JPS6328912A - Production of highly water absorbing fiber - Google Patents

Abstract

PURPOSE:To obtain the titled fibers, capable of losing the strength in a water absorption state, readily disposable and useful as sanitary products, by spinning an aqueous solution containing a polycarboxylic acid having a specific content of carboxyl groups and weight-average polymerization degree and polyhydric alcohol in a high concentration and heat-treating the resultant fibers. CONSTITUTION:An aqueous solution containing a polycarboxylic acid, e.g. polyacrylic acid, etc., having at least 7 mequiv./g carboxyl groups and containing 25-90% thereof in the form of an alkali metal salt and/or monovalent amine salt and 1,000-30,000 average polymerization degree and a polyhydric alcohol, e.g. glycerol, etc., in an amount of 0.1-10wt% based on the carboxylic acid as components in a concentration as high as >=35wt% as a spinning solution is spun by a dry spinning method while applying at least 2 times draft and the resultant fibers are heat-treated to afford the aimed highly water absorbing fibers.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to the production of highly absorbent fibers, such as synthetic polymer fibers suitable for use in sanitary products, disposable diapers, and other products that require high water absorbency and water retention. This is related to the method.

[Conventional technology]

In recent years, the development of polymeric materials used for applications that take advantage of their water absorption and water retention properties has become active.

These have a chemical structure in which a small amount of cross-linking or a hydrophobic, yet crystalline segment is introduced into a water-soluble polymer, particularly a polyelectrolyte, to make it water-insoluble.

Among these, for applications that require high water absorption and fast water absorption speed, such as sanitary napkins and disposable diapers, lightly cross-linked sodium polyacrylate and partially hydrolyzed acrylonitrile polymers are used. Polycarboxylic acid salts are commonly used, and most of them are supplied as powders or granules.

For example, JP-A No. 55-84304 proposes a method in which a small amount of polyhydric alcohol is coexisting as a crosslinking agent, a partial alkali metal salt is polymerized in an acrylic solution in an aqueous solution, the resulting stubble is divided into pieces, and then heated and dried. has been done.

10,000 Attempts are being made to make fibers into fibers in hopes of increasing water absorption speed due to their large specific surface area and diversifying their usage.

An attempt at fiberization was made by the present inventors in JP-A-49-752.
As shown in No. 6, the mainstream method is to use acrylic fibers as a starting material and introduce calzexyl groups into this by a slight crosslinking structure and a hydrolysis reaction of the nitrile groups contained therein.

Compared to these methods of chemically modifying fibers, the method of directly fiberizing polycardic acid, typified by polyacrylic acid, into superabsorbent fibers is an extremely rational process, and has already been reported in JP-A-49-70741. There is a description that a water-soluble We of a calzexyl polymer electrolyte and a cross-linking agent reactive with the carxyl group such as a polyhydric alcohol is extruded into a bath such as acetone to form fibers and then subjected to dry heat treatment, suggesting the possibility of this. .

[Problem that the invention seeks to solve]

However, for direct fiberization of polycarboxylate, 1) To obtain high water absorption, it is necessary to use a spinning dope containing a water-soluble polycarboxylate and a crosslinking agent to make it water-insoluble. The presence of a crosslinking agent may cause gelation of the spinning dope or cause deterioration of spinnability and stretchability.

2) Among polycarboxylate salts, alkali metal salts have hidden and strong water absorption properties, and are effective dehydrating agents (coagulants) for this purpose.
Furthermore, even if it is slightly dehydrated (or gelled), it does not easily gel (or solidify) due to the extremely strong dissolving power of the residual water, so it has been extremely difficult to spin it not only by the wet method but also by the dry method.

3) Polycarboxylic acid has strong hydrogen bonds and cannot be hot stretched.

Fibers obtained without drawing do not have fiber strength and are glass-like brittle when dried, and these properties are extremely unfavorable in handling as fibers.

There are fundamental problems such as these, and the current situation is that it has not yet been industrialized.

In view of the current situation, the present inventor is currently conducting extensive research into the production of water-absorbing fibers using polycarboxylate as a raw material.
Fibers can be efficiently produced by discharging a heated, highly concentrated aqueous solution of polycarboxylate into hot air, and a spinning stock solution that is stable for a long period of time can be obtained using a system that uses polycarboxylate and polyhydric alcohol as raw materials. It was also discovered that the previously fragile physical properties of fibers can be significantly improved by spinning with a draft above a certain level, and as a result of further research into the details, the present invention was arrived at.

[Means for solving problems]

That is, the present invention provides (1) a weight-average polymerization degree of 1000 to 1,000, which has at least 7 meq/g of carxyl groups, and 25 to 90% of which is an alkali metal and/or monovalent amine salt;
30,000 polycarboxylic acid and (2) a highly concentrated aqueous solution of 35 wt % or more containing 01 to 10 wt % polyhydric alcohol and the total substantial component of the polycarboxylic acid as the spinning stock solution, and at least twice as much by dry spinning method. There is a method for producing superabsorbent fibers, which is characterized by spinning the fibers in a draft and heat-treating them.

The present invention will be specifically explained in detail below.

In the method of the present invention, the main raw material polycarboxylic acids include monovinyl monomers having a ruzexyl group, such as acrylic acid, methacrylic acid, crotonic acid, fumaric acid, and maleic anhydride; alkali metal salts of these vinyl monomers; Homopolymers of monomers selected from amine salts, or copolymers of these monomers with acrylonitrile, styrene, acrylic, amide, methacrylamide, etc.; also acrylamide, methacrylamide, acrylonitrile, acrylic There is polycarzenic acid obtained by hydrolyzing a polymer obtained by polymerizing at least one monomer selected from acid esters and methacrylic esters as a main component in the presence of an alkali.

These polycarboxylic acids are less than 7 meq/
It has a calzexyl group of more than g and the average degree of polymerization is 1000~
Must be 30000. Sarani, So's 25-95
% of the calzexyl group, a monovalent alkali metal such as lithium, potassium, and sodium, or a monovalent amine such as ammonia, monoethanolamine, jetanolamine, and triethanolamine.

That is, when the other monomer is a polymer without carxyl groups and has a carxyl group content of 7 meq/g or less, a high degree of water absorption cannot be obtained. Also, if the average degree of polymerization is less than 1000, the fibers will have low strength, low elongation, and there will be problems such as a large amount of components eluted from the fibers when absorbing water. However, even if the concentration is lowered and the viscosity is adjusted to a range suitable for spinning, spinning becomes difficult because the water content increases.

A preferred example of polycarboxylic acid that satisfies the above conditions is polyacrylic acid with a polymerization degree of 2,000 to 10,000.
Examples include those in which 0 to 85 mole calzexyl groups form a salt with at least one of potassium ion, sodium ion, monoethanolamine, jetanolamine, and triethanolamine.

Polyhydric alcohols that can be used as crosslinking agents for these partially neutralized salts of polycarboxylic acids include those having two or more hydroxyl groups, such as ethylene glycol, diethylene glycol, triethylene glycol, ethylene glycol, chrycerin, and propylene glycol. , jetanolamine, triethanolamine, polyoxypropylene, sorbitan, D-sorbitol, crucose,
Examples include mannitol, pentaerythritol, mannitan, sucrose, glucose, and low polymerization degree PVA.

These polyhydric narcols have a 0.1
~lQwt% is used. Q: If it is less than 1wt%, the fiber cannot be made water-insoluble even if the heat treatment conditions are strengthened.
On the other hand, if it exceeds 1Qwt%, an appropriate degree of crosslinking can be achieved under weak heat treatment conditions, but excessive polyhydric alcohol acts as a plasticizer and significantly impairs the fiber properties, which is not preferable.

A more preferable amount of polyhydric alcohol is 0.2 to 2 wt%.

Polycardiic acid and polyhydric alcohol that satisfy the above conditions are made into a highly concentrated aqueous solution, and this is spun by a dry spinning method.

The polycarboxylic acid and polyhydric alcohol are dissolved together with water using a dissolving machine such as a kneader to obtain a spinning stock solution. At this time, if unneutralized polycarboxylic acid is used as a raw material, in this dissolution step, a predetermined amount of alkali metal hydroxide or ethanolamine is added and mixed with water and polyhydric alcohol to directly achieve the desired neutralization. A spinning dope of polycarboxylic acid salt can be obtained. The spinning dope thus obtained is kept warm in a dope tank, and is constantly guided to the nozzle section by a syringe pump through a piping system that is also kept warm.

Alternatively, the raw material polycarboxylic acid powder or pellets may be impregnated with a predetermined proportion of water and polyhydric alcohol, which is then continuously fed to the extruder and melted in the heating section (all of the molten material is It is supplied to the nozzle section and spun.

In principle, it is possible to use a melt spinning apparatus for this method.

This spinning stock solution is required to have a higher concentration and temperature than normal dry spinning, for example, when using polyvinyl alcohol using water as a solvent. In other words, water is a solvent that shows extremely strong affinity for polycarboxylate salts, and at low concentrations, it can cause problems during the fiber formation process.
Even a small amount of moisture prior to drying-gelation can easily break the spun fibers due to its strong dissolving power. Therefore, it is important to dry and solidify quickly after spinning using a stock solution adjusted to high concentration and high temperature.

Therefore, the concentration of the stock solution is 35 wt% or more, and the temperature is 8.
It is desirable that the temperature is 0°C or higher, more preferably 4Qw
The temperature ranges from t to 55wt and from 90 to 140°C.

゛The spinning dope that satisfies these conditions is then discharged from a nozzle into hot air and becomes fibrous, but if the draft (ratio of winding speed to discharge linear velocity) is small, the fibers are so brittle that they cannot be wound. The power increases as the draft increases. The required draft is at least 2x dust, preferably 10-50x.

There are no particular restrictions on the fineness and cross-sectional shape of the resulting fibers.

Finally, the fibers are heat treated to impart high water absorption properties. The water absorption ability depends on the content of carzexyl group, its degree of neutralization, the amount of polyhydric alcohol added, and the heat treatment conditions (temperature and time).The heat treatment temperature ranges from 150℃ to 250℃, and the heat treatment time ranges from a few seconds to several tens of seconds. Water absorption as high as 100 to 1000 times can be obtained in the range of minutes.

The structure, operation, and effects of the present invention will be clarified by Examples and Comparative Examples below. In addition, W5 in the examples means parts by weight.

Practical row 1 1 part for 3 parts of polyacrylic acid (manufactured by Toagosei Kagaku Co., Ltd., trade name Aron A-10H) with an average degree of polymerization s, ooo
28 parts of granular caustic soda, 0.015 parts of glycerin, and 5 parts of water were put into a Nigu, and the mixture was uniformly dissolved, transferred to a sealed tank, and left at 100'6 overnight for degassing.

The spinning stock solution prepared in this way was quantitatively pumped out by a gear pump and allowed to leak, and then spun into a dry air stream at 120°C through a 20-hole nozzle with a hole diameter of 200 microns, and while drying, a 15-fold or higher raft was applied to wind it up. Ta.

Next, this was passed through an oven at 230°C for a residence time of 13 seconds to obtain 830g/g of pure water at 0.27N.
-A water-absorbing fiber having a water absorption capacity of 78 g/g for Na0L artificial urine was obtained. This fiber is 20℃50%R
It had fiber properties that could withstand the necessary handling as a fiber, such as knitting, blending, and spinning in a humidity-controlled room.

In this example, the water absorption capacity of the fibers obtained when the heat treatment time (oven residence time) was 30.20 and 15 seconds, respectively, was 42.85.520 g/g, and 1
When the time was set to 0 seconds, the fibers did not exhibit water absorbency and were water soluble. In addition, when the heat treatment time was set to 13 seconds at 240°C, the water absorption was 164 g/g, which was also 22
When the temperature was 0°C, the fibers showed no water absorption and were water-soluble.

comparison column 1 (1) Draft is multiplied by 15 times.

(2) Use a 20-hole nozzle with a hole diameter of 60 microns to increase the draft by 18 times.

All the fibers obtained under the same conditions as in Example 1 had no strength and could not be handled as fibers.

Example 2 A complete aqueous solution was prepared consisting of 100 parts of polyacrylic acid (same as in Example 1) with a degree of polymerization of 5,000, triethanolamine equivalent to 5 volumes per polyacrylic acid, and 120 parts of water. After leaving it in a pressure vessel at 105°C for a day and night to degas it, it was spun using a 50-hole nozzle with a hole diameter of 120 microns in a dry air stream at 110°C while applying a draft of 25 times, and immediately passed through a pair of Nelnon rolls. Heat treatment was performed at 230° C. for 11 seconds in a heat treatment zone.

The thus obtained fibers had physical properties that allowed the fibers to be rolled and knitted in a humidity-controlled room, and exhibited full water absorbency of absorbing pure water at s 60 g/g at room temperature.

〔Effect of the invention〕

According to the method of the present invention, a spinning dope can be obtained that can maintain good spinnability and stretchability for a long period of time without gelation when kept at 100°C or higher, and the obtained fiber can be used in the knitting and weaving process in a dry state. It has durable fiber physical properties and a high degree of water absorption, while in a water-absorbing state it loses strength and can be easily disposed of as an aqueous dispersion. In addition, since the target product can be obtained as a filament, it can be directly used in the knitting and weaving process without a spinning process, and it can also be cut into short fibers to form cotton lumps, non-woven fabrics, etc. It is also possible to mix it with other fiber materials depending on the situation.

As described above, according to the present invention, it is possible to obtain a material with high water absorbency and water absorption rate as a fibrous material, so the field of application is significantly expanded compared to conventional powder or granular materials, and it is extremely useful in industry. Beneficial.

Claims (1)

[Claims] It has at least 7 meq/g of carboxyl groups, 25 to 90% of which are alkali metal salts and/or monovalent amine salts, and a weight average degree of polymerization of 1000 to 300.
00 polycarboxylic acid and 0.1 to 0.1 to the carboxylic acid
3 whose substantial component is 10 wt% polyhydric alcohol
A method for producing superabsorbent fibers, which comprises using a highly concentrated aqueous solution of 5 wt % or more as a spinning stock solution, spinning the fiber by applying a draft of at least twice as much by a dry spinning method, and heat-treating it.