Four influencing factors to pay attention to when die-cutting overflow glue appears!
Design of tag shape
Tags with irregular shapes are more prone to overflow glue than square or rectangular tags.
Several basic judgment standards for pre-printing overflow glue
When the self-adhesive material of the roll-to-roll label is unwound on the printing press, if there is no pulling or a slight pulling phenomena between the upper and lower layers, the material can be judged as qualified. Of course, the temperature and humidity of the site should also be taken into consideration.
When the self-adhesive material of the single sheet label is fed on the feeder of the flexographic printing press, if there are pulls or adhesions between the upper and lower layers, the material can be judged as unqualified. Because the phenomenon of pulling between the upper and lower layers on the feeder will cause the self-adhesive material to run off, resulting in inaccurate overprinting.
Overflow glue after printing and die-cutting
If there is serious adhesion on the end face of the backing paper, and if there is obvious pulling phenomena during printing, it is very likely that glue will seep around the tag after die-cutting. It should be pointed out that overflow glue is also related to the displacement and shrinkage of tags on the backing paper. During the die-cutting process or the winding process after die-cutting, tag movement will cause single-sided overflow glue, and tag shrinkage will cause overflow glue around the tag.
Control of winding and unwinding tensions
Since the processed materials, production processes, and printing presses used are different, it is unrealistic to provide a "correct" tension data. The result of tension control is reflected in the tightness of the roll. Within the premise of confirming with the customer, it is best to wind the roll as loose as possible.
During printing (including inline die-cutting), the winding and unwinding tensions should be controlled as small as possible without affecting the accuracy of overprinting and post-processing. The tension of the winding should be smaller than that of the unwinding, and there should not be a significant difference in tension. When picking up a small roll after die-cutting, it should be possible to push up and down with the thumb at least. If the small roll cut after die-cutting is like an "iron pancake", the winding tension is definitely too large.
Acrylic emulsion adhesive and hot melt adhesive are commonly used adhesives for self-adhesive label materials.
The difficulty of die-cutting with hot melt adhesive is higher than that of acrylic emulsion adhesive. This is because the softer the adhesive, the sharper the die cuter needs to be so that it can quickly cut into the surface material during die-cutting without being hindered, and thus avoid overflow glue caused by the surface material squeezing the adhesive layer.
The softer the adhesive, the better the fluidity, and the faster the adhesive layer flows back after die-cutting. Therefore, when using hot-melt adhesive self-adhesive label materials, the shorter the distance between die-cutting and waste removal stations, the better. Waste removal should be done as soon as possible before the cut adhesive layer flows back and adheres together.
Since the melting point of hot melt adhesive is low (starting from 65°C), controlling the temperature of die-cutting can play a big role. Practice has proven that reducing the temperature during die-cutting can effectively prevent the hot melt adhesive from flowing back, allowing smooth waste removal (die-cutting is smoother in winter than in other seasons).
The initial viscosity of hot-melt adhesive is not conducive to die-cutting. High initial viscosity means that once the flowing adhesive touches, it will melt together (the time is shorter than that of acrylic emulsion adhesive), and the pulling phenomenon generated during waste removal is almost the same as that generated by uncut adhesive layer. The high initial viscosity of hot melt adhesive will cause the die cuter to firmly adhere to the adhesive during cutting, gradually accumulating a lot of adhesive on the surface of the tool. If the adhesive accumulated on the die cuter is not cleaned up in time, it will transfer to the tag and cause overflow glue during repeated die-cutting. Therefore, the die-cutting tool of hot melt adhesive needs to be treated with fluorine, and the adhesive on the tool needs to be cleaned up in time.
