<H1><B><center>Controlling Static Electricity in Offset Printing</H1></B></center>

Static electricity in paper can be controlled whether you work on a sheet fed or web offset printing press.  I have worked on both and during the dry weather it can make for terrible running conditions.  But you can't control the weather so you must resort to other ways to manage static electricity on your offset press.  

There are three main problems that static electricity causes. Here they are:

• Shocks to workers (all)
• Sheets double feeding (sheetfed)
• Jams (on all offset presses, bindery)

In my experience, these are the main causes of static electricity in offset printing:

• No grounding of the equipment. On days where it is particularly strong, properly grounded equipment will make a difference and dissipate the electricity. 

• Low humidity: Static can build on a sheet or web as it travels through a press.  This happens particularly in dry weather. This is because the water in the air conducts electricity and when the sheet comes in contact with it, the charge dissipates.  Not so in dry weather.

• Pressure - Paper is considered a semi-conductor of electricity.  The more that a stack of sheet is compressed, the lower the conductivity will be.  So the higher the stack of paper, the more compressed it will be. This causes static particularly at the bottom of a pile. Many sheet fed offset press operators will fan out these lower sheets before loading to reduce the static.

• Climate.   Since you can't control the weather, you need to create it. This is closely related to the low humidity point, but includes temperature.  Relative humidity is a huge factor in controlling static electricity.

• A combination of everything.  Usually it is the perfect storm that hits.  All of the above come into plate. On those days being a press operator is no fun.

Now let's talk about how to control it.  We have used all of these ways in our press room.  Even when printing with aqueous coatings (which hold a major static charge after being cured with UV light) they have helped.  Here are the top ways of controlling the static charge:

How to control static electricity on your web and sheet fed printing press.

1. All press and post-press equipment should be grounded.  A steel rod in the ground that goes quite deep, more than 6 feet (this is important to be effective).  On web presses, this is particularly important early on in the press line, such as the roll stands. There may be local electrical standards to comply with as well.

 

2. Install a complete climate control system with humidifiers.  These are considered the optimum conditions:

• Relative humidity: 45% +/- 5 degrees
• Temperature: 70-84 degrees farenheit (21-29 celcius)

This is mostly done for sheet fed press rooms but the same applies to all forms of offset printing. 

Winter is the worst time for dealing with static in paper.  Higher elevations also tend to be dry.  If you live in a cold climate or high elevation, I recommend making the biting the bullet. It's one of those long term investments but pays back quickly in downtime and waste.

Climate controlled offset printing press room.

 

Tip: a cheaper solution to controlling the climate can work on offset sheet fed printing presses. Install an air ionizer in the feeder area of the press. I've seen them. They work great. An air ionizer produces a charge that repels the charged paper. As it blows between the sheets it negates the charge and allows the sheets to separate.

 

Air ionizer to reduce static at the feeder
of this offset printing press.

3. Static bars.  Another investment which is minimal compared with climate control. It is a simple bar that runs along the path of the paper.  Here is an example of what it looks like on a web printing press.

Anti static bar on web offset printing press.

We used to use these on our web offset press inline sheeter.  Two static bars that run along the length of the paper while it is moving. It is a high-voltage electric current to ionize the surrounding air.  They remove static where essential to prevent jams and allow proper stacking.  They can be installed at almost any point the paper travels.  Caution: the electric shock from them gives a good jolt.  Beware!

4. Copper tinsel.  Probably the cheapest solution but pretty "mickey mouse".  Copper conducts electricity very well.  If the strands are grounded and dragged along the path of the paper it can remove the charge. We have done it with good results. We used it on a web printing press as the paper leaves the folder and is going to the inline trimming system. They simply drag on top of the product.

We have also used it on the web.  It looks something like this:

 

Yes, I said it was mickey mouse. But it worked.

Here are some more tips:

• Do not use paper from rolls on a sheet fed. Web paper rolls are manufactured to a lower moisture content than sheet fed paper.  Some offset printers will cut these rolls into sheets to run though the sheet fed press - bad idea!  

• Keep paper in it's vapor barrier until it's ready to use.  Removing the barrier will cause the paper to lose moisture and have more static electricity. Have a paper moisture content reader.  They have come down significantly in price over the years.  Here is a good one that works well.  

• Mix a cocktail. If your offset printing press is a heatset web, you probably have some sort of silicone applicator.  Try adding a fabric softener to the cocktail.  We use Downy. It makes a big difference.

So that's what I've seen in my experience that has gotten results.  I hope you find something helpful.