Splicing efficiency on coaters averages about 98%. Most papermakers use 2" or 3" wide single line splice tape products.
Variables that affect the splicing process include primary roll speed match, paster roll speed match, paster roll gap, paster roll pressure, paper caliper/hardness profiles, splice tape pattern and tail length. Primary roll speed should be set at 5-10 fpm slower than the coater speed to prevent a low tension wave from going through the coater that may cause sheet steering at the coating heads.
One way to control the primary unwind speed is the use of a laser surface speed tachometer. The initial primary unwind speed is established by inputting the roll diameter or inches of paper into the computer or by using an ultrasonic measuring device. Once up to speed the laser tachometer takes over and trims the speed to the desired speed setting. The desired speed setting is determined by analyzing high frequency unwind sheet tension trends during splicing (SIGMA data analysis software). If the unwind tension drops, the primary unwind is running too fast. If it increases, the primary unwind is running too slow.
Paster roll speed should be set at line speed - 0 fpm draw. Paster roll gap should be set at about 3/8" (10mm).
Paper caliper/hardness profiles are determined by watching splice failure modes. If the problem is splice tape not sticking in a certain area or folding over, this indicates that the primary jumbo roll is softer in that area. Most coaters will find they have to run a slight frown caliper/hardness profile to compensate for paster roll deflection during pasting. If the splice tape doesn't stick or folds over in the center of the roll, the ends are too hard, and the center too soft or vice versa.
Splice tape patterns vary by machine and mill. The most common pattern is a straight line of tape across the entire roll at a very slight angle. If edge pickup is a problem, try a pattern where the main tape run stops about 6" from the end of the pattern, with a short strip of tape that runs up at an angle to the edge of the roll. Or try stiffer pieces of paper located under the splice tape for better pickup.
Tail length should be controlled to about 25". Too long of a tail causes more wrinkles going through the coater stations.
For those that have jet applicator coaters, the jet will actually lift the tail off the sheet as it passes through one of the coating stations (tail side out) and slam it into the coating return plate. This causes CD accordion type wrinkles high in coat weight. The higher coat weight can deposit on rolls and felts down the line and cause pieces of the splice tail to get lodged under the coater blade. This causes wet lines that will either break the sheet or cause blade lines in the paper. An easy way to prevent this type of problem is to use a spray adhesive on the sheet just behind the splice tape where the tail will be. A good product for this application is 3M Repositionable 75 - similar to 3M's Post-it notes in a can. It doesn’t build up on any rolls or felts and does not affect repulping.
For more information about splicing, contact your Valmet representative.