High-barrier polypropylene packaging film and method for preparing the same

Abstract

This invention discloses a high-barrier polypropylene packaging film and its preparation method, belonging to the field of polypropylene film processing. It includes a barrier layer, a bridging agent, and a color-developing layer. The barrier layer comprises 70-80 parts of polypropylene copolymer, 15-20 parts of high-density polyethylene, 4-6 parts of stearic acid-modified nano-silica, and 0.5-0.8 parts of silane coupling agent A. The bridging agent comprises 1.5-2 parts of ionic liquid and 0.8-1 parts of silane coupling agent B, wherein the ionic liquid exists in the form of microcapsules. The color-developing layer comprises 85-90 parts of polar modified low-density polyethylene, 5-7 parts of metal ion color-developing-adsorption complex, and 10-12 parts of polymer polyol-modified nano-silica. This application introduces a color-developing layer on the outer surface of the barrier layer capable of adsorbing and developing color in metal ions, thereby capturing, blocking, and identifying certain metal ions, serving as a warning and barrier.

Description

Technical Field

[0001] This invention belongs to the field of polypropylene film processing, and relates to a high-barrier polypropylene packaging film and its preparation method. Background Technology

[0002] Polypropylene has a high melting point and excellent comprehensive performance, making it one of the most promising thermoplastic polymer materials today. Compared with other general-purpose thermoplastics, it has the advantages of low price, low specific gravity, superior mechanical properties such as yield strength, tensile strength, and surface strength, outstanding stress cracking resistance and wear resistance, good chemical stability, easy molding and processing, and wide range of applications. It has been widely used in chemical, electrical, automotive, construction, packaging and other industries.

[0003] Currently, polypropylene and polyethylene can be blended to produce films with high barrier properties, which are strong against substances such as O2, H2O, and CO2. However, they do not have significant identification and barrier properties against metal ions. When packaging certain chemical products (items that can produce physical and chemical reactions with metal ions through adsorption or complexation), it is difficult to visually identify whether external metal ions pose a risk of contamination to the inner packaged items. Once the packaging film is damaged, such as by gaps, externally detectable metal ions can easily penetrate the packaging film and contaminate the inner items. Currently, it is only easy to detect the contamination after the inner items have been contaminated, and it does not have a monitoring function for the contamination process. Summary of the Invention

[0004] The purpose of this invention is to provide a high-barrier polypropylene packaging film and its preparation method, thereby solving the problem of how to achieve a high-barrier polypropylene film with significant recognition and blocking functions for metal ions.

[0005] The technical solution adopted in this invention is as follows: A high-barrier polypropylene packaging film includes a barrier layer, a bridging agent, and a color developing layer; The barrier layer comprises the following components by weight fraction: 70-80 parts polypropylene copolymer, 15-20 parts high-density polyethylene, 4-6 parts stearic acid modified nano silica, and 0.5-0.8 parts silane coupling agent A, wherein the particle size of the nano silica in the stearic acid modified nano silica is 10-20 nm. The bridging agent comprises the following components in parts by weight: 1.5-2 parts ionic liquid and 0.8-1 parts silane coupling agent B, wherein the ionic liquid exists in the form of microcapsules; The color-developing layer comprises the following components in parts by weight: 85-90 parts of polar modified low-density polyethylene, 5-7 parts of metal ion color-developing-adsorption complex, and 10-12 parts of polymer polyol modified nano silica; wherein the nano silica in the polymer polyol modified nano silica has a particle size of 70-80 nm.

[0006] This application prepares a barrier layer using polypropylene copolymer and high-density polyethylene as the main materials. This barrier layer contacts the packaging material and significantly improves its basic oxygen and water barrier properties. Furthermore, this application introduces a color-developing layer on the outer surface of the barrier layer, capable of adsorbing and developing color for metal ions. The barrier layer is a non-polar layer and needs to possess strong chemical inertness, generally not reacting with the contents. However, the color-developing layer needs to capture metal ions and develop color, requiring a polar environment. This results in poor compatibility between the barrier layer and the color-developing layer, making it difficult to bond them together. Due to the strong chemical inertness of the barrier layer, even when an adhesive is used between the two layers, bonding between the adhesive and the barrier layer remains challenging. Therefore, in order to achieve a tight bond between the barrier layer and the color development layer, this application uses stearic acid-modified nano-silica and polymer polyol-modified nano-silica as the connection points of the bilayer film. Under the catalysis of ionic liquid, stearic acid and polymer polyol react to form a nanoscale connection and interlocking of two nanoparticles with different particle sizes, forming a micro-connection layer that replaces the macroscopic adhesive effect of existing adhesives. The nanoparticles have a filling and anchoring effect on the micro-gaps in the film layer, which weakens the influence of the polarity or non-polarity of the film layer on the adhesive strength, and achieves a tight bond between the bilayer film. Furthermore, due to the filling of nano-silica with different particle sizes, the overall film density is enhanced, and the overall barrier properties of the film are improved.

[0007] In this application, the metal ion colorimetric-adsorption complex involves the adsorption and color development of metal ions, comprising a metal ion adsorbent and a metal ion colorimetric agent. The metal ion adsorbent adsorbs metal ions, not only blocking their penetration but also enriching them at the metal ion colorimetric agent, thus amplifying the colorimetric response of the agent to metal ions. The color development of the metal ions in the metal ion colorimetric-adsorption complex and the metal ions treated by the adsorbent must overlap.

[0008] Further, the metal ion colorimetric-adsorption complex is an alizarin red-maleic anhydride-grafted graphene oxide complex, which is prepared by the following method: maleic anhydride-grafted graphene oxide is prepared using maleic anhydride and graphene oxide in a mass ratio of 3:1. The maleic anhydride-grafted graphene oxide is dispersed in anhydrous pyridine, ultrasonically treated, and then alizarin red is added. Under nitrogen protection and light protection, the mixture is magnetically stirred and refluxed in an oil bath at 100°C for 7-8 hours. After the reaction is completed, it is cooled to room temperature and transferred to acetone, filtered, and the precipitate is obtained. The precipitate is then washed and dried to obtain alizarin red-maleic anhydride-grafted graphene oxide. The mass ratio of maleic anhydride-grafted graphene oxide to alizarin red is 1:0.4.

[0009] The packaging film of this application is mainly used for the barrier and protection against acidic pollutants containing copper ions, and can be used for packaging products that react with copper ions, such as some chelating agents; alizarin red is used as a color developer, and maleic anhydride-grafted graphene oxide is used as an adsorbent.

[0010] Further, the polymer polyol-modified nano silica is prepared by the following method: nano silica with a particle size of 70-80 nm is dispersed in anhydrous toluene, stirred evenly, and then propyltriethoxysilane is added. After heating and refluxing for 3-4 hours, polymer polyol and dibutyltin dilaurate are added. After heating and refluxing under nitrogen for 6-8 hours, the mixture is centrifuged, washed, and dried to obtain polymer polyol-modified nano silica; wherein the mass ratio of nano silica, polymer polyol, propyltriethoxysilane, and dibutyltin dilaurate is 1:2:1.5:0.1.

[0011] Furthermore, the polar modified low-density polyethylene is a mixture obtained by melt blending ethylene-vinyl acetate copolymer as a polar material with low-density polyethylene, and the mixture is polar modified low-density polyethylene; wherein, the content of vinyl acetate in the ethylene-vinyl acetate copolymer is 36-38%.

[0012] Furthermore, the polypropylene copolymer is a propylene-ethylene random copolymer, wherein the ethylene content is 4-5 wt%.

[0013] Furthermore, the stearic acid modified nano-silica is prepared by the following method: hydrophilic nano-silica with a particle size of 10-20 nm is dispersed in ethanol, stearic acid is added, the mixture is heated and stirred to react, and after the reaction is completed, it is centrifuged, washed, and dried to obtain stearic acid modified nano-silica; wherein, the mass ratio of hydrophilic nano-silica to stearic acid is 2:1.

[0014] Furthermore, the silane coupling agent A is γ-aminopropyltriethoxysilane.

[0015] Furthermore, the ionic liquid microcapsule is a microcapsule containing 1-butylsulfonic acid-3-methylimidazolium p-toluenesulfonate ionic liquid encapsulated in a polysulfuric acid ester shell, wherein the polysulfuric acid ester shell is obtained through an isocyanate-thiol interfacial reaction, and the molar ratio of -NCO to -SH is 1:1.2.

[0016] Furthermore, the silane coupling agent B is γ-glycidoxypropyltrimethoxysilane.

[0017] The method for preparing a high-barrier polypropylene packaging film includes the following steps: S1. Preparation of the barrier layer Polypropylene copolymer, high-density polyethylene, stearic acid modified nano silica, and silane coupling agent A are put into a high-speed mixer and mixed at 800-1000 rpm for 12-15 minutes. The uniformly mixed material is melt-extruded through an extruder at 185-200℃, and then cast through a T-die onto the surface of a cooling roller. The material is then pulled and wound to obtain a barrier layer with a thickness of 30-50μm. S2, Preparation of the color development layer Polar modified low-density polyethylene, metal ion color-developing-adsorption composite, and polymer polyol modified nano-silica are put into a high-speed mixer and mixed at 600-800 rpm for 10-12 minutes. The mixture is then melt-extruded through an extruder at 135-150℃, cast through a T-die onto the surface of a cooling roller, and pulled and wound to obtain a color-developing layer with a thickness of 20-25μm. S3, Bridging agent coating and lamination Ionic liquid microcapsules and silane coupling agent B are dispersed in anhydrous ethanol to obtain a bridging agent coating solution. The bridging agent coating solution is uniformly coated on the surface of the barrier layer, and then dried at 50-60℃ for 30-40 seconds. The color development layer and the barrier layer coated with the bridging agent are then hot-pressed together using laminating rollers at a temperature of 80-85℃ and a pressure of 0.4-0.6 MPa to obtain a film preform. The film preform is then placed in a curing chamber at 50-55℃ and cured for 12-13 hours to obtain a high-barrier polypropylene packaging film.

[0018] This application requires hot pressing during lamination to cause the ionic liquid microcapsules to rupture and release the internal ionic liquid, and also requires a certain curing time to ensure that the double membranes adhere tightly.

[0019] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1. This invention discloses a high-barrier polypropylene packaging film. To achieve a tight bond between the barrier layer and the color development layer, stearic acid-modified nano-silica and polymer polyol-modified nano-silica are used as the connection points of the double-layer film. Under the catalysis of ionic liquid, stearic acid and polymer polyol react, causing the two nanoparticles of different sizes to form a nanoscale connection and interlocking, forming a micro-connection layer that replaces the macroscopic adhesive effect of existing adhesives. The nanoparticles have a filling and anchoring effect on the micro-gaps in the film layer, weakening the influence of the polarity or non-polarity of the film layer on the adhesive strength, and achieving a tight bond between the double-layer film. 2. The present invention enhances the overall membrane density and improves the overall membrane barrier properties by filling it with nano-silica of different particle sizes; 3. The present invention adds a color-developing layer to one side of the barrier layer. The metal ion color-developing-adsorption complex in the color-developing layer is for the adsorption and color development of metal ions, including a metal ion adsorbent and a metal ion color developer. The metal ion adsorbent adsorbs metal ions, which not only blocks the inward penetration of metal ions, but also realizes the enrichment of metal ions at the metal ion color developer, amplifying the color response of the metal ion color developer to metal ions. 4. The method for preparing a high-barrier polypropylene packaging film of the present invention is adapted to the use of ionic liquid microcapsules, avoiding premature release of ionic liquid from the ionic liquid microcapsules and thus preventing waste of ionic liquid. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort, wherein: Figure 1 This is a physical image of the product of the present invention (Example 2); Figure 2 This is a graph showing the changes in the product of the present invention (Example 2) after it has been immersed in a copper ion solution. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described embodiments are merely some embodiments of the invention, and not all embodiments. The components of the embodiments of the invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0022] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0023] It should be noted that relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0024] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0025] Example 1:

[0026] A preferred embodiment of the present invention provides a high-barrier polypropylene packaging film, comprising a barrier layer, a bridging agent, and a color developing layer; The barrier layer comprises the following components in weight fractions: 70 parts polypropylene copolymer, 15 parts high-density polyethylene, 4 parts stearic acid modified nano silica, and 0.5 parts silane coupling agent A, wherein the particle size of the nano silica in the stearic acid modified nano silica is 10-20 nm. The bridging agent comprises the following components in parts by weight: 1.5 parts ionic liquid and 0.8 parts silane coupling agent B, wherein the ionic liquid exists in the form of microcapsules; The color-developing layer comprises the following components in parts by weight: 85 parts of polar modified low-density polyethylene, 5 parts of metal ion color-developing-adsorption complex, and 10 parts of polymer polyol modified nano silica; wherein the nano silica in the polymer polyol modified nano silica has a particle size of 70-80 nm. The metal ion colorimetric-adsorption complex is an alizarin red-maleic anhydride-grafted graphene oxide complex, which is prepared by the following method: maleic anhydride-grafted graphene oxide is prepared using maleic anhydride and graphene oxide in a mass ratio of 3:1. The maleic anhydride-grafted graphene oxide is dispersed in anhydrous pyridine, ultrasonically treated, and then alizarin red is added. Under nitrogen protection and light protection, the mixture is magnetically stirred and refluxed in an oil bath at 100°C for 8 hours. After the reaction is completed, the mixture is cooled to room temperature and transferred to acetone. The precipitate is filtered, washed, and dried to obtain alizarin red-maleic anhydride-grafted graphene oxide. The mass ratio of maleic anhydride-grafted graphene oxide to alizarin red is 1:0.4. The polymer polyol-modified nano-silica was prepared by the following method: nano-silica with a particle size of 70-80 nm was dispersed in anhydrous toluene, stirred evenly, and then propyltriethoxysilane was added. After heating and refluxing for 3 hours, polymer polyol and dibutyltin dilaurate were added. After heating and refluxing for 7 hours under nitrogen, the mixture was centrifuged, washed, and dried to obtain polymer polyol-modified nano-silica; wherein the mass ratio of nano-silica, polymer polyol, propyltriethoxysilane, and dibutyltin dilaurate was 1:2:1.5:0.1. The polar modified low-density polyethylene is a mixture obtained by melt blending ethylene-vinyl acetate copolymer as the polar material with low-density polyethylene, wherein the mixture is polar modified low-density polyethylene; wherein the ethylene-vinyl acetate copolymer contains 37% vinyl acetate; The polypropylene copolymer is a propylene-ethylene random copolymer, wherein the ethylene content is 5 wt%; The stearic acid modified nano-silica was prepared by the following method: hydrophilic nano-silica with a particle size of 10-20 nm was dispersed in ethanol, stearic acid was added, the mixture was heated and stirred to react, and after the reaction was completed, it was centrifuged, washed, and dried to obtain stearic acid modified nano-silica; wherein the mass ratio of hydrophilic nano-silica to stearic acid was 2:1.

[0027] The silane coupling agent A is γ-aminopropyltriethoxysilane.

[0028] The ionic liquid microcapsules are microcapsules containing 1-butylsulfonic acid-3-methylimidazolium p-toluenesulfonate ionic liquid encapsulated in a polysulfuric acid ester shell. The polysulfuric acid ester shell is obtained through an isocyanate-thiol interfacial reaction, and the molar ratio of -NCO to -SH is 1:1.2.

[0029] The silane coupling agent B is γ-glycidoxypropyltrimethoxysilane.

[0030] The method for preparing a high-barrier polypropylene packaging film includes the following steps: S1. Preparation of the barrier layer Polypropylene copolymer, high-density polyethylene, stearic acid modified nano silica, and silane coupling agent A are put into a high-speed mixer and mixed at 900 rpm for 13 minutes. The uniformly mixed material is melt-extruded through an extruder at 200°C, and then cast through a T-die onto the surface of a cooling roller. The material is then pulled and wound to obtain a barrier layer with a thickness of 40 μm. S2, Preparation of the color development layer Polar modified low-density polyethylene, metal ion color-adsorption composite, and polymer polyol modified nano silica were put into a high-speed mixer and mixed at 800 rpm for 10 minutes. The mixture was then melt-extruded through an extruder at 140°C, cast through a T-die onto the surface of a cooling roller, and pulled and wound to obtain a color layer with a thickness of 25 μm. S3, Bridging agent coating and lamination Ionic liquid microcapsules and silane coupling agent B were dispersed in anhydrous ethanol to obtain a bridging agent coating solution. The bridging agent coating solution was uniformly coated on the surface of the barrier layer and then dried at 50°C for 40 seconds. The color development layer and the barrier layer coated with the bridging agent were then hot-pressed together using a laminating roller at a temperature of 85°C and a pressure of 0.5 MPa to obtain a film preform. The film preform was then placed in a curing chamber at 55°C and cured for 13 hours to obtain a high-barrier polypropylene packaging film.

[0031] This embodiment is mainly applicable to factories such as semiconductor processing plants, where there are large amounts of acidic pollutants (wastewater) containing copper ions, and where packaging and protection are provided for metal-sensitive products.

[0032] Example 2:

[0033] This embodiment differs from Embodiment 1 in that it provides a high-barrier polypropylene packaging film, comprising a barrier layer, a bridging agent, and a color developing layer. The barrier layer comprises the following components in weight fractions: 75 parts polypropylene copolymer, 18 parts high-density polyethylene, 5 parts stearic acid modified nano silica, and 0.7 parts silane coupling agent A, wherein the particle size of the nano silica in the stearic acid modified nano silica is 10-20 nm. The bridging agent comprises the following components in parts by weight: 1.7 parts ionic liquid and 0.9 parts silane coupling agent B, wherein the ionic liquid exists in the form of microcapsules; The color-developing layer comprises the following components in parts by weight: 88 parts of polar modified low-density polyethylene, 6 parts of metal ion color-developing-adsorption complex, and 11 parts of polymer polyol modified nano-silica; wherein the nano-silica in the polymer polyol modified nano-silica has a particle size of 70-80 nm. The rest is consistent with Example 1.

[0034] Example 3:

[0035] This embodiment differs from Embodiment 1 in that it provides a high-barrier polypropylene packaging film, comprising a barrier layer, a bridging agent, and a color developing layer. The barrier layer comprises the following components in weight fractions: 80 parts polypropylene copolymer, 20 parts high-density polyethylene, 6 parts stearic acid modified nano silica, and 0.8 parts silane coupling agent A, wherein the particle size of the nano silica in the stearic acid modified nano silica is 10-20 nm. The bridging agent comprises the following components in parts by weight: 2 parts ionic liquid and 1 part silane coupling agent B, wherein the ionic liquid exists in the form of microcapsules; The color-developing layer comprises the following components in parts by weight: 90 parts polar modified low-density polyethylene, 7 parts metal ion color-developing-adsorption complex, and 12 parts polymer polyol modified nano-silica; wherein the nano-silica in the polymer polyol modified nano-silica has a particle size of 70-80 nm. The rest is consistent with Example 1.

[0036] Example 4:

[0037] This embodiment differs from Embodiment 2 in that the polar modified low-density polyethylene described in this embodiment is a mixture obtained by melt blending ethylene-vinyl acetate copolymer as the polar material with low-density polyethylene. The mixture is polar modified low-density polyethylene; wherein, the vinyl acetate content in the ethylene-vinyl acetate copolymer is 36%.

[0038] Example 5:

[0039] This embodiment differs from Embodiment 2 in that the polar modified low-density polyethylene described in this embodiment is a mixture obtained by melt blending ethylene-vinyl acetate copolymer as the polar material with low-density polyethylene. The mixture is polar modified low-density polyethylene; wherein, the vinyl acetate content in the ethylene-vinyl acetate copolymer is 38%.

[0040] Example 6:

[0041] This embodiment is based on Embodiment 2, but differs from Embodiment 2 in that the thickness of the barrier layer is 30 μm and the thickness of the color developing layer is 20 μm.

[0042] Example 7:

[0043] This embodiment is based on Embodiment 2, but differs from Embodiment 2 in that the thickness of the barrier layer is 50 μm and the thickness of the color developing layer is 25 μm.

[0044] Comparative Example 1 Based on Example 2, the difference from Example 2 is that this comparative example of a high-barrier polypropylene packaging film only includes a barrier layer and does not include a bridging agent and a color developing layer. The preparation method is the same as that of Example 2.

[0045] Comparative Example 2 Based on Example 2, the difference from Example 2 is that the bridging agent in this comparative example is PP-specific instant adhesive (product model JL-406AB), which is used according to the existing method to bond the barrier layer and the color development layer, replacing the bridging agent in Example 2. All other aspects are the same.

[0046] Comparative Example 3 Based on Example 2, the difference is that the nano-silica in this comparative example barrier layer was not modified with stearic acid; instead, nano-silica with a particle size of 10-20 nm was directly added. All other aspects are the same.

[0047] Comparative Example 4 Based on Example 2, the difference is that the nano-silica in this comparative example's colorimetric layer was not modified with polymer polyols; instead, nano-silica with a particle size of 70-80 nm was directly added. All other aspects are the same.

[0048] Comparative Example 5 Based on Example 2, the difference from Example 2 is that the stearic acid modified nano-silica in the barrier layer of this comparative example and the polymer polyol modified nano-silica in the color development layer have the same particle size range, which is 10-20 nm.

[0049] Comparative Example 6 Based on Example 2, the difference from Example 2 is that the stearic acid modified nano-silica in the barrier layer of this comparative example and the polymer polyol modified nano-silica in the color development layer have the same particle size range, which is 70-80nm.

[0050] Comparative Example 7 Based on Example 2, the difference from Example 2 is that the low-density polyethylene in the color development layer of this comparative example is not polarized and low-density polyethylene is used directly, while the rest are the same.

[0051] Comparative Example 8 Based on Example 2, the difference from Example 2 is that the ionic liquid in this comparative bridging agent is not in capsule form, but is directly coated; all other aspects are the same.

[0052] Comparative Example 9 Based on Example 2, the difference from Example 2 is that the bridging agent in this comparative example does not include ionic liquid, but all other aspects are the same.

[0053] Experimental Example 1 Examples 1-7 and Examples 2-9 were tested to evaluate their workability. The workability of the barrier layer and color-developing layer during lamination was observed by visual inspection. Any defects such as inability to bond, delamination after curing, or large-area defects were noted during upper film lamination. If any of these occurred, it indicated that the workability did not meet the requirements. The evaluation results are shown in Table 1. Table 1. Constructability Assessment Results Example 1 After hot pressing, the film adheres tightly, and after curing, the film surface is smooth and flat. Constructable Example 2 After hot pressing, the film adheres tightly, and after curing, the film surface is smooth and flat. Constructable Example 3 After hot pressing, the film adheres tightly, and after curing, the film surface is smooth and flat. Constructable Example 4 After hot pressing, the film adheres tightly, and after curing, the film surface is smooth and flat. Constructable Example 5 After hot pressing, the film adheres tightly, and after curing, the film surface is smooth and flat. Constructable Example 6 After hot pressing, the film adheres tightly, and after curing, the film surface is smooth and flat. Constructable Example 7 After hot pressing, the film adheres tightly, and after curing, the film surface is smooth and flat. Constructable Comparative Example 2 A few air bubbles were present during hot pressing, and the double-layer film was bonded together, but the edges warped slightly after curing. Constructable Comparative Example 3 Some areas are not sticky and cannot be laminated. Does not meet construction requirements Comparative Example 4 Some areas are not sticky and cannot be laminated. Does not meet construction requirements Comparative Example 5 The lamination process went smoothly, but the film surface had a grainy texture. Constructable Comparative Example 6 The lamination process went smoothly, but the film surface had a grainy texture. Constructable Comparative Example 7 Large-area delamination after maturation Does not meet construction requirements Comparative Example 8 Localized areas cannot be laminated, film voids, and delamination during winding. Does not meet construction requirements Comparative Example 9 Unable to reconcile Does not meet construction requirements Experimental Example 2 Adsorption and color development performance of copper ions of thin films: The adsorption and color development performance of copper ions of the thin films of Examples 1-7 and Comparative Examples 1, 2, 5 and 6 were tested. Test method: Prepare a 10 mg / L Cu solution using copper sulfate. 2+ A copper ion solution was prepared, and the pH was adjusted to 4.0 with dilute sulfuric acid to simulate the test environment (an acidic environment rich in copper ions). A 5 cm × 5 cm film sample was immersed in 50 mL of the copper ion solution and allowed to stand at 25 °C. Samples were taken at 0, 3, and 24 hours to detect the copper ion adsorption rate, colorimetric response of the developing layer, and visual effect of the developing layer at 3 and 24 hours. The results are shown in Table 2. Copper ion adsorption rate: The concentration of copper ions in the solution was measured using an inductively coupled plasma mass spectrometer (ICP-MS, Agilent 7900), and the adsorption rate was calculated (adsorption rate = (initial concentration - remaining concentration) / initial concentration × 100%). Color response: The color difference (ΔE, average value) on the surface of the film color development layer was measured using a colorimeter (HunterLab ColorQuest XE), with an unimmersed sample as the reference (ΔE > 5 indicates significant color change). Visual observation: Record the color change of the film development layer after immersion and compare it with the unimmersed sample. For Examples 1-7 and Comparative Examples 2, 5, and 6, the films were all light yellowish-brown when unimmersed (the actual product obtained in Example 2 is shown in the image). Figure 1 As shown), Comparative Example 1 is colorless.

[0054] Table 2. Test results of adsorption and color development performance of the thin film for copper ions. Example 1 70.5-71% 90.2-91% ＞5 ＞5 Numerous scattered reddish-brown spots Example 2 80.3-81% 98.1-98.8% ＞5 ＞5 Dense dark reddish-brown spots Example 3 75.2-76% 95.2-95.5% ＞5 ＞5 Dense dark reddish-brown spots Example 4 78.1-79% 96.0-96.5% ＞5 ＞5 Dense dark reddish-brown spots Example 5 77.3-78% 95.3-96% ＞5 ＞5 Dense dark reddish-brown spots Example 6 72.4-73% 92.1-92.6% ＞5 ＞5 Scattered dark reddish-brown spots Example 7 78.5-79% 96.3-97% ＞5 ＞5 Dense dark reddish-brown spots Comparative Example 1 ＜0.6 ＜1 ＜0.5 ＜0.5 No color change Comparative Example 2 ＜45% ＜50% ＜5 ＞5 Scattered and few light brown spots Comparative Example 5 65.1-66% 85.2-85.5% ＜5 ＞5 Scattered dark brown spots Comparative Example 6 62.1-63% 83.2-83.5% ＜5 ＞5 Scattered dark brown spots contrast Figure 1 , Figure 2 As shown, the present invention exhibits significant changes in copper ion solution, indicating that the film of this application has a significant response to copper ions and can serve as a warning, indicating that the product may pose a pollution risk in the current environment. In this application, copper ions are adsorbed and colored in the color development layer and will not permeate through the entire film, that is, they will not penetrate from the outer layer of the film to the inner layer. It can be understood that the color development layer is a warning layer for copper ions, indicating that there is a pollution source in the current environment and that there may be a risk of pollution. The color development layer in this application has a certain protective effect on the barrier layer. The color development layer can both serve as a warning and as a sacrificial layer to protect the barrier layer. In addition, even if there are minor cracks in the entire film, metal ions will be actively captured by the color development layer during the process of penetrating from the outside to the inside, blocking the penetration path.

[0055] Experimental Example 3 The films of Examples 1-7 and Comparative Examples 1, 2, 5, and 6 were tested for oxygen barrier properties, water barrier properties, and peel strength between the color development layer and the barrier layer. The results are shown in Table 3.

[0056] Oxygen barrier performance testing method: The oxygen barrier performance testing method of the film directly adopts the existing technology. The oxygen permeability of the film is measured by the OX2 / 230 oxygen permeability testing system. The unit is cm³ / m²·24h·0.1MPa. An oxygen permeability of less than 2 indicates good barrier performance. Water barrier performance testing method: The water vapor transmission rate tester is used to determine the water vapor barrier performance of the film. The measurement method of the water vapor transmission rate tester is existing technology and will not be explained in detail here. The lower the water vapor transmission rate value, the better the barrier performance of the film. A water vapor transmission rate below 1 g / m2.day.1 atm indicates good water barrier performance.

[0057] Peel strength test method between color layer and barrier layer: According to ASTM D903 standard, a 180° peel test was performed using a universal testing machine (Instron 3365), with a sample width of 15 mm and a tensile speed of 100 mm / min. The average peel strength (N / 15 mm) was measured.

[0058] Table 3. Thin Film Performance Test Results Example 1 ＜1 ＜1 >30N / 15mm Example 2 ＜1 ＜1 >30N / 15mm Example 3 ＜1 ＜1 >30N / 15mm Example 4 ＜1 ＜1 >30N / 15mm Example 5 ＜1 ＜1 >30N / 15mm Example 6 ＜1 ＜1 >30N / 15mm Example 7 ＜1 ＜1 >30N / 15mm Comparative Example 1 1-2 ＜1 - Comparative Example 2 1-2 ＜1 <15N / 15mm Comparative Example 5 ＞2 ＞1 <10N / 15mm Comparative Example 6 ＞2 ＞1 <10N / 15mm Based on the data in the table above, this invention exhibits high barrier properties and high peel strength between the bilayer films. Furthermore, it responds quickly and shows clear color development to copper ions, making it suitable for adsorbing and color developing detectable copper ions in the environment. Sufficient adsorption of copper ions hinders their further penetration. Even with minute gaps in the film, any permeated copper ions will be captured by the color development layer, preventing further infiltration. In addition, the tensile strength and other mechanical properties of this application are consistent with those of cast polypropylene films. Unlike the adsorption and color development of metal ions on one side of the film, where water vapor and oxygen permeate from one side, surface adsorption and color development of metal ions do not affect the evaluation of the film's barrier properties.

[0059] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high barrier polypropylene packaging film, characterized by: Includes barrier layer, bridging agent, and color developing layer; The barrier layer comprises the following components by weight fraction: 70-80 parts polypropylene copolymer, 15-20 parts high-density polyethylene, 4-6 parts stearic acid modified nano silica, and 0.5-0.8 parts silane coupling agent A, wherein the particle size of the nano silica in the stearic acid modified nano silica is 10-20 nm. The bridging agent comprises the following components in parts by weight: 1.5-2 parts ionic liquid and 0.8-1 parts silane coupling agent B, wherein the ionic liquid exists in the form of microcapsules; The color-developing layer comprises the following components in parts by weight: 85-90 parts of polar modified low-density polyethylene, 5-7 parts of metal ion color-developing-adsorption complex, and 10-12 parts of polymer polyol modified nano-silica; wherein the particle size of the nano-silica in the polymer polyol modified nano-silica is 70-80 nm; the polar modified low-density polyethylene is a mixture obtained by melt blending ethylene-vinyl acetate copolymer as a polar material with low-density polyethylene, and the mixture is polar modified low-density polyethylene; wherein the vinyl acetate content in the ethylene-vinyl acetate copolymer is 36-38%.

2. A high barrier polypropylene packaging film according to claim 1, characterized in that: The metal ion colorimetric-adsorption complex is an alizarin red-maleic anhydride-grafted graphene oxide complex, which is prepared by the following method: maleic anhydride-grafted graphene oxide is prepared using maleic anhydride and graphene oxide in a mass ratio of 3:

1. The maleic anhydride-grafted graphene oxide is dispersed in anhydrous pyridine, ultrasonically treated, and then alizarin red is added. Under nitrogen protection and light protection, the mixture is magnetically stirred and refluxed in an oil bath at 100°C for 7-8 hours. After the reaction is completed, the mixture is cooled to room temperature and transferred to acetone. The precipitate is obtained by suction filtration, washed, and dried to obtain alizarin red-maleic anhydride-grafted graphene oxide. The mass ratio of maleic anhydride-grafted graphene oxide to alizarin red is 1:0.

4.

3. The high-barrier polypropylene packaging film according to claim 1, characterized in that: The polymer polyol-modified nano-silica was prepared by the following method: nano-silica with a particle size of 70-80 nm was dispersed in anhydrous toluene, stirred evenly, and then propyltriethoxysilane is added. After heating and refluxing for 3-4 hours, polymer polyol and dibutyltin dilaurate were added. After heating and refluxing under nitrogen for 6-8 hours, the mixture was centrifuged, washed, and dried to obtain polymer polyol-modified nano-silica; wherein the mass ratio of nano-silica to polymer polyol was 1:

2.

4. The high barrier polypropylene packaging film according to claim 1, characterized in that: The polypropylene copolymer is a propylene-ethylene random copolymer, wherein the ethylene content is 4-5 wt%.

5. The high barrier polypropylene packaging film according to claim 1, characterized in that: The stearic acid modified nano-silica was prepared by the following method: hydrophilic nano-silica with a particle size of 10-20 nm was dispersed in ethanol, stearic acid was added, the mixture was heated and stirred to react, and after the reaction was completed, it was centrifuged, washed, and dried to obtain stearic acid modified nano-silica; wherein the mass ratio of hydrophilic nano-silica to stearic acid was 2:

1.

6. A high barrier polypropylene packaging film according to claim 1, characterized in that: The silane coupling agent A is γ-aminopropyltriethoxysilane.

7. The high-barrier polypropylene packaging film according to claim 1, characterized in that: The ionic liquid microcapsules are microcapsules containing 1-butylsulfonic acid-3-methylimidazolium p-toluenesulfonate ionic liquid encapsulated in a polysulfuric acid ester shell. The polysulfuric acid ester shell is obtained through an isocyanate-thiol interfacial reaction, and the molar ratio of -NCO to -SH is 1:1.

2.

8. A high barrier polypropylene packaging film according to claim 1, characterized in that: The silane coupling agent B is γ-glycidoxypropyltrimethoxysilane.

9. The method for preparing a high-barrier polypropylene packaging film according to claim 1, characterized in that: Includes the following steps: S1. Preparation of the barrier layer Polypropylene copolymer, high-density polyethylene, stearic acid modified nano silica, and silane coupling agent A are put into a high-speed mixer and mixed at 800-1000 rpm for 12-15 minutes. The uniformly mixed material is melt-extruded through an extruder at 185-200℃, and then cast through a T-die onto the surface of a cooling roller. The material is then pulled and wound to obtain a barrier layer with a thickness of 30-50μm. S2, Preparation of the color development layer Polar modified low-density polyethylene, metal ion color-developing-adsorption composite, and polymer polyol modified nano-silica are put into a high-speed mixer and mixed at 600-800 rpm for 10-12 minutes. The mixture is then melt-extruded through an extruder at 135-150℃, cast through a T-die onto the surface of a cooling roller, and pulled and wound to obtain a color-developing layer with a thickness of 20-25μm. S3, Bridging agent coating and lamination Ionic liquid microcapsules and silane coupling agent B are dispersed in anhydrous ethanol to obtain a bridging agent coating solution. The bridging agent coating solution is uniformly coated on the surface of the barrier layer, and then dried at 50-60℃ for 30-40 seconds. The color development layer and the barrier layer coated with the bridging agent are then hot-pressed together using laminating rollers at a temperature of 80-85℃ and a pressure of 0.4-0.6 MPa to obtain a film preform. The film preform is then placed in a curing chamber at 50-55℃ and cured for 12-13 hours to obtain a high-barrier polypropylene packaging film.

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