Offset ink measurement and adjustment technology

In recent years, the printing industry applied colorimetry to evaluate printed matter, especially when it comes to the color management of all processes in the standardization and digital production chain. In spot color printing, color analysis can be used to accurately assess the final color effect.

For this purpose, Manroland has developed Color-Pilot's new measuring system for the integration of density and color measurement and regulation.

For more than 20 years, printing companies have used measurement and adjustment techniques in order to achieve the desired effects of the original and to make it stable. Densitometry (measurement of ink density) plays an important role in this process. The ink density bar on the substrate was measured optically. As a result of the determination, the system determines if more or less ink is needed in the measured ink zone. Complex adjustment algorithms eventually lead to precise opening/closing of the ink metering elements controlling these ink zones. Within this range, a little more or less ink is printed on the paper to control the amount of ink.

The first ink adjustment device appeared in 1977

Manroland demonstrated the first generation RolandCCI ink conditioning device in 1977. Since then, such devices have continued to improve in terms of speed, measurement accuracy and reliability. In the late 1980s, with the adoption of the third-generation regulating device, the measuring time was greatly reduced: the measuring and control bar with a length of 1020 mm can be measured within 14 seconds, and there are more measuring blocks on the measuring and controlling bar. The width is only 3 mm. , so more information is available on the entire sheet (340 gauge blocks on medium-sized sheets).

In 1990, with the Roland 700 offset press application, the time required to control the quantitative slide in the ink fountain was greatly reduced: if the previous six-color machine required 6 seconds, it is now less than this time. When the fourth-generation Roland CCI was introduced in 1998, it was already possible to use a measuring head to measure printing strips measuring only 3 mm wide.

Color-Pilot integration density measurement and colorimetric determination

In 2002, Color-Pilot integrated the density adjustment of colorimetric measurement into the measurement system, thus taking the most important step.

In order to measure and adjust according to the ink density, the Color-Pilot simultaneously determines the colorimetric value from each small measuring block of only 3 mm×4 mm of the printing control strip, without additional time. A nominal color space position can be entered for each printing unit and each fountain slide area.

Record color difference

The color measurement results are graphically displayed as the color difference records of figures and numbers (ΔE-recording), so that the tolerance range (permissible color difference) and the excess tolerance range can be immediately seen.

Each printing unit can choose the so-called zoom display. Each ink zone can be displayed by a single ink control element. The color difference between the nominal value and the actual value is displayed with numbers, graphics and a square control block to visually check the authenticity of the color.

Color difference statistics

The "statistical record" function of the Color-Pilot system makes statistics from all record measurements of a job, and creates a histogram based on delta E. In the "Statistics" function, the smallest, larger, and medium color difference can be calculated from all measurements for each fountain slide area (each with a measurement block), and displayed numerically and graphically.

The “rectogram” function also calculates the smallest, larger, and medium color differences from all fountain slide areas for each measured sheet, and displays them graphically and numerically. Graphs and digital records can be printed as reports.

The advantages of density adjustment

Densitometry is a technique suitable for measuring the amount of ink. This density is directly related to the thickness of the ink layer on the printed sheet: usually within the range of the color ink layer thickness (up to 1/1000 mm), there is an almost linear relationship between the density and the ink layer thickness, making the density suitable for printing sheets. Measure and adjust the ink layer thickness. The measured value is directly affected by the adjustment of the fountain slider so that the measured value becomes the thickness of the ink layer.

The use of a front polarizing filter for density measurement eliminates the diffuse gloss effect caused by ink drying. This almost eliminates the density difference between the ink dry and wet, however, the use of polarizing filters in colorimetry is problematic.

Automatically adjusting the position of the ink fountain slide relieves the burden on the printer: he only needs to pull out one page at a time and measure and make adjustment recommendations. In this way, in formal printing, he can hand over the amount of ink to the computer's control algorithm. The quality of the entire batch of prints was evaluated by statistical analysis and provided as proof of quality to the customer along with the prints to confirm the print quality.

Its advantage is that through the density adjustment of important process parameters, that is, the ink layer thickness, to bring stability to the printing process, to maintain the stability of the printing effect achieved.

For commercial printers that use only four-color printed dot images, pure density measurement and adjustment systems are sufficient in most cases because they rarely print in spot colors. Standardization processes in prepress and printing can increase the productivity and economic efficiency of the entire printing system.

Colorimetric determination of complementary density

Packaging and printing plants require additional aids because of the high demands placed on the color vision of packaging prints. They often evaluate spot color inks in the field, and their color should be the same color as the manufacturer or the product. To be able to evaluate impressions objectively, people need a measurement and evaluation system that mimics the visual impression of the eye. This system is the colorimetric method. If only the density value is used, it cannot be accurately recognized whether the hue of an ink is accurate. In this case, even if the position of the ink fountain slide is changed, it does not help.

The same inking, depending on the different substrates used (thickness, absorbency, paper color), will also produce different visual impressions on the printed sheets at the same density. The color of the substrate (ie, the different whiteness of the paper) plays a major role as a cause of different color vision.

During the formal printing process, due to a failure, it is necessary to reconfirm that the printed sample has changed its rated density. In this case, using the Color-Pilot system to provide colorimetric supplemental density measurements is a suitable solution.

Reprinted from: China Printed Materials Network