BYK-Gardnerīs New Coating Test Charts
Higher Quality Consistent Drawdown
Charts Improves QC Test Results |
Quality testing of paints, 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 coa tings as well as the end user.
But what about the quality of the chart itself? What
happens when you discover that the new shipment of
draw down charts that you are using is different from the
previous supply that you had been using? Do you ever test
that, or do you rely on the supplier to supply you a consis -
tent chart? 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 opacity of
the coating is measured by the lightness (L*) differences of
the coating on the white and black areas of a drawdown
chart. Differences in the L* values between charts can result
in false opacity determinations and cause costly batch
adjustments or allow for below-spec paint to be approved. |
Case 1: The absolute difference between the L* value of
the black and white area of the charts is less than that
on the chart used to determine the standard hiding of
the product:
A quality control test on a batch of paint with this smaller
difference in L* values will show that the batch hides more
than it should (less TiO2 needed) and QC makes an adjust -
ment to the batch, increasing the yield of the total batch
but lowering the hide to match the standard. However,
when a painting contractor uses this paint on the wall to
hide stains, the stains show through. The contractor has to
apply a second coat of paint, increasing his costs for
material and labor. Those costs may be charged back to
and accepted by the paint manufacturer if the contractor is
a good customer. |
Case 2: The absolute difference between the L* value on
the black and white area of the charts is greater than
that on the chart used to determine the standard hiding
of the product:
A quality control test on a batch of paint with this greater
difference in L* values will show that the batch hides less
than it should (moreTiO2 needed) and QC makes an adjust -
ment to the batch, increasing the cost of the total batch to
match the hide of the standard. Pigment is wasted and the
hiding power of the paint does not improve when the paint
is applied on the wall. In fact, if the contractor is using two
different lots on the same job, he may complain about the
lot that has lower hide (normal hide) because it doesn’t
hide as well as the off-spec lot. |
Case 3: Either Case 1 or Case 2 has occurred and testing
is performed on a batch of paint that is below-spec and
has been sent to the QC Lab.
In this case there is a strong possibility that the below-spec
will be approved and the problem won’t be discovered until
the customer uses it and finds the difference. This could be
both costly and embarrassing.
Inconsistency in chart production can lead to unnecessary
costs, production adjustments, customer complaints and retesting
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-chartsŪ over a period of 5 years. |
White Area Tests
The following graphs show the variation of CIE L*a* b*
color and gloss values for the white coated portion of the
charts used in the tests. |
