JP2004124160A - Silver powder consisting of silver grain with indeterminate shape, method for selectively producing the silver powder, and functional material obtained by using the silver powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide silver powder consisting of unshapened silver grains having many projections improving the function of a functional material as for silver powder used as a metallic filler exerting considerable influence upon the function of a functional material, particularly, an electrically conductive adhesive, to provide a method for selectively producing the silver powder, and to provide a functional material obtained by using the silver powder. <P>SOLUTION: In the method for producing silver powder consisting of unshapened silver grains having many projections, a silver nitrate solution (e.g., a silver nitrate aqueous solution), and a reducing agent which does not comprise acrylic acid monomers (e.g., an L-ascorbic acid aqueous solution) are mixed and reacted under an environment where conditions of electromagnetic waves such as X-rays, ultraviolet-rays or the like, liquid temperature conditions in the reaction or the like are controlled. <P>COPYRIGHT: (C)2004,JPO

Description

【０１９５】
【表２】

【０１９６】
【表３】

【０１９７】
【表４】

【０１９８】
【表５】

【０１９９】
不定形な形状の銀粒子が形成される理論的根拠は、基本的に不明であるが、硝酸銀溶液と、Ｌ−アスコルビン酸溶液とを１：１の割合に近い対比で混合したが、還元剤であるＬ−アスコルビン酸量の多い方が不定形な形状の銀粉を析出した。
【０２００】
実施例１５　不定形な形状の銀粒子の洗浄を下記の通り行った。
【０２０１】
多数の突起物を有する不定形な形状の銀粒子を水洗浄するとき、洗浄中の不定形な形状の銀粒子が水中で相互に激しく衝突することにより、不定形な形状の突起物が折れる。
【０２０２】
本発明では、２リットルのビ−カー（直径１４５ｍｍ、高さ（深さ２５０ｍｍ））の中に析出した不定形な形状の銀粒子２００ｇと、洗浄水として純水１．５リットルを入れ、電熱器でビ−カーを加熱しながら不定形な形状の銀粉をゆっくり（１分間２０回転程度）とガラス攪拌棒（直径６ｍｍ、長さ２７０ｍｍ）で一定方向に手動にて回転させた。
【０２０３】
純水の温度が６０℃程度になるまで加熱とゆっくり攪拌し、洗浄の第１工程とした。
【０２０４】
洗浄した純水を捨て、又、新たな純水と不定形な形状の銀粉をビ−カーに入れ洗浄し、この工程を繰り返し、リトマス試験紙による計測で洗浄用の純水のｐＨが７を示した時点で洗浄の完了とした。
【０２０５】
不定形な形状の銀粒子が水中で衝突することを避けるため、ガラス攪拌棒を一方向へゆっくりと回転させたが、この方法により突起物の損傷を回避できることを確認した。
【０２０６】
また、加熱しながら洗浄することにより、加熱しない洗浄方法との比較により洗浄回数が半分で済むことも分かった。
【０２０７】
実施例１６　分粒は以下のように行った。
【０２０８】
前記実施例１の方法で得られた反応生成物を上記実施例１３の方法で洗浄し、その洗浄後の不定形な形状の銀粒子は、例えば未処理の下水道や工場廃液遺棄物が海岸に集まってどろどろに固まったヘドロ状であり、乾燥後においては、不定形な形状の銀粒子は、乾燥収縮により全体が１個又は数個の塊となっている。
【０２０９】
分粒工程は、乾燥がまだ完了していない状態で、まだ僅か水分を含有（含水率５％程）している状態の時、スクリーン印刷の版枠に７００，１２００，１８００メッシュの紗（ポリエステル）を張り、最初に一次分粒として、７００メッシュの紗を張ったアルミ製スクリーン印刷用版枠の上にまだ僅かに水分を含有している不定形な形状の銀粒子を置き、スキージを用いて前後に動かすことにより粗銀粒子（一次分粒銀粒子）を得た。
【０２１０】
一次分粒銀粒子から同様な方法で１２００メッシュの紗を用い、スキージし、二次分粒銀粒子を得た。
【０２１１】
二次分粒銀粒子から、最終分粒工程として、１８００メッシュの紗を用い、スキージし、微細分粒銀粒子を得た。
【０２１２】
分粒作業が完了して得た不定形な形状の銀粒子をＳＥＭにて形状が破損していないことを確認した後、最終分粒工程により得られた銀粒子から、僅か残っていた水分を乾燥することにより除去した。
【０２１３】
得られた銀粒子は花状の形状であり、粒径は６μｍであった。
【０２１４】
実施例１７　導電性接着剤は以下のようにして製造した。
【０２１５】
前記実施例２で得た１０μｍの粒径を有する多数の突起を有する花状の銀粒子を導電性接着剤の金属フィラーとして使用し、樹脂としてエポキシ樹脂を使用し、金属フィラーとエポキシ樹脂との配合比を金属フィラー６５％／Ｗｔ、エポキシ樹脂を３５％／Ｗｔとなるように設定した。
【０２１６】
導電性接着剤の混練方法は以下のようにした。
【０２１７】
最初に直径が１０ｃｍのシリコンゴム製の乳鉢に、不定形な形状の銀粒子とエポキシ樹脂とを上記割合で入れ、シリコンゴム製攪拌棒にて軽く全体が濡れるまで混ぜ一次混練とした。
【０２１８】
次に市販の金属製三本ロール混練機のロール表面を厚さ２ｍｍのシリコンゴムで覆ったロールを作成し、不定形な形状の銀粒子専用の混練機とした。この混練機のロール間の上に一次混練された導電性接着剤を置き、ロール間のクリアランスを取り徐々に回転させ、不定形な形状の銀粒子とエポキシ樹脂とが均一になるまで回転させた。
【０２１９】
導電性接着剤は、金属フィラーとエポキシ樹脂を多数の突起物を持つ花状を保ちつつ充分混練することにより得られた。
【０２２０】
実施例１８　実施例１５で製造した導電性接着剤をアルミナ基板上に印刷し、１５０℃１０分加熱した熱硬化後の導電性接着剤の抵抗値は１０ｍΩであり、前述した引張り強度試験機による接着強度は１８Ｎ／ｍｍ^２を示し、従来の導電牲接着剤と比較して遥かに優れた特性を持っていた。
【０２２１】
従来の粒径３μｍの球形の銀粒子を同じ割合で配合した導電性接着剤の場合の抵抗値（Ω）は１０^６オーダーであり、接着強度は１７Ｎ／ｍｍ^２であった。
【０２２２】
実施例１９　厚膜ガラスペーストは以下のようにして製造した。
【０２２３】
前記実施例２で得た１０μｍの粒径を有する多数の突起を有した花状の銀粒子を厚膜ガラスペーストの金属フィラーとして使用し、バインダーとして無鉛窯業上絵用フリットを使用し、金属フィラーと無鉛窯業用フリットとの配合比を、金属フィラー９５％／Ｗｔ、無鉛窯業上絵用フリットを５％／Ｗｔとなるように設定した。
【０２２４】
ついで、金属フィラーと無鉛窯業上絵用フリットとの配合品を６５％／Ｗｔ、ペースト化のための窯業用アクリル樹脂を３５％／Ｗｔの割合で配合し、多数の突起物を持つ花状銀粉の形状を保ちつつ充分混練して厚膜ガラスペーストを得た。
【０２２５】
この厚膜ガラスペーストをアルミナ基坂上に印刷し、８００℃、１０分焼成することにより得られた厚膜ガラスペーストの抵抗値は１０μΩであり、優れた導電性を示した。
【０２２６】
尚、ペースト化のための窯業用アクリル樹脂は３００℃程度で重解合し、焼成後には存在しないものである。
【０２２７】
実施例２０　ソルダーペーストは以下のようにして製造した。
【０２２８】
前記実施例２で得た１０μｍの粒径を有する多数の突起を有した花状の銀粒子をソルダーペーストの金属フィラーとして使用した。
【０２２９】
市販の錫・鋼合金ソルダーペースト（小島半田製造製）を９５％／Ｗｔ使用し、金属フィラーを５％／Ｗｔとなるように設定した。
【０２３０】
ソルダーペーストは、上記割合の配合物を花状である不定形な形状の銀粒子の多数の突起物を保ちつつ充分に混練することにより得られた。
【０２３１】
このソルダーペーストをアルミナ基板上に印刷し、２４０℃，１分焼成することにより得られたソルダーペーストの抵抗値は５μΩあり、優れた導電性を示した。
【０２３２】
実施例２１　糸はんだは以下のようにして製造した。
【０２３３】
前記実施例２で得た１０μｍの粒径を有する多数の突起を有した花状の銀粒子を糸はんだの添加金属フィラーとして使用した。
【０２３４】
糸はんだを製造するために、錫・銅合金からなる中空の円筒棒の中空部分にフラックスと供に詰め込むよう設定した。
【０２３５】
直径１０ｍｍ内径４ｍｍ長さ３００ｍｍ重量１８０ｇの錫銅合金からなる中空の円筒棒の中空部分に、該銀粒子１８ｇ、フラックス５ｇを充分混練し、且つ真空脱泡した後、市販のプラスチック注射器に入れ、この注射器にて押し込み、後中空の円筒棒における上下の口を塞いだ。
【０２３６】
その後、糸はんだ製造機で直径０．３ｍｍになるよう引き伸ばし、糸はんだとした。
【０２３７】
この糸はんだを、はんだゴテ（約３００℃）で電極間をはんだ付けした。
【０２３８】
該糸はんだの抵抗値は５μΩであり、優れた導電性を示した。
【０２３９】
実施例２２　銀粒子入り合成織錐の糸は以下のようにして製造した。
【０２４０】
前記実施例５で得た３μｍの粒径を有する多数の突起を有した花状の銀粒子を合成織錐の金属フィラーとして使用した。
【０２４１】
ナイロン製ペレットと金属フィラーの配合比を８０％／Ｗｔ：２０％／Ｗｔとし、紡糸後数本の糸を１本に合糸し、該銀粒子が連続性を保つことにより導電牲が得られるよう、また、紡糸用ノズル形状も該銀粒子が糸表面に現れやすいよう設定した。
【０２４２】
この配合物を溶融紡糸装置に入れ、２２０℃に加熱した。ナイロンペレットが溶融するとともに、金属フィラーがナイロンペレット中に分散され、ステンレス製十字孔ノズル（１ｍｍ）からナイロンペレットが金属フィラーを含んだ合繊糸として抽出するとともに、巻とり機により引き伸ばし直径５μｍの糸５本を１本に合糸することにより、該銀粒子の連続性を充分保つことになり導電性が得られた。
【０２４３】
得られた合成繊維の抵抗値は１Ωの優れた数値を示した。
【０２４４】
この合成繊維の最大の特徴は導電性等の機能が洗濯回数と関係なく、機能性が劣化しないこと及び染色が可能なことである。
【０２４５】
【発明の効果】
本発明に係る銀粉、該銀粉の製造方法及び該銀粉を用いた機能材料、例えば、該銀粉を金属フィラーとした導電性接着剤は、金属フィラーとバインダー樹脂との配合比の範囲を従来よりも拡大できるという効果を有する。
【０２４６】
この結果、導電性接着剤における電気特性及び接着剤強度の機能の向上を図ることができるという効果が得られる。
【０２４７】
すなわち、従来の銀粉を配合した導電性接着剤では配合比が抵抗値、基板への接着性及び作業性から合成樹脂２５％／Ｗｔ：銀粉７５％／Ｗｔが限界とされている。
【０２４８】
しかし本発明の銀粒子を金属フィラーとした導電性接着剤では、金属フィラーと樹脂との配合比の範囲を従来よりも、樹脂量を飛躍的に増量でき、この結果、導電性接着剤における電気特性及び接着強度等の特性向上、又作業性の向上、製品歩留まり向上等を図ることができ、良好な結果が得られた。
【０２４９】
これは、銀粒子が絡み合い嵌合するテトラポット効果による形状どうしの接触機会の多さと接触面積の大きさに由来するものであり、本発明の銀粒子の機能材料としての優秀さを示す一つの証である。
【０２５０】
従来製法による銀粒子を使用した導電性接着剤では、隣接する銀粒子と銀粒子の接点は点接点一点であり、その隣接する接点部分に樹脂が入り込むことにより導電性の確保が困難となる。
【０２５１】
使用する樹脂量を少なくすると導電性の確保は保証されるが基板に対する接着性は確保できず、また粘性がないため作業性が得られない。
【０２５２】
本発明は、従来の素材を形状を変化させることにより新素材とし、銀粒子を使用した従来の導電性接着剤の技術的課題を一気に解決したものである。
【０２５３】
もっとも、本発明に係る多数の突起を有する不定形の銀粉は、導電性接着剤に使用する以外にも、ガラスペースト、合成繊維、糸はんだ及びソルダーペースト等の分野における機能材料の新素材として使用できることから、導電性接着剤のみならず、各種機能材料の機能向上を図ることができるものである。
【０２５４】
また、本発明に係る銀粒子からなる銀粉、その銀粉の製造方法及びその銀粉を用いた機能材料によると、多岐にわたる形状と広範囲にわたる粒径をもつ銀粒子からなる銀粉を簡易かつ選択的に製造できるため、該銀粉を使用する機能材料の機能に適した銀粉をその銀粉を構成する銀粒子の形状と粒径の観点から選択できるという効果が得られる。
【図面の簡単な説明】
【図１】本発明に係る銀粒子（花状・粒径６μｍ）からなる銀粉の電子顕微鏡写真（図面代用写真）。
【図２】本発明に係る銀粒子（シダ草状・粒径２０μｍ）からなる銀粉の電子顕微鏡写真（図面代用写真）。
【図３】本発明に係る銀粒子（花状・粒径１０μｍ）からなる銀粉の電子顕微鏡写真（図面代用写真）。
【図４】本発明に係る銀粒子（針状・粒径４０μｍ）からなる銀粉の電子顕微鏡写真（図面代用写真）。
【図５】本発明に係る銀粒子（シダ草状・粒径６μｍ）からなる銀粉の電子顕微鏡写真（図面代用写真）。
【図６】本発明に係る銀粒子（キノコ類の胞子状・粒径６μｍ）からなる銀粉の電子顕微鏡写真（図面代用写真）。
【図７】本発明に係る銀粒子（シダ草状・粒径６μｍ）からなる銀粉の電子顕微鏡写真（図面代用写真）。
【図８】本発明に係る銀粒子（その他の形状・粒径２０μｍ）からなる銀粉の電子顕微鏡写真（図面代用写真）。
【図９】本発明に係る銀粒子（花状・粒径１μｍ）からなる銀粉の電子顕微鏡写真（図面代用写真）。
【図１０】本発明に係る銀粒子（針状・粒径１０μｍ）からなる銀粉の電子顕微鏡写真（図面代用写真）。
【図１１】（ａ）本発明に係る白熱灯を真上から照射することにより得られた銀粒子（針状・粒径１０μｍ）からなる銀粉の電子顕微鏡写真（図面代用写真）。
（ｂ）本発明に係る白熱灯を真横から照射することにより得られた銀粒子（その他の形状・粒径特定できない）からなる銀粉の電子顕微鏡写真（図面代用写真）。
【図１２】本発明に係る銀粒子（花状・粒径３μｍ）からなる銀粉の電子顕微鏡写真（図面代用写真）。
【図１３】本発明に係る銀粒子（花状・粒径０．５μｍ）からなる銀粉の電子顕微鏡写真（図面代用写真）。
【図１４】本発明に係る銀粒子（シダ草状・粒径２０μｍ）からなる銀粉の電子顕微鏡写真（図面代用写真）。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention selectively produces silver powder composed of irregularly shaped silver particles having a large number of projections that are neither spherical nor thin, and silver powder composed of such irregularly shaped silver particles under electromagnetic wave irradiation. And a functional material comprising the silver powder.
[0002]
[Prior art]
Silver powder has been used for a long time in the fields of brazing and conductive materials, but in recent years, with the development of electronic industry technology, silver powder has been used as a conductive resin material by mixing and dispersing it in resin as a metal filler. There are many.
[0003]
Among conductive resin materials, conductive adhesives are attracting attention in the fields of repair of circuit conductors, mounting of device terminals, shielding, etc. as printed circuits and electronic components become more complicated, denser and smaller. Have been.
[0004]
In addition, the development of lead-free solder is urgently required at present to protect the environment, and from such a viewpoint, conductive adhesives using silver powder have attracted much attention.
[0005]
As the conductive adhesive, the functions of the electrical properties and the adhesive strength are particularly important, but the relationship between the electrical properties and the adhesive strength is that the electrical properties based on the metal filler (so-called conductivity) and the adhesive strength based on the binder resin. Because of the conflicting relationship, the amount of metal filler must be increased to reduce the amount of binder resin used to increase the electrical properties of conductivity, and the amount of binder resin used must be reduced to increase the adhesion. The amount had to be increased and the amount of metal filler had to be reduced.
[0006]
Therefore, in order to develop a conductive adhesive that maintains conductivity and also has adhesiveness to circuit boards, etc., the compounding ratio between the metal filler and the resin is extremely important. It was necessary to set within a range not exceeding a boundary where conductivity was not recognized and a boundary where conductivity was recognized but adhesion was not recognized.
[0007]
For example, when round spherical silver particles having an average particle diameter of 4 μm and having no protrusion are used as the metal filler and an epoxy resin is used as the binder resin, the metal filler is 75% / Wt and the epoxy resin is 25%. When the metal filler is below this value with respect to the blending ratio at% / Wt, conductivity sufficient for practical use was not recognized.
[0008]
When the metal filler exceeds 90% / Wt and the mixing ratio of the epoxy resin is 10% / Wt, the adhesiveness sufficient for practical use was not observed.
[0009]
In addition, in the application field of silver powder, for example, use as a pressure-resistant glass paste to improve the glass function, use in synthetic fibers to produce sterilizing fiber products, to improve the function of solder The use of silver powder in functional materials is wide.
[0010]
As a method for producing silver powder used for brazing, a conductive adhesive, and the like, a physical method and a reduction method are known.
[0011]
Here, the physical method is a method of obtaining silver powder by pulverizing silver foil, and the reducing method is a method of depositing silver dissolved in an aqueous nitric acid solution as a simple silver by adding a reducing agent.
[0012]
As a reduction method, for example, as a method for producing a silver fine powder used for a conductive paste or a paint, in order to improve the dispersibility of the silver fine powder, after adding a fatty acid to a silver nitrate solution and a mixed aqueous solution of formalin and stirring, In order to precipitate a fine silver powder having an average particle diameter of 0.8 to 0.9 μm by adding an alkaline solution (for example, see Patent Document 1), There is a method of adding an aqueous solution of L-ascorbic acid obtained by adding an acrylic acid monomer to an aqueous solution of silver nitrate as a reducing agent and stirring to precipitate highly crystalline silver particles having an average particle size of 2 to 4 μm (for example, see Patent Document 2). .
[0013]
The silver particles constituting the silver powder produced by these physical methods or reduction methods have a spherical shape or a thin plate shape (also called a flake shape; hereinafter, a flake shape) without protrusions.
[0014]
The flake shape without protrusions can also be obtained by stretching a round sphere without protrusions with a mill.
[0015]
[Patent Document 1]
JP-B-57-21001
[Patent Document 2]
JP-A-2000-1706
[0016]
[Problems to be solved by the invention]
In the development of the conductive adhesive, under the restriction that the compounding ratio of the metal filler and the binder resin is within the range of the boundary, it has basic and important functions such as electric characteristics and adhesive strength, and can sufficiently exhibit these functions. It is extremely difficult to design a conductive adhesive because the electrical properties based on the metal filler and the adhesive strength based on the binder resin are in conflict with each other as described above.
[0017]
On the other hand, the present inventor focused on the shape and particle size of silver particles of silver powder used as a metal filler, and investigated and studied the relationship between the electrical properties based on the metal filler and the adhesive strength based on the binder resin. It has been found that the shape and particle size of the silver particles constituting the silver powder have an influence on the electrical properties and the adhesive strength of the conductive adhesive.
[0018]
The problem to be solved by the present invention is to provide a functional material such as a conductive adhesive with characteristics superior to the conventional ones, that is, satisfying at least both the contradictory electric characteristics and the adhesive strength at a higher level than the conventional ones. It is to create a silver powder composed of silver particles having a shape and a particle diameter having characteristics.
[0019]
Silver powder is used for functional materials such as pressure-resistant glass paste, synthetic fiber, solder, and solder paste in addition to the conductive adhesive, and silver powder plays a large role in expressing the functions of these functional materials.
[0020]
In particular, the shape and particle size of the silver particles forming the silver powder greatly affect the function of the functional material, and the shape and particle size of the silver particles forming the silver powder play an important role in the development of the functional material.
[0021]
Therefore, from the viewpoint of improving the function of functional materials such as conductive adhesives, a method for producing silver powder is a method that can easily and selectively produce silver powder composed of silver particles having a wide variety of shapes and a wide range of particle sizes. Is desired.
[0022]
The present invention relates to a silver powder used as a functional material, particularly a silver powder used as a metal filler that has a great effect on the function of a conductive adhesive. Another object of the present invention is to provide a method for selectively producing the silver powder and a functional material using the silver powder.
[0023]
[Means for Solving the Problems]
The invention according to claim 1 or 2 created by the inventor, that is, “silver powder composed of irregularly shaped silver particles having a large number of projections” is not a spherical or flake-shaped silver particle. A single silver particle is formed of a central nucleus portion and projections radiating from the center in multiple directions including one direction, and the integrated shape is a radiation spine.
[0024]
The particle size varies depending on the manufacturing conditions, and is about 0.1 to 50 μm.
[0025]
The silver powder composed of irregularly shaped silver particles having a large number of projections is produced by the invention according to claim 3, that is, by reacting a silver nitrate solution with a reducing agent under irradiation of electromagnetic waves.
[0026]
This reaction is preferably performed at a temperature of 30 ° C. or lower, particularly preferably −2 ° C. to 25 ° C., to obtain irregularly shaped silver particles having a large number of projections.
[0027]
This reaction does not require the presence of an acrylic acid monomer in the reaction system as in the conventional method. Rather, positive removal is preferred because the purity of the generated silver powder is improved.
[0028]
The silver powder composed of irregularly shaped silver particles having a large number of projections has excellent characteristics and can be used for various conventionally known functional materials. The invention according to claim 4 is a functional material using silver powder composed of irregularly shaped silver particles having a large number of projections.
[0029]
The silver powder composed of irregularly shaped silver particles having a large number of projections is particularly suitable for a conductive adhesive. This is because even if the compounding ratio as the metal filler is set to a region lower than the above-mentioned boundary, for example, 70% / Wt (30% / Wt for epoxy resin), the conductivity and adhesiveness sufficient for practical use are sufficient. This is because an acceptable conductive adhesive can be obtained. The invention according to claim 5 is a conductive adhesive using silver powder composed of irregularly shaped silver particles having a large number of projections.
[0030]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
[0031]
The silver particles in the “silver powder composed of irregularly shaped silver particles having a large number of protrusions” created by the present inventor are such that the shape of one silver particle is neither spherical nor flake-like, and the center of one silver particle is It is formed from a core part and projections that radiate in multiple directions including one direction from the center (hereinafter, these projections are referred to as spines). It is.
[0032]
The radial spine-shaped silver particles are characterized in that they have protruding spines, and typical spines are 1.1 times or more the diameter of the central nucleus corresponding to the central part of the silver particles. Having
[0033]
When it is difficult to directly confirm the central nucleus corresponding to the central portion of the radial spine-shaped silver particles using an electron microscope, for example, in the case of FIG. 9, the central portion estimated to correspond to the central nucleus is defined as the central nucleus. did.
[0034]
The shape of the spines varies depending on the reaction conditions. When the shapes of the spines are roughly classified into needle-like, flower-like, fern-like, mushroom-like spore-like, and other shapes, the needle-like shape is, for example, as shown in FIGS. 1, 3, 9, 13, and 14 as flower-like ones, and those shown in FIGS. 2, 5, 7, and 15 as fern-like ones, and spore-like ones For example, there is a shape shown in FIG. 6 and other shapes shown in FIGS. 8 and 12, for example. FIG. 8 shows a mixed shape of a flower shape and a fern grass shape.
[0035]
As for the particle and particle size, for example, in the case of a flower shape, one piece from the tip of a petal, which is one protrusion of silver particles having many radially extending protrusions, to the tip of the petal of a protrusion at the opposite pole is one. The particle size between the poles of the petals of the protrusion was determined.
[0036]
The particle size of the irregularly shaped silver particles having a large number of projections constituting the silver powder of the present invention was 0.1 to 50 μm.
[0037]
A silver powder composed of irregularly shaped silver particles having a large number of projections can be produced by mixing silver nitrate and a reducing agent in a solution state under irradiation of an electromagnetic wave to cause a reaction.
[0038]
Specifically, it is a method for producing silver powder in which a silver nitrate solution is reacted with a reducing agent containing no acrylic acid monomer, and is not spherical or flake-like by changing conditions of electromagnetic waves or liquid temperature during the reaction. This method selectively produces silver powder having an irregular shape having projections.
[0039]
As a reaction method, when reacting the silver nitrate solution and the reducing agent solution, they are instantaneously mixed and reacted in a container, or the silver nitrate solution and the reducing agent solution are put into separate sprayers, and after the spraying, near both sprayers. After positioning the angles of the atomizers so that they are mixed with each other, a reaction system in which different atomizers are simultaneously operated to react in the atmosphere can be adopted. As a result, silver powder composed of silver particles having an irregular shape is obtained.
[0040]
FIG. 6 shows silver powder composed of silver particles obtained by the method of operating this atomizer.
[0041]
Here, the method of instantly mixing the silver nitrate solution and the reducing agent solution in the container includes: (1) a method of mixing and stirring while simultaneously pouring the silver nitrate solution and the reducing agent solution into the container; and (2) a method of mixing and stirring. Or a method in which a reducing agent solution is dropped or injected into the silver nitrate solution.
[0042]
However, as a mixing method, from the viewpoint of obtaining a product having a higher yield and a good crystal shape, a method of mixing and stirring while simultaneously pouring a silver nitrate solution and a reducing agent solution into a container; 2) a method of dropping or injecting a silver nitrate solution into a reducing agent solution, and (3) a method of dropping or injecting a reducing agent solution into a silver nitrate solution are preferred.
[0043]
FIG. 5 shows silver powder composed of silver particles obtained by injecting a silver nitrate solution into a reducing agent solution.
[0044]
As the reducing agent, an inorganic compound and an organic compound can be used. Examples of the former include potassium borohydride, sodium borohydride, lithium aluminum hydride, and the like, examples of the latter include borane compounds such as dimethylamine borane and pyridine borane, and ascorbic acids. Of these, preferred are organic compounds, and among them, L-ascorbic acid is particularly preferred.
[0045]
A preferable silver nitrate solution is a silver nitrate solution having a concentration of 0.1 to 30% by weight in which silver nitrate crystals are dissolved in distilled water, alcohol, or the like. Similarly, a preferable L-ascorbic acid solution is L-ascorbic acid in distilled water, alcohol, or the like. L-ascorbic acid solution having a concentration of 0.1 to 30% dissolved in water, and these are mixed at a ratio of about 0.2: 1 to 1: 1.
[0046]
As a solvent used for preparing a silver nitrate solution or a reducing agent solution, water, alcohol (such as methanol and ethanol), and ketones (such as acetone and methyl ethyl ketone) can be used. Of these, water, alcohol and the like are preferable, and they can be used even if they are mixed (FIG. 7).
[0047]
The reaction is completed in a short time, but is irradiated with electromagnetic waves during the reaction. As the electromagnetic waves to be irradiated, electromagnetic waves in the entire electromagnetic wave range (radio waves, infrared rays, visible rays, ultraviolet rays, X-rays, γ-rays) can be used.
[0048]
Here, the intensity of the radiated electromagnetic wave is preferably in the range of 1 lux to 2500 lux for illuminance, 100 V or more for electric field, and in the range of 60 mT to 145 mT for magnetic field. This is because if the reaction is performed outside this range, it is difficult to generate crystals.
[0049]
Further, when the reaction is carried out within this range, the form of the generated crystals is good and the yield is high.
[0050]
Note that the applied electromagnetic wave may be continuously applied during substantial work.
[0051]
The wavelength range is controlled by selecting and using various types of lighting equipment and the like.
[0052]
Various kinds of illumination light, which is a kind of electromagnetic wave, irradiate various kinds of illumination light having the above-mentioned wavelength at an illuminance of 1 lux to 2,500 lux. Even at 2,500 lux or more, for example under direct sunlight (60,000 lux), the results were similar to those at 2,500 lux.
[0053]
Illuminance was measured using a YOKOGAWA 501-01 illuminance meter.
[0054]
Also, a plurality of the above conditions can be combined.
[0055]
The silver powder composed of irregularly shaped silver particles having a large number of protrusions can be produced by reacting a silver nitrate solution and a reducing agent under irradiation of electromagnetic waves. It is particularly preferably carried out under a temperature condition of -2 ° C to 25 ° C.
[0056]
It is preferable to use a thermostat for setting the temperature.
[0057]
When the mixture is reacted under the above conditions, silver particles having an irregular shape with a particle size in the range of about 0.1 to 50 μm are obtained.
[0058]
However, the range of the particle size when a crystal having a high yield and a good shape is obtained is 0.5 to 40 μm as shown in the following Examples.
[0059]
As a material of the reaction vessel used for the mixing, glass, ceramics, plastic, wooden, paper, and the like are more preferable. This is to avoid adverse effects due to a chemical reaction with the metal when the metal container is used.
[0060]
In addition, the shape of the reaction vessel is such that the shape of the inner bottom surface at the bottom is an arc shape (for example, wine glass) in a cut sectional view, but the two kinds of liquids to be mixed at the time of short-time mixing are complicated rotational motions. It is preferable because it has a stirring action.
[0061]
However, this is not the case when the stirring motion is forcibly performed using a device or the like that rotates while reversing the left and right. This is because the yield is improved by such a stirring motion.
[0062]
This reaction does not require the presence of an acrylic acid monomer in the reaction system as in the conventional method (for example, see Patent Document 2).
[0063]
That is, in the method described in Patent Document 2, which is a conventional method, an acrylic acid monomer is added when a silver nitrate aqueous solution and an L-ascorbic acid aqueous solution are mixed and reacted, but in the present invention, The need for its use is not recognized. On the contrary, it is preferable that the use of the acrylic acid monomer be positively excluded from the viewpoint of improving the purity of the generated silver powder.
[0064]
However, the shape of the silver particles generated in the present invention is different from that of the conventional method (Patent Document 2).
[0065]
The formed silver particles are separated from the reaction system as precipitates, washed and sized. The irregularly shaped silver particles having a large number of deposited protrusions are subjected to traction (rolling, sliding) phenomena due to turbulent water flows that generate additional energy for cleaning in the washing process, for example, when washing with water. As a result, the projections having an irregular shape may be broken, and the desired irregularly shaped silver particles may not be obtained.
[0066]
For this reason, in the cleaning step, it is necessary to avoid a traction phenomenon due to energy for cleaning and to prevent damage to the projections. As a washing method for avoiding such a phenomenon, a method in which the powder is gradually rotated in a fixed direction with a stirring bar is preferable. By this washing method, silver powder composed of silver particles having an irregular shape can be obtained.
[0067]
Further, by washing while heating (boiling, warm water, hot water), the acid in the silver nitrate adhering to the irregularly shaped silver particles after precipitation easily dissolves into the heated water and does not heat. The number of times of washing can be reduced by half as compared with the washing method using water at about ° C.
[0068]
When the irregularly shaped silver particles that have been washed are dried, the whole silver particles shrink due to evaporation of water. The irregularly shaped silver particles shrunk by the drying are entangled in the opposite way, so that it is difficult to size them. Therefore, in the sizing step, it is preferable to perform sizing when the irregularly shaped silver particles having a large number of projections slightly contain water.
[0069]
Specifically, a screen printing screen frame is put on a screen printing plate frame, and irregular shaped silver particles having a large number of projections still slightly containing water are placed thereon, Use a squeegee to move back and forth to size.
[0070]
Usually, the particle size is divided into three stages. In this case, for example, 700, 1200, or 1800 mesh gauze may be used.
[0071]
First, place irregularly shaped silver particles, which still contain a small amount of water, on a frame covered with a gauze of 700 mesh as the primary particle size, and move the coarse silver particles back and forth using a squeegee. The primary sized silver particles were similarly squeezed using a 1200 mesh gauze to obtain secondary sized silver particles, and the secondary sized silver particles were squeegeeed using a 1800 mesh gauze to obtain a final squeegee. Fine sized silver particles can be obtained by sizing.
[0072]
Further, a small amount of remaining water is dried and removed from the silver particles obtained in the final sizing step. This prevents secondary aggregation of silver particles during storage and helps to prevent migration, which is a problem of silver as a bonding material for electronic devices.
[0073]
The amorphous silver particles of the present invention are intended to be used in electronic device bonding materials by utilizing entanglement.However, in the washing, sizing, and storage stages, the irregularly shaped silver particles are used. Is preferably avoided.
[0074]
The functional material of the present invention is a functional material using silver powder composed of irregularly shaped silver particles having a large number of projections. It is particularly important to use the functional material as a conductive adhesive.
[0075]
For example, when the irregularly shaped silver particles having a large number of protrusions of the present invention are mixed with a functional material as a metal filler, a conductive adhesive and a paint having improved functions can be obtained.
[0076]
However, the particle size of the irregularly shaped silver particles having a large number of projections constituting the silver powder of the present invention is 0.1 to 50 μm, but a large particle size exceeding 4 μm is not necessarily required on all surfaces. It's not that good.
[0077]
For example, even in the case of silver powder having silver particles having an average particle diameter of 4 μm or less, the conductive adhesive is superior to silver powder having silver particles having an average particle diameter of more than 4 μm in terms of dispersibility in resin and the like. In some cases.
[0078]
For this reason, even with silver powder having silver particles having an average particle size of 4 μm or less, sufficient conductivity and adhesiveness sufficient for practical use can be obtained depending on the shape of the silver particles. Is good.
[0079]
In addition, from the viewpoint of minimizing an electronic device or a printed circuit, silver powder having a small particle size may be preferable.
[0080]
The effect brought about by the silver powder composed of irregularly shaped silver particles having a large number of projections was produced by the conventional physical method or reduction method, for example, the method described in Patent Document 1 or Patent Document 2 described above. It could not be obtained with silver powder composed of round spheres or flake-shaped silver particles having an average particle diameter of 4 μm or less and having no projections.
[0081]
In addition, it can be used by mixing it with glass frit for ceramics in thick film glass paste, dispersing in synthetic fiber yarn to produce sterilizing power, and conductive fiber products, To manufacture solder, a solder paste with a hollow cylindrical rod made of an alloy based on tin and used with a hollow part filled with flux, new functions, or improved conventional functions Can be used by kneading it with a solder paste composed of an alloy based on tin.
[0082]
The conductive adhesive of the present invention is obtained by mixing silver particles having an irregular shape having a particle size in the range of 0.1 to 50 μm obtained by the method of the present invention with a resin as a metal filler. .
[0083]
As the resin, it is possible to use various kinds of resins such as a natural curing type and a hot melt type.However, in order to obtain good electric characteristics, a thermosetting epoxy which can be expected to shrink the resin by heating is used. Preferably, a resin is used.
[0084]
For the conductive adhesive, the mixing ratio of the resin to the metal filler is set within a range of 1 to 99% / Wt, and the distance between the electrodes set on the alumina substrate is 100 mm (length) × 100 mm using a metal mask plate. After screen printing on the (horizontal) pattern and heating at 150 ° C. for about 10 minutes, the adhesive properties and the conductive properties were measured.
[0085]
The electrical properties of the conductive adhesive were measured by a method defined in JIS K 6911 <Thermosetting Plastics General Test Method>. The silver particles of the present invention were mixed with the epoxy resin as a metal filler, Although the compounding ratio was 65% / Wt for the silver particles of the present invention and 35% / Wt for the epoxy resin, the resistance value was 50 mΩ.
[0086]
As described above, the silver powder composed of irregularly shaped silver particles having a large number of protrusions created by the present inventor has a compounding ratio as a metal filler having a conductivity sufficient for practical use even in a region lower than the boundary range. Thus, the conductive adhesive was confirmed to have adhesiveness.
[0087]
In addition, since the adhesive strength does not have a particular provision in JIS, it was performed by a method determined by us.
[0088]
That is, a small nut is embedded in a conductive adhesive printed on a substrate, and after heating and curing, a bolt is screwed into the nut and pulled by a tensile strength tester.
[0089]
Here, when the alumina substrate was used for the measurement of the adhesive strength, the alumina substrate was damaged and delamination occurred in the glass epoxy substrate. Therefore, a single copper plate which was flexible and did not peel was used.
[0090]
When kneading irregularly shaped silver particles and a resin, there is a possibility that a large number of projections of the irregularly shaped silver particles may be damaged depending on a machine or a member used. Therefore, the contact surface of the kneading machine with the irregularly shaped silver powder is preferably a soft material such as rubber, and it is preferable to avoid metals and ceramics.
[0091]
This requires strong pressure and rotational movement during kneading, but in order to protect the irregular shaped silver powder from strong pressure, it is better to make the material of the pressing member elastic at least a little. It is.
[0092]
Hereinafter, the present invention will be described in detail with reference to examples. However, the scope of the present invention is not limited to the following examples.
[0093]
The shape and particle size of the silver particles in the present invention were confirmed by a photograph taken with a scanning electron microscope (hereinafter referred to as SEM).
[0094]
【Example】
Example 1 (Method for producing silver powder composed of silver particles having an irregular shape having a large number of protrusions and having a flower shape and a particle diameter of 6 μm)
17 g of silver nitrate crystals were dissolved in distilled water to obtain a 100 ml silver nitrate aqueous solution. To this aqueous solution, 18 g of L-ascorbic acid was dissolved in distilled water to make 100 ml, and an equal amount of an L-ascorbic acid aqueous solution was mixed.
[0095]
At this time, the liquid temperature was set to 14 ° C. while irradiating a fluorescent lamp having an illuminance of 750 lux as a condition for accelerating the reaction.
[0096]
Thereafter, the deposited precipitate was washed with water and dried under vacuum to obtain silver powder. As a result, it was confirmed by a SEM photograph that silver powder having a so-called flower shape and a particle diameter of 6 μm was obtained (FIG. 1).
[0097]
Example 2 (Method for producing silver powder composed of silver particles having an irregular shape having a large number of protrusions and having a flower shape and a particle diameter of 10 μm)
17 g of silver nitrate is dissolved in distilled water to make a total of 100 ml.
Dissolve 18 g of L-ascorbic acid in distilled water to make a total of 100 ml.
[0098]
Keep A and B at 14 ° C.
[0099]
After sunset, adjust the temperature of the room to 14 ° C and irradiate a 200 lux incandescent lamp 30 cm above the wine glass (except for work lighting equipment). And mixed.
[0100]
After 2 seconds, the reaction was completed, and after 1 minute, it separated into a murine precipitate deposited on the bottom of the wine glass and a clear water layer above the precipitate.
[0101]
This murine colored precipitate was collected, washed, dried, and sized to confirm that the irregularly shaped silver particles having a large number of protrusions obtained by SEM were in a flower-like shape.
[0102]
The particle size was 10 μm (FIG. 3).
[0103]
Example 3 (A method for producing silver powder composed of silver particles having an irregular shape having a large number of projections and having a fern grass shape and a particle size of 20 μm)
17 g of silver nitrate is dissolved in distilled water to make a total of 100 ml. 17.7 g of L-ascorbic acid is dissolved in distilled water to make a total of 100 ml.
[0104]
Keep A and B at 14 ° C.
[0105]
After adjusting the temperature of the room to 14 ° C, both sides in the vertical direction (300 mm) of a 300 mm (length) x 200 mm (width) x 200 (thickness) mm cardboard box (open state without a lid at the top) A 200 mm (vertical) x 150 mm (horizontal) copper plate was attached to the surface and connected to the copper plate with a 2,000 mm lead wire from a DC power supply.
[0106]
Further, a φ200 × φ120 × 20 donut-shaped magnet (120 mT) is installed at the center of the box, a wine glass is installed at the center of the hole of the donut-shaped magnet, and A is applied with a voltage of 10,000 V applied. The solution and the solution B were simultaneously poured into a wine glass and mixed.
[0107]
After 2 seconds, the reaction was completed, and after 1 minute, the solution was separated into a murine precipitate on the bottom of the wine glass and clear water in the upper layer.
[0108]
This murine colored precipitate was collected, and after washing, drying and sizing, it was confirmed by SEM that the irregularly shaped silver particles having a large number of protrusions were in the shape of ferns (FIG. 2).
[0109]
The particle size was 20 μm.
[0110]
Example 4 (Method for producing silver powder composed of silver particles having a needle-like irregular shape having a large number of projections and a particle diameter of 40 μm)
26 g of silver nitrate is dissolved in distilled water to make a total of 100 ml.
27 g of L-ascorbic acid is dissolved in distilled water to make a total of 100 ml.
[0111]
Keep A and B at 2 ° C.
[0112]
After sunset, the temperature of the room was adjusted to 2 ° C. A 200 mm x 150 mm copper plate was attached to both sides of a 300 mm x 200 mm x 200 mm cardboard box (open state without a lid at the top). Connected to the copper plate with 2,000mm lead wires.
[0113]
Irradiate 200 lux (10 W incandescent bulb) from 30 cm above the box, place the wine glass in the center of the box, apply the voltage of 10,000 V, and simultaneously apply the liquid A and the liquid B to the wine glass. And mixed.
[0114]
After 2 seconds, the reaction was completed, and after 1 minute, it separated into a murine precipitate deposited on the bottom of the wine glass and a clear water layer above the precipitate.
[0115]
This murine-colored precipitate is collected, washed, dried, and after sizing, has a large number of protrusions obtained by SEM, and the irregular-shaped silver particles having a plurality of layers have a needle-like shape. It was confirmed (FIG. 4).
[0116]
The particle size was 40 μm.
[0117]
Example 5 (Method for producing silver powder composed of silver particles having an irregular shape having a large number of protrusions and having a flower shape and a particle diameter of 3 μm)
8.5 g of silver nitrate is dissolved in distilled water to make a total of 100 ml.
[0118]
Dissolve 18 g of L-ascorbic acid in distilled water to make a total of 100 ml.
[0119]
Keep A and B at 14 ° C.
[0120]
The wine glass was placed under 750 lux of a fluorescent lamp as a ceiling lighting device, and the solution A and the solution B were simultaneously poured into the wine glass and mixed.
[0121]
After 2 seconds, the reaction was completed, and after 1 minute, it separated into a murine precipitate deposited on the bottom of the wine glass and a clear water layer above the precipitate.
[0122]
This murine colored precipitate was collected, and after washing, drying, and sizing, it was confirmed by SEM that the irregularly shaped silver particles having a large number of protrusions had a flower-like shape (FIG. 13). .
[0123]
The particle size was 3 μm.
[0124]
Example 6 (Method for producing silver powder composed of silver particles having an irregular shape having a large number of protrusions and having a flower shape and a particle diameter of 1 μm)
3.5 g of silver nitrate is dissolved in distilled water to make a total of 100 ml.
[0125]
Dissolve 18 g of L-ascorbic acid in distilled water to make a total of 100 ml.
[0126]
Keep A and B at 14 ° C.
[0127]
Select a place of natural light that is not exposed to direct sunlight, place the wine glass in the center of a φ200 × φ120 × 20 donut-shaped magnet (120 mT) under 2300 lux, and place solution A and solution B in the wine glass at the same time. And mixed.
[0128]
After 2 seconds, the reaction was completed, and after 1 minute, it separated into a murine precipitate deposited on the bottom of the wine glass and a clear water layer above the precipitate.
[0129]
After collecting the rat-colored precipitate, after washing, drying and sizing, it was confirmed by SEM that the irregularly shaped silver particles having a large number of protrusions were in a flower-like shape (FIG. 9). .
[0130]
The particle size was 0.1 μm.
[0131]
For reference, in the above experiment, when only natural light is irradiated, flower-shaped silver particles having a particle diameter of 0.1 μm are obtained, and when only magnetic field lines are irradiated in a dark state, flower-shaped silver particles having a particle diameter of 6 μm are obtained. Obtained.
[0132]
Example 7 (Method for producing silver powder composed of silver particles having an irregular shape having a large number of protrusions and having a flower shape and a particle size of 0.5 μm)
3.5 g of silver nitrate is dissolved in distilled water to make a total of 100 ml.
[0133]
Dissolve 18 g of L-ascorbic acid in distilled water to make a total of 100 ml.
[0134]
Keep A and B at 14 ° C.
[0135]
Select a place that is well exposed to direct sunlight through the glass, place a wine glass in the center of a donut-shaped magnet (120 mT) of φ200 × φ120 × 20 under 60,000 lux, and wine A liquid and B liquid simultaneously. Poured into a glass and mixed.
[0136]
After 2 seconds, the reaction was completed, and after 1 minute, it separated into a murine precipitate deposited on the bottom of the wine glass and a clear water layer above the precipitate.
[0137]
The mouse-colored precipitate was recovered, and after washing, drying, and sizing, it was confirmed by SEM that the irregularly shaped silver particles having a large number of protrusions had a flower-like shape (FIG. 14). .
[0138]
The particle size was 0.5 μm.
[0139]
Example 8 (Production method of silver powder composed of silver particles having an irregular shape having a large number of protrusions and having a fern grass shape and a particle size of 20 μm)
17 g of silver nitrate crystals were dissolved in distilled water to obtain a 100 ml silver nitrate aqueous solution, and 17.7 g of L-ascorbic acid was dissolved in distilled water to make 100 ml of an aqueous solution of L-ascorbic acid. It was kept cool and mixed in equal amounts.
[0140]
During this mixing, a 250 cc wine glass was placed in the center of a φ200 × φ120 × 20 donut magnet (120 mm terrace) under a 750 lux fluorescent lamp, and reacted for 2 seconds.
[0141]
The precipitate was recovered, and after washing, drying and sizing, it was confirmed by SEM that the irregularly shaped silver particles having a large number of protrusions were in the shape of ferns (FIG. 15).
[0142]
The particle size was 20 μm.
[0143]
Example 9 (Production method of silver powder composed of silver particles having a mushroom spore shape and a particle size of 6 μm in an irregular shape having a large number of protrusions)
17 g of silver nitrate is dissolved in distilled water to make a total of 100 ml.
[0144]
Dissolve 18 g of L-ascorbic acid in distilled water to make a total of 100 ml.
[0145]
A and B were kept cool to 14 ° C.
[0146]
Two commercially available plastic trigger-type small atomizers were prepared, one of which was charged with the liquid A in the tank of the atomizer, and the other with the liquid B in the tank of the atomizer.
[0147]
Separately, a large-diameter plastic lidless container was prepared and used as a saucer.
[0148]
After holding two sprayers containing liquid A and liquid B separately in the left and right hands, and adjusting the angle of the sprayer so that the liquid sprayed from both sides is mixed in the air about 5 cm from the tip of the nozzle of the sprayer The two nebulizers were operated simultaneously with the intention that the reaction solution was put into the tray.
[0149]
Since the mixed periphery was felt dark, it was presumed that Solution A and Solution B had a reaction in the atmosphere. The reaction in the saucer was a rat-colored sponge.
[0150]
The mouse-colored sponge-like reactant was recovered, and after washing, drying, and sizing, it was confirmed by SEM that the irregularly shaped silver particles having a large number of protrusions were in the form of mushroom spores. However, the grain shape was not uniform (FIG. 6).
[0151]
The diameter was 6 μm.
[0152]
The operation was performed under a 750 lux fluorescent light.
[0153]
Example 10 (Production method of silver powder composed of silver particles having an irregular shape having a large number of protrusions and having a fern grass shape and a particle size of 6 μm)
17 g of silver nitrate is dissolved in distilled water to make a total of 100 ml.
[0154]
Dissolve 18 g of L-ascorbic acid in distilled water to make a total of 100 ml. Keep A and B at 14 ° C.
[0155]
The whole amount of the solution B was put in a wine glass as a reaction container in advance, and then the whole amount of the solution A was instantaneously injected into the wine glass from above the wine glass (about 5 cm).
[0156]
After 2 seconds, the reaction was completed, and after 1 minute, it separated into a murine precipitate deposited on the bottom of the wine glass and a clear water layer above the precipitate.
[0157]
This murine colored precipitate was recovered, and after washing, drying and sizing, it was confirmed by SEM that the irregularly shaped silver particles having a large number of protrusions were in the shape of ferns (FIG. 5). ). However, the yield of the shape was low.
[0158]
The particle size was 10 μm.
[0159]
The operation was performed under a 750 lux fluorescent light.
[0160]
Example 11 (Production method of silver powder composed of silver particles having an irregular shape having a large number of protrusions and having a fern grass shape and a particle diameter of 6 μm)
17 g of silver nitrate is dissolved in distilled water to make a total of 100 ml.
Dissolve 18 g of L-ascorbic acid in distilled water to make a total of 100 ml, and use this solution as solution B.
[0161]
100 ml of ethanol was further added to both the solution A and the solution B to make each 200 ml, and then cooled to 14 ° C.
[0162]
After the temperature of the room was adjusted to 14 ° C., the solution A and the solution B were simultaneously poured into a wine glass and mixed under a fluorescent lamp of 750 lux.
[0163]
After 2 seconds, the reaction was completed, and after 1 minute, it separated into a murine precipitate deposited on the bottom of the wine glass and a clear water layer above the precipitate.
[0164]
This murine colored precipitate was recovered, and after washing, drying and sizing, it was confirmed by SEM that the irregularly shaped silver particles having a large number of projections were in the shape of ferns (FIG. 7). ).
[0165]
The particle size was 6 μm (FIG. 7).
[0166]
Example 12 (Production method of silver powder composed of silver particles having an irregular shape having a large number of protrusions and having a particle size of 20 μm in a shape other than a flower shape or the like)
The reaction was attempted at room temperature and a liquid temperature of 25 ° C.
[0167]
17 g of silver nitrate is dissolved in distilled water to make a total of 100 ml. Dissolve 18 g of L-ascorbic acid in distilled water to make a total of 100 ml, and use this solution as solution B.
[0168]
The solution A and the solution B were kept cool at 25 ° C., and the temperature of the room was also adjusted to 25 ° C.
[0169]
The wine glass was placed under a fluorescent lamp of 750 lux, a donut-shaped magnet of 120 mT was placed around the outside of the wine glass, and the solution A and the solution B were simultaneously poured into the wine glass and mixed.
[0170]
After 2 seconds, the reaction was completed, and after 1 minute, it separated into a murine precipitate deposited on the bottom of the wine glass and a clear water layer above the precipitate.
[0171]
After collecting the rat-colored precipitate, after washing, drying and sizing, it was confirmed by SEM that the irregularly shaped silver particles having a large number of protrusions were in a mixed shape of flower and fern grass. (FIG. 8), and it was determined that it belonged to other shapes other than shapes such as flower shape and fern grass shape.
[0172]
The size of the silver particles was about 20 μm.
[0173]
Example 13 (Method for producing silver powder comprising irregularly shaped silver particles having a large number of protrusions)
The following experiment was performed according to the second embodiment.
[0174]
17 g of silver nitrate is dissolved in distilled water to make a total of 100 ml.
Dissolve 18 g of L-ascorbic acid in distilled water to make a total of 100 ml.
[0175]
Keep A and B at 14 ° C.
[0176]
After sunset, adjust the temperature of the room to 14 ° C, place a wine glass in the center of a φ200 × φ120 × 20 donut magnet (120 mT), and irradiate a 200 lux incandescent lamp 30 cm above the wine glass (for work) Solution A and Solution B were simultaneously poured into a wine glass and mixed together.
[0177]
After 2 seconds, the reaction was completed, and after 1 minute, it separated into a murine precipitate deposited on the bottom of the wine glass and a clear water layer above the precipitate.
[0178]
The mouse-colored precipitate was recovered, and after washing, drying and sizing, it was confirmed by SEM that the irregularly shaped silver particles having a large number of protrusions were needle-shaped. This was different from the flower-like shape obtained in Example 2.
[0179]
The particle size was 10 μm (FIG. 10).
[0180]
Example 14 (Method for producing silver powder comprising irregularly shaped silver particles having a large number of projections)
Example 14a 17 g of silver nitrate was dissolved in distilled water to make a total of 100 ml.
[0181]
Dissolve 18 g of L-ascorbic acid in distilled water to make a total of 100 ml. Keep A and B at 14 ° C.
[0182]
After sunset, adjust the temperature of the room to 14 ° C, and irradiate a 100W incandescent lamp from the place 30cm directly above the wine glass (except for work lighting equipment), and simultaneously drink the A liquid and the B liquid. Poured into glass and mixed.
[0183]
After 2 seconds, the reaction was completed, and after 1 minute, it separated into a murine precipitate deposited on the bottom of the wine glass and a clear water layer above the precipitate.
[0184]
The mouse-colored precipitate was recovered, and after washing, drying and sizing, it was confirmed by SEM that the irregularly shaped silver particles having a large number of protrusions were needle-shaped.
[0185]
The particle size was 10 μm (FIG. 11A).
[0186]
Example 14b 17 g of silver nitrate was dissolved in distilled water to make a total of 100 ml.
[0187]
Dissolve 18 g of L-ascorbic acid in distilled water to make a total of 100 ml. Keep A and B at 14 ° C.
[0188]
After sunset, adjust the temperature of the room to 14 ° C, and irradiate a 100W incandescent lamp (except for work lighting equipment) from a location 30 cm beside the wine glass (except for work lighting equipment), and simultaneously mix the liquid A and the liquid B with the wine glass And mixed.
[0189]
After 2 seconds, the reaction was completed, and after 1 minute, it separated into a murine precipitate deposited on the bottom of the wine glass and a clear water layer above the precipitate.
[0190]
This murine colored precipitate was recovered, and after washing, drying, and sizing, it was confirmed by SEM that the irregularly shaped silver particles having a large number of protrusions had other shapes (deformed shapes).
[0191]
The particle size could not be specified because the shape was a deformed shape (FIG. 11B).
[0192]
As described above, the silver nitrate aqueous solution and the L-ascorbic acid aqueous solution were reacted under the reaction conditions shown in Examples 1 to 14, and as a result, silver powder composed of irregularly shaped silver particles having many projections was obtained.
[0193]
Tables 1 to 5 summarize the reaction conditions shown in Examples 1 to 14 and the shapes and particle diameters of the silver particles obtained by the reaction.
[0194]
[Table 1]

[0195]
[Table 2]

[0196]
[Table 3]

[0197]
[Table 4]

[0198]
[Table 5]

[0199]
Although the theoretical basis for the formation of the irregularly shaped silver particles is basically unknown, the silver nitrate solution and the L-ascorbic acid solution were mixed at a ratio close to 1: 1. The larger the amount of L-ascorbic acid was, the more the amorphous silver powder was precipitated.
[0200]
Example 15 Washing of irregularly shaped silver particles was performed as follows.
[0201]
When washing irregularly shaped silver particles having a large number of projections with water, the irregularly shaped projections are broken by violent collision of the irregularly shaped silver particles with each other in water during washing.
[0202]
In the present invention, 200 g of amorphous silver particles precipitated in a 2 liter beaker (diameter 145 mm, height (depth: 250 mm)) and 1.5 liters of pure water as washing water are added. While heating the beaker with a vessel, the irregularly shaped silver powder was slowly rotated (about 20 rotations per minute) and manually rotated in a certain direction with a glass stirring rod (diameter 6 mm, length 270 mm).
[0203]
The mixture was heated and slowly stirred until the temperature of the pure water reached about 60 ° C., and this was the first washing step.
[0204]
The washed pure water is discarded, and fresh pure water and an irregularly shaped silver powder are put in a beaker for washing. This process is repeated, and the pH of the pure water for washing shows 7 by measurement with litmus paper. At that point, the washing was completed.
[0205]
The glass stirrer was slowly rotated in one direction to avoid collision of irregularly shaped silver particles in water, but it was confirmed that this method could avoid damage to projections.
[0206]
In addition, it was also found that by performing cleaning while heating, the number of times of cleaning was only half as compared with the cleaning method without heating.
[0207]
Example 16 The sizing was performed as follows.
[0208]
The reaction product obtained by the method of Example 1 is washed by the method of Example 13 described above, and the silver particles having an irregular shape after the washing are, for example, untreated sewers or industrial waste liquid waste on the coast. Agglomerated and lumpy in a sludge shape, and after drying, the irregularly shaped silver particles are all or one or several lumps due to drying shrinkage.
[0209]
In the sizing process, when drying has not been completed yet and the water content is still a little (about 5%), 700, 1200, 1800 mesh gauze (polyester) ), First, as primary sizing, place irregularly shaped silver particles still slightly containing water on an aluminum screen printing frame with 700 mesh gauze, using a squeegee. To obtain coarse silver particles (primary-sized silver particles).
[0210]
A squeegee was prepared from the primary-sized silver particles using a 1200-mesh gauze in a similar manner to obtain secondary-sized silver particles.
[0211]
From the secondary sized silver particles, a squeegee was used as a final sizing step using a 1800 mesh gauze to obtain fine sized silver particles.
[0212]
After confirming that the shape of the irregularly shaped silver particles obtained by the completion of the sizing operation is not damaged by SEM, a small amount of remaining water is removed from the silver particles obtained by the final sizing process. It was removed by drying.
[0213]
The obtained silver particles had a flower-like shape, and the particle size was 6 μm.
[0214]
Example 17 A conductive adhesive was manufactured as follows.
[0215]
The flower-like silver particles having a large number of protrusions having a particle diameter of 10 μm obtained in Example 2 were used as a metal filler of a conductive adhesive, and an epoxy resin was used as a resin. The compounding ratio was set so that the metal filler was 65% / Wt and the epoxy resin was 35% / Wt.
[0216]
The method of kneading the conductive adhesive was as follows.
[0217]
First, the irregularly shaped silver particles and the epoxy resin were placed in a silicone rubber mortar having a diameter of 10 cm at the above ratio, and mixed with a silicon rubber stirrer until the whole was lightly wet, thereby performing primary kneading.
[0218]
Next, a roll was prepared by covering the roll surface of a commercially available three-roll kneader made of metal with silicon rubber having a thickness of 2 mm, and used as a kneader exclusively for silver particles having an irregular shape. The primary kneaded conductive adhesive was placed between the rolls of this kneading machine, the clearance between the rolls was taken, and the mixture was gradually rotated until the silver particles of irregular shape and the epoxy resin became uniform. .
[0219]
The conductive adhesive was obtained by sufficiently kneading the metal filler and the epoxy resin while maintaining a flower shape having many projections.
[0220]
Example 18 The conductive adhesive manufactured in Example 15 was printed on an alumina substrate, and the resistance of the conductive adhesive after heat curing at 150 ° C. for 10 minutes was 10 mΩ, which was measured by the tensile strength tester described above. Adhesion strength is 18N / mm ² And had much better properties than the conventional conductive adhesive.
[0221]
The resistance (Ω) of a conventional conductive adhesive containing spherical silver particles having a particle size of 3 μm in the same ratio is 10 ⁶ Order, adhesive strength is 17N / mm ² Met.
[0222]
Example 19 A thick film glass paste was produced as follows.
[0223]
The flower-like silver particles having a large number of protrusions having a particle diameter of 10 μm obtained in Example 2 were used as a metal filler of a thick-film glass paste, and a frit for lead-free ceramic painting was used as a binder. The blending ratio between the metal frit and the lead-free ceramic industry frit was set to 95% / Wt for the metal filler, and to 5% / Wt for the lead-free ceramic industry frit.
[0224]
Next, a blend of a metal filler and a frit for lead-free ceramics over-the-top painting at 65% / Wt and an acrylic resin for ceramics for pasting at a ratio of 35% / Wt, and flower-like silver powder having a large number of protrusions Was sufficiently kneaded while maintaining the same shape to obtain a thick film glass paste.
[0225]
This thick film glass paste was printed on an alumina-based surface and baked at 800 ° C. for 10 minutes. The resistance value of the thick film glass paste obtained was 10 μΩ, indicating excellent conductivity.
[0226]
In addition, the acrylic resin for ceramics for pasting is heavily disintegrated at about 300 ° C. and does not exist after firing.
[0227]
Example 20 A solder paste was produced as follows.
[0228]
The flower-like silver particles having a large number of protrusions having a particle diameter of 10 μm and obtained in Example 2 were used as metal fillers of the solder paste.
[0229]
A commercially available tin / steel alloy solder paste (manufactured by Kojima Solder Co., Ltd.) was used at 95% / Wt, and the metal filler was set at 5% / Wt.
[0230]
The solder paste was obtained by sufficiently kneading the mixture in the above proportions while maintaining a large number of irregularly shaped silver particles having a flower shape.
[0231]
This solder paste was printed on an alumina substrate and baked at 240 ° C. for 1 minute. The solder paste obtained had a resistance of 5 μΩ and exhibited excellent conductivity.
[0232]
Example 21 A thread solder was manufactured as follows.
[0233]
The flower-like silver particles having a large number of protrusions and having a particle diameter of 10 μm obtained in Example 2 were used as an additive metal filler for the thread solder.
[0234]
In order to manufacture the thread solder, it was set so that the hollow portion of a hollow cylindrical rod made of a tin-copper alloy was packed together with the flux.
[0235]
18 g of the silver particles and 5 g of the flux were sufficiently kneaded in the hollow portion of a hollow cylindrical rod made of a tin-copper alloy having a diameter of 10 mm, an inner diameter of 4 mm, a length of 300 mm, and a weight of 180 g. The syringe was pushed in, and the upper and lower ports of the hollow cylindrical rod were closed.
[0236]
Then, it was stretched to have a diameter of 0.3 mm by a thread soldering machine to obtain a thread solder.
[0237]
This wire solder was soldered between electrodes using a soldering iron (about 300 ° C.).
[0238]
The resistance value of the thread solder was 5 μΩ, indicating excellent conductivity.
[0239]
Example 22 A yarn of a synthetic woven cone containing silver particles was produced as follows.
[0240]
The flower-shaped silver particles having a number of protrusions and having a particle diameter of 3 μm and obtained in Example 5 were used as the metal filler of the synthetic woven cone.
[0241]
The blending ratio of the nylon pellet and the metal filler is set to 80% / Wt: 20% / Wt, and after spinning, several yarns are united into one and the silver particles maintain continuity, thereby obtaining conductivity. In addition, the shape of the spinning nozzle was also set so that the silver particles easily appeared on the yarn surface.
[0242]
This blend was placed in a melt spinning apparatus and heated to 220 ° C. The nylon pellets are melted, the metal filler is dispersed in the nylon pellets, and the nylon pellets are extracted as a synthetic fiber containing the metal filler from a stainless steel cross-hole nozzle (1 mm) and stretched by a winding machine to a yarn having a diameter of 5 μm. By tying the five to one, the continuity of the silver particles was sufficiently maintained and conductivity was obtained.
[0243]
The resistance value of the obtained synthetic fiber showed an excellent value of 1Ω.
[0244]
The most significant features of this synthetic fiber are that its function such as conductivity does not deteriorate regardless of the number of washings, and that it can be dyed.
[0245]
【The invention's effect】
Silver powder according to the present invention, a method for producing the silver powder and a functional material using the silver powder, for example, a conductive adhesive using the silver powder as a metal filler, the mixing ratio of the metal filler and the binder resin is more than the conventional range. It has the effect of being able to expand.
[0246]
As a result, it is possible to obtain an effect that the electrical characteristics and the adhesive strength of the conductive adhesive can be improved.
[0247]
That is, in the conventional conductive adhesive containing silver powder, the mixing ratio is limited to 25% / Wt: silver powder 75% / Wt from the viewpoint of resistance value, adhesion to a substrate, and workability.
[0248]
However, in the conductive adhesive of the present invention using silver particles as a metal filler, the range of the mixing ratio of the metal filler and the resin can be significantly increased as compared with the conventional case, and as a result, the electric conductivity of the conductive adhesive can be increased. Improvements in characteristics such as characteristics and adhesive strength, improvement in workability, improvement in product yield, and the like were achieved, and good results were obtained.
[0249]
This is due to the large number of contact opportunities and the size of the contact area between the shapes due to the tetrapot effect in which the silver particles are entangled and fitted, and is one of the silver particles of the present invention showing an excellent function material. It is proof.
[0250]
In a conductive adhesive using silver particles according to a conventional manufacturing method, the point of contact between adjacent silver particles and silver particles is one point contact, and it is difficult to secure conductivity by the resin entering the adjacent contact points.
[0251]
When the amount of resin used is reduced, the conductivity is ensured, but the adhesion to the substrate cannot be ensured, and the workability cannot be obtained due to lack of viscosity.
[0252]
The present invention provides a new material by changing the shape of a conventional material and solves the technical problem of the conventional conductive adhesive using silver particles at a stretch.
[0253]
However, the amorphous silver powder having a large number of protrusions according to the present invention is used as a new material for functional materials in fields such as glass paste, synthetic fiber, thread solder, and solder paste, in addition to being used for conductive adhesives. Therefore, not only the conductive adhesive but also various functional materials can be improved in function.
[0254]
Further, according to the silver powder composed of silver particles according to the present invention, the method for producing the silver powder and the functional material using the silver powder, silver powder composed of silver particles having a wide variety of shapes and a wide range of particle sizes can be easily and selectively produced. Therefore, an effect is obtained that silver powder suitable for the function of the functional material using the silver powder can be selected from the viewpoint of the shape and particle size of the silver particles constituting the silver powder.
[Brief description of the drawings]
FIG. 1 is an electron micrograph (a substitute for a drawing) of silver powder composed of silver particles (flower-shaped, particle size: 6 μm) according to the present invention.
FIG. 2 is an electron micrograph (a photograph substituted for a drawing) of a silver powder composed of silver particles (fern grass, particle size: 20 μm) according to the present invention.
FIG. 3 is an electron micrograph (a substitute for a drawing) of a silver powder composed of silver particles (flower-shaped, particle size: 10 μm) according to the present invention.
FIG. 4 is an electron micrograph (a photograph as a substitute for a drawing) of silver powder composed of silver particles (acicular, particle diameter: 40 μm) according to the present invention.
FIG. 5 is an electron micrograph (a photograph substituted for a drawing) of silver powder composed of silver particles (fern grass, particle size: 6 μm) according to the present invention.
FIG. 6 is an electron micrograph (a drawing substitute photograph) of a silver powder composed of silver particles (spore-like mushrooms, particle size: 6 μm) according to the present invention.
FIG. 7 is an electron micrograph (a photograph substituted for a drawing) of a silver powder composed of silver particles (fern grass, particle size: 6 μm) according to the present invention.
FIG. 8 is an electron micrograph (a photograph as a substitute for a drawing) of silver powder composed of silver particles (other shapes and particle diameters of 20 μm) according to the present invention.
FIG. 9 is an electron micrograph (a photograph as a substitute for a drawing) of silver powder composed of silver particles (flower shape, particle diameter: 1 μm) according to the present invention.
FIG. 10 is an electron micrograph (a substitute for a drawing) of a silver powder composed of silver particles (acicular, particle size: 10 μm) according to the present invention.
FIG. 11 (a) is an electron micrograph (a photograph as a substitute for a drawing) of silver powder composed of silver particles (acicular, particle diameter 10 μm) obtained by irradiating the incandescent lamp according to the present invention from directly above.
(B) An electron micrograph (a photograph as a substitute for a drawing) of silver powder composed of silver particles (other shapes and particle diameters cannot be specified) obtained by irradiating the incandescent lamp according to the present invention from the side.
FIG. 12 is an electron micrograph (a photograph as a substitute for a drawing) of silver powder composed of silver particles (flower-shaped, particle diameter: 3 μm) according to the present invention.
FIG. 13 is an electron micrograph (a photograph as a substitute for a drawing) of silver powder composed of silver particles (flower-shaped, particle size: 0.5 μm) according to the present invention.
FIG. 14 is an electron micrograph (a substitute for a drawing) of a silver powder composed of silver particles (fern grass, particle size: 20 μm) according to the present invention.

Claims (5)

A silver powder composed of irregularly shaped silver particles having a large number of protrusions. The silver powder according to claim 1, wherein the silver particles have a particle size of 0.1 to 50 µm. 3. The method for producing silver powder according to claim 1, wherein the silver nitrate solution and a reducing agent containing no acrylic acid monomer are reacted under irradiation of electromagnetic waves. A functional material comprising the silver powder according to claim 1. A conductive adhesive comprising the silver powder according to claim 1.

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