Knife over roll

In knife-over-roll or blade coating, the coating material is placed on the fabric surface behind a knife, or doctor blade, and metered according to the gap set between the blade and the fabric surface. This method is used to apply thick coatings of highly viscous materials such as pastes, plastisols, or foams. 

Knedel micelles, 20 489 Knelson concentrator, 16 632 Knife coatings, 7 7-8, 10-11 method summarized, 7 5t Knife-over-roll chemical finishing,... 

Recently, hot melt PSA systems have been introduced and radiation curable PSA systems are at the commercial development stage. High solids (50%-70% by wt.) nonaqueous dispersion acrylic PSA systems have also been reported(1). Unlike the hot melt and radiation cured systems which require new capital outlay in coating head and/or curing (drying) equipment, BFG has developed PSA systems, based on Hycar 2100R reactive acrylic liquid polymers and isocyanate terminated prepolymer, which can be processed at 80% solids (by wt.) with equipment presently used in the PSA industry, namely, the reverse roll and knife-over-roll coater. 

Figures VI and VII illustrate the initial viscosity of both the Hycar 2103 and Hycar 2106 systems as well as the viscosity increase with time due to the reactive nature of the 2-component system. These figures will help in determining the percent solids necessary for processing on a given piece of equipment depending upon its viscosity handling capability. Since the 100% solids PSA systems have high initial viscosities of over 100 Pa s (100,000 cps), the conventional knife-over-roll and reverse roll coaters can not process them.

Knife Over-Roll Coater Horizontal Pad Coating Floating Knife Coater Extrusion Coating... 

For the dyeing or finishing of pile fabrics, such as carpets, flocked goods, velvets or sliver knits, the foam can be applied to the face of the fabric by means of a knife over-roll or knife over table coater (Figure l). 

Knife over roll coaler. Reproduced from Textile Finishing,... 

The most common coating application method is the knife over roll system (Fig. 2.16). The shape and angle of the coating blade, the gap between the blade and the fabric and the viscosity of the coating all affect the amount of coating applied and the penetration into the fabric. 

REZTHANES 1980A 1980B, aqueous polyurethane base or single coat, is designed for knife over roll or floating knife application on goods normally coated with solvent coatings where either recovery or protected environment is in place. 

Krebs, F.C. (2009) Polymer solar cell modules prepared using roll-to-roU methods knife-over-edge coating, slot-die coating and screen printing. Sol. Eneigy Mater. Sol. Cells, 93 (4), 465—475. 

The knife over roll coater (Fig. 4b) is probably the most common of the knife coaters. It is simple and compact. The driven back-up roll may be precision-made... 

Figure 15. Standard coating equipment for PSAs A) Knife over roU B) Reverse roll coater... 

Standard equipment for solution based PSAs are knife over roll and reverse roll coaters (Fig. 15) [255, p. 13 ff]. For high-speed application, a closed reservoir or a slot die is preferred for better control of air bubbles [260]. Especially the knife over roll coater allows for an easy change of the coating material. 

Drying Lines. Oven drying lines represent large capital investments, of the order of several million dollars, and the same line is frequently used to handle both solutions and latices. The metering equipment may be either reverse roll coaters, which offer maximum flexibility, or knife-over-roll coaters, which are less expensive. For thin films a wire-wound rod to remove excess material can be used. Because of coating difficulties encountered with latex vehicles such devices as an air knife or flexible blade are sometimes used with these products. 

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