Puncture-resistant marine product freezing thermal forming film and preparation method thereof

Abstract

The invention discloses a puncture-resistant marine product freezing thermal forming film and a preparation method thereof, and relates to the technical field of packaging films. According to the invention, homopolymerized nylon and copolymerized nylon are blended, at the same time, a polar-treated rigid filler taking nano boron nitride as a main material is added, a supercritical assisted extrusion process is utilized, puncture resistance and low-temperature resistance of the membrane material are improved, then through a multi-layer nylon distribution structure, toughness of the material is increased, and multi-layer low-density polyethylene is used in the middle, so that the performance of the membrane material is improved. And the bonding layer is a maleic anhydride grafted copolymer of an EVA (Ethylene Vinyl Acetate) matrix, and relatively strong Van der Waals' force and hydrogen-bond interaction can be generated between polar groups of the nylon layer and the bonding layer according to the principle of'similar intermiscibility ', so that good infiltration and bonding are realized, the deformation caused by a large stretch ratio is met, and the tensile strength of the film material is improved. The puncture resistance and the low-temperature resistance of the membrane material are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of packaging film, in particular to a puncture-resistant frozen marine product thermoforming film and a preparation method thereof. BACKGROUND

[0002] The seafood market is developing towards quality, convenience, digitization and sustainability. Foam boxes, aluminum foil lunch boxes, transparent bags, vacuum packaging and oxygen-filled fresh-keeping packaging are all common and important packaging methods at present, each of which has its own advantages and disadvantages and is suitable for different products and scenarios. The salmon seafood industry is developed in Norway, Chile, Canada and other regions, and a large number of products need to be exported. Fine segmentation is not conducive to export sales. After export in large pieces, segmentation and packaging are carried out in the local market. When large pieces of salmon seafood are packaged by thermoforming vacuum packaging, the requirements for the thermoforming film are higher, and special application requirements need to be considered when packaging large pieces of salmon seafood.

[0003] The existing thermoforming packaging film has a small draw ratio, is usually applied to the To C end, mainly packs some leisure snacks or medium-sized meat products, has a small packaging volume, and the draw ratio is generally controlled to be less than 2.5. The requirements for the tensile properties and puncture resistance of the film are not high. After excessive stretching, the thickness of the four sides is thin, and the puncture resistance is obviously decreased. The packaging is easily broken by collision or fish thorn, and cannot meet the packaging requirements of high-value products. The thermoforming film with excessive PA content to compensate for the puncture resistance is hard, the vacuum is not complete, the preheating time of thermoforming is long, and the production efficiency is reduced. After excessive stretching, the interface is easily separated due to different material shrinkage rates during long-term storage of the product, which causes the packaging to be layered and affects the product quality. Therefore, it is particularly necessary to invent a thermoforming film capable of large-draw stretching and meeting the requirements of low-temperature freezing resistance and high puncture resistance. SUMMARY

[0004] The present application aims to provide a puncture-resistant frozen marine product thermoforming film and a preparation method thereof to solve the problems in the prior art.

[0005] To solve the above technical problems, the present application provides the following technical scheme: a preparation method of a puncture-resistant frozen marine product thermoforming film, comprising the following steps: (1) uniformly mixing homopolymer nylon, copolymer nylon and rigid filler after polarity treatment, the temperature is 250-290 DEG C, the time is 30-90 min, and then the supercritical auxiliary extrusion process is used, the supercritical ammonia gas is injected into the mixed material melt in the pressurization section of the screw, and then mixed to form a homogeneous system, and then in the decompression section of the screw, the supercritical ammonia gas is extracted by the vacuum pump, and the material is extruded by the extruder to obtain a blended nylon material; (2) the low-density polyethylene, the blended nylon material and the adhesive EVA-g-MAH are extruded by using 9-13 layer multi-layer co-extrusion film blowing equipment, the extrusion temperature is 240-260 DEG C, and the melt state film is rapidly cooled by water ring cooling water through the down blowing process, the crystallization temperature interval is rapidly jumped over, the crystallinity is reduced, and the puncture-resistant frozen seafood thermoforming film is obtained; The mass ratio of the homopolymer nylon, the copolymer nylon and the polar treated rigid filler is 50:2.5-7.5:0.01-0.08. The copolymer nylon is prepared by the reaction of PA12 prepolymer, caprolactam, terephthalic acid, hexamethylene diamine and a catalyst, and the mass ratio is 4:7:3:2:0.004. The structure of the multi-layer extrusion from the surface layer to the inner layer is: blended nylon material-adhesive-1-5 layers of low-density polyethylene-adhesive-blended nylon material-adhesive-blended nylon material-adhesive-low-density polyethylene.

[0006] Further, the homopolymer nylon in step (1) is at least one of PA6, PA66, PA11 and PA12.

[0007] Further, the polar treated rigid filler in step (1) is prepared by polar treatment of nano boron nitride and other nano particles; the mass ratio of the nano boron nitride and the other nano particles is 6:4.

[0008] Further, the other nano particles are at least one of silicon dioxide, titanium dioxide, calcium carbonate and aluminum oxide.

[0009] Further, the parameters of the supercritical assisted extrusion process in step (1) are as follows: the pressure is 12-20 MPa, the ammonia injection amount is 3-10% of the material mass, the temperature is 240-270 DEG C, and the screw rotation speed is 100 rpm.

[0010] Further, the density of the low-density polyethylene in step (2) is 0.895-0.915 g / cm 3 .

[0011] Further, the cooling water in step (2) is 20 wt% ethylene glycol aqueous solution at 0-5 DEG C.

[0012] Compared with the prior art, the present application has the following beneficial effects: The present application utilizes homopolymer nylon and copolymer nylon blending, breaks the regularity of molecular chain through copolymer nylon, increases the difficulty of crystallization, limits the formation of large spherulites, and further absorbs and disperses more impact energy, and the copolymer PA segment provides greater plastic deformation capacity, thereby enhancing the tensile strength of the matrix, introducing aromatic heterocycle into the copolymer nylon, which can limit the rigidity of the polyamide molecular backbone and improve the tensile properties of the polyamide through the special aromatic ring structure and heteroatom, thereby improving the low temperature resistance of the film material, and adding a polar modified rigid filler mainly of nano boron nitride during the blending process, and then using supercritical assisted extrusion process, the boron nitride is uniformly dispersed in the nylon matrix through physical intercalation and swelling, reducing the low temperature thermal stress concentration, and the low crystalline region of the copolymer nylon maintains toughness at low temperature, greatly improving the puncture resistance and low temperature resistance of the film material. The supercritical ammonia gas system reacts with the polarity of the surface of the rigid filler, and then combines with the nylon segment through hydrogen bond or amide bond, and the stress dispersion effect of boron nitride further avoids the formation of large crystalline spheroids, optimizes the crystalline structure, and further enhances the puncture resistance and low temperature resistance.

[0013] The present application increases the toughness of the material through the multi-layer nylon distribution structure, uses multi-layer low density polyethylene in the middle to control the crystallinity of the film material, and the adhesive layer is a maleic anhydride grafted copolymer of EVA matrix. According to the principle of "like dissolves like", the polar groups between the nylon layer and the adhesive layer can produce strong van der Waals force and hydrogen bond effect, thereby realizing good wetting and adhesion, meeting the deformation generated by large draw ratio, and improving the puncture resistance and low temperature resistance of the film material. DETAILED DESCRIPTION

[0014] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0015] In order to more clearly illustrate the method provided by the present application, the following embodiments are described in detail. In the following embodiments, the test methods of various indexes of the puncture-resistant sea product cold-formed film are as follows: Puncture resistance: Take the same size of the examples and the comparative examples, and test their puncture force according to GB / T 10004.

[0016] Low temperature resistance: Take the same size of the examples and the comparative examples, and test their tensile strength at 25 DEG C normal temperature and-30 DEG C frozen environment respectively according to ASTM D638, and measure the tensile strength retention rate.

[0017] Stretching ratio: take the same size of the embodiment and the comparative example to form the limit depth, when the limit forming depth changes, the stretching ratio will change, therefore, according to the formula: 2 (long （拉伸后） ⋅high （拉伸后） + wide （拉伸后） ⋅high （拉伸后） ) + long （拉伸前） ⋅wide （拉伸前） / long （拉伸前） ⋅wide （拉伸前） , calculate its stretching ratio.

[0018] Example 1; (1) PA12 and deionized water were mixed in a mass ratio of 1:2, and under the conditions of 180℃ and 1.2MPa, the initial polymerization was carried out for 2h to obtain a PA12 prepolymer; the PA12 prepolymer, caprolactam, terephthalic acid, hexamethylene diamine and a catalyst were protected by nitrogen gas with a flow rate of 100sccm, and then the temperature was raised to 200℃ and reacted for 1h, then the temperature was raised to 230℃ and reacted for 2h, then the temperature was raised to 270℃ and reacted for 2h, and then the unreacted monomers were removed by filtration to obtain a copolymerized nylon; the mass ratio of the PA12 prepolymer, caprolactam, terephthalic acid, hexamethylene diamine and the catalyst was 4:7:3:2:0.004; the catalyst was sodium hypophosphite; the rigid filler was immersed in a 10wt% sodium hydroxide solution at a bath ratio of 1:10 and reacted at 90℃ for 4h, then mixed with 25wt% ammonia water and 50wt% nitric acid solution at a volume ratio of 1:5:2, stirred at 60℃ and 200rpm for 8h, centrifuged at 8000rpm for 5min, washed with deionized water for 3 times, and dried at 80℃ for 8h to obtain a polar treated rigid filler; the rigid filler was composed of nano boron nitride and silicon dioxide, and the mass ratio was 6:4; PA6, copolymerized nylon and polar treated rigid filler were premixed at a temperature of 250℃ for 30min, and then treated by supercritical assisted extrusion process, the parameters of which were: pressure 12MPa, ammonia injection amount 3% of the mass of the material, temperature 240℃, screw rotation speed 100rpm, supercritical ammonia was injected into the mixture melt in the pressurization section of the screw and mixed to form a homogeneous system, and then in the decompression section of the screw, the supercritical ammonia was extracted by a vacuum pump, and the material was extruded by an extruder to obtain a blended nylon material; the mass ratio of PA6, copolymerized nylon and polar treated rigid filler was 50:2.5:0.01; (2) the low-density polyethylene, the blended nylon material and the adhesive EVA-g-MAH are extruded by using a 9-layer multi-layer co-extrusion film blowing device, the structure of the film material from the surface layer to the inner layer is: blended nylon material-adhesive-low-density polyethylene-adhesive-blended nylon material-adhesive-blended nylon material-adhesive-low-density polyethylene, the extrusion temperature is 240℃, and the film in the molten state is rapidly cooled by the water ring cooling water through the downward blowing process, so that the film rapidly jumps through the crystallization temperature interval and the crystallinity is reduced, so that the puncture-resistant seafood frozen thermoforming film is obtained; the density of the low-density polyethylene is 0.895 g / cm 3 ; the cooling water is 0℃ 20wt% ethylene glycol aqueous solution.

[0019] Example 2; (1) PA12 is mixed with deionized water at a mass ratio of 1:2, and is subjected to initial polymerization at 180℃ and 1.2MPa for 2h to obtain PA12 prepolymer; PA12 prepolymer, caprolactam, terephthalic acid, hexamethylene diamine and catalyst are subjected to reaction under the protection of nitrogen gas with a flow rate of 100sccm, the temperature is raised to 200℃ and reaction is carried out for 1h, the temperature is raised to 230℃ and reaction is carried out for 2h, the temperature is raised to 270℃ and reaction is carried out for 2h, and then unreacted monomers are removed by filtration to obtain copolymerized nylon; the mass ratio of the PA12 prepolymer, caprolactam, terephthalic acid, hexamethylene diamine and catalyst is 4:7:3:2:0.004; the catalyst is sodium hypophosphite; the rigid filler is immersed in 10wt% sodium hydroxide solution at a bath ratio of 1:10, and is reacted at 90℃ for 4h, and then is mixed with 25wt% ammonia water and 50wt% nitric acid solution at a volume ratio of 1:5:2, and is stirred at 60℃ at 200rpm for 8h, is centrifuged at 8000rpm for 5min, is washed with deionized water for 3 times, and is dried at 80℃ for 8h to obtain the polar treated rigid filler; the rigid filler is composed of nano boron nitride and silicon dioxide, and the mass ratio is 6:4; PA6, copolymerized nylon and the polar treated rigid filler are premixed at a temperature of 270℃ for 60min, and then are treated by supercritical assisted extrusion process, and the parameters are: the pressure is 16MPa, the ammonia gas injection amount is 7% of the mass of the material, the temperature is 260℃, and the screw rotation speed is 100rpm; the supercritical ammonia gas is injected into the molten mixture of the material in the pressurization section of the screw, and is mixed with the molten mixture to form a homogeneous system, and then in the decompression section of the screw, the supercritical ammonia gas is extracted by the vacuum pump, and the material is extruded by the extruder to obtain the blended nylon material; the mass ratio of the PA6, copolymerized nylon and the polar treated rigid filler is 50:5:0.04; (2) the low-density polyethylene, the blended nylon material and the adhesive EVA-g-MAH are extruded by using an 11-layer multi-layer co-extrusion film blowing device, the structure of the film material from the surface layer to the inner layer is: blended nylon material-adhesive-3 layers of low-density polyethylene-adhesive-blended nylon material-adhesive-blended nylon material-adhesive-low-density polyethylene, the extrusion temperature is 250℃, and the film in a molten state is rapidly cooled by a water ring cooling water through a downward blowing process, rapidly jumps through a crystallization temperature interval, reduces the crystallinity, and a puncture-resistant seafood frozen thermoforming film is obtained; the density of the low-density polyethylene is 0.905 g / cm 3 ; the cooling water is a 20wt% ethylene glycol aqueous solution with a temperature of 3℃.

[0020] Example 3; (1) PA12 is mixed with deionized water at a mass ratio of 1:2, and is subjected to initial polymerization at 180℃ and 1.2MPa for 2h to obtain a PA12 prepolymer; the PA12 prepolymer, caprolactam, terephthalic acid, hexamethylene diamine and a catalyst are subjected to reaction under the protection of nitrogen gas with a flow rate of 100sccm, the temperature is raised to 200℃ for 1h, to 230℃ for 2h, and to 270℃ for 2h, and then unreacted monomers are removed by filtration to obtain a copolymerized nylon; the mass ratio of the PA12 prepolymer, caprolactam, terephthalic acid, hexamethylene diamine and the catalyst is 4:7:3:2:0.004; the catalyst is sodium hypophosphite; a rigid filler is immersed in a 10wt% sodium hydroxide solution at a bath ratio of 1:10 and reacted at 90℃ for 4h, and then mixed with 25wt% ammonia water and 50wt% nitric acid solution at a volume ratio of 1:5:2, stirred at 60℃ at 200rpm for 8h, centrifuged at 8000rpm for 5min, washed with deionized water for 3 times, and dried at 80℃ for 8h to obtain a polar-treated rigid filler; the rigid filler is composed of nano-boron nitride and silicon dioxide, and the mass ratio is 6:4; PA6, the copolymerized nylon and the polar-treated rigid filler are premixed at a temperature of 290℃ for 90min, and then subjected to a supercritical assisted extrusion process, the parameters of which are: a pressure of 20MPa, an ammonia gas injection amount of 10% of the mass of the material, a temperature of 270℃, and a screw rotation speed of 100rpm, the supercritical ammonia gas is injected into the molten mixture in the pressurization section of the screw and mixed with the molten mixture to form a homogeneous system, and then in the decompression section of the screw, the supercritical ammonia gas is extracted by a vacuum pump, and the material is extruded by an extruder to obtain a blended nylon material; the mass ratio of the PA6, the copolymerized nylon and the polar-treated rigid filler is 50:7.5:0.08; (2) the low-density polyethylene, the blended nylon material and the adhesive EVA-g-MAH are extruded by using a 13-layer multi-layer co-extrusion film blowing device, the structure of the film material from the surface layer to the inner layer is: blended nylon material-adhesive-5 layers of low-density polyethylene-adhesive-blended nylon material-adhesive-blended nylon material-adhesive-low-density polyethylene, the extrusion temperature is 260°C, and the film in a molten state is rapidly cooled by a water ring cooling water through a downward blowing process, rapidly jumps through a crystallization temperature interval, reduces the crystallinity, and a puncture-resistant frozen seafood thermoforming film is obtained; the density of the low-density polyethylene is 0.915 g / cm 3 ; the cooling water is a 20wt% ethylene glycol aqueous solution with a temperature of 5°C.

[0021] Example 4; (1) PA12 is mixed with deionized water at a mass ratio of 1:2, and is subjected to initial polymerization at 180°C and 1.2 MPa for 2h to obtain a PA12 prepolymer; the PA12 prepolymer, caprolactam, terephthalic acid, hexamethylene diamine and a catalyst are subjected to reaction under the protection of nitrogen gas with a flow rate of 100sccm, the temperature is raised to 200°C for 1h, to 230°C for 2h, and to 270°C for 2h, and then unreacted monomers are removed by filtration to obtain a copolymerized nylon; the mass ratio of the PA12 prepolymer, caprolactam, terephthalic acid, hexamethylene diamine and the catalyst is 4:7:3:2:0.004; the catalyst is sodium hypophosphite; a rigid filler is immersed in a 10wt% sodium hydroxide solution at a bath ratio of 1:10 and reacted at 90°C for 4h, and then mixed with 25wt% ammonia water and 50wt% nitric acid solution at a volume ratio of 1:5:2, stirred at 60°C at 200rpm for 8h, centrifuged at 8000rpm for 5min, washed with deionized water for 3 times, and dried at 80°C for 8h to obtain a polar-treated rigid filler; the rigid filler is composed of nano-boron nitride and silicon dioxide, and the mass ratio is 6:4; PA6, the copolymerized nylon and the polar-treated rigid filler are premixed at a temperature of 270°C for 60min, and then subjected to a supercritical assisted extrusion process, the parameters of which are: a pressure of 16 MPa, an ammonia gas injection amount of 7% of the mass of the material, a temperature of 260°C, and a screw rotation speed of 100rpm, the supercritical ammonia gas is injected into the molten mixture in the pressurization section of the screw and mixed with the molten mixture to form a homogeneous system, and then in the decompression section of the screw, the supercritical ammonia gas is extracted by a vacuum pump, and the material is extruded by an extruder to obtain a blended nylon material; the mass ratio of the PA6, the copolymerized nylon and the polar-treated rigid filler is 50:1:0.04; (2) the low-density polyethylene, the blended nylon material and the adhesive EVA-g-MAH are extruded by using an 11-layer multi-layer co-extrusion film blowing device, the structure of the film material from the surface layer to the inner layer is: blended nylon material-adhesive-3 layers of low-density polyethylene-adhesive-blended nylon material-adhesive-blended nylon material-adhesive-low-density polyethylene, the extrusion temperature is 250°C, and the film in a molten state is rapidly cooled by a water ring cooling water through a downward blowing process, rapidly jumps through a crystallization temperature interval, reduces the crystallinity, and a puncture-resistant frozen seafood thermoforming film is obtained; the density of the low-density polyethylene is 0.905 g / cm 3 ; the cooling water is a 20wt% ethylene glycol aqueous solution at 3°C.

[0022] Example 5; (1) PA12 is mixed with deionized water at a mass ratio of 1:2, and is subjected to initial polymerization at 180°C and 1.2 MPa for 2h to obtain a PA12 prepolymer; the PA12 prepolymer, caprolactam, terephthalic acid, hexamethylene diamine and a catalyst are subjected to reaction under the protection of nitrogen gas at a flow rate of 100sccm, the temperature is raised to 200°C for 1h, to 230°C for 2h, and to 270°C for 2h, and then unreacted monomers are removed by filtration to obtain a copolymerized nylon; the mass ratio of the PA12 prepolymer, caprolactam, terephthalic acid, hexamethylene diamine and the catalyst is 4:7:3:2:0.004; the catalyst is sodium hypophosphite; a rigid filler is immersed in a 10wt% sodium hydroxide solution at a bath ratio of 1:10, and is reacted at 90°C for 4h, and then is mixed with 25wt% ammonia water and 50wt% nitric acid solution at a volume ratio of 1:5:2, and is stirred at 60°C at 200rpm for 8h, is centrifuged at 8000rpm for 5min, is washed with deionized water for 3 times, and is dried at 80°C for 8h to obtain a polar-treated rigid filler; the rigid filler is composed of nano-boron nitride and silicon dioxide, and the mass ratio is 6:4; PA6, the copolymerized nylon and the polar-treated rigid filler are premixed at a temperature of 270°C for 60min, and then are treated by a supercritical assisted extrusion process, the parameters of which are: the pressure is 16 MPa, the ammonia gas injection amount is 7% of the mass of the material, the temperature is 260°C, and the screw rotation speed is 100rpm, the supercritical ammonia gas is injected into the molten mixture in the pressurization section of the screw and is mixed with the molten mixture to form a homogeneous system, the supercritical ammonia gas is then extracted by a vacuum pump in the decompression section of the screw, and the material is extruded by an extruder to obtain a blended nylon material; the mass ratio of the PA6, the copolymerized nylon and the polar-treated rigid filler is 50:5:0.005; (2) the low-density polyethylene, the blended nylon material and the adhesive EVA-g-MAH are extruded by using an 11-layer multi-layer co-extrusion film blowing device, the structure of the film material from the surface layer to the inner layer is: blended nylon material-adhesive-3 layers of low-density polyethylene-adhesive-blended nylon material-adhesive-blended nylon material-adhesive-low-density polyethylene, the extrusion temperature is 250°C, and the film in a molten state is rapidly cooled by a water ring cooling water through a downward blowing process, rapidly jumps through a crystallization temperature interval, reduces the crystallinity, and a puncture-resistant frozen seafood thermoforming film is obtained; the density of the low-density polyethylene is 0.905 g / cm 3 ; the cooling water is a 20wt% ethylene glycol aqueous solution at 3°C.

[0023] Example 6; (1) PA12 is mixed with deionized water at a mass ratio of 1:2, and is subjected to initial polymerization at 180°C and 1.2 MPa for 2h to obtain a PA12 prepolymer; the PA12 prepolymer, caprolactam, terephthalic acid, hexamethylene diamine and a catalyst are subjected to reaction under the protection of nitrogen gas at a flow rate of 100sccm, the temperature is raised to 200°C for 1h, to 230°C for 2h, and to 270°C for 2h, and then unreacted monomers are removed by filtration to obtain a copolymerized nylon; the mass ratio of the PA12 prepolymer, caprolactam, terephthalic acid, hexamethylene diamine and the catalyst is 4:7:3:2:0.004; the catalyst is sodium hypophosphite; a rigid filler is immersed in a 10wt% sodium hydroxide solution at a bath ratio of 1:10, and is reacted at 90°C for 4h, and then is mixed with 25wt% ammonia water and 50wt% nitric acid solution at a volume ratio of 1:5:2, and is stirred at 60°C at 200rpm for 8h, is centrifuged at 8000rpm for 5min, is washed with deionized water for 3 times, and is dried at 80°C for 8h to obtain a polar-treated rigid filler; the rigid filler is composed of nano-boron nitride and silicon dioxide, and the mass ratio is 6:4; PA6, the copolymerized nylon and the polar-treated rigid filler are premixed at a temperature of 270°C for 60min, and then are treated by a supercritical assisted extrusion process, the parameters of which are: the pressure is 16 MPa, the ammonia gas injection amount is 1% of the mass of the material, the temperature is 260°C, and the screw rotation speed is 100rpm, the supercritical ammonia gas is injected into the molten mixture in the pressurization section of the screw and is mixed with the molten mixture to form a homogeneous system, the supercritical ammonia gas is then extracted by a vacuum pump in the decompression section of the screw, and the material is extruded by an extruder to obtain a blended nylon material; the mass ratio of the PA6, the copolymerized nylon and the polar-treated rigid filler is 7:5:0.04; (2) the low-density polyethylene, the blended nylon material and the adhesive EVA-g-MAH are extruded by using an 11-layer multi-layer co-extrusion film blowing device, the structure of the film material from the surface layer to the inner layer is: blended nylon material-adhesive-3 layers of low-density polyethylene-adhesive-blended nylon material-adhesive-blended nylon material-adhesive-low-density polyethylene, the extrusion temperature is 250℃, and the film in a molten state is rapidly cooled by a water ring cooling water through a downward blowing process, rapidly jumps through a crystallization temperature interval, reduces the crystallinity, and the puncture-resistant sea product frozen thermoforming film is obtained; the density of the low-density polyethylene is 0.905 g / cm 3 ; the cooling water is a 20wt% ethylene glycol aqueous solution with a temperature of 3℃.

[0024] Comparative Example 1; the difference between Comparative Example 1 and Example 2 is that no copolymerized nylon is added; the remaining steps are the same as those in Example 2.

[0025] Comparative Example 2; the difference between Comparative Example 2 and Example 2 is that no rigid filler is added; the remaining steps are the same as those in Example 2.

[0026] Comparative Example 3; the difference between Comparative Example 3 and Example 2 is that step (1) is different, and step (1) is changed to: PA12 and deionized water are mixed at a mass ratio of 1:2, and a PA12 prepolymer is obtained under the conditions of 180℃ and 1.2MPa for 2h; the PA12 prepolymer, caprolactam, terephthalic acid, hexamethylene diamine and a catalyst are protected by nitrogen gas with a flow rate of 100sccm, and the temperature is raised to 200℃ for 1h, to 230℃ for 2h, and to 270℃ for 2h, and then the unreacted monomers are removed by filtration to obtain the copolymerized nylon; the mass ratio of the PA12 prepolymer, caprolactam, terephthalic acid, hexamethylene diamine and the catalyst is 4:7:3:2:0.004; the catalyst is sodium hypophosphite; the rigid filler is immersed in a 10wt% sodium hydroxide solution at a bath ratio of 1:10, reacted at 90℃ for 4h, then mixed with 25wt% ammonia water and 50wt% nitric acid solution at a volume ratio of 1:5:2, stirred at 60℃ at 200rpm for 8h, centrifuged at 8000rpm for 5min, washed with deionized water for 3 times, and dried at 80℃ for 8h to obtain the polar treated rigid filler; the rigid filler is composed of nano boron nitride and silicon dioxide, and the mass ratio is 6:4; the PA6, the copolymerized nylon and the polar treated rigid filler are premixed at a temperature of 270℃ for 60min, and then treated by an extrusion process at a temperature of 260℃ to obtain the blended nylon material; the mass ratio of the PA6, the copolymerized nylon and the polar treated rigid filler is 50:5:0.04; the remaining steps are the same as those in Example 2.

[0027] Effect Example The performance analysis results of the puncture-resistant sea product frozen thermoforming films obtained by using Examples 1 to 6 and Comparative Examples 1 to 3 of the present application are shown in Table 1 below.

[0028] Table 1

[0029] From the comparison of the experimental data of the examples and the comparative examples in Table 1, it can be found that, by blending homopolymer nylon and copolymer nylon, the regularity of the molecular chain is disturbed by the copolymer nylon, the crystallization difficulty is increased, the formation of large spherulites is limited, and more impact energy is absorbed and dispersed, and the copolymer PA segment provides greater plastic deformation capacity, thereby enhancing the tensile strength of the matrix, the aromatic heterocycle is introduced into the copolymer nylon, and through the special aromatic ring structure and heteroatom, the rigidity of the polyamide molecular backbone can be limitedly weakened, the tensile properties of the polyamide are improved, thereby the low-temperature resistance of the film material is improved, and the polar modified rigid filler mainly of nano boron nitride is added in the blending process, and then the supercritical assisted extrusion process is used, the puncture resistance and low-temperature resistance of the film material are greatly improved, the supercritical ammonia system reacts with the surface polarity of the rigid filler, and then is combined with the nylon segment through hydrogen bond or amide bond, and the stress dispersion effect of boron nitride is added, the crystallization structure is optimized, and the puncture resistance and low-temperature resistance are further improved.

[0030] It is apparent for those skilled in the art that the present application is not limited to the details of the above exemplary embodiments but can be implemented in other embodiments without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be considered in all respects as illustrative and not restrictive, the scope of the present application being indicated by the appended claims rather than by the above description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference signs in the claims should not be construed as limiting the claims.

Claims

1. A method for preparing a puncture-resistant, seafood chiller thermoformed film, characterized in that, The method comprises the following steps: (1) uniformly mixing homopolymer nylon, copolymer nylon and rigid filler after polarity treatment, and then treating by supercritical assisted extrusion process to obtain blended nylon material; (2) extruding low-density polyethylene, blended nylon material and adhesive EVA-g-MAH by 9-13 layer multi-layer co-extrusion film blowing equipment and then cooling by water ring cooling water to obtain puncture-resistant seafood frozen thermoforming film by down blowing process; The mass ratio of the homopolymer nylon, copolymer nylon and rigid filler after polarity treatment is 50:2.5-7.5:0.01-0.08; The copolymer nylon is prepared by reaction of PA12 prepolymer, caprolactam, terephthalic acid, hexamethylene diamine and catalyst, and the mass ratio is 4:7:3:2:0.004; The structure of the multi-layer extrusion from the surface layer to the inner layer is: blended nylon material-adhesive-1-5 layers of low-density polyethylene-adhesive-blended nylon material-adhesive-blended nylon material-adhesive-low-density polyethylene.

2. The method of claim 1, wherein the method further comprises the step of: The homopolymer nylon in step (1) is at least one of PA6, PA66, PA11 and PA12.

3. The method of claim 1, wherein the method further comprises the step of: 3-1) drying the frozen film at a temperature of 20 to 30°C for 1 to 3 days. The rigid filler after polarity treatment in step (1) is prepared by polarity treatment of nano boron nitride and other nano particles, and the mass ratio of the nano boron nitride and other nano particles is 6:

4.

4. The method of claim 3, wherein the method further comprises the step of applying a coating of a material to the surface of the film. The other nano particles are at least one of silica, titanium dioxide, calcium carbonate and aluminum oxide.

5. The method of claim 1, wherein the method further comprises the step of: 5.

1. drying the frozen film at a temperature of 20-30°C for 1-3 days. The parameters of the supercritical assisted extrusion process in step (1) are: pressure 12-20 MPa, ammonia injection amount 3-10% of the mass of the material, temperature 240-270℃, and screw rotation speed 100 rpm.

6. The method of claim 1, wherein the method further comprises the step of: The low density polyethylene of step (2) has a density of 0.895 to 0.915 g / cm 3 .

7. The method of claim 1, wherein the method further comprises the step of: 5 applying a coating of a material to the surface of the film. The cooling water in step (2) is 20wt% ethylene glycol aqueous solution at 0-5℃.

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