PP / PE biaxially oriented synthetic paper and preparation method thereof

Abstract

The invention discloses PP / PE biaxially oriented synthetic paper and a preparation method thereof, and belongs to the technical field of synthetic paper. The synthetic paper consists of an outer surface layer, a middle layer and an inner surface layer, wherein the outer surface layer comprises the following raw materials in parts by weight: 30-50 parts of PP, 20-40 parts of PE, 3-5 parts of a modified flame-retardant anti-aging agent and 2-3 parts of calcium carbonate; the middle layer is prepared from the following raw materials in parts by weight: 20 to 40 parts of PP (Polypropylene), 30 to 50 parts of PE (Polyethylene), 3 to 5 parts of modified flame-retardant anti-aging agent and 2 to 3 parts of calcium carbonate; the inner surface layer and the outer surface layer are the same in raw material and part. The PP / PE biaxially oriented synthetic paper prepared by the invention has excellent mechanical property, anti-aging property and flame retardant property by adding the modified flame-retardant anti-aging agent.

Description

Technical Field

[0001] The present invention relates to the technical field of synthetic paper, and in particular to a PP / PE biaxially stretched synthetic paper and a preparation method thereof. Background Art

[0002] Synthetic paper is widely known as an environmentally friendly product as a material that replaces ordinary fiber papermaking. The base material of synthetic paper is polymer plastic, especially polyolefin resin such as polypropylene, polyethylene or a blend of the two. PP / PE synthetic paper has the characteristics of light weight, high strength, good printing, light shielding, durability, economy and environmental protection. PP / PE synthetic paper has been widely used in high-quality printing, high-end packaging and special uses because it has the characteristics of both plastic and paper. With the increase in the application scenarios of synthetic paper, such as easy breakage after long-term exposure to the outdoors, yellowing and fading, more requirements are put forward for PP / PE synthetic paper, such as higher flame retardancy and anti-aging properties.

[0003] A Chinese invention patent with publication number CN118061637A discloses a polyethylene-blended polypropylene biaxially stretched synthetic paper and a preparation method thereof. The synthetic paper comprises an outer layer, an intermediate layer and an inner layer. The outer layer comprises the following raw materials in parts by weight: 30-40 parts of polyethylene, 40-50 parts of polypropylene, 2-3 parts of modified N-isopropyl-N-'phenyl-p-phenylenediamine antioxidant, 1-2 parts of calcium stearate, 1-2 parts of calcium carbonate, and 0.8-1.5 parts of nano titanium dioxide; the intermediate layer comprises the following raw materials in parts by weight: 20-25 parts of polyethylene, 40-50 parts of polypropylene, and 1-2 parts of calcium carbonate. The synthetic paper has excellent mechanical properties, but its flame retardant performance is poor. Summary of the invention

[0004] In view of the deficiencies in the prior art, an object of the present invention is to provide a PP / PE biaxially oriented synthetic paper and a preparation method thereof.

[0005] To achieve the above object, the present invention is implemented through the following technical solutions: A PP / PE biaxially stretched synthetic paper, consisting of an outer layer, an intermediate layer and an inner layer, wherein the outer layer comprises the following raw materials in parts by weight: PP: 30-50 parts, PE: 20-40 parts, modified flame retardant antioxidant: 3-5 parts, calcium carbonate: 2-3 parts; The middle layer comprises the following raw materials in parts by weight: PP: 20-40 parts, PE: 30-50 parts, modified flame retardant antioxidant: 3-5 parts, calcium carbonate 2-3 parts; The material and number of the inner surface layer are the same as those of the outer surface layer; The modified flame retardant antioxidant is prepared by the following method: S1: Hexamethylenetetramine reacts with p-aminophenol under the action of glacial acetic acid as a catalyst to obtain a brown polymer. The reaction equation is as follows:

[0006] S2: Under nitrogen protection, DMSO, brown polymer, and anhydrous potassium carbonate were added to the reactor in sequence, stirred and dissolved, and the temperature was raised to 50-60°C. Then, N,N'-((6-chloro-1,3,5-triazine-2,4-diyl)bis(methylene))bis(N-butyl-2,2,6,6-tetramethylpiperidin-4-amine) was added, and the reaction was continued for 8-10 hours. After cooling, ice water was added to precipitate, filtered, and recrystallized three times with petroleum ether to obtain intermediate 1. The reaction equation is shown as follows:

[0007] S3: Under nitrogen protection, DMF, intermediate 1, [(6-oxo-6H-dibenzo[C,E][1,2]oxaphosphorin-6-yl)methyl]succinic acid are added to the reactor, heated in an oil bath to 120-130°C, and then pyridinepropylsulfonic acid ionic liquid is added, refluxed for 4-6h, and vacuum distilled and dried to obtain a modified flame retardant antioxidant. The reaction equation is as follows:

[0008] Among them, m, r, s, o, and p are natural numbers, m=r+s, s=o+p.

[0009] The mass ratio of the DMSO, brown polymer, N,N'-((6-chloro-1,3,5-triazine-2,4-diyl)bis(methylene))bis(N-butyl-2,2,6,6-tetramethylpiperidin-4-amine), and anhydrous potassium carbonate is 30:(5-7):(10-15):(3-6).

[0010] The feed mass ratio of DMF, intermediate 1, [(6-oxo-6H-dibenzo[C,E][1,2]oxaphosphorin-6-yl)methyl]succinic acid, and pyridinepropylsulfonic acid ionic liquid is 20:(5-8):(5-10):(0.1-0.3).

[0011] A method for preparing PP / PE biaxially oriented synthetic paper comprises the following steps: S1: Extruding the outer layer raw material, the middle layer raw material and the inner layer raw material through an extruder respectively; S2: extruding each layer of raw materials extruded by the extruder through a T-type die, and then longitudinally stretching and transversely stretching, followed by cooling, corona treatment, and trimming; Among them, the extrusion temperature of the outer layer raw material and the inner layer raw material is 230°C, and the extrusion temperature of the middle layer raw material is 250°C; the preheating section temperature of longitudinal stretching is 130°C, the stretching section temperature is 142°C, the shaping section temperature is 145°C, the longitudinal stretching ratio is 4.9, the preheating section temperature of transverse stretching is 167°C, the stretching section temperature is 155°C, the shaping section temperature is 171°C, the transverse stretching ratio is 9 times, and the corona is 34.

[0012] Due to the adoption of the above technical solution, the beneficial effects of the present invention include: The invention prepares a brown polymer by using urotropine and p-aminophenol, then the brown polymer is subjected to a grafting reaction with N,N'-((6-chloro-1,3,5-triazine-2,4-diyl)bis(methylene))bis(N-butyl-2,2,6,6-tetramethylpiperidin-4-amine) to obtain an intermediate 1, and finally [(6-oxo-6H-dibenzo[C,E][1,2]oxaphosphorin-6-yl)methyl]succinic acid is grafted onto the intermediate 1 to obtain a modified flame retardant and antioxidant.

[0013] The substrate N,N'-((6-chloro-1,3,5-triazine-2,4-diyl)bis(methylene))bis(N-butyl-2,2,6,6-tetramethylpiperidin-4-amine) used in the modified flame retardant and antioxidant prepared by the present invention contains a piperidine group, but due to its small molecular weight, it is not resistant to migration. By grafting it with a brown polymer, the molecular weight is increased. Under the irradiation of ultraviolet rays, the piperidine amine group is first converted into a stable nitroxide free radical, and then captures the active free radical generated in the polymer, the chain reaction is terminated, and after the generated free radical is captured, the generated ester and peroxyester compounds continue to combine with the free radical generated in the polymer material, and finally generate nitroxide free radicals. This cycle is repeated, and the chain reaction is effectively cut off for a long time, thereby achieving an anti-aging effect.

[0014] The [(6-oxo-6H-dibenzo[C,E][1,2]oxaphosphorin-6-yl)methyl]succinic acid used in the modified flame retardant and antioxidant prepared by the invention contains phosphorus element and is decomposed into polymetaphosphoric acid and orthophosphoric acid by heat during combustion. The polymetaphosphoric acid and orthophosphoric acid are not easy to volatilize and can form a protective film on the surface of PP / PE material to prevent the material from continuing to burn. The polymetaphosphoric acid has strong hygroscopicity and can promote the material to form a carbon layer of a certain thickness during combustion. Moreover, the phosphorus-containing flame retardant can capture free radicals to terminate the combustion reaction, thereby playing a good flame retardant role. DETAILED DESCRIPTION

[0015] The invention will be further described below in conjunction with the embodiments, but the invention is not limited to these embodiments.

[0016] Example 1 Preparation of N,N'-((6-chloro-1,3,5-triazine-2,4-diyl)bis(methylene))bis(N-butyl-2,2,6,6-tetramethylpiperidin-4-amine): Dissolve 18.44g of cyanuric chloride in 200mL of toluene, slowly add 42.42g of N-n-butyl-2,2,6,6-tetramethyl-4-piperidinamine in an ice-water bath, and react for 2h; then drop 20mL of 40wt% sodium hydroxide solution for 5min, and heat to 70℃ to continue reacting for 14h. After the reaction, add deionized water and ethyl acetate for extraction 3 times (200mL of deionized water and 100mL of ethyl acetate are used each time), then dry with anhydrous sodium sulfate for 2h, rotary evaporate at 50℃ for 3h, and vacuum dry at 70℃ for 5h to obtain N,N'-((6-chloro-1,3,5-triazine-2,4-diyl)bis(methylene))bis(N-butyl-2,2,6,6-tetramethylpiperidin-4-amine), and the reaction equation is as follows:

[0017] Example 2 Preparation of modified flame retardant antioxidant: S1: 1 kg of deionized water, 0.25 kg of urotropine, 0.1 kg of p-aminophenol, and 0.08 kg of glacial acetic acid were added to a reactor in sequence, stirred and dissolved, heated to 75°C, reacted for 3 h, cooled to room temperature, separated, and washed with deionized water for 3 times (200 g of deionized water each time) to obtain a brown polymer; S2: Under nitrogen protection, 3 kg DMSO, 0.5 kg brown polymer, and 0.3 kg anhydrous potassium carbonate were added to the reactor in sequence, stirred and dissolved, and the temperature was raised to 50°C. Then, 1 kg N,N'-((6-chloro-1,3,5-triazine-2,4-diyl)bis(methylene))bis(N-butyl-2,2,6,6-tetramethylpiperidin-4-amine) was added, and the reaction was continued for 10 h. After cooling, 2 kg ice water was added for precipitation, filtered, and recrystallized with petroleum ether three times (1 kg of petroleum ether was used each time) to obtain intermediate 1; S3: Under nitrogen protection, 2kgDMF, 0.5kg intermediate 1 and 0.5kg [(6-oxo-6H-dibenzo[C,E][1,2]oxaphosphorin-6-yl)methyl]succinic acid were added into the reactor and heated in an oil bath to 120°C. Then, 0.01kg pyridinepropylsulfonic acid ionic liquid was added, and the reaction was refluxed for 6h. The reaction was carried out under reduced pressure distillation at 60°C for 5h and vacuum dried at 80°C for 4h to obtain the modified flame retardant and antioxidant.

[0018] Example 3 Preparation of modified flame retardant antioxidant: S1: 1 kg of deionized water, 0.25 kg of urotropine, 0.1 kg of p-aminophenol, and 0.08 kg of glacial acetic acid were added to a reactor in sequence, stirred and dissolved, heated to 75°C, reacted for 3 h, cooled to room temperature, separated, and washed with deionized water for 3 times (200 g of deionized water each time) to obtain a brown polymer; S2: Under nitrogen protection, 3 kg DMSO, 0.6 kg brown polymer, and 0.5 kg anhydrous potassium carbonate were added to the reactor in sequence, stirred and dissolved, and the temperature was raised to 55°C. Then, 1.25 kg N, N'-((6-chloro-1,3,5-triazine-2,4-diyl)bis(methylene))bis(N-butyl-2,2,6,6-tetramethylpiperidin-4-amine) was added, and the reaction was carried out for 9 hours. After cooling, 2 kg ice water was added for precipitation, filtered, and recrystallized with petroleum ether three times (1 kg of petroleum ether was used each time) to obtain intermediate 1; S3: Under nitrogen protection, 2kgDMF, 0.65kg intermediate 1 and 0.8kg [(6-oxo-6H-dibenzo[C,E][1,2]oxaphosphorin-6-yl)methyl]succinic acid were added into the reactor and heated in an oil bath to 125°C. Then, 0.02kg pyridinepropylsulfonic acid ionic liquid was added and refluxed for 5h. The reaction was carried out under reduced pressure distillation at 70°C for 4h and vacuum dried at 90°C for 3h to obtain the modified flame retardant and antioxidant.

[0019] Example 4 Preparation of modified flame retardant antioxidant: S1: 1 kg of deionized water, 0.25 kg of urotropine, 0.1 kg of p-aminophenol, and 0.08 kg of glacial acetic acid were added to a reactor in sequence, stirred and dissolved, heated to 75°C, reacted for 3 h, cooled to room temperature, separated, and washed with deionized water for 3 times (200 g of deionized water each time) to obtain a brown polymer; S2: Under nitrogen protection, 3 kg DMSO, 0.7 kg brown polymer, and 0.6 kg anhydrous potassium carbonate were added to the reactor in sequence, stirred and dissolved, and the temperature was raised to 60°C. Then, 1.5 kg N,N'-((6-chloro-1,3,5-triazine-2,4-diyl)bis(methylene))bis(N-butyl-2,2,6,6-tetramethylpiperidin-4-amine) was added, and the reaction was carried out for 8 hours. After cooling, 2 kg ice water was added for precipitation, filtered, and recrystallized with petroleum ether three times (1 kg of petroleum ether was used each time) to obtain intermediate 1; S3: Under nitrogen protection, 2kgDMF, 0.8kg intermediate 1 and 1.0kg [(6-oxo-6H-dibenzo[C,E][1,2]oxaphosphorin-6-yl)methyl]succinic acid were added into the reactor, heated in an oil bath to 130°C, and then 0.03kg pyridinepropylsulfonic acid ionic liquid was added, refluxed for 4h, distilled at 80°C under reduced pressure for 3h, and vacuum dried at 100°C for 2h to obtain a modified flame retardant and antioxidant.

[0020] Example 5 A PP / PE biaxially stretched synthetic paper has a thickness of 0.20 mm, an outer layer and an inner layer having a thickness of 0.06 mm, and a middle layer having a thickness of 0.08 mm; the outer layer is made of 3000 g PP, 2000 g PE, 300 g modified flame retardant and antioxidant (prepared in Example 2), and 200 g calcium carbonate; the middle layer is made of 2000 g PP, 3000 g PE, 300 g modified flame retardant and antioxidant (prepared in Example 2), and 200 g calcium carbonate; the inner layer has the same raw materials and proportions as the outer layer.

[0021] Example 6 A PP / PE biaxially stretched synthetic paper has a thickness of 0.20 mm, an outer layer and an inner layer having a thickness of 0.06 mm, and a middle layer having a thickness of 0.08 mm; the outer layer is made of 4000 g PP, 3000 g PE, 400 g modified flame retardant and antioxidant (prepared in Example 3), and 250 g calcium carbonate; the middle layer is made of 3000 g PP, 4000 g PE, 400 g modified flame retardant and antioxidant (prepared in Example 3), and 250 g calcium carbonate; the inner layer has the same raw materials and proportions as the outer layer.

[0022] Example 7 A PP / PE biaxially stretched synthetic paper has a thickness of 0.20 mm, an outer layer and an inner layer having a thickness of 0.06 mm, and a middle layer having a thickness of 0.08 mm; the outer layer is made of 5000 g PP, 4000 g PE, 500 g modified flame retardant and antioxidant (prepared in Example 4), and 300 g calcium carbonate; the middle layer is made of 4000 g PP, 5000 g PE, 500 g modified flame retardant and antioxidant (prepared in Example 4), and 300 g calcium carbonate; the inner layer has the same raw materials and proportions as the outer layer.

[0023] Comparative Example 1 A PP / PE biaxially oriented synthetic paper is basically the same as Example 6, except that no modified flame retardant and antioxidant are added to the outer layer and the inner layer.

[0024] Comparative Example 2 A PP / PE biaxially oriented synthetic paper is basically the same as Example 6, except that the modified flame retardant and antioxidant added to the outer layer and the inner layer are replaced by an equal weight of the intermediate 1 prepared in step S2 of Example 3.

[0025] Comparative Example 3 A PP / PE biaxially oriented synthetic paper is basically the same as Example 6, except that the modified flame retardant and antioxidant added to the outer layer and the inner layer are replaced by an equal weight of [(6-oxo-6H-dibenzo[C,E][1,2]oxaphosphorin-6-yl)methyl]succinic acid.

[0026] Comparative Example 4 A PP / PE biaxially oriented synthetic paper is basically the same as Example 6, except that the modified flame retardant and antioxidant added to the outer layer and the inner layer are replaced by 180 g of the intermediate 1 prepared in step S2 of Example 3 and 220 g of [(6-oxo-6H-dibenzo[C,E][1,2]oxaphosphorin-6-yl)methyl]succinic acid.

[0027] Comparative Example 5 A PP / PE biaxially oriented synthetic paper is basically the same as Example 6, except that the modified flame retardant and antioxidant added to the outer layer and the inner layer are replaced by an antioxidant of equal weight prepared in Example 2 of Chinese invention patent with publication number CN118438763A.

[0028] Comparative Example 6 A PP / PE biaxially stretched synthetic paper, wherein the raw materials and proportions of the outer layer, the middle layer and the inner layer are the raw materials and proportions of Example 3 of the Chinese invention patent with publication number CN118061637A.

[0029] The PP / PE biaxially oriented synthetic papers of Examples 5-7 and Comparative Examples 1-6 were prepared by the following process: S1: Extruding the outer layer raw material, the middle layer raw material and the inner layer raw material through an extruder respectively; S2: extruding each layer of raw materials extruded by the extruder through a T-type die, and then longitudinally stretching and transversely stretching, followed by cooling, corona treatment, and trimming; Among them, the extrusion temperature of the outer layer raw material and the inner layer raw material is 230°C, and the extrusion temperature of the middle layer raw material is 250°C; the preheating section temperature of longitudinal stretching is 130°C, the stretching section temperature is 142°C, the shaping section temperature is 145°C, the longitudinal stretching ratio is 4.9, the preheating section temperature of transverse stretching is 167°C, the stretching section temperature is 155°C, the shaping section temperature is 171°C, the transverse stretching ratio is 9 times, and the corona is 34.

[0030] The PP used in the examples and comparative examples of the present application is CJS-700 homopolypropylene produced by Sinopec, and the PE grade is Yangzi Petrochemical 5000S.

[0031] The specific preparation method of the pyridinepropyl sulfonic acid ionic liquid used in the examples and comparative examples of the present application is as follows: Pyridine and an equal molar amount of propyl sultone were mixed in a three-necked flask, refluxed at 40°C for 2 hours to obtain a white solid, and vacuum dried at 80°C to obtain a zwitterion; the obtained zwitterion and an equal molar amount of H2SO4 were added to a three-necked flask, reacted at 50°C for 3 hours, and vacuum dried at 70°C to obtain a pyridinepropyl sulfonic acid ionic liquid.

[0032] The PP / PE biaxially oriented synthetic papers prepared in Examples 5-7 and Comparative Examples 1-6 were subjected to UV aging tests, and the test method was carried out in accordance with the method of GB / T16422.3-2014 "Plastic Laboratory Light Source Exposure Test Method".

[0033] The tensile strength of the PP / PE biaxially oriented synthetic paper prepared in Examples 5-7 and Comparative Examples 1-6 and the aged PP / PE biaxially oriented synthetic paper were tested according to the method of GB13022-91; the test results of Examples 5-7 of the present application are shown in Table 1.

[0034] The PP / PE biaxially oriented synthetic paper prepared in Examples 5-7 and Comparative Examples 1-6 and the aged synthetic paper were subjected to a vertical burning (UL-94) test. According to the ASTM D3801 standard, the vertical burning grade of the sample was evaluated using a CZF-3 instrument. The sample size was 130×13×3.2 mm. 3 (Its thickness is achieved by stacking layers of synthetic paper). The test results are shown in Table 1.

[0035] Table 1

[0036] It can be seen from Examples 5, 6 and 7 in Table 1 that the PP / PE biaxially oriented synthetic paper prepared by the present invention has transverse and longitudinal mechanical strengths greater than 105 MPa and 85 MPa, respectively, and the transverse and longitudinal mechanical strengths after aging are greater than 92 MPa and 75 MPa, respectively, and has excellent transverse and longitudinal mechanical properties, and the flame retardant grade remains at V-0 level after aging.

[0037] Comparative Example 1 is a comparative example in which no modified flame retardant and antioxidant is added. After aging, its transverse mechanical strength is 70 MPa, its longitudinal tensile strength is 56 MPa, and its flammability rating (UL-94) after aging is V-2.

[0038] Comparative Example 2 is different from Example 6, and the difference is that the modified flame retardant and antioxidant is replaced by the intermediate 1 prepared in step S2 of Example 3. After aging, the transverse mechanical strength is 79 MPa, the longitudinal tensile strength is 68 MPa, and the combustion grade (UL-94) after aging is V-2.

[0039] Comparative Example 3 is different from Example 6, and the difference is that the modified flame retardant and antioxidant is replaced by [(6-oxo-6H-dibenzo[C,E][1,2]oxaphosphorin-6-yl)methyl]succinic acid. It can be seen from the data in Table 1 that after aging, the transverse tensile strength is 71 MPa, the longitudinal tensile strength is 61 MPa, the mechanical strength loss is serious, and the combustion grade (UL-94) after aging is V-1.

[0040] Comparative Example 4 is different from Example 6, except that the modified UV inhibitor replaces 200 g of the intermediate 1 prepared in step S2 of Example 3, 200 g of [(6-oxo-6H-dibenzo[C,E][1,2]oxaphosphorin-6-yl)methyl]succinic acid, and the transverse mechanical strength after aging is 80 MPa, the longitudinal tensile strength is 68 MPa, and the flammability grade (UL-94) after aging is V-1.

[0041] Comparative Example 5 uses the antioxidant prepared in Example 2 of the Chinese invention patent with publication number CN118438763A. Its transverse tensile strength after aging is 80 MPa, its longitudinal tensile strength is lower than 69 MPa, and its combustion grade (UL-94) after aging is V-2.

[0042] Comparative Example 6 uses the raw materials and proportions in Example 3 of the Chinese invention patent with publication number CN118061637A to prepare synthetic paper. Its transverse tensile strength after aging is 90 MPa, its longitudinal tensile strength is lower than 77 MPa, and its flammability rating (UL-94) after aging is V-2.

[0043] In summary, it can be seen from the data of the comparative examples and embodiments in Table 1 that the PP / PE biaxially oriented synthetic paper prepared by the present invention has excellent transverse and longitudinal mechanical properties, still maintains relatively good mechanical properties after aging, and has excellent flame retardant properties.

[0044] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. However, any equivalent changes, modifications and evolutions made by ordinary technicians in the field without departing from the scope of the technical solution of the present invention by using the technical content disclosed above are all equivalent embodiments of the present invention. At the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the technical solution of the present invention.

Claims

1. A PP / PE biaxially oriented synthetic paper, consisting of an outer layer, an intermediate layer and an inner layer. It is characterized in that The outer layer comprises the following raw materials in parts by weight: PP: 30-50 parts, PE: 20-40 parts, modified flame retardant antioxidant: 3-5 parts, calcium carbonate: 2-3 parts; The middle layer comprises the following raw materials in parts by weight: PP: 20-40 parts, PE: 30-50 parts, modified flame retardant antioxidant: 3-5 parts, calcium carbonate 2-3 parts; The material and number of the inner surface layer are the same as those of the outer surface layer; The modified flame retardant antioxidant is prepared by the following method: S1: Hexamethylenetetramine reacts with p-aminophenol in the presence of glacial acetic acid as a catalyst to obtain a brown polymer; S2: Under nitrogen protection, DMSO, brown polymer, and anhydrous potassium carbonate were added to the reactor in sequence, stirred and dissolved, and the temperature was raised to 50-60°C, and then N,N'-((6-chloro-1,3,5-triazine-2,4-diyl)bis(methylene))bis(N-butyl-2,2,6,6-tetramethylpiperidin-4-amine) was added, and the reaction was carried out for 8-10 hours. After cooling, ice water was added to precipitate, filtered, and recrystallized three times with petroleum ether to obtain intermediate 1; S3: Under nitrogen protection, DMF, intermediate 1, [(6-oxo-6H-dibenzo[C,E][1,2]oxaphosphorin-6-yl)methyl]succinic acid are added to the reactor, heated to 120-130°C, and then pyridinepropylsulfonic acid ionic liquid is added, refluxed for 4-6 hours, and vacuum distilled and dried to obtain the modified flame retardant antioxidant.

2. The PP / PE biaxially oriented synthetic paper according to claim 1, It is characterized in that The mass ratio of DMSO, brown polymer, N,N'-((6-chloro-1,3,5-triazine-2,4-diyl)bis(methylene))bis(N-butyl-2,2,6,6-tetramethylpiperidin-4-amine), and anhydrous potassium carbonate in step S2 is 30:(5-7):(10-15):(3-6).

3. The PP / PE biaxially oriented synthetic paper according to claim 1, It is characterized in that The mass ratio of DMF, intermediate 1, [(6-oxo-6H-dibenzo[C,E][1,2]oxaphosphorin-6-yl)methyl]butanedioic acid, and pyridinepropylsulfonic acid ionic liquid in step S3 is 20:(5-8):(5-10):(0.1-0.3).

4. A method for preparing the PP / PE biaxially oriented synthetic paper according to any one of claims 1 to 3, It is characterized in that The following steps are involved: S1: Extruding the outer layer raw material, the middle layer raw material and the inner layer raw material through an extruder respectively; S2: extruding each layer of raw materials extruded by the extruder through a T-type die, and then longitudinally stretching and transversely stretching, followed by cooling, corona treatment, and trimming; Among them, the extrusion temperature of the outer layer raw material and the inner layer raw material is 230°C, and the extrusion temperature of the middle layer raw material is 250°C; the preheating section temperature of longitudinal stretching is 130°C, the stretching section temperature is 142°C, the shaping section temperature is 145°C, the longitudinal stretching ratio is 4.9, the preheating section temperature of transverse stretching is 167°C, the stretching section temperature is 155°C, the shaping section temperature is 171°C, the transverse stretching ratio is 9 times, and the corona is 34.

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