Plastic film labels improve stability through surface treatment

in In the label market, although the paper label has a market share of 75%, in recent years, plastic film labels have also shown a high growth trend. The commonly used film materials are mainly polypropylene (PP) and polyethylene (PE), and the former is used twice as much as the latter. Other film materials, including the highly regarded polyethylene terephthalate (PET), together account for only 10% of the market.

Good Printability to the film label materials is absolutely necessary, but the commonly used PE and PP film itself does not meet the requirements, in order to ensure such a label material with fewer problems or no problem in the printing process, the printing having good The ink fixability requires pretreatment of the surface. The most common methods are corona pretreatment and coating pretreatment.

Prerequisites for film label printing

As a carrier for printing information, a plastic film label material not only needs to ensure that the ink can be well wetted on its surface, but also firmly adheres to the surface of the ink layer after it is cured.

The importance of ink wetting

The wetting properties of the ink on the film material are largely influenced by the surface tension of the ink and the free energy of the surface of the film. If the surface tension of the ink and the free energy of the surface of the film are the same, it means that it can be wetted; if the surface tension of the ink is greater than the free energy of the surface of the film, the ink will shrink on the surface of the film and will not wet; if the free energy of the surface of the film is higher than The surface tension of the ink allows the ink to spread on the surface of the film for wetting.

This leads to a very important criterion for film printing: the surface tension of the ink is at least as large as the surface free energy of the film, otherwise the ink cannot be wetted or the surface of the film cannot be sufficiently wetted, and the transfer of the ink to the film cannot be achieved, or Causes the printed image to be missing.

The importance of ink fixation

The fixing effect of the ink on the substrate plays an important role in the perfection of the label quality. This not only considers the adhesion effect in a short time after printing, but also considers the adhesion of the ink after a sufficiently long time.

The basic adhesion mechanisms of the ink on the surface of the substrate include mechanical attachment, chemical attachment, and physical attachment. If the appropriate roughness and porosity of the substrate surface contributes to the mechanical fixation of the ink, it is necessary to form a polar functional group on the plastic surface for physical and chemical adhesion of the ink. Since the functional groups are mostly polar, which helps to increase the surface energy of the material, it is very important that the functional groups themselves are fully integrated with the polymer network. Degradation products or other materials that are on the surface of the plastic film but are not bonded to the polymer network, although also having a certain polarity, do not allow the ink to adhere well.