Hue Control of Gold and Silver Card Paper Printing

At present, there are many kinds of cigarette labels in the domestic market. Different papers use different inks, and in combination with different printing processes, different cigarette labels are printed. Among them, the use of an offset printing process to print UV ink on gold and silver card paper is more common.

Due to the laser metallic luster on the surface of the gold and silver cardboard, the color during the printing process is not easily controlled. How to ensure that the same batch of cigarettes, even different batches of cigarettes, is consistent with the spot color, which is a difficult point for printing companies.

1 Smoke detection environment control

1) Light source The light source is a prerequisite for observing the color. The quality of the light source directly affects the visual sense of the color. The smoke label is a reflection sample. According to the International Commission on Illumination (CIE) regulations, the standard light source D65 and the correlated color temperature of 6504K daylight should be used, the illuminance uniformity ≥ 80%, and the light source color rendering index Ra ≥ 90.

2) Environmental requirements The testing environment requires no dust, temperature 20 ~ 25 °C, humidity 50% ~ 60%.

2 ink thickness control

The ink layer thickness refers to the average thickness of the ink layer attached to the surface of the paper in a direction perpendicular to the paper. The thickness of the ink layer is an important factor affecting the hue of the smoke mark. At present, the main means for controlling the thickness of the ink layer by various printing companies is the field density test, that is, the relative contrast value (K value).

The formula for the relative contrast (K value):
K=(DS-DT)/DS
Where: DS is the density of the field DT is 75% or 80% of the dot integral density value

In the case of constant printing conditions, the solid density is a single function of the thickness of the ink layer. Therefore, the optimum thickness of the ink layer can be determined by measuring the solid density when the relative contrast is maximum.

3 Paper and ink control

The surface of the gold and silver cardboard is very smooth and has a strong laser metallic luster, which produces a strong specular reflection when illuminated. Therefore, the color of the surface of the smoke mark changes with the observation angle.

Gold and silver cardboard cigarettes generally use UV ink printing, UV ink particle size, transparency, viscosity, adhesion, etc. have a greater impact on the hue. Therefore, the characteristics of the inks produced by different manufacturers are also different. Even inks produced by the same manufacturer on different production dates will have differences in color difference, viscosity, and the like.

Therefore, the use of paper and ink in cigarette marking should grasp the following principles: The production of a batch of cigarette labels should use the same kind of paper and ink produced by the same manufacturer on the same production date.

4 Establish a reasonable standard of color difference detection standards

Due to the influence of many factors, the hue of the gold and silver paperboard printing ink will inevitably fluctuate. How to ensure the consistency between the printing hue and the standard color sample, and how to ensure the stability of the production of large-volume prints, is every one The problems that printing companies must face. Determining the color difference detection standard can effectively solve this problem.

At present, most tobacco companies will select standard proofs from the qualified products for proofing, directly specify a color difference detection standard, and require the printing company to print according to this standard. At this time, the printing company should correct the color difference detector of the company and the color difference detector of the cigarette factory to ensure the consistency of the color difference detected by the instrument. In addition, the printing company should determine the up-and-down fluctuation range of the color difference based on its own actual situation and based on the color difference detection standard.

Source: "Printing World" Author: Wang Jun