JPH03277635A - Production of moisture-absorbing and-emitting stretched molded article - Google Patents

Abstract

PURPOSE:To obtain the title article excellent in moisture-absorbing and -emitting properties and having mechanical strengths, water resistance, and dimensional stability by stretching a molded article obtd. from an aq. soln. of a PVA resin and a free carboxyl groups containing polymer and neutralizing the article. CONSTITUTION:A molded article is produced from an aq. soln. of a PVA resin (pref. having a degree of polymn. of 3100 or higher) and a carboxylated polymer having free carboxyl groups in the molecule (e.g. a polyacrylic acid or an acrylic acid-sodium acrylate copolymer contg. less than 5mol.% sodium acrylate) in a wt. ratio of the former to latter of (90:10)-(20:80). The article is stretched at least double in at least one direction when it is linear, or at least double in terms of the areal stretching ratio in at least one direction when it is sheetlike. Then, the free carboxyl groups of the polymer contained in the stretched article are neutralized to give the title article.

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Field of Application The present invention produces a moisture-absorbing and desorbing stretched molded product that has excellent moisture absorption and moisture release properties, as well as mechanical strength, water resistance, and dimensional stability. It is about the method.

Conventional technology Linear or sheet-shaped molded products that have the property of absorbing and releasing moisture depending on the environmental humidity are used in clothing, sanitary products, agricultural and horticultural materials, interior materials, packaging materials, dehydrating agents, It is expected to be used in applications such as sealing materials.

JP-A No. 63-219618 has 3 meq.

Polycarboxylic acid (A
), polyvinyl alcohol with a degree of polymerization of 500 to 3000 (
B) and polyhydric alcohol (C) in an amount of 0.1 to 5% by weight based on (A) as an essential component, and (A) and (B) are microscopically incompletely mixed immediately before the nozzle or at the nozzle part. A method for producing water absorbent fibers is disclosed by mixing, dry spinning, and heat treatment.

JP-A-1-103643 discloses salts of carboxyl group-containing polymers (I), polyvinyl alcohol (■), polyhydric alcohols (m), and polyhydric epoxy compounds (IV).
A film-like or fibrous water-absorbing composition obtained by molding and heat-treating a mixture consisting of four components is shown.

Although it is not for the purpose of absorbing and desorbing moisture,
Publication No. 0 discloses a water-soluble film made of a homogeneous mixture of water-soluble polyvinyl alcohol and polyacrylic alcohol, and claims that this water-soluble film is useful for packaging dry detergents and similar water-soluble products. .

Problems to be Solved by the Invention In the method described in JP-A No. 63-219618, (A) and (B) are added in order to smoothly stretch and obtain the desired water absorbency and elongation. A method of spinning an incompletely mixed spinning stock solution is used. However, such a special method is hardly desirable from an industrial standpoint.

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 a polyvinyl alcohol (II).
The polyhydric alcohol (m) ensures toughness, the polyhydric alcohol (m) ensures flexibility, and the polyhydric epoxy compound (ff) performs crosslinking 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 applications are limited. Sometimes.

Furthermore, since a trace amount of polyvalent epoxy compound (IV) is added and crosslinking is attempted by heat treatment, there is also the problem that it is difficult to stably produce products with a constant degree of crosslinking.

The purpose of the water-soluble film described in JP-A-57-125240 is to provide a water-soluble film suitable for uses such as detergent packaging, and therefore is not suitable as a moisture-absorbing and desorbing molded product.

As a result of extensive research to find a moisture absorbing and desorbing stretched molded product that has excellent moisture absorbing and desorbing properties as well as mechanical strength, water resistance, and dimensional stability, the applicant has already filed a patent application. No. 1-328919, a polyvinyl alcohol resin (A) (especially one with a degree of polymerization of 3100 or more) and a polymer containing a salt-type carboxyl group (
A composition having a blending ratio of Bo) of 90:10 to 20:80 by weight is prepared, the composition is molded, and the molded product is then doubled in at least one axial direction if it is linear. As described above, an application has been filed to produce a moisture-absorbing and desorbing stretched molded product by stretching it in at least one axis direction to an area magnification of 2 times or more when the sheet is in the form of a sheet.

However, in the above-mentioned prior application in which the molding stock solution is a composition in which polyvinyl alcohol resin (A) and a polymer containing salt-type carboxyl groups (Bo) are mixed at a specific blending ratio, the moisture absorption and desorption properties obtained are The degree of polymerization of the resin (A) is increased as much as possible in consideration of the balance with the properties of the stretched product, so if the polymer concentration is relatively low, no particular problem will occur, but the When the polymer concentration in the stock solution increases beyond a certain limit, (A
) and (Bo), which impairs the stability of the stock solution for molding, and as a result, the stock solution may undergo phase separation over time and the strength of the molded product may decrease. .

The present invention is based on the polymer concentration and polyvinyl alcohol resin (
A) has good stability regardless of the degree of polymerization, has industrial productivity, and has excellent moisture absorption and desorption properties; 5. mechanical strength;
The purpose of this invention is to provide a method for obtaining a moisture-absorbing and desorbing stretched molded product that has both water resistance and dimensional stability.

Note that in this specification, the term "sheet" includes a film.

Means for Solving the Problems The method for producing a moisture-absorbing and desorbing stretched molded product of the present invention is to use a polyvinyl alcohol resin (A) and a polymer (B) containing free carboxyl groups in the molecule in a weight ratio of 90: 10-2
A process of forming a molded article using a mixed aqueous solution containing a ratio of 0:80 as a stock solution for molding. In some cases, a step of stretching at least uniaxially to an area ratio of 2 times or more, and a step of neutralizing free carboxyl groups contained in the polymer (B) in the obtained stretched product. It is characterized by:

In this case, it is desirable to provide a step of crosslinking the stretched product before or after the neutralization step, or simultaneously with the neutralization step.

The present invention will be explained in detail below.

L spoon 1 The polyvinyl alcohol resin (A) may have various degrees of polymerization (for example, 300 or more) and saponification degrees (for example, 70 to 100) as long as it is water-soluble or water-swellable.
mol%) of polyvinyl alcohol is used. In this case, for the purpose of the present invention, it is desirable that the degree of polymerization is higher, and the degree of polymerization is preferably 3100 or more, particularly 3500 or more, and especially 40
A value of 00 or more is preferred.

In addition to polyvinyl alcohol, 1,000 polymers that can be copolymerized with vinyl acetate (α-olefins, ethylenically unsaturated carboxylic acid salts, alkyl esters, anhydrides, nitriles, amides, ethylenically unsaturated sulfonic acids, vinyl ethers, vinyl acetate) "Copolymerized modified" polyvinyl alcohol that has been copolymerized and modified with other vinyl esters, vinyl chloride, etc.
"Post-modified" polyvinyl alcohol, which is obtained by acylating or urethanizing polyvinyl alcohol or copolymerized modified polyvinyl alcohol, can also be used.

Examples of the polymer (B) containing a free carboxyl group in the molecule include ethylenically unsaturated monocarboxylic acids (acrylic acid, methacrylic acid, crotonic acid, etc.).

At least one heptad polymer selected from ethylenically unsaturated carboxylic acids such as ethylenically unsaturated dicarboxylic acids (maleic acid, fumaric acid, itaconic acid, etc.) or their anhydrides and partial alkyl esters, or the above-mentioned Examples include copolymers of nanatsumer and other copolymerizable monomers (ethylenic unsaturated carboxylic acid esters, α-olefins, styrenic monomers, vinyl esters, (meth)acrylonitrile, vinyl ethers, vinyl chloride, etc.). It will be done.

It is preferable that all the carboxyl groups in the molecule of the polymer (B) be free carboxyl groups from the viewpoint of compatibility with (A) and (B), but it is less than 5 mol%, especially 3 mol%. There is no problem even if it is partially neutralized and in the form of a salt, as long as the amount is less than 100%.Salt refers to water-soluble salts such as alkali metal salts, alkaline earth metal salts, amine salts, and ammonium salts.

Among the above, particularly preferred are polyacrylic acid or acrylic acid-sodium acrylate copolymers in which the copolymerization ratio of sodium acrylate is less than 5 mol%.

The blending ratio of the polyvinyl alcohol resin (A) and the polymer (B) containing free carboxyl groups in the molecule is as follows:
Weight ratio of 90:10 to 20:80, especially 80:
20-30: It is desirable to select from the range of 70. Too much of the former (A) and too little of the latter (B) will lead to insufficient moisture absorption and desorption properties, while too little of the former (^) and too much of the latter (B) This results in a lack of mechanical strength and dimensional stability.

By using a mixed aqueous solution containing a polyvinyl alcohol resin (A) and a polymer (B) containing a free carboxyl group in the molecule in the above ratio as a stock solution for molding,
Molded products in the form of fibers, sheets, and other shapes are manufactured.

As a molding method, an extrusion method or a casting method is usually adopted. That is, a solvent, a softening agent (polyhydric alcohol, etc.), a crosslinking agent (polyepoxy compound, dialdehyde,
methylolmelamine, etc.), fillers, colorants, stabilizers,
After blending functional drugs, etc., it is discharged from a die or nozzle into the air or into a coagulation bath, or it is cast onto a base material.
Dry if necessary. Typically, the aqueous solution of (A) and the aqueous solution of (B) are mixed, other additives are added as necessary, and the mixture is discharged from a goo or nozzle or cast onto a substrate. ,dry.

Stretching JLIJ In the present invention, the obtained molded product is subjected to stretching. In this case, there is no problem even if water remains at the natural moisture absorption rate.

The stretching ratio should be 2 times or more (especially 3 times or more) in the uniaxial direction if the molded product is linear, and if the molded product is sheet-like (including sheets for vacuum forming or deep drawing). is set to an area magnification of 2 times or more (particularly 3 times or more) in at least one axial direction (that is, the -axial direction, biaxial direction, or even multiaxial direction). When the stretching ratio is small, mechanical strength, water resistance, and dimensional stability are insufficient, and the intended purpose cannot be achieved.

The stretching temperature during the above stretching operation is 100 to 300.
℃, especially 140 to 250°C is suitable. Heat treatment can be performed before the stretching operation to an extent that does not impair the stretching operation, and heat setting can also be performed after the stretching operation.

The hot water dissolution rate of the stretched product is 30% by weight or less, and even 2% by weight.
It is preferable that it is less than 0% by weight, especially less than 10% by weight.

Tokoko 1 In the present invention, free carboxyl groups contained in the polymer (B) in the stretched product obtained as described above are neutralized.

Neutralization can be achieved by bringing the stretched product into contact with a neutralizing agent which is an aqueous solution of sodium hydroxide, potassium hydroxide, sodium carbonate, ethanolamine, etc. at a concentration of about 0.0 l-IN. The temperature conditions during neutralization are often from room temperature to about 80° C. During neutralization, it is preferable to keep the stretched product in a tensioned state. Heat treatment can also be performed after the neutralization treatment.

By this neutralization operation, the carboxyl groups contained in the polymer (B) in the stretched product are neutralized to a high degree of neutralization (particularly 30 mol % or more). If the degree of neutralization is insufficient, properties such as moisture absorption rate will be impaired.

1 Natsumeko 1 In the present invention, it is desirable to subject the stretched molded product obtained above to a crosslinking treatment. This can be done by heat treatment. Such a crosslinking treatment further improves the mechanical properties such as tensile strength of the target product, resulting in a more practical target product.

As the crosslinking agent, any known crosslinking agent for polyvinyl alcohol or polyacrylic acid can be used, such as polyvalent epoxy compounds, dialdehydes, polyvalent incyanates, methylolmelamine, methylolurea, metal Salts, metal chelates, etc. are used.

Further, without using a crosslinking agent in particular, crosslinking treatment can also be carried out by irradiation with active energy rays such as electron beams and ultraviolet rays.

Shiriju The moisture-absorbing and desorbing stretched molded product obtained by the method of the present invention can be used alone or in combination with other materials to produce textile products (mono- or multifilament, yarn, cotton-like material, woven fabric, etc.).
(non-woven fabrics, knitted fabrics, etc.), sanitary products, agricultural and horticultural materials, interior materials (
wallpaper, etc.), packaging materials (condensation prevention sheets for fresh food or fast food packaging, etc.), dehydration/dehumidification materials, sealing materials,
It can be suitably used for various purposes including civil engineering materials (concrete curing sheets, etc.).

Actions and Effects of the Invention The method of the present invention is characterized in that a polyvinyl alcohol resin (A) and a polymer (B) containing a free carboxyl group in the molecule
A molded article made from a composition having a specific blending ratio is first stretched, and then free carboxyl groups contained in the polymer (B) are neutralized. The moisture-absorbing and desorbing stretched molded product obtained by this method has excellent moisture-absorbing and desorbing properties (
It has mechanical strength, water resistance, and dimensional stability while also having hygroscopic and moisture-releasing properties.

If a crosslinking step is further added, the mechanical strength of the target object is further improved, so that a moisture-absorbing and desorbing stretched molded product with even higher practical value can be obtained.

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

Examples (Stability of stock solution for molding, moldability) Examples 1 to 3 Polyvinyl alcohol (^) aqueous solution with a degree of polymerization of 3500 adjusted to a concentration of 15% by weight or 25% by weight, and a concentration of 15% by weight or 20% by weight % or a polyacrylic acid (B) aqueous solution with a degree of polymerization of 5000 adjusted to a concentration of 25% by weight in the combinations and ratios shown in Table 1 below to obtain a stock solution for molding.

Comparative Examples 1-2 Polyacrylic acid (B) was 0, IN
Except that an aqueous solution containing an acrylic acid-sodium acrylate copolymer neutralized to about 90 mol% with an aqueous sodium hydroxide solution at a concentration of 15% by weight or 25% by weight was used.
A stock solution for molding was obtained in the same manner as in Examples 1 to 3.

The above stock solution for molding was left at ambient temperatures of 20° C. and 60° C. for 12 hours and 48 hours, respectively, and the stability of the stock solution for molding was examined.

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

O: No separation, Δ: Separation tendency, X: Separation Table 1 (A) Concentration (wtX) (B) Concentration (wtX) (A)/(B) Weight ratio Stability of stock solution at 20°C 12hr 60℃X 48hr 15 25 25 15 2515
25 20 15 257/3
7/3 515 7/3 7/30 0 0
Δ x 000 x x Further, the above-mentioned stock solution for molding was discharged from a nozzle into acetone, air-dried, and wound up on a winder.

In Examples 1 to 3, the stringiness was very good and it was possible to wind the yarn without causing yarn breakage.

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

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

<Manufacture of wire pyramid-shaped molded product> Example 4 Polyvinyl alcohol resin (A) with a degree of polymerization of 3500. Polyvinyl alcohol having a saponification degree of 38.7 mol% was dissolved in water to prepare an aqueous polyvinyl alcohol solution having a S degree of 12% by weight.

Also, as an example of polymer (B), the degree of polymerization is soo.

Polyacrylic acid was dissolved in water to prepare an aqueous polyacrylic acid solution having a concentration of 12% by weight.

Polyvinyl alcohol aqueous solution 7 with the above concentration of 12% by weight
0 parts by weight and 30 parts by weight of the above polyacrylic acid aqueous solution having a concentration of 12% by weight are mixed to form a homogeneous solution, the solution is supplied to a container equipped with a piston and a nozzle, and is discharged from the nozzle in the form of fibers. The mixture was introduced into an acetone bath at a temperature of 20°C to solidify, and then air-dried. The thickness of the single yarn of the obtained fibrous molded product was 69 denier.

Next, the above 69 denier fibrous molded product was stretched 7 times in the length direction at a stretching temperature of 180°C using a roll drawing machine, and then stretched 3 times in the length direction at a stretching temperature of 220°C.
．． After stretching to 1x, heat setting was performed for 1 minute.

This was then introduced into a 0.2N aqueous sodium hydroxide solution at a temperature of 50°C and run under tension to neutralize it, washed with water, dried, and heat treated at 220°C under tension.

As a result, a fibrous moisture-absorbing and desorbing stretched molded product having a thickness of 3.9 deniers was obtained. The polymer (
The degree of neutralization of carboxyl groups in B) was about 90 mol%.

Example 5 In Example 4, a homogeneous solution obtained by mixing polyvinyl alcohol aqueous solution and polyacrylic acid aqueous solution with the concentrations changed to 30% by weight was discharged into the air from a nozzle, and then dried with hot air at a temperature of 180°C. Stretching, neutralization, water washing, drying and heat treatment were carried out under the same conditions as in Example 4 to obtain a fibrous stretched molded product.

Example 6 The fibrous moisture-absorbing and desorbing stretched molded product obtained in Example 4 after stretching and neutralization was further treated with a methylolated melamine aqueous solution (Sumimar M- manufactured by Sumitomo Chemical Co., Ltd.) at a temperature of 50°C and a concentration of 2% by weight. 30W) and run under tension, then 220
The crosslinking operation was carried out by heat treatment at °C.

Example 7 Stretching, neutralization, water washing,
Drying and heat treatment were performed to obtain a fibrous stretched molded product.

Example 8 The concentration of sodium hydroxide aqueous solution was 0. Stretching, neutralization, water washing, drying and heat treatment were carried out under the same conditions as in Example 4, except that IN was used, to obtain a fibrous stretched molded product.

Examples 9 to 11 Polyvinyl alcohol resin (A) had a polymerization degree of 56
00 (Example 9), degree of polymerization 4300 (Example 10)
, polyvinyl alcohol having a polymerization degree of 1800 (Example 11) was used, but stretching, neutralization, water washing, drying and heat treatment were carried out under the same conditions as in Example 4 to obtain a fibrous stretched molded product.

Comparative Example 3 A fibrous stretched molded product (3.3 denier) in which the neutralization step was omitted in Example 4 was used.

Comparative Example 4 70 parts by weight of the polyvinyl alcohol aqueous solution of Example 4 with a concentration of 12% by weight and the polyacrylic acid of Example 4 were partially neutralized in advance with an aqueous sodium hydroxide solution to a neutralization degree of 50% by weight, and then the polyvinyl alcohol aqueous solution of Example 4 with a concentration of 12% by weight % and 30 parts by weight of an aqueous solution of acrylic acid-sodium acrylate copolymer, the solution was supplied to a container equipped with a piston and a nozzle, and was discharged from the nozzle in the form of fibers. ℃
After solidifying it in an acetone bath, it was air-dried.

The thickness of the single yarn of the obtained fibrous molded product was 3.9 denier.

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

<Characteristics Evaluation) Multifilament yarns of 1560 d/400 f were produced from the fibrous molded products obtained in Examples 4 to 11 and Comparative Examples 3 to 5, and then plain-woven to produce woven fabrics.

The woven fabric obtained in this way has moisture absorption and desorption properties (moisture absorption rate,
Moisture release rate, equilibrium moisture absorption rate) 1 Mechanical strength (tensile strength), water resistance (hot water insolubility rate), and dimensional stability were measured by the following methods, and from the viewpoint of practicality, 3 stages of O1Δ, × It was evaluated by

However, the tensile strength and dimensional stability are measured values for single yarns.

Moisture absorption and release properties were measured over 24 hours under low humidity conditions (40°C, 40% RH) and high humidity conditions (40°C, 90% RH) using a tabletop constant temperature and humidity chamber manufactured by Nagano Scientific Machinery Co., Ltd. The average change (X/■in) in the moisture absorption rate during the initial 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. The tensile strength was similarly measured after being immersed in water at 20°C for 1 hour and after being immersed in hot water at 95°C for 1 hour.

The rate of insolubility in hot water is determined by accurately weighing 1.0±0.1g of the sample (absolute dry weight), keeping it at 20℃ and 65%RH for more than 48 hours, and then weighing it in a beaker containing water 5001 at a temperature of 98℃. After stirring at 50 rpm for 60 minutes, the sample was taken out, and the weight (b) after absolute drying was measured and calculated using the following formula.

Hot water insolubility rate ($) -100b/a For dimensional stability, sample fibers were heated at 20°C and 65% RH.
After keeping it for more than 48 hours, cut it into 100m layer length,
Next, this was put into a beaker containing water 5001 at a temperature of 20°C and stirred at 50 rpm for 60 minutes, then taken out and the moisture attached to the surface was removed with a filter paper, and the change in length (z) was determined. .

The results are shown in Table 2.

<Manufacture of sheet-shaped molded product> Example 12 Polyvinyl alcohol resin (A) with a degree of polymerization of 3500 and a degree of saponification of 99.7 mol% is dissolved in water to form polyvinyl alcohol with a concentration of 5% by weight. An alcohol aqueous solution was prepared.

Further, polyacrylic acid having a degree of polymerization of 5000 as an example of polymer (B) was dissolved in water to prepare an aqueous polyacrylic acid solution having a concentration of 5% by weight.

Polyvinyl alcohol aqueous solution with the above concentration of 5% by weight 70
Parts by weight and 30 parts by weight of the above 5% by weight aqueous polyacrylic acid solution were mixed to form a homogeneous solution, which was cast onto a 120 mm thick polyester sheet as a base material and dried with hot air to obtain a uniform solution. A sheet-like molded product of 50 Bm was obtained.

Next, this sheet-like molded product was stretched by 2.12 times (area magnification: 4.5 times) in each direction at a stretching temperature of 180°C using a tenter-type stretching machine, and for 10 seconds at a temperature of 240°C. Heat fixation was performed.

The obtained sheet-shaped rolled product was heated at a temperature of 50°C.

After neutralization by immersing it in a 0.2N aqueous sodium hydroxide solution under tension for 20 seconds, it was washed with water, dried, and then heat-set at a temperature of 240° C. for 10 seconds.

As a result, a sheet-like moisture absorbing and desorbing stretched molded product was obtained. The degree of neutralization of carboxyl groups in the polymer (B) in the stretched product was about 90 mol%.

Example 13 The stretched and neutralized sheet-like moisture-absorbing and desorbing stretched product obtained in Example 12 was further placed in a methylolated melamine aqueous solution (used in Example 6) at a temperature of 50°C and a concentration of 2% by weight. The sample was immersed under tension in water, and then heat-treated at 240°C for 10 seconds to perform a crosslinking operation.

Comparative Example 6 The sheet-shaped stretched product in Example 12 before neutralization was used.

Comparative Example 7 80 parts by weight of the polyvinyl alcohol aqueous solution of Example 12 with a concentration of 5% by weight and the polyacrylic acid of Example 12 were neutralized in advance with an aqueous sodium hydroxide solution to a degree of neutralization of 50 mol%,
Next, 30 parts by weight of an aqueous solution of acrylic acid-sodium acrylate copolymer whose concentration was adjusted to 5% by weight was mixed uniformly, and the solution was cast onto a 120p thick polyester sheet as a base material, followed by hot air drying. A sheet-like molded product having a thickness of 50 mm was obtained.

<Characteristic evaluation> Examples 12 to 13 and comparative examples 6 to 13 obtained in this way
Regarding the sheet-shaped molded product No. 7, moisture absorption and desorption properties (moisture absorption rate, moisture desorption rate, equilibrium moisture absorption rate), mechanical strength (tensile strength), and water resistance (hot water insolubility rate) were measured in the same manner as above. In addition to measuring stability, O1
Evaluation was made in three stages: Δ and ×.

However, for one-dimensional stability, the sample sheet was heated at 20°C.
After keeping it at 65% RH for more than 48 hours, it was cut into pieces of 50 layers x 50 cm, and then soaked in 50 cm of water at a temperature of 20°C.
Pour it into a beaker containing 01 and set it to 6 at 50 rpm.
After stirring for 0 minutes, the sample was taken out, water adhering to the surface was removed using filter paper, and the change in area (z) was determined.

The results are shown in Table 3.

From the results 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, the production method of the example can yield a stock solution for molding with excellent stability. It can also be seen that the obtained moisture absorbing and desorbing stretched molded product has a good balance of moisture absorbing and desorbing properties, mechanical strength, water resistance, and dimensional stability.

Claims (1)

[Claims] 1. Molding a mixed aqueous solution containing a polyvinyl alcohol resin (A) and a polymer (B) containing free carboxyl groups in a weight ratio of 90:10 to 20:80. A step of molding the molded product into a molded product using the stock solution as a stock solution; Moisture-absorbing and desorbing stretch-molding, characterized by comprising the steps of stretching the obtained stretched product by more than twice the amount, and then neutralizing free carboxyl groups contained in the polymer (B) in the obtained stretched-molded product. How things are manufactured. 2. The production method according to claim 1, wherein free carboxyl groups contained in the polymer (B) in the stretched product are neutralized to a degree of neutralization of 30 mol% or more. 3. Polyvinyl alcohol resin (A) has a polymerization degree of 31
Claim 1: The resin is a polyvinyl alcohol-based resin having a molecular weight of 00 or more.
Manufacturing method described. 4. Polymers containing free carboxyl groups in the molecule (
The method according to claim 1, wherein B) is polyacrylic acid or an acrylic acid-sodium acrylate copolymer in which the copolymerization ratio of sodium acrylate is less than 5 mol%. 5. A method for producing a moisture-absorbing and desorbing stretched molded product, which comprises a step of crosslinking the moisture-absorbing and desorbing stretched molded product according to claim 1 by bringing it into contact with a crosslinking agent solution.