Metal ink
11149161 · 2021-10-19
Assignee
Inventors
- Yuusuke Ohshima (Tsukuba, JP)
- Yuichi Makita (Tsukuba, JP)
- Teruhisa Iwai (Tsukuba, JP)
- Hitoshi Kubo (Tsukuba, JP)
- Shigeki Yamanaka (Hiratsuka, JP)
- Masahiro Ito (Hiratsuka, JP)
- Shingo Watanabe (Hiratsuka, JP)
Cpc classification
H01B1/00
ELECTRICITY
International classification
Abstract
A metal ink containing metal particles including silver, a protective agent A including an amine compound, and a protective agent B including a fatty acid. The metal ink is configured such that the protective agent A includes at least one C.sub.4-12 amine compound, and the protective agent B includes at least one C.sub.22-26 fatty acid. It is preferable that the amine compound content is 0.2 mmol/g or more and 1.5 mmol/g or less on a silver particle mass basis. In addition, it is preferable that the fatty acid content is 0.01 mmol/g or more and 0.06 mmol/g or less on a silver particle mass basis.
Claims
1. A metal ink comprising: metal particles including silver; a protective agent A including an amine compound; and a protective agent B including a fatty acid, wherein the protective agent A includes at least one C.sub.4-12 amine compound, and the protective agent B consists of at least one C.sub.22-26 fatty acid, but optionally contains at least one C.sub.14-21 fatty acid, a content of the C.sub.4-12 amine compound serving as the protective agent A is 0.2 mmol/g or more and 1.5 mmol/g or less on a silver particle mass basis, a content of the fatty acid serving as the protective agent B of is 0.01 mmol/g or more and 0.06 mmol/g or less on a silver particle mass basis, and wherein all fatty acids present in the metal ink consist of protective agent B.
2. The metal ink according to claim 1, wherein a ratio of an amine compound content to a fatty acid content is 5.0 or more and 120.0 or less.
3. The metal ink according to claim 2, wherein a proportion of coarse agglomerates having a particle size of 500 nm or more in a particle size distribution based on dynamic light scattering method is 5% or less in volume fraction.
4. The metal ink according to claim 2, wherein the silver particles have an average particle size of 5 nm or more and 100 nm or less.
5. The metal ink according to claim 2, wherein a content of the silver particles is 20 mass % or more and 70 mass % or less relative to an entire mass of the metal ink.
6. The metal ink according to claim 2, wherein when 100 μL of the metal ink is applied by spinning at a rotation speed of 2,000 rpm for 1 minute by a spin coat method and then calcined at 120° C. for 30 minutes or more, a resultant electrical conductor has a volume resistance of 5 μΩcm or more and 20 μΩcm or less.
7. The metal ink according to claim 1, wherein a proportion of coarse agglomerates having a particle size of 500 nm or more in a particle size distribution based on dynamic light scattering method is 5% or less in volume fraction.
8. The metal ink according to claim 7, wherein the silver particles have an average particle size of 5 nm or more and 100 nm or less.
9. The metal ink according to claim 7, wherein a content of the silver particles is 20 mass % or more and 70 mass % or less relative to an entire mass of the metal ink.
10. The metal ink according to claim 7, wherein when 100 μL of the metal ink is applied by spinning at a rotation speed of 2,000 rpm for 1 minute by a spin coat method and then calcined at 120° C. for 30 minutes or more, a resultant electrical conductor has a volume resistance of 5 μΩcm or more and 20 μΩcm or less.
11. The metal ink according to claim 1, wherein the silver particles have an average particle size of 5 nm or more and 100 nm or less.
12. The metal ink according to claim 11, wherein a content of the silver particles is 20 mass % or more and 70 mass % or less relative to an entire mass of the metal ink.
13. The metal ink according to claim 11, wherein when 100 μL of the metal ink is applied by spinning at a rotation speed of 2,000 rpm for 1 minute by a spin coat method and then calcined at 120° C. for 30 minutes or more, a resultant electrical conductor has a volume resistance of 5 μΩcm or more and 20 μΩcm or less.
14. The metal ink according to claim 1, wherein a content of the silver particles is 20 mass % or more and 70 mass % or less relative to an entire mass of the metal ink.
15. The metal ink according to claim 14, wherein when 100 μL of the metal ink is applied by spinning at a rotation speed of 2,000 rpm for 1 minute by a spin coat method and then calcined at 120° C. for 30 minutes or more, a resultant electrical conductor has a volume resistance of 5 μΩcm or more and 20 μΩcm or less.
16. The metal ink according to claim 1, wherein when 100 μL of the metal ink is applied by spinning at a rotation speed of 2,000 rpm for 1 minute by a spin coat method and then calcined at 120° C. for 30 minutes or more, a resultant electrical conductor has a volume resistance of 5 μΩcm or more and 20 μΩcm or less.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1)
(2)
(3)
DESCRIPTION OF EMBODIMENTS
First Embodiment
(4) Hereinafter, preferred embodiments of the present invention will be described. In the present embodiment, a metal ink (silver ink) applying erucic acid (C.sub.22) as a fatty acid was produced and printed on a substrate to form silver lines, and the presence of printing defects was evaluated. In the evaluation of printing defects, a comparison was made with a conventional metal ink.
(5) [Production of Silver Ink]
(6) In the present embodiment, silver particles produced by a thermal decomposition method were dispersed in a solvent to produce a metal ink. In the production of silver particles, 0.651 g of methanol was added to 1.519 g of silver oxalate (silver: 1.079 g) serving as a starting material to cause wetting. Then, amine compounds and a fatty acid each serving as a protective agent were added to the silver oxalate. Specifically, first, N,N-dimethyl-1,3-diaminopropane (0.778 g (7.61 mmol)) was added and kneaded for a while, and then hexylamine (1.156 g (11.42 mmol)), dodecylamine (0.176 g (0.95 mmol)), and erucic acid (0.0443 g (0.131 mmol)) were added and kneaded, followed by heating and stirring at 110° C. During this heating and stirring, the cream-colored silver complex gradually became brown and further became black. This heating/stirring operation was performed until the occurrence of bubbling from the reaction system stopped.
(7) After the completion of the reaction, the reaction system was allowed to cool to room temperature, and then methanol (2 g) was added and thoroughly stirred, followed by centrifugation (2,000 rpm, 60 s). The supernatant was removed, solid-liquid separation was performed, methanol (2 g) was added again and stirred, centrifugation was performed, and the supernatant was removed. Finally, methanol was added once again, and the same washing operation was performed. Like this, the washing operation with a solvent was repeated three times, whereby excess protective agents were removed, and the silver particles were purified.
(8) Then, to the produced silver fine particles, a mixed solvent of octane and butanol (octane:butanol=4:1 (volume ratio)) was added to give a silver ink. The metal ink produced through the above steps has a silver concentration of 50 mass %.
(9) The contents of the amine compounds and the fatty acid, which are protective agents, in the silver ink produced through the above steps were analyzed. In the present embodiment, the analysis was performed by GC-MS. As the GC-MS analyzer, 7890B manufactured by Agilent Technologies, Inc., was used for the GC part, and JMS-Q1500GC manufactured by JEOL Ltd., which is a quadrupole mass spectrometer, was used for the MS part. As the ionizing method, photoionization was used. In addition, for the GC sample introduction part, a pyrolyzer manufactured by Frontier Laboratories Ltd., was installed and used. At the time of analysis, the metal ink was diluted 12.5-fold by volume, and then 5 μL was subjected to the analysis. Other measurement conditions were as follows.
(10) <GC Conditions>
(11) Column: UA-530M-0.25F (manufactured by Frontier Laboratories Ltd.)
(12) Column flow rate: 1.0 ml/min. He
(13) Split ratio: 30
(14) Oven temperature setting: 40° C., 6 min..fwdarw.heating (10° C./min.).fwdarw.360° C., 2 min.
(15) Inlet temperature: 250° C.
(16) <MS Conditions>
(17) Q-pole temperature: 70° C.
(18) Ion source temperature: 200° C.
(19) Mode: Scan (m/z=10 to 350)
(20) Photoionization energy: 10.18 eV or higher
(21) As a result of the quantitative analysis by GC-MS described above, the amine compound content (the total amount of N,N-dimethyl-1,3-diaminopropane, hexylamine, and dodecylamine) was 0.73 mmol/g on a silver mass basis, and the fatty acid (erucic acid) content was 0.025 mmol/g on a silver mass basis. The ratio of the amine compound content to the fatty acid content was 29.2.
Comparative Example
(22) As a conventional metal ink, a metal ink containing oleic acid (C.sub.18) as a protective agent was prepared (the amine compounds are the same as in the embodiment). The method for producing this metal ink is almost the same as in the metal ink production step of the present embodiment. In the comparative example, N,N-dimethyl-1,3-diaminopropane was added to silver oxalate in a wet state and kneaded, and then hexylamine, dodecylamine, and oleic acid (0.037 g (0.131 mmol)) were added and kneaded. The amounts of silver oxalate and amine compounds used are the same as in the present embodiment. Then, the operation after the addition of oleic acid was also the same as in the embodiment, and the metal ink was thus produced.
(23) Also, in this comparative example, as in the first embodiment, the amine compound content and the fatty acid content were analyzed (GC-MS). As a result, the amine compound content (the total amount of N,N-dimethyl-1,3-diaminopropane, hexylamine, and dodecylamine) was 0.71 mmol/g on a silver mass basis, and the fatty acid (erucic acid) content was 0.028 mmol/g on a silver mass basis. The ratio of the amine compound content to the fatty acid content was 25.35.
(24) [Evaluation of Particle Size Distribution of Metal Ink]
(25) The metal inks produced above were subjected to the measurement of particle size distribution by DLS. As the analyzer for the particle size distribution by DLS, VASCO2 manufactured by CORDOUAN (laser wavelength: 657 nm) was used. The viscosity of an octane-butanol mixed solvent necessary for the calculation of particle size distribution was set at an actual measured value of 0.635 cP, while the refractive index was set at the literature data (1.391), and the measurement was performed at 25° C. After the measurement, the obtained data were analyzed with the software stored in the device. SBL was selected as the analysis method, and a particle size distribution on a volume basis was prepared. This measurement was performed on a metal ink after one day from production and a metal ink after 20 days from production.
(26)
(27) Meanwhile, in the metal ink of the present embodiment containing erucic acid as a protective agent, the formation of coarse agglomerates as in the comparative example was not seen. In the case of the metal ink of the present embodiment, even after 20 days from production, the number of peaks observed in the particle size distribution profile was only one, and a peak of coarse agglomerates was not seen.
(28) [Metal Line Production Test]
(29) Next, the metal inks of the present embodiment and the comparative example, each after 20 days from implementation/production, were used to produce metal lines. Here, metal lines were formed based on the method of Patent Document 2 described above, and the presence of printing defects was studied.
(30) As a substrate for the formation of metal lines, a transparent resin substrate made of polyethylene naphthalate (PET) (dimension: 150 mm×150 mm, thickness: 100 μm) was prepared. In the present embodiment, in a predetermined region of this substrate (125 mm in length×6 mm in width), grid-like metal lines were formed. Specifically, grid-like metal lines having a line width (L) of 2 μm at intervals (S) of 300 μm (L/S=2 m/300 μm) were formed.
(31) According to the metal line formation method in accordance with the method of Patent Document 2 described above, an amorphousness perfluorobutenyl ether polymer (CYTOP (registered trademark): manufactured by Asahi Glass Co., Ltd.), which is a liquid-repellant fluorine-containing resin, was applied to a substrate by a spin coat method (rotation speed: 2,000 rpm, 20 s), then heated at 50° C. for 10 minutes and subsequently at 80° C. for 10 minutes, further heated in an oven at 100° C. for 60 minutes, and calcined.
(32) Next, a photomask having a grid-like line pattern (line width: 2.0 μm) was closely attached to the surface of the substrate having formed thereon a fluororesin layer (contact exposure at a mask-substrate distance of 0), followed by irradiation with UV light (VUV light). The VUV light irradiation was performed at a wavelength of 172 nm and 11 mW/cm.sup.−2 for 20 seconds.
(33) To the substrate having a functional group formed by exposing the fluorine resin layer surface to light as described above, the metal ink was applied. Application was performed such that three drops of 1 μL of the ink were equally disposed on the substrate, and the drops were swept in one direction with a blade (applicator). Here, the sweep rate was set at 2 mm/s. It was confirmed that as a result of the application with a blade, the ink adhered only to the UV light irradiation part (functional group formation part) of the substrate. Then, the substrate was dried with hot air at 120° C., and silver lines (L/S=2 μm/300 μm) were formed.
(34) The silver lines formed as above were observed under an optical microscope and an electron microscope (SEM), and the presence of printing defects, such as faint printing of lines or appearance defects, was studied. In the metal lines formed from the metal ink of the present embodiment, printing defects were not observed, and the conditions were entirely clear (
(35) As described above, printing defects were observed in the comparative example, in which a metal ink containing C.sub.18 oleic acid as a protective agent was used. When the example and the comparative example are compared, the difference between them is only the number of carbon atoms in a fatty acid, and the amine compounds serving as a protective agent A are the same. In addition, in view of the amounts of protective agents, the amine compound content and the fatty acid content are not much different between the example and the comparative example. In the comparative example, with respect to the protective agent contents, even when the suitable values applied in the examples were applied, printing defects occurred.
Second Embodiment
(36) Here, the kind of fatty acid serving as a protective agent was varied to produce metal inks. In addition, a metal ink in which, in addition to silver oxalate, silver carbonate was also used as a silver compound serving as a raw material was also produced. Then, the stability of the produced metal inks, which presumably relates to the occurrence of printing defects, was evaluated.
(37) In the present embodiment, the metal ink production step using silver oxalate is approximately the same as in the first embodiment. That is, N,N-dimethyl-1,3-diaminopropane was added to silver oxalate in a wet state and kneaded, and then hexylamine, dodecylamine, and 0.131 mmol of each fatty acid were added and kneaded. The amounts of silver oxalate and amine compounds used are the same as in the present embodiment. In addition, the operation after the addition of each fatty acid was also the same as in the embodiment, and the metal inks were thus produced.
(38) In addition, the metal ink production step using silver carbonate as a raw material was performed as follows. 0.651 g of methanol was added to 1.379 g of silver carbonate (silver: 1.079 g) to cause wetting. Then, to this silver carbonate, octylamine (0.478 g (3.705 mmol)), hexylamine (1.156 g (11.42 mmol)), dodecylamine (0.176 g (0.95 mmol)), and 0.131 mmol of each fatty acid were added and kneaded. Then, this silver-amine complex was heated and stirred at 110° C. After the completion of the reaction, silver fine particles were washed and recovered in the same manner as in the first embodiment. Then, a solvent (octane:butanol=4:1 (volume ratio)) was added to the silver fine particles to produce a silver ink (silver concentration: 50 mass %).
(39) With respect to the metal ink produced in the present embodiment, the protective agent contents were measured by GC-MS in the same manner as in the first embodiment. Then, after 20 days from production, the particle size distribution was measured by the DLS method under the same measurement conditions as in the first embodiment.
(40) In the DLS measurement of particle size distribution in the present embodiment, with respect to each metal ink, the average particle size based on all the particles dispersed in the ink (DLS average particle size) was calculated. Then, the volume fraction of agglomerates having a particle size of 500 nm or more was measured. At this time, when the volume fraction of coarse agglomerates having a particle size of 500 nm or more was 5% or less, a rating of “acceptable (◯)” was given.
(41) (A) Evaluation of Printability
(42) Next, the same substrate as in the first embodiment was prepared, metal lines were formed, and the printability of the metal ink was evaluated. By the same method as in the first embodiment, metal lines (grid-like metal lines having L/S=2 μm/300 μm) were formed in a region of 125 mm in length×6 mm in width. Then, the formed metal lines were first subjected to the evaluation of printability by the observation of appearance. Here, the entire metal lines were observed, and when printing defects, such as faint printing and liquid gathering, were seen even partially, a rating of “unacceptable (×)” was given, while when there were completely no defects, a rating of “acceptable (◯)” was given.
(43) Next, the conduction of the metal lines was measured to confirm the soundness of the lines, which cannot be judged from appearance only. In this test, within the region where metal lines were formed (region of 125 mm in length×6 mm in width), terminals of a digital tester were brought into contact with two arbitrary points of the metal lines, where conduction is supposed to occur according to the pattern shape, and the electrical resistance was measured to confirm the presence of conduction. Ten sets of this measurement were performed. When conduction was confirmed in all, a rating of “◯” was given, when conduction was confirmed in 8 or more points, “Δ” was given, and “×” was given to other cases.
(44) Then, the results of the appearance test and the results of the conduction test were put together to judge the printability. In this overall evaluation, inks rated as “◯” both in appearance and conduction were rated as “excellent (⊙)”. Meanwhile, inks rated as “Δ” in the conduction test were rated as “non-defective (◯)” in the overall evaluation. Inks rated as “×” in either the appearance test or the conduction test were rated as “defective (×)” in the overall evaluation.
(45) (B) Evaluation of Electrical Characteristics
(46) Further, in the present embodiment, an electrical conductor was formed from each metal ink, and its electrical characteristics (electrical resistance) were measured. The reason why electrical conductors are produced and evaluated like this in addition to the conduction test for printability is that the scope of application of the metal ink was taken into consideration. That is, the metal lines produced in the present embodiment as described above are lines having a relatively small line width (2 μm). Here, in metal lines, in addition to the demand for smaller line width/line pitch, it is sometimes demanded to achieve a three-dimensional structure by applying a metal ink a plurality of times, for example. It can be said that in order to meet such various demands, it is preferable to understand the tendency of the electrical characteristics of the metal ink itself. Thus, in the present embodiment, onto a PET substrate having no pattern formed, a certain amount of metal ink was applied to form an electrical conductor, and, from its electrical characteristics, the suitability as a metal line precursor was evaluated.
(47) In this evaluation test, 100 μL of a metal ink was spin-coated to a PET substrate (2,000 rpm) and then calcined in air at 120° C. for 30 minutes, thereby forming an electrical conductor having a dimension of ×25×25 mm. The volume resistance of this electrical conductor (μΩm) was measured by use of a resistivity meter (Loresta-GP MCP-T610 manufactured by Mitsubishi Chemical Analytech Co., Ltd.). Then, a volume resistance of 20 μΩm or less was rated as “acceptable (◯)”.
(48) With respect to each of the metal inks produced in the present embodiment, Table 1 shows the measurement results of particle size distribution, the evaluation results upon the formation of metal lines, and the evaluation results of electrical characteristics.
(49) TABLE-US-00001 TABLE 1 Protective agent Particle size Fatty acid content (mmol/g) distribution*.sup.2 Silver Number of Fatty Amine/ DLS average No. compound Name carbon atoms Amines*.sup.1 acid fatty acid particle size*.sup.3 1 Silver Oleic acid 18 0.71 0.028 25.4 93 nm oxalate 2 Silver 1.13 0.018 62.8 213 nm carbonate 3 Silver Eicosanoic 20 0.88 0.022 40.0 64 nm oxalate acid 4 Silver Erucic acid 22 0.73 0.025 29.2 10 nm oxalate 5 Silver 1.08 0.016 67.5 48 nm carbonate 6 Silver Lignoceric 24 0.61 0.02 30.5 12 nm oxalate acid 7 Silver 1.28 0.014 91.4 32 nm carbonate 8 Silver Hexacosanoic 26 0.51 0.019 26.8 14 nm oxalate acid 9 Silver Octacosanoic 28 Unmeasurable*.sup.6 — Unmeasurable*.sup.6 oxalate acid 10 Silver Triacontanoic 30 Unmeasurable*.sup.6 — Unmeasurable*.sup.6 oxalate acid Particle size Electrical distribution*.sup.2 characteristics Aggregation Printability Resistance No. rating*.sup.4 Appearance Conduction Evaluation*.sup.5 (μΩcm) Rating 1 X X X X 10 ◯ 2 X X X X 13 ◯ 3 X X X X 11 ◯ 4 ◯ ◯ ◯ ⊙ 11 ◯ 5 ◯ ◯ ◯ ⊙ 6 ◯ 6 ◯ ◯ ◯ ⊙ 18 ◯ 7 ◯ ◯ ◯ ⊙ 11 ◯ 8 ◯ ◯ ◯ ⊙ 10 ◯ 9 — Unmeasurable*.sup.6 — Unmeasurable*.sup.6 — 10 — Unmeasurable*.sup.6 — Unmeasurable*.sup.6 — *.sup.1As amines, the same plurality of amines as in the first embodiment were applied in each case. *.sup.2Measurement results after 20 days from production. *.sup.3Average particle size of all dispersed particles by DLS. *.sup.4When the volume fraction of agglomerates having a particle size of 500 nm or more was 5% or less, “◯” was given, while a volume fraction was more than 5%, “X” was given. *.sup.5The evaluation method was as follows. ⊙: Entirely excellent ◯: Excellent. However, defects may occur depending on the shape of metal lines. X: Entirely defective *.sup.6The ink became an agar-like solid matter in several days after synthesis, and measurement/evaluation was not possible.
(50) From Table 1, it can be seen that when the number of carbon atoms in the fatty acid is 22 or more (No. 4 to No. 8), metal lines without printing defects can be formed. In addition, in electrical conductors produced from these metal inks, increases in resistance were also within the acceptable range. Meanwhile, it was confirmed that when a C.sub.18 or C.sub.20 fatty acid is applied (No. 1 to No. 3), although the application can contribute to the formation of an electrical conductor having low resistance, the printability is poor. It has been already confirmed in the first embodiment (oleic acid) that a metal ink containing a low-carbon fatty acid has poor printability, and it was also confirmed from the present embodiment that the same also applies to C.sub.20 eicosanoic acid.
(51) Meanwhile, an ink containing a C.sub.26 or higher high-carbon fatty acid (C.sub.28: octacosanoic acid, C.sub.30: triacontanoic acid) turned into an agar-like solid matter within one to several days after production. In the present embodiment, it became difficult to apply the ink for a printing use. From the above study results, it turned out that the number of carbon atoms in a fatty acid should be 22 or more and 26 or less.
(52) In addition, in view of the relationship between the aggregation of silver particles in a metal ink and printability, when a C.sub.20 or lower fatty acid was applied (No. 1 to No. 3), the volume fraction of coarse agglomerates having a particle size of 500 nm or more was more than 5%, and the aggregation rating was “unacceptable”. It was already confirmed that a metal ink applying such a low-carbon fatty acid has poor printability, and thus relevance with the presence of coarse agglomerates is estimated.
(53) Incidentally, with respect to silver oxalate and silver carbonate used as starting materials for silver particles, it was confirmed that the results do not differ depending on the difference in kind, and both raw materials are usable.
Third Embodiment
(54) In this embodiment, a plurality of metal inks containing erucic acid (C.sub.22) as a fatty acid in various amounts were produced. Then, the same test/evaluation as in the second embodiment was performed.
(55) As in the first embodiment, silver oxalate or silver carbonate was used as a starting material to produce a metal ink. In this production step, as in the first embodiment, erucic acid was added at the timing corresponding to the kind of raw material. At this time, the amounts of erucic acid added were, based on the amount added in the second embodiment (0.131 mmol), ⅓ times (0.0436 mmol), ½ times (0.0655 mmol), 1 time (0.131 mmol), 2 times (0.262 mmol), and 3 times (0.393 mmol) the amount.
(56) In addition, also with respect to amine compounds, as in the first embodiment, when silver oxalate was used as a raw material, N,N-dimethyl-1,3-diaminopropane, hexylamine, and dodecylamine were applied, while when silver carbonate was used as a raw material, octylamine, hexylamine, and dodecylamine were applied. The amine compounds are also added at the same timing as in the first embodiment. Then, the amounts thereof added were, based on the amount added in the first embodiment (19.98 mmol or 16.075 mmol in total), ⅕ times, ⅓ times, 1 time, 3 times, and 4 times the amount. Incidentally, the proportion of each amine compound was made common to the first embodiment.
(57) After the addition of each protective agent, a metal ink was produced through the same steps as in the first embodiment. Then, particle size distribution, printability evaluation, and resistance measurement were performed. The results are shown in Table 2.
(58) TABLE-US-00002 TABLE 2 Protective agent content (mmol/g) Particle size Amines*.sup.1 Fatty acid*.sup.2 distribution*.sup.3 Silver Amount used Amount used Amine/ DLS average No. compound in production Content in production Content fatty acid particle size*.sup.4 11 Silver 1 time 0.95 ⅓ times 0.006 158.3 65 nm oxalate 12 Silver 1 time 0.63 1 time 0.025 25.2 10 nm oxalate 13 Silver 1 time 1.08 1 time 0.016 67.5 48 nm carbonate 14 Silver 1 time 0.86 2 times 0.052 16.5 9 nm oxalate 15 Silver 1 time 0.58 3 times 0.061 9.5 9 nm oxalate 16 Silver ⅓ times 0.31 2 times 0.050 6.2 52 nm oxalate 17 Silver ⅕ times 0.23 2 times 0.055 4.2 53 nm oxalate 18 Silver 3 times 1.42 ½ times 0.012 118.3 55 nm oxalate 19 Silver 4 times 1.68 ½ times 0.010 168.0 7 nm oxalate Particle size Electrical distribution*.sup.3 characteristics Aggregation Printability Resistance No. rating*.sup.5 Appearance Conduction Evaluation*.sup.6 (μΩcm) Rating 11 X X Δ X 7 ◯ 12 ◯ ◯ ◯ ⊙ 11 ◯ 13 ◯ ◯ ◯ ⊙ 6 ◯ 14 ◯ ◯ ◯ ⊙ 11 ◯ 15 ◯ ◯ ◯ ⊙ 28 X 16 ◯ ◯ ◯ ⊙ 12 ◯ 17 ◯ ◯ Δ ◯ 7 ◯ 18 ◯ ◯ ◯ ⊙ 18 ◯ 19 ◯ X X X 22 X *.sup.1As amines, the same plurality of amines as in the first embodiment were applied in each case. The amount of each amine used was based on the amount used in the first embodiment (1 time), and the mixing ratio of amines was the same as in the first embodiment. *.sup.2Erucic acid (C.sub.22) was used as a fatty acid in each case. The amount used was based on the amount used in the second embodiment (1 time) *.sup.3Measurement results after 20 days from production. *.sup.4Average particle size of all dispersed particles by DLS. *.sup.5When the volume fraction of agglomerates having a particle size of 500 nm or more was 5% or less, “◯” was given, while a volume fraction was more than 5%, “X” was given. *.sup.6The evaluation method was as follows. ⊙: Entirely excellent ◯: Excellent. However, defects may occur depending on the shape of metal lines. X: Entirely defective
(59) From Table 2, in the metal ink containing erucic acid in an amount of more than 0.06 gmmol/g on a mass basis relative to silver (No. 15), when an electrical conductor was produced, the resistance rapidly increased. The electrical conductor from this metal ink has resistance that is twice or more that of the electrical conductor from the metal ink No. 14, whose erucic acid content is slightly lower than 0.06 gmmol/g. From the previous study, it has been confirmed that the application of erucic acid suppresses aggregation in a metal ink and ensures printability. From the study results, it can be said that when Ag particles are sintered at the time of electrical conductor formation, it is preferable the amount is suitably adjusted to such a degree that sintering is not inhibited.
(60) In addition, in view of the metal ink (No. 11) in which the amount of erucic acid added was ⅓ that in the second embodiment, it was confirmed that the printability is poor in this metal ink. Erucic acid is a long-chain fatty acid having higher molecular weight than in the conventional art, and is a compound that is originally capable of sufficiently exerting effects as a protective agent. However, it was confirmed that when the amount of erucic acid mixed is small, the protective action in the state of a metal ink is insufficient. In the case of this metal ink, the occurrence of coarse agglomerates is observed, and agglomerates having a particle size of 500 nm or more were contained in a volume fraction of 5% or more.
(61) In view of the ratio of the content of the amine compounds to the content of the fatty acid (amine compound/fatty acid), which are protective agents, the metal ink (No. 16), in which the ratio is 6.2 that is slightly higher than 5.0, the printability was excellent, and the electrical characteristics were also excellent. In contrast, in the metal ink (No. 17) having a ratio of less than 5.0, although the electrical characteristic were excellent, with respect to printability, there were some areas where conduction cannot be locally obtained. In this respect, the line pattern of the present embodiment provides relatively thin lines (line width: 2 μm), and the conditions are severe in that even a slight lack of bonding (lack of sintering) between silver particles and the substrate leads to conduction defects. With respect to the metal ink No. 17, when its good electrical characteristics in the form of an electrical conductor are taken into consideration, presumably, depending on the conditions, the metal ink can be used as an excellent metal line precursor. However, when the formation of high-precision metal lines, which are ultrathin with a narrow pitch, is taken into consideration, it is considered to be more preferable that the ratio of the amine compound content to the fatty acid content is 5.0 or more.
INDUSTRIAL APPLICABILITY
(62) As described above, in the metal ink according to the present invention, as a result of pursuing the configuration regarding a fatty acid serving as a protective agent, the relationship between the problem with printability and the problem with the resistance of a formed electrical conductor is optimized. The present invention is useful for the formation of electrodes/lines on circuit boards of various electronic devices or on transparent substrates of touch panels, for example, and high-precision/high-quality metal lines can be efficiently formed on these substrates.