Mat material and method for making it

#This invention relates generally to melt spun polymeric filaments and, more particularly, to a mat material containing a plurality of such filaments fuse bonded together at points where they contact each other and to a process for making such a mat material.

#One mat material of this general type is disclosed in U.S. Pat. No. 3,691,004. This mat material is produced by extruding a polymer melt through a spinneret having at least three staggered rows of equally spaced spinning orifices to form a bundic of filaments onto a cooling liquid which is preferably water. The distance between spinneret face and bath surface is 2 to 30 cm, preferably 4 to 20 cm. The filaments produced by this process are deposited as loops onto the water bath. They sink into the water and fuse at mutual points of intersection, due to the inherent tackiness produced by the transition from the melted to the solid state. The resulting mat material is withdrawn from the water bath, shaken, dried and wound.

#According to another process (GPD No. 1,922,460 and U.S. Pat. No. 3,837,988) a similar material is produced by extruding a polymer melt through several rows of spinning orifices in such a manner that the still tacky filaments drop partly onto the surface of a roller which is about half submerged in a water bath, located some 20 to 25 cm below the spinneret, and partly directly into the water bath where they are fused together. The rolls may be provided with spikes to insure continuous transport of the mat as it is forming through the water bath. To obtain a patterned web of mat material, the roller may be provided with transverse struts or other irregular elements, instead of the spikes. Mat material obtained according to this process is compacted on one side.

#Other objects will become apparent from the following description with reference to the accompanying drawing wherein

#FIG. 1 illustrates schematically spinning apparatus suitable for making the mat material of the invention;

#FIGS. 2 and 3 are illustrations in cross-section of embodiments of the filaments having a circular cross-section and a plurality of adjacent, separate, discontinuous cavities used to make the mat material of the invention; and

#The foregoing objects and others are accomplished in accordance with this invention, generally speaking, by providing a mat material prepared by extruding in a substantially vertical direction filaments of a synthetic polymeric melt containing a gas onto a moving member having an embossed surface, the filaments are permitted to fuse together at mutual points of contact, cooled and removed from the moving member. Filaments of the type contemplated by the invention and a method for making them are disclosed in our copending U.S. Patent Application Ser. No. 738,985, filed Nov. 4, 1976, now U.S. Pat. No. 4,164,603, the disclosure of which is incorporated herein by reference. Such filaments contain a plurality of adjacent uniform, individual discontinuous cavities.

#The filaments of the mat material of the invention are not provided with a single, large diameter cavity or bore which extends over the entire length of the filament, but rather with a plurality of adjacent or end-to-end, approximately needle-shaped cavities, having an essentially circular cross-section and a diameter, depending on the yarn thickness and cavity constituent, of generally between 0.5.mu. and 6.mu., but which may also reach up to 20 or more .mu.. The cross-section of the filaments may vary from 0.2 to 3 mm. The cavities are largely non-communicating and are enclosed by a shell.

#Since all of the needle-shaped cavities are enclosed by thin polymer walls, the yarn cross-section is not markedly deformed either during the mat formation process or under extensive loading of the mat of the invention. Thus, the filaments essentially retain their shape and geometrical dimensions while the mat is used. The filaments furthermore possess a specific strength as a result of which the longitudinal and transverse strengths of the mat are distinctly higher than if made from hollow filaments. The filaments contain preferably up to 1 weight %, most preferably 0.1 to 0.4 weight %, based on the weight of the melt, of a silicone oil. This leads to a substantial improvement in the spinnability of the polymer, increases the running time of the spinnerets and provides mainly for a uniform distribution of the cavities in the filaments.