WO2007072788A1 - Cellular fiber and method for production thereof - Google Patents

Abstract

[PROBLEMS] To provide a high-quality cellular fiber having a small fiber fineness, having no large air bubble therein, and is uniform in fiber diameter in the lengthwise direction. [MEANS FOR SOLVING PROBLEMS] Disclosed is a cellular fiber comprising a thermoplastic polymer and has an average fiber diameter of 1 to 50 μm inclusive, wherein air bubbles constitute 10 to 90% inclusive of the cross-section of the fiber, the ratio of the maximum diameter of an air bubble to the diameter of the fiber is 0.08 or less, and the fiber has a U% (half) of 2 or less. The cellular fiber can be produced by: kneading a thermoplastic polymer and nitrogen and/or carbon dioxide in a molten state to prepare a mixed polymer, introducing the mixed polymer to a spinning die; applying a shear rate (ϜH) of 50,000 to 1,000,000 sec-1 to the mixed polymer at the spinning die; discharging the mixed polymer into a low-pressure area to decrease the pressure of the mixed polymer, thereby causing to foam the polymer; cooling the foamed polymer; drawing the polymer; and winding the polymer.

Description

 Specification

 Foamed fiber and method for producing the same

 Technical field

 The present invention relates to a foamed fiber excellent in fiber uniformity and light weight and a method for producing the same. More specifically, in the present invention, the bubbles inside the fiber are fine and uniform, and the foamed structure is uniform in the longitudinal direction of the fiber. For this reason, the present invention relates to a high-quality foamed fiber having a uniform fiber diameter in the longitudinal direction of the fiber and free of thick spots, and a method for producing the same.

 Background art

 [0002] In recent years, from the viewpoint of energy saving, a wide variety of foam materials containing bubbles in the thermoplastic resin are widely used. Foamed material is excellent in lightness, heat retention, heat insulation, elasticity, etc. due to the effect of having independent air bubbles inside, so it is practical in the field of molding materials such as food containers, packing materials and building materials. It has become.

 [0003] A general foam molding material is manufactured by a manufacturing method in which a foaming agent is added to thermoplastic resin, melted and mixed, and foamed during or after discharge. These foam molding materials have closed cells of about several mm to several hundreds / zm inside. Conventionally, low-boiling compounds such as butane and organic / inorganic compounds that generate decomposition gas by thermal decomposition have been used as blowing agents. However, the former low-boiling compound has a problem that it has an explosive risk and has a large environmental load. Power! In addition, since the low-boiling compound has low solubility in the molten resin, there is a problem that the bubble diameter in the obtained foam molding material tends to be large. In addition, since it is difficult to uniformly dissolve the low-boiling compound in the molten resin, there is a problem in that the foam size of the obtained foam molding material tends to be non-uniform. On the other hand, when using the latter organic and inorganic compounds

However, there is a restriction on the use temperature, and the foaming efficiency is poor. In addition, the organic / inorganic compound and the polymer react to discolor the polymer.

[0004] In recent years, inert gases such as carbon dioxide and nitrogen have attracted attention as foaming agents that have low environmental impact, high foaming efficiency, and no reaction with thermoplastic polymers. And the inert gas A foam molding material with a cell diameter of about several tens of meters can be obtained by mixing a molten polymer (carbon dioxide or nitrogen dioxide) in a supercritical state with a molten polymer, dissolving it uniformly in the polymer, and then foaming. ing.

 [0005] In order to improve characteristics such as lightness and heat retention, it is desired to produce a foamed fiber having a practical level with high productivity even with synthetic fibers. However, no practical foamed fiber has been obtained yet. There are two reasons for this.

[0006] The first is that many of the fibers used for clothing and industrial use are thin fibers with a diameter of 50 m or less. For this reason, at the bubble size of a few tens of μm achieved with molding materials, the physical properties were significantly reduced and practically useless.

[0007] The second reason is that uniformity (fiber diameter, fiber physical properties) in the longitudinal direction of the fiber is required. In this case, bubbles of a size of several tens / zm level are not practical because they cause thick fibers.

[0008] Until now, the following proposal has been made for foamed fibers!

[0009] For example, a method for producing a string-like aromatic polyester foam has been proposed (see Patent Document 1). O This proposal involves adding a low-boiling compound as a foaming agent to a thermoplastic polymer, Foamed fibers are obtained by foaming when discharged from the spinneret. But the resulting foamed fibers, the cross-sectional area of the fiber was as low as L～200mm ² of the large instrument versatility. Further, as described above, low boiling point compounds are poorly soluble in thermoplastic polymers, and are therefore difficult to mix uniformly. For this reason, the foam formed is large, and the foamed structure is likely to be uneven in the longitudinal direction.

[0010] Similarly, a technique has also been proposed in which an aliphatic polyester to which a low-boiling compound is added is foamed at the time of spinning to obtain a string-like material having a cross-sectional area of 1 to 100 mm ² subjected to uniaxial elongation. (Refer to Patent Document 2.) _{0 In} this proposal, it is stated that the absolute strength is insufficient if the cross-sectional area is less than 1 mm ² , so that a known foaming agent is added to the fiber so as to be stiff. Even when foamed fibers with a small diameter are formed, only foamed fibers with low mechanical properties can be obtained. The present inventors also tried to apply the proposal of Patent Document 2 to foamed fibers with fineness. However, thread breakage occurred frequently just after the die was discharged, and it was impossible to wind the foamed fiber stably. As a result of observing the yarn breakage of the spun yarn, there are coarse bubbles inside the fiber that are comparable to the fiber diameter. This has been found to be the cause of poor yarn production.

[0011] Further, the organic-inorganic blowing agent is added to the thermoplastic polymer has also been proposed a technique for obtaining a foamed fiber by foaming during discharge (see Patent Documents 3 to 5.) ₀ However, in these proposals Further, the foaming agent or the remaining chain generated by thermal decomposition of the foaming agent and the thermoplastic polymer reacted with each other, so that the quality of the fiber being easily colored was lowered and the strength was increased. In addition, the base was frequently soiled due to the remaining chain of the foaming agent, and the spinning performance was poor. Furthermore, Patent Document 5 discloses a foamed fiber having a convex portion on the fiber surface. The convex portion on the surface of the fiber is formed by having coarse bubbles inside the fiber and the foam structure being non-uniform in the longitudinal direction of the fiber. Therefore, although it can be used for a specific purpose, it has not been widely used as a foamed fiber for clothing or industry.

[0012] As synthetic fibers, foamed fibers using carbon dioxide or nitrogen have been proposed. For example, foamed fibrous structure having an average diameter within the fibers have an independent air bubbles substantially spherical 1Z1,000~1Z5 fiber diameter has been proposed (see Patent Document 6.) ₀ The foamed fiber structure Zotai is After a low molecular compound such as carbon dioxide or nitrogen is exhausted to a fiber structure prepared in advance under high pressure, the fiber structure containing the low molecular compound is subjected to a treatment such as heating to obtain a low molecular compound. Obtained by inflating. According to this proposal, it is possible to form sub-micron-order substantially spherical closed cells inside the fiber, and it is possible to obtain foamed fibers with high cushioning and heat retention properties. However, in order to impregnate the low molecular weight compound, since it is necessary to hold it under a high pressure for a long time, the productivity is low. In addition, in order to obtain a foamed fiber structure with high productivity, a huge high-pressure vessel is required, which is a technology that requires high equipment costs. Furthermore, since the low molecular weight compound easily escapes the fiber force before the treatment for expanding the low molecular weight compound, it was difficult to increase the expansion ratio. In addition, since the bubbles inside the foamed fiber are almost spherical, the cushioning property is high. The strength of the fiber is low.

[0013] Therefore, a technique for continuously obtaining foamed fibers has also been proposed. Specifically, an inert gas such as carbon dioxide or nitrogen is used as a foaming agent, inorganic particles are contained as a foam nucleating agent, the back pressure in the base is set to 50 to 300 kgZcm ^2, and the mixed polymer stays in the base. A foamed fiber in which fine bubbles are formed inside the fiber is proposed by setting the interval to 1 to 15 milliseconds (see Patent Document 7). _{0 In} this proposal, the inert gas is held under high pressure. Later, by discharging with a shorter residence time in the die, that is, by reducing the pressure at a high speed, a foamed monofilament having a fiber diameter of 500 / zm or less can be obtained. In the examples, it is shown that foamed fibers having a bubble diameter of about 20 m and a fiber diameter of 60 m can be obtained. However, it had a diameter variation of 7 m in the longitudinal direction of the fiber. This was because the bubble diameter was larger than the fiber diameter of the foamed fiber, and the bubble diameter was non-uniform. Therefore, it was not used as a general-purpose fiber. This is a technique that is easy to deteriorate the spinning performance due to the large diameter of the bubbles and poor uniformity.

[0014] Therefore, in order to improve the spinning property and suppress the coarsening of bubbles after spinning, a core-sheath composite yarn is used, and a polymer added with carbon dioxide or nitrogen at a high concentration is arranged in the core. Therefore, a technique for obtaining foamed fibers has been proposed (see Patent Document 8). ₀ According to this proposal, the yarn-making property is improved by the existence of a sheath component having a low carbon dioxide gas concentration and which is not foamed. The effect of suppressing the growth of bubbles by the sheath component was low, and the inside of the fibers had coarsened bubbles, and thickness spots in the longitudinal direction of the fibers were likely to occur. In addition, since it has a sheath component that does not contain air bubbles, there are inherent limitations in improving characteristics such as lightness and heat retention.

[0015] In addition, a supercritical fluid such as carbon dioxide or nitrogen is injected into a polymer at the time of spinning and foamed at the time of spinning, so that the volume expansion coefficient is 1.2 to 50 and the cell density is 10 ^7. A microcellular fiber having a cell / cm ³ or more, a cell length to diameter ratio of 2 or more, and a fiber diameter of 5 μm or more has been proposed (see Patent Document 9;). This proposal improves fiber properties by quenching the spun yarn to suppress gas outflow from the spun yarn and coalescence of the bubbles, and stretching the bubbles in the longitudinal direction by a spinning draft. According to this proposal, a foamed fiber having a high volume expansion coefficient and improved mechanical properties can be obtained. However, as can be seen from the cell density of the foam fibers disclosed in the examples, the cell density tends to decrease particularly when trying to obtain foam fibers having a fineness of 50 m or less. Atsuta. This is because the fiber surface area per volume increases when the spun yarn is cooled. For this reason, it is difficult to suppress the outflow of the foaming agent to the outside of the spun yarn. For this reason, it was a technology that did not generate enough bubble nuclei and the cell density decreased. Further, with the outflow of the foaming agent, foaming agent concentration spots and viscosity spots are produced inside the spun yarn. For this reason, this is a technique in which the bubble growth becomes uneven, coarse bubbles are formed, and the foam structure becomes uneven. Therefore, the obtained foamed fiber has a large thickness variation in the longitudinal direction and a low effect of improving mechanical properties.

 Patent Document 1: Japanese Patent Laid-Open No. 57-34931

 Patent Document 2: JP-A-11-92583

 Patent Document 3: Japanese Patent Laid-Open No. 55-93831

 Patent Document 4: Japanese Patent Laid-Open No. 4-214407

 Patent Document 5: Japanese Unexamined Patent Application Publication No. 2004-19013

 Patent Document 6: Japanese Unexamined Patent Application Publication No. 2002-154463

 Patent Document 7: JP-A-7-252724

 Patent Document 8: Japanese Unexamined Patent Publication No. 2003-129342

 Patent Document 9: WO2004—35884 pamphlet

 Disclosure of the invention

 Problems to be solved by the invention

[0016] An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a foamed fiber that is suitable for clothing and industrial use and has a fineness and excellent longitudinal uniformity of the fiber. is there. Another object of the present invention is to provide a production method for producing the foamed fiber with high productivity.

 Means for solving the problem

 [0017] The present inventors give a high shear rate to the mixed polymer of carbon dioxide or nitrogen and a thermoplastic polymer so that it cannot be applied by ordinary melt spinning in the discharge hole. The number of bubble nuclei generated at the time of spinning is remarkably increased, and a foamed fiber having a finer foam diameter and a uniform foamed structure in the longitudinal direction of the fiber can be obtained. Has reached

That is, the foamed fiber of the present invention is a foamed fiber having thermoplastic polymer strength, It is a foamed fiber characterized by satisfying (1) to (5).

 (1) Fiber diameter is 1 μm or more and 50 μm or less

 (2) Bubble occupancy in fiber cross section is 10% or more and 90% or less

 (3) Maximum bubble diameter Z fiber diameter ≤ 0.08

 (4) Average bubble diameter is 1 μm or less

 (5) U% (half) is 2 or less.

 According to a preferred embodiment of the foamed fiber of the present invention, the relationship between the strength and the elongation of the foamed fiber satisfies the relationship of the following formula.

Strength X (Elongation) ⁵ ≥15

 The method for producing foamed fiber according to the present invention introduces a mixed polymer obtained by kneading a thermoplastic polymer and carbon dioxide or nitrogen in a molten state to a spinneret, and discharges it to a low pressure region to cause foaming by reducing the pressure. The foamed fiber manufacturing method is characterized by satisfying the following (6) to (8) by cooling the foamed polymer and taking it out after taking it out.

(6) Shear rate in discharge hole (γ H) 50,000 ～ l, 000, OOOsec ^_1

 (7) Spinning speed lOOOOmZ min ~ 6000mZ min

 (8) Back pressure of the base is 8MPa or more lOOMPa or less

 According to a preferred embodiment of the method for producing foamed fibers of the present invention, the shear rate of the mixed polymer in the spinneret hole is the shear rate (Ύ) of the first stage.

H is 50,000 to 1,000,000 sec- ¹ , and the second stage is a multistage discharge hole diameter so that the shear rate (γ) is smaller than γ.

 H L

 It is discharging using the spinneret which expands.

[0020] According to another preferred embodiment of the method for producing a foamed fiber of the present invention, after the spun yarn is drawn, it is wound by applying a heat treatment before winding.

 The invention's effect

[0021] The foamed fiber of the present invention is a foamed fiber having fine bubbles inside the fiber and having a highly uniform foamed structure. In addition, it is possible to produce foamed fibers at a low cost with a low environmental load. In addition, the foamed fiber of the present invention has a uniform fiber diameter in the longitudinal direction and good mechanical properties, and is excellent in lightness, heat retention, sound insulation, cushioning, touch, and product safety. It is. Therefore, it is particularly suitable for sports clothing, outdoor clothing, uniform clothing such as white clothing, formal clothing and clothing such as winter underwear, swimwear and lining, and various vehicle interior materials such as seat skins, ceiling skins, and inline carpets. It is also suitable for industrial use such as cushions, duvets, blankets, pillows, carpets and curtains, and is also suitable for general consumption materials such as diapers, raw materials and used towels, and hand towels.

 BEST MODE FOR CARRYING OUT THE INVENTION

 [0022] The fiber in the foamed fiber of the present invention refers to a thin, long and shaped fiber. Examples thereof include long fibers (filaments), short fibers (stable), and short fibers and piles used for electric flocking. A filament is preferred because it has a feature of high uniformity in the longitudinal direction and is vibrant.

 [0023] When the foamed fiber is a multifilament, the number of single fibers may be set as appropriate according to the purpose of use such as apparel use or industrial material use. Depending on the application, monofilament may be used.

 [0024] The cross-sectional shape of the single fiber of the foamed fiber of the present invention may be appropriately selected according to the intended use. Examples include round, polygonal, gear, petal, multileaf, star, and C types. Depending on the purpose, a composite fiber such as a core-sheath type, a sea-island type, or a bimetal type in which the same or different thermoplastic polymers are bonded can be obtained. The blend fiber can be blended at any stage of discharging the same or different thermoplastic polymer from the spinneret. From the viewpoint of low cost and good recyclability, it is preferably a foamed fiber formed from a single type of thermoplastic polymer.

[0025] The foamed fiber of the present invention has a fiber diameter of 1 µm or more and 50 µm or less. Here, the fiber diameter means the diameter of a single fiber. If the cross-section of a single fiber is a perfect circle, it is the diameter. In the foamed fiber of the present invention, since it is necessary to simultaneously measure the form of bubbles and the diameter of the fiber, the fiber diameter is obtained by the method shown in the Examples. Specifically, the cross section of the fiber is first observed, and the cross-sectional area surrounded by the outer periphery of the fiber is calculated by image analysis. Then, the diameter corresponding to the circle is obtained from the cross-sectional area, and this is defined as the fiber diameter. At this time, the cross-section of the fiber was observed at 10 random locations, and the fiber diameters obtained from each were averaged to obtain the fiber diameter. [0026] When the fiber diameter is 50 µm or less, a high-quality foamed fiber having appropriate flexibility is obtained. Therefore, it can be used widely for clothing and industrial use! In addition, when the fiber diameter is 1 μm or more, the mechanical properties of the foamed fiber are maintained and the foamed fiber has practical durability. As long as the foamed fiber satisfies the above range, the fiber diameter may be appropriately selected according to the intended use. For example, when used for clothing, the fiber diameter is preferably 30 μm or less, more preferably 20 μm or less, and even more preferably 15 / zm or less. For industrial applications, the fiber diameter is preferably 40 m or less, more preferably 30 m or less. On the other hand, the fiber diameter is preferably 3 m or more, more preferably 5 μm or more, and 8 μm is more preferable because it suppresses fluctuations in the fiber diameter due to the presence of bubbles and makes it easier to obtain uniform fibers. More preferably, it is more preferably 10 μm or more.

 [0027] The foamed fiber in the present invention has bubbles inside the fiber. Preferably, it has ten or more independent bubbles divided by thermoplastic polymer walls in the fiber cross section. These bubbles have a shape extending in the longitudinal direction of the fiber and are discontinuous. The foamed fiber in the present invention is obtained by introducing a mixed polymer in which fiber thermoplastic polymer and carbon dioxide or nitrogen or nitrogen are mixed at the spinneret in melt spinning, and reducing the pressure when discharged from the spinneret. It can be obtained by generating bubbles inside.

 [0028] Next, the foam structure of the foam fiber of the present invention will be described in more detail.

[0029] The foam occupancy of the foamed fiber of the present invention has a bubble occupancy of 10% or more and 90% or less in the fiber cross section. By making the bubble occupancy 10% or more, various properties such as heat retention can be improved. In addition, by setting the bubble occupancy to 90% or less, the mechanical properties as fibers can maintain a practical level. It is preferable that the ratio of air bubbles in the cross section of the fiber is 20% or more, more preferably 30% or more, and more preferably, in terms of becoming a highly expanded foam fiber with characteristics such as light weight and heat retention. Is 40% or more, particularly preferably 50% or more. In addition, since foamed fibers with a high bubble occupancy rate tend to deteriorate in mechanical properties, the bubble occupancy rate is preferably 85% or less, more preferably 80% or less, and even more preferably 75% or less. Yes, particularly preferably 70% or less. [0030] The number of bubbles in the fiber cross section of the foamed fiber of the present invention is preferably 10 or more. Due to the foam structure having 10 or more fine bubbles, external force is dispersed in the thermoplastic polymer. Due to this effect, the bubble has excellent durability and becomes a structure that is not easily crushed by bending or abrasion. Moreover, it becomes a foamed fiber excellent in cushioning properties and elasticity. The foamed fiber of the present invention maintains the bubbles that are difficult to collapse even during yarn processing such as drawing and false twisting or when the product is used. It is preferable that the number of bubbles is large in that the durability of the foam structure is more excellent, and the number of bubbles is preferably 50 or more, more preferably 100 or more, and The number is preferably 400 or more, particularly preferably 1000 or more. About 1,000,000 is appropriate for the upper limit of the number of voids. The number of voids can be confirmed by the method of the example.

 [0031] The foamed fiber of the present invention satisfies the relationship between the maximum bubble diameter and the fiber diameter in the fiber cross section. The maximum bubble diameter Z fiber diameter ≤ 0.08. Uniformity in the longitudinal direction of the fiber can be enhanced by the foamed structure in which the maximum diameter of the bubbles is sufficiently smaller than the fiber diameter. The mechanical properties can also be maintained at a practical level. Maximum bubble diameter The smaller the Z-fiber diameter, the more uniform the foam in the longitudinal direction of the fiber. And even if the bubble occupation rate mentioned above is made high, it becomes a foamed fiber with favorable mechanical properties. In view of the above, the relationship between the maximum bubble diameter and fiber diameter is preferably the maximum bubble diameter Z fiber diameter ≤ 0.07. The maximum bubble diameter Z fiber diameter ≤ 0.06. More preferably, the maximum bubble diameter Z fiber diameter ≤ 0.05 is more preferred, and the maximum bubble diameter Z fiber diameter ≤ 0.04 is more preferred. As for the lower limit of the value of the maximum bubble diameter Z fiber diameter, the maximum bubble diameter Z fiber diameter ≥0.0001 is currently the manufacturing limit.

[0032] The finer the maximum bubble diameter in the fiber cross section of the foamed fiber of the present invention, the more uniform the foamed fiber and the better the mechanical properties. Therefore, the maximum bubble diameter is 10 μm. More preferably, it is 5 μm or less, more preferably 3 μm or less, particularly preferably 1 μm or less, and most preferably 0.5 m or less. The smaller the maximum bubble diameter, the better. The lower limit is preferably 0.001 / zm or more. [0033] In addition, the average diameter of the bubbles in the cross section of the fiber is 1 μm or less from the viewpoint of good uniformity and mechanical properties of the fiber. It is preferable that the average diameter of the bubbles is small, preferably 0.7 / zm or less, more preferably 0.6 m or less, and even more preferably 0.5 m or less. The lower limit of the average diameter of the bubbles, the smaller the average diameter of the bubbles, the more suitable the lower limit of the average diameter of the bubbles, so that the foamed fiber has high durability of the bubbles. For this reason, the average diameter of the bubbles is preferably 0.001 μm or more, more preferably 0.005 μm or more, and further preferably 0.01 μm or more.

 [0034] As described above, the foamed fiber of the present invention has bubbles stretched in the longitudinal direction of the fiber. In the foamed fiber manufacturing method described later, this is formed by extending the bubbles in the longitudinal direction of the fiber in the process of drawing the spun yarn and in the process of stretching the spun. It is preferable that the bubbles existing inside the fiber are in the form extended in the longitudinal direction because the decrease in the mechanical properties of the fiber is reduced. The larger the bubbles, the easier it is to reduce the mechanical properties! The largest in the cross section of the fiber! The diameter of the bubble (the maximum diameter of the bubble) and the length of the bubble in the longitudinal direction of the fiber It is preferable that the ratio with (bubble length) is large. That is, the maximum length of the bubble length Z bubble is preferably 3 or more, more preferably 5 or more, and even more preferably 10 or more. On the other hand, since the maximum length of the bubble length Z bubble is an appropriate size, it is preferable because the bubbles are not easily crushed by the external force applied from the side of the fiber. Therefore, the maximum diameter of the bubble length Z bubble is preferably 10000 or less, more preferably 5000 or less, and even more preferably 1000 or less.

 In the foamed fiber of the present invention, the smaller the bubble diameter distribution in the fiber cross section, that is, the smaller the standard deviation of the bubble diameter, the more uniformly the external force is dispersed in the thermoplastic polymer. It is preferable because it becomes a foamed fiber excellent in. The standard deviation of the bubble diameter is preferably 1 μm or less, more preferably 0.7 m or less, even more preferably 0.5 m or less, and particularly preferably 0. It is as follows. As for the lower limit, 0.01 μm is the current manufacturing limit.

[0036] Since the foamed fiber of the present invention has a fine and uniform foamed structure, U% (half) indicating fluctuation of the fiber diameter in the longitudinal direction is 2 or less. By reducing U% (half) to 2 or less, The processability of the foam fiber is improved. For example, in the case of suppressing fluff during false twisting or making a woven fabric, it becomes a fiber excellent in versatility as a fiber for clothing or industrial use that suppresses the generation of wrinkles and is less likely to cause shading in dyeing.

 [0037] Conventional foam fibers have coarse bubbles inside the fibers, and the foam structure in the longitudinal direction of the fibers is non-uniform, so that only foam fibers with U% (half) greater than 2 can be obtained. I had a great power. However, in the present invention, by applying a high shear rate to the mixed polymer of the thermoplastic polymer and carbon dioxide or nitrogen, which is not assumed in ordinary melt spinning, in the discharge hole of the spinneret. They found that the number of bubble nuclei generated can be dramatically increased. For the first time, an expanded fiber having uniform fine bubbles inside the fiber was obtained. It is preferable that the U% (half) of the foamed fiber of the present invention is 1.5 or less in that it is a highly versatile foam fiber with high processability and quality. Is more preferably 1 or less, and even more preferably 0.8 or less. Since U% (half) is preferably as low as possible, the lower limit for production is currently 0.01 or more.

 [0038] Next, the thermoplastic polymer constituting the foamed fiber of the present invention will be described.

[0039] The thermoplastic polymer forming the foamed fiber of the present invention has fiber-forming ability. For example, polyester polymers, polyamide polymers, polyimide polymers, polyolefin polymers and other vinylenopolymers, fluorine polymers, senorelose polymers, silicone polymers, elastomers, and a variety of other engineering plastics. I'll do it.

[0040] More specifically, the thermoplastic polymer is synthesized by a mechanism in which a monomer having a bur group, such as radical polymerization, ion polymerization, and cationic polymerization, is produced by an addition polymerization reaction. Polyolefin-based polymers and other bur polymers such as polyethylene, polypropylene, polybutylene, polymethylpentene, polystyrene, polyacrylic acid, polymethacrylic acid, polymethyl methacrylate, polyacrylonitrile, polytetrafluoroethylene , Polyvinylidene fluoride, polysalt vinylidene, polycyanide vinylidene and the like. These may be polymers by homopolymerization, such as polyethylene only or polypropylene only! /, Or a plurality of monomers. It may be a copolymerized polymer formed by carrying out a polymerization reaction in the presence of one copolymer. For example, if polymerization is carried out in the presence of styrene and methyl methacrylate, a copolymerized polymer called poly (styrene methacrylate) is obtained. The force which produces | generates may be a polymer which is such a copolymer.

 [0041] Further, examples of the thermoplastic polymer include a polyamide polymer formed by the reaction of carboxylic acid or carboxylic acid chloride with amine. Specifically, nylon 6, nylon 7, nylon 9, nylon 11, nylon 12, nylon 6, 6, nylon 4, 6, nylon 6, 9, nylon 6, 10, nylon 6, 12, nylon 5, 7 Nylon 5, 6 and nylon 5, 10 and the like. And within the range not detracting from the gist of the present invention, other aromatic, aliphatic, alicyclic dicarboxylic acid, other aromatic, aliphatic and alicyclic diamine components, or other aromatic, aliphatic and An alicyclic aminocarboxylic acid compound (one compound having both sulfonic acid and amino groups) may be used. Alternatively, it may be a polyamide polymer obtained by copolymerization of the third and fourth copolymer components.

 [0042] Examples of the thermoplastic polymer include polyester polymers formed by esterification reaction of carboxylic acid and alcohol. Specific examples include polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and polycyclohexane dimethanol terephthalate. And the main point of the present invention is not impaired! Other components are copolymerized within the range!

 [0043] The dicarboxylic acid compound of the copolymerization component includes terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, diphenyl dicarboxylic acid, anthracene dicarboxylic acid, phenanthrene dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenoxyethanedicarboxylic acid. , Diphenylethanedicarboxylic acid, adipic acid, sebacic acid, 1,4-cyclohexanedicarboxylic acid, 5-sodium sulfoisophthalic acid, 5-tetrabutylphosphonium isophthalic acid, azelaic acid, dodecanedioic acid, hexahydroterephthalate Aromatic, aliphatic, and cycloaliphatic dicarboxylic acids such as acids and their derivatives, adducts, structural isomers, and optical isomers such as alkyl, alkoxy, aryl, aryl, and imi-imido halides. be able to. Of these dicarboxylic acid compounds, one may be used alone, or two or more may be used in combination.

[0044] Examples of the diol compound of the copolymer component include ethylene glycol and propylene glycol. , Butyleneglycolanol, pentanediol, hexanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, hydroquinone, resorcin, dihydroxybiphenyl, naphthalenediol, anthracenediol, phenanthreneol, 2, 2-bis Aromatic, aliphatic and cycloaliphatic diol compounds such as (4-hydroxyphenol) propane, 4,4'-dihydroxydiphenyl ether and bisphenol S and their alkyl, alkoxy, aryl, aryl, Derivatives, adducts, structural isomers and optical isomers such as amino-imino and halides can be mentioned. You can use one of these Zeo-Lui compounds alone or in combination of two or more.

[0045] Examples of the copolymer component include hydroxycarboxylic acids (one compound having a hydroxyl group and a carboxylic acid). Examples of the hydroxycarboxylic acid include lactic acid, 3-hydroxypropionate, 3-hydroxybutyrate, 3-hydroxybutyrate valerate, hydroxybenzoic acid, hydroxynaphthoic acid, hydroxyanthracenecarboxylic acid, and hydroxyphenanthrene. Aromatic, aliphatic and alicyclic diol compounds such as carboxylic acids, (hydroxyphenol) vinyl carboxylic acids, and their alkyl, alkoxy, aryl, aryl, and amide-containing halogenated compounds Derivatives, adducts, structural isomers and optical isomers. Of these hydroxycarboxylic acids, one kind may be used alone, or two or more kinds may be used in combination.

 [0046] The polyester polymer may be a polymer having hydroxycarboxylic acid as a main repeating unit. Hydroxycarboxylic acids include aromatic, aliphatic and alicyclic. These hydroxycarboxylic acid polymerized polymers include polylactic acid, poly (3-hydroxypropionate), poly (3-hydroxybutyrate) and poly (3-hydroxybutyrate valerate). Mention may be made of poly (hydroxycarboxylic acids). In addition, other aromatic, aliphatic and alicyclic dicarboxylic acids, other aromatic, aliphatic and alicyclic diol components, and other hydroxycarboxylic acids are copolymerized without departing from the spirit of the present invention. Also good.

[0047] In addition, the thermoplastic polymer of the present invention includes polycarbonate polymers (polymerized by transesterification of alcohol and carbonic acid derivatives), polyimide polymers (carbons). (Polymerized by cyclized polycondensation of acid anhydride and diamine), polybenzimidazole polymer (polymerized by reaction of dicarboxylic acid ester and diamine), polysulfone polymer, polyethylenee polymer, polyphenylene sulfide Examples thereof include synthetic polymers such as polymers, polyether ether ketone polymers, and polyetherol ketone ketone polymers, and polymers derived from natural polymers such as chitin and chitosan derivatives.

 [0048] The thermoplastic polymer may be appropriately selected depending on the use of the foamed fiber, but is well balanced in fiber physical properties such as mechanical properties and thermal properties, excellent in versatility, and heat resistant in the foam structure. Of these, polyester polymers, polyamide polymers, and polyolefin polymers are preferred. Polyesterol polymers and polyamide polymers are more preferred.

 [0049] Among polyester polymers, polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, and polylactic acid are more preferable in that the foamed structure of the foamed fiber has high heat resistance and high durability. . Polyethylene terephthalate and polytrimethylene terephthalate are even more preferred. Polyethylene terephthalate is particularly preferred.

 [0050] Similarly, nylon 6 and nylon 6, 6 are more preferably used as the polyamide polymer from the viewpoint of durability of the foamed fiber.

 [0051] The foamed fiber of the present invention preferably has a better mechanical property and a highly versatile fiber, and the relationship between strength (cNZdtex) and elongation (%) preferably satisfies the following formula.

Strength X (Elongation) ⁵ ≥15

Strength X (Elongation) · The value of ⁵ is an index for evaluating the energy required for a fiber to break. Higher values indicate better mechanical properties and higher practicality. In the prior art, the fibers contained coarse bubbles with respect to the fiber diameter, and the size of the bubbles was not uniform. . However, in the present invention, by increasing the number of bubble nuclei generated by a specific manufacturing method, it is possible to obtain a foam fiber that is sufficiently small relative to the fiber diameter and includes only soot bubbles. Therefore, a foamed fiber satisfying the above formula can be obtained. Strength X (elongation) ° · ⁵ is preferably 16 or more in terms of becoming a foamed fiber with better mechanical properties and practicality. More preferred is 17 or more. It is more preferable that it is 18 or more, and it is particularly preferably 20 or more. On the other hand, if the strength X (elongation) · ⁵ is too large, the fiber may become too stiff and the fiber may become stiff. Therefore, the strength X (elongation) ⁵ is preferably 40 or less, more preferably 35 or less, and even more preferably 30 or less.

 [0052] The fiber strength of the foamed fiber in the present invention is preferably 2. OcNZdtex or more. When used as a sports uniform or outdoor clothing, and when used as an industrial material, it should be a strong material. In addition, even when the processability of fibers or fiber products is taken into consideration, the yarn properties are required to have high fiber strength. Therefore, it is more preferable that the fiber strength is 2.5 cNZdtex or more. 3. It is more preferable that the fiber strength is OcNZdtex or more. Particularly preferable is 3.5 cNZdtex or more. In general, fibers having high strength tend to have low elongation. Therefore, the strength is preferably 10c NZdtex or less, more preferably 9cNZdtex or less, more preferably 8cN Zdtex or less, and even more preferably 7cNZdtex or less.

 [0053] The foamed fiber in the present invention has excellent lightness because it has bubbles inside the fiber.

 Here, excellent lightness is defined as the apparent specific gravity of the fiber being 90% or less of the specific gravity of the thermoplastic polymer. For example, in the case of polyethylene terephthalate, the apparent specific gravity is 1.24 or less, 1.12 or less for polytrimethylene terephthalate, 1.22 or less for polybutylene terephthalate, 1.13 or less for polylactic acid, 1.02 or less for polyamide, 0. 81 or less, or 0.85 or less for polyethylene. It is preferable that the apparent specific gravity of the fiber is 85% or less with respect to the specific gravity of the thermoplastic polymer, more preferably 80% or less, and even more preferably 75% or less in terms of becoming a lighter fiber. . The specific gravity of the foamed fiber of the present invention is measured by the method of the example. However, for foamed fibers for which it is difficult to measure the specific gravity by this method, the apparent specific gravity is calculated using the bubble occupancy in the fiber cross section and the amorphous density of the thermoplastic polymer.

[0054] The foamed fiber of the present invention has a quenching agent, a flame retardant, a lubricant, an anti-oxidation agent, an ultraviolet absorber, an infrared absorber, a crystal nucleating agent, a foaming nucleating agent, a fluorescent substance within a range not impairing the gist of the invention. Brighteners, end group sealants (compounds or reactive compounds such as epoxy groups, carpositimide groups, etc.) Ma) and a small amount of additives such as thickeners may be retained.

[0055] Hereinafter, the production method of the foamed fiber of the present invention will be specifically described.

[0056] The foamed fiber of the present invention uses diacid carbon and / or nitrogen as a foaming agent, and after mixing the diacid carbon and / or nitrogen with a molten thermoplastic polymer. Then, the mixed polymer is guided to the spinneret, discharged at a high shear rate in the spinneret discharge hole, foamed by lowering the pressure, and the foamed spun yarn is cooled and then wound. Manufactured by the method of taking.

[0057] In the method for producing foamed fiber of the present invention, carbon dioxide and / or nitrogen is used as a foaming agent, which is relatively low in critical temperature and critical pressure of carbon dioxide and nitrogen. Therefore, it is easy to form a single phase of the thermoplastic polymer and carbon dioxide or nitrogen by dissolving in the thermoplastic polymer by mixing in the thermoplastic polymer as a supercritical state. As a result, a fine and uniform foam structure can be formed inside the foam fiber.

[0058] The critical temperature of carbon dioxide is 31 ° C and the critical pressure is 7.4MPa, while the critical temperature of nitrogen is -147 ° C and the critical pressure is 3.4MPa. If the requirements above the critical temperature and above the critical pressure are met, the fluid will be in a supercritical state. Carbon dioxide or nitrogen used as a foaming agent can be used alone or in combination with carbon dioxide and nitrogen. The mixing ratio can be arbitrarily selected. In view of obtaining a foamed fiber having a higher foaming ratio, that is, having a higher cell occupation ratio in the foamed fiber, it is preferable to use carbon dioxide.

[0059] In the method for producing foamed fibers of the present invention, it is preferable that carbon dioxide or nitrogen dioxide is brought into a supercritical state at least inside the spinning pack. The configuration of the flow path, filter layer and filter in the spin pack is arbitrary, but it is preferable that the pressure in the spin pack increases. For this reason, it is essential that each component of the spin pack has a mechanical design that can withstand the pressure. The bubbles in the foamed fibers become finer as carbon dioxide or nitrogen dioxide dissolves in the thermoplastic polymer to form a single phase. Therefore, it is preferable that the pressure in the spin pack is 10 MPa or more. The pressure in the spin pack is more preferably 20 MPa or more. More preferably, it is 30 MPa or more. More preferably, it is 40 MPa or more. Than Particularly preferred is 50 MPa or more. The higher the pressure in the spinning pack, the better. However, if the pressure is too high, the equipment becomes large due to pressure-resistant design of the spinning pack, the base, the polymer flow path, and the gear pump. And the versatility of the foamed fiber obtained will become low. Therefore, it is preferable to set it to 200 MPa or less. The pressure inside the spin pack can be measured by placing a pressure gauge in the polymer flow path to the spin pack as well as the gear pump.

 [0060] In the method for producing foamed fibers of the present invention, the back pressure in the die (hereinafter, sometimes abbreviated as the die back pressure) is 8 MPa or more and lOOMPa or less. First, the foaming mechanism of the foamed fiber of the present invention will be outlined. The amount of carbon dioxide or nitrogen dissolved in the thermoplastic polymer (hereinafter sometimes abbreviated as “solubility”) is higher at higher pressures and lower at lower pressures. For this reason, under high pressure conditions, the mixed polymer forms a single phase in which carbon dioxide or nitrogen is dissolved in the thermoplastic polymer. The solubility of carbon dioxide or nitrogen in the thermoplastic polymer is lowered by the pressure drop when the mixed polymer is discharged. For this reason, carbon dioxide or nitrogen is present in a supersaturated state in the spun yarn immediately after discharge. Inside the supersaturated spun yarn, carbon dioxide or nitrogen is released and bubble nuclei are formed. Dioxide carbon or nitrogen dissolved in the spun yarn flows into the bubble nucleus, and the bubble grows and becomes larger. Thereafter, the spun yarn is solidified by cooling to complete foaming. This is the foaming mechanism in the foamed fiber. At this time, the higher the pressure applied to the mixed polymer before ejection, the greater the difference in the solubility of carbon dioxide or nitrogen before and after ejection, so that more bubbles are formed. For this reason, it is necessary that the back pressure at the base is 8 MPa or more. In this way, it is preferable to apply a high pressure to the mixed polymer until immediately before discharge, since the foaming phenomenon is stabilized and the yarn-forming property is improved. From the above, it is preferable that the back pressure of the base is high. It is more preferable that it is lOMPa or more. More preferable is 15 MPa or more. More preferable is 20 MPa or more. Particularly preferable is 30 MPa or more. Is the best. In addition, the upper limit of the back pressure of the base is preferably set to lOOMPa or less from the viewpoint of pressure resistance design. Note that the back pressure of the base is calculated from the pressure in the spin pack by the method of the example.

[0061] In the manufacturing method of the foamed fiber of the present invention, a mixed polymer of the diacid I匕炭oxygen or nitrogen and a thermoplastic polymer in the spinneret holes, the shear rate _{(Ύ) 50,000~l, 000, OOOsec} _1 To discharge. In the present invention, the region to which the shear rate (γ) is applied is defined as the high shear rate region.

 Η

 This is called the area. The shear rate (γ) in the present invention is calculated by the following equation.

 Η

(Note) When the high shear rate region is a round hole,

y = 32Q / π Ό ³

 Η Η Η

 (Note) When the high shear rate region is a slit hole,

y = 6Q / TW ²

 H H H H

 (C) When the high shear rate region is Y hole,

y = 6Q Z3T W ²

 H H H H

 However,

 y: shear rate applied in the high shear rate region

 H

Q: Volume discharge per single hole ( _cm ³ Zsec)

 H

 D: Diameter of the hole (cm) when the high shear rate region is a round hole

 H

 T: Slit length in the high shear rate region (cm)

 H

 W: Slit width (cm) in the high shear rate region.

 H

 [0062] Also, for example, when the hole shape is a hole shape other than a round hole, a slit hole and a Y hole, the cross-sectional area of the hole is calculated to obtain the diameter D corresponding to the cross-sectional area, and the above (A )

 H

 To calculate.

[0063] Volume discharge per single hole (Q) (cmVsec) is the weight discharge per single hole (gZsec

 H

) Divided by the melt density (g / cm ³ ) of the thermoplastic polymer only. For example, 1.18 for polyethylene terephthalate, 1.14 for polytrimethylene terephthalate, 1.08 for polylactic acid, and 1.00 for nylon 6 It was. For polymers other than the above thermoplastic polymers, adjust the pressure at the inlet and outlet of the gear pump so that the discharge efficiency of the gear pump is 100%, and use the discharge volume per rotation of the gear pump and the rotation speed. Calculated by calculation.

[0064] In the melt spinning comprising only a thermoplastic polymer, which is usually l, OOOsec- ¹ ~ 10, it is common to discharge at OOOsec ^_1 extent of shear rate. This is because when a high shear rate is applied as in the present invention, the base becomes dirty due to bending and uneven discharge occurs, resulting in poor yarn production. It is because it is easy to do. However, in the method for producing foamed fiber of the present invention, as a result of earnestly examining the formation of fine foam in the foamed fiber by generating a large number of cell nuclei, the result is far beyond the normal range. By imparting a high shear rate, rather, the spinning property is improved, and a foamed fiber having highly uniform fine bubbles can be obtained.

 [0065] The reason is presumed to be as follows. Presumably, bubble nuclei are formed by contacting carbon dioxide or nitrogen in the mixed polymer. For this reason, fluctuations in the concentration of carbon dioxide or nitrogen in the mixed polymer are involved in the formation of bubble nuclei. Usually, bubble nuclei are generated only in the region where the concentration of carbon dioxide or nitrogen is relatively high in the fiber. On the other hand, when a high cutting speed is imparted in the discharge hole as in the present invention, a large amount of carbon dioxide or nitrogen dissolved in the thermoplastic polymer is brought into contact with each other. It is also presumed that bubble nuclei are generated even in a relatively low concentration region of nitrogen. As a result, it is estimated that it is formed uniformly in a much larger number of bubble nuclear spinning yarns. Even when a high shear rate is applied, it is presumed that the yarn can be stably produced without causing the base stain or non-uniform discharge.

[0066] A force that can generate a large number of bubble nuclei even by increasing the pressure drop during discharge described above. Further, by applying the high shear rate shown above, a much larger number of bubble nuclei are generated. To do. For the same reason, it is preferable to increase the back pressure of the die even when the same shear rate is applied. By shear rate to be applied to the mixed polymer at the discharge hole is to 50, OOOsec ^{_ 1} or more, the foam fibers finely foamed for cell nuclei is sufficiently generated bubbles do not grow excessively is obtained. Shear rate is more favorable Mashiku is at 60,000Sec ^_1, even more preferably 70,000Sec ^_1 or more. The upper limit of the pruning disconnection speed, it is preferable than that force is preferred instrument 800,000Sec ^_1 from the viewpoint of productivity and the spinning stability l, 000, is OOOsec ^_1, 500, more favorable it is OOOsec ^_1 Mashigu particularly preferably 300, OOOsec ^_1.

 [0067] Giving a shear rate (γ) within the range of the present invention means that the high shear rate region is a round hole.

 Η

 If the hole diameter is calculated as a round hole, adjust the hole diameter D (cm), slit

 H

 If the hole is a Y hole, adjust the slit length (T) and slit width (W), or simply

 H H

This can be achieved by adjusting the volume discharge amount per hole. [0068] Further, the pore depth (L) in the high shear rate region in the present invention is carbon dioxide or nitrogen.

 H

 A hole depth (L) of 0.1 mm or more is preferred because it is desirable to apply a uniform shear rate to the mixed polymer of thermoplastic polymer and to easily generate cell nuclei uniformly inside the mixed polymer.

 H

 Is more preferably 0.2 mm or more, and even more preferably 0.3 mm or more, and particularly preferably 0.4 mm or more. For the upper limit of the hole depth (L),

 H

 The gold back pressure should not exceed lOOMPa! / Choose the appropriate range! ,.

[0069] die used in the production of foamed fiber of the present invention, the mixed polymer 50,000Sec ^_1 least 1, after applying the shear rate (gamma) below 000,000 _SeC ^_1, smaller than its shear rate (gamma)

 Η Η

 V, preferred to have a region that imparts a shear rate (γ). In the present invention, the shear rate

 Shi

 Degree (0

 The region to which (i) is given is called the low shear rate region. By having a low shear rate region after a high shear rate region, more bubble nuclei are generated, and a large number of generated bubble nuclei can be uniformly and moderately grown. Therefore, it is possible to increase the occupancy rate of bubbles in the fiber cross section of the obtained foamed fiber. Further, by having a low shear region, the discharge linear velocity of the mixed polymer can be slowed, and the bubbles inside the spun yarn are easily stretched. Therefore, there is an advantage that the mechanical properties of the foam fiber are improved.

[0070] The cell occupancy is high !, that is, the shear rate (γ) and the trimming in terms of high foamed fiber.

 Η

 It is preferable that γ /, which is the ratio of the breaking speed (0), is 1.5 or more.

 L H L

 It is more preferably 2.0 or more, particularly preferably 2.5 or more. Shear rate (γ)

 L is the shear rate (γ)

 Similar to Η, it can be calculated by the following formula. Shear rate (0

 H) gives pore shape and shear rate (0

 The hole shapes for imparting L) may be the same or different.

 (D) When the low shear rate region is a round hole,

y = 32Q / π Ό ³

 L L L

 (E) When the low shear rate region is a slit hole,

y = 6Q / TW ²

 L L L L

 (F) When the low shear rate region is a Y hole,

y = 6Q Z3T W ²

 L L L L

However, Ύ

 Shi: Shear rate applied in the low shear rate region

Q: Volume discharge in the low shear rate region (cm ³ Zsec)

 Shi

 D: Hole diameter in the low shear rate region (cm)

 Shi

 T: Slit length in the low shear rate region (cm)

 Shi

 W: Slit width in the low shear rate region (cm)

 Shi

 For example, when the hole shape in the low shear rate region is a hole shape other than a round hole, slit hole, and Y hole, the cross-sectional area of the hole is calculated to obtain the diameter D corresponding to the cross-sectional area, and the above (

 Shi

 It shall be calculated using the formula of D). The volume discharge volume (Q) is the volume per single hole.

 Shi

 Discharge rate (Q)

 It can be calculated by the same method as H.

 [0071] In the present invention, the pore depth (L) in the low shear rate region can be heated with carbon dioxide or nitrogen.

 Shi

 It is preferable that the plastic polymer mixed polymer is long in terms of imparting a uniform shear rate, generating bubble nuclei uniformly inside the mixed polymer, and allowing the bubbles to grow easily. Hole depth (L)

 The thickness is preferably at least 0.1 mm, more preferably at least 0.2 mm, and even more preferably at least 0.3 mm, particularly preferably at least 0.4 mm. Above hole depth (L)

 However, the pressure on the back of the base should not exceed lOOMPa! ,.

FIGS. 1 to 3 are schematic views of a round hole cap having a high shear rate region and a low shear rate region which are preferable in the present invention. With the die illustrated in Figs. 1-3, the shear rate (y

 H) and shear rate (γ)

 L can be given. Using this schematic cross-sectional view, the shear rate (γ) when a die having a high shear rate region and a low shear rate region is used.

 Η and shear rate (y

 The calculation method of (ii) will be specifically described.

 [0073] As shown in Fig. 1, when the high shear rate region force ^ hole has one hole in the low shear rate region and each has a tube shape, the hole diameter D ( In the figure, reference numeral 1)

 H

 Volume discharge volume per single hole in high shear rate region Q

 Using H, shear rate (0

 H) is calculated. Then, the pore diameter D (reference numeral 3 in the figure) in the low shear rate region in FIG.

 Shi

 The shear rate (γ) is calculated using the volume discharge amount Q per hole. At this time, high shear rate

 Lion

 Q and Q are the same because the strength region is a low shear rate region force ^ hole for one hole.

 H L

Further, as shown in FIG. 2, when the high shear rate region has a plurality of holes and the low shear rate region has one hole, the volume discharge amount (Q) and the volume discharge amount (Q) are different. Caution must be taken . That is, when the high shear rate region is 2 holes and the low shear rate region is 1 hole, Q becomes 1Z2 of Q.

 H L

 [0075] Further, as shown in Fig. 3, when the low shear rate region has a shape extending in a direction perpendicular to the direction in which the polymer proceeds, the shear rate (γ) is a parameter of the portion where the shear rate is lowest.

 Shi

 Calculate using a meter. That is, in the case of FIG. 3, the pore diameter D in the low shear rate region is

 However, the hole diameter indicated by reference numeral 3 in FIG. 3 is used.

 [0076] In the present invention, a die having a high shear rate region and a die having a low shear rate region can be used in an overlapping manner.

 [0077] The thermoplastic polymer used in the present invention is a force formed by a melt-viscosity thermoplastic polymer that is usually used for synthetic fibers. In the method for producing foamed fibers described later, the thermoplastic polymer and carbon dioxide or nitrogen dioxide are used. A high shear stress is generated when melt and kneading and the carbon dioxide or nitrogen dioxide is easily dissolved in the thermoplastic polymer, and the bubbles are coalesced when the spun yarn is cooled. * From the standpoint that foam breakage hardly occurs, a thermoplastic polymer having a high melt viscosity is preferable.

[0078] The melt viscosity is the melt shear viscosity at a shear rate of 20 s _ec ^_1 (below below) measured at a temperature 30 ° C higher than the melting point (Τ) when the thermoplastic polymer used for the foamed fiber is a crystalline polymer. , Sometimes abbreviated as shear viscosity). The shear viscosity is preferably lOOPa-sec or more, more preferably 300 Pa'sec or more, and even more preferably 500 Pa'sec or more. In order to grow bubbles, the shear viscosity is preferably ΙΟ, ΟΟΟΡ a 'sec or less, more preferably 8,000 Pa' sec or less, and even more preferably 5,000 Pa 'sec or less. . For amorphous polymers not showing a melting point, the shear viscosity was measured at the same temperature as the spinning temperature.

[0079] A mixed polymer of carbon dioxide or nitrogen and a thermoplastic polymer is kneaded by mechanical kneading such as a 1-axis etatruder or 2-axis etatruder, or by stationary kneading such as a static mixer or a high mixer. It is preferred that This is preferable because carbon dioxide or nitrogen dioxide is easily dissolved uniformly. It is more preferable to knead by mechanical kneading such as a 1-axis etha ruder or a 2-shaft eta-truder. These kneading mechanisms may use only one type, or two or more types May be used in combination, or a plurality of types may be used.

 [0080] Carbon dioxide or nitrogen dioxide is preferably injected by a nozzle tube or the like at an arbitrary stage before discharging the molten thermoplastic polymer. As a result, carbon dioxide or nitrogen dioxide can be added with high productivity and can be added to the thermoplastic polymer at a high concentration. In the case of using a spinning machine attached with an etastruder, which is preferred in the present invention, a nozzle tube is attached to any position where the thermoplastic polymer is melted and kneaded with the etastruder. It is preferred to inject carbon or nitrogen directly into the molten thermoplastic polymer. This facilitates uniform dissolution in carbon dioxide or nitrogen thermoplastic polymers, and is preferred.

 [0081] Carbon dioxide or nitrogen, or a mixture of both, and a thermoplastic polymer is supercritical in all regions where the polymer is introduced into the spin pack and foamed during spinning. Preferred to be in the state. This can be achieved by a spinning machine with an etustruder, which is preferred in the present invention. For example, the amount of thermoplastic polymer supplied can be adjusted by adjusting the discharge rate of the gear pump and the mixed polymer existing in the polymer flow path can be increased to maintain high pressure, and the clearance of the elasto ruder and the polymer flow path can be designed narrowly. It is preferable to employ a method of maintaining the mixed polymer at a high pressure.

 [0082] In the present invention, when a spinning machine attached with an etastruder, which is preferably used, is used, an extruder is used because carbon dioxide or nitrogen dioxide is easily dissolved in a thermoplastic polymer uniformly. In the polymer flow path between the gear pump and the gear pump, it is preferable that the pressure at the outlet of the etastruder (hereinafter abbreviated as the tip pressure) be 8 MPa or more, more preferably 9 MPa or more, and lOMPa or more. Is a more preferred embodiment.

[0083] Carbon dioxide or nitrogen used for injection can be in any of a gaseous state, a liquid state, and a supercritical state, but has a high diffusion rate into the molten thermoplastic polymer and is easily dissolved uniformly. Therefore, it is preferable to inject in a supercritical state. Injection with a supercritical fluid means that the temperature of the molten thermoplastic polymer is 31 ° C or higher when carbon dioxide is used, 147 ° C or higher when nitrogen is used, and 31 ° C when both are used in combination. 7.4MPa or more if the injection pressure is carbon dioxide carbon, satisfying the condition of C or higher, and 3.4MPa or higher if nitrogen is used, or 7.4MPa or higher if both are used in combination. To be achieved. [0084] The greater the amount of carbon dioxide and / or nitrogen added to the thermoplastic polymer, the more dioxygen carbon or nitrogen mixed when the die force is discharged becomes supersaturated, resulting in more bubble nuclei. Is formed. For this reason, it is preferable that the amount of added force of carbon dioxide and / or nitrogen is larger. Specifically, it is more preferable that the amount of applied force is 1.5 wt% or more. 2. More preferably, it is more preferably Owt% or more, and more preferably 2.5 wt% or more. If too much carbon dioxide and / or nitrogen is added, the bubbles tend to coalesce easily. Therefore, the amount of carbon dioxide and / or nitrogen added is preferably 10 wt% or less, more preferably 9 wt% or less, and even more preferably 8 wt% or less.

 In the method for producing foamed fiber of the present invention, it is easy to generate bubble nuclei by imparting a high shear rate to the thermoplastic polymer and carbon dioxide or nitrogen, or a mixed polymer of both in the discharge hole. ing. Therefore, carbon dioxide or nitrogen dioxide is consumed mainly by the formation of bubble nuclei. Therefore, even if the addition amount of carbon dioxide and / or nitrogen is large, the bubble growth rate does not become excessively high, and the bubbles are not easily coalesced. For this reason, it is possible to spin stably.

 [0086] The discharged spun yarn is cooled. If the spun yarn is not cooled, the bubble nuclei from which carbon dioxide or nitrogen dioxide easily flows out from the spun yarn will not grow, resulting in poor foaming efficiency. The rate may go down. The cooling method V is achieved by a technique in which a material having a temperature lower than that of the spun yarn is brought into contact with the spun yarn. For example, a method of spraying cooling air onto the spun yarn, a method of immersing the spun yarn in cold water, a method of spraying water vapor onto the spun yarn, and the like. A method of cooling the spun yarn by blowing cooling air on the spun yarn with advantages such as uniform cooling of the spun yarn and high spinning speed is preferred. In this case, as the temperature of the cooling air is lower, the spun yarn is cooled more rapidly as the distance from the cooling air spray start point to the base is shorter.

[0087] The temperature of the cooling air is preferably 30 ° C or less from the viewpoint that the outflow of carbon dioxide or nitrogen can be further suppressed, and the bubble occupation ratio in the fiber cross section of the foamed fiber can be increased. It is more preferable that the temperature is 25 ° C or lower, and further preferable is 20 ° C or lower. The lower limit of the temperature of the cooling air! It is too low! If the temperature is too low, water vapor will freeze in the cooling air flow path, causing clogging. Since there are concerns about rubbing, o ° c or higher is appropriate. Further, as described above, the spun yarn is cooled more rapidly as the distance between the cooling air blowing start point and the base is shorter.

 [0088] The distance between the cooling air spray start point and the base is preferably 20 cm or less, more preferably 10 cm or less, and even more preferably 5 cm or less, particularly preferably 3 cm or less. It is. Direct force under the base When cooling air is blown, the base itself may be cooled and the temperature of the base may drop. When the temperature of the die surface is excessively lowered, unmelted polymer is discharged, and as a result, the foam structure of the foamed fiber may become non-uniform. Therefore, it is also preferable to use a heater that locally heats the vicinity of the die. It is a technique.

 [0089] In the method for producing foamed fibers of the present invention, after cooling after discharge, the fiber is taken up at a speed of 1000 to 6,000 mZ (hereinafter sometimes abbreviated as "spinning speed"). As a result, the spun yarn is cooled below the glass transition temperature (T) in a short time.

 g

 Therefore, the growth of bubbles is suppressed and excessively large bubbles do not grow. In addition, carbon dioxide or nitrogen dioxide will flow out of the system from the spun yarn, increasing the number of bubble nuclei generated. And by suppressing the outflow, the bubble diameter is made uniform because there is no concentration of carbon dioxide or nitrogen. In addition, there is an advantage that the mechanical properties of the foamed fibers are improved by extending and lengthening the bubbles in the longitudinal direction of the foamed fibers. Spinning speed l is more preferably 300 mZ or more l, 500 mZ or more Force S More preferably 2,000 mZ or more is particularly preferable.

 [0090] In addition, the higher the spinning speed, the more the bubble growth is suppressed, and the lower the occupancy rate of the bubbles, the more tend to become foamed fibers. Therefore, by setting the amount to 6,000 mZ or less, it is possible to obtain a foamed fiber having moderately grown bubbles. The spinning speed is more preferably 5,500 mZ or less, more preferably 5, OOmZ or less, and even more preferably 4,500 mZ, in terms of forming a foam fiber with a higher cell occupation ratio. It is as follows.

[0091] In the method for producing foamed fiber of the present invention, it is preferable that the spun yarn is cooled and the foamed fiber taken up at the above spinning speed is heat-treated without being wound. Since the solubility of carbon dioxide or nitrogen in thermoplastic polymers is usually greater at lower temperatures, the carbon dioxide or nitrogen may be dissolved inside the drawn foam fibers. Therefore, by applying heat treatment, carbon dioxide or nitrogen dissolved in the foamed fiber was dissolved. It is possible to increase the number of bubbles inside the foamed fiber by reducing the solubility of and generating bubble nuclei. At the same time, the dissolved carbon dioxide or nitrogen flows into bubbles that already exist, and the bubbles grow, resulting in a foam fiber with a high bubble occupancy rate. Such a change in the foam structure due to the heat treatment is a phenomenon peculiar to the foamed fiber immediately after spinning, and is thus achieved by heat-treating the taken-up foamed fiber before winding.

 [0092] It is preferable that the heat treatment temperature is T or higher of the thermoplastic polymer. T + 10 ° C or higher.

 g g

 More preferably, it is T + 20 ° C or more. Heat treatment temperature is too high

 g

 If the thermoplastic polymer is a crystalline polymer, the fluidity of the thermoplastic polymer becomes too high, which may lead to bubble coalescence and bubble breakage. In this case, the treatment is preferably performed at a temperature lower than T + 150 ° C. More preferably crystalline polymer g

 In the case of, the melting point is 30 ° C or less, and in the case of an amorphous polymer, T + 120 ° C or less. Even better

 g

 For crystalline polymers, the melting point is less than 50 ° C, and for amorphous polymers, T + 100 ° C

 g or less. Further, the longer the heat treatment time is, the better. However, if it is 10 msec or more, a sufficient effect is exhibited.

 [0093] The heating method for the heat treatment is preferably a heating method using a general-purpose apparatus and high heat transfer capability. Therefore, an apparatus using a heating roller, a heating pin, a heating plate, a heating liquid and heating steam, Alternatively, it is preferable to employ a heating method using excitation of molecular vibration represented by a carbon dioxide laser or the like. One heat source can be used for heat treatment in one step !, or multiple heat sources can be combined for heat treatment in multiple steps.

 [0094] In the method for producing foamed fiber of the present invention, it is preferable that the spun yarn is drawn and then drawn. This is because, by stretching, the bubbles inside the foamed fiber are elongated in the longitudinal direction, and the uniformity of the foamed structure in the longitudinal direction is enhanced. In addition, by stretching, the wall of the thermoplastic polymer existing between the bubbles of the foamed fiber is stretched in the fiber axis direction and oriented in the longitudinal direction to have sufficient mechanical properties.

[0095] The heating method during stretching is represented by a heating pin, a heating plate, a device using a heating liquid or a heating gas, a carbon dioxide laser, or the like, which uses a general-purpose device and a heating method having a high heat transfer capability. It is possible to employ a heating method that utilizes the excitation of molecular vibration. In view of easy uniform stretching, the stretching temperature is preferably T + 10 ° C or higher. High stretching temperature If the thermoplastic polymer is too high, the fluidity of the thermoplastic polymer may become so high that bubbles may be coalesced and broken, so if the thermoplastic polymer is a crystalline polymer, it should be processed below the melting point, and if it is an amorphous polymer, It is preferable to process at a temperature lower than T + 150 ° C.

 g

 [0096] In addition, a method of heat treatment at a temperature of T + 10 ° C or higher again after stretching is preferred. Stretching g

 By performing a heat treatment later, the periphery of the bubbles is heat-set, and the foamed fiber has excellent heat resistance. When the thermoplastic polymer is a crystalline polymer, it should be processed below the melting point, and when it is an amorphous polymer, it should be processed at a temperature lower than T + 150 ° C.

 Is preferred. More preferably, the melting point is 30 ° C or lower for a crystalline polymer, and T + 120 ° C or lower for an amorphous polymer. More preferably, for crystalline polymers, the melting point is 50 ° C g

 In the case of an amorphous polymer, T + 100 ° C or less. Also, the heat treatment time is long g

 V is more preferable, but if it is 10 msec or more, a sufficient effect is exhibited.

 [0097] The method of re-heat treatment after stretching uses a general-purpose apparatus, and the higher the heating efficiency, the more the structure inside the fiber is fixed without being relaxed, and the foamed fiber with high bubble durability is obtained. Therefore, a heating pin, a heating roller, a heating plate, a device using a heating liquid or a heating gas, or a heating method using excitation of molecular vibration represented by a carbon dioxide laser can be employed.

 [0098] Stretching and reheat treatment after stretching may be performed at any stage after winding the foamed fiber and before winding, but as described above, before the wound foamed fiber is wound, heat treatment is performed. In view of the fact that the effect can be realized at the same time, a method of heating and extending after winding and then reheating after winding is particularly preferable.

 [0099] Specifically, after drawing the spun yarn, when drawing using a roller speed difference between a plurality of rollers, heat treatment is performed by heating several rollers. A stretching method or a heating pin, a heating plate, or a heat source such as a heated liquid between the rollers and a method of stretching while performing heat treatment can be employed. The draw ratio should be adjusted so that the foamed fiber has the desired residual elongation.

[0100] Further, the above-described spun yarn may be false twisted without being stretched or after being stretched. When drawn yarn is used in false twisting, it is heated by a contact or non-contact method, and false twisting is performed with a disk, belt, or pin. Is done. When undrawn yarn is used, it is similarly heated with a contact or non-contact type heater or the like, while being stretched without being heated, and with a twisted body (disk, pin, belt). It is Although the false-twisted foamed fiber can be wound as it is, it is wound after being heat-set again.

 Example

 [0101] Hereinafter, the foamed fiber of the present invention and the method for producing the same will be described specifically and in detail with reference to Examples. The physical property values in the examples were measured by the following methods.

 A. Measurement of melting point (T) and glass transition temperature (T) of thermoplastic polymer

 m g

 Τ under the following conditions

 m and τ were measured.

 g

 [0102] Measuring device: Differential scanning calorimeter (DSC-2), manufactured by PerkinElmer

 Direct sample amount: Sample lOmg

 Temperature increase rate: 16 ° CZ min.

 [0103] The definitions of T and T are described below. Once observed at a temperature increase rate of 16 ° CZ

 m g

 After observing the endothermic peak temperature (Τ), hold at a temperature of T + 20 ° C for 5 minutes. afterwards

 ml ml

 Cool to room temperature (keep cooling time and room temperature holding time together for 5 minutes). The endothermic peak temperature observed as the deviation of the stepped baseline when the temperature was measured again at a temperature of 16 ° CZ was defined as the glass transition temperature (T). The endotherm observed as the melting temperature of the crystal

 g

 The peak temperature was taken as the melting point (T).

 B. Measurement of melt viscosity of thermoplastic polymer

 The melt shear viscosity was measured under the following conditions.

 [0104] Measuring device: Capillograph type 1 manufactured by Toyo Seiki Co., Ltd.

Shear rate: 20sec ^_1

Measurement temperature: T + 30 ° C for crystalline polymer _o Spinning temperature for amorphous polymer.

 C. U% (half) measurement

 U% (half) was measured under the following conditions.

[0105] Measuring device: Zellweger, UT-4

 Yarn feeding speed: 200mZ min

Measurement time: 1 minute. D. Measurement of foam fiber strength and elongation

The strength and elongation of the foamed fiber were measured under the following conditions. The strength and elongation were measured, and the average value measured five times was taken as each measured value. Using the average value of strength and elongation, strength X (elongation) ° ⁵ was calculated.

 [0106] Measurement conditions: Tensilon tensile tester (TENSIRON UCT—100) manufactured by Orientec

 Initial sample length: 50mm for undrawn yarn, 200mm for drawn yarn

 I Tension speed: 400mmZ for undrawn yarn, 200mmZ for drawn yarn Temperature: 25 ° C

 Relative humidity: 65%

 E. Measurement of apparent specific gravity of foam fiber

 (a) The apparent specific gravity of the fiber was measured based on the float / sink method defined in JIS-L-1013: 1999 8.1.7.1 (published by the Japanese Standards Association, chemical fiber filament yarn test method). 20 ° C ± 0

Check the floating state after immersing the fiber in the specific gravity liquid at a temperature of 1 ° C for 30 minutes. Then, adjust the specific gravity liquid that does not float or sink as described in Section 8.1.1, and measure the specific gravity value of the specific gravity liquid. An average value of specific gravity values obtained by measuring five fibers was measured. At this time, as the specific gravity liquid, an aqueous NaBr solution was used if the apparent specific gravity of the fiber was 1 or more. When the apparent specific gravity of the fiber was between 1 and 0.789, a mixed liquid using water as a heavy liquid and ethyl alcohol as a light liquid was used. When the apparent specific gravity of the fibers was between 0.789 and 659, a mixed liquid using ethyl alcohol as a heavy liquid and _n- hexane as a light liquid was used.

 (b) When the apparent specific gravity of the fiber is less than 0.659

 A tubular knitted fabric of 100 g ± 10 g consisting only of the foamed fiber of the present invention is prepared. Then, the apparent specific gravity was determined by measuring the weight and volume of the tubular knitted fabric.

First, the weight of the tubular knitted fabric is measured in advance. Then, the weight and volume of the weight-balanced weight are fixed to the tubular knitted fabric, immersed in ion-exchanged water adjusted to a temperature of 4 ° C ± 1 ° C, and defoamed with ultrasonic waves for 5 minutes. After that, the volume of the tubular knitted fabric is measured. Tube knitted fabric 10 The average value of the specific gravity values of 10 pieces of cloth was measured.

F. Observation of foam structure of foam fiber A single fiber is placed on the carbon tape affixed to the sample stage, and a platinum deposition process (deposition film pressure: 25-50 angstroms processing time: about 120 seconds) is performed. Then, the focused ion beam (FIB) cutting is performed with a Ga focused ion beam accelerated at an acceleration voltage of 30 kV with a scanning electron microscope (SEM) observation device (STRAIDB235 5 manufactured by FEI). Cutting was performed in two steps. In the first stage, rough cutting (current: about 7000 pA treatment time: about 20 minutes, degree of vacuum: ^1.4 X 10 ^_13 Pa) was performed. The second stage was subjected to precision cutting (current: about 30 OOpA treatment time: about 4 minutes, vacuum: ^1.4 X 10 ^_13 Pa). When observing the cross section of the fiber, the sample was cut perpendicular to the fiber axis direction. When performing fiber longitudinal section observation, the sample was cut parallel to the fiber axis direction.

[0108] After cutting, the cross section of the fiber and the longitudinal section of the fiber were observed using a scanning electron microscope possessed by the apparatus (vacuum degree 1.4 X 10 ^{_ 19} Pa, sample inclination 52 degrees , Acceleration voltage 5kV, magnification 80000 times). At this time, when the whole image of the fiber cross section and the vertical cross section could not be taken at the magnification, partial pictures were taken at the respective positions, and the whole image was obtained by pasting them using image software.

 (a) Measurement of fiber cross-sectional area (A) and fiber diameter (D)

 F F

 Using the cross-sectional photograph of the fiber, the computer software "WinROOF" (registered trademark) (version 2.3) manufactured by Mitani Shoji Co., Ltd. was analyzed by image analysis, and the fiber cross-sectional area (A), fiber diameter

 F

 (D) was determined. The cross-sectional area (A) of the fiber means the cross-sectional area of the region that forms one fiber.

F F

 To do. A diameter corresponding to a circle was calculated from the cross-sectional area (A). The above fiber cross-section observation

 F

 The fiber diameter (D) was calculated by averaging the fiber diameters obtained at 10 power stations.

 F

 (b) Measurement of maximum bubble diameter (D) and bubble length (L)

 M M

 In the cross-sectional photograph of the fiber, the cross-sectional area of the bubble with the largest area is similarly calculated by image analysis, and the diameter corresponding to the circle is calculated from the cross-sectional area to calculate the maximum bubble diameter (D

 M

 )

 [0109] Further, the fiber was cut so that it passed through the center of gravity of the bubble having the largest area and was parallel to the fiber axis, and the bubble length (L), which is the length of the bubble in the fiber axis direction, was obtained.

 M

[0110] Maximum bubble diameter Z Fiber diameter = D ZD Bubble length Z bubble maximum diameter = L ZD

 M M

 (c) Measurement of total cross-sectional area (A) and number of bubbles (N)

 all

 The number of bubbles (N) was determined by counting all the bubbles present in the fiber cross section. For all bubbles, the cross-sectional area of the bubbles was calculated by image analysis, and the sum (A) was obtained.

 all

 [0111] Bubble occupancy = A / A

 all F

 (d) Measurement of average bubble diameter (D) and standard deviation of bubble diameter (σ)

 A

 The average bubble diameter (D) corresponds to the circle of all the bubbles present in the fiber cross section

 A

 The diameter to calculate was calculated and the number average was taken. The standard deviation (σ) of the bubbles was calculated by taking the standard deviation of the diameter corresponding to all the bubble circles.

 G. Measurement of pressure inside spin pack and back pressure of base

 In the polymer flow path between the gear pump and the spinning pack, a pressure gauge is attached so that the pressure in the spinning pack during spinning (Ρ

 1), back pressure of base (Ρ)

 Measure 2

 [0112] First, the spinning pack is attached, and the measured value of the pressure gauge is measured until the mixed polymer of thermoplastic polymer and carbon dioxide or nitrogen is introduced into the spinning pack and the spinneret mixed polymer is discharged. Put it on the chart. Based on this chart, the pressure (Ρ) in the spinning pack immediately after discharge is expressed as the pressure loss (Ρ) in the polymer flow path.

 B, filtration layer pressure loss (Ρ)

 A C, filter pressure loss (Ρ)

 D, back pressure

(P) + P + P + P)

 Separate into E (P = P

 A B C D E. After 1 hour has elapsed from the start of discharge, the pressure in the stable spinning pack is reduced to P

 It was set to 1. Back pressure of base (P)

 2 is P = P / P X P

 2 E A 1 Calculated from the formula.

 H. Evaluation of yarn production and stretchability

 When producing 100 kg of foamed fibers, the spinning performance in the spinning process was evaluated. Thread-making performance is evaluated based on the number of thread breaks. Excellent when no thread breakage occurs (◎), good when thread breakage is 1-5 times (○), and when thread breakage is 6-20 times Inferior (△), can't wind up at all! /, Case not allowed (X).

[0113] In the drawing step, the drawability was evaluated by the number of times that a single yarn breakage occurred and the single yarn was wound around a roller. Excellent when the single yarn has no wrapping force (◎), good when the single yarn wrapping force is ~~ 5 times (○), inferior when it is 6-20 times (△), and cannot be drawn at all Impossible (X). I. Preparation of thermoplastic polymer

 (a) Preparation of polyethylene terephthalate (PET-1 and PET-2)

To a low polymer obtained by the usual esterification reaction of 166 parts by weight of terephthalic acid and 75 parts by weight of ethylene glycol, 0.03 part by weight of a 85% aqueous solution of phosphoric acid as an anti-coloring agent and triacid as a polycondensation catalyst A polycondensation reaction was carried out by adding 0.06 parts by weight of antimony and 0.06 parts by weight of cobalt acetate tetrahydrate as a toning agent. The melting point (T) is 260 ° C, the glass transition temperature (T) is 80 ° C, and the melting point (T) is 290 ° C and the shear rate is 20 ^sec_1 .

 g

PET-1 having a melt viscosity of 250 Pa 'sec was obtained.

 PET-1 was further solid-phase polymerized at a temperature of 220 ° C under a nitrogen stream and solid-phase polymerized for 15 hours. The melting point (T) was 260 ° C and the glass transition temperature (T) was 83 ° C and 290

 m g

PET-2 with a high viscosity of lOOOPa · sec- ^{1 at} a temperature of ° C was obtained.

(b) Preparation of polytrimethylene terephthalate (PTT)

 Dimethyl terephthalate 130 parts (6.7 mole parts), 1,3-prononediol 114 parts (15 mole parts), calcium acetate monohydrate 0.24 parts (0.014 mole parts), lithium acetate 2 water A low polymer obtained by transesterifying 0.1 parts (0.01 mole parts) of a Japanese salt and distilling off methanol was added to 0.065 parts of trimethyl phosphate and 0.14 parts of titanium tetrabutoxide. The polycondensation reaction was carried out while distilling off 1,3-propanediol, to obtain chip-shaped preborima. The obtained prepolymer was further solid-phase polymerized at a temperature of 220 ° C under a nitrogen stream, and had a glass transition temperature (T) of 52 ° C and a melting point (T) of 230 ° C.

 g m

, A melt viscosity at a temperature of 260 ° C at a shear rate of 20sec ^{_ 1} was obtained lOOOPa 'sec- ¹ of PTT.

 (c) Preparation of polylactic acid (PLA)

 After adding 0.005 parts by weight of tin octylate as a catalyst to 300 parts by weight of L-lactide and replacing with nitrogen, the reaction was carried out at a temperature of 170 ° C, resulting in a weight average molecular weight of 153,000 and a glass transition temperature. (T) is 58 ° C, melting point (T) is 170 ° C, shear rate 20 at a temperature of 200 ° C

 g m

melt viscosity at ^sec-1 was obtained PLA of 2000 Pa 'sec ^_1.

Example 1

Directly into the molten polymer at 1Z3 position from the most upstream part of the cylinder of the 2-axis ETASRUDER An undrawn yarn of foamed fiber was produced using a spinning machine with a nozzle for injecting carbon dioxide. Using PET-1 as the thermoplastic polymer, injecting diacid-carbon into the molten polymer with a biaxial etatruder, and mechanically kneading the molten polymer and diacid-carbon in the etatruder, The mixed polymer was weighed with a gear pump and supplied to the spinning pack. The spun yarn foamed when discharged from the discharge hole of the spinneret was cooled with cooling air, taken up with a roller, and wound up with a winder to produce a foam undrawn yarn (fineness). 124. 8dtex, filament number 24). The spinning conditions at this time are shown below. The shear rate was calculated using the above equation (A) using 1.18 gZcm ³ , which is the melt density of PET.

 [Spinning conditions of Example 1]

 'Spinning temperature: 290 ° C

 • Kneader temperature: 280 ° C

 'Etast Ruder speed: 300rpm

 • Etastruder tip pressure: lOMPa

 • Foaming agent: carbon dioxide

 • Foaming agent addition amount: 3wt% with respect to the spun yarn discharged from the die

'Foaming agent injection pressure: 8MPa

 • Base: Round base with a hole diameter of 0.15 mm, a hole depth of 0.16 mm, and a hole number of 24

-y: 88711sec ^_1

 H

 Filter layer: 30 # Morundum Sand

• Filter: 10m non-woven filter

• Discharge rate: 49.9gZ

'Pack internal pressure: 20MPa

 • Back pressure of the base: 15MPa

 • Cooling: Uses Uniflow with a cooling length of lm. Cooling air temperature 20 ° C, wind speed 0.5m / min

Oil: 10% aliphatic ester emulsion oil adheres 10% to the yarn

'Spinning speed: 4000m / min

When drawing the foam undrawn yarn, the first heating roller is a low temperature of 90 ° C. The second heated roller was drawn between rollers having a temperature of 130 ° C., cooled to room temperature with a third roller, and wound on a bobbin with a spindle to obtain foamed fibers. At this time, the draw ratio was set to 1.4 times. Table 1 shows the physical properties of the foamed fiber of Example 1.

[table 1]

Example 2, Comparative Examples 1-3

 In Example 1, the internal pressure of the pack and the back pressure of the base were the same, and the bases with different hole diameters and hole depths were used as described below, except that the shear rate γ was changed as shown in Table 1.

 Η

A foamed unstretched yarn was prepared in the same manner as in Example 1, and the foamed unstretched yarn was treated in the same manner as in Example 1. The foamed fibers of Example 2 and Comparative Examples 1 to 3 were produced by stretching.

 [0117] When a shear rate within the range applicable to the normal melt spinning of Comparative Example 3 was applied while compressing, the bubbles generated inside the spun yarn at the spout discharge section made a noise and bubbled. Because the discharge became unstable, it was unable to wind at the same spinning speed. Therefore, when the spinning speed was lowered, although the spinning performance was poor, it was able to wind up at a spinning speed of 200 mZ. The unstretched foamed fiber of Comparative Example 3 is a foamed fiber that is thick and thin in the longitudinal direction, and many yarn breaks occurred during stretching. For this reason, unstretched foamed fiber was used, and the force was not obtained. Table 1 shows the results of Example 2 and Comparative Examples 1 to 3.

 Example 2: Hole diameter = 0.18mm, hole depth = 0.26mm, y = 5133, sec

 H

 • Comparative Example 1: Hole diameter = 0.20mm, hole depth = 0.3omm, y = d7425sec

 H

 • Comparative Example 2: Hole diameter = 0.23mm, hole depth = 0.5mm, y = 24607sec

 H

 Comparative Example 3: Hole diameter = 0.35mm, hole depth = 1.6mm, y = 6983sec,

 Spinning speed = 200mZ min

 As can be seen from Table 1, the foamed fiber of the present invention contains only fine bubbles as compared with the fiber diameter with a smaller ratio of the maximum bubble diameter to the Z fiber diameter, and has coarse bubbles. It was not. For this reason, it was a high-quality foam fiber that was uniform in the longitudinal direction of the fiber with a small U% (half). Also, the variation in bubble diameter, that is, the standard deviation of the bubble diameter was small. For this reason, the mechanical properties were also excellent. The foamed fiber of the present invention uses a die that gives a shear rate much higher than the shear rate applied in ordinary melt spinning to a mixed polymer of thermoplastic polymer and carbon dioxide-dioxide carbon. Achieved for the first time.

 [0118] In Comparative Examples 1 and 2, the shear rate was insufficient. For this reason, the maximum diameter Z fiber diameter with a small number of bubble nuclei generated during ejection and coarse bubbles with a large average bubble diameter were included. Therefore, it was a foamed fiber that was inferior in uniformity in the longitudinal direction, and was a foamed fiber that was not at a practical level.

 [0119] In Comparative Example 3, although the bubble occupancy ratio was high, the fiber was thick and hard and low quality. Further, it was a foam fiber that was clearly impregnated in the longitudinal direction, had insufficient mechanical properties, and was impractical.

Examples 3-8, Comparative Examples 4-6 In Example 1, an undrawn expanded yarn was produced under the same conditions as in Example 1 except that the spinning speed was changed as follows. Further, when the unfoamed yarn was stretched in the same manner as in Example 1, the stretch ratio was adjusted as follows to obtain foamed fibers. The results of Examples 4 to 8 and Comparative Examples 3 to 4 are shown in Table 2.

Example 3: Spinning speed lOOOOmZ, draw ratio 3.0 times

Example 4: Spinning speed 1500 mZ min, draw ratio 2.8 times

 Example 5: Spinning speed 2000 mZ min, draw ratio 2.5 timesExample 6: Spinning speed 3000 mZ min, draw ratio 1. 8 timesExample 7: Spinning speed 5000 mZ min, draw ratio 1.2 times

, Example 8: Unstretched

 • Comparative Example 4: Spinning speed 500mZ, draw ratio 4.0 times

• Comparative Example 5: Spinning speed 700mZ min, draw ratio 3.5 times

• Comparative Example 6: Spinning speed 7000mZ min, unstretched

[Table 2]

As shown in Table 2, in the present invention, uniform foamed fibers with smaller maximum diameter of bubbles and smaller U% (half) were obtained. In addition, the maximum diameter of bubbles Z The diameter of fibers is small The average diameter of bubbles is small The standard deviation of the diameter of bubbles is small, the mechanical properties are Also became an excellent foamed fiber. In other words, in the method for producing foamed fibers of the present invention, it is obvious that the higher the spinning speed, the more the foamed fibers can have many fine bubbles. This is because cooling of the spun yarn occurs quickly, and the growth of bubbles, which is difficult to cause carbon dioxide concentration spots, is suppressed. However, as in Comparative Example 6, when the spinning speed was too high, the foamed fiber had almost no bubbles. This is because the cooling rate tends to be too high and bubble growth tends not to occur sufficiently.

Examples 9-11

 In Example 1, the shear rate (γ

 H) after applying shear rate (γ

 Spinning was carried out in the same manner as in Example 1 except that the base for imparting L) was used to obtain a foam undrawn yarn. In Examples 9 to 11, the shear rate (γ) and the back pressure of the base were the same as in Example 1.

 Η

As shown, the following hole spec base was used. The obtained foam undrawn yarn was drawn in the same manner as in Example 1 to obtain foamed fibers. The results of Examples 9-11 are shown in Table 3.

• Example 9:.. D = 0 15mm , L = 0 15mm, y = 88711sec _1

 H H H

D = 0.35mm, L = 0.10mm, y = 6983sec ^_1

 L L L

• Example 10:.. D = 0 15mm , L = 0 15mm, y = 88711sec _ 1

 H H H

D = 0.50mm, L = 0.24mm, y = 2395sec ^_1

 L L L

• Example 11:.. D = 0 15mm , L = 0 15mm, y = 88711sec _ 1

 H H H

D = 0.80mm, L = 0.90mm, y = 585sec ^_1

 L L L

[Table 3]

 As shown in Table 3, in the present invention, in the discharge hole, the mixed polymer has a shear rate (Ύ) as the first step and a shear rate (γ) lower than the shear rate (γ) as the second step. Hole

 L

It can be seen that by using a base that expands in multiple stages, the bubble occupancy of the foamed fiber can be increased. This is because many bubble nuclei are generated inside the spun yarn and grow appropriately. The larger the ratio of γ /, the higher the bubble occupancy ratio. Example 9 1 1 has a high bubble occupancy, but the bubbles are sufficiently elongated in the fiber axis direction Therefore, the foamed fiber was excellent in mechanical properties.

Example 12

 In Example 11, a heat-drawing roller that rotates at a speed higher than the spinning speed is disposed after the take-up roller for spinning, and the spinning yarn is drawn between the heating rollers without winding up the spun yarn. I went there. The results of Example 12 are shown in Table 3.

'Spinning speed: 4000m / min

• Stretch ratio: 1.4 times

'First stretching roller temperature: 90 ° C

'Second stretching roller temperature: 130 ° C

 Comparing Examples 11 and 12, it can be seen that a foamed fiber having a high cell occupancy is obtained by drawing without spinning the spun yarn. This is because the carbon dioxide dissolved in the taken-out spun yarn flows into the bubbles, so that the bubbles grow appropriately. The obtained foamed fiber was uniform in the longitudinal direction because of fine air bubbles, and had excellent mechanical properties.

Examples 13-15, Comparative Example 7

 In Example 1, the foam fibers of Examples 13 to 15 and Comparative Example 7 were the same as Example 1 except that the hole depth of the base was changed as shown below, and the back pressure of the base and the internal pressure of the pack were changed. Got. The results of Examples 13 to 15 and Comparative Example 7 are shown in Table 3.

• Base of Example 13: hole diameter 0.15mm, hole depth 0.08mm

 • Base of Example 14: hole diameter 0.15 mm, hole depth 0.1 lmm 'Example 15 base: hole diameter 0.15 mm, hole depth 0.45 mm

 • Base of Comparative Example 7: Hole diameter 0.15mm, hole depth 0.05mm

As compared with Example 1, Examples 13 to 15 and Comparative Example 7, in the present invention, by setting the pressure on the back surface of the die to 8 MPa or more, the bubbles of the obtained foamed fibers are fine and uniform. Become. This is because the carbon dioxide is in a supercritical state even in the mixed polymer immediately before being discharged, so that the carbon dioxide is easily dissolved uniformly. The higher the back pressure of the base and the internal pressure of the pack, the more the foamed fibers having finer bubbles and smaller U% (half). Examples 16-20 In Example 1, spinning and drawing were performed in the same manner as in Example 1 except that the addition amount of carbon dioxide and carbon dioxide was changed, and foamed fibers were obtained. The results of Examples 16-20 are shown in Table 4. As is clear from Example 1 and Examples 16 to 20, the addition of carbon dioxide in the range of the preferred addition amount in the present invention makes the bubbles in the foam fibers finer and U% (half) became a small foam-free foamed fiber. The maximum diameter of bubbles, Z fiber diameter, average diameter of bubbles, standard deviation force of bubble diameter, the toughness of the foamed fibers increased, and the foamed fibers were excellent in mechanical properties.

[Table 4]

Example 21

In producing the foamed fiber by the method of spinning and drawing in Example 12 in a continuous process, PET-2 was used as the thermoplastic polymer. Parts different from Example 12 regarding spinning and drawing conditions Is shown below. The results of Example 21 are shown in Table 4.

[Example 21 (PET-2) spinning 'drawing conditions']

Spinning temperature: 305 ° C

• Kneader temperature: 295 ° C

• Base specification: D = 0.20mm, L = 0.20mm, y = 88711sec ^{_ 1}

 H H H

D = 0.80mm, L = 0.90mm, y = 585sec ^_1

 L L L

 'Pack internal pressure: 80MPa

 • Back pressure of base: 60MPa

'Spinning speed: 3000mZ min

 As shown in the comparison between Example 12 and Example 21, it is preferable to use a thermoplastic polymer having a high melt viscosity, which is preferable in the present invention. A foamed fiber having a small and uniform foamed structure can be obtained. This is because the coalescence of carbon dioxide is uniformly dissolved in the thermoplastic polymer and the coalescence of bubbles is difficult to occur during the process of cooling the spun yarn. The obtained foamed fibers were uniform in the longitudinal direction and excellent in mechanical properties, and thus were suitable for clothing and industrial applications.

Examples 22-24

 When producing foamed fibers by the method of spinning and drawing in Example 12 in a continuous process, as a thermoplastic polymer, PTT in Example 22, PLA in Example 23, Toray Co., Ltd. in Example 24 Nylon 6 “Amilan” (registered trademark) (type CM1017, hereinafter abbreviated as nylon 6) was used. Regarding the spinning and drawing conditions of Examples 22 to 24, the parts different from Example 12 are shown below. The results of Examples 22 to 24 are shown in Table 4.

[Example 22 (PTT) spinning 'drawing conditions]

'Spinning temperature: 265 ° C

• Kneader temperature: 255 ° C

、 Base specification: D = 0.15mm, L = 0.15mm, y = 91823sec ^{_ 1}

 H H H

D = 0.80mm, L = 0.90mm, y = 605sec ^_1

 L L L

 (γ and γ are calculated assuming the melt density of PTT is 1.14)

 H L

• Pack internal pressure: 65MPa • Back pressure of the base: 45MPa

'Spinning speed: 3000mZ min

 'First stretching roller temperature: 70 ° C

• Second stretching roller temperature: 140 ° C

[Example 23 (PLA) spinning 'drawing conditions]

'Spinning temperature: 230 ° C

• Kneader temperature: 220 ° C

• the base specs:.. D = 0 15mm, L = 0 15mm, y = 96925sec _ 1

 H H H

D = 0.80mm, L = 0.90mm, y = 639sec ^_1

 L L L

 (γ and γ are calculated assuming PLA melt density as 1.08)

 H L

 'Pack internal pressure: 65MPa

 • Back pressure of base: 50MPa

 [Example 24 (Nylon 6) spinning 'drawing conditions]

'Spinning temperature: 245 ° C

• Kneader temperature: 235 ° C

, Base spec: D = 0.15mm, L = 0.15mm, y = 104679sec ^{_ 1}

 H H H

D = 0.80mm, L = 0.90mm, y = 690sec ^_1

 L L L

 (γ and γ are calculated assuming that nylon 6 has a melt density of 1.00)

 H L

 'Pack internal pressure: 30MPa

 • Back pressure of base: 20MPa

'Spinning speed: 3000mZ min

 'First stretching roller temperature: 60 ° C

'Second stretching roller temperature: 150 ° C

 As shown in Table 4, by using PTT, PLA, and nylon 6 which are preferable thermoplastic polymers in the present invention, foamed fibers having fine bubbles can be obtained. The obtained foamed fiber was a high-quality foamed fiber, and was a foamed fiber excellent in durability of the foamed structure because it was a heat-resistant high-temperature thermoplastic polymer.

Examples 25-27 In Example 12, the discharge amount was 14.8gZ, the pack internal pressure was 18MPa, the back pressure of the base was 15MPa, and the base hole spec was changed as shown below. 25-27 foam fibers were obtained. The results of Examples 25 to 27 are shown in Table 5. • Example 25: D = 0.10mm, L = 0.10mm, y = 88711sec _1

 H H H

D = 0.20mm, L = 0.10mm, y = 11089sec ^_1

 L L L

• Example 26: D = 0.10mm, L = 0.10mm, y = 88711sec _1

 H H H

D = 0.35mm, L = 0.40mm, y = 2069sec ^_1

 L L L

• Example 27: D = 0.10mm, L = 0.10mm, y = 88711sec _1

 H H H

D = 0.50mm, L = 1.00mm, y = 710sec ^_1

 L L L

[Table 5]

In the present invention, it is possible to obtain a foamed fiber having a thin fiber diameter and uniform in the longitudinal direction of the fiber by adopting a die that provides a high shear rate and a low shear rate in multiple stages. It was. The foamed fiber was particularly suitable for use in clothing because it was high-grade, excellent in lightness and heat retention, and had no staining spots.

 Industrial applicability

 [0128] The foamed fiber of the present invention does not have coarse bubbles, and therefore has good mechanical properties. It is excellent in lightness, fiber uniformity, heat retention, cushioning and touch. Therefore, it is particularly suitable for sports clothing, outdoor clothing, uniform clothing such as white clothing, formal clothing, and clothing such as winter underwear, swimwear and lining. It is also useful and useful for industrial applications such as various vehicle interior materials (sheet skin, ceiling skin, in-line carpet), cushions, futons, blankets, pillows, carpets and curtains.

 Brief Description of Drawings

 [0129] [FIG. 1] FIG. 1 shows a round hole which gives a shear rate (γ) and a shear rate (γ) in multiple stages in the present invention.

 H L

 It is a schematic cross section for demonstrating an example of a nozzle | cap | die.

 [FIG. 2] FIG. 2 shows a round hole which gives a shear rate (γ) and a shear rate (γ) in multiple stages in the present invention.

 H L

 It is a schematic cross section for demonstrating another example of a nozzle | cap | die.

 [FIG. 3] FIG. 3 shows a round hole which gives a shear rate (γ) and a shear rate (γ) in multiple stages in the present invention.

 H L

 It is a schematic cross section for demonstrating another example of a nozzle | cap | die.

 Explanation of symbols

[0130] 1: D (pore diameter in the high shear rate region)

 H

 2: L (hole depth in high shear rate region)

 H

 3: D (pore diameter in the low shear rate region)

 Shi

 4: L (hole depth in low shear rate region)

Claims

Claims [1] A foamed fiber that also has thermoplastic polymer strength, and satisfies the following (1) to (5).

 (1) Fiber diameter is 1 μm or more and 50 μm or less

 (2) Bubble occupancy in fiber cross section is 10% or more and 90% or less

 (3) Maximum bubble diameter Z fiber diameter ≤ 0.08

 (4) Average bubble diameter is 1 μm or less

 (5) U% (half) is 2 or less

 2. The foamed fiber according to claim 1, wherein the relationship between the strength and the elongation of the foamed fiber satisfies the relationship of the following formula.

Strength X (Elongation) ⁵ ≥15

 [3] Foaming is achieved by introducing a mixed polymer obtained by kneading a thermoplastic polymer and carbon dioxide or nitrogen, or both of them in a molten state, to a spinneret and discharging it to a low pressure region to reduce the pressure. The foamed fiber manufacturing method is characterized by satisfying the following (6) to (8), wherein the foamed polymer is cooled and taken off after being cooled.

(6) Shear rate in discharge hole (γ H) 50,000 ～ l, 000, OOOsec ^_1

 (7) Spinning speed lOOOOmZ min ~ 6000mZ min

 (8) Back pressure of the base is 8MPa or more lOOMPa or less

 [4] The shear rate of the mixed polymer in the discharge hole is 50,000 to 1 as the first stage shear rate (γ).

 Η

l, 000,000sec ^_1 , as the second stage, discharge at a shear rate (γ) smaller than γ

 H L

 The method for producing a foamed fiber according to claim 3, wherein:

[5] The method for producing a foamed fiber according to [3] or [4], wherein after the spun yarn is taken up, it is wound by applying a heat treatment before taking off the spun yarn.