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A, failure phenomenon:
In thousands of packaging substrates, such as soft polyvinyl chloride or cellulose plastics, the ink film softens after ink printing or varnish coating, adhesion after printing of other substrates, migration, and back Viscosity phenomenon, in contrast to some plasticizer containing inks or glazing oils, softening point of the ink system binder resin, after a period of time, the ink film or oil film layer is brittle (adding excess plasticizer, once printed Absorption is anti-migration).
B. Reasons:
The migration of the resin binder or excessive plasticizer with too low a softening point between the plastic and the ink layer is often restricted by various factors. We know that this restriction should have the following conditions: (1) with the substrate Type and type, when only adding a small amount of plasticizer to increase the elasticity of the substrate, the migration is small, and soft plastic packaging products often contain more plasticizers, it is inevitable that migration does not occur. Of course, 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. As we all know, the migration of plasticizers is inversely proportional to the square of their own viscosity, which is related to the molecular weight is too small, the molecular structure, whether the oligomer plasticizer with branches, etc., plasticizers and plastic substrates The closer the cohesive energy is to each other, the higher the degree of mutual integration and the less migratory. (3) It is related to the processing methods and printing, coating, finishing and production processes of the substrate plastic twice or three times. If the temperature is high and the time is long, adhesion and migration will occur easily.
C. Countermeasures:
In packaging and printing products, in order to solve the problem of low adhesion and migration of plasticizers due to the low softening point of inks and varnish systems, we should consider two aspects: printing plastics, printing inks, or varnish: (1) It is possible to use resins with a high softening point as the binder for the ink or coating, with as little or no plasticizer as possible. (2) Use plasticizers with small or no migration as much 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 little chance of changing the substrate itself, and in many cases the parameters of the softening point of plasticizers and binder resins in packaging printing products are unknown. The practice of experiments is required to regulate the compatibility of ink or varnish formulation components in research institutions or manufacturing companies that require inks or coatings.
2.5 adhesion, migration: