After the soft pack factory is steamed, the packaging bag is delaminated and wrinkled. What is going on?

After the soft pack factory is steamed, the packaging bag is delaminated and wrinkled. What is going on?

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A color printing factory uses retort-resistant polyurethane ink, prints nylon and then composites CPP. After the bag is not subjected to the cooking test, it is sent to the food factory for packaging food, but after cooking, it is found that the packaging bag has printing ink where the nylon delamination wrinkles, how What about it?

Experts suggest that the first analysis of polyurethane ink systems

Composition of polyurethane ink: pigment, polyurethane resin, auxiliary agent, solvent, etc. The diluent solvent composition of the polyurethane ink generally includes butanone, ethyl ester, butyl ester, isopropanol, toluene, and the like.

Adhesive Mechanism of Polyurethane Adhesive: The main agent is a polyurethane with a -OH end-capping and a curing agent-NCO-terminated polyurethane, which reacts to form a larger molecular weight polyurethane to form an adhesive force. Therefore, the alcohol with -OH and the material with -NH2 interfere with the post-composite processing.

By the same token, the polyurethane resin in the ink itself 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

First, the solution to the dilution solvent in the polyurethane ink is solved first, and the solvent is not diluted as much as possible. If alcohol-based thinners must be used for printing, it is also necessary to minimize residual solvents during printing.

Second, if there is a white ink printed film, it is best to add a small amount of hardener in the white ink to increase the composite fastness. However, the ink with the hardener is used for a short period of time. If there is any remaining, and the interval is longer, it should not be used in principle. (But this kind of operation is wasteful, just for reference.)

3. The purity of ethyl acetate used for the dilution of the adhesive is high, and the moisture and alcohol content are as low as possible. This is the quality assurance of the retort pouch. In addition, when the adhesive is prepared, the amount of the curing agent is appropriately increased (the increase ratio is Between 5% and 10% of the curing dose, that is, adding 0.05 to 0.1 kg of curing agent to add 1 kg of curing agent to ensure sufficient crosslinking of the adhesive main agent and curing agent.

The ink of polyurethane system is the development direction of printing ink, and the ink of chlorinated polypropylene system will be gradually eliminated. Therefore, only by grasping the characteristics of polyurethane system ink well, it can effectively avoid some quality problems in compounding.