Vacuum coating
Encyclopedia
Vacuum coating is a mechanized process for applying coatings to lengths of materials.
Paint is drawn from a reservoir by a diaphragm pump, filtered for large particles, and delivered through a hole into the bottom of the coater head. The fluid delivery diaphragm pump is by definition low shear and under low pressure. The level of the coating then rises within the head until the part passing through is completely surrounded or immersed.
A vacuum is applied to the reservoir and the application chamber. The reservoir is a sealed environment attached to the coating head. The coating head contains the only area for air to inrush and that is the space between the product and the template profile. It is this inrush of air that is used to strip excess coating from the product and this removal of excess coating is what determines the wet film thickness applied. The amount removed is subject to the vacuum relief valve, the size of the templates, the linear speed of the product, and the viscosity of the coating. This application and removal method stratifies the coating on removal and then it is drawn up and over a baffle and drains to the reservoir.
The amount of vacuum applied to the system regulates the resulting coating thickness applied to the board. In a perfect system too much vacuum would remove all the coating from the board leaving none behind at all. Conversely a non-existent vacuum would allow the coating head to fill sufficiently with coating where it would run out of the space created between template and product.
Vacuum coating differs from vacuum deposition in that the vacuum employed here is intended to vary the amount of coating by sucking off the excess and creating varying coating thicknesses between 0.001 inch in thickness. Vacuum deposition is applying a coating while the substrate is under a vacuum and applies the coating in very precise layers.
Process
The product passes through the portion of the coater known as the application chamber at a constant speed of up to 500' per minute.. As it enters the chamber it passes through a template which has the same shape hole, or profile, in itself to the shape of the product passing through. As it exits the chamber, it passes through another template called the exit template that also has a similar matching profile.Paint is drawn from a reservoir by a diaphragm pump, filtered for large particles, and delivered through a hole into the bottom of the coater head. The fluid delivery diaphragm pump is by definition low shear and under low pressure. The level of the coating then rises within the head until the part passing through is completely surrounded or immersed.
A vacuum is applied to the reservoir and the application chamber. The reservoir is a sealed environment attached to the coating head. The coating head contains the only area for air to inrush and that is the space between the product and the template profile. It is this inrush of air that is used to strip excess coating from the product and this removal of excess coating is what determines the wet film thickness applied. The amount removed is subject to the vacuum relief valve, the size of the templates, the linear speed of the product, and the viscosity of the coating. This application and removal method stratifies the coating on removal and then it is drawn up and over a baffle and drains to the reservoir.
The amount of vacuum applied to the system regulates the resulting coating thickness applied to the board. In a perfect system too much vacuum would remove all the coating from the board leaving none behind at all. Conversely a non-existent vacuum would allow the coating head to fill sufficiently with coating where it would run out of the space created between template and product.
Vacuum coating differs from vacuum deposition in that the vacuum employed here is intended to vary the amount of coating by sucking off the excess and creating varying coating thicknesses between 0.001 inch in thickness. Vacuum deposition is applying a coating while the substrate is under a vacuum and applies the coating in very precise layers.
Disadvantages
- Difficult to change colors
- Must have matching template for every profile
- Limited coating choices