Multi-layer co-extrusion linear easy-to-tear heat-sealable BOPA film and preparation method thereof

Abstract

The invention relates to the field of film packaging, in particular to a multi-layer co-extrusion linear easy-to-tear heat-sealable BOPA film and a preparation method thereof. According to the multilayer co-extruded linear easy-to-tear heat-sealable BOPA film provided by the invention, the film layer structure comprises the toughening anti-sticking layer, the linear easy-to-tear layer, the barrier core layer, the bonding layer and the heat-sealing layer, the toughening anti-sticking layer can enhance the toughness of the film and improve the mechanical property, and the linear easy-to-tear layer not only provides the linear easy-to-tear property for the film, but also provides the heat-sealing property for the film. Aromatic polyamide resin or long-carbon-chain aliphatic polyamide resin in the raw materials further improves the barrier property in cooperation with the barrier core layer, the bonding layer adopts maleic anhydride grafted polyolefin to bond the barrier core layer and the heat sealing layer, and the material compatibility is high. The invention further provides a preparation method of the multi-layer co-extruded linear easy-to-tear heat-sealable BOPA film, and the packaging film with good barrier property, linear easy-to-tear property, heat sealability and mechanical property is prepared through one-step molding by adopting a multi-layer co-extrusion and two-way stretching technology.

Description

Technical Field

[0001] The invention relates to the field of film packaging, and in particular to a multi-layer co-extruded linear easy-tear heat-sealable BOPA film and a preparation method thereof. Background Art

[0002] BOPA film is widely used in the field of film flexible packaging due to its excellent mechanical strength, puncture resistance, transparency, oil and chemical solvent resistance, and non-toxicity. However, due to the high melting point of nylon, it does not have heat sealability. In the prior art, nylon is usually compounded with heat-sealable materials such as polyolefins such as polypropylene and polyethylene using solvent-based adhesives for application in the packaging field. However, the heat-sealable layer obtained by this method is usually thicker, and the production cost of the product is increased due to the addition of the glue compounding process, which also limits the advantages of the nylon film itself to a certain extent.

[0003] In addition, as a packaging material, it is also necessary to have good barrier properties and tear-away properties to extend the shelf life of the contents and protect the quality of the contents, while also focusing on optimizing the customer experience. In actual production, in order to integrate the above functions, it is necessary to add production processes such as coating and lamination, which will also increase the production cost of the product and affect the production capacity efficiency.

[0004] On May 4, 2021, Chinese patent CN213108563U disclosed a composite film for packaging, whose film layer structure includes a polyester layer, an ink layer, a first adhesive layer, an aluminum foil layer, a second adhesive layer, a toughened nylon layer, a third adhesive layer, a polyethylene layer, a fourth adhesive layer and a heat-sealable nylon layer, and has excellent barrier properties, mechanical strength and toughness. The total thickness of the film layer is 68~148 μm, wherein the polyethylene layer has a thickness of 12~30 μm, the fourth adhesive layer is a water-based acrylic adhesive or a two-component polyurethane adhesive, and the independent thickness is 2~5 μm, and the heat-sealable nylon layer has a thickness of 15~30 μm, including a heat-sealable nylon surface layer, a nylon core layer and a nylon surface layer. It can be seen that in the prior art, in order to achieve the heat sealability of nylon, there is a sacrifice that has to increase the thickness of the film.

[0005] Therefore, how to achieve good barrier properties, linear tearability, heat sealing and mechanical properties of the film through one-step processing and molding is still an urgent problem to be solved in order to further expand the application field of the film. Summary of the invention

[0006] In order to solve the technical problem of how to achieve good barrier, linear tear, heat sealing and mechanical properties of the film by one-step processing, the present invention provides a multi-layer co-extruded linear tearable heat-sealable BOPA film, the film layer structure of which includes a toughening anti-adhesive layer, a linear tearable layer, a barrier core layer, an adhesive layer and a heat sealing layer arranged in sequence from top to bottom; In terms of weight percentage, the toughened anti-adhesive layer comprises 0.01% to 1% of an anti-adhesive agent, 0.01% to 1% of a slip agent, and 98% to 99.98% of a toughened nylon resin; The linear tearable layer comprises 10% to 30% of special nylon resin and 70% to 90% of nylon 6 resin; The barrier core layer comprises 100% EVOH resin; The bonding layer comprises 100% maleic anhydride grafts; The heat-sealing layer comprises 0.5% to 2% of an anti-adhesive agent, 0.5% to 2% of a lubricant and 96% to 99% of a heat-sealing resin.

[0007] In one embodiment, the anti-adhesive agent is any one of silicon dioxide, talc and calcium carbonate, or any combination thereof.

[0008] In one embodiment, the lubricant is any one of PE wax, erucamide and oleamide, or any combination thereof.

[0009] In one embodiment, the toughened nylon resin is any one or a combination of any two of PA6-b-12 copolymer, PA6-b-1010 copolymer and PA6-b-PEG copolymer.

[0010] In one embodiment, the special nylon resin is an aromatic polyamide resin or a long carbon chain aliphatic polyamide resin, or a mixture of the two in a weight percentage ratio of (5-7): (3-5).

[0011] Furthermore, the aromatic polyamide resin is formed by condensation of an aliphatic dicarboxylic acid having 6 to 12 carbon atoms and an aromatic diamine, or by condensation of an aromatic diacid and an aliphatic diamine having 6 to 12 carbon atoms; the long-chain aliphatic polyamide resin is formed by condensation of an aliphatic dicarboxylic acid having 4 to 18 carbon atoms and an aliphatic diamine having 4 to 18 carbon atoms.

[0012] In one embodiment, the maleic anhydride grafted compound is any one of PE-g-MHA and PP-g-MHA.

[0013] In one embodiment, the heat-sealing resin is any one of PE, modified PE, terpolymer PP and modified PP, or any combination thereof.

[0014] In one embodiment, the total thickness of the multi-layer co-extruded linear easy-tear heat-sealable BOPA film layer is 30~60μm; wherein the thickness ratio of the toughened anti-sticking layer, the linear easy-tear layer, the barrier core layer, the adhesive layer and the heat-sealing layer is (1~2):(2~3):(4~5):(1~2):(2~3).

[0015] The present invention also provides a method for preparing the multi-layer co-extruded linear easy-tear heat-sealable BOPA film as described above, comprising the following steps: The raw materials of the toughened anti-sticking layer, the linear easy-tear layer, the barrier core layer, the adhesive layer and the heat-sealing layer are respectively put into extruder 1, extruder 2, extruder 3, extruder 4 and extruder 5 according to weight percentage, melted, plasticized, extruded, and flowed out through a T-die to form a molten thick sheet; It is cooled and solidified into a cast thick sheet by the action of chilled rollers and high-pressure air knives; The cast thick sheet is subjected to water treatment and then subjected to synchronous biaxial stretching; The stretched film is subjected to heat setting treatment, and then cooled and corona treated, and then rolled up to obtain the multi-layer co-extruded linear easy-tear heat-sealable BOPA film; Among them, the melting temperature of the extruder is 220~250℃, the temperature of the chilled roller is 30~60℃, the bidirectional synchronous stretching temperature is 150~205℃, the stretching ratio is (3.0~3.6)×(3.0~3.6), and the heat setting treatment temperature is 160~210℃.

[0016] The multi-layer co-extruded linear easy-tear heat-sealable BOPA film provided by the present invention has a film layer structure comprising a toughened anti-sticking layer, a linear easy-tear layer, a barrier core layer, an adhesive layer and a heat-sealing layer. The toughened anti-sticking layer can enhance the toughness of the film and improve the mechanical properties; the linear easy-tear layer not only provides the film with linear easy tearing property and enhances the user experience, but the aromatic polyamide resin or long-carbon chain aliphatic polyamide resin in the raw material can also improve the barrier property to a certain extent, and synergize with the barrier core layer to enable the film to obtain excellent oxygen barrier performance, which is beneficial to the quality and freshness preservation during food packaging; and the adhesive layer particularly adopts maleic anhydride grafted polyolefin as the adhesive resin to bond the barrier core layer and the heat-sealing layer, thereby increasing the material compatibility, avoiding the occurrence of film stratification, and improving the quality and appearance of the film.

[0017] The invention provides a method for preparing a multi-layer co-extruded linear easy-tear heat-sealable BOPA film, which adopts a multi-layer co-extrusion and biaxial stretching technology and can be formed in one step without glue compounding, thereby obtaining a packaging film with good barrier properties, linear easy tearing properties, heat sealing properties and mechanical properties.

[0018] In summary, compared with the prior art, the multi-layer co-extruded linear easy-tear heat-sealable BOPA film and the preparation method thereof provided by the present invention can be formed in one step without glue compounding to prepare a packaging film with barrier properties, linear easy-tear properties, heat-seal properties and mechanical properties. The material compatibility is good and the film quality is high, and it has sufficient practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 This is a schematic diagram of the film layer structure of the multi-layer co-extruded linear easy-tear heat-sealable BOPA film provided in Example 1 of the present invention.

[0021] Reference numerals: DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] In the description of the present invention, it should be noted that the terms "upper", "lower", "inside", "outside", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0024] Example 1 This embodiment provides a multi-layer co-extruded linear easy-tear heat-sealable BOPA film, such as Figure 1 As shown, the film layer structure includes a toughened anti-sticking layer 10, a linear easy-tear layer 20, a barrier core layer 30, an adhesive layer 40 and a heat-sealing layer 50 arranged in sequence from top to bottom; the total thickness of the film layer is 33 μm, wherein the thickness ratio of the toughened anti-sticking layer, the linear easy-tear layer, the barrier core layer, the adhesive layer and the heat-sealing layer is 1:2:4:1:3.

[0025] The multi-layer co-extruded linear easy-tear heat-sealable BOPA film is prepared according to the following steps: The raw materials of the toughened anti-sticking layer, the linear easy-tear layer, the barrier core layer, the adhesive layer and the heat-sealing layer are respectively put into extruder 1, extruder 2, extruder 3, extruder 4 and extruder 5 according to weight percentage, melted, plasticized and extruded at 220-250° C., and flowed out through a T-die to form a molten thick sheet; It is cooled and solidified into a cast thick sheet by the action of a 45°C chilled roller and a high-pressure air knife; The cast thick sheet is subjected to water treatment and then subjected to synchronous biaxial stretching at a stretching temperature of 180° C. and a stretching ratio of 3.2×3.2; The stretched film is heat-set at 200° C., cooled, corona-treated, and then rolled up to obtain the multi-layer co-extruded linear easy-tear heat-sealable BOPA film.

[0026] In this embodiment, preferably, the raw materials of the toughened anti-sticking layer are as follows by weight: 0.5% anti-adhesive agent, 0.5% lubricant and 99% toughened nylon resin; wherein the anti-adhesive agent is silicon dioxide, the lubricant is a mixture of erucamide and oleamide in a weight percentage of 4:1; the toughened nylon resin is PA6-b-12 copolymer.

[0027] In this embodiment, preferably, the raw materials of the linear tearable layer are as follows: 10% special nylon resin and 90% nylon 6 resin by weight percentage; wherein the special nylon resin is an aromatic polyamide resin, which is formed by condensation of an aliphatic dicarboxylic acid having 6 carbon atoms and meta-xylylenediamine.

[0028] In this embodiment, preferably, the raw material of the barrier core layer is 100% EVOH resin by weight.

[0029] In this embodiment, preferably, the raw material of the bonding layer is 100% by weight of maleic anhydride grafted material; wherein the maleic anhydride grafted material is a PE-g-MHA copolymer.

[0030] In this embodiment, preferably, the raw materials of the heat sealing layer are 1% anti-blocking agent, 1% lubricant and 98% heat sealing resin in weight percentage; wherein the anti-blocking agent is talcum powder, the lubricant is PE wax, and the heat sealing resin is LLDPE resin.

[0031] Example 2 This embodiment provides a multi-layer co-extruded linear easy-tear heat-sealable BOPA film; wherein the toughened nylon resin in the toughened anti-adhesive layer is a PA6-b-1010 copolymer; the raw materials of the linear easy-tear layer are 15% by weight of a special nylon resin and 85% by weight of a nylon 6 resin, and the special nylon resin is an aromatic polyamide resin. The remaining raw materials, proportions and preparation steps are the same as those in Example 1.

[0032] Example 3 This embodiment provides a multi-layer co-extruded linear easy-tear heat-sealable BOPA film; wherein the toughened nylon resin in the toughened anti-adhesive layer is a PA6-b-PEG copolymer; the raw materials of the linear easy-tear layer are 20% by weight of a special nylon resin and 80% by weight of a nylon 6 resin, and the special nylon resin is a long carbon chain aliphatic polyamide resin, which is polycondensed from sebacic acid and pentamethylenediamine. The remaining raw materials, proportions and preparation steps are the same as those in Example 1.

[0033] Comparative Example 1 This comparative example is a commercially available EHA film product, which is prepared by co-extrusion and biaxial stretching of five layers of PA6, PA6, EVOH, PA6 and PA6, and does not have heat sealing properties and linear tearability.

[0034] Comparative Example 2 The difference between this comparative example and Example 1 of the present invention is that the toughened anti-adhesive layer is replaced by an anti-adhesive layer, and the raw materials of the anti-adhesive layer are 0.5% anti-adhesive agent, 0.5% slip agent and 99% PA6 resin by weight percentage, wherein the anti-adhesive agent is silicon dioxide, and the slip agent is erucic acid amide and oleic acid amide mixed in a weight percentage ratio of 4:1; the raw materials of the linear easy-tear layer are 15% special nylon resin and 85% nylon 6 resin by weight percentage, and the special nylon resin is aromatic polyamide resin. The remaining raw materials, proportions and preparation steps are the same as those of Example 1.

[0035] Comparative Example 3 The difference between this comparative example and Example 1 of the present invention is that the linear easy-tear layer is replaced by a nylon resin layer, and the raw material of the nylon resin layer is 100% nylon 6 resin by weight. The remaining raw materials, proportions and preparation steps are the same as those of Example 1.

[0036] Comparative Example 4 The difference between this comparative example and Example 1 of the present invention is that the bonding layer is replaced by a nylon resin layer, and the raw material of the nylon resin layer is 100% nylon 6 resin by weight. The remaining raw materials, proportions and preparation steps are the same as those of Example 1.

[0037] Comparative Example 5 The difference between this comparative example and Example 1 of the present invention is that the heat seal layer is replaced by a nylon resin layer, and the raw materials of the nylon resin layer are 1% anti-blocking agent, 1% lubricant and 98% nylon 6 resin by weight, wherein the anti-blocking agent is talcum powder and the lubricant is PE wax. The remaining raw materials, proportions and preparation steps are the same as those of Example 1.

[0038] The performance tests were performed on the multi-layer co-extruded linear easy-tear heat-sealable BOPA films prepared in Examples 1 to 3, the EHA films provided in Comparative Example 1, and the BOPA films prepared in Comparative Examples 2 to 5; Among them, tensile strength and elongation at break are tested in accordance with GB / T 20218-2021 Biaxially oriented polyamide (nylon) film; Oxygen transmission rate is tested according to ASTM F1927; Evaluation of linear tearing performance: 25 film samples were taken for measurement. Films with a length (MD direction) and width (TD direction) of 220 mm × 40 mm were cut. A 20 mm tear was cut in the middle of the film. The film was torn 200 mm along the crack direction at a constant speed. The maximum distance that the tear deviated from the center line of the tear opening during the tearing process was measured, i.e., the deviation displacement S. β , if the tear displacement S0 is 200 mm, the average deviation displacement S β ≤6 mm, the film has good linear tearing property, which is marked as ▲; otherwise, the film has poor linear tearing property or no linear tearing property, which is marked as ×; Heat sealability evaluation: Heat sealability test was conducted according to QB / T 2358-1998 Test method for heat sealability of plastic film packaging bags. Good heat sealability was recorded as ▲, poor heat sealability or no heat sealability was recorded as ×. The film performance test results provided by Examples 1 to 3 and Comparative Examples 1 to 5 are shown in Table 1: Table 1 Test results of film properties provided by Examples 1 to 3 and Comparative Examples 1 to 5

[0039] According to the data in Table 1, the tensile strength, elongation at break and oxygen permeability of the multi-layer co-extruded linear easy-tear heat-sealable BOPA films prepared in Examples 1 to 3 of the present invention are significantly better than those of the commercially available EHA film provided in Comparative Example 1. In addition, the BOPA film provided by the present invention not only meets the requirements of film packaging toughness and barrier properties, but also has linear easy tearing and heat sealing properties, and can be formed into a finished product in one step without the need for glue compounding, which effectively solves the technical problem of how to achieve good barrier, linear easy tearing, heat sealing and mechanical properties of the film in one step of processing and forming.

[0040] Furthermore, according to the data in Table 1, replacing any of the toughened anti-sticking layer, the linear tear-away layer, the adhesive layer and the heat-sealing layer in the film structure with a nylon resin layer will have a negative impact on the film performance, including but not limited to the impact on the film's mechanical properties, heat sealing properties or film quality.

[0041] Although the terms such as toughened anti-adhesive, linear tear, bonding, heat seal, barrier property, heat sealability, multi-layer co-extrusion, biaxial stretching, etc. are used more frequently in this article, the possibility of using other terms is not excluded. The use of these terms is only for more convenient description and explanation of the essence of the present invention; interpreting them as any additional limitation is contrary to the spirit of the present invention.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements 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 multi-layer co-extruded linear easy-tear heat-sealable BOPA film, characterized in that: The film layer structure includes a toughening anti-sticking layer, a linear easy-tear layer, a barrier core layer, an adhesive layer and a heat-sealing layer arranged in sequence from top to bottom; In terms of weight percentage, the toughened anti-adhesive layer comprises 0.01% to 1% of an anti-adhesive agent, 0.01% to 1% of a slip agent, and 98% to 99.98% of a toughened nylon resin; The linear tearable layer comprises 10% to 30% of special nylon resin and 70% to 90% of nylon 6 resin; The barrier core layer comprises 100% EVOH resin; The bonding layer comprises 100% maleic anhydride grafts; The heat-sealing layer comprises 0.5% to 2% of an anti-adhesive agent, 0.5% to 2% of a lubricant and 96% to 99% of a heat-sealing resin.

2. The multi-layer co-extruded linear easy-tear heat-sealable BOPA film according to claim 1, characterized in that: The anti-adhesive agent is any one of silicon dioxide, talcum powder and calcium carbonate or any combination thereof.

3. The multi-layer co-extruded linear easy-tear heat-sealable BOPA film according to claim 1, characterized in that: The lubricant is any one of PE wax, erucamide and oleamide, or any combination thereof.

4. The multi-layer co-extruded linear easy-tear heat-sealable BOPA film according to claim 1, characterized in that: The toughened nylon resin is any one or any combination of PA6-b-12 copolymer, PA6-b-1010 copolymer and PA6-b-PEG copolymer.

5. The multi-layer co-extruded linear easy-tear heat-sealable BOPA film according to claim 1, characterized in that: The special nylon resin is an aromatic polyamide resin or a long carbon chain aliphatic polyamide resin, or a mixture of the two in a weight percentage ratio of (5-7): (3-5).

6. The multi-layer co-extruded linear easy-tear heat-sealable BOPA film according to claim 5, characterized in that: The aromatic polyamide resin is formed by polycondensation of an aliphatic dicarboxylic acid having 6 to 12 carbon atoms and an aromatic diamine, or by polycondensation of an aromatic diacid and an aliphatic diamine having 6 to 12 carbon atoms; The long carbon chain aliphatic polyamide resin is prepared by polycondensation of an aliphatic dicarboxylic acid having 4 to 18 carbon atoms and an aliphatic diamine having 4 to 18 carbon atoms.

7. The multi-layer co-extruded linear easy-tear heat-sealable BOPA film according to claim 1, characterized in that: The maleic anhydride grafted product is any one of PE-g-MHA and PP-g-MHA.

8. The multi-layer co-extruded linear easy-tear heat-sealable BOPA film according to claim 1, characterized in that: The heat-sealing resin is any one of PE, modified PE, ternary copolymer PP and modified PP, or any combination thereof.

9. The multi-layer co-extruded linear easy-tear heat-sealable BOPA film according to claim 1, characterized in that: The total thickness of the multi-layer co-extruded linear easy-tear heat-sealable BOPA film layer is 30-60 μm; The thickness ratio of the toughened anti-sticking layer, the linear tear-away layer, the barrier core layer, the adhesive layer and the heat-sealing layer is (1-2): (2-3): (4-5): (1-2): (2-3).

10. A method for preparing the multi-layer co-extruded linear easy-tear heat-sealable BOPA film according to any one of claims 1 to 9, characterized in that: The following steps are involved: The raw materials of the toughened anti-sticking layer, the linear easy-tear layer, the barrier core layer, the adhesive layer and the heat-sealing layer are respectively put into extruder 1, extruder 2, extruder 3, extruder 4 and extruder 5 according to weight percentage, melted, plasticized, extruded, and flowed out through a T-die to form a molten thick sheet; It is cooled and solidified into a cast thick sheet by the action of chilled rollers and high-pressure air knives; The cast thick sheet is subjected to water treatment and then subjected to synchronous biaxial stretching; The stretched film is subjected to heat setting treatment, and then cooled and corona treated, and then rolled up to obtain the multi-layer co-extruded linear easy-tear heat-sealable BOPA film; Among them, the melting temperature of the extruder is 220~250℃, the temperature of the chilled roller is 30~60℃, the bidirectional synchronous stretching temperature is 150~205℃, the stretching ratio is (3.0~3.6)×(3.0~3.6), and the heat setting treatment temperature is 160~210℃.

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