A similar example is shown in Table
4 for a set of the formulated paints. The
performance for the formulated paints is
even broader showing a drastic disparity
in stain repellency values. Tables 3 and
4 highlight the broad range of stain re-
pellency data found in this study that is
better for determining correlations since
small differences are not magnified.
The samples shown in Tables 3 and 4
are also shown in Tables 5 and 6, respec-
tively, except that these tables highlight the
contact angles and subsequent calculated
surface energy values used to determine if
any correlation to stain repellency exists.
The range of values for contact angle and
surface energy are not as different within
each set of paint samples.
However, Table 7 shows the complete
range of data for contact angle measurements and calculated surface energy data.
Again, the broad range indicates a good
spread of data for determining whether a
correlation exists.
The sheer volume of data and the
broad range of data should have the effect of reducing variation errors in the
correlation coefficient calculations.
Correlation coefficients were calculated
for diiodomethane, however, the information is of spurious value since only
a small number of very similar samples
were measured using this solvent.
The summarized stain repellency data
shown in Table 8 represents a very broad
range of data with the minimum values
for most stains at or below L* of 0.5 or
less, and maximum values in excess of 10,
and in some cases in excess of 20.
The ASTM black stain media, red lipstick, and red wine were the most deleterious stains and should be considered as
being very aggressive for stain repellency
testing. Conversely, while ketchup, soybean oil and cola all have average L* values > 1.0, they show the lowest average
staining with values < 2.0. Thus, in some
cases, these materials may either not stain
or be easy to clean even though the test
substrate may not be very stain repellent.
Since contact angle of a liquid correlates to its surface energy, a relationship is expected between the chemistry
of the staining agents and the surfaces to
which they are applied. A discussion of
the chemical nature of the staining agents
is needed to understand why staining or
attraction (adhesion) occurs. Coffee contains over 20 different chemicals but the
more common components are acidic,
and thus polar (caffeic acid, chlorogenic
acid, and quinic acid). 18, 19
The main ingredients in tomato ketchup are ascorbic acid, acetic acid, sugars,
and lycopene, some of which are polar and
others are non-polar. 19, 20 Soy sauces contain many chemicals as well but primarily are comprised of multiple amino acids
and peptides, both of which have polar
Table 5: Example of commercial paint contact angle and surface energy data
Sample 56 57 58 59 60
Watercontactangle(°) 65. 26 64.02 68. 69 65. 28 73. 59
Dodecanecontactangle(°) 56.06 55. 93 65. 72 55. 44 54. 70
Diiodomethane contact
angle (°)
NA NA NA NA NA
Dispersiveenergy(mN/m) 15. 42 15. 46 12. 65 15. 60 15. 81
Polarenergy(mN/m) 21. 74 22. 65 21. 39 21. 59 15. 50
Total surface energy
(mN/m)
37. 16 38. 11 34.03 37. 19 31. 31
Table 4: Example of formulated paint stain repellency data
Sample 163 164 165 166 167
Ketchup 1.12 0.95 0.82 1.19 0.64
Redwine 3. 96 2.94 3. 95 3. 97 3. 14
Mustard 1.21 1.88 1.10 2.53 1.39
Soybeanoil 0.89 0.84 0.54 1.53 0.53
Soysauce 0.53 1.25 0.89 1.03 0.36
Coffee 0.54 1.65 1.12 1.53 1.08
Cola 0.99 2.57 0.93 1.17 1.12
Redlipstick 15. 12 11. 49 12. 50 13. 85 11. 51
ASTMblackstainmedia 16. 87 18. 88 16. 51 15. 46 15. 71
Total 41. 26 42. 45 38. 36 42. 26 35. 48
Table 6: Example of formulated paint contact angle and surface energy data
Sample 163 164 165 166 167
Water contact angle (°) 90. 77 91. 61 91. 66 100. 89 98. 85
Dodecane contact angle (°) NA 48. 14 57. 97 64. 70 64. 78
Diiodomethane contact
angle (°)
49. 18 NA NA NA NA
Dispersiveenergy(mN/m) 34. 73 17. 65 14. 87 12. 94 12. 92
Polarenergy(mN/m) 1.38 4. 87 5. 90 3. 18 3. 85
Total surface energy
(mN/m)
36. 11 22. 52 20. 77 16. 12 16. 77
