The different styles of paper on the market today introduces many challenges for printers. First of all, try to match your paper with your ink. If you are printing on styrene (or any synthetic paper), you must use an ink that will dry by oxidation. These inks are typically called non-porous inks are available from any reputable ink manufacturer. Be sure to wash your ink off the rollers as soon as the job has beeen completed—or you will be using a chisel soon.

We find that all inks are not drying like they used to. We have also found that the paper companies are using less pulp and more filler compounds (calcium carbonate), selling the paper at a higher price and claiming that the paper is whiter. True, it is, but the paper is more difficult to finish (more prone to cracking) and that inks don't dry as well. The calcium carbonate will change the Ph of your water and will build up in your rollers.
It is my opinion that ink companies haven't caught up to the changes in paper and that the paper companies are making a lesser product than they used to. That the increase in calcium carbonate in paper is creating a drying problem, keeping inks soft longer and reeking havoc on print shops all across the board.

As with all litho inks, the ability for the emulsified fountain solution to be carried completely out of the ink is necessary for ink to set. Be sure that water and ink trains in your print units are maintained and set properly to help pressman run minimum water and ink balances to achieve the desired ink density. Also, work with your ink supplier to insure that your inks are formulated for the proper water holding properties for your particular application. Even slightly over emulsified ink can retard dry times enough to cause a problem through the bindery process in a rush situation.

I recently had this problem and added a Harris and Bruno IR dryer to my Ryobi. It was a great value and really improved the quality of my jobs.