Technical defects and remedies of ink in printing (6)

Adhesion, migration:

Fault phenomenon:

In thousands of packaging substrates, such as soft polyvinyl chloride or cellulosic plastics, the ink film softens after ink printing or varnish coating, and adhesion, migration, and backing of other substrates occur after surface printing. Viscosity phenomenon. On the contrary, some binder resins containing plasticizers, inks or polishes, and softening points are too low. After a period of time, the ink film or oil film layer becomes brittle. If excessive plasticizers are added, once absorbed by the substrate, It is anti-migration.

cause:

The mobility of resin binders or excessive plasticizers with too low a softening point between the plastic and the ink layer is often constrained by a number of factors. This constraint has the following conditions: (1) The type and type of the substrate Relevant, when only adding a small amount of plasticizer to increase the flexibility of the substrate, the migration is small, and soft plastic packaging products often contain more plasticizers, it is inevitable that migration does not occur. However, substrates with good chemical stability and high molecular weight are less likely to experience this phenomenon. (2) It is related to the type of plasticizer. The migration of the plasticizer is inversely proportional to the square of its own viscosity, which is related to the molecular weight is too small, the molecular structure, whether the oligomer plasticizer with branching and so on. The closer the cohesive energy between the plasticizing aid and the plastic substrate, the higher the mutual binding and the smaller the mobility. (3) It is related to the multiple processing methods of substrate plastics and packaging printing or coating finishing and production processes. If the temperature is high and the time is long, adhesion and migration will occur easily.

Countermeasures:

In packaging printing products, in order to solve the problem of migration of plasticizers due to the low softening point of inks and varnish systems, we should consider two aspects: printing materials plastics and printing inks or coating oils:

(1) Use as high a softening point resin as possible as an ink or varnish binder with as little or no plasticizer as possible.
(2) Use plasticizers that are as small or non-migrating as possible.

(3) Strive to achieve the best state of balance (balance) between the ink or varnish and the substrate. In the daily production, for the purpose of packaging and printing, we often have very little possibility of changing the substrate itself, and in many cases the parameters of the softening point of the plasticizer and binder resin in the packaging printing products are unknown. In practice, the research unit or manufacturing company that requires inks or coating oils, in combination with the surface pretreatment, adjusts the compatibility of the ink or varnish in the formula design.




Hunan Packaging Liu Jiaju