JP3783555B2 - Hygroscopic material and method for producing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention absorbs and absorbs moisture in the ambient air when the humidity is high, and dissipates the moisture absorbed in the ambient air when the humidity is low, thereby reducing moisture fluctuations in the ambient air. It relates to materials and is particularly useful as an interior material for buildings.
[0002]
[Prior art]
Modern buildings are remarkably airtight compared to former Japanese architecture due to the spread of reinforced concrete structures and prefabricated construction methods, new building materials made of synthetic materials such as resin-processed plywood, and the development of metal sashes on doors and windows. It is expensive. It can be said that the high airtightness of such a building is very desirable from the viewpoints of saving energy resources by improving the cooling and heating effect and preventing noise pollution by improving soundproofing. On the other hand, the moisture generated by the resident's daily activities (human exhalation, cooking, bathing, showering, etc.) in the room can easily be trapped in the room without escaping to the outside, and the moisture that has lost its place can be removed from the walls and windows. Condensation on the surface of glass, window frame sashes, etc. is not only aesthetically and tactilely undesired, but it can cause building materials to become dirty and corroded, and can also shorten the life of buildings. is there.
[0003]
As a solution to this problem, methods such as installing a forced ventilation device or air conditioner in a building to keep the indoor humidity within a certain range have been studied in some areas. In order to make forced ventilation or air conditioning for the entire interior of the building including the storage space, the initial capital investment burden becomes significantly heavy, and the equipment is operated for 24 hours including at night and when going out. However, it is not considered to be a very practical method for general households because the burden of electricity costs is heavy, and the maintenance and maintenance of facilities are also expensive.
[0004]
Therefore, as a method of adjusting the humidity in the room without using special equipment as described above, the function of absorbing moisture in the ambient air at high humidity while releasing the moisture absorbed in the ambient air at low humidity. A method has been devised in which moisture absorption / release materials are installed in a room to mitigate indoor humidity fluctuations. Although various modes of installation of the moisture absorbing / releasing material are conceivable, it is considered that the larger the surface area in contact with the environmental air, the more advantageous in order to quickly and sufficiently exhibit the moisture absorbing / releasing function. The most promising method is to finish wall surfaces, ceiling surfaces, and the like that occupy a large surface area in the interior of an object with interior materials such as wallpaper using a hygroscopic material.
[0005]
Specifically, the wallpaper using the moisture absorbing / releasing material is, for example, a normal wallpaper in which a foamed resin layer such as polyvinyl chloride resin is provided on a backing paper such as a flame retardant paper. Alternatively, a material having moisture absorption / release properties has been devised by blending a hygroscopic inorganic powder such as zeolite, or a highly water-absorbing polymer such as acrylic resin or polyvinyl alcohol resin. However, those using hygroscopic inorganic powders have a small absolute amount of moisture absorption, so the ability to alleviate indoor humidity fluctuations is not always sufficient, and in that respect, a superabsorbent polymer with a large absolute amount of water absorption. On the other hand, because the highly water-absorbing polymer swells and softens due to water absorption, the surface of the wallpaper is easily sticky at high humidity. There are problems such as being easily deformed and scratched.
[0006]
In order to solve such problems, a protective layer made of a resin composition that does not contain a superabsorbent polymer and does not easily deteriorate in strength even at high humidity on the surface of the hygroscopic resin layer containing a superabsorbent polymer. It is also conceivable to provide However, if the surface of the hygroscopic resin layer is covered with a protective layer made of a hydrophobic resin with excellent water resistance, the protective layer will transfer moisture between the ambient air and the hygroscopic resin layer. Since it is difficult to obtain sufficient moisture absorption / release properties, it is considered desirable to form the protective layer with a highly moisture-permeable aqueous resin. However, when an aqueous coating solution composed of an aqueous resin aqueous solution or aqueous dispersion is applied to the surface of the hygroscopic resin layer to provide a protective layer, during application of the aqueous coating solution, Since the water contained in the aqueous coating solution is absorbed by the highly water-absorbing polymer in the hygroscopic resin layer and swells, there is a problem that a good coating state cannot be obtained.
[0007]
[Problems to be solved by the invention]
The present invention has been made paying attention to the above-mentioned problems in the prior art, and the problem is that it has excellent moisture absorption and desorption properties and has a sticky surface even at high humidity. Another object of the present invention is to provide a moisture-absorbing / releasing material and a method for producing the same, which can easily produce a product having a good surface condition without being easily damaged.
[0008]
[Means for Solving the Problems]
The moisture-absorbing / releasing material of the present invention is characterized in that a moisture-absorbing / releasing resin layer containing a water-absorbing substance, a moisture-permeable waterproof resin film, and an aqueous resin layer are sequentially provided on a substrate. In particular, the aqueous resin layer is a foamed layer.
[0009]
In the method for producing a moisture absorbing / releasing material of the present invention, a moisture absorbing / releasing resin layer containing a water absorbing substance is formed on a substrate, a moisture permeable waterproof resin film is formed on the moisture absorbing / releasing resin layer, and thereafter , Characterized in that an aqueous coating solution containing an aqueous resin is applied onto the moisture-permeable waterproof resin coating to provide an aqueous resin layer, and in particular, an aqueous coating solution containing the aqueous resin. Is added with a foaming agent, and the water-based resin layer is formed into a foamed layer by heating and foaming after coating on the moisture-permeable waterproof resin film.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing an embodiment of a hygroscopic material of the present invention.
[0011]
As shown in FIG. 1, the moisture absorbing / releasing material of the present invention comprises a resin composition containing a water absorbing substance 21 such as a super absorbent polymer on the surface of an appropriate base material 1 serving as a support. The moisture resin layer 2 has moisture permeability that does not hinder the movement of moisture between the moisture-absorbing / releasing moisture resin layer 2 and the ambient air. Moisture-permeable waterproof resin film 3 having waterproof properties to the extent that moisture can be prevented from penetrating into moisture-absorbing / releasing resin layer 2, and water-based resin having high moisture permeability that does not interfere with the moisture-absorbing / releasing function of moisture-absorbing and releasing resin layer An aqueous resin layer 4 as a protective layer made of the composition is provided and configured in this order.
[0012]
The specific material and shape of the base material 1 in the moisture-absorbing / releasing material of the present invention are not limited at all. For example, a fibrous sheet such as paper, woven fabric or non-woven fabric, a polyolefin resin sheet or a polyester resin Synthetic resin sheets such as sheets, synthetic rubber sheets, acrylic resin plates, polycarbonate resin plates, ABS resin plates, synthetic resin base materials such as FRP, plywood and laminated materials, fiber boards, wood base materials such as particle boards, steel Arbitrary materials such as metal base materials such as agate, brass plate, aluminum plate, gypsum plate, calcium silicate plate, cement plate, concrete plate, etc. can be used. Accordingly, for example, appropriate surface treatment such as sealing treatment, base coat treatment, primer treatment, corona discharge treatment, ozone treatment, flame treatment, and polishing treatment may be performed. There.
[0013]
In particular, when the moisture-absorbing / releasing material of the present invention is used as wallpaper, any sheet-like material conventionally used as a base material for synthetic resin-based wallpaper can be used. Specifically, for example, pulp paper flame retardant paper impregnated with water-soluble flame retardant such as guanazine sulfanilate or guanazine phosphate on paper made of cellulose fiber such as wood pulp, or carbonic acid during paper making of cellulose fiber. Flame retardant paper or non-flammable paper such as inorganic mixed paper made by mixing inorganic agents such as calcium, aluminum hydroxide or magnesium hydroxide, inorganic fiber paper made from inorganic fibers such as glass fiber or alumina fiber, and similarly flame retardants and inorganics Any flame-retardant or non-flammable woven or non-woven fabric prepared by adding an agent or manufactured from inorganic fibers can be used.
[0014]
The moisture absorbing / releasing resin layer 2 in the moisture absorbing / releasing material of the present invention is formed by dispersing a water absorbing substance 22 in a substrate resin 21. The substrate resin 21 may be any resin as long as it is a resin material that has a film-forming property, a low water-swelling property, and can maintain the form of the film even when the water-absorbing substance 22 absorbs water. For example, an acrylic resin, a urethane resin, an SBR resin, a vinyl acetate resin, an ethylene-vinyl acetate copolymer so as not to impede the absorption and release of moisture between the active substance 22 and the ambient air. Resins, silicone resins, polyamide resins, polybutene resins, polyvinyl alcohol resins, and the like are preferred to use a resin with high moisture permeability, and any one of these may be used alone, Two or more resin mixtures can also be used.
[0015]
The water-absorbing substance 22 added to the hygroscopic resin layer 2 is a substance having a relatively sparse structure containing many hydrophilic functional groups such as hydroxyl groups and carboxyl groups, and a large amount of water exceeding its own volume. May be used as long as it is a substance capable of absorbing and storing the inside, and specifically, a known general superabsorbent polymer or the like is used. For example, starch-acrylic acid graft polymer, starch-acrylonitrile graft polymer, cellulose- An acrylonitrile graft polymer, a polyvinyl alcohol cross-linked polymer, a sodium polyacrylate cross-linked product, a methyl acrylate-vinyl acetate copolymer saponified product, and the like are used. In addition, natural products such as potato starch and dextrins can be used, and these water-absorbing substances can be used alone or in admixture of two or more.
[0016]
The compounding ratio of the substrate resin 21 and the water-absorbing substance 22 in the hygroscopic resin layer 2 is not particularly limited in the present invention, but generally 20 to 80% by weight of the substrate resin 21 and the water-absorbing substance. It is desirable that 22 be about 80 to 20% by weight. When the content of the substrate resin 21 is less than 20% by weight, it is difficult to sufficiently suppress remarkable deformation and strength reduction due to water absorption swelling of the water absorbent material 22 at high humidity. Is less than 20% by weight, it is difficult to obtain a sufficient moisture absorption / release function. The thickness of the moisture-absorbing / releasing resin layer 2 is not particularly limited in the present invention, but considering the expression of a sufficient moisture-releasing / releasing function, processability during manufacturing, flexibility during handling, and the like, Generally, it is desirable to set it within a range of about 10 to 100 μm.
[0017]
If necessary, a hygroscopic substance 23 made of porous hydrophilic inorganic substance particles having a large specific surface area, such as silica gel, zeolite, diatomaceous earth, and calcined talc, is added to the hygroscopic resin layer 2 as necessary. Thus, the moisture absorption / release rate when the humidity in the ambient air changes can be improved, and the humidity adjusting function can be more effectively exhibited. The reason is that the water-absorbing substance 22 such as a highly water-absorbing polymer only absorbs moisture spontaneously condensing around it, whereas the hygroscopic substance 23 positively adsorbs gaseous water molecules at high humidity. It is presumed that the water is condensed and delivered to the water-absorbing substance 22, and on the other hand, when the humidity is low, the water content of the water-absorbing substance 22 is received and vaporized and evaporated.
[0018]
The amount of the hygroscopic substance 23 added is not particularly limited in the present invention, but the hygroscopic substance 23 itself absorbs less moisture than the water absorbent substance 22, and thus absorbs more moisture than the water absorbent substance 22. If a large amount of the water-soluble substance 23 is added, the saturated water absorption amount is small, but the moisture absorption / release speed when the environmental humidity changes is high. Conversely, if the water-absorbing substance 22 is added more than the hygroscopic substance 23, the environmental humidity changes. However, the saturated water absorption amount increases, so that it may be appropriately designed according to the purpose of use. In general, the hygroscopic substance 23 has a catalytic meaning of the water-absorbing substance 22, and may be smaller than the water-absorbing substance 22. The hygroscopic substance 23 is 30 to 100 wt% with respect to 100 parts by weight of the water-absorbing substance 22. It is desirable that the composition be about a part.
[0019]
The moisture-permeable waterproof resin coating 3 provided on the moisture-absorbing / releasing resin layer 2 described above has a moisture permeability that does not hinder the movement of moisture between the moisture-releasing / releasing resin layer 2 and the ambient air. In addition, the hydrophilic and water-resistant material has waterproofness to such an extent that moisture contained in the aqueous coating solution at the time of application of the aqueous resin layer 4 to be described later can be prevented from penetrating into the hygroscopic resin layer 2. However, the composition is not particularly limited. Specifically, for example, it is the same as that exemplified as the substrate resin 21 of the hygroscopic resin layer 2 described above. Acrylic resin, urethane resin, SBR resin, vinyl acetate resin, ethylene-vinyl acetate copolymer resin, silicone resin, polyamide resin, polybutene resin, polyvinyl alcohol resin, etc. can be used. No Even one single or a mixture or multilayer coating of two or more thereof.
[0020]
When the thickness of the moisture-permeable waterproof resin coating 3 is too thin, the waterproof property is insufficient, and the swelling of the water-absorbing substance 22 in the moisture-absorbing / releasing resin layer 2 is sufficiently prevented when the aqueous resin layer 4 is applied. However, if the thickness is too thick, the moisture permeability is lowered and the moisture absorbing / releasing performance of the moisture absorbing / releasing resin layer 2 is diminished. When the resin composition constituting the moisture-permeable waterproof resin coating 3 is, for example, one selected from the various resins listed above, the thickness of the moisture-permeable waterproof resin coating 3 is generally in the range of about 0.2 to 20 μm. It is preferable to be inside.
[0021]
The water-borne resin layer 4 provided on the moisture-permeable waterproof resin coating 3 covers the surface of the moisture-absorbing / releasing resin layer 2 and serves as a protective layer for preventing stickiness of the surface at high humidity or when wet and deterioration of surface strength. It is provided and can be applied in the form of an aqueous coating solution such as an aqueous solution or an aqueous dispersion so as not to impede the moisture absorbing / releasing function of the moisture absorbing / releasing resin layer 2, and after coating and drying. May be made of water-soluble resin 41 that can form a water-insoluble and water-resistant film while being hydrophilic, and may have a laminated structure of two or more layers made of the same or different materials.
[0022]
Specific examples of the aqueous resin 41 that is the main component of the aqueous resin layer 4 include water-soluble resins such as water-soluble acrylic resins, polyacrylamide, polyvinyl alcohol, polyvinylpyrrolidone, casein, cellulose derivatives, and dextrins. Compounds, blocked isocyanate compounds, epoxy compounds, hydrazine derivatives, aziridines, those which have been made water-insoluble by cross-linking by means such as addition of cross-linking agents such as organic peroxides or irradiation with ionizing radiation, such as acrylic resins and polyurethane resins , SBR resin, vinyl acetate resin, ethylene vinyl acetate copolymer resin, silicone resin, water-insoluble resin particles such as polybutene resin dispersed in water at least one or two of them More resin mixtures can be used . In view of stability of the coating liquid, surface physical properties after coating and drying, and high moisture permeability due to a microporous state, it is desirable to use an aqueous emulsion resin. Of course, the aqueous emulsion resin may be cross-linked by blending a cross-linking agent or ionizing radiation.
[0023]
If necessary, the aqueous resin layer 4 may be foamed into a porous cellular shape by a known appropriate means such as a mechanical foaming method or a method of blending the foaming agent 42, and by doing so, the aqueous resin layer 4 The moisture permeability of 4 can be further improved, and the moisture absorption / release function of the moisture absorption / release resin layer 2 can be more fully exhibited. When the moisture-absorbing / releasing material of the present invention is used as an interior material such as wallpaper in a building such as a house, the water-based resin layer 4 is foamed to facilitate the formation of the uneven pattern 6 by embossing, and the design property There is also an advantage that an excellent interior material can be easily obtained.
[0024]
Examples of the foaming agent 42 include organic foaming agents such as azo compounds such as azodicarbonamide (ADCA), nitroso compounds such as P and P′-oxybis (benzenesulfonylhydrazide) (OBSH), and sodium hydrogen carbonate. Thermal expansion chemical foaming agents such as inorganic foaming agents, and expansion by encapsulating a low-boiling liquid such as isobutane inside a heat-softening flexible shell such as polyacrylonitrile resin, phenolic resin, epoxy resin, etc. A type microcapsule foaming agent or the like can be used.
[0025]
The addition amount of the foaming agent 42 is not particularly limited in the present invention, but generally 2 to 20 weights with respect to 100 parts by weight of the solid content of the aqueous resin 41 which is the main component of the aqueous resin layer 4. Part is preferably added, more preferably 4 to 10 parts. When the amount is less than 2 parts by weight, the expansion ratio is low, the effect of improving moisture absorption / release is not expected so much, and improvement in design by the embossed uneven pattern 6 is difficult. On the other hand, when the amount is more than 20 parts by weight, the foamed cells are extremely rough and the surface strength of the sheet may be weakened.
[0026]
The aqueous resin layer 4 may include other inorganic fillers such as calcium carbonate, barium sulfate, aluminum hydroxide, and magnesium hydroxide, color pigments such as titanium oxide and zinc oxide, dispersants, etc. Antifoaming agent, wetting agent, flame retardant, flameproofing agent, antibacterial agent, antifungal agent, UV absorber, light stabilizer, heat stabilizer, lubricant, gloss adjusting agent, antistatic agent, antiblocking agent, thickener One or more selected from various additives such as these can also be added as appropriate.
[0027]
The thickness of the aqueous resin layer 4 is not particularly limited in the present invention. However, if it is too thin, the effect of preventing stickiness and surface protection is poor. Since the moisture absorption / release function of the layer 2 is diminished, it is necessary to design appropriately considering these. Generally, in the case of non-foaming, it is preferably in the range of about 5 to 100 μm, and in the case of foaming, it is preferably in the range of about 20 to 2000 μm.
[0028]
The method for forming the moisture absorbing / releasing resin layer 2, the moisture permeable waterproof resin coating 3, and the aqueous resin layer 4 described above is not particularly limited in the present invention, but the moisture absorbing / releasing resin layer 2 and the moisture permeable waterproof resin are not limited. The coating 3 is an oil-based coating solution using a hydrophobic organic solvent as a dispersion medium, and the aqueous resin layer 4 is coated using an aqueous coating solution using water or a mixture of water and alcohol as a dispersion medium. Generally, it is based on a method of forming sequentially by a construction method. Examples of coating methods include knife coating, nozzle coating, gravure coating, micro gravure coating, rotary screen coating, reverse roast coating, comma coating, lip coating, die coating, spray coating, and dip coating. Conventionally known arbitrary coating methods such as a coating method and a flow coating method can be adopted. As a drying method after coating each layer, for example, a heat source such as hot air or an infrared heater is used alone or a plurality of these are used. It can also be used in combination.
[0029]
If necessary, the moisture-absorbing / releasing material of the present invention can be provided with a design printing layer 5 on the surface of the aqueous resin layer 4 to impart design properties by the design. As a printing method of the pattern printing layer 5, a normal printing method such as a gravure printing method, a rotary screen printing method, a flexographic printing method, an ink jet printing method, a transfer printing method, or the like can be used. Moreover, in order to provide a three-dimensional design property, the surface which consists of a moisture-permeable resin composition on the surface in order to provide the uneven | corrugated pattern 6 process by a mechanical embossing method or a chemical embossing method, or to improve surface strength further A protective layer can also be provided arbitrarily.
[0030]
【Example】
Examples of the present invention and comparative examples will be shown below to explain the present invention in more detail.
[0031]
<Example 1>
First, a moisture absorbing / releasing resin composition having the following composition was applied on the surface of an inorganic paper having a basis weight of 90 g / m ² by a comma coating method and dried at about 90 ° C., and the coating amount after drying was about 20 g. A moisture absorbing / releasing resin layer of / m ² was provided. Subsequently, a solvent-based urethane resin is applied on the moisture-absorbing / releasing moisture-absorbing resin layer by a gravure coating method to a coating amount after drying of about 1 g / m ² and dried to form a moisture-permeable waterproof resin film. On the resin coating, an ethylene-vinyl acetate copolymer aqueous emulsion resin to which 6 parts by weight of a microcapsule foaming agent is added is applied to a coating amount of about 140 g / m ² after drying by a comma coating method to about 90 ° C. And dried to form an aqueous resin layer. Then, after printing an abstract pattern on the surface of the aqueous resin layer by a gravure printing method, the aqueous resin layer is foamed about 5 times in a foaming heating furnace having a furnace temperature of about 150 ° C. An embossed pattern was formed on the surface of the resin layer using a cooling embossing roll to prepare a wallpaper which is a moisture absorbing / releasing material of the present invention.
[0032]
[Composition table of hygroscopic resin composition]
Water-absorbing substance Urethane-based superabsorbent polymer 40 parts by weight Hygroscopic substance Colloidal synthetic silica 30 parts by weight Substrate resin Polyurethane 90 parts by weight
The obtained wallpaper was free from defects such as coating unevenness in each layer and had a good design in appearance. In addition, for this wallpaper, commercially available vinyl chloride based anti-condensation wallpaper (with a polyvinyl chloride resin foam layer with a superabsorbent polymer added on the backing paper) and commercially available ordinary products not subjected to anti-condensation processing As a result of measuring moisture absorption / release performance by the following test method together with the vinyl chloride wallpaper (with a polyvinyl chloride resin foam layer to which a superabsorbent polymer is not added on the backing paper), It was confirmed that the wallpaper of Example 1 which is a moisture absorbing / releasing material has very excellent moisture absorbing / releasing performance as shown in FIG.
[0034]
<Method for testing moisture absorption / release performance>
The sample is cut into a size of 6 cm × 27 cm, covered with 1 cm square of the front edge of the front surface and the entire back surface with aluminum tape, and treated to prevent moisture permeation from the side surface and the back surface. From the above treatment, the moisture permeable surface area of the sample is set to 100 m ^{2 of} 4 cm × 25 cm. The test piece thus prepared is left in a constant temperature and humidity test machine set at a temperature of 25 ° C. and a relative humidity of 50% for 4 days, and then the weight (a) of the test piece is measured and used as an initial value. . Next, after leaving the test piece in a constant temperature and humidity tester set at a temperature of 25 ° C. and a relative humidity of 90% for 144 hours, in a constant temperature and high humidity test set at a temperature of 25 ° C. and a relative humidity of 50%. The sample is left for 144 hours, and the weight (b) of the test piece is measured at an appropriate time interval. The amount of moisture absorption of the test piece at each time is calculated by the following equation (1).
Moisture absorption [g / m ² ] = (test specimen weight (b) [g] −test specimen weight (a) [g]) / moisture permeable surface area [m ² ] (1)
[0035]
<Comparative Example 1>
In Example 1 described above, the step of forming the moisture-permeable waterproof resin coating was omitted, and the rest was the same as in Example 1, and an attempt was made to produce a wallpaper that is a moisture-absorbing / releasing material. Immediately after coating the aqueous coating solution of the aqueous emulsion resin for the aqueous resin layer, the moisture absorbing / releasing resin layer swells by a thickness ratio of about 5 to 10 times by the moisture in the aqueous coating solution, and the surface state A good hygroscopic material could not be obtained.
[0036]
【The invention's effect】
As described above in detail, the moisture-absorbing / releasing material of the present invention has a structure in which an aqueous resin layer is provided on a moisture-absorbing / releasing resin layer containing a water-absorbing substance via a moisture-permeable waterproof resin film. When the aqueous coating liquid for forming the aqueous resin layer is applied, the water-absorbing substance in the moisture-absorbing / releasing moisture-absorbing resin layer effectively absorbs and swells due to moisture contained in the aqueous coating liquid. Therefore, it is possible to stably obtain a moisture absorbing / releasing material having a good surface state. In addition, the moisture-absorbing / releasing material thus obtained absorbs moisture in the ambient air at high humidity, while releasing moisture that was absorbed at low humidity. Does not contain a water-absorbing substance, so that the surface does not become sticky or the surface strength does not decrease at high humidity. For example, it has a surface property and design that are exactly the same as those of conventional wallpaper. It has an excellent effect that a moisture-releasing material can be easily obtained.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing an embodiment of a hygroscopic material of the present invention.
FIG. 2 is a graph showing moisture absorption / release performance test results of examples of the moisture absorption / release material of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Base material 2 ... Hygroscopic resin layer 21 ... Substrate resin 22 ... Water-absorbing substance 23 ... Hygroscopic substance 3 ... Moisture-permeable waterproof resin film 4 ... Aqueous resin layer 41 ... Aqueous resin 42 ... Foaming agent 5 …… Picture printing layer 6 …… Uneven pattern

Claims (4)

A moisture-absorbing / releasing material comprising a substrate and a moisture-absorbing / releasing resin layer containing a water-absorbing substance, a moisture-permeable waterproof resin film, and an aqueous resin layer. The hygroscopic material according to claim 1, wherein the aqueous resin layer is a foam layer. A moisture-absorbing / releasing resin layer containing a water-absorbing substance is formed on the substrate, a moisture-permeable waterproof resin film is formed on the moisture-absorbing / releasing resin layer, and then an aqueous resin is formed on the moisture-permeable waterproof resin film. A method for producing a moisture-absorbing / releasing material, characterized in that an aqueous resin layer is provided by coating an aqueous coating solution containing the aqueous coating solution. A foaming agent is added to the aqueous coating liquid containing the aqueous resin, and the aqueous resin layer is formed into a foamed layer by heating and foaming after coating on the moisture-permeable waterproof resin film. The manufacturing method of the hygroscopic material of Claim 3.

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