Doctor blades

Fig. 8. Schematic of methods for MLC manufacturing (a) belt casting (b) carrier film casting using a doctor blade.

J. C. Williams, "Doctor-Blade Process," in F. F. Y. Wang, ed.. Treatise on Materials Science and Technology, Vol. 9, Academic Press, New York, 1976. 

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. 

Fig. 15. Flexographic printing station, where the fountain pan suppHes ink to the mbber fountain roU, which in turn suppHes ink to the anilox roU. The doctor blade removes excess ink from the surface of the anilox roU so that it transfers a uniform layer of ink to the printing plate. The printing plate then...

The thickness of the tape is controUed by the sHp characteristics, the height of the doctor blade, the casting rate, and the pressure head of the sHp reservoir behind the doctor blade. SHp viscosities in the range of 1 5 Pa-s (10—50 P) are used to cast tapes at 5—100 cm/s. To achieve the desired strength and flexibUity in the green tape, tape casting slurries contain more binder than those used in sHp casting, as weU as a plasticizer to ensure flexibUity. 

A conventional valve that is piped, including its blow-back section, to be open to vacuum during polishing. When the precoat is consumed its blow-back section is turned on to remove the remaining precoat heel over the doctor blade. 

The flow scheme for a conventional precoat filter station typically looks like that shown in Figure 9. The doctor blade discharge configuration for this machine is illustrated in Figure 10. 

Figure 10. Doctor blade discharge for precoat filter.

Abstreicher, m. scraper akimmer. Abstreich-lbffel, n. skimming ladle, skimmer, -messer, n. (literally, scraping-off knife) scraper (Calico, etc.) doctor, abstreifen, v.t. strip off. strip skin. Abstreifmesser, n. (Mach.) doctor blade, doctor flaying knife. 

Rakel, m., f. Calico, etc.) doctor, wiper, -ap-pretur,/. doctor finish, -lineal, n. doctor rule, -messcr, n. doctor blade, doctor, -starkema-schine, /. starching machine with doctor, -streifen, m. doctor streak. 

Schaber, m. scraper, etc. (see schaben) doetor blade, doctor, -messer, n. doctor blade, doetor. 

Extrusion coating is ideal for rods, tube and wire. The article is passed through a paint reservoir and then out via a die, which leaves only the correct thickness of paint in place. There are further techniques suitable for flat articles in sheet or web form. Knife coating is ideal for very thin coats, especially on continuous paper or plastic webs. The knife is either a metal doctor blade or a curtain of high velocity air (an air knife) directed onto the surface and it removes surplus material applied previously. 

The polymer films were prepared by dissolving the polymer in a suitable solvent (chloroform) to form 7 wt% solutions. The solution was then poured over a clean glass plate and spread out evenly to a uniform thickness with the aid of a doctor blade. The films were air dried, removed from the glass plate and further vacuum dried at 60 C for 72 hours. 

Application of controlled amounts of foam to the substrate is by knife-on-roller, knife-on-blanket, floating knife, horizontal pad or furnishing roller with doctor blade, or by squeegee across a printing screen. 

The electrodes for examination were produced by smearing of suspension of active materials in the solution of binding substance -po 1 yviny 1 idcncfluoride (PVDF) - on the metal substrate by means of applicator "Doctor Blade" by Hohsen Corp. N-methyl-2-pyrrolidone was used as the solvent for the binding substance. 

The anodes of these two graphite samples were fabricated from a slurried mixture which contains 92 wt% of active graphite powder and 8wt% polyvinylidene difluoride (PVDF) polymer binder (Kureha 9130) and using 1 -methyl-2-pyrrolidinone (NMP) (Aldrich, >99%) as the solvent. After getting the homogenous slurry, the electrode laminates were coated on Cu current collector foil using a doctor blade in the laboratory-made laminate-coater. The laminates were then dried first at 75°C in air for 3 hrs and then the final heat treatment was carried out in a vacuum oven at 75 C for 10 hrs. Finally, the laminates were calendared to about 35% porosity in a dry room. 

The spreader most commonly found in the rubber industry has a working width across the application roller/blade of 1.5 metres. Wider spreaders (up to 4 metres) exist for very wide cloth coating but they require special control of the bending of the doctor blade and have compensatory mechanisms to overcome this problem. 

Alternatively, the doctor blade can impinge onto a small conveyor belt system which supports the travelling fabric. This mechanism is less commonly used than the rigid roller as it leads to reduced control of the thickness of the spread. For precision work, using very consistent cloth, an accurately machined chromium plated steel roll can replace the rubber covered roller. 

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