JPH0718066B2 - Water absorption shrinkage yarn - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a yarn that shrinks by absorbing water. More specifically, the present invention relates to a yarn that rapidly shrinks in the lengthwise direction due to water absorption and has a high contracting stress expression rate, and further exhibits high strength and rubber-like elasticity for a long time even after water-absorption contraction.

<Prior Art> A yarn that shrinks due to water absorption, or a knitted fabric or a woven fabric using the yarn is useful for various applications. For example, when the shrinkable yarn is used for the longitudinal edge portion of the disposable diaper, by absorbing the water excreted by the user of the disposable diaper (mainly water contained in urine, other diarrhea / feces, etc.) and shrinking,
It is possible to prevent urine, feces, etc. from leaking out of the disposable diaper. Further, when the shrinkable yarn is used as various binding strings and the binding strings are made to absorb water, it is possible to prevent loosening of the binding part due to shrinkage stress at the time of absorbing water. When a cloth made of the shrinkable yarn is used as a cover material for a water rod of an offset printing machine, a tubular material having a diameter slightly larger than that of the core roller is prepared in advance from the cloth, and the core roller is mounted on the tubular material. And it can be brought into close contact with the core roller by immersion in water,
The mounting work can be extremely simplified. Further, if the shrinkable yarn is formed into a coarse-cylindrical material or a cord shape and is used as a root wrapping material at the time of transplanting a plant, for the same reason as the case of the cover material for the water rod of the offset printing machine, the root of the plant is It can be easily attached to the part. In addition, it is also useful as a net for hams and as a thread. Further, a fabric for civil engineering work, for example, a fabric once subjected to a water-absorption contraction treatment, has a high elongation and an extremely large impact resistance, and can be used as an excellent revetment base scour prevention sheet. It is also useful as a humidity sensor.

As is clear from these applications, the water-absorbing shrinkable yarn has a high shrinkage rate and a high shrinkage stress development rate during water absorption,
In addition, it is important that high strength is maintained for a long time even after water-absorption contraction, and that it exhibits appropriate rubber-like elasticity, and that it has all of the above four characteristics.

Various yarns have been proposed as yarns that shrink due to water absorption. However, the conventional water-absorbing shrinkable yarn lacks at least one of the above four characteristics and is not satisfactory. For example, in the case of increasing the shrinkage rate during water absorption and the rate of contraction stress development, a hydrophilic polymer is used as the fiber-constituting polymer, and the structure is such that water easily penetrates into the fiber. In order to contribute to the contraction of the swollen fiber in the axial direction of the fiber, the degree of orientation of the fiber constituent molecules is increased, but since such a fiber has a structure that can be swollen freely by absorbing water, the The internal structure of the is likely to collapse, and the strength and shrinkage stress after water-absorption contraction decrease sharply. In order to increase the strength and shrinkage stress after water absorption shrinkage, a method of twisting the fiber so that the number of twists is high to make a yarn whose internal structure does not easily collapse is considered, but such a yarn has a compact structure. Since water does not easily penetrate into the yarn and the free space where the fibers that make up the yarn absorb water will decrease, the shrinkage rate during water absorption and contraction stress during water absorption will develop. The speed will be significantly reduced. That is, the conventionally known water-absorptive yarn lacks at least one of the contraction rate upon absorption of water, the contraction stress developing rate, the strength after water-absorption contraction, and the rubber-like elasticity of the water-absorption contractile yarn, as described above. It is a problem when used for many purposes.

<Problems to be Solved by the Invention> The present invention has the above-mentioned characteristics, that is, the shrinkage rate at the time of water absorption is high, and the shrinkage stress development rate is also high, and the strength after the water absorption shrinkage is high, and further the water absorption shrinkage occurs. The purpose is to obtain a water-absorbing shrinkable yarn having rubber-like elasticity and having all of the above four characteristics.

<Means for Solving Problems> That is, according to the present invention, the maximum shrinkage ratio in water at 20 ° C. is 30%.
The water-absorbing shrinkable yarn is obtained by kneading or twisting the fibers which are contracted rapidly by water absorption and the fibers which have a maximum contraction rate in water at 20 ° C. of 30% or more and are contracted slowly by water absorption.

Fibers that shrink rapidly due to water absorption have the characteristics of high shrinkage rate during water absorption and high contraction stress development rate, but have the drawback that the strength and shrinkage stress after water absorption shrinkage decrease in a short time. . On the other hand, a fiber that shrinks and shrinks slowly by absorbing water has high strength and shrinkage stress after absorbing water, but has the drawback that it shrinks slowly when absorbing water and the shrinkage stress develops slowly. The present invention has found that by combining and integrating two types of fibers having such advantages and disadvantages, the advantages possessed by the respective fibers can be further expanded and the disadvantages can be eliminated. . In the present invention, a method of kneading or blending is used as a means for integrating two types of fibers into a yarn.
This unifying means is preferable in expanding the advantages of individual fibers and eliminating the disadvantages.

Next, the case of using the water-absorbing shrinkable yarn of the present invention for the longitudinal edge of a disposable diaper will be described as an example. In this case, it is particularly required that the shrinkage rate at the time of water absorption and the shrinkage stress development rate are high. To be done. This is because when the water-absorbing shrinkage yarn has a slow water-absorbing contraction speed or contraction force development speed, when the user of the disposable diaper suddenly excretes body fluid (for example, when the user excretes severe diarrhea or sideways). Excretion while the absorbent shrinkage thread attached to the disposable diaper does not function sufficiently (that is, before the edge of the disposable diaper is sufficiently adhered to the user's thigh), such as when sleeping and urinating. Is leaked from the edge of the disposable diaper to the outside. Furthermore, since the user of the disposable diaper usually moves frequently, the water-absorption contraction yarn undergoes repeated expansion-contraction, but the edge of the disposable diaper must always be in close contact with the thigh. The absorbent shrinkage thread should not break when it is used in a proper shape (for example, when the disposable diaper is not worn or maintained in a normal shape and the user moves violently). In order to satisfy these requirements, it is necessary that the fiber after water-absorption shrinkage has an appropriate rubber-like elasticity and sufficient strength. The water-absorption contraction thread used for the edge of the disposable diaper absorbs water in the excrement of the user and contracts, but the excreted bodily fluid does not always reach the water-absorption contraction thread immediately, and the excrement does not come in advance. It should also be taken into consideration that new excrement is excreted and mixed in the absorbent body of the disposable diaper while the temperature is lowered, and then reaches the water-absorbing shrinkable yarn. As a matter of course, the shrinkage rate, shrinkage rate, shrinkage stress, shrinkage stress manifestation rate, swelling degree, stress relaxation after swelling, etc. of the organic polymer material due to water absorption depend on temperature, and become higher as the temperature rises. , Temperature dependence depends on the material. The water-absorbing shrinkable yarn used for the edge of the diaper after use must be able to sufficiently function even in the worst use condition, and therefore (A) Immediately required water-absorbing water absorption The initial performance of shrinkage rate, shrinkage rate, shrinkage stress, and shrinkage stress onset rate is required to function even at around 20 ° C, which is considerably lower than body temperature, in consideration of environmental temperature, and (B) after water absorption shrinkage. Sustainability (especially rubber-like elasticity and strength) functions for a long time even in a temperature range close to body temperature, and no remarkable stress relaxation should be observed.

Considering the above points, it is desirable that the water-absorbing shrinkable yarn used for the edge portion of the diaper after use has the following substitute characteristics.

(1) Shrinkage upon absorption of water: Maximum shrinkage in water at 20 ° C (hereinafter referred to as shrinkage upon absorption of water) is 30% or more, and time to reach 30% shrinkage (hereinafter referred to as shrinkage rate upon absorption of water) is 10 seconds or less. Preferably there is. If the contraction rate upon absorption of water is less than 30%, there is a possibility that the thigh of the user cannot be sufficiently adhered.

(2) Shrinkage stress when absorbing water: The shrinkage stress in water at 20 ° C in the original length state (hereinafter referred to as shrinkage stress when absorbing water) is 30 mg / d or more in consideration of the thickness of the thread used and economic efficiency. The time at which 30 mg / d is expressed (hereinafter referred to as contraction stress development rate during water absorption) is preferably 10 seconds or less. If the shrinkage stress during water absorption is low, there is insufficient force to bring the edge of the disposable diaper into close contact with the thigh, and the entire material that makes up the edge absorbs water and must be soft before it can shrink. , Contraction will be delayed. Although it is possible to increase the shrinkage stress by thickening the thread to be used, in this case, a convex portion due to the shrink thread is generated and the wearing feeling is deteriorated, and it is not economically preferable.

(3) The yarn after shrinking when absorbing water has rubber-like elasticity. Specifically, the shrinkage stress in the absorbing state when immersed in water at 20 ° C for 16 hours in a state of contracting 30% from the original length (hereinafter referred to as absorbing water) The post-shrinkage stress) is preferably 10 mg / d or more. Again 35
It is more preferable that the shrinkage stress in the water-absorbed state when immersed in water at 8 ° C for 8 hours (hereinafter referred to as shrinkage stress after absorbing at 35 ° C) is 10 mg / d or more. If the contraction stress after water absorption in the temperature range from 20 ° C to near the body temperature decreases during use, the edge of the diaper cannot be stretched-contracted according to the user's movement, and the thigh does not reach the thigh. The state of close contact is poor. If the yarn used to increase the shrinkage stress after water absorption is thick, an unfavorable result is obtained for the same reason as described in (2) above.

(4) Strength after water-absorption contraction: Means the tensile rupture strength in the water-absorption state (hereinafter referred to as the water-absorption strength) after dipping for 16 hours in water that has been shrunk by 30% from the original length in 20 ° C. 300 mg / d or more is preferable. It is necessary to take care so that the absorbent shrinkage yarn does not cut due to the user's vigorous movement after the absorbent shrinkage yarn shrinks and swells with water when the disposable diaper is not worn properly. Because there is.

The required characteristics have been described in detail above by taking the water-absorbing shrinkable yarn for disposable diapers as an example, but these properties are also useful when the water-absorbing shrinkable yarn is applied to the other uses described above. For example, even when the water-absorbing shrinkable yarn of the present invention is used as a tie string, a root wrapping material, a net for hams or a sewn yarn, the work efficiency is greatly improved when it has the above-mentioned performance. Further, even when it is used as a material for a cover material for water roller rollers of an offset printing machine, the replacement efficiency of the cover material is remarkably improved. When used as a humidity sensor, more sensitive data can be obtained.

As described above, the present invention succeeds in highly functionalizing the above-mentioned four characteristics by allowing the rapidly shrinking fiber and the softly shrinking fiber to share the role of making the best use of the characteristics of each fiber and to expand them. In other words, the initial performances due to water absorption (shrinkage rate during water absorption and contraction stress development rate during water absorption) are expressed by fibers that shrink rapidly due to water absorption, and the sustained performance after water absorption (shrinkage stress after water absorption, 35 ° C The shrinkage force after water absorption and the strength after water absorption) are shared by the fibers that undergo water-absorption contraction later (usually within 5 minutes) than the fibers that contract rapidly due to water absorption. As is clear from this, the fibers that rapidly shrink due to water absorption and the fibers that slowly shrink due to water absorption, which compose the present invention, have the above-mentioned four characteristics when integrated. Desirably, for this purpose, each fiber preferably has the properties shown in Table 1 below. In the table, the ability of a fiber that rapidly shrinks due to water absorption to retain shrinkage stress at 30% shrinkage 5 minutes after water absorption shrinks until the fiber that shrinks loosely due to water absorption develops shrinkage stress (usually within about 5 minutes). It is for sharing the stress. Also the first
The table also shows the fibers that do not substantially shrink due to water absorption.

The method of measuring these performances will be described later.

As the fiber that rapidly shrinks and the fiber that gently shrinks by absorbing water, those having the characteristics shown in Table 1 above are preferable, and examples of the polymer that constitutes these fibers include polyvinyl alcohol, carboxyl group-containing modified polyvinyl alcohol, and water degradation polyacrylonitrile (-COOX the nitrile group: X = Li, K, obtained by introducing Na, the NH _4), carboxymethylated cellulose, acrylic acid grafted products of cellulose.

Next, a fiber that shrinks rapidly by absorbing water and a fiber that shrinks slowly by absorbing water will be described below by taking a polyvinyl alcohol fiber as a typical example.

A. Fiber that shrinks rapidly due to water absorption The present inventors have studied production of a fiber that shrinks rapidly, and a polyvinyl alcohol (hereinafter abbreviated as PVA) -based fiber produced under a certain special condition is converted into water at 20 ° C. We have found that it is a fiber material that reacts extremely sensitively when it comes into contact with it, and exhibits a large shrinkage behavior with almost no dissolution, and has already filed a patent application (hereinafter referred to as a prior patent). That is, the fiber described in the prior application patent is a water-shrinkable fiber having a shrinkage ratio upon water absorption of 30% or more and a shrinkage rate upon water absorption of 10 seconds or less, and a shrinkage stress upon water absorption of 150 mg / d or more, The shrinkage stress development rate of 150 mg / d is 10 seconds or less, and the shrinkage stress in 20 ° C water is 30 mg / d or more when it is shrunk by 30% from the original length. It is a high-speed shrinkable fiber which is less soluble in water and satisfies 25% or less, and it is specified in the prior patent that the following production method is suitable for obtaining a PVA fiber having such performance. Has been done.

Raw material PVA: containing 0.5 to 10 mol% of carboxyl groups, having an average degree of polymerization of 500 to 3000 and a degree of saponification of 77 to 99.9%. The carboxyl group-containing mol% means all the raw material monomer units constituting the modified polyvinyl alcohol, that is, vinyl acetate and carboxyl group-containing monomers (for example, itaconic acid and maleic acid) in the total amount of the carboxyl group-containing monomers. It is the molar ratio.

Stock solution for spinning: Aqueous solution with PVA concentration of 35-60% by weight Spinning method: Dry spinning Cooling and drying conditions after spinning: 20 ° C-70 immediately after exiting the spinneret
Once cooled in a cooling zone of ℃, passed through a preliminary drying zone of 80 ℃ ~ 170 ℃, then dried at 110 ℃ ~ 180 ℃.

Stretching heat treatment conditions: Stretching 4 to 7 times at a temperature of 190 ° C to 230 ° C.

The fibers obtained by such a method can be preferably used in the present invention, but can be, of course, produced by other methods.

B. Fibers that shrink and shrink due to water absorption In the Japanese Patent Laid-Open No. Sho 60-2709, the inventors of the present invention
It proposes a high shrinkage yarn in water. The skeleton advances the molecular orientation in the fiber as much as possible in a non-uniform state, minimizes crystallization, and relaxes the non-uniform strain latent in the fiber with a slight swelling action at the moment of contact with water. However, the morphological deformation developed in this process is utilized as a water-absorption shrinkage thread. As described in JP-A-60-2709, this material is characterized by shrinking 10% to 60% within 30 seconds at a water temperature of 30 ° C to 40 ° C. When measured in water at ℃
Seconds or more, and the rate of contraction stress development during water absorption requires 45 seconds or more. However, the shrinkage stress after water absorption is about 10 mg / d, the shrinkage stress after water absorption at 35 ° C is about 12 mg / d, and the strength after water absorption is 1.0 g / d or more,
These two characteristics match the requirements of the present invention.
Therefore, this fiber can usually be preferably used in the present invention.

The specific method for producing such a fiber is described in the above-mentioned publication, but it will be described below again.

Raw material PVA: Normal PVA with a degree of polymerization of 1,200 to 3,000 and a saponification degree of 98.0 mol% or more Spinning method: Wet spinning Stretching / heat treatment after spinning: Stretching 4 times or more at 130 ° C or less in a state where the fiber contains salts and water , The maximum shrinkage temperature is 65
Heat treatment under tension so that the maximum shrinkage rate is ~ 80 ° C and 50% or more. The maximum shrinkage temperature and the maximum shrinkage ratio can be freely changed by changing the stretching ratio and the stretching heat treatment temperature.

The fiber obtained by such a method can be preferably used in the present invention, or can be, of course, produced by another method.

The present invention is one in which fibers that shrink rapidly due to water absorption and fibers that shrink slowly due to water absorption are integrated, but yarns obtained by mixing and twisting fibers that shrink due to water absorption and fibers that do not substantially shrink due to water absorption are known. is there. FIG. 1 shows a mixed twisted state of a fiber (1) that shrinks due to water absorption and a fiber (2) that does not substantially shrink due to water absorption, and FIG. 2 schematically shows a state when the mixed twisted yarn is contracted by water absorption. It is shown. Third
The figure shows a fiber which shrinks rapidly by water absorption according to the present invention (3)
FIG. 4 schematically shows the mixed twisted state of the fiber (4) which shrinks and shrinks due to water absorption, and FIG. 4 schematically shows the mixed twisted yarn when it absorbs water. In the case of the twisted yarn according to the combination shown in FIG. 1, the yarn is contracted by absorbing water to form the shape shown in FIG. That is, only the fibers that contract due to water absorption contract, and the fibers that do not contract due to water absorption are simply wrapped around the former. As shown in Fig. 2, only the water-absorbing shrinkage yarns are responsible for the shrinking stress of the twisted yarns that have undergone water-absorbing shrinkage and have a shape as shown in Fig. 2. Therefore, when the water-absorbing shrinkage yarns relax due to water swelling, the shrinkage stress will no longer shrink. The stress will be lost (that is, the contraction stress after absorbing water will be insufficient). In order to prevent this drawback, as mentioned above, it is possible to take a method of suppressing the swelling by giving a twist that greatly exceeds the number of twists required for integration, but on the other hand, the shrinkage rate at water absorption, shrinkage at water absorption The stress onset rate decreases significantly. The strength after water absorption is tentatively maintained by the fibers that do not shrink.

Japanese Unexamined Patent Publication (Kokai) No. 57-11231 describes a mixed-twisted yarn obtained by twisting fibers that shrink due to water absorption and fibers that do not substantially shrink due to water absorption. According to our tracing experiment, the mixed twisted yarn has a shrinkage stress of 12 mg / d after absorption of water, which seems to have a seemingly satisfactory function, but when the water temperature rises, stress relaxation is likely to occur rapidly. For example, water absorption shrinkage stress at 35 ℃ is relaxed to 4 mg / d or less (3% shrinkage from original length
Even if it is soaked in water at 5 ° C for 2 hours, it becomes 5 mg / d.) It no longer shows rubber-like elasticity. Further, the rate of contraction stress development during water absorption of the mixed twisted yarn is 20 seconds, and it cannot be said that the mixed twisted yarn always has sufficient performance as a water absorbent shrinkage yarn for diapers.

On the other hand, the twisted yarn according to the present invention (Fig. 3) has a shape similar to that shown in Fig. 2 temporarily at the very early stage of water absorption shrinkage (usually 10 seconds to 5 minutes as shown in Table 1), but thereafter. Since the fibers that are contracted by shrinking follow and shrink, the shape is as shown in FIG. As is clear from FIG. 4, in the water-absorbing shrinkable yarn according to the present invention, both the rapidly shrinking fibers and the loosely shrinking fibers share the shrinking stress, and after a long time, the rapidly shrinking fibers swell and shrink. The fibers that shrink and shrink even after losing the stress share the shrinkage stress, and exhibit high shrinkage stress after absorbing water and shrinkage stress after absorbing water at 35 ° C. Moreover, the shrinkage stress after absorption of water and the shrinkage stress after absorption of water at 35 ° C. are respectively the shrinkage stress after absorption of water or the shrinkage stress after absorption of 35
It becomes much higher than the value after adding shrinkage stress after absorbing water. Furthermore, the strength after absorbing water is sufficiently high.

The characteristics of the present invention cannot be obtained simply by combining fibers that shrink rapidly with water absorption and fibers that shrink and shrink slowly with water absorption. That is, it is necessary to integrate these fibers by kneading or blending, and to use the fiber that shrinks rapidly with water absorption and to utilize the shrinkage rate at water absorption and the contraction stress development rate at water absorption as they are. In particular, the number of twists becomes a problem when combined with a fiber that shrinks and shrinks due to water absorption. In other words, if the twist number is high, the shrinkage rate of the yarn upon water absorption and the shrinkage stress development rate upon water absorption will decrease. As a result of examining the proper number of twists, the present inventors,
The angle θ formed by the rapidly shrinking fiber with the longitudinal direction of the water-absorbing shrinkable yarn
(Hereinafter referred to as twist angle θ, the method for obtaining it will be described later)
It has been found that it is preferable to set it to be less than or equal to ° in order to obtain a yarn having a performance conforming to the invention. Therefore, it is preferable that the water-absorbing shrinkable yarn according to the present invention is used with a twist number less than the twist angle of 18 ° and with a twist sufficient to integrate the yarn.
If the number of twists is increased, in addition to the above-mentioned drawbacks, the following problems will occur.

A: Snare is generated in the form of twisted yarn, and troubles such as yarn breakage occur in the manufacturing process, weaving process, or knitting process in which the twisted yarn is incorporated into the end edge of the disposable diaper, and the operation rate of the manufacturing process decreases.

B: When water shrinks, the yarn becomes kinked and uniform shrinkage cannot be obtained.

The twist angle θ indicates an angle θ formed by a single fiber, which is a rapidly shrinking fiber among the constituents of the water-absorbing shrinkable yarn, with the length direction of the water-absorbing shrinkable yarn, and the value is calculated by the following formula. The obtained value shall be used. FIG. 5 shows the water-absorbing shrinkable yarn 5.
FIG. 6 is a schematic diagram showing a state in which a fiber component 6 that rapidly shrinks in (thread radius rcm, twist pitch dcm) is twisted at a twist angle θ, and FIG. 6 is a development view thereof. 5 and 6
As can be easily understood from the figure, the twist angle θ is obtained as follows. Here, the thread is assumed to be a perfect cylinder, and voids between single fibers are ignored.

Twisting pitch d: 2.54 / T (cm) (T: Number of twists expressed in t / in) dr: Normal amount fineness of water-absorbing shrinkable yarn ρ: Density of water-absorbing shrinkable yarn (weighted average is calculated when different kinds of fibers are mixed-spun or mixed-twisted) As the value of ρ, vinylon = 1.26 cotton yarn = 1.54 rayon = 1.50 Use acrylonitrile = 1.15.

Θ (°) is obtained from

However, the single fibers do not pass on the outer circumference of the thread, Treat as passing through.

If the component of the water-absorbing shrinkable yarn that shrinks rapidly is the plied yarn, the twist angle θ in the lower twisted yarn
₁ and upper twisted yarn twist angle θ ₂ are calculated separately by the above formula, and when lower twist and upper twist are in the same direction (see FIG. 7), θ = θ ₁ +
When the lower twist and the upper twist are in the opposite directions at θ ₂ , θ = θ ₁ −θ ₂
Ask as.

Although the reason is not clear, when a fiber that shrinks rapidly due to water absorption and a fiber that shrinks slowly due to water absorption are twisted together, the shrinkage stress after absorption of water and the shrinkage stress after absorption at 35 ° C of the twisted yarn are It is also confirmed that there is a peculiar phenomenon that the shrinkage stress after absorption of water or the shrinkage stress after absorption of water at 35 ° C. is more than doubled.

When integrating fibers that shrink rapidly and fibers that shrink slowly by absorbing water, the form of each fiber may be filament + filament, filament + spun yarn, spun yarn + filament, spun yarn + spun yarn, As described above, it is usually used by twisting with a twist angle of 18 ° or less.
Further, both may be mixed at the time of spinning, and it is also possible to perform mixing in a cotton shape or a sliver shape, and mixing at the time of spinning (so-called core yarn).

Of course, the water-absorbing shrinkable yarn may be used as it is in the form of a cord depending on the purpose of use, or may be used after being processed into a woven fabric or a knitted fabric.

Next, the performance measurement of the water-absorptive shrinkable yarn, the fiber rapidly shrinking by the water absorption, and the fiber tightly shrinking by the water absorption will be described in detail. The fibers and yarns (hereinafter referred to as “fibers” as a representative of both) to be used for the measurement are in advance in a standard state (20
After leaving it in an atmosphere of ℃ ± 2 ℃, relative humidity 65 ± 2%) to reach water equilibrium, measure under standard conditions.

1. Shrinkage rate when absorbing water and shrinkage rate when absorbing water Immerse the fiber in water at 20 ± 1 ℃ so that a load of 1 mg / d is applied to the fiber in water, dipping time (sec) and shrinkage rate (shrinkage with respect to original length) Rate). And the contraction rate at that time 30
The time (seconds) to reach% is defined as the shrinkage rate upon water absorption, and the maximum shrinkage rate after 5 minutes of water immersion is defined as the shrinkage rate upon water absorption.

2. Shrinkage stress at water absorption and shrinkage stress development time at water absorption A tension of 5 mg / d is applied to the fiber and it is attached to a constant-speed elongation type tensile tester with a gripping interval of 10 cm, then the fiber is 20 ± 1 ° C.
Immersed in water and the relationship between shrinkage stress and immersion time (seconds) is measured with the gripping interval unchanged. And then water immersion 5
The maximum shrinkage stress within minutes is the shrinkage stress when absorbing water (unit: mg / d)
When the sample is a yarn, the contraction stress is 150 mg / d or 50 mg / d, and when the sample is a cord, the time (sec) required until the contraction stress reaches 30 mg / d is defined as the contraction stress development rate during water absorption.

3. Shrinkage stress at 30% contraction when absorbing water, same retention capacity While the fiber is slackened by 30% from the original length, it is attached to a constant-speed extension type tensile tester with a gripping interval of 10 cm, and then the fiber is 20 ± 1 ° C. The test piece is dipped in water and the relationship between shrinkage stress and immersion time (seconds) is measured with the gripping interval unchanged. At that time, the maximum shrinkage stress value within 5 minutes of water immersion is defined as the shrinkage stress at the time of water absorption of 30% (unit: mg / d), and the shrinkage stress at the time of 5 minutes after water immersion is 30% of the water absorption. Retaining capacity for shrinkage stress (unit: mg / d).

4. Shrinkage stress after absorption of water By the same method as the contraction stress measurement method at 30% contraction when absorbing water,
Shrinkage stress after soaking for 16 hours after shrinkage (unit: m
g / d).

5.35 ° C Shrinkage stress after absorption of water The shrinkage stress when measured by the same method as the shrinkage stress after absorption of water, except that the water temperature is 35 ± 1 ° C and the immersion time is 8 hours.
℃ Shrinkage stress after absorbing water (unit: mg / d)

6. Strength after absorption of water By the same method as the contraction stress measurement method at 30% contraction when absorbing water,
The tensile rupture strength is measured using a constant-speed elongation type tensile tester while the sample immersed for 16 hours is kept containing water. Apply 5 mg / d of initial load when attaching to the check part.

Hereinafter, the present invention will be described with reference to examples.

Examples and Comparative Examples (1) Production of rapidly shrinking fibers Itaconic acid 2 mol% modified PVA (average polymerization degree 1800, saponification degree 97
Mol%) to prepare a stock solution with a concentration of 50% PVA in water,
The spun raw yarn discharged from the spinneret into the air was cooled, pre-dried and dried under the following conditions.

Spinneret temperature (cooling zone): 30 ℃ 〃 (preliminary drying zone): 110 ℃ Cooling zone length: 0.25m Predrying zone length: 2.35m Drying temperature: 125 ℃ Moisture content of the dried spinning raw yarn is 0.1% It was as follows. This spinning raw yarn was drawn 5.5 times through a drawing furnace at 200 ° C, and 650d
I got a yarn of 72f. This fiber was designated as A yarn and the performance is shown in Table 2.

(2) Manufacture of fibers that shrink and shrink slowly An aqueous solution of PVA with a polymerization degree of 1700 and a saponification degree of 99.9 mol% is saturated with Na ₂
After wet spinning in SO ₄ aqueous solution was stretched to 4.5 times in a 40 ° C. in air and 90 ° C. saturated Na ₂ SO ₄ aqueous solution, as the hot air drying and 170 ° C. of 130 ° C. until the absolute dry at a constant length state Heat treatment was performed. Since this fiber is significantly swelled and shrunk by water, it is washed with water at 30 ° C for the purpose of removing Na ₂ SO ₄ adhering to the fiber while applying sufficient tension to maintain a fixed length, and a wet treatment such as oiling. And was dried under tension with hot air at 80 ° C. and then 120 ° C. until the moisture content to fiber reached 40%. Using the obtained monofilament denier 1.5-dr thread, after cutting with a parlock system, using a ring spinning machine, cotton count 10's / 1,
A spun yarn having a twist number of 6.8 t / in (Z) was obtained. This spun yarn was used as B yarn, and the performance is shown in Table 2.

(3) Fibers that do not substantially shrink due to water absorption Commercially available cotton yarn 10's / 1 (referred to as C yarn) was used. The performance is shown in Table 2.

(4) Preparation of water-absorbing shrinkable yarn Using the yarns obtained in (1), (2) and (3) above, a twisted yarn having the following constitution was produced.

Examples 1 to 4 One rapidly-shrinking yarn 650d / 72f and ten loosely-shrinking fibers 10's / 12 two were twisted in the S direction by a ring twisting machine =
5,8,10.5,14t / in (twisting angles of rapidly shrinking fibers are 8.1 °, 12.8 °, 16.9 °, 22.4 ° respectively)
The obtained yarns were designated as Examples 1, 2, 3, and 4, respectively.

Example 5 The same yarn constitution as in Examples 1 to 4 above was used, and the twist number was 5 t / in.
Twisting in the same direction as the spun yarn (Z direction) was applied as (twist angle of rapidly shrinking fiber is 8.0 °).

Comparative Example 1 Using only 3 yarns 10's / 1 that are loose and shrinkable, twisting was performed with a ring twisting machine at a twist number of 4.8 t / in (S direction).

Comparative Example 2 Only three rapidly shrinking yarns 650d / 72f were used and twisted in a S direction with a ring twisting machine to a twist number of 4.6 t / in (the rapidly shrinking fiber has a twist angle of 7.6 °).

Comparative Example 3 A rapidly contracting yarn 650d / 72f / 1 × 2 ply cord was twisted into a lower twist number of 14 t / in ^(s) × upper twist number of 5 t / in ^(s) . The twist angle of the rapidly shrinking fiber is 20.7 °. The reason for twisting in the same twisting direction is to make the shape of the twisted yarn compact and to increase the strength after absorbing water.

Comparative Example 4 One yarn 650d / 72f that rapidly shrinks and 10 ′s / two yarns (cotton yarn) that do not substantially shrink are S
Twisted to 5 t / in in the direction. The twist angle of the rapidly shrinking fiber is 7.4 °. Examples 1 to 5 and Comparative Example 1 described above
Various properties of the yarn obtained in No. 4 are shown in Table 3.

From these results, Examples 1, 2, 3 and 5 are cases in which the fibers which shrink rapidly due to water absorption and the fibers which shrink slowly due to water absorption are combined and the twist angle θ is twisted to 18 ° or less. In this case, it is clear that all the preferred characteristics of the water-absorbing shrinkable yarn according to the present invention are satisfied. Even if the twisting direction is changed, the characteristics of the water-absorbing shrinkable yarn hardly change (Example 5). Further, Example 4 is a case in which a fiber that rapidly shrinks due to water absorption and a fiber that shrinks softly are combined, but the twist angle is increased and the yarn is made compact. In this case, the rate of shrinkage upon absorption of water and the rate of development of contraction stress upon absorption of water are slightly reduced, indicating that the preferred requirements of the present invention are not satisfied. Can be used for.

On the other hand, Comparative Example 1 is a yarn composed of only fibers that shrink and shrink slowly by absorbing water, but in this case, the shrinkage rate upon absorption of water and the contraction stress development rate upon absorption of water are extremely low. Further, Comparative Example 2 is a case where the fiber is composed only of fibers that rapidly shrink due to water absorption, but in this case, there is no strength after water absorption,
The shrinkage stress after absorbing water and the shrinkage stress after absorbing water at 35 ° C are not satisfactory either. Comparative Example 3 is a case in which the cord is made compact by using only the yarn that rapidly shrinks due to water absorption, and the strength after water absorption is increased. In this case as well, the contraction speed upon water absorption decreases and the contraction stress upon water absorption occurs. Extremely slow speed. Further, Comparative Example 4 is a case where a yarn that rapidly shrinks by absorbing water and a yarn that does not shrink substantially by absorbing water are combined, and it is shown that the shrinkage stress after absorbing water and the shrinking stress after absorbing water at 35 ° C. are too low. In addition, a trial-made disposable diaper was produced by using the yarns shown in Table 3 for the longitudinal edge of the diaper (with two identical yarns aligned in parallel to one edge). As a result of carrying out a practical test by wearing it on a baby aged for 10 months, the water-absorbing shrinkable yarn according to the present invention showed good results as follows.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a yarn in which a fiber (1) that shrinks by absorbing water and a fiber (2) that does not substantially shrink are twisted together, and FIG. 2 is a schematic diagram of the yarn when the yarn of FIG. 1 is contracted. , Fig. 3 is a schematic diagram of a yarn in which a fiber (3) that rapidly shrinks by absorbing water and a fiber (4) that shrinks slowly by absorbing water (4) are twisted together, and Fig. 4 shows a case where the yarn of Fig. 3 is contracted. It is a schematic diagram of a thread. Fifth
The figure schematically shows the state of the monofilament (6) of rapidly shrinking fibers in the water-absorption shrinkable yarn (5).
Is the radius of the water-absorbing shrinkable yarn, d is the twist pitch, and θ is the twist angle. FIG. 6 is a development view of FIG. FIG. 7 schematically shows the state of a single fiber of rapidly shrinking fibers when the water-absorbing shrinkage yarn is twisted in the same direction as the lower twist and the upper twist, and is a single fiber. The twisted yarn is 6, a monofilament of rapidly shrinking fibers, θ ₁ is the twist angle of the monofilament of rapidly shrinking fibers in the undertwisted yarn, and θ ₂ is the twisted angle of the undertwisted yarn in the upper twisted yarn.

Claims (6)

[Claims] 1. A fiber having a maximum shrinkage of 20% or more in water at 30 ° C. and rapidly shrinking by water absorption, and a fiber having a maximum shrinkage of 20% in water at 20 ° C. or more and slowly shrinking by water absorption. Water-absorbing shrinkable yarn. 2. The maximum shrinkage rate in 20 ° C. water is 30% or more, the time to reach 30% shrinkage is 10 seconds or less, and the shrinkage stress in 20 ° C. water in the original length state is 30 mg / d or more, 30 mg. / d
The time until the contraction stress develops is 10 seconds or less, and the contraction stress in the water absorption state when immersed in water at 20 ° C for 16 hours in a state of contracting 30% from the original length is 10 mg / d or more. Claim 1 whose strength is 300 mg / d or more
The water-absorbing shrinkable yarn according to item. 3. The water absorbing shrinkable yarn according to claim 1 or 2, wherein the twisting angle of the rapidly shrinking fiber is 18 ° or less. 4. In water at 20 ° C., the fibers that shrink rapidly due to water absorption have a maximum shrinkage of 30% or more, and the income time to reach 30% shrinkage is 10 seconds or less. When the shrinkage stress is 150 mg / d or more, the time until the 150 mg / d shrinkage stress develops is 10 seconds or less, and the shrinkage stress in water at 20 ° C is 30 mg / d or more when contracted by 30% from the original length. The water-absorbing shrinkable yarn according to any one of claims 1 to 3, which has a shrinkage stress of 20 mg / d or more when left for 5 minutes in this state. 5. A fiber that shrinks slowly due to water absorption is 20 ° C.
In water, the maximum shrinkage rate is 30% or more, the time required to reach 30% shrinkage rate is 10 seconds to 5 minutes, and 20 ° C in the original length state
The contraction stress in water is 50 mg / d or more, the time until the contraction stress of 50 mg / d appears is 10 seconds to 5 minutes, and it is 30 from the original length.
% Contraction stress in the water absorption state when immersed in 20 ° C. water for 16 hours in a contracted state is 5 mg / d or more, and strength in this state is 500 mg / d or more.
The water-absorptive shrinkable yarn according to any one of 3 above. 6. The water absorption according to any one of claims 1 to 5, wherein the fiber which shrinks rapidly with water absorption is a modified polyvinyl alcohol containing a carboxyl group, and the fiber which shrinks slowly with water absorption is an unmodified polyvinyl alcohol. Shrink yarn.