JP2008081883A - Lightweight acrylic fiber and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lightweight acrylic fiber having sufficient strength and percentage of hollowness even after being formed into a fiber product, and also having excellent handleability; and to provide a method for producing the same. <P>SOLUTION: The lightweight acrylic fiber has a multilayered structure consisting of a layer (I) composed of an acrylonitrile-based polymer (A), and a layer (II) composed of an acrylonitrile-based polymer (A) having pores with an average diameter of ≥0.1 μm and ≤1 μm, and is obtained by laminating the layers (I) and (II) so that the average number of the total layers (N) of the layers (I) and (II) in a fiber cross-section may be larger than three, and the layers may form a stripe shape. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a lightweight acrylic fiber and a method for producing the same.

  In recent years, needs for weight reduction of clothing and bedding for elderly people and children are increasing as social demands. In particular, among various synthetic fibers, acrylic fibers are widely used in clothing and bedding because they are excellent in flexibility, heat retention, color development, weather resistance, etc., and technological development aimed at weight reduction is actively carried out. ing. One of them is a porous acrylic fiber having a large number of pores in the cross section of the acrylic fiber. Porous acrylic fibers have pores inside, so that the fibers themselves are lighter than normal acrylic fibers, and heat retention is improved, so it can be applied to products such as clothing and bedding and is necessary It has the merit that the amount of fibers can be reduced.

  As a technique for producing this porous acrylic fiber, for example, a method in which a water-soluble polymer is added to a stock solution of an acrylonitrile-based polymer and removed in a yarn-making process (see Patent Document 1), a dissimilar polymer is added, and emptying is performed by interfacial peeling. Methods for forming pores (see Patent Document 2), methods for adding a foaming agent (see Patent Document 3), and the like are known as known techniques.

  However, acrylic fibers prepared by these techniques have low fiber strength due to the presence of pores throughout the fiber, and the fiber fibrillation significantly deteriorates, making it unusable.

Therefore, as a technique for increasing the strength by combining porous acrylic fibers, a method of making a layer having pores and a layer not containing pores a core-sheath composite type (see Patent Document 4), a method of making a three-layer laminate type (See Patent Document 5), there is a method of making a side-by-side composite type (see Patent Document 6), but as a method of forming pores in any of the methods, interfacial peeling is performed by mixing incompatible dissimilar polymers. This is a technology for generating voids by causing The porous acrylic fibers prepared by these methods have problems in terms of color developability, crimp fastness, and texture due to the presence of different polymer components in the fibers. Also, when cutting, carding, weaving and knitting of fibers, or when the product is used, the friction and compression that the fiber receives causes separation of different polymers from the pores, generating dust and crushing the holes. It was. Furthermore, when a composite die is used as a manufacturing method, there is a problem that it is difficult to increase the number of holes and productivity is low. In addition, all of the above methods form pores in the fiber before crimping, so the subsequent processes from crimping, setting, cutting, carding, spinning, weaving, and dyeing There is a problem that the pores are crushed and the characteristic expression due to the porous shape is impaired. In addition, it is possible to maintain the porous shape to a certain extent by improving the processing method, but in that case special processing conditions are required, so there are problems such as requiring capital investment and reducing productivity. there were.
Japanese Patent Laid-Open No. 3-124811 (page 4) Japanese Examined Patent Publication No. 60-11124 (page 4) JP 2001-131821 (page 2) JP2002-13029 (1-6 pages) JP 2000-45126 A (pages 1 to 11) JP-B 63-060129 (1-13 pages)

  The subject of this invention is improving the intensity | strength of a fiber and the hollow rate which were mentioned as a problem of the said prior art, and providing the lightweight acrylic fiber which is excellent in productivity, and its manufacturing method.

  In order to achieve the above object, the present invention is summarized as follows.

  The first invention of the present invention is a layer (I) comprising an acrylonitrile polymer (A) and a layer comprising an acrylonitrile polymer (A) having pores having an average diameter (Dv) of 0.1 μm or more and 1 μm or less ( II), and has a multilayer composite structure in which the total average number of layers (N) of layers (I) and (II) exceeds 3 in a fiber cross section Lightweight acrylic fiber.

  The second invention of the present invention comprises a layer (III) of an acrylonitrile polymer (A) and a layer (IV) in which an ester polymer (B) is dispersed in the acrylonitrile polymer (A). A multilayer composite acrylic fiber characterized by having a multilayer composite structure in which a total average number of layers (N) of layers (III) and (IV) exceeds 3 layers in a plane is laminated. .

  According to a third aspect of the present invention, in the method for producing a lightweight acrylic fiber according to the first aspect, the ester-based polymer (B) is eluted from the multilayer composite acrylic fiber according to the second aspect with an alkaline solution. is there.

  According to a fourth aspect of the present invention, an undiluted solution (a) of an acrylonitrile-based polymer (A) and a undiluted solution (b) obtained by mixing an ester-based polymer (B) with an acrylonitrile-based polymer (A) are divided into multiple layers to form a spinneret. 3. The method for producing a multilayer composite acrylic fiber according to claim 2, wherein the yarn is introduced and yarn-formed.

  The lightweight acrylic fiber of the present invention is a lightweight lightweight heat-insulating fiber that achieves both high hollowness and high mechanical properties without impairing the properties of the acrylic fiber. Contributes to weight reduction. By the production method of the present invention, the collapse of holes in the fiber product production process after the yarn production process is suppressed, and a lightweight acrylic fiber having the above-described excellent characteristics is provided by a method excellent in productivity.

  Hereinafter, the lightweight acrylic fiber of the present invention will be described in detail.

  The acrylonitrile-based polymer (A) in the present invention is an acrylonitrile homopolymer and / or a copolymer of an acrylonitrile monomer and another monomer depending on the application. Examples of other types of monomers include styrene, vinyl toluene, vinyl acetate, vinyl chloride, vinylidene chloride, vinyl bromide, vinylidene bromide, vinyl fluoride, vinylidene fluoride, etc., for the purpose of changing the texture and dyeability of acrylic fibers. Unsaturated monomers, p-sulfophenyl methallyl ether, methallyl sulfonic acid, allyl sulfonic acid, styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid and alkali metal salts thereof may be mentioned. In addition, when a lightweight acrylic fiber is used as a carbon fiber precursor, a monomer or acrylamide type having a carboxylic acid group or an esterified product thereof for the purpose of promoting the progress of cyclization of the acrylonitrile polymer (A) in the flameproofing step The monomer may be copolymerized. The ratio of the acrylonitrile monomer to the other monomer can be appropriately selected according to the use of the fiber, but preferably the acrylonitrile monomer in the acrylonitrile copolymer is 50% by weight or more, more preferably 85% by weight or more, and most preferably Is 90% by weight or more. By increasing the ratio of acrylonitrile monomer, the excellent properties unique to acrylic fibers can be maintained even in lightweight acrylic fibers.

  The lightweight acrylic fiber of the present invention comprises a layer (I) comprising an acrylonitrile polymer (A) and a layer (II) comprising an acrylonitrile polymer (A) having pores having an average diameter (Dv) of 0.1 μm or more and 1 μm or less. Consists of. The layer (I) comprising the acrylonitrile-based polymer (A) is densified through a normal spinning process, and the presence of this layer (I) cannot be achieved only by the layer (II) having pores. Sufficient strength is obtained. Moreover, lightweight property is provided to an acrylic fiber by the layer (II) which has a void | hole.

  Both layers may contain 20% by weight or less of different components other than acrylonitrile polymer (A) for the purpose of imparting functions such as water absorption, water retention, and heat retention. It does not contain foreign components that are easy to wake up and form voids. Thereby, compared with the light weight acrylic fiber which forms a void | hole by the conventional interfacial peeling, it is hard to generate | occur | produce dust at the time of processing of a fiber or use of a product, it is excellent in coloring property, and it is excellent also in handleability. Examples of the heterogeneous component that easily causes interface peeling include cellulose acetate and polyvinyl acetate.

  The lightweight acrylic fiber of the present invention has a multilayer composite structure in which the total number of layers (N) of layers (I) and (II) exceeds 3 in a fiber cross section. The multilayer composite structure referred to in the present invention is a structure in which layers (I) and (II) are laminated in a striped manner in the fiber cross section. By adopting a structure in which stripes are stacked, the fiber side surface is composed of components constituting both layers. In addition to the lightness and heat retention derived from the pores due to the presence of the layer (II) on the side of the fiber, water absorption, quick drying properties, etc. are manifested, and the presence of the layer (I) ensures fibril resistance and fibers Strength is maintained.

  Further, by laminating so that the total average number of layers (N) exceeds three layers, the uniformity of the fiber structure is improved, and fiber properties such as stable strength and excellent color developability can be obtained. The total average number of layers (N) is preferably 3.5 or more and 15 or less, more preferably 4 or more and 8 or less. By making the total average number of layers (N) 15 or less, the strength and lightness derived from the components constituting both layers are maximized. Here, the total average number of layers (N) referred to here is that in Example C.I. It is a value obtained by the method described in the item.

  In addition, the area fraction of the layer (II) with respect to the area surrounded by the outer periphery of the single fiber in the cross section of the lightweight acrylic fiber is 20% or more and 90% or less for the purpose of maintaining the strength of the lightweight acrylic fiber and expressing the lightness. Is more preferable, and more preferably 30% or more and 80% or less.

  In the present invention, the average diameter (Dv) of the pores in the layer (II) is from 0.1 μm to 1 μm, and the average diameter (Dv) of the pores is from 0.1 μm to 1 μm. As a result, lightness is exhibited in a state where the strength of the fiber is sufficiently maintained. More preferably, it is 0.5 μm or more and 1 μm or less. In order to give lightness to the fiber by pores having an average diameter (Dv) of less than 0.1 μm, a large number of pores must be formed. The separating polymer layer becomes thin and the strength of the fiber is reduced. If the average diameter (Dv) exceeds 1 μm, the fiber structure becomes non-uniform due to the presence of many pores larger than 1 μm in the fiber, leading to a decrease in strength, as well as causes such as fiber staining spots and crimped spots. It becomes.

  The ratio (Dvmax / Dv) of the maximum hole diameter (Dvmax) to the average hole diameter (Dv) is 1 to 20 and preferably 1 to 10 with high mechanical properties and light weight. It is more preferable from the standpoint of compatibility. The hollow ratio expressed as a percentage of the ratio of the total area (Sv) of pores in the cross section of the fiber and the area surrounded by the outer periphery of the single fiber (Sf) is 5 from the viewpoint that both high mechanical properties and light weight can be achieved. % Is preferably 40% or less and more preferably 10% or more and 40% or less. The number of pores is preferably 30 or more, more preferably 60 or more in the cross section of the fiber from the viewpoint of lightness. In the present invention, the number of holes, the maximum hole diameter (Dvmax), the average hole diameter (Dv), the total area (Sv) of holes in the fiber cross section, the area surrounded by the outer periphery of the single fiber ( Sf) and the hollowness ratio are described in the examples. The value obtained by the method described in the section.

  The lightweight acrylic fiber according to the present invention has a single yarn fineness of 1.0 dtex to 100 dtex, a strength of 1.0 cN / dtex to 10 cN / dtex, and an elongation of 10% to 100% from the viewpoint of processability in yarn production and high-order processing. Is preferred.

  Since the lightweight acrylic fiber of the present invention has a layer having a large number of pores and a layer having substantially no pores, it is a fiber excellent in lightweight heat retention that achieves both a high hollow ratio and high mechanical properties. The lightweight acrylic fiber of the present invention may be used alone, natural fiber such as cotton, hemp, wool, etc., chemical fiber such as rayon, acetate, etc., blended with synthetic fiber with polyester or nylon, mixed fiber, interwoven, knitted Can also be used. Examples of applications include curtains, blankets, carpets, foot towel mats, towels, dryer canvas, sweaters, underwear, socks and the like. Further, by adsorbing a functional substance to the pores inside the fiber and the fiber surface, it can be used for antibacterial clothing, drug solution sustained-release materials, cell culture media and the like.

  Next, the multilayer composite type acrylic fiber having the multilayer composite structure of the present invention will be described in detail.

  The acrylonitrile-based polymer (A) in the present invention is an acrylonitrile homopolymer and / or a copolymer of an acrylonitrile monomer and another monomer depending on the application. Examples of other types of monomers, copolymerization ratios, and the like are as described above.

  The ester-based polymer (B) in the present invention is not particularly limited as long as it is a polymer having an ester bond in the main chain, but the ester can be obtained by treating a multilayer composite acrylic fiber with an alkaline solution. From the viewpoint of increasing the elution rate, a block polyether ester copolymerized with a polyol, particularly a polyalkylene glycol, is more preferable for the purpose of elution and removal of the polymer (B). Further, an ester polymer (B) obtained by graft copolymerizing the block polyether ester with an acrylonitrile polymer (A) for the purpose of maintaining the water resistance of the fiber is most preferable.

  The molecular weight of the copolymerized polyalkylene glycol is preferably 1000 to 20000, more preferably 3000 to 6000, from the viewpoint of promoting elution rate. The mixing ratio of the polyalkylene glycol is preferably 1 to 60% by weight based on the total weight of the ester polymer (B). When the content is 1% by weight or more, the decomposition rate of the ester polymer (B) when the multilayer composite acrylic fiber is treated with an alkaline solution is promoted, and when the content is 60% by weight or less, the water resistance of the multilayer composite acrylic fiber is increased. Improves. Specific examples of the polyalkylene glycol include polyethylene glycol, polypropylene glycol, polytetramethylene glycol and the like. Among these, polyethylene glycol is particularly preferable from the viewpoint of elution rate.

  As for the composition of the polyester part of the block polyether ester, an aliphatic dicarboxylic acid or an aliphatic dicarboxylic acid is compared with an aliphatic diol for the purpose of suppressing the crystallinity of the ester-based polymer (B) and improving the decomposability during alkali treatment. What combined the mixture of an acid and aromatic dicarboxylic acid is preferable. Examples of aliphatic diols include ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, neopentyl glycol and the like, and aliphatic dicarboxylic acids include succinic acid, glutaric acid, adipic acid, suberic acid, Examples of azelaic acid, sebacic acid, dodecanedioic acid and aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, orthophthalic acid, 2,6-naphthalenedicarboxylic acid, paraphenylene dicarboxylic acid and the like. In particular, it is more preferable to include an aliphatic dicarboxylic acid component having 6 or less carbon atoms.

  The multilayer composite acrylic fiber of the present invention comprises a layer (III) of an acrylonitrile polymer (A) and a layer (IV) in which an ester polymer (B) is dispersed in the acrylonitrile polymer (A). The layer (III) composed of the acrylonitrile-based polymer (A) is densified through a normal spinning process, and the presence of this layer (III) allows the ester-based polymer (B) to be contained in the acrylonitrile-based polymer (A). Sufficient strength that cannot be achieved by the dispersed layer (IV) alone is obtained. In addition, the presence of the layer (IV) allows alkali treatment to remove the ester-based polymer (B) to form pores, thereby obtaining a porous lightweight acrylic fiber.

  Both layers may contain 20% by weight or less of different components other than acrylonitrile polymer (A) and ester polymer (B) for the purpose of imparting functions such as water absorption, water retention and heat retention. It is preferable not to include a heterogeneous component that tends to cause interfacial peeling and form pores with (A). By doing so, dust is not easily generated during fiber processing or product use, and the handleability is excellent. Examples of the heterogeneous component that easily causes interface peeling include cellulose acetate and polyvinyl acetate.

  The acrylic fiber of the present invention has a multilayer composite structure in which the total number of layers (N) of the layers (III) and (IV) exceeds 3 in the fiber cross section. The multilayer composite structure referred to in the present invention is a structure in which layers (III) and (IV) are laminated in a striped manner in the fiber cross section. By adopting such a striped multilayer composite structure, three-dimensional crimps can be expressed due to the difference in shrinkage between the two layers. By laminating so that the total average number of layers (N) exceeds 3 layers, the uniformity of the fiber structure is improved, and stable fiber properties are obtained with little variation in the number of crimps. Improves. Further, excellent color developability of the fiber can be obtained. The total average number of layers (N) is preferably 3.5 or more and 15 for the purpose of maintaining a laminated structure of layers having different components and expressing a special crimp derived from the three-dimensional and bulky properties. Or less, more preferably 4 or more and 8 or less. The total average number of layers (N) here is a value determined by the method described in the examples.

  As the area fraction of the layer (IV) with respect to the area surrounded by the outer periphery of the single fiber in the cross section of the multilayer composite fiber, the high mechanical properties and lightness of the lightweight acrylic fiber obtained by alkali treatment of the multilayer composite fiber 20% or more and 90% or less are preferable from the point which can be compatible, More preferably, they are 30% or more and 80% or less.

  In addition, the average diameter (De) of the island part which consists of ester-type polymer (B) is 0.1 micrometer or more in order to make the high mechanical characteristic and lightweight property of the lightweight acrylic fiber obtained by alkali-treating a multilayer composite type fiber. It is preferably 1 μm or less, more preferably 0.5 μm or more and 1 μm or less. Further, the ratio (Demax / De) of the maximum diameter (Demax) of the island part made of the ester polymer (B) and the average diameter (De) of the island part is preferably 1 or more and 20 or less, more preferably 1 or more. 10 or less. In addition, the sea island ratio expressed as a percentage of the ratio of the total area (Se) of the island portion made of the ester polymer (B) in the fiber cross section to the area surrounded by the outer periphery of the single fiber (Sf) is also a multi-layer composite. It is preferably 5% or more and 40% or less, more preferably 10% or more and 40% or less, from the viewpoint that both high mechanical properties and light weight of the lightweight acrylic fiber obtained by alkali treatment of the mold fiber can be achieved. Moreover, it is preferable that the island part which consists of ester polymer (B) exists 30 or more in a fiber cross section, More preferably, it is 60 or more. Surrounded by the number of island parts made of the ester polymer (B) in the present invention, the maximum diameter (Demax), the average diameter (De), the total area of the island parts in the fiber cross section (Se), and the outer periphery of the single fiber Area (Sf) and sea island ratio are shown in Example D.3. The value obtained by the method described in the section.

  The multilayer composite acrylic fiber of the present invention has a single yarn fineness of 1.0 dtex or more and 100 dtex or less, a strength of 1.0 cN / dtex or more and 10 cN / dtex or less, and an elongation of 10% or more and 100 from the viewpoint of processability in yarn production and high-order processing. % Or less is preferable.

  The multilayer composite acrylic fiber of the present invention exhibits excellent crimpability by having a multilayer composite structure, and is superior in texture, bulkiness, and color development as compared with conventional acrylic fibers not having a multilayer composite structure. Moreover, since the ester polymer (B) which can be easily eluted with an alkali is used, it can be used as a suitable precursor fiber of a lightweight acrylic fiber.

  Hereinafter, the manufacturing method of the lightweight acrylic fiber of this invention is demonstrated in detail.

  In the present invention, a lightweight acrylic fiber having pores is obtained by eluting the ester-based polymer (B) from the multilayer composite acrylic fiber with an alkaline solution. In the present invention, “to obtain a light acrylic fiber having pores by elution” means that the weight of the fiber is reduced by treating the fiber with an alkaline solution, and substantially before the alkali treatment in the fiber cross section. In this case, the state changes from a state in which no pores exist to a state in which a large number of pores exist in the fiber cross section after the alkali treatment. In the present invention, substantially no pores exist before the alkali treatment, and the pores are not crushed even if the same yarn production and higher-order processing as those for ordinary acrylic fibers are performed.

  Furthermore, in the present invention, the ester-based polymer (B) is eluted with an alkaline solution. At this time, the ester-based polymer (B) is hydrolyzed and rapidly eluted in a low molecular state. For this reason, compared with the extraction of the polymer with an organic solvent or hot water, the utility and energy required for the elution step can be greatly reduced, which is the most preferable mode. In addition, the lightweight acrylic fiber obtained by the production method of the present invention has an excellent feature that dust is less likely to be generated during processing and use as compared with the conventional production method in which pores are formed by interfacial peeling.

  The alkaline solution used in the present invention is a solution having a pH higher than 7, and is preferably pH 12 or higher, more preferably pH 13 or higher from the viewpoint of improving the processing speed. As the alkaline solution, an aqueous solution of barium hydroxide, calcium hydroxide, copper hydroxide, aluminum hydroxide, ammonia, sodium hydrogen carbonate, or the like can be used, but it is a strong alkali, has a high degree of ionization, and is industrially inexpensive. The aqueous solution using sodium hydroxide or potassium hydroxide is most preferable.

  The treatment time with the alkali solution varies depending on the form of the fiber and the concentration of the alkali solution, but 1 to 180 min is preferable from industrial practicality, and 10 to 120 min is more preferable. The treatment temperature is 10 to 98 ° C., preferably 20 to 70 ° C., from the viewpoint of shortening the elution time and suppressing the evaporation of water from the alkaline solution.

  The alkali treatment can be carried out in any form such as continuous yarn, crimped yarn, cut cotton, spun yarn and other forms such as cotton, a wound package, and a tow, and a sheet and product such as non-woven fabric, knitted fabric, and woven fabric. The alkali treatment may be continuously passed through an alkaline solution bath, or may be a batch treatment in which a skein of fiber, raw cotton, spun yarn cheese, or fabric is immersed in a liquid bath.

  The process of alkali treatment includes post-yarning, crimping, cutting, spinning, weaving and knitting, after scouring, etc. Subsequent and subsequent steps are preferred.

  The production method of the present invention suppresses crushing of pores in the fiber product production process after the yarn production process, and a layer (I) made of the acrylonitrile-based polymer (A) and a void having an average diameter (Dv) of 0.1 μm to 1 μm. It consists of layer (II) made of acrylonitrile-based polymer (A) having pores, and is laminated in stripes so that the total average number of layers (N) of layer (I) and layer (II) exceeds 3 layers in the fiber cross section A lightweight acrylic fiber characterized by having a multilayered composite structure can be obtained with high productivity.

  Hereafter, the manufacturing method of the multilayer composite type acrylic fiber of this invention is demonstrated in detail.

  The acrylonitrile-based polymer (A) in the present invention is an acrylonitrile homopolymer and / or a copolymer of an acrylonitrile monomer and another monomer depending on the application. Examples of other types of monomers, copolymerization ratios, and the like are as described above.

  The acrylonitrile-based polymer (A) preferably has a viscosity of 100 to 2000 poise of a 20% by weight dimethyl sulfoxide solution at 45 ° C., which is an index of molecular weight, from the viewpoint of obtaining excellent mechanical properties.

  The stock solution (a) of the acrylonitrile polymer (A) of the present invention is a polymer solution in which the acrylonitrile polymer (A) is dissolved in a soluble solvent. Examples of the soluble solvent include dimethyl sulfoxide, dimethylformamide, dimethylacetamide, and the like. The concentration of the stock solution (a) is preferably a concentration at which the solution has a viscosity of 100 to 2000 poise at 45 ° C. from the viewpoint of spinning stability.

  The ester polymer (B) in the present invention is as described above.

    As a method for preparing a stock solution (b) in which an ester polymer (B) is mixed with an acrylonitrile polymer (A), it is sufficient that the acrylonitrile polymer (A), the ester polymer (B) and a solvent can be mixed uniformly. After mixing both polymers, they may be dissolved in a good solvent common to both polymers, the other polymer may be mixed with a polymer solution in which one polymer is dissolved, or the solutions of both polymers may be mixed together. As a mixing method, for example, mixing with a stirring blade or a homomixer may be used in a container such as a flask or tank, mixing and stirring of a polymer solution with an extruder or the like, or mixing with a static in-tube mixer in a pipe Etc. can be used alone or in combination. For the purpose of maintaining excellent crimp characteristics of the resulting multilayer composite fiber and high mechanical properties and light weight of the lightweight acrylic fiber after elution of the ester polymer (B), the mixing ratio of the ester polymer (B) is as follows. Is preferably 5% by weight or more and 70% by weight or less, more preferably 10% by weight or more and 60% by weight or less based on the total weight of the acrylonitrile-based polymer (A) and the ester-based polymer (B) in the stock solution (b). is there. The concentration of the stock solution (b) is preferably a concentration at which the viscosity of the solution at 45 ° C. is 100 to 2000 poise.

  In addition, the same acrylonitrile-based polymer (A) used for the stock solution (a) and the stock solution (b) is used for the purpose of preventing delamination between the resulting multilayer composite acrylic fibers and maintaining uniform color development. It is preferable.

  In order to divide the stock solution (a) of the acrylonitrile-based polymer (A) and the stock solution (b) obtained by mixing the ester-based polymer (B) with the acrylonitrile-based polymer (A) into multiple layers, both stock solutions are placed in a pipe immediately before the die. Use a static in-tube mixer. As a static type in-pipe mixer to be used, "High Mixer" manufactured by Toray Industries, Inc., "Static Mixer" manufactured by Noritake Co., Ltd., "Skeya Mixer" manufactured by Sakura Seisakusho, " Loss ISG mixer ". Among these devices, the constituent elements are not complicated, the flow resistance of the spinning dope is relatively small, and the change in the effective cross-sectional area in the spinning dope channel is small, so that the abnormal stay of the spinning dope hardly occurs in the device. Therefore, “static mixer” and “skaya mixer” are preferably used.

  The number of elements of the static type in-pipe mixer should be selected so that the theoretical number of layers in single yarn (Ncal) by calculation shown in the example is greater than 3 and 15 or less, corresponding to the number of holes in the cap used. Is preferred. By selecting the number of elements so that Ncal exceeds 3, the total average number of layers (N) in the resulting fiber exceeds 3, resulting from the difference in shrinkage between layers (III) and (IV). When crimped, a three-dimensional and bulky crimp is developed. Moreover, by making Ncal 15 or less, the laminated structure of the layer (III) and the layer (IV) in the cross section of the obtained fiber is maintained, and excellent crimp expression is maintained. Further, Ncal is preferably 3.5 or more and 15 or less, and most preferably 4 or more and 8 or less for the purpose of improving the uniformity of the fiber structure and obtaining stable fiber properties and excellent color developability.

  In the present invention, the undiluted solution divided into multiple layers is introduced into a spinneret to produce a yarn. Specifically, the undiluted multi-layer solution is extruded from a spinneret, and in a coagulation bath filled with a solvent capable of solidifying both the acrylonitrile polymer (A) and the ester polymer (B), that is, a coagulation solvent. Wet spinning can be applied, and dry and wet spinning can be applied after running in the air and then leading to a coagulation bath. In addition, as a spinneret, the normal round shape used for the conventional acrylic fiber, a rectangular die, etc. can be used. For this reason, it is not necessary to use a special composite die, and it is very easy to increase the number of holes in the spinneret.

  The discharge rate of the stock solution is preferably set so that the single fiber fineness of the obtained fiber is 1.0 to 100 dtex from the viewpoints of yarn production and processability of the obtained fiber. In addition, for the purpose of maintaining the physical properties of the obtained multilayer composite fiber, the ratio of the discharge amount of the stock solution (a) and the stock solution (b) is the weight of the polymer contained in the stock solution (b) discharged in a certain time, It is preferably set to be 20% by weight or more and 90% by weight or less, more preferably 30% by weight or more and 80% by weight or less, with respect to the total weight of the polymers contained in both stock solutions.

  The coagulation solvent may be a solution containing a poor solvent for both components of the acrylonitrile polymer (A) and the ester polymer (B). From the viewpoint of solvent recovery, it is used for preparing the poor solvent and the polymer stock solution for both components. A mixed solvent with a solvent is particularly preferred. Examples thereof include alcohols such as methanol, ethanol, and propanol, and a mixed solution of a poor solvent such as water and a solvent used for preparing the stock solution. It is most preferable to use a mixed solution of water and a solvent used in the preparation of the stock solution from the viewpoint of reduction of environmental burden and equipment cost for safely handling the coagulation solvent. The concentration of the mixed solution is preferably 10% by weight or more and 90% by weight or less when the stock solution is prepared in the coagulation solvent. By setting the concentration of the solvent at the time of preparing the stock solution in the coagulation solvent to 10% by weight or more, it is possible to reduce the cost for recovery, purification, separation and reuse of the coagulation solvent. Can be solidified. More preferably, it is 20 weight% or more and 80 weight% or less. The temperature of the coagulation bath is preferably 0 to 90 ° C., more preferably 5 to 70 ° C. from the viewpoint of operability. The take-up speed of the solidified yarn obtained by solidifying the stock solution in a coagulation bath is preferably 1 to 100 m / min from the viewpoint of operability. The obtained coagulated yarn is preferably stretched for the purpose of increasing fiber strength. Stretching is preferably performed in multiple stages by liquid bath stretching following coagulation, and the total stretching ratio can be appropriately adjusted according to the purpose, but is preferably about 2 to 20 times. Moreover, you may perform drying, oil supply, and washing | cleaning suitably in the middle of the process or at the end. It is most preferable to carry out crimping such as stuffing or steam setting after rinsing and drying following stretching. By applying the crimping process, a special crimp that is three-dimensional and excellent in bulkiness appears due to the multilayer composite structure of fibers.

  From the layer (III) of the acrylonitrile-based polymer (A) and the layer (IV) in which the ester-based polymer (B) is dispersed in the acrylonitrile-based polymer (A) by the method for producing a multilayer composite acrylic fiber of the present invention. A multi-layer composite acrylic characterized by having a multi-layer composite structure in which the total number of layers (N) of layers (III) and (IV) exceeds three in a fiber cross section. It is possible to produce fibers without using a special base, and it is possible to obtain the above-mentioned excellent multilayer composite acrylic fiber with high productivity compared to a composite acrylic fiber using a conventional composite base. it can.

  The most preferred example of the method for producing lightweight acrylic fibers of the present invention is a stock solution (a) having a viscosity of 100 to 2000 poise at 45 ° C. comprising a 20% by weight dimethyl sulfoxide solution of acrylonitrile polymer (A), and 15 at 45 ° C. A stock solution (b) composed of a dimethyl sulfoxide solution of an acrylonitrile polymer (A) mixed with an ester polymer (B) having a viscosity of 2000 poise of a weight% dimethyl sulfoxide solution is used. After dividing into multiple layers so that the theoretical number of layers in single yarn (Ncal) is more than 3 and 15 or less using an in-pipe mixer, the mixture is introduced into a spinneret and 20-20 wt% dimethyl sulfoxide aqueous solution at 5 to 70 ° C. After being discharged into a coagulation bath, solidified and taken up at 1 to 100 m / min, Shin, washed with water to obtain a multilayer composite acrylic fibers with crimps excellent steric and bulkiness by performing crimping after the drying. By immersing this multilayer composite acrylic fiber in an aqueous sodium hydroxide solution having a pH of 13 or more and 20 to 70 ° C. for 10 to 120 minutes, there are 60 or more holes in the cross section of the fiber, and the average diameter of the holes (Dv) is a method of obtaining a porous acrylic fiber having 0.1 to 1 μm and a hollowness of 10 to 40%.

  Hereinafter, the present invention will be described in more detail with reference to examples. In addition, each characteristic value in an Example was calculated | required with the following method.

A. Viscosity of Polymer Solution Using a DV-II + Pro VISCOMETER manufactured by BROOKFIELD, the viscosity was measured at a shear rate of 10 to 20 sec ⁻¹ under the condition that the temperature was controlled constant with TC500 manufactured by BROOKFIELD.

B. Calculation of the number of theoretical layers in a single yarn The number of theoretical layers in a single yarn (Ncal) was determined by the following equation.

Here, K is a constant determined by the external shape of the spinneret. The value of K is 1 for a rectangular base and the value of K is 1.1 for a circular base. The number of divided layers in the spinning raw liquid flow depends on the elements constituting the static in-tube mixer and the number of elements. In the case of a static mixer, if the number of elements is n, It becomes street.
Number of divided layers of spinning dope stream = 2 ⁿ
C. Measurement of the total average number of layers and the area fraction of the layers in the fiber cross section After embedding the sample fiber in paraffin, use a microtome to make a slice sliced on a plane perpendicular to the fiber axis, and use this slice as an optical fiber. Observation was performed at a magnification of 400 times with a microscope (manufactured by Olympus Corporation, BX60), and a photograph was obtained. The total number of layers (N) was obtained by averaging the values obtained by counting the number of layers laminated in a stripe shape in the cross section of each of 30 fibers in total from the obtained photographs. At this time, a layer that was not in contact with the outer peripheral line of the fiber cross section and was taken into another layer was not added to the number of layers.

In addition, for the measurement of the area fraction of layer (II) or layer (IV), an ultra-thin slice of a plane perpendicular to the fiber axis is prepared using a microtome after impregnating the epoxy fiber with a sample fiber and transmitted. A photograph was obtained by observation with a scanning electron microscope (Hitachi, Ltd., H-7100FA) at a magnification of 4000 times. Using the obtained photograph, cut out fiber cross-section surrounded by the outer periphery of the fiber, the value obtained by measuring the weight of the paper (unit: g) of the set to W _1. Furthermore, it was cut along the boundary portion of the layer that was almost striped in the fiber cross section, divided into layers, and the weight of the layer (II) or layer (IV) collected and measured (unit: g) It was referred to as _{W 2.} At this time, a layer that was not in contact with the outer peripheral line of the fiber cross section and was taken into another layer was not cut out.

The area fraction occupied by the layer (II) or layer (IV) contained in the cross section of the fiber was calculated using the following formula, and the average value was obtained from a total of five fibers.
Area fraction occupied by layer (II) or layer (IV) = W ₂ / W ₁ × 100
D. Observation of fiber cross-section and measurement of islands and pores After impregnating the sample fiber with epoxy resin, a microtome was used to make an ultrathin section perpendicular to the fiber axis, and a transmission electron microscope (Corporation) Hitachi, H-7100FA) was observed at a magnification of 4000 times to obtain a total of five cross-sectional photographs of the fibers. The obtained photograph was enlarged and printed on paper so that the length corresponding to 5 μm was 5 cm. The tracing paper was placed on the enlarged printed photograph, and the outer peripheral line of the fiber cross section and the outer peripheral line of the holes or islands were copied using an aqueous pen with a thickness of 0.5 mm. This copied figure is read with a scanner, and graphic separation is performed on each fiber cross section using image processing software (Mitani Corporation, Winroof), and the following measurements are performed for each single fiber, for a total of 5 The average value of the fibers of the book was determined.
Number of holes: The number of independent holes was measured.
Hole diameter: The equivalent circle diameter was determined for each hole.
Maximum diameter of holes (Dvmax): A hole having the largest equivalent circle diameter was adopted.
Average diameter of holes (Dv): A value obtained by averaging the equivalent circle diameters of all holes was obtained.
Total area of pores in fiber cross section (Sv): A value obtained by summing the areas of all pores was used.
Number of islands: The number of independent islands was measured.
Diameter of island part: The equivalent circle diameter was determined for each island part.
Maximum diameter of island portion (Demax): The island portion having the largest equivalent circle diameter was adopted.
Average diameter of island (De): The average of equivalent circle diameters of all islands was obtained.
Total area of islands in fiber cross section (Se): A value obtained by summing the areas of all islands was used.
Area surrounded by the outer periphery of the single fiber (Sf): The area of the portion surrounded by the outer periphery of the fiber was determined.

The hollowness ratio and sea island ratio were determined by the following equations.
Hollow ratio (%) = (Sv / Sf) × 100
Sea island rate (%) = (Se / Sf) × 100
E. Single fiber fineness and strength The single fiber fineness was measured using a Denier Computer manufactured by Search, and the average value of ten single yarn finenesses was defined as the single fiber fineness. The strength was measured using Tensilon UTC-100 manufactured by Orientec Co., Ltd. at an initial length of 20 mm and a tensile speed of 20 mm / min, and the average value of five measurements was taken as the strength. Moreover, although the fluctuation rate of intensity | strength was calculated | required about the lightweight acrylic fiber, the fluctuation ratio of an intensity | strength is a value represented by dividing the standard deviation of intensity | strength by the average value of intensity | strength, and expressed as a percentage. In the present invention, the strength was 2.0 cN / dtex or more and the variation in strength was 15% or less.

F. Crimp number and crimp number fluctuation rate According to JIS L1015 (revised in 1999), the length La (mm) and the number of peaks (M) were measured with a load of 1.8 mg / dtex applied to a single fiber. The number of crimps was calculated by the following formula, and an average value of 20 was obtained.
Number of crimps (mountain / 25 mm) = M × 25 / La
In addition, the variation rate (%) of the number of crimps representing the variation in the number of crimps was obtained by dividing the standard deviation of the number of crimps by the average value of the number of crimps and expressing it as a percentage. In the present invention, the crimp number fluctuation rate (%) is 30% or less.

Example 1
As the stock solution (a), an acrylonitrile-based polymer (A) comprising 94% by weight of acrylonitrile, 5% by weight of methyl acrylate, and 1% by weight of sodium methallyl sulfonate by a solution polymerization method using dimethyl sulfoxide (DMSO) as a solvent. Polymerization was performed to obtain a 20 wt% DMSO solution of the component (A) as a stock solution (a). The viscosity of the stock solution (a) at 45 ° C. was 200 poise.

  As the ester polymer (B), first, 12 parts of ethylene glycol was added to 5 parts of adipic acid and 12 parts of azelaic acid, and an esterification reaction was performed to obtain a prepolymer. Next, 48 parts of polyethylene glycol (molecular weight 4000) was added to this prepolymer and subjected to polycondensation to obtain a block polyether ester composed of polyethylene adipate, polyethylene azelate, and polyethylene glycol. Further, 100 parts of this block polyether ester was dissolved in 737 parts of DMSO and 30 parts of acrylonitrile was graft-polymerized to obtain an ester polymer (B). When a 15.0 wt% DMSO solution of this ester polymer (B) was prepared, the viscosity of the solution showed 15 poise at 45 ° C.

  The stock solution (b) was measured with an independent gear pump so that the stock solution (a) was 17.4 mL / min, and the 15.0 wt% DMSO solution of the ester polymer (B) was 18.9 mL / min. Both were mixed in a pipe using a static mixer having 14 elements to obtain a stock solution (b).

  Next, the stock solution (a) is weighed using a gear pump so as to be 13.4 mL / min, combined with the stock solution (b) just before the die, and the stock solution is layered in the pipe using a static mixer with 8 elements. And extruded from a circular die having a number of nozzle holes of 1000 and a diameter of 0.065 mmφ, and discharged into a coagulation bath made of a 40 wt% DMSO / water mixed solution at 40 ° C. At this time, the number of divided layers of the spinning dope flow is 256, and the number of theoretical layers in single yarn (Ncal) is 7.4. After the solidification, the yarn is taken up at 5.0 m / min, and then 6.0 in a two-stage drawing bath composed of a 30 wt% DMSO / water mixed solution at 70 ° C. and a 10 wt% DMSO / water mixed solution at 90 ° C. After being stretched twice, it was washed with water in a 25 ° C. water bath and then passed through a 160 ° C. hot drum to obtain acrylic fibers having a single yarn fineness of 3 dtex.

  The obtained fiber is preheated with atmospheric pressure steam so that the yarn temperature becomes 75 ° C. and introduced into a stuffing box having an inlet pressure of 0.06 MPa and an outlet pressure of 0.01 MPa, and the number of crimps is 12 peaks / 25 mm. Was granted. Thereafter, crimp expression treatment was performed at 113 ° C. in a relaxed state. Further, the yarn after the crimp expression treatment is redrawn at a steam temperature of 100 ° C. at a magnification of 1.2 times to eliminate the crimp, and further in a stuffing box to improve the entanglement at the time of spinning. A 12 crimps / 25 mm mechanical crimp was applied and dried with hot air at 70 ° C.

  From observation of the cross section of the obtained fiber, the layer (III) composed of the acrylonitrile-based polymer (A) component and the layer (IV) in which the ester-based polymer (B) is dispersed in the acrylonitrile-based polymer (A) are alternated. As a result, it was found that a multilayer composite acrylic fiber was obtained. Further, in the layer (IV), a sea-island structure in which the acrylonitrile-based polymer (A) is the sea and the ester-based polymer (B) is the island was observed, but no clear pores were observed in any layer, At that time, the acrylic fiber was not made porous. According to cross-sectional observation, the total average number of layers (N) was 7.2, and the area fraction occupied by the layer (IV) included in the cross-section was 68%. In addition, the number of island parts made of the ester polymer (B) was 162, the average diameter (De) was 0.83 μm, the maximum diameter (Demax) was 3.6 μm, and the sea-island ratio was 29.8%.

  In addition, after the resulting multilayer composite acrylic fiber was treated in boiling water for 10 minutes to reveal crimps, it was dried with a hot air dryer at 70 ° C. for 30 minutes, and then the single yarn strength, the number of crimps, Table 1 shows the results of measuring the crimp fluctuation rate. After the boiling water treatment, a three-dimensional crimp was developed, and a multilayer composite acrylic fiber excellent in bulkiness was obtained.

Example 2
The same stock solution (a) as in Example 1 was used.

  The stock solution (b) was measured with an independent gear pump so that the stock solution (a) was 52.3 mL / min and the ester-based polymer (B) 15.0 wt% DMSO solution was 56.6 mL / min. Both were mixed in a pipe using a static mixer having 14 elements to obtain a stock solution (b).

  Next, the stock solution (a) is weighed with a gear pump so as to be 40.3 mL / min, combined with the stock solution (b) just before the die, and the stock solution is layered in the pipe using a static mixer with 8 elements. And extruded from a circular die having a die hole number of 3000 and a diameter of 0.065 mmφ, and discharged into a coagulation bath made of a 40 wt% DMSO / water mixed solution at 40 ° C. At this time, the number of divided layers of the spinning dope is 256, and the number of theoretical layers in single yarn (Ncal) is 4.2. Following the solidification, the yarn is taken up at 5.0 m / min, and then is stretched in a two-stage drawing bath composed of a 30 wt% DMSO / water mixed solution at 70 ° C. and a 10 wt% DMSO / water mixed solution at 90 ° C. After stretching by 0 times, it was washed with a water bath at 25 ° C. and then passed through a hot drum at 160 ° C. to obtain an acrylic fiber having a single yarn fineness of 3 dtex.

  The obtained fiber is preheated with atmospheric pressure steam so that the yarn temperature becomes 75 ° C. and introduced into a stuffing box having an inlet pressure of 0.06 MPa and an outlet pressure of 0.01 MPa, and the number of crimps is 12 peaks / 25 mm. Was granted. Thereafter, crimp expression treatment was performed at 113 ° C. in a relaxed state. Further, the yarn after the crimp expression treatment is redrawn at a steam temperature of 100 ° C. at a magnification of 1.2 times to eliminate the crimp, and further in a stuffing box to improve the entanglement at the time of spinning. A 12 crimps / 25 mm mechanical crimp was applied and dried with hot air at 70 ° C.

  In the cross-sectional observation of the obtained fiber, the layer (III) composed of the acrylonitrile polymer (A) component and the layer (IV) in which the ester polymer (B) is dispersed in the acrylonitrile polymer (A) are alternately arranged. The structure laminated | stacked in stripe form was confirmed, and it turned out that the multilayer composite type acrylic fiber is obtained. Further, in the layer (IV), a sea-island structure in which the acrylonitrile-based polymer (A) is the sea and the ester-based polymer (B) is the island was observed, but no clear pores were observed in any layer, At that time, the acrylic fiber was not made porous. According to cross-sectional observation, the total average number of layers (N) was 4.1, and the area fraction occupied by the layer (IV) contained in the cross-section was 73%. Further, the number of island portions made of the ester polymer (B) was 157, the average diameter (De) was 0.82 μm, the maximum diameter (Demax) was 3.9 μm, and the sea-island ratio was 31.5%.

  In addition, the resulting multilayer composite acrylic fiber was treated in boiling water for 10 minutes to reveal crimps, dried at 100 ° C., and then measured for single yarn strength, number of crimps, and crimp fluctuation rate. Is shown in Table 1. After the boiling water treatment, a three-dimensional crimp was developed, and a multilayer composite acrylic fiber excellent in bulkiness was obtained.

Example 3
The same stock solution (a) as in Example 1 was used.

  The stock solution (b) was measured with an independent gear pump so that the stock solution (a) was 348.5 mL / min and the 15.0 wt% DMSO solution of the ester polymer (B) was 377.5 mL / min. Both were mixed in a pipe using a static mixer having 14 elements to obtain a stock solution (b).

  Next, the stock solution (a) is weighed using a gear pump so as to be 268.5 mL / min, and is combined with the stock solution (b) just before the die, and the stock solution is layered in the pipe using a static mixer with 9 elements. Were extruded from a circular die having a number of nozzle holes of 20000 and a diameter of 0.065 mmφ, and discharged into a coagulation bath made of a 40 wt% DMSO / water mixed solution at 40 ° C. At this time, the number of divided layers of the spinning dope is 512, and the number of theoretical layers in single yarn (Ncal) is 3.3. Following the solidification, the yarn is taken up at 5.0 m / min, and then is stretched in a two-stage drawing bath composed of a 30 wt% DMSO / water mixed solution at 70 ° C. and a 10 wt% DMSO / water mixed solution at 90 ° C. After stretching by 0 times, it was washed with a water bath at 25 ° C. and then passed through a hot drum at 160 ° C. to obtain an acrylic fiber having a single yarn fineness of 3 dtex.

  The obtained fiber is preheated with atmospheric pressure steam so that the yarn temperature becomes 75 ° C. and introduced into a stuffing box having an inlet pressure of 0.06 MPa and an outlet pressure of 0.01 MPa, and the number of crimps is 12 peaks / 25 mm. Was granted. Thereafter, crimp expression treatment was performed at 113 ° C. in a relaxed state. Further, the yarn after the crimp expression treatment is redrawn at a steam temperature of 100 ° C. at a magnification of 1.2 times to eliminate the crimp, and further in a stuffing box to improve the entanglement at the time of spinning. A 12 crimps / 25 mm mechanical crimp was applied and dried with hot air at 70 ° C.

  In the cross-sectional observation of the obtained fiber, the layer (III) composed of the acrylonitrile polymer (A) component and the layer (IV) in which the ester polymer (B) is dispersed in the acrylonitrile polymer (A) are alternately arranged. The structure laminated | stacked in stripe form was confirmed, and it turned out that the multilayer composite type acrylic fiber is obtained. Further, in the layer (IV), a sea-island structure in which the acrylonitrile-based polymer (A) is the sea and the ester-based polymer (B) is the island was observed, but no clear pores were observed in any layer, At that time, the acrylic fiber was not made porous. According to cross-sectional observation, the total average number of layers (N) was 3.5, and the area fraction occupied by the layer (IV) included in the cross-section was 73%. The number of island parts made of ester polymer (B) was 141, the average diameter (De) was 0.84 μm, the maximum diameter (Demax) was 3.8 μm, and the sea-island ratio was 30.7%.

  In addition, the resulting multilayer composite acrylic fiber was treated in boiling water for 10 minutes to reveal crimps, dried at 100 ° C., and then measured for single yarn strength, number of crimps, and crimp fluctuation rate. Is shown in Table 1. After the boiling water treatment, a three-dimensional crimp was developed, and a multilayer composite acrylic fiber excellent in bulkiness was obtained.

Comparative Example 1
The same stock solution (a) as in Example 1 was used.

  The stock solution (b) was measured with an independent gear pump so that the stock solution (a) was 8.7 mL / min and the ester-based polymer (B) 15.0 wt% DMSO solution was 9.4 mL / min. Both were mixed in a pipe using a static mixer having 14 elements to obtain a stock solution (b).

  Next, the stock solution (a) is weighed using a gear pump so as to be 6.7 mL / min, combined with the stock solution (b) just before the die, and the stock solution is layered in the pipe using a static mixer with 6 elements. And extruded from a circular die having a die number of 500 and a diameter of 0.065 mm. At this time, the number of divided layers of the spinning dope is 64, and the number of theoretical layers (Ncal) in single yarn is 2.6. After the solidification, the yarn is taken up at 5.0 m / min, and then 6.0 in a two-stage drawing bath composed of a 30 wt% DMSO / water mixed solution at 70 ° C. and a 10 wt% DMSO / water mixed solution at 90 ° C. After being stretched, it was washed in a water bath at 25 ° C. and then passed through a hot drum at 160 ° C. to obtain an acrylic fiber having a single yarn fineness of 3 dtex.

  The obtained fiber is preheated with atmospheric pressure steam so that the yarn temperature becomes 75 ° C. and introduced into a stuffing box having an inlet pressure of 0.06 MPa and an outlet pressure of 0.01 MPa, and the number of crimps is 12 peaks / 25 mm. Was granted. Thereafter, crimp expression treatment was performed at 113 ° C. in a relaxed state. Further, the yarn after the crimp expression treatment is redrawn at a steam temperature of 100 ° C. at a magnification of 1.2 times to eliminate the crimp, and further in a stuffing box to improve the entanglement at the time of spinning. A 12 crimps / 25 mm mechanical crimp was applied and dried with hot air at 70 ° C.

  In the cross-sectional observation of the obtained fiber, the layer (III) composed of the acrylonitrile polymer (A) component and the layer (IV) in which the ester polymer (B) is dispersed in the acrylonitrile polymer (A) are 2 In addition to the structure in which more than one layer is laminated, a cross section composed only of the layer (III) composed of the acrylonitrile polymer (A) component and a cross section having no layer structure composed only of the ester polymer (B) were observed. . As a result of cross-sectional observation, the total average number of layers (N) was 2.8, and the area fraction occupied by the layer (IV) contained in the cross-section was 74%. The number of island parts made of ester polymer (B) was 136, the average diameter (De) was 0.87 μm, the maximum diameter (Demax) was 3.7 μm, and the sea-island ratio was 30.4%. Further, in the layer (IV), a sea-island structure in which the acrylonitrile-based polymer (A) is the sea and the ester-based polymer (B) is the island was observed, but no clear pores were observed in any layer, At that time, the acrylic fiber was not made porous.

  In addition, the resulting multilayer composite acrylic fiber was treated in boiling water for 10 minutes to reveal crimps, dried at 100 ° C., and then measured for single yarn strength, number of crimps, and crimp fluctuation rate. Is shown in Table 1. Crimps were developed after the boiling water treatment, but the number of crimps varied by one fiber, and as shown in Table 1, the crimp number fluctuation rate was very large as compared with Examples 1 to 3. This is because the number of theoretical layers (Ncal) in a single yarn is as low as 2.6, so that the composition of the polymer constituting the cross section of the obtained fiber is greatly different for each fiber, and the total average number (N) is 2. It is estimated that there was a large difference in crimp development between each fiber.

Examples 4-6
The multilayer composite acrylic fiber obtained in Examples 1 to 3 was used as a skein and immersed in a 1.5 wt% (pH 13.5) sodium hydroxide aqueous solution so that the bath ratio was 1: 100 or more, and 60 ° C., 120 min. The alkali treatment was performed. Table 2 shows the weight loss of the fiber (skein) before and after the alkali treatment. When the cross section of the fiber after the alkali treatment was observed, the layer (I) made of acrylonitrile polymer (A) and the layer (II) made of acrylonitrile polymer (A) having many vacancies were alternately found in each fiber. It was found that lightweight acrylic fibers having a multilayer composite structure were obtained. For each fiber, the total average number of layers (N), the area fraction occupied by the layer (II) contained in the cross section, the number of holes, the average diameter (Dv) of the holes, the maximum diameter (Dvmax), hollow The results of the rate are shown in Table 2.

  As shown in Table 2, all of the obtained lightweight acrylic fibers showed high strength and a stable fluctuation rate, and had excellent mechanical properties.

Comparative Example 2
The same alkali treatment as in Examples 4 to 6 was performed using the acrylic fiber obtained in Comparative Example 1 as a skein. Table 2 shows the weight loss of the fiber (skein) before and after the alkali treatment. When the cross section of the fiber after the alkali treatment was observed, two or more layers (I) composed of the acrylonitrile polymer (A) and two (II) layers composed of the acrylonitrile polymer (A) having many pores were laminated. In addition to the structure described above, a multilayer composite structure consisting only of a layer consisting of only the layer (I) composed of the acrylonitrile-based polymer (A) component, or a layer (II) composed of the acrylonitrile-based polymer (A) having many pores A cross-section having no A was observed, and the total average number of layers (N) was 2.9. For this fiber, the area fraction occupied by the layer (II) contained in the cross section, the number of holes, the average diameter (Dv) of the holes, the maximum diameter (Dvmax), the hollow ratio, the strength, and the strength fluctuation rate were determined. The results are shown in Table 2. Compared with the fibers of Examples 4 to 6, the strength is low, the fluctuation rate of strength is large, and the variation in strength is large for each single yarn. This is because the total average number of layers (N) is as small as 2.9, and the composition of the polymer constituting the cross section of the fiber is greatly different for each fiber. It is speculated that a big difference has occurred.

  The lightweight acrylic fiber of the present invention has both sufficient strength and hollowness even when used as a textile product, and is excellent in handleability and color development without generation of dust compared to conventional products, curtains, blankets, carpets, Suitable for antibacterial clothing, chemical solution sustained-release materials, cell culture media, etc. by adsorbing functional agents on the surface of mats, towels, dryer canvas, sweaters, underwear, socks, and pores and porous fibers Can do. In addition, the multilayer composite acrylic fiber of the present invention has excellent crimp developability, excellent color developability, and the ester polymer (B) is easily eluted by alkali. It can be suitably used as a precursor fiber. Moreover, the lightweight acrylic fiber manufacturing method of the present invention can obtain the lightweight acrylic fiber as described above with high productivity without requiring special processing conditions and capital investment. In addition, according to the method for producing a multilayer composite acrylic fiber of the present invention, an excellent multilayer composite acrylic fiber as described above can be obtained with high productivity without requiring special processing conditions and capital investment.

Claims (4)

  A layer (I) made of acrylonitrile polymer (A) and a layer (II) made of acrylonitrile polymer (A) having pores with an average diameter (Dv) of 0.1 μm or more and 1 μm or less, A lightweight acrylic fiber characterized by having a multilayer composite structure in which the total average number of layers (N) of layers (I) and (II) exceeds 3 layers is laminated.   The layer (III) of the acrylonitrile-based polymer (A) and the layer (IV) in which the ester-based polymer (B) is dispersed in the acrylonitrile-based polymer (A) are composed of layers (III) and ( A multilayer composite acrylic fiber having a multilayer composite structure in which the total number of layers (N) of (IV) exceeds 3 layers, and is laminated in a striped pattern.   The method for producing a lightweight acrylic fiber according to claim 1, wherein the ester-based polymer (B) is eluted from the multilayer composite acrylic fiber according to claim 2 with an alkaline solution.   A stock solution (a) of an acrylonitrile-based polymer (A) and a stock solution (b) obtained by mixing an ester-based polymer (B) with an acrylonitrile-based polymer (A) are divided into multiple layers, introduced into a spinneret, and then formed. The manufacturing method of the multilayer composite type acrylic fiber of Claim 2.