A flame-retardant biaxially oriented polyamide film and its preparation method

Abstract

This invention relates to the field of polyamide film flexible packaging technology, and particularly to a flame-retardant biaxially oriented polyamide film and its preparation method. The polyamide film, from top to bottom, consists of a flame-retardant upper layer, a flame-retardant polyamide core layer, and a flame-retardant lower layer. By mass parts: the flame-retardant upper layer comprises 1-10 parts of anti-sticking masterbatch and 90-99 parts of flame-retardant nylon composite material; the flame-retardant polyamide core layer comprises 1-15 parts of 3-ethylidene bis(ethylphosphonic acid) aluminum salt and 85-99 parts of flame-retardant nylon composite material; the flame-retardant lower layer comprises 1-10 parts of anti-sticking masterbatch and 90-99 parts of flame-retardant nylon composite material. The flame-retardant biaxially oriented polyamide film provided by this invention not only has excellent flame-retardant properties but also superior mechanical properties, is environmentally friendly and pollution-free, and is particularly suitable for the field of electronic product packaging.

Description

Technical Field

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

[0002] BOPA film, or biaxially oriented nylon film, is one of the three most popular films currently available. Besides its high tensile strength and excellent puncture resistance, it also boasts outstanding gas barrier properties, pinhole resistance, transparency, and printability. It meets the requirements for high barrier properties, high strength, high transparency, thinness, lightweight, and an extremely wide operating temperature range (-60℃ to 150℃) in packaging materials, and is therefore widely used in many packaging fields, including food packaging, pharmaceutical packaging, cosmetic packaging, and mechanical and electronic product packaging.

[0003] With the continuous development of society and the economy, BOPA film has been developed for applications in other new fields, such as aluminum-plastic encapsulation film for lithium batteries and packaging for electronic products. Lithium batteries and electronic products may pose a risk of spontaneous combustion or explosion, or even fire, during use. Therefore, the nylon film used for packaging these products also needs to have good flame retardancy. However, nylon material itself has a low flame retardancy rating, only reaching UL94 V-2, with an oxygen index of approximately 24, which does not meet the application standards for lithium batteries and electronic products.

[0004] In existing technologies, halogenated flame retardants are commonly used to improve the flame retardancy of BOPA films. However, halogenated flame retardants produce a large amount of corrosive fumes and toxic gases during combustion. These substances not only pollute the environment but also threaten life and property safety.

[0005] Furthermore, due to the bulging and deformation issues of battery products such as lithium batteries, the tensile strength of their packaging is particularly important. If the packaging breaks due to bulging or deformation of lithium batteries, it will pose a safety hazard. To enhance flame retardancy, conventional flame-retardant films typically employ inorganic or halogenated flame retardants, such as the flame-retardant matte polyamide film disclosed in CN 116100895 A. However, when these existing flame retardants are added to BOPA films, they not only fail to meet the biaxial tensile strength requirements of battery products such as lithium batteries, but some flame retardants may even reduce their biaxial tensile strength, compromising safety. Summary of the Invention

[0006] To address the issue of simultaneously achieving flame retardancy and meeting biaxial tensile strength requirements in biaxially oriented polyamide films, this invention provides a flame-retardant biaxially oriented polyamide film, wherein the film comprises, from top to bottom, a flame-retardant upper surface layer, a flame-retardant polyamide core layer, and a flame-retardant lower surface layer.

[0007] By weight parts:

[0008] The flame-retardant upper surface layer comprises 1 to 10 parts of anti-sticking masterbatch and 90 to 99 parts of flame-retardant nylon composite material;

[0009] The flame-retardant polyamide core layer comprises 1 to 15 parts of 3-ethylidene bis(ethylphosphonic acid) aluminum salt and 85 to 99 parts of flame-retardant nylon composite material.

[0010] The flame-retardant lower surface layer comprises 1 to 10 parts of anti-sticking masterbatch and 90 to 99 parts of flame-retardant nylon composite material;

[0011] The flame-retardant nylon composite material is polymerized from caprolactam, purified water, flame-retardant units, glacial acetic acid, and molecular chain extender in a mass ratio of 62-89.8:5-10:5-20:0.1-3:0.1-5.

[0012] In one embodiment, the flame retardant unit is a compound of an active dicarboxylic acid phosphine oxide flame retardant monomer, a polyhydroxyphosphonate ester, and methyl 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-propionate 10-oxide in a mass ratio of 20-40:30-50:10-50.

[0013] In one embodiment, the polymerization of the flame-retardant nylon composite material includes the following steps:

[0014] Add caprolactam, purified water, flame retardant unit, glacial acetic acid, and molecular chain extender to a high-pressure reactor, evacuate for 10 to 120 minutes, purge with nitrogen for 5 to 40 minutes, and circulate 3 to 10 times to ensure that all components are under nitrogen protection and control the pressure in the high-pressure reactor to maintain at 0.1 to 1.5 MPa.

[0015] Heat the high-pressure reactor to 50-100°C, and simultaneously turn on the stirrer. Control the stirring speed at 20-150 r / min, and keep it under these conditions for 1-10 hours to ensure that it is completely melted and becomes a homogeneous fluid.

[0016] The high-pressure reactor is heated to 210–290°C and reacted under these conditions for 2–24 hours. The pressure is then released and reduced to atmospheric pressure, while the temperature is lowered to 30–100°C to obtain the polymer.

[0017] The desired flame-retardant nylon composite material is obtained by extruding the polymer, cutting it into pellets using a casting belt, drying it at 80–120°C, and controlling the moisture content to be below 600 ppm.

[0018] In one embodiment, the dicarboxylic acid phosphine oxide flame retardant monomer is a substance comprising the following structure:

[0019] ;

[0020] The polyhydroxyphosphonate is a substance comprising the following structure:

[0021] ;

[0022] The 9,10-dihydro-9-oxa-10-phosphaphenanthrene oxide is a substance comprising the following structure:

[0023] or .

[0024] In one embodiment, the particle size D of the 3-ethylidene bis(ethylphosphonic acid) aluminum salt is... 50 ≤1.2μm, particle size D 95 ≤3.0μm, and the phosphorus content of aluminum salts is ≥23%.

[0025] In one embodiment, the anti-sticking masterbatch is composed of polyamide 6 and / or lubricant and / or opening agent and / or antioxidant and / or nucleating agent.

[0026] In one embodiment, the anti-sticking masterbatch, by weight, consists of 70-91.6 parts polyamide 6, 3-10 parts lubricant, 5-15 parts opening agent, 0.3-3 parts antioxidant and 0.1-2 parts nucleating agent.

[0027] In one embodiment, the lubricant is selected from any one or a mixture of at least two of oleamide, erucamide, ethylene dilauramide, stearamide, silicone powder, ethylene dioleamide, and ethylene distearamide in any proportion;

[0028] The opening agent is selected from any one or at least two of the following: organosilicon resin, magnesium carbonate, alumina, talc, silica, calcium carbonate, titanium dioxide, kaolin, barium carbonate, and diatomaceous earth, mixed in any proportion.

[0029] The antioxidant is selected from any one or a mixture of at least two of antioxidants 1010, 1098, 168, SEED, and DNP in any proportion.

[0030] The nucleating agent is selected from any one or a mixture of at least two of the following: autolactam ring dimer and sodium 2,2′-methylene-bis-(4,6-di-tert-butylphenyl) phosphate;

[0031] The molecular chain extender is 1,2-cyclohexanediol diglycidyl ether.

[0032] In one embodiment, the thickness of the polyamide film is 10–50 μm;

[0033] The thickness of the flame-retardant upper and lower surface layers is 1–4 μm; the thickness of the flame-retardant polyamide core layer is 2–48 μm.

[0034] The present invention also provides a method for preparing a flame-retardant biaxially oriented polyamide film as described above, comprising the following steps:

[0035] S100: Polyamide 6 and / or lubricant and / or opening agent and / or antioxidant and / or nucleating agent are mixed in a high-speed mixer according to a set ratio, and then melt-blended, extruded, drawn into strands, and pelletized in a twin-screw extruder to obtain the required anti-sticking masterbatch, which is then dried for later use;

[0036] The extruder temperature is 225–275℃, the drying temperature is 70–100℃, and the moisture content of the final anti-sticking masterbatch is below 800 ppm.

[0037] S200: Mix flame-retardant nylon composite material and 3-ethylidene bis(ethylphosphonic acid) aluminum salt in a set ratio, and put them into a high-speed mixer for uniform mixing to ensure even dispersion. Then, melt-blend, extrude, stretch, and pelletize the mixture through a twin-screw extruder to obtain the required flame-retardant polyamide core material, and dry it for later use.

[0038] The extruder temperature is 225–265℃, the drying temperature is 70–110℃, and the final moisture content is below 600 ppm.

[0039] S300: Different raw materials are added to the extruders for the flame-retardant upper surface layer, flame-retardant polyamide core layer, and flame-retardant lower surface layer, respectively, and then melted and plasticized through their respective extruders at a temperature of 240-280°C, and flowed out through a T-die.

[0040] S400: A low-pressure air knife is used to attach the melt onto a cooling drum to form a thick sheet, wherein the thickness of the sheet is 90-600 μm and the temperature of the cooling drum is 10-45℃.

[0041] S500: Immerse the thick sheet in a water bath at 30-85°C for pretreatment;

[0042] S600: After heating the thick sheet, synchronous biaxial stretching is performed using a Bruckner magnetic levitation synchronous biaxial stretching device, wherein the stretching temperature is 145~210℃ and the stretching ratio is 2.9×2.9~4.0×4.0.

[0043] S700. The stretched film is heat-set at a temperature of 170–228°C for 1–50 seconds. The film is then cooled and subjected to corona treatment at a power of 5–16 W / min / m², and then wound up.

[0044] S800. The wound biaxially oriented polyamide film is cut as required to obtain the flame-retardant biaxially oriented polyamide film.

[0045] The flame-retardant biaxially oriented polyamide film provided by this invention has the following beneficial effects:

[0046] It adopts a multi-layer flame-retardant design structure, which has outstanding flame-retardant performance and builds three flame-retardant defenses for the film; and the flame retardant of the flame-retardant polyamide core layer is selected from different types of flame retardants, which has a synergistic effect of multiple components and avoids the flame-retardant defects of a single material.

[0047] The flame retardant used has good compatibility, which can effectively avoid the problem of decreased mechanical properties caused by large addition. In addition, the flame retardant is not easy to precipitate, and has little impact on mechanical properties.

[0048] In a preferred embodiment, 1,2-cyclohexanediol diglycidyl ether is selected as the molecular chain extender in the flame-retardant biaxially oriented polyamide film of the present invention. Combined with other technical features of the biaxially oriented polyamide film of the present invention, adding a small amount of 1,2-cyclohexanediol diglycidyl ether can increase the viscosity of the material, significantly improve the melt strength, and ultimately further enhance the mechanical properties of the material. Attached Figure Description

[0049] 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.

[0050] Figure 1 This is a schematic diagram of a flame-retardant biaxially oriented polyamide film structure provided by the present invention.

[0051] Figure Labels

[0052] 10. Flame-retardant upper surface layer

[0053] 20. Flame-retardant polyamide core layer

[0054] 30. Flame-retardant lower surface layer Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0056] This invention provides the following embodiments of flame-retardant biaxially oriented polyamide films, such as... Figure 1 As shown, from top to bottom, it consists of a flame-retardant upper surface layer 10, a flame-retardant polyamide core layer 20, and a flame-retardant lower surface layer 30.

[0057] Example 1

[0058] The total thickness of the polyamide film is 15 μm; of which, the thickness of the flame-retardant upper and lower surface layers is 2 μm each; and the thickness of the flame-retardant polyamide core layer is 11 μm.

[0059] Flame-retardant biaxially oriented polyamide film by weight:

[0060] Flame-retardant top layer: consists of 5 parts of anti-sticking masterbatch and 95 parts of flame-retardant nylon composite material;

[0061] The flame-retardant polyamide core layer comprises 8 parts of 3-ethylidene bis(ethylphosphonic acid) aluminum salt and 92 parts of flame-retardant nylon composite material;

[0062] The flame-retardant lower surface layer consists of 5 parts of anti-sticking masterbatch and 95 parts of flame-retardant nylon composite material.

[0063] Flame-retardant nylon composite material: comprising 80.2 parts caprolactam, 6 parts purified water, 12 parts flame-retardant units, 0.8 parts glacial acetic acid, and 1 part molecular chain extender; wherein the molecular chain extender is 1,2-cyclohexanediol diglycidyl ether.

[0064] The flame retardant unit consists of 30 parts of active dicarboxylic acid phosphine oxide flame retardant monomer, 40 parts of polyhydroxyphosphonate ester and 30 parts of 9,10-dihydro-9-oxa-10-phosphaphenanthrene oxide.

[0065] The preparation method of flame-retardant nylon composite material is as follows:

[0066] Add caprolactam, purified water, flame retardant unit, glacial acetic acid, and molecular chain extender to a high-pressure reactor, evacuate for 60 minutes, purge with nitrogen for 20 minutes, and circulate 6 times to ensure that each component is under nitrogen protection and control the pressure in the high-pressure reactor to maintain at 0.8 MPa.

[0067] The high-pressure reactor is heated to 80°C, and stirring is started at a speed of 90 r / min. Under these conditions, the reactor is kept in the reactor for 6 hours to ensure that it is completely melted and becomes a homogeneous fluid.

[0068] The high-pressure reactor was heated to 260°C and reacted under these conditions for 18 hours. The pressure was then released and reduced to atmospheric pressure, while the temperature was lowered to 80°C to obtain the polymer.

[0069] The polymer is discharged, granulated by casting, dried at 90°C, and the moisture content is controlled to be below 500 ppm to obtain the flame-retardant nylon composite material required in this embodiment.

[0070] Anti-sticking masterbatch: by weight, it contains 82.5 parts polyamide 6, 5 parts lubricant, 10 parts opening agent, 1.5 parts antioxidant and 1 part nucleating agent.

[0071] The lubricant is selected from stearamide; the opening agent is selected from silica; the antioxidant is selected from antioxidant 1098 and antioxidant 168 mixed in a 2:1 ratio; the nucleating agent is caprolactam cyclic dimer.

[0072] The preparation method of the flame-retardant biaxially oriented polyamide film in this embodiment is as follows:

[0073] Step 1: Polyamide 6 and / or lubricant and / or opening agent and / or antioxidant and / or nucleating agent are mixed in a high-speed mixer according to a set ratio. The mixture is then melt-blended, extruded, drawn into strands, and pelletized in a twin-screw extruder to obtain the required anti-sticking masterbatch, which is then dried for later use. The extruder temperature is 250℃, the drying temperature is 80℃, and the moisture content of the final anti-sticking masterbatch is kept below 700ppm.

[0074] Step 2: The flame-retardant nylon composite material and 3-ethylidene bis(ethylphosphonic acid) aluminum salt are mixed in a set ratio and placed in a high-speed mixer for homogenization to ensure uniform dispersion. Then, the mixture is melt-blended, extruded, drawn into strands, and pelletized using a twin-screw extruder to obtain the desired flame-retardant polyamide core material, which is then dried for later use. The extruder temperature is 245℃, the drying temperature is 80℃, and the final moisture content is kept below 550ppm.

[0075] Step 3: According to the formula design requirements, add different raw materials into the extruders of the flame-retardant upper surface layer, flame-retardant polyamide core layer and flame-retardant lower surface layer respectively, and then melt and plasticize them through their respective extruders at a temperature of 260°C, and flow out through the T-die;

[0076] Step 4: Use a low-pressure air knife to attach the melt onto the cooling drum to form a thick sheet, wherein the thickness of the sheet is 195μm and the temperature of the cooling drum is 20℃;

[0077] Step 5: Immerse the thick sheet in a 55℃ water bath for pretreatment;

[0078] Step 6: After heating the thick sheet, synchronous biaxial stretching is performed using a Bruckner magnetic levitation synchronous biaxial stretching device, where the stretching temperature is 190℃ and the stretching ratio is 3.1×3.5.

[0079] Step 7: The stretched film is heat-set at a temperature of 210℃ for 30 seconds. Then the film is cooled and subjected to corona treatment at a power of 9Wmin / m², and then wound up.

[0080] Step 8: Cut the wound biaxially oriented polyamide film as required to obtain the flame-retardant biaxially oriented polyamide film with a thickness of 15 μm.

[0081] Example 2

[0082] The total thickness of the polyamide film is 12 μm; of which, the thickness of the flame-retardant upper and lower surface layers is 1 μm; and the thickness of the flame-retardant polyamide core layer is 10 μm.

[0083] Flame-retardant biaxially oriented polyamide film by weight:

[0084] Flame-retardant top layer: consists of 2 parts of anti-sticking masterbatch and 98 parts of flame-retardant nylon composite material;

[0085] Flame-retardant polyamide core layer: comprising 3 parts of 3-ethylidene bis(ethylphosphonic acid) aluminum salt and 97 parts of flame-retardant nylon composite material;

[0086] The flame-retardant lower surface layer consists of 2 parts of anti-sticking masterbatch and 98 parts of flame-retardant nylon composite material.

[0087] Flame-retardant nylon composite material: comprising 88.5 parts caprolactam, 5 parts purified water, 6 parts flame-retardant unit, 0.2 parts glacial acetic acid, and 0.3 parts molecular chain extender; wherein the molecular chain extender is 1,2-cyclohexanediol diglycidyl ether.

[0088] The flame retardant unit consists of 20 parts of active dicarboxylic acid phosphine oxide flame retardant monomer, 30 parts of polyhydroxyphosphonate ester and 50 parts of 9,10-dihydro-9-oxa-10-phosphaphenanthrene oxide.

[0089] The preparation method of flame-retardant nylon composite material is as follows:

[0090] Add caprolactam, purified water, flame retardant unit, glacial acetic acid, and molecular chain extender to a high-pressure reactor, evacuate for 10 minutes, purge with nitrogen for 5 minutes, and circulate 3 times to ensure that each component is under nitrogen protection and control the pressure in the high-pressure reactor to maintain at 0.2 MPa.

[0091] The high-pressure reactor is heated to 60°C, and stirring is started at a speed of 20 r / min. The reactor is stirred for 1.5 hours under these conditions to ensure that it is completely melted and becomes a homogeneous fluid.

[0092] The high-pressure reactor was heated to 220°C and reacted under these conditions for 5 hours. The pressure was then released and reduced to atmospheric pressure, while the temperature was lowered to 35°C to obtain the polymer.

[0093] The desired flame-retardant nylon composite material is obtained by extruding the polymer, cutting it into pellets using a casting belt, drying it at 80°C, and controlling the moisture content to be below 600 ppm.

[0094] Anti-sticking masterbatch: by weight, it contains 91.6 parts polyamide 6, 3 parts lubricant, 5 parts opening agent, 0.3 parts antioxidant and 0.1 parts nucleating agent.

[0095] The lubricant is selected from erucamide; the opening agent is selected from talc; the antioxidant is selected from antioxidant 1010 and antioxidant 168 mixed in a 3:1 ratio; the nucleating agent is sodium salt of 2,2′-methylene-bis-(4,6-di-tert-butylphenyl) phosphate.

[0096] The preparation method of the flame-retardant biaxially oriented polyamide film in this embodiment is as follows:

[0097] Step 1: Polyamide 6 and / or lubricant and / or opening agent and / or antioxidant and / or nucleating agent are mixed in a high-speed mixer according to a set ratio. The mixture is then melt-blended, extruded, drawn into strands, and pelletized in a twin-screw extruder to obtain the required anti-sticking masterbatch, which is then dried for later use. The extruder temperature is 225℃, the drying temperature is 70℃, and the moisture content of the final anti-sticking masterbatch is kept below 800ppm.

[0098] Step 2: The flame-retardant nylon composite material and 3-ethylidene bis(ethylphosphonic acid) aluminum salt are mixed in a set ratio and placed in a high-speed mixer for homogenization to ensure uniform dispersion. Then, the mixture is melt-blended, extruded, drawn into strands, and pelletized using a twin-screw extruder to obtain the desired flame-retardant polyamide core material, which is then dried for later use. The extruder temperature is 225℃, the drying temperature is 70℃, and the final moisture content is kept below 600ppm.

[0099] Step 3: According to the formula design requirements, add different raw materials into the extruders of the flame-retardant upper surface layer, flame-retardant polyamide core layer and flame-retardant lower surface layer respectively, and then melt and plasticize them through their respective extruders at a temperature of 245°C, and flow out through the T-die;

[0100] Step 4: Use a low-pressure air knife to attach the melt onto the cooling drum to form a thick sheet, wherein the thickness of the sheet is 145μm and the temperature of the cooling drum is 12℃;

[0101] Step 5: Immerse the thick sheet in a 45℃ water bath for pretreatment;

[0102] Step 6: After heating the thick sheet, synchronous biaxial stretching is performed using a Bruckner magnetic levitation synchronous biaxial stretching device, where the stretching temperature is 160℃ and the stretching ratio is 3.0×3.0.

[0103] Step 7: The stretched film is heat-set at a temperature of 195℃ for 5 seconds. Then the film is cooled and subjected to corona treatment at a power of 6Wmin / m², and then wound up.

[0104] Step 8: Cut the wound biaxially oriented polyamide film as required to obtain the flame-retardant biaxially oriented polyamide film with a thickness of 12 μm.

[0105] Example 3

[0106] The total thickness of the polyamide film is 25 μm; of which, the thickness of the flame-retardant upper and lower surface layers is 2.5 μm each; and the thickness of the flame-retardant polyamide core layer is 20 μm.

[0107] Flame-retardant biaxially oriented polyamide film by weight:

[0108] Flame-retardant top layer: consists of 8 parts of anti-sticking masterbatch and 92 parts of flame-retardant nylon composite material;

[0109] The flame-retardant polyamide core layer comprises 13 parts of 3-ethylene bis(ethylphosphonic acid) aluminum salt and 87 parts of flame-retardant nylon composite material;

[0110] The flame-retardant lower surface layer consists of 9 parts of anti-sticking masterbatch and 91 parts of flame-retardant nylon composite material.

[0111] Flame-retardant nylon composite material: comprising 64.7 parts caprolactam, 9 parts purified water, 19 parts flame-retardant units, 2.8 parts glacial acetic acid, and 4.5 parts molecular chain extender; wherein the molecular chain extender is 1,2-cyclohexanediol diglycidyl ether.

[0112] The flame retardant unit consists of 40 parts of active dicarboxylic acid phosphine oxide flame retardant monomer, 50 parts of polyhydroxyphosphonate ester and 10 parts of 9,10-dihydro-9-oxa-10-phosphaphenanthrene oxide.

[0113] The preparation method of flame-retardant nylon composite material is as follows:

[0114] Add caprolactam, purified water, flame retardant unit, glacial acetic acid, and molecular chain extender to a high-pressure reactor, evacuate for 110 minutes, purge with nitrogen for 35 minutes, and circulate 9 times to ensure that each component is under nitrogen protection and control the pressure in the high-pressure reactor to maintain at 1.2 MPa.

[0115] The high-pressure reactor is heated to 90°C, and stirring is started at a speed of 150 r / min. Under these conditions, the reactor is kept in the reactor for 9 hours to ensure that it is completely melted and becomes a homogeneous fluid.

[0116] The high-pressure reactor was heated to 280°C and reacted under these conditions for 23 hours. The pressure was then released and reduced to atmospheric pressure, while the temperature was lowered to 90°C to obtain the polymer.

[0117] The desired flame-retardant nylon composite material is obtained by extruding the polymer, cutting it into pellets using a casting belt, drying it at 110°C, and controlling the moisture content to be below 500 ppm.

[0118] Anti-sticking masterbatch: by weight, it contains 74.7 parts polyamide, 6 parts lubricant, 9 parts opening agent, 12 parts antioxidant, 2.5 parts antioxidant and 1.8 parts nucleating agent.

[0119] The lubricant is selected from erucamide and stearamide mixed in a 1:2 ratio; the opening agent is selected from silica; the antioxidant is selected from antioxidant 1010, antioxidant 168 and antioxidant SEED mixed in a 3:1:1 ratio; the nucleating agent is selected from autolactam ring dimer and sodium salt of 2,2′-methylene-bis-(4,6-di-tert-butylphenyl) phosphate mixed in a 1:1 ratio.

[0120] The preparation method of the flame-retardant biaxially oriented polyamide film in this embodiment is as follows:

[0121] Step 1: Polyamide 6 and / or lubricant and / or opening agent and / or antioxidant and / or nucleating agent are mixed in a high-speed mixer according to a set ratio. The mixture is then melt-blended, extruded, drawn into strands, and pelletized in a twin-screw extruder to obtain the required anti-sticking masterbatch, which is then dried for later use. The extruder temperature is 265℃, the drying temperature is 95℃, and the moisture content of the final anti-sticking masterbatch is kept below 500ppm.

[0122] Step 2: The flame-retardant nylon composite material and 3-ethylidene bis(ethylphosphonic acid) aluminum salt are mixed in a set ratio and placed in a high-speed mixer for homogenization to ensure uniform dispersion. Then, the mixture is melt-blended, extruded, drawn into strands, and pelletized using a twin-screw extruder to obtain the desired flame-retardant polyamide core layer material, which is then dried for later use. The extruder temperature is 260℃, the drying temperature is 105℃, and the final moisture content is kept below 450ppm.

[0123] Step 3: According to the formula design requirements, add different raw materials into the extruders of the flame-retardant upper surface layer, flame-retardant polyamide core layer and flame-retardant lower surface layer respectively, and then melt and plasticize them through their respective extruders at a temperature of 270°C, and flow out through the T-die;

[0124] Step 4: Use a low-pressure air knife to attach the melt onto the cooling drum to form a thick sheet, wherein the thickness of the sheet is 300μm and the temperature of the cooling drum is 40℃;

[0125] Step 5: Immerse the thick sheet in an 80℃ water bath for pretreatment;

[0126] Step 6: After heating the thick sheet, synchronous biaxial stretching is performed using a Bruckner magnetic levitation synchronous biaxial stretching device, where the stretching temperature is 205℃ and the stretching ratio is 3.3×3.8.

[0127] Step 7: The stretched film is heat-set at a temperature of 225℃ for 40 seconds. Then the film is cooled and subjected to corona treatment at a power of 15Wmin / m², and then wound up.

[0128] Step 8: Cut the wound biaxially oriented polyamide film as required to obtain the flame-retardant biaxially oriented polyamide film with a thickness of 25 μm.

[0129] In Examples 1, 2, and 3 above, the particle size D of 3-ethylidene bis(ethylphosphonic acid) aluminum salt was... 50 ≤1.2μm, particle size D 95 ≤3.0μm; the phosphorus content of 3-ethylidene bis(ethylphosphonic acid) aluminum salt is ≥23%.

[0130] Active dicarboxylic acid phosphine oxide flame retardant monomers refer to substances with the following structure:

[0131]

[0132] Polyhydroxyphosphonates are substances having the following structure:

[0133]

[0134] In Examples 1 and 2, 9,10-dihydro-9-oxa-10-phosphaphenanthrene oxide is a substance having the following structure:

[0135] ;

[0136] The 9,10-dihydro-9-oxa-10-phosphaphenanthrene oxide in Example 3 refers to a substance having the following structure:

[0137]

[0138] The present invention also provides the following comparative examples:

[0139] Comparative Example 1

[0140] Compared with Example 1, the difference is that, by mass parts, the flame-retardant biaxially oriented polyamide film comprises 5 parts of anti-sticking masterbatch and 95 parts of polyamide 6 in the upper flame-retardant layer; 100 parts of polyamide 6 in the flame-retardant polyamide core layer; and 5 parts of anti-sticking masterbatch and 95 parts of polyamide 6 in the lower flame-retardant layer.

[0141] The preparation method is as follows:

[0142] Step 1: Polyamide 6 and / or lubricant and / or opening agent and / or antioxidant and / or nucleating agent are mixed in a high-speed mixer according to a set ratio. The mixture is then melt-blended, extruded, drawn into strands, and pelletized in a twin-screw extruder to obtain the required anti-sticking masterbatch, which is then dried for later use. The extruder temperature is 250℃, the drying temperature is 80℃, and the moisture content of the final anti-sticking masterbatch is kept below 700ppm.

[0143] Step 2: According to the formula design requirements, add different raw materials into the extruders of the flame-retardant upper surface layer, flame-retardant polyamide core layer and flame-retardant lower surface layer respectively, and then melt and plasticize them through their respective extruders at a temperature of 260°C, and flow out through the T-die;

[0144] Step 3: Use a low-pressure air knife to attach the melt to the cooling drum to form a thick sheet, wherein the thickness of the sheet is 195μm and the temperature of the cooling drum is 20℃;

[0145] Step 4: Immerse the thick sheet in a 55℃ water bath for pretreatment;

[0146] Step 5: After heating the thick sheet, synchronous biaxial stretching is performed using a Bruckner magnetic levitation synchronous biaxial stretching device, where the stretching temperature is 190℃ and the stretching ratio is 3.1×3.5.

[0147] Step 6: The stretched film is heat-set at a temperature of 210℃ for 30 seconds. Then the film is cooled and corona treated with a power of 9Wmin / m², and then wound up.

[0148] Step 7: Cut the wound biaxially oriented polyamide film as required to obtain the flame-retardant biaxially oriented polyamide film with a thickness of 15 μm.

[0149] The remaining conditions remain the same as in Example 1.

[0150] Comparative Example 2

[0151] Compared with Example 1, the difference is that the flame-retardant polyamide core layer is composed of 100 parts of flame-retardant nylon composite material;

[0152] The preparation method is as follows:

[0153] Step 1: Polyamide 6 and / or lubricant and / or opening agent and / or antioxidant and / or nucleating agent are mixed in a high-speed mixer according to a set ratio. The mixture is then melt-blended, extruded, drawn into strands, and pelletized in a twin-screw extruder to obtain the required anti-sticking masterbatch, which is then dried for later use. The extruder temperature is 250℃, the drying temperature is 80℃, and the moisture content of the final anti-sticking masterbatch is kept below 700ppm.

[0154] Step 2: According to the formula design requirements, add different raw materials into the extruders of the flame-retardant upper surface layer, flame-retardant polyamide core layer and flame-retardant lower surface layer respectively, and then melt and plasticize them through their respective extruders at a temperature of 260°C, and flow out through the T-die;

[0155] Step 3: Use a low-pressure air knife to attach the melt to the cooling drum to form a thick sheet, wherein the thickness of the sheet is 195μm and the temperature of the cooling drum is 20℃;

[0156] Step 4: Immerse the thick sheet in a 55℃ water bath for pretreatment;

[0157] Step 5: After heating the thick sheet, synchronous biaxial stretching is performed using a Bruckner magnetic levitation synchronous biaxial stretching device, where the stretching temperature is 190℃ and the stretching ratio is 3.1×3.5.

[0158] Step 6: The stretched film is heat-set at a temperature of 210℃ for 30 seconds. Then the film is cooled and corona treated with a power of 9Wmin / m², and then wound up.

[0159] Step 7: Cut the wound biaxially oriented polyamide film as required to obtain the flame-retardant biaxially oriented polyamide film with a thickness of 15 μm.

[0160] The remaining conditions remain the same as in Example 1.

[0161] Comparative Example 3

[0162] Compared with Example 1, the difference is that the flame-retardant upper surface layer and the flame-retardant lower surface layer include 5 parts of anti-sticking masterbatch and 95 parts of polyamide 6;

[0163] The flame-retardant polyamide core layer comprises 8 parts of 3-ethylidene bis(ethylphosphonic acid) aluminum salt and 92 parts of polyamide 6;

[0164] The preparation method is as follows:

[0165] Step 1: Polyamide 6 and / or lubricant and / or opening agent and / or antioxidant and / or nucleating agent are mixed in a high-speed mixer according to a set ratio. The mixture is then melt-blended, extruded, drawn into strands, and pelletized in a twin-screw extruder to obtain the required anti-sticking masterbatch, which is then dried for later use. The extruder temperature is 250℃, the drying temperature is 80℃, and the moisture content of the final anti-sticking masterbatch is kept below 700ppm.

[0166] Step 2: Polyamide 6 and 3-ethylidene bis(ethylphosphonic acid) aluminum salt are mixed in a set ratio and placed in a high-speed mixer for homogenization to ensure uniform dispersion. Then, the mixture is melt-blended, extruded, drawn into strands, and pelletized using a twin-screw extruder to obtain the desired flame-retardant polyamide core layer material, which is then dried for later use. The extruder temperature is 245℃, the drying temperature is 80℃, and the final moisture content is kept below 550ppm.

[0167] Step 3: According to the formula design requirements, add different raw materials into the extruders of the flame-retardant upper surface layer, flame-retardant polyamide core layer and flame-retardant lower surface layer respectively, and then melt and plasticize them through their respective extruders at a temperature of 260°C, and flow out through the T-die;

[0168] Step 4: Use a low-pressure air knife to attach the melt onto the cooling drum to form a thick sheet, wherein the thickness of the sheet is 195μm and the temperature of the cooling drum is 20℃;

[0169] Step 5: Immerse the thick sheet in a 55℃ water bath for pretreatment;

[0170] Step 6: After heating the thick sheet, synchronous biaxial stretching is performed using a Bruckner magnetic levitation synchronous biaxial stretching device, where the stretching temperature is 190℃ and the stretching ratio is 3.1×3.5.

[0171] Step 7: The stretched film is heat-set at a temperature of 210℃ for 30 seconds. Then the film is cooled and subjected to corona treatment at a power of 9Wmin / m², and then wound up.

[0172] Step 8: Cut the wound biaxially oriented polyamide film as required to obtain the flame-retardant biaxially oriented polyamide film with a thickness of 15 μm.

[0173] The remaining conditions remain the same as in Example 1.

[0174] Comparative Example 4

[0175] Compared with Example 1, the difference is that the flame-retardant unit in the flame-retardant nylon composite material is composed of active dicarboxylic acid phosphine oxide flame-retardant monomers;

[0176] Among them, active dicarboxylic acid phosphine oxide flame retardant monomers refer to substances with the following structure:

[0177]

[0178] The remaining conditions remain the same as in Example 1.

[0179] Comparative Example 5

[0180] Compared with Example 1, the difference is that the flame-retardant unit in the flame-retardant nylon composite material is composed of polyhydroxyphosphonate;

[0181] Polyhydroxyphosphonates refer to substances having the following structure:

[0182] .

[0183] The remaining conditions remain the same as in Example 1.

[0184] Comparative Example 6

[0185] Compared with Example 1, the difference is that the flame-retardant unit in the flame-retardant nylon composite material is composed of methyl 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-propionate 10-oxide.

[0186] Among them, 9,10-dihydro-9-oxa-10-phosphaphenanthrene oxide refers to substances having the following structure:

[0187] .

[0188] The remaining conditions remain the same as in Example 1.

[0189] Comparative Example 7

[0190] Compared with Example 1, the difference is that the flame-retardant unit in the flame-retardant nylon composite material is composed of active dicarboxylic acid phosphine oxide flame-retardant monomer and polyhydroxy phosphonate.

[0191] Among them, active dicarboxylic acid phosphine oxide flame retardant monomers refer to substances with the following structure:

[0192]

[0193] Polyhydroxyphosphonates are substances having the following structure:

[0194] .

[0195] The remaining conditions remain the same as in Example 1.

[0196] Comparative Example 8

[0197] Compared with Example 1, the difference is that the flame-retardant unit in the flame-retardant nylon composite material is composed of an active dicarboxylic acid phosphine oxide flame-retardant monomer and methyl 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-propionate 10-oxide.

[0198] Among them, active dicarboxylic acid phosphine oxide flame retardant monomers refer to substances with the following structure:

[0199] ;

[0200] 9,10-dihydro-9-oxa-10-phosphaphenanthrene oxide refers to substances having the following structure:

[0201] .

[0202] The remaining conditions are the same as in Example 1.

[0203] Comparative Example 9

[0204] Compared to Example 1, the difference lies in that the flame-retardant unit in the flame-retardant nylon composite material is composed of polyhydroxyphosphonate and methyl 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-propionate 10-oxide;

[0205] Polyhydroxyphosphonates refer to substances having the following structure:

[0206]

[0207] 9,10-dihydro-9-oxa-10-phosphaphenanthrene oxide refers to substances having the following structure:

[0208] .

[0209] The remaining conditions are the same as in Example 1.

[0210] Comparative Example 10

[0211] Compared with Example 1, the difference is that no flame-retardant unit was added to the flame-retardant nylon composite material;

[0212] The flame-retardant nylon composite material comprises 92.2 parts caprolactam, 6 parts purified water, 0.8 parts glacial acetic acid, and 1 part molecular chain extender;

[0213] The remaining conditions are the same as in Example 1.

[0214] Comparative Example 11

[0215] Compared with Example 1, the difference is that no molecular chain extender was added to the flame-retardant nylon composite material;

[0216] The flame-retardant nylon composite material comprises 81.2 parts caprolactam, 6 parts purified water, 12 parts flame-retardant units, and 0.8 parts glacial acetic acid;

[0217] The remaining conditions remain the same as in Example 1.

[0218] The present invention tested the relevant performance of the above embodiments and comparative examples, and the specific results are shown in Table 1:

[0219] Table 1

[0220]

[0221] In Table 1:

[0222] (1) Flame retardant performance test: The test shall be conducted in accordance with the requirements of standard ISO 9773 "Plastics - Determination of burning behavior of thin f1exible vertical specimens in contact with a small-flame retardation source". The flame retardant ratings from high to low are represented by VTM-0, VTM-1 and VTM-2 respectively, while × indicates that the flame retardant rating does not reach VTM-2, and □ indicates that the flame retardant rating is between VTM-2 and VTM-1.

[0223] (2) Tensile strength test: The test shall be conducted in accordance with the requirements of GB / T 1040.3 "Determination of tensile properties of plastics (Part 3: Test conditions for films and sheets)".

[0224] As can be seen from the comparison of Example 1 and Comparative Examples 1-3 in the table above, replacing all or any one of the flame-retardant nylon composite materials in the upper surface layer, flame-retardant polyamide core layer and lower surface layer with the existing polyamide 6 will reduce the flame-retardant properties and tensile strength of the polyamide film.

[0225] As can be seen from Example 1 and Comparative Examples 4-10, the flame-retardant unit prepared by the synergistic use of active dicarboxylic acid phosphine oxide flame-retardant monomer, polyhydroxy phosphonate and 9,10-dihydro-9-oxa-10-phosphaphenanthrene oxide in the technical solution of the present invention can significantly improve the flame-retardant properties and tensile strength of polyamide films.

[0226] As can be seen from Example 1 and Comparative Example 11, the use of the molecular chain extender of the present invention plays a key role in improving the biaxial tensile strength of polyamide films. In particular, the use of 1,2-cyclohexanediol diglycidyl ether as a molecular chain extender in the present invention, combined with other technical features of the present invention, has the effect of increasing the viscosity of the material with a small amount of addition, significantly improving the melt strength, and ultimately improving the mechanical properties of the material.

[0227] In summary, it can be seen that the multi-layer flame-retardant design structure of the film prepared by this invention has outstanding flame-retardant performance, constructing three lines of flame-retardant protection for the film. Furthermore, the flame retardant agents in the flame-retardant polyamide core layer of the substrate film are selected from different types of flame retardants, exhibiting a synergistic effect among multiple components and avoiding the flame-retardant defects of a single material. Compared with biaxially oriented polyamide films produced by traditional methods, the flame-retardant biaxially oriented polyamide film produced by this invention has functional layers that work in harmony to form an inseparable organic whole. It not only possesses outstanding flame-retardant performance but also excellent tensile strength, meeting the demands of markets such as lithium-ion battery packaging and electronic product packaging.

[0228] Furthermore, the film prepared by this invention has a wide range of applications and strong applicability. Its production process is simple, easy to process, has high production efficiency, and is easy to achieve industrial production. The film product prepared by this invention has a delicate appearance, no graininess, and does not affect transparency.

[0229] Preferably, the flame retardant is added through a polymerization reaction, which has the characteristics of good flame retardant effect, less flame retardant component added, and the flame retardant unit used is not easy to precipitate and has little impact on mechanical properties. Compared with conventional flame retardants, this flame retardant material has good compatibility and can effectively avoid the problem of decreased mechanical properties caused by large addition.

[0230] Meanwhile, compared to polyamide films using conventional halogenated flame retardants, which produce large amounts of corrosive fumes and toxic gases during combustion, the raw materials in the polyamide film provided by this invention not only do not pollute the environment but also do not pose a threat to life and property. This has significant social implications.

[0231] Although terms such as upper surface layer, lower surface layer, and flame-retardant polyamide core 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 be contrary to the spirit of the invention.

[0232] 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 flame-retardant biaxially oriented polyamide film, characterized in that: The film is composed of a flame-retardant upper surface layer, a flame-retardant polyamide core layer and a flame-retardant lower surface layer from top to bottom; By weight parts: The flame-retardant upper surface layer comprises 1 to 10 parts of anti-sticking masterbatch and 90 to 99 parts of flame-retardant nylon composite material; The flame-retardant polyamide core layer comprises 1 to 15 parts of 3-ethylidene bis(ethylphosphonic acid) aluminum salt and 85 to 99 parts of flame-retardant nylon composite material. The flame-retardant lower surface layer comprises 1 to 10 parts of anti-sticking masterbatch and 90 to 99 parts of flame-retardant nylon composite material; The flame-retardant nylon composite material is polymerized from caprolactam, purified water, flame-retardant units, glacial acetic acid, and molecular chain extender in a mass ratio of 62-89.8:5-10:5-20:0.1-3:0.1-5. The flame retardant unit is a compound of active dicarboxylic acid phosphine oxide flame retardant monomer, polyhydroxy phosphonate and methyl 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-propionate 10-oxide in a mass ratio of 20-40:30-50:10-50. The dicarboxylic acid phosphine oxide flame retardant monomer comprises a substance with the following structure: ； The polyhydroxyphosphonate is a substance comprising the following structure: ； The 9,10-dihydro-9-oxa-10-phosphaphenanthrene oxide is a substance comprising the following structure: or .

2. The flame-retardant biaxially oriented polyamide film according to claim 1, characterized in that: The polymerization of flame-retardant nylon composite materials includes the following steps: Add caprolactam, purified water, flame retardant unit, glacial acetic acid, and molecular chain extender to a high-pressure reactor, evacuate for 10 to 120 minutes, purge with nitrogen for 5 to 40 minutes, and circulate 3 to 10 times to ensure that all components are under nitrogen protection and control the pressure in the high-pressure reactor to maintain at 0.1 to 1.5 MPa. Heat the high-pressure reactor to 50-100°C, and simultaneously turn on the stirrer. Control the stirring speed at 20-150 r / min, and stir under these conditions until it is completely melted and becomes a homogeneous fluid. The high-pressure reactor is heated to 210–290°C and reacted under these conditions for 2–24 hours. The pressure is then released and reduced to atmospheric pressure, while the temperature is lowered to 30–100°C to obtain the polymer. The polymer is discharged, granulated by casting, dried at 80–120°C with the moisture content controlled below 600 ppm, and the desired flame-retardant nylon composite material is obtained.

3. The flame-retardant biaxially oriented polyamide film according to claim 1, characterized in that: The particle size D of the 3-ethylidene bis(ethylphosphonic acid) aluminum salt 50 ≤1.2μm, particle size D 95 ≤3.0μm, and the phosphorus content of aluminum salts is ≥23%.

4. The flame-retardant biaxially oriented polyamide film according to claim 1, characterized in that: The anti-sticking masterbatch is composed of polyamide 6 and / or lubricant and / or opening agent and / or antioxidant and / or nucleating agent.

5. The flame-retardant biaxially oriented polyamide film according to claim 1, characterized in that: The anti-sticking masterbatch, by weight, consists of 70-91.6 parts polyamide 6, 3-10 parts lubricant, 5-15 parts opening agent, 0.3-3 parts antioxidant and 0.1-2 parts nucleating agent.

6. The flame-retardant biaxially oriented polyamide film according to claim 4, characterized in that: The lubricant is selected from any one or a mixture of at least two of oleamide, erucamide, ethylene dilauramide, stearamide, silicone powder, ethylene dioleamide, and ethylene distearamide in any proportion; The opening agent is selected from any one or at least two of the following: organosilicon resin, magnesium carbonate, alumina, talc, silica, calcium carbonate, titanium dioxide, kaolin, barium carbonate, and diatomaceous earth, mixed in any proportion. The antioxidant is selected from any one or a mixture of at least two of antioxidants 1010, 1098, 168, SEED, and DNP in any proportion. The nucleating agent is selected from any one or a mixture of at least two of the following: autolactam ring dimer and sodium 2,2′-methylene-bis-(4,6-di-tert-butylphenyl) phosphate; The molecular chain extender is 1,2-cyclohexanediol diglycidyl ether.

7. The flame-retardant biaxially oriented polyamide film according to claim 1, characterized in that: The thickness of the polyamide film is 10–50 μm; The thickness of the flame-retardant upper and lower surface layers is 1–4 μm; the thickness of the flame-retardant polyamide core layer is 2–48 μm.

8. A method for preparing a flame-retardant biaxially oriented polyamide film according to any one of claims 1-7, comprising the following steps: S100: Polyamide 6 and / or lubricant and / or opening agent and / or antioxidant and / or nucleating agent are mixed in a high-speed mixer according to a set ratio, and then melt-blended, extruded, drawn into strands, and pelletized in a twin-screw extruder to obtain the required anti-sticking masterbatch, which is then dried for later use; The extruder temperature is 225–275℃, the drying temperature is 70–100℃, and the moisture content of the final anti-sticking masterbatch is below 800 ppm. S200: Mix flame-retardant nylon composite material and 3-ethylidene bis(ethylphosphonic acid) aluminum salt in a set ratio, and put them into a high-speed mixer for uniform mixing to ensure even dispersion. Then, melt-blend, extrude, stretch, and pelletize the mixture through a twin-screw extruder to obtain the required flame-retardant polyamide core material, and dry it for later use. The extruder temperature is 225–265℃, the drying temperature is 70–110℃, and the final moisture content is below 600 ppm. S300: Different raw materials are added to the extruders for the flame-retardant upper surface layer, flame-retardant polyamide core layer, and flame-retardant lower surface layer, respectively, and then melted and plasticized through their respective extruders at a temperature of 240-280°C, and flowed out through a T-die. S400: A low-pressure air knife is used to attach the melt onto a cooling drum to form a thick sheet, wherein the thickness of the sheet is 90-600 μm and the temperature of the cooling drum is 10-45℃. S500: Immerse the thick sheet in a water bath at 30-85°C for pretreatment; S600: After heating the thick sheet, synchronous biaxial stretching is performed using a Bruckner magnetic levitation synchronous biaxial stretching device, wherein the stretching temperature is 145~210℃ and the stretching ratio is 2.9×2.9~4.0×4.

0. S700. The stretched film is heat-set at a temperature of 170–228°C for 1–50 seconds. The film is then cooled and subjected to corona treatment at a power of 5–16 W / min / m², and then wound up. S800. The wound biaxially oriented polyamide film is cut as required to obtain the flame-retardant biaxially oriented polyamide film.

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