Film coating technology analysis

Composite strength

Refers to the adhesive fastness between the plastic film and the paper (board) print in the film product, and its size depends on the adhesive force between the plastic film, the paper (board) print and the adhesive (or hot melt adhesive). When laminating, the adhesive force is mainly derived from the mechanical bonding force and physicochemical bonding force between the plastic film, the paper (plate) and the adhesive (or hot melt adhesive).

The key to film fastness lies in the affinity of the glue with the print (ink and substrate). As a film coating industry, printing inks are not optional, that is, only the film that is adapted to the ink market is the only choice, so as a pre-coating film, only the performance of all inks can be considered as high quality. The composite strength of the film products is affected not only by the process parameters in the film production process, such as the temperature, pressure, speed, coating conditions of the adhesive, film tension, and environmental factors of the film coating process. At the same time, it is also affected by the printing process, such as the surface state of the printed product after printing, such as the thickness of the ink layer, the area and distribution of the graphics, the ink characteristics, the use of diluting agents, dusting, and the state of ink drying.

Factors affecting film quality
1. The state of the ink on the printed matter refers to the nature of the paper, ink properties, ink layer thickness, graphic area, and print graphic density. When the printed ink layer is thick and the graphic area is large, many paper fiber capillary pores are closed, which impedes the penetration and diffusion of the adhesive, making it difficult for the printed matter and the plastic film to be bonded, and problems such as delamination and blistering tend to occur.

2. Environmental humidity

Between the adhesive and the plastic film and print, the moisture content changes with the relative humidity of the air. Humidity-sensitive prints can cause internal stress due to dimensional changes. For example, the longitudinal stretch rate of printed materials is 0.5%, and the longitudinal thermal shrinkage of BOPP film is 4%. If the water absorption capacity of the printed material is too large and the film stretches, the internal stress caused by heat shrinkage of the film will cause the film products to curl, wrinkle, and bond. Not strong. In addition, in a relatively high humidity environment, the equilibrium moisture content of the printed matter will also change, and a large amount of water absorbed from the air medium will be released from the surface during the hot-pressing compounding process, stagnating at the adhesive interface, and locally forming non-adhesion. phenomenon. Moreover, changes in the equilibrium moisture content of the printed matter (absorbing moisture from the air medium or releasing moisture into the air medium) mostly occur at the edge of the printed matter, making it to form a flounced or tight edge, and it is not easy to form a good film with the film in the hot press composite. Bonding and creases cause production to fail.

3. Temperature control

Heating can soften the film and allow the paper to adhere to the plastic film. However, the temperature is too high, the film is easily broken, and the quality of the product is seriously affected. Therefore, measures should be taken to cool the fan and close the heating wire.

Plastic film green trend

The coated paper becomes a kind of white pollution because it cannot be recycled, and toxic substances such as toluene and thinner etc. evaporate during the film coating process, and harm people's health. In advocating the protection of the environment and the protection of resources today, plastic film coating technology has been eliminated in Europe and the United States and other countries. European and American countries have even refused to import plastic packaging films. Although the water-based plastic coating process and the hot-melt pre-coating dry plastic composite process are currently available, the former still fails to solve the problem that non-degradable and non-recoverable waste of the film-covered printed matter. The latter requires a large amount of heat in the production process and it is abandoned. Materials need to be separated from paper and plastic in water at 60°C, and the cost is high.

With the improvement of environmental protection awareness, new scientific and technological achievements will eliminate old-processed products and make the lamination process undergo qualitative changes. Non-toxic, harmless, and green environmental protection will naturally become the inevitable development trend of the lamination process. In addition, the glazing process is also optimistic about it. Glossing is the use of painting, spraying or printing methods to add a layer of colorless and transparent coating on the surface of the printed matter, that is, coating oil, after calendering, drying treatment, increase the gloss of the surface of the printing product, but also improve the stiffness, while After the glazing, the printed waste can be recycled or self-decomposed and does not pollute the environment. Therefore, glazing is a processing technology with great development potential, and it may gradually occupy the market of plastic film coating technology. Although the dilution machines used for oily and alcoholic glazing on the market are toluene and alcohol respectively, which are also harmful to the human body and unfavorable to the environment, waterborne glazing has gradually become the mainstream of glazing processes. The water-based UV glazing process that has been developed so far is an ideal environment-friendly glazing process and is also the development direction of glazing processes in the future.