When it comes to developing products such as paints, cosmetics, glues or varnishes for example; it’s typical to test their properties as part of their development. It’s important therefore to ensure that consistent, repeatable and reproducible films can be made in order to undertake fair and accurate tests.
One method of doing this, which is ideal for when you want to create incredibly thin films, is the spiral bar coater.
The spiral bar coater consists of a cylindrical bar wound with stainless steel wire of a defined diameter; the product you wish to make a sample film of is placed in front of the bar coater and as the bar coater is moved across the substrate (again this could be done manually or automatically using the Elcometer 4340 Automatic Film Applicator) the product flows between the turns of the stainless steel wire. This simulates how a coating is applied when using a paint brush. The product should then settle, or level off, to the wet film thickness defined by the bar coater. As a result, this method only works with products that have high levelling characteristics, with a low viscosity. It is best suited to materials with a viscosity range from about 1 to 1000 centipoise, subject to them flowing out after coating.
CONTENTS
0:00 - Introduction
1:10 - How a Spiral Bar Coater works
2:45 - Setting up the Elcometer 4340 for a Spiral Bar Coater
6:10 - Creating a film using a Spiral Bar Coater
Made of stainless steel, the Elcometer 4360 and 4361 Spiral Bar Coaters are available in two widths, and are perfect for creating incredibly thin films from just 4-500μm thick.
To begin, place the supplied bubble level on the table, and adjust the feet of the unit, until the table is level. Next, switch the Elcometer 4340 on using the switch at the back of the machine, followed by the green button on the control panel.
Now you can set your carriage speed – in other words, how quickly the film is applied. Simply set the dial from 1 to 11, to choose your desired speed. This should only be done when the carriage is stationary, not while the carriage is moving.
With the speed set, you now set the carriage start and stop positions, which defines the length of your film.
With the applicator’s speed and distance set, it’s time to add your spiral bar coater to the carriage.
To fit a spiral bar coater, ensure the combined carriage is in its raised position, remove the applicator pushing bar if it’s fitted, remove the weights, open the clamps, and fit the spiral bar coater. Then close the clamps. Make sure when you are closing the clamps, they are closed on the plain end pieces of the bar, not on the spiral or the weld, as this can damage the bar coater. Also, depending on the width of the spiral bar coater you are using, you may also have to adjust the horizontal position of the clamps.
Once the bar is clamped in place, refit the weights and then it’s time to mount the provided rubber matt to the table. The rubber matt, also known as an impression bed, is designed to elevate the substrate to a suitable height for the spiral bar coater, while gripping both the table and the substrate. Its properties also aid the flowing out and levelling of the product once the drawdown has been completed, increasing repeatability.
Make sure the table and both sides of the soft rubber mat are clean, then place the rubber mat on the table, securing in place using the spring clamp. Next, rotate the carriage to the lower position, and check the spiral bar coater is touching the surface of the rubber mat.
With the spiral bar coater correctly positioned, make sure the underside of the substrate you are using is clean, then place the substrate on the rubber matt and secure using the clamp. Additionally, you may want place a thin piece of paper at the end of your substrate, between the substrate and the rubber mat, in order to catch any excess product, making it easier to clean up. You are now ready to test.
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STANDARDS:
ASTM D 823, ASTM D 4147
For more information on the Elcometer 4340 Automatic Film Applicator, or Elcometer’s full range of applicators, please contact Elcometer at
[email protected] or visit our website: