High-toughness biaxially oriented polyamide film and preparation method thereof

Abstract

The invention relates to the technical field of film packaging, in particular to a high-toughness biaxially oriented polyamide film and a preparation method thereof. According to the high-toughness biaxially oriented polyamide film and the preparation method thereof, the polyamide flexibilizer is specially blended to overcome the incompatibility between the flexibilizer and a nylon material and improve the toughness of the polyamide film, and the dehydration rate of the material at low temperature is regulated and controlled by regulating and controlling the component proportion of the polyamide flexibilizer, so that the low-temperature embrittlement phenomenon is reduced; besides, the polyamide copolymer with weak hydrogen-bond interaction between molecular chains and lower crystallization speed and melting point is matched to reduce the formation of a polyamide crystal region, and the polyamide 12 with low water absorption rate is matched to reduce the performance and size change of the material caused by water absorption, so that the technical problem of how to avoid incompatibility to prepare the high-toughness polyamide film is solved; the technical effects of high toughness, low temperature resistance, high tensile strength, excellent punching depth, puncture resistance and easiness in ultrathin processing are comprehensively achieved, and good market application prospects are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of film packaging, and in particular to a high-toughness biaxially oriented polyamide film and a preparation method thereof. Background Art

[0002] Biaxially oriented polyamide film, also known as biaxially stretched nylon film, or BOPA, has excellent mechanical properties, optical properties, electrical insulation and gas barrier properties. It is also easy to print, oil-resistant, chemical solvent-resistant and has a wide temperature range. 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 field.

[0003] However, under low temperature conditions, ordinary nylon 6 materials have the problem of insufficient toughness. Nylon used for frozen food packaging, especially for food packaging with edges and corners after vacuuming, is prone to bag breakage, which makes the packaging bag lose its shelf life and causes the packaged product to deteriorate. Similarly, in the pharmaceutical blister packaging and lithium-ion battery industries, in order to protect the aluminum foil layer in the multi-layer composite structure, the product needs to have a certain deep-drawing and forming performance. Therefore, improving the toughness of biaxially oriented polyamide film has become an urgent need.

[0004] In the modification industry, a common method to improve the toughness of products is to add polyolefin elastomers and rubber elastomers, but the above methods often have little effect on very thin film products. Because the film is very thin, and polyolefin elastomers and rubber elastomers are non-polar materials, even after grafting, their compatibility with polyamide films is still greatly lacking. Therefore, even if grafted polyolefin elastomers and rubber elastomers are added, due to poor compatibility with the nylon system, not only is the toughening effect not obvious, but it will lead to a sharp drop in tensile properties. Furthermore, the addition of polyolefin elastomers and rubber elastomers will also have a certain impact on the barrier properties of the film, greatly reducing the shelf life of the packaging products.

[0005] Therefore, it is often difficult for existing BOPA films to simultaneously take into account compatibility, barrier properties, deep-drawing formability and toughness, which greatly limits the application of BOPA films in the lithium-ion battery industry, pharmaceutical blister packaging industry and frozen food packaging industry. It can be seen that how to avoid incompatibility and prepare a high-toughness polyamide film has become a problem that needs to be solved urgently. Summary of the invention

[0006] In order to solve the technical problem of how to avoid incompatibility and prepare a high-toughness polyamide film, the present invention provides a high-toughness biaxially oriented polyamide film, the film layer structure includes a lower surface layer, an intermediate layer and an upper surface layer arranged in sequence from bottom to top; The lower surface layer comprises, by weight, 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 middle layer comprises 5 to 50 parts of a polyamide toughening agent, 5 to 20 parts of a polyamide copolymer, 5 to 15 parts of polyamide 12 and 15 to 85 parts of polyamide 6; The upper 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.

[0007] In one embodiment, the thickness of the high-toughness biaxially oriented polyamide film is 10-30 μm; Wherein, the thickness of the lower surface layer and the upper surface layer are both 1-4 μm; The thickness of the intermediate layer is 2-28 μm.

[0008] In one embodiment, the polyamide copolymer is any one of polyamide 6 / 66 copolymer, polyamide 6 / 1010 copolymer, polyamide 6 / 12 copolymer and polyamide 66 / 12 copolymer, or a combination of any two of them.

[0009] In one embodiment, the polyamide toughening agent is prepared by the following steps: S100, adding 3-amino-4,4,4-trifluorobutyric acid, 2,2'-iminobis(ethylamine), 2,3-diaminotoluene and a catalyst into a reaction container, and performing a heating reflux dehydration reaction; S101, removing 2,3-diaminotoluene and water from the S100 reaction system by vacuum distillation; S102, adding α-chlorotoluene and carrying out heat preservation reaction; S103, after the heat preservation reaction is completed, adding a mixed solution of acetone and toluene for recrystallization to obtain a toughening agent prepolymer; S104, adding the toughening agent prepolymer to polyamide 6 resin, putting into a twin-screw extruder for melt mixing, extruding from a nozzle through a die plate, drawing into strips, cutting into pellets, and drying to obtain the polyamide toughening agent.

[0010] Furthermore, the catalyst is any one of aluminum trichloride, boron trifluoride, sulfur trioxide and ferric bromide, or a combination of any two of them.

[0011] Furthermore, the weight ratio of the 3-amino-4,4,4-trifluorobutyric acid, 2,2'-iminobis(ethylamine), 2,3-diaminotoluene and 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); the weight ratio of the polyamide 6 resin and the toughening agent prepolymer is (20-80):(20-80).

[0012] Furthermore, in step S100, the reaction temperature is 100-160°C, and the reaction time is 6-15 h; in step S102, the insulation reaction temperature is 90-120°C, and the reaction time is 4-8 h; in step S104, the mixing temperature is 245-260°C, and the mixing time is 0.5-10 min.

[0013] In one embodiment, 1 to 5 parts of a lubricant, 2 to 15 parts of an anti-blocking agent and 80 to 97 parts of polyamide 6 are put into a twin-screw extruder, melt-extruded at 230 to 270° C., drawn into strips, cooled, pelletized and dried to obtain the anti-sticking masterbatch.

[0014] Furthermore, the lubricant is any one of erucamide, PE wax, ethylene bisstearamide and oleamide, or a combination of any two of them; the anti-blocking agent is any one of kaolin, silicon dioxide, calcium carbonate, diatomaceous earth and talc, or a combination of any two of them.

[0015] The present invention also provides a method for preparing the high-toughness biaxially oriented polyamide film as described above, comprising the following steps: Dry the raw materials and control the moisture content of the raw materials to ≤800 ppm; The raw materials of the lower surface layer, the middle layer and the upper surface layer are mixed according to the proportions, and then respectively put into the extruder, melted and plasticized at 230-270°C, and flowed out through the hanger-shaped die head; The melt is attached to the cold drum using a low-pressure air knife to form a thick sheet with a thickness of 100-350 μm and a cold drum temperature of 6-30°C. The thick sheet is sent into a longitudinal tenter for stretching, with a preheating temperature of 45-60°C, a stretching temperature of 45-65°C, a stretching ratio of 2.5-3.5 times, and then cooled for shaping; The longitudinally stretched film is sent to a transverse tenter for stretching, with a preheating temperature of 60-85°C, a stretching temperature of 70-150°C, and a stretching ratio of 3.0-4.5 times; The stretched film is subjected to heat setting treatment, the setting temperature is 190-220°C, and the setting time is 1-50 s; The film is cooled and corona treated, with a corona treatment power of 6~15 Wmin / m 2 After the treatment, the film is rolled up and cut according to specifications to obtain the high-toughness biaxially oriented polyamide film.

[0016] Compared with the prior art, the high-toughness biaxially oriented polyamide film and the preparation method thereof provided by the present invention have the following advantages: (1) Under the action of high temperature, the active hydrogen atoms on the secondary amine 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, and then form a three-dimensional cross-linking network structure, thereby achieving the reinforcement and toughening of the polyamide.

[0017] (2) By adjusting the composition ratio of the polyamide toughening agent, the dehydration rate of the final high-toughness biaxially oriented polyamide film at low temperature is controlled, the brittleness of the material is reduced or even avoided, and the toughness and punching depth of the system can be further improved.

[0018] (3) Polyamide copolymers are designed in the raw material composition. The chemical structure of polyamide copolymers is quite related to polyamide 6, but the hydrogen bond interaction between its molecular chains is weaker than that of polyamide 6. In addition, the crystallization rate, melting point, crystallization temperature, etc. of polyamide copolymers are also lower than those of polyamide 6. This can reduce the formation of polyamide crystal areas, maintain the original properties of polyamide, and give it better toughness and processability.

[0019] (4) Polyamide 12 is specially designed in the composition of the middle layer raw materials. There are a large number of non-polar methylene groups in the molecular chain of polyamide 12, 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 decrease in tensile strength of polyamide 12 after water absorption is very small, which is much smaller 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 polyamide products with high water absorption and difficult to ensure dimensional stability.

[0020] (5) The polyamide copolymer, polyamide toughening agent and polyamide 12 used in the present invention have excellent compatibility with polyamide 6. When used for the toughening modification of polyamide films, the problem of poor film toughening effect caused by dispersion or agglomeration between different components can be avoided. 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 stability, low moisture absorption rate, good softness and high elastic recovery rate. In particular, the impact strength and flexibility can be maintained unchanged in a low temperature environment of -40~0℃, and they have excellent low-temperature toughening effect. Under relatively low stress, the high-toughness biaxially oriented polyamide film provided by the present invention has better tensile stress than ordinary polyamide films, thereby achieving thinning of the product thickness, and is particularly suitable for the toughening modification of ultra-thin polyamide film products.

[0021] (6) In the preparation process, biaxial orientation technology is used to stretch the material in two mutually perpendicular directions. Through biaxial orientation, the polymer chains are arranged in a direction parallel to the plane, and the material strength is more uniform in all directions, which greatly improves the overall strength and further represents the improvement of material performance.

[0022] In summary, the high-toughness biaxially oriented polyamide film and the preparation method thereof provided by the present invention improve the toughness of the polyamide film through formula design and film layer structure design, avoid material incompatibility, and prepare a high-toughness biaxially oriented polyamide film with excellent comprehensive performance, easy processing, and excellent punching depth. The film can be widely used in different packaging fields and has good market application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] 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.

[0024] Figure 1 This is a schematic diagram of the structure of the high-toughness biaxially oriented polyamide film provided in Examples 1 to 3 of the present invention.

[0025] Reference numerals: DETAILED DESCRIPTION

[0026] 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.

[0027] In the description of the present invention, it should be noted that the terms "upper", "lower", "inner", "outer", "middle", "lateral", "longitudinal" and the like 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 limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0028] Example 1 This embodiment provides a high-toughness biaxially oriented polyamide film, such as Figure 1 As shown, the film structure includes a lower surface layer 10, an intermediate layer 20 and an upper surface layer 30 arranged in sequence from bottom to top, with a thickness of 25 μm, wherein the thickness of the lower surface layer 10 and the upper surface layer 30 are both 2 μm, and the thickness of the intermediate layer 20 is 21 μm, and is prepared by the following steps: Preparation of polyamide toughening agent: S100, adding 3-amino-4,4,4-trifluorobutyric acid, 2,2'-iminobisethylamine, 2,3-diaminotoluene and a catalyst into a reaction container, and performing a heating reflux dehydration reaction; S101, removing 2,3-diaminotoluene and from the S100 reaction system by vacuum distillation; S102, adding α-chlorotoluene and carrying out heat preservation reaction; S103, after the heat preservation reaction is completed, adding a mixed solution of acetone and toluene for recrystallization to obtain a toughening agent prepolymer; S104, adding the toughening agent prepolymer to polyamide 6 resin, putting into a twin-screw extruder for melt mixing, extruding from a nozzle through a die plate, drawing into strips, cutting into pellets, and drying to obtain the polyamide toughening agent.

[0029] In this embodiment, preferably, the catalyst is aluminum chloride.

[0030] In this embodiment, preferably, the weight ratio of the 3-amino-4,4,4-trifluorobutyric acid, 2,2'-imidobis(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; the weight ratio of the polyamide 6 resin and the toughening agent prepolymer is 60:40.

[0031] In this embodiment, preferably, in step S100, the reaction temperature is 130°C and the reaction time is 10 h; in step S102, the insulation 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.

[0032] Preparation of anti-sticking masterbatch 3 parts of lubricant, 10 parts of anti-blocking agent and 87 parts of polyamide 6 are put into a twin-screw extruder, melt-extruded at 250° C., drawn into strips, cooled, pelletized and dried to obtain the anti-sticking masterbatch.

[0033] In this embodiment, preferably, the lubricant is ethylene bisstearamide; and the opening agent is silicon dioxide.

[0034] Preparation of high toughness biaxially oriented polyamide film Dry the raw materials and control the moisture content of the raw materials to ≤600 ppm; The raw materials of the lower surface layer, the middle layer and the upper surface layer are mixed according to the proportions, and then respectively put into the extruder, melted and plasticized at 260°C, and flowed out through the hanger-shaped die head; The melt was attached to the cold drum using a low-pressure air knife to form a thick sheet with a thickness of 280 μm and a cold drum temperature of 15°C. The thick sheet is sent into a longitudinal tenter for stretching, with a preheating temperature of 50°C, a stretching temperature of 60°C, a stretching ratio of 3.0 times, and then shaped and cooled; The longitudinally stretched film was sent to a transverse tenter for stretching, with a preheating temperature of 75°C, a stretching temperature of 125°C, and a stretching ratio of 4.0 times; The stretched film was heat-set at a temperature of 210°C and a setting time of 20 s. The film was cooled and corona treated at a power of 10 Wmin / m 2 After the treatment, the film is rolled up and cut according to specifications to obtain the high-toughness biaxially oriented polyamide film.

[0035] In this embodiment, preferably, 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, by weight; the raw materials of the middle 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.

[0036] In this embodiment, preferably, the polyamide copolymer is a polyamide 6 / 12 copolymer.

[0037] Example 2 This embodiment provides a high-toughness biaxially oriented polyamide film, such as Figure 1 As shown, the film structure includes a lower surface layer 10, an intermediate layer 20 and an upper surface layer 30 arranged in sequence from bottom to top, with a thickness of 15 μm, wherein the thickness of the lower surface layer 10 and the upper surface layer 30 are both 1.5 μm, and the thickness of the intermediate layer 20 is 12 μm, and is prepared by the following steps: Preparation of polyamide toughening agent: S100, adding 3-amino-4,4,4-trifluorobutyric acid, 2,2'-iminobisethylamine, 2,3-diaminotoluene and a catalyst into a reaction container, and performing a heating reflux dehydration reaction; S101, removing 2,3-diaminotoluene and water from the S100 reaction system by vacuum distillation; S102, adding α-chlorotoluene and carrying out heat preservation reaction; S103, after the heat preservation reaction is completed, adding a mixed solution of acetone and toluene for recrystallization to obtain a toughening agent prepolymer; S104, adding the toughening agent prepolymer to polyamide 6 resin, putting into a twin-screw extruder for melt mixing, extruding from a nozzle through a die plate, drawing into strips, cutting into pellets, and drying to obtain the polyamide toughening agent.

[0038] In this embodiment, preferably, the catalyst is sulfur trioxide.

[0039] In this embodiment, preferably, the weight ratio of the 3-amino-4,4,4-trifluorobutyric acid, 2,2'-imidobis(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 and toluene is 40:60; the weight ratio of the polyamide 6 resin and the toughening agent prepolymer is 75:25.

[0040] In this embodiment, preferably, in step S100, the reaction temperature is 110°C and the reaction time is 7 h; in step S102, the insulation 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.

[0041] Preparation of anti-sticking masterbatch 2 parts of lubricant, 5 parts of anti-blocking agent and 93 parts of polyamide 6 are put into a twin-screw extruder, melt-extruded at 235° C., drawn into strips, cooled, pelletized and dried to obtain the anti-sticking masterbatch.

[0042] In this embodiment, preferably, the lubricant is erucamide; and the opening agent is talcum powder.

[0043] Preparation of high toughness biaxially oriented polyamide film Dry the raw materials and control the moisture content of the raw materials to ≤450 ppm; The raw materials of the lower surface layer, the middle layer and the upper surface layer are mixed according to the proportions, and then respectively put into the extruder, melted and plasticized at 250°C, and flowed out through the hanger-shaped die head; The melt was attached to the cold drum using a low-pressure air knife to form a thick sheet with a thickness of 180 μm and a cold drum temperature of 8°C. The thick sheet is sent into a longitudinal tenter for stretching, with a preheating temperature of 48°C, a stretching temperature of 58°C, a stretching ratio of 2.6 times, and then shaped and cooled; The longitudinally stretched film was sent to a transverse tenter for stretching, with a preheating temperature of 65°C, a stretching temperature of 75°C, and a stretching ratio of 3.5 times; The stretched film was heat-set at a temperature of 195°C and a setting time of 5 s. The film was cooled and corona treated at a power of 7 Wmin / m 2 After the treatment, the film is rolled up and cut according to specifications to obtain the high-toughness biaxially oriented polyamide film.

[0044] 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 middle 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.

[0045] In this embodiment, preferably, the polyamide copolymer is a polyamide 6 / 1010 copolymer.

[0046] Example 3 This embodiment provides a high-toughness biaxially oriented polyamide film, such as Figure 1 As shown, the film structure includes a lower surface layer 10, an intermediate layer 20 and an upper surface layer 30 arranged in sequence from bottom to top, with a thickness of 25 μm, wherein the thickness of the lower surface layer 10 and the upper surface layer 30 are both 1.8 μm, and the thickness of the intermediate layer 20 is 21.4 μm, and is prepared by the following steps: Preparation of polyamide toughening agent: S100, adding 3-amino-4,4,4-trifluorobutyric acid, 2,2'-iminobisethylamine, 2,3-diaminotoluene and a catalyst into a reaction container, and performing a heating reflux dehydration reaction; S101, removing 2,3-diaminotoluene and water from the S100 reaction system by vacuum distillation; S102, adding α-chlorotoluene and carrying out heat preservation reaction; S103, after the heat preservation reaction is completed, adding a mixed solution of acetone and toluene for recrystallization to obtain a toughening agent prepolymer; S104, adding the toughening agent prepolymer to polyamide 6 resin, putting into a twin-screw extruder for melt mixing, extruding from a nozzle through a die plate, drawing into strips, cutting into pellets, and drying to obtain the polyamide toughening agent.

[0047] In this embodiment, preferably, the catalyst is ferric bromide.

[0048] In this embodiment, preferably, the weight ratio of the 3-amino-4,4,4-trifluorobutyric acid, 2,2'-imidobis(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 and toluene is 70:30; the weight ratio of the polyamide 6 resin and the toughening agent prepolymer is 30:70.

[0049] In this embodiment, preferably, in step S100, the reaction temperature is 150°C and the reaction time is 13 h; in step S102, the insulation 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.

[0050] Preparation of anti-sticking masterbatch 4 parts of lubricant, 13 parts of anti-blocking agent and 83 parts of polyamide 6 were put into a twin-screw extruder, melt-extruded at 260° C., drawn into strips, cooled, pelletized and dried to obtain the anti-sticking masterbatch.

[0051] In this embodiment, preferably, the lubricant is erucamide; and the opening agent is talcum powder.

[0052] Preparation of high toughness biaxially oriented polyamide film Dry the raw materials and control the moisture content of the raw materials to ≤400 ppm; The raw materials of the lower surface layer, the middle layer and the upper surface layer are mixed according to the proportions, and then respectively put into the extruder, melted and plasticized at 265°C, and flowed out through the hanger-shaped die head; The melt was attached to the cold drum using a low-pressure air knife to form a thick sheet with a thickness of 300 μm and a cold drum temperature of 18°C. The thick sheet was sent to a longitudinal tenter for stretching, with a preheating temperature of 52°C, a stretching temperature of 62°C, a stretching ratio of 3.1 times, and then shaped and cooled; The longitudinally stretched film was sent to a transverse tenter for stretching, with a preheating temperature of 80°C, a stretching temperature of 145°C, and a stretching ratio of 4.3 times; The stretched film was heat-set at a temperature of 215°C and a setting time of 45 s. The film was cooled and corona treated at a power of 12 Wmin / m 2 After the treatment, the film is rolled up and cut according to specifications to obtain the high-toughness biaxially oriented polyamide film.

[0053] In this embodiment, preferably, 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, by weight; the raw materials of the middle 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; the upper surface layer 30 includes 9 parts of anti-sticking masterbatch, 45 parts of polyamide toughening agent and 46 parts of polyamide 6.

[0054] In this embodiment, preferably, the polyamide copolymer is obtained by mixing a polyamide 6 / 1010 copolymer and a polyamide 6 / 12 copolymer in a ratio of 1:1.

[0055] Comparative Example 1 This comparative example provides a polyamide film, which is different from Example 1 in that: the lower surface layer and the upper surface layer do not contain a polyamide toughening agent, and the raw materials of the lower surface layer and the upper surface layer are 4 parts of anti-sticking masterbatch and 96 parts of polyamide 6; the middle layer does not contain a polyamide toughening agent, a polyamide copolymer and polyamide 12, and the raw material of the middle layer is 100 parts of polyamide 6. The rest of the content, preparation steps and process parameters are consistent with Example 1.

[0056] Comparative Example 2 This comparative example provides a polyamide film, which is different from Example 1 in that: the lower surface layer and the upper surface layer do not contain a polyamide toughening agent, and the raw materials of the lower surface layer and the upper surface layer are 4 parts of anti-sticking masterbatch and 96 parts of polyamide 6; the middle layer does not contain a polyamide toughening agent, and the raw materials of the middle layer are 12 parts of a polyamide copolymer, 10 parts of polyamide 12 and 78 parts of polyamide 6. The remaining contents, preparation steps and process parameters are consistent with those of Example 1.

[0057] Comparative Example 3 This comparative example provides a polyamide film, which is different from Example 1 in that the middle layer does not contain a polyamide copolymer, and the raw materials of the middle layer are 40 parts of a polyamide toughening agent, 10 parts of polyamide 12 and 50 parts of polyamide 6. The rest of the content, preparation steps and process parameters are consistent with Example 1.

[0058] Comparative Example 4 This comparative example provides a polyamide film, which is different from Example 1 in that the middle layer does not contain polyamide 12, and the raw materials of the middle layer are 40 parts of polyamide toughening agent, 12 parts of polyamide copolymer and 48 parts of polyamide 6. The rest of the content, preparation steps and process parameters are consistent with Example 1.

[0059] Comparative Example 5 This comparative example provides a polyamide film, which is different from Example 1 in that the polyamide toughening agent is replaced by polyolefin elastomer POE, and the raw materials of the lower surface layer and the upper surface layer are 4 parts of anti-sticking masterbatch, 30 parts of polyolefin elastomer POE and 66 parts of polyamide 6, and the raw materials of 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. The rest of the content, preparation steps and process parameters are consistent with Example 1.

[0060] Comparative Example 6 This comparative example provides a polyamide film, which is different from Example 1 in that the polyamide toughening agent is replaced by EPDM, and the raw materials of the lower surface layer and the upper surface layer are 4 parts of anti-sticking masterbatch, 30 parts of EPDM and 66 parts of polyamide 6, and the raw materials of the middle layer are 40 parts of EPDM, 12 parts of polyamide copolymer, 10 parts of polyamide 12 and 38 parts of polyamide 6. The rest of the content, preparation steps and process parameters are consistent with Example 1.

[0061] The high toughness biaxially oriented polyamide films prepared in the above Examples 1 to 3 and the polyamide films prepared in the above Comparative Examples 1 to 6 were tested for performance of punch depth, puncture force, tensile strength and elongation at break; Among them, the punching depth performance test is as follows: 40 film samples are taken for punching depth test, and the maximum punching depth when no cracks appear in the film is the test value. In particular, during the low temperature test, the sample needs to be placed at -18℃ for 48 hours before being taken out for testing; The puncture force performance test is carried out in accordance with ASTM D4833-2007 Index Puncture Resistance of Geomembranes and Related Products; The tensile strength performance test is carried out in accordance with GB / T 1040.3 Determination of tensile properties of plastics-Part 3: Test conditions for films and sheets; The test results of the polyamide film properties provided by Examples 1 to 3 and Comparative Examples 1 to 6 are shown in Table 1: Table 1 Performance test table of polyamide films provided in Examples 1 to 3 and Comparative Examples 1 to 6

[0062] Note: “◎” indicates excellent, “○” indicates excellent, “□” indicates good, “△” indicates fair, “☆” indicates poor, “×” indicates extremely poor, and “-” indicates not tested or no test is required and no relevant data is available.

[0063] According to the performance test results in Table 1, the high-toughness biaxially oriented polyamide films provided in Examples 1 to 3 have good tensile strength, puncture force and punch depth; the polyamide films provided in Comparative Examples 1 to 4 have reduced raw material compositions compared to Example 1, but no matter which component is reduced, the film performance is reduced. In addition, according to the performance test results of Comparative Examples 5 and 6 and Example 1, it can be understood that replacing the polyamide toughening agent with other toughening agents, such as polyolefin elastomer POE or ethylene propylene diene monomer rubber EPDM, cannot effectively improve the toughness of the film, and due to the poor compatibility of POE and EPDM with nylon materials, it will also reduce the effect of other materials in the raw material formula.

[0064] In addition, according to the low-temperature punching depth data in Table 1, it can be seen that the high-toughness biaxially oriented polyamide films provided by Examples 1 to 3 of the present invention have better low-temperature toughness, while the punching performance of ordinary products at low temperatures is significantly deteriorated.

[0065] Based on the above, it can be seen that the high-toughness biaxially oriented polyamide film provided by the present invention has better toughness and processing performance, while maintaining excellent tensile strength, and can meet the needs of different high-end market fields.

[0066] Although the terms such as lower surface layer, middle layer, upper surface layer, etc. are used more frequently in this article, the possibility of using other terms is not excluded. These terms are used only to more conveniently describe and explain the essence of the present invention; interpreting them as any additional restrictions is contrary to the spirit of the present invention.

[0067] 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 high-toughness biaxially oriented polyamide film, characterized in that: The membrane layer structure includes a lower surface layer, a middle layer and an upper surface layer arranged in sequence from bottom to top; The lower surface layer comprises, by weight, 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 middle layer comprises 5 to 50 parts of a polyamide toughening agent, 5 to 20 parts of a polyamide copolymer, 5 to 15 parts of polyamide 12 and 15 to 85 parts of polyamide 6; The upper 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.

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; Wherein, the thickness of the lower surface layer and the upper surface layer are both 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 of polyamide 6 / 66 copolymer, polyamide 6 / 1010 copolymer, polyamide 6 / 12 copolymer and polyamide 66 / 12 copolymer, or a combination of any two of them.

4. The high-toughness biaxially oriented polyamide film according to claim 1, characterized in that: The polyamide toughening agent is prepared by the following steps: S100, adding 3-amino-4,4,4-trifluorobutyric acid, 2,2'-iminobis(ethylamine), 2,3-diaminotoluene and a catalyst into a reaction container, and performing a heating reflux dehydration reaction; S101, removing 2,3-diaminotoluene and water from the S100 reaction system by vacuum distillation; S102, adding α-chlorotoluene and carrying out heat preservation reaction; S103, after the heat preservation reaction is completed, adding a mixed solution of acetone and toluene for recrystallization to obtain a toughening agent prepolymer; S104, adding the toughening agent prepolymer to polyamide 6 resin, putting into a twin-screw extruder for melt mixing, extruding from a nozzle through a die plate, drawing into strips, cutting into pellets, and drying to obtain the polyamide toughening agent.

5. The high toughness biaxially oriented polyamide film according to claim 4, characterized in that: The catalyst is any one of aluminum trichloride, boron trifluoride, sulfur trioxide and ferric bromide, or a combination of any of them.

6. The high toughness biaxially oriented polyamide film according to claim 4, characterized in that: The weight ratio of the 3-amino-4,4,4-trifluorobutyric acid, 2,2'-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 and the toughening agent prepolymer is (20-80): (20-80).

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

8. 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 anti-blocking agent and 80-97 parts of polyamide 6 are put into a twin-screw extruder, melt-extruded at 230-270° C., drawn into strips, cooled, pelletized and dried to obtain the anti-sticking masterbatch.

9. The high-toughness biaxially oriented polyamide film according to claim 8, characterized in that: The lubricant is any one of erucamide, PE wax, ethylene bisstearamide and oleamide, or any combination of several thereof; The anti-blocking agent is any one of kaolin, silicon dioxide, calcium carbonate, diatomaceous earth and talc, or a combination of any two of them.

10. A method for preparing a high-toughness biaxially oriented polyamide film according to any one of claims 1 to 9, characterized in that: The following steps are involved: Dry the raw materials and control the moisture content of the raw materials to ≤800 ppm; The raw materials of the lower surface layer, the middle layer and the upper surface layer are mixed according to the proportions, and then respectively put into the extruder, melted and plasticized at 230-270°C, and flowed out through the hanger-shaped die head; The melt is attached to the cold drum using a low-pressure air knife to form a thick sheet with a thickness of 100-350 μm and a cold drum temperature of 6-30°C. The thick sheet is sent into a longitudinal tenter for stretching, with a preheating temperature of 45-60°C, a stretching temperature of 45-65°C, a stretching ratio of 2.5-3.5 times, and then cooled for shaping; The longitudinally stretched film is sent to a transverse tenter for stretching, with a preheating temperature of 60-85°C, a stretching temperature of 70-150°C, and a stretching ratio of 3.0-4.5 times; The stretched film is subjected to heat setting treatment, the setting temperature is 190-220°C, and the setting time is 1-50 s; The film is cooled and corona treated, with a corona treatment power of 6~15 Wmin / m 2 After the treatment, the film is rolled up and cut according to specifications to obtain the high-toughness biaxially oriented polyamide film.

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