Color Experiment Analysis of Water-free, Water-based Offset Printing Inks

Waterless offset printing refers to a type of lithographic printing method that uses special ink to complete the printing without the need for the traditional aqueous solution dampening, using the ink-repellent silicone rubber layer as the non-graphical part of the printing plate. Waterless offset printing has higher quality due to the elimination of fountain solution. Such a promising printing method has relatively high requirements for various materials. Ink is the two major types of printing materials and plays a key role in this printing process. At present, the more common waterless offset printing ink in the world is Germany's K+E. The key parameter for evaluating the quality of the ink is to analyze the color quality of the print in the dynamic printing process. Because the quality of prints directly determines the quality of prints. This article uses the German K+E water and waterless offset printing ink as an example to analyze the color quality of the ink, so as to compare the two inks.

1 Test

1) Test material: Test strip printed by Heidelberg QKDI-46 waterless printing press, Test strip printed by Heidelberg GTO 4 colour with water offset press.
2) Test equipment: X-Rite 508 Densitometer [1].
3) Test conditions and data test: Select coated paper with a basis weight of 157g/m2 [2]. The number of screens added is 69 lines/cm. Under standard printing conditions [3], the temperature is 20°C, relative humidity. It is a 56% test strip. Under standard test conditions, the temperature is 20°C and the relative humidity is 65%. Randomly selected six of the 500 proofs for testing, and finally averaged them. See Tables 1 and 2.

2 Data Analysis

The indicators for the evaluation of the three primary inks [4] are usually color intensity, hue error, saturation, and color efficiency [5].

1) Color Intensity: The highest density value for each ink measured. The higher the color intensity value, the higher the color quality of the ink.

2) Hue Error: An index used to describe the ink color deviation, which can be expressed by the ratio of the difference in the reflectivity of the ink hue and the difference in the density of the absorption area.

Hue error={(ML)/(HL)}×100% (1)

In the formula: H is the maximum density value of the ink; L is the minimum density value of the ink; M is the density value between H, L.

The smaller the hue error value of the ink, the purer the ink and the better the color performance.

3) Saturation: It is closely linked to the gray scale of the ink, and the gray scale of the ink, that is, the ratio of the ink hue to the minimum density of the absorption area and the maximum density of the absorption area, represents the gray scale. Saturation and grayscale are the opposite concepts.
Saturation = (1-L/H) × 100% (2)

Saturation is an important indicator of hue, the greater the value, the higher the saturation of the ink, the more pure and bright the color is.

4) Color efficiency: refers to the percentage of the normal absorption and abnormal absorption of the color of the color.

Color efficiency = {1-(L+M)/2H}×100% (3)

The higher the color efficiency, the more pure the hue of the color.

According to the test data of Tables 1 and 2, the color intensity, hue error, color saturation, and color efficiency analysis of the K+E ink with water and the anhydrous K+E ink are shown in Tables 3 and 4.

3 Conclusion

It can be seen from Tables 3 and 4 that the waterless offset printing ink has higher color intensity than a water offset printing ink, a small hue error, slightly poor color saturation, and high color efficiency. From the results of the data comparison, it can be seen that the color reproduction quality of waterless offset ink prints is better than that of water offset printing. It is imperative to promote waterless offset printing.

(Author/Guo Linghua Luo Guanglin)
Source: "Packaging Project"