Splittable multi-component fiber, method for producing it, and fibrous article comprising it

#The present invention relates to a splittable multi-component fiber of good splittability, a method for producing it, and a fibrous article comprising it. More precisely, the invention relates to a splittable multi-component fiber of good splittability favorable for use in the field of industrial materials for battery separators, wipers, filters, etc., and also in the field of sanitary materials for napkin, etc., and relates to a method for producing it, and a fibrous article comprising it.

#Heretofore known is a method of using sea-island or splittable multi-component fibers for producing fine fibers. In the method of using sea-island multi-component fibers, a plurality of different components are combined and spun into multi-component fibers, and one component of the resulting multi-component fibers is dissolved and removed to give fine fibers. The method gives extremely fine fibers, but is uneconomical as requiring the step of dissolving and removing one component of the multi-component fibers. In the other method of using splittable multi-component fibers, a plurality of different resins are combined and spun into multi-component fibers, and the resulting multi-component fibers are split into a large number of fine fibers by applying physical stress to them or by processing them with a chemical reagent with which the resins constituting each fiber shrink to different degrees. Known are various types of multi-component fibers made from a plurality of different resins, including, for example, a combination of a polyester resin and a polyolefin resin, a combination of a polyester resin and a polyamide resin, a combination of a polyamide resin and a polyolefin resin, etc. However, in the process of splitting the splittable multi-component fibers into fine fibers followed by further processing the resulting fine fibers to give non-woven fabrics and others, the step of splitting the multi-component fibers into fine fibers by processing them with high-pressure liquid jets takes a lot of time, and this is the rate-determining step for the subsequent step of processing the resulting fine fibers to give non-woven fabrics. In addition, the energy cost for the step of splitting the multi-component fibers into fine fibers is high. Moreover, the thus split fine fibers and fibrous articles comprising them inevitably contain different types of polymers, and, at present, their applications in the field of industrial materials that are required to be resistant to chemicals are limited.

#On the other hand, in splittable multi-component fibers from a combination of a plurality of resins of the same type, for example, from a combination of polyolefin resins, that of polyester resins, or that of polyamide resins or the like, the constituent polymers are more highly miscible with each other, as compared with those in splittable multi-component fibers from a combination of a plurality of different types of resins such as that mentioned above. Therefore, the multi-component fibers of the former type need greater physical impact for splitting them into fine fibers. As a result, the multi-component fibers thus having received such greater physical impact will be split into uneven fibers, some of which are thick but some others are thin. Such uneven fibers are problematic in that non-woven fabrics made from them have a bad uniformity, and the line speed for processing them with high-pressure liquid jets must be significantly lowered. To that effect, the multi-component fibers are problematic and are not satisfactory.

#FIG. 1 is a schematic cross-sectional view showing the completely conjugated part of a radially-aligned, splittable multi-component fiber of the first aspect of the invention.

#FIG. 2 is a schematic cross-sectional view showing the partially conjugated part of a radially-aligned, splittable multi-component fiber of the first aspect of the invention.

#FIG. 3 is a schematic cross-sectional view showing the non-conjugated part of a radially-aligned, splittable multi-component fiber of the first aspect of the invention.

#The invention is described in detail hereinunder. The splittable multi-component fiber of the first aspect of the invention comprises components (A) and (B) of thermoplastic resin in which the components are alternately aligned in its cross section. In this, the component (A) is formed continuously in the direction of the fiber axis, and the component (B) is so randomly formed that some of it is conjugated to the component (A) in the direction of the fiber axis to give a completely conjugated part (in FIG. 1 illustrating the cross section of the fiber, 1 indicates the component (A) and 2 indicates the component (B)) and some others of it are broken in the direction of the fiber axis to give a partially conjugated part in which the area conjugated to the component (A) is smaller than that in the completely conjugated part (in FIG. 2 illustrating the cross section of the fiber, 2b, 2b′ and 2b″ all indicate the partially conjugated part) and/or a non-conjugated part in which the component (B) lacks in the direction of the fiber axis and is not conjugated to the component (A) (in FIG. 3 illustrating the cross section of the fiber, 2b′″ indicates the non-conjugated part). In one fiber, all these completely-conjugated part, partially-conjugated part and non-conjugated part of the component (B) exist at random.

#As having the structure defined herein, the splittable multi-component fiber of the first aspect of the invention can readily receive concentrated physical stress from high-pressure liquid jets or the like applied thereto. In other words, in the fiber, the segments of the component (A) run continuously throughout the fiber in the direction of the fiber axis to thereby ensure the essential fiber strength, while some of the segments of the component (B) are partially lacked to such a degree that at least one segment of the component (A) is not completely exposed outside, thereby forming the partially-conjugated parts 2b, 2b′ and 2b″ in the cross section of the fiber (FIG. 2) and/or completely lacked to such a degree that at least one segment of the component (A) is completely exposed outside, thereby forming the non-conjugated part 2b′″ therein (FIG. 3), and in one fiber, all these completely-conjugated part, partially-conjugated part and non-conjugated part of the component (B) exist at random. Therefore, the fiber shall have discontinuous hollow in the direction of the fiber axis. Accordingly, when compared with any other fibers not having such hollow on the surface, the fiber of the invention can more readily receive physical stress applied thereto and therefore can be readily split into fine fibers by any small impact energy applied thereto.

#The discontinuous hollow include regular and irregular hollow with respect to their length and depth in the direction of the fiber axis, and their shape, length and depth are not defined in any way. In other words, the hollow may be inclined at an acute angle, a right angle or an obtuse angle to the adjacent component (A) in the cross section in the direction of the fiber axis. Regarding their depth, they may be shallow (like 2b in FIG. 2), or deep to such a degree that the adjacent component (A) is completely exposed outside (like 2b′″ in FIG. 3). It is rather desirable that the component (A) is exposed outside as much as possible, as in FIG. 3. If the discontinuous parts in the segments of the component (B) shall be at least formed, the discontinuous hollow therein are not specifically defined with respect to their shape and form.