A high-barrier, fresh-keeping, low-temperature heat-sealing composite film and its production process and application

Abstract

The present invention provides a high-barrier, fresh-keeping, low-temperature heat-sealing composite film, and its production process and application. The composite film of the present invention is composed of a heat-sealing layer, a barrier layer, a reinforcement layer and a surface-treated layer from the inner layer to the outer layer, and the layers are bonded by an adhesive layer. The heat-sealing layer is made of modified polyethylene, polypropylene and a heat-sealing aid, and the barrier layer is made of a composite material of nano-alumina, polyvinylidene fluoride and ethylene-vinyl alcohol copolymer. The reinforcement layer is a polyester film, and the surface-treated layer is corona-treated. The composite film is prepared by a specific production process, including the steps of preparing the heat-sealing layer and the barrier layer, compounding, aging treatment and surface treatment. The composite film of the present invention has excellent barrier properties and low-temperature heat-sealing ability, is suitable for vacuum packaging or modified atmosphere packaging of food, and effectively extends the shelf life and quality assurance period of food.

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 food packaging sector, existing packaging materials have numerous deficiencies in terms of barrier properties and low-temperature heat-sealing performance. On the one hand, many common packaging materials offer poor barrier properties against gases like oxygen and water vapor, making food susceptible to oxidation and moisture loss during storage, thereby shortening its shelf life. On the other hand, traditional packaging materials are difficult to heat-seal at low temperatures and have low seal strength, making them prone to problems such as loose seals and leakage. This not only affects food packaging quality but can also cause food spoilage. Furthermore, some packaging materials have poor preservation properties, failing to effectively preserve food's freshness, taste, and nutritional content.

[0004] In addition, existing composite packaging materials need to be improved in terms of bonding strength between layers and overall mechanical properties. 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 existing technology 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 needs 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 its production process and application 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 comprises a heat-seal layer, a barrier layer, a reinforcement layer, and a surface-treated layer, the heat-seal layer, the barrier layer, and the reinforcement layer being bonded to each other by at least one adhesive layer; the heat-seal layer comprises the following raw materials in parts by weight: 40-60 parts modified polyethylene, 22-35 parts polypropylene, and 8-12 parts heat-seal aid; the heat-seal aid comprises epoxy soybean oil, silicone oil, and xylitol ester in a mass ratio of (32-50):(12-25):(5-10); the film achieves low-temperature rapid heat sealing while maintaining good sealing strength; 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), thereby improving the barrier properties against 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 with 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 drying polyethylene and ethylene-α-olefin copolymer in an oven, mixing them in a mass ratio of 50-80:15, and simultaneously adding 5-10% carbon tetrachloride (based on the mass of the mixture) for melt blending at a mixing temperature of 120-135°C. The melt blend is pelletized by extrusion, cooled, and then cross-linked using cobalt-60 irradiation for 15-30 minutes to obtain the modified polyethylene. This significantly improves the polyethylene's heat resistance, mechanical strength, and environmental stress cracking resistance.

[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. Preparation of heat seal layer: uniformly mix the modified polyethylene, polypropylene and heat seal additive according to a proportion, and extrude the mixture into a film through an extruder to form a heat seal layer;

[0016] S2. Preparation of barrier layer: Nano-alumina, polyvinylidene fluoride, and ethylene-vinyl alcohol copolymer are premixed according to a ratio at a premixing stirring rate of 200-400 rpm. The premixed materials are added to a high-speed mixer, and 5-15% of ammonium polyacrylate by weight of the materials is added. The mixture is mixed at a speed of 1000-2000 rpm and a temperature of 50-80° C. for 40-90 minutes. The mixture is extruded and granulated to obtain a barrier layer material. The extrusion temperature is controlled at 180-220° C. The prepared barrier layer material is extruded through 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 reinforcement layer on the barrier film coated with the adhesive, and placed in an aging device for aging treatment at a aging temperature of 40-60°C for 24-48 hours. During the aging process, the relative humidity is controlled at 40-60%.

[0019] S5. Surface treatment: The outermost layer of the composite film is subjected to multi-stage 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: By combining a specific ratio of heat sealing aids with modified polyethylene and polypropylene, the composite film can achieve good heat sealing effects at low temperatures. Furthermore, it can maintain a high heat sealing strength even at low temperatures.

[0024] (2) High barrier performance: The composite material of nano-alumina, polyvinylidene fluoride and ethylene-vinyl alcohol copolymer is used as the barrier layer, which effectively improves the barrier performance 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-stage 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) Broad 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, maintaining its effectiveness and safety. DETAILED DESCRIPTION

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

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

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

[0031] Example 1

[0032] A high-barrier, fresh-keeping, low-temperature heat-seal composite film: from the inner layer to the outer layer, there are a heat-seal layer, a barrier layer, a reinforcement layer and a surface-treated layer, and the heat-seal layer, barrier layer and 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 parts of modified polyethylene, 22 parts of polypropylene, and 8 parts of a heat-seal auxiliary agent; the heat-seal auxiliary agent 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-treated 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, placing them into a mixing device at a mass ratio of 50:15, adding 5% carbon tetrachloride by mass of the mixture for melt blending at a mixing temperature of 120° C., granulating the melted blend by extrusion, cooling, and cross-linking with cobalt-60 radiation for 15 minutes. The irradiation dose of the cobalt-60 cross-linking is 80 kGy and the dose rate is 0.01 Gy / s to obtain the modified polyethylene.

[0034] Example 2

[0035] A high-barrier, fresh-keeping, low-temperature heat-seal composite film: from the inner layer to the outer layer, there are a heat-seal layer, a barrier layer, a reinforcement layer and a surface-treated layer, and the heat-seal layer, barrier layer and 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: 60 parts of modified polyethylene, 35 parts of polypropylene, and 12 parts of a heat-seal auxiliary agent; the heat-seal auxiliary agent 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-treated layer is a corona-treated surface; 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-α-olefin copolymer into an oven for drying, placing them into a mixing device at a mass ratio of 80:15, adding 10% carbon tetrachloride by mass of the mixture for melt blending at a mixing temperature of 120-135° C., granulating the melted blend by extrusion, cooling, and cross-linking with cobalt-60 radiation for 30 minutes. The irradiation dose of the 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-seal composite film: from the inner layer to the outer layer, there are a heat-seal layer, a barrier layer, a reinforcement layer and a surface-treated layer, and the heat-seal layer, barrier layer and 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: 50 parts of modified polyethylene, 30 parts of polypropylene, and 10 parts of a heat-seal auxiliary agent; the heat-seal auxiliary agent 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-treated layer is a corona-treated surface; 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-alpha olefin copolymer into an oven for drying, placing them into a mixing device at a mass ratio of 70:15, adding 5-10% carbon tetrachloride by mass of the mixture for melt blending at a mixing temperature of 130° C., extruding the melt blend into pellets, cooling the melt blend, and cross-linking the melt blend with cobalt-60 irradiation for 22 minutes at an irradiation dose of 100 kGy and a dose rate of 3.5 Gy / s to obtain the modified polyethylene.

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

[0041] S1. Preparation of heat seal layer: uniformly mix the modified polyethylene, polypropylene and heat seal additive according to a proportion, and extrude the mixture into a film through an extruder to form a heat seal layer;

[0042] S2. Preparation of barrier layer: Nano-alumina, polyvinylidene fluoride, and ethylene-vinyl alcohol copolymer were premixed according to a ratio at a premixing stirring rate of 300 rpm. The premixed materials were added to a high-speed mixer, and 10% of ammonium polyacrylate by weight of the materials was added. The mixture was mixed at a speed of 1500 rpm and a temperature of 70°C for 65 minutes. The mixture was extruded and granulated to obtain a barrier layer material. The extrusion temperature was controlled at 200°C. The prepared barrier layer material was extruded through 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 at a wind speed of 13 m / s, a drying temperature of 90°C, and a drying time of 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 reinforcement layer on the barrier film coated with the adhesive, and placed in an aging device for aging treatment at a aging temperature of 50°C for 36 hours. During the aging process, the relative humidity is controlled at 50%.

[0045] S5. Surface treatment: The outermost layer of the composite film is subjected to three-stage surface treatment using corona equipment: the first stage: the output power is 3kW, the 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 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.

[0046] Example 4

[0047] A high-barrier, fresh-keeping, low-temperature heat-seal composite film: from the inner layer to the outer layer, it comprises a heat-seal layer, a barrier layer, a reinforcement layer and a surface-treated layer, and the heat-seal layer, barrier layer and 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: 50 parts of modified polyethylene, 30 parts of polypropylene, and 10 parts of a heat-seal auxiliary agent; the heat-seal auxiliary agent 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-treated 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 drying polyethylene and ethylene-α-olefin copolymer in an oven, placing them in 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. After cooling, the mixture is cross-linked with cobalt-60 irradiation for 22 minutes. The irradiation dose of the cobalt-60 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. Preparation of heat seal layer: uniformly mix the modified polyethylene, polypropylene and heat seal additive according to a proportion, and extrude the mixture into a film through an extruder to form a heat seal layer;

[0051] S2. Preparation of barrier layer: Nano-alumina, polyvinylidene fluoride, and ethylene-vinyl alcohol copolymer were premixed according to a ratio at a premixing stirring rate of 200 rpm. The premixed materials were added to a high-speed mixer, and 5% of ammonium polyacrylate by weight of the materials was added. The mixture was mixed at a speed of 1000 rpm and a temperature of 50° C. for 40 minutes, and extruded into granules to obtain a barrier layer material. The extrusion temperature was controlled at 180° C. The prepared barrier layer material was extruded through 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 at a wind speed of 10 m / s, a drying temperature of 80°C, and a drying time of 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 reinforcement layer on the barrier film coated with the adhesive, and placed in an aging device for aging treatment at a aging temperature of 40°C for 24 hours. During the aging process, the relative humidity is controlled at 40%.

[0054] S5. Surface treatment: The outermost layer of the composite film is subjected to three-stage surface treatment using corona equipment: the first stage: the output power is 3kW, the 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 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.

[0055] Example 5

[0056] A high-barrier, fresh-keeping, low-temperature heat-seal composite film: from the inner layer to the outer layer, it comprises a heat-seal layer, a barrier layer, a reinforcement layer and a surface-treated layer, and the heat-seal layer, barrier layer and 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: 50 parts of modified polyethylene, 30 parts of polypropylene, and 10 parts of a heat-seal auxiliary agent; the heat-seal auxiliary agent 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-treated 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-alpha olefin copolymer into an oven for drying, placing the mixture into a mixing device at a mass ratio of 70:15, adding 10% carbon tetrachloride by mass of the mixture for melt blending at a mixing temperature of 130° C., extruding the melt blend into pellets, cooling the melt blend, and cross-linking the melt blend with cobalt-60 irradiation for 22 minutes at an irradiation dose of 100 kGy and a dose rate of 3.5 Gy / s to obtain the modified polyethylene.

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

[0059] S1. Preparation of heat seal layer: uniformly mix the modified polyethylene, polypropylene and heat seal additive according to a proportion, and extrude the mixture into a film through an extruder to form a heat seal layer;

[0060] S2. Preparation of barrier layer: Nano-alumina, polyvinylidene fluoride, and ethylene-vinyl alcohol copolymer were premixed according to a ratio at a premixing stirring rate of 400 rpm. The premixed materials were added to a high-speed mixer, and 15% of ammonium polyacrylate by weight of the materials was added. The mixture was mixed at a speed of 2000 rpm and a temperature of 80° C. for 90 minutes. The mixture was extruded and granulated to obtain a barrier layer material. The extrusion temperature was controlled at 220° C. The prepared barrier layer material was extruded through 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 reinforcement layer on the barrier film coated with the adhesive, and placed in an aging device for aging treatment at a aging temperature of 60°C for 48 hours. During the aging process, the relative humidity is controlled at 60%.

[0063] S5. Surface treatment: The outermost layer of the composite film is subjected to three-stage surface treatment using corona equipment: the first stage: the output power is 3kW, the 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 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.

[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 the film with polyvinyl alcohol, and the coating thickness is 5 μm.

[0070] Effect verification

[0071] 1. Barrier performance verification

[0072] 1. Oxygen Transmission Rate Test: Using an oxygen transmission rate tester, measure the amount of oxygen that passes through a composite film per unit area per unit time at 23±2°C and 50±5% humidity. A low oxygen transmission rate indicates that the composite film effectively prevents oxygen from entering the package, delaying food oxidation and deterioration.

[0073] 2. Water Vapor Transmission Rate (WVTR): A gas permeometer measures the amount of water vapor that permeates a composite film per unit area per unit time at a temperature of 38 ± 0.6°C and a relative humidity of 90 ± 2%. A low WVTR ensures that the packaged food remains dry, reducing moisture loss and the risk of microbial growth.

[0074] 3. Carbon Dioxide Transmission Rate Test: Similar to the oxygen transmission rate test, the test temperature is 23±2°C and the humidity is 50±5%. The test measures the amount of carbon dioxide gas that permeates a unit area per unit time. This test measures the composite film's barrier ability to carbon dioxide, thereby ensuring product quality and taste.

[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. The heat sealing area was ensured to reach the set temperature at 60°C, 80°C, 100°C, and 120°C, respectively. The heat sealing effect and heat sealing strength data at each temperature point were recorded.

[0081] Table 2:

[0082]

[0083]

[0084] The data in the table above clearly show that at low temperatures of 60°C and 80°C, the heat seal strength of the Example group was much higher than that of the Comparative Example group. As the temperature increased to 100°C and 120°C, the heat seal strength of the Example group continued to increase. However, while the heat seal strength of the Comparative Example group also increased somewhat, the increase was smaller than that of the Example group, and the final heat seal strength was still lower than that of the Example group.

[0085] Table 3:

[0086]

[0087]

[0088] By comparing the heat-sealing appearance of the examples and comparative examples, it can be clearly seen that the heat-sealing appearance of the low-temperature heat-sealing composite film is superior to that of traditional heat-sealing materials at different temperatures. In particular, 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, with 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, demonstrating 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 rot rate and weight loss rate of the cabbage were tested after 5 days, 7 days, 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-retention properties and are suitable for low-temperature fresh-keeping packaging of vegetables such as cabbage.

[0097] As can be seen from the test results in Tables 1-4 above, when Example 3 is compared with Comparative Example 1, the specific modification treatment of polyethylene, namely, mixing with an ethylene-α-olefin copolymer, melt blending with carbon tetrachloride, and cross-linking by cobalt-60 irradiation, significantly improves its heat sealing performance, allowing the composite film to remain tightly sealed even at low temperatures. Furthermore, the modification also enhances the barrier properties of the polyethylene, improving its gas and moisture barrier capabilities. Furthermore, 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 properties of the polyethylene, improving production efficiency and product quality, and enhancing its weather resistance.

[0098] Comparing Example 3 with Comparative Example 2, epoxy soybean oil, silicone oil, and xylitol ester, mixed in a specific mass ratio as a heat-sealing aid, can effectively reduce the heat-sealing temperature of the composite film, allowing the composite film to achieve a good heat-sealing effect at a lower temperature. Due to the reduced heat-sealing temperature, the time required for the heat-sealing process is also correspondingly shortened, thereby improving production efficiency. The epoxy soybean oil in the heat-sealing aid has good bonding properties, which can form a strong bond between the heat-sealing layer and the packaged object during the heat-sealing process. Silicone oil can act as a lubricant and filler, making the heat seal more flat and smooth, reducing poor sealing caused by surface unevenness. Xylitol ester can increase the flexibility and elasticity of the heat-sealing layer, making it less likely to break when subjected to external forces, thereby maintaining good sealing strength.

[0099] Comparison of Example 3 and Comparative Example 3 shows that the surface polarity of the composite film is significantly improved by the three-stage corona treatment. When the composite film contacts other materials, it can form a stronger intermolecular force, 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, further improving 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, forming a cross-linked structure, thereby enhancing the mechanical strength of the composite film. This makes the composite film more durable during use, able to 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 principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A high-barrier, fresh-keeping, low-temperature heat-sealing composite film, characterized by: The heat-sealing layer, barrier layer, reinforcement layer, and surface treatment layer are sequentially arranged from the inner layer to the outer layer. The heat-sealing layer, barrier layer, and reinforcement layer are bonded to each other via 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). The modified polyethylene is prepared by placing polyethylene and ethylene-α-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 by mass of the mixture for melt blending at a mixing temperature of 120-135° C., granulating the melted blend by extrusion, cooling, and cross-linking for 15-30 minutes using cobalt-60 irradiation to obtain the modified polyethylene.

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

4. The high-barrier, fresh-keeping, low-temperature heat-seal 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 / m².

5. The high-barrier, fresh-keeping, low-temperature heat-seal composite film according to claim 1, 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.

6. The process for producing a high-barrier, fresh-keeping, low-temperature heat-seal composite film according to claim 1, wherein: The following steps are involved: S1. Preparation of heat seal layer: uniformly mix the modified polyethylene, polypropylene and heat seal additive according to a proportion, and extrude the mixture into a film through an extruder to form a heat seal layer; S2. Preparation of barrier layer: Nano-alumina, polyvinylidene fluoride, and ethylene-vinyl alcohol copolymer are premixed according to a ratio at a premixing stirring rate of 200-400 rpm. The premixed materials are added to a high-speed mixer, and 5-15% of ammonium polyacrylate by weight of the materials is added. The mixture is mixed at a speed of 1000-2000 rpm and a temperature of 50-80° C. for 40-90 minutes. The mixture is extruded and granulated to obtain a barrier layer material. The extrusion temperature is controlled at 180-220° C. The prepared barrier layer material is extruded through an extruder to form a barrier layer film. S3. Lamination: Apply polyurethane adhesive on one side of the heat-sealing film at a coating amount of 2-4g / m², then laminate the barrier film onto the heat-sealing film and dry it at a wind speed of 10-15m / s, a drying temperature of 80-100°C, and a drying time of 5-10 minutes. S4. Curing treatment: Apply polyurethane adhesive to the other side of the barrier film, also controlling the coating amount to 2-4g / m². Then, laminate the polyester film as a reinforcement layer on the barrier film coated with adhesive. Place the film in a curing equipment for curing treatment at a curing temperature of 40-60°C for 24-48 hours. During the curing process, control the relative humidity to 40-60%. S5. Surface treatment: The outermost layer of the composite film is subjected to multi-stage surface treatment using corona equipment.

7. The process for producing a high-barrier, fresh-keeping, low-temperature heat-seal composite film according to claim 6, characterized in that: Surface treatment of S5: first stage: output power 3kW, frequency 15kHz, electrode gap adjusted to 2mm, treatment speed 10m / min, corona treatment time 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.

8. Use of the high-barrier, fresh-keeping, low-temperature heat-seal composite film according to any one of claims 1 to 5, characterized in that: Used for vacuum packaging or modified atmosphere packaging of food.

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