Polyvinyl alcohol fiber and its manufacturing method

Abstract

The present invention addresses the problem of providing a polyvinyl alcohol fiber which has excellent secondary workability and solubility in water, in particular, solubility in water at low temperatures.　The present invention relates to a polyvinyl alcohol fiber comprising: a polyvinyl alcohol A having a degree of saponification of at least 90 mol% and an ethylene modification rate of 4-15 mol%; and a polyvinyl alcohol B having a degree of saponification that satisfies the following expression (1) of 0<αA−αB≤20. In expression (1), αA represents the degree of saponification of the polyvinyl alcohol A and αB represents the degree of saponification of the polyvinyl alcohol B.

Description

[Technical field]

[0001] The present invention relates to polyvinyl alcohol fibers containing polyvinyl alcohols having different degrees of saponification, long-fiber nonwoven fabrics made of said fibers, and a method for producing said fibers or long-fiber nonwoven fabrics. More specifically, the present invention relates to polyvinyl alcohol fibers containing ethylene-modified polyvinyl alcohol and polyvinyl alcohol having a degree of saponification in a specific range, long-fiber nonwoven fabrics made of said fibers, and a method for producing said fibers and long-fiber nonwoven fabrics made of said fibers by melt spinning.

[0002] In polyvinyl alcohol fibers, the hydroxyl groups in the polyvinyl alcohol molecules form intramolecular and intermolecular hydrogen bonds, and these bonds are extremely strong. Therefore, polyvinyl alcohol fibers have high strength and excellent mechanical strength. Taking advantage of this excellent mechanical strength, polyvinyl alcohol fibers are used in a wide range of applications, such as packaging, wound dressings, and textile materials.

[0003] On the other hand, polyvinyl alcohol fibers have excellent solubility in water and are useful as water-soluble fibers or water-soluble packaging materials. Since such water-soluble fibers or water-soluble packaging materials dissolve in water, they impose little burden on the environment when disposed of, and further expansion of their applications is expected.

[0004] Polyvinyl alcohol fibers are usually produced by a wet spinning method in which the polyvinyl alcohol is dissolved in a solvent and spun. However, since the wet spinning method uses a solvent, a process for removing the solvent is required, which can make the production process complicated. Furthermore, trace amounts of solvent may remain in the fibers, and it may be necessary to remove the remaining solvent when the fibers are disposed of. On the other hand, since the melt spinning method does not use a solvent, the process of removing the solvent is omitted and no solvent remains in the fibers. Therefore, there is a need to develop polyvinyl alcohol suitable for the melt spinning method rather than the wet spinning method. As one of the polyvinyl alcohols suitable for the melt spinning method, ethylene-modified polyvinyl alcohol has been proposed (for example, Patent Documents 1 and 2).

[0005] Patent Document 1 discloses a fiber that is composed of an α-olefin-modified polyvinyl alcohol (A) that is a melt-spinnable resin and has a degree of polymerization of 200 to 500, a degree of saponification of 90 to 99.99 mol %, a molar fraction of the central hydroxyl group of three chains of hydroxyl groups in a vinyl alcohol unit expressed as a triad of 70 to 99.9 mol %, and a melting point of 160°C to 230°C, and an alkali metal ion (B), in which the content of component (B) per 100 parts by mass of component (A) is 0.0003 to 1 part by mass.

[0006] Patent Document 2 discloses a thermoplastic polyvinyl alcohol fiber containing, as at least one component, polyvinyl alcohol having a 1,2-glycol bond content of 1.8 mol % to 3.5 mol %. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2000-234214 A [Patent Document 2] JP 2001-248014 A Summary of the Invention [Problem to be solved by the invention]

[0008] The ethylene-modified polyvinyl alcohol described in these documents must have a high degree of saponification in order to improve melt spinnability, but the secondary processability of fibers made of ethylene-modified polyvinyl alcohol with a high degree of saponification tends to be lower than that of polyvinyl alcohol that is not ethylene-modified.

[0009] Furthermore, ethylene-modified polyvinyl alcohol with a high degree of saponification has low solubility in water, especially in low-temperature water, and when made into fibers, its water solubility decreases. Therefore, it may be necessary to treat it with high-temperature water when disposing of it.

[0010] An object of the present invention is to provide polyvinyl alcohol fibers which are excellent in secondary processability and solubility in water, particularly in solubility in water at low temperatures, and a long-fiber nonwoven fabric made of said fibers. The present inventors have discovered that secondary processability and solubility in water are improved by producing polyvinyl alcohol fibers containing two types of polyvinyl alcohol and a long-fiber nonwoven fabric made from said fibers, and have thus completed the present invention. [Means for solving the problem]

[0011] That is, the present invention provides: [1] The present invention relates to a polyvinyl alcohol fiber comprising polyvinyl alcohol A having a saponification degree of 90 mol % or more and an ethylene modification rate of 4 to 15 mol %, and polyvinyl alcohol B having a saponification degree satisfying the following formula (1): 0<α A -α B <= 20 (1) In formula (1), α A is the degree of saponification of the polyvinyl alcohol A, α B represents the degree of saponification of the polyvinyl alcohol B.

[0012] Further, as a preferred embodiment of the present invention, [2] The polyvinyl alcohol fiber according to the above [1], wherein the difference between the melting point and the decomposition temperature is 40° C. or more. [3] The polymerization degree of the polyvinyl alcohol A is from 200 to 600. Polyvinyl alcohol fiber , and [4] The polyvinyl alcohol fiber according to any one of [1] to [3], wherein the degree of polymerization of the polyvinyl alcohol B is 200 to 600. [5] The polyvinyl alcohol fiber according to any one of [1] to [4], wherein the saponification degree of the polyvinyl alcohol B is 80 mol % or more. [6] The polyvinyl alcohol fiber according to any one of [1] to [5], wherein the polyvinyl alcohol B is 15% by mass or more and 95% by mass or less, where the total mass of the polyvinyl alcohol A and the polyvinyl alcohol B is 100% by mass; and, [7] The polyvinyl alcohol fiber according to any one of [1] to [6] above, which has an underwater melt-cutting temperature of 70° C. or less; Regarding.

[0013] The present invention also provides [8] The present invention relates to a method for producing a polyvinyl alcohol fiber according to any one of the above [1] to [7], comprising melting a composition containing polyvinyl alcohol A having a saponification degree of 90 mol % or more and an ethylene modification rate of 4 to 15 mol %, and polyvinyl alcohol B having a saponification degree satisfying the following formula (2), discharging the composition from a nozzle, and cooling the composition: 0<α A -α B <= 20 (2) In the formula (2), α A is the degree of saponification of the polyvinyl alcohol A, α B represents the degree of saponification of the polyvinyl alcohol B. Further, the present invention relates to [9] A long-fiber nonwoven fabric made of the polyvinyl alcohol fiber according to any one of [1] to [7] above.

[10] A method for producing a long-fiber nonwoven fabric, comprising depositing the polyvinyl alcohol fiber according to any one of [1] to [7] above to form a nonwoven fabric web; Regarding. Effect of the Invention

[0014] According to the present invention, there are provided polyvinyl alcohol fibers and long-fiber nonwoven fabrics which are excellent in secondary processability and solubility in water, particularly in solubility in water at low temperatures, and methods for producing the polyvinyl alcohol fibers and long-fiber nonwoven fabrics. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The polyvinyl alcohol A in the present invention is an ethylene-modified polyvinyl alcohol having a degree of saponification of 90 mol % or more and an ethylene modification rate of 4 to 15 mol %. The ethylene-modified polyvinyl alcohol includes an ethylene-vinyl alcohol copolymer obtained by saponifying an ethylene-vinyl ester copolymer obtained by copolymerizing ethylene and a vinyl ester. The ethylene-vinyl alcohol copolymer is a copolymer of ethylene, a vinyl ester as described below, and Copolymerizable The ethylene-vinyl alcohol copolymer may be a saponified copolymer of the ethylene-vinyl alcohol copolymer and a vinyl ester. The ethylene-modified polyvinyl alcohol may be a so-called polyvinyl acetal resin obtained by crosslinking a part of the hydroxyl groups of the ethylene-vinyl alcohol copolymer with an aldehyde such as formalin, butylaldehyde, or benzaldehyde. Among these ethylene-modified polyvinyl alcohols, ethylene-vinyl alcohol copolymers are preferred from the viewpoints of lowering the melting point and improving strength.

[0016] The vinyl esters used in the production of ethylene-modified polyvinyl alcohol may be one or more of them, and it is preferable to use one type of vinyl ester. Examples of vinyl esters include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl valerate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, vinyl versatate, etc. Among these, vinyl acetate is preferred.

[0017] Examples of monomers copolymerizable with the vinyl ester include olefins having 3 to 30 carbon atoms, such as propylene, 1-butene, and isobutene; acrylic acid or a salt thereof; acrylic acid esters, such as methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, and octadecyl acrylate; methacrylic acid or a salt thereof; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, and the like. methacrylic acid esters such as propyl, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, and octadecyl methacrylate; acrylamides such as acrylamide, N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetone acrylamide, acrylamidopropanesulfonic acid or a salt thereof, acrylamidopropyldimethylamine or a salt thereof, and N-methylolacrylamide or a derivative thereof; acrylamide derivatives; methacrylamide derivatives such as methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid or a salt thereof, methacrylamidepropyldimethylamine or a salt thereof, N-methylolmethacrylamide or a derivative thereof; N-vinylamides such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether; vinyl cyanides such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid or a salt, ester, or acid anhydride thereof; itaconic acid or a salt, ester, or acid anhydride thereof; vinyl silyl compounds such as vinyltrimethoxysilane; and isopropenyl acetate. Among these, olefins having 3 to 30 carbon atoms are preferred, and propylene, 1-butene, 1-pentene and 1-hexene are more preferred.

[0018] The saponification degree of polyvinyl alcohol A is 90 mol% or more. From the viewpoint of the mechanical strength of the obtained polyvinyl alcohol fiber, the saponification degree is preferably 95 mol% or more, more preferably 98 mol% or more. The saponification degree is usually 100 mol% or less, preferably 99.5 mol% or less, and further preferably 99 mol% or less.

[0019] The degree of saponification of polyvinyl alcohol A refers to the ratio (mol %) of the number of moles of vinyl alcohol units to the total number of moles of structural units that can be converted to vinyl alcohol units by saponification, typically vinyl ester monomer units and vinyl alcohol units. The degree of saponification of polyvinyl alcohol can be measured in accordance with the description of JIS K 6726-1994.

[0020] The ethylene modification rate of polyvinyl alcohol A is 4 to 15 mol % from the viewpoints of water solubility and strength. The ethylene modification rate is the proportion of structural units derived from ethylene to all structural units, with all structural units constituting polyvinyl alcohol A being 100 mol %. Based on the number of moles of all structural units constituting the vinyl ester polymer, the ethylene modification rate is preferably 12 mol% or less, more preferably 9 mol% or less, and from the viewpoint of strength, the ethylene modification rate is preferably 6 mol% or more, more preferably 7 mol% or more. The ethylene modification rate is, for example, the ratio of an ethylene-vinyl ester copolymer, which is a precursor or reesterification product of an ethylene-modified polyvinyl alcohol. 1 It can be determined from H-NMR. Specifically, the ethylene modification rate can be determined using the peak attributable to the main chain methylene of the vinyl ester in the range of 4.7 to 5.2 ppm and the peak attributable to the main chain methylene of ethylene, the vinyl ester, and other monomers copolymerizable with the vinyl ester in the range of 0.8 to 1.6 ppm.

[0021] From the viewpoint of melt spinnability, the difference between the melting point and the decomposition temperature of the polyvinyl alcohol A is preferably 40° C. or more. The difference between the melting point and the decomposition temperature of the polyvinyl alcohol A is more preferably 50° C. or more. When the difference between the melting point and the decomposition temperature of the polyvinyl alcohol A is equal to or more than the lower limit, the polyvinyl alcohol A has excellent melt spinnability. There is no particular restriction on the upper limit of the difference between the melting point and the decomposition temperature of the polyvinyl alcohol A, but it is preferably 150° C. or less. The melting point of the polyvinyl alcohol A is preferably 180° C. or higher, more preferably 190° C. or higher, from the viewpoint of melt spinnability, and is preferably 220° C. or lower, more preferably 210° C. or lower, from the viewpoint of secondary processability when made into fibers. From the viewpoint of melt spinnability, the decomposition temperature of the polyvinyl alcohol A is preferably 250° C. or higher, more preferably 260° C. or higher. There is no particular upper limit to the decomposition temperature of the polyvinyl alcohol A, but it is preferably 350° C. or lower. The melting point is the peak temperature of the main endothermic peak observed in a differential scanning calorimeter (DSC), and the decomposition temperature is the temperature at which the thermal weight decreases by 3% when heated at a rate of 10°C / min in thermogravimetry (TG).

[0022] The degree of polymerization (viscosity average degree of polymerization) of the polyvinyl alcohol A is preferably 600 or less, more preferably 500 or less, from the viewpoint of melt spinnability. If the degree of polymerization is too high, the melt viscosity may be too high to extrude the polymer from the spinning nozzle. In addition, from the viewpoint of suppressing the decrease in spinnability and inter-fiber sticking during spinning and maintaining the mechanical properties and quality of the fibers and fiber structures, the degree of polymerization is preferably 200 or more, more preferably 300 or more.

[0023] The degree of polymerization means an average degree of polymerization measured in accordance with the description of JIS K 6726-1994. That is, in this specification, the degree of polymerization is calculated from the intrinsic viscosity [η] (unit: deciliter / g) measured in water at 30° C. after resaponifying the residual acetate groups of polyvinyl alcohol A and purifying it, according to the following formula (3). Degree of polymerization P = ([η]×10 4 / 8.29) (1 / 0.62) (3)

[0024] The polyvinyl alcohol B in the present invention is a polyvinyl alcohol having a degree of saponification that satisfies the following formula (1). 0<α A -α B <= 20 (1) In the above formula (1), α A is the degree of saponification of the polyvinyl alcohol A, α B represents the degree of saponification of the polyvinyl alcohol B. It is preferable that the saponification degree of polyvinyl alcohol B further satisfies the following formula (4) from the viewpoints of the secondary processability and water solubility of the obtained fiber. 0<α A -α B <= 15 (4) In the above formula (4), α A , α B has the same meaning as above.

[0025] From the viewpoints of secondary processability and water solubility of the resulting fiber, the saponification degree of polyvinyl alcohol B satisfies the above formula (4) and is preferably 80 mol% or more, more preferably 85 mol% or more. When the saponification degree of polyvinyl alcohol B is as above, the saponification degree of polyvinyl alcohol A is preferably 95 mol% or more, more preferably 98 mol% or more.

[0026] Polyvinyl alcohol B may be an ethylene-modified polyvinyl alcohol similar to polyvinyl alcohol A, a saponification product of the vinyl ester polymer, or a copolymer of a vinyl ester and a copolymerizable monomer, as long as the degree of saponification satisfies the above formula (1). Examples of the vinyl ester and the monomer copolymerizable with the vinyl ester include ethylene and the same vinyl esters and monomers as those exemplified for the polyvinyl alcohol A, and the preferred vinyl esters and monomers are also the same as those mentioned above.

[0027] Polyvinyl alcohol B is preferably an ethylene-unmodified polyvinyl alcohol having a degree of saponification that satisfies the above formula (1) and is not modified with ethylene. The ethylene-unmodified polyvinyl alcohol includes polyvinyl alcohol that is a saponification product of the above vinyl ester polymer, or polyvinyl alcohol that is a saponification product of a copolymer of a vinyl ester and a monomer other than ethylene that is copolymerizable with the above vinyl ester. Among the ethylene-unmodified polyvinyl alcohols, polyvinyl alcohol that is a saponification product of the above vinyl ester polymer is preferred. Examples of the vinyl esters and monomers copolymerizable with the vinyl esters include the same vinyl esters and monomers as those exemplified for the polyvinyl alcohol A, and the preferred vinyl esters and monomers are the same as those mentioned above except for ethylene.

[0028] From the viewpoint of melt spinnability, the difference between the melting point and the decomposition temperature of the polyvinyl alcohol B is preferably 40° C. or more. The difference between the melting point and the decomposition temperature of the polyvinyl alcohol B is more preferably 50° C. or more. When the difference between the melting point and the decomposition temperature of the polyvinyl alcohol B is equal to or more than the lower limit, the melt spinnability is excellent. There is no particular restriction on the upper limit of the difference between the melting point and the decomposition temperature of the polyvinyl alcohol B, but it is preferably 150° C. or less. The melting point of the polyvinyl alcohol B is preferably 170° C. or higher, more preferably 180° C. or higher, from the viewpoint of melt spinnability, and is preferably 200° C. or lower, more preferably 190° C. or lower, from the viewpoint of secondary processability when made into fibers. From the viewpoint of melt spinnability, the decomposition temperature of the polyvinyl alcohol B is preferably 250° C. or higher, more preferably 260° C. or higher. The decomposition temperature of the polyvinyl alcohol B is not particularly limited, but is preferably 350° C. or lower.

[0029] The degree of polymerization (viscosity average degree of polymerization) of the polyvinyl alcohol B is preferably 600 or less, more preferably 500 or less, from the viewpoint of melt spinnability. If the degree of polymerization is too high, the melt viscosity may be too high to extrude the polymer from the spinning nozzle. In addition, from the viewpoint of suppressing the decrease in spinnability and inter-fiber agglutination and maintaining the mechanical properties and quality of the fibers and fiber structures, the degree of polymerization is preferably 200 or more, more preferably 300 or more.

[0030] The polyvinyl alcohol fiber of the present invention contains the polyvinyl alcohol A and the polyvinyl alcohol B. The polyvinyl alcohol fiber of the present invention preferably contains the polyvinyl alcohol B in an amount of 15% by mass or more and 95% by mass or less, with the total mass of the polyvinyl alcohol A and the polyvinyl alcohol B being 100% by mass. When the content of polyvinyl alcohol B is within the above range, the balance between the low-temperature solubility in water and secondary processability of the fiber is excellent. The content of polyvinyl alcohol B is more preferably 30% by mass or more and 80% by mass or less, with the total mass of the polyvinyl alcohol A and the polyvinyl alcohol B being 100% by mass.

[0031] From the viewpoint of secondary processability, the melting point of the polyvinyl alcohol fiber of the present invention is preferably 190° C. or more and 210° C. or less. The upper limit of the melting point is more preferably 208° C. or less, and even more preferably 205° C. or less. Moreover, from the viewpoint of secondary processability, the difference between the melting point and the decomposition temperature of the polyvinyl alcohol fiber is preferably 40° C. or more, more preferably 50° C. or more, and even more preferably 60° C. or more. The melting point and decomposition temperature of the polyvinyl alcohol fiber can be obtained by spinning polyvinyl alcohol A and polyvinyl alcohol B by the method described below, and measuring the obtained fiber by the above-mentioned method. By adjusting the ethylene modification rate and saponification degree of the polyvinyl alcohol A and the saponification degree and content of the polyvinyl alcohol B within the above ranges, the melting point and decomposition temperature of the obtained fibers can be within the above ranges.

[0032] The tensile strength of the polyvinyl alcohol fiber of the present invention is preferably 1 cN / dtex or more, more preferably 3 cN / dtex or more, from the viewpoint of secondary processability. There is no particular upper limit to the tensile strength, but it is usually 25 cN / dtex or less. The tensile strength of the polyvinyl alcohol fiber can be adjusted to a desired value by controlling the stretching conditions, such as the stretching temperature and the stretching ratio, in the fiber manufacturing method described below.

[0033] The melt-cutting temperature of the polyvinyl alcohol fiber of the present invention in water is preferably as low as possible, and from the viewpoint of reducing the environmental load, it is preferably 70° C. or lower, more preferably 50° C. or lower, and even more preferably 30° C. or lower. Moreover, from the viewpoint of handling the fiber, it is preferably 5° C. or higher. The meltdown temperature was determined by applying a load of 2 mg / dtex to a 100 mm long fiber, keeping it in water, and raising the water temperature at a rate of 2°C / min. The temperature was measured at the point when the fiber melted and the load dropped. The severing temperature can be adjusted to a desired level by adjusting the ethylene modification rate of the polyvinyl alcohol A in the polyvinyl alcohol fiber, the ratio of the polyvinyl alcohol B, the degree of saponification of the polyvinyl alcohol A or the polyvinyl alcohol B, and the like within the above-mentioned ranges.

[0034] The polyvinyl alcohol fiber of the present invention has a crystallinity of preferably 50% or less, more preferably 40% or less, from the viewpoint of water solubility, and preferably 15% or more, more preferably 25% or more, from the viewpoints of fiberization and mechanical strength. The degree of crystallinity of the fibers can be controlled by the degree of polymerization of the polyvinyl alcohol A and the polyvinyl alcohol B, the degree of saponification, the type and content of functional groups, and the like. The crystallinity of the fiber can be determined by the following method: Using a Mettler differential scanning calorimeter (DSC-20), 10 mg of a fiber sample was heated at a rate of 10°C / min in a nitrogen atmosphere, the endothermic heat ΔH (J / g) at the endothermic peak was measured, and the crystallinity was calculated from the ratio to 174.5 J / g, which is the heat of fusion of the complete crystal of polyvinyl alcohol, using the following formula (6). Crystallinity (%)=ΔH(J / g) / 174.5(J / g)×100 (6)

[0035] In addition to the above, the polyvinyl alcohol fiber of the present invention may contain various additives that are commonly used, such as a plasticizer, a crosslinking agent, an antioxidant, a stabilizer, a lubricant, a processing aid, an antistatic agent, a colorant, an impact resistance aid, and a foaming agent. When these additives are added, the total amount of the polyvinyl alcohol A and the polyvinyl alcohol B in the polyvinyl alcohol fiber is preferably 60% by mass or more, more preferably 70 to 99% by mass.

[0036] The polyvinyl alcohol fiber of the present invention can be produced by any of wet spinning, dry spinning and melt spinning methods. From the viewpoints of simplifying the spinning process and reducing the environmental load by not using a solvent during the process, the melt spinning method is preferred. In the melt spinning method, the raw material polyvinyl alcohol is melted, and the filaments discharged from a spinning nozzle are drawn and spun. The melt spinning method also includes the melt blowing method or the spunbonding method, in which the fibers discharged from the spinning nozzle are directly formed into a sheet. The melt blowing method is preferred because it produces a nonwoven fabric with fine fibers and a fine mesh.

[0037] Since the polyvinyl alcohol fiber of the present invention contains the polyvinyl alcohol A and the polyvinyl alcohol B, a composition containing predetermined amounts of the polyvinyl alcohol A and the polyvinyl alcohol B may be prepared in advance, and the composition may be melt-spun, or the polyvinyl alcohol A and the polyvinyl alcohol B may be melted separately, and then the two may be combined to form a single fiber when extruded from a spinning nozzle. When a composition containing predetermined amounts of the polyvinyl alcohol A and the polyvinyl alcohol B is to be prepared, the composition containing both polyvinyl alcohols may be taken out of a melt mixer and then melt spun, or the composition may be melt mixed in a melt spinning machine and spun as it is without being taken out. When polyvinyl alcohol A and polyvinyl alcohol B are melted and extruded separately, the contents of polyvinyl alcohol A and polyvinyl alcohol B in the polyvinyl alcohol fibers can be adjusted to predetermined amounts by controlling the extrusion amount, etc.

[0038] In the case of melt spinning, the polyvinyl alcohol melts at a temperature higher than its melting temperature and lower than its decomposition temperature. It is preferable that the polyvinyl alcohol is melted at a temperature that is at least 10° C. higher than the melting temperature of the polyvinyl alcohol and at least 20° C. lower than the decomposition temperature. In the present invention, it is sufficient that the polyvinyl alcohol A and the polyvinyl alcohol B are melted at a temperature range that is higher than the higher melting temperature and lower than the lower decomposition temperature of the polyvinyl alcohol A and the polyvinyl alcohol B, and it is preferable that the polyvinyl alcohol A and the polyvinyl alcohol B are melted at a temperature range of 220°C or higher and 240°C or lower.

[0039] The temperature of the spinning nozzle when it is discharged from the spinning nozzle is at least 10° C. higher than the melting point of polyvinyl alcohol. In the present invention, the polyvinyl alcohol A and the polyvinyl alcohol B may be discharged at a temperature higher than the higher melting temperature and lower than a temperature 10°C or higher than the melting temperature, and it is preferable to discharge the polyvinyl alcohol A and the polyvinyl alcohol B at a temperature in the range of 230°C to 240°C.

[0040] The filaments discharged from the spinning nozzle may be taken up as they are without being stretched, or may be subsequently stretched. The stretching is carried out at a temperature equal to or higher than the glass transition point (Tg) of polyvinyl alcohol, and is carried out at a temperature higher than the higher Tg of polyvinyl alcohol A and polyvinyl alcohol B. From the viewpoint of the strength of the resulting fiber, the draw ratio is preferably 2 times or more, and more preferably 3 times or more.

[0041] The stretching is usually carried out by hot stretching, and the hot stretching may be carried out using any of hot air, a hot plate, a hot roller, a water bath, or the like. The stretching temperature is usually about 70 to 100°C. In addition, non-contact devices such as a heating tube are used. When using a heater for heat stretching, the temperature is even higher, about 110 to 150℃. It is preferable to set the temperature condition at 100°C.

[0042] In the case of the melt spinning method, the cross section of the fiber can be circular, hollow, or of an irregular cross section depending on the shape of the spinning nozzle. From the viewpoint of processability in fiberization and weaving, a circular shape is preferred.

[0043] The fineness of the single fiber of the polyvinyl alcohol fiber of the present invention is not particularly limited, but the fineness is preferably 0.01 dtex or more, more preferably 0.1 dtex or more, and even more preferably 0.2 dtex or more. The fineness is preferably 1000 dtex or less, more preferably 100 dtex or less, and even more preferably 10 dtex or less. Finenesses of 0.1 to 1000 dtex, particularly 0.2 to 100 dtex, and further 0.5 to 10 dtex can be widely used. Also Polyvinyl alcohol fiber There is no particular limitation on the cross-sectional shape of the fibers, but simple, substantially circular fibers are preferred over complicated shapes in terms of water dispersibility, product uniformity, and the like.

[0044] The polyvinyl alcohol fiber of the present invention is excellent in various properties such as mechanical properties such as strength, and is also excellent in water solubility, so that any fiber structure can be obtained by using the fiber. For example, it can be processed into fiber structures such as cut fibers, filaments, spun yarns, woven and knitted fabrics or dry nonwoven fabrics, ropes, string-like materials, etc. Furthermore, such fabrics may be molded into a desired shape. In this case, other fibers may be used in combination, but from the viewpoint of efficiently obtaining the effects of the present invention, it is preferable that 40% by mass or more, more preferably 60% by mass or more, particularly 80 to 100% by mass of the fiber structure is the polyvinyl alcohol fiber of the present invention. Note that other fibers include water-soluble fibers, water-insoluble fibers, and polyvinyl alcohol fibers other than those of the present invention. Furthermore, it may be used in combination with other materials such as metals or films.

[0045] The fiber length of the polyvinyl alcohol fiber of the present invention may be appropriately set depending on the application, but when it is processed into a short fiber nonwoven fabric such as paper or spun yarn, the fiber length is preferably about 1 to 100 mm. The obtained short fibers can be made into a nonwoven fabric by a dry method. On the other hand, when the polyvinyl alcohol fiber of the present invention is used as a long fiber to form a long-fiber nonwoven fabric, the fiber length may be several meters to several hundreds of meters. As a method for producing a long-fiber nonwoven fabric, the long fibers obtained by the above method are spread and deposited on a collecting surface to form a nonwoven fabric web, and the nonwoven fabric can be produced by a spunbonding method or a meltblowing method in which the web is partially compressed and wound up.

[0046] The polyvinyl alcohol fiber and the fiber structure of the present invention can be used for various purposes, but taking advantage of the characteristics of water solubility and secondary processability, they can be particularly suitably used as a processing aid for textile products and as a base fabric for embroidery of chemical lace.

[0047] When the fiber structure of the present invention is used as a base fabric for embroidery, it is preferable to use at least a cloth from the viewpoint of mechanical properties. 2 Above 100g / m 2 From the viewpoint of production efficiency, it is preferable that the thickness is 300 g / m or more. 2 Below that, 200g / m 2 From the viewpoint of mechanical properties, the breaking length of the fabric is preferably 2.5 N / 25 mm or more, and more preferably 2.6 N / 25 mm or more.

[0048] The method for producing such a fabric is not particularly limited, but it is preferable to produce a dry nonwoven fabric by treating a fiber web in terms of feel, flexibility, etc. Polyvinyl alcohol fiber Suitable examples of such a method include opening filaments or the like by the repulsive action caused by frictional charging, or opening crimped or cut staples with a card or the like to form a web, which is then thermally bonded in a hot air dryer at 150°C to 200°C.

[0049] Another method for producing a dry nonwoven fabric is, for example, a method of producing a nonwoven fabric by entangling processing using a needle punching process. In this case, a known needle punching machine is used, and conditions such as needle density, needle type, needle depth, and number of punches can be adjusted according to the properties of the fibers to produce a dry nonwoven fabric with excellent strength and flexibility. If necessary, entangling may be optimized using multiple needle punching machines. EXAMPLES

[0050] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0051] [Ethylene modification rate] The ethylene-vinyl ester copolymer was purified by reprecipitation with n-hexane / acetone three times or more, and then dried under reduced pressure at 80°C for three days to prepare the ethylene-vinyl ester copolymer for analysis. The obtained polymer was dissolved in DMSO-d6 and analyzed by a 500 MHz spectrometer. 1 Measurements were performed using H-NMR at 80° C. The ethylene modification rate was calculated using the peaks attributable to the main chain methylene of the vinyl ester in the range of 4.7 to 5.2 ppm and the peaks attributable to ethylene and the vinyl ester in the range of 0.8 to 1.6 ppm.

[0052] [Degree of polymerization] In accordance with JIS K 6726-1994, it was calculated from the measured value of the limiting viscosity [η] of an aqueous solution at 30° C. using the following formula (7), where P is the average degree of polymerization of polyvinyl alcohol. P = ([η] × 10 4 / 8.29) (1 / 0.62) (7)

[0053] [Saponification degree (mol%)] Measurement was performed according to JIS K 6726-1994.

[0054] [Fiber strength (cN / dtex)] The tensile strength of the fibers was measured according to JIS L 1013.

[0055] [Water melting temperature of fiber (℃)] A load of 2 mg / dtex was applied to the end of a 100 mm long fiber, which was then held in water with the load facing down. The water temperature was raised at a rate of 2°C / min, and the temperature was measured at the point when the fiber melted and the load dropped. The meltdown temperature in water is the meltdown temperature for the fiber diameter at the time of measurement. In the case of long fiber nonwoven fabric, the nonwoven fabric was cut to a length of 50 mm and a width of 50 mm, and the water temperature was raised at a rate of 2°C / min while stirring in water. The temperature at the point when the nonwoven fabric disintegrated and dispersed in the water was measured.

[0056] [Secondary processability of fibers] The fibers are formed into a web and heat-treated at 160°C for 1 minute using a hot air dryer to produce a web with a basis weight of 100g / m 2 In this case, those that could not be processed into nonwoven fabric were marked with an ×, those with a breaking strength of 2.5N / 25mm or less were marked with an ◯, and those with a breaking strength of over 2.5N / 25mm were marked with an ⊚. In the case of long fiber nonwoven fabrics, those for which no nonwoven fabric was obtained were rated as x, and those with a basis weight of about 40 g / m 2 The nonwoven fabrics obtained were rated as follows: those with a breaking strength of 3.0 N / 25 mm or less were rated as ◯, and those with a breaking strength exceeding 3.0 N / 25 mm were rated as ⊚.

[0057] [Thickness of nonwoven fabric (mm)] The thickness of the long fiber nonwoven fabric was measured in accordance with JIS L 1913.

[0058] [Example 1] A polyvinyl alcohol composition was prepared by mixing 90% by mass of polyvinyl alcohol having a saponification degree of 98.5 mol%, a polymerization degree of 380, and an ethylene modification rate of 8 mol% as polyvinyl alcohol A and 10% by mass of polyvinyl alcohol having a saponification degree of 88 mol% and a polymerization degree of 300 as polyvinyl alcohol B. The obtained polyvinyl alcohol composition was discharged from a round hole nozzle at 230 ° C. using a melt spinning machine and spun. The spun raw yarn was dry-heat stretched at a magnification of 2.7 times using a hot air oven to obtain a multifilament of 50 dtex / 24 filaments. The spinnability was good with no breaks in the yarn for 6 hours, and the stretchability was good with no problems without any single yarn breakage or sticking.

[0059] [Examples 2 to 9] Polyvinyl alcohol fibers were obtained in the same manner as in Example 1, except that the ratio of polyvinyl alcohol A to polyvinyl alcohol B was changed as shown in Table 1. The results are shown in Table 1.

[0060] [Example 10] Polyvinyl alcohol fibers were obtained in the same manner as in Example 1, except that a polyvinyl alcohol composition was prepared by mixing 70 mass% of polyvinyl alcohol having a saponification degree of 98.5 mol%, a polymerization degree of 380, and an ethylene modification rate of 8 mol% as polyvinyl alcohol A and 30 mass% of polyvinyl alcohol having a saponification degree of 80 mol% and a polymerization degree of 300 as polyvinyl alcohol B. The results are shown in Table 1.

[0061] [Example 11] The polyvinyl alcohol composition described in Example 1 was used and extruded from a round-hole nozzle at 260°C using a melt-blowing machine to give a mass of about 40 g / m 2 The results are shown in Table 2.

[0062] [Examples 12 and 13] A long-fiber nonwoven fabric was obtained in the same manner as in Example 11, except that the ratio of polyvinyl alcohol A to polyvinyl alcohol B was changed as shown in Table 2. The results are shown in Table 2.

[0063] [Example 14] A long-fiber nonwoven fabric was obtained in the same manner as in Example 11, except for using the polyvinyl alcohol composition described in Example 10. The results are shown in Table 2.

[0064] [Comparative Example 1] Polyvinyl alcohol fibers were obtained in the same manner as in Example 1, except that polyvinyl alcohol A was used instead of polyvinyl alcohol B used in Example 1. The results are shown in Table 1. The melting point of the obtained fibers was high, and it was impossible to process them into a nonwoven fabric.

[0065] [Comparative Example 2] Polyvinyl alcohol fibers were obtained in the same manner as in Example 1, except that polyvinyl alcohol A used in Example 1 was not used and only polyvinyl alcohol B was used. The results are shown in Table 1. The strength of the obtained fibers was low and it was impossible to process them into a nonwoven fabric.

[0066] [Comparative Example 3] A polyvinyl alcohol fiber was obtained in the same manner as in Example 1, except that a polyvinyl alcohol having a saponification degree of 74 mol % and a polymerization degree of 500 was used as polyvinyl alcohol B instead of the polyvinyl alcohol B used in Example 1, and the ratio of polyvinyl alcohol A to polyvinyl alcohol B was changed as shown in Table 1. The results are shown in Table 1. The obtained fiber had a high water melt-cutting temperature.

[0067] [Comparative Example 4] Instead of using the polyvinyl alcohol A used in Example 1, polyvinyl alcohol with a saponification degree of 88 mol% and a polymerization degree of 1700 was used as polyvinyl alcohol B, and only polyvinyl alcohol B was dissolved in DMSO at 90 ° C. to a concentration of 20 mass % to prepare a stock solution. This stock solution was passed through a nozzle with 3000 holes and a hole diameter of 0.08 mmφ, and wet-spun at a bath draft of 0.5 times in a solidification bath at 5 ° C. with a composition of methanol / DMSO in a mass ratio of 7 / 3. DMSO was extracted with methanol at 20 ° C. while applying wet stretching at 3 times. Thereafter, the product was immersed in a bath containing 10 mass % of glycerin as an additive, 45 mass % of methyl isobutyl ketone (hereinafter abbreviated as MIBK), and the remainder of methanol so that the amount of glycerin applied was 10 mass % relative to the polyvinyl alcohol in the obtained spinning raw yarn, and dried at 150 ° C. to obtain a spinning raw yarn. The spun raw yarn was hot-drawn at 160°C to a total draw ratio of 6 and then wound up. The resulting fiber had a high melting point and could not be processed into a nonwoven fabric. The results are shown in Table 1.

[0068] [Comparative Example 5] Polyvinyl alcohol fibers were obtained in the same manner as in Example 3, except that polyvinyl alcohol A having a saponification degree of 98 mol% and a polymerization degree of 500 was used instead of the polyvinyl alcohol A used in Example 1. Since the polyvinyl alcohol A was not ethylene-modified, the melting point of the obtained fibers was high, and it was difficult to process them into a nonwoven fabric. The results are shown in Table 1.

[0069] [Table 1]

[0070] [Comparative Example 6] A long-fiber nonwoven fabric was obtained in the same manner as in Example 11, except that polyvinyl alcohol A was used instead of polyvinyl alcohol B used in Example 1. The results are shown in Table 2.

[0071] [Comparative Example 7] A long-fiber nonwoven fabric was obtained in the same manner as in Example 11, except that a polyvinyl alcohol having a saponification degree of 74 mol % and a polymerization degree of 500 was used as polyvinyl alcohol B instead of polyvinyl alcohol B used in Example 1, and the ratio of polyvinyl alcohol A to polyvinyl alcohol B was changed as shown in Table 2. The results are shown in Table 2.

[0072] [Table 2]

[0073] As is clear from Table 1, the polyvinyl alcohol fiber of the present invention is excellent in water solubility and strength. It is also excellent in secondary processability such as nonwoven fabric processing. Furthermore, as is clear from Table 2, the polyvinyl alcohol fiber of the present invention is excellent in the possibility of forming a long-fiber nonwoven fabric by melt-blowing or the like, and the obtained long-fiber nonwoven fabric is also excellent in water solubility and mechanical properties. Therefore, the fiber structure at least partially containing the vinyl alcohol fiber of the present invention can be suitably used as a water-soluble fiber or a water-soluble nonwoven fabric.

Claims

1. A polyvinyl alcohol fiber comprising polyvinyl alcohol A having a saponification degree of 90 mol % or more and an ethylene modification rate of 4 to 15 mol %, and polyvinyl alcohol B having a saponification degree satisfying the following formula (1): ０＜α Ａ －α Ｂ ≦２０ （１） In the formula (1), α Ａ is the degree of saponification of the polyvinyl alcohol A, α Ｂ represents the degree of saponification of the polyvinyl alcohol B.

2. 2. The polyvinyl alcohol fiber according to claim 1, wherein the difference between the melting point and the decomposition temperature is 40° C. or more.

3. 3. The polyvinyl alcohol fiber according to claim 1, wherein the degree of polymerization of the polyvinyl alcohol A is from 200 to 600.

4. 3. The polyvinyl alcohol fiber according to claim 1, wherein the degree of polymerization of the polyvinyl alcohol B is from 200 to 600.

5. 3. The polyvinyl alcohol fiber according to claim 1, wherein the polyvinyl alcohol B has a degree of saponification of 80 mol % or more.

6. 3. The polyvinyl alcohol fiber according to claim 1, wherein the polyvinyl alcohol B is contained in an amount of 15% by mass or more and 95% by mass or less, where the total mass of the polyvinyl alcohol A and the polyvinyl alcohol B is 100% by mass.

7. 3. The polyvinyl alcohol fiber according to claim 1, which has a melt-cutting temperature in water of 70° C. or lower.

8. 3. The method for producing a polyvinyl alcohol fiber according to claim 1 or 2, comprising melting a composition containing polyvinyl alcohol A having a saponification degree of 90 mol % or more and an ethylene modification rate of 4 to 15 mol %, and polyvinyl alcohol B having a saponification degree satisfying the following formula (2), discharging the composition from a nozzle, and cooling the composition: ０＜α Ａ －α Ｂ ≦２０ （２） In the formula (2), α Ａ is the degree of saponification of the polyvinyl alcohol A, α Ｂ represents the degree of saponification of the polyvinyl alcohol B.

9. 3. A long-fiber nonwoven fabric comprising the polyvinyl alcohol fiber according to claim 1 or 2.

10. A method for producing a long-fiber nonwoven fabric, comprising depositing the polyvinyl alcohol fibers according to claim 1 or 2 to form a nonwoven fabric web.

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