A composite material for retort food packaging and a method for preparing the same

Abstract

The application belongs to the technical field of food packaging, and particularly relates to a composite material for water-boiling-resistant food packaging and a preparation method thereof. The application provides a composite material for water-boiling-resistant food packaging, which is formed by compounding a silicon-plated nylon layer, a polyethylene terephthalate layer and a composite polyethylene layer through a solvent-free adhesive. The polyethylene terephthalate layer can provide a basic barrier function of a barrier layer for aroma preservation, and can also anchor the adhesive penetration to significantly improve the peeling strength, and further improve the mechanical impact resistance. The silicon-plated nylon layer can have oxygen barrier and mechanical cushioning effects. The composite polyethylene layer can significantly improve the impact strength. Through the synergistic effect of the layers, the prepared packaging material has high efficiency of barrier property, high-temperature water-boiling resistance, mechanical impact resistance and environmental protection and recycling.

Description

Technical Field

[0001] This application belongs to the field of food packaging technology, specifically relating to a composite material for water-resistant food packaging and its preparation method. Background Technology

[0002] As living standards continue to improve, people are paying more and more attention to food quality and safety, and therefore the field of food packaging materials related to food safety has also received considerable attention.

[0003] To improve the barrier properties of food packaging materials, packaging films are often used in the form of composite films. Traditional composite seasoning packaging uses aluminum foil composite films, which offer excellent barrier properties but are costly, opaque, not resistant to folding, and difficult to recycle. Transparent high-barrier packaging materials, such as silica-coated films (SiOx), can partially replace aluminum foil, but they suffer from defects such as brittle coatings and poor resistance to boiling. Furthermore, while ordinary solvent-free composite packaging materials are healthy and environmentally friendly, differences in material thermal shrinkage can cause coating cracking, affecting barrier stability. Therefore, there is a need to develop a composite food packaging material with good thermal stability and resistance to boiling. Summary of the Invention

[0004] This application provides a composite material for water-resistant food packaging and its preparation method. The composite material is made by sequentially bonding a polyethylene terephthalate (PET) barrier layer, a silicone nylon (MX) reinforcing layer, and a composite polyethylene (HTPE) heat-sealing layer with a solvent-free adhesive. The functions of each layer work together to make the resulting packaging material have high-efficiency barrier properties, high-temperature water resistance, mechanical impact resistance, and environmental recyclability.

[0005] In a first aspect, this application provides a composite material for water-resistant food packaging, comprising a silicone-coated nylon layer, a polyethylene terephthalate layer, and a composite polyethylene layer. The silicone-coated nylon layer includes a nylon substrate and nano-silicon layers on both surfaces of the nylon substrate. The polyethylene terephthalate layer is located above the silicone-coated nylon layer, and the composite polyethylene layer is located below the silicone-coated nylon layer. The composite polyethylene layer comprises nano-calcium carbonate and ethylene-butyl acrylate copolymer. The silicone-coated nylon layer, the polyethylene terephthalate layer, and the composite polyethylene layer are sequentially bonded together using a solvent-free adhesive to form the composite material for water-resistant food packaging. The polyethylene terephthalate layer provides basic barrier and aroma retention functions, while also allowing adhesives to penetrate and anchor, significantly improving peel strength and thus enhancing resistance to mechanical impact. The silicone-coated nylon layer combines oxygen barrier and mechanical cushioning, and the composite polyethylene layer significantly improves impact strength. Through the synergistic function of each layer, the resulting packaging material possesses high-efficiency barrier properties, high-temperature water resistance, mechanical impact resistance, and is environmentally friendly and recyclable.

[0006] In some embodiments, the thickness of the nano-silicon layer on a single surface is 80-150 nm, and the surface roughness Ra of the nano-silicon layer is ≤0.1 μm. When this condition is met, an amorphous silicon layer can be deposited on a nylon substrate. During boiling in water, the coefficient of thermal expansion of the silicon layer matches that of the nylon, preventing the coating from cracking. This allows the material to have both oxygen barrier and mechanical cushioning properties, resulting in packaging materials with high-efficiency barrier properties, high-temperature boiling resistance, mechanical impact resistance, and environmental recyclability.

[0007] In some embodiments, the thickness of the nylon substrate is 15-20 μm. When this condition is met, the resulting packaging material can have high barrier properties, high-temperature water resistance, mechanical impact resistance, and environmental recyclability.

[0008] In some embodiments, the surface of the polyethylene terephthalate layer has a spaced-apart pit structure, wherein the depth of the pit structure is 50-200 nm and the diameter is 100-500 nm. When this condition is met, the adhesive can penetrate and anchor, significantly improving the peel strength, thereby providing basic barrier and aroma retention functions. This results in packaging materials with high barrier properties, high-temperature water resistance, mechanical impact resistance, and environmental recyclability.

[0009] In some embodiments, the surface tension of the polyethylene terephthalate layer is ≥50 dyn / cm. When this condition is met, it can provide basic barrier and aroma retention functions, enabling the resulting packaging material to have high barrier properties, high-temperature water resistance, mechanical impact resistance, and environmental recyclability.

[0010] In some embodiments, the thickness of the polyethylene terephthalate layer is 12-25 μm. When this condition is met, the resulting packaging material can possess high barrier properties, high-temperature water resistance, mechanical impact resistance, and environmental recyclability.

[0011] In some embodiments, the mass percentage of nano-calcium carbonate is 5-8% and the mass percentage of ethylene-butyl acrylate copolymer is 10-35%, depending on the mass of the composite polyethylene layer. When the mass percentages of nano-calcium carbonate and ethylene-butyl acrylate copolymer are controlled to meet the above ranges, the nano-calcium carbonate can be distributed in a sheet-like orientation to form a "brick-and-mortar" structure with the matrix, significantly improving the impact strength. This results in packaging materials with high barrier properties, high-temperature boiling resistance, mechanical impact resistance, and environmental recyclability.

[0012] In some embodiments, the mass percentage of the ethylene-butyl acrylate copolymer is 20-25% based on the mass of the composite polyethylene layer. When the mass percentage of the ethylene-butyl acrylate copolymer is controlled within the above range, the resulting packaging material can have high barrier properties, high-temperature boiling resistance, mechanical impact resistance, and environmental recyclability.

[0013] In some embodiments, the thickness of the composite polyethylene layer is 50-100 μm. Meeting this condition enables the resulting packaging material to possess high barrier properties, high-temperature water resistance, mechanical impact resistance, and environmental recyclability.

[0014] In some embodiments, the water vapor transmission rate of the composite material used for water-resistant food packaging is H cc / (m 2 (×24h×0.1Mpa), oxygen permeability is O g / (m 2 ×24h×0.1Mpa), H≤3, and O≤0.5; the water vapor permeability of the composite material for water-resistant food packaging after being boiled in water at 100℃ for 30 minutes is H'cc / (m 2 (×24h×0.1Mpa), oxygen permeability is O'g / (m 2 ×24h×0.1Mpa), (H'-H) / H<10%, (O'-O) / O<10%. When these conditions are met, the resulting packaging material can have high barrier properties, high temperature water resistance, mechanical impact resistance, and environmental recyclability.

[0015] Secondly, this application also provides a method for preparing a composite material for water-resistant food packaging, comprising the following steps: a silicone-coated nylon layer and a polyethylene terephthalate layer are composited using a solvent-free adhesive, followed by a curing treatment to obtain an intermediate composite layer; the curing temperature is 38-42℃, and the time is 36-72 hours; then the intermediate composite layer and the composite polyethylene layer are composited using a solvent-free adhesive to obtain the composite material for water-resistant food packaging. Based on the above preparation method, by sequentially composited with a solvent-free adhesive the polyethylene terephthalate barrier layer, the silicone-coated nylon reinforcing layer, and the composite polyethylene heat-sealing layer into a single unit, the functions of each layer work synergistically, resulting in a packaging material with high-efficiency barrier properties, high-temperature water resistance, mechanical impact resistance, and environmental recyclability.

[0016] In some embodiments, the composite strength of the intermediate composite layer after curing treatment is not less than 2.5 N / 15 mm.

[0017] The beneficial effects of this application are:

[0018] 1. The packaging material obtained in this application is formed by sequentially composited a polyethylene terephthalate (PET) barrier layer, a silicone nylon (MX) reinforcing layer, and a composite polyethylene (HTPE) heat-sealing layer. The functions of each layer work together to make the packaging material have high-efficiency barrier properties, high-temperature water resistance, mechanical impact resistance, and environmental recyclability.

[0019] 2. The polyethylene terephthalate (PET) barrier layer, through plasma surface treatment, significantly improves surface tension, thereby providing the basic barrier layer function of aroma retention and fragrance retention, and also allows adhesives to penetrate and anchor, significantly improving peel strength.

[0020] 3. Silicon-coated nylon (MX) reinforcement layer: By depositing an amorphous silicon layer on a nylon substrate, the coefficient of thermal expansion of the silicon layer matches that of the nylon during boiling in water (the difference in coefficient of thermal expansion (CTE) is ≤0.5×10⁻⁶). -6 / ℃), to prevent coating cracking, thus providing both oxygen barrier and mechanical buffering.

[0021] 4. The composite polyethylene (HTPE) heat-sealing layer contains nano-calcium carbonate distributed in a sheet-like orientation, forming a "brick-and-mortar" structure with the matrix, which significantly improves impact strength.

[0022] 5. Solvent-free adhesives: The composite layers are bonded using solvent-free adhesives, resulting in excellent safety and environmental performance. Furthermore, the silicone-coated nylon layer and polyethylene terephthalate layer are bonded together and then cured to improve the composite strength of the intermediate composite layer. Finally, the composite polyethylene layer is bonded together, allowing each layer to function synergistically. This results in packaging materials with high barrier properties, high-temperature water resistance, mechanical impact resistance, and environmental recyclability.

[0023] Therefore, the packaging material obtained in this application has high barrier properties, high temperature resistance to boiling water, resistance to mechanical impact, and is environmentally friendly and recyclable, and has important application value in the field of food packaging technology. Attached Figure Description

[0024] Figure 1 This is a structural schematic diagram of a water-resistant food packaging composite material provided in Embodiment 1 of this application. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0026] Example 1

[0027] Preparation of polyethylene terephthalate (PET) barrier layer materials

[0028] S1, Biaxially stretched 12μm PET layer (Toray Lumirror) ®X43) undergoes plasma surface treatment, specifically including: cleaning and modifying the material surface of the corona-electrode film using ionized gas generated by high-energy electromagnetic radiation. After plasma surface treatment, the surface of the ethylene terephthalate layer has a spaced-out pit structure, wherein the pit structure has a depth of 50 nm, a diameter of 100 nm, and a surface tension ≥50 dyn / cm, providing basic water-blocking and aroma-preserving functions.

[0029] Preparation of silicon-coated nylon (MX) reinforcing layer material

[0030] S2. The substrate is 15μm 6-layer nylon (Silicone-plated nylon from Lucky Group). The chemical vapor deposition method specifically includes: plasma treatment of the corona-treated surface of the PA film material, vaporization deposition of liquid polyether siloxane on a vacuum coating machine, and introduction of high-purity oxygen to form a nano-silicon layer (thickness 80nm). The surface roughness Ra of the nano-silicon layer is ≤0.1μm.

[0031] Preparation of composite polyethylene (HTPE) heat-sealing layer material

[0032] S3, 60μm thick metallocene linear low-density polyethylene (HTPE) co-extruded film (Dow Affinity) TM PL1880G), containing 5wt% nano-calcium carbonate and 20wt% ethylene-butyl acrylate copolymer, can withstand a drop of -40℃ without cracking.

[0033] Composite process

[0034] S4. Using Wilt 4028 adhesive, composite unit temperature 50℃, pressure 0.4MPa (coating amount 1.8g / m²). 2 The PET / MX composite was achieved by five-roll transfer coating, followed by curing at 40°C. After curing, the composite strength of PET / MX was 2.5 N / 15 mm. Then, it was laminated with an HTPE layer for a second time. The total curing time was 48 h.

[0035] Example 2

[0036] The preparation method is similar to that in Example 1, except that plasma surface treatment is omitted in S1.

[0037] Example 3

[0038] Similar to the preparation method in Example 1, the difference is that in S4, the curing treatment is omitted, and after the PET / MX is composited, it is directly composited with the HTPE layer for a second time.

[0039] Comparative Example 1

[0040] The preparation method is similar to that in Example 1, except that in S2, a biaxially stretched 12μm PET layer (Toray Lumirror) is used.® X43 replaces 6 layers of nylon.

[0041] Test case

[0042] The packaging materials of each embodiment and comparative example were subjected to a boiling test at 100°C for 30 minutes. The water vapor transmission rate, oxygen transmission rate, and heat seal strength were measured before and after the boiling test. The water vapor transmission rate test involved cutting the composite film material to the dimensions of an oxygen-permeable mold and testing the water vapor transmission amount according to the infrared detector method in GB / T 26253-2010, under conditions of 38°C and 90% Rh. The oxygen transmission rate test involved cutting the composite film material to the dimensions of an oxygen-permeable mold and testing the oxygen transmission rate according to the gas permeability test method in GB / T1038.2-2022, under the isobaric method, under conditions of 23°C and 50% Rh. The heat seal strength test involved sealing the film at 170°C for the top seal and 90°C for the bottom seal for 1 second, at a pressure of 274 kPa, and then testing the heat seal strength according to the heat seal strength test method for plastic film packaging bags in QB / T 2358-1998. The test results are shown in Table 1.

[0043] Table 1

[0044]

[0045] As shown in the table above, the packaging material prepared in the embodiments of this application has high barrier properties, high-temperature boiling resistance, and mechanical impact resistance. In particular, using nylon 6 layers as the silicon-coated substrate can improve barrier properties, high-temperature boiling resistance, and mechanical impact resistance; plasma surface treatment can further improve barrier properties, high-temperature boiling resistance, and mechanical impact resistance; and curing treatment after PET / MX lamination is beneficial to further improve barrier properties, high-temperature boiling resistance, and mechanical impact resistance.

[0046] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the principles of this application should be included within the protection scope of this application.

Claims

1. A composite material for packaging food that is resistant to boiling, characterized in that, The material comprises a silicone-coated nylon layer, a polyethylene terephthalate layer, and a composite polyethylene layer; the silicone-coated nylon layer includes a nylon substrate and nano-silicon layers on both surfaces of the nylon substrate; the polyethylene terephthalate layer is located above the silicone-coated nylon layer; the composite polyethylene layer is located below the silicone-coated nylon layer; the composite polyethylene layer comprises nano-calcium carbonate and ethylene-butyl acrylate copolymer. The silicon-coated nylon layer, the polyethylene terephthalate layer, and the composite polyethylene layer are sequentially bonded together using a solvent-free adhesive to form the composite material for water-resistant food packaging. The thickness of the nano-silicon layer on a single surface of the two surfaces is 80~150nm; the surface roughness Ra of the nano-silicon layer is ≤0.1μm; The thickness of the nylon substrate is 15~20μm; In the composite polyethylene layer, based on the mass of the composite polyethylene layer, the mass percentage of nano-calcium carbonate is 5-8%, and the mass percentage of ethylene-butyl acrylate copolymer is 10-35%. The surface of the polyethylene terephthalate layer has a recessed structure with spaced intervals; the depth of the recessed structure is 50~200nm and the diameter is 100~500nm; The surface tension of the polyethylene terephthalate layer is ≥50 dyn / cm; The thickness of the polyethylene terephthalate layer is 12~25μm.

2. The composite material for water-resistant food packaging according to claim 1, characterized in that, Based on the mass of the composite polyethylene layer, the mass percentage of the ethylene-butyl acrylate copolymer is 20-25%.

3. The composite material for water-resistant food packaging according to claim 1, characterized in that: Includes the following steps: Step 1: Preparation of polyethylene terephthalate barrier layer material S1, a biaxially stretched 12μm polyethylene terephthalate layer, specifically Toray Lumirror. ® X43 undergoes plasma surface treatment, specifically including: cleaning and modifying the material surface of the corona surface of the thin film using ionized gas generated by high-energy electromagnetic radiation; after plasma surface treatment, the surface of the ethylene terephthalate layer has a recessed structure with spaced intervals, wherein the depth of the recessed structure is 50nm, the diameter is 100nm, and the surface tension is ≥50dyn / cm, providing basic water-blocking and fragrance-preserving functions. Step 2: Preparation of silicon-coated nylon reinforcing layer material S2. The substrate is 15μm nylon 6 layers, specifically Lucky Group silicon-plated nylon. It is formed by chemical vapor deposition, specifically including: plasma treatment of the corona-treated surface of PA film material, vaporization and deposition of liquid polyether siloxane on a vacuum coating machine and introduction of high-purity oxygen to form a nano-silicon layer with a thickness of 80nm and a surface roughness Ra≤0.1μm. Step 3: Preparation of composite polyethylene heat-sealing layer material S3, a 60μm thick metallocene linear low-density polyethylene co-extruded film, specifically Dow Affinity. TM PL1880G contains 5wt% nano-calcium carbonate and 20wt% ethylene-butyl acrylate copolymer, and can withstand a drop of -40℃ without breaking. Step 4: Composite Process S4. Using Wilt 4028 adhesive, the composite unit temperature is 50℃, the pressure is 0.4MPa, and the coating amount is 1.8g / m². 2 The polyethylene terephthalate layer / silicone nylon layer was composited by five-roll transfer coating, and then cured at 40°C. After curing, the composite strength of the polyethylene terephthalate layer / silicone nylon layer was 2.5 N / 15 mm. Then it was composited with a composite polyethylene layer for a second time. The total curing time was 48 h.

Images