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Re: Flexography



I can only give you general responses. First, if the ink is water based,
there is no savings in VOC emissions.

Second, if it is solvent based, there is a savings. The savings is related
to the film thickness of the ink or coating transferred to the substrate
with each method. If the film thickness is identical, no savings. If, as is
often the case, the film thickness is greater with a two roll system than
with a doctor blade system, there will be a savings. A rule of thumb (but
with a wide range of variability) is that a two roll system will apply a
film three times as thick as would a doctor blade system. Assuming the same
VOC content of the ink, there would be a 2/3 reduction in VOC emissions.

One must be quite careful in making these generalities, however. The goal
of printing is to place an image on a substrate that has certain visual and
technical characteristics. If a printer reduces the ink film thickness by
2/3, he also reduces the amount of pigment transferred, resulting in a
washed out image. Now he must modify the ink formulation to compensate for
low ink density, which then causes performance problems on the press,
requiring even more adjustments. Only after all adjustments have been made
can you again attempt to make a comparison. Now all bets are off as the the
% savings (there will still be some, but it will have to be measured
instead of estimated).

Regarding the rest of the questions, there will be savings with each. With
high solids inks, the reduction will be proportionate to the percent
reduction in solvent content. An enclosed chamber ink system minimizes the
amount of VOCs lost due to evaporation from an open tray or pan. The
evaporation rate times the surface area of the pan would give you a sense
of the amount of savings. Reduced volume anilox rolls place a thinner film
of ink on the substrate. The above discussion applies. Automatic viscosity
control systems improve color control on press. If one were using a manual
system, one would periodically add solvent to make an adjustment. If the
tendancy of the operator is to overshoot the solvent additions, more VOCs
would be emitted as the ink dries. If the tendency is to undershoot, then
less VOCs would be emitted. I've seen both. Automatic viscosity controls
are used for improved operational and quality control, however.

Hope this is helpful.

wjw/

>
>I am looking for studies on estimations (in percentage of reduction of
>VOCemitted) of P2 mesures in flexography, namely what is the percentage of
>VOC reduction due to the use of doctor blades in comparison with printing
>without doctor blades. Same question about : use of high solids inks, use of
>enclosed doctor blades chamber, use of anilox roll with reduced volumes,
>automated ink mixing system, automated viscosity control system, etc...
>
>Thank you for your help,

wjw5@psu.edu

Warren J. Weaver
PENNTAP
227 W. Market St.
York, PA 17401

ph: (717) 848-6669

fax: (717) 854-0087

website: www.penntap.psu.edu

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