Canned powder food packaging easy-to-uncover film and preparation method thereof

Abstract

The invention discloses an easy-to-uncover film for packaging canned powder food and a preparation method of the easy-to-uncover film. The easy-to-uncover film is of a three-layer composite structure and comprises a printing layer with the thickness of 8-30 microns, a blocking layer with the thickness of 60-100 microns and a polyolefin heat sealing layer with the thickness of 18-50 microns. According to the preparation method, the printing layer-barrier layer and the barrier layer-heat sealing layer are compounded step by step through a dry type / solvent-free compounding process, and low solvent residue between layers is realized in combination with curing treatment. The cover film can keep stable easy-to-uncover force at the heat sealing temperature of 130-180 DEG C, solves the problems of powder falling and coating missing of a traditional coating structure, is free of wiredrawing or rough selvedge after being uncovered, has excellent barrier property and use safety, and is suitable for metal can packaging of powder food such as milk powder and coffee.

Description

Technical Field

[0001] The present invention relates to the technical field of food packaging, in particular to an easy-to-peel cover film, in particular to an easy-to-peel cover film suitable for canned powdered food, and a preparation method of the cover film. Background Art

[0002] Food packaging made of sheet metal, categorized by material, includes iron cans and aluminum cans. Due to its extremely low water and oxygen permeability, this type of packaging completely blocks the penetration of moisture and oxygen, maintaining low humidity and oxygen levels within the package. Furthermore, metal packaging can withstand significant pressure, making it particularly suitable for transporting and protecting the food inside. It is commonly used in canned foods, beverages, milk powder, protein powder, coffee, and other packaging, ensuring maximum quality and safety of the contents while significantly extending their shelf life.

[0003] Metal packaging, depending on how the lid is opened, includes sterile caps (Sanitary End), easy-open caps (Easy-Open End), and peel-off caps (Peel-Off End). As sterile caps lack pull rings, they must be cut from the can body with a sharp tool. Easy-open caps, on the other hand, have a separation line pre-set between the lid and the can body during stamping, allowing the lid to be removed by pulling the pull ring. While both types of lids are still in use, the former is difficult to open, while the latter's separation line can easily scratch users. Therefore, the market is more inclined towards easy-open caps with a pre-set opening and a tight fit.

[0004] Traditional easy-tear lids typically include a protective coating, an aluminum foil layer, and a heat-seal coating (HSL) layer stacked in sequence. When used for canned powdered foods, these easy-tear lids are subject to the risk of heat-seal coating powder shedding and coating leaks. Powder shedding can easily leave coating material on the inside of the easy-tear lid, while coating leaks can cause the easy-tear lid to leak, both of which can easily lead to food safety issues.

[0005] The utility model patent with announcement number CN207207324U provides a transparent easy-tear sealing film. Summary of the Invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art. In a first aspect, a canned powder food packaging easy-to-open cover film is provided, which has safe and reliable heat-sealing performance, is completely combined with the canned powder food, and is easy to open.

[0007] To achieve the above-mentioned purpose, the technical solution provided by the present invention is as follows: a canned food packaging easy-to-peel cover film, comprising a printing layer, a barrier layer and a heat-sealing layer made of a polyolefin film stacked in sequence, the three-layer structure being connected as one, and the total thickness of the easy-to-peel cover film being less than 150 μm.

[0008] Compared with the existing technology, the above technical features are designed with functional zoning of a three-layer structure. The printing layer can be used as a film material for printing on the surface, and can also serve as surface protection for the barrier layer. The heat-sealing layer replaces the risk of powder loss in traditional coatings, reducing the hidden dangers of food contamination. The form of the composite film relies on its mature process and has no risk of composite omissions, thereby avoiding the problem of leaking when the easy-to-peel cover film is used to seal the metal can through heat sealing.

[0009] As a preferred technical solution, the printing layer is at least one of polyethylene terephthalate film, polypropylene film, and polyethylene film, with a thickness of 8-30 μm. The printing layer is made of a film with high mechanical strength and print resistance, balancing the requirements of surface printing with the barrier layer's protective function. The thickness is selected to balance mechanical strength with the overall lightweight requirements of the cover film.

[0010] As a preferred technical solution, the barrier layer is at least one of aluminum foil, aluminum oxide coating, silicon oxide coating, and liquid crystal polymer film, with a thickness of 60-100 μm. The high-barrier material prevents water and oxygen penetration, extending the shelf life of the powdered food. The thickness of the barrier layer ensures a balance between barrier performance and mechanical strength.

[0011] As a preferred technical solution, the polyolefin film is at least one of linear low-density polyethylene (LLDPE), cast polypropylene (PP), metallocene polypropylene (MP), and ethylene-acrylic acid copolymer (EAC). The heat-seal layer has a thickness of 18-50 μm. The polyolefin material used in the heat-seal layer achieves controllable heat-seal strength, ensuring a balance between ease of opening and sealing. The thickness of the heat-seal layer ensures both flexibility and prevents breakage or residue when the lid is opened.

[0012] As a preferred technical solution, the barrier layer contains at least one layer of liquid crystal polymer film, and the heat sealing layer contains at least one layer of cast polypropylene film. The thickness ratio of the liquid crystal polymer film to the cast polypropylene film is (1-4):1.

[0013] Liquid crystal polymer (LCP) film refers to a high-performance polymer with a highly oriented molecular chain structure. It is formed into a film through melt extrusion and has high barrier properties, high temperature resistance, and excellent dimensional stability. Cast polypropylene film refers to a polypropylene film made through a melt casting process, which has high transparency, excellent heat sealing properties, and flexibility. The barrier layer contains at least one layer of LCP film, and the heat sealing layer contains at least one layer of CPP film. The thickness ratio of the two ranges from 1:1 to 4:1. The low thermal expansion coefficient of LCP (CTE≈10 ppm / ℃) and the higher thermal expansion coefficient of CPP (CTE≈100 ppm / ℃) differ by nearly ten times. The present invention compensates for the difference in thermal deformation by adjusting the thickness, reducing the risk of delamination. At the same time, LCP has a high elastic modulus and is combined with the high-ductility CPP to form a "rigid-flexible composite structure" to avoid brittle fracture when the lid is opened.

[0014] As an explanation, the glass transition temperature of LCP is usually between 120-150°C, and its surface will soften slightly at conventional heat sealing temperatures. The melting temperature of CPP is between 130-180°C. After melting, it has high fluidity and can easily form a tight fit with the surface of the metal can. When the two are bonded to each other, the molten CPP will penetrate the microporous structure of the softened LCP surface, forming a mechanical interlock after cooling. The softened LCP surface molecular chains are partially entangled with the molten CPP molecules, and the interfacial bonding between the two cans can be enhanced. Control the CPP melting depth and the thickness of the LCP softened layer to prevent thermal degradation of the LCP.

[0015] To illustrate, LCPs are mostly composed of rigid, rod-shaped aromatic monomers that form a highly oriented backbone structure through polycondensation. The backbone rigid monomers are preferably p-hydroxybenzoic acid (PHB), while the flexible spacer monomers are preferably terephthalic acid (TA) and isophthalic acid (IPA). They may also contain copolymerized modifying monomers such as 4,4'-biphenyldicarboxylic acid (HNA).

[0016] For illustration, LCP raw materials, by weight, include 50-70% PHB, 20-40% TA, and 30-50% HNA. Preparation methods include, but are not limited to, using a twin-screw extruder at a feed stage of 280-300°C, a melt stage of 320-340°C, and a homogenization stage of 340-360°C to form a cast film or blown film into a barrier layer.

[0017] As a preferred technical solution, the thickness ratio of liquid crystal polymer film to cast polypropylene film is 2:1. During heat sealing, the heat transfer from molten CPP to LCP is more uniform, reducing local LCP temperature melting.

[0018] As an explanation, the easy-peel mechanism of the easy-peel film is that the heat-sealing layer itself is destroyed and peeled off, with part of the heat-sealing layer remaining on the surface of the barrier layer and the other part remaining on the heat-sealed substrate (metal can). The peeled area will turn white, and when peeling, the heat-sealing layer itself will produce interfacial damage and internal peeling of the film will occur.

[0019] In a second aspect, the present invention provides a method for preparing an easy-to-peel cover film for canned food packaging having at least one of the above technical features, comprising the following steps: S1, performing dry lamination or solvent-free lamination on the printing layer and the barrier layer to integrally connect the two to form a primary product; S2, ripening the primary product; S3, dry-compounding or solvent-free-compounding the primary product with the heat-sealing layer to integrally connect the two to form a finished film; S4, aging the finished film.

[0020] To explain, the purpose of the dry / solventless lamination process combined with step-by-step aging is to reduce solvent residue and enhance interlayer bonding. Dry lamination is a traditional lamination process that uses an adhesive containing an organic solvent. This adhesive is evenly applied to the adhesive-carrying base film using an anilox roller coating method, dried in an oven, and pressed together in the lamination section to form a composite film. The adhesive used in dry lamination is typically solvent-based. Solventless lamination uses an adhesive that does not contain organic solvents. This adhesive is applied via multi-roll transfer coating, resulting in a thin and uniform adhesive layer. The coating amount is primarily determined by the speed of each roller and can be adjusted continuously online. The adhesive used in solvent-free lamination is typically a two-component reactive adhesive. Both lamination processes typically use polyurethane as the primary component, supplemented by a curing agent. The solvent-based adhesive used in dry lamination often uses organic solvents such as ethyl acetate.

[0021] As a preferred embodiment, dry lamination or solvent-free lamination is carried out on a corresponding laminating machine. In S1, the printing layer is placed in the first unwinding unit and the barrier layer is placed in the second unwinding unit, and the corresponding unwinding tension and laminating pressure are set for lamination; in S3, the primary product is placed in the first unwinding unit and the heat sealing layer is placed in the second unwinding unit, and the corresponding unwinding tension and laminating pressure are set for lamination.

[0022] As an explanation, step S1 combines the printing layer and the barrier layer into a primary product through a dry lamination or solvent-free lamination process. Dry lamination uses a solvent-based adhesive with a coating weight of 3.0-4.5 g / m 2 After the solvent is dried in three drying tunnels, the lamination is carried out under a pressure of 0.3-0.5 MPa. The winding tension is controlled to be 45-55 N for the printing layer and 50-60 N for the barrier layer. For solvent-free lamination, 100% solid content adhesive is used, and the coating amount is 1.4-2.0 g / m 2, directly through 0.4-0.6 MPa pressure compounding, no need for drying tunnel.

[0023] As a preferred embodiment, the adhesive used in the dry composite process is a two-component polyurethane adhesive, the mass ratio of the main agent to the curing agent is (8-10):1, the solid content after mixing is 25-33%, and the viscosity range is 300-800 mPa·s (25°C); the adhesive used in the solvent-free composite process is a polyurethane adhesive, especially an aliphatic polyurethane adhesive, and the glass transition temperature of the aliphatic polyurethane adhesive is -50°C to 80°C; the adhesive coating process parameters include: the dry composite coating roller line count is 120-180 lines / foot; the solvent-free composite coating roller temperature is 50-70°C, the coating roller pressure is 0.2-0.4MPa, the coating speed is 120-200m / min, and the ambient humidity of the solvent-free composite is controlled below 60%RH.

[0024] As a preferred embodiment, the aging process is typically carried out in an aging chamber. The aging parameters are a temperature of 40-60°C, a humidity of 50-80% RH, and an aging time of ≥ 24 hours, preferably ≥ 48 hours. When the barrier layer comprises a liquid crystal polymer film, the difference between the two aging times is ≤ 4 hours.

[0025] A powder food packaging having a packaging cover material made of an easy-to-peel cover film according to at least one of the above technical features.

[0026] The advantages and beneficial effects of the present invention are: the structure of integrated composite connection of the printing layer, the barrier layer and the heat-sealing layer solves the risk of powder loss and coating leakage when the coating type easy-to-open lid is connected by the coating, and the heat sealing is used to connect it to the metal can body packaging, which greatly reduces the risk of leakage. As a cover film, the connection between the metal can body and it can be made without sharp edges through processes such as flanging and chamfering, which reduces the risk of scratching the user when taking out the contents of the metal can, and is more labor-saving when opening than the easy-to-open lid with a pull ring structure. When dry lamination is used, the amount of residual solvent between the layers is low, which meets the needs of food safety. Compared with cover films with structures such as epoxy resin and coating, this type of cover film has no bad appearance such as brushing or fuzzing on the base material after being opened. The same easy-to-open force value can be achieved at different heat sealing temperatures of 130℃-180℃. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a structural schematic diagram of the easy-to-peel cover film of the present invention; Figure 2 This is a process flow chart for preparing the easy-to-peel cover film of the present invention; Figure 3 This is a photo of the easy-to-peel cover film of the present invention connected to the can body (top surface); Figure 4This is a photograph of the easy-to-peel cover film of the present invention being peeled off from the can body (top surface). DETAILED DESCRIPTION

[0028] The following embodiments are further described in conjunction with the accompanying drawings and examples. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0029] Example 1 A film for packaging powdered foods that can be easily peeled off comprises a printing layer, a barrier layer, and a heat-sealing layer stacked in sequence. The printing layer is a 12μm-thick biaxially oriented polypropylene film, the barrier layer is an 80μm-thick aluminum foil, and the heat-sealing layer is a 25μm-thick cast polypropylene film, for a total thickness of 117μm.

[0030] The preparation method of the easy-to-peel cover film is as follows: S1: The BOPP layer and the aluminum foil are connected on the laminating machine through a dry laminating process to obtain the initial product. A two-component polyurethane adhesive is applied between the two layers with a coating amount of 4.0g / m 2 , composite pressure 0.4MPa; S2: Transfer the primary product to a curing chamber and perform the first curing at 55°C / 65%RH for 48 hours; S3: The primary product and the CPP layer are connected by a solvent-free composite process to obtain a finished film, and a solvent-free adhesive is applied between the two with a coating amount of 2.0g / m 2 , composite pressure 0.5MPa; S4: The finished film is transferred to an aging chamber and aged for a second time at 50°C / 70% RH for 48 hours.

[0031] Example 2 A film for packaging powdered foods that can be easily peeled off comprises a printing layer, a barrier layer, and a heat-seal layer stacked in sequence. The printing layer is a 20-μm-thick polyethylene terephthalate film, the barrier layer is a 70-μm-thick aluminum oxide film, and the heat-seal layer is a 28-μm-thick metallocene polypropylene film, for a total thickness of 118 μm.

[0032] The preparation method of the easy-to-peel cover film is as follows: S1: The PET layer and the aluminum oxide coating are connected on a laminating machine through a solvent-free laminating process to obtain the initial product. A solvent-free polyurethane adhesive is applied between the two with a coating amount of 1.8g / m 2 , composite pressure 0.6MPa; S2: Transfer the primary product to a curing chamber and perform the first curing at 60°C / 75%RH for 24 hours; S3: The primary product and the mPP layer are connected by a dry lamination process to obtain the finished film. A two-component polyurethane adhesive is applied between the two layers with a coating amount of 4.0 g / m 2 , composite pressure 0.45MPa; S4: The finished film is transferred to an aging chamber and aged for a second time at 55°C / 70% RH for 48 hours.

[0033] Example 3 A peelable film for powdered food packaging comprises a laminated printing layer, a barrier layer, and a heat-seal layer. The printing layer is an 18μm-thick biaxially oriented polypropylene film. The barrier layer is a 60μm-thick liquid crystal polymer film (PHB 60% + TA 40%), and the heat-seal layer is a 22μm-thick cast polypropylene film, for a total thickness of 100μm.

[0034] The preparation method of the easy-to-peel cover film is as follows: S1: The BOPP layer and the LCP film are connected on a laminating machine through a dry lamination process to obtain the initial product. A two-component polyurethane adhesive is applied between the two layers with a coating amount of 3.4g / m 2 , composite pressure 0.5MPa; S2: Transfer the primary product to a curing chamber and perform the first curing at 55°C / 65%RH for 48 hours; S3: The primary product and the CPP layer are connected by a solvent-free composite process to obtain a finished film, and a solvent-free polyurethane adhesive is applied between the two with a coating amount of 2.0g / m 2 , composite pressure 0.5MPa; S4: The finished film is transferred to an aging chamber and aged for a second time at 50°C / 70% RH for 20 hours.

[0035] Example 4 A peelable film for powdered food packaging, comprising a laminated printing layer, a barrier layer, and a heat-seal layer. The printing layer is a 30μm-thick polyethylene terephthalate film, the barrier layer is a 95μm-thick aluminum oxide film (deposited by magnetron sputtering, with a thickness tolerance of ±5%), and the heat-seal layer is a 25μm-thick metallocene polypropylene film, for a total thickness of 150μm.

[0036] The preparation method of the easy-to-peel cover film is as follows: S1: The PET layer and the aluminum oxide coating are connected on a laminating machine through a solvent-free laminating process to obtain the initial product. A solvent-free polyurethane adhesive is applied between the two with a coating amount of 2.2g / m 2 , composite pressure 0.6MPa; S2: Transfer the primary product to a curing chamber and perform the first curing at 60°C / 70%RH for 16 hours; S3: The primary product and the mPP layer are connected by a dry lamination process to obtain the finished film. A two-component polyurethane adhesive is applied between the two layers with a coating amount of 4.0 g / m 2 , composite pressure 0.45MPa; S4: The finished film was transferred to an aging chamber and aged for a second time at 55°C / 65%RH for 18 hours.

[0037] Example 5 A film for packaging powdered foods that can be easily peeled off comprises a printing layer, a barrier layer, and a heat-sealing layer stacked in sequence. The printing layer is an 8-μm-thick polyethylene terephthalate film, the barrier layer is a 90-μm-thick aluminum foil, and the heat-sealing layer is an 18-μm-thick linear low-density polyethylene film, for a total thickness of 116 μm.

[0038] The preparation method of the easy-to-peel cover film is as follows: S1: After the PET layer and aluminum foil were plasma treated (argon / oxygen = 4:1, power 80W, time 15 seconds), they were dry-laminated on a laminating machine to obtain the initial product. A two-component polyurethane adhesive was applied between the two layers at a coating weight of 4.3g / m 2 , composite pressure 0.35MPa; S2: Transfer the primary product to a curing chamber and perform the first curing at 50°C / 75%RH for 48 hours; S3: The primary product and the LLDPE layer are connected by a solvent-free composite process to obtain a finished film, and a solvent-free polyurethane adhesive is applied between the two with a coating amount of 2.0g / m 2 , composite pressure 0.6MPa; S4: The finished film is transferred to an aging chamber and aged for a second time at 45°C / 80% RH for 72 hours.

[0039] Example 6 A film for packaging powdered food that is easy to peel off, comprising a printing layer, a barrier layer, and a heat-sealing layer stacked in sequence. The printing layer is a 23 μm thick polyethylene terephthalate film, and the barrier layer is a 60 μm thick silicon oxide coating (vapor chemical deposition, SiO x Thickness 200nm, substrate is PET film), heat sealing layer is 18μm thick cast polypropylene film, total thickness 101.2μm.

[0040] The preparation method of the easy-to-peel cover film is as follows: S1: The PET layer and the silicon oxide coating are connected on a laminating machine through a dry laminating process to obtain the initial product. A polyester adhesive is applied between the two with a coating amount of 3.4g / m 2 , composite pressure 0.4MPa; S2: Transfer the primary product to a curing chamber and perform the first curing at 55°C / 70%RH for 48 hours; S3: The primary product and the CPP layer are connected by a solvent-free composite process to obtain a finished film, and a solvent-free polyurethane adhesive is applied between the two with a coating amount of 2.0g / m 2 , composite pressure 0.55MPa; S4: The finished film is transferred to an aging chamber and aged for a second time at 50°C / 65% RH for 24 hours.

[0041] Example 7 This easy-to-peel lidding film for powdered food packaging consists of a laminated printing layer, a barrier layer, and a heat-sealing layer. The printing layer is a 24μm-thick polyethylene terephthalate film, the barrier layer is a 30μm-thick liquid crystal polymer film (55% PHB + 45% HNA) and a 40μm-thick aluminum foil, and the heat-sealing layer is a 28μm-thick cast polypropylene film, for a total thickness of 122μm.

[0042] The preparation method of the easy-to-peel cover film is as follows: S1: The PET layer and the aluminum foil are connected on the laminating machine through a dry laminating process to obtain the first primary product. A two-component polyurethane adhesive is applied between the two layers with a coating amount of 2.4g / m 2 , composite pressure 0.5MPa; S2: The first product is transferred to the curing chamber and cured for the first time at 58°C / 68%RH for 20 hours; S3: The aluminum foil of the first primary product and the LCP film are connected through a solvent-free composite process to obtain the second primary product, and a solvent-free acrylic adhesive is applied between the two with a coating amount of 1.0g / m 2 , composite pressure 0.6MPa; S4: Transfer the second primary product to the curing chamber and perform a second curing at 55°C / 70%RH for 18 hours; S5: The second primary product and the CPP layer are connected by a dry lamination process to obtain a finished film, and a two-component polyurethane adhesive is applied between the two with a coating amount of 2.0g / m 2 , composite pressure 0.45MPa; S6: The finished film was transferred to an aging chamber and aged for the third time at 50°C / 75%RH for 22 hours.

[0043] Example 8 This easy-to-peel lidding film for powdered food packaging consists of a laminated printing layer, a barrier layer, and a heat-sealing layer. The printing layer is a 20μm-thick polyethylene terephthalate film, the barrier layer is a 56μm-thick liquid crystal polymer film (50% PHB + 50% HNA) and a 40μm-thick aluminum foil, and the heat-sealing layer is a 28μm-thick cast polypropylene film, for a total thickness of 144μm.

[0044] The preparation method of the easy-to-peel cover film is as follows: S1: The PET layer and the aluminum foil are connected on the laminating machine through a dry laminating process to obtain the first primary product. A two-component polyurethane adhesive is applied between the two layers with a coating amount of 2.0g / m 2 , composite pressure 0.4MPa; S2: Transfer the first product to the curing room and perform the first curing at 50°C / 70%RH for 24 hours; S3: The aluminum foil of the first primary product and the LCP film are connected through a solvent-free composite process to obtain the second primary product. A solvent-free acrylic adhesive is applied between the two with a coating amount of 1.7g / m 2 , composite pressure 0.4MPa; S4: Transfer the second primary product to the curing chamber and perform a second curing at 40°C / 50%RH for 24 hours; S5: The second primary product and the CPP layer are connected by a dry lamination process to obtain a finished film. A two-component polyurethane adhesive is applied between the two, with a coating amount of 2.3g / m 2 , composite pressure 0.45MPa; S6: The finished film was transferred to an aging chamber and aged for a third time at 50°C / 70% RH for 48 hours.

[0045] Example 9 A peelable film for powdered food packaging comprises a printing layer, a barrier layer, and a heat-seal layer stacked in sequence. The printing layer is a 12-μm-thick polybutylene terephthalate film, the barrier layer is a 100-μm-thick aluminum foil, and the heat-seal layer is a 25-μm-thick cast polypropylene film, for a total thickness of 137 μm.

[0046] The preparation method of the easy-to-peel cover film is as follows: S1: The PET layer and the aluminum foil are connected on the laminating machine through a dry laminating process to obtain the initial product. A two-component polyurethane adhesive is applied between the two layers with a coating amount of 5.0g / m 2 , composite pressure 0.45MPa; S2: Transfer the primary product to a curing chamber and perform the first curing at 55°C / 65%RH for 48 hours; S3: The primary product and the CPP layer are connected by a solvent-free composite process to obtain the finished film. A solvent-free adhesive is applied between the two layers with a coating amount of 1.4 g / m 2 , composite pressure 0.5MPa; S4: The finished film is transferred to an aging chamber and aged for a second time at 40°C / 66% RH for 48 hours.

[0047] Example 10 This easy-to-peel lidding film for powdered food packaging consists of a laminated printing layer, a barrier layer, and a heat-sealing layer. The printing layer is a 20μm-thick polyethylene terephthalate film, the barrier layer is an 80μm-thick liquid crystal polymer film (70% PHB + 30% HNA), and the heat-sealing layer is a 20μm-thick cast polypropylene film, for a total thickness of 120μm.

[0048] The preparation method of the easy-to-peel cover film is as follows: S1: The PET layer and the aluminum foil are connected on the laminating machine through a dry laminating process to obtain the first primary product. A two-component polyurethane adhesive is applied between the two layers with a coating amount of 4.0g / m 2 , composite pressure 0.5MPa; S2: Transfer the first product to the curing room and perform the first curing at 50°C / 60%RH for 48 hours; S3: The aluminum foil of the first primary product and the LCP film are connected through a solvent-free composite process to obtain the second primary product. A solvent-free acrylic adhesive is applied between the two with a coating amount of 1.7g / m 2 , composite pressure 0.4MPa; S4: Transfer the second primary product to the curing chamber and perform a second curing at 40°C / 50%RH for 48 hours; S5: The second primary product and the CPP layer are connected by a dry lamination process to obtain a finished film. A two-component polyurethane adhesive is applied between the two, with a coating amount of 1.4g / m 2 , composite pressure 0.6MPa; S6: The finished film was transferred to an aging chamber and aged for a third time at 40°C / 50% RH for 48 hours.

[0049] The above examples were subjected to interlaminar strength testing using the GB / T 8808-1988 test method. The heat seal layer was peeled from the barrier layer at a peel speed of 300 mm / min. Peel stability was measured using the coefficient of variation (CV), where CV = standard deviation / average value × 100%. The test results are shown in the table below. Each example was heat-sealed at a temperature of 130-180°C in increments of 10°C. The heat seal strength range is reported below. The heat-sealed cover film was then attached to the can body (top surface) and the seal was visually inspected after removal. Test items Interlaminar strength, N Peel stability Heat seal strength (N / 15mm) Uncovering effect Example 1 14.2±0.8 CV=8.2% 6.5±0.3 Even whitening, no burrs Example 2 7.8±1.1 CV=11.5% 6.2±0.4 Slightly whitish, no burrs Example 3 11.5±0.6 CV=5.8% 5.1±0.2 Evenly white, smooth edges Example 4 9.5±1.3 CV=15.7% 5.8±0.5 Slightly white, slightly burred Example 5 13.3±0.9 CV=12.1% 6.5±0.3 Slightly white, slightly burred Example 6 8.6±0.7 CV=7.9% 7.8±0.4 Even whitening, no burrs Example 7 12.2±0.5 CV=4.2% 6.5±0.3 Even whitening, no burrs Example 8 14.1±1.2 CV=6.3% 7.3±0.3 Even whitening, no burrs Example 9 15.2±0.8 CV=7.2% 7.2±0.5 Even whitening, no burrs Example 10 13.2±1.2 CV=8.8% 4.2±0.3 Even whitening, no burrs The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. An easy-to-peel cover film for canned powder food packaging, characterized in that: The easy-to-peel cover film comprises a printing layer, a barrier layer and a heat-sealing layer made of a polyolefin film which are stacked in sequence. The three layers are connected as one. The total thickness of the easy-to-peel cover film is less than 150 μm.

2. The easy-to-peel cover film according to claim 1, wherein: The printing layer is selected from at least one of polyethylene terephthalate film, polypropylene film and polyethylene film, and has a thickness of 8-30 μm.

3. The easy-to-peel cover film according to claim 1, wherein: The barrier layer is selected from at least one of aluminum foil, aluminum oxide coating, silicon oxide coating, and liquid crystal polymer film, and has a thickness of 60-100 μm.

4. The easy-to-peel cover film according to claim 1, wherein: The polyolefin film is selected from at least one of linear low-density polyethylene film, cast polypropylene film, metallocene polypropylene film, and ethylene-acrylic acid copolymer film, and the thickness of the heat-sealing layer is 18-50 μm.

5. The easy-to-peel cover film according to claim 1, wherein: The barrier layer comprises at least one layer of liquid crystal polymer film, the heat sealing layer comprises at least one layer of cast polypropylene film, and the thickness ratio of the liquid crystal polymer film to the cast polypropylene film is (1-4):

1.

6. The easy-to-peel cover film according to claim 1, wherein: The thickness ratio of the liquid crystal polymer film to the cast polypropylene film is 2:

1.

7. A method for preparing an easy-to-peel cover film for canned powder food packaging according to any one of claims 1 to 6, comprising the following steps: S1: The printing layer and the barrier layer are integrally connected through a dry lamination or solvent-free lamination process to form a primary product; S2: Ripening treatment of the primary product; S3: The primary product and the heat seal layer are integrally connected through a dry lamination or solvent-free lamination process to form a finished film; S4: performing a aging treatment on the finished film.

8. The preparation method according to claim 7, characterized in that: In step S1, the printing layer is placed in the first unwinding unit, and the barrier layer is placed in the second unwinding unit, and the lamination is completed by adjusting the unwinding tension and laminating pressure; In step S3, the primary product is placed in the first unwinding unit, and the heat-sealing layer is placed in the second unwinding unit, and the lamination is completed by adjusting the unwinding tension and the laminating pressure.

9. The preparation method according to claim 7, characterized in that The aging treatment conditions are: temperature 40-60° C., humidity 50-80% RH, and aging time ≥ 24 hours.

10. A canned powder food package, characterized in that: The easy-to-peel cover film according to any one of claims 1 to 6 is used as a packaging cover material.

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