JP2004068072A

JP2004068072A - Manufacturing method of silver particulate colloid dispersion solution

Info

Publication number: JP2004068072A
Application number: JP2002228112A
Authority: JP
Inventors: Masaya Yukinobu; 行延　雅也; Yukiko Suekane; 末兼　有希子
Original assignee: Sumitomo Metal Mining Co Ltd
Current assignee: Sumitomo Metal Mining Co Ltd
Priority date: 2002-08-06
Filing date: 2002-08-06
Publication date: 2004-03-04

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of colloidal dispersion solution of a silver particulate suitable as liquid paint for transparent conductive layer forming and antibacteria coating forming, with high productivity while the particle size of the silver particulate is easily controlled. <P>SOLUTION: Mixture solution 3 of aqueous solution containing ferrous ions, and aqueous solution containing citric acid ions, and aqueous solution 4 containing a silver salt are made to flow out of different nozzles 1 and 2 respectively, and they are made to join in the middle of running down, and are mixed, and are made to react in natural running down, to produce the silver particulate. Natural running down height H from junction of the mixed-solution 3 and the aqueous solution 4 containing the silver salt to surface 5 of a remaining reaction solution is set in the range of 10 cm-2 m. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、透明基板上に透明導電層を形成するための透明導電層形成塗液や、抗菌コーティング形成塗液等に用いられる銀微粒子コロイド分散液の製造方法に関するものである。
【０００２】
【従来の技術】
銀は貴金属類の中では安価であり、優れた導電特性や抗菌作用を有することから、電子機器、医薬など幅広い分野で使用されている。特に粒子をナノサイズにまで微細化させると、バルクの状態では見られなかった機能なども発現するようになるため、その用途は更に広がりを見せている。
【０００３】
かかる銀微粒子の用途として、例えば、特開平１１−３２９０７１号公報や特開２０００−２６８６３９号公報には、コンピュータディスプレイの漏洩電磁波防止用の透明導電膜がある。この透明導電膜は、銀を含む貴金属微粒子を溶媒に分散させた透明導電層形成塗液を、陰極線管（ＣＲＴ）の前面ガラス（前面板）に塗布・乾燥後、２００℃程度の温度で焼成して形成される。また、特開平４−３２１６２８号公報には、銀微粒子を溶媒に分散させた抗菌コーティング形成塗液が提案されている。
【０００４】
ナノサイズの銀微粒子を作製する方法はいろいろあるが、水溶液中において化学的に銀イオンを還元させて銀微粒子コロイド分散液を得る方法が、簡便且つ安価に製造できることから広く用いられている。
【０００５】
代表的な銀微粒子コロイド分散液の製造方法としては、Ｃａｒｅｙ−Ｌｅａ法［Ａｍ．　Ｊ．　Ｓｃｉ．，３７，４７（１８８９）、Ａｍ．　Ｊ．　Ｓｃｉ．，３８（１８８９）参照］がよく知られている。この方法によれば、硫酸鉄（ＩＩ）水溶液とクエン酸ナトリウム水溶液の混合液に、硝酸銀水溶液を混合して反応させ、得られた銀微粒子凝集体を濾過・洗浄した後、そのケーキに純水を加えることにより、簡単に比較的高濃度な銀微粒子コロイド分散液（Ａｇ：０．１〜１０重量％）を得ることができる。
【０００６】
【発明が解決しようとする課題】
上記Ｃａｒｅｙ−Ｌｅａ法による銀微粒子コロイド分散液の製造では、硫酸鉄（ＩＩ）水溶液とクエン酸ナトリウム水溶液の混合液と、硝酸銀水溶液とを混合する際に、片方の水溶液が入った容器に他方の水溶液を一気に加える方法が採られている。（以後、硫酸鉄（ＩＩ）水溶液とクエン酸ナトリウム水溶液の混合液、及び／又は硝酸銀水溶液を、原料水溶液と称する場合がある。）
しかし、両方の原料水溶液を容器内で一気に混合する従来のバッチ式の混合方法では、原料水溶液の混合状態の制御が困難であるため、得られる銀微粒子コロイド分散液の品質、特に銀微粒子の粒径の制御が容易ではなく、バッチ間で粒径を一定に保つことはほとんど不可能であった。
【０００７】
また、両方の原料水溶液の混合が容器内での液−液混合のため、それぞれの液量が多くなるほど完全な混合状態を得ることが困難となり、不均一な混合状態で銀微粒子の生成反応が起こってしまう。その結果として、同一バッチ内においても、得られる銀微粒子の粒径が不均一になりやすかった。
【０００８】
しかも、バッチ式の混合方法であるため、多量の銀微粒子コロイド分散液を製造するためには、小規模のバッチ式製造を繰り返し行う必要があり、生産性・生産効率が悪いという問題もあった。
【０００９】
本発明は、このような従来の事情に鑑み、従来の銀微粒子コロイド分散液の製造方法に比べて、銀微粒子の粒径制御が容易であり、且つ生産性に優れた銀微粒子コロイド分散液の製造方法を提供することを目的とする。
【００１０】
【課題を解決するための手段】
上記目的を達成するため、本発明が提供する銀微粒子コロイド分散液の製造方法は、第一鉄イオンを含む水溶液とクエン酸イオンを含む水溶液の混合液と、銀塩を含む水溶液とを混合して、銀微粒子を生成させる反応工程を有する銀微粒子コロイド分散液の製造方法において、上記混合液と銀塩を含む水溶液とをそれぞれ別のノズルから流出させ、流下途中で合流させて混合し、自然流下中に反応させることを特徴とするものである。
【００１１】
上記本発明の銀微粒子コロイド分散液の製造方法においては、前記混合液と銀塩を含む水溶液との合流点から下方の滞留反応液の液面までの自然流下高さを、１０ｃｍ〜２ｍの範囲に設定することが好ましい。
【００１２】
また、上記本発明における銀微粒子コロイド分散液の製造方法は、前記反応工程で得られた銀微粒子を濾過して銀微粒子凝集体のケーキを得る濾過工程と、上記ケーキに純水を加えて純水中に銀微粒子を分散させる分散工程を具備することができる。
【００１３】
【発明の実施の形態】
前述のＣａｒｅｙ−Ｌｅａ法における銀微粒子の生成反応は、下記化学式１のように表される：
【００１４】
【化１】
Ａｇ^＋　＋　Ｆｅ^２ ^＋　→　Ａｇ　＋　Ｆｅ^３＋
【００１５】
生成した銀微粒子は共存するクエン酸イオンの保護作用を受けると同時に、高濃度の鉄イオン、ナトリウムイオン等により急速に凝集するため、クエン酸イオンで保護された銀微粒子の凝集体を形成する。これら一連の反応は、各原料水溶液の混合後１〜２秒以内に起きるため、得られる銀微粒子の粒径等の特性は原料水溶液の混合状態に大きく依存することとなる。
【００１６】
従来法ではバッチ式により、片方の原料水溶液が入った容器に他方の原料水溶液を一気に加えるため、液の混合状態が不均一となりやすかった。そのため、生成する銀微粒子の粒径制御が難しく、特に処理液量が多い場合には銀微粒子の粗大粒子が生じやすいため、製造規模を大きくすることが困難であった。
【００１７】
これに対して、本発明方法では、硫酸鉄（ＩＩ）のような第一鉄イオンを含む水溶液とクエン酸イオンを含む水溶液の混合液と、硝酸銀のような銀塩を含む水溶液とを混合して反応させる反応工程において、上記混合液と銀塩を含む水溶液をそれぞれ別のノズルから流出させ、流下途中で合流させることにより混合し、自然流下中に反応させて銀微粒子を生成させる。
【００１８】
例えば、図１に示すように、２つのノズル１、２を対向させてやや下向きに設置して、片方のノズル１から第一鉄イオンを含む水溶液とクエン酸イオンを含む水溶液の混合液３を、他方のノズル２からは銀塩を含む水溶液４を空中に流出させ、両方の流れを流下の途中で合流させる。合流した混合液３と銀塩を含む水溶液４は、自然流下する間に混合と反応が進行して銀微粒子が生成される。
【００１９】
混合液３と銀塩を含む水溶液４の合流点から滞留反応液の液面５までの高さ（自然流下高さ）Ｈは、ノズルの径や原料水溶液の流速等にもよるが、一般的には１０ｃｍ〜２ｍの範囲が好ましく、２０ｃｍ〜１ｍの範囲が更に好ましい。この自然流下高さＨが１０ｃｍ未満では、原料水溶液同士の混合と反応が不十分となり、均一な粒径の銀微粒子が得られない。また、自然流下高さＨが２ｍを超えても、それまでの流下中に原料水溶液の混合と反応がほとんど終了してしまうため、設備が大掛かりとなるだけで、製造面でのメリットが得られない。
【００２０】
尚、下方に設置する容器６は、滞留反応液を溜めておくだけでも良いが、オーバーフロー等により滞留反応液を順じ次工程に供給することが好ましい。オーバーフロー等により滞留反応液を順じ次工程に供給できる容器の場合には、比較的小さい容器であっても、自然流下高さＨの設定が自由で且つ簡単であるという利点もある。しかし、出口がなく滞留反応液を溜めておくだけの容器では、時間の経過に伴って液面が上昇するため、自然流下高さＨの範囲内で全原料水溶液の合流流下が終了するように注意する必要がある。
【００２１】
この本発明方法によれば、従来のバッチ式製造法と異なり、連続式であるため常に液の混合状態が一定であるうえ、銀微粒子の生成反応時に原料水溶液が容器の壁面等に接触することもないため、容器壁面での銀微粒子の核発生・付着等も防止できるので、均一な粒径の銀微粒子を容易に、且つ効率的に製造することが可能となる。
【００２２】
上記の反応工程で得られた銀微粒子は、その後、濾過工程において濾過され、銀微粒子凝集体のケーキとして回収される。次の分散工程において、このケーキに純水を加えると、凝集要因となる液中の鉄イオンやナトリウム濃度が大幅に低下するため、クエン酸イオンで保護された銀微粒子は液中に再分散して、銀微粒子コロイド分散液が得られる。尚、このようなコロイドの製造方法は、一般的に「洗い出し法」と呼ばれている。
【００２３】
尚、銀微粒子凝集体の濾過工程では、銀微粒子が洗い出されない程度の少量の純水で上記ケーキの洗浄を行うことも可能である。また、上記銀微粒子凝集体の濾過には、メンブレンフィルター濾過、遠心分離、フィルタープレス等の常用の方法を用いることができる。
【００２４】
ところで、従来のＣａｒｅｙ−Ｌｅａ法を用いた場合には、一般的に粒径５〜１５ｎｍ程度の広い粒径範囲の銀微粒子が、一度の処理ごとに得られる。これに対して本発明方法によれば、例えば粒径２〜７ｎｍ、あるいは粒径１０〜１５ｎｍという具合に、粒径範囲を狭く制御しながら連続製造が可能となる。粒径の制御は、原料水溶液の液温や、ノズルからの流出速度、原料水溶液が合流する際の角度（ノズルの交差角度）等によるが、これらを適切に設定することにより、粒径が均一な銀微粒子を得ることが可能となる。尚、ここで言う銀微粒子の粒径とは、透過電子顕微鏡（ＴＥＭ）で観察される粒径をいう。
【００２５】
【実施例】
以下、本発明の実施例を具体的に説明するが、本発明はこれら実施例に限定されるものではない。また、本文中の「％」は、銀の収率を除き「重量％」を意味している。
【００２６】
［実施例１］
２３．１％硫酸鉄（ＦｅＳＯ_４・７Ｈ_２Ｏ）水溶液と３７．５％クエン酸ナトリウム（Ｃ_３Ｈ_４（ＯＨ）（ＣＯＯＮａ）_３・２Ｈ_２Ｏ）水溶液の混合液を片方のノズルから流速８７０ｇ／分で流出させると同時に、９．１％硝酸銀（ＡｇＮＯ_３）水溶液を他方のノズルから流速３３０ｇ／分で流出させ、空中で合流させて混合し、そのまま自然に流下させた。
【００２７】
尚、使用した２つのノズルは共に内径５ｍｍであり、それぞれ対向させて下方約４５度の方向にセットした。それぞれの原料水溶液は約７０度の交差角度で混合され、自然流下高さＨは３０ｃｍ（一定）になるように設定した。また、硫酸鉄水溶液とクエン酸ナトリウム水溶液の混合液の液温は１０℃に、硝酸銀水溶液の液温は５℃に設定した。
【００２８】
１０分間に合計で４８００ｇの混合液と３３００ｇ硝酸銀水溶液を合流混合させ、銀微粒子凝集体を含む反応液を得た。その後、容器内に滞留した反応液から銀微粒子凝集体を遠心分離機で濾過し、銀微粒子凝集体のケーキを回収した後、そのケーキに純水を加えて洗い出しを行い、銀微粒子コロイド分散液（Ａｇ：０．５％）３０５００ｇを得た。得られた銀微粒子の粒径をＴＥＭで測定し、その結果を下記表１に示した。
【００２９】
［実施例２］
硫酸鉄水溶液とクエン酸ナトリウム水溶液の混合液と硝酸銀水溶液の液温を、いずれも３０℃に設定した以外は上記実施例１と同様にして、銀微粒子コロイド分散液（Ａｇ：０．５％）３０９００ｇを得た。この実施例２の銀微粒子について、上記と同様に測定した粒径を下記表１に併せて示した。
【００３０】
［比較例１］
２３．１％硫酸鉄（ＦｅＳＯ_４・７Ｈ_２Ｏ）水溶液１３０ｇと、３７．５％クエン酸ナトリウム（Ｃ_３Ｈ_４（ＯＨ）（ＣＯＯＮａ）_３・２Ｈ_２Ｏ）水溶液１６０ｇの混合液をビーカーに入れ、この混合液を撹拌しながら９．１％硝酸銀（ＡｇＮＯ_３）水溶液１１０ｇを一気に加えて混合し、銀微粒子凝集体を含む反応液を得た。尚、硫酸鉄水溶液とクエン酸ナトリウム水溶液の混合液の液温は１０℃に、及び硝酸銀水溶液の液温は５℃に設定した。
【００３１】
この反応液から銀微粒子凝集体を遠心分離機で濾過し、回収した銀微粒子凝集体のケーキに純水を加えて洗い出しを行い、比較例１に係る銀微粒子コロイド分散液（Ａｇ：０．５％）９３０ｇを得た。得られた比較例１の銀微粒子について、上記と同様に測定した粒径を下記表１に併せて示した。
【００３２】
［比較例２］
２３．１％硫酸鉄水溶液３９００ｇと３７．５％クエン酸ナトリウム水溶液４８００ｇの混合液をステンレス容器に入れ、この混合液を撹拌しながら９．１％硝酸銀水溶液３３００ｇを一気に加えた以外は上記比較例１と同様にして、銀微粒子コロイド分散液（Ａｇ：０．５％）３１１００ｇを得た。この比較例２の銀微粒子について、上記と同様に測定した粒径を下記表１に併せて示した。
【００３３】
【表１】

【００３４】
表１に示された結果から分るように、本発明の各実施例に係る銀微粒子コロイド分散液では、粗大な銀微粒子はいっさい観察されず、極めて均一な粒径を有する銀微粒子が得られた。しかも、一度の処理で液量約３００００ｇの銀微粒子コロイド分散液が得られ、銀微粒子コロイド分散液の製造効率にも優れていることが分る。
【００３５】
一方、比較例１は、生産性を犠牲にした極めて少ない液量であるため、バッチ式にもかかわらず、粒径５〜１５ｎｍ程度の比較的均一な銀微粒子が得られている。しかしながら、同じバッチ式で液量を上記実施例と同程度に増やした比較例２では、粒径５〜１５ｎｍの通常粒子と共に粒径２５〜３０ｎｍの粗大な銀微粒子が観察され、粒径が極めて不均一であった。
【００３６】
【発明の効果】
本発明によれば、粒径制御が容易で、極めて均一な粒径の銀微粒子が得られ、生産性に優れた銀微粒子コロイド分散液の製造が可能となる。従って、本発明に係る銀微粒子コロイド分散液は、透明基板上に透明導電層を形成するための透明導電層形成塗液、抗菌コーティング形成塗液等として好適であると同時に、これら塗液の低価格化並びに品質安定化を実現することができる。
【図面の簡単な説明】
【図１】本発明方法の一具体例を示す概略の説明図である。
【符号の説明】
１、２　　　ノズル
３　　　混合液
４　　　銀塩を含む水溶液
５　　　液面
６　　　容器[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a silver fine particle colloidal dispersion used for a transparent conductive layer forming coating solution for forming a transparent conductive layer on a transparent substrate, an antimicrobial coating forming coating solution, and the like.
[0002]
[Prior art]
Silver is inexpensive among precious metals, and has excellent conductive properties and antibacterial action, and is therefore used in a wide range of fields such as electronic devices and pharmaceuticals. In particular, when the particles are miniaturized to a nano size, functions that are not seen in a bulk state are also exhibited, and the use thereof is further expanding.
[0003]
As an application of such silver fine particles, for example, JP-A-11-329071 and JP-A-2000-268639 include a transparent conductive film for preventing leakage of electromagnetic waves from a computer display. This transparent conductive film is coated with a transparent conductive layer forming coating liquid in which silver-containing noble metal fine particles are dispersed in a solvent, applied to the front glass (front plate) of a cathode ray tube (CRT), dried, and fired at a temperature of about 200 ° C. Formed. Japanese Patent Application Laid-Open No. 4-321628 proposes a coating liquid for forming an antibacterial coating in which silver fine particles are dispersed in a solvent.
[0004]
Although there are various methods for producing nano-sized silver fine particles, a method of chemically reducing silver ions in an aqueous solution to obtain a silver fine particle colloidal dispersion is widely used because it can be easily and inexpensively manufactured.
[0005]
As a typical method for producing a silver fine particle colloidal dispersion, the Carey-Lea method [Am. J. Sci. , 37, 47 (1889), Am. J. Sci. , 38 (1889)] are well known. According to this method, a silver nitrate aqueous solution is mixed and reacted with a mixed solution of an aqueous solution of iron (II) sulfate and an aqueous solution of sodium citrate, and the obtained fine silver particle aggregates are filtered and washed, and then the cake is added to pure water. , A silver microparticle colloidal dispersion (Ag: 0.1 to 10% by weight) having a relatively high concentration can be easily obtained.
[0006]
[Problems to be solved by the invention]
In the production of the silver fine particle colloidal dispersion by the Carey-Lea method, when mixing a mixed solution of an aqueous solution of iron (II) sulfate and an aqueous solution of sodium citrate with an aqueous solution of silver nitrate, one of the aqueous solutions is placed in a container containing the other aqueous solution. A method of adding an aqueous solution at once is adopted. (Hereinafter, a mixed solution of an aqueous solution of iron (II) sulfate and an aqueous solution of sodium citrate, and / or an aqueous solution of silver nitrate may be referred to as a raw material aqueous solution.)
However, in a conventional batch-type mixing method in which both raw material aqueous solutions are mixed at once in a container, it is difficult to control the mixing state of the raw material aqueous solutions. Controlling the diameter was not easy and it was almost impossible to keep the particle size constant between batches.
[0007]
In addition, since the mixing of both raw material aqueous solutions is a liquid-liquid mixture in a container, it becomes more difficult to obtain a perfect mixed state as the amount of each liquid increases, and the generation reaction of silver fine particles in an uneven mixed state is difficult. Will happen. As a result, even within the same batch, the particle size of the obtained silver fine particles was likely to be non-uniform.
[0008]
In addition, since it is a batch-type mixing method, it is necessary to repeatedly perform a small-scale batch-type production in order to produce a large amount of silver fine particle colloidal dispersion, and there is a problem that productivity and production efficiency are poor. .
[0009]
In view of such a conventional circumstance, the present invention makes it easier to control the particle size of silver fine particles, and to produce a silver fine particle colloidal dispersion having excellent productivity, as compared with a conventional method for producing a silver fine particle colloidal dispersion. It is intended to provide a manufacturing method.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, a method for producing a silver microparticle colloidal dispersion provided by the present invention comprises mixing a mixed solution of an aqueous solution containing ferrous ions and an aqueous solution containing citrate ions, and an aqueous solution containing a silver salt. In the method for producing a silver fine particle colloidal dispersion having a reaction step of generating silver fine particles, the mixed solution and the aqueous solution containing a silver salt are flowed out from different nozzles, respectively, mixed and mixed in the middle of the flow, and naturally mixed. It is characterized by reacting in the flow down.
[0011]
In the method for producing a silver fine particle colloidal dispersion liquid of the present invention, the natural flow height from the confluence of the mixed solution and the aqueous solution containing a silver salt to the liquid level of the staying reaction liquid below is in the range of 10 cm to 2 m. It is preferable to set
[0012]
Further, the method for producing a silver fine particle colloidal dispersion liquid according to the present invention includes a filtration step of filtering the silver fine particles obtained in the reaction step to obtain a cake of silver fine particle aggregates, and adding pure water to the cake to obtain pure water. A dispersing step of dispersing silver fine particles in water can be provided.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
The reaction of forming the fine silver particles in the Carey-Lea method described above is represented by the following chemical formula 1:
[0014]
Embedded image
^{^{^{Ag + + Fe 2 + → Ag}}} + Fe 3+
[0015]
The generated silver fine particles are protected by the coexisting citrate ions, and are also rapidly aggregated by high-concentration iron ions, sodium ions and the like, so that aggregates of the silver fine particles protected by the citrate ions are formed. Since these series of reactions occur within 1 to 2 seconds after the mixing of each raw material aqueous solution, the characteristics such as the particle size of the obtained silver fine particles greatly depend on the mixing state of the raw material aqueous solutions.
[0016]
In the conventional method, since the other raw material aqueous solution is added at a stretch to a container containing one raw material aqueous solution by a batch method, the mixing state of the liquids tends to be uneven. Therefore, it is difficult to control the particle size of the generated silver fine particles, and particularly when the amount of the processing solution is large, coarse silver fine particles are likely to be generated, and it is difficult to increase the production scale.
[0017]
On the other hand, in the method of the present invention, a mixed solution of an aqueous solution containing ferrous ions such as iron (II) sulfate and an aqueous solution containing citrate ions, and an aqueous solution containing a silver salt such as silver nitrate are mixed. In the reaction step, the mixed solution and the aqueous solution containing a silver salt are flowed out from different nozzles, are mixed by being merged in the middle of the flow, and are allowed to react in the natural flow to generate silver fine particles.
[0018]
For example, as shown in FIG. 1, two nozzles 1 and 2 are installed to face each other slightly downward, and a mixed solution 3 of an aqueous solution containing ferrous ions and an aqueous solution containing citrate ions is supplied from one nozzle 1. From the other nozzle 2, an aqueous solution 4 containing a silver salt is caused to flow out into the air, and both flows are merged on the way down. The mixed liquid 3 and the aqueous solution 4 containing a silver salt are mixed and reacted with each other while flowing naturally to produce silver fine particles.
[0019]
The height H from the confluence of the mixed solution 3 and the aqueous solution 4 containing the silver salt to the liquid level 5 of the staying reaction solution (natural flow height) depends on the diameter of the nozzle, the flow rate of the raw material aqueous solution, and the like. Is preferably in the range of 10 cm to 2 m, more preferably in the range of 20 cm to 1 m. If the natural flow height H is less than 10 cm, the mixing and the reaction of the raw material aqueous solutions become insufficient, and silver fine particles having a uniform particle size cannot be obtained. Further, even if the natural flow height H exceeds 2 m, the mixing and reaction of the raw material aqueous solution is almost completed during the flow down to that time, so that the equipment becomes large-scale, and there is an advantage in production. Absent.
[0020]
Note that the container 6 installed below may simply store the staying reaction solution, but it is preferable to supply the staying reaction solution to the next step in order by overflow or the like. In the case of a container which can supply the staying reaction solution to the next step in order due to overflow or the like, there is also an advantage that the setting of the natural flow height H is free and simple even for a relatively small container. However, in the case of a vessel having no outlet and merely storing the staying reaction liquid, the liquid level rises with the passage of time, so that the combined flow of all the raw material aqueous solutions is completed within the range of the natural flow height H. You need to be careful.
[0021]
According to the method of the present invention, unlike the conventional batch-type manufacturing method, the mixing state of the liquid is always constant because the method is continuous, and the raw material aqueous solution comes into contact with the wall surface of the container or the like during the silver fine particle generation reaction. Therefore, nucleation and adhesion of silver fine particles on the container wall surface can be prevented, so that silver fine particles having a uniform particle size can be easily and efficiently manufactured.
[0022]
The silver fine particles obtained in the above reaction step are then filtered in a filtration step and recovered as a cake of silver fine particle aggregates. In the next dispersing step, when pure water is added to this cake, the concentration of iron ions and sodium in the liquid, which is a coagulation factor, is greatly reduced, so that the silver fine particles protected by citrate ions are redispersed in the liquid. Thus, a silver fine particle colloidal dispersion is obtained. Incidentally, such a method for producing a colloid is generally called a “washing-out method”.
[0023]
In the step of filtering the aggregated silver fine particles, the cake can be washed with a small amount of pure water that does not wash out the silver fine particles. In addition, a common method such as filtration with a membrane filter, centrifugation, or a filter press can be used for filtering the aggregated silver fine particles.
[0024]
By the way, when the conventional Carey-Lea method is used, generally, silver fine particles having a wide particle size range of about 5 to 15 nm are obtained for each processing. On the other hand, according to the method of the present invention, continuous production is possible while controlling the particle size range to be narrow, for example, 2 to 7 nm in particle size or 10 to 15 nm in particle size. The particle size is controlled by the liquid temperature of the raw material aqueous solution, the outflow speed from the nozzle, the angle at which the raw material aqueous solution joins (crossing angle of the nozzle), and the like. Silver fine particles can be obtained. Here, the particle size of the silver fine particles means a particle size observed by a transmission electron microscope (TEM).
[0025]
【Example】
Hereinafter, examples of the present invention will be specifically described, but the present invention is not limited to these examples. Further, “%” in the text means “% by weight” except for the yield of silver.
[0026]
[Example 1]
23.1% iron sulfate _(FeSO 4 · _7H 2 O) solution and 37.5% sodium citrate _{_{(C 3 H 4 (OH)}} (COONa) 3 · 2H 2 O) flow rate mixture of the aqueous solution from one of the nozzles At the same time as flowing out at 870 g / min, a 9.1% aqueous solution of silver nitrate (AgNO ₃ ) was flowed out from the other nozzle at a flow rate of 330 g / min, merged and mixed in the air, and allowed to flow naturally.
[0027]
The two nozzles used each had an inner diameter of 5 mm, and were set facing downward at about 45 degrees. Each raw material aqueous solution was mixed at an intersection angle of about 70 degrees, and the natural falling height H was set to be 30 cm (constant). The temperature of the mixture of the aqueous solution of iron sulfate and the aqueous solution of sodium citrate was set at 10 ° C, and the temperature of the aqueous solution of silver nitrate was set at 5 ° C.
[0028]
A total of 4800 g of the mixed solution and 3300 g of silver nitrate aqueous solution were mixed and mixed in 10 minutes to obtain a reaction solution containing silver fine particle aggregates. Thereafter, the silver fine particle aggregates are filtered from the reaction solution retained in the container with a centrifugal separator, and a cake of the silver fine particle aggregates is recovered.Pure water is added to the cake to wash out the silver fine particle aggregates. (Ag: 0.5%) 30500 g was obtained. The particle size of the obtained silver fine particles was measured by TEM, and the results are shown in Table 1 below.
[0029]
[Example 2]
A silver fine particle colloidal dispersion (Ag: 0.5%) in the same manner as in Example 1 except that the temperature of the mixture of the aqueous solution of iron sulfate and the aqueous solution of sodium citrate and the aqueous solution of silver nitrate were all set at 30 ° C. 30900 g were obtained. The particle size of the silver fine particles of Example 2 measured in the same manner as described above is also shown in Table 1 below.
[0030]
[Comparative Example 1]
And 23.1% iron sulfate _(FeSO 4 · _7H 2 O) aqueous solution 130 g, a mixture of 37.5% sodium citrate _{_{(C 3 H 4 (OH)}} (COONa) 3 · 2H 2 O) aqueous solution of 160g in a beaker Then, while stirring the mixture, 110 g of a 9.1% silver nitrate (AgNO ₃ ) aqueous solution was added at a stretch and mixed to obtain a reaction solution containing silver fine particle aggregates. The temperature of the mixture of the aqueous solution of iron sulfate and the aqueous solution of sodium citrate was set at 10 ° C, and the temperature of the aqueous solution of silver nitrate was set at 5 ° C.
[0031]
The silver fine particle aggregates were filtered from the reaction solution by a centrifuge, and pure water was added to the recovered silver fine particle aggregate cake to wash out the silver fine particle aggregates. The silver fine particle colloidal dispersion (Ag: 0.5 %) 930 g were obtained. Table 1 below also shows the particle diameters of the obtained silver fine particles of Comparative Example 1 measured in the same manner as described above.
[0032]
[Comparative Example 2]
The above comparative example except that a mixed solution of 3900 g of a 23.1% iron sulfate aqueous solution and 4800 g of a 37.5% sodium citrate aqueous solution was put in a stainless steel container, and 3300 g of a 9.1% silver nitrate aqueous solution was added at a stretch while stirring the mixed solution. In the same manner as in Example 1, 31100 g of a silver fine particle colloidal dispersion (Ag: 0.5%) was obtained. The particle size of the silver fine particles of Comparative Example 2 measured in the same manner as above is also shown in Table 1 below.
[0033]
[Table 1]

[0034]
As can be seen from the results shown in Table 1, in the silver fine particle colloidal dispersion according to each example of the present invention, no coarse silver fine particles were observed, and silver fine particles having an extremely uniform particle size were obtained. Was. Moreover, it can be seen that a silver fine particle colloidal dispersion having a liquid amount of about 30,000 g can be obtained by one treatment, and that the production efficiency of the silver fine particle colloidal dispersion is excellent.
[0035]
On the other hand, in Comparative Example 1, since the liquid amount was extremely small at the expense of productivity, relatively uniform silver fine particles having a particle size of about 5 to 15 nm were obtained despite the batch method. However, in Comparative Example 2 in which the liquid volume was increased to the same level as in the above example in the same batch system, coarse silver fine particles having a particle size of 25 to 30 nm were observed together with ordinary particles having a particle size of 5 to 15 nm, and the particle size was extremely large. It was uneven.
[0036]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, silver particle | grain of a particle size control is easy and a very uniform particle size is obtained, and it becomes possible to manufacture the silver fine particle colloid dispersion liquid excellent in productivity. Therefore, the colloidal dispersion liquid of fine silver particles according to the present invention is suitable as a coating liquid for forming a transparent conductive layer for forming a transparent conductive layer on a transparent substrate, a coating liquid for forming an antibacterial coating, etc. Price and quality stabilization can be realized.
[Brief description of the drawings]
FIG. 1 is a schematic explanatory view showing one specific example of the method of the present invention.
[Explanation of symbols]
1, 2 Nozzle 3 Mixed solution 4 Aqueous solution containing silver salt 5 Liquid level 6 Container

Claims

第一鉄イオンを含む水溶液とクエン酸イオンを含む水溶液の混合液と、銀塩を含む水溶液とを混合して、銀微粒子を生成させる反応工程を有する銀微粒子コロイド分散液の製造方法において、上記混合液と銀塩を含む水溶液とをそれぞれ別のノズルから流出させ、流下途中で合流させて混合し、自然流下中に反応させることを特徴とする銀微粒子コロイド分散液の製造方法。In the method for producing a silver fine particle colloidal dispersion having a reaction step of mixing a mixed solution of an aqueous solution containing ferrous ions and an aqueous solution containing citrate ions and an aqueous solution containing a silver salt to generate silver fine particles, A method for producing a silver fine particle colloidal dispersion, wherein a mixed liquid and an aqueous solution containing a silver salt are flowed out from different nozzles, mixed together in the course of flow, mixed and allowed to react naturally.

前記混合液と銀塩を含む水溶液との合流点から下方の滞留反応液の液面までの自然流下高さを、１０ｃｍ〜２ｍの範囲に設定することを特徴とする、請求項１に記載の銀微粒子コロイド分散液の製造方法。The spontaneous flow height from the junction of the mixed solution and the aqueous solution containing a silver salt to the liquid level of the staying reaction solution below is set in a range of 10 cm to 2 m, according to claim 1, wherein A method for producing a colloidal dispersion of fine silver particles.

前記反応工程で得られた銀微粒子を濾過して銀微粒子凝集体のケーキを得る濾過工程と、上記ケーキに純水を加えて純水中に銀微粒子を分散させる分散工程を具備することを特徴とする、請求項１又は２に記載の銀微粒子コロイド分散液の製造方法。A filtering step of filtering the silver fine particles obtained in the reaction step to obtain a cake of silver fine particle aggregates; and a dispersion step of adding pure water to the cake and dispersing the silver fine particles in pure water. The method for producing a silver fine particle colloidal dispersion according to claim 1 or 2.