JPH0112848B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing water-swellable highly shrinkable fibers that exhibit a large shrinkage rate and shrinkage force in a short period of time in hot water in a relatively low temperature range of 30 to 40°C or hot water containing salts. be. BACKGROUND OF THE INVENTION Fiber materials and sheet materials that absorb water and swell or dissolve when immersed in water are known. For example, polyvinyl alcohol-based water-soluble fibers obtained from resins with hydrophilic groups and superabsorbent fibers with hydrophilic groups introduced in fibrous form are widely known; It is used as a material, used to maintain the workability of other materials, and is ultimately dissolved and removed, or its purpose is to absorb water. Therefore, contraction during the process of expressing each effect often becomes an impediment to achieving the purpose. Furthermore, heat-shrinkable fibers using hydrophobic resins are known. All of these fibers shrink only at relatively high temperatures of 60° C. or higher, and solidify after cooling, so they are unable to exhibit rubber-like elasticity like the low-temperature, highly shrinkable fibers of the present invention. The present inventor conducted various studies on the possibility of producing a material that exhibits a large shrinkage behavior that is extremely sensitive to hot water at body temperature or bath temperature, or hot water containing salts such as blood and urine. polyvinyl alcohol (hereinafter abbreviated as PVA)
It has been found that fibers can achieve the above objectives. In other words, in order to use hydrophilic PVA fibers and shorten the time required for contraction to occur without causing partial dissolution of the fiber surface in hot water in a relatively low temperature range, and to obtain a large contractile force, fiber breakage due to water absorption and swelling is necessary. Rather than trying to increase the area, we try to advance the molecular orientation inside the fiber in a non-uniform state as much as possible in advance, while suppressing crystallization to the necessary minimum, and the slight swelling effect at the moment of contact with water creates the potential inside the fiber. Alleviates uneven distortion caused by
The idea that it is more effective to utilize morphological changes such as crimp that occur during this process is the basis for inventing the fiber material. That is, in the present invention, a polyvinyl alcohol aqueous solution having a degree of polymerization of 1,200 to 3,000 and a degree of saponification of 98.0 mol% or more is wet-spun, and the resulting spun yarn is spun in an atmosphere of 130°C or lower with moisture and salts attached. After stretching more than twice as much, it is dried, then heat treated at a temperature of 170°C or less and under tension, and then washed with washing water of 35°C or less under tension, and the fiber moisture is reduced to 50% under tension.
This is a method for producing low-temperature, highly shrinkable fibers, which is characterized by drying at 80°C or lower until the There are two methods for producing PVA fibers: dry spinning and wet spinning, but the wet spinning method is used. The reason for this is that although it is suitable for producing fibers for nonwoven fabrics, it tends to form a non-uniform structure in the fiber cross-sectional direction during coagulation. If the degree of polymerization of PVA exceeds 3000, the viscosity of the aqueous solution will increase significantly and the productivity will drop significantly, which is not preferable. On the other hand, if it is less than 1200, the molecular orientation during stretching will be poor and it will be difficult to obtain a predetermined shrinkage force.
Furthermore, if the degree of saponification is 98 mol% or less, it is difficult to obtain the minimum degree of crystallinity in the fibers necessary to remove salts of the coagulating liquid adhering to the fibers by washing with water. As a coagulating liquid in wet spinning of a PVA aqueous solution, a concentrated aqueous solution of salts such as sodium sulfate and ammonium sulfate is usually used, and there is also a method of gelling with sodium hydroxide and then neutralizing and coagulating. Either method is fine, but the former is more preferable. preferable. Next, the PVA fibers leaving the coagulation bath are treated with swelling water and an aqueous solution of salt brought from the coagulation solution.
Non-uniform strain is imparted to the inside of the fiber by stretching it four times or more in an atmosphere below 130°C, economically below 100°C. In order for the resulting fibers to exhibit strong shrinkage behavior upon water absorption at relatively low temperatures, the internal strain must be kept as unstable as possible. To achieve this objective, conditions are desirable that suppress crystallization of the fibers and maximize molecular orientation. A high stretching ratio is required to increase molecular orientation, and increasing the fiber temperature is effective in this regard. However, when the fiber temperature rises to 150°C or higher under conditions close to bone dry, the degree of crystallinity increases rapidly, resulting in a decrease in internal strain. Conversely, if the fiber temperature is low, the draw ratio decreases and the necessary shrinkage force cannot be obtained. In order to prevent crystallization by increasing the molecular spacing and to obtain a large stretching ratio, the present inventor developed a method in which water, which is a solvent for PVA, is contained in and around the fibers at a temperature of 130°C or less in a state where the fibers contain at least 40% of the fibers. We have discovered the possibility of obtaining the desired shrinkage behavior by stretching 4 times or more. During stretching, the adhering salts with coagulation ability, such as sodium sulfate and ammonium sulfate, should be used in an amount sufficient to prevent a decrease in actual stretching efficiency due to excessive swelling of the fibers, or to suppress adhesion between fibers due to partial dissolution. Requires. Note that the temperature of the fiber itself during stretching is 70°C or higher and lower than 100°C, preferably 80°C since it is accompanied by a large amount of moisture.
It is desirable to control the ambient temperature within a range of 95°C to 95°C. The salts adhering to the drawn fibers are washed away with water to less than 0.5% in the scouring process, and after applying the necessary oil for the spinning or non-woven process, they are dried to produce a stable material that retains latent shrinkage when water is absorbed. The prerequisite is to produce fibers in the form of fibers, but even if the fibers after stretching are placed under tension, salts can be washed away with water without any partial dissolution of the fiber surface, and dry fibers can be economically produced. That is difficult. Therefore, the drawn fibers are left to dry completely with the salts attached, and heat treatment is required to achieve the minimum necessary level of crystallization. As a result of investigating the shrinkage behavior of the fibers by varying the heat treatment conditions, it was confirmed that fibers exhibiting the desired water absorption and shrinkage properties could be obtained under extremely limited conditions. To measure the shrinkage behavior of fibers in water,
First, in order to make the fibers straight, an initial load of 1/500 (g) per denier of the fibers was applied, the fibers were placed in water at 20°C, and the shrinkage rate at each temperature was read while heating at 1°C/min. did. The shrinkage rate of the fibers increases as the water temperature rises, reaching an equilibrium at the temperature at which the fibers exhibit the maximum shrinkage rate, and beyond this temperature the fibers cannot resist the load and begin to elongate rapidly and break. The cutting temperature will be called the melting temperature. An object of the present invention is to provide a fiber material that exhibits remarkable rubber elasticity, shrinkage rate of 10% or more in an extremely short period of time at water temperatures close to body temperature, and moderate strength in use. Therefore, no problematic dissolution of PVA should occur up to at least 50°C. This region corresponds to a maximum shrinkage temperature of 65°C. However, assuming the above-mentioned stretching conditions, this degree of heat treatment coincides with the limit condition under which adhering salts can be economically removed by water washing over a fixed length and hot air drying over a fixed length without causing adhesion between fibers. Next, increasing the heat treatment effect will not only reduce the maximum shrinkage rate and increase its temperature, but also increase the difference in the corresponding temperature between the minimum shrinkage rate of 15% required at the fiber stage and the maximum shrinkage rate. It's shrinking. In addition, in order for the spun yarn or nonwoven fabric using the fibers of the present invention to exhibit a rapid shrinkage behavior of 10% or more in water at 40°C or water containing 5% or less salt, the PVA fibers constituting it must However, when immersed in water at the fiber stage, approximately 15% shrinkage is required. The maximum shrinkage temperature of fibers with this physical property is 75°C. However, if a room temperature stretch cutting method (such as parlock spinning) is used in the process of manufacturing spun yarn or nonwoven fabric, the maximum shrinkage temperature of the fiber is 80°C because internal strain increases during stretch cutting.
Tolerable up to ℃. The maximum shrinkage rate is 50%.
The above is required, and the maximum shrinkage temperature is 75℃ from 65℃.
(In the tension cutting method, 75°C can be read as 80°C.) Heat treatment conditions must be selected within a range that satisfies the following three limiting conditions. For this purpose, heat treatment is carried out at a temperature of 170° C. or lower and under tension, as carried out in the Examples described later. Salts adhering to the heat-treated PVA fibers as described above must be removed in order to be spun or made into a non-woven fabric, and treated with a water-based emulsion oil. Washing with water is the most economical way to remove water-soluble adhering salts, but swelling in water cannot greatly reduce the internal strain of fibers, which is the driving force behind crimp development. As a result of various studies on the possibility of washing with water, the present inventor took advantage of the fact that molecular orientation is not disturbed much when strong tension is applied even in a wet state under limited conditions, and set the temperature of the washing water and oil treatment solution to 35°C or less. As well as the heat treatment process, water washing, oil treatment,
It has been found that drying until the fiber moisture content is 10% or less can be carried out under tension greater than the constant length state. In particular, in the drying process after removing salts, it is effective to keep the hot air temperature below 80°C until the moisture content of the fibers is below 50% in order to prevent adhesion between the fibers. There are no restrictions on the single fineness of the PVA fiber as long as it satisfies the above physical properties. However, under the conditions of the wet spinning method that is normally used for production, the coagulation state decreases as the single fiber size increases, and the drawing effect decreases, so the range is preferably 7 denier (dr) or less. Next, the spun yarn and nonwoven fabric made of the PVA fiber will be described. It is assumed that the spun yarn made of low-temperature high shrinkage fibers obtained by the method of the present invention will sensitively contract with a force of 0.1 g/dr or more when it comes into contact with urine or blood, and that it will shrink sensitively with a force of 0.1 g/dr or more when it comes into contact with urine or blood. It shrinks by 10-60% within 30 seconds in water containing salt, and exhibits rubber-like elasticity in the wet state. The measurement method is water at 30℃, 5% sodium chloride aqueous solution at 30℃, and artificial urine (aqueous solution of urea 1.94℃, sodium chloride 0.80%, magnesium sulfate heptahydrate 0.11%, calcium chloride 0.06%) and 1/500. (g/dr) and read the change in shrinkage rate over time. 30
The shrinkage rate increases at 40℃ compared to ℃.
Spun yarn may be produced by a card method using the above-mentioned fibers, which are crimped and cut to a length suitable for the spinning process, but the parlock method, in which the fibers are cut in a tow shape, reduces the internal strain of the fibers. It is effective in improving the shrinkage rate and shrinkage force in water in terms of a decrease in structural density due to a decrease in the number of twists due to an increase in the fiber length and a decrease in the number of twists. Note that other fibers can also be blended. The water-absorbent highly shrinkable nonwoven fabric has the ability to shrink by 10 to 60% within 30 seconds when it comes into contact with water at 40°C or lower or water containing 5% or less salt, and has the same effect as the above-mentioned spun yarn in the form of a sheet. This is what we provide. Therefore, in order to efficiently develop crimp, it is more desirable to arrange the fibers in the uniaxial direction as much as possible within the range that exhibits the physical properties of a practical nonwoven fabric, but this is not limiting. To obtain a sheet-like material, the web after carding or random webs may be fixed with a needle punch, or binder fibers with a melting temperature of less than 150°C and showing very little shrinkage upon melting (for example, binder fibers manufactured by Kanebo Co., Ltd.) It is desirable to adopt a process such as blending with composite binder fibers such as Belt Combi and heat bonding. The feel after water absorption can be improved by blending around 10 to 20% hydrophobic fibers such as polyester, if necessary, without significantly impairing desired physical properties such as shrinkage behavior in water and rubber elasticity upon water absorption. These spun yarns or non-woven fabrics take advantage of their high wet shrinkage in relatively low temperature regions and are secured to the longitudinal edges, usually at the thighs, in place of the rubber-like materials used in disposable diapers, for example. Reinforcement of casts, including applications that prevent urine from leaking out of diapers, without tightening, once urine is drained, and when the spun yarn (including cloth-like materials whose constituent elements are spun yarn) or nonwoven fabric gets wet, it quickly shrinks and prevents urine from leaking outside the diaper. It can be used in fabrics and other fields that require the ability to rapidly shrink when wet. The low-temperature, high-shrinkage fiber obtained by the method of the present invention is also extremely flexible, being relatively flexible in a dry state and, in the presence of water, immediately absorbing water and exhibiting rubber elasticity with an elongation of more than 100%. It can also be used for sheet-like or bulk materials that exhibit excellent performance and are reversible in both wet and dry conditions. Conventionally, foamed sponges made of formalized PVA resin or nonwoven fabrics made by shrinking PVA fibers at high temperatures of 60°C or higher have existed as materials that exhibit flexible rubber-like elasticity when water is absorbed. However, since all of these materials harden significantly in the dry state, their uses are limited to wide ranges, and there is a strong demand in the market for improvements in their physical properties. In the case of formalized PVA resin sponges, the reason for hardening is that when water, which has a plasticizing effect, is no longer present, the resin itself is extremely hard, and the sponge structure has no flexibility, resulting in a significant decrease in toughness. On the other hand, in the case of nonwoven fabrics made of high-temperature shrink PVA fibers, as mentioned above, the water temperature required to ensure a predetermined shrinkage rate and the water temperature or melting temperature corresponding to the maximum shrinkage rate are close to each other, so some portions of the fiber surface may
PVA dissolves or localized excessive swelling similar to dissolution occurs, and when it dries, it hardens. This hardening phenomenon is based on pseudo-adhesion between fibers, and a certain degree of softening effect can be seen after kneading, but after reabsorbing water and drying at room temperature, the hardness remains the same as before kneading. Restore. The nonwoven fabric made of the PVA fiber of the present invention was heated at 30 to 50℃.
It has been discovered that a high-density nonwoven fabric obtained by shrinking the area by 50°C or more in a relatively low temperature region can improve the above-mentioned drawbacks of conventional products. The surface of this high-density nonwoven fabric becomes smoother as the fineness becomes finer, but 0.5 dr or more is required to ensure card passage. There are no restrictions on the manufacturing method of the nonwoven fabric as long as it is a dry method, and any method suitable for the purpose of use may be selected. In order to avoid directing the shrinkage, a random web or 45° cross method is used, needle punching is used for adhesion, and heat treatment is used in the blended state of heat-adhesive fibers that have a melting point of 150℃ or less and have low shrinkage when melted. Either method may be used. The basis weight and thickness of the nonwoven fabric can be set depending on the application, from sheet-like to bulk raw materials. The obtained nonwoven fabric exhibits rubber elasticity and extremely flexible physical properties when water is absorbed, and maintains flexibility even when dry, but depending on the conditions used, it may have a slightly slimy feel when wet. There are also applications where a smooth feel is required even when wet. As a countermeasure for this, mixing 10 to 20% of commonly produced hydrophobic fibers or hydrophobic composite fibers such as polyester, polyacrylonitrile, or polypropylene into the PVA fiber will almost change the desired physical properties. It can be improved without any problems. Further, other hydrophilic fibers may be mixed depending on the purpose. However, if the blending ratio of other fibers increases to more than 70%, the desired shrinkability cannot be obtained in the nonwoven fabric. As mentioned above, the high-density nonwoven fabric made by sufficiently shrinking the nonwoven fabric made of the PVA fiber of the present invention in relatively low-temperature water of 30 to 50°C exhibits rubber-like elasticity immediately upon absorption of water, and has extremely excellent flexibility. It exhibits unprecedented physical properties, with almost no loss of flexibility even after drying. Utilizing this physical property, it can be used for tools for applying or wiping off makeup on the face, etc., base fabrics such as poultices, high-grade wipers, and civil engineering materials such as sheets for preventing scouring during land reclamation on the coast. EXAMPLES The excellent performance of the fibers and fiber structures obtained by the present invention will be explained below using Examples. Example 1 A PVA aqueous solution with a polymerization degree of 1700 and a saponification degree of 99.9 mol% was wet-spun in a saturated Na ₂ SO ₄ aqueous solution and then stretched 4.5 times in air at 40°C and in a saturated Na ₂ SO ₄ aqueous solution at 90°C. , leave it at a constant length until completely dry.
Hot air drying at 130℃ and maximum shrinkage temperature in water is 70℃
Heat treatment was performed using hot air at 170°C to achieve a temperature of 170°C.
This fiber undergoes significant swelling and contraction due to water, so when sufficient tension is applied to maintain a constant length,
Washing with water at 30℃ for the purpose of removing Na ₂ SO ₄ attached to the fibers.
Performs moisture treatment such as oiling, and further reduces the fiber moisture content to 40%.
It was dried under tension with hot air at 80°C and then 120°C until reaching %. The obtained fibers with a single fineness of 2 dr showed no adhesion between fibers and exhibited good splitting properties.
The maximum shrinkage rate in water was 72%, and the dissolution temperature was 79°C. Also, in distilled water, artificial urine and saline at 30°C.
The shrinkage rate when immersed for 30 seconds is 31% and 30%, respectively.
and 16%. Reference example PVA fiber alone obtained by crimping the thread obtained in Example 1 and cutting it to a fiber length of 51 mm, and
A dry nonwoven fabric with a fabric weight of 80 g/m 2 and a needle count of 200 p/cm ² was made by blending PVA fiber with 10% polyester fiber with a single fineness of 2 dr and a fiber length of 51 mm using a ^random web and needle punch method. The nonwoven fabric exhibited shrinkage behavior as shown in the following table in distilled water, artificial urine, and 5% saline. In addition, the nonwoven fabric exhibits extremely excellent flexibility and rubber elasticity in the wet state after shrinkage, and PVA
The slimy feeling on the surface that can be seen in the case of 100% fiber was almost completely eliminated by blending a small amount of polyester fiber.

[Table] Measurements were made with no load in the direction.
In addition, PVA fibers alone and PVA fibers obtained by crimping the yarn obtained in Example 1 and cutting them into fiber lengths of 51 mm and
A dry non-woven fabric with a fabric weight of 80 g/m ² and a needle count of 200 p/cm ² was made by mixing PVA fiber with 20% polyester fiber with a single fineness of 2 dr and a fiber length of 51 mm using a random web and needle punch method. Furthermore, when the nonwoven fabric was immersed in water at 40°C for 1 minute, the area of the nonwoven fabric shrunk by 35% of that before dipping, and by 41% in the latter case, showing extremely excellent flexibility and wet cutting elongation of nearly 200%. It exhibits a high degree of rubber elasticity. In particular, the latter does not feel slimy when water is absorbed. It was confirmed that the nonwoven fabric, which has been made highly densified by shrinkage, remains flexible even after being dried with hot air at 80°C, and that the tactile sensation in the re-conditioned state can be reproduced when it is repeatedly immersed in water (water temperature 40°C) and dried. . The strength and elongation properties of the obtained high-density nonwoven fabric are shown in the following table.

[Table] Comparative Example After wet spinning, stretching, and drying in the same manner as in Example 1, heat treatment was performed in hot air at 190°C so that the maximum shrinkage temperature of the obtained fiber was 85°C, and the fiber was washed with water at a fixed length.
Oiled, dried, crimped and cut
We prototyped a nonwoven fabric made of PVA fiber alone. The conditions for the trial production of the nonwoven fabric were as in the above reference example. In order to shrink the area of the nonwoven fabric in water to 35% of its pre-immersion water temperature, a water temperature of 71°C is required, and while the resulting high-density nonwoven fabric exhibits excellent flexibility and rubber elasticity in a water-absorbing state, it has a very slimy feel. It was strong, and especially when dried, it took on a very hard plate-like shape even when hot air of 80°C or less was used. 20% to the PVA fiber
A high-density nonwoven fabric containing polyester fibers can reduce the slimy feeling, but hardly any improvement in hardness after drying is observed. When the nonwoven fabric, which has a plate-like shape in the dry state, is kneaded, it becomes somewhat flexible, but when it is re-immersed in water below 40°C and dried, its hardness returned to the level before kneading.

Claims (1)

[Claims] 1 Wet-spun a polyvinyl alcohol aqueous solution with a degree of polymerization of 1200 to 3000 and a degree of saponification of 98.0 mol% or more, and the resulting spun yarn with water and salts attached to it.
Stretched at least 4 times in an atmosphere of 130℃ or less, dried, then heat treated at a temperature of 170℃ or less under tension, washed with washing water at 35℃ or less under tension, and then dried under tension. Fiber moisture is 50%
A method for producing low-temperature, high-shrinkable fibers, which is characterized by drying at 80°C or lower until the following.