Solvent-free lightning protection composite film, preparation method and application thereof

Abstract

The application discloses a kind of solventless lightning protection composite film, the composite film includes conductive metal net, hot melt adhesive film and backing, the conductive metal net is fixed on backing by hot melt adhesive film, and the hot melt adhesive film is infiltrated and bonded the backing and fills into the aperture of the conductive metal net.The lightning protection composite film of the application is smooth and smooth on surface, and the initial surface viscosity of colloid is moderate, which can modify the phenomenon of surface lack of glue, poor glue and pinhole after prepreg curing, and also has excellent lightning protection performance.The viscosity of hot melt adhesive is adjusted by controlling temperature during preparation process, to realize the integrated molding of colloid and backing material and expanded metal net, and there is no introduction of any solvent during production process, and the process is time-saving, simple, and environmentally friendly.

Description

Technical Field

[0001] This invention belongs to the field of composite material manufacturing, specifically relating to a solvent-free lightning protection composite film for aerospace composite material structures and its preparation method. Background Technology

[0002] In the aerospace field, composite materials are playing an increasingly important role in aircraft manufacturing due to their superior properties in specific strength, specific modulus, fatigue resistance, corrosion resistance, and lightweighting. Statistics show that the proportion of composite materials in the structural weight of Airbus aircraft has been steadily increasing, from 5% in the A310-300, to 25% in the A380, 35% in the A400M, and 53% in the A350XWB which entered service in 2013. This upward trend is expected to become increasingly pronounced in the future aerospace industry. Compared to metallic materials, composite materials have significantly lower electrical conductivity. Especially when struck by lightning, they are susceptible to damage from the combined effects of electrothermal and mechanical forces, leading to ablation, perforation, and delamination, thus affecting aircraft safety.

[0003] Traditional lightning protection designs in the aerospace industry involve laying metal mesh, spraying aluminum onto the surface, and bonding metal foil. However, these designs have shortcomings in terms of manufacturing process, conductivity, aircraft weight gain, and ease of repair.

[0004] Metal mesh installation method: The installation process involves laying the insulating glass layer, adhesive film, and metal mesh separately, making the construction process complex. Furthermore, the lightweight metal mesh is prone to wrinkling and deformation during installation, affecting its electrical conductivity.

[0005] Surface coating with aluminum: results in significant weight gain, high cost, and low bonding strength with composite material components;

[0006] Bonding metal foil: Although metal foil is lighter and has the advantage of weight reduction, the laying process of metal foil is complicated, the bonding strength is low, and the overall lightning protection effect is poor.

[0007] With the development of new materials technology and processes, traditional lightning protection methods are gradually being replaced by a new type of lightning protection composite membrane that integrates a surface film and a ductile metal mesh. In contrast, the metal mesh of this new lightning protection composite membrane can be impregnated with resin and molded together with the composite material, avoiding metal exposure and contributing to the formation of a stable protective layer. This new type of lightning protection composite membrane has been widely used due to its advantages of simple construction, easy repair, high bonding strength with composite material components, and adaptability to components with large curvature shapes.

[0008] However, existing new lightning protection composite membranes require the addition of epoxy diluents or volatile solvents during production to create a low-viscosity adhesive, which is then formed using vacuum injection. The resulting composite membrane has a high surface viscosity, which is detrimental to subsequent construction operations. Furthermore, the introduction of volatile solvents increases the difficulty of subsequent solvent recovery processes and can easily cause pollution and damage to the natural environment. Summary of the Invention

[0009] The purpose of this invention is to solve the problems of high surface viscosity, poor construction convenience, difficulty in recovering volatile solvents during the molding process, and easy environmental pollution of lightning protection composite membranes after molding, and to provide a solvent-free lightning protection composite membrane for aerospace composite material structures and its preparation method.

[0010] The first aspect of the present invention provides a solvent-free lightning protection composite film, the composite film comprising a conductive metal mesh, a hot melt adhesive film and a backing, wherein the conductive metal mesh is bonded and fixed to the backing by the hot melt adhesive film, and the hot melt adhesive film impregnates and bonds the backing and fills the pores of the conductive metal mesh;

[0011] The hot melt adhesive film comprises the following components, wherein, by weight,

[0012] 55-95 parts of modified epoxy resin

[0013] 15-40 parts of core-shell toughened epoxy resin

[0014] 5-13 parts of curing agent;

[0015] The modified epoxy resin includes liquid modified epoxy resin and solid modified epoxy resin.

[0016] Preferably, by weight, the modified epoxy resin comprises 30 to 50 parts of liquid modified epoxy resin and 25 to 45 parts of solid modified epoxy resin.

[0017] According to the composite membrane of the first aspect, wherein the liquid-modified epoxy resin is selected from bisphenol A type epoxy resin and / or amino tetrafunctional epoxy resin; and / or

[0018] The solid epoxy resin is selected from one or more of biphenyl-type epoxy resin, bisphenol A-type epoxy resin, and phenoxy-type epoxy resin.

[0019] According to the composite membrane of the first aspect, wherein the core-shell toughened epoxy resin is selected from one or more of EPX-140, RE728, and XP-425; and / or

[0020] The curing agent is selected from dicyandiamide-based curing agents.

[0021] According to the composite film of the first aspect, the hot melt adhesive film further includes a thixotropic agent, an accelerator, and / or a coupling agent;

[0022] Preferably, the thixotropic agent is fumed silica;

[0023] Preferably, the accelerator is selected from organic urea-type accelerators and / or imidazole-type accelerators; and / or

[0024] Preferably, the coupling agent is selected from one or more of γ-(2,3-epoxypropoxy)propyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, and N-(β-aminoethyl)-γ-aminopropyltriethoxysilane;

[0025] More preferably, the hot melt adhesive film comprises, by weight, 1 to 6 parts of thixotropic agent, 1 to 8 parts of accelerator and / or 0.5 to 2 parts of coupling agent.

[0026] According to the composite membrane of the first aspect, the backing material is polyester, glass fiber mat or non-woven fabric;

[0027] Preferably, the backing has a weight of 8-25g per square meter.

[0028] According to the composite film of the first aspect, at least one side of the composite film is further provided with a double silicone release paper;

[0029] Preferably, the average peel strength of the dual-silicone release paper on both sides is 10-25 g / m². 2 .

[0030] A second aspect of the present invention provides a method for preparing the solvent-free lightning protection composite film described in the first aspect, comprising the following steps:

[0031] (1) Preparation of hot melt colloid:

[0032] Component A is obtained by uniformly mixing core-shell toughened epoxy resin, solid modified epoxy resin and 60-85% by weight of liquid modified epoxy resin at a first temperature.

[0033] The remaining liquid modified epoxy resin is mixed uniformly with curing agent, optional thixotropic agent, optional accelerator and optional coupling agent at a second temperature to obtain component B.

[0034] Component A and component B are mixed and stirred evenly under vacuum conditions and a third temperature to obtain a hot melt colloid, preferably with a vacuum degree ≤ -0.08 MPa;

[0035] (2) Preparation of hot melt adhesive film:

[0036] The hot melt adhesive obtained in step (1) is hot melt coated onto the surface of the backing to form a film, thereby obtaining a hot melt adhesive film; preferably, a double silicone release paper is provided on the back of the backing.

[0037] (3) Preparation of solvent-free lightning protection composite membrane:

[0038] The hot melt adhesive film obtained in step (2) is combined with the metal mesh by a flat plate hot pressing method to obtain a solvent-free lightning protection composite film.

[0039] According to the preparation method of the second aspect, in step (1), the first temperature is 130-150℃;

[0040] The second temperature is 50–70°C; and / or

[0041] The third temperature is ≤70℃.

[0042] According to the preparation method of the second aspect, in step (2), the hot melt coating temperature is 50±5℃; and / or

[0043] The hot melt coating speed is 1 to 4 m / min.

[0044] According to the preparation method of the second aspect, in step (3), the hot pressing temperature of the flat plate is 38-60°C; and / or

[0045] The pressure of the hot pressing of the plate is 0.05 to 0.1 MPa.

[0046] Applications of the solvent-free lightning protection composite film of the first aspect or the solvent-free lightning protection composite film prepared by the preparation method described in the second aspect in the aerospace field.

[0047] The beneficial effects of the solvent-free lightning protection composite film of the present invention include, but are not limited to:

[0048] 1. This invention involves preparing a solvent-free hot melt adhesive, first laminating it with a backing material via hot melt coating, and then using a flatbed heated pressure forming machine to laminate the hot melt adhesive film with an extended metal mesh to form a lightning protection composite film. The entire preparation process controls the temperature to adjust the viscosity of the hot melt adhesive, achieving integrated molding of the adhesive, backing material, and extended metal mesh. No solvents are introduced during production, making the process time-saving, simple, and environmentally friendly.

[0049] 2. The lightning protection surface film of the present invention has a smooth and flat surface and moderate initial surface viscosity of the colloid. It can not only correct the phenomena of insufficient glue, poor glue and pinholes on the surface of the prepreg after curing, but also has excellent lightning protection performance. Attached Figure Description

[0050] Figure 1 A schematic diagram of the structure of the solvent-free lightning protection composite film with double silicon release paper on the lower surface of the present invention is shown.

[0051] Figure 2 A schematic diagram of the structure of the solvent-free lightning protection composite film of the present invention, in which double silicone release paper is provided on both the upper and lower surfaces, is shown.

[0052] Explanation of reference numerals in the attached figures:

[0053] 1. Conductive metal mesh; 2. Hot melt adhesive film; 3. Backing adhesive layer; 4, 4'. Double silicone release paper. Detailed Implementation

[0054] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. Through these descriptions, the features and advantages of the present application will become clearer and more apparent.

[0055] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments. Although various aspects of embodiments are shown in the accompanying drawings, the drawings are not necessarily drawn to scale unless specifically indicated otherwise.

[0056] Furthermore, the technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0057] The present invention provides a solvent-free lightning protection composite membrane, the composite membrane comprising a conductive metal mesh, a hot melt adhesive film and a backing, wherein the conductive metal mesh is bonded and fixed to the backing by the hot melt adhesive film, and the hot melt adhesive film impregnates and bonds the backing and fills the pores of the conductive metal mesh;

[0058] The hot melt adhesive film comprises the following components, wherein, by weight,

[0059] 55-95 parts of modified epoxy resin

[0060] 15-40 parts of core-shell toughened epoxy resin

[0061] 5-13 parts of curing agent;

[0062] The modified epoxy resin includes liquid modified epoxy resin and solid modified epoxy resin.

[0063] Preferably, by weight, the modified epoxy resin comprises 30 to 50 parts of liquid modified epoxy resin and 25 to 45 parts of solid modified epoxy resin.

[0064] This invention relates to a solvent-free lightning protection composite film, which is a hot melt adhesive film comprising a core-shell toughened epoxy resin to enhance its toughness. By compounding liquid-modified epoxy resin and solid-modified epoxy resin, this invention achieves a suitable viscosity for the hot melt adhesive film, enabling the integral molding of the adhesive, backing material, and extended metal mesh. This results in a lightning protection surface film with a smooth and flat surface and moderate initial surface viscosity, effectively correcting defects such as insufficient adhesive, pinholes, and lack of adhesive on the cured prepreg surface, while also providing excellent lightning protection performance. In one embodiment, the liquid-modified epoxy resin is selected from bisphenol A type epoxy resin and / or amino tetrafunctional epoxy resin; and / or

[0065] The solid epoxy resin is selected from one or more of biphenyl-type epoxy resin, bisphenol A-type epoxy resin, and phenoxy-type epoxy resin.

[0066] In one specific embodiment, the liquid modified epoxy resin is selected from one or more of bisphenol A type epoxy resins E-51, YB301, 328, and amino tetrafunctional epoxy resins AG80, AG70; and / or

[0067] The solid epoxy resin is selected from one or more of the following: biphenyl type epoxy resin YX4000, EBA-50; bisphenol A type epoxy resin YD-014U; and phenoxy type epoxy resin JER1256. In one embodiment, the core-shell toughening epoxy resin is selected from one or more of the following: EPX-140, RE728, and XP-425; and / or

[0068] The curing agent is selected from dicyandiamide-based curing agents.

[0069] In one specific embodiment, the curing agent is selected from one or more of dicyandiamide curing agents 1010P, AH-154, and AH-156.

[0070] In one embodiment, the hot melt adhesive film further includes a thixotropic agent, an accelerator, and / or a coupling agent;

[0071] Preferably, the thixotropic agent is fumed silica;

[0072] Preferably, the accelerator is selected from organic urea-type accelerators and / or imidazole-type accelerators; and / or

[0073] Preferably, the coupling agent is selected from one or more of γ-(2,3-epoxypropoxy)propyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, and N-(β-aminoethyl)-γ-aminopropyltriethoxysilane;

[0074] More preferably, the hot melt adhesive film comprises, by weight, 1 to 6 parts of thixotropic agent, 1 to 8 parts of accelerator and / or 0.5 to 2 parts of coupling agent.

[0075] In one specific embodiment, the thixotropic agent is fumed silica HB139 and / or fumed silica HDK H18.

[0076] In one specific embodiment, the accelerator is selected from one or more of the organic urea type accelerators 5050P and 3030P, and the imidazole type accelerators PN50 and PN23.

[0077] In one specific embodiment, the coupling agent is selected from γ-(2,3-epoxypropoxy)propyltrimethoxysilane KH-560, Z-6011, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane KH-792, and N-(β-aminoethyl)-γ-aminopropyltriethoxysilane KH-791.

[0078] The hot melt adhesive film of the present invention may further include a thixotropic agent, an accelerator, and / or a coupling agent, wherein the thixotropic agent is used to adjust the flowability of the adhesive, the accelerator is used to adjust the curing activity of the hot melt adhesive film, and the coupling agent is used to improve the interfacial properties of the hot melt adhesive film and prevent debonding. In one embodiment, the backing material is polyester, fiberglass mat, or nonwoven fabric;

[0079] Preferably, the backing has a weight of 8-25g per square meter.

[0080] In one embodiment, at least one side of the composite film is further provided with a double-silicone release paper;

[0081] Preferably, the average peel strength of the dual-silicone release paper on both sides is 10-25 g / m². 2 .

[0082] The present invention also provides a method for preparing the solvent-free lightning protection composite film, the method comprising the following steps:

[0083] (1) Preparation of hot melt colloid:

[0084] Component A is obtained by uniformly mixing core-shell toughened epoxy resin, solid modified epoxy resin and 60-85% by weight of liquid modified epoxy resin at a first temperature.

[0085] The remaining liquid modified epoxy resin is mixed uniformly with curing agent, optional thixotropic agent, optional accelerator and optional coupling agent at a second temperature to obtain component B.

[0086] Component A and component B are mixed and stirred evenly under vacuum conditions and a third temperature to obtain a hot melt colloid, preferably with a vacuum degree ≤ -0.08 MPa;

[0087] (2) Preparation of hot melt adhesive film:

[0088] The hot melt adhesive obtained in step (1) is hot melt coated onto the surface of the backing to form a film, thereby obtaining a hot melt adhesive film; preferably, a double silicone release paper is provided on the back of the backing.

[0089] (3) Preparation of solvent-free lightning protection composite membrane:

[0090] The hot melt adhesive film obtained in step (2) is combined with the metal mesh by a flat plate hot pressing method to obtain a solvent-free lightning protection composite film.

[0091] The method for preparing the solvent-free lightning protection composite film of the present invention utilizes the hot-melt properties of the hot melt adhesive film itself and uses a flat plate hot pressing method to prepare the composite film. The process is simple, time-saving, and convenient, and avoids environmental pollution and solvent recovery problems caused by the introduction of volatile solvents. The preparation method of the present invention is applicable to backings and / or metal meshes of different materials and specifications. By controlling the hot-melt properties of the hot melt adhesive film, lightning protection composite films can be rapidly prepared in batches under mild conditions without causing deformation of the metal mesh. In one embodiment, in step (1), the first temperature is 130-150°C;

[0092] The second temperature is 50–70°C; and / or

[0093] The third temperature is ≤70℃.

[0094] In one embodiment, in step (2), the hot melt coating temperature is 50±5℃; and / or

[0095] The hot melt coating speed is 1 to 4 m / min.

[0096] In one embodiment, in step (3), the hot-pressing temperature of the flat plate is 38–60°C; and / or

[0097] The pressure of the hot pressing of the plate is 0.05 to 0.1 MPa.

[0098] The present invention also provides the application of the solvent-free lightning protection composite film in the aerospace field.

[0099] The present invention can prepare a solvent-free lightning protection composite film through the following steps.

[0100] Step 1: Preparation of hot melt colloid

[0101] A portion (e.g., 60%–85% by weight) of the liquid modified epoxy resin, all of the solid modified epoxy resin, and the core-shell toughened epoxy resin are stirred and mixed evenly at 130–150°C to form component A. Then, the remaining liquid modified epoxy resin is mixed evenly with the thixotropic agent, curing accelerator, and coupling agent at 50–70°C. Finally, it is mixed evenly with component A at a temperature not exceeding 70°C under vacuum, with a vacuum degree ≤-0.08MPa.

[0102] Step 2: Prepare hot melt adhesive film

[0103] The adhesive material from step 1 is laminated with a backing material and a double-silicone release paper using a hot-melt coating method to obtain a hot-melt adhesive film coated with release paper. The temperature of the hot-melt coating melting box and the die head is set to 50±5℃, preheated for 20 minutes, and the machine speed is 1~4m / min.

[0104] The backing material is polyester, fiberglass mat, or non-woven fabric, with a weight of 8-25g per square meter.

[0105] The average peel strength of the dual-silicone release paper on both sides is 10-25 g / m². 2 .

[0106] Step 3: Preparation of lightning protection composite membrane

[0107] 3.1 The flat plate heating pressure forming machine is set with the upper and lower plate heating temperatures at 38-60℃ and kept at that temperature for 20 minutes.

[0108] 3.2 Set the pressure value according to the width of the hot melt adhesive film, with the pressure between 0.05-0.1 MPa.

[0109] 3.3 According to the required hot melt adhesive film thickness, place pads of corresponding thickness on both sides of the lower plate.

[0110] 3.4 The hot melt adhesive film obtained in step 2, the extended metal mesh, and the double-sided silicone release paper are sequentially laid on the lower platen of the flatbed heating and pressure forming machine. Then, the upper and lower plates of the flatbed heating and pressure forming machine are pressurized and heat-sealed for 4-10 seconds. Under the action of temperature and pressure, the viscosity of the hot melt adhesive decreases, allowing it to impregnate and fill the extended metal mesh, thus bonding it together. After lifting the upper platen of the flatbed heating and pressure forming machine, a solvent-free lightning protection composite film is obtained. It can be directly cut into slices and packaged according to the required dimensions, or the upper silicone release paper can be removed for roll packaging. The packaged finished product must be stored in a sealed environment below -10℃.

[0111] The pad is made of 304 stainless steel, with a width of 2-5cm and a length consistent with the width of the lower plate of the flatbed heating pressure forming machine. The pad thickness ranges from 0.1-2mm, with a thickness accuracy of 0.001mm.

[0112] In one specific embodiment, the backing material in step 2 is polyester, fiberglass mat, or nonwoven fabric, with a weight of 8-25g per square meter.

[0113] The average peel strength of the dual-silicone release paper on both sides in step 2 is 10-25 g / m². 2 .

[0114] Step 3, the preparation method of the lightning protection composite film, is as follows: The upper and lower plates of the flatbed heating and pressure forming machine are set to a heating temperature of 38-60℃ and held at that temperature for 20 minutes. The pressure value is set according to the width of the hot melt adhesive film, with a pressure of 0.05-0.1 MPa. According to the required hot melt adhesive film thickness, pads of corresponding thickness are placed on both sides of the lower platen's edge. The hot melt adhesive film obtained in Step 2, the extended metal mesh, and the double-silicone release paper are sequentially laid on the lower platen of the flatbed heating and pressure forming machine. Then, the upper and lower plates of the flatbed heating and pressure forming machine are pressed and heat-sealed for 4-10 seconds. Under the action of temperature and pressure, the viscosity of the hot melt adhesive decreases, allowing it to wet and fill the extended metal mesh and bond with it. After lifting the upper plate of the flatbed heating and pressure forming machine, a solvent-free lightning protection composite film is obtained. It can be directly cut into slices and packaged according to the required dimensions, or the upper double-silicone release paper can be removed for roll packaging. The packaged finished product must be stored in a sealed environment below -10℃.

[0115] The pad mentioned in step 3.3 is made of 304 stainless steel, with a width of 2-5cm and a length consistent with the width of the lower plate of the flatbed heating pressure forming machine. The thickness of the pad ranges from 0.1-2mm, with a thickness accuracy of 0.001mm.

[0116] The structure of the solvent-free lightning protection composite membrane prepared by this invention is as follows: Figure 1 and Figure 2 As shown, where Figure 1 This illustrates a structure with dual silicone release paper on the lower surface. Figure 2 The structure shown depicts a double-sided silicone release paper on both the upper and lower surfaces. The solvent-free lightning protection composite film of the present invention comprises a conductive metal mesh 1, a hot melt adhesive film 2, and a backing adhesive layer 3. At least one side of the solvent-free lightning protection composite film is provided with double-sided silicone release paper 4 and 4'. In the solvent-free lightning protection composite film of the present invention, the conductive metal mesh 1 is bonded and fixed to the backing by the hot melt adhesive film 2. The hot melt adhesive film 2 impregnates and bonds the backing to form the backing adhesive layer 3, and the hot melt adhesive film 2 fills the pores of the conductive metal mesh. The present invention forms a composite film by fixing and bonding the backing and conductive metal mesh with a solvent-free hot melt adhesive film. The preparation process is simple and environmentally friendly, applicable to various specifications of conductive metal mesh and backing materials, and exhibits good bonding performance.

[0117] Unless otherwise specified, the raw materials used in the following embodiments are commercially available products, and the operations or instruments and equipment used in the following embodiments are common in the art unless otherwise specified.

[0118] Example 1

[0119] This embodiment illustrates the preparation method of the solvent-free lightning protection composite film of the present invention, comprising the following components in parts by weight:

[0120]

[0121] The specific preparation steps of the solvent-free lightning protection composite membrane in this embodiment are as follows:

[0122] Step 1: Preparation of hot melt colloid

[0123] First, 80% by weight of bisphenol A type epoxy resin E-51, amino tetrafunctional epoxy resin AG80, all of the core-shell toughened epoxy resin RE-728, solid epoxy resin YD-014U, and biphenyl-terminated epoxy resin YX4000 are mixed evenly at 145°C to obtain component A. Then, the remaining epoxy resin E-51 and amino tetrafunctional epoxy resin AG80 are mixed evenly with fumed silica HB139, modified dicyandiamide 1010P, organic urea type accelerator 5050P, and silane coupling agent KH-560 at 50°C to obtain component B. Then, component B is mixed evenly with component A at a vacuum of -0.08MPa and a temperature not exceeding 70°C.

[0124] Step 2: Prepare hot melt adhesive film

[0125] The adhesive from step 1 is laminated using a hot melt coating method to form a film with a basis weight of 10 g / m². 2 Polyester backing and dual-silicone release paper (average peel strength on both sides 15g / m²) 2 The hot melt adhesive film with release paper is formed. The temperature of the hot melt coating box and the die head is set to 50±5℃, preheated for 20min, and the speed is 1~4m / min.

[0126] Step 3: Preparation of lightning protection composite membrane

[0127] 3.1 The flat plate heating pressure forming machine is set to heat the upper and lower plates at 50℃ and maintain the temperature for 20 minutes.

[0128] 3.2 Set the pressure value according to the width of the hot melt adhesive film, with a pressure setting of 0.05-0.1 MPa.

[0129] In this embodiment, the width of the hot melt adhesive film is 980cm, and the pressure is set to 0.1MPa. 3.3 According to the required hot melt adhesive film thickness, place pads of corresponding thickness on both sides of the lower plate.

[0130] In this embodiment, the thickness of the hot melt adhesive film is 0.15 mm. 3.4 The hot melt adhesive film obtained in step 2 and the extended metal mesh (material is copper mesh, width 980 cm, surface density 73±10 g / m²) are sequentially laid on the lower plate of the flatbed heating pressure forming machine. 2 The film consists of a 0.05mm thick double-sided silicone release paper. Then, the upper and lower plates are heat-sealed for 5 seconds using a flatbed heating and pressure forming machine, after which the upper plate is lifted to obtain a solvent-free lightning protection composite film.

[0131] Example 2

[0132] This embodiment provides a method for preparing a solvent-free lightning protection composite film, comprising the following components in parts by weight:

[0133]

[0134]

[0135] The specific preparation steps of the solvent-free lightning protection composite membrane in this embodiment are as follows:

[0136] Step 1: Preparation of hot melt colloid

[0137] First, 70% by weight of bisphenol A type epoxy resin YB301, amino tetrafunctional epoxy resin AG80, all of the core-shell toughened epoxy resin XP-425, solid epoxy resin YD-014U, and phenoxy type epoxy resin JER1256 are mixed evenly at 138℃ and set as component A for later use. Then, the remaining bisphenol A type epoxy resin YB301 and amino tetrafunctional epoxy resin AG80 are mixed evenly with fumed silica HDK H18, modified dicyandiamide 1010P and AH-154, organic urea type accelerator 3030P, imidazole type accelerator PN23, and silane coupling agent KH-792 at 45℃. Then, component B is mixed evenly with component A at a vacuum degree of -0.08 and the temperature does not exceed 70℃.

[0138] Step 2: Prepare hot melt adhesive film

[0139] The adhesive material from step 1 is laminated using a hot melt coating method to achieve a basis weight of 20 g / m². 2 Fiberglass mat and double-sided silicone release paper (average peel strength on both sides 10g / m²) 2 The hot melt adhesive film with release paper is formed. The temperature of the hot melt coating box and the die head is set to 50±5℃, preheated for 20min, and the speed is 1~4m / min.

[0140] Step 3: Preparation of lightning protection composite membrane

[0141] 3.1 The flat plate heating pressure forming machine is set to heat the upper and lower plates at 45℃ and maintain the temperature for 20 minutes.

[0142] 3.2 Set the pressure value according to the width of the hot melt adhesive film, with a pressure setting of 0.05-0.1 MPa.

[0143] In this embodiment, the width of the hot melt adhesive film is 1000cm and the pressure is set to 0.08MPa.

[0144] 3.3 According to the required hot melt adhesive film thickness, place pads of corresponding thickness on both sides of the lower plate.

[0145] In this embodiment, the thickness of the hot melt adhesive film is 0.2 mm.

[0146] 3.4 The hot melt adhesive film obtained in step 2 and the extended metal mesh (material is copper mesh, width 1000cm, surface density 120±10g / m²) are sequentially laid on the lower plate of the flatbed heating pressure forming machine. 2 (0.05mm thick) and double-silicone release paper. Then, the upper and lower plates are heat-sealed in a flatbed heating and pressure forming machine for 6 seconds, and the upper plate is lifted to obtain a solvent-free lightning protection composite film.

[0147] The solvent-free lightning protection composite film obtained from Examples 1-2 can be directly cut into slices and packaged according to the required dimensions, or packaged in rolls after removing the top layer of double-silicone release paper. The packaged product must be stored in a sealed environment below -10°C.

[0148] Experimental Example 1

[0149] The performance of the solvent-free lightning protection composite membranes prepared in Examples 1 and 2 was tested, and the results are shown in Table 1.

[0150] Table 1. Performance of solvent-free lightning protection composite films prepared in Examples 1 and 2*

[0151]

[0152] *The test standard for shear strength is GB / T 7124-2008, the test standard for peel strength of floating rolls is GB / T7122-1996, and the test standard for electrical properties is GB / T 351-2019.

[0153] As shown in Table 1, the solvent-free lightning protection composite membrane prepared by the method of this invention exhibits good shear strength and floating roll peel strength, good bonding performance, low sheet resistance, and excellent conductivity. The lightning protection composite membrane of this invention has good conductivity and bonding performance, a simple preparation method, and is suitable for lightning protection of components with different shapes and environments.

[0154] The present application has been described above with reference to preferred embodiments; however, these embodiments are merely exemplary and illustrative. Various substitutions and modifications can be made to the present application based on these embodiments, all of which fall within the protection scope of the present application.

Claims

1. A lightning strike resistant composite film of the solvent-free type, characterized in that, The composite film includes a conductive metal mesh, a hot melt adhesive film, and a backing. The conductive metal mesh is bonded and fixed to the backing by the hot melt adhesive film, and the hot melt adhesive film impregnates and bonds the backing and fills the pores of the conductive metal mesh. The hot melt adhesive film comprises the following components, wherein, by weight, 55-95 parts of modified epoxy resin 15-40 parts of core-shell toughened epoxy resin 5-13 parts of curing agent; The modified epoxy resin includes liquid modified epoxy resin and solid modified epoxy resin. The hot melt adhesive film further includes a thixotropic agent, an accelerator, and a coupling agent; The method for preparing the composite membrane includes the following steps: (1) Preparation of hot melt colloid: Component A is obtained by uniformly mixing core-shell toughened epoxy resin, solid modified epoxy resin and 60-85% by weight of liquid modified epoxy resin at a first temperature. The remaining liquid modified epoxy resin was mixed uniformly with curing agent, thixotropic agent, accelerator and coupling agent at the second temperature to obtain component B; Component A and component B are mixed and stirred evenly under vacuum conditions and a third temperature to obtain a hot melt colloid. (2) Preparation of hot melt adhesive film: The hot melt adhesive obtained in step (1) is hot melt coated onto the backing surface to form a film, thus obtaining a hot melt adhesive film. In step (1), the first temperature is 130-150℃; the second temperature is 50-70℃; and the third temperature is ≤70℃.

2. The composite film according to claim 1, characterized by By weight, the modified epoxy resin comprises 30-50 parts of liquid modified epoxy resin and 25-45 parts of solid modified epoxy resin.

3. The composite film of claim 1, wherein The liquid modified epoxy resin is selected from bisphenol A type epoxy resin and / or amino tetrafunctional epoxy resin; and / or The solid modified epoxy resin is selected from one or more of biphenyl-type epoxy resin, bisphenol A-type epoxy resin, and phenoxy-type epoxy resin.

4. The composite film of claim 1, wherein The core-shell toughening epoxy resin is selected from one or more of EPX-140, RE728, and XP-425; and / or The curing agent is selected from dicyandiamide-based curing agents.

5. The composite film of claim 1, wherein The thixotropic agent is fumed silica; The accelerator is selected from organic urea-type accelerators and / or imidazole-type accelerators; and / or The coupling agent is selected from one or more of γ-(2,3-epoxypropoxy)propyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, and N-(β-aminoethyl)-γ-aminopropyltriethoxysilane.

6. The composite film of claim 5, wherein, The hot melt adhesive film comprises, by weight, 1 to 6 parts of thixotropic agent, 1 to 8 parts of accelerator and / or 0.5 to 2 parts of coupling agent.

7. The composite membrane according to claim 1, characterized in that, The backing material is polyester, fiberglass mat, or nonwoven fabric.

8. The composite film of claim 7, wherein, The backing material weighs 8-25g per square meter.

9. The composite film of claim 1, wherein, The composite film is further provided with a double silicone release paper on at least one side.

10. The method of producing a lightning strike resistant composite film without solvent according to any one of claims 1 to 9, characterized by, The method includes the following steps: (1) Preparation of hot melt colloid: Component A is obtained by uniformly mixing core-shell toughened epoxy resin, solid modified epoxy resin and 60-85% by weight of liquid modified epoxy resin at a first temperature. The remaining liquid modified epoxy resin was mixed uniformly with curing agent, thixotropic agent, accelerator and coupling agent at the second temperature to obtain component B; Component A and component B are mixed and stirred evenly under vacuum conditions and a third temperature to obtain a hot melt colloid. (2) Preparation of hot melt adhesive film: The hot melt adhesive obtained in step (1) is hot melt coated onto the backing surface to form a film, thus obtaining a hot melt adhesive film. (3) Preparation of solvent-free lightning protection composite membrane: The hot melt adhesive film obtained in step (2) is combined with the metal mesh by a flat plate hot pressing method to obtain a solvent-free lightning protection composite film; In step (1), the first temperature is 130-150℃; the second temperature is 50-70℃; and the third temperature is ≤70℃.

11. The method of claim 10, wherein, In step (1), the vacuum degree of the vacuum condition is ≤-0.08MPa.

12. The preparation method according to claim 10, characterized in that, In step (2), the back of the backing is provided with double silicone release paper.

13. The preparation method according to claim 10, characterized in that, In step (2), the hot melt coating temperature is 50±5℃; and / or The hot melt coating speed is 1 to 4 m / min.

14. The method of claim 10, wherein, In step (3), the hot pressing temperature of the flat plate is 38~60℃; and / or The pressure of the hot pressing of the plate is 0.05~0.1MPa.

15. The application of the solvent-free lightning protection composite film according to any one of claims 1 to 9 or the solvent-free lightning protection composite film prepared by the preparation method according to any one of claims 10 to 14 in the aerospace field.

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