In daily life, we can see composite film packaging products everywhere. Technically demanding foil-coated films are usually used for color printing. In order to produce composite films with different firmness requirements, the interaction between multiple materials is required—the interaction between the synthetic film, the drilling compound, and the printing oil.
A growing market
In recent years, the total amount of flexible packaging has been increasing, which also fully shows the trend of flexible packaging to replace bulky packaging such as glass bottles and metal cans. This is not only because of its cost advantage, but also because it can adapt to changes in market demand and demand faster and better. The increasingly complex multi-layer composite process (three-layer and four-layer composite) makes it adapt to the ever-expanding application fields and the growing variety of related requirements. The composite film market can be divided into the off-end market for packaging liquid goods according to the characteristics: the middle market for packaging cheese, fresh meat, etc., and the low-end market for fast-food or instant noodles.
Barrier characteristics of composite film
Through the interaction of different materials in the composite film. The advantages of each layer are accumulated. The following are the functions of the composite film:
1. Water vapor barrier, prevent wet goods from drying, and add wet wipes for cooling: protect dry goods from moisture, such as baked products, powder products.
2. Acidic substance barrier. Prevent oxidation such as fat and fresh goods.
3. Carbon dioxide barrier. In MAP packaging, prevent the loss of carbon dioxide to achieve a stable packaging gas to constitute carbonated beverages.
4. Fragrance barrier. Protect the aroma from the package and lose it like coffee.
5. Odor barrier. Prevent absorption of external odors or loss of fragrance.
6. Light blocking. Prevent light oxidation such as dairy products.
7. The seal is firm. To seal the composite film, hot-press sealing is used.
Aluminized film has the best barrier properties. Vaporizing the metal onto the PET plastic film can also match the characteristics that are very close to that of the aluminum coating. The vaporization of aluminum vapor or silicon oxide to PET or OPP plastics also has a good barrier function. But there is no good light blocking ability.
Composite film formation
It is composed of two or more layers! The combined film must be inseparable like a film. This not only involves the drilling compound between the two films. It is also related to the ink film. Drilling compound is a synthetic product. Most drilling compound is a two-component poly (nitrogen vinegar) (PU) drilling compound. The chemical reaction in the drilling process solidifies the drilling compound. The drilling compound on the surface of the substrate is mainly a physical process, and only a small part is a chemical process. At this time, the components of the drilling compound and the components in the plastic film are drilled together and further cured.
If a film is already printed during the drilling process, the drilling compound and ink must meet more requirements. The most basic requirement is that the inner layer before compounding should have good adhesion fastness and thorough drying. This tastes better. No solvent residues are allowed in the printed film. However, solvents or alcohols often remain in the connecting material of the ink. For this reason, the performance of the drilling compound must be able to combine with free radicals (-OH groups). Otherwise, the drilling compound and the curing agent will have a drilling reaction by themselves and lose the feline nature that they should have. For example, in the compounding process, the film has been printed with PVB ink, and the isocyanate remains in the ink. The chemical base of the salt (NCO group) will react with the free radical OH of alcohol and water. No residue causes the drilling compound to fail to fully react. What followed was an insufficient curing and drilling effort.
Among the drilling compounds, there are differences between solvent-based drilling compounds and solvent-free drilling compounds such as UV drilling compounds. The solvent-based drilling compound requires a drying tunnel to evaporate the agent. When using a UV drilling compound, UV light passes through the film to reach the drilling compound to polymerize the bonding agent together.
Ink suitable for composite film
The ink suitable for the composite film should not only have good adhesion on a variety of films (OPA, OPP, PET-ALOX, PET-SiOX, PE, Alu), fully drill with the drilling compound, and strong Cohesion (cohesion of ink) and non-toxic safety are also very important. In addition, the further requirements in the composite film printing oil are: long-lasting patterns can be printed, aseptic and pasteurized simple stamping and perfect color processing and fast solvent volatility.
For composite film printing. Nitrocellulose (NC), Polybutene Butene (PVC), Polyvinyl Butyral (PVB) Nitrocellulose-Polynitrogen Vinegar (NC / PU) oil pan system should be considered first. It can be seen that the more plastic the system is adjusted, the more firmly the oil adheres to the substrate, so the better the compound fastness. The PVB ink system is suitable for almost all drilling applications. This system is currently the most widely used.
The NC / PU oil star system appeared late. But it has better performance in stamping, color processing and cleaning. It is a "universal" oil-in-oil system suitable for flexo and gravure printing. It is very environmentally friendly, with few failures under high-speed printing, rapid solvent evaporation, long-lasting sterilization and pasteurization. No plasticizer ingredients. At present, its market position is still relatively low but has shown a growing trend. The PU ink system widely used in Asia has similar characteristics and trends as the NC / PU ink system. It needs to be printed with a layer of white ink first when printing.
The market share of PVC ink systems is gradually declining. Because the ink used in it contains 'grade' ingredients, it cannot be used in packaging. In addition, the "vinegar" component contained in it will weaken the performance of the photopolymerization plate, so this ink system has not been considered in flexo printing. Therefore, it is currently only used in gravure printing.
Defect handling
Relevant laws and regulations have restricted this because of the susceptibility to environmental pollution caused by the penetration and transfer of ingredients in the oil and drilling compound, especially in the area of ​​composite film packaging for food and medicine.
In daily life, consumers should be particularly cautious when purchasing foods packed with composite film, because whether food packaging is environmentally friendly is related to their own health. If juice, soy sauce, olives, vinegar alcoholic beverages, skin care products, detergents, disinfection If unsuitable inks and drilling compounds are used for agents, bleaching agents, etc., it is possible that these inks or drilling compounds will be incorporated into beverages or food, which will affect the health of consumers.
Also monomeric plasticizers from oil walls or drilling compounds may penetrate (migrate) into the product. In addition, the durability of pasteurization, sterilization or heat sealing and drilling of composite membranes will be reduced if an unsuitable oil system and drilling compound are used.
Conclusion
When producing a variety of composite films that not only meet the legal requirements but also meet customer requirements, it is very meaningful to integrate the advantages of different materials in the composite film. But the production process of such composite membranes is also very complicated. It requires manufacturers to have a comprehensive understanding of the relevant tomb materials, oil systems and drilling compounds. And the interaction between these materials should also have a deep understanding to avoid problems with the post-processing of the composite membrane.
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