Лако-красочные материалы — производство

The single most important component on an edgebander is the gravure wheel applicator. All other components of the machine support the performance of the gravure wheel applicator. It is the gravure wheel application that controls the amount of hot-melt adhe­sive that is applied to the substrates, which, in turn, determines the number of calories of heat present to keep the hot-melt liquid until the time of bond formation.

Of the hot-melt adhesive that is located between the peaks and the doctor blade, only 1% is transferred to the substrate; the balance becomes nothing more than squeeze-out. The volume of adhesive that is found in the groove area is the actual material that is transferred to the substrate edge. The purpose of the doctor blade is not to act as an adjustment to increase or decrease adhesive transfer to the substrate; rather, it serves to replace in the grooves the adhesive that has transferred to the substrate. An incorrect doctor-blade setting will either cause excess squeeze-out or insufficiently fill the grooves, which will result in less than maximum adhesive transfer. The volume of adhesive that is transferred to the substrate is the single major controlling factor in determining the open time of the hot-melt adhesive. The volume of adhesive that does transfer is preset at the factory and is determined by the actual dimensions and geometry of the groove area.

If the adhesive is too cohesively strong (too cold) or too cohesively weak (too hot), the adhesive will break out of the top of the groove in the gravure applicator wheel, reducing the adhesive transfer. This is exactly why the open time of the hot-melt adhesive is determined by the amount of adhesive transferred, not by raising the application tem­perature. If the shear force is too low to move the adhesive from the gravure applicator wheel (slow line speed), adhesive transfer is reduced from maximum; too high a shear force (fast line speed) also reduces transfer. Shear force affects the cohesive strength of the hot melt exactly like temperature.