Low-temperature frozen high-temperature cooking polyolefin anti-fog film and preparation method thereof

Abstract

The present application relates to a kind of low-temperature frozen high-temperature cooking polyolefin anti-fog film, from top to bottom in turn includes surface layer, core layer and heat sealing layer;Wherein, the heat sealing layer includes ternary random copolymerization polypropylene 65~80wt%, propylene-ethylene copolymer 10~35wt%, nano-silica 0.5~3.0wt%;Propylene-ethylene copolymer in monomer ratio of propylene and ethylene is 80:20.The heat sealing layer of the present application is mainly ternary random copolymerization polypropylene and propylene-ethylene copolymer, the melting point of ternary random copolymerization polypropylene is high, can resist high-temperature cooking, can provide good high-temperature heat sealing function for film, but it has the problem of being easy to be brittle at low temperature.The present application introduces propylene-ethylene copolymer with specific monomer ratio, its melting point is more than 128℃, higher than 121℃ of high-temperature cooking, can be used for high-temperature cooking packaging, it is used to modify ternary random copolymerization polypropylene, the ethylene component in it can strengthen the heat sealing function of ternary random copolymerization polypropylene at low temperature, improve its low-temperature heat sealing strength, prevent polypropylene brittle at low temperature.

Description

Technical Field

[0001] This invention relates to the field of heat-sealing film technology, and in particular to a low-temperature freeze-and-high-temperature cookable polyolefin anti-fog film and its preparation method. Background Technology

[0002] With the accelerating pace of life and the gradual improvement of living standards, pre-prepared meals have developed rapidly in my country in recent years. Various frozen foods, steamed foods, and instant foods are increasingly appearing on people's menus, and the volume is enormous. With the development of pre-prepared meals, the requirements for packaging are becoming increasingly stringent, especially in the field of flexible plastic packaging materials. Currently, frozen foods and steamed foods often use different materials due to the different functional attributes of their packaging. Frozen products commonly use polyethylene flexible plastic packaging materials, which can withstand temperatures as low as -28℃ or higher, while steamed foods commonly use polypropylene flexible plastic packaging materials, which require high temperature resistance of 121℃ or higher. As consumer demands continue to diversify, pre-prepared meals are now often frozen, refrigerated, and stored at low temperatures, and then consumed without opening the packaging, directly heated in a water bath or steamed. The limitations of the aforementioned traditional packaging materials are becoming increasingly apparent. Polyethylene, used for the heat-sealing layer, has a low melting point and cannot meet the requirements of high-temperature heat-sealing packaging; while polypropylene becomes brittle at low temperatures, has low heat-sealing strength, and the packaging is easily opened.

[0003] The increasing complexity of pre-prepared food applications has placed new demands on packaging materials. In practical applications, packaging materials must be able to withstand both low-temperature freezing and high-temperature cooking; they must have high strength, and their heat-sealing strength must be unaffected by temperature changes; furthermore, condensation inside the bag must be prevented during low-temperature freezing, refrigeration, and high-temperature boiling or cooking, thus protecting the product's visual appeal. In addition, because packaging materials generally employ composite structures of different materials, they are difficult to degrade, cannot be regenerated or recycled, and are detrimental to sustainable development.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The technical problem to be solved by the present invention is: the present invention provides a polyolefin anti-fog film that can be frozen at low temperature and cooked at high temperature and its preparation method. The recyclable polyolefin single material film material obtained by the present invention can simultaneously meet the requirements of low temperature freezing resistance and high temperature cooking resistance of packaging materials, and has high heat sealing strength, which is suitable for the requirements of complex application scenarios of pre-prepared food.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] This invention provides a polyolefin anti-fog film that can be frozen at low temperatures and cooked at high temperatures, comprising, from top to bottom, a surface layer, a core layer, and a heat-sealing layer;

[0008] The heat-sealing layer comprises 65-80 wt% ternary random copolymer polypropylene, 10-35 wt% propylene-ethylene copolymer, and 0.5-3.0 wt% nano-silica.

[0009] The monomer ratio of propylene to ethylene in the propylene-ethylene copolymer is 80:20.

[0010] This invention proposes a low-temperature freeze-and-high-temperature retortible polyolefin anti-fog film. The heat-sealing layer is primarily composed of ternary random copolymer polypropylene and propylene-ethylene copolymer. Ternary random copolymer polypropylene has a high melting point and can withstand high-temperature retort, providing excellent high-temperature heat-sealing performance for the film; however, it is prone to brittleness at low temperatures. This invention introduces a propylene-ethylene copolymer with a specific monomer ratio. Its melting point exceeds 128°C, higher than the 121°C required for high-temperature retort packaging, and it is used to modify the ternary random copolymer polypropylene. The ethylene component enhances the heat-sealing function of the ternary random copolymer polypropylene at low temperatures, improving its low-temperature heat-sealing strength and preventing low-temperature brittleness. Different propylene-ethylene copolymers have different melting points; higher ethylene content results in better low-temperature heat-sealing performance, but excessively high ethylene content lowers the melting point of the propylene-ethylene copolymer. Therefore, a suitable ratio of propylene-ethylene copolymer significantly affects film performance. Furthermore, nano-silica is added to the heat-sealing layer, which can improve the film's stickiness after the addition of propylene-ethylene copolymer and enhance its opening properties. This invention optimizes the design of the components in the heat-sealing layer, enabling packaging materials to simultaneously possess excellent high and low temperature heat-sealing effects, thus meeting the heat-sealing performance requirements in different scenarios.

[0011] Optionally, the melting point of the ternary random copolymer polypropylene is higher than 150°C.

[0012] As can be seen from the above description, the present invention uses high-temperature resistant ternary random copolymer polypropylene, which has a very good high-temperature heat-sealing effect. Compared with conventional heat-sealing polyethylene, its melting point is generally lower than 120°C, and it is not suitable for heat-sealing packaging under high temperature conditions. Compared with high-temperature resistant high-density polyethylene, its viscosity is low and its heat-sealing function is poor, and it is not suitable for heat-sealing layers.

[0013] Optionally, the ratio of the surface layer, core layer, and heat-sealing layer is 10-30 wt%: 50-75 wt%: 15-35 wt%.

[0014] Optionally, the surface layer comprises 92-96.5 wt% high-density polyethylene, 3-5 wt% micron-sized silica masterbatch, and 0.5-3 wt% antistatic agent.

[0015] Optionally, the core layer comprises 91.5–95.5 wt% high-density polyethylene, 3–5 wt% micron-sized silica masterbatch, and 1.5–3.5 wt% high- and low-temperature compound anti-fogging agent masterbatch.

[0016] As described above, both the outer and core layers of this invention are primarily composed of high-density polyethylene, which can withstand temperatures above 130°C. High-density polyethylene also possesses excellent moisture barrier properties, making it particularly suitable for packaging foods containing water. By adding micron-sized silica inorganic materials, the micron-level particle size is increased. This has several advantages: firstly, it raises the temperature resistance of the outer and core layers by 2-3°C, further improving their temperature resistance; secondly, it enhances the film's stiffness and strength; and thirdly, it provides anti-adhesion, preventing layer-to-layer adhesion during film winding. Furthermore, because the heat-sealing layer of this invention contains a propylene-ethylene copolymer, which is compatible with both polypropylene and polyethylene, the bonding strength between the core layer and the heat-sealing layer is high, preventing delamination during heating and cooking. Furthermore, the main materials selected for the surface layer, core layer, and heat-sealing layer of this invention are PP and PE, which belong to the same type of polyolefin material. Therefore, the polyolefin anti-fog film that can be frozen at low temperatures and cooked at high temperatures obtained by this invention also has the advantages of being recyclable and reusable, reducing the waste pollution of plastic bags, and saving petrochemical resources.

[0017] Optionally, the micron-sized silica masterbatch is a high-density polyethylene masterbatch containing 20 wt% micron-sized silica.

[0018] Optionally, the high and low temperature compound antifogging agent masterbatch is a high-density polyethylene masterbatch containing 20 wt% high and low temperature compound antifogging agent, wherein the high and low temperature compound antifogging agent includes 30-40 wt% sorbitan monostearate, 30-40 wt% polyoxyethylene sorbitan palmitate, and 20-40 wt% sorbitol monopalmitate.

[0019] As described above, this invention, by adding a high- and low-temperature compound anti-fogging agent to the core layer, allows the agent to migrate to the heat-sealing layer after the three-layer co-extrusion composite of the film, thus enabling the film to simultaneously possess high and low-temperature anti-fogging properties. Specifically, dehydrated sorbitan monostearate provides high-temperature anti-fogging effects, polyoxyethylene sorbitan palmitate provides low-temperature anti-fogging effects, and sorbitol monostearate improves the initial anti-fogging effect, effectively meeting the needs for low-temperature anti-fogging during food refrigeration, high-temperature anti-fogging during high-temperature cooking, and rapid initial anti-fogging.

[0020] Another aspect of the present invention provides a method for preparing the above-mentioned low-temperature freezeable and high-temperature cookable polyolefin anti-fog film, comprising the following steps: the surface layer, core layer and heat-sealing layer are respectively formulated and mixed evenly, and co-extruded using a three-layer co-extrusion casting method to obtain the low-temperature freezeable and high-temperature cookable polyolefin anti-fog film.

[0021] Optionally, the equipment used in the three-layer co-extrusion casting method is a three-layer co-extrusion casting machine, with each main machine speed being 15 rpm, the casting roller speed being 10 m / min, the traction roller speed being 11 m / min, the winding roller speed being 11.5 m / min, and the cooler temperature being 25°C. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the polyolefin anti-fog film that can be frozen at low temperatures and cooked at high temperatures in an embodiment of the present invention.

[0023] [Explanation of Labels in the Attached Image]

[0024] 1. Top layer; 2. Core layer; 3. Heat seal layer. Detailed Implementation

[0025] To better understand the above technical solutions, exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present invention can be understood more clearly and thoroughly, and that the scope of the present invention can be fully conveyed to those skilled in the art.

[0026] Reference Figure 1 This invention provides a polyolefin anti-fog film that can be frozen at low temperatures and boiled at high temperatures, comprising, from top to bottom, a surface layer, a core layer and a heat-sealing layer;

[0027] The heat-sealing layer comprises 65-80 wt% ternary random copolymer polypropylene, 10-35 wt% propylene-ethylene copolymer, and 0.5-3.0 wt% nano-silica.

[0028] The monomer ratio of propylene to ethylene in the propylene-ethylene copolymer is 80:20.

[0029] The melting point of the ternary random copolymer polypropylene is higher than 150°C.

[0030] The ratio of the surface layer, core layer, and heat-sealing layer is 10–30 wt%: 50–75 wt%: 15–35 wt%.

[0031] The surface layer comprises 92-96.5 wt% high-density polyethylene, 3-5 wt% micron-sized silica masterbatch, and 0.5-3 wt% antistatic agent.

[0032] The core layer comprises 91.5–95.5 wt% high-density polyethylene, 3–5 wt% micron-sized silica masterbatch, and 1.5–3.5 wt% high- and low-temperature compound anti-fogging agent masterbatch.

[0033] The micron-sized silica masterbatch is a high-density polyethylene masterbatch containing 20 wt% micron-sized silica.

[0034] In some preferred embodiments of the present invention, the micron-sized silica masterbatch may also contain appropriate amounts of dispersant and adhesive.

[0035] A typical method for preparing micron-sized silica masterbatch includes the following steps: mixing 20 wt% micron-sized silica, 75 wt% high-density polyethylene, 2 wt% dispersant and 3 wt% adhesive evenly, and then granulating the mixture in a granulator to obtain the micron-sized silica masterbatch.

[0036] The granulation conditions are as follows: the temperatures of the extruder in zones 1, 2, and 3 are set to 160℃, the temperature in zone 4 to 165℃, the temperature in zone 5 to 170℃, the temperatures in zones 6 and 7 to 175℃, the temperatures in zones 8 and 9 to 180℃, the die head temperature to 180℃, the main machine speed to 80 rpm, and the feeding speed to 6 rpm.

[0037] The high and low temperature compound antifogging agent masterbatch is a high-density polyethylene masterbatch containing 20 wt% high and low temperature compound antifogging agent. The high and low temperature compound antifogging agent includes 30-40 wt% sorbitan monostearate, 30-40 wt% polyoxyethylene sorbitan palmitate, and 20-40 wt% sorbitol monostearate.

[0038] In some preferred embodiments of the present invention, the high and low temperature compound antifogging agent masterbatch may also contain an appropriate amount of antioxidant.

[0039] A typical method for preparing a high-low temperature compound antifogging agent masterbatch includes the following steps: 20 wt% of a high-low temperature compound antifogging agent (containing 30-40 wt% of dehydrated sorbitan monostearate, 30-40 wt% of polyoxyethylene sorbitan palmitate, and 20-40 wt% of sorbitol monostearate), 79.5 wt% of high-density polyethylene, and 0.5 wt% of an antioxidant are mixed evenly, and then granulated in a granulator to obtain the high-low temperature compound antifogging agent masterbatch.

[0040] The granulation conditions are as follows: the temperatures of the first, second, and third zones of the extruder are set to 160℃, the fourth zone to 165℃, the fifth zone to 165℃, the sixth and seventh zones to 170℃, the eighth and ninth zones to 175℃, the die head temperature to 175℃, the main machine speed to 80 rpm, and the feeding speed to 6 rpm.

[0041] It is prepared by the following steps: the surface layer, core layer and heat-sealing layer are formulated and mixed evenly, and then co-extruded using a three-layer co-extrusion casting method to obtain a polyolefin anti-fog film that can be frozen at low temperature and cooked at high temperature.

[0042] The equipment used in the three-layer co-extrusion casting method is a three-layer co-extrusion casting machine with a main machine speed of 15 rpm, a casting roller speed of 10 m / min, a traction roller speed of 11 m / min, a winding roller speed of 11.5 m / min, and a cooler temperature of 25℃.

[0043] In some preferred embodiments of the present invention, the process temperature parameters for the co-extrusion process are set as shown in Table 1.

[0044] Table 1 Processing Temperature Settings

[0045]

[0046] Example 1

[0047] A polyolefin anti-fog film that can be frozen at low temperatures and boiled at high temperatures comprises, from top to bottom, a 20wt% surface layer, a 60wt% core layer, and a 20wt% heat-sealing layer.

[0048] The heat-sealing layer comprises 75 wt% ternary random copolymer polypropylene, 23.5 wt% propylene-ethylene copolymer, and 1.5 wt% nano-silica.

[0049] The monomer ratio of propylene to ethylene in the propylene-ethylene copolymer is 80:20.

[0050] The melting point of the ternary random copolymer polypropylene is higher than 150°C.

[0051] The surface layer comprises 93.5 wt% high-density polyethylene, 3.5 wt% micron-sized silica masterbatch, and 3 wt% antistatic agent.

[0052] The core layer comprises 91.5 wt% high-density polyethylene, 5 wt% micron-sized silica masterbatch, and 3.5 wt% high and low temperature compounded anti-fogging agent masterbatch.

[0053] The micron-sized silica masterbatch is a high-density polyethylene masterbatch containing 20 wt% micron-sized silica.

[0054] The high and low temperature compound antifogging agent masterbatch is a high-density polyethylene masterbatch containing 20 wt% high and low temperature compound antifogging agent. The high and low temperature compound antifogging agent includes 40 wt% dehydrated sorbitan monostearate, 40 wt% polyoxyethylene sorbitan palmitate, and 20 wt% sorbitan monopalmitate.

[0055] It is prepared by the following steps: the surface layer, core layer and heat-sealing layer are formulated and mixed evenly, and then co-extruded using a three-layer co-extrusion casting method to obtain a polyolefin anti-fog film that can be frozen at low temperature and cooked at high temperature.

[0056] The equipment used in the three-layer co-extrusion casting method is a three-layer co-extrusion casting machine with a main machine speed of 15 rpm, a casting roller speed of 10 m / min, a traction roller speed of 11 m / min, a winding roller speed of 11.5 m / min, and a cooler temperature of 25℃.

[0057] The polyolefin anti-fog film that can be frozen at low temperatures and cooked at high temperatures obtained in this embodiment has a thickness of 35 μm, of which the surface layer thickness is 5 μm, the core layer thickness is 20 μm, and the heat-sealing layer thickness is 10 μm.

[0058] Example 2

[0059] The difference between this embodiment and Embodiment 1 is that the amounts of each component are different.

[0060] A polyolefin anti-fog film that can be frozen at low temperatures and boiled at high temperatures comprises, from top to bottom, a 10wt% surface layer, a 65wt% core layer, and a 25wt% heat-sealing layer.

[0061] The heat-sealing layer comprises 70 wt% ternary random copolymer polypropylene, 28 wt% propylene-ethylene copolymer, and 2 wt% nano-silica.

[0062] The monomer ratio of propylene to ethylene in the propylene-ethylene copolymer is 80:20.

[0063] The melting point of the ternary random copolymer polypropylene is higher than 150°C.

[0064] The surface layer comprises 94 wt% high-density polyethylene, 3 wt% micron-sized silica masterbatch, and 3 wt% antistatic agent.

[0065] The core layer comprises 92.5 wt% high-density polyethylene, 4.5 wt% micron-sized silica masterbatch, and 3 wt% high and low temperature compound anti-fogging agent masterbatch.

[0066] The micron-sized silica masterbatch is a high-density polyethylene masterbatch containing 20 wt% micron-sized silica.

[0067] The high and low temperature compound antifogging agent masterbatch is a high-density polyethylene masterbatch containing 20 wt% high and low temperature compound antifogging agent. The high and low temperature compound antifogging agent includes 35 wt% dehydrated sorbitan monostearate, 35 wt% polyoxyethylene sorbitan palmitate, and 30 wt% sorbitol monopalmitate.

[0068] The polyolefin anti-fog film that can be frozen at low temperatures and cooked at high temperatures obtained in this embodiment has a thickness of 40 μm, of which the surface layer thickness is 8 μm, the core layer thickness is 20 μm, and the heat-sealing layer thickness is 12 μm.

[0069] Example 3

[0070] The difference between this embodiment and Embodiment 1 is that the amounts of each component are different.

[0071] A polyolefin anti-fog film that can be frozen at low temperatures and boiled at high temperatures comprises, from top to bottom, a 15wt% surface layer, a 67wt% core layer, and an 18wt% heat-sealing layer.

[0072] The heat-sealing layer comprises 78 wt% ternary random copolymer polypropylene, 20 wt% propylene-ethylene copolymer, and 2 wt% nano-silica.

[0073] The monomer ratio of propylene to ethylene in the propylene-ethylene copolymer is 80:20.

[0074] The melting point of the ternary random copolymer polypropylene is higher than 150°C.

[0075] The surface layer comprises 93.8 wt% high-density polyethylene, 3.2 wt% micron-sized silica masterbatch, and 3 wt% antistatic agent.

[0076] The core layer comprises 92.2 wt% high-density polyethylene, 4.5 wt% micron-sized silica masterbatch, and 3.3 wt% high and low temperature compounded anti-fogging agent masterbatch.

[0077] The micron-sized silica masterbatch is a high-density polyethylene masterbatch containing 20 wt% micron-sized silica.

[0078] The high and low temperature compound antifogging agent masterbatch is a high-density polyethylene masterbatch containing 20 wt% high and low temperature compound antifogging agent. The high and low temperature compound antifogging agent includes 38 wt% dehydrated sorbitan monostearate, 38 wt% polyoxyethylene sorbitan palmitate, and 24 wt% sorbitan monopalmitate.

[0079] The polyolefin anti-fog film that can be frozen at low temperatures and cooked at high temperatures obtained in this embodiment has a thickness of 38 μm, of which the surface layer thickness is 10 μm, the core layer thickness is 20 μm, and the heat-sealing layer thickness is 8 μm.

[0080] Comparative Example 1

[0081] This comparative example uses ordinary CPE heat-sealing film.

[0082] Comparative Example 2

[0083] This comparative example uses ordinary CPP heat-sealing film.

[0084] The heat-sealing films obtained in Examples 1-3 and Comparative Examples 1-2 were subjected to performance tests, and the results are recorded in Table 2.

[0085] Table 2 Performance Test Results

[0086]

[0087] As can be seen from Table 2, the low-temperature freezeable and high-temperature cookable polyolefin antifog film prepared in the embodiments of the present invention has the following advantages: (1) excellent resistance to low-temperature freezing and high-temperature cooking and high heat sealing strength; (2) good antifog effect at high and low temperatures and long antifog time; (3) good mechanical properties and other properties.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention 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; and these 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 the present invention.

Claims

1. A polyolefin anti-fog film that can be frozen at low temperatures and cooked at high temperatures, characterized in that, From top to bottom, it includes the surface layer, core layer, and heat seal layer; The heat-sealing layer comprises 65-80 wt% ternary random copolymer polypropylene, 10-28 wt% propylene-ethylene copolymer, and 0.5-3.0 wt% nano-silica. The monomer ratio of propylene to ethylene in the propylene-ethylene copolymer is 80:20; The melting point of the ternary random copolymer polypropylene is higher than 150°C; The core layer comprises 91.5-95.5 wt% high-density polyethylene, 3-5 wt% micron-sized silica masterbatch, and 1.5-3.5 wt% high- and low-temperature compound anti-fogging agent masterbatch. The high and low temperature compound antifogging agent masterbatch is a high-density polyethylene masterbatch containing 20 wt% high and low temperature compound antifogging agent. The high and low temperature compound antifogging agent includes 30-40 wt% sorbitan monostearate, 30-40 wt% polyoxyethylene sorbitan palmitate, and 20-40 wt% sorbitol monopalmitate.

2. The low-temperature freeze-and-high-temperature cookable polyolefin anti-fog film as described in claim 1, characterized in that, The ratio of the surface layer, core layer and heat seal layer is 10~30wt%: 50~75wt%: 15~35wt%.

3. The low-temperature freeze-and-high-temperature cookable polyolefin anti-fog film as described in claim 1, characterized in that, The surface layer comprises 92-96.5 wt% high-density polyethylene, 3-5 wt% micron-sized silica masterbatch, and 0.5-3 wt% antistatic agent.

4. The low-temperature freeze-and-high-temperature cookable polyolefin anti-fog film as described in claim 1 or 3, characterized in that, The micron-sized silica masterbatch is a high-density polyethylene masterbatch containing 20 wt% micron-sized silica.

5. A method for preparing a low-temperature freeze-and-high-temperature cookable polyolefin anti-fog film as described in claim 1, comprising the following steps: The surface layer, core layer and heat-sealing layer are formulated and mixed evenly, and then co-extruded using a three-layer co-extrusion casting method to obtain a low-temperature freeze-proof and high-temperature cookable polyolefin anti-fog film.

6. The method for preparing the low-temperature freeze-high-temperature cookable polyolefin anti-fog film as described in claim 5, characterized in that, The equipment used in the three-layer co-extrusion casting method is a three-layer co-extrusion casting machine with a main machine speed of 15 rpm, a casting roller speed of 10 m / min, a traction roller speed of 11 m / min, a winding roller speed of 11.5 m / min, and a cooler temperature of 25℃.

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