The Mystery of the Declining Print Plate Durability

As is well known, the factors that mainly affect the print plate's durability include excessive pressure from the inking rollers on the plate, excessive cushioning of the blanket, too much fountain solution, wear and play in the machine's cylinder bearings, uneven photosensitive coating on the plate, and excessive accumulation of paper dust on the blanket. The situation we encountered this time is relatively special, and the specific circumstances are as follows.

In late December last year, during the peak season of book and periodical production, our company's two 4787 eight-color web offset presses ran continuously day and night. However, the press operators generally reported that the paper quality was not very good, and there was a lot of paper dust on the blankets. When touched by hand, it felt like a layer of sand (which was actually coarser pulp fibers), causing severe wear on the plates and low print run durability. Usually, after about 40,000 to 50,000 prints, a new plate had to be installed, especially for the lower group, which required more frequent plate changes. As a result, daily machine output could not increase, seriously affecting the production schedule. Since paper turnover also required some time, everyone had to grit their teeth and continue using this batch of paper until it was finished.

Five days later, we switched to a high-quality domestic brand of paper, but the situation still did not improve significantly. Strange? The current paper quality is absolutely fine, so why can't the print plate's durability improve? Could it be a problem with the press operators' operation?

With these doubts in mind, we sequentially checked the fountain solution ratio, the pressure of the inking rollers on the plate, the blanket cushioning, etc., and found no issues. The operators also assured us that all adjustment data were the same as last quarter and could not have been changed arbitrarily. After much consideration, we compared the old plates from the previous batch with the current old plates and found that the surface wear was similar, with shallow vertical scratches. Obviously, the plate wear still existed. After ruling out factors such as paper and machine adjustments, the only components in close contact with the plate were the plate rollers. We initially concluded that the coarse fibers from the previous batch of paper had been continuously transferred to the plates and rubber rollers via the blanket. After millions of rotations and compressions, these fibers had become firmly embedded in the surface of the rubber rollers, as shown in Figure 1.

Figure 1 Rubber roller surface pressed with coarse fiber sand particlesSince time was limited, we first conducted experiments on the lower set of the first color group, replacing two backing rollers and wiping the other rubber rollers clean one by one, and then started printing. After half a day of testing, the printing plate's durability returned to normal. Then, the backing rollers of the remaining sets were replaced one by one. At this point, the problem of printing plate wear caused by coarse fibers in the paper was finally resolved.