JP2007270312A - Method for manufacturing silver powder, and silver powder - Google Patents
Method for manufacturing silver powder, and silver powder Download PDFInfo
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- JP2007270312A JP2007270312A JP2006100229A JP2006100229A JP2007270312A JP 2007270312 A JP2007270312 A JP 2007270312A JP 2006100229 A JP2006100229 A JP 2006100229A JP 2006100229 A JP2006100229 A JP 2006100229A JP 2007270312 A JP2007270312 A JP 2007270312A
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- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 title claims abstract description 175
- 238000000034 method Methods 0.000 title claims abstract description 56
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 52
- 239000003638 chemical reducing agent Substances 0.000 claims abstract description 58
- FOIXSVOLVBLSDH-UHFFFAOYSA-N Silver ion Chemical compound [Ag+] FOIXSVOLVBLSDH-UHFFFAOYSA-N 0.000 claims abstract description 54
- SQGYOTSLMSWVJD-UHFFFAOYSA-N silver(1+) nitrate Chemical compound [Ag+].[O-]N(=O)=O SQGYOTSLMSWVJD-UHFFFAOYSA-N 0.000 claims abstract description 36
- 230000009467 reduction Effects 0.000 claims abstract description 32
- CIWBSHSKHKDKBQ-JLAZNSOCSA-N Ascorbic acid Chemical compound OC[C@H](O)[C@H]1OC(=O)C(O)=C1O CIWBSHSKHKDKBQ-JLAZNSOCSA-N 0.000 claims abstract description 20
- 229910001961 silver nitrate Inorganic materials 0.000 claims abstract description 18
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 15
- 235000010323 ascorbic acid Nutrition 0.000 claims abstract description 10
- 229960005070 ascorbic acid Drugs 0.000 claims abstract description 10
- 239000011668 ascorbic acid Substances 0.000 claims abstract description 10
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 claims abstract description 7
- LSNNMFCWUKXFEE-UHFFFAOYSA-N Sulfurous acid Chemical compound OS(O)=O LSNNMFCWUKXFEE-UHFFFAOYSA-N 0.000 claims abstract description 6
- 239000002245 particle Substances 0.000 claims description 100
- 229910052709 silver Inorganic materials 0.000 claims description 46
- 239000004332 silver Substances 0.000 claims description 46
- 238000005245 sintering Methods 0.000 claims description 22
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims description 17
- 238000001000 micrograph Methods 0.000 claims description 15
- 238000009826 distribution Methods 0.000 claims description 14
- 239000011164 primary particle Substances 0.000 claims description 13
- QIGBRXMKCJKVMJ-UHFFFAOYSA-N Hydroquinone Chemical compound OC1=CC=C(O)C=C1 QIGBRXMKCJKVMJ-UHFFFAOYSA-N 0.000 claims description 12
- 108010010803 Gelatin Proteins 0.000 claims description 8
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims description 8
- 229910021529 ammonia Inorganic materials 0.000 claims description 8
- 229920000159 gelatin Polymers 0.000 claims description 8
- 239000008273 gelatin Substances 0.000 claims description 8
- 235000019322 gelatine Nutrition 0.000 claims description 8
- 235000011852 gelatine desserts Nutrition 0.000 claims description 8
- 229910017604 nitric acid Inorganic materials 0.000 claims description 8
- GEHJYWRUCIMESM-UHFFFAOYSA-L sodium sulfite Chemical compound [Na+].[Na+].[O-]S([O-])=O GEHJYWRUCIMESM-UHFFFAOYSA-L 0.000 claims description 6
- 235000003891 ferrous sulphate Nutrition 0.000 claims description 5
- 239000011790 ferrous sulphate Substances 0.000 claims description 5
- 238000010191 image analysis Methods 0.000 claims description 5
- BAUYGSIQEAFULO-UHFFFAOYSA-L iron(2+) sulfate (anhydrous) Chemical compound [Fe+2].[O-]S([O-])(=O)=O BAUYGSIQEAFULO-UHFFFAOYSA-L 0.000 claims description 5
- 229910000359 iron(II) sulfate Inorganic materials 0.000 claims description 5
- BHZRJJOHZFYXTO-UHFFFAOYSA-L potassium sulfite Chemical compound [K+].[K+].[O-]S([O-])=O BHZRJJOHZFYXTO-UHFFFAOYSA-L 0.000 claims description 5
- 235000019252 potassium sulphite Nutrition 0.000 claims description 5
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 claims description 4
- 235000011114 ammonium hydroxide Nutrition 0.000 claims description 4
- PQUCIEFHOVEZAU-UHFFFAOYSA-N Diammonium sulfite Chemical compound [NH4+].[NH4+].[O-]S([O-])=O PQUCIEFHOVEZAU-UHFFFAOYSA-N 0.000 claims description 3
- 235000010265 sodium sulphite Nutrition 0.000 claims description 3
- LSNNMFCWUKXFEE-UHFFFAOYSA-L sulfite Chemical class [O-]S([O-])=O LSNNMFCWUKXFEE-UHFFFAOYSA-L 0.000 claims description 3
- 238000002156 mixing Methods 0.000 abstract description 8
- 230000008569 process Effects 0.000 abstract description 8
- 238000009766 low-temperature sintering Methods 0.000 abstract description 4
- 239000000243 solution Substances 0.000 description 96
- 238000006722 reduction reaction Methods 0.000 description 31
- 230000000052 comparative effect Effects 0.000 description 21
- 239000004020 conductor Substances 0.000 description 16
- 239000000843 powder Substances 0.000 description 16
- 239000000758 substrate Substances 0.000 description 16
- 239000011521 glass Substances 0.000 description 12
- 230000002829 reductive effect Effects 0.000 description 12
- 239000007864 aqueous solution Substances 0.000 description 11
- 238000001556 precipitation Methods 0.000 description 11
- -1 silver ions Chemical class 0.000 description 9
- 238000006243 chemical reaction Methods 0.000 description 8
- 239000010419 fine particle Substances 0.000 description 8
- 238000009499 grossing Methods 0.000 description 8
- 238000010304 firing Methods 0.000 description 7
- 230000015572 biosynthetic process Effects 0.000 description 6
- 230000002776 aggregation Effects 0.000 description 5
- 238000010438 heat treatment Methods 0.000 description 5
- 239000000463 material Substances 0.000 description 5
- 239000011259 mixed solution Substances 0.000 description 5
- 239000006228 supernatant Substances 0.000 description 5
- 238000004220 aggregation Methods 0.000 description 4
- 230000008901 benefit Effects 0.000 description 4
- 229910052751 metal Inorganic materials 0.000 description 4
- 239000002184 metal Substances 0.000 description 4
- 238000012856 packing Methods 0.000 description 4
- 239000013078 crystal Substances 0.000 description 3
- 239000006185 dispersion Substances 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 239000007788 liquid Substances 0.000 description 3
- 239000002244 precipitate Substances 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- 239000012159 carrier gas Substances 0.000 description 2
- 238000001816 cooling Methods 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
- 239000000203 mixture Substances 0.000 description 2
- 230000001376 precipitating effect Effects 0.000 description 2
- 239000000047 product Substances 0.000 description 2
- 150000003378 silver Chemical class 0.000 description 2
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 238000005054 agglomeration Methods 0.000 description 1
- 230000004931 aggregating effect Effects 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- 239000012298 atmosphere Substances 0.000 description 1
- 238000000889 atomisation Methods 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 239000013522 chelant Substances 0.000 description 1
- 239000002738 chelating agent Substances 0.000 description 1
- 230000009920 chelation Effects 0.000 description 1
- 239000011362 coarse particle Substances 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 239000002270 dispersing agent Substances 0.000 description 1
- 238000005485 electric heating Methods 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 239000000835 fiber Substances 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 239000012530 fluid Substances 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- 230000001788 irregular Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 239000000155 melt Substances 0.000 description 1
- YPJKMVATUPSWOH-UHFFFAOYSA-N nitrooxidanyl Chemical compound [O][N+]([O-])=O YPJKMVATUPSWOH-UHFFFAOYSA-N 0.000 description 1
- 239000011148 porous material Substances 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
- 239000002994 raw material Substances 0.000 description 1
- 238000001953 recrystallisation Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 230000000930 thermomechanical effect Effects 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
Abstract
Description
湿式還元法を用いた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 using a wet reduction method and silver powder.
銀粉は、電子機器の配線回路、電極等に用いられるセラミック部品（基板）の電極・配線用材料、フラットディスプレイパネルの導体等の形成に導電性インクまたは導電性ペースト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、微細且つ高密度な配線回路の形成に対応する為、一定の分散性を持ち、且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が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、アトマイズ粉の微粒レベルのものが使用されてきた。 Silver powder is used as a conductive ink or conductive paste for forming electrodes and wiring materials for ceramic parts (substrates) used for wiring circuits of electronic equipment, electrodes, etc., conductors of flat display panels, and the like. With the downsizing of electronic parts and the like and the fine lines of substrates, in order to cope with the formation of fine and high-density wiring circuits, it is required to have a certain dispersibility and to have a certain degree of fineness. 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 fire at around 500 ° C. to form a conductor circuit or an electrode. 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 thing of the fine particle level of atomized powder 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、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には、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には、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。 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 are converted into fine particles having a narrow particle size distribution by a classification operation using a precision sieve. 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 to form droplets, and the particle size is reduced by thermally decomposing the droplets. A technique for producing silver powder having a size of 2 μm to 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 silver powder having fine and high dispersibility and a method for producing the same are disclosed.
フラットディスプレイパネルのパネル等の製造において、ガラス基板上に導体を形成する為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、アトマイズ法により得られる平均粒径が５μｍ前後の高分散性アトマイズ粉が一般的に利用されている。アトマイズ法で製造した銀粉は、粒子径が１０μｍ〜数十μｍの粗粒域の量産性に優れているが、５μｍ程度の微粒域を直接製造することは困難であるため、分級により５μｍ前後の粒径の銀粉を得ている。従って、製造コストが高くなる点が難点である。また、アトマイズ粉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。 In the manufacture of flat display panel panels, etc., silver powder, which is a conductive ink or conductive paste material for forming conductors on glass substrates, has a high dispersibility with an average particle size of about 5 μm obtained by the atomization method. Atomized powder is generally used. The silver powder produced by the atomizing method is excellent in mass productivity in a coarse particle region having a particle diameter of 10 μm to several tens of μm, but it is difficult to directly produce a fine particle region of about 5 μm. Obtained silver powder of particle size. Therefore, the manufacturing cost is high. Atomized powder also has good heat shrinkage due to the characteristics of the crystal structure of the particles due to the thermal history up to the melting point due to the characteristics of the manufacturing process, but good low temperature sintering characteristics can be obtained even when atomized. However, heating at least at 800 ° C. or more is required.
一方、湿式法により得られる銀粉は低温焼結特性に優れ、更に微粒且つ分散性に優れている。しかし、湿式法により得られる銀粉は、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、粒径３μｍ以下の製品が一般的に製造されている。ここで、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すぎるため、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。 On the other hand, silver powder obtained by a wet method is excellent in low-temperature sintering characteristics, and further excellent in fine particles and dispersibility. However, since silver powder obtained by a wet method could not stably produce a product having a particle size exceeding 3 μm, a product having a particle size of 3 μm or less is generally produced. Here, in applications such as when a circuit is formed on a glass substrate, sintering at around 500 ° C. is required. 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 unsuitable for forming a fine pitch circuit.
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及び銀粉の製造方法が望まれてきた。 For these reasons, there has been a demand for a silver powder and a method for producing silver powder that ensure low temperature sinterability and electrical conductivity of about 500 ° C. and have excellent conductor shape stability after firing.
そこで、本発明者等は、鋭意研究を行った結果、湿式還元法を用いた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 using a wet reduction method.
本件発明に係る銀粉の製造方法： 即ち、本件発明に係る銀粉の湿式製造方法は、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を含み、前記還元剤含有溶液はアスコルビン酸、アスコルビン酸の異性体、還元能を備えた硫酸塩、還元能を備えた亜硫酸塩の群から選ばれたいずれか一種以上を水に溶解させたものを含むことを特徴とする。 Silver powder production method according to the present invention: That is, the silver powder wet 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, The silver ion-containing solution contains silver nitrate, and the reducing agent-containing solution is any one or more selected from the group of ascorbic acid, an isomer of ascorbic acid, a sulfate having a reducing ability, and a sulfite having a reducing ability. In which water is dissolved in water.
上記銀粉の湿式製造方法において、前記銀イオン含有溶液は、銀１ｍｏｌ当たりアンモニアが１〜５ｍｏｌとなる量比のアンモニア水と、銀１ｍｏｌ当たり１〜２ｍｏｌの硝酸とを含有していることが望ましい。 In the silver powder wet manufacturing method, the silver ion-containing solution preferably contains ammonia water in a quantitative ratio of 1 to 5 mol of ammonia per 1 mol of silver and 1 to 2 mol of nitric acid per 1 mol of silver.
そして、上記銀粉の湿式製造方法に用いる前記銀イオン含有溶液がゼラチンを含有していることが好ましい。 And it is preferable that the said silver ion containing solution used for the wet manufacturing method of the said silver powder contains gelatin.
上記銀粉の湿式製造方法において、前記還元能を備えた硫酸塩あるいは亜硫酸塩としては、硫酸第一鉄、亜硫酸カリウム、亜硫酸アンモニウム、亜硫酸ナトリウムのうちのいずれか一種以上を用いることが好ましい。 In the silver powder wet manufacturing method, it is preferable to use at least one of ferrous sulfate, potassium sulfite, ammonium sulfite, and sodium sulfite as the sulfate or sulfite having the reducing ability.
そして、上記銀粉の湿式製造方法に用いる前記還元剤含有溶液はヒドロキノンを含有していることが好ましい。 And it is preferable that the said reducing agent containing solution used for the wet manufacturing method of the said silver powder contains hydroquinone.
上記銀粉の湿式製造方法において、前記銀イオン含有溶液と還元剤含有溶液を、３０℃以下の温度で一括で接触混合させることが好ましい。 In the silver powder wet manufacturing method, the silver ion-containing solution and the reducing agent-containing solution are preferably contact-mixed at a temperature of 30 ° C. or less.
更に、前記銀イオン含有溶液及び前記還元剤含有溶液のそれぞれの溶液を１６℃以下に冷却して用いる事が好ましい。 Furthermore, it is preferable to use each of the silver ion-containing solution and the reducing agent-containing solution after cooling to 16 ° C. or lower.
本件発明に係る銀粉： 本件発明に係る銀粉は、湿式還元法を用いて製造された銀粉であって、走査型電子顕微鏡（ＳＥＭ）像の画像解析により得られる一次粒子平均径（ＤＩＡ）が４．０μｍ〜６．５μｍ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 silver powder produced by a wet reduction method, and has an average primary particle diameter (D IA ) obtained by image analysis of a scanning electron microscope (SEM) image. It is characterized by being 4.0 μm to 6.5 μm.
そして、本件発明に係る銀粉は、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 450-550 degreeC.
また、本件発明に係る銀粉は、望ましくは上述の銀粉はレーザー回折散乱式粒度分布測定法によるＤ５０＝４μｍ〜８μｍである特性を併せ持つものである。 In addition, the silver powder according to the present invention desirably has the characteristics that the above-mentioned silver powder has a D 50 = 4 μm to 8 μm by a laser diffraction / scattering particle size distribution measurement method.
本件発明に係る銀粉の湿式製造方法は、従来、製造することが難しかった低温焼結性及び導電性に優れたＤＩＡが５μｍ前後の銀粉を低コストで製造することができる。 Wet production method for silver powder according to the present invention, conventionally, can be D IA superior in low temperature sinterability and conductivity it is difficult to produce to produce a 5μm around silver powder at a low cost.
また、本件発明に係る銀粉は、湿式還元法を用いて製造され、５μｍ前後の平均粒子径を有し、焼結性及び導電性に優れるものである。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。 Moreover, the silver powder which concerns on this invention is manufactured using the wet reduction method, has an average particle diameter of around 5 micrometers, and is excellent in sinterability and electroconductivity. Such silver powder is useful in applications that require firing at temperatures around 500 ° C.
以下、本発明に係る銀粉の湿式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 wet manufacturing method of silver powder and the best embodiment of the silver powder according to the present invention will be described.
＜本件発明に係る銀粉の製造形態＞
本発明は、湿式還元法を用いた銀粉の製造方法である。ここで、湿式還元法は、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湿式製造方法は、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、一次粒子の平均粒径が５μｍ前後の銀粉の製造を行うものである。確かに、銀イオン含有溶液中の銀濃度を高くすると、どのような製造方法を採用しても粒径を２μｍ〜３μｍ程度まで大きくする事が可能である。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アトマイズ粉の微粒レベル（一次粒子径５μｍ前後）の銀粉を湿式法で得ることは出来ない。
<Production form of silver powder according to the present invention>
The present invention is a method for producing silver powder using a wet reduction method. Here, in the wet reduction method, 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 to precipitate and precipitate particles obtained by precipitation. In this method, silver powder is obtained by removing, filtering, and washing. That is, the silver powder wet manufacturing method according to the present invention is a silver powder manufacturing method in which a silver ion-containing solution and a reducing agent-containing solution described below are contact-mixed to generate particles by reduction precipitation, and the average of primary particles Silver powder having a particle size of about 5 μm is produced. Certainly, if the silver concentration in the silver ion-containing solution is increased, it is possible to increase the particle size to about 2 μm to 3 μm regardless of any manufacturing method. However, even if the silver concentration in the reaction solution is simply increased by a normal production method, the agglomeration phenomenon between the precipitated particles only becomes remarkable, and the atomized powder having good particle dispersibility and uniform particle shape. Silver powder (primary particle diameter of about 5 μm) cannot be obtained by a wet method.
このような湿式製造プロセスを経て得られる銀粉は、アトマイズ法等の製造方法で得られる乾式銀粉が製造過程で熱履歴を受けるのに対し、それがない。即ち、乾式銀粉は、一旦、金属の溶湯を製造しこれを冷却凝固させるものである。これに対し、湿式還元法で得られる銀粉は、溶液中の銀粉を銀イオンの状態から還元析出させて得られるものであるため、その製造方法に起因して粒子内に内包する結晶歪みのレベルが異なる。一般的には、加熱により粒子の再結晶化が起こりやすいほど、粒子間の焼結を起こす相互拡散現象が容易となる。この観点から考えるに、乾式法で得られる銀粒子は、再結晶組織に近い状態にある。これに対し、湿式還元法で得られる銀粒子は、その粒子に内包する孔子欠陥が多く、加熱による格子移動が容易で、再結晶化に向けた動きがおこりやすく、焼結が容易になると言える。その結果、本件発明に係る銀粒子が、アトマイズ法等に代表される乾式法で得られた銀粉と同等の粒子径を有するとしても、乾式法で得られた銀粉を遙かに超える低温焼結性能を示し、よりバルクに近い良好な導電性を持つ焼成膜の形成を可能とするのである。以下、本件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。 The silver powder obtained through such a wet manufacturing process does not have a dry history while a dry silver powder obtained by a manufacturing method such as an atomizing method receives a thermal history during the manufacturing process. In other words, dry silver powder is one in which a molten metal is once produced and cooled and solidified. On the other hand, since the silver powder obtained by the wet reduction method is obtained by reducing and precipitating the silver powder in the solution from the state of silver ions, the level of crystal distortion included in the particles due to the production method Is different. In general, the more easily the particles are recrystallized by heating, the easier the interdiffusion phenomenon that causes sintering between the particles. From this point of view, the silver particles obtained by the dry method are in a state close to a recrystallized structure. On the other hand, silver particles obtained by the wet reduction method have many pore defects encapsulated in the particles, facilitate lattice movement by heating, easily move toward recrystallization, and can be said to be easy to sinter. . As a result, even if the silver particles according to the present invention have a particle size equivalent to that of the silver powder obtained by the dry method represented by the atomizing method, the low temperature sintering far exceeds the silver powder obtained by the dry method. It shows performance and enables the formation of a fired film having good conductivity close to the bulk. 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： 本件発明に係る銀粉の製造において、銀イオン含有溶液には、硝酸銀を含む水溶液を用いることが好ましい。まず、銀イオン含有溶液の銀濃度は、３０ｇ／ｌ〜６０ｇ／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３０ｇ／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、本件発明の目的とするアトマイズ粉の微粒レベル（一次粒子径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６０ｇ／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。 Silver ion-containing solution: In the production of silver powder according to the present invention, an aqueous solution containing silver nitrate is preferably used as the silver ion-containing solution. First, the silver concentration of the silver ion-containing solution is preferably in the range of 30 g / l to 60 g / l. Here, when the silver concentration of the silver ion-containing solution is less than 30 g / l, not only the industrially required productivity can be maintained, but also the atomized powder fine particle level (primary particle diameter of around 5 μm) which is the object of the present invention. ) Silver powder cannot be obtained. On the other hand, when the silver concentration of the silver ion-containing solution exceeds 60 g / l, aggregation of particles that are reduced and precipitated becomes remarkable, and silver powder having excellent particle dispersibility cannot be obtained.
当該銀イオン含有溶液の成分構成としては、硝酸銀を銀の供給源として用いて、銀１ｍｏｌ当たりのアンモニア成分が１ｍｏｌ〜５ｍｏｌ、銀１ｍｏｌ当たりの硝酸成分が１ｍｏｌ〜２ｍｏｌの量比として用いることが好ましい。このように、アンモニア成分と硝酸成分とを併用するのは、アンモニア成分が銀イオンのキレート（錯体）として反応し、硝酸根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を起こさせることで、析出核の形成数を適正量にして、余分な析出核の形成を抑制し、銀イオンを粒子の成長に振り向けさせることで、析出粒子の成長促進ができると考える。 As a component constitution of the silver ion-containing solution, it is preferable to use silver nitrate as a silver supply source, and use it as an amount ratio of 1 mol to 5 mol of ammonia component per mol of silver and 1 mol to 2 mol of nitric acid component per mol of silver. . As described above, the ammonia component and the nitric acid component are used together because the ammonia component reacts as a chelate (complex) of silver ions, the redox potential is lowered by the nitrate radical, and the reduction reaction is unlikely to occur at the formation stage of the precipitation nucleus. By forming an atmosphere and causing a gradual reduction reaction, the number of precipitation nuclei formed is set to an appropriate amount, the formation of excess precipitation nuclei is suppressed, and silver ions are directed to the growth of the particles, I think we can promote growth.
ここで、アンモニアはキレート剤として機能して、銀イオンと反応して銀アンミン錯体を形成する。このとき、アンモニアの濃度が１ｍｏｌ未満の場合には、溶液中に存在する銀イオンとの間でのキレート化が不十分となり、銀イオン含有溶液としての品質のバラツキが大きくなるため、結果として粒度分布のバラツキが大きな銀粉が得られやすくなる。一方、アンモニア濃度を５ｍｏｌを超えるものとしても、キレート化する銀イオンが無くなり資源の無駄遣いともなり、しかも、溶液ｐＨの変動幅も大きくなるため、得られる銀粉の一次粒子径のバラツキも大きくなる。 Here, ammonia functions as a chelating agent and reacts with silver ions to form a silver ammine complex. At this time, when the concentration of ammonia is less than 1 mol, chelation with the silver ions present in the solution becomes insufficient, and the quality variation as the silver ion-containing solution becomes large. Silver powder with large variation in distribution is easily obtained. On the other hand, even if the ammonia concentration exceeds 5 mol, the chelating silver ions are eliminated, resources are wasted, and the fluctuation range of the solution pH is increased, so that the dispersion of the primary particle diameter of the obtained silver powder increases.
そして、硝酸成分の濃度が１ｍｏｌ未満の場合には、得られる粒子が小さくなり所望の大きさの粒子を得られない傾向が顕著となる。一方、硝酸成分の濃度が２ｍｏｌを超えると、アトマイズ粉の微粒レベル（一次粒子径５μｍ前後）を超える粒径の銀粒子が得られるが、粒径のバラツキが大きく、品質安定性に欠けるものとなる。 And when the density | concentration of a nitric acid component is less than 1 mol, the tendency for the particle | grains obtained to become small and to obtain the particle | grains of a desired magnitude | size becomes remarkable. On the other hand, if the concentration of the nitric acid component exceeds 2 mol, silver particles having a particle size exceeding the fine particle level of the atomized powder (primary particle size of around 5 μm) can be obtained, but the particle size variation is large and the quality stability is poor. Become.
更に、銀イオン含有溶液は、ゼラチンを含有する事が好ましい。その理由としては、銀イオン含有溶液と還元剤含有溶液との混合後に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、析出粒子の分散状態を好適に保つことができるからである。更に、ゼラチンが保護剤として機能し、製造過程において粒子表面を損傷から保護する効果も奏する。このゼラチンは、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。このゼラチン含有量が１ｇ／ｌ未満の場合には、還元析出粒子の立体障害として寄与する事が出来ないため、凝集を防止する効果が得られない。一方、このゼラチン含有量が５ｇ／ｌ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が劣化する。 Furthermore, the silver ion-containing solution preferably contains gelatin. The reason for this is that it contributes as steric hindrance of the particles that are reduced and precipitated after mixing the silver ion-containing solution and the reducing agent-containing solution, prevents the particles from aggregating and can keep the dispersed state of the precipitated particles suitably. Because. Furthermore, gelatin functions as a protective agent, and has an effect of protecting the particle surface from damage in the production process. This gelatin is preferably used in a silver ion-containing solution in the range of 1 g / l to 5 g / l in consideration of the amount of silver particles that are reduced and precipitated. If the gelatin content is less than 1 g / l, 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 this gelatin content exceeds 5 g / l, it becomes a factor inhibiting silver reductive precipitation reaction, the reductive precipitation reaction becomes slow, and the particle size distribution of the obtained silver powder deteriorates.
還元剤含有溶液： 本件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、アスコルビン酸の異性体、還元能を備えた硫酸塩、還元能を備えた亜硫酸塩の群から選ばれたいずれか一種以上を水に溶解させたものを用いる。これらの還元剤と上記銀イオン含有溶液とを用いることにより、一次粒子の平均粒径が５μｍ前後の銀粉を湿式還元法で効率よく製造出来るのである。以上に列挙した還元剤は、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無くし、均一な分散状態が得られる。ここに挙げた還元剤は、比較的還元力の弱いものを選択している。緩やかな還元反応を起こさせることで、析出核の成長を促進させるためである。 Reducing agent-containing solution: In the production of silver powder according to the present invention, the reducing agent-containing solution is selected from the group consisting of ascorbic acid, an isomer of ascorbic acid, a sulfate having a reducing ability, and a sulfite having a reducing ability. Any one or more of them dissolved in water is used. By using these reducing agents and the silver ion-containing solution, silver powder having an average primary particle size of about 5 μm can be efficiently produced by a wet reduction method. The reducing agents listed above are 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, there is no uneven distribution of the reducing agent in the reaction system, and a uniform dispersion state is obtained. It is done. The reducing agents listed here are selected with a relatively weak reducing power. This is to promote the growth of precipitation nuclei by causing a gradual reduction reaction.
上記還元能を備えた硫酸塩あるいは亜硫酸塩としては、硫酸第一鉄、亜硫酸カリウム、亜硫酸アンモニウム、亜硫酸ナトリウムのうちのいずれか一種以上を用いることが好ましい。これらの還元力の弱い亜硫酸塩を用いて還元析出する粒子数を抑制させることによって、その分、析出した粒子を成長させることができる。更に、この還元剤含有溶液にヒドロキノンを混合して溶解すると、上記亜硫酸塩のいずれかと異なる還元能を発揮し、還元析出反応速度が抑えられて、粒子の成長を促進させることができる。このようにして、従来の湿式還元法で得られる銀粒子より粗粒となる５μｍ前後の銀粒子を得ることができるのである。 As the sulfate or sulfite having the reducing ability, it is preferable to use at least one of ferrous sulfate, potassium sulfite, ammonium sulfite, and sodium sulfite. By suppressing the number of particles that are reduced and precipitated using these sulfites having a weak reducing power, it is possible to grow the precipitated particles accordingly. Furthermore, when hydroquinone is mixed and dissolved in this reducing agent-containing solution, the reducing ability different from any of the above sulfites is exhibited, the reduction precipitation reaction rate is suppressed, and the growth of particles can be promoted. In this way, silver particles of about 5 μm that are coarser than silver particles obtained by the conventional wet reduction method can be obtained.
そして、この還元剤含有溶液は、上記還元剤を、反応させる銀イオン含有溶液の１リットル当たりに含まれる銀の当量を基準として、その１倍当量／ｌ〜３倍当量／ｌの範囲で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トータル量によって異なる。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／ｌ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／ｌ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。 And this reducing agent containing solution contains the said reducing agent in the range of the 1 equivalent / l-3 times equivalent / l on the basis of the equivalent of the silver contained per liter of the silver ion containing solution made to react. It is preferable to use it as an aqueous solution. 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, when the reducing agent concentration of the reducing agent-containing solution is less than 1 equivalent / l, 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 reducing agent concentration of the reducing agent-containing solution exceeds 3 times equivalent / l, when the silver ion-containing solution and the reducing agent-containing solution are contact-mixed, the reducing agent concentration is high. It becomes difficult to quickly eliminate the uneven distribution of the reducing agent in the inside, 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： 上述の銀イオン含有溶液と還元剤含有溶液とを接触混合し、撹拌することにより銀粒子を還元析出させる。本件発明に係る銀粉の製造方法においては、銀イオン含有溶液と還元剤含有溶液とを３０℃以下の温度で一括で接触混合させる事が好ましい。 Method of mixing silver ion-containing solution and reducing agent-containing solution: The above-described silver ion-containing solution and reducing agent-containing solution are contact-mixed and stirred to reduce and precipitate silver particles. In the method for producing silver powder according to the present invention, the silver ion-containing solution and the reducing agent-containing solution are preferably contact-mixed at a temperature of 30 ° C. or less.
そして、接触混合を行う場合には、一括で混合すると記載している。この一括で混合するとは、銀イオン含有溶液に対し還元剤含有溶液を一定の時間（例えば、３０分等）をかけて徐々に添加する概念の反対を意味するものである。即ち、銀イオン含有溶液の入った容器に対し還元剤含有溶液を一気に全量注入添加する場合、一つの容器に対し銀イオン含有溶液と還元剤含有溶液とを同時に注入添加する場合、還元剤含有溶液の入った容器に対し銀イオン含有溶液を一気に全量注入添加する場合、のそれぞれの概念を意味する。 And when performing contact mixing, it describes that it mixes collectively. This batch mixing means the opposite of the concept of gradually adding a reducing agent-containing solution over a certain time (for example, 30 minutes) to a silver ion-containing solution. That is, when a reducing agent-containing solution is injected and added all at once to a container containing a silver ion-containing solution, when a silver ion-containing solution and a reducing agent-containing solution are simultaneously injected and added to one container, the reducing agent-containing solution When the whole amount of the silver ion-containing solution is injected and added to the container containing, the respective concepts are meant.
最初に混合時の液温に関して説明する。本件発明者の研究の結果、混合時の溶液の温度が高温となる程、析出粒子が微粒化する傾向があり、粒径を大きくするためには反応時の温度を適正な温度以下にする必要があることが判明した。この混合時の銀イオン含有溶液及び還元剤含有溶液の温度を３０℃を超えるものとすると、還元速度が早くなり、初期析出する粒子核の量が増加し、得られる銀粒子が小さくなり、適正な粒径の銀粒子が得られない。 First, the liquid temperature during mixing will be described. As a result of the inventor's research, the higher the temperature of the solution at the time of mixing, the more the precipitated particles tend to be atomized. In order to increase the particle size, the temperature at the time of reaction needs to be lower than the appropriate temperature. Turned out to be. If the temperature of the silver ion-containing solution and the reducing agent-containing solution at the time of mixing exceeds 30 ° C., the reduction rate increases, the amount of particle nuclei that initially precipitate increases, the resulting silver particles become smaller, Silver particles with a small particle size cannot be obtained.
そして、より好ましくは、この硝酸銀水溶液及び還元剤含有溶液をそれぞれ１６℃以下に冷却して用いることによって、飛躍的に製造安定性を向上させ、析出する粒子の粒径をアトマイズ粉の微粒レベル（一次粒子径５μｍ前後）とすることが、更に容易となる。 More preferably, the silver nitrate aqueous solution and the reducing agent-containing solution are each cooled to 16 ° C. or less to dramatically improve production stability, and the particle size of the precipitated particles is reduced to a fine particle level of atomized powder ( It becomes even easier to have a primary particle diameter of 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混合した以降は、速やかに混合溶液を攪拌して、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 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.
上記方法で銀イオン含有溶液（硝酸銀水溶液）と還元剤含有溶液とを一括して接触混合して撹拌した後は、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 the silver ion-containing solution (silver nitrate aqueous solution) and the reducing agent-containing solution are brought into contact and mixed together and stirred by the above method, the particles are settled, the supernatant is removed, filtered, and washed in the same manner as in the conventional wet reduction method. Silver powder is obtained through the process.
＜本件発明に係る銀粉の形態＞
本件発明に係る湿式還元法を用いて製造された銀粉は、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平均径がＤＩＡ＝４．０μｍ〜６．５μｍである。加えて、この銀粉はレーザー回折散乱式粒度分布測定法によるＤ５０＝４μｍ〜８μｍという粉体特性を備えるものとなる。従来、湿式還元法で製造することが難しかった粒径が５μｍ前後の銀粉を得ることができる。
<Form of silver powder according to the present invention>
The silver powder produced using the wet reduction method according to the present invention has a primary particle average diameter obtained by image analysis of a scanning electron microscope image of D IA = 4.0 μm to 6.5 μm. In addition, this silver powder has a powder characteristic of D 50 = 4 μm to 8 μm by a laser diffraction / scattering particle size distribution measurement method. Conventionally, it is possible to obtain silver powder having a particle size of around 5 μm, which has been difficult to manufacture by a wet reduction method.
このように５μｍ前後の一次粒子平均径を有する湿式銀粉は、湿式還元法による銀粉の特徴である高分散、高充填密度に加えて、粒径を５μｍ前後とすることによって焼結開始温度が４５０℃〜５５０℃となる粉体特性を備えるものである。 As described above, the wet silver powder having an average primary particle diameter of about 5 μm has a sintering start temperature of 450 by setting the particle diameter to about 5 μm in addition to the high dispersion and high packing density characteristic of the silver powder by the wet reduction method. It has a powder characteristic of 550 ° C to 550 ° C.
このような銀粉は粒径の均一性に優れ且つ粒子分散性に優れた銀粉であるので、この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、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、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。 Since such silver powder is a silver powder having excellent particle size uniformity and particle dispersibility, when this silver powder is processed into a conductive ink or the like, a conductor film is formed and fired, the particle size variation and Roughness of the conductor film surface due to the aggregation of particles can be suppressed, and a sintered body (conductive film) having a uniform surface state can be formed. And since it is excellent in low-temperature sinterability and baking which particle | grains connect by the heating around 500 degreeC is possible, it is suitable for formation of the low resistance conductor film excellent in the electroconductivity in the said temperature range.
以下、実施例及び比較例を示して本件発明を具体的に説明する。なお、本件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. The present invention is not limited to the following examples.
実施例１では、銀イオン含有溶液として、硝酸銀５ｋｇを純水５０Ｌに溶解させ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２．６ｋｇを純水５０Ｌに溶解させたものを用いた。この銀イオン含有溶液（硝酸銀水溶液）と、還元剤含有溶液とを、３０℃の温度で一括して接触混合して反応させる。この時、混合溶液の均一化のために５分間撹拌した。その後、粒子を沈降させた上澄みを抜き、濾過、洗浄することによって銀粉を得た。 In Example 1, a silver nitrate aqueous solution in which 5 kg of silver nitrate was dissolved in 50 L of pure water was used as the silver ion-containing solution. As the reducing agent-containing solution, a solution obtained by dissolving 2.6 kg of ascorbic acid in 50 L of pure water was used. This silver ion-containing solution (silver nitrate aqueous solution) and the reducing agent-containing solution are brought into contact and mixed at a temperature of 30 ° C. for reaction. At this time, the mixture was stirred for 5 minutes to make the mixed solution uniform. Thereafter, the supernatant on which the particles were settled was removed, filtered and washed to obtain silver powder.
なお、上記銀イオン含有溶液の銀濃度は３１．８ｇ／ｌとなり、この銀濃度に対して、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 31.8 g / l, and the usage-amount of ascorbic acid will be 1.0 time equivalent with respect to this silver concentration.
こうして得られた銀粉について、以下の方法にて諸特性を評価した。即ち、倍率２０００倍における走査型電子顕微鏡像を画像解析して任意に１００個の一次粒子径を測定し、一次粒子平均径を算出した。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、Ｄ５０、Ｄ９０、Ｄｍａｘを測定し、Ｄ９０／Ｄ１０を算出した（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）。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と、６００℃における収縮率を調べた。 Various properties of the silver powder thus obtained were evaluated by the following methods. That is, an image of a scanning electron microscope image at a magnification of 2000 was subjected to image analysis, and 100 primary particle diameters were arbitrarily measured to calculate an average primary particle diameter. In order to evaluate the particle size distribution, D 10 , D 50 , D 90 , and D max were measured using a Micro Trac HRA9320-X100 type (Leeds + Northrup), which is a laser diffraction / scattering type particle size distribution measuring device. 90 / D 10 was calculated (0.1 g of silver powder was mixed with a 0.1% aqueous solution of SN Dispersant 5468 (manufactured by San Nopco) and dispersed with an ultrasonic homogenizer (US-300T, manufactured by Nippon Seiki Seisakusho) for 5 minutes. Use sample). 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 and the shrinkage rate at 600 ° C. were examined 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に示す。図１を見ると、複数の繊維が巻き付いた様に表面が形成された粒子が見られ、大きさは粒径が５μｍ程度で比較的揃っていることが分かる。なお、諸特性の評価結果については表１に示す。 A scanning electron microscope image of the silver powder obtained in Example 1 is shown in FIG. Referring to FIG. 1, it can be seen that particles having a surface formed like a plurality of fibers are wound, and the sizes are relatively uniform with a particle size of about 5 μm. The evaluation results of various characteristics are shown in Table 1.
実施例２は銀イオン含有溶液に硝酸銀１６．５ｋｇを純水３０Ｌに溶解させた硝酸銀水溶液を用い、還元剤含有溶液は、硫酸第一鉄（７水和物）４９．５ｋｇを純水１５０Ｌに溶解させたものを用いた。なお、上記銀イオン含有溶液の銀濃度は５８．２ｇ／ｌとなり、この銀濃度に対して、硫酸第一鉄の使用量は１．２６倍当量となる。この銀イオン含有溶液と還元剤含有溶液とを３０℃の温度で一括して接触混合し、この混合した溶液の均一化のために５分間撹拌した。その後、粒子を沈降させた上澄みを抜き、洗浄、濾過することによって粗粒銀粉を得た。 Example 2 uses a silver nitrate aqueous solution in which 16.5 kg of silver nitrate is dissolved in 30 L of pure water in a silver ion-containing solution, and the reducing agent-containing solution is 49.5 kg of ferrous sulfate (7 hydrate) in 150 L of pure water. What was dissolved was used. In addition, the silver concentration of the said silver ion containing solution will be 58.2 g / l, and the usage-amount of ferrous sulfate will be 1.26 times equivalent with respect to this silver concentration. The silver ion-containing solution and the reducing agent-containing solution were collectively contact-mixed at a temperature of 30 ° C., and stirred for 5 minutes to homogenize the mixed solution. Thereafter, the supernatant on which the particles were settled was removed, washed and filtered to obtain coarse silver powder.
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、表面が小さなフレーク状のもので形成された粒子が粒径５μｍ程度に大きさが揃っていることが分かる。なお、その他の諸特性については表１に示す。 A scanning electron microscope image of the silver powder obtained in Example 2 is shown in FIG. Referring to FIG. 2, it can be seen that the particles formed of flakes having a small surface have a size of about 5 μm. Other characteristics are shown in Table 1.
実施例３は、銀イオン含有溶液として、硝酸銀３．０６ｋｇを純水３．６Ｌに溶かした硝酸銀水溶液に、別途、濃度２５ｗｔ％のアンモニア水５３６０ｍｌと硝酸２５８３ｇを溶かした溶液を加え１６℃まで冷却したものを用いた。還元剤含有溶液は、ヒドロキノン７０１ｇと亜硫酸カリウム２４５３ｇを純水５４．４Ｌに溶解させたものを用いた。別途、ゼラチン１７５ｇを純水３Ｌに溶かした溶液を作製し、還元剤含有溶液に添加して１６℃まで冷却する。冷却した銀イオン含有溶液と、還元剤含有溶液とを一括で接触混合して５分間撹拌した後、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粗粒銀粉を得た。 In Example 3, as a silver ion-containing solution, a solution obtained by dissolving 5360 ml of 25 wt% ammonia water and 2583 g of nitric acid was added to a silver nitrate aqueous solution in which 3.06 kg of silver nitrate was dissolved in 3.6 L of pure water and cooled to 16 ° C. What was done was used. As the reducing agent-containing solution, a solution obtained by dissolving 701 g of hydroquinone and 2453 g of potassium sulfite in 54.4 L of pure water was used. Separately, a solution in which 175 g of gelatin is dissolved in 3 L of pure water is prepared, added to the reducing agent-containing solution, and cooled to 16 ° C. The cooled silver ion-containing solution and the reducing agent-containing solution were contacted and mixed together and stirred for 5 minutes, and then the particles were settled, the supernatant was removed, filtered, and washed to obtain coarse silver powder.
なお、上記銀イオン含有溶液の銀濃度は３１．９ｇ／ｌとなり、還元剤としてのヒドロキノンと亜硫酸カリウムの使用量は、銀濃度に対して、１．６倍当量である。また、アンモニア成分の使用量は、銀濃度に対して、３．１倍当量であり、硝酸の使用量は１．３倍当量である。 In addition, the silver concentration of the said silver ion containing solution will be 31.9 g / l, and the usage-amount of hydroquinone and potassium sulfite as a reducing agent is 1.6 times equivalent with respect to silver concentration. Moreover, the usage-amount of an ammonia component is 3.1 times equivalent with respect to silver concentration, and the usage-amount of nitric acid is 1.3 times equivalent.
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、粒径が比較的揃っているのが確認でき、また、表面に凹凸が少なく滑らかで大きい粒径の粒子が混在していることが分かる。その他の諸特性については表１に示す。 A scanning electron microscope image of the silver powder obtained in Example 3 is shown in FIG. When FIG. 3 is seen, it can confirm that the particle size is comparatively uniform, and it turns out that there are few unevenness | corrugations on the surface, and the particle | grains of smooth and large particle size are mixed. Other characteristics are shown in Table 1.
実施例４は、実施例３で得られた銀粉に表面平滑化処理を施した例であり、製造条件は実施例３と同じなので説明を割愛する。表面平滑化処理にはハイブリタイザー（奈良機械製作所製）を用いて回転数５０００ｒｐｍの条件で表面平滑化処理を施した。得られた銀粉の走査型電子顕微鏡像を図４に示す。その他の諸特性については表１に示す。 Example 4 is an example in which the surface of the silver powder obtained in Example 3 was subjected to a surface smoothing process, and the manufacturing conditions are the same as those in Example 3. The surface smoothing treatment was performed using a hybridizer (manufactured by Nara Machinery Co., Ltd.) under the condition of a rotational speed of 5000 rpm. A scanning electron microscope image of the obtained silver powder is shown in FIG. Other characteristics are shown in Table 1.
［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溶かし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純水１７０Ｌ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で得られた銀粉の粉体特性を表１に示す。
[Comparative Example 1]
In Comparative Example 1, silver powder was produced using a conventional wet reduction method. That is, as the silver ion-containing solution, a solution obtained by dissolving 10 L of ammonia water in a solution of 5 kg of silver nitrate in 25 L of pure water and cooling to 16 ° C. was used, and the reducing agent-containing solution was dissolved in 170 L of hydroquinone 1.6 kg of pure water. What was cooled to 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 the powder was filtered and washed to obtain silver powder. Table 1 shows the powder characteristics of the silver powder obtained in Comparative Example 1.
［比較例２］
比較例２では、アトマイズ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 2]
In Comparative Example 2, silver powder was manufactured using an atomizing method. That is, 110 g of silver nitrate was put in a crucible and heated to 315 ° C. by electric heating. Then, argon gas was used as a carrier gas for a two-fluid nozzle (manufactured by SUS), and silver nitrate was added under the conditions of carrier gas pressure 5 kg / cm 2 and flow rate 10 L / min. Sprayed and introduced into a quartz tube heated to 1100 ° C. The silver powder after pyrolysis was collected by a cyclone.
比較例２で得られた銀粉の走査型電子顕微鏡像を図６に示す。そして、比較例２の銀粉の粉体特性を表１に示す。なお、図６を見ても分かるように、比較例２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。従って、走査型電子顕微鏡像の画像解析の結果を用いても、上記実施例１〜実施例３との比較に有効性は認められないので測定は省略した。また、収縮率については、上記実施例１〜実施例４および比較例１ではガラス基板との焼結特性の整合性を検討する上で、６００℃の収縮率を測定していたが、本比較例２の場合、６００℃の段階では未焼結なので記載は省略した。 A scanning electron microscope image of the silver powder obtained in Comparative Example 2 is shown in FIG. Table 1 shows the powder characteristics of the silver powder of Comparative Example 2. As can be seen from FIG. 6, the silver powder of Comparative Example 2 has many agglomerated particles and irregular particle sizes. Therefore, even if the result of the image analysis of the scanning electron microscope image was used, the effectiveness was not recognized in the comparison with Examples 1 to 3, and thus the measurement was omitted. As for the shrinkage rate, in Examples 1 to 4 and Comparative Example 1 described above, the shrinkage rate at 600 ° C. was measured for examining the consistency of the sintering characteristics with the glass substrate. In the case of Example 2, since it was unsintered at the stage of 600 ° C., the description was omitted.
表１から明らかなように、実施例１〜実施例４に示す銀粉は、いずれも５μｍ前後の粗粒域であり、且つ、粒径が揃い、分散性に優れ、充填密度も高い、高性能な銀粉であると言える。また、従来の湿式銀粉より熱収縮率を低減出来たので、焼結前後の寸法安定性が向上し、より高品質な導体を形成できる。即ち、湿式還元法の利点であった、高分散性、高導電性を活かしながら、焼結開始温度を高くすることができる銀粉を低コストで製造することができる。特に、高分散性、高充填密度による高導電性を有するので、導体形成の焼成温度が５００℃前後とする基板に印刷、塗布する導電性インクまたは導電性ペーストの材料として好適な銀粉を低コストで製造することができる。 As is clear from Table 1, the silver powders shown in Examples 1 to 4 are all coarse-grained regions of around 5 μm, have a uniform particle size, excellent dispersibility, and high packing density. It can be said that it is a silver powder. Moreover, since the thermal shrinkage rate can be reduced as compared with the conventional wet silver powder, the dimensional stability before and after sintering is improved, and a higher quality conductor can be formed. That is, it is possible to produce silver powder that can increase the sintering start temperature at low cost while taking advantage of the high dispersibility and high conductivity that are advantages of the wet reduction method. In particular, since it has high conductivity due to high dispersibility and high packing density, silver powder suitable as a material for conductive ink or conductive paste to be printed and applied on a substrate having a firing temperature of about 500 ° C. is low cost. Can be manufactured.
次に、実施例３と実施例４について比較する。ここで、表面平滑化処理は、高速回転している気流中に粒子を投入することにより粒子どうしが衝突する衝撃によって粒子表面を平滑化させる処理であるが、粒子どうしの衝突によって凝集した粒子が解砕される効果もある。従って、一般的に、表面平滑化処理後の粉体は、表面平滑化処理前のものと比べると、平均粒径Ｄ５０や粒度分布が変化する傾向がある。しかし、実施例３と実施例４とでは、タップ密度（Ｔ．Ｄ）が高くなった他は、粒径、粒度分布、焼結開始温度について大きな差が生じなかった。この結果から、表面平滑化処理を行う前から凝集した粒子が少なく、粒子分散性に優れた粉体であったと言える。しかしながら、表面平滑化処理を行うことにより、焼結開始温度を維持したままに、高密度でより導電性の高い銀粉を製造することができる。なお、実施例３の銀粉より実施例４の銀粉の比表面積（ＳＳＡ）が低くなっているのは、粒子衝突によって表面が滑らかになっているものと考えられる。 Next, Example 3 and Example 4 will be compared. Here, the surface smoothing process is a process of smoothing the particle surface by the impact of particles colliding with each other by putting the particles into an air stream rotating at high speed. There is also an effect of being crushed. Therefore, in general, powder after surface smoothing treatment, as compared to the previous surface smoothing treatment, tends to average particle size D 50 and particle size distribution changes. However, in Example 3 and Example 4, there was no significant difference in particle size, particle size distribution, and sintering start temperature except that the tap density (TD) was increased. From this result, it can be said that the powder was excellent in particle dispersibility with few aggregated particles before the surface smoothing treatment. However, by performing the surface smoothing treatment, it is possible to produce silver powder having a higher density and higher conductivity while maintaining the sintering start temperature. The specific surface area (SSA) of the silver powder of Example 4 is lower than that of the silver powder of Example 3 because the surface is smooth due to particle collision.
そして、実施例１〜実施例３と比較例１とを比べると、Ｄ９０／Ｄ１０の値は大きく変わらないことから、従来の湿式銀粉と同様に粒子分散性に優れていながら、平均粒径Ｄ５０が大きい銀粉を製造できたと言える。一方、比較例１で得られた銀粉は、実施例１〜実施例４に比べて平均粒径が小さい銀粉である為に、焼結開始温度は２２０℃と低温となると考えられる。従って、銀粉の粗粒化の実現によって焼結開始温度が顕著に変化し、焼成温度が５００℃前後で導体形成する場合に対応できたと言える。 And when Examples 1 to 3 and Comparative Example 1 are compared, since the value of D 90 / D 10 does not change greatly, the average particle size is excellent while being excellent in particle dispersibility like conventional wet silver powder. It can be said that silver powder having a large D 50 could be produced. On the other hand, since the silver powder obtained in Comparative Example 1 is a silver powder having an average particle size smaller than those in Examples 1 to 4, the sintering start temperature is considered to be as low as 220 ° C. Therefore, it can be said that the sintering start temperature has changed remarkably by realizing the coarsening of the silver powder, and the case where the conductor is formed at a firing temperature of around 500 ° C. can be said.
また、実施例１〜実施例４で得られた銀粉の比表面積は、比較例１に比べて小さい値となっているが、比表面積の値が小さいほど滑らかで平滑な表面を持つ銀粉と言え、比表面積が滑らかであるほど、ペーストに加工した時のペースト粘度を低くすることができる。 Moreover, although the specific surface area of the silver powder obtained in Examples 1 to 4 has a smaller value than that of Comparative Example 1, it can be said that the smaller the specific surface area, the smoother and smoother the surface of the silver powder. As the specific surface area is smoother, the paste viscosity when processed into a paste can be lowered.
そして、実施例１〜実施例４と比較例２とを比べると、Ｄ９０／Ｄ１０の値は実施例１〜実施例４が低い値となっており、比較例２と比べて粒度分布がシャープな銀粉が作製できていると言える。また、図１〜図４と図６とを比較しても、実施例１〜実施例４の方が、比較例２よりも凝集が少なく粒径が揃っていることは瞭然である。 When compared with Comparative Example 2 and Example 1 to Example 4, the value of D 90 / D 10 is a low value first to fourth embodiments, the particle size distribution in comparison with Comparative Example 2 It can be said that sharp silver powder has been produced. Further, even when FIGS. 1 to 4 are compared with FIG. 6, it is obvious that Examples 1 to 4 are less aggregated and have a uniform particle size than Comparative Example 2.
従って、導電性インクまたは導電性ペースト等によりフラットディスプレイパネルのガラス基板上に導体形成する場合等を想定すると、焼成温度は５００℃前後であるが、比較例１で得られた銀粉を導電性インクまたは導電性ペーストに用いた場合、焼成の際に銀粉が焼けすぎとなるだけでなく、６００℃での収縮率が高いので寸法安定性が劣り、ガラス基板上の金属導体材料としては適さないと言える。一方、比較例２で得られた銀粉の焼結開始温度は、ガラス基板の焼結開始温度より非常に高く、ガラス基板の焼成後もこの銀粉は未焼結となるのでガラス基板上に形成する金属導体として使用出来ないと言える。 Accordingly, assuming a case where a conductor is formed on a glass substrate of a flat display panel using a conductive ink or a conductive paste, the firing temperature is around 500 ° C., but the silver powder obtained in Comparative Example 1 is used as the conductive ink. Or when used as a conductive paste, not only does the silver powder burn too much during firing, but the shrinkage at 600 ° C. is high, resulting in poor dimensional stability, and is not suitable as a metal conductor material on a glass substrate. I can say that. On the other hand, the sintering start temperature of the silver powder obtained in Comparative Example 2 is much higher than the sintering start temperature of the glass substrate, and the silver powder becomes unsintered even after the glass substrate is fired, so it is formed on the glass substrate. It can be said that it cannot be used as a metal conductor.
従来、湿式還元法を用いた銀粉の製造では得られなかった５μｍ前後の粒径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製造することができる。更に、従来より熱収縮率を低減出来るので、焼結前後の寸法安定性が向上し、より高品質な導体を形成できる。また、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。即ち、湿式還元法の利点であった、高分散性、高導電性を活かしながら、焼結開始温度を高くすることができるので、基板と銀粉との焼結挙動の整合可能範囲を広げることができ、導体材料として求められる高分散性、高充填密度である高品質な銀粉を低コストで製造することができる。従って、本件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 particle size of around 5 μm, which has not been obtained by the production of silver powder using a wet reduction method, it is possible to produce excellent silver powder with excellent dispersibility and improved sintering characteristics. it can. Furthermore, since the thermal shrinkage rate can be reduced as compared with the prior art, the dimensional stability before and after sintering is improved, and a higher quality conductor can be formed. Moreover, 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. In other words, it is possible to increase the sintering start temperature while taking advantage of the high dispersibility and high conductivity, which were the advantages of the wet reduction method, so that the matching range of the sintering behavior of the substrate and the silver powder can be expanded. In addition, high-quality silver powder having high dispersibility and high packing density required as a conductor material can be produced at low cost. Therefore, when using conductive ink or conductive paste using silver powder according to the present invention for glass substrate formation 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 (10)
前記銀イオン含有溶液は硝酸銀を含み、
前記還元剤含有溶液はアスコルビン酸、アスコルビン酸の異性体、還元能を備えた硫酸塩、還元能を備えた亜硫酸塩の群から選ばれたいずれか一種以上を水に溶解させたものを含むことを特徴とする銀粉の湿式製造方法。 A method for producing silver powder using a wet reduction method in which a silver ion-containing solution and a reducing agent-containing solution are contact-mixed,
The silver ion-containing solution contains silver nitrate,
The reducing agent-containing solution contains ascorbic acid, an isomer of ascorbic acid, a sulfate having a reducing ability, or a solution in which at least one selected from the group of sulfites having a reducing ability is dissolved in water. A method for wet production of silver powder.
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平均径（ＤＩＡ）が４．０μｍ〜６．５μｍであることを特徴とする銀粉。 Silver powder produced using a wet reduction method,
A silver powder having an average primary particle diameter (D IA ) obtained by image analysis of a scanning electron microscope image of 4.0 μm to 6.5 μm.
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