A water-boiling type heat-sealing barrier polyamide film and its preparation method

Abstract

This application relates to the field of packaging film technology, specifically to a boil-proof heat-sealing barrier polyamide film and its preparation method. The boil-proof heat-sealing barrier polyamide film comprises a four-layer structure, from top to bottom: a polyamide surface layer, a polyamide core layer, a heat-sealing barrier layer, and a heat-sealing polyamide surface layer. The polyamide surface layer comprises polyamide 6 resin, an opening agent, and a slip agent; the polyamide core layer comprises polyamide 6 resin; the heat-sealing barrier layer comprises polyolefin hot melt adhesive resin and nanosheet materials; and the heat-sealing polyamide surface layer comprises copolymer polyamide resin and a metal compound. This boil-proof heat-sealing barrier polyamide film exhibits significantly reduced oxygen and water vapor permeability, possesses excellent barrier properties, heat-sealing performance, and dimensional stability, making it suitable for boil-proof packaging. The content of non-polyamide materials is ≤5%, meeting the limitation requirements for heterogeneous components in single-material packaging, thus providing a feasible solution for single-material polyamide film packaging.

Description

Technical Field

[0001] This application relates to the field of packaging film technology, specifically to a boil-in-water heat-sealing barrier polyamide film and its preparation method. Background Technology

[0002] Currently, the most commonly used base materials for packaging films are PE, PP, PET, and PA, with some PS and PVC also used. Due to the significant differences in the properties of these different materials, the film-forming processes, complexity, and final film performance vary considerably. To meet the requirements of packaging materials, multiple film materials need to be laminated. In other words, the packaging bags we see in retail outlets (supermarkets, etc.) are generally composed of multiple layers of materials, each with a different function. For example, the base material needs heat-sealing properties, typically using LDPE; the middle layer needs barrier properties, usually using aluminum foil, metallized film / alumina film (metallization deposition on PP, PET, etc.); and the surface layer needs printing capabilities, typically using BOPP, BOPET, etc.

[0003] Single-material packaging refers to unifying the multiple layers of different substrate films in traditional packaging bags into a single material. According to the definition of the European Circular Economy for Flexible Packaging (CEFLEX), single material mainly refers to a single polyolefin material (PP and PE), with other components accounting for no more than 5%. This structure of single-material packaging not only reduces the use of different materials, thus reducing environmental pollution and resource waste, and conforms to the trend of sustainable development and environmental protection; moreover, this material is easy to separate and recycle later, which helps to improve the overall recycling efficiency.

[0004] Microbial sterilization is an important method for long-term food preservation, and it can be classified by temperature into pasteurization, boiling sterilization, and high-temperature cooking sterilization. Therefore, packaging bags suitable for boiling and cooking sterilization have a promising market prospect. However, the performance of existing single polyolefin materials is limited, and they are not suitable for boiling or cooking sterilization.

[0005] Biaxially oriented polyamide film (BOPA) possesses excellent tensile strength, puncture resistance, low-temperature resistance, oil resistance, and flexibility, and is highly suitable for boiling and retorting sterilization, leading to its widespread use in food packaging. However, pure biaxially oriented nylon 6 (polyamide 6) material lacks high barrier and heat-sealing properties, making it difficult to overcome food spoilage caused by oxygen, temperature, water, and pH levels.

[0006] Therefore, the development of a single-material polyamide film that can be sterilized by boiling and can also prevent heat sealing, suitable for both boiling and steam sterilization, and easy to separate and recycle later, has significant market value. Summary of the Invention

[0007] To address the shortcomings of the existing technology, namely that biaxially oriented nylon 6 material, being a single material, lacks high barrier and heat-sealing properties and struggles to overcome food spoilage caused by oxygen, temperature, water, and pH levels, this application provides a boil-proof, heat-sealing barrier polyamide film, the technical solution of which is as follows:

[0008] This boil-in type heat-sealing barrier polyamide film comprises a four-layer structure, consisting of a polyamide surface layer, a polyamide core layer, a heat-sealing barrier layer, and a heat-sealing polyamide surface layer from top to bottom. By weight, the polyamide surface layer comprises 98–99.8 parts of polyamide 6 resin, 0.1–1 parts of an opening agent, and 0.1–1 parts of a slip agent; the polyamide core layer comprises polyamide 6 resin; the heat-sealing barrier layer comprises 98–99.5 parts of polyolefin hot melt adhesive resin and 0.5–2 parts of nanosheet material; and the heat-sealing polyamide surface layer comprises 97–99 parts of copolymer polyamide resin and 1–3 parts of a metal compound.

[0009] In some embodiments, by weight percentage, the polyamide surface layer comprises 98-99.8% polyamide 6 resin, 0.1-1% opening agent, and 0.1-1% slip agent; the polyamide core layer is composed of polyamide 6 resin; by weight percentage, the heat-sealable barrier layer comprises 98-99.5% polyolefin hot melt adhesive resin and 0.5-2% nanosheet material; by weight percentage, the heat-sealable polyamide surface layer comprises 97-99% copolymer polyamide resin and 1-3% metal compound.

[0010] In some embodiments, it comprises a four-layer film structure, which, from top to bottom, consists of a polyamide surface layer, a polyamide core layer, a heat-sealing barrier layer, and a heat-sealing polyamide surface layer; the polyamide surface layer is composed of polyamide 6 resin, an opening agent, and a slip agent; the polyamide core layer is composed of polyamide 6 resin; the heat-sealing barrier layer is composed of polyolefin hot melt adhesive resin and nanosheet material; and the heat-sealing polyamide surface layer is composed of copolymer polyamide resin and a metal compound.

[0011] In some embodiments, the opening agent is one or more combinations of silica, talc, calcium carbonate, PMMA particles, and hollow glass microspheres; the slip agent is one or more combinations of erucamide, oleamide, ethylene bis-stearamide, polyester silicone wax, polyethylene wax, and amide silicone wax; the polyolefin hot melt adhesive resin is one or more combinations of maleic anhydride-grafted metallocene polyethylene wax hot melt adhesive and maleic anhydride-grafted metallocene polypropylene wax hot melt adhesive; and the nanosheet material is one or more combinations of montmorillonite, titanium dioxide, graphene, mica, and talc.

[0012] In some embodiments, the particle size of the nanosheet material is 50–200 nm.

[0013] In some embodiments, the metal compound has the general formula MX. mWhere M is one of the metallic elements Li, K, Na, Ti, Zr, Zn, Mg, Ca, Fe, and Cu, X is one of the following: methoxy, ethoxy, isopropoxy, n-butoxy, sec-butoxy, tert-butoxy, acetylacetone, acetate ion, formate ion, nitrate ion, F group, Cl group, Br group, and I group, and m is a positive integer from 1 to 4.

[0014] In some embodiments, the particle size of the metal compound is 50–100 nm.

[0015] In some embodiments, the copolyamide is formed by copolymerizing at least two monomers selected from polyamide-6, polyamide-66, polyamide-11, polyamide-12, polyamide-1010, and polyamide-1212; the melting point of the copolyamide is ≤135°C.

[0016] In some embodiments, the total thickness of the boil-in heat-sealing barrier polyamide film is 25–60 μm; the thickness of the heat-sealing barrier layer is 1–2 μm; and the thickness of the heat-sealing polyamide surface layer is 3–6 μm.

[0017] This application also provides a method for preparing the water-boiling type heat-sealing barrier polyamide film described above, characterized by comprising the following preparation steps:

[0018] The components of the polyamide surface layer are mixed in proportion, melt-blended, extruded and granulated by a twin-screw extruder to obtain polyamide surface layer masterbatch, which is then dried for later use.

[0019] The components of the heat-sealing barrier layer are mixed in proportion, melt-blended, extruded and granulated by a twin-screw extruder to obtain the heat-sealing barrier layer masterbatch, which is then dried for later use.

[0020] The components of the heat-sealing polyamide surface layer are mixed in proportion, melt-blended, extruded and granulated by a twin-screw extruder to obtain heat-sealing polyamide surface layer masterbatch, which is then dried for later use.

[0021] Polyamide surface layer masterbatch is fed into the first extruder to produce the polyamide surface layer; polyamide 6 is fed into the second extruder to produce the polyamide core layer; heat-sealing barrier layer masterbatch is fed into the third extruder to produce the heat-sealing barrier layer; heat-sealing polyamide surface layer masterbatch is fed into the fourth extruder to produce the heat-sealing polyamide surface layer; wherein, the extruder temperature and T-die temperature of the polyamide surface layer and polyamide core layer are controlled between 220 and 240°C, and the extruder temperature of the heat-sealing barrier layer and heat-sealing polyamide surface layer are controlled between 135 and 180°C;

[0022] Using the LISIM synchronous stretching method, the polyamide surface layer, polyamide core layer, heat-sealing barrier layer, and heat-sealing polyamide surface layer are extruded, rapidly cooled, and cast. After being humidified and cleaned in a 60-80℃ hot steam bath, and the surface of the cast sheet is removed with hot air, biaxial stretching is then performed at a stretching temperature of 160-190℃ and a setting temperature of 180-210℃, with a stretching ratio of 2.6×2.3-3.3×3.3, thus obtaining a water-boiling type heat-sealing barrier polyamide film.

[0023] Based on the above, compared with the prior art, the water-boiling type barrier heat-sealing polyamide film provided in this application has the following beneficial effects:

[0024] The boil-in heat-sealable barrier polyamide film provided in this application has significantly reduced oxygen and water vapor permeability. It has good barrier properties, heat-sealing properties and dimensional stability, making it suitable for boil-in packaging. Furthermore, the content of non-polyamide materials in the boil-in heat-sealable barrier polyamide film is ≤5%, which meets the restriction requirements of single material on heterogeneous components, providing a feasible solution for single-material polyamide film packaging. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Unless otherwise specified, the positional relationships in the drawings described below are based on the direction in which the components are drawn in the figures.

[0026] Figure 1 This is a structural diagram of a water-boiling heat-sealing barrier polyamide film.

[0027] Figure reference numerals: 10, polyamide surface layer; 20, polyamide core layer; 30, heat-sealing barrier layer; 40, heat-sealing polyamide surface layer. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. The technical features designed in the different implementations of this application described below can be combined with each other as long as they do not conflict with each other. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0029] In the description of this application, it should be noted that all terms used in this application (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains, and should not be construed as limiting this application; it should be further understood that the terms used in this application should be understood to have the same meaning as those in the context of this specification and the relevant field, and should not be understood in an idealized or overly formal sense, except as expressly defined in this application.

[0030] This application provides a water-boiling type heat-sealing barrier polyamide film, the technical solution of which is as follows:

[0031] like Figure 1 As shown, the water-boiling type heat-sealing barrier polyamide film consists of a four-layer film structure, which, from top to bottom, consists of a polyamide surface layer 10, a polyamide core layer 20, a heat-sealing barrier layer 30, and a heat-sealing polyamide surface layer 40.

[0032] The polyamide surface layer 10 comprises, by mass percentage, 98–99.8% polyamide 6 resin, 0.1–1% opening agent, and 0.1–1% slip agent; the polyamide core layer 20 is composed of polyamide 6 resin; the heat-sealing barrier layer 30 comprises, by mass percentage, 98–99.5% polyolefin hot melt adhesive resin and 0.5–2% nanosheet material; and the heat-sealing polyamide surface layer 40 comprises, by mass percentage, 97–99% copolymer polyamide resin and 1–3% metal compound.

[0033] In this embodiment, the method for preparing the water-boiling type heat-sealing barrier polyamide film is as follows:

[0034] Step 1: Mix the components of polyamide surface layer 10 in proportion, melt-blend, extrude and granulate them through a twin-screw extruder to obtain polyamide surface layer 10 masterbatch, and dry the masterbatch for later use.

[0035] Step 2: Mix the components in the heat-sealing barrier layer 30 in proportion, melt-blend, extrude and granulate them through a twin-screw extruder to obtain the heat-sealing barrier layer 30 masterbatch, and dry the masterbatch for later use.

[0036] Step 3: Mix the components of heat-sealable polyamide surface layer 40 in proportion, melt-blend, extrude and granulate through a twin-screw extruder to obtain heat-sealable polyamide surface layer 40 masterbatch, and dry the masterbatch for later use;

[0037] Step 4: Feed the polyamide surface layer 10 masterbatch into the first extruder to produce polyamide surface layer 10; feed the polyamide 6 into the second extruder to produce polyamide core layer 20; feed the heat-sealing barrier layer 30 masterbatch into the third extruder to produce heat-sealing barrier layer 30; feed the heat-sealing polyamide surface layer 40 masterbatch into the fourth extruder to produce heat-sealing polyamide surface layer 40; wherein, the extruder temperature of polyamide surface layer 10 and polyamide core layer 20 and the temperature of their T-die are controlled between 220 and 240°C, and the extruder temperature of heat-sealing barrier layer 30 and heat-sealing polyamide surface layer 40 is controlled between 135 and 180°C;

[0038] Step 5: Using the LISIM synchronous stretching method, extrude and rapidly cool the polyamide surface layer 10, polyamide core layer 20, heat-sealing barrier layer 30, and heat-sealing polyamide surface layer 40 into a cast sheet. After humidifying and cleaning the surface in a 60-80℃ hot steam bath, remove the evaporated slurry from the cast sheet surface with hot air, and then perform biaxial stretching at a stretching temperature of 160-190℃ and a setting temperature of 180-210℃. The stretching ratio is 2.6×2.3-3.3×3.3, thus obtaining a water-boiling type heat-sealing barrier polyamide film.

[0039] This application provides the following embodiments:

[0040] Example 1

[0041] 1. Structure and Formulation

[0042] The boil-in type heat-sealing barrier polyamide film consists of a four-layer structure, which from top to bottom are polyamide surface layer, polyamide core layer, heat-sealing barrier layer, and heat-sealing polyamide surface layer;

[0043] The polyamide surface layer is composed of 99% polyamide 6 resin, 0.5% silica, and 0.5% erucamide by mass percentage; the polyamide core layer is composed of 100% polyamide 6 resin; the heat-sealing barrier layer is composed of 98.5% maleic anhydride-grafted metallocene polyethylene wax hot melt adhesive and 1.5% nano-montmorillonite; and the heat-sealing polyamide surface layer is composed of 98% copolymer polyamide 6 / 10 / 12 and 2% nano-magnesium oxide.

[0044] The thicknesses of the polyamide surface layer, polyamide core layer, heat-sealing barrier layer, and heat-sealing polyamide surface layer are 1.5μm, 22μm, 1.5μm, and 5μm, respectively; the total thickness of the film is 30μm.

[0045] 2. The thin film preparation process is as follows:

[0046] Step 1: Mix the components of the polyamide surface layer in proportion, melt-blend, extrude, and granulate them using a twin-screw extruder to obtain polyamide surface layer masterbatch, and dry the masterbatch for later use;

[0047] Step 2: Mix the components of the heat-sealing barrier layer in proportion, melt-blend, extrude, and granulate them using a twin-screw extruder to obtain the heat-sealing barrier layer masterbatch. Dry the masterbatch for later use.

[0048] Step 3: Mix the components of the heat-sealing polyamide surface layer in proportion, melt-blend, extrude, and granulate them using a twin-screw extruder to obtain the heat-sealing polyamide surface layer masterbatch. Dry the masterbatch for later use.

[0049] Step 4: Feed the polyamide surface masterbatch into the first extruder to make the polyamide surface layer; feed the polyamide 6 into the second extruder to make the polyamide core layer; feed the heat-sealing barrier layer masterbatch into the third extruder to make the heat-sealing barrier layer; feed the heat-sealing polyamide surface masterbatch into the fourth extruder to make the heat-sealing polyamide surface layer.

[0050] Among them, the extruder temperature of the polyamide surface layer and the polyamide core layer and the temperature of the T-die are controlled at 235℃, and the extruder temperature of the heat-sealing barrier layer and the heat-sealing polyamide surface layer is controlled at 165℃.

[0051] Step 5: Using the LISIM synchronous stretching method, the polyamide surface layer, polyamide core layer, heat-sealing barrier layer, and heat-sealing polyamide surface layer are extruded, rapidly cooled, and cast. After being humidified and cleaned in a 65℃ hot steam bath, the surface of the cast film is removed with hot air. Then, biaxial stretching is performed at a stretching temperature of 175℃ and a setting temperature of 195℃, with a stretching ratio of 2.8×3.2, to obtain a water-boiling type heat-sealing barrier polyamide film.

[0052] Example 2

[0053] 1. Structure and Formulation

[0054] The boil-in type heat-sealing barrier polyamide film consists of a four-layer structure, which from top to bottom are polyamide surface layer, polyamide core layer, heat-sealing barrier layer, and heat-sealing polyamide surface layer;

[0055] The polyamide surface layer, by mass percentage, consists of 98% polyamide 6 resin, 1% talc, and 1% EBS (ethylene bis-stearamide); the polyamide core layer consists of 100% polyamide 6 resin; the heat-sealing barrier layer consists of 98% maleic anhydride-grafted metallocene polypropylene wax hot melt adhesive and 2% mica; and the heat-sealing polyamide surface layer consists of 97% copolymer polyamide 6 / 66 / 10 and 3% nano zinc oxide.

[0056] The thicknesses of the polyamide surface layer, polyamide core layer, heat-sealing barrier layer, and heat-sealing polyamide surface layer are 1.5μm, 22μm, 1.5μm, and 5μm, respectively; the total thickness of the film is 30μm.

[0057] 2. The thin film preparation process is as follows:

[0058] Step 1: Mix the components of the polyamide surface layer in proportion, melt-blend, extrude, and granulate them using a twin-screw extruder to obtain polyamide surface layer masterbatch, and dry the masterbatch for later use;

[0059] Step 2: Mix the components of the heat-sealing barrier layer in proportion, melt-blend, extrude, and granulate them using a twin-screw extruder to obtain the heat-sealing barrier layer masterbatch. Dry the masterbatch for later use.

[0060] Step 3: Mix the components of the heat-sealing polyamide surface layer in proportion, melt-blend, extrude, and granulate them using a twin-screw extruder to obtain the heat-sealing polyamide surface layer masterbatch. Dry the masterbatch for later use.

[0061] Step 4: Feed the polyamide surface masterbatch into the first extruder to make the polyamide surface layer; feed the polyamide 6 into the second extruder to make the polyamide core layer; feed the heat-sealing barrier layer masterbatch into the third extruder to make the heat-sealing barrier layer; feed the heat-sealing polyamide surface masterbatch into the fourth extruder to make the heat-sealing polyamide surface layer.

[0062] Among them, the extruder temperature of the polyamide surface layer and the polyamide core layer and the temperature of the T-die are controlled at 235℃, and the extruder temperature of the heat-sealing barrier layer and the heat-sealing polyamide surface layer is controlled at 165℃.

[0063] Step 5: Using the LISIM synchronous stretching method, the polyamide surface layer, polyamide core layer, heat-sealing barrier layer, and heat-sealing polyamide surface layer are extruded, rapidly cooled, and cast. After being humidified and cleaned in a 65℃ hot steam bath, the surface of the cast film is removed with hot air. Then, biaxial stretching is performed at a stretching temperature of 175℃ and a setting temperature of 195℃, with a stretching ratio of 2.8×3.2, to obtain a water-boiling type heat-sealing barrier polyamide film.

[0064] Example 3

[0065] 1. Structure and Formulation

[0066] The boil-in type heat-sealing barrier polyamide film consists of a four-layer structure, which, from top to bottom, are a polyamide surface layer, a polyamide core layer, a heat-sealing barrier layer, and a heat-sealing polyamide surface layer.

[0067] The polyamide surface layer, by mass percentage, consists of 99.8% polyamide 6 resin, 0.1% calcium carbonate, and 0.1% PE wax; the polyamide core layer consists of 100% polyamide 6 resin; the heat-sealing barrier layer consists of 99.5% maleic anhydride-grafted metallocene polypropylene wax hot melt adhesive and 0.5% nano-graphene; and the heat-sealing polyamide surface layer consists of 99% copolymer polyamide 6 / 66 / 11 and 1% calcium chloride.

[0068] The thicknesses of the polyamide surface layer, polyamide core layer, heat-sealing barrier layer, and heat-sealing polyamide surface layer are 1.5μm, 22μm, 1.5μm, and 5μm, respectively; the total thickness of the film is 30μm.

[0069] 2. The thin film preparation process is as follows:

[0070] Step 1: Mix the components of the polyamide surface layer in proportion, melt-blend, extrude, and granulate them using a twin-screw extruder to obtain polyamide surface layer masterbatch, and dry the masterbatch for later use;

[0071] Step 2: Mix the components of the heat-sealing barrier layer in proportion, melt-blend, extrude, and granulate them using a twin-screw extruder to obtain the heat-sealing barrier layer masterbatch. Dry the masterbatch for later use.

[0072] Step 3: Mix the components of the heat-sealing polyamide surface layer in proportion, melt-blend, extrude, and granulate them using a twin-screw extruder to obtain the heat-sealing polyamide surface layer masterbatch. Dry the masterbatch for later use.

[0073] Step 4: Feed the polyamide surface masterbatch into the first extruder to make the polyamide surface layer; feed the polyamide 6 into the second extruder to make the polyamide core layer; feed the heat-sealing barrier layer masterbatch into the third extruder to make the heat-sealing barrier layer; feed the heat-sealing polyamide surface masterbatch into the fourth extruder to make the heat-sealing polyamide surface layer.

[0074] Among them, the extruder temperature of the polyamide surface layer and the polyamide core layer and the temperature of the T-die are controlled at 235℃, and the extruder temperature of the heat-sealing barrier layer and the heat-sealing polyamide surface layer is controlled at 165℃.

[0075] Step 5: Using the LISIM synchronous stretching method, the polyamide surface layer, polyamide core layer, heat-sealing barrier layer, and heat-sealing polyamide surface layer are extruded, rapidly cooled, and cast. After being humidified and cleaned in a 65℃ hot steam bath, the surface of the cast film is removed with hot air. Then, biaxial stretching is performed at a stretching temperature of 175℃ and a setting temperature of 195℃, with a stretching ratio of 2.8×3.2, to obtain a water-boiling type heat-sealing barrier polyamide film.

[0076] This application provides the following comparative examples:

[0077] Comparative Example 1

[0078] Commercially available biaxially oriented nylon film (BOPA).

[0079] Comparative Example 2 (The heat-sealing barrier layer lacks sheet material, and the heat-sealing polyamide surface layer lacks metal compounds)

[0080] The only difference between this comparative example and Example 1 is the composition of the heat-sealing barrier layer and the heat-sealing polyamide surface layer:

[0081] The boil-in type heat-sealable barrier polyamide film consists of a four-layer structure, from top to bottom: a polyamide surface layer, a polyamide core layer, a heat-sealable barrier layer, and a heat-sealable polyamide surface layer. Specifically, by mass percentage, the polyamide surface layer comprises 99% polyamide 6 resin, 0.5% silica, and 0.5% erucamide; the polyamide core layer comprises 100% polyamide 6 resin; the heat-sealable barrier layer comprises 100% maleic anhydride-grafted metallocene polyethylene wax hot melt adhesive; and the heat-sealable polyamide surface layer comprises 100% copolymer polyamide 6 / 10 / 12. Other film formulations and preparation methods are the same as in Example 1.

[0082] Comparative Example 3 (Heat-sealable polyamide surface lacks metal compounds)

[0083] The only difference between this comparative example and Example 1 is the surface component of the heat-sealable polyamide:

[0084] The boil-in type heat-sealing barrier polyamide film consists of a four-layer structure, from top to bottom: a polyamide surface layer, a polyamide core layer, a heat-sealing barrier layer, and a heat-sealing polyamide surface layer. Specifically, by mass percentage, the polyamide surface layer comprises 99% polyamide 6 resin, 0.5% silica, and 0.5% erucamide; the polyamide core layer comprises 100% polyamide 6 resin; the heat-sealing barrier layer comprises 98.5% maleic anhydride-grafted metallocene polyethylene wax hot melt adhesive and 1.5% nano-montmorillonite; and the heat-sealing polyamide surface layer comprises 100% copolymer polyamide 6 / 10 / 12. Other film formulations and preparation methods are the same as in Example 1.

[0085] Comparative Example 4 (the polyolefin hot melt adhesive resin of the heat-sealing barrier layer was replaced with EVA resin)

[0086] The only difference between this comparative example and Example 1 is the composition of the heat-sealing barrier layer:

[0087] The boil-in type heat-sealing barrier polyamide film consists of a four-layer structure, from top to bottom: a polyamide surface layer, a polyamide core layer, a heat-sealing barrier layer, and a heat-sealing polyamide surface layer. Specifically, by mass percentage, the polyamide surface layer comprises 99% polyamide 6 resin, 0.5% silica, and 0.5% erucamide; the polyamide core layer comprises 100% polyamide 6 resin; the heat-sealing barrier layer comprises 98.5% EVA resin and 1.5% nano-montmorillonite; and the heat-sealing polyamide surface layer comprises 98% copolymer polyamide 6 / 10 / 12 and 2% nano-magnesium oxide. Other film formulations and preparation methods are the same as in Example 1.

[0088] Comparative Example 5 (different formulation ratios of heat-sealing barrier layer components)

[0089] The only difference between this comparative example and Example 1 is that the heat-sealing barrier layer consists of 95% maleic anhydride-grafted metallocene polyethylene wax hot melt adhesive and 5% nano-montmorillonite. Other membrane formulations and preparation methods are the same as in Example 1.

[0090] The films prepared in the examples and comparative examples were subjected to performance tests according to the following standards:

[0091] Thickness: According to GB / T20220-2006, the average thickness of plastic film and sheet samples, the average thickness of rolls, and the surface area per unit mass;

[0092] Heat seal strength: The film heat seal strength was tested according to QB / T 2358-98, with a heat seal temperature of 125℃, a heat seal pressure of 400kpa, and a heat seal time of 1s.

[0093] Moisture absorption elongation: The initial size of the film is L0. After being placed in an environment of 23℃ / 50% humidity for 48 hours, the size is L1. The rate of no change in film size is measured as: [(L1~L0) / L0]×100%;

[0094] Heat shrinkage rate: GB / T12027-2004 Test method for dimensional change rate of plastic films and sheets upon heating;

[0095] Water vapor transmission rate: The water vapor transmission rate of the thin film was tested according to GB / T 1037-1988;

[0096] Oxygen permeability: The oxygen permeability of the membrane was tested according to GB / T 1038-2000; the test conditions were 23℃ and 50%RH.

[0097] The test evaluation results are shown in Table 1:

[0098] Table 1

[0099]

[0100] Notes: 1. The heat-sealing barrier layer is 1.5 micrometers thick, and the heat-sealing polyamide surface layer is 5 micrometers thick; 2. Boiling conditions: boil at 100℃ for 30 minutes.

[0101] As can be seen from Table 1, compared with the comparative examples, the water-boiling heat-sealing barrier polyamide films prepared in Examples 1-3 have better barrier properties, heat-sealing properties and dimensional stability, and the barrier properties are further improved after boiling.

[0102] It is known that the oxygen permeability and water vapor permeability of the boil-in-water heat-sealing barrier polyamide film provided in this application are significantly reduced, and it has good barrier properties, heat-sealing properties and dimensional stability, making it suitable for boil-in-water packaging.

[0103] In summary, compared with the prior art, the water-boiling heat-sealing barrier polyamide film solution provided in this application has the following design concept and beneficial effects:

[0104] 1. The heat-sealing barrier layer component in the film is designed with maleic anhydride-grafted metallocene polyethylene wax hot melt adhesive or maleic anhydride-grafted metallocene polypropylene wax hot melt adhesive, which makes reasonable use of the hydrophobic properties of polyolefins. At the same time, after grafting maleic anhydride, it has good compatibility with polyamide and enhances the interlayer adhesion strength.

[0105] 2. The addition of nanosheet materials to the heat-sealing barrier layer in the film can reduce the path of oxygen and water vapor through the substrate, thereby improving the barrier performance. The nano-metal compounds can effectively fill the voids in the polymer, further enhancing the barrier performance.

[0106] 3. Nano-metal compounds are added to the surface layer of the heat-sealable polyamide in the film. During the boiling process, the nano-metal compounds are excited by water vapor to generate polyvalent metal ions. These metal ions can be transferred and cross-linked with maleic anhydride, which further improves the barrier performance of the heat-sealable barrier layer.

[0107] 4. The nanosheet material particles in this film can improve the dimensional stability of the film under different temperature and humidity conditions; the water-boiling heat-sealing barrier polyamide film has a non-polyamide material content of ≤5%, which meets the restriction requirements of a single material on heterogeneous components.

[0108] In summary, the boil-in-water heat-sealing barrier polyamide film provided in this application has significantly reduced oxygen and water vapor permeability, and possesses excellent barrier properties, heat-sealing properties, and dimensional stability, making it suitable for boil-in-water packaging. Furthermore, the content of non-polyamide materials in this boil-in-water heat-sealing barrier polyamide film is ≤5%, which meets the restriction requirements for heterogeneous components in single-material packaging, providing a feasible solution for single-material polyamide film packaging.

[0109] It should be noted that:

[0110] In this article, polyamide-6, polyamide-66, polyamide-11, polyamide-12, polyamide-1010, polyamide-1212, copolyamide 6 / 10 / 12, copolyamide 6 / 66 / 10, and copolyamide 6 / 66 / 11 are commonly referred to in the industry as PA-6, PA-66, PA-11, PA-12, PA-1010, PA-1212, PA6 / 10 / 12, PA6 / 66 / 10, and PA6 / 66 / 11, respectively. These values ​​refer to existing materials.

[0111] As the fourth generation of BOPA film technology, LISIM technology is the most advanced synchronous stretching technology in the industry. It combines the advantages of step stretching and mechanical synchronous stretching with magnetic levitation technology to produce linear synchronous films that have good mechanical strength, good ductility and good uniformity.

[0112] In this article, “~” is used to represent the range of values, and the range of values ​​represented by this expression includes two endpoint values.

[0113] In summary, the specific parameters or some commonly used reagents or raw materials in the above embodiments are specific or preferred embodiments under the concept of this application, and not limitations thereof; where no specific technology or conditions are specified in the embodiments, they shall be carried out in accordance with the technology or conditions described in the literature in this field or in accordance with the product instructions; where the manufacturers of the reagents or instruments used are not specified, they are all conventional products that can be obtained commercially.

[0114] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A water-boiling type heat-sealing barrier polyamide film, characterized in that, It includes a four-layer membrane structure, from top to bottom: polyamide surface layer, polyamide core layer, heat-sealing barrier layer, and heat-sealing polyamide surface layer; By weight, the components of the polyamide surface layer include 98-99.8 parts of polyamide 6 resin, 0.1-1 parts of opening agent, and 0.1-1 parts of slip agent; The polyamide core layer comprises polyamide 6 resin; The heat-sealing barrier layer comprises 98-99.5 parts of polyolefin hot melt adhesive resin and 0.5-2 parts of nanosheet material; The heat-sealable polyamide surface layer comprises 97-99 parts of copolyamide resin and 1-3 parts of metal compound; The polyolefin hot melt adhesive resin is one or more of maleic anhydride-grafted metallocene polyethylene wax hot melt adhesive and maleic anhydride-grafted metallocene polypropylene wax hot melt adhesive; the nanosheet material is one or more of montmorillonite, titanium dioxide, graphene, mica, and talc. The general formula of the metal compound is MX. m ; Wherein, M is one of the metallic elements Li, K, Na, Ti, Zr, Zn, Mg, Ca, Fe, and Cu, X is one of the following: methoxy, ethoxy, isopropoxy, n-butoxy, sec-butoxy, tert-butoxy, acetylacetone, acetate ion, formate ion, nitrate ion, F group, Cl group, Br group, and I group, and m is a positive integer from 1 to 4.

2. The water-boiling heat-sealing barrier polyamide film according to claim 1, characterized in that, By weight percentage, the polyamide surface layer comprises 98-99.8% polyamide 6 resin, 0.1-1% opening agent, and 0.1-1% slip agent; The polyamide core layer is composed of polyamide 6 resin; By weight percentage, the heat-sealing barrier layer comprises 98–99.5% polyolefin hot melt adhesive resin and 0.5–2% nanosheet material; By mass percentage, the components of the heat-sealable polyamide surface layer include 97-99% copolyamide resin and 1-3% metal compound.

3. The water-boiling heat-sealing barrier polyamide film according to claim 1, characterized in that, It consists of a four-layer membrane structure, which, from top to bottom, consists of a polyamide surface layer, a polyamide core layer, a heat-sealing barrier layer, and a heat-sealing polyamide surface layer. The polyamide surface layer is composed of polyamide 6 resin, an opening agent, and a slip agent; The polyamide core layer is composed of polyamide 6 resin; The heat-sealing barrier layer is composed of polyolefin hot melt adhesive resin and nanosheet material; The heat-sealable polyamide surface layer is composed of copolyamide resin and metal compounds.

4. The water-boiling heat-sealing barrier polyamide film according to claim 1, characterized in that: The opening agent is one or more of the following: silica, talc, calcium carbonate, PMMA particles, and hollow glass microspheres. The slip agent is one or more of the following: erucamide, oleamide, ethylene bis-stearamide, polyester silicone wax, polyethylene wax, and amide silicone wax.

5. The water-boiling heat-sealing barrier polyamide film according to claim 1, characterized in that: The particle size of the nanosheet material is 50–200 nm.

6. The water-boiling heat-sealing barrier polyamide film according to claim 1, characterized in that, The particle size of the metal compound is 50–100 nm.

7. The water-boiling heat-sealing barrier polyamide film according to claim 1, characterized in that, The copolyamide is formed by copolymerizing at least two monomers selected from polyamide-6, polyamide-66, polyamide-11, polyamide-12, polyamide-1010, and polyamide-1212. The melting point of the copolyamide is ≤135℃.

8. The water-boiling heat-sealing barrier polyamide film according to claim 1, characterized in that: The total thickness of the boil-in heat-sealable barrier polyamide film is 25–60 μm; The thickness of the heat-sealing barrier layer is 1–2 μm; The thickness of the heat-sealable polyamide surface layer is 3–6 μm.

9. A method for preparing a water-boiling type heat-sealing barrier polyamide film as described in any one of claims 1-8, characterized in that, The preparation steps include the following: The components of the polyamide surface layer are mixed in proportion, melt-blended, extruded and granulated by a twin-screw extruder to obtain polyamide surface layer masterbatch, which is then dried for later use. The components of the heat-sealing barrier layer are mixed in proportion, melt-blended, extruded and granulated by a twin-screw extruder to obtain the heat-sealing barrier layer masterbatch, which is then dried for later use. The components of the heat-sealing polyamide surface layer are mixed in proportion, melt-blended, extruded and granulated by a twin-screw extruder to obtain heat-sealing polyamide surface layer masterbatch, which is then dried for later use. The polyamide surface masterbatch is fed into the first extruder to produce the polyamide surface layer; polyamide 6 is fed into the second extruder to produce the polyamide core layer. The heat-sealing barrier layer masterbatch is fed into the third extruder to produce the heat-sealing barrier layer; the heat-sealing polyamide surface layer masterbatch is fed into the fourth extruder to produce the heat-sealing polyamide surface layer; wherein, the extruder temperature of the polyamide surface layer and the polyamide core layer and the temperature of the T-die are controlled between 220 and 240°C, and the extruder temperature of the heat-sealing barrier layer and the heat-sealing polyamide surface layer is controlled between 135 and 180°C. Using the LISIM synchronous stretching method, the polyamide surface layer, polyamide core layer, heat-sealing barrier layer, and heat-sealing polyamide surface layer are extruded, rapidly cooled, and cast. After being humidified and cleaned in a 60-80℃ hot steam bath, and the surface of the cast sheet is removed with hot air, biaxial stretching is then performed at a stretching temperature of 160-190℃ and a setting temperature of 180-210℃, with a stretching ratio of 2.6×2.3-3.3×3.3, thus obtaining a water-boiling type heat-sealing barrier polyamide film.

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