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Direct electrostatic coating of paper Robert H. Marchessault, Patrice Rioux and Ilie Saracovan, Keywords: Coated papers, Polyolefins, Poly-P-hydroxyal- kanoates, Electrostatic coating, Corona discharge, Xerogra- phy, Toners, Adhesive strength, Barrier properties, Moisture transmission. SUMMARY: Direct Electrostatic Coating (DEC) of paper uses "as polymerized" reactor polyolefin and an electrostatic spraying applicator. A glossyltransparent polymer coat was obtained after hot-pressing the electrostatically deposited pow- der layer on the paper surface

. Chemical composition of coated 1 : 105 paper surfaces determined by means of ESCA Interactions between dissolved and 1:226 colloidal substances and a cationic fixing agent in mechanical pulp suspensions Sundberg, A. Ekman, R. Holmbom, B. Sundberg, K. Thornton, J. Marchessault, R.H.Direct electrostatic coating of 1:211 Rioux, P. paper Saracovan, I. Sundstrom, L. Fibrillation and its importance for 4:379 Middleton, S. R. Partial umen loading 1 :204 Scallan, A. M. Brolin, A. the properties of mechanical pulp Hartler, N. fiber sheet Neimo, L

, especial- ly barrier properties and printability. Conclusions The feasibility of the Direct Electrostatic Coating (DEC) process using thermoplastic polymer powders has been demonstrated. Two key-elements enable this new approach: simple and efficient corona charging equipment to provide a high volume throughput of coating material; inexpensive polymer powder (e.g. "as polymerized" polyolefin) with suitable characteristics (i.e., particle diameter, electrostatic charging characteristics, rnelt- ing point, etc.). These results open new approaches to speciality

- porating an anti-electrostatic agent, most commonly on the surface. Therefore, anti-electrostatic surfaces are either manufactured from metal, or covered with an anti- electrostatic coating. Wood is often the preferred building material for con- structing a room or furniture that houses electronic equipment and flammable materials. However, wood must be treated with an anti-electrostatic agent before it can be used in applications requiring anti-electrostatic properties since wood is an electrical insulator and prone to the buildup of electrostatic charge. Graphite is

/sq, whereas for electrostatic coating, only small electrical resistivity of ~10 7 –10 8 Ω/sq is necessary [ 3 ]. Therefore, the control of the electrical resistivity in polymers has become a main challenge for the development of conductive polymer composites (CPCs). Muller et al. [ 4 ] and Villmow’s group [ 5 ] demonstrated that the addition of conductive particles to polymers simply makes them conductive. A wide variety of conductive particles are available, such as metal particles, carbon fibers, carbon nanotubes (CNTs), grapheme, etc. Nowadays, the most mature

. Pimchuai A , Dutta A , Basu P . Torrefaction of agriculture residue to enhance combustible properties . Energy Fuel 2010 ; 24 : 4638 – 45 . 10.1021/ef901168f 17. Szafran RG , Ludwig W , Kmiec A. New spout-fluid bed apparatus for electrostatic coating of fine particles and encapsulation . Powder Technol 2012 ; 225 : 52 – 7 . 10.1016/j.powtec.2012.03.031 18. Li R , Zhong Z , Jin B. Influence of reaction conditions and red brick on fast pyrolysis of rice residue (husk and straw) in a spout-fluid bed . Can J Chem Eng 2012a ; 90 : 1202 – 11 . 10.1002/cjce.20623 19

dioxide established itself as the leading white pigment when it went into mass production in 1919. These developments in coating chemistry were paralleled (finally) by advances in coating technology. The various methods of brush application and spraying were supplemented by electrodeposition, electrostatic coating and powder coating techniques. Ambient air drying was joined by infrared and radiation drying methods (UV, electron beam), and the automation of coating processes continued to advance. It is also worth mentioning environmental technologies for the

- ciency and the so-called wrap around the work piece (see Chapter 4.3: Primers, Figure 4.4: Principle of the electrostatic coating method). For this method conductive substrates are necessary as well. The conductivity can be achieved by the use of conductive primers as explained in Chapter. 4.3. High speed bell atomizer The equipment manufacturers have further increased operating and transfer efficiencies by increasing brush speed (up to 1000 mm/s), increased fluid flows (>600 ml/min) and developed more reliable air bearing turbines so that transfer efficiency can

rather than internal charging (see above) or • insulating the entire spraying plant, including the coating supply system (a cumbersome proc- ess), or • insulating the spray gun only and supplying restricted quantities of coating by means of ”shut- tles” or similar vessels which are to be insulated separately (”canister system”) Spray application processes spray gun spray gun without electrostatic assistance workpiece coating film with electrostatic assistance Figure 6.16: Coating droplet deposition without/with electrostatic coating charging, according to [9] VIN

the barrier effect against sol- vents and inward water diffusion under humid climate conditions. Primers are made conductive by the use of conductive pigments (carbon black, doped mate- rials). Conductive primers allow the electrostatic coating of the non-conductive plastic. In the electrostatic coating process the coating is electrically charged at the atomizer (pneu- matic or high speed rotation), the work piece is grounded. The charged paint droplets move along the electrical field lines to the part where the static is discharged to the ground (see Figure 4