JP2000328352A - Polyvinyl alcohol-based water-soluble fiber and paper and solidification state determination method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a PVA-based fiber which hardly causes agglutination and excellent in water dispersibility, a paper obtained by using the fiber, and a P-based fiber.
Provided is a simple method for determining the solidification state of VA-based fibers. SOLUTION: This is a polyvinyl alcohol-based fiber having a dissolution temperature in water of 55 ° C. or lower, having a skin core structure, and having a skin layer thickness of 4 to 25% with respect to the fiber diameter. I do.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyvinyl alcohol (PVA) -based water-soluble fiber which is particularly suitable as a stock, and a paper using the fiber. The present invention relates to a method for easily determining the solidification state of a solid.

[0002]

2. Description of the Related Art Conventionally, PVA-based fibers have high hydrophilicity in chemical structure, and thus have been widely used in paper materials (paper constituent materials) such as binder fibers. However, since the fibers have high hydrophilicity, there is a problem that the surface of the fibers is softened and dissolved in the presence of water to cause sticking, and when sticking occurs, not only the quality of the fibers is impaired, but also the water dispersibility is insufficient. Become. In particular, the tendency is remarkable for water-soluble fibers having a low dissolution temperature in water, and since the water-soluble fibers have a low dissolution temperature, welding tends to occur in the drying step.
In addition, water-soluble fibers are generally used in low saponification PVA or modified PV.
Although it is composed of A, when the degree of saponification and the degree of denaturation increase, the phase separation ability (solidification ability) tends to decrease significantly, so that sticking is more likely to occur.

[0003] If the drying temperature of Ishino is lowered, the occurrence of agglutination can be suppressed. However, if the drying temperature is lowered, the production efficiency is reduced and the cost is increased. In addition, the occurrence of agglutination at elevated temperatures during long-term storage or transportation cannot be suppressed. It has also been considered to add an anti-sticking agent, but at present, the conventional technology does not sufficiently prevent the sticking. From the above, it is practically difficult to lower the water dissolution temperature of the fiber to a certain degree or more. In order to maintain the fiber quality, water dispersibility, etc., the water dissolution temperature is substantially 60 ° C.
It was necessary to do above. Adopting a spinning method using an undiluted spinning solution containing an organic solvent as an organic solvent suppresses the occurrence of agglomeration, and a PVA-based fiber having a low dissolution temperature in water can be obtained, but is disadvantageous in terms of cost and production efficiency.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a PVA-based water-soluble fiber which is less likely to cause sticking, is excellent in water dispersibility and quality, and is also advantageous in terms of cost. An object of the present invention is to provide high quality paper by using fibers.

[0005]

The present invention relates to (1) a polyvinyl alcohol-based fiber having a dissolution temperature in water of 55 ° C. or less, having a skin core structure, and having a skin layer thickness of 4% with respect to the fiber diameter. (2) a polyvinyl alcohol-based fiber having a dissolution temperature in water of 55 ° C. or less, having a skin core structure, and a skin layer having a fiber diameter of 25% or less. Paper made of polyvinyl alcohol-based water-soluble fiber in an amount of 4 to 25%, and (3) dipping a semipermeable membrane tube having a diameter of 5 to 50 mm filled with an undiluted solution of spinning polyvinyl alcohol in an arbitrary solidifying solution. And a method of observing the cross section of the tube after immersion to determine the solidification state of the fiber when spun using the spinning solution and the solidification solution.

[0006]

DETAILED DESCRIPTION OF THE INVENTION The present invention is to form a specific skin core structure on the surface of a water-soluble fiber, thereby suppressing sticking between fibers and remarkably improving water dispersibility. In other words, by covering the surface layer of the fiber with a strong and hardly dissolvable skin layer, sticking between fibers in the spinning process is prevented, and furthermore, dissolution of the fiber is suppressed even in the disaggregation process during paper production, and excellent water dispersibility is obtained. And the foaming is further reduced, so that an excellent effect can be obtained. In order to sufficiently obtain the effects of the present invention, the water-soluble fiber must have a dissolution temperature in water of 55 ° C. or lower, preferably 52 ° C. or lower. Excellent effects can be obtained by applying the present invention to such water-soluble fibers in which sticking is likely to occur. From the standpoint of spinnability and prevention of sticking, the dissolution temperature of the fiber in water is preferably 10 ° C. or higher, more preferably 30 ° C. or higher. 3
The dissolution rate of fiber in water at 0 ° C. (% by weight / fiber) is 20
% By weight or less, and the water content is 200 to 10%.
Preferably it is 00% by weight / fiber.

In the present invention, the thickness of the skin layer needs to be 4 to 25%, particularly 5 to 20% of the fiber diameter. By setting the thickness ratio of the skin layer (thickness of skin layer / diameter of fiber) to a specific range, inter-fiber sticking is efficiently suppressed, and fibers excellent in water dispersibility and quality can be obtained. Although it is preferable to increase the thickness of the skin layer from the viewpoint of suppressing inter-fiber sticking, if the skin layer is too thick, there is a problem that the stretchability is impaired. The fiber having a skin core structure referred to in the present invention refers to a fiber having a two-layer structure of a dense skin structure and a sparse core structure in a cross section of the fiber. The presence or absence of the skin core structure can be confirmed by confirming that the sheath portion becomes darker than the core portion. The presence or absence of a skin core structure can also be confirmed by examining the densities of both layers.

The PVA-based fibers used in the present invention are fibers containing a vinyl alcohol-based polymer, and may contain other polymers or the like. For example, fibers obtained by blending PVA and other polymers (sea-island structure fibers, etc.) and composite spun fibers composed of PVA and other polymers (core-sheath type composite fibers, side-by-side type composite fibers, etc.)
And the like. From the viewpoint of obtaining the effect of the present invention more remarkably, it is preferable that the fiber surface is composed of at least a vinyl alcohol-based polymer, and the vinyl alcohol-based polymer is at least 30% by weight / fiber, more preferably at least 50% by weight / fiber, Further, those containing 80% by weight or more / fiber are preferable.

A modified P modified by another unit
VA may be used. For example, by replacing the hydroxyl group constituting PVA with another functional group such as a carboxylic acid, an amide group or an ethylene group, the water solubility of the polymer is increased,
Water-soluble PVA-based fibers can be obtained efficiently. The modification rate may be set as appropriate, but for example, about 0.1 to 20 mol% can be widely applied. Further, it may be a block copolymer with polyacrylamide or the like. At this time, the proportion of the copolymer component is preferably set to about 60% by weight or less. The degree of saponification of the vinyl alcohol-based polymer may be set as appropriate, but since the dissolution temperature of the polymer in water can be lowered by lowering the degree of saponification, 97
Mol% or less, and a degree of polymerization of 300 to 300.
In the case of PVA which is substantially zero and does not substantially contain a copolymerization component, the saponification degree is preferably 90 mol% or less. From the standpoint of spinnability and prevention of sticking, it is preferably at least 70 mol%, particularly preferably at least 80 mol%. The average degree of polymerization of the vinyl alcohol-based polymer, the handling properties of the spinning solution, spinnability,
300-5000, especially 500-
It is preferably 3000.

The method for obtaining the PVA-based fiber of the present invention is not particularly limited. However, since the skin core structure is easily formed and the cost is excellent, a spinning solution comprising an aqueous PVA solution is wet-spun or wet-dried into a coagulation bath. It is preferable to employ a method of discharging by a spinning method. Although spinning is performed while actually changing various conditions, the presence or absence of a skin core structure and the thickness ratio of the skin layer are measured, and production conditions suitable for forming a specific skin layer may be determined. Since the water-soluble fiber has low crystallinity, the solidification condition (spinning solution concentration, spinning solution temperature, solidification solution concentration, solidification solution temperature) has a slight difference, and the solidification state (skin core structure state) changes greatly depending on the PVA used. Unless very limited conditions are adopted, a desired skin core structure cannot be formed. Therefore, it is necessary to spin under various spinning conditions to find a condition capable of forming a desired skin solidified structure. It takes a lot of time and effort. From the above, it is preferable to perform the following simple solidification test to determine the solidification state of the PVA-based fiber when spun using the spinning stock solution and the solidification solution used in the test.

More specifically, a tube made of a semipermeable membrane (preferably made of cellulose, particularly preferably cellophane) filled with a spinning solution is immersed in a solidification bath and left for a certain period of time to promote the solidification reaction. Thereafter, the tube is taken out and cut into slices, and the solidified state (skin core structure) is visually observed or confirmed by a phase contrast optical microscope to confirm the cross section of the tube. This is a method of determining the solidification state of the fiber. In particular, it is preferable to use a tube having a diameter of 5 to 50 mm (more preferably, 1 to 2 cm) and to determine the solidification state by immersing the tube in a solidification bath. If the tube diameter is too small, the time required to complete the solidification becomes short, and the variation between samples becomes large, and it is difficult to determine the solidification state, which is not preferable.If the tube diameter is too large, the solidification state can be determined. It is not efficient because the immersion time is too long. The immersion time in the solidification solution may be set as appropriate, but is generally 5 minutes or more, particularly 10 minutes or more, and preferably 15 minutes or more from the viewpoint of sufficiently complete solidification, and from the viewpoint of efficiency, The immersion time is preferably 60 minutes or less, and more preferably 30 minutes or less. Further, the length of the tube may be appropriately set according to the tube diameter and the like, but is preferably 3 to 15 cm, particularly preferably 5 to 10 cm from the viewpoint of the size of the test apparatus, etc. What is necessary is just to tie and seal. The amount of the solidifying solution in which the tube is immersed may be appropriately set, and may be any amount that can completely immerse the tube. For example, 500 ~
It may be about 2000 ml.

The solidification state determined from the cross section of the tube obtained by the above solidification test and the skin core state obtained by observing the cross section of the fiber obtained by actual spinning with a microscope are in very good agreement. Is an extremely excellent method for determining the solidification state of PVA-based fibers. When the solidification is good, it can be clearly determined that a sparse core structure is formed at the core of the tube and a dense skin structure is formed around the core (the sheath). If the skin core structure becomes unclear and the solidification state is extremely poor, the core of the tube may remain undiluted. When a desired skin core structure is formed by a solidification test, a PVA-based fiber having a desired skin core structure can be efficiently obtained by actually spinning using the same spinning solution and solidifying solution.

Further, by forming the protruding portion on the fiber surface, the sticking between the fibers can be suppressed more effectively, and the water dispersibility of the fiber can be remarkably enhanced. That is, when a specific protrusion is present on the fiber surface, the contact area between the fibers is reduced, so that even when moisture is present, sticking is less likely to occur. And the like can easily penetrate into the fibers, so that the fibers are easily disintegrated into single fibers, and the dispersibility in water is remarkably increased in combination with the effect of preventing sticking.

The protrusion is preferably formed when the spinning solution is discharged from the spinning nozzle. Particularly, when producing fibers by wet spinning or dry-wet spinning, a more remarkable effect can be obtained. In other words, when the spinning solution is discharged from the spinning nozzle into the solidification bath, the spinning solution is solidified to form a shinoshi. However, when a plurality of the shinoshis discharged from the nozzle holes are integrated, the solidification reaction does not proceed sufficiently, and the solidification proceeds. This may cause sticking in a process or a subsequent process. However, by providing the protrusions on the surface of the yarn, the contact between the yarns is effectively suppressed, and the solidification reaction proceeds sufficiently by facilitating penetration of the solidification bath into the space between the yarns, thereby causing sticking. Generation can be further suppressed.

From the viewpoint of the effect of preventing sticking and the dispersibility in water, the average height of the projections must be 0.1 to 10%, preferably 0.8 to 8% of the fiber diameter. If the protrusion is too small, the desired effect cannot be obtained.On the other hand, if the protrusion is too large, the contact area between the single fibers and the coefficient of friction become large, so that the effect of preventing sticking becomes difficult to obtain, and in water and the like. Uniform dispersibility also tends to be impaired. The PVA fiber is cocoon-shaped,
Although it may have an irregular cross section such as an elliptical shape, the fiber diameter according to the present invention is the arithmetic mean of the maximum diameter and the minimum diameter in the same fiber cross section, and the average height of the protrusion is This is a value obtained by the method described in the example.

As a method of forming the projecting portion on the fiber surface, it is effective to form the projecting portion by exposing fine particles to the fiber surface because the projecting portion is easy to form and has an excellent anti-sticking effect. It is a target. Of course, some or all of the fine particles may be coated with another substance (such as a vinyl alcohol-based polymer). However, from the viewpoint of efficiently obtaining the effect of preventing sticking and improving the water dispersibility without impairing the fiber performance, it is preferable to form the protruding portion by substantially exposing the fine particles to the fiber surface.

The fine particles to be used are not specified, but it is preferable to use fine particles made of a polymer, since they do not easily damage adjacent fibers, and the spinnability and the mechanical performance of the fibers are hardly impaired. Specifically, polyamide resins (nylon 6, nylon 66, etc.), polyester resins (polyethylene terephthalate, polybutylene terephthalate, etc.), acrylic resins (polymethyl methacrylate, methyl methacrylate / methacrylic acid copolymer, methyl Examples thereof include methacrylate / methacrylic acid / styrene copolymers, acrylic acid / styrene copolymers), silicone-based resins (eg, alcon rubber), and urethane-based resins. Among them, polyester resins and / or acrylic resins are preferred. Of course, a plurality of resins may be used in combination.

The average particle size of the fine particles is from 0.05 to 50 μm, particularly from 0.06 to
It is preferably 4 μm, more preferably 0.07 to 2 μm.
From the viewpoint of suppressing secondary aggregation of fine particles, the average particle size is 0.1.
It is preferably at least 0.2 μm, more preferably at least 0.2 μm.
Of course, fine particles having different particle diameters may be used in combination. In terms of spinnability and the size and shape of the protrusion,
The diameter of the fine particles is preferably 1 to 30%, particularly preferably 2 to 25% of the fiber diameter.

In order to efficiently prevent the fine particles from falling off from the fiber and to form a projection suitable for preventing sticking on the fiber surface, 1 to 28% of the fine particle diameter is exposed from the fiber surface. In this case, it is preferable that the protrusion is formed. When the exposed portion of the fine particles increases, not only the particles easily fall off, but also the contact area with other adjacent fibers tends to increase, and the friction coefficient tends to increase. The shape of the fine particles is not particularly limited, but is preferably spherical because the uniform dispersibility in the fibers is high and the fibers are not easily damaged, and furthermore, a protrusion having an excellent effect of preventing sticking is easily formed. Further, the fine particles may be solid fine particles or hollow fine particles. When the hollow fine particles are used, high concealing property and lightening of the fiber can be realized at the same time.

The method for producing the fine particles is not particularly limited. For example, a method of physically pulverizing a polymer chip or powder into a fine powder by freeze-pulverization using a known pulverizer, or a method of preparing a polymerizable monomer from a polymerizable monomer. Fine particles can be produced by a polymerization technique such as a method of forming particles in a polymerization process and a method of forming particles from a polymer solution formed into fine droplets. For example, in order to obtain fine particles having a particle size of about 0.05 to 1 μm, an emulsion polymerization method, a soap-free emulsion polymerization method, and a seed emulsion polymerization method are preferably employed.
In this case, a seed emulsion polymerization method, a two-stage swelling method, a dispersion polymerization method and the like are preferred.

Hereinafter, a specific spinning method of the fiber of the present invention will be described. First, the spinning solution must be a PVA aqueous solution. A method using an organic solvent as a solvent is not preferable in terms of cost and production efficiency, and does not form a skin core structure. The PVA concentration in the spinning dope may be appropriately set, but is usually 10 to 3 in view of spinnability, solidification, fiber performance, and the like.
It is preferably about 0% by weight, especially about 15 to 28% by weight. Increasing the concentration of the spinning dope tends to increase the thickness of the skin layer.However, if the concentration is high, the viscosity of the spinning dope may increase and the spinnability may decrease. Is preferred. It is necessary to appropriately set the temperature of the spinning dope depending on the PVA used, the solidification conditions, and the like.
The temperature is preferably set to -100 ° C. In spinning, it is important to defoam the stock solution, and if the defoaming is insufficient, the spinnability will decrease. It is preferable to leave the mixture for 16 to 30 hours to remove bubbles and to remove the bubbles for 1 to 24 hours in vacuum. Of course, other additives may be added to the spinning dope for various purposes, and for example, a surfactant or the like can be added.

When it is desired to form protrusions on the fiber surface, it is preferable to add fine particles to the spinning dope. The blending amount of the fine particles may be appropriately changed according to the fine particle diameter, the fiber diameter, etc., but if the blending amount is too large, the spinnability and the mechanical performance of the fiber are impaired. 0.6 to 45% by weight because the effect of the invention cannot be sufficiently obtained
/ Fiber, especially 0.7 to 30% by weight / fiber. The method for preparing the spinning dope is not particularly limited, but from the viewpoint of uniform dispersibility of the fine particles, PVA is used.
A method of gradually adding fine particles while stirring the aqueous solution is preferably employed. Specifically, it is preferable to stir at a high speed of about 400 RPM or more and to mix under the condition that the fine particles do not agglomerate. If foaming occurs, the spinnability is reduced, and the yarn breakage occurs and the quality of the yarn is reduced. It is preferred to stir at the maximum number of revolutions that does not allow air to enter.

Spinning may be performed using such a spinning solution, but it is necessary to employ a wet spinning method or a dry-wet spinning method from the viewpoint of forming a specific skin core structure. As the solidification liquid (coagulation liquid) used in the spinning method, an aqueous solution obtained by adding a salt having a coagulation ability to PVA is preferably used. Examples of suitable salts include sodium sulfate (Glauber's salt), ammonium sulfate, and sodium carbonate. And the like. The concentration of the aqueous solution is preferably from 200 g / L or more to the saturation concentration, particularly preferably 300 g / L or more, more preferably 320 g / L or more, and preferably the saturation concentration from the viewpoint of solidification. From the viewpoint of solidification properties, cost, etc., a saturated aqueous sodium sulfate solution can be particularly preferably used.

The temperature of the solidification solution must be appropriately set in accordance with the PVA used, other solidification conditions, and the like.
The temperature is preferably in the range of 00 ° C, particularly 45 to 80 ° C, in view of solidification reactivity, spinnability and the like. The higher the solidifying solution concentration, the higher the solidifying solution temperature, the higher the ratio of the thickness of the skin layer tends to be.However, these conditions are slightly reduced along with the used PVA, spinning solution concentration, and spinning solution temperature. The solidification state of the fiber is greatly affected only by changing, and the skin core structure is not substantially formed, or the thickness ratio of the skin layer becomes too large, so that the desired skin core structure is formed. It is necessary to adopt extremely limited conditions. Such conditions may be found by the above-described solidification test. For example, by employing the conditions described in Examples, a desired skin core structure can be formed.

The spinning solution is discharged into a coagulating liquid to perform dehydration and coagulation, and then, if necessary, roller stretching and / or wet heat stretching. From the viewpoint of fiber performance, it is preferable to perform both stretching, roller stretching to about 2 to 3 times, and wet heat stretching to 1.
It is preferable to carry out about 1 to 2 times. At this time, by performing the wet heat stretching in an aqueous solution (particularly preferably sodium sulfate solution) containing a salt capable of coagulating PVA, the thickness of the skin layer does not change much, but the solidification reaction proceeds further and the skin Preferred results are obtained because the layers are more dense. The salt concentration of the wet heat stretching bath is preferably 300 to 400 g / liter, and the bath temperature is preferably 70 to 100 ° C. By setting the temperature slightly higher than the temperature of the solidification liquid, the solidification reaction can be more efficiently promoted.

Next, it is preferable to perform dry heat drawing in order to enhance the mechanical performance and anti-sticking property of the fiber. Dry heat stretching is 2
The stretching is preferably performed at a temperature of 20 to 240 ° C., and the total stretching ratio is preferably about 3 to 8 times. Further, it is preferable to further perform a heat treatment to obtain a desired melting temperature. The heat treatment temperature is preferably from 150 to 200 ° C., and the heat treatment time is preferably from about 10 to 60 seconds. If the heat treatment conditions become severe, the fiber dissolution temperature in water becomes too high to obtain the fiber of the present invention, so it is preferable to pay attention to the heat treatment conditions. In some cases, an additional 22
A heat shrinkage treatment of 0 to 15% may be performed under a temperature condition of about 0 to 240 ° C, and a heat shrinkage treatment of 0 to 15% is preferably performed from the viewpoint of water resistance.

The denier of the fiber may be appropriately set according to the purpose. In general, the denier is preferably 0.01 to 100 denier, and 0.1 to 5 d when used for paper stock. The fiber length may be appropriately set according to the purpose. For example, when used as a stock, it is preferable to use the fiber by cutting it to a length of about 1 to 10 mm.

The fiber of the present invention can be used in any form, for example, any fiber structure such as cut fiber, yarn (spun yarn, filament yarn), string, cloth (woven and knitted, non-woven fabric, etc.). Can be processed. At this time, it may be used in combination with a fiber other than the PVA-based fiber of the present invention (including a PVA-based fiber having no protruding portion formed on the surface), or may be dyed after being processed into a fiber structure. Absent. The fibers of the present invention can be used for all kinds of fabrics, such as those for industrial use, clothing, and medical use. Specifically, stencil paper, decorative paper, wrapping paper, decorative paper, curtains, sheets, covers, adhesive tape, It can be suitably used for heat insulating materials, wet tissues, wiping cloths and the like.

In particular, the fiber of the present invention is suitable as a stock (paper constituent material) because of its excellent water dispersibility. The fiber may be used to make a desired paper by a known method. For example, one or more types of main fibers such as PVA-based fibers, pulp, rayon and the like having a high dissolution temperature in water,
A paper excellent in various performances can be obtained by using it together with A-based water-soluble fibers. From the viewpoint of sufficiently obtaining the effects of the present invention, it is preferable to use a paper containing the PVA-based water-soluble fiber of the present invention in an amount of 5% by weight or more, more preferably 10% by weight or more.
The paper obtained by such a method is excellent in uniform dispersibility of the fiber, and has high formation and quality, and can be suitably used for stencil paper, decorative paper, wrapping paper, wrapping paper, wet tissue, and the like.

[0030]

EXAMPLES The present invention will be described more specifically with reference to the following examples, but the present invention is not limited thereto.

[Skin layer thickness ratio: solidification test] VISLASE
SALES semi-permeable cellophane tube "Semless Cell
Each of the undiluted PVA spinning solutions was injected into a cellophane tube with a syringe into "ulose Tubing (diameter 18 mm x length 7 cm)". To promote the coagulation reaction. In a coagulation bath maintained at a constant temperature (1500 ml)
The tube was immersed for about 20 minutes in a state where the entire tube was immersed in the tube, taken out, and sliced so as to have a thickness of about 3 mm, and 5 or more test pieces were collected. The surface of the test piece (cross section of the tube) was observed at a magnification of 100 to 200 times with a phase contrast microscope, and the percentage of the thickness of the skin layer with respect to the tube diameter (skin layer thickness ratio) was calculated. Were determined by arithmetically averaging the skin ratios determined for the test specimens.

According to such a test method, the thickness of the skin layer is substantially uniform in the same cross-sectional shape, but when the thickness is not uniform, the average value of the maximum thickness and the minimum thickness is determined by the skin layer. Thickness. The temperature of the spinning solution and the coagulation solution can be adjusted by immersing the spinning solution and the coagulation solution in a thermostatic layer set at a desired temperature for 60 minutes or more. [Skin layer thickness ratio: fiber] It was determined by observing the fiber cross section by the method described in the above-mentioned solidification test.

[Average Particle Size of Fine Particles] With respect to the fine particles observed in the cross section of the fiber magnified 5,000 to 20,000 times by an electron microscope, when the fine particle shape is a perfect circle or a substantially circular shape, the diameter is changed to a non-circular shape. In the case of (1), the major axis is measured, the average value of the diameters of the fine particles present in one cross section is obtained, and the average value is obtained in five or more cross sections. Also,
In the state of the fine particle dispersion, the particle size distribution is measured using a Microtrac particle size distribution analyzer, and the highest peak point particle size (MV value) is defined as the average particle size. [Particle content (% of PVA added)% by weight] PVA-based fiber weighed in advance is dissolved in hot water, and the solution is filtered through a Teflon membrane filter or ultrafiltration membrane to separate dyeable fine particles.・ Dry to obtain the weight, fiber 1
The content (g) per g was determined.

[Average height ratio of protrusions (ratio of protrusion height to fiber diameter)%] Using an electron microscope, 1,000 to 2
The side surface of the fiber magnified 0000 times was observed, and the height of the protrusion formed by the fine particles was measured. This was carried out on five or more sides, and the average was calculated by dividing the average value by the fiber diameter. [Dissolution temperature in water ° C] 500mg / dr for fiber sample
Was immersed in water with a suspended weight, and the temperature at which the fiber sample broke when the temperature was raised at a rate of 1 ° C./min was observed, and the temperature was determined as the water dissolution temperature.

[Elution rate wt% / fiber moisture content (wt%
/ Fiber)] The sample fiber was immersed in water at a water temperature of 30 ° C. (bath
After immersion under the conditions of (water) 1/100 and immersion time of 15 minutes, the sample fiber and water were separated by filtration, the filtrate was evaporated to dryness, and the weight of the residue (Ag) was measured. Separately, 30 wet fibers after filtration
The mixture was treated with a centrifugal dehydrator at 00 rpm for 10 minutes to measure the weight (Bg) of the wet fiber after removing water adhering to the surface, and then evaporated to dryness to determine the weight (Cg) of the fiber residue. . The dissolution rate was calculated from A / (A + C) × 100, and the water content (% by weight / fiber) was calculated from (B−C) / (A + C) × 100.

[Agglutination] The fiber obtained after spinning was evaluated as ○ when substantially no agglutination occurred, and evaluated as × when the agglomeration occurred. [Water dispersibility] After the fiber was cut to a predetermined length, the fiber / water mixture ratio was adjusted to 6 g / 1.1 liter, and 500
A counting process was performed, and then 100 cc of fiber-dispersed water was collected, and 900 cc of water was added thereto and stirred. Further, after collecting 100 cc from the further stirred dispersion water, 900 cc of water was further added and the mixture was gently stirred, and the dispersion state of the fibers in the obtained dispersion water was visually evaluated. Next, 100 cc of the finally obtained dispersion water was collected, and 40 cc was added thereto.
After adding 0 ccc of water and stirring gently, the mixture was poured on a filter-coated nutsche and allowed to stand for about 30 seconds to precipitate fibers to some extent, followed by suction filtration with an aspirator or the like.
The obtained sample was observed with a microscope, and the dispersibility was evaluated based on whether there was any single fiber adhered (glued). The number of bonded fibers visible in the field of view is 50
% Or less is regarded as poor dispersibility, the case of 25% or more and less than 50% is slightly poor, and the case of less than 25% is good.

Examples 1 to 6 and Comparative Examples 1 to 3 Each spinning solution using PVA having a degree of saponification of 88 mol% and an average degree of polymerization of 1700 was applied to each concentration of sodium sulfate from a nozzle having a diameter of 0.08 mm and a number of holes of 2,000. Into a coagulation bath composed of an aqueous solution of sodium sulfate having a temperature of sodium sulfate and wet spinning. Then, the bath is separated from the coagulation bath and stretched by 2.5 times with a roller.
(1.5 g of wet heat stretching in 50 g / liter, 90 ° C.), and after drying, drying at 170 ° C. so that the total stretching ratio becomes 5 times.
And stretched by dry heat. Furthermore, constant-length heat treatment was performed under the conditions shown in Table 1 to produce PVA-based water-soluble fibers.
According to the examples, substantially no sticking occurred, and fibers having excellent quality and water dispersibility were obtained. However, in Comparative Examples 1 and 2, sticking occurred due to the small thickness ratio of the skin layer. It was not sufficiently suppressed, resulting in low quality and low water dispersibility. In Comparative Example 3, since the thickness ratio of the skin layer was too large, the fiber structure was destroyed in the stretching step, and fluff occurred frequently, resulting in low quality and low water dispersibility. Further, the solidification state in the solidification test and the solidification state when actually spun were in good agreement, and the solidification test was an excellent method for determining the solidification state of the fiber. Table 1 shows the results.

Example 7 Acrylic polymer fine particles (“HP91” manufactured by Rohm and House Co., Ltd., average particle size: 1 μm) were gradually added to an aqueous PVA solution so as to have a compounding ratio shown in Table 1, and 980 / min. The same procedure as in Example 1 was carried out except that the mixture was stirred and mixed by using a rotating high-speed stirrer, and left still for 30 minutes to obtain a defoaming solution. The average height of the protrusions of the obtained fibers was 5.5% of the fiber diameter, and the average protrusion height was 25% of the diameter of the fine particles. Since the fibers obtained by this example had specific projections formed on the surface, they were more excellent in terms of preventing sticking and improving water dispersibility, and had extremely high performance. Table 1 shows the results.

Examples 8, 9 and Comparative Example 4 Itaconic acid-modified PVA (degree of saponification: 95 mol%, average degree of polymerization: 1700)
Was performed in the same manner as in Example 1 except that was used. The modification rate of PVA was 10 mol% in Example 8, Example 9 and Comparative Example 4
Is 2 mol%. Table 1 shows the results. [Examples 10 and 11, Comparative Examples 5 and 6] Polyacrylamide block copolymerized PVA (polyacrylamide 50)
%, A saponification degree of 85 mol%, and an average polymerization degree of 1700). Table 1 shows the results.

[0040]

[Table 1]

[0041]

[Table 2]

Examples 12 to 22 Binder fibers 1 each having a fiber length of 2 mm and obtained in Examples 1 to 11
0 parts by weight and PVA-based fiber (Kuraray “V
90 parts by weight of PB103) were dispersed in water to prepare a slurry, which was wet-processed with a tappi paper machine to produce paper having a basis weight of 10 g / m ² . All the obtained papers were homogeneous and had good formation, and were high quality papers without pinholes due to sticking of binder fibers.

Claims (3)

[Claims] 1. A polyvinyl alcohol fiber having a dissolution temperature in water of 55 ° C. or less, having a skin core structure, and having a skin layer thickness of 4 to 25% of the fiber diameter. Alcohol-based water-soluble fiber. 2. A polyvinyl alcohol-based fiber having a dissolution temperature in water of 55 ° C. or lower, having a skin core structure and having a skin layer thickness of 4 to 25% of the fiber diameter. Made of paper. 3. A semipermeable membrane tube having a diameter of 5 to 50 mm and filled with a polyvinyl alcohol spinning solution is immersed in an arbitrary solidifying solution, and the cross section of the immersed tube is observed. A method for determining the solidification state of a fiber when spun using the solidification liquid.