A transparent high-barrier food packaging composite film and its preparation method

Abstract

The present invention belongs to the technical field of food packaging material preparation, and particularly relates to a transparent high-barrier food packaging composite film and a preparation method thereof. The transparent high-barrier food packaging composite film comprises a first film layer, a coating layer, an adhesive layer, a second film layer, a coating layer, an adhesive layer, and a third film layer which are arranged in sequence; the coating layer is a waterborne polyurethane-nano silicon hybrid coating layer. The transparent high-barrier food packaging composite film prepared by the present invention still has excellent barrier properties after being sterilized by high-temperature cooking at 121 °C for 30 minutes, greatly prolongs the shelf life of food, and ensures the safety and hygiene of food.

Description

Technical Field

[0001] The present invention belongs to the technical field of food packaging material preparation, and particularly relates to a transparent high-barrier food packaging composite film and a preparation method thereof. Background Art

[0002] In the food industry, to ensure the safety and hygiene of food, maintain the flavor of food, and extend the shelf life of food, two aspects are required: one is the sterilization of the food itself. Among them, meat products are very likely to contain Clostridium botulinum. The spores of Clostridium botulinum have strong resistance, and it is necessary to maintain high-temperature cooking at 121 °C for 30 minutes to kill the spores and ensure food safety. This also means that its packaging material needs to be adapted to high-temperature cooking sterilization at 121 °C for 30 minutes. The other is to block the intrusion of external oxygen and other gases and water vapor. In food flexible packaging, the use of high-barrier materials can prevent the reproduction of microorganisms and the oxidation of the contents caused by the penetration of oxygen and other gases, prevent the mildew of the contents caused by the penetration of water vapor, prevent the loss of fragrance and the adsorption of peculiar smell, etc., and extend the shelf life of food.

[0003] Currently, among food flexible packaging materials, the best barrier property is aluminum foil, but aluminum foil is opaque and has poor folding resistance. Commonly used transparent food flexible packaging barrier materials include: 1. ethylene-vinyl alcohol copolymer, 2. silicon oxide-coated film and aluminum oxide-coated film, 3. polyvinylidene chloride-coated film, 4. polyvinyl alcohol-coated film, 5. polyethylene terephthalate film, 6. polyamide film.

[0004] Among them, imported ethylene-vinyl alcohol copolymer films have excellent gas barrier properties, but the price is very expensive, and their barrier properties will deteriorate rapidly with the increase of humidity; polyvinylidene chloride-coated films and polyvinyl alcohol-coated films have very poor heat resistance, and the barrier properties of polyvinyl alcohol-coated films will also drop sharply under high humidity. Both are not suitable for high-temperature cooking; the composite film laminated and compounded by polyamide film, aluminum oxide-coated film based on polyethylene terephthalate film, and cast polypropylene film is already a composite film structure with relatively high barrier properties for high-temperature cooking grade at present. However, after high-temperature cooking sterilization at 121 °C for 30 minutes, its oxygen transmission rate is 6.2 cm 3 / (m 2 ·24h·0.1MPa), and the water vapor transmission rate is 6.9 g / (m 2 ·24h). After being placed at room temperature for 4 months, the change in the fragrance of the food can already be smelled. Such barrier properties are not ideal.

[0005] In the prior art, it has always been a difficult problem urgently needed to be solved in the industry to prepare a packaging film that still has excellent barrier properties after high-temperature cooking sterilization at 121 °C for 30 minutes, and at the same time has transparent visibility and meets the food packaging safety and hygiene standards. Summary of the Invention

[0006] In view of this, the present invention provides a transparent high-barrier food packaging composite film and a preparation method thereof. The transparent high-barrier food packaging composite film of the present invention still has excellent barrier properties after high-temperature cooking and sterilization at 121 °C for 30 minutes, greatly extending the shelf life of food and ensuring the safety and hygiene of food.

[0007] The technical solution of the present invention is as follows:

[0008] A transparent high-barrier food packaging composite film, characterized in that it comprises a first film layer, a coating layer, an adhesive layer, a second film layer, a coating layer, an adhesive layer, and a third film layer arranged in sequence; the coating layer is a waterborne polyurethane-nano-silica hybrid coating layer.

[0009] Further, the first film layer is a polyethylene terephthalate film layer.

[0010] Further, the adhesive layer is an ester-soluble polyurethane adhesive layer.

[0011] Further, the second film layer is a polyamide film layer.

[0012] Further, the third film layer is a polypropylene film layer.

[0013] Further, the polypropylene film layer is a cooking-grade cast polypropylene film layer.

[0014] The transparent high-barrier food packaging composite film provided by the present invention combines each layer organically. The polyethylene terephthalate film is located on the outermost side, the cooking-grade cast polypropylene film is located on the innermost side, and the hygroscopic polyamide film and the hydrophilic waterborne polyurethane-nano-silica hybrid coating layer are compounded inside. A two-component ester-soluble polyurethane adhesive is used to bond between the two film layers. The polyethylene terephthalate film, the cooking-grade cast polypropylene film, and the two-component ester-soluble polyurethane adhesive layer are all hydrophobic. This arrangement can effectively prevent the damage of high-temperature and high-pressure water vapor to the polyamide film and the waterborne polyurethane-nano-silica hybrid coating layer during high-temperature cooking and sterilization. By coating the waterborne polyurethane-nano-silica hybrid coating layer on the polyethylene terephthalate film and the polyamide film respectively and controlling a certain coating amount, not only the barrier effect is better than that of coating on only one of the films with the same coating amount, but also the drying and crosslinking and curing of the coating are easier and more complete. The waterborne polyurethane-nano-silica hybrid coating liquid and the two-component ester-soluble polyurethane adhesive used in the preparation method are both reaction systems. The curing method adopted in the embodiments of the present invention effectively forms a specific crosslinked polymer at the composite interface, which can resist the damage of high-temperature and high-pressure water vapor to the composite film during high-temperature cooking and sterilization and improve the barrier effect against oxygen and water vapor.

[0015] The present invention also provides a method for preparing a transparent high-barrier food packaging composite film, which is characterized by comprising the following steps:

[0016] S1. Add nano-silicon, waterborne polyurethane, and a water-dispersed isocyanate curing agent into deionized water to prepare a waterborne polyurethane-nano-silicon mixed coating layer liquid.

[0017] S2. Coat the above-mentioned waterborne polyurethane-nano-silicon mixed coating layer liquid on the corona surface of a polyethylene terephthalate film and one side of a biaxially oriented polyamide film.

[0018] S3. Cure and dry the above-mentioned coated polyethylene terephthalate film and polyamide film, and cool for later use.

[0019] S4. Use a two-component ester-soluble polyurethane adhesive to laminate and composite the above-mentioned coated and cured polyethylene terephthalate film and polyamide film, and a cast polypropylene film for cooking in sequence. The side of the polyethylene terephthalate film without a coating is located on the outermost side, and the heat-sealing surface of the cast polypropylene film for cooking is located on the innermost side.

[0020] S5. Cure and cool the above-mentioned composite film to obtain a packaging composite film product.

[0021] Further, in the step S1, the preparation method of the waterborne polyurethane-nano-silicon mixed coating layer liquid is as follows:

[0022] S11. Add 15-20 parts of nano-silicon into 59.6-64.6 parts of deionized water and stir for 10-20 minutes.

[0023] S12. Then add 17.5-22.5 parts of waterborne polyurethane and stir for 10-20 minutes.

[0024] S13. Then add 0.5-1.5 parts of the water-dispersed isocyanate curing agent and stir for 15-25 minutes.

[0025] S14. Perform ultrasonic dispersion for 8-15 minutes.

[0026] S15. Filter with a 200-500 mesh filter screen to obtain the waterborne polyurethane-nano-silicon mixed coating layer liquid.

[0027] Further, in step S2, coating is performed on a dry laminator, with the coating amount controlled at 1.0 - 2.0 grams per square meter. The three-stage temperatures of the drying oven of the dry laminator are set at 75°C, 85°C, and 100°C in sequence, and the machine speed is set at 70 - 100 revolutions per minute. The above-mentioned aqueous polyurethane-nano-silica hybrid coating liquid is coated on the corona-treated surface of the polyethylene terephthalate film and one side of the biaxially oriented polyamide film.

[0028] In the present invention, the prepared aqueous polyurethane-nano-silica hybrid coating liquid is a water dispersion system. Since the evaporation rate of water is lower than that of organic solvents, the drying and curing of the water dispersion system are slower. The presence of water will also affect the effect of the two-component ester-soluble polyurethane adhesive used in the subsequent steps. Therefore, the control of the coating amount, drying oven temperature, machine speed, and exhaust system during coating is very important.

[0029] Further, in step S3, the above-mentioned coated polyethylene terephthalate film and polyamide film are placed in a forced-air drying oven at 50 - 70°C for curing, taken out after 36 - 48 hours, and placed in an air-conditioned room at 20 - 25°C for cooling and standby.

[0030] In step S3 of the present invention, since the main solid component of the aqueous polyurethane is hydrophilic, if the dried coating does not undergo a certain degree of crosslinking, the water resistance will be poor and the barrier property will also be insufficient. The water-dispersed isocyanate curing agent added in the embodiments of the present invention is to play a role in crosslinking and curing. Therefore, an effective curing process must be carried out after coating.

[0031] In step S4 of the present invention, a two-component ester-soluble polyurethane adhesive is used for lamination. Since the above-mentioned coated and cured polyethylene terephthalate film and polyamide film may contain a small amount of water and the crosslinking and curing are incomplete, when preparing the coating liquid of the two-component ester-soluble polyurethane adhesive, the ratio of the curing agent component should be appropriately increased.

[0032] In one embodiment of the present invention, in step S4, the polyamide film and the cast polypropylene film for retort packaging are first laminated. The bonding surface is one side of the polyamide film and the corona-treated surface of the cast polypropylene film for retort packaging. Then, the polyethylene terephthalate film is laminated. The bonding surface is the other side of the polyamide film and the coated side of the polyethylene terephthalate film.

[0033] In another embodiment of the present invention, in step S4, the polyethylene terephthalate film and the polyamide film are first laminated. The bonding surface is the coated side of the polyethylene terephthalate film and one side of the polyamide film. Then, the cast polypropylene film for retort packaging is laminated. The bonding surface is the other side of the polyamide film and the corona-treated surface of the cast polypropylene film for retort packaging.

[0034] Further, in step S5, lamination is carried out on a dry laminator using a two-component ester-soluble polyurethane adhesive. The curing agent component is increased by 15-25% based on the specified ratio of this adhesive. The coating amount is controlled at 3.5-5.5 grams per square meter. The three-stage temperature settings of the drying oven of the dry laminator are 65°C, 85°C, and 98°C in sequence. The machine speed is set at 120-180 revolutions per minute. The above-mentioned poly(ethylene terephthalate) film and polyamide film that have been coated and cured, and the cooking-grade cast polypropylene film are laminated in sequence. The side without coating of the poly(ethylene terephthalate) film is located on the outermost side, and the heat-sealing side of the cooking-grade cast polypropylene film is located on the innermost side.

[0035] Further, in step S5, the above-mentioned composite film after lamination is placed in a forced-air drying oven at 60-75°C for curing. After 36-48 hours, the temperature is adjusted to 45-55°C for further curing. After another 36-48 hours of curing, it is taken out and placed in an air-conditioned room at 20-25°C for cooling.

[0036] In step S5 of the present invention, the crosslinking and curing effect of the high-temperature cooking two-component ester-soluble polyurethane adhesive directly affects the high-temperature cooking resistance and barrier property. Therefore, the curing process after lamination is very important.

[0037] Through the preparation method of the present invention, the prepared waterborne polyurethane-nano-silicon hybrid coating layer is the main barrier functional layer, which has excellent oxygen barrier property and the coating is transparent. The three film substrates used in the preparation method are all films with relatively high transparency and suitable for high-temperature cooking at 121°C. The poly(ethylene terephthalate) film and polyamide film itself have medium barrier properties, and the cooking-grade cast polypropylene film has good water vapor barrier property. And these three film substrates are all plastic resins allowed to come into contact with food in the national standard GB4806.6—2016 "National Food Safety Standard Plastic Resins for Food Contact". The two-component ester-soluble polyurethane adhesive selected in the preparation method is a high-temperature cooking type polyurethane adhesive, which has the characteristics of strong adhesion, high softening point, hydrolysis resistance, and good solvent release property. The solvent residue is far lower than the upper limit specified in the national food safety standard. The formed adhesive layer has high transparency, and the peel strength does not decrease after cooking. The hydrophobic effect of the ester-soluble polyurethane adhesive layer has a certain water vapor barrier property.

[0038] The beneficial effects of the present invention are as follows:

[0039] Compared with the prior art, in the preparation method of the transparent high-barrier food packaging composite film provided by the present invention, a waterborne polyurethane-nano-silicon hybrid coating layer with barrier function is coated on the polyethylene terephthalate film and the polyamide film, and then the coated polyethylene terephthalate film and polyamide film are organically combined with the cast polypropylene film to form a transparent food packaging composite film that can withstand high-temperature cooking and sterilization and has excellent oxygen barrier property and water vapor barrier property. From the test results, it can be seen that after high-temperature cooking and sterilization at 121 °C for 30 minutes, the oxygen barrier property and water vapor barrier property of the transparent food packaging composite film provided by the present invention are significantly better than those of the transparent food packaging composite film prepared by the prior art, and can reach the packaging film of aluminum foil and plastic composite. However, the aluminum foil is opaque and has poor folding resistance, while the food packaging composite film provided by the present invention is transparent, allowing consumers to directly see the contents, and has good folding resistance, and there is no restriction on the shape of the contents in use.

[0040] In terms of economy, in the preparation method of the transparent high-barrier food packaging composite film provided by the present invention, the materials, equipment, processes, transportation and storage costs used are relatively low. In the prior art, imported multilayer coextruded films with ethylene-vinyl alcohol copolymer as the barrier functional layer are compounded with polyethylene terephthalate films, polyamide films, cast polypropylene films, etc. to form transparent multilayer composite films. After high-temperature cooking and sterilization at 121 °C for 30 minutes, the oxygen transmission rate can reach 1.0 - 2.0 cm 3 / (m 2 ·24h·0.1MPa), but the imported multilayer coextruded films with ethylene-vinyl alcohol copolymer as the barrier functional layer are very expensive and have high requirements for the storage environment. In contrast, the transparent food packaging composite film provided by the present invention has no worse barrier property but much lower cost. Brief Description of the Drawings

[0041] Figure 1 It is a schematic structural diagram of the transparent high-barrier food packaging composite film of the present invention. Detailed Embodiments

[0042] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0043] Example 1

[0044] A transparent high-barrier food packaging composite film, characterized in that it comprises a first film layer 1, a coating layer 2, an adhesive layer 3, a second film layer 4, a coating layer 2, an adhesive layer 3, and a third film layer 5 arranged in sequence; the coating layer is a waterborne polyurethane-nano-silica hybrid coating layer.

[0045] Further, the first film layer is a polyethylene terephthalate film layer.

[0046] Further, the adhesive layer is an ester-soluble polyurethane adhesive layer.

[0047] Further, the second film layer is a polyamide film layer.

[0048] Further, the third film layer is a polypropylene film layer.

[0049] Further, the polypropylene film layer is a cast polypropylene film layer for cooking.

[0050] Example 2

[0051] This example provides a method for preparing the transparent high-barrier food packaging composite film of Example 1, comprising the following steps:

[0052] First step, add 7.5 kg of nano-silica to 32.3 kg of deionized water, stir for 15 minutes, then add 9.7 kg of waterborne polyurethane, stir for 15 minutes, then add 0.5 kg of water-dispersed isocyanate curing agent, stir for 20 minutes, then ultrasonically disperse for 10 minutes, and then filter with a 300-mesh filter screen to obtain the waterborne polyurethane-nano-silica hybrid coating layer liquid.

[0053] Second step, perform coating on a dry laminator, control the coating amount at 1.5 grams per square meter, set the three-stage temperature of the drying oven of the dry laminator to 75 °C, 85 °C, and 100 °C in sequence, set the machine speed to 80 revolutions per minute, and coat the above-mentioned waterborne polyurethane-nano-silica hybrid coating layer liquid on the corona surface of the polyethylene terephthalate film and one side of the double-corona polyamide film.

[0054] Third step, place the above-mentioned coated polyethylene terephthalate film and polyamide film in a blast drying oven at 55 °C for curing, take them out after 48 hours, and place them in an air-conditioned room at 23 °C for cooling and standby.

[0055] Step 4: Conduct lamination on a dry laminator using a two-component ester-soluble polyurethane adhesive. Increase the curing agent component by 20% based on the specified ratio of this adhesive. Control the coating amount at 4.5 grams per square meter. The three-stage temperature settings of the drying oven of the dry laminator are 65°C, 85°C, and 98°C in sequence. Set the machine speed at 150 revolutions per minute. First, laminate the polyamide film and the cooking-grade cast polypropylene film. The bonding surface is the coated side of the polyamide film and the corona-treated side of the cooking-grade cast polypropylene film. Then, laminate the polyethylene terephthalate film. The bonding surface is the other side of the polyamide film and the coated side of the polyethylene terephthalate film.

[0056] Step 5: Place the above-completed composite film in a forced-air drying oven at 65°C for curing. After 48 hours, change the temperature to 50°C for further curing. After another 48 hours of curing, take it out and place it in an air-conditioned room at 23°C for cooling for 24 hours.

[0057] Example 3

[0058] This example provides a method for preparing the composite film of the transparent high-barrier food packaging of Example 1, including the following steps:

[0059] Step 1: Add 10.0 kg of nano-silicon to 29.8 kg of deionized water, stir for 15 minutes, then add 9.7 kg of waterborne polyurethane, stir for 15 minutes, then add 0.5 kg of water-dispersed isocyanate curing agent, stir for 20 minutes, then perform ultrasonic dispersion for 10 minutes, and then filter through a 300-mesh filter screen to obtain the waterborne polyurethane-nano-silicon mixed coating liquid.

[0060] Step 2: Conduct coating on a dry laminator. Control the coating amount at 1.5 grams per square meter. The three-stage temperature settings of the drying oven of the dry laminator are 75°C, 85°C, and 100°C in sequence. Set the machine speed at 80 revolutions per minute. Coat the above waterborne polyurethane-nano-silicon mixed coating liquid on the corona-treated surface of the polyethylene terephthalate film and one side of the double-corona polyamide film.

[0061] Step 3: Place the above-coated polyethylene terephthalate film and polyamide film in a forced-air drying oven at 55°C for curing. After 48 hours, take it out and place it in an air-conditioned room at 23°C for cooling and standby.

[0062] Step 4: Conduct lamination on a dry laminator using a two-component ester-soluble polyurethane adhesive. Increase the curing agent component by 20% based on the specified ratio of this adhesive. Control the coating amount at 4.5 grams per square meter. Set the three-stage temperature of the drying oven of the dry laminator to 65°C, 85°C, and 98°C in sequence, and set the machine speed to 150 revolutions per minute. First, laminate the polyethylene terephthalate film and the polyamide film. The bonding surface is the side of the polyethylene terephthalate film with a coating and the side of the polyamide film without a coating. Then, laminate the retort cast polypropylene film. The bonding surface is the side of the polyamide film with a coating and the corona-treated surface of the retort cast polypropylene film.

[0063] Step 5: Place the above-completed composite film in a forced-air drying oven at 65°C for curing. After 48 hours, change the temperature to 50°C for further curing. After another 48 hours of curing, take it out and place it in an air-conditioned room at 23°C for cooling for 24 hours.

[0064] Example 4

[0065] This example provides a method for preparing the composite film for transparent high-barrier food packaging in Example 1, which is characterized by including the following steps:

[0066] S1. Add nano-silicon, waterborne polyurethane, and a water-dispersed isocyanate curing agent to deionized water to prepare a waterborne polyurethane-nano-silicon mixed coating layer solution.

[0067] S2. Coat the above-prepared waterborne polyurethane-nano-silicon mixed coating layer solution on the corona-treated surface of the polyethylene terephthalate film and one side of the double-corona-treated polyamide film.

[0068] S3. Cure and dry the above-coated polyethylene terephthalate film and polyamide film, and cool for later use.

[0069] S4. Use a two-component ester-soluble polyurethane adhesive to sequentially laminate the above-coated and cured polyethylene terephthalate film and polyamide film, and the retort cast polypropylene film. The side of the polyethylene terephthalate film without a coating is located on the outermost side, and the heat-sealing surface of the retort cast polypropylene film is located on the innermost side.

[0070] S5. Cure and cool the above-completed composite film to obtain the packaging composite film product.

[0071] Further, in the step S1, the preparation method of the waterborne polyurethane-nano-silicon mixed coating layer solution is as follows:

[0072] S11. Add 15 parts of nano-silicon to 59.6 parts of deionized water and stir for 10 minutes.

[0073] S12. Add another 17.5 parts of waterborne polyurethane and stir for 10 minutes;

[0074] S13. Add another 0.5 part of water-dispersed isocyanate curing agent and stir for 15 minutes;

[0075] S14. Perform ultrasonic dispersion for 8 minutes;

[0076] S15. Filter through a 200-mesh filter screen to obtain a waterborne polyurethane-nano-silicon hybrid coating layer solution.

[0077] Further, in step S2, coating is carried out on a dry laminator, the coating amount is controlled at 1.0 gram per square meter, the three-stage temperature settings of the drying oven of the dry laminator are 75 °C, 85 °C, and 100 °C in sequence, the machine speed is set at 70 revolutions per minute, and the above-mentioned waterborne polyurethane-nano-silicon hybrid coating layer solution is coated on the corona-treated surface of the polyethylene terephthalate film and one side of the double-corona polyamide film.

[0078] Further, in step S3, the coated polyethylene terephthalate film and polyamide film are placed in a forced-air drying oven at 50 °C for curing, taken out after 48 hours, and placed in an air-conditioned room at 20 °C for cooling and standby.

[0079] In step S4, first laminate the polyamide film and the cast polypropylene film for cooking, the bonding surface is one side of the polyamide film and the corona-treated surface of the cast polypropylene film for cooking, and then laminate the polyethylene terephthalate film, the bonding surface is the other side of the polyamide film and the coated side of the polyethylene terephthalate film.

[0080] Further, in step S5, laminating and compounding are carried out on a dry laminator, using a two-component ester-soluble polyurethane adhesive, the curing agent component is increased by 15% on the basis of the specified ratio of this adhesive, the coating amount is controlled at 3.5 grams per square meter, the three-stage temperature settings of the drying oven of the dry laminator are 65 °C, 85 °C, and 98 °C in sequence, the machine speed is set at 120 revolutions per minute, and the above-mentioned coated and cured polyethylene terephthalate film and polyamide film, and the cast polypropylene film for cooking are sequentially subjected to laminating and compounding, the side without coating of the polyethylene terephthalate film is located on the outermost side, and the heat-sealing surface of the cast polypropylene film for cooking is located on the innermost side.

[0081] Further, in step S5, the compounded composite film is placed in a forced-air drying oven at 60 °C for curing, after 48 hours, the temperature is adjusted to 45 °C for curing, and after curing for another 48 hours, it is taken out and placed in an air-conditioned room at 20 °C for cooling.

[0082] Example 5

[0083] This embodiment provides a method for preparing the composite film of the transparent high-barrier food packaging in Embodiment 1, which is characterized by including the following steps:

[0084] S1. Add nano-silicon, waterborne polyurethane, and water-dispersed isocyanate curing agent into deionized water to prepare a waterborne polyurethane-nano-silicon mixed coating layer solution.

[0085] S2. Coating the above-mentioned waterborne polyurethane-nano-silicon mixed coating layer solution on the corona-treated surface of the polyethylene terephthalate film and one side of the biaxially oriented polyamide film;

[0086] S3. Cure and dry the above-mentioned coated polyethylene terephthalate film and polyamide film, and cool for later use;

[0087] S4. Use a two-component ester-soluble polyurethane adhesive to laminate and compound the above-mentioned coated and cured polyethylene terephthalate film and polyamide film, and the cast polypropylene film for retort pouch in sequence. The side of the polyethylene terephthalate film without coating is located on the outermost side, and the heat-sealing surface of the cast polypropylene film for retort pouch is located on the innermost side;

[0088] S5. Cure and cool the above-mentioned compounded composite film to obtain the packaging composite film product.

[0089] Further, in the step S1, the preparation method of the waterborne polyurethane-nano-silicon mixed coating layer solution is as follows:

[0090] S11. Add 18 parts of nano-silicon into 61.6 parts of deionized water and stir for 12 minutes;

[0091] S12. Then add 19.5 parts of waterborne polyurethane and stir for 13 minutes;

[0092] S13. Then add 0.7 part of water-dispersed isocyanate curing agent and stir for 18 minutes;

[0093] S14. Perform ultrasonic dispersion for 11 minutes;

[0094] S15. Filter with a 300-mesh filter screen to obtain the waterborne polyurethane-nano-silicon mixed coating layer solution.

[0095] Further, in the step S2, the coating is carried out on a dry laminator, and the coating amount is controlled at 1.2 grams per square meter. The three-stage temperature settings of the drying channel of the dry laminator are 75°C, 85°C, and 100°C in sequence, and the machine speed is set at 85 revolutions per minute. Coat the above-mentioned waterborne polyurethane-nano-silicon mixed coating layer solution on the corona-treated surface of the polyethylene terephthalate film and one side of the biaxially oriented polyamide film.

[0096] Further, in step S3, the above-mentioned coated polyethylene terephthalate film and polyamide film are placed in a forced-air drying oven at 60 °C for curing, taken out after 42 hours, and placed in an air-conditioned room at 22 °C for cooling for standby.

[0097] In step S4, first, the polyethylene terephthalate film and the polyamide film are laminated. The bonding surface is one side of the polyethylene terephthalate film with a coating and one side of the polyamide film. Then, the cast polypropylene film for retort pouch is laminated. The bonding surface is the other side of the polyamide film and the corona-treated surface of the cast polypropylene film for retort pouch.

[0098] Further, in step S5, lamination is carried out on a dry laminator using a two-component ester-soluble polyurethane adhesive. The curing agent component is increased by 17% based on the specified ratio of this adhesive. The coating amount is controlled at 4.0 g per square meter. The three-stage temperature settings of the drying channel of the dry laminator are 65 °C, 85 °C, and 98 °C in sequence. The machine speed is set at 140 revolutions per minute. The above-mentioned coated and cured polyethylene terephthalate film and polyamide film, and the cast polypropylene film for retort pouch are laminated in sequence. The side of the polyethylene terephthalate film without a coating is located on the outermost side, and the heat-sealed surface of the cast polypropylene film for retort pouch is located on the innermost side.

[0099] Further, in step S5, the above-mentioned laminated composite film is placed in a forced-air drying oven at 65 °C for curing. After 42 hours, the temperature is adjusted to 48 °C for further curing. After another 42 hours of curing, it is taken out and placed in an air-conditioned room at 22 °C for cooling.

[0100] Example 6

[0101] This example provides a method for preparing a transparent high-barrier food packaging composite film of Example 1, which is characterized by including the following steps:

[0102] S1. Add nano-silicon, waterborne polyurethane, and a water-dispersed isocyanate curing agent to deionized water to prepare a waterborne polyurethane-nano-silicon mixed coating liquid.

[0103] S2. Coat the above-mentioned waterborne polyurethane-nano-silicon mixed coating liquid on the corona-treated surface of the polyethylene terephthalate film and one side of the double-corona polyamide film.

[0104] S3. Cure and dry the above-mentioned coated polyethylene terephthalate film and polyamide film, and cool for standby.

[0105] S4. Use a two-component ester-soluble polyurethane adhesive to sequentially laminate and compound the above-mentioned polyethylene terephthalate film and polyamide film that have been coated and cured, and the cast polypropylene film for cooking, with the uncoated side of the polyethylene terephthalate film on the outermost side and the heat-sealing side of the cast polypropylene film for cooking on the innermost side;

[0106] S5. Cure and cool the above-mentioned compounded film to obtain a packaged composite film product.

[0107] Further, in the step S1, the preparation method of the aqueous polyurethane-nano-silicon mixed coating layer liquid is as follows:

[0108] S11. Add 20 parts of nano-silicon to 64.6 parts of deionized water and stir for 20 minutes;

[0109] S12. Then add 22.5 parts of aqueous polyurethane and stir for 20 minutes;

[0110] S13. Then add 1.5 parts of a water-dispersed isocyanate curing agent and stir for 25 minutes;

[0111] S14. Perform ultrasonic dispersion for 15 minutes;

[0112] S15. Filter with a 500-mesh filter screen to obtain the aqueous polyurethane-nano-silicon mixed coating layer liquid.

[0113] Further, in the step S2, coating is carried out on a dry laminator, and the coating amount is controlled at 2.0 grams per square meter. The three-stage temperature settings of the drying oven of the dry laminator are 75°C, 85°C, and 100°C in sequence, and the machine speed is set at 100 revolutions per minute. Coat the above-mentioned aqueous polyurethane-nano-silicon mixed coating layer liquid on the corona-treated surface of the polyethylene terephthalate film and one side of the double-corona-treated polyamide film.

[0114] Further, in the step S3, place the above-mentioned coated polyethylene terephthalate film and polyamide film in a forced-air drying oven at 70°C for curing, take them out after 36 hours, and place them in an air-conditioned room at 25°C for cooling and standby.

[0115] In step S4, first compound the polyethylene terephthalate film and the polyamide film, with the bonding surface being the coated side of the polyethylene terephthalate film and one side of the polyamide film, and then compound the cast polypropylene film for cooking, with the bonding surface being the other side of the polyamide film and the corona-treated surface of the cast polypropylene film for cooking.

[0116] Further, in step S5, laminating and compounding are carried out on a dry laminator, using a two-component ester-soluble polyurethane adhesive, and the curing agent component is increased by 25% on the basis of the specified ratio of this adhesive. The coating amount is controlled at 5.5 grams per square meter. The three-stage temperature settings of the drying channel of the dry laminator are 65 °C, 85 °C, and 98 °C in sequence, and the machine speed is set at 180 revolutions per minute. The above-mentioned poly(ethylene terephthalate) film and polyamide film that have been coated and cured, and the cast polypropylene film for cooking, are laminated and compounded in sequence. The side without coating of the poly(ethylene terephthalate) film is located on the outermost side, and the heat-sealing surface of the cast polypropylene film for cooking is located on the innermost side.

[0117] Further, in step S5, the above-mentioned compounded composite film is placed in a forced-air drying oven at 75 °C for curing. After 36 hours, the temperature is adjusted to 55 °C for further curing. After another 36 hours of curing, it is taken out and placed in an air-conditioned room at 25 °C for cooling.

[0118] Example 7

[0119] This example provides a method for preparing a transparent high-barrier food packaging composite film of Example 1, which is characterized by including the following steps:

[0120] S1. Add nano-silicon, waterborne polyurethane, and a water-dispersed isocyanate curing agent to deionized water to prepare a waterborne polyurethane-nano-silicon mixed coating layer liquid.

[0121] S2. Coat the above-mentioned waterborne polyurethane-nano-silicon mixed coating layer liquid on the corona-treated surface of the poly(ethylene terephthalate) film and one side of the double-corona-treated polyamide film.

[0122] S3. Cure and dry the above-mentioned coated poly(ethylene terephthalate) film and polyamide film, and cool for later use.

[0123] S4. Use a two-component ester-soluble polyurethane adhesive to laminate and compound the above-mentioned coated and cured poly(ethylene terephthalate) film and polyamide film, and the cast polypropylene film for cooking in sequence. The side without coating of the poly(ethylene terephthalate) film is located on the outermost side, and the heat-sealing surface of the cast polypropylene film for cooking is located on the innermost side.

[0124] S5. Cure and cool the above-mentioned compounded composite film to obtain a packaging composite film product.

[0125] Further, in step S1, the preparation method of the waterborne polyurethane-nano-silicon mixed coating layer liquid is as follows:

[0126] S11. Add 19.2 parts of nano-silicon to 62.8 parts of deionized water and stir for 18 minutes.

[0127] S12. Add 21.6 parts of waterborne polyurethane and stir for 18 minutes;

[0128] S13. Add 1.3 parts of water-dispersed isocyanate curing agent and stir for 22 minutes;

[0129] S14. Carry out ultrasonic dispersion for 13 minutes;

[0130] S15. Filter with a 400-mesh filter screen to obtain a waterborne polyurethane-nano-silicon mixed coating layer liquid.

[0131] Further, in step S2, coating is carried out on a dry laminator, the coating amount is controlled at 1.8 grams per square meter, the three-stage temperature settings of the drying channel of the dry laminator are 75 °C, 85 °C, and 100 °C in sequence, the machine speed is set at 95 revolutions per minute, and the above-mentioned waterborne polyurethane-nano-silicon mixed coating layer liquid is coated on the corona surface of the polyethylene terephthalate film and one side of the double-corona polyamide film.

[0132] Further, in step S3, the above-mentioned coated polyethylene terephthalate film and polyamide film are placed in a forced-air drying oven at 68 °C for curing, taken out after 45 hours, and placed in an air-conditioned room at 23 °C for cooling and standby.

[0133] In step S4, first laminate the polyamide film and the cast polypropylene film for cooking, the bonding surface is one side of the polyamide film and the corona surface of the cast polypropylene film for cooking, and then laminate the polyethylene terephthalate film, the bonding surface is the other side of the polyamide film and the coated side of the polyethylene terephthalate film.

[0134] Further, in step S5, laminating and compounding are carried out on a dry laminator, using a two-component ester-soluble polyurethane adhesive, the curing agent component is increased by 22% on the basis of the specified ratio of this adhesive, the coating amount is controlled at 5.0 grams per square meter, the three-stage temperature settings of the drying channel of the dry laminator are 65 °C, 85 °C, and 98 °C in sequence, the machine speed is set at 170 revolutions per minute, and the above-mentioned coated and cured polyethylene terephthalate film and polyamide film, and the cast polypropylene film for cooking are sequentially subjected to laminating and compounding, the non-coated side of the polyethylene terephthalate film is located on the outermost side, and the heat-sealing surface of the cast polypropylene film for cooking is located on the innermost side.

[0135] Further, in step S5, the above-mentioned compounded composite film is placed in a forced-air drying oven at 70 °C for curing, after 45 hours, the temperature is adjusted to 52 °C for curing, and after curing for another 45 hours, it is taken out and placed in an air-conditioned room at 23 °C for cooling.

[0136] Comparative Example 1

[0137] This comparative example provides a method for preparing a food packaging composite film, which includes the following steps:

[0138] First step, provide an aluminum oxide-coated film of polyethylene terephthalate film substrate, a polyamide film, and a cooking-grade cast polypropylene film.

[0139] Second step, perform lamination and compounding on a dry laminator, use a two-component ester-soluble polyurethane adhesive, increase the curing agent component by 20% based on the specified ratio of this adhesive, control the coating amount at 4.5 grams per square meter, set the three-stage temperature of the drying oven of the dry laminator to 65°C, 85°C, and 98°C in sequence, set the machine speed to 150 revolutions per minute. First, compound the polyamide film and the cooking-grade cast polypropylene film, with the bonding surface being one side of the polyamide film and the corona-treated surface of the cooking-grade cast polypropylene film. Then, compound the aluminum oxide-coated film of the polyethylene terephthalate film substrate, with the bonding surface being the other side of the polyamide film and the aluminum oxide-coated side of the polyethylene terephthalate film.

[0140] Third step, place the above-completed composite film in a forced-air drying oven at 65°C for curing, change to curing at 50°C after 48 hours, take it out after curing for another 48 hours, and place it in an air-conditioned room at 23°C for cooling for 24 hours.

[0141] Comparative Example 2

[0142] This comparative example provides a method for preparing a food packaging composite film, which includes the following steps:

[0143] First step, provide a polyethylene terephthalate film, an aluminum foil of 9 µm, and a cooking-grade cast polypropylene film.

[0144] Second step, perform lamination and compounding on a dry laminator, use a two-component ester-soluble polyurethane adhesive, increase the curing agent component by 20% based on the specified ratio of this adhesive, control the coating amount at 4.5 grams per square meter, set the three-stage temperature of the drying oven of the dry laminator to 65°C, 85°C, and 98°C in sequence, set the machine speed to 150 revolutions per minute. First, compound the polyethylene terephthalate film and the aluminum foil, with the bonding surface being the corona-treated surface of the polyethylene terephthalate film and one side of the aluminum foil. Then, compound the cooking-grade cast polypropylene film, with the bonding surface being the other side of the aluminum foil and the corona-treated surface of the cooking-grade cast polypropylene film.

[0145] Third step, place the above-completed composite film in a forced-air drying oven at 65°C for curing, change to curing at 50°C after 48 hours, take it out after curing for another 48 hours, and place it in an air-conditioned room at 23°C for cooling for 24 hours.

[0146] Experimental effect test

[0147] For the packaging composite films prepared in Examples 2-3 and Comparative Examples 1-2, after high-temperature cooking and sterilization at 121 °C for 30 minutes, the water vapor transmission rate was tested in accordance with the national standard GB / T 1037—1988 "Test Method for Water Vapor Transmission of Plastic Films and Sheets - Cup Method", and the oxygen transmission rate was tested in accordance with the national standard GB / T 1038—2000 "Test Method for Gas Permeability of Plastic Films and Sheets - Differential Pressure Method". The test results are shown in Table 1 below.

[0148] Table 1

[0149] Test item Unit Example 2 Example 3 Comparative Example 1 Comparative Example 2 Water vapor transmission rate <![CDATA[g / (m 2 ·24h)]]> 4.5 4.4 6.9 0.6 Oxygen transmission rate <![CDATA[cm 3 / (m 2 ·24h·0.1MPa)]]> 0.8 0.6 6.2 0.5

[0150] As can be seen from Table 1, the food packaging composite film provided by the present invention still has excellent oxygen barrier properties and water vapor barrier properties after high-temperature cooking and sterilization at 121 °C for 30 minutes.

[0151] The food packaging composite film provided by Comparative Example 1 is a commonly used high-barrier food packaging composite film for high-temperature cooking. However, after high-temperature cooking and sterilization at 121 °C for 30 minutes, its oxygen barrier property and water vapor barrier property are significantly inferior to those of the food packaging composite film provided by the examples of the present invention.

[0152] The aluminum foil used in the preparation method of Comparative Example 2 is the soft packaging material with the best barrier property at present. Through the comparison of the test results, it can be seen that the oxygen transmission rate of the food packaging composite film provided by the examples of the present invention is comparable to that of the aluminum foil. However, the aluminum foil is opaque and has poor folding resistance. If it is filled with food and then subjected to high-temperature cooking and sterilization, pinholes are likely to occur, and its barrier property will drop sharply. Therefore, for the food packaging film laminated with aluminum foil, there are certain restrictions on the shape of the contents in use. In contrast, the food packaging composite film provided by the present invention is highly transparent and does not have the problem of poor folding resistance, and there are no restrictions on the shape of the contents in use.

[0153] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, in any aspect, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention. Any reference signs in the claims should not be regarded as limiting the claimed rights.

[0154] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art. It should be noted that the technical features not detailedly described in the present invention can all be implemented by any existing technology.

Claims

1. A preparation method of a transparent high-barrier food packaging composite film, characterized in that, The transparent high-barrier food packaging composite film includes a first film layer, a coating layer, an adhesive layer, a second film layer, a coating layer, an adhesive layer, and a third film layer arranged in sequence; the coating layer is an aqueous polyurethane-nano-silicon hybrid coating layer containing a water-dispersible isocyanate curing agent; the first film layer is a polyethylene terephthalate film layer; the adhesive layer is an ester-soluble polyurethane adhesive layer; the second film layer is a polyamide film layer; the third film layer is a polypropylene film layer. The preparation method includes the following steps: S1. Add nano-silicon, aqueous polyurethane, and water-dispersible isocyanate curing agent to deionized water to prepare an aqueous polyurethane-nano-silicon hybrid coating layer liquid; S2. Coat the above-mentioned aqueous polyurethane-nano-silicon hybrid coating layer liquid on the corona-treated surface of the polyethylene terephthalate film and one side of the biaxially oriented polyamide film; S3. Cure and dry the above-mentioned coated polyethylene terephthalate film and polyamide film, and cool for later use; S4. Use a two-component ester-soluble polyurethane adhesive to laminate the above-mentioned coated and cured polyethylene terephthalate film and polyamide film, and a cooking-grade cast polypropylene film in sequence. The side of the polyethylene terephthalate film without coating is located on the outermost side, and the heat-sealed side of the cooking-grade cast polypropylene film is located on the innermost side; S5. Cure and cool the composite film after lamination to obtain a packaging composite film product; in step S1, the preparation method of the aqueous polyurethane-nano-silicon hybrid coating layer liquid is as follows: S11. Add 15-20 parts of nano-silicon to 59.6-64.6 parts of deionized water and stir for 10-20 minutes; S12. Then add 17.5-22.5 parts of aqueous polyurethane and stir for 10-20 minutes; S13. Then add 0.5-1.5 parts of water-dispersible isocyanate curing agent and stir for 15-25 minutes; S14. Ultrasonic disperse for 8-15 minutes; S15. Filter with a 200-500 mesh filter screen to obtain an aqueous polyurethane-nano-silicon hybrid coating layer liquid; In step S2, coating is carried out on a dry laminator, and the coating amount is controlled at 1.0-2.0 grams per square meter. The three-stage temperature settings of the drying oven of the dry laminator are 75°C, 85°C, and 100°C in sequence, and the machine speed is set at 70-100 revolutions per minute. Coat the above-mentioned aqueous polyurethane-nano-silicon hybrid coating layer liquid on the corona-treated surface of the polyethylene terephthalate film and one side of the biaxially oriented polyamide film; In step S3, place the above-mentioned coated polyethylene terephthalate film and polyamide film in a forced-air drying oven at 50-70°C for curing, take them out after 36-48 hours, and place them in an air-conditioned room at 20-25°C for cooling and later use.

2. The preparation method of the transparent high-barrier food packaging composite film according to claim 1, characterized in that, In step S4, first laminate the polyamide film and the cooking-grade cast polypropylene film, and the bonding surface is one side of the polyamide film and the corona-treated surface of the cooking-grade cast polypropylene film. Then laminate the polyethylene terephthalate film, and the bonding surface is the other side of the polyamide film and the coated side of the polyethylene terephthalate film.

3. The preparation method of the transparent high-barrier food packaging composite film according to claim 1, characterized in that, In step S4, first, the polyethylene terephthalate film and the polyamide film are laminated. The bonding surfaces are the coated side of the polyethylene terephthalate film and one side of the polyamide film. Then, the retort cast polypropylene film is laminated. The bonding surface is the other side of the polyamide film and the corona-treated surface of the retort cast polypropylene film.

4. The preparation method of the transparent high-barrier food packaging composite film according to claim 1, characterized in that In the said step S5, lamination is carried out on a dry laminator. A two-component ester-soluble polyurethane adhesive is used, and the curing agent component is increased by 15 - 25% based on the specified ratio of this adhesive. The coating amount is controlled at 3.5 - 5.5 grams per square meter. The three-stage temperature settings of the drying channel of the dry laminator are 65°C, 85°C, and 98°C in sequence, and the machine speed is set at 120 - 180 revolutions per minute. The above-mentioned polyethylene terephthalate film and polyamide film that have been coated and cured, and the retort cast polypropylene film are laminated in sequence. The non-coated side of the polyethylene terephthalate film is located on the outermost side, and the heat-sealed side of the retort cast polypropylene film is located on the innermost side.

5. The preparation method of the transparent high-barrier food packaging composite film according to claim 4, characterized in that, In the said step S5, the above-mentioned laminated composite film is placed in a forced-air drying oven at 60 - 75°C for curing. After 36 - 48 hours, the temperature is adjusted to 45 - 55°C for further curing. After another 36 - 48 hours of curing, it is taken out and placed in an air-conditioned room at 20 - 25°C for cooling.

6. The preparation method of the transparent high-barrier food packaging composite film according to claim 5, characterized in that, The polypropylene film layer is a retort cast polypropylene film layer.

Images