Rubber rollers play an essential role in printing press performance. They are largely responsible for the proper transport of ink and dampening fluid to the printing plate.
Sheetfed rollers, running three shifts per day, five days a week or about 30 million impressions, should last about two years before replacement. Web presses, running a similar shift schedule, should last about one-and-a-half years. If you are not getting this performance from your rollers it may have to do with the quality of your rollers or the way your rollers are maintained. In order to learn more about how to get better performance from your rollers I spoke with Chuck Hands from Bottcher. Bottcher supplies rollers to many of the press manufactures and is a leading roller, chemistry and blanket supplier to printers around the world.
The major ingredients in rollers are polymer, vulcanization agents, plasticizer, filler and processing aids. Rollers are vulcanized during the manufacturing process. Both heat and pressure are applied to the rollers over time. This vulcanization process forms cross links that help lock the plasticizer into the rollers. A variety of things can cause the plasticizer to come out of the roller. This causes harder durometer, a tendency for shrinkage and a loss of good ink transfer. In a 25 durometer roller plasticizes can make up 46% of the roller.
Roller swelling is happening when you notice heat buildup, reduced ink viscosity and disturbance of water transport. This can lead to greater plate wear and eventually the destruction of the roller.
Roller shrinkage is happening when you notice insufficient ink transfer, “flaring” at the ends, increased need to adjust the rollers, increase in shore hardness. This will lead to poor ink transfer and destruction of the roller.
The chemistry you use on press can have a big impact on roller life. Press wash, fountain solutions, ink, and maintenance products all have an effect on the life of your rollers. Make sure all the chemicals you are using are tested by the roller manufacturer. If you change products have the new product tested before you use it.
If you view a new rubber roller under a microscope you will see a nap or “mountains and valleys” ground into their surface. This provides uniform ink and water distribution. Rollers should have a dull, velvety appearance and they should feel velvety smooth as you drag your finger across the surface. As plasticizers leave the roller, the roller can become hard and a glaze forms. This means you have to run higher levels of ink and water. In addition, dot gain, hickies, mottled solids and other unwanted problems may appear.
Roller glaze can be caused by a number of issues although improper wash up and over all cleanliness are the main culprits. Paper dust, residual chemicals, calcium from water or paper fillers can all contribute.
Consult your roller manufacturer for their recommended wash up procedure. Pressman may not be given enough time or may develop bad habits around wash up that greatly contribute poor roller life. Paste products are best used to deglaze rollers or help keep the plasticizers in the rollers. These should be used when the press will sit overnight or over a weekend. There are a variety of cleaning products out there to help keep rollers at their proper durometer. Again, make sure these products are compatible with the rollers.
Every time a roller goes in or comes out of the press it should be logged along with the reason the roller came out. This will allow you to evaluate roller life and see if you are getting the most from your rollers.
Pressrooms usually have durometers to measure the roller hardness. In order to get an accurate reading the durometer must have a weight on the top. Otherwise you can get variable readings on the same roller. The proper procedure for measuring durometer on a roller out of the press is to place the durometer on the long edge of the footer just off center line of the top of the roller. Keep the footer in contact. Roll forward to the vertical position parallel to the center line of the roller. Do not pass vertical. Do not rock.
Everyone is looking at how to get more out of their investment. Rollers are an investment in your printing quality and raw material usage. Proper wash up and care procedures along with a good quality roller will reduce your operating costs.