Anti-Fingerprint Strategies
June 2014 www.coatingsworld.com Coatings World | 37
found on the groves of frictional ridge skins, and these skin types
are the most frequently used contact areas for electronic devices
(Figure 2).
A description of common compositions for latent print residue
has been reported in several studies (see Ramotowski, Advances in
Fingerprint Technology, 2001 CRC Press LLC, source of Table 1).
A substantial weight percent of the latent print residue is attributed
to lipid components and lipids are susceptible to ester hydrolysis.
Knowing the composition and spatial distribution of the contaminating fingerprint residue on touch screen surfaces, Reactive
Surfaces engineered these additives and developed these coatings as
a useful counter strategy.
Quantifying functional coatings efficacy in a laboratory set-
ting was performed using the indicator, 4-nitrophenyl acetate
(pNp-OAc) possessing an ester linkage. The catalytic reaction
rate using pNP-OAc was monitored using UV absorption at 401
nm and these values correspond directly with the degree of chemi-
cal conversion versus time while monitoring for the absorbance
of the hydrolyzed product p-Nitrophenyl. Increase in absorbance
per unit time can then be converted to a concentration using the
extinction coefficient of 4-nitrophenol (ε = 3.2 x 10-5 M cm-1 at
pH 7.1) as a conversion factor. The routine analysis sample size
was standardized to 1 cm2 and all assays results contain tripli-
cate data values within the same assay. Control coating materials
lacked the functional additive as an internal standard of the assay
conditions. The functional coating activity levels shown in Figure
3, indicated by the 4-nitrophenyl acetate hydrolysis rates for a
series of solvent based polyurethane overcoated commercially
available screen protectors. The results support robust coating
functionality over multiple substrate types. The urethane coating
was applied directly to the unprotected screen protectors as re-
ceived. The samples were cured for 30 minutes at 60°C, cooled to
ambient, and cut into 1cm2 test coupons. Coupons were assayed
over a one hour period to obtain the relative functionality of each
screen protector. The activity ranged between 9. 6 to 19.67 μmole/
min cm2 with at the same additive loading level of 1.5% based
upon total resin solids. The hydrophilic or hydrophobic character
of the varying film materials exhibited minimal effect on the coat-
ing functionality.
Table 2 shows the fingerprint removing capabilities of eRACE™
in an acrylic copolymer waterborne coating applied to a PET sub-
strate. Note the difference in the eRACE™ sample after 24 hours
as compared to the control where the fingerprint became more vis-
ible over the observation period.
Reactive Surfaces have launched a line of touch screen protec-
tive and self-cleaning functional coatings and these appliques are
being marketed under the trademark eRACE™. It is now possible
to convert the lipid components of the fingerprint and other related
contaminants to soap-like and glycerin hydrolysis products using
functionalized screen protectors on touch screen devices. The new
technology facilitates the removal of subsequent latent residues,
and maintains clearer and cleaning touch screen surfaces. Reactive
Surfaces is currently producing screen protectors for leading cell
phone brands, other handheld devices, and automotive surfaces. CW
A. Organic (major)
Triglycerides 30–40%
Free fatty acids 15–25%
Saturated 50%
Monounsaturated 48%
Polyunsaturated 2%
Wax esters 20–25%
Squalene 10–12%
Cholesterol 1–3%
Cholesterol esters 2–3%
B. Organic (trace)
ldehydes, Ketones, Amines, Amides, Alkanes, Alkenes, Alcohols, Phospholipids, Pyrroles, Pyridines, Piperidines, Pyrazines, Furans, Haloalkanes,
Mercaptans, and Sulfides
Table 1. Organic Composition of Sebaceous Secretions
Control eRace TM with DeGreez TM
Time
0
Time
24 Hr
Table 2.
1 The University of Southern Mississippi, 2 Reactive Surfaces
*Fig 1-3 Photos Courtesy of Dr. Jorn Chi-Chung Yu, Forensic Science Program,
College of Criminal Justice, Sam Houston State University
