Effect of film surface properties on printing and compounding

1. Non-polar molecular structure

In general, the adsorption and adhesion of inks and adhesives on the surface of plastic films is mainly achieved by the interaction between the two molecules. Most plastic film packaging materials have no polar groups or only weak polar groups in the molecular structure, and have a small critical surface tension and strong inertness. They are typical non-polar polymer materials, inks and adhesives. The wettability and affinity of the surface are poor, and the intermolecular forces between the two are very weak.

2. Surface energy of plastic film

The surface energy of plastic film is usually very low. For example, the critical surface tension of polyethylene is only 3.1 × 10-2N/m, and the critical surface tension of polypropylene is only 3.4 × 10-2N/m. The surface energy is low and it is not easy to be ink. Or the adhesive is wetted, so the critical surface tension of the plastic film must be greater than or equal to the surface tension of the ink or adhesive to ensure sufficient wetting of the ink or adhesive on its surface.

3. Crystallinity of plastic film

Many plastic films not only have a smooth surface, but also have high crystallinity, the molecules are in a thermodynamically stable state, and have stable chemical properties. It is difficult for ink or adhesive molecules to diffuse on the surface, so that inks and adhesives are in the film. The adhesion of the surface is not ideal.

4. Weak surface layer

In the process of processing polyolefin and other films, in order to make the film have better opening, antistatic, anti-aging, anti-ultraviolet radiation and other properties, it is necessary to add a certain amount of additives, such as an opening agent, an antistatic agent, plasticizing. Agents, stabilizers, etc., these additives are very easy to precipitate, and migrate to the surface and form oil stains, so that the surface of the film forms a weak surface layer with low strength, because the cohesive strength of the weak surface layer is lower than the cohesive strength of the main body. More, it will have an adverse effect on the printing and composite processes.

5. Cleanliness of plastic film surface If the environmental sanitation conditions are relatively poor and the air cleanliness is low, the surface of the plastic film is very easy to adsorb dust, grease and other substances in the air, and these adsorbents may hinder the ink and the adhesive and the film. The mutual contact of the surfaces affects their wetting on the surface of the plastic film, so the cleanliness of the film surface must be taken seriously.

Jiuzhi Plastics Network

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