A method for preparing modified polyester film

Abstract

The present invention provides a method for preparing a modified polyester film, comprising: dissolving thiourea in an ethanol solution, slowly dropping an ethanol solution containing p-hydroxybenzaldehyde and acetic acid into an ethanol solution containing thiourea, reacting at 85-95°C for 4-6h to obtain an intermediate product; dispersing the intermediate product obtained in step S1 and sodium bicarbonate in tetrahydrofuran, then dropping a tetrahydrofuran solution containing diphenyl chlorophosphate, reacting at a temperature of 75-85°C for 5-8h to obtain a phosphorus / nitrogen / sulfur Schiff base multifunctional modifier; S3, mixing the phosphorus / nitrogen / sulfur Schiff base multifunctional modifier with polyester, and obtaining a flame-retardant, anti-melting, antibacterial and multifunctional polyester film by extrusion, casting, stretching and heat setting. The present invention adopts a two-step reaction of p-hydroxybenzaldehyde, thiourea and diphenylphosphinyl chloride to synthesize a phosphorus / nitrogen / sulfur Schiff base multifunctional modifier, and the phosphorus / nitrogen / sulfur Schiff base multifunctional modifier has high flame retardant efficiency and antibacterial efficiency for polyester film.

Description

[Technical field]

[0001] The invention belongs to the technical field of textiles and relates to a method for preparing a modified polyester film. [Background technology]

[0002] Polyester film is a film material made of polyethylene terephthalate as raw material, which is made by extrusion and biaxial stretching. Polyester film has excellent properties such as high mechanical strength, excellent optical properties, chemical corrosion resistance and dimensional stability, and is widely used in food packaging, electronic power, automobile and other transportation equipment fields. However, polyester material is highly flammable, with a limiting oxygen index of only about 21%, and there is a serious droplet phenomenon; in addition, the antibacterial properties of polyester film are poor, and bacteria are easily bred on its surface.

[0003] Chinese invention patent CN109252240B discloses a melt-spinning preparation method for flame-retardant antibacterial polyester fiber, wherein a metal-modified hyperbranched polymer is prepared by using a metal salt and a hyperbranched phosphorus-containing polymer containing carboxylic acid at the end group, and a flame-retardant antibacterial masterbatch is added online during the polyester melt-spinning process to prepare a flame-retardant antibacterial polyester fiber. Reference (Wu Zhihao, Li Lili, Yu Senlong, et al. Research on flame-retardant and antibacterial modification of recycled polyester [C]. / / 2014 Annual Academic Meeting of Chemical Fiber Professional Committee of China Textile Engineering Society and Proceedings of Strategic Emerging Industries and Bio-based Fiber Materials Summit Forum. 2014: 237-240) Recycled polyester (RPET) is melt-blended and extruded by using an organophosphorus flame retardant OP and silver-loaded organophosphate zirconium AgOZ to prepare flame-retardant and antibacterial multifunctional recycled polyester fiber by melt spinning. However, the prepared flame-retardant and antibacterial polyester fiber has the potential to release metal salts during use, and the metal salt antibacterial agent is easy to fall off, which endangers the water body and people's health and safety.

[0004] Schiff base compounds and their ligands contain imine or azomethine characteristic groups and have a wide range of applications in the fields of antibacterial and catalytic applications. However, the development of a multifunctional modifier for polyester composites that combines flame retardant and antibacterial functions is still a major challenge.

[0005] Chinese invention patent CN109988335B discloses a ferrocenyl Schiff base and its preparation method and application. A ferrocenyl Schiff base is synthesized using compounds such as pentaerythritol phosphate, phosphorus oxychloride, melamine, ferrocenyl dicarboxaldehyde, and applied to bio-based PLA, PBAT, PE, PP and PET materials. However, the preparation process of the ferrocenyl Schiff base is complicated, and the flame retardant efficiency and antibacterial efficiency of the product are poor. The limiting oxygen index of the modified PLA is increased from the original 19.1% to 23.7%, and the antibacterial rate against Staphylococcus aureus is only 92.07%. Both the flame retardant efficiency and antibacterial efficiency need to be improved.

[0006] Therefore, it is necessary to provide a new technical solution. [Summary of the invention]

[0007] In order to solve the above technical problems and overcome the shortcomings of the prior art, the present invention provides a method for preparing a modified polyester film, which adopts a two-step reaction of p-hydroxybenzaldehyde, thiourea and diphenylphosphine chloride to synthesize a phosphorus / nitrogen / sulfur Schiff base multifunctional modifier. The phosphorus / nitrogen / sulfur Schiff base multifunctional modifier has high flame retardant efficiency and antibacterial efficiency for the polyester film.

[0008] In order to achieve the above purpose, the following technical solutions are adopted:

[0009] A method for preparing modified polyester comprises the following steps:

[0010] S1. Dissolve thiourea in an ethanol solution, slowly drop an ethanol solution containing p-hydroxybenzaldehyde and acetic acid into the ethanol solution containing thiourea, and react at 85-95° C. for 4-6 hours to obtain an intermediate product;

[0011] S2, dispersing the intermediate product obtained in step S1 and sodium bicarbonate in tetrahydrofuran, then dropwise adding a tetrahydrofuran solution containing diphenyl chlorophosphate, and reacting at a temperature of 75 to 85° C. for 5 to 8 hours to obtain a phosphorus / nitrogen / sulfur Schiff base multifunctional modifier;

[0012] S3. The phosphorus / nitrogen / sulfur Schiff base multifunctional modifier is mixed with polyester, and a flame-retardant, anti-drip and antibacterial multifunctional polyester film is prepared by extrusion, casting, stretching and heat setting.

[0013] Furthermore, in step S1, the mass ratio of thiourea to ethanol is 1:10-20, the mass ratio of p-hydroxybenzaldehyde to ethanol is 1:10-20, the molar ratio of p-hydroxybenzaldehyde to thiourea is 2.1-2.3:1, and the mass of acetic acid is 1-1.5% of the mass of p-hydroxybenzaldehyde.

[0014] Furthermore, in step S2, the molar ratio of the intermediate product to diphenyl chlorophosphate is 1:2.1-2.3, the molar ratio of diphenyl chlorophosphate to sodium bicarbonate is 1:1.5-2, the mass ratio of the intermediate product to tetrahydrofuran is 1:15-25, and the mass ratio of diphenyl chlorophosphate to tetrahydrofuran is 1:10-20.

[0015] Furthermore, step S3 specifically includes:

[0016] S31, drying the phosphorus / nitrogen / sulfur Schiff base multifunctional modifier to obtain phosphorus / nitrogen / sulfur Schiff base multifunctional modifier powder, and drying the polyester powder to obtain polyester dry powder;

[0017] S32, mixing the phosphorus / nitrogen / sulfur Schiff base multifunctional modifier powder obtained in step S31 with the polyester dry powder to obtain a mixture;

[0018] S33, preparing modified polyester masterbatch from the mixture obtained in step S32 through a screw extruder, and preparing a flame-retardant, anti-drip, antibacterial and multifunctional polyester film by casting the modified polyester masterbatch into sheets, biaxially stretching the sheets, and heat-setting the sheets.

[0019] Furthermore, in step S31, the drying temperature of the polyester powder is 140-160° C. for 2-4 hours; the drying temperature of the phosphorus / nitrogen / sulfur Schiff base multifunctional modifier is 70-90° C. for 5-7 hours, ensuring that the final moisture content of the polyester masterbatch and the multifunctional modifier is less than 100 ppm.

[0020] Furthermore, in step S32, the amount of the phosphorus / nitrogen / sulfur Schiff base multifunctional modifier powder in the mixed powder is 3-6%.

[0021] Furthermore, in step S33, the processing temperature of the twin-screw extruder is 240-280°C, the stretching temperature is 100-140°C, and the heat setting temperature is 200-250°C.

[0022] Furthermore, in step S1, the structure of the intermediate product is formula (1):

[0023]

[0024] Furthermore, in step S2, the structure of the phosphorus / nitrogen / sulfur Schiff base multifunctional modifier is formula (2):

[0025]

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] The present invention generates an intermediate product by a Schiff base condensation reaction between the aldehyde group of p-hydroxybenzaldehyde and the amino group of thiourea under acidic conditions, and then the hydroxyl group of the intermediate product reacts with diphenyl chlorophosphate to generate a phosphorus / nitrogen / sulfur Schiff base multifunctional modifier. The thiourea structure in the multifunctional modifier molecule generates sulfur-containing free radicals during the heating process to capture combustible free radicals, and the Schiff base structure decomposes to generate non-flammable nitrogen-containing gas to dilute the free radical and oxygen concentration. In addition, the aromatic phosphorus-containing flame retardant group generates a phosphorus-containing carbon layer with high thermal stability during the thermal decomposition process, which helps to protect the underlying matrix, thereby achieving an excellent flame retardant effect. Therefore, the aromatic phosphorus-containing group, the sulfur-containing group, the nitrogen-containing group, etc. improve the flame retardant and anti-melting droplet performance of the modified polyester film through a synergistic flame retardant effect. In addition, the Schiff base structure has excellent biological activity, and the multifunctional modified polyester film has good antibacterial properties. The multifunctional modified polyester film has good antibacterial properties. The phosphorus / nitrogen / sulfur Schiff base multifunctional modifier is rich in aromatic groups and has high compatibility with polyester. Therefore, the addition of the phosphorus / nitrogen / sulfur Schiff base multifunctional modifier has little effect on the mechanical properties of the polyester film.

Brief Description of the Drawings

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 The infrared spectrum of the phosphorus / nitrogen / sulfur Schiff base multifunctional modifier prepared in Example 1 of the present invention;

[0030] Figure 2 The heat release rate curves of the unmodified and the multifunctional modified polyester films prepared in Example 1 of the present invention after microcalorimetry testing. [Specific implementation method]

[0031] To further help understand the technical solution of the present invention, the technical solution of the present invention is described in more detail below by providing several specific implementation examples. All of the described embodiments are only partial embodiments of the present invention, not all of them. The following specific embodiments may be combined with each other, and the same or similar concepts or processes therein may not be repeated in some embodiments.

[0032] Example 1

[0033] The present invention provides a method for preparing a modified polyester film, comprising the following steps:

[0034] (1) First, thiourea is dissolved in an ethanol solution, and then an ethanol solution containing p-hydroxybenzaldehyde and acetic acid catalyst is slowly added dropwise to the ethanol solution of thiourea, heated to a certain temperature, and refluxed for a certain time to obtain an intermediate product. In step (1), the mass ratio of thiourea to ethanol is 1:10, and the mass ratio of p-hydroxybenzaldehyde to ethanol is 1:20. Theoretically, the amino group of one mole of thiourea can react with the aldehyde group of two moles of p-hydroxybenzaldehyde to generate a Schiff base structure. A slightly excessive amount of p-hydroxybenzaldehyde helps to promote the reaction; acetic acid is a catalyst, and terephthalaldehyde and thiourea are conducive to Schiff base reaction under acidic conditions. The amount of acetic acid is 1% of the mass of p-hydroxybenzaldehyde; the reaction temperature is 85°C, and the boiling point of ethanol is 78.3°C. Under the set temperature conditions, the ethanol solvent boils and reacts under reflux conditions for 4 hours; after the reaction liquid is cooled, a yellow solid is precipitated, which is distilled under reduced pressure and washed with ethanol to obtain an intermediate product.

[0035] In step (1), the structure of the intermediate product is as follows:

[0036]

[0037] (2) The intermediate product and sodium bicarbonate are dispersed in tetrahydrofuran, and then a tetrahydrofuran solution containing diphenyl chlorophosphate is slowly added dropwise, heated to a certain temperature, refluxed for a certain time, and distilled under reduced pressure, and washed with distilled water and ethanol to obtain a phosphorus / nitrogen / sulfur Schiff base multifunctional modifier. The molar ratio of the intermediate product to diphenyl chlorophosphate is 1:2.1. Theoretically, each mole of the intermediate product reacts with two moles of diphenyl chlorophosphate. A slight excess of diphenyl chlorophosphate helps to promote the complete reaction. The molar ratio of diphenyl chlorophosphate to sodium bicarbonate is 1:1.5. Hydrochloric acid is produced during the reaction of the intermediate product and diphenyl chlorophosphate. Sodium bicarbonate can neutralize the hydrochloric acid. An excess of sodium bicarbonate helps to promote the reaction. The mass ratio of the intermediate product to tetrahydrofuran is 1:15, and the mass ratio of diphenyl chlorophosphate to tetrahydrofuran is 1:10. The reaction temperature is 75°C, and the boiling point of tetrahydrofuran is 66°C. Under the set temperature conditions, the tetrahydrofuran solvent boils and reacts under reflux conditions for 5 hours. The phosphorus / nitrogen / sulfur Schiff base multifunctional modifier prepared in this step (2) has a yield of 62%. The molecular structure of the phosphorus / nitrogen / sulfur Schiff base multifunctional modifier is as follows (2):

[0038]

[0039] (3) Then, the phosphorus / nitrogen / sulfur Schiff base multifunctional modifier is dried to obtain phosphorus / nitrogen / sulfur Schiff base multifunctional modifier powder, and the polyester powder is dried to obtain polyester dry powder; the obtained phosphorus / nitrogen / sulfur Schiff base multifunctional modifier powder and polyester dry powder are mixed to obtain a mixture; the mixture is passed through a screw extruder to prepare a flame-retardant, anti-melting, antibacterial and multifunctional polyester masterbatch, and then a flame-retardant, anti-melting, antibacterial and multifunctional polyester film is obtained by casting, biaxial stretching, and heat setting. In step (3), the drying temperature of the polyester powder is 140°C and the time is 2 hours; the drying temperature of the phosphorus / nitrogen / sulfur Schiff base multifunctional modifier is 90°C and the drying time is 5 hours, ensuring that the final moisture content of the polyester powder and the multifunctional modifier is less than 100 ppm. The processing temperature of the twin-screw extruder is 240°C, the stretching temperature is 100°C, and the setting temperature is 200°C. If the processing temperature is too low, the flame retardant and the polyester powder cannot be mixed evenly, which is not conducive to granulation. If the temperature is too high, energy will be wasted. The temperature range provided by the present invention can smoothly prepare uniform flame retardant polyester masterbatch. In the mixed powder, the amount of the phosphorus / nitrogen / sulfur Schiff base multifunctional modifier powder is 3%.

[0040] Example 2

[0041] (1) First, thiourea is dissolved in an ethanol solution, and then an ethanol solution containing p-hydroxybenzaldehyde and acetic acid catalyst is slowly added dropwise to the ethanol solution of thiourea, heated to a certain temperature, and refluxed for a certain time to obtain an intermediate product. In step (1), the mass ratio of thiourea to ethanol is 1:20, and the mass ratio of p-hydroxybenzaldehyde to ethanol is 1:10. Theoretically, the amino group of one mole of thiourea can react with the aldehyde group of two moles of p-hydroxybenzaldehyde to generate a Schiff base structure. A slight excess of p-hydroxybenzaldehyde helps to promote the reaction; acetic acid is a catalyst, and terephthalaldehyde and thiourea are conducive to Schiff base reaction under acidic conditions. The amount of acetic acid is 1.5% of the mass of p-hydroxybenzaldehyde; the reaction temperature is 95°C, and the boiling point of ethanol is 78.3°C. Under the set temperature conditions, the ethanol solvent boils and reacts for 6 hours under reflux conditions; after the reaction liquid is cooled, a yellow solid is precipitated, which is distilled under reduced pressure and washed with ethanol to obtain an intermediate product.

[0042] In step (1), the structure of the intermediate product is as follows:

[0043]

[0044] (2) The intermediate product and sodium bicarbonate are dispersed in tetrahydrofuran, and then a tetrahydrofuran solution containing diphenyl chlorophosphate is slowly added dropwise, heated to a certain temperature, refluxed for a certain time, and distilled under reduced pressure, and washed with distilled water and ethanol to obtain a phosphorus / nitrogen / sulfur Schiff base multifunctional modifier. The molar ratio of the intermediate product to diphenyl chlorophosphate is 1:2.3. Theoretically, each mole of the intermediate product reacts with two moles of diphenyl chlorophosphate. A slight excess of diphenyl chlorophosphate helps to promote the complete reaction. The molar ratio of diphenyl chlorophosphate to sodium bicarbonate is 1:2. Hydrochloric acid is produced during the reaction of the intermediate product and diphenyl chlorophosphate. Sodium bicarbonate can neutralize the hydrochloric acid. An excess of sodium bicarbonate helps to promote the reaction. The mass ratio of the intermediate product to tetrahydrofuran is 1:25, and the mass ratio of diphenyl chlorophosphate to tetrahydrofuran is 1:20. The reaction temperature is 85°C, and the boiling point of tetrahydrofuran is 66°C. Under the set temperature conditions, the tetrahydrofuran solvent boils and reacts under reflux conditions for 8 hours. The phosphorus / nitrogen / sulfur Schiff base multifunctional modifier prepared in this step (2) has a yield of 60%. The molecular structure of the phosphorus / nitrogen / sulfur Schiff base multifunctional modifier is as follows (2):

[0045]

[0046] (3) Then, the phosphorus / nitrogen / sulfur Schiff base multifunctional modifier is dried to obtain phosphorus / nitrogen / sulfur Schiff base multifunctional modifier powder, and the polyester powder is dried to obtain polyester dry powder; the obtained phosphorus / nitrogen / sulfur Schiff base multifunctional modifier powder and polyester dry powder are mixed to obtain a mixture; the mixture is passed through a screw extruder to prepare a flame-retardant, anti-melting, antibacterial and multifunctional polyester masterbatch, and then a flame-retardant, anti-melting, antibacterial and multifunctional polyester film is obtained by casting, biaxial stretching, and heat setting. In step (3), the drying temperature of the polyester powder is 150°C and the time is 4 hours; the drying temperature of the phosphorus / nitrogen / sulfur Schiff base multifunctional modifier is 70°C and the drying time is 6 hours, ensuring that the final moisture content of the polyester powder and the multifunctional modifier is less than 100 ppm. The processing temperature of the twin-screw extruder is 260°C, the stretching temperature is 120°C, and the setting temperature is 220°C. If the processing temperature is too low, the flame retardant and the polyester powder cannot be mixed evenly, which is not conducive to granulation. If the temperature is too high, energy will be wasted. The temperature range provided by the present invention can smoothly prepare uniform flame retardant polyester masterbatch. In the mixed powder, the amount of the phosphorus / nitrogen / sulfur Schiff base multifunctional modifier powder is 5%.

[0047] Example 3

[0048] (1) First, thiourea is dissolved in an ethanol solution, and then an ethanol solution containing p-hydroxybenzaldehyde and acetic acid catalyst is slowly added dropwise to the ethanol solution of thiourea, heated to a certain temperature, and refluxed for a certain time to obtain an intermediate product. In step (1), the mass ratio of thiourea to ethanol is 1:15, and the mass ratio of p-hydroxybenzaldehyde to ethanol is 1:15. Theoretically, the amino group of one mole of thiourea can react with the aldehyde group of two moles of p-hydroxybenzaldehyde to generate a Schiff base structure. The p-hydroxybenzaldehyde is slightly excessive, which helps to promote the reaction; acetic acid is a catalyst, and terephthalaldehyde and thiourea are conducive to Schiff base reaction under acidic conditions. The amount of acetic acid is 1.2% of the mass of p-hydroxybenzaldehyde; the reaction temperature is 90°C, and the boiling point of ethanol is 78.3°C. Under the set temperature conditions, the ethanol solvent boils and reacts under reflux conditions for 5 hours; after the reaction liquid is cooled, a yellow solid is precipitated, which is distilled under reduced pressure and washed with ethanol to obtain an intermediate product.

[0049] In step (1), the structure of the intermediate product is as follows:

[0050]

[0051] (2) The intermediate product and sodium bicarbonate are dispersed in tetrahydrofuran, and then a tetrahydrofuran solution containing diphenyl chlorophosphate is slowly added dropwise, heated to a certain temperature, refluxed for a certain time, and distilled under reduced pressure, and washed with distilled water and ethanol to obtain a phosphorus / nitrogen / sulfur Schiff base multifunctional modifier. The molar ratio of the intermediate product to diphenyl chlorophosphate is 1:2.2. Theoretically, each mole of the intermediate product reacts with two moles of diphenyl chlorophosphate. A slight excess of diphenyl chlorophosphate helps to promote the complete reaction. The molar ratio of diphenyl chlorophosphate to sodium bicarbonate is 1:1.6. Hydrochloric acid is produced during the reaction of the intermediate product and diphenyl chlorophosphate. Sodium bicarbonate can neutralize the hydrochloric acid. An excess of sodium bicarbonate helps to promote the reaction. The mass ratio of the intermediate product to tetrahydrofuran is 1:20, and the mass ratio of diphenyl chlorophosphate to tetrahydrofuran is 1:15. The reaction temperature is 80°C, and the boiling point of tetrahydrofuran is 66°C. Under the set temperature conditions, the tetrahydrofuran solvent boils and reacts under reflux conditions for 6 hours. The phosphorus / nitrogen / sulfur Schiff base multifunctional modifier prepared in this step (2) has a yield of 66%. The molecular structure of the phosphorus / nitrogen / sulfur Schiff base multifunctional modifier is as follows (2):

[0052]

[0053] (3) Then, the phosphorus / nitrogen / sulfur Schiff base multifunctional modifier is dried to obtain phosphorus / nitrogen / sulfur Schiff base multifunctional modifier powder, and the polyester powder is dried to obtain polyester dry powder; the obtained phosphorus / nitrogen / sulfur Schiff base multifunctional modifier powder and polyester dry powder are mixed to obtain a mixture; the mixture is passed through a screw extruder to prepare a flame-retardant, anti-melting, antibacterial and multifunctional polyester masterbatch, and then a flame-retardant, anti-melting, antibacterial and multifunctional polyester film is obtained by casting, biaxial stretching, and heat setting. In step (3), the drying temperature of the polyester powder is 160°C and the time is 3 hours; the drying temperature of the phosphorus / nitrogen / sulfur Schiff base multifunctional modifier is 80°C and the drying time is 7 hours, ensuring that the final moisture content of the polyester powder and the multifunctional modifier is less than 100 ppm. The processing temperature of the twin-screw extruder is 280°C, the stretching temperature is 130°C, and the setting temperature is 250°C. If the processing temperature is too low, the flame retardant and the polyester powder cannot be mixed evenly, which is not conducive to granulation. If the temperature is too high, energy will be wasted. The temperature range provided by the present invention can smoothly prepare uniform flame retardant polyester masterbatch. In the mixed powder, the amount of the phosphorus / nitrogen / sulfur Schiff base multifunctional modifier powder is 6%.

[0054] Example 4

[0055] (1) First, thiourea is dissolved in an ethanol solution, and then an ethanol solution containing p-hydroxybenzaldehyde and acetic acid catalyst is slowly added dropwise to the ethanol solution of thiourea, heated to a certain temperature, and refluxed for a certain time to obtain an intermediate product. In step (1), the mass ratio of thiourea to ethanol is 1:18, and the mass ratio of p-hydroxybenzaldehyde to ethanol is 1:18. Theoretically, the amino group of one mole of thiourea can react with the aldehyde group of two moles of p-hydroxybenzaldehyde to generate a Schiff base structure. A slight excess of p-hydroxybenzaldehyde helps to promote the reaction; acetic acid is a catalyst, and terephthalaldehyde and thiourea are conducive to Schiff base reaction under acidic conditions. The amount of acetic acid is 1.3% of the mass of p-hydroxybenzaldehyde; the reaction temperature is 85°C, and the boiling point of ethanol is 78.3°C. Under the set temperature conditions, the ethanol solvent boils and reacts under reflux conditions for 4.5 hours; after the reaction liquid is cooled, a yellow solid is precipitated, which is distilled under reduced pressure and washed with ethanol to obtain an intermediate product.

[0056] In step (1), the structure of the intermediate product is as follows:

[0057]

[0058] (2) The intermediate product and sodium bicarbonate are dispersed in tetrahydrofuran, and then a tetrahydrofuran solution containing diphenyl chlorophosphate is slowly added dropwise, heated to a certain temperature, refluxed for a certain time, and distilled under reduced pressure, and washed with distilled water and ethanol to obtain a phosphorus / nitrogen / sulfur Schiff base multifunctional modifier. The molar ratio of the intermediate product to diphenyl chlorophosphate is 1:2.1. Theoretically, each mole of the intermediate product reacts with two moles of diphenyl chlorophosphate. A slight excess of diphenyl chlorophosphate helps to promote the complete reaction. The molar ratio of diphenyl chlorophosphate to sodium bicarbonate is 1:1.8. Hydrochloric acid is produced during the reaction of the intermediate product and diphenyl chlorophosphate. Sodium bicarbonate can neutralize the hydrochloric acid. An excess of sodium bicarbonate helps to promote the reaction. The mass ratio of the intermediate product to tetrahydrofuran is 1:22, and the mass ratio of diphenyl chlorophosphate to tetrahydrofuran is 1:18. The reaction temperature is 80°C, and the boiling point of tetrahydrofuran is 66°C. Under the set temperature conditions, the tetrahydrofuran solvent boils and reacts for 7 hours under reflux conditions. The phosphorus / nitrogen / sulfur Schiff base multifunctional modifier prepared in this step (2) has a yield of 65%. The molecular structure of the phosphorus / nitrogen / sulfur Schiff base multifunctional modifier is as follows (2):

[0059]

[0060] (3) Then, the phosphorus / nitrogen / sulfur Schiff base multifunctional modifier is dried to obtain phosphorus / nitrogen / sulfur Schiff base multifunctional modifier powder, and the polyester powder is dried to obtain polyester dry powder; the obtained phosphorus / nitrogen / sulfur Schiff base multifunctional modifier powder and polyester dry powder are mixed to obtain a mixture; the mixture is passed through a screw extruder to prepare a flame-retardant, anti-melting, antibacterial and multifunctional polyester masterbatch, and then a flame-retardant, anti-melting, antibacterial and multifunctional polyester film is obtained by casting, biaxial stretching and heat setting. In step (3), the drying temperature of the polyester powder is 155°C and the time is 2.5h; the drying temperature of the phosphorus / nitrogen / sulfur Schiff base multifunctional modifier is 85°C and the drying time is 5.5h, ensuring that the final moisture content of the polyester powder and the multifunctional modifier is less than 100ppm. The processing temperature of the twin-screw extruder is 250°C, the stretching temperature is 140°C, and the setting temperature is 240°C. If the processing temperature is too low, the flame retardant and the polyester powder cannot be mixed evenly, which is not conducive to granulation. If the temperature is too high, energy will be wasted. The temperature range provided by the present invention can smoothly prepare uniform flame retardant polyester masterbatch. In the mixed powder, the amount of the phosphorus / nitrogen / sulfur Schiff base multifunctional modifier powder is 4%.

[0061] The thickness of the flame-retardant, anti-drip, antibacterial and multifunctional polyester film prepared by the embodiment of the present invention is 100-200 μm.

[0062] The multifunctional nylon 6 film prepared in Example 1 was subjected to combustion, tensile and antibacterial tests, and the test standards used were:

[0063] Vertical combustion: refer to GB / T 2408-2021 standard.

[0064] Limiting oxygen index: Tested in accordance with GB / T 2406-2009 standard.

[0065] Tensile strength: tested according to GB / T 1040.3-2018 standard, clamping length is 150mm, tensile speed is 100mm / min.

[0066] Antibacterial rate test: Refer to GB / T 20944.3-2008 "Evaluation of antibacterial properties of textiles Part 3: Oscillation method" to test the antibacterial rate of modified polyester film against Escherichia coli and Staphylococcus aureus.

[0067] The above test standards were used for testing. The indicators of the modified polyester films prepared in various embodiments of the present invention are shown in Table 1.

[0068]

[0069] It can be seen from Table 1 that the LOI of the flame retardant, anti-drip and antibacterial multifunctional modified polyester film in Example 1 is not less than 29.5%, and the flame retardant grade is V-0 (the LOI of the unmodified polyester film is 21.3%, and the flame retardant grade is V-2), the antibacterial rate of the multifunctional polyester film against Escherichia coli and Staphylococcus aureus is 91.3~99.9%, and the tensile strength of the multifunctional polyester film is 183~198MPa (the tensile strength of the unmodified polyester film is 215MPa), indicating that the multifunctional modified polyester film has excellent flame retardant and anti-drip properties and antibacterial properties.

[0070] See also Figure 1 , Figure 1 This is the infrared spectrum of the phosphorus / nitrogen / sulfur Schiff base multifunctional modifier prepared in Example 1 of the present invention. Figure 1 As shown, 3423 and 3187cm -1 The absorption peaks at 1687, 1654 and 1589 cm are caused by the stretching vibration of aromatic CH and thiourea NH. -1 The absorption peaks at 1489 and 1401 cm are caused by the stretching vibrations of C=O, C=S and Schiff base C=N structures. -1 The absorption peak at 1161cm is caused by the bending vibration of aromatic CH. -1 The absorption peaks at 1294, 1187, 1011, 968 cm are caused by the stretching vibration of the CN structure. -1 The absorption peaks at are caused by the stretching vibrations of structures such as OPO, P=O, PO and POC. The above results indicate that the multifunctional modifier containing phosphorus / nitrogen / sulfur Schiff base is successfully synthesized.

[0071] See also Figure 2 , Figure 2 1 is the heat release rate curve of the unmodified multifunctional modified polyester film and the multifunctional modified polyester film prepared in Example 1 of the present invention after microcalorimetry test. Figure 2 As shown, the peak heat release of the unmodified polyester film is higher, reaching 488 W / g, indicating that it has a high fire hazard; while the peak heat release of the modified polyester film is reduced to 297 W / g, indicating that its fire safety is significantly improved.

[0072] The present invention generates an intermediate product by a Schiff base condensation reaction between the aldehyde group of p-hydroxybenzaldehyde and the amino group of thiourea under acidic conditions, and then the hydroxyl group of the intermediate product reacts with diphenyl chlorophosphate to generate a phosphorus / nitrogen / sulfur Schiff base multifunctional modifier. The thiourea structure in the multifunctional modifier molecule generates sulfur-containing free radicals during the heating process to capture combustible free radicals, and the Schiff base structure decomposes to generate non-flammable nitrogen-containing gas to dilute the free radical and oxygen concentration. In addition, the aromatic phosphorus-containing flame retardant group generates a phosphorus-containing carbon layer with high thermal stability during the thermal decomposition process, which helps to protect the underlying matrix, thereby achieving an excellent flame retardant effect. Therefore, the aromatic phosphorus-containing group, the sulfur-containing group, the nitrogen-containing group, etc. improve the flame retardant and anti-melting droplet performance of the modified polyester film through a synergistic flame retardant effect. In addition, the Schiff base structure has excellent biological activity, and the multifunctional modified polyester film has good antibacterial properties. The multifunctional modified polyester film has good antibacterial properties. The phosphorus / nitrogen / sulfur Schiff base multifunctional modifier is rich in aromatic groups and has high compatibility with polyester. Therefore, the addition of the phosphorus / nitrogen / sulfur Schiff base multifunctional modifier has little effect on the mechanical properties of the polyester film.

[0073] It should be noted that any changes made by those skilled in the art to the specific embodiments of the present invention do not deviate from the scope of the claims of the present invention. Accordingly, the scope of the claims of the present invention is not limited to the above specific embodiments.

Claims

1. A method for preparing a modified polyester film, characterized in that: It includes the following steps: S1. Dissolve thiourea in an ethanol solution, slowly drop an ethanol solution containing p-hydroxybenzaldehyde and acetic acid into the ethanol solution containing thiourea, and react at 85-95° C. for 4-6 hours to obtain an intermediate product, wherein the molar ratio of p-hydroxybenzaldehyde to thiourea is 2.1-2.3:1, and the structure of the intermediate product is formula (1): S2, dispersing the intermediate product obtained in step S1 and sodium bicarbonate in tetrahydrofuran, then dropwise adding a tetrahydrofuran solution containing diphenyl chlorophosphate, and reacting at a temperature of 75-85° C. for 5-8 hours to obtain a phosphorus / nitrogen / sulfur Schiff base multifunctional modifier, wherein the molar ratio of the intermediate product to diphenyl chlorophosphate is 1:2.1-2.3, and the structure of the phosphorus / nitrogen / sulfur Schiff base multifunctional modifier is formula (2): S3. The phosphorus / nitrogen / sulfur Schiff base multifunctional modifier is mixed with polyester, and a flame-retardant, anti-drip and antibacterial multifunctional polyester film is prepared by extrusion, casting, stretching and heat setting.

2. The method for preparing a modified polyester film according to claim 1, characterized in that: In step S1, the mass ratio of thiourea to ethanol is 1:10-20, the mass ratio of p-hydroxybenzaldehyde to ethanol is 1:10-20, and the mass of acetic acid is 1-1.5% of the mass of p-hydroxybenzaldehyde.

3. The method for preparing the modified polyester film according to claim 1, characterized in that: In step S2, the molar ratio of diphenyl chlorophosphate to sodium bicarbonate is 1:1.5-2, the mass ratio of the intermediate product to tetrahydrofuran is 1:15-25, and the mass ratio of diphenyl chlorophosphate to tetrahydrofuran is 1:10-20.

4. The method for preparing the modified polyester film according to claim 1, characterized in that: Step S3 specifically includes: S31, drying the phosphorus / nitrogen / sulfur Schiff base multifunctional modifier to obtain phosphorus / nitrogen / sulfur Schiff base multifunctional modifier powder, and drying the polyester powder to obtain polyester dry powder; S32, mixing the phosphorus / nitrogen / sulfur Schiff base multifunctional modifier powder obtained in step S31 with the polyester dry powder to obtain a mixture; S33, preparing modified polyester masterbatch from the mixture obtained in step S32 through a screw extruder, and preparing a flame-retardant, anti-drip, antibacterial and multifunctional polyester film by casting the modified polyester masterbatch into sheets, biaxially stretching the sheets, and heat-setting the sheets.

5. The method for preparing the modified polyester film according to claim 4, characterized in that: In step S31, the drying temperature of the polyester powder is 140-160°C for 2-4 hours; the drying temperature of the phosphorus / nitrogen / sulfur Schiff base multifunctional modifier is 70-90°C for 5-7 hours to ensure that the final moisture content of the polyester masterbatch and the multifunctional modifier is less than 100 ppm.

6. The method for preparing the modified polyester film according to claim 4, characterized in that: In step S32, the amount of the phosphorus / nitrogen / sulfur Schiff base multifunctional modifier powder in the mixed powder is 3-6%.

7. The method for preparing a modified polyester film according to claim 4, characterized in that: In step S33, the processing temperature of the twin-screw extruder is 240-280°C, the stretching temperature is 100-140°C, and the heat setting temperature is 200-250°C.

Images