JP3751154B2 - Silver powder manufacturing method - Google Patents
Silver powder manufacturing method Download PDFInfo
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- JP3751154B2 JP3751154B2 JP30136398A JP30136398A JP3751154B2 JP 3751154 B2 JP3751154 B2 JP 3751154B2 JP 30136398 A JP30136398 A JP 30136398A JP 30136398 A JP30136398 A JP 30136398A JP 3751154 B2 JP3751154 B2 JP 3751154B2
- Authority
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- Prior art keywords
- silver
- silver powder
- aqueous
- reaction system
- reducing agent
- Prior art date
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- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 title claims description 112
- 238000004519 manufacturing process Methods 0.000 title claims description 17
- 238000006243 chemical reaction Methods 0.000 claims description 45
- 229910052709 silver Inorganic materials 0.000 claims description 41
- 239000004332 silver Substances 0.000 claims description 41
- 239000003638 chemical reducing agent Substances 0.000 claims description 31
- 239000007864 aqueous solution Substances 0.000 claims description 28
- 238000006722 reduction reaction Methods 0.000 claims description 28
- 239000002245 particle Substances 0.000 claims description 25
- NDVLTYZPCACLMA-UHFFFAOYSA-N silver oxide Chemical compound [O-2].[Ag+].[Ag+] NDVLTYZPCACLMA-UHFFFAOYSA-N 0.000 claims description 20
- 230000009467 reduction Effects 0.000 claims description 18
- 229910001923 silver oxide Inorganic materials 0.000 claims description 10
- GGCZERPQGJTIQP-UHFFFAOYSA-N sodium;9,10-dioxoanthracene-2-sulfonic acid Chemical compound [Na+].C1=CC=C2C(=O)C3=CC(S(=O)(=O)O)=CC=C3C(=O)C2=C1 GGCZERPQGJTIQP-UHFFFAOYSA-N 0.000 claims description 8
- 239000002563 ionic surfactant Substances 0.000 claims description 3
- 238000000034 method Methods 0.000 description 31
- 239000000243 solution Substances 0.000 description 23
- 239000002736 nonionic surfactant Substances 0.000 description 17
- SQGYOTSLMSWVJD-UHFFFAOYSA-N silver(1+) nitrate Chemical compound [Ag+].[O-]N(=O)=O SQGYOTSLMSWVJD-UHFFFAOYSA-N 0.000 description 16
- WSFSSNUMVMOOMR-UHFFFAOYSA-N Formaldehyde Chemical compound O=C WSFSSNUMVMOOMR-UHFFFAOYSA-N 0.000 description 13
- QGZKDVFQNNGYKY-UHFFFAOYSA-N ammonia Natural products N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 13
- 239000007788 liquid Substances 0.000 description 11
- 239000011248 coating agent Substances 0.000 description 9
- 238000000576 coating method Methods 0.000 description 9
- 230000002776 aggregation Effects 0.000 description 8
- 229910001961 silver nitrate Inorganic materials 0.000 description 8
- OAKJQQAXSVQMHS-UHFFFAOYSA-N Hydrazine Chemical compound NN OAKJQQAXSVQMHS-UHFFFAOYSA-N 0.000 description 6
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 description 6
- 238000004220 aggregation Methods 0.000 description 6
- 239000000203 mixture Substances 0.000 description 6
- 239000002002 slurry Substances 0.000 description 6
- 229910021529 ammonia Inorganic materials 0.000 description 5
- 239000004020 conductor Substances 0.000 description 5
- 238000001035 drying Methods 0.000 description 5
- 239000010419 fine particle Substances 0.000 description 5
- 239000011521 glass Substances 0.000 description 5
- 238000002156 mixing Methods 0.000 description 5
- 235000014113 dietary fatty acids Nutrition 0.000 description 4
- 239000006185 dispersion Substances 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 229930195729 fatty acid Natural products 0.000 description 4
- 239000000194 fatty acid Substances 0.000 description 4
- 150000004665 fatty acids Chemical class 0.000 description 4
- 230000002209 hydrophobic effect Effects 0.000 description 4
- 238000005259 measurement Methods 0.000 description 4
- 239000000843 powder Substances 0.000 description 4
- 150000003839 salts Chemical class 0.000 description 4
- -1 silver ions Chemical class 0.000 description 4
- 239000004094 surface-active agent Substances 0.000 description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 4
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 3
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 description 3
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- 239000003513 alkali Substances 0.000 description 3
- 239000003093 cationic surfactant Substances 0.000 description 3
- 239000008139 complexing agent Substances 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 238000001556 precipitation Methods 0.000 description 3
- 239000012279 sodium borohydride Substances 0.000 description 3
- 229910000033 sodium borohydride Inorganic materials 0.000 description 3
- 239000000758 substrate Substances 0.000 description 3
- 230000003746 surface roughness Effects 0.000 description 3
- CIWBSHSKHKDKBQ-JLAZNSOCSA-N Ascorbic acid Chemical compound OC[C@H](O)[C@H]1OC(=O)C(O)=C1O CIWBSHSKHKDKBQ-JLAZNSOCSA-N 0.000 description 2
- 238000005054 agglomeration Methods 0.000 description 2
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 2
- 239000011230 binding agent Substances 0.000 description 2
- 239000003985 ceramic capacitor Substances 0.000 description 2
- 238000007796 conventional method Methods 0.000 description 2
- 239000002270 dispersing agent Substances 0.000 description 2
- 238000001914 filtration Methods 0.000 description 2
- 238000007561 laser diffraction method Methods 0.000 description 2
- BDAGIHXWWSANSR-UHFFFAOYSA-N methanoic acid Natural products OC=O BDAGIHXWWSANSR-UHFFFAOYSA-N 0.000 description 2
- 239000002244 precipitate Substances 0.000 description 2
- 238000000790 scattering method Methods 0.000 description 2
- 238000000926 separation method Methods 0.000 description 2
- HAAYBYDROVFKPU-UHFFFAOYSA-N silver;azane;nitrate Chemical compound N.N.[Ag+].[O-][N+]([O-])=O HAAYBYDROVFKPU-UHFFFAOYSA-N 0.000 description 2
- 238000003756 stirring Methods 0.000 description 2
- 239000000725 suspension Substances 0.000 description 2
- 238000005406 washing Methods 0.000 description 2
- OSWFIVFLDKOXQC-UHFFFAOYSA-N 4-(3-methoxyphenyl)aniline Chemical compound COC1=CC=CC(C=2C=CC(N)=CC=2)=C1 OSWFIVFLDKOXQC-UHFFFAOYSA-N 0.000 description 1
- KWSLGOVYXMQPPX-UHFFFAOYSA-N 5-[3-(trifluoromethyl)phenyl]-2h-tetrazole Chemical compound FC(F)(F)C1=CC=CC(C2=NNN=N2)=C1 KWSLGOVYXMQPPX-UHFFFAOYSA-N 0.000 description 1
- 239000004925 Acrylic resin Substances 0.000 description 1
- 229920000178 Acrylic resin Polymers 0.000 description 1
- 238000004438 BET method Methods 0.000 description 1
- QPLDLSVMHZLSFG-UHFFFAOYSA-N Copper oxide Chemical compound [Cu]=O QPLDLSVMHZLSFG-UHFFFAOYSA-N 0.000 description 1
- 239000005751 Copper oxide Substances 0.000 description 1
- FEWJPZIEWOKRBE-JCYAYHJZSA-N Dextrotartaric acid Chemical compound OC(=O)[C@H](O)[C@@H](O)C(O)=O FEWJPZIEWOKRBE-JCYAYHJZSA-N 0.000 description 1
- ZZSNKZQZMQGXPY-UHFFFAOYSA-N Ethyl cellulose Chemical compound CCOCC1OC(OC)C(OCC)C(OCC)C1OC1C(O)C(O)C(OC)C(CO)O1 ZZSNKZQZMQGXPY-UHFFFAOYSA-N 0.000 description 1
- 239000001856 Ethyl cellulose Substances 0.000 description 1
- WQZGKKKJIJFFOK-GASJEMHNSA-N Glucose Natural products OC[C@H]1OC(O)[C@H](O)[C@@H](O)[C@@H]1O WQZGKKKJIJFFOK-GASJEMHNSA-N 0.000 description 1
- 239000001358 L(+)-tartaric acid Substances 0.000 description 1
- 235000011002 L(+)-tartaric acid Nutrition 0.000 description 1
- FEWJPZIEWOKRBE-LWMBPPNESA-N L-(+)-Tartaric acid Natural products OC(=O)[C@@H](O)[C@H](O)C(O)=O FEWJPZIEWOKRBE-LWMBPPNESA-N 0.000 description 1
- 239000002211 L-ascorbic acid Substances 0.000 description 1
- 235000000069 L-ascorbic acid Nutrition 0.000 description 1
- 239000004280 Sodium formate Substances 0.000 description 1
- LSNNMFCWUKXFEE-UHFFFAOYSA-N Sulfurous acid Chemical compound OS(O)=O LSNNMFCWUKXFEE-UHFFFAOYSA-N 0.000 description 1
- FEWJPZIEWOKRBE-UHFFFAOYSA-N Tartaric acid Natural products [H+].[H+].[O-]C(=O)C(O)C(O)C([O-])=O FEWJPZIEWOKRBE-UHFFFAOYSA-N 0.000 description 1
- 239000012190 activator Substances 0.000 description 1
- 150000001298 alcohols Chemical class 0.000 description 1
- 239000012670 alkaline solution Substances 0.000 description 1
- 229920000180 alkyd Polymers 0.000 description 1
- WUOACPNHFRMFPN-UHFFFAOYSA-N alpha-terpineol Chemical compound CC1=CCC(C(C)(C)O)CC1 WUOACPNHFRMFPN-UHFFFAOYSA-N 0.000 description 1
- VZTDIZULWFCMLS-UHFFFAOYSA-N ammonium formate Chemical compound [NH4+].[O-]C=O VZTDIZULWFCMLS-UHFFFAOYSA-N 0.000 description 1
- 150000003863 ammonium salts Chemical class 0.000 description 1
- 229940101006 anhydrous sodium sulfite Drugs 0.000 description 1
- 239000007900 aqueous suspension Substances 0.000 description 1
- 229960005070 ascorbic acid Drugs 0.000 description 1
- 239000012298 atmosphere Substances 0.000 description 1
- WQZGKKKJIJFFOK-VFUOTHLCSA-N beta-D-glucose Chemical compound OC[C@H]1O[C@@H](O)[C@H](O)[C@@H](O)[C@@H]1O WQZGKKKJIJFFOK-VFUOTHLCSA-N 0.000 description 1
- 229910000416 bismuth oxide Inorganic materials 0.000 description 1
- 229920002678 cellulose Polymers 0.000 description 1
- 235000010980 cellulose Nutrition 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
- 239000011362 coarse particle Substances 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 229910000431 copper oxide Inorganic materials 0.000 description 1
- 230000018044 dehydration Effects 0.000 description 1
- 238000006297 dehydration reaction Methods 0.000 description 1
- SQIFACVGCPWBQZ-UHFFFAOYSA-N delta-terpineol Natural products CC(C)(O)C1CCC(=C)CC1 SQIFACVGCPWBQZ-UHFFFAOYSA-N 0.000 description 1
- TYIXMATWDRGMPF-UHFFFAOYSA-N dibismuth;oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[Bi+3].[Bi+3] TYIXMATWDRGMPF-UHFFFAOYSA-N 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 239000002612 dispersion medium Substances 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 150000002148 esters Chemical class 0.000 description 1
- 150000002170 ethers Chemical class 0.000 description 1
- 235000019325 ethyl cellulose Nutrition 0.000 description 1
- 229920001249 ethyl cellulose Polymers 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 239000012530 fluid Substances 0.000 description 1
- 238000005187 foaming Methods 0.000 description 1
- 238000005755 formation reaction Methods 0.000 description 1
- 235000019253 formic acid Nutrition 0.000 description 1
- 239000008103 glucose Substances 0.000 description 1
- 150000002429 hydrazines Chemical class 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 description 1
- 238000003384 imaging method Methods 0.000 description 1
- 238000004898 kneading Methods 0.000 description 1
- 239000012528 membrane Substances 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
- 239000005011 phenolic resin Substances 0.000 description 1
- 230000000704 physical effect Effects 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 230000002250 progressing effect Effects 0.000 description 1
- 238000010298 pulverizing process Methods 0.000 description 1
- 238000006479 redox reaction Methods 0.000 description 1
- 230000007261 regionalization Effects 0.000 description 1
- 238000010079 rubber tapping Methods 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- HLBBKKJFGFRGMU-UHFFFAOYSA-M sodium formate Chemical compound [Na+].[O-]C=O HLBBKKJFGFRGMU-UHFFFAOYSA-M 0.000 description 1
- 235000019254 sodium formate Nutrition 0.000 description 1
- 229910001379 sodium hypophosphite Inorganic materials 0.000 description 1
- GEHJYWRUCIMESM-UHFFFAOYSA-L sodium sulfite Chemical compound [Na+].[Na+].[O-]S([O-])=O GEHJYWRUCIMESM-UHFFFAOYSA-L 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 230000001629 suppression Effects 0.000 description 1
- 229940116411 terpineol Drugs 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 238000001291 vacuum drying Methods 0.000 description 1
Landscapes
- Parts Printed On Printed Circuit Boards (AREA)
- Manufacture Of Metal Powder And Suspensions Thereof (AREA)
- Powder Metallurgy (AREA)
- Ceramic Capacitors (AREA)
Description
【０００１】
【発明の属する技術分野】
本発明は還元析出法により得られる銀粉の製造方法および当該方法により得られる銀粉に関する。詳しくは、部品電極または回路基板用パターンなどの電子部品に好適に使用される銀粉の製造方法および当該方法により製造される銀粉に関する。
【０００２】
【従来の技術】
従来積層セラミックコンデンサの電極など電子機器部品の一部や回路導体パターンなどに銀粉をガラスフリットとともに有機ビヒクル中に加え混練することによって得られる銀含有ペーストが使用されており、このようなペーストの銀粉には粒子径が適当に小さく粒度が揃っていることが要求されている。
上記の銀粉の製造には銀含有溶液にアルカリを加え酸化銀を生成させ、さらに還元剤を加えて銀粉を得る方法、もしくは銀含有溶液に錯化剤を加え錯体を生成させ、さらに還元剤を加えることで銀粉を得る方法が用いられている。
【０００３】
しかしながら、これらの方法で製造された銀粉は凝集が激しく、ファインライン化が進む導体パターンや積層セラミックコンデンサの内部電極の薄膜化に対応できないという欠点があった。
そのため、得られる銀粉をより凝集の少ないものとすべく改善が行われ、それらの改善結果が例えば特開昭５４−１２１２７０号公報、特開昭６１−２４３１０５号公報および特開平１０−８８２０６号公報などに開示されている。
【０００４】
特開昭５４−１２１２７０号公報には、硝酸銀溶液とホルマリンの混合水溶液に析出銀量に対して０．１〜５重量％の脂肪酸を添加攪拌し、これにアルカリ性溶液を添加して、銀粉末を析出させる方法が開示され、還元反応により銀微粒子が析出した時点で、脂肪酸が銀微粒子を被覆することで微細に分散した銀粉が得られると記載されている。
特開昭６１−２４３１０５号公報には、疎水性反応槽内で還元剤を用いてアンモニア性硝酸銀錯体溶液を還元し、銀微粒子を製造する方法において、反応溶液中にカチオン系界面活性剤を添加することで、単分散した銀微粒子を得る方法が開示され、疎水性反応槽を使用する理由は、親水性の場合、析出反応が容器の壁面で起こるために凝集した粒度分布の幅の広い銀粒子しか得られないと記載している。
【０００５】
また、反応溶液中にカチオン系界面活性剤を添加する理由は、アンモニア性硝酸銀錯体溶液を還元することによって、水溶液中に析出した銀微粒子が凝集しないで単分散状態を保つようにするためと記載されている。この方法と同様にして、特開昭６１−２７６９０５号公報には、非イオン系界面活性剤を用いた方法が記載されている。しかし、非イオン系界面活性剤は反応槽内を疎水性に保つため用いており、銀粒子の分散についてはカチオン系界面活性剤を用いて凝集を防いでいる。また、特開平１０−８８２０６では以上の諸問題を解決するべく、還元剤を高速で添加し得られたウェットケーキに分散剤の処理を施す方法が記載されている。
【０００６】
【発明が解決しようとする課題】
しかしながら、これらの方法で製造された銀粉でも、電子機器部品においてより細い導体パターンやより薄い電極が要求されるに従い、分散性等の特性が必ずしも十分ではなくなってきた。またペースト製造技術の多様化によって、イオン系界面活性剤や脂肪酸を用いた銀粉では、これら界面活性剤の影響でペースト組成中の分散性が不十分となることがあった。従って本発明の目的は、分散性の優れた銀粉で、しかもこの銀粉を用いて作製したペーストにこの銀粉からのイオン系界面活性剤や脂肪酸の混入のない分散性のよいペーストが得られる銀粉の製造方法とそれにより得られる銀粉を提供することにある。
【０００７】
【課題を解決するための手段】
本発明者らは上記目的を達成するため鋭意研究した結果、銀塩（銀錯体）あるいは酸化銀を含有する水溶液あるいは水性懸濁液あるいは両者の混合体からなる水性反応系に銀粒子の凝集を防ぎ、還元剤の拡散を促進するため非イオン性界面活性剤を加えておき、その系に対して還元剤含有水溶液を加える際、還元された銀粒子の凝集を防ぐため還元剤含有水溶液の添加速度を早くし、還元反応当量で１当量／分以上の速度で還元剤を添加し、銀粉を得ることで、前記の課題が解消されて優れた分散性を有する銀粉が得られることを見出し本発明に到達した。
【０００８】
すなわち本発明は、第１に、銀塩と酸化銀の少なくとも一方を含有する水性反応系に還元剤含有水溶液を添加することにより混合し、銀粒子を還元析出させる銀粉の製造方法において、還元前にＨＬＢ値が６〜１７の非イオン性界面活性剤を前記水性反応系に含有されている還元前の銀量に対して０．０１〜３重量％添加し、かつ、前記還元剤含有水溶液の添加速度が、前記水性反応系に含有されている還元前の銀量に対して、還元反応当量で、還元剤の添加速度として１当量／分以上であることを特徴とする銀粉の製造方法；第２に、前記水性反応系が銀塩として銀錯体を含有する水溶液であることを特徴とする第１記載の銀粉の製造方法を提供するものである。
【０００９】
【発明の実施の形態】
本発明の製造方法の特徴は、還元工程において銀イオン（銀塩）または酸化銀を含む水性反応系に還元前に分散剤として非イオン性界面活性剤を添加すること、好ましくは非イオン性界面活性剤のＨＬＢ値が６〜１７であること、さらに好ましくは還元剤水溶液を１当量／分以上の速度で添加すること、あるいは反応系内における銀の還元反応すなわち銀粉の生成反応が１分以内程度で終了するようにすることにある。
本発明における製造方法で、水性反応系中の銀粉に還元する前の銀形態は特に限定するものではない。具体的には、銀錯体塩含有水溶液の場合は例えば硝酸銀水溶液に錯化剤を加えて得られ、錯化剤にはアンモニア水、アンモニウム塩、キレート化合物等が使用できる。一方、酸化銀含有懸濁液（スラリー）の場合は、例えば硝酸銀水溶液にアルカリ例えば水酸化ナトリウム、水酸化カリウム等の水酸化物を添加することにより得ることができる。また、このようにして得られた銀錯体塩含有水溶液、酸化銀含有懸濁液を混合してから還元しても何ら差し支えない。
【００１０】
次に還元剤であるが、水溶液中の酸化還元反応を利用して、銀粉を製造する公知の方法で用いる還元剤であれば何ら問題はなく、水性反応系中の銀を還元するのに足りうる量の還元剤を用いる。具体例としては、ヒドラジン、ヒドラジン化合物、ホルマリン、ぶどう糖、水素化ほう素ナトリウム、次亜リン酸ナトリウム、亜硫酸塩、ギ酸、ギ酸ナトリウム、無水亜硫酸ナトリウム、Ｌ（＋）酒石酸、ギ酸アンモニウム、ロンガリット、Ｌ−アスコルビン酸、またはこれらの混合物である。これらの中で還元力の強い水素化ほう素ナトリウム、ヒドラジン、ホルマリンなどが特に好ましい。
【００１１】
そして、これらの還元剤のうち液体状のものはそのままあるいは水溶液として、固体状のものは水溶液として使用するので、本発明では液体状の還元剤を希釈せずに用いる場合も還元剤含有水溶液に含める。使用の際には水溶液とした際に分解してしまう物質については、溶液ｐＨをアルカリ側にするなどの処理を行う。還元時の温度については２０〜８０℃の温度範囲で行うのが望ましい。水性反応系の液温は５〜７０℃に調整する。この調整を行うことで還元反応が発熱反応の場合還元時の温度が２０〜８０℃の範囲にできる。水性反応系を５℃未満にすると、液の粘性が増し析出する銀粉の分散性が低下したり、冷却コストの面から好ましくない。また７０℃より高温にすると発熱反応で液温が更に上昇するため、銀粉の二次凝集が促進されることと、また取扱い上から７０℃以下が好ましい。以上の理由から水性反応系の温度は特に２０〜４０℃に調整するのが望ましい
。
【００１２】
銀塩と酸化銀の少なくとも一方を含有する水性反応系と還元剤含有水溶液とを混合する場合、水性反応系に還元剤含有水溶液を添加する方法、還元剤含有水溶液に水性反応系を添加する方法、両溶液を同時に接触する方法のいずれも可能である。
両溶液を混合することで還元反応が生じ銀粒子が析出する。この混合前に、即ち、還元前に分散剤である非イオン性界面活性剤を水性反応系に添加しておくと水性反応系中の流体の動きを適正化させることができ、混合した還元剤を水性反応系中によりよく拡散させることが可能となり、分散性の良好な銀粉を得ることができる。還元前に非イオン性界面活性剤を還元剤含有水溶液に添加することも可能であるが、ヒドラジン、水素化ほう素ナトリウム、ホルマリンなどの強い還元力を有する還元剤では非イオン性界面活性剤が還元されて銀塩、酸化銀の還元効率を低下させるため、このような場合は非イオン性界面活性剤は水性反応系に添加することが好ましい。
【００１３】
この非イオン系界面活性剤としては、界面活性剤の親水性親油性バランスを示すＨＬＢ値が６〜１７の範囲にある非イオン性界面活性剤が好ましい。これは非イオン性界面活性剤が粒子表面を被覆することでさらに凝集を押さえることができ、より分散性が向上するものと考えられる。なお、使用する非イオン性界面活性剤についてはそのＨＬＢ値が６を下回ると界面活性剤が洗浄されずに残ってしまい、得られる銀粉の含量が低下してしまう。また、ＨＬＢ値が１７を超えても反応中に発泡してしまい実作業上好ましくない上に、添加する効果が現れないためである。また、非イオン系界面活性剤の添加量としては、還元前の銀量に対して０．０１〜３重量％が好ましい。添加量が０．０１重量％未満では十分な分散効果が得られず、３重量％を超えると分散効果が飽和してしまいコストが不必要にかかることになるとともに銀粉析出後に銀粉に過剰に付着する分を固液分離後の水洗等で十分に洗い流すことができなくなる。これらの点から添加量は特に０．１〜１重量％が好ましい。
【００１４】
両溶液を混合する速度としては水性反応系に含有されている還元前の銀量に対して、還元反応当量で還元剤の混合速度として１当量／分以上の速さあるいは反応当量の還元剤が１分以内に反応系全体に行き渡る速さで混合すると、析出する銀粉の凝集を防ぎ、分散性のよい銀粉を得られる。
還元剤含有水溶液を水性反応系に添加する場合、還元剤が添加される水性反応系の大きさが実操業で使用する反応槽程度の大きさのものである限り、その反応系の大きさによって厳密に添加速度を変更する必要はなく１当量／分以上の速度で添加すれば効果があることが確認された。
【００１５】
この操作の理由は定かではないが、還元剤を短時間で添加することで銀粒子への還元析出が一挙に生じ、短時間で還元反応が終了するために発生した核同士の凝集が生じにくく、より分散性が向上するものと考えられる。また還元の際には、より短時間で反応が終了するように反応液を攪拌することが好ましい。なお、反応槽としては内壁が必ずしも疎水性のものを必要としない。
【００１６】
こうして得られた銀粉含有スラリーを、濾過、水洗、脱水工程を経て銀粉ウェットケーキとする。ウェットケーキは取り扱いやすさから含水率１０〜６０重量％が好ましい。含水率が低いほど乾燥時間が短く、また乾燥温度が低くてすみ、銀粉の凝集が抑えられるため、また脱水の効率から特に１０〜３０重量％が好ましい。こうして得られた銀粉ウェットケーキは、乾燥工程を経て銀粉となる。濾過、水洗の方法は通常の固液分離に使用する装置を用いれば何ら問題はない。乾燥方法については公知の方法および設備を用いれば良く、雰囲気も特に限定されるものではないが、真空乾燥のものがより好ましく、乾燥温度も８０℃以下が好ましい。
なお、水性反応系での銀（錯体）塩や、酸化銀の濃度は最終的な水性反応系の液量として銀濃度として０．０１〜０．４mol/dm3が好ましい。０．０１mol/dm3より低濃度では生産性が低下し、０．４mol/dm3より高濃度では球状の形状が崩 れるためである。これらの点から特に０．０５〜０．２mol/dm3が好ましい。
【００１７】
銀濃度が０．０１〜０．４mol/dm3となる硝酸銀水溶液にアンモニアを加えて、銀錯体塩を含有した水性反応系を得る場合は、この硝酸銀水溶液に含有している銀に対してモル比で４〜８のアンモニアを添加する。アンモニアの添加量がモル比で４より少ないと錯体が不安定となり、モル比で８より多いと銀錯体が安定化し過ぎてしまい、析出する銀粉の収率が低下する。
このアンモニアを添加した硝酸銀水溶液を５〜５０℃に温度を調整する。液温が５℃未満では溶液の粘性が高くなり十分に分散した銀粉が得られず、５０℃より高温ではアンモニアが飛散して銀錯体の安定度が低下し好ましくない。これらの点から特に２０〜４０℃で還元反応を行うのが好ましい。
【００１８】
これら工程を通して製造された銀粉は、タップ密度が２．５g/cm3以上、レー ザー回折・散乱法による平均粒径が１〜６μｍ、比表面積が５m2/ｇ以下の物性 を有するものである。タップ密度はＪIＳ Ｋ５１０１−１９９１の２０．２の タップ法に準じた方法により測定した。タッピング回数は１，０００回である。従来方法により製造した銀粉は分散性が不十分でありこの方法で測定したタップ密度は２．５g/cm3未満であるのに対し、本発明により得られる銀粉は単分散に より近い状態のためタップ密度は２．５g/cm3以上となる。
銀粉の平均粒径については、レーザー回折・散乱法により測定しており、装置は日機装製マイクロトラック粒度分析計9320-X100を用いた。分散媒はIPA（イソプロピルアルコール）を用いている。
【００１９】
この方法で測定した場合、本発明により得られた銀粉は平均粒径が１〜６μm となるのに対し、従来法による銀粉は６μmを超える値となり分散性が劣ってい る。１μm未満の銀粉は技術的に本発明では得るのが難しい。比表面積はBET法で測定した。本発明法で製造した銀粉は５m2/g以下となる。上記特性を持つ銀粉を、その主用途であるペーストとして評価すると、その銀粉の優れた面を知ることができる。
【００２０】
ペースト化の方法については、公知の例に従って実施すれば、特に問題はない。ここではハイブリッドICなどの導体パターン形成に使用される厚膜銀ペーストを例とする。まずペーストに使用するビヒクルであるが、一般的には各種セルロース、アクリル樹脂、フェノール樹脂、アルキッド樹脂などを、アルコール系、エステル系、エーテル系、炭化水素等の溶剤に溶解したものが用いられる。また導体パターンとアルミナ基板などのセラミック基板を結着するために、各種無機バインダーがペーストに添加される。無機バインダーとしては、酸化銅、酸化ビスマスといった金属酸化物や、ガラスを微細に粉砕したガラスフリットといわれるものが用いられる。
【００２１】
評価のための試験においては、上記ペースト構成物の多くの組み合わせの中より、ごく一般的な組成でペーストを調製し、銀粉の評価を行った。ビヒクルはエチルセルロースをターピネオールに溶解し、10％溶液を調製した。このビヒクルと日本電気ガラス製GA-8ガラス粉および銀粉をビヒクル23.4％、銀粉75％、GA-8ガラス粉1.6％の組成となるように秤量する。
【００２２】
これらペースト構成物をビーカー中で予備混合後、３本ロールにて分散、ペーストを得る。96％アルミナ基板上に、スクリーンにてペーストを引き延ばして印刷し、ペースト塗膜を10分間のレベリング後、熱風循環乾燥機で150℃、10分間 の乾燥を行う。乾燥させた塗膜は次の方法により評価した。
1)グラインドゲージにてそのペーストの４thスクラッチ（第４スクラッチ）と平均粒径（D50）を測定した。
なお、第４スクラッチとはグラインドゲージによるペーストの粒度測定で最大粗粒から数えて４番目の粒径をいう。
2)表面粗さは触針式表面粗さ計で測定できるが、ここでは（株）ミツトヨ製Surftest-501を用いて測定した。測定モードはRaとし、測定レンジ80μm、カット オフ値0.3mm、測定区間３とした。
【００２３】
これらの方法により銀粉を評価したところ次のことを見出した。分散性の優れた銀粉を用いたペーストはグラインドゲージで第４スクラッチが12μm以下、D50値が9μm以下となり、さらに塗膜はRaが0.8μm以下となり、特に優れた銀粉は0.5μm以下と小さい値を示し、平滑な塗膜になるのである。このような凝集粒が少なく均一で、しかも表面が滑らかな塗膜は、タップ密度2.5g/cm3以上、マイクロトラックによる平均粒径が１〜６μmで、比表面積５m2/g以下の銀粉から得られ ることは言うまでもない。
このように、凝集体が少ない表面粗度が低くなる銀粉を用いることは、撮像法などによるパターン形成時の精度を高め、その結果として得られる応用製品の高特性化に大きく寄与することとなり、イオン性などの界面活性剤を嫌うペースト組成などにおいても、それらと同等の特性を得ることができる点も本発明の製造方法の特徴であり、銀粉の特徴でもある。以下実施例により本発明をさらに詳細に説明する。しかし本発明の範囲は以下の実施例により制限されるものではない。
【００２４】
【実施例】
銀イオンとして10g/dm3の硝酸銀水溶液1OOdm3に、25％アンモニア水7.5dm3を 加え、銀アンミン錯体水溶液を得た。この水溶液を液温40℃とし、HLB値＝8の第一工業製薬（株）社製非イオン性界面活性剤ノイゲンET-80Eを3.4ｇ加えて攪拌 しながら、37％ホルマリン水溶液4.5dm3を10秒間加え、銀粉を析出させ銀粉含有スラリ一を得た。このスラリーをブフナー漏斗で濾過水洗しウェットケーキを得、これを真空中70℃、24時間乾燥して銀粉を得た。
得られた銀粉はタップ密度4.Og/cm3、マイクロトラックによる粒径が4.6μm、比表面積0.25m2/gであった。さらにこの粉末をペースト化し、評価を行った。方法は前項「発明の実施の形態」の項で記述した方法である。その結果、グラインドゲージ、第４スクラッチ＝6.3μm、平均粒径D50=5.3μm、塗膜Ra＝0.5μmで良好な結果が得られた。
【００２５】
【比較例】
銀イオンとして10g/dm3の硝酸銀水溶液1OOdm3に、25％アンモニア水7.5dm3を 加え、銀アンミン錯体水溶液を得た。この水溶液を液温40℃として攪拌しながら、37％ホルマリン水溶液4.5dm3を10秒間で加え、銀粉を析出させ銀粉含有スラリーを得た。
このスラリーをブフナー漏斗で濾過水洗しウェットケーキを得、これを真空中70℃、24時間乾燥して銀粉を得た。得られた銀粉はタップ密度2.2g/cm3、マイクロトラックによる粒径が10.2μm、比表面積0.25m2/gであった。さらにこの粉末 をペースト化し、評価を行った。方法は前項「発明の実施の形態」の項で記述した方法である。その結果、グラインドゲージ、第４スクラッチ＝13.8μm、平均 粒径D50＝9.7μm、塗膜Ra＝0.9μmで分散が進んでいないという結果が得られた
。
【００２６】
【発明の効果】
以上説明したように、還元前に非イオン性界面活性剤を添加しない方法では大きな凝集体があり、分散性の良くない場合があり、分散性を必要とする用途への使用が限定されてしまうのに対し、本発明の方法によれば、非イオン界面活性剤を加えて還元剤含有水溶液の添加速度を１当量／分以上として反応した銀粉は分散性に優れ、ペースト化して回路基板の導体パターン等に好適な塗膜または焼成膜とすることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing silver powder obtained by a reduction precipitation method and a silver powder obtained by the method. Specifically, the present invention relates to a method for producing silver powder suitably used for electronic components such as component electrodes or circuit board patterns, and silver powder produced by the method.
[0002]
[Prior art]
Conventionally, a silver-containing paste obtained by adding silver powder to an organic vehicle together with a glass frit and kneading a part of an electronic device component such as an electrode of a multilayer ceramic capacitor or a circuit conductor pattern has been used. Is required to have a suitably small particle size and uniform particle size.
In the production of the silver powder, alkali is added to the silver-containing solution to form silver oxide, and further a reducing agent is added to obtain silver powder, or a complexing agent is added to the silver-containing solution to form a complex, and a reducing agent is further added. The method of obtaining silver powder by adding is used.
[0003]
However, the silver powder produced by these methods has a strong agglomeration, and has a disadvantage that it cannot cope with the thinning of the conductive pattern and the internal electrode of the multilayer ceramic capacitor which are becoming finer.
Therefore, improvements have been made so that the resulting silver powder has less agglomeration, and the results of such improvements are disclosed in, for example, JP-A Nos. 54-121270, 61-243105 and 10-88206. And the like.
[0004]
In Japanese Patent Laid-Open No. 54-121270, silver powder is prepared by adding 0.1 to 5% by weight of a fatty acid to a mixed aqueous solution of a silver nitrate solution and formalin with stirring, and adding an alkaline solution thereto. Is disclosed, and when silver fine particles are precipitated by the reduction reaction, it is described that a finely dispersed silver powder is obtained by coating the silver fine particles with a fatty acid.
In JP-A-61-243105, a cationic surfactant is added to a reaction solution in a method for producing silver fine particles by reducing an ammoniacal silver nitrate complex solution using a reducing agent in a hydrophobic reaction tank. Thus, a method for obtaining monodispersed silver fine particles is disclosed, and the reason for using a hydrophobic reaction vessel is that, in the case of hydrophilicity, the precipitation reaction occurs on the wall surface of the container, so that the aggregated particle size distribution is wide. It states that only particles can be obtained.
[0005]
In addition, the reason for adding a cationic surfactant to the reaction solution is to reduce the ammoniacal silver nitrate complex solution so that the silver fine particles deposited in the aqueous solution can be kept in a monodispersed state without aggregation. Has been. Similarly to this method, JP-A-61-276905 describes a method using a nonionic surfactant. However, a nonionic surfactant is used to keep the inside of the reaction vessel hydrophobic, and a cationic surfactant is used for dispersion of silver particles to prevent aggregation. Japanese Patent Application Laid-Open No. 10-88206 describes a method for treating a wet cake obtained by adding a reducing agent at a high speed to solve the above problems.
[0006]
[Problems to be solved by the invention]
However, even with silver powder produced by these methods, characteristics such as dispersibility have not always been sufficient as electronic device parts require thinner conductor patterns and thinner electrodes. Further, due to diversification of paste manufacturing techniques, dispersibility in the paste composition may be insufficient due to the influence of these surfactants in silver powder using ionic surfactants and fatty acids. Therefore, an object of the present invention is a silver powder having excellent dispersibility, and a paste having a good dispersibility without mixing ionic surfactant and fatty acid from the silver powder into a paste prepared using the silver powder. It is in providing a manufacturing method and the silver powder obtained by it.
[0007]
[Means for Solving the Problems]
As a result of intensive studies to achieve the above object, the present inventors have found that silver particles are aggregated in an aqueous reaction system comprising an aqueous solution or aqueous suspension containing silver salt (silver complex) or silver oxide, or a mixture of both. In order to prevent and promote the diffusion of the reducing agent, add a nonionic surfactant, and when adding the reducing agent-containing aqueous solution to the system, add the reducing agent-containing aqueous solution to prevent aggregation of the reduced silver particles It is found that the above problem is solved and silver powder having excellent dispersibility can be obtained by increasing the speed, adding a reducing agent at a reduction reaction equivalent rate of 1 equivalent / min or more, and obtaining silver powder. The invention has been reached.
[0008]
That is, the present invention firstly relates to a silver powder production method in which an aqueous reaction system containing at least one of a silver salt and silver oxide is mixed by adding a reducing agent-containing aqueous solution to reduce and precipitate silver particles. A nonionic surfactant having an HLB value of 6 to 17 is added in an amount of 0.01 to 3% by weight with respect to the amount of silver before reduction contained in the aqueous reaction system, and The method for producing silver powder, wherein the addition rate is equivalent to a reduction reaction equivalent to the silver amount before reduction contained in the aqueous reaction system, and the addition rate of the reducing agent is 1 equivalent / min or more; Second, the aqueous reaction system is an aqueous solution containing a silver complex as a silver salt. The method for producing silver powder according to the first aspect is provided.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
A feature of the production method of the present invention is that a nonionic surfactant is added as a dispersant to the aqueous reaction system containing silver ions (silver salt) or silver oxide before the reduction in the reduction step, preferably a nonionic interface. The HLB value of the activator is 6 to 17, more preferably an aqueous reducing agent solution is added at a rate of 1 equivalent / min or more, or the silver reduction reaction in the reaction system, that is, the silver powder formation reaction is within 1 minute. It is to be finished with a degree.
In the production method of the present invention, the silver form before being reduced to silver powder in the aqueous reaction system is not particularly limited. Specifically, in the case of an aqueous solution containing a silver complex salt, for example, it is obtained by adding a complexing agent to an aqueous silver nitrate solution. As the complexing agent, aqueous ammonia, ammonium salt, chelate compound and the like can be used. On the other hand, in the case of a silver oxide-containing suspension (slurry), for example, it can be obtained by adding a hydroxide such as an alkali such as sodium hydroxide or potassium hydroxide to a silver nitrate aqueous solution. Further, the silver complex salt-containing aqueous solution and the silver oxide-containing suspension thus obtained may be mixed and then reduced.
[0010]
Next, as a reducing agent, there is no problem as long as it is a reducing agent used in a known method for producing silver powder using an oxidation-reduction reaction in an aqueous solution, and it is sufficient to reduce silver in an aqueous reaction system. Use as much reducing agent as possible. Specific examples include hydrazine, hydrazine compounds, formalin, glucose, sodium borohydride, sodium hypophosphite, sulfite, formic acid, sodium formate, anhydrous sodium sulfite, L (+) tartaric acid, ammonium formate, longgarit, L -Ascorbic acid or a mixture thereof. Of these, sodium borohydride, hydrazine, formalin and the like having a strong reducing power are particularly preferable.
[0011]
Of these reducing agents, liquid ones are used as they are or as aqueous solutions, and solid ones are used as aqueous solutions. In the present invention, the reducing agent-containing aqueous solution can be used even when the liquid reducing agent is used without being diluted. include. For a substance that decomposes when used as an aqueous solution during use, a treatment such as bringing the solution pH to the alkali side is performed. About the temperature at the time of reduction | restoration, it is desirable to carry out in the temperature range of 20-80 degreeC. The liquid temperature of the aqueous reaction system is adjusted to 5 to 70 ° C. By performing this adjustment, when the reduction reaction is an exothermic reaction, the temperature during the reduction can be in the range of 20 to 80 ° C. When the aqueous reaction system is lower than 5 ° C., the viscosity of the liquid increases and the dispersibility of the precipitated silver powder decreases, and it is not preferable from the viewpoint of cooling cost. Further, when the temperature is higher than 70 ° C., the liquid temperature further increases due to an exothermic reaction, so that the secondary aggregation of silver powder is promoted, and 70 ° C. or lower is preferable in terms of handling. For the above reasons, the temperature of the aqueous reaction system is particularly preferably adjusted to 20 to 40 ° C.
[0012]
When mixing an aqueous reaction system containing at least one of silver salt and silver oxide and a reducing agent-containing aqueous solution, a method of adding the reducing agent-containing aqueous solution to the aqueous reaction system, a method of adding the aqueous reaction system to the reducing agent-containing aqueous solution Any method of contacting both solutions simultaneously is possible.
By mixing both solutions, a reduction reaction occurs and silver particles are precipitated. Before the mixing, that is, before the reduction, a nonionic surfactant that is a dispersing agent is added to the aqueous reaction system, so that the movement of the fluid in the aqueous reaction system can be optimized. Can be diffused better in the aqueous reaction system, and silver powder with good dispersibility can be obtained. It is possible to add a nonionic surfactant to the reducing agent-containing aqueous solution before the reduction, but in the case of a reducing agent having a strong reducing power such as hydrazine, sodium borohydride, formalin, etc., a nonionic surfactant is used. In such a case, it is preferable to add the nonionic surfactant to the aqueous reaction system because it reduces the reduction efficiency of the silver salt and silver oxide.
[0013]
The nonionic surfactant is preferably a nonionic surfactant having an HLB value in the range of 6 to 17 indicating the hydrophilic / lipophilic balance of the surfactant. It is considered that this is because the nonionic surfactant can further suppress aggregation by covering the particle surface, and the dispersibility is further improved. In addition, about the nonionic surfactant to be used, when the HLB value is less than 6, the surfactant remains without being washed, and the content of the obtained silver powder is lowered. Further, even if the HLB value exceeds 17, foaming occurs during the reaction, which is not preferable in actual work, and the effect of addition does not appear. Moreover, as an addition amount of a nonionic surfactant, 0.01 to 3 weight% is preferable with respect to the silver amount before a reduction | restoration. If the added amount is less than 0.01% by weight, a sufficient dispersion effect cannot be obtained. If the added amount exceeds 3% by weight, the dispersion effect is saturated and the cost becomes unnecessary, and the silver powder is excessively deposited after the silver powder is deposited. The portion to be removed cannot be sufficiently washed away with water after solid-liquid separation. From these points, the addition amount is particularly preferably 0.1 to 1% by weight.
[0014]
The mixing speed of the two solutions is a reduction reaction equivalent of 1 equivalent / min or more of the reducing agent equivalent to the amount of silver before the reduction contained in the aqueous reaction system, or a reaction equivalent of the reducing agent. When mixed at a speed that reaches the entire reaction system within 1 minute, the silver powder that precipitates is prevented from agglomerating, and silver powder with good dispersibility can be obtained.
When adding a reducing agent-containing aqueous solution to an aqueous reaction system, depending on the size of the reaction system, as long as the size of the aqueous reaction system to which the reducing agent is added is about the size of a reaction tank used in actual operation. It was not necessary to strictly change the addition rate, and it was confirmed that the addition was effective at a rate of 1 equivalent / min or more.
[0015]
The reason for this operation is not clear, but by adding the reducing agent in a short time, reduction precipitation on the silver particles occurs all at once, and the reduction reaction is completed in a short time, so it is difficult for the generated nuclei to aggregate. Therefore, it is considered that the dispersibility is further improved. In the reduction, the reaction solution is preferably stirred so that the reaction is completed in a shorter time. Note that the reaction vessel does not necessarily have a hydrophobic inner wall.
[0016]
The silver powder-containing slurry thus obtained is made into a silver powder wet cake through filtration, water washing and dehydration steps. The wet cake preferably has a water content of 10 to 60% by weight for ease of handling. The lower the moisture content, the shorter the drying time, the lower the drying temperature, and the suppression of the aggregation of the silver powder. The silver powder wet cake thus obtained becomes silver powder through a drying step. There is no problem with the methods of filtration and water washing if an apparatus used for ordinary solid-liquid separation is used. As the drying method, known methods and equipment may be used, and the atmosphere is not particularly limited, but vacuum drying is more preferable, and the drying temperature is preferably 80 ° C. or less.
The concentration of silver (complex) salt and silver oxide in the aqueous reaction system is preferably 0.01 to 0.4 mol / dm 3 as the silver concentration as the final liquid volume of the aqueous reaction system. This is because the productivity is lowered at a concentration lower than 0.01 mol / dm 3 , and the spherical shape collapses at a concentration higher than 0.4 mol / dm 3 . From these points, 0.05 to 0.2 mol / dm 3 is particularly preferable.
[0017]
In the case where an aqueous reaction system containing a silver complex salt is obtained by adding ammonia to an aqueous silver nitrate solution having a silver concentration of 0.01 to 0.4 mol / dm 3 , the molar ratio relative to the silver contained in the aqueous silver nitrate solution is Ammonia in a ratio of 4-8 is added. If the added amount of ammonia is less than 4 in molar ratio, the complex becomes unstable, and if it is more than 8 in molar ratio, the silver complex is overstabilized and the yield of precipitated silver powder decreases.
The temperature of the aqueous silver nitrate solution added with ammonia is adjusted to 5 to 50 ° C. If the liquid temperature is less than 5 ° C., the viscosity of the solution becomes high, and a sufficiently dispersed silver powder cannot be obtained. If the temperature is higher than 50 ° C., ammonia is scattered and the stability of the silver complex decreases, which is not preferable. From these points, it is particularly preferable to carry out the reduction reaction at 20 to 40 ° C.
[0018]
The silver powder produced through these processes has physical properties such that the tap density is 2.5 g / cm 3 or more, the average particle size by laser diffraction / scattering method is 1 to 6 μm, and the specific surface area is 5 m 2 / g or less. . The tap density was measured by a method according to the 20.2 tap method of JIS K5101-1991. The number of tapping is 1,000 times. The silver powder produced by the conventional method has insufficient dispersibility, and the tap density measured by this method is less than 2.5 g / cm 3 , whereas the silver powder obtained by the present invention is closer to monodispersion. The tap density is 2.5 g / cm 3 or more.
The average particle diameter of the silver powder was measured by a laser diffraction / scattering method, and a Nikkiso Microtrack Particle Size Analyzer 9320-X100 was used as the apparatus. IPA (isopropyl alcohol) is used as the dispersion medium.
[0019]
When measured by this method, the silver powder obtained according to the present invention has an average particle diameter of 1 to 6 μm, whereas the silver powder obtained by the conventional method has a value exceeding 6 μm and is inferior in dispersibility. A silver powder of less than 1 μm is technically difficult to obtain in the present invention. The specific surface area was measured by the BET method. The silver powder produced by the method of the present invention is 5 m 2 / g or less. When the silver powder having the above characteristics is evaluated as a paste which is the main application, the excellent surface of the silver powder can be known.
[0020]
The pasting method is not particularly problematic as long as it is carried out according to known examples. Here, a thick film silver paste used for forming a conductor pattern such as a hybrid IC is taken as an example. First, the vehicle used for the paste is generally used by dissolving various celluloses, acrylic resins, phenol resins, alkyd resins and the like in solvents such as alcohols, esters, ethers, and hydrocarbons. Various inorganic binders are added to the paste in order to bind the conductor pattern and a ceramic substrate such as an alumina substrate. As the inorganic binder, a metal oxide such as copper oxide or bismuth oxide, or a so-called glass frit obtained by finely pulverizing glass is used.
[0021]
In the test for evaluation, a paste was prepared with a very general composition from among many combinations of the paste components, and silver powder was evaluated. As a vehicle, ethylcellulose was dissolved in terpineol to prepare a 10% solution. This vehicle, and Nippon Electric Glass GA-8 glass powder and silver powder are weighed to a composition of 23.4% vehicle, 75% silver powder and 1.6% GA-8 glass powder.
[0022]
These paste components are premixed in a beaker and then dispersed by a three roll to obtain a paste. Print on a 96% alumina substrate by stretching the paste on a screen, level the paste coating for 10 minutes, and then dry at 150 ° C for 10 minutes in a hot air circulating dryer. The dried coating film was evaluated by the following method.
1) The 4th scratch (fourth scratch) and average particle diameter (D 50 ) of the paste were measured with a grind gauge.
The fourth scratch means the fourth particle size counted from the largest coarse particle in the particle size measurement of the paste with a grind gauge.
2) The surface roughness can be measured with a stylus type surface roughness meter, but here, it was measured using Surftest-501 manufactured by Mitutoyo Corporation. The measurement mode was Ra, the measurement range was 80 μm, the cutoff value was 0.3 mm, and the measurement section was 3.
[0023]
When silver powder was evaluated by these methods, the following was found. The paste using silver powder with excellent dispersibility is a grind gauge, the fourth scratch is 12 μm or less, the D 50 value is 9 μm or less, the coating film has Ra of 0.8 μm or less, and the particularly excellent silver powder is as small as 0.5 μm or less. It shows a value and becomes a smooth coating film. Such a coating film with a small number of agglomerated particles and a smooth surface is made of silver powder having a tap density of 2.5 g / cm 3 or more, an average particle size of 1 to 6 μm by Microtrac, and a specific surface area of 5 m 2 / g or less. Needless to say, it can be obtained.
Thus, using silver powder with low surface roughness with few aggregates increases the accuracy during pattern formation by imaging methods and the like, and greatly contributes to the enhancement of the characteristics of the applied products obtained as a result. Even in paste compositions that dislike surfactants such as ionicity, the same characteristics as those can be obtained, which is a feature of the production method of the present invention and a feature of silver powder. Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited by the following examples.
[0024]
【Example】
The aqueous silver nitrate solution 1OOdm 3 of 10 g / dm 3 as silver ions, 25% aqueous ammonia 7.5Dm 3 to give a silver ammine complex solution. The aqueous solution was a liquid temperature of 40 ° C., while the Dai-ichi Kogyo Seiyaku Co., Ltd. nonionic surfactant Noigen ET-80E of HLB value = 8 and stirred with 3.4 g, 37% formaldehyde aqueous solution 4.5Dm 3 For 10 seconds, silver powder was precipitated to obtain a silver powder-containing slurry. This slurry was filtered and washed with a Buchner funnel to obtain a wet cake, which was dried in vacuum at 70 ° C. for 24 hours to obtain silver powder.
The obtained silver powder had a tap density of 4.Og / cm 3 , a particle size measured by Microtrac of 4.6 μm, and a specific surface area of 0.25 m 2 / g. Further, this powder was made into a paste and evaluated. The method is the method described in the preceding section “Embodiments of the Invention”. As a result, good results were obtained with a grind gauge, fourth scratch = 6.3 μm, average particle diameter D 50 = 5.3 μm, and coating film Ra = 0.5 μm.
[0025]
[Comparative example]
The aqueous silver nitrate solution 1OOdm 3 of 10 g / dm 3 as silver ions, 25% aqueous ammonia 7.5Dm 3 to give a silver ammine complex solution. While stirring this aqueous solution at a liquid temperature of 40 ° C., 4.5 dm 3 of 37% formalin aqueous solution was added over 10 seconds to precipitate silver powder to obtain a silver powder-containing slurry.
This slurry was filtered and washed with a Buchner funnel to obtain a wet cake, which was dried in vacuum at 70 ° C. for 24 hours to obtain silver powder. The obtained silver powder had a tap density of 2.2 g / cm 3 , a particle size by Microtrac of 10.2 μm, and a specific surface area of 0.25 m 2 / g. Furthermore, this powder was made into a paste and evaluated. The method is the method described in the preceding section “Embodiments of the Invention”. As a result, it was found that the dispersion was not progressing with the grind gauge, the fourth scratch = 13.8 μm, the average particle diameter D 50 = 9.7 μm, and the coating film Ra = 0.9 μm.
[0026]
【The invention's effect】
As explained above, the method in which the nonionic surfactant is not added before the reduction has large aggregates, and the dispersibility may not be good, and the use in applications requiring dispersibility is limited. On the other hand, according to the method of the present invention, the silver powder reacted by adding a nonionic surfactant and adding the reducing agent-containing aqueous solution at 1 equivalent / min or more is excellent in dispersibility, and pasted into a conductor of a circuit board. It can be set as the coating film or baking film | membrane suitable for a pattern etc.
Claims (2)
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| JP30136398A JP3751154B2 (en) | 1998-10-22 | 1998-10-22 | Silver powder manufacturing method |
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| JP30136398A JP3751154B2 (en) | 1998-10-22 | 1998-10-22 | Silver powder manufacturing method |
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| JP3751154B2 true JP3751154B2 (en) | 2006-03-01 |
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| JP4526200B2 (en) * | 2001-02-20 | 2010-08-18 | バンドー化学株式会社 | Method for producing metal colloid liquid |
| JP4320447B2 (en) * | 2004-02-03 | 2009-08-26 | Ｄｏｗａエレクトロニクス株式会社 | Silver powder and method for producing the same |
| JP4583063B2 (en) * | 2004-04-14 | 2010-11-17 | 三井金属鉱業株式会社 | Silver compound-coated silver powder and method for producing the same |
| JP4583147B2 (en) * | 2004-11-19 | 2010-11-17 | 三井金属鉱業株式会社 | Conductive composite powder and method for producing the same |
| JP5028695B2 (en) * | 2004-11-25 | 2012-09-19 | Ｄｏｗａエレクトロニクス株式会社 | Silver powder and method for producing the same |
| JP5032005B2 (en) * | 2005-07-05 | 2012-09-26 | 三井金属鉱業株式会社 | High crystal silver powder and method for producing the high crystal silver powder |
| KR101235873B1 (en) * | 2008-04-28 | 2013-02-21 | 타타 케미칼스 리미티드 | A process for the preparation of silver nano particles |
| JP2011080094A (en) * | 2009-10-02 | 2011-04-21 | Toda Kogyo Corp | Fine silver particle, method for producing same, conductive paste containing the fine silver particles, conductive film, and electronic device |
| JP5288063B2 (en) | 2011-06-08 | 2013-09-11 | 住友金属鉱山株式会社 | Silver powder and method for producing the same |
| WO2012176831A1 (en) | 2011-06-21 | 2012-12-27 | 住友金属鉱山株式会社 | Silver dust and manufacturing method thereof |
| MY185528A (en) | 2011-11-18 | 2021-05-19 | Sumitomo Metal Mining Co | Silver powder, method for producing silver powder, and conductive paste |
| JP5500237B1 (en) | 2012-12-05 | 2014-05-21 | 住友金属鉱山株式会社 | Silver powder |
| JP5505535B1 (en) | 2012-12-07 | 2014-05-28 | 住友金属鉱山株式会社 | Silver powder |
| JP6143627B2 (en) * | 2013-10-03 | 2017-06-07 | 住友金属鉱山株式会社 | Ammonia recovery method |
| CN105345024B (en) * | 2015-10-30 | 2017-12-26 | 溧阳市立方贵金属材料有限公司 | The preparation method of leaf shape silver powder |
| JP7215047B2 (en) * | 2018-09-28 | 2023-01-31 | 住友金属鉱山株式会社 | Conductive paste, electronic parts, and laminated ceramic capacitors |
| CN111599507A (en) * | 2020-06-02 | 2020-08-28 | 江西贝特利新材料有限公司 | Conductive silver paste based on smooth ultrathin flake silver powder and preparation method thereof |
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| JPS61276905A (en) * | 1985-05-31 | 1986-12-06 | Tanaka Kikinzoku Kogyo Kk | Production of fine silver particle |
| JP4025839B2 (en) * | 1996-09-12 | 2007-12-26 | Ｄｏｗａエレクトロニクス株式会社 | Silver powder and method for producing silver powder |
| JP4012960B2 (en) * | 1996-09-12 | 2007-11-28 | Ｄｏｗａエレクトロニクス株式会社 | Silver powder manufacturing method |
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