Modacrylic Fiber, Flame-Retardant Fiber Assembly Containing Same, and Method for Manufacturing Same

One or more embodiments of the present invention relate to a modacrylic fiber, a flame-retardant fiber composite including the modacrylic fiber, and a method for producing the modacrylic fiber.

Conventionally, modacrylic fibers have generally been made flame retardant by adding about 1 to about 50 parts by mass of antimony compounds as flame retardants with respect to 100 parts by mass of the polymer (for example, Patent Document 1). However, since antimony compounds may affect the environment and the human body, flame retardants other than the antimony compound are being considered. For example, Patent Document 2 proposes incorporating a zinc stannate compound to halogen-containing fibers as a compound that impart flame retardancy, and the halogen-containing fibers used together with cellulose fibers. Patent Document 3 describes a flame-retardant synthetic fiber containing a halogen containing polymer, a halogen containing substance, and a zinc compound.

However, when the zinc stannate compound is used as a flame retardant, flame retardancy of the modacrylic fiber is inferior to when an antimony compound is used as a flame retardant.

To address the above, a modacrylic fiber with enhanced flame retardancy while being environmentally friendly, a flame-retardant fiber composite including the modacrylic fiber, and a method for producing the modacrylic fiber are provided.

One or more embodiments of the present invention relate to a modacrylic fiber including a modacrylic polymer, a halogen-containing compound other than the modacrylic polymer, and a compound containing tin and zinc, where the halogen-containing compound contains halogen in an amount of 50 mass % or more, the modacrylic fiber contains halogen in an amount of 40 mass % or more with respect to a total of 100 mass % of the modacrylic polymer and the halogen-containing compound, and a molar ratio (halogen/tin) of halogen element derived from the modacrylic polymer and the halogen-containing compound to tin element derived from the compound containing tin and zinc is 32 or more.

One or more embodiments of the present invention relate to a flame-retardant fiber composite including the modacrylic fiber.

One or more embodiments of the present invention relate to a method for producing the modacrylic fiber, the method including wet-spinning a spinning solution containing the modacrylic polymer, the halogen-containing compound other than the modacrylic polymer, the compound containing tin and zinc, and a solvent.

One or more embodiments of the present invention can provide a modacrylic fiber with enhanced flame retardancy while being environmentally friendly, a flame-retardant fiber composite including the modacrylic fiber, and a method for producing the modacrylic fiber.

The inventors of one or more embodiments of the present invention have conducted in-depth studies to improve the flame retardancy of a modacrylic fiber that contains the modacrylic polymer while considering environmentally friendly. As a result, the inventors found that the flame retardancy of the modacrylic fiber was improved by using the modacrylic polymer together with a halogen-containing compound other than the modacrylic polymer (hereinafter, also referred to as the other halogen-containing compound), and a compound containing tin and zinc and setting a molar ratio (halogen/tin) of halogen element derived from the modacrylic polymer and the other halogen-containing compound to tin element derived from the compound containing tin and zinc to a specified value or more.

When a modacrylic fiber that contains a compound containing tin and zinc as a flame retardant was combusted, tin reacts with halogens, e.g. chloride to generate tin (IV) halide, e.g. tin tetrachloride (SnCl) and tin (II) halide, e.g. tin dichloride (SnCl), and tin (IV) halide, e.g. tin tetrachloride (SnCl) exhibits gas-phase flame retardancy, while tin (II) halide, e.g. tin dichloride (SnCl) exhibits solid-phase flame retardancy. The inventors of one or more embodiments of the present invention found that the low generating amount of tin (IV) halide, e.g. tin tetrachloride (SnCl) in a case using the compound containing tin and zinc as a flame retardant, results in inferior gas-phase flame retardancy compared to in a case using the antimony compound as a flame retardant, and that this is the reason why the flame retardancy is inferior when the compound containing tin and zinc is used as a flame retardant compared to when the antimony compound is used. The inventors of one or more embodiments of the present invention then found that in the modacrylic fiber containing the modacrylic polymer, the halogen-containing compound other than the modacrylic polymer, and the compound containing stannate and zinc, by setting a molar ratio (halogen/tin) of halogen element derived from the modacrylic polymer and the other halogen-containing compound to tin element derived from the compound containing tin and zinc is 32 or more, when the modacrylic fiber was combusted, a generating amount of tin (IV) halide, e.g. tin tetrachloride (SnCl) that generated by reaction halogens, e.g. chloride with tin and that exhibit gas-phase flame retardancy, become higher than a generating amount of tin (II) halide, e.g. tin dichloride (SnCl) that generated by reaction halogens, e.g. chloride with tin and that exhibit solid-phase flame retardancy, thus flame retardancy of the modacrylic fiber was improved.

In this specification, when a numerical range is shown using “to”, that includes the values at both ends (i.e., the upper limit and the lower limit). For example, a numerical range “A to B” is a range that includes A and B, which are the values at the two ends of the range, and is the same as “A or more and B or less”. Also, when a plurality of numerical ranges is described in this specification, numerical ranges obtained by using the upper limits and the lower limits of the different numerical ranges in combination as appropriate are included.

The modacrylic fiber contains the modacrylic polymer, the other halogen-containing compound, and the compound containing tin and zinc.

The modacrylic polymer contains acrylonitrile and a halogen-containing monomer, and is not particularly limited as long as the acrylonitrile content is less than 85 mass %. The modacrylic polymer may contain acrylonitrile in an amount of 30 to 70 mass %, and the halogen-containing monomer in an amount of 30 to 70 mass %, may contain acrylonitrile in an amount of 35 to 65 mass %, and the halogen-containing monomer in an amount of 35 to 65 mass %, or may contain acrylonitrile in an amount of 40 to 60 mass %, and the halogen-containing monomer in an amount of 40 to 60 mass %, from the viewpoint of flame retardancy and heat resistance.

Examples of the halogen-containing monomer include a halogen-containing vinyl monomer and a halogen-containing vinylidene monomer. Examples of the halogen-containing vinyl monomer include vinyl chloride and vinyl bromide, and examples of the halogen-containing vinylidene monomer include vinylidene chloride and vinylidene bromide. The halogen-containing monomer may be used alone or in combination of two or more. Among them, the halogen-containing monomer may be one or more selected from the group consisting of vinyl chloride and vinylidene chloride, and from the viewpoint of the synergistic effect with the compound containing tin and zinc for flame retardancy, vinyl chloride is more preferable.

The modacrylic polymer may contain one or more other copolymerizable monomers in an amount of 0 to 3 mass % in addition to the acrylonitrile and the halogen-containing monomer.

The other copolymerizable monomers are not particular limited as long as it is copolymerizable with acrylonitrile. Examples of the other copolymerizable monomers include, but not particularly limited to: unsaturated carboxylic acids typified by acrylic acids and methacrylic acids, as well as salts thereof; esters of unsaturated carboxylic acids, typified by methacrylic esters (e.g. methyl methacrylate), glycidyl methacrylate and the like; vinyl esters typified by vinyl acetate and vinyl butyrate; and sulfonic acid group-containing monomers. Examples of the sulfonic acid group-containing monomers include, but not particularly limited to, allylsulfonic acid, methallylsulfonic acid, styrenesulfonic acid, isoprenesulfonic acid, and 2-acrylamide-2-methylpropanesulfonic acid, as well as metal salts, such as sodium salts, and amine salts thereof. The other copolymerizable vinyl monomers may be used alone, or two or more of them may be used in combination. Among them, the sulfonic acid group-containing monomers may be used from the viewpoint of improving dye-affinity.

The other halogen-containing compound is not particular limited as long as it contains halogen in an amount of 50 mass % or more. For example, a halogen-containing polymer containing halogen in an amount of 50 mass % or more can be used. The halogen-containing polymer may contain halogen in an amount of 50 to 73 mass %, 50 to 68 mass %, or 50 to 61 mass %. Examples of the halogen-containing polymer include homopolymers or copolymers of halogen monomers include halogen-containing vinyl monomer, e.g., vinyl chloride and vinyl bromide, and a halogen-containing vinylidene monomer, e.g., vinylidene chloride and vinylidene bromide. The halogen-containing polymer may also include copolymers of one or more the halogen monomers and one or more other copolymerizable monomers. The other copolymerizable monomers include ethylene, propylene, vinyl acetate, allyl chloride, allyl glycidyl ether, acrylic esters, and vinyl ethers, but are not particularly limited thereto. More specifically, the halogen-containing polymer includes polyvinyl chloride, and chlorinated polyvinyl chloride. Polyvinyl chloride may a homopolymer of vinyl chloride or a copolymer of vinyl chloride and one or more monomer selected from group consisting of the other halogen-containing monomer and the other copolymerizable monomers.

The modacrylic fiber may contain halogen in an amount of 40 mass % or more with respect to a total of 100 mass % of the modacrylic polymer and the halogen-containing compound, 41 mass % or more, or 42 mass % or more. Thus, when the modacrylic fiber is combusted, the generating amount of the tin (IV) halide, e.g., tin tetrachloride (SnCl) is remarkably increase, and become higher than the generating amount of the tin (II) halide, e.g., tin dichloride (SnCl), so the flame retardancy, more specifically the gas-phase flame retardancy of the modacrylic fiber is improved. In the modacrylic fiber, the upper limit amount of halogen with respect to a total of 100 mass % of the modacrylic polymer and the halogen-containing compound is not particularly limited, but from the viewpoint of the heat resistance, it may be 60 mass % or less, or 50 mass % or less. More specifically, the modacrylic fiber may contain halogen in an amount of 40 to 60 mass %, 41 to 60 mass %, or 41 to 50 mass % with respect to a total of 100 mass % of the modacrylic polymer and the halogen-containing compound.

The modacrylic fiber may contain the modacrylic polymer in an amount of 50 to 75 mass % and the halogen-containing compound in an amount of 25 to 50 mass %, or may contain the modacrylic polymer in an amount of 55 to 75 mass % and the halogen-containing compound in an amount of 25 to 45 mass %, with respect to a total of 100 mass % of the modacrylic polymer and the halogen-containing compound. Thus, the flame retardancy of the modacrylic fiber is improved while maintaining the heat resistance. In addition, the modacrylic fiber can be obtained by wet spinning with good spinnability.

The zinc stannate compound may be used as the compound containing tin and zinc, from view point of general-purpose, and there is no particular limitation thereto. The zinc stannate compound may be zinc stannate (ZnSnO) or zinc hydroxystannate (ZnSn(OH)). Among them, for example, zinc hydroxystannate is preferable from the viewpoint of more improving flame retardancy of the modacrylic fiber.

The modacrylic fiber may contain the compound containing tin and zinc in an amount of 1 to 20 mass %, from the viewpoint of flame retardancy and fiber strength. The modacrylic fiber may contain the compound containing tin and zinc in an amount of 2 mass % or more, 4 mass % or more, 6 mass % or more, or 8 mass % or more, from the viewpoint more improving flame retardancy. The modacrylic fiber may contain the compound containing tin and zinc in an amount of 18 mass % or less, 16 mass % or less, or 14 mass % or less, from the viewpoint of fiber strength and fabric strength. In this specification, the content of the compound containing tin and zinc in the modacrylic fiber can be measured by fluorescence X-ray analysis.

In the modacrylic fiber, the molar ratio (halogen/tin) of halogen element derived from the modacrylic polymer and the halogen-containing compound to tin element derived from the compound containing tin and zinc is 32 or more. Thus the flame retardancy, more specifically the gas-phase flame retardancy of the modacrylic fiber can be improved. The molar ratio of halogen/tin may be 33 or more, 34 or more, or 35 or more. The upper limit of the molar ratio of halogen/tin is not particularly limited, and may be 59 or less, 55 or less, 49 or less, 46 or less, or 44 or less, for example. More specifically, the molar ratio of halogen/tin is 32 to 59, 32 to 55, 33 to 49, 33 to 46, or 33 to 44.

The modacrylic fiber contains substantially no antimony compound. This can reduce the environmental impact and costs. In this specification, the wording “containing substantially no antimony compound” means that an antimony compound serving as a flame retardant is not added to a modacrylic fiber or a flame-retardant fiber composite on purpose, and accordingly, the state where an antimony compound is contained as a contaminant or the like is considered as “containing substantially no antimony compound”.

The modacrylic fiber may contain other additives e.g., an antistatic agent, a thermal coloration inhibitor, a light resistance improver, a whiteness improver, a devitrification inhibitor, and a colorant, as needed. The other additives may be used in an amount of 10 mass % or less, 5 mass % or less, 3 mass % or less, or 1 mass % or less.

The modacrylic fiber may contain the modacrylic polymer and the halogen-containing compound in a total amount of 80 to 99 mass %, the compound containing tin and zinc in an amount of 1 to 20 mass %, and the other additives in an amount of 0 to 10 mass %, may contain the modacrylic polymer and the halogen-containing compound in a total amount of 82 to 98 mass %, the compound containing tin and zinc in an amount of 2 to 18 mass %, and the other additives in an amount of 0 to 5 mass %, may contain the modacrylic polymer and the halogen-containing compound in a total amount of 84 to 96 mass %, the compound containing tin and zinc in an amount of 4 to 16 mass %, and the other additives in an amount of 0 to 3 mass %, or may contain the modacrylic polymer and the halogen-containing compound in a total amount of 86 to 92 mass %, the compound containing tin and zinc in an amount of 8 to 14 mass %, and the other additives in an amount of 0 to 1 mass %.

The modacrylic fiber may be either a short fiber or a long fiber, and can be selected as appropriate depending on the method of use. The single fiber fineness of the modacrylic fiber, which is selected as appropriate depending on the intended use and the like of the flame-retardant fiber composite, may be 1 to 50 dtex, 1.5 to 30 dtex, or 1.7 to 15 dtex. The fiber length of the modacrylic fiber is selected as appropriate depending on the intended use and the like of the flame-retardant fiber composite. For example, a short cut fiber (fiber length: 0.1 to 5 mm), a short fiber (fiber length: 15 to 176 mm, 20 to 160 mm, 25 to 138 mm, or 30 to 128 mm), or a long fiber (filament fiber) can be used.

The single fiber strength of the modacrylic fiber may be 1.0 to 4.0 cN/dtex or 1.5 to 3.5 cN/dtex, for example, from the viewpoint of durability. The elongation at break of the modacrylic fiber may be 15 to 40% or 20 to 30%, for example, from the viewpoint of practicality. In this specification, the single fiber strength and the elongation at break of the modacrylic fiber can be measured accordance with JIS L 1013:2010 or JIS L 1015:2010.

When the modacrylic fiber is combusted at 350° C. for 30 minutes, it may be that tin (IV) halide is generated in an amount of 55 mass % or more and tin (II) halide is generated in an amount of 45 mass % or less, from the viewpoint of enhancing the flame retardancy, more particularly the gas-phase flame retardancy. Further, tin (IV) halide may be generated in an amount of 55 to 80 mass % and tin (II) halide may be generated in an amount of 20 to 45 mass %, from the viewpoint both of the gas-phase flame retardancy and thermal resistance. In this specification, the respective generating amount of the tin (IV) halide and the tin (II) halide can be calculated by the following formulas (1) and (2), respectively, based on the mass of tin contained in the modacrylic fiber and the mass of tin contained in a combustion residue after a combustion test. In this specification, the mass of tin contained in a sample can be measured by ICP-AES. In this specification, the respective generating amount of the tin (IV) halide and the tin (II) halide can be specifically measured and calculated as described in Examples.

In the formulas 1 and 2, W0 represent the mass of tin contained in the modacrylic fiber subjected to the combustion test, and W1 represent the mass of tin contained in the combustion residue after the combustion test.

The modacrylic fiber may have a limiting oxygen index (LOI), which is measured according to the E method (E-1) of JIS L 1091, more than 45, 45.5 or more, 46.0 or more, 46.5 or more, 47.0 or more, or 47.5 or more. In this specification, the LOI value can be specifically measured as described in Examples.

The modacrylic fiber can be produced by, but not particularly limited to, spinning a composition that contains the modacrylic polymer, the other halogen-containing compound, and the compound containing tin and zinc. The modacrylic fiber may be produced by wet spinning a spinning solution that contains the modacrylic polymer, the other halogen-containing compound, the compound containing tin and zinc, and a solvent. The spinning solution may be obtained by dissolving the modacrylic polymer in the solvent and adding the other halogen-containing compound, the compound containing tin and zinc, and other additives as needed, to the obtained solution of the modacrylic polymer. The modacrylic fiber can be produced by the general wet spinning for modacrylic fibers, except using the above-described spinning solution. Specifically, the modacrylic fiber can be produced by extruding the spinning solution into a coagulation bath through a nozzle to coagulate it, then subjecting the coagulated filaments to drawing, washing with water, and drying. After drying, as needed, the obtained filaments may be subject to drawing and heat relaxing treatment. Further, the obtained filaments may be crimped and cut into any desired length as needed. The spinning solution may also be obtained by adding a dispersion of the compound containing tin and zinc dispersed in a solvent to a solution of the modacrylic polymer and the other halogen-containing compound dissolved in a solvent. Examples of the solvent include organic solvents e.g., dimethyl sulfoxide, dimethylformamide, dimethylacetamide, and acetone, and inorganic solvents e.g., a rhodan salt aqueous solution, and a nitric acid aqueous solution.

In one or more embodiments of the present invention, the flame-retardant fiber composite contains the modacrylic fiber. Thus, the flame-retardant fiber composite has excellent flame retardancy, particularly excellent gas-phase flame retardancy. The flame-retardant fiber composite may include a flame-retardant fiber mixture.

The flame-retardant fiber composite may include a cellulose fiber in addition to the modacrylic fiber, from the viewpoint of imparting excellent texture, moisture absorption, and touch, in addition to the flame retardancy. By using the modacrylic fiber, the flame-retardant fiber composite can exhibit excellent flame retardancy, particularly excellent gas phase flame retardancy in the combustion test, even when used together with the cellulose fiber. The flame-retardant fiber composite may contain the modacrylic fiber in an amount of 25 to 75 mass % and the cellulose fiber in an amount of 25 to 75 mass %, may contain the modacrylic fiber in an amount of 30 to 70 mass % and the cellulose fiber in an amount of 30 to 70 mass %, or may contain the modacrylic fiber in an amount of 35 to 65 mass % and the cellulose fiber in an amount of 35 to 65 mass %, from the viewpoint of flame retardancy and texture.

The cellulose fiber may be one or more selected from group consisting of a natural cellulose fiber and a regenerated cellulose fiber.

Examples of the natural cellulose fiber include a cotton fiber, a kapok fiber, a linen fiber, a hemp fiber, a ramie fiber, a jute fiber, a Manila hemp fiber, and a kenaf fiber.

Examples of the regenerated cellulose fiber include a rayon fiber, a flame-retardant rayon fiber, a lyocell fiber, and a flame-retardant lyocell fiber. The rayon fiber is obtained by dissolving, in caustic soda, cellulose xanthate produced by the reaction of an alkali and carbon disulfide with a cellulose raw material, followed by wet spinning. The lyocell fiber is obtained by dissolving a cellulose raw material in N-methylmorpholine N-oxide without performing a step of denaturing the cellulose raw material, followed by dry wet spinning.

The cellulose fiber may be either a short fiber or a long fiber, and can be selected as appropriate depending on the method of use. The single fiber fineness of the cellulose fiber, which is selected as appropriate depending on the intended use and the like of the flame-retardant fiber composite to be used, may be 1 to 50 dtex, 1.5 to 30 dtex, or 1.7 to 15 dtex. The fiber length of the cellulose fiber is selected as appropriate depending on the intended use and the like of the flame-retardant fiber composite. For example, a short cut fiber (fiber length: 0.1 to 5 mm), a short fiber (fiber length: 15 to 176 mm, 20 to 160 mm, 25 to 138 mm, or 30 to 128 mm), or a long fiber that is not cut at all (filament fiber) can be used.

The flame-retardant fiber composite may contain one or more other fibers in addition to the modacrylic fiber and the cellulose fiber. The other fibers include a natural fiber, a regenerated fiber, and a synthetic fiber. The other fibers may be one or more selected from group consisting of a polyester fiber, an aramid fiber, a melamine fiber, and the like. The flame-retardant fiber composite may contain the other fibers in an amount of 20 mass % or less, 10 mass % or less, or 1 mass % or less.

The other fibers may be either short fibers or long fibers, and can be selected as appropriate depending on the method of use. The single fiber fineness of the other fibers, which is selected as appropriate depending on the intended use and the like of the flame-retardant fiber composite, may be 1 to 50 dtex, 1.5 to 30 dtex, or 1.7 to 15 dtex. The fiber length of the other fibers is selected as appropriate depending on the intended use and the like of the flame-retardant fiber composite. For example, a short cut fiber (fiber length: 0.1 to 5 mm), a short fiber (fiber length: 15 to 176 mm, 20 to 160 mm, 25 to 138 mm, or 30 to 128 mm), or a long fiber (filament fiber) can be used.

The flame-retardant fiber composite may include those obtained by fiber blending, mixed spinning, and filament blending, conjugated yarns such as paralleled yarns, folded yarns, and sheath-core yarns, and those obtained by mixed weaving, mixed knitting, and laminating. The specific form of the flame-retardant fiber composite may be cotton for use as stuffing or the like, a spun yarn, a nonwoven fabric, a fabric e.g., a woven fabric, and a knitted fabric, a braided fabric, or the like.

Examples of the cotton for use as stuffing or the like include opened cotton, ball-like cotton, webs, and molded cotton.

Examples of the spun yarn include ring spun yarns, air spun yarns, and air jet spun yarns.

Examples of the nonwoven fabric include wet-laid nonwoven fabrics, carded nonwoven fabrics, air-laid nonwoven fabrics, thermal bonded nonwoven fabrics, chemical bonded nonwoven fabrics, needle-punched nonwoven fabrics, hydro-entangled nonwoven fabrics, and stitch bonded nonwoven fabrics. Thermal bonded nonwoven fabrics and needle-punched nonwoven fabrics are industrially inexpensive. The nonwoven fabric may have any structure that is uniform in the thickness, width, and length directions, a distinctive laminate structure, and an indistinct laminated structure.

Examples of the woven fabric include plain weave fabrics, twill weave fabrics, satin weave fabrics, irregular plain weave fabrics, irregular twill weave fabrics, irregular satin weave fabrics, fancy weave fabrics, Jacquard weave fabrics, woven fabrics using two or more types of yarn for either one of the warp and the weft, double weave fabrics, multiple weave fabrics, warp pile woven fabrics, weft pile woven fabrics, and leno weave fabrics. Plain weave fabrics, satin weave fabrics, and Jacquard weave fabrics exhibit excellent texture, strength, and the like as commercial products.

Examples of the knitted fabric include circular knitted fabrics, weft knitted fabrics, warp knitted fabrics, and pile knitted fabrics, and more specific examples thereof include plain stitch fabrics, jersey stitch fabrics, rib stitch fabrics, smooth knitted fabrics (interlock stitch fabrics), elastic rib stitch fabrics, purl stitch fabrics, denbigh stitch structures, cord stitch structures, atlas stitch structures, chain stitch structures, and laid-in structures. Of these, jersey stitch fabrics and rib stitch fabrics are excellent in texture as commercial products.

The modacrylic fiber and the flame-retardant fiber composite may be used in various textile products (applications). Examples of textile products include the following products.

Clothes (including jackets, underwear, sweaters, vests, trousers, and the like), gloves, socks, mufflers, hats, bedding, pillows, cushions, stuffed toys, and the like

Work clothing worn by workers who handle fire including protective clothing and firefighting clothing, cold weather clothing, and the like