In the dry compounding of plastic films, edging failures often occur. The so-called sticky edge, that is, in the dry composite, the plastic film after coating gluing by the drying tunnel heating and drying, and then squeezed by hot-pressed steel roller after the winding, winding the finished product on both sides of the phenomenon of adhesion together. After the rolling-up of the rolled product occurs, the film is tightly bonded at both ends of the roll and the film is difficult to separate. Especially in the use of two-component two-liquid reactive adhesives are most likely to occur, severe composite products will be pulled off, pull deformation, the product scrapped, quite a headache.

I have a deep understanding of the dangers of sticky edge failure. After a long period of practical exploration, it has been found that there are various forms of sticky edge failures, but as long as they are taken seriously, early prevention can minimize sticking edge failures.

1. The relationship between the amount of glue applied and the sticky edge

We know that the amount of sizing is determined by the depth of the sizing and depth of glue on the anilox roller.

At present, many small-scale printing companies use the compound machine whose gluing system is still non-scraper. The biggest difference between the non-squeegee type sizing system and the squeegee type sizing system is that the non-squeegee type sizing system adjusts the amount of gluing through the threaded rods at both ends of the squeegee roller, and the squeegee type sizing system is adjusted by the squeegee and the anilox roller. The amount of glue.

For a compounder using a squeegee type sizing system, the pressure and angle of the squeegee are important. Squeegee pressure is not enough, the amount of glue is bound to be more, often because of this, resulting in a composite finished product sticky edge. The angle between the scraper and the anilox roller is 35°, and the angle is too easy to damage the anilox roller and shorten the service life of the anilox roller. When the angle is too small, the glue is more, and the edge is easy to stick. The pressure of the scraper is regulated by a handwheel and the angle of the scraper is adjusted by the thread wheel on the knife holder.

A compound machine that does not use a squeegee type gluing system controls the amount of sizing by adjusting the pressure between the squeegee roller and the anilox roller. Light pressure, large amount of glue, or small amount of glue. In the course of operation, if the pressure on both sides is improperly adjusted, the adhesive layer must be thick and thin on one side, and the thick side of the adhesive layer is squeezed out by the hot-pressing roller and the adhesive is squeezed out, and a sticky edge failure occurs.

There are two steps to resolve this failure:

(1) Before gluing, first press the threaded rod on both ends of the gluing roller tightly, and then slowly adjust the gluing amount during the operation. The amount of glue should not be too large.

(2) Detect the amount of glue on the rubber roller. The most direct method is to use the index finger to squeeze the rubber roller and observe the thickness of the glue that is squeezed. It must be ensured that both sides are consistent and safety must be observed. It is best done by skilled workers.

2. The relationship between drying temperature and sticky edge

Drying machine drying system is divided into three areas, namely: evaporation area, hardening area, eliminate odor areas. The energy consumed in these three areas is almost equal. The evaporation zone temperature is generally controlled at 60-70°C, and the hardening zone and the exclusion of the deodorization zone are generally controlled at 70-80°C. Of course, with the changes in ambient temperature and humidity and the structure of composite products, adjustments need to be made accordingly.

In practice, we have noticed that when the width of the composite substrate is more than 60cm and the thickness is more than 38μm, the evaporation zone temperature should not be lower than 65°C, and the hardening zone temperature should be increased accordingly. Otherwise, stickiness will occur due to the stickiness. In addition, if the speed reaches 80m/min, the drying lane should also increase the temperature accordingly, which is beneficial to the volatilization of the flux, leaving no odor; secondly, it can also make rapid reactions between molecules of the glue, which is good for improving the quality. If the drying temperature does not meet the requirements, after the hot-pressed steel rolls are pressed, the edges of the composite film are prone to sticking failures. Insiders often say such a sentence: the two sides of the film are sticky, speed and temperature are related. Visible temperature control is very important.

3. The relationship between the width and the width of composite materials

Sticking edge failure is directly related to the width of the composite material. If the width of the printed substrate is greater than the width of the composite substrate, sticking will definitely occur. At the same time glue will stick to the hot roller, seriously affecting product quality.

The solution is to increase the width of the composite substrate. Under normal circumstances, the width of the composite substrate is 1 cm wider than that of the printed film, that is, 0.5 mm on both sides, which is beneficial to avoid the occurrence of sticky edge failure.

There is also a solution - "reversal" method, that is: the printing film as a "composite substrate" for composite, you can avoid the "sticky edge" failure. However, this method is only applicable to BOPP/OPP composite structures or OPP/PET composite structures.

When gluing the composite substrate, care must be taken to ensure that the coating surface cannot be reversed and must be coated on the corona treatment surface of the film.

4. Sticky edges caused by other factors

In dry compounding, the role of the pressure roller is to compact the film and the coating roller so that the coating is uniform and no bubbles are generated. The width of the pressure roller is generally narrower than the width of the film by 0.5mm. If the width is the same or is too large, the glue liquid on the rubber roller is easily pressed by the hot steel roller when the glue is applied. When the composite structure is PA/CPE, sticky edges are most likely to occur.

In addition, the printed substrate is uneven, and it swings left and right during operation. Displacement during compounding also easily leads to sticky edges. The solution is: the printing substrate is first rolled with a flat-rolling machine to ensure that it will not be displaced during compounding, and no glue will be attached, so that the sticky edge failure of the rolled product can be avoided. For high-speed dry laminating machines, there is no need for roll-leveling because of the electric eye tracking.

Sticky edge failure is also related to the hardness of the rubber roller. Two-component rubber rollers are prone to "hardening" after being used for a period of time. The lack of elasticity makes it easy to produce glue spillage when the glue is applied. The spilled glue liquid "runs" toward both sides, creating conditions for sticky edges. The solution is: aging the rubber roll in a maturation room at about 50°C for 1 to 2 hours to reduce the degree of hardening and improve its surface elasticity, so that the glue can be coated evenly to ensure that the glue does not overflow, thereby reducing the occurrence of sticky edges. Chance.

Traction roller cleaning is also an important factor. If the glue is inadvertently adhered, it must be wiped clean to avoid sticking and sticking.

In summary, there are many kinds of sticky edge failures, but as long as they are summed up and the right medicine is prescribed, the sticky edge failure can be minimized.

Source: Guangzhou Food Safety Network