Ink adhesion
1. The adhesion of ink on paper
The main components of paper are cellulose, rubber, fillers, etc. Cellulose is a polymer with a long-chain ring structure with many hydroxyl groups. The fluid part of the ink is the connecting material, and the ink depends on the connecting material
The conjunctiva on the surface of the paper is dry and adheres. Commonly used binders are dry vegetable oils and various natural or synthetic resins.
The main components of paper and ink are asymmetric molecules. When their molecules are close to each other, the inherent dipoles are repelled by the same sex and attracted by the opposite sex, so that the molecules are oriented in the space adjacent to the different polarities in the space, resulting in orientation first Force, and subsequently induce force and dispersion force. The secondary binding force between the molecules makes the ink adhere to the paper. The greater the secondary binding force, the better the adhesion effect.
On the other hand, the paper is made of interwoven fibers, the surface is uneven and porous, and the ink has good flow properties. Therefore, when the ink is transferred to the paper, there is a significant mechanical anchor effect, which promotes the ink on the paper Attach.
The adhesion of the ink on the paper depends on the secondary binding force between the molecules and the mechanical anchor effect of the ink on the paper. For paper with higher smoothness, the adhesion of ink mainly depends on the secondary binding force between molecules; for rougher paper, the adhesion of ink relies more on the mechanical anchor effect.
In addition, most of the fillers (calcium oxide, titanium oxide, etc.) and paints (white clay, calcium carbonate, etc.) contained in the paper are inorganic compounds. These inorganic compounds greatly increase the specific surface energy of the paper, so the paper is a high-energy surface. When the ink with low surface tension covers the surface of the paper, the surface free energy of the paper is reduced to form a stable system, so the ink can firmly adhere 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 molecules and the electrostatic attraction of the interface. There is no mechanical anchor 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, it can greatly reduce the surface free energy of the metal, so it has a larger adhesion work and makes the ink adhesion effect better.
Like metal poultry, the polymer film material with high surface smoothness, the adhesion of ink can only rely on the secondary binding force between molecules. However, the surface of the polymer is a low-energy surface. Whether the ink adheres well depends largely on the energy of the surface of the polymer. In order to improve the adhesion effect of the ink on the surface of the polymer, the surface of the polymer should be treated to increase the surface free energy, increase the surface roughness, and improve the wettability of the ink.
In order to make the ink adhere to the surface of the metal foil and polymer, the UV offset printing now developed has achieved good results.
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