JP6375125B2 - Polyvinyl alcohol fiber - Google Patents

Description

  The present invention relates to a reinforcing fiber having an excellent matrix reinforcing effect.

  Conventionally, asbestos has been used as a fiber for cement reinforcement, but due to environmental problems in recent years, various inorganic fibers and synthetic fibers have been proposed as cement reinforcing fibers to replace asbestos. As synthetic fibers, polyvinyl alcohol fibers ( Hereinafter, it may be referred to as PVA fiber), polypropylene fiber, acrylic fiber, and the like have been mainly used. Among these, PVA fibers are preferably used because they have good alkali resistance and relatively excellent mechanical properties.

  It is said that the performance required for reinforcing fibers is primarily strength and elasticity. When the fiber does not have sufficient strength and elasticity, the resulting fiber-reinforced molded product does not have toughness as a matter of course.

  The second required performance is adhesiveness with the matrix. If the adhesion between the reinforcing fiber and the matrix is insufficient, the strength and elasticity of the reinforcing fiber against the external stress are not fully utilized, and the fiber reinforced molded product may crack or break without obtaining a reinforcing effect. It will be. In order to improve the adhesion between the fiber and the matrix, it is effective to increase the surface area of the fiber, and specifically, methods such as flattening the fiber cross-section, making it atypical, and making fine denier are being studied.

  Various studies have been conducted as methods for obtaining high-strength PVA fibers (for example, Patent Documents 1 to 4). However, although the fibers obtained by these methods are greatly improved in strength and elasticity, they are homogeneous, so that their cross sections are almost circular and have a small surface area. In general, as the strength of the reinforcing fiber increases, the limit fiber length becomes longer, so that the fiber tends to come off when subjected to stress. Since the fibers that have been studied so far have a long limit fiber length and a small surface area, the reinforcing effect cannot be obtained as much as expected for the strength of the fiber.

  On the other hand, as a means of increasing the surface area of the fiber, there is a method of spinning using a variant nozzle to make the fiber cross-section atypical. It is hard to get something. Further, the surface area per unit amount can be increased by reducing the fineness of the fiber, but in this case, the dispersibility in the matrix is deteriorated, so that the mechanical properties of the fiber reinforced molded article are not improved.

Further, as another form of increasing the surface area of the fiber, there is a fiber having a fold extending in the fiber axis direction on the fiber surface (Patent Document 6), a strength of 90 kg / mm ² or more, and a width of 0.5 to A polyvinyl alcohol fiber and a fiber-reinforced cement molded article including the same are disclosed, characterized in that at least pleats having a diameter of 2 microns, height or depth of 0.5 to 1 microns are present. However, although it has a certain degree of strength as a fiber, other reinforcing materials such as asbestos are also used as the fiber reinforced cement molded product, and there is room for further improvement in the reinforcing effect of the fiber alone. It was.

  As described above, it has been difficult to achieve the two performances required for reinforcing fibers, that is, strength / elasticity and adhesiveness, and the mechanical properties of the resulting fiber-reinforced molded article have not been sufficiently satisfactory. .

Japanese Patent Publication No. 48-32623 Japanese Patent Publication No.53-1368 Japanese Patent Publication No. 60-126312 JP-A-61-108712 JP-A-10-53918 Japanese Patent Publication No.62-32144

  An object of the present invention is to provide a reinforcing fiber having excellent strength / elasticity and adhesiveness and excellent reinforcing efficiency, and a molded body reinforced with the fiber.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have introduced a streak-like recess on the fiber surface without extremely making the fiber atypical cross section, while maintaining strength and elasticity, The inventors have found that the abundance ratio of the recesses is particularly important when trying to improve the adhesion to the matrix, and have completed the present invention.

That is, the present invention is a polyvinyl alcohol fiber having a streak-like recess parallel to the fiber length direction on the fiber surface and satisfying the following (1) to (4).
(1) The average depth of the streak-shaped recess is 0.05 to 2 μm (2) The average width of the opening of the streak-shaped recess is 0.1 to 4 μm (3) The streak (4) The breaking strength is 8 cN / dtex or more.

  The polyvinyl alcohol fiber may have a crystallinity of 40% or more and an orientation of 60% or more.

  The polyvinyl alcohol fiber may be manufactured by a manufacturing method including a step of solidifying in a solidification bath having high solidification property and a step of solidifying in a solidification bath having low solidification property.

  The polyvinyl alcohol fiber may be manufactured by a manufacturing process in which a compound having an aspect ratio of 2 or more is contained in a spinning dope.

  ADVANTAGE OF THE INVENTION According to this invention, since the adhesiveness with a matrix can be improved, maintaining the intensity | strength and elasticity of a fiber, the reinforcing fiber excellent in reinforcement efficiency and the molded object reinforced with this fiber are provided. Can do.

  It is important for the present invention to be a polyvinyl alcohol fiber having a streak-like recess parallel to the fiber length direction on the fiber surface. By having a streak-like recess parallel to the length direction of the fiber on the fiber surface, the adhesion area can be increased and the adhesion to the matrix can be improved.

It is important that the average depth of the recesses is 0.05 to 2 μm. If it is less than 0.05 μm, the adhesion area with the matrix is small, and the matrix may not be effectively reinforced. If it is larger than 2 μm, the fiber strength may decrease. The average depth is preferably 0.08 to 1.9 μm, more preferably 0.1 to 1.8 μm, and still more preferably 0.2 to 1.7 μm.
The average depth of the recess can be obtained by the method described later.

It is important that the average width of the opening of the recess is 0.1 to 4 μm. If it is less than 0.1 μm, not only the bonding area becomes small, but in the case of cement-based materials, for example, CSH gel (hardened cement paste) is difficult to efficiently enter and bond into the recess, so that sufficient adhesion cannot be obtained. There is. If the average width of the recesses is larger than 4 μm, the fiber strength may be lowered. The average width is preferably 0.2 to 3.9 μm, more preferably 0.3 to 3.8 μm, and still more preferably 0.4 to 3.7 μm.
The average width of the opening of the recess can be determined by the method described later.

In the PVA fiber according to the present invention, it is important that the abundance ratio of the recesses is 5% or more. When the concave portion is less than 5%, the adhesion area becomes small. The abundance ratio of the recesses is preferably 10% or more, more preferably 15% or more, and further preferably 20% or more. The abundance ratio of the recesses is preferably 80% or less, more preferably 60% or less, still more preferably 50% or less, and particularly preferably 40% or less.
The abundance ratio of the recesses can be determined by the method described later.

The PVA fiber of the present invention preferably has a crystallinity of 40% or more and an orientation of 60% or more. If the crystallinity is less than 40%, the mechanical properties and heat and humidity resistance of the fiber may be inferior. Further, when the degree of orientation is less than 60%, the heat resistance, mechanical properties, and heat and humidity resistance may be inferior. The crystallinity is more preferably 50% or more, and further preferably 60% or more. The degree of orientation is more preferably 70% or more, and further preferably 75% or more from the viewpoint of mechanical properties.
The degree of crystallinity and the degree of orientation can be determined by the methods described below.

  The breaking strength of the PVA fiber of the present invention is preferably 8 cN / dtex or more. When the breaking strength is less than 8 cN / dtex, in the molded body to which the fiber is added, even when the matrix and the fiber are sufficiently bonded, the fiber itself is broken, so that sufficient reinforcing effect in bending strength and the like is obtained. May not be obtained. The breaking strength is more preferably 9 cN / dtex or more, further preferably 10 cN / dtex or more, particularly preferably 12 cN / dtex or more, and particularly preferably 13 cN / dtex or more.

  The breaking elongation of the PVA fiber of the present invention is preferably 3 to 20%. When the elongation at break is less than 3%, not only the impact strength is lowered in the molded article to which the fiber is added, but also the drawing processability may be deteriorated in the production of the fiber. On the other hand, if the elongation at break exceeds 20%, the impact resistance is improved, but a sufficient reinforcing effect may not be obtained in bending strength. The breaking elongation is more preferably 4 to 15%, still more preferably 5 to 10%.

The cross-sectional shape of the PVA fiber of the present invention is not particularly limited as long as the effect of the present invention is not affected, but from the viewpoint of mechanical strength, a circular shape having a recess or a substantially circular shape is preferable. When the average degree of cross-section is calculated as an index of the cross-sectional shape, it is preferably 60 to 99%, more preferably 65 to 98%, and still more preferably 70 to 97%. The degree of cross-section fulfillment is calculated by the following equation, where S1 is the cross-sectional area of the fiber and S2 is the area of the minimum circle surrounding the fiber.
Cross-sectional quality (%) = (S1 / S2) × 100
More specifically, the average cross-section fulfillment degree can be obtained by a method described later.

  FIG. 1 is a fiber side view photograph of the PVA fiber of the present invention, and FIG. 2 is a cross-sectional photograph of the fiber. As shown in FIG. 1, streaky concave portions are present on the surface of the PVA fiber of the present invention in parallel to the length direction of the fiber. In addition, as shown in FIG. 2, each concave portion has a certain depth, but the cross-sectional shape of the fiber is substantially circular. Therefore, the PVA fiber of the present invention has high adhesiveness and maintains mechanical characteristics. ing.

  The form of the fiber of this invention can be made into forms as needed, such as a shortcut, a multifilament, a monofilament, a mesh fabric.

  Although the fineness of the fiber of this invention is not specifically limited, It is preferable that it is 0.1-10000 dtex. When blended with slate, it is preferably 0.1 to 100 dtex, and when blended with mortar, it is preferably 1 to 2000 dtex in terms of the reinforcing effect due to dispersibility and the number of fibers. When mix | blending with concrete, since it is hard to break a fiber, it is preferable that it is 100-10000 dtex. When used as a mesh fabric, a multifilament yarn having a total fineness of 50 to 2,000 dtex or a monofilament of 2 to 5,000 dtex is preferable. The aspect ratio when used as a shortcut is preferably 50 to 2000, more preferably 150 to 600.

  The PVA polymer constituting the PVA fiber of the present invention is not particularly limited, but from the viewpoint of polymer crystallinity, mechanical performance, flame retardancy, etc., the viscosity average polymerization degree is preferably 1000 or more, particularly preferably 1500 or more. In view of spinnability and cost, it is preferably 5000 or less. For the same reason, the saponification degree is preferably 98 mol% or more, more preferably 99 mol% or more, and particularly preferably 99.5 mol% or more.

  Other monomers may be copolymerized in the PVA polymer, and examples of the copolymer component include ethylene, vinyl acetate, itaconic acid, vinylamine, acrylamide, vinyl pivalate, maleic anhydride, and sulfonic acid-containing vinyl compounds. Can be mentioned. From the viewpoint of fiber performance, flame retardancy, etc., it is preferable to contain a vinyl alcohol unit in an amount of 70 mol% or more of all constituent units.

  Moreover, as long as the effect of the present invention is not impaired, the fiber may contain a polymer other than the PVA polymer and other additives. From the viewpoint of fiber performance and the like, the content of the PVA polymer is preferably 30% by mass or more / fiber, particularly 50% by mass or more / fiber.

  Moreover, in this invention, the fiber which has a streak-like recessed part on the fiber surface can be obtained more efficiently by finely disperse | distributing the compound with L / D of 2 or more aspect ratio in a PVA-type polymer stock solution. . Since the spinning stock solution in which the compound having the aspect ratio is finely dispersed takes a share in the discharge direction when discharged from the nozzle, the compound is arranged with anisotropy in the fiber direction in the discharged fiber. . Therefore, in the process of solidifying while forming a skin layer and volume shrinkage, it is easy to form a deep and wide concave part because the presence of the compound inhibits volume shrinkage.

  The compound preferably has a smaller average particle diameter in terms of efficient formation of recesses and spinning processability. Specifically, it is preferably in the range of 0.01 to 10 μm, more preferably 0.02 to 9 μm, and still more preferably 0.03 to 8 μm. The amount added is preferably in the range of 0.01 to 30% by mass, more preferably 0.02 to 29% by mass, and still more preferably 0.03 to 28% by mass with respect to the fiber. .

  The compound may have any aspect ratio as long as the L / D has an aspect ratio of 2 or more and the average particle diameter is 0.01 to 10 μm, but the hardness is high in order to effectively inhibit volume shrinkage during the solidification process. More preferred are inorganic fibrous, needle-like, whisker-like fillers, and layered compounds. Specifically, fibrous materials such as carbon carbon fiber and carbon nanotube, whisker-like materials such as graphite whisker, aluminum borate whisker, potassium titanate whisker, montmorillonite, saponite, hydelite, nontronite, hectorite, and viro Smectite clay compounds such as sites and stave sites, vermiculite clay compounds such as di-vermiculite, tri-vermiculite and fluorine vermiculite, mica clay compounds such as muscovite, paragonite and illite, Li-type fluorine teniolite, Na-type Layered compounds such as fluorine teniolite and synthetic fluorine mica (Li-type tetrasilicon fluorine mica, Na-type tetrasilicon fluorine mica, etc.) can be exemplified, and these are natural products or synthetic products. Good.

Next, the manufacturing method of the PVA type fiber of this invention is demonstrated.
In the present invention, in order to obtain a PVA-based fiber having a streak-like recess parallel to the fiber length direction on the fiber surface, control of fiber solidification is important. As a method of forming a streak-like recess on the surface, first, a thin skin layer is formed on the fiber surface at the initial stage of solidification, and then volume shrinkage is caused slowly. The circumference of the thin skin layer is the circumference after volume shrinkage. If a substantially longer state is created, the surface skin layer is folded, resulting in the formation of recesses on the fiber surface. For example, it is possible to set a spinning condition so as to increase the difference in time required for solidification between the outer peripheral portion and the inside of the fiber by reducing the concentration of the stock solution for spinning, but solidification for solidifying the stock solution for spinning. A method of adjusting the concentration of the bath is more preferably selected.

Specifically, first, in order to form a skin layer on the surface, the spinning dope immediately after being discharged from the nozzle is solidified in a solidifying bath having a high solidification property, and then slowly solidified in a spinning cylinder.
As a method of slowly solidifying, a method of allowing a solvent that lowers the solidification property to flow into the spinning cylinder, a method of separating after forming a skin layer in a solidification bath having a high solidification property, and then slowly in a solidification bath having a low solidification property. And a method of solidifying. The concentration of the spinning dope is preferably low, and more preferably the slow bathing rate is low.

  If the above elements can be controlled, the spinning method is not particularly limited, and the spinning solution containing a PVA polymer is produced by solution spinning, specifically, wet spinning, dry wet spinning, and dry spinning. Solvents used in the spinning dope include solvents conventionally used in the production of PVA fibers, such as water, dimethyl sulfoxide (DMSO), dimethylformamide, dimethylacetamide, glycerin, ethylene glycol, triethylene glycol and other polyhydric alcohols. 1 type, or 2 or more types can be used in combination. Among these, water and DMSO are particularly preferable from the viewpoint of supplyability and influence on environmental load. Since the lower concentration of the polymer in the spinning dope is preferable as described above, the polymer concentration varies depending on the composition, polymerization degree, and solvent of the PVA polymer, but is preferably in the range of 6 to 25% by mass. As long as the effects of the present invention are not impaired, the spinning dope includes a surfactant, a decomposition inhibitor, an antifreezing agent, a pH adjuster, a concealing agent, a colorant, in addition to the PVA polymer, depending on the purpose. An additive such as an oil may be included.

The solidification bath used in 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 dope is an aqueous solution, a solidification bath composed of an aqueous solution of sodium sulfate is used. For the stock solution to which boric acid is added, a mixed aqueous solution of caustic soda and mirabilite is used. In this case, since solidification is due to dehydration, the higher the concentration of sodium sulfate, the higher the solidification property. The concentration of salt cake of the solidification bath having high solidification property is preferably 200 to 400 g / L, more preferably 210 to 390 g / L, and still more preferably 220 g / L to 380 g / L.
In the case of an undiluted solution using an organic solvent, a mixed solution composed of a solidified solvent and a undiluted solvent is preferable, and as the solidified solvent, for PVA such as alcohols such as methanol and ethanol, and ketones such as acetone and methyl ethyl ketone. An organic solvent having a solidifying ability is preferable. In this case, the higher the ratio of the solidification solvent in the solidification bath, the higher the solidification property. The ratio of the solidification solvent in the solidification bath having a high solidification property is preferably 50% or more, more preferably 55% or more, and further preferably 60% or more.

  The solidified yarn obtained by the spinning method is extracted / washed, dried, stretched / heat treated.

  The PVA fiber of the present invention is subjected to a drawing heat treatment so that the breaking strength is 8 cN / dtex or more. This stretching heat treatment is generally performed at a temperature of 210 ° C. or higher, preferably 220 ° C. to 260 ° C., and when stretched at a total stretching ratio of 8 times or more, preferably 10 to 25 times. The crystallinity and orientation of the fiber are improved, and the mechanical properties of the fiber are improved accordingly.

  The PVA fiber of the present invention can be subjected to acetalization treatment and other crosslinking treatments generally performed for PVA fibers for the purpose of improving hot water resistance depending on applications and purposes. That is, the fiber can be hydrophobized by treating the PVA fiber in an aqueous solution containing a crosslinking agent such as formaldehyde that reacts with the hydroxyl group of the PVA polymer to block the hydroxyl group.

The PVA fiber of the present invention can be widely used for reinforcement of slate, board, panel, etc., reinforcement of mortar / concrete, FRP and the like.
Further, depending on the application, for example, natural fibers such as pulp, other PVA fibers, acrylic fibers, aramid fibers, carbon fibers, PPS fibers, synthetic fibers such as PBO fibers, and other fibers can be used in combination.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited to these examples. In the following, parts and% refer to parts by mass and% by mass unless otherwise specified. Various measuring methods and methods for producing cement moldings are as follows.

[Fracture strength of fiber cN / dtex, elongation at break%]
Measurement was performed in accordance with JIS L1013.

[Crystallinity (Xc)%]
The fiber crystallinity was measured by measuring the melting enthalpy of the sample using a Pyris-1 differential scanning calorimeter manufactured by Perkin Elmer. The measurement conditions were a heating rate of 80 ° C./min, and the weight crystallinity was calculated from the following formula. In addition, correction of melting point and heat of fusion was performed using indium and lead as standard materials.
Xc (%) = ΔHobs / ΔHcal × 100
ΔHobs: Actual heat of fusion (J / g)
ΔHcal: heat of fusion of complete crystal (174.5 J / g)

[Orientation%]
Using a pulse direct-reading viscoelasticity measuring instrument DDV-5-B manufactured by Orientec Co., Ltd., the velocity C of 10 KHz sound wave along the fiber axis of the fiber sample was measured, and the non-oriented obtained from the cast film of polyvinyl alcohol Compared with the sound velocity Cu (2.20 km / sec) of the sample, the degree of orientation was calculated by the Mosley equation (degree of orientation = 1-Cu2 / C2).

[Average width μm of openings of streaky recesses on fiber surface, average depth of recesses μm, presence ratio of recesses]
A fiber cross-sectional image was taken with a scanning electron microscope, and a tangent line was drawn so as to circumscribe the concave portion seen on the outer periphery of the cross-section with image analysis software, and the length of the tangent line was apparently defined as a concave portion width W1. In addition, a perpendicular line was drawn from the bottom of the recess to the tangent line, and the perpendicular length was defined as the apparent depth L1 of the recess. After performing this operation for each recess, add all recesses for each width and depth (ΣW, ΣL), and divide by the number n of extracted recesses to obtain the average width W and average depth L of all recesses. Was calculated. Further, ΣW was divided by a substantially polygonal circumferential length C surrounded by the tangent line and the actual fiber circumference to calculate the abundance ratio of the recesses on the fiber surface.
Average width W [μm] = ΣW [μm] / n [pieces]
Average depth L [μm] = ΣL [μm] / n [pieces]
Abundance ratio [%] = ΣW [μm] / C [μm] × 100

[Average cross-sectional area%]
The cross-sectional shape of the fiber is measured with a scanning electron microscope, the cross-sectional area of the fiber is S1, and the area of the smallest perfect circle surrounding the fiber is S2, as shown in FIG. The degree of cross-section was calculated by the formula and the average value was obtained.
Cross-sectional quality (%) = (S1 / S2) × 100

[Cement molded board production method]
(1) Compounding fiber: 2wt%
Pulp (Cellofiber, Partec Co.): 3wt%
Cement (ordinary Portland cement): 95wt%
(2) Creation After adding the required amount of fiber, pulp, cement and water and dispersing with a TAPPI disintegrator, it is poured onto a cotton cloth to make paper. 10 sheets of the obtained paper sheets are laminated on a mold and dehydrated under pressure at a pressure of 75 kg / cm ² with a press machine to form a molded plate having a length of 20 cm × width of 25 cm and a thickness of 0.4 cm. This was obtained by curing for 14 hours under a 20 ° C. wet air after curing for 24 hours under a 50 ° C. wet air.

[Bending test of molded cement board]
In accordance with JIS A1408, a test piece cut into a width of 2.5 cm, a length of 8 cm, and a thickness of 0.4 cm was subjected to a bending test with a span of 5 cm, and indicated by bending strength and bending deflection in MOR (Modulus of Rapture). The bending strength indicates the maximum stress of the stress strain curve, and the bending deflection indicates the amount of strain at the maximum stress.
The bending strength was a corrected strength normalized to a bulk density of 1.7 from the following equation.
Corrected bending strength = Measured bending strength × (1.7 / bulk specific gravity) ²
(Reference Example 1 )

PVA having a viscosity average degree of polymerization of 1700 and a saponification degree of 99.9 mol% was added to water to a concentration of 16.5% by mass, and then 3.0% by mass of boric acid / PVA was added and dissolved at 90 ° C. As a result, a PVA spinning dope was obtained. The obtained spinning solution was passed through a nozzle with 1000 holes and wet-spun into a solidification bath consisting of an aqueous solution at 70 ° C. containing 15 g / L of caustic soda and 350 g / L of sodium sulfate at a separation bath speed of 3 m / min. Thereafter, water at 70 ° C. is injected so that the volume ratio becomes 75% in the middle of the spinning cylinder, and the solidification bath composition after water injection is adjusted to 11 g / L of caustic soda and 260 g / L of sodium sulfate to solidify. After delaying, he took a bath. Next, after neutralization, wet stretching, washing with water and drying, dry heat stretching was performed at 230 ° C. to obtain PVA fibers. The single fiber fineness of the obtained fiber was 2.0 dtex. The total draw ratio was 20 times. Moreover, the obtained fiber was cut into 6 mm, and a molded product was obtained according to the above-described method for producing a cement molded body. Table 1 shows the physical properties of the obtained fiber, and Table 2 shows the physical properties of a molded product obtained using this fiber. The bending strength of the molded product was higher than that of Comparative Example 1 having the same fiber strength, and the adhesive effect was exhibited.
(Reference Example 2 )

Fibers and cement moldings were obtained in the same manner as in Reference Example 1 except that the PVA concentration was 10.0% by mass when obtaining the PVA spinning dope and that water was not injected in the middle of the spinning cylinder. Table 1 shows the physical properties of the obtained fiber, and Table 2 shows the physical properties of a molded product obtained using this fiber. The bending strength of the molded product was higher than that of Comparative Example 1 having the same fiber strength, and the adhesive effect was exhibited.
(Reference Example 3 )

Fibers and cement moldings were obtained in exactly the same manner as in Reference Example 1, except that the PVA concentration was 10.0% by mass when obtaining the PVA spinning dope. Table 1 shows the physical properties of the obtained fiber, and Table 2 shows the physical properties of the molded product. The bending strength of the molded product was higher than that of Comparative Example 1 having the same fiber strength, and the adhesive effect was exhibited.
( Example 1)

A fiber and cement molded product were obtained in the same manner as in Reference Example 2 except that 3% by mass of an aluminum borate whisker (trade name: Arbolex Y) manufactured by Shikoku Kasei Kogyo Co., Ltd. was added to PVA when obtaining the spinning dope. Got. Table 1 shows the physical properties of the obtained fiber, and Table 2 shows the physical properties of the molded product. The bending strength of the molded product was higher than that of Comparative Example 1 having the same fiber strength, and the adhesive effect was exhibited.
( Example 2)

Fibers and cement moldings were obtained in exactly the same manner as in Reference Example 2 except that 3% by mass of montmorillonite (trade name: Kunipia F) manufactured by Kunimine Kogyo Co., Ltd. was added to PVA when obtaining the spinning dope. Table 1 shows the physical properties of the obtained fiber, and Table 2 shows the physical properties of the molded product. The bending strength of the molded product was higher than that of Comparative Example 1 having the same fiber strength, and the adhesive effect was exhibited.

Comparative Example 1
Fibers and cement moldings were obtained in exactly the same manner as in Reference Example 2 except that the stock solution concentration was 18% and the bathing speed was 8 m / min. Table 1 shows the physical properties of the obtained fiber, and Table 2 shows the physical properties of the molded product. Since there was no wrinkle, the bending strength of the molded product was low although the fiber strength was high.

Comparative Example 2
In Example 1, fibers and cement moldings were obtained in the same manner as in Reference Example 2 except that the total draw ratio was 6. Table 1 shows the physical properties of the obtained fiber, and Table 2 shows the physical properties of the molded product. Although a predetermined wrinkle was obtained, since the fiber strength was low, the bending strength of the molded product was low, and the bending deflection was also low.

The fiber side surface photograph of the PVA type fiber of this invention On the surface of a PVA type fiber, a stripe-shaped recessed part exists in parallel with the length direction of a fiber. Fiber cross-sectional photograph of the PVA-based fiber of the present invention The fiber cross-sectional shape is substantially circular, while each recess has a certain depth. Schematic diagram showing the degree of cross-section The fiber cross-sectional schematic diagram and the smallest perfect circle surrounding the fiber cross-section are shown.

1 Concave part 2 Fiber cross-sectional schematic diagram (cross-sectional area: S1)
3 The smallest perfect circle that surrounds the fiber cross section (area: S2)

Claims (4)

A polyvinyl alcohol-based fiber having a streak-shaped recess along the length of the fiber on the fiber surface and satisfying the following (1) to (4), which contains a compound having an aspect ratio of 2 or more, A polyvinyl alcohol fiber, wherein the compound having an aspect ratio of 2 or more is a whisker-like material or a smectite clay compound .
(1) The average depth of the streak-shaped recess is 0.05 to 2 μm (2) The average width of the opening of the streak-shaped recess is 0.1 to 4 μm (3) The streak (4) The breaking strength is 8 cN / dtex or more.   The polyvinyl alcohol fiber according to claim 1, wherein the degree of crystallinity is 40% or more and the degree of orientation is 60% or more. Including a step of solidifying a polyvinyl alcohol spinning dope in a solidification bath having a high solidification property, and a step of solidifying in a solidification bath having a low solidification property thereafter, a streak-like concave portion is formed on the fiber surface along the length direction of the fiber. A method for producing a polyvinyl alcohol fiber, which satisfies the following (1) to (4).
(1) The average depth of the streak-shaped recess is 0.05 to 2 μm (2) The average width of the opening of the streak-shaped recess is 0.1 to 4 μm (3) The streak (4) The breaking strength is 8 cN / dtex or more. Look including the aspect ratio of 2 or more compounds in the spinning solution, the aspect ratio of 2 or more compounds is a whisker-like product or smectite clay compounds, method for producing a polyvinyl alcohol fiber of claim 3.