Doctor roll

Wearing gloves, the doctor rolls a sheet of sandpaper around a round object (e.g. a bottle of pre-peel cleanser). The skin is held taut with one hand, and intersecting, careful, gentle and repeated passes are made with the sandpaper. Pressure must be firm and even. If the pressure is too light, the skin will not be abraded properly. On the other hand, if the pressure is too firm, it will take off more skin and make it too permeable. 

Although virtually any type of roll coater may be used, reverse roll coating is the most common. This may incorporate a doctor roll, doctor blade, or Mayer bar to meter the spread rate. With tapes, adhesive is usually applied directly to the tape, which then passes through a drying station incorporating countercurrent air, usually warm. The dried tape is then rolled and slit. With label stock, adhesive is normally applied to the release paper, dried, and then transferred to the label when the label stock is united with the release paper in a nip roll. 

Control devices must be used to ensure that the proper resin impregnation occurs and is held within the required limits. Simple devices, such as doctor rolls or squeeze rolls, are usually sufficient. It is important to control the resin viscosity. The most difficult part to set up is the shape of the opening in the die/mold. Experience and/or trial and error are required. 

Doctor roll—A roller mechanism that revolves at a different surface speed, in a direction opposite to that of the spreader roll, resulting in a wiping action to control the amount of adhesive supplied to the spreader roll. 

Doctor roll. The gap between the pick up roll and the coating roll is adjustable and this determines the adhesive add-on. It is possible to apply thick adhesives up to 50,000 mPas and control accurately the adhesive thickness which may vary from 10 to 150 g/m. This system allows also to apply fluid adhesives at very high speed and low add-on (2 to 50 g/m ) (Fig. 40 and 48). The doctor roll reduces foaming because it squeezes the foam bubbles which could result from the agitation of the adhesive. Doctor rolls are always used in sophisticated roll coaters, when an accurate add-on is required and for high speeds. 

Doctor Roll Doctor Bar. A device for regulating the amount of liquid material on the rollers of a spreader. 

The coating sol is deposited on a doctor roll by a sol dispenser and is transferred from there to an anilox roll with small cavities. From this roll, the sol is transported to the printing... 

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