High-temperature-cooking-resistant PA (Polyamide) film and preparation method thereof

Abstract

The invention discloses a high-temperature cooking resistant PA film and a preparation method thereof, and relates to the technical field of packaging materials. The preparation method comprises the following steps: carrying out substitution reaction on surface active hydroxyl of a hydroxylated layered zeolite molecular sieve and p-chlorostyrene, and then initiating free radical polymerization to prepare modified zeolite; the hydroxylated layered zeolite molecular sieve and polystyrene are introduced, so that the thermal stability of the system can be remarkably improved, and the rigid structures of the layered zeolite molecular sieve and polystyrene improve the overall glass-transition temperature of the PA membrane; the modified zeolite and polyamide are subjected to melt blending to prepare the PA membrane resistant to high-temperature steaming and boiling, polystyrene is combined with a PA matrix through physical entanglement, the interfacial tension of a hydroxylated layered zeolite molecular sieve and PA is reduced, the compatibility of the matrix is improved, defects are reduced, the hydroxylated layered zeolite molecular sieve prolongs the permeation path of gas and liquid, and the heat resistance of the membrane is improved. The barrier property is obviously improved. The PA film prepared by the invention has the performance of resisting high-temperature steaming and boiling.

Description

Technical Field

[0001] The present invention relates to the technical field of packaging materials, and particularly to a PA film resistant to high-temperature cooking and a preparation method thereof. Background Art

[0002] With the rapid development of the food industry, consumers' requirements for food packaging are increasing day by day, especially in terms of food safety, extended shelf life, and packaging convenience. As an important packaging material, high-temperature cooking films are widely used in fields such as food soft cans and ready-to-eat foods. Such packaging materials not only need to have good mechanical properties, such as tensile strength, tear resistance, and impact resistance, but also need to maintain stable physical and chemical properties under high-temperature cooking conditions to ensure that the food does not leak or deteriorate during the sterilization process.

[0003] Traditional high-temperature cooking films mostly adopt multi-layer composite structures, such as combinations of materials like polyester (PET), nylon (PA), and polypropylene (PP). However, the existing technologies still have some limitations. For example, although polyamide (PA) has excellent barrier properties and high-temperature resistance, its water absorption is relatively strong, which easily leads to a decline in the performance of the film material after high-temperature cooking, such as delamination or deformation. In addition, traditional composite processes usually rely on adhesives to bond different material layers, which not only increases production costs but may also result in adhesive failure during high-temperature cooking, leading to packaging damage or content leakage.

[0004] Existing modification technologies mostly improve thermal stability by adding inorganic particles such as nano-silica and montmorillonite, but there are problems of decreased optical properties caused by poor dispersion; or use glass fiber reinforcement, but at the expense of the flexibility and processability of the film. Some blending modification schemes introduce high-temperature resistant resins such as polyether ether ketone (PEEK), but the cost is high and the control of interfacial compatibility is complex, making it difficult to achieve large-scale industrial applications. With the increasing demand for high-temperature sterilization processes in the food processing industry and the strengthening of environmental protection regulations on the safety of packaging materials, the development of PA films with both high heat resistance, excellent barrier properties, and processing adaptability has important practical significance and market value. Summary of the Invention

[0005] The purpose of the present invention is to provide a PA film resistant to high-temperature cooking and a preparation method thereof to solve the problems existing in the prior art.

[0006] To solve the above technical problems, the present invention provides the following technical solution: A PA film resistant to high-temperature cooking is prepared by melt-blending and blow-molding and stretching a modified zeolite, a functional additive, and polyamide. The modified zeolite is prepared by subjecting zeolite to an esterification reaction with 4-vinylbenzoic acid and then initiating free radical polymerization.

[0007] Further, the zeolite is a hydroxylated layered zeolite molecular sieve, and the pore diameter of the layered zeolite molecular sieve is 0.3 nm.

[0008] Further, the functional auxiliary agent is at least one of an anti-blocking agent, a slip agent, an antistatic agent, an antioxidant, and a toughening agent.

[0009] Further, a preparation method of a PA film resistant to high-temperature cooking includes the following preparation steps: (1) Dissolve 4-vinylbenzoic acid in methanol which is 3 to 5 times the mass of 4-vinylbenzoic acid, add a hydroxylated layered zeolite molecular sieve which is 0.5 to 0.7 times the mass of 4-vinylbenzoic acid, stir at 300 to 400 r / min for 10 to 15 min to obtain a mixture, add p-toluenesulfonic acid which is 0.05 to 0.1 times the mass of the mixture, perform ultrasonic treatment at 30 to 40 kHz for 20 to 30 min, raise the temperature to 78 to 79 °C, stir at 700 to 800 r / min for 6 to 8 h, filter, and wash with ethanol 2 to 3 times to obtain pretreated zeolite; (2) Under nitrogen protection, mix absolute ethanol and pretreated zeolite in a mass ratio of 100 to 110:1, raise the temperature to 70 to 80 °C, add maleic acid which is 0.10 to 0.15 times the mass of 4-vinylbenzoic acid, stir at 300 to 400 r / min for 30 to 40 min, dropwise add a toluene solution of azobisisobutyronitrile which is 0.10 to 0.15 times the mass of 4-vinylbenzoic acid, raise the temperature to 75 to 85 °C, react for 2.5 to 3.0 h, naturally cool to room temperature, precipitate with methanol, filter, and dry at 50 °C to obtain modified zeolite; (3) By mass, mix 40 to 50 parts of polyamide chips, 2 to 5 parts of modified zeolite, and 1 to 3 parts of functional auxiliary agent, perform melt blending and extrusion, and blow molding and stretching to prepare a PA film resistant to high-temperature cooking.

[0010] Further, in the step (1), the hydroxylated layered zeolite molecular sieve is obtained by soaking the layered zeolite molecular sieve in a 7 wt% nitric acid solution for 100 to 130 min, filtering, then soaking in a 10 wt% potassium nitrate solution for 100 to 130 min, filtering, washing with deionized water and ethanol 2 to 3 times respectively, and grinding to a particle size of 1 to 3 μm.

[0011] Further, in the step (2), the toluene solution of azobisisobutyronitrile is prepared by dissolving azobisisobutyronitrile in toluene at a concentration of 5 g / L.

[0012] Further, in the step (3), the polyamide chips are melt-blended from two or more of nylon 66, nylon 6, nylon 610, nylon 611, nylon 612, nylon 6I, nylon 11, and nylon 46.

[0013] Further, in the step (3), the melt blending and extrusion temperature is 240~280°C.

[0014] Further, in the step (3), the blown film stretching and forming is carried out by blowing and stretching under heating at 90~145°C, the blow-up ratio is 1.5~3.5, it is shaped at 160~180°C for 10~15 s, and the film thickness is 15~40 μm.

[0015] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: The present invention prepares a PA film resistant to high-temperature cooking by melt blending modified zeolite and polyamide to achieve the effect of high-temperature cooking resistance.

[0016] First, utilize the surface active hydroxyl groups of the hydroxylated layered zeolite molecular sieve to undergo a substitution reaction with 4-vinylbenzoic acid, and then initiate free radical polymerization to prepare the modified zeolite. Melt blend the modified zeolite and polyamide to prepare a PA film resistant to high-temperature cooking; the lamellar structure of the hydroxylated layered zeolite molecular sieve provides a larger specific surface area and more surface hydroxyl active sites, improving the chemical bonding efficiency with 4-vinylbenzoic acid, enhancing the loading amount and dispersibility of the zeolite in polystyrene. Introducing the hydroxylated layered zeolite molecular sieve and polystyrene can significantly improve the thermal stability of the system. The rigid structures of the layered zeolite molecular sieve and polystyrene increase the overall glass transition temperature of the PA film, making the PA film not easily deformed, decomposed, etc. under high-temperature cooking conditions. After polystyrene coats the hydroxylated layered zeolite molecular sieve, a core-shell structure is formed, preventing the zeolite particles from agglomerating during melt blending and ensuring their uniform distribution in the PA matrix to maximize the functional effect. Polystyrene is also combined with the PA matrix through physical entanglement, reducing the interfacial tension between the hydroxylated layered zeolite molecular sieve and PA, improving the compatibility of the matrix, reducing defects, and the hydroxylated layered zeolite molecular sieve can extend the penetration paths of gases and liquids through the "labyrinth effect", significantly enhancing the barrier performance. The hydrophobicity of PS and the hydrophilicity of the layered zeolite molecular sieve are synergistically regulated to form a hydrophobic-hydrophilic gradient barrier layer, further improving the barrier performance. Specific Embodiments

[0017] The following will combine the embodiments of the present invention to clearly and completely describe the technical solutions 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 of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0018] In order to more clearly illustrate the method provided by the present invention, the following examples are used for detailed description. The test methods for each index of the PA film resistant to high-temperature cooking prepared in the following examples are as follows: High temperature resistance performance: The high temperature resistant cooking PA films prepared from the examples and comparative examples with the same mass were tested for their high temperature resistance performance in accordance with BB / T 0003-1994 "High Temperature Resistant Cooking Films and Bags".

[0019] Water vapor transmission rate: The high temperature resistant cooking PA films prepared from the examples and comparative examples with the same mass were tested for their water vapor transmission rate in accordance with GB / T 10004-1998 "Resistant Cooking Composite Films and Bags".

[0020] Oxygen transmission rate: The high temperature resistant cooking PA films prepared from the examples and comparative examples with the same mass were tested for their oxygen transmission rate in accordance with GB / T 28118-2011 "Plastic and Aluminum Foil Composite Films and Bags for Food Packaging".

[0021] Example 1 A preparation method of a high temperature resistant cooking PA film, comprising the following preparation steps: (1) Immerse the layered zeolite molecular sieve in a 7wt% nitric acid solution for 100 min, filter, then immerse it in a 10wt% potassium nitrate solution for 100 min, filter and wash it twice with deionized water and ethanol respectively, and grind it to a particle size of 1 μm to obtain hydroxylated layered zeolite molecular sieve; (2) Dissolve 4-vinylbenzoic acid in methanol with a mass 3 times that of 4-vinylbenzoic acid, add hydroxylated layered zeolite molecular sieve with a mass 0.5 times that of 4-vinylbenzoic acid, stir at 300 r / min for 10 min to obtain a mixture, add p-toluenesulfonic acid with a mass 0.05 times that of the mixture, ultrasonically treat at 30 kHz for 20 min, raise the temperature to 78 °C, stir at 700 r / min for 6 h, filter, and wash with ethanol twice to obtain pretreated zeolite; (3) Under nitrogen protection, mix absolute ethanol and pretreated zeolite in a mass ratio of 100:1, raise the temperature to 70 °C, add maleic acid with a mass 0.10 times that of 4-vinylbenzoic acid, stir at 300 r / min for 30 min, dropwise add a toluene solution of 5 g / L azobisisobutyronitrile with a mass 0.10 times that of 4-vinylbenzoic acid, raise the temperature to 75 °C, react for 2.5 h, naturally cool to room temperature, precipitate with methanol, filter, and dry at 50 °C to obtain modified zeolite; (4) By mass, mix 40 parts of polyamide, 2 parts of modified zeolite, 0.5 part of Irganox 1098 antioxidant, 0.5 part of erucamide slip agent, and 0.5 part of POM antistatic agent, melt blend and extrude at 240 °C. The polyamide chips are prepared by co-extrusion of nylon 66, nylon 6, and nylon 610 in a mass ratio of 1:1.2:1, and blow film and stretch to form a high temperature resistant cooking PA film. The blow film and stretch are carried out under heating at 90 °C, the blow-up ratio is 2.5, and it is shaped at 160 °C for 10 s, and the film thickness is 25 μm.

[0022] Example 2 A preparation method of a PA film resistant to high-temperature cooking, comprising the following preparation steps: (1) Immerse the layered zeolite molecular sieve in a 7 wt% nitric acid solution for 120 min, filter, then immerse it in a 10 wt% potassium nitrate solution for 120 min, filter, wash 3 times with deionized water and ethanol respectively, and grind to a particle size of 2 μm to obtain hydroxylated layered zeolite molecular sieve; (2) Dissolve 4-vinylbenzoic acid in methanol which is 4 times the mass of 4-vinylbenzoic acid, add hydroxylated layered zeolite molecular sieve which is 0.6 times the mass of 4-vinylbenzoic acid, stir at 350 r / min for 13 min to obtain a mixture, add p-toluenesulfonic acid which is 0.07 times the mass of the mixture, ultrasonicate at 35 kHz for 25 min, heat up to 78 °C, stir at 750 r / min for 7 h, filter, and wash 3 times with ethanol to obtain pretreated zeolite; (3) Under nitrogen protection, mix absolute ethanol and pretreated zeolite at a mass ratio of 1005:1, heat up to 75 °C, add maleic acid which is 0.13 times the mass of 4-vinylbenzoic acid, stir at 35 r / min for 35 min, dropwise add a toluene solution of 5 g / L azobisisobutyronitrile which is 0.13 times the mass of 4-vinylbenzoic acid, heat up to 80 °C, react for 3.0 h, naturally cool to room temperature, precipitate with methanol, filter, and dry at 50 °C to obtain modified zeolite; (4)By mass, mix 45 parts of polyamide chips, 4 parts of modified zeolite, 1 part of Irganox 1098 antioxidant, 0.8 part of erucamide slip agent, and 0.7 part of POM antistatic agent, melt-blend and extrude at 260 °C. The polyamide chips are prepared by co-extrusion of nylon 66, nylon 6, and nylon 610 at a mass ratio of 1:1.1:1, and blow-mold and stretch to form a PA film resistant to high-temperature cooking. The blow-molding and stretching are carried out under heating at 125 °C, the blow-up ratio is 3.0, it is shaped at 170 °C for 13 s, and the film thickness is 30 μm.

[0023] Example 3 A preparation method of a PA film resistant to high-temperature cooking, comprising the following preparation steps: (1)Immerse the layered zeolite molecular sieve in a 7 wt% nitric acid solution for 130 min, filter, then immerse it in a 10 wt% potassium nitrate solution for 130 min, filter, wash 3 times with deionized water and ethanol respectively, and grind to a particle size of 3 μm to obtain hydroxylated layered zeolite molecular sieve; (2) Dissolve 4-vinylbenzoic acid in methanol at 5 times the mass of 4-vinylbenzoic acid, add hydroxylated layered zeolite molecular sieve at 0.7 times the mass of 4-vinylbenzoic acid, stir at 400 r / min for 15 min to obtain a mixture, add p-toluenesulfonic acid at 0.1 times the mass of the mixture, ultrasonicate at 40 kHz for 30 min, heat up to 79 °C, stir at 800 r / min for 8 h, filter, and wash with ethanol 3 times to obtain pretreated zeolite; (3) Under nitrogen protection, mix absolute ethanol and pretreated zeolite at a mass ratio of 110:1, heat up to 80 °C, add maleic acid at 0.15 times the mass of 4-vinylbenzoic acid, stir at 400 r / min for 40 min, dropwise add a toluene solution of azobisisobutyronitrile at 5 g / L and 0.15 times the mass of 4-vinylbenzoic acid, heat up to 85 °C, react for 3.0 h, naturally cool to room temperature, precipitate with methanol, filter, and dry at 50 °C to obtain modified zeolite; (4) By mass, mix 50 parts of polyamide chips, 5 parts of modified zeolite, 2 parts of Irganox 1098 antioxidant, 1.5 parts of erucamide slip agent, and 1 part of POM antistatic agent, melt-blend and extrude at 280 °C. The polyamide chips are prepared by co-extrusion of nylon 66, nylon 6, and nylon 610 at a mass ratio of 1:1.3:1, and blow-molding and stretching are carried out to obtain a high-temperature cooking-resistant PA film. The blow-molding and stretching are carried out under heating at 145 °C, the blow-up ratio is 3.5, and it is shaped at 180 °C for 5 s, and the film thickness is 40 μm.

[0024] Comparative Example 1 The difference between Comparative Example 1 and Example 2 is that steps (2) and (3) are not included, and the modified zeolite in step (4) is changed to: hydroxylated layered zeolite molecular sieve; the other steps are the same as in Example 2.

[0025] Comparative Example 2 The difference between Comparative Example 2 and Example 2 is that step (1) is not included, and the hydroxylated layered zeolite molecular sieve in step (2) is changed to: layered zeolite molecular sieve; the other steps are the same as in Example 2.

[0026] Comparative Example 3 The difference between Comparative Example 3 and Example 2 is that step (3) is not included, and the modified zeolite in step (4) is changed to: pretreated zeolite; the other steps are the same as in Example 2.

[0027] Effect Example The following Table 1 gives the performance analysis results of the high-temperature cooking-resistant PA films of Examples 1 to 3 and Comparative Examples 1 to 3 of the present invention.

[0028] Table 1

[0029] From the comparison of the experimental data of Example 2 with Comparative Examples 1 and 3, it can be found that in the present invention, the surface active hydroxyl groups of the hydroxylated layered zeolite molecular sieve react with p-chlorostyrene by substitution reaction, and then free radical polymerization is initiated to prepare the modified zeolite. The introduction of the hydroxylated layered zeolite molecular sieve and polystyrene can significantly improve the thermal stability of the system. The rigid structures of the layered zeolite molecular sieve and polystyrene increase the glass transition temperature of the overall PA membrane, making the PA membrane not easily deformed, decomposed, etc. under high-temperature cooking conditions. After the hydroxylated layered zeolite molecular sieve is coated with polystyrene, a core-shell structure is formed to prevent the aggregation of zeolite particles during melt blending, ensuring their uniform distribution in the PA matrix and maximizing the functional effect. Polystyrene is also combined with the PA matrix through physical entanglement, reducing the interfacial tension between the hydroxylated layered zeolite molecular sieve and PA, improving the compatibility of the matrix, reducing defects, and the hydroxylated layered zeolite molecular sieve can extend the penetration paths of gases and liquids through the "labyrinth effect", significantly enhancing the barrier performance. The hydrophobicity of PS and the hydrophilicity of the layered zeolite molecular sieve are synergistically regulated to form a hydrophobic-hydrophilic gradient barrier layer, further improving the barrier performance. From the comparison of the experimental data of Example 2 with Comparative Example 2, it can be found that in the present invention, the layered zeolite molecular sieve is first hydroxylated. The lamellar structure of the hydroxylated layered zeolite molecular sieve provides a larger specific surface area and more surface hydroxyl active sites, improving the chemical bonding efficiency with p-chlorostyrene and enhancing the loading amount and dispersibility of the zeolite in polystyrene.

[0030] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, 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.

Claims

1. A PA film resistant to high-temperature cooking, characterized in that, The PA film resistant to high-temperature cooking is prepared by melt-blending modified zeolite, functional additives and polyamide and then blow-molding and stretching. The modified zeolite is prepared by carrying out an esterification reaction between zeolite and 4-vinylbenzoic acid and then initiating radical polymerization.

2. The PA film resistant to high-temperature cooking according to claim 1, wherein The zeolite is a hydroxylated layered zeolite molecular sieve, and the pore diameter of the layered zeolite molecular sieve is 0.3 nm.

3. The PA film capable of high-temperature cooking according to claim 2, wherein, The functional additives are at least one of an anti-blocking agent, a slip agent, an antistatic agent, an antioxidant and a toughening agent.

4. A preparation method of a PA film resistant to high-temperature cooking, characterized in that, It includes the following preparation steps: (1) Dissolve 4-vinylbenzoic acid in methanol which is 3-5 times the mass of 4-vinylbenzoic acid, add hydroxylated layered zeolite molecular sieve which is 0.5-0.7 times the mass of 4-vinylbenzoic acid, stir at 300-400 r / min for 10-15 min to obtain a mixture, add p-toluenesulfonic acid which is 0.05-0.1 times the mass of the mixture, carry out ultrasonic treatment at 30-40 kHz for 20-30 min, raise the temperature to 78-79 °C, stir at 700-800 r / min for 6-8 h, filter, and wash with ethanol 2-3 times to obtain pretreated zeolite; (2) Under nitrogen protection, mix absolute ethanol and pretreated zeolite in a mass ratio of 100-110:1, raise the temperature to 70-80 °C, add maleic acid which is 0.10-0.15 times the mass of 4-vinylbenzoic acid, stir at 300-400 r / min for 30-40 min, dropwise add a toluene solution of azobisisobutyronitrile which is 0.10-0.15 times the mass of 4-vinylbenzoic acid, raise the temperature to 75-85 °C, react for 2.5-3.0 h, naturally cool to room temperature, precipitate with methanol, filter, and dry at 50 °C to obtain modified zeolite; (3) By mass, mix 40-50 parts of polyamide chips, 2-5 parts of modified zeolite and 1-3 parts of functional additives, carry out melt-blending and extrusion, and blow-mold and stretch to obtain the PA film resistant to high-temperature cooking.

5. The preparation method of a PA film resistant to high-temperature cooking according to claim 4, characterized in that, In the step (1), the hydroxylated layered zeolite molecular sieve is obtained by soaking the layered zeolite molecular sieve in a 7 wt% nitric acid solution for 100-130 min, filtering, then soaking in a 10 wt% potassium nitrate solution for 100-130 min, filtering, washing with deionized water and ethanol 2-3 times respectively, and grinding to a particle size of 1-3 μm.

6. The preparation method of a PA film resistant to high-temperature cooking according to claim 4, characterized in that, In the step (2), the toluene solution of azobisisobutyronitrile is prepared by dissolving azobisisobutyronitrile in toluene with a concentration of 5 g / L.

7. The preparation method of a PA film resistant to high-temperature cooking according to claim 4, characterized in that, In the step (3), the polyamide chips are melt-blended from two or more of nylon 66, nylon 6, nylon 610, nylon 611, nylon 612, nylon 6I, nylon 11 and nylon 46.

8. The preparation method of a PA film resistant to high-temperature cooking according to claim 4, characterized in that, In the step (3), the melt-blending and extrusion temperature is 240-280 °C.

9. The preparation method of a PA film resistant to high-temperature cooking according to claim 4, characterized in that, In the step (3), the blow-molding and stretching is carried out under heating at 90-145 °C, the blow-up ratio is 1.5-3.5, and it is shaped at 160-180 °C for 10-15 s, and the film thickness is 15-40 μm.

Images