A high-temperature resistant, easy-to-peel PP film, a composite film, and its preparation method.

Abstract

This invention relates to the field of composite membrane technology, providing a high-temperature resistant, retortable, and easily peelable PP film, a composite film, and its preparation method. The invention uses polypropylene as the main matrix material to prepare the PP film. The resulting PP film has good compatibility, excellent mechanical properties, and is not prone to stringing when peeled off. Furthermore, the invention incorporates a high-impact modified polymer material in the middle layer, significantly improving the impact resistance of the PP film. Two high-temperature resistant, retortable, and easily peelable materials are selected and combined in the inner layer, resulting in a PP film with moderate heat-sealing strength and easy peeling. The composite film obtained by combining the PP film of this invention with a printing layer and a barrier layer shows no delamination after retorting at 121°C for 30 minutes, has a wide heat-sealing window, and maintains a stable heat-sealing strength of 10–15 N / mm within the range of 130–240°C. The seal is easy to tear, without stringing or residue, and ensures no leakage. The heat-sealing strength changes little after retorting.

Description

Technical Field

[0001] This invention relates to the field of composite film technology, and in particular to a high-temperature resistant, easy-to-peel PP film, a composite film, and a preparation method thereof. Background Technology

[0002] PP film is made of polypropylene, a non-toxic, odorless, and tasteless milky-white, highly crystalline polymer. It is typically thicker and tougher, with high tensile strength and low water absorption. Polypropylene film plays a crucial role in packaging materials among plastic products. Currently, packaging materials used for food and daily necessities, in addition to good mechanical properties and sealing performance, also need to be easy to open and resistant to high-temperature retort processes to prevent loss of contents when opened or softening, deformation, and seal failure during high-temperature retort processes. Furthermore, PP is a semi-crystalline material; although its strength is higher than PE, it is more brittle at low temperatures and has poor impact resistance.

[0003] Chinese patent CN112373076A discloses a high-barrier, retort-resistant, easy-to-peel film. The disclosed product structure is PP / SUYLN / PA / PVDC / PA / SUYLN / easy-to-peel material. It requires a 9-layer co-extrusion equipment for preparation, has a complex product structure, uses many types of raw materials, and has a high cost.

[0004] Chinese patent CN113442532A discloses an antibacterial, milky-white, high-temperature retort PP easy-open sealing film. This easy-open film comprises a corona layer, a middle layer, and an inner layer. The corona layer is a blend of homopolymer polypropylene resin and processing aids; the middle layer is a blend of random block copolymer polypropylene, white masterbatch, and processing aids; and the inner layer is a blend of random block copolymer polypropylene, low-density polyethylene, polyethylene terephthalate, modified chitosan powder, erucamide, opening agent, and processing aids. Although the easy-open film disclosed in this patent has fewer layers, its composition is still very complex, especially the inner layer, making the film's preparation difficult and costly.

[0005] Chinese patent CN113427871A discloses an easy-peel film material that can withstand high-temperature cooking. It is co-extruded from a corona layer, an intermediate layer, and a heat-sealing layer. The corona layer material is metallocene polypropylene or a mixture of metallocene medium-density polyethylene and high-density polyethylene; the intermediate layer material is metallocene high-density polyethylene; and the heat-sealing layer material is a copolymer of high-density polyethylene (HDPE), polypropylene (PP), and polybutene (PB). While the easy-peel film material disclosed in this patent exhibits good peelability, its impact resistance is not mentioned. Furthermore, due to the co-extrusion of PE and PP, their compatibility is poor, leading to stringing during peeling. Summary of the Invention

[0006] In view of this, the present invention provides a high-temperature resistant retortable easy-peel PP film, a composite film, and a preparation method thereof. The high-temperature resistant retortable easy-peel PP film provided by the present invention is resistant to high-temperature retorting, has good mechanical properties, and the composite film prepared using it is not prone to delamination after retorting. It is easy to tear open after sealing, without stringing or residue, and has excellent impact resistance at different temperatures.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] A high-temperature resistant, easy-to-peel PP film is made by co-extrusion blown film of three layers: outer layer, middle layer and inner layer;

[0009] The outer layer is prepared from 100 parts by weight of polypropylene and 0.5 to 1.5 parts by weight of processing aids.

[0010] By mass, the raw materials for preparing the middle layer include 50-95 parts of polypropylene, 10-15 parts of high-impact modified polymer, and 0.5-1.5 parts of processing aid; the high-impact modified polymer is a vinyl polymer.

[0011] The raw materials for preparing the inner layer, by mass, include 55-95 parts of a first high-temperature resistant retortable and easy-to-remove material, 10-25 parts of a second high-temperature resistant and easy-to-remove material, and 0.5-1.5 parts of processing aids; the first high-temperature resistant and easy-to-remove material is a propylene-based polymer modified with the brand name AT2912 produced by Mitsui Chemicals Co., Ltd.; the second high-temperature resistant and easy-to-remove material is a propylene-based polymer modified with the brand name AT2913 produced by Mitsui Chemicals Co., Ltd.

[0012] The weight ratio of the outer layer, middle layer and inner layer is (1-2):(1-3):1;

[0013] The processing aids used in the outer, middle, and inner layers are all functional masterbatches made from fluoropolymers and polyolefin resins.

[0014] Preferably, the polypropylene used in the outer layer has a melt index of 1.0–2.0 g / 10 min and a density of 0.900–0.910 g / cm³. 3 .

[0015] Preferably, the polypropylene used in the middle layer has a melt index of 1.0–2.0 g / 10 min and a density of 0.900–0.910 g / cm³. 3 The high-impact modified polymer material used in the middle layer has a melt index of 2.0–4.0 g / 10 min and a density of 0.880–0.890 g / cm³. 3 .

[0016] Preferably, the first high-temperature resistant, easy-to-remove material used in the inner layer has a melt index of 5.0–6.5 g / 10 min and a density of 0.890–0.910 g / cm³. 3 The second high-temperature resistant, easy-to-remove material used in the inner layer has a melt index of 6.0–7.5 g / 10 min and a density of 0.890–0.910 g / cm³. 3 .

[0017] Preferably, the processing aids used in the outer, middle, and inner layers have a melt index of 5.0–7.0 g / 10 min and a density of 0.890–0.910 g / cm³. 3 .

[0018] Preferably, the polypropylene used in the outer layer is polypropylene with the grade RB709CF produced by Borouge Chemical, the polypropylene used in the middle layer is polypropylene with the grade RB707CF produced by Borouge Chemical, and the high-impact modified polymer used in the middle layer is a vinyl polymer modified with the grade A-4085S produced by Mitsui Chemicals Co., Ltd.; the processing aid used in the outer, middle and inner layers is a processing aid with the grade PA0833PPR produced by Suzhou Constance Engineering Plastics Co., Ltd.

[0019] This invention also provides a method for preparing the high-temperature resistant, easy-to-peel PP film described above, comprising the following steps:

[0020] The raw materials for the outer, middle, and inner layers are co-extruded in three layers to obtain the high-temperature resistant, easy-to-peel PP film.

[0021] The present invention also provides a high-temperature resistant retortable easy-to-peel composite film, comprising a heat-sealing layer, a barrier layer and a printing layer stacked sequentially; the heat-sealing layer is the high-temperature resistant retortable easy-to-peel PP film described in the above scheme or the high-temperature resistant retortable easy-to-peel PP film prepared by the preparation method described in the above scheme; the printing layer is a polyester film, and the barrier layer is an aluminum film or a polyester aluminized film.

[0022] This invention also provides a method for preparing the high-temperature resistant, easy-to-peel composite film described above, comprising the following steps:

[0023] (1) The printed layer and the barrier layer are dry-laminated with an adhesive and then cured to obtain a printed layer / barrier layer composite film.

[0024] (2) The printed layer / barrier layer composite film and the high temperature resistant retort easy-to-peel PP film are dry-laminated with adhesive and then cured to obtain a high temperature resistant retort easy-to-peel composite film.

[0025] Preferably, the amount of adhesive applied in step (1) is 3.8–4.8 g / m³. 2In step (2), the amount of adhesive applied is 3.5–4.5 g / m³. 2 .

[0026] This invention provides a high-temperature resistant, retortable, and easily peelable PP film, which is made by co-extrusion blown film of three layers: an outer layer, a middle layer, and an inner layer. The outer layer is prepared from 100 parts by weight of polypropylene and 0.5-1.5 parts by weight of processing aids. The middle layer is prepared from 50-95 parts by weight of polypropylene, 10-15 parts by weight of high-impact modified polymer material, and 0.5-1.5 parts by weight of processing aids. The high-impact modified polymer material is a vinyl-modified polymer. The inner layer is prepared from 55-95 parts by weight of a first high-temperature resistant, retortable, and easily peelable material. The composition includes 5 parts of a first high-temperature resistant retortable easy-to-peel material, 10-25 parts of a second high-temperature resistant retortable easy-to-peel material, and 0.5-1.5 parts of a processing aid. The first high-temperature resistant retortable easy-to-peel material is a propylene-based polymer modified with the brand name AT2912 produced by Mitsui Chemicals Co., Ltd.; the second high-temperature resistant retortable easy-to-peel material is a propylene-based polymer modified with the brand name AT2913 produced by Mitsui Chemicals Co., Ltd.; the weight ratio of the outer layer, middle layer, and inner layer is (1-2):(1-3):1; the processing aids used in the outer layer, middle layer, and inner layer are all functional masterbatches prepared from fluoropolymers and polyolefin resins. This invention uses polypropylene as the main matrix material to prepare PP film. The resulting PP film has good compatibility, excellent mechanical properties, and is not easily stringy when peeled off. Furthermore, this invention adds a high-impact modified polymer material to the middle layer, significantly improving the impact resistance of the PP film. This invention selects two high-temperature resistant retortable easy-to-peel materials for the inner layer, resulting in a PP film with moderate heat-sealing strength after heat sealing and easy peeling.

[0027] This invention also provides a high-temperature resistant, retortable, easy-to-peel composite film, comprising a heat-sealing layer, a barrier layer, and a printing layer stacked sequentially; the heat-sealing layer is the high-temperature resistant, retortable, easy-to-peel PP film described in the above-described scheme or the high-temperature resistant, retortable, easy-to-peel PP film prepared by the preparation method described in the above-described scheme; the printing layer is a polyester film, and the barrier layer is an aluminum film or a polyester aluminized film. The composite film provided by this invention is resistant to high-temperature retorting, showing no delamination after retorting at 121°C for 30 minutes, and has a wide heat-sealing window. Its heat-sealing strength remains stable at 10–15 N / mm within the range of 120–230°C, and the seal is easy to tear open without stringing or residue, while ensuring no leakage at the seal. The heat-sealing strength changes little after retorting. Attached Figure Description

[0028] Figure 1 The results show the heat-sealing strength of the composite films prepared in Examples 1-3 and Comparative Examples 1-2 at different heat-sealing temperatures before cooking.

[0029] Figure 2The results show the heat-sealing strength of the composite films prepared in Examples 1-3 and Comparative Examples 1-2 after cooking at different heat-sealing temperatures. Detailed Implementation

[0030] This invention provides a high-temperature resistant, easy-to-peel PP film, which is made of three layers: an outer layer, a middle layer, and an inner layer, through co-extrusion blown film blowing.

[0031] The outer layer is prepared using the following raw materials by weight: 100 parts polypropylene and 0.5 to 1.5 parts processing aids.

[0032] By mass, the raw materials for preparing the middle layer include 50-95 parts of polypropylene, 10-15 parts of high-impact modified polymer, and 0.5-1.5 parts of processing aid; the high-impact modified polymer is a vinyl polymer.

[0033] The inner layer is prepared by means of 55-95 parts by weight of a first high-temperature resistant retortable and easy-to-remove material, 10-25 parts by weight of a second high-temperature resistant and easy-to-remove material, and 0.5-1.5 parts by weight of a processing aid. The first high-temperature resistant and easy-to-remove material is a propylene-based polymer modified with the brand name AT2912 produced by Mitsui Chemicals Co., Ltd.; the second high-temperature resistant and easy-to-remove material is a propylene-based polymer modified with the brand name AT2913 produced by Mitsui Chemicals Co., Ltd.

[0034] The weight ratio of the outer layer, middle layer and inner layer is (1-2):(1-3):1;

[0035] The processing aids used in the outer, middle, and inner layers are all functional masterbatches made from fluoropolymers and polyolefin resins.

[0036] The outer layer comprises 100 parts by weight of polypropylene. In this invention, the polypropylene used in the outer layer is a block copolymer polypropylene, specifically a block copolymer of propylene and ethylene; the melt index of the polypropylene used in the outer layer is preferably 1.0–2.0 g / 10 min, more preferably 1.5–1.8 g / 10 min, and the density is preferably 0.900–0.910 g / cm³. 3 More preferably, it is 0.902–0.905 g / cm³. 3 In a specific embodiment of the present invention, the polypropylene used for the outer layer is preferably block copolymer upblown PP produced by Borouge Chemical, grade RB709CF, with a melt index of 1.5 g / 10 min and a density of 0.905 g / cm³. 3 It has the characteristics of good transparency, good impact resistance and easy processing; the polypropylene used in the outer layer of the present invention is preferably ethylene-propylene block polypropylene, which has high toughness and stiffness, as well as a wide operating temperature range, and can be frozen or boiled.

[0037] Based on the mass fraction of polypropylene used in the outer layer, the raw materials for preparing the outer layer include 0.5 to 1 part of processing aids, preferably 0.6 to 0.8 parts. In this invention, the processing aids used in the outer layer are preferably functional masterbatches prepared from fluoropolymers and polyolefin resins, with a melt index preferably of 5.0 to 7.0 g / 10 min, more preferably 5.5 to 6.0 g / 10 min, and a density preferably of 0.890 to 0.910 g / cm³. 3 More preferably, it is 0.895–0.900 g / cm³. 3 In a specific embodiment of the present invention, the functional additive used in the outer layer is preferably PA0833PPR, manufactured by Suzhou Constance Engineering Plastics Co., Ltd., with a melt index of 6.0 g / min and a density of 0.900 g / cm³. 3 It has high temperature resistance, which can effectively reduce die buildup, reduce crystal points, lower extrusion pressure, and improve production efficiency.

[0038] The raw materials for preparing the intermediate layer, by mass parts, include 50-95 parts of polypropylene, preferably 60-80 parts. In this invention, the polypropylene used in the intermediate layer is a block copolymer polypropylene, specifically a block copolymer of propylene and ethylene; the melt index of the polypropylene used in the intermediate layer is preferably 1.0-2.0 g / 10 min, more preferably 1.5-1.8 g / 10 min, and the density is preferably 0.900-0.910 g / cm³. 3 More preferably, it is 0.902–0.905 g / cm³. 3 In a specific embodiment of the present invention, the polypropylene used in the middle layer is preferably Borouge Chemical's block copolymer upblown PP, grade RB707CF, with a melt index of 1.5 g / 10 min and a density of 0.905 g / cm³. 3 It has the characteristics of high tensile strength, high stiffness, good temperature resistance and easy processing.

[0039] Based on the mass fraction of polypropylene used in the middle layer, the raw materials for preparing the middle layer include 10-15 parts, preferably 12-13 parts, of a high-impact modified polymer. In this invention, the high-impact modified polymer is a vinyl-modified polymer; the melt index of the high-impact modified polymer is preferably 2.0-4.0 g / 10 min, more preferably 2.5-3.0 g / 10 min, and the density is preferably 0.880-0.890 g / cm³. 3 More preferably, it is 0.882–0.885 g / cm³. 3 In a specific embodiment of the present invention, the high-impact modified polymer material used for the outer layer is preferably a product of Mitsui Chemicals Co., Ltd., with the product name A-4085S, having a melt index of 3.0 g / 10 min and a density of 0.885 g / cm³. 3It has excellent low-temperature impact resistance and good processing performance.

[0040] Based on the mass fraction of polypropylene used in the middle layer, the raw materials for preparing the middle layer include 0.5 to 1 part of processing aids, preferably 0.6 to 0.8 parts. In this invention, the melt index, density, and specific grade of the processing aids used in the middle layer are preferably the same as those used in the outer layer, and will not be repeated here.

[0041] The raw materials for preparing the inner layer, by weight, include 55-95 parts, preferably 60-85 parts, of a first high-temperature retortable and easily removable material. In this invention, the first high-temperature retortable and easily removable material is a propylene-based modified polymer with the brand name AT2912 manufactured by Mitsui Chemicals Co., Ltd.; the melt index of the first high-temperature retortable and easily removable material is preferably 5.0-6.5 g / 10 min, more preferably 5.5-5.6 g / 10 min, and the density is preferably 0.890-0.910 g / cm³. 3 More preferably, it is 0.895–0.900 g / cm³. 3 In a specific embodiment of the present invention, the AT2912 has a melt index of 5.6 g / 10 min and a density of 0.900 g / cm³. 3 It has excellent heat resistance and easy peeling properties, and the heat seal strength decreases little after cooking.

[0042] Based on the mass fraction of the first high-temperature retortable and easy-to-remove material used in the inner layer, the raw materials for preparing the inner layer include 10 to 25 parts of a second high-temperature retortable and easy-to-remove material, preferably 15 to 20 parts. In this invention, the second high-temperature retortable and easy-to-remove material is a propylene-based polymer modified with the brand name AT2913 produced by Mitsui Chemicals Co., Ltd.; the melt index of the second high-temperature retortable and easy-to-remove material is preferably 5 to 7.5 g / 10 min, and the density is preferably 0.890 to 0.910 g / cm³. 3 More preferably, it is 0.895–0.900 g / cm³. 3 In a specific embodiment of the present invention, the AT2913 has a melt index of 6.8 g / 10 min and a density of 0.900 g / cm³. 3 It has excellent heat resistance and easy peeling properties, and the heat seal strength decreases little after cooking.

[0043] Based on the mass fraction of the first high-temperature retortable and easily peelable material used in the inner layer, the raw materials for preparing the inner layer include 0.5 to 1.5 parts of processing aids, preferably 0.6 to 1 part. In this invention, the melt index, density, and specific grade of the processing aids used in the inner layer are preferably the same as those used in the outer layer, and will not be repeated here.

[0044] In this invention, the weight ratio of the outer layer, middle layer, and inner layer is (1-2):(1-3):1, preferably 3:4:3, 3:5:2, 1:2:1, or 1:3:1; in this invention, the weight ratio of the outer layer, middle layer, and inner layer is also its thickness ratio. In a specific embodiment of this invention, the mass of raw materials required for each layer can be determined based on the total thickness of the target PP film and the thickness ratio of the three layers; the total thickness of the high-temperature resistant, easy-to-peel PP film is preferably 50-120 μm, more preferably 60-100 μm, and even more preferably 80 μm.

[0045] This invention also provides a method for preparing the high-temperature resistant, easy-to-peel PP film described above, comprising the following steps:

[0046] The raw materials for the outer, middle, and inner layers are co-extruded in three layers to obtain the high-temperature resistant, easy-to-peel PP film.

[0047] In a specific embodiment of the present invention, the three-layer co-extrusion process specifically includes: feeding the raw materials for the preparation of the outer layer, middle layer and inner layer into the outer layer, middle layer and inner layer extruders respectively for melt plasticization; conveying the obtained adhesive liquid to the die head; extruding and blowing film using the top blowing process to obtain a film bubble; after the film bubble is cooled by air, it passes through a stabilizing ring and herringbone arrangement to the upper traction rotation; after flattening the film bubble, it enters the corona treatment device through the guide roller for corona treatment; then the edges are trimmed; and then it enters the front and rear winding device through the lower traction clamping roller for front and rear winding, thus obtaining a high-temperature resistant, easy-to-peel PP film.

[0048] In this invention, the outer extruder, the middle extruder, and the inner extruder are preferably each provided with 5 heating zones, which are numbered 1 to 5 according to the order in which the raw materials pass through; the die head is provided with 4 heating zones, which are numbered 1 to 4 according to the order in which the raw materials pass through.

[0049] In this invention, the extrusion temperatures of the outer extruder, middle extruder, inner extruder, and each zone of the die are shown in Table 1:

[0050] Table 1. Extrusion temperatures of various zones in the outer, middle, and inner layer extruders and die.

[0051]

[0052]

[0053] In this invention, the extrusion pressure of the outer extruder is preferably 275-370 bar, the extrusion pressure of the middle extruder is preferably 305-430 bar, and the extrusion pressure of the inner extruder is preferably 290-385 bar.

[0054] This invention also provides a high-temperature resistant, retortable, easy-to-peel composite film, comprising a heat-sealing layer, a barrier layer, and a printing layer stacked sequentially; the heat-sealing layer is the high-temperature resistant, retortable, easy-to-peel PP film described in the above-described scheme or the high-temperature resistant, retortable, easy-to-peel PP film prepared by the preparation method described in the above-described scheme; the printing layer is a polyester film, and the barrier layer is an aluminum film or a polyester aluminized film. In this invention, the heat-sealing layer, the barrier layer, and the printing layer are preferably bonded together by a retortable adhesive, specifically, the outer layer of the PP film and the barrier layer are in contact.

[0055] In this invention, the polyester film, aluminum film, and aluminized polyester film are all commercially available products; specifically, the aluminized polyester film is prepared by vacuum aluminizing technology to coat the surface of the polyester film with a layer of aluminum. The aluminum layer is obtained; in this invention, the thickness of both the polyester film and the aluminized polyester film is preferably 12 μm, and the corona value of the printed surface of the polyester film is preferably 52 dynes or more, more preferably 52 to 56 dynes; the thickness of the aluminum film is preferably 7 μm. In a specific embodiment of this invention, the polyester film is purchased from Anhui Guofeng, specifically a printing polyester film with a corona value greater than 52 and a thickness of 12 μm. This invention controls the corona value of the printed surface within the above range, which can improve the composite adhesion; the aluminum film used is purchased from Nanfang Aluminum, specifically a grade A aluminum foil film with a thickness of 7 μm, which increases the barrier properties of the aluminum foil.

[0056] In this invention, the heat-sealing window of the high-temperature resistant retort easy-to-peel composite film is 120-230℃, the heat-sealing strength is 10-15N / 15mm, the seal is easy to tear, without stringing or residue, and there is no delamination after being boiled at 121℃ for 30 minutes; in a specific embodiment of this invention, the high-temperature resistant retort easy-to-peel composite film can be used for heat sealing of PP bowls, cups, plates, etc.

[0057] This invention also provides a method for preparing the high-temperature resistant, easy-to-peel composite film described above, comprising the following steps:

[0058] (1) The printed layer and the barrier layer are dry-laminated with adhesive and then cured to obtain a printed layer / barrier layer composite film.

[0059] (2) The printed layer / barrier layer composite film and the high temperature resistant retort easy-to-peel PP film are dry-laminated with adhesive and then cured to obtain a high temperature resistant retort easy-to-peel composite film.

[0060] This invention uses an adhesive to dry-laminate a printing layer and a barrier layer, followed by curing, to obtain a printing layer / barrier layer composite film. In this invention, the printing layer is preferably printed before bonding with the barrier layer, according to requirements. This invention does not have special requirements for the printing method; gravure printing, a process well-known to those skilled in the art, is acceptable. The printing ink is preferably a retort-resistant ink. In this invention, the adhesive used in step (1) is a retort-resistant adhesive, specifically preferably Dow Chemical's high-performance retort polyurethane adhesive 811A with a solid content of 60%, and the curing agent is 9L10 with a solid content of 75%. The preferred mass ratio of high-performance retort polyurethane adhesive 811A to curing agent 9L10 is 100:8. This invention does not have special requirements for the specific operating conditions of the dry lamination in step (1); a dry lamination process well-known to those skilled in the art is acceptable. In a specific embodiment of this invention, the adhesive is applied to the printing layer, and then the barrier layer is laminated. In a specific embodiment of the present invention, the preferred operating parameters for the lamination process in step (1) include: a coating solid content of 35% (diluted to the required solid content with ethyl acetate), a lamination heating roller temperature of approximately 70°C, a lamination speed of 120 m / min, and an adhesive application rate of 3.8–4.8 g / m. 2 The preferred value is 4.5 g / m 2 .

[0061] In this invention, the ripening temperature in step (1) is preferably 50±5℃, and the ripening time is preferably 12 to 24 hours.

[0062] After obtaining the printed layer / barrier layer composite film, the present invention uses an adhesive to dry-laminate the printed layer / barrier layer composite film and the PP film, followed by curing, to obtain a high-temperature resistant, easy-to-peel composite film. In the present invention, the adhesive used in step (2) is preferably a retort-resistant adhesive, the specific type of which is the same as in step (1), and will not be repeated here; the dry lamination operation parameters in step (2) are the same as in step (1), except that the lamination speed is adjusted to 130 g / min and the amount of adhesive applied is adjusted to 3.5-4.5 g / min. 2 More preferably 4.0 g / m 2 .

[0063] In this invention, the curing temperature in step (2) is preferably 50±5℃, and the curing time is preferably 48~72h. After curing, this invention preferably cools the cured composite film for 24h before slitting or bag making. This invention does not specifically limit the slitting or bag making process; any process well known to those skilled in the art can be used. In a specific embodiment of this invention, when making bags, the preferred operating conditions are: temperature 120~230℃, heat sealing pressure preferably 2.5~5kg, more preferably 3kg, and heat sealing time preferably 0.5~1.5 seconds, more preferably 1 second.

[0064] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments thereof, but this should not be construed as limiting the scope of protection of the present invention.

[0065] The sources of raw materials and performance parameters used in the examples are shown in Table 2.

[0066] Table 2 shows the source of raw materials and performance parameters used in the examples.

[0067]

[0068] Example 1

[0069] The raw material usage and layer thickness ratio for each layer are shown in Table 6. The total thickness of the high-temperature resistant, retortable, and easily peelable PP film is 80 μm. The preparation method is as follows:

[0070] The raw materials for the outer, middle, and inner layers are mixed in proportion by an automatic batching system and then fed into the outer, middle, and inner layer extruders. The raw materials for the outer, middle, and inner layers are melted and plasticized and then fed into the die head for extrusion and upward blowing. After being cooled by air, the cylinder is flattened by the stabilizing ring and herringbone arrangement and then enters the corona treatment device for corona treatment via guide rollers. After being trimmed, the cylinder is wound into the front and rear winding device via the lower traction clamping rollers for front and rear winding, thus obtaining a 75μm high-temperature resistant, easy-to-peel PP film.

[0071] The temperatures and pressures of the outer, middle, and inner layer extruders and dies are shown in Table 3.

[0072] Table 3 Extruder Temperature and Pressure

[0073] condition Zone 1 / ℃ Zone 2 / ℃ Zone 3 / ℃ 4 zones / ℃ 5 zones / ℃ Pressure / bar outer layer 205 215 220 210 206 313 Middle layer 200 210 215 208 200 345 Inner layer 193 200 210 205 197 321 mold head 210 220 225 215

[0074] The composite film was prepared using the above-mentioned high-temperature resistant, easy-to-peel PP film. The polyester film (PET) used was a printing polyester film with a corona value greater than 52 dynes on the printing surface, produced by Anhui Guofeng, and a thickness of 12μm. The aluminum foil used was a grade A aluminum foil film produced by Southern Aluminum Industry, with a thickness of 7μm.

[0075] The printed polyester film is printed using gravure printing according to the customer's specifications, using retort-resistant ink. The printed polyester film is then laminated with aluminum foil using a dry lamination process. The adhesive used is Dow Chemical's high-performance retort polyurethane adhesive 811A (60% solids content), and the curing agent is 9L10 (75% solids content). The mixing ratio of 811A and 9L10 is 100:8. The coating solids content is 35% (diluted with ethyl acetate). The temperature of the lamination heating roller is controlled at 70℃, the lamination speed is 120m / min, and the adhesive application rate is 4.5g / m². 2 After lamination, the film is placed in a curing room at 50℃±5℃ for 12 hours to obtain a PET / Al composite film.

[0076] The PET / AL composite film and PP film are laminated using a dry lamination process. The adhesive used is Dow Chemical's high-performance retortable polyurethane adhesive 811A (60% solids content), and the curing agent is 9L10 (75% solids content). The mixing ratio of 811A to 9L10 is 100:8. The coating solids content is 35%. The temperature of the lamination heating roller is controlled at 70℃, the lamination speed is 130 m / min, and the adhesive application rate is 4.0 g / m³. 2 After lamination, the film is placed in a curing room at 50℃±5℃ for 72 hours, cooled for 24 hours, and then cut to obtain a high-temperature resistant, easy-to-peel composite film.

[0077] Examples 2-3

[0078] The raw material usage and layer thickness ratio of each layer are shown in Table 6. The total thickness of the high-temperature resistant, easy-to-peel PP film is 80 μm. The preparation method is the same as in Example 1, and the high-temperature resistant, easy-to-peel PP film and composite film are obtained.

[0079] Comparative Example 1

[0080] Traditional methods use PE and PP co-extrusion to prepare PP easy-peel film. The raw materials used for each layer are shown in Table 4. The thickness ratio of the outer layer, middle layer and inner layer is 3:4:3, and the total thickness of the film is 80μm.

[0081] Table 4 Comparative Example 1: Raw material usage for each layer

[0082]

[0083] In Table 4, 5960G is metallocene high-density polyethylene, purchased from Dow Chemical; PE104-001 is a processing aid, purchased from Daikin Industries, Ltd.; 2103C is a high-temperature resistant easy-peel material, purchased from LyondellBasell; and PA0833PPR is a processing aid, purchased from Constantech.

[0084] The film preparation method is the same as in Example 1, except that the temperature and pressure of each extruder are adjusted, as shown in Table 5.

[0085] Table 5 Comparative Example 1: Extruder Temperature and Pressure

[0086] temperature Zone 1 Zone 2 Zone 3 4th District 5th District Pressure (bar) outer layer 180 185 195 190 180 335 Middle layer 185 190 195 195 185 355 Inner layer 195 205 215 210 198 328 mold head 205 210 220 208

[0087] The PP film prepared under the above conditions was then used to prepare a composite film according to the method in Example 1.

[0088] Comparative Example 2

[0089] The amount of raw materials used in each layer and the layer thickness ratio are shown in Table 6. The total thickness of the PP film is 80 μm. The preparation method is the same as in Example 1, and PP film and composite film are obtained.

[0090] Table 6. Raw material usage (parts by mass) for Examples 1-3 and Comparative Example 2

[0091] raw material Example 1 Example 2 Example 3 Comparative Example 2 RB709CF 100 100 100 100 PA0833PPR 0.8 1.2 1.5 1.5 RB707CF block copolymer PP 55 75 93 93 A-4085S 10 12 15 PA0833PPR 0.8 1.2 1.5 1.5 AT2912 57 72 95 43 AT2913 25 18 12 38 PA0833PPR 0.8 1.0 1.2 0.8 Layer thickness ratio (mass ratio of each layer) 3 / 5 / 2 1:2:1 1:3:1 1:2:1

[0092] Performance testing:

[0093] The tensile strength and elongation at break of the high-temperature resistant retortable easy-peel PP films prepared in Examples 1-3 and Comparative Examples 1-2 were tested before and after retorting. The retorting temperature was 121℃ and the time was 60min.

[0094] The peel strength of the composite films prepared in Examples 1-3 and Comparative Examples 1-2 before and after cooking was tested, including the peel strength of PET / Al and the peel strength of Al / PP. The cooking temperature was 121°C and the cooking time was 45 min.

[0095] The PET / AL / PP composite films prepared in Examples 1-3 and Comparative Examples 1-2 were heat-sealed with PP cups, and the heat-sealing strength before and after cooking was tested. The heat-sealing conditions were: heat-sealing temperature 170℃, pressure 3kg, time 1 second, cooking temperature 121℃, time 45min.

[0096] Observe the surface of the heat-sealed line after heat sealing to see if it is smooth and whether it is stringy when peeled off; test the sealing performance of the composite film after heat sealing.

[0097] The impact strength of PP was tested at room temperature, 0℃ and -10℃.

[0098] The test results are shown in Tables 7 and 8.

[0099] Table 7. Test Results of Mechanical Properties of High-Temperature Resistant and Resistant Removable PP Film

[0100]

[0101] Table 8. Performance Test Results of Composite Membrane

[0102]

[0103]

[0104] As can be seen from the data in Tables 7 and 8, the high-temperature resistant PP film prepared by this invention exhibits minimal change in mechanical properties after cooking, indicating excellent high-temperature cooking resistance. Furthermore, the composite film prepared using the PP film of this invention shows relatively stable peel strength in both the PET / Al layer and the Al / PP layer before and after cooking. The composite film also exhibits stable strength after heat sealing, with the heat sealing strength remaining stable at 10–15 N / 15 mm before and after cooking. Although the PP films obtained in Comparative Examples 1 and 2 have acceptable mechanical properties, the resulting composite films have low heat sealing strength, resulting in leakage at the seal. Moreover, the composite film prepared in Comparative Example 1 shows delamination and stringing when peeled off, and the impact strength of the composite films prepared in Comparative Examples 1 and 2 is relatively low.

[0105] In addition, the PET / AL / PP composite films and PP cups obtained in Examples 1-3 and Comparative Examples 1-2 were heat-sealed at different temperatures (120-230°C, pressure 3 kg, time 1 second) to test the heat-sealing strength before and after cooking. The cooking temperature was 121°C and the time was 45 min. The results are as follows: Figures 1-2 As shown. According to Figures 1-2 It can be seen that, within the range of 120 to 230°C, the high-temperature resistant and easy-to-peel PP films prepared by this invention all have moderate heat-sealing strength, indicating that they have a wide heat-sealing window and good high-temperature resistance. In contrast, the composite films prepared by Comparative Examples 1 and 2 have low heat-sealing strength, and their strength decreases significantly after high-temperature cooking, making them prone to leakage at the seal.

[0106] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A high-temperature resistant, retortable, and easy-to-peel PP film, characterized in that, It is made of three layers: outer layer, middle layer and inner layer, through co-extrusion blown film. By mass, the outer layer is prepared from 100 parts of polypropylene and 0.5 to 1.5 parts of processing aids; the polypropylene used in the outer layer is ethylene-propylene block polypropylene. By mass, the raw materials for preparing the middle layer are 50-95 parts polypropylene, 10-15 parts high-impact modified polymer, and 0.5-1.5 parts processing aids; the high-impact modified polymer is a vinyl polymer; the polypropylene used in the middle layer is ethylene-propylene block polypropylene. By weight, the raw materials for preparing the inner layer are 55-95 parts of a first high-temperature resistant retortable and easy-to-remove material, 10-25 parts of a second high-temperature resistant and easy-to-remove material, and 0.5-1.5 parts of processing aids; the first high-temperature resistant and easy-to-remove material is a propylene-based polymer modified with the brand name AT2912 produced by Mitsui Chemicals Co., Ltd.; the second high-temperature resistant and easy-to-remove material is a propylene-based polymer modified with the brand name AT2913 produced by Mitsui Chemicals Co., Ltd. The weight ratio of the outer layer, middle layer and inner layer is (1-2):(1-3):1; The processing aids used in the outer, middle and inner layers are all functional masterbatches made of fluoropolymers and polyolefin resins. The outer layer uses polypropylene with a melt index of 1.0–2.0 g / 10 min and a density of 0.900–0.910 g / cm³. 3 The polypropylene used in the middle layer has a melt index of 1.0–2.0 g / 10 min and a density of 0.900–0.910 g / cm³. 3 The high-impact modified polymer material used in the middle layer has a melt index of 2.0–4.0 g / 10 min and a density of 0.880–0.890 g / cm³. 3 ; The outer layer uses polypropylene of grade RB709CF produced by Borouge Chemicals; the middle layer uses polypropylene of grade RB707CF produced by Borouge Chemicals; and the middle layer uses vinyl-modified polymer of grade A-4085S produced by Mitsui Chemicals Co., Ltd., a high-impact modified polymer. The processing aids used in the outer, middle, and inner layers are processing aids of grade PA0833PPR produced by Suzhou Constance Engineering Plastics Co., Ltd. The total thickness of the high-temperature resistant, easy-to-peel PP film is 50–120 μm.

2. The high-temperature resistant, easy-to-peel PP film according to claim 1, characterized in that, The first high-temperature resistant, easy-to-remove material used in the inner layer has a melt index of 5.0–6.5 g / 10 min and a density of 0.890–0.910 g / cm³. 3 The second high-temperature resistant, easy-to-remove material used in the inner layer has a melt index of 6.0–7.5 g / 10 min and a density of 0.890–0.910 g / cm³. 3 .

3. The high-temperature resistant, easy-to-peel PP film according to claim 1, characterized in that, The processing aids used in the outer, middle, and inner layers have an independent melt index of 5.0–7.0 g / 10 min and an independent density of 0.890–0.910 g / cm³. 3 .

4. The method for preparing the high-temperature resistant, easy-to-peel PP film according to any one of claims 1 to 3, characterized in that, Includes the following steps: The raw materials for the outer, middle, and inner layers are co-extruded in three layers to obtain the high-temperature resistant, easy-to-peel PP film.

5. A high-temperature resistant, retortable, and easily peelable composite film, comprising a heat-sealing layer, a barrier layer, and a printing layer stacked sequentially; wherein the heat-sealing layer is the high-temperature resistant, retortable, and easily peelable PP film according to any one of claims 1 to 3 or the high-temperature resistant, retortable, and easily peelable PP film prepared by the preparation method according to claim 4; wherein the printing layer is a polyester film, and the barrier layer is an aluminum film or a polyester aluminized film.

6. The method for preparing the high-temperature resistant, easy-to-peel composite film according to claim 5, characterized in that, Includes the following steps: (1) The printed layer and the barrier layer are dry-laminated with an adhesive and then cured to obtain a printed layer / barrier layer composite film. (2) The printed layer / barrier layer composite film and the high temperature resistant retort easy-to-peel PP film are dry-laminated with adhesive and then cured to obtain a high temperature resistant retort easy-to-peel composite film.

7. The preparation method according to claim 6, characterized in that, In step (1), the amount of adhesive applied is 3.8–4.8 g / m³. 2 In step (2), the amount of adhesive applied is 3.5–4.5 g / m³. 2 .

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