In the packaging and printing industry, the effect of lamination is not only related to the raw materials and operation methods of lamination, but more importantly, it is related to the condition of the ink layer of the printed matter to be offset. The condition of the ink layer of the printed matter is mainly determined by the nature of the paper, the ink performance, the thickness of the ink layer, the graphic area and the overall density of the printed graphics and texts. These factors affect the formation conditions of the adhesive mechanical adhesion, physical and chemical adhesion, etc., which causes a change in the adhesion properties of the printed surface.
1.The thickness of the ink layer of the printed matter. Solid prints with thick ink layers often struggle to bond to plastic film and quickly delaminate and blister. This is because the thicker ink layer alters the porous surface properties of the paper, making the fibrous pores of the paper closed, severely hindering the penetration and diffusion of the adhesive. A certain degree of penetration of the adhesive is conducive to the adhesion of the coating film.
2.Types of printing inks. The coated print should be made of fast-setting bright offset ink, which is composed of synthetic resin, dry vegetable oil, high-boiling kerosene and a small amount of gum. The synthetic resin molecule contains polar groups, which are easy to diffuse and penetrate with the polar groups in the adhesive molecule, and cross-link to form physical and chemical binding force, which is conducive to lamination. However, it is not advisable to add too much drier when using, otherwise the surface of the ink layer will crystallize, which will affect the coating effect.
3.Add powder coating. Spray powders are mostly composed of cereals, starches and natural suspensions. The anti-stick effect of powder spraying is mainly to form an irreversible cushion on the surface of the ink layer, thereby reducing adhesion. Due to the coarser size of the particles, if they are sprayed too much during the printing process, these particles will float on the surface of the print. When laminating, the adhesive will not be bonded to the ink layer everywhere, but will be bonded to this layer of powder, which will cause false sticking and seriously affect the quality of the lamination.
4.The drying of the inner layer on the surface of the printed matter. Poor drying of the ink layer of printed matter is very harmful to the quality of the coating film. In addition to the type of ink, the amount and type of drier used during the printing process, and the ambient temperature and humidity between printing and storage, the structure of the paper itself is also important. If the structure of coated paper and offset paper is different, the drying conditions of the ink layer are also different.
