Sichuan color printing plant using a retort polyurethane inks, printing and nylon composite CPP, into the compound prepared in the bag and no cooker test, it is sent to the food packaging food plants, but after retort pouch have found local delamination of the printing ink nylon Wrinkled, what's going on?
Experts suggest that we must first analyze the polyurethane ink system
Composition of polyurethane ink: pigment, polyurethane resin, additives, solvents, etc. The dilution solvent components of polyurethane ink are generally: butanone, ethyl ester, butyl ester, isopropyl alcohol, toluene and so on.
Adhesive mechanism of polyurethane adhesive: The main agent is polyurethane with -OH end capping and polyurethane with -NCO end capping agent , which react to form polyurethane with larger molecular weight to form adhesive force. Therefore , alcohols with -OH and substances with -NH2 have a greater interference on post-composite processing.
For the same reason, the polyurethane resin itself in the ink is also -OH- terminated, and can also react with the polyurethane adhesive curing agent. Therefore, it is not difficult to explain the phenomena in the above two examples.
solution
1. The first is to solve the problem of diluting the solvent in polyurethane ink, try not to dilute the solvent without alcohol. If alcohol diluent must be used during printing, it is also necessary to minimize residual solvents during printing.
2. If there is a printed composite film with white ink on the bottom , it is best to add a small amount of hardener in the white ink to increase the composite fastness. However, the use period of the ink added with the hardener is short. If there is surplus, and the interval time is longer, it should not be used in principle. (However, this operation is wasteful, and it is for reference only.)
3. The purity of the ethyl acetate used for the dilution of the prepared adhesive is high, and the content of water and alcohol is as low as possible. This is the quality assurance of high-temperature cooking bags . In addition, when preparing the adhesive, the amount of curing agent is appropriately increased (increasing the proportion It is between 5% and 10% of the curing dose , that is to say, adding 1kg of curing agent requires adding 0.05 to 0.1kg of curing agent) to ensure that the main agent of the adhesive and the curing agent are fully cross-linked.
The ink of polyurethane system is the current development direction of printing ink. The ink of chlorinated polypropylene system will be gradually phased out. Therefore, only a good grasp of the characteristics of the ink of polyurethane system can effectively avoid some quality problems in compounding.
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