The main ink factor that affects the glossiness of packaging printed matter is the smoothness of the ink film, which is determined by the nature and dosage of the binder. The ink should contain evenly dispersed fine pigments and have sufficient viscosity and fast drying speed to avoid excessive penetration of the adhesive into the paper pores. In addition, the ink should have good fluidity to form a smooth ink film after printing
1) The effect of ink film thickness on the gloss of printed matter
After the paper absorbs the ink binder to the maximum extent, the remaining binder remains in the ink film, which can effectively improve the gloss of the printed matter. The thicker the film, the more adhesive is left, which helps improve the gloss of the print. Glossiness increases with ink film thickness. Although the ink is the same, the glossiness of the printed matter formed on different papers varies with the thickness of the ink film. When the ink film of high-gloss coated paper is thin, the glossiness of the printed matter decreases as the thickness of the ink film increases. This is because the ink film masks the original high gloss of the paper itself, and the gloss formed by the ink film itself is reduced due to the absorption of the paper. As the thickness of the ink film gradually increases, after the absorption of the adhesive by the paper is basically saturated, the amount of adhesive remaining on the surface of the paper increases, and the gloss also continues to increase. The glossiness of coated cardboard prints increases rapidly with the increase of ink film thickness. When the ink film thickness increases to 3.8μm, the glossiness no longer increases with the increase of ink film thickness.
2) Fluidity of ink
If the ink fluidity is too large, the dots will expand, the printing size will become larger, the ink layer will become thinner, and the printing gloss will be poor; if the ink fluidity is too small, the gloss will be high, and the ink will not be easily transferred, which is not conducive to printing. Therefore, in order to obtain better gloss, the fluidity of the ink must be controlled well, not too large or too small.
3) Leveling of ink
During the printing process, if the leveling property of the ink is good, the gloss will be good; if the leveling property is poor, it will be easy to draw and the gloss will be poor.
4) Pigment content in ink
The pigment content of the ink is high, and a large number of tiny capillaries can be formed in the ink film. However, the ability of these tiny capillaries to retain adhesive is much greater than the ability of the fiber gaps on the surface of the paper to absorb adhesive. Therefore, an ink with a high pigment content can retain more binder in the ink film than an ink with a low pigment content. Prints using high pigment content inks have a higher gloss than prints using low pigment content inks.