Higher-Quality, Consistent Drawdown Charts Improve QC Test Results

By Sherry Walter

Quality testing of coatings, inks and raw materials is required to ensure consistent production. Drawdown charts have been used for many years for checking color, gloss, opacity, hiding power, adhesion and many other physical properties that are important to the manufacturer of coatings as well as the end-user.

Figure 1. Click image for larger view.

What happens when you discover that the new shipment of drawdown charts that you are using is different from the previous supply that you had been using? Can changes in the color of the paper stock that was used to produce the drawdown chart affect your results? What about changes in the color of the coated white or black sections of the chart? How can changes in the gloss properties affect your testing?

Any of these physical changes in the drawdown chart can negatively influence your testing results and the reliability of your standards. For example, hiding power or coating opacity is measured by the lightness (L*) differences of the coating on the white and black areas of a drawdown chart. With a new batch of charts two possibilities can happen if the L* of the white and black areas are not kept consistent.

Figure 2. Click image for larger view.

Case 1: If the black has a higher L* value than usual, the difference between black and white is smaller. Less hiding pigments are needed in the paint to make this difference disappear; however when this paint is used on the wall to hide stains, the stains show through. The contractor has to apply a second paint layer, leading to increased material and labor cost.

Case 2: If the black has a lower L* value, the difference between black and white is larger. The QC lab then orders production to add more pigment to make the difference disappear. Pigment is wasted, and the hiding power of the paint does not improve when the paint is applied on the wall.

Inconsistent charts can lead to unnecessary costs, production adjustments and re-testing, only to discover that the problems detected were due to variances in the chart itself and NOT in the product being tested.

To illustrate the magnitude of the problem, consistency tests were conducted on different production lots of a leading brand of drawdown charts as well as our own byko-charts® over a period of 54 months.

Figures 3-4. Click image for larger view.

White Area Tests

Figures 1-3 show the variation of CIE L*a* b* color values for the white-coated portion of the competitive drawdown charts used in the tests. The variance in color values for the white-coated section of the competitive test chart was found to be:

L* (Min. 91.13 to Max. 92.94) = Range 1.51 units

a* (Min. -1.28 to Max. -0.12) = Range 1.16 units

b* (Min. 2.61 to Max 4.93) = Range 2.32 units

Figures 5-6. Click image for larger view.

Black Area Tests

Significantly greater color variance was found for the black sections of the competitive charts tested in this study (Figures 4-6). The variance in color values for the black coated section of the competitive test charts was found to be:

L* (Min. 3.64 to Max. 8.16) = Range 4.52 units

a* (Min. -0.23 to Max. 1.80) = Range 2.03 units

b* (Min. -0.58 to Max. 3.44) = Range 4.02 units

BYK-Gardner goes to great lengths to assure the quality of all the charts before, during and after the productions process. A quality technician is on site testing the charts as lots are being produced. Prior to a lot being released for sale to customers, random samples are collected across the entire chart run and subjected to extensive testing in the BYK-Gardner laboratory.

Figures 7-8. Click image for larger view.

Storage

Drawdown chart storage has also been found to be a serious problem when less than "ideal" storage conditions are used. For instance, in the hot, humid days of summer, boxes of drawdown charts that are stacked in a warehouse or a delivery truck can quickly deteriorate, making them totally unusable. Charts can stick together, causing the coatings to be pulled off when attempts are made to separate the charts.

ASTM D 4946 is a procedure to test for blocking (resistance of surfaces to stick together). BYK-Gardner had an independent laboratory conduct a test on our charts and the competitive drawdown charts using the ASTM D 4926 method. The byko-charts passed the test and the competitive charts failed. To prevent blocking, BYK-Gardner wraps each box of byko-charts with a protective film that guards against humidity in the warehouse and during shipment.

BYK-Gardner has solved all these serious problems with our byko-chart family of charts. Our charts set high standards for the most desirable features in drawdown charts:

most consistent color and gloss values in the industry;
superior blocking resistance;
industry best moisture resistance during storage; and
environmentally friendly topcoat.

Figures 9-12. Click image for larger view.

All the familiar drawdown charts are available in the byko-chart family (Figures 7-12).

1. Opacity Charts - comprised of simple combinations of black and white areas with ample space for reflectance measurement to test hiding power.

2. Penopac Charts - Penetration and opacity testing combined in one simple chart.

3. Spreading Rate Charts - Designed for visually comparing hiding power and calculating coating spreading rate.

4. Sag and Leveling Test Charts - Designed for use with anti-sag meters.

5. Display Charts - Bold diagonally striped black patterns visually emphasize variations in opacity.

6. Plain White Charts - Plain white charts with the coating on one side with no text or label on top.

Now you can test your coatings or inks with the greatest degree of reliability in the industry. We also have private label charts available. Customize your charts with your own logo and custom header.

For further information or a sample pack of charts, contact BYK-Gardner USA at 1-800-343-7721.