Patent Publication Number: US-2023139423-A1

Title: Humidity controlling material and humidity controlling apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to a humidity controlling material and a humidity controlling apparatus. The present application claims priority to Japanese Patent Application No. 2020-061765, filed on Mar. 31, 2020, the contents of which are incorporated herein by reference in its entirety. 
     BACKGROUND ART 
     Conventionally, hygroscopic materials made of polymeric materials and formed into beads are known (see, for example, Patent Document 1). A hygroscopic material (hygroscopic millimeter-beads) described in Patent Document 1 is characterized by high hygroscopicity and small dimensional change upon absorbing and releasing moisture. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Document 1: Japanese Unexamined Patent Application Publication No. 2017-056404 
       
    
     SUMMARY OF INVENTION 
     Technical Problems 
     However, because of the above characteristic, it is difficult for a user who uses the above hygroscopic material to understand how much moisture the hygroscopic material has absorbed by the appearance of the hygroscopic material in use. Hence, for example, a problem of the hygroscopic material is that it is difficult for the user to understand when to replace the hygroscopic material. 
     In addition, regardless of the hygroscopic material described above, if the user could understand how much moisture has been absorbed by the moisture-absorbing material in use, the hygroscopic material would be easy to use. That is why improvement has been required of the hygroscopic material. 
     In view of the above circumstances, an aspect of the present invention is intended to provide a humidity controlling material with which the amount of absorbed moisture is easily understood. Another aspect of the present invention is intended to provide a humidity controlling apparatus including the above humidity controlling material with which the amount of absorbed moisture is easily understood. 
     Solution to Problems 
     In order to solve the above problems, an embodiment of the present invention includes the aspects below. 
     [1] A humidity controlling material comprising: a first particle capable of absorbing or discharging moisture in air; and a second particle capable of absorbing or discharging moisture in the air, wherein the first particle includes: a first humidity controlling liquid containing a hygroscopic substance; and a first holding portion holding the first humidity controlling liquid, the second particle includes: a second humidity controlling liquid containing the hygroscopic substance; and a second holding portion holding the second humidity controlling liquid, the first holding portion and the second holding portion are formed of a polymeric material, the first humidity controlling liquid includes a first indicator a color of Which changes according to an amount of moisture contained in the first humidity controlling liquid, and the second humidity controlling liquid includes a second indicator a color of which changes, in a transition range different from a transition range of the first indicator, according to an amount of moisture contained in the second humidity controlling liquid. 
     [2] The humidity controlling material according to [1], wherein at least one of the first humidity controlling liquid or the second humidity controlling liquid contains two or more kinds of the hydroscopic substances. 
     [3] The humidity controlling material according to [2], wherein the hydroscopic substance contains a hygroscopic polyalcohol and a hygroscopic inorganic salt. 
     [4] The humidity controlling material according to any one of [1] to [3], wherein the polymeric material forming the first holding portion and the second holding portion is a water-absorbing polymer. 
     [5] The humidity controlling material according to any one of [1] to [3], wherein the first particle has a core-shell structure including: a core containing the first humidity controlling liquid; 
     and the first holding portion formed of the polymeric material and shaped into a shell, and the second particle has a core-shell structure including: a core containing the second humidity controlling liquid; and the second holding portion formed of the polymeric material and shaped into a shell. 
     [6] The humidity controlling material according to any one of [1] to [3], wherein the first particle has a core-shell structure including: a core containing the first humidity controlling liquid; and the first holding portion formed of the polymeric material and shaped into a shell, and the second holding portion included in the second particle is a water-absorbing polymer. 
     [7] The humidity controlling material according to any one of [1] to [6, further comprising a fixed color particle configured to indicate a certain color. 
     [8] The humidity controlling material according to [7], wherein the fixed color particle includes: a humidity controlling liquid containing the hygroscopic substance; and a holding portion holding the humidity controlling liquid in a form of a particle. 
     [9] A humidity controlling apparatus, comprising: the humidity controlling material according to any one of [1] to [8]; and a housing portion housing the humidity controlling material, wherein the housing portion is at least partially transparent to light. 
     [10] The humidity controlling material according to [9], wherein the housing portion includes: a first housing portion housing the first particle; and a second housing portion housing the second particle. 
     [11] The humidity controlling material according to claim  10 , further comprising a removing portion configured to remove moisture contained in the humidity controlling material. 
     [12] The humidity controlling material according to [11], wherein the first particle has a core-shell structure including: a core containing the first humidity controlling liquid; and the first holding portion formed of the polymeric material and shaped into a shell, the second holding portion included in the second particle is a water-absorbing polymer, and the removing portion is disposed closer to the first housing portion than to the second housing portion. 
     Advantageous Effects of Invention 
     An aspect of the present invention can provide a humidity controlling material with which the amount of absorbed moisture can be easily understood. An aspect of the present invention can provide a hygroscopic material with which the amount of absorbed moisture can be easily understood. Moreover, an aspect of the present invention can provide a humidity controlling apparatus including the above humidity controlling material so that the amount of absorbed moisture is easily understood. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a schematic view of a humidity controlling material  1  according to a first embodiment. 
         FIG.  2    is a schematic view of a first particle  1 A or a second particle  1 B according to the first embodiment. 
         FIG.  3    is a schematic view of a humidity controlling material  2  according to a second embodiment. 
         FIG.  4    is an illustration of a humidity controlling material  3  according to a third embodiment. 
         FIG.  5    is an illustration of a humidity controlling apparatus  100  according to a fourth embodiment. 
         FIG.  6    is an illustration of a humidity controlling apparatus  200  according to a fifth embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
       FIGS.  1  and  2    are illustrations of a humidity controlling material  1  according to this embodiment. Note that, in all the drawings below, the constituent features vary in dimensions and proportions as appropriate so that the drawings are easy to see. 
       FIG.  1    is a schematic view of the humidity controlling material  1  according to this embodiment. The humidity controlling material  1  according to this embodiment includes: first particles  1 A capable of absorbing or discharging moisture in the air; and second particles  1 B capable of absorbing or discharging moisture in the air. The humidity controlling material  1  according to this embodiment absorbs or releases moisture contained in the air in which the humidity controlling material  1  is placed, depending on the humidity of an environment in which the humidity controlling material  1  placed. 
     The humidity controlling material  1  will be described below in sequence. 
     &lt;First Particle and Second Particle&gt; 
       FIG.  2    is a schematic view of a first particle  1 A or a second particle  1 E according to this embodiment. Each of the first particle  1 A and the second particle  1 B includes: a humidity controlling liquid  11 ; and a holding portion  12  holding the humidity controlling liquid  11 . 
     In this DESCRIPTION, the term “humidity control” means to adjust the amount of water vapor contained in the air. The humidity control includes both “moisture absorption” that involves removing water vapor in the air to relatively reduce the amount of the water vapor contained in the air, and “humidification” that involves supplying water vapor to the air to relatively increase the amount of the water vapor contained in the air. 
     In the description below, the humidity controlling liquid included in the first particle  1 A may be referred to as a “first humidity controlling liquid”, and the holding portion included in the first particle  1 A may be referred to as a “first holding portion”. 
     Likewise, the humidity controlling liquid included in the second particle  1 B may be referred to as a “second humidity controlling liquid”, and the holding portion included in the second particle  1 B may be referred to as a “second holding portion”. 
     Moreover, if the first humidity controlling liquid and the second humidity controlling liquid are described without di stint ti on, the term “humidity controlling liquid” is used in common. 
     Likewise, if the first holding portion and the second holding portion are described without distinction, the term “holding portion” is used in common. 
     &lt;Humidity Controlling Liquid&gt; 
     The humidity controlling liquid  11  included in the first particle  1 A and the second particle  1 B has a property of absorbing moisture contained in the surrounding air (hygroscopicity) until the humidity controlling liquid  11  reaches an equilibrium with the humidity of the air in which the first particle  1 A and the second particle  1 B are placed, if the air in which the first particle  1 A and the second particle  1 B are placed is relatively wet compared with the humidity controlling liquid  11 . 
     In addition, the humidity controlling liquid  11  has a property of releasing in the air moisture contained in the humidity controlling liquid  11  until the humidity controlling liquid  11  reaches an equilibrium with the humidity of the air in which the first particle  1 A and the second particle  1 B are placed, if the air in which the first particle and the second particle  1 B are placed is relatively dry compared with the humidity controlling liquid. 
     Note that, when also heated, the humidity controlling liquid  11  releases in the air moisture contained in the humidity controlling liquid  11 . 
     The humidity controlling liquid  11  contains: a hygroscopic substance; and an indicator a color of which changes according to the amount of moisture contained in the humidity controlling liquid  11 . 
     (Hygroscopic Substance) 
     The hygroscopic substance can include an organic material and an inorganic material. 
     Examples of the hygroscopic organic material to be used as the hygroscopic substance include divalent or more than divalent alcohols (polyalcohols), ketones, organic solvents having amide groups, saccharides, and known materials to be used as raw materials of moisturizing cosmetics. Among these materials, the organic materials to be preferably used as the hygroscopic substance include polyalcohols, organic solvents having amid groups, saccharides, and known materials to be used as raw materials of moisturizing cosmetics. Such organic materials are high in hydrophilicity. 
     Examples of the polyalcohols include glycerin, propanediol, butanediol, pentanediol, trimethylolpropane, butanetriol, ethylene glycol, diethylene glycol, and tri ethylene glycol. Moreover, the hygroscopic polyalcohols may be dimers or polymers of the polyalcohols. 
     Examples of the organic solvents having amid groups include formamide and acetamide. 
     Examples of the saccharides include sucrose, pullulan, glucose, xylol, fructose, mannitol, and sorbitol. 
     Examples of the known materials to be used as raw materials of moisturizing cosmetics include 2-methacryloyloxyethyl phosphorylcholine (MPC), betaine, hyaluronic acid, and collagen. 
     Examples of the hygroscopic inorganic material to be used as the hygroscopic substance include hygroscopic inorganic salts. These inorganic salts include: 
     chlorides such as calcium chloride, lithium chloride, magnesium chloride, potassium chloride, sodium chloride, zinc chloride, aluminum chloride, strontium chloride, and barium chloride; 
     bromides such as lithium bromide, calcium bromide, and potassium bromide; 
     nitrates such as magnesium nitrate, calcium nitrate, strontium nitrate, and barium nitrate; 
     and 
     metal salts such as magnesium sulfate, sodium hydroxide, and sodium pyrrolidone carboxylic acid. 
     Among the inorganic salts, lithium chloride and calcium chloride are preferable. 
     In addition, the hygroscopic inorganic materials include phosphorus oxide, silica gel, alunite, and zeolite. 
     Silica gel, alunite, and zeolite are dispersed in a dispersing medium to form a dispersion liquid. The dispersion liquid can constitute the humidity controlling liquid  11 . As the dispersion medium, a polar solvent can be used. Examples of the polar solvent includes water, ethanol, methanol, glycerin, diglycerin, polyglycerin, and ethylene glycol. 
     The humidity controlling liquid  11  preferably contains two or more kinds of hygroscopic substances. When the humidity controlling liquid  11  contains two or more kinds of hygroscopic substances, physical properties of the humidity controlling liquid  11  are easily adjusted. 
     If the hygroscopic substance contains two or more kinds of hygroscopic substances, for example, two or more kinds of polyalcohols may be used, two or more kinds of inorganic salts may be used, or a polyalcohol and an inorganic salt may be used in combination. 
     The humidity controlling liquid  11  preferably contains a hygroscopic polyalcohol and a hygroscopic inorganic salt. 
     (Indicator) 
     As the indicator included in the humidity controlling liquid  11  according to this embodiment, a pH indicator can be preferably used. The humidity controlling liquid  11  changes in pH as concentration of the humidity controlling liquid  11  changes. That is, the humidity controlling liquid  11  changes in pH in accordance with the amount of absorbed moisture. Hence, when the humidity controlling liquid  11  includes the pH indicator, the first particle  1 A and the second particle  1 B change in color in accordance with the amount of moisture absorbed by the humidity controlling liquid  11 . 
     Moreover, the humidity controlling material  1  (the first particle  1 A and the second particle  1 B) according to this embodiment absorbs or releases moisture until the humidity controlling material  1  reaches an equilibrium with the humidity of the air in which the humidity controlling material  1  is placed. Hence, when a correspondence relationship is examined in advance between a color of the pH indicator and the humidity of the environment in which the first particle  1 A and the second particle  1 B are placed, the humidity of the environment in which the humidity controlling material  1  is placed can be understood in a simple manner by the colors of the first particle  1 A and the second particle  1 B. 
     In the descriptions below, an indicator included in the first particle  1 A may be referred to as a “first indicator”, and an indicator included in the second particle  1 B may be referred to as a “second indicator”. 
     Examples of the pH indicator includes known pH indicators such as methyl yellow, bromophenol blue, conga red, methyl orange, bromocresol green, methyl red, litmus, bromocresol purple, bromothymol blue, phenol red, thymol blue, neutral red, cresol red litmus, paranitrophenol, methyl purple, and phenolphthalein. 
     Moreover, as the pH indicator, triarylmethane derivatives, fluoran derivatives, pyrazolone derivatives, azo derivatives, and xanthene derivatives can also be used. 
     Each of the first indicator and the second indicator to be used may be of one kind alone. Alternatively, two or more kinds of the first indicators and the second indicators may be used in combination. 
     If two or more kinds of pH indicators are mixed and used, a compound ratio for use of the pH indicators can be a known mixing ratio. For example, as an indicator included in the humidity controlling liquid  11  of this embodiment, among the above pH indicators, a Yamada-type universal indicator (a universal pH indicator) containing thymol blue, methyl red, bromothymol blue, and phenolphthalein may be used. 
     In the humidity controlling material  1  of this embodiment, the first index and the second index have different transition ranges. Hence, the first particle  1 A and the second particle  1 B can be different from each other in a correspondence relationship between the colors of the indicators and the humidity of the environment in which the humidity control ling material  1  is placed. 
     Usually, when exhibiting color reaction, a pH indicator exhibits a color change with a slight change in pH. Meanwhile, the pH indicator exhibits a dull color change in a range other than the transition range. Hence, when the humidity controlling material  1  has only one kind of indicator, there is one transition range, and it is difficult to detect a change in concentration of the humidity controlling liquid in a pH range other than the transition range (concentration of the humidity controlling liquid). 
     In contrast, as seen in the humidity controlling material  1  of this embodiment, if the first indicator of the first particle  1 A and the second indicator of the second particle  1 B have different transition ranges, it is possible to establish a relationship in which the color change of one of the indicators is sharp in a pH range while the color change of the other indicator is dull in the pH range. Hence, it is easy to detect the concentration change of the humidity controlling liquid, and to understand the humidity of the environment in which the humidity controlling material  1  is placed. 
     It is preferable that the colors of the first indicator and the second indicator are different from each other. It is also preferable that the colors of the first index and the second index have a pH range in which the colors of the first index and the second index are different from each other in an angle of 30 degrees or more on the color circle in color change depending on pH. With the humidity controlling material  1  using such a first index and a second index, it is easy to check the color change. 
     A combination of the first indicator and the second indicator can be, for example, bromocresol green as the first indicator and a universal pH indicator as the second indicator. 
     (Other Substances) 
     Moreover, the humidity control ling liquid  11  may contain a solvent as another substance. The solvent includes a solvent in which the above hygroscopic substance dissolves, or a solvent with which the hygroscopic substance is mixed. An example of such a solvent can include water. 
     Furthermore, as the solvent, the polyalcohol or the organic solvent mentioned above as the hygroscopic organic material may be used. 
     When the humidity controlling liquid  11  contains the solvent, a mixing ratio (a mass ratio) of the solvent to the indicator is preferably in a range of (solvent): (indicator)=100:1 to 50:1. 
     In addition, the humidity controlling liquid  11  may contain a dye for color adjustment as another substance. 
     &lt;Holding Portion&gt; 
     The holding portion  12  included in the first particle  1 A and the second particle  1 B has a function of holding the humidity controlling liquid  11  described above. 
     The holding portion  12  of this embodiment is formed of a known water-absorbing polymeric material (a water-absorbing polymer). Examples of the material for forming the holding portion  12  include polyacrylate, starch-acrylate graft polymer, vinyl acetate copolymer, maleic anhydride copolymer, and polyvinyl alcohol. 
     &lt;Method for Manufacturing Humidity Controlling Material&gt; 
     A method fix manufacturing the humidity controlling material  1  according to this embodiment can include a step of manufacturing the holding portion  12  and a step of swelling the humidity controlling liquid  11  with the obtained holding portion  12 . 
     In the step of manufacturing the holding portion  12 , the holding portion  12  can be manufactured by a known inversed phase suspension polymerization technique. Specifically, the holding portion  12  can be manufactured of: a continuous phase such as a hydrophobic organic solvent containing a surfactant and a dispersant; and a disperse phase such as a liquid mixture containing a monomer including a repeating unit of the water-absorbing polymeric material described above, a polymerization initiator, and a crosslinking agent. The continuous phase and the liquid mixture are subjected to suspension polymerization to form the holding portion  12 . 
     Examples of the monomer can include acrylic acid, vinyl acetate, vinyl alcohol, and maleic anhydride. 
     Examples of the polymerization initiator can include an organic peroxide and an azo compound, each known as a radical polymerization initiator. 
     The crosslinking agent is used to adjust the water absorption performance of the holding portion  12  to be obtained. The larger the amount of the crosslinking agent to be copolymerized with the monomer is, the denser the crosslinking of the polymeric material included in the holding portion  12  is, thereby decreasing the hygroscopicity. The smaller the amount of the crosslinking agent to be copolymerized with the monomer is, the coarser the crosslinking of the polymeric material included in the holding portion  12  is, thereby increasing the hygroscopicity. 
     Examples of the organic solvent as the continuous phase can include aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, aliphatic alcohols, aliphatic ketones, and aliphatic esters. 
     The surfactant that can be used shall not be limited to a particular surfactant, and any of an anionic surfactant, a cationic surfactant, an amphoteric surfactant, and a nonionic surfactant can be used. 
     The dispersant shall not be limited to a particular dispersant as long as the dispersant can stably disperse the monomer in the organic solvent. The dispersant may be a known dispersant. Examples of the dispersant can include fatty acid ester, cellulose ether, and cellulose ester. 
     The holding portion  12  manufactured by the inversed phase suspension polymerization technique is preferably dried. 
     Note that, in the polymerization, silica (colloidal crystals) arranged regularly may be added to the holding portion  12 . After the polymerization, the silica is etched and removed so that the holding portion  12  may be colored with a structural color. The holding portion  12  having the structural color can be manufactured in the same manner as a known technique of manufacturing an inverse opal gel. 
     Before immersed in the humidity controlling liquid  11 , the holding portion  12  may have a size (a diameter) of, for example, 1 mm or more and 30 mm or less. The size of the holding portion  12  can be controlled by changing at least one selected from the group consisting of the agitation speed, the amount of the surfactant, the amount of the dispersant, and the amount of the polymerization initiator in the above-mentioned inversed phase suspension polymerization. 
     Moreover, the first particle  1 A and the second particle  1 B obtained by immersing the holding portion  12  in the humidity controlling liquid  11  become larger than the holding portion  12  before being immersed in the humidity controlling liquid  11 , because the humidity controlling liquid  11  swells. For example, the first particle  1 A and the second particle  1 B can have a size (a diameter) of 4 mm or more and 150 mm or less. 
     The first particle  1 A and the second particle  1 B included in the humidity controlling material  1  absorb moisture from the surrounding air when the air in which the humidity controlling material  1  is placed is relatively wet compared with the humidity controlling liquid  11 . Moreover, the first particle  1 A and the second particle  1 B release the absorbed moisture when the air in which the humidity controlling material  1  is placed is relatively dry compared with the humidity controlling liquid  11 . 
     When the amount of the held moisture changes in this manner, the humidity controlling liquid  11  included in the first particle  1 A and the second particle  1 B changes in concentration, and in pH. As a result, the indicator included in the humidity controlling liquid  11  exhibits color reaction, making it possible to detect that the first particle  1 A and the second particle  1 B have absorbed, or released, moisture. 
     The first particle  1 A and the second particle  1 B respectively include the first indicator and the second indicator having different transition ranges. Hence, the first particle  1 A and the second particle  1 B easily detect the concentration change of the humidity controlling liquid, and the humidity of the environment in which the humidity controlling material  1  is placed. 
     Moreover, the first particle  1 A and the second particle  1 B swell by absorbing moisture, and become larger in diameter than the first particle  1 A and the second particle  1 B before absorbing the moisture. In addition, the first particle  1 A and the second particle  1 B contract by releasing moisture, and become smaller in diameter than the first particle  1 A and the second particle TB before releasing the moisture. Hence, the humidity controlling material  1  can detect that the humidity controlling material  1  has absorbed or released moisture, in accordance with the sizes of the first particle  1 A and the second particle  1 B. Furthermore, the humidity controlling material  1  can easily detect the humidity in which the humidity controlling material  1  is placed, in accordance with the sizes of the first particle  1 A and the second particle  1 B. 
     A ratio of the first particles  1 A to the second particles  1 B that constitute the humidity controlling material  1  may be set appropriately, in view of the colors of the first indicator and the second indicator to be used and of how easily the first particles  1 A and the second particles  1 B can be checked for the color change. For example, a mass ratio of the first particles  1 A to the second particles  1 B may be set as follows: (the first particles): (the second particles) may be 10:90 to 90:10, 25:75 to 75:25, or 40:60 to 60:40. 
     The humidity controlling material  1  of the above-described configuration can be provided as a moisture absorbing material with which the amount of absorbed moisture can be easily understood. 
     Second Embodiment 
       FIG.  3    is an illustration of a humidity controlling material  2  according to a second embodiment.  FIG.  3    is an illustration of a first particle  2 A or a second particle  2 B included in the humidity controlling material  2 . 
     Each of the first particle  2 A and the second particle  2 B included in the humidity controlling material  2  according to this embodiment includes: a humidity controlling liquid  21 ; and a holding portion  22  holding the humidity controlling liquid  21 . The humidity controlling material  2  according to this embodiment absorbs or releases moisture contained in the air in which the humidity controlling material  2  is placed, in accordance with the humidity of an environment in which the humidity controlling material  2  is placed. 
     The first particle  2 A included in the humidity controlling material  2  of this embodiment has a core-shell structure including: a core containing the humidity controlling liquid  21 ; and a first holding portion formed of a polymeric material and shaped into a shell. 
     The second particle  2 B included in the humidity controlling material  2  of this embodiment has a core-shell structure including: a core containing the humidity controlling liquid  21 ; and a second holding portion formed of a polymeric material and shaped into a shell. 
     &lt;Humidity Controlling Liquid&gt; 
     The humidity controlling liquid  21  contains: a hygroscopic substance; an indicator a color of which changes according to the amount of moisture contained in the humidity controlling liquid  21 ; and a material to form the holding portion  22 . 
     As the hygroscopic substance and the indicator, each of the substances exemplified in the first embodiment can be used. 
     The material for forming the holding portion  22  contained in the humidity controlling liquid  21  will be described later. 
     &lt;Holding Portion&gt; 
     The holding portion  22  corresponds to the shell (the first holding portion) of the first particle  2 A, or the shell (the second holding portion) of the second particle  2 B, The first particle  2 A and the second particle  2 B have a core-shell structure. The holding portion  22  is a hollow particle having a space to hold therein the humidity controlling liquid  21 . 
     The holding portion  22  can be formed of a polymeric material that reacts with a gelling agent to form a gel. Specifically, as the material for forming the holding portion  22 , monovalent alginate, polysaccharides such as carboxymethyl cellulose and methyl cellulose, and polyalcohols such as polyvinyl alcohol can be used. 
     In this DESCRIPTION, the above materials to be used as the materials for forming the holding portion  22  are not included in the “water-absorbing polymer”; that is, a material for forming the holding portion  12 . 
     The gelling agent, which reacts with the above polymeric material so that the polymeric material forms a gel, includes a polyvalent metal salt aqueous solution, an acidic aqueous solution, and a sodium tetraborate aqueous solution. 
     The polyvalent metal salt includes polyvalent metal ion salts such as calcium salts, magnesium salts, barium salts, and aluminum salts. 
     Combinations of the gel-forming polymeric material and the gelling agent include the following: 
     (1) a combination of monovalent alginate and a polyvalent metal salt solution;
 
(2) a combination of monovalent alginate and an acidic aqueous solution;
 
(3) a combination of (carboxy) methyl cellulose and a polyvalent metal salt solution; and
 
(4) a combination of polyvinyl alcohol and a sodium tetraborate aqueous solution.
 
     Note that the “(carboxy) methyl cellulose” means both methyl cellulose and carboxymethyl cellulose. 
     The holding portion  22  may contain the above humidity controlling liquid. 
     The holding portion  22  is permeable to moisture. 
     &lt;Method for Manufacturing Humidity Controlling Material&gt; 
     A method for manufacturing the first particle  2 A and the second particle  2 B includes a step of preparing a humidity controlling liquid, a step of obtaining a liquid mixture in which a material for forming the holding portion is mixed with the humidity controlling liquid, and a step of dripping the liquid mixture into a gelling agent. 
     The step of preparing the humidity controlling liquid involves mixing together the hygroscopic substance, the indicator, the solvent, and another substance, all of which are described above. 
     The step of obtaining the liquid mixture involves mixing an aqueous solution, which is separately prepared to contain a material for forming the holding portion, with the humidity controlling liquid. For example, in the case where sodium alginate is used as the material for forming the holding portion, a sodium alginate aqueous solution of, in mass percent, 1% or more and 5% or less is prepared and mixed with the humidity controlling liquid. 
     A proportion of the humidity controlling liquid to the Whole liquid mixture can be, in mass percent, 10% or more and 90% or less. 
     The step of dripping the liquid mixture into the gelling agent involves dripping the obtained liquid mixture into a galling agent aqueous solution. In the case where sodium alginate is used as the material for forming the holding portion, for example, a calcium chloride aqueous solution is used as the gelling agent. A concentration of the calcium chloride aqueous solution can be, in mass percent, 1% or more and 10% or less, for example. 
     When the liquid mixture is dripped into the gelling agent, the sodium alginate contained in the surface of a droplet of the dripped liquid mixture reacts with the gelling agent to form a gel. As a result, the gelled surface of the droplet becomes the shell (the holding portion  22 ) of the humidity controlling material  2 ; and the non-gelled interior of the droplet becomes the core of the first particle  2 A or the second particle  2 B. 
     After dripping the liquid mixture into the gelling agent, the particles to be obtained may be removed from the gelling agent within 24 hours. This feature can reduce a problem of which the gelling agent penetrates into the center of the first particle  2 A and the second particle  2 B such that the particles are entirely gelled. The time period for removing the first particle  2 A and the second particle  2 B may be changed in accordance with the composition and the size of the particles after a preliminary experiment is conducted in advance and a time period during Which no problem occurs is checked. 
     Moreover, the method may include a step of freeze-drying the particles obtained at the step of dripping the liquid mixture into the gelling agent. The freeze-drying involves freezing the above particles, and, after that, sublimating frozen moisture in a reduced pressure environment. Hence, the moisture in the holding portion is partially removed, and the portions from which the moisture is removed are deemed pores. As a result, the particles after the freeze-drying are deemed wider in surface area than the particles before the freeze-drying, and the Obtained particles (the humidity controlling material  2 ) are deemed more likely to absorb moisture than the particles before the freeze-drying. 
     Furthermore, the freeze-drying can also be expected to have an advantageous effect of cutting off a portion of the polymeric material included in the holding portion  22  to reduce the molecular weight of the polymeric material. Hence, the cross-linking of the polymeric material included in the holding portion  22  becomes coarse, thereby increasing the hygroscopicity. 
     The humidity controlling material  2  of the above-described configuration can also be provided as a humidity controlling material with which the amount of absorbed moisture or the amount of released moisture is easily understood. 
     Note that, in this embodiment, both the first particle  2 A and the second particle  2 B have a core-shell structure; however, the first particle  2 A and the second particle  2 B shall not be limited to have such a structure. The first particle  2 A may have the core-shell structure described in the second embodiment, and the second particle  2 B may have the same structure as the structure of the second particle  1 B described in the first embodiment. 
     In the description below, the particles described in the first embodiment are referred to as “swollen particles”. Moreover, the particles described in the second embodiment are referred to as “core-shell particles”. 
     A ratio of the swollen particles to the core-shell particles included in the humidity controlling material may be set appropriately. For example, a mass ratio of the swollen particles to the core-shell particles may be set as follows: (the swollen particles): (the core-shell particles) may be 10:90 to 90:10, 25:75 to 75:25, or 40:60 to 60:40. 
     Third Embodiment 
       FIG.  4    is an illustration of a humidity controlling material  3  according to a third embodiment of the present invention. The humidity controlling material  3  according to this embodiment includes: first particles  3 A; second particles  3 B; and fixed color particles  3 C. 
     As a first particle  3 A, either the first particle  1 A of the first embodiment or the first particle  2 A of the second embodiment can be employed. 
     As a second particle  3 B, either the second particle  1 B of the first embodiment or the second particle  2 B of the second embodiment can be employed. 
     A fixed color particle  3 C is a particle that indicates a certain color, regardless of the amount of moisture absorbed by the humidity controlling material  3 . The fixed color particle  3 C may or may not have a function of absorbing or releasing the moisture contained in the air in which the humidity controlling material  3  is placed, depending on the humidity of an environment in which the humidity controlling material  3  is placed. 
     In the description below, the function of “absorbing or releasing the moisture contained in the air in which the humidity controlling material  3  is placed” may be referred to as a “humidity control function”. 
     If the fixed color particle  3 C does not have the humidity control function, glass or a polymeric material can be used as a material for forming the fixed color particle  3 C. 
     If the fixed color particle  3 C has the humidity control function, the fixed color particle  3 C includes: a humidity controlling liquid containing a hygroscopic substance; and a holding portion holding the humidity controlling liquid in the form of a particle. 
     As the humidity controlling liquid included in the fixed color particle  3 C, the humidity controlling liquid described above can be employed. 
     As the holding portion included in the fixed color particle  3 C, the holding portion described above can be employed. 
     That is, the fixed color particle  3 C may be a particle obtained by removing the indicator from the first particle  1 A of the first embodiment, or a particle obtained by removing the indicator from the first particle  2 A of the second embodiment. 
     A color of the fixed color particle  3 C may be the same as, or different from, a color of the first particle or the second particle. 
     Moreover, if there is a target of the humidity to be adjusted using the humidity controlling material  3 , the color of the fixed color particle  3 C is the same as the color of the first particle or the second particle at the target humidity. If the fixed color particle  3 C has such a color, it is easy to determine whether the environment in which the humidity controlling material is placed has reached the target humidity. 
     Because the humidity controlling material  3  contains the filed color particle  3 C, the color change of the first particle  3 A and the second particle  3 B can be easily recognized. 
     A ratio of the first particles  3 A to the second particles  3 B to the fixed color particles  3 C that constitute the humidity controlling material  3  may be set appropriately, in view of the colors of the first indicator and the second indicator to be used, of the color of the fixed color particles  3 C, and of how easily the first particles  3 A and the second particles  3 B can be checked for the color change. For example, a mass ratio of a sum of the first particles  3 A and the second particles  3 B to the fixed color particles  3 C may be set as follows: (the first particles+the second particles): (the fixed color particles)=10:90 to 90:10, 25:75 to 75:25, or 40:60 to 60:40. 
     A ratio of the first particles  3 A to the second particles  3 B can be appropriately set as described in the first embodiment. 
     The humidity controlling material  3  of the above configuration can also be provided as a hygroscopic material with which the amount of absorbed moisture is easily understood. 
     Fourth Embodiment 
       FIG.  5    is an illustration of a humidity controlling apparatus  100  according to a fourth embodiment of the present invention. The humidity controlling apparatus  100  includes: a humidity controlling material  110 ; and a housing portion  120 . The housing portion  120  includes: a container  121 ; and a lid  122 . 
     As the humidity controlling material  110 , any of the humidity controlling materials  1  to  3  described above can be employed. The humidity controlling material  110  is filled in the container  121 . 
     The container  121  includes an internal space for filling the humidity controlling material  110 , and an upper portion of the container  121  is open to have an opening portion  121   a . The container  121  illustrated in  FIG.  5    is a flat thin container having a rectangular shape in plan view and a height direction dimension smaller than a plane direction dimension. 
     The container  121  is preferably transparent to light so that a state of the humidity controlling material  110  can be visually recognized. As a material for forming the container  121 , a light-transparent material can be preferably used. For example, as the material for forming the container  121 , a known polymeric material such as glass, polystyrene, polyolefin, polyethylene terephthalate (PET), polymethyl methacrylate (PMMA), or polyvinyl chloride (PVC) can be used. 
     The container  121  may be totally, or only partially, transparent to light. 
     The lid  122  covers the container  121  from above the container  121  to close the opening portion  121   a . As a result, the housing portion  120  houses the humidity controlling material  110  inside the housing portion  120 . 
     The lid  122  includes a plurality of through holes  112   a  penetrating the lid  112  in the thickness direction. Through the through holes  122   a , the air in which the humidity controlling apparatus  100  is placed flows into, and out of, the housing portion  120 . 
     A size of the through holes  122   a  can be set appropriately as long as the humidity controlling material  110  cannot pass through the through holes  122   a , and as long as the air flow is not obstructed. Moreover, the shape of the through holes  122   a  in plan view can also be set appropriately as long as the function of the through holes  122   a  is not obstructed. 
     The lid  122  may or may not be transparent to light. 
     As a material for forming the lid  122 , a polymeric material can be preferably used. 
     The above humidity controlling apparatus  100  includes the humidity controlling material described above. With the humidity controlling apparatus  100 , it is easy to understand the amount of absorbed moisture. 
     Fifth Embodiment 
       FIG.  6    is an illustration of a humidity controlling apparatus  200  according to a fifth embodiment of the present invention. The humidity controlling apparatus  200  includes: a humidity controlling material  210 ; and a housing portion  220 . 
     As the humidity controlling material  210 , any of the humidity controlling materials  1  to  3  described above can be employed. 
     The housing portion  220  includes: a first housing portion  221 ; a second housing portion  222 ; and a removing portion  223 . 
     The first housing portion  221  is a space housing first particles  210 A included in the humidity controlling material  210 . 
     The second housing portion  222  is a space housing second particles  210 B included in the humidity control ling material  210 . 
     The first housing portion  221  and the second housing portion  222  each include: an inlet for taking in external air into the first housing portion  221  and the second housing portion  222 ; and an outlet for discharging air of the first housing portion  221  and the second housing portion  222  to the outside. The inlet and the outlet may be provided in any given position as long as the advantageous effects of the humidity controlling apparatus  200  are not obstructed. 
     Moreover, a plurality of through holes may be provided to wall surfaces of the first housing portion  221  and the second housing portion  222 , and the through holes may function inlets and outlets. The through holes may be in the form of a mash or slits. 
     The first housing portion  221  and the second housing portion  222  are adjacent to each other through a partition  228  including a through hole through which air can flow. In the humidity controlling apparatus  200 , the first housing portion  221  and the second housing portion  222  are arranged in the height direction (a vertical direction) across the partition  228 . 
     A wall of the first housing portion  221  and a wall of the second housing portion  222  are at least partially transparent to light. 
     As a material for forming the first housing portion  221  and the second housing portion  222 , the material for forming the container  121  in the fourth embodiment described above can be employed. 
     The removing portion  223  removes moisture from the humidity controlling material  210 . The removing portion  223  is located below the first housing portion  221 . That is, the removing portion  223  is disposed closer to the first housing portion  221  than to the second housing portion  222 . 
     The removing portion  223  includes an air blower that blows air to the first housing portion  221  and the second housing portion  222 . The removing portion  223  can blow air to the first housing portion  221  and the second housing portion  222 , and partially remove moisture from the first particles  210 A housed in the first housing portion  221  and the second particles  210 B housed in the second housing portion  222 . 
     Moreover, the removing portion  223  may include a heat source. The removing portion  223  including the heat source sends warm air or hot air to the first housing portion  221  and the second housing portion  222  to heat the first particles  210 A and the second particles  210 B. As a result, moisture partially evaporates from the first particles  210 A and the second particles  2106 . 
     Moreover, the removing portion  223  may include a light source that irradiates the first particles  210 A and the second particles  210 B with light. When the first particles  210 A and the second particles  210 B are irradiated with light, the first particles  210 A and the second particles  210 B absorb the light and generate heat. Because of the generated heat, moisture partially evaporates from the first particles  210 A and the second particles  210 B. 
     When the removing portion  223  includes the light source, a bottom portion  221   a  of the first housing portion  221  may be transparent to light. 
     Furthermore, when the removing portion  223  includes the light source, the first housing portion  221  and the second housing portion  222  may each have a stirring device that stirs the first particles  210 A and the second particles  210 B. As a result, the humidity controlling material  210  (the first particles  210 A or the second particles  210 B) changes in position in each housing portion, and the entire humidity controlling material  210  is more likely to be irradiated with light. 
     In addition, when the removing portion  223  includes the light source, black fixed color particles may be mixed in either one of, or both, the first housing portion  221  and the second housing portion  222 . The black fixed color particles suitably absorb light and generate heat, thereby making it possible to accelerate evaporation of a portion of moisture from the first particles  210 A and the second particles  210 B. 
     In the configuration described above, the first particles  210 A housed in the first housing portion  221  near the removing portion  223  are preferably particles having a core-shell structure similar to the first particles  2 A described in the second embodiment. 
     Moreover, the second particles  210 B housed in the second accommodating portion  222  far from the removing portion  223  are preferably particles in which the humidity controlling liquid  11  is swollen with the holding portion  12 , similar to the first particles  1 A described in the first embodiment. 
     The core-shell particles are relatively less likely to dry than the swollen particles. Hence, the core-shell particles are disposed in a position near the removing portion  223 , so that moisture can be suitably removed from the core-shell particles. 
     Moreover, the humidity controlling apparatus  200  may include a fan that allows air to flow inside the humidity controlling apparatus  200 . The fan, for example, takes air into the humidity controlling apparatus  200  from the outside of the humidity controlling apparatus  200 , and allows the air to flow inside the humidity controlling apparatus  200 . As a result, the air around the humidity controlling material  210  included in the humidity controlling apparatus  200  is easily replaced, and humidity control is easily carried out. 
     The above humidity controlling apparatus  200  includes the humidity controlling material described above. With the humidity controlling apparatus  200 , it is easy to understand the amount of absorbed moisture. 
     Although preferred embodiments according to the present invention have been described above with reference to the accompanying drawings, it is needless to say that the present invention is not limited to such embodiments. Various shapes and combinations of the constituent members shown in the examples described above are merely examples, and can be modified in various manners in accordance with design requirements unless otherwise departing from the subject matter of the present invention.