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Opaque Microspheres for Coatings

Opaque Polyethylene Microspheres for Coatings Applications - PCI Feature Article - Jan 2010



Hemispherically-Coated Bicolor Microspheres, Microparticles

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

Opaque White Microspheres for Coatings Applications

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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