A high-toughness biaxially oriented polyamide film and its preparation method

Abstract

This invention relates to the field of film packaging technology, and particularly to a high-toughness biaxially oriented polyamide film and its preparation method. The high-toughness biaxially oriented polyamide film and its preparation method provided by this invention specifically utilize a polyamide toughening agent to overcome the incompatibility between the toughening agent and nylon materials, improving the toughness of the polyamide film. Furthermore, by controlling the composition ratio of the polyamide toughening agent, the dehydration rate of the material at low temperatures can be controlled, reducing low-temperature embrittlement. In addition, by combining a polyamide copolymer with weaker inter-chain hydrogen bonding and lower crystallization speed and melting point, the formation of polyamide crystalline regions is reduced. The low water absorption rate of polyamide 12 further reduces the changes in performance and size caused by water absorption. This solves the technical problem of how to prepare a high-toughness polyamide film without incompatibility, comprehensively achieving high toughness, low-temperature resistance, high tensile strength, excellent drawing depth, puncture resistance, and ease of ultra-thin processing, demonstrating good market application prospects.

Description

Technical Field

[0001] This invention relates to the field of film packaging technology, and in particular to a high-toughness biaxially oriented polyamide film and its preparation method. Background Technology

[0002] Biaxially oriented polyamide film, also known as biaxially oriented nylon film (BOPA), possesses excellent mechanical, optical, electrical insulation, and gas barrier properties. It is also easy to print, oil-resistant, chemical solvent-resistant, and has a wide operating temperature range. As a result, it is widely used in various fields such as food packaging, daily necessities packaging, electronic product packaging, and pharmaceutical product packaging, and occupies a pivotal position in the packaging industry.

[0003] However, under low-temperature conditions, ordinary nylon 6 materials suffer from insufficient toughness. Nylon used in frozen food packaging, especially in vacuum-sealed food packaging with sharp edges, is prone to tearing, leading to loss of the packaging's shelf-life and product spoilage. Similarly, in the pharmaceutical blister packaging and lithium-ion battery industries, products require certain deep-drawing performance to protect the aluminum foil layer in multi-layered composite structures. Therefore, improving the toughness of biaxially oriented polyamide films has become an urgent need.

[0004] In the modification industry, a common method to improve the toughness of products is by adding polyolefin elastomers and rubber-based elastomers. However, these methods are often ineffective for very thin films. Because the films are very thin, and polyolefin and rubber-based elastomers are non-polar materials, even after grafting, their compatibility with polyamide films remains significantly lacking. Therefore, even with the addition of grafted polyolefin and rubber-based elastomers, due to their poor compatibility with the nylon system, not only is the toughening effect insignificant, but it can also lead to a sharp decline in tensile properties. Furthermore, the addition of polyolefin and rubber-based elastomers can also affect the barrier properties of the film, significantly reducing the shelf life of packaged products.

[0005] Therefore, existing BOPA films often struggle to simultaneously achieve compatibility, barrier properties, deep-drawing formability, and toughness, significantly limiting their application in the lithium-ion battery, pharmaceutical blister packaging, and frozen food packaging industries. Clearly, developing a high-toughness polyamide film while avoiding incompatibilities has become a pressing issue. Summary of the Invention

[0006] To address the technical problem of how to avoid incompatibility in the preparation of a high-toughness polyamide film, this invention provides a high-toughness biaxially oriented polyamide film, the film structure of which includes a lower surface layer, an intermediate layer and an upper surface layer arranged sequentially from bottom to top;

[0007] By weight, the lower surface layer comprises 1 to 10 parts of anti-sticking masterbatch, 5 to 50 parts of polyamide toughening agent and 40 to 94 parts of polyamide 6;

[0008] The intermediate layer comprises 5-50 parts of polyamide toughening agent, 5-20 parts of polyamide copolymer, 5-15 parts of polyamide 12 and 15-85 parts of polyamide 6;

[0009] The upper surface layer comprises 1-10 parts of anti-sticking masterbatch, 5-50 parts of polyamide toughening agent, and 40-94 parts of polyamide 6.

[0010] In one embodiment, the thickness of the high-toughness biaxially oriented polyamide film is 10~30 μm;

[0011] The thickness of both the lower and upper surface layers is 1~4 μm;

[0012] The thickness of the intermediate layer is 2~28 μm.

[0013] In one embodiment, the polyamide copolymer is any one or a combination of several of the following: polyamide 6 / 66 copolymer, polyamide 6 / 1010 copolymer, polyamide 6 / 12 copolymer, and polyamide 66 / 12 copolymer.

[0014] In one embodiment, the polyamide toughening agent is prepared by the following steps:

[0015] S100. Add 3-amino-4,4,4-trifluorobutyric acid, 2,2ˊ-iminobis(ethylamine), 2,3-diaminotoluene and catalyst to the reaction vessel, and carry out a dehydration reaction by heating and reflux.

[0016] S101. Remove 2,3-diaminotoluene and water from the S100 reaction system using vacuum distillation.

[0017] S102, add α-chlorotoluene and carry out the reaction under heat preservation;

[0018] S103. After the heat preservation reaction is completed, a mixed solution of acetone and toluene is added for recrystallization to obtain the toughening agent prepolymer.

[0019] S104. The toughening agent prepolymer is added to polyamide 6 resin, melt-mixed in a twin-screw extruder, extruded from the nozzle through a die, stretched, pelletized, and dried to obtain the polyamide toughening agent.

[0020] Furthermore, the catalyst is any one or any combination of aluminum trichloride, boron trifluoride, sulfur trioxide, and ferric bromide.

[0021] Furthermore, the weight ratio of 3-amino-4,4,4-trifluorobutyric acid, 2,2ˊ-iminobis(ethylamine), 2,3-diaminotoluene, and the catalyst is (25~59.9):(30~50):(10~20):(0.1~5); the amount of α-chlorotoluene added is 20~50 parts by weight; the weight ratio of acetone and toluene is (30~70):(30~70); and the weight ratio of polyamide 6 resin and toughening agent prepolymer is (20~80):(20~80).

[0022] Furthermore, in step S100, the reaction temperature is 100~160℃ and the reaction time is 6~15 h; in step S102, the heat preservation reaction temperature is 90~120℃ and the reaction time is 4~8 h; in step S104, the mixing temperature is 245~260℃ and the mixing time is 0.5~10 min.

[0023] In one embodiment, 1-5 parts of lubricant, 2-15 parts of opening agent and 80-97 parts of polyamide 6 are fed into a twin-screw extruder, melt-extruded at 230-270°C, drawn into strands, cooled, pelletized and dried to obtain the anti-sticking masterbatch.

[0024] Furthermore, the lubricant is any one or a combination of several of erucamide, PE wax, ethylene bis-stearamide, and oleamide; the opening agent is any one or a combination of several of kaolin, silica, calcium carbonate, diatomaceous earth, and talc.

[0025] The present invention also provides a method for preparing a high-toughness biaxially oriented polyamide film as described above, comprising the following steps:

[0026] The raw materials are dried to control the moisture content to ≤800 ppm;

[0027] The raw materials for the lower, middle, and upper layers are mixed according to the specified ratio, and then fed into an extruder separately. They are melted and plasticized at 230~270℃ and then flowed out through a coat hanger-shaped die.

[0028] The melt is attached to the cooling drum using a low-pressure air knife to form a thick sheet with a thickness of 100~350 μm and a cooling drum temperature of 6~30℃.

[0029] The thick sheet is fed into a longitudinal tenter frame for stretching. The preheating temperature is 45~60℃, the stretching temperature is 45~65℃, the stretching ratio is 2.5~3.5 times, and then it is shaped and cooled.

[0030] The longitudinally stretched film is fed into a transverse tenter for stretching. The preheating temperature is 60~85℃, the stretching temperature is 70~150℃, and the stretching ratio is 3.0~4.5 times.

[0031] The stretched film is subjected to heat setting treatment at a temperature of 190~220℃ for a time of 1~50 s.

[0032] The thin film is cooled and corona treated with a power of 6~15 Wmin / m. 2 After processing, the film is wound up and cut according to specifications to obtain the high-toughness biaxially oriented polyamide film.

[0033] Compared with the prior art, the high-toughness biaxially oriented polyamide film and its preparation method provided by the present invention have the following advantages:

[0034] (1) Under high temperature, the active hydrogen atoms on the secondary amino groups generated between some adjacent terminal amino groups of the linear polyamide molecular chain react with the amino groups in the polyamide toughening agent to form cross-linking points, thereby forming a three-dimensional cross-linked network structure to achieve the reinforcement and toughening of polyamide.

[0035] (2) By adjusting the composition ratio of polyamide toughening agent, the dehydration rate of the final high-toughness biaxially oriented polyamide film at low temperature can be controlled, thereby reducing or even avoiding the occurrence of material brittleness, and further improving the toughness and drawing depth of the system.

[0036] (3) A polyamide copolymer was designed in the raw material composition. The chemical structure of the polyamide copolymer is quite related to that of polyamide 6, but the interaction of hydrogen bonds between its molecular chains is weaker than that of polyamide 6. In addition, the crystallization rate, melting point and crystallization temperature of the polyamide copolymer are also lower than those of polyamide 6. This can reduce the formation of polyamide crystal regions and maintain the original properties of polyamide while giving it better toughness and processability.

[0037] (4) Polyamide 12 was specially designed into the composition of the intermediate layer raw materials. There are a large number of non-polar methylene groups in the polyamide 12 molecular chain, which makes the polymer molecular chain more flexible and has good toughness. At the same time, polyamide 12 has the lowest water absorption rate among polyamide products, and the tensile strength of polyamide 12 decreases very little after water absorption, which is much less than the performance change of conventional polyamides such as polyamide 6 or polyamide 66 after water absorption. Due to the increase of methylene molecules in polyamide 12, the influence of hydrophilic groups can be greatly reduced, thereby reducing the changes in performance and size of the product caused by water absorption, thus overcoming the technical difficulties of high water absorption and difficult dimensional stability of polyamide products.

[0038] (5) The polyamide copolymer, polyamide toughening agent and polyamide 12 used in this invention have excellent compatibility with polyamide 6. Using them for toughening modification of polyamide films can avoid the problem of poor toughening effect of films caused by dispersion or agglomeration between different components. In addition, the polyamide copolymer, polyamide toughening agent and polyamide 12 themselves have the advantages of high temperature resistance, friction resistance, good dimensional stability, creep resistance, low moisture absorption, good softness and high elastic recovery rate. In particular, they can maintain the impact strength and flexibility without change in the low temperature environment of -40~0℃, and have excellent low temperature toughening effect. Under relatively low stress, the high toughness biaxially oriented polyamide film provided by this invention has better tensile stress than ordinary polyamide films, so the thickness of the product can be reduced, which is particularly suitable for toughening modification of ultra-thin polyamide film products.

[0039] (6) In terms of preparation process, biaxial orientation technology is adopted, and stretching is performed in two mutually perpendicular directions. Through biaxial orientation, the polymer chains are arranged in directions parallel to the plane, and the material strength is more uniform in all directions, which greatly improves the overall strength and further characterizes the improvement of material performance.

[0040] In summary, the high-toughness biaxially oriented polyamide film and its preparation method provided by this invention improve the toughness of the polyamide film through formulation design and film layer structure design, avoid material incompatibility, and produce a high-toughness biaxially oriented polyamide film with excellent comprehensive performance, easy processing, and excellent drawing depth. It can be widely used in different packaging fields and has good market application prospects. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 The diagram shows the high-toughness biaxially oriented polyamide film structure provided in Embodiments 1-3 of the present invention.

[0043] Figure label:

[0044] Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0046] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," "outer," "middle," "lateral," and "longitudinal," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0047] Example 1

[0048] This embodiment provides a high-toughness biaxially oriented polyamide film, such as Figure 1 As shown, the membrane structure includes a lower surface layer 10, an intermediate layer 20, and an upper surface layer 30 arranged sequentially from bottom to top, with a thickness of 25 μm. The lower surface layer 10 and the upper surface layer 30 are both 2 μm thick, and the intermediate layer 20 has a thickness of 21 μm. It is prepared by the following steps:

[0049] Preparation of polyamide toughening agents:

[0050] S100. Add 3-amino-4,4,4-trifluorobutyric acid, 2,2ˊ-iminodiethylamine, 2,3-diaminotoluene and catalyst to the reaction vessel and carry out a dehydration reaction by heating and reflux.

[0051] S101, 2,3-diaminotoluene and 2,3-diaminotoluene in the S100 reaction system are removed by vacuum distillation;

[0052] S102, add α-chlorotoluene and carry out the reaction under heat preservation;

[0053] S103. After the heat preservation reaction is completed, a mixed solution of acetone and toluene is added for recrystallization to obtain the toughening agent prepolymer.

[0054] S104. The toughening agent prepolymer is added to polyamide 6 resin, melt-mixed in a twin-screw extruder, extruded from the nozzle through a die, stretched, pelletized, and dried to obtain the polyamide toughening agent.

[0055] In this embodiment, preferably, the catalyst is aluminum trichloride.

[0056] In this embodiment, preferably, the weight ratio of 3-amino-4,4,4-trifluorobutyric acid, 2,2ˊ-iminobis(ethylamine), 2,3-diaminotoluene and the catalyst is 42:40:15:3; the amount of α-chlorotoluene added is 35 parts by weight; the weight ratio of acetone and toluene is 50:50; and the weight ratio of polyamide 6 resin and toughening agent prepolymer is 60:40.

[0057] In this embodiment, preferably, in step S100, the reaction temperature is 130°C and the reaction time is 10 h; in step S102, the heat preservation reaction temperature is 105°C and the reaction time is 6 h; in step S104, the mixing temperature is 255°C and the mixing time is 6 min.

[0058] Preparation of anti-sticking masterbatch

[0059] Three parts of lubricant, ten parts of opening agent and 87 parts of polyamide 6 were put into a twin-screw extruder, melt-extruded at 250°C, stretched into strands, cooled, pelletized and dried to obtain the anti-sticking masterbatch.

[0060] In this embodiment, preferably, the lubricant is ethylene bis-stearamide; and the opening agent is silicon dioxide.

[0061] Preparation of high-toughness biaxially oriented polyamide films

[0062] The raw materials are dried to control the moisture content to ≤600 ppm;

[0063] The raw materials for the lower, middle, and upper layers are mixed according to the specified ratio, and then fed into an extruder separately. They are melted and plasticized at 260°C and then flowed out through a coat hanger-shaped die.

[0064] The melt is attached to the cooling drum using a low-pressure air knife to form a thick sheet with a thickness of 280 μm. The temperature of the cooling drum is 15℃.

[0065] The thick sheet is fed into a longitudinal tenter frame for stretching. The preheating temperature is 50℃, the stretching temperature is 60℃, the stretching ratio is 3.0 times, and then it is shaped and cooled.

[0066] The longitudinally stretched film is fed into a transverse tenter for stretching. The preheating temperature is 75℃, the stretching temperature is 125℃, and the stretching ratio is 4.0 times.

[0067] The stretched film was subjected to heat setting at a temperature of 210℃ for 20 seconds.

[0068] The thin film was cooled and corona treated with a corona treatment power of 10 Wmin / m. 2After processing, the film is wound up and cut according to specifications to obtain the high-toughness biaxially oriented polyamide film.

[0069] In this embodiment, preferably, by weight, the raw materials of the lower surface layer 10 are 4 parts of anti-sticking masterbatch, 30 parts of polyamide toughening agent, and 66 parts of polyamide 6; the raw materials of the intermediate layer 20 are 40 parts of polyamide toughening agent, 12 parts of polyamide copolymer, 10 parts of polyamide 12, and 38 parts of polyamide 6; the upper surface layer 30 includes 4 parts of anti-sticking masterbatch, 30 parts of polyamide toughening agent, and 66 parts of polyamide 6.

[0070] In this embodiment, preferably, the polyamide copolymer is a polyamide 6 / 12 copolymer.

[0071] Example 2

[0072] This embodiment provides a high-toughness biaxially oriented polyamide film, such as Figure 1 As shown, the membrane structure includes a lower surface layer 10, an intermediate layer 20, and an upper surface layer 30 arranged sequentially from bottom to top, with a thickness of 15 μm. The thickness of the lower surface layer 10 and the upper surface layer 30 is 1.5 μm each, and the thickness of the intermediate layer 20 is 12 μm. It is prepared by the following steps:

[0073] Preparation of polyamide toughening agents:

[0074] S100. Add 3-amino-4,4,4-trifluorobutyric acid, 2,2ˊ-iminodiethylamine, 2,3-diaminotoluene and catalyst to the reaction vessel and carry out a dehydration reaction by heating and reflux.

[0075] S101. Remove 2,3-diaminotoluene and water from the S100 reaction system using vacuum distillation.

[0076] S102, add α-chlorotoluene and carry out the reaction under heat preservation;

[0077] S103. After the heat preservation reaction is completed, a mixed solution of acetone and toluene is added for recrystallization to obtain the toughening agent prepolymer.

[0078] S104. The toughening agent prepolymer is added to polyamide 6 resin, melt-mixed in a twin-screw extruder, extruded from the nozzle through a die, stretched, pelletized, and dried to obtain the polyamide toughening agent.

[0079] In this embodiment, preferably, the catalyst is sulfur trioxide.

[0080] In this embodiment, preferably, the weight ratio of 3-amino-4,4,4-trifluorobutyric acid, 2,2ˊ-iminobis(ethylamine), 2,3-diaminotoluene, and the catalyst is 52.5:35:12:0.5; the amount of α-chlorotoluene added is 25 parts by weight; the weight ratio of acetone to toluene is 40:60; and the weight ratio of polyamide 6 resin to toughening agent prepolymer is 75:25.

[0081] In this embodiment, preferably, in step S100, the reaction temperature is 110°C and the reaction time is 7 h; in step S102, the heat preservation reaction temperature is 95°C and the reaction time is 4.5 h; in step S104, the mixing temperature is 250°C and the mixing time is 1 min.

[0082] Preparation of anti-sticking masterbatch

[0083] Two parts of lubricant, five parts of opening agent, and 93 parts of polyamide 6 were fed into a twin-screw extruder and melt-extruded at 235°C. The mixture was then stretched, cooled, pelletized, and dried to obtain the anti-sticking masterbatch.

[0084] In this embodiment, preferably, the lubricant is erucamide and the opening agent is talc.

[0085] Preparation of high-toughness biaxially oriented polyamide films

[0086] The raw materials are dried to control the moisture content to ≤450 ppm;

[0087] The raw materials for the lower, middle, and upper layers are mixed according to the specified ratio, and then fed into an extruder separately. They are melted and plasticized at 250°C and then flowed out through a coat hanger-shaped die.

[0088] The melt is attached to the cooling drum using a low-pressure air knife to form a thick sheet with a thickness of 180 μm. The temperature of the cooling drum is 8℃.

[0089] The thick sheet is fed into a longitudinal tenter frame for stretching. The preheating temperature is 48℃, the stretching temperature is 58℃, the stretching ratio is 2.6 times, and then it is shaped and cooled.

[0090] The longitudinally stretched film is fed into a transverse tenter for stretching. The preheating temperature is 65℃, the stretching temperature is 75℃, and the stretching ratio is 3.5 times.

[0091] The stretched film was subjected to heat setting at a temperature of 195℃ for 5 seconds.

[0092] The thin film was cooled and corona treated with a corona treatment power of 7 Wmin / m. 2 After processing, the film is wound up and cut according to specifications to obtain the high-toughness biaxially oriented polyamide film.

[0093] In this embodiment, preferably, by weight, the raw materials of the lower surface layer 10 are 2 parts of anti-sticking masterbatch, 10 parts of polyamide toughening agent, and 88 parts of polyamide 6; the raw materials of the intermediate layer 20 are 9 parts of polyamide toughening agent, 6 parts of polyamide copolymer, 6 parts of polyamide 12, and 79 parts of polyamide 6; the upper surface layer 30 includes 2 parts of anti-sticking masterbatch, 10 parts of polyamide toughening agent, and 88 parts of polyamide 6.

[0094] In this embodiment, preferably, the polyamide copolymer is a polyamide 6 / 1010 copolymer.

[0095] Example 3

[0096] This embodiment provides a high-toughness biaxially oriented polyamide film, such as Figure 1 As shown, the membrane structure includes a lower surface layer 10, an intermediate layer 20, and an upper surface layer 30 arranged sequentially from bottom to top, with a thickness of 25 μm. The thickness of the lower surface layer 10 and the upper surface layer 30 is 1.8 μm each, and the thickness of the intermediate layer 20 is 21.4 μm. It is prepared by the following steps:

[0097] Preparation of polyamide toughening agents:

[0098] S100. Add 3-amino-4,4,4-trifluorobutyric acid, 2,2ˊ-iminodiethylamine, 2,3-diaminotoluene and catalyst to the reaction vessel and carry out a dehydration reaction by heating and reflux.

[0099] S101. Remove 2,3-diaminotoluene and water from the S100 reaction system using vacuum distillation.

[0100] S102, add α-chlorotoluene and carry out the reaction under heat preservation;

[0101] S103. After the heat preservation reaction is completed, a mixed solution of acetone and toluene is added for recrystallization to obtain the toughening agent prepolymer.

[0102] S104. The toughening agent prepolymer is added to polyamide 6 resin, melt-mixed in a twin-screw extruder, extruded from the nozzle through a die, stretched, pelletized, and dried to obtain the polyamide toughening agent.

[0103] In this embodiment, preferably, the catalyst is ferric bromide.

[0104] In this embodiment, preferably, the weight ratio of 3-amino-4,4,4-trifluorobutyric acid, 2,2ˊ-iminobis(ethylamine), 2,3-diaminotoluene, and the catalyst is 35.5:45:18:1.5; the amount of α-chlorotoluene added is 45 parts by weight; the weight ratio of acetone to toluene is 70:30; and the weight ratio of polyamide 6 resin to toughening agent prepolymer is 30:70.

[0105] In this embodiment, preferably, in step S100, the reaction temperature is 150°C and the reaction time is 13 h; in step S102, the heat preservation reaction temperature is 115°C and the reaction time is 7 h; in step S104, the mixing temperature is 258°C and the mixing time is 9 min.

[0106] Preparation of anti-sticking masterbatch

[0107] Four parts of lubricant, 13 parts of opening agent and 83 parts of polyamide 6 were put into a twin-screw extruder, melt-extruded at 260°C, stretched into strands, cooled, pelletized and dried to obtain the anti-sticking masterbatch.

[0108] In this embodiment, preferably, the lubricant is erucamide and the opening agent is talc.

[0109] Preparation of high-toughness biaxially oriented polyamide films

[0110] The raw materials are dried to control the moisture content to ≤400 ppm;

[0111] The raw materials for the lower, middle, and upper layers are mixed according to the specified ratio, and then fed into an extruder separately. They are melted and plasticized at 265°C and then flowed out through a coat hanger-shaped die.

[0112] The melt is attached to the cooling drum using a low-pressure air knife to form a thick sheet with a thickness of 300 μm. The temperature of the cooling drum is 18℃.

[0113] The thick sheet is fed into a longitudinal tenter frame for stretching. The preheating temperature is 52℃, the stretching temperature is 62℃, the stretching ratio is 3.1 times, and then it is shaped and cooled.

[0114] The longitudinally stretched film is fed into a transverse tenter for stretching. The preheating temperature is 80℃, the stretching temperature is 145℃, and the stretching ratio is 4.3 times.

[0115] The stretched film was subjected to heat setting at a temperature of 215℃ for 45 seconds.

[0116] The thin film was cooled and corona treated with a corona treatment power of 12 Wmin / m. 2 After processing, the film is wound up and cut according to specifications to obtain the high-toughness biaxially oriented polyamide film.

[0117] In this embodiment, preferably, by weight, the raw materials of the lower surface layer 10 are 9 parts of anti-sticking masterbatch, 45 parts of polyamide toughening agent, and 46 parts of polyamide 6; the raw materials of the intermediate layer 20 are 46 parts of polyamide toughening agent, 48 parts of polyamide copolymer, 13 parts of polyamide 12, and 23 parts of polyamide 6; and the upper surface layer 30 includes 9 parts of anti-sticking masterbatch, 45 parts of polyamide toughening agent, and 46 parts of polyamide 6.

[0118] In this embodiment, preferably, the polyamide copolymer is obtained by mixing polyamide 6 / 1010 copolymer and polyamide 6 / 12 copolymer in a 1:1 ratio.

[0119] Comparative Example 1

[0120] This comparative example provides a polyamide film, which differs from Example 1 in that: neither the lower nor upper surface layer contains a polyamide toughening agent; the raw materials for both the lower and upper surface layers are 4 parts of anti-sticking masterbatch and 96 parts of polyamide 6; the intermediate layer does not contain a polyamide toughening agent, a polyamide copolymer, or polyamide 12; the raw material for the intermediate layer is 100 parts of polyamide 6. All other contents, preparation steps, and process parameters are the same as in Example 1.

[0121] Comparative Example 2

[0122] This comparative example provides a polyamide film, which differs from Example 1 in that: neither the lower nor upper surface layer contains a polyamide toughening agent; the raw materials for both the lower and upper surface layers are 4 parts of anti-sticking masterbatch and 96 parts of polyamide 6; the intermediate layer does not contain a polyamide toughening agent; the raw materials for the intermediate layer are 12 parts of a polyamide copolymer, 10 parts of polyamide 12, and 78 parts of polyamide 6. All other contents, preparation steps, and process parameters are the same as in Example 1.

[0123] Comparative Example 3

[0124] This comparative example provides a polyamide film, which differs from Example 1 in that the interlayer does not contain a polyamide copolymer, and the raw materials for the interlayer are 40 parts of polyamide toughening agent, 10 parts of polyamide 12, and 50 parts of polyamide 6. All other contents, preparation steps, and process parameters are the same as in Example 1.

[0125] Comparative Example 4

[0126] This comparative example provides a polyamide film, which differs from Example 1 in that the interlayer does not contain polyamide 12, and the raw materials for the interlayer are 40 parts of polyamide toughening agent, 12 parts of polyamide copolymer, and 48 parts of polyamide 6. All other contents, preparation steps, and process parameters are the same as in Example 1.

[0127] Comparative Example 5

[0128] This comparative example provides a polyamide film, which differs from Example 1 in that the polyamide toughening agent is replaced with polyolefin elastomer POE. The raw materials for the lower and upper layers are 4 parts of anti-sticking masterbatch, 30 parts of polyolefin elastomer POE, and 66 parts of polyamide 6. The raw materials for the middle layer are 40 parts of polyolefin elastomer POE, 12 parts of polyamide copolymer, 10 parts of polyamide 12, and 38 parts of polyamide 6. All other contents, preparation steps, and process parameters are the same as in Example 1.

[0129] Comparative Example 6

[0130] This comparative example provides a polyamide film, which differs from Example 1 in that the polyamide toughening agent is replaced with ethylene propylene diene monomer (EPDM). The raw materials for the lower and upper layers are 4 parts of anti-sticking masterbatch, 30 parts of EPDM, and 66 parts of polyamide 6. The raw materials for the middle layer are 40 parts of EPDM, 12 parts of polyamide copolymer, 10 parts of polyamide 12, and 38 parts of polyamide 6. All other contents, preparation steps, and process parameters are the same as in Example 1.

[0131] The high-toughness biaxially oriented polyamide films prepared in Examples 1-3 and the polyamide films prepared in Comparative Examples 1-6 were tested for their punching depth, puncture force, tensile strength and elongation at break.

[0132] Among them, the drawing depth performance test is as follows: 40 film samples are taken for each test and the maximum drawing depth when the film does not crack is the test value. In particular, for low temperature test, the sample must be placed at -18℃ for 48 hours before it is taken out for test.

[0133] Puncture resistance testing was conducted in accordance with ASTM D4833-2007 Index Puncture Resistance of Geomembranes and Related Products.

[0134] The tensile strength test was conducted in accordance with GB / T 1040.3 Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets;

[0135] The performance test results of the polyamide films provided in Examples 1-3 and Comparative Examples 1-6 are listed in Table 1:

[0136] Table 1 Performance test table of polyamide films provided in Examples 1-3 and Comparative Examples 1-6

[0137]

[0138] Note: "◎" indicates excellent, "○" indicates good, "□" indicates fair, "△" indicates fair, "☆" indicates poor, "×" indicates very poor, and "-" indicates untested or no test required, or no relevant data.

[0139] According to the performance test results in Table 1, the high-toughness biaxially oriented polyamide films provided in Examples 1-3 exhibit good tensile strength, puncture force, and drawing depth. The polyamide films provided in Comparative Examples 1-4 have reduced raw material compositions compared to Example 1, but regardless of the reduction of any component, their film performance decreases. Furthermore, based on the performance test results of Comparative Examples 5 and 6 compared to Example 1, it can be seen that replacing the polyamide toughening agent with other toughening agents, such as polyolefin elastomer POE or ethylene propylene diene monomer (EPDM), does not effectively improve film toughness. Moreover, due to the poor compatibility of POE and EPDM with nylon materials, it also reduces the effectiveness of other materials in the raw material formulation.

[0140] Furthermore, according to the low-temperature drawing depth data in Table 1, the high-toughness biaxially oriented polyamide films provided in Examples 1-3 of this invention have better low-temperature toughness, while the drawing performance of ordinary products deteriorates significantly at low temperatures.

[0141] As can be seen from the above, the high-toughness biaxially oriented polyamide film provided by the present invention has better toughness and processing performance, while maintaining excellent tensile strength, which can meet the needs of different high-end markets.

[0142] Although terms such as lower layer, intermediate layer, and upper layer are frequently used herein, the possibility of using other terms is not excluded. These terms are used merely for the convenience of describing and explaining the essence of the invention; interpreting them as any additional limitation would contradict the spirit of the invention.

[0143] 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 high-toughness biaxially oriented polyamide film, characterized in that: The membrane structure includes a lower surface layer, an intermediate layer, and an upper surface layer arranged sequentially from bottom to top; By weight, the lower surface layer comprises 1 to 10 parts of anti-sticking masterbatch, 5 to 50 parts of polyamide toughening agent and 40 to 94 parts of polyamide 6; The intermediate layer comprises 5-50 parts of polyamide toughening agent, 5-20 parts of polyamide copolymer, 5-15 parts of polyamide 12 and 15-85 parts of polyamide 6; The upper surface layer comprises 1-10 parts of anti-sticking masterbatch, 5-50 parts of polyamide toughening agent and 40-94 parts of polyamide 6; The polyamide toughening agent is prepared by the following steps: S100. Add 3-amino-4,4,4-trifluorobutyric acid, 2,2ˊ-iminobis(ethylamine), 2,3-diaminotoluene and catalyst to the reaction vessel, and carry out a dehydration reaction by heating and reflux. S101. Remove 2,3-diaminotoluene and water from the S100 reaction system using vacuum distillation. S102, add α-chlorotoluene and carry out the reaction under heat preservation; S103. After the heat preservation reaction is completed, a mixed solution of acetone and toluene is added for recrystallization to obtain the toughening agent prepolymer. S104. The toughening agent prepolymer is added to polyamide 6 resin, melt-mixed in a twin-screw extruder, extruded from the nozzle through the die, stretched, pelletized, and dried to obtain the polyamide toughening agent. The catalyst is any one or any combination of aluminum trichloride, boron trifluoride, sulfur trioxide and ferric bromide; The weight ratio of 3-amino-4,4,4-trifluorobutyric acid, 2,2ˊ-iminobis(ethylamine), 2,3-diaminotoluene and the catalyst is (25~59.9):(30~50):(10~20):(0.1~5). The amount of α-chlorotoluene added is 20 to 50 parts by weight; The weight ratio of acetone to toluene is (30~70):(30~70); The weight ratio of the polyamide 6 resin to the toughening agent prepolymer is (20~80):(20~80).

2. The high-toughness biaxially oriented polyamide film according to claim 1, characterized in that: The thickness of the high-toughness biaxially oriented polyamide film is 10~30 μm; The thickness of both the lower and upper surface layers is 1~4 μm; The thickness of the intermediate layer is 2~28 μm.

3. The high-toughness biaxially oriented polyamide film according to claim 1, characterized in that: The polyamide copolymer is any one or a combination of several of the following: polyamide 6 / 66 copolymer, polyamide 6 / 1010 copolymer, polyamide 6 / 12 copolymer, and polyamide 66 / 12 copolymer.

4. The high-toughness biaxially oriented polyamide film according to claim 1, characterized in that: In step S100, the reaction temperature is 100~160℃ and the reaction time is 6~15 h; In step S102, the heat preservation reaction temperature is 90~120℃, and the reaction time is 4~8 h; In step S104, the mixing temperature is 245~260℃ and the mixing time is 0.5~10 min.

5. The high-toughness biaxially oriented polyamide film according to claim 1, characterized in that, The anti-sticking masterbatch is prepared by the following steps: 1-5 parts of lubricant, 2-15 parts of opening agent and 80-97 parts of polyamide 6 are put into a twin-screw extruder, melt-extruded at 230-270°C, drawn into strands, cooled, pelletized and dried to obtain the anti-sticking masterbatch.

6. The high-toughness biaxially oriented polyamide film according to claim 5, characterized in that: The lubricant is any one or a combination of any of the following: erucamide, PE wax, ethylene bis-stearamide and oleamide; The opening agent is any one or any combination of kaolin, silica, calcium carbonate, diatomaceous earth and talc.

7. A method for preparing a high-toughness biaxially oriented polyamide film according to any one of claims 1 to 6, characterized in that, Includes the following steps: The raw materials are dried to control the moisture content to ≤800 ppm; The raw materials for the lower, middle, and upper layers are mixed according to the specified ratio, and then fed into an extruder separately. They are melted and plasticized at 230~270℃ and then flowed out through a coat hanger-shaped die. The melt is attached to the cooling drum using a low-pressure air knife to form a thick sheet with a thickness of 100~350 μm and a cooling drum temperature of 6~30℃. The thick sheet is fed into a longitudinal tenter frame for stretching. The preheating temperature is 45~60℃, the stretching temperature is 45~65℃, the stretching ratio is 2.5~3.5 times, and then it is shaped and cooled. The longitudinally stretched film is fed into a transverse tenter for stretching. The preheating temperature is 60~85℃, the stretching temperature is 70~150℃, and the stretching ratio is 3.0~4.5 times. The stretched film is subjected to heat setting treatment at a temperature of 190~220℃ for a time of 1~50 s. The thin film is cooled and corona treated with a power of 6~15 Wmin / m. 2 After processing, the film is wound up and cut according to specifications to obtain the high-toughness biaxially oriented polyamide film.

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