Perspective Process Technology and Influencing Factors of Film Coating Technology (II)

Factors affecting film quality

1. The status of the print ink

The condition of the ink layer in the printed matter mainly refers to the nature of the paper, the ink properties, the thickness of the ink layer, the area of ​​the graphic and the density of the printed graphic, etc. Their influence on the quality of the film is mainly the influence on the adhesive strength of the printed matter and the film. When the printed ink layer is thick and the area of ​​the graphic is large, the ink changes the porous surface characteristics of the paper, and many paper fiber capillary pores are closed, impeding the penetration and diffusion of the adhesive, making it difficult for the printed matter and the plastic film. Bonding, prone to delamination, blistering and other failures. Offset printing adopts the method of dusting to avoid the dirtying of the printed matter. The powder is sprayed on the ink layer and forms a layer of fine particles on the surface. When the film is coated, the adhesive does not adhere to the ink layer at every place, but adheres to these powders to form a false-stick phenomenon, which seriously affects the quality of the film. When the ink is not completely dried, the high boiling point solvent contained in the ink can easily cause the plastic film to expand and elongate. This is the most important reason for blistering and delamination of the product after the film is covered.

2. environment humidity

The environmental humidity of the film shop also has an impact on the quality of the coating. The main reason is that the moisture content changes with the relative humidity of the air between the adhesive and the plastic film and the printed matter. Humidity-sensitive prints can develop internal stresses due to dimensional changes. If the longitudinal stretch rate of the printed matter is 0.5%, the longitudinal shrinkage of the BOPP film is 4%. If the water absorption of the printed material is excessive and the film stretches, and the internal stress is caused by the heat shrinkage of the film, the film product may curl, wrinkle and adhere. Not strong. In addition, in a high humidity environment, the equilibrium moisture content of the printed matter will also change, and the large amount of moisture absorbed from the air medium will be released from the surface during the hot-press compounding process, stagnating at the adhesive interface, and being formed locally. Non-adhesive phenomenon. Moreover, changes in the balance of moisture in the printed matter (absorbing moisture from the air medium or releasing moisture into the air medium) often occur at the edge of the print, making it a scalloped edge or a tight edge, and it is not easy to form a film with the film during hot press compounding. Good adhesion produces wrinkles, making production unsuccessful.

3. temperature control

Heating can soften the film and bond the paper to the plastic film. However, the temperature is too high and the film is easily broken, which seriously affects the quality of the product. Fan cooling and closing of the heating wire should be adopted.

Plastic film green development trend

Plastic film is favored by the printing industry and consumers because of its folding resistance, wear resistance, ability to protect prints, increased gloss, and low cost. However, due to the fact that the coated paper cannot be recovered, it becomes a kind of white pollution, and the toxic substances such as toluene and thinner etc. are volatilized during the film coating process and damage human health. Today, in advocating "protecting the environment and protecting resources," 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 there is now a water-based plastic coating technology. And the hot-melt adhesive precoating film dry plastic composite technology, these two types of film are called "environmentally friendly laminating machine", but the former still can not solve the problem of the non-degradable and non-recoverable waste of the filmed printed matter. In the production process, a large amount of heat is required, energy consumption is large, the working environment is unsatisfactory, and the waste can only be separated by paper and plastic in water at 60° C., and the separation cost is high.

With the awareness of environmental protection, health awareness, and the renewal and development of the concept of operators, new scientific and technological achievements will eliminate the products of the old technology and make the coating process undergo a qualitative change. “Non-toxic, harmless, and green” will become a cover. The inevitable development trend of membrane technology. For example: water-based film glue, which uses water-soluble high-molecular polyester material and water as a solvent, and is basically an environmentally-friendly product. At present, there is a problem of poor stability of domestic water-based film adhesives, but such defects as WDT-3300, WDT-2200 and WDT-1100 produced in Korea can completely replace the oil-based film adhesive products. In terms of machinery, laminating machine manufacturers in Guangdong, Hebei, and Zhejiang have successively introduced several semi-automatic desktop dry laminating machine products. South Korea Yongxin also introduced FLCD-S1020, 1090, 1350 and 1450 four fully automatic water-based dry laminating machines to the Chinese market. The operation process is fully automated, which greatly reduces the human-machine contact time, and the use of plastic non-toxic, no Harm, green, and these new products have just been introduced by the domestic leading and highly conscious companies, such as Haier Fon Choi, HK and so on.

The glazing process is also optimistic about this. Glossing is the use of painting, spraying or printing methods to add a layer of colorless and transparent paint on the surface of the print, that is, coating oil, after calendering, drying, a layer of colorless and transparent bright layer on the surface of the print, The glossiness of the surface of the printed product is increased, and the stiffness of the printed product is also increased, which also serves to protect the printed product and increase the appearance. Better still, the printed waste after polishing can be recycled or recycled, and it will not pollute the environment. Therefore, it is a kind of surface decoration processing technology with great development potential, and it is possible to gradually occupy the market of plastic coating technology. However, the diluents used in the oil-based glazing and alcohol-based glazing on the market are toluene and alcohol, respectively, which are harmful to the human body and are also harmful to environmental protection. Therefore, an aqueous coating process has emerged. Waterborne glazing has gradually become the mainstream of glazing processes, but this process needs further development in technology to make it more suitable for the dual requirements of environmental protection and printing quality. 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.