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Opaque Polyethylene Microspheres for Coatings Applications - PCI Feature Article - Jan 2010
Microspheres
are well known in the coatings industry for their use as low-surface-area fillers
that offer benefits in viscosity and density control, solids content,
application and flow characteristics. Cospheric LLC, a Santa Barbara-based
microtechnology company, recently launched a line of opaque polyethylene
microspheres that act as a superior opacifying agent and provide maximum hiding
power with just one monolayer of microspheres as small as 40 microns in
diameter. Microspheres are manufactured in any color imaginable and even in
combinations of two differently colored hemispheres.
Microsphere Characteristics
When light strikes an interface between two
substances, in general some may be reflected, some absorbed, some scattered and
the rest transmitted. An opaque substance transmits very little light, and
therefore reflects, scatters or absorbs most of it. High level of opacity
becomes more difficult to achieve for microscopic particles, because opacity is
proportional to the thickness of the material. An opaque microsphere does not
allow any light to pass through, which means every single particle has maximum
hiding power.
Opaque microspheres provide superior coverage with one invisible and
feather-light layer – revolutionizing coatings products. Today Cospheric is the
only company in the world to manufacture truly opaque
microspheres.
“While sourcing materials for one of our
projects, we searched the globe for microspheres that were truly opaque in a
monolayer arrangement. We found a handful of companies that sent us
samples, but under the microscope we saw poor opacity, dust, debris and
non-spherical particles. “Frustrated with the lack of opaque microspheres on
the market, we developed our own proprietary process to produce polymer
microspheres with tightly controlled particle size, opacity, color, sphericity,
as well as internal and surface charge and magnetic properties,” says
Brian Gobrogge, CEO and co-founder of Cospheric.
Cospheric microparticles are guaranteed to be >90% spherical and
within specified particle size range. The exceptional smoothness, sphericity
and particle size uniformity are responsible for the ball-bearing effect, which
imparts the finished product with a silky texture, enhanced slip, glide
and omni-directional spreadability. Outstanding roundness enhances lubrication.
Red, green, blue, yellow or
even multi-color microspheres make a product that is not only functional but
fun and exciting by adding a hint of color, sparkle or even a color changing
effect, without dealing with difficult-to-disperse pigments.
Composition
Opaque microspheres are made from polyethylene. The
polymer is pigmented to achieve the exact color and opacity level desired by
the customer. Particle size ranges from 10-25 microns up to 850-1,000 microns
are available and supplied as a dry powder that can be easily mixed into
coatings, adhesives and oils. Just like clear polyethylene microspheres, opaque
grades are inert in most solvents.
Cospheric uses eco-friendly manufacturing practices. There are absolutely
no solvents or waste in the spherical microparticle manufacturing process.
Microparticles that do not meet tight specifications are recycled back into the
process.
Orientation of Dual-Functional Microspheres in an Electromagnetic Field
High-quality,
dual-functionalized microspheres recently became available on the market in
bulk quantities and reasonable prices. There are numerous applications for this
amazing product, with most of them still waiting to be
discovered.
One particularly interesting and unique feature of these miracle microspheres
is their ability to orient themselves in response to electromagnetic fields and
show a visual response. This is achieved by making spheres both bipolar and
bichromal, with dipole precisely aligned with two differently colored
hemispheres. Due to the dipole the sphere will rotate in an electromagnetic
field to align the more positive hemisphere to the negatively charged stimuli
and vise versa. As the spheres align themselves, the viewer will observe the
color of one hemisphere, while the other hemisphere will be hidden from view,
providing an obvious strong visible indication of the presence of the field. In
an alternating electromagnetic field, these microspheres can spin at hundreds
of times per second.
This superior functionality is achieved with a proprietary and patented process
that allows extremely precise coating on one hemisphere without affecting the
other. Each coating is custom formulated for color, charge, magnetic, electric
and surface properties, and solvent resistance per customers’ needs.
Hemispherical coatings of less than 1 micron with tolerances as low as 0.25
micron have been routinely demonstrated. Color combinations are truly
unlimited. White, black, silver, blue, green, red, yellow, brown, purple as
well as transparent microspheres have been made. Sphericity of greater than 90%
and custom particle size ranges are offered.
The spheres were originally developed for
very high-tolerance electronic paper reflective digital displays, where
functionalized microspheres are used to create an image that appears to the
viewer. To achieve high resolution in display applications it is critical that
every single sphere responds to the electromagnetic field in the same way at
the same time and aligns precisely with the other spheres. It is also critical
that there are no color gradients in the display.
High-quality opaque polyethylene microspheres are now available in sample and
bulk quantities and reasonable prices to scientists and engineers who would
like to add color and functionality to new generations of their products.
For more information, visit www.cospheric.com
or call 805/687.3747 to discuss your application.
Yelena Lipovetskaya
CTO, Cospheric LLC, Santa Barbara, CA
Original Article Printed in PCI Magazine, January 2010
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