Because porcelain enamel is a glass-based
coating, it is much more scratch-, abrasion-, and heat-resistant than
organic paints. However, burned-on
food residue forms hydrogen bonds and strongly adheres to enamel. The
cleanability of enamel can be improved by maximizing the acid resistance,
catalyzing the transformation of burned-on residue into ash, pyrolyzing
the residue into ash, or applying an easy-to-clean top-coat to the
enamel [1,2]. However, none of these have the cleanability of organic
The two major families of organic non-stick coatings are those
composed of either fluoropolymers such as polytetrafluoroethylene
(PTFE) or of silicone-polyesters.
PTFE-based coatings have been widely used on small appliances, cooktop
grills, cookware, and bakeware. Middle-market PTFE coatings are two-ply
with a binder-containing base coat and a fluoropolymer-rich finish coat.
The most durable PTFE coatings for high-end cookware are three-coat systems
with a ceramic oxide-containing intermediate coat for scratch resistance
. Silicone-polyesters are widely used on bakeware as well as the exterior
of cookware in a variety of colors. These two families of organic materials
have a low surface energy, which prevents the adhesion of burned-on foods.
Thus, for example, only water and paper towel can be used to remove residue
with the application of minimal force. However, both types of coating
are soft and easily scratched or gouged. The abrasion resistance
of the PTFE
coatings tends to be much less than porcelain enamel. Additionally, there
are two health and environmental concerns with PTFE. The first involves
a surfactant used in the manufacture of fluoropolymer resins, but this
material is not present in cured PTFE coatings . The second is the
emission of toxic by-products from PTFE during thermal decomposition,
occur if, for example, cookware is overheated .
a ceramic-based, non-stick coating developed by Ferro. This new coating
technology marries the cleanability of the organic non-sticks
to the durability of vitreous enamel. In a single coat, it offers the
scratch resistance of enamel and the cleanability of PTFE. It is a patented
that stands to bridge the gap between the organic non-sticks and low-temperature
The new coating technology is applied to degreased and roughened
aluminum, aluminized steel, brass, or copper. Unlike conventional enamel,
be applied to die-cast aluminum. Roughening can be done with sandblasting
or acid etching. It can be applied to mild steel, stainless steel, cast
iron, glass, or ceramics after the application of special patented hard-bases.
Hard-bases consist of an enamel base coat with a rough surface .
new coating technology is supplied as a wet, ready-to-use (RTU) system.
The RTU slip requires no adjustment of set, gravity, or color.
and unlike PTFE, the overspray can be reclaimed and re-used at 30 percent.
The coating is dried at about 125ºF (52ºC). Once dried, it may be screen
printed with other non-stick enamel colors and fired in a single process.
The coating fires at less than 1,000ºF (538ºC). The time varies with
the metal thickness and thermal conductivity, and a convection-type oven
preferred. Volatile emissions during curing are 70 to 80 percent less
Figure 1. Liquid
Droplet on a Hydrophobic Surface
Typically, the non-stick enamel is about 2-mils (50-60 µm) thick
without hard-base and as low as 1.5-mils (40 µm) with hard-base.
The hard-base is typically 1.5-mil (40-µm)
thick and requires an additional fire.
This new coating technology can
be supplied in many colors, except bright white. Generally, the color
palette is similar to that for aluminum enamels.
The new coating has a satin finish with a 60-degree gloss of 2-10, depending
on firing conditions. Possible effects are mottles, stipples, shadow
application, and recently developed metallic colors.
The new coating
technology has lower surface energy than conventional enamel and is,
therefore, hydrophobic and easy-to-clean. The balance
arising from a sessile drop of liquid water (l) on the coating surface
(s) under a vapor (v) is schematically shown in Figure 1 and is described
with Young’s equation, which is:
||is the energy per unit area of the appropriate interface, and
||is the contact angle between the liquid and the substrate.
surface will be wetted to decrease the area of the higher energy s/v
interface; this is the situation with conventional enamel.
balling up of the water will occur to reduce the area of the higher energy
Typically, is only 60 degrees for conventional enamel,
about 120 degrees for PTFE, and about 110 degrees for the new coating
of water wet and spread on a dual-purpose black ground coat. On non-stick
enamel, they are repelled by the surface and form beads.
Figure 2. Cleanability Results
has been assessed by the European FAN (Facile à Nettoyer,
translated to Easy-to-Clean) test. First, five steel rings are glued
to the coating surface. Second, salted whole milk, gravy, lemon juice,
yolk, and ketchup are placed in each ring. Third, the test panel is baked
at 482°F (250°C) for 30 min. Then, the glue thermally decomposes,
which allows the ring to be removed. Finally, the cleaning is rated using
the fan system.
The results for the new coating technology, PTFE, stainless
steel, and a typical porcelain enamel are shown in Figure 2. The new
achieves a perfect score and shows cleanability equal to PTFE and much
better than stainless steel or traditional enamel.
The new coating technology
exhibits good acid and alkali resistance. It achieves a rating of AA
on the PEI T-21 citric acid spot resistance
It is UV-stable and unaffected by solvents. It has excellent scratch
and abrasion resistance.
Figure 3. Pencil Hardness
Scratch resistance is evaluated using ASTMD3363-00 “Standard
Test Method for Film Hardness by Pencil Test.” The force required
to gouge a coating with a drawing lead of calibrated hardness is assessed.
coating shows a rating of 8H compared to an average of 4H for PTFE coatings.
Results are shown in Figure 3.
Abrasion resistance is measured using ASTMD4060-95 “Standard
Test Method for Abrasion Resistance of Organic Coatings by the Taber
weight loss before and after 2,000 cycles under the most abrasive CS-17
wheels under a 1-kg load was measured and normalized to the coating thickness.
Results are shown in Figure 4. On average, the new coating technology
was less damaged by abrasion than PTFE and significantly less than silicone-polyesters.
Figure 4. Taber Abrasion Results
The new coating technology has more heat resistance than the organic
non-stick coatings. It can be used in service at 600° F (315°C)
for extended periods of time. Figure 5 shows the color stability of non-stick
compared to a high-temperature silicone-polyester paint. After 100 hours
at either 662°F (350ºC) or 752ºF (400ºC), non-stick enamel showed
little color change versus a ?E as high as 51.17 for the silicone-polyester
after 100 hours at 752º F (400ºC). PTFE shows similar degradation at
Potential applications for non-stick enamel include
the interior or exterior of all types of cookware, including ceramic
bakeware. The new coating
is listed with NSF International as compliant with Standard 51. It is
as safe for food contact (acidic, aqueous, < 8-percent alcohol beverages,
dairy, dry solids, and other) up to 750°F (398ºC). With superior
heat resistance, it is very promising for heavy-duty use environments
commercial kitchen restaurants. It would be very suitable for small appliances
such as toaster ovens, waffle irons, and microwaves. For large cooking
appliances, it is an alternative to silicone-polyesters and PTFE on grills,
griddles, and simmer plates.
In summary, the new coating technology is
the first true, non-stick porcelain enamel. It is water-based and applied
as a single coat. Compared to silicone-polyesters
and PTFE, it is much more scratch-, abrasion-, and heat-resistant.
5. Color Stability of RealEase™ vs Silicone Paint
 H. Berkenkoetter
et al., “Method of making a temperature
and scratch-resistant anti-sticking coating,” USP 6372290, April
 “U-Jin’s Coating System”,
U-Jin Porcelain Enamel Limited 2001. (12 April 2004)
 P. Thomas, “The Use of Fluoropolymers
for Non-Stick Coating Utensils,” Surface
Coatings International 12, 1998.
 “PFOA-Facts.com” The
Society of the Plastics Industry, Inc. (SPI) (14 September 2004).
 David A. Ellis
et al. “Themolysis
of Fluropolymers as a Potential Source of Halogenated Organic Acids in
the Environment,” Nature
 William D. Faust, “Ceramic Substrate for Non-Stick
of the Porcelain Enamel Institute Technical Forum, 63, 2001
This is an
edited version of a paper delivered at the Porcelain Enamel Institute
Forum, held April 27-29, 2004 in Nashville, TN,
Baldwin is a research engineer at Ferro
Corporation in Cleveland,
OH, U.S. He has a B.S. and M.S. in Materials
Science from Case Western Reserve University. Mr. Baldwin
currently oversees technical support for new product development
in porcelain enamel research.
Aronica is director of Technical Support in Appliance
Design for Ferro
Europe in Saint-Dizier, France. He holds a
B.S. in Physics and Chemistry from Reims University (France).
Mr. Aronica has more than 25 years of experience in porcelain
enamel research and development.
Devine holds a B.S. in Ceramic Engineering from Alfred
NY, U.S., and has more than 20 years
of experience in porcelain enamel research and development.
he is the market development director for porcelain enamel
product development and marketing activities for the
Ferro Corp. in Cleveland, OH, U.S.
Rose holds an honors degree in Chemistry from the University
Sheffield, UK, and has more than 20
in porcelain enamel product development. Currently,
he is the worldwide market director for New Products
for the Ferro Corp. based in the UK.