The Development And Manufacture Of The Electromagnetic Shielding Coated Paper

Electromagnetic wave brings great convenience to people, but it still causes inevitable harm. To decrease electromagnetic pollution which has long been recognized as one kind of the four pollutions, electromagnetic shielding is possibly the best way. In the area of electromagnetic shielding, the method of surface coating with conductive pigments has been developing very rapidly due to the advantages such as simple, low cost, and suitability for various applications.In this paper, based on the understanding of mechanisms regarding electromagnetic shielding and paper coating, the material capable of electromagnetic shielding was coated on the base paper to obtain coated paper with unique attributes.For the coating color used for the preparation of coated paper with electromagnetic shielding properties, nickel powder was used as the conductive pigment, and different binding agents were also used. In addition to nickel powder and binding agents, dispersing agents and coupling agents were also used for the preparation of the coating color. The effects of various parameters regarding the type and dosage of binding agents, mixing of different types of binding agents, preparation of coating colors, paper coating, and drying of the coated paper, on the conductivity, electromagnetic shielding, and physical properties of the coated paper, as well as the strength of coating layer, were studied.It was found that, the use of nickel powder in combination with polyacrylate and carbxymethyl cellulose gave good results. When the dosage of binding agents (polyacrylate and carbxymethyl cellulose) was 26%(based on the dry weight of nickel powder), and when the weight ratio of polyacrylate to carboxymethyl cellulose was 9 to 1, excellent viscosity of the coating color was achieved, and the pigment particles was well dispersed. The use of the coating color in paper coating gave uniform coating layer, and the coated paper exhibited excellent conducting and electromagnetic shielding properties.The influence of different parameters including dispersant dosage, dispersing time, stirring speed, and solids content of the coating color on paper coating was investigated, and the optimum conditions were as follows:dispersant dosage of 0.5%, dispersing time of 1h, stirring speed of 1000r/min, and solids content of 45%. Under the optimum conditions, excellent conducting and electromagnetic shielding properties of the coated paper was achieved when the amount of coating, temperature for paper drying, and time for paper drying were 55g/m2,65℃, and 5min, respectively.When the dosage of binding agents (weight ratio of polyacrylate to carboxymethyl cellulose of 9 to 1), dosage of dispersant, time for dispersing, and stirring speed were 26%, 0.5%, 1h, and 1000r/min, respectively, conductive coating color with solids content of 45% was easily prepared. The conductive coating color was then successfully used for the preparation of coated paper when the amount of coating, temperature for paper drying, and time for paper drying were 55g/m2,65℃, and 5 min, and sheet resistivity, electromagnetic shielding, and weight loss (the strength of the coating layer of the coated paper) were measured to be 105mΩ/□,40dB, and 0.344%, equivalent to medium electromagnetic shielding (the standard values of materials for electromagnetic shielding for Chinese military purposes are in the range of 30-60dB). Additionally, the physical properties of the coated paper were found to have good stability.Scanning electron microscope (SEM) observations showed that the coating layer of the coated paper was compact and uniform, indicating good filming effect of the coating color. Also, the penetration of pigment particles and binding agents into the paper sheet was observed, further confirming the good strength of the coating layer.