Weyerhaeuser increased pre-press production by 100 percent, cut downtime between runs, reduced pre-press waste and improved safety with a new digital vision plate mounter/proofer system.
Flexographic printing has long been considered a low-quality printing system, but a mainstay for the printing of packaging containers, including flexible packages like food bags, shopping bags and self-adhesive labels. Technical developments over the past few decades in the flexo printing process have improved print quality, by enhancing the ability to reproduce highlight tonal values - working around the very high dot gain associated with flexo printing, and by making accessible four-plus-color applications. But the systems for the mounting and calibration of flexographic plates onto printing cylinders have not evolved enough technologically to provide for quick and highly accurate mounting of the flexible printing plates.
Plate Mounting Bottleneck
The quality of a flexo printing job depends, to a large degree, on the care in which pre-press preparations are carried out. This includes mounting the flexible plate on the printing cylinder, checking color registration and proofing. The mounting of the printing plates onto printing cylinders requires a high degree of alignment accuracy. The image on the printing plate must be perfectly square and in register with the printing cylinder in order to print clearly. The arrangement of the printing plates in the exact predetermined relationship with one another requires that their position be accurately determined prior to mounting.
After the plates are mounted onto the cylinders, the printing press operator must stop the press to examine the print results for acceptability. If out of registration, the operator must remove the plates from the cylinders and start over from the beginning. This activity is very time consuming resulting in substantial press downtime.
A common method to mount and align the printing plates on the printing cylinder involves the drawing of a line around the printing cylinder. This line is then aligned by eye with a longitudinal line along the length of the photopolymer or other printing plate. The plate is then wrapped around the cylinder. This method is somewhat accurate but can be extremely time consuming for the operator, leading to delays between print runs.
Other plate mounting and calibration systems have been devised for flexo printing using manual or semi-manual systems, such as employing rods for rolling the plate onto the cylinder, light projection to position the plates, plate vacuum suction devices, and registration pins and holes to align the plates on the cylinder. Each of these methods have proved error prone in registration.
In response to these challenges, Leader Engineering-Fabrication, Inc. developed a new high-tech, fully-automated, digital system of plate mounting and proofing for use on flexographic printing equipment. The system, called theVision Plate Mounter/Proofer, delivers quick and precise mounting for both horizontal and vertical alignment, accommodates a variety of different sizes of printing plates and cylinders, and is also easy to operate.
Passing the Field Test
Leader’s digital system was tested and ultimately selected by Weyerhaeuser Co. as the plate mounter/proofer system of choice for use within several of its flexo printing facilities in the United States.
“We were looking for increased throughput and improved quality in our mounting area because of the constraints that mounting was having on our printing presses,” says Harry Matthews, superintendent of the Weyerhaeuser pre-print plant in Tucker, Ga. “We are challenged with shorter lead times, smaller order quantities and tighter registration, and we felt that the Leader Vision system could address all of these issues at the same time. We purchased one of these mounters back in 2005. Initially, we looked at the machine because our Hillsborough sister-plant in Oregon had been using the same machine for about three years and done real well with it.”
Previously, the mounting process took more than one hour foe one plate.
“With the Leader machine, they can do it in about ten minutes. From a quality standpoint, one of our biggest downtime problems was sending jobs to the printing press that were not in registration, or were not quite right, and we would have to go back and re-work it. With the Leader machine we can actually see mathematically before we go to press whether or not the plates are in the proper position,” he adds.
The pre-press workers have the ability to stop and re-work something before it goes to the press, saving substantial downtime.
“The machine measures four decimal points to the right, so it is extremely accurate,” Matthews says. “The tolerance of that machine is well beyond the tolerance of our printing presses. So, if we can get a job mounted correctly on the Leader, then we know it will run efficiently on the press.”
The company has experienced a sizable improvement in the number of jobs delivered to the press, which affords the printer more run time, resulting in customers receiving a better product.
A Better Mounting SolutionThe Leader system is a state-of-the-art vision system capable of mounting almost every type of flexographic printing plate. The computer and its software take electronic data from the art department and send it directly to the mounter/proofer computer to mount the plate with only two clicks from the mounter operator. It utilizes a dual camera system, with a large view camera that locates microdots or reference points on a pre-press table holding the plate to be mounted.
The narrow view camera then magnifies the microdots 70 times and pinpoints the exact center-point for accurate registration. The plate is then positioned, and the system brings the plate up against the press cylinder with a pressure roller and applies the plate exactly to a corresponding micro-dot position on the press. Operator variations are removed because this system does not require the operator to position the microdots.
Unusual with plate mounting and proofing systems, the Leader machine ensures good prints from the first revolution of the print cylinder. Excessive plate handling, which causes damaged plates, is eliminated, as is misalignment of plates due to parallax from positioning of the human eye. Vacuum grooves secure the plate to the pre-press work station, eliminating punch holes.
Tighter Plate Registration & Production Downtime ReducedThe Leader Vision system is so tight on its registration that Weyerhaeuser has uncovered tolerance aberrations in its printing plates that it did not realize existed while using its prior manual plate mounting method.
“We are working with plates that are 50-inches x 80-inches in size, large sheets of material,” says Matthews. “It is not unreasonable to think that there was going to be some tolerance variations in the plate making process. The plate makers can introduce variation in the way the plates are made: the timing of the exposure, the timing of the washout, the timing between the washout and the drying, etc. If these sequences vary at all in the plate manufacturing process, then one plate will be longer or shorter than the other.
“These variations affect the registration on press, which are not always evident in traditional mounting systems. The Leader equipment showed up the aberrations immediately, and allowed us to compensate for the deviations accordingly. It really brought it to our attention how much unknown variance was occurring on our prior system,” he says.
The amount of time it takes to get a job on press is typically the same whether it is a one-roll job or a twenty-roll job. Weyerhaeuser runs a lot of smaller orders of one and two rolls. Instead of spending up to four hours mounting plates for a new one- or two-roll job like before - and running another job as a fill while the next job is being set up - they simply pull the cylinders out of the press, go back to the mounter and have the cylinders back and ready to go back on the press in a fraction of the time. Down-time has been greatly eliminated with the Leader system.