Bubbles due to insufficient coating
Insufficient coating is a relative concept. For composite non printing transparent film, the coating amount of 1.8-2.2 G is enough, and the composite printing film is better than 2.8 G.
When determining the coating amount, not only the peeling strength, but also the leveling of coating should be considered. The leveling is also related to the use of even cots, the surface tension of base materials and adhesives, and the viscosity of working fluid. If the comprehensive conditions are good, the coating amount can be reduced properly.
If the coating amount is not enough, bubbles will be produced, and the peel strength will be decreased. However, if the coating amount is too large, the ink will fall off and transfer from the printing substrate. Local coating is difficult to identify, the reason is also very complex.
Bubbles caused by poor drying of adhesive
Compound found after the bubble, the operator's first reflection is to increase the coating amount, in general, it is still very effective. But the coating amount increases after drying more difficult, sometimes if you do not adjust the drying capacity, or there are bubbles. However, the bubble is not the original coating caused by insufficient, into a poor drying bubble.
Generally speaking, due to the coating state is poor (including coating amount is insufficient) and generated bubbles, the atmosphere bubble after aging is small, small bubble. However, the air bubble of the composite film with poor drying will be larger after aging, because the solvent evaporated from the coating will gather to the surface. The structure of BOPP / CPP was BOPP / CPP. If the bubble is small enough and the barrier of a certain layer of film is poor, the small bubble can disappear after aging.
If the barrier property of a film is poor, such as BOPP / Al, the solvent gathered on the surface of the adhesive layer will permeate the film and volatilize, and the smaller bubbles can disappear after aging. However, it is not so lucky when the same process is applied to PET / Al structure, and the bubbles can not disappear. The structure of PET / Al has good barrier property on both sides of the substrate, and the bubbles caused by solvent residue can not disappear.
The key to solve the problem is to accurately determine the causes of bubbles
The main solution is to adjust the drying capacity of the compound machine. Many compound operators only want to increase the temperature of the drying oven. However, most of the poor drying problems are caused by poor ventilation. The exhaust air volume is small, and the inlet air volume is also small, otherwise the drying oven will overflow the air. At this time, although the temperature is high, the drying capacity is still very low.
Another method is to reduce the compound speed, but sometimes the effect is good, sometimes it is not obvious. The reason is that the change of speed leads to the change of coating amount. If the glue concentration is low, the speed reduction is effective; when the glue concentration is high, the effect of speed reduction is not obvious.
It is a good method to reduce the coating amount, but it is very complicated to do so, and it is not simply to reduce the working concentration of the glue solution.
Bubbles caused by poor ink drying
Poor ink drying will also produce bubbles in the composite, this reason is often ignored. The bubbles produced by high ink residue are characteristic: bubbles often appear in the part with high overprint rate, and there are few bubbles where the overprint rate is low.
In order to eliminate this kind of bubble, we can only deal with the printing film. For example, the printing film can be dried again with a printing machine or a compound machine, and then the bubbles can be eliminated smoothly.
Poor drying does not necessarily produce bubbles, generally speaking, the residue is not too serious, or other conditions do not have no bubble, it will show in other forms, we should attach great importance to it.
Air bubbles caused by clogging of Cots
However, it is different from that of printing, which often leads to misjudgment.
The first type of blocking is that the gluing roller is not cleaned with washing solution for a long time, and the amount of glue is gradually decreased, and finally bubbles are produced. Strictly speaking, this type of blocking is not an accident, with the extension of the cot use time, the coating amount continues to decline is an inevitable phenomenon.

In order to maintain the amount of glue and constantly improve the working concentration of adhesive. If you have been monitoring the amount of coating, then when there will be bubbles will have a premonition.

In normal production, when a product is changed, there will be bubbles or white spots, which is a common phenomenon of blocking accidents of cots. Different products, different films and even different inks have different requirements for the amount of glue applied. If we lack the monitoring of the coating amount, we will be puzzled and can't imagine that it is the glue roller blocking. The bubble produced by the clogging of the cot is not different from other kinds of bubbles, so it needs to be distinguished carefully.
Bubbles produced by incomplete drying. Bubble formed by coating roller blockage
In the high temperature season, the evaporation rate of solvent becomes faster. For example, the relative evaporation rate of ethyl acetate is 6 at 25 ℃ and increases to 9 at 35 ℃.
Printers are familiar with this situation, they will adjust the proportion of ink solvent, increase the proportion of slow drying solvent to prevent blocking.
Whether domestic or imported polyurethane adhesives, no use of mixed solvents, the reason is that the residual solvents exceed the standard, so summer is the high incidence season of composite blocking plate.
Fine anilox roll in summer prone to block, because the number of lines of high coating roller mesh is relatively shallow; in order to maintain the coating amount, but also to improve the working concentration.
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