WOOD RESEARCH Volume 67, Number 4, 2022
Juraj Gigac, Mária Fišerová, and Radko Tiňo

Effect of paperboard surface modifications on electrical conductivity of printed UHF RFID antennas

The effect of surface roughness and water contact angle of commercial paperboard before and after surface modification by calendering, coating and calendering and plasma treatment on the functionality of UHF RFID antennas printed with thermal transfer aluminum ribbon was evaluated. A hydrophilic surface was created by coating or plasma treatment, which improved the wettability of the paperboard surface, the spreading of the thermoplastic tie layer and the adhesion of the conductive aluminum layer. A new paper product was created with permanent surface wettability by coating, without the need for plasma treatment before printing. The plasma treatment provided time-limited wettability, needed only during printing, and made it possible to restore the original hydrophobic surface of the paperboard. In addition to the meaning of these surface modifications, the importance and need to reduce the surface roughness was confirmed, as the higher surface roughness of the paperboard limited the effect of the plasma treatment in terms of its printability and the functionality of the printed aluminum antenna. The printability of the paperboard and the functionality of the printed antennas were evaluated using electrical conductivity. The electrical conductivities of the dipole and inductor loop of the UHF RFID antennas printed on modified paperboards varied depending on the antenna design.

WOOD RESEARCH Volume 62, Number 6, 2017
Christian Brischke, Antje Gellerich, Holger Militz, and Michael Starck

Performance of coated and uncoated horizontal lap-joint members during 20 years of outdoor exposure

Horizontal lap-joint trials were set up using eleven different wood species representing a wide range of natural durability. Coated and uncoated lap-joint specimens as well as non-jointed reference specimens were exposed for up to 20 years and evaluated with respect to decay, formation of cracks and performance of the coating. The tropical wood species Tatajuba, Cedrorana, and Dark Red Meranti performed still very well and also some Europe-grown softwoods with coloured heardwood were still in good shape. The lap-joint set up turned out to be a method that can be used also for determining the durability and performance of untreated naturally durable wood, but suffered from several drawbacks such as time-consuming and costly specimen preparation, difficult to detect onset of decay, and generally long exposure times needed for a reliable durability assessment. Cracks were often the starting point for internal decay, but did not exclusively occur in the lap area.

WOOD RESEARCH Volume 65, Number 3, 2020
Darius Albrektas, Milda Jucienė, Vaida Dobilaitė, and Raimondas Bliūdžius

The influence of thermal modification on the resistance to water impact properties and strength of wood used in outdoor conditions

In this study the influence of thermal modification on the resistance of wood to the impact of water and mechanical properties and to compare the durability of thermally modified and coated wood products operating in wet conditions was investigated. It was found that the weight of thermally unmodified non-coated oak wood after 48 h of soaking increased on average up to ~ 15%, and the weight of coated oak wood increased up to ~ 8%. If wood was thermally modified, the weight of non-coated oak wood increased up to ~ 9%, and the weight of coated oak wood increased up to ~ 5%. After 168 h of soaking these change is about 2 times larger. In the case of pine wood compared to oak wood these change of weight after 48 h is about 2.0 – 2.4 times and after 168 h about 1.4 – 2.0 larger. It can be stated that wooden constructions intended to be used in very wet conditions should be made of thermally modified wood without coating. Thermally modified wood will have greater dimensional and shape stability. Thermal modification reduces the swell up to 1.6 times in the case of oak, more than 2 times in the case of pine.

WOOD RESEARCH Volume 65, Number 3, 2020
Matej Holc, Igor Karlovits, David Ravnjak, Aleš Palatinus, and Ita Junkar

Influence of gaseous plasma treatment on functional properties of coated papers

Three different types of paper with different coatings have been used in order to study the influence of gaseous plasma treatment on surface properties of paper. Radio frequency (RF) oxygen plasma was used for treatment of papers that contain different parts of organic and inorganic components in their coatings. Surface properties like surface morphology, roughness, surface energy, wettability, and chemistry were studied. The influence of plasma modification was also studied in terms of printability and paper gloss, which are one of the key parameters that dictate the use of such paper in desired applications. The results indicate that plasma modification of different types of coatings indeed influences paper printability as well as gloss function, which was shown to be highly connected with surface morphology, as micro- and nanopores were opened or formed due to selective plasma etching of organic part of the coating. Moreover, significant increase in surface energy was observed on all plasma treated papers, however this seemed not to influence much on the printing and gloss properties.

WOOD RESEARCH Volume 65, Number 1, 2020
Juraj Gigac, Mária Fišerová, Maroš Kováč, and Monika Stankovská

Paper substrates for inkjet printing of uhf rfid antennas

Conventional papers are not suitable for printed electronics because they have a rougher surface than the plastic film commonly used for electronics printing. The paper surfaces were modified by coating and calendering processes to reduce surface roughness and electrical resistance of inkjet-printed UHF RFID antennas. The composition of coatings, the main component which included aluminum oxide pigment, had an influence on the surface roughness, the surface pore content and the electrical resistance of the inkjet-printed UHF RFID antennas on coated papers. Papers coated with a mixture containing 25% polyvinyl alcohol binder in combination with the cationic polymer PDADMAC without glyoxal crosslinker had the lowest surface roughnesses and the lowest electrical resistances of the inkjet-printed antennas. As the coating basis weight increased, the electrical resistance of the antennas increased. Reduction of the electrical resistance of the antennas was achieved after calendering coated paper. The design of the antennas had a significant effect on their electrical resistance, which increased with the length of the antenna.

WOOD RESEARCH Volume 66, Number 1, 2021
Juraj Gigac, Mária Fišerová, and Svetozár Hegyi

Comparison of thermal transfer and inkjet printing of UHF RFID tag antennas on paper substrates

UHF RFID printed antennas on conventional and experimentally coated papers by thermal transfer and inkjet technique were not conductive due to high surface roughness. Reducing the surface roughness of paper and hence the electrical resistance of the antennas printed by thermal transfer and inkjet printing was achieved by coating and subsequent calendering process. Papers for thermal transfer and inkjet printed of aluminum and silver antennas were prepared by coating with top functional coating, whose main component was pigment – precipitated calcium carbonate with addition of polyvinyl alcohol, cationic polymer PDADMAC and glyoxal. The desired quality of inkjet-printed silver antennas was achieved by using coated paper with a polyvinyl alcohol barrier layer and a top functional hydrophilic layer. Silver nanoparticles of inkjet ink require a sintering process to obtain a conductive printed trace. The microstructure and thickness of antennas printed by thermal transfer and inkjet technique were compared. Thermal transfer printing created a more homogeneous antenna with greater sharpness of drawing compared to inkjet printing.