Our customers' specifications for unique material applications and performances may require a suitable coating process provided by any of the following types:
The gravure coating process relies on an engraved roller running in a coating bath, which fills the engraved dots or lines of the roller with the coating material. The excess coating on the roller is wiped off by the Doctor Blade and the coating is then deposited onto the substrate as it passes between the Engraved roller and a Pressure Roller.
Reverse Roll Coating
In this procedure, the coating material is measured onto the applicator roller by precision setting of the gap between the upper metering roller and the application roller below it. The coating is 'wiped' off the application roller by the substrate as it passes around the support roller at the bottom. The diagram illustrates a 3-roll reverse roll coating process, although 4-roll versions are common.
Knife-Over-Roll Coating "Gap Coating"
This process relies on a coating being applied to the substrate which then passes through a 'gap' between a 'knife' and a support roller. As the coating and substrate pass through, the excess is scraped off. This process can be used for high viscosity coatings and very high coat weights, such as plastisols and rubber coatings. There are innumerable variants of the relatively simple process which is rugged, hard-working and somewhat inaccurate.
Metering Rod (Meyer Rod) Coating
In this coating process, an excess of the coating is deposited onto the substrate as it passes over the bath roller. The wire-wound metering rod, sometimes known as a Meyer Rod, allows the desired quantity of the coating to remain on the substrate. The quantity is determined by the diameter of the wire used on the rod. This process is remarkably tolerant of non-precision engineering of the other components of the coating machine.
Slot Die (Slot, Extrusion) Coating
In the Slot Die process, the coating is squeezed out by gravity or under pressure through a slot and onto the substrate. If the coating is 100% solids, the process is termed 'Extrusion' and in this case, the line speed is frequently much faster than the speed of the extrusion. This enables coatings to be considerably thinner than the width of the slot.
Immersion (Dip) Coating
In this simple process, the substrate is dipped into a bath of the coating, which is normally of a low viscosity to enable the coating to run back into the bath as the substrate emerges. This process is frequently used on porous substrates.
In the Curtain Coating process, a bath with a slot in the base allows a continuous curtain of the coating to fall into the gap between two conveyors. The object to be coated, such as a door, is passed along the conveyor at a controlled speed and so receives the coating on its upper face. Smelly and crude versions of these machines were once common.
Air Knife Coating
A simple process where the coating is applied to the substrate and the excess is 'blown off' by a powerful jet from the air knife. This procedure is typically used for aqueous coatings and is particularly noisy.
Note: Technical Coating International, Inc. has the capability to coat via Direct Gravure, Metering (Mayer) Rod, Immersion, and Knife-over Roll.
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