Printech Archive, February, 2000
Reduction of VOCs from Flexography


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From: Wayne Pferdehirt (pferdehi@epd.engr.wisc.edu)
Date: Fri Feb 04 2000 - 08:20:48 CST


I am forwarding a question and response from the P2Tech listserv. Do
any
Printechies have any further suggestions? I will forward posted
responses
to the P2Tech listserv.
-Wayne

>X-Authentication-Warning: superior.great-lakes.net: majordom set sender to
>owner-p2tech@great-lakes.net using -f
>Date: Tue, 1 Feb 2000 23:42:59 -0500
>To: "Logé, Hervé" <Herve.Loge@cum.qc.ca>
>From: wjw5@email.psu.edu (Warren J. Weaver)
>Subject: Re: Flexography
>Cc: <P2tech@great-lakes.net>
>Sender: owner-p2tech@great-lakes.net
>Reply-To: wjw5@email.psu.edu (Warren J. Weaver)
>List-Name: p2tech
>X-Loop: p2tech
>
>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
>
>Recycle Electrons
>Use E-commerce

Wayne P. Pferdehirt
Director, MEPP, http://epdweb.engr.wisc.edu/mepp/
Co-Director, PNEAC http://www.pneac.org
Specialist, SHWEC, http://www.uwex.edu/shwec/
tel 608.265.2361
fax 608.262.6250


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