The newest generation of laser marking “smart additives” incorporated into polymers is a quantum leap in technology which is both enabling and cost-saving.

1. t e c h n o l o g y r e p o r t
“Smart additives”
enhance plastics laser marking
SCOTT R. SABREEN
IMPROVED CONTRAST, LINE EDGE DETAIL, AND SPEED
and custom color yellow-gold on
T
ABS (right).
he newest generation of laser mark- FIGURE 1 also demonstrates three unique surface reaction
ing “smart additives” incorporated mechanisms. First, the charring process occurs when the
into polymers is a quantum leap in energy absorbed raises the local temperature of the material
technology, which is both surrounding the absorp-
enabling and cost-saving. tion site high enough to
These advanced mate- cause thermal degra-
rial science formulations dation of the polymer.
achieve unprecedented marking contrast, line While this can result in
edge detail, and speed on plastics that burning of the polymer
have traditionally been difficult, if in the presence of oxy-
not impossible, to laser mark. gen, the limited supply
Designed for thermal chemical of oxygen in the interior
surface reactions, these formu- of the substrate results
lations are ideal for fiber, YAG, in charring of the poly-
and vanadate lasers operating at mer to form a black or
a wavelength of 1060 to 1070 nm dark marking contrast.
(near infrared spectrum). The darkness of the
Polymers that can be marked by mark is depen-
lasers are those that absorb laser
light and convert it from light
energy to thermal energy. Since
most polymers do not possess
absorption properties at 1060
to 1070 nm, experts utilize addi-
tives, fillers, pigments, and dyes
that enhance the absorption of
laser energy for localized color
changes. The material science
chemistry for achieving high con-
trast and color laser marking is FIGURE 1. Dark marking contrast (top),
both art and science. Contrary to white marking contrast (left), and custom
popular belief, a single laser addi- color (right).
tive that solves all marking prob-
lems does not exist. Vastly different formulation chemistries, dent on the energy absorbed as well as
laser type (fiber, YAG, vanadate), and laser optics/setup param- the material’s unique thermal degradation pathway.
eters are used depending upon the desired marking contrast When blended into the resin colorant matrix, additives that
and functionality. FIGURE 1 shows “dark marking contrast” on yield dark marking contrast often contain mixtures of either
polyethylene (left), “white marking contrast” on nylon (center), antimony-doped tin oxide, antimony trioxide, or aluminum
www.industrial-lasers.com JANUARY/FEBRUARY 2012 Industrial Laser Solutions 21
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2. t e c h n o l o g y r e p o r t
particles. All are easily dispersed in polymers. Typical loading creates the laser mark. The
concentration levels by weight are 0.01% to 3.0%. Many of the higher temperature polymer
final formulations have received FDA approval for use under con- will require more laser
ditions A-H of 21 CFR 178.3297 Colorant for Polymers. energy, lower mark-
A second surface reaction is chemical change, through use ing speeds, or more
of additives that release steam during degradation, resulting in absorbing additive
foaming of the polymer. During the foaming process, the laser to achieve the same
energy is absorbed by an additive that is in close proximity to the mark appearance.
foaming agent. The heat from the absorber causes the foaming Smart additives are
agent to degrade, releasing steam. Examples of foaming agents cost-saving and dem-
are aluminum hydroxide or various carbonates. To prevent char- onstrating 15% and faster
ring, the mechanism requires the polymer to degrade at a tem- marking speeds versus
perature higher than that of the foaming additive. Through tight non-optimized material for-
control of the laser-operating parameters, high quality and dura- mulations. One interesting appli-
ble light marks can be generated on dark substrates. Poor laser cation is “on-the-fly” laser marking
control can generate a friable or low-contrast mark, which can be for undercap promotions on linerless
FIGURE 3. Laser
easily scratched (poor durability). beverage closures. Turnkey systems
marking undercap
Third, laser energy is used to heat/degrade one colorant in a col- are capable of marking unique graphics
promotions on
orant mixture, resulting in a color change. An example is a mixture and alphanumeric text at speeds up to
linerless beverage
of carbon black and a stable inorganic colorant. When heated, the 1,500 closures per minute. Examples are
closures at speeds up
carbon black is removed, leaving behind the inorganic colorant. shown in FIGURE 3.
to 1,500 per minute.
These mixed colorant systems are dependent on specific colorant
stabilities, and not all color changes are possible. Laser technology
Laser formulations cannot be toxic or adversely affect the prod- The advancements in laser technol-
ucts appearance, physical, or functional properties. They must ogy have been instrumental in the rapid
absorb enough laser energy to raise the local temperature of the development of smart laser additives.
polymer to a sufficiently high Nanosecond fiber laser technology is
level to achieve charring or Change in weight (%) an emerging field and one of the most
foaming of the polymer, thus 262°C significant advancements in lasers for
0 364°C
creating the mark. This tem- marking, welding, and cutting. Fiber
perature will vary for different 258°C lasers are fundamentally different
-20
polymers, even within a poly- 357°C than other solid state marking lasers.
mer family. With fiber lasers, the active medium
-40
HDPE A that generates the laser beam is dis-
Achieving faster HDPE B persed within a specialized fiber optic
-60
marking speeds cable. In contrast to fiber-delivered
The time required to mark a lasers, the entire path of the beam is
-80
part is a function of the poly- 567°C within the fiber optic cable all the way
meric substrate, the number 436°C to the beam delivery optics.
-100
of vector lines drawn, and Fiber lasers yield superior beam
488°C 565°C
how fast the laser beam/gal- quality and brightness. The metric for
vanometer scan head draws 0 200 400 600 800 1000 beam quality is M2. The smaller the
all of the lines. Laser soft- Temperature (°C) M2 value, the better the beam quality,
ware and the type of vec- whereas M2 = 1 is the ideal Gauss-
tor fill, unidirectional, bidi- FIGURE 2. Thermal gravimetric analyses (TGA) from ambient ian laser beam. A laser with superior
rectional or serpentine, can to 1000°C of two HDPE samples showing differences in beam quality can be focused to a
also affect the marking time. thermal degradation temperatures. HDPE B will mark more small spot size, which leads to high
New independent studies are easily and faster than HDPE A. energy density. MOPA fiber lasers
showing that statistically sig- with pulse energy up to 1 mJ and
nificant faster marking speeds are achievable by incorporating high power density can mark many historically difficult poly-
laser additive formulations at very low concentration levels, typi- mers including nylons, urethanes, and acetals.
cally 0.01% to 2.0%. All beam-steered fiber, YAG and vanadate lasers are not cre-
FIGURE 2 shows a thermal gravimetric analyses (TGA) plot for ated equal. The hardware and software components a laser man-
two high density polyethylenes. The two polymers exhibit dif- ufacturer incorporates into its systems makes significant differ-
ferent temperatures of thermal degradation – the process that ence in marking contrast, quality and speed. A primary attribute
22 Industrial Laser Solutions JANUARY/FEBRUARY 2012 www.industrial-lasers.com
1201ILS_22 22 1/5/12 3:57 PM

3. t e c h n o l o g y r e p o r t
is the power density (W/cm2) at the mark surface (which is dif- increases, a lower peak power produces minimal vaporization
ferent than the raw output power of the laser). The output mode but conducts more heat.
of the laser beam is critical to the marking performance. These
output modes relate to factors including the beam divergence Conclusion
and power distribution across the diameter of the laser beam. The newest generation of laser marking “smart additives” incorpo-
Power density is a function of rated into polymers yields unprecedented marking contrast, line
focused laser spot size. Focused edge detail, and speed. These benefits rapidly offset the incremental
laser spot size for any given material additive cost. Achieving optimal material-science chemistry
focal length lens and laser formulation for plastics laser marking requires expertise in polymers,
wavelength is a func- property grades within polymeric families, colorants, pigments, and
tion of laser beam dyes relative to solubility, particle sizes, threshold concentration lim-
divergence, which is its, color match and regulatory certifications (GRAS, FDA Direct/
controlled by laser Indirect Food Contact). Material-science solutions must be cost-
configuration, mode- effective and easy to use, and possess no deleterious effects on
selecting aperture size, the polymer’s physical and chemical properties. ✺
and upcollimator (beam
expander) magnification. References
Pulse repetition rate and 1. Engelhard Corporation Mark-it™ Laser Marking Pigment Technical Bulletin 2002, with
technical content contributions from The Sabreen Group Inc.
peak power density are crit- 2. Bruce Mulholland (Hoechst Technical Polymers) and Scott Sabreen (The Sabreen Group Inc.),
ical parameters in forming the “Enlightened Laser Marking,” Lasers&Optronics, July 1997.
mark and achieving optimal contrast 3. Daniel S. Burgess, Scott R. Sabreen, & Carl Baasel Lasertechnik GmbH, “Laser Marking: A
Clean Economical Packaging Solution,” Photonics Spectra, November 2001.
and speed. High peak power at low frequency increases the
surface temperature rapidly, vaporizing the material while con- SCOTT R. SABREEN (ssabreen@sabreen.com) is founder and president of The
ducting minimal heat into the substrate. As the pulse repetition Sabreen Group Inc., Plano, TX.
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