Opacity Measurement of Coating

When working with metallized films the term "optical density" is used. It is a scale of 0 to 4 with 0 being completely transparent and 4 being completely opaque.

If it is not relevant, I'm sorry. Giving more detail is needed for a decent answer.

Black in real terms is white with low intensity. If the coating is on a black surface, one can perhaps measure the reflectivity of the substrate as baseline and correlate with the reflectivity of coatings of known thicknesses on the base. May involve a lot of validation.

I work more with measurements of paper (where opacity is also an important value) but maybe my explanation can help.

Opacity is essentially the degree to which something will hide what is underneath it. Usually it is a comparison of two values: For paper, the values are a pad-backed (preferable) or white-backed measurement, and a black-backed or even open-backed measurement. Pad-backed would mean a pad of the same kind of paper with enough sheets so that adding another sheet wouldn't affect the measured values. White-backed would mean measuring a single sheet over a white plate. Black-back would mean measuring a single sheet over a black plate or even a light-absorbing device (so that the only reflectance that would be measured would be that from the paper).

The opacity is then calculated in percent as Reflectance (black)/Reflectance (pad). This is also called the contrast ratio C.

For coatings, you would still need two reflectance measurements: One over a white substrate, and one over a black substrate. I did a little searching, and found a book excerpt on Google books related to paint and coating testing in the section on hiding power.

Hope this helps.

densitometer, transmission

http://www.google.ca/#hl=en&source=hp&q=%22transmission+densitometer%22&btnG=Google+Search&meta=&aq=f&oq=%22transmission+densitometer%22&fp=c7677315ecfd5b5c

I am not sure where you are or the exact nature of your application. Take a look @ schenkvision.com. They have a new product called Eastmeasure. It is a line scan camera with the appropriate lighting that can make an opacity measurement on line with several web products.

Good luck, mkh

Hi Maimuki,

In the coating industry, we compare the capacity to hide one colour with another colour on top of the first.

First, we have a chart, one of them is a Leneta Chart, available on the market worldwide, with white and black or white and grey stripes, and we maintain in horizontal position the chart.

Second, we apply a couting with a draw-down blade (we have different sizes and types) in a controlled thickness, let say 6 mils wet film, and let dry the coating.

We can judge the hiding capacity of the coating on the chart by seeing or not the black or grey stripes. When we cannot see the underneat stripes, the coating has a good wet hiding. It can be equal or different when the coating dries. Again, judgement needed to have or not have good hiding.

For example, we have a white paint, the hiding pigment is TiO2, let say 2 lbs/US gallon or 240 gram per litre. Let say the wet film doesn't hide satisfactorily. In this coating we have to increase to TiO2 level to let say 3 lbs/US gallon or 360 gram/litre, and we apply film, 6 mils wet with draw-down blade, judge the wet hiding and let dry and judge the final film capacity to hide the black or grey stripes. If we have satisfaction, the coating has a good hiding. The coating can be coloured in any colour and tested for hiding as mentionned. Some coatings with certain pigment hide well, and another, mainly organic pigment has the tendency to hide les or very little.

This is a simple explanation how check the hiding capacity of a coating. If you need QC procedures, let me know, Gil.

NB: Raw material suppliers can help you locally or through the Internet.

Contact www.rohmhaas.com and you get documentation about.

I understand your explanation. Thus can I say that black in leneta chart is meant for hiding power/color constract? Do you ever use the white part to check it's opacity? I have an opacity measure kit and I usually use black/white to check the opacity.