JP2004018891A - Process for preparing colloidal dispersion of silver fine particle - Google Patents
Process for preparing colloidal dispersion of silver fine particle Download PDFInfo
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- JP2004018891A JP2004018891A JP2002172191A JP2002172191A JP2004018891A JP 2004018891 A JP2004018891 A JP 2004018891A JP 2002172191 A JP2002172191 A JP 2002172191A JP 2002172191 A JP2002172191 A JP 2002172191A JP 2004018891 A JP2004018891 A JP 2004018891A
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- 229910052709 silver Inorganic materials 0.000 title claims abstract description 93
- 239000004332 silver Substances 0.000 title claims abstract description 93
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 title claims abstract description 92
- 239000010419 fine particle Substances 0.000 title claims abstract description 87
- 238000001246 colloidal dispersion Methods 0.000 title claims abstract description 25
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 19
- 239000007864 aqueous solution Substances 0.000 claims abstract description 73
- 238000002156 mixing Methods 0.000 claims abstract description 28
- 230000003068 static effect Effects 0.000 claims abstract description 17
- 239000000243 solution Substances 0.000 claims abstract description 13
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 12
- GGCZERPQGJTIQP-UHFFFAOYSA-N sodium;9,10-dioxoanthracene-2-sulfonic acid Chemical compound [Na+].C1=CC=C2C(=O)C3=CC(S(=O)(=O)O)=CC=C3C(=O)C2=C1 GGCZERPQGJTIQP-UHFFFAOYSA-N 0.000 claims abstract description 10
- 239000000203 mixture Substances 0.000 claims abstract description 8
- CWYNVVGOOAEACU-UHFFFAOYSA-N Fe2+ Chemical compound [Fe+2] CWYNVVGOOAEACU-UHFFFAOYSA-N 0.000 claims abstract description 7
- 229910001448 ferrous ion Inorganic materials 0.000 claims abstract description 6
- 238000006243 chemical reaction Methods 0.000 claims description 14
- 239000011259 mixed solution Substances 0.000 claims description 13
- -1 citrate ions Chemical class 0.000 claims description 12
- 238000001914 filtration Methods 0.000 claims description 7
- 239000011859 microparticle Substances 0.000 claims description 4
- 239000006185 dispersion Substances 0.000 claims description 3
- 239000011248 coating agent Substances 0.000 abstract description 11
- 238000000576 coating method Methods 0.000 abstract description 11
- 230000000844 anti-bacterial effect Effects 0.000 abstract description 3
- 239000012295 chemical reaction liquid Substances 0.000 abstract description 2
- 239000008367 deionised water Substances 0.000 abstract 2
- 229910021641 deionized water Inorganic materials 0.000 abstract 2
- KRKNYBCHXYNGOX-UHFFFAOYSA-K Citrate Chemical compound [O-]C(=O)CC(O)(CC([O-])=O)C([O-])=O KRKNYBCHXYNGOX-UHFFFAOYSA-K 0.000 abstract 1
- 239000002245 particle Substances 0.000 description 37
- SQGYOTSLMSWVJD-UHFFFAOYSA-N silver(1+) nitrate Chemical compound [Ag+].[O-]N(=O)=O SQGYOTSLMSWVJD-UHFFFAOYSA-N 0.000 description 28
- 239000007788 liquid Substances 0.000 description 27
- 238000000034 method Methods 0.000 description 19
- 229910001961 silver nitrate Inorganic materials 0.000 description 14
- BAUYGSIQEAFULO-UHFFFAOYSA-L iron(2+) sulfate (anhydrous) Chemical compound [Fe+2].[O-]S([O-])(=O)=O BAUYGSIQEAFULO-UHFFFAOYSA-L 0.000 description 13
- 239000002994 raw material Substances 0.000 description 12
- NLJMYIDDQXHKNR-UHFFFAOYSA-K sodium citrate Chemical compound O.O.[Na+].[Na+].[Na+].[O-]C(=O)CC(O)(CC([O-])=O)C([O-])=O NLJMYIDDQXHKNR-UHFFFAOYSA-K 0.000 description 12
- 239000001509 sodium citrate Substances 0.000 description 12
- 230000000052 comparative effect Effects 0.000 description 10
- 239000012530 fluid Substances 0.000 description 9
- 229910000358 iron sulfate Inorganic materials 0.000 description 8
- 239000010944 silver (metal) Substances 0.000 description 7
- 238000002347 injection Methods 0.000 description 6
- 239000007924 injection Substances 0.000 description 6
- 229910000359 iron(II) sulfate Inorganic materials 0.000 description 5
- 239000010946 fine silver Substances 0.000 description 4
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 4
- 239000000084 colloidal system Substances 0.000 description 3
- 238000011156 evaluation Methods 0.000 description 3
- 230000000845 anti-microbial effect Effects 0.000 description 2
- 239000004599 antimicrobial Substances 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 238000007796 conventional method Methods 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 229910001415 sodium ion Inorganic materials 0.000 description 2
- 239000002904 solvent Substances 0.000 description 2
- 238000003756 stirring Methods 0.000 description 2
- 239000000758 substrate Substances 0.000 description 2
- 238000011144 upstream manufacturing Methods 0.000 description 2
- 101710134784 Agnoprotein Proteins 0.000 description 1
- 102000015081 Blood Coagulation Factors Human genes 0.000 description 1
- 108010039209 Blood Coagulation Factors Proteins 0.000 description 1
- 239000003114 blood coagulation factor Substances 0.000 description 1
- 238000005119 centrifugation Methods 0.000 description 1
- 239000011362 coarse particle Substances 0.000 description 1
- 239000003814 drug Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000010828 elution Methods 0.000 description 1
- 238000005755 formation reaction Methods 0.000 description 1
- 230000008014 freezing Effects 0.000 description 1
- 238000007710 freezing Methods 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 239000012528 membrane Substances 0.000 description 1
- 239000002105 nanoparticle Substances 0.000 description 1
- 229910000510 noble metal Inorganic materials 0.000 description 1
- 230000002093 peripheral effect Effects 0.000 description 1
- 239000010970 precious metal Substances 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 230000006641 stabilisation Effects 0.000 description 1
- 238000011105 stabilization Methods 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
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- 238000011077 uniformity evaluation Methods 0.000 description 1
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- Manufacture Of Metal Powder And Suspensions Thereof (AREA)
- Application Of Or Painting With Fluid Materials (AREA)
- Colloid Chemistry (AREA)
Abstract
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った場合に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の銀微粒子の生成反応が起こってしまう。その結果、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に、銀塩を含む水溶液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有する水溶液とをスタティックミキサーを用いて混合することを特徴とする。
【００１１】
上記本発明の銀微粒子コロイド分散液の製造方法では、前記反応工程において、微細な銀粒子を生成させること、液の取り扱い易さ、溶出の析出、液の凍結などを考慮すると、前記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の温度を５〜８０℃、及び銀塩を含有する水溶液の温度を０〜８０℃とすることが好ましい。
【００１２】
また、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＋ ＋ Ｆｅ２ ＋ → Ａｇ ＋ Ｆｅ３＋
【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に、硝酸銀のような銀塩を含む水溶液を混合する際に、スタティックミキサーを用いて混合・反応させる。この本発明方法によれば、従来のバッチ式混合法と異なり連続式であるため、常に液の混合状態が一定となり、均一な粒径の銀微粒子を容易に、しかも効率良く製造することが可能となる。
【００１８】
ここで、「スタティックミキサー」とは、機械的可動部分が存在しない混合装置である。例えば、従来から一般に用いられているスタティックミキサーとしては、９０度捻った捻り翼（固定スクリュ−）を１エレメントと称し、それら捻り翼の捻り方向を変えたものを交互に数エレメント流体流路中に収納したものが知られている。また、これとは別のタイプのスタティックミキサーとして、流体流路中に混合室及びその内部に衝突盤を有し、衝突盤の流体流入面に多数の凹部が設けられているもの（特開平１１−８２９１９号公報参照）が挙げられる。
【００１９】
後者のスタティックミキサーは、例えば図１に示す構造を有している。具体的には、流入路１の途中に注入管２を連結し、この注入管２の下流側に流入路１より大径の混合室３が同心状に設けてあり、混合室３の下流側に流出路４を有している。混合室３内には流入路１の内径より大きい外径の衝突盤５が同心状に収納固定され、衝突盤５の外周縁部には流入路１側に向けて突き出た筒部６を備えている。また、衝突盤５の流入路１側の表面や、混合室３の軸方向に直角な側面には、多数の小さな凹部７が設けてある。
【００２０】
流入路１と注入管から導入された流体は、混合室３の衝突盤５に衝突してその外周方向に放射状に流れ、一部は筒部６に当り逆流して複雑な乱流となり、混合室３の上流側で渦流を発生させる。また、混合室３の上流側では、順次流入してくる流体と逆流してくる流体とが衝突し、激しく撹拌・混合される。更に、衝突盤５等に設けた多数の小さな凹部７に衝突することで、流体はより複雑な流れとなる。このようにして、十分に撹拌・混合された流体は、混合室３を出て下流側に回り、流出路４から排出される。
【００２１】
このようなスタティックミキサーを用いて、例えば、流入路１に硫酸鉄（ＩＩ）水溶液とクエン酸ナトリウム水溶液の混合液を流し、注入管２から硝酸銀水溶液を導入することによって、両方の原料水溶液を常に一定の混合状態で十分に混合することができるため、均一な粒径の銀微粒子を得ることができる。しかも、スタティックミキサーを用いることで連続運転が可能となり、多量の銀微粒子を高い生産効率で製造することができる。
【００２２】
従来から行われているバッチ式の混合方法では、同一バッチ内での銀微粒子の粒径は一般的に粒径５〜１５ｎｍ程度であった。これに対して、本発明のスタティックミキサーを用いた混合方法によれば、連続的に得られる銀微粒子の粒径の範囲をより狭い範囲内に制御することができ、例えば粒径２〜７ｎｍの範囲あるいは１０〜１５ｎｍの範囲の銀微粒子を連続して製造するが可能となる。尚、ここで言う粒径とは、透過電子顕微鏡（ＴＥＭ）で観察される銀微粒子の粒径を示している。
【００２３】
銀微粒子の粒径は、原料水溶液の液温や流量（流入速度）、スタティックミキサーの構造等によって変化し、これらを適切に設定することで粒径を制御することが可能でなる。例えば、原料水溶液の液温を上げると粒径は大きくなり、流量を多くすると粒径は小さくなる傾向にある。また、スタティックミキサーの構造に関しては、従来型のねじり羽根を交互に配置したタイプよりも、図１に示す特開平１１−８２９１９号公報記載のスタティックミキサーを用いた方が小さな粒径が得られる。
【００２４】
特に原料水溶液の液温については、３０℃を超えるとバッチ式で少量ずつ混合した場合と同程度の大きな粒径の銀微粒子が含まれるようになるため、微細な銀微粒子を得るためには、３０℃以下に保持することが望ましい。具体的には、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の温度は、５〜８０℃とすることが好ましく、５〜２０℃が更に好ましい。また、銀塩を含有する水溶液の温度は、０〜８０℃とすることが好ましく、０〜１０℃が更に好ましい。このように温度管理することによって、粒径が１０ｎｍ以下で且つ粒径幅が５ｎｍ程度の銀微粒子を安定して得ることができる。
【００２５】
上記した反応工程により得られた銀微粒子凝集体は、濾過することにより銀微粒子凝集体のケーキが得られる。このケーキに純水を加えると、液中の鉄イオン及びナトリウムイオン濃度は大幅に低下し、凝集要因がなくなるため、クエン酸イオンで保護されていた銀微粒子が液中に再分散して、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。
【００２６】
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。
【００２７】
【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。
【００２８】
［実施例１］
図１に示すスタティックミキサー（シンユー技研製、特開平１１−８２９１９号公報記載の構造）を用いて、２３．１％硫酸鉄（ＦｅＳＯ４・７Ｈ２Ｏ）水溶液と３７．５％クエン酸ナトリウム（Ｃ３Ｈ４（ＯＨ）（ＣＯＯＮａ）３・２Ｈ２Ｏ）水溶液の混合液に、９．１％硝酸銀（ＡｇＮＯ３）水溶液を混合して、銀微粒子を製造した。
【００２９】
即ち、上記硫酸鉄水溶液３９００ｇとクエン酸ナトリウム水溶液４８００ｇの混合液を流入路１から８７０ｇ／分の流量で導入し、同時に上記硝酸銀水溶液３３００ｇを注入管２から３３０ｇ／分の流量で供給しながら、滞留時間１０分間で混合・反応させることによって、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℃、及び硝酸銀水溶液の液温は５℃に設定した。
【００３０】
上記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って、実施例１に係る銀微粒子コロイド分散液（Ａｇ：０．５％）３０７００ｇを得た。
【００３１】
得られた実施例１の銀微粒子について、銀微粒子コロイド分散液を透過電子顕微鏡（日本電子製）で観察して粒径を測定し、その結果を粒径の均一性の評価と共に、下記表１に示した。尚、粒径の均一性評価は、粒径２５ｎｍ以上の粗大粒子が見られなかった場合を均一とした。
【００３２】
［実施例２］
上記実施例１と同様にして、スタティックミキサーで硫酸鉄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、銀微粒子の製造を行ったが、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及び硝酸銀水溶液の液温を共に３０℃に設定した。
【００３３】
得られた銀微粒子凝集体を含む反応液を実施例１と同様に処理して、実施例２の銀微粒子コロイド分散液（Ａｇ：０．５％）３０８００ｇを得た。この実施例２の銀微粒子について、実施例１と同様に粒径を測定し、その結果を粒径の均一性の評価と共に、下記表１に示した。
【００３４】
［比較例１］
上記実施例１と同じ硫酸鉄水溶液とクエン酸ナトリウム水溶液、及び硝酸銀水溶液を用い、バッチ式により銀微粒子を製造した。
【００３５】
即ち、硫酸鉄水溶液１３０ｇとクエン酸ナトリウム水溶液１６０ｇの混合液をビーカーに入れ、撹拌しながら硝酸銀水溶液１１０ｇを一気に加え、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℃、及び硝酸銀水溶液の液温は５℃に設定した。
【００３６】
この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得た後、そ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、実施例１と同様に測定及び評価した結果を下記表１に示した。
【００３７】
［比較例２］
比較例１と同様にバッチ式で混合したが、効率を高めるため液量を増やした。即ち、硫酸鉄水溶液３９００ｇと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、撹拌しながら硝酸銀水溶液３３００ｇを一気に加えた以外は、比較例１と同様に実施した。
【００３８】
得られた銀微粒子凝集体を含む反応液を実施例１と同様に処理して、比較例２の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も、実施例１と同様に測定及び評価した結果を下記表１に示した。
【００３９】
【表１】
表１に示された結果から分るように、各実施例に係る銀微粒子コロイド分散液では、粗大銀微粒子が観察されず、均一な粒径を有する銀微粒子が得られ、特に液温を１０°以下に保持した実施例１では粒径２〜８ｎｍの極めて均一な銀微粒子が得られた。また、各実施例とも、約３００００ｇの液量が一度の処理で得られており、銀微粒子コロイド分散液の製造効率が高いことが分る。
【００４１】
一方、比較例１に係る銀微粒子コロイド分散液においては、粒径５〜１５ｎｍ程度の比較的均一な銀微粒子が得られているものの、一度に得られる液量が９３０ｇと極めて少ない。また、比較例２に係る銀微粒子コロイド分散液では、得られる液量を上記実施例と同程度にしたため、銀微粒の粒径が大幅にばらつき、粒径２５〜３０ｎｍ程度の粗大銀微粒子が含まれていた。
【００４２】
【発明の効果】
本発明によれば、銀微粒子の粒径制御が容易であり、均一な粒径の銀微粒子を含む銀微粒子コロイド分散液を、生産性良く製造することができる。従って、本且つ名によ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、あるいは抗菌コーティング形成塗液等に用いたとき、これら塗液の品質の安定化と、低価格化を実現することができる。
【図面の簡単な説明】
【図１】スタティックミキサーの一具体例を示す概略の断面図である。
【符号の説明】
１ 流入路
２ 注入管
３ 混合室
４ 流出路
５ 衝突盤
６ 筒部
７ 凹部[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 the two raw material aqueous solutions is a liquid-liquid mixture in a container, it is difficult to obtain a complete mixed state when the respective liquid amounts are large, and the silver fine particles in an uneven mixed state are difficult to obtain. The formation reaction occurs. As a result, even in 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 situation, the present invention makes it easier to control the particle size of silver fine particles and to produce a silver fine particle colloidal dispersion excellent in productivity as compared with a conventional method for manufacturing a silver fine particle colloidal dispersion. The aim is to provide a method.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, a method for producing a silver fine particle colloidal dispersion provided by the present invention comprises mixing an aqueous solution containing a silver salt with a mixed solution of an aqueous solution containing ferrous ions and an aqueous solution containing citrate ions. A method for producing a silver fine particle colloidal dispersion having a reaction step of generating silver fine particles, wherein the mixed liquid and an aqueous solution containing a silver salt are mixed using a static mixer.
[0011]
In the method for producing a silver fine particle colloidal dispersion liquid of the present invention, in the reaction step, considering the generation of fine silver particles, ease of handling of the liquid, precipitation of elution, freezing of the liquid, the ferrous iron, The temperature of the mixed solution of the aqueous solution containing ions and the aqueous solution containing citrate ions is preferably 5 to 80 ° C, and the temperature of the aqueous solution containing the silver salt is preferably 0 to 80 ° C.
[0012]
In the method for producing a silver fine particle colloidal dispersion liquid of the present invention, 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. A dispersing step of dispersing silver fine particles in pure water can be provided.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
The reaction of forming silver fine particles in the above Carey-Lea method 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]
In contrast, according to the present invention, when an aqueous solution containing a silver salt such as silver nitrate is mixed with a mixed solution of an aqueous solution containing ferrous ions such as iron (II) sulfate and an aqueous solution containing citrate ions. Mix and react using a static mixer. According to the method of the present invention, unlike the conventional batch-type mixing method, a continuous type is used, so that the mixing state of the liquid is always constant, and silver fine particles having a uniform particle size can be easily and efficiently produced. It becomes.
[0018]
Here, the “static mixer” is a mixing device having no mechanically movable part. For example, as a static mixer generally used conventionally, a twisted blade (fixed screw) twisted by 90 degrees is referred to as one element, and one in which the twisting direction of the twisted blade is changed is alternately used in several element fluid flow paths. Is known. As another type of static mixer, a mixer having a mixing chamber in a fluid flow path and an impingement plate therein, and having a large number of recesses in a fluid inflow surface of the impingement plate (Japanese Patent Laid-Open No. -82919).
[0019]
The latter static mixer has, for example, the structure shown in FIG. Specifically, an injection pipe 2 is connected in the middle of the inflow path 1, and a mixing chamber 3 having a larger diameter than the inflow path 1 is provided concentrically downstream of the injection pipe 2. Has an outflow channel 4. A collision plate 5 having an outer diameter larger than the inner diameter of the inflow passage 1 is accommodated and fixed concentrically in the mixing chamber 3, and the outer periphery of the collision plate 5 is provided with a cylindrical portion 6 protruding toward the inflow passage 1. ing. Further, a large number of small
[0020]
The fluid introduced from the inflow path 1 and the injection pipe collides with the collision plate 5 of the mixing chamber 3 and radially flows in the outer peripheral direction thereof, and a part of the fluid hits the cylinder 6 and flows backward to form a complex turbulent flow. A vortex is generated upstream of the chamber 3. Further, on the upstream side of the mixing chamber 3, the fluid flowing sequentially and the fluid flowing backward collide and are vigorously stirred and mixed. Further, by colliding with a number of small
[0021]
By using such a static mixer, for example, a mixed solution of an aqueous solution of iron (II) sulfate and an aqueous solution of sodium citrate is flowed into the inflow path 1 and an aqueous solution of silver nitrate is introduced from the injection pipe 2 so that both the aqueous solutions of the raw materials are constantly kept. Since the particles can be sufficiently mixed in a constant mixing state, silver fine particles having a uniform particle size can be obtained. In addition, continuous operation becomes possible by using a static mixer, and a large amount of fine silver particles can be produced with high production efficiency.
[0022]
In a conventional batch-type mixing method, the particle size of silver fine particles in the same batch is generally about 5 to 15 nm. On the other hand, according to the mixing method using the static mixer of the present invention, the range of the particle size of the continuously obtained silver fine particles can be controlled within a narrower range. It is possible to continuously produce silver fine particles in the range or in the range of 10 to 15 nm. In addition, the particle size here indicates the particle size of the silver fine particles observed by a transmission electron microscope (TEM).
[0023]
The particle size of the silver fine particles varies depending on the liquid temperature and flow rate (flow rate) of the raw material aqueous solution, the structure of the static mixer, and the like, and the particle size can be controlled by appropriately setting these. For example, increasing the liquid temperature of the raw material aqueous solution tends to increase the particle size, and increasing the flow rate tends to decrease the particle size. Regarding the structure of the static mixer, a smaller particle size can be obtained by using the static mixer described in JP-A-11-82919 shown in FIG. 1 than by using the conventional type in which the twisting blades are alternately arranged.
[0024]
In particular, regarding the liquid temperature of the raw material aqueous solution, if the temperature exceeds 30 ° C., silver fine particles having a particle size as large as that obtained by mixing the small amounts in a batch manner will be included. It is desirable to keep the temperature at 30 ° C. or lower. Specifically, the temperature of the mixture of the aqueous solution containing ferrous ions and the aqueous solution containing citrate ions is preferably 5 to 80 ° C, more preferably 5 to 20 ° C. The temperature of the aqueous solution containing the silver salt is preferably 0 to 80 ° C, more preferably 0 to 10 ° C. By controlling the temperature in this manner, silver fine particles having a particle size of 10 nm or less and a particle size width of about 5 nm can be stably obtained.
[0025]
The silver fine particle aggregate obtained by the above-described reaction step is filtered to obtain a silver fine particle aggregate cake. When pure water is added to the cake, the concentration of iron ions and sodium ions in the liquid is greatly reduced, and the coagulation factor is eliminated, so that the silver fine particles protected by citrate ions are redispersed in the liquid, and A fine particle colloidal dispersion is obtained. Incidentally, such a method for producing a colloid is generally called a “washing-out method”.
[0026]
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.
[0027]
【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.
[0028]
[Example 1]
Static mixer shown in FIG. 1 using (Xinyu Giken, the structure of JP-A-11-82919 JP), 23.1% iron sulfate (FeSO 4 · 7H 2 O) solution and 37.5% sodium citrate ( A 9.1% silver nitrate (AgNO 3 ) aqueous solution was mixed with a mixed solution of a C 3 H 4 (OH) (COONa) 3 .2H 2 O aqueous solution to produce silver fine particles.
[0029]
That is, a mixed solution of 3900 g of the aqueous solution of iron sulfate and 4,800 g of the aqueous solution of sodium citrate was introduced at a flow rate of 870 g / min from the inflow channel 1, and 3300 g of the silver nitrate aqueous solution was simultaneously supplied from the injection pipe 2 at a flow rate of 330 g / min. By mixing and reacting for a residence time of 10 minutes, a reaction solution containing silver fine particle aggregates was obtained. 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.
[0030]
The silver fine particle aggregate was filtered from the above reaction liquid by a centrifugal separator, and a cake of the silver fine particle aggregate was recovered. Then, pure water was added to the cake to wash out the silver fine particle aggregate. (Ag: 0.5%) 30700 g was obtained.
[0031]
With respect to the obtained silver fine particles of Example 1, the silver fine particle colloidal dispersion was observed with a transmission electron microscope (manufactured by JEOL Ltd.) to measure the particle diameter. It was shown to. In addition, the uniformity evaluation of the particle diameter was regarded as uniform when no coarse particles having a particle diameter of 25 nm or more were observed.
[0032]
[Example 2]
In the same manner as in Example 1 above, a silver nitrate aqueous solution was mixed with a mixed solution of an aqueous solution of iron sulfate and an aqueous solution of sodium citrate using a static mixer to produce silver fine particles. The liquid temperature of the liquid and the liquid temperature of the aqueous silver nitrate solution were both set to 30 ° C.
[0033]
The reaction solution containing the obtained silver fine particle aggregates was treated in the same manner as in Example 1 to obtain 30,800 g of a silver fine particle colloidal dispersion (Ag: 0.5%) of Example 2. The particle size of the silver fine particles of Example 2 was measured in the same manner as in Example 1, and the results are shown in Table 1 below together with the evaluation of the uniformity of the particle size.
[0034]
[Comparative Example 1]
Using the same iron sulfate aqueous solution, sodium citrate aqueous solution, and silver nitrate aqueous solution as in Example 1, silver fine particles were produced by a batch method.
[0035]
That is, a mixed solution of 130 g of an aqueous solution of iron sulfate and 160 g of an aqueous solution of sodium citrate was placed in a beaker, and 110 g of an aqueous solution of silver nitrate was added at a stretch with stirring to obtain a reaction solution containing fine silver 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.
[0036]
The silver fine particle aggregate was filtered from the reaction solution by a centrifugal separator to obtain a cake of silver fine particle aggregates, and the cake was washed by adding pure water to the silver fine particle aggregate according to Comparative Example 1. (Ag: 0.5%) 930 g was obtained. The results of measurement and evaluation of the obtained silver fine particles of Comparative Example 1 in the same manner as in Example 1 are shown in Table 1 below.
[0037]
[Comparative Example 2]
Mixing was performed in a batch manner as in Comparative Example 1, but the amount of liquid was increased to increase efficiency. That is, the procedure was performed in the same manner as in Comparative Example 1 except that a mixed solution of 3900 g of an aqueous solution of iron sulfate and 4800 g of an aqueous solution of sodium citrate was placed in a stainless steel container, and 3300 g of an aqueous solution of silver nitrate was added all at once while stirring.
[0038]
The reaction solution containing the obtained silver fine particle aggregates was treated in the same manner as in Example 1 to obtain 31100 g of a silver fine particle colloidal dispersion (Ag: 0.5%) of Comparative Example 2. The results of measurement and evaluation of the silver fine particles of Comparative Example 2 in the same manner as in Example 1 are shown in Table 1 below.
[0039]
[Table 1]
As can be seen from the results shown in Table 1, no coarse silver fine particles were observed in the silver fine particle colloidal dispersions according to the examples, and silver fine particles having a uniform particle size were obtained. In Example 1 where the temperature was kept at or below, extremely uniform silver fine particles having a particle size of 2 to 8 nm were obtained. In each of the examples, a liquid amount of about 30,000 g was obtained by one treatment, which indicates that the production efficiency of the silver fine particle colloidal dispersion is high.
[0041]
On the other hand, in the silver microparticle colloid dispersion liquid according to Comparative Example 1, although relatively uniform silver microparticles having a particle size of about 5 to 15 nm were obtained, the amount of liquid obtained at one time was extremely small at 930 g. Further, in the silver fine particle colloid dispersion liquid according to Comparative Example 2, since the obtained liquid volume was substantially the same as that in the above example, the particle diameter of silver fine particles fluctuated greatly, and coarse silver fine particles having a particle diameter of about 25 to 30 nm were included. Had been.
[0042]
【The invention's effect】
According to the present invention, it is easy to control the particle size of silver fine particles, and it is possible to produce a silver fine particle colloidal dispersion containing silver fine particles having a uniform particle size with high productivity. Therefore, the silver fine particle colloidal dispersion according to the present invention is used in a transparent conductive layer forming coating liquid for forming a transparent conductive layer on a transparent substrate, or an antimicrobial coating forming coating liquid, etc. Stabilization and cost reduction can be realized.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view showing a specific example of a static mixer.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Inflow path 2 Injection pipe 3 Mixing chamber 4 Outflow path 5 Collision plate 6
Claims (3)
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| WO2005088652A1 (en) * | 2004-03-10 | 2005-09-22 | Asahi Glass Company, Limited | Metal-containing fine particle, liquid dispersion of metal-containing fine particle, and conductive metal-containing material |
| US7390440B2 (en) | 2004-03-10 | 2008-06-24 | Asahi Glass Company, Limited | Process for producing metal-containing particles having their surface coated with at least two dispersants different in vaporization temperature |
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| JP2016148089A (en) * | 2015-02-13 | 2016-08-18 | 三菱マテリアル株式会社 | Silver powder and paste-like composition and method for producing silver powder |
| WO2016129368A1 (en) * | 2015-02-13 | 2016-08-18 | 三菱マテリアル株式会社 | Silver powder, paste composition and method for producing silver powder |
| US11587695B2 (en) | 2015-02-13 | 2023-02-21 | Mitsubishi Materials Corporation | Silver powder, paste composition, and method of producing silver powder |
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