The thickness of the substrate determines the type of roller coater machine configuration, which will allow for optimal performance in part coating. Parts must be able to make full contact with the coating rollers to achieve consistent coating, but should not cause the coating to transfer to the feed rollers (or feed rollers).
Thin, flexible substrates (such as paper) are usually best coated with a biased pressure roller or a double-feed roller arrangement, and a single sheet of paper coating will require the use of a peel pointer. Extremely soft substrates such as fabrics, thin foams, non-woven fabrics, thin rubbers, etc. may be very difficult to coat as they often come together and fold up when leaving the coating point. In some cases, these types of materials can only be coated using a backplane with sufficient stiffness, coated into a roll form, or leaving an unsprayed part on the front edge and using it to pull the substrate across the coating point. This can be done by loading the parts into the coating machine with the feed rollers open.
Thicker or harder substrates on roller coater machines can be driven by single feed rollers or double feed rollers. In some cases, hard substrates such as plywood or fiberboard may pose problems because they may have high and low points that bridge on the coating roller and create gaps in the coating. For these types of materials, a soft surface coating roll may be needed to contact the entire surface and apply the coating.
Once a part has been coated with an adhesive, it becomes more difficult to handle than when it was dry, so it is important to consider how the part will be handled after coating. The simplest and cheapest roll coating machine to coat parts on the bottom. This means that the parts must be handled immediately upon leaving the roll coating machine and must be processed by the coating surface. For many types of parts, this is not a problem, but the potential problem of wet glue sticking to the operator's fingers needs to be addressed. If the operator can handle and position the parts without contaminating the clean surface, there will be no problem, but in some cases, the operator will need to use special tools to handle the parts, or wipe the glue off their fingers. Gluing and assembly operations.
Using a machine designed to apply adhesive or coating to the top surface of parts greatly reduces the problem of glue contamination. The top of the part has a coating, and the bottom remains clean for processing. Parts can be placed directly on the roll coating machine conveyor (which is not possible for parts with a bottom coating). This may be important for large parts that are difficult to handle through the coating surface. Clearcoat is essential for parts that have been coated with clearcoat, as the clearcoat must have time to self-level and flow into a smooth coating after application.