Big Presses Need Roll Attention

Large publishing houses are buying big presses or specifying their use for the long-run publication grades' "bread and butter" work. The new, oversize presses greatly expand capacity, doubling it in some cases, which has a big impact on ordering, storing, and moving paper rolls to and from the production floor.

Production quality can be affected, too. Big rolls running so fast and wide require even greater uniformity to avoid print quality variation, especially for centralized operations with big central distributions.

Papermaking has inherent natural variability because of the natural materials used in the process. Wood fiber, starch, and water are all natural materials that have some slight quality differences that can affect final product quality. Too, coating and filling materials like clay, carbonate, and titanium dioxide have some variability as a result of how they're processed, that is, crushing and refining steps that produce particle size differences and distributions.

The only material that is inherently uniform is latex, which is a synthetic chemical. Other synthetic chemicals like lubricants, dyes, and tinting agents are also purely uniform, as long as the kitchen staff makes them the same each time.

Because of these slight variations, and the pressroom's desire for unchanging quality from one roll to the next, paper mills invest millions of dollars in equipment to produce perfectly uniform rolls.

The paper machine itself can contribute to variability, particularly regarding the removal of water. Depending on the incoming furnish and the way the machine is running, there can be small variations in thickness (caliper), moisture, weight, and smoothness.

Computers scan the sheet in the cross- and machine-directions (CD, MD). When there is an upset, the computer sends a signal to an "actuator," a device that makes a small adjustment in a specific zone along the paper width. The actuator usually emits some form of energy like steam, infrared (IR) heat, or heat to a contact roll, which makes the change to the paper in just a few seconds.

These profiles, along with the two-sigma variation, can be made available to the consumer upon request. The goal is to make paper with a flat profile of weight, moisture, and caliper.

CD actuators are very sophisticated. For example, electric IR dryers can correct a moisture peak in milliseconds, while a coating head CD actuator can correct coat weight and thickness in real time. A roll produced with flat profiles has the greatest potential to best reproduce graphic images and text repeatedly on long print runs.

Bigger presses may use rolls of larger diameter and width. Many mills will have trouble cutting those larger rolls and may refuse because of the production of waste rolls.

The problem for pressrooms may occur in the tension settings, which may need adjustments more often. To reduce the need for adjustments, press operators use rolls along the positions in the tambour, which the mill marks. Using larger rolls will create more odd-position rolls.

Large rolls also will have more temperature variation through the roll, from core to the skin. Temperature and humidity control becomes more critical. The storage room should be 60°F to 74°F and 50% to 55% relative humidity.

If the pressroom is in a cold climate, the rolls may stay very cold at their cores, which can cause problems unwinding (you will hear your drives whining), and ink density may be affected. If the pressroom is in a humid climate, moisture will attack the outer paper first and the edges.

In both cases, condition the rolls by keeping them in their wrappers in a room with constant temperature and humidity for a few days. Repair any damage to the wrapper on the edge or shield immediately after it occurs or upon receipt.

The same procedure is advised for splicing tapes and tabs.

Most damage to rolls occurs when moved by a forklift. It is very important not to neglect the forklift driver's abilities. Training should be annual or better, and do not overtax the drivers with other duties.

Rolls should be stored on a clean, dry, level floor in a bright, open space with floor markings for use and storage. The rolls should be stacked on ends, evenly in the same unwind direction, with protective guards to prevent contact or leaning. Poor stacking may lead to warped rolls. Edge damage creates waste.

Try to use the whole roll at one time. It is better to run out the roll rather than store it. Once the wrapper is off and the roll is moved around, it will suffer damage both on the outside and will accept moisture to the core.

If you must store the used roll, take a wrapper and shield out of the waste and re-wrap the used roll. Use these first in preparation of splice patterns loaded onto the paster and run them for adjusting settings on press.

All rolls should be documented when received and consumed. This data should be communicated with the paper sales representative periodically for review. This evaluation should lead to recommendations and improvement in roll usage, which is important when moving onto larger presses.