Seeing this topic, you may say that now everyone is using solvent-free compounding, what is the focus of dry compounding? In fact, according to the survey, dry composite is still the main processing method of flexible packaging composite film in China. The demand for quality management, cost control and equipment upgrade of soft packaging enterprises is still high, so today we will bring you An article by Teacher Chen Zhixiong, he analyzed the inadequacy of domestic dry composite equipment and the unique design of imported dry composite equipment.
Coating method
In the adhesive transfer coating, the traditional domestic dry composite equipment still uses the anilox roller coating method, which makes the dry composite coating amount often difficult to break the limitation of floating at 4.0g/m2, which cannot meet the high limit. Application requirements for composite strength flexible packaging products. Moreover, the anilox coating method also causes the problem of uneven coating of the adhesive, although this problem can be improved by the action of a uniform roll, but the composite effect is still not satisfactory. Here are two of the most common negative cases: First, dry composite high temperature cooking bags. If the adhesive is not coated uniformly, after the high temperature sterilization process, it can be clearly seen that the surface of the high temperature cooking bag is large. the emergence of the phenomenon of uneven, due to the sterilization process at high temperatures, the stresses caused by uneven curing of the adhesive; the second is the production of flexible packaging printing in the composite film, when the adhesive is applied, since a uniform The action of the roller will have a certain negative impact on the adhesion of the ester-soluble ink.
In contrast, imported dry composite equipment, which can provide two or more kinds of glue coating methods for users to choose, one is the traditional anilox roller coating method; the other is similar to the flexo printing unit printing glue The method is two-roll or three-roll transfer coating. The latter allows the user to easily obtain a larger amount of glue and a more uniform coating effect. In addition, the glue unit can also be designed with a trolley structure to facilitate the installation, cleaning and replacement of the glue unit.
Routing route
In terms of the routing route, the traditional domestic dry composite equipment also has an unreasonable design. For example, after the substrate is coated, the drying unit is vertically raised, and when the coating amount is large, the base after coating is easily caused. The material has not yet entered the drying process, and the adhesive has been cast, which will further aggravate the uneven coating of the adhesive. In contrast, imported dry composite equipment, which has changed the vertical ascending route to the 45° climb mode, can easily and effectively avoid adhesive casting defects.
Drying method
In the drying method, the traditional domestic dry composite equipment uses the hot air directly to the surface of the adhesive to achieve the purpose of solvent evaporation, but this often brings some negative effects. For example, in the hot air with high wind speed, the surface of the adhesive will have “water ripple†phenomenon; the solvent of the surface of the adhesive which is first transferred by heat will first volatilize, and the solvent of the inner layer of the adhesive is not volatile, resulting in adhesiveness. There is scar on the surface of the agent, and the residual amount of the solvent exceeds the standard.
The volatilization of the solvent in the adhesive requires two basic conditions: first, the temperature, after the substrate is heated, when the solvent in the adhesive reaches the volatilization temperature, it can be volatilized; second, it is necessary to create a solvent concentration difference around the substrate. The conditions are such that the solvent in the adhesive is transferred to a low concentration oven and then carried away by the gas stream flowing in the oven. It can be seen that heating from the surface of the adhesive is not a reasonable heat transfer method.
In contrast, imported dry composite equipment, the oven design has used the method of heating from the substrate instead of heating from the surface of the adhesive. Design methods are: increasing from a bottom-heated oven at 45 ° climb the base station, the substrate is heated first, and then into the main oven, the main oven has upper and lower heat transfer tuyeres, wherein a The air nozzle is located between the lower guide rollers of the main oven. In addition to heat transfer, it can also play the role of floating the substrate. The other air nozzle is located on the upper part of the main oven to balance the floating of the substrate. "Semi-suspension oven design method". Another design method is referred to as a "full suspension oven design" in which the guide rolls in the oven are all eliminated and the substrate is completely in a floating state under the action of the up and down nozzles in the oven.
DONG GUAN CITY CHING XIN INDUSTRIAL CO LTD , https://www.chingxin.com