JP4281060B2 - Absorbent / release paper and method for producing the same - Google Patents

Description

The present invention relates to a moisture-absorbing / releasing paper having both high moisture-absorbing / releasing properties and high dimensional stability and a method for producing the same.

Much research and development has been conducted on moisture-absorbing / releasing paper, that is, paper having moisture-absorbing / releasing properties, and paper containing moisture-absorbing / releasing material is well known. As a material having moisture absorption / release properties, fibers having moisture absorption / release properties and fine particles having moisture absorption / release properties are often used. In general, there are organic and inorganic substances having such hygroscopic properties, but the former is highly hygroscopic but swells, while the latter is not swollen but has low moisture absorption. There is. For this reason, it is not easy to obtain moisture-absorbing / releasing paper having both high moisture-absorbing / releasing properties and high dimensional stability.

Moisture-absorbing / releasing paper using moisture-absorbing / releasing fibers includes moisture-absorbing / absorbing fibers obtained by adding crosslinks and carboxyl groups to acrylic fibers and adding sodium ions, polyester binder fibers, and softwood pulp. A moisture-releasing paper or the like is known (see Patent Document 1). The moisture-absorbing / releasing fibers can contain a large amount of carboxyl groups, so that they have excellent moisture-absorbing / releasing properties, and can suppress the swelling of fibers more than ordinary moisture-absorbing / releasing fibers by crosslinking. Therefore, the dimensional stability of the moisture-absorbing / releasing paper can be maintained with a small amount of use. However, when the amount used is increased in order to obtain a moisture-absorbing / releasing paper having a high moisture absorption rate, the swelling suppression effect cannot be said to be sufficient, and a reduction in dimensional stability is inevitable. For this reason, in the moisture-absorbing / releasing paper disclosed in this document, dimensional stability is improved by using a large amount of binder fibers or by applying a hot press after making the paper. However, if a large amount of binder fiber is used, the moisture absorbing / releasing fiber is covered and bound by the fused binder fiber, so even if the moisture absorbing / releasing property of the moisture absorbing / releasing fiber is excellent, its performance is fully demonstrated. Therefore, it is difficult to improve the moisture absorption / release properties of the moisture absorbent paper.

Known examples of utilizing fine particles having moisture absorption / release properties include inorganic particles such as silica gel and zeolite, moisture absorption / release paper made of wood pulp and heat-fusible fibers (see Patent Document 2). The moisture-absorbing / releasing paper is excellent in terms of dimensional stability because inorganic particles such as silica gel and zeolite, which are responsible for moisture-absorbing / releasing properties, do not swell even when they absorb moisture. However, as described above, since the inorganic particles have a low moisture absorption amount, it is difficult to obtain a highly moisture-absorbing and moisture-absorbing paper, and the moisture absorption rate is slow, a high temperature is required for moisture desorption, or repeated moisture absorption and desorption There is a problem that the field of use is limited due to the drawbacks such as crushing to cause performance degradation.
JP-A-6-207398 Japanese Patent Laid-Open No. 10-212692

As described above, in the prior art, it has been extremely difficult to obtain moisture-absorbing / releasing paper having both high moisture-absorbing / releasing properties and high dimensional stability. An object of the present invention is to provide a moisture-absorbing / releasing paper and a method for producing the same that can achieve both high moisture-absorbing / releasing properties and high dimensional stability that overcomes such problems.

As a result of diligent investigation to achieve the above-mentioned object, the present inventor suppresses the amount of binder fibers used by adopting inorganic fibers having excellent dimensional stability, and in addition, as a substance having moisture absorption / release properties Adopting a fiber having a cross-linked structure and an acidic group, and making the fiber absorb and release moisture as much as possible even after papermaking by devising the papermaking method, achieving both high moisture absorption and release and high dimensional stability. The present inventors have found that a moisture-absorbing and releasing paper can be obtained, and have reached the present invention.

That is, the present invention is achieved by the following means.
(1) It has a crosslinked structure and 1 to 10 mmol / g acidic group, and the acidic group contains at least 1 mmol / g or more of metal ions selected from the group consisting of Li, Na, K, Mg, and Ca. A cation excluding metal ions bonded to the acidic group, which is a moisture absorbent paper composed of bonded fibers (hereinafter also referred to as fibers having a crosslinked structure and acidic groups), inorganic fibers, and pulp-like fibers. An aqueous slurry containing a fiber having a crosslinked structure and an acidic group, an inorganic fiber, and a pulp-like fiber was prepared using water having a concentration of 1 ppm or less, and the paper was made and has a crosslinked structure and an acidic group. fibers, are acrylic acid type moisture absorptive and desorptive fiber consisting subjected to hydrolysis treatment with acrylonitrile fiber crosslinking introducing treatment by a hydrazine compound and an alkali metal salt Absorbing and wet paper characterized the door.
( 2 ) The moisture absorbing / releasing paper according to ( 1 ), wherein a part or all of the fiber having a crosslinked structure and an acidic group is fibrillated.
( 3 ) The moisture absorbent paper according to (1) or (2) , wherein the pulp-like fiber is a fibrillated acrylic fiber.
( 4 ) The moisture-absorbing / releasing paper according to any one of (1) to ( 3 ), wherein a saturated moisture absorption rate in a 20 ° C.-65% RH atmosphere is 15% or more.
( 5 ) The moisture-absorbing / releasing paper according to any one of (1) to ( 4 ), wherein the content of the heat-fusible fiber is 20% by weight or less.
( 6 ) The moisture absorbing / releasing paper according to any one of (1) to ( 5 ), wherein the water swelling rate is 50% or less.
( 7 ) having a crosslinked structure and 1 to 10 mmol / g acidic group, and at least 1 mmol / g or more of metal ions of at least one metal selected from the group consisting of Li, Na, K, Mg and Ca in the acidic group In the preparation of an aqueous slurry containing bonded fibers, inorganic fibers, and pulp-like fibers, and in the papermaking process by a wet papermaking method using the aqueous slurry, metal ions bonded to the acidic groups are removed. Water having a cation concentration of 1 ppm or less is used. The method for producing a moisture absorbent paper according to any one of (1) to ( 6 ).

The moisture-absorbing / releasing paper of the present invention has both high moisture-absorbing / releasing properties and high dimensional stability. Therefore, even in applications where the moisture-absorbing / releasing properties must be suppressed to maintain the dimensions, It is possible to provide moisture release. Further, since the change in dimensions due to repeated moisture absorption and desorption is small, the moisture absorption and desorption paper itself has high durability and can be suitably used for a moisture absorption element for a dehumidifying air conditioner.

The present invention is described in detail below. The moisture-absorbing / releasing paper of the present invention has a cross-linked structure and an acidic group of 1 to 10 mmol / g, and the acidic group has at least one metal selected from the group consisting of Li, Na, K, Mg, and Ca. A moisture-absorbing / releasing paper composed of fibers (hereinafter also referred to as fibers having a crosslinked structure and acidic groups) in which ions are bonded at 1 mmol / g or more, inorganic fibers, and pulp-like fibers, and bonded to the acidic groups. An aqueous slurry containing a fiber having a cross-linked structure and an acidic group, an inorganic fiber, and a pulp-like fiber is prepared using water having a cation concentration excluding metal ions of 1 ppm or less, and is made into paper.

The fiber having a crosslinked structure and an acidic group according to the present invention is a main component responsible for moisture absorption / release in the moisture absorbent paper of the present invention. Typical examples of the acidic group include a carboxyl group and a sulfonic acid group. These acidic groups copolymerize monomers containing these acidic groups when polymerizing the polymer constituting the fiber, or, in the case of carboxyl groups, contain nitrile groups or carboxylic acid esters. The monomer can be introduced by copolymerization and then hydrolysis.

Moreover, the amount of acidic groups in the fiber having a crosslinked structure and acidic groups is 1 to 10 mmol / g, preferably 3 to 10 mmol / g, more preferably 3 to 8 mmol / g. When the amount of acidic groups is less than 1 mmol / g, only a small amount of metal ions described below can be bound, so that sufficient moisture absorption / release properties may not be obtained, and when the amount exceeds 10 mmol / g. In some cases, the swelling during moisture absorption becomes severe and the dimensional stability of the moisture-absorbing / releasing paper becomes insufficient, or the fiber physical properties that are practically satisfactory cannot be obtained.

Furthermore, at least part of the acidic groups in the fiber having a crosslinked structure and acidic groups is bound with metal ions of at least one metal selected from the group consisting of Li, Na, K, Mg, and Ca. is required. By adopting these metal ions, it is possible to exhibit high moisture absorption / release properties. In particular, when sodium ions are employed, the saturated moisture absorption amount can be excellent, and when potassium ions are employed, the moisture absorption / release rate can be excellent.

In order to obtain moisture absorption and desorption, the total amount of the metal ions is desirably 1 mmol / g or more. That is, if sodium ions and potassium ions are bonded, the total amount of sodium ions and potassium ions is preferably 1 mmol / g or more. In addition, about the upper limit of the coupling | bonding amount, it is the maximum amount which can couple | bond with the acidic group in the fiber which has a crosslinked structure and an acidic group.

In addition, even when the amount of acidic groups is greater than 1 mmol / g in the fiber having a crosslinked structure and acidic groups, moisture absorption and desorption can be obtained if the metal ions are bonded at 1 mmol / g as described above. However, many acidic groups are present without effectively utilizing their potential moisture absorption / release properties, and the advantage of having a large amount of acid groups does not appear on the moisture absorption / release properties. In order to realize this advantage, it is desirable that metal ions are bonded to at least 50 mol% or more, preferably 70 mol% or more of the entire acidic group.

Since the metal ion bonded to the acidic group in the fiber having a crosslinked structure and an acidic group described above has an ionic bond with the acidic group, after making the paper raw material into an aqueous slurry having a concentration of 1 to 3% by weight, Further, when a large amount of water is used as in the so-called paper making process in which the paper is diluted to 0.1 to 1% by weight, the metal ions may exchange with other cations present in the water. For this reason, in making the moisture-absorbing / releasing paper of the present invention, it is necessary to consider such exchange with other cations.

That is, in the case of the wet papermaking method, it is important to use water having a cation concentration of 1 ppm or less excluding metal ions bonded to acidic groups in the preparation of the aqueous slurry and the subsequent papermaking process. Here, water having a cation concentration of 1 ppm or less excluding metal ions bonded to acidic groups is, for example, when other ions than sodium ions are excluded if sodium ions are bonded to acidic groups. It refers to water with a total concentration of 1 ppm or less. With such water, exchange between the metal ion bonded to the acidic group and another cation can be minimized. On the other hand, if water containing a large amount of cations such as industrial water, such as about 50 to 100 ppm, is used, exchange with other cations occurs to some extent, and in some cases, the desired moisture absorption / release properties cannot be obtained. Sometimes.

It is recommended to use distilled water or ion-exchanged water as water having a cation concentration of 1 ppm or less excluding metal ions bonded to acidic groups. These have little influence on moisture absorption and desorption, and are easy to use industrially. In the present invention, ion-exchanged water refers to water having a conductivity of 3 μS / cm or less. Usually, in the case of 3 μS / cm, the total cation concentration is about 0.6 ppm. Moreover, not only distilled water and ion-exchanged water but also water containing only the same ions as the metal ions bonded to the acidic group can be used.

In the fiber having a crosslinked structure and an acidic group according to the present invention, since the polymers constituting the fiber are linked to each other by the crosslinked structure, swelling at the time of moisture absorption can be suppressed.

As the fiber having a cross-linked structure and an acidic group, an acrylic acid-based moisture absorbing / releasing fiber obtained by subjecting an acrylonitrile-based fiber to a cross-linking introduction treatment with a hydrazine compound and a hydrolysis treatment with an alkali metal salt is employed . The fiber is relatively easy to adjust the amount of the cross-linked structure and the amount of carboxyl groups, and can contain a large amount of carboxyl groups, so that the moisture absorption and release properties and dimensional stability required for moisture absorbent paper are improved. It can respond flexibly. The acrylic acid-based moisture absorbing / releasing fiber will be described in detail below.

The acrylonitrile fiber used as the raw fiber of the acrylic acid-based moisture-absorbing / releasing fiber is an acrylonitrile copolymer containing acrylonitrile homopolymer or acrylonitrile in an amount of 40% by weight or more, preferably 50% by weight or more, more preferably 80% by weight or more. A fiber formed by coalescence can be employed. The monomer copolymerized with acrylonitrile is not particularly limited and may be appropriately selected.

The acrylonitrile fiber is subjected to a crosslinking introduction treatment with a hydrazine compound. In this treatment, a nitrile group of the acrylonitrile fiber reacts with an amino group of the hydrazine compound to form a crosslinked structure. Nitrogen content increases. This increase in nitrogen content is a measure of the degree of crosslinking, but when employed in the moisture-absorbing and releasing paper of the present invention, it is preferably 1.0 to 10% by weight.

As a method for adjusting the increase in nitrogen content to 1.0 to 10% by weight, the above-mentioned acrylonitrile fiber is used in an aqueous solution having a hydrazine compound concentration of 5 to 60% by weight at a temperature of 50 to 120 ° C. within 5 hours. The method of treating with is industrially preferred.

The hydrazine-based compound used here is not particularly limited, and hydrazine derivatives such as hydrazine hydrate, hydrazine sulfate, hydrazine hydrochloride, hydrazine hydrobromide, hydrazine carbonate, ethylenediamine, guanidine sulfate, guanidine hydrochloride, and phosphoric acid. Examples thereof include compounds containing a plurality of amino groups such as guanidine and melamine.

The fiber subjected to the cross-linking introduction treatment with the hydrazine compound may be subjected to an acid treatment after sufficiently removing the hydrazine compound remaining in the treatment. The acid used here is not particularly limited, and examples thereof include mineral acids such as nitric acid, sulfuric acid, and hydrochloric acid, and organic acids. The conditions for the acid treatment are not particularly limited, but the treated fiber is immersed in an aqueous solution having an acid concentration of 3 to 20% by weight, preferably 7 to 15% by weight, at a temperature of 50 to 120 ° C. for 0.5 to 10 hours. Examples are given.

The fiber that has undergone the cross-linking introduction treatment with the hydrazine-based compound or the fiber that has undergone the acid treatment is subsequently subjected to a hydrolysis treatment with an alkaline metal salt. By this hydrolysis treatment, the nitrile group remaining without being involved in the cross-linking introduction treatment with the hydrazine-based compound, or the residual nitrile group in the case of performing the acid treatment after the cross-linking introduction treatment, is partially acid-treated. The amide group generated by hydrolysis is converted into a carboxyl group, and the carboxyl group is in a state in which a metal ion corresponding to the alkaline metal salt used is bonded.

Examples of the alkaline metal salt used here include alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal carbonates, etc., and the metal species include alkali metals such as Li, Na, and K, Mg, Mention may be made of alkaline earth metals such as Ca.

The amount of the carboxyl group generated by the hydrolysis treatment is 1 to 10 mmol / g, preferably 3 to 10 mmol / g, more preferably 3 to 8 mmol / g. When the amount of the carboxyl group is less than 1 mmol / g, sufficient moisture absorption / release characteristics may not be obtained. When the amount exceeds 10 mmol / g, the swelling during moisture absorption becomes severe and the dimensions of the moisture absorption / release paper. There may be problems such as insufficient stability or failure to obtain fiber properties that are practically satisfactory.

The conditions for the hydrolysis treatment may be appropriately set so that a necessary amount of carboxyl groups is generated, but preferably 0.5 to 10% by weight, more preferably 1 to 5% by weight in an aqueous alkaline metal salt solution, A method of treating at a temperature of 50 to 120 ° C. for 1 to 10 hours is preferable from an industrial and fiber property viewpoint. The fiber that has undergone the hydrolysis treatment may or may not have a nitrile group remaining. If the nitrile group remains, there is a possibility that a further function can be imparted using its reactivity.

The fiber subjected to the hydrolysis treatment may be subjected to a treatment for adjusting a metal ion to be bonded to a carboxyl group using a metal salt, if necessary. The metal species of the metal salt employed in the metal ion adjustment treatment is selected from Li, Na, K, Ca, and Mg, and Na, K, and Ca are particularly recommended. The salt used for the treatment may be a water-soluble salt of these metals, and examples thereof include hydroxides, halides, nitrates, sulfates and carbonates. Specifically, as typical metals, NaOH, Na ₂ CO ₃ as Na salt, KOH as K salt, Ca (OH) ₂ , Ca (NO ₃ ) ₂ , CaCl as Ca salt ₂ is preferred.

In addition, as described above, the metal ion to be bonded to the carboxyl group of the acrylic acid-based moisture-absorbing / releasing fiber is sodium ion for increasing the saturated moisture absorption amount, and potassium ion for increasing the moisture absorption / release rate. It is desirable.

Further, the acrylic acid-based moisture-absorbing / releasing fiber has been subjected to further treatment in addition to the above-described cross-linking introduction treatment with a hydrazine-based compound, acid treatment, hydrolysis treatment with an alkali metal salt, and metal ion adjustment treatment. Alternatively, the cross-linking introduction treatment and the hydrolysis treatment may be performed at the same time.

Furthermore, it is more desirable that a part or all of the fiber having a crosslinked structure and acidic group according to the present invention is fibrillated. If some or all of the fibers having a cross-linked structure and acidic groups are fibrillated, the entanglement between fibers becomes stronger when paper is made, and the resulting moisture-absorbing paper is more excellent in dimensional stability. Can be. Further, since the surface area is increased by subdividing the fibers, the moisture absorption rate can be improved. In addition, as a method for obtaining the fibrillated fiber for the above-described acrylic acid-based moisture-absorbing / releasing fiber, in addition to the method for directly fibrillating the acrylic acid-based moisture-absorbing / releasing fiber obtained by the above method, raw fiber It is possible to employ a method in which the above-described treatment is performed after fibrillation of the acrylonitrile-based fiber.

There is no restriction | limiting in particular as the method of fibrillation, A normal beating method can be employ | adopted. A typical example is a fibrillation method using a beater such as a beater or refiner.

As mentioned above, although the fiber which has a crosslinked structure and an acidic group has been described, even if it is a fiber which has a crosslinked structure and an acidic group as mentioned above, a certain amount of dimensional change occurs by moisture absorption / release or heating. For this reason, it is extremely difficult to construct the moisture-absorbing / releasing paper of the present invention, which is intended to exhibit high dimensional stability, only with fibers having a crosslinked structure and acidic groups. Therefore, in the present invention, inorganic fibers are used in combination as a measure for developing high dimensional stability. Inorganic fibers are extremely effective in improving the dimensional stability of moisture-absorbing / releasing paper, since the dimensional change due to moisture-absorbing / releasing and heating is extremely small. Such inorganic fibers are not particularly limited, and examples thereof include glass fibers, carbon fibers, alumina fibers, and metal fibers.

In the present invention, a pulp-like fiber is used in addition to a fiber having a crosslinked structure and an acidic group and an inorganic fiber. If pulp-like fibers are not used, the entanglement between the fibers will be insufficient, and the restraint of each fiber will be loosened. It becomes difficult. The pulp fiber is not particularly limited, and wood pulp such as softwood pulp and hardwood pulp, non-wood pulp such as hemp pulp, cotton pulp and kenaf pulp, and fibrillated synthetic fiber such as rayon, vinylon and acrylic. Can be adopted. In particular, when acrylic pulp is used, water resistance increases compared to cellulosic pulp, and a paper having high strength when containing water can be obtained, so durability such as repeated moisture absorption and desorption is required. Suitable for use.

Needless to say, the fibrillated cross-linked structure and the fiber having an acidic group can also be used as the pulp-like fiber. In this case, since the amount of the fiber having a cross-linked structure and an acidic group that substantially constitute the moisture-absorbing / releasing paper is increased, it is possible to exhibit high moisture-absorbing / releasing properties. Furthermore, if the cross-linked structure and the fiber having the acidic group and the fiber having the acidic group are fibrillated in both the fiber having the cross-linked structure and the acidic group, the moisture absorption and release can be further improved and the dimensional stability is improved. It is also possible to make it.

As described above, the fiber having a crosslinked structure and an acidic group, the inorganic fiber, and the pulp-like fiber, which are constituents of the moisture-absorbing and releasing paper of the present invention, have been described. It is desirable that the fiber having a crosslinked structure and an acidic group is 5 to 80% by weight, the inorganic fiber is 10 to 40% by weight, and the pulp-like fiber is 10 to 55% by weight. Outside these ranges, it may be impossible to achieve both high moisture absorption and release and high dimensional stability.

Further, in the case where higher dimensional stability is desired, it is possible to use a heat-fusible fiber in addition to the above-described configuration. The heat-fusible fiber is not particularly limited, and synthetic fibers such as polyester, polyethylene, polypropylene, polyamide, and vinylon can be used. However, the heat-fusible fiber is not sufficient for its use because it reduces the moisture absorption / release property by covering or constraining the fiber having a crosslinked structure and an acidic group when heat-sealing. Care should be taken and it is desirable not to use it if possible. Even when it is unavoidably used, it is desirable that the amount used be 20% by weight or less, more preferably 10% by weight or less, and still more preferably 5% by weight or less.

The moisture-absorbing / releasing paper of the present invention uses other natural fibers or synthetic fibers in addition to the above-mentioned fibers having a crosslinked structure and acidic groups, inorganic fibers, pulp-like fibers, and heat-fusible fibers. It goes without saying that it doesn't matter.

The saturated moisture absorption rate of the moisture-absorbing / releasing paper of the present invention is preferably 15% or more, more preferably 20% or more in a 20 ° C.-65% RH atmosphere. When the saturated moisture absorption is 15% or less, it is not very useful as a moisture absorbent paper. Furthermore, the water swelling rate of the moisture-absorbing / releasing paper of the present invention is preferably 50% or less, more preferably 40% or less. When the water swelling rate is 50% or more, the change in dimensions at the time of moisture absorption and moisture release becomes too large, so that there are many applications that cannot be used. In addition, the saturated moisture absorption rate and water swelling rate said to this invention are calculated | required by the measuring method mentioned later.

Next, the manufacturing method of the moisture absorption / release paper of this invention is demonstrated. In general, the following wet papermaking methods can be employed.

First, it has a crosslinked structure and an acidic group of 1 to 10 mmol / g, and metal ions of at least one metal selected from the group consisting of Li, Na, K, Mg, and Ca are bonded to the acidic group in an amount of 1 mmol / g or more. The fibers, inorganic fibers, and pulp fibers are uniformly mixed and dispersed in water to form an aqueous slurry. Next, the aqueous slurry is subjected to paper making using a paper machine such as a circular net, a short net, a long net, or a composite machine thereof. After paper making, the moisture-absorbing / releasing paper of the present invention can be obtained by drying using a normal dryer such as a cylinder dryer, Yankee dryer or air dryer. Here, as the water used in the aqueous slurry and the papermaking process, as described above, water having a cation concentration of 1 ppm or less excluding metal ions bonded to acidic groups is used. It is preferred to use distilled water.

In the above-described production method, other fibers, a sticking agent used in normal wet papermaking, a sizing agent, a dye, a paper strength enhancer, and the like may be added to the aqueous slurry. If necessary, a fixing agent can be added in order to suppress the loss of the filler. Examples of the fixing agent include polyethyleneimine modified products, polyacrylamide modified products, sodium alginate, gum arabic, positive starch, aluminum sulfate, and potassium alum.

EXAMPLES Hereinafter, the present invention will be specifically described by way of examples. However, these are merely illustrative, and the gist of the present invention is not limited thereto. In addition, unless otherwise indicated, the part and percentage in an Example are shown on a weight basis. In addition, the ion-exchanged water in the examples has a cation concentration of 0.6 ppm. The measurement methods and evaluation methods in the examples are shown below.

(1) Amount of acidic groups (total amount of carboxyl groups)
About 1 g of a well-dried sample is precisely weighed (W1 [g]), 200 ml of water is added thereto, 1 mol / l hydrochloric acid aqueous solution is added to the mixture while being heated to 50 ° C. to pH 2, and then 0.1 mol A titration curve was determined according to a conventional method with an aqueous / 1 sodium hydroxide solution. From the titration curve, the amount of aqueous sodium hydroxide consumed (V1 [ml]) consumed by carboxyl groups was determined, and the total amount of carboxyl groups (A1 [mmol / g]) was calculated according to the following equation.

Total carboxyl group amount [mmol / g] = 0.1 × V1 / W1

(2) Amount of metal ion-bonded carboxyl groups The titration curve was determined in the same manner without adjusting to pH 2 by adding a 1 mol / l aqueous hydrochloric acid solution during the above total carboxyl group content measurement procedure, and H-type carboxyl groups contained in the sample. The amount of (COOH) (A2 [mmol / g]) was determined. From these results, the amount of carboxyl groups bound to metal ions was calculated by the following formula.

Metal ion bond carboxyl group amount [mmol / g] = A1-A2

(3) The amount of metal ions was precisely weighed and then wet-decomposed, and the amount of metal ions was determined using an atomic absorption method.

(4) About 5.0 g of saturated moisture absorption sample is absolutely dried and the weight is measured (W2 [g]). Next, the sample is placed in a constant humidity bath at a temperature of 20 ° C. and 65% RH for 24 hours. The weight of the sample thus absorbed is measured (W3 [g]). From the above measurement results, calculation was performed according to the following equation.

Saturated moisture absorption [%] = (W3-W2) / W2 × 100

(5) The water swelling rate sample is absolutely dried and the thickness is measured (T1). The sample was immersed in water for 24 hours, then dehydrated with a centrifugal dehydrator (TYPE H-770A manufactured by Kokusan Centrifuge Co., Ltd.) for 2 minutes under a centrifugal acceleration of 160G (G indicates gravitational acceleration), and the thickness was measured again. (T2). From these measured values, it calculated by the following formula.

Water swelling rate [%] = (T2-T1) / T1 × 100

Moreover, the preparation method of the fiber and acrylic pulp which have a crosslinked structure and an acidic group in an Example is as follows.

<Fiber A having cross-linked structure and acidic group>
A spinning stock solution in which 10 parts of an acrylonitrile polymer consisting of 90% by weight of acrylonitrile and 10% by weight of vinyl acetate was dissolved in 90 parts of a 48% aqueous sodium thiocyanate solution was spun and stretched according to a conventional method (total stretching ratio: 10 times). Thereafter, after drying in an atmosphere of dry bulb / wet bulb = 120 ° C./60° C., through wet heat treatment and cutting, a raw fiber a having a fiber length of 7 mm and a single fiber fineness of 0.9 dtex was obtained. The raw fiber a was subjected to 98 ° C. × 5 Hr cross-linking introduction treatment in a 20 wt% aqueous solution of hydrazine and washed with water. Next, 90 ° C. × 2 Hr acid treatment was performed in a 3 wt% aqueous solution of nitric acid. Subsequently, hydrolysis was performed at 90 ° C. × 2 Hr in a 1% by weight aqueous solution of sodium hydroxide and washed with ion-exchanged water to obtain a fiber of fiber A having a crosslinked structure and acidic groups. The fiber had an acid group amount of 1.2 mmol / g, a metal ion-bonded carboxyl group amount of 1.1 mmol / g, and a sodium ion amount of 1.1 mmol / g.

<Fiber B having cross-linked structure and acidic group>
A fiber B having a crosslinked structure and an acidic group was obtained in the same manner as the fiber A having a crosslinked structure and an acidic group, except that the raw material fiber a was hydrolyzed with a 3% by weight aqueous solution of potassium hydroxide. The fiber had an acid group amount of 6.1 mmol / g, a metal ion-bonded carboxyl group amount of 5.4 mmol / g, and a potassium ion amount of 5.3 mmol / g.

<Fiber C having crosslinked structure and acidic group>
A fiber C having a crosslinked structure and an acidic group was obtained in the same manner as the fiber A having a crosslinked structure and an acidic group, except that the raw material fiber a was hydrolyzed with a 10% by weight aqueous solution of sodium hydroxide. The fiber had an acid group amount of 8.8 mmol / g, a metal ion-bonded carboxyl group amount of 7.7 mmol / g, and a sodium ion amount of 7.9 mmol / g.

<Fiber D having cross-linked structure and acidic group>
A raw material fiber having a single fiber fineness of 0.9 dtex is obtained by dissolving a spinning stock solution obtained by dissolving 10 parts of acrylonitrile-based polymer composed of 98% by weight of acrylonitrile and 2% by weight of acrylic acid in 90 parts of a 48% rhodium soda aqueous solution by a wet spinning method according to a conventional method. d was obtained. Next, the raw fiber d was cut into 5 mm, and then beaten using a Niagara-type beater (type BE-10) manufactured by Kumagai Riki Kogyo Co., Ltd. to prepare a fibrillated raw fiber d having a Canadian standard freeness of 180 ml. The fibrillated raw fiber d was subjected to 98 ° C. × 5 Hr cross-linking introduction treatment in a 20 wt% aqueous solution of hydrazine and washed with water. Next, 90 ° C. × 2 Hr acid treatment was performed in a 3 wt% aqueous solution of nitric acid. Subsequently, a hydrolysis treatment was performed at 90 ° C. × 2 Hr in a 3 wt% aqueous solution of potassium hydroxide and washed with ion-exchanged water to obtain a fiber D having a crosslinked structure and an acidic group. The fiber contained an acid group amount of 5.8 mmol / g, a metal ion-bonded carboxyl group amount of 5.2 mmol / g, and a potassium ion amount of 5.3 mmol / g.

[Examples 1 to 5]
Fibers having a crosslinked structure and acidic groups in the proportions shown in Table 1, inorganic fibers, pulp-like fibers and heat-fusible fibers were dispersed in ion-exchanged water to prepare an aqueous slurry having a concentration of 0.5%. Papermaking the prepared aqueous slurry using a square sheet machine manufactured by Kumagaya Riki Kogyo Co., Ltd., sandwiching between the filter papers, and drying at 145 ° C. using a rotary dryer manufactured by Kumagaya Riki Kogyo Co., Ltd. A moisture-absorbing / releasing paper was prepared. With respect to the obtained moisture absorbing / releasing paper, the water swelling rate was measured as an index of dimensional stability, and the saturated moisture absorption rate was measured as an index of moisture absorbing / releasing property. These evaluation results are shown in Table 1. In addition, the detail of the inorganic fiber in the table | surface, a pulp-like fiber, and a heat-fusible fiber is as follows.
・ Glass fiber: Fiber diameter 6μm, fiber length 6mm
・ Bi-PUL: Nippon Exlan Industrial Co., Ltd. acrylic pulp, Canadian standard freeness 150ml
・ Conifer kraft pulp: Canadian standard freeness 600ml
・ VPB-105: Kuraray Co., Ltd. vinylon binder fiber, fineness 1T, fiber length 3mm

All of the moisture absorbent papers of Examples 1 to 5 had a low water swelling rate and a high saturated moisture absorption rate. In particular, the moisture-absorbing / releasing paper of Example 5 uses a fibrillated fiber having a cross-linked structure and an acidic group, and since the entanglement of the fibers is strong, the moisture absorption paper of Example 2 having an equivalent saturated moisture absorption rate. It seems that the water swelling rate is lower than that of moisture-absorbing and releasing paper.

[Comparative Examples 1-3]
In the same manner as in Examples 1 to 5, moisture-absorbing and releasing paper was prepared from fibers having a cross-linked structure and acidic groups, inorganic fibers, pulp-like fibers, and heat-fusible fibers in the proportions shown in Table 2. Table 2 shows the evaluation results of the moisture absorbent paper obtained. In addition, about the comparative example 3, it replaced with ion-exchange water and used industrial water.

In Comparative Example 1, although pulp-like fibers were increased, it was considered that water swelling could not be sufficiently suppressed because inorganic fibers were not used. In Comparative Example 2, the amount of heat-fusible fiber used was increased, so that the water swelling rate could be suppressed. However, since the inhibition of moisture absorption by the heat-fusible fiber was increased, the saturated moisture absorption rate was greatly reduced. It seems to have done. The moisture-absorbing / releasing paper of Comparative Example 3 has exactly the same fiber configuration as that of Example 1, but was prepared using industrial water. Therefore, the sodium ion of fiber A having a cation, a crosslinked structure, and an acidic group in industrial water. Seems to have caused ion exchange and reduced saturated moisture absorption.

Claims (7)

It has a crosslinked structure and an acidic group of 1 to 10 mmol / g, and metal ions of at least one metal selected from the group consisting of Li, Na, K, Mg, and Ca are bonded to the acidic group by 1 mmol / g or more. A moisture absorbing / releasing paper composed of fibers (hereinafter also referred to as fibers having a crosslinked structure and acidic groups), inorganic fibers, and pulp-like fibers, and having a cation concentration of 1 ppm excluding metal ions bound to the acidic groups Using the following water, a fiber having a crosslinked structure and an acidic group, an inorganic fiber, and an aqueous slurry containing a pulp-like fiber were prepared and paper-made, and the fiber having a crosslinked structure and an acidic group was that the acrylonitrile fiber acrylic becomes subjected to hydrolysis treatment with hydrazine-based crosslinking introducing treatment and alkali metal salts with the compounds in hygroscopicity fibers Absorbing and wet paper and butterfly. 2. The moisture-absorbing / releasing paper according to claim 1 , wherein a part or all of the fiber having a crosslinked structure and an acidic group is fibrillated. The moisture-absorbing / releasing paper according to claim 1 or 2 , wherein the pulp-like fibers are fibrillated acrylic fibers. The moisture-absorbing / releasing paper according to any one of claims 1 to 3, wherein a saturated moisture absorption rate in a 20 ° C-65% RH atmosphere is 15% or more. The moisture-absorbing / releasing paper according to any one of claims 1 to 4 , wherein the content of the heat-fusible fiber is 20% by weight or less. The moisture-absorbing / releasing paper according to any one of claims 1 to 5 , wherein the water swelling rate is 50% or less. It has a crosslinked structure and an acidic group of 1 to 10 mmol / g, and metal ions of at least one metal selected from the group consisting of Li, Na, K, Mg, and Ca are bonded to the acidic group by 1 mmol / g or more. Cation concentration excluding metal ions bound to the acidic groups in the preparation of aqueous slurry containing fibers, inorganic fibers, and pulp-like fibers, and in the papermaking process by wet papermaking using the aqueous slurry The method for producing moisture-absorbing and releasing paper according to any one of claims 1 to 6 , wherein water having a concentration of 1 ppm or less is used.