Nissio Gravure Co., Ltd.’s new MULTI EX was developed to further improve the quality and ease of use of their gravure proof presses. In the previous article, we looked at the background to the development and some of the advantages of this machine, the most important of which is the proof press’s ability to increase the operational ability of the production machines. In this article, we will look at the specific modifications that were made to develop the MULTI EX.
Nissio Gravure began by focussing on solving some of the problems found with the existing MULTI proof press. The first of these was that the CCD camera for printing registration was fixed on the left side of the machine, as was the monitor. Although Nissio Gravure engraves printer’s marks on both the left and right side of their printing cylinder, some of their customers only engrave printers marks on one side of their cylinders. As such, when a customer would request that they place the monitor on the right side of the machine, they would simply install a second monitor on that side. In the new model, the CCD camera and monitor are attached to a common guide rail so that both can be shifted to the printer’s marks positions on either side of the printing cylinder.
Naturally, only one monitor is required and it increased the size of the monitor from 13 inches to 19 inches. At the same time it upgraded the CCD camera from monochrome to color, allowing the printer’s marks to be more clearly identified for registration.
The MULTI proof presses installed at Nissio Gravure can only handle cylinder lengths of 1,100 mm, or a maximum length of 1,150 mm, but the new machine can be mounted with 1,300 mm long cylinders. A jig can also be attached so that the machine can be mounted with shorter cylinders having a minimum length of 700 mm. MULTI proof presses sold to other companies can typically handle cylinder lengths of 900 to 1,300 mm.
Functionalized touch screen operations panel
Mounted on the right side of the machine, the control panel, which had previously been an analog system, is now a touch screen with greater functionality. Specifically, the printing pressure (MPa), doctor pressure (MPa), printing speed (metres a minute), assist pressure (MPa), register calibration value (PLS), and doctor angle (degree), can be directly inputted using the touch screen. The setting conditions, which had been recorded by hand in the past, can now be stored in the sequencer memory.
The touch screen can also display settings from the previous two jobs, making changes from earlier jobs easy to recognize. The settings can also be saved by inputting a code number. These data can also be saved on the sequencer’s SD card so that they can be easily modified on a PC. Previous setting data are also recorded, which can be recalled and displayed on the screen by inputting the required job product code (maximum 11 digits).
Touching the desired cylinder number on the screen, for example No. 6, moves the cylinder into the printing position and stops the cylinder at the desired location. Previously, each cylinder had to be set individually in order.
The number of colors has also been increased from eight to nine, but if requested, Nissio Gravure says that they intend to build and supply proof presses for printing up to 12 colors. The MULTI EX proof press, like the MULTI proof press, however, is only able to hold eight cylinders at one time due to physical limitations. When printing the ninth color, for example, the operator selects the No. 9 cylinder from the touch screen, after which the machine removes the fourth printing cylinder, located opposite the eighth printing cylinder, and sets in the ninth cylinder for printing. To print ten colors, the third printing cylinder is replaced with the tenth cylinder, and so on. This function was designed to work with the newer gravure printing machines which print using more colors.
Push-pull air curtain
One approach Nissio took to improving the work environment was to strengthen the local exhaust capability. The conventional machine also has a local exhaust duct, which draws the volatile organic compounds (VOCs) generated during proof printing out of the proofing room using a blower. The new system reduces the risk that proofing workers will be exposed to the local exhaust by blowing an air current through a slit located above the proof press. This air current is then sucked out of a slit at the bottom of the machine in a push-pull method that creates an air curtain.
Minoru Nishino, managing director of Nissio Gravure, explains that previously there would be a solvent odour below the impression cylinder after proof printing, but the new approach reduces this odour. Specifically, VOCs are likely to diffuse when the tiny volume of ink is supplied to the space between the printing cylinder and doctor blade and before it is transferred to the film fixed to the impression cylinder. As such, the machine has a separate suction slit at the bottom of the printing unit, which creates an air flow that exhausts the solvents so that the VOCs are mostly sucked into the local exhaust duct. This push-pull air current flows simultaneously with the cylinder rotation and prevents any odour from diffusing. The strength of the air can be manually or automatically controlled from the sub-control panel.
Near-production quality at 80 metres a minute
MULTI EX has not only been improved in terms of ecology and safety; the registration precision is also better than the conventional machine. According to Jun Ito, one of the operators, although gravure printing machines operate at 150 to 200 metres a minute, MULTI proof press printing speeds are generally 60 metres a minute. This is a problem because at low speed the adhesion of mid-tone inks is poor. Moreover, over-printing white ink on the highlight sections can cause ink lifting or result in dissolving caused by ink back trapping. In contrast, MULTI EX is able to print at speeds exceeding 80 metres a minute, so the ink adhesion of mid-tones and the halftone highlight sections are more similar to those of production machines.
It has also made improvements to the impression cylinder blanket. According to Mr. Tochizawa, the older machine uses a rubber blanket with a cushioning property, but the high printing pressures mean that the blanket will stop returning to its original thickness after about six months. Therefore, the new machine uses a blanket made of rubber without a cushioning property for the surface and a cushioning material for the underside. Whereas the conventional machine used a driven impression cylinder to drive the printing cylinder, MULTI EX uses driven impression and printing cylinders, which eases registration. Specifically, driving both cylinders mitigates the problem of cylinder slipping, which was seen in the older machines when printing full-coverage inks.
Thus far, renewal demand for delivered MULTI proof press has been non-existent. Although this fact is frustrating for Nissio, it also proves the high reliability of the machine’s precision. Because gravure proof presses are not production machines—the new MULTI EX being no exception—it takes a significant amount of time in Japan before a company will make a purchase. On the other hand, although it can be difficult to sell the first machine to a new customer, those that have installed a unit and verified the results come back for more, with some companies having installed 10 machines. This gives Mr. Ako the confidence to say that once a company installs a new MULTI EX they will install more. Mr. Ako also says there is room for growth in the global market and so he has high expectations for both MULTI and MULTI EX.
Mr. Ako closes by saying that although the next generation MULTI project members wanted to implement all of the ideas they received, given the fact that they kept the structure of the original machine, they had to make choices. In fact, there were even conflicts between the project members who wanted to realize all of these ideas and those on the production side. Even though the company was not able to implement all of these ideas this time, they hope to take the ideas that they were not able to implement and use these to develop peripheral equipment in the future.
Reprinted by permission from Convertech and e-Print, July-August 2015