Optimizing the Performance of Your CTP Plates

Computer-to-plate (CTP) printing proves its value to printers every day. The latest refinements in CTP let you spend less for pre-press and plate-making and get your plates on press faster.

At the same time, printers often face problems with runnability and compatibility. Most involve incompatibility between the new, "unbaked" CTP plates and the fountain solutions, plate cleaners and press washes developed for "baked" plates.

Suppliers of pressroom chemicals need to find innovative ways to make their products work more effectively with your CTP plates, finding ingredients and combinations of ingredients that do the job effectively and economically without interacting negatively with plates. The answers can make a huge difference in helping you get more from CTP technology.

Most CTP plate runnability and compatibility problems fit into one of three categories:

1. Image loss: Chemical attack on the image area caused by incompatible chemicals.
2. Ink/water balance: CTP plates often have a narrower "operating window" between sensitivity and ink washout.
3. Plate sensitivity: The newer CTP plates are more sensitive than predecessors.

Image Loss

In most cases, image loss is caused by aggressive polar-type solvents, especially glycol ethers and isopropyl alcohol. Reducing or eliminating them in your fountain solutions, plate cleaners and press washes will probably be the most important thing you can do to prevent or improve image loss.

• Fountain solutions. Replacing glycol ethers and alcohol with surfactants, surface tension modifiers and/or other compatible solvents reduces or eliminates image loss.
• Plate cleaners. Alkaline cleaners are usually the culprits. Use acid/emulsion type cleaners instead. There’s a trade-off: acid/emulsion cleaners don’t cause problems but they aren’t usually as effective. You can’t have it both ways. You have to make a choice.
• Press washes. Check out your wash’s MSDS. If it contains glycol ethers or alcohol, stop using it. For instance, water-miscible washes are notorious for containing glycol ethers and/or alcohol.

Conventional press washes that don’t use these solvents cause fewer problems and are usually just as effective in every area except removing paper coatings. In those cases, it will take a little more elbow grease to do the job, but the end result will be the same. Adding a small amount of water to the wash will usually make it more effective in removing paper coatings.

Ink/Water Balance

• Fountain solution. Optimizing fountain solution chemistry is crucial to keeping the narrowed "operating window" as far open as possible. Work closely with your pressroom chemistry supplier to ensure that you’re using the right combination of ink, fountain solution and water.

This is an area where constant vigilance and routine maintenance play a big role. Monitor pH and conductivity at least daily and maintain fresh chemistry.

Plate Sensitivity

CTP plates are more sensitive than other types. Using new-age desensitizers and polymer film formers will help keep your non-image areas clean and desensitized.

• Fountain solutions are key. The big thing is preventing ink breakdown and image attack. Changing to a less acidic formula reduces ink breakdown and image attack. Your ink/water balance also will remain correct longer.

Changes in CTP plate technology will continue for a long time to come. With those changes come opportunities and problems. Today’s solutions probably won’t work forever, but if your suppliers of pressroom chemicals are on their toes, they’ll keep finding new ways to help you optimize the printing performance of your CTP plates.