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1. IN6520/DELNP/2008 - SILVER ORGANO-SOL INK FOR FORMING ELECTRICALLY CONDUCTIVE PATTERNS

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Description SILVER ORGANO-SOL INK FOR FORMING ELECTRICALLYCONDUCTIVE PATTERNSTechnical Field[ 1] The present invention relates to silver organo-sol ink, more specifically inkcontaining a silver precursor for forming electrically conductive patterns. Background Art[2] In semiconductor and display industries, pattern forming technologies are classifiedinto 3 categories. One is a subtractive method mainly applied to thin film technologies such as CVD, PVD and sputtering wherein a functional layer is deposited on a substrate, a photo-resist layer is patterned by lithography on the functional layer, and then the functional layer is etched into a pattern. Another is an additive method used in thick film technologies such as screen-printing. The other is a subtractive-additive method adopting both of a subtractive method and an additive method. Pattern forming by an additive methodis an economical process, which spares material and reduces number of steps, but additive methods of thick filmtechnologies such as screen-printing are not so fine as thin filmtechnologies, and thus are applied to different processes.[3] If an additive method accomplishes finer patterns, it is more favorable in aspects ofenvironment and cost reduction. In this context, pattern forming by inkjet printing has been recently noted.For example, attempts to apply an additive method to pattern forming for color filters originally formed by thin filmtechnologies have been made.[4] MOD material has been researched since Vest, R.W. tested inks made of MODmateria] (IEEE Transactions on Components, Hybrids and Manufacturing Technology, 12(4), 545-549, 1987). Kydd, et al in W098-37133 disclosed inkjet-printing ink consisting of MOD material and particulate metal. US Patent No. 6878184 owned by Kovio Inc. disclosed metal ink of nano-size particle prepared from MOD and a reductant (for example, aldehydes). Many attempts have been made to use ink containing dispersed fine metal particles, especially silver particles for forming electrically conductive patterns. A new inkjet- printing system including nozzles should be devised with inks dispersed with fine metal particles, i.e., fine silver particles because those behave differently from ordinary inks. In addition, additives added to sustain suspension would do harm to the physical properties of patterns formed.[5] In the above-mentioned respect, inks containing MOD (metallo-organic de-composition materialman be applied to traditional inkjet printing devices without severe modification of the system if those are thoroughly solution. Solution inkscontaining MOD, in addition, can lower the temperature of metallization, and thus can be applied on flexible substrates such as plastic.[6] Korean Patent Publication No. 2004-85470 applied by Haeuncomtec disclosed ametal ink for inkjet-printing consisting of 5~40t% of silver oxide, 10-20 wt% of lactam, lactone or carbonate and 20-85 wt% of amine. The ink prepared in the example is likely suspension rather than solution considering the dark color of the ink. Emulsifier which may do harm to the physical properties of patterns formed, should be added to the ink to sustain suspension, In addition, maintenance problems concerning nozzle clog caused by particles may arise.[7] Prior arts published to date are listed below.[81[9][10][11] Table 1Patent Pocumepts(TableRemove) [121[13][14] Table 2Non-patent Documents(Table Removed) [151Disclosure of Invention Technical Problem[ 16] The object of the present invention is to provide silver organo-sol ink for formingelectrically conductive patterns with good physical properties.[17] Another object of the present invention is to provide silver organo-sol ink, whichcan be applied to traditional printing methods including inkjet-printing.[ 18] The other object of the present invention is to provide silver organo-sol ink, whichcan be reduced and metallized at a relatively lower temperature.[19]Technical Solution[20] The present invention provides silver organo-sol ink of solution type for formingelectrically conductive pattern comprising effective amount of silver CO to CI 6 aliphatic carboxylate saturated or unsaturated, linear or branched, unsubstituted or substituted with amino, nitro and/or hydroxy group(s) having 1 to 3 carboxyl groups or silver aromatic carboxylate defined as Formulas 1; and organic solvent[21][221Formula 1(Formula Removed)[23] in which R R R R and R are respectively COO Ag+, H, OH, amino, nitro or CI1, 2. 3. 4 5 r Jto C9 alkyl.[24] Herein, "organo-sol" means that silver exist as solution state bound to organicmaterial. The silver carboxylate in the ink of the present invention acts as a precursor for forming metal silver by heat-treasting or reducing. The said organic solvent desirably consists of a reactive organic solvent, which can form chelate or complex with silver, and polar or nonpolar organic solvent for control of viscosity. The reactive organic solvents, which can form chelate or complex with silver, are, for example, organic solvents having keton, mercapto, carboxyl, aniline or sulfurous functional group, substituted or unsubstituted. The silver aliphatic carboxylate or silver aromatic carboxylate is typically 5~70 wt% of the total ink composition.[25] As a preferred embodiment, the present invention provides silver organo-sol ink ofsolution type comprising 10 to 50 wt% of silver CO to C16 aliphatic carboxylate saturated or unsaturated, linear or branched, unsubstituted or substituted with with amino, nitro and/or hydroxy group(s) having 1 to 3 carboxyl groups; 10 to 60 wt% ofreactive organic solvent selected from the group consisting of amine substituted by one or more CI to C6 hydroxy alkyl and CI to C16 aliphatic thiol, linear or branched; and residual polar or nonpolar organic solvent.[26] The silver CO to CI6 saturated or unsaturated aliphatic carboxylate is desirablysaturated or has one or two double bonds. The silver aliphatic carboxylate, for example, silver malate, silver maleate, silver succinate, silver acetate, silver maloate, siver mathacrylate, silver propionate, silver sorbate, silver citrate, silver undecylenate, silver neododecanate, silver oleate, silver oxalate, silver formate or silver gluconate[27] As another preferred embodiment, the present invention provides silver organo-solink of solution type comprising 10 to 50 wt% of silver aromatic carboxylate defined as Formulas la; 10 to 60 wt% of reactive organic solvent selected from the group consisting of amine substituted by one or more CI to C6 hydroxy alkyl and CI to C16 aliphatic thiol, linear or branched; and residual polar or nonpolar organic solvent[28][291Formula la(Formula Removed)[30] in which R R R R and R are respectively H, OH,amino nitro or CI to C9 alkyl.1,2,3,4 5[31 ] Said silver aromatic carboxylate defined as Formulas la is, for example, silverbenzoate or silver 4-aminobenzoate.[32][33] As another preferred embodiment, the present invention provides silver organo-solink of solution type comprising 10 to 50 wt% of silver aromatic carboxylate defined as Formulas lb; 10 to 60 wt% of reactive organic solvent selected from the group consisting of amine substituted by one or more CI to C6 hydroxy alkyl and CI to C16 aliphatic thiol, linear or branched; and residual polar or nonpolar organic solvent[34][35]Formula lb(Formula Removed)[36] in which one among R R R R and R is COO~Ag+' and the others are re-1,2,3,4 5spectively H, OH, amino, nitro or CI to C9 alkyl, but desirably R is COO~Ag+and the others are respectively H, OH, CI to C9 alkyl.[37] Said silver aromatic carboxylate defined as Formulas lb is, for example, silverphthalate. The silver aromatic carboxylate having two carboxyl groups has the merit of higher contents of silver.[38] As another preferred embodiment, the present invention provides silver organo-solink of solution type comprising 10 to 50 wt% of silver aromatic carboxylate defined as Formulas lc; 10 to 60 wt% of reactive organic solvent selected from the group consisting of amine substituted by one or more CI to C6 hydroxy alkyl and CI to C16 aliphatic thiol, linear or branched; and residual polar or nonpolar organic solvent[39][40]Formula lc(Formula Removed)[41] in which two or more among R R R R and R are COO"Ag+, and the others arerespectively H, OHor amino, nitro CI to C9 alkyl, but desirably R and R are COOAg+.[42] Said silver aromatic carboxylate defined as Formulas lc is, for example, silvertrimesate. The silver aromatic carboxylate defined as Formulas lc has higher in contents of silver than those defined as Formulas la and Formulas lb.[431[44] The organo-sol ink of the present invention may further comprise surfactants and/orviscosity controlling agents. In addition, it may comprise further nonconductive polymeric or glassy material as matrix or flux material for silver conductor. The organo-sol ink of the present invention can be applied not only to processes for display manufacturing such as PDP and Rfid but also to other processes such as solar cells wherein conductive patterns are required.[45] Silver aromatic carboxylate defined as Formulas 1 has higher contents of silver,especially, silver benzoate has about 47 wt% of silver per mole of the compound. It has a merit of higher content of metallized silver even if small quantity is adopted.[46] Silver aromatic carboxylate defined as Formulas 1 in the organo-sol ink of thepresent invention desirably ranges from 5 wt % to 70 wt% of the total ink composition since silver content becomes small below 5 w% and making solution with it becomes difficult above 70 wt%. The preferred range is 10 wt % to 50 wt%. The most preferred range is 20 wt % to 40 wt%. Silver aromatic carboxylate defined as Formulas 1 is prepared by reacting silver inorganic acid salt such as silver nitrate with alkali metal salt corresponding to Formulas 1 with silver replaced by alkali metal.[47] The said reactive organic solvent is broadly organic solvent which can form chelateor complex with silver through hetero atom N, O and S ,more preferably, hydrocarbons having keton, mercapto, carboxyl, aniline or sulfurous functional group, substituted or unsubstituted. The most preferred are monoethanolamine, diethanolamine and tri-ethanolamine. The organo-sol ink of the present invention has light color but is basically clear. The viscosity of the initial solution which is prepared by dissolving the silver organic salt in a reactive organic solvent such as ethanolamine ranges about 10,000 to 100,000cp, and thus it can be used in screen-printing, offset-printing and imprinting. It also can be diluted with diluent such as ethanol or water according to the object of use.[48] Silver organo-sol prepared by dissolving silver aromatic carboxylate in reactivesolvent, for example, amine substituted by one or more ethanol may be further diluted with ethylene glycol or water to be deposited on a hydrophilic substrate. On the other hand, it may be diluted with an alcohol of short chain alcohol such as ethanol to be deposited on a substrate having a hydrophobic metal oxide film thereon. It is presumed that the solubility increases drastically because the reactive organic solvent forms complex with the silver aromatic carboxylate by chelating or coordinate covalent bonding.[49] A preferred nonpolar organic solvent is an aliphatic or aromatic hydrocarbon ormixture thereof. A preferred polar organic solvent is water or CI to CI2, saturated or unsaturated, mono to tri functional aliphatic alcohol. The organic solvent, for example, is 2-methoxy ethanol, 1,2-hexanediol, benzene, toluene, xylene, dimethylcarbithol, kerosene ethanol, methanol, 2-propanol, chloroform or ethylene glycol. [50]Advantageous Effects[51] By the present invention, silver organo-sol ink of solution type basically havinghigher content of silver is obtained. The solution type ink of the present invention can be used for forming conductive patterns in flat panel display such as plasma display panel(PDP) to reduce the numbers of steps for pattern forming. Some of the solution type ink of the present invention can be used for forming conductive patterns on a milder substrate such as thermoset plastic at a lower reducing temperatuture.[52]Brief Description of the Drawings[53] Figure 1 through Figure 3 show FT-IR spectrometer graphs of synthesized organo-silver precursors prepared in Examples 1 through 19 except Examples 12.[54] Figure 4 through Figure 7 are TGA graphs of synthesized organo-silver precursorsprepared in Examples 1 through 19.[55] Figure 8 through 10 show SEM images(l 000 times enlarged) of a sample preparedin Examples 1 through 18 after heat-treatment at respectivereducing temperatures for 10 minutes.[56] Figure 11 shows microscopic images of calcined patterns on glass panels usingorganosol ink prepared by Example 1.[57]Best Mode for Carrying Out the Invention[58] The present invention is illustrated by examples below. However, such examplespresented for the purpose of illustration do not serve as a basis to decide the scope of the invention.[59][60] Example 1[61] 50mmol 4-aminobenzoic acid is dissolved in 50mL of methanol. 50mmol NaOHdissolved in 50mL water is added slowly to the 4-aminobenzoic acid solution prepared while stirring to obtain sodium 4-aminobenzoate emulsion. 50mmol silver nitrate dissolved in 50mL water is added to the sodium 4-aminobenzoate emulsion controlled at —5°C, and then white precipitate forms fast. The precipitate is washed to remove unreacted silver nitrate and NaOH with water, filtered and washed several times to remove unreacted 4-aminobenzoic acid with methanol. The filtrant is dried at roomtemerature to finally prepare silver 4-aminobenzoate. Silver content was measured by the characteristic peak of TGA graph(TA instrument, SDT Q600). Also with FT-IR(Perkin Elmer, Spectrum GX), the reaction process for forming silver 4-aminobenzoate was confirmed by observing that the peak characteristic of C=0 bond is shifted from 1700cm" to around 1500cm" and the broad peaks between 3500~4000cm" characteristic for hydoxyl group in -COOH. disappear. The shift is presumably caused by resonanc effect of carboxyl group. The yield of silver carboxylate powder is 93%.[62] O.lmol prepared powder of silver 4-aminobenzoate is dissolved in 0.12moltriethanol amine and ethanol is added and stirred for 30 minutes to control viscosity lOcPs at 25°C. lg of such prepared organo-sol ink is coated on a glass substrate with a bar coater, dried at room temerature and then heat-treated for 10 minutes at 372°C. The final siver content is decided by the weights of the solution coated and residual solid after heat-treatment. The facial resistance is measured with 4-probe device. The micro-structure of the silver layer was analyzed with SEM(Hitachi, S-4300). The image is shown in Figure 8. Amounts of reagents and measured values are listed in table 3.[63] By using SE-128 head with a inkjet printer made by Litrex Corp, (a)72.2um dotsare drawn on glass panels. By using SX-128 head with the same inkjet printer (b)56(im dots, (c)a 60um line and (d)more complex circuit patterns are drawn on glass panels respectively. Nozzle head condtions of drawing are under -20mmHg pressure of meniscus and under 1.2kHz frequency, 119.5V applied and working time 9.8[is of piezo. Drawing speeds are 20mm/sec. The panels are dried at room temerature and then heat-treated for 10 minutes at 372°C. Calcined pattern microscopic images are shown Figure 11.[64][65] Example 2[66] Example 2 is carried out the same way as Example 1 except that malic acid is usedinstead of 4-aminobenzoic acid. The yield of the silver carboxylate powder is 93%.[67] An image of the micro-structure of the silver layer analyzed with SEM is shown inFigure 8. Amounts of reagents and measured values are listed in table 3.[68][69] Example 3[70] Example 3 is carried out the same way as Example 1 except that maleic acid is usedinstead of 4-aminobenzoic acid. The yield of the silver carboxylate powder is 89%.[71] An image of the micro-structure of the silver layer analyzed with SEM is shown inFigure 8. Amounts of reagents and measured values are listed in table 3.[72][73] Example 4[74] Example 4 is carried out the same way as Example 1 except that succinic acid isused instead of 4-aminobenzoic acid. The yield of the silver carboxylate powder is46.5%.[75] An image of the micro-structure of the silver layer analyzed with SEM is shown inFigure 8. Amounts of reagents and measured values are listed in table 3. [76][77] Example 5[78] Example 5 is carried out the same way as Example 1 except that acetic acid is usedinstead of 4-aminobenzoic acid. The yield of the silver carboxylate powder is 87.7%.[79] An image of the micro-structure of the silver layer analyzed with SEM is shown inFigure 8. Amounts of reagents and measured values are listed in table 3. [80][81] Example 6[82] Example 6 is carried out the same way as Example 1 except that malonic acid isused instead of 4-aminobenzoic acid. The yield of the silver carboxylate powder is87.5%.[83] An image of the micro-structure of the silver layer analyzed with SEM is shown inFigure 8. Amounts of reagents and measured values are listed in table 3. [84][85] Example 7[86] Example 7 is carried out the same way as Example 1 except that methacrylic acid isused instead of 4-aminobenzoic acid. The yield of the silver carboxylate powder is74.3%.[87] An image of the micro-structure of the silver layer analyzed with SEM is shown inFigure 9. Amounts of reagents and measured values are listed in table 3. [88][89] Example 8[90] Example 8 is carried out the same way as Example 1 except that propionic acid isused instead of 4-aminobenzoic acid. The yield of the silver carboxylate powder is63%.[91 ] An image of the micro-structure of the silver layer analyzed with SEM is shown inFigure 9. Amounts of reagents and measured values are listed in table 3. [92][93] Example 9[94] Example 9 is carried out the same way as Example 1 except that sorbic acid is usedinstead of 4-aminobenzoic acid. The yield of the silver carboxylate powder is 82%.[95] An image of the micro-structure of the silver layer analyzed with SEM is shown inFigure 9. Amounts of reagents and measured values are listed in table 3.[96][97] Example 10[98] Example 10 is carried out the same way as Example 1 except that citric acid is usedinstead of 4-aminobenzoic acid. The yield of the silver carboxylate powder is 88%.[99] An image of the micro-structure of the silver layer analyzed with SEM is shown inFigure 9. Amounts of reagents and measured values are listed in table 3. [100][101] Example 11[102] Example 11 is carried out the same way as Example 1 except that(E)-undec-2-enoic acid is used instead of 4-aminobenzoic acid. The yield of the silvercarboxylate powder is 93%.[ 103] An image of the micro-structure of the silver layer analyzed with SEM is shown inFigure 9. Amounts of reagents and measured values are listed in table 3. [104][105] Example 12[106] Example 12 is carried out the same way as Example 1 except that neododecanoicacid is used instead of 4-aminobenzoic acid. The yield of the silver carboxylate powderis 98%.[ 107] An image of the micro-structure of the silver layer analyzed with SEM is shown inFigure 9. Amounts of reagents and measured values are listed in table 3. [108][109] Example 13[110] Example 13 is carried out the same way as Example 1 except that oleic acid is usedinstead of 4-aminobenzoic acid. The yield of the silver carboxylate powder is 95.3%.[111] An image of the micro-structure of the silver layer analyzed with SEM is shown inFigure 10. Amounts of reagents and measured values are listed in table 3. [112][113] Example 14[114] Example 14 is carried out the same way as Example 1 except that oxalic acid isused instead of 4-aminobenzoic acid. The yield of the silver carboxylate powder is96%.[115] An image of the micro-structure of the silver layer analyzed with SEM is shown inFigure 10. Amounts of reagents and measured values are listed in table 3. [116][117] Example 15[118] Example 15 is carried out the same way as Example 1 except that formic acid isused instead of 4-aminobenzoic acid and the sodium formate emulsion is controlled at—15°C while silver nitrate dissolved in 50mL water is added. The yield of the silvercarboxylate powder is 77%.[119] An image of the micro-structure of the silver layer analyzed with SEM is shown inFigure 10. Amounts of reagents and measured values are listed in table 3. [120][121] Example 16[122] Example 16 is carried out the same way as Example 1 except that gluconic acid isused instead of 4-aminobenzoic acid. The yield of the silver carboxylate powder is80%.[123] An image of the micro-structure of the silver layer analyzed with SEM is shown inFigure 10. Amounts of reagents and measured values are listed in table 3. [124][125] Example 17[126] Example 17 is carried out the same way as Example 1 except that benzoic acid isused instead of 4-aminobenzoic acid. The yield of the silver carboxylate powder is87.7%.[127] An image of the micro-structure of the silver layer analyzed with SEM is shown inFigure 10. Amounts of reagents and measured values are listed in table 3. [128][129] Example 18[130] Example 18 is carried out the same way as Example 1 except that terephthalic acidis used instead of 4-aminobenzoic acid. The yield of the silver carboxylate powder is98%.[131] An image of the micro-structure of the silver layer analyzed with SEM is shown inFigure 10. Amounts of reagents and measured values are listed in table 3. [132][133] Example 19[134] Example 19 is carried out the same way as Example 1 except that trimesic acid isused instead of 4-aminobenzoic acid. The yield of the silver carboxylate powder is87.7%.[135] Amounts of reagents and measured values are listed in table 3.[136] Table 3(Table Removed)physical properties of silver precursors, silver inks, and silver films.[137] [138] [139]Industrial Applicability[140] The solution type ink of the present invention can be used for forming conductivepatterns by traditional printing technology, especially by inkjet-printing, in flat panel display such as plasma display panel(PDP) to reduce the numbers of steps for pattern forming.[1411]