High-barrier fresh-keeping low-temperature heat-sealing composite film as well as preparation process and application thereof

Abstract

The invention provides a high-barrier fresh-keeping low-temperature heat-sealing composite film and a manufacturing process and application thereof, the composite film sequentially comprises a heat-sealing layer, a barrier layer, a reinforcing layer and a surface treatment layer from the inner layer to the outer layer, and the layers are bonded through bonding layers. The heat-sealing layer is prepared from modified polyethylene, polypropylene and a heat-sealing auxiliary agent, and the barrier layer is made of a composite material of nano aluminum oxide, polyvinylidene fluoride and an ethylene-vinyl alcohol copolymer. The enhancement layer is a polyester film, and the surface treatment layer is subjected to corona treatment. The composite film is prepared through a specific manufacturing process, and the specific manufacturing process comprises the steps of preparation of the heat sealing layer and the blocking layer, compounding, curing treatment, surface treatment and the like. The composite film disclosed by the invention has excellent barrier property and low-temperature heat-sealing capability, is suitable for vacuum packaging or modified atmosphere packaging of foods, and effectively prolongs the fresh-keeping period and the shelf life of the foods.

Description

Technical Field

[0001] The present invention relates to the technical field of composite films, and in particular to a high-barrier, fresh-keeping, low-temperature heat-sealing composite film and a manufacturing process and application thereof. Background Art

[0002] In the modern packaging industry, the research and development and application of high-barrier fresh-keeping packaging materials have attracted much attention. As people's requirements for food quality and safety continue to increase, the limitations of traditional packaging materials are becoming increasingly prominent.

[0003] In the field of food packaging, existing packaging materials have many deficiencies in terms of barrier properties and low-temperature heat-sealing properties. On the one hand, many common packaging materials have poor barrier effects against gases such as oxygen and water vapor, which makes food susceptible to oxidation and water loss during storage, thereby shortening the shelf life of food. On the other hand, traditional packaging materials are difficult to heat-seal at low temperatures, have low heat-seal strength, and are prone to problems such as loose sealing and leakage, which not only affects the packaging quality of food, but may also cause food deterioration. In addition, some packaging materials have poor preservation properties and cannot effectively maintain the freshness, taste and nutritional content of food.

[0004] In addition, the existing composite packaging materials need to be improved in terms of bonding strength between layers, overall mechanical properties, etc. Some composite films are prone to delamination and cracking during use, affecting the integrity and reliability of the packaging.

[0005] In summary, the packaging materials in the prior art have deficiencies in terms of high barrier properties, low temperature heat sealing properties, freshness preservation performance, safety and overall performance, and are unable to meet the growing demands of the food industry. Summary of the invention

[0006] In view of this, the present invention proposes a high-barrier fresh-keeping low-temperature heat-sealing composite film and a manufacturing process and application thereof to solve the above problems.

[0007] The technical solution of the present invention is achieved as follows: a high barrier fresh-keeping low temperature heat-seal composite film: from the inner layer to the outer layer, it is a heat-seal layer, a barrier layer, a reinforcement layer and a surface treatment layer, and the heat-seal layer, the barrier layer and the reinforcement layer are bonded to each other by at least one adhesive layer; the heat-seal layer is made of the following raw materials in parts by weight: 40-60 parts of modified polyethylene, 22-35 parts of polypropylene, and 8-12 parts of heat-seal aids; the heat-seal aids are epoxy soybean oil, silicone oil and xylitol ester in a mass ratio of (32-50): (12-25): (5-10); low-temperature rapid heat sealing is achieved while maintaining good sealing strength, and the barrier layer is made of a composite material of nano-alumina, polyvinylidene fluoride and ethylene-vinyl alcohol copolymer in a mass ratio of (2-5): (1-3): (4-8). To improve the barrier properties of oxygen, carbon dioxide and water vapor.

[0008] Furthermore, the reinforcing layer is a polyester (PET) film with a thickness of 10-20 μm, the tensile strength of the polyester film layer is not less than 200 MPa, and the elongation at break is 100-150%. It is used to improve the mechanical strength and dimensional stability of the film.

[0009] Furthermore, the surface treatment layer is a surface treated by corona treatment.

[0010] Furthermore, the adhesive layer is a polyurethane adhesive, and the coating amount of the adhesive is 2-4 g / m 2 .

[0011] Furthermore, the modified polyethylene is prepared by placing polyethylene and ethylene-alpha olefin copolymer into an oven for drying, placing them into a mixing device at a mass ratio of 50-80:15, adding 5-10% carbon tetrachloride of the mass of the mixture for melt blending, and the mixing temperature is 120-135° C. The melt blend is extruded and granulated, and after cooling, cobalt-60 irradiation cross-linking is used for 15-30 minutes to obtain the modified polyethylene. The heat resistance, mechanical strength, and environmental stress cracking resistance of polyethylene are significantly improved.

[0012] Furthermore, the irradiation dose of the cobalt-60 irradiation cross-linking is 80-120 kGy, and the dose rate is 0.01-6.86 Gy / s.

[0013] Furthermore, a process for producing a high barrier fresh-keeping low temperature heat-sealing composite film is provided.

[0014] The following steps are involved:

[0015] S1, heat sealing layer preparation: the modified polyethylene, polypropylene and heat sealing aid are mixed evenly according to a ratio, and the mixture is extruded into a film by an extruder to form a heat sealing layer;

[0016] S2, preparation of barrier layer: nano alumina, polyvinylidene fluoride and ethylene-vinyl alcohol copolymer are premixed according to the ratio, the premixing stirring rate is 200-400rpm, the premixed materials are added into a high-speed mixer, 5-15% of ammonium polyacrylate by mass of the materials are added, the mixture is mixed at a speed of 1000-2000rpm and a temperature of 50-80°C for 40-90min, extruded and granulated to obtain a barrier layer material, the extrusion temperature is controlled at 180-220°C, and the prepared barrier layer material is extruded and formed by an extruder to form a barrier layer film;

[0017] S3, Composite: Apply polyurethane adhesive on one side of the heat seal film, with a coating amount of 2-4g / m 2Then, the barrier layer film is laminated on the heat-sealing layer film and dried. The wind speed of the drying process is 10-15m / s, the drying temperature is 80-100℃, and the drying time is 5-10 minutes.

[0018] S4, aging treatment: Apply polyurethane adhesive on the other side of the barrier film, and also control the coating amount to 2-4g / m 2 Then, the polyester film is laminated as a reinforcing layer on the barrier film coated with the adhesive, and placed in a curing device for curing at a temperature of 40-60°C for 24-48 hours. During the curing process, the relative humidity is controlled at 40-60%.

[0019] S5. Surface treatment: The outermost layer of the composite film is subjected to multi-level surface treatment using corona equipment.

[0020] Furthermore, the surface treatment of S5 is as follows: first stage: output power is 3kW, frequency is 15kHz, electrode gap is adjusted to 2mm, processing speed is 10m / min, and corona treatment time is 2s; second stage: output power is 4kW, frequency is 20kHz, electrode gap is 1.5mm, processing speed is adjusted to 8m / min, and corona treatment time is 3s; third stage: output power is 5kW, frequency is 25kHz, electrode gap is 1mm, processing speed is 6m / min, and corona treatment time is 4s.

[0021] Furthermore, a high-barrier, fresh-keeping, low-temperature heat-sealing composite film is used for vacuum packaging or modified atmosphere packaging of food, effectively extending the shelf life.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) Low-temperature heat-sealing performance: Through the combination of a specific ratio of heat-sealing aids with modified polyethylene and polypropylene, the composite film can achieve good heat-sealing effect at low temperatures. It can also maintain a high heat-sealing strength under low-temperature heat-sealing conditions.

[0024] (2) High barrier properties: The composite material of nano-alumina, polyvinylidene fluoride and ethylene-vinyl alcohol copolymer is used as the barrier layer, which effectively improves the barrier properties of the composite film, can effectively prevent the penetration of oxygen, moisture, microorganisms, etc., and extend the shelf life of food.

[0025] (3) Good mechanical properties: The reinforcement layer is made of polyester film, which has high tensile strength and appropriate elongation at break, providing the composite film with good mechanical strength and flexibility. The heat-sealing layer, barrier layer, and reinforcement layer are tightly bonded by polyurethane adhesive. The synergistic effect between the layers makes the composite film have good overall structural stability.

[0026] (4) Significant surface treatment effect: After multi-level corona surface treatment, the bonding performance and mechanical strength of the composite film are improved, which can better block the penetration of substances such as oxygen, water vapor, and odor, further improving the barrier performance of the composite film.

[0027] (5) Wide application prospects: It can be used for vacuum packaging or modified atmosphere packaging of food, which can effectively maintain the quality and nutritional content of food and extend the shelf life of food. Whether it is meat, fruit, vegetables or processed food, it can be well protected to ensure that the product is not contaminated during storage and transportation, and maintain its effectiveness and safety. DETAILED DESCRIPTION

[0028] In order to better understand the technical content of the present invention, specific embodiments are provided below to further illustrate the present invention.

[0029] Unless otherwise specified, the experimental methods used in the embodiments of the present invention are all conventional methods.

[0030] Unless otherwise specified, the materials, reagents, etc. used in the embodiments of the present invention can be obtained from commercial sources.

[0031] Example 1

[0032] A high-barrier, fresh-keeping, low-temperature heat-sealing composite film: from the inner layer to the outer layer, there are a heat-sealing layer, a barrier layer, a reinforcement layer and a surface treatment layer, and the heat-sealing layer, the barrier layer and the reinforcement layer are bonded to each other by at least one adhesive layer; the heat-sealing layer is made of the following raw materials in parts by weight: 40 parts of modified polyethylene, 22 parts of polypropylene, and 8 parts of a heat-sealing aid; the heat-sealing aid is epoxy soybean oil, silicone oil and xylitol ester in a mass ratio of 32:12:5; the barrier layer is made of a composite material of nano-alumina, polyvinylidene fluoride and ethylene-vinyl alcohol copolymer in a mass ratio of 2:1:4; the reinforcement layer is a polyester (PET) film with a thickness of 10 μm, the tensile strength of the polyester film layer is not less than 200 MPa, and the elongation at break is 100%; the surface treatment layer is a corona-treated surface; the adhesive layer is a polyurethane adhesive, and the coating amount of the adhesive is 2 g / m 2 ;

[0033] The modified polyethylene is prepared by placing polyethylene and ethylene-α-olefin copolymer into an oven for drying, respectively, and then placing them into a mixing device at a mass ratio of 50:15, and simultaneously adding 5% carbon tetrachloride by mass of the mixture for melt blending, the mixing temperature being 120° C. The molten blend is granulated by extrusion, cooled, and cross-linked by cobalt-60 radiation for 15 minutes, the radiation dose of cobalt-60 radiation cross-linking being 80 kGy, and the dose rate being 0.01 Gy / s, to obtain the modified polyethylene.

[0034] Example 2

[0035] A high-barrier, fresh-keeping, low-temperature heat-sealing composite film: from the inner layer to the outer layer, there are a heat-sealing layer, a barrier layer, a reinforcement layer and a surface treatment layer, and the heat-sealing layer, the barrier layer and the reinforcement layer are bonded to each other by at least one adhesive layer; the heat-sealing layer is made of the following raw materials in parts by weight: 60 parts of modified polyethylene, 35 parts of polypropylene, and 12 parts of a heat-sealing aid; the heat-sealing aid is epoxy soybean oil, silicone oil and xylitol ester in a mass ratio of 50:25:10; the barrier layer is made of a composite material of nano-alumina, polyvinylidene fluoride and ethylene-vinyl alcohol copolymer in a mass ratio of 5:3:8; the reinforcement layer is a polyester (PET) film with a thickness of 20 μm, the tensile strength of the polyester film layer is not less than 200 MPa, and the elongation at break is 150%; the surface treatment layer is a surface treated with corona; the adhesive layer is a polyurethane adhesive, and the coating amount of the adhesive is 4 g / m 2 ;

[0036] The modified polyethylene is prepared by placing polyethylene and ethylene-alpha olefin copolymer into an oven for drying treatment respectively, placing the mixture into a mixing device at a mass ratio of 80:15, and adding 10% carbon tetrachloride by mass of the mixture for melt blending at a mixing temperature of 120-135° C. The molten blend is granulated by extrusion, cooled, and cross-linked by cobalt-60 radiation for 30 minutes. The radiation dose of cobalt-60 radiation cross-linking is 120 kGy, and the dose rate is 6.86 Gy / s to obtain the modified polyethylene.

[0037] Example 3

[0038] A high-barrier, fresh-keeping, low-temperature heat-sealing composite film: from the inner layer to the outer layer, there are a heat-sealing layer, a barrier layer, a reinforcement layer and a surface treatment layer, and the heat-sealing layer, the barrier layer and the reinforcement layer are bonded to each other by at least one adhesive layer; the heat-sealing layer is made of the following raw materials in parts by weight: 50 parts of modified polyethylene, 30 parts of polypropylene, and 10 parts of a heat-sealing aid; the heat-sealing aid is epoxy soybean oil, silicone oil and xylitol ester in a mass ratio of 45:18:8; the barrier layer is made of a composite material of nano-alumina, polyvinylidene fluoride and ethylene-vinyl alcohol copolymer in a mass ratio of 4:2:6; the reinforcement layer is a polyester (PET) film with a thickness of 15 μm, the tensile strength of the polyester film layer is not less than 200 MPa, and the elongation at break is 130%; the surface treatment layer is a surface treated with corona; the adhesive layer is a polyurethane adhesive, and the coating amount of the adhesive is 3 g / m 2 ;

[0039] The modified polyethylene is prepared by placing polyethylene and ethylene-α-olefin copolymer into an oven for drying, respectively, and placing them into a mixing device at a mass ratio of 70:15, and adding 5-10% carbon tetrachloride by mass of the mixture for melt blending at a mixing temperature of 130° C. The melt blend is extruded and granulated, and after cooling, cobalt-60 irradiation cross-linking is performed for 22 minutes, the irradiation dose of cobalt-60 irradiation cross-linking is 100 kGy, and the dose rate is 3.5 Gy / s, to obtain the modified polyethylene;

[0040] The above-mentioned embodiments 1-3 adopt the following manufacturing process:

[0041] S1, heat sealing layer preparation: the modified polyethylene, polypropylene and heat sealing aid are mixed evenly according to a ratio, and the mixture is extruded into a film by an extruder to form a heat sealing layer;

[0042] S2, preparation of barrier layer: nano-alumina, polyvinylidene fluoride and ethylene-vinyl alcohol copolymer are premixed according to the ratio, the premixing stirring rate is 300 rpm, the premixed materials are added into a high-speed mixer, 10% of ammonium polyacrylate by mass of the materials is added, the mixture is mixed at a speed of 1500 rpm and a temperature of 70°C for 65 minutes, and the barrier layer material is obtained by extrusion granulation. The extrusion temperature is controlled at 200°C, and the prepared barrier layer material is extruded and formed by an extruder to form a barrier layer film;

[0043] S3, Composite: Apply polyurethane adhesive on one side of the heat seal film, with a coating amount of 3g / m 2 Then, the barrier layer film is laminated on the heat-sealing layer film and dried. The wind speed of the drying process is 13 m / s, the drying temperature is 90°C, and the drying time is 8 minutes.

[0044] S4, aging treatment: Apply polyurethane adhesive on the other side of the barrier film, and also control the coating amount to 3g / m 2 Then, the polyester film is laminated as a reinforcing layer on the barrier film coated with the adhesive, and placed in a curing device for curing at a temperature of 50°C for 36 hours. During the curing process, the relative humidity is controlled at 50%.

[0045] S5. Surface treatment: The outermost layer of the composite film is subjected to three-level surface treatment using corona equipment: the first level: output power is 3kW, frequency is 15kHz, the electrode gap is adjusted to 2mm, the processing speed is 10m / min, and the corona treatment time is 2s; the second level: output power is 4kW, frequency is 20kHz, the electrode gap is 1.5mm, the processing speed is adjusted to 8m / min, and the corona treatment time is 3s; the third level: output power is 5kW, frequency is 25kHz, the electrode gap is 1mm, the processing speed is 6m / min, and the corona treatment time is 4s.

[0046] Example 4

[0047] A high-barrier, fresh-keeping, low-temperature heat-sealing composite film: from the inner layer to the outer layer, there are a heat-sealing layer, a barrier layer, a reinforcement layer and a surface treatment layer, and the heat-sealing layer, the barrier layer and the reinforcement layer are bonded to each other by at least one adhesive layer; the heat-sealing layer is made of the following raw materials in parts by weight: 50 parts of modified polyethylene, 30 parts of polypropylene, and 10 parts of a heat-sealing aid; the heat-sealing aid is epoxy soybean oil, silicone oil and xylitol ester in a mass ratio of 45:18:8; the barrier layer is made of a composite material of nano-alumina, polyvinylidene fluoride and ethylene-vinyl alcohol copolymer in a mass ratio of 4:2:6; the reinforcement layer is a polyester (PET) film; the surface treatment layer is a corona-treated surface; the adhesive layer is a polyurethane adhesive, and the coating amount of the adhesive is 3g / m 2 ;

[0048] The modified polyethylene is prepared by placing polyethylene and ethylene-α-olefin copolymer into an oven for drying, respectively, and placing them into a mixing device at a mass ratio of 70:15, and adding 5% carbon tetrachloride by mass of the mixture for melt blending at a mixing temperature of 130° C. The melt blend is extruded and granulated, and after cooling, cobalt-60 irradiation cross-linking is performed for 22 minutes, the irradiation dose of cobalt-60 irradiation cross-linking is 100 kGy, and the dose rate is 3.5 Gy / s, to obtain the modified polyethylene;

[0049] The above-mentioned embodiment 4 adopts the following manufacturing process:

[0050] S1, heat sealing layer preparation: the modified polyethylene, polypropylene and heat sealing aid are mixed evenly according to a ratio, and the mixture is extruded into a film by an extruder to form a heat sealing layer;

[0051] S2, preparation of barrier layer: nano-alumina, polyvinylidene fluoride and ethylene-vinyl alcohol copolymer are premixed according to the ratio, the premixing stirring rate is 200rpm, the premixed materials are added into a high-speed mixer, 5% of ammonium polyacrylate by mass of the materials is added, the mixture is mixed at a speed of 1000rpm and a temperature of 50°C for 40min, extruded and granulated to obtain a barrier layer material, the extrusion temperature is controlled at 180°C, and the prepared barrier layer material is extruded and formed by an extruder to form a barrier layer film;

[0052] S3, Composite: Apply polyurethane adhesive on one side of the heat seal film, with a coating amount of 2g / m 2 Then, the barrier layer film is laminated on the heat-sealing layer film and dried. The wind speed of the drying process is 10 m / s, the drying temperature is 80°C, and the drying time is 5 minutes.

[0053] S4, aging treatment: Apply polyurethane adhesive on the other side of the barrier film, and also control the coating amount to 2-4g / m 2 Then, the polyester film is laminated as a reinforcing layer on the barrier film coated with the adhesive, and placed in a curing device for curing at a temperature of 40°C for 24 hours. During the curing process, the relative humidity is controlled at 40%.

[0054] S5. Surface treatment: The outermost layer of the composite film is subjected to three-level surface treatment using corona equipment: the first level: output power is 3kW, frequency is 15kHz, the electrode gap is adjusted to 2mm, the processing speed is 10m / min, and the corona treatment time is 2s; the second level: output power is 4kW, frequency is 20kHz, the electrode gap is 1.5mm, the processing speed is adjusted to 8m / min, and the corona treatment time is 3s; the third level: output power is 5kW, frequency is 25kHz, the electrode gap is 1mm, the processing speed is 6m / min, and the corona treatment time is 4s.

[0055] Example 5

[0056] A high-barrier, fresh-keeping, low-temperature heat-sealing composite film: from the inner layer to the outer layer, there are a heat-sealing layer, a barrier layer, a reinforcement layer and a surface treatment layer, and the heat-sealing layer, the barrier layer and the reinforcement layer are bonded to each other by at least one adhesive layer; the heat-sealing layer is made of the following raw materials in parts by weight: 50 parts of modified polyethylene, 30 parts of polypropylene, and 10 parts of a heat-sealing aid; the heat-sealing aid is epoxy soybean oil, silicone oil and xylitol ester in a mass ratio of 45:18:8; the barrier layer is made of a composite material of nano-alumina, polyvinylidene fluoride and ethylene-vinyl alcohol copolymer in a mass ratio of 4:2:6; the reinforcement layer is a polyester (PET) film; the surface treatment layer is a corona-treated surface; the adhesive layer is a polyurethane adhesive, and the coating amount of the adhesive is 3g / m 2 ;

[0057] The modified polyethylene is prepared by placing polyethylene and ethylene-α-olefin copolymer into an oven for drying, respectively, and placing them into a mixing device at a mass ratio of 70:15, and adding 10% carbon tetrachloride by mass of the mixture for melt blending at a mixing temperature of 130° C. The melt blend is extruded and granulated, and after cooling, cobalt-60 irradiation cross-linking is performed for 22 minutes, the irradiation dose of cobalt-60 irradiation cross-linking is 100 kGy, and the dose rate is 3.5 Gy / s, to obtain the modified polyethylene;

[0058] The above-mentioned embodiment 5 adopts the following manufacturing process:

[0059] S1, heat sealing layer preparation: the modified polyethylene, polypropylene and heat sealing aid are mixed evenly according to a ratio, and the mixture is extruded into a film by an extruder to form a heat sealing layer;

[0060] S2, preparation of barrier layer: nano-alumina, polyvinylidene fluoride and ethylene-vinyl alcohol copolymer are premixed according to the ratio, the premixing stirring rate is 400rpm, the premixed materials are added into a high-speed mixer, 15% of ammonium polyacrylate by mass of the materials is added, the mixture is mixed at a speed of 2000rpm and a temperature of 80°C for 90min, extruded and granulated to obtain a barrier layer material, the extrusion temperature is controlled at 220°C, and the prepared barrier layer material is extruded and formed by an extruder to form a barrier layer film;

[0061] S3, Composite: Apply polyurethane adhesive on one side of the heat seal film, with a coating amount of 4g / m 2 Then, the barrier layer film is laminated on the heat-sealing layer film and dried at a wind speed of 15 m / s, a drying temperature of 100°C, and a drying time of 10 minutes;

[0062] S4, aging treatment: Apply polyurethane adhesive on the other side of the barrier film, and also control the coating amount to 4g / m 2 Then, the polyester film is laminated as a reinforcing layer on the barrier film coated with the adhesive, and placed in a curing device for curing at a temperature of 60°C for 48 hours. During the curing process, the relative humidity is controlled at 60%.

[0063] S5. Surface treatment: The outermost layer of the composite film is subjected to three-level surface treatment using corona equipment: the first level: output power is 3kW, frequency is 15kHz, the electrode gap is adjusted to 2mm, the processing speed is 10m / min, and the corona treatment time is 2s; the second level: output power is 4kW, frequency is 20kHz, the electrode gap is 1.5mm, the processing speed is adjusted to 8m / min, and the corona treatment time is 3s; the third level: output power is 5kW, frequency is 25kHz, the electrode gap is 1mm, the processing speed is 6m / min, and the corona treatment time is 4s.

[0064] Comparative Example 1

[0065] The difference between this comparative example and Example 3 is that the polyethylene in the raw material of the heat sealing layer is not modified.

[0066] Comparative Example 2

[0067] The difference between this comparative example and Example 3 is that the heat sealing layer does not contain a heat sealing aid.

[0068] Comparative Example 3

[0069] The difference between this comparative example and Example 3 is that the surface treatment of the composite film is to coat the surface of a film of polyvinyl alcohol with a coating thickness of 5 μm.

[0070] Effect verification

[0071] 1. Barrier performance verification

[0072] 1. Oxygen permeability test: Use an oxygen permeability tester to measure the amount of oxygen that passes through a unit area per unit time at 23±2℃ and humidity 50±5%. Low oxygen permeability indicates that the composite film can effectively prevent oxygen from entering the package and delay the oxidation and deterioration of food.

[0073] 2. Water vapor transmission rate test: The water vapor permeability test is performed by using a gas permeometer to measure the amount of water vapor that permeates through a unit area of ​​the composite film per unit time at a temperature of 38±0.6℃ and a relative humidity of 90±2%. Low water vapor transmission rate ensures that the food in the package remains dry, reducing the risk of moisture loss and microbial growth.

[0074] 3. Carbon dioxide permeability test: Same as oxygen permeability test, test temperature 23±2℃, humidity 50±5%, the amount of carbon dioxide gas permeating per unit area per unit time. This test measures the barrier capacity of composite film to carbon dioxide to ensure the quality and taste of the product.

[0075] 4. Test results

[0076] Table 1:

[0077]

[0078]

[0079] 2. Heat sealing performance test

[0080] 1. The composite films of Examples 1-5 and Comparative Examples 1-3 were heat-sealed using a heat sealer to ensure that the heat-sealing area reached the set temperature at 60°C, 80°C, 100°C, and 120°C, respectively, and the heat-sealing effect and heat-sealing strength data at each temperature point were recorded.

[0081] Table 2:

[0082]

[0083]

[0084] It can be clearly seen from the above table data that under low temperature conditions of 60°C and 80°C, the heat sealing strength of the embodiment group is much higher than that of the comparative example group. As the temperature rises to 100°C and 120°C, the heat sealing strength of the embodiment group continues to increase, but although the heat sealing strength of the comparative example group also increases, its growth rate is smaller than that of the embodiment group, and the final heat sealing strength is still lower than that of the embodiment group.

[0085] Table 3:

[0086]

[0087]

[0088] By comparing the heat-sealing appearance evaluation of the embodiments and comparative examples, it can be clearly seen that the heat-sealing appearance of the low-temperature heat-sealing composite film at different temperatures is better than that of the traditional heat-sealing material. Especially under low temperature conditions of 60°C and 80°C, the low-temperature heat-sealing composite film exhibits a smoother and more uniform heat-sealing appearance, without obvious wrinkles and melt overflow, neat edges, and good bonding effect. As the temperature increases, the heat-sealing appearance of traditional heat-sealing materials also improves, but at 120°C, the low-temperature heat-sealing composite film still maintains an excellent heat-sealing appearance, showing its advantages in low-temperature heat-sealing applications. These results highlight the application potential of low-temperature heat-sealing composite films in areas such as food packaging, especially in situations where rapid packaging and low-temperature storage are required.

[0089] 3. Freshness preservation performance test

[0090] The composite films of Examples 1-5 and Comparative Examples 1-3 were made into packaging bags of appropriate sizes using a heat sealer, and the bags were filled with cabbage for packaging. The bags were placed in a refrigerator at 6° C. for 2 weeks, and the decay rate and weight loss rate of the cabbage were tested after 5, 7, and 14 days, respectively.

[0091] Decay rate = (mass of the decayed part / initial total mass) × 100%;

[0092] Weight loss rate = [(initial total weight - weight after storage) / initial total weight] × 100%;

[0093] Table 4:

[0094]

[0095]

[0096] The composite films of Examples 1-5 performed well in terms of decay rate and weight loss rate, indicating that these film materials have excellent fresh-keeping and water-retaining properties and are suitable for low-temperature fresh-keeping packaging of vegetables such as cabbage.

[0097] From the results of the above test tables 1-4, it can be seen that, compared with Example 1, after the polyethylene is subjected to a specific modification treatment, namely, mixed with an ethylene-α-olefin copolymer, melt-blended with carbon tetrachloride, and cross-linked by cobalt-60 irradiation, its heat sealing performance is significantly improved, so that the composite film can still be tightly sealed at low temperatures; at the same time, the modification also enhances the barrier properties of the polyethylene, and improves the barrier capacity for gas and moisture; in addition, the physical and mechanical properties such as tensile strength and elongation at break are also significantly improved, ensuring the stability and integrity of the film when subjected to external forces; the modification process also optimizes the processing performance of the polyethylene, improves production efficiency and product quality, and enhances its weather resistance;

[0098] Compared with Example 2, epoxy soybean oil, silicone oil and xylitol ester are mixed in a specific mass ratio as heat-sealing aids, which can effectively reduce the heat-sealing temperature of the composite film, so that the composite film can achieve a good heat-sealing effect at a lower temperature; due to the reduction in heat-sealing temperature, the time required for the heat-sealing process is also shortened accordingly, thereby improving production efficiency; the epoxy soybean oil in the heat-sealing aid has good bonding properties, and can form a strong bond between the heat-sealing layer and the packaged object during the heat-sealing process. Silicone oil can play a role in lubrication and filling, making the heat-sealed area smoother and reducing poor sealing caused by uneven surfaces. Xylitol ester can increase the flexibility and elasticity of the heat-sealing layer, making it difficult to break when subjected to external forces, thereby maintaining good sealing strength.

[0099] Compared with Comparative Example 3, the surface polarity of the composite film is significantly improved by the three-stage corona treatment, and the composite film can form a stronger intermolecular force when in contact with other materials, thereby greatly improving the bonding performance. In the vacuum packaging or modified atmosphere packaging of food, good bonding performance can ensure the sealing of the packaging, prevent gas leakage, and extend the shelf life of the food. After the three-stage corona treatment, the surface structure of the composite film is tighter, which can better block the penetration of substances such as oxygen, water vapor, and odor, and further improve the barrier performance of the composite film. At the same time, the plasma generated during the corona treatment can trigger some chemical reactions on the surface of the composite film to form a cross-linked structure, thereby enhancing the mechanical strength of the composite film. This makes the composite film more durable during use, can withstand greater external forces, and reduces the risk of package damage.

[0100] 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, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A high barrier fresh-keeping low temperature heat-sealing composite film, characterized in that: The inner layer to the outer layer are a heat sealing layer, a barrier layer, a reinforcement layer and a surface treatment layer, and the heat sealing layer, the barrier layer and the reinforcement layer are bonded to each other by at least one adhesive layer; the heat sealing layer is made of the following raw materials in parts by weight: 40-60 parts of modified polyethylene, 22-35 parts of polypropylene, and 8-12 parts of a heat sealing aid; the heat sealing aid is epoxy soybean oil, silicone oil and xylitol ester in a mass ratio of (32-50):(12-25):(5-10); the barrier layer is made of a composite material of nano-alumina, polyvinylidene fluoride and ethylene-vinyl alcohol copolymer in a mass ratio of (2-5):(1-3):(4-8).

2. A high barrier fresh-keeping low temperature heat-sealing composite film as claimed in claim 1, characterized in that: The reinforcing layer is a polyester film with a thickness of 10-20 μm. The tensile strength of the polyester film layer is not less than 200 MPa and the elongation at break is 100-150%.

3. The high barrier fresh-keeping low temperature heat-sealing composite film according to claim 1, characterized in that: The surface treatment layer is a surface treated by corona treatment.

4. The high barrier fresh-keeping low temperature heat-sealing composite film according to claim 1, characterized in that: The adhesive layer is a polyurethane adhesive, and the coating amount of the adhesive is 2-4 g / m 2 .

5. The high barrier fresh-keeping low temperature heat-sealing composite film according to claim 1, characterized in that: The modified polyethylene is prepared by placing polyethylene and ethylene-alpha olefin copolymer into an oven for drying, respectively, and then placing them into a mixing device at a mass ratio of 50-80:15, and simultaneously adding 5-10% of carbon tetrachloride by mass of the mixture for melt blending, the mixing temperature being 120-135° C., extruding the melt blend into granules, cooling it, and then cross-linking it with cobalt-60 radiation for 15-30 minutes to obtain the modified polyethylene.

6. A high barrier fresh-keeping low temperature heat-sealing composite film as claimed in claim 5, characterized in that: The irradiation dose of the cobalt-60 irradiation cross-linking is 80-120 kGy, and the dose rate is 0.01-6.86 Gy / s.

7. The process for producing a high barrier fresh-keeping low temperature heat-sealing composite film according to claim 1, characterized in that: The following steps are involved: S1, heat sealing layer preparation: the modified polyethylene, polypropylene and heat sealing aid are mixed evenly according to a ratio, and the mixture is extruded into a film by an extruder to form a heat sealing layer; S2, preparation of barrier layer: nano alumina, polyvinylidene fluoride and ethylene-vinyl alcohol copolymer are premixed according to the ratio, the premixing stirring rate is 200-400rpm, the premixed materials are added into a high-speed mixer, 5-15% of ammonium polyacrylate by mass of the materials are added, the mixture is mixed at a speed of 1000-2000rpm and a temperature of 50-80°C for 40-90min, extruded and granulated to obtain a barrier layer material, the extrusion temperature is controlled at 180-220°C, and the prepared barrier layer material is extruded and formed by an extruder to form a barrier layer film; S3, Composite: Apply polyurethane adhesive on one side of the heat seal film, with a coating amount of 2-4g / m 2 Then, the barrier layer film is laminated on the heat-sealing layer film and dried. The wind speed of the drying process is 10-15m / s, the drying temperature is 80-100℃, and the drying time is 5-10 minutes. S4, aging treatment: Apply polyurethane adhesive on the other side of the barrier film, and also control the coating amount to 2-4g / m 2 Then, the polyester film is laminated as a reinforcing layer on the barrier film coated with the adhesive, and placed in a curing device for curing at a temperature of 40-60°C for 24-48 hours. During the curing process, the relative humidity is controlled at 40-60%. S5. Surface treatment: The outermost layer of the composite film is subjected to multi-level surface treatment using corona equipment.

8. The process for producing a high barrier fresh-keeping low temperature heat-sealing composite film according to claim 7, characterized in that: Surface treatment of S5: first stage: output power is 3kW, frequency is 15kHz, electrode gap is adjusted to 2mm, treatment speed is 10m / min, and corona treatment time is 2s; The second stage: the output power is 4kW, the frequency is 20kHz, the electrode gap is 1.5mm, the processing speed is adjusted to 8m / min, and the corona treatment time is 3s; the third stage: the output power is 5kW, the frequency is 25kHz, the electrode gap is 1mm, the processing speed is 6m / min, and the corona treatment time is 4s.

9. Application of a high barrier fresh-keeping low temperature heat-sealing composite film, characterized in that: Used for vacuum packaging or modified atmosphere packaging of food.

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