Pittsfield, MA-The coated diffuser films used to mange the light in liquid
crystal displays can give manufacturers a real headache. Usually made from
polyester film coated with micron-sized optical beads, these films can lose bits
of coating and develop optical defects as they make their way through the LCD
manufacturing process, driving down yields substantially. GE Advanced Materials
has come up with a new line of polycarbonate diffuser films that can eliminate
these coating-related failures.
Called Illuminex and based on
Lexan optical quality polycarbonate, these monolithic diffuser films have no
coating at all. "There's nothing to flake off," says Todd Hoff, industry manager
for displays. Instead of the coating, Illuminex films get their optical
properties from two proprietary technologies developed by GE scientists. The
first uses additives to incorporate diffusion properties into the resin itself.
The second involves a surface modification to the films as part of the
melt-calendaring process. According to Hoff, this texturing process creates a
"random surface profile" that helps distribute light evenly, one of the primary
functions of diffuser films
In terms of optical performance-which LCD makers measure in terms of "hiding
power, luminescence, and viewing angle-the Illuminex films "meet or exceed the
performance of coated products," Hoff says.† And the films may offer
another kind of performance edge as well. With an HDT of about 135 C, versus
80-85 C for many polyester products, the new Illuminex films promise to do a
better job resisting the permanent waviness that can develop when displays go
into high-heat and -humidity environments.
But it's in the yield department that these films really start to shine. A
handful of display makers have quietly adopted GE's new technology over the past
year and generally seen 10% yield improvements, Hoff reports.† "That all
comes down to the elimination of coating failures from handling," he says. There
are other sources of coating failure too, such as CTE mismatch between the
coating and film substrate. Overall yield losses from diffuser films can top 20%
in some operations.
GE has developed several grades of Illuminex films for use as bottom and top
diffusers in a wide variety of consumer electronics and automotive displays.
Current products come in thicknesses of 127 and 203 microns for products ranging
in size from PDAs up to large television sets. Right now, there's no Illuminex
product for the smallest displays, such as those used in some cell phones, but
Hoff says these are in the works.
For more information, go to www.geadvancedmaterials.com.
Illuminex films do away with the coatings
that typically give LCD diffuser films their optical properties. Instead,
GE scientists came up with proprietary technologies to modify the polymer
used in the film as well as the surface of the film.