JP4879762B2 - Silver powder manufacturing method and silver powder - Google Patents
Silver powder manufacturing method and silver powder Download PDFInfo
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- JP4879762B2 JP4879762B2 JP2007013394A JP2007013394A JP4879762B2 JP 4879762 B2 JP4879762 B2 JP 4879762B2 JP 2007013394 A JP2007013394 A JP 2007013394A JP 2007013394 A JP2007013394 A JP 2007013394A JP 4879762 B2 JP4879762 B2 JP 4879762B2
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- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 title claims description 171
- 238000004519 manufacturing process Methods 0.000 title claims description 53
- 239000002245 particle Substances 0.000 claims description 108
- FOIXSVOLVBLSDH-UHFFFAOYSA-N Silver ion Chemical compound [Ag+] FOIXSVOLVBLSDH-UHFFFAOYSA-N 0.000 claims description 58
- 239000003638 chemical reducing agent Substances 0.000 claims description 54
- 238000000034 method Methods 0.000 claims description 44
- 238000009826 distribution Methods 0.000 claims description 32
- 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 26
- 238000005245 sintering Methods 0.000 claims description 23
- 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 22
- -1 nitrite ions Chemical class 0.000 claims description 16
- 229910001961 silver nitrate Inorganic materials 0.000 claims description 13
- KKKDGYXNGYJJRX-UHFFFAOYSA-M silver nitrite Chemical compound [Ag+].[O-]N=O KKKDGYXNGYJJRX-UHFFFAOYSA-M 0.000 claims description 13
- 229960005070 ascorbic acid Drugs 0.000 claims description 11
- 235000010323 ascorbic acid Nutrition 0.000 claims description 11
- 239000011668 ascorbic acid Substances 0.000 claims description 11
- 239000007788 liquid Substances 0.000 claims description 11
- 108010010803 Gelatin Proteins 0.000 claims description 10
- IOVCWXUNBOPUCH-UHFFFAOYSA-M Nitrite anion Chemical compound [O-]N=O IOVCWXUNBOPUCH-UHFFFAOYSA-M 0.000 claims description 10
- 229920000159 gelatin Polymers 0.000 claims description 10
- 239000008273 gelatin Substances 0.000 claims description 10
- 235000019322 gelatine Nutrition 0.000 claims description 10
- 235000011852 gelatine desserts Nutrition 0.000 claims description 10
- 229940005654 nitrite ion Drugs 0.000 claims description 10
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 10
- 230000001186 cumulative effect Effects 0.000 claims description 8
- 239000000843 powder Substances 0.000 claims description 7
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims description 6
- 229910017604 nitric acid Inorganic materials 0.000 claims description 6
- 238000002441 X-ray diffraction Methods 0.000 claims description 4
- 239000000243 solution Substances 0.000 description 91
- 238000006722 reduction reaction Methods 0.000 description 28
- 230000000052 comparative effect Effects 0.000 description 20
- 230000009467 reduction Effects 0.000 description 19
- 238000006243 chemical reaction Methods 0.000 description 17
- 239000011259 mixed solution Substances 0.000 description 17
- 230000002829 reductive effect Effects 0.000 description 12
- 239000004020 conductor Substances 0.000 description 10
- 238000001000 micrograph Methods 0.000 description 10
- 239000000758 substrate Substances 0.000 description 9
- 230000002776 aggregation Effects 0.000 description 8
- 239000007864 aqueous solution Substances 0.000 description 8
- 238000001556 precipitation Methods 0.000 description 8
- 238000004220 aggregation Methods 0.000 description 7
- 239000010419 fine particle Substances 0.000 description 7
- 239000011521 glass Substances 0.000 description 7
- 230000015572 biosynthetic process Effects 0.000 description 6
- 230000000694 effects Effects 0.000 description 6
- 239000006228 supernatant Substances 0.000 description 5
- 238000010304 firing Methods 0.000 description 4
- 238000010438 heat treatment Methods 0.000 description 4
- 238000005259 measurement Methods 0.000 description 4
- 239000000203 mixture Substances 0.000 description 4
- 238000002156 mixing Methods 0.000 description 3
- 239000002994 raw material Substances 0.000 description 3
- 239000002904 solvent Substances 0.000 description 3
- 238000003756 stirring Methods 0.000 description 3
- 230000008719 thickening Effects 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- QIGBRXMKCJKVMJ-UHFFFAOYSA-N Hydroquinone Chemical compound OC1=CC=C(O)C=C1 QIGBRXMKCJKVMJ-UHFFFAOYSA-N 0.000 description 2
- 238000000889 atomisation Methods 0.000 description 2
- 239000012159 carrier gas Substances 0.000 description 2
- 239000006185 dispersion Substances 0.000 description 2
- 238000001914 filtration Methods 0.000 description 2
- 239000012535 impurity Substances 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 238000000691 measurement method Methods 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 238000012856 packing Methods 0.000 description 2
- 239000000047 product Substances 0.000 description 2
- 238000001953 recrystallisation Methods 0.000 description 2
- 239000011347 resin Substances 0.000 description 2
- 229920005989 resin Polymers 0.000 description 2
- 238000005118 spray pyrolysis Methods 0.000 description 2
- 230000000007 visual effect Effects 0.000 description 2
- 238000005406 washing Methods 0.000 description 2
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 229910002651 NO3 Inorganic materials 0.000 description 1
- 230000002378 acidificating effect Effects 0.000 description 1
- 238000005054 agglomeration Methods 0.000 description 1
- 230000005260 alpha ray Effects 0.000 description 1
- 235000011114 ammonium hydroxide Nutrition 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- 239000012298 atmosphere Substances 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 239000011362 coarse particle Substances 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 239000002270 dispersing agent Substances 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 238000005485 electric heating Methods 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 238000011049 filling Methods 0.000 description 1
- 239000012530 fluid Substances 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 239000007952 growth promoter Substances 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 238000009766 low-temperature sintering Methods 0.000 description 1
- 230000010534 mechanism of action Effects 0.000 description 1
- 239000000155 melt Substances 0.000 description 1
- 239000005416 organic matter Substances 0.000 description 1
- 230000033116 oxidation-reduction process Effects 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 230000001376 precipitating effect Effects 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 239000003223 protective agent Substances 0.000 description 1
- 238000000197 pyrolysis Methods 0.000 description 1
- 239000010453 quartz Substances 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- 150000003378 silver Chemical class 0.000 description 1
- 238000007711 solidification Methods 0.000 description 1
- 230000008023 solidification Effects 0.000 description 1
- 230000000930 thermomechanical effect Effects 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
- 239000002351 wastewater Substances 0.000 description 1
Description
湿式還元法による銀粉の製造方法及び銀粉に関する。 The present invention relates to a method for producing silver powder by a wet reduction method and silver powder.
銀粉は、セラミック部品（基板）等の電子機器の配線回路、電極、フラットディスプレイパネルの導体等の形成において、導電性インクまたは導電性ペーストの原材料として使用されている。そして、電子部品等の小型化、基板のファインライン化に伴い、微細かつ高密度な配線回路の形成に対応するため、一定の分散性を持ち、かつある程度微粒であることが要求されている。一方、フラットディスプレイパネルの電極等を形成する場合には、ガラス基板上に導電性インクで回路等を形成し、５００℃前後で焼成して導体回路や電極を形成することが望まれる。このとき、ガラス基板の焼成温度に応じて、導電性インクまたは導電性ペースト用の銀粉には低温焼成可能な性能が望まれるのは当然である。そして、このような用途においては、焼結開始温度及び加工性能への要求を両立可能な銀粉が望まれ、その要求に近い銀粉として、微粒レベルのアトマイズ粉が使用されてきた。 Silver powder is used as a raw material for conductive ink or conductive paste in the formation of wiring circuits of electronic devices such as ceramic parts (substrates), electrodes, conductors of flat display panels, and the like. With the downsizing of electronic components and the finer lines of substrates, it is required to have a certain degree of dispersibility and have a certain degree of fineness in order to cope with the formation of fine and high-density wiring circuits. On the other hand, when forming an electrode or the like of a flat display panel, it is desirable to form a circuit or the like with a conductive ink on a glass substrate and to form a conductor circuit or an electrode by baking at around 500 ° C. At this time, it is natural that the silver powder for the conductive ink or conductive paste is desired to have the ability to be fired at a low temperature in accordance with the firing temperature of the glass substrate. And in such a use, the silver powder which can satisfy the request | requirement with respect to sintering start temperature and processing performance is desired, and the atomized powder of the fine particle level has been used as a silver powder close | similar to the request | requirement.
銀粉の従来技術として、特許文献１では、乾式法の一種であるアトマイズ法を用いて製造された銀粒子（金属微粒子）を、精密ふるいを用いた分級操作で粒子径分布が狭い微粒子とする技術が開示されている。特許文献２は、導体ペーストの原料となる銀粉末の製造方法に関するものであり、硝酸銀結晶を加熱溶融した溶融物を噴霧して液滴にし、この液滴を熱分解させることによって粒子径が２μｍ〜４μｍの大きさの銀粉末を製造する技術が開示されている。また、特許文献３は、導電ペースト用途に適した高分散性球状銀粉末及びその製造方法に関する発明であり、アンミン錯体水溶液と還元剤水溶液とを用いて銀粒子を還元析出させることにより得られ、微細で高分散性を有する銀粉末及びその製造方法が開示されている。そして、本発明者等は、特許文献４に開示したように、微粒で、分散性が良く、結晶子が大きい高結晶性銀粉について従来より検討してきた。 As a conventional technique of silver powder, Patent Document 1 discloses a technique in which silver particles (metal fine particles) produced by using an atomizing method, which is a kind of dry method, are made into fine particles having a narrow particle size distribution by classification using a precision sieve. Is disclosed. Patent Document 2 relates to a method for producing a silver powder as a raw material for a conductive paste. A melt obtained by heating and melting silver nitrate crystals is sprayed into droplets, and the droplets are thermally decomposed to have a particle diameter of 2 μm. A technique for producing a silver powder having a size of ˜4 μm is disclosed. Patent Document 3 is an invention relating to a highly dispersible spherical silver powder suitable for conductive paste applications and a method for producing the same, and is obtained by reducing and precipitating silver particles using an ammine complex aqueous solution and a reducing agent aqueous solution. A fine and highly dispersible silver powder and a method for producing the same are disclosed. Then, as disclosed in Patent Document 4, the present inventors have conventionally studied highly crystalline silver powder having fine particles, good dispersibility, and large crystallites.
フラットディスプレイパネルのパネル等の製造に用いられる、ガラス基板上に導体を形成するための導電性インクまたは導電性ペーストの材料となる銀粉には、例えば、乾式法の一種であるアトマイズ法により得られ、レーザー回折散乱式粒度分布測定法による体積累積平均粒径Ｄ５０値（以下、「Ｄ５０値」と記す。）が５μｍ前後の高分散性銀粉が一般的に利用されている。アトマイズ法による銀粉の製造方法は、粒子径が１０μｍ〜数十μｍ程度の比較的粒度の大きな銀粉の量産性に優れているが、Ｄ５０値が５μｍ程度の銀粉を直接製造することは困難であるため、分級を行う必要がある。従って、製造コストが高くなる点が難点である。また、アトマイズ法、噴霧熱分解還元法等の乾式法では製造プロセスの特性上融点までの熱履歴を受けることによる粒子の結晶組織の特性故に良好な耐熱収縮性を有する反面、微粒化しても良好な低温焼結特性を得ることが出来ず、少なくとも８００℃以上での加熱が要求される。 Silver powder used as a material for conductive ink or conductive paste for forming a conductor on a glass substrate used in the manufacture of flat display panel panels and the like is obtained by, for example, an atomizing method which is a kind of dry method. Highly dispersible silver powder having a volume cumulative average particle diameter D 50 value (hereinafter referred to as “D 50 value”) measured by a laser diffraction / scattering particle size distribution measuring method of about 5 μm is generally used. The method for producing silver powder by the atomization method is excellent in mass production of silver powder having a relatively large particle size of about 10 μm to several tens of μm, but it is difficult to directly produce silver powder having a D 50 value of about 5 μm. There is a need for classification. Therefore, the manufacturing cost is high. In addition, dry methods such as atomization and spray pyrolysis reduction have good heat shrinkage due to the characteristics of the crystalline structure of the particles due to the heat history up to the melting point due to the characteristics of the manufacturing process, but they are good even when atomized. High temperature sintering characteristics cannot be obtained, and heating at least at 800 ° C. or more is required.
一方、湿式還元法により得られる銀粉は低温焼結特性に優れ、更に微粒かつ分散性に優れている。しかし、湿式還元法により得られる銀粉は、Ｄ５０値が３μｍを超える粒径の製品を安定的に生産することが出来なかったため、Ｄ５０値が３μｍ以下の製品が一般的に製造されている。 On the other hand, the silver powder obtained by the wet reduction method has excellent low-temperature sintering characteristics, and further has excellent fineness and dispersibility. However, since the silver powder obtained by the wet reduction method could not stably produce a product having a particle size with a D 50 value exceeding 3 μm, a product having a D 50 value of 3 μm or less is generally produced. .
通常、ガラス基板上で回路形成する場合等の用途においては、５００℃前後での焼結が要求される。このような要求を想定すると、従来の湿式銀粉では焼結開始温度が低過ぎるため、５００℃付近で焼成した導体は形状安定性に欠け、ファインピッチ回路の形成には不適であった。更に、湿式還元法により得られる銀粉は、製造プロセスの特性上、乾式法により得られる銀粉と比べて有機物を多く含むので、導電性の阻害要因となっていた。このようなことから、特に５００℃程度の低温焼結性及び導電性を確保し、焼成後の導体形状の安定性に優れた銀粉が望まれていた。 Usually, sintering is required at around 500 ° C. in applications such as when forming a circuit on a glass substrate. Assuming such a requirement, the conventional wet silver powder has a sintering start temperature that is too low, so that the conductor fired at around 500 ° C. lacks shape stability and is not suitable for forming a fine pitch circuit. Furthermore, the silver powder obtained by the wet reduction method contains a larger amount of organic matter than the silver powder obtained by the dry method due to the characteristics of the manufacturing process, and thus has been an impediment to conductivity. For this reason, a silver powder that secures low-temperature sinterability and electrical conductivity of about 500 ° C. and has excellent conductor shape stability after firing has been desired.
また、特許文献４に開示の高結晶性銀粉は、粒度分布が比較的ブロードであることにより、従前の銀粉と比べて、当該銀粉を用いた導電性ペーストで回路を形成すると、銀粉の充填性に優れ、その結果、導電性の確保に有利である。しかし、粒度分布がブロードであることから、形成した回路の平滑性や形状安定性にバラツキが生じ易いものであった。 In addition, the highly crystalline silver powder disclosed in Patent Document 4 has a relatively broad particle size distribution, and therefore, when a circuit is formed with a conductive paste using the silver powder as compared with the conventional silver powder, the filling property of the silver powder is As a result, it is advantageous for ensuring conductivity. However, since the particle size distribution is broad, the smoothness and shape stability of the formed circuit tend to vary.
そこで、本発明者等は、鋭意研究を行った結果、以下の銀粉の製造方法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 intensive studies, the present inventors have achieved the above-mentioned problem by adopting the following silver powder production method.
銀粉の製造方法： 即ち、本発明に係る銀粉の製造方法は、銀イオン含有溶液と還元剤含有溶液とを接触混合させる湿式還元法を用いた銀粉の製造方法であって、前記銀イオン含有溶液は硝酸銀と亜硝酸イオンとを含み、前記還元剤含有溶液はアスコルビン酸またはアスコルビン酸の異性体のいずれか１種以上からなる還元剤を水に溶解させたものを用い、還元剤含有溶液を銀イオン含有溶液に対して添加することを特徴とする。 Silver powder production method: That is, the silver powder production method according to the present invention is a silver powder production method using a wet reduction method in which a silver ion-containing solution and a reducing agent-containing solution are contact-mixed, and the silver ion-containing solution. and a silver nitrate and nitrite ions, the reducing agent-containing solution used after a reducing agent comprising any one or more of the isomers of ascorbic acid or ascorbic acid is dissolved in water, silver reducing agent-containing solution It is added to the ion-containing solution .
上記銀粉の製造方法において、前記銀イオン含有溶液は、銀１ｍｏｌ当たり１ｍｏｌ〜２ｍｏｌの硝酸を含有するものを用いることが望ましい。 In the method for producing silver powder, the silver ion-containing solution is preferably a solution containing 1 mol to 2 mol of nitric acid per mol of silver.
上記銀粉の製造方法において、前記亜硝酸イオンは、銀イオン含有溶液に、０．０１ｍｏｌ／ｌ〜２．０ｍｏｌ／ｌ濃度で含むことが望ましい。 In the silver powder production method, the nitrite ions are preferably contained in the silver ion-containing solution at a concentration of 0.01 mol / l to 2.0 mol / l.
そして、上記銀粉の製造方法において、前記銀イオン含有溶液は、亜硝酸銀を添加することにより亜硝酸イオンを得ることが好ましい。 And in the manufacturing method of the said silver powder, it is preferable that the said silver ion containing solution obtains nitrite ion by adding silver nitrite.
更に、上記銀粉の製造方法に用いる前記銀イオン含有溶液は、ゼラチンを添加したものを用いることが好ましい。 Furthermore, the silver ion-containing solution used in the method for producing silver powder is preferably a gelatin-added solution.
上記銀粉の製造方法において、液温を４０℃〜６０℃に保ちながら、前記銀イオン含有溶液と前記還元剤含有溶液とを接触混合させることが好ましい。 In the said silver powder manufacturing method, it is preferable to contact-mix the said silver ion containing solution and the said reducing agent containing solution, keeping liquid temperature at 40 to 60 degreeC.
銀粉： 本発明に係る銀粉は、上記方法を用いて製造された銀粉であって、粉末法Ｘ線解析分析により得られる結晶子径が５４０Å〜６００Åであることを特徴とする。 Silver powder: The silver powder according to the present invention is a silver powder produced by using the above-described method, and has a crystallite diameter of 540 to 600 mm obtained by powder method X-ray analysis.
上述の結晶子径は、粉末法Ｘ線回折分析に基づくものであり、測定機器として株式会社リガク製のＲＩＮＴ２０００を用い、ＣｕＫα線測定角度２０／２θ〜１００／２θの条件で測定したものである。 The above-mentioned crystallite diameter is based on the powder method X-ray diffraction analysis and is measured under the condition of CuK α ray measurement angle 20 / 2θ to 100 / 2θ using RINT2000 manufactured by Rigaku Corporation as a measuring instrument. is there.
そして、本発明に係る銀粉は、焼結開始温度が４５０℃〜５５０℃である特性を有するものであることが好ましい。 And it is preferable that the silver powder which concerns on this invention has a characteristic whose sintering start temperature is 450 to 550 degreeC.
また、本発明に係る銀粉は、望ましくはレーザー回折散乱式粒度分布測定法による体積累積平均粒径Ｄ５０値が４μｍ〜６μｍである特性を備えるものである。 Further, silver powder according to the present invention, preferably the volume accumulated average particle diameter D 50 value using a laser diffraction scattering particle size distribution measuring method are those having a property of being 4Myuemu～6myuemu.
更に、本発明に係る銀粉は、レーザー回折散乱式粒度分布測定法による１０％体積累積粒径Ｄ１０値（以下、「Ｄ１０値」と記す。）が３μｍ以上であることが望ましい。 Further, silver powder according to the present invention, a laser diffraction scattering particle size distribution measurement by 10% volume cumulative particle diameter D 10 value according to method (hereinafter, referred to as "D 10 value".) It is preferable that 3μm or more.
また、本発明に係る銀粉は、比表面積（ＳＳＡ）が０．２ｍ２／ｇ以下であることが望ましい。 The silver powder according to the present invention preferably has a specific surface area (SSA) of 0.2 m 2 / g or less.
本発明に係る銀粉の製造方法によって、従来、製造することが難しかった、Ｄ５０値が５μｍ程度の粒度分布がシャープな銀粉を安定的に製造することができる。そして、本発明に係る銀粉は、上記製造方法により得られ、Ｄ５０値が５μｍ前後の平均粒子径を有し、非常にシャープな粒度分布を示すものである。この結果、結晶子径が大きくかつ狭い範囲で揃った銀粉が得られるので、焼結性及び導電性に優れるのみならず、安定した形状の回路形成が可能である。このような銀粉は、５００℃前後の温度での焼成が求められる用途においては有用なものである。また、比表面積（ＳＳＡ）が０．２ｍ２／ｇ以下であり、かつ１０％体積累積粒径Ｄ１０値が３μｍ以上という特性を備える銀粉は、これを用いてペーストを作製する場合に、ペーストの組成物である樹脂等の溶媒量を極限に減らすことができる。この結果、ペーストのコンテントを上げることができるので粘度調節がしやすく、かつ製造コストを削減できる。 By the manufacturing method of the silver powder according to the present invention, conventionally it has been difficult to manufacture, D 50 value can be the particle size distribution of about 5μm to produce a sharp silver powder stably. Then, the silver powder according to the present invention is obtained by the above manufacturing method, D 50 value has an average particle size of about 5 [mu] m, it shows a very sharp particle size distribution. As a result, a silver powder having a large crystallite diameter and a narrow range can be obtained, so that not only the sinterability and conductivity are excellent, but also a circuit having a stable shape can be formed. Such silver powder is useful in applications that require firing at temperatures around 500 ° C. Silver powder having the characteristics that the specific surface area (SSA) is 0.2 m 2 / g or less and the 10% volume cumulative particle diameter D 10 value is 3 μm or more is used when a paste is produced using this silver powder. The amount of the solvent such as a resin that is the composition can be reduced to the limit. As a result, since the content of the paste can be increased, the viscosity can be easily adjusted, and the manufacturing cost can be reduced.
以下、本発明に係る銀粉の製造方法及び銀粉の最良の実施の形態に関して説明する。 Hereinafter, the silver powder production method and the best embodiment of the silver powder according to the present invention will be described.
＜銀粉の製造形態＞
本発明は、湿式還元法を用いた銀粉の製造方法に関するものである。ここでいう、湿式還元法とは、銀イオンを含有する銀イオン含有溶液と、還元剤含有溶液とを、接触混合させることによって水素還元反応を起こさせて析出させることにより粒子を得て、この得られた粒子を沈降させて上澄みを抜き、濾過、洗浄することによって銀粉を得る方法である。即ち、本発明に係る銀粉の製造方法は、以下に述べる銀イオン含有溶液と還元剤含有溶液とを接触混合させて、還元析出によって粒子を生成させる銀粉の製造方法であり、Ｄ５０値が５μｍ前後の銀粉を製造するものである。確かに、銀イオン含有溶液中の銀濃度を高くすると、他の製造方法を採用してもＤ５０値を２μｍ〜３μｍ程度まで大きくすることが可能である。しかしながら、通常の製造方法を以て、単に反応液中の銀濃度を上昇させても、析出粒子同士の凝集現象が顕著になるだけであり、良好な粒子分散性及び均一な粒子形状を備えたＤ５０値が５μｍ前後の銀粉を安定的に得ることは出来ない。
<Manufacturing form of silver powder>
The present invention relates to a method for producing silver powder using a wet reduction method. As used herein, the wet reduction method refers to a method in which a silver ion-containing solution containing silver ions and a reducing agent-containing solution are brought into contact with each other to cause a hydrogen reduction reaction and precipitate, thereby obtaining particles. In this method, the obtained particles are settled, the supernatant is removed, filtered and washed to obtain silver powder. That is, the silver powder production method according to the present invention is a silver powder production method in which a silver ion-containing solution and a reducing agent-containing solution described below are contact-mixed to produce particles by reduction precipitation, and the D 50 value is 5 μm. It produces silver powder before and after. Certainly, if the silver concentration in the silver ion-containing solution is increased, the D 50 value can be increased to about 2 μm to 3 μm even if another manufacturing method is adopted. However, even if the silver concentration in the reaction solution is simply increased by a normal production method, only the agglomeration phenomenon between the precipitated particles becomes remarkable, and D 50 having good particle dispersibility and uniform particle shape. A silver powder having a value of about 5 μm cannot be obtained stably.
ところで、乾式法にて得られる銀粉（以下、「乾式銀粉」と記す。）は、製造過程において、一旦溶融金属にして、これを粉体化させるため、その凝固過程において粒子の再結晶化が起こりやすく、結晶子径が大きくなる傾向がある。従って、湿式銀粉に比べて焼結開始温度が高い。一方、従来の湿式法で得られる銀粉（以下、「湿式銀粉」と記す。）は、還元析出させて直接形成するため、結晶子径が小さい。その結果、加熱による再結晶化がおこりやすく、乾式銀粉より焼結開始温度がはるかに低いのが通常である。ところが、本発明に係る銀粉の製造方法では、従来の湿式銀粉と比べて結晶子径が大きく、焼結開始温度を５００℃程度に上昇させ、乾式銀粉により近い焼結特性を得ることができるのである。 By the way, silver powder obtained by a dry method (hereinafter referred to as “dry silver powder”) is once made into a molten metal in the production process and pulverized, so that the recrystallization of particles in the solidification process. It tends to occur and the crystallite diameter tends to increase. Therefore, the sintering start temperature is higher than that of wet silver powder. On the other hand, silver powder obtained by a conventional wet method (hereinafter referred to as “wet silver powder”) has a small crystallite diameter because it is directly formed by reduction precipitation. As a result, recrystallization by heating is likely to occur, and the sintering start temperature is usually much lower than that of dry silver powder. However, in the method for producing silver powder according to the present invention, the crystallite diameter is larger than that of the conventional wet silver powder, the sintering start temperature is increased to about 500 ° C., and sintering characteristics closer to dry silver powder can be obtained. is there.
以下、本発明に係る銀粉の製造で用いる銀イオン含有溶液、還元剤含有溶液等に関して詳細に説明する。 Hereinafter, the silver ion-containing solution, the reducing agent-containing solution and the like used in the production of the silver powder according to the present invention will be described in detail.
銀イオン含有溶液： 本発明に係る銀粉の製造方法において、銀イオン含有溶液には、硝酸銀と亜硝酸イオンとを含むものである。このように、銀イオン含有溶液に亜硝酸イオンを加えることによって、銀粉粒子の大粒径化のみならず銀粉の粒度分布をシャープにすることが可能となるのである。亜硝酸イオンの作用機構は明確ではないが、析出した銀粒子の成長を促進するためには反応速度が重要であり、亜硝酸イオンが前記混合溶液中における酸化還元電位を低下させ、析出粒子の成長を促進させるものと考えられる。亜硝酸イオンは、言わば、析出する銀粒子の成長促進剤として機能し、その結果、比較的粒度が大きく、かつシャープな粒度分布を有する銀粉を得ることができる。 Silver ion-containing solution: In the method for producing silver powder according to the present invention, the silver ion-containing solution contains silver nitrate and nitrite ions. Thus, by adding nitrite ions to the silver ion-containing solution, it becomes possible not only to increase the particle size of the silver powder particles but also to sharpen the particle size distribution of the silver powder. Although the mechanism of action of nitrite ions is not clear, the reaction rate is important to promote the growth of the precipitated silver particles, and nitrite ions lower the redox potential in the mixed solution, It is thought to promote growth. Nitrite ions function as a growth promoter for the precipitated silver particles, and as a result, a silver powder having a relatively large particle size and a sharp particle size distribution can be obtained.
当該銀イオン含有溶液は、銀１ｍｏｌ当たり１ｍｏｌ〜２ｍｏｌの硝酸を含有することが好ましい。このような硝酸溶液であれば、硝酸イオンによって酸化還元電位を下げ、析出核の形成段階では還元反応を起こしにくい雰囲気を形成し、緩やかな還元反応とすることができ、余分な析出核の形成を抑制して析出核の形成数を適量にし、銀イオンを粒子の成長に振り向けさせることで、析出粒子の成長が促進できると考える。 The silver ion-containing solution preferably contains 1 mol to 2 mol of nitric acid per mol of silver. With such a nitric acid solution, the oxidation-reduction potential is lowered by nitrate ions, an atmosphere in which a reduction reaction is difficult to occur in the formation stage of precipitation nuclei can be formed, and a gradual reduction reaction can be formed. It is considered that the growth of the precipitated particles can be promoted by suppressing the above and adjusting the number of formed precipitation nuclei to the appropriate amount and directing the silver ions to the growth of the particles.
また、本発明に係る銀粉の製造方法において、銀イオン含有溶液には、０．０１ｍｏｌ／ｌ〜２．０ｍｏｌ／ｌの濃度の亜硝酸イオンを含むものを用いる。 Moreover, in the manufacturing method of the silver powder which concerns on this invention, what contains nitrite ion of the density | concentration of 0.01 mol / l-2.0 mol / l is used for a silver ion containing solution.
本発明に係る銀粉の製造方法では、還元剤含有溶液としてアスコルビン酸を用いているので、銀イオン含有溶液において亜硝酸イオンを用いると、酸性下での反応効率が良い。そして、亜硝酸イオンの含有量として、銀イオン含有溶液中の亜硝酸イオン濃度が２．０ｍｏｌ／ｌを超えると、亜硝酸イオンの量が多くなり過ぎて反応が安定せず、得られる銀粉に凝集が生じる。一方、銀イオン含有溶液中の亜硝酸イオン濃度が０．０１ｍｏｌ／ｌを下回ると、析出させる銀粉の大粒径化の効果が得られない。 In the method for producing silver powder according to the present invention, ascorbic acid is used as the reducing agent-containing solution. When nitrite ions are used in the silver ion-containing solution, the reaction efficiency under acidic conditions is good. And as content of nitrite ion, when the concentration of nitrite ion in the silver ion-containing solution exceeds 2.0 mol / l, the amount of nitrite ion increases too much and the reaction is not stabilized, and the resulting silver powder Aggregation occurs. On the other hand, when the nitrite ion concentration in the silver ion-containing solution is less than 0.01 mol / l, the effect of increasing the particle size of the silver powder to be deposited cannot be obtained.
そして、亜硝酸イオンの供給源としては、亜硝酸銀を添加することにより得ることが好ましい。亜硝酸銀は、前記混合溶液中で銀イオンと亜硝酸イオンとなり、この亜硝酸イオンが還元反応において上述の効果を奏する。なお、亜硝酸銀を用いると、亜硝酸銀から生じた銀イオンは還元反応により銀粉として析出するので、混合溶液中に不純物成分を導入することにならず、不純物の影響を回避することができる。 And it is preferable to obtain by adding silver nitrite as a supply source of nitrite ion. Silver nitrite becomes silver ion and nitrite ion in the mixed solution, and this nitrite ion has the above-mentioned effect in the reduction reaction. When silver nitrite is used, silver ions generated from the silver nitrite are precipitated as silver powder by a reduction reaction, so that an impurity component is not introduced into the mixed solution and the influence of impurities can be avoided.
更に、銀イオン含有溶液は、ゼラチンを含有することが好ましい。ゼラチンが銀イオン含有溶液と還元剤含有溶液との混合溶液中の反応における立体障害として寄与して反応の進行を妨げるので粒子の析出数を抑制することができる。その結果、緩やかな反応となり析出した粒子を成長させることができる。また、ゼラチンは保護剤として機能し、混合溶液中に析出した粒子の分散状態を良好な状態に保つことができるので、析出粒子間の凝集を防ぐことができる。ゼラチンの含有量は還元析出する銀粒子量を考慮して、銀イオン含有溶液中で１ｇ／ｌ〜５ｇ／ｌの範囲で用いることが好ましい。ゼラチン含有量が１ｇ／ｌ未満の場合には、還元析出粒子の立体障害としての効果が得られず、また、混合溶液の分散性が得られずに凝集が生じやすくなる。一方、ゼラチン含有量が５ｇ／ｌを超える場合には、銀粒子の還元析出反応を阻害する要因となり、還元析出反応が過度に遅くなると共に得られる銀粉の粒度分布がブロード化する。 Furthermore, the silver ion-containing solution preferably contains gelatin. Since gelatin contributes as a steric hindrance in the reaction in the mixed solution of the silver ion-containing solution and the reducing agent-containing solution and hinders the progress of the reaction, the number of deposited particles can be suppressed. As a result, it becomes a slow reaction and the deposited particles can be grown. In addition, gelatin functions as a protective agent and can maintain the dispersed state of the particles precipitated in the mixed solution in a good state, so that aggregation between the precipitated particles can be prevented. The gelatin content is preferably in the range of 1 g / l to 5 g / l in the silver ion-containing solution in consideration of the amount of silver particles to be reduced and precipitated. When the gelatin content is less than 1 g / l, the effect of steric hindrance of the reduced precipitated particles cannot be obtained, and the dispersibility of the mixed solution cannot be obtained and aggregation easily occurs. On the other hand, when the gelatin content exceeds 5 g / l, it becomes a factor that inhibits the reductive precipitation reaction of silver particles, and the reductive precipitation reaction becomes excessively slow and the particle size distribution of the obtained silver powder becomes broad.
なお、銀イオン含有溶液の銀濃度は、０．５ｍｏｌ／ｌ〜０．６ｍｏｌ／ｌの範囲であることが好ましい。ここで、銀イオン含有溶液の銀濃度が０．５ｍｏｌ／ｌ未満の場合には、工業的に求められる生産性を維持できないばかりか、本発明の目的とするアトマイズ粉の微粒レベル（Ｄ５０値が５μｍ前後）の銀粉を得ることも出来なくなる。一方、銀イオン含有溶液の銀濃度が０．６ｍｏｌ／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銀粉を得ることが出来なくなる。 In addition, it is preferable that the silver concentration of a silver ion containing solution is the range of 0.5 mol / l-0.6 mol / l. Here, when the silver concentration of the silver ion-containing solution is less than 0.5 mol / l, not only the industrially required productivity can be maintained, but also the fine particle level (D 50 value) of the atomized powder targeted by the present invention. Cannot be obtained. On the other hand, when the silver concentration of the silver ion-containing solution exceeds 0.6 mol / l, aggregation of particles that are reduced and precipitated becomes remarkable, and silver powder having excellent particle dispersibility cannot be obtained.
還元剤含有溶液： 本発明に係る銀粉の製造方法には、還元剤含有溶液として、アスコルビン酸、アスコルビン酸の異性体から選ばれたいずれか１種以上からなる還元剤を水に溶解させたものを用いる。上記還元剤は、比較的還元力の弱いものを選択している。還元力の弱い還元剤を用いて緩やかな還元反応を起こさせることで、還元析出する粒子数を抑制させ、その分、析出した核の成長を促進させるためである。そして、上記還元剤は還元剤含有溶液として用いる。このように溶媒としての水に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、均一な分散状態が得られる。これらの還元剤を上記銀イオン含有溶液に添加することにより、従来の湿式還元法で得られる銀粒子より粒径大となるＤ５０値が５μｍ前後の平均粒径の銀粉を効率良く製造出来るのである。 Reducing agent-containing solution: In the method for producing silver powder according to the present invention, as the reducing agent-containing solution, a reducing agent comprising at least one selected from ascorbic acid and an isomer of ascorbic acid is dissolved in water. Is used. As the reducing agent, one having a relatively weak reducing power is selected. This is because by causing a gentle reduction reaction using a reducing agent having a weak reducing power, the number of particles to be reduced and precipitated is suppressed, and the growth of the deposited nuclei is promoted accordingly. The reducing agent is used as a reducing agent-containing solution. By using it in a state dissolved in water as a solvent in this way, when the silver ion-containing solution and the reducing agent-containing solution are mixed, the uneven distribution of the reducing agent in the reaction system is eliminated, and a uniform dispersion state is obtained. It is done. By adding these reducing agents to the silver ion-containing solution, it is possible to efficiently produce silver powder having an average particle diameter of a D 50 value of about 5 μm, which is larger than the silver particles obtained by the conventional wet reduction method. is there.
そして、この還元剤含有溶液は、反応させる銀イオン含有溶液に含まれる銀１当量あたり１倍当量〜３倍当量の上記還元剤を含む水溶液として用いることが好ましい。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濃度を前提として考えると、還元剤含有溶液の還元剤濃度が１倍当量未満の場合には、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、還元剤含有溶液の還元剤濃度が３倍当量を超える場合には、銀イオン含有溶液と還元剤含有溶液とを接触混合する際に、還元剤濃度が濃いため、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、得られる銀粒子の均一な分散性を阻害する。 The reducing agent-containing solution is preferably used as an aqueous solution containing 1 to 3 equivalents of the above reducing agent per equivalent of silver contained in the silver ion-containing solution to be reacted. The amount of reducing agent required depends on the total amount of silver ions to be reduced. However, considering the silver concentration contained in the silver ion-containing solution, if the reducing agent concentration of the reducing agent-containing solution is less than 1 equivalent, the reducing precipitation rate becomes slower than the reducing agent-containing solution. This is not preferable because the amount of wastewater used increases and the load of waste liquid treatment becomes significant. On the other hand, when the reducing agent concentration of the reducing agent-containing solution exceeds 3 times equivalent, the reducing agent concentration is high when the silver ion-containing solution and the reducing agent-containing solution are contact-mixed. It becomes difficult to quickly eliminate the uneven distribution of the reducing agent, and the uniform dispersibility of the resulting silver particles is hindered.
銀イオン含有溶液と還元剤含有溶液との混合方法： 上述の還元剤含有溶液と銀イオン含有溶液とを接触混合する。混合の際は、還元剤含有溶液を銀イオン含有溶液に添加するのが好ましい。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方法を用いると、前記混合溶液内の反応を緩やかにすることができ、かつ、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、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１回当たりの添加量が多くなると、反応速度が早くなって、粒子の成長より粒子の析出数が多くなり、Ｄ５０値が５μｍ前後の大きさの粒子を得ることが難しくなる。加えて、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。 Method of mixing silver ion-containing solution and reducing agent-containing solution: The above-described reducing agent-containing solution and silver ion-containing solution are contact-mixed. In mixing, it is preferable to add the reducing agent-containing solution to the silver ion-containing solution. The addition time of the reducing agent-containing solution is not particularly limited, but if a method of adding gradually and gradually over time is used, the reaction in the mixed solution can be moderated, and the reducing agent-containing solution The effect of temperature change of the reaction system due to the addition of is prevented, the reduction reaction is stabilized, the precipitated particles can be homogenized, and the production stability is excellent. Note that, for example, when the amount of the reducing agent-containing solution added to the silver ion-containing solution of the reducing agent-containing solution per batch increases, for example, the reaction rate increases, and the number of precipitated particles is larger than the particle growth. It becomes difficult to obtain particles having a D 50 value of around 5 μm. In addition, the liquid temperature variation of the silver ion-containing solution tends to be large, which affects the reaction, tends to cause variation in particle diameter, and tends to broaden the particle size distribution.
更に、この銀イオン含有溶液と還元剤含有溶液との混合溶液の液温が４０℃〜６０℃に保たれるように接触混合することがより好ましい。ここで、上記混合溶液の液温を４０℃未満とすると、銀イオン含有溶液に含むゼラチンの粘度が高くなり、銀イオン含有溶液の分散状態を良好に保てなくなる。一方、混合溶液の液温が６０℃を超えると、還元剤含有溶液との反応速度が増し、析出粒子の粒径混合溶液の分散状態を良好な状態に保てなくなる。従って、前記混合溶液の液温が４０℃〜６０℃の範囲に保たれることにより、反応速度を好適な状態に制御することができ、製造安定性を向上させ、析出する粒子の粒径を目的とする微粒レベル（Ｄ５０値が５μｍ前後）とすることが容易となるのである。 Furthermore, it is more preferable to perform contact mixing so that the liquid temperature of the mixed solution of the silver ion-containing solution and the reducing agent-containing solution is maintained at 40 ° C to 60 ° C. Here, when the liquid temperature of the mixed solution is less than 40 ° C., the viscosity of gelatin contained in the silver ion-containing solution becomes high, and the dispersion state of the silver ion-containing solution cannot be maintained well. On the other hand, when the liquid temperature of the mixed solution exceeds 60 ° C., the reaction rate with the reducing agent-containing solution increases, and the dispersed state of the mixed solution of precipitated particles cannot be maintained in a good state. Therefore, by maintaining the liquid temperature of the mixed solution in the range of 40 ° C. to 60 ° C., the reaction rate can be controlled to a suitable state, the production stability is improved, and the particle size of the precipitated particles is increased. This makes it easy to achieve the target fine particle level (D 50 value is around 5 μm).
以上のようにして、銀イオン含有溶液と還元剤含有溶液とを接触混合した以降は、速やかに混合溶液を撹拌して、混合溶液内における銀イオンと還元剤との偏在を解消するのである。そして、還元反応の起こっている混合液の撹拌は、そのまま継続して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。 As described above, after the silver ion-containing solution and the reducing agent-containing solution are contact-mixed, the mixed solution is rapidly stirred to eliminate the uneven distribution of silver ions and the reducing agent in the mixed solution. And it is preferable to continue stirring of the liquid mixture which has undergone the reduction reaction as it is. 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.
還元反応終了後は、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、洗浄工程を経て銀粉を得る。 After completion of the reduction reaction, the particles are settled in the same manner as in the conventional wet reduction method, the supernatant is removed, and silver powder is obtained through filtration and washing steps.
＜銀粉の形態＞
本発明に係る湿式還元法を用いて製造された銀粉は、粉末法Ｘ線解析分析により得られる結晶子径が５４０Å〜６００Åであり、結晶子径が大きいので、焼結温度の高温化を図ることができる。
<Form of silver powder>
The silver powder produced using the wet reduction method according to the present invention has a crystallite diameter of 540 to 600 mm obtained by powder method X-ray analysis analysis and a large crystallite diameter, so that the sintering temperature is increased. be able to.
また、本発明に係る銀粉の焼結開始温度は４５０℃〜５５０℃である。焼結開始温度が当該範囲の銀粉は、上述の通り、ガラス基板上に回路形成する場合等の用途に好適である。 Moreover, the sintering start temperature of the silver powder according to the present invention is 450 ° C to 550 ° C. As described above, the silver powder having a sintering start temperature in the above range is suitable for applications such as when a circuit is formed on a glass substrate.
加えて、前記銀粉は、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について、以下の特徴を示す。まず、Ｄ５０値が４μｍ〜６μｍである。これは従来の湿式法により得られる銀粉では難しかったＤ５０値が５μｍ前後の銀粉であり、このようなＤ５０値が５μｍ前後の粒径の銀粉を導電性ペーストに用いると、５００℃付近での焼成により形成された導体の形状安定性に貢献できる。 In addition, the said silver powder shows the following characteristics about the volume cumulative particle diameter by the laser diffraction scattering type particle size distribution measuring method. First, the D 50 value is 4 μm to 6 μm. This is a silver powder having a D 50 value of around 5 μm, which was difficult with a silver powder obtained by a conventional wet method, and when such a D 50 value of silver powder having a particle size of around 5 μm is used as a conductive paste, the D 50 value is around 500 ° C. This contributes to the shape stability of the conductor formed by firing.
更に、Ｄ１０値については３μｍ以下である。Ｄ５０値が４μｍ〜６μｍであり、かつ、Ｄ１０値が３μｍ以下である銀粉は、粒径が揃った非常にシャープな粒度分布を備えるものであると言える。 Furthermore, it is 3μm or less for D 10 value. It can be said that the silver powder having a D 50 value of 4 μm to 6 μm and a D 10 value of 3 μm or less has a very sharp particle size distribution with a uniform particle size.
また、前記銀粉の粒度分布の幅は、レーザー回折散乱式粒度分布測定法による９０％体積累積粒径Ｄ９０値（以下、「Ｄ９０値」と記す。）並びに粒径Ｄ５０とを用いたＤ９０値／Ｄ１０値により表すことができる。このＤ９０値／Ｄ１０値が小さい程に粒度分布の幅が狭いと言える。そして、本発明に係る銀粉は、Ｄ９０値／Ｄ１０値≦３．０を満足するものが好ましい。Ｄ９０値／Ｄ１０値≦３．０であると、粗大粒子や凝集塊が非常に少なく、粒度分布の幅が狭い銀粉であると言える。 The width of the particle size distribution of the silver powder was 90% volume cumulative particle size D 90 value (hereinafter referred to as “D 90 value”) and particle size D 50 as measured by a laser diffraction scattering particle size distribution measurement method. it can be represented by D 90 value / D 10 value. The width of the particle size distribution to the extent this D 90 value / D 10 value is small it can be said that narrow. The silver powder according to the present invention preferably satisfies D 90 value / D 10 value ≦ 3.0. When D 90 value / D 10 value ≦ 3.0, it can be said that the silver powder has a very small number of coarse particles and aggregates and a narrow particle size distribution.
更に、本発明に係る銀粉は、比表面積（ＳＳＡ）は０．２ｍ２／ｇ以下である。比表面積が０．２ｍ２／ｇ以下であれば、表面が平滑であり、ペーストに加工したときのペースト粘度の低減化が可能となるのである。 Furthermore, the silver powder according to the present invention has a specific surface area (SSA) of 0.2 m 2 / g or less. When the specific surface area is 0.2 m 2 / g or less, the surface is smooth and the paste viscosity when processed into a paste can be reduced.
以上、説明したように、本発明に係る銀粉は、Ｄ５０値が５μｍ前後で、微粒が少なく、粒度分布が非常にシャープで、かつ、粒子分散性に優れた銀粉である。 As described above, the silver powder according to the present invention is a silver powder having a D 50 value of around 5 μm, few fine particles, a very sharp particle size distribution, and excellent particle dispersibility.
上述のような特性を備える銀粉を用いて導電性インク等に加工し、導体膜形成を行い焼成すると、ペーストのコンテントが上げられるので、ペーストの組成物である樹脂等の溶媒量を減らすことができ、ペーストの粘度調節が容易となる。この結果、当該銀粉を用いたペーストにより形成された回路の抵抗を低くすることができる。しかも、低温焼結性に優れ、５００℃前後の加熱により粒子同士が連結する焼成が可能であるため、粒径のバラツキ及び粒子の凝集に起因した導体膜表面の粗れを抑制でき、表面状態が均質な焼結体（導電膜）を形成することができ、当該温度域における導電性に優れた低抵抗の導体膜の形成に好適である。 When the silver powder having the characteristics as described above is processed into a conductive ink or the like, and the conductor film is formed and baked, the content of the paste is raised, so that the amount of the solvent such as a resin as a paste composition can be reduced. The viscosity of the paste can be easily adjusted. As a result, the resistance of the circuit formed by the paste using the silver powder can be reduced. Moreover, since it is excellent in low-temperature sinterability and can be fired in which particles are connected by heating at around 500 ° C., it is possible to suppress the roughness of the conductor film surface due to particle size variation and particle aggregation, and the surface state Can form a homogeneous sintered body (conductive film), and is suitable for forming a low-resistance conductor film excellent in conductivity in the temperature range.
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。しかし、本発明は以下の実施例に制限されるものではない。なお、以下の実施例及び比較例における銀粉の製造条件の概略を一覧にして表１に掲載する。 Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. However, the present invention is not limited to the following examples. In addition, the outline of the manufacturing conditions of the silver powder in the following Examples and Comparative Examples is listed and listed in Table 1.
実施例１では、銀イオン含有溶液として、硝酸銀５０ｋｇ、ゼラチン１ｋｇ、硝酸２６．４ｋｇ、亜硝酸銀２００ｇを純水２５０Ｌに入れ、５０℃まで溶解させ、撹拌した硝酸銀水溶液を用いた。還元剤含有溶液は、アスコルビン酸２６．４ｋｇを純水２５０Ｌに溶解させたものを用いた。銀イオン含有溶液（硝酸銀水溶液）に、上記還元剤含有溶液を、連続的に３０分かけて添加する。この工程において、混合溶液の液温を５０℃に保つ。添加終了後、１０分間撹拌して熟成させる。その後、粒子を沈降させた上澄みを抜き、濾過、洗浄、乾燥することによって銀粉を得た。 In Example 1, as a silver ion-containing solution, 50 kg of silver nitrate, 1 kg of gelatin, 26.4 kg of nitric acid, and 200 g of silver nitrite were put in 250 L of pure water, dissolved to 50 ° C., and a stirred silver nitrate aqueous solution was used. As the reducing agent-containing solution, a solution obtained by dissolving 26.4 kg of ascorbic acid in 250 L of pure water was used. The reducing agent-containing solution is continuously added to the silver ion-containing solution (silver nitrate aqueous solution) over 30 minutes. In this step, the liquid temperature of the mixed solution is maintained at 50 ° C. After the addition is complete, stir for 10 minutes. Thereafter, the supernatant on which the particles were settled was taken out, filtered, washed and dried to obtain silver powder.
なお、上記銀イオン含有溶液の銀濃度は０．５７ｍｏｌ／ｌとなり、この銀の当量に対して、アスコルビン酸の使用量は、１．０倍当量となる。 In addition, the silver concentration of the said silver ion containing solution will be 0.57 mol / l, and the usage-amount of ascorbic acid will be 1.0 time equivalent with respect to the equivalent of this silver.
こうして得られた銀粉について、結晶子径、Ｄ１０値、Ｄ５０値、Ｄ９０値、Ｄｍａｘ値（レーザー回折散乱式粒度分布測定法による体積累積最大粒径）、Ｄ９０値／Ｄ１０値、（Ｄ９０値−Ｄ１０値）／Ｄ５０値、比表面積（ＳＳＡ）、タップ充填密度（Ｔ．Ｄ）を測定した。これら諸特性の測定方法を以下に示す。 For the silver powder thus obtained, the crystallite diameter, D 10 value, D 50 value, D 90 value, D max value (volume cumulative maximum particle diameter by laser diffraction scattering type particle size distribution measurement method), D 90 value / D 10 value. , (D 90 value−D 10 value) / D 50 value, specific surface area (SSA), tap packing density (TD) were measured. The measuring method of these characteristics is shown below.
結晶子径は株式会社リガク製のＲＩＮＴ２０００を用い、測定角度２０／２θ〜１００／２θの条件で測定した。また、粒度分布を評価するため、レーザー回折散乱式粒度分布測定装置であるＭｉｃｒｏ Ｔｒａｃ ＨＲＡ９３２０−Ｘ１００型（Ｌｅｅｄｓ＋Ｎｏｒｔｈｒｕｐ社製）を用いて、Ｄ１０値、Ｄ５０値、Ｄ９０値、Ｄｍａｘ値を測定した（銀粉０．１ｇをＳＮディスパーサント５４６８の０．１％水溶液（サンノプコ社製）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分間分散させた試料を使用）。この測定値を用いて、Ｄ９０値／Ｄ１０値、（Ｄ９０値−Ｄ１０値）／Ｄ５０値を算出した。そして、タップ密度（Ｔ．Ｄ）をホソカワミクロン製パウダーテスターＰＴ−Ｅ型にて測定し、比表面積（ＳＳＡ）を島津−マイクロメリッテクス製２２００型ＢＥＴ計にて測定した。更に、セイコーインスツルメンツ社製の熱機械分析装置（ＴＭＡ装置）であるＴＭＡ／ＳＳ６０００を用いて焼結開始温度を調べた。 The crystallite diameter was measured using RINT2000 manufactured by Rigaku Corporation under the conditions of a measurement angle of 20 / 2θ to 100 / 2θ. Further, in order to evaluate the particle size distribution, using a Micro Trac HRA9320-X100 type is a laser diffraction scattering particle size distribution analyzer (Leeds + Northrup Co.), D 10 value, D 50 value, D 90 value, the D max value Measurement was performed (0.1 g of silver powder was mixed with a 0.1% aqueous solution of SN Dispersant 5468 (manufactured by Sannopco) and dispersed with an ultrasonic homogenizer (US-300T, manufactured by Nippon Seiki Seisakusho Co., Ltd.) for 5 minutes). Using this measured value, D 90 value / D 10 value and (D 90 value−D 10 value) / D 50 value were calculated. Then, the tap density (TD) was measured with a powder tester PT-E type manufactured by Hosokawa Micron, and the specific surface area (SSA) was measured with a 2200 type BET meter manufactured by Shimadzu-Micromeritics. Furthermore, the sintering start temperature was investigated using TMA / SS6000 which is a thermomechanical analyzer (TMA apparatus) manufactured by Seiko Instruments Inc.
実施例１で得られた銀粉の走査型電子顕微鏡像を図１に示し、諸特性の評価結果については表２に示す。図１を見ると、実施例１の銀粉は、表面が滑らかな多面形状の粒子が見られ、目視による粒径が５μｍ程度の大きさで揃っていることが分かる。また、粒子の凝集がほとんど見られないことも特徴である。 A scanning electron microscope image of the silver powder obtained in Example 1 is shown in FIG. 1, and the evaluation results of various properties are shown in Table 2. When FIG. 1 is seen, it turns out that the silver powder of Example 1 has the smooth surface and the multi-sided-shaped particle | grains are seen, and the particle diameter by visual observation has a uniform size of about 5 micrometers. Another feature is that the particles are hardly aggregated.
実施例２は実施例１と比べ、銀イオン含有溶液における亜硝酸銀量が異なる。即ち、実施例１の亜硝酸銀量が２００ｇであるのに対し、亜硝酸銀量が１００ｇである点が異なり、この亜硝酸銀量以外の条件は全て実施例１と同じであるので製造方法の説明を省略する。 Example 2 differs from Example 1 in the amount of silver nitrite in the silver ion-containing solution. That is, the amount of silver nitrite in Example 1 is 200 g, whereas the amount of silver nitrite is 100 g. The conditions other than this amount of silver nitrite are all the same as in Example 1, so the explanation of the production method is as follows. Omitted.
実施例２で得られた銀粉の走査型電子顕微鏡像を図２に示す。図２を見ると、表面が滑らかな多面体形状の粒子が形成され、実施例１に比べると目視による粒径が小さくなるものの、大きさが揃っていることが分かる。 A scanning electron microscope image of the silver powder obtained in Example 2 is shown in FIG. When FIG. 2 is seen, although the surface of a polyhedron shape particle | grains with a smooth surface is formed, although the particle size by visual observation becomes small compared with Example 1, it turns out that the magnitude | size is equal.
実施例３は、銀イオン含有溶液における亜硝酸銀量を２５ｇとする以外の条件は、実施例１と全て同じである。従って、製造方法についての説明を省略する。 Example 3 is the same as Example 1 except that the amount of silver nitrite in the silver ion-containing solution is 25 g. Therefore, the description about the manufacturing method is omitted.
実施例３で得られた銀粉の走査型電子顕微鏡像を図３に示す。図３を見ると、実施例１及び実施例２に比べると大きさが小さくなるものの、大きさが揃っていることが確認できる。いずれの実施例においても、表２に示す粒度分布が非常にシャープであることからも言える。 A scanning electron microscope image of the silver powder obtained in Example 3 is shown in FIG. When FIG. 3 is seen, although a magnitude | size becomes small compared with Example 1 and Example 2, it can confirm that the magnitude | size is equal. In any of the examples, it can be said that the particle size distribution shown in Table 2 is very sharp.
［比較例１］
比較例１では、従来の湿式還元法を用いて銀粉を製造した。即ち、銀イオン含有溶液として、硝酸銀５ｋｇを純水２５Ｌに溶かした溶液にアンモニア水１０Ｌを溶かして１６℃まで冷却したものを用い、還元剤含有溶液はヒドロキノン１．６ｋｇを純水２００Ｌに溶解させ、１６℃まで冷却したものを用いた。この銀イオン含有溶液と還元剤含有溶液とを一括して接触混合して５分間撹拌した後、粒子を沈降させ上澄みを抜き、濾過、洗浄、乾燥することによって銀粉を得た。比較例１で得られた銀粉の走査型電子顕微鏡像を図４に示す。比較例１の銀粉は、相当微粒かつ分散性に優れており、湿式還元法により得られる従来の銀粉の特徴を示している例である。
[Comparative Example 1]
In Comparative Example 1, silver powder was produced using a conventional wet reduction method. That is, as a silver ion-containing solution, a solution obtained by dissolving 5 L of silver nitrate in 25 L of pure water and dissolving 10 L of ammonia water and cooling to 16 ° C., the reducing agent-containing solution dissolves 1.6 kg of hydroquinone in 200 L of pure water. What was cooled to 16 degreeC was used. The silver ion-containing solution and the reducing agent-containing solution were collectively contact-mixed and stirred for 5 minutes, and then the particles were settled, the supernatant was removed, and silver powder was obtained by filtering, washing and drying. A scanning electron microscope image of the silver powder obtained in Comparative Example 1 is shown in FIG. The silver powder of the comparative example 1 is an example which shows the characteristic of the conventional silver powder obtained by the wet reduction method, which is considerably fine and excellent in dispersibility.
［比較例２］
比較例２は、特許文献４に示す銀粉をトレースした例であり、アスコルビン酸を３０分掛けて添加した例である。まず、銀イオン含有溶液として、硝酸銀５０ｋｇ、ゼラチン１ｋｇ、硝酸２６．４ｋｇを純水２５０Ｌに入れ、５０℃で溶解させ、撹拌した硝酸銀水溶液を用いた。還元剤含有溶液は、アスコルビン酸２６．４ｋｇを純水２５０Ｌに溶解させたものを用いた。銀イオン含有溶液（硝酸銀水溶液）に、上記還元剤含有溶液を、連続的に３０分かけて添加する。この工程において、混合溶液の液温を５０℃に保つ。添加終了後、１０分間撹拌して熟成させる。その後、粒子を沈降させた上澄みを抜き、濾過、洗浄、乾燥することによって銀粉を得た。即ち、比較例２は、実施例１〜実施例３と比べ、銀イオン含有溶液に亜硝酸イオン（亜硝酸銀）を含まない点が異なる。
[Comparative Example 2]
Comparative Example 2 is an example in which the silver powder shown in Patent Document 4 is traced, and ascorbic acid is added over 30 minutes. First, as a silver ion-containing solution, 50 kg of silver nitrate, 1 kg of gelatin, and 26.4 kg of nitric acid were put in 250 L of pure water, dissolved at 50 ° C., and a stirred silver nitrate aqueous solution was used. As the reducing agent-containing solution, a solution obtained by dissolving 26.4 kg of ascorbic acid in 250 L of pure water was used. The reducing agent-containing solution is continuously added to the silver ion-containing solution (silver nitrate aqueous solution) over 30 minutes. In this step, the liquid temperature of the mixed solution is maintained at 50 ° C. After the addition is complete, stir for 10 minutes. Thereafter, the supernatant on which the particles were settled was taken out, filtered, washed and dried to obtain silver powder. That is, Comparative Example 2 is different from Examples 1 to 3 in that the silver ion-containing solution does not contain nitrite ions (silver nitrite).
［比較例３］
比較例３では、噴霧熱分解還元法を用いて銀粉を製造した。即ち、硝酸銀１１０ｇをるつぼに入れ、電気加熱で３１５℃にした後、二流体ノズル（ＳＵＳ製）にキャリアガスとしてアルゴンガスを用い、キャリアガス圧力５ｋｇ／ｃｍ２、流速１０ｌ／ｍｉｎの条件で硝酸銀を噴霧し、１１００℃に加熱された石英管に導入した。熱分解後の銀粉末はサイクロンにより捕集した。
[Comparative Example 3]
In Comparative Example 3, silver powder was produced using a spray pyrolysis reduction method. That is, 110 g of silver nitrate is put in a crucible and heated to 315 ° C. by electric heating. Then, argon gas is used as a carrier gas in a two-fluid nozzle (manufactured by SUS), and the silver nitrate is used under the conditions of a carrier gas pressure of 5 kg / cm 2 and a flow rate of 10 l / min. Was sprayed and introduced into a quartz tube heated to 1100 ° C. The silver powder after pyrolysis was collected by a cyclone.
比較例３で得られた銀粉の走査型電子顕微鏡像を図５に示す。図５を見ても分かるように、比較例３の銀粉は凝集した粒子が多く見られ、粒径が不揃いである。 A scanning electron microscope image of the silver powder obtained in Comparative Example 3 is shown in FIG. As can be seen from FIG. 5, the silver powder of Comparative Example 3 has many agglomerated particles, and the particle sizes are not uniform.
[実施例と比較例の対比]
表２から明らかなように、実施例の銀粉は、Ｄ５０値が５μｍ程度であり、Ｄ９０値／Ｄ１０値や（Ｄ９０値−Ｄ１０値）／Ｄ５０値が小さく、シャープな粒度分布を呈していることから、比較的粒径大なる銀粉でありながら、回路形成用途に用いた際の回路の平滑性や形状安定性に優れた原材料として好適である。また、焼結開始温度が４００℃台で、かつ、結晶子径がほぼ６００Å近傍と大きいことにより、耐収縮性等、熱的な影響も受けにくく、５００℃程度の焼結温度でガラス基板上に回路形成するような用途に好適である。また、比較的粒径大、かつ比表面積も小さく、粒子表面の平滑性も高いことがうかがえることから、ペースト化した際の増粘等も抑制できる。
[Contrast between Example and Comparative Example]
As is clear from Table 2, the silver powder of the example has a D 50 value of about 5 μm, a small D 90 value / D 10 value or (D 90 value−D 10 value) / D 50 value, and a sharp particle size. Since it exhibits a distribution, it is suitable as a raw material excellent in circuit smoothness and shape stability when used for circuit formation, although it is a silver powder having a relatively large particle size. In addition, since the sintering start temperature is in the range of about 400 ° C. and the crystallite diameter is as large as about 600 mm, it is hardly affected by thermal effects such as shrinkage resistance. It is suitable for applications such as circuit formation. Further, since it can be seen that the particle size is relatively large, the specific surface area is small, and the smoothness of the particle surface is high, it is possible to suppress thickening and the like when it is made into a paste.
これに対し、比較例１の銀粉は粒度分布がシャープであるものの、Ｄ５０値が小さく、５００℃程度の焼結温度で用いるには不適であり、充填性の面（タップ密度小）、耐収縮性の面（結晶子径小）、ペースト化した際の増粘性の面等でも劣ることが予測される。 On the other hand, the silver powder of Comparative Example 1 has a sharp particle size distribution, but has a small D50 value and is unsuitable for use at a sintering temperature of about 500 ° C. It is expected that the shrinkable surface (crystallite diameter is small), the surface of thickening when made into a paste, and the like are also inferior.
また、比較例２の銀粉は、粒径（Ｄ５０値）が小さいながら、５００℃程度の焼結温度で用いることも可能な特性（焼結開始温度４００℃台、結晶子径５００Å超）を有するものである。しかし、粒径（Ｄ５０値）が小さく、粒度分布がブロードであり、凝集の程度で実施例より劣り、本発明の目的とする比較的粒度の大きな粒子からなる銀粉ではないのみならず、ペースト化した際の増粘等が生じやすいものと予測される。 Further, the silver powder of Comparative Example 2 has characteristics (sintering start temperature range of about 400 ° C., crystallite diameter of more than 500 mm) that can be used at a sintering temperature of about 500 ° C. while the particle size (D 50 value) is small. It is what you have. However, the particle size (D 50 value) is small, a particle size distribution broad, inferior than Example in the degree of aggregation, not only is not a silver powder of relatively size large particles is an object of the present invention, the paste It is predicted that thickening and the like are likely to occur.
また、比較例３の銀粉は、粒径（Ｄ５０値）が５μｍ程度であり、結晶子径が大きく、耐収縮性等、熱的な影響を受けにくいものである。しかし、粒度分布がかなりブロードであり、回路形成用途に用いた際の回路の平滑性や形状安定性に劣るものと予測される。また、焼結開始温度が高く５００℃程度では焼結しない為、５００℃程度の焼結温度が求められる用途では不適である。 Further, silver powder of Comparative Example 3 is about 5μm particle size (D 50 value), the crystallite diameter is large, but less prone resistance shrinkage or the like, a thermal effect. However, the particle size distribution is quite broad, and it is predicted that the circuit is inferior in smoothness and shape stability when used for circuit formation. In addition, since the sintering start temperature is high and sintering is not performed at about 500 ° C., it is not suitable for applications requiring a sintering temperature of about 500 ° C.
従来の湿式還元法では得られなかったＤ５０値が５μｍ前後の銀粉を製造可能としたことにより、分散性に優れ、焼結特性を改善した優れた銀粉を得ることができる。また、表面形状が滑らかな銀粉とすることにより、当該銀粉をペースト材料として用いた場合の、充填密度を高めることができる。更に、アトマイズ法による銀粉で必要となる分級を行う必要がないので、アトマイズ法と比べて製造コストを抑えることができる。従って、本発明に係る銀粉を用いた導電性インクまたは導電性ペースト等をフラットディスプレイパネルのガラス基板形成に用いると、ガラス基板上に導体形成する際の焼結温度との整合性を有し、寸法安定性に優れ、導電性が高く、高性能なフラットディスプレイパネルの製造コスト低減に貢献することができる。 By making it possible to produce silver powder having a D 50 value of around 5 μm, which could not be obtained by the conventional wet reduction method, it is possible to obtain excellent silver powder with excellent dispersibility and improved sintering characteristics. Moreover, by using silver powder having a smooth surface shape, the packing density when the silver powder is used as a paste material can be increased. Furthermore, since it is not necessary to perform the classification required for the silver powder by the atomizing method, the manufacturing cost can be suppressed as compared with the atomizing method. Therefore, when using conductive ink or conductive paste using silver powder according to the present invention for forming a glass substrate of a flat display panel, it has consistency with the sintering temperature when a conductor is formed on the glass substrate, It is excellent in dimensional stability, has high conductivity, and can contribute to a reduction in manufacturing cost of a high performance flat display panel.
Claims (11)
前記銀イオン含有溶液は硝酸銀と亜硝酸イオンとを含み、
前記還元剤含有溶液はアスコルビン酸またはアスコルビン酸の異性体のいずれか１種以上からなる還元剤を水に溶解させたものを用い、
還元剤含有溶液を銀イオン含有溶液に対して添加することを特徴とする銀粉の製造方法。 A method for producing silver powder in which a silver ion-containing solution and a reducing agent-containing solution are contact-mixed,
The silver ion-containing solution contains silver nitrate and nitrite ions,
The reducing agent-containing solution is a solution obtained by dissolving a reducing agent consisting of at least one of ascorbic acid or an isomer of ascorbic acid in water,
A method for producing silver powder, comprising adding a reducing agent-containing solution to a silver ion-containing solution .
粉末法Ｘ線解析分析により得られる結晶子径が５４０Å〜６００Åであることを特徴とする銀粉。 A silver powder produced by the production method according to claim 1,
A silver powder having a crystallite diameter of 540 to 600 mm obtained by powder method X-ray analysis.
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