JP7714910B2 - composite fiber - Google Patents

Description

The present invention relates to composite fibers composed of two or more components.

Synthetic fibers made from polyester, polyamide, and other materials have excellent mechanical properties and dimensional stability, making them widely used in a variety of applications, from clothing to non-clothing. However, as people's lifestyles have become more sophisticated in recent years, there is a demand for fibers with advanced sensibilities and functions not found in conventional synthetic fibers, for a variety of uses, including clothing. The sensibilities and functions woven into fibers vary widely, and one direction in research and technological development of synthetic fibers is the pursuit of fiber materials that possess the morphological diversity seen in natural fibers, while also possessing a certain degree of regularity and a warm texture. Through this research, a variety of fiber materials and fiber-related elemental technologies have been created.

Traditionally, textile products such as woven and knitted fabrics made from synthetic filaments have required uniformity, primarily from the perspective of quality control. Naturally, compared to natural fibers such as cotton, linen, and wool, the color tone, luster, and texture tend to be monotonous. In order to pursue natural-looking textiles, it is necessary to innovate and make the yarn processing and weaving/knitting structures more complex. As a result, various technologies have been proposed for the spinning and advanced processing stages, including modifying the polymer raw material.

One spinning technique aimed at producing natural-like fibers involves creating an irregular cross-sectional structure for the single yarns that make up the multifilament. For example, one proposed technique involves first constructing a single yarn from multiple components, and then dissolving one component during a high-level processing step, thereby achieving the natural variations and soft feel of natural fibers.

Patent Document 1 proposes a multifilament composed of composite fibers whose cross section is layered with multiple components. The single yarns that make up this multifilament have different composite ratios and composite shapes in the cross section, and it is stated that by dissolving one component, a multifilament composed of single yarns with irregular cross sections can be obtained, resulting in a textile product with excellent texture and a wide variety of color, luster, and texture. This technology uses a static mixing element to divide the composite polymer flow into layers and distribute them accidentally to each discharge hole in different states. This results in a multifilament in which the components are layered in irregular shapes in the cross section of the single yarn, but the composite ratios and composite shapes differ between the single yarns.

Patent Document 2 also proposes a multifilament in which the cross section is a composite fiber in which multiple components are layered, with the composite ratio and composite structure differing between single yarns. Like Patent Document 1, this technology uses static mixing elements, and by increasing the number of mixing elements, a composite polymer flow with a greater number of layers is formed. By distributing this to each discharge hole, the components are layered in an irregular shape in the cross section of the single yarn, resulting in a multifilament in which the composite ratio and composite structure differ between single yarns.

Patent Document 3 proposes a multifilament containing composite fibers in which the cross section of a single fiber has a multi-branched composite shape consisting of a trunk and branches extending radially from it, by devising a distribution path when distributing a composite polymer flow separated into layers by a static mixing element to each discharge hole. With this technology, some of the single fibers that make up the multifilament become multi-branched composite fibers, while the remaining single fibers become layered composite fibers as exemplified in Patent Documents 1 and 2. By dissolving one component, a multifilament made up of single fibers with a more irregular cross section can be obtained, resulting in a textile product with an excellent texture similar to that of natural fibers.

JP-A-59-100717 (pages 5-7) JP 2002-309449 A (Claims) JP-A-10-237715 (pages 2-5)

In Patent Documents 1 and 2, the static mixing elements mix the composite polymer streams by repeatedly dividing and converting them, which naturally results in the composite polymer streams being stacked in layers. As a result, the cross-sectional structure of the resulting single yarn is one in which the shapes and directions of each component are aligned and stacked.

Meanwhile, Patent Document 3, which applies this static mixing element and aims to increase the complexity of the cross section by devising distribution channels, produces composite fibers with a multi-branched composite cross section not seen in Patent Documents 1 and 2. However, in the end, each component is layered with some degree of change in direction, and does not go much beyond the realm of composite fibers layered in a uniform shape.

As such, with composite fibers that utilize the phenomenon of incomplete mixing caused by conventional static mixing elements, the principles of static mixing elements mean that even if the spinning pack is modified, the shapes and lamination patterns of the components that make up the composite cross section remain relatively uniform, making it difficult to achieve the complex appearance and texture that can be achieved with natural fibers. As a result, processed yarns that utilize these fibers often require complex processing or require post-blending with other materials, which can impose restrictions on advanced processing.

For this reason, there is a strong demand for fibers that are suitable for achieving the complex appearance and texture of natural fibers. For example, there is a desire for composite fibers that have a certain degree of regularity in the cross section of a single yarn, while still allowing for diversity in the morphology of each component.

The above object can be achieved by the following means:
(1) A composite fiber in which two or more types of components constitute a cross section, each of the components having a diverse marbled composite morphology, the composite morphology being continuous in the fiber axial direction, the cross section of at least one of the components constituting the fiber having an average circularity of 0.20 or more and 0.80 or less, the difference between the minimum and maximum circularity values being 0.30 or more, and U% being 1.0% or less .
(2) A composite fiber according to (1), characterized in that segments having a cross-sectional circularity of 0.10 or less account for 1 to 20% of the total number of segments.
(3) A conjugated fiber according to (1) or (2) , characterized in that all of the constituent components are polyester.
( 4 ) A textile product at least partly containing the conjugate fiber according to any one of (1) to ( 3 ).

The present invention relates to a composite fiber having a cross section in which two or more components are kneaded in a so-called marbled pattern, and provides a composite fiber suitable for producing natural-look textured yarn. Utilizing the composite fiber of the present invention, it is possible to produce textiles with the natural patterns and soft feel of natural fibers. Furthermore, due to its characteristic cross section, the composite fiber is less likely to fluff during advanced processing, such as repeated abrasion with yarn guides or compression deformation under heat. It also has excellent high-level processing properties, making it possible to process high-quality natural-look textiles.

1 is a schematic diagram of an example of the cross-sectional structure of a marbled fiber of the present invention. 1 is a schematic diagram of the cross-sectional structure of a marbled fiber of the present invention in which the components are mixed to a low degree. 1 is a schematic diagram of a cross-sectional structure of a marbled fiber of the present invention in which each component is strongly mixed. 1 is a schematic diagram of a cross-sectional structure of a conventional heterogeneously mixed layered composite fiber. 1 is a cross-sectional view illustrating a method for producing marbled fiber according to the present invention. FIG.

The present invention will be described in detail below, along with preferred embodiments.

The composite fiber of the present invention is a fiber whose cross section is made up of two or more components, and while the morphology of each component is diverse in the cross section, it has a regular, marbled composite morphology.

The marble-patterned composite shape in the cross section refers to a shape in which the various components are kneaded together, as shown in Figure 1, with components of irregular shapes and orientations scattered throughout.

For example, it has a composite shape that is dotted with circular components (C in Figure 1), stripe-shaped components (D in Figure 1), triangular components (E in Figure 1), and even components with complex shapes that appear to be multiple of these joined together (F in Figure 1).

The complex composite morphology of the cross section can be determined by the circularity of the scattered components, and the present invention requires that at least one component constituting the fiber has an average circularity of 0.20 or more and 0.80 or less, and that the difference between the minimum and maximum circularity values is 0.30 or more.

The circularity here is an index that represents the complexity of the shapes of components scattered in a cross section, and is expressed in a two-dimensional image of the cross section of a fiber.
(Circularity of component) = {4π × area of component / (perimeter of component) ² }
In the present invention, it is determined as follows.

That is, the cross section of the fiber is photographed two-dimensionally using a stereomicroscope or similar at a magnification that allows the interfaces of the components that make up the cross section of the fiber to be observed. In this case, it is preferable to stain only specific components among those that make up the fiber, as this will result in clear contrast at the component interfaces and allow for efficient image processing, as described below.

The photographed image of the fiber cross section is converted to a grayscale image using image analysis software, and the threshold is adjusted to perform binarization. The cross-sectional parameters of segments of a specific component are read from the binarized image, and the circularity of all segments is determined. "Segment" here refers to a component that is separated and surrounded by a different component in the binarized image. The arithmetic mean of the circularity of each segment thus determined is the average circularity referred to in this invention.

The composite fiber of the present invention is intended to have the natural variegation and soft feel of natural fibers. The marbled cross-sectional structure described above imparts variations in the yarn properties, color tone, luster, etc., to each single yarn, resulting in a natural-like texture and appearance. For example, if polyester and cationic dyeable polyester are used as components of the composite fiber of the present invention and the resulting textile is then cationic dyed, the components with different shades will be exposed on the surface in a variety of states, creating subtle differences in shade on the surface and resulting in a wide range of color and luster variations. Furthermore, if one of the components constituting the composite fiber of the present invention is made into an easily soluble component in advance and then eluted after the composite fiber of the present invention is formed, ultrafine fibers with irregular cross sections will be produced. These ultrafine fibers with irregular cross sections not only impart variations in color tone, luster, texture, etc., but also form unique, irregular voids in various locations between the ultrafine fibers, resulting in a natural variegation and soft feel. When considering the use of these ultrafine fibers in textiles such as woven and knitted fabrics, it is desirable for the cross section of the composite fiber to have a variety of shapes, with no single component being uniformly aligned in a specific shape. In other words, the key point is that the circularity, which indicates the complexity of the shape, is distributed evenly over a wide area, resulting in irregularities.

As circularity varies widely from a minimum of 0 to a maximum of 1, the average circularity approaches 0.50, which is halfway between the minimum and maximum values, and the difference between the minimum and maximum circularity values tends to become larger.

The first and second requirements for achieving the effects of the present invention are that the average circularity of the cross section of at least one component constituting the fiber must be 0.20 or more and 0.80 or less, and the difference between the minimum and maximum circularity values must be 0.30 or more.

Within this range, the cross section of the composite fiber will contain a variety of shapes, from complex, branched shapes with a circularity close to 0 to simple circular shapes with a circularity close to 1, without the components of that type being uniform in shape. By dissolving the other component, it is possible to produce fibers with irregular cross sections. Furthermore, due to the composite shape in which the components defined by their circularity are irregularly kneaded together, the composite fiber also exhibits excellent suitability for advanced processing. This is because the wide distribution of circularity results in the presence of components with complex shapes (F in Figure 1) in the cross section of the composite fiber. This increases the contact area between components, and creates an anchoring effect where the complex-shaped components penetrate other components, making interfacial peeling between the components of the composite fiber less likely to occur. The anchoring effect here refers to the phenomenon in which a component penetrates into an object, making mechanical peeling difficult and increasing peel strength.

To enhance the natural unevenness and high-level processing ability obtained from the composite fiber, it is preferable to emphasize the irregularities of the complex-shaped components. To achieve this, it is preferable to have slightly more complex-shaped components than simple circular components, and it is preferable that the average circularity be 0.20 or more and 0.50 or less. If it is desired to further emphasize the natural unevenness, it is preferable that the circularity be distributed over a wider range, and it is preferable that the difference between the minimum and maximum circularity values be 0.50 or more.

Furthermore, in composite fibers characterized in that at least one component constituting the cross section does not have a specific uniform shape, the greater the number of segments of the component constituting the cross section, the more irregularly shaped components can be obtained, and by dissolving the other component, fibers with more irregular cross sections can be produced. In other words, it is preferable that the number of segments of at least one component constituting the cross section of the fiber is large. The number of segments here refers to the number of segments constituting one single yarn cross section in the binarized image described above. In this case, it is preferable that the number of segments in the binarized cross section be 10 or more.

As described above, the composite fiber of the present invention has a regular, marbled composite morphology, even though the components that make up its cross section have diverse morphologies. This characteristic cross-sectional morphology is suitable for producing natural-look textiles that have the natural mottling and soft feel of natural fibers, and also has favorable effects in terms of ease of processing in advanced stages.

In other words, as mentioned above, the key point is that the single type of component that makes up the cross section of the composite fiber does not align to a specific shape, but rather forms a variety of forms. The proportion of segments with a complex, root-like shape (G in Figure 1) relative to the total number of segments is a notable requirement from the perspective of exerting an anchoring effect and enhancing the interfacial delamination suppression effect. Incidentally, due to the complexity of their shape, these segments with a complex, root-like shape have a circularity of 0.10 or less, as defined in the present invention. In the composite fiber obtained by the present invention, segments with a circularity of 0.10 or less are effective in suppressing interfacial delamination.

For this reason, in the present invention, in order to improve the processability in advanced processing and to ensure high quality when made into a textile, it is preferable that segments with a circularity of 0.10 or less account for 1 to 20% of the total number of segments.

If the number of segments with a circularity of 0.10 or less is 1% or more of the total number of segments, interfacial delamination is suppressed even when the composite fiber is subjected to compressive deformation under heat, such as in the twisting process of false twisting. This not only maintains good fuzzing of the composite fiber and the quality of the resulting textile, but also reduces the likelihood of yarn breakage during advanced processing, maintaining good operability. Furthermore, if the number of segments with a circularity of 0.10 or less is 20% or less of the total number of segments in the cross section, there will be fewer areas where a specific component excessively surrounds another component. For example, even when one component is dissolved after the textile is made, the irregular cross-section ultrafine fibers that are a feature of the present invention are efficiently produced, resulting in the effect of completing the process in a short time.

In addition, while the components that make up the composite cross section of the composite fiber of the present invention have irregular cross-sectional shapes, they are continuous along the fiber axis, and the unstable phenomenon of thinning immediately below the spinneret seen in general blend spinning, etc., is not observed. This results in stable extrusion, and the resulting composite fiber has excellent thickness uniformity along the fiber axis, making it suitable for processing into high-quality, natural-look textiles.

Generally, in composite fibers containing two or more components, the elongation deformation behavior of each component differs, making the elongation deformation unstable during the spinning and drawing processes. This instability is exacerbated, particularly when the components constituting the composite fiber are discontinuous in the fiber axis direction, and thickness unevenness along the fiber axis tends to increase. When at least one component constituting the composite fiber is continuous in the fiber axis direction, elongation deformation during the spinning and drawing processes is stable, suppressing the occurrence of excessive thickness unevenness along the fiber axis. As a result, when the fiber is processed into a textile, large color variations and unevenness can be avoided, allowing for the production of high-quality natural-look textiles. For this reason, in order to process high-quality natural-look textiles in the present invention, it is preferable that at least one component constituting the composite fiber be continuous in the fiber axis direction.

The thickness unevenness in the fiber axis direction referred to here can be expressed as the Worcester (fineness unevenness) U% value, which is an index of fineness unevenness. To process high-quality natural-look textiles, U% is preferably 1.0% or less. If U% is 1.0% or less, the degree of color unevenness and unevenness that appears when the textile is made into a textile will be more natural, resulting in a high-quality natural-look textile. In particular, when the goal is a natural-look textile, fineness unevenness can easily result in noticeable dye unevenness, which can induce defects in advanced processing such as streaks. Therefore, it is preferable to be able to control this fineness unevenness. Furthermore, when at least one component constituting the composite fiber, a feature of the present invention, is continuous in the fiber axis direction, the elongation deformation during the spinning and drawing processes is stabilized, thereby suppressing the occurrence of yarn breakage and stabilizing operability.

When the conjugated fiber of the present invention is produced by melt spinning, excellent processability is achieved when the constituent components are thermoplastic polymers, and therefore, it is advisable to select the polymers from a group of polymers such as polyesters, polyethylenes, polypropylenes, polystyrenes, polyamides, polycarbonates, polymethyl methacrylates, and polyphenylene sulfides.
Furthermore, from the viewpoint of suppressing interfacial peeling and improving the composite cross section, it is preferable that the difference in solubility parameters between the components constituting the fiber is small, and it is advisable to select polymers such that the difference in solubility parameters between the two components forming the interface is 3.0 or less. The solubility parameter (SP value) difference referred to here refers to a parameter that reflects the cohesive strength of a substance, defined as (evaporation energy/molar volume) ^1/2 , and can be, for example, the value described in "Plastics Data Book," co-edited by Asahi Kasei Amidas Corporation and the Plastics Editorial Department, page 189, etc. In particular, when one type of component is dissolved after the composite fiber of the present invention is made into a textile to generate ultrafine fibers with an irregular cross section, it is advisable to use an alkali-soluble polymer and an alkali-slightly soluble polymer as the components constituting the fiber and perform an alkali reduction treatment. For example, if the components constituting the fiber are a polyester that is easily soluble in alkali and a polyester that is hardly soluble in alkali, or a polyester that is easily soluble in alkali and a polyamide (slightly soluble in alkali), then the alkali reduction treatment will produce ultrafine fibers with irregular cross sections made of the hardly soluble in alkali polymer, which is preferable because natural unevenness resulting from the cross-sectional shape can be obtained.
By utilizing the conjugated fiber of the present invention, a textile having natural patterns and a soft feel like natural fibers can be obtained, and therefore the present invention can be used in a wide range of clothing and apparel applications, from general clothing applications such as innerwear and outerwear to interior applications such as curtains and cloth.

An example of a method for producing the composite fiber of the present invention is described in detail below.

The composite fiber of the present invention, i.e., a composite fiber composed of two or more components, each of which has an irregular cross section and a marbled pattern, can be produced by spinning using a composite spinneret. From the perspective of increasing productivity, melt spinning is a suitable method for spinning such composite fiber.

The composite spinneret used for the composite fiber of the present invention is preferably the spinneret described in JP 2018-154934 A, adapted to composite spinneret specifications. The composite spinneret shown in Figure 5 is assembled into a spinning pack with three types of components stacked from top to bottom: metering plate H, confluence plate I, and discharge plate J, and is used for spinning. Incidentally, Figure 5 shows an example using two types of components, component A and component B, but if necessary, three or more types of components can be used for spinning.

In the composite spinneret shown in Figure 5, the metering plate H measures the amount of component (polymer) per hole in the confluence plate I, and the confluence plate I combines and mixes the measured different polymers any number of times, resulting in a marbled pattern of the polymers combined in the cross section of the polymer flow. The discharge plate J then compresses and discharges the polymer flow mixed in the confluence plate I.

The confluence plate is described in JP 2018-154934 A, so details are omitted here. However, it combines multiple flow paths carrying different polymers, resulting in a mixture of the different polymers as the polymers flowing from each flow path repeatedly merge. Specifically, the confluence plate has multistage confluence microchannels K, as shown in Figure 5, corresponding to each discharge hole of the discharge plate J. At each stage of these multistage confluence microchannels K, the confluence patterns, such as the confluence position and angle of the different polymer streams, vary. Therefore, repeated confluence results in a marbled pattern of various shapes for each component in the cross section of the polymer stream. Furthermore, by changing the number of confluence stages of the multistage confluence microchannels K in the confluence plate I, the composite cross section can be easily altered. For example, a small number of confluence stages results in a coarse marbled structure, as shown in Figure 2. Increasing the number of confluence stages results in a more delicate marbled structure, as shown in Figure 1, and further increasing the number of confluence stages results in a more delicate marbled structure, as shown in Figure 3. Furthermore, this composite cross section can be formed continuously in the fiber axis direction, and compared to the method described in JP 59-100717 A, in which a non-uniformly mixed polymer flow is accidentally distributed to each nozzle hole using a static mixing element (the cross-sectional structure resulting from this method is as shown in Figure 4), the composite ratio of each single yarn and the composite cross section do not change over time, allowing for stable spinning without yarn breakage.

To avoid confusing the explanation of the composite spinneret, components stacked above the metering plate H (not shown) can be components that form flow paths in accordance with the spinning machine and spin pack. By designing the metering plate H to match existing flow path components, the existing spin pack and its components can be used as is. Therefore, there is no need to dedicate a spinning machine specifically to this spinneret. In practice, it is also advisable to stack multiple flow path plates between the flow path and metering plate H or between the metering plate H and merging plate I. The purpose of this is to create a flow path that efficiently transports the polymer in the cross-sectional direction of the spinneret and the cross-sectional direction of the single yarn, and to configure it so that it is introduced into the merging plate I. After cooling and solidifying, the composite polymer stream discharged from the discharge plate J is given an oil agent and taken up by rollers at a specified peripheral speed to become composite fiber.

The composite fiber of the present invention can be produced using the composite spinneret described above. It goes without saying that, if this composite spinneret is used, the composite fiber of the present invention can also be produced using a spinning method that uses a solvent, such as solution spinning.

When melt spinning is selected, the components constituting the composite fiber of the present invention are as described above. Examples include melt-processable polymers such as polyethylene terephthalate or its copolymers, polyethylene naphthalate, polybutylene terephthalate, polytrimethylene terephthalate, polypropylene, polyolefin, polycarbonate, polyacrylate, polyamide, polylactic acid, and thermoplastic polyurethane. Polycondensation polymers, such as polyester and polyamide, have high melting points and are particularly preferred. The polymer may also contain various additives, such as inorganic substances such as titanium oxide, silica, and barium oxide; colorants such as carbon black, dyes, and pigments; flame retardants; fluorescent brighteners; antioxidants; and ultraviolet absorbers. Furthermore, from the viewpoint of suppressing interfacial delamination and achieving a good composite cross section, it is preferable that the difference in solubility parameters between the components constituting the fiber be 3.0 or less. In particular, when it is desired to form a textile from the composite fiber of the present invention and then dissolve one component to produce ultrafine fibers with irregular cross sections, which is a feature of the present invention, it is preferable that the fiber contains an alkali-soluble polymer and a poorly alkali-soluble polymer. For example, an alkali-soluble polyester and a poorly alkali-soluble polyester, or an alkali-soluble polyester and a polyamide (poorly alkali-soluble) can be used. In particular, as the easily soluble polyester, it is preferable to use a polyester copolymerized with polyethylene glycol and sodium sulfoisophthalic acid, either alone or in combination, from the viewpoint of spinnability and ease of solubility in low-concentration aqueous solvents. Examples of suitable polymer combinations for generating ultrafine fibers with irregular cross sections from the composite fibers of the present invention include polyethylene terephthalate copolymerized with 5 mol% to 15 mol% of 5-sodium sulfoisophthalic acid as the readily soluble component, due to their melting points, and polyethylene terephthalate copolymerized with the aforementioned 5-sodium sulfoisophthalic acid and 5 wt% to 15 wt% of polyethylene glycol having a weight average molecular weight of 500 to 3000, and polyethylene terephthalate or polyamide-6 as the poorly soluble component.

The spinning temperature when spinning the composite fiber of the present invention is set to a temperature at which the two or more components, primarily the high-melting-point or high-viscosity polymer, exhibits fluidity. The temperature at which this fluidity is exhibited varies depending on the molecular weight, but it is preferably set between the melting point of the polymer and the melting point + 60°C. A temperature below this level is preferable because it prevents thermal decomposition of the polymer in the spinning head or spin pack and suppresses a decrease in molecular weight.

When spinning the composite fiber of the present invention, a throughput of 0.1 g/min-hole to 20.0 g/min-hole is required to ensure stable production. A single-hole throughput rate that results in a single-fiber fineness of less than 4 dtex after drawing is particularly preferred, as the fineness of the fiber results in a soft texture when woven into a fabric. The ratio of component A to component B when spinning the composite fiber of the present invention can be selected from a component A/component B ratio of 5/95 to 95/5 based on the throughput rate. When using a slightly soluble component as component A and a readily soluble component as component B to produce ultrafine fibers with irregular cross sections from the composite fiber of the present invention, a higher ratio of the slightly soluble component is preferable in terms of ultrafine fiber productivity. When the component A/component B ratio is 30/70 to 20/80, the slightly soluble component does not excessively surround the readily soluble component in the cross section of the fiber, and the dissolution process can be completed in a short time.

The polymer stream discharged in this manner is cooled and solidified, and is then applied with an oil and taken up by rollers with a specified peripheral speed to form composite fibers. The take-up speed can be determined based on the discharge rate and the desired fiber diameter, but a speed in the range of 100 to 7000 m/min is preferred for stable production of the composite fibers used in the present invention. From the perspective of highly orienting the composite fibers and improving their mechanical properties, it is advisable to draw them. This drawing can be carried out after they have been wound up in the spinning process, or it can be carried out immediately without winding them.

As for the drawing conditions, for example, in a drawing machine consisting of one or more pairs of rollers, for fibers made from a polymer exhibiting thermoplasticity that can generally be melt-spun, the fibers can be comfortably drawn in the fiber axis direction by using a peripheral speed ratio between the first roller set at a temperature above the glass transition temperature and below the melting point and the second roller set at the crystallization temperature, and then heat-set and wound up to obtain a composite fiber with a composite cross section as shown in Figure 1. The upper limit of the temperature of the first roller is preferably set to a temperature that does not cause fiber path disturbance during the preheating process. For example, in the case of polyethylene terephthalate, whose glass transition temperature is around 70°C, the preheating temperature is usually set to around 80 to 95°C.

The composite polymer stream discharged from the discharge plate 3 is cooled and solidified according to the manufacturing method described above, and then an oil agent is applied. The stream is then taken up by rollers set at a specified peripheral speed, and then stretched by heated rollers to produce the desired composite fiber.

The composite fiber of the present invention obtained in this manner has a marbled cross-sectional structure that varies the yarn properties, color tone, luster, etc., for each single yarn, resulting in a natural-looking texture and appearance. Furthermore, to obtain ultrafine fibers with irregular cross sections from the composite fiber of the present invention, the composite fiber can be immersed in a solvent capable of dissolving the readily soluble components to remove the readily soluble components, thereby obtaining ultrafine fibers with irregular cross sections composed of sparingly soluble components. When the readily soluble component is copolymerized polyethylene terephthalate copolymerized with 5-sodium sulfoisophthalic acid or the like, an alkaline aqueous solution such as a sodium hydroxide aqueous solution can be used. For example, the composite fiber of the present invention can be treated with an alkaline aqueous solution by immersing the composite fiber or a textile made thereof in the alkaline aqueous solution. In this case, it is preferable to heat the alkaline aqueous solution to 50°C or higher, as this accelerates the progress of hydrolysis. The method for generating ultrafine fibers with irregular cross sections from the composite fiber of the present invention is not limited to the dissolution treatment described above, but can also be carried out by physical methods such as drawing, kneading, and raising, or chemical methods such as heat treatment, boiling water treatment, and swelling treatment, or a combination of these.

As mentioned above, the method for producing the composite fiber of the present invention has been explained based on the general melt spinning method, but it goes without saying that it can also be produced using the meltblowing method and the spunbonding method, and it can also be produced using solution spinning methods such as wet and dry-wet methods.

The conjugate fiber of the present invention will be specifically described below with reference to examples.
The examples and comparative examples were evaluated as follows.

A. Melt viscosity of polymer The measurement temperature was the same as the spinning temperature, and a melt viscosity of 1216 s ^-1 was recorded in the examples and comparative examples. The measurement was carried out in a nitrogen atmosphere, with a 5-minute time lapse between the time the sample was placed in the heating furnace and the start of the measurement.

B. Melting Point of Polymer Chip-shaped polymer was adjusted to a moisture content of 200 ppm or less using a vacuum dryer, and approximately 5 mg was weighed out. Using a TA Instruments differential scanning calorimeter (DSC) Model Q2000, the temperature was raised from 0°C to 300°C at a heating rate of 16°C/min, and then held at 300°C for 5 minutes for DSC measurement. The melting point was calculated from the melting peak observed during the heating process. Measurements were performed three times per sample, and the average value was taken as the melting point. When multiple melting peaks were observed, the melting point was determined to be the top of the melting peak with the highest temperature.

C. Solubility Parameter Difference The solubility parameter (SP value) is a parameter that reflects the cohesive strength of a substance, defined as the square root of (evaporation energy/molar volume). It can be determined by immersing a polymer in various solvents and taking the value of (evaporation energy/molar volume) of the solvent at which the swelling pressure is maximized as the (evaporation energy/molar volume) of the polymer. The SP value determined in this manner is described, for example, in "Plastics Data Book," co-edited by Asahi Kasei Amidas Corporation and the Plastics Editorial Department, page 189, and this value can be used. The solubility parameter difference between the polymers to be combined is calculated as the absolute value of (SP value of component A - SP value of component B).

D. Fineness The weight of 100 m of the composite fiber was measured, and the weight was multiplied by 100 to calculate the fineness (dtex). This measurement was repeated 10 times, and the average value was taken as the fineness (dtex). The value obtained by dividing the fineness by the number of filaments was taken as the single yarn fineness (dtex).

E. Worcester U%
Using a fineness unevenness measuring device (UT-4) manufactured by Zellweger, the Worcester U% (H) of the composite fiber was measured under the conditions of a yarn supply speed of 100 m/min, a twister rotation speed of 6000 rpm, and a measurement length of 100 m.

F. Average circularity and difference between maximum and minimum circularity values. Immediately after extrusion, the composite fiber was cut approximately perpendicular to the fiber axis at an arbitrary position along the fiber axis, and the cut surface was photographed using an optical microscope manufactured by Olympus at a magnification that allowed observation of the interface between the components constituting the single yarn cross section. Using image processing software (WINROOF), one single yarn cross section was extracted, converted into a grayscale image, and binarized by adjusting the threshold value. From the binarized image, the cross-sectional parameters of segments representing a specific component were read, and the circularity of all extracted segments was measured. The same process was repeated for five single yarn cross sections, and the calculated circularity of each segment was arithmetically averaged and rounded to two decimal places to obtain the average circularity. The circularity of each segment was calculated using the image processing software using the following formula:
(Circularity of segment)={4π×area of segment/(perimeter of segment) ² }
Of all the extracted segments, the difference in circularity between the segment with the maximum circularity and the segment with the minimum circularity was calculated.

G. Ratio of Segments with a Circularity of 0.10 or Less to the Total Number of Segments Of all the segments extracted from the image subjected to the above-described binarization processing, the ratio of the number of segments with a circularity of 0.10 or less to the total number of segments was calculated.

H. Appearance (dyed fabric)
The number of fibers in the composite fiber was adjusted so that the weave density was 180/2.54 cm, and a plain woven fabric was produced. The obtained plain woven fabric was scoured at 80°C for 20 minutes and dyed under the following dyeing conditions.
Dye: NICHILON BLUE (manufactured by Nissei Kasei) 3.0% owf
Auxiliary agent: Ultra N-2 (Mitejima Chemical Co., Ltd.) 0.5 g/L
Dispersant: RAP-250 (manufactured by Meisei Chemical Industry Co., Ltd.) 0.5 g/L
Dyeing conditions: 50°C x 20 minutes → 100°C x 30 minutes.

The appearance of the dyed plain weave fabric was evaluated by five inspectors on three levels based on the following criteria:
A: There is a clear difference in shade.
B: Somewhat unclear but with some shading.
C: Monotonous.

I. Appearance (alkali-treated fabric)
A plain weave fabric was prepared by adjusting the number of fibers in the composite fiber to a weave density of 180 fibers/2.54 cm. The resulting plain weave fabric was immersed in a 1% sodium hydroxide aqueous solution heated to 90°C for 30 minutes, rinsed with water, and dried in a hot air dryer set to 60°C for 30 minutes. The appearance of the alkali-treated plain weave fabric was evaluated by five inspectors on a four-point scale based on the following criteria:
S: Has a natural, glossy sheen.
A: It has a natural luster.
B: There is fine flickering.
C: There is glare.

J. Hand feel (alkali-treated fabric)
The alkali-treated plain weave fabric used in the appearance evaluation was evaluated for feel by five examiners, who rated the feel of the fabric on a four-point scale based on the following criteria.
S: Soft and has a good feel.
A: Feels good to the touch.
B: A level that can be used for clothing.
C: Feels bad to the touch.

K. Peel Resistance Plain woven fabrics were prepared by adjusting the number of fibers in the composite fiber to a weave density of 180 fibers/2.54 cm. The resulting plain woven fabrics were subjected to a frosting treatment under strong conditions (wet state, load: 7.36 N) or weak conditions (dry state, load: 4.12 N). The plain woven fabrics were then cut perpendicular to the fiber axis, and the fiber cross sections were photographed using a Hitachi scanning electron microscope (SEM). The cut surfaces of the resulting fiber cross sections were observed for the presence of interfacial peeling. Peel resistance was then evaluated based on the following three criteria:
A: No interfacial peeling even after frosting under severe conditions.
B: Interfacial peeling occurs after frosting under strong conditions, but no interfacial peeling occurs under weak conditions. C: Interfacial peeling occurs even after frosting under weak conditions.

L. Advanced processing passability (number of yarn breakages during false twist processing)
The high-level processability of the composite fiber was evaluated on a three-level scale based on the number of yarn breakages that occurred when a 3 kg wound pirn was false-twisted. The false-twisting conditions were a processing speed of 500 m/min, a draw ratio of 1.05, a false-twisting temperature of 130°C (hot plate length of 2.0 m), and a false-twist number of 3000 T/M. The high-level processability was evaluated based on the number of yarn breakages, including single yarn breakages, that occurred during false-twisting. A preferable range for minimizing interference with false-twisting operations was one in which the number of yarn breakages during processing was four or less. Furthermore, if the number of yarn breakages was one or less, it could be said that there was no interference with false-twisting operations, and the fiber was therefore judged to have excellent high-level processability.
A: 0 to 1 thread breakage. B: 2 to 4 thread breakages. C: 5 or more thread breakages.

[Example 1]
Polyethylene terephthalate (PET, melt viscosity: 120 Pa s, melting point: 254°C, SP value: 21.4 MPa ^1/2 ) was prepared as component A, and polyethylene terephthalate copolymerized with 8.0 mol % of 5-sodium sulfoisophthalic acid and 9 wt % of polyethylene glycol (SSIA-PEG copolymerized PET, melt viscosity: 95 Pa s, melting point: 233°C, SP value: 22.9 MPa ^1/2 ) was prepared as component B. The difference in solubility parameters of the combined polymers was 1.5 MPa.

These components were melted separately at 290°C, then introduced into a spinning pack incorporating a composite spinneret (shown in Figure 5) with a 50/50 component A/B ratio. A composite polymer stream was then extruded from the extrusion holes. A two-stage multi-stage microchannel A was used for the extrusion plate, and the composite polymer stream was extruded to form a marbled composite cross-sectional shape as shown in Figure 1. The extruded composite polymer stream was cooled and solidified, then oiled and wound at a spinning speed of 1000 m/min to obtain an undrawn yarn of 200 dtex-8 filaments (total output of 20 g/min). The wound undrawn fiber was drawn 3.5 times between rollers heated to 90°C and 130°C, yielding a drawn fiber of 56 dtex-8 filaments. The U% (index of fineness unevenness) was 0.6%, demonstrating excellent thickness uniformity along the fiber axis. Furthermore, when 100 kg of this composite fiber was spun, no thread breakage occurred and spinnability was good.

When the cross section of the resulting composite fiber was observed, it was found to have a structure in which the components were kneaded together in a marbled pattern. Focusing on component A, there was no bias toward any particular shape, and it was widely distributed, ranging from complex, branched shapes to simple, circular shapes. The average circularity was 0.37, and the difference between the maximum and minimum circularity values was 0.71. Segments with root-like, embedded shapes were also observed, with 6% of segments having a circularity of 0.1 or less. The number of segments in the cross section of one single yarn was 18. The marbled composite morphology in the cross section was continuous in the fiber axis direction.

When a 3 kg wound pirn of the resulting composite fiber was false-twisted, the cross-sectional shape showed that each component was interwoven in a marbled pattern, resulting in no yarn breakage and good passability through advanced processing. Furthermore, when the peel resistance of fabric woven from the resulting composite fiber was evaluated, no interfacial peeling was observed, even after frosting under severe conditions.

The resulting composite fiber was woven into a fabric, which was then scoured at 80°C for 20 minutes and cationic dyed to obtain a dyed fabric. The dyed fabric had natural shades and a wide range of color variations, as the components with different dyeability that make up the single yarns were exposed on the surface in a variety of states.

A fabric woven from the resulting composite fiber was immersed in a 1% sodium hydroxide aqueous solution (bath ratio 1:50) heated to 90°C for 30 minutes, removing over 99% of the SSIA-PEG copolymerized PET (component B), generating ultrafine fibers with irregular cross-sections, and a fabric composed of these was obtained. Evaluation of this ultrafine fiber fabric revealed that the irregular cross-sections gave the fabric a natural, lustrous sheen on the surface. Furthermore, the unique voids formed between the single yarns with irregular cross-sections gave the fabric an excellent feel and a warm texture reminiscent of natural fibers. The results are shown in Table 1.

[Examples 2, 3, 4, and 5]
The same procedure as in Example 1 was repeated, except that the number of confluence plates was changed to one (Example 2), three (Example 3), six (Example 4), and seven (Example 5). The evaluation results for these composite fibers are shown in Table 1. Regardless of the number of confluence plates, the components formed a marbled structure in the cross section of the composite fiber. The marbled composite morphology in the cross section was continuous in the fiber axis direction. In Examples 2 and 4-5, there were no segments with a circularity of 0.1 or less. Therefore, interfacial peeling was observed under severe frosting conditions, and peel resistance was slightly reduced. However, the high-level processing passability was good. Furthermore, in Examples 4-6, an increase in the number of confluence plates resulted in a finer marbled structure. Consequently, the ultrafine fibers with irregular cross sections obtained after dissolution treatment had nanofiber-order diameters and a particularly soft and supple texture. In all of Examples 2 to 5, when 100 kg of composite fiber was spun, no yarn breakage occurred, and the spinnability was good.

[Examples 6 and 7]
The same procedure as in Example 1 was repeated, except that the A/B component conjugation ratio was changed to 30/70 (Example 5) and 70/30 (Example 6). The evaluation results of these conjugated fibers are shown in Table 1. They had a marbled composite cross section similar to that of Example 1, and exhibited good peel resistance and high-level processing passability. In Example 6, a structure in which the poorly soluble component PET surrounded the easily soluble component SSIA-PEG copolymerized PET was observed in some parts of the cross section. Under the dissolution treatment conditions used in Examples 1 to 5, 30% of the SSIA-PEG copolymerized PET remained. This resulted in slightly inferior appearance and feel, although not problematic. Furthermore, in Examples 5 and 6, no yarn breakage occurred when 100 kg of the conjugated fibers were spun, and spinnability was good.

[Example 8]
The same procedure as in Example 1 was repeated except that, in the method described in Example 1, component A was polyamide-6 (N6, melt viscosity: 100 Pa·s, melting point: 225°C, SP value: 23.7 MPa ^1/2 ), and component B was polyethylene terephthalate copolymerized with 8.0 mol% 5-sodium sulfoisophthalic acid and 9 wt% polyethylene glycol (SSIA-PEG copolymerized PET, melt viscosity: 95 Pa·s, melting point: 233°C, SP value: 22.9 MPa ^1/2 ), and these were spun at 280°C. The difference in solubility parameters between the combined polymers was 0.8 MPa. The evaluation results of these composite fibers are shown in Table 1. Even when the composite polymer was changed, the components formed a structure in the cross section of the fiber in which they were kneaded into a marbled pattern as shown in Figure 1. Due to the presence of segments with a circularity of 0.1 or less, no interfacial peeling was observed even under strong frosting conditions, and peel resistance was good. When the woven fabric in which ultrafine fibers with irregular cross sections had been generated by the dissolution treatment was evaluated, it was found that the irregular cross-sectional shape gave the woven fabric a natural, glossy luster on its surface, and that the unique gaps formed between the single yarns with irregular cross sections gave the fabric an excellent feel. Furthermore, when 100 kg of the composite fiber was spun into yarn, no yarn breakage occurred, and the spinnability was good.

[Example 9]
The same procedure as in Example 1 was repeated except that, in the method described in Example 1, Component A was polypropylene (PP, melt viscosity: 70 Pa·s, melting point: 165°C, SP value: 16.8 MPa ^1/2 ), and Component B was polyethylene terephthalate copolymerized with 8.0 mol% 5-sodium sulfoisophthalic acid and 9 wt% polyethylene glycol (SSIA-PEG copolymerized PET, melt viscosity: 95 Pa·s, melting point: 233°C, SP value: 22.9 MPa ^1/2 ), and these were spun at 280°C. The difference in solubility parameters between the combined polymers was 6.1 MPa ^1/2 . The evaluation results of these composite fibers are shown in Table 1. Although the components formed a marbled structure in the fiber cross section, the large difference in solubility parameters between the combined polymers resulted in the formation of simple circular segments with high circularity, resulting in an average circularity of 0.69. Since there were no segments with a circularity of 0.1 or less, interfacial peeling was observed under strong frosting conditions, and peel resistance was reduced. Furthermore, when 100 kg of the composite fiber was spun, no yarn breakage occurred, and spinnability was good.

[Examples 10, 11, 12, and 13]
The method described in Example 1 was repeated except that a confluence plate consisting of multistage confluence microchannels B, which differed from multistage confluence microchannels A in the confluence position and confluence angle of the polymer streams, was used, and the number of confluence stages was changed to two (Example 10), one (Example 11), three (Example 12), and six (Example 13). The evaluation results for these composite fibers are shown in Table 2. Regardless of the number of confluence stages, the cross section of the composite fiber showed a structure in which each component was kneaded into a marbled pattern, and this structure was continuous in the fiber axis direction. In Examples 10 to 13, the difference between the minimum and maximum circularity values was smaller than in Examples 1 to 5, and although the fabrics were composed of segments with relatively similar shapes, the alkali-treated fabrics had a natural luster on their surfaces. In Examples 10 and 12, segments with a circularity of 0.1 or less were present, so no interfacial peeling was observed even under severe frosting conditions, and peel resistance was good. In all of Examples 10 to 13, when 100 kg of composite fiber was spun, no yarn breakage occurred and spinnability was good.

[Comparative Example 1]
The same procedure as in Example 1 was repeated, except that a composite spinneret equipped with two static mixing elements (number of mixing elements: 2) as described in Japanese Patent Application Laid-Open Nos. 10-237715 and 59-100717 was used. The results of the composite fiber obtained in Comparative Example 1 are shown in Table 1. The components had an irregular cross-sectional structure with four to five laminated layers, and the cross-sectional structure varied along the fiber axis. The U% was 1.2%, and there was significant thickness variation along the fiber axis. The difference between the minimum and maximum circularity values was only 0.14, and the shape distribution was poor. In addition, the number of segments was very small (2). Therefore, the appearance of the woven fabric after dissolution treatment was monotonous and cold, and the feel was stiff and stiff. Furthermore, because the cross-section was irregular but the monotonous laminated structure occurred, interfacial delamination occurred even with weak frosting conditions, and yarn breakage frequently occurred during false twisting, resulting in problems with high-level processing passability. Furthermore, since this method involves accidentally distributing a non-uniformly mixed composite polymer flow to each nozzle, there are differences in the composite ratio between single yarns, and the composite ratio also changes over time, so yarn breakage occurred eight times when spinning 100 kg of this composite fiber.

[Comparative Example 2]
In Comparative Example 1, the same experiment was conducted except that the number of static mixing elements was increased to four. Compared to Comparative Example 1, a composite fiber was obtained with a cross-sectional structure in which each component was layered in more layers and irregularly. The cross-sectional structure varied along the fiber axis. The difference between the minimum and maximum circularity values was very small at 0.09, resulting in a cross-section with little shape distribution, with only complex-shaped segments present. The appearance of the fabric after dissolution treatment varied slightly, but was monotonous and cold. Furthermore, although no interfacial delamination was observed in the weak frosting condition, there were differences in the conjugation ratio between the single yarns, and the conjugation ratio changed over time. Therefore, yarn breakage occurred six times during the spinning of 100 kg of composite fiber, and yarn breakage also occurred frequently during the false twisting process.

A: Component A B: Component B C: An example of a circular component (Component A) D: An example of a streak-shaped component (Component A) E: An example of a triangular component (Component A) F: An example of a component (Component A) with a complex shape that combines various shapes G: An example of a component (Component A) with a shape that penetrates like tree roots H: Metering plate I: Merging plate J: Discharge plate K: Multi-stage merging fine flow channel

Claims (4)

A composite fiber having a cross section made up of two or more types of components, characterized in that the components have a diverse, marbled composite morphology, the composite morphology is continuous in the fiber axial direction, the average circularity of segments of at least one type of component constituting the fiber is 0.20 or more and 0.80 or less, the difference between the minimum and maximum circularity values is 0.30 or more, and U% is 1.0% or less . The composite fiber described in claim 1, characterized in that segments with a circularity of 0.10 or less account for 1 to 20% of the total number of segments. 3. The conjugated fiber according to claim 1, wherein all of the constituent components are polyester. A textile product at least partly comprising the conjugated fiber according to any one of claims 1 to 3 .