JP2942597B2 - Method for producing moisture-absorptive split fibers - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing hygroscopic split fibers having excellent hygroscopic and hygroscopic properties.

2. Description of the Related Art Split fibers, which have the property of absorbing and releasing moisture (absorbing and releasing moisture) according to environmental humidity, can be applied to applications such as clothing, sanitary products, agricultural and horticultural materials, interior materials, dehydrating agents, sealing materials, etc. Be expected.

JP-A-63-219618 discloses a polycarboxylic acid (A) having a carboxyl group of at least 3 meq./g and 5 to 75% of which is an alkali metal salt or an amine salt, and a degree of polymerization of 500 to 3000. Of polyvinyl alcohol (B) and polyhydric alcohol (C) in an amount of 0.1 to 5% by weight based on (A), and (A) and (B) are not microscopically observed immediately before or at the nozzle. A method of producing a water-absorbent fiber by thoroughly mixing, spinning by a dry method, and heat-treating is described.

JP-A-1-103643 discloses salts of a carboxyl group-containing polymer (I), polyvinyl alcohol (II), polyhydric alcohol (III) and polyhydric epoxy compound (IV).
A film-like or fibrous water-absorbing composition obtained by subjecting a mixture of components to a molding heat treatment is shown.

Although not for the purpose of absorbing and releasing moisture, JP-A-57-125240 discloses a water-soluble film composed of a uniform mixture of water-soluble polyvinyl alcohol and polyacrylic acid, and this water-soluble film is It is said to be useful for packaging of dry detergents and similar water-soluble products.

In addition, the present applicant has filed Japanese Patent Application Nos.
No.-80354, filed an application relating to the present invention.

Problems to be Solved by the Invention In the method described in JP-A-63-219618 described above, (A) and (B) must be used in order to smoothly stretch and obtain desired water absorption and elongation. A method of spinning a completely mixed spinning solution is employed. However, such special methods are less than desirable from an industrial point of view. Further, in the invention of this publication, splitting of the obtained filament is not considered.

The film-like or fibrous water-absorbing composition described in Japanese Patent Application No. 1-103643 secures toughness with polyvinyl alcohol (II) based on a salt (I) of a carboxyl group-containing polymer, and has a high flexibility. The flexibility is ensured by the polyhydric alcohol (III), and crosslinking is performed by the polyvalent epoxy compound (IV) to control the water absorption capacity. However, it is difficult for this film-like or fibrous water-absorbing composition to have all the properties of moisture absorption / desorption, mechanical strength, water resistance and dimensional stability in a well-balanced manner, and its application is limited. Sometimes. In addition, since a small amount of the polyvalent epoxy compound (IV) is added and the crosslinking is attempted by heat treatment, there is also a problem that it is difficult to stably produce a product having a constant crosslinking degree. Further, in the invention of this publication, splitting of the obtained film or fiber is not considered.

The water-soluble film described in JP-A-57-125240,
Since the purpose is to provide a water-soluble film suitable for uses such as detergent packaging, it is not suitable as a moisture-absorbing and releasing molded article.

Under such a background, the present invention is to obtain a moisture-absorbing and stretched stretched product having industrial productivity and having excellent moisture-absorbing and releasing properties, mechanical strength, water resistance and dimensional stability. It is intended to provide a method that can be used.

Means for Solving the Problems The method for producing a moisture-absorbing and desorbing split fiber according to the present invention is characterized in that the copolymerization ratio of the polyvinyl alcohol-based resin (A) and polyacrylic acid or sodium acrylate is 5 mol%.
Less than 90:10 by weight of a polyacrylic acid-based polymer (B) comprising an acrylic acid-sodium acrylate copolymer
Step 1: Forming into a molded article using a mixed aqueous solution containing the mixture in a ratio of about 20:80 as a stock solution, Step 2 of stretching the molded article, Step 4 of splitting the obtained stretched molded article, Step 1 The process is performed in the order of → step 2 → step 4.

In this case, a free carboxyl group contained in the polyacrylic acid-based polymer (B) in the obtained stretch-formed product is obtained between the above steps 2 and 4 or after the above step 4. Step 3 for neutralizing to a degree of neutralization of 30 mol% or more is provided, and these steps are referred to as Step 1 → Step 2 → Step 3 → Step 4
Or the order of Step 1 → Step 2 → Step 4 → Step 3 is particularly desirable.

 Hereinafter, the present invention will be described in detail.

<Step 1 (Molding Step)> As the polyvinyl alcohol-based resin (A), various degrees of polymerization (for example, 300 or more) and degrees of saponification (for example, 70 to 100) are provided as long as they have water solubility or water lubricity.
Mol%) of polyvinyl alcohol. In this case, a higher degree of polymerization is desirable for the purpose of the present invention, and a degree of polymerization of 3100 or more, particularly 3500 or more, especially 4000 or more is suitable.

In addition to polyvinyl alcohol, monomers copolymerizable with vinyl acetate (α-olefins, ethylenically unsaturated carboxylic acids, salts, alkyl esters, anhydrides, nitriles, amides, ethylenically unsaturated sulfonic acids, vinyl ethers,
Use of “copolymerized” polyvinyl alcohol copolymerized with vinyl esters other than vinyl acetate, vinyl chloride, etc.), and “post-modified” polyvinyl alcohol obtained by acylating or urethane-forming polyvinyl alcohol or copolymerized modified polyvinyl alcohol. Can be.

As the polyacrylic acid-based polymer (B), an acrylic acid-sodium acrylate copolymer having a copolymerization ratio of polyacrylic acid or sodium acrylate of less than 5 mol% (especially less than 3 mol%) is used. .

The mixing ratio of the polyvinyl alcohol-based resin (A) and the polyacrylic acid-based polymer (B) is 90:10 to 20:80 by weight.
It is particularly preferable to select from the range of 80:20 to 30:70. An excessive amount of the former (A) and an excessive amount of the latter (B) cause insufficient moisture absorption and desorption, and an insufficient amount of the former (A) and excessive amount of the latter (B) cause insufficient mechanical strength and dimensional stability.

By using a mixed aqueous solution containing the polyvinyl alcohol-based resin (A) and the polyacrylic acid-based polymer (B) at the above ratio as a stock solution, a sheet (including a film) or a linear shaped product is produced. You.

As a molding method, an extrusion method or a casting method is usually employed. That is, a solvent, a plasticizer (polyhydric alcohol, etc.), a crosslinking agent (polyhydric epoxy compound, dialdehyde, methylolmelamine, etc.), gelation, if necessary, are added to the mixed aqueous solution of the polymer components (A) and (B). After blending agents (boric acid, boric acid, metal salts, etc.), fillers, coloring agents, stabilizers, functional chemicals, etc., discharge them from the die or nozzle into the air or into a coagulation bath, or onto the substrate Cast and dry if necessary. Typically, after mixing the aqueous solution of (A) and the aqueous solution of (B), further blending other additives as necessary, and then discharging from a die or nozzle or casting on a substrate ,dry.

<Step 2 (Stretching Step)> In the present invention, the obtained molded product is subjected to stretching. In this case, moisture of about the natural moisture absorption rate may remain.

When the molded product is in the form of a sheet, the stretch ratio is at least 2 times (particularly 3 times or more, especially 4 times) at least in the uniaxial direction (that is, in the uniaxial or biaxial direction, and more preferably in the multiaxial direction). In the above, when the molded product is linear, it is set to be at least twice (especially at least three times) in one axial direction. When the draw ratio is small, the mechanical strength, water resistance, and dimensional stability are insufficient, and the intended purpose cannot be achieved.

The stretching temperature in the above stretching operation is suitably about 100 to 300 ° C, especially 140 to 250 ° C. Before the stretching operation, heat treatment can be performed to the extent that the stretching operation is not impaired, and heat setting can be performed after the stretching operation.

The hot water dissolution rate of the stretch molded product is 30% by weight or less,
It is preferably at most 10% by weight, especially at most 10% by weight.

<Step 4 (Split Step)> Step 4 is a step of splitting the stretch-formed product obtained above.

Splitting of the stretch-formed product is performed by various methods including a method using a friction machine, a method using a file, a method using a beater, and a method using compressed air.

<Step 3 (Neutralization Step)> Step 3 is a step of neutralizing a free carboxyl machine contained in the polyacrylic acid-based polymer (B) in the stretch-formed product obtained as described above. It is.

Neutralization can be achieved by bringing the above stretched product into contact with a neutralizing agent in which an aqueous solution of sodium hydroxide, potassium hydroxide, sodium carbonate, ethanolamine or the like has a concentration of about 0.01 to 1N. Temperature conditions for neutralization should be between room temperature and
Often around 80 ° C. At the time of neutralization, it is preferable to keep the stretched product in a tensioned state. Heat treatment can be performed after the neutralization treatment.

By this neutralization operation, the carboxyl group contained in the polymer (B) in the stretch molded product is neutralized to a high degree of neutralization (particularly 30 mol% or more). If the degree of neutralization is insufficient, it has a disadvantageous effect on hygroscopicity.

This step 3 is not an essential step, but it is a step that is definitely required to improve water absorption.

<Crosslinking Step> In the present invention, the stretch molded product obtained above can be subjected to a crosslinking treatment. The crosslinking treatment is performed in the neutralization step 3 described above.
Before or after or simultaneously with the neutralization step 3, or before or after the splitting step 4, the stretched molded product is brought into contact with a crosslinking agent solution by dipping, spraying, or the like, and further, if necessary, heat-treated. it can. By such a cross-linking treatment, the mechanical properties such as the tensile strength of the object are further improved, and the object having higher practicality is obtained.

As the cross-linking agent, any of those known as a cross-linking agent for polyvinyl alcohol or polyacrylic acid can be used, for example, polyepoxy compounds, dialdehydes, polyisocyanates, methylol melamine, methylol urea, metal salts And metal chelates.

The crosslinking treatment can be performed by irradiating an active energy ray such as an electron beam or an ultraviolet ray without using a crosslinking agent.

<Step Operation> Each of the above steps is performed in the order of step 1 → step 2 → step 4, step 1 → step 2 → step 3 → step 4, or step 1 → step 2 → step 4 → step 3.

As described above, the step 3 is not an essential step, but it is preferable to provide the step 3. When the process 3 is provided,
The order of Step 3 and Step 4 is arbitrary, but when the thickness of the molded product is relatively large or the thickness is relatively large, it is more advantageous to carry out Step 3 after Step 4.

<Uses> The moisture-absorbing and desorbing split fibers obtained by the method of the present invention, alone or in combination with other materials, are used for textile products (yarns, linear materials, woven fabrics, non-woven fabrics, knitted fabrics, etc.), sanitary products, agricultural Suitable for horticultural materials, interior materials (wall materials, etc.), dewatering / dehumidifying materials, water / moisture retaining materials, civil engineering materials, air conditioning materials, heat exchanger elements, evaporating plates, and other various applications. Can be.

Function and Effect of the Invention The method of the present invention provides a polyvinyl alcohol resin (A)
And a polyacrylic acid-based polymer (B) to form a molded article, then stretch the molded article, split the stretched molded article, or before or after splitting the polymer ( It neutralizes the free carboxyl groups contained in B).

According to the present invention, even when the polymer concentration in the stock solution for molding is considerably increased, or when a polyvinyl alcohol-based resin (A) having a high degree of polymerization is used, the stability of the stock solution for molding is good. In addition, smooth molding can be performed.

Since the molded product is composed of a blend of two types of polymers (A) and (B) and the polyacrylic acid-based polymer (B) is not a crystalline polymer, the stretched molded product that has undergone the stretching step has a low degree of crystallinity. A high region and a low region are formed. Therefore, a smooth splitting in the splitting step becomes possible, and a split fiber having a small thickness can be easily obtained.

Since each step of drawing and splitting is provided, and preferably a further neutralization step is provided, the moisture-absorbing and desorbing split fiber obtained by the method of the present invention has excellent moisture-absorbing and desorbing properties (hygroscopic and Water resistance and dimensional stability.

EXAMPLES Example 1 As an example of a polyvinyl alcohol-based resin (A), polyvinyl alcohol having a degree of polymerization of 4000 and a saponification degree of 99.9 mol% was used and dissolved in water to prepare a 5% by weight aqueous solution of polyvinyl alcohol. did.

As an example of the polyacrylic acid-based polymer (B), polyacrylic acid having a polymerization degree of 5,000 was used, and dissolved in water to prepare a 5% by weight aqueous solution of polyacrylic acid.

5% by weight aqueous solution of polyvinyl alcohol 70
Parts by weight and 30 parts by weight of the above polyacrylic acid aqueous solution having a concentration of 5% by weight were mixed to form a uniform solution, cast on a polyester sheet having a thickness of 120 μm as a substrate, dried with hot air, and dried with a hot air of 40 μm in thickness. A sheet-like molded product was obtained.

Next, using a tenter type stretching machine, the sheet-like molded product was stretched 10 times in the machine direction at a stretching temperature of 180 ° C.
Heat fixation was performed at 1 ° C. for 1 minute.

The obtained sheet-shaped stretched product was supplied to a friction machine, and subjected to a frictional force for 1 minute to split the fiber. The average thickness of the obtained split fibers was 21 μm.

Then, the split fiber is neutralized by immersing it under tension in a 0.2N aqueous sodium hydroxide solution at a temperature of 50 ° C. for 20 seconds, washed with water, dried, and then heat-treated at a temperature of 200 ° C. for 10 seconds. did.

As a result, the desired moisture-absorbing / releasing split fiber was obtained. The degree of neutralization of carboxyl groups in the polyacrylic acid-based polymer (B) in this split fiber is about 50 mol%
Met.

Example 2 Example 1 was repeated except that 50 parts by weight of a 5% by weight aqueous solution of polyvinyl alcohol and 50 parts by weight of an aqueous solution of polyacrylic acid having a concentration of 5% by weight were mixed to form a uniform solution. Repeated. The average thickness of the obtained split fibers was 15 μm. The degree of neutralization of the carboxyl groups in the polyacrylic acid-based polymer (B) in this split fiber was about 50 mol%.

Example 3 The split fiber obtained in Example 1 was further subjected to a temperature of 50 ° C.
It was introduced into an aqueous solution of methylolated melamine having a concentration of 2% by weight (Sumimar M-30W manufactured by Sumitomo Chemical Co., Ltd.), allowed to run under tension, and then heat-treated at 220 ° C. to perform a crosslinking operation.

Examples 4 to 6 As a polyvinyl alcohol-based resin (A), a polymerization degree of 56 was used.
00 (Example 4), degree of polymerization 3500 (Example 5), degree of polymerization 1800
Example 1 was repeated except that the polyvinyl alcohol of (Example 6) was used to obtain split fibers.

Example 7 As an example of the polyvinyl alcohol-based resin (A), polyvinyl alcohol having a degree of polymerization of 4,000 and a degree of saponification of 99.9 mol% was used and dissolved in water to prepare a 12% by weight aqueous solution of polyvinyl alcohol.

Further, as an example of the polyacrylic acid-based polymer (B), polyacrylic acid having a polymerization degree of 5,000 was used and dissolved in water to prepare a 12% by weight aqueous solution of polyacrylic acid.

The above-mentioned 12% by weight aqueous solution of polyvinyl alcohol 70
30 parts by weight of the above polyacrylic acid aqueous solution having a concentration of 12% by weight
Parts by weight to form a uniform solution, the solution was supplied to a container equipped with a piston and a nozzle, discharged from the nozzle in the form of a strand, and then introduced into an acetone bath at a temperature of 20 ° C. for coagulation. Naturally dried. The thickness of the obtained strand was 115 denier.

Next, using a roll-type stretching machine,
After stretching 6 times in the length direction at a stretching temperature of 180 ° C., and subsequently stretching twice in the length direction at a stretching temperature of 220 ° C.,
Heat set for 1 minute.

Then, the stretched strand was neutralized by running it under tension in a 0.2N aqueous sodium hydroxide solution at a temperature of 50 ° C., washed with water, dried, and then heat-treated at a temperature of 220 ° C. under tension.

The stretched strand after the neutralization was supplied to a friction machine, and the fiber was split by applying a friction force for 1 minute. The average thickness of the obtained split fibers was 12 μm.

As a result, the desired moisture-absorbing / releasing split fiber was obtained. The degree of neutralization of the carboxyl group in the polymer (B) in this split fiber was about 50 mol%.

Comparative Example 1 A film of polyvinyl alcohol having a polymerization degree of 4000 and a saponification degree of 99.9 mol% and a thickness of 40 μm was drawn and split under the same conditions as in Example 1. The average thickness of the obtained split fibers was 32 μm.

Comparative Example 2 A 5% by weight aqueous solution of polyvinyl alcohol of Example 1
70 parts by weight of the polyacrylic acid of Example 1 was partially neutralized in advance with an aqueous sodium hydroxide solution to a degree of neutralization of 50 mol%, and then an aqueous solution of an acrylic acid-sodium acrylate copolymer adjusted to a concentration of 5% by weight 30 parts by weight were mixed to form a uniform solution, and then molded, stretched and heat-set under the same conditions as in Example 1 to obtain a stretched film.

<Characteristics Evaluation> For the split fibers, films or shreds obtained in Examples 1 to 7 and Comparative Examples 1 and 2 (in the case of split fibers and shreds, a multifilament system of 1560 d was prepared, and ), Moisture absorption / release properties, water resistance (insoluble ratio of hot water), and dimensional stability were measured by the following methods.

The moisture absorption and desorption properties were measured using a table-top constant temperature and humidity device manufactured by Nagano Scientific Machinery Co., Ltd. at 40 ° C, 90
It was brought to a high humidity condition of% RH, and the value after 24 hours was defined as the equilibrium moisture absorption rate, and the hygroscopicity was judged. In addition, the sample used for the measurement of hygroscopicity was brought to low humidity conditions of 40 ° C and 40% RH,
The value after the time was regarded as the equilibrium moisture absorption, and the moisture release was determined.

The hot water insolubility rate was determined by precisely weighing a sample in an absolutely dry weight of 1.0 ± 0.1 g (a) and keeping it at 20 ° C. and 65% RH for 48 hours or more.
Into a beaker containing 500 ml of water at 50 ° C and at 50 rpm
After stirring for 60 minutes, it was taken out and the weight (b) after absolute drying was measured and calculated by the following equation.

Hot water insolubility (%) = 100b / a For dimensional stability, sample fiber (or film)
After being kept at 20 ° C and 65% RH for 48 hours or more, it is cut into a length of 100 mm (or a size of 50 mm x 50 mm). After stirring for 60 minutes under the conditions described above, the water was taken out and removed from the surface with a filter paper, and the change in length (%) (or change in area (%)) was determined.

 The results are shown in Table 1.

From the results in Table 1, it can be seen that in Examples, even when the degree of polymerization of polyvinyl alcohol is high or the concentration of the stock solution for molding is high, a stock solution for molding with excellent stability is obtained, and the resulting split is obtained. It can be seen that the fibers have a good balance of moisture absorption / release properties, water resistance and dimensional stability.

Example 8 In Example 1, only the neutralization step was omitted.

In this case, the insolubility in hot water and the dimensional stability are the same as in Example 1, the data on the hygroscopicity is about 50% as compared with Example 1, and the data on the moisture release is about 7% as compared with Example 1. About 30% of the data was obtained. However, the split fiber obtained in Example 8 also has a practically sufficient use.

Example 9 In Example 2, only the neutralization step was omitted.

In this case, the insolubility in hot water and the dimensional stability are equivalent to those in Example 2, the data on the hygroscopicity is about 50% as compared with Example 2, and the data on the moisture release is 7% as compared with Example 2. About 30% of the data was obtained. However, the split fiber obtained in Example 9 also has practically sufficient use.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) D01F ^6/ 14-6/ ¹⁶ D01F ⁶ /34-6/36 D01D 5/42

Claims (4)

(57) [Claims] 1. A polyacrylic acid-based polymer (B) comprising an acrylic acid-sodium acrylate copolymer having a copolymerization ratio of a polyvinyl alcohol-based resin (A) and polyacrylic acid or sodium acrylate of less than 5 mol%. ) Is used as a stock solution for molding, using a mixed aqueous solution containing the mixed solution at a weight ratio of 90:10 to 20:80, a step 1 of forming a molded article, a step 2 of stretching the molded article, A method for producing a moisture-absorbing and releasing split fiber, wherein the splitting step 4 is performed in the order of step 1 → step 2 → step 4. 2. The method according to claim 1, wherein the free carboxyl groups contained in the polyacrylic acid polymer (B) in the obtained stretch-formed product are neutralized. 30 mol%
2. The method according to claim 1, wherein Step 3 for neutralizing is provided as described above, and these steps are performed in the order of Step 1 → Step 2 → Step 3 → Step 4. 3. After the step 4 of claim 1, the free carboxyl groups contained in the polyacrylic acid-based polymer (B) in the obtained stretch-formed product are reduced to a degree of neutralization of 30 mol% or more. 2. The method according to claim 1, wherein a step 3 for neutralizing the mixture is provided, and these steps are performed in the order of step 1 → step 2 → step 4 → step 3. 4. The method according to claim 1, wherein the polyvinyl alcohol resin (A) is a polyvinyl alcohol resin having a degree of polymerization of 3100 or more.