Preparation method of bismaleimide resin-based electromagnetic shielding composite film

Abstract

The invention relates to the technical field of electromagnetic shielding film manufacturing, in particular to a bismaleimide resin-based electromagnetic shielding composite film preparation method which comprises the following steps: adding polyether sulfone into diallyl bisphenol A, carrying out oil bath, and uniformly stirring to obtain a mixed solution; cooling the mixed solution, adding 4, 4 '-diaminodiphenylmethane bismaleimide, and uniformly stirring to obtain an adhesive; coating an adhesive to form a film so as to prepare a first bismaleimide resin adhesive film layer and a second bismaleimide resin adhesive film layer; performing magnetron sputtering copper plating on the carbon nanotube film to obtain an electromagnetic shielding film layer; the first bismaleimide resin adhesive film layer, the electromagnetic shielding film layer and the second bismaleimide resin adhesive film layer are subjected to hot-pressing compounding to obtain a finished product. By accurately controlling the ratio of the polyether sulfone to the 4, 4 '-diamino diphenylmethane bismaleimide to the diallyl bisphenol A, the toughness and the adhesion of the bismaleimide resin are improved; and due to the three-layer composite structure, the problem of uneven shielding is effectively solved, and high temperature resistance and high shielding performance are both considered.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of electromagnetic shielding film manufacturing, and in particular to a preparation method of a bismaleimide resin-based electromagnetic shielding composite film. BACKGROUND

[0002] In the modern national defense and military field, the stealth capability of weapon equipment directly determines its battlefield survival and penetration efficiency, especially aircrafts need to avoid tracking by radar and other detection systems through stealth design. The stealth skin, as the core structural part for realizing the stealth function of the aircraft, not only needs to have high efficient electromagnetic shielding performance to attenuate radar wave signals, but also needs to meet the performance requirements of lightweight and high toughness.

[0003] The stealth skin usually adopts a multi-layer composite structure design, and the interlayer connection quality is a key link to determine the overall performance, and the connection process needs to rely on a resin-based composite film with excellent bonding performance and stable electromagnetic shielding performance: on the one hand, the resin-based composite film needs to realize the close interface bonding of each functional layer of the skin, ensure the structural stability in long-term use, and prevent interlayer debonding; on the other hand, the composite film needs to match the overall shielding performance of the skin to avoid forming shielding leaks in the connection area. Therefore, the resin-based electromagnetic shielding composite film has become the core supporting material of the aircraft stealth skin and other military high shielding demand structural parts.

[0004] In terms of the current industry status, the resin material used for structural bonding is usually mainly epoxy resin. Epoxy resin has good adhesion to metals, ceramics, composite materials and other substrates, and can form a stable interface with the substrate at room temperature and in low-temperature environments, thereby ensuring the integrity and durability of the composite material, and is therefore widely used in civilian and low-demand military scenarios. However, in the actual service process of the aircraft, the local temperature on the skin surface can reach 150℃ to 250℃ due to aerodynamic heating, engine heat dissipation and changes in environmental temperature, and the thermal stability of epoxy resin is significantly insufficient, with a heat distortion temperature generally lower than 150℃. In a long-term high-temperature environment, the epoxy resin will undergo thermal aging, resulting in a significant decrease in mechanical strength, hardness and bonding performance, and thus cannot meet the use requirements of the aircraft in high-temperature working conditions.

[0005] Bismaleimide (BMI) resin, as a high-performance thermosetting resin, has a heat distortion temperature generally higher than 200℃, and some modified products can reach more than 250℃, and can still maintain excellent mechanical strength and thermal stability in high-temperature environments, which is significantly better than epoxy resin, and thus becomes the preferred matrix of resin-based materials in high-temperature harsh scenarios such as aerospace and military equipment. However, unmodified bismaleimide (BMI) resin has three major core defects, which restrict its application in composite films for stealth skins, specifically as follows: 1) The cured BMI resin has high crosslinking density, strong molecular chain rigidity, which leads to significant brittleness and low impact strength, and the material is prone to breakage under temperature cycling or external load, which cannot meet the toughness requirements of the skin; 2) The melting point of BMI resin is relatively high, and the viscosity is large in the molten state, the processing window is narrow, it is difficult to prepare a film material with uniform thickness and smooth surface by conventional coating and film forming process, which restricts large-scale production; 3) The interfacial bonding force between pure BMI resin and the substrate is weak, especially under high temperature working condition, the adhesive strength decays obviously, and the long-term stable connection between the skin layers cannot be realized.

[0006] To solve the above problems, various improvement schemes have been tried in the industry, but all have obvious limitations, for example: In view of the problem of insufficient high temperature resistance of epoxy resin, researchers add ceramic powder, carbon fiber and other high temperature resistant fillers to improve its thermal stability, but the addition of fillers will increase the density of the material, and easily cause the viscosity of the resin system to rise, reduce the processing fluidity, and at the same time cannot fundamentally solve the problem of adhesive performance decay under high temperature; In view of the brittleness problem of BMI resin, rubber elastomer and thermoplastic resin are used for toughening modification, but after modification, the contradiction between toughness improvement and temperature resistance reduction often occurs. For example, although the addition of excessive thermoplastic resin can improve the toughness, it will cause the thermal deformation temperature of BMI resin to decrease by 10-30℃, losing its high temperature resistance advantage; in addition, the combination of modified BMI resin and electromagnetic shielding function still lacks effective scheme; In view of the realization of electromagnetic shielding function, the existing resin-based composite film mostly uses a mixed system of "resin matrix + powder conductive filler", but the powder filler has high surface energy and poor compatibility with the resin matrix, and is prone to agglomeration during mixing, leading to uneven distribution of conductive network: on the one hand, the agglomeration area is prone to form stress concentration points, reducing the mechanical properties of the material; on the other hand, the conductive path in the non-agglomeration area is insufficient, leading to fluctuation of shielding efficiency, and the addition of powder filler will further increase the processing difficulty of the resin system, making it difficult to prepare large-area film material with a width of >1m, which cannot meet the large-scale assembly requirements of aircraft stealth skin. SUMMARY

[0007] The purpose of the present application is to provide a bismaleimide resin-based electromagnetic shielding composite film preparation method, which aims to solve the problems of large brittleness and insufficient adhesion of bismaleimide resin in existing designs, agglomeration of powder conductive filler leading to uneven shielding, and difficulty in preparing large-area film material to adapt to military equipment, and cannot meet the requirements of high temperature resistance, high adhesion, high shielding, light weight and easy processing.

[0008] The application relates to a preparation method of a bismaleimide resin-based electromagnetic shielding composite film. The preparation method of the bismaleimide resin-based electromagnetic shielding composite film comprises the following steps: S1: according to the mass ratio of 4,4'-diamino diphenyl methane type bismaleimide to polyether sulfone being 100:10-30, polyether sulfone is added into diallyl bisphenol A, and stirring and dispersion are carried out for 30-50 min under the condition of an oil bath environment at 170 DEG C, so that a polyether sulfone-diallyl bisphenol A mixed solution is obtained; S2: the polyether sulfone-diallyl bisphenol A mixed solution obtained in step S1 is cooled to 140 DEG C, 4,4'-diamino diphenyl methane type bismaleimide is added according to the mass ratio of 4,4'-diamino diphenyl methane type bismaleimide to diallyl bisphenol A being 100:70-80, and stirring and dispersion are carried out for 20-30 min until the mixture is uniform, so that a bismaleimide resin adhesive is prepared; S3: the bismaleimide resin adhesive obtained in step S2 is coated into a film on an electric heating plate at 80 DEG C by using a wire bar coater, and the first bismaleimide resin adhesive film layer and the second bismaleimide resin adhesive film layer are obtained after treatment; S4: the electromagnetic shielding film layer is prepared by carrying out copper plating treatment on the surface of the carbon nanotube film by using a magnetron sputtering device; S5: the first bismaleimide resin adhesive film layer and the second bismaleimide resin adhesive film layer obtained in step S3 and the electromagnetic shielding film layer obtained in step S4 are hot-pressed by using a hot-pressing composite machine, so that a bismaleimide resin-based electromagnetic shielding composite film product is obtained.

[0009] As a further improvement of the disclosed technical scheme, in step S1, the polyether sulfone is added into the diallyl bisphenol A in a batch adding mode, the adding amount of each batch is 25-35% of the total mass of the polyether sulfone, and the interval between the adding times of the adjacent two batches is 8-12 min.

[0010] As a further improvement of the disclosed technical scheme, in step S1, inert gas protection is adopted during the stirring and dispersion process, the inert gas is introduced at a rate of 8-18 sccm; and in step S2, the oil bath temperature control cooling and the local air cooling are combined in the cooling process, and the cooling rate is controlled at 6-9 DEG C / min.

[0011] As a further improvement of the disclosed technical solution, in step S2, after the 4,4'-diamino diphenyl methane type bismaleimide is added, the stirring process adopts a phased speed regulation mode, the speed is maintained at 500 rpm in the early stage for 10 min, the speed is adjusted to 460-490 rpm in the middle stage for 5-8 min, and the speed is maintained at 510-530 rpm in the late stage for 5-12 min.

[0012] As a further improvement of the disclosed technical solution, in step S3, the coating thickness of the wire bar coater is controlled to be 50-80 μm, and the heating temperature fluctuation range is not more than ±2℃.

[0013] As a further improvement of the disclosed technical solution, in step S3, after the film is coated and formed, the film is placed in an environment with a temperature of 30-40℃ and a relative humidity of 35-55% for 15-25 min for curing treatment, and then naturally cooled to room temperature to obtain the first bismaleimide resin film layer and the second bismaleimide resin film layer.

[0014] As a further improvement of the disclosed technical solution, in step S4, the sputtering power of the magnetron sputtering device is controlled to be 90-120 W, and the vacuum degree is maintained at 3×10 -3 -5×10 -3 Pa during the sputtering process.

[0015] As a further improvement of the disclosed technical solution, in step S4, the carbon nanotube film is subjected to plasma cleaning treatment before use, the cleaning time is 5-10 min, and the cleaning power is 80-100 W.

[0016] As a further improvement of the disclosed technical solution, in step S5, when the hot pressing operation is performed, the pressure of the hot pressing roller is controlled to be 0.8-1.5 MPa, the rotating speed is 1-3 m / min, and after the hot pressing operation, a natural cooling mode is adopted, and after cooling to room temperature, the edge of the bismaleimide resin-based electromagnetic shielding composite film is cut, and the cutting precision is controlled to be ±0.5 mm.

[0017] In actual application, the bismaleimide resin-based electromagnetic shielding composite film preparation method disclosed by the present application can at least achieve the following beneficial technical effects, specifically: 1) In the resin preparation stage, the mass ratio of 4,4'-diamino diphenyl methane type BMI and polyether sulfone is accurately controlled, the polyether sulfone can form a micro-phase separation structure with the BMI as a toughening agent, which significantly improves the brittleness of the resin without reducing the thermal stability of the resin; further, the diallyl bisphenol A is used as a crosslinking agent and compounded with the BMI according to a set mass ratio, which not only regulates the crosslinking density of the resin, but also improves the interfacial bonding force, solves the problems of insufficient bonding strength and easy debonding at high temperature of the traditional BMI resin, and ensures the high-temperature resistance, high toughness and high adhesion of the bismaleimide resin-based electromagnetic shielding composite film; 2) The three-layer composite structure fundamentally solves the problems of uneven shielding and decreased mechanical properties caused by the aggregation of conductive powder. Among them, the middle layer of the electromagnetic shielding film is prepared by a magnetron sputtering copper plating process, a uniform and dense copper layer is formed on the surface of the carbon nanotube film to construct a conductive network, which not only retains the lightweight advantage of carbon nanotubes, but also reasonably utilizes the high conductivity of copper to improve the shielding effectiveness; the first bismaleimide resin adhesive film layer and the second bismaleimide resin adhesive film layer are used as supporting and bonding carriers to realize the close combination with the skin base material and avoid the occurrence of shielding leakage phenomenon, and the layered structure is convenient for continuous processing by wire bar coating and hot pressing, which breaks through the process limitation of large-area film preparation; 3) In step S1, 170℃ oil bath and 30-50min stirring ensure the dispersion of polyether sulfone, avoiding the fluctuation of resin performance; in step S3, 80℃ electric heating plate coating and wire rod thickness control ensure the uniformity and surface flatness of the adhesive film; in step S5, the hot pressing process realizes the close combination of the three-layer structure without complex post-treatment. The whole preparation process uses mature equipment with strong controllability, which can realize mass production of wide-area film and meet the application requirements of large structural parts such as aircraft stealth skin. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0019] Figure 1 is the microscopic image of the carbon nanotube film disclosed by the present application before being treated by magnetron sputtering copper plating.

[0020] Figure 2 is the microscopic image of the carbon nanotube film disclosed by the present application after being treated by magnetron sputtering copper plating.

[0021] Figure 3The adhesive shear strength test result curve of the bismaleimide resin-based electromagnetic shielding composite film prepared in Example 1 of the present application under different temperature conditions.

[0022] Figure 4 The electromagnetic shielding performance test result map of the bismaleimide resin-based electromagnetic shielding composite film prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0023] The preparation technical solution of the bismaleimide resin-based electromagnetic shielding composite film of the present application will be further described below in combination with specific examples.

[0024] In the thickness direction, the bismaleimide resin-based electromagnetic shielding composite film is composed of a first bismaleimide resin adhesive film layer, an electromagnetic shielding film layer and a second bismaleimide resin adhesive film layer in sequence, and the preparation method thereof is as follows by precisely controlling the process parameters of each link: Example One: The bismaleimide resin-based electromagnetic shielding composite film is realized by the following steps: S1, according to the mass ratio of 4,4'-diamino diphenyl methane type bismaleimide to polyether sulfone of 100:10, polyether sulfone is added into diallyl bisphenol A in four batches, and the addition amount of each batch is 25% of the total mass of polyether sulfone; the addition time interval of adjacent two batches is 12 min; under the condition of 170℃ oil bath environment, nitrogen gas is introduced at a rate of 10sccm for protection, and stirring and dispersion are carried out for 30 min to obtain polyether sulfone-diallyl bisphenol A mixed solution; S2, the polyether sulfone-diallyl bisphenol A mixed solution obtained in S1 is cooled by adopting the combination of oil bath temperature control cooling and local air cooling, and the cooling rate is controlled at 7℃ / min; when the temperature is reduced to 140℃, 4,4'-diamino diphenyl methane type bismaleimide is added according to the mass ratio of 4,4'-diamino diphenyl methane type bismaleimide to diallyl bisphenol A of 100:70; the stirring process adopts phased speed regulation: the rotation speed is maintained at 500 rpm for the first 10 min, adjusted to 470 rpm for the next 5 min, and maintained at 520 rpm for the last 3-5 min, until the mixture is uniform, and the bismaleimide resin adhesive is prepared; S3, the obtained bismaleimide resin adhesive is heated to 80℃ (constant temperature heating, temperature fluctuation range ±2℃) by adopting a wire bar coater, the coating thickness is controlled at 60μm, and the bismaleimide resin adhesive is coated on release paper; the release paper loaded with the adhesive is placed in an environment of 35℃ and relative humidity of 45% for 20 min, and after cooling and hardening, the surface is covered with a protective film to prepare the first bismaleimide resin adhesive film layer and the second bismaleimide resin adhesive film layer, respectively; S4, select carbon nanotube film, after plasma cleaning treatment (cleaning time 8 min, cleaning power 90 W), copper plating treatment is carried out on the surface of the film by using magnetron sputtering equipment: set the sputtering power to 100 W, and maintain the vacuum degree at 4x10 -3 Pa, electromagnetic shielding film layer is prepared; S5, the first bismaleimide resin adhesive film layer, the electromagnetic shielding film layer and the second bismaleimide resin adhesive film layer are stacked in order by using a hot press compounding machine, the hot press roller pressure is controlled to be 1.0 MPa, and the rotating speed is 2 m / min, after hot press compounding, natural cooling to room temperature, and edge cutting, a bismaleimide resin-based electromagnetic shielding composite film product is obtained.

[0025] Example two: The bismaleimide resin-based electromagnetic shielding composite film provided in the example is realized by the following steps: S1, according to the mass ratio of 4,4'-diamino diphenyl methane type bismaleimide to polyether sulfone of 100:20, polyether sulfone is added into diallyl bisphenol A in four batches, and the amount of each batch is 25% of the total mass of polyether sulfone, and the interval between adjacent two batches is 12 min; under the condition of 170℃ oil bath environment, argon gas is introduced at a rate of 15 sccm for protection, and stirring and dispersion are carried out for 40 min to obtain polyether sulfone-diallyl bisphenol A mixed solution; S2, the obtained polyether sulfone-diallyl bisphenol A mixed solution is cooled by combining oil bath temperature control cooling and local air cooling, and the cooling rate is controlled at 6℃ / min, when the temperature is reduced to 140℃, 4,4'-diamino diphenyl methane type bismaleimide is added according to the mass ratio of 4,4'-diamino diphenyl methane type bismaleimide to diallyl bisphenol A of 100:75; the stirring process adopts phased speed regulation: the rotating speed is maintained at 500 rpm for the first 10 min, adjusted to 480 rpm for the next 6 min, and maintained at 530 rpm for the last 4-6 min, until the mixture is uniform, and a bismaleimide resin adhesive is prepared; S3, the obtained bismaleimide resin adhesive is heated to 80℃ (constant temperature heating, temperature fluctuation range ±2℃) by using a wire bar coater, and the coating thickness is controlled to be 70μm, and then coated on release paper; the release paper loaded with adhesive is placed in an environment of 30℃ and relative humidity of 50% for 15 min, and after cooling and hardening, the surface is covered with a protective film, and the first bismaleimide resin adhesive film layer and the second bismaleimide resin adhesive film layer are prepared respectively; S4, select carbon nanotube film, after plasma cleaning treatment (cleaning time 5 min, cleaning power 80 W), copper plating treatment is carried out on the surface of the film by using magnetron sputtering equipment: set the sputtering power to 90 W, and maintain the vacuum degree at 3x10 -3 Pa, electromagnetic shielding film layer is prepared; S5, using a hot press compounding machine, the obtained first bismaleimide resin adhesive film layer, electromagnetic shielding film layer and second bismaleimide resin adhesive film layer are stacked in order, the hot press roller pressure is controlled to be 0.8 MPa, the rotating speed is 1 m / min, hot press compounding is performed, and after natural cooling to room temperature, edge cutting is performed, to obtain a bismaleimide resin-based electromagnetic shielding composite film product.

[0026] Example three: The bismaleimide resin-based electromagnetic shielding composite film provided in the embodiment is realized by the following steps: S1, according to the mass ratio of 4,4'-diamino diphenyl methane type bismaleimide to polyether sulfone of 100:25, polyether sulfone is added into diallyl bisphenol A in three batches, and the addition amount of each batch is 33% (error allowance ±2%) of the total mass of polyether sulfone, and the addition time interval of adjacent two batches is 15 min; nitrogen gas is introduced at a rate of 8 sccm under the protection of nitrogen gas at 170 ℃ oil bath environment, and stirring and dispersion are performed for 50 min to obtain a polyether sulfone-diallyl bisphenol A mixed solution; S2, the obtained polyether sulfone-diallyl bisphenol A mixed solution is cooled by combining oil bath temperature control cooling and local air cooling, the cooling rate is controlled to be 9 ℃ / min, when the temperature is reduced to 140 ℃, 4,4'-diamino diphenyl methane type bismaleimide is added according to the mass ratio of 4,4'-diamino diphenyl methane type bismaleimide to diallyl bisphenol A of 100:78; the stirring process adopts phased speed regulation: the rotating speed is maintained to be 500 rpm for 10 min in the early stage, the rotating speed is adjusted to be 460 rpm for 8 min in the middle stage, and the rotating speed is maintained to be 510 rpm for 4-12 min in the late stage, until the mixture is uniformly prepared, to obtain a bismaleimide resin adhesive; S3, the obtained bismaleimide resin adhesive is heated to 80 ℃ (constant temperature heating, temperature fluctuation range ±2 ℃) by using a wire bar coater, the coating thickness is controlled to be 50 μm, and the bismaleimide resin adhesive is coated on release paper; the release paper loaded with the adhesive is placed in an environment of 40 ℃ and 35% relative humidity for 25 min, and after cooling and hardening, a protective film is coated on the surface, to respectively prepare a first bismaleimide resin adhesive film layer and a second bismaleimide resin adhesive film layer; S4, after plasma cleaning treatment (cleaning time 10 min, cleaning power 100 W), a carbon nanotube film is selected, copper plating treatment is performed on the surface of the carbon nanotube film by using a magnetron sputtering device: the sputtering power is set to be 120 W, and the vacuum degree is maintained to be 5×10 -3 Pa, to obtain an electromagnetic shielding film layer; S5, using a hot press compounding machine, the obtained first bismaleimide resin adhesive film layer, electromagnetic shielding film layer and second bismaleimide resin adhesive film layer are stacked in order, the hot press roller pressure is controlled to be 1.5 MPa, the rotating speed is 3 m / min, hot press compounding is performed, and after natural cooling to room temperature, edge cutting is performed, to obtain a bismaleimide resin-based electromagnetic shielding composite film product.

[0027] Example Four: The bismaleimide resin-based electromagnetic shielding composite film provided in the embodiment is realized by the following steps: S1, according to the mass ratio of 4,4'-diamino diphenyl methane type bismaleimide to polyether sulfone of 100:30, polyether sulfone is added into diallyl bisphenol A in three batches, and the addition amount of each batch is 33% (error allowance ±1%) of the total mass of polyether sulfone, and the addition time interval of adjacent two batches is 10 min; under the condition of 170℃ oil bath environment, argon gas is introduced at a rate of 12 sccm for protection, and stirring and dispersion are performed for 45 min to obtain a polyether sulfone-diallyl bisphenol A mixed solution; S2, the obtained polyether sulfone-diallyl bisphenol A mixed solution is cooled by combining oil bath temperature control cooling and local air cooling, and the cooling rate is controlled at 8℃ / min; when the temperature is reduced to 140℃, 4,4'-diamino diphenyl methane type bismaleimide is added according to the mass ratio of 4,4'-diamino diphenyl methane type bismaleimide to diallyl bisphenol A of 100:80; the stirring process adopts phased speed regulation: the rotating speed is maintained at 500 rpm for 10 min in the early stage, adjusted to 490 rpm for 7 min in the middle stage, and maintained at 525 rpm for 4-10 min in the later stage, until the mixture is uniform, to prepare a bismaleimide resin adhesive; S3, the obtained bismaleimide resin adhesive is heated to 80℃ (constant temperature heating, temperature fluctuation range ±2℃) by using a wire bar coater, and the coating thickness is controlled to be 80μm, and coated on release paper; the release paper loaded with the adhesive is placed in an environment of 32℃ and relative humidity of 55% for 18 min, and after cooling and hardening, a protective film is coated on the surface, to prepare a first bismaleimide resin adhesive film layer and a second bismaleimide resin adhesive film layer, respectively; S4, after plasma cleaning treatment (cleaning time 7 min, cleaning power 95 W), a carbon nanotube film is selected, copper plating treatment is performed on the surface of the carbon nanotube film by using a magnetron sputtering equipment: the sputtering power is set to be 110 W, and the vacuum degree is maintained at 4.5×10 -3 Pa, to obtain an electromagnetic shielding film layer; S5, using a hot press laminator, the obtained first bismaleimide resin adhesive film layer, electromagnetic shielding film layer and second bismaleimide resin adhesive film layer are stacked in order, the hot press roller pressure is controlled to be 1.2 MPa, the rotating speed is 2.5 m / min, hot press lamination is performed, and then natural cooling is performed to room temperature, and then edge cutting is performed, to obtain a bismaleimide resin-based electromagnetic shielding composite film product.

[0028] Comparative Example One The difference between the present comparative example and Example One is that the batch addition of polyether sulfone, inert gas protection and phase speed regulation of stirring are omitted, and the specific steps are as follows: S1, according to the mass ratio of 4,4'-diamino diphenyl methane type bismaleimide to polyether sulfone being 100:10, polyether sulfone is added to diallyl bisphenol A at one time; under the condition of no inert gas protection in 170℃ oil bath environment, stirring and dispersing for 30 min, to obtain polyether sulfone-diallyl bisphenol A mixed solution; S2, using the combination of oil bath temperature control cooling and local air cooling, the polyether sulfone-diallyl bisphenol A mixed solution obtained in S1 is cooled to 140℃, 4,4'-diamino diphenyl methane type bismaleimide is added according to the mass ratio of 4,4'-diamino diphenyl methane type bismaleimide to diallyl bisphenol A being 100:70, and the whole process is maintained at 500 rpm uniform stirring for 30 min, to prepare a bismaleimide resin adhesive; S3 to S5, the process parameters are completely consistent with those of S3 to S5 of Example One, and finally a comparative bismaleimide resin-based electromagnetic shielding composite film is prepared.

[0029] It is detected that the bismaleimide resin-based electromagnetic shielding composite film prepared in Comparative Example One has multiple performance problems due to the one-time addition of polyether sulfone, uneven dispersion, and the influence of no inert gas protection on the stability of the resin, including insufficient toughness of the adhesive film (impact strength is 8.6 kJ / m², which is 28% lower than 11.9 kJ / m² of Example One), decreased adhesive shear strength (13.90 MPa, which is 15.3% lower than 16.41 MPa of Example One), and large fluctuation of electromagnetic shielding effectiveness (shielding effectiveness is 40.23-45.76 dB, difference is 1.5 dB larger than 3.23 dB of Example One), as shown in Table 1.

[0030] Comparative Example Two The difference between the present comparative example and Example One is that the electromagnetic shielding film layer directly uses a carbon nanotube film without copper plating, and the specific steps are as follows: S1 to S3, the process parameters are completely consistent with those of S1 to S3 of Example One; S4, directly selecting a carbon nanotube film as the electromagnetic shielding film layer (omitting the magnetron sputtering copper plating treatment); S5, the process parameters are completely consistent with S5 of example one, finally, the bismaleimide resin-based electromagnetic shielding composite film for comparison is prepared.

[0031] It is detected that the electromagnetic shielding efficiency of the composite film prepared in the comparative example is reduced by 37% (in the frequency range of 1-18 GHz, the shielding efficiency of example one is ≥46 dB, and the shielding efficiency of the comparative example two is ≤31 dB) compared with example one, as shown in Table 1.

[0032] Table 1 Figure 1 、 Figure 2 The microscopic images of the carbon nanotube film before and after the magnetic control sputtering copper treatment disclosed in the present application are disclosed respectively, it can be known that before the magnetic control sputtering copper treatment, the carbon nanotube film is dark and the surface texture is relatively rough and loose, and the carbon nanotube is relatively dispersed; and after the magnetic control sputtering copper treatment, a uniform copper layer is covered on the surface, the texture is more flat and dense, and the carbon nanotube is combined closely with the copper layer, which indicates that the copper layer is successfully deposited on the surface of the carbon nanotube film by the magnetic control sputtering process, and lays a foundation for subsequent construction of an efficient electromagnetic shielding path.

[0033] Figure 3 The curve graph of the adhesive shear strength test results of the bismaleimide resin-based electromagnetic shielding composite film prepared in example 1 of the present application under different temperature conditions can be known that the adhesive shear strength of the bismaleimide resin-based electromagnetic shielding composite film decreases regularly with the increase of the test temperature: the shear strength reaches 16.41 MPa at room temperature of 25 DEG C, which meets the normal temperature bonding demand of scenes such as stealth skin; when the temperature rises to 200 DEG C, the strength decreases to 12.09 MPa; when the temperature further rises to 225 DEG C, the strength decreases to 13.00 MPa (note: the slight increase of the strength here is caused by the temporary recombination of the resin molecular chain, which is normal fluctuation); when the temperature rises to 250 DEG C, the strength decreases to 7.52 MPa. Such trend is caused by the fact that the molecular chain movement of the bismaleimide resin adhesive film layer is intensified under high temperature, and the interfacial bonding force between the adhesive film and the shielding layer is weakened, thereby indirectly proving the excellent adhesive stability of the bismaleimide resin-based electromagnetic shielding composite film in the medium and low temperature environment, and providing the performance basis of the temperature dimension for the scene adaptation.

[0034] Figure 4 The electromagnetic shielding performance test result graph of the bismaleimide resin-based electromagnetic shielding composite film prepared in example 1 of the present application can be known that the electromagnetic shielding efficiency of the composite film prepared in example 1 is always stable in the interval of 46.12-49.35 dB in the test frequency range of 1-18 GHz. It can be known that the interfacial bonding between the first bismaleimide resin adhesive film layer, the second bismaleimide resin adhesive film layer and the electromagnetic shielding film layer is uniform, and the conductive path constructed by the carbon nanotube and the copper plating layer is stable, which provides the actual measurement basis for realizing the efficient and stable electromagnetic shielding of the composite film in a wide frequency range.

[0035] The foregoing description of the disclosed embodiments enables a person skilled in the art to make or use the application. Numerous modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other embodiments without the use of the inventive faculty. Therefore, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a bismaleimide resin-based electromagnetic shielding composite film, wherein the bismaleimide resin-based electromagnetic shielding composite film is sequentially composed of a first bismaleimide resin film layer, an electromagnetic shielding film layer and a second bismaleimide resin film layer along its thickness direction. The preparation method of bismaleimide resin-based electromagnetic shielding composite film includes the following steps: S1: According to the mass ratio of 4,4'-diaminodiphenylmethane type bismaleimide to polyethersulfone of 100:10~30, polyethersulfone is added to diallyl bisphenol A and stirred and dispersed in an oil bath at 170°C for 30~50 min to obtain a polyethersulfone-diallyl bisphenol A mixture. S2: Cool the polyethersulfone-diallyl bisphenol A mixture obtained in step S1 to 140°C, add 4,4'-diaminodiphenylmethane bismaleimide at a mass ratio of 100:70-80 to 4,4'-diaminodiphenylmethane bismaleimide, and stir and disperse for 20-30 minutes until the mixture is uniform to obtain bismaleimide resin adhesive; S3: The bismaleimide resin adhesive obtained in step S2 is coated onto an electric heating plate at 80°C using a wire bar coater to form a film. After processing, the first bismaleimide resin film layer and the second bismaleimide resin film layer are obtained. S4: Copper plating is performed on the surface of the carbon nanotube film using magnetron sputtering equipment to obtain the electromagnetic shielding film layer; S5: Using a hot-press laminating machine, the first bismaleimide resin film layer and the second bismaleimide resin film layer obtained in step S3, and the electromagnetic shielding film layer obtained in step S4 are hot-pressed together to obtain the finished bismaleimide resin-based electromagnetic shielding composite film.

2. The method for preparing the bismaleimide resin-based electromagnetic shielding composite film according to claim 1, characterized in that, In step S1, polyethersulfone is added to diallyl bisphenol A in batches, with each batch containing 25-35% of the total mass of polyethersulfone, and the time interval between two adjacent batches is 8-12 minutes.

3. The method for preparing the bismaleimide resin-based electromagnetic shielding composite film according to claim 1, characterized in that, In step S1, inert gas protection is used during the stirring and dispersion process, and the inert gas introduction rate is 8 to 18 sccm; and in step S2, the cooling process adopts a combination of oil bath temperature control and local air cooling, and the cooling rate is controlled at 6 to 9℃ / min.

4. The method for preparing the bismaleimide resin-based electromagnetic shielding composite film according to claim 1, characterized in that, In step S2, after adding 4,4'-diaminodiphenylmethane bismaleimide, the stirring process adopts a staged speed adjustment method. In the first 10 minutes, the speed is maintained at 500 rpm, in the middle 5-8 minutes, the speed is adjusted to 460-490 rpm, and in the later 5-12 minutes, it is maintained at 510-530 rpm.

5. The method for preparing the bismaleimide resin-based electromagnetic shielding composite film according to claim 1, characterized in that, In step S3, the coating thickness of the bar coater is controlled between 50 and 80 μm, and the heating temperature fluctuation range does not exceed ±2℃.

6. The method for preparing the bismaleimide resin-based electromagnetic shielding composite film according to claim 1, characterized in that, In step S3, after coating and forming the film, the film is placed in an environment of 30-40°C and 35-55% relative humidity for 15-25 minutes for curing treatment, and then naturally cooled to room temperature to obtain the first bismaleimide resin film layer and the second bismaleimide resin film layer.

7. The method for preparing the bismaleimide resin-based electromagnetic shielding composite film according to claim 1, characterized in that, In step S4, the sputtering power of the magnetron sputtering equipment is controlled between 90 and 120 W, and the vacuum level is maintained at 3 × 10⁻⁶ W during the sputtering process. -3 ~5×10 -3 Pa.

8. The method for preparing the bismaleimide resin-based electromagnetic shielding composite film according to claim 1, characterized in that, In step S4, the carbon nanotube membrane undergoes plasma cleaning treatment before use, with a cleaning time of 5 to 10 minutes and a cleaning power of 80 to 100 W.

9. The method for preparing the bismaleimide resin-based electromagnetic shielding composite film according to claim 1, characterized in that, In step S5, when performing the hot-pressing composite operation, the pressure of the hot-pressing roller is controlled at 0.8 to 1.5 MPa, the rotation speed is 1 to 3 m / min, and after hot-pressing composite, natural cooling is adopted. After cooling to room temperature, the edge of the bismaleimide resin-based electromagnetic shielding composite film is cut, and the cutting accuracy is controlled within ±0.5 mm.

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