Reasons for color difference of spot color in packaging printing

1.The effect of paper on color

The influence of paper on the color of ink layer is mainly reflected in three aspects.

(1) Paper whiteness: Paper with different whiteness (or with certain color) has different effects on the color appearance of printing ink layer. Therefore, in actual production, the paper with the same whiteness should be selected as far as possible to reduce the influence of paper whiteness on printing color.

(2) Absorbency: When the same ink is printed on paper with different absorbency under the same conditions, it will have different printing gloss. Compared with coated paper, the black ink layer of uncoated paper will appear gray and matt, and the color ink layer will drift. The color prepared by cyan ink and magenta ink is the most obvious.

(3) Gloss and smoothness: The glossiness of the printed matter depends on the glossiness and smoothness of the paper. The surface of printing paper is semi-glossy, especially coated paper.

2.Effect of surface treatment on color

The surface treatment methods of packaging products mainly include film covering (bright film, matt film), glazing (cover bright oil, matt oil, uv varnish), etc. After these surface treatments, the printed matter will have different degrees of color change and color density change. When the light film, light oil and uv oil are coated, the color density increases; When coated with matt film and matt oil, the color density decreases. The chemical changes mainly come from a variety of organic solvents contained in the film covering adhesive, UV primer and UV oil, which will change the color of the printing ink layer.

3.Impact of system differences

The process of making color cards with ink leveler and ink spreader is a dry printing process, without the participation of water, while printing is a wet printing process, with the participation of wetting liquid in the printing process, so the ink must undergo oil-in-water emulsification in offset printing. The emulsified ink will inevitably produce color difference because it changes the distribution of pigment particles in the ink layer, and the printed products will also appear dark and not bright.

In addition, the stability of the ink used for mixing spot colors, the thickness of the ink layer, the accuracy of weighing the ink, the difference between the old and new ink supply areas of the printing machine, the speed of the printing machine, and the amount of water added during printing will also have different effects on the color difference.

4.Printing control

During printing, the printer controls the thickness of the spot color ink layer with the printing standard color card, and assists in measuring the main density value and bk value of the color with a densimeter to overcome the difference between the dry and wet color density of the ink.

Post time: Mar-14-2023