JP3066043B2 - Method for producing moisture-absorbing and stretched stretched products - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention is to produce a moisture-absorbent and moisture-absorbent stretch molded article having excellent moisture-absorbing properties and moisture-releasing properties, and also having mechanical strength, water resistance and dimensional stability. It is about the method.

2. Description of the Related Art Linear or sheet-like molded products having the property of absorbing and releasing moisture (absorbing and releasing moisture) in accordance with environmental humidity are used for clothing, sanitary products, agricultural and horticultural materials, interior materials, packaging materials, dehydrating agents, It is expected to be applied to applications such as sealing materials.

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 portion. 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.

The film-like or fibrous water-absorbing composition described in JP-A-1-103643 is based on a salt (I) of a carboxyl group-containing polymer, and secures toughness with polyvinyl alcohol (II) to obtain a polyvalent resin. The flexibility is ensured by the 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 of the properties of moisture absorption / desorption, mechanical strength, water resistance and dimensional stability in a well-balanced manner, and its application is limited. Sometimes.

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.

In this specification, the term “sheet” is a concept including a film.

Means for Solving the Problems The method for producing a moisture-absorbing and releasing stretch-formed product of the present invention comprises a polyvinyl alcohol-based resin (A) and a polymer (B) containing a free carboxyl group in a molecule in a weight ratio.
Using a mixed aqueous solution containing the gelling agent (C) of the resin (A) in a ratio of 90:10 to 20:80 as a stock solution for molding, and molding the molded product into a molded product; A step of stretching at least twice in the uniaxial direction when it is linear, and at least twice or more at an area ratio in a uniaxial direction if it is sheet-like, and then the polymer in the obtained stretched product (B) a step of neutralizing a free carboxyl group contained in the compound (B).

 Hereinafter, the present invention will be described in detail.

Molding Step The polyvinyl alcohol-based resin (A) has various degrees of polymerization (for example, 300 or more) and degrees of saponification (for example, 70 to 100) as long as it has water solubility or water swellability.
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.

Polymer containing free carboxyl group in molecule (B)
Examples include ethylenically unsaturated monocarboxylic acids (acrylic acid, methacrylic acid, crotonic acid, etc.), ethylenically unsaturated dicarboxylic acids (maleic acid, fumaric acid, itaconic acid, etc.) or their anhydrides and partial alkyl esters such as ethylene. Polymers of at least one monomer selected from unsaturated unsaturated carboxylic acids, or monomers copolymerizable with the above monomers (ethylenically unsaturated carboxylic acid esters, α-olefins, styrene monomers, vinyl esters, ( (Meth) acrylonitrile, vinyl ether, vinyl chloride, etc.).

The carboxyl groups in the molecule of the polymer (B) are preferably free carboxyl groups (A) and (B).
However, if it is less than 5 mol%, especially less than 3 mol%, it may be partially neutralized to be in a salt form. Note that the salt refers to a water-soluble salt such as an alkali metal salt, an alkaline earth metal salt, an amine salt, and an ammonium salt.

Among them, particularly preferred is polyacrylic acid or an acrylic acid-sodium acrylate copolymer having a copolymerization ratio of sodium acrylate of less than 5 mol% (particularly less than 3 mol%).

The mixing ratio of the polyvinyl alcohol resin (A) and the polymer (B) having a free carboxyl group in the molecule is 90:10 to 20:80, especially 80:20 to 30:70 by weight. It is desirable to select from a range. Excessive amounts of the former (A) and excessively small amounts of the latter (B) cause insufficient moisture absorption and desorption, and insufficient amounts of the former (A) and excessively large amounts of the latter (B) lead to insufficient mechanical strength and dimensional stability.

As the gelling agent (C), a substance capable of gelling the polyvinyl alcohol-based resin (A) is used. Typical examples are boric acid, borax, metal salts,
An ammonium salt is mentioned, and boric acid is particularly important.

Among the above, metal salts such as iron, cobalt, nickel, manganese, chromium, vanadium, tin, zirconium, titanium, aluminum, zinc, cadmium, magnesium, calcium, strontium, barium, copper, lithium, sodium, potassium, etc. Inorganic or organic acid salts (chloride, bromide, nitrate, sulfate, sulfite, acid sulfate, thiosulfate, carbonate, phosphate, acetate, oxalate, citrate, malic acid Salts, gluconates, etc.) having water solubility are used, and double salts such as potassium aluminum sulfate may be used.

The compounding ratio of the gelling agent (C) is desirably 0.01 to 30% by weight, particularly 0.1 to 10% by weight, based on the polyvinyl alcohol resin (A). If the amount of the gelling agent (C) is too small, the compounding effect is insufficient, and if the amount of the gelling agent (C) is too large, the moldability is impaired.

By using a mixed aqueous solution containing the polyvinyl alcohol-based resin (A), the polymer (B) containing a free carboxyl group in the molecule and the gelling agent (C) in the above ratio as the stock solution, the fibrous form is obtained. Sheet and other shaped articles are produced.

As a forming method, an extrusion method or a casting method is usually employed. That is, a solvent, a plasticizer (polyhydric alcohol or the like), a crosslinking agent (polyhydric epoxy compound, dialdehyde, methylolmelamine or the like), a filler, After blending a colorant, a stabilizer, a functional agent, and the like, the mixture is discharged from the die or nozzle into the air or a coagulation bath, or cast on a substrate, and dried if necessary. Typically, the aqueous solution of (A), the aqueous solution of (B), and (C) are mixed, and further, if necessary, other additives are compounded and discharged from a die or a nozzle, After casting, dry.

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 be left.

The stretching ratio is 2 in the uniaxial direction when the molded product is linear.
When the molded article is in the form of a sheet (including a sheet for vacuum forming or deep drawing) at least one-fold (especially three times or more), at least in the uniaxial direction (that is, in the uniaxial or biaxial direction, or even more). 2 times or more (especially 3 times or more) in area magnification in the axial direction)
Set to. 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.

Neutralization Step In the present invention, the free carboxyl groups contained in the polymer (B) in the stretch molded product obtained as described above are neutralized.

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, characteristics such as the rate of moisture absorption are impaired.

Crosslinking Step In the present invention, it is desirable to subject the stretch molded article obtained above to a crosslinking treatment. The cross-linking treatment can be carried out by bringing the stretched product into contact with a cross-linking agent solution by dipping, spraying or the like before or after the above-mentioned neutralization step or simultaneously with the neutralization, and further performing a heat treatment if necessary. 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.

Here, 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, a polyvalent epoxy compound, dialdehyde, polyvalent isocyanate, methylolmelamine, methylolurea, or the like is used. Can be

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.

UseThe moisture-absorbing and releasing stretch molded product obtained by the method of the present invention is
Textile products (mono or multifilaments, yarns, linear materials, woven fabrics, non-woven fabrics, knitted fabrics, etc.), hygiene products, agricultural and horticultural materials, interior materials (wallpaper, etc.), and packaging materials by themselves or in combination with other materials (Dew-prevention sheet for fresh food or fast food packaging, etc.), dewatering / dehumidifying material, sealing material, civil engineering material (concrete curing sheet, etc.), and various other uses can be suitably used.

Function and Effect of the Invention The method of the present invention is a molding method comprising molding a composition comprising a polyvinyl alcohol resin (A), a polymer (B) containing a free carboxyl group in the molecule, and a gelling agent (C). The product is first stretched, and then neutralizes the free carboxyl groups contained in the polymer (B).

When the gelling agent (C) is not used together, the OH group of the polyvinyl alcohol-based resin (A) and the COOH group of the polymer (B) react during molding or stretching to form an ester bond. The formation of an ester bond is necessary for water resistance and dimensional stability, but limits the upper limit of the moisture absorption. However, the combined use of the gelling agent (C) prevents the OH group of the polyvinyl alcohol-based resin (A) from being blocked by the gelling agent (C), thereby preventing the COOH group from being esterified more than necessary. , Contribute to higher moisture absorption and desorption properties.

The moisture-absorbing and stretched stretched product obtained by the above method has excellent moisture-absorbing and desorbing properties (hygroscopic and moisture-releasing properties),
It has both mechanical strength, water resistance and dimensional stability.

If a cross-linking step is further added, the mechanical strength of the target product is further improved, so that a moisture-absorbing and desorbing stretch molded product having a higher practical value can be obtained.

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

Examples <Stability of the stock solution for molding and moldability> Examples 1 to 3 Polymerization degree adjusted to 15% by weight or 25% by weight
Polyvinyl alcohol (A) aqueous solution of 00, concentration 15% by weight, polymerization degree adjusted to concentration 20% by weight or concentration 25% by weight
An aqueous solution of polyacrylic acid (B) of 5000 and 2 wt% of boric acid with respect to polyvinyl alcohol (A) were mixed in the combinations and ratios shown in Table 1 below to obtain a stock solution for molding.

Comparative Examples 1-2 Polymerization degree 35 adjusted to 15% by weight or 25% by weight
Aqueous polyvinyl alcohol (A) aqueous solution and acrylic acid-sodium acrylate copolymer obtained by neutralizing polyacrylic acid as polyacrylic acid (B) by about 90 mol% with 0.1 N aqueous sodium hydroxide solution at a concentration of 15% by weight Alternatively, an aqueous solution having a concentration of 25% by weight was mixed in the combinations and ratios shown in Table 1 below to obtain a stock solution for molding.

The stock solution for molding was allowed to stand at 20 ° C. and 60 ° C. for 12 hours and 48 hours, respectively, to examine the stability of the stock solution for molding.

Table 1 shows the conditions and results. The meanings of the symbols in Table 1 are as follows.

：: not separated, △: tends to separate, ×: separated Further, the stock solution was discharged from a nozzle into acetone, air-dried, and wound up by a winder.

In Examples 1 to 3, the spinnability was good, and the yarn could be wound without causing yarn breakage.

On the other hand, in Comparative Example 1, smooth spinning was not possible due to poor spinnability, and yarn breakage often occurred. When the coagulation bath was methanol, an aqueous sodium sulfate solution, or when discharged into the air, the moldability was similarly poor.

In Comparative Example 2, the molding itself could not be performed.

<Production of Fibrous Molded Product> Example 4 Polyvinyl alcohol having a polymerization degree of 4000 and a saponification degree of 99.9 mol% as an example of a polyvinyl alcohol resin (A) is dissolved in water, and a polyvinyl alcohol aqueous solution having a concentration of 12% by weight is dissolved. Prepared.

Further, polyacrylic acid having a polymerization degree of 5000 as an example of the polymer (B) was 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, and 0.17 parts by weight of boric acid as a gelling agent (C) (2% by weight based on polyvinyl alcohol) were mixed to form a uniform solution, and the solution was supplied to a container equipped with a piston and a nozzle to form a nozzle. From the fiber, and then the temperature
After being introduced into a 20 ° C. acetone bath for coagulation, it was air-dried. The single thread of the obtained fibrous molded article had a thickness of 69 denier.

Next, the above-mentioned 69-denier fibrous molded article was stretched 7 times in the length direction at a stretching temperature of 180 ° C. using a roll-type stretching machine. After stretching twice, it was heat-set for 1 minute.

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

As a result, a fibrous hygroscopic stretch-formed product having a thickness of 3.9 denier was obtained. The degree of neutralization of the carboxyl group in the polymer (B) in the stretch molded product was about 90 mol%.

Example 5 Example 4 was repeated except that the compounding amount of boric acid as the gelling agent (C) was 0.43 parts by weight (5% by weight based on polyvinyl alcohol).

Example 6 In Example 4, the concentration of each of the aqueous solution of polyvinyl alcohol and the aqueous solution of polyacrylic acid was changed to 30% by weight, and a boric acid as a gelling agent (C) was mixed at 2% by weight with respect to polyvinyl alcohol. Was discharged from a nozzle into the air, dried with hot air at a temperature of 180 ° C., and stretched, neutralized, washed with water, dried and heat-treated under the same conditions as in Example 4 to obtain a fibrous stretch-formed product.

Example 7 The stretched and neutralized fibrous moisture-absorbing stretched product obtained in Example 4 after stretching and neutralization was further treated with a methylolated melamine aqueous solution at a temperature of 50 ° C and a concentration of 2% by weight (Sumimar M- manufactured by Sumitomo Chemical Co., Ltd.). 30W), and after running under tension, a heat treatment was performed at 220 ° C. to perform a crosslinking operation.

Example 8 In Example 4, the ratio of the aqueous solution of polyvinyl alcohol to the aqueous solution of polyacrylic acid was changed to 80:20 by weight, and boric acid as the gelling agent (C) was mixed at 2% by weight with respect to polyvinyl alcohol. Was stretched, neutralized, washed with water, dried and heat-treated under the same conditions as in Example 4 to obtain a fibrous stretch-formed product.

Examples 9 to 11 As a polyvinyl alcohol resin (A), a polymerization degree of 56 was used.
00 (Example 9), degree of polymerization 4300 (Example 10), degree of polymerization 1800
Stretching, neutralization, washing with water, drying and heat treatment were carried out under the same conditions as in Example 4 except that the polyvinyl alcohol of (Example 11) was used, respectively, to obtain a fibrous stretch-formed product.

Comparative Example 3 A fibrous stretch-formed product (3.9 denier) in which the neutralization step was omitted in Example 4 was used. The formulation of the gelling agent (C) was omitted when preparing the stock solution.

Comparative Example 4 70 parts by weight of a 12% by weight aqueous solution of polyvinyl alcohol of Example 4 and the polyacrylic acid of Example 4 were partially neutralized in advance to a degree of neutralization of 50 mol% with an aqueous solution of sodium hydroxide. % Of an aqueous solution of an acrylic acid-sodium acrylate copolymer adjusted to a concentration of 30% by weight, and the solution is supplied to a container equipped with a piston and a nozzle and discharged from the nozzle in a fibrous form. After being introduced into an acetone bath at ℃ for coagulation, it was air-dried. The single yarn of the obtained fibrous molded article had a thickness of 3.9 denier.

Comparative Example 5 Comparative Example 4 was repeated except that the mixed solution was discharged from the nozzle into the air to obtain a fibrous molded product having a single yarn thickness of 3.9 denier.

Reference Example 1 Example 4 except that only the compounding of the gelling agent (C) was omitted.
Was repeated.

<Characteristics Evaluation> From the fibrous molded products obtained in Examples 4 to 11, Comparative Examples 3 to 5, and Reference Example 1, a multifilament yarn of 1560d / 400f was produced, and moisture absorption / desorption properties (moisture absorption rate, moisture release Speed, equilibrium moisture absorption), mechanical strength (tensile strength), water resistance (hot water insolubility), and dimensional stability are measured by the following methods.
From the viewpoint of practicality, evaluation was made in three stages of ○, Δ, and ×. However, the tensile strength and dimensional stability are measured values for a single yarn.

The moisture absorption rate was measured at 40 ° C and 90 ° C for a sample in a dry state using a table-top constant temperature and humidity chamber manufactured by Nagano Kagaku Kikai Seisakusho
% RH from an absolutely dry state to a high humidity condition, the average change rate (% / min) of the moisture absorption rate during the first 10 minutes was defined as the moisture absorption rate, and the value after 24 hours was defined as the equilibrium moisture absorption rate.

The moisture absorption and desorption properties were measured for 24 hours under low humidity conditions (40 ° C, 40% RH) and high humidity conditions (40 ° C, 90% RH) using a desktop thermo-humidifier manufactured by Nagano Kagaku Kikai Seisakusho Co., Ltd. The average change (% / min) in the moisture absorption rate during the first 10 minutes was defined as the moisture absorption / desorption rate, and the value after 24 hours was defined as the equilibrium moisture absorption rate.

The tensile strength was measured using a tensile tester after keeping the sample at 20 ° C. and 65% RH for 48 hours or more. After immersion in water at 20 ° C. for 1 hour, the tensile strength was similarly measured.

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, the sample fiber was placed at 20 ° C and 65% RH for 48 hours.
After keeping it for more than an hour, cut it into a length of 100 mm, then put it in a beaker containing 500 ml of water at a temperature of 20 ° C. and rotate it at 50 rpm
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 (%) was determined.

 The results are shown in Table 2.

<Production of sheet-shaped molded product> Example 12 Polyvinyl alcohol having a polymerization degree of 3500 and a saponification degree of 99.7 mol% as an example of a polyvinyl alcohol-based resin (A) was dissolved in water, and a 5% by weight aqueous solution of polyvinyl alcohol was dissolved in water. Prepared.

Further, polyacrylic acid having a polymerization degree of 5000 as an example of the polymer (B) was 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, the above-mentioned 5% by weight aqueous solution of polyacrylic acid 30
Parts by weight and boric acid as a gelling agent (C) are mixed with polyvinyl alcohol in an amount of 3% by weight to form a uniform solution, cast onto a polyester sheet having a thickness of 120 μm as a base material, and then dried with hot air. A sheet-like molded product having a thickness of 50 μm was obtained.

Next, this sheet-like molded product is stretched 2.12 times (4.5 times in area ratio) in each of the longitudinal and transverse directions at a stretching temperature of 180 ° C. using a tenter type stretching machine, and heat-set at a temperature of 240 ° C. for 10 seconds. Was.

The obtained sheet-like stretch-formed product was neutralized by immersing it in a 0.2 N aqueous sodium hydroxide solution at a temperature of 50 ° C. under tension for 20 seconds, followed by washing with water and drying, followed by a temperature of 240 ° C.
Heat set at 10 ° C. for 10 seconds.

As a result, a sheet-shaped moisture-absorbing and releasing stretch-formed product was obtained. The degree of neutralization of the carboxyl group in the polymer (B) in the stretch molded product was about 75 mol%.

Example 13 The sheet-shaped moisture-absorbing and stretched stretched product obtained in Example 12 after stretching and neutralization was further treated with a methylolated melamine aqueous solution (the one used in Example 6) at a temperature of 50 ° C and a concentration of 2% by weight. , And then heat-treated at 240 ° C. for 10 seconds to perform a crosslinking operation.

Example 14 Example 12 was repeated except that cupric acetate was used instead of boric acid as the gelling agent (C) in an amount of 2% by weight based on polyvinyl alcohol.

Example 15 Example 12 was repeated except that as the gelling agent (C), nickel nickel acetate was used instead of boric acid and mixed with polyvinyl alcohol in an amount of 2% by weight.

Comparative Example 6 The sheet-like stretch-formed product before neutralization in Example 12 was used. The formulation of the gelling agent (C) was omitted when preparing the stock solution.

Comparative Example 7 70 parts by weight of a 5% by weight aqueous solution of polyvinyl alcohol of Example 12 and the polyacrylic acid of Example 12 were previously neutralized with an aqueous solution of sodium hydroxide to a degree of neutralization of 50 mol%, and then a concentration of 5% by weight was obtained. Acrylic acid-concentration-adjusted acrylic acid-sodium acrylate copolymer aqueous solution 30 parts by weight was uniformly mixed, and the solution was cast on a 120 μm-thick polyester sheet as a substrate, followed by hot-air drying, and a 50 μm-thick A sheet-like molded product was obtained.

<Characteristics Evaluation> Examples 12 to 15 and Comparative Examples 6 and 7 obtained in this manner.
In the same manner as above, moisture absorption / desorption properties (moisture absorption rate, moisture release rate, equilibrium moisture absorption rate), mechanical strength (tensile strength), water resistance (hot water insoluble rate), dimensional stability ○, and from the viewpoint of practicality etc.,
The evaluation was made in three stages of Δ and X.

However, for dimensional stability, the sample sheet was kept at 20 ° C.
After keeping at 65% RH for more than 48 hours, cut into a size of 50 mm x 50 mm, then put this into a beaker containing 500 ml of water at a temperature of 20 ° C, stir for 60 minutes at 50 rpm, and take out The water attached to the surface was removed with a filter paper, and the area change (%) was determined.

 The results are shown in Table 3.

From the results shown in Tables 1 to 3, even when the degree of polymerization of polyvinyl alcohol is high and the concentration of the stock solution for molding is high by the production method of Example, a stock solution for molding having excellent stability is obtained. Further, it can be seen that the obtained moisture-absorbing and releasing stretched product has a good balance of moisture-absorbing and releasing properties, mechanical strength, water resistance and dimensional stability.

Claims (6)

(57) [Claims] 1. A polyvinyl alcohol resin (A) and a polymer (B) containing a free carboxyl group in the molecule.
Using a mixed aqueous solution containing the gelling agent (C) of the resin (A) and the gelling agent (C) in a ratio of 90:10 to 20:80 by weight as a stock solution for molding, and molding the molded product. Is stretched at least twice in the uniaxial direction if it is linear, or twice or more in area ratio in the uniaxial direction if it is sheet-like. Neutralizing a free carboxyl group contained in the polymer (B) contained therein. 2. The process according to claim 1, wherein the free carboxyl groups contained in the polymer (B) in the stretch molded product are neutralized to a degree of neutralization of 30 mol% or more. . 3. The method according to claim 1, wherein the polyvinyl alcohol resin (A) is a polyvinyl alcohol resin having a polymerization degree of 3100 or more. 4. The polymer (B) containing a free carboxyl group in the molecule is polyacrylic acid or acrylic acid having a copolymerization ratio of sodium acrylate of less than 5 mol%.
The method according to claim 1, which is a sodium acrylate copolymer. 5. The process according to claim 1, wherein the gelling agent (C) is boric acid, borate, metal salt or ammonium salt. 6. The method of claim 1, further comprising the step of contacting the moisture-absorbing and releasing stretch molded product with a crosslinking agent solution to perform a crosslinking treatment before, after or simultaneously with the neutralizing step of claim 1. A method for producing a wet stretch molded product.