JP2004075434A - Titanium oxide sol and its preparation process - Google Patents

Titanium oxide sol and its preparation process Download PDF

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Publication number
JP2004075434A
JP2004075434A JP2002235979A JP2002235979A JP2004075434A JP 2004075434 A JP2004075434 A JP 2004075434A JP 2002235979 A JP2002235979 A JP 2002235979A JP 2002235979 A JP2002235979 A JP 2002235979A JP 2004075434 A JP2004075434 A JP 2004075434A
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titanium oxide
oxide sol
fine particles
acidic compound
range
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JP4115203B2 (en
Inventor
Yasuro Fukui
福井 靖郎
Takashi Nishikawa
西川 貴志
Daisuke Ito
伊藤 大介
Shoichi Akita
秋田 彰一
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Ishihara Sangyo Kaisha Ltd
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Ishihara Sangyo Kaisha Ltd
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a titanium oxide sol with a pH of 3-5 showing excellent dispersion stability. <P>SOLUTION: The titanium oxide sol with a pH of 3-5 is prepared by adjusting the pH of an aqueous titanium oxide sol to 0-2 with an acidic compound and performing anion exchange of the aqueous titanium oxide sol, e.g. by contacting it with an anion-exchange resin, to impart a conductivity of ≤300 mS/m and a pH of 3-5 to it. The sol thus prepared is substantially composed of a dispersion medium essentially comprising water, titanium oxide fine particles and the acidic compound. Preferably, an inorganic acid such as hydrochloric acid, sulfuric acid, nitric acid or hydrofluoric acid is used as the acidic compound. <P>COPYRIGHT: (C)2004,JPO

Description

【0001】
【発明の属する技術分野】
本発明は、分散安定性に優れた酸化チタンゾル及びその製造方法に関する。
【0002】
【従来の技術】
粒子径が0.1μm以下の酸化チタン微粒子は、透明性が高く、紫外線遮蔽能が優れており、従来より、紫外線保護塗料等に用いられてきた。また、酸化チタン微粒子は光触媒活性が強く、バンドギャップ以上の光を照射することにより、有機化合物や一部の無機化合物を、効率良く分解できるので、近年、防汚や脱臭に利用されている。これらの機能を効果的に発現させるには、酸化チタン微粒子をほぼ一次粒子にまで分散させる必要があるが、微粒子であるが故に表面エネルギーが大きく、分散が困難である。このため、酸化チタン微粒子を含むをコーティング剤、塗料等の組成物を工業的に有利に製造するには、酸化チタン微粒子を予め水、有機溶剤等の分散媒に分散させて酸化チタンゾルとし、この酸化チタンゾルを前記組成物に配合する方法が用いられている。
【0003】
酸化チタンは水中ではpHが強酸性または強アルカリ性の領域で分散安定化するため、酸でpHを2以下にした酸化チタンゾル、あるいはアルカリでpHを12以上にした酸化チタンゾルが知られている。また、pHが6〜9の中性域で安定した酸化チタンゾルも知られているが、この場合、酸化チタン微粒子の凝集を防止するため、分散安定化剤を加える必要がある。分散安定化剤として例えば、水溶性の高分子有機化合物や界面活性剤等を用いものが特開昭64−3020号公報に、アルキルシリケートを用いたものが特開2000−53421号公報に開示されている。
【0004】
【発明が解決しようとする課題】
前記の強酸性酸化チタンゾル、あるいは、強アルカリ性酸化チタンゾルを用いる場合、被塗物が著しく限定されたり、あるいは、コーティング剤、塗料等の組成物に配合される添加剤の種類によっては、pH調整に用いる酸またはアルカリと相互作用を生じ、酸化チタン微粒子が凝集してしまうという問題がある。また、分散安定化剤を用いた中性の酸化チタンゾルでは、被塗物の制限は無いものの、コーティング剤、塗料等の組成物の添加剤が分散安定化剤の分散安定化能に影響を与えたり、酸化チタン微粒子の表面に分散安定化剤が強く吸着し、光学特性や光触媒活性等の酸化チタン微粒子の表面機能を損うという問題が生じる場合がある。
【0005】
【課題を解決するための手段】
そこで、本発明者らは、中性域の酸化チタンゾルに配合される通常の分散安定化剤を用いずに、しかも、被塗物に影響を与え難い酸化チタンゾルを得るべく鋭意研究を重ねた結果、意外にも、分散媒のpHを3〜5の範囲としても分散安定性に優れた、所望の酸化チタンゾルが得られること、このような酸化チタンゾルは、強酸性の水性酸化チタンゾルを特定の導電率及びpH領域になるまで陰イオンを交換することにより得られることを見出し、本発明を完成した。すなわち、本発明は以上に述べた従来技術の問題点を克服し、強酸性下または強アルカリ性下でなくとも、分散安定化剤を用いずに、酸化チタン微粒子を分散安定化させた水性の酸化チタンゾル及びその製造方法を提供するものである。
【0006】
本発明は酸化チタン微粒子、水を主成分とする分散媒、酸性化合物から実質的に構成され、pHが3〜5の範囲であることを特徴とする酸化チタンゾルである。また、本発明は、酸性化合物によりpHを0〜2の範囲に調整した水性酸化チタンゾルを導電率が300mS/m以下でpHが3〜5の範囲になるまで陰イオン交換することを特徴とする酸化チタンゾルの製造方法である。
【0007】
【発明の実施の形態】
本発明は、pHが3〜5の範囲で酸化チタン微粒子を分散安定化した酸化チタンゾルであって、酸化チタン微粒子、水を主成分とする分散媒、酸性化合物から実質的に構成される。pHが3より低い酸性の領域、あるいはpHが12以上の強アルカリ性の領域では、酸化チタン微粒子は分散安定化するものの、目的とする汎用性が損なわれ、pHが5より高く12より低い領域では、酸化チタン微粒子が凝集・沈降してしまう。本発明における酸化チタン微粒子の分散安定性を、具体的な指標で、例えば、以下の方法で測定した550nmの波長を有する光の分光透過率で表すと、好ましくは20〜60%、より好ましくは20〜40%の範囲にある。
(分光透過率の測定方法)
酸化チタン微粒子の濃度を0.5重量%に水で調整した試料を、光路が1cmの石英セルに充填して、水を対象試料とし、550nmの波長を有する光の分光透過率を、分光光度計(UV−2200A型:島津製作所製)を用いて測定する。
【0008】
本発明の酸化チタンゾルは、陰イオンが比較的少ない状態で酸化チタン微粒子を分散安定化できる。陰イオンの含有量を導電率で示すと、好ましくは300mS/m以下、より好ましくは200mS/m以下である。陰イオンの含有量が少ないと、後述するように酸化チタン微粒子の分散安定化が確保し易いほかに、陰イオンの被塗物への影響、あるいは、コーティング剤、塗料等の組成物に配合される添加剤への影響が少ないため好ましい態様である。
【0009】
また、本発明では、酸化チタン微粒子を比較的高濃度に配合しても、微粒子同士の相互作用による凝集が生じ難く、酸化チタンゾル中に酸化チタン微粒子を10〜50重量%、好ましくは10〜30重量%の範囲で配合できる。このため、最終の組成物に配合される酸化チタン微粒子の濃度等、組成物の成分処方が制限を受け難くなる。
【0010】
本発明で用いる酸化チタン微粒子は、酸化チタンの有する光触媒活性、光学特性等の表面特性が損なわれないように、無機化合物、有機化合物等の表面被覆を行っていないものが好ましい。その内部には、異種の元素、または異種元素の酸化物等の化合物が含まれても良い。酸化チタン微粒子には、無水酸化チタン、含水酸化チタン、水酸化チタン、チタン酸等を用いることができ、これらはルチル型、アナターゼ型等の結晶性のものや、不定形であっても良く、その形状は球状、紡錘状、棒状、針状、樹枝状、不定形等、特に制限は無く、組成物の用途に応じて適宜選択できる。酸化チタン微粒子の平均粒子径が0.001〜0.1μmの範囲にあれば、特に光触媒能、紫外線遮蔽能、透明性等の特性が優れているので好ましい。尚、ここで言う平均粒子径は、電子顕微鏡法による50%粒子径(算術平均)であり、酸化チタン微粒子が紡錘状、棒状、針状等の非球状粒子の場合、短軸径を平均粒子径とする。
【0011】
水を主成分とする分散媒とは、本発明においては水を50重量%以上、好ましくは80重量%以上含む分散媒であり、水以外の成分としては、アルコール類、ケトン類等の親水性有機溶媒が、本発明の効果を損なわない範囲で含まれていても良い。酸性化合物には酢酸、ギ酸等の有機酸を用いることもできるが、塩酸、硫酸、硝酸、フッ酸等の無機酸は水中での解離度が大きく、分散安定化の効果が高いので好ましい。中でも塩酸、硫酸、硝酸であれば、取り扱い易く工業的に有利に実施できるので更に好ましく、酸化チタンゾルを配合する組成物の用途に応じて、適宜選択できる。
【0012】
本発明は、酸化チタン微粒子、水を主成分とする分散媒、酸性化合物の3成分から実質的に構成されるものであるが、本発明の効果を損なわない範囲で、第4の成分が含まれていても良い。例えば、酸化チタン微粒子の製造に由来する不純物が含まれていても良く、あるいは、酸化チタンゾルを用いる際に添加される材料、例えば、コーティング剤、塗料等の組成物に配合される添加剤の少なくとも一種を加えても良い。
【0013】
本発明の酸化チタンゾルは、pHが3〜5の範囲と弱酸性領域にあり、また、分散安定化剤を用いていないので、各種のコーティング剤、塗料、成形体、担体等の組成物に用いると、組成物に配合されるバインダー、添加剤等の成分の種類や、塗布する基材が制限され難く、広範囲に適用できる。例えば、本発明の酸化チタンゾルと、有機シリケート等の無機系硬化性成分とを混合すると、光触媒コーティング剤とするとことができ、酸化チタンのバンドギャップ以上の光を照射すれば、被塗物の防汚や、環境中に発生した有害物資の分解・除去に用いることができる。アクリル樹脂、アルキド樹脂、フッ素樹脂等の公知の塗料用硬化性成分を加え、紫外線保護塗料とすることもできる。あるいは、粘土鉱物等の無機バインダーで成形された成形体または担体に、本発明の酸化チタンゾルを含浸させた後、加熱焼成することで、その表面に酸化チタン微粒子を担持させることもできる。
【0014】
次に、本発明は酸化チタンゾルの製造方法であって、酸性化合物によりpHを0〜2の範囲に調整した水性酸化チタンゾルを、導電率が300mS/m以下でpHが3〜5の範囲になるまで陰イオン交換することを特徴とする。この方法により、分散安定化剤を用いなくても、pHが3〜5の範囲の水を主成分とする弱酸性の分散媒中に、酸化チタン微粒子を分散安定化させることができる。その理由は、次のように考えられる。
【0015】
一般的に、酸化チタンはその表面に水酸基を有し、pHが酸性領域の水中では、Hイオンと水酸基とが結合し、−OH としてプラスの電荷を帯びるので、強酸性になりHイオンの濃度が高くなる程、静電的な斥力が生じ、酸化チタンが分散安定化すると言われている。しかし、酸性化合物は水中で解離し、Hイオンと陰イオンとを生成するので、強酸性にするため、酸性化合物を多量に加えると、陰イオンの量も多くなり、斥力を弱める方向に働くと考えられる。
【0016】
予め、酸性化合物で強酸性にして酸化チタン微粒子を分散させた後、本発明のように、導電率が300mS/m以下になるまで陰イオン交換すると、Hが酸化チタン微粒子表面の水酸基に結合したまま、即ち、−OH の状態のままで、ゾル中の陰イオンが減少するため、静電的な斥力が保持されると推測される。陰イオン交換により、ゾル中のOHイオンが増加するため、pHは0〜2の範囲から上昇するが、酸性化合物の解離度が維持されるpH領域、即ちpHが3〜5の範囲にすると、表面の−OH 量は一定であるため、このような弱酸酸性のpH下でも、酸化チタン微粒子が安定して分散すると考えられる。
【0017】
本発明の製造方法において用いる強酸性の水性酸化チタンゾル、その水性酸化チタンゾルに配合する酸化チタン微粒子は、公知の方法で得られたものを用いることができる。酸化チタン微粒子としては、例えば、四塩化チタン、硫酸チタニル、硫酸チタン等のチタン化合物を、加熱加水分解したり、アルカリ中和すると、含水酸化チタン、水酸化チタン、またはチタン酸の微粒子が得られる。これらを加熱焼成することで、無水酸化チタンの微粒子が得られる。あるいは、四塩化チタンの気相加水分解、チタンアルコキシドの加水分解によっても、無水酸化チタン微粒子を得ることができる。含水酸化チタンを水酸化ナトリウムで処理した後、塩酸で処理すると、無水酸化チタンの紡錘状または針状の微粒子が得られることが知られている。本発明では、これらの含水酸化チタン、水酸化チタン、チタン酸または無水酸化チタンを酸化チタン微粒子として用いることができる。
【0018】
pHが0〜2の範囲に調整した水性酸化チタンゾルは、前記の酸化チタン微粒子を、水を主成分とする分散媒にpHが0〜2の範囲で分散させたものである。具体的には、前記のように酸化チタン微粒子を得た反応液のpHが2以下であればその状態のものを必要に応じて分散機で分散させて酸化チタンゾルとしたり、反応液のpHが2以上であれば、酸性化合物を添加してpHを0〜2の範囲に調整し分散して酸化チタンゾルとしたり、あるいは、前記の酸化チタン微粒子を水を主成分とする分散媒に懸濁し、酸性化合物を添加してpHを0〜2の範囲に調整し分散して酸化チタンゾルとしたり、更には、前記酸化チタン微粒子を、酸性化合物によりpHを0〜2の範囲に調整した水を主成分とする分散媒に分散して酸化チタンゾルとすることができる。本発明においては、酸性化合物によりpHを0〜2の範囲に調整した水を主成分とする分散媒に酸化チタン微粒子を分散して酸化チタンゾルとするのが好ましい。
【0019】
本発明においては、前記のpHが0〜2の水性酸化チタンゾルを、導電率が300mS/m以下でpHが3〜5の範囲になるまで陰イオン交換する。陰イオン交換は、例えば、前記水性酸化チタンゾルを陰イオン交換樹脂に接触させることで行うことができ、具体的には、陰イオン交換樹脂を酸化チタンゾルに投入した後、固液分離したり、陰イオン交換樹脂を充填したカラム内に、酸化チタンゾルを通過させる等、その方法は適宜選択できる。陰イオン交換樹脂としては、公知の、イオン交換基として四級アンモニウムを有する強塩基性のものや、1〜3級アミンを有する弱塩基性のものを用いることができ、また、ゲル型、ポーラス型のいずれを用いても良く、その性状は特に制限されない。導電率が300mS/m以下、好ましくは導電率が200mS/m以下であれば、分散安定性に優れた酸化チタンゾルが得られる。
【0020】
【実施例】
本発明を実施例により、更に詳細に説明するが、これらは本発明を限定するものではない。
【0021】
実施例1
四塩化チタンの中和により得られた平均粒子径が0.05μmの含水酸化チタンの微粒子を、硝酸でpHを1に調整したイオン交換水に、TiOとして15重量%の濃度になるように分散させ、強酸性の水性懸濁液を調製した。この懸濁液100gに、予めイオン交換水で湿潤させた陰イオン交換樹脂(アンバーライトIRA−910:オルガノ社製)450gを撹拌しながら添加し、陰イオンを除去した。酸化チタンゾルのpHが4、導電率が62.7mS/mになった時点で、イオン交換樹脂を濾過し、本発明の酸化チタンゾル(試料A)を得た。
【0022】
実施例2
硫酸チタンの加熱加水分解により得られた平均粒子径が0.05μmのメタチタン酸の微粒子を、硝酸でpHを1.5に調整したイオン交換水に、TiOとして15重量%の濃度になるように分散させ、強酸性の水性懸濁液を調製した。この懸濁液を用いた以外は、実施例1と同様にして本発明の酸化チタンゾル(試料B)を得た。
【0023】
実施例3
酸化チタンゾルのpHが4.9、導電率が26.1mS/mになった時点で、イオン交換樹脂を濾過したこと以外は、実施例2と同様にして、本発明の酸化チタンゾル(試料C)を得た。
【0024】
比較例1
実施例2で用いた強酸性水性懸濁液を比較例1(試料D)とする。この試料Dの導電率は測定器の測定限界(2000mS/m)を越え、測定不能であった。
【0025】
比較例2
酸化チタンゾルのpHが5.4、導電率が10.2mS/mで、陰イオン交換樹脂を濾過した以外は、実施例2と同様にして酸化チタンゾル(試E)を得た。
【0026】
評価1
実施例1〜3及び比較例1、2の酸化チタンゾル(試料A〜E)の、550nmの波長での分光透過率を、前記の方法に従って測定した。また、沈降物の有無を、目視により判定した。結果を表1に示す。本発明の酸化チタンゾルは、550nmの波長での透過率が高く、従来の強酸性の酸化チタンゾルと同等の、優れた酸化チタン微粒子の分散安定性が得られていることが判る。
【0027】
【表1】

Figure 2004075434
【0028】
【発明の効果】
本発明の酸化チタンゾルは、pHが3〜5の範囲の弱酸性の水を主体とする分散媒中に、分散安定化剤を用いずに、酸化チタン微粒子を分散安定化させているので、広範囲の組成物に適用でき、特に光触媒コーティング剤、紫外線保護塗料に有用である。また、本発明の製造方法は、酸性化合物によりpHを0〜2の範囲に調整した水性酸化チタンゾルを、導電率が300mS/m以下でpHが3〜5の範囲になるまで陰イオン交換する方法であり、pHが3〜5の範囲の弱酸性下でも、分散安定性に優れた酸化チタンゾルを製造することができる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a titanium oxide sol having excellent dispersion stability and a method for producing the same.
[0002]
[Prior art]
Titanium oxide fine particles having a particle diameter of 0.1 μm or less have high transparency and excellent ultraviolet shielding ability, and have been conventionally used in ultraviolet protection paints and the like. In addition, titanium oxide fine particles have a strong photocatalytic activity and can efficiently decompose organic compounds and some inorganic compounds by irradiating light having a band gap or more, and thus have been used in recent years for antifouling and deodorization. In order to effectively exhibit these functions, it is necessary to disperse the titanium oxide fine particles almost to the primary particles. However, the fine particles have a large surface energy and are difficult to disperse. For this reason, in order to industrially produce a composition such as a coating agent or a paint containing titanium oxide fine particles in an industrially advantageous manner, the titanium oxide fine particles are previously dispersed in a dispersion medium such as water or an organic solvent to form a titanium oxide sol. A method of blending a titanium oxide sol with the composition has been used.
[0003]
Titanium oxide is dispersed and stabilized in water in a strongly acidic or strongly alkaline region. Therefore, a titanium oxide sol having a pH of 2 or less with an acid or a titanium oxide sol having a pH of 12 or more with an alkali is known. Titanium oxide sols having a stable pH in the neutral range of 6 to 9 are also known. In this case, however, it is necessary to add a dispersion stabilizer to prevent aggregation of the titanium oxide fine particles. JP-A-64-3020 discloses a dispersion stabilizer using, for example, a water-soluble high-molecular organic compound or a surfactant, and JP-A-2000-53421 discloses an alkyl silicate. ing.
[0004]
[Problems to be solved by the invention]
When using the strongly acidic titanium oxide sol, or the strongly alkaline titanium oxide sol, the object to be coated is significantly limited, or, depending on the type of additives to be added to the composition such as a coating agent or a paint, the pH may be adjusted. There is a problem that interaction occurs with the acid or alkali used, and the titanium oxide fine particles aggregate. In addition, in a neutral titanium oxide sol using a dispersion stabilizer, although there is no limitation on an object to be coated, additives of a composition such as a coating agent and a paint affect the dispersion stabilization ability of the dispersion stabilizer. In addition, there may be a problem that the dispersion stabilizer is strongly adsorbed on the surface of the titanium oxide fine particles and impairs the surface function of the titanium oxide fine particles such as optical characteristics and photocatalytic activity.
[0005]
[Means for Solving the Problems]
Therefore, the present inventors have conducted intensive studies to obtain a titanium oxide sol that does not easily affect an object to be coated without using a normal dispersion stabilizer that is blended in a titanium oxide sol in a neutral region. Surprisingly, it is possible to obtain a desired titanium oxide sol having excellent dispersion stability even when the pH of the dispersion medium is in the range of 3 to 5. Such a titanium oxide sol is obtained by converting a strongly acidic aqueous titanium oxide sol into a specific conductive material. The present invention was found to be obtained by exchanging anions until the rate and pH range were reached, and the present invention was completed. That is, the present invention overcomes the above-mentioned problems of the prior art, and does not use a dispersion stabilizer, even under strong acidity or strong alkalinity. A titanium sol and a method for producing the same are provided.
[0006]
The present invention is a titanium oxide sol substantially composed of titanium oxide fine particles, a dispersion medium containing water as a main component, and an acidic compound, and having a pH in the range of 3 to 5. Further, the present invention is characterized in that the aqueous titanium oxide sol whose pH has been adjusted to a range of 0 to 2 with an acidic compound is anion-exchanged until the conductivity is 300 mS / m or less and the pH is in a range of 3 to 5. This is a method for producing a titanium oxide sol.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention is a titanium oxide sol in which titanium oxide fine particles are dispersed and stabilized in a pH range of 3 to 5, and is substantially composed of titanium oxide fine particles, a dispersion medium containing water as a main component, and an acidic compound. In the acidic region where the pH is lower than 3, or in the strongly alkaline region where the pH is 12 or more, the titanium oxide fine particles are dispersed and stabilized, but the intended versatility is impaired. In the region where the pH is higher than 5 and lower than 12, As a result, the titanium oxide fine particles aggregate and settle. When the dispersion stability of the titanium oxide fine particles in the present invention is expressed by a specific index, for example, as a spectral transmittance of light having a wavelength of 550 nm measured by the following method, preferably 20 to 60%, more preferably It is in the range of 20-40%.
(Method of measuring spectral transmittance)
A sample in which the concentration of titanium oxide fine particles was adjusted to 0.5% by weight with water was filled in a quartz cell having an optical path of 1 cm, and water was used as a target sample, and the spectral transmittance of light having a wavelength of 550 nm was measured. It is measured using a total meter (UV-2200A: manufactured by Shimadzu Corporation).
[0008]
The titanium oxide sol of the present invention can stably disperse the titanium oxide fine particles with a relatively small amount of anions. When the content of the anion is represented by conductivity, it is preferably 300 mS / m or less, more preferably 200 mS / m or less. When the content of the anion is small, the dispersion stabilization of the titanium oxide fine particles is easily ensured as described later, and the effect of the anion on the object to be coated, or a coating agent, is incorporated into a composition such as a paint. This is a preferred embodiment because the influence on the additive is small.
[0009]
Further, in the present invention, even when the titanium oxide fine particles are blended at a relatively high concentration, aggregation due to the interaction between the fine particles hardly occurs, and the titanium oxide fine particles contain 10 to 50% by weight, preferably 10 to 30% by weight in the titanium oxide sol. It can be blended in the range of weight%. For this reason, the component formulation of the composition such as the concentration of the titanium oxide fine particles blended in the final composition is less likely to be restricted.
[0010]
The titanium oxide fine particles used in the present invention are preferably not coated with a surface such as an inorganic compound or an organic compound so that the surface characteristics such as photocatalytic activity and optical characteristics of the titanium oxide are not impaired. The inside thereof may contain a different element or a compound such as an oxide of a different element. For the titanium oxide fine particles, anhydrous titanium oxide, hydrous titanium oxide, titanium hydroxide, titanic acid and the like can be used, and these may be crystalline such as rutile type, anatase type, etc., or may be amorphous. The shape is not particularly limited, such as a sphere, a spindle, a rod, a needle, a dendrite, and an irregular shape, and can be appropriately selected depending on the use of the composition. It is preferable that the average particle diameter of the titanium oxide fine particles is in the range of 0.001 to 0.1 μm because the characteristics such as photocatalytic ability, ultraviolet shielding ability, and transparency are particularly excellent. Here, the average particle diameter is a 50% particle diameter (arithmetic average) determined by electron microscopy. When the titanium oxide fine particles are non-spherical particles such as spindle-shaped, rod-shaped, and needle-shaped particles, the minor axis diameter is calculated as the average particle diameter Diameter.
[0011]
In the present invention, the dispersion medium containing water as a main component is a dispersion medium containing 50% by weight or more, preferably 80% by weight or more of water. As a component other than water, hydrophilic media such as alcohols and ketones are used. An organic solvent may be contained within a range that does not impair the effects of the present invention. Organic acids such as acetic acid and formic acid can be used as the acidic compound. However, inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, and hydrofluoric acid are preferred because they have a high degree of dissociation in water and a high effect of stabilizing dispersion. Among them, hydrochloric acid, sulfuric acid, and nitric acid are more preferable because they are easy to handle and can be industrially advantageously carried out, and can be appropriately selected according to the use of the composition containing the titanium oxide sol.
[0012]
The present invention is substantially composed of three components of titanium oxide fine particles, a dispersion medium containing water as a main component, and an acidic compound, but contains a fourth component as long as the effects of the present invention are not impaired. It may be. For example, impurities derived from the production of titanium oxide fine particles may be contained, or a material added when using titanium oxide sol, for example, a coating agent, at least an additive added to a composition such as a paint. One kind may be added.
[0013]
The titanium oxide sol of the present invention has a pH in the range of 3 to 5 and is in a weakly acidic region, and does not use a dispersion stabilizer, so that it is used for various coating agents, paints, molded articles, compositions such as carriers, and the like. In addition, the types of components such as binders and additives to be blended in the composition and the base material to be applied are hardly limited and can be widely applied. For example, when the titanium oxide sol of the present invention is mixed with an inorganic curable component such as an organic silicate, a photocatalyst coating agent can be obtained. It can be used to decompose and remove dirt and harmful substances generated in the environment. Known UV curable components such as acrylic resins, alkyd resins, and fluororesins may be added to the composition to provide a UV protection paint. Alternatively, after a titanium oxide sol of the present invention is impregnated into a molded article or a carrier molded with an inorganic binder such as a clay mineral, and then heated and calcined, titanium oxide fine particles can be carried on the surface.
[0014]
Next, the present invention relates to a method for producing a titanium oxide sol, in which an aqueous titanium oxide sol whose pH is adjusted to a range of 0 to 2 with an acidic compound has a conductivity of 300 mS / m or less and a pH of 3 to 5. It is characterized by performing anion exchange up to. According to this method, the titanium oxide fine particles can be stably dispersed in a weakly acidic dispersion medium containing water as a main component and having a pH in the range of 3 to 5 without using a dispersion stabilizer. The reason is considered as follows.
[0015]
In general, titanium oxide has a hydroxyl group on its surface, and in water having an acidic pH range, H + ion and hydroxyl group are combined to take a positive charge as —OH 2 +. It is said that the higher the concentration of + ions, the more electrostatic repulsion occurs and the more stable the dispersion of titanium oxide. However, since acidic compounds dissociate in water and generate H + ions and anions, in order to make them strongly acidic, adding a large amount of acidic compounds increases the amount of anions and acts to weaken the repulsive force. it is conceivable that.
[0016]
After the titanium oxide fine particles are made highly acidic with an acidic compound and dispersed in advance, and then anion exchange is performed until the conductivity becomes 300 mS / m or less as in the present invention, H + binds to hydroxyl groups on the surface of the titanium oxide fine particles. while the, i.e., while the -OH 2 + state, to reduce the anions in the sol, electrostatic repulsion is presumed to be maintained. By anion exchange, OH in the sol - for ions increases, pH is increased from a range of 0 to 2, pH region dissociation degree is maintained acidic compounds, i.e. when the pH is in the range of 3-5 since -OH 2 + amount of surface is constant, even in pH under such weak acid, titanium oxide fine particles is considered to be stably dispersed.
[0017]
As the strongly acidic aqueous titanium oxide sol used in the production method of the present invention and the titanium oxide fine particles to be added to the aqueous titanium oxide sol, those obtained by a known method can be used. As the titanium oxide fine particles, for example, titanium compounds such as titanium tetrachloride, titanyl sulfate, and titanium sulfate are heated and hydrolyzed or neutralized with alkali to obtain fine particles of hydrous titanium oxide, titanium hydroxide, or titanic acid. . By heating and firing these, fine particles of anhydrous titanium oxide can be obtained. Alternatively, anhydrous titanium oxide fine particles can be obtained by gas phase hydrolysis of titanium tetrachloride or hydrolysis of titanium alkoxide. It is known that when hydrous titanium oxide is treated with sodium hydroxide and then treated with hydrochloric acid, spindle-shaped or needle-shaped fine particles of anhydrous titanium oxide are obtained. In the present invention, these hydrous titanium oxide, titanium hydroxide, titanic acid or anhydrous titanium oxide can be used as titanium oxide fine particles.
[0018]
The aqueous titanium oxide sol having a pH adjusted to the range of 0 to 2 is obtained by dispersing the above-mentioned titanium oxide fine particles in a dispersion medium containing water as a main component at a pH of 0 to 2. Specifically, if the pH of the reaction solution from which the titanium oxide fine particles are obtained as described above is 2 or less, the state is dispersed by a disperser as necessary to obtain a titanium oxide sol, or the pH of the reaction solution is reduced. If it is 2 or more, an acidic compound is added to adjust the pH to a range of 0 to 2 and dispersed to obtain a titanium oxide sol, or the titanium oxide fine particles are suspended in a dispersion medium containing water as a main component, An acidic compound is added to adjust the pH to a range of 0 to 2 and dispersed to form a titanium oxide sol. Further, the titanium oxide fine particles are mainly composed of water whose pH is adjusted to a range of 0 to 2 by an acidic compound. To a titanium oxide sol. In the present invention, it is preferable to form titanium oxide sol by dispersing titanium oxide fine particles in a dispersion medium containing water as a main component and having a pH adjusted to a range of 0 to 2 with an acidic compound.
[0019]
In the present invention, the above-mentioned aqueous titanium oxide sol having a pH of 0 to 2 is anion-exchanged until the conductivity is 300 mS / m or less and the pH is in a range of 3 to 5. The anion exchange can be performed, for example, by bringing the aqueous titanium oxide sol into contact with an anion exchange resin. Specifically, after the anion exchange resin is charged into the titanium oxide sol, solid-liquid separation or anion exchange is performed. The method can be appropriately selected, such as passing a titanium oxide sol through a column filled with an ion exchange resin. As the anion exchange resin, a known strong base having a quaternary ammonium as an ion exchange group or a weak base having a tertiary amine can be used. Any type may be used, and the properties thereof are not particularly limited. When the conductivity is 300 mS / m or less, preferably 200 mS / m or less, a titanium oxide sol having excellent dispersion stability can be obtained.
[0020]
【Example】
The present invention will be described in more detail by way of examples, which do not limit the present invention.
[0021]
Example 1
Fine particles of hydrous titanium oxide having an average particle diameter of 0.05 μm obtained by neutralization of titanium tetrachloride are added to ion-exchanged water adjusted to pH 1 with nitric acid so as to have a concentration of 15% by weight as TiO 2. Dispersed to prepare a strongly acidic aqueous suspension. To 100 g of this suspension, 450 g of an anion exchange resin (Amberlite IRA-910: manufactured by Organo) pre-wetted with ion-exchanged water was added while stirring to remove anions. When the pH of the titanium oxide sol reached 4 and the conductivity reached 62.7 mS / m, the ion-exchange resin was filtered to obtain a titanium oxide sol of the present invention (sample A).
[0022]
Example 2
Fine particles of metatitanic acid having an average particle diameter of 0.05 μm obtained by heating and hydrolyzing titanium sulfate are added to ion-exchanged water adjusted to pH 1.5 with nitric acid so as to have a concentration of 15% by weight as TiO 2. To prepare a strongly acidic aqueous suspension. Except for using this suspension, a titanium oxide sol of the present invention (sample B) was obtained in the same manner as in Example 1.
[0023]
Example 3
The titanium oxide sol of the present invention (sample C) was prepared in the same manner as in Example 2 except that the ion exchange resin was filtered when the pH of the titanium oxide sol reached 4.9 and the conductivity reached 26.1 mS / m. Got.
[0024]
Comparative Example 1
The strongly acidic aqueous suspension used in Example 2 is referred to as Comparative Example 1 (Sample D). The conductivity of this sample D exceeded the measurement limit (2000 mS / m) of the measuring instrument and was not measurable.
[0025]
Comparative Example 2
A titanium oxide sol (test E) was obtained in the same manner as in Example 2, except that the pH of the titanium oxide sol was 5.4, the conductivity was 10.2 mS / m, and the anion exchange resin was filtered.
[0026]
Evaluation 1
The spectral transmittance of the titanium oxide sols of Examples 1 to 3 and Comparative Examples 1 and 2 (samples A to E) at a wavelength of 550 nm was measured according to the method described above. In addition, the presence or absence of sediment was visually determined. Table 1 shows the results. It can be seen that the titanium oxide sol of the present invention has a high transmittance at a wavelength of 550 nm and has excellent dispersion stability of titanium oxide fine particles equivalent to that of a conventional strongly acidic titanium oxide sol.
[0027]
[Table 1]
Figure 2004075434
[0028]
【The invention's effect】
The titanium oxide sol of the present invention stabilizes the dispersion of titanium oxide fine particles in a dispersion medium mainly composed of weakly acidic water having a pH in the range of 3 to 5 without using a dispersion stabilizer. And particularly useful for photocatalytic coating agents and ultraviolet protective coatings. Further, the production method of the present invention is a method of anion-exchanging an aqueous titanium oxide sol having a pH adjusted to 0 to 2 with an acidic compound until the conductivity is 300 mS / m or less and the pH is in a range of 3 to 5. It is possible to produce a titanium oxide sol having excellent dispersion stability even under a weak acidity having a pH in the range of 3 to 5.

Claims (8)

酸化チタン微粒子、水を主成分とする分散媒、酸性化合物から実質的に構成され、pHが3〜5の範囲であることを特徴とする酸化チタンゾル。A titanium oxide sol substantially comprising titanium oxide fine particles, a dispersion medium containing water as a main component, and an acidic compound, and having a pH of 3 to 5. 下記の条件で測定した、550nmの波長を有する光の分光透過率が20〜60%の範囲であることを特徴とする請求項1記載の酸化チタンゾル。
分光透過率の測定条件
酸化チタン微粒子の濃度を0.5重量%に調整し、光路が1cmの石英セルに充填し、測定する。対象試料は水とする。
The titanium oxide sol according to claim 1, wherein the spectral transmittance of light having a wavelength of 550 nm measured under the following conditions is in the range of 20 to 60%.
Measurement Conditions of Spectral Transmittance The concentration of the titanium oxide fine particles was adjusted to 0.5% by weight, and a quartz cell having an optical path of 1 cm was filled and measured. The target sample is water.
導電率が300mS/m以下であることを特徴とする請求項1記載の酸化チタンゾル。2. The titanium oxide sol according to claim 1, wherein the conductivity is 300 mS / m or less. 酸化チタン微粒子を10〜50重量%の範囲で含むことを特徴とする請求項1に記載の酸化チタンゾル。The titanium oxide sol according to claim 1, wherein the titanium oxide fine particles are contained in a range of 10 to 50% by weight. 酸性化合物が無機酸であることを特徴とする請求項1記載の酸化チタンゾル。The titanium oxide sol according to claim 1, wherein the acidic compound is an inorganic acid. 酸性化合物によりpHを0〜2の範囲に調整した水性酸化チタンゾルを導電率が300mS/m以下でpHが3〜5の範囲になるまで陰イオン交換することを特徴とする酸化チタンゾルの製造方法。A method for producing a titanium oxide sol, comprising subjecting an aqueous titanium oxide sol, whose pH has been adjusted to 0 to 2 with an acidic compound, to anion exchange until the electric conductivity is 300 mS / m or less and the pH is in a range of 3 to 5. 水性酸化チタンゾルを陰イオン交換樹脂に接触させて、陰イオン交換することを特徴とする請求項6記載の酸化チタンゾルの製造方法。The method for producing a titanium oxide sol according to claim 6, wherein the aqueous titanium oxide sol is brought into contact with an anion exchange resin to perform anion exchange. 酸性化合物が無機酸であることを特徴とする請求項6記載の酸化チタンゾルの製造方法。The method for producing a titanium oxide sol according to claim 6, wherein the acidic compound is an inorganic acid.
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