Converting considerations for flexible materials
Converting considerations
for flexible materials
by Josh Chernin, Web Industries, Boston, MA, USA
‘Converting’ refers to the manipulation and selection of blade geometries and depths,
The thin-film photovoltaic finishing of flexible materials. It encompass- and sometimes by either contact- or non-
(TFPV) industry is beginning
es processes such as slitting, sheeting and contact web cleaning systems. Thin films are
to scale up. Hundreds of mil-
traverse winding; coating, printing (includ- susceptible to dusting, especially hard-coated
lions of dollars are being in-
ing conductive printing), laminating, and as-
films, and they are also subject to some
vested in production facilities.
sembly of multi-layer substrates; die-cutting,
edge fracture. Dusting causes subsequent
Much attention is going to
encapsulation, and similar processes. Other
problems in downstream operations such
the front-end (the chemistry,
industries have failed to consider these
as printing, coating and laminating, and
physics and efficiencies of the
aspects of the process until it was too late
fracture can sometimes be fatal to the per-
to design for optimal manufacturability and
formance of the films. In addition, belling
films and the production of
lowest cost. Avoiding this error will be espe-
(lipping at the edges of a slit roll, indicat-
the films themselves) and to
cially important in industries such as TFPV,
ing uneven rewind tension, unsupported
the back-end (integration into
where the substrates are generally produced
edges in the slitting process or uneven blade
finished products and utility-
at fixed widths and require conversion
depth) can put a permanent ‘set’ into rolls
scale installations, and retail
before integration into final production.
that cannot be erased or easily dealt with.
economics), but sometimes
The best place to start is ‘with the end
Rewind tensions need to be high enough to
less attention is paid to the in mind.’ TFPV companies should consider
insure the integrity of the package, while low
steps in between, including the entire range of end-products they plan
enough to not deform the materials. Metals
the converting of the flexible
to bring to market before designing their
can generally be rewound at higher tensions
converting capabilities. They should build as
than films.
materials.
much flexibility into converting capabilities
When the converting of TFPV re-
This article will examine
as possible in order for this function not to
quires coating, printing or laminating, it is
some of the more important
be a bottleneck in either production efficien-
important to recognize the differences in
considerations that go into
cies or in the ability to bring products with
the requirements of these materials versus
these intermediate process
new configurations into the market.
what might be expected from more common
steps, including technical and
So, for example, in choosing a method
flexible substrates. The printing and coating
economic aspects, some of the
of sheeting, they may want to consider
that people are more familiar with are often
hidden costs, and the pros
having both programmable blades in the
trying to achieve an aesthetic objective that
and cons of outsourcing this machine direction and a programmable guil-
can be subjective. This is not the case when
important suite of manufac- lotine in the cross-machine direction. This
you are trying to accomplish functional
turing capabilities.
combination will provide almost any size
electrical properties. The materials being
sheet. Similarly, those TFPV companies that
printed or coated and the coatings being
are using glass as a carrier may find that this
applied are often novel and unique and have
limits flexibility downstream and may want
been developed to produce specific effects.
Keywords: Flexible Materials,
to consider a true roll-to-roll process.
Whenever possible, the chemistry being
Slitting, Sheeting, Spooling,
In general, the thin-film products need
applied should be modified to promote its
Printing, Coating, Laminating,
to be kept clean and should be run in a
uniform metering and transfer throughout
Die Cutting
cleanroom. Static needs to be minimized,
the metering and application process. Many
because it will attract dust. Plastic cores
coatings are developmental and have been
should be made of materials that don’t
formulated for electrical properties without
cause static, or coated with anti-stat coatings;
regard to the rheology and surface energy
rewinds with various cores ‘clutching’ at dif-
needed for optimum transfer and leveling
ferent rates are notorious sources of static.
needed for printing or coating. Firms should
Some films are sensitive to arcing caused
select methods that don’t compromise the
by static electricity, and there are a number
sometimes delicate properties of the base
of methods to deal with that. Some are
substrate or the functional characteristics
sensitive to humidity; they can literally grow
of the ink or coating. Printing and coat-
in a humid environment.
ing methods that achieve a degree of shear
Other considerations include the quality
during the metering process will achieve a
of slitting, especially the quality of slit edges.
smoother and more uniform result, but one
Slitter dust needs to be minimized by careful
must be careful that this does not negatively
18 – Global Solar Technology – November/December 2008 www.globalsolartechnology.com
issue_2.1.indd 18 2/22/09 9:39:55 PM
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