JP2020204104A - Polyvinyl alcohol fiber and method for producing the same - Google Patents

Abstract

To provide a polyvinyl alcohol fiber obtained by a production method in which a draw ratio is low and having excellent strength, and a method for producing the same.SOLUTION: In a polyvinyl alcohol fiber, regarding the value A and the value B obtained when the long periodic image of X-ray small angle scattering intensity is measured, A/B satisfies 1.6 or more. A: the X-ray small angle scattering intensity of the polyvinyl alcohol fiber is measured, among four images composing the long period image of the X-ray small angle scattering intensity, any one image (X1) is selected, an another image (X2) at the side same as the image (X1) viewed from an equatorial line among the four images is decided, and the average value of the two of the maximum value of the peak scattering intensity derived from the image (X1) (X1-maxvalue) and the maximum value of the peak scattering intensity derived from the image (X2) (X1-maxvalue) is defined as A,and B: between the pixel number position of the maximum value of the peak scattering intensity derived from the image (X1) and the pixel number position of the maximum value of the peak scattering intensity derived from the image (X2), the minimum value of the scattering intensity is defined as the value B.SELECTED DRAWING: Figure 1

Description

The present invention relates to polyvinyl alcohol-based fibers and methods for producing the same. More specifically, the present invention relates to a polyvinyl alcohol-based fiber containing a polyvinyl alcohol resin having a narrow molecular weight distribution and having significantly reduced defects, and a method for producing the same.

Polyvinyl alcohol-based fibers have a higher strength and elasticity than general-purpose synthetic fibers such as polyamide fibers and polyester fibers, and are not only used as fibers for industrial materials, but also cement reinforcing materials, rubber reinforcing materials, or plastics that replace asbestos. Used as a reinforcing material.

In recent years, as a method for further increasing the strength and elastic modulus of polyvinyl alcohol-based fibers, a method of using polyvinyl alcohol having a molecular weight of 500,000 or more has been proposed based on the same concept as gel spinning-ultra-stretching of high molecular weight polyethylene. (Patent Document 1). As a result, fibers having high strength and high elastic modulus comparable to polyparaphenylene terephthalamide fibers, which are representative of high strength and high elastic modulus fibers, have been obtained, although they are not as good as polyethylene fibers produced by the so-called gel spinning method. .. However, this method has problems of cost increase and spinning stability.

As a method of improving the strength of the conventional polyvinyl alcohol-based fiber, there are a method of increasing the degree of polymerization and a method of improving the draw ratio. However, if the degree of polymerization is increased, the cost can be increased.

Further, in general, high orientation and high crystallization of molecular chains are indispensable for improving the strength, and for that purpose, high-magnification stretching is required (Patent Document 2).

By the way, in recent years, with the progress of so-called living radical polymerization technology, some methods for controlling the radical polymerization reaction of vinyl acetate have been proposed. For example, a method has been proposed in which a radical polymerization reaction of vinyl acetate is carried out in the presence of a radical polymerization initiator and a specific control agent to obtain polyvinyl acetate having a narrow molecular weight distribution and a high molecular weight. In such a polymerization reaction, the growth radical terminal of the molecular chain of polyvinyl acetate covalently bonds with a control agent to form a dormant species, and an equilibrium is formed between the dormant species and the radical species generated by dissociation thereof. Polymerization proceeds while forming. Such a polymerization reaction is called controlled radical polymerization.

According to Patent Document 3, a number average molecular weight (Mn) of 92,000 and a molecular weight distribution (Mw / Mn) are obtained by carrying out a radical polymerization reaction of vinyl acetate in the presence of a radical polymerization initiator and a control agent composed of an iodine compound. ) Synthesized polyvinyl acetate of 1.57, and saponified it to produce polyvinyl alcohol. However, it is known that an aldehyde group is formed at the polymerization terminal of polyvinyl acetate in the polymerization method using an iodine compound as a control agent (see, for example, Non-Patent Document 1). It is known that when polyvinyl acetate having such an aldehyde group at the end is saponified, a conjugated polyene structure in which a plurality of carbon-carbon double bonds are conjugated is formed, and polyvinyl alcohol with remarkable coloring can be obtained. Polyvinyl alcohol colored in this way is not suitable as a fiber.

Recently, a method for synthesizing polyvinyl acetate by controlled radical polymerization using an organic cobalt complex as a control agent has been proposed. In this polymerization reaction, the growth radical terminal of the molecular chain of polyvinyl acetate covalently bonds with the cobalt atom of the organic cobalt complex to form a dormant species, and between the dormant species and the radical species generated by dissociation thereof. Polymerization proceeds while forming equilibrium. For example, Non-Patent Document 2 describes that by polymerizing vinyl acetate in the presence of cobalt (II) acetylacetonate, the number average molecular weight (Mn) is 99,000 and the molecular weight distribution (Mw / Mn) is 1.33. An example of synthesizing polyvinyl acetate has been reported.

Non-Patent Document 3 describes that a polyvinyl acetate chain obtained by polymerizing vinyl acetate in the presence of cobalt (II) acetylacetonate is treated with 1-propanethiol. The polyvinyl acetate chain forms a dormant species with a cobalt (III) complex bonded to the end, and the terminal radical formed by cleavage of the dormant species reacts with 1-propanethiol to cause polyacetate. The cobalt complex can be separated from the vinyl chain. The polyvinyl acetate forming the Dormant species is green, but it is described that the polyvinyl acetate with reduced coloring was obtained by precipitating the separated cobalt complex and then filtering it off with Celite. ing. Further, by using TEMPO (2,2,6,6-tetramethylpiperidin1-oxyl) which is a stable radical compound instead of 1-propanethiol, TEMPO is bound to the terminal radical to capture the radical. You can also. Also in this case, it is described that a colorless polyvinyl acetate was obtained by filtering and removing the cobalt complex with acidic alumina.

As described above, according to the method described in Non-Patent Document 3, it is said that polyvinyl acetate with reduced coloring can be obtained. However, it is not described in Non-Patent Document 3 that the polyvinyl acetate thus obtained is saponified to obtain polyvinyl alcohol. As a result of experiments by the present inventors, it was found that the polyvinyl alcohol obtained by saponifying the polyvinyl acetate obtained in Non-Patent Document 3 is colored.

Therefore, Patent Document 4 proposes a method for producing a polyvinyl alcohol resin having a narrow molecular weight distribution and not being colored. However, Patent Document 4 does not describe fibrosis.

JP-A-59-130314 Japanese Unexamined Patent Publication No. 2-155008 Japanese Unexamined Patent Publication No. 11-147914 International Publication No. 2019/13267

Controlled / Living Radical Polymerization of Vinyl Acetate by Degenerative Transfer with Alkyl Iodides, Macromolecules, 2003, vol.36, Issue 25, p9346-9354 Highly Efficient Cobalt-Mediated Radical Polymerization of Vinyl Acetate, Angewandte Chemie International Edition, 2005, vol.44, p1101-1104 Synthesis of End-Functional Poly (vinyl acetate) by Cobalt-Mediated Radical Polymerization, Macromolecules, 2005, vol.38, Issue 13, p5452-5458

An object of the present invention is to solve the above-mentioned problems, to provide a polyvinyl alcohol-based fiber having excellent strength even when the draw ratio is low, and to provide a method for producing the same.

As a result of intensive research to solve the above problems, the present inventors have focused on a technique for narrowing the molecular weight distribution as a method for reducing fiber defects during drawing, further advanced the research, and completed the present invention. I came to do it.

That is, the present invention includes the following inventions.
[1] A polyvinyl alcohol-based fiber having an A / B of 1.6 or more with respect to the following values A and B obtained when a long-period image of small-angle X-ray scattering intensity is measured.
A: A long-period image of the small-angle X-ray scattering intensity of the polyvinyl alcohol fiber is measured so that the fiber axis direction of the polyvinyl alcohol-based fiber is the meridional direction, and a long-period image of the small-angle X-ray scattering intensity that can be obtained by the measurement is performed. Observe the four images that make up the. One of the four images (X1) is selected, and the point (X1max) having the highest peak scattering intensity in the image (X1) is specified. It passes through the point (X1max) and another image (X2) on the same side as the image (X1) when viewed from the equator line among the four images, and is parallel to the equator line. The linear region (Y) is determined. The maximum value (X1-maxvalue) of the peak scattering intensity derived from the image (X1) and the maximum value of the peak scattering intensity derived from the image (X2) (X1-maxvalue) obtained by observing the peak scattering intensity in the linear region (Y). Let the two average values of X2-maxvalue) be the value A.
B: The number of pixels (X1P) at the point (X1max) that gives the maximum value (X1-maxvalue) of the peak scattering intensity derived from the image (X1) when the peak scattering intensity is observed in the linear region (Y). And the minimum value of the scattering intensity in the pixel number range between the maximum value (X2-maxvalue) of the peak scattering intensity derived from the image (X2) and the pixel number position (X2P) is defined as the value B.
[2] The polyvinyl alcohol-based fiber according to the above [1], which has a tensile strength of 10.0 cN / dtex or more.
[3] The polyvinyl alcohol-based fiber according to the above [1] or [2], which comprises a polyvinyl alcohol resin having a molecular weight distribution (Mw / Mn) of 1.05 to 1.95.
[4] The polyvinyl alcohol-based fiber according to the above [3], wherein the degree of saponification of the polyvinyl alcohol resin is 95.0 to 99.9 mol%.
[5] The polyvinyl alcohol-based fiber according to the above [3] or [4], wherein the polyvinyl alcohol resin has a terminal group represented by the following formula (I).
(In the formula, R ¹ represents an aromatic group having 6 to 20 carbon atoms which may have a substituent, and R ² may have a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or a substituent. Represents a good aromatic group with 6 to 20 carbon atoms.)
[6] The polyvinyl alcohol-based fiber according to any one of [3] to [5], wherein the polyvinyl alcohol resin has a weight average molecular weight (Mw) of 100,000 to 555,000.
[7] The method for producing a polyvinyl alcohol-based fiber according to any one of [1] to [6] above, which comprises a spinning step of spinning by a wet spinning method.
[8] Production of polyvinyl alcohol-based fiber comprising a step of immersing an aqueous solution containing a polyvinyl alcohol resin having a molecular weight distribution (Mw / Mn) of 1.05 to 1.95 in a coagulation bath of inorganic salts to dehydrate and solidify it. Method.
[9] The method for producing a polyvinyl alcohol-based fiber according to the above [8], wherein the coagulation bath of the inorganic salts further contains an alkaline aqueous solution.
[10] The method for producing a polyvinyl alcohol-based fiber according to [8] or [9], wherein the coagulation bath for the inorganic salts is a saturated aqueous solution of the inorganic salts.
[11] The method for producing a polyvinyl alcohol-based fiber according to any one of [7] to [10], further comprising a stretching step, wherein the total stretching ratio in the stretching step is less than 18.0 times.

According to the present invention, it is possible to provide a polyvinyl alcohol-based fiber having excellent strength and a method for producing the same even when the draw ratio is low.

FIG. 1 is an explanatory diagram of a method for measuring the small-angle X-ray scattering intensity according to the present invention. FIG. 2 is an explanatory diagram illustrating a method of calculating a value A (the average value of two maximum values of the peak scattering intensity in a linear region parallel to the equator line) from the measurement result of the small-angle X-ray scattering intensity according to the present invention. is there. FIG. 3 is a diagram showing the measurement results of the small-angle X-ray scattering intensity of Examples 1 to 5 and Comparative Examples 1 to 5. FIG. 4 is a diagram showing the peak scattering intensity obtained from the small-angle X-ray scattering image of the linear region parallel to the equator line of the polyvinyl alcohol fiber sample in Example 1 and Comparative Example 1. FIG. 5 is a diagram showing peak scattering intensities obtained from small-angle X-ray scattering images in a linear region parallel to the equator line of the polyvinyl alcohol fiber samples in Examples 2 and 3 and Comparative Examples 2 and 3. FIG. 6 is a diagram showing peak scattering intensities obtained from small-angle X-ray scattering images in a linear region parallel to the equator line of the polyvinyl alcohol fiber samples in Examples 4 and 5 and Comparative Examples 4 and 5.

The polyvinyl alcohol-based fiber of the present invention has an A / B of 1.6 or more with respect to the following values A and B obtained when a long-period image of small-angle X-ray scattering intensity is measured.
A: A long-period image of the small-angle X-ray scattering intensity of the polyvinyl alcohol-based fiber is measured so that the fiber axis direction of the polyvinyl alcohol-based fiber is the meridional direction, and a long-period image of the small-angle X-ray scattering intensity that can be obtained by the measurement is performed. Observe the four images that make up the. One of the four images (X1) is selected, and the point (X1max) having the highest peak scattering intensity in the image (X1) is specified. It passes through the point (X1max) and another image (X2) on the same side as the image (X1) when viewed from the equator line among the four images, and is parallel to the equator line. The linear region (Y) is determined. The maximum value (X1-maxvalue) of the peak scattering intensity derived from the image (X1) and the maximum value of the peak scattering intensity derived from the image (X2) obtained by observing the peak scattering intensity in the linear region (Y) (X1). Let the two average values of X2-maxvalue) be the value A.
B: The number of pixels (X1P) at the point (X1max) that gives the maximum value (X1-maxvalue) of the peak scattering intensity derived from the image (X1) when the peak scattering intensity is observed in the linear region (Y). And the minimum value of the scattering intensity in the pixel number range between the maximum value (X2-maxvalue) of the peak scattering intensity derived from the image (X2) and the pixel number position (X2P) is defined as the value B.

In the present specification, the upper limit value and the lower limit value of the numerical range (content of each component, each condition in the manufacturing method, etc., value calculated from each component, each physical property, etc.) can be appropriately combined.

In the present invention, the small-angle X-ray scattering intensity can be measured according to a known small-angle X-ray scattering method (SAXS). For example, under the conditions described in the examples described later, as shown in FIG. 1, a sample of polyvinyl alcohol-based fiber 1 is placed in a slit 2 having a predetermined size so that the fiber axis direction is the meridional direction, and the sample is predetermined. A long period of X-ray small-angle scattering intensity is obtained by irradiating incident X-rays 3 and measuring scattered X-rays using a nanoscale X-ray structure evaluation device (for example, NANO-Viewer (manufactured by Rigaku)). The image can be measured. In the present specification, the four interference images measured by the small-angle X-ray scattering method are collectively referred to as a long-period image. As shown in FIG. 3, in the polyvinyl alcohol-based fibers containing the conventional polyvinyl alcohol resins of Comparative Examples 1 to 5, no image separated into four is observed.

Next, the value A (the average value of the two maximum values of the peak scattering intensity in the linear region parallel to the equator line) will be described. For the measurement result of the long-period image of the X-ray small-angle scattering intensity obtained by the small-angle X-ray scattering method, one interference image (X1) is selected from the four leaf-shaped interference images, and the image (X1) is selected. The point (X1max) having the highest peak scattering intensity in X1) is specified. It passes through the point (X1max) and another image (X2) on the same side as the image (X1) when viewed from the equator line among the four images, and is parallel to the equator line. The linear region (Y) is determined.
In FIG. 2, in the portion surrounded by the dotted line, the axial region indicated by the alternate long and short dash line is the linear region (Y) parallel to the equator line 30. In FIG. 2, the interference image on the upper left in the drawing is selected as the interference image (X1) from the four interference images, and the point (X1max: in FIG. 2) having the highest peak scattering intensity in the image (X1). The point indicated by "+") is specified. In this case, the interference image at the lower left in the drawing becomes another image (X2).
When the peak scattering intensity is observed in the linear region (Y), the result as shown in FIG. 4 can be obtained. FIG. 4 shows the peak scattering intensity obtained from the small-angle X-ray scattering images in the linear region parallel to the equator line of the polyvinyl alcohol-based fiber samples of Example 1 and Comparative Example 1. In FIG. 4, the horizontal axis represents the number of pixels and the vertical axis represents the scattering intensity. As shown in FIG. 4, the maximum value (X1-maxvalue) of the peak scattering intensity derived from the image (X1) (point 4 in FIG. 4) and the maximum value (X2-maxvalue) of the peak scattering intensity derived from the image (X2). ) (Point 5 in FIG. 4) is the value A.

As shown in FIG. 4, the value B gives a maximum value (X1-maxvalue) of the peak scattering intensity derived from the image (X1) when the peak scattering intensity is observed in the linear region (Y). The minimum value of the scattering intensity in the pixel number range between the pixel number position (X1P) of (X1max) and the pixel number position (X2P) of the maximum value (X2-maxvalue) of the peak scattering intensity derived from the image (X2). (Point 6 in FIG. 4).

In the polyvinyl alcohol-based fiber of the present invention, the A / B is 1.6 or more, and 1.7 or more is preferable, and 1.8 or more is more preferable, from the viewpoint of excellent strength. The A / B is not particularly limited, but may be 20 or less, 10 or less, or 6 or less.

The polyvinyl alcohol-based fiber of the present invention preferably has a tensile strength of 10.0 cN / dtex or more, more preferably 11.0 cN / dtex or more, and even more preferably 12.0 cN / dtex or more. The tensile strength can be measured by the method described in Examples described later.

The polyvinyl alcohol-based fiber of the present invention preferably contains a polyvinyl alcohol resin having a molecular weight distribution (Mw / Mn) of 1.05 to 1.95. By polymerizing by controlled radical polymerization, a polyvinyl alcohol resin having a narrow molecular weight distribution can be obtained. By using a polyvinyl alcohol resin having a narrow molecular weight distribution (Mw / Mn), the strength of the polyvinyl alcohol fiber obtained is the conventional polyvinyl alcohol type obtained by using a polyvinyl alcohol resin having the same weight average molecular weight (Mw). Surprisingly noticeable improvement compared to fiber. Therefore, it is possible to increase the strength of the obtained polyvinyl alcohol-based fiber while suppressing the decrease in moldability. The molecular weight distribution (Mw / Mn) is preferably 1.90 or less, more preferably 1.85 or less, and even more preferably 1.70 or less. The molecular weight distribution (Mw / Mn) is preferably 1.10 or more, more preferably 1.15 or more, and even more preferably 1.20 or more. The molecular weight distribution (Mw / Mn) can be measured by the method described in Examples described later.

The weight average molecular weight (Mw) of the polyvinyl alcohol resin is preferably 100,000 to 1,000,000. When the weight average molecular weight (Mw) is 100,000 or more, a polyvinyl alcohol-based fiber having excellent strength can be obtained. The weight average molecular weight (Mw) is preferably 150,000 or more, more preferably 180,000 or more, and even more preferably 190,000 or more. On the other hand, when the weight average molecular weight (Mw) is 1,000,000 or less, the moldability is improved. The weight average molecular weight (Mw) is preferably 800,000 or less, and more preferably 500,000 or less. The weight average molecular weight (Mw) and the molecular weight distribution (Mw / Mn) in the present invention are measured by gel permeation chromatography (GPC) method. In this measurement, polymethylmethacrylate is used as a standard substance. Further, HFIP (hexafluoroisopropanol) is used as the mobile phase, and a column for HFIP is used as the column. Specifically, the measurement by the GPC method in the present invention is performed by the method described in the examples.

The saponification degree of the polyvinyl alcohol resin is preferably 95.0 to 99.99 mol% from the viewpoint of more excellent fiber strength. The saponification degree is preferably 98 mol% or more, more preferably 99 mol% or more, and further preferably 99.9 mol% or more. On the other hand, if the degree of saponification exceeds 99.99 mol%, it may be difficult to produce a polyvinyl alcohol resin. The saponification degree is preferably 99.95 mol% or less. The degree of saponification of the polyvinyl alcohol resin in the present specification is the total number of moles of the structural unit (typically a vinyl ester unit) and the vinyl alcohol unit of the polyvinyl alcohol resin that can be converted into vinyl alcohol units by saponification. The ratio (mol%) of the number of moles of the vinyl alcohol unit to the vinyl alcohol unit. The saponification degree of the polyvinyl alcohol resin can be measured by the method described in Examples described later.

The total amount of the vinyl ester unit and the vinyl alcohol unit with respect to all the monomer units in the polyvinyl alcohol resin is preferably 50 mol% or more, more preferably 80 mol% or more, further preferably 90 mol% or more, and particularly preferably 95 mol% or more. Preferably, it may be 100 mol%.

The content of the 1,2-glycol bond in the polyvinyl alcohol resin is preferably 0.7 to 1.5 mol%. When the content of 1,2-glycol bond is 1.5 mol% or less, the strength of the obtained fiber is further improved. The content of 1,2-glycol bond is more preferably 1.4 mol% or less. On the other hand, if the content of the 1,2-glycol bond is less than 0.7 mol%, the water solubility may decrease and it may become difficult to handle. The content of 1,2-glycol bond is more preferably 1 mol% or more.

The polyvinyl alcohol resin preferably has a terminal group represented by the following formula (I).
(In the formula, R ¹ represents an aromatic group having 6 to 20 carbon atoms which may have a substituent, and R ² may have a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or a substituent. Represents a good aromatic group with 6 to 20 carbon atoms.)

In the above formula (I), R ¹ represents an aromatic group having 6 to 20 carbon atoms which may have a substituent. When R ¹ is an aromatic group having a substituent, the number of carbon atoms including the carbon of the substituent needs to be in the above range. The number of carbon atoms of the aromatic group used as R ¹ is preferably 10 or less. The aromatic group used as R ¹ may be either an aromatic hydrocarbon group or a complex aromatic group, but the former is preferable. Examples of the aromatic hydrocarbon group used as R ¹ include a phenyl group, a biphenyl group, a naphthyl group, an anthryl group, a phenanthryl group and the like, and a phenyl group is preferable.

R ¹ may be an aromatic group having a substituent. Examples of the substituent at this time include an alkyl group and the like. Examples of the alkyl group include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, isopentyl group, neopentyl group and tert. -Pentyl group, n-hexyl group, isohexyl group, 2-ethylhexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group and the like can be mentioned. From the viewpoint of obtaining a polyvinyl alcohol resin having a narrower molecular weight distribution, hue and water solubility, R ¹ is preferably an aromatic group having no substituent.

In the above formula (I), R ² represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or an aromatic group having 6 to 20 carbon atoms which may have a substituent. The number of carbon atoms of the alkyl group used as R ² is preferably 10 or less, more preferably 5 or less, and even more preferably 3 or less. Examples of the alkyl group include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, isopentyl group, neopentyl group and tert. -Pentyl group, n-hexyl group, isohexyl group, 2-ethylhexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group and the like can be mentioned, with methyl group being preferable.

From the viewpoint of obtaining a polyvinyl alcohol resin having a narrower molecular weight distribution, R ² is preferably an aromatic group. The aromatic group of R ² is preferably the same as the aromatic group used as R ¹ .

The terminal group is preferably derived from a polymerization terminator represented by the following formula (II).
(In the formula, R ¹ and R ² have the same meaning as those shown in the above formula (I).)

It is considered that the polymerization terminator reacts with the radical of the polyvinyl ester chain, binds to the terminal of the polyvinyl ester chain, and then the newly generated radical is protonated to form the terminal group. ..

Specific examples of the polymerization terminator represented by the above formula (II) include 1,1-diphenylethylene, styrene, α-methylstyrene, 4-tert-butylstyrene and the like, and among them, 1,1-diphenylethylene. , Styrene and α-methylstyrene are preferred, 1,1-diphenylethylene and styrene are more preferred, and 1,1-diphenylethylene is even more preferred.

The polyvinyl alcohol resin used in the present invention satisfies the following formula (Z) in terms of the molar ratio (X) and number average molecular weight (Mn) of the terminal groups represented by the above formula (I) to all monomer units. Is.

X · Mn / 44 ≧ 0.5 (Z)

In the above formula (Z), the left side (X · Mn / 44) is the polyvinyl in the molar ratio (X) of the terminal group represented by the above formula (I) to all the monomer units in the polyvinyl alcohol resin. It is the product of the number average degree of polymerization (Mn / 44) of the alcohol resin. That is, X · Mn / 44 corresponds to the ratio of the polyvinyl alcohol chain having the terminal group to the total polyvinyl alcohol chain. Therefore, when X · Mn / 44 is a certain value or more, it means that the ratio of the polyvinyl alcohol chain having the terminal group to the total polyvinyl alcohol chain is a certain value or more. As described above, the polymerization terminator represented by the above formula (II) is bound to the terminal of the polyvinyl ester chain to conjugate and stabilize the radical, whereby a polyvinyl alcohol resin having a narrow molecular weight distribution can be obtained.

When the polymerization reaction represented by the above formula (II) is added to stop the polymerization reaction of the vinyl ester monomer and the terminal group represented by the above formula (I) is introduced into the polyvinyl ester chain, The content of the carbon-carbon double bond of the main chain in the polyvinyl alcohol resin after saponification is reduced, and a polyvinyl alcohol resin having a good hue can be obtained, and the polyvinyl alcohol-based fiber using the polyvinyl alcohol resin has excellent strength. X · Mn / 44 is preferably 0.65 or more, and more preferably 0.8 or more. On the other hand, X · Mn / 44 is usually 2 or less. Even if the terminal group is bonded to all polyvinyl alcohol chains, X · Mn / 44 is calculated to be 1, but the value actually obtained may exceed 1 due to a measurement error of the number average molecular weight (Mn) or the like. is there.

The method for producing a polyvinyl alcohol-based fiber of the present invention is not particularly limited, and examples thereof include a method for producing a polyvinyl alcohol-based fiber including a spinning step of spinning by a wet spinning method.

In the method for producing a polyvinyl alcohol-based fiber of the present invention, an aqueous solution containing a polyvinyl alcohol resin having a molecular weight distribution (Mw / Mn) of 1.05 to 1.95 is immersed in a coagulation bath of inorganic salts to dehydrate and solidify. A method of providing a process can be mentioned. The production method is one aspect of a method for producing a polyvinyl alcohol-based fiber, which comprises a spinning step of spinning by a wet spinning method.

A suitable method for producing a polyvinyl alcohol resin having a molecular weight distribution (Mw / Mn) of 1.05 to 1.95 is to polymerize a vinyl ester monomer by controlled radical polymerization in the presence of a radical initiator and an organic cobalt complex. Polymerization step; After the polymerization step, a polymerization terminator represented by the above formula (I) or a proton-donating polymerization terminator is added to terminate the polymerization to obtain a polyvinyl ester; and the terminator step. It has a saponification step; in which the polyvinyl ester obtained in the above step is saponified to obtain a polyvinyl alcohol resin. According to this method, a polyvinyl alcohol resin having a narrow molecular weight distribution, a high weight average molecular weight, and a good hue can be obtained. Hereinafter, a method for producing a polyvinyl alcohol resin will be described in detail.

First, the polymerization process will be described. In the polymerization step, the vinyl ester monomer is polymerized by controlled radical polymerization in the presence of a radical initiator and an organic cobalt complex. Controlled radical polymerization is a polymerization reaction in which the growth radical terminal (active species) is placed in equilibrium with a covalent bond species (dormant species) bound to a control agent and the reaction proceeds. By performing controlled radical polymerization, side reactions are suppressed, so that a polyvinyl ester having a high weight average molecular weight (Mw) and a narrow molecular weight distribution (Mw / Mn) can be obtained. In the above production method, an organic cobalt complex is used as a control agent.

Examples of the vinyl ester monomer used in the above-mentioned production method include vinyl formate, vinyl acetate, trifluoroacetic acid vinyl acetate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, and laurin. Examples thereof include vinyl acetate, vinyl stearate, vinyl benzoate, vinyl versatic acid and the like, but vinyl acetate is preferably used from an economical point of view.

The produced polyvinyl ester may contain a monomer unit derived from an ethylenically unsaturated monomer copolymerizable with the vinyl ester monomer as long as the effects of the present invention are not impaired. Examples of the ethylenically unsaturated monomer include olefins such as ethylene, propylene, 1-butene and isobutene; acrylic acid, methacrylic acid, crotonic acid, (anhydrous) phthalic acid, (anhydrous) maleic acid, (anhydrous) itaconic acid and the like. Unsaturated carboxylic acid, its salt, its mono or dialkyl ester or its anhydride; acrylamide, N-alkylacrylamide, N, N-dimethylacrylamide, 2-acrylamide propanesulfonic acid or its salt, acrylamidepropyldimethylamine or its acid Acrylonitrile such as a salt or a quaternary salt thereof; methacrylamide, N-alkylmethacrylicamide, N, N-dimethylmethacrylate, 2-methacrylamide propanesulfonic acid or a salt thereof, methacrylicamidepropyldimethylamine or an ester thereof or its 4 Methacrylates such as grade salts; N-vinylamides such as N-vinylpyrrolidone, N-vinylformamide, N-vinylacetamide; vinyl cyanide such as acrylonitrile and methacrylonitrile; alkylvinyl ethers, hydroxyalkylvinyl ethers, alkoxyalkylvinyl ethers and the like Vinyl ether; vinyl halide such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, vinyl bromide; vinylsilane such as trimethoxyvinylsilane, allyl acetate, allyl chloride, allyl alcohol, dimethylallyl alcohol, trimethyl- (3-) Acrylo-3-dimethylpropyl) -ammonium chloride, acrylamide-2-methylpropanesulfonic acid and the like can be mentioned. The number of carbon atoms of the ethylenically unsaturated monomer to be copolymerized is not particularly limited, but the number of carbon atoms is preferably 2 to 20. The content of the monomer unit derived from the ethylenically unsaturated monomer with respect to all the monomer units in the polyvinyl alcohol resin is preferably 20 mol% or less, more preferably 10 mol% or less, and 1 mol%. The following is more preferable, and 0.1 mol% or less is particularly preferable.

Examples of the method for polymerizing the vinyl ester monomer include known methods such as a massive polymerization method, a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method. Among them, a massive polymerization method in which polymerization is carried out without a solvent or a solution polymerization method in which polymerization is carried out in various organic solvents is usually adopted. In order to obtain a polymer having a narrow molecular weight distribution, a massive polymerization method that does not use a solvent or a dispersion medium that may cause side reactions such as chain transfer is preferable. On the other hand, solution polymerization may be preferable from the viewpoint of adjusting the viscosity of the reaction solution and controlling the polymerization rate. Examples of the organic solvent used as a solvent in solution polymerization include esters such as methyl acetate and ethyl acetate; aromatic hydrocarbons such as benzene and toluene; lower alcohols such as methanol and ethanol; and the like. Of these, esters and aromatic hydrocarbons are preferably used to prevent chain transfer. The amount of the solvent used may be determined in consideration of the viscosity of the reaction solution according to the weight average molecular weight of the target polyvinyl alcohol resin. For example, the mass ratio (solvent / monomer) is selected from the range of 0.01-10. The mass ratio (solvent / monomer) is preferably 0.1 or more, and preferably 5 or less.

As the radical initiator used in the polymerization step, conventionally known azo-based initiators, peroxide-based initiators, redox-based initiators and the like are appropriately selected. Examples of the azo-based initiator include 2,2'-azobis (isobutyronitrile), 2,2'-azobis (2,4-dimethylvaleronitrile), and 2,2'-azobis (4-methoxy-2,4). -Dimethylvaleronitrile) and the like. Peroxide-based initiators include percarbonate compounds such as diisopropylperoxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and diethoxyethylperoxydicarbonate; t-butylperoxyneodecanate, α-kumi. Perester compounds such as ruperoxyneodecanate and t-butylperoxyneodecanate; acetylcyclohexylsulfonyl peroxide, diisobutyryl peroxide; 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate and the like. .. Further, potassium persulfate, ammonium persulfate, hydrogen peroxide and the like can be combined with the above-mentioned initiator to prepare the initiator. In addition, examples of the redox-based initiator include a combination of the above-mentioned peroxide and a reducing agent such as sodium hydrogen sulfite, sodium hydrogen carbonate, tartaric acid, L-ascorbic acid, and longalite. The amount of the initiator used differs depending on the polymerization catalyst and cannot be unconditionally determined, and is arbitrarily selected according to the polymerization rate.

The organic cobalt complex used as a control agent in the polymerization step preferably contains a divalent cobalt atom and an organic ligand. Suitable organic cobalt complexes include, for example, cobalt (II) acetylacetonate [Co (acac) 2], cobalt (II) porphyrin complex and the like. Of these, cobalt (II) acetylacetonate is preferable from the viewpoint of manufacturing cost.

For example, in controlled radical polymerization, first, the radicals generated by the decomposition of the radical initiator combine with a small number of vinyl ester monomers, and the radicals at the growth ends of the short-chain polymer are combined with the organic cobalt (II) complex. Bonding produces a dormant species in which the organic cobalt (III) complex is covalently bonded to the polymer terminal. For a certain period of time after the start of the reaction, a short-chain polymer is produced and only converted into a dormant species, and the degree of polymerization does not substantially increase. This period is called the induction period. After the organic cobalt (II) complex is consumed, the growth period in which the degree of polymerization increases progresses, and the molecular weight of most of the molecular chains in the reaction system increases in proportion to the polymerization time in the same manner. As a result, a polyvinyl ester having a narrow molecular weight distribution can be obtained.

In the controlled radical polymerization, theoretically, one polyvinyl ester chain is generated from one molecule of the added organic cobalt complex. Therefore, the amount of the organic cobalt complex added to the reaction solution is determined in consideration of the target polymerization average molecular weight and the polymerization rate. Usually, it is preferable to use 0.001 to 1 mol of an organic cobalt complex with respect to 100 mol of the vinyl ester monomer.

The number of moles of the radical initiator used in the controlled radical polymerization is preferably 1 times or more, more preferably 1.5 times or more the number of moles of the organic cobalt complex. On the other hand, if the number of moles of radicals generated is too large to be larger than the number of moles of the organic cobalt complex, the proportion of uncontrolled radical polymerization increases and the molecular weight distribution widens. The number of moles of the radical initiator used is preferably 10 times or less, more preferably 6 times or less, the number of moles of the organic cobalt complex.

The method for mixing the radical initiator, the organic cobalt complex and the vinyl ester monomer is not particularly limited as long as the dormant species can be produced and the degree of polymerization of the polyvinyl ester can be controlled. For example, a method of mixing the obtained mixture and a vinyl ester monomer after mixing the radical initiator and the organic cobalt complex, a method of mixing the radical initiator, the organic cobalt complex and the vinyl ester monomer at once, an organic method. Examples thereof include a method of mixing the cobalt complex and the vinyl ester monomer, and then mixing the obtained mixture with the radical initiator. Further, the radical initiator, the organic cobalt complex and the vinyl ester monomer may be divided and mixed. For example, by mixing a radical initiator and an organic cobalt complex with a part of a vinyl ester monomer, a dormant species in which the organic cobalt (III) complex is covalently bonded to the short-chain polyvinyl ester terminal is generated, and then the dormant species is generated. Examples thereof include a method of mixing the dormant species and the remainder of the vinyl ester monomer to increase the degree of polymerization. The dormant species may be isolated as a macroinitiator and then mixed with the rest of the vinyl ester monomer to increase the degree of polymerization.

The polymerization temperature is preferably, for example, 0 ° C to 80 ° C. When the polymerization temperature is less than 0 ° C., the polymerization rate becomes insufficient and the productivity tends to decrease. From this point of view, the polymerization temperature is more preferably 10 ° C. or higher, and even more preferably 20 ° C. or higher. On the other hand, when the polymerization temperature exceeds 80 ° C., the molecular weight distribution of the obtained polyvinyl ester tends to be widened. From this point, the polymerization temperature is more preferably 65 ° C. or lower, and even more preferably 50 ° C. or lower. The time required for the polymerization step of the vinyl ester monomer is usually 3 to 50 hours.

When the desired polymerization rate is reached in the polymerization step, the polymerization reaction is stopped by adding a polymerization terminator represented by the above formula (I) or a proton-donating polymerization terminator.

The proton donating polymerization terminator is a polymerization terminator capable of providing a proton radical to the radical at the end of the polyvinyl acetate chain, and preferably has a chain transfer constant of 0.1 or more with respect to vinyl acetate at 60 ° C. .. For example, sorbic acid and the like can be mentioned. Further, an organometallic compound having a metal-hydrogen bond or the like can also be used.

The number of moles of the polymerization inhibitor represented by the above formula (II) to be added is preferably 1 to 100 mol with respect to 1 mol of the added organic cobalt complex. If the number of moles of the polymerization inhibitor is too small, the radicals at the polymer ends cannot be sufficiently captured, and the color tone of the obtained polyvinyl alcohol resin may deteriorate. Therefore, the number of moles of the polymerization inhibitor is more preferably 3 mol or more with respect to 1 mol of the organic cobalt complex. On the other hand, if the number of moles of the polymerization inhibitor is too large, the production cost may increase. The number of moles of the polymerization inhibitor is more preferably 50 mol or less with respect to 1 mol of the organic cobalt complex.

The temperature of the reaction solution in the termination step is the temperature at which the polymerization inhibitor represented by the above formula (II) can react with the radical at the end of the polyvinyl acetate chain, or the proton-donating polymerization inhibitor is the radical at the end of the polyvinyl acetate chain. The temperature may be any temperature at which proton radicals can be provided, preferably 0 to 80 ° C. If the temperature of the reaction solution is less than 0 ° C., the stopping step takes too much time and the productivity is lowered. From this point of view, the temperature of the reaction solution in the stopping step is more preferably 10 ° C. or higher, further preferably 20 ° C. or higher. On the other hand, when the temperature of the reaction solution exceeds 80 ° C., unnecessary polymerization of vinyl acetate proceeds and the molecular weight distribution (Mw / Mn) tends to increase. From this point, the temperature is more preferably 70 ° C. or lower, and even more preferably 60 ° C. or lower. The time required for the stopping process is usually 10 minutes to 5 hours.

After the stopping step, it is preferable to carry out an extraction step of bringing the obtained polyvinyl ester solution into contact with an aqueous solution containing a water-soluble ligand to extract and remove the cobalt complex from the polyvinyl ester solution. As described above, by performing the saponification step after removing the cobalt complex contained in the polyvinyl ester solution in advance, a polyvinyl alcohol resin having a good hue and being hard to gel can be obtained. Specifically, the aqueous solution and the polyvinyl ester solution, which are insoluble in each other, are vigorously stirred so that the area of the interface between the two is large, and then allowed to stand, separated into an oil layer and an aqueous layer, and then the aqueous layer is formed. All you have to do is remove it. This operation may be repeated a plurality of times.

The water-soluble ligand used in the extraction step is preferably an acid having a pKa of 0 to 12 at 25 ° C. When a strong acid having a pKa of less than 0 is used, it is difficult to efficiently extract the cobalt complex, and the pKa is preferably 2 or more. Further, it is difficult to efficiently extract the cobalt complex even when a weak acid having a pKa of more than 12 is used, and the pKa is preferably 7 or less. When the acid is a polyvalent acid, the first dissociation constant (pKa1) needs to be in the above range. The acid having a pKa of 0 to 12 is preferably a carboxylic acid or a phosphoric acid (pKa1 is 2.1), and more preferably a carboxylic acid. Of these, acetic acid (pKa is 4.76) is particularly preferable.

The pH of the aqueous solution containing the water-soluble ligand is preferably 0 to 5. The pH is more preferably 1 or more, and even more preferably 1.5 or more. The pH is more preferably 4 or less, and even more preferably 3 or less.

In the saponification step, the polyvinyl ester obtained in the stop step is saponified to obtain a polyvinyl alcohol resin. At this time, the saponification step may be performed after the extraction step is performed after the stop step.

In the saponification step, the polyvinyl ester produced by the above method is saponified in a state of being dissolved in alcohol or hydroalcohol to obtain a polyvinyl alcohol resin. Examples of the alcohol used in the saponification reaction include lower alcohols such as methanol and ethanol, and methanol is particularly preferably used. The alcohol used in the saponification reaction may contain acetone, an ester such as methyl acetate or ethyl acetate, or a solvent such as toluene. Examples of the catalyst used in the saponification reaction include hydroxides of alkali metals such as potassium hydroxide and sodium hydroxide, alkaline catalysts such as sodium methylate, and acid catalysts such as mineral acid. The temperature of the saponification reaction is, for example, in the range of 20 to 60 ° C. When a gel-like product precipitates as the saponification reaction progresses, the product is pulverized at that time, washed, and dried to obtain a polyvinyl alcohol resin.

In producing the polyvinyl alcohol-based fiber, the method for spinning the polyvinyl alcohol resin is not particularly limited, but the wet spinning method is preferable. Among the wet spinning methods, there are a dehydration gelling method and a dehydration solidification method. As the solvent used in the spinning stock solution, the solvents conventionally used in the production of polyvinyl alcohol-based fibers, such as water, dimethyl sulfoxide (DMSO), dimethylformamide, dimethylacetamide, glycerin, ethylene glycol, triethylene glycol, and the like are polyvalent. One kind or a combination of two or more kinds such as alcohol can be used. Of these, water and DMSO are particularly preferable from the viewpoint of supplyability and influence on environmental load. The concentration of the polyvinyl alcohol resin in the spinning stock solution varies depending on the composition, degree of polymerization, and solvent of the polyvinyl alcohol resin, but is preferably in the range of 6 to 25% by mass. In addition to the polyvinyl alcohol resin, the spinning stock solution contains a gelling agent, a surfactant, a decomposition inhibitor, an antifreezing agent, a pH adjuster, and a concealing agent, as long as the effects of the present invention are not impaired. , Colorants, additives such as oils, etc. may be included. Examples of the gelling agent include boric acid, calcium borate, cobalt borate, zinc borate, potassium aluminum borate, ammonium borate, cadmium borate, potassium borate, copper borate, lead borate, nickel borate, barium borate, bismuth borate, magnesium borate. , Manganese borate, lithium borate, borosand, carnite, inyoite, koto stone, suian stone, zyberite and other boron compounds; tripotassium citrate and the like. Among these, boron compounds are preferable, and boric acid and borax are more preferable. The content of the gelling agent is preferably 0.01 to 5% by mass, more preferably 0.1 to 3% by mass, based on the polyvinyl alcohol resin.

In water-based wet spinning in which water is used as the solvent used for the spinning stock solution, the adjustment can be made from 0.5 to 15 detx / f by changing the nozzle diameter and the concentration of the aqueous solution. Further, even in water-based dry spinning, it is possible to adjust up to 3 to 4,000 dtex / f by changing the nozzle diameter and the concentration of chips contained.

The method for producing a polyvinyl alcohol-based fiber of the present invention includes a step of permeating an aqueous solution containing a polyvinyl alcohol resin having the above-mentioned predetermined molecular weight distribution (Mw / Mn) into a coagulation bath of inorganic salts to dehydrate and solidify it. preferable. In this method, the manufacturing process is simple, the equipment is compact, and in general, the thread shinob is brought into the drying process because it is allowed to pass through the drying and heat drawing steps while the inorganic salts having dehydration and coagulation ability are adhered and contained in the thread shinobi. There is an advantage that the amount of water is reduced, the drying process is easy, and sticking is unlikely to occur. Furthermore, since drying can be performed efficiently, the thickness of the thread shino (focusing degree, total denier) can be increased, which is suitable for mass production.

The coagulation bath used in the method for producing a polyvinyl alcohol-based fiber of the present invention differs depending on whether the spinning stock solution is an aqueous solution or the stock solution solvent is an organic solvent. When the spinning stock solution is an aqueous solution (preferably an aqueous solution containing the polyvinyl alcohol resin), it is preferable to permeate it into a coagulation bath of inorganic salts. Examples of the inorganic salts include sodium sulfate, sodium sulfate decahydrate, ammonium sulfate, sodium carbonate and the like. As the coagulation bath for inorganic salts, it is more preferable to use a saturated aqueous solution of inorganic salts. Further, when the spinning stock solution is an aqueous solution, the coagulation bath is more excellent in the coagulation action, and the strength of the obtained polyvinyl alcohol-based fiber becomes higher. Therefore, it is preferable to further contain an alkaline aqueous solution.

Examples of the alkaline substance used in the alkaline aqueous solution include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide and potassium hydroxide; alkaline earth metal hydroxides such as calcium hydroxide, strontium hydroxide and barium hydroxide; tetraethyl. Examples thereof include ammonium hydroxide, and sodium hydroxide is preferable. When the aqueous solution containing the polyvinyl alcohol resin is used as a spinning stock solution, the composition of the coagulation bath is preferably an aqueous solution of sodium sulfate or a mixed aqueous solution of sodium hydroxide and sodium sulfate. Further, as the spinning stock solution to which boric acid is added, it is preferable to use a mixed aqueous solution of sodium hydroxide and sodium sulfate. In this case, since the solidification is due to dehydration, the higher the sodium sulfate concentration, the higher the solidification property. The sodium sulfate concentration of the highly solidifying coagulation bath is preferably 200 to 400 g / L, more preferably 210 to 390 g / L, and even more preferably 220 g / L to 380 g / L.

In the case of a stock solution using an organic solvent, a mixed solution consisting of a solidifying solvent and a stock solution solvent is preferable, and the solidifying solvent is a polyvinyl alcohol resin such as alcohols such as methanol and ethanol and ketones such as acetone and methyl ethyl ketone. On the other hand, an organic solvent having a solidifying ability is preferable. In this case, the higher the ratio of the solidifying solvent in the coagulation bath, the higher the solidifying property. The ratio of the solidifying solvent in the coagulation bath having high solidifying property is preferably 50% or more, more preferably 55% or more, and further preferably 60% or more.

The temperature of the coagulation bath is not particularly limited, but is preferably 20 to 100 ° C, more preferably 25 to 90 ° C, and even more preferably 30 to 80 ° C.

The solidified yarn obtained by the above spinning method is extracted, washed, dried, and then subjected to a draw heat treatment.

The polyvinyl alcohol-based fiber of the present invention is preferably stretch-heat-treated in order to have a breaking strength of 10 cN / dtex or more. The temperature of this stretching heat treatment is generally 210 ° C. or higher, preferably 220 ° C. to 260 ° C. The total draw ratio of the draw heat treatment is preferably 8.0 times or more, more preferably 10.0 times, from the viewpoint that the crystallinity and orientation of the fibers are improved and the mechanical properties of the fibers are improved accordingly. That is all. The total draw ratio of the draw heat treatment is preferably less than 20.0 times, more preferably less than 18.0 times, and even more preferably less than 16.0 times.

The present invention includes embodiments in which the above configurations are variously combined within the scope of the technical idea of the present invention as long as the effects of the present invention are exhibited.

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples, and many modifications are applicable within the scope of the technical idea of the present invention. It is possible by someone with ordinary knowledge in the field.

[Measurement of weight average molecular weight (Mw) and molecular weight distribution (Mw / Mn)]
The weight average molecular weight (Mw) and the molecular weight distribution (Mw / Mn) were measured using a size exclusion high performance liquid chromatograph "HLC-8320GPC" manufactured by Tosoh Corporation. The measurement conditions are as follows.
Column: HFIP-based column "TSKgel GMHR-H (S)" manufactured by Tosoh Corporation, connected in series Standard sample: Polymethylmethacrylate Solvent and mobile phase: Sodium trifluoroacetate-HFIP solution (concentration 20 mM)
Flow rate: 0.2 mL / min
Temperature: 40 ° C
Sample solution concentration: 0.1 wt% (filtered with a filter with an opening diameter of 0.45 μm)
Injection volume: 10 μL
Detector: RI

[Measurement of saponification degree]
Regarding the polyvinyl alcohol resin used in Example 1 and Comparative Example 1, the polyvinyl alcohol resin dried under reduced pressure at 90 ° C. for 2 days was dissolved in DMSO-d ₆ and a few drops of trifluoroacetic acid were added to prepare a sample. It was used for measurement. ¹ H-NMR measurement was performed at 80 ° C. using a nuclear magnetic resonance apparatus "LAMBDA 500" manufactured by JEOL Ltd. The degree of saponification was calculated from the ratio of the peak integral values of the residual acetyl group in the polyvinyl alcohol resin and the methine group derived from the vinyl group.

[Fineness measurement]
For each polyvinyl alcohol-based fiber obtained in Examples and Comparative Examples, the average value of the number of samples 4 (n = 4) was calculated from the absolute dry weight of a trial length of 30 m with reference to JIS L 1013: 2010, and the average value was an integer. The fineness (dtex) was calculated by rounding off. The single yarn fineness was calculated by dividing the fineness by the number of nozzle holes.

[Tensile strength measurement]
Each polyvinyl alcohol-based fiber obtained in Examples and Comparative Examples was twisted at 80 TPM and measured under the conditions of a grip interval of 20 cm and a tensile speed of 10 cm / min with reference to JIS L 1015: 2010, and the number of samples. The average value of 20 (n = 20) was rounded to the nearest whole number. The obtained strength (cN) value was divided by the fineness (dtex) to calculate the tensile strength (cN / dtex).

[How to obtain the total draw ratio of water-based wet spinning]
Total draw ratio = draw outlet roller speed / 1st roller speed

[Measurement of peak interval from small-angle X-ray scattering intensity]
For each polyvinyl alcohol-based fiber obtained in Examples and Comparative Examples, an image of small-angle X-ray scattering intensity was obtained by the small-angle X-ray scattering method (SAXS) under the following conditions. As shown in FIG. 1, a sample of polyvinyl alcohol-based fiber was placed and measured.
Device: Nanoscale X-ray structure evaluation device "NANO-Viewer" (manufactured by Rigaku)
Detector: 2D semiconductor detector PILATUS-100K
X-ray source: Cu
Current: 20mA
Voltage: 40kv
Camera distance: 987.78mm
Measurement mode: Normal measurement Exposure time: 30 minutes or more Slit conditions; 1st = 0.4mm, 2nd = 0.2mm, 3rd = 0.45mm
Beam stopper diameter: 4 mm
Vacuum path: Vacuum state analysis software: 2DP (manufactured by Rigaku)
Sample set position: After 3rd slit Sample setting method: Set one yarn horizontally

(How to find the scattering intensity peak interval in the linear region parallel to the equator line)
By image processing the obtained two-dimensional images (FIGS. 2 and 3) using general-purpose two-dimensional data processing software (2DP manufactured by Rigaku Co., Ltd.), the images become parallel to the equatorial line of the polyvinyl alcohol fiber sample. The scattering intensity profile of the linear region (Y) was obtained. The straight line region (Y) is used to calculate the value A and the value B by the method described above. For image processing, the measurement data with the sample minus the data measured without the sample was used.
Conversion method; Convert Image to Slit Profile
Conversion mode; Pixel vs intensity
Conversion conditions; step = 0.5pixel
In addition, in order to select one of the four images (X1) and identify the point (X1max) having the highest peak scattering intensity in the image (X1), the center is determined by the image (sample). Positions are different Region (pixel) Left = 85, Right = 95, Top = 10, Bottom = 10
Rotation (deg) 270
Smoothing process; Smoothing factor = 10
1PixelSIZE = 0.172mm
The profile obtained by the above conversion has two chevron shapes.
The peak top distance between these two peaks was calculated in pixels, and the value of the peak scattering intensity in the linear region (Y) parallel to the equator line was obtained in 0.5 pixel increments.
The value A and the value B were calculated by the method described above, and A / B was obtained. For each sample, the average of the peak values of the two peaks shown in FIGS. 4 to 6 is the value A, and the minimum value between the two peaks is the value B.
The wider the peak interval, which is the interval between the values A and B, means that the fibers are regularly arranged. Therefore, information on the regularity of the fiber arrangement can be obtained by the peak interval analysis. That is, if the A / B value is large, it can be said that the fibers are regularly arranged.

[Synthesis Example 1]
A reactor equipped with a stirrer, a reflux condenser, a nitrogen introduction tube, and an initiator addition port is charged with 100 parts by mass of vinyl acetate and 0.04 parts by mass of cobalt (II) acetylacetonate as an organic cobalt complex, and nitrogen bubbling. The inside of the reactor was replaced with an inert gas for 30 minutes. The temperature of the reactor was started by heating the water bath, and when the internal temperature reached 40 ° C., 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile) was added as a radical initiator. 13 parts by mass was added and the mixture was stirred for 2 hours, the temperature was lowered, and the internal temperature was maintained at 30 ° C. to initiate polymerization. Sampling was performed as appropriate, the progress of polymerization was confirmed from the solid content concentration, and when the conversion rate of vinyl acetate reached 20%, 0.13 parts by mass of 1,1-diphenylethylene was added as a polymerization inhibitor, and the temperature was 30 ° C. Was stirred with. The reaction was carried out for 3 hours from the start of polymerization until the target polymerization rate was reached. After adding the polymerization inhibitor, 92 parts by mass of an acetic acid aqueous solution having a concentration of 25% by mass was further added, and the mixture was stirred for 5 minutes and then allowed to stand for 30 minutes to separate into two layers, and the aqueous layer was removed. After repeating the above liquid separation operation a total of 3 times, the acetic acid aqueous solution was changed to deionized water and the same liquid separation operation was repeated a total of 3 times. After that, a vacuum line was connected to the reactor, and the remaining vinyl acetate was distilled off under reduced pressure at 30 ° C. together with methanol. While visually checking the inside of the reactor, when the viscosity increased, distillation was continued while appropriately adding methanol to obtain a 20% by mass methanol solution of polyvinyl acetate. Next, 100 parts by mass of the obtained 20% by mass methanol solution of polyvinyl acetate and 20 parts by mass of methanol are added and dissolved in the same reactor as above, and then the water bath is heated to bring the internal temperature to 40 ° C. Was heated and stirred until. To this, 13.3 parts by mass (1.9 parts by mass as sodium hydroxide) of a methanol solution of sodium hydroxide (concentration 14% by mass) was added, and saponification was carried out at 40 ° C. The produced gelled product was pulverized with a pulverizer and left at 40 ° C. for 1 hour to proceed with saponification. To the obtained saponified product, 1.9 parts by mass of a methanol solution of sodium hydroxide (concentration: 14% by mass) was further added, and a saponification reaction was further carried out under heating at 65 ° C. for 1 hour. Then, 30 parts by mass of methyl acetate was added to neutralize the remaining alkali. After confirming that the neutralization was completed using a phenolphthalein indicator, a solid was obtained by filtration, 75 parts by mass of methanol was added thereto, and the mixture was heated under reflux for 1 hour. Then, the solid obtained by centrifugal dehydration was dried in a vacuum dryer at 40 ° C. for 24 hours to obtain the desired polyvinyl alcohol resin <polymer type I>. As shown in Table 1, the weight average molecular weight (Mw) was 197,000, the degree of saponification was 99.9 mol%, and the molecular weight distribution (Mw / Mn) was 1.6.

[Example 1]
Using the polyvinyl alcohol resin prepared in Synthesis Example 1 and water as a solvent, an aqueous solution was prepared so as to have a concentration of 16.5% by mass. Boric acid was added to this in an amount of 1.8% by mass with respect to the polyvinyl alcohol resin to prepare a spinning stock solution, and water-based wet spinning was carried out. The undiluted spinning solution was discharged from a nozzle into a coagulation bath of inorganic salts (saturated aqueous solution of sodium sulfate / sodium hydroxide, temperature 40 ° C.), immersed in the solution, and then desorbed on a 1st roller to dehydrate and solidify. Then, roller stretching, neutralization, moist heat stretching, washing with water and drying were carried out, stretching treatment was carried out in a wet state (stretching ratio 5 times), and then stretching treatment was carried out at 235 ° C. using a stretching outlet roller. The total draw ratio was 15.5 times as a result of calculating from the draw outlet roller speed and the 1st roller speed ratio. Table 2 below shows the results obtained by the above method for the A / B and tensile strength of the obtained polyvinyl alcohol fiber sample. The measurement results of the small-angle X-ray scattering intensity of the obtained polyvinyl alcohol-based fiber sample are shown in FIG. 3, and the peak scattering intensity obtained from the small-angle X-ray scattering image of the linear region parallel to the equatorial line of the sample is shown in FIG. Shown in.

[Comparative Example 1]
Polyvinyl alcohol resin to be compared (weight average molecular weight is 197,400, saponification degree is 99.9 mol%, molecular weight distribution (Mw / Mn) is 2.2, <polymer type II> in Table 1) and as a solvent. The aqueous solution was prepared to a concentration of 16.5% by mass using the water of. Boric acid was added to this in an amount of 1.8% by mass with respect to the polyvinyl alcohol resin to prepare a spinning stock solution, and water-based wet spinning was carried out. The undiluted spinning solution was discharged from a nozzle into a coagulation bath of inorganic salts (saturated aqueous solution of sodium sulfate / sodium hydroxide, temperature 40 ° C.), immersed in the solution, and then desorbed on a 1st roller to dehydrate and solidify. Then, roller stretching, neutralization, moist heat stretching, washing with water and drying were carried out, stretching treatment was carried out in a wet state (stretching ratio 5 times), and then stretching treatment was carried out at 235 ° C. using a stretching outlet roller. The total draw ratio was 15.5 times as a result of calculating from the draw outlet roller speed and the 1st roller speed ratio. Table 2 below shows the results obtained by the above method for the A / B and tensile strength of the obtained polyvinyl alcohol fiber sample. The measurement results of the small-angle X-ray scattering intensity of the obtained polyvinyl alcohol-based fiber sample are shown in FIG. 3, and the peak scattering intensity obtained from the small-angle X-ray scattering image of the linear region parallel to the equatorial line of the sample is shown in FIG. Shown in.

[Example 2]
Polyvinyl alcohol-based fibers were produced under the same conditions as in Example 1 except that the coagulation bath temperature was changed to 70 ° C. and the total draw ratio was changed. The total draw ratio was 17.8 times as a result of calculating from the draw outlet roller speed and the 1st roller speed ratio. Table 2 below shows the results obtained by the above method for the A / B and tensile strength of the obtained polyvinyl alcohol fiber sample. The measurement result of the small-angle X-ray scattering intensity of the obtained polyvinyl alcohol fiber sample is shown in FIG. 3, and the peak scattering intensity obtained from the small-angle X-ray scattering image of the linear region parallel to the equatorial line of the sample is shown in FIG. Shown in.

[Comparative Example 2]
Polyvinyl alcohol-based fibers were produced under the same conditions as in Comparative Example 1 except that the coagulation bath temperature was changed to 70 ° C. and the total draw ratio was changed. The total draw ratio was 17.8 times as a result of calculating from the draw outlet roller speed and the 1st roller speed ratio. Table 2 below shows the results obtained by the above method for the A / B and tensile strength of the obtained polyvinyl alcohol fiber sample. The measurement result of the small-angle X-ray scattering intensity of the obtained polyvinyl alcohol fiber sample is shown in FIG. 3, and the peak scattering intensity obtained from the small-angle X-ray scattering image of the linear region parallel to the equatorial line of the sample is shown in FIG. Shown in.

[Example 3]
Polyvinyl alcohol-based fibers were produced under the same conditions as in Example 2 except that the temperature during the stretching treatment was changed to 240 ° C. Table 2 below shows the results obtained by the above method for the A / B and tensile strength of the obtained polyvinyl alcohol fiber sample. The measurement result of the small-angle X-ray scattering intensity of the obtained polyvinyl alcohol fiber sample is shown in FIG. 3, and the peak scattering intensity obtained from the small-angle X-ray scattering image of the linear region parallel to the equatorial line of the sample is shown in FIG. Shown in.

[Comparative Example 3]
Polyvinyl alcohol-based fibers were produced under the same conditions as in Comparative Example 2 except that the temperature during the stretching treatment was changed to 240 ° C. Table 2 below shows the results obtained by the above method for the A / B and tensile strength of the obtained polyvinyl alcohol fiber sample. The measurement result of the small-angle X-ray scattering intensity of the obtained polyvinyl alcohol fiber sample is shown in FIG. 3, and the peak scattering intensity obtained from the small-angle X-ray scattering image of the linear region parallel to the equatorial line of the sample is shown in FIG. Shown in.

[Example 4]
Using the polyvinyl alcohol resin prepared in Synthesis Example 1 and water as a solvent, an aqueous solution was prepared as a spinning stock solution so as to have a concentration of 16.5% by mass. The undiluted spinning solution was discharged from a nozzle into a coagulation bath for inorganic salts (saturated aqueous solution of sodium sulfate, temperature 40 ° C.), immersed in the solution, and then desorbed on a 1st roller to dehydrate and solidify. Then, roller stretching, moist heat stretching, washing with water and drying were performed, stretching treatment was performed in a wet state (stretching ratio 4 times), and then stretching treatment was performed using a 235 ° C. stretching outlet roller. The total draw ratio was 11.7 times as a result of calculating from the draw outlet roller speed and the 1st roller speed ratio. Table 2 below shows the results obtained by the above method for the A / B and tensile strength of the obtained polyvinyl alcohol fiber sample. The measurement results of the small-angle X-ray scattering intensity of the obtained polyvinyl alcohol-based fiber sample are shown in FIG. 3, and the peak scattering intensity obtained from the small-angle X-ray scattering image of the linear region parallel to the equatorial line of the sample is shown in FIG. Shown in.

[Comparative Example 4]
Using polyvinyl alcohol resin <polymer type II> to be compared and water as a solvent, an aqueous solution was prepared as a spinning stock solution so as to have a concentration of 16.5% by mass. The undiluted spinning solution was discharged from a nozzle into a coagulation bath for inorganic salts (saturated aqueous solution of sodium sulfate, temperature 40 ° C.), immersed in the solution, and then desorbed on a 1st roller to dehydrate and solidify. Then, roller stretching, moist heat stretching, washing with water and drying were performed, stretching treatment was performed in a wet state (stretching ratio 4 times), and then stretching treatment was performed using a 235 ° C. stretching outlet roller. The total draw ratio was 11.7 times as a result of calculating from the draw outlet roller speed and the 1st roller speed ratio. Table 2 below shows the results obtained by the above method for the A / B and tensile strength of the obtained polyvinyl alcohol fiber sample. The measurement results of the small-angle X-ray scattering intensity of the obtained polyvinyl alcohol-based fiber sample are shown in FIG. 3, and the peak scattering intensity obtained from the small-angle X-ray scattering image of the linear region parallel to the equatorial line of the sample is shown in FIG. Shown in.

[Example 5]
Polyvinyl alcohol-based fibers were produced under the same conditions as in Example 4 except that the temperature at the time of stretching was 240 ° C. and the total stretching ratio calculated from the stretching outlet roller speed and the 1st roller speed ratio was 12.0 times. .. Table 2 below shows the results obtained by the above method for the A / B and tensile strength of the obtained polyvinyl alcohol fiber sample. The measurement results of the small-angle X-ray scattering intensity of the obtained polyvinyl alcohol-based fiber sample are shown in FIG. 3, and the peak scattering intensity obtained from the small-angle X-ray scattering image of the linear region parallel to the equatorial line of the sample is shown in FIG. Shown in.

[Comparative Example 5]
Polyvinyl alcohol-based fibers were produced under the same conditions as in Comparative Example 4 except that the temperature at the time of stretching was 240 ° C. and the total draw ratio calculated from the stretching outlet roller speed and the 1st roller speed ratio was 12.0 times. .. Table 2 below shows the results obtained by the above method for the A / B and tensile strength of the obtained polyvinyl alcohol fiber sample. The measurement results of the small-angle X-ray scattering intensity of the obtained polyvinyl alcohol-based fiber sample are shown in FIG. 3, and the peak scattering intensity obtained from the small-angle X-ray scattering image of the linear region parallel to the equatorial line of the sample is shown in FIG. Shown in.

As described above, in Examples 1 to 5, the strength was superior to that of Comparative Examples 1 to 5 even when the total draw ratio at the time of production was less than 20 times. From the above results, it was confirmed that the polyvinyl alcohol-based fiber of the present invention has excellent strength even in a production method having a low draw ratio.

The polyvinyl alcohol-based fiber of the present invention has excellent strength even in a production method having a low draw ratio.

1 Polyvinyl alcohol fiber 2 Slit 3 Incident X-ray 30 Equatorial line 4 Maximum value of peak scattering intensity derived from image (X1) (X1-maxvalue)
Maximum value of peak scattering intensity derived from 5 images (X2) (X2-maxvalue)
6 The number of pixels (X1P) at the point (X1max) that gives the maximum value (X1-maxvalue) of the peak scattering intensity derived from the image (X1) and the maximum value (X2-maxvalue) of the peak scattering intensity derived from the image (X2). Minimum value of scattering intensity in the pixel number range between the pixel number position (X2P) of

Claims (11)

A polyvinyl alcohol-based fiber having an A / B of 1.6 or more with respect to the following values A and B obtained when a long-period image of small-angle X-ray scattering intensity is measured.
A: A long-period image of the small-angle X-ray scattering intensity of the polyvinyl alcohol-based fiber is measured so that the fiber axis direction of the polyvinyl alcohol-based fiber is the meridional direction, and a long-period image of the small-angle X-ray scattering intensity that can be obtained by the measurement is performed. Observe the four images that make up the. One of the four images (X1) is selected, and the point (X1max) having the highest peak scattering intensity in the image (X1) is specified. It passes through the point (X1max) and another image (X2) on the same side as the image (X1) when viewed from the equator line among the four images, and is parallel to the equator line. The linear region (Y) is determined. The maximum value (X1-maxvalue) of the peak scattering intensity derived from the image (X1) and the maximum value of the peak scattering intensity derived from the image (X2) obtained by observing the peak scattering intensity in the linear region (Y) (X1). Let the two average values of X2-maxvalue) be the value A.
B: The number of pixels (X1P) at the point (X1max) that gives the maximum value (X1-maxvalue) of the peak scattering intensity derived from the image (X1) when the peak scattering intensity is observed in the linear region (Y). And the minimum value of the scattering intensity in the pixel number range between the maximum value (X2-maxvalue) of the peak scattering intensity derived from the image (X2) and the pixel number position (X2P) is defined as the value B. The polyvinyl alcohol-based fiber according to claim 1, which has a tensile strength of 10.0 cN / dtex or more. The polyvinyl alcohol-based fiber according to claim 1 or 2, which comprises a polyvinyl alcohol resin having a molecular weight distribution (Mw / Mn) of 1.05 to 1.95. The polyvinyl alcohol-based fiber according to claim 3, wherein the polyvinyl alcohol resin has a saponification degree of 95.0 to 99.9 mol%. The polyvinyl alcohol-based fiber according to claim 3 or 4, wherein the polyvinyl alcohol resin has a terminal group represented by the following formula (I).
(In the formula, R ¹ represents an aromatic group having 6 to 20 carbon atoms which may have a substituent, and R ² may have a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or a substituent. Represents a good aromatic group with 6 to 20 carbon atoms.) The polyvinyl alcohol-based fiber according to any one of claims 3 to 5, wherein the polyvinyl alcohol resin has a weight average molecular weight (Mw) of 100,000 to 555,000. The method for producing a polyvinyl alcohol-based fiber according to any one of claims 1 to 6, further comprising a spinning step of spinning by a wet spinning method. A method for producing a polyvinyl alcohol-based fiber, comprising a step of immersing an aqueous solution containing a polyvinyl alcohol resin having a molecular weight distribution (Mw / Mn) of 1.05 to 1.95 in a coagulation bath of inorganic salts to dehydrate and solidify it. The method for producing a polyvinyl alcohol-based fiber according to claim 8, wherein the coagulation bath of the inorganic salts further contains an alkaline aqueous solution. The method for producing a polyvinyl alcohol-based fiber according to claim 8 or 9, wherein the coagulation bath of the inorganic salts is a saturated aqueous solution of the inorganic salts. The method for producing a polyvinyl alcohol-based fiber according to any one of claims 7 to 10, further comprising a stretching step, wherein the total stretching ratio in the stretching step is less than 18.0 times.