- 學位論文
電磁遮蔽之無電鍍銅硫粉末/EVA複合材料之研究
Investigation of Electroless Plating CuxSy powders/EVA composites for EMI shielding
摘要
本研究利用無電鍍法以析鍍時間一小時，CuSO4Na2S2O3NaHSO3 (2:1:1)鍍液組成的條件下製備銅硫粉末，且經測試後得知該粉末具高導電特點。故應用銅硫粉末的特性，以混煉的方式將其添加高分子基材(EVA)中，並且在混煉的過程添加適當的添加劑使基材內的導電顆粒更容易形成導電通路以賦予複材具電磁波遮蔽效果。 本實驗以無電鍍過程中的溫度與攪拌速度作為影響銅硫粉末導電性的兩大變數，並且以不同的添加劑種類與含量作為混煉過程的變數。利用HP-XRD、SEM、EDS等分析，探討導電顆粒的導電性與粒徑、顆粒在基材內的分散情況以及機械性質影響等等，來解釋此類型高分子複合材料抗電磁波遮蔽值的變化。 由實驗結果顯示，無電鍍過程中的溫度對其製備出粉末的導電性有顯著的影響。雖然攪拌速度增加能將粉末平均粒徑由370.5nm降低至276.67nm，但對粉末其導電性的影響卻呈現具反曲點的趨勢。本實驗中所製備出的銅硫粉末其電阻值最低可達約0.86 mΩ。 不過即使粉末添加量高達200 phr，複材仍無明顯的抗電磁波遮蔽效果。但在混煉過程中加入125 phf的甘油，即使導電粉末添加量僅60 phr，複材抗電磁波遮蔽效果可提升至20~25 dB左右。但當導電粉末添加量提高至100 phr時，只需添加15 phf甘油就可以使複材達到最佳的電磁遮蔽能力，約35~40dB左右。並且當甘油添加量由5 phf 增加到125phf，在基材內一部份區域的粉末凝聚團之間的平均距離由53.9 μm減少到25 μm，但在另一部份區域內的粉末有減少的趨勢，也就是基材和粉末相分離的現象越嚴重。這些現象代表著在混煉過程中添加適量的甘油可藉由甘油高內聚力導致被甘油包覆的導電顆粒在基材內產生團聚現象，進而拉近顆粒間的距離且在複材內形成導電路徑因而改善複材遮蔽電磁波能力，即使導電粉末添加量尚未達到理論填充體積滲透值。當粉末添加量增加到150 phr時，複材抗電磁波遮蔽效果更可大幅提升到約50~60dB左右。 在添加粉末含量在100 phr且甘油含量達到15 phf以上時可在EMI曲線上明顯觀察到共振現象。經由SEM觀察後推測是由於導電顆粒在基材內形成適當的團聚現象導致電磁波通過複材時具有某種程度的共振現象。而此共振現象會隨著試片厚度的增加而有更顯著的趨勢。這是因為當試片厚度增加，電磁波通過試片時撞擊凝聚團產生的反射波再次撞擊另一凝聚團的機率隨之增加。並且當試片厚度較薄(≦2mm)，複材在低頻範圍內會有較低的電磁遮蔽能力，這是由於較高波長的電磁波其穿透力較強所致。
並列摘要
In this investigation, the CuxSy (CuS, Cu4O3, Cu1.8S, CuS2 and Cu9S8) powders were produced by electroless plating as plating time was 1 hour with a bath of CuSO4．5H2ONa2S2O3NaHSO3 (2:1:1) and the electric conductivity of these particles could be affirmed that electric conductivity by the way of measuring. Then the CuxSy conductive powders were used as conductive fillers and were blended with EVA (ethylene-vinyl acetate) and additives (Zn-ST, Lica38 and glycerol) by the mixer (Brabender Plasti-Corder PLE-330) in order to form polymeric composites those owned the Electronmagnetic Interference Shielding Effectiveness (EMI SE) due to the connected network of the conductive particles in matrix. In our electroless plating, the temperatures (65, 80, 95℃) and the stirring speeds (300, 600, 900rpm) were chosen as operating parameters. By the way, the effects of different type and variety content of additives in the compounding process were also investigated. Meanwhile, the influences of the fillers contents and the sample thickness on the absorption resonances phenomenon of composites were observed. The resistance and particle sizes of fillers, cross section morphology and CuxSy powders dispersion, mechanical properties and electronmagnetic interference shielding effectiveness (EMI SE) of polymeric composites were detected by 4-point-probe method, SEM, FE-SEM, HP-XRD, EDS, EMI measurements, respectively. Experimental results revealed that temperature has significant effect on electric conductivity of powders. However, stirring speed had the varied effect on the resistance of fillers even if it can reduce effectively average particle size from 370.5nm to 276.67nm. The minimum resistance value of CuxSy powders can reach 0.86 mΩ in the operating parameters (300rpm/95℃). After CuxSy powders were mixed with EVA by brabender, it was in vain to possess EMI SE effect even if fillers contents rise up to 200 phr. However, EMI SE value improved obviously to 20~25dB with the fillers contents only retained 60 phr as 125 phf glycerol was added into composites. However, it only needed 15 phf contents of glycerol that EMI SE of composites achieved maximum effect (35-40dB) as the fillers content increased as 100 phr. When the glycerol contents were increased from 5 phf to 125 phf, the average distance between agglomerates in a partial regions of matrix will decrease from 53.9 μm to 25 μm but the dispersing density of fillers in others regions of matrix will decrease. The phenomenon means that the network could be formed in the composites due to glycerol has strong cohesion even if fillers volume contents does not reach percolation value. Consequently, EMI SE value will reach 50~60dB as the fillers content increased to 150 phr and the glycerol content was 15 phf. Meanwhile, the resonance phenomenon occurred as the fillers contents ran up to 100 phr and glycerol contents ran up to 15 phf. The phenomenon resulted from agglomerates of conductive fillers and was observed by SEM. And the thickness of sample also affected directly the resonances phenomenon. It is assumed that the probability of the electromagnetic wave, which is reflected by one filler agglomerate, impacts on another filler agglomerate will increase with the increasing of sample thickness. Meanwhile, it had inferior EMI SE in lower frequency (30~500MHz) as the sample thickness is thinner (≦2mm) due to the longer wavelength electromagnetic wave has stronger transmittance.