Ask NHGAA's Experts

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NHGAA is a network of resources for our members and industry participants. Below are many frequently asked questions. If you have a specific question that you would like answered, please email us here: Ask NHGAA!

Q: What is the cause of Scumming?
A: Scumming is caused by the ink adhering to the non image areas of the printing plate. It is usually caused by running too little water or not enough acid, gum or both in the fountain solution.

Q: While running a job the ink would not flow to the ink ball. Why?
A: Ink hanging back in the fountain is usually caused by too high a yield factor in the ink. The problem can be fixed by adding a small amount of alkyd, linseed or similar material to the ink.

Q: At what humidity level should I try to keep my paper at so as to avoid problems with static?
A: Paper at humidity less than 35 percent becomes less electrically conductive and can no loger dissipate it's electical charge, causing static build-up.

Q: What could be the cause of non-uniform ink coverage especially printing in the solids?
A: You are probably seeing a mottling problem. This is usually caused by an uneven absorbency of the pager. You may be able to solve this problem by increasing or decreasing the body of the ink so that all the will be either held out on, or absorbed by, the paper.

Q: What is the cause of ink piling on the blanket?
A: Piling will usually occur if the ink lacks the proper amount of varnish, contains too much dryer or is emulsified.

Q: How can I stop the image from transferring to the back of the sheet on top of it in a pile?
There are several simple solutions to your setoff problem. Increasing the amount of spray powder or using a courser powder are the easiest. Use of infrared dryers to accelerate the ink setting time is also an option.

Q: We are experiencing a problem where ink is stripping off of the rollers. What is the cause?
A: Common caused of stripping are glazed rollers, too acidic fountain solution, over emulsified ink or insufficient ink on the rollers. Try deglazing your rollers with a deglazing compound or acetic acid. Also, keep your fountain solution pH between 4.0 and 5.0.

Q: What can cause overall plate scumming, loss of image and loss of image clarity?
A: It appears you have a plate wear problem. This can be caused by excessive plate to blanket pressure or having your form rollers adjusted too tight to the plate. Too acidic a fountain solution or under developed plates could also be the cause.

Q: What is cause of ink misting at the nip of the ink rollers and what can I do to minimize it?
A: Misting can be caused by too much ink on the rollers, too low a viscosity of the ink or excessive press speeds. Misting can be minimized by reducing the amount of ink in the ink train, increasing the body of ink and slowing the press down.