Process for the production of biaxially oriented polypropylene film

Abstract

This invention relates to the field of polypropylene film technology and discloses a preparation process for biaxially oriented polypropylene film. The invention involves melting, extruding, and water-cooling polypropylene resin and polymer-loaded silver nanoparticles in an extrusion casting machine, followed by transverse and longitudinal stretching, heat setting, and winding in a biaxial tensile testing machine to obtain a biaxially oriented polypropylene film. The polymer-loaded silver nanoparticles exhibit good compatibility with polypropylene and have minimal impact on the mechanical properties of the polypropylene film. The polymer-loaded silver nanoparticles are uniformly dispersed in the polypropylene film matrix, and the smaller particle size of the silver nanoparticles exposes more antibacterial sites, significantly improving the antibacterial properties of the film. Furthermore, polyitacrylamide contains hydrophilic carboxyl groups, amide bonds, and bisphenol groups; its addition to the polypropylene film helps reduce the water contact angle and improve surface hydrophilicity.

Description

Technical Field

[0001] This invention relates to the field of polypropylene film technology, specifically to a process for preparing biaxially oriented polypropylene film. Background Technology

[0002] Polypropylene can be processed into film materials through processes such as casting, blow molding, and biaxial stretching. Among these, biaxially oriented polypropylene film has advantages such as high mechanical strength, good airtightness, high transparency and gloss, and is widely used in printing films, agricultural films, food and pharmaceutical packaging, and building insulation and waterproofing materials. Improving the antibacterial properties of polypropylene film will help expand its practical applications in food packaging, medical supplies, and other fields.

[0003] Nano-silver is a high-performance antibacterial agent with strong inhibitory and bactericidal effects against pathogenic microorganisms such as Escherichia coli and Neisseria gonorrhoeae. It is also non-toxic, environmentally friendly, and biocompatible. The preparation of nano-silver typically requires the addition of stabilizers such as polyvinylpyrrolidone and polyvinyl alcohol, followed by reduction to obtain nano-silver with smaller particle size and better antibacterial properties. Nano-silver has important applications in materials such as polypropylene, polyacrylate, polyurethane, and silicone rubber. Chinese patent CN112094431B discloses a method of uniformly mixing a thiol-modified polymer with a nano-silver antibacterial agent to obtain a polypropylene wax-based nano-silver antibacterial material, which can improve the surface antibacterial effect of polypropylene products. However, this nano-silver antibacterial agent does not improve the surface hydrophilicity or other properties of polypropylene products. Summary of the Invention

[0004] This invention provides a process for preparing a biaxially oriented polypropylene film with good antibacterial properties and excellent hydrophilicity.

[0005] The preparation process of a biaxially oriented polypropylene film is as follows: (1) Add pyridine, itaconic anhydride, and dopamine hydrochloride to a flask and react at 20-30℃ for 12-18 h. Dissolve the product in ethyl acetate by rotary evaporation, place it in a separatory funnel, extract and wash with water, combine the organic phases, dry with anhydrous sodium sulfate, filter, and evaporate the filtrate by rotary evaporation. Recrystallize the crude product from dichloromethane to obtain itaconic acid-based dopamine monomer. The reaction formula is as follows: .

[0006] (2) Add ethanol and itaconic acid-based dopamine monomer to the flask, stir and then introduce nitrogen gas, add azobisisobutyronitrile, heat to 60-80℃, react for 3-5 hours, filter, wash with ethanol, and dry to obtain polyitaconic acid-based dopamine.

[0007] (3) Add water and polyitacrylamide to the flask, stir and then add silver nitrate. Stir for 0.5-1h in the dark, then heat to 60-75℃ and react for 1-2h. After cooling, add ethanol, filter and wash with ethanol, and dry to obtain polymer-supported silver nanoparticles.

[0008] (4) Mix polypropylene resin, polymer-loaded nano-silver and antioxidant, melt and extrude in an extrusion casting machine, water-cool and cast into a sheet, and then simultaneously stretch in the transverse and longitudinal direction in a biaxial tensile testing machine. The stretching temperature is 160-170℃, the transverse stretching ratio is 3, and the longitudinal stretching ratio is 3. Then heat set at 160-165℃ for 30s, and then wind up to obtain a biaxially oriented polypropylene film.

[0009] In (1), the ratio of pyridine, itaconic anhydride and dopamine hydrochloride is (14-16)g:1g:(0.7-0.76)g.

[0010] In (2), the ratio of itaconic acid-based dopamine monomer to azobisisobutyronitrile is 1g:(0.006-0.008)g.

[0011] In (3), the ratio of polyitacrylic acid dopamine to silver nitrate is 1g: (0.12-0.3)g.

[0012] In (4), the ratio of polypropylene resin to polymer-loaded nano-silver is 100g: (2-5)g.

[0013] Beneficial technical effects: This invention reacts itaconic anhydride and dopamine hydrochloride to obtain itaconic dopamine monomer, which is then polymerized by azobisisobutyronitrile to obtain polyitaconic dopamine, which contains carboxyl groups that can complex silver ions, allowing silver ions to be uniformly loaded onto the polyitaconic dopamine molecular chain, thus stabilizing the silver ions. Then, it is reduced by catechol groups to generate uniformly dispersed, small-particle-size silver nanoparticles.

[0014] This invention involves melting and biaxially stretching polypropylene resin and polymer-loaded silver nanoparticles to obtain a biaxially stretched polypropylene film. The polyitaconic acid-based dopamine in the polymer-loaded silver nanoparticles is an alkenyl polymer, which has good compatibility with polypropylene. Therefore, it has little impact on the mechanical properties of the polypropylene film, allowing the polypropylene film to maintain good tensile strength.

[0015] In this invention, polymer-loaded silver nanoparticles are uniformly dispersed in a polypropylene membrane matrix. The smaller particle size of the silver nanoparticles exposes more antibacterial sites, significantly improving the antibacterial properties of the membrane. Furthermore, polyitacrylamide contains hydrophilic carboxyl, amide, and bisphenol groups; its addition to the polypropylene membrane helps reduce the water contact angle and improves surface hydrophilicity. Detailed Implementation

[0016] To make the technical solutions of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. It should be noted that the following embodiments are only used to better understand the technical solutions of the present invention and should not be construed as limiting the present invention.

[0017] Example 1: (1) Add 70g pyridine, 5g itaconic anhydride and 3.5g dopamine hydrochloride to a flask, react at 30°C for 12h, evaporate by rotary evaporation, dissolve in ethyl acetate, place in a separatory funnel, extract and wash with water, combine the organic phases, dry with anhydrous sodium sulfate, filter, evaporate the filtrate by rotary evaporation, recrystallize the crude product in dichloromethane to obtain itaconic acid-based dopamine monomer.

[0018] (2) Add 120-150 mL of ethanol and 20 g of itaconic acid dopamine monomer to the flask, stir and then introduce nitrogen gas, add 0.14 g of azobisisobutyronitrile, heat to 70 °C, react for 5 h, filter, wash with ethanol, and dry to obtain polyitaconic acid dopamine.

[0019] (3) Add 500 mL of water and 10 g of polyitacrylamide to the flask, stir, add 1.2 g of silver nitrate, stir for 1 h in the dark, then heat to 75 °C and react for 1 h. After cooling, add ethanol, filter, wash with ethanol, and dry to obtain polymer-supported silver nanoparticles.

[0020] (4) Mix 1kg of polypropylene resin, 20g of polymer-loaded nano silver and 0.5g of antioxidant 1010, melt and extrude in an extrusion casting machine, water-cool and cast into a sheet, and then simultaneously stretch in the transverse and longitudinal directions in a biaxial tensile testing machine. The stretching temperature is 165℃, the transverse stretching ratio is 3, and the longitudinal stretching ratio is 3. Then heat set at 160℃ for 30s, and then wind up to obtain a biaxially oriented polypropylene film.

[0021] Example 2: (1) Add 80g pyridine, 5g itaconic anhydride and 3.8g dopamine hydrochloride to a flask, react at 25°C for 12h, evaporate by rotary evaporation, dissolve in ethyl acetate, place in a separatory funnel, extract and wash with water, combine the organic phases, dry with anhydrous sodium sulfate, filter, evaporate the filtrate by rotary evaporation, recrystallize the crude product in dichloromethane to obtain itaconic acid-based dopamine monomer.

[0022] (2) Add 150 mL of ethanol and 20 g of itaconic acid dopamine monomer to a flask, stir and then introduce nitrogen gas, add 0.16 g of azobisisobutyronitrile, heat to 60 °C, react for 5 h, filter, wash with ethanol, and dry to obtain polyitaconic acid dopamine.

[0023] (3) Add 800 mL of water and 10 g of polyitacrylamide to the flask, stir, add 3 g of silver nitrate, stir for 1 h in the dark, then heat to 60 °C and react for 2 h. After cooling, add ethanol, filter, wash with ethanol, and dry to obtain polymer-supported silver nanoparticles.

[0024] (4) Mix 1kg of polypropylene resin, 35g of polymer-loaded nano silver and 0.5g of antioxidant 1010, melt and extrude in an extrusion casting machine, water-cool and cast into a sheet, and then simultaneously stretch in the transverse and longitudinal direction in a biaxial tensile testing machine. The stretching temperature is 160℃, the transverse stretching ratio is 3, and the longitudinal stretching ratio is 3. Then heat set at 165℃ for 30s, and then wind up to obtain a biaxially oriented polypropylene film.

[0025] Example 3: (1) Add 80g pyridine, 5g itaconic anhydride and 3.7g dopamine hydrochloride to a flask, react at 20°C for 18h, evaporate by rotary evaporation, dissolve in ethyl acetate, place in a separatory funnel, extract and wash with water, combine the organic phases, dry with anhydrous sodium sulfate, filter, evaporate the filtrate by rotary evaporation, recrystallize the crude product in dichloromethane to obtain itaconic acid-based dopamine monomer.

[0026] (2) Add 150 mL of ethanol and 20 g of itaconic acid dopamine monomer to a flask, stir and then introduce nitrogen gas, add 0.12 g of azobisisobutyronitrile, heat to 80 °C, react for 3 h, filter, wash with ethanol, and dry to obtain polyitaconic acid dopamine.

[0027] (3) Add 500 mL of water and 10 g of polyitacrylamide to the flask, stir, add 2 g of silver nitrate, stir for 0.5 h in the dark, then heat to 70 °C and react for 2 h. After cooling, add ethanol, filter, wash with ethanol, and dry to obtain polymer-supported silver nanoparticles.

[0028] (4) Mix 1kg of polypropylene resin, 50g of polymer-loaded nano-silver, and 0.6g of antioxidant 1010, melt and extrude in an extrusion casting machine, water-cool and cast into a sheet, and then simultaneously stretch in the transverse and longitudinal directions in a biaxial tensile testing machine. The stretching temperature is 170℃, the transverse stretching ratio is 3, and the longitudinal stretching ratio is 3. Then heat set at 160℃ for 30s, and then wind up to obtain a biaxially oriented polypropylene film.

[0029] Comparative Example 1: (1) 1 kg of polypropylene resin and 0.5 g of antioxidant 1010 were mixed, melted, extruded and water-cooled in an extrusion casting machine, and then stretched in both the transverse and longitudinal directions in a biaxial tensile testing machine. The temperature during stretching was 165°C, the transverse stretching ratio was 3, and the longitudinal stretching ratio was 3. Then, the film was heat-set at 160°C for 30 seconds and wound up to obtain a biaxially stretched polypropylene film.

[0030] Comparative Example 2: (1) Polyitacrylic acid-based dopamine was prepared according to the process of Example 1.

[0031] (2) Mix 1kg of polypropylene resin, 20g of polyitacrylamide, and 0.5g of antioxidant 1010, melt and extrude them in an extrusion casting machine, and then water-cool them into a sheet. Then, stretch them in both the transverse and longitudinal directions simultaneously in a biaxial tensile testing machine. The temperature during stretching is 165℃, the transverse stretching ratio is 3, and the longitudinal stretching ratio is 3. Then, heat set at 160℃ for 30s and rewind to obtain a biaxially oriented polypropylene film.

[0032] Comparative Example 3: (1) Add 120-150 mL of ethanol and 20 g of 3-methacryloyldopamine (CAS No. 471915-89-6, structural formula is) to a flask. After stirring, nitrogen gas was introduced, 0.14 g of azobisisobutyronitrile was added, the mixture was heated to 70°C, and reacted for 5 h. After filtration, the mixture was washed with ethanol and dried to obtain polymethacrylamide dopamine.

[0033] (2) Add 500 mL of water and 10 g of polymethacrylamide to the flask, stir, add 2 g of silver nitrate, stir for 1 h in the dark, then heat to 75 °C and react for 1 h. After cooling, add ethanol, filter, wash with ethanol, and dry to obtain polymer-supported silver nanoparticles.

[0034] (3) Mix 1kg of polypropylene resin, 20g of polymer-loaded nano silver and 0.5g of antioxidant 1010, melt and extrude in an extrusion casting machine, water-cool and cast into a sheet, and then simultaneously stretch in the transverse and longitudinal directions in a biaxial tensile testing machine. The stretching temperature is 165℃, the transverse stretching ratio is 3, and the longitudinal stretching ratio is 3. Then heat set at 160℃ for 30s, and then wind up to obtain a biaxially oriented polypropylene film.

[0035] Comparative Example 4: (1) Add 100 mL of water and 10 g of polyvinyl alcohol to a flask, heat to 95 °C, stir to dissolve, then add 700 mL of aqueous solution containing 1.2 g of silver nitrate, react at 80 °C for 1 h, cool, filter, wash with water to obtain polyvinyl alcohol-supported silver nanoparticles.

[0036] (2) Mix 1kg of polypropylene resin, 20g of polyvinyl alcohol loaded with nano silver and 0.5g of antioxidant 1010, melt and extrude in an extrusion casting machine, water-cool and cast into a sheet, and then simultaneously stretch in the transverse and longitudinal direction in a biaxial tensile testing machine. The stretching temperature is 165℃, the transverse stretching ratio is 3, and the longitudinal stretching ratio is 3. Then heat set at 160℃ for 30s, and then wind up to obtain a biaxially oriented polypropylene film.

[0037] The average particle size of the silver nanoparticles in the polymer-supported silver nanoparticles was measured using a nanolaser particle size analyzer, as shown in Table 1 below.

[0038] Table 1: Test results of each embodiment and Comparative Examples 3 and 4

[0039] As shown in Table 1, the silver nanoparticles in the polymer-supported silver nanoparticles prepared in Examples 1-3 have a particle size of only 17.3-56.9 nm, good dispersibility, and are not prone to agglomeration. This is because polyitacrylamide contains carboxyl groups, which can complex silver ions, so that silver ions are uniformly loaded onto the polyitacrylamide molecular chain, which plays a role in stabilizing silver ions. Then, after reduction by catechol groups, uniformly dispersed silver nanoparticles with small particle size are generated.

[0040] The polymethacryloyldopamine in Comparative Example 3 does not contain a carboxyl group, so it cannot play a role in complexing and stabilizing silver ions, resulting in poor dispersion of the generated silver nanoparticles, easy agglomeration, and large particle size.

[0041] Comparative Example 4, which used polyvinyl alcohol as a stabilizer and reducing agent, produced nano-silver with good dispersibility and small particle size.

[0042] The tensile properties of polypropylene film were tested according to the national standard GB / T 1040.3-2006.

[0043] The water contact angle of polypropylene film was tested according to the national standard GB / T 30693-2014.

[0044] The antibacterial properties of polypropylene films were tested according to standard QB / T 2591-2003. The test bacteria were *Escherichia coli* and *Staphylococcus aureus*. The polypropylene film of Comparative Example 1 served as a blank control. The polypropylene films of Examples 1-3 and Comparative Examples 2-4 were used as antibacterial plastic film samples.

[0045] The antibacterial rate R = (BC) / B × 100%. B is the average number of recovered bacteria (cfu / tablet) in the blank control sample. C is the average number of recovered bacteria (cfu / tablet) in the antibacterial plastic film sample. The test data obtained by the above method are shown in Table 2 below.

[0046] Table 2: Test results of each embodiment and comparative example

[0047] As shown in Table 2, compared with Comparative Example 1, the biaxially oriented polypropylene films of Examples 1-3 still maintained good tensile strength, and the surface water contact angle decreased, indicating improved hydrophilicity. They also exhibited excellent antibacterial properties against *Escherichia coli* and *Staphylococcus aureus*. This is because the polyitacrylamide in the polymer-loaded silver nanoparticles is an alkenyl polymer, which has good compatibility with polypropylene, thus having little impact on the mechanical properties of the polypropylene film. The polymer-loaded silver nanoparticles are uniformly dispersed in the polypropylene film matrix, and the smaller particle size of the silver nanoparticles exposes more antibacterial sites, significantly improving the antibacterial properties of the film. Furthermore, polyitacrylamide contains hydrophilic carboxyl groups, amide bonds, and bisphenol groups, which, when added to the polypropylene film, help reduce the water contact angle and improve the surface hydrophilicity.

[0048] Comparative Example 2 only added polyitacrylic acid dopamine. The film had good tensile strength, which was very similar to that of Comparative Example 1. The water contact angle was significantly reduced, and the hydrophilicity was improved. However, it did not contain nano-silver, so the antibacterial properties of the film were very poor.

[0049] In Comparative Example 3, the polymer-loaded silver nanoparticles were added. These silver nanoparticles had a larger particle size and fewer antibacterial sites, resulting in a lower antibacterial rate of the polypropylene film. Furthermore, the silver nanoparticles were poorly dispersible and easily agglomerated into large particles, which affected the tensile strength of the film. Additionally, polymethacryloyl dopamine does not contain carboxyl groups and has lower hydrophilicity than polyitacrylic acid dopamine, resulting in a higher water contact angle for the film.

[0050] Comparative Example 4 included polyvinyl alcohol-loaded silver nanoparticles. It is possible that the poor compatibility between polyvinyl alcohol and polypropylene resulted in the polyvinyl alcohol-loaded silver nanoparticles not being uniformly dispersed in the film matrix, leading to a low antibacterial rate.

[0051] The preferred embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and any practices not described in detail should be understood as implementations in the ordinary manner known in the art. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, without departing from the scope of the present invention, using the methods and techniques disclosed above. This does not affect the essential content of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the present invention, still fall within the protection scope of the present invention.

Claims

1. A process for preparing biaxially oriented polypropylene film, characterized in that, The preparation process is as follows: (1) Add pyridine, itaconic anhydride and dopamine hydrochloride to a flask, react and evaporate by rotary evaporation, extract and wash, recrystallize to obtain itaconic dopamine monomer; (2) Add ethanol and itaconic acid-based dopamine monomer to a flask, stir and then introduce nitrogen gas, add azobisisobutyronitrile, filter after reaction, wash and dry to obtain polyitaconic acid-based dopamine; (3) Add water and polyitacrylamide to the flask, stir and then add silver nitrate. Stir under the dark, then heat to react. After cooling, add ethanol, filter, wash and dry to obtain polymer-loaded silver nanoparticles. (4) Mix polypropylene resin, polymer-loaded nano-silver and antioxidant, melt, extrude and water-cool the mixture in an extrusion casting machine, and then stretch, heat-set and wind it in a biaxial tensile testing machine to obtain a biaxially oriented polypropylene film.

2. The preparation process of a biaxially oriented polypropylene film according to claim 1, characterized in that, The ratio of pyridine, itaconic anhydride and dopamine hydrochloride in (1) is (14-16)g:1g:(0.7-0.76)g.

3. The preparation process of a biaxially oriented polypropylene film according to claim 1, characterized in that, The reaction temperature in (1) is 20-30℃ and the reaction time is 12-18h.

4. The preparation process of a biaxially oriented polypropylene film according to claim 1, characterized in that, The ratio of itaconic acid dopamine monomer and azobisisobutyronitrile in (2) is 1g:(0.006-0.008)g.

5. The preparation process of a biaxially oriented polypropylene film according to claim 1, characterized in that, The reaction temperature in (2) is 60-80℃ and the reaction time is 3-5h.

6. The preparation process of a biaxially oriented polypropylene film according to claim 1, characterized in that, The ratio of polyitaconic acid dopamine and silver nitrate in (3) is 1g:(0.12-0.3)g.

7. The preparation process of a biaxially oriented polypropylene film according to claim 1, characterized in that, The stirring time in (3) is 0.5-1h; the reaction temperature is 60-75℃ and the reaction time is 1-2h.

8. The preparation process of a biaxially oriented polypropylene film according to claim 1, characterized in that, In step (4), the ratio of polypropylene resin to polymer-loaded nano-silver is 100g:(2-5)g.

9. The preparation process of a biaxially oriented polypropylene film according to claim 1, characterized in that, The stretching temperature in (4) is 160-170℃, and the heat setting temperature is 160-165℃.

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