An eleven-layer co-extruded film, a preparation process and application in an aviation cable

Abstract

The present application relates to the technical fields of functional film research and manufacturing, and discloses a kind of eleven-layer co-extrusion film, preparation process and application in aviation cable, specifically: with seven methyl hydrogen-containing POSS, diallylamine, diethyl phosphite and 10-undecenal as raw material, through silicium hydrogen addition, Kabachnik-Fields and alkenyl epoxidation reaction, synthesis of halogen-free reactive phosphorus-POSS-nitrogen synergistic flame retardant, it is with the end amino functional group in PA6 resin, PA66 resin through epoxy-amino ring-opening reaction Covalent bond effect, prepare flame-retardant PA masterbatch;Flame-retardant PA masterbatch is used as the raw material of eleven-layer co-extrusion film, adopts eleven-layer co-extrusion blow molding process, and eleven-layer co-extrusion film is prepared.The present application significantly improves the flame-retardant performance of eleven-layer co-extrusion film, and also achieves the beneficial technical effect of significantly enhancing the high-temperature resistance of eleven-layer co-extrusion film.

Description

Technical Field

[0001] This invention relates to the field of functional film research and manufacturing technology, and in particular to an eleven-layer co-extruded film, its preparation process, and its application in aerospace cables. Background Technology

[0002] As a core component of aircraft electrical systems, aviation cables perform crucial functions in power transmission and signal control. Modern passenger aircraft avionics systems contain thousands of cables. If a distributed wiring method is used, it not only occupies a huge amount of space but also fails to meet the requirements of system reliability and maintainability. Through harness design, employing multi-layered bundled and branched structures, the orderly integration of high-density cables and space optimization can be achieved.

[0003] In terms of wire harness protection, aviation wire harnesses are typically wrapped and secured with tape. For high-temperature areas such as engine compartments and landing gear bays, polyimide (PI) tape remains the standard protective material for hot-end areas due to its excellent high-temperature resistance (long-term operating temperature can reach over 200°C) and self-extinguishing properties. However, for general-purpose wire harnesses in normal temperature environments (such as cockpit control panels and seat adjustment systems), the high-temperature resistance of PI tape is excessive.

[0004] Currently, polyimide (PI), which is used to manufacture PI tape, is one of the most expensive engineering plastics. In contrast, polyamide (commonly known as nylon, or PA for short), as a bulk general-purpose engineering plastic, has a much lower raw material cost than polyimide, but its basic models have insufficient flame retardant properties and need to be modified.

[0005] Therefore, this invention aims to develop a novel tape based on modified PA, a low-cost material, which also possesses excellent flame-retardant properties, to replace traditional PI tape for wrapping and fixing wire harnesses under normal temperature conditions. Summary of the Invention

[0006] This invention independently synthesizes a halogen-free reactive phosphorus-POSS-nitrogen synergistic flame retardant, which is grafted onto the main chain of PA molecules through covalent bonding to obtain a flame-retardant PA masterbatch. The flame-retardant PA masterbatch is used as the raw material for an eleven-layer co-extruded film. The eleven-layer co-extruded film obtained by the eleven-layer co-extruded blow molding process is a flame-retardant PA film material. The flame-retardant PA film material is used as the substrate of the tape to manufacture tape for wrapping and fixing aviation wire harnesses used in normal temperature environments.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A process for preparing an eleven-layer co-extruded film includes the following steps:

[0009] Step 1: Preparation of flame-retardant PA masterbatch, specifically: An epoxy-amino ring-opening reaction is conducted between a halogen-free reactive phosphorus-POSS-nitrogen synergistic flame retardant and the terminal amino functional groups in PA6 and PA66 resins to obtain the flame-retardant PA masterbatch; the content of the flame retardant in the flame-retardant PA masterbatch is 3.0-6.9 wt%.

[0010] Step 2: Using flame-retardant PA masterbatch as raw material, set the product structure, film layer formula and dosage of eleven-layer co-extruded film, and use eleven-layer co-extruded film forming process to obtain eleven-layer co-extruded film.

[0011] Preferably, the preparation method of the halogen-free reactive phosphorus-POSS-nitrogen synergistic flame retardant is as follows:

[0012] Intermediate a was prepared by hydrosilylation reaction of 2-2.03 molar equivalents of heptamethylhydrogen-containing POSS with 1 molar equivalent of diallylamine under the action of platinum catalyst.

[0013] Based on the Kabachnik-Fields reaction mechanism, intermediate a, 10-undecenal and diethyl phosphite undergo a condensation reaction to prepare intermediate b;

[0014] Under the action of glacial acetic acid, hydrogen peroxide is used to oxidize the alkenyl functional group in intermediate b into an epoxy functional group to prepare a halogen-free reactive phosphorus-POSS-nitrogen synergistic flame retardant.

[0015] Preferably, the platinum catalyst is a chloroplatinic acid-isopropanol catalyst or a Karstedt catalyst.

[0016] Preferably, the method for preparing the heptamethyl hydrogen-containing POSS is as follows:

[0017] Incompletely condensed trihydroxyheptamethyl cage-like silsesquioxane was prepared by direct hydrolysis condensation using methyltrichlorosilane as a raw material.

[0018] Using incompletely condensed trihydroxyheptamethyl cage-like silsesquioxane as a raw material and trichlorosilane as a apex-capping monomer, heptamethyl hydrogen-containing POSS was prepared through an apex-capping ring-closing reaction.

[0019] Preferably, the method for preparing the flame-retardant PA masterbatch is as follows: PA6 resin, PA66 resin and halogen-free reactive phosphorus-POSS-nitrogen synergistic flame retardant are added to a high-speed mixer, stirred evenly, and then placed in a twin-screw extruder for melt reaction extrusion granulation to obtain the flame-retardant PA masterbatch.

[0020] Preferably, the extrusion temperature of the twin-screw extruder is 250-260℃.

[0021] Preferably, the product structure of the eleven-layer co-extruded film is PA layer a / PA layer b / PA layer c / PA layer d / PA layer e / PA layer f / PA layer g / PA layer h / PA layer i / PA layer j / PA layer k, and the corresponding raw material amounts are 5-15 parts by weight / 5-10 parts by weight / 5-10 parts by weight / 5-10 parts by weight / 5-10 parts by weight / 5-10 parts by weight / 5-10 parts by weight / 5-10 parts by weight / 5-10 parts by weight / 5-10 parts by weight / 15-25 parts by weight, and the raw material for any PA layer is 100wt% flame-retardant PA masterbatch.

[0022] Preferably, the process parameters of the screw extruder corresponding to any PA layer are set as follows: zone 1 temperature is 255-265℃, zone 2 temperature is 265-275℃, zone 3 temperature is 280-290℃, zone 4 temperature is 290-300℃, and screw speed is 35-45 r / min.

[0023] Preferably, the thickness of the eleven-layer co-extruded film is 50-150 μm.

[0024] Preferably, the eleven-layer co-extruded film is used as a substrate, and a pressure-sensitive adhesive is coated on one side of the substrate to obtain PA tape. The PA tape is used to wrap and fix aviation wire harnesses used in normal temperature environments.

[0025] The beneficial effects of this invention are as follows:

[0026] Based on the molecular design mechanism, a halogen-free reactive phosphorus-POSS-nitrogen synergistic flame retardant was synthesized using self-made heptamethyl hydrogen-containing POSS, diallylamine, diethyl phosphite and 10-undecenal as raw materials through hydrosilylation, Kabachnik-Fields and alkenyl epoxidation reactions.

[0027] A halogen-free reactive phosphorus-POSS-nitrogen synergistic flame retardant containing epoxy functional groups is covalently bonded to the terminal amino functional groups in PA6 resin and PA66 resin through an epoxy-amino ring-opening reaction to obtain flame-retardant PA masterbatch.

[0028] Flame-retardant PA masterbatch is used as raw material for eleven-layer co-extruded film. Eleven-layer co-extruded film, i.e. flame-retardant PA film, is produced by using eleven-layer co-extruded blow molding process.

[0029] Experimental results confirm that the flame retardant performance of the eleven-layer co-extruded film prepared by this invention reaches the V-0 level in the GB / T 2408-2021 standard, demonstrating excellent flame retardant performance.

[0030] The flame-retardant mechanism of the eleven-layer co-extruded film is as follows: when phosphorus is heated, it decomposes to produce phosphorus-containing compounds, which promotes the dehydration of the eleven-layer co-extruded film material to form a dense char layer. The silicon in POSS is converted into a stable silica protective layer at high temperature, covering the surface of the char layer and improving the thermal stability and density of the char layer. When the nitrogen source is heated, it releases non-combustible gas, dilutes the concentration of combustible gas and interrupts the combustion chain reaction. Under the synergistic effect of the three, phosphorus promotes char formation, nitrogen expands the char layer and dilutes combustibles, and POSS enhances the stability of the char layer. Together, they can form a stable and dense high-efficiency barrier layer, which can inhibit the transfer of heat and oxygen into the interior of the eleven-layer co-extruded film material, thereby achieving the beneficial technical effect of significantly improving the fire resistance of the eleven-layer co-extruded film. Detailed Implementation Example 1:

[0031] The synthesis mechanism of a halogen-free reactive phosphorus-POSS-nitrogen synergistic flame retardant is as follows:

[0032] Step 1: Under the action of a platinum catalyst, a hydrosilylation reaction occurs between the heptamethylhydrogen-containing POSS (which is a self-made raw material of this invention) and the alkenyl functional group in diallylamine, and the molar ratio of heptamethylhydrogen-containing POSS to diallylamine is controlled to be (2-2.03):1, preferably 2.01:1 in this embodiment, to obtain intermediate a, whose chemical structural formula is:

[0033] ;

[0034] The chemical structural formula of heptamethylhydrogen-containing POSS is as follows:

[0035] ;

[0036] Step 2: Based on the Kabachnik-Fields reaction mechanism, intermediate b is prepared by a condensation reaction involving intermediate a (providing the amine source), 10-undecenal (providing the aldehyde source), and diethyl phosphite (providing the active hydrogen source). Its chemical structural formula is as follows:

[0037] ;

[0038] Step 3: Under the action of glacial acetic acid, hydrogen peroxide is used to oxidize the alkenyl functional group in intermediate b to an epoxy functional group, thus preparing a halogen-free reactive phosphorus-POSS-nitrogen synergistic flame retardant, the chemical structural formula of which is:

[0039] ;

[0040] The specific experimental steps for halogen-free reactive phosphorus-POSS-nitrogen synergistic flame retardants are as follows:

[0041] Step 1: Add 200 mL of acetone and 20 mL of methyltrichlorosilane to a 500 mL three-necked flask equipped with a reflux device. Place a magnetic stir bar in the flask and, when the oil bath temperature stabilizes at 60 °C, start magnetic stirring for 30 min. Then, slowly add 90 mL of distilled water dropwise to the mixture of acetone and methyltrichlorosilane using a 125 mL separatory funnel. Reflux for 24 h, cool to room temperature, filter, wash the resulting solid three times with acetone and filter, then suspend it in pyridine and stir magnetically overnight. Filter to remove insoluble matter, then wash the filter with an equal volume of concentrated hydrochloric acid and ice water mixture, wash with distilled water until neutral, and vacuum dry at 50 °C for 10 h to obtain incompletely condensed trihydroxyheptamethyl cage-like silsesquioxane.

[0042] Add 3g of incompletely condensed trihydroxyheptamethyl cage-like silsesquioxane, 50mL of triethylamine and 100mL of tetrahydrofuran to a 500mL three-necked flask. Stir magnetically for 3min in a stable oil bath at 65℃. Then slowly add the prepared mixed solution of 1.74g of trichlorosilane and 50mL of tetrahydrofuran dropwise to the three-necked flask. Continue reflux for 24h. Cool to room temperature, filter, wash, and dry in a vacuum drying oven at 50℃ for 8h to obtain heptamethyl hydrogen-containing POSS.

[0043] The 1H NMR spectrum of heptamethyl hydrogen-containing POSS is characterized as follows:

[0044] 1 H NMR (CDCl3, 400MHz) δ: 0.04 (s, 12H), 0.14 (s, 9H), 2.93 (s, 1H);

[0045] 5.3 g of heptamethyl hydrogen-containing POSS was added to 80 mL of tetrahydrofuran and mechanically stirred until homogeneous. Then, 4 mL of N,N-dimethylformamide solution containing 0.49 g of diallylamine was added. Nitrogen gas was purged into the system for 30 min to ensure that the reaction was carried out under a nitrogen atmosphere. Next, 0.05 g of Karstedt catalyst was added and stirred until homogeneous. The temperature was raised to 66 °C and refluxed for 48 h. After the reaction was completed, the solvent was removed by rotary evaporation, the product precipitate was separated, and the product was dried under vacuum at 40 °C for 24 h to prepare intermediate a.

[0046] Step 2: Add 9.13g of intermediate a, 2.7g of 10-undecenal and 100mL of anhydrous ethanol to a 500mL three-necked flask, and raise the temperature of the system to 80℃ under a nitrogen atmosphere. Stir the reaction for 4h, add 10mL of anhydrous ethanol solution containing 1.1g of diethyl phosphite, and stir the reaction for 8h. After the reaction is completed, remove the anhydrous ethanol by rotary evaporation, wash, and vacuum dry at 40℃ for 12h to prepare intermediate b.

[0047] Step 3: Add 5g of intermediate b to 60mL of chloroform, add 5mL of glacial acetic acid and 0.25mL of concentrated sulfuric acid, stir and heat to 70℃ under nitrogen protection, add 10mL of 50% hydrogen peroxide dropwise, reflux for 6h, wash after the reaction is complete, and dry in a vacuum drying oven at 40℃ for 24h to prepare halogen-free reactive phosphorus-POSS-nitrogen synergistic flame retardant;

[0048] The 1H NMR spectrum characterization of the halogen-free reactive phosphorus-POSS-nitrogen synergistic flame retardant is as follows:

[0049] 1 H NMR (CDCl3, 400MHz) δ: 0.02 (s, 18H), 0.06 (s, 24H), 0.63-0.67 (t, 4H), 1.26-1.39 (m, 18H), 1.51-1.65 ( m, 6H), 1.75-1.85 (m, 2H), 2.56-2.76 (m, 6H), 2.85-2.91 (m, 1H), 3.31-3.34 (m, 1H), 4.04-4.18 (m, 4H). Example 2:

[0050] Flame-retardant PA masterbatch I was prepared using the following raw material formulation: 100 parts by weight of PA6 resin (model F136 / NA99001 / 4229D, terminal amino content 0.051 mmol / g), 100 parts by weight of PA66 resin (model 75HF, terminal amino content 0.12 mmol / g), and 6.2 parts by weight of halogen-free reactive phosphorus-POSS-nitrogen synergistic flame retardant.

[0051] The specific experimental steps are as follows:

[0052] PA6 resin, PA66 resin, and halogen-free reactive phosphorus-POSS-nitrogen synergistic flame retardant were added to a high-speed mixer and stirred evenly. The mixture was then placed in a twin-screw extruder for melt reaction extrusion granulation. The extrusion temperature of the twin-screw extruder was 255℃. The mixture was dried at 90℃ for 4 hours to prepare flame-retardant PA masterbatch I. Example 3:

[0053] Flame-retardant PA masterbatch II was prepared, and its only difference from flame-retardant PA masterbatch I was that 14.8 parts by weight of halogen-free reactive phosphorus-POSS-nitrogen synergistic flame retardant were used instead of 6.2 parts by weight of halogen-free reactive phosphorus-POSS-nitrogen synergistic flame retardant. Example 4:

[0054] The preparation of eleven-layer co-extruded film I includes the following steps:

[0055] Step 1: Set the film structure, formulation, and dosage of the eleven-layer co-extruded film I. The specific experiments are shown in Table 1 below:

[0056] Table 1. Membrane structure, formulation, and dosage of eleven-layer co-extruded film I

[0057]

[0058] Step 2: The raw materials of each film layer in Step 1 are respectively fed into the hoppers of the eleven screw extruders of the eleven-layer co-extrusion film blow molding unit. After stirring and mixing, the molten resin is gathered at the die head through the distributor, extruded through the die head and blow molded, and then cooled and wound up to obtain an eleven-layer co-extrusion film I with a thickness of 75μm.

[0059] The process parameters for the screw extruders corresponding to each layer are set as follows: Zone 1 temperature is 260℃, Zone 2 temperature is 270℃, Zone 3 temperature is 285℃, Zone 4 temperature is 295℃, and screw speed is 40r / min.

[0060] The application experiment of the eleven-layer co-extruded film is as follows:

[0061] PA tape is prepared by coating one side of an eleven-layer co-extruded film with a pressure-sensitive adhesive (one of silicone or acrylic). Example 5:

[0062] Eleven-layer co-extruded film II was prepared. The only difference between it and eleven-layer co-extruded film I is the film layer formulation, which is shown in Table 2 below.

[0063] Table 2. Membrane structure, formulation, and dosage of eleven-layer co-extruded film II

[0064]

[0065] Comparative example:

[0066] An unmodified eleven-layer co-extruded film was prepared, which differed from the eleven-layer co-extruded film I only in the film layer formulation, as shown in Table 3 below.

[0067] Table 3. Membrane structure, formulation, and dosage of unmodified eleven-layer co-extruded film

[0068]

[0069] Among them, the specification model of PA66 is 75HF; the specification model of PA6 is F136 / NA99001 / 4229D;

[0070] Each film layer raw material is fed into the hopper of eleven screw extruders of the eleven-layer co-extrusion film blow molding unit. After stirring and mixing, the molten resin is gathered at the die head through the distributor, extruded through the die head and blow molded, then cooled and wound up to obtain an unmodified eleven-layer co-extrusion film with a thickness of 75μm.

[0071] The process parameters for the screw extruders corresponding to each layer are set as follows: Zone 1 temperature is 250℃, Zone 2 temperature is 260℃, Zone 3 temperature is 275℃, Zone 4 temperature is 285℃, and screw speed is 40r / min.

[0072] Performance testing:

[0073] I. Flame retardant performance test: The eleven-layer co-extruded film sample (size 125mm×13mm×0.075mm) prepared in this invention was tested according to Test Method B - Vertical Burning Test Method in GB / T 2408-2021 "Determination of Burning Performance of Plastics - Horizontal and Vertical Methods".

[0074] II. Mechanical property testing:

[0075] According to GB / T 1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets", a sample with dimensions of 150mm×20mm×0.075mm was subjected to tensile testing along the blown film direction at a speed of 50mm / min at room temperature of 25℃, and the longitudinal tensile strength was recorded.

[0076] The sample measuring 150mm×20mm×0.075mm was treated in an oven at 210℃ for 12 hours and then subjected to a tensile test along the blown film direction at a speed of 50mm / min. The longitudinal tensile strength was recorded.

[0077] The test results are shown in Table 4 below;

[0078] Table 4 Performance test results of eleven-layer co-extruded film

[0079]

[0080] The experimental results above show that:

[0081] The halogen-free reactive phosphorus-POSS-nitrogen synergistic flame retardant developed in this invention not only significantly improves the flame retardant performance of eleven-layer co-extruded films, but also achieves the beneficial technical effect of significantly enhancing the high-temperature resistance of eleven-layer co-extruded films.

Claims

1. A process for preparing an eleven-layer co-extruded film, characterized in that, Includes the following steps: Step 1: Preparation of flame-retardant PA masterbatch, specifically as follows: First, a halogen-free reactive phosphorus-POSS-nitrogen synergistic flame retardant was synthesized, and the synthesis method included: (a) Using methyltrichlorosilane as a raw material, an incompletely condensed trihydroxyheptamethyl cage-like silsesquioxane was prepared by direct hydrolysis-condensation; using the incompletely condensed trihydroxyheptamethyl cage-like silsesquioxane as a raw material and trichlorosilane as the apex-capping monomer, a heptamethyl hydrogen-containing POSS was prepared through an apex-capping ring-closing reaction, the chemical structural formula of which is: ； (b) Intermediate a was prepared by hydrosilylation reaction of 2-2.03 molar equivalents of heptamethylhydrogen-containing POSS with 1 molar equivalent of diallylamine under the action of a platinum catalyst. The chemical structural formula of intermediate a is as follows: ； (c) Based on the Kabachnik-Fields reaction mechanism, intermediate a, 10-undecenal, and diethyl phosphite undergo a condensation reaction to prepare intermediate b, whose chemical structural formula is: ； (d) Under the action of glacial acetic acid, hydrogen peroxide is used to oxidize the alkenyl functional group in intermediate b to an epoxy functional group to prepare a halogen-free reactive phosphorus-POSS-nitrogen synergistic flame retardant, the chemical structural formula of which is: ； Then, PA6 resin, PA66 resin, and halogen-free reactive phosphorus-POSS-nitrogen synergistic flame retardant are added to a high-speed mixer and stirred evenly. The mixture is then placed in a twin-screw extruder for melt reaction extrusion granulation. The flame retardant is grafted onto the PA molecular backbone via a covalent bond through an epoxy-amino ring-opening reaction between the epoxy functional groups in the flame retardant and the terminal amino functional groups in the PA6 and PA66 resins, thus obtaining flame-retardant PA masterbatch. The content of the flame retardant in the flame-retardant PA masterbatch is 3.0-6.9 wt%. Step 2: Using flame-retardant PA masterbatch as raw material, the product structure of the eleven-layer co-extruded film is set as follows: PA layer a / PA layer b / PA layer c / PA layer d / PA layer e / PA layer f / PA layer g / PA layer h / PA layer i / PA layer j / PA layer k, with the corresponding raw material amounts being 5-15 parts by weight / 5-10 parts by weight / 5-10 parts by weight / 5-10 parts by weight / 5-10 parts by weight / 5-10 parts by weight / 5-10 parts by weight / 5-10 parts by weight / 5-10 parts by weight / 15-25 parts by weight. The raw material for any PA layer is 100wt% flame-retardant PA masterbatch. The eleven-layer co-extruded film with a thickness of 50-150μm is obtained by using the eleven-layer co-extruded blow molding process. The process parameters for the screw extruder corresponding to any PA layer are set as follows: Zone 1 temperature is 255-265℃, Zone 2 temperature is 265-275℃, Zone 3 temperature is 280-290℃, Zone 4 temperature is 290-300℃, and screw speed is 35-45 r / min.

2. The preparation process of an eleven-layer co-extruded film according to claim 1, characterized in that, The platinum catalyst is a chloroplatinic acid-isopropanol catalyst or a Karstedt catalyst.

3. The preparation process of an eleven-layer co-extruded film according to claim 1, characterized in that, The extrusion temperature of the twin-screw extruder is 250-260℃.

4. An eleven-layer co-extruded film prepared by the process according to any one of claims 1-3.

5. The eleven-layer co-extruded film according to claim 4, characterized in that, The eleven-layer co-extruded film serves as the substrate, and a pressure-sensitive adhesive is coated on one side of the substrate to produce PA tape. The PA tape is used to wrap and fix aviation wire harnesses used in normal temperature environments.

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