Dry compounding refers to a method of compounding the adhesive in a dry state. It is a process of coating the adhesive on a substrate, drying it through a drying path, drying all the solvents in the adhesive, melting the adhesive in a heated state, then bonding another substrate with it, then cooling it, and then aging to produce a composite material with excellent performance.

Dry composite products often have "small pockmarks" similar to bubbles, which are not bubbles after careful analysis. The distribution of small pits is uneven, but the size and thickness are almost the same, which can be seen in the blank of the substrate. This kind of "small pockmarks" has puzzled many soft packaging enterprises. We have dealt with it before. The probability of producing small pockmarks of two-component and two-liquid reactive adhesives is higher than that of single component hot-melt adhesives, and the composite structure of BOPP / OPP is higher than that of BOPP / CPP and PET / PE. There are three reasons.

(1) The adhesive is mixed with dust and other particles. There is too much dust in the air of the workshop environment. There is also dust in the hot air blown out of the drying channel after gluing. The dust is stuck on the surface of the adhesive layer and sandwiched between the two layers of base film when compounding, resulting in the opacity of the composite finished product. The solution is to use 180 mesh to filter the adhesive and remove the insoluble particles in the adhesive. At the same time, we should pay attention to the cleanliness of the workshop and keep the floor clean and clean without floating dust. In dry compounding, the glue barrel and glue tray must be cleaned before work. Especially in summer, the indoor temperature is high and the drying is fast. Before each shift leaves work, the residual adhesive should be poured into the bucket and sealed separately. In addition, a high mesh filter screen or other filter materials shall be used at the air inlet of the drying channel to remove the dust in the hot air. The two-component reactive adhesives are easy to turn white and turbid due to the influence of temperature. The "Turbid white" adhesives can not be reused, otherwise, the uneven distribution of adhesive layer will occur, resulting in the increase of "small pockmarks".

(2) The quality of basement membrane and composite membrane is not up to standard. If OPP hot compound is yellow and old, it should be checked carefully. Firstly, the surface tension should be measured. The surface tension of BOPP and pet should reach 38mn / M and 50Mn / m respectively. Low surface tension will lead to poor wetting effect of the material surface, uneven coating of glue solution, resulting in voids and small pockmarks in the finished product after compounding. Therefore, if the surface tension value of the film fails to meet the requirements, the film shall be treated as qualified before use. Secondly, the smoothness of the base film and the composite film is tested with a magnifying glass, and there is no concave convex phenomenon. If the surface of the material is uneven and the depth is different, the hot pressing roll can not fully adhere to the adhesive film after extrusion, and "small pockmarks" will appear. So it's crucial to choose the right material.

(3) The poor flatness of the upper rubber roller, the insufficient liquidity of the glue liquid and the poor flattening will result in "small pockmarks". It is required that the upper rubber roller is fine and smooth, preferably made of silicone rubber. With good fluidity, good flattening and even coating, the probability of "small pockmarks" can be reduced, and the transparency of composite products can also be improved.

[Dongguan Beite packaging material Co., Ltd.] located in Dongguan, a world famous manufacturing city, is an enterprise of gravure soft packaging, which has a complete set of advanced domestic production equipment: computer printing machine, dry compound machine, high-speed slitting machine, multi-functional bag making machine, hydraulic punch machine and all kinds of matching machinery; complete production of printing, laminating, slitting, bag making and manual production Production line: our company provides customers with high-quality products and first-class services with the support of scientific and human-oriented management system and a group of experienced technical personnel.