Closed-loop color control technology during printing (1)

Industry people seem no stranger to the term “closed loop.” However, when it comes to the application of closed loop technology in print control, it is far from being familiar with the terms CIP3, CIP4, and color management. With the continuous improvement of society's requirements for multi-color and rapid short-run printing, people have put forward higher requirements for printing production efficiency. The pre-printing work preparation and test-printing time are more and more strictly controlled, so the automatic control of the printing process is It is very important.

For a long time, the automation of printing and related processes is a very important means for people to continuously explore for efficient and stable quality, and has achieved remarkable results. Automation was achieved in many areas such as paper roll bonding, automatic paper feeding, and postpress processing (such as stacking and shipping). Other aspects, such as automatic register control, were not available until after the closed-loop control system had emerged. Great development.

History background

In the control of printing quality, color control is a very important factor, and closed-loop color control is an important embodiment of the automatic control of the printing process. Since Gutenberg invented modern printing technology, people have paid great attention to the quality of printed color.

From the use of tools to monitor and control the quality of prints, people rely mainly on the eyes to subjectively evaluate colors using a magnifying glass.

In the 1930s, Frank Preucil produced the first printing densitometer to evaluate the printing color, which was an important milestone. However, the density meter had not yet been commercialized at the time.

In the 1970s, many brands of color measuring instruments (densitometers and colorimeters), such as Macbeth, Gretag, and X-Rite, emerged. Densitometry methods and tools began to be widely adopted by the printing industry.

In the 1980s, the color measurement technology used in printing was continuously developed. From the diversified functions of densitometers to the colorimeters that display test data and graphs on the screen, scanning color meters soon emerged, greatly improving the speed of color measurement and control in the printing process. The development of semi-automatic control technology for printing presses puts forward requirements for closed-loop control technology. With the overall development of the printing press and color measurement technology, the emergence of the concept of digital control, mutual consistency between different measuring instruments has also been emphasized and improved, such as the widespread use and recognition of CIE L*a*b*, at the same time, These standards and norms have been increasingly strengthened and promoted.

In the 1990s, a variety of color measurement instruments were widely used. The instrument itself was also cheaper, and the test was faster and easier to use. Color closed-loop control technology is used in web offset printing.

Closed-loop color control technology

The first-generation closed-loop color control system was introduced on Drupa 95. It was mainly used on rotary presses. According to statistics, starting from Drupa 95, about 300 sets of closed-loop control systems were installed on rotary presses. About 60% are improved installations on old equipment, and the remaining 40% are on new equipment. Of this, about 50% are used for publishing and about 30% for commercial printing. At Drupa 2000, sheet-fed press makers have developed closed-loop technology with real-world development. Printer suppliers pay special attention to the innovative use of closed-loop technology in the development of new technologies. Heidelberg, Manroland, Komori, Mitsubishi, and Agfa have all paid close attention to closed-loop technologies. Printing companies are also looking for tools that can help to achieve low-cost, high-efficiency, rapid, high-quality production tools. Minimize the "guess" as the goal of automated technology developed by the sheet-fed press manufacturer and applied to the new press now . These automation technologies become standard accessories for new presses. Some systems have also been retrofitted to earlier presses.

The working principle of the closed-loop color control system: This system scans and tests the color mark (also known as the color target) on the printed sheet (web or sheet) during the printing process, and continuously feeds the test data back to the printing machine. Ink console for instant adjustment and compensation of ink layer thickness. This system can not only guarantee the stability of printing color, but also provide real-time data for statistical process control and guaranteeing the quality of customers.

The closed-loop color control system ColorQuick is used as an example to illustrate the working process of the closed-loop control system: A printing machine console that is compatible with the CIP4 receives a description of the workpiece and electronically performs ink presetting; then, these digital information The ColorQuick console is sent to the press; a spectrophotometer is installed next to the camera behind the chill roll on the press. This spectrophotometer scans the color scale horizontally and compares it with the preset target density. The ink density deviation, and then automatically adjust the amount of ink.

A closed-loop color control system helps control the built-in variables of the press. In the printing process, in order to maintain the consistency and accuracy of the printing color, the printing worker should constantly adjust on the printing machine. However, the printing worker cannot control the wear and tear of the printing plate and the blanket, the change of the paper and ink, and the loss of the paper. Factors such as powder, lint and temperature fluctuations. Other variables, such as ink balance, fountain solution pH, ink bars, blanket height, and tension, can all be controlled but not always controlled well, depending on equipment maintenance or training for the printer The situation, therefore, very much hopes that the printer can use the energy to control these tasks, and give the color control to the machine.

In addition, the closed-loop system not only plays a role in the printing press. From the point of view of the entire printing production process, an automatic report generated by the closed-loop color control system will finally be fed back to different departments of the entire printing large-scale system, thus truly forming a large system of printing. System, closed-loop control, production management environment. The feedback results of these information are as follows:

Prepress - Improve color management;

Material suppliers - measuring density, dot gain, etc.

Technical service and engineering staff - improving press settings;

Equipment maintenance and engineering staff - track changes in the state of the press.

(to be continued)