[Technology] When Using Polyurethane Ink, Pay Special Attention to This Point During Lamination!
- In the PET12/VMPET12/CPP60 sample, the outer PET/VMPET peel strength is 1.5 N/15 mm, with ink separating from the aluminum coating and the adhesive remaining tacky and incompletely cured, still tacky after 24 h at 80°C and 24 h humid-air exposure.
- The inner VMPET/CPP layer formed by one-pass lamination has a peel strength of 3.5 N/15 mm and shows no tackiness or incomplete curing.
- The conclusion identifies the non-drying component as -OH, indicating that part of the curing agent in the adhesive has been consumed, so the effect of polyurethane ink on incomplete curing requires close attention.
- The ink is a benzene-free and ketone-free polyurethane ink with a solvent ratio of ethanol:ethyl acetate:n-propyl acetate = 2:3:5, a total residual of 3.6 mg/m2, and alcohol solvents accounting for 0.2 mg/m2.
- The solution is to add ink curing agent during printing and, based on actual curing, appropriately add 10%–20% more curing agent when mixing the adhesive.
Incomplete curing of adhesive is one of the most common quality problems in the lamination process.
There are many causes of this problem. For example, inaccurate mixing ratio, excessive moisture or alcohol content in the solvent, too high ambient humidity, improper storage of leftover adhesive, and insufficient crosslinking degree of the adhesive itself can all lead to incomplete curing. Among them, particular attention should be paid to the effect of polyurethane ink on the incomplete curing of adhesive.
The following is a specific case:
The structure of the sample is: PET12/VMPET12/CPP60
The sample analysis is as follows:
- The peel strength of the outer layer PET/VMPET is 1.5N/15mm. During peeling, the ink separates from the aluminum coating. Depending on the peeling angle, a minor amount of ink or aluminum transfer may occur. The adhesive exhibits tackiness and incomplete curing. After continued curing in an 80℃ oven for 24h, the tackiness showed no obvious change. After the peeled strip was exposed to humid air for 24h, the strip was still tacky.
- The peel strength of the inner layer VMPET/CPP formed by one-pass lamination is 3.5N/15mm, with no tackiness or incomplete curing.
Conclusion: The non-drying component is an -OH component, indicating that part of the curing agent in the adhesive has been consumed.
Several products from the customer all show this phenomenon.
Cause analysis:
- The processing was done in a single pass, and no additional adhesive mixing was carried out during production.
- The ink is a benzene-free and ketone-free polyurethane ink. The solvent is ethanol:ethyl acetate:n-propyl acetate = 2:3:5. The total residual amount is 3.6mg/m2, of which alcohol solvents account for 0.2mg/m2.
How should such problems be addressed?
Since the problem point is very clear, the solution is actually not complicated. As long as such problems are noticed and vigilance is maintained, issues generally will not arise.
The specific solutions are as follows:
- Choose suppliers with stable product quality
- Keep the combination of ink and adhesive relatively stable
- Conduct compatibility tests when changing ink or adhesive
- Add ink curing agent during printing, and according to the actual curing situation, appropriately add 10%~20% more curing agent when mixing adhesive.
Of course, in order to better help customers solve such problems, Beijing Huateng has also been making continuous efforts to improve adhesives. Relying on strong technical support, it has developed a fast-curing adhesive UK3160DK/UK5060, which also delivers very good results in solving such problems.
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