JP2013119683A - Water-soluble fiber and nonwoven fabric - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water-soluble fiber that is excellent in mechanical strength and suitable for a nonwoven fabric for soil improvement and vegetation, and a nonwoven fabric using the same.SOLUTION: The water-soluble fiber contains an alkyl modified vinyl alcohol-based polymer. The alkyl modified vinyl alcohol-based polymer comprises a monomer unit (a) represented by the general formula (I), the viscosity average polymerization degree is 1,000 or more to 5,000 or less, the saponification degree is 80 mol% or more and 99.99 mol% or less, and the monomer unit (a) is contained in a ratio of 0.05 mol% or more and 5 mol% or less. (In the formula (I), Rrepresents an 8-29C linear or branched alkyl group. Rrepresents a hydrogen atom or a 1-8C alkyl group.)

Description

  The present invention relates to a water-soluble fiber and a nonwoven fabric using the same.

  Vinyl alcohol polymers (hereinafter also referred to as “PVA”) are water-soluble, and PVA fibers are used for nonwoven materials such as chemical lace and soil-improved vegetation sheets. PVA fibers are required to have mechanical strength and chemical resistance that can withstand processing into a nonwoven fabric or the like. In order to meet such a demand, for example, a PVA fiber (Japanese Patent Laid-Open No. 2005-194666) impregnated with a compound having an ionic group has been developed.

  However, the PVA fibers are intended for use in chemical lace fabrics and the like, and higher mechanical strength is required for use in soil-improved vegetation sheets. In addition, the soil improvement vegetation sheet suppresses the outflow of contained soil improvement agents and fertilizers, and allows the soil improvement agent and the like to exist in or near the sheet for a long period of time and has excellent adhesion to the ground surface. Is desired.

JP-A-2005-194666

  The present invention has been made based on the circumstances as described above, and has an object to provide a water-soluble fiber excellent in mechanical strength and the like and suitable for a nonwoven fabric for soil improvement vegetation, and a nonwoven fabric using the same. And

（式（Ｉ）中、Ｒ^１は炭素数８〜２９の直鎖状又は分岐状アルキル基を表す。Ｒ^２は水素原子又は炭素数１〜８のアルキル基を表す。） The invention made to solve the above problems is
Containing an alkyl-modified vinyl alcohol polymer,
The alkyl-modified vinyl alcohol polymer includes a monomer unit (a) represented by the following general formula (I), has a viscosity average polymerization degree of 1,000 to 5,000, and a saponification degree of 80 mol%. The water-soluble fiber has a content of the monomer unit (a) of 0.05 mol% or more and 5 mol% or less.

(In formula (I), R ¹ represents a linear or branched alkyl group having 8 to 29 carbon atoms. R ² represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms.)

  The water-soluble fiber contains alkyl-modified PVA containing the monomer unit (a), and has a high mechanical strength due to the long chain alkyl group of the alkyl-modified PVA forming an association state. it can. Moreover, since the said alkyl modified PVA has such a monomer unit, it is excellent in the uniform miscibility with the viscosity at the time of setting it as aqueous solution, water retention, a soil improvement agent, etc. Therefore, when the water-soluble fiber is used for a nonwoven fabric for soil improvement vegetation, when the fiber is melted, the PVA, the soil improvement agent, etc. are unlikely to flow out due to rainfall, etc. it can. Moreover, since the viscosity of aqueous solution is high, this nonwoven fabric for soil improvement vegetation is excellent in adhesiveness with the ground surface. Therefore, the said water-soluble fiber can be used suitably for the nonwoven fabric for soil improvement vegetation.

  The 4% by weight aqueous solution viscosity of the water-soluble fiber is preferably 50,000 mPa · s or more. Thus, when the viscosity of aqueous solution is high, the outflow of the said PVA, a soil improvement agent, etc. at the time of using for the nonwoven fabric for soil improvement vegetation can be suppressed more.

  The tensile strength of the water-soluble fiber is preferably 3.0 cN / dtex or more and 7.5 cN / dtex or less. By having such tensile strength, the mechanical properties of the water-soluble fiber can be further enhanced.

  The nonwoven fabric of this invention is a nonwoven fabric formed from the said water-soluble fiber. The nonwoven fabric is formed from PVA which has excellent mechanical strength, viscosity when it is used as an aqueous solution, water retention, and uniform miscibility with a soil improver. Suitable for vegetation.

  As described above, since the water-soluble fiber of the present invention contains alkyl-modified PVA which is excellent in mechanical strength and excellent in viscosity when used as an aqueous solution, it can be suitably used for nonwoven fabrics for soil improvement vegetation. .

  Hereinafter, embodiments of the water-soluble fiber and the nonwoven fabric of the present invention will be described in detail.

<Water-soluble fiber>
The water-soluble fiber of the present invention contains a specific alkyl-modified PVA and can further contain other components. Hereinafter, each component will be described.

(Alkyl-modified PVA)
The alkyl-modified PVA contains a monomer unit (a) represented by the following general formula (I). That is, the alkyl-modified PVA is a copolymer of the monomer unit (a) and a vinyl alcohol monomer unit (—CH ₂ —CHOH—), and further has other monomer units. It may be. However, in order to effectively express the action of the monomer unit (a), the alkyl-modified PVA is a co-polymer consisting only of the monomer unit (a), the vinyl alcohol unit and the remaining vinyl ester unit. A polymer is preferred.

In formula (I), R ¹ represents a linear or branched alkyl group having 8 to 29 carbon atoms. R ² represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms. The R ¹ and R ² may have a substituent such as a halogen atom as long as the effect of the present invention is not impaired, but preferably does not have these substituents. .

The linear or branched alkyl group represented by R ¹ has 8 to 29 carbon atoms, preferably 10 to 28, more preferably 12 to 27, and 15 to 26. More preferably, 17 or more and 24 or less are particularly preferable. When R ¹ is such a long-chain alkyl group, an appropriate interaction between the alkyl groups is exhibited, and high viscosity and water retention can be exhibited when an aqueous solution is used. When the number of carbon atoms is less than 8, the interaction between the alkyl groups in the alkyl-modified PVA does not appear, and thus the above properties cannot be exhibited. On the contrary, when this carbon number exceeds 29, the water solubility etc. of the said alkyl-modified PVA fall.

R ² is a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and a hydrogen atom or a methyl group is preferable from the viewpoint of ease of synthesis.

  The content of the monomer unit (a) in the alkyl-modified PVA is 0.05 mol% or more and 5 mol% or less. Further, the content is preferably 0.1 mol% or more, and more preferably 0.2 mol% or more. Further, the content is preferably 2 mol% or less, and more preferably 1 mol% or less. In addition, the content rate of this monomer unit (a) is a content rate of the monomer unit (a) represented by the said Formula (I) which occupies for all the structural units which comprise the alkyl-modified PVA. When the alkyl-modified PVA does not contain any other alkyl-modified monomer unit other than the monomer unit (a) represented by the above formula (I), the content of the monomer unit (a) Is the so-called alkyl modification rate.

  When the content of the monomer unit (a) exceeds 5 mol%, the proportion of hydrophobic groups contained in one molecule of the alkyl-modified PVA increases, and the water solubility and the like of the alkyl-modified PVA decreases. On the other hand, when the content of the monomer unit (a) is less than 0.05 mol%, the water content of the alkyl-modified PVA is excellent, but the number of alkyl units contained in the alkyl-modified PVA is small. In addition, physical properties based on alkyl modification such as high viscosity when used as an aqueous solution are not sufficiently exhibited.

The content of the monomer unit (a) may be obtained from the alkyl-modified PVA or may be obtained from an alkyl-modified vinyl ester polymer that is a precursor thereof, and both can be obtained from proton NMR. . For example, when obtaining from an alkyl-modified vinyl ester polymer, specifically, after reprecipitation and purification of the alkyl-modified vinyl ester polymer with n-hexane / acetone three or more times sufficiently, under reduced pressure at 50 ° C. Dry for 2 days to prepare a sample for analysis. This sample is dissolved in CDCl ₃ and measured at room temperature using proton NMR.

In this case, for example, when the alkyl-modified monomer unit other than the monomer unit (a) is not included, R ¹ is linear, and R ² is a hydrogen atom, the calculation is performed by the following method. it can. That is, the peak α (4.7 to 5.2 ppm) derived from the main chain methine of the alkyl-modified vinyl ester polymer and the peak β (0.8 to 1.0 ppm) derived from the terminal methyl group of the alkyl group R ¹ From the above, the content S of the monomer unit (a) is calculated using the following formula.
S (mol%)
= {(Number of protons of β / 3) / (number of protons of α + (number of protons of β / 3))} × 100

  The viscosity average polymerization degree of the alkyl-modified PVA is 1,000 or more and 5,000 or less. The viscosity average degree of polymerization may be simply referred to as the degree of polymerization. If the degree of polymerization exceeds 5,000, water solubility is lowered, and polymerization becomes difficult, which is not practical. On the contrary, when the degree of polymerization is less than 1,000, the mechanical strength and the like are not sufficiently exhibited.

This viscosity average degree of polymerization (P) is measured according to JIS-K6726. That is, after re-saponifying and purifying the alkyl-modified PVA, it is obtained by the following formula from the intrinsic viscosity [η] (unit: deciliter / g) measured in water at 30 ° C.
P = ([η] × 10 ³ /8.29) ^{(1 / 0.62)}

  The saponification degree of the alkyl-modified PVA is from 80 mol% to 99.99 mol%, preferably from 88 mol% to 99.9 mol%, more preferably from 94 mol% to 99.9 mol%.

  When this saponification degree is less than 80 mol%, the water solubility etc. of the said alkyl modified PVA fall, and the viscosity at the time of using aqueous solution also falls. On the contrary, if the degree of saponification exceeds 99.99 mol%, production of alkyl-modified PVA becomes difficult, which is not practical. The saponification degree of the alkyl-modified PVA is a value that can be measured according to JIS-K6726.

  As content of the said alkyl-modified PVA in the said water-soluble fiber, 30 mass% or more is preferable, 60 mass% or more is more preferable, 90 mass% or more is further more preferable, 96 mass% or more is especially preferable. When this content is less than 30% by mass, the effect of the alkyl-modified PVA may not be sufficiently exhibited.

The water-soluble fiber contains the alkyl-modified PVA, and the alkyl-modified PVA is, as described above, due to the presence of the hydrophobic R ¹ and the hydrophilic amide bond of the monomer unit (a). High water solubility and mechanical strength. In addition, due to the presence of the hydrophobic R ^{1 and the} like, the water-soluble fiber is excellent in viscosity when formed into an aqueous solution, water retention, and uniform miscibility with a soil conditioner. Therefore, when the water-soluble fiber is used in a nonwoven fabric for soil improvement vegetation, when the fiber is melted, the alkyl-modified PVA and the soil improvement agent do not easily flow out due to rain or the like and stay in the vicinity of the nonwoven fabric for a long time. Can do. Moreover, since the said alkyl-modified PVA aqueous solution has high viscosity, this nonwoven fabric for soil improvement vegetation is excellent in adhesiveness with the ground surface. Therefore, the said water-soluble fiber can be used suitably for the nonwoven fabric for soil improvement vegetation.

(Method for producing alkyl-modified PVA)
The method for producing the alkyl-modified PVA is not particularly limited, but the alkyl-modified vinyl ester obtained by copolymerizing an unsaturated monomer represented by the following general formula (II) with a vinyl ester monomer. A method of saponifying the polymer is preferred. Here, the above copolymerization is preferably performed in an alcohol solvent or without a solvent.

In the formula (II), the definitions of R ¹ and R ² are the same as those in the above formula (I).

  Specific examples of the unsaturated monomer represented by the above formula (II) include N-octylacrylamide, N-decylacrylamide, N-dodecylacrylamide, N-octadecylacrylamide, N-hexacosylacrylamide, and N-octyl. Examples include methacrylamide, N-decyl methacrylamide, N-dodecyl methacrylamide, N-octadecyl methacrylamide, N-hexacosyl methacrylamide and the like. Among these, N-octadecylacrylamide, N-octylmethacrylamide, N-decylmethacrylamide, N-dodecylmethacrylamide, N-octadecylmethacrylamide, and N-hexacosylmethacrylamide are preferable, and N-octadecylacrylamide, N -Dodecyl methacrylamide and N-octadecyl methacrylamide are more preferable, and N-octadecyl acrylamide and N-octadecyl methacrylamide are more preferable.

  Examples of the vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatate, vinyl caproate, vinyl caprylate, vinyl laurate, and vinyl palmitate. , Vinyl stearate, vinyl oleate, vinyl benzoate and the like, among which vinyl acetate is preferred.

When the unsaturated monomer represented by the general formula (II) and the vinyl ester monomer are copolymerized, other monomers may be copolymerized within a range not impairing the gist of the present invention. Examples of monomers that can be used include:
Α-olefins such as ethylene, propylene, n-butene, isobutylene;
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, 2,3-diacetoxy-1-vinyloxypropane;
Nitriles such as acrylonitrile and methacrylonitrile;
Vinyl halides such as vinyl chloride and vinyl fluoride;
Vinylidene halides such as vinylidene chloride and vinylidene fluoride;
Allyl compounds such as allyl acetate, 2,3-diacetoxy-1-allyloxypropane, allyl chloride;
Vinylsilyl compounds such as vinyltrimethoxysilane;
And isopropenyl acetate.

In addition, in the copolymerization of the unsaturated monomer represented by the general formula (II) and the vinyl ester monomer, the purpose of the present invention is to adjust the degree of polymerization of the obtained copolymer. Copolymerization may be carried out in the presence of a chain transfer agent within a range that does not impair. As this chain transfer agent,
Aldehydes such as acetaldehyde and propionaldehyde;
Ketones such as acetone and methyl ethyl ketone;
Mercaptans such as 2-hydroxyethanethiol;
Halogenated hydrocarbons such as trichlorethylene and perchlorethylene;
Examples thereof include phosphinic acid salts such as sodium phosphinate monohydrate, among which aldehydes and ketones are preferably used.

  The amount of the chain transfer agent added can be determined according to the chain transfer constant of the chain transfer agent to be added and the degree of polymerization of the target alkyl-modified vinyl ester polymer. 0.1-10 mass% is preferable with respect to it.

  The temperature employed when copolymerizing the unsaturated monomer represented by the general formula (II) and the vinyl ester monomer is preferably 0 to 200 ° C, more preferably 30 to 140 ° C. When the copolymerization temperature is lower than 0 ° C., it is difficult to obtain a sufficient polymerization rate. Moreover, when the temperature which superposes | polymerizes is higher than 200 degreeC, it is difficult to obtain the alkyl modified PVA which satisfies the content rate of the monomer unit (a) prescribed | regulated by this invention. As a method for controlling the temperature employed in the copolymerization to 0 to 200 ° C., for example, by controlling the polymerization rate, the heat generated by the polymerization is balanced with the heat released from the surface of the reactor. Examples thereof include a method and a method of controlling by an external jacket using an appropriate heat medium, but the latter method is preferable from the viewpoint of safety.

  The polymerization method employed for the copolymerization of the unsaturated monomer represented by the general formula (II) and the vinyl ester monomer is batch polymerization, semi-batch polymerization, continuous polymerization, or semi-continuous polymerization. Either of these may be used. As the polymerization method, any known method such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, or an emulsion polymerization method can be employed. Among these, a bulk polymerization method or a solution polymerization method in which polymerization is performed in a solvent-free or alcohol-based solvent is preferably employed, and an emulsion polymerization method is employed for the purpose of producing a copolymer having a high degree of polymerization. .

  Examples of the alcohol solvent include methanol, ethanol, n-propanol, and the like, but are not limited thereto. Moreover, these solvents can be used by mixing two or more kinds.

  As the initiator used for copolymerization, conventionally known azo initiators, peroxide initiators, redox initiators and the like are appropriately selected according to the polymerization method. As the azo initiator, 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis (4-methoxy-2,4- Dimethyl valeronitrile) and the like, and peroxide initiators include perisopropyl compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate and diethoxyethyl peroxydicarbonate; t-butyl Perester compounds such as peroxyneodecanate, α-cumylperoxyneodecanate, t-butylperoxydecanate; acetylcyclohexylsulfonyl peroxide; 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate, etc. Is mentioned. Furthermore, the initiator can be combined with potassium persulfate, ammonium persulfate, hydrogen peroxide, or the like to form an initiator. Moreover, as a redox-type initiator, what combined said peroxide and reducing agents, such as sodium hydrogen sulfite, sodium hydrogencarbonate, tartaric acid, L-ascorbic acid, Rongalite, is mentioned.

  In addition, when copolymerization of the unsaturated monomer represented by the general formula (II) and the vinyl ester monomer is performed at a high temperature, the coloring of the alkyl-modified PVA caused by the decomposition of the vinyl ester monomer Etc. may be seen. In this case, an antioxidant such as tartaric acid may be added to the polymerization system in an amount of about 1 to 100 ppm based on the vinyl ester monomer for the purpose of preventing coloring.

  The saponification reaction of the alkyl-modified vinyl ester polymer obtained by the above copolymerization is publicly known using a basic catalyst such as sodium hydroxide, potassium hydroxide or sodium methoxide or an acidic catalyst such as p-toluenesulfonic acid. An alcoholysis reaction or a hydrolysis reaction can be applied. Examples of the solvent that can be used in this reaction include alcohols such as methanol and ethanol; esters such as methyl acetate and ethyl acetate; ketones such as acetone and methyl ethyl ketone; aromatic hydrocarbons such as benzene and toluene; These can be used alone or in combination of two or more. Among these, it is simple and preferable to perform the saponification reaction using methanol or a methanol / methyl acetate mixed solution as a solvent and sodium hydroxide as a catalyst.

(Other ingredients)
The said water-soluble fiber can contain another component in the range which does not impair the objective and effect of this invention. Other components include stabilizers such as copper compounds, colorants, UV absorbers, light stabilizers, antioxidants, antistatic agents, flame retardants, plasticizers, lubricants, crystallization rate retarders, and other Examples thereof include resins such as PVA. In particular, when an organic stabilizer such as hindered phenol, a copper halide compound such as copper iodide, or an alkali metal halide compound such as potassium iodide is added as a heat stabilizer, the melt retention stability during fiberization can be improved. Since it improves, it is preferable.

  Further, the water-soluble fiber can contain fine particles having an average particle diameter of 0.01 μm or more and 5 μm or less, preferably 0.02 μm or more and 1 μm or less, as necessary. The water-soluble fiber can improve spinnability and stretchability by containing such fine particles. The content of the fine particles can be, for example, 0.05% by mass or more and 10% by mass or less. The kind of fine particles is not particularly limited, and examples thereof include inert fine particles such as silica, alumina, titanium oxide, calcium carbonate, and barium sulfate. These may be used alone or in combination of two or more.

(Production method)
The method for producing the water-soluble fiber is not particularly limited, and spinning of known PVA fibers such as a wet spinning method, a dry spinning method, a dry wet spinning method, a gel spinning method, a melt spinning method, etc., using the alkyl-modified PVA as a material. It can be obtained by a method.

  The water-soluble fiber preferably has a total draw ratio of 3 times or more. If the draw ratio is less than 3, the mechanical properties of the fiber may be lowered. In addition, the draw ratio here is the product of the wet draw in the solidification bath before drying and the draw ratio after drying. For example, when the wet stretching is 3 times and the subsequent stretching is 2 times, the total stretching ratio is 6 times.

(Quality, usage, etc.)
As a 4 mass% aqueous solution viscosity of the said water-soluble fiber, 50,000 mPa * s or more is preferable and 100,000 mPa * s or more is more preferable. Thus, when the viscosity of aqueous solution is high, the outflow of the said PVA, a soil improvement agent, etc. at the time of using for the nonwoven fabric for soil improvement vegetation etc. can be suppressed more, for example. This aqueous solution viscosity is a value measured using a B-type viscometer under the conditions of a rotor speed of 6 rpm and a temperature of 20 ° C.

  The tensile strength of the water-soluble fiber is preferably 3.0 cN / dtex or more and 7.5 cN / dtex or less, more preferably 5.0 cN / dtex or more and 7.5 cN / dtex or less. By having such tensile strength, the mechanical properties of the water-soluble fiber can be enhanced. When the tensile strength is less than the above lower limit, the mechanical strength may be insufficient. On the contrary, when the tensile strength exceeds the above upper limit, the handleability may be lowered. This tensile strength is a value measured according to JIS-L1013.

  The fineness of the water-soluble fiber is not particularly limited, and can be, for example, 0.1 to 10,000 dtex, preferably 1 to 1,000 dtex.

  The water-soluble PVA fibers can be used in the form of, for example, cut fibers, filaments, spun yarns, strings, ropes, fibrils, and the like. Moreover, a nonwoven fabric, a knitted fabric, etc. can also be produced using the said fiber, for example. From the viewpoint of applications that require water-solubility, it is preferable to use it as a non-woven fabric for chemical lace base fabric or soil improvement vegetation.

<Nonwoven fabric>
The nonwoven fabric is formed from the water-soluble fiber. A conventionally well-known method is used for the manufacturing method of the said nonwoven fabric. Specifically, the needle punch method, emboss method, foam bond method, heating method (embossing, hot air, mold molding, etc.) mixed with heat-bonding fibers, binder bonding method, hydroentanglement method, melt blown method and spun bond method Examples thereof include bonding with a manufactured nonwoven fabric and combinations thereof. These can be appropriately selected according to the desired quality of the nonwoven fabric.

  The content of the water-soluble PVA fiber in the nonwoven fabric is preferably 5% by mass or more and 100% by mass or less, more preferably 30% by mass or more, and still more preferably 60% by mass or more. When the content is less than 5% by mass, it becomes difficult to use in applications that require water-soluble properties. In addition, since the water-soluble fiber has fiber properties such as high mechanical strength, it can be embossed or needle punched using the water-soluble fiber as a 100% by mass nonwoven fabric. . However, you may use together with another fiber according to the target quality and cost.

  Examples of other fibers include natural fibers such as pulp and cotton, regenerated fibers such as rayon and cupra, semi-synthetic fibers such as acetate and promix, polyester fibers, acrylic fibers, polyamide fibers (nylon, aramid, etc.), Examples thereof include synthetic fibers such as other PVA fibers. In the said nonwoven fabric, the said water-soluble fiber and these other fibers can be mixed or laminated | stacked and used. Moreover, the nonwoven fabric formed from the said water-soluble fiber can also be combined with another raw material, for example, a film, a metal, resin etc. as needed.

  The said nonwoven fabric can be used as what is called a soil improvement vegetation sheet etc. by containing a soil improvement agent, a fertilizer, a seed, etc., for example. The nonwoven fabric is formed from PVA which has excellent mechanical strength, viscosity when it is used as an aqueous solution, water retention, and uniform miscibility with a soil improver. Suitable for vegetation.

  Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. In the following examples and comparative examples, “part” and “%” mean mass basis unless otherwise specified.

  The obtained PVA (alkyl-modified PVA and non-modified PVA) was evaluated according to the following method.

[Modification rate]
The content rate (modification rate) of the monomer unit (a) represented by the formula (I) in PVA was determined according to the above-described method using proton NMR. For proton NMR, 500 MHz JEOL GX-500 was used.

[Degree of polymerization]
The degree of polymerization of PVA was determined by the method described in JIS-K6726.

[Saponification degree]
The degree of saponification of PVA was determined by the method described in JIS-K6726.

<Manufacture of PVA>
[Production Example 1] (Production of PVA1)
A 3 L reactor equipped with a stirrer, a reflux condenser, a nitrogen inlet, a comonomer addition port and an initiator addition port was charged with 750 g of vinyl acetate, 250 g of methanol and 1.1 g of N-octadecyl methacrylamide and bubbling nitrogen. Then, the system was purged with nitrogen for 30 minutes. Further, a comonomer solution in which N-octadecylmethacrylamide was dissolved in methanol to a concentration of 5% was prepared as a delay solution, and nitrogen substitution was performed by bubbling nitrogen gas. The temperature of the reactor was increased, and when the internal temperature reached 60 ° C., 0.25 g of 2,2′-azobisisobutyronitrile (AIBN) was added to initiate polymerization. The delay solution was added dropwise to polymerize the monomer composition (ratio of vinyl acetate and N-octadecyl methacrylamide) in the polymerization solution at a constant temperature for 3 hours at 60 ° C., and then cooled to stop the polymerization. The total amount of comonomer added until the polymerization was stopped was 4.8 g. The solid content concentration when the polymerization was stopped was 29.9%. Subsequently, unreacted vinyl acetate monomer was removed while occasionally adding methanol under reduced pressure at 30 ° C. to obtain a methanol solution (concentration 35%) of an alkyl-modified vinyl ester polymer (alkyl-modified PVAc). Furthermore, 27.9 g of an alkali solution (10% methanol solution of sodium hydroxide) was added to 771.4 g of an alkyl-modified PVAc methanol solution prepared by adding methanol thereto (200.0 g of alkyl-modified PVAc in the solution). Saponification was performed. Here, the alkyl-modified PVAc concentration in the saponification solution was 25%, and the molar ratio of sodium hydroxide to vinyl acetate units in the alkyl-modified PVAc was 0.03. A gel-like product was formed in about 1 minute after the addition of the alkaline solution. This was pulverized with a pulverizer and allowed to stand at 40 ° C. for 1 hour to proceed with saponification, and then 500 g of methyl acetate was added to leave the remaining alkali. Neutralized. After confirming that the neutralization was completed using a phenolphthalein indicator, a white solid was obtained by filtration, 2,000 g of methanol was added thereto, and the mixture was allowed to stand and washed at room temperature for 3 hours. After the above washing operation was repeated three times, the white solid obtained by centrifugal drainage was left in a dryer at 65 ° C. for 2 days to obtain alkyl-modified PVA (PVA1).

[Production Examples 2 to 14] (Production of PVA 2 to 14)
Charge amount of vinyl acetate and methanol, polymerization conditions such as kind and addition amount of unsaturated monomer having alkyl group used during polymerization, concentration of alkyl-modified PVAc during saponification, molar ratio of sodium hydroxide to vinyl acetate unit Various alkyl-modified PVA (PVA2 to 14) were produced in the same manner as in Example 1 except that the saponification conditions such as those were changed as shown in Table 1. The unsaturated monomer in Table 1 is a compound represented by the above formula (II), and Table 1 shows R ¹ and R ² in the formula (II).

[Production Example 15] (Production of PVA15)
750 g of vinyl acetate and 250 g of methanol were charged into a 3 L reactor equipped with a stirrer, reflux condenser, nitrogen inlet tube and initiator addition port, and the system was purged with nitrogen for 30 minutes while bubbling nitrogen. The temperature of the reactor was increased, and when the internal temperature reached 60 ° C., 0.5 g of 2,2′-azobisisobutyronitrile (AIBN) was added to start polymerization, and polymerization was performed at 60 ° C. for 3 hours. Then, the polymerization was stopped by cooling. The solid content concentration when the polymerization was stopped was 31.4%. Subsequently, unreacted vinyl acetate monomer was removed while sometimes adding methanol under reduced pressure at 30 ° C. to obtain a methanol solution (concentration 30%) of polyvinyl acetate (PVAc). Furthermore, saponification was performed by adding 27.9 g of an alkaline solution (sodium hydroxide in 10% methanol) to 772.1 g of PVAc methanol solution prepared by adding methanol thereto (200.0 g of PVAc in the solution). It was. Here, the PVAc concentration of the saponification solution was 25%, and the molar ratio of sodium hydroxide to vinyl acetate units in PVAc was 0.03. A gel-like product was formed in about 1 minute after the addition of the alkaline solution. This was pulverized with a pulverizer and allowed to stand at 40 ° C. for 1 hour to proceed with saponification, and then 500 g of methyl acetate was added to leave the remaining alkali. Neutralized. After confirming that the neutralization was completed using a phenolphthalein indicator, a white solid was obtained by filtration, 2,000 g of methanol was added thereto, and the mixture was allowed to stand and washed at room temperature for 3 hours. After repeating the above washing operation three times, the white solid obtained by centrifugal drainage was left in a dryer at 65 ° C. for 2 days to obtain unmodified PVA (PVA15).

[Examples 1-9, Comparative Examples 1-6]
Each of the obtained PVA was added to DMSO so as to have a PVA concentration of 23% by mass, and heated and dissolved at 90 ° C. in a nitrogen atmosphere. The obtained spinning solution was dry-wet-spun into a solidification bath of methanol / DMSO = 70/30 (mass ratio) at a liquid temperature of 5 ° C. through a nozzle having a hole diameter of 0.08 mm and a hole number of 108.

  The obtained solidified yarn was dipped in a second bath having the same methanol / DMSO composition as the solidified bath, and then wet-stretched 3 times in a methanol bath having a liquid temperature of 25 ° C. Then, it dried with the hot air of 120 degreeC, and obtained the spinning original yarn. Subsequently, the obtained spinning yarn was drawn in a hot air drawing furnace at 160 ° C. so that the total draw ratio (wet draw ratio × hot air furnace draw ratio) was 6 times. Examples 1 to 9 and Comparative Examples 1 to 6 water-soluble fibers were obtained.

  The obtained water-soluble fiber was evaluated as follows.

[4% aqueous solution viscosity]
4 g of water-soluble fiber was added to 96 g of distilled water at room temperature, the temperature was raised to 90 ° C., stirred as it was for 1 hour, and then cooled to room temperature to prepare a PVA aqueous solution with a concentration of 4%. Thereafter, the viscosity at a temperature of 20 ° C. was measured at a rotor rotation speed of 6 rpm using a B-type viscometer.

[Tensile strength]
According to JIS-L1013, a yarn conditioned in advance was measured under the conditions of a test length of 20 cm, an initial load of 0.25 cN / dtex and a tensile speed of 50% / min, and an average value of n = 20 was adopted. The fiber fineness (dtex) was determined by a mass method.

  Table 2 shows the evaluation results of the produced PVA and water-soluble fibers. In Table 2, “−” in the viscosity of a 4% aqueous solution indicates that there was an undissolved residue and no evaluation was possible.

  As shown in Table 2, it can be seen that the water-soluble fiber of the present invention has a high viscosity when made into an aqueous solution and has a high tensile strength.

  As described above, since the water-soluble fiber of the present invention contains PVA which is excellent in mechanical strength and excellent in viscosity and the like when used as an aqueous solution, it can be suitably used for a nonwoven fabric for soil improvement vegetation.

Claims (5)

Containing an alkyl-modified vinyl alcohol polymer,
The alkyl-modified vinyl alcohol polymer includes a monomer unit (a) represented by the following general formula (I), has a viscosity average polymerization degree of 1,000 to 5,000, and a saponification degree of 80 mol%. A water-soluble fiber having a content of the monomer unit (a) of 0.05 mol% or more and 5 mol% or less.

(In formula (I), R ¹ represents a linear or branched alkyl group having 8 to 29 carbon atoms. R ² represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms.)   The water-soluble fiber according to claim 1, wherein the viscosity of a 4% by mass aqueous solution is 50,000 mPa · s or more.   The water-soluble fiber according to claim 1 or 2, wherein the tensile strength is 3.0 cN / dtex or more and 7.5 cN / dtex or less.   The nonwoven fabric formed from the water-soluble fiber of Claim 1, Claim 2, or Claim 3. The nonwoven fabric according to claim 4, which is used for soil improvement vegetation.