CN115558304A - Preparation method of ultralight composite electromagnetic shielding material based on carbon fiber solid waste modification and insulation coating - Google Patents

Abstract

The invention discloses a preparation method of an ultralight composite electromagnetic shielding material based on carbon fiber solid waste modification and insulation coating, which is based on the one-dimensional characteristic of chopped carbon fiber waste and through the adjustment of the surface conductivity of carbon fibersAnd the insulating outer layer coating scheme is combined, so that the eddy current size on the surface of the carbon fiber is reduced, the shielding capability of a reverse magnetic field is improved, and macroscopic conductive connection caused by overlapping of one-dimensional carbon fibers is avoided. The material of the invention can be directly fused with a polymer matrix used by a device, and the integral resistivity can still be kept at 10 ⁹ ‑10 ²⁰ The higher level of Ω · m can ensure the electrical safety and performance of surrounding connectors and circuits. The invention can be applied to electromagnetic wave shielding of DC-42.5 GHz frequency band in various devices and products.

Description

Development of ultra-light composite electromagnetic shielding material based on carbon fiber solid waste modification and insulation coating Preparation

technical field

The invention belongs to the field of electromagnetic functional materials, and in particular relates to a preparation method of an ultra-light composite electromagnetic shielding material based on carbon fiber solid waste modification and insulation coating.

Background technique

Electromagnetic compatibility (EMC) of electrical products has become a mandatory standard for market access in countries all over the world. In the growing field of electronics and communications, electromagnetic radiation and external electromagnetic interference generated during device operation have become industry pain points that affect important factors such as product performance, reliability, and safety. The problems are found in new energy vehicles, consumer electronics, etc. Products, intelligent IoT products, 5G and other communication products, wearable electronic products, aviation, aerospace and other key fields. For example, in new energy vehicles, the multi-band electromagnetic waves generated by the dense three-electric system are superimposed on each other, which can easily lead to the failure of vehicle driving systems and sensors, threatening driving safety; electromagnetic emissions from electronic components in aircraft will affect radar, communication and The operation of the sensing system leads to flight safety accidents; the intelligent IoT system receives interference from external stray signals, causing distortion of sensors and receivers, affecting the linkage of multiple devices, and even the collapse of the Internet of Things, etc. Therefore, in response to the development of miniaturized and integrated devices, the key technologies of ultra-light and efficient electromagnetic shielding materials need to be solved urgently.

The electromagnetic shielding materials currently used are mainly concentrated in the 1-18GHz frequency band, especially the 8-12GHz (X-band) and 5G frequency band (C-band), and there are few electromagnetic shielding materials suitable for a wide frequency range. The electromagnetic shielding method for the microwave frequency band is mainly conductive shielding, that is, the reverse magnetic field generated by the electromagnetic induction effect of the conductor in the microwave can offset the entry and influence of the external electromagnetic field. Related products and devices in the industry mostly use metal conductive shielding shells or conductive coatings for external overall shielding. However, this method is extremely difficult for the shielding design of miniaturized and miniaturized devices, and leakage waves will still appear in key positions such as connectors and connectors, which cannot meet the current strict EMC standards and integration requirements. Developing a new type of insulating electromagnetic shielding material with high resistivity, so that it can be seamlessly integrated with the device substrate, while ensuring electromagnetic performance, also meets the requirements of electrical performance, which has been considered as a new solution to the EMC problems of future micro-devices and special-shaped connectors solution.

Contents of the invention

The present invention aims at providing a method for preparing an ultra-light composite electromagnetic shielding material based on carbon fiber solid waste modification and insulation coating, aiming at the problems existing in the application of conductive shielding materials in small and integrated devices at present. Based on the one-dimensional characteristics of chopped carbon fiber waste, the invention not only reduces the size of the eddy current on the surface of the carbon fiber, improves the reverse magnetic field shielding ability, but also avoids the one-dimensional carbon fiber The macroscopic conductive connection caused by the overlap between them. The material of the invention can be directly fused with the polymer matrix used in the device, and the overall resistivity can still be maintained at a high level of 10 ⁹ -10 ²⁰ Ω·m, which can ensure the electrical safety and performance of the surrounding connectors and circuits. The invention can be applied to electromagnetic wave shielding in the frequency range of DC to 42.5 GHz in various devices and products.

The invention is based on the preparation method of the ultra-light composite electromagnetic shielding material based on carbon fiber solid waste modification and insulation coating. Through the regulation and control of the electrical conductivity of the surface of the chopped carbon fiber, combined with the insulation material coating, the microscopic electromagnetic shielding is enhanced, and the macroscopic conductive transmission is cut off. Transport, specifically include the following steps:

Step 1: Evenly disperse 0.05-3g of the cleaned chopped carbon fiber solid waste in 20ml of absolute ethanol, add a certain amount of dispersant to it, and continue ultrasonic treatment for 0.5-3h to improve the charge distribution on the surface through functional groups, so that the carbon fiber The solid waste is uniformly dispersed; then, after suction filtration or centrifugal separation, the modified chopped carbon fiber powder with good polar solution dispersibility is obtained;

Step 2: Disperse 0.05-3g of the modified chopped carbon fiber powder obtained in step 1 in 10mL-50mL conductive polymer monomer solution with a concentration of 0.0001-1g/mL and stir for 1h until uniform, and adjust the pH of the system to ≤ 5. Obtain the precursor solution;

Step 3: Add 3-10ml of initiator dropwise to the precursor solution obtained in Step 2 under continuous stirring, and continue to stir and react for 0.5-10 hours under ice bath conditions. The obtained product is washed with distilled water and absolute ethanol, and filtered with suction Or centrifugal separation to obtain carbon fiber powder with surface modification of conductive polymer;

Step 4: Take the conductive polymer surface-modified carbon fiber powder obtained in step 3, and use step 4a or 4b to coat the particles with insulating amorphous silicon oxide or an insulating polymer shell:

4a: Uniformly disperse the carbon fiber powder with conductive polymer surface modification in a mixed solution composed of water, alcohol and ammonia water, stir at room temperature for 0.5-2 hours, slowly add tetraethyl orthosilicate (TEOS) into the system dropwise, And keep the room temperature and continue to stir the reaction for 1-20h; after the reaction product is washed with water and ethanol, it is suction filtered or centrifuged and dried to obtain the insulating amorphous _SiO2 -coated biomass carbon-based shielding material powder;

4b: Evenly disperse the carbon fiber powder with conductive polymer surface modification in the aqueous solution of insulating polymer monomer with a concentration of 0.05-8mol/L, stir at room temperature for 0.5-5h, slowly add the initiator into the system, and Continue to stir and react at 90°C for 1-20 hours. After the reaction product is washed with water and ethanol, it is suction filtered or centrifuged and dried to obtain the insulating polymer-coated biomass carbon-based shielding material powder;

Step 5: Mix the carbon fiber one-dimensional material coated with the insulating shell obtained in step 4 with the device matrix, and obtain an electromagnetic shielding material and device with high resistivity insulating coating after molding.

The device matrix includes resin, rubber, paint, colloid, paraffin and the like.

The added mass of the carbon fiber one-dimensional material covered by the insulating shell is 10-50% of the mass of the device matrix.

Mixing methods include direct mixing, banburying or open refining, etc.

Forming methods include injection molding, extrusion molding, compression molding, blow molding, extrusion, rotational molding, coating, and the like.

In step 1, the length of the chopped carbon fiber is 0.5-3mm, and the diameter is 2-5um.

In step 1, the dispersant can be polyvinylpyrrolidone (PVP), sodium dodecylbenzenesulfonate (SDS), sodium dodecylbenzenesulfonate (SDBS), KH550, polyethylene glycol (PEG) , oleic acid, Tween, etc., or other types that are compatible with the carbon fiber surface; the addition ratio of the dispersant is 0.001-3mol/L.

In step 2, reagents such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, and acetic acid can be used to adjust the pH value.

In step 2, the conductive polymer monomer is one or more of aniline, thiophene, and pyrrole.

In step 3, the initiator is 0.02-4mol/L persulfate solution, or other reagents that can cause monomer polymerization.

In step 4a, the volume ratio of ammonia water (concentration: 25-28%), water and alcohol in the mixed solution is 1:2-30:25-60.

In step 4a, the proportion of the conductive polymer surface-modified carbon fiber powder dispersed in the mixed solution is 0.01-0.075 g/mL.

In step 4a, the added volume of tetraethyl orthosilicate is 2-20% of the total solution volume.

In step 4b, the insulating polymer monomer is selected from polystyrene (PS), polymethyl methacrylate (PMMA), polyphenylene sulfide (PPS), polyamide (PA), polypropylene (PP) , polybutylene terephthalate (PBT), polyimide (PI), polycarbonate (PC), polyoxymethylene (POM), polyethylene (PE), polyvinyl chloride (PVC), polylactic acid ( PLA) and other polymer monomers with high resistivity and precursor monomers for doping or derivatives.

In step 4b, the ratio of the conductive polymer surface-modified carbon fiber powder dispersed in the insulating polymer monomer aqueous solution is 0.01-0.075 g/mL.

In step 4b, the initiator is a persulfate or a reagent that can polymerize the above monomers, and the added volume is 1-12% of the total solution volume.

Advantage of the present invention and beneficial effect are embodied in:

1. The present invention forms a conductive/insulating one-dimensional heterogeneous structure through amorphous or polymer-coated carbon fibers with insulating properties. While forming an effective electromagnetic shielding effect inside, the external conductive connection is avoided, and a novel insulating electromagnetic shielding substrate;

2. The present invention modulates the reverse magnetic field of the eddy current in different frequency bands through the surface modification of the conductive polymer intermediate layer, thereby modulating the surface impedance and the applicable frequency band of electromagnetic shielding. The present invention can cover the electromagnetic shielding of the widely used frequency band from DC to 42.5GHz;

3. The high-resistivity composite material of the present invention can be directly fused with the matrix material of the device, and directly used as a raw material for product or device molding, thereby replacing the external metal shielding shell without affecting the internal circuit connection. Carbon fiber-based materials can also be Greatly improve the mechanical properties of the device;

4. Carbon fiber solid waste is industrial waste produced in the production of carbon fiber related parts. The technology of the present invention can make the difficult-to-handle carbon fiber solid waste obtain new applications, save the energy consumption of incineration, and the process cost is extremely low, energy-saving and economical ,Environmental friendly.

Description of drawings

Fig. 1 is the SEM image of the 1mm chopped carbon fiber/PANI/PS prepared in embodiment 3; The SEM morphology image shows that the 0.5mm chopped carbon fiber/PANI/PS is a cylinder with a diameter of 5 μm, and the surface of the cylinder is smooth and flat, It shows the double-layer dense insulating coating of PANI/PS, and the gap of the shell layer shows the PANI coated on the surface of the carbon fiber.

Fig. ₂ is the SEM image of 0.5mm chopped carbon fiber/PANI/SiO prepared in Example 4; SEM topography image shows that 1mm chopped carbon fiber/PANI/SiO is a cylinder with a diameter of ₅ μm, and the surface of the cylinder is smooth It is flat, indicating the dense insulation coating of PANI/SiO ₂ , and the gap of the shell layer shows the PANI coated on the surface of the carbon fiber.

Fig. 3 is in embodiment 1-5, the dielectric constant real part of sample respectively in (a) 1～18GHz, (b) 18～26.5GHz, (c) 26.5～40GHz frequency band; Embodiment 1-5 corresponding sample ε' is at a relatively high level in 1-40GHz, and it can reach more than 20 in some frequency bands of 1-18GHz, and the highest can reach 30, indicating that despite the coating of the insulating shell, there is A large number of dielectric dipoles.

Fig. 4 is in embodiment 1-5, the imaginary part of the dielectric constant of sample respectively in (a) 1～18GHz, (b) 18～26.5GHz, (c) 26.5～40GHz frequency band; Embodiment 1-5 corresponding sample The value of ε" at 1-40GHz is also relatively large, among which the whole frequency band in the 1-40GHz frequency band reaches more than 20, and the part in the 1-18GHz frequency band reaches 200, and the highest value can reach 500, which shows that despite the covering of the insulating shell, the short Cut carbon fiber and chopped carbon fiber/PANI conductive core still have excellent dielectric loss properties, and the imaginary part is greater than the real part, indicating that the conductive/insulating interface forms an effective shielding that causes multiple reflections of electromagnetic waves inside the carbon fiber.

Fig. 5 shows the shielding effectiveness of samples in (a) 1-18 GHz, (b) 18-26.5 GHz, (c) 26.5-40 GHz frequency bands in Examples 1-5. The SE of the high-resistivity insulating sample in Examples 1-5 has exceeded 10dB in the C-Ku frequency band of 1-18GHz and the full frequency band of 18-26.5GHz, and the SE of some frequency bands of 26.5-40GHz has exceeded 35dB. Three's SE can reach up to 70dB. Combined with the higher resistivity (greater than 10 ⁹ Ω·m) of the samples in Examples 1-5, it shows that the biomass carbon and the biomass carbon/PANI conductive core have high dielectric properties, so that the insulating shell is coated and between the particles. In the case of no conductive connection, excellent and effective shielding of electromagnetic waves in the 1-40GHz frequency band can still be formed. Among them, Example 6 in Figure (a) is the shielding performance of carbon fiber without covering the conductive core and insulating material. Compared with Examples 1-5, it can be seen that the double-layer coating of conductive core/insulating material will not reduce the shielding performance of the material.

detailed description

Example 1:

(1) Clean and dry 0.3g of carbon fiber solid waste with a diameter of 5μm and a chopped length of 0.5mm, and evenly disperse it in 20mL of absolute ethanol, and add 1g of PVP and 0.3g of PEG to it, continue ultrasonic treatment for 0.5h, and then filter with suction seperate;

(2) Disperse the modified carbon fiber obtained in step (1) in 20 mL of 5 mol/L styrene monomer aqueous solution, and add 0.5 ml of 0.15 mol/L dropwise to the solution under stirring in a water bath at 70°C Aqueous ammonium persulfate solution, and continuously stirred for 3 hours; the product was washed with water and absolute ethanol and then vacuum-dried for 8 hours to obtain carbon fiber/PS powder;

(3) The carbon fiber/PS powder obtained in step (2) was mixed with paraffin wax at a ratio of 20%, and its electromagnetic parameters and shielding effectiveness at 1-18GHz, 18-26.5GHz, and 26.5-40GHz were tested.

Example 2:

(1) Wash and dry 0.3g of carbon fiber solid waste with a diameter of 5μm and a chopped length of 1mm, and evenly disperse it in 20mL of absolute ethanol, and add 1g of PVP and 0.3g of PEG to it, continue ultrasonic treatment for 0.5h, and then separate by suction filtration come out;

(2) Disperse the modified carbon fiber obtained in step (1) in 20mL of absolute ethanol, add 0.2g of PVP and 0.8ml of ammonia water to the solution, and stir for 0.5h until uniform; then slowly add 0.3ml of Tetraethyl orthosilicate (TEOS), and keep stirring for 5h; the product is vacuum-dried for 8h after washing with water and absolute ethanol to obtain carbon fiber/SiO ₂ powder;

(3) The carbon fiber/SiO ₂ powder obtained in step (2) was mixed with paraffin at a ratio of 20% to form it, and its electromagnetic parameters and shielding effectiveness at 1-18GHz, 18-26.5GHz, and 26.5-40GHz were tested.

Example 3:

(1) Clean and dry 0.3g of carbon fiber solid waste with a diameter of 5μm and a chopped length of 0.5mm, and evenly disperse it in 20mL of absolute ethanol, and add 1g of PVP and 0.3g of PEG to it, continue ultrasonic treatment for 0.5h, and then filter with suction seperate;

(2) Put the modified carbon fiber powder obtained in step (1) into 30 mL of 1 mol/L aniline aqueous solution, and add 5 ml of hydrochloric acid solution with a concentration of 0.2 mol/L dropwise therein, and continue ultrasonic treatment for 1 h;

(3) under continuous stirring, to the precursor solution of step (2), slowly dripping 5ml concentration is the ammonium persulfate aqueous solution of 1mol/L, and continuous stirring 5h; Reaction product suction filtration separates after washing with water and dehydrated alcohol and Dry for 8 hours to obtain carbon fiber/PANI powder;

(4) Disperse the carbon fiber/PANI powder obtained in step (3) in 20mL of absolute ethanol, add 0.2g of PVP and 0.8ml of ammonia water to the solution, and stir well; then slowly add 0.3ml of Tetraethyl orthosilicate (TEOS), and keep stirring for 5h; the product is vacuum-dried for 8h after being washed with water and absolute ethanol to obtain carbon fiber/PANI/SiO ₂ powder;

(5) Mix the carbon fiber/PANI/ _SiO2 powder obtained in step (4) with paraffin wax at a ratio of 20%, and test its electromagnetic parameters and shielding effectiveness at 1-18GHz, 18-26.5GHz, 26.5-40GHz .

Example 4:

(1) Wash and dry 0.3g of carbon fiber solid waste with a diameter of 5μm and a chopped length of 1mm, and evenly disperse it in 20mL of absolute ethanol, and add 1g of PVP and 0.3g of PEG to it, continue ultrasonic treatment for 0.5h, and then separate by suction filtration come out;

(2) Put the modified carbon fiber powder obtained in step (1) into 30 mL of 1 mol/L aniline aqueous solution, and add 5 ml of hydrochloric acid solution with a concentration of 0.2 mol/L dropwise therein, and continue ultrasonic treatment for 1 h;

(3) under continuous stirring, to the precursor solution of step (2), slowly dripping 5ml concentration is the ammonium persulfate aqueous solution of 1mol/L, and continuous stirring 5h; Reaction product suction filtration separates after washing with water and dehydrated alcohol and Dry for 8 hours to obtain carbon fiber/PANI powder;

(4) Disperse the carbon fiber/PANI powder obtained in step (3) in 20 mL of an aqueous solution of 5 mol/L styrene monomer, and add 0.5 ml of 0.15 mol /L ammonium persulfate aqueous solution, and continuously stirred for 3 hours; the product was washed with water and absolute ethanol and then vacuum-dried for 58 hours to obtain carbon fiber/PANI/PS powder;

(5) Mix the carbon fiber/PANI/PS powder obtained in step (4) with paraffin wax at a ratio of 20%, and test its electromagnetic parameters and shielding effectiveness at 1-18GHz, 18-26.5GHz, and 26.5-40GHz.

Example 5:

(1) Wash and dry 0.3g of carbon fiber solid waste with a diameter of 5μm and a chopped length of 3mm, and evenly disperse it in 20mL of absolute ethanol, and add 1g of PVP and 0.3g of PEG to it, continue ultrasonic treatment for 0.5h, and then separate by suction filtration come out;

(2) Put the modified carbon fiber powder obtained in step (1) into 30 mL of 1 mol/L aniline aqueous solution, and add 5 ml of hydrochloric acid solution with a concentration of 0.2 mol/L dropwise therein, and continue ultrasonic treatment for 1 h;

(3) under continuous stirring, to the precursor solution of step (2), slowly dripping 5ml concentration is the ammonium persulfate aqueous solution of 1mol/L, and continuous stirring 5h; Reaction product suction filtration separates after washing with water and dehydrated alcohol and Dry for 8 hours to obtain carbon fiber/PANI powder;

(4) Disperse the carbon fiber/PANI powder obtained in step (3) in a mixed solution composed of 2ml MMA, 18ml distilled water and 50ml absolute ethanol, add 0.052g ammonium persulfate to the solution, and place in a 70°C water bath Stirring was continued for 10 h under ambient conditions, and the product was washed with water and ethanol and then vacuum-dried for 8 h to obtain carbon fiber/PANI/PMMA powder.

(5) Mix the carbon fiber/PANI/PMMA powder obtained in step (4) with paraffin wax at a ratio of 20%, and test its electromagnetic parameters and shielding effectiveness at 1-18GHz, 18-26.5GHz, and 26.5-40GHz.

Claims (10)

1. The preparation method of the ultralight composite electromagnetic shielding material based on carbon fiber solid waste modification and insulation coating is characterized by comprising the following steps of:

step 1: uniformly dispersing 0.05-3g of cleaned chopped carbon fiber solid waste into 20ml of absolute ethyl alcohol, adding a dispersing agent, continuously carrying out ultrasonic treatment for 0.5-3 h, and improving the surface charge distribution through functional groups to uniformly disperse the carbon fiber solid waste; then carrying out suction filtration or centrifugal separation to obtain modified chopped carbon fiber powder with good polar solution dispersibility;

step 2: dispersing 0.05-3g of modified chopped carbon fiber powder obtained in the step 1 into 10-50 mL of conductive polymer monomer solution with the concentration of 0.0001-1 g/mL, stirring for 1h until the solution is uniform, and adjusting the pH value of the system to be less than or equal to 5 to obtain a precursor solution;

and step 3: under continuous stirring, dropwise adding 3-10ml of initiator into the precursor solution obtained in the step 2, continuously stirring and reacting for 0.5-10 h under an ice bath condition, cleaning the obtained product by using distilled water and absolute ethyl alcohol, and performing suction filtration or centrifugal separation to obtain carbon fiber powder with the surface modified by the conductive polymer;

and 4, step 4: taking the carbon fiber powder with the modified conductive polymer surface obtained in the step 3, and coating the particles with insulating amorphous silicon oxide or an insulating polymer shell layer by adopting the method in the step 4a or 4b:

4a: uniformly dispersing carbon fiber powder with the surface modified by a conductive polymer into a mixed solution consisting of water, alcohol and ammonia water, stirring at room temperature for 0.5-2 h, slowly dropwise adding tetraethyl orthosilicate into the system, and keeping the room temperature to continue stirring and reacting for 1-20 h; washing the reaction product with water and ethanol, filtering or centrifugally separating and drying to obtain the insulating amorphous SiO ₂ Coated biomass carbon-based shielding material powder;

4b: uniformly dispersing carbon fiber powder with the surface modified by a conductive polymer into an insulating polymer monomer aqueous solution with the concentration of 0.05-8 mol/L, stirring at room temperature for 0.5-5 h, slowly adding an initiator into the system, continuously stirring at 0-90 ℃ for reaction for 1-20 h, washing a reaction product by water and ethanol, and performing suction filtration or centrifugal separation and drying to obtain insulating polymer coated biomass carbon-based shielding material powder;

and 5: and (4) mixing the carbon fiber one-dimensional material coated by the insulating shell layer obtained in the step (4) with a device substrate, and forming to obtain the electromagnetic shielding material coated with high-resistivity insulation and the device.

2. The production method according to claim 1, characterized in that:

in the step 1, the length of the chopped carbon fiber is 0.5-3mm, and the diameter is 2-5um.

3. The method of claim 1, wherein:

in the step 1, the dispersant is one or more of polyvinylpyrrolidone, sodium dodecyl benzene sulfonate, KH550, polyethylene glycol, oleic acid and tween; the addition ratio of the dispersant is 0.001-3mol/L.

4. The method of claim 1, wherein:

in the step 2, the conductive polymer monomer is one or more of aniline, thiophene and pyrrole.

5. The method of claim 1, wherein:

in the step 3, the initiator is persulfate solution, and the addition amount is 0.02-4mol/L.

6. The method of claim 1, wherein:

in the step 4a, the volume ratio of ammonia water, water and alcohol in the mixed solution is 1:2 to 30:25 to 60.

7. The method of claim 1, wherein:

in the step 4a, the proportion of the carbon fiber powder with the surface modified by the conductive polymer dispersed in the mixed solution is 0.01-0.075 g/mL; the addition volume of the tetraethyl orthosilicate is 2-20% of the volume of the total solution.

8. The method of claim 1, wherein:

in step 4b, the insulating polymer monomer is selected from monomers constituting a polymer having a high resistivity of polystyrene, polymethylmethacrylate, polyphenylene sulfide, polyamide, polypropylene, polybutylene terephthalate, polyimide, polycarbonate, polyoxymethylene, polyethylene, polyvinyl chloride, or polylactic acid, and precursor monomers of a dopant or derivative thereof.

9. The production method according to claim 1, characterized in that:

in the step 4b, the proportion of the carbon fiber powder modified by the conductive polymer surface dispersed in the insulating polymer monomer aqueous solution is 0.01-0.075 g/mL.

10. The production method according to claim 1, characterized in that:

in the step 5, the adding mass of the one-dimensional carbon fiber material coated by the insulating shell layer is 10-50% of the mass of the device matrix.

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