1.Causes, Rectification, and Misconceptions
In solvent-free lamination production, ink dissolution, pattern blurring, and core blurring are frequent quality problems and the most easily misdiagnosed "difficult cases." The root cause is not a single equipment malfunction, but a systemic deviation in materials, processes, environment, and operation.
I. Five Core Causes
1. Insufficient Adhesive Curing Speed (Most Common): Slow-curing PU adhesives have a slow cross-linking reaction, resulting in a longer liquid state and easier penetration and compression of the ink layer. Pressure is concentrated at the core of large-diameter products, making ink dissolution particularly severe.
2. Inadequate Corona Value on Printed Film Surface: When the corona value is <38 dyn, ink adhesion is weak, and the flowing adhesive layer easily causes the ink layer to shift and detach.
3. Imbalanced Temperature and Humidity in the Workshop: Low temperature and high humidity delay curing, while high temperature exacerbates adhesive layer fluidity-both extremes aggravate ink dissolution.
4. Special Pattern Structures: Full-page solid backgrounds, large areas of overlapping colors, and light-colored halftone patterns are the most problematic areas. The thicker the ink layer, the more obvious the pigment dispersion after adhesive penetration.
5. Excessive speed: Uneven glue application, concentrated pressure at the moment of winding, and adhesive directionally washing over the ink layer.
II. Targeted Rectification Plan
• Conduct ink-adhesive compatibility simulation tests, replicating actual working conditions (adhesive application amount, speed, winding pressure, curing conditions), and observe for at least 72 hours.
• Fix the adhesive brand and batch; small-batch trial runs are required before any change.
• Select solvent-free special adhesives with low permeability and high initial tack.
Process (On-site Implementation):
• Adhesive application amount: Less is not always better. Too little will cause white spots, while too much will lead to excessive adhesive flow. Adjust the amount appropriately for high-risk patterns and avoid adhesive buildup.
• Curing: Use stepped heating; extend curing time for larger roll diameters.
• Winding: Gradually reduce the taper setting, "tight at the beginning, loose at the end," prioritizing loose winding for curing of larger roll diameters.
• Lamination speed: Appropriately reduce speed for high-risk patterns, allowing time for adhesive layer setting.
• Temperature 25-35℃, Humidity 50%-65%
• Allow sufficient settling time after printing; laminate only after the ink is completely dry.
III. Quick Differentiation in Three Minutes (To Avoid Misjudgment)
IV. Summary in One Sentence
Ink dissolution is not an equipment malfunction. The key is to control the entire process: "ink-resin compatibility → curing process → winding pressure → temperature and humidity." Adjustments can be made for high-risk pattern variations, and small-roll testing can be conducted to verify the results. This can significantly reduce ink dissolution failure rates.
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