Pearlised film with flame-retardant and antibacterial functions as well as preparation method and application of pearlised film

Abstract

The invention discloses a pearlized film with flame-retardant and antibacterial functions as well as a preparation method and application thereof, and the specific scheme is as follows: a KH550 silane coupling agent is hydrolyzed and grafted on the surface of titanium dioxide (TiO2), and cinnamyl aldehyde (CA) is further grafted to prepare a CA-TiO2 composite antibacterial material; the pearlized film has the characteristics of strong activity, high stability, long acting time, safety, environmental protection and the like in the antibacterial process. Meanwhile, the APP flame-retardant microcapsule is prepared through a strategy of preparing ammonium polyphosphate (APP) through polyimide (PI) coating, so that the compatibility problem of polypropylene is solved, and the pearlized film is endowed with the flame-retardant characteristic. Furthermore, based on a three-layer co-extrusion process, the pearlized film with the flame-retardant and antibacterial functions is prepared by taking an APP flame-retardant microcapsule layer as a core layer and CA-TiO2 composite antibacterial material layers as two side skin layers, and systematic, diversified and standardized development of pearlized film product types is accelerated.

Description

Technical Field

[0001] The present invention belongs to the technical field of biaxially oriented polypropylene (BOPP) films, and specifically relates to a method for preparing a three-layer co-extruded pearlescent film based on CA-TiO2 composite antibacterial material and APP flame retardant microcapsules. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance some understanding of the overall background of the invention and should not be necessarily regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] BOPP pearlescent film is a polyolefin plastic film product produced by casting polypropylene melt into a sheet and then biaxially stretching it. Due to its low cost, high mechanical strength, excellent dimensional stability, and unique pearlescent luster, BOPP pearlescent film is widely used in electronics, machinery, food, and pharmaceutical packaging. However, pearlescent film faces two challenges in its practical application.

[0004] One issue is a common problem with polyolefin products: pearlescent film is prone to flammability when exposed to high temperatures. The resulting drippings can also cause other objects to burn, posing a significant risk to life and property. Furthermore, the carbonization and smoke produced by incomplete combustion of the pearlescent film can seriously impact the environment. Directly adding flame retardants can address the flammability issues of plastic products, and environmentally friendly flame retardants, such as ammonium polyphosphate (APP), have become a key research focus. However, APP's high water absorption and poor compatibility with polyolefins make it difficult to directly apply to pearlescent film production.

[0005] Secondly, the surface of BOPP pearlescent film is susceptible to large numbers of microorganisms, which not only affects the quality of the packaged products but can also infect mechanical surfaces such as instruments, posing a safety hazard. In particular, with growing concern for food safety, the demand for high-quality, green, safe, and long-shelf-life foods is increasing. Traditional preservatives not only alter the flavor of food but can also lead to nutrient loss. Adding antimicrobial materials to packaging materials can inhibit microbial growth and maintain the quality of the packaged products. Titanium dioxide (TiO2), as an inorganic antimicrobial material, offers advantages such as excellent thermal stability and resistance to migration. However, its antimicrobial effect relies on a photocatalytic process, making it weak in the dark. Cinnamaldehyde (CA), a natural antimicrobial material, is safe, environmentally friendly, and exhibits strong antimicrobial activity, but its inherent migration tendency leads to poor antimicrobial stability and a short duration of action. Conventional single or blended antimicrobial materials fail to combine the advantages of different antimicrobial materials. Therefore, developing composite antimicrobial materials that combine strong activity, high stability, long duration of action, and safety and environmental friendliness to achieve the superior antimicrobial efficacy of pearlescent films is becoming increasingly important. Summary of the Invention

[0006] To address the above issues, the present invention first prepares APP flame-retardant microcapsules to address polypropylene compatibility issues and impart flame-retardant properties to the pearlescent film. Simultaneously, CA is grafted onto the surface of TiO2 to create a composite antibacterial material, CA-TiO2. By integrating the advantages of different antibacterial materials, the pearlescent film achieves strong antibacterial activity, high stability, long-lasting action, and safety and environmental protection. Furthermore, based on a three-layer co-extrusion process, a flame-retardant and antibacterial pearlescent film is prepared with an APP flame-retardant microcapsule layer as the core layer and CA-TiO2 composite antibacterial material layers as the two side skin layers. This advances the development and transformation of flame-retardant and antibacterial composite technologies and accelerates the systematic, diversified, and standardized development of pearlescent film product categories.

[0007] The technical solution adopted in the present invention is as follows: In a first aspect of the present invention, a method for preparing a three-layer co-extruded pearlescent film based on a CA-TiO2 composite antibacterial material and APP flame retardant microcapsules is provided, the method comprising the following steps: (1) Dissolving KH550 silane coupling agent in water and hydrolyzing it, dispersing TiO2 in water and then adding it to the above solution to carry out KH550 grafting TiO2 reaction, centrifuging, washing and drying after the reaction to obtain KH550 grafted TiO2; dispersing KH550 grafted TiO2 in anhydrous ethanol, adding CA to carry out CA grafting TiO2 reaction; after the reaction, centrifuging, washing and drying to obtain CA-TiO2 composite antibacterial material; (2) APP was dissolved in anhydrous ethanol, the pH was adjusted to 5.5-6.5, polyimide (PI) was dissolved in dimethylacetamide and added to the APP solution, stirred, and the reaction solution was spray-dried to obtain APP flame-retardant microcapsules; (3) CA-TiO2 composite antibacterial material, APP microcapsules, pearlescent masterbatch and polypropylene were premixed and added to different twin-screw extruders for melting and plasticization. Cast sheets were prepared by three-layer co-extrusion process, and pearlescent films were prepared by biaxial stretching. The pearlescent film had an APP flame retardant microcapsule layer as the core layer and CA-TiO2 composite antibacterial material layers as the skin layers on both sides.

[0008] In one or some embodiments of the present invention, in step (1), the ratio of the KH550 silane coupling agent to water is (4.42-8.84) g: (150-250) mL; the hydrolysis temperature is 50-75°C, and the hydrolysis time is 4-12 h. Using water as the solvent results in a longer and more stable hydrolysis reaction.

[0009] In one or some embodiments of the present invention, in step (1), the average particle size of TiO2 is 100~300 nm, the ratio of TiO2, water and CA is (7~15) g: (150~250) mL: (35~60) mL, the reaction time of KH550 grafting TiO2 is 3~8 h, and the corresponding reaction temperature is 50~75 °C, and the reaction time of CA grafting TiO2 is 12~36 h, and the corresponding reaction temperature is 50~75 °C.

[0010] In one or some embodiments of the present invention, in step (2), the ratio of APP, anhydrous ethanol, PI and dimethylacetamide is (15-30) g: (250-350) mL: (8-15) g: (150-250) mL; the stirring time is 120-240 min, the spray drying feed rate is 12-25 mL / min, the inlet air temperature is 70-90 °C, and the outlet air temperature is 50-75 °C.

[0011] In one or some embodiments of the present invention, in step (3), in the three-layer structure of the pearlescent film, the skin layers on both sides contain 4~8 wt% CA-TiO2 composite antibacterial material, 15~25 wt% pearlescent masterbatch, and 67~81 wt% polypropylene; the core layer contains 8~15 wt% APP microcapsule flame retardant, 15~25 wt% pearlescent masterbatch, and 60~77 wt% polypropylene.

[0012] Preferably, the pearlescent masterbatch is composed of the following raw materials in mass fractions: 40-55 wt% of polypropylene, 40-55 wt% of calcium carbonate, 2.5-3.5 wt% of alkyl sulfonate surfactant, 0.3-0.8 wt% of 1010 antioxidant, and 0.3-0.7 wt% of magnesium stearate lubricant.

[0013] In one or some embodiments of the present invention, in step (3), the melt index of the polypropylene is 0.5-6 g / min (230°C, 2.16 kg), and the isotacticity is 97%-99%.

[0014] In one or some embodiments of the present invention, in step (3), the die extrusion temperature is 200-240°C, the die draw ratio is 6-14, and the casting temperature is 30°C.

[0015] In one or some embodiments of the present invention, in step (3), the longitudinal stretching temperature is 120~150°C, the stretching ratio is 500%~800%, and the stretching rate is 25~60% / s; the transverse stretching temperature is 140~160°C, the stretching ratio is 600%~900%, and the stretching rate is 25~60% / s.

[0016] In a second aspect of the present invention, a three-layer co-extruded pearlescent film based on CA-TiO2 composite antibacterial material and APP flame retardant microcapsules prepared by the above method is provided.

[0017] In a third aspect of the present invention, there is provided application of the three-layer co-extruded pearlescent film based on the CA-TiO2 composite antibacterial material and APP flame-retardant microcapsules in the field of packaging and / or decoration.

[0018] In the field of packaging, the three-layer co-extruded pearlescent film based on CA-TiO2 composite antibacterial material and APP flame-retardant microcapsules is often used to prepare food packaging bags and / or daily chemical product packaging bags.

[0019] In the field of decoration, the three-layer co-extruded pearlescent film based on CA-TiO2 composite antibacterial material and APP flame retardant microcapsules is often used to prepare gift boxes, greeting cards, book covers and / or holiday decorations.

[0020] Compared with the related art known to the inventors, one of the technical solutions of the present invention has the following beneficial effects: (1) The CA-TiO2 composite antibacterial material prepared in this invention combines the advantages of strong antibacterial activity, high heat stability, anti-migration, and safety and environmental protection by grafting CA onto the TiO2 surface. The prepared three-layer co-extruded pearlescent film can effectively inhibit the growth of Escherichia coli, Staphylococcus aureus, and Candida albicans under simulated light and dark conditions, ensuring the stability of product quality within the package.

[0021] (2) The flame-retardant microencapsulation of APP prepared by the present invention improves hygroscopicity and affinity with the polypropylene matrix, achieving uniform dispersion of the flame retardant. Furthermore, the microcapsule structure and the three-layer structure of the pearlescent film avoid problems such as flame retardant failure and product contamination caused by precipitation of the flame retardant in the core layer of the pearlescent film. The prepared three-layer co-extruded pearlescent film has a limiting oxygen index (GB / T 2406-2009) of 31.8%, a vertical combustion heat rating of V-0, and no droplet formation.

[0022] (3) The present invention is based on the three-layer co-extrusion method to prepare pearlescent film with good flame retardant and antibacterial effects. The method is simple and easy to implement and can be mass-produced. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings, which constitute a part of the specification of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0024] Figure 1 Schematic diagram of the prepared pearlescent film structure.

[0025] Figure 2 The thermogravimetric temperature rise curve of the CA-TiO2 composite antibacterial material in Example 1 is shown.

[0026] Figure 3 It represents the limiting oxygen index of the pearlescent film prepared in different examples. DETAILED DESCRIPTION

[0027] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0028] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations and / or combinations thereof.

[0029] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0030] The polypropylene used in the examples is T38F, purchased from PetroChina Lanzhou Petrochemical Company.

[0031] APP used in the examples was purchased from Aladdin Reagent Network as a white powder with a molecular weight of 1500-3500 Da.

[0032] The PI used in the examples was purchased from Aladdin Reagent Network as a light yellow powder with a molecular weight of 50,000-80,000 Da.

[0033] The pearlescent masterbatch used in the embodiment is composed of the following raw materials in mass fractions: 45 wt % of polypropylene, 50 wt % of calcium carbonate, 3.5 wt % of alkyl sulfonate surfactant, 0.8 wt % of 1010 antioxidant, and 0.7 wt % of magnesium stearate lubricant.

[0034] Example 1 A method for preparing a three-layer co-extruded pearlescent film based on CA-TiO2 composite antibacterial material and APP flame retardant microcapsules, the method comprising the following steps: (1) 5.53 g of KH550 silane coupling agent was dissolved in 200 mL of deionized water and hydrolyzed at 70 °C for 8 h. 10 g of TiO2 with an average particle size of 100 nm was dispersed in 200 mL of deionized water and added to the above solution. The grafting reaction was carried out at 70 °C for 5 h. After centrifugation and washing three times, the mixture was vacuum dried at 70 °C for 24 h. KH550-modified TiO2 was dispersed in 200 mL of anhydrous ethanol, 50 mL of CA was added, and the grafting reaction was carried out at 60 °C for 24 h. After centrifugation and washing three times, the mixture was vacuum dried at 70 °C for 24 h to obtain CA-TiO2 composite antibacterial material.

[0035] (2) 20 g of APP was dissolved in 300 mL of anhydrous ethanol and the pH was adjusted to 6 using 5 wt% dilute hydrochloric acid. 8 g of PI was dissolved in 200 mL of dimethylacetamide and added to the APP solution. The mixture was stirred at 60 °C for 180 min and then spray-dried to obtain APP flame-retardant microcapsules. The spray drying feed rate was 20 mL / min, the inlet air temperature was 75 °C, and the outlet air temperature was 55 °C.

[0036] (3) 4 wt% CA-TiO2 composite antibacterial material, 18 wt% pearlescent masterbatch, and 77 wt% polypropylene were premixed and added to the skin layer extruder. 10 wt% APP flame retardant microcapsules, 20 wt% pearlescent masterbatch, and 70 wt% polypropylene were premixed and added to the core layer extruder. Cast sheets were prepared by three-layer coextrusion process with a die head temperature of 220 °C, a die mouth draw ratio of 8, and a casting temperature of 30 °C. The pearlescent film was obtained by biaxial stretching with a longitudinal stretching temperature of 135 °C, a stretching ratio of 600%, and a stretching rate of 25% / s; and a transverse stretching temperature of 150 °C, a stretching ratio of 800%, and a stretching rate of 35% / s.

[0037] The three-layer structure of the pearlescent film prepared in this embodiment is shown in FIG. Figure 1 As shown, the thickness is 28 μm, the flame-retardant core layer is 22 μm thick, and the skin layers on both sides are 3 μm thick. The pearlescent film has a limiting oxygen index of 27.7%, a vertical burning rating (UL94) of V-0, and no dripping. The CA-TiO2 composite antibacterial material prepared in this example has a thermal decomposition temperature of 379°C, meeting the thermal stability requirements of the pearlescent film extrusion process. Under LED simulated sunlight, the pearlescent film prepared in this example has antibacterial rates (GB / T 31402-2015) against Escherichia coli, Staphylococcus aureus, and Candida albicans of 97.8%, 96.4%, and 96.9%, respectively. Under dark conditions, the antibacterial rates against Escherichia coli, Staphylococcus aureus, and Candida albicans remained stable at 94.3%, 93.8%, and 94.7%, respectively (see Table 1).

[0038] Example 2 A method for preparing a three-layer co-extruded pearlescent film based on CA-TiO2 composite antibacterial material and APP flame retardant microcapsules, the method comprising the following steps: (1) 6.63 g of KH550 silane coupling agent was dissolved in 200 mL of deionized water and hydrolyzed at 60 °C for 5 h. 12 g of TiO2 with an average particle size of 150 nm was dispersed in 200 mL of deionized water and added to the above solution. The grafting reaction was carried out at 60 °C for 8 h. After centrifugation and washing three times, the mixture was vacuum dried at 70 °C for 24 h. KH550-modified TiO2 was dispersed in 200 mL of anhydrous ethanol, 60 mL of CA was added, and the grafting reaction was carried out at 60 °C for 36 h. After centrifugation and washing three times, the mixture was vacuum dried at 70 °C for 24 h to obtain CA-TiO2 composite antibacterial material.

[0039] (2) 25 g of APP was dissolved in 300 mL of anhydrous ethanol and the pH was adjusted to 6 using 5 wt% dilute hydrochloric acid. 13 g of PI was dissolved in 200 mL of dimethylacetamide and added to the APP solution. The mixture was stirred at 60 °C for 240 min and then spray-dried to obtain APP flame-retardant microcapsules. The spray drying feed rate was 25 mL / min, the inlet air temperature was 80 °C, and the outlet air temperature was 60 °C.

[0040] (3) 7 wt% CA-TiO2 composite antibacterial material, 15 wt% pearlescent masterbatch, and 78 wt% polypropylene were premixed and added to the skin layer extruder. 13 wt% APP flame retardant microcapsules, 22 wt% pearlescent masterbatch, and 65 wt% polypropylene were premixed and added to the core layer extruder. Cast sheets were prepared by three-layer coextrusion process with a die head temperature of 200 °C, a die mouth draw ratio of 6, and a casting temperature of 30 °C. The pearlescent film was obtained by biaxial stretching with a longitudinal stretching temperature of 140 °C, a stretching ratio of 700%, and a stretching rate of 30% / s; and a transverse stretching temperature of 155 °C, a stretching ratio of 700%, and a stretching rate of 50% / s.

[0041] The pearlescent film prepared in this example has a thickness of 27 μm, a flame-retardant core layer thickness of 22 μm, and a skin layer thickness of 2.5 μm on both sides. The limiting oxygen index of the pearlescent film is 29.4%, the vertical combustion grade is V-0, and there is no droplet phenomenon. The thermal decomposition temperature of the CA-TiO2 composite antibacterial material prepared in this example is 368 ° C, which meets the thermal stability requirements of the pearlescent film extrusion process. The antibacterial rates of the prepared pearlescent film against Escherichia coli, Staphylococcus aureus, and Candida albicans under LED simulated sunlight irradiation are 99.1%, 98.4%, and 98.5%, respectively. Under dark conditions, the antibacterial rates against Escherichia coli, Staphylococcus aureus, and Candida albicans remain stable at 98.7%, 96.9%, and 97.3%, respectively, as shown in Table 1.

[0042] Example 3 A method for preparing a three-layer co-extruded pearlescent film based on CA-TiO2 composite antibacterial material and APP flame retardant microcapsules, the method comprising the following steps: (1) 8.84 g of KH550 silane coupling agent was dissolved in 200 mL of deionized water and hydrolyzed at 75 °C for 12 h. 15 g of TiO2 with an average particle size of 250 nm was dispersed in 200 mL of deionized water and added to the above solution. The mixture was grafted at 75 °C for 8 h. After centrifugation and washing three times, the mixture was vacuum dried at 70 °C for 24 h. KH550-modified TiO2 was dispersed in 200 mL of anhydrous ethanol, 50 mL of CA was added, and the mixture was grafted at 75 °C for 24 h. After the reaction, the mixture was centrifuged and washed three times, and vacuum dried at 70 °C for 24 h to obtain CA-TiO2 composite antibacterial material.

[0043] (2) 30 g of APP was dissolved in 300 mL of anhydrous ethanol and the pH was adjusted to 6 using 5 wt% dilute hydrochloric acid. 15 g of PI was dissolved in 200 mL of dimethylacetamide and added to the APP solution. The mixture was stirred at 60 °C for 240 min and then spray-dried to obtain APP flame-retardant microcapsules. The spray drying feed rate was 20 mL / min, the inlet air temperature was 75 °C, and the outlet air temperature was 65 °C.

[0044] (3) 8 wt% CA-TiO2 composite antibacterial material, 18 wt% pearlescent masterbatch, and 74 wt% polypropylene were premixed and added to the skin layer extruder. 15 wt% APP flame retardant microcapsules, 20 wt% pearlescent masterbatch, and 65 wt% polypropylene were premixed and added to the core layer extruder. Cast sheets were prepared by three-layer coextrusion process with a die head temperature of 230 °C, a die mouth draw ratio of 12, and a casting temperature of 30 °C. Pearlescent films were obtained by biaxial stretching with a longitudinal stretching temperature of 140 °C, a stretching ratio of 600%, and a stretching rate of 25% / s; and a transverse stretching temperature of 145 °C, a stretching ratio of 900%, and a stretching rate of 30% / s.

[0045] The pearlescent film prepared in this embodiment has a thickness of 24 μm, a flame retardant core layer thickness of 20 μm, and a skin thickness of 2 μm on both sides. The limiting oxygen index of the pearlescent film is 31.8%, the vertical combustion grade is V-0, and there is no droplet phenomenon. The thermal decomposition temperature of the CA-TiO2 composite antibacterial material prepared in this embodiment is 381 ° C, which meets the thermal stability requirements of the pearlescent film extrusion process. The antibacterial rates of the prepared pearlescent film against Escherichia coli, Staphylococcus aureus and Candida albicans under LED simulated sunlight irradiation are 99.3%, 98.2% and 98.8% respectively, while the antibacterial rates against Escherichia coli, Staphylococcus aureus and Candida albicans under dark conditions remain stable at 97.2%, 96.1% and 96.4% respectively, as shown in Table 1.

[0046] Example 4 A method for preparing a three-layer co-extruded pearlescent film based on CA-TiO2 composite antibacterial material and APP flame retardant microcapsules, the method comprising the following steps: (1) 4.41 g of KH550 silane coupling agent was dissolved in 200 mL of deionized water and hydrolyzed at 70 °C for 10 h. 12 g of TiO2 with an average particle size of 300 nm was dispersed in 200 mL of deionized water and added to the above solution. The grafting reaction was carried out at 70 °C for 5 h. After centrifugation and washing three times, the mixture was vacuum dried at 70 °C for 24 h. KH550-modified TiO2 was dispersed in 200 mL of anhydrous ethanol, 35 mL of CA was added, and the grafting reaction was carried out at 70 °C for 14 h. After the reaction, the mixture was centrifuged and washed three times, and vacuum dried at 70 °C for 24 h to obtain CA-TiO2 composite antibacterial material.

[0047] (2) 18 g of APP was dissolved in 300 mL of anhydrous ethanol and the pH was adjusted to 6 using 5 wt% dilute hydrochloric acid. 8 g of PI was dissolved in 200 mL of dimethylacetamide and added to the APP solution. The mixture was stirred at 60 °C for 120 min and then spray-dried to obtain APP flame-retardant microcapsules. The spray drying feed rate was 25 mL / min, the inlet air temperature was 70 °C, and the outlet air temperature was 60 °C.

[0048] (3) 5 wt% CA-TiO2 composite antibacterial material, 15 wt% pearlescent masterbatch, and 80 wt% polypropylene were premixed and added to the skin layer extruder. 8 wt% APP flame retardant microcapsules, 22 wt% pearlescent masterbatch, and 70 wt% polypropylene were premixed and added to the core layer extruder. Cast sheets were prepared by three-layer coextrusion process with a die head temperature of 240 °C, a die mouth draw ratio of 14, and a casting temperature of 30 °C. Pearlescent films were obtained by biaxial stretching with a longitudinal stretching temperature of 125 °C, a stretching ratio of 600%, and a stretching rate of 25% / s; and a transverse stretching temperature of 150 °C, a stretching ratio of 700%, and a stretching rate of 40% / s.

[0049] The pearlescent film prepared in this embodiment has a thickness of 32 μm, a flame retardant core layer thickness of 26 μm, and a skin thickness of 3 μm on both sides. The limiting oxygen index of the pearlescent film is 26.9%, the vertical combustion grade is V-0, and there is no droplet phenomenon. The thermal decomposition temperature of the CA-TiO2 composite antibacterial material prepared in this embodiment is 388 ° C, which meets the thermal stability requirements of the pearlescent film extrusion process. The antibacterial rates of the prepared pearlescent film against Escherichia coli, Staphylococcus aureus and Candida albicans under LED simulated sunlight irradiation are 97.4%, 97.1% and 96.5%, respectively, while the antibacterial rates against Escherichia coli, Staphylococcus aureus and Candida albicans under dark conditions remain stable at 95.6%, 94.7% and 95.2%, respectively, as shown in Table 1.

[0050] Example 5 A method for preparing a three-layer co-extruded pearlescent film based on CA-TiO2 composite antibacterial material and APP flame retardant microcapsules, the method comprising the following steps: (1) 5.53 g of KH550 silane coupling agent was dissolved in 200 mL of deionized water and hydrolyzed at 70 °C for 4 h. 8 g of TiO2 with an average particle size of 100 nm was dispersed in 200 mL of deionized water and added to the above solution. The grafting reaction was carried out at 70 °C for 6 h. After centrifugation and washing three times, the mixture was vacuum dried at 70 °C for 24 h. KH550-modified TiO2 was dispersed in 200 mL of anhydrous ethanol, 45 mL of CA was added, and the grafting reaction was carried out at 60 °C for 20 h. After the reaction, the mixture was centrifuged and washed three times, and vacuum dried at 70 °C for 24 h to obtain CA-TiO2 composite antibacterial material.

[0051] (2) 22 g of APP was dissolved in 300 mL of anhydrous ethanol and the pH was adjusted to 6 using 5 wt% dilute hydrochloric acid. 10 g of PI was dissolved in 200 mL of dimethylacetamide and added to the APP solution. The mixture was stirred at 60 °C for 160 min and then spray-dried to obtain APP flame-retardant microcapsules. The spray drying feed rate was 25 mL / min, the inlet air temperature was 80 °C, and the outlet air temperature was 70 °C.

[0052] (3) 6 wt% CA-TiO2 composite antibacterial material, 13 wt% pearlescent masterbatch, and 81 wt% polypropylene were premixed and added to the skin layer extruder. 12 wt% APP flame retardant microcapsules, 20 wt% pearlescent masterbatch, and 68 wt% polypropylene were premixed and added to the core layer extruder. Cast sheets were prepared by three-layer coextrusion process with a die head temperature of 220 °C, a die mouth draw ratio of 7, and a casting temperature of 30 °C. The pearlescent film was obtained by biaxial stretching with a longitudinal stretching temperature of 145 °C, a stretching ratio of 700%, and a stretching rate of 50% / s; and a transverse stretching temperature of 158 °C, a stretching ratio of 800%, and a stretching rate of 60% / s.

[0053] The pearlescent film prepared in this embodiment has a thickness of 23 μm, a flame retardant core layer thickness of 19 μm, and a skin layer thickness of 2 μm on both sides. The limiting oxygen index of the pearlescent film is 28.6%, the vertical combustion grade is V-0, and there is no droplet phenomenon. The thermal decomposition temperature of the CA-TiO2 composite antibacterial material prepared in this embodiment is 374 ° C, which meets the thermal stability requirements of the pearlescent film extrusion process. The antibacterial rates of the prepared pearlescent film against Escherichia coli, Staphylococcus aureus and Candida albicans under LED simulated sunlight irradiation are 98.3%, 97.7% and 97.4%, respectively, while the antibacterial rates against Escherichia coli, Staphylococcus aureus and Candida albicans under dark conditions remain stable at 97.6%, 95.9% and 96.3%, respectively, as shown in Table 1.

[0054] Table 1 Antibacterial rates of different BOPP antibacterial pearlescent films under light and dark conditions The present invention is not limited to the embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing a three-layer co-extruded pearlescent film based on CA-TiO2 composite antibacterial material and APP flame retardant microcapsules, characterized in that: The method comprises the following steps: (1) Dissolving KH550 silane coupling agent in water and hydrolyzing it, dispersing TiO2 in water and then adding it to the above solution to carry out KH550 grafting TiO2 reaction, centrifuging, washing and drying after the reaction to obtain KH550 grafted TiO2; dispersing KH550 grafted TiO2 in anhydrous ethanol, adding CA to carry out CA grafting TiO2 reaction; after the reaction, centrifuging, washing and drying to obtain CA-TiO2 composite antibacterial material; (2) APP was dissolved in anhydrous ethanol, the pH was adjusted to 5.5-6.5, PI was dissolved in dimethylacetamide and added to the APP solution, stirred, and the reaction solution was spray-dried to obtain APP flame-retardant microcapsules; (3) CA-TiO2 composite antibacterial material, APP microcapsules, pearlescent masterbatch and polypropylene were premixed and added to different twin-screw extruders for melting and plasticization. Cast sheets were prepared by three-layer co-extrusion process, and pearlescent films were prepared by biaxial stretching. The pearlescent film had an APP flame retardant microcapsule layer as the core layer and CA-TiO2 composite antibacterial material layers as the skin layers on both sides.

2. The method for preparing a three-layer co-extruded pearlescent film based on CA-TiO2 composite antibacterial material and APP flame retardant microcapsules according to claim 1, characterized in that: In step (1), the ratio of the KH550 silane coupling agent to water is (4.42-8.84) g: (150-250) mL; the hydrolysis temperature is 50-75 °C, and the hydrolysis time is 4-12 h.

3. The method for preparing a three-layer co-extruded pearlescent film based on CA-TiO2 composite antibacterial material and APP flame retardant microcapsules according to claim 1, characterized in that: In step (1), the average particle size of TiO2 is 100~300 nm, the ratio of TiO2, water and CA is (7~15) g: (150~250) mL: (35~60) mL, the reaction time of KH550 grafting TiO2 is 3~8 h, and the corresponding reaction temperature is 50~75 ℃, and the reaction time of CA grafting TiO2 is 12~36 h, and the corresponding reaction temperature is 50~75 ℃.

4. The method for preparing a three-layer co-extruded pearlescent film based on CA-TiO2 composite antibacterial material and APP flame retardant microcapsules according to claim 1, characterized in that: In step (2), the ratio of APP, anhydrous ethanol, PI and dimethylacetamide is (15~30) g: (250~350) mL: (8~15) g: (150~250) mL; the stirring time is 120~240 min, the spray drying feed rate is 12~25 mL / min, the inlet air temperature is 70~90 ℃, and the outlet air temperature is 50~75 ℃.

5. The method for preparing a three-layer co-extruded pearlescent film based on CA-TiO2 composite antibacterial material and APP flame retardant microcapsules according to claim 1, characterized in that: In step (3), in the three-layer structure of the pearlescent film, the skin layers on both sides contain 4~8 wt% CA-TiO2 composite antibacterial material, 15~25 wt% pearlescent masterbatch, and 67~81 wt% polypropylene; the core layer contains 8~15 wt% APP microcapsule flame retardant, 15~25 wt% pearlescent masterbatch, and 60~77 wt% polypropylene.

6. The method for preparing a three-layer co-extruded pearlescent film based on CA-TiO2 composite antibacterial material and APP flame retardant microcapsules according to claim 5, characterized in that: The pearlescent masterbatch is composed of the following raw materials in mass fractions: 30-45 wt% of polypropylene, 45-50 wt% of calcium carbonate, 1.5-3.5 wt% of alkyl sulfonate surfactant, 0.3-0.8 wt% of 1010 antioxidant, and 0.3-0.7 wt% of magnesium stearate lubricant.

7. The method for preparing a three-layer co-extruded pearlescent film based on CA-TiO2 composite antibacterial material and APP flame retardant microcapsules according to claim 1, characterized in that: In step (3), the melt index of polypropylene is 0.5-6 g / min (230°C, 2.16 kg), and the isotacticity is 97%-99%.

8. The method for preparing a three-layer co-extruded pearlescent film based on CA-TiO2 composite antibacterial material and APP flame retardant microcapsules according to claim 1, characterized in that: In step (3), the die extrusion temperature is 200~240℃, the die mouth drawing ratio is 6~14, and the casting temperature is 30℃; the longitudinal stretching temperature is 120~150℃, the stretching ratio is 500%~800%, and the stretching rate is 25~60% / s; the transverse stretching temperature is 140~160℃, the stretching ratio is 600%~900%, and the stretching rate is 25~60% / s.

9. A three-layer co-extruded pearlescent film based on CA-TiO2 composite antibacterial material and APP flame retardant microcapsules prepared by the method according to any one of claims 1 to 8.

10. Use of the three-layer co-extruded pearlescent film based on the CA-TiO2 composite antibacterial material and APP flame-retardant microcapsules according to claim 9 in the field of packaging and / or decoration.

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