JP5074837B2 - Method for producing flat silver powder, flat silver powder, and conductive paste - Google Patents
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- JP5074837B2 JP5074837B2 JP2007174662A JP2007174662A JP5074837B2 JP 5074837 B2 JP5074837 B2 JP 5074837B2 JP 2007174662 A JP2007174662 A JP 2007174662A JP 2007174662 A JP2007174662 A JP 2007174662A JP 5074837 B2 JP5074837 B2 JP 5074837B2
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- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 title claims description 124
- 238000004519 manufacturing process Methods 0.000 title claims description 24
- 239000002245 particle Substances 0.000 claims description 100
- 239000003638 chemical reducing agent Substances 0.000 claims description 48
- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Chemical compound OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 claims description 41
- CIWBSHSKHKDKBQ-JLAZNSOCSA-N Ascorbic acid Chemical compound OC[C@H](O)[C@H]1OC(=O)C(O)=C1O CIWBSHSKHKDKBQ-JLAZNSOCSA-N 0.000 claims description 33
- FOIXSVOLVBLSDH-UHFFFAOYSA-N Silver ion Chemical compound [Ag+] FOIXSVOLVBLSDH-UHFFFAOYSA-N 0.000 claims description 31
- 238000000034 method Methods 0.000 claims description 30
- 229910052709 silver Inorganic materials 0.000 claims description 26
- 239000004332 silver Substances 0.000 claims description 26
- SQGYOTSLMSWVJD-UHFFFAOYSA-N silver(1+) nitrate Chemical compound [Ag+].[O-]N(=O)=O SQGYOTSLMSWVJD-UHFFFAOYSA-N 0.000 claims description 24
- 239000011164 primary particle Substances 0.000 claims description 21
- 238000009826 distribution Methods 0.000 claims description 19
- 235000010323 ascorbic acid Nutrition 0.000 claims description 16
- 229960005070 ascorbic acid Drugs 0.000 claims description 16
- 239000011668 ascorbic acid Substances 0.000 claims description 16
- 230000009467 reduction Effects 0.000 claims description 15
- -1 silver ions Chemical class 0.000 claims description 14
- 108010010803 Gelatin Proteins 0.000 claims description 13
- 229920000159 gelatin Polymers 0.000 claims description 13
- 239000008273 gelatin Substances 0.000 claims description 13
- 235000019322 gelatine Nutrition 0.000 claims description 13
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- 229910001961 silver nitrate Inorganic materials 0.000 claims description 12
- 238000001000 micrograph Methods 0.000 claims description 8
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- YASYEJJMZJALEJ-UHFFFAOYSA-N Citric acid monohydrate Chemical compound O.OC(=O)CC(O)(C(O)=O)CC(O)=O YASYEJJMZJALEJ-UHFFFAOYSA-N 0.000 description 2
- 229960002303 citric acid monohydrate Drugs 0.000 description 2
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- 159000000000 sodium salts Chemical class 0.000 description 2
- OAYXUHPQHDHDDZ-UHFFFAOYSA-N 2-(2-butoxyethoxy)ethanol Chemical compound CCCCOCCOCCO OAYXUHPQHDHDDZ-UHFFFAOYSA-N 0.000 description 1
- 239000004925 Acrylic resin Substances 0.000 description 1
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- CIWBSHSKHKDKBQ-DUZGATOHSA-N D-isoascorbic acid Chemical compound OC[C@@H](O)[C@H]1OC(=O)C(O)=C1O CIWBSHSKHKDKBQ-DUZGATOHSA-N 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
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- YWXYYJSYQOXTPL-SLPGGIOYSA-N isosorbide mononitrate Chemical compound [O-][N+](=O)O[C@@H]1CO[C@@H]2[C@@H](O)CO[C@@H]21 YWXYYJSYQOXTPL-SLPGGIOYSA-N 0.000 description 1
- 238000009766 low-temperature sintering Methods 0.000 description 1
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- XAEFZNCEHLXOMS-UHFFFAOYSA-M potassium benzoate Chemical compound [K+].[O-]C(=O)C1=CC=CC=C1 XAEFZNCEHLXOMS-UHFFFAOYSA-M 0.000 description 1
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Landscapes
- Conductive Materials (AREA)
- Non-Insulated Conductors (AREA)
- Manufacture Of Metal Powder And Suspensions Thereof (AREA)
- Powder Metallurgy (AREA)
Description
本件出願に係る発明は、扁平銀粉の製造方法、扁平銀粉、並びにその扁平銀粉を含有する導電性ペーストに関し、特に、湿式還元法による微粒な扁平銀粉の製造方法に関する。 The invention according to the present application relates to a method for producing flat silver powder, flat silver powder, and a conductive paste containing the flat silver powder, and particularly relates to a method for producing fine flat silver powder by a wet reduction method .
近年、電子機器等において形成する配線回路等は、微細配線下での低抵抗化と接続信頼性がより重要になってきている。スクリーン印刷法等により、導電性ペーストを用いて形成した回路（導体）は、粒子間の物理的な接触によって電気的導電性を得ている。したがって、導電性ペーストに含まれる粒子の粒径や形状等によって、粒子相互の接触状態が大きな影響を受け、形成導体の抵抗値が変動する。また同時に、低温焼結でも高い導電性を示すことが求められる。 In recent years, in a wiring circuit formed in an electronic device or the like, low resistance and connection reliability under fine wiring have become more important. A circuit (conductor) formed using a conductive paste by screen printing or the like obtains electrical conductivity by physical contact between particles. Therefore, the contact state between the particles is greatly influenced by the particle size and shape of the particles contained in the conductive paste, and the resistance value of the formed conductor varies. At the same time, high conductivity is required even at low temperature sintering.
従来、湿式法、アトマイズ法、電解法等により得られる球状銀粉に各種樹脂や分散剤等を配合し、導電性ペーストに加工されて用いられることが多い。導電性ペーストの原料に球状銀粉を用いた場合、ペーストの材料である樹脂中への分散性は高く、ペースト粘度の制御は容易である。その一方で、当該導電性ペーストを使用して形成した導体を流れる電流は球状粒子相互の物理的接触により伝達されるため、球状銀粉を用いると、導通パスが三次元網目状の複雑な経路となり、電気抵抗が比較的高くなる傾向にある。 Conventionally, a spherical silver powder obtained by a wet method, an atomizing method, an electrolytic method, or the like is often used by blending various resins or dispersants into a conductive paste. When spherical silver powder is used as the raw material for the conductive paste, the dispersibility in the resin that is the paste material is high, and the paste viscosity can be easily controlled. On the other hand, since the current flowing through the conductor formed using the conductive paste is transmitted by physical contact between the spherical particles, using spherical silver powder makes the conduction path a complicated three-dimensional network. The electric resistance tends to be relatively high.
上述した球状銀粉の欠点を補うものとして、粒子形状を扁平化したフレーク状銀粉がある。従来、フレーク状銀粉は、銀粒子を物理的に塑性加工することにより製造される。このフレーク状銀粉は、粒子同士が面と面とで接触できるので、球状銀粉に比べて、より大きな接触面積を確保できる。そのため、このような銀粉を材料とした導電性ペーストは、球状銀粉を材料とした導電性ペーストを用いて形成した導体膜と比べて、銀濃度が同じであっても、導電性の高い導電膜の形成が可能で、電気抵抗の低い導電膜が得やすくなる。 To compensate for the above-described drawbacks of the spherical silver powder, there is a flaky silver powder whose particle shape is flattened. Conventionally, flaky silver powder is produced by physically plastically processing silver particles. This flaky silver powder can ensure a larger contact area than the spherical silver powder because the particles can contact each other between the surfaces. Therefore, a conductive paste made of such silver powder is a conductive film having high conductivity even if the silver concentration is the same as that of a conductive film formed using a conductive paste made of spherical silver powder. It is easy to obtain a conductive film with low electrical resistance.
例えば、特許文献１は、フレーク状銀粉末の製造方法に関するものであって、湿式法を用いて製造した銀粒子を洗浄、乾燥させ、この銀粒子を粉砕してフレーク状にする技術が開示されている。また、特許文献２は、アトマイズ法、電解法または化学還元法などの方法で得られた粒状銀粉のフレーク化技術に関し、より薄くて細かいフレーク状銀粉を製造するために、高遠心力下でボールミルを用いてフレーク化を促進させる技術が開示されている。一方で、従来のフレーク状銀粉は、ビーズミルや振動ミル等を用いて、原料粉に強い応力を加えて扁平状にするため、長辺が１μｍを上回る大きなものしか得られない上に、複数個の粒子が重なり合って扁平化された数十ミクロンの粗大な粒子を含むブロードな粒度となる傾向がある。このような粗大フレーク状銀粒子が多く含まれる場合には、スクリーンの目詰まりが生じ、スクリーン印刷法での使用に耐えない。したがって、高度な微細配線を描画するための導電性ペーストの材料として適さない。 For example, Patent Document 1 relates to a method for producing flaky silver powder, and discloses a technique in which silver particles produced using a wet method are washed and dried, and the silver particles are pulverized to form a flaky shape. ing. Further, Patent Document 2 relates to a flaking technique of granular silver powder obtained by an atomizing method, an electrolytic method, a chemical reduction method, or the like. In order to produce a thinner and finer flaky silver powder, a ball mill is used under a high centrifugal force. Techniques that use it to promote flaking are disclosed. On the other hand, since the conventional flaky silver powder is flattened by applying a strong stress to the raw material powder using a bead mill or a vibration mill, only a large one having a long side exceeding 1 μm can be obtained. Tend to have a broad particle size including coarse particles of several tens of microns that are flattened by overlapping particles. When many such coarse flaky silver particles are contained, the screen is clogged and cannot be used in the screen printing method. Therefore, it is not suitable as a material for a conductive paste for drawing advanced fine wiring.
上記以外には、特許文献３に極薄板状銀粉に関する開示があり、また、特許文献４には、湿式法により略板状の銀粒子を得る技術が開示されている。 In addition to the above, Patent Document 3 discloses an ultrathin plate-like silver powder, and Patent Document 4 discloses a technique for obtaining substantially plate-like silver particles by a wet method.
上記の通り、フレーク状、極薄板状、板状等、比較的扁平な形状を呈する銀粉、あるいは物理処理法や湿式法等の手段による銀粉の製造方法に関して、種々の先行技術が開示されている。しかし、面方向径（本発明でいう平均長径）だけみても、特許文献２または特許文献３開示の銀粉では、粒度が大きすぎて、２０μｍ以下の超微細回路形成への利用には不向きである。また、特許文献４に開示の銀粉では、粒子径は細かいものの、粒度のバラツキが大きく、微細配線形成時に配線幅のバラツキや、配線の表面粗さの不均一性の原因となり、設計に応じた抵抗値が得られにくい傾向がある。 As described above, various prior arts have been disclosed regarding silver powder having a relatively flat shape such as flakes, ultrathin plates, plates, or the like, or methods for producing silver powder by means of a physical treatment method or a wet method. . However, the silver powder disclosed in Patent Document 2 or Patent Document 3 is too large to be used for forming an ultrafine circuit of 20 μm or less even when only the surface direction diameter (the average major axis in the present invention) is viewed. . In addition, the silver powder disclosed in Patent Document 4 has a small particle size, but has a large variation in particle size, which causes a variation in wiring width and a non-uniformity in the surface roughness of the wiring at the time of forming a fine wiring. It tends to be difficult to obtain a resistance value.
したがって、従来技術における銀粉は、粒子形状が均整で、サブミクロンレベルの面方向径と数十ｎｍ程度の厚みを有し、かつ粒子径のバラツキが少なくシャープな粒度分布を有するものとは言いがたく、所望の導電性ペーストに好適な銀粉並びにその製造方法が望まれていた。 Therefore, it can be said that the silver powder in the prior art has a uniform particle shape, a submicron level surface direction diameter and a thickness of about several tens of nanometers, and has a sharp particle size distribution with little variation in particle diameter. Therefore, a silver powder suitable for a desired conductive paste and a method for producing the same have been desired.
本発明の目的は、上記特性を満足する扁平銀粉、その好適な製造方法、並びに、導電性ペーストを提供することにある。 The objective of this invention is providing the flat silver powder which satisfies the said characteristic, its suitable manufacturing method, and an electrically conductive paste.
そこで、本発明者は、鋭意研究を行った結果、以下の扁平銀粉の製造方法、扁平銀粉、及びこの扁平銀粉を含む導電性ペーストを採用することで上記課題を達成するに到った。 Thus, as a result of earnest research, the present inventor has achieved the above-described problems by employing the following method for producing flat silver powder, flat silver powder, and conductive paste containing the flat silver powder.
本発明に係る扁平銀粉の製造方法： 本発明に係る扁平銀粉の製造方法であって、硝酸銀と、銀イオン１ｍｏｌあたり０．５ｍｏｌ〜１．０ｍｏｌのクエン酸と、銀イオン１ｍｏｌあたり２０ｇ〜４０ｇのゼラチンとを含む銀イオン含有溶液に、前記銀イオン含有溶液の銀イオン１ｍｏｌに対して０．４ｍｏｌ〜０．７ｍｏｌのアスコルビン酸系還元剤を含む還元剤含有溶液を添加することを特徴とする。 Method for producing flat silver powder according to the present invention : Method for producing flat silver powder according to the present invention, comprising silver nitrate, 0.5 mol to 1.0 mol of citric acid per mol of silver ions, and 20 g to 40 g of mol of silver ions A reducing agent-containing solution containing 0.4 to 0.7 mol of an ascorbic acid reducing agent is added to a silver ion-containing solution containing gelatin with respect to 1 mol of silver ions in the silver ion-containing solution.
また、本発明に係る扁平銀粉の製造方法では、前記銀イオン含有溶液が、０．０１ｍｏｌ／ｌ〜０．３ｍｏｌ／ｌの硝酸銀を含有することが好ましい。In the method for producing flat silver powder according to the present invention, the silver ion-containing solution preferably contains 0.01 mol / l to 0.3 mol / l silver nitrate.
本発明に係る銀粉： 本発明に係る銀粉は、湿式還元法により得られる扁平形状の粒子からなる扁平銀粉であって、走査型電子顕微鏡像（ＳＥＭ）の画像解析により得られる一次粒子の平均長径が０．１μｍ〜１．０μｍであり、前記一次粒子の平均厚さが１０ｎｍ〜１００ｎｍであり、前記平均長径のＣＶ値が０．３以下であることを特徴とする。 Silver powder according to the present invention: The silver powder according to the present invention is a flat silver powder comprising flat particles obtained by a wet reduction method, and the average major axis of primary particles obtained by image analysis of a scanning electron microscope image (SEM). Is 0.1 μm to 1.0 μm, the average thickness of the primary particles is 10 nm to 100 nm, and the CV value of the average major axis is 0.3 or less.
そして、本発明に係る扁平銀粉は、より好ましくは、レーザー回折散乱式粒度分布測定法によるＤ５０＝０．１μｍ〜０．８μｍである。 The flat silver powder according to the present invention is more preferably D 50 = 0.1 μm to 0.8 μm by a laser diffraction / scattering particle size distribution measurement method.
本発明の導電性ペースト： 本発明に係る導電性ペーストは、上述の扁平銀粉を含有することを特徴とする。 Conductive paste of the present invention: The conductive paste according to the present invention contains the above-described flat silver powder.
本発明に係る扁平銀粉の製造方法は、粒子形状が均整で、サブミクロンレベルの面方向径と数十ｎｍ程度の厚みを有し、かつ粒子径のバラツキが少なくシャープな粒度分布を有する扁平銀粉を得ることができ、かかる扁平銀粉は、超微細回路形成可能な導電性ペースト用に好適である。 Method for producing a flat silver powder according to the present invention is a proportioned particle shape, flat silver powder having sub-surface direction size of the micron level and have a thickness of about several tens of nm, and the variation is less sharp particle size distribution of the particle size Such flat silver powder is suitable for a conductive paste capable of forming an ultrafine circuit.
以下、本発明に係る扁平銀粉、扁平銀粉の製造方法及び導電性ペーストの最良の実施の形態に関して説明する。 Hereinafter, the flat silver powder according to the present invention, the method for producing the flat silver powder, and the best mode of the conductive paste will be described.
＜扁平銀粉の形態＞
本発明に係る扁平銀粉は、湿式還元法によって得られ、粒子形状が扁平形状である。ここで言う扁平形状とは、粒子が扁平化し、略平板状の形状である。更に、この扁平銀粉は、走査型電子顕微鏡像の画像解析により得られる一次粒子の平均長径が０．１μｍ〜１．０μｍ、前記一次粒子の平均厚さが１０ｎｍ〜１００ｎｍ、前記平均長径のＣＶ値が０．３以下である非常に微粒な扁平銀粉である。
<Form of flat silver powder>
The flat silver powder according to the present invention is obtained by a wet reduction method, and the particle shape is a flat shape. The flat shape referred to here is a substantially flat shape with particles flattened. Further, in this flat silver powder, the average major axis of primary particles obtained by image analysis of a scanning electron microscope image is 0.1 μm to 1.0 μm, the average thickness of the primary particles is 10 nm to 100 nm, and the CV value of the average major axis is Is a very fine flat silver powder having a particle size of 0.3 or less.
平均長径が０．１μｍ未満の場合には、相対的に粒子の厚さも薄く、粒子の粒度が小さくなるため、ペースト化した時の粘度が高くなり、導電性ペーストの材料として適さない。一方、平均長径が１．０μｍを上回ると、スクリーン印刷で目詰まりが生じるような大きな粒度の粒子となり、導電性ペーストとして適さない。なお、一次粒子の平均長径は、より好ましくは、０．２μｍ〜０．５μｍである。 When the average major axis is less than 0.1 μm, the thickness of the particles is relatively thin and the particle size of the particles is small, so that the viscosity when made into a paste is high, which is not suitable as a material for the conductive paste. On the other hand, when the average major axis exceeds 1.0 μm, the particles have a large particle size that causes clogging in screen printing, and are not suitable as a conductive paste. The average major axis of the primary particles is more preferably 0.2 μm to 0.5 μm.
また、一次粒子の平均厚さが１０ｎｍ〜１００ｎｍであるので、充填性、導通確保の点で、導電性ペーストの材料として好適である。一次粒子の平均厚さが１０ｎｍ未満であると、粒子が薄すぎて、相対的に粒子の粒度も小さくなるため、ペースト化した時の粘度が高くなり導電性ペーストの材料として適さない。一方、一次粒子の平均厚さが１００ｎｍを上回る扁平粒子は、相対的に粒子の粒度も大きくなるため、スクリーン印刷での目詰まりの原因となるために適さない。なお、一次粒子の平均厚さは、より好ましくは、３０ｎｍ〜１００ｎｍである。 In addition, since the average thickness of the primary particles is 10 nm to 100 nm, it is suitable as a material for the conductive paste in terms of ensuring filling properties and conduction. If the average thickness of the primary particles is less than 10 nm, the particles are too thin and the particle size of the particles is relatively small, so that the viscosity when made into a paste is high and not suitable as a material for a conductive paste. On the other hand, flat particles having an average primary particle thickness exceeding 100 nm are not suitable because they cause a clogging in screen printing because the particle size of the particles is relatively large. The average thickness of the primary particles is more preferably 30 nm to 100 nm.
そして、ＣＶ値は、粉体の一次粒子の平均長径とその標準偏差σとを用いて、ＣＶ値＝標準偏差σ／平均長径で表される関係式で算出されるものであり、このＣＶ値の値が小さい程、粉粒の粒径が揃っており、大きなバラツキがないことを意味している。本発明に係る扁平銀粉の平均長径のＣＶ値は０．３以下と小さく、粒径が揃っており、粒度のバラツキが小さいものである。 The CV value is calculated by a relational expression represented by CV value = standard deviation σ / average major axis using the average major axis of the primary particles of the powder and the standard deviation σ. The smaller the value of, the more uniform the particle size of the particles, which means that there is no large variation. The CV value of the average major axis of the flat silver powder according to the present invention is as small as 0.3 or less, the particle size is uniform, and the variation in particle size is small.
また、本発明に係る扁平銀粉は、レーザー回折散乱式粒度分布測定法による平均粒径がＤ５０＝０．１μｍ〜０．８μｍとすることが好ましい。このような扁平銀粉であれば、ＣＶ値が０．３以下であることとあいまって、凝集度合も小さく、かつ粒度分布が非常にシャープな扁平銀粉と言える。このような扁平銀粉は、導電性ペーストの材料として考えると、ペースト粘度の変動が少なく、かつ、粒子同士の接触面積が大きく、接触効率が高くなるので導通を確保しやすくなる。その結果、導電性ペースト中の銀粉の充填量を少なくしても、良好な導電性能が得られる。したがって、導電性ペーストのコストを削減することができる。更に、導電性ペーストのフィラーの量の設計幅が広くなり、導電性ペーストの粘度の制御が容易で、導電性ペーストのチキソ性を良好な状態にコントロールできる。 In addition, the flat silver powder according to the present invention preferably has an average particle diameter of D 50 = 0.1 μm to 0.8 μm as measured by a laser diffraction / scattering particle size distribution measurement method. Such a flat silver powder can be said to be a flat silver powder having a small degree of aggregation and a very sharp particle size distribution, combined with a CV value of 0.3 or less. When considered as a material for a conductive paste, such flat silver powder is less susceptible to fluctuations in paste viscosity, has a large contact area between particles, and has high contact efficiency, so that it is easy to ensure conduction. As a result, even if the filling amount of the silver powder in the conductive paste is reduced, good conductive performance can be obtained. Therefore, the cost of the conductive paste can be reduced. Furthermore, the design range of the amount of filler of the conductive paste is widened, the viscosity of the conductive paste can be easily controlled, and the thixotropy of the conductive paste can be controlled in a good state.
更に、本発明に係る扁平銀粉は、アスペクト比（［平均長径（ｎｍ）］／［平均厚さ（ｎｍ）］）が２〜２０であると、より好ましい。アスペクト比がこの範囲内にあると、粒子が扁平形状である特徴を損なわず、導電性が確保できると同時に、スクリーン印刷での微細配線に好適なペーストを製造できる。なお、より好ましいアスペクト比の値は２〜１０の範囲である。 Furthermore, it is more preferable that the flat silver powder according to the present invention has an aspect ratio ([average major axis (nm)] / [average thickness (nm)]) of 2 to 20. When the aspect ratio is within this range, the characteristics of the flat shape of the particles can be maintained, conductivity can be ensured, and at the same time, a paste suitable for fine wiring in screen printing can be produced. A more preferable aspect ratio value is in the range of 2 to 10.
本発明に係る扁平銀粉は湿式還元法により得られるものである。物理的作用により扁平粒子化する銀粉は、原材料である銀粉粒子の大きさにより、扁平粒子の大きさの下限が規定されることとなるので、本発明に係る形状混合銀粉の様な微細形状の扁平粒子の製造は困難である。したがって、本発明に係る扁平銀粉は、極めて微細な粒子で、かつ、粒度分布がシャープな特徴を有し、導電性ペーストの様な高い導電性が求められる用途に好適である。 The flat silver powder according to the present invention is obtained by a wet reduction method. Since the silver powder that is flattened by physical action is defined by the size of the silver powder particles that are the raw material, the lower limit of the size of the flat particles is defined. Production of flat particles is difficult. Therefore, the flat silver powder according to the present invention is characterized by extremely fine particles and a sharp particle size distribution, and is suitable for applications requiring high conductivity such as a conductive paste.
本発明において、一次粒子の平均長径とは、走査型電子顕微鏡像により得られる任意の一次粒子５０個の面方向長径から算出した平均値である。同様に、平均厚さとは、まず銀粉をエポキシ樹脂で固めた試料の断面を走査型電子顕微鏡（倍率１００００倍）で直接観察し、任意の一次粒子５０個の厚さから算出した平均値である。なお、本件明細書においては、上記平均長径及び平均厚さは、２０００倍の走査型電子顕微鏡写真を、画像解析装置ＩＰ−１０００ＰＣ（旭エンジニアリング株式会社製）を用いて、粒子解析することにより求められる。 In the present invention, the average major axis of primary particles is an average value calculated from the major axis of 50 arbitrary primary particles obtained from a scanning electron microscope image. Similarly, the average thickness is an average value calculated from the thickness of 50 arbitrary primary particles by directly observing a cross-section of a sample obtained by solidifying silver powder with an epoxy resin with a scanning electron microscope (10,000 times magnification). . In addition, in this specification, the said average major axis and average thickness are calculated | required by carrying out particle | grain analysis of the scanning electron micrograph of 2000 times using image analyzer IP-1000PC (made by Asahi Engineering Co., Ltd.). It is done.
なお、本件明細書におけるレーザー回折散乱式粒度分布測定法は、銀粉０．１ｇをＳＮディスパーサント５４６８（サンノプコ社製）の０．１％水溶液と混合し、超音波ホモジナイザ（日本精機製作所製 ＵＳ−３００Ｔ）で５分間分散させた後、屈折率に１．５１を採用して日機装社製マイクロトラック９３２０ＨＲＡ Ｘ−１００を用いて測定したものである。 In this specification, the laser diffraction scattering type particle size distribution measurement method is performed by mixing 0.1 g of silver powder with a 0.1% aqueous solution of SN Dispersant 5468 (manufactured by San Nopco), and ultrasonic homogenizer (US-made by Nippon Seiki Seisakusho). 300T) for 5 minutes, and a refractive index of 1.51 was adopted, and the measurement was performed using a Nikkiso Microtrack 9320HRA X-100.
＜扁平銀粉の製造形態＞
本発明の扁平銀粉の製造方法は、湿式還元法を採用しており、銀イオンを含有する銀イオン含有溶液と還元剤含有溶液とにより還元反応を行わせる方法による。以下、本発明に係る扁平銀粉の製造に用いる銀イオン含有溶液、還元剤含有溶液に関して詳細に説明する。
<Manufacturing form of flat silver powder>
The method for producing flat silver powder of the present invention employs a wet reduction method, and is based on a method in which a reduction reaction is performed using a silver ion-containing solution containing silver ions and a reducing agent-containing solution. Hereinafter, the silver ion-containing solution and the reducing agent-containing solution used for producing the flat silver powder according to the present invention will be described in detail.
銀イオン含有溶液： 本発明に係る扁平銀粉の製造において、銀イオン含有溶液には、硝酸銀と、クエン酸とゼラチンとを含む溶液を用いる。 Silver ion-containing solution: In the production of flat silver powder according to the present invention, a solution containing silver nitrate, citric acid and gelatin is used as the silver ion-containing solution.
クエン酸は、錯化剤として銀イオン含有溶液に添加され、クエン酸錯体が形成される。この結果、還元剤含有溶液と混合すると、還元反応による粒子析出を安定化させることができる。クエン酸としては、無水クエン酸の他、例えば、クエン酸一水和物、クエン酸のナトリウム塩、カリウム塩、アンモニウム塩等を用いることも可能である。なお、クエン酸は、銀イオン含有溶液中に、銀イオン１ｍｏｌあたり０．５ｍｏｌ〜１．０ｍｏｌ含有していることが必要である。クエン酸含有量が上記範囲を外れると、粒度分布のバラツキが大きくなり、均一な扁平粒子が得られず、球状粉や異形粉等が混在することになる。すなわち、クエン酸をこのような範囲で添加することにより、還元反応時に、反応液のｐＨが下がり、還元反応速度を制御しやすくなる。また、扁平粒子を形成する結晶面の成長が促進されるので、扁平粒子が、微粒且つ粒径が揃った状態で形成される。 Citric acid is added to the silver ion-containing solution as a complexing agent to form a citric acid complex. As a result, when mixed with the reducing agent-containing solution, particle precipitation due to the reduction reaction can be stabilized. In addition to anhydrous citric acid, for example, citric acid monohydrate, sodium salt, potassium salt, ammonium salt and the like of citric acid can also be used. Citric acid must be contained in a silver ion-containing solution in an amount of 0.5 mol to 1.0 mol per mol of silver ions. If the citric acid content is out of the above range, the dispersion of the particle size distribution becomes large, uniform flat particles cannot be obtained, and spherical powder, irregular powder and the like are mixed. That is, by adding citric acid in such a range, the pH of the reaction solution is lowered during the reduction reaction, and the reduction reaction rate can be easily controlled. In addition, since the growth of the crystal planes that form the flat particles is promoted, the flat particles are formed in a state of fine particles and uniform particle sizes.
ゼラチンは、銀イオン含有溶液と還元剤含有溶液との反応により還元析出する粒子の立体障害として寄与し、粒子同士の凝集を防止して、析出した粒子の分散状態を好適に保つことができる。量的には、還元析出する銀粒子量を考慮して、銀イオン含有溶液は、銀イオン１ｍｏｌあたりゼラチンを２０ｇ〜４０ｇ含有していることが必要である。このゼラチン含有量が２０ｇを下回る場合には、還元析出粒子の立体障害として寄与することができないため、凝集を防止する効果が得られない。一方、ゼラチン含有量が４０ｇを超える場合には、銀の還元析出反応を阻害する要因となり、還元析出反応が遅くなると共に、得られる銀粉の粒度分布はブロードとなる。したがって、ゼラチン含有量が上記範囲から外れると、均一な扁平粒子が得られなくなる。なお、銀イオン含有溶液に含む硝酸銀は、銀の供給源として用い、硝酸銀濃度が０．０１ｍｏｌ／ｌ〜０．３ｍｏｌ／ｌの範囲であることが好ましい。ここで、硝酸銀濃度が０．０１ｍｏｌ／ｌを下回る場合には、工業的に求められる生産性を維持できない。一方、硝酸銀濃度が０．３ｍｏｌ／ｌを超えると、還元析出する粒子同士の凝集が顕著となり、粒子分散性に優れた扁平銀粉を得ることができなくなる。 Gelatin contributes as steric hindrance of the particles that are reduced and precipitated by the reaction between the silver ion-containing solution and the reducing agent-containing solution, and prevents the particles from aggregating with each other, so that the dispersed state of the precipitated particles can be suitably maintained. Quantitatively, the silver ion-containing solution needs to contain 20 g to 40 g of gelatin per mol of silver ions in consideration of the amount of silver particles to be reduced and precipitated. If the gelatin content is less than 20 g, it cannot contribute to the steric hindrance of the reduced precipitated particles, so that the effect of preventing aggregation cannot be obtained. On the other hand, when the gelatin content exceeds 40 g, it becomes a factor that inhibits the silver reductive precipitation reaction, the reductive precipitation reaction becomes slow, and the particle size distribution of the obtained silver powder becomes broad. Therefore, when the gelatin content is out of the above range, uniform flat particles cannot be obtained. In addition, it is preferable that the silver nitrate contained in a silver ion containing solution is used as a supply source of silver, and the silver nitrate density | concentration is the range of 0.01 mol / l-0.3 mol / l. Here, when the silver nitrate concentration is less than 0.01 mol / l, the industrially required productivity cannot be maintained. On the other hand, when the silver nitrate concentration exceeds 0.3 mol / l, aggregation of particles that are reduced and precipitated becomes remarkable, and flat silver powder excellent in particle dispersibility cannot be obtained.
還元剤含有溶液： 本発明に係る銀粉の製造においては、還元剤含有溶液として、アスコルビン酸系還元剤を含む水溶液を用いる点が特徴の一つである。アスコルビン酸系還元剤は、比較的還元力が弱いので緩やかな還元反応を起こさせる。これにより、還元析出する核生成を適正にし、析出した核の成長を促進させることができる。そして、溶媒としての水に還元剤としてのアスコルビン酸系還元剤を溶解させた状態で用いることにより、銀イオン含有溶液と還元剤含有溶液とを混合する際の、反応系内における還元剤の偏在をなくし、均一な反応が可能となる。アスコルビン酸系還元剤としてはアスコルビン酸の他、例えば、アスコルビン酸の異性体であるイソアスコルビン酸、及びそれらのナトリウム塩等を用いることも可能である。 Reducing agent-containing solution: In the production of silver powder according to the present invention, one of the features is that an aqueous solution containing an ascorbic acid-based reducing agent is used as the reducing agent-containing solution. Ascorbic acid-based reducing agents cause a mild reduction reaction because of their relatively low reducing power. Thereby, the nucleation which carries out reduction precipitation can be made appropriate, and the growth of the deposited nucleus can be promoted. Then, by using the ascorbic acid reducing agent as the reducing agent dissolved in water as the solvent, the reducing agent is unevenly distributed in the reaction system when the silver ion-containing solution and the reducing agent-containing solution are mixed. And uniform reaction becomes possible. As the ascorbic acid reducing agent, for example, isoascorbic acid, which is an isomer of ascorbic acid, and sodium salts thereof can be used in addition to ascorbic acid.
そして、この還元剤含有溶液は、銀イオン含有溶液の銀イオン１ｍｏｌに対して０．４〜０．７ｍｏｌのアスコルビン酸系還元剤を含む水溶液を用いることが必要である。必要とする還元剤の量は、還元対象となる銀イオンの総量によって異なる。しかしながら、上記銀イオン含有溶液に含まれる銀イオン１ｍｏｌに対して、還元剤含有溶液のアスコルビン酸系還元剤濃度が０．４ｍｏｌ未満の場合には、還元析出速度が遅くなる以上に、還元剤含有溶液としての使用量が増加して、廃液処理の負荷が顕著となるために好ましくない。これに対し、銀イオン含有溶液中の銀イオン１ｍｏｌに対する還元剤含有溶液のアスコルビン酸系還元剤濃度が０．７ｍｏｌを超える場合には、銀イオン含有溶液と還元剤含有溶液とを反応させる際に、アスコルビン酸系還元剤濃度が濃いために、反応系内における還元剤の偏在を速やかに消失させることが困難となり、得られる銀粒子の分散性を阻害し、その結果、均一な扁平粒子とならず、球状粉や異形粉等が混在することとなる。 And this reducing agent containing solution needs to use the aqueous solution containing 0.4-0.7 mol ascorbic acid type reducing agent with respect to 1 mol of silver ions of a silver ion containing solution. The amount of reducing agent required depends on the total amount of silver ions to be reduced. However, when the ascorbic acid-based reducing agent concentration of the reducing agent-containing solution is less than 0.4 mol with respect to 1 mol of silver ions contained in the silver ion-containing solution, the reducing agent is contained more than the reduction rate of reduction precipitation. This is not preferable because the amount used as a solution increases and the load of waste liquid treatment becomes significant. On the other hand, when the ascorbic acid-based reducing agent concentration of the reducing agent-containing solution with respect to 1 mol of silver ions in the silver ion-containing solution exceeds 0.7 mol, the silver ion-containing solution and the reducing agent-containing solution are reacted. The concentration of the ascorbic acid-based reducing agent is so high that it is difficult to quickly eliminate the uneven distribution of the reducing agent in the reaction system, thereby inhibiting the dispersibility of the resulting silver particles, resulting in uniform flat particles. Therefore, spherical powder, irregular powder, etc. will be mixed.
還元剤含有溶液添加から扁平銀粉を得るまでの工程： 上述の銀イオン含有溶液に還元剤含有溶液を撹拌しつつ添加して、銀粒子を還元析出させる。本発明に係る扁平銀粉の製造方法においては、反応性の観点から、銀イオン含有溶液と還元剤含有溶液とをそれぞれ４０℃〜８０℃の液温で混合するのが好ましい。 Step from addition of reducing agent-containing solution to obtaining flat silver powder: The reducing agent-containing solution is added to the above-described silver ion-containing solution while stirring to reduce and precipitate silver particles. In the method for producing flat silver powder according to the present invention, the silver ion-containing solution and the reducing agent-containing solution are preferably mixed at a liquid temperature of 40 ° C. to 80 ° C., respectively, from the viewpoint of reactivity.
また、還元剤含有溶液の添加時間については特に限定しないが、時間を掛けて連続して徐々に添加することにより最終的に所定量を添加する方法を用いると、還元剤含有溶液の添加に伴う反応系の温度変化の影響を防止して、還元反応が安定し、析出粒子の均質化を図ることができて製造安定性に優れるものとなる。なお、例えば、一括添加等、還元剤含有溶液の銀イオン含有溶液への還元剤含有溶液の添加が早急な場合、銀イオン含有溶液の液温変動が大きくなりやすく、これが反応に影響して粒子径のバラツキが生じやすくなり、粒度分布がブロードになる傾向がある。したがって、反応時の液温変動の影響を考慮した還元剤含有溶液の好ましい添加方法としては、１５分〜１２０分掛けて徐々に添加することが好ましい。 Further, the addition time of the reducing agent-containing solution is not particularly limited, but when a method of adding a predetermined amount by adding gradually and gradually over time is used, it is accompanied by the addition of the reducing agent-containing solution. The effect of temperature change in the reaction system is prevented, the reduction reaction is stabilized, the precipitated particles can be homogenized, and the production stability is excellent. In addition, for example, when the addition of the reducing agent-containing solution to the silver ion-containing solution of the reducing agent-containing solution is urgent, such as batch addition, the liquid temperature fluctuation of the silver ion-containing solution tends to increase, which affects the reaction and causes particles There is a tendency that the variation in diameter tends to occur and the particle size distribution tends to be broad. Therefore, as a preferable addition method of the reducing agent-containing solution in consideration of the influence of the liquid temperature fluctuation during the reaction, it is preferable to gradually add over 15 minutes to 120 minutes.
そして、銀イオン含有溶液に還元剤含有溶液を添加した以降も、還元反応の起こっている混合溶液は、還元析出反応が充分に終了するまで撹拌を行うことが好ましい。このような操作により当該混合溶液において還元析出反応が進み、析出した粒子同士の接触を防止して、凝集を起こさず、粒子分散性の高い状態を保つことができる。その後、従来の湿式還元法と同様に粒子を沈降させ、上澄みを抜き、濾過、洗浄、乾燥工程を経て扁平銀粉を得る。 And even after adding a reducing agent containing solution to a silver ion containing solution, it is preferable to stir the mixed solution in which the reduction reaction has occurred until the reduction precipitation reaction is sufficiently completed. By such an operation, the reduction precipitation reaction proceeds in the mixed solution, the contact between the precipitated particles is prevented, aggregation is not caused, and the state of high particle dispersibility can be maintained. Thereafter, particles are settled in the same manner as in the conventional wet reduction method, the supernatant is removed, and flat silver powder is obtained through filtration, washing, and drying steps.
本発明に係る扁平銀粉の製造方法では、銀イオン含有溶液にクエン酸とゼラチンとを含み、かつ、還元剤含有溶液にアスコルビン酸系還元剤を含ませ、これらを上述の組成及び配合量で用いることにより、核粒子の生成とその成長とのバランスが好適に保たれる。その結果、微細な粒子からなる扁平銀粉を、優れた粒度分布で析出させることができる。 In the method for producing flat silver powder according to the present invention, the silver ion-containing solution contains citric acid and gelatin, and the reducing agent-containing solution contains an ascorbic acid-based reducing agent, which are used in the above-described composition and blending amount. Thus, the balance between the generation of the nuclear particles and the growth thereof is suitably maintained. As a result, flat silver powder composed of fine particles can be precipitated with an excellent particle size distribution.
即ち、従来技術では、扁平粒子を得ることは可能であっても、還元速度のバラツキや反応諸条件の選択が不適切なことに起因して、得られる粒子の粒度や形状にバラツキが生じやすかった。本発明に係る扁平銀粉は、還元剤の選択並びに使用量を検討した結果、クエン酸とゼラチンとを含む銀イオン含有溶液及びアスコルビン酸系還元剤を含む還元剤含有溶液を上記の配合とすることにより、還元速度を一定に制御すると同時に、扁平粒子を形成する結晶面の優先的な成長を促すことが可能となる結果、微粒均一な扁平銀粉の生成を可能とした。更に、厚さ方向の成長を実現でき、特許文献３に示されるような極薄板状品より、厚みと面方向の成長のバランスが取れた扁平銀粉を得ることができる。このような扁平銀粉であれば、導電性ペーストに用いた場合に、粒子分散性に優れるとともに、接触面を確保できるので、導電性を向上させることができる。 That is, in the prior art, even though it is possible to obtain flat particles, the particle size and shape of the obtained particles are likely to vary due to variation in reduction rate and inappropriate selection of reaction conditions. It was. As for the flat silver powder according to the present invention, as a result of studying selection and use amount of a reducing agent, a silver ion-containing solution containing citric acid and gelatin and a reducing agent-containing solution containing an ascorbic acid-based reducing agent are combined as described above. As a result, it is possible to control the reduction rate to be constant and to promote the preferential growth of the crystal planes forming the flat particles, thereby enabling the generation of flat silver powder with uniform fine particles. Furthermore, the growth in the thickness direction can be realized, and a flat silver powder having a balance between the thickness and the growth in the surface direction can be obtained from the ultrathin plate-shaped product as disclosed in Patent Document 3. Such a flat silver powder is excellent in particle dispersibility when used in a conductive paste and can secure a contact surface, thereby improving conductivity.
＜導電性ペーストの形態＞
本発明に係る導電性ペーストは、上記扁平銀粉と、樹脂成分と、有機溶剤とを含んでなるものである。ここで、上記扁平銀粉を導電性ペーストに用いることで、上述の通り、形成される導体の低抵抗化を図ることができるので、導電性ペーストを構成する成分に特段の限定は必要ない。しかし、上記扁平銀粉をフィラーとして用いる場合に、良好な分散性を保ち、ファインピッチ回路の形成に好適な組成を採用することが好ましい。そのような好適な樹脂成分としては、エポキシ樹脂、ポリエステル樹脂、ケイ素樹脂、ユリア樹脂、アクリル樹脂、セルロース樹脂、フェノール樹脂、シリコーン樹脂から選ばれる１種以上を含む組成が挙げられる。
<Form of conductive paste>
The conductive paste according to the present invention comprises the above flat silver powder, a resin component, and an organic solvent. Here, by using the above flat silver powder for the conductive paste, as described above, the resistance of the formed conductor can be reduced, so that the components constituting the conductive paste are not particularly limited. However, when the above flat silver powder is used as a filler, it is preferable to employ a composition suitable for forming a fine pitch circuit while maintaining good dispersibility. As such a suitable resin component, the composition containing 1 or more types chosen from an epoxy resin, a polyester resin, a silicon resin, a urea resin, an acrylic resin, a cellulose resin, a phenol resin, and a silicone resin is mentioned.
そして、上記樹脂成分を含む導電性ペーストに含まれる扁平銀粉の含有量は、導電性や、回路の膜密度を考慮すると８０ｗｔ％以上が好ましい。ここで、扁平銀粉の含有量が８０ｗｔ％未満だと、焼結後の回路の膜密度が低下して比抵抗が高くなる。ペーストの膜密度を確保しつつ、ペーストの粘度上昇を抑制するためには、８５ｗｔ％〜９０ｗｔ％がより好ましい。 The content of the flat silver powder contained in the conductive paste containing the resin component is preferably 80 wt% or more in consideration of conductivity and the film density of the circuit. Here, when the content of the flat silver powder is less than 80 wt%, the film density of the circuit after sintering is lowered and the specific resistance is increased. In order to suppress the increase in the viscosity of the paste while ensuring the film density of the paste, 85 wt% to 90 wt% is more preferable.
以下、実施例及び比較例を示して本発明を具体的に説明する。なお、本発明は以下の実施例に制限されるものではない。 Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. In addition, this invention is not restrict | limited to a following example.
０．３ｍｏｌ／ｌの硝酸銀溶液２Ｌに、クエン酸一水和物１００ｇ及びゼラチン１５ｇを添加し、この銀イオン含有溶液を５０℃に加熱保持した。また、還元剤含有溶液としてアスコルビン酸５３ｇを２Ｌの水に溶解させたものを作成し、この還元剤含有溶液も５０℃に加熱保持した。次に、銀イオン含有溶液を撹拌しながら還元剤含有溶液を３０分掛けて連続添加した。添加終了後も、５０℃に保温した状態で１時間撹拌し、扁平銀粒子を得た。これを限外濾過によって洗浄し、余分な不純物を除去した後、乾燥させて扁平銀粉を得た。本実施例における主な調製条件を表１に示す。 100 g of citric acid monohydrate and 15 g of gelatin were added to 2 L of a 0.3 mol / l silver nitrate solution, and this silver ion-containing solution was heated and held at 50 ° C. A reducing agent-containing solution was prepared by dissolving 53 g of ascorbic acid in 2 L of water, and this reducing agent-containing solution was also heated and held at 50 ° C. Next, the reducing agent-containing solution was continuously added over 30 minutes while stirring the silver ion-containing solution. After completion of the addition, the mixture was stirred for 1 hour while being kept at 50 ° C. to obtain flat silver particles. This was washed by ultrafiltration to remove excess impurities and then dried to obtain flat silver powder. Table 1 shows main preparation conditions in this example.
本実施例で得られた扁平銀粉の粉体特性に関して、一次粒子の平均長径、一次粒子の平均厚さ、アスペクト比、比表面積、タップ密度、レーザー回折散乱式粒度分布測定法による体積累積粒径Ｄ５０の値を表２に示す。 Regarding the powder characteristics of the flat silver powder obtained in this example, the average major axis of primary particles, the average thickness of primary particles, the aspect ratio, the specific surface area, the tap density, and the volume cumulative particle size by laser diffraction scattering type particle size distribution measurement method. the value of D 50 shown in Table 2.
なお、タップ密度は、パウダーテスターＰＴ−Ｅ（ホソカワミクロン株式会社製）を用いて測定したものである。比表面積は、試料３．００ｇを７０℃で１０分間脱気処理を行った後、モノソーブ（カンタクロム社製）を用いてＢＥＴ１点法で測定したものである。 The tap density is measured using a powder tester PT-E (manufactured by Hosokawa Micron Corporation). The specific surface area was measured by a BET 1-point method using a monosorb (manufactured by Kantachrome Co., Ltd.) after deaerating a sample of 3.00 g at 70 ° C. for 10 minutes.
また、以下の方法でＣＶ値を算出した。即ち、粉体の一次粒子の平均長径とその標準偏差σとを用いて、ＣＶ値＝標準偏差σ／平均長径で算出した。一次粒子の平均長径及びこれに基づく標準偏差σは、前述の画像解析装置を用いることにより得られる。実施例の場合、平均長径は２８１ｎｍ、標準偏差σは６９．６８であり、その結果、ＣＶ値は０．２５と小さな値となり、粒度分布のバラツキが小さく、粒径の均一性に優れた銀粉であった。実施例の銀粉のＣＶ値の結果を表３に示す。 Further, the CV value was calculated by the following method. That is, the average major axis of the primary particles of the powder and the standard deviation σ thereof were used to calculate CV value = standard deviation σ / average major axis. The average major axis of the primary particles and the standard deviation σ based thereon are obtained by using the above-described image analysis apparatus. In the case of the examples, the average major axis is 281 nm and the standard deviation σ is 69.68. As a result, the CV value is a small value of 0.25, the dispersion of the particle size distribution is small, and the silver powder having excellent particle size uniformity. Met. Table 3 shows the results of the CV values of the silver powders of the examples.
また、本実施例で得られた扁平銀粉の走査型電子顕微鏡像を図１に示す。図１を見ると、扁平形状で、粒子の表面が滑らかであり、粒径が比較的揃った扁平銀粉であることが分かる。更に、図１に示す扁平銀粉は、凝集がほとんど見られない点も特徴である。 Moreover, the scanning electron microscope image of the flat silver powder obtained by the present Example is shown in FIG. As can be seen from FIG. 1, it is a flat silver powder having a flat shape, a smooth particle surface, and a relatively uniform particle size. Furthermore, the flat silver powder shown in FIG. 1 is also characterized by almost no aggregation.
また、本実施例で得られた扁平銀粉５０ｇと、エポキシ樹脂２ｇと、ブチルカルビトール５ｇとを、３本ロールで混練してペーストを作成した。このペーストの粘度を、東機産業社製の粘度計であるＲＥ−１０５Ｕを用いて、温度２５℃、１ｒｐｍの回転数で測定した。次に、このペーストを用いてスクリーン印刷によって、幅１００μｍ、厚み１０μｍのパターンをガラス基板上に印刷し、空気中２５０℃で１時間焼成を行った。得られたパターンの比抵抗値をＨＥＷＬＥＴＴ ＰＡＣＫＡＲＤ社製ミリオームメーター４３３８Ｂで測定した。以上の結果は表２にまとめて示す。 Also, 50 g of the flat silver powder obtained in this example, 2 g of epoxy resin, and 5 g of butyl carbitol were kneaded with three rolls to prepare a paste. The viscosity of this paste was measured at a temperature of 25 ° C. and a rotation speed of 1 rpm using RE-105U, a viscometer manufactured by Toki Sangyo Co., Ltd. Next, a pattern having a width of 100 μm and a thickness of 10 μm was printed on the glass substrate by screen printing using this paste, and baked at 250 ° C. for 1 hour in the air. The specific resistance value of the obtained pattern was measured with a milliohm meter 4338B manufactured by HEWLETT PACKARD. The above results are summarized in Table 2.
実施例の導電性ペーストは、粒子形状が均整で、サブミクロンレベルの面方向径と数１０ｎｍ程度の厚みを有し、かつ、シャープな粒度分布を有している扁平銀粉を用いたので、微粒な扁平銀粉を用いているにも拘わらず比抵抗、粘度共に、実用性に優れたレベルの値を示していると言える。したがって、実施例の扁平銀粉は、微細配線等の形成に優れ、かつ、良好な導電性及び印刷性能を備えており、微細配線形成のための導電性ペーストの材料として好適である。 The conductive paste of the example uses flat silver powder having a uniform particle shape, a submicron level surface direction diameter and a thickness of about several tens of nanometers, and a sharp particle size distribution. In spite of the use of flat silver powder, it can be said that both the specific resistance and viscosity show values of excellent practicality. Therefore, the flat silver powder of the examples is excellent in forming fine wiring and the like, and has good conductivity and printing performance, and is suitable as a conductive paste material for forming fine wiring.
［比較例１］
比較例１は、実施例で銀イオン含有溶液に添加したクエン酸を添加しない例である。即ち、硝酸銀溶液にゼラチンのみ添加した銀イオン含有溶液を用いた。なお、還元剤含有溶液及び扁平銀粉の取得手順は実施例と同様であるので説明を割愛し、調製条件を表１に示す。
[Comparative Example 1]
The comparative example 1 is an example which does not add the citric acid added to the silver ion containing solution in the Example. That is, a silver ion-containing solution obtained by adding only gelatin to a silver nitrate solution was used. In addition, since the acquisition procedure of a reducing agent containing solution and flat silver powder is the same as that of an Example, description is omitted and preparation conditions are shown in Table 1.
比較例１で得られた銀粉の走査型電子顕微鏡像を図２に示す。なお、本比較例１で得られた銀粉の粉体特性については、実施例と比較可能な粉体特性が得られないため、粉体特性の評価は行わなかった。 A scanning electron microscope image of the silver powder obtained in Comparative Example 1 is shown in FIG. In addition, about the powder characteristic of the silver powder obtained by this comparative example 1, since the powder characteristic comparable with an Example was not obtained, evaluation of the powder characteristic was not performed.
［比較例２］
比較例２では、特許文献４に開示の実施例をトレースして銀粉を製造した。即ち、水１００重量部に、高分子化合物として、ゼラチンを０．３重量部溶解させ、得られた水溶液に、硝酸銀を０．２４重量部添加、溶解し、液温を６０℃に保持した後、還元剤としてアスコルビン酸を０．０３重量部添加し、２時間撹拌させながら反応させた。
[Comparative Example 2]
In Comparative Example 2, silver powder was produced by tracing the example disclosed in Patent Document 4. That is, after dissolving 0.3 parts by weight of gelatin as a polymer compound in 100 parts by weight of water, 0.24 parts by weight of silver nitrate was added and dissolved in the resulting aqueous solution, and the liquid temperature was maintained at 60 ° C. Then, 0.03 part by weight of ascorbic acid was added as a reducing agent and reacted while stirring for 2 hours.
比較例２で得られた銀粉を、実施例と同じ方法で評価を行った。この結果、平均長径は１２７ｎｍ、標準偏差σは６０．２１、ＣＶ値は０．４７となった。 The silver powder obtained in Comparative Example 2 was evaluated in the same manner as in the Examples. As a result, the average major axis was 127 nm, the standard deviation σ was 60.21, and the CV value was 0.47.
表２から明らかなように、実施例の扁平銀粉は、サブミクロンレベルの面方向径と数１０ｎｍ程度の厚みを有しており、微粒ながら面方向と厚み方向の粒度バランスが取れている。また、表３に示した通り、ＣＶ値が低いことから、一次粒子径のバラツキが少なく、シャープな粒度分布を有するのみならず、写真やＤ５０値からも明らかなように低凝集なものである。 As is clear from Table 2, the flat silver powder of the examples has a submicron level surface direction diameter and a thickness of about several tens of nanometers. Further, as shown in Table 3, since the CV value is low, less variation in primary particle diameter, not only have a sharp particle size distribution, as is clear from the photograph and D 50 values but low cohesive is there.
これに対し、図２から明らかなように、比較例１の銀粉は凝集の大きな塊状を呈するものであり、その他評価を行うまでもなく、実施例より粉体特性の劣るものであった。これは、クエン酸を反応液に添加していないことに起因して、キレート効果が得られず、核粒子の量と粒子の成長とのバランスが崩れているものと考えられる。 On the other hand, as is clear from FIG. 2, the silver powder of Comparative Example 1 exhibits a large aggregated mass, and the powder characteristics were inferior to those of the examples without performing other evaluations. This is probably because the chelate effect cannot be obtained due to the fact that citric acid is not added to the reaction solution, and the balance between the amount of core particles and the growth of the particles is lost.
また、比較例２の銀粉は、ＣＶ値が高く、一次粒子径のバラツキが大きく、粒度分布がブロードで、Ｄ５０値も大きく、凝集気味であることがうかがえる。 Further, silver powder of Comparative Example 2, CV value is high, a large variation in the primary particle size, particle size distribution is broad, D 50 value is large, suggesting that a flocculation slightly.
本発明に係る扁平銀粉は、湿式還元法を用いて良好な反応条件で製造することにより、微細かつ表面平滑な粒子で、粒度分布がシャープな扁平銀粉となり、導電性に優れた扁平銀粉を製造することができる。したがって、本発明は、高品質化と低コスト化を併せて実現できる導電性材料の提供に貢献することができる。 The flat silver powder according to the present invention is produced under good reaction conditions using a wet reduction method, thereby producing a flat silver powder with fine and smooth particles and a sharp particle size distribution, and having excellent conductivity. can do. Therefore, the present invention can contribute to the provision of a conductive material that can realize both high quality and low cost.
Claims (5)
硝酸銀と、銀イオン１ｍｏｌあたり０．５ｍｏｌ〜１．０ｍｏｌのクエン酸と、銀イオン１ｍｏｌあたり２０ｇ〜４０ｇのゼラチンとを含む銀イオン含有溶液に、In a silver ion-containing solution containing silver nitrate, 0.5 mol to 1.0 mol of citric acid per mol of silver ions, and 20 g to 40 g of gelatin per mol of silver ions,
前記銀イオン含有溶液の銀イオン１ｍｏｌに対して０．４ｍｏｌ〜０．７ｍｏｌのアスコルビン酸系還元剤を含む還元剤含有溶液を添加することを特徴とする扁平銀粉の製造方法。A method for producing flat silver powder, comprising adding a reducing agent-containing solution containing 0.4 to 0.7 mol of an ascorbic acid-based reducing agent with respect to 1 mol of silver ions in the silver ion-containing solution.
走査型電子顕微鏡像（ＳＥＭ）の画像解析により得られる一次粒子の平均長径が０．１μｍ〜１．０μｍであり、The average major axis of primary particles obtained by image analysis of a scanning electron microscope image (SEM) is 0.1 μm to 1.0 μm,
前記一次粒子の平均厚さが１０ｎｍ〜１００ｎｍであり、The average thickness of the primary particles is 10 nm to 100 nm,
前記平均長径のＣＶ値が０．３以下であることを特徴とする扁平銀粉。A flat silver powder having a CV value of the average major axis of 0.3 or less.
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| JP5715355B2 (en) * | 2010-08-11 | 2015-05-07 | 三井金属鉱業株式会社 | Flat silver particles and method for producing the same |
| CN103260795B (en) * | 2010-11-08 | 2015-10-07 | 纳美仕有限公司 | Metallic and manufacture method thereof |
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| JP5763869B2 (en) | 2013-06-25 | 2015-08-12 | 化研テック株式会社 | Flaky silver powder, conductive paste, and method for producing flaky silver powder |
| JP6115406B2 (en) * | 2013-08-28 | 2017-04-19 | 住友金属鉱山株式会社 | Silver powder manufacturing method |
| CN107206485B (en) * | 2015-02-06 | 2020-06-02 | 特线工业株式会社 | Conductive fine particles |
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| WO2007065154A2 (en) * | 2005-12-02 | 2007-06-07 | Nanodynamics Inc. | Method of manufacturing silver platelets |
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