorption rate and improved water resistance and damp heat resistance, which can meet the mechanical and protective requirements of electronic potting under complex working conditions.

[0030] (V) The bio-based flame retardant synthesis route provided by this invention is simple, the reaction conditions are mild, the raw materials are readily available and the cost is low; the production of components A and B only requires conventional heating, vacuum dehydration, stirring and mixing processes, the process parameters are easy to control, and no special equipment is required. After components A and B are mixed in proportion, they can be directly used for continuous operation of dispensing machines, which is convenient for construction and has the advantages of low cost, high stability and large-scale production, making it suitable for the large-volume and high-efficiency potting and encapsulation processing needs of the electronics industry. Detailed Implementation

[0031] Example 1 The first aspect of this example provides a bio-based flame-retardant polyurethane potting compound, which includes component A and component B, with a mass ratio of component A to component B of 1:2.

[0032] The raw materials for preparing component A, by weight, include: 60 parts liquefied MDI, 35 parts bio-based flame retardant bis(tolyl)-cashew phenolic ester, and 5 parts epoxidized soybean oil (epoxidation value 2.0±0.5%). The raw materials for preparing component B, by weight, include: 50 parts castor oil, 38 parts modified soybean oil, 12 parts epoxidized soybean oil (epoxidation value 2.0±0.5%), 0.05 parts catalyst dibutyltin dilaurate, and 0.01 parts BYK-A535 defoamer.

[0033] The preparation method of the bio-based flame retardant includes the following steps: S1. Add phosphorus oxychloride to the reactor and cool it down to 10°C; S2. Add mixed cresols (a mixture of o-cresol, m-cresol, and p-cresol) dropwise, with a molar ratio of mixed cresols to phosphorus oxychloride of 1:1. After the addition is complete, keep the reaction at 30°C for 2 hours. During the reaction, maintain a pressure of -0.05 to -0.06 MPa and remove the byproduct HCl under negative pressure. After the reaction is complete, cresoloxyphosphoryl dichloride is obtained. S3. Add a mixture of cashew phenol and cresol dropwise, with a molar ratio of cashew phenol, cresol and cresoloxyphosphoryl dichloride of 1.01:1:1. Keep the mixture at 30°C for 2 hours, while maintaining a pressure of -0.05 to -0.06 MPa during the reaction. Remove the byproduct HCl under negative pressure. After the reaction is completed, remove the low-boiling substances by vacuum distillation at -0.095 MPa to obtain the bio-based flame retardant bis(tolyl)-cashew phenol ester.

[0034] The second aspect of this example provides a method for preparing a bio-based flame-retardant polyurethane potting compound, comprising the following steps: The bio-based flame retardant and epoxidized soybean oil were mixed evenly, heated to 100°C, and dehydrated under vacuum at -0.095MPa. The mixture was then cooled to 55°C, liquefied MDI was added, and the mixture was stirred evenly. The mixture was then cooled to 40°C, filtered, and discharged to obtain component A. Castor oil, modified soybean oil, and epoxidized soybean oil are mixed, heated to 100°C, and then dehydrated under vacuum at -0.095 MPa. The mixture is then cooled to 50°C, and BYK-A535 defoamer and dibutyltin dilaurate are added. After stirring evenly, the mixture is cooled to 40°C, filtered, and discharged to obtain component B.

[0035] Example 2 The first aspect of this example provides a bio-based flame-retardant polyurethane potting compound, which includes component A and component B, with a mass ratio of component A to component B of 1:2.

[0036] The raw materials for preparing component A, by mass parts, include: 60 parts liquefied MDI, 40 parts bio-based flame retardant bis(tolyl) cashew nut ester; the raw materials for preparing component B, by mass parts, include: 50 parts castor oil, 38 parts modified soybean oil, 12 parts epoxidized soybean oil (epoxidation value 2.0%), 0.05 parts catalyst dibutyltin dilaurate, and 0.01 parts BYK-A535 defoamer.

[0037] The preparation method of the bio-based flame retardant includes the following steps: S1. Add phosphorus oxychloride to the reactor and cool it down to 10°C; S2. Add mixed cresols (a mixture of o-cresol, m-cresol, and p-cresol) dropwise, with a molar ratio of mixed cresols to phosphorus oxychloride of 1:1. After the addition is complete, keep the reaction at 30°C for 2 hours. During the reaction, maintain a pressure of -0.05 to -0.06 MPa and remove the byproduct HCl under negative pressure. After the reaction is complete, cresoloxyphosphoryl dichloride is obtained. S3. Add a mixture of cashew phenol and cresol dropwise, with a molar ratio of cashew phenol, cresol and cresoloxyphosphoryl dichloride of 1.02:1:1. Keep the mixture at 30°C for 2 hours, while maintaining a pressure of -0.05 to -0.06 MPa during the reaction. Remove the byproduct HCl under negative pressure. After the reaction is completed, remove the low-boiling substances by vacuum distillation at -0.095 MPa to obtain the bio-based flame retardant bis(tolyl)-cashew phenol ester.

[0038] The second aspect of this example provides a method for preparing a bio-based flame-retardant polyurethane potting compound, comprising the following steps: The bio-based flame retardant was heated to 100°C, then dehydrated under vacuum at -0.095 MPa, and then cooled to 55°C. Liquefied MDI was added, stirred evenly, and then cooled to 40°C. The mixture was filtered out to obtain component A. Castor oil, modified soybean oil, and epoxidized soybean oil are mixed, heated to 100°C, and then dehydrated under vacuum at -0.095 MPa. The mixture is then cooled to 50°C, and BYK-A535 defoamer and dibutyltin dilaurate are added. After stirring evenly, the mixture is cooled to 40°C, filtered, and discharged to obtain component B.

[0039] Comparative Example 1 The specific implementation method in this example is the same as in Example 2, except that: an equal mass fraction of toluene-bis(cainol) phosphate is used instead of bis(toluene)-cainol phosphate, wherein the preparation method of toluene-bis(cainol) phosphate includes the following steps: S1. Add phosphorus oxychloride (POCl3) to the reactor and cool it down to 10~15℃ (lower temperature is more conducive to controlling monosubstitution). S2. Add a mixture of cresol and cashew phenol (POCl3:cresol:cashew phenol = 1:1:2~1:1.05:2) dropwise, maintaining a negative pressure of -0.01~-0.08MPa to remove HCl; S3. After the addition is complete, keep the temperature at 20~30℃ for 1~2 hours to allow the reaction to proceed. S4. Post-treatment: Remove low-boiling substances by vacuum distillation at -0.095MPa.

[0040] Comparative Example 2 The specific implementation method in this example is the same as in Example 2, except that: an equal mass fraction of tricalycanthate phosphate is used instead of bis(tolyl)-calycanthate phosphate, wherein the preparation method of tricalycanthate phosphate includes the following steps: S1. Add phosphorus oxychloride (POCl3) to the reactor and cool it down to 10~15℃ (lower temperature is more conducive to controlling monosubstitution). S2. Add cashew phenol (POCl3: cashew phenol = 1:3~1:3.05) dropwise, maintaining a negative pressure of -0.01~-0.08 MPa to remove HCl; S3. After the addition is complete, keep the temperature at 20~30℃ for 1~2 hours to allow the reaction to proceed. S4. Post-treatment: Remove low-boiling substances by vacuum distillation at -0.095MPa.

[0041] Comparative Example 3 The first aspect of this example provides a flame-retardant polyurethane potting compound, which includes component A and component B, with a mass ratio of component A to component B of 1:2.

[0042] The raw materials for preparing component A, by mass parts, include: 60 parts liquefied MDI, 35 parts tricresyl phosphate, and 5 parts epoxidized soybean oil (epoxidation value 6.0%); the raw materials for preparing component B, by mass parts, include: 50 parts castor oil, 38 parts modified soybean oil, 12 parts epoxidized soybean oil (epoxidation value 6.0%), 0.05 parts catalyst dibutyltin dilaurate, and 0.01 parts BYK-A535 defoamer.

[0043] The second aspect of this example provides a method for preparing a flame-retardant polyurethane potting compound, comprising the following steps: Epoxidized soybean oil and flame retardant tricresyl phosphate were mixed, heated to 100°C, then dehydrated under vacuum at -0.095 MPa, and then cooled to 55°C. Liquefied MDI was added, stirred evenly, and then cooled to 40°C. The mixture was filtered out to obtain component A. Castor oil, modified soybean oil, and epoxidized soybean oil are mixed, heated to 100°C, and then dehydrated under vacuum at -0.095 MPa. The mixture is then cooled to 50°C, and BYK-A535 defoamer and dibutyltin dilaurate are added. After stirring evenly, the mixture is cooled to 40°C, filtered, and discharged to obtain component B.

[0044] In Examples 1-2 and Comparative Examples 1-3 above, the castor oil was refined Grade 1 commercially available castor oil; the modified soybean oil polyol with a hydroxyl value of 150 mgKOH / g was purchased from Zhangjiagang Feihang Technology Co., Ltd., brand name FH-150; epoxidized soybean oil (epoxidation value of 6.0%) and epoxidized soybean oil (epoxidation value of 2.0±0.5%) were both purchased from Nantong Haierma Technology Co., Ltd.; and BYK-A535 defoamer was purchased from BYK Chemical Company.

[0045] Performance Evaluation Curing conditions: Mix components A and B evenly (mass ratio of components A to B is 1:2), and cure at room temperature (23±2℃) for 7 days.

[0046] 1. Hardness test: Tested according to national standard GB / T 531.1-2008.

[0047] 2. Tensile test: Tested according to national standard GB / T 1040.3-2006.

[0048] 3. Shear strength test: Tested according to national standard GB / T 7124-2008, the test substrate is ABS material.

[0049] 4. Shore hardness test: Tested according to national standard GB / T 531.1-2008.

[0050] 5. Water absorption rate test: Tested according to national standard GB / T 1034-2008.

[0051] 6. Flame retardancy test (UL-94): Tested according to national standard GB / T 2408-2021, with a sample thickness of 3mm.

[0052] 7. Resistance Test: Mix components A and B thoroughly and pour into a mold containing a comb-shaped plate (0.3mm wide between electrodes). The adhesive layer on top of the comb-shaped plate should be 4mm thick. Cure at room temperature (approximately 25℃) for 7 days, then test the resistance. The environmental chamber should be set at 85℃ and 85%RH, and the comb-shaped plate should be connected to a DC regulated power supply at 50V. Observe the appearance and measure the resistance every 100 hours, for a total of 500 hours of testing.

[0053] The experimental results of the above tests are detailed in Table 1.

[0054] Table 1

[0055] Test data shows that the use of cashew phenol ester flame retardant has little impact on the hardness of the cured product. Both mono- and TCP flame retardants achieved a V-0 rating, while di- and tri-cashew phenol esters only reached V-2, possibly due to their low phosphorus content. Simultaneously, mono-cashew phenol ester showed improvements in mechanical properties, adhesion, and water absorption, and also maintained good electrical resistance after aging with double 85 esters.

[0056] In addition, the resistance of Examples 1 and 2 and Comparative Examples 1 and 2 was higher than that of Comparative Example 3 after the double 85 test. This was because Comparative Example 3 used TCP flame retardant and high epoxy value soybean oil.

Claims

1. A bio-based flame-retardant polyurethane potting compound, characterized in that, The bio-based flame-retardant polyurethane potting compound comprises component A and component B; The raw materials for preparing component A include isocyanate and bio-based flame retardant; The raw materials for preparing component B include bio-based polyols, plasticizers, catalysts, and defoamers; The preparation method of the bio-based flame retardant includes the following steps: S1. Add phosphorus oxychloride to the reactor and cool it to 10-15℃; S2. Add cresol dropwise. After the addition is complete, keep the reaction at 20-30℃ for 1-2 hours. During the reaction, maintain a pressure of -0.01~-0.08MPa and remove the byproduct HCl under negative pressure. After the reaction is complete, cresoloxyphosphoryl dichloride is obtained. S3, a mixture of cashew phenol and cresol is added dropwise to cresoloxyphosphoryl dichloride, and the reaction is carried out at 20-30℃ for 1-2 hours. During the reaction, the pressure is maintained at -0.01~-0.08MPa. The byproduct HCl is removed under negative pressure. After the reaction is completed, the low-boiling substances are removed by vacuum distillation to obtain the bio-based flame retardant.

2. The bio-based flame-retardant polyurethane potting compound according to claim 1, characterized in that, The raw materials for component A also include plasticizers.

3. The bio-based flame-retardant polyurethane potting compound according to claim 2, characterized in that, The plasticizers mentioned include one or more of DOA, DINP, DPHP, and epoxidized soybean oil.

4. The bio-based flame-retardant polyurethane potting compound according to claim 1, characterized in that, The molar ratio of phosphorus oxychloride and cresol is 1:(2-2.05).

5. The bio-based flame-retardant polyurethane potting compound according to claim 1, characterized in that, The molar ratio of cresoloxyphosphoryl dichloride and cashew phenol is 1:(1-1.05).

6. The bio-based flame-retardant polyurethane potting compound according to claim 1, characterized in that, The isocyanate includes one or more of MDI, MDI derivatives, HDI, IPDI, or hydrogenated MDI.

7. The bio-based flame-retardant polyurethane potting compound according to claim 1, characterized in that, The mass ratio of component A to component B is 1:(1-5).

8. The bio-based flame-retardant polyurethane potting compound according to claim 1, characterized in that, The bio-based polyols include one or more of castor oil, modified castor oil polyols, modified soybean oil polyols, modified cashew nut shell oil polyols, and modified palm oil polyols.

9. The bio-based flame-retardant polyurethane potting compound according to claim 3, characterized in that, The epoxy value of the epoxidized soybean oil is 2.0 ± 0.5%.

10. A method for preparing a bio-based flame-retardant polyurethane potting compound according to any one of claims 2-9, characterized in that, Includes the following steps: The plasticizer and bio-based flame retardant are mixed, heated to 100-120℃, and dehydrated under vacuum at -0.09~-0.095MPa. The mixture is then cooled to below 60℃, isocyanate is added, stirred evenly, cooled, filtered, and discharged to obtain component A. The bio-based polyol and plasticizer are mixed, heated to 100-120℃, and dehydrated under vacuum at -0.09~-0.095MPa. The mixture is then cooled to below 60℃, and defoamer and catalyst are added. After stirring evenly, the mixture is cooled, filtered, and discharged to obtain component B.

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