Recyclable composite membrane material and application thereof in dry food packaging

Abstract

The invention discloses a recoverable composite film material and application thereof in dry food packaging, the recoverable composite film material comprises a protective layer, a high barrier layer and a heat sealing inner layer which are sequentially arranged from outside to inside, reversible weak bonding interface layers are arranged between the protective layer and the high-barrier layer and between the high-barrier layer and the heat-sealing inner layer; the reversible weak bonding interface layer has bonding force for bonding the layers in an initial state, and the bonding force of the reversible weak bonding interface layer is remarkably reduced or disappears under specific external stimulation, so that physical separation of the functional layers is realized. According to the recoverable composite membrane material, the reversible weak bonding interface layer is arranged between the layers, so that the unification of high-performance packaging and easy recoverability is realized; the material can be rapidly separated into a single material component under specific physical stimulation while meeting the requirements of dry food on barrier property, strength and heat sealability, and is compatible with an existing polyolefin recovery system; complicated chemical treatment is not needed in the separation process.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, specifically to a recyclable composite film material and its application in dried food packaging. Background Technology

[0002] Currently, dried foods (such as potato chips, biscuits, dried fruits, and milk powder) have extremely high requirements for the moisture barrier, oxygen barrier, mechanical strength, and heat-sealing performance of their packaging materials. Multilayer composite films are commonly used in the market, with typical structures such as polyester (PET) / aluminum foil (Al) / polyethylene (PE) or biaxially oriented polypropylene (BOPP) / metallized cast polypropylene (VMCPP). These materials use adhesives to bond polymer layers with different properties but incompatible chemical structures to achieve the required comprehensive performance.

[0003] However, this traditional approach has led to serious environmental problems. Due to the large differences in chemical properties of the various layers of materials and their firm bonding with permanent chemical adhesives, the discarded composite membrane is difficult to separate effectively by physical or chemical methods. It cannot enter the existing single-material plastic recycling stream and can usually only be landfilled or incinerated for energy, resulting in resource waste and "white pollution". Summary of the Invention

[0004] Therefore, the present invention provides a recyclable composite film material and its application in dry food packaging to solve the problem of non-recyclability of multilayer composite films used in dry food packaging in the prior art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A recyclable composite membrane material includes a protective layer, a high-barrier layer, and a heat-sealing inner layer arranged sequentially from the outside to the inside. A reversible weak bonding interface layer is provided between the protective layer and the high-barrier layer, and between the high-barrier layer and the heat-sealing inner layer. The reversible weakly bonded interface layer has an adhesive force that binds the layers together in the initial state. Under specific external stimuli, its adhesive force is significantly reduced or disappears, thereby achieving physical separation of the functional layers.

[0006] Furthermore: the reversible weakly bonded interface layer is selected from at least one of the following modes: Mode A: Thermally responsive elastomer adhesive layer, which softens and loses its adhesiveness at a specific temperature; Mode B: pH-responsive hydrosol interface layer, which absorbs water and swells in a solution with a specific pH, resulting in loss of adhesion; Mode C: Mechanically responsive microstructure interlocking interface, which achieves bonding through microstructure interlocking and separation through mechanical stress.

[0007] Furthermore, the protective layer is one of biaxially oriented polypropylene, high-density polyethylene, or biaxially oriented polyethylene film, and its surface is provided with a functional coating.

[0008] Furthermore, the high barrier layer is one of the following: vapor-deposited silica cast polypropylene film, vapor-deposited alumina biaxially oriented polypropylene film, or co-extruded polyethylene / ethylene-vinyl alcohol copolymer island structure barrier film.

[0009] Furthermore: the heat-sealed inner layer is one of metallocene linear low-density polyethylene, anti-fouling metallocene polyethylene, or low-temperature heat-sealing polypropylene, with a thickness of 25-40 mm. .

[0010] To achieve the above objectives, the present invention also provides an application of a recyclable composite film material in dry food packaging, comprising the following steps: (1) Composite membrane processing: The layers are bonded by dry lamination or co-extrusion lamination process, and the process conditions are controlled during the lamination process to maintain the responsive activity of the reversible weak bonding interface layer; (2) Packaging bag making and heat sealing: Optimize the heat sealing process parameters according to the heat sealing layer material, and adopt a two-stage heat sealing to avoid the heat affecting the interface layer; (3) Gas-filled packaging: Protective gas is filled into easily oxidized foods during packaging; (4) Post-consumer recycling guidelines: Print recycling labels and pre-treatment instructions on the packaging to guide users to achieve interlayer separation through physical stimulation.

[0011] Furthermore: when the reversible weakly bonded interface layer is thermally responsive, the recycling method is to soak it in warm water at 65-70℃ for 3-5 minutes to achieve interlayer separation.

[0012] Furthermore: when the reversible weakly bound interface layer is pH-responsive, the recovery method is to soak it in a weak alkaline solution with pH 9-10 for 5-8 minutes to achieve interlayer separation.

[0013] Furthermore: when the reversible weakly bonded interface layer is mechanically responsive, the recycling method is to achieve dry separation by applying micro-bending stress through mechanical rollers.

[0014] The present invention has the following advantages: the recyclable composite membrane material of the present invention achieves the unity of high-performance packaging and easy recyclability by setting a reversible weak bonding interface layer between the layers; while meeting the requirements of dry food for barrier properties, strength and heat sealing, the material can be rapidly separated into single material components under specific physical stimuli, and is compatible with existing polyolefin recycling systems; its separation process does not require complex chemical treatment, reducing recycling energy consumption and cost, reducing composite membrane waste from the source, and effectively alleviating "white pollution".

[0015] Other features and advantages of the present invention will be set forth in the following description. Attached Figure Description

[0016] To more intuitively illustrate the prior art and this application, exemplary drawings are provided below. It should be understood that the specific shapes and structures shown in the drawings should not generally be regarded as limiting conditions for implementing this application; for example, based on the technical concept disclosed in this application and the exemplary drawings, those skilled in the art are able to easily make conventional adjustments or further optimizations to the addition / reduction / classification, specific shapes, positional relationships, connection methods, size ratios, etc. of certain units (components).

[0017] Figure 1 This is a schematic diagram of the hierarchical structure of a recyclable composite membrane material provided in an embodiment of this application. Detailed Implementation

[0018] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. It should be understood that these embodiments are merely for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above-described content.

[0019] Please see Figure 1 A recyclable composite membrane material includes a protective layer 1, a high-barrier layer 2, a heat-sealing inner layer 3, and a reversible weak bonding interface layer 4; the protective layer 1 is located on the outer side, the high-barrier layer 2 is located in the middle layer, the heat-sealing inner layer 3 is located on the inner side, and the protective layer 1, the high-barrier layer 2, and the heat-sealing inner layer 3 are connected together by the reversible weak bonding interface layer 4.

[0020] The reversible weakly bonded interface layer 4 has sufficient initial adhesion to ensure processing and performance, but under specific external stimuli (such as hot water at a specific temperature, solution at a specific pH, or specific physical action), its adhesion can be significantly reduced or disappear, thereby achieving non-destructive or low-destructive physical separation of each functional layer.

[0021] The protective layer 1 provides printing support and the necessary stiffness; it is made of biaxially oriented polypropylene (BOPP); in addition, to meet different needs, surface functional coatings (such as abrasion-resistant coatings and antistatic coatings) can be added to the surface of the protective layer 1 for modification, and these functional coatings are themselves compatible with polyolefins or can be washed away with water.

[0022] The high-performance barrier layer 2 is a co-extruded polymer alloy barrier membrane. Through multi-layer co-extrusion technology, a "sea-island structure" film is prepared, with polyethylene (PE) or polypropylene (PP) as the continuous phase and ultra-high barrier polymers (such as ethylene-vinyl alcohol copolymer EVOH) as the dispersed phase. By precisely controlling the flow channels and phase states, EVOH is arranged in parallel within the membrane in a discontinuous, ultra-fine sheet-like form, creating a tortuous barrier path. The structure of the co-extruded polymer alloy barrier membrane not only leverages the extreme oxygen barrier properties of EVOH but also, due to its discontinuous encapsulation by polyolefins, ensures that the entire membrane can be treated as a single polyolefin material during recycling. The EVOH content is strictly controlled below 5% to meet the impurity content requirements of mainstream recycling systems.

[0023] The heat-sealed inner layer 3 is preferably metallocene linear low-density polyethylene (mLLDPE) or low-temperature heat-sealed polypropylene (LTSCPP), with a thickness of 25-40 mm. The heat-sealing inner layer 3 provides excellent low-temperature heat-sealing properties, heat-adhesion strength, and resistance to sealing contamination.

[0024] The reversible weakly bonded interface layer 4 is selected from one or a combination of the following three modes; Mode A: Thermally responsive elastomer adhesive layer; using a thermoplastic elastomer (TPO) based on polyolefin block copolymer as the adhesive resin; this adhesive resin exhibits high modulus and strong adhesion at room temperature, ensuring the interlayer stability of the composite film during transportation and storage; however, it has a defined "viscosity collapse temperature" (e.g., 65°C); when the waste composite film enters a hot water or hot air treatment line at a specific temperature, the adhesive layer softens rapidly, loses its cohesive strength, and the functional layers can be completely separated under slight external force, like peeling a banana. Mode B: pH-responsive hydrosol interface layer; a modified polyvinyl alcohol (PVA) and polyacrylic acid (PAA) interpenetrating network hydrogel is coated between the layers; this interpenetrating network hydrogel layer provides strong adhesion through hydrogen bonds and van der Waals forces in the dry state; when placed in a warm aqueous solution with a specific pH value (such as weakly alkaline, pH 9-10), the carboxylic acid groups in the polymer network ionize, generating strong electrostatic repulsion and absorbing a large amount of water, causing the gel volume to expand and the adhesion to drop to near zero within minutes; the separated layers can be directly recycled after washing and drying; Mode C: Mechanically responsive microstructure interlocking interface; using laser micromachining or precision embossing rollers, complementary micron-level tenon-and-mortise structure arrays are constructed on the surfaces of the contacting films respectively; during lamination, under moderate heating and pressure, these microstructures interlock with each other, generating a strong mechanical interlocking force; during separation, a roller group with specific waveform protrusions applies local, high-frequency micro-bending stress to the composite film, causing the micro-interlocking structure to "spring apart" due to elastic deformation.

[0025] The overview of the embodiments is shown in the table below:

[0026] Example 1: High-barrier composite membrane using a thermally responsive interface (Mode A) This embodiment aims to provide a composite membrane with top-notch oxygen and moisture barrier properties, specifically designed for packaging nitrogen-filled foods that are highly susceptible to oxidation and spoilage, such as premium fried potato chips and nuts; the purpose is to ensure that the flavor remains unaffected during a long shelf life, while also enabling convenient warm water soaking for recycling.

[0027] The specific layer structure from the outside in is as follows: (1) Protective layer 1: using 20 Thick biaxially oriented polypropylene (BOPP) film; surface treated with corona discharge and coated with a water-washable abrasion-resistant coating to protect printed patterns and improve film stiffness.

[0028] (2) Reversible weakly bonded interface layer 4, mode A is selected, and 8 is used. The thick, heat-responsive polyolefin elastomer TPO adhesive layer has a precisely designed "tack collapse temperature" of 65°C.

[0029] (3) High barrier layer 2, using 30 A thick vapor-deposited silicon oxide cast polypropylene SiOx-CPP film; this film layer is formed by plasma vapor deposition of a nano-SiOx coating on a CPP substrate, with an oxygen permeability (OTR) < 0.5 cm⁻¹. 3 / (m 2 (day atm), water vapor transmission rate WVTR < 1.0 g / (m 2 ·day).

[0030] (4) Reversible weakly bonded interface layer 4, select mode A, same as above, is 8 Thick TPO adhesive layer.

[0031] (5) Heat-sealed inner layer 3, using 35 Thick metallocene linear low-density polyethylene (mLLDPE) has excellent low-temperature heat-sealing properties and high thermal adhesion strength, ensuring reliable sealing at high-speed filling and sealing.

[0032] A dry lamination process is adopted; after coating the BOPP protective layer with TPO adhesive, it is dried and cured in a low-temperature oven at 70°C, and then laminated with the SiOx-CPP barrier film; similarly, the barrier layer is laminated with the mLLDPE heat-sealing layer; this low-temperature process aims to maintain the thermal responsiveness of the TPO adhesive layer and avoid premature irreversible cross-linking.

[0033] The bag making and packaging process is as follows: a. Bag making: The bags are made into stand-up pouches using a two-stage heat-sealing process; the pre-sealing conditions are 115℃ for 0.3 seconds; the main sealing conditions are 128℃ for 0.5 seconds; precise temperature control prevents heat damage to the TPO interface.

[0034] b. Filling: On the high-speed automatic packaging line, after filling, nitrogen gas with a purity of over 99% is immediately introduced, and the final sealing is completed.

[0035] When consumers cut open the empty bag and soak it in 65℃ warm water for 3-5 minutes, the TPO adhesive layer softens completely and loses its stickiness. The BOPP layer, SiOx-CPP layer, and mLLDPE layer can be completely separated by gentle rubbing. After washing and drying, each individual material film can be sent to the PP and PE recycling streams for granulation and regeneration.

[0036] Example 2: An economical composite membrane using a pH-responsive interface (Mode B) This embodiment addresses powdered food packaging requiring high cost-effectiveness and excellent moisture-proof performance, such as small-packet packaging of milk powder, protein powder, and seasonings. The aim is to balance performance and cost, and to provide a recycling solution based on common weak alkaline solutions.

[0037] The specific layer structure from the outside in is as follows: (1) Protective layer 1, using 25 Thick uniaxially stretched high-density polyethylene (HDPE) film; it has good stiffness and low cost, making it suitable for high-speed printing; (2) Reversible weakly bonded interface layer 4, using film type B, coated with a layer of pH-responsive interpenetrating network hydrogel formed by modified polyvinyl alcohol (PVA) and polyacrylic acid (PAA), with a dry gel thickness of approximately 5 mm. ; (3) High barrier layer 2, using 40 A thick co-extruded PE / EVOH "island structure" barrier membrane; in which PE is the continuous phase, and EVOH is dispersed in a discontinuous sheet-like form as the barrier phase, with the EVOH content strictly controlled at 4%; the membrane's oxygen permeability (OTR) is <2.0 cm⁻¹. 3 / (m 2 (day·atm), with excellent water vapor barrier properties; (4) Reversible weakly bonded interface layer 4, membrane type B: same as above, is a pH-responsive hydrogel layer; (5) Heat-sealed inner layer 3, using 30 Thick, stain-resistant metallocene polyethylene (mPE) forms a reliable seal even when trace amounts of powder adhere to the sealing area.

[0038] A dry lamination process is adopted; PVA-PAA hydrogel solution is coated onto HDPE film and slowly dried at a low temperature of ≤55℃ to form a responsive gel network, which is then laminated with PE / EVOH barrier film, and the inner layer is laminated using the same process.

[0039] It is then made into back-sealed bags or pillow bags, suitable for high-speed powder filling machines; ultrasonic sealing technology is used as the main sealing method, which can completely avoid the thermal impact of heat sealing on the interface layer.

[0040] Scrap materials generated during the production process can be collected and soaked in a 1% sodium carbonate (edible alkali) solution (pH≈10) to achieve separation of each layer and immediate recycling.

[0041] The packaging bag is printed with a recycling symbol: "To help with recycling, please soak the empty bag in a small amount of edible alkali water"; consumers should follow the instructions to soak the bag in a warm water solution with a pH of 9-10 for 5-8 minutes. The hydrogel layer will swell and lose its stickiness, and the layers will peel off automatically. The separated HDPE, PE / EVOH composite membrane (which is recycled as PE as a whole) and mPE membrane can be recycled after rinsing with clean water.

[0042] Example 3: High-strength composite membrane using mechanical interlocking interface (Mode C) This embodiment is designed for packaging scenarios requiring ultra-high mechanical strength, such as pasta, hard candy, and roasted coffee beans with sharp edges; the aim is to provide excellent puncture and tear resistance and achieve purely physical dry recycling without the need for water or chemical reagents.

[0043] The specific layer structure from the outside in is as follows: (1) Protective / strength layer 1 is made of 18μm thick biaxially oriented polyethylene (BOPE) film, and its surface is formed by precision laser micromachining to form a micron-level array of protrusions.

[0044] (2) Reversible weak bonding interface layer 4, mode C is selected, that is, mechanical interlocking interface achieved by physical pressure; (3) High-barrier layer 2, using a 25μm thick BOPP membrane with double-sided alumina vapor deposition. This membrane is double-sided vapor-deposited, with symmetrical and excellent barrier properties, and a water vapor transmission rate (WVTR) of <0.3g / (m). 2 ·day), and provides good light blocking properties.

[0045] (4) Reversible weak bonding interface layer 4, mode C is selected, same as above; the surface of the double-sided vapor-deposited alumina BOPP film is formed by a precision embossing roller to form a groove array structure that complements the protrusions of the BOPE layer. (5) Heat-sealed inner layer 3 is made of 40μm thick high-toughness low-temperature heat-sealing polypropylene LTSCPP to ensure good sealing performance while providing high strength.

[0046] A one-step molding process combining co-extrusion casting and online embossing is adopted. BOPE and LTSCPP are melt-extruded separately. In the molten state, a pre-prepared double-sided alumina-deposited BOPP barrier film is introduced as an intermediate layer. The film is then rolled by a set of embossing rollers with complementary microstructures under appropriate temperature and pressure, so that the three layers are cold-pressed together at the interface through microstructure.

[0047] It can be made into three-side seal bags or coffee bags with vent valves; due to the extremely high strength of the material itself, conventional heat sealing parameters (130-135℃) can be used, resulting in narrower sealing edges and saving material; the structure can effectively resist punctures by the contents, and the impact of hard objects such as coffee beans during transportation will not cause the packaging to break.

[0048] After the waste packaging enters the recycling system, it does not require chemical treatment and is directly separated by a specially designed wave roller separation device. This device applies local, high-frequency micro-bending stress to the film, causing the interlocking micro-mortise and tenon structure to undergo elastic deformation and "spring open", thereby achieving dry and non-destructive separation of the three layers of BOPE, double-sided vapor-deposited alumina BOPP film and LTSCPP. The separated material is clean and can be directly melted and granulated.

[0049] The application of a recyclable composite film material in dry food packaging includes the following steps: (1) Composite film processing: The layers are bonded by dry lamination or co-extrusion lamination process; if the lamination is done by several methods, after coating the interface material of mode A or mode B, it needs to be dried at low temperature (e.g., ≤80℃) to prevent the interface from curing too early; if co-extrusion lamination is used, the interface of mode A or mode C is laminated online. (2) Packaging bag making and heat sealing: Optimize the heat sealing process parameters according to the heat sealing layer material (mLLDPE or LTSCPP); adopt a two-stage heat sealing method. First, pre-seal and shape at a lower temperature (110-120℃), and then perform main sealing at an optimized temperature (125-135℃) to ensure strength, while avoiding excessive heat conduction that could affect the reversible weak bonding interface layer. (3) Gas-filled packaging: For easily oxidized foods, nitrogen or mixed protective gas is filled during packaging; the high barrier layer of the present invention can effectively maintain the gas atmosphere inside the packaging; (4) Post-consumer recycling guidelines: Print a label on the packaging that includes a recyclable symbol and simple pretreatment instructions; for example, for Mode A, indicate that “empty bags can be separated by soaking in warm water at XX℃”; for Mode B, indicate that “they can be separated by soaking in a small amount of edible alkali water”.

[0050] The packaging material of the present invention allows for interlayer separation after consumption through simple physical stimulation (soaking in warm water, treatment with a weak alkaline solution, or mechanical treatment), without the need for complex chemical dissociation or high-temperature and high-pressure treatment. The separated single polyolefin film can be directly entered into the existing recycling system for granulation and regeneration.

[0051] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A recyclable composite membrane material, characterized in that, It includes a protective layer, a high barrier layer and a heat-sealing inner layer arranged sequentially from the outside to the inside, and a reversible weak bonding interface layer is provided between the protective layer and the high barrier layer, and between the high barrier layer and the heat-sealing inner layer. The reversible weakly bonded interface layer has an adhesive force that binds the layers together in the initial state. Under specific external stimuli, its adhesive force is significantly reduced or disappears, thereby achieving physical separation of the functional layers.

2. The recyclable composite membrane material according to claim 1, characterized in that, The reversible weakly bonded interface layer is selected from at least one of the following modes: Mode A: Thermally responsive elastomer adhesive layer, which softens and loses its adhesiveness at a specific temperature; Mode B: pH-responsive hydrosol interface layer, which absorbs water and swells in a solution with a specific pH, resulting in loss of adhesion; Mode C: Mechanically responsive microstructure interlocking interface, which achieves bonding through microstructure interlocking and separation through mechanical stress.

3. The recyclable composite membrane material according to claim 1, characterized in that, The protective layer is one of biaxially oriented polypropylene, high-density polyethylene, or biaxially oriented polyethylene film, and its surface is provided with a functional coating.

4. The recyclable composite membrane material according to claim 1, characterized in that, The high barrier layer is one of the following: vapor-deposited silica cast polypropylene film, vapor-deposited alumina biaxially oriented polypropylene film, or co-extruded polyethylene / ethylene-vinyl alcohol copolymer island structure barrier film.

5. The recyclable composite membrane material according to claim 1, characterized in that, The heat-sealed inner layer is one of metallocene linear low-density polyethylene, anti-fouling metallocene polyethylene, or low-temperature heat-sealing polypropylene, with a thickness of 25-40 mm. .

6. The application of a recyclable composite film material in dry food packaging, characterized in that, Includes the following steps: (1) Composite membrane processing: The layers are bonded by dry lamination or co-extrusion lamination process, and the process conditions are controlled during the lamination process to maintain the responsive activity of the reversible weak bonding interface layer; (2) Packaging bag making and heat sealing: Optimize the heat sealing process parameters according to the heat sealing layer material, and adopt a two-stage heat sealing to avoid the heat affecting the interface layer; (3) Gas-filled packaging: Protective gas is filled into easily oxidized foods during packaging; (4) Post-consumer recycling guidelines: Print recycling labels and pre-treatment instructions on the packaging to guide users to achieve interlayer separation through physical stimulation.

7. The application of a recyclable composite film material according to claim 6 in dry food packaging, characterized in that, When the reversible weakly bonded interface layer is thermally responsive, the recycling method is to achieve interlayer separation by immersing it in warm water at 65-70℃ for 3-5 minutes.

8. The application of a recyclable composite film material according to claim 6 in dry food packaging, characterized in that, When the reversible weakly bound interface layer is pH-responsive, the recovery method is to soak it in a weak alkaline solution with pH 9-10 for 5-8 minutes to achieve interlayer separation.

9. The application of a recyclable composite film material according to claim 6 in dry food packaging, characterized in that, When the reversible weakly bonded interface layer is mechanically responsive, the recycling method is to achieve dry separation by applying micro-bending stress through mechanical rollers.

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