Abstract: A bag for packing powder, permeable for gases and comprising a plurality of inwards protrudent hole-forming portions. Preferably, the bag comprises a film having holes (B) of predetermined thickness (d) furnished with protrudent hole-forming portions of predetermined height (h), the height (h) of the protrudent hole-forming portions being in the range of 2 to 200, still preferably 5 to 100, times the thickness (d) of the film having holes (B). By virtue of this structure, the soaring of powder at the time of powder filling can be prevented to thereby facilitate the filling operation. Furthermore, not only is the sticking of powder to seal portion reduced at the time of sealing the mouth of the bag to thereby ensure obtaining satisfactory seal strength but also the environmental pollution by the soaring of powder can be avoided.

Abstract: The improved nonwoven fabric in an electret state is composed of monofilaments with an average fiber diameter of 0.5-100 .mu.m that are formed of a polymer composition containing no more than 1 mol % of polar groups; the fabric has a weight of 5-100 g/m.sup.2, a bulk density of 0.05-0.40 g/cm.sup.3 and an average surface charge density of at least 0.1.times.10.sup.-9 C/cm.sup.2. This nonwoven fabric is capable of efficient dust collection and its trapping ability is retained for a prolonged time even in a hot and humid condition. Also disclosed are a process for producing this nonwoven fabric, as well as a filtering and an air masking material which are composed of that nonwoven fabric.

Abstract: A filter comprising a composite sheet bent like a pleat and composed of a laminate of at least two monolayer sheets, in which the bent portions are fusion-welded, is provided in order to improve filtering properties while carrying out the composing and pleating processes in one process. A device for manufacturing the filter is also provided. The device comprises, for example: a pair of star-shaped gear type ribbed rolls engaged with each other for heating the composite sheet to temperatures suitable to fusion-weld the same at the front end of the gear while bending the composite sheet like a pleat having a bent width corresponding to the depth or height of the gear; star-shaped gear type bending roll for further bending the heated composite sheet like a pleat; and a pair of heating plates positioned opposed each other at a distance corresponding to the bent width of the pleat.