An improved milk product packaging box and method of production

Abstract

The application provides an improved milk product packaging box, which comprises a PP outer layer and an HDPE inner layer for contacting the content, and the inner wall surface of the HDPE inner layer has a micro-nano composite rough structure, which comprises micron-level main protrusions and nano-level protrusions attached to the surface of the micron-level main protrusions; and the application also provides a method for producing the improved milk product packaging box. The improved milk product packaging box and the production method have the advantages of good anti-sticking performance, only a small amount of mature additives for modification, no risk of material migration, and more controllable food safety.

Description

Technical Field

[0001] This invention relates to the field of dairy product packaging technology, and more specifically, to an improved dairy product packaging box and its production method. Background Technology

[0002] Currently, dairy products are frequently packaged in plastic boxes. To meet requirements for food safety, preservation, and production efficiency, the raw materials are generally food-grade resins such as polypropylene (PP), high-density polyethylene (HDPE), and polystyrene (PS). However, when consumers consume these products, the dairy products easily stick to the inner wall of the packaging box, leading to inconvenience and significant waste, thus affecting the user experience.

[0003] To improve user experience, anti-stick performance has gradually become an important research direction for modern dairy product packaging boxes. Currently, the mainstream technical means are mainly the following three: (1) Selecting plastics with low surface energy (such as HDPE), or adding slip agents (such as oleamide) to the resin raw materials to reduce adhesion, but the anti-stick effect of this method is limited; (2) Coating the inner wall of the packaging box with an anti-stick coating based on fluoropolymers or silicone resin. Although this method can effectively reduce adhesion, the coating material may migrate into the food, and the coating has a small bonding force with the substrate, making it easy to fall off locally, resulting in failure of the anti-stick function, and there is also a risk of foreign matter; (3) Changing the geometry of the packaging box, such as using an arc-shaped bottom and a large area transition, relying on gravity to make the product easier to gather, but its improvement effect is also limited and cannot cope with the contents adhering to the vertical sidewalls.

[0004] Furthermore, patent CN118024637A discloses a preparation process and application of modified polypropylene packaging sheets. It utilizes the synergistic effect of silicone oil (anti-stick agent) and POSS-modified SiO2 nanoparticles to modify polypropylene sheets, achieving excellent anti-stick properties. Patent CN118063832A discloses a non-stick yogurt packaging composite material and its preparation method. It utilizes the Schiff base reaction mechanism, using amino-terminated poly(dimethylsiloxane) as raw material, modifying it with aldehyde-terminated functional monomers, and then end-capping it with a monoaldehyde linear saturated aliphatic hydrocarbon end-capping agent to prepare an anti-stick agent. This anti-stick agent is then used to modify a polypropylene film, achieving good anti-stick properties. However, both patents use a relatively large number of chemical additives in their polypropylene modification processes, and these are relatively new additives. The migration safety of these chemical additives requires careful evaluation.

[0005] In order to solve the above problems, people have been seeking an ideal technological solution. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing an improved dairy product packaging box and its production method that offers superior anti-stick properties, uses only a small amount of mature additives for modification, eliminates the risk of material migration, and ensures more controllable food safety.

[0007] In a first aspect, the present invention provides an improved dairy product packaging box, comprising a PP outer layer and an HDPE inner layer for contacting the contents, wherein the inner wall surface of the HDPE inner layer has a micro-nano composite rough structure, the micro-nano composite rough structure comprising micron-level main protrusions and nano-level protrusions attached to the surface of the micron-level main protrusions. The micron-scale main protrusion is formed by a two-step replication process: First replication: The first injection mold is composed of an upper mold with a micro-protrusion array texture engraved on the core and a lower mold with a smooth cavity. The functional film is injection molded to form a micro-pit structure on the inner wall of the functional film. The back of the functional film is laminated with an HDPE film. The diameter of the protrusions in the micro-protrusion array is 3-7μm, the height is 11-19μm, and the minimum distance between the outer edges of adjacent protrusions is 5-15μm. Second replication: During injection molding, the micro-dimpled structure on the front side of the functional film is used as the inner mold core. The molten PP and the back side of the HDPE film are fused together. Under the action of injection pressure, the surface of the HDPE film bulges forward to form a micro-protrusion structure due to the push of the micro-dimpled structure on the functional film. The nanoscale protrusions are formed from food-grade silica nanospheres modified with alkylsilane, and the average particle size of the food-grade silica nanospheres is 50-150 nm.

[0008] Based on the above, the food-grade silica nanospheres are uniformly dispersed in the HDPE, and the mass fraction of the food-grade silica nanospheres is 1%-2%.

[0009] Based on the above, the alkylsilane is octadecyltrimethoxysilane.

[0010] Based on the above, the thickness of the HDPE inner layer is 70-150 μm.

[0011] Based on the above, the height of the micron-sized main protrusion is 2-5 times its diameter.

[0012] Secondly, the present invention also provides a method for producing the above-mentioned improved dairy product packaging box, characterized by comprising the following steps: Step S1, the preparation of the PP functional film, includes the following sub-steps: A1) A micro-protrusion array texture is engraved on the core of a steel upper mold using a laser. The diameter of the protrusions in the micro-protrusion array is 3-7μm, the height is 11-19μm, and the minimum distance between the outer edges of adjacent protrusions is 5-15μm. The steel upper mold and a steel lower mold with a smooth cavity are used to form a first injection mold. A2) Melt food-grade PP resin granules and inject them into the first injection mold. The injection pressure is 80-120 MPa and the injection speed is 200-300 mm / s. A3) Reduce the pressure to 35%-40% of the injection pressure, hold the pressure for 2-4 seconds, complete the cooling and shaping, and after demolding, obtain a PP film with a micro-pit structure on the inner wall. The thickness of the PP film is 40-60μm. Step S2, the preparation of the modified HDPE film, includes the following sub-steps: B1) Prepare food-grade silica nanospheres with octadecyltrimethoxysilane surface modification, wherein the average particle size of the silica nanospheres is 50-150 nm; B2) Prepare a premix by using the alkylsilane-modified silica nanospheres, dispersant, antioxidant and some HDPE resin particles prepared in step B1. Then, melt-blend the premix through an extruder. After cooling, the extruded strip material is cut into uniform functional masterbatches. B3) A second injection mold is formed by an upper mold with a smooth core and a lower mold with a smooth cavity. The functional masterbatch prepared in step B2 is mixed with a certain amount of HDPE resin, melted and plasticized in an extruder, and then injected into the second injection mold. After cooling and solidification, the modified HDPE film is demolded to obtain a modified HDPE film with a thickness of 70-150 μm and a mass fraction of 1%-2% of silica nanospheres in the modified HDPE film. Step S3: Prepare an ethanol aqueous solution with a mass fraction of 5%-10% and keep it at a temperature of 60-80℃ for later use; Step S4: The modified HDPE film from step S2 is overlaid on the outside of the PP functional film from step S1. An ethanol aqueous solution prepared in step S3 is used to form a liquid film between the modified HDPE film and the PP functional film. Process edges are provided at the openings of both the PP functional film and the modified HDPE film to obtain a functional insert. Step S5: A third injection mold is formed by using an upper mold with a smooth core and a lower mold with a smooth cavity. The parting surface edge of the third injection mold is provided with a process edge clamping mechanism to perform the final injection molding, including the following sub-steps: C1) The functional surface of the functional insert with micro-dimpled structure in step S4 is tightly attached to the smooth core on the upper mold. After the mold is closed, the process edge pressing mechanism presses the process edge. C2) Molten PP is injected into the cavity at an injection pressure of 80-150MPa and an injection speed of 200-300mm / s. It is formed on the back of the functional insert. The heat causes the PP and HDPE to fuse. The high pressure pushes the micro-dimpled structure on the PP functional film to fit the smooth core. At the same time, the surface of the modified HDPE film bulges forward to form a micro-protrusion structure, thus completing the injection molding. C3) Reduce the pressure to 50%-80% of the injection pressure, hold the pressure for 3-8 seconds, and complete the cooling and shaping process; Step S6: After cooling and solidification, open the mold and cut off the process edges; Step S7: Immerse the packaging box in warm water, peel off the PP functional film, and expose the micro-protrusion structure on the modified HDPE film layer.

[0013] Based on the above, step B1 includes the following steps: The silica nanosphere hydrosol with a solid content of 20% was solvent-displaced with ethanol, and centrifuged and washed several times to form a stable ethanol dispersion. Octadecyltrimethoxysilane was mixed with a small amount of glacial acetic acid and anhydrous ethanol, and then added dropwise to the above silica nanosphere ethanol dispersion under a nitrogen atmosphere. The mixture was refluxed at 60-80℃ for 6-12 hours until the reaction was completed. The reaction solution was cooled to room temperature, filtered, and washed. The resulting precipitate was food-grade silica nanospheres modified with octadecyltrimethoxysilane.

[0014] Based on the above, in the functional masterbatch prepared in step B2, the mass fraction of silica nanospheres is 20%, and the dispersant is maleic anhydride-grafted polyethylene; the weight of HDPE resin in step B3 is 9-19 times the weight of the functional masterbatch.

[0015] Based on the above, the temperature of the warm water in step S7 is 80-85℃.

[0016] This invention has outstanding substantive features and significant progress compared to the prior art. Specifically, the packaging box produced by the method of this invention not only has a huge improvement in anti-stick performance, but also uses only a small amount of mature additives (in the food industry) during the production process, so there is no risk of material migration to the contents. At the same time, its material still uses PP and HDPE commonly used in dairy product packaging, and its strength and other physical properties remain basically unchanged. Attached Figure Description

[0017] Figure 1 This is a block diagram of the main structure of the dairy product packaging box production equipment in this invention.

[0018] Figure 2 This is a schematic diagram of the functional thin film preparation module in this invention.

[0019] Figure 3 This is a schematic diagram of the HDPE film preparation module in this invention.

[0020] Figure 4 This is a schematic diagram of the functional insert preparation module in this invention.

[0021] Figure 5 This is a structural schematic diagram of the product forming module in this invention.

[0022] Figure 6 This is a schematic diagram of the layout structure of the workbench in this invention.

[0023] Figure 7 This is a schematic diagram of the transfer robot in this invention.

[0024] Figure 8 This is a schematic diagram of the structure of the first injection mold in this invention.

[0025] Figure 9 This is a schematic diagram of the structure of the second injection mold in this invention.

[0026] Figure 10 This is a schematic diagram of the pressing mold in this invention.

[0027] Figure 11 This is a schematic diagram of the structure of the third injection mold in this invention.

[0028] Figure 12 This is a schematic diagram of the structure in which the functional film and the HDPE film are stacked together in this invention.

[0029] In the diagram: 1. First extruder; 2. First injection unit; 3. First injection mold; 31. First upper mold; 32. First lower mold; 33. First gate; 34. First core; 35. First cavity; 36. First molding cavity; 4. Second extruder; 5. Second injection unit; 6. Second injection mold; 61. Second upper mold; 62. Second lower mold; 63. Second gate; 64. Second core; 65. Second cavity; 66. Second molding cavity; 7. High-speed mixer; 8. Premixed material extruder; 9. Cooling water tank; 10. Dryer; 11. Pelletizer; 12. Liquid storage tank; 13. Injection mechanism; 131. Metering pump; 132. Flat nozzle; 14. Pressing mold; 141. Pressing upper mold; 142. Pressing lower mold; 143. Pressing core; 144. 15. Pressing cavity; 16. Third extruder; 17. Third injection unit; 18. Third injection mold; 19. Third upper mold; 10. Third lower mold; 11. Third gate; 12. Third core; 13. Third cavity; 14. Third molding cavity; 15. Clamping mechanism; 16. Transfer robot; 17. Thin gripper; 18. Negative pressure suction cup; 19. Trimming mechanism; 10. Annular punch; 11. Annular blade plate; 22. Immersion tank; 23. Worktable; 24. Ejector rod; 25. Venting channel. Detailed Implementation

[0030] The technical solution of the present invention will be further described in detail below through specific embodiments.

[0031] Using known precision laser processing techniques (such as picosecond laser micromachining systems), a micro-protrusion array texture was engraved on the cores of three steel upper dies, wherein: The first steel upper mold core has micro-protrusions with a diameter of 3μm, a height of 11μm, and a minimum distance of 5μm between the outer edges of adjacent protrusions; The core of the second steel upper mold has micro-protrusions with a diameter of 5μm, a height of 15μm, and a minimum distance of 10μm between the outer edges of adjacent protrusions; The core of the third steel upper mold has micro-protrusions with a diameter of 7μm, a height of 19μm, and a minimum distance of 15μm between the outer edges of adjacent protrusions.

[0032] To extend service life, in other embodiments, a hard coating (such as TiN or DLC) can be deposited on the core surface of the steel upper mold, with a coating thickness of 1-3 μm. Example 1

[0033] This embodiment provides an improved dairy product packaging box and its production method.

[0034] The production method includes the following steps: Step S1, the preparation of the PP functional film, includes the following sub-steps: A1) The first injection mold 3 is formed by the second steel upper mold and the steel lower mold with a smooth cavity. The steel upper mold is the first upper mold 31 and the steel lower mold is the first lower mold 32.

[0035] A2) Melt food-grade PP resin granules and inject them into the first injection mold 3. The injection pressure is 80-120 MPa and the injection speed is 200-300 mm / s.

[0036] A3) Reduce the pressure to 35%-40% of the injection pressure, hold the pressure for 2-4 seconds, and complete the cooling and shaping. After demolding, a PP film with a micro-pit structure on the inner wall is obtained. The thickness of the PP film is 40-60μm.

[0037] In this step, the injection temperature can be the commonly used temperature for PP injection molding. Using a higher injection speed and higher injection pressure can ensure that the PP fills the space on the micro-protrusion array before cooling and molding, which is the key to the molding of the micro-dimple structure.

[0038] There are two main reasons why PP material is used for functional films. First, it is a commonly used material in dairy product packaging boxes and will not affect the safety of the packaging. Second, it has high melt strength, sharp outlines of the micro-pit structure when pressed, and a heat distortion temperature much higher than room temperature. After being removed from the press, it can cool and solidify quickly to prevent springback or loosening.

[0039] Step S2, the preparation of the modified HDPE film, includes the following sub-steps: B1) Food-grade silica nanospheres were prepared by surface modification with octadecyltrimethoxysilane, so that the particle surface energy is close to that of HDPE, which is beneficial for subsequent dispersion. The average particle size of the silica nanospheres was 100 nm.

[0040] The specific preparation process is as follows: The silica nanosphere hydrosol with a solid content of 20% was solvent-displaced with ethanol, and centrifuged and washed several times to form a stable ethanol dispersion. Octadecyltrimethoxysilane was mixed with a small amount of glacial acetic acid and anhydrous ethanol, and then added dropwise to the above-mentioned silica nanosphere ethanol dispersion under a nitrogen atmosphere. The mixture was refluxed at 60-80℃ for 6-12 hours until the reaction was complete. During this process, glacial acetic acid catalyzed the hydrolysis of the methoxy group (-OCH3) of the silane to generate an active silanol (-Si(OH)3). The silanol generated by hydrolysis undergoes a dehydration condensation reaction with the silanol (Si-OH) on the surface of the silica nanospheres to form a stable siloxane bond (Si-O-Si), thus completing the reaction. After the reaction was completed, the mixture was cooled to room temperature and filtered to obtain a precipitate. The precipitate was washed with ethanol and acetone alternately until no chloride ions were detected in the washing solution. The precipitate was food-grade silica nanospheres modified with octadecyltrimethoxysilane.

[0041] B2) Prepare a premix by using the alkylsilane-modified silica nanospheres, dispersant, antioxidant and some HDPE resin particles prepared in step B1. Then, melt-blend the premix through an extruder, which is the premix extruder 8. After cooling, the extruded strip material is cut into uniform functional masterbatches.

[0042] The dispersant is maleic anhydride-grafted polyethylene, which prevents the aggregation of silica nanospheres and improves their dispersion uniformity in the functional masterbatch. The antioxidant is a combination of hindered phenolic primary antioxidant and phosphite secondary antioxidant, with a ratio of primary antioxidant to secondary antioxidant of 1:1 or 1:2 (mass ratio). The hindered phenolic primary antioxidant is selected from at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate. The phosphite secondary antioxidant is selected from at least one of tris(2,4-di-tert-butylphenyl) phosphite and pentaerythritol distearate diphosphite. Its function is to prevent the catalytic degradation of silica nanospheres under high-temperature shear, ensure the stability of the masterbatch melt index, and avoid nanoparticle aggregation due to degradation.

[0043] In this embodiment, the mass fraction of silica nanospheres is 20%, the mass fraction of dispersant is 2%, the mass fraction of antioxidant is 0.2%, and the remainder is HDPE resin.

[0044] B3) A second injection mold 6 is formed by an upper mold with a smooth core and a lower mold with a smooth cavity. The upper mold serves as the second upper mold 61, and the lower mold serves as the second lower mold 62. The functional masterbatch prepared in step B2 is mixed with 12.3 times its weight of HDPE resin. After melting and plasticizing in an extruder (the second extruder 4), the mixture is injected into the second injection mold 6 at an injection pressure of 100-140 MPa and an injection speed of 50-150 mm / s. After cooling and solidification, the mixture is demolded to obtain a modified HDPE film with a thickness of 70-150 μm and a silica nanosphere mass fraction of 1.5%. In other embodiments, functional masterbatches with different silica nanosphere concentrations can also be prepared. By adjusting the ratio of functional masterbatch to HDPE resin, the same modified HDPE film can be obtained.

[0045] By first pre-dispersing silica nanospheres in functional masterbatch, and then utilizing the good flowability of functional masterbatch to mix them evenly with a large amount of HDPE resin, the silica nanospheres are ensured to be evenly dispersed in the final film.

[0046] Step S3: Prepare an ethanol aqueous solution with a mass fraction of 5%-10% and maintain its temperature at 60-80℃ for later use. The main function of ethanol is to reduce the surface tension of water, facilitating air expulsion during the liquid film formation in step S4.

[0047] Step S4: The modified HDPE film from step S2 is placed over the outside of the PP functional film from step S1. An ethanol aqueous solution prepared in step S3 is used to form a liquid film between the modified HDPE film and the PP functional film. Process edges are provided at the openings of both the PP functional film and the modified HDPE film. After the process edges of the two films are adsorbed together by the liquid film, a functional insert is obtained.

[0048] Step S5: A third injection mold 17 is formed by using an upper mold with a smooth core and a lower mold with a smooth cavity. The upper mold serves as the third upper mold 171, and the lower mold serves as the second lower mold 172. The parting surface edge of the third injection mold 17 is provided with a process edge clamping mechanism 177 for final injection molding, including the following sub-steps: C1) The functional surface of the functional insert with the micro-dimpled structure in step S4 is tightly attached to the smooth core on the upper mold. After the mold is closed, the process edge pressing mechanism 177 presses the process edge.

[0049] C2) Molten PP is injected into the mold cavity at an injection pressure of 80-150MPa and an injection speed of 200-300mm / s. It is formed on the back of the functional insert. The heat causes the PP and HDPE to fuse. The high pressure pushes the micro-dimpled structure on the PP functional film to fit the smooth core. At the same time, the surface of the modified HDPE film bulges forward to form a micro-protrusion structure, thus completing the injection molding.

[0050] C3) Reduce the pressure to 50%-80% of the injection pressure, hold the pressure for 3-8 seconds, and complete the cooling and shaping.

[0051] In this step, the injection temperature is also the commonly used temperature for PP injection molding. The higher injection speed and higher injection pressure are the key to the high-pressure pushing of the micro-pit structure of the PP functional film and the formation of the micro-protrusion structure on the surface of the modified HDPE film. When the HDPE melt pushes to form the micro-protrusion structure, driven by flow and cooling crystallization, the nanospheres tend to migrate and accumulate towards the surface and interface. After cooling and solidification, the nanospheres form a nano-scale secondary rough structure on the surface of the micron-scale main protrusion.

[0052] During injection molding, because HDPE has a higher coefficient of thermal expansion than PP, the micron-sized main protrusions formed on the surface of the modified HDPE film will embed into the back of the PP functional film. The liquid film between the two protects the nanoscale rough structure from embedding into the PP functional film. During the cooling and shaping process, the modified HDPE film has a higher shrinkage rate. Together with the liquid film, it will not damage the micro-protrusion structure on the surface of the modified HDPE film when the PP functional film is peeled off in the future.

[0053] Step S6: After cooling and solidification, open the mold and cut off the process edges.

[0054] Step S7: Immerse the packaging box in warm water (80-85℃) to peel off the PP functional film, exposing the micro-protrusion structure on the modified HDPE film layer. In this step, the temperature is slightly higher than the ethanol-water solution storage temperature in Step S3, ensuring that the physical properties are consistent during the preparation of the functional insert and the peeling off of the PP functional film.

[0055] After drying, an improved dairy product packaging box is obtained, which includes a PP outer layer and an HDPE inner layer for contacting the contents. The inner wall surface of the HDPE inner layer has a micro-nano composite rough structure, which includes micron-level main protrusions and nano-level protrusions attached to the surface of the micron-level main protrusions. The micron-scale main protrusion is formed by the above two-step replication process: First replication: The first injection mold 3 is composed of an upper mold with a micro-protrusion array texture engraved on the core and a lower mold with a smooth cavity. The functional film is injection molded to form a micro-pit structure on the inner wall of the functional film. The back of the functional film is laminated with an HDPE film. The diameter of the protrusions in the micro-protrusion array is 5μm, the height is 15μm, and the minimum distance between the outer edges of adjacent protrusions is 10μm. Second replication: During injection molding, the micro-dimpled structure on the front side of the functional film is used as the inner mold core. The molten PP and the back side of the HDPE film are fused together. Under the action of injection pressure, the surface of the HDPE film bulges forward to form a micro-protrusion structure due to the push of the micro-dimpled structure on the functional film. The nanoscale protrusions are formed from food-grade silica nanospheres modified with alkylsilane, and the average particle size of the food-grade silica nanospheres is 100 nm.

[0056] Anti-stick performance test Test method: Pour whole milk into the test box, seal it, and let it stand at 3-5℃ for 24 hours. Then open it and invert the box for 10 minutes at 20-25℃ to allow the milk to flow out naturally. The calculation formula is: Residual rate (%) = (mass of carton after dumping - mass of empty carton) / initial mass of milk x 100%.

[0057] Experiments showed that the milk residue rate in the packaging box in this embodiment was 0.48%.

[0058] Comparative Example 1-1: Ordinary PP packaging boxes obtained by smooth injection molding; the milk residue rate was 2.81% as shown in the experiment.

[0059] Comparative Examples 1-2: Ordinary HDPE packaging boxes obtained by smooth injection molding; the milk residue rate was 2.40% as shown in the experiment.

[0060] The comparison shows that the packaging box made in this embodiment has an anti-stick performance that is about 80% better than that of traditional packaging boxes. This is because a micro-nano superhydrophobic structure is formed on its inner wall. Example 2

[0061] The difference between this embodiment and Embodiment 1 is that the average particle size of the silica nanospheres used in the packaging box is 50 nm; according to experiments, the milk residue rate of the packaging box in this embodiment is 1.31%.

[0062] Comparative Example 2: The average particle size of the silica nanospheres used in the packaging box was reduced to 30 nm; the milk residue rate was 2.10% as shown in the experiment.

[0063] The comparison shows that when the average particle size of the silica nanospheres is too low, the anti-sticking performance will drop rapidly. This may be because the gaps are filled too densely, causing liquid film to permeate and forming a Wenzel state. Example 3

[0064] The difference between this embodiment and Embodiment 1 is that the average particle size of the silica nanospheres used in the packaging box is 150 nm; according to experiments, the milk residue rate of the packaging box in this embodiment is 0.93%.

[0065] Comparative Example 3: The average particle size of the silica nanospheres used in the packaging box was increased to 180 nm; the milk residue rate was 2.08% as tested.

[0066] The comparison shows that when the average particle size of the silica nanospheres is too high, the anti-sticking performance will also decrease rapidly. This may be because the gap filling is insufficient and the air pad is unstable. Example 4

[0067] The difference between this embodiment and embodiment 1 is that in step B3, the weight ratio of functional masterbatch to HDPE resin is 1:9, and the mass fraction of silica nanospheres in the generated modified HDPE film is 2%; according to experiments, the milk residue rate of the packaging box in this embodiment is 0.95%.

[0068] Comparative Example 4: The mass fraction of silica nanospheres in the modified HDPE film was increased to 2.5%; according to experiments, the milk residue rate of the packaging box in this example was 1.98%.

[0069] The comparison shows that when the mass fraction of silica nanospheres is too high, the anti-sticking performance decreases rapidly. This may be because the excessive amount of nanoparticles leads to large-size aggregation, which induces the Wenzel state. Example 5

[0070] The difference between this embodiment and Embodiment 1 is that in step B3, the weight ratio of functional masterbatch to HDPE resin is 1:19, and the mass fraction of silica nanospheres in the generated modified HDPE film is 1%; according to experiments, the milk residue rate of the packaging box in this embodiment is 0.72%.

[0071] Comparative Example 5: The mass fraction of silica nanospheres in the modified HDPE film was reduced to 0.5%; the milk residue rate of the packaging box in this example was 1.76% as shown in the experiment.

[0072] The comparison shows that when the mass fraction of silica nanospheres is too low, the anti-sticking performance will also drop rapidly. This may be because the nanoscale secondary structure is not dense enough and the air cushion is unstable. Example 6

[0073] The difference between this embodiment and Embodiment 1 is that in step A1, a first steel upper mold and a steel lower mold with a smooth cavity are used to form the first injection mold. Experiments showed that the milk residue rate was 0.78%. Example 7

[0074] The difference between this embodiment and Embodiment 1 is that in step A1, a third steel upper mold and a steel lower mold with a smooth cavity are used to form the first injection mold. Experiments showed that the milk residue rate was 0.66%.

[0075] Due to the high cost of molds, the applicant did not make many molds for comparison. Based on existing experiments and theoretical deductions, it is believed that the height of the micron-level main protrusion is more suitable to be 2-5 times its diameter. If it is less than 2, the pit may be too shallow, and the droplet cannot form a stable air cushion at the pit opening. Moreover, this design can still retain most of the structural height even if the surface is slightly worn, and the function is more durable. Example 8

[0076] The difference between this embodiment and Embodiment 1 is that in step S1, the thickness of the PP functional film is 25 μm, and in step S2, the thickness of the modified HDPE film is 50 μm; the experiment showed that its milk residue rate was 2.42%.

[0077] In another embodiment, the difference from Embodiment 1 is that in step S1, the thickness of the PP functional film is 75 μm, and in step S2, the thickness of the modified HDPE film is 180 μm; the milk residue rate was found to be 2.57% in the experiment.

[0078] The comparison shows that both excessively thin and excessively thick PP functional films and modified HDPE films will lead to failure in the fabrication of microstructures and failure to obtain good anti-stick properties. This may be because if the thickness is too thin, the cooling and setting will be too fast, resulting in insufficient time for the microtexture to be replicated, while if the thickness is too thick, the heat transfer during injection molding will be slow, and the microtexture cannot be effectively formed. Example 9

[0079] The difference between this embodiment and Embodiment 1 is that in step A2, the injection pressure is reduced to 50-70 MPa, and the injection speed is also reduced to 80-100 mm / s, which are commonly used injection molding parameters for ordinary melt PP; according to experiments, its milk residue rate is 2.27%.

[0080] In another embodiment, the difference from Embodiment 1 is that in step C2, the injection pressure is reduced to 50-70 MPa and the injection speed is reduced to 80-100 mm / s; the milk residue rate was found to be 2.51% in the experiment.

[0081] The comparison shows that using the injection pressure and injection speed commonly used in ordinary molten PP in any step will lead to the loss of microstructure during the replication process, resulting in failure of microstructure production and failure to obtain good anti-stick properties. Example 10

[0082] like Figures 1-12 As shown in the figure, this embodiment provides a production equipment and process for dairy product packaging boxes.

[0083] The production equipment includes: The functional film preparation module includes a first extruder 1, a first injection unit 2, and a first injection mold 3 sequentially connected. The first injection mold 3 includes a first core 34 and a first cavity 35 disposed opposite to each other. The gap between the first core 34 and the first cavity 35 forms a first molding cavity 36. The functional film includes a box-shaped body with inclined sidewalls and a process edge located at the box opening. The first molding cavity 36 includes a box body area for molding the box-shaped body and a process edge area for molding the process edge. The surface of the first core 34 is engraved with a micro-protrusion array texture. The diameter of the protrusions in the micro-protrusion array is 3-7 μm, the height is 11-19 μm, and the minimum distance between the outer edges of adjacent protrusions is 5-15 μm. The inner wall of the first cavity 35 is smooth. The functional film is injection molded in the first molding cavity 36, and its inner wall has a micro-pit structure corresponding to the micro-protrusion array, and its outer wall has a smooth structure.

[0084] The HDPE film preparation module includes a functional masterbatch preparation unit and a second extruder 4, a second injection unit 5, and a second injection mold 6 connected in sequence. The functional masterbatch preparation unit includes a high-speed mixer 7, a premixed extruder 8, a cooling water tank 9, a blower 10, and a pelletizer 11 connected in sequence. In the functional masterbatch preparation unit, pre-made food-grade silica nanospheres modified with octadecyltrimethoxysilane, a dispersant, an antioxidant, and a portion of HDPE resin particles are mixed at high speed, and then sequentially melted, cooled, dried, and pelletized to obtain HDPE resin particles containing silica nanospheres as the functional masterbatch.

[0085] The second injection mold 6 includes a second core 64 and a second cavity 65 disposed opposite to each other. The gap between the second core 64 and the second cavity 65 forms a second molding cavity 66. The HDPE film also includes a box-shaped body with inclined sidewalls and a process edge located at the box opening. The second molding cavity 66 also includes a box body area for molding the box-shaped body and a process edge area for molding the process edge. The surface of the second core 64 and the inner wall of the second cavity 65 are both smooth. The HDPE film is configured to adhere to the outside of the functional film. The functional masterbatch and the remaining HDPE resin particles are fed into the second extruder 4, melted, and injected into the second molding cavity 66 to obtain a modified HDPE film with smooth inner and outer walls.

[0086] The functional insert preparation module includes a liquid storage tank 12, a liquid injection mechanism 13, and a pressing mold 14. The pressing mold 14 includes a pressing core 143 and a pressing cavity 144 arranged opposite to each other. The pressing cavity 144 is configured to support the outer wall of the HDPE film. The liquid storage tank 12 injects liquid into the HDPE film through the liquid injection mechanism 13. The pressing core 143 is configured to press the functional film slowly into the HDPE film to form a liquid film between the films. When the functional film is slowly pressed into the HDPE film, the inclined sidewalls on the box-shaped body facilitate air discharge and make it easier for the liquid film to fill the interlayer. Specifically, the inclination angle of the sidewalls of the functional film and the box-shaped body in the HDPE film is between 10-15°.

[0087] The product molding module includes a third extruder 15, a third injection unit 16, and a third injection mold 17 connected sequentially. The third injection mold 17 includes a third core 174 and a third cavity 175 arranged opposite each other. The gap between the third core 174 and the third cavity 175 forms a third molding cavity 176. The surface of the third core 174 is smooth and matches the inner wall of the functional insert. A clamping mechanism 177 for clamping the process edge of the functional insert is provided at the root of the third core 174 and the opening end of the third cavity 175. During molding, the functional insert is fitted onto the third core 174, using the micro-dimpled structure on the front side of the functional film as the inner mold core. The third injection unit 16 injects melt into the third molding cavity 176 with a high injection speed and high injection pressure. The molten PP fuses with the back side of the HDPE film. Under the action of injection pressure, the surface of the HDPE film bulges forward to form a micro-protrusion structure due to the pushing action of the micro-dimpled structure on the functional film.

[0088] A transfer robot 18 is used to transfer the functional film, the HDPE film, and the functional insert between the first injection mold 3, the second injection mold 6, the pressing mold 14, and the third injection mold 17. The end effector of the transfer robot 18 includes a horizontally opening and closing thin gripper 181 and a negative pressure suction cup 182. The thin gripper 181 is used to hold, press, or release the process edge. The negative pressure suction cup 182 is configured to selectively apply suction force to the outer or inner bottom surface of the box-shaped body to achieve lifting or pressing relative to the box-shaped body. The negative pressure suction cup 182 can be supported by multiple arm sections and joints connected between the arm sections. A negative pressure channel is opened in the arm section to provide negative pressure. The position and orientation of the negative pressure suction cup 182 are controlled by the rotation of the joints.

[0089] The edge-cutting mechanism 19 is configured to cut off the process edges remaining on the molded product. Specifically, the edge-cutting mechanism 19 includes an annular punch 191 and an annular cutting edge plate 192. The inner side of the cutting edge of the annular cutting edge plate 192 is provided with a tapered guide surface, which is configured to radially position the box-shaped body. The annular punch 191 and the annular cutting edge plate 192 are coaxially arranged.

[0090] Immersion tank 20 is used to immerse the molded product to remove the functional film and expose the inner wall of the HDPE film, resulting in a packaging box with a micro-nano composite rough structure on the inner wall.

[0091] Preferably, the first injection mold 3 includes a first upper mold 31 supporting the first core 34 and a first lower mold 32 supporting the first cavity 35, the first upper mold 31 and the first lower mold 32 opening and closing in the vertical direction; the second injection mold 6 includes a second upper mold 61 supporting the second core 64 and a second lower mold 62 supporting the second cavity 65, the second upper mold 61 and the second lower mold 62 opening and closing in the vertical direction; the pressing mold 14 includes a pressing upper mold 141 supporting the pressing core 143 and a pressing lower mold 142 supporting the pressing cavity 144, the pressing upper mold 141 and the pressing lower mold 142 opening and closing in the vertical direction; the third injection mold 17 includes a third upper mold 171 supporting the third core 174 and a third lower mold 172 supporting the third cavity 175, the third upper mold 171 and the third lower mold 172 opening and closing in the vertical direction. All four molds open and close vertically, which facilitates the discharge of gas from the cavity, the filling of the melt, the transfer of the molded parts, the clamping of the process edges, and the formation of the liquid film.

[0092] Preferably, the equipment further includes a worktable 21, on which the first lower mold 32, the second lower mold 62, the pressing lower mold 142, the third lower mold 172, the transfer robot 18, and the liquid injection mechanism 13 are all mounted. The first lower mold 32 and the second lower mold 62 are located on the front and rear sides of the pressing lower mold 142, the transfer robot 18 and the liquid injection mechanism 13 are located on the left and right sides of the pressing lower mold 142, and the third lower mold 172 is located on the other side of the transfer robot 18. This layout is more compact and the movement is more reasonable. The transfer robot 18 can bring the PP functional film and modified HDPE film together from the front and rear sides into the pressing mold, while the liquid injection mechanism 13 injects liquid from the other side. The functional inserts pressed by the pressing mold are then transferred by the transfer robot 18 to the third injection mold 17 on the other side for injection molding to obtain the final product. Furthermore, the trimming mechanism 19 can also be set on one side of the transfer robot 18 where there is a gap. After the product is injection molded, the transfer robot 18 will transfer it to the trimming mechanism 19 to complete the trimming of the process edge.

[0093] Preferably, the first lower mold 32 has a first gate 33 at the center of its bottom end, the second lower mold 62 has a second gate 63 at the center of its bottom end, and the third lower mold 172 has a third gate 173 at the center of its bottom end; this is conducive to more uniform melt filling.

[0094] The first injection mold 3, the second injection mold 6, and the third injection mold 17 are all equipped with cooling mechanisms to cool the melt during injection molding. The first upper mold 31 is equipped with an ejector mechanism for ejecting the functional film process edge, the second lower mold 62 is equipped with an ejector mechanism for ejecting the HDPE film process edge, the pressing lower mold 142 is equipped with an ejector mechanism for ejecting the functional insert process edge, and the third lower mold 172 is equipped with an ejector mechanism for ejecting the molded product process edge. The ejector mechanisms of the first upper mold 31, the second lower mold 62, and the third lower mold 172 are all equipped with venting structures for venting gas during injection molding. Specifically, the ejector mechanism can be an ejector rod 22, and the venting structure is a venting channel 23 opened in the ejector rod.

[0095] The production process includes the following steps: S1. Prepare a PP functional film using the aforementioned functional film module, including the following sub-steps: A1) Food-grade PP resin granules are fed into the first extruder 1, melted, and extruded into the first injection unit 2; A2) The first injection unit 2 injects the melt into the first injection mold 3 at an injection pressure of 80-120 MPa and an injection speed of 200-300 mm / s; A3) Reduce the pressure to 35%-40% of the injection pressure, hold the pressure for 2-4 seconds, and complete the cooling and shaping. After demolding, a PP film with a micro-pit structure on the inner wall is obtained. The thickness of the PP film is 40-60μm.

[0096] In this step, the injection temperature can be the conventional injection temperature of PP, but the injection speed and injection pressure are higher than the conventional injection pressure and injection speed of PP. This ensures that the PP can fill the space on the micro-protrusion array before cooling and molding, which is the key to the molding of the micro-dimple structure.

[0097] There are two main reasons why PP material is used for functional films. First, it is a commonly used material in dairy product packaging boxes and will not affect the safety of the packaging. Second, it has high melt strength, sharp outlines of the micro-pit structure when pressed, and a heat distortion temperature much higher than room temperature. After being removed from the press, it can cool and solidify quickly to prevent springback or loosening.

[0098] S2. Prepare modified HDPE films using the HDPE film preparation module, including the following sub-steps: B1) Food-grade silica nanospheres (pre-made) modified with octadecyltrimethoxysilane, dispersant, antioxidant and some HDPE resin particles are put into high-speed mixer 7 and mixed evenly. The average particle size of the silica nanospheres is 50-150nm. The dispersant is maleic anhydride-grafted polyethylene, which prevents the aggregation of silica nanospheres and improves their dispersion uniformity in the functional masterbatch. The antioxidant is a combination of hindered phenolic primary antioxidant and phosphite secondary antioxidant, with a ratio of primary antioxidant to secondary antioxidant of 1:1 or 1:2 (mass ratio). The hindered phenolic primary antioxidant is selected from at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate. The phosphite secondary antioxidant is selected from at least one of tris(2,4-di-tert-butylphenyl) phosphite and pentaerythritol distearate diphosphite. Its function is to prevent the catalytic degradation of silica nanospheres under high-temperature shear, ensure the stability of the masterbatch melt index, and avoid nanoparticle aggregation due to degradation.

[0099] B2) The mixture in step B1 is fed into the premixed material extruder 8 for melting. The extruded strips are cooled by the cooling water tank 9 and dried by the dryer 10, and then cut into uniform functional masterbatches by the pelletizer 11. B3) The functional masterbatch prepared in step B2 is mixed with a certain amount of HDPE resin, melted in the second extruder 4 and extruded into the second injection unit 5; B4) The second injection unit 5 injects the melt into the second injection mold 6 at an injection pressure of 100-140MPa and an injection speed of 50-150mm / s. After cooling and solidification, the mold is demolded to obtain a modified HDPE film with a thickness of 70-150μm and a mass fraction of 1%-2% of silica nanospheres in the modified HDPE film.

[0100] In this step, silica nanospheres are first pre-dispersed in a small amount of functional masterbatch, and then the good flowability of the functional masterbatch is used to mix it evenly with a large amount of HDPE resin, ensuring that the silica nanospheres are uniformly dispersed in the final film. Since the inner and outer walls of the film are smooth, it can be molded using the injection temperature, injection pressure, and injection speed commonly used for HDPE resin.

[0101] S3. Prepare an ethanol aqueous solution with a mass fraction of 5%-10% and store it in the storage tank 12 for later use, maintaining its temperature at 60-80℃. The role of ethanol is mainly to reduce the surface tension of water, which facilitates the expulsion of air when the liquid film is formed in step S4.

[0102] S4. The functional insert is prepared using the functional insert preparation module, including the following sub-steps: C1) The transfer robot 18 transfers the prepared PP functional film and places it on the pressing core 143. The transfer robot 18 also transfers the prepared modified HDPE film and places it in the pressing cavity 144. C2) Inject 1-1.5 ml of the ethanol-water solution from step S3 into the modified HDPE film using the injection mechanism 13; the injection mechanism 13 can be powered by a metering pump 131 and output liquid using a flat nozzle 132 to facilitate liquid dispersion. C3) The pressing core 143, carrying the functional film, is slowly pressed into the HDPE film to form a liquid film between the films.

[0103] S5. Prepare the molded packaging box using the product molding module, including the following sub-steps: D1) The prepared functional insert is transferred to the third injection mold 17 using the transfer robot 18, and the inner wall of the functional insert is pressed against the surface of the third core 174. The process edge of the functional insert is clamped by the clamping mechanism 177. D2) Food-grade PP resin granules are fed into the third extruder 15, melted, and extruded into the third injection unit 16; D3) The third injection unit 16 injects the melt into the third injection mold 17 at an injection pressure of 80-150MPa and an injection speed of 200-300mm / s. It forms on the back of the functional insert. The heat causes PP and HDPE to fuse. The high pressure pushes the micro-dimpled structure on the PP functional film to fit the smooth core. At the same time, the surface of the modified HDPE film bulges forward to form a micro-protrusion structure, thus completing the injection molding. D4) Reduce the pressure to 50%-80% of the injection pressure, hold the pressure for 3-8 seconds, and complete the cooling and shaping.

[0104] In this step, the injection temperature is also the commonly used temperature for PP injection molding, and the injection speed and injection pressure are higher than the conventional injection pressure and injection speed of PP. By pushing the micro-dimpled structure of the PP functional film under high pressure (making it adhere to the smooth surface of the third core 174), the modified HDPE film surface is compressed towards the mold core to form a micro-protrusion structure. When the HDPE melt is pushed to form a micro-protrusion structure, driven by flow and cooling crystallization, the nanospheres tend to migrate and accumulate towards the surface and interface. After cooling and solidification, the nanospheres form a nano-scale secondary rough structure on the surface of the micron-scale main protrusion.

[0105] During injection molding, because HDPE has a higher coefficient of thermal expansion than PP, the micron-sized main protrusions formed on the surface of the modified HDPE film will embed into the back of the PP functional film. The liquid film between the two protects the nanoscale rough structure from embedding into the PP functional film. During the cooling and shaping process, the modified HDPE film has a higher shrinkage rate. Together with the liquid film, it will not damage the micro-protrusion structure on the surface of the modified HDPE film when the PP functional film is peeled off in the future.

[0106] Step S6: After cooling and shaping, open the mold and use the edge-cutting mechanism 19 to cut off the remaining process edges on the molded product.

[0107] Step S7: Immerse the packaging box in the soaking pool 20 and soak it in warm water at 80-85℃ to peel off the PP functional film and expose the micro-protrusion structure on the modified HDPE film layer.

[0108] Preferably, step C1 includes the following sub-steps: Transfer of PP functional films: (1) After the mold is opened, the PP functional film is in the state of being sleeved on the outside of the first core 34. The transfer robot 18 holds the process edge through a thin gripper 181 and the transfer robot 18 adsorbs and holds the bottom of the outer side of the box-shaped body through a negative pressure suction cup 182. (2) The PP functional film is separated from the first core 34 by an ejection mechanism, and the transfer robot 18 transfers the PP functional film to the area directly below the pressing core 143; (3) The transfer robot 18 slowly lifts the PP functional film so that it is tightly fitted onto the pressing core 143, and removes the thin gripper 181 and the negative pressure suction cup 182; Transfer of modified HDPE film: (1) After the mold is opened, the modified HDPE film is embedded in the second cavity 65. The transfer robot 18 holds the process edge through the thin gripper 181. The transfer robot 18 adsorbs and presses the bottom of the inner side of the box-shaped body through the negative pressure suction cup 182. (2) The modified HDPE film is separated from the second cavity 65 by an ejection mechanism, and the transfer robot 18 transfers the modified HDPE film to the top of the pressing cavity 144. (3) The transfer robot 18 slowly presses down the modified HDPE film to embed it into the pressing cavity 144, and removes the thin gripper 181 and the negative pressure suction cup 182.

[0109] Preferably, step D1 includes the following sub-steps: (1) The transfer robot 18 presses the process edge with the thin gripper 181. After the mold is opened, the functional insert is in the state of being embedded in the pressing cavity 144 and the thin gripper 181 is removed. (2) The functional insert is slowly pushed away from the pressing cavity 144 by the ejection mechanism. The transfer robot 18 holds the process edge by the thin gripper 181 and the transfer robot 18 adsorbs and holds the bottom of the outer side of the box-shaped body by the negative pressure suction cup 182, and transfers the functional insert to the bottom of the third core 174. (3) The transfer robot 18 slowly lifts the functional insert so that its inner wall is tightly fitted onto the third core 174; (4) The third core 174 and the transfer robot 18 together carry the functional insert down and before entering the third cavity 175, the negative pressure suction cup 182 is removed. (5) The third core 174 and the thin clamp 181 carry the functional insert and continue to descend until the clamping mechanism 177 clamps the process edge and the mold is closed, and then the thin clamp 181 is removed.

[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. An improved dairy product packaging box, characterized in that: It includes a PP outer layer and an HDPE inner layer for contacting the contents. The inner wall surface of the HDPE inner layer has a micro-nano composite rough structure, which includes micron-scale main protrusions and nano-scale protrusions attached to the surface of the micron-scale main protrusions. The micron-scale main protrusion is formed by a two-step replication process: First replication: The first injection mold is composed of an upper mold with a micro-protrusion array texture engraved on the core and a lower mold with a smooth cavity. The functional film is injection molded to form a micro-pit structure on the inner wall of the functional film. The back of the functional film is laminated with an HDPE film. The diameter of the protrusions in the micro-protrusion array is 3-7μm, the height is 11-19μm, and the minimum distance between the outer edges of adjacent protrusions is 5-15μm. Second replication: During injection molding, the micro-dimpled structure on the front side of the functional film is used as the inner mold core. The molten PP and the back side of the HDPE film are fused together. Under the action of injection pressure, the surface of the HDPE film bulges forward to form a micro-protrusion structure due to the push of the micro-dimpled structure on the functional film. The nanoscale protrusions are formed from food-grade silica nanospheres modified with alkylsilane, and the average particle size of the food-grade silica nanospheres is 50-150 nm.

2. The improved dairy product packaging box according to claim 1, characterized in that: The food-grade silica nanospheres are uniformly dispersed in the HDPE, and the mass fraction of the food-grade silica nanospheres is 1%-2%.

3. The improved dairy product packaging box according to claim 2, characterized in that: The alkylsilane is octadecyltrimethoxysilane.

4. The improved dairy product packaging box according to any one of claims 1-3, characterized in that: The thickness of the HDPE inner layer is 70-150 μm.

5. The improved dairy product packaging box according to claim 4, characterized in that: The height of the micron-sized main protrusion is 2-5 times its diameter.

6. A method for producing the improved dairy product packaging box according to any one of claims 1-5, characterized in that, Includes the following steps: Step S1, the preparation of the PP functional film, includes the following sub-steps: A1) A micro-protrusion array texture is engraved on the core of a steel upper mold using a laser. The diameter of the protrusions in the micro-protrusion array is 3-7μm, the height is 11-19μm, and the minimum distance between the outer edges of adjacent protrusions is 5-15μm. The steel upper mold and a steel lower mold with a smooth cavity are used to form a first injection mold. A2) Melt food-grade PP resin granules and inject them into the first injection mold. The injection pressure is 80-120 MPa and the injection speed is 200-300 mm / s. A3) Reduce the pressure to 35%-40% of the injection pressure, hold the pressure for 2-4 seconds, complete the cooling and shaping, and after demolding, obtain a PP film with a micro-pit structure on the inner wall. The thickness of the PP film is 40-60μm. Step S2, the preparation of the modified HDPE film, includes the following sub-steps: B1) Prepare food-grade silica nanospheres with octadecyltrimethoxysilane surface modification, wherein the average particle size of the silica nanospheres is 50-150 nm; B2) Prepare a premix by using the alkylsilane-modified silica nanospheres, dispersant, antioxidant and some HDPE resin particles prepared in step B1. Then, melt-blend the premix through an extruder. After cooling, the extruded strip material is cut into uniform functional masterbatches. B3) A second injection mold is formed by an upper mold with a smooth core and a lower mold with a smooth cavity. The functional masterbatch prepared in step B2 is mixed with a certain amount of HDPE resin, melted and plasticized in an extruder, and then injected into the second injection mold. After cooling and solidification, the modified HDPE film is demolded to obtain a modified HDPE film with a thickness of 70-150 μm and a mass fraction of 1%-2% of silica nanospheres in the modified HDPE film. Step S3: Prepare an ethanol aqueous solution with a mass fraction of 5%-10% and keep it at a temperature of 60-80℃ for later use; Step S4: The modified HDPE film from step S2 is overlaid on the outside of the PP functional film from step S1. An ethanol aqueous solution prepared in step S3 is used to form a liquid film between the modified HDPE film and the PP functional film. Process edges are provided at the openings of both the PP functional film and the modified HDPE film to obtain a functional insert. Step S5: A third injection mold is formed by using an upper mold with a smooth core and a lower mold with a smooth cavity. The parting surface edge of the third injection mold is provided with a process edge clamping mechanism to perform the final injection molding, including the following sub-steps: C1) The functional surface of the functional insert with micro-dimpled structure in step S4 is tightly attached to the smooth core on the upper mold. After the mold is closed, the process edge pressing mechanism presses the process edge. C2) Molten PP is injected into the cavity at an injection pressure of 80-150MPa and an injection speed of 200-300mm / s. It is formed on the back of the functional insert. The heat causes the PP and HDPE to fuse. The high pressure pushes the micro-dimpled structure on the PP functional film to fit the smooth core. At the same time, the surface of the modified HDPE film bulges forward to form a micro-protrusion structure, thus completing the injection molding. C3) Reduce the pressure to 50%-80% of the injection pressure, hold the pressure for 3-8 seconds, and complete the cooling and shaping process; Step S6: After cooling and solidification, open the mold and cut off the process edges; Step S7: Immerse the packaging box in warm water, peel off the PP functional film, and expose the micro-protrusion structure on the modified HDPE film layer.

7. The production method according to claim 6, characterized in that, Step B1 includes the following steps: The silica nanosphere hydrosol with a solid content of 20% was solvent-displaced with ethanol, and centrifuged and washed several times to form a stable ethanol dispersion. Octadecyltrimethoxysilane was mixed with a small amount of glacial acetic acid and anhydrous ethanol, and then added dropwise to the above silica nanosphere ethanol dispersion under a nitrogen atmosphere. The mixture was refluxed at 60-80℃ for 6-12 hours until the reaction was completed. The reaction solution was cooled to room temperature, filtered, and washed. The resulting precipitate was food-grade silica nanospheres modified with octadecyltrimethoxysilane.

8. The production method according to claim 6, characterized in that: In the functional masterbatch prepared in step B2, the mass fraction of silica nanospheres is 20%, and the dispersant is maleic anhydride-grafted polyethylene. In step B3, the weight of HDPE resin is 9-19 times the weight of the functional masterbatch.

9. The production method according to any one of claims 6-8, characterized in that: In step S7, the temperature of the warm water is 80-85℃.

Images