Film applicator
A Film applicator is a device used to spread a substance, such as paint, ink or cosmetics, evenly over a substrate. A standard procedure for testing substances that are applied in a liquid form, and then dry to a solid film, is to create a controlled, standardized test film of the substance, usually on a standardized substrate, such as a metal, plastic or paper panel. To provide the uniform film thickness, a Film applicator is normally used to maintain a constant film thickness. The applicators are used to spread a substance such as paint, ink or cosmetics, evenly over a substrate such as a drawdown cards. The applicators are usually metal bars with that are manufactured to high tolerances to give consistent, repeatable results. These applicators can either be used manually or by automatic film applicators. Each bar will give a theoretical wet film thickness or, in other words, the thickness of the coating that should remain on the drawdown card after application. Even with high manufacturing tolerances, the actual wet film thickness can vary from 50% to 90% of the gap. There are multiple kinds of bar applicators, their forms and uses are shown below. Film applicators follow the ASTM standard D823.[1]
Types
Four-sided applicator
Used for high viscous coatings, this type of applicator has four different clearances built in, one on each horizontal surface.
Applicator frame
Used for low viscous coatings, this applicator also has four different clearances built in. It is used for non-rigid substances and has a two sided opening in the center of the bar.
Bar type or Bird applicator
This applicator has one, two or four clearances and contains a slanted trailing edge, also used for high viscous coatings. This is the most common type of film applicator.
U shaped
This applicator also has two clearances but features a U-shaped form instead of a straight bar.
Square applicator or Octoplex applicator
The square applicator is the more versatile than previously mentioned applicators. It has 8 clearances in the form of a square frame. This tool combines the accuracy of fixed applicators with the versatility of adjustable applicators.
Film applicator knife
This adjustable applicator has a metal frame with an adjustable "knife" that acts as the gap clearance. These applicators are the most versatile manual applicator, but is also the least precise.
Wire-wound applicator
These applicators differ from the bar applicators as they consist of a metal rod wound with wire of varying thickness. The coating will pass through the gaps between the wires and level off at a uniform thickness. There are two main types of wire bars. Close wire wound bars will produce coating layers from 4 to 120μm. Higher coating thickness up to 500μm can be obtained using open wound bars.
References
- ↑ ASTM D823 - 95(2007) Standard Practices for Producing Films of Uniform Thickness of Paint, Varnish, and Related Products on Test Panels