There is provided a dust collecting unit of a vacuum cleaner, the dust collecting unit being designed to increase the density of foreign substances collected in a dust collection container. A non-metallic, substantially deformable, proppant particle is \u201celastically flexible\u201d or \u201cplastically compressible\u201d and adapted for use at concentrations which will substantially create a partial monolayer. The roller carries the plated liquid toner and applied the plated toner to a substrate. Secondary welding is carried out with the rotation of the glass tube around an axis.