Doctor blade coating

Screen Preparations, 100 micron thick x-ray intensifying screens were prepared using standard doctor blade coating techniques. The final phosphor volume was 50% when the coatings were dried. In most instances, the phosphor suspensions were prepared using polyvinyl butyral binders with viscosities adjusted to 2000 centipoise for the doctor blade operation and care was taken to avoid convection cell formation (9). A cross section of the screen construction is shown in Figure I. The completed screens consist of polyester (Mylar) base about 10 mil. thick, a 50 micron thick (TI02 (rutile) reflector layer, a 100 micron thick phosphor layer, a 10 micron thick clear cellulose acetate butyrate top protective layer. 

Figure 6.12 The Doctor Blade coating method for the laminating of electrolyte and cathode membranes for LPB.

Interference pigments based on liquid crystalline materials are prepared by a doctor-blade coating of the polymers in the liquid or liquid crystalline state on an even surface. The doctor-blade process leads to a thin film wherein a homogeneous orientation of the molecules takes place. It is only after this orientation process that the film shows an interference color. The films are then cured and crushed by special techniques to yield platelets of liquid crystalline polymers showing interference effects. 

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. 

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 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. 

The coatings were applied to one side of a steel substrate by means of a spray gun for the lower viscosity coatings, or by doctor blading with an adjustable Gardner knife for the higher viscosity materials. A casting technique was also used in which a known volume of the coating material was poured into a known area defined by heavy tape and was allowed to spread while on a level surface. 

Preparation of P(UA)-2 Coating. In lOOg of PBH solution, 45g of Desmodur N-lOO and Ig of Dabco XDM catalyst were added. Using a doctor blade, clear films were drawn on glass and steel panels and were cured using the same conditions as in the case of P(UA)-1. 

Film thickness can govern the morphology, stability, and surface-chemical expression of polymeric thin films. NIST researchers developed a process for producing gradients, termed flow coating, which is a modified blade-casting technique [3-5]. How coater instrumentation and the flow coating process are illustrated in Fig. 2. To create the library, a dilute solution of polymer in solvent (1-5% mass fraction) is injected into the gap between a doctor blade positioned over a flat substrate... 

The basic poly(phenylene vinylene) (PPV) polymer is commonly prepared by the sufonium prepolymer route developed by WessUng and Zimmerman in 1968 but much modified by subsequent workers. The synthesis starts from 1,4-bis(chloromethyl)benzene, via the bis-sulfonium salt formed by reaction with tetrahydrothiophene, and then polymerisation is effected to give the prepolymer by reaction with lithium hydroxide (Figure 3.39). Because of the inherent insolubility of PPV it is this prepolymer that is used to form the film coating on the substrate, for example by using a doctor blade technique. The prepolymer is converted into PPV on the substrate by heating in an oven under vacuum at 200 °C for 8-10 h. 

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