In the dry compounding of plastic film, the edge-gluing failure often occurs. The so-called sticky edge refers to the phenomenon that the plastic film is heated and dried by the drying channel after being coated and glued, and then squeezed by the hot-pressing steel roller and then wound up. The two sides of the wound up product are stuck together. After the adhesive failure of the finished product is wound, the film layers are firmly bonded between the two ends of the coil material, which will make the separation of the finished film difficult. Especially when the two-component two-liquid reactive adhesive is used, it is most likely to occur. In severe cases, it will cause the composite product to be broken or deformed, making the product scrapped, which is quite a headache.
I have a deep understanding of the hazards of sticky edge failures. After long-term practice and exploration, it is found that there are many forms of adhesive edge faults, but as long as it is taken seriously and early prevention, the adhesive edge faults can be minimized.
1. The relationship between the amount of glue applied and the edge
We know that the amount of glue is determined by the depth of the anilox roller and the concentration of glue.
At present, the gluing system of compound machines used by many small printing enterprises is still non-squeegee type. The biggest difference between the non-squeegee gluing system and the squeegee gluing system is that the non-scraper gluing system adjusts the amount of gluing through the threaded rods at both ends of the gluing roller, while the squeegee gluing system is adjusted by the squeegee and anilox roller The amount of glue.
For the compound machine adopting the doctor blade gluing system, the pressure and angle of the doctor blade are very important. If the pressure of the scraper is not enough, the amount of glue must be large, often because of this, resulting in the bonding of the composite product. The angle between the doctor blade and the anilox roller is preferably 35 °. If the angle is too large, the anilox roller will be easily damaged and the service life of the anilox roller will be shortened. If the angle is too small, more glue will be applied and the edge will be easy to stick. The pressure of the scraper is adjusted by a hand wheel, and the angle of the scraper is adjusted by the threaded wheel on the knife holder.
The laminating machine that does not use the scraper gluing system controls the amount of gluing by adjusting the pressure between the gluing roller and the anilox roller. Light pressure, large amount of glue, otherwise small amount of glue. During the operation, if the pressure on both sides is improperly adjusted, the adhesive layer must be thick on one side and thin on the other. After the thick side of the adhesive layer is squeezed out by the hot pressing roller, the adhesive failure will occur.
Two steps can be taken to solve this problem:
(1) Before gluing, press the threaded rods at both ends of the gluing roller tightly, and then slowly adjust the amount of gluing during operation. The amount of glue should not be too large.
(2) Detect the amount of glue applied by the rubber roller. The most direct method is to squeeze the glue roller with your index finger and observe the thickness of the glue at the place where it is squeezed. You must ensure that both sides are consistent, and you must pay attention to safety. It is best done by skilled workers. [next]
2. The relationship between drying temperature and sticky edge
The drying system of the dry compound machine is divided into 3 areas, namely: evaporation area, hardening area, and odor elimination area. The energy consumed by these three sections is almost equal. The temperature of the evaporation zone is generally controlled at 60-70 ° C, and the temperature of the hardening zone and the odor-exclusion zone is generally controlled at 70-80 ° C. Of course, with the changes in the surrounding temperature and humidity and the structure of the composite product, it needs to be adjusted accordingly.
In practice, we have noticed that when the width of the composite substrate exceeds 60cm and the thickness is above 38μm, the temperature in the evaporation zone should not be lower than 65 ° C, and the temperature in the hardening zone should also be increased accordingly, otherwise it will easily stick and cause sticking. In addition, if the machine speed reaches 80m / min, the drying tunnel should also increase the temperature accordingly. Firstly, it is conducive to the volatilization of the flux without leaving odors; secondly, it can also cause rapid reaction between the glue molecules, which is good for improving the quality. If the drying temperature does not meet the requirements, after being extruded by the hot-pressed steel roller, the two sides of the composite film are prone to adhesive edge failure. Experts often say that the two sides of the membrane are sticky or not, and the speed and temperature are related. It can be seen that temperature control is very important.
3. The relationship between the width of the composite material and the sticky edge
The edge sticking fault is directly related to the width of the composite material. If the width of the printed substrate is larger than the width of the composite substrate, edge sticking will definitely occur. At the same time, the glue will stick to the hot roller, which seriously affects the quality of the product.
The solution is to increase the width of the composite substrate. Under normal circumstances, the width of the composite substrate is 1cm wider than the printed film, that is, each side is 0.5mm wider, which is beneficial to avoid the occurrence of edge adhesion failure.
There is also a solution-the "inverted" method, that is, to use the printed film as a "composite substrate" to compound, you can avoid the "sticking" failure. But this method is only applicable to BOPP / OPP composite structure or OPP / PET composite structure.
When coating the composite substrate, please pay attention: the surface of the glue can not be reversed, and the glue must be coated on the corona treatment surface of the film. [next]
4. Sticky edges caused by other factors
In dry lamination, the role of the pressure roller is to compact the film and the coating roller to make it evenly coated without generating bubbles. The width of the pressure roller is generally 0.5mm narrower than the width of the film. If the width is consistent or too large, when the glue is applied, the glue on the rubber roller is squeezed by the hot steel roller, which may easily cause the edge of the finished product to be wound, especially when When the composite structure is PA / CPE, sticking is most likely to occur.
In addition, the printed substrate is not flat, swings left and right during operation, and displacement during compounding can easily lead to sticking. The solution is to roll the printed substrate with a roll-leveling machine to ensure that it does not move during compounding, so that no glue will be attached, and the edge-winding failure of the finished product can be avoided. For high-speed dry laminating machine, there is no need to wind flattening because of the electric eye tracking.
The edge sticking fault is also related to the hardness of the top roller. After being used for a period of time, the two-component rubber roller is prone to "hardening" and lacks elasticity. It is easy to cause glue overflow when gluing. The overflowed glue "runs" to both sides, which creates conditions for the adhesive edge. The solution is: place the glue roller in the curing room at about 50 ℃ for 1 to 2 hours to reduce the degree of hardening and improve its surface elasticity, so that the glue is coated evenly, ensure that the glue does not overflow, thereby reducing the occurrence of adhesive edge faults Odds.
Whether the traction roller is clean is also an important factor. If the glue is accidentally attached, it must be wiped clean to avoid sticking to the rollers and edges.
To sum up, there are many kinds of sticky edge failures, but as long as they are carefully summarized and treated properly, the sticky edge failures can be reduced to the lowest point
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