Offset printing ink adhesion

Ink adhesion

1. Adhesion of ink to paper The main components of paper are cellulose, rubber, and fillers. Cellulose is a long-chain cyclic structure polymer with many hydroxyl groups. The fluid part of the ink is the binder, and the ink is dried and attached to the surface of the paper by the binder. Commonly used binders are dry vegetable oils and various natural or synthetic resins. The main components of paper and ink are all asymmetric molecules. When their molecules are close to each other, the inherent dipoles repel each other due to homosexuality, and the opposite phase attracts molecules to align the molecules in space in a state of heteropolarity. As a result, the orientation is first generated. Force, then induce force and dispersion force. The secondary binding force between the molecules allows the ink to adhere to the paper, and the greater the secondary binding force, the better the adhesion effect.

On the other hand, the paper is made of fibers intertwined with uneven surface and porosity, and the ink has good flow properties. Therefore, when the ink is transferred to the paper, there is a clear mechanical anchoring effect, which promotes ink on the paper. Attached. The adhesion of the ink on the paper depends not only on the secondary binding force between the molecules but also on the mechanical anchoring effect of the ink on the paper. For paper with a higher degree of smoothness, the adhesion of the ink depends mainly on the secondary binding force between the molecules; on a rougher paper, the adhesion of the ink is more dependent on the mechanical anchoring effect. In addition, fillers (calcium oxide, titanium oxide, etc.) and coatings (white clay, calcium carbonate, etc.) contained in paper are mostly inorganic compounds. These inorganic compounds greatly increase the specific surface energy of the paper so that the paper is a high-energy surface. When the low surface tension ink covers the surface of the paper, the surface free energy of the paper is reduced to form a stable system, so the ink can be firmly attached to the surface of the paper.

2. The adhesion of ink on metal foil and polymer film. Metal mooring is a printing material with high smoothness. The adhesion of ink can only rely on the secondary binding force between the molecules and the interface electrostatic attraction, and there is no mechanical anchoring effect. However, the metal surface is a high-energy surface, and the surface energy is much higher than the surface tension of the ink. When the ink is attached, the surface free energy of the metal can be greatly reduced, so that there is a larger adhesion work and the adhesion effect of the ink is better. Like metal moorings, polymer film materials with a very high degree of surface smoothness can only adhere to the intermolecular binding forces of the ink. However, the surface of the polymer is a low-energy surface, and the ink can adhere well to a large extent depending on the energy of the polymer surface.

In order to improve the adhesion of the ink on the polymer surface, the surface of the polymer must be treated to increase the surface free energy, increase the surface roughness, and improve its wettability with the ink. In order to make the ink adhere to the surface of metal foil and polymer, UV offset printing developed now has achieved good results.