JP7336282B2 - Polyvinyl alcohol fiber and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polyvinyl alcohol-based fiber suitable as a packaging material for alkaline substances such as soap, and a fiber structure using the fiber.

Conventionally, paper or plastic boxes have been used as packaging materials for alkaline substances such as soap powder. Furthermore, in recent years, a method has been adopted in which a desired amount of soap is wrapped in a water-soluble film, fabric, or the like, and the soap is put into water together with the package. According to such a method, powder soap or the like can be used without weighing a predetermined amount of soap or touching the soap or the like. Moreover, since the packaging material dissolves in water, an excellent effect can be obtained in terms of reducing the amount of waste. Moreover, since it is convenient to carry, a form in which a desired amount of soap is wrapped in a water-soluble film, fabric, or the like can be suitably used as a portable detergent for traveling.
It is known that polyvinyl alcohol can be suitably used as a material for such a packaging material because of its excellent water solubility and mechanical strength.

However, in order to lower the dissolution temperature of polyvinyl alcohol in water, it is necessary to lower the degree of saponification. Melting temperature rises. As a result, although it has excellent water-solubility immediately after being filled with a detergent or the like, the water-solubility deteriorates with the lapse of time, and there is a possibility that sufficient performance cannot be exhibited during use.

In order to solve the above problems, it has been proposed to use a film using polyvinyl alcohol containing a copolymer unit composed of a carboxyl group or a sulfonic acid group as a packaging material (for example, Patent Document 1). By introducing such copolymer units, it is possible to obtain detergent packaging materials that are resistant to saponification even in an alkaline environment. It is difficult to prevent extreme fluctuations in mechanical properties under low and high humidity conditions. In particular, when a film using modified polyvinyl alcohol absorbs moisture under high humidity conditions, tacking occurs and the films stick to each other. Therefore, it was necessary to store each bag in an aluminum dehumidifying bag and then store it in a dehumidifying box, which made storage and management complicated and inefficient.

On the other hand, the use of a cloth made of polyvinyl alcohol fibers as a packaging material for alkaline substances has also been investigated. For example, as a high-quality polyvinyl alcohol fiber capable of providing excellent water solubility even in an alkaline environment, a fiber containing 1.0 mol % or more of a copolymer unit having a sulfonic acid group and/or a sulfonate group is used. A water-soluble fiber containing a vinyl alcohol copolymer having a degree of conversion of 94 mol % or more has been proposed (for example, Patent Document 2).

However, although the above-mentioned water-soluble fibers exhibit good water-solubility, the water-solubility after alkali treatment is still insufficient, and there is a demand for water-soluble fibers that exhibit good water-solubility even at low temperatures. ing.

JP-A-9-272773 JP-A-2002-235236

In recent years, from the viewpoint of environmental problems, especially from the viewpoint of countermeasures against plastic pollution in the ocean, the demand for packaging materials with excellent water solubility is increasing, and the required performance of water-soluble fibers that provide such packaging materials is increasing year by year. ing.

An object of the present invention is to provide a water-soluble fiber having excellent water-solubility even in an alkaline environment and excellent water-solubility at extremely low temperatures, a fiber structure comprising the same, and a method for producing the water-soluble fiber. .

That is, the present invention provides [1] a polyvinyl alcohol fiber containing 1.0 mol% or more of a sulfonic acid group and having a saponification degree of 80 to 93 mol%, wherein the polyvinyl alcohol in the polyvinyl alcohol fiber It relates to a polyvinyl alcohol-based fiber having a degree of polymerization of 500 or more .

Furthermore, as a preferred form of the present invention,
[2] The polyvinyl alcohol-based fiber according to [1] above, characterized in that the time for fusing the fiber at −1.0° C. in a 3.5% by mass sodium chloride aqueous solution is less than 60 minutes.
[3] The polyvinyl alcohol-based fiber according to any one of [1] to [2] above, characterized in that the fiber has an underwater fusion temperature of 25°C or less after alkali treatment, and [4] Crystallinity The polyvinyl alcohol-based fiber according to any one of [1] to [3] above, wherein is 20 to 30%.

Further, as a preferred embodiment of the present invention, [5] the polyvinyl alcohol-based fiber according to any one of [1] to [4] composed of at least two polyvinyl alcohols, and [6] polyvinyl alcohol-based copolymer A polyvinyl alcohol-based fiber comprising a combination (A) and a polyvinyl alcohol-based polymer (B), wherein the polyvinyl alcohol-based copolymer (A) contains 1.0 mol% or more of sulfonic acid groups and is saponified. degree is 80 to 96 mol%, the polyvinyl alcohol copolymer (A) is 60 to 90% by mass, and the polyvinyl alcohol polymer (B) is 10 to 40% by mass, It relates to the polyvinyl alcohol-based fiber described in [5] above.

Furthermore, the present invention
[7] A fiber structure at least partially including the polyvinyl alcohol-based fiber according to any one of [1] to [6] above.

The present invention also provides [8] a polyvinyl alcohol-based copolymer (A) containing 1.0 mol% or more of sulfonic acid groups and having a degree of saponification of 80 to 96 mol%, and a polyvinyl alcohol-based polymer (B ), and [9] the method for producing a polyvinyl alcohol-based fiber according to [6] above, which includes at least the step of mixing ) to prepare a spinning dope, and [9] the spinning dope having the ability to solidify polyvinyl alcohol The above [8] is characterized by wet or dry-wet spinning in a solidification bath mainly composed of an organic solvent, and the total draw ratio in all steps is 3 times or more in any of the steps of drying, drawing, and heat treatment. 2. A method for producing the polyvinyl alcohol-based fiber according to 1. is provided.

ADVANTAGE OF THE INVENTION According to this invention, the water-soluble fiber which is excellent in water solubility especially at low temperature, the fiber structure which consists of it, and the manufacturing method of this water-soluble fiber are provided.

In the present invention, at least one functional group selected from the group consisting of a sulfonic acid group, a sulfonate group, a maleic acid group, an itaconic acid group, an acrylic acid group and a methacrylic acid group is contained in an amount of 1.0 mol % or more, By using a polyvinyl alcohol fiber having a degree of conversion of 80 to 93 mol%, it is possible to obtain a polyvinyl alcohol fiber that exhibits excellent water solubility (water solubility) even in an alkaline environment and is excellent in water solubility even at extremely low temperatures. It becomes possible.

In the present invention, the polyvinyl alcohol-based fiber has the above-described functional group, and its content and degree of saponification should satisfy the above ranges. It may be composed of two or more types of polyvinyl alcohol. Moreover, other polymers than polyvinyl alcohol may be included. When the polyvinyl alcohol-based fiber is composed of two or more types of polyvinyl alcohol, or when it contains other polymers, the amount of functional groups contained in the entire polyvinyl alcohol-based fiber may be within the above range. The degree of saponification of the entire polyvinyl alcohol-based fiber (hereinafter sometimes simply referred to as the degree of saponification) obtained as described later may be within the above range.

The functional group contained in the polyvinyl alcohol-based fiber of the present invention is at least one selected from the group consisting of sulfonic acid group, sulfonate group, maleic acid group, itaconic acid group, acrylic acid group and methacrylic acid group. Polyvinyl alcohol fibers can be produced by spinning polyvinyl alcohol having these functional groups. The method for producing the polyvinyl alcohol having the above functional group is a method of copolymerizing a monomer having these functional groups and a vinyl ester monomer and saponifying the obtained polyvinyl ester copolymer, or a method of synthesizing it in advance. For example, a method of introducing these functional groups into the polyvinyl alcohol obtained later.

A monomer containing a sulfonic acid group or a sulfonate group is a monomer that can be copolymerized with a vinyl ester to form a sulfonic acid group or a sulfonate group, which is a salt thereof, after saponification. Specifically, 2-acrylamido-2-ethylpropanesulfonic acid or its alkali metal salt, 2-acrylamido-1-methylpropanesulfonic acid or its alkali metal salt, 2-methacrylamido-2-methylpropanesulfonic acid or its Examples thereof include alkali metal salts, olefinsulfonic acids such as ethylenesulfonic acid, allylsulfonic acid and methallylsulfonic acid, and metal salts thereof. Among them, 2-acrylamido-2-methylpropanesulfonic acid or an alkali metal salt thereof is preferable from the viewpoint of reactivity with vinyl ester and stability during saponification.

A sulfonic acid group or a sulfonate group may be subsequently introduced into the polyvinyl alcohol. For example, pre-synthesized polyvinyl alcohol is dissolved in an organic solvent such as DMSO and reacted with an aromatic aldehyde sulfonic acid such as sodium orthobenzaldehyde sulfonate or a salt thereof to replace the hydroxyl group portion of polyvinyl alcohol with a sulfonic acid group or its salt. It may be modified with a metal salt.
At this time, an aromatic sulfonic acid such as p-toluenesulfonic acid may be used as a catalyst.

A monomer containing a maleic acid group is one that is copolymerizable with the vinyl ester and the maleic acid group is present in the resulting copolymer. Specific examples include maleic acid or salts thereof, maleic acid esters such as monomethyl maleate, dimethyl maleate, monoethyl maleate and diethyl maleate, maleic anhydride and derivatives thereof, and the like. Among them, maleic acid, monomethyl maleate, and dimethyl maleate are preferable from the viewpoint of copolymerization reaction with vinyl ester and stability during saponification.

Monomers containing itaconic acid groups are those which are copolymerizable with the vinyl ester and where the itaconic acid groups are present in the resulting copolymer. Specific examples include itaconic acid or salts thereof, itaconic acid esters such as monomethyl itaconate, dimethyl itaconate, monoethyl itaconate and diethyl itaconate, itaconic anhydride and derivatives thereof, and the like. Among them, itaconic acid, monomethyl itaconate, and dimethyl itaconate are preferable from the viewpoint of copolymerization reaction with vinyl ester and stability during saponification.

A monomer containing an acrylic acid group is one that is copolymerizable with the vinyl ester and the acrylic acid group is present in the resulting copolymer. Specific examples include acrylic acid or its salts, and acrylic acid esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate and isopropyl acrylate. Among them, acrylic acid and methyl acrylate are preferable from the viewpoint of copolymerization reaction with vinyl ester and stability during saponification.

A monomer containing a methacrylic acid group is one that is copolymerizable with the vinyl ester and the methacrylic acid group is present in the resulting copolymer. Specific examples include methacrylic acid or salts thereof, and methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate and isopropyl methacrylate. Among them, methacrylic acid and methyl methacrylate are preferable from the viewpoint of copolymerization reaction with vinyl ester and stability during saponification.

One or two or more monomers having these functional groups may be used, but it is preferable to use one monomer.

Vinyl ester monomers to be copolymerized include, for example, vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl versatate. can be done. Among these, vinyl acetate is preferred.

Although one or two or more vinyl ester monomers may be used, it is preferable to use one vinyl ester monomer.

A polyvinyl alcohol having at least one functional group selected from the group consisting of a sulfonic acid group, a sulfonate group, a maleic acid group, an itaconic acid group, an acrylic acid group and a methacrylic acid group is obtained by the above-described method. In the case of production by copolymerization, the content of functional groups in the polyvinyl alcohol obtained can be adjusted by appropriately adjusting the amount of monomers during copolymerization.
When these functional groups are subsequently introduced into polyvinyl alcohol, the desired functional group content can be obtained by adjusting the amount of polyvinyl alcohol and the amount of the compound having the functional group.

The content of such functional groups is 1.0 mol % or more in polyvinyl alcohol. From the viewpoint of alkali resistance, it is preferably 1.5 mol % or more, more preferably 2.0 mol % or more. If the content is too low, the saponification reaction of polyvinyl alcohol will readily proceed in an alkaline environment, making it impossible to maintain the desired water solubility.

From the viewpoint of cost, process passability, and yarn quality, the functional group content is preferably 20 mol % or less, more preferably 10 mol % or less, and even more preferably 6 mol % or less.

When the polyvinyl alcohol-based fiber is composed of two or more types of polyvinyl alcohol and when it contains another polymer, the amount of functional groups contained in the finally obtained polyvinyl alcohol-based fiber should be within the above range. , the amount of functional groups contained in each polyvinyl alcohol may be adjusted.

The polyvinyl alcohol of the present invention contains copolymer units other than sulfonic acid groups, sulfonate groups, maleic acid groups, itaconic acid groups, acrylic acid groups and methacrylic acid groups, as long as the effects of the present invention are not impaired. may be modified with other components. Other copolymers or components include allylsulfonic acid, vinylpyrrolidone, ethylene, and the like.

The degree of saponification of the polyvinyl alcohol-based fiber of the present invention is 80 mol % or more and 93 mol % or less. If the degree of saponification is less than the above lower limit, the polyvinyl alcohol obtained and the polyvinyl alcohol-based fiber obtained therefrom will be inferior in mechanical strength, resulting in poor practicality when used as a package. On the other hand, if the degree of saponification exceeds the above upper limit, the water solubility at extremely low temperatures is poor. The degree of saponification of the polyvinyl alcohol fiber is preferably 83 mol % or more and 93 mol % or less, more preferably 88 mol % or more and 93 mol % or less.

As described above, the polyvinyl alcohol fiber of the present invention may contain one or more polyvinyl alcohols. When polyvinyl alcohol is used alone, polyvinyl alcohol having a degree of saponification within the above range can be spun by a method described later to obtain the intended polyvinyl alcohol-based fiber.

When two or more types of polyvinyl alcohol are used, the degree of saponification of each polyvinyl alcohol is subject to additivity. The degree of saponification of the entire alcohol-based fiber is determined, and the blending amount of the polyvinyl alcohol used may be adjusted so that the obtained degree of saponification falls within the above range.
The degree of saponification of polyvinyl alcohol can be usually determined by the method described in JIS K6726.

(Number 1)
Saponification degree (mol%) of polyvinyl alcohol-based fiber = Σ (ni × Mi) / 100 (1)
ni: Degree of saponification of each polyvinyl alcohol (mol%)
Mi: Proportion of each polyvinyl alcohol in the polyvinyl alcohol fiber (% by weight)

When the polyvinyl alcohol-based fiber contains a polymer other than polyvinyl alcohol, in the above formula (1), the ratio of the polymer other than polyvinyl alcohol to Mi, and ni to 0 (zero ) should be substituted.

Using two or more types of polyvinyl alcohol in this way, spinning can be performed by the method described below to obtain the intended polyvinyl alcohol-based fiber.

The degree of polymerization (viscosity-average degree of polymerization) of polyvinyl alcohol used in the present invention is not particularly limited, but from the viewpoint of mechanical strength and suppression of fiber insolubilization due to shrinkage and gelation when dissolved in water, 2400 or less is preferred. Preferably, 1800 or less is more preferable. If the degree of polymerization is too high, treatment with high-temperature water or immersion in water for a long time may be required. In addition, from the viewpoint of suppressing deterioration of spinnability and adhesion between fibers and maintaining mechanical performance and quality of fibers and fiber structures, the degree of polymerization is preferably 500 or more, more preferably 700 or more, and particularly preferably 1000 or more. .

In order to evaluate that the polyvinyl alcohol-based fiber of the present invention is excellent in water solubility even at extremely low temperatures below freezing point, considering the purpose of lowering the freezing point of water and applicability in seawater, It was evaluated using a certain 3.5 mass % sodium chloride aqueous solution. From the viewpoint of water solubility at low temperatures, it is preferable that the fiber melts for less than 60 minutes at −1.0° C. in a 3.5 mass % sodium chloride aqueous solution. It is more preferable that the fiber is melted for less than 40 minutes at −1.0° C. in a 3.5 mass % sodium chloride aqueous solution.
The fusing time of the fiber at -1.0°C in a 3.5 wt% sodium chloride aqueous solution is controlled by the degree of polymerization, the degree of saponification, the type and content of the functional group, etc. of the polyvinyl alcohol constituting the polyvinyl alcohol fiber. can be done.

It is preferable that the polyvinyl alcohol-based fiber of the present invention has a melting temperature in water of 25° C. or less after alkali treatment, because it is suitable for use in packaging detergents such as powdered soap. The melting temperature in water of the fiber after alkali treatment is more preferably 20° C. or less.
The melting temperature in water of the fiber after alkali treatment can be controlled by the degree of polymerization, the degree of saponification, the type and content of the functional group, etc. of the polyvinyl alcohol constituting the polyvinyl alcohol fiber.

From the viewpoint of water solubility, the polyvinyl alcohol-based fiber of the present invention preferably has a crystallinity of 30% or less, more preferably 28% or less. From the viewpoint of fiberization and mechanical strength, it is preferably 20% or more.
The degree of crystallinity can be controlled by the degree of polymerization, the degree of saponification, the type and content of functional groups, etc. of the polyvinyl alcohol constituting the polyvinyl alcohol fiber.

From the viewpoint of water solubility, the water solubility temperature (WTb) of the polyvinyl alcohol-based fiber of the present invention is preferably 50° C. or lower, more preferably 20° C. or lower, and particularly preferably 10° C. or lower. The dissolution temperature of the polyvinyl alcohol-based fiber in water can be controlled by the degree of polymerization, degree of saponification, type and content of functional groups, etc. of the polyvinyl alcohol constituting the fiber. Also, from the viewpoint of suppressing gelation during water dissolution and lowering the water solubility and ensuring high water solubility, it is preferable to have a small shrinkage rate when dissolving in water. Specifically, the maximum shrinkage rate when dissolving in water ( The shrinkage ratio in water) is preferably 30% or less, particularly 10% or less.

When the polyvinyl alcohol-based fiber of the present invention is composed of two or more types of polyvinyl alcohol, such polyvinyl alcohol-based fiber includes:
(1) Polyvinyl alcohol (hereinafter referred to as a polyvinyl alcohol copolymer ( Polyvinyl alcohol-based fiber composed of two or more of (sometimes referred to as A)),
(2) Polyvinyl alcohol fibers composed of polyvinyl alcohol copolymer (A) and polyvinyl alcohol having no functional group (hereinafter sometimes referred to as polyvinyl alcohol polymer (B)). .
Also, if it contains a polymer other than polyvinyl alcohol, for example,
(3) Polyvinyl alcohol fiber composed of polyvinyl alcohol copolymer (A), polyvinyl alcohol polymer (B), and a polymer other than polyvinyl alcohol, or polyvinyl alcohol copolymer (A) and polyvinyl alcohol and polyvinyl alcohol-based fibers composed of polymers other than the above.

In (1) above, the plurality of types of polyvinyl alcohol copolymers (A) differ in at least one of the types of functional groups, their content, the degree of saponification, and the degree of polymerization. In (2), the degree of saponification and the degree of polymerization of the polyvinyl alcohol copolymer (A) and the polyvinyl alcohol polymer (B) may be different or the same.

In a 3.5 mass% sodium chloride aqueous solution, from the viewpoint that it is easy to control each of the fiber fusing time at -1.0 ° C., the water fusing temperature of the fiber after alkali treatment, and the mechanical strength, the polyvinyl alcohol-based of the present invention The fibers are preferably composed of two or more kinds of polyvinyl alcohol, and the polyvinyl alcohol-based fiber composed of the above-mentioned (2) polyvinyl alcohol-based copolymer (A) and polyvinyl alcohol-based polymer (B) is more preferred.

The polyvinyl alcohol-based copolymer (A) contains at least 1 mol of at least one functional group selected from the group consisting of sulfonic acid groups, sulfonate groups, maleic acid groups, itaconic acid groups, acrylic acid groups and methacrylic acid groups. % have. More preferably, the amount of the functional group is 2 mol % or more. Moreover, the amount of the functional group is usually 20 mol % or less.

The degree of saponification of the polyvinyl alcohol-based copolymer (A) depends on the blending ratio with the polyvinyl alcohol-based polymer (B), but the saponification degree of the resulting polyvinyl alcohol-based fiber is controlled to 80 to 93 mol%. 80 mol % or more and 96 mol % or less is preferable from the viewpoint that it is easy to

The degree of polymerization of the polyvinyl alcohol-based copolymer (A) is preferably 2400 or less, more preferably 1800 or less, as described above. Moreover, the degree of polymerization is preferably 500 or more, more preferably 700 or more, and particularly preferably 1000 or more.

The degree of saponification of the polyvinyl alcohol polymer (B) may be appropriately selected according to the degree of saponification of the polyvinyl alcohol (A) and the mixing ratio. % or more and 93 mol % or less, it is preferably 87 mol % or more and 100 mol % or less.

The mixing ratio of the polyvinyl alcohol-based copolymer (A) and the polyvinyl alcohol-based polymer (B) is set so that the copolymer content and saponification degree of the polyvinyl alcohol-based fiber to be obtained are within the above ranges. Although it is good, usually, the polyvinyl alcohol copolymer (A) is 60% by mass or more and 90% by mass or less, and the polyvinyl alcohol polymer (B) is 10% by mass or more and 40% by mass or less (however, the entire polyvinyl alcohol fiber 100% by mass).

In addition to the above, other commonly used additives may be added to the polyvinyl alcohol fiber of the present invention. When added, the content of polyvinyl alcohol in the polyvinyl alcohol fiber is preferably 60% by mass or more, particularly 70 to 100% by mass.

When producing the polyvinyl alcohol-based fiber of the present invention, first, a spinning dope containing polyvinyl alcohol satisfying the above requirements is prepared. The solvent constituting the spinning dope may be water. It is preferable to use an organic solvent as the constituent solvent of the spinning dope because the dissolution temperature in water can be lowered as a result.

Examples of organic solvents include polar solvents such as dimethyl sulfoxide (hereinafter abbreviated as DMSO), dimethylacetamide, dimethylformamide and N-methylpyrrolidone; polyhydric alcohols such as glycerin and ethylene glycol; Examples include mixtures of swelling metal salts such as calcium and zinc chloride, mixtures of these solvents together, and mixtures of these solvents and water. Among them, DMSO is most preferable in terms of low-temperature solubility, low toxicity, low corrosiveness, and the like.

The concentration of the polymer in the spinning dope varies depending on the composition, degree of polymerization, and solvent, but is generally in the range of 8-40% by mass. When the constituent solvent of the spinning dope is an organic solvent, dissolution is preferably carried out while stirring under reduced pressure after purging with nitrogen from the viewpoint of preventing oxidation, decomposition, cross-linking reaction, etc., and suppressing foaming. The liquid temperature at the time of discharging the spinning dope is preferably in the range of 50 to 150° C., and the range is such that the dope does not gel, decompose or color.

When the polyvinyl alcohol-based fiber of the present invention is composed of the polyvinyl alcohol-based copolymer (A) and the polyvinyl alcohol-based polymer (B), the polyvinyl alcohol-based copolymer (A) and polyvinyl A spinning stock solution of the alcohol-based polymer (B) is prepared. When preparing the spinning stock solution, the polyvinyl alcohol copolymer (A) and the polyvinyl alcohol polymer (B) may be mixed in advance and the above solvent may be used to prepare the spinning stock solution, or the above solvent may be used to prepare the spinning stock solution. A liquid containing the system copolymer (A) and a liquid containing the polyvinyl alcohol polymer (B) may be separately prepared, and then the two liquids may be mixed to obtain a spinning dope.

The polyvinyl alcohol-based fiber of the present invention can be produced by spinning the spinning dope prepared as described above. The spinning method is not particularly limited, and examples thereof include a dry spinning method, a wet spinning method, and a dry-wet spinning method. Among them, wet spinning or dry-wet spinning is preferable because of its high productivity, and it may be discharged into a solidifying liquid capable of solidifying polyvinyl alcohol. In particular, when the spinning dope is discharged from multiple holes, the wet spinning method is preferable to the dry-wet spinning method from the viewpoint of preventing the fibers from sticking together during the discharge. The wet spinning method is a method in which the spinning stock solution is discharged directly from the spinneret into a solidifying bath, while the dry-wet spinning method is a method in which the spinning stock solution is once discharged from the spinneret into air or an inert gas. is discharged and then introduced into the solidification bath. The term “solidification” as used in the present invention refers to the transformation of a fluid spinning dope into a non-fluid solid, i.e., gelation, in which the dope composition does not change, and solidification, in which the dope composition changes and solidifies. includes both

When the constituent solvent of the spinning dope is water, for example, a saturated sodium sulfate solution may be ejected as the solidification liquid. , acetone, methyl ethyl ketone, and methyl isobutyl ketone, fatty acid esters such as methyl acetate and ethyl acetate, aromatics such as benzene and toluene, and mixtures of two or more of these may be discharged as the solidified liquid. In order to sufficiently solidify the inside of the fiber, it is preferable to use a mixture of the solidifying solvent and the solvent constituting the spinning dope, and the mixing mass ratio of the solidifying solvent/the dope solvent is preferably 95/5 to 40/60, preferably 90/10. ~50/50 is more preferred, and 85/15 to 55/45 is most preferred. Further, by mixing the undiluted solvent in the solidification bath, it is possible to adjust the solidification ability and reduce the separation and recovery cost of the undiluted solvent and the solidified solvent. Although the temperature of the solidification bath is not limited, when the spinning dope constituent solvent is an organic solvent, solidification is usually carried out at a solidification bath temperature of -15 to 30°C. From the viewpoint of uniform solidification and energy saving, the solidification bath temperature is preferably -10 to 20°C, more preferably -5 to 15°C, and particularly preferably 0 to 10°C. If the temperature of the solidification bath is outside this temperature range, the tensile strength of the obtained fiber may be lowered. When the spinning dope is heated to a high temperature, it is preferable to cool the solidification bath in order to keep the solidification bath temperature low.

Then, the fibers after being removed from the solidification bath may be wet-drawn as needed. From the viewpoint of the mechanical performance of the fiber and the prevention of sticking, it is preferable to apply wet stretching of 1.5 to 7.0 times, particularly 2.5 to 5.5 times. It is preferable to increase the wet draw ratio within a range that does not In order to increase the wet draw ratio, it is effective to carry out the wet drawing in two or more stages during the extraction step.

When the spinning stock solution constituent solvent is an organic solvent, it is preferable to extract and remove the stock solution solvent from the thread by bringing it into contact with an extraction bath mainly containing a solidifying solvent. Also, wet stretching and extraction may be performed in the same step. This extraction process can shorten the residence time in the extraction bath by continuously flowing the pure solidifying solvent in the direction countercurrent to the running direction of the thread. This extraction treatment can reduce the amount of the spinning dope solvent contained in the filaments to 1% or less, particularly 0.1% or less of the mass of filaments, and thus such a method is preferred. The contact time is preferably 5 seconds or more, particularly 15 seconds or more. In order to increase the extraction speed and improve the extraction, it is preferable to loosen the filaments in the extraction bath. Prior to drying, polyvinyl alcohol is replaced with a solvent having a high solidifying ability, such as acetone, methyl ethyl ketone, methyl isobutyl ketone, or a hydrophobic solvent such as mineral oil, polyethylene oxide, silicone, or fluorine. It is also effective to prevent sticking by applying an oil agent in the form of a solution or an emulsion, or by shrinking the material to alleviate shrinkage stress during drying.

The fibers may then be dried, preferably at 180° C. or less, and the mechanical properties of the fibers can be enhanced by further dry heat drawing. The dry heat treatment conditions can be appropriately selected according to the properties of the polyvinyl alcohol, particularly the melting point and the desired dissolution temperature in water. It is preferably 80 to 250°C. From the standpoint of process passability and the effect of dry heat stretching and/or dry heat treatment, the temperature is preferably 100 to 235°C, more preferably 120 to 180°C. From the viewpoint of efficient drawing by suppressing agglutination between fibers, it is preferable to perform hot drawing in multiple stages of 2 times or more, and it is particularly preferable to perform multistage drawing at elevated temperature.

From the viewpoint of the crystallinity of the polyvinyl alcohol-based fiber to be obtained, it is preferable to set the total draw ratio to 3 times or more in any one of the drying, drawing, and heat treatment steps.

Although the fineness of the single fiber of the polyvinyl alcohol-based fiber of the present invention is not particularly limited, those of 0.1 to 1000 dtex, particularly 0.2 to 100 dtex, and further 0.5 to 10 dtex can be widely used. The fiber length of the fiber may be appropriately set according to the application. For example, when the fiber is processed into paper or spun yarn, the fiber length is preferably about 1 to 30 mm. Although there is no particular limitation on the cross-sectional shape of the polyvinyl alcohol-based fiber, a simple substantially circular fiber is preferable to a complicated shape from the viewpoints of water dispersibility, product homogeneity, and the like. Further, the strength of the polyvinyl alcohol-based fiber of the present invention is preferably 1.5 cN/dtex or more, particularly 3 cN/dtex or more.

The polyvinyl alcohol-based fiber of the present invention is excellent in various performances such as mechanical performance, and any fiber structure can be obtained by using this fiber. For example, it can be processed into fiber structures such as cut fibers, filaments, spun yarns, fabrics (woven or knitted fabrics, dry nonwoven fabrics, wet nonwoven fabrics), ropes, cords, and the like. Among them, fabrics, especially nonwoven fabrics, and especially dry nonwoven fabrics are more preferable because they are excellent in mechanical performance, flexibility, and the like. Also, such a fabric may be formed into a desired shape. At this time, other fibers (water-soluble fibers, water-insoluble fibers: including polyvinyl alcohol fibers other than the present invention) may be used in combination. The polyvinyl alcohol-based fiber of the present invention preferably accounts for 40 mass % or more, more preferably 60 mass % or more, particularly 80 to 100 mass % of the structure. It may also be used in combination with other materials (metal, film, etc.).

Since the polyvinyl alcohol-based fiber of the present invention is excellent in water solubility, particularly at low temperatures, the fiber structure obtained therefrom can be easily dissolved and removed by treatment with water, hot water, or the like. Liquids other than water may be used as necessary, and liquids containing additives and the like may also be used. Treatment with water (hot water) or an aqueous solution is preferred from the viewpoint of easy treatment and environmental friendliness. In addition, depending on the application, it can be dissolved and removed by throwing it into a bath, a flush toilet, a washing machine bathtub, or the like.

The polyvinyl alcohol-based fiber and the fiber structure of the present invention can be used for all purposes, and since excellent water solubility is maintained even when placed under alkaline conditions, it is suitable for packaging materials for alkaline substances. It can be used particularly preferably, and can be used as a package in which an alkaline substance is packaged with a fiber structure. Alkaline substances applicable to the present invention are not particularly limited, but examples thereof include detergents (for laundry, industrial use, etc.), agricultural chemicals, carbonates, water-soluble solid acids, high-boiling solvents, surfactants, and the like. Among others, the fiber and packaging material of the present invention can be suitably used for solids, particularly granular materials. Ordinary polyvinyl alcohol fibers lose their water-solubility when they come into contact with such alkaline substances or are left in contact under high humidity conditions. , and can be suitably applied to such alkaline substances.

When the fiber structure of the present invention is used as a packaging material, at least a fiber fabric is preferably used from the viewpoint of mechanical performance, flexibility, solubility in water, packaging performance, and the like. Non-woven fabrics are particularly preferable from the viewpoints of production processability, cost, solubility in water, and the like. The basis weight of such fabric is preferably 10 g/m ² or more, particularly 40 g/m 2 or more from the viewpoint of mechanical performance and packaging performance, and is preferably 80 g/m ^{2 or} less from the viewpoint of production efficiency and flexibility. It is preferably 60 g/m ² or less. In terms of mechanical performance, the breaking length of the fabric is preferably 5 N/25 cm or more.

Although the method for producing a nonwoven fabric suitable for such a packaging material is not particularly limited, it is preferable to use a dry-laid nonwoven fabric obtained by treating a fibrous web in terms of feel, softness and the like. For example, filament tows of polyvinyl alcohol-based fibers are opened by the repulsive action of triboelectrification, or crimped and cut staples are opened with a card or the like to form a web, and the area compression rate is 10 to 50%. (particularly preferably 10 to 30%), that is, a method of thermally compressing 10 to 50% (particularly preferably 10 to 30%) of the surface area of the nonwoven fabric with a hot embossing roller. By subjecting a portion of the nonwoven fabric to a thermocompression bonding treatment, the mechanical performance and shape stability can be enhanced without impairing the feel, flexibility and water solubility of the nonwoven fabric. The area of each thermocompression bonding portion is preferably 4 cm ² or less, particularly 2 cm ² or less, and more preferably 1 cm 2 or less from the viewpoint of texture and water solubility, and 1 mm ^{2 or} more from the viewpoint of the mechanical performance of the nonwoven fabric. It is preferable to have The thermocompression bonding temperature may be, for example, approximately 180 to 230° C., and the pressure may be approximately 1 to 6 MPa. In addition, since the polyvinyl alcohol-based fiber of the present invention exhibits adhesion ability by dry heat treatment, such embossing treatment can efficiently increase the mechanical performance of the nonwoven fabric by bonding between fibers, and can be easily bonded by thermocompression bonding. It can also be molded into any desired shape. For example, it may be molded into a desired shape such as bag-like or box-like. As the packaging material, a bag-like material can be preferably used. For example, it may be a bag-like object with a side of about 3 to 10 cm.

Further, in the present invention, by further laminating a water-soluble film, it is possible to further improve the mechanical performance and shape stability of the packaging material and the leakage prevention of the contents. At this time, it is preferable to laminate so that the inner side of the packaging material (side on which the inclusion is filled) becomes a water-soluble film. In general, low-temperature water-soluble films are two-dimensional materials with low crystallinity and low orientation. However, in the present invention, since a specific fiber or fiber structure is used in combination, such a phenomenon is suppressed and a high-performance packaging material can be obtained. As the water-soluble film, for example, a polyvinyl alcohol film can be preferably used, and in particular, a polyvinyl alcohol film composed of polyvinyl alcohol constituting the fibers of the present invention can be used more preferably. Such a film has high adhesion to the fibrous structure of the present invention, has excellent water solubility, and is less likely to lose its water solubility even in an alkaline environment, so excellent effects can be obtained. Although the method of laminating the films is not particularly limited, the films can be laminated and integrated efficiently by, for example, thermocompression bonding. Also, such a laminate may be formed into a desired shape such as a bag.

EXAMPLES The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to these Examples.

[Degree of polymerization]
Based on JIS K6726, it was calculated by the following formula (2) from the measured value of the intrinsic viscosity [η] of an aqueous solution at 30°C. Incidentally, P is the average degree of polymerization of polyvinyl alcohol.
(Number 2)
log P = 1.613 log ([η] x 104/8.29) (2)

[Saponification degree (mol%)]
Measured according to JIS K6726.

[Crystallinity of Polyvinyl Alcohol Fiber]
Using a Mettler differential scanning calorimeter (DSC-20), 10 mg of the fiber sample was heated at a rate of 20 ° C./min under nitrogen, and the endothermic amount ΔH (J / g) at the endothermic peak was measured. The degree of crystallinity was calculated by the following formula (3) from the ratio to 174.5 J/g, which is the heat of fusion of complete crystals of polyvinyl alcohol.
(Number 3)
Crystallinity (%) = ΔH (J / g) / 174.5 (J / g) × 100 (3)

[Fiber cutting temperature in water (°C)] (WTb in water)
A fiber bundle with a length of 10 cm is suspended in water at 0°C with a load of 2.2 mg/dtex, the water temperature is raised at a rate of 2°C/min, and the temperature at which the fiber melts and the load drops. was taken as the melting temperature in water.

[Fiber shrinkage rate in water (%)]
A fiber bundle with a length of 10 cm was suspended in water at 0 ° C. with a load of 2.2 mg / dtex, and the water temperature was raised at a rate of 2 ° C./min, before the fiber melted and the load dropped. Second, the value obtained by dividing the length of the fiber when it was most shrunk by the original length was taken as the shrinkage rate in water.

[Fusing time at −1.0° C. in 3.5% by mass sodium chloride aqueous solution of fiber] (3.5% NaCl aqueous solution WTb)
A fiber bundle with a length of 10 cm was suspended in a 3.5% by mass sodium chloride aqueous solution at -1.0 ° C. with a load of 2.2 mg / dtex, and the time at which the fiber dissolved and the load dropped was 3. 0.5% by mass of sodium chloride aqueous solution.

[Water solubility after alkali treatment] (WTb after alkali treatment)
Leave the fiber bundle in contact with an alkaline substance (commercially available powder detergent) in a thermo-hygrostat at a temperature of 30°C and a humidity of 93% for 5 weeks. was measured.

[Reference example 1]
[Additional saponification of polyvinyl alcohol]
Polyvinyl alcohol having a degree of polymerization of 1700 ("22-88" manufactured by Kuraray) was added to a methanol solution containing 10% by mass of sodium hydroxide at a molar ratio of 0.01 to sodium hydroxide, and the mixture was immersed at 45°C for 1 hour. . After that, the polyvinyl alcohol was neutralized at room temperature for 30 minutes using a solution having a mass ratio of methyl acetate and water of 95/5. The neutralized polyvinyl alcohol was washed with methanol and dried at 80° C. for 10 hours.

[Synthesis of sulfonic acid-modified polyvinyl alcohol]
Polyvinyl alcohol having a degree of polymerization of 1700 ("22-88" manufactured by Kuraray) was further saponified by the above method, and the polyvinyl alcohol having a degree of saponification of 92 mol% was dissolved in DMSO with stirring at 90°C for 4 hours to obtain a polyvinyl alcohol concentration of 18 mass. % stock solution was obtained. To this stock solution, 3 mol % of sodium orthobenzaldehyde sulfonate with respect to polyvinyl alcohol and 0.065 mol of p-toluenesulfonic acid per 1 kg of the stock solution were added and stirred at 90° C. for 1 hour. 0325 mol was added and neutralized to synthesize a spinning dope containing sulfonic acid groups.

[Example 1]
Polyvinyl alcohol-based copolymer (A) ("S -1113”) and a polyvinyl alcohol polymer (B) (“25-100” manufactured by Kuraray) having a degree of polymerization of 1700 and a degree of saponification of 99.9 mol% (A) / (B) = 80/20 (weight was dissolved in DMSO at 90° C. for 5 hours with stirring to obtain a spinning dope having a polyvinyl alcohol concentration of 23% by mass. This spinning dope is dry-wet spun in a solidification bath of methanol/DMSO=80/20 at 5°C through a nozzle having 80 holes and a hole diameter of 0.1 mmφ, and subjected to wet-heat drawing of 3.0 times in a methanol bath at 20°C. did. Then, after extracting DMSO in the filament with methanol, a spinning oil was applied and dried at 120°C. 0 times) to produce a polyvinyl alcohol-based fiber. Spinnability was good. Table 1 shows the measurement results of the melting temperature in water, the shrinkage rate in water, the melting time in a 3.5% by mass sodium chloride aqueous solution, and the melting temperature in water after alkali treatment.

[Example 2]
Polyvinyl alcohol-based copolymer (A) ("S-2217" manufactured by Kuraray) containing 2.0 mol% of AMPS and having a degree of polymerization of 1700 and a degree of saponification of 88 mol% and a copolymer having a degree of polymerization of 1700 and a degree of saponification of 88 mol% Polyvinyl alcohol polymer (B) ("22-88" manufactured by Kuraray) was dissolved in DMSO at a ratio of (A)/(B) = 70/30 (weight ratio) with stirring at 90°C for 5 hours to determine the polyvinyl alcohol concentration. A spinning stock solution of 22% by weight was obtained. This spinning dope is dry-wet spun in a solidification bath of methanol/DMSO=80/20 at 5°C through a nozzle having 80 holes and a hole diameter of 0.1 mmφ, and subjected to wet-heat drawing of 3.0 times in a methanol bath at 20°C. did. Then, after extracting DMSO in the filament with methanol, a spinning oil was applied and dried at 120°C. 0 times) to produce a polyvinyl alcohol-based fiber. Spinnability was good. Table 1 shows the measurement results of the melting temperature in water, the shrinkage rate in water, the melting time in a 3.5% by mass sodium chloride aqueous solution, and the melting temperature in water after alkali treatment.

[Example 3]
Polyvinyl alcohol-based copolymer (A) ("S-2217" manufactured by Kuraray) containing 2.0 mol% of AMPS and having a degree of polymerization of 1700 and a degree of saponification of 88 mol% and a degree of polymerization of 2400 and a degree of saponification of 99.9 mol. % polyvinyl alcohol-based polymer (B) ("60-98" manufactured by Kuraray) and (A)/(B) = 90/10 (weight ratio) were dissolved in DMSO at 90°C for 5 hours with stirring. A spinning dope having an alcohol concentration of 22% by mass was obtained. This spinning dope is dry-wet spun in a solidification bath of methanol/DMSO=80/20 at 0°C through a nozzle having 80 holes and a hole diameter of 0.1 mmφ, and subjected to wet-heat stretching of 3.0 times in a methanol bath at 20°C. did. Then, after extracting DMSO in the filament with methanol, a spinning oil was applied and dried at 120°C. 0 times) to produce a polyvinyl alcohol-based fiber. Spinnability was good. Table 1 shows the measurement results of the melting temperature in water, the shrinkage rate in water, the melting time in a 3.5% by mass sodium chloride aqueous solution, and the melting temperature in water after alkali treatment.

[Example 4]
A polyvinyl alcohol-based copolymer (A) containing 4.0 mol% of AMPS and having a degree of polymerization of 1200 and a degree of saponification of 88 mol% and a polyvinyl alcohol-based polymer (B) having a degree of polymerization of 1700 and a degree of saponification of 98 mol% ( Kuraray Co., Ltd. "28-98") and (A)/(B) = 70/30 (weight ratio) were dissolved in DMSO with stirring at 90°C for 5 hours to obtain a spinning dope having a polyvinyl alcohol concentration of 24% by mass. . This spinning dope is dry-wet spun in a solidification bath of methanol/DMSO=80/20 at 5°C through a nozzle having 80 holes and a hole diameter of 0.1 mmφ, and subjected to wet-heat drawing of 3.0 times in a methanol bath at 20°C. did. Then, after extracting DMSO in the filament with methanol, a spinning oil was applied and dried at 120°C. 0 times) to produce a polyvinyl alcohol-based fiber. Spinnability was good. Table 1 shows the measurement results of the melting temperature in water, the shrinkage rate in water, the melting time in a 3.5% by mass sodium chloride aqueous solution, and the melting temperature in water after alkali treatment.

[Example 5]
Polyvinyl alcohol-based copolymer (A) containing 3.0 mol% of sulfonic acid groups modified with sulfonic acid in Reference Example 1 and having a degree of polymerization of 1700 and a degree of saponification of 92 mol% and a polyvinyl alcohol-based copolymer (A) having a degree of polymerization of 1000 and a degree of saponification of 98 mol % polyvinyl alcohol polymer (B) ("11-98" manufactured by Kuraray) and (A)/(B) = 90/10 (weight ratio) were dissolved in DMSO at 90°C for 5 hours with stirring. A spinning dope having an alcohol concentration of 22% by mass was obtained. This spinning dope is dry-wet spun in a solidification bath of methanol/DMSO=80/20 at 5°C through a nozzle having 80 holes and a hole diameter of 0.1 mmφ, and subjected to wet-heat drawing of 3.0 times in a methanol bath at 20°C. did. Then, after extracting DMSO in the filament with methanol, a spinning oil was applied and dried at 120°C. 0 times) to produce a polyvinyl alcohol-based fiber. Spinnability was good. Table 1 shows the measurement results of the melting temperature in water, the shrinkage rate in water, the melting time in a 3.5% by mass sodium chloride aqueous solution, and the melting temperature in water after alkali treatment.

[Example 6]
Polyvinyl alcohol-based copolymer (A) (“S-2217” manufactured by Kuraray) containing 2.0 mol% of AMPS and having a degree of polymerization of 1700 and a degree of saponification of 88 mol% and a copolymer having a degree of polymerization of 1700 and a degree of saponification of 96 mol% Polyvinyl alcohol polymer (B) ("27-96" manufactured by Kuraray) was dissolved in DMSO at a ratio of (A)/(B) = 60/40 (weight ratio) with stirring at 90°C for 5 hours to determine the polyvinyl alcohol concentration. A spinning stock solution of 22% by weight was obtained. This spinning dope is dry-wet spun in a solidification bath of methanol/DMSO=80/20 at 5°C through a nozzle having 80 holes and a hole diameter of 0.1 mmφ, and subjected to wet-heat drawing of 3.0 times in a methanol bath at 20°C. did. Next, after extracting DMSO in the filament with methanol, a spinning oil was applied and dried at 120°C. 0 times) to produce a polyvinyl alcohol-based fiber. Spinnability was good. Table 1 shows the measurement results of the melting temperature in water, the shrinkage rate in water, the melting time in a 3.5% by mass sodium chloride aqueous solution, and the melting temperature in water after alkali treatment.

[Example 7]
Polyvinyl alcohol copolymer (A) ("S-2217" manufactured by Kuraray) containing 2.0 mol% of AMPS and having a degree of polymerization of 1700 and a degree of saponification of 88 mol% was dissolved in DMSO with stirring at 90°C for 5 hours. , to obtain a spinning dope having a polyvinyl alcohol concentration of 24% by mass. This spinning dope was dry-wet spun in a methanol solidification bath at 0°C through a nozzle having 80 holes and a hole diameter of 0.1 mmφ, and subjected to wet-heat drawing of 3.0 times in a methanol bath at 5°C. Next, after extracting DMSO in the thread with methanol at 5°C, a spinning oil is applied and dried at 120°C. = 6.0 times) to produce a polyvinyl alcohol-based fiber. Spinnability was good. Spinnability was inferior to Examples 1-6. Table 1 shows the measurement results of the melting temperature in water, the shrinkage rate in water, the melting time in a 3.5% by mass sodium chloride aqueous solution, and the melting temperature in water after alkali treatment.

[Example 8]
Polyvinyl alcohol-based copolymer (A) ("S-2217" manufactured by Kuraray) containing 2.0 mol% of AMPS and having a degree of polymerization of 1700 and a degree of saponification of 88 mol% and a copolymer having a degree of polymerization of 1700 and a degree of saponification of 88 mol% Polyvinyl alcohol polymer (B) ("22-88" manufactured by Kuraray) was dissolved in DMSO at a ratio of (A)/(B) = 95/5 (weight ratio) with stirring at 90°C for 5 hours to determine the polyvinyl alcohol concentration. A spinning stock solution of 23% by weight was obtained. This spinning dope was dry-wet spun in a methanol solidification bath at 0°C through a nozzle having 80 holes and a hole diameter of 0.1 mmφ, and subjected to wet-heat drawing of 3.0 times in a methanol bath at 5°C. Next, after extracting DMSO in the thread with methanol at 5°C, a spinning oil is applied and dried at 120°C. = 6.0 times) to produce a polyvinyl alcohol-based fiber. Spinnability was better than Example 7 but worse than Examples 1-6. Table 1 shows the measurement results of the melting temperature in water, the shrinkage rate in water, the melting time in a 3.5% by mass sodium chloride aqueous solution, and the melting temperature in water after alkali treatment.

[Comparative Example 1]
Polyvinyl alcohol-based copolymer (A) ("S-2217" manufactured by Kuraray) containing 2.0 mol% of AMPS and having a degree of polymerization of 1700 and a degree of saponification of 88 mol% and a degree of polymerization of 1700 and a degree of saponification of 99.9 mol. % polyvinyl alcohol polymer (B) ("25-100" manufactured by Kuraray) and (A)/(B) = 50/50 (weight ratio) were dissolved in DMSO at 90°C for 5 hours with stirring. A spinning dope having an alcohol concentration of 21% by mass was obtained. This spinning dope is dry-wet spun in a solidification bath of methanol/DMSO=80/20 at 5°C through a nozzle having 80 holes and a hole diameter of 0.1 mmφ, and subjected to wet-heat drawing of 3.0 times in a methanol bath at 20°C. did. Then, after extracting DMSO in the filament with methanol, a spinning oil was applied and dried at 120°C. 0 times) to produce a polyvinyl alcohol-based fiber. Spinnability was good. Table 1 shows the measurement results of the melting temperature in water, the shrinkage rate in water, the melting time in a 3.5% by mass sodium chloride aqueous solution, and the melting temperature in water after alkali treatment.

[Comparative Example 2]
Polyvinyl alcohol-based copolymer (A) ("S-2217" manufactured by Kuraray) containing 2.0 mol% of AMPS and having a degree of polymerization of 1700 and a degree of saponification of 88 mol% and a copolymer having a degree of polymerization of 1700 and a degree of saponification of 98 mol% Polyvinyl alcohol polymer (B) ("28-98" manufactured by Kuraray Co., Ltd.) was dissolved in DMSO at a ratio of (A)/(B) = 30/70 (weight ratio) with stirring at 90°C for 5 hours to determine the polyvinyl alcohol concentration. A spinning stock solution of 20% by weight was obtained. This spinning dope is dry-wet spun in a solidification bath of methanol/DMSO=80/20 at 5°C through a nozzle having 80 holes and a hole diameter of 0.1 mmφ, and subjected to wet-heat drawing of 3.0 times in a methanol bath at 20°C. did. Then, after extracting DMSO in the filament with methanol, a spinning oil was applied and dried at 120°C. 0 times) to produce a polyvinyl alcohol-based fiber. Spinnability was good. Table 1 shows the measurement results of the melting temperature in water, the shrinkage rate in water, the melting time in a 3.5% by mass sodium chloride aqueous solution, and the melting temperature in water after alkali treatment.

[Comparative Example 3]
A polyvinyl alcohol-based copolymer (A) ("S-2117" manufactured by Kuraray) containing 2.0 mol% of AMPS and having a degree of polymerization of 1700 and a degree of saponification of 95 mol% was dissolved in DMSO with stirring at 90°C for 5 hours. , to obtain a spinning dope having a polyvinyl alcohol concentration of 20% by mass. This spinning dope is dry-wet spun in a solidification bath of methanol/DMSO=80/20 at 5°C through a nozzle having 80 holes and a hole diameter of 0.1 mmφ, and subjected to wet-heat drawing of 3.0 times in a methanol bath at 20°C. did. Then, after extracting DMSO in the filament with methanol, a spinning oil was applied and dried at 120°C. 0 times) to produce a polyvinyl alcohol-based fiber. Spinnability was good. Table 1 shows the measurement results of the melting temperature in water, the shrinkage rate in water, the melting time in a 3.5% by mass sodium chloride aqueous solution, and the melting temperature in water after alkali treatment.

As is clear from Table 1 above, the polyvinyl alcohol-based fiber of the present invention has excellent water solubility and water solubility after alkali treatment, and also has a short fusing time at −1.0° C. in a 3.5% by mass sodium chloride aqueous solution. Therefore, it has excellent water solubility at extremely low temperatures.
The polyvinyl alcohol-based fiber of the present invention has a fiber structure, and the structure contains alkaline substances such as detergents (for laundry, industrial use, etc.), agricultural chemicals, carbonates, water-soluble solid acids, high-boiling solvents, and surfactants. It can be suitably used as a raw material for a package formed by packaging.

Claims (9)

A polyvinyl alcohol fiber containing 1.0 mol % or more of a sulfonic acid group and having a saponification degree of 80 to 93 mol %, wherein the polyvinyl alcohol in the polyvinyl alcohol fiber has a polymerization degree of 500 or more. Polyvinyl alcohol fiber . 2. The polyvinyl alcohol fiber according to claim 1, wherein the fiber has a melting time of less than 60 minutes at −1.0° C. in a 3.5% by mass sodium chloride aqueous solution. The polyvinyl alcohol-based fiber according to claim 1 or 2, wherein the water melting temperature of the fiber after alkali treatment is 25°C or less. The polyvinyl alcohol-based fiber according to any one of claims 1 to 3, characterized in that the degree of crystallinity is 20-30%. The polyvinyl alcohol-based fiber according to any one of claims 1 to 4, which is composed of at least two polyvinyl alcohols. A polyvinyl alcohol-based fiber comprising a polyvinyl alcohol-based copolymer (A) and a polyvinyl alcohol-based polymer (B), wherein the polyvinyl alcohol-based copolymer (A) contains 1.0 mol% or more of sulfonic acid groups . containing, the degree of saponification is 80 to 96 mol%, the polyvinyl alcohol copolymer (A) is 60 to 90% by mass, and the polyvinyl alcohol polymer (B) is 10 to 40% by mass. The polyvinyl alcohol-based fiber according to claim 5, characterized by: A fiber structure comprising at least a portion of the polyvinyl alcohol-based fiber according to any one of claims 1 to 6. A polyvinyl alcohol-based copolymer (A) containing 1.0 mol% or more of a sulfonic acid group and having a degree of saponification of 80 to 96 mol% and a polyvinyl alcohol-based polymer (B) are mixed and spun. 7. The method for producing a polyvinyl alcohol fiber according to claim 6, comprising at least the step of preparing a stock solution. The spinning stock solution is subjected to wet or dry-wet spinning in a solidification bath mainly composed of an organic solvent capable of solidifying polyvinyl alcohol, and the total draw ratio in all steps is set to 3 in any of drying, drawing, and heat treatment. The method for producing a polyvinyl alcohol-based fiber according to claim 8, characterized in that it is doubled or more.