JP4177920B2 - Method for producing high-purity titanium oxide powder - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、優れた分散性を有し、焼結材料あるいは紫外線遮蔽材料等汎用的に利用しうる高純度酸化チタン粉末に関する。
【０００２】
【従来の技術】
酸化チタン粉末は、白色顔料として古くから利用されており、近年はコンデンサ、サーミスタの構成材料、チタン酸バリウムの原料等の電気・電子材料に用いられる焼結材料に広く利用されている。また、酸化チタンは可視光付近の波長領域において大きな屈折率を示すため、可視光領域では殆ど光吸収は起こらない。このことから、最近、化粧料、医薬あるいは塗料等の紫外線遮蔽が要求されるような材料にも広く使用されている。さらに、酸化チタンにそのバンドギャップ以上のエネルギーを持つ光を照射することによって酸化チタンが励起されて、伝導帯に電子、価電帯に正孔が生じるが、この電子による還元力及び正孔による酸化力を利用した光触媒反応の用途開発が盛んに行われている。この酸化チタン光触媒の用途は非常に多岐に渡っており、水の分解による水素の発生、排ガス処理、空気清浄、防臭、殺菌、抗菌、水処理、照明機器等の汚れ防止等、数多くの用途開発が行われている。
【０００３】
このように酸化チタンの用途は多岐に渡るが、顔料、塗料あるいは焼結材料などに酸化チタン粉末を利用する場合、水あるいは有機溶剤等に懸濁し分散させて使用する場合が多く、その場合酸化チタン粉末の溶媒への分散性が問題となる。上記のような用途、特に電子材料用酸化チタンは、近年の電子材料の超小型化に対応するため酸化チタン粒子を１μm 以下、さらには０．１μm 以下の超微粒にする必要がある。また、光触媒用酸化チタンについては、その光触媒活性を向上させ、さらに光触媒材に利用するとき酸化チタンを基材にコーティングするが、そのときの酸化チタン被膜の透明性を向上させるために、酸化チタン粒子を数nm〜数十nmというような超微粒子にする必要がある。このように、酸化チタンを微粒化するにともない、溶媒への分散性が悪くなり、溶媒に懸濁すると凝集が起こり、逆に電子材料や光触媒の特性に悪影響を与え、また紫外線遮蔽材においては酸化チタン粒子の凝集により紫外線の遮蔽特性が悪くなるという問題が生じる。
【０００４】
酸化チタン粉末を溶媒に懸濁する際、高度に分散させ、粒子同士の凝集を防ぐ方法としては、塩酸、硫酸あるいは有機酸などの酸を存在させ、懸濁液のｐＨを酸性側に調整するか、あるいは水酸化ナトリウム等のアルカリを存在させ懸濁液のｐＨをアルカリ側に調整する方法がある。これは、酸化チタン粒子表面に存在する水酸基に起因するもので、従来の酸化チタン粉末は、酸性側では酸化チタン粉末のゼータ電位（界面電位）がプラスとなり、またアルカリ性側ではマイナスの電位を帯びるため粒子同士の凝集を防ぎ分散性が向上する。
【０００５】
また、さらに分散性を向上させる方法には、酸化チタンの懸濁液をボールミル等の粉砕機や分級機を用い調整する方法、懸濁液中に例えばヘキサメタリン酸ナトリウム等の分散剤を存在させ、酸化チタン懸濁液を調製する方法がある。さらに、シリカ、アルミナのような元来分散性の高い疎水性物質を、酸化チタンの粒子表面にコーティングし、分散性の問題を解決する試みもなされている。例えば特開平5-28672 号公報では、アルミニウム塩基性塩の水溶液に酸を添加することによりｐＨを１０．５〜１２．０に調節し、これに二酸化チタンスラリーを混合し、次いでこれを酸にて中和し二酸化チタン粒子表面に酸化アルミニウム水和物を均一に析出させる方法が開示されている。
【０００６】
【発明が解決しようとする課題】
しかしながら、上記従来技術のような酸化チタン粒子の分散性を向上させる方法は、酸、アルカリ、分散剤あるいは酸化チタン粒子表面の異物質によるコーティングというような酸化チタン以外の成分を用いるため、酸化チタン本来の特性が変化したり、また電子材料、顔料、紫外線遮蔽材あるいは光触媒等に利用した場合、このような他成分が混入するため、その利用材に悪影響を及ぼすという問題があった。
【０００７】
したがって、本発明の目的は、分散溶媒を酸やアルカリに調整する必要がなく、また、分散剤の添加やコーティング処理をする必要のない、それ自体が優れた分散性を有する高純度酸化チタン粉末を提供することにある。
【０００８】
【発明を解決するための手段】
かかる実情において、本発明者は、鋭意検討を行った結果、ゼータ電位の等電点が特定のｐＨ範囲であり、且つｐＨ５．５のゼータ電位の絶対値が特定範囲にある高純度酸化チタンが、水中での分散性に優れ、焼結材料あるいは紫外線遮蔽材料等汎用的に利用し得ることを見出し、本発明を完成するに至った。
【０００９】
すなわち、本発明は、気相法あるいは火炎加水分解法により酸化チタン粉末を生成させ、次いで、ボールミル、振動ミル、ピンミル、タワーミル、ターボミル又はペイントシェーカーを用いて解砕あるいは粉砕することを特徴とする高純度酸化チタン粉末の製造方法を提供するものである。
【００１０】
【発明の実施の形態】
以下、本発明をさらに詳しく説明する。
本発明の高純度酸化チタン粉末は、電気泳動を利用したレーザードップラー法によるゼータ電位の等電点がｐＨ２．０〜ｐＨ４．５であり、且つｐＨ５．５におけるゼータ電位の絶対値が１５ｍＶ以上であり、好ましくは、前記の同法によるゼータ電位の等電点がｐＨ２．５〜ｐＨ４．０であり、且つｐＨ５．５におけるゼータ電位の絶対値が２０ｍＶ以上、６０ｍＶ以下である。ゼータ電位は固体と液体の界面に生じる電位差であり、物質によりその値は異なり、酸化チタンのような金属酸化物においては、その粒子表面の水酸基の酸・アルカリ特性を示す一つの指標である。酸化チタンの表面は酸・アルカリの両性を示す代表的な物質であり、酸化チタン粉末についてのゼータ電位について多くの報告がなされている。それらの報告の値を平均すると、酸化チタン粉末のゼータ電位の等電点は、アナターゼ型酸化チタンがｐＨ６．１、ルチル型酸化チタンがｐＨ５．６である［参考文献：清野 学著「酸化チタン」（技報堂出版）4.4.4 、 60-62頁、およびG.D. Parfitt, Prog. Surface Membrane Sci. 11, 181 (1976)］。このように、従来の酸化チタン粉末のゼータ電位の等電点はｐＨ５〜６程度であり、通常使用される水のｐＨと同様のほぼ中性の領域にある。
【００１１】
これに対して、本発明の高純度酸化チタン粉末は、ゼータ電位の等電点がｐＨ２．０〜ｐＨ４．５と酸性側にあり、且つｐＨ５．５におけるゼータ電位の絶対値が１５ｍＶ以上と、酸性あるいはアルカリ性側にｐＨ調整していない通常の水中においてゼータ電位を示すものである。さらに、本発明の高純度酸化チタン粉末のｐＨ５．５におけるゼータ電位は、マイナス側の電位を示す。すなわち、ｐＨ５．５というｐＨ領域であっても絶対値で１５ｍＶ以上のゼータ電位を示すので、焼結材料、顔料、紫外線遮蔽材料あるいは光触媒など溶媒に懸濁して利用される場合、溶媒のｐＨを調整することなく、あるいは従来のようにｐＨ調整した場合においても優れた分散性を示す。
【００１２】
前記ゼータ電位は、試料を適量蒸留水に加えて３分間超音波分散させたものについて、電気泳動ゼータ電位計を用い、１０ｍ規定の塩化ナトリウム水溶液中、２５℃で安定させた後、測定したものを示す。
【００１３】
また、本発明の酸化チタン粉末は、不純物として酸化チタン粉末中に含まれるＦｅ、Ａｌ、ＳｉおよびＮａが各々２０ｐｐｍ以下であり、かつＣｌが２００ｐｐｍ以下であるような不純物の少ない高純度のものであることが、酸化チタン本来の焼結特性、紫外線遮蔽特性あるいは光触媒活性を発現させるために望ましい。さらに望ましくは、酸化チタン粉末中に含まれるＦｅ、Ａｌ、ＳｉおよびＮａが各々１０ｐｐｍ以下であり、またＣｌが１００ｐｐｍ以下である。このように本発明の酸化チタン粉末は、従来技術に見られるようなシリカあるいはアルミナのごとき疎水性物質を表面コーティングするなどの他成分による処理を施しておらず、酸化チタン以外の他成分を殆ど含有していない高純度の酸化チタン粉末であるので、各分野に利用した際、酸化チタン本来の特性が変化せず作用するため、優れた効果を得ることができる。
【００１４】
本発明の酸化チタン粉末の粒径、比表面積などの粒子性状については、その用途により異なり、一概には特定はできないが、平均粒径は好ましくは０．０１〜１０μm 、より好ましくは０．０５〜５μm 、さらに好ましくは０．１〜３μm である。表面積は好ましくは０．５〜５００m2/ g 、より好ましくは１〜３００m2/ g 、さらに好ましくは０．５〜１００m2/ g である。また、結晶型についても一概に特定はできず、その用途により調整すればよいが、例えば、焼結材料、顔料あるいは紫外線遮蔽材料用ではルチル化率１０〜１００％のルチル型が好ましく、一方、光触媒用としてはアナターゼ型が好ましい。
【００１５】
本発明の酸化チタン粉末は、種々の方法により製造することができ、例えば（１）硫酸チタニル、硫酸チタンなどの含チタン溶液の加水分解法、（２）チタンアルコキシドなどの有機チタン化合物の加水分解法、（３）三塩化チタンあるいは四塩化チタンなどのハロゲン化チタン水溶液の中和法又は加水分解法、（４）四塩化チタンを気相中で酸素及び／又は水蒸気と接触させ酸化させる気相法あるいは（５）燃焼して水を生成する水素ガス等の可燃性ガスと酸素を燃焼バーナーに供給し火炎を形成し、この中に四塩化チタンを導入する火炎加水分解法などの方法により製造できる。このなかでも、より高純度の酸化チタン粉末を得る方法としては（４）の気相法あるいは（５）の火炎加水分解法が有効である。
【００１６】
上記気相法は、具体的には、先ず、液状の四塩化チタンを予め加熱し、気化させ反応炉に導入する。四塩化チタンの導入と同時に、酸素ガスを反応炉に導入し、酸化反応を行うが反応温度は通常５００〜１２００℃、好ましくは８００〜１１００℃である。本発明の高純度の酸化チタン粉末を得るためにはこのように比較的高温で酸化反応を行うことが望ましい。また、酸化反応の際、第三成分として、ルチル化率あるいは粒径の制御のため水素ガスあるいは水蒸気を上記四塩化チタンおよび酸素と同時に反応炉に供給し、酸化反応を行うこともできる（酸化工程）。
【００１７】
上記の酸化反応により酸化チタン粉末を生成させ、その後酸化チタン粉末を冷却する。この冷却方法についは種々の方法が取り得るが、通常冷却ジャケットを具備した冷却槽等が用いられ、空気あるいは窒素ガス等の不活性ガスを生成酸化チタン粉末と接触させ冷却する（冷却工程）。その後生成した酸化チタン粉末を捕集し、酸化チタン粉末中に残留する塩素ガスを、真空加熱、空気あるいは窒素ガス雰囲気中での加熱あるいはスチーム処理等の加熱処理により除去し、本発明の高純度酸化チタン粉末を得ることができる（加熱工程）。ここで、酸化チタン粉末が生成した後は、水分をなるべく接触させないことが望ましく、また得られた酸化チタン粉末の保存または貯蔵においてもチッソ雰囲気に保持するなど、湿気を避けた状態で保存、貯蔵することが望ましい。
【００１８】
上記のような方法で本発明の酸化チタン粉末を得ることができるが、さらに得られた酸化チタン粉末を解砕あるいは粉砕することも有効である。この解砕あるいは粉砕は、ボールミル、振動ミル、ピンミル、タワーミル、ターボミル、ペイントシェーカー等を用い、乾式方法または溶媒を存在させる湿式方法により行われる（解砕工程）。上記の加熱工程後に得られた酸化チタン粉末は一次粒子が凝集し二次粒子を形成しているが、この凝集した二次粒子をある程度崩すことにより水酸基の少ない酸化チタン粒子表面を発現させる。従って、解砕又は粉砕は、得られる酸化チタンのゼータ電位の等電点がｐＨ２．０〜ｐＨ４．５と酸性側にあり、且つｐＨ５．５におけるゼータ電位の絶対値が１５ｍＶ以上となるような条件を適宜選択することにより行われる。
【００１９】
元来酸化チタンはその粒子表面に水酸基を有しており、この水酸基がゼータ電位に影響することは前に述べたが、従来の酸化チタン粉末はこの粒子表面の水酸基が多く含まれるため、ゼータ電位の等電点がほぼ中性の領域にあり、水中での分散性が悪くなる。これに対し、本発明の高純度酸化チタンは、従来の酸化チタンよりも粒子表面の水酸基が極めて少ないため、従来にないｐＨ−ゼータ電位曲線を示し、その結果、非常に優れた分散性を示す。
【００２０】
本発明の酸化チタン粉末は、焼結材料、顔料、紫外線遮蔽材料あるいは光触媒などの溶媒に分散して使用するあらゆる用途に利用可能であり、特にコンデンサなどの電子材料用や紫外線遮蔽材としての顔料用、塗料用また化粧料用として有効である。
【００２１】
【実施例】
以下、本発明を実施例および比較例によりさらに具体的に説明する。
また、高純度酸化チタン粉末のゼータ電位、平均粒径、粒度分布、比表面積、不純物の定量および分散度は以下の方法により測定した。
【００２２】
（電気泳動を利用したレーザードップラー法によるゼータ電位）
試料を予め蒸留水に懸濁させた後、超音波で３分振動分散させ、ゼータ電位測定装置（型式「ＤＥＬＳＡ ４４０ＳＸ」コールター社製）のセルに注入する。その後２５℃で安定させた後、ゼータ電位を測定する。
（水中に分散させたときの粒度分布）
レーザー光散乱法粒度測定機（型式「ＬＡ７００」堀場製作所製）を用いて測定する。
（比表面積及び平均粒径）
ＢＥＴ法により測定する。
（不純物の定量）
Ｆｅ、Ａｌ、ＳｉおよびＮａ成分については、原子吸光法により測定する。酸化チタン中のＣｌ成分については、吸光光度法により測定する。
（分散度）
目開き４５μｍのステンレス製フィルター付濾過容器に、酸化チタン粉末試料を入れ、その上から水を１０分間流す。その後フィルター上に残留した試料を乾燥してその重量を計測し、下記式により分散度を算出する。従って、分散度は数値が小さい程、分散性に優れることを示す。
分散度（％）＝（フィルター上に残留した試料重量／試料投入重量）×１００
【００２３】
実施例１
四塩化チタンを気相中で酸素と接触させ酸化させる気相法により酸化チタン粉末を調製した。まず、内径４００mmの多重管バーナーを上部に具備した気相反応管において、多重管バーナーに、約１０００℃に予熱し気化させた四塩化チタン、酸素ガスおよび水蒸気を供給し、気相反応管内で約１０００℃にて酸化反応させ、酸化チタン粉末を生成させた。その後、気相反応管の底部から空気を導入し、生成した酸化チタン粉末を冷却した後、得られた酸化チタン粉末をロータリーキルンに移送し、窒素雰囲気中で３００℃〜４００℃で２時間加熱処理した。次いで得られた酸化チタン粉末１２０ｋｇを、振動ミルにて３時間の解砕を施した。このようにして得られた高純度酸化チタン粉末Ａのゼータ電位、比表面積、不純物の含量、分散度および粒度分布を表１に示した。
【００２４】
実施例２
酸素ガスを用いず、水蒸気を添加した以外は、実施例１と同様に酸化反応させ、高純度酸化チタン粉末を得た。このようにして得られた高純度酸化チタン粉末Ｂの各物性を表１に示した。
【００２５】
比較例１
振動ミルでの解砕処理を行わなかった以外は、実施例１と同様に高純度酸化チタン粉末を調製した。得られた酸化チタン粉末Ｃの各物性を表１に示した。
【００２６】
比較例２
振動ミルでの解砕処理を行なわなかった以外は実施例２と同様に酸化チタン粉末を調製した。得られた高純度酸化チタン粉末Ｄの各物性を表１に示した。
【００２７】
【表１】
表１より明らかなように、高純度酸化チタンＡ及びＢは電気泳動を利用したレーザードップラー法によるゼータ電位の等電点がｐＨ２．０〜ｐＨ４．５と酸性側にあり、且つｐＨ５．５におけるゼータ電位の絶対値が１５ｍＶ以上であるため分散性に優れる。一方、高純度酸化チタンＣ及びＤはゼータ電位の等電点が各々ｐＨ５．１及び５．７であり、ｐＨ５．５におけるゼータ電位の絶対値が１１．１及び２．８５ｍＶであるため、それぞれ分散性で劣る。
【００２９】
【発明の効果】
以上説明したように、本発明の高純度酸化チタン粉末は、従来の酸化チタンとは異なり、電気泳動を利用したレーザードップラー法によるゼータ電位の等電点がｐＨ２．０〜ｐＨ４．５と酸性側にあり、且つｐＨ５．５におけるゼータ電位の絶対値が１５ｍＶ以上という特性をもち、水、有機溶媒等の溶媒に懸濁した際に優れた分散性を示すという効果が得られる。従って、本発明の高純度酸化チタン粉末は、電子材料用、顔料用、紫外線遮蔽材用あるいは光触媒用として好適である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high-purity titanium oxide powder that has excellent dispersibility and can be used for general purposes such as a sintered material or an ultraviolet shielding material.
[0002]
[Prior art]
Titanium oxide powder has long been used as a white pigment, and in recent years, it has been widely used as a sintering material used for electric and electronic materials such as capacitors, thermistor constituent materials, and barium titanate raw materials. Further, since titanium oxide exhibits a large refractive index in the wavelength region near visible light, light absorption hardly occurs in the visible light region. For this reason, it has recently been widely used in materials that require UV shielding such as cosmetics, medicines, and paints. Furthermore, when titanium oxide is irradiated with light having energy greater than its band gap, the titanium oxide is excited, generating electrons in the conduction band and holes in the valence band. Development of applications for photocatalytic reactions using oxidizing power has been actively conducted. This titanium oxide photocatalyst has a wide variety of uses. Development of many applications such as generation of hydrogen due to water decomposition, exhaust gas treatment, air purification, deodorization, sterilization, antibacterial, water treatment, and prevention of dirt from lighting equipment, etc. Has been done.
[0003]
In this way, titanium oxide has a wide variety of uses. When titanium oxide powder is used in pigments, paints or sintered materials, it is often suspended and dispersed in water or an organic solvent. Dispersibility of the titanium powder in the solvent becomes a problem. In the above applications, particularly titanium oxide for electronic materials, it is necessary to make titanium oxide particles 1 μm or less, and further 0.1 μm or less, in order to cope with recent miniaturization of electronic materials. In addition, for titanium oxide for photocatalyst, the photocatalytic activity is improved, and when used as a photocatalyst material, titanium oxide is coated on the substrate. In order to improve the transparency of the titanium oxide film at that time, titanium oxide is used. The particles need to be ultrafine particles of several nm to several tens of nm. In this way, as titanium oxide is atomized, the dispersibility in the solvent deteriorates, and when suspended in the solvent, aggregation occurs, adversely affecting the characteristics of the electronic material and photocatalyst. There arises a problem that the ultraviolet shielding property deteriorates due to aggregation of the titanium oxide particles.
[0004]
When suspending titanium oxide powder in a solvent, as a method of highly dispersing and preventing aggregation between particles, acid such as hydrochloric acid, sulfuric acid or organic acid is present, and the pH of the suspension is adjusted to the acidic side. Alternatively, there is a method in which an alkali such as sodium hydroxide is present to adjust the pH of the suspension to the alkali side. This is due to the hydroxyl groups present on the surface of the titanium oxide particles. Conventional titanium oxide powder has a positive zeta potential (interface potential) of the titanium oxide powder on the acidic side and a negative potential on the alkaline side. Therefore, aggregation of particles is prevented and dispersibility is improved.
[0005]
Further, in the method of further improving dispersibility, a method of adjusting the suspension of titanium oxide using a pulverizer or classifier such as a ball mill, a dispersant such as sodium hexametaphosphate is present in the suspension, There is a method for preparing a titanium oxide suspension. Furthermore, attempts have been made to solve the problem of dispersibility by coating the surface of titanium oxide particles with a hydrophobic material that is inherently highly dispersible, such as silica and alumina. For example, in Japanese Patent Application Laid-Open No. H5-28672, the pH is adjusted to 10.5 to 12.0 by adding an acid to an aqueous solution of an aluminum basic salt, and a titanium dioxide slurry is mixed therewith. And a method for uniformly depositing aluminum oxide hydrate on the surface of titanium dioxide particles is disclosed.
[0006]
[Problems to be solved by the invention]
However, the method for improving the dispersibility of the titanium oxide particles as in the above prior art uses components other than titanium oxide such as acid, alkali, dispersant, or coating with a foreign substance on the surface of the titanium oxide particles. When the original characteristics are changed, or when used as an electronic material, pigment, ultraviolet shielding material, photocatalyst, or the like, there is a problem in that such other components are mixed, which adversely affects the used material.
[0007]
Accordingly, an object of the present invention is to provide a high-purity titanium oxide powder that itself has excellent dispersibility without the need for adjusting the dispersion solvent to acid or alkali, and without the need for adding a dispersant or coating treatment. Is to provide.
[0008]
[Means for Solving the Invention]
In this situation, the present inventor has intensively studied. As a result, the high-purity titanium oxide in which the isoelectric point of the zeta potential is in a specific pH range and the absolute value of the zeta potential at pH 5.5 is in the specific range. The present inventors have found that it is excellent in dispersibility in water and can be used for general purposes such as a sintered material or an ultraviolet shielding material, and the present invention has been completed.
[0009]
That is, the present invention is characterized in that a titanium oxide powder is produced by a gas phase method or a flame hydrolysis method, and then pulverized or pulverized using a ball mill, a vibration mill, a pin mill, a tower mill, a turbo mill, or a paint shaker. A method for producing high-purity titanium oxide powder is provided.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail.
The high-purity titanium oxide powder of the present invention has an isoelectric point of zeta potential measured by laser Doppler method using electrophoresis of pH 2.0 to pH 4.5, and an absolute value of zeta potential at pH 5.5 of 15 mV or more. Preferably, the isoelectric point of the zeta potential according to the same method is pH 2.5 to pH 4.0, and the absolute value of the zeta potential at pH 5.5 is 20 mV or more and 60 mV or less. The zeta potential is a potential difference generated at the interface between a solid and a liquid, and its value varies depending on the substance. In the case of a metal oxide such as titanium oxide, it is an index indicating the acid / alkali characteristics of the hydroxyl group on the particle surface. The surface of titanium oxide is a representative material exhibiting both acid and alkali properties, and many reports have been made on the zeta potential of titanium oxide powder. When the reported values are averaged, the isoelectric point of the zeta potential of the titanium oxide powder is pH 6.1 for anatase type titanium oxide and pH 5.6 for rutile type titanium oxide [Reference: Manabu Seino, “Titanium oxide”. (Gihodo Shuppan) 4.4.4, pp. 60-62, and GD Parfitt, Prog. Surface Membrane Sci. 11, 181 (1976)]. Thus, the isoelectric point of the zeta potential of the conventional titanium oxide powder is about pH 5 to 6, and is in a substantially neutral region similar to the pH of water that is usually used.
[0011]
On the other hand, the high-purity titanium oxide powder of the present invention has an isoelectric point of zeta potential on the acidic side of pH 2.0 to pH 4.5, and an absolute value of zeta potential at pH 5.5 of 15 mV or more, It exhibits a zeta potential in normal water whose pH is not adjusted to the acidic or alkaline side. Furthermore, the zeta potential at pH 5.5 of the high-purity titanium oxide powder of the present invention indicates a negative potential. That is, even in the pH range of pH 5.5, it shows a zeta potential of 15 mV or more in absolute value, so when suspended in a solvent such as a sintered material, a pigment, an ultraviolet shielding material or a photocatalyst, the pH of the solvent is set. Excellent dispersibility is exhibited without adjustment or even when the pH is adjusted as in the prior art.
[0012]
The zeta potential was measured after stabilizing a sample in an aqueous 10 m sodium chloride solution at 25 ° C. using an electrophoretic zeta potentiometer for a sample added to distilled water in an appropriate amount and ultrasonically dispersed for 3 minutes. Indicates.
[0013]
In addition, the titanium oxide powder of the present invention is a high-purity product with few impurities such that Fe, Al, Si and Na contained in the titanium oxide powder as impurities are each 20 ppm or less and Cl is 200 ppm or less. It is desirable to have titanium oxide inherent sintering characteristics, ultraviolet shielding characteristics or photocatalytic activity. More desirably, Fe, Al, Si and Na contained in the titanium oxide powder are each 10 ppm or less, and Cl is 100 ppm or less. As described above, the titanium oxide powder of the present invention is not treated with other components such as surface coating with a hydrophobic material such as silica or alumina as found in the prior art, and most other components than titanium oxide are not treated. Since it is a high-purity titanium oxide powder not contained, when it is used in various fields, the original characteristics of titanium oxide act without change, so that an excellent effect can be obtained.
[0014]
The particle properties such as the particle size and specific surface area of the titanium oxide powder of the present invention vary depending on the application and cannot be specified. However, the average particle size is preferably 0.01 to 10 μm, more preferably 0.05. -5 μm, more preferably 0.1-3 μm. The surface area is preferably 0.5 to 500 m 2 / g, more preferably 1 to 300 m 2 / g, and still more preferably 0.5 to 100 m 2 / g. Further, the crystal type cannot be generally specified, and may be adjusted depending on the application. For example, a rutile type having a rutile ratio of 10 to 100% is preferable for a sintered material, a pigment, or an ultraviolet shielding material, Anatase type is preferable for photocatalysts.
[0015]
The titanium oxide powder of the present invention can be produced by various methods, for example, (1) hydrolysis of titanium-containing solutions such as titanyl sulfate and titanium sulfate, and (2) hydrolysis of organic titanium compounds such as titanium alkoxide. (3) Neutralization method or hydrolysis method of titanium halide aqueous solution such as titanium trichloride or titanium tetrachloride, (4) Gas phase in which titanium tetrachloride is contacted with oxygen and / or water vapor in the gas phase and oxidized. Manufactured by a method such as the flame hydrolysis method in which a combustible gas such as hydrogen gas or oxygen that burns to produce water and oxygen is supplied to a combustion burner to form a flame, and titanium tetrachloride is introduced into this. it can. Of these, the vapor phase method (4) or the flame hydrolysis method (5) is effective as a method for obtaining a higher purity titanium oxide powder.
[0016]
Specifically, in the gas phase method, first, liquid titanium tetrachloride is heated in advance, vaporized, and introduced into the reaction furnace. Simultaneously with the introduction of titanium tetrachloride, oxygen gas is introduced into the reaction furnace to carry out the oxidation reaction, but the reaction temperature is usually 500 to 1200 ° C, preferably 800 to 1100 ° C. In order to obtain the high-purity titanium oxide powder of the present invention, it is desirable to carry out the oxidation reaction at such a relatively high temperature. In addition, during the oxidation reaction, as a third component, hydrogen gas or water vapor can be supplied to the reaction furnace simultaneously with the titanium tetrachloride and oxygen to control the rutile ratio or particle size, and the oxidation reaction can be carried out (oxidation). Process).
[0017]
Titanium oxide powder is produced by the above oxidation reaction, and then the titanium oxide powder is cooled. Various methods can be used for this cooling method. Usually, a cooling tank equipped with a cooling jacket or the like is used, and cooling is performed by bringing an inert gas such as air or nitrogen gas into contact with the produced titanium oxide powder (cooling step). Thereafter, the produced titanium oxide powder is collected, and the chlorine gas remaining in the titanium oxide powder is removed by heat treatment such as vacuum heating, heating in air or nitrogen gas atmosphere or steam treatment, and the high purity of the present invention. Titanium oxide powder can be obtained (heating step). Here, after the titanium oxide powder is formed, it is desirable not to allow moisture to come into contact with it as much as possible, and the titanium oxide powder obtained is stored and stored in a state avoiding moisture, such as being kept in a nitrogen atmosphere during storage or storage. It is desirable to do.
[0018]
Although the titanium oxide powder of the present invention can be obtained by the method as described above, it is also effective to crush or pulverize the obtained titanium oxide powder. This crushing or crushing is performed by a dry method or a wet method in which a solvent is present using a ball mill, a vibration mill, a pin mill, a tower mill, a turbo mill, a paint shaker, or the like (crushing step). In the titanium oxide powder obtained after the heating step, primary particles are aggregated to form secondary particles. By breaking the aggregated secondary particles to some extent, the surface of titanium oxide particles with few hydroxyl groups is expressed. Therefore, in the crushing or pulverization, the isoelectric point of the zeta potential of the obtained titanium oxide is on the acidic side of pH 2.0 to pH 4.5, and the absolute value of the zeta potential at pH 5.5 is 15 mV or more. This is done by appropriately selecting the conditions.
[0019]
Titanium oxide originally has a hydroxyl group on the particle surface, and it has been described before that this hydroxyl group affects the zeta potential. However, since conventional titanium oxide powder contains many hydroxyl groups on the particle surface, The isoelectric point of the potential is in a substantially neutral region, resulting in poor dispersibility in water. On the other hand, the high-purity titanium oxide of the present invention has an unprecedented pH-zeta potential curve because the number of hydroxyl groups on the particle surface is extremely smaller than that of conventional titanium oxide, and as a result, exhibits excellent dispersibility. .
[0020]
The titanium oxide powder of the present invention can be used for any application that is used by being dispersed in a solvent such as a sintered material, a pigment, an ultraviolet shielding material, or a photocatalyst, and in particular, a pigment for an electronic material such as a capacitor or an ultraviolet shielding material. It is effective for use in paints, paints and cosmetics.
[0021]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.
Further, the zeta potential, average particle size, particle size distribution, specific surface area, quantification of impurities and degree of dispersion of the high purity titanium oxide powder were measured by the following methods.
[0022]
(Zeta potential by laser Doppler method using electrophoresis)
The sample is suspended in distilled water in advance, and is then vibrated and dispersed with ultrasonic waves for 3 minutes, and injected into a cell of a zeta potential measurement device (model “DELSA 440SX” manufactured by Coulter). After stabilization at 25 ° C., the zeta potential is measured.
(Particle size distribution when dispersed in water)
Measurement is performed using a laser light scattering particle size analyzer (model “LA700” manufactured by Horiba, Ltd.).
(Specific surface area and average particle size)
Measured by BET method.
(Quantification of impurities)
Fe, Al, Si and Na components are measured by atomic absorption method. The Cl component in titanium oxide is measured by absorptiometry.
(Dispersity)
A titanium oxide powder sample is put into a filter container with a stainless steel filter having an opening of 45 μm, and water is allowed to flow from there for 10 minutes. Thereafter, the sample remaining on the filter is dried, its weight is measured, and the degree of dispersion is calculated by the following equation. Therefore, the smaller the numerical value, the better the dispersibility.
Dispersity (%) = (sample weight remaining on filter / sample input weight) × 100
[0023]
Example 1
Titanium oxide powder was prepared by a gas phase method in which titanium tetrachloride was contacted with oxygen in the gas phase and oxidized. First, in a gas phase reaction tube equipped with a multi-tube burner having an inner diameter of 400 mm at the top, titanium tetrachloride, oxygen gas and water vapor preheated to about 1000 ° C. and vaporized are supplied to the multi-tube burner. An oxidation reaction was performed at about 1000 ° C. to produce a titanium oxide powder. Then, after introducing air from the bottom of the gas phase reaction tube and cooling the produced titanium oxide powder, the obtained titanium oxide powder is transferred to a rotary kiln and heated at 300 ° C. to 400 ° C. for 2 hours in a nitrogen atmosphere. did. Next, 120 kg of the obtained titanium oxide powder was crushed by a vibration mill for 3 hours. Table 1 shows the zeta potential, specific surface area, impurity content, dispersity, and particle size distribution of the high-purity titanium oxide powder A thus obtained.
[0024]
Example 2
Except that oxygen gas was not used and water vapor was added, an oxidation reaction was performed in the same manner as in Example 1 to obtain a high-purity titanium oxide powder. The physical properties of the high purity titanium oxide powder B thus obtained are shown in Table 1.
[0025]
Comparative Example 1
A high-purity titanium oxide powder was prepared in the same manner as in Example 1 except that the crushing treatment with a vibration mill was not performed. The physical properties of the obtained titanium oxide powder C are shown in Table 1.
[0026]
Comparative Example 2
Titanium oxide powder was prepared in the same manner as in Example 2 except that the crushing treatment with a vibration mill was not performed. Table 1 shows the physical properties of the obtained high-purity titanium oxide powder D.
[0027]
[Table 1]
As is clear from Table 1, high-purity titanium oxides A and B have an isoelectric point of zeta potential measured by laser Doppler method using electrophoresis on the acidic side of pH 2.0 to pH 4.5, and at pH 5.5. Since the absolute value of the zeta potential is 15 mV or more, the dispersibility is excellent. On the other hand, high-purity titanium oxides C and D have zeta potential isoelectric points of pH 5.1 and 5.7, respectively, and zeta potential absolute values at pH 5.5 are 11.1 and 2.85 mV, respectively. It is inferior in dispersibility.
[0029]
【The invention's effect】
As described above, the high-purity titanium oxide powder of the present invention is different from the conventional titanium oxide in that the isoelectric point of zeta potential by the laser Doppler method using electrophoresis is pH 2.0 to pH 4.5 and the acidic side. And the absolute value of the zeta potential at pH 5.5 is 15 mV or more, and the effect of exhibiting excellent dispersibility when suspended in a solvent such as water or an organic solvent is obtained. Therefore, the high-purity titanium oxide powder of the present invention is suitable for electronic materials, pigments, ultraviolet shielding materials or photocatalysts.
Claims (5)
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