How To Maximize 5-Roll Transfer Coater Performance

There are a variety of coating technologies on the market today, each designed to achieve different results while using an infinite number of coating formulations. Each formulation can be applied with many types of coaters. The objective of the converter (and their equipment supplier) is to establish which coater best accomplishes the converter's goals.

When using UV curable silicones, film substrates and low coatweights, the 5-Roll Transfer Coater is ideally suited to create the best possible product. The 5-Roll Coater's use of multiple rolls to reduce the wet film thickness and smooth the laydown of the coating are main reasons why this coater provides the best results.

Theory of Operation

5-Roll Coater Configuration:

Roll #	Roll Name	Roll Material	Roll Purpose
#5	Back-up Roll	Chrome	Web support, tension control
#4	Applicator Roll	Rubber	Application of silicone, final appearance
#3	Intermediate Roll	Chrome	Appearance
#2	Innergate Roll	Rubber	Coatweight control
#1	Outergate Roll	Chrome	Pond support

Roll #5

Controls web tension.
The nip, also referred to as the footprint, is set to different widths (dependent on the substrate.)

For paper substrates, a large footprint is needed to force the silicone to penetrate the surface of the web and apply a uniform coating.

If this does not happen, the effect is known as "pinhole" coating.
Film substrates are typically smoother so a lighter nip will be adequate.

Roll #4

Applies the silicone to the web.
The speed of this roll is varied +/- 5% to achieve optimum coating appearance.

Roll #3

Used to shear thin the silicone.
Affects the appearance.
This roll supports the 4-3 and 3-2 nips, which are varied to provide a shear force to the coating.
The amount of shear needed is dependent upon the viscosity of the silicone.
Higher viscosity requires more shear to achieve lower coatweights.

Roll #2

Main coatweight controlling device after the 2-1 nip has been set.
The speed of the roll determines the coatweight.
The faster the roll, the higher the coatweight.
The degree of change in coatweight is dependent upon the width of the footprint in nip 2-1.

Roll #1

Maintains a coating feed pond with the help of end dams located at both ends of nip 2-1.
Speed is very slow.
Not used to control coatweight.

Run Conditions

Below are suggested starting conditions: (CHART) The first step is to determine the desired coatweight. Using film as an example, set the footprints as indicated on the chart (5-4 = 3/8"), (4-3 = 3/8") etc.
Set the roll speeds to: #5 (insp.), #4 (95% of insp.), #3 (50% of insp.), #2 (varied) and #1 (2 crawl).
Select a line speed and run 6 speed parameters on the innergate roll from 5% to 30% in increments of 5%. A coatweight curve will be produced in the shape of the sample graph below.

The above graph demonstrates a theoretical curve; an actual curve should look similar. The degree of incline will vary depending on the silicone viscosity and/or the footprint setting of rolls 2-1.

If a coatweight curve is established in the desired range, proceed to step two. If the range is not correct, then increase or decrease the footprint (depending if the curve was high or low.) Then repeat the six innergate parameters and re-plot the curve.

The second step is to adjust the other roll settings, one at a time. Select a roll and adjust the speed or the nip. After all the rolls have been adjusted, the optimum product should be close. The other factors listed above can be adjusted or substituted one by one.

Note: When a condition is altered, a previous step may need to be performed again.

Black Clawson's recently renovated Coating Lab facility features 5-Roll Coating capabilities to experiment with a multitude of coating applications. The lab features multiple coater configurations, 60' long convection dryer, modular drying nozzle configuration, Steamex remoisturizer and many other state-of-the-art technologies.

The only Tandem Coating pilot facility in North America, Black Clawson's lab is ready for trials in Spring, 1998.
For more information on Black Clawson's 5-Roll Coater, please contact a Black Clawson sales engineer at (315) 598-7121. To book Coating Lab time, please contact Jeff Lawler at (315) 598-7121.

Questions? Call Black Clawson Converting Machinery at 315-598-7121 or e-mail us at bc@bc-egan.com

BC Publications is a technical newsletter designed to provide operational and maintenance information to improve the performance of your Black Clawson equipment.