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Coating Methods Used in UV/EB Technology
Published in Jiri George Drobny, Radiation Technology for Polymers, 2020
Curtain coating is widely used in the coating of flat sheets of substrate, such as wood panels. A coating is pumped through a slot in the coating head so that it flows as a continuous curtain of liquid. The material to be coated is moved under the curtain by a conveyor belt. The curtain is always wider than the substrate and therefore a recirculating system is necessary for the overflow from the sides.
Manufacture of Pressure-Sensitive Products
Published in István Benedek, Mikhail M. Feldstein, Technology of Pressure-Sensitive Adhesives and Products, 2008
Contactless Coating Devices In contactless coating devices the mechanical device that regulates the thickness of the adhesive layer can be replaced by air [13]. An air knife uses an air jet, which comes almost horizontally, with a pressure of 6.9 × 10−3 N/mm2. The coating weight is regulated by the air pressure. Air-knife coating devices need a viscosity of 100–300 mPa · s and solids content of about 30% (w/w). The actual coating weight range covers 20–25 g/m2, that is, 2–3 g/m2 dry. In kiss-roll coating the adhesive is coated with a reverse smooth roll and the excess of latex is eliminated with an air knife. The kiss coat is used up to 30 Pa · s. In curtain coating a continuous stream of liquefied coating falls onto the moving material. Curtain coating uses a web width of 600–3,000 mm, running speed up to 500 m/min, viscosity lower than 10 Pa · s; and minimum coating weight of 2 g/m2 and maximum coating weight of 100 g/m2 [23].
Uses of anti-foaming agents in paints and surface coatings
Published in David R. Karsa, Surfactants in Polymers, Coatings, Inks and Adhesives, 2020
The most efficient ones should be selected for special application tests. These tests try to mimic the final application. Roller testA small volume of paint is spread by felt or sponge roller preferably on a closed surface such as glass, plastic film or sealed hardboard. After drying, the appearance of the film is evaluated. Transparent surfaces can be rated above a lamp and be checked for small holes which are due to very small air bubbles, called microfoam. Also, the influence of the defoamer on levelling and gloss can be rated here. Some modem defoamers are very active in destroying foam bubbles very rapidly, such as the newly introduced FoamStar® products [41]. Here the bubble break time in seconds is an indication of effectiveness.Airless spray testThis application means for aqueous coatings a process which produces a very intensive microfoam. It can be simulated in the laboratory by using electrical hand pistols which give comparable results. Microfoam causes very small defects which, if not eliminated, are a starting point for corrosion. These pinholes can be seen best when the panel is held over a strong light, where they appear as little stars shining through the film.Curtain coatingThis application method is often found in wood and paper coating. Here, defoamers must be very shear stable and not lose efficiency during continuous pumping of the paint. On the other hand, the defoamer must not cause disruption of the curtain by incompatibility at any time.Automatic testingThe market provides an automatic defoamer testing machine which measures the foam height by photo cells also depending on time. Foam is induced by either vigorous stirring, blowing air through the substance from the bottom through a frit or circular pumping, splashing the liquid back into the cylinder (Sita Messtechnik GmbH, Dresden, Germany).
Graphene-based electrodes for ECG signal monitoring: Fabrication methodologies, challenges and future directions
Published in Cogent Engineering, 2023
Rimita Dey, Pravin Kumar Samanta, Ram Pramod Chokda, Bishnu Prasad De, Bhargav Appasani, Avireni Srinivasulu, Nsengiyumva Philibert
In 2017, Karim et al., (2017) have reported fabrication of inkjet-printed environment-friendly, comfortable and breathable graphene e-textiles which are surface pre-treated with organic nanoparticles. In case of inkjet printing of the surface pre-treat, ink or coating material can be deposited on a specific targeted position which is advantageous compared to other techniques such as curtain coating and screen printing. The surface pre-treatment decreases the chance of heat-sensitive fabrics getting damaged since the pre-treatment acts as receptor of water-contained rGO inks, reducing the drying temperature of the fabric as low as 100°C. An organic nanoparticle which is hydroxyl functionalised cross-linked styrene/divinylbenzene was inkjet printed on the surface of the textile fabric. Then this fabric was coated with rGO water-based ink. In the presence of polyvinyl alcohol (PVA), the rGO water-based ink was synthesised using L-ascorbic acid which is a green and nontoxic reducing agent. In comparison with untreated textiles, the sheet resistance of the graphene-based inkjet-printed e-textiles decreased from 1.09 × 106 Ω/sq to 2.14 × 103 Ω/sq due to inkjet printing onto the pre-treated coating. The SNR value of the extracted ECG signal when this fabricated electrode was used was measured to be 21 dB.
Foam forming of fiber products: a review
Published in Journal of Dispersion Science and Technology, 2020
Tuomo Hjelt, Jukka A. Ketoja, Harri Kiiskinen, Antti I. Koponen, Elina Pääkkönen
Higher surface porosity or deep surface pores can be a disadvantage if paper is coated. Forsström et al.[157] coated water-formed and foam-formed papers and noticed that a more porous foam-formed structure led to a higher coat weight. Moreover, the coating penetrated deeper into the structure than in the case of water-formed papers when a traditional coating process was used. Koskela et al.[158] aimed to improve the coating quality of foam-formed webs by closing the paper surface by pre-calendering or by applying starch-foam coating before pigment coating, which was done either with a metered size press (MSP) or curtain coating. Coating penetration was reduced both by pre-calendering and by starch-foam coating, while pre-calendering improved coating hold-out and smoothness more than starch but simultaneously density was increased. High bulk was maintained with starch-foam coating, and this operation closed the surface well. In their research, it seemed that the non-contact curtain coating led to lower coating penetration, maintained bulk well, and improved coating hold-out compared to MSP that uses a high-pressure pulse.