JP2024179437A - Split type composite fiber - Google Patents

Abstract

To provide a split-type composite fiber low in cost, having preferable handleability, having preferable spinnability in fiber production and exhibiting excellent splitting performance, and with which a nonwoven fabric having a soft texture can be obtained.SOLUTION: Provided is a split-type composite fiber composed of polypropylene and polyester, and having a split-type composite form in which the contents of calcium, aluminum and sodium as inorganic substances in the polypropylene are each 60 ppm or less, and the total content of these inorganic substances is 100 ppm or less, one component is divided into a plurality of segments by the other component in a cross section and both components are exposed on the fiber surface. The area ratio of polypropylene to the fiber surface is smaller than that of polyester to the fiber surface, the fineness of the composite fiber is 1 to 6 dtex, the total number of segments is 10 to 30, and the fineness of each segment is 0.30 dtex or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to a splittable composite fiber made of polypropylene and polyester, which has excellent splittability and can be suitably used in the fields of industrial materials such as wipers and filters, sanitary materials such as diapers, and artificial leather.

Conventionally, there have been developments related to ultrafine fibers derived from splittable composite fibers in order to obtain nonwoven fabrics and woven and knitted fabrics with soft texture, wiping properties, drape properties, etc. For example, Patent Document 1 discloses a method of splitting composite fibers consisting of an alkali-soluble polymer and an alkali-insoluble polymer by alkali treatment. Patent Document 2 discloses a method of forming a nonwoven fabric from splittable composite fibers consisting of two olefin resin components such as polypropylene and polyethylene using a high-pressure liquid flow or a papermaking method. Furthermore, Patent Document 3 discloses a method of forming a nonwoven fabric from splittable composite fibers consisting of polyester and polyolefin resin using a water jet method.

Japanese Unexamined Patent Publication No. 62-57981 JP 2002-88580 A Japanese Patent Application Publication No. 6-313215

The above-mentioned cited document 1 requires a solvent, which makes handling and recovery difficult and increases production costs. The cited document 2 has problems such as poor spinning stretchability due to the complex composite cross-sectional shape, and poor stability of the cross-sectional shape, which reduces the quality of the resulting fiber products such as nonwoven fabrics. The cited document 3 has problems such as a high exposure of olefin resin, which has a relatively low melting point, to the fiber surface, which makes it impossible to raise the heat setting temperature in the fiber manufacturing process, resulting in a high thermal shrinkage rate of the fiber and poor texture.

The present invention aims to solve the above problems and provide a splittable composite fiber that is low-cost, easy to handle, has good spinnability in fiber production, and exhibits excellent splitting performance, and also provides a splittable composite fiber from which a nonwoven fabric with a soft feel can be obtained.

The present inventors have conducted extensive research to solve the above problems and have arrived at the present invention.
(1) A splittable composite fiber composed of polypropylene and polyester, in which the ratio of polypropylene to polyester is 30/70 to 70/30 wt%, the content of inorganic substances calcium, aluminum, and sodium in the polypropylene is each 60 ppm or less, and the total content of these inorganic substances calcium, aluminum, and sodium inorganic substances is 100 ppm or less;
In the cross section, one of the two components, polypropylene and polyester, is divided into a plurality of segments by the other component,
Both the polypropylene and the polyester are exposed on the fiber surface in a split-type composite form, and the area ratio of the polypropylene on the fiber surface is smaller than the area ratio of the polyester on the fiber surface.
A splittable conjugate fiber, characterized in that the conjugate fiber has a fineness of 1 to 6 dtex, the total number of segments is 10 to 30, and the fineness of each segment is 0.30 dtex or less.
(2) The splittable conjugate fiber according to (1) above, characterized in that the cross section of the splittable conjugate fiber is formed by radially alternatingly arranging segments made of polypropylene and segments made of polyester.
(3) The splittable conjugate fiber according to (1) above, wherein the area ratio of polypropylene to the fiber surface is 5 to 30%.
(4) The splittable conjugate fiber according to (1) above, characterized in that a peeled portion is present at the boundary between the polypropylene segment and the polyester segment of the splittable conjugate fiber.
(5) The splittable conjugate fiber according to (1) above, which has a heat shrinkage rate of less than 5% when heat-treated at 110° C. for 15 minutes.
(6) A method for producing the splittable conjugate fiber described in (1) above,
A polypropylene having a content of calcium, aluminum, and sodium, which are inorganic substances, of 60 ppm or less each and a total content of calcium, aluminum, and sodium, which are inorganic substances, of 100 ppm or less in total, and a melt viscosity of 650 to 850 dPa·S at 285° C. and a shear rate of 1000 S ^-1 is prepared;
A polyester having a melt viscosity of 1000 to 2000 dPa·S at 285° C. and a shear rate of 1000S ^-1 is prepared.
A method for producing splittable composite fibers, comprising conjugating the polypropylene and polyester to form composite fibers using a splittable composite spinneret in which one component is split into a plurality of segments by the other component.
(7) A method for producing a spunlace nonwoven fabric, comprising: preparing a nonwoven web containing the splittable conjugate fiber according to any one of (1) to (5) above; subjecting the nonwoven web to a hydroentanglement treatment to split the splittable conjugate fiber to produce ultrafine fibers and entangle the constituent fibers to obtain a spunlace nonwoven fabric.

The present invention is described in detail below.

The present invention is a splittable composite fiber composed of polypropylene and polyester. Since polypropylene and polyester are not compatible with each other, by applying a physical impact, the fiber is split at the boundary between the polypropylene segment and the polyester segment without solvent treatment, and ultrafine fibers composed of each segment can be obtained. Examples of physical impact include impact with a fiber spreader or carding machine when the composite fiber is a staple fiber, a method of subjecting the composite fiber of the present invention to a high-pressure water flow after making it into a fabric, a needle punching method, a method of passing the composite fiber through a liquid flow dyeing machine to apply an impact, and a buckling method.

Examples of polypropylene include propylene homopolymers and copolymers of propylene and α-olefins other than propylene. Examples of copolymers of propylene and α-olefins other than propylene include ethylene-propylene copolymers and ethylene-propylene-butene copolymers. Specific examples of such polypropylene include syndiotactic polypropylene and isotactic polypropylene polymerized with a Ziegler-Natta catalyst, a metallocene catalyst, or the like. Ethylene-bisstearic acid amide or the like may be added to the polypropylene during spinning to the extent that the effect of the present invention is not impaired. The antioxidant contained in the polypropylene is preferably a component having discoloration resistance.

In the present invention, the content of calcium, aluminum, and sodium in the polypropylene constituting the fiber is 60 ppm or less, and more preferably 40 ppm or less. The total content of calcium, aluminum, and sodium in the polypropylene is 100 ppm or less. These inorganic substances are derived from catalysts and neutralizing agents added during the polymerization of polypropylene, and therefore are contained in a certain amount in the polypropylene. However, these inorganic substances accumulate in the nozzle hole over time during the spinning process in the manufacturing process of the composite split fiber. Since the composite cross section for obtaining the composite split fiber has many and complex split segments, with 10 to 30 segments, if inorganic substances accumulate in the nozzle hole, the composite cross section shape will collapse, making it difficult to obtain fibers with a split composite cross section of the desired shape, and the splittability of the obtained composite fiber will deteriorate. Therefore, in the present invention, by setting the content of each of the calcium, aluminum, and sodium contained in the polypropylene to 60 ppm or less, and the total content of calcium, aluminum, and sodium to 100 ppm or less, even in continuous production, inorganic matter is less likely to accumulate in the nozzle holes during the spinning process, so that the composite cross-sectional shape is less likely to deform or collapse, and it becomes possible to continuously produce splittable composite fibers while stably maintaining the composite cross-sectional shape, even if the composite cross-sectional shape has a large number of split segments and is complex. In addition, because the composite cross-section of the splittable composite fiber is less likely to deform or collapse, fibers with a splittable composite cross-section of the desired shape can be obtained, and the desired ultrafine fibers can be obtained with good splittability.

The splittable composite fiber of the present invention is composed of the above-mentioned polypropylene and polyester. The polyester is a polyester whose main repeating unit is alkylene terephthalate, and examples of alkylene terephthalate include ethylene terephthalate, butylene terephthalate, and ethylene naphthalate. Among them, ethylene terephthalate is preferred from the viewpoints of economy and heat resistance, and homopolyester is also preferred. To the polyester, one or more types of various additives such as stabilizers such as phosphate ester compounds and hindered phenol compounds, color tone improvers such as cobalt compounds, fluorescent whitening agents, and dyes, matting agents such as titanium dioxide, plasticizers, pigments, antistatic agents, flame retardants, and dye-improving agents may be added within a range that does not impair the effects of the present invention.

In splittable composite fibers, the composite ratio (mass ratio) of polypropylene and polyester is preferably 30/70 to 70/30, and more preferably 40/60 to 60/40. By making the polypropylene ratio 30 wt% or more, the proportion of polypropylene on the fiber surface does not become too small and can be exposed moderately, resulting in good splittability and the desired ultrafine fibers. On the other hand, by making the polypropylene ratio 70 wt% or less, not much polypropylene with a low melting point is exposed on the fiber surface, allowing the heat setting temperature after drawing to be set high, and the obtained composite fiber has a low thermal shrinkage rate and is a fiber with dimensional stability.

The cross-sectional shape of the splittable composite fiber is a splittable composite form in which one of the two components, polypropylene and polyester, is split into multiple segments by the other component, and both polypropylene and polyester are exposed on the fiber surface, and the area ratio of polypropylene to the fiber surface is smaller than the area ratio of polyester to the fiber surface. Since one component is split into multiple segments by the other component, when a physical impact is applied, the polypropylene and polyester, which are incompatible with each other, split at the interface where they are joined, and ultrafine fibers consisting of each segment are developed. And since both the polypropylene and polyester components are exposed on the fiber surface, they split well due to physical impact. In addition, since the area ratio of polypropylene to the fiber surface is smaller than the area ratio of polyester, the exposure rate of polyester, which has excellent heat resistance, is high, the exposure rate of polypropylene, which has a low melting point, can be suppressed, and the heat setting temperature after drawing can be set high, and the resulting composite fiber can have a low heat shrinkage rate and has dimensional stability.

Examples of the cross-sectional shape include a cross-sectional shape in which segments of one component and segments of the other component are alternately arranged radially, a cross-sectional shape in which segments of one component and segments of the other component are alternately stacked to form a striped pattern, and a multi-leaf cross-sectional shape in which one component forms a core segment and the other component surrounds the core and is divided into multiple leaf segments. If the number of segments is 10 or more, the structure of the composite spinneret becomes complicated, but this is preferable because the shape of the ultra-fine fibers expressed by splitting is approximately wedge-shaped, and a textile product with scraping properties, wiping properties, and softness can be obtained. Examples of such cross-sectional shapes arranged radially alternately include the so-called fruit split type and the cross-sectional shape shown in Figure 1, in which one component has multiple petal-shaped petal segments and the other component has multiple non-petal-shaped non-petal segments that exist by dividing the petal segments. In the present invention, it is more preferable that the cross-sectional shape be composed of petal and non-petal parts as shown in Figure 1, and it is preferable that polypropylene is arranged in the petal parts that are less exposed to the fiber surface, and polyester is arranged in the non-petal parts.

In splittable composite fibers, the area ratio of polypropylene on the fiber surface is smaller than the composite ratio of polypropylene in the fiber, and is preferably 10-40%, more preferably 15-35%. By making the area ratio of polypropylene on the fiber surface 10% or more, the splitting performance is improved, and ultrafine fibers are successfully produced by splitting. On the other hand, by making the area ratio of polypropylene on the fiber surface 40% or less, the exposure rate of low-melting polypropylene is suppressed, and the heat setting temperature after stretching can be set high, and the heat shrinkage rate of the obtained composite fiber can be reduced, resulting in a fiber with dimensional stability. The area ratio on the fiber surface may be measured from the fiber cross section.

The fineness of the splittable composite fiber is 1 to 6 dtex, and preferably 2 to 4 dtex. By making the composite fiber fineness 1 dtex or more, the splittable composite fiber is less likely to break during spinning or during drawing in the manufacturing process, resulting in a fiber of good quality, and this composite fiber can be used to obtain high-quality textile products such as nonwoven fabrics. On the other hand, by making the fineness 6 dtex or less, the fineness of the individual segments that make up the composite fiber can be made small, at 0.30 dtex or less as specified by the present invention, and textile products such as nonwoven fabrics with good texture and wiping properties can be obtained.

In the splittable composite fiber, the total number of segments made of polyester and segments made of polypropylene is 10 to 30, and preferably 14 to 26. By making the total number of segments 10 or more, it is easy to obtain the desired fineness of each segment as specified by the present invention, and it is possible to obtain a fiber product such as a nonwoven fabric with good texture and wiping properties. On the other hand, by making the total number of segments 30 or less, it is possible to form the desired split shape during spinning, resulting in a composite fiber with good spinnability and stretchability, and excellent splitting performance.

The fineness of each segment constituting the splittable composite fiber is 0.30 dtex or less, preferably 0.25 dtex or less, and more preferably 0.20 dtex or less. By making it 0.30 dtex or less, the fineness of the ultrafine fibers produced by splitting is small, and a fiber product such as a nonwoven fabric having excellent texture and wiping properties can be obtained.

In the splittable composite fiber, it is preferable that a peeled portion exists at the boundary between the segment made of polypropylene and the segment made of polyester. The boundary between the segment made of one component and the segment made of the other component is not completely in contact with each other, and a gap is formed in a part, and a peeled portion exists. When a physical impact due to an external force is applied during the splitting and splitting process, the peeled portion becomes the starting point for the start of splitting, and the impact is easily transmitted to the whole, and the segments are satisfactorily split, the desired ultrafine fibers are expressed, and a fiber product such as a nonwoven fabric having excellent texture and wiping properties is easily obtained. The peeled portion refers to such a gap between segments. Figure 2 is an SEM photograph showing the state of the side of the splittable composite fiber of the present invention. On the fiber side in Figure 2, the segment that is black is polypropylene, and the segment that is white is polyester. In Figure 2, for example, in the center of the photograph, in the area around the center of the fiber that is diagonally extending from the upper left to the lower right, the polypropylene segment and the polyester segment are not in contact with each other, and a gap is formed, and a peeled portion exists. In addition, such peeled areas can be formed by drawing the fiber at an appropriate draw ratio under heated conditions in the drawing process after melt spinning in the process of manufacturing the composite fiber. In other words, peeling occurs at the interface due to the difference in fluidity between polypropylene and polyester during hot drawing. More specifically, the peeled areas can be formed well by hot drawing at a drawing temperature of 60 to 80°C and a draw ratio of 2 to 4 times. In addition, peeled areas can also be formed when an appropriate number of crimps is imparted to the splittable composite fiber through a process of imparting mechanical crimps. The number of crimps will be described later.

The number of crimps in the splittable composite fiber is preferably 8 to 16 crimps/25 mm, and more preferably 9 to 15 crimps/25 mm. A crimp number of 8 crimps/25 mm or more is preferable because when a web is made using the composite fiber, the fibers are well entangled and the shape of the web is well retained, resulting in good processability. In addition, the number of peeling points that serve as the starting points for splitting is maintained, resulting in a composite fiber with good splitting performance. On the other hand, a crimp number of 16 crimps/25 mm or less does not deteriorate the opening property during the carding process when making the web, and a web and nonwoven fabric with good texture can be obtained.

The crimp rate of the splittable composite fiber is preferably 7 to 17%, and more preferably 8 to 16%. A crimp rate of 7% or more is preferable because the fibers are well entangled when the composite fiber is used to produce a web, and the web has good shape retention, which makes it easy to pass through the process. On the other hand, a crimp rate of 17% or less does not deteriorate the opening property during the carding process when producing the web, and a web and nonwoven fabric with good texture can be obtained.

The elongation of the splittable composite fiber is preferably 20-70%, and more preferably 25-60% or less. With an elongation of 20% or more, single thread breakage or cutting is unlikely to occur during the drawing process, and the quality of the resulting composite fiber and the fiber products such as nonwoven fabrics obtained using the composite fiber is good. On the other hand, composite fibers with an elongation of more than 70% are difficult to handle due to their high elongation. In addition, in order to obtain fibers with an elongation of more than 70%, a small draw ratio of more than 1.5 is sufficient in the drawing process during fiber production. At such a draw ratio, no difference in fluidity occurs at the interface between polypropylene and polyester during hot drawing, and peeling points cannot be formed well, making it difficult to develop ultrafine fibers through splitting processing. The elongation of the composite fiber is measured based on the elongation rate described in JIS L1015 using a constant-speed elongation tensile tester under conditions of a grip interval of 20 mm and a tensile speed of 20 mm/min.

The dry heat shrinkage rate of splittable composite fibers when treated at 110°C for 15 minutes is preferably 5% or less, and more preferably 4% or less. If it exceeds 5%, the splittable composite fibers will shrink more due to the heat treatment when making a nonwoven fabric using the composite fibers, resulting in a nonwoven fabric with poor texture.

Next, we will explain the method for producing the splittable composite fiber of the present invention.

First, polypropylene and polyester are prepared as the raw materials for the splittable composite fiber. The polypropylene is the above-mentioned polypropylene, in which the contents of the inorganic substances calcium, aluminum, and sodium are all 60 ppm or less, and the total content of these inorganic substances calcium, aluminum, and sodium is 100 ppm or less. The reason why the contents of the inorganic substances calcium, aluminum, and sodium contained in the polypropylene are all 60 ppm or less, and the total content of these inorganic substances calcium, aluminum, and sodium is 100 ppm or less, is as described above, and even in continuous production, the deposition of inorganic substances in the nozzle holes during the spinning process is unlikely to occur, so that the composite cross-sectional shape is unlikely to deform or collapse, and even if the composite cross-sectional shape has a large number of split segments and is complicated, it is possible to continuously produce splittable composite fibers while stably maintaining the composite cross-sectional shape, and since a splittable composite cross-section fiber of the desired shape is obtained, it is possible to obtain the desired ultrafine fibers with good splittability.

The polypropylene preferably has a melt viscosity of 650 to 850 dPa·S at 285°C and a shear rate of 1000S ^{- 1} . When the polypropylene has a melt viscosity of 650 dPa·S or more at 285°C and a shear rate of 1000S-1, the melt viscosity during spinning does not become too low, making it possible to form a desired split shape, and the conjugate split fiber of the present invention is obtained. On the other hand, when the melt viscosity is 850 dPa·S or less, the elongation of the undrawn yarn after spinning does not become too low, and drawing can be performed at a desired high draw ratio in the drawing step, so that a splittable conjugate fiber of a desired fineness can be obtained, rather than a large fineness.

The polyester, which is the other raw material of the composite fiber, is the above-mentioned polyester, and the melt viscosity at 285°C and a shear rate of 1000S ^-1 is preferably 1000 to 2000 dPa·S. Also, it is preferably 1200 to 1800 dPa·S. By having the melt viscosity of the polyester at 285°C and a shear rate of 1000S ^-1 of 1000 dPa·S or more, the melt viscosity during spinning is not too low, making it possible to form a desired split shape, and the composite split fiber of the present invention is obtained. On the other hand, by having the melt viscosity of 2000 dPa·S or less, the elongation of the undrawn yarn after spinning is not too low, and drawing can be performed at a desired high draw ratio in the drawing process, so that the drawability is good, and the obtained composite fiber can have a desired fineness rather than a large fineness.

Next, the prepared polypropylene and polyester are composite-spun in a composite spinning device using a split composite spinneret in which one component is split into multiple segments by the other component. The resulting undrawn yarn is then collected into a yarn bundle of 500,000 to 1,000,000 denier, and the undrawn yarn is heat-drawn, after which the fiber is heat-set by heat treatment using a heat drum heated to a temperature of 110 to 140°C, to obtain the split composite fiber of the present invention. As described above, the conditions for heat-drawing the undrawn yarn are preferably a drawing temperature of 60 to 80°C and a draw ratio of 2 to 4 times.

The splittable composite fiber obtained by heat setting may be mechanically crimped using a push-in crimper, and after applying a finishing oil, the yarn bundle may be cut to the desired length to produce short fibers. The finishing oil applied is preferably weakly acidic, with a pH of 5.0 to 6.5. This is because making the finishing oil have a weakly acidic pH can reduce discoloration of the polypropylene.

The resulting composite fiber can be twisted or spun into yarn, and the resulting yarn can be woven into a woven fabric, or other textile product.

In addition, in the present invention, it is preferable to use splittable composite fibers to make a nonwoven fabric. A preferred method for obtaining a nonwoven fabric using splittable composite fibers will be described. The fibers (splittable composite fibers of the present invention) that will be the constituent fibers of the nonwoven fabric are carded using a carding machine or the like to produce a carded web, and the resulting carded web is subjected to a high-pressure liquid flow treatment to three-dimensionally entangle and integrate the constituent fibers to obtain a spunlace nonwoven fabric. During carding, more peeling points are formed in the splittable composite fibers. As a method for producing a web, in addition to the method using a carding machine, a wet papermaking method and an airlaid method can be mentioned. The obtained web is subjected to a high-pressure liquid flow to split and split the splittable composite fibers to produce ultrafine fibers and entangle the constituent fibers. In addition, the degree of splitting can be increased by increasing the water pressure of the high-pressure liquid flow. The high-pressure water flow entanglement method is preferable because the high-pressure water flow is applied uniformly over the entire web, and therefore splitting can be uniformly performed over the entire nonwoven fabric obtained and also over the entire fiber. In addition, the above-mentioned fiber products, such as yarns and woven/knitted fabrics, can also be split and split into ultrafine fibers by applying a physical impact. Examples of splitting and splitting methods include the hydroentanglement method, which uses a high-pressure liquid flow, the needle punch method, which applies a physical impact by piercing and removing a needle, the method of applying an impact through a liquid flow dyeing machine, and the buckling method.

No solvent is required to produce ultrafine fibers, and splittable composite fibers can be obtained that are low-cost, easy to handle, have good spinnability in fiber production, and exhibit excellent splitting performance.

1 shows an example of a cross section of a splittable conjugate fiber of the present invention, which has a cross-sectional shape consisting of petal portions and non-petal portions. 1 is a SEM photograph showing the state of a side surface of a splittable conjugate fiber of the present invention.

The present invention will be described in more detail below with reference to examples. The measurement methods for the characteristics and the like in the examples are as follows.
(1) Single fiber fineness: Measured according to JIS L1015 8.5.1 B method.
(2) Segment Fineness This was calculated from the single fiber fineness obtained by the above-mentioned measuring method, the number of segments, and the composite ratio.
(3) Inorganic content The polyester in the obtained splittable composite fiber was dissolved in a solvent consisting of an equal weight mixture of phenol and tetrachloroethane, and only the polypropylene was recovered. The recovered polypropylene was thermally decomposed with nitric acid and sulfuric acid, and the amount of inorganic matter in the polypropylene was measured by ICP-MS analysis. When measuring the inorganic content in the raw polypropylene, the polypropylene raw material was subjected to ICP-MS analysis.
(4) Melt Viscosity: Using a flow tester (Shimadzu Corporation, Model CFT-500), the melt viscosity was measured under conditions of a temperature of 285° C. and a shear rate of 1000 s ⁻¹ .
(5) Fiber Observation Observation was carried out using a scanning electron microscope (SEM).
(6) Heat shrinkage: Measured based on JIS L1015 8.15 Dry heat dimensional change rate. The temperature was 110°C, and the time in the dryer was 15 minutes. A shrinkage rate of less than 5% was considered to be acceptable (◯), and a shrinkage rate of 5% or more was considered to be unacceptable (×).
(7) Number of crimps and crimp rate: Measured according to JIS L1015 8.12.1 and 8.12.2.
(8) Spinnability With regard to the number of times of yarn breakage during the fiber spinning process, less than 3 times per ton of spun yarn was evaluated as pass (◯), and 3 times or more was evaluated as fail (×).
(9) Stretchability If the number of times that a single filament broke during the fiber stretching process was less than 3 times per ton of stretching amount, it was evaluated as pass (◯), and if it was 3 times or more, it was evaluated as fail (×).
(10) Air permeability Continuous production was carried out for three days in a batch of one lot per day, and composite fibers produced in each batch (approximately 24 hours, 48 hours, and 72 hours after the start of production) were sampled. The air permeability was measured according to JIS L1015 8.5.1 B method.
(6) Fluctuation rate (%) of fiber diameter
The fiber cross section was observed under an optical microscope, and the fiber diameters of 50 fibers were measured. The standard deviation and average value of the fiber diameters were then calculated, and the rate of variation was calculated according to the following formula.
Fluctuation rate of fiber diameter (%) = (standard deviation of fiber diameter / average value of fiber diameter) x 100
(7) Fiber length: Measured according to JIS L1015 8.4.1 Method A.
(8) Dry heat shrinkage: Measured according to JIS L1015 8.15. The measurement temperature was 170. (9) Number of crimps: Measured according to JIS L1015 8.12.1 and 8.12.2. At this time, the standard condition (25 (1) _XB / _XA (10) Spinnability: Regarding the number of times of yarn breakage in the fiber spinning process, less than 3 times per ton of spinning amount was considered to be pass (◯), and 3 times or more was considered to be fail (×).
(11) Stretchability If the number of times that a single yarn broke during the fiber stretching process was less than 3 times per ton of stretching amount, it was evaluated as pass (◯), and if it was 3 times or more, it was evaluated as fail (×).
(12) Processability 10 kg of fiber was sequentially put into the box of a CH-500 hopper feeder manufactured by Takeuchi Seisakusho Co., Ltd., and the fiber was transported by a spike lattice lifting method (raised to a height of about 2.3 m from the installation surface), and the amount of transported fiber (mass) was measured. The value obtained by dividing the "amount of transported fiber" by the "amount of fiber put in (10 kg)" and multiplying the result by 100 was taken as the transport rate, and a transport rate of 95% or more was considered to be pass (◯), and a transport rate of less than 95% was considered to be fail (×). Using the composite fiber group, spunlace nonwoven fabrics of each lot were produced so that the basis weight was 50 g/ ^m2 . Thereafter, the air permeability was measured by the Frazier method described in JIS L1096.
The air permeability of each lot of the spunlace nonwoven fabric was measured, and nonwoven fabrics of the three lots in which all had air permeability values of less than 80 cc/ ^cm2 ·s were judged to be pass (◯), since the ultrafine fibers were sufficiently expressed and dense, resulting in low air permeability.

Example 1
As raw materials, polypropylene with MFR of 14 and melt viscosity of 709 dPa·s at 285° C. and shear rate of 1000 s ^-1 , and polyester with melt viscosity of 1300 dPa·s at 285° C. and shear rate of 1000 ^s-1 were prepared. The inorganic contents in the polypropylene raw material were calcium 27 ppm, aluminum 32 ppm, and sodium 27 ppm.

These raw materials were melt spun using a 20-split spinneret with 850 holes and a hole diameter of 0.5 mm (a spinneret that produces fibers with a split composite cross-sectional shape as shown in Figure 1, with 10 segments each of petal and non-petal parts, totaling 20 segments) under conditions of a discharge rate of 580 g/min, composite ratio of 55/45 wt% (polypropylene/polyester), spinning temperature of 285°C, and spinning speed of 865 m/min. The polypropylene was arranged in a petal shape, and the polyester in a non-petal shape.

The undrawn yarn obtained was converged to a 60 ktex tow, which was hot-drawn at a drawing temperature of 75°C and a draw ratio of 2.4 times, and then passed through a heat drum at 130°C for heat setting. Next, mechanical crimping was imparted using a push-in crimper, and a finishing oil was applied to the fiber. The fiber was then heat-treated in a dryer at a temperature of 68°C and cut to a fiber length of 38 mm to obtain a splittable composite fiber with a fineness of 3.3 dtex. The number of crimps in the resulting splittable composite fiber was 13/25 mm, the crimp rate was 11%, and the content of inorganic substances in the polypropylene was 27 ppm calcium, 32 ppm aluminum, and 27 ppm sodium. There was almost no accumulation of inorganic substances on the spinneret during production. The segment fineness of the resulting splittable composite fiber and the area ratio of polypropylene on the fiber surface are shown in Table 1.

The obtained splittable composite fiber was used to prepare a carded web by carding using a carding machine, and the obtained carded web was subjected to a high-pressure liquid flow treatment, and then a dry heat treatment at 130°C for 2 minutes to obtain a spunlace nonwoven fabric having a basis weight of 50 g/ ^m2 . The high-pressure liquid flow treatment conditions were 2 MPa x 1 time, 4 MPa x 1 time, and 8 MPa x 3 times. The air permeability of the obtained spunlace nonwoven fabric was as shown in Table 1.

Example 2
A splittable conjugate fiber was obtained in the same manner as in Example 1, except that the discharge rate was 440 g/min and the single fiber fineness of the splittable conjugate fiber was 2.5 dtex.

Example 3
A splittable conjugate fiber was obtained in the same manner as in Example 1, except that the conjugation ratio of polypropylene and polyester was 45/55 wt %.

Example 4
A splittable conjugate fiber was obtained in the same manner as in Example 11, except that a polypropylene having an MFR of 11, a melt viscosity of 782 dPa·s at 285° C. and a shear rate of 1000 s ⁻¹ was used as the polypropylene.

Comparative Example 1
The same procedure as in Example 1 was performed except that the discharge rate was set to 140 g/min and the single fiber fineness of the splittable conjugate fiber was set to 0.8 dtex. However, due to the influence of the reduction in the discharge rate in order to set the fineness to 0.8 dtex, the spinnability and drawability were deteriorated, and it was not possible to obtain a splittable conjugate fiber.

Comparative Example 2
A splittable conjugate fiber was obtained in the same manner as in Example 1, except that the discharge rate was 1142 g/min and the single fiber fineness of the splittable conjugate fiber was 6.5 dtex.

Comparative Example 3
A split type composite fiber was obtained in the same manner as in Example 1, except that an eight-split type spinneret (each of the petal portion and the non-petal portion having four segments, for a total of eight segments) was used.

Comparative Example 4
An attempt was made to carry out the same procedure as in Example 1, except that a 40-segment spinneret (each of the petal portion and the non-petal portion had 20 segments, for a total of 40 segments) was used. However, since the total number of segments was 40, it became difficult to form the desired split shape during spinning, and spinnability and drawability were deteriorated, making it impossible to obtain a splittable conjugate fiber.

Comparative Examples 5 and 6
Splittable conjugate fibers were obtained in the same manner as in Example 1, except that the conjugation ratio of polypropylene and polyester in Example 1 was as shown in Table 1.

In Comparative Example 6, when the heat setting temperature after drawing was set to 130°C, the same as in Example 1, the yarns became tightly adhered, so the heat setting was performed at 110°C.

Comparative Example 7
A splittable conjugate fiber was obtained in the same manner as in Example 1, except that polypropylene having inorganic substance contents of 80 ppm calcium, 63 ppm aluminum, and 86 ppm sodium in the polypropylene raw material was used.

Comparative Examples 8 and 9
A splittable conjugate fiber was obtained in the same manner as in Example 1, except that the polypropylene used had an MFR and a melt viscosity at 285° C. and a shear rate of 1000 s ⁻¹ as shown in Table 1.

In Comparative Example 9, the MFR of the polypropylene was low, and the melt viscosity at 285°C and a shear rate of 1000 s ^-1 was too high, so that the elongation of the undrawn yarn after spinning was too low, and therefore it was not possible to apply a high draw ratio of 2.4 times in the drawing step as in Example 1, and drawing was not possible. Therefore, the production of the fiber was discontinued.

As shown in Table 1, the splittable composite fibers obtained in Examples 1 to 4 had good spinnability, stretchability, heat shrinkage, and nonwoven fabric air permeability.

In Comparative Example 2, the single fiber fineness was 6.5 dtex, and the fineness after splitting was also high, so that the breathability was high, which is not what is desired in the present invention, and the flexibility and softness were also poor.

In Comparative Example 3, the total number of segments was 8, resulting in a large fineness after division, high breathability, and poor flexibility and softness.

In Comparative Example 5, the composite ratio was 20/80 wt%, and because the polypropylene ratio was small, there was no exposure of polypropylene on the fiber surface, and the splitting performance was poor, so the fiber did not split well, the breathability was high, and the flexibility and softness were poor, resulting in poor nonwoven fabric performance.

In Comparative Example 6, the composite ratio was 80/20 wt%, and the proportion of polypropylene on the fiber surface was high due to the large proportion of polypropylene, so the heat setting temperature after drawing could not be increased, resulting in a splittable composite fiber with a high thermal shrinkage rate.

In Comparative Example 7, the inorganic matter content in the polypropylene was high, and as a result, inorganic matter accumulated in the nozzle holes over time during the spinning process, causing the cross-sectional shape to collapse, the splitting performance of the splittable composite fiber to deteriorate, the desired ultrafine fibers not being produced, the air permeability to increase, and the flexibility and softness to deteriorate, resulting in poor nonwoven fabric performance. In addition, the inorganic matter content in the polypropylene of the obtained splittable composite fiber was more than 100 ppm in total for calcium, aluminum, and sodium.

In Comparative Example 8, the MFR of the polypropylene was high and the melt viscosity at 285°C and a shear rate of 1000 s ^-1 was too low, so that the desired split shape could not be formed, and the splitting performance of the obtained splittable conjugate fiber was poor, the air permeability was high, and the flexibility and softness were also poor, resulting in poor nonwoven fabric performance.

Claims (7)

A splittable conjugate fiber made of polypropylene and polyester, the ratio of polypropylene to polyester being 30/70 to 70/30 wt %, the contents of inorganic substances calcium, aluminum and sodium in the polypropylene being each 60 ppm or less, and the total content of these inorganic substances calcium, aluminum and sodium being 100 ppm or less,
In the cross section, one of the two components, polypropylene and polyester, is divided into a plurality of segments by the other component,
Both the polypropylene and the polyester are exposed on the fiber surface in a split-type composite form, and the area ratio of the polypropylene on the fiber surface is smaller than the area ratio of the polyester on the fiber surface.
A splittable conjugate fiber, characterized in that the conjugate fiber has a fineness of 1 to 6 dtex, the total number of segments is 10 to 30, and the fineness of each segment is 0.30 dtex or less. The splittable composite fiber according to claim 1, characterized in that the cross section of the splittable composite fiber is a cross section in which segments made of polypropylene and segments made of polyester are radially arranged alternately. The splittable composite fiber according to claim 1, characterized in that the area ratio of polypropylene on the fiber surface is 10 to 40%. The splittable composite fiber according to claim 1, characterized in that there is a peeling site at the interface between the polypropylene segment and the polyester segment of the splittable composite fiber. The splittable composite fiber according to claim 1, characterized in that the heat shrinkage rate upon heat treatment at 110°C for 15 minutes is less than 5%. A polypropylene having a content of calcium, aluminum, and sodium, which are inorganic substances, of 60 ppm or less each and a total content of calcium, aluminum, and sodium, which are inorganic substances, of 100 ppm or less in total, and a melt viscosity of 650 to 850 dPa·S at 285° C. and a shear rate of 1000 S ^-1 is prepared;
A polyester having a melt viscosity of 1000 to 2000 dPa·S at 285° C. and a shear rate of 1000S ^-1 is prepared.
2. The method for producing a splittable conjugate fiber according to claim 1, wherein the polypropylene and polyester are conjugated and spun using a splittable conjugate spinneret in which one component is divided into a plurality of segments by the other component, and the spun undrawn yarn is then hot-drawn. A method for producing a spunlace nonwoven fabric, comprising: preparing a nonwoven web containing the splittable conjugate fiber according to any one of claims 1 to 5; subjecting the nonwoven web to a high-pressure liquid flow treatment to split the splittable conjugate fiber to produce ultrafine fibers and entangle the constituent fibers to obtain a spunlace nonwoven fabric.