EP0854213B1

EP0854213B1 - Heat-fusible composite fiber, and non-woven fabrics and absorbent products produced from the same

Info

Publication number: EP0854213B1
Application number: EP98100922A
Authority: EP
Inventors: Mitsuru Kojima; Yukinori Kataoka; Masayasu Suzuki
Original assignee: Chisso Corp
Current assignee: JNC Corp
Priority date: 1997-01-20
Filing date: 1998-01-20
Publication date: 2002-06-05
Anticipated expiration: 2018-01-20
Also published as: JP3741180B2; EP0854213A1; JPH10259522A; DE69805664D1; DE69805664T2; CN1195040A

Description

The present invention relates to a heat-fusible composite fiber having a profiled cross-section, and to non-woven fabrics and absorbent products produced from such a composite fiber. In particular, the present invention relates to a polyolefin-based heat-fusible composite fiber having a profiled cross-section, requiring a low heat-treatment temperature for producing non-woven fabrics, and having an excellent hiding property; and to non-woven fabrics and absorbent products produced from such a composite fiber.
Non-woven fabrics manufactured from a low-melting-point resin serving as the sheath component and a high-melting-point resin serving as the core component have been well received for their properties such as feeling (touch) and non-woven tenacity, and have widely been used as the surface materials for hygienic products such as paper diapers and sanitary napkins. When produced from short fibers, such non-woven fabrics are typically manufactured by processing a heat-fusible composite fiber into a web through carding or air-flow opening, then melting the sheath component by heat and pressure and bonding fiber intermingling points.
In contrast, typical non-woven fabrics can be easily produced from long fibers by spun bonding. Long fibers discharged from a spinneret are typically introduced into an air sucker or the like, stretched and elongated, opened, accumulated on a collecting conveyor and processed into a web, and then the sheath component is melted by heat and pressure and fiber intermingling points are bonded.
Processes for bonding fiber intermingling points are roughly divided into the heat-pressure method, which uses heat embossing rolls, and the hot-air bonding method, which uses a suction band dryer or a suction drum dryer. Non-woven fabrics manufactured by these methods are called point-bonded non-woven fabrics and through-air non-woven fabrics, respectively, and are used according to their applications.
Such fibers known as heat-fusible (sheath-and-core) composite fibers include, for example, a composite fiber consisting of high-density polyethylene/polypropylene (hereafter referred to as HDPE/PP), a composite fiber consisting of high-density polyethylene/polyester (hereafter referred to as HDPE/PET), and a composite fiber consisting of a sheath component of a propylene-based copolymer and a core component of polypropylene (hereafter referred to as co-PP/PP), as disclosed in Japanese Patent Publication No. 55-26203, and Japanese Patent Application Laid-open Nos. 2-91217 and 2-191720.
Among these fibers, since the co-PP/PP has propylene components in both resins constituting the sheath and those constituting the core, strong affinity exists between the sheath and core components, and, in contrast to HDPE/PP or HDPE/PET, the sheath and the core are not prone to delamination. In addition, since, relative to HDPE, co-PP in the sheath component excels in the ability of heat-sealing with other resins, non-woven fabrics produced from the co-PP/PP-based heat fusible composite fiber are highly evaluated for their high strength when processed into paper diapers or other hygienic products together with non-woven fabrics or films produced from other resins.
When a non-woven fabric is produced from a heat fusible composite fiber, the feeling (touch) of the non-woven fabric is incompatible with its tenacity. Conventionally, since non-woven fabrics used for hygienic materials are required to have sufficient tenacity and as fast a production speed as possible, they have often been produced through heat treatment at a relatively high temperature. As a recent trend, however, softer feeling (touch) has been demanded in non-woven fabrics used as the surface material of hygienic products. Therefore, a lower temperature is often employed for the heat treatment of non-woven fabrics produced from co-PP/PP, resulting in a problem of the non-woven fabrics having lower tenacity.
For this reason, the development of co-PP/PP is required for producing non-woven fabrics which satisfy the two incompatible demands for high tenacity and soft feeling (touch).
Non-woven fabrics used for surface materials; for example, those used for the manufacture of disposable diapers and hygienic napkins, become marked with yellowish stain from infants' excrement or urine, or reddish stain from women's menstrual discharge. Since such stain has significant influence on the comfort of use, the hiding property, which is a function of making such stain less visible, is essential for recent surface materials. For this reason, methods for improving the hiding property in conventional non-woven fabrics include the increase of whiteness by adding pigments such as TiO₂ in fibers constituting the non-woven fabrics. However, if the amount of TiO₂ or the like is excessive, whiteness increases, but spinning properties of the fibers and the processability into non-woven fabrics are degraded, cutting long fibers into staples becomes difficult, and the manufacturing costs increase. Although a method in which the weight per unit area is increased to improve the hiding property has also been proposed, such a method involves difficulty in decreasing the weight, size, and manufacturing costs of non-woven fabrics.
JP-A-63 295712 describes a fiber, containing (A) a high-melting polymer component 1 consisting of a polyester which contains ≥ 80 mol.% ethylene terephthalate units based on the total repeating units and having a melting point of ≥ 200°C and (B) a low-melting polymer component 2 consisting of a low-melting polyester consisting essentially of terephthalic acid and isophthalic acid in a 40-80:60-20 molar ratio as a dicarboxylic acid component in 80:20-20:80 weight ratio of components 1 to 2, wherein components (A) and (B) form two or more blocks in a side-by-side or sheath-core form in the perpendicular cross-section of fiber, wherein the component (B) is exposed to the periphery of the fiber.
JP-A-62 085025 describes a polyester A having a softening point of 90 - 160°C and a polyester B having a softening point of ≥ 230°C which are dried under reduced pressure and subjected to conjugate spinning with a melt-spinning apparatus for conjugated yam furnished with a spinneret for producing a symmetrical tri-lobal fiber to obtain the objective hot-melt type polyester conjugated yam having 3-4 ridges, made of polyester B at the tip of the ridge and of polyester A at the core part of the fiber and satisfying the formula I: CR/PR = 1.5 - 6 wherein CR is the diameter of the circumscribed circle of the cross-section of the fiber and PR is the diameter of the inscribed circle of the cross-section of the fiber, and satisfying formula II: SR/PR = 1.3 - 4 wherein SR is the diameter of the circumscribed circle of the core part of the fiber cross-section, and satisfying formula III: CR/SR = 1.1 - 1.8.
An object of the present invention is to provide a composite fiber which can be processed into a non-woven fabric having high strength and soft feeling even by heat treatment at a low temperature and a high speed, and which has a good heat-sealing property and a good hiding property.
The inventors of the present invention conducted repeated examinations for solving the above problems, and found that the above object was achieved by a heat-fusible composite fiber having the constitution described below.
According to a first aspect of the present invention, there is provided a heat-fusible composite fiber comprising a component A consisting of a high-melting-point, crystalline polypropylene resin having a melting point of 158°C or above, and a component B consisting of at least one low-melting-point resin selected from propylene-based copolymers having a melting point of 120 to 158°C, which is lower than that of the component A, characterized in that the cross-section of said composite fiber has a profiled structure wherein the component A consisting of the high-melting-point resin forms branch portions of strands radially extending from the center portion outward, and the component B consisting of the low-melting-point resin forms projecting portions connected to the branch portions, wherein the weight ratio of components A and B is within a range between 30/70 and 80/20.
According to a second aspect of the present invention, there is provided a heat-fusible composite fiber according to the first aspect, wherein the propylene-based copolymer component is a binary copolymer consisting of 85 to 99 percent by weight of propylene and 1 to 15 percent by weight of ethylene.
According to a third aspect of the present invention, there is provided a heat-fusible composite fiber according to the first aspect, wherein the propylene-based copolymer component is a binary copolymer consisting of 50 to 99 percent by weight of propylene and 1 to 50 percent by weight of butene-1.
According to a fourth aspect of the present invention, there is provided a heat-fusible composite fiber according to the first aspect, wherein the propylene-based copolymer component is a terpolymer consisting of 84 to 98 percent by weight of propylene, 1 to 10 percent by weight ethylene, and 1 to 15 percent by weight of butene-1.
According to a fifth aspect of the present invention, there is provided a short fiber non-woven fabric formed of a heat-fusible composite fiber according to any of the first through fourth aspects, whose intersections are thermally fused.
According to a sixth aspect of the present invention, there is provided a long fiber non-woven fabric formed of a heat-fusible composite fiber according to any of the first through fourth aspects, whose intersections are thermally fused.
According to a seventh aspect of the present invention, there is provided an absorbent product, at least a part of which is produced from a non-woven fabric according to the fifth or sixth aspect.
The present invention will be described in detail below.
Crystalline polypropylene, a high-melting-point resin used in the present invention as the component A of the heat-fusible composite fiber, is a homopolymer of propylene, or a crystalline copolymer of propylene as the main constituent and a small amount of α-olefins such as ethylene, butene-1, hexene-1, octene-1, and 4-methyl pentene-1, and preferably having an MFR (230°C, 2.16 kg) of 2 to 150 and having a melting point of 158°C or above. Such polymers are obtained by methods well known to those skilled in the art, such as the polymerization of propylene through use of a Ziegler-Natta catalyst.
A propylene-based copolymer which serves as a low-melting-point resin used in the present invention as the component B of the heat-fusible composite fiber is a crystalline copolymer of propylene as the main constituent and a small amount of α-olefins such as ethylene, butene-1, hexene-1, octene-1, and 4-methyl pentene-1, and preferably having an MFR (230°C, 2.16 kg) of 3 to 50 and having a melting point of 120 to 158°C, which melting point is lower than that of crystalline polypropylene used as the component A. In a preferred embodiment, the propylene-based copolymer is a propylene-based propylene-ethylene binary copolymer consisting of 85 to 99 percent by weight of propylene and 1 to 15 percent by weight of ethylene, a propylene-based propylene-butene binary copolymer consisting of 50 to 99 percent by weight of propylene and 1 to 50 percent by weight of butene-1, or a propylene-ethylene-butene-1 terpolymer consisting of 84 to 98 percent by weight of propylene, 1 to 10 percent by weight of ethylene, and 1 to 15 percent by weight of butene-1. Such copolymers are obtained by methods well known to those skilled in the art, such as the copolymerization of olefins through use of a Ziegler-Natta catalyst.
If the content of any of the co-monomers (ethylene and butene-1) in the copolymer is less than 1 percent by weight, the resultant fiber will become less heat-fusible. If the melting point of the copolymer is above or below the above-mentioned range, the balance between processing speed, tenacity, and feeling of the non-woven fabric will be deteriorated. The cross-section of the heat-fusible composite fiber of the present invention has a profiled structure in which the component A consisting of the high-melting-point resin forms branch portions of strands radially extending outwardly from the center portion, and the component B consisting of the low-melting-point resin forms projecting portions connected to the branch portions.
If a part of the low-melting-point resin component constituting the heat-fusible composite fiber is delaminated during the manufacturing process, the number of heat-bonded fiber intermingling points will decrease, resulting in poor adhesion. In particular, since the composite fiber of the present invention has a cross-section of a profiled structure, it is rather easily delaminated, and therefore, the combination of the resin components A and B constituting the composite fiber is more important. Specifically, the resin components A and B must have affinity with each other, and even if an external force is applied, they must not be separated. Examples of the cross-sections of heat-fusible fibers according to the present invention are shown in Figs. 1 through 4. However, the cross-sections of fibers described below are not intended to limit the present invention thereto.
The heat-fusible composite fiber (a1) shown in Fig. 1 is a composite fiber in which the component A (1) consisting of the high-melting-point resin forms branch portions of three strands radially extending outwardly from the center portion, and the component B (2) of the low-melting-point resin forms projecting portions extending from the end of each strand of the branch portions in the lengthwise direction along an extension line.
The heat-fusible composite fiber (a2) shown in Fig. 2 is a composite fiber in which the component A (1) of the high-melting-point resin forms branch portions of four strands radially extending outwardly from the center portion, and the component B (2) of the low-melting-point resin forms projecting portions extending from the end of each strand of the branch portions in the lengthwise direction along an extension line.
The heat-fusible composite fiber (a3) shown in Fig. 3 is a composite fiber in which the component A (1) consisting of the high-melting-point resin forms branch portions of four strands radially extending outwardly from the center portion, and the component B (2) consisting of the low-melting-point resin forms two projecting portions extending from the vicinity of the end of each strand in opposite directions along a line intersecting the strand. (In this case the directions are perpendicular to the strand, but any intersecting angle can be adopted. This principle is also applicable to the following description.) Also, in this case, one of the projecting portions extends from a location very close to the end of the strand, and the other extends from a location slightly closer to the root of the strand. However, both projecting portions may extend from substantially the same location in directions that are substantially opposite.
The heat-fusible composite fiber (a4) shown in Fig. 4 is a composite fiber in which the component A (1) consisting of the high-melting-point resin forms branch portions of four strands radially extending outwardly from the center portion, and the component B (2) consisting of the low-melting-point resin forms two projecting portions extending from the vicinity of the end of each strand in opposite directions along a line intersecting the strand. (In this case the directions are somewhat oblique to the strand.)
As the above Figs. 1 through 4 show, the heat-fusible composite fiber of the present invention has a unique profiled cross-sectional structure. That is, the component A consisting of the high-melting-point resin projects outwardly as fine strands to form a branching skeleton, and the component B consisting of the low-melting-point resin is partly joined to the branch portions of the component A to form projecting portions. Thus, the component B has extremely fine projecting portions, and its surface is exposed, except for those portions that join with the component A as described above.
When a composite fiber having such a form and structure is subjected to heat treatment, heat is transferred through the exposed surface of the component B consisting of the low-melting-point resin, facilitating heat transfer to the component B as it changes from a softened state to fusion.
Especially, since the percentage of the exposed surface area of the low-melting-point resin (component B) relative to volume is significantly larger than corresponding figures for ordinary sheath-and-core type fibers and other fibers having a circular cross-section as shown in Fig. 5, heat is transferred from the exposed surface, and uniform fusion is achieved. In other words, the fiber of the present invention excels in adhesion at low temperature.
This effect becomes more pronounced as the projecting portions of the component B become finer and the exposed surface area becomes larger.
For the purpose of the present invention, excellent adhesion at low temperature means that the heat-fusible fiber of the present invention can be heat-bonded uniformly at a temperature 3 to 4°C lower than that for the heat-bonding of normal composite fibers having circular cross-sections as shown in Fig. 5, and that under these conditions no unevenly joined fiber intermingling points are produced.
As a result, a non-woven fabric produced by heat treatment of the heat-fusible composite fiber of the present invention at a low temperature has a large number of voids between fibers, and thus a very soft feeling. In addition, since the fibers are firmly heat-bonded at fiber intermingling points, the resultant non-woven fabric has an improved bonding force as the amalgamation of fibers, and high tenacity.
Compared with the composite fiber of the present invention, an ordinary sheath-and-core type composite fiber having a circular cross-section as shown in Fig. 5 requires a higher temperature for sufficiently melting the sheath component thereof.
Although heat treatment of ordinary fibers under such conditions imparts greater tenacity by heat fusion, entire fibers become fused because the temperature of the core component approaches its melting point. This inevitably leads to loss of bulk, and the feeling (soft touch) of the non-woven fabric becomes impaired.
Also, since the heat-fusible composite fiber of the present invention has a polyfoliate structure in which strands branch radially outward from the center, scattered and reflected incident light can be seen in the field of view.
Therefore, when the heat-fusible composite fiber of the present invention is processed into cloth such as non-woven fabrics and knitted fabrics, there is exerted the effect of making colors underneath such cloth difficult to see, known as a diaphanousness prevention effect. In other words, the heat-fusible composite fiber of the present invention excels in hiding power.
In order to produce the heat-fusible composite fiber of the present invention, when in the form of a short fiber, the components A and B described above are spun, drawn, and crimped by any well-known composite spinning method, through use of a nozzle plate having a cross-section represented by the above-mentioned cross-sectional shapes of fibers. The weight ratio of the components A and B is within a range between 30/70 and 80/20. If the content of the component B is less than 20 percent, the thermal adhesion of the resultant fiber is lowered, thereby compromising the desired tenacity and low temperature adhesiveness of the non-woven fabric produced from such a fiber. If the content of the component B exceeds 70 percent, the heat shrinkage of the fiber is increased and dimensional stability tends to lower when the resultant fiber is processed into a non-woven fabric, although the thermal adhesion is sufficiently high. The fineness of the composite fiber is preferably 0.5 to 10.0 d/f, and the number of crimps is preferably about 3 to 60/25 mm in view of favorable carding properties.
In order to produce a typical long fiber, the components A and B described above are spun by any well-known spun-bonding method, through use of a nozzle plate having a cross-section represented by the above-mentioned cross-sectional shapes of fibers. The weight ratio of the components A and B is within a range between 30/70 and 80/20. If the content of the component B is less than 20 percent, the thermal adhesion of the resultant fiber is lowered, thus compromising the desired tenacity and low temperature adhesiveness of the non-woven fabric produced from such a fiber. If the content of the component B exceeds 70 percent, the heat shrinkage of the fiber is increased and dimensional stability tends to lower when the resultant fiber is processed into a non-woven fabric, although the thermal adhesion is sufficiently high. The fineness of the composite fiber is preferably 0.5 to 10.0 d/f. When required, the fiber may be crimped.
The short fiber non-woven fabric of the present invention may be produced by a well-known method in which a web having a desired weight per unit area (METSUKE) is produced from the above composite fiber by carding, and the web in turn is processed into a non-woven fabric through use of the needle-punch method, the suction dryer method, or the hot-roll method.
A typical long fiber non-woven fabric may be produced by a well-known method, such as the spun-bonding method.
These non-woven fabrics are useful for producing the surface material of paper diapers or sanitary napkins. When these non-woven fabrics are to be used for producing paper diapers or sanitary napkins, the single yarn fineness is preferably 0.5 to 10.0 d/f, and the weight per unit area (METSUKE) of the non-woven fabric is preferably 8 to 50 g/m², more preferably 10 to 30 g/m². If the single yarn fineness is less than 0.5 d/f, stable spinning is difficult to achieve, and uniform webs are difficult to obtain; if the single yarn fineness exceeds 10.0 d/f, the texture of the non-woven fabric becomes coarse, and even if such a non-woven fabric is used as the surface material of a hygienic product, the product will have undesirably rough and rigid feeling. If the weight per unit area (METSUKE) is less than 8 g/m², sufficient tenacity of the non-woven fabric cannot be achieved because the non-woven fabric becomes excessively thin; if it exceeds 50 g/m², the non-woven fabric becomes impractical because of poor feeling and high costs despite favorable tenacity.
The present invention will be described in further detail with reference to examples; however, the present invention should not be construed as limited thereto.
Various physical properties described in relation to the following examples were measured through use of the following methods:

Cross-sectional shape retention (short fibers) Fifty single yarns were sampled after drawing, the cross-sections thereof were photographed through an optical microscope, and the shapes of profiled cross-sections at the joints between the component A consisting of the high-melting-point resin and the component B consisting of the low-melting-point resin over a field of view were observed. When the shape was retained in an amount of 90 percent or more, shape retention was evaluated as Excellent; when the shape was retained in an amount of 80 percent or more, shape retention was evaluated as Fair; and when the shape was retained in an amount of less than 80 percent, shape retention was evaluated as Poor. The results of shape retention measurement are shown in Table 1, in which Excellent, Fair, and Poor are represented by ○, Δ, and ×, respectively.
Cross-sectional shape retention (long fibers) The cross-sections of non-woven fabrics were photographed through an optical microscope, and fibers other than those subjected to heat bonding and the shapes of profiled cross-sections at the joints of the component A consisting of the high-melting-point resin and the component B consisting of the low-melting-point resin over a field of view were observed. When the shape was retained in amount of 90 percent or more, shape retention was evaluated as Excellent; when the shape was retained in an amount of 80 percent or more, shape retention was evaluated as Fair; and when the shape was retained in an amount of less than 80 percent, shape retention was evaluated as Poor. The results of shape retention measurement are shown in Table 1, in which Excellent, Fair, and Poor are represented by ○, Δ, and ×, respectively.
Hiding power (whiteness of web) Ten grams of the web were sampled and whiteness was measured through use of a color difference meter (SM Color Computer, Suga Testing Machine Co., Ltd.). Higher values indicate higher hiding power. Table 1 shows the results of hiding power measurement.
Hiding power (contrast ratio of non-woven fabric) Non-woven test samples prepared for the measurement of tenacity were used. A white tile and a black tile were placed behind the test sample, brightness was measured through use of a color difference meter, and the contrast ratio (ΔL) was calculated according to the following equation. Lower contrast ratio indicates higher hiding power. Table 1 shows the results of hiding power measurement. Contrast ratio (ΔL) = L* W - L* B Where
L^* _W: Brightness when the white tile was placed behind the non-woven fabric
L^* _B: Brightness when the black tile was placed behind the non-woven fabric
Tenacity of non-woven fabric Test specimens each having a length of 15 cm and a width of 5 cm were prepared, and the tensile tenacity was measured with a tensile testing machine under conditions of a clamp distance of 10 cm and a pulling speed of 10 cm/min.
Feeling of non-woven fabric A sensuous test was conducted by 5 panelists, and the samples for which all the panelists judged as "soft," those for which 3 or more panelists judged as "soft," and those for which 3 or more panelists judged as "lacking in soft feeling" were evaluated as Excellent, Fair, and Poor, respectively. Excellent, Fair, and Poor are represented by○, Δ, and ×, respectively.
Heat-sealing property

From the non-woven fabric used for the measurement of tenacity, there were cut test specimens each having a length along the traveling direction of the machine (MD) of 7.5 cm, and a width along the direction normal to the traveling direction of the machine (CD) of 2.5 cm. The end portion of each specimen was overlaid in the amount of 1 cm over the end portion of a specimen having a length of 7.5 cm and a width of 2.5 cm cut from the same type of non-woven fabric, or from a non-woven fabric made of polypropylene fibers (2 d/f) having a weight per unit area (METSUKE) of about 20 g/m², and the overlaid specimens were heat-sealed under a pressure of 3 kg/cm² for 3 seconds at a predetermined temperature. The peeling tenacity of the heat-sealed portion of each specimen was measured with a tensile tester under conditions of a clamp distance of 10 cm and a tensile speed of 10 cm/min.

Example 1, Comparative Example 1

Through use of composite spinning equipment with nozzle plates having desired cross-sections as shown in Fig. 1 (Example 1) and Fig. 5 (Comparative Example 1), a non-stretched fiber of a weight ratio of 40/60 (component B/component A) and a single-yarn fineness of 4 d/f was produced from a binary copolymer consisting of 5 percent by weight of butene-1 and 95 percent by weight of propylene having an MFR of 15 serving as the component B, and crystalline polypropylene (homopolymer) having an MFR of 10 serving as the component A. The non-stretched fiber was then stretched to 2.4 times its original length through use of hot rolls at 95°C, mechanically crimped through use of a stuffer box, dried at 90°C, and cut to form a composite fiber of 2 d × 38 mm. Non-woven fabrics of a weight per unit area (METSUKE) of about 20 g/m² were produced by subjecting webs produced by a carding machine to heat treatment with thermocompression bonding equipment consisting of a metal back roll and an embossing roll having a 24 percent land area that was heated to 120°C (Example 1) or 124°C (Comparative Example 1), under conditions of a line pressure of 20 kg/cm, and a speed of 6 m/min. When these non-woven fabrics were used as the surface material of diapers for adults, the non-woven fabric of Example 1 excelled in whiteness, feeling (soft touch), as well as in tenacity and heat sealing properties, while the non-woven fabric of Comparative Example 1 had relatively poor whiteness, tenacity, and heat sealing properties. Thus, difference in suitability to absorbent products was obvious.

Examples 2 and 3

Through use of composite spinning equipment with nozzle plates having desired cross-sections as shown in Fig. 3 (Example 2) and Fig. 4 (Example 3), a composite fiber of 2 d / 38 mm was produced in the same manner as in Example 1 except that a terpolymer consisting of 3 percent by weight of ethylene, 5 percent by weight of butene-1, and 92 percent by weight of propylene having an MFR of 15 was used as the component B, and crystalline polypropylene (homopolymer) having an MFR of 10 was used as the component A. Non-woven fabrics of a weight per unit area (METSUKE) of about 20 g/m² were produced by subjecting webs produced by a carding machine to heat treatment with thermocompression bonding equipment consisting of a metal back roll and an embossing roll having a 24 percent land area that was heated to 120°C (Examples 2 and 3), under conditions of a line pressure of 20 kg/cm, and a speed of 6 m/min.

Comparative Examples 2 and 3

Through use of composite spinning equipment with nozzle plates having desired cross-sections as shown in Fig. 1 (Comparative Example 2) and Fig. 5 (comparative Example 3), a composite fiber of 2 d × 38 mm was produced in the same manner as in Example 1 except that a high-density polyethylene having an MI of 19 was used as the component B, and crystalline polypropylene (homopolymer) having an MFR of 10 was used as the component A. Non-woven fabrics were produced from these composite fibers in the same manner as in Example 1 except that the processing temperature was 124°C (Comparative Example 2) or 128°C (Comparative Example 3). Comparative Example 2 was produced through use of the same nozzle plate as in the present invention, and resin components beyond the scope of the present invention were combined.

Comparative Example 4

Through use of a nozzle plate having a desired cross-section as shown in Fig. 2, a composite fiber of 2 d × 38 mm was produced in the same manner as in Example 1 except that polyethylene terephthalate having an IV value of 0.65 was used as the component B, and polyethylene terephthalate having an IV value of 0.49 was used as the component A. This composite fiber could not be subjected to evaluation, because components A and B delaminated and split after stretching.

Comparative Example 5

Through use of a nozzle plate having a desired cross-section as shown in Fig. 1, a composite fiber of 2 d × 38 mm was produced in the same manner as in Example 1 except that a high-density polyethylene having an MI of 19 was used as the component B, and polyethylene terephthalate having an IV value of 0.49 was used as the component A. This composite fiber could not be subjected to evaluation, because components A and B delaminated and split after stretching.

Example 4, Comparative Example 6

Composite fibers were formed from a binary copolymer consisting of 5 percent by weight of butene-1 and 95 percent by weight of propylene, having an MFR of 15, and serving as the component B; and crystalline polypropylene (homopolymer) having an MFR of 10 serving as the component A, and were discharged from a nozzle plate as shown in Fig. 1 (Example 4) or Fig. 5 (Comparative Example 6). The resultant fibers were introduced into an air sucker and stretched to obtain long composite fibers. These long fibers discharged from the air sucker were electrically charged through use of an electric charger and opened by being allowed to collide against a reflector board, and the opened long fibers were collected as long fiber webs on an endless net conveyor having a suction device on its back side. The collected long fiber webs were transferred with the endless conveyor, and subjected to heat treatment through use of thermocompression equipment consisting of a metal back roll and an embossing roll having a 24 percent land area that was heated to 120°C, under conditions of a line pressure of 20 kg/cm, and a speed of 30 m/min to form a non-woven fabric of a weight per unit area (METSUKE)of about 20 g/m². When these non-woven fabrics were used as the surface material of diapers for adults, the non-woven fabric of Example 4 excelled in whiteness, feeling (soft touch) , as well as in tenacity and heat sealing properties, while the non-woven fabric of Comparative Example 6 had relatively poor whiteness, tenacity, and heat sealing properties. Thus, difference in suitability to absorbent products was obvious.
Tenacity, feeling, and contrast ratio of non-woven fabric, and heat-sealing properties.
The samples evaluated as Fair (Δ) or better in the cross-sectional shape retention test were evaluated. In order to produce short fiber non-woven fabrics, each fiber was carded through use of a roller carding machine at a speed of 20 m/min to form webs of a weight per unit area (METSUKE) of about 20 g/m². The webs were in turn processed at a predetermined temperature into non-woven fabrics through use of an embossing roll having a 24 percent land area. Properties of these non-woven fabrics are shown in Table 1.
In contrast, long fiber non-woven fabrics were produced by the spun-bonding method. Webs of a weight per unit area (METSUKE) of about 20 g/m² were processed at a predetermined temperature into non-woven fabrics, through use of an embossing roll having a 24 percent land area. Properties of these non-woven fabrics are shown in Table 1.
The heat-fusible composite fiber having a profiled cross-section according to the present invention can be processed into a non-woven fabric of high tenacity by heat treatment at a low temperature for a short time. The non-woven fabric produced from this heat-fusible composite fiber has a soft feeling. In addition, the heat-sealing properties with other polyolefin-based non-woven fabric are good, and hiding power is high. Such a non-woven fabric is useful as the surface material for paper diapers and sanitary napkins.
Fig. 1 is a sectional view showing an exemplary shape of a heat-fusible composite fiber of the present invention.
Fig. 2 is a sectional view showing another exemplary shape of a heat-fusible composite fiber of the present invention.
Fig. 3 is a sectional view showing still another exemplary shape of a heat-fusible composite fiber of the present invention.
Fig. 4 is a sectional view showing yet another shape of a heat-fusible composite fiber of the present invention.
Fig. 5 is a sectional view showing the shape of a heat-fusible composite fiber of Comparative Examples 1, 3, and 6.
a1...Heat-fusible composite fiber of the present invention
a2...Heat-fusible composite fiber of the present invention
a3...Heat-fusible composite fiber of the present invention
a4...Heat-fusible composite fiber of the present invention
a5...Heat-fusible composite fiber of Comparative Examples 1, 3, and 6
1...High-melting-point resin (component A)
2...Low-melting-point resin (component B)

Claims

A heat-fusible composite fiber comprising a component A consisting of a high-melting-point, crystalline polypropylene resin having a melting point of 158°C or above, and a component B consisting of at least one low-melting-point resin selected from propylene-based copolymers having a melting point of 120 to 158°C, which is lower than that of the component A, characterized in that the cross-section of said composite fiber has a profiled structure wherein the component A consisting of the high-melting-point resin forms branch portions of strands radially extending from the center portion outward, and the component B consisting of the low-melting-point resin forms projecting portions connected to the branch portions, wherein the weight ratio of components A and B is within a range between 30/70 and 80/20.
A heat-fusible composite fiber according to claim 1, wherein the propylene-based copolymer component is a binary copolymer consisting of 85 to 99 percent by weight of propylene and 1 to 15 percent by weight of ethylene.
A heat-fusible composite fiber according to claim 1, wherein the propylene-based copolymer component is a binary copolymer consisting of 50 to 99 percent by weight propylene and 1 to 50 percent by weight of butene-1.
A heat-fusible composite fiber according to claim 1, wherein the propylene-based copolymer component is a terpolymer consisting of 84 to 98 percent by weight propylene, 1 to 10 percent by weight of ethylene, and 1 to 15 percent by weight of butene-1.
A short fiber non-woven fabric formed of a heat-fusible composite fiber according to any of claims 1 through 4, whose intersections are thermally fused.
A long fiber non-woven fabric formed of a heat-fusible composite fiber according to any of claims 1 through 4, whose intersections are thermally fused.
An absorbent product, at least a part of which is produced from a non-woven fabric according to claims 5 or 6.