High-strength flame-retardant phenolic moulding plastic and preparation method thereof

Abstract

The invention discloses a high-strength flame-retardant phenolic molding compound and a preparation method thereof, and belongs to the technical field of phenolic molding compounds. Comprising the following raw materials in parts by weight: 70-90 parts of phenolic resin, 5-8 parts of hexamethylenetetramine, 10-20 parts of pretreated glass fibers, 8-16 parts of a flame retardant and 1-3 parts of a lubricant. Wherein the pretreated glass fiber reinforced molding compound solves the problem of interfacial compatibility between fibers and a resin matrix, reduces stress concentration, and improves the strength of the molding compound; wherein the flame retardant has a phosphorus-boron-nitrogen synergistic flame retardant effect, the flame retardant property of the phenolic molding plastic can be remarkably improved, the problem of insufficient flame retardant property of the traditional phenolic molding plastic is solved, and the flame retardant is halogen-free and environment-friendly; therefore, the phenolic moulding plastic prepared by the invention has both flame retardance and high strength, and has important application value in the technical field of phenolic moulding plastics.

Description

Technical Field

[0001] The present invention belongs to the technical field of phenolic molding compounds, and in particular relates to a high-strength flame-retardant phenolic molding compound and a preparation method thereof. Background Art

[0002] As a thermosetting plastic with a long history, phenolic molding compounds have been widely used in the fields of electrical electronics, automobiles, aerospace, etc. due to their excellent mechanical properties, heat resistance, electrical insulation and dimensional stability. However, with the continuous improvement of modern industry's requirements for material performance, traditional phenolic molding compounds have gradually exposed some defects. For example, in the field of electrical insulation, the material not only needs to withstand long-term current loads, but also needs to have the ability to prevent the spread of flames in the event of a short circuit or overload. Although ordinary phenolic molding compounds have certain flame retardant properties, in the face of high flame retardant standards, the flame retardancy of phenolic molding compounds still needs to be improved. The flame retardants currently used in phenolic molding compounds, such as decabromodiphenyl ethane, are halogen-containing flame retardants. This type of flame retardant will cause serious pollution to the environment during preparation, use and post-processing, which is not in line with the current green and environmentally friendly development concept.

[0003] From a strength perspective, the industry typically uses fiber filling or inorganic filler blending to enhance mechanical properties. For example, while glass fiber-reinforced phenolic plastics can significantly improve tensile strength and impact toughness, interfacial compatibility issues between the fiber and matrix often lead to stress concentration, and uneven fiber orientation is prone to occur during the molding process of complex shapes. Commonly used fillers such as wood flour and mineral powder are low-cost, but adding more than 30% can increase the material's brittleness and reduce its fluidity, affecting its molding processability.

[0004] In summary, there is an urgent need to invent a phenolic molding compound with both high strength and flame retardant properties to meet the higher technical requirements in the field of phenolic molding compounds. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide a high-strength flame-retardant phenolic molding compound and a preparation method thereof.

[0006] The purpose of the present invention can be achieved through the following technical solutions: A high-strength flame-retardant phenolic molding compound comprises the following raw materials in parts by weight: 70-90 parts of phenolic resin, 5-8 parts of hexamethylenetetramine, 10-20 parts of pretreated glass fibers, 8-16 parts of flame retardant, and 1-3 parts of lubricant.

[0007] As a further technical solution, the lubricant is one of polyethylene wax, zinc stearate and stearic acid.

[0008] As a further technical solution, the pretreated glass fiber is prepared by the following steps: The chopped glass fiber, silane coupling agent and anhydrous ethanol were mixed, acetic acid solution was added dropwise, the pH was adjusted to 4-5, ultrasonic treatment was performed for 10-15 minutes, the fibers were separated with a filter, excess liquid was drained, and the fibers were dried in an oven at 80-100°C for 2-3 hours to obtain pretreated glass fibers.

[0009] As a further technical solution, the weight proportions of the raw materials are as follows: 20-30 parts of chopped glass fibers, 1-2 parts of silane coupling agents, and 80-100 parts of anhydrous ethanol.

[0010] As a further technical solution, the silane coupling agent is KH-550.

[0011] As a further technical solution, the flame retardant is prepared by the following steps: A1. Add pentaerythritol, boric acid, toluene, and p-toluenesulfonic acid to a three-necked flask, purge with nitrogen for 10 minutes to exclude air, start stirring, and slowly heat to 80°C. Maintain the temperature for 30 minutes to partially dissolve the boric acid. Then, heat to 130-140°C, stir, and reflux to react. Remove the generated water through an oil-water separator. When no water droplets are generated in the water separator, continue the reaction for 1-2 hours to ensure complete esterification. After the reaction is complete, cool to 80°C, distill under reduced pressure to recover toluene, dissolve the product in hot ethanol, filter while hot to remove unreacted boric acid, cool the filtrate to precipitate a white solid, filter, wash with cold ethanol, and vacuum dry to obtain a borate ester product. A2. Add 2-chloro-4,6-diamino-1,3,5-triazine, 4-dimethylaminopyridine and tetrahydrofuran to a three-necked flask, pass nitrogen for 10 minutes to exclude air, start stirring, and slowly heat to 40°C, stir until the solid is completely dissolved, then dissolve diethylphosphoacetic acid and dicyclohexylcarbodiimide in tetrahydrofuran, and slowly add dropwise through a constant pressure dropping funnel in an ice bath at 0-5°C. After the addition is complete, remove the ice bath, raise the temperature to 25-30°C, continue stirring and react for 10-12 hours. After the reaction is complete, filter with suction, wash the filter cake with cold tetrahydrofuran, combine the filtrates, concentrate under reduced pressure, add ice water to precipitate the solid, filter with suction, wash with cold water and cold ethanol, and dry to obtain an amidated product; A3. Add the borate product, amidation product, tetrahydrofuran and triethylamine to a three-necked flask in sequence, pass nitrogen for 10 minutes to exclude air, and stir for 10-20 minutes under ice bath condition of 0-5°C. Heat to 40-60°C to promote the reaction. The reaction time is controlled at 6-8 hours. After the reaction is completed, water is added to quench the reaction, and the mixture is extracted with ethyl acetate. The organic phases are combined, dried over anhydrous sodium sulfate, filtered, and the solvent is removed by rotary evaporation. The mixture is separated by column chromatography to obtain a flame retardant.

[0012] As a further technical solution, the ratio of pentaerythritol, boric acid, toluene and p-toluenesulfonic acid in step A1 is 13.6 g:14.1-15.7 g:75 mL:0.1-0.2 g.

[0013] As a further technical solution, in step A2, the ratio of 2-chloro-4,6-diamino-1,3,5-triazine, 4-dimethylaminopyridine, tetrahydrofuran, diethylphosphinoacetic acid, and dicyclohexylcarbodiimide is 14.5 g: 2.4 g: 150 mL: 39.0-40.6 g: 42.2-47.4 g.

[0014] As a further technical solution, in step A3, the ratio of the amount of the borate product, the amidation product, tetrahydrofuran, and triethylamine is 18.6 g:105.7-110.9 g:200 mL:20.2 g.

[0015] The reaction formulas of steps A1 and A2 of the present invention are as follows: During the preparation of the flame retardant, it should be noted that in step A1, the molar ratio of pentaerythritol to boric acid must be strictly controlled to be close to 1:2, and the boric acid must be in excess to ensure complete reaction. Similarly, in step A2, the molar ratio of 2-chloro-4,6-diamino-1,3,5-triazine to diethylphosphinoacetic acid must be strictly controlled to be close to 1:2, and the diethylphosphinoacetic acid must be in excess to ensure complete reaction. Similarly, in step A3, the molar ratio of the borate ester product to the amidation product must be strictly controlled to be close to 1:2, and the amidation product must be in excess to ensure complete reaction.

[0016] It is not difficult to infer from the above reaction formula that the flame retardant prepared by the present invention constructs a phosphorus-boron-nitrogen synergistic flame retardant structure, and the symmetry of the molecule and the presence of multiple phosphoric acid structures further enhance the flame retardant performance of the flame retardant; the introduced pentaerythritol skeleton can not only inhibit the hydrolysis of borate esters and improve the stability of the flame retardant, but also promote the formation of a dense carbon layer in the matrix, further improving the flame retardancy.

[0017] The present invention also provides a method for preparing a high-strength flame-retardant phenolic molding compound, comprising the following steps: The phenolic resin is heated to 80-90°C to soften it, and then hexamethylenetetramine (curing agent) is added and stirred for 5-10 minutes for preliminary mixing. Then, a flame retardant and a lubricant are added in sequence and stirred at high speed to ensure uniform dispersion. Then, pretreated glass fiber is added and stirred at low speed to prevent fiber breakage to obtain a mixture. The mixture is fed into a twin-screw extruder and pelletized after extrusion to obtain molding compound particles. The molding compound particles are placed in a mold and compression molded to obtain a high-strength flame-retardant phenolic molding compound.

[0018] As a further technical solution, the rotation speed of the high-speed stirring is 1000-1200 rpm, and the time is 10-20 min.

[0019] As a further technical solution, the rotation speed of the low-speed stirring is 300-500 rpm, and the time is 5-10 min.

[0020] As a further technical solution, the temperature of the mold in the compression molding is 170-180° C., the molding time is 5-10 minutes, and the pressure is 15-20 MPa.

[0021] Beneficial effects of the present invention: 1. The present invention solves the problem of interfacial compatibility between the fiber and the resin matrix by pre-treating the glass fiber reinforced molding compound, reduces stress concentration, and improves the strength of the molding compound; 2. The present invention constructs a phosphorus-boron-nitrogen synergistic flame retardant that significantly improves the flame retardancy of phenolic molding compounds, overcoming the problem of insufficient flame retardancy of traditional phenolic molding compounds. In addition, the flame retardant is halogen-free and environmentally friendly. In summary, the phenolic molding compound prepared by the present invention has both flame retardancy and high strength, and has important application value in the technical field of phenolic molding compounds. DETAILED DESCRIPTION

[0022] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0023] Example 1 Preparation of pretreated glass fiber: Mix 20 parts of chopped glass fibers, 1 part of KH-550 and 80 parts of anhydrous ethanol, add acetic acid solution dropwise, adjust the pH to 4, and ultrasonically treat for 10 minutes. Separate the fibers with a filter, drain the excess liquid, and dry in an oven at 80°C for 2 hours to obtain pretreated glass fibers.

[0024] Example 2 Preparation of pretreated glass fiber: 30 parts of chopped glass fibers, 2 parts of KH-550 and 100 parts of anhydrous ethanol were mixed, acetic acid solution was added dropwise, the pH was adjusted to 5, ultrasonic treatment was performed for 15 minutes, the fibers were separated with a filter, the excess liquid was drained, and the mixture was dried in an oven at 100°C for 3 hours to obtain pretreated glass fibers.

[0025] Example 3 Preparation of flame retardant: A1. Add 13.6 g of pentaerythritol, 14.1 g of boric acid, 75 mL of toluene, and 0.1 g of p-toluenesulfonic acid to a three-necked flask, purge with nitrogen for 10 min to exclude air, start stirring, and slowly raise the temperature to 80° C., keep warm for 30 min to partially dissolve the boric acid, then raise the temperature to 130° C., stir and reflux to react, remove the generated water through an oil-water separator. When no water droplets are generated in the water separator, continue the reaction for 1 h to ensure complete esterification. After the reaction is complete, cool to 80° C., distill under reduced pressure to recover toluene, dissolve the product in hot ethanol, filter while hot to remove unreacted boric acid, cool the filtrate to precipitate a white solid, filter, wash with cold ethanol, and dry in vacuo to obtain a borate ester product; A2, 29.0g2-chloro-4,6-diamino-1,3,5-triazine, 4.8g4-dimethylaminopyridine and 60mL tetrahydrofuran were added to a three-necked flask, nitrogen was passed for 10min to exclude air, stirring was turned on, and the temperature was slowly raised to 40°C, and stirred until the solid was completely dissolved. Then 78.0g diethylphosphoacetic acid and 84.4g dicyclohexylcarbodiimide were dissolved in 240mL tetrahydrofuran and slowly added dropwise through a constant pressure dropping funnel under 0°C ice bath conditions. After the addition was complete, the ice bath was removed, the temperature was raised to 30°C, and the stirring reaction was continued for 10h. The reaction was completed, filtered, the filter cake was washed with cold tetrahydrofuran, the filtrate was combined, concentrated under reduced pressure, added to ice water to precipitate the solid, filtered, then washed with cold water and cold ethanol, and dried to obtain an amidated product; A3. 18.6 g of the borate ester product, 105.7 g of the amidation product, 200 mL of tetrahydrofuran, and 20.2 g of triethylamine were sequentially added to a three-necked flask, purged with nitrogen for 10 min to exclude air, and stirred for 10 min in an ice bath at 0°C. The mixture was heated to 40°C to promote the reaction. The reaction time was controlled within 8 h. After the reaction was complete, water was added to quench the reaction, and the mixture was extracted with ethyl acetate. The organic phases were combined, dried over anhydrous sodium sulfate, filtered, and the solvent was removed by rotary evaporation. The mixture was separated by column chromatography (volume ratio of petroleum ether / ethyl acetate = 9:1) to obtain a flame retardant. A method for preparing a high-strength flame-retardant phenolic molding compound comprises the following steps: 70 parts of phenolic resin were heated to 80° C. to soften it, and then 5 parts of hexamethylenetetramine were added and stirred for 5 minutes for preliminary mixing; then 8 parts of flame retardant and 1 part of polyethylene wax were added in sequence, and stirred at 1000 rpm for 10 minutes to ensure uniform dispersion; then 10 parts of the pretreated glass fiber prepared in Example 1 were added and stirred at 300 rpm for 5 minutes to prevent fiber breakage, to obtain a mixture; the mixture was fed into a twin-screw extruder, extruded, and pelletized to obtain molding compound particles; the molding compound particles were placed in a mold at 170° C. and compression molded at 15 MPa for 5 minutes to obtain a high-strength flame-retardant phenolic molding compound.

[0026] Example 3 Preparation of flame retardant: A1. Add 13.6 g of pentaerythritol, 15.7 g of boric acid, 75 mL of toluene, and 0.2 g of p-toluenesulfonic acid to a three-necked flask, purge with nitrogen for 10 min to exclude air, start stirring, and slowly heat to 80° C., keep warm for 30 min to partially dissolve the boric acid, then heat to 130-140° C., stir and reflux to react, remove the generated water through an oil-water separator. When no water droplets are generated in the water separator, continue the reaction for 1-2 h to ensure complete esterification. After the reaction is complete, cool to 80° C., distill under reduced pressure to recover toluene, dissolve the product in hot ethanol, filter while hot to remove unreacted boric acid, cool the filtrate to precipitate a white solid, filter, wash with cold ethanol, and dry in vacuo to obtain a borate ester product; A2, 29.0g2-chloro-4,6-diamino-1,3,5-triazine, 4.8g4-dimethylaminopyridine and 60mL tetrahydrofuran were added to a three-necked flask, nitrogen was passed for 10min to exclude air, stirring was turned on, and the temperature was slowly raised to 40°C, and stirred until the solid was completely dissolved. Then 81.2g diethylphosphinoacetic acid and 94.8g dicyclohexylcarbodiimide were dissolved in 240mL tetrahydrofuran and slowly added dropwise through a constant pressure dropping funnel under 5°C ice bath conditions. After the addition was complete, the ice bath was removed, the temperature was raised to 25°C, and the stirring reaction was continued for 12h. The reaction was completed, filtered, the filter cake was washed with cold tetrahydrofuran, the filtrate was combined, concentrated under reduced pressure, added to ice water to precipitate a solid, filtered, washed with cold water and cold ethanol, and dried to obtain an amidated product; A3. 18.6 g of the borate ester product, 110.9 g of the amidation product, 200 mL of tetrahydrofuran, and 20.2 g of triethylamine were sequentially added to a three-necked flask, purged with nitrogen for 10 min to exclude air, and stirred for 20 min in an ice bath at 0-5°C. The mixture was heated to 60°C to promote the reaction. The reaction time was controlled within 6 h. After the reaction was complete, water was added to quench the reaction, and the mixture was extracted with ethyl acetate. The organic phases were combined, dried over anhydrous sodium sulfate, filtered, and the solvent was removed by rotary evaporation. The mixture was separated by column chromatography (volume ratio of petroleum ether / ethyl acetate = 9:1) to obtain a flame retardant. A method for preparing a high-strength flame-retardant phenolic molding compound comprises the following steps: 80 parts of phenolic resin were heated to 90° C. to soften it, and then 6.5 parts of hexamethylenetetramine were added and stirred for 10 minutes for preliminary mixing; then 12 parts of flame retardant and 2 parts of zinc stearate were added in sequence, and stirred at 1100 rpm for 15 minutes to ensure uniform dispersion, and then 15 parts of pretreated glass fiber prepared in Example 2 were added and stirred at 400 rpm for 7.5 minutes to prevent fiber breakage, to obtain a mixture; the mixture was fed into a twin-screw extruder, extruded, and pelletized to obtain molding compound particles; the molding compound particles were placed in a mold at 170° C. and compression molded at 20 MPa for 10 minutes to obtain a high-strength flame-retardant phenolic molding compound.

[0027] Example 5 The only difference between this embodiment and the fourth embodiment is that in this embodiment, a method for preparing a high-strength flame-retardant phenolic molding compound includes the following steps: 90 parts of phenolic resin were heated to 90° C. to soften it, and then 8 parts of hexamethylenetetramine were added and stirred for 10 minutes to achieve preliminary mixing; then 16 parts of flame retardant and 3 parts of stearic acid were added in sequence, and stirred at 1200 rpm for 20 minutes to ensure uniform dispersion, and then 20 parts of pretreated glass fiber prepared in Example 2 were added and stirred at 500 rpm for 10 minutes to prevent fiber breakage, to obtain a mixture; the mixture was fed into a twin-screw extruder, extruded, and pelletized to obtain molding compound particles; the molding compound particles were placed in a mold at 180° C. and compression molded at 20 MPa for 10 minutes to obtain a high-strength flame-retardant phenolic molding compound.

[0028] Comparative Example 1 The only difference between this comparative example and Example 5 is that in this comparative example, an equal amount of DOPO is used to replace the flame retardant to prepare the molding compound.

[0029] Comparative Example 2 The only difference between this comparative example and Example 5 is that in this comparative example, an equal amount of untreated chopped glass fibers is used to replace the pretreated glass fibers to prepare the molding compound.

[0030] The following performance tests were performed on Examples 3, 4, and 5 and Comparative Examples 1 and 2: GB / T 2406.2-2009 standard is used to determine the oxygen index; GB / T 1040.2-2006 standard was used to determine the tensile strength; The performance test results are shown in Table 1: Table 1 Test items Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 Limiting oxygen index / % 42.4 43.8 45.2 29.6 44.5 Tensile strength MPa 59.7 62.5 65.1 64.8 51.9 As can be seen from the above table, the flame retardancy and strength of the phenolic molding materials prepared in the examples of the present invention are higher than those of the comparative examples. Therefore, the present invention has important application value in the technical field of phenolic molding materials.

[0031] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

Claims

1. A high-strength flame-retardant phenolic molding compound, characterized in that: The invention comprises the following raw materials in parts by weight: 70-90 parts of phenolic resin, 5-8 parts of hexamethylenetetramine, 10-20 parts of pretreated glass fiber, 8-16 parts of flame retardant and 1-3 parts of lubricant.

2. The high-strength flame-retardant phenolic molding compound according to claim 1, characterized in that: The flame retardant is prepared by the following steps: A1. Add pentaerythritol, boric acid, toluene, and p-toluenesulfonic acid to a flask, purge with nitrogen, start stirring, raise the temperature to 80°C, maintain the temperature for 30 minutes, then raise the temperature to 130-140°C, and reflux. When no water droplets are generated in the water separator, continue the reaction for 1-2 hours. The reaction is complete to obtain a borate ester product. A2. Add 2-chloro-4,6-diamino-1,3,5-triazine, 4-dimethylaminopyridine, and tetrahydrofuran to a flask, purge with nitrogen, start stirring, heat to 40°C, and stir to dissolve. Then, dissolve diethylphosphoacetic acid and dicyclohexylcarbodiimide in tetrahydrofuran and add dropwise at 0-5°C. After the addition is complete, react at 25-30°C for 10-12 hours. The reaction is complete to obtain an amidated product. A3. Add the borate product, amidation product, tetrahydrofuran and triethylamine into a flask, pass nitrogen, stir at 0-5°C for 10-20 minutes, heat to 40-60°C, and react for 6-8 hours. The reaction is completed to obtain a flame retardant.

3. The high-strength flame-retardant phenolic molding compound according to claim 2, characterized in that: In step A1, the ratio of pentaerythritol, boric acid, toluene, and p-toluenesulfonic acid is 13.6 g:14.1-15.7 g:75 mL:0.1-0.2 g.

4. The high-strength flame-retardant phenolic molding compound according to claim 2, characterized in that: In step A2, the ratio of 2-chloro-4,6-diamino-1,3,5-triazine, 4-dimethylaminopyridine, tetrahydrofuran, diethylphosphinoacetic acid, and dicyclohexylcarbodiimide is 14.5 g: 2.4 g: 150 mL: 39.0-40.6 g: 42.2-47.4 g.

5. The high-strength flame-retardant phenolic molding compound according to claim 2, characterized in that: In step A3, the ratio of the amount of borate product, amidation product, tetrahydrofuran, and triethylamine used is 18.6 g:105.7-110.9 g:200 mL:20.2 g.

6. The high-strength flame-retardant phenolic molding compound according to claim 1, characterized in that: The lubricant is one of polyethylene wax, zinc stearate and stearic acid.

7. The high-strength flame-retardant phenolic molding compound according to claim 1, characterized in that: The pretreated glass fiber is prepared by the following steps: The chopped glass fibers, silane coupling agent and anhydrous ethanol are mixed, acetic acid solution is added dropwise, the pH is adjusted to 4-5, ultrasonic treatment is performed for 10-15 minutes, the fibers are separated, excess liquid is drained, and the mixture is dried to obtain pretreated glass fibers.

8. The high-strength flame-retardant phenolic molding compound according to claim 7, characterized in that: The weight proportions of the raw materials are as follows: 20-30 parts of chopped glass fibers, 1-2 parts of silane coupling agents and 80-100 parts of anhydrous ethanol.

9. A method for preparing a high-strength flame-retardant phenolic molding compound, for preparing the high-strength flame-retardant phenolic molding compound according to any one of claims 1 to 8, characterized in that: The following steps are involved: The phenolic resin is heated to soften it, and then hexamethylenetetramine is added and stirred for preliminary mixing; then a flame retardant and a lubricant are added in sequence and stirred at high speed to be uniformly mixed, and then pretreated glass fiber is added with stirring at low speed to obtain a mixture; the mixture is fed into a twin-screw extruder, extruded and pelletized to obtain molding compound particles; the molding compound particles are placed in a mold and compression molded to obtain a high-strength flame-retardant phenolic molding compound.

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