JP3786230B2 - Manufacturing method of alumina humidity conditioning material - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、アルミナ系調湿材料の製造方法に関し、特に水酸化アルミニウムの熱処理によって形成される細孔の吸放湿特性を利用することにより、結露やカビ・ダニの発生を防止する建築材料として有用なアルミナ系調湿材料の製造方法に関する。なお、本明細書において調湿材料とは、吸湿機能及び放湿機能を有し、例えば本発明の調湿材料を壁材として用いた場合に、室内の湿度が高くなると水蒸気を吸収して貯え（吸湿）、逆に環境湿度が低くなると保有する水分を室内に放出し（放湿）、室内の湿度を一定に保つような機能を有する微多孔質材料をいう。
【０００２】
【従来の技術】
従来の日本の家屋では、木材や土壁等の調湿性能の良い建築材料が用いられ、また気密性もあまり良くないため隙間風による自然換気が行われていた。しかし、最近の建築物では吸湿性の劣る新建材が使用され、さらに高断熱化・高気密化の促進により、以下のような問題が生じている。
（１）内部結露により建材に腐朽菌が繁殖し、強度が低下する。
（２）ダニ・カビの繁殖によりアレルギー問題が発生する。
（３）梅雨時等、室内が高湿度になり易く、居住者が不快感を感じる。
このような問題を解決するために、一般に除湿器やエアコン等の空調設備が用いられている。しかし、設備費が高価で、しかも快適さを保つためには常時運転しなければならないため、運転コストも高いという難点がある。さらに、このような空調設備を用いても、押し入れや隅部等の局所的な場所の湿度の制御は難しいという問題があった。そのため、これまで種々の吸湿性能の高い調湿建材の開発が行われてきた。
【０００３】
【発明が解決しようとする課題】
従来の調湿材料の吸着量（吸湿量）と相対湿度の関係は、一般に図１１に示すような３種類のパターンに分類される。図１１において、曲線Ａは、湿度の上昇とともに吸着量がほぼ比例的に増大するパターンであり、一般にはこのような吸湿特性を示すものが多く、その代表例はシリカゲルである。なお、シリカゲルは、相対湿度に比例して吸着量が大きくなるが、脱着温度は約１１０℃以上と言われており、その放湿機能に難点がある。曲線Ｂのパターンの吸湿特性を示すものの代表例はゼオライトであり、相対湿度が約２０〜３０％位の低湿度で吸着量が急峻に増大するが、それ以上は湿度が高くなってもほとんど吸着しなくなる。最後に、曲線Ｃは、約８０〜９０％以上の高湿度で吸着量が急峻に増大するパターンであり、そのような吸湿特性を示す材料の例としてはカオリナイトが挙げられる。
しかしながら、特にカビの繁殖防止の観点からは、８０％以下の湿度で吸着量が急峻に増大する材料が好ましい。また、快適性等の観点からは約６０％で、また場合に応じては約４０％のように、所望の任意の湿度において吸着量が急峻に増大する材料が望ましい。
【０００４】
従って、本発明の目的は、制御された任意の湿度で吸着量が急峻に増大する調湿材料を得ることができ、それによって、例えば局所的に低湿度が要求される場所（隅部等の結露し易い場所）においても、任意のほぼ一定の湿度に保つことができ、結露やカビ・ダニの繁殖を防止することができるアルミナ系調湿材料を生産性よく低コストで製造できる方法を提供することにある。
【０００５】
【課題を解決するための手段】
前記目的を達成するために、本発明の第１の態様によれば、水酸化アルミニウム粉末を減圧雰囲気下で熱処理することを特徴とする吸着・脱着性アルミナ系調湿材料の製造方法が提供される。
さらに好適な本発明の第２の態様によれば、平均粒径が５０μｍ以下の水酸化アルミニウム粉末を減圧雰囲気下で熱処理することを特徴とする吸着・脱着性アルミナ系調湿材料の製造方法が提供される。
前記いずれの態様においても、好ましくは、前記熱処理を３００〜８００℃の温度で行う。
【０００６】
【発明の実施の形態】
吸湿作用は、微多孔質材料の細孔への水蒸気の吸着によって行われる。ケルビンの式より明らかなように、細孔径の大きさによって、吸着量が増大する湿度の位置が決まる。すなわち、ゼオライトのような細孔径がほぼ一定で小さい材料では、図１１の曲線Ｂで示されるように低湿度で吸着量が増大する。また、例えばカオリナイトの表面とその二次粒子からなる細孔がほぼ一定で大きい材料では、図１１の曲線Ｃで示されるように高湿度で吸着量が増大する。さらにシリカゲルのような細孔径が幅広い分布をもつ材料では、図１１の曲線Ａで示されるように湿度の増大とともに吸着量は単調に増大する。
そこで、希望する湿度範囲において吸着量が急峻に増大するような調湿材料を得るためには、細孔径を制御する必要がある。適切に細孔径を制御された調湿材料では、環境湿度が高くなると材料の細孔に水蒸気を水にして貯え（吸湿）、環境湿度が低くなると水を蒸発させ（放湿）、湿度を一定の最適値に保つことができる。
【０００７】
本発明者らは、上記のような吸放湿特性を示す調湿材料を製造すべく鋭意研究の結果、調湿材料の原料として水酸化アルミニウム（以下、水酸化アルミという）の粉末を用い、これを減圧雰囲気下、好ましくは０．９気圧以下の減圧雰囲気下で熱処理すれば、細孔径分布のピーク幅が狭くてシャープな分布となり、或る一定の比較的狭い湿度範囲で吸着量が急峻に増大する吸放湿特性を示すことを見い出し、しかも、出発材料の水酸化アルミの平均粒径及び／又は熱処理雰囲気の圧力、あるいはさらに熱処理温度を変えることにより、吸着量が急峻に増大する湿度位置を任意に変え得ることを見い出し、本発明を完成するに至ったものである。
以下、本発明の方法による水酸化アルミ粉末の細孔径分布及び吸放湿特性の制御に関して、さらに詳しく説明する。
【０００８】
例えば、ゼオライト、珪藻土等の天然材料は細孔径が一義的に決まっており、その制御を行うことは困難である。
これに対して、水酸化アルミ（ギブサイトＡｌ2Ｏ3・３Ｈ2Ｏ）の場合、加熱により脱水反応が起こり、ベーマイト（Ａｌ2Ｏ3・Ｈ2Ｏ）を経てアルミナ（Ａｌ2Ｏ3）に変化し、この過程で放出された水の通り道（脱水経路）に細孔が生じるので、熱処理条件を変えることにより、細孔の数及び細孔径を変化させることができる。
例えば、熱処理温度を変化させた場合、２００℃で既に一部ベーマイトが生じ、３５０℃でギブサイトが全てベーマイトになり、５００℃以上ではアルミナになっている。従って、吸放湿に必要な細孔を生じさせるためには、水酸化アルミ粉末の熱処理は３００℃以上で行うことが望ましい。
熱処理温度の上昇に伴い、脱水による細孔形成のため、粉末の比表面積は増大するが、一方、細孔の融合も起こり始めるため、５００℃以後は温度の上昇とともに漸次減少し、雰囲気圧力や出発材料の平均粒径によっても若干異なるが、約７００〜８００℃付近から急激に減少する。従って、水酸化アルミ粉末の熱処理は８００℃以下で行うことが望ましい。なお、熱処理時間は所望の吸放湿特性に応じて任意に選定できるが、通常は数時間程度以下で充分である。
【０００９】
吸着（吸湿）は、材料の細孔中の毛細管凝縮作用によって起こると考えられるため、細孔の数や細孔径によって吸着の挙動が変化する。熱処理温度と吸着量の関係についても、熱処理温度が３００℃から５００℃にかけて上昇するに伴い、粉末の比表面積が増大すると共に、吸着量も大幅に上昇し、例えば大気圧下での熱処理においては約５００℃付近の熱処理温度で吸着量はピークを示し、その後、熱処理温度が上昇するに伴って比表面積が減少するため漸次減少し、約７００〜８００℃から吸着量は急激に減少する。また、高温での熱処理はそれだけ加熱エネルギーも必要となり、経済的にも不利となる。このような吸着量や経済性等の観点からみて、より好ましい熱処理温度は３００℃以上、７００℃以下であり、特に好ましくは４００℃以上、６００℃以下である。
また、水酸化アルミ粉末の平均粒径及び熱処理雰囲気の圧力が同一であっても、熱処理温度によって吸着量が急峻に増大する湿度位置（より正確には所定幅の湿度域）が変化し、高温になる程、高湿度側に移行し、またその湿度域における吸着量の増大度合（立ち上がり）も急激になる。
【００１０】
また、本発明者らの研究によれば、水酸化アルミ粉末の熱処理による脱水反応（熱分解反応）の促進には、減圧によって分解生成気体（水蒸気）を材料内から除去することが効果的であることが確認された。すなわち、熱処理雰囲気の水蒸気分圧を減少させて熱処理することにより、細孔径を制御することができる。例えば、雰囲気圧力を０．９気圧以下、好ましくは０．１気圧以下の減圧雰囲気下で熱処理した場合、細孔径分布のピーク幅が狭くてシャープな分布となり、その結果、熱処理温度に応じて相対湿度が約３０〜約６０％の任意の値で、吸着量の立ち上がりが急峻な調湿材料を得ることができる。
また、概して雰囲気圧力が低くなる程、調湿材料の細孔径分布のピーク幅が狭く、かつシャープなものとなり、また比表面積が増大し、平均細孔径が小さくなる傾向にある。
なお、熱処理を減圧雰囲気下で行う場合、出発材料の水酸化アルミ粉末の平均粒径は多少大きくてもよく、例えば１００μｍ以下でも吸着量の増大が急峻な調湿材料を得ることができるが、この場合にも、水酸化アルミ粉末の平均粒径は後述するように５０μｍ以下であることが好ましい。
【００１１】
さらに本発明者らの研究によれば、大気圧下で熱処理を行った場合においても、水酸化アルミ粉末の平均粒径を５０μｍ以下、好ましくは２５μｍ以下、より好ましくは２μｍ以下に調整した場合、同様の傾向を示し、熱処理温度に応じた所定の湿度域で吸着量が急峻に増大する調湿材料が得られることが見い出された。また、水酸化アルミ粉末の平均粒径が小さい程、得られる調湿材料の吸着量は全体的に増大する。さらに、減圧雰囲気下で、平均粒径の小さな水酸化アルミ粉末を用いて熱処理を行うと、上記効果が助長されることは言うまでもない。
【００１２】
以上のように、本発明の方法によれば、熱処理温度、雰囲気圧力、水酸化アルミ粉末の粒径を変えることにより、得られる粉末の細孔径分布、従って吸放湿特性を比較的に簡単に、任意に制御することができる。
得られる粉末状のアルミナ系調湿材料は、適当なバインダー、補強材等を混合し、加圧成形してシート材、板材等任意の形状に成形した固形材や、コーティング材など、任意の形態で用いることができ、壁材等の建築用材料に好適に利用することができる。また、所望の湿度に応じて、適切な湿度域で吸着量が急峻に増大する調湿材料を選択して使用することができる。例えば、換気が困難で高湿度になり易い押し入れ、下駄箱など、局所的に低湿度が要求される場所においても、低湿度域で吸着量が急激に増大する調湿材料を選択使用することにより、任意の空間を常に任意の適切な湿度状態に保つことができる。それによって、結露やカビ・ダニなどの繁殖を防止でき、しかも、センサーや電気機器を用いていないため、極めて安全で経済的に調湿が行われる。
【００１３】
【実施例】
以下、実施例を示して本発明についてより具体的に説明するが、本発明が下記実施例に限定されるものでないことはもとよりである。
【００１４】
実施例１
平均粒径約２５μｍの水酸化アルミ粉末を６００℃、０．１気圧の減圧雰囲気下で熱処理した。熱処理は、水酸化アルミ粉末をセラミック製緻密円筒管内に入れ、円筒管を真空ポンプに接続して０．１気圧に維持し、これを環状電気炉内に設置し、熱電対で試料温度を測定しながら行った。昇降温速度は２００℃／ｈとし、熱処理温度での保持時間は２時間とした。得られた粉末の細孔径分布を図１に、またその吸放湿特性（吸着等温線）を図２に示す。
なお、得られた粉末の細孔径分布は、窒素吸着法を用いて測定した。また、吸放湿特性は、測定系内の温度を一定（２５℃）にして、水蒸気圧を変化させて平衡状態に達した時の試料重量の変化から吸着量を求める（重量法）吸着平衡測定装置を用いて測定した。吸着量は、絶乾状態の粉末重量に対する水の吸着重量の割合を示す。
図１から明らかなように、得られた調湿材料の細孔径分布はピーク幅が狭くてシャープな分布であり、また図２から明らかなように、吸着量は相対湿度約６０％で立ち上がっている。従って、この調湿材料を用いることにより、環境湿度を約６０％に調湿できる。
【００１５】
実施例２
平均粒径約２５μｍの水酸化アルミ粉末を５００℃、０．１気圧の減圧雰囲気下で実施例１と同様に熱処理した。得られた粉末の細孔径分布を図３に、またその吸放湿特性を図４に示す。
図３から明らかなように、得られた調湿材料の細孔径分布はピーク幅が狭くてシャープな分布であり、また図４から明らかなように、吸着量は相対湿度約５０％で立ち上がっている。従って、この調湿材料を用いることにより、環境湿度を約５０％に調湿できる。
【００１６】
実施例３
実施例１で用いた平均粒径約２５μｍの水酸化アルミ粉末をボールミルで粉砕して得た平均粒径約２μｍの水酸化アルミ粉末を６００℃、０．１気圧の減圧雰囲気下で熱処理した。得られた粉末の細孔径分布を図５に、またその吸放湿特性を図６に示す。
図５から明らかなように、得られた調湿材料の細孔径分布はピーク幅が狭くてシャープな分布であり、また図６から明らかなように、吸着量は相対湿度約５０％で立ち上がっている。
【００１７】
実施例４
実施例３で用いた平均粒径約２μｍの水酸化アルミ粉末を４００℃、０．１気圧の減圧雰囲気下で熱処理した。得られた粉末の細孔径分布を図７に、またその吸放湿特性を図８に示す。得られた調湿材料には微細な細孔が含まれるため、４０％位の湿度位置で吸着量が急峻に増大している。
【００１８】
実施例５
平均粒径約２５μｍの水酸化アルミ粉末を６００℃、０．０１気圧の減圧雰囲気下で実施例１と同様に熱処理した。得られた粉末の細孔径分布を図９に、またその吸放湿特性を図１０に示す。
図９から明らかなように、得られた調湿材料の細孔径分布はピーク幅が狭くてシャープであり、また図１０から明らかなように、吸着量は相対湿度約６０％で立ち上がっている。従って、この調湿材料を用いることにより、環境湿度を約６０％に調湿できる。
上記各実施例から明らかなように、減圧雰囲気下で、あるいは水酸化アルミ粉末の粒径を小さく調整し、熱処理することにより、細孔径分布がシャープで、吸着量が所定の湿度位置で急峻に立ち上がる調湿材料を得ることができ、また熱処理条件を適宜変えることにより、任意の吸放湿特性が得られるように制御することができる。
【００１９】
【発明の効果】
以上のように、本発明のアルミナ系調湿材料の製造方法に従って水酸化アルミ粉末を適切に熱処理することにより、細孔径分布を任意に制御でき、任意の湿度で吸着量が急峻に増大する調湿材料を得ることができる。本発明により得られる調湿材料を適宜選択して用いることによって、例えば局所的に低湿度が要求される場所（隅部等の結露し易い場所）においても、任意の所望の湿度に保つことができ、結露やカビ・ダニの繁殖を防止することができる。また、本発明の方法は単に熱処理のみによるため、その工程が比較的簡単であり、従って前記したような優れた吸放湿特性を示すアルミナ系調湿材料を生産性良く低コストで製造することができる。
【図面の簡単な説明】
【図１】 実施例１で作製したアルミナ系調湿材料の細孔径分布を示すグラフである。
【図２】 実施例１で作製したアルミナ系調湿材料の吸放湿特性を示すグラフである。
【図３】 実施例２で作製したアルミナ系調湿材料の細孔径分布を示すグラフである。
【図４】 実施例２で作製したアルミナ系調湿材料の吸放湿特性を示すグラフである。
【図５】 実施例３で作製したアルミナ系調湿材料の細孔径分布を示すグラフである。
【図６】 実施例３で作製したアルミナ系調湿材料の吸放湿特性を示すグラフである。
【図７】 実施例４で作製したアルミナ系調湿材料の細孔径分布を示すグラフである。
【図８】 実施例４で作製したアルミナ系調湿材料の吸放湿特性を示すグラフである。
【図９】 実施例５で作製したアルミナ系調湿材料の細孔径分布を示すグラフである。
【図１０】 実施例５で作製したアルミナ系調湿材料の吸放湿特性を示すグラフである。
【図１１】 従来の調湿材料の吸湿特性パターンを示すグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing an alumina-based humidity conditioning material, and in particular, as a building material that prevents the formation of condensation and mold / tick by utilizing the moisture absorption / release characteristics of pores formed by heat treatment of aluminum hydroxide. The present invention relates to a method for producing a useful alumina-based humidity conditioning material. In the present specification, the humidity control material has a moisture absorption function and a moisture release function. For example, when the humidity control material of the present invention is used as a wall material, it absorbs and stores water vapor when the indoor humidity increases. (Hygroscopic), conversely, refers to a microporous material having a function of releasing the retained moisture into the room (moisture release) and keeping the room humidity constant when the environmental humidity becomes low.
[0002]
[Prior art]
In traditional Japanese houses, building materials with good humidity control such as wood and earth walls are used, and the airtightness is not so good. However, new buildings with poor hygroscopicity are used in recent buildings, and the following problems have arisen due to the promotion of higher thermal insulation and higher airtightness.
(1) Due to internal condensation, decaying fungi grow on the building material and the strength decreases.
(2) Allergic problems occur due to the growth of mites and molds.
(3) During the rainy season, etc., the room tends to be highly humid and the resident feels uncomfortable.
In order to solve such problems, air conditioning equipment such as a dehumidifier and an air conditioner is generally used. However, since the equipment cost is expensive and it is necessary to always operate in order to maintain comfort, there is a problem that the operation cost is high. Furthermore, even if such an air conditioning equipment is used, there is a problem that it is difficult to control the humidity in a local place such as a close-in or a corner. For this reason, various humidity-controlling building materials having high moisture absorption performance have been developed so far.
[0003]
[Problems to be solved by the invention]
Adsorption of conventional humidity control material (moisture absorption) and the relationship of relative humidity, are generally classified into three types of patterns as shown in FIG. 11. In FIG. 11 , a curve A is a pattern in which the amount of adsorption increases almost proportionally with an increase in humidity. In general, there are many that exhibit such moisture absorption characteristics, and a typical example is silica gel. Silica gel increases in the amount of adsorption in proportion to the relative humidity, but the desorption temperature is said to be about 110 ° C. or higher, and its moisture releasing function is difficult. A typical example of the moisture absorption characteristics of the curve B pattern is zeolite, and the adsorption amount increases sharply at a relative humidity of about 20 to 30%, but it is almost absorbed even at higher humidity. No longer. Finally, curve C is a pattern in which the amount of adsorption sharply increases at a high humidity of about 80 to 90% or higher, and an example of a material exhibiting such moisture absorption characteristics is kaolinite.
However, in particular, from the viewpoint of preventing mold growth, a material whose adsorption amount sharply increases at a humidity of 80% or less is preferable. Further, from the viewpoint of comfort and the like, a material whose adsorption amount sharply increases at an arbitrary desired humidity is desirable, such as about 60% and, depending on the case, about 40%.
[0004]
Therefore, the object of the present invention is to obtain a humidity control material whose amount of adsorption sharply increases at an arbitrary controlled humidity, and thereby, for example, a place where low humidity is locally required (such as a corner). Providing a low-cost, high-productivity alumina-based humidity-conditioning material that can be kept at an almost constant humidity even in areas where condensation is likely to occur, and that prevents condensation and mold and mite reproduction. There is to do.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, there is provided a method for producing an adsorbable / desorbable alumina-based humidity conditioning material, characterized by heat-treating aluminum hydroxide powder in a reduced-pressure atmosphere. The
According to a further preferred second aspect of the present invention, there is provided a method for producing an adsorbable / desorbable alumina-based humidity conditioning material, characterized in that an aluminum hydroxide powder having an average particle size of 50 μm or less is heat-treated in a reduced-pressure atmosphere. Provided.
In any of the above embodiments, the heat treatment is preferably performed at a temperature of 300 to 800 ° C.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
The hygroscopic action is performed by adsorption of water vapor into the pores of the microporous material. As apparent from the Kelvin equation, the position of the humidity at which the amount of adsorption increases depends on the size of the pore diameter. That is, in the material having a small pore size at a substantially constant, such as zeolite, the adsorption amount of low humidity as shown by the curve B in FIG. 11 is increased. Further, for example, in large material pores comprising kaolinite surface and its secondary particles have substantially constant, the adsorption amount at high humidity, as shown by the curve C in FIG. 11 is increased. The material further having a pore size of wide distribution such as silica gel, adsorption with increasing humidity as shown by the curve A in FIG. 11 increases monotonically.
Therefore, in order to obtain a humidity control material whose amount of adsorption sharply increases in a desired humidity range, it is necessary to control the pore diameter. In a humidity control material with appropriately controlled pore diameter, water vapor is stored in the material pores as water (moisture absorption) when the environmental humidity is high, and water is evaporated (moisture release) when the environmental humidity is low. Can be kept at the optimum value.
[0007]
As a result of intensive studies to produce a humidity control material exhibiting the moisture absorption / release characteristics as described above, the present inventors used aluminum hydroxide (hereinafter referred to as aluminum hydroxide) powder as a raw material of the humidity control material. This low-pressure atmosphere, preferably be heat-treated under a reduced pressure atmosphere of less 0.9 atm, it becomes sharp distribution narrow peak width of the pore size distribution, steep adsorption amount at a certain relatively narrow humidity range The humidity at which the amount of adsorption increases sharply by changing the average particle diameter of aluminum hydroxide as the starting material and / or the pressure of the heat treatment atmosphere, or further the heat treatment temperature. The present inventors have found that the position can be arbitrarily changed and have completed the present invention.
Hereinafter, the control of the pore size distribution and moisture absorption / release characteristics of the aluminum hydroxide powder by the method of the present invention will be described in more detail.
[0008]
For example, natural materials such as zeolite and diatomaceous earth have a unique pore size and are difficult to control.
On the other hand, in the case of aluminum hydroxide (Gibsite Al 2 O 3 .3H 2 O), a dehydration reaction occurs by heating, and boehmite (Al 2 O 3 .H 2 O) is passed through to alumina (Al 2 O 3 ). Since the pores are formed in the passage (dehydration pathway) of the water released in this process, the number of pores and the pore diameter can be changed by changing the heat treatment conditions.
For example, when the heat treatment temperature is changed, some boehmite is already generated at 200 ° C., all the gibbsite is boehmite at 350 ° C., and alumina is above 500 ° C. Therefore, in order to generate pores necessary for moisture absorption / release, it is desirable to perform the heat treatment of the aluminum hydroxide powder at 300 ° C. or higher.
As the heat treatment temperature rises, the specific surface area of the powder increases due to the formation of pores due to dehydration. On the other hand, the fusion of the pores also begins to occur. Although it slightly varies depending on the average particle diameter of the starting material, it rapidly decreases from around 700 to 800 ° C. Therefore, the heat treatment of the aluminum hydroxide powder is desirably performed at 800 ° C. or lower. The heat treatment time can be arbitrarily selected according to the desired moisture absorption / release characteristics, but usually about several hours or less is sufficient.
[0009]
Adsorption (moisture absorption) is considered to occur due to capillary condensation in the pores of the material, so the adsorption behavior varies depending on the number of pores and the pore diameter. Regarding the relationship between the heat treatment temperature and the amount of adsorption, as the heat treatment temperature increases from 300 ° C. to 500 ° C., the specific surface area of the powder increases and the amount of adsorption increases significantly. For example, in heat treatment under atmospheric pressure, The amount of adsorption shows a peak at a heat treatment temperature of about 500 ° C., and then gradually decreases because the specific surface area decreases as the heat treatment temperature rises, and the amount of adsorption decreases rapidly from about 700 to 800 ° C. In addition, heat treatment at a high temperature requires heating energy, which is economically disadvantageous. From the viewpoint of such an adsorption amount and economic efficiency, a more preferable heat treatment temperature is 300 ° C. or more and 700 ° C. or less, and particularly preferably 400 ° C. or more and 600 ° C. or less.
Moreover, even if the average particle size of the aluminum hydroxide powder and the pressure of the heat treatment atmosphere are the same, the humidity position (more precisely, the humidity range of the predetermined width) where the amount of adsorption sharply increases with the heat treatment temperature changes, resulting in a high temperature. As it becomes, it shifts to the high humidity side, and the degree of increase (rise) of the adsorption amount in the humidity region also becomes steep.
[0010]
Further, according to the study by the present inventors, it is effective to remove the decomposition product gas (water vapor) from the material by reducing the pressure in order to accelerate the dehydration reaction (thermal decomposition reaction) by heat treatment of the aluminum hydroxide powder. It was confirmed that there was. That is, the pore diameter can be controlled by reducing the water vapor partial pressure in the heat treatment atmosphere and performing the heat treatment. For example, when heat treatment is performed under a reduced pressure atmosphere with an atmospheric pressure of 0.9 atm or less, preferably 0.1 atm or less, the peak width of the pore diameter distribution is narrow and sharp, and as a result, the relative pressure depends on the heat treatment temperature. A humidity-controlling material having a steep rise in the amount of adsorption can be obtained at an arbitrary value of about 30 to about 60%.
In general, the lower the atmospheric pressure, the narrower and sharper the peak width of the pore size distribution of the humidity control material, and the specific surface area increases and the average pore size tends to decrease.
When the heat treatment is performed in a reduced-pressure atmosphere, the average particle diameter of the starting aluminum hydroxide powder may be somewhat large, for example, a humidity-controlling material with a sharp increase in the amount of adsorption can be obtained even at 100 μm or less, Also in this case, the average particle diameter of the aluminum hydroxide powder is preferably 50 μm or less as described later.
[0011]
Further, according to the study by the present inventors, even when the heat treatment is performed under atmospheric pressure, when the average particle size of the aluminum hydroxide powder is adjusted to 50 μm or less, preferably 25 μm or less, more preferably 2 μm or less, It has been found that a humidity control material that exhibits the same tendency and has a steep increase in the amount of adsorption in a predetermined humidity range according to the heat treatment temperature can be obtained. Further, the smaller the average particle size of the aluminum hydroxide powder, the greater the amount of adsorption of the resulting humidity control material. Furthermore, it goes without saying that the above effect is promoted when heat treatment is performed using an aluminum hydroxide powder having a small average particle diameter in a reduced-pressure atmosphere.
[0012]
As described above, according to the method of the present invention, by changing the heat treatment temperature, the atmospheric pressure, and the particle size of the aluminum hydroxide powder, the pore size distribution of the resulting powder, and thus the moisture absorption / release characteristics, can be made relatively simple. Can be controlled arbitrarily.
The resulting powdery alumina-based humidity conditioning material can be mixed in a suitable binder, reinforcing material, etc., pressed and molded into any shape, such as a solid material or a coating material, such as a sheet material or plate material, or any form, such as a coating material. And can be suitably used for building materials such as wall materials. Further, it is possible to select and use a humidity control material whose adsorption amount sharply increases in an appropriate humidity range according to the desired humidity. For example, even in places where low humidity is required locally, such as intrusions and shoeboxes that are difficult to ventilate and become highly humid, by selectively using a humidity control material whose adsorption amount increases rapidly in the low humidity range Any space can always be kept in any suitable humidity state. As a result, it is possible to prevent condensation and mold / mite breeding, and because it uses no sensors or electrical equipment, humidity control is extremely safe and economical.
[0013]
【Example】
EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated more concretely, it cannot be overemphasized that this invention is not what is limited to the following Example.
[0014]
Example 1
Aluminum hydroxide powder having an average particle size of about 25 μm was heat-treated in a reduced pressure atmosphere at 600 ° C. and 0.1 atm. For heat treatment, put aluminum hydroxide powder in a ceramic dense cylindrical tube, connect the cylindrical tube to a vacuum pump and maintain it at 0.1 atm, install it in an annular electric furnace, and measure the sample temperature with a thermocouple I went there. The temperature raising / lowering speed was 200 ° C./h, and the holding time at the heat treatment temperature was 2 hours. The pore size distribution of the obtained powder is shown in FIG. 1, and its moisture absorption / release characteristics (adsorption isotherm) are shown in FIG.
The pore size distribution of the obtained powder was measured using a nitrogen adsorption method. In addition, the moisture absorption and desorption characteristics are obtained by determining the adsorption amount from the change in the sample weight when the temperature in the measurement system is constant (25 ° C) and the water vapor pressure is changed to reach the equilibrium state (gravimetric method). It measured using the measuring apparatus. The amount of adsorption indicates the ratio of the weight of water adsorbed to the weight of powder in the absolutely dry state.
As is clear from FIG. 1, the pore size distribution of the obtained humidity control material is a sharp distribution with a narrow peak width, and as is clear from FIG. 2, the adsorption amount rises at a relative humidity of about 60%. Yes. Therefore, the humidity can be adjusted to about 60% by using this humidity control material.
[0015]
Example 2
Aluminum hydroxide powder having an average particle size of about 25 μm was heat-treated in the same manner as in Example 1 in a reduced pressure atmosphere at 500 ° C. and 0.1 atm. FIG. 3 shows the pore size distribution of the obtained powder, and FIG. 4 shows its moisture absorption / release characteristics.
As is clear from FIG. 3, the pore size distribution of the obtained humidity control material is a sharp distribution with a narrow peak width. As is clear from FIG. 4, the adsorption amount rises at a relative humidity of about 50%. Yes. Therefore, the humidity can be adjusted to about 50% by using this humidity conditioning material.
[ 0016 ]
Example 3
The aluminum hydroxide powder having an average particle size of about 2 μm obtained by pulverizing the aluminum hydroxide powder having an average particle size of about 25 μm used in Example 1 with a ball mill was heat-treated in a reduced pressure atmosphere at 600 ° C. and 0.1 atm. FIG. 5 shows the pore size distribution of the obtained powder, and FIG. 6 shows its moisture absorption / release characteristics.
As is clear from FIG. 5 , the pore size distribution of the obtained humidity control material is a sharp distribution with a narrow peak width, and as is clear from FIG. 6 , the adsorption amount rises at a relative humidity of about 50%. Yes.
[ 0017 ]
Example 4
The aluminum hydroxide powder having an average particle diameter of about 2 μm used in Example 3 was heat-treated in a reduced pressure atmosphere at 400 ° C. and 0.1 atm. FIG. 7 shows the pore size distribution of the obtained powder, and FIG. 8 shows its moisture absorption / release characteristics. Since the obtained humidity control material contains fine pores, the amount of adsorption sharply increases at a humidity position of about 40%.
[ 0018 ]
Example 5
Aluminum hydroxide powder having an average particle size of about 25 μm was heat-treated in the same manner as in Example 1 under a reduced pressure atmosphere at 600 ° C. and 0.01 atm. Figure 9 a pore size distribution of the resulting powder, also shows the Hygroscopic properties in FIG.
As is clear from FIG. 9 , the pore size distribution of the obtained humidity control material is sharp with a narrow peak width, and as is clear from FIG. 10 , the adsorption amount rises at a relative humidity of about 60%. Therefore, the humidity can be adjusted to about 60% by using this humidity control material.
As is clear from each of the above examples, by adjusting the particle size of the aluminum hydroxide powder to be small in a reduced pressure atmosphere or by heat treatment, the pore size distribution is sharp and the adsorption amount is sharp at a predetermined humidity position. A rising humidity control material can be obtained, and by appropriately changing the heat treatment conditions, it can be controlled to obtain any moisture absorption / release characteristics.
[ 0019 ]
【The invention's effect】
As described above, by appropriately heat-treating the aluminum hydroxide powder according to the method for producing an alumina humidity-controlling material of the present invention, the pore size distribution can be arbitrarily controlled, and the amount of adsorption can be increased sharply at any humidity. A wet material can be obtained. By appropriately selecting and using the humidity control material obtained according to the present invention, for example, it can be kept at any desired humidity even in places where low humidity is required locally (places such as corners where condensation is likely to occur). It is possible to prevent condensation and mold / tick breeding. In addition, since the method of the present invention is based only on heat treatment, the process is relatively simple. Therefore, an alumina-based humidity conditioning material exhibiting excellent moisture absorption / release characteristics as described above can be produced with high productivity and low cost. Can do.
[Brief description of the drawings]
1 is a graph showing the pore size distribution of an alumina-based humidity conditioning material produced in Example 1. FIG.
FIG. 2 is a graph showing moisture absorption / release characteristics of the alumina-based humidity control material produced in Example 1.
3 is a graph showing the pore size distribution of the alumina-based humidity conditioning material produced in Example 2. FIG.
4 is a graph showing the moisture absorption / release characteristics of the alumina-based humidity control material produced in Example 2. FIG.
5 is a graph showing the pore size distribution of the alumina-based humidity conditioning material produced in Example 3. FIG.
6 is a graph showing the moisture absorption / release characteristics of the alumina-based humidity control material produced in Example 3. FIG.
7 is a graph showing the pore size distribution of the alumina-based humidity conditioning material produced in Example 4. FIG.
FIG. 8 is a graph showing moisture absorption / release characteristics of the alumina-based humidity control material produced in Example 4.
9 is a graph showing the pore size distribution of the alumina-based humidity conditioning material produced in Example 5. FIG.
10 is a graph showing the moisture absorption / release characteristics of the alumina-based humidity control material produced in Example 5. FIG.
FIG. 11 is a graph showing a moisture absorption characteristic pattern of a conventional humidity control material.
Claims (3)
Priority Applications (1)
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|---|---|---|---|
| JP17780297A JP3786230B2 (en) | 1997-06-19 | 1997-06-19 | Manufacturing method of alumina humidity conditioning material |
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|---|---|---|---|
| JP17780297A JP3786230B2 (en) | 1997-06-19 | 1997-06-19 | Manufacturing method of alumina humidity conditioning material |
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| JP2005125984A Division JP2005320233A (en) | 2005-04-25 | 2005-04-25 | Method of manufacturing alumina-based humidity conditioning material |
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| JPH1111939A JPH1111939A (en) | 1999-01-19 |
| JP3786230B2 true JP3786230B2 (en) | 2006-06-14 |
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| JP3681923B2 (en) | 1999-06-18 | 2005-08-10 | 株式会社クボタ | Swivel work machine |
| JP5255836B2 (en) * | 2005-07-06 | 2013-08-07 | 靖雄 芝崎 | Method for producing ceramic porous body |
| US7927406B2 (en) | 2007-06-01 | 2011-04-19 | Denso Corporation | Water droplet generating system and method for generating water droplet |
| JP2011504867A (en) * | 2007-11-30 | 2011-02-17 | ナノロジカ エービー | Method for producing nanoporous alumina material having controlled structure and particle size, and nanoporous alumina obtained by the method |
| CN104370297B (en) * | 2014-10-27 | 2015-09-30 | 浙江理工大学 | A kind of preparation method of aluminium sesquioxide humidity adjusting material |
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