Spot color printing inks must pay attention to these points!
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In order to improve the design and quality of printed matter, printing companies often use spot color inks when printing trademarks, packaging and publicity materials to ensure the color consistency of printed products and meet the requirements of customers. The reason for the printing color difference of the color ink.
First, the printing process
Ink layer thickness and ink balance
The control of the hue of the ink during printing is mainly achieved by controlling the thickness of the ink layer. When the thickness of the ink layer changes by about 0.1 μm, a chromatic aberration of ΔE = 1.5 to 4.5 NBS is caused, and this effect is apparently large. Offset ink color reproduction is closely related to ink balance. Under the same amount of ink, small water and small water will affect the color depth. Properly mastering the ink balance, it is important to pay special attention to the pH of the dampening fluid. The principle of the amount of water used is that the amount of water supply is as small as possible without being dirty.
Printing pressure
The size of the printing pressure has a great influence on the extent to which the ink is transferred from the printing plate to the paper. When the printing pressure is insufficient, the transfer of the ink is insufficient and it is not suitable for printing; when the printing pressure is too large, due to the printing plate The ink spreads to the blank part outside the graphic, and the ink transfer rate is not improved, but also brings other disadvantages, and is also unsuitable for printing. Prints with thick ink layers, sharp images, rich tone and good color reproducibility can be printed only within the appropriate printing pressure range.
Printing speed
The increase in printing speed shortens the contact time between printing surfaces, the dot is imaginary, the ink transfer rate is lowered, and the printing quality is degraded. In order to ensure sufficient contact of the printing surface and improve the printing quality, it is required to control the printing speed under a certain printing pressure to obtain a stable ink layer thickness.
Dry back density difference
On the same paper, the density of the sample just printed is higher, and after a period of time, the density value decreases as the drying smoothness of the ink decreases. The printed image exhibits a different hue due to the difference in density values before and after drying of the ink layer.
The ink that has just been printed, the ink is still in a wet state, and there is a difference from the dry state. This is because the ink layer just printed has a certain leveling property, so the surface reflection is mainly specular reflection, which looks bright and lustrous. When the ink layer is in a dry state, the surface reflection is mainly diffuse reflection, and the color is naturally duller than when it is just printed. Therefore, the ink color of the general printed proof is slightly deeper than the standard proof, but how much deeper should be controlled by data. When proofing, the density values of the newly printed colors are measured. When printing, refer to these density values for printing, so that two The ink color is close to the same. A densitometer with a polarizing filter can eliminate the light generated by the specular reflection on the surface of the ink layer. The measured wet density is very close to the dry density, and the measured density value is little affected by the wet and dry of the ink layer.
Second, the surface finishing of printed matter
The surface finishing is to properly process the surface of the printed matter to improve the light resistance, heat resistance, water resistance, abrasion resistance, folding resistance and chemical resistance of the printed surface; increase the gloss and artistic sense of the printed matter; And beautify the role of printed matter to enhance the value of printed matter.
The surface finishing methods of packaging products mainly include glazing (printing varnish, coating varnish, matt oil, UV varnish, water varnish, etc.), waxing, filming (bright film, matt film) , bump embossing, bronzing, etc. After the surface treatment of the printed matter, there will be varying degrees of change in hue and saturation, ie, density. These changes can be divided into physical and chemical changes. Physical changes are mainly reflected in the increased specular and diffuse reflectivity of the product surface. In general, when the light film is coated, the varnish is coated with the varnish, and the color density is increased; when the matte film is coated and the matte oil is applied, the color density is lowered. The chemical changes mainly come from the organic solvents contained in the film glue, water-based varnish, and UV varnish, which combine with the ink particles on the printed matter to change the color of the ink layer.
Third, the printing materials
Paper whiteness
The factors that affect the whiteness of paper are:
1 Whiteness of the slurry: the most important factor.
2 Dyes: The dye should be selected so that it is near the dominant wavelength of whiteness measurement, without affecting its reflectivity, that is, it does not affect the whiteness of the paper.
3 Filler: Depends on its type and grade.
4 Coating: The whiteness of the coating printing paper is determined by the whiteness of the base paper, the whiteness of the coating, and the amount of coating.