JP2558277B2 - Band-shaped molded article having high-speed shrinkability and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention is applied to an object when contacted with water at room temperature, causing rapid contraction and less stress relaxation for a long time after contraction, and when wound around an object. The present invention relates to a belt-shaped molded article that exhibits no stress concentration and exhibits functions such as rubber elasticity, and a manufacturing method thereof.

<Prior Art> As a Japanese Patent Application No. 60-246914, we have already applied for a patent for a fiber that shrinks due to water absorption. The water-absorptive shrinkable fiber has a high shrinkage rate and has no stress relaxation for a short time after shrinkage, but a large stress relaxation is observed with the passage of time after water absorption. In addition, the water-absorbing shrinkable fiber described in Japanese Patent Laid-Open No. 60-2709, which is different from this, does not show stress relaxation for a long time, but in terms of shrinkage rate, even in water having a water temperature of 30 ° C.
It takes 30 seconds until it shrinks at room temperature (at around 20 ° C)
When using the above water, the contraction speed becomes extremely slow. As described above, it is extremely difficult for the fiber alone to satisfy both the contraction rate and the stress relaxation after contraction, and it has not been found until now that the above two requirements are simultaneously satisfied.

In addition, the largest use of the shrinkable fiber is to attach the fiber to the edge of the diaper and use it to shrink after absorbing liquid so that the diaper can be closely attached to the crotch to prevent liquid leakage. It is used as a thigh clamp.
Then, as a specific usage form at that time, Japanese Patent Laid-Open No. 57-
As disclosed in Japanese Patent No. 35002, an aggregate of a plurality of fibers is formed, or as shown in Japanese Patent Application Laid-Open No. 60-72548, a nonwoven fabric is formed into a tape. However, an aggregate of a plurality of fibers, for example, a multifilament twisted, or a fiber cut into raw cotton and twisted in a normal spinning process to form a yarn, which is cut by the tow spinning method. , When twisted into a thread, when the fiber assembly is wound around a certain object and put into a wet state, the shrinkage stress applied to the object is concentrated in the fiber assembly, that is, the thickness portion of the thread, and shrinks. There are drawbacks such as marking of threads and deformation of the surface of the object such as dents. In the case of a diaper that is specifically used, a strong streak is attached to the thigh by tightening. In order to prevent such a situation, the above-mentioned JP-A-60
In the −72548 publication, the water-absorption shrinkable fiber is woven or woven into a plane,
Although the stress concentration is dispersed in the width direction by making it into a non-woven fabric, since the yarns of the knitted fabric mutually regulate each other, sufficient shrinkage stress cannot be obtained, and the non-woven fabric is not completely fixed by the single fibers. However, there is a drawback in that the material easily behaves freely with shrinkage, and as a result, shrinkage is small. That is, the conventional technique has not obtained a material having a large shrinkage stress and having the shrinkage stress dispersed in the width direction.

Further, in JP-A-60-72548, a water-absorbent PVA film slit and stretched is described as a water-absorbent shrinkable tape. There is a drawback that the stress relaxation is large. Actually, in the invention of JP-A-60-72548,
In order to prevent low shrinkage stress of the tape and high stress relaxation after shrinkage, it is essential to use the slit film and a rubber band together.

<Problems to be Solved by the Invention> The inventors of the present invention react very sensitively to water at 20 ° C., exhibit a large shrinkage behavior with almost no dissolution, and relax stress. PVA produced under certain special conditions as a result of diligent research on a material that does not have stress and does not cause stress such as shrinkage yarns to be attached to the bound object It was found that a band-shaped molded product of the system solves the above-mentioned problems.

<Means for Solving Problems> That is, the present invention provides a water-absorbing shrinkable band-shaped molded article at 20 ° C.
When the maximum shrinkage rate in water is 30% or more, the time required to reach 30% shrinkage rate is 10 seconds or less, and the shrinkage stress in the original length state is 10 g or more per 1 mm width. Is less than 10 seconds, the subsequent stress relaxation is less than 15% of the maximum shrinkage stress after 1 hour, and is less than 30% from the original length.
When the shrinkage stress in water at 20 ℃ is 2g or more per 1mm width when it is dispersed in water at 20 ℃, the weight loss on dissolution is 25
% Or less, and is a high-speed shrinkable band-shaped molded product which is hardly soluble in water.

More specifically, the present invention is a band-shaped molded article that shrinks upon absorption of water, and has a volume increase rate of 50% or more when absorbing water with a constant length having a width of 1 mm or more, which is made of carboxyl group-modified PVA,
Further, the dissolution loss is 25% or less, which is a band-shaped molded product.

There is an increasing number of fields that require a material that contracts quickly by contacting normal temperature water by sensing it.

Using the time required to reach a shrinkage rate of 30% in order to display the shrinkage rate required for practical use, the high-speed shrinkable band-shaped molded article referred to here is 10 seconds or less, preferably 7 seconds or less. Moreover, since it is premised on the contraction exhibiting rubber elasticity, it is desirable that the contraction stress in the state of being contracted by 30% is higher than the volume and economical efficiency of the band-shaped molded body. In the present invention, the maximum contraction rate in water at 20 ° C is 30% or more, the time required to reach the 30% contraction rate is 10 seconds or less, and the contraction stress in the original length state is 10 g or more per 10 mm width.
The time until the contraction stress of g is expressed is 10 seconds or less, the stress relaxation after that is 15% or less of the maximum contraction stress after 1 hour, and 20 ° C. in the condition of contracting 30% from the original length.
The performance that the shrinkage stress in water is more than 2g per 1mm width could be obtained.

However, even if these contraction speed and contraction stress are secured, excessive swelling must be suppressed in order to maintain the contracted state, particularly the contraction stress for a long time. Therefore, a strip-shaped compact cut into a length of about 10 mm in water with a bath ratio of 200 or more and 20 ° C is dispersed in a free state and left for 60 minutes, the solubility of the compact is 25% or less, preferably 15% or less. It is necessary to be.

It is necessary that the width of the band-shaped molded product should be designed so that when it is wound around a certain object and immersed in water, shrinkage stress is not partially concentrated and does not give rise to deformation such as dents. Therefore, the width of the strip-shaped compact (the length of the long side of the cross section perpendicular to the length direction of the strip-shaped compact) is preferably 1 mm or more, particularly 2 mm or more. If this width is less than 1 mm, it is no different from the conventional twisted fiber, and stress is concentrated to give marks such as marks and dents. When used in a diaper after use, the width is preferably 7 mm or less.

In addition, the shape of the cross section perpendicular to the length direction of the strip-shaped molded body needs to be flat, and the flatness (ratio of cross-sectional width (long side) to cross-sectional height) at that time is 5 to 250. The range is preferable in terms of handleability. It is widely known that, in a PVA-based molded product having a strip-like shape and showing strength for practical use, in order to improve the affinity for water, it is preferable to use PVA having various modified groups introduced as a raw material. ing. The preferred raw material used in the present invention is PVA in which a carboxyl group-containing monomer is copolymerized, that is, a carboxyl group-modified PVA, from the viewpoints of high-speed shrinkage in water and poor solubility, but itaconic acid-modified PVA is most preferred.

From the viewpoint of production and performance of the band-shaped molded product, the carboxyl group modification degree is preferably 0.5 mol% to 10 mol%, the average polymerization degree is 500 to 3000, and the saponification degree is 79 mol% to 99.9 mol%, but the modification degree is particularly 1.
5 mol% to 5 mol%, average degree of polymerization 1000 to 2000, degree of saponification 86
Those having a mol% to 99 mol% are preferable. The degree of carboxyl group modification (content mol%) in the modified polyvinyl alcohol referred to in the present invention means the molar ratio of the carboxyl group-containing monomer to the total amount of vinyl acetate and the carboxyl group-containing monomer used when synthesizing the modified polyvinyl alcohol. That is.

Specifically, an aqueous solution of 35% by weight to 70% by weight of denatured polyvinyl alcohol is used as the spinning dope, and is ejected in the form of a band from the nozzle into the air. Immediately after that, a cooling zone adjusted to a temperature of 20 ° C to 70 ° C and 80 ° C to After forming a band using a spinning cylinder consisting of a pre-drying zone of 170 ℃, the temperature 110 ℃ ~ 180
The strip-shaped molded body thus obtained is dried to a nearly dry state at a temperature of 190 ° C to 230 ° C, and the draw ratio is 4 times or more.
A 7-fold stretching heat treatment is performed. This way,
By using the water content, the temperature range and the draw ratio, a band-shaped molded product having the above-mentioned performance can be obtained. And these conditions are necessary in order to obtain the belt-shaped molded object which has the said performance. That is, a heated modified polyvinyl alcohol aqueous solution is discharged from a nozzle, a film is first formed on the surface of the discharge product in a cooling zone, and then a preliminary drying zone (the inlet side temperature is preferably less than 100 ° C) and a subsequent drying zone. In this method, the moisture inside the molded body is removed by evaporation to bring the molded body to an almost dry state. By using such a manufacturing method, the inside of the belt-shaped molded body becomes uniform and the subsequent stretching heat treatment becomes possible.

Generally, either a dry method or a wet method can be used to form a carboxyl group-modified PVA into a strip shape, but since this polymer has high hydrophilicity, it is economical to use the dry method, and further it is excellent in terms of performance. Things are obtained.
Using these carboxyl group-modified PVA, the concentration is 35% by weight to 60%.
A stock solution having an aqueous solution concentration of 50% by weight, preferably 50% by weight to 55% by weight, is used, and a molding method which is completely different from the usual dry production method of PVA-based fibers is adopted. Then, the formed original strip is further subjected to a stretching heat treatment. The stretching ratio after that is required to be 4 times or more in order to retain the internal strain in the strip-shaped molded body and to secure the shrinkage rate. Japanese Patent Publication Sho 53-10
Although a similar method is proposed in Japanese Patent No. 174, this proposal is aimed at obtaining a fiber soluble in low temperature water, and is characterized by a low temperature drawing heat treatment of 100 ° C to 180 ° C.
The object and conditions are completely different from those of the present invention.

In the production of PVA-based fibers, a method of partially blocking hydroxyl groups with an aldehyde or the like is generally used to impart water resistance. When strong hydrophilicity is required as in the present invention, it is necessary to extremely reduce the degree of acetalization, and in order to make it hardly soluble or insoluble, it is necessary to use dialdehyde which is premised on intermolecular crosslinking. Although effective, in the case of a carboxyl group-modified PVA band-shaped molded product having a strong hydrophilicity unlike the case of a normal PVA-based band-shaped molded product, it is impossible to react an aldehyde with hydrogen, which is not economically preferable.

On the other hand, in the case of a general PVA-based band-shaped molded product, it is possible to improve water resistance also by increasing the crystallinity of the constituent molecules of the band-shaped molded product by increasing the temperature during the stretching heat treatment. However, since this method involves crystallization, it is known that the shrinkage behavior at a low temperature is markedly lower than the effect of increasing the melting temperature. However, surprisingly, in the case of the modified PVA band-shaped molded product using the carboxyl group-modified PVA, the stretching heat treatment temperature was 20 ° C even at 190 ° C.
It was found that the water solubility at the same temperature was remarkably improved with almost no change in the rapid contraction property in water.

On the other hand, as shown in JP-B-53-10174, even if the fiber obtained from the carboxyl group-modified PVA, if the spinning method is an ordinary spinning method, the stretching heat treatment temperature is 190 ℃. With the above, the maximum draw ratio drops sharply to 3.5 times or less, making it extremely difficult to secure the required poor water solubility and shrinkage ratio.

As a result of earnest research, the present inventors have made it possible to adopt a maximum draw ratio of 4 times or more and a drawing heat treatment temperature of 190 ° C. or more by adopting a special spinning method, and as a result, it has a high-speed shrinkage performance. The present invention has led to the invention of a band-shaped molded article that is poorly soluble in water. More preferably, the present invention is 35% to 60% by weight of carboxyl group-modified polyvinyl alcohol.
Immediately after being discharged from the nozzle at a stock solution temperature of 95 ℃ to 160 ℃, the temperature of the solution was adjusted to 20 ℃ to 50 ℃.
A cooling zone of ~ 1.0m (residence time of the strip in this zone of about 0.05 seconds to 2 seconds) and a temperature of 80 ° C to 170 ° C, more preferably 9 ° C
After forming a band-shaped compact using a special spinning cylinder consisting of a pre-drying zone of 1 m to 8 m adjusted to 0 ° C to 140 ° C (residence time of the band in this zone of about 0.5 seconds to 20 seconds), 11
At a temperature of 0 ° C to 145 ° C, a stretching heat treatment condition necessary for imparting poor water solubility and high-speed shrinkability by drying to an almost dry state, that is, a stretching temperature of 190 ° C to 230 ° C which was thought to be impossible in the past This makes it possible to extremely easily carry out a heat treatment at a draw ratio of 4 to 7 times at a temperature of 0 ° C.
If the stretching temperature is less than 190 ° C, it is impossible to impart satisfactory poor water solubility, and if the stretching temperature exceeds 220 ° C, the fibers start to be colored, which is an obstacle to the appearance quality. More preferably, it is in the range of 195 ° C to 210 ° C.

The draw ratio is in the range of 4 to 7 times from the viewpoint of performance and productivity, but it is desirable to increase the draw ratio as the processing temperature becomes higher.

By using such a method, the condition that the volume increase rate when absorbing water with a constant length is 50% or more is satisfied, and this condition is extremely important for achieving high-speed shrinkage and high shrinkage ratio. is there. When the volume increase rate does not reach 50%, it is possible to satisfy the above condition of 50% or more by reducing the draw ratio or increasing the degree of carbosyl group modification.

As a method for producing a band-shaped molded body, which already has a band-shaped state discharged from a nozzle as in the method of the present invention, a method for obtaining a band-shaped molded body by simply drying, stretching and heat treating There is a method in which the film of (1) is first prepared, it is slit into several tens to several thousands, and the individual tapes obtained are stretched and heat-treated, but in the case of this method, the present invention is usually aimed. Such high speed shrinkage and high shrinkage cannot be obtained. Probably, it is because the molecular chains shift due to water swelling and easy movement. In addition,
The strip generally obtained by using the method of the present invention has a corner with a round cross section in a plane perpendicular to the lengthwise direction, while the tape obtained by slitting the film has a corner in a cutting relation. Are square, and the two can be distinguished in this respect.

As a method of using the band-shaped molded article of the present invention, in addition to the side tightening straps of the above-mentioned disposable diaper, a moisture detection sensor, a fishing tackle tightening thread, a tightening thread for grafting plants, a water stick for printing a binding thread for root winding, A grip tightening strap for a racket bat or the like may be considered. Next, a method for measuring physical property values specified in the present invention will be described.

Dissolution loss: After cutting the sample to a length of approximately 10 mm, JIS L-101
3 by the absolute dry state, performs sampling of 1 to 2 g, and the initial weight omega ₀ and accurately weighed it. Bath ratio 20 of 20
Disperse a precisely weighed sample in ion-exchanged water at ℃, leave it for 60 minutes, and filter using a filter paper of quantitative No. 5A-11 cmφ.
When the water droplets that have stopped dripping are completely dried and weighed precisely to give ω, the dissolution weight loss is Required by.

Shrinkage required time, maximum shrinkage rate ..............................................
Suspend the sample with the number as the initial load, immerse it in pure water at 20 ° C, and read the shrinkage rate every hour to make a chart. The time required to reach the required shrinkage is determined from this chart. In addition, the maximum shrinkage ratio in water immersion for 5 minutes or less is also obtained. However, the sample used here was used for the test after being made into a standard state according to JIS L-1013.

Shrinkage stress and stress relaxation in a fixed length state: The sample was held in a pulling tester with a gripping length of 10 cm vertically and immersed in pure water at 20 ° C to measure the maximum shrinkage stress, and then the sample was held as it was. In this state, the shrinkage stress after 1 hour is measured, and the decrease amount of the shrinkage stress after 1 hour with respect to the maximum shrinkage stress is obtained to determine the stress relaxation.

Shrinkage stress in pure water at 20 ° C in a state of contracting 30 from the original length …… The sample was attached to a constant-speed extension type tensile tester with a gripping interval of 10 cm in a state of being slackened by 30% from the original length, and then the fiber Is immersed in pure water at 20 ° C and the relationship between shrinkage stress and immersion time (seconds) is measured with the gripping interval unchanged. Then, the maximum shrinkage stress within 5 minutes of water immersion is determined. However, the sample used here was used for the test after being made into a standard state by the method according to JIS L-1013.

Volume increase rate in a fixed length: A sample in a standard state is fixed to a frame so that it is in a fixed length state, immersed in pure water at 20 ° C, taken out after 2 minutes, the width and thickness are measured, and the cross-sectional area is measured. Find the rate of increase of.

Examples (1) to (3) Comparative Examples (1) to (3) Itaconic acid 2 mol% modified PVA (average degree of polymerization 1800, saponification degree 97 mol%) and low saponification degree PVA (average degree of polymerization 1700, saponification degree) 98 mol%) was used to prepare a stock solution having a PVA aqueous solution concentration of 50%, and a strip-shaped body discharged from a die having a thickness of 0.1 mm and a width of 10 mm was dried under the following conditions.

All the dried strips had a water content of 0.1% or less.
The above-mentioned two kinds of strips thus obtained were heat-treated at various stretching furnace temperatures while the stretching ratio was 5.5 times, and the following characteristics were measured in water at 20 ° C. by a predetermined method. In addition, the cross-sectional shape of the obtained band-shaped molded product in the length direction is 3.5 m in width.
The corners were 1700 denier with a m of 0.04 mm and had roundness.

Examples (4) to (5) Comparative Examples (4) to (7) Using shrink materials having various shapes that shrink due to water absorption, the wrists are bound together with 30% slack, and then submerged in water. It was dipped to absorb water and contracted, and after 3 minutes, it was removed to compare the degree of depression of the binding portion.

In Comparative Examples (4) and (5), the water absorption shrinkage was sufficient, but as a result of the concentration of stress in the binding portion, a dent occurred. Further, in Comparative Examples (6) and (7), the shrinkage did not sufficiently occur, and the binding was not achieved.

Continuation of front page (56) References JP-A-60-72548 (JP, A) JP-B-53-10174 (JP, B2)

Claims (8)

(57) [Claims] 1. A band-shaped molded article having a flat cross section that shrinks by absorbing water,
The maximum shrinkage rate is 30% or more in water at 20 ° C, the time required to reach 30% shrinkage rate is 10 seconds or less, and the shrinkage stress in the original length state is 10 g or more per 1 mm width, until the shrinkage stress of 10 g appears. Is less than 10 seconds, stress relaxation is less than 15% of the maximum shrinkage force after 1 hour, and is also less than 30% of the original length.
Shrinkage stress in water at 20 ° C in a shrunk state is 2 g or more per 1 mm width, and dissolution loss when dispersed in water at 20 ° C is 25
High-speed shrinkable band-shaped molded product that is less soluble in water at less than 50%. 2. The band-shaped molded product according to claim 1, which has a width of 1 mm or more. 3. The strip-shaped molded product according to claim 1, wherein the polymer constituting the molded product is a modified polyvinyl alcohol containing 0.5 mol% to 10 mol% of a carboxyl group. 4. The band-shaped molded article according to claim 3, wherein the modified polyvinyl alcohol is modified with itaconic acid. 5. A band-shaped molded product which shrinks upon absorption of water, and the following conditions: made of carboxyl group-modified PVA, having a width of 1 mm or more, a volume increase rate of 50% or more when absorbing water at a constant length, and a dissolution weight loss. Of 25% or less, a high-speed shrinkable band-shaped molded product. 6. A spinning process comprising an aqueous solution containing 35% by weight to 70% by weight of denatured polyvinyl alcohol as a spinning stock solution, ejected in a band form from a nozzle into the air, and immediately thereafter, a cooling zone adjusted to a temperature of 20 ° C. to 70 ° C. After forming a band using a cylinder, it is dried at a temperature of 110 ℃ ~ 180 ℃ to almost dry state,
A method for producing a band-shaped molded product, which comprises subjecting the band-shaped molded product thus obtained to a stretching heat treatment at a temperature of 190 ° C to 230 ° C at a draw ratio of 4 to 7 times. 7. A modified polyvinyl alcohol containing 0.5 mol% to 10 mol% of carboxyl groups and having an average degree of polymerization of 500 to 300.
The production method according to claim 6, wherein the saponification degree is 0 to 77% to 99.9%. 8. The method according to claim 7, wherein the modified polyvinyl alcohol is modified with itaconic acid.