Microsoft Word - 001.docx CHEMICAL ENGINEERING TRANSACTIONS VOL. 66, 2018 A publication of The Italian Association of Chemical Engineering Online at www.aidic.it/cet Guest Editors: Songying Zhao, Yougang Sun, Ye Zhou Copyright © 2018, AIDIC Servizi S.r.l. ISBN 978-88-95608-63-1; ISSN 2283-9216 Preparation and Performance of Conductive Copper Ink Based on Chemical Deoxidization Tianhua Li*, Hongbo Hu Zunyi Normal College, Zunyi 563006, China lthyy@163.com This paper adopts the improved liquid-phase chemical deoxidization to prepare nano-copper powder used as principal conducting material instead of nano-silver particles in conductive ink of printed electronics. The prepared nano copper particles are analyzed for their microstructure and electrical conductivity. Studies show that the prepared nano-copper particles are mainly distributed chain-like, with an average particle size of 26 nm, of which, those with 20-25nm amount to 42%, 25-30nm to 29%. The PVP surfactant can effectively organize the oxidation of nano-copper. After the sintering temperature exceeds 412°C, the organic materials mixed in the nano-copper have completely volatilized. The content of nano copper decomposition product hits upon 46.5% of the original sample. The higher the sintering temperature, the lower the sheet resistance of the conductive copper film. After the sintering temperature exceeds the melting point of nano-copper, a stable conductivity channel will be formed on the surface of the film. Subsequently, continuous sintering of the film has an insignificant effect on its conductivity. 1. Introduction In the past century, a plurality of electronic products were made from micron-level electrocondution slurry. With the progressive advancement of modern technology, current electronic products tend to be refined, small-sized, flexible, and highly integrated. Up to now, the traditional micron-level electrocondution slurry has fallen well short of what’s needed (Kumashiro et al., 2009; Zhang et al., 2009). Conductive ink for printed electronic technology is the core material of the current electronic printing industry and has been widely applied in many fields such as RFID, electronic product monitors, batteries, printed circuits, etc. (Sergeev et al., 2018; Dang and Fribourgblanc, 2013). In the past, there are some gaps such as a lot of industrial waste water, high costs, and low efficiency in the manufacture technologies for conductive inks. Nano- metal-based conductive ink emerges to effectively fill the above gaps. Some fine electronics can be efficiently printed out with various types of conductive materials (carbon nanotubes, graphene, conductive polymers, nano- metals (Cui et al., 2010; Kumar et al., 2009; Titkovr et al., 2015; Dang and Fribourgblanc, 2015; Tam et al.,2016; Yang et al., 2013). Due to expensive cost of heavy metals such as carbon nanotubes, graphene, gold and silver, the concept that the nano copper particles are used as a conductive ink has been the future trend of R&D in the field (Lee et al., 2006; Tang et al., 2010; Lim et al., 2015; Yang et al., 2012). Currently, Nano-copper particles are mainly prepared by gas-phase evaporation, electrolysis, plasma coagulation, mechanical grinding and other methods (Lee et al., 2009; Joo et al., 2014). However, the copper ions available by the above methods are easily oxidized and unstable (Zhang et al., 2014). This paper adopts an improved liquid-phase chemical deoxidization to prepare nano-copper powders used the principal conducting materials to replace nano-silver particles in conductive inks (Haneda and Towata, 2015). The prepared nano copper particles are analyzed and explored for their microstructure and conductivity. Here, the conclusions can provide a new idea for the development of printed electronics. DOI: 10.3303/CET1866006 Please cite this article as: Li T., Hu H., 2018, Preparation and performance of conductive copper ink based on chemical deoxidization, Chemical Engineering Transactions, 66, 31-36 DOI:10.3303/CET1866006 31 2. Preparation of nano-copper-based conductive ink Raw materials: copper chloride dihydrate, hydrazine hydrate, ammonia hydroxide, sodium hydroxide, polyvinylpyrrolidone, trimethylammonium bromide, ascorbic acid, carboxylated carbon nanotubes. Test instrument: ultrasonic cleaner, magnetic electric mixer, electronic scale, centrifuge, vacuum drying oven, electron microscope, X-ray diffractometer. The process for preparing nano-copper powder based on the liquid-phase chemical deoxidization is shown in Fig. 1. Chemical reaction process of nano copper conducting ink: The hydrazine hydrate in the solution acts as an oxidant and a reductant for chemical reaction, respectively. The reaction process is given as follows: - 2 2 4 2 2NH +2OH =N H +2H O+2e (1) - 2 4 2 2 N H 4OH =N 4H O+4e  (2) In practices, the nano-copper colloids are prepared mainly by Eq. 2, pH>9, and the reduction reaction of Cu2+ can be expressed as 2 2Cu +4e=2Cu  (3) CuCL2 solution CTAB powder CuCL2 solution after complexation Concentrated ammonia PVP powder Copper ammonia solution Copper ammonia solution after dispersion Hydrazine hydrate solution Nano copper colloid Figure 1: Preparation process of nano-copper colloids Nano copper colloid Nano copper (with impurities) Anhydrous ethanol Nano copper (with impurities) Washing Centrifugal Vacuum drying Pure nano copper powder Repeat Figure 2: Preparation process of nano-copper powder According to the relevancy theory of thermodynamics, the free energy ΔG<0 in the reaction process, then the following equation is true: 32 1 E =0.56-0.05412pH (4) 2+ 2 E =0.36-0.02708lg Cu =0.1458V   (5) 2 1 G=E E =0.05412pH 0.4142   (6) According to Eqs. 1~6, the nano copper in the reaction solution is prepared by the following formula:   2 3 2 4 2 2 3 4 24 2 2 4 4Cu NH N H H O Cu N NH NH H O          (7) The resulting copper colloids prepared by Fig. 1 are subjected to secondary treatment in the process as shown in Fig. 2. Nano copper powder is obtained after the treatment. 3. Detection and analysis of nano-copper properties As shown in Fig. 3, the X-ray diffraction pattern is plotted for the prepared nano copper powder. It is obvious that the diffraction peaks of the copper crystal appear at 2θ=42.9°, 2θ=50.8° and 2θ=73.8°, respectively; while the diffraction peaks of the copper oxide crystal appear at 2θ=36.2°. It is testified that film on the nano copper powder surface exists as Cu2O. The nanoparticles mainly distribute chain-ball-like. In te n si ty 2¦ È/(¡ã) 30 40 50 60 70 80 Cu Cu2O Figure 3: X-ray diffraction pattern of nano copper powder Figure 4: Statistics of nano copper particle size distribution As shown in Fig. 4, the sizes of the prepared nano copper particles are counted up. on the whole, the average particle size of nano copper is 26 nm, those with 20-25 nm reaches up to 42%, and the 25-30 nm is 29%. As shown in Fig. 5, the results from the analysis of nanoparticles are obtained using an infrared spectrum analyzer, see Fig. 5 (a) for the infrared spectrum of the nano copper particles after secondary treatment; Fig. 5 (b) for the infrared spectrum of the original nano copper particles, and Fig. 5 (c) for the infrared spectrum of the PVP dispersant. 1 2 3 4 5 6 0 10 20 30 40 55-6045-5035-4035-4025-3020-2515-20  d is tr ib u te d /% D grain /nm 33 T /% ¦ Ò/cm -1 (a) 20 30004000 2000 1000 0 40 60 80 100 T /% ¦ Ò/cm -1 (b) 20 30004000 2000 1000 0 40 60 80 100 T /% ¦ Ò/cm -1 (c) 20 30004000 2000 1000 0 40 60 80 100 29 31 28 78 16 56 34 90 29 55 2 91 6 16 61 1 46 2 13 73 14 39 Figure 5: Infrared spectrum analysis of nano copper powder and PVP As shown in Fig. 3(b), there is a broad absorption peak in the range of 2950-3500/cm, which corresponds to the -OH bond of the aqueous solution. It is suggested that the original nano-copper particles prepared in this paper still remain some organic solvent on the surface. While the diffraction peak in Fig. 3(a) disappears completely; Figure 3(b) shows relatively lower peak shift of -C=O and -C-H groups at 1650/cm and 2925/cm as compared to Figure 3(a). As described above, both cases suggest that the nano copper particles after the secondary treatment have shed off residues on the surface. As shown in Fig. 6, the thermogravimetric curve of nano copper inks is given. It is obvious that nano copper has a significant mass loss at 145°C, 207°C, 341°C, and 412°C. However, when the temperature exceeds 412°C, the mass of nano copper remains intact, which implies that at 412°C, the organic matters mixed in the nano- copper have completely volatilized. So eventually, the content of decomposition product of nano coppers reaches 46.5% of the original sample. W e ig h t p e rc e n ta g e /% 400 90 Temperature/¡ æ 5003002001000 100 80 70 60 50 (a) Figure 6: Thermogravimetric curve of nano copper conductive ink 34 S q u a re r e si st a n c e /( m ¦ )̧ 400 Temperature/¡ æ 300 350300250 250 200 150 100 50 0 Figure 7: Curve of sheet resistance of nano-copper conductive ink as a function of sintering temperatures (sintered for 15 min) The prepared nano-copper conductive ink is smeared on the polyimide surface to form a thin film. See Fig. 7 for the sheet resistance curve of the film sintered at different temperatures. Fig. 8 shows the relationship between the sintering time and the sheet resistance when fixed sintering temperatures are 350° C and 400° C, respectively. As shown in the figure, as the sintering temperature rises, the sheet resistance of the film swoops at 250°C ~ 350°C, from 297mΩ to 75.6mΩ; but significantly retards at 350°C ~ 400°C, and down to 56.1 mΩ at 400°C. As the sintering extends, the sheet resistance of the film gets less and less. It is suggested that when the sintering temperature exceeds the melting point of nano-copper, a stable conductivity channel is formed on the surface of the film. After that, the film sintering has no obvious effect on the conductivity any more. S q u a re r e si st a n c e /( m ¦ )̧ Time/min 80 15 20 100 60 40 30 45 60 400¡ æ 350¡ æ Figure 8: Curve of sheet resistance of nano copper conductive ink as a function of sintering time 4. Conclusions In this paper, an improved liquid-phase chemical deoxidization is used to prepare nano-copper powde as main conductive material to replace nano-silver particles in the conductive ink. The prepared nano copper particles are analyzed to probe into their microstructure and conductivity. The findings come here as follows: (1) The prepared nano-copper particles are chain-like with an average particle size of 26 nm. As for particle distribution, those with 20-25nm amount to 42%, 25-30nm to 29%. PVP surfactant can effectively organize the oxidation of nano-copper. (2) After the sintering temperature exceeds 412°C, the organic matters mixed in the nano-copper have completely volatilized. The content of final decomposition product of nano coppers is 46.5% of the original sample. The higher the sintering temperature, the lower the sheet resistance of the conductive copper film. After the sintering temperature exceeds the melting point of nano-copper, there will be a stable conductivity channel formed on the surface of the film. Afterwards, the film sintering has no obvious effect on its conductivity any more. 35 Acknowledgments This work is supported by the Natural Science Research Project of Guizhou Province under Grant (No. KY [2017] 052), Funded by Natural Science Research of Science and Technology Department of Guizhou Province Qiankehe J word No LH [2015] 7011. References Chien Dang M., Dung Dang T.M., Fribourgblanc E., 2013, Inkjet printing technology and conductive inks synthesis for microfabrication techniques, Advances in Natural Sciences Nanoscience & Nanotechnology, 4(1), 015009, DOI: 10.1088/2043-6262/4/1/015009 Chien Dang M., Dung Dang T.M., Fribourgblanc E., 2015, Silver nanoparticles ink synthesis for conductive patterns fabrication using inkjet printing technology, Advances in Natural Sciences Nanoscience & Nanotechnology, 6(1), DOI: 10.1088/2043-6262/6/1/015003 Cui W., Lu W., Zhang Y., Lin G., Wei T., Jiang L., 2010, Gold nanoparticle ink suitable for electric-conductive pattern fabrication using in ink-jet printing technology, Colloids & Surfaces A Physicochemical & Engineering Aspects, 358(1–3), 35-41, DOI: 10.1016/j.colsurfa.2010.01.023 Haneda M., Towata A., 2015, Catalytic performance of supported ag nano-particles prepared by liquid phase chemical reduction for soot oxidation, Catalysis Today, 242, 351-356, DOI: 10.1016/j.cattod.2014.05.044 Joo S.J., Hwang H.J., Kim H.S., 2014, Highly conductive copper nano/microparticles ink via flash light sintering for printed electronics, Nanotechnology, 25(26), 265601, DOI: 10.1088/0957-4484/25/26/265601 Kumar B., Tan H.S., Ramalingam N., Mhaisalkar S.G., 2009, Integration of ink jet and transfer printing for device fabrication using nanostructured materials. Carbon, 47(1), 321-324, DOI: 10.1016/j.carbon.2008.10.029 Kumashiro Y., Nakako H., Inada M., Yamamoto K., Izumi A., Ishihara M., 2009, Novel materials for electronic device fabrication using ink-jet printing technology, Applied Surface Science, 256(4), 1019-1022, DOI: 10.1016/j.apsusc.2009.05.134 Lee B., Kim Y., Yang S., Jeong I., Moon J., 2009, A low-cure-temperature copper nano ink for highly conductive printed electrodes, China Printing & Packaging Study, 9(2), e157-e160, DOI: 10.1016/j.cap.2009.03.008 Lee K.J., Jun B.H., Lee Y.I., Cho H.J., 2006, Metal nano particle and method for manufacturing them and conductive ink, US, US20060254387. Lim S., Joyce M., Fleming P.D., Aijazi A.T., Atashbar M., 2015, Inkjet printing and sintering of nano-copper ink, Journal of Imaging Science & Technology, 57(5), 50506-1-50506-7(7), DOI: 10.2352/j.imagingsci.technol.2013.57.5.050506 Sergeev A.S., Tameev A.R., Zolotarevskii V.I., Vannikov A.V., 2018, Electrically conductive inks based on polymer composition for inkjet printing, Inorganic Materials Applied Research, 9(1), 147-150, DOI: 10.1134/s2075113318010239 Tam S.K., Fung K.Y., Poon G.S.H., Ng K.M., 2016, Product design: metal nanoparticle-based conductive inkjet inks, Aiche Journal, 62(8), 2740-2753, DOI: 10.1002/aic.15271 Tang X.F., Yang Z.G., Wang W.J., 2010, A simple way of preparing high-concentration and high-purity nano copper colloid for conductive ink in inkjet printing technology, Colloids & Surfaces A Physicochemical & Engineering Aspects, 360(1–3), 99-104, DOI: 10.1016/j.colsurfa.2010.02.011 Titkov A.I., Bukhanets O.G., Gadirov R.M., Yukhin Y.M., Lyakhov N.Z., 2015, Conductive inks for inkjet printing based on composition of nanoparticles and organic silver salt, Inorganic Materials Applied Research, 6(4), 375-381, DOI: 10.1134/s2075113315040243 Yang W., Liu C., Zhang Z., Liu Y., Nie S., 2013, Preparation and conductive mechanism of copper nanoparticles ink, Journal of Materials Science Materials in Electronics, 24(12), 5175-5182, DOI: 10.1007/s10854-013- 1541-3 Yang X.J., He W., Wang S.X., Zhou G.Y., Tang Y., 2012, Preparation of high-performance conductive ink with silver nanoparticles and nanoplates for fabricating conductive films, Advanced Manufacturing Processes, 28(1), 1-4, DOI: 10.1080/10426914.2012.709344 Zhang Y., Westland S., Cheung V., Burkinshaw S.M., Blackburn R.S., 2009, A custom ink-jet printing system using a novel pretreatment method, Coloration Technology, 125(6), 357-365, DOI: 10.1111/j.1478- 4408.2009.00218.x Zhang Y., Zhu P., Li G., Zhao T., Fu X., Sun R., Zhou F., Wong C.P., 2014, Facile preparation of monodisperse, impurity-free, and antioxidation copper nanoparticles on a large scale for application in conductive ink, Acs Applied Materials & Interfaces, 6(1), 560-567, DOI: 10.1021/am404620y 36 https://doi.org/10.1088/2043-6262/4/1/015009 https://doi.org/10.1088/2043-6262/6/1/015003 https://doi.org/10.1016/j.colsurfa.2010.01.023 https://doi.org/10.1016/j.cattod.2014.05.044 https://doi.org/10.1088/0957-4484/25/26/265601 https://doi.org/10.1016/j.carbon.2008.10.029 https://doi.org/10.1016/j.apsusc.2009.05.134 https://doi.org/10.1016/j.cap.2009.03.008 https://doi.org/10.2352/j.imagingsci.technol.2013.57.5.050506 https://doi.org/10.1134/s2075113318010239 https://doi.org/10.1002/aic.15271 https://doi.org/10.1016/j.colsurfa.2010.02.011 https://doi.org/10.1134/s2075113315040243 https://doi.org/10.1007/s10854-013-1541-3 https://doi.org/10.1007/s10854-013-1541-3 https://doi.org/10.1080/10426914.2012.709344 https://doi.org/10.1111/j.1478-4408.2009.00218.x https://doi.org/10.1111/j.1478-4408.2009.00218.x https://doi.org/10.1021/am404620y