Solvent-free laminating process implementation, the composite film appeared “point” is a relatively common anomaly. Its causes are physical and chemical reasons.

Physical causes of the “point” and chemical causes of the “point” from the external appearance, formation mechanism and solutions are different. Therefore, this “point” is not the other “point”, should be carefully screened and treated separately, can not be “the same”.

1, the physical causes of the formation of “points”
(1) Appearance: irregular distribution, often the number of different areas of the ink layer thickness is different.
Cause analysis: the amount of glue is too small. Coated glue is not enough to fill the gap in the ink layer in the composite film and the pits on the surface of the material, the formation of the “point”. In fact, no glue and the formation of the “gap”.
Solution: increase the amount of glue.
(2) Appearance characteristics: some “points” periodically concentrated and repeated in a fixed area of the pattern.
Reason analysis: because in the transfer steel roller, transfer roller, coating steel roller, coating roller, a roller on the adhesion of foreign objects, or a roller on the mechanical defects, resulting in a specific area on the amount of glue transfer bad, and the formation of the “point”.
Solution: According to the length of the periodic recurrence, compared to the circumference of the rollers, to find out where the problem is the roller, and clean up foreign objects or repair defects.

2、Chemical reasons for the formation of the “point”
External characteristics: irregular distribution, but the distribution of a wide range of “points” of different sizes, especially in wet weather, good barrier (such as aluminized film) is more likely to occur when the material structure of the composite.
Cause analysis:
Two-component solvent-free adhesive in the isocyanate (-NCO) component and the water in the air to produce derivatization reaction, the generation of carbon dioxide gas, because these gases can not be precipitated from the barrier of good composite film, silt collection in the formation of composite film between the “point”.
Therefore, these points are actually carbon dioxide “bubbles”.

3, how to avoid the composite membrane “point”?
(1) Avoid “points” in the laminated film caused by insufficient glue or uneven glue application by the following measures:
Reasonably set the amount of glue applied to various composite structures.
Pay attention to keep the coating unit rollers clean, clean up the adhering foreign matter in time.
Often check the surface condition of each roller of the coating unit, and replace the roller with defective surface in time.
Reasonably set the level of glue in the storage tank, often observe the status of the glue in the tank, and deal with the abnormal phenomena such as the mixture of glue siltation, viscosity, lumps, and so on in a timely manner.
(2) through the following measures to avoid the composite film due to the reaction of water and glue in the air caused by the “bubble”:
Control composite operation, curing environment humidity, general relative humidity control in 70% or less;.
Regularly replace the glue mixer storage drum desiccant, to ensure that the air inside the storage drum is dry.
Glue drums (especially curing agent components) open, if there is a surplus of glue, should be closed tightly in time, and as soon as possible will be the surplus of glue with out;
Create a relatively closed space for solvent-free laminating process, which is conducive to the control of temperature and humidity.