Preparation method of an integrated shielding foam with two-sided anisotropy

Abstract

The present invention provides a preparation method of an integrated shielding foam with two-sided anisotropy, comprising: obtaining a reinforced polyimide foam with a sheet stack structure by subjecting the polyimide foam to isothermal gradient compression treatment; performing surface colloidal palladium activation, peptization treatment, and electroless plating conductive treatment on the reinforced polyimide foam to form a first metal layer; performing electro-deposition on one side of the first metal layer to obtain a second metal layer with a thickness gradient, wherein the first metal layer uniformly adheres to the inner and outer surfaces of the reinforced polyimide foam to form a three-dimensional continuous conductive structure, and the second metal layer grows on one side of the outer surface of the first metal layer; this integrated shielding foam has good bending resistance while achieving a good shielding effect; due to the inconsistent metal layer structures on both sides, the loss modes and paths of electromagnetic waves are also inconsistent, which can well meet the requirements of some special devices for materials with two-sided anisotropic shielding performance.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic shielding materials, and particularly relates to a preparation method of an integrated shielding foam with two-sided anisotropy. Background Art

[0002] The rapid development of science and information technology has brought people an efficient and convenient life. However, the widespread use of electromagnetic waves has brought serious electromagnetic pollution. Electromagnetic waves can interfere with the communication system and driving system of airplanes, affecting the safety of airplane travel; electromagnetic waves can also affect the signal transmission of equipment, making it unable to work properly; electromagnetic waves can also carry information, posing a risk of information leakage; and if the human body is exposed to strong electromagnetic waves for a long time, it will also cause harm to the body. As a good conductor, metal materials have excellent electromagnetic wave shielding ability, but their disadvantages such as high density, difficult processing, and easy corrosion limit their application in the field of electromagnetic shielding. With the development of science and technology, people have begun to pursue lightweight and efficient electromagnetic shielding materials, and traditional pure metal materials as electromagnetic shielding materials can no longer meet people's needs.

[0003] Polymers have the advantage of low density. Combining metal materials with polymer materials as electromagnetic shielding materials can significantly reduce the density of the composite material. A metal shielding film can be prepared on the surface of the polymer matrix by methods such as electroless plating and magnetron sputtering. The shielding of electromagnetic waves by such shielding structures is mainly based on reflection loss, which is likely to cause serious secondary electromagnetic pollution. Summary of the Invention

[0004] In view of this, the present invention provides a preparation method of an integrated shielding foam with two-sided anisotropy. By adjusting the thickness of the metal layers on both sides of the foam, the loss modes and paths of electromagnetic waves on both sides of the foam are inconsistent, which can well meet the requirements of some special devices for materials with two-sided anisotropic shielding performance.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] An embodiment of the present invention provides a preparation method of an integrated shielding foam with two-sided anisotropy, and the method includes:

[0007] Subjecting a polyimide foam to isothermal gradient compression treatment to obtain a strengthened polyimide foam, and the strengthened polyimide foam is a three-dimensional structure in the form of sheet stacking;

[0008] Performing surface colloidal palladium activation, degumming treatment, and electroless plating conductivity treatment on the strengthened polyimide foam to form a first metal layer;

[0009] Electrodeposit on one side of the first metal layer to obtain a second metal layer with a thickness gradient, wherein the first metal layer uniformly adheres to the inner and outer surfaces of the reinforced polyimide foam to form a three-dimensional continuous conductive structure, and the second metal layer grows on one side of the outer surface of the first metal layer.

[0010] Preferably, obtaining the reinforced polyimide foam by subjecting the polyimide foam to isothermal gradient compression treatment includes:

[0011] a) At a temperature of 180 - 220 °C, compress the polyimide foam to 3 / 5 - 4 / 5 of its original thickness, and keep the pressure and temperature for 3 - 5 minutes;

[0012] b) Keep the temperature unchanged, adjust the compression degree to 1 / 5 - 2 / 5 of the original thickness, and keep the pressure and temperature for 3 - 5 minutes.

[0013] Preferably, subjecting the reinforced polyimide foam to surface colloidal palladium activation, decolloiding treatment, and electroless plating for conductivity treatment to form the first metal layer includes:

[0014] Immerse the reinforced polyimide foam in a Triton solution with a volume fraction of 0.2% for hydrophilization treatment; then immerse the hydrophilized reinforced polyimide foam in a colloidal palladium activation solution, adjust the solution environment to a negative pressure state, stir with a rotor, and keep for 1 - 5 minutes; then immerse the reinforced polyimide foam after colloidal palladium activation treatment in a decolloiding solution, adjust the solution environment to a negative pressure state, stir with a rotor, and keep for 1 - 5 minutes; then place the reinforced polyimide foam after decolloiding treatment in an electroless plating metal solution, adjust the solution environment to a negative pressure state, stir with a rotor, and keep for 20 - 40 minutes to complete the electroless plating for conductivity treatment and form the first metal layer.

[0015] Preferably, the stirring speed of the rotor is 800 - 1200 revolutions per minute.

[0016] Preferably, the negative pressure state means that the reading of the vacuum gauge is -0.1 to 0 MPa.

[0017] Preferably, electrodepositing on one side of the first metal layer to obtain a second metal layer with a thickness gradient includes:

[0018] Place the reinforced polyimide foam after electroless plating for conductivity treatment in an electroplating solution, perform single-sided electrodeposition on one side of the first metal layer, keep air stirring during the electroplating process, and keep the temperature of the electroplating solution at 35 - 45 °C to prepare a second metal layer with a thickness gradient of 0.1 - 3 μm.

[0019] Preferably, the density of the polyimide foam is 15 - 35 kg / m³.

[0020] Preferably, the polyimide foam is an open-cell foam with a porosity of 70-90%.

[0021] Preferably, the single-sided electrodeposition is pulse electrodeposition, with an average current density of 1.0-5.0 A / dm², a duty cycle of 0.1-0.3, a frequency of 50-200 Hz, and an electrodeposition time of 1-5 minutes.

[0022] Compared with the prior art, it has the following beneficial effects:

[0023] (1) Different from the conventional foam structure, the integrated shielding foam with two-sided anisotropy has a stacked three-dimensional structure. After metallization, it can reflect the incident electromagnetic wave more times, greatly improving the absorption loss of the electromagnetic wave. At the same time, the isothermal gradient compression treatment can effectively remove the blowing agent remaining in the foaming process, improve the roughness of the foam inner wall, so that the foam can omit the roughening step in the subsequent "chemical plating for conductivity treatment" step.

[0024] (2) Usually, the flexibility of the composite material obtained after metallization of a soft polymer substrate (such as the bending resistance) will be greatly reduced. However, in the present invention, by combining chemical plating and electrodeposition, a copper layer of nanocrystals is uniformly attached to the inner and outer surfaces of the polyimide foam, and then by adjusting the parameters of electrodeposition, a copper layer with the same order of magnitude of grain size is plated outside the nanocrystalline copper layer on the outer side of the foam, achieving good shielding effectiveness of the foam while having good bending resistance.

[0025] (3) Through the design of the lamellar stacked structure and the composite of the thickness gradient metal layer, the two sides of the foam of the present invention have different characteristics in protecting against electromagnetic waves. When the electromagnetic wave is incident from side Ⅰ and passes through the foam of the present invention, the electromagnetic wave is dissipated through "absorption-reflection-re-absorption". When the electromagnetic wave is incident from side Ⅱ and passes through the foam of the present invention, the electromagnetic wave is dissipated through "reflection-absorption". When the electromagnetic wave is incident from side Ⅰ, the shielding effectiveness of the foam of the present invention is better, realizing the two-sided anisotropy of the electromagnetic wave shielding effect, which can well meet the requirements of some special devices for materials with two-sided anisotropic shielding performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a cross-sectional SEM image of the polyimide foam after isothermal gradient compression treatment provided in Embodiment 1 of the present invention.

[0027] Figure 2 It is a cross-sectional schematic diagram of the integrated shielding foam with two-sided anisotropy provided in Embodiment 1 of the present invention, where side Ⅰ refers to the first metal layer surface, and side Ⅱ refers to the composite metal layer surface of the first metal layer and the second metal layer.

[0028] Figure 3This is a comparison chart of the shielding effectiveness of the integrated shielding foam with two-sided anisotropy provided in the first embodiment of the present invention, where the electromagnetic wave incident surfaces are surface I and surface II. Detailed implementation mode

[0029] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0030] The present invention provides a preparation method of an integrated shielding foam with two-sided anisotropy. Among them, for the integrated shielding foam, a first metal layer is uniformly attached to the inner and outer surfaces of the polyimide foam, and a second metal layer grows on one side of the outer surface of the first metal layer. In this way, the two sides of the integrated shielding foam are surface I and surface II: surface I refers to the first metal layer surface; surface II refers to the composite metal layer surface of the first metal layer and the second metal layer. Specifically, the first metal layer can be a metal such as copper, nickel, silver, zinc, cobalt, tin, etc. that can be electrolessly plated, and the second metal layer can be a metal such as copper, nickel, silver, cadmium, chromium, tin, cobalt, etc. that can be electroplated. In the following embodiments of the present invention, the first metal layer and the second metal layer are taken as an example of metal copper or metal nickel or their combination. The specific preparation method is as follows:

[0031] (1) Place the polyimide foam in a hot press. At a temperature of 180 - 220 degrees Celsius, compress the polyimide foam to 3 / 5 - 4 / 5 of its original thickness, and keep the temperature for 3 - 5 minutes; then keep the temperature unchanged, adjust the compression degree to 1 / 5 - 2 / 5 of its original thickness, and keep the temperature for 3 - 5 minutes to obtain a laminated reinforced polyimide foam.

[0032] (2) Immerse the reinforced polyimide foam in a Triton solution with a volume fraction of 0.2% for hydrophilic treatment; then immerse the hydrophilized reinforced polyimide foam in a colloidal palladium activation solution, adjust the solution environment to negative pressure, use a rotor to stir, and keep it for 1 - 5 minutes; then immerse the reinforced polyimide foam after the colloidal palladium activation treatment in a peptizing solution, adjust the solution environment to negative pressure, use a rotor to stir, and keep it for 1 - 5 minutes; then place the reinforced polyimide foam after the peptizing treatment in an electroless plating metal solution, adjust the solution environment to negative pressure, use a rotor to stir, and keep it for 20 - 40 minutes to complete the electroless plating and conductivity treatment.

[0033] (3) Place the reinforced polyimide foam after the conductivity treatment in an electroplating solution for single-sided electro-deposition to obtain the integrated shielding foam with two-sided anisotropy.

[0034] Among them, the stirring speed of the rotor is 800 - 1200 revolutions per minute;

[0035] Among them, the negative pressure state refers to the reading of the vacuum gauge being -0.1 to 0 MPa.

[0036] Among them, the density of the polyimide foam is 15 to 35 kg / m³.

[0037] Among them, the polyimide foam is an open-cell foam with a porosity of 70 to 90%.

[0038] Among them, the average current density of electrodeposition is 1.0 to 5.0 A / dm², the duty cycle is 0.1 to 0.3, more preferably 0.2, the frequency is 50 to 200 Hz, more preferably 100 Hz, the temperature of the electroplating solution is 45 to 55 °C, and the electroplating time is 1 to 5 minutes.

[0039] The present invention provides a preparation method of an integrated shielding foam with two-sided anisotropy, relating to the technical field of electromagnetic shielding materials. The steps include: obtaining a strengthened polyimide foam with a lamellar stacked structure by subjecting the polyimide foam to isothermal gradient compression treatment; then conducting a conductivity treatment on it by electroless plating to attach a uniform metal layer on the surface and inner surface of the foam; finally, designing a thickness gradient metal layer structure, and obtaining an integrated shielding foam with a thickness gradient metal layer structure by regulating the electrodeposition parameters, which can have good flexibility while achieving a good shielding effect; when electromagnetic waves are incident from different sides of the integrated shielding foam, due to the inconsistent metal layer structures on both sides, the loss methods and paths of electromagnetic waves are also inconsistent. Therefore, when this composite foam is used as an electromagnetic shielding and protection material, it has different electromagnetic protection characteristics on both sides, which can well meet the requirements of some special devices for materials with two-sided anisotropic shielding performance.

[0040] Example 1

[0041] An integrated shielding foam with two-sided anisotropy prepared in an embodiment of the present invention is as follows:

[0042] (1) Place the polyimide foam in a hot press. At a temperature of 200 °C, compress the polyimide foam to 2 / 3 of its original thickness and keep it warm for 3 minutes; then keep the temperature unchanged, adjust the compression degree to 1 / 3 of its original thickness, and keep it warm for 3 minutes to obtain a lamellar stacked strengthened polyimide foam with a thickness of 1 mm.

[0043] (2) Immerse the reinforced polyimide foam in a Triton solution with a volume fraction of 0.2% for hydrophilization treatment; then immerse the hydrophilized reinforced polyimide foam in a colloidal palladium activation solution, adjust the solution environment to negative pressure, with the vacuum gauge reading -0.1 MPa and the rotor stirring speed of 1000 revolutions per minute, and hold for 2 minutes; then immerse the reinforced polyimide foam after colloidal palladium activation treatment in a peptizing solution, adjust the solution environment to negative pressure, with the vacuum gauge reading -0.1 MPa and the rotor stirring speed of 1000 revolutions per minute, and hold for 2 minutes; then place the reinforced polyimide foam after peptizing treatment in an electroless copper plating solution, adjust the solution environment to negative pressure, with the vacuum gauge reading -0.1 MPa and the rotor stirring speed of 1000 revolutions per minute, and hold for 30 minutes to complete the electroless copper plating for conductivity treatment.

[0044] (3) Place the reinforced polyimide foam after conductivity treatment in an electroplating copper solution, with the solution temperature of 45 °C, adopt single-sided pulse electrodeposition, with an average current density of 3 A / dm², a duty cycle of 0.2, a frequency of 100 Hz, and an electrodeposition time of 3 minutes. Keep air stirring during the electrodeposition process to obtain a metal copper layer with a gradient thickness, and obtain the described integrated shielding foam with two-sided anisotropy.

[0045] Example Two

[0046] An integrated shielding foam with two-sided anisotropy prepared in the embodiment of the present invention, the specific implementation manner is the same as that of Example One, only in the "isothermal gradient compression treatment" step, the hot pressing temperature is adjusted to 100 °C for experiments.

[0047] Example Three

[0048] An integrated shielding foam with two-sided anisotropy prepared in the embodiment of the present invention, the specific implementation manner is the same as that of Example One, only in the "isothermal gradient compression treatment" step, the hot pressing temperature is adjusted to 300 °C for experiments.

[0049] Example Four

[0050] An integrated shielding foam with two-sided anisotropy prepared in the embodiment of the present invention, the specific implementation manner is the same as that of Example One, only in the "electroless plating for conductivity treatment" step, the electroless plating time is adjusted to 20 minutes for experiments.

[0051] Example Five

[0052] An integrated shielding foam with two-sided anisotropy prepared in the embodiment of the present invention, the specific implementation manner is the same as that of Example One, only in the "electroless plating for conductivity treatment" step, the electroless plating time is adjusted to 40 minutes for experiments.

[0053] Example VI

[0054] An integrated shielding foam with two-sided anisotropy prepared in an embodiment of the present invention. The specific implementation manner is the same as that of Example I, and only the electro-deposition time is adjusted to 1 minute in the step of "electro-depositing on one side of the first metal layer" for the experiment.

[0055] Example VII

[0056] An integrated shielding foam with two-sided anisotropy prepared in an embodiment of the present invention. The specific implementation manner is the same as that of Example I, and only the electro-deposition time is adjusted to 5 minutes in the step of "electro-depositing on one side of the first metal layer" for the experiment.

[0057] Example VIII

[0058] An integrated shielding foam with two-sided anisotropy prepared in an embodiment of the present invention. The specific implementation manner is the same as that of Example I, and only the electro-deposition parameters are adjusted to an average current density of 1 ampere per square decimeter and an electro-deposition time of 9 minutes in the step of "electro-depositing on one side of the first metal layer" for the experiment.

[0059] Example IX

[0060] An integrated shielding foam with two-sided anisotropy prepared in an embodiment of the present invention. The specific implementation manner is the same as that of Example I, and only the electro-deposition parameters are adjusted to an average current density of 5 amperes per square decimeter and an electro-deposition time of 1.8 minutes in the step of "electro-depositing on one side of the first metal layer" for the experiment.

[0061] Example X

[0062] An integrated shielding foam with two-sided anisotropy prepared in an embodiment of the present invention. The specific implementation manner is the same as that of Example I, and only the duty cycle in the electro-deposition parameters is adjusted to 0.1 in the step of "electro-depositing on one side of the first metal layer" for the experiment.

[0063] Example XI

[0064] An integrated shielding foam with two-sided anisotropy prepared in an embodiment of the present invention. The specific implementation manner is the same as that of Example I, and only the duty cycle in the electro-deposition parameters is adjusted to 0.3 in the step of "electro-depositing on one side of the first metal layer" for the experiment.

[0065] Example XII

[0066] An integrated shielding foam with two-sided anisotropy prepared in an embodiment of the present invention. The specific implementation manner is the same as that of Example I, and only the frequency in the electro-deposition parameters is adjusted to 50 Hz in the step of "electro-depositing on one side of the first metal layer" for the experiment.

[0067] Example XIII

[0068] An integrated shielding foam with two-sided anisotropy prepared in the embodiment of the present invention. The specific implementation manner is the same as that of Example 1, except that in the step of "electrodepositing on one side of the first metal layer", the frequency in the electrodeposition parameters is adjusted to 200 Hz for the experiment.

[0069] Comparative Example 1

[0070] The constant temperature gradient compression step is omitted in the comparative example of the present invention, and the modification and subsequent steps are directly carried out on the polyimide foam;

[0071] After the step of "chemical plating for conductivity treatment", it can be clearly observed by the naked eye that very little metallic copper is plated on the polyimide foam. Using a multimeter to test both ends of the foam, it is found that it is not conductive, indicating that a continuous conductive path is not formed inside the foam, resulting in the inability to smoothly carry out the subsequent electrodeposition step, which fully reflects the importance of the hot pressing step.

[0072] Comparative Example 2

[0073] An integrated shielding foam with two-sided anisotropy prepared in the comparative example of the present invention. The specific implementation manner is the same as that of Example 1, except that in the step of "chemical plating for conductivity treatment", the chemical copper plating time is adjusted to 60 minutes for the experiment;

[0074] The integrated shielding foam prepared with this experimental parameter has a high shielding effectiveness, but its texture is hard and brittle and no longer has flexibility.

[0075] Comparative Example 3

[0076] The step of "electrodepositing on one side of the first metal layer" is omitted in the comparative example of the present invention, and the prepared integrated shielding foam does not have the shielding performance with different phases on both sides. The specific experimental steps are as follows:

[0077] (1) Place the polyimide foam in a hot press. At a temperature of 200 °C, compress the polyimide foam to 2 / 3 of its original thickness and keep it warm for 3 minutes; then keep the temperature unchanged, adjust the compression degree to 1 / 3 of its original thickness, and keep it warm for 3 minutes to obtain a laminated reinforced polyimide foam;

[0078] (2) Immerse the reinforced polyimide foam in a Triton solution with a volume fraction of 0.2% for hydrophilization treatment; then immerse the hydrophilized reinforced polyimide foam in a colloidal palladium activation solution, adjust the solution environment to negative pressure, with the vacuum gauge reading -0.1 MPa and the rotor stirring speed at 1000 revolutions per minute, and hold for 2 minutes; then immerse the reinforced polyimide foam after the colloidal palladium activation treatment in a peptizing solution, adjust the solution environment to negative pressure, with the vacuum gauge reading -0.1 MPa and the rotor stirring speed at 1000 revolutions per minute, and hold for 2 minutes; then place the reinforced polyimide foam after the peptizing treatment in a electroless copper plating solution, adjust the solution environment to negative pressure, with the vacuum gauge reading -0.1 MPa and the rotor stirring speed at 1000 revolutions per minute, and hold for 30 minutes to complete the electroless copper plating for conductivity treatment.

[0079] Characterize the shielding effectiveness of the integrated shielding foam sample using a network vector analyzer;

[0080] Characterize the bending resistance by testing the resistance increment of the integrated shielding foam sample before and after bending 100 times.

[0081] Refer to Table 1 for a comparative summary of the effects of hot pressing temperature, electroless plating time, and electroplating time on the shielding effectiveness in the examples of the present invention. In the table, the hot pressing temperature refers to the temperature of the isothermal gradient compression treatment, the shielding effectiveness in the table refers to the average shielding effectiveness of this integrated shielding foam in the frequency range of 0.3 MHz to 2 GHz, the shielding effectiveness of surface I in the table refers to the shielding effectiveness of this integrated shielding foam when the electromagnetic wave is incident from the first metal layer; the shielding effectiveness of surface II in the table refers to the shielding effectiveness of this integrated shielding foam when the electromagnetic wave is incident from the composite metal layer of the first metal layer and the second metal layer. It can be seen from the table that:

[0082] 1) In Example 1, when the hot pressing temperature is 200 °C, the electroless plating time is 30 minutes, and the electroplating parameters are an average current density of 3 A / dm², a duty cycle of 0.2, and a frequency of 100 Hz, and electroplating for 3 minutes, the integrated shielding foam with two-sided anisotropy prepared is the foam with the best parameters. When the electromagnetic wave is incident from surface I, the average shielding effectiveness reaches 39.2 dB; when the electromagnetic wave is incident from surface II, the average shielding effectiveness reaches 37.5 dB; from Figure 1 it can be seen that this foam has a three-dimensional structure of sheet stacking; combined with Figure 2 、 Figure 3 it can be intuitively seen the two-sided anisotropy of the electromagnetic wave protection effect of this foam;

[0083] 2) By comparing Examples 1, 2, and 3, it can be concluded that the hot pressing temperature directly affects the shielding effectiveness of the integrated shielding foam. It can be seen that 200 °C in Example 1 is the optimal temperature. Omitting the hot pressing step in Comparative Example 1 will directly lead to a very poor effect in the "electroless plating for conductivity treatment" step, and no conductive path can be formed inside the foam, resulting in the inability to smoothly carry out the subsequent electroplating step. This reflects the importance of the hot pressing step;

[0084] 3) By comparing Examples 1, 4, and 5, the electroless copper plating time directly affects the shielding effectiveness. When the electroless copper plating time is short, insufficient conductive paths cannot be formed inside the composite foam, affecting the subsequent electroplating effect. After bending, the internal conductive paths will be damaged, resulting in a large increase in resistance; while when the electroless copper plating time is too long, the copper layer inside the composite foam will be too thick, affecting the overall bendability of the composite foam. In Example 1, the resistance increase is only 0.02 ohms / cm after bending 100 times, and the resistance change after bending is the smallest, indicating that the metal layer remains the best after bending. It can be concluded that Example 1 has the optimal parameters. By further analyzing Comparative Example 2, long-term electroless plating can continue to improve the shielding effectiveness, but it will cause the composite foam to lose its bendability and directly result in the overall fracture of the composite foam;

[0085] 4) By comparing Examples 1, 6, and 7, the electroplating time has a greater impact on the shielding effectiveness. At the same time, by comparing the increase in resistance after bending, it can be seen that electroplating for 3 minutes in Example 1 is the optimal parameter. By observing Comparative Example 3, omitting the electroplating step will cause a significant decrease in the shielding effectiveness, and there is no difference in the shielding effectiveness on both sides. This reflects the importance of the electroplating step;

[0086] 5) By comparing Examples 1, 8, 9, 10, 11, 12, and 13, the electroplating parameters have little impact on the shielding effectiveness and mainly affect the bend resistance. By comparing the resistance changes of the composite foam samples before and after bending 100 times, the resistance increase in Example 1 after bending 100 times is the smallest, only increasing by 0.02 ohms / cm. After bending, the metal layer remains the best. It can be concluded that the electroplating parameters in Example 1 are the best, maintaining excellent bend resistance while having a good shielding effect.

[0087]

[0088] Table 1

[0089] In summary, the present invention discloses a preparation method of an integrated shielding foam with two-sided anisotropy. The steps include: obtaining a strengthened polyimide foam with a lamellar stacked structure by subjecting the polyimide foam to isothermal gradient compression treatment; then conducting a conductivity treatment on it by electroless plating to attach a uniform metal layer on the surface and inner surface of the foam; finally, designing a thickness gradient metal layer structure and obtaining an integrated shielding foam with a thickness gradient metal layer structure by regulating the electrodeposition parameters. While achieving a good shielding effect, it can have good flexibility. When electromagnetic waves are incident from different sides of the integrated shielding foam, due to the inconsistent metal layer structures on both sides, the loss modes and paths of the electromagnetic waves are also inconsistent. Therefore, when this composite foam is used as an electromagnetic shielding protection material, it has different electromagnetic protection characteristics on both sides and can well meet the requirements of some special devices for materials with two-sided anisotropic shielding performance.

[0090] The above is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and scope of the present invention are all included in the protection scope of the present invention.

Claims

1. A preparation method of an integrated shielding foam with two-sided anisotropy, characterized in that, The method includes: Subjecting polyimide foam to isothermal gradient compression treatment to obtain strengthened polyimide foam, where the strengthened polyimide foam is a three-dimensional structure in the form of stacked lamellae; Performing surface colloidal palladium activation, peptization treatment, and electroless plating conductivity treatment on the strengthened polyimide foam to form a first metal layer; the performing surface colloidal palladium activation, peptization treatment, and electroless plating conductivity treatment on the strengthened polyimide foam to form a first metal layer includes: Immersing the strengthened polyimide foam in a Triton solution with a volume fraction of 0.2% for hydrophilization treatment; then immersing the hydrophilized strengthened polyimide foam in a colloidal palladium activation solution, adjusting the solution environment to a negative pressure state, stirring with a rotor for 1 - 5 minutes; then immersing the strengthened polyimide foam after colloidal palladium activation treatment in a peptizing solution, adjusting the solution environment to a negative pressure state, stirring with a rotor for 1 - 5 minutes; then placing the strengthened polyimide foam after peptization treatment in an electroless plating metal solution, adjusting the solution environment to a negative pressure state, stirring with a rotor for 20 - 40 minutes to complete the electroless plating conductivity treatment and form a first metal layer; Electrodepositing on one side of the first metal layer to obtain a second metal layer with a thickness gradient, where the first metal layer uniformly adheres to the inner and outer surfaces of the strengthened polyimide foam to form a three-dimensional continuous conductive structure, and the second metal layer grows on one side of the outer surface of the first metal layer.

2. The preparation method of the integrated shielding foam with two-sided anisotropy according to claim 1, characterized in that, The subjecting polyimide foam to isothermal gradient compression treatment to obtain strengthened polyimide foam includes: a) At a temperature of 180 - 220 °C, compressing the polyimide foam to 3 / 5 - 4 / 5 of its original thickness, with a pressure holding and heat preservation time of 3 - 5 minutes; b) Keeping the temperature unchanged, adjusting the compression degree to 1 / 5 - 2 / 5 of the original thickness, with a pressure holding and heat preservation time of 3 - 5 minutes.

3. The preparation method of the integrated shielding foam with two-sided anisotropy according to claim 1, characterized in that, The stirring speed of the rotor is 800 - 1200 revolutions per minute.

4. The preparation method of the integrated shielding foam with two-sided anisotropy according to claim 1, characterized in that, The negative pressure state means the reading of the vacuum gauge is -0.1 - 0 MPa.

5. The preparation method of the integrated shielding foam with two-sided anisotropy according to claim 1, characterized in that, The electrodepositing on one side of the first metal layer to obtain a second metal layer with a thickness gradient includes: Placing the strengthened polyimide foam after electroless plating conductivity treatment in an electroplating solution, performing single-sided electrodeposition on one side of the first metal layer, maintaining air stirring during the electroplating process, keeping the electroplating solution temperature at 35 - 45 °C, and preparing a second metal layer with a thickness gradient of 0.1 - 3 μm.

6. The preparation method of the integrated shielding foam with two-sided anisotropy according to claim 1, characterized in that, The density of the polyimide foam is 15 - 35 kg / m³.

7. The preparation method of the integrated shielding foam with two-sided anisotropy according to claim 1, characterized in that, The polyimide foam is an open-cell foam with a porosity of 70 - 90%.

8. The preparation method of an integrated shielding foam with two-sided anisotropy according to claim 5, characterized in that, The single-sided electrodeposition is pulse electrodeposition, with an average current density of 1.0 - 5.0 A / dm², a duty cycle of 0.1 - 0.3, a frequency of 50 - 200 Hz, and an electrodeposition time of 1 - 5 minutes.

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