Aluminum-foil-free full-opaque high-temperature retort RCPP film, packaging film and preparation method thereof

Abstract

This invention relates to the field of packaging film technology, and discloses a high-temperature retortable RCPP film with no aluminum foil and full light blocking, a packaging film, and a preparation method. The film comprises layers A, B, and C stacked sequentially. Layers A and C contain polypropylene resin and nano-titanium dioxide white masterbatch; layer B contains polypropylene resin, near-infrared identifiable black masterbatch, surface-coupled talc powder, and rheology modifier masterbatch. A SiOCH buffer layer, a dense inorganic silica barrier layer, and a protective undercoat layer are sequentially disposed on the surface of layer A. During preparation, the three substrates are co-extruded, and then the barrier system is constructed by plasma vapor deposition. The SiOCH buffer layer can disperse the interlayer thermal stress caused by high-temperature retorting, preventing cracking of the inorganic barrier layer; the black masterbatch in layer B, together with the outer white masterbatch, achieves full light blocking of the film and allows it to be identified by near-infrared sorting equipment. This invention eliminates traditional aluminum foil, solving the problems of packaging films being unable to be microwaved and difficult to classify and recycle, and possesses high barrier performance.

Description

Technical Field

[0001] This invention relates to the field of packaging film technology, specifically to a high-temperature retortable RCPP film without aluminum foil that provides complete light blocking, the packaging film, and its preparation method. Background Technology

[0002] Existing high-temperature retort packaging typically relies on aluminum foil as a high-barrier and light-blocking layer. However, packaging containing aluminum foil layers not only cannot be microwaved, but also makes material separation and recycling difficult after disposal.

[0003] To achieve microwave heating, current technologies often attempt to deposit an inorganic silica layer directly on the surface of a polypropylene substrate to replace aluminum foil and provide oxygen and water barrier functions. However, due to the significant difference in the coefficients of thermal expansion between organic polypropylene and inorganic silica, severe shear stress is generated between the two layers when they expand under high-temperature cooking. This causes the inorganic barrier layer to easily crack or peel off, thus losing its barrier properties.

[0004] Meanwhile, after removing the aluminum foil, conventional carbon black pigment is often added to the film to block ultraviolet and visible light and prevent oxidation of the contents. However, conventional carbon black completely absorbs near-infrared light, causing the underlying material of the waste packaging to be unidentifiable by near-infrared optical sorting equipment on the recycling line, resulting in the inability to classify and recycle it. Furthermore, the pure black film layer is difficult to meet the conventional requirement of white appearance for most food packaging.

[0005] Furthermore, due to the loss of the rigid framework support of aluminum foil, pure polypropylene films are prone to severe thermal shrinkage deformation during high-temperature cooking. Although adding a large amount of inorganic powder inside the film can improve rigidity and limit thermal shrinkage, this will lead to a sharp increase in melt friction resistance during extrusion processing, which can easily cause melt fracture and die accumulation, severely damaging the smoothness of the film surface and the continuity of production. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a foil-free, fully light-blocking high-temperature retortable RCPP film, packaging film, and preparation method. This solves the problems that existing high-temperature retortable flexible packaging typically relies on aluminum foil as a high-barrier and light-blocking layer, which makes it impossible to microwave-heat the packaging and difficult to recycle it using near-infrared optical sorting equipment after disposal. Furthermore, the different internal stresses of the multilayer composite film during high-temperature retorting can easily cause interlayer peeling and inorganic layer shedding.

[0007] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a high-temperature retortable RCPP film and a packaging film that is completely light-blocking without aluminum foil, comprising: an RCPP film having an A layer, a B layer and a C layer, wherein the packaging film comprises the RCPP film; Layer A consists of 90-95% highly crystalline homopolymer polypropylene and 5-10% nano-titanium dioxide white masterbatch by weight percentage. Layer B consists of 62.5–72.75% block copolymer polypropylene, 15–20% near-infrared identifiable black masterbatch, 3% maleic anhydride grafted polypropylene, 1.25–2.5% rheology modifier masterbatch, and 8–12% surface-coupled talc by weight percentage. Layer C consists of 90-95% random copolymer polypropylene and 5-10% nano-titanium dioxide white masterbatch by weight percentage. A SiOCH buffer layer with a thickness of 10-20 nm is provided on the surface of layer A; The surface of the SiOCH buffer layer is provided with a dense inorganic silicon oxide barrier layer with a thickness of 40-60 nm. A protective undercoat is applied to the surface of the dense inorganic silica barrier layer, with a dry coating weight of 0.5–1.0 g / m². 2 ; The nano titanium dioxide white masterbatch contains 40% titanium dioxide by weight.

[0008] By adopting the above technical solution, due to the combination of multilayer co-extruded polypropylene film with plasma vapor deposition buffer and barrier layers, the effects of full light blocking, high oxygen and water vapor barrier, high temperature resistance to cooking, and material recycling are achieved.

[0009] In terms of light blocking and optical recognition, the near-infrared identifiable black masterbatch added to layer B can absorb visible light and block ultraviolet and visible light from penetrating. The nano-titanium dioxide particles in layers A and C cover the black inside by reflecting and scattering light, keeping the film white in appearance.

[0010] Regarding interlayer bonding and stress buffering, the polypropylene substrate itself is non-polar. When an inorganic silica layer is directly deposited on its surface, the difference in thermal expansion coefficients between the two is significant, making the inorganic layer prone to cracking after heating and cooking. First, a SiOCH buffer layer is deposited on the surface of layer A, followed by a dense inorganic silica barrier layer, forming a structure that transitions from organic to inorganic materials. The SiOCH buffer layer retains some organic groups such as methyl groups, physically cross-linking with the polypropylene of layer A on its bottom surface and chemically bonding with the dense inorganic silica barrier layer on its top surface. Under high-temperature thermal shock, this buffer layer can absorb and disperse the shear force caused by thermal expansion, preventing the barrier layer from cracking.

[0011] During the plasma deposition stage, hexamethyldisiloxane gas molecules undergo bond breaking due to electron bombardment, generating silanyl groups, siloxane radicals, and fragment ions. A small amount of oxygen is introduced in the early stages of deposition, allowing carbon elements to be retained in the deposit, forming a SiOCH network. In the later stages of deposition, the oxygen flow rate is increased to fully oxidize and remove organic groups, ultimately generating a tightly packed siloxane inorganic barrier layer.

[0012] In terms of structural stability, the surface-coupled talc powder added to layer B is distributed in a lamellar state within the polypropylene matrix, forming a physical labyrinth that blocks gas permeation. It also increases the film stiffness and limits the shrinkage of layers A and C when heated. A protective undercoat is coated on the outer side of the dense inorganic silica barrier layer, primarily to prevent frictional damage to the inorganic layer during subsequent winding and printing processes.

[0013] Preferably, the thickness ratio of layer A, layer B and layer C is 15-25:50-70:15-25, and the total thickness of the RCPP film is 50-200 μm.

[0014] By adopting the above technical solution, a reasonable layer thickness ratio maintains the symmetrical stress distribution on both sides of the film. The thickness of layers A and C is sufficient to completely cover the dark color of layer B. Layer B provides mechanical support and total light blocking, preventing edge curling deformation of the film during winding and subsequent lamination processing.

[0015] Preferably, the surface-coupled talc powder is prepared by the following steps: Flake talc powder with a median particle size of 1.5–2.5 μm and a diameter-to-thickness ratio of 20–30:1 was placed in a forced-air drying oven and dehydrated at 100–120°C for 3–5 hours. The dehydrated flake talc powder is fed into a high-speed mixer and heated to 100-110°C through friction. Anhydrous ethanol containing distearyloxyisopropoxyaluminate coupling agent is sprayed onto the surface of dehydrated flake talc powder through a spraying device. After spraying, the internal temperature of the high-speed mixer is maintained at 100-110°C. Ethanol vapor is discharged and the mixture is mixed at a constant temperature for 10-15 minutes. The mixture is then cooled and discharged. The weight of the distearyloxyisopropoxyaluminate coupling agent is 1.5 to 2.5% of the total weight of the flake talc.

[0016] By employing the above technical solution, heating and dehydration eliminates free water introduced by the talc powder, preventing moisture from vaporizing and forming microbubbles within the membrane during extrusion heating. The spray method ensures the coupling agent is uniformly adhered to the surface of the talc particles. The distearyloxyisopropoxyaluminate coupling agent used reacts with the hydroxyl groups on the talc surface at one end, removing alcohols and forming chemical bonds; the distearyloxy group at the other end is a long-chain aliphatic structure that can entangle with the polypropylene molecular chains. After this treatment, the talc surface changes from hydrophilic to lipophilic, making it less prone to agglomeration in the polypropylene melt and resulting in better dispersion.

[0017] Preferably, the near-infrared identifiable black masterbatch is made of the following components in weight percentage: 35-40% copper chromium manganese composite oxide spinel black pigment; 5% maleic anhydride grafted polypropylene, wherein the grafting rate of the maleic anhydride grafted polypropylene is 0.8-1.2%; and 55-60% block copolymer polypropylene resin. The preparation method of near-infrared identifiable black masterbatch is as follows: copper chromium manganese composite oxide spinel black pigment, maleic anhydride grafted polypropylene and block copolymer polypropylene resin are put into a low-speed kneader for premixing to obtain black polymer premix. The black polymer premix is ​​put into a co-rotating twin-screw extruder and melt extruded and vacuum degassing in a temperature range of 160-210℃. After water cooling and pelletizing, it is produced.

[0018] By adopting the above technical solution, ordinary carbon black absorbs near-infrared light, making it impossible for sorting equipment to obtain reflected signals. Using copper-chromium-manganese composite oxide spinel black pigment, which absorbs visible light but reflects near-infrared light, waste packaging film can be identified as polypropylene by near-infrared equipment on the recycling line, facilitating classification. Maleic anhydride-grafted polypropylene contains polar groups, which can improve the bonding state between pigment particles and non-polar polypropylene resin. The preparation process clearly defines the equipment and process scope for premixing and extrusion granulation, ensuring the full disclosure and feasibility of the masterbatch preparation scheme.

[0019] Preferably, the rheology modifier masterbatch is prepared by feeding ultra-high molecular weight polydimethylsiloxane colloid and block copolymer polypropylene powder in a weight ratio of 40:60 into an internal mixer, mixing at 185°C for 18 minutes for dynamic high-shear dispersion, crushing in a pulverizer, and then extruding and granulating in a single-screw extruder; the weight average molecular weight of the ultra-high molecular weight polydimethylsiloxane colloid is 500,000 to 800,000 g / mol.

[0020] By adopting the above technical solution, the ultra-high molecular weight polydimethylsiloxane colloid moves towards the interface between the melt and the die surface during extrusion, playing a lubricating role and reducing the frictional resistance of the melt when passing through the die lip. This solves the problems of melt fracture or die accumulation caused by adding too much inorganic powder. The shearing force provided by the internal mixer breaks down the high-viscosity polydimethylsiloxane colloid and disperses it into the polypropylene powder, avoiding excessively high local concentrations that could cause crystal points to appear on the film surface.

[0021] Preferably, the protective primer layer is formed by film formation from an aqueous protective primer liquid, which is prepared by mixing components comprising the following parts by weight: 60-70 parts of aqueous chlorinated polypropylene dispersion; 30-40 parts of waterborne aliphatic polyurethane dispersion; 0.3 to 0.7 parts of polyether siloxane copolymer.

[0022] By employing the above technical solutions, the chlorinated polypropylene in the waterborne chlorinated polypropylene dispersion possesses a hydrocarbon backbone similar to the substrate, and the polar chlorine atoms further enhance its adhesion to the dense inorganic silica barrier layer. The waterborne aliphatic polyurethane dispersion provides relatively flexible molecular chains and temperature resistance, buffering external mechanical forces after film formation, and is not prone to softening or becoming sticky under high-temperature cooking conditions. The polyether siloxane copolymer is used to reduce the surface tension of the coating liquid, allowing the coating liquid to spread rapidly on the inorganic layer surface, forming a smooth coating.

[0023] Secondly, the present invention provides a method for preparing a high-temperature retortable RCPP film and packaging film that is completely light-blocking without aluminum foil, comprising the following steps: The A-layer feed, B-layer main feed, B-layer side feed and C-layer feed are melted and extruded in their respective extruders, and then fed into a T-shaped flat die through a co-extrusion distributor to form a three-layer co-extrusion melt. The RCPP film is obtained by cooling and shaping the surface of the quench roll. The RCPP film was placed in a vacuum plasma deposition apparatus for plasma activation, and hexamethyldisiloxane gas and argon gas were introduced for vapor phase deposition to obtain a SiOCH buffer layer on the surface of layer A. Under continuous arc conditions, oxygen is introduced and the flow rate of hexamethyldisiloxane gas is adjusted to increase the plasma power of the vacuum plasma deposition equipment and the working pressure of the deposition chamber, and a dense inorganic silicon oxide barrier layer is obtained by continuing vapor phase deposition. A water-based protective primer is uniformly coated on the surface of a dense inorganic silica barrier layer, and then dried in a hot air convection oven at a temperature of 85-95°C to form a protective primer layer. The primer layer is then rolled up to obtain a high-temperature retortable RCPP film and packaging film that is completely light-blocking without aluminum foil.

[0024] By adopting the above technical solution, multilayer co-extrusion completes the molding of a three-layer substrate film in one step. Plasma vapor deposition continuously performs surface activation, deposition of buffer layer, and deposition of inorganic barrier layer in a vacuum chamber, avoiding interface contamination caused by material exposure to air during the process.

[0025] The specific working process is as follows: First, argon plasma is used to bombard the polypropylene surface of layer A, breaking the carbon-hydrogen bonds or carbon-carbon bonds of the surface molecular chains, generating surface free radicals, making the surface rough and reactive. Then, without interrupting the plasma flow, hexamethyldisiloxane gas is introduced. The gaseous monomers are decomposed in the plasma into active fragments containing silanyl methyl groups and siloxane free radicals. Because oxygen has not yet been introduced, the hydrocarbon groups in the fragments remain, depositing on the film surface and combining with the free radicals generated in the previous step to crosslink into a relatively flexible SiOCH buffer network. Finally, oxygen is directly introduced while reducing the amount of hexamethyldisiloxane. The oxygen plasma oxidizes and decomposes the methyl groups in the monomer fragments into carbon dioxide and water, which are then discharged. The remaining siloxane free radicals polymerize on the buffer layer to form a dense inorganic barrier network. This continuous arc operation creates a gradual transition in composition between the buffer layer and the barrier layer, without a clear physical interface, which is more conducive to preventing gas permeation.

[0026] Preferably, the process for preparing RCPP film satisfies the following parameter settings: The A-layer and C-layer ingredients are extruded separately in independent single-screw extruders with a temperature gradient of 180–250°C. The B-layer main feed and B-layer side feed are extruded in a twin-screw extruder with a side feed port. The B-layer main feed is added from the main feed port of the twin-screw extruder, and the B-layer side feed is added from the side feed port. The temperature range of the twin-screw extruder is 190-210℃. The die lip temperature of the T-type flat die head is controlled at 215~220℃; The surface water temperature of the quenching roller is 20-25℃, and the traction speed is set to 30-80m / min.

[0027] By adopting the above technical solution, extrusion temperatures were set according to the melting characteristics of each layer. Layers A and C were extruded using a single screw to provide stable surface pressure. Layer B, containing a relatively large amount of inorganic talc and pigment masterbatch, was extruded using a twin-screw extruder with a side-feed method. The resin was first melted in the main feeding section, and then the powder was added from the side feeding port. This avoided dry friction of the powder in the feeding section, which could lead to equipment wear or localized overheating and decomposition of the material. The shearing force of the twin screws was used to mix the powder evenly. The water temperature and traction speed of the quench roller were coordinated to allow the polypropylene melt to cool rapidly after leaving the die, forming fine crystals and improving the overall toughness of the film.

[0028] Preferably, the process for preparing the SiOCH buffer layer satisfies the following parameter settings: The background vacuum level of the deposition chamber of the vacuum plasma deposition equipment was evacuated to 4.0 × 10⁻⁶. -3 ~5.0×10 -3 Pa, argon gas was introduced to adjust the working pressure of the deposition chamber to 1.0-2.0 Pa, and plasma activation was performed on the surface of layer A under a radio frequency power of 1.0-2.0 kW; After plasma activation, hexamethyldisiloxane gas with a flow rate of 200–300 sccm and argon gas with a flow rate of 50–100 sccm are introduced. Under the conditions of radio frequency power of 1.5–2.5 kW and working pressure of 2.0–4.0 Pa in the deposition chamber, a SiOCH buffer layer is deposited.

[0029] By employing the above technical solution, the base vacuum is used to remove impurity gases. A radio frequency power of 1.0–2.0 kW is used to activate the surface, preventing excessive power from burning the substrate. During the deposition of the buffer layer, hexamethyldisiloxane is introduced at a relatively low operating pressure and power, controlling the degree of gas molecule dissociation. This allows only partial breakage of monomers, preserving a certain proportion of silicon-carbon bonds, ultimately forming a cross-linked film with low hardness and some flexibility.

[0030] Preferably, the process of depositing a dense inorganic silica barrier layer satisfies the following parameter settings: oxygen is introduced at a flow rate of 1500-2200 sccm, the flow rate of hexamethyldisiloxane gas is adjusted to 100-150 sccm, the plasma power is increased to 3.5-5.0 kW, the working pressure of the deposition chamber is adjusted to 3.0-6.0 Pa, and a dense inorganic silica barrier layer is deposited.

[0031] By employing the above technical solution, increasing the oxygen flow rate while reducing the monomer flow rate creates a reaction environment with excess oxygen. Increasing the power to 3.5–5.0 kW and inputting greater radio frequency energy causes the hexamethyldisiloxane molecules in the reaction chamber to completely dissociate. The higher operating pressure and power allow silicon-oxygen free radicals to densely accumulate on the substrate surface, completing deep oxidation, removing organic components, and generating an inorganic layer with fewer pores, thus cutting off the channels for oxygen and water vapor to enter and exit, meeting the high-barrier requirements of high-temperature cooking.

[0032] This invention provides a high-temperature retortable RCPP film without aluminum foil, a packaging film, and a preparation method thereof. It has the following beneficial effects: 1. This invention constructs a gradient structure transitioning from organic to inorganic by first vapor-depositing a SiOCH buffer layer retaining some organic groups on the surface of the polypropylene A layer, followed by continuous deposition of a dense inorganic silica barrier layer. Utilizing the physical cross-linking and chemical bonding of the SiOCH layer, the shear stress caused by the difference in thermal expansion between the polypropylene substrate and the inorganic layer during high-temperature cooking is absorbed and dispersed, preventing the barrier layer from cracking or detaching due to heat. This achieves the high oxygen and water barrier standards required for high-temperature cooking while eliminating the need for a traditional aluminum foil layer and meeting microwave heating conditions.

[0033] 2. This invention achieves a balance between high light-blocking properties and material recyclability by adding a near-infrared identifiable black masterbatch made from copper-chromium-manganese composite oxide spinel black pigment to the middle B layer, and adding nano-titanium dioxide white masterbatch to the inner and outer A and C layers. The black pigment in the middle layer absorbs ultraviolet and visible light to prevent oxidation of the contents, while reflecting near-infrared light, allowing the waste packaging to be accurately identified and sorted by near-infrared optical sorting equipment on a recycling line. The outer titanium dioxide layer serves to cover the black interior and maintain the appearance of the conventional white packaging.

[0034] 3. This invention improves the thermal dimensional stability and extrusion smoothness of the film by adding surface-coupled modified flake talc to the intermediate B layer and using ultra-high molecular weight polydimethylsiloxane rheology modifier masterbatch. The uniformly dispersed flake talc constructs a physical barrier within the film and increases overall rigidity, limiting the thermal shrinkage of the film during high-temperature cooking. The rheology modifier masterbatch migrates towards the die junction during extrusion to form lubrication, reducing melt friction resistance and solving the problems of melt fracture and die accumulation caused by adding a large amount of inorganic powder, thus ensuring a smooth film surface. Attached Figure Description

[0035] Figure 1 The near-infrared reflectance spectra of the thin film samples from Examples 1 to 3 of the present invention are shown below. Figure 2 This is a graph showing the cumulative oxygen permeation curve of a thin film sample under constant temperature and humidity conditions, as an embodiment of the present invention. Figure 3 The cumulative water vapor transmission curve of the thin film sample under constant temperature and humidity conditions is shown in the embodiment of the present invention. Figure 4 The attenuated total reflectance Fourier transform infrared spectra of the inner surface of the thin film samples of Example 2 and Comparative Example 3 of the present invention are shown. Figure 5 The images show the near-infrared reflectance spectra of the thin film samples from Example 2 and Comparative Example 4 of the present invention. Detailed Implementation

[0036] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] Preparation Examples 1-10: Preparation Example 1: This preparation example provides a surface-coupled talc powder, including the following steps: Flake talc powder (median particle size of 1.5 μm and aspect ratio of 20:1) was placed in a forced-air drying oven and dehydrated at 100°C for 3 hours; the dehydrated flake talc powder was then fed into a high-speed mixer, and the speed of the high-speed mixer was set to allow the dehydrated flake talc powder to be heated to 100°C by friction. Distearate isopropoxyaluminate, weighed at 1.5% of the total mass of talc powder, was used as a coupling agent. The coupling agent was dissolved in anhydrous ethanol, and the anhydrous ethanol containing the coupling agent was evenly sprayed onto the surface of the dehydrated flake talc powder through a spraying device. After spraying, the temperature of the dehydrated flake talc powder was maintained at 100℃, the exhaust valve was opened to release ethanol vapor, and the mixture was kept at a constant temperature and high speed for 10 minutes. The mixture was then cooled and discharged to obtain surface-coupled talc powder.

[0038] Preparation Example 2: This preparation example provides a surface-coupled talc powder, including the following steps: Flake talc powder (median particle size of 2.0 μm and aspect ratio of 25:1) was placed in a forced-air drying oven and dehydrated at 110℃ for 4 hours; the dehydrated flake talc powder was then fed into a high-speed mixer, and the speed of the high-speed mixer was set so that the dehydrated flake talc powder was heated to 105℃ by friction. Distearate isopropoxyaluminate, weighed at 2.0% of the total mass of talc powder, was used as a coupling agent. The coupling agent was dissolved in anhydrous ethanol, and the anhydrous ethanol containing the coupling agent was evenly sprayed onto the surface of the dehydrated flake talc powder through a spraying device. After spraying, the temperature of the dehydrated flake talc powder was maintained at 105℃, the exhaust valve was opened to release ethanol vapor, and the mixture was kept at a constant temperature and high speed for 12 minutes. The mixture was then cooled and discharged to obtain surface-coupled talc powder.

[0039] Preparation Example 3: This preparation example provides a surface-coupled talc powder, including the following steps: Flake talc powder (median particle size of 2.5 μm and aspect ratio of 30:1) was placed in a forced-air drying oven and dehydrated at 120°C for 5 hours; the dehydrated flake talc powder was then fed into a high-speed mixer, and the speed of the high-speed mixer was set so that the dehydrated flake talc powder was heated to 110°C by friction. Distearate isopropoxyaluminate, weighed at 2.5% of the total mass of talc powder, was used as a coupling agent. The coupling agent was dissolved in anhydrous ethanol, and the anhydrous ethanol containing the coupling agent was evenly sprayed onto the surface of the dehydrated flake talc powder through a spraying device. After spraying, the temperature of the dehydrated flake talc powder was maintained at 110℃, the exhaust valve was opened to release ethanol vapor, and the mixture was kept at a constant temperature and high speed for 15 minutes. The mixture was then cooled and discharged to obtain surface-coupled talc powder.

[0040] Preparation Example 4: This preparation example provides a near-infrared identifiable black masterbatch, including the following steps: Weigh out 35% copper chromium manganese composite oxide spinel black pigment, 5% maleic anhydride grafted polypropylene (grafting rate 0.8wt%) and 60% block copolymer polypropylene resin by mass percentage, put them into a low-speed kneader and premix them evenly to obtain black polymer premix. Black polymer premix is ​​fed into a co-rotating twin-screw extruder, and the temperature of each zone of the co-rotating twin-screw extruder is set as follows: 160°C for the feeding zone, 190°C for the melting zone, and 200°C for the homogenization zone. The black polymer premix is ​​melt-extruded at the set temperature of each zone. Vacuum degassing is performed during the melt extrusion process. After extrusion, the premix is ​​water-cooled and pelletized to obtain near-infrared identifiable black masterbatch.

[0041] Preparation Example 5: This preparation example provides a near-infrared identifiable black masterbatch, including the following steps: Weigh out 37.5% of copper chromium manganese composite oxide spinel black pigment, 5% of maleic anhydride grafted polypropylene (grafting rate 1.0 wt%) and 57.5% of block copolymer polypropylene resin by mass percentage, put them into a low-speed kneader and premix them evenly to obtain black polymer premix. Black polymer premix is ​​fed into a co-rotating twin-screw extruder, and the temperature of each zone of the co-rotating twin-screw extruder is set as follows: 170°C for the feeding zone, 200°C for the melting zone, and 200°C for the homogenization zone. The black polymer premix is ​​melt-extruded at the set temperature of each zone. Vacuum degassing is performed during the melt extrusion process. After extrusion, the premix is ​​water-cooled and pelletized to obtain near-infrared identifiable black masterbatch.

[0042] Preparation Example 6: This preparation example provides a near-infrared identifiable black masterbatch, including the following steps: Weigh out 40% of copper chromium manganese composite oxide spinel black pigment, 5% of maleic anhydride grafted polypropylene (grafting rate 1.2wt%) and 55% of block copolymer polypropylene resin by mass percentage, put them into a low-speed kneader and premix them evenly to obtain black polymer premix. Black polymer premix is ​​fed into a co-rotating twin-screw extruder, and the temperature of each zone of the co-rotating twin-screw extruder is set as follows: 180°C for the feeding zone, 210°C for the melting zone, and 200°C for the homogenization zone. The black polymer premix is ​​melt-extruded at the set temperature of each zone. Vacuum degassing is performed during the melt extrusion process. After extrusion, the premix is ​​water-cooled and pelletized to obtain near-infrared identifiable black masterbatch.

[0043] Preparation Example 7: This preparation example provides a rheology-modified masterbatch, including the following steps: Weigh ultra-high molecular weight polydimethylsiloxane colloid (weight average molecular weight of 500,000-800,000 g / mol) and block copolymer polypropylene powder at a mass ratio of 40:60. Put the ultra-high molecular weight polydimethylsiloxane colloid and block copolymer polypropylene powder into an internal mixer and perform dynamic high-shear dispersion by mixing at 185°C for 18 min to obtain a mixed blend of silicone and polypropylene. After crushing the mixed blend of silicone and polypropylene by a pulverizer, put it into a single screw extruder for extrusion granulation to obtain rheology modifier masterbatch.

[0044] Preparation Example 8: This preparation example provides a protective primer, including the following steps: In a stainless steel reactor equipped with an anchor stirrer, 60 parts by weight of aqueous chlorinated polypropylene dispersion and 40 parts by weight of aqueous aliphatic polyurethane dispersion were added. Stirring was started and the stirring speed was set to 150 rpm. 0.3 parts of polyether siloxane copolymer were slowly added dropwise through a dropping funnel as a leveling agent to obtain a coating mixture. The coating mixture was stirred continuously at room temperature for 20 minutes. The material was collected and filtered through a 200-mesh filter to obtain a homogeneous, precipitate-free aqueous protective primer for later use.

[0045] Preparation Example 9: This preparation example provides a protective primer, including the following steps: In a stainless steel reactor equipped with an anchor stirrer, 65 parts by weight of aqueous chlorinated polypropylene dispersion and 35 parts by weight of aqueous aliphatic polyurethane dispersion were added. Stirring was started and the stirring speed was set to 200 rpm. 0.5 parts of polyether siloxane copolymer were slowly added dropwise through a dropping funnel as a leveling agent to obtain a coating mixture. The coating mixture was stirred continuously at room temperature for 30 minutes. The material was collected and filtered through a 200-mesh filter to obtain a homogeneous, precipitate-free aqueous protective primer for later use.

[0046] Preparation Example 10: This preparation example provides a protective primer, including the following steps: In a stainless steel reactor equipped with an anchor stirrer, 70 parts by weight of aqueous chlorinated polypropylene dispersion and 30 parts by weight of aqueous aliphatic polyurethane dispersion were added. Stirring was started and the stirring speed was set to 250 rpm. 0.7 parts of polyether siloxane copolymer were slowly added dropwise through a dropping funnel as a leveling agent to obtain a coating mixture. The coating mixture was stirred continuously at room temperature for 40 minutes. The material was collected and filtered through a 200-mesh filter to obtain a homogeneous, precipitate-free aqueous protective primer for later use.

[0047] Examples 1-3: Example 1: This embodiment provides a method for preparing a high-temperature retortable RCPP packaging film with no aluminum foil and full light blocking properties, including the following steps: 95 wt% of highly crystalline homopolymer polypropylene and 5 wt% of nano-titanium dioxide white masterbatch (titanium dioxide accounts for 40% of the total mass of white masterbatch) are mixed evenly as the A layer ingredients. 72.75 wt% of block copolymer polypropylene, 15 wt% of near-infrared identifiable black masterbatch prepared in Preparation Example 4, 3 wt% of maleic anhydride grafted polypropylene, and 1.25 wt% of rheology modifier masterbatch prepared in Preparation Example 7 were mixed evenly as the main feed for layer B, and 8 wt% of surface-coupled talc prepared in Preparation Example 1 was weighed as the side feed for layer B. 95 wt% random copolymer polypropylene and 5 wt% nano titanium dioxide white masterbatch were mixed evenly as the C layer material.

[0048] Three extruders were used for co-extrusion. Layers A and C each used independent single-screw extruders with temperature gradients set at 180℃, 220℃, and 230℃. Layer B used a twin-screw extruder with a side feed port, and the temperature of each zone of the twin-screw extruder was set at 190℃. The main feed for layer B was added from the main feed port of the twin-screw extruder, and the side feed for layer B was added from the side feed port at the rear of the barrel of the twin-screw extruder.

[0049] Layer A feed, layer B main feed, layer B side feed, and layer C feed are melt-extruded in their respective single-screw and twin-screw extruders to form layer A melt, layer B melt, and layer C melt. These three melts are then co-extruded through a co-extrusion distributor into a T-die to form a three-layer co-extruded melt. The die lip temperature is controlled at 215℃. The three-layer co-extruded melt is vertically extruded onto the surface of a quench roll, with the quench roll water temperature controlled at 20℃ and the traction speed set at 80m / min. After cooling and shaping, a retort-grade cast polypropylene (RCPP) film is obtained. The thickness ratio of layers A, B, and C is set to 15:70:15, and the total thickness of the RCPP film is 50μm.

[0050] The RCPP film was placed in a roll-to-roll vacuum plasma deposition apparatus, the chamber door was closed, and the vacuum level in the deposition chamber was evacuated to 5.0 × 10⁻⁶. -3 Pa; then argon gas was introduced and the working pressure of the deposition chamber was adjusted to 1.0 Pa. The radio frequency power supply was started and the power was set to 1.0 kW to perform online plasma activation on the surface of layer A.

[0051] Hexamethyldisiloxane (HMDSO) gas at 200 sccm (standard mL / min) and argon gas at 50 sccm were introduced. Under conditions of 1.5 kW RF power and 2.0 Pa operating pressure, a 10 nm thick SiOCH (silicon oxide carbon) buffer layer was deposited on the surface of layer A. Under continuous arc control, oxygen at 1500 sccm was introduced, the HMDSO gas flow rate was adjusted to 100 sccm, the plasma power was increased to 3.5 kW, and the deposition chamber operating pressure was adjusted to 3.0 Pa. A dense inorganic silicon oxide barrier layer with a thickness of 40 nm was then deposited on the surface of the SiOCH buffer layer.

[0052] The protective primer prepared in Example 8 was uniformly coated onto the surface of the silicon oxide barrier layer using a gravure coating machine. The coated layer was then dried in an 85°C hot air convection oven to form a film, with the dry coating amount controlled at 0.5 g / m². 2 High-temperature retort RCPP packaging film with no aluminum foil and full light blocking is produced by winding.

[0053] Example 2: This embodiment provides a method for preparing a high-temperature retortable RCPP packaging film with no aluminum foil and full light blocking properties, including the following steps: 92.5 wt% of highly crystalline homopolymer polypropylene and 7.5 wt% of nano-titanium dioxide white masterbatch (titanium dioxide accounts for 40% of the total mass of white masterbatch) are mixed evenly as the A layer ingredients. 67.625 wt% of block copolymer polypropylene, 17.5 wt% of near-infrared identifiable black masterbatch prepared in Preparation Example 5, 3 wt% of maleic anhydride grafted polypropylene, and 1.875 wt% of rheology modifier masterbatch prepared in Preparation Example 7 were mixed evenly as the main feed for layer B, and 10 wt% of surface-coupled talc prepared in Preparation Example 2 was weighed as the side feed for layer B. 92.5 wt% of random copolymer polypropylene and 7.5 wt% of nano-titanium dioxide white masterbatch were mixed evenly as the C layer material.

[0054] Three extruders were used for co-extrusion. Layers A and C each used independent single-screw extruders with temperature gradients set at 185℃, 230℃, and 240℃. Layer B used a twin-screw extruder with a side feed port, and the temperature of each zone of the twin-screw extruder was set at 200℃. The main feed for layer B was added from the main feed port of the twin-screw extruder, and the side feed for layer B was added from the side feed port at the rear of the barrel of the twin-screw extruder.

[0055] Layer A feed, layer B main feed, layer B side feed, and layer C feed are melt-extruded in their respective single-screw and twin-screw extruders to form layer A melt, layer B melt, and layer C melt. These three melts are then co-extruded through a co-extrusion distributor into a T-die to form a three-layer co-extruded melt. The die lip temperature is controlled at 218℃. The three-layer co-extruded melt is vertically extruded onto the surface of a quench roll, with the quench roll water temperature controlled at 22℃ and the traction speed set at 50m / min. After cooling and shaping, an RCPP film is obtained. The thickness ratio of layers A, B, and C is set to 20:60:20, and the total thickness of the RCPP film is 125μm.

[0056] The RCPP film was placed in a roll-to-roll vacuum plasma deposition apparatus, the chamber door was closed, and the vacuum level in the deposition chamber was evacuated to 4.5 × 10⁻⁶. -3 Pa; then argon gas was introduced and the working pressure of the deposition chamber was adjusted to 1.5 Pa. The radio frequency power supply was started and the power was set to 1.5 kW to perform online plasma activation on the surface of layer A.

[0057] HMDSO gas at 250 sccm and argon gas at 75 sccm were introduced, and a 15 nm thick SiOCH buffer layer was deposited on the surface of layer A under the conditions of RF power of 2.0 kW and working pressure of 3.0 Pa. Under the condition of continuous arcing, oxygen at 1800 sccm was introduced, the HMDSO gas flow rate was adjusted to 125 sccm, the plasma power was increased to 4.2 kW, and the working pressure of the deposition chamber was adjusted to 4.5 Pa, and a dense inorganic silicon oxide barrier layer with a thickness of 50 nm was deposited on the surface of the SiOCH buffer layer.

[0058] The protective primer prepared in Example 9 was uniformly coated onto the surface of the silicon oxide barrier layer using a gravure coating machine. The coated layer was then dried in a 90°C hot air convection oven to form a film, with the dry coating amount controlled at 0.75 g / m². 2 High-temperature retort RCPP packaging film with no aluminum foil and full light blocking is produced by winding.

[0059] Example 3: This embodiment provides a method for preparing a high-temperature retortable RCPP packaging film with no aluminum foil and full light blocking properties, including the following steps: 90 wt% of highly crystalline homopolymer polypropylene and 10 wt% of nano-titanium dioxide white masterbatch (titanium dioxide accounts for 40% of the total mass of white masterbatch) are mixed evenly as the A layer ingredients. 62.5 wt% of block copolymer polypropylene, 20 wt% of near-infrared identifiable black masterbatch prepared in Preparation Example 6, 3 wt% of maleic anhydride grafted polypropylene, and 2.5 wt% of rheology modifier masterbatch prepared in Preparation Example 7 were mixed evenly as the main feed for layer B, and 12 wt% of surface-coupled talc prepared in Preparation Example 3 was weighed as the side feed for layer B. 90 wt% random copolymer polypropylene and 10 wt% nano titanium dioxide white masterbatch were mixed evenly as the C layer material.

[0060] Three extruders were used for co-extrusion. Layers A and C each used independent single-screw extruders with temperature gradients set at 190℃, 240℃, and 250℃. Layer B used a twin-screw extruder with a side feed port, and the temperature of each zone of the twin-screw extruder was set at 210℃. The main feed for layer B was added from the main feed port of the twin-screw extruder, and the side feed for layer B was added from the side feed port at the rear of the barrel of the twin-screw extruder.

[0061] Layer A feed, layer B main feed, layer B side feed, and layer C feed are melt-extruded in their respective single-screw and twin-screw extruders to form layer A melt, layer B melt, and layer C melt. These three melts are then co-extruded through a co-extrusion distributor into a T-die to form a three-layer co-extruded melt. The die lip temperature is controlled at 220℃. The three-layer co-extruded melt is vertically extruded onto the surface of a quench roll, with the quench roll water temperature controlled at 25℃ and the traction speed set at 30m / min. After cooling and shaping, an RCPP film is obtained. The thickness ratio of layers A, B, and C is set to 25:50:25, and the total thickness of the RCPP film is 200μm.

[0062] The RCPP film was placed in a roll-to-roll vacuum plasma deposition apparatus, the chamber door was closed, and the vacuum level in the deposition chamber was evacuated to 4.0 × 10⁻⁶. -3Pa; then argon gas was introduced and the working pressure of the deposition chamber was adjusted to 2.0 Pa. The radio frequency power supply was started and the power was set to 2.0 kW to perform online plasma activation on the surface of layer A.

[0063] HMDSO gas at 300 sccm and argon gas at 100 sccm were introduced, and a 20 nm thick SiOCH buffer layer was deposited on the surface of layer A under the conditions of RF power of 2.5 kW and working pressure of 4.0 Pa. Under the condition of continuous arcing, oxygen at 2200 sccm was introduced, the HMDSO gas flow rate was adjusted to 150 sccm, the plasma power was increased to 5.0 kW, and the working pressure of the deposition chamber was adjusted to 6.0 Pa, and a dense inorganic silicon oxide barrier layer with a thickness of 60 nm was deposited on the surface of the SiOCH buffer layer.

[0064] The protective primer prepared in Example 10 was uniformly coated onto the surface of the silicon oxide barrier layer using a gravure coating machine. The coated layer was then dried in a 95°C hot air convection oven to form a film, with the dry coating amount controlled at 1.0 g / m². 2 High-temperature retort RCPP packaging film with no aluminum foil and full light blocking is produced by winding.

[0065] Comparative Examples 1-5: Comparative Example 1: Compared with Example 2, the difference is that the amount of block copolymer polypropylene added in the B layer main feed is increased to 77.625 wt%, and the surface-coupled talc powder prepared in Example 2 is not added as the B layer side feed, while the rest are the same.

[0066] Comparative Example 2: Compared with Example 2, the difference is that in the plasma vapor deposition step, after online plasma activation of the surface of layer A, the SiOCH buffer layer is not deposited. Instead, oxygen and hexamethyldisiloxane gas are directly introduced under continuous arc conditions to deposit a dense inorganic silicon oxide barrier layer with a thickness of 50 nm on the surface of layer A. All other steps are the same.

[0067] Comparative Example 3: Compared with Example 2, the difference is that 1.875 wt% of the rheology modifier masterbatch prepared in Preparation Example 7 in the B layer main feed was replaced with an equal mass of ethylene bis-stearamide dispersant, and all other aspects were the same.

[0068] Comparative Example 4: Compared with Example 2, the difference is that 17.5 wt% of the near-infrared identifiable black masterbatch prepared in Preparation Example 5 in the B layer main feed was replaced with an equal mass of conventional carbon black masterbatch, and all other aspects were the same.

[0069] Comparative Example 5: Compared with Example 2, the difference is that the plasma vapor deposition step and the surface protective coating step are not included. The RCPP film obtained by cooling and shaping is directly wound up to obtain the packaging film. All other aspects are the same.

[0070] Test Examples 1-4: This test case provides specific operational details and verification data for the feasibility test of optical closed-loop sorting, including the following steps: (1) Take the aluminum foil-free, light-blocking, high-temperature retort RCPP packaging films prepared in Examples 1 to 3, and cut them into film samples with a size of 40mm × 40mm. Fix the film samples in the test chamber support of the UV-Vis spectrophotometer. Set the scanning wavelength range of the spectrophotometer to 380nm to 780nm. Select five different positions evenly on the surface of the film sample for transmission scanning, record the transmittance data of each position, and calculate the arithmetic mean.

[0071] (2) The reflectance spectrum of the thin film sample was scanned using a UV-Vis-NIR spectrophotometer equipped with an integrating sphere. The scanning wavelength range was set to 800 nm to 1700 nm, and the test spot size was set to 10 mm × 10 mm. The thin film sample was flatly attached to the reflectance test port of the integrating sphere. Using a standard white plate as a reference, the reflectance curve data in different wavelength ranges were continuously scanned and recorded, and the absorption peak coordinates and baseline values ​​were derived.

[0072] (3) The aluminum foil-free, light-blocking, high-temperature retortable RCPP packaging films prepared in Examples 1 to 3 were fed into a mechanical pulverizer and pulverized into fragments with a side length of approximately 50 mm. 1.0 kg of film fragments were weighed and mixed with 10.0 kg of transparent homopolymer polypropylene fragments to obtain a mixed test material. The mixed test material was evenly spread on a commercial near-infrared plastic sorting machine with a conveyor belt running at a speed of 2.0 m / s. The optical recognition band of the sorting machine was set to 1000 nm to 1700 nm, and the target material for the high-pressure air valve blowing action was set to polypropylene. After the sorting process was completed, the film fragments that fell into the target hopper were collected and weighed. The collected weight was divided by the initial weight of 1.0 kg to calculate the photoelectric sorting accuracy.

[0073] Table 1. Optical transmission and reflection and sorting / recognition rate data of the thin films in the examples Test conclusion: According to the data in Table 1, the average transmittance of Examples 1 to 3 in the visible light band of 380nm to 780nm was 0.03%, 0.01%, and 0.00%, respectively, with transmittance close to zero. The copper-chromium-manganese composite oxide spinel black pigment added to the B layer of the aluminum foil-free, fully light-blocking RCPP packaging film absorbs photons in the visible light band, and combined with the multi-layer co-extruded film structure, it provides a physical light-blocking effect.

[0074] Within the near-infrared band of 800nm ​​to 1700nm, the average reflectivities of Examples 1 to 3 reached 46.8%, 52.4%, and 55.7%, respectively, and the identification accuracy of the near-infrared sorting machine for waste film fragments reached 95.2%, 97.6%, and 98.9%, respectively. Figure 1 The spectral characteristics show that polypropylene characteristic absorption valleys appear near wavelengths of 1190 nm and 1390 nm.

[0075] The electronic transition characteristics of the transition metal ions within the copper-chromium-manganese composite oxide spinel black pigment determine its absorption in the visible light band, while exhibiting low absorption and high scattering rates for low-energy near-infrared electromagnetic waves. Incident near-infrared photons penetrate the surface pigment and undergo diffuse reflection within the polypropylene polymer chains, returning an optical signal carrying the characteristic vibrational frequencies of the polypropylene groups to the detector.

[0076] The increased overall thickness of the thin film lengthens the physical path through which the light beam undergoes multiple scatterings within the polymer entity. Figure 1 The mid-to-near infrared baseline shifts upwards with increasing thickness, causing reflectivity to increase with thickness, thus improving the probability of the photoelectric sorting equipment capturing effective feature signals. Test results confirm that the material system composed of metal oxides and polypropylene meets the light-shielding requirements and is compatible with the photoelectric automated sorting and recycling system.

[0077] Test Example 2: This test case provides specific operational procedures and verification data for the feasibility test of high barrier properties and high temperature resistance in a single substrate homogeneous material, including the following steps: (1) Take the aluminum foil-free, light-blocking, high-temperature retortable RCPP packaging films prepared in Examples 1 to 3, and cut them into sizes of 200 mm in length and 150 mm in width. Adhere the inner layers of two film samples to each other, and use a heat sealer to heat seal three sides at a temperature of 145°C, a pressure of 0.3 MPa, and a time of 1.0 s. After injecting 50 mL of purified water, seal the package to obtain a sealed water bag. Place the sealed water bags in a high-temperature retort chamber under reverse pressure, and set the retort conditions to 121°C for 30 min and 135°C for 15 min, respectively. After retort, cool and depressurize, remove the film, wipe off the surface moisture, and let it stand for 24 hours at an ambient temperature of 23°C and a relative humidity of 50%. Visually observe the wrinkling, delamination, and deformation on the surface of the water bag.

[0078] (2) Take the film samples from Examples 1 to 3 that have not undergone high-temperature cooking treatment, and the film samples that have undergone high-temperature cooking treatment under different conditions than in step (1) and have been left to stand. Cut them into circular areas suitable for the fixture of the testing instrument. Load the circular film samples into the isobaric oxygen permeability tester. Set the temperature of the test chamber to 25°C and the relative humidity to 80%. The test gas is high-purity oxygen, and the carrier gas is high-purity nitrogen. Continuously monitor the gas permeation process. After the oxygen permeation rate reaches a stable state, record the oxygen permeability data.

[0079] (3) Take a film sample that has undergone the same treatment conditions as in step (2) and load it into an infrared sensor method water vapor transmission rate tester. Set the temperature of the test chamber to 40°C and the relative humidity to 90%. Monitor the concentration change of water vapor molecules passing through the film to the dry carrier gas side during the test process. After the transmission rate stabilizes, record the water vapor transmission rate data.

[0080] Table 2. Appearance evaluation and barrier performance data of the films before and after high-temperature cooking in the examples. Test conclusion: According to the data in Table 2, in the initial state without cooking treatment, the gas permeability of Examples 1 to 3 was at a low level. Table 2 shows that the oxygen permeability of Example 3 was 0.06 cc / (m³). 2 ·d·atm), water vapor transmission rate is 0.32g / (m 2 ·d).

[0081] Polypropylene polymer materials, due to the free volume between molecular chain segments, form a physical barrier against gas and water molecules. The surface of the foil-free, fully light-blocking high-temperature retortable RCPP packaging film is activated by plasma and deposited with a dense inorganic silica barrier layer, constructing a physical barrier layer that prolongs the penetration path of oxygen and water vapor molecules. The protective primer on the surface, after film formation, fills the pores in the microstructure of the inorganic deposition layer, improving the overall water and oxygen barrier capability of the foil-free, fully light-blocking high-temperature retortable RCPP packaging film. Combined with… Figure 2 and Figure 3 It can be seen that as the test time goes on, the cumulative permeation curve shows a time lag characteristic, indicating that the resistance to gas molecules dissolving and diffusing through the multi-layer interface increases.

[0082] Under high-temperature reverse-pressure retorting conditions of 121℃ and 135℃, the aluminum foil-free, fully light-blocking high-temperature retorting RCPP packaging film did not exhibit macroscopic delamination. Oxygen and water vapor permeability remained within a relatively stable range, maintaining a stable barrier state. As shown in Table 2, in Example 3, the oxygen permeability increased to 0.08 cc / (m³) after retorting at 135℃ for 15 min. 2 The water vapor transmission rate is 0.39 g / (m·d·atm). 2 •d). The dense inorganic silica barrier layer has a low coefficient of linear expansion, while the polypropylene substrate is prone to volume expansion when heated. The difference in deformation will induce shear stress at the interface.

[0083] The surface-coupled talc powder added to layer B is a micron-sized rigid sheet-like filler that, under the tensile stress field of the casting process, is oriented along the plane and forms a physically cross-linked constraint network with the polypropylene matrix. This rigid network restricts the movement and volume expansion of the polypropylene polymer chains under heating, reducing the overall coefficient of thermal expansion within the film surface.

[0084] The SiOCH buffer layer, formed by the reaction of hexamethyldisiloxane and oxygen, retains some organic side chains, giving it a tensile modulus lower than that of the dense inorganic silica barrier layer but higher than that of the polypropylene substrate. The SiOCH buffer layer provides a mechanical buffer zone at the interface, absorbing and dissipating residual internal stress generated during thermal expansion. The rigid filler constraint system, combined with the modulus transition layer, reduces the tensile stress applied to the nanoscale inorganic coating during heat treatment, minimizing the possibility of microcracks in the dense inorganic silica barrier layer and ensuring the integrity of the barrier network after high-temperature cooking.

[0085] Test Example 3: This test example provides specific operation and verification data for a comparative test of the overall degradation of high-temperature cooking resistance, including the following steps: (1) The aluminum foil-free, light-blocking, high-temperature retortable RCPP packaging films prepared in Example 2, Comparative Examples 1 to 3, and Comparative Example 5 were cut into sealed water bags filled with 50 mL of purified water. Some of the sealed water bags made from the packaging films were placed in a high-temperature retort under reverse pressure and treated at a constant temperature of 121°C for 30 min. After the retort was completed, the films were cooled and depressurized, the surface moisture of the films was wiped dry, and the films were left to stand for 24 hours. Another portion of the films that had not undergone the retort treatment was retained as a control sample.

[0086] (2) Circular samples were cut from the film samples that underwent high-temperature cooking and those that did not, and loaded into the isobaric oxygen transmission rate tester and the infrared sensor water vapor transmission rate tester, respectively. The oxygen transmission rate test environment was set to 25°C and 80% relative humidity, and the water vapor transmission rate test environment was set to 40°C and 90% relative humidity. After the gas transmission rate reached a stable state, the barrier performance data were recorded.

[0087] (3) Take the thin film samples from Example 2 and Comparative Example 3 that have undergone high-temperature cooking treatment and those that have not. Place the inner layer of the thin film sample towards the test window on the sample stage of the attenuated total reflectance Fourier transform infrared spectrometer, ensuring that the test crystal is in close contact with the surface of the inner layer of the thin film. Set the spectral scanning range to 4000 cm⁻¹. -1 Up to 600cm -1 The absorbance data of the infrared spectrum were continuously scanned and recorded.

[0088] (4) The film samples of Examples 2, Comparative Examples 1 to 3, and Comparative Examples 5, which underwent high-temperature cooking treatment and those that did not, were cut into strips with a width of 15 mm. The inner layers of two strips were bonded together and heat-sealed for 1.0 s at 145 °C and 0.3 MPa. Using an electronic tensile testing machine, the unsealed free end was clamped, and the tensile speed was set to 300 mm / min. A peel test was performed along the T-direction, and the average peel load during the fracture process was recorded as the peel heat seal strength.

[0089] Table 3. Test data on the comprehensive high-temperature cooking resistance of Example 2 and the comparative example. Test conclusion: According to the data in Table 3, in Example 2, the oxygen permeability and water vapor permeability remained at similar levels before and after the cooking treatment. In Comparative Example 1, without the addition of surface-coupled talc, the oxygen permeability and water vapor permeability increased after high-temperature cooking. The lack of a physical cross-linked network constructed within the polypropylene matrix by surface-coupled talc prevented the establishment of a rigid silicate constraint system, causing the polymer polymer chains to expand in volume under heat. In this state, the interfacial shear stress generated by the expansion deformation triggered the fracture of the dense inorganic silica barrier layer, and the generation of microcracks destroyed the original physical barrier network.

[0090] Comparative Example 2 lacked a SiOCH buffer layer during the plasma vapor deposition step, resulting in increased gas permeability after cooking. The absence of a low-modulus SiOCH buffer layer containing organic side chains prevented the provision of a transition region at the interface to absorb and dissipate residual internal stress caused by the difference in thermal expansion deformation between the substrate and the inorganic coating. This stress concentration led to cracking and failure of the dense inorganic silica barrier layer. Comparative Example 5, which did not include the plasma vapor deposition and surface protective coating steps, exhibited a higher base gas permeability, confirming that a single polypropylene film bulk cannot meet the water and oxygen barrier standards.

[0091] In the heat-sealing performance test, Example 2 maintained stable peel heat-sealing strength before and after cooking. Comparative Example 3, using ethylene bis-stearamide dispersant instead of the rheology modifier masterbatch, showed a decrease in peel heat-sealing strength after cooking. Figure 4 Spectral characteristics and data analysis in Table 3 show that, after cooking, Comparative Example 3 was tested at 1640 cm⁻¹. -1 With 1540cm -1 An absorption peak appeared near the wavenumber, corresponding to the molecular vibration of the amide group. The small molecule additives experienced intensified molecular thermal motion at high temperatures, migrating and precipitating towards the film surface. The precipitates covering the inner surface formed a weak interfacial layer, hindering the interdiffusion and physical entanglement of polypropylene polymer segments during the heat-sealing process.

[0092] In Example 2, the rheology modulator masterbatch uses ultra-high molecular weight polydimethylsiloxane. Due to its thermodynamic incompatibility with the polypropylene melt, phase separation occurs, which enriches the inorganic particle surface and melt interface, reducing the apparent shear viscosity. At the same time, after cooling and crystallization, the macromolecular chains are limited by the size of the polypropylene crystal region, resulting in a low apparent migration rate to the film surface. This avoids the surface precipitation problem during high-temperature cooking and ensures the heat sealing reliability of the contact layer interface.

[0093] Test Example 4: This test case provides specific operational procedures and verification data for a comparative test of the optical recognition advantages of a particular light-blocking agent, including the following steps: (1) Take the aluminum foil-free, fully light-blocking high-temperature retort RCPP packaging films prepared in Example 2 and Comparative Example 4, and cut them into film samples with a size of 40mm × 40mm. Fix the film samples in the test chamber support of the UV-Vis spectrophotometer. Set the scanning wavelength range of the spectrophotometer to 380nm to 780nm. Select 5 different positions on the surface of the film sample for transmission scanning, record the transmittance data of each position, and calculate the average value.

[0094] (2) The reflectance spectrum of the thin film sample was scanned using a UV-Vis-NIR spectrophotometer equipped with an integrating sphere. The scanning wavelength range was set to 800 nm to 1700 nm, and the test spot size was set to 10 mm × 10 mm. The thin film sample was attached to the reflectance test port of the integrating sphere, and a standard white plate was used as a reference. The reflectance curve data in different wavelength ranges were continuously scanned and recorded.

[0095] (3) The film samples obtained in Example 2 and Comparative Example 4 were respectively put into a mechanical pulverizer and pulverized into fragments with a side length of about 50 mm. 1.0 kg of film fragments from different samples were weighed and mixed with 10.0 kg of transparent homopolymer polypropylene fragments to obtain a mixed test material. The mixed test material was evenly spread on a commercial near-infrared plastic sorting machine with a conveyor belt running at a speed of 2.0 m / s. The optical recognition band of the sorting machine was set to 1000 nm to 1700 nm, and the target material was set to polypropylene. After the sorting process was completed, the film fragments that fell into the target hopper were collected and weighed. The collected weight was divided by the initial weight of 1.0 kg to calculate the photoelectric sorting accuracy.

[0096] Table 4. Comparison of optical characteristics and sorting / recognition rates between Example 2 and Comparative Example 4 Test conclusion: According to the data in Table 4, the average transmittance of Example 2 and Comparative Example 4 in the visible light band from 380 nm to 780 nm was 0.01% and 0.02%, respectively, with transmittance close to zero. The test results indicate that the copper-chromium-manganese composite oxide spinel black pigment added to both conventional carbon black particles and the aluminum foil-free, fully light-blocking high-temperature retort RCPP packaging film provides physical light-blocking properties when combined with a multilayer co-extruded film structure.

[0097] Within the near-infrared band of 800nm ​​to 1700nm, the average reflectance of Example 2 was 51.8%, while the average reflectance of Comparative Example 4 was only 4.6%. In actual photoelectric sorting tests, the sorting accuracy of Example 2 reached 96.5%, while the accuracy of Comparative Example 4 decreased to 1.8%. Figure 5The near-infrared reflectance spectra of the thin film samples from Example 2 and Comparative Example 4 are shown in the figure. The solid line represents the spectral curve of Example 2, and the dashed line represents the spectral curve of Comparative Example 4. It can be seen that the near-infrared spectral curve of Comparative Example 4 is generally flat and in a low reflectance state, without the characteristic absorption valley of polypropylene. The conventional carbon black particles used in Comparative Example 4 have broadband absorption characteristics, absorbing visible light while also absorbing low-energy near-infrared electromagnetic waves. The incident near-infrared photons are absorbed by the carbon black particles in the surface and intermediate layers and cannot penetrate into the interior of the polypropylene polymer chain to undergo physical diffuse reflection. The infrared sensor cannot receive the optical reflection signal carrying the characteristic vibrational frequency of polypropylene groups, causing the sorting equipment to be unable to identify the target material.

[0098] Example 2 uses copper-chromium-manganese composite oxide spinel black pigment as a light-shielding filler. From Figure 5 It can be seen that the spectral curve of Example 2, while maintaining a high reflectance baseline, retains the characteristic absorption valleys of polypropylene near wavelengths of 1190 nm and 1390 nm. The electronic transition energy levels of transition metal ions within the lattice of the copper-chromium-manganese composite oxide spinel black pigment determine its main absorption of photons in the visible light band, while exhibiting low absorption and high scattering rates for electromagnetic waves in the near-infrared band.

[0099] After incident near-infrared photons pass through the pigment-containing polymer layer, they undergo diffuse reflection within the polymer entity and return to the detector. This enables the photoelectric sorting equipment to stably capture the characteristic spectral signal of polypropylene, ensuring the homogeneous sorting and identification of high-temperature retortable RCPP packaging film without aluminum foil and with full light blocking after entering the plastic recycling end.

Claims

1. A high-temperature retortable RCPP film and packaging film with no aluminum foil and full light blocking properties, characterized in that, include: An RCPP film having layers A, B, and C is provided, and the packaging film comprises the RCPP film; The A layer is composed of 90-95% highly crystalline homopolymer polypropylene and 5-10% nano-titanium dioxide white masterbatch by weight percentage. The B layer is composed of 62.5-72.75% block copolymer polypropylene, 15-20% near-infrared identifiable black masterbatch, 3% maleic anhydride grafted polypropylene, 1.25-2.5% rheology modifier masterbatch and 8-12% surface-coupled talc by weight percentage. The C layer is composed of 90-95% random copolymer polypropylene and 5-10% nano-titanium dioxide white masterbatch by weight percentage. The surface of layer A is provided with a SiOCH buffer layer with a thickness of 10-20 nm; The surface of the SiOCH buffer layer is provided with a dense inorganic silicon oxide barrier layer with a thickness of 40-60 nm. The dense inorganic silicon oxide barrier layer is provided with a protective primer layer on the surface, and the dry coating amount of the protective primer layer is 0.5-1.0 g / m 2 ; The nano-titanium dioxide white masterbatch contains 40% titanium dioxide by weight.

2. The high-temperature retort RCPP film and packaging film according to claim 1, characterized in that, The thickness ratio of the A layer, the B layer and the C layer is (15-25):(50-70):(15-25), and the total thickness of the RCPP film is 50-200 μm.

3. The high-temperature retort RCPP film and packaging film according to claim 1, characterized in that, The surface-coupled talc powder is prepared by the following steps: Flake talc powder with a median particle size of 1.5–2.5 μm and a diameter-to-thickness ratio of (20–30):1 was placed in a forced-air drying oven and dehydrated at 100–120°C for 3–5 h. The dehydrated flake talc powder is fed into a high-speed mixer and heated to 100-110°C through friction. Anhydrous ethanol containing distearyloxyisopropoxyaluminate coupling agent is sprayed onto the surface of the dehydrated flake talc powder through a spraying device. After spraying, the internal temperature of the high-speed mixer is maintained at 100-110°C. Ethanol vapor is discharged and the mixture is mixed at a constant temperature for 10-15 minutes. The mixture is then cooled and discharged. The weight of the distearate isopropoxyaluminate coupling agent is 1.5 to 2.5% of the total weight of the flake talc.

4. The high-temperature retort RCPP film and packaging film according to claim 1, characterized in that, The preparation method of the near-infrared identifiable black masterbatch is as follows: 35-40% of copper-chromium-manganese composite oxide spinel black pigment, 5% of maleic anhydride-grafted polypropylene, and 55-60% of block copolymer polypropylene resin are premixed in a low-speed kneader to obtain a black polymer premix. The black polymer premix is ​​fed into a co-rotating twin-screw extruder and subjected to melt extrusion and vacuum degassing at a temperature range of 160-210°C. The mixture is then water-cooled and pelletized. The grafting rate of the maleic anhydride-grafted polypropylene is 0.8-1.2%.

5. The high-temperature retort RCPP film and packaging film according to claim 1, characterized in that, The rheology modifier masterbatch is prepared by feeding ultra-high molecular weight polydimethylsiloxane colloid and block copolymer polypropylene powder in a weight ratio of 40:60 into an internal mixer, mixing at 185°C for 18 minutes for dynamic high shear dispersion, crushing in a pulverizer and then feeding into a single screw extruder for extrusion granulation. The ultra-high molecular weight polydimethylsiloxane colloid has a weight-average molecular weight of 500,000 to 800,000 g / mol.

6. The high-temperature retort RCPP film and packaging film according to claim 1, characterized in that, The protective primer coating is formed by film formation from an aqueous protective primer liquid, which is prepared by mixing components comprising the following parts by weight: 60-70 parts of aqueous chlorinated polypropylene dispersion; 30-40 parts of waterborne aliphatic polyurethane dispersion; 0.3 to 0.7 parts of polyether siloxane copolymer.

7. A method for preparing a high-temperature retortable RCPP film and packaging film with no aluminum foil and full light blocking properties, characterized in that, The method for preparing the high-temperature retortable RCPP film and packaging film as described in any one of claims 1-6 includes the following steps: The A-layer feed, B-layer main feed, B-layer side feed and C-layer feed are melted and extruded in their respective extruders, and then fed into a T-shaped flat die through a co-extrusion distributor to form a three-layer co-extrusion melt. The RCPP film is obtained by cooling and shaping the surface of the quench roll. The RCPP film was placed in a vacuum plasma deposition apparatus for plasma activation, and hexamethyldisiloxane gas and argon gas were introduced for vapor phase deposition to obtain the SiOCH buffer layer on the surface of the A layer. Under continuous arc conditions, oxygen is introduced and the flow rate of the hexamethyldisiloxane gas is adjusted to increase the plasma power and working pressure of the deposition chamber of the vacuum plasma deposition equipment, and a dense inorganic silicon oxide barrier layer is obtained by continuing vapor phase deposition. A water-based protective primer is uniformly coated on the surface of the dense inorganic silicon oxide barrier layer, and then dried in a hot air convection oven at a temperature of 85-95°C to form a film to obtain the protective primer coating. The film is then rolled up to obtain the aluminum foil-free, light-blocking, high-temperature retortable RCPP film and packaging film.

8. The preparation method according to claim 7, characterized in that, The process for obtaining the RCPP film satisfies the following parameter settings: The A-layer ingredients and the C-layer ingredients are extruded in separate single-screw extruders, and the temperature gradient of the single-screw extruders is 180-250°C. The B-layer main feed and the B-layer side feed are extruded in a twin-screw extruder with a side feed port. The B-layer main feed is added from the main feed port of the twin-screw extruder, and the B-layer side feed is added from the side feed port. The temperature range of the twin-screw extruder is 190-210°C. The temperature of the die lip of the T-shaped flat die head is controlled at 215-220℃; The surface water temperature of the quenching roller is 20-25℃, and the traction speed is set to 30-80m / min.

9. The preparation method according to claim 7, characterized in that, The process of obtaining the SiOCH buffer layer satisfies the following parameter settings: The background vacuum of the deposition chamber of the vacuum plasma deposition equipment is pumped to 4.0x10 -3 ~5.0x10 -3 Pa, the argon gas is introduced to adjust the working pressure of the deposition chamber to 1.0~2.0Pa, and the surface of the A layer is plasma activated under 1.0~2.0kW radio frequency power. After plasma activation, hexamethyldisiloxane gas with a flow rate of 200-300 sccm and argon gas with a flow rate of 50-100 sccm are introduced. Under the conditions of radio frequency power of 1.5-2.5 kW and working pressure of 2.0-4.0 Pa in the deposition chamber, the SiOCH buffer layer is deposited.

10. The preparation method according to claim 7, characterized in that, The process of depositing the dense inorganic silicon oxide barrier layer satisfies the following parameter settings: oxygen is introduced at a flow rate of 1500-2200 sccm, the flow rate of hexamethyldisiloxane gas is adjusted to 100-150 sccm, the plasma power is increased to 3.5-5.0 kW, the working pressure of the deposition chamber is adjusted to 3.0-6.0 Pa, and the dense inorganic silicon oxide barrier layer is deposited.

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