Research On Preparation And Electromagnetic Shielding Performance Of Flexible Printable Magnetic Films

With the development of modern science and technology,more and more electronic devices appear in people's daily lives,bringing great convenience to modern society.However,these electronic devices will generate electromagnetic radiation,which is harmful to human health.Using electromagnetic shielding materials can solve electromagnetic radiation problems well.In recent years,flexible electronic devices have developed rapidly.Wearable and foldable devices are constantly appearing in people's lives.These flexible devices have put forward new requirements for electromagnetic shielding materials,where the traditional inflexible electromagnetic shielding materials are unsuitable.At present,research on flexible electromagnetic shielding material mainly focuses on conductive polymer composites.However,many disadvantages such as large thickness,poor flexibility and high preparation cost have always restricted practical applications.In this paper,a preparation method of high-efficiency flexible electromagnetic shielding material is designed and flexible electromagnetic shielding films are prepared and characterized.Also,some electromagnetic shielding films are prepared by screen printing method.These electromagnetic shielding films prepared by different methods were compared.Preparation and electromagnetic shielding performance of non-magnetic flexible electromagnetic shielding films were studied.Silver particles were prepared by chemical reduction first,then dispersed in ethylene glycol to form a metal ink,and a flexible electromagnetic shielding film was prepared by sintering metal ink on a flexible substrate.The Ag particles were forming a metal layer tightly bonded to the substrate.This structure gives the material good flexibility and efficient electromagnetic shielding ability.The electromagnetic shielding effectiveness at 8.1 GHz was maintained over 88% after bending to a radius of 2 mm for 200,000 times.The absorption loss of the film was greater than the reflection loss,indicating that this shielding film is absorption-dominant electromagnetic shielding material.The electromagnetic shielding effectiveness of films with different conductivity are close to theoretical values.Screen printing method for fabricating grid-type flexible electromagnetic shielding film and its electromagnetic shielding performance were studied.Three kinds of conductive pastes,silver/thermoplastic resin,silver/dibasic esters/acrylic resin and commercial silver paste,were used to fabricate different films.Both sheet resistance and electromagnetic shielding effectiveness of these films were measured and compared.Results show that film made of silver/thermoplastic resin has the lowest sheet resistance and the highest electromagnetic shielding effectiveness.The effect of the change of film pattern on the electromagnetic shielding performance was studied.The results show that when line width was fixed and line spacing was increased,sheet resistance of film was increased,but the electromagnetic shielding effectiveness was decreased;Instead,when line spacing was fixed and line width was increased,sheet resistance of film was reduced,but the electromagnetic shielding effectiveness was increased.Most of grid-type electromagnetic shielding films have lower electromagnetic shielding effectiveness than theoretical values of electromagnetic shielding effectiveness of non-mesh shielding materials.The preparation of magnetic shielding film fabricated by coating method and its electromagnetic shielding performance were studied.The silver-nickel blend were prepared by chemical reduction method frist,then they were dispersed in ethylene glycol to form metal ink,followed by sintering metal ink on a flexible substrate.A flexible magnetic electromagnetic shielding film in which silver is continuously bonded to a substrate as a metal layer and granular nickel is dispersed in the layer was obtained.This special structure gives the film flexibility,magnetic property,high electrical conductivity,and high electromagnetic shielding effectiveness.According to the calculation and analysis,the addition of a small amount of nickel can not only improve the absorption capacity of the material for electromagnetic waves,but also improve the flexibility of the film.After bending to a radius of 2 mm for 200,000 times,sheet resistance of the film at bending area was only increased by 1.2 ?/?,and the electromagnetic shielding effectiveness at 8.1 GHz has only dropped by 4.5%.The electromagnetic shielding effectiveness of nickel-containing magnetic films with different conductivity is significantly higher than theoretical values of the electromagnetic shielding effectiveness of the corresponding non-magnetic materials.