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Question
#1137
Subject: We are having a problem of static charge in
BOPP
We need to know how the temperature and ambient conditions
affect the BOPP film roll. We are having a problem of static charge in
BOPP which gets neutralized sometimes when kept under airconditioning.
Also, we may need to look into anti-blocking agents and slip agents
for the sticking of the BOPP film during running on the machine. what
are the best methods of storing BOPP films?
Answers (links jump to full text of answer below)
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#1139
Author: Charles A. Bishop, C.A.Bishop Consulting Ltd.
Email: cabuk1@freenetname.co.uk
Subject: Static electricity is generated whenever two materials are brought together and separated.
Static electricity is generated whenever two materials are brought together and separated. Depending upon the materials involved will depend the amount of static generated. Materials far apart in the triboelectric series will generate more static than those that are close together. It is for this reason that walking on carpets can charge up a person so that when they reach for a metal door handle they get an electric shock.
Typically when winding polymers the rolls are either metal or rubber. The polymer web will charge up and retain the charge because the polymer is non-conducting and cannot dissipate the charge. Using static neutralisation can help. The static neutralisation may be active or passive. The active systems try to measure the amount of static generated on the surface of the web and produce just enough opposing charge to neutralise the surface to near zero charge. The passive systems just produce a set amount of opposing charge and hopefully it is near enough to offset most of the charge on the surface.
The amount of charge on the surface not only can vary with different materials but also is related to the humidity. A high humidity will lead to a lower static charge. This is because the moisture within the air can leak charge away whereas a very dry environment has not this leakage mechanism and so the charge generated retained on the surface will be much higher.
Thus there are a couple of things that are worth checking. One is that if the polymer web has had some static neutralisation, check where the static neutralisation is positioned. If it is not near the rewind it may well be that although immediately after the neutralisation there is little charge on the web once the web has been over a couple of more rollers it will have generated a new charge on the surface. The ideal position for the static neutralisation is immediately before the rewind roll. If it has been positioned elsewhere it may be that it has been placed there to assist in some other process such as coating & it may be that a second static neutralisation system is needed.
The other possible thing to check is the humidity control. It may be more comfortable to have a dry environment but it increases the static problem therefore a slightly higher humidity may be preferred.
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