JP2020070489A - Conductive fine particle dispersion, method for forming conductive pattern and method for producing conductive substrate - Google Patents

Abstract

To provide a conductive fine particle dispersion which is excellent in conductivity under high temperature sintering conditions at 650°C or more, and is suitable for forming a thin film having a thickness of 5 μm or less and a thin line having a width of 50 μm or less.SOLUTION: There is provided a conductive fine particle dispersion which contains conductive fine particles, a metal oxide and dispersant, wherein the content ratio (the conductive fine particles: the metal oxide) between the conductive fine particles and the metal oxide is 75:25 to 98:2 by mass ratio.SELECTED DRAWING: None

Description

The present invention relates to a conductive fine particle dispersion, a method for manufacturing a conductive pattern, and a method for manufacturing a conductive substrate.

In recent years, printed electronics technology, which forms electronic circuits, devices, and the like using printing technology, has been drawing attention. In the printed electronics technology, as a simpler and cheaper method of forming a conductive pattern, it has been considered to use a printing method such as a letterpress printing method, an intaglio printing method, a screen printing method or an inkjet printing method. Conductive inks and conductive pastes suitable for the printing method have been researched and developed.

In addition, a printed electronics technology has attracted attention, in which a conductive paste containing fine metal particles is printed on a base material and fired to form an extremely fine fine wire or thin layer into an electronic circuit or device. The metal fine particles used for the conductive paste that forms such fine lines and thin layers are nanometer-sized particles that are much smaller than the conductive filler in the conventionally known conductive paste. Silver nanoparticles are known as metal fine particles that can be sintered at a low temperature due to a decrease in melting point and exhibit high conductivity close to that of a metal foil.

By the way, as the metal particles used for the conductive ink conductive paste suitable for the above-mentioned various printing methods, use of alloys or metal oxides as metal fine particles has been studied in addition to the silver nanoparticles.

For example, Patent Document 1 discloses a binder resin containing an epoxy resin having a total chlorine concentration of 300 ppm or less, preferably 50 ppm or less, as an electrically conductive particle dispersion for forming a conductive film, which has high productivity and is excellent in long-term insulation performance, and an organic solvent. In the mixed liquid with, metal fine particles and / or metal oxide fine particles are dispersed as conductive particles to form a conductive particle dispersion for forming a conductive film, which is applied to the surface of the electric insulator layer by screen printing and baked by microwave. It is described that a conductive film pattern is formed.

Further, Patent Document 2 proposes a conductive paste used for bonding electrode terminals of a semiconductor element or electrode terminals of a circuit board, and a bonded body obtained by firing the conductive paste. It is described that the fine metal particles contained in the conductive paste are composed of one kind or two or more kinds selected from metals, alloys and metal oxides.

JP, 2013-69475, A JP2012-28136A

As described above, it has been conventionally proposed to use a metal oxide as the fine metal particles used in the conductive fine particle dispersion. However, since the metal oxide is inferior in conductivity as compared with the metal fine particles such as silver, gold, platinum and copper, the choice of the metal fine particles used in the conductive fine particle dispersion as described in Patent Documents 1 and 2 above. Although a metal oxide is described as one of the above, a test example using metal particles containing a metal oxide is not shown in the examples. Further, the unique effect of using a metal oxide in the conductive fine particle dispersion has not been known.

Here, the metal fine particles such as silver have a characteristic that the melting point becomes lower as the size thereof becomes smaller. Particularly, in the case of nanoparticles having a size of about several tens of nanometers or less, the melting point effect becomes more remarkable. The appearance is known as described above. When a conductive wiring or the like printed with fine silver particles having a low melting point is burned at a high temperature of 650 ° C. or higher, the fine silver particles are over-sintered, melted, and evaporated, and a rapid volume contraction or disconnection is observed.

Further, in recent years, the density of electronic circuits has increased, and further miniaturization of wiring has been studied. In particular, it is required to form a conductive pattern having a line width of 50 μm or less, and in a more precise electronic circuit, it is required to form a conductive pattern having a line width of 30 μm or less and 10 μm or less. Therefore, it is possible to form a fine wire having a line width of 50 μm or less and a thin film having a layer thickness of 5 μm or less under a high temperature sintering condition of 650 ° C. or higher using a conductive fine particle dispersion containing conductive fine particles such as silver fine particles. It was wanted. However, when the fine wire or thin film as described above is formed using the conductive fine particle dispersion and the conductive pattern is formed under the high temperature sintering condition of 650 ° C. or more, disconnection due to volume contraction is apt to appear, and these measures are taken. Was required.

However, the conductive particle dispersion for forming a conductive film described in Document 1 above was printed by printing an IPC standard IPC-C comb pattern with a # 250 mesh polyester plate in the Examples, and printing. A conductive pattern was formed by drying the latter film at 80 ° C. for 30 minutes, and the pattern linearity was 0.040 mm, which could not be used in a precision electronic circuit. Further, the conductive paste described in the above-mentioned Document 2 is used for joining the electrode terminals as described above, and is not intended to form a conductive pattern, and this is also a precise electronic circuit. It could not be used.

The present invention has been made in view of the above circumstances, and has excellent conductivity even under high-temperature sintering conditions of 650 ° C. or higher, and conductive fine particles suitable for forming a thin film having a thickness of 5 μm or less and a fine wire having a width of 50 μm or less. The purpose is to provide a dispersion.

The present inventors have made various studies on conductive fine particle dispersions capable of exhibiting sufficient conductivity even when applied in the form of a thin film having a thickness of 5 μm or less and / or a fine wire having a width of 50 μm or less and baked at high temperature. As a result, by dispersing the metal oxide in the conductive fine particle dispersion, it is possible to prevent rapid volume shrinkage due to oversintering, melting, and evaporation of the conductive fine particles even at a high temperature of 650 ° C. or higher. As a result, they have found that it is possible to form a conductive pattern such as a highly conductive wiring that can be baked at a high temperature, and completed the present invention.

The conductive fine particle dispersion of the present invention contains conductive fine particles, a metal oxide, and a dispersion medium, and the content ratio of the conductive fine particles and the metal oxide (conductive fine particles: metal oxide) is The mass ratio is 75:25 to 98: 2.

The conductive fine particle dispersion of the present invention is preferably used for forming a conductive pattern.

The average particle size of the metal oxide is preferably 700 nm or less.

The conductive fine particles are preferably at least one selected from the group consisting of silver, copper and gold.

The metal oxide is preferably a doped metal oxide and / or a single metal oxide.

The doped metal oxide comprises antimony-doped tin oxide, phosphorus-doped tin oxide, antimony-doped titanium oxide, tin oxide-doped indium oxide, zinc oxide-doped indium oxide, tin oxide-zinc oxide-doped indium oxide, and gallium oxide-doped zinc oxide. It is preferably at least one selected from the group.

The single metal oxide is preferably at least one selected from the group consisting of tin oxide, indium oxide, aluminum oxide, titanium oxide, zinc oxide, and nickel oxide.

The conductive fine particle dispersion of the present invention is preferably a conductive paste for offset printing.

The method of forming a conductive pattern of the present invention comprises a first step of applying the conductive fine particle dispersion of the present invention to at least a part of a substrate, and external heating of the conductive fine particles contained in the conductive fine particle dispersion. And a second step of forming a conductive pattern by sintering, the sintering temperature in the second step being 650 ° C. or higher.

In the first step, the conductive fine particle dispersion is preferably applied by a gravure offset printing method using a gravure plate.

It is preferable that the gravure plate has a concave portion on the printed surface which is filled with the conductive fine particle dispersion for gravure offset printing, and the width of the concave portion is 50 μm or less.

The method for producing a conductive substrate of the present invention is characterized in that a conductive pattern is drawn on a base material by using the method for forming a conductive pattern of the present invention.

The electroconductive fine particle dispersion of the present invention has excellent electroconductivity and can form a thin film having a thickness of 5 μm or less and a fine wire having a width of 50 μm or less even if the sintering temperature is fired in a high temperature region of 650 ° C. or more. A fine particle dispersion can be provided. Therefore, by using the conductive fine particle dispersion of the present invention, fine line printing is possible even in firing in a high temperature region. Further, according to the method for forming a conductive pattern of the present invention, a conductive pattern having a film thickness of 5 μm or less and / or a line width of 50 μm or less can be formed even in a high temperature region where the sintering temperature is 650 ° C. or higher. it can. According to the method for forming a conductive pattern of the present invention, even a conductive pattern having a line width of 30 μm or less can be formed without breaking. According to the method for producing a conductive substrate of the present invention, a precise conductive pattern having a film thickness of 5 μm or less and / or a line width of 50 μm or less is printed even when the sintering temperature condition is a high temperature region of 650 ° C. or higher. It is possible to manufacture a conductive substrate having the above structure.

It is a conceptual diagram which showed typically an example of the gravure offset printing method.

[Conductive fine particle dispersion]
The conductive fine particle dispersion of the present invention contains conductive fine particles, a metal oxide, and a dispersion medium, and the content ratio of the conductive fine particles and the metal oxide (conductive fine particles: metal oxide) is The mass ratio is 75:25 to 98: 2. Since the content of the metal oxide is 2% or more with respect to the entire metal component including the conductive fine particles and the metal oxide, the excess of the conductive fine particles in the high temperature region where the sintering temperature condition is 650 ° C. or higher. It is possible to sufficiently prevent sudden volume contraction due to sintering, melting, and evaporation. Further, when the content of the conductive fine particles is 75% or more with respect to the entire metal component, a conductive pattern having a high conductive fine particle content can be formed. Since the conductive fine particles are excellent in chemical stability, the conductive fine particles as a main component can form a conductive pattern that is difficult to oxidize and the volume resistance value is not easily lowered. Since the conductive fine particle dispersion of the present invention contains the conductive fine particles and the metal oxide in the above-mentioned specific content ratio (mass ratio), it has high heat resistance even if the sintering temperature condition is a high temperature region of 650 ° C. or higher. Compatibility and high conductivity can be achieved at the same time.

The conductive fine particle dispersion of the present invention is preferably used for forming a conductive pattern. Since the conductive fine particle dispersion of the present invention does not undergo rapid volume shrinkage or wire breakage due to oversintering, melting, or evaporation of the conductive fine particles even when the sintering temperature condition is in a high temperature range of 650 ° C. or higher, It is suitable for forming a thin line having a width of 50 μm or less and / or a thin film having a film thickness of 5 μm or less. Further, the conductive fine particle dispersion of the present invention is preferably used for forming a conductive pattern having a sintering temperature condition of 650 ° C. or higher.

(Conductive particles)
The conductive fine particles are preferably at least one selected from the group consisting of silver, copper and gold, and more preferably silver. The average particle size of the conductive fine particles is not particularly limited as long as the effect of the present invention is not impaired, but it is preferable that the average particle size is such that a melting point effect occurs, for example, 1 It may be ˜3000 nm. More preferably, it is 1 to 1000 nm. When the average particle diameter of the conductive fine particles is 1 nm or more, the manufacturing cost of the conductive fine particles can be suppressed, which is practical. Further, when the average particle diameter of the conductive fine particles is 1000 nm or less, it can be suitably used for offset printing such as gravure offset printing and screen offset printing. The particle size of the conductive fine particles in the conductive fine particle dispersion according to the present invention may not be constant.

The average particle diameter in the present invention means the average primary particle diameter. The average primary particle diameter can be measured from a photograph taken using a scanning electron microscope or a transmission electron microscope. Specifically, with SEM (S-4800 manufactured by Hitachi, Ltd.), dried particles are attached to a carbon tape, platinum is vapor-deposited, and observation and measurement can be performed at an acceleration voltage of 5.0 KV.

(Metal oxide)
The average particle size of the metal oxide may be within a range that does not impair the effects of the present invention, but is preferably 700 nm or less, more preferably 300 nm or less. When the average particle diameter of the metal oxide is 700 nm or less, the dispersion stability of the metal oxide is less likely to change over time, and the metal oxide can be effectively dispersed in the conductive paste. In addition, the more preferable average particle diameter of the said metal oxide is 10 nm or more and 100 nm or less. By reducing the particle size of the metal oxide, the specific surface area of the metal oxide increases and the number of contact points between the metal oxides increases. Therefore, oversintering of the metal oxide can be suppressed more sufficiently.

As the metal oxide, various metal oxides can be used as long as the effects of the present invention are not impaired, and metal oxides having a melting point of 1000 ° C. or higher can be used. The conductive fine particle dispersion of the present invention contains a metal oxide, so that even if the sintering temperature condition is in a high temperature range of 650 ° C. or higher, the conductive fine particles are rapidly sintered, resulting in rapid volume contraction due to melting and evaporation. It is possible to prevent breakage and disconnection and obtain high conductivity.

The metal oxide is preferably a doped metal oxide and / or a single metal oxide. This is because the metal oxide has relatively high conductivity.

Examples of the doped metal oxide include antimony-doped tin oxide, phosphorus-doped tin oxide, antimony-doped titanium oxide, tin oxide-doped indium oxide (ITO), zinc oxide-doped indium oxide (IZO), tin oxide-zinc oxide-doped indium oxide (ITZO). Examples thereof include gallium oxide-doped zinc oxide (GZO) and the like, but metal oxides obtained by adding a dopant to metal oxides other than the above can also be suitably used.

The doped metal oxides include antimony-doped tin oxide, phosphorus-doped tin oxide, antimony-doped titanium oxide, tin oxide-doped indium oxide (ITO), zinc oxide-doped indium oxide (IZO), tin oxide-zinc oxide-doped indium oxide (ITZO), and It is preferably at least one selected from the group consisting of gallium oxide-doped zinc oxide (GZO).
The doped metal oxide is preferably antimony-doped tin oxide and / or tin oxide-doped indium oxide.

As the above-mentioned single metal oxide, various single metal oxides can be used within a range in which the effect of the present invention can be obtained, and tin oxide, indium oxide, aluminum oxide, titanium oxide, zinc oxide, and nickel oxide can be used. It is preferably at least one selected from the group consisting of

The metal oxide is particularly preferably a doped metal oxide. This is because the conductivity is high.

(Organic component)
An organic component is preferably attached to at least a part of the surface of the conductive fine particles. The surface of the conductive fine particles is more preferably coated with an organic component. The form of the coating is not particularly limited, but the organic component substantially constitutes an inorganic colloid particle together with the conductive fine particles as a so-called dispersant. The organic component includes a trace amount of organic substances contained as impurities in the conductive fine particles from the beginning, a trace amount of organic substances mixed in the conductive fine particles adhering to the conductive fine particles to be described later, a residual reducing agent not completely removed in the cleaning process, and a residual dispersion. It is a concept that does not include organic substances and the like that are attached in trace amounts to the conductive fine particles, such as agents. The "trace amount" is specifically intended to be less than 1% by mass in the inorganic colloid particles.

The organic component is an organic substance that can coat the conductive fine particles to prevent aggregation of the conductive fine particles and form inorganic colloid particles. From the viewpoint of dispersibility and conductivity, amine and carboxylic acid are It is preferable to include. Incidentally, when these organic components are chemically or physically bound to the conductive fine particles, it is considered that they are converted into anions or cations, and ions or complexes derived from these organic components are also described above. Included in organic components.

The amine may be linear or branched, and may have a side chain. Specifically, N- (3-methoxypropyl) propane-1,3-diamine, 1,2-ethanediamine, 2-methoxyethylamine, 3-methoxypropylamine, 3-ethoxypropylamine, 1,4-butane Diamines such as diamine, 1,5-pentanediamine, pentanolamine, aminoisobutanol, alkoxyamines or aminoalcohols, alkylamines such as propylamine, butylamine, pentylamine, hexylamine, hexylamine (linear alkylamines , May have a side chain); cycloalkylamines such as cyclopentylamine and cyclohexylamine; primary amines such as aniline and allylamine; secondaries such as dipropylamine, dibutylamine, piperidine and hexamethyleneimine. Primary amine; tripropy Amine, dimethyl propanediamine, cyclohexyldimethylamine, pyridine, tertiary amines such as quinoline. Of these, alkylamine or alkoxyamine is preferable.

The amine may be a compound containing a functional group other than amine such as a hydroxy group, a carboxyl group, an alkoxy group, a carbonyl group, an ester group, and a mercapto group. The above amines may be used alone or in combination of two or more. The amine preferably has a boiling point at atmospheric pressure of 300 ° C or lower, more preferably 250 ° C or lower.

To the extent that the effects of the present invention are not impaired, a carboxylic acid may be contained in addition to the above amine. The carboxyl group in one molecule of the carboxylic acid has a relatively high polarity and is likely to cause interaction by hydrogen bonding, but the moieties other than these functional groups have a relatively low polarity. Further, the carboxyl group tends to show acidic properties.

As the carboxylic acid, a compound having at least one carboxyl group can be widely used, and examples thereof include formic acid, oxalic acid, acetic acid, hexanoic acid, acrylic acid, octylic acid, and oleic acid. Part of the carboxyl groups of the carboxylic acid may form a salt with a metal ion. In addition, about the said metal ion, 2 or more types of metal ions may be contained.

The carboxylic acid may be a compound containing a functional group other than the carboxyl group, such as an amino group, a hydroxy group, an alkoxy group, a carbonyl group, an ester group, and a mercapto group. In this case, it is preferable that the number of carboxyl groups is equal to or larger than the number of functional groups other than the carboxyl groups. The carboxylic acids may be used alone or in combination of two or more. The carboxylic acid preferably has a boiling point at atmospheric pressure of 300 ° C or lower, more preferably 250 ° C or lower. Also, amine and carboxylic acid form an amide group. Since the amide group is also appropriately adsorbed on the surface of the conductive fine particles, the organic component may contain an amide group.

The content of the organic component in the inorganic colloid in the conductive fine particle dispersion of the present invention is preferably 0.5 to 50% by mass. When the content of the organic component is 0.5% by mass or more, the storage stability of the obtained conductive fine particle dispersion tends to be good, and when it is 50% by mass or less, the conductivity of the conductive pattern tends to be good. There is. The more preferable content of the organic component is 1 to 30% by mass, and the further preferable content is 2 to 15% by mass.

When the amine and the carboxylic acid are used in combination, the composition ratio (mass) of the amine and the carboxylic acid can be arbitrarily selected within the range of 1/99 to 99/1. The composition ratio of the amine and the carboxylic acid is preferably 20/80 to 98/2, and more preferably 30/70 to 97/3. A plurality of types of amine or carboxylic acid may be used as the amine or carboxylic acid, respectively.

As a method for producing the conductive fine particles having the organic component adhered to the surface, for example, when silver is used as the conductive fine particles, a silver compound capable of decomposing by reduction to generate silver, an amine, and a dispersant are used. A method including a mixed solution preparing step of preparing a mixed solution and a silver fine particle producing step of producing silver fine particles in which the amine is attached to at least a part of the surface by reducing the silver compound in the mixed solution is mentioned. Be done.

In the mixed liquid preparation step, it is preferable to add 2 mol or more of amine to 1 mol of silver. By setting the addition amount of the amine to 2 mol or more with respect to 1 mol of silver, an appropriate amount of the amine can be attached to the surface of the silver fine particles produced by reduction, and the silver fine particles can be excellently dispersed in various dispersion media. And low-temperature sinterability can be imparted.

The composition of the mixed solution in the mixed solution preparation step and the reducing conditions (for example, heating temperature and heating time) in the silver fine particle producing step are such that the particle diameter of the obtained silver fine particles is nanometer size. It is preferable to adjust. This is because when the particle size of the silver particles is nanometer, the melting point is lowered and the silver particles can be fired at a low temperature. The particle size of the obtained silver fine particles is more preferably 1 to 3000 nm. If necessary, micron-sized particles may be included. The method for taking out the silver fine particles from the colloidal liquid containing the silver fine particles obtained in the silver fine particle producing step is not particularly limited, and examples thereof include a method of washing the colloidal liquid.

The colloidal liquid obtained in the silver fine particle production step contains a dispersant and the like in addition to the silver fine particles, and the electrolyte concentration of the entire solution tends to be high. In the colloidal liquid in such a state, the fine silver particles are coagulated and tend to be precipitated because of high electric conductivity. Therefore, it is preferable to wash this colloidal solution to remove excess electrolyte.

As a method of washing the colloidal solution, for example, a step of removing the supernatant by allowing the prepared colloidal solution to stand for a certain period of time to remove the supernatant liquid, adding pure water to the solution and stirring it, and leaving it for a certain period of time to remove the supernatant liquid There is a method of repeating it several times. Other washing methods include, for example, a method of performing centrifugation instead of the above-mentioned standing, a method of desalting with an ultrafiltration device, an ion exchange device, and the like. Of these, the method of desalting is preferable. The desalted liquid may be appropriately concentrated.

As the silver compound, various known silver compounds can be used, and for example, a silver salt or a hydrate of a silver salt can be used. Specific examples thereof include silver salts such as silver nitrate, silver sulfate, silver chloride, silver oxide, silver acetate, silver oxalate, silver formate, silver nitrite, silver chlorate, and silver sulfide. These are not particularly limited as long as they can be reduced, and may be dissolved in an appropriate solvent or may be used while being dispersed in the solvent. These may be used alone or in combination. Of these, silver oxalate is preferable. Silver oxalate is the simplest silver dicarboxylate, and the silver oxalate amine complex synthesized using silver oxalate is capable of reduction at low temperature and in a short time, so it is suitable for the synthesis of nanometer-sized silver fine particles. It is suitable. Furthermore, when silver oxalate is used, no by-product is generated during the synthesis, and only carbon dioxide derived from the oxalate ion is released to the outside of the system.

As the dispersant, for example, a commercially available wetting dispersant can be used. Examples of commercially available wetting and dispersing agents include Solsperse 11200, Solsperse 13940, Solsperse 16000, Solsperse 17,000, Solsperse 18000, Solsperse 20000, Solsperse 24000, Solsperse 26000, Solsperse 27000, Solsperse 28000 (manufactured by Nippon Lubrizol); DISPERBYK-102, 110, 111, 170, 190.194N, 2015, 2090, 2096 (manufactured by Big Chemie Japan); EFKA-46, EFKA-47, EFKA-48, EFKA-49 (manufactured by EFKA Chemical Co.); polymer 100, polymer 120, polymer 150, polymer 400, polymer 401, polymer 402, polymer 403, polymer 450 Polymer 451, Polymer 452, Polymer 453 (manufactured by EFKA Chemical Co.); Addisper PB711, Addisper PA111, Addisper PB811, Addisper PW911 (manufactured by Ajinomoto Co.); Floren DOPA-15B, Floren DOPA-22, Floren DOPA-17, Floren TG-. 730W, Floren G-700, Floren TG-720W (manufactured by Kyoeisha Chemical Industry Co., Ltd.) and the like. Also, TEGO Dispers series 610, 610S, 630, 651, 655, 750W, 755W and the like of Evonik Co .; Disparlon series DA-375, DA-1200 and the like of Kusumoto Kasei Co. may be used. From the viewpoint of low-temperature sinterability and dispersion stability, it is preferable to use DISPERBYK-102, Solsperse 11200, Solsperse 13940, Solsperse 16000, Solsperse 17000, Solsperse 18000, Solsperse 28000 and the like.

As a method for reducing the silver compound, a heating method is preferable. The heating method is not particularly limited. As a method of reducing the silver compound by the heating, for example, a complex compound generated from a silver compound such as silver oxalate and an organic component such as an amine is heated to remove oxalate ions or the like contained in the complex compound. A method of aggregating atomic silver produced by decomposing a metal compound may be mentioned. By the above method, it is possible to produce fine silver particles protected by a protective film of an organic component such as amine.

Thus, in the metal amine complex decomposition method for producing silver particles coated with an amine by thermally decomposing a complex compound of a silver compound in the presence of an amine, decomposition of a silver amine complex, which is a single type of molecule, is performed. Since atomic silver is generated by the reaction, it is possible to uniformly generate atomic silver in the reaction system, and constitutes a reaction as compared with the case where silver atoms are generated by the reaction between a plurality of components. The non-uniformity of the reaction due to the compositional fluctuation of the components is suppressed, which is advantageous especially when a large amount of silver powder is produced on an industrial scale.

Further, in the metal amine complex decomposition method, an amine molecule is coordinate-bonded to a silver atom to be produced, and the action of the amine molecule coordinated to the silver atom controls the movement of the silver atom when aggregation occurs. It is presumed to be a thing. As a result, the metal amine complex decomposition method makes it possible to produce very fine metal particles having a narrow particle size distribution.

Furthermore, a large number of amine molecules form coordination bonds with a relatively weak force on the surface of the silver fine particles to be produced, and these form a dense protective film on the surface of the silver fine particles, and thus have excellent storage stability. It is possible to produce organic-coated silver fine particles having a clean surface. Moreover, since the amine molecules forming the above-mentioned coating can be easily desorbed by heating or the like, it becomes possible to produce silver fine particles that can be sintered at a very low temperature.

(Dispersion medium)
The dispersion medium contained in the conductive fine particle dispersion of the present invention disperses the conductive fine particles, and various materials can be used within a range not impairing the effects of the present invention. It can be selected according to the coating method and application of the fine particle dispersion.

Hereinafter, in the description of the present invention, although it may be described by taking the gravure offset printing method as a specific example of the method for printing the conductive pattern, an inkjet method, a relief printing method, an intaglio printing method, a screen printing method, etc. Printing methods known in the art can be used as well.

It is preferable that the conductive fine particle dispersion of the invention contains an organic solvent. By using an organic solvent as the dispersion medium, aggregation of the conductive fine particles can be suppressed. In addition, since it generally has a high boiling point and is difficult to dry, it is easy to adjust the viscosity so that it can be ejected by inkjet printing, and the coating property of the conductive fine particle dispersion (for example, the ejection property from an inkjet head) can be improved.

(Dispersion medium such as an organic solvent having a hydroxy group)
As the dispersion medium, an organic solvent having at least a hydroxy group can be used, and examples thereof include alcohol and glycol ether having a hydroxy group at one end.

Examples of the alcohol include methanol, ethanol, propanol, isopropanol, butanol, isobutanol, 2-butanol, hexanol, isoamyl alcohol, furfuryl alcohol, tert-butanol, 1-pentanol, 2-pentanol, 4-methyl. Examples include 2-pentanol, 3-methyl-1-pentanol, 3-methyl-2-pentanol, 2-butanol, 1-hexanol, 2-hexanol, and 2-hexyloxyethanol.

The alcohol may be a polyhydric alcohol. Examples of the polyhydric alcohol include glycerin, 1,2,4-butanetriol, 1,2,6-hexanetriol, ethylene glycol, diethylene glycol, 1,2-butanediol, propylene glycol, 2-methylpentane-2, 4-diol, butyltriglycol, isobutyldiglycol, 2-butoxyethanol, 3-methoxy-3-methylbutanol, 2- (2-methoxyethoxy) ethanol, 2- (2-hexyloxyethoxy) ethanol, 2,4 -Diethyl-1,5-pentanediol, 3-methyl-1,5-pentanediol, 2-ethyl-1,3-hexanediol.

Examples of the glycol ether include tripropylene glycol, triethylene glycol, 1,2-hexanediol, 1,3 butylene glycol, 1,3-propanediol, dipropylene glycol, and 2-butene-1,4-diol. Can be mentioned.

As the alcohol, aliphatic alcohol, cyclic alcohol, alicyclic alcohol and the like can be used.

Examples of the aliphatic alcohol include heptanol, octanol (1-octanol, 2-octanol, 3-octanol, etc.), decanol (1-decanol, etc.), tridecanol (isotridecanol, etc.), lauryl alcohol, tetradecyl alcohol. And saturated or unsaturated aliphatic alcohols having 6 to 30 carbon atoms such as cetyl alcohol, 2-ethyl-1-hexanol, octadecyl alcohol, hexadecenol, and oleyl alcohol.

Examples of the cyclic alcohol include cresol, eugenol, terpineol and the like.

Examples of the alicyclic alcohol include cycloalkanol such as cyclohexanol, terpineol (including α, β, γ isomers, or any mixture thereof), terpene alcohol such as dihydroterpineol (monoterpene alcohol, etc.) , Dihydroterpineol, myrtenol, sobrerol, menthol, carveol, perillyl alcohol, pinocarveol, sobrerol, berbenol and the like.

The dispersion medium preferably has a boiling point of 170 ° C. or higher at normal pressure. When the boiling point of the dispersion medium at atmospheric pressure is 170 ° C. or higher, excessive drying of the silver particle dispersion can be suppressed after coating.

The content of the above dispersion medium in the whole conductive fine particle dispersion of the present invention can be appropriately adjusted according to the coating method (printing method) of the conductive fine particle dispersion and the application.
When the viscosity is adjusted to be low as in an inkjet ink, the conductive fine particle dispersion (conductive ink) preferably contains the dispersion medium in an amount of 40 to 80% by mass. Further, in the case of adjusting to a high viscosity like a conductive paste for offset printing, the conductive fine particle dispersion (conductive paste) preferably contains the dispersion medium in an amount of about 10 to 30% by mass.

The conductive fine particle dispersion of the present invention is preferably a conductive paste for offset printing such as gravure offset printing and screen offset printing, and more preferably a conductive paste for gravure offset printing. Offset printing is a printing method that is capable of clear printing and is suitable for forming a film having a film thickness of 5 μm or less and a fine line having a line width of 50 μm or less. Among them, the gravure offset printing is a gravure plate having a concave portion. The shape of the printing pattern can be freely set by the shape of the (intaglio), and the transfer rate of the film of the conductive fine particle dispersion from the blanket to the substrate is also good if the conductive fine particle dispersion of the present invention is used. The fine conductive pattern as described above can be accurately formed.
Hereinafter, the dispersion medium in the case where the conductive fine particle dispersion of the invention is a conductive paste for gravure offset printing, and the water-soluble polymer contained in the conductive paste will be described.

(Dispersion medium of conductive paste)
The conductive paste for gravure offset printing contains an organic solvent as a dispersion medium of the conductive fine particles. By using an organic solvent as the dispersion medium, aggregation of the conductive fine particles can be suppressed. In addition, since it generally has a high boiling point and is difficult to dry, transfer to a blanket is easy. Further, since it has a low surface tension, it is well compatible with silicone rubber generally used as a blanket. When water is used as the dispersion medium, the silver fine particles may aggregate and clog the concave portions of the gravure plate. Further, water is unsuitable as a dispersion medium for a conductive paste used for gravure offset printing having a transfer step because of its high surface tension, poor wettability to a blanket, low boiling point and easy drying.

It is preferable that the organic solvent in the conductive paste for gravure offset printing contains a hydroxyl group and a first organic solvent having a boiling point of 200 ° C. or higher at normal pressure. The conductive paste for gravure offset printing, which is one form of the conductive fine particle dispersion of the present invention, is suitable for thin line printing having a line width of 10 μm or less, and particularly a line width of 3 μm or less. It is preferable to use. When the boiling point of the first organic solvent at atmospheric pressure is 200 ° C. or higher, it is possible to prevent the conductive paste from being excessively dried on the gravure plate. Further, when the first organic solvent contains a hydroxy group, the silver fine particles are well dispersed, and the polarity of the organic solvent is increased, so that the swelling of the blanket tends to be suppressed.

Examples of the first organic solvent include 2,4-diethyl-1,5-pentanediol, 3-methyl-1,5-pentanediol, 2-ethyl-1,3-hexanediol, tripropylene glycol, It is preferable to use a diol solvent such as triethylene glycol, 1,2-hexanediol, 1.3 butylene glycol, 1,3-propanediol, dipropylene glycol or 2-butene-1,4-diol.

The content of the first organic solvent with respect to the entire conductive paste is preferably 3 to 30 mass%. A more preferable upper limit of the content of the first organic solvent is 25% by mass, and a still more preferable upper limit thereof is 20% by mass.

The organic solvent preferably contains 3.0 to 30 mass% of a second organic solvent having a blanket swelling ratio of 2.0% or less. The second organic solvent having a blanket swelling ratio of 2.0% or less is also referred to as "low swelling organic solvent". The second organic solvent may also serve as the first organic solvent. By using the low swelling organic solvent having an extremely low blanket swelling ratio of 2.0% or less, the absorption of the organic solvent into the blanket can be reduced, and the drying of the conductive paste on the blanket surface can be significantly suppressed. it can. When a fine line is printed using a conductive paste, the fine line-shaped conductive paste is very easy to dry, and it is difficult to form a good conductive pattern. On the other hand, by setting the blanket swelling ratio of the organic solvent to 2.0% or less, for example, it is possible to cope with the formation of a fine line conductive pattern having a line width of 3 μm or less. A more preferable blanket swelling ratio is 0.4% or less.

(Organic solvent having a blanket swelling ratio of 2.0% or less)
Examples of the polyhydric alcohol having 2 to 3 hydroxy groups include glycerin, 1,2,4-butanetriol, 1,2,6-hexanetriol, ethylene glycol, diethylene glycol, 1,2-butanediol and propylene. Examples thereof include glycol and 2-methylpentane-2,4-diol.

Further, by setting the content rate of the second organic solvent to the entire conductive paste to be 3.0% by mass or more, it is possible to impart appropriate coatability (fluidity) to the conductive paste, and further, For example, it is possible to suppress drying at the time of printing a fine line having a line width of 3 μm or less. By setting the content to 30% by mass or less, it is possible to prevent the spread during printing. The more preferable upper limit of the content of the low-swelling organic solvent is 25.0% by mass, and the further preferable upper limit thereof is 20.0% by mass.

Generally, the outermost surface of a printing plate used for gravure offset printing is made of silicone rubber, and the “blanket swelling ratio” in the present invention means the swelling ratio when the silicone rubber is immersed in an organic solvent. Here, the "blanket swelling rate" is synonymous with the mass change rate of the blanket (silicone rubber) before and after the immersion when the blanket (silicone rubber) is immersed in the organic solvent. Specifically, a blanket (silicone rubber) is cut into 1 cm squares to give a test piece, and the test piece is immersed in an organic solvent under room temperature conditions (25 ° C. ± 5 ° C.), taken out after 10 hours, and mass before and after immersion. The “blanket swelling ratio” can be evaluated by obtaining the increase ratio. It has been experimentally proved that, as long as the silicone blanket is used as a standard for printing the conductive paste, the swelling rate measured with respect to a specific organic solvent does not significantly differ.

As the low swelling organic solvent having a blanket swelling ratio of 2.0% or less, various solvents can be used as long as the effects of the present invention are not impaired. Among them, a solvent having a hydroxy group as a functional group is preferable, and examples thereof include a polyhydric alcohol having a plurality of hydroxy groups and other monohydric alcohol solvents. Further, by using a highly polar solvent such as diol having an extremely low blanket swelling rate, it is possible to more effectively suppress the drying of the fine line pattern on the blanket. These solvents may be used alone or in combination of two or more.

Examples of the monohydric alcohol include butyltriglycol, isobutyldiglycol, 2-butoxyethanol, 3-methoxy-3-methylbutanol, 2- (2-methoxyethoxy) ethanol, 2- (2-hexyloxyethoxy) ethanol. Etc.

Further, although overlapping with the first organic solvent, 2,4-diethyl-1,5-pentanediol, 3-methyl-1,5-pentanediol, 2-ethyl-1,3-hexanediol, tripropylene A diol solvent such as glycol, triethylene glycol, 1,2-hexanediol, 1.3 butylene glycol, 1,3-propanediol, dipropylene glycol or 2-butene-1,4-diol may be used.

Various organic solvents can be used as long as the effects of the present invention are not impaired. In addition to the first organic solvent and the second organic solvent, the blanket swelling rate is adjusted by adjusting the drying property. A solvent having a high swelling ratio exceeding 2.0% may be mixed and used. The number and combination of solvents to be mixed are not particularly limited.

(Organic solvent having a blanket swelling ratio of more than 2.0%)
Examples of the organic solvent having a blanket swelling ratio of more than 2.0% include glycol ether, glycol ester, terpene solvent, hydrocarbon solvent, alcohol solvent and the like. These solvents may be used alone or in combination of two or more. If the concentration of the terpene solvent in the organic solvent is too high, the amount of solvent absorbed in the blanket increases, and since drying easily proceeds on the blanket during transfer printing, the diol solvent and the terpene solvent are well balanced. It is preferable to mix them.

Specific examples of the organic solvent having a blanket swelling ratio exceeding 2.0% include, for example, tripropylene glycol-n-butyl ether, butyl carbitol, diethylene glycol monomethyl ether, tripropylene glycol methyl ether, diethylene glycol monoethyl ether acetate, diethylene glycol. Monobutyl ether acetate, triethylene glycol dimethyl ether, dipropylene glycol methyl ether acetate, ethylene glycol monohexyl ether, dipropylene glycol methyl ether, propylene glycol diacetate, 1,4-butanediol divinyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl Ether acetate etc. are mentioned.

The hydrocarbon solvent may contain an aliphatic hydrocarbon compound, may contain a cyclic hydrocarbon compound, or may contain an alicyclic hydrocarbon compound. ..

Examples of the aliphatic hydrocarbon compound include saturated or unsaturated aliphatic compounds such as tetradecane, octadecane, heptamethylnonane, tetramethylpentadecane, hexane, heptane, octane, nonane, decane, tridecane, methylpentane, normal paraffin, and isoparaffin. Hydrocarbon compounds may be mentioned.

Examples of the cyclic hydrocarbon compound include toluene and xylene.

Examples of the alicyclic hydrocarbon compound include limonene, dipentene, terpinene, terpinene (also referred to as terpinene), nesole, sinen, orange flavor, terpinolene, terpinolene (also referred to as terpinolene), ferrandrene, menthadiene, tereben, and the like. Examples thereof include dihydrocymene, moslene, isoterpinene, isoterpinene (also referred to as isoterpinene), klitmen, coutcine, cajeptene, oilymen, pinene, turpentine, menthane, pinane, terpene, cyclohexane and the like.

The alcohol solvent is a compound containing one or more hydroxy groups in its molecular structure, and examples thereof include aliphatic alcohols, cyclic alcohols and alicyclic alcohols. These alcohols may be used alone or in combination of two or more. Further, part of the hydroxy group may be derivatized with an acetoxy group or the like as long as the effect of the present invention is not impaired.

Examples of the aliphatic alcohol include heptanol, octanol (1-octanol, 2-octanol, 3-octanol, etc.), decanol (1-decanol, etc.), lauryl alcohol, tetradecyl alcohol, cetyl alcohol, 2-ethyl-1. -Saturated or unsaturated aliphatic alcohols having 6 to 30 carbon atoms such as hexanol, octadecyl alcohol, hexadecenol, and oleyl alcohol.

Examples of the cyclic alcohol include cresol and eugenol.

Examples of the alicyclic alcohol include cycloalkanol such as cyclohexanol, terpineol (including terpineol, α, β, γ isomers, or any mixture thereof), terpene alcohol such as dihydroterpineol (monoterpene alcohol). Etc.), dihydroterpineol, myrtenol, sobrerol, menthol, carveol, perillyl alcohol, pinocarveol, sobrerol, berbenol and the like. The alicyclic alcohol may overlap with the terpene solvent.

(Water-soluble polymer)
The conductive paste for gravure offset printing preferably contains a water-soluble polymer. The inclusion of the water-soluble polymer enhances the adsorption action on the interface between the blanket and the adherend. Therefore, by using the gravure offset printing method, even if the conductive pattern has a line width of 3 μm or less, it does not break. Can be formed. In the present specification, “water-soluble” refers to one having a solubility of 1 g or more in 1 L of water.

The water-soluble polymer is preferably a polymer that is soluble in both organic solvents and water. Further, the above water-soluble polymer is required to have adhesiveness to a base material, transferability to the base material, and difficulty in spreading a line on a blanket. When the adherend (base material) of the conductive paste is, for example, polyethylene terephthalate (PET), it is preferable that the adherence to PET is good.

The water-soluble polymer preferably contains a polymerizable compound having a cyclic structure. Polyvinyl alcohol can also be used, although its solubility in organic solvents is limited. The cyclic structure is preferably γ-lactam, and preferably has a vinyl group. Above all, the water-soluble polymer more preferably contains polyvinylpyrrolidone. Polyvinylpyrrolidone is a polymer represented by the following chemical formula (1).

（式中、ｎは自然数である。）

(In the formula, n is a natural number.)

Polyvinylpyrrolidone has high solubility in highly polar polyhydric alcohols (especially diol solvents) and can be well dissolved in solvents such as esters and ketones. Can be dispersed. In particular, it dissolves well in the first organic solvent containing a hydroxy group and having a boiling point of 200 ° C. or higher at normal pressure.

Further, since polyvinylpyrrolidone is also soluble in water, it is possible to remarkably enhance the adsorbing action on the base material interface. Further, as a feature of gravure offset printing, a semi-solid / semi-liquid paste is transferred and printed on a blanket, but polyvinylpyrrolidone has a very high tackiness (adhesiveness) in the semi-solid / semi-liquid state. Therefore, it is very excellent in the transfer from the blanket to the substrate. Therefore, it is possible to remarkably improve printability in fine line printing having a line width of, for example, 3 μm or less, which cannot be printed by the conventional conductive paste.

The polyvinylpyrrolidone preferably has an average molecular weight of 100,000 or less. When the average molecular weight is 100,000 or less, the viscosity of the conductive paste is not excessively increased, and the transferability to the blanket or the base material can be improved. Examples of such polyvinylpyrrolidone include polyvinylpyrrolidone K25 (average molecular weight: 25000), polyvinylpyrrolidone K30 (average molecular weight: 40000) (both manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and the like. The average molecular weight is a mass average molecular weight and is measured by liquid chromatography. For the measurement of the mass average molecular weight, Shimadzu LC-6AD pump, RID-10A RI detector, CLASS-LC10 Chromatopac data processor, and DGU-20A3 degasser are used. Further, TSK-GEL G1000H, G2000H and G2500H are used as columns, and the temperature of the oven is set to 40 ° C. and tetrahydrofuran (THF) is flown at a flow rate of 1.0 mL / min. The mass average molecular weight is calculated by calibrating polystyrene as a standard.

The content of the water-soluble polymer is preferably 3 to 8 mass% with respect to the entire conductive paste. When the content of the water-soluble polymer is less than 3% by mass, the adhesiveness to the adherend may decrease. On the other hand, when the content of the water-soluble polymer exceeds 8% by mass, the volume resistance value of the conductive pattern formed by the conductive paste of one embodiment of the present invention may increase. The more preferable upper limit of the content of the water-soluble polymer is 7% by mass.

The conductive fine particle dispersion of the present invention may contain a surfactant. In a multi-component solvent-based inorganic colloidal dispersion, the surface of the coating film becomes rough and the solid content tends to be uneven due to the difference in the volatilization rate during drying. By adding a surfactant to the conductive fine particle dispersion of the present invention, these disadvantages can be suppressed and a uniform conductive pattern can be formed.

The surfactant is not particularly limited, and an anionic surfactant, a cationic surfactant, a nonionic surfactant and the like can be used. Specific examples thereof include alkylbenzene sulfonate and quaternary ammonium salt. From the viewpoint of obtaining the effect with a small amount of addition, a fluorine-based surfactant is more preferable.

The method for producing the conductive fine particle dispersion of the present invention is not particularly limited, and examples thereof include the following methods. First, a colloidal liquid containing conductive fine particles having an organic component attached to the surface as a solid content is prepared. Then, the obtained colloidal liquid, the metal oxide, the dispersion medium, and the above-mentioned optional components are mixed to obtain the conductive fine particle dispersion of the present invention.

A method of forming a conductive pattern is also one of the present invention, the first step of applying the conductive fine particle dispersion of the present invention to at least a part of the substrate, and the conductive contained in the conductive fine particle dispersion A second step of sintering the fine particles by external heating to form a conductive pattern, wherein the sintering temperature in the second step is 650 ° C. or higher.
Since the conductive fine particle dispersion of the present invention contains a metal oxide in a specific ratio with respect to the conductive fine particles, the conductive fine particles are over-sintered or melted even in a high temperature range of 650 ° C. or higher. Further, it is possible to sufficiently prevent a rapid volume contraction due to evaporation, and it is possible to form a conductive pattern having excellent conductivity.

The conductive fine particle dispersion of the present invention can be suitably used as a conductive ink or a conductive paste in the field of printed electronics. The conductive film can be used as an electronic circuit board (for example, a semiconductor integrated circuit), a printed wiring board, a wiring of a thin film transistor substrate, an electrode, or the like.

As the material of the above-mentioned base material to which the conductive fine particle dispersion of the present invention is applied, various base materials can be used as long as the effects of the present invention are not impaired. A substrate having heat resistance that can be used even in the region is preferable. Examples of such a base material include alumina ceramics. The surface of the base material may be provided with a surface layer (primer layer) for the purpose of enhancing the adhesion to the conductive film, or may be subjected to a surface treatment such as a hydrophilic treatment. Examples of the surface treatment method include dry treatment such as corona treatment, plasma treatment, UV treatment, and electron beam treatment. Further, as the base material, in addition to the alumina ceramic substrate, specifically, an oxide substrate, a PZT substrate, an alumina substrate, a zirconia substrate, a ceramic substrate, a ceramic green sheet, or the like can be used.

The above-mentioned coating is a concept including both the case where the conductive fine particle dispersion is applied in a plane and the case where the conductive fine particle dispersion is applied (drawn) linearly. The coating film (conductive film) formed by applying the conductive fine particle dispersion may have a planar shape, a linear shape, or a combination thereof. The coating film (conductive film) may have a continuous pattern, a discontinuous pattern, or a combination of these.

The method for applying the conductive fine particle dispersion of the present invention is not particularly limited, and for example, gravure offset printing method, inkjet printing method, screen printing method, screen offset printing method, letterpress printing method, intaglio printing method, reverse printing method, Examples thereof include a microcontact printing method, a dipping method, a spray method, a bar coating method, a spin coating method, a dispenser method, a casting method, a flexo method, a gravure method, a syringe method, and a coating method using a brush. Among them, the conductive fine particle dispersion of the invention is preferably a conductive paste for offset printing or a conductive ink for inkjet printing, and more preferably a conductive paste for gravure offset printing.

In the second step, the bonding between the conductive fine particles contained in the coating film formed in the first step is increased and the particles are sintered. In the method for forming a conductive pattern of the present invention, since the conductive fine particle dispersion of the present invention is used, the metal oxide is dispersed in the coating film and the sintering temperature is 650 ° C. or higher even in a high temperature region. The metal oxide prevents abrupt volume contraction of the conductive fine particles due to oversintering, melting and evaporation. The sintering temperature is preferably 1000 ° C. or lower. The sintering temperature is preferably 700 ° C or higher. Further, the temperature may be 850 ° C. or higher. The firing time of the coating film is not particularly limited and may be appropriately set according to the sintering temperature.

The method for firing the coating film is not particularly limited, and examples thereof include a method using a conventionally known gear oven and the like.

The film thickness of the conductive pattern is, for example, 0.1 to 5 μm, preferably 0.2 to 3 μm. The line width of the conductive pattern is, for example, 50 μm or less, preferably 30 μm or less, and more preferably 10 μm or less. The volume resistance value of the conductive pattern is preferably 20 μΩ · cm or less, more preferably 10 μΩ · cm or less, and further preferably 5 μΩ · cm or less.

The film thickness t of the conductive pattern can be measured with a laser microscope (for example, laser microscope VK-9510 manufactured by Keyence Corporation). Further, the film thickness t of the conductive pattern can be obtained using the following formula.
Formula: t = m / (d × M × w)
m: conductive pattern mass (weigh the conductive pattern formed on the slide glass with an electronic balance)
d: Conductive pattern density (g / cm ³ ) (10.5 g / cm ^{3 for} silver)
M: Conductive pattern length (cm) (measures the length of the conductive pattern formed on the slide glass on a scale equivalent to JIS class 1)
w: conductive pattern width (cm) (width of the conductive pattern formed on the slide glass is measured on a scale equivalent to JIS class 1)

The volume resistance value of the conductive pattern obtained by the conductive pattern forming method of the present invention can be measured, for example, by the following method. First, the conductive fine particles of the present invention are formed on a 2.5 cm square glaze-processed alumina ceramic with an applicator aiming at a wet film thickness of 30 μm, and 900 ° C. at a heating rate of 8 ° C./min in a muffle furnace. The temperature is raised to 100 ° C., and thereafter, the conductive film is formed by sintering by heating and firing under the condition of cooling to room temperature. The surface resistance (R) of this coating is measured using Loresta GP MCP-T610 manufactured by Mitsubishi Chemical Anateric Co., Ltd., and the volume resistance value is calculated by multiplying this by the film thickness (t). The film thickness (t) can be measured using, for example, a shape measurement laser microscope “VK-X100” manufactured by Keyence Corporation. The formula used to calculate the volume resistance value is as follows.
Formula (1): (volume resistance value ρv) = (surface resistance value R) × (film thickness t)

The conductive pattern obtained by the method for forming a conductive pattern of the present invention contains a metal oxide having an average particle size of 700 nm or less.

Further, when the conductive fine particle dispersion of the present invention is a conductive paste for gravure offset printing, within a range that does not impair the effects of the present invention, appropriate viscosity, adhesiveness, dryability or printability according to the purpose of use. In order to impart functions such as the above, an optional component such as a wetting dispersant, an oligomer component, a surfactant, a thickener or a surface tension adjusting agent may be added. The optional component is not particularly limited.
As the above-mentioned wetting dispersant, the same dispersant as the above-mentioned commercially available wetting dispersant can be used.

The content of the wetting and dispersing agent is preferably 0.1 to 15 mass% with respect to the entire conductive paste. If the content of the above-mentioned wetting dispersant with respect to the entire conductive paste is 0.1% by mass or more, the dispersion stability of the obtained conductive paste will be good, but if the content is too large, the dispersion stability will decrease. It will be. From such a viewpoint, the more preferable content of the wetting and dispersing agent is 0.3 to 3% by mass, and the more preferable content is 0.5 to 2% by mass.

Examples of the thickener include clay minerals such as clay, bentonite and hectorite; emulsions of polyester emulsion resins, acrylic emulsion resins, polyurethane emulsion resins or blocked isocyanates; methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, Examples thereof include cellulose derivatives such as hydroxypropyl cellulose and hydroxypropyl methyl cellulose; polysaccharides such as xanthan gum and guar gum. These may be used alone or in combination of two or more kinds.

The conductive paste preferably has a viscosity of 500 cP to 50,000 cP. When the viscosity of the conductive paste is within the above range, the concave portions of the gravure plate can be easily filled and the conductive paste is less likely to bleed after transfer to the adherend, and thus fine line printing is possible. The viscosity can be measured with a cone-plate type viscometer (for example, Rheometer MCR301 manufactured by Anton Paar). The measurement is performed at a temperature of 25 ° C., and the viscosity at a cone rotation speed of 50 rpm can be adopted. The viscosity can also be expressed as a shear viscosity, and the paste viscosity at a share rate of 1 s ⁻¹ is 50 Pa · s or less and the paste viscosity at a share rate of 100 s ⁻¹ is 0.5 Pa · s or more. Is preferable in terms of.

Although screen printing is generally used for printing the conductive pattern, screen printing is stencil printing, so if the viscosity is low, the paste will flow and it will be difficult to print according to the pattern, so gravure offset A conductive paste having a higher viscosity than that for printing is used. Generally, many conductive pastes used for screen printing have a viscosity range of about 50,000 to 100,000 cP. If the conductive paste for screen printing is filled in the gravure offset printing gravure plate, the viscosity is too high to make transfer to the blanket difficult, and the concave portion of the gravure plate is clogged.

[Method for producing conductive paste for gravure offset printing]
The method for producing the conductive paste for gravure offset printing of one embodiment of the present invention is not particularly limited, but first, a colloid containing conductive fine particles is prepared, and the conductive fine particle dispersion, an organic solvent and a water-soluble polymer are prepared. By mixing the above-mentioned various components as necessary, the conductive paste for gravure offset printing according to one aspect of the present invention can be obtained. The method for preparing the conductive fine particle dispersion is as described above.

The method of mixing the conductive fine particle dispersion obtained by the method described above, the dispersion medium, and the water-soluble polymer is not particularly limited, and can be performed by a conventionally known method using a stirrer, a stirrer, or the like. An ultrasonic homogenizer having an appropriate output may be applied by stirring with a thing such as a spatula.

[Method of forming conductive pattern]
By using the conductive paste for gravure offset printing, a fine conductive pattern can be formed by the gravure offset printing method using a gravure plate. That is, using a gravure offset printing method using a gravure plate, the gravure plate has a concave portion filled with a conductive paste for gravure offset printing (conductive fine particle dispersion) on the printing surface, the width of the concave portion is , 50 μm or less, and the conductive paste for gravure offset printing is the conductive paste for gravure offset printing (conductive particle dispersion) of the present invention. A method for forming a conductive pattern is also an aspect of the present invention. is there.

A method of applying the conductive paste to the base material 60 using the gravure offset printing method will be described below with reference to FIG. FIG. 1 is a conceptual diagram schematically showing an example of the gravure offset printing method. As shown in FIG. 1, the printing apparatus 100 for gravure offset printing includes a gravure plate 40 and a blanket 50. The printing apparatus 100 for gravure offset printing preferably further includes a pickup roll 20 for applying the conductive paste 10 for gravure offset printing to the gravure plate 40, and a blade 30 for removing the excess conductive paste 10.

The gravure plate 40 has a recess 41 on the printed surface, which is filled with the gravure offset printing conductive paste 10. The width W of the recess 41 is 50 μm or less. By setting the width W of the recess 41 to 50 μm or less, a conductive pattern having a line width of 50 μm or less can be formed. The width W of the recess 41 is preferably 30 μm or less. By using the gravure offset printing conductive paste (conductive particle dispersion) of the present invention, even if a gravure plate having a width W of the recess 41 of 50 μm or less is used, the line width is 50 μm or less without breaking. A fine conductive pattern can be formed. The gravure plate 40 may have a plate shape or a cylindrical shape.

The blanket 50 preferably has a silicone rubber layer. As the blanket 50, for example, Silblanc series manufactured by Kinyosha Co., Ltd., # 700-STD manufactured by Fujikura Rubber Co., Ltd., or the like can be used. The blanket 50 may have a plate shape or a cylindrical shape.

The base material 60 is not particularly limited as long as it has at least one main surface on which the conductive paste 10 for gravure offset printing is applied and baked by heating so that a conductive pattern can be mounted. However, it is preferable that the substrate has excellent heat resistance.

As a material for forming the base material 60, as described above, an oxide substrate, a PZT substrate, an alumina substrate, a zirconia substrate, an alumina ceramic substrate, a ceramic substrate, a ceramic green sheet, or the like can be used. The base material 60 may have various shapes such as a plate shape or a strip shape, and may be rigid or flexible. The thickness of the base material 60 can be appropriately selected. A substrate having a surface layer formed thereon or a substrate subjected to a surface treatment such as a hydrophilization treatment may be used for the purpose of improving the adhesiveness or adhesion or for other purposes.

The method for forming the conductive pattern is a conductive pattern in which the conductive paste 10 for gravure offset printing is applied to the base material 60 and the conductive paste 10 for gravure offset printing applied to the base material 60 is baked. And a firing step for forming.

An example of the coating process will be described below with reference to FIG. In FIG. 1, the arrows shown on the pickup roll 20, the gravure plate 40, and the blanket 50 indicate the respective rotation directions. The arrow below the base material 60 indicates the moving direction of the base material 60. First, the conductive paste 10 is applied to the gravure plate 40 by the pick-up roll 20, and the excess conductive paste 10 is removed by the blade 30, so that the conductive paste 10 is formed in the concave portion 41 provided on the printing surface of the gravure plate 40. Are filled ((a) in FIG. 1). Next, the conductive paste 10 filled in the recess 41 is transferred to the blanket 50 ((b) of FIG. 1). After that, the semi-solid / semi-liquid state (wet state or semi-dry state) conductive paste 10 transferred to the blanket 50 is transferred to the base material (adherend) 60 ((c) of FIG. 1). Through the above steps, a pattern that is the reverse of the print pattern formed on the surface of the gravure plate 40 is printed on the base material 60.

When a fine line is printed using the conductive paste 10, a transfer failure is likely to occur during transfer from the gravure plate 40 to the blanket 50 and transfer from the blanket 50 to the substrate 60. Since the electroconductive paste for offset printing (electroconductive fine particle dispersion) contains a water-soluble polymer, the electroconductive paste 10 transferred onto the blanket 50 is difficult to spread, and the adhesiveness to the base material 60 is sufficient. Further, since it has transferability, even a conductive pattern having a line width of 10 μm or less, particularly a line width of 3 μm or less can be formed without breaking.

When the conductive paste 10 is transferred onto the surface of the blanket 50 and left for a short time, the low boiling point solvent may volatilize and be absorbed in the blanket 50, so that the viscosity of the conductive paste 10 may increase. On the other hand, the organic solvent that constitutes the conductive paste 10 for gravure offset printing contains a hydroxy group and has a first organic solvent having a boiling point of 200 ° C. or higher at normal pressure and / or a blanket swelling rate. When the content of the second organic solvent is 2.0% or less, the absorption of the organic solvent into the blanket 50 is reduced, so that the drying of the conductive paste 10 on the surface of the blanket 50 can be significantly suppressed. .. Therefore, for example, a fine wire conductive pattern having a line width of 50 μm or less can be more preferably formed.

The firing temperature of the conductive paste in the firing step is preferably 650 ° C or higher, more preferably 700 ° C or higher, and may be 850 ° C or higher. The firing temperature is preferably 1000 ° C or lower. By using the conductive fine particle dispersion of the present invention, it is possible to suppress the volume shrinkage of the conductive fine particles even when firing at a temperature of 650 ° C. or higher, and it is possible to maintain the line width during printing.

A method for manufacturing a conductive substrate in which a conductive pattern is drawn on a base material using the conductive pattern forming method of the present invention is also an aspect of the present invention. As the base material, the same base material as described in the method for forming a conductive pattern of the present invention can be used. Since the method for producing a conductive substrate of the present invention uses the method for forming a conductive pattern using the conductive paste (conductive fine particle dispersion) for gravure offset printing of the present invention, for example, the line width is 50 μm or less, particularly A fine line conductive pattern having a line width of 30 μm or less can be formed. Therefore, a conductive substrate having a precise electronic circuit can be manufactured. Examples of the conductive substrate include an electronic circuit board and the like. The conductive pattern is, for example, a wiring formed on the electronic circuit board.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

<Synthesis example 1>
(Preparation of fine silver particles)
3-Methoxypropylamine (4.0 g), dodecylamine (0.5 g) and 2- (2-aminoethoxy) ethanol (5.5 g) were mixed and well stirred with a magnetic stirrer to form an amine mixed solution. Then, 3.0 g of silver oxalate was added with stirring. After the addition of silver oxalate, by continuing stirring at room temperature, the silver oxalate was changed into a viscous white substance, and the stirring was terminated when it was recognized that the above change was apparently completed (preparation of mixed solution). Process).

The obtained mixed liquid was transferred to an oil bath and heated and stirred at 100 ° C. A reaction involving the generation of carbon dioxide was started immediately after the start of stirring, and then stirring was performed until the generation of carbon dioxide was completed to obtain a suspension in which fine silver particles were suspended in the amine mixture (silver). Fine particle generation step).

In order to replace the dispersion medium of the suspension, 10 mL of a mixed solvent of methanol and water was added and stirred, and then silver fine particles were precipitated and separated by centrifugation. Next, 10 mL of a mixed solvent of methanol and water was added to the separated fine silver particles, and the fine silver particles were precipitated and purified and separated by stirring and centrifuging, and the separated fine particles were collected to obtain a silver slurry. ..

The average primary particle diameter of the silver fine particles contained in the obtained slurry was measured. The average primary particle diameter can be observed and measured at an acceleration voltage of 5.0 KV by adhering particles dried with SEM (S-4800 manufactured by Hitachi, Ltd.) to a carbon tape and performing platinum vapor deposition. The calculation was performed using the particle image thus photographed. From 5 or more SEM images at different photographing points, a total of 200 or more particles were measured for primary particle size by using image processing software (MITINI CORPORATION, Win ROOF), and the average primary particle size was calculated by arithmetic mean.
The obtained silver slurry was air dried to obtain fine silver particles.

(Example 1)
To 76 parts by mass of the silver fine particles obtained in Synthesis Example 1, 4 parts by mass of antimony-doped tin oxide (product name SN-100P manufactured by Ishihara Sangyo Co., Ltd.) was added as a metal oxide, and 2 ethyl-1 as an organic solvent. After adding 20 parts by mass of a mixed solution in which 3 parts by mass of polyvinylpyrrolidone K30 as a resin material was dissolved in 17 parts by mass of the 3-hexanediol isomer mixture, the mixture was mixed with a stirring rod and mixed by a rotation / revolution mixer. Deformation was performed to obtain a silver fine particle dispersion 1.

(Example 2)
Example except that the metal oxide was changed from 4 parts by mass of antimony-doped tin oxide (reagent first grade manufactured by Ishihara Sangyo Co., Ltd.) to 4 parts by mass of tin oxide-doped indium oxide (Mitsubishi Materials Denshi Kasei Co., Ltd., product name E-ITO). A fine silver particle dispersion 2 was obtained in the same manner as in 1.

(Example 3)
Example 1 except that the metal oxide was changed from 4 parts by mass of antimony-doped tin oxide (reagent first grade manufactured by Ishihara Sangyo Co., Ltd.) to 4 parts by mass of phosphorus-doped tin oxide (Mitsubishi Materials Denshi Kasei Co., Ltd. product name SP-2). Similarly, a silver fine particle dispersion 3 was obtained.

(Example 4)
The silver fine particles obtained in Synthesis Example 1 were changed from 76 parts by mass to 64 parts by mass, and the metal oxide was changed from 4 parts by mass of antimony-doped tin oxide (Ishihara Sangyo Co., Ltd. reagent first grade) to aluminum oxide (Sumitomo Chemical Co., Ltd. product name. A silver fine particle dispersion 4 was obtained in the same manner as in Example 1 except that the amount of AKP-50) was changed to 16 parts by mass.

(Example 5)
The silver fine particles obtained in Synthesis Example 1 was changed from 76 parts by mass to 60 parts by mass, and the metal oxide was changed from 4 parts by mass of antimony-doped tin oxide (reagent first grade manufactured by Ishihara Sangyo Co., Ltd.) to antimony-doped titanium oxide / tin oxide (Ishihara). Sangyo KK Product name ET-500W) A silver fine particle dispersion 5 was obtained in the same manner as in Example 1 except that the amount was changed to 20 parts by mass.

(Example 6)
Similar to Example 1 except that the metal oxide was changed from 4 parts by mass of antimony-doped tin oxide (reagent first grade manufactured by Ishihara Sangyo Co., Ltd.) to 4 parts by mass of tin oxide (product name S-2000 of Mitsubishi Materials Electronics Corporation). A silver fine particle dispersion 6 was obtained.

(Example 7)
The silver fine particles obtained in Synthesis Example 1 was changed from 76 parts by mass to 78.4 parts by mass, and antimony-doped tin oxide (reagent first grade manufactured by Ishihara Sangyo Co., Ltd.), which is a metal tin oxide, was added from 4 parts by mass to 1.6 parts by mass. A silver fine particle dispersion 7 was obtained in the same manner as in Example 1 except that the above was changed.

(Comparative Example 1)
Example 1 except that the silver fine particles obtained in Synthesis Example 1 was changed from 76 parts by mass to 80 parts by mass and antimony-doped tin oxide (product name SN-100P manufactured by Ishihara Sangyo Co., Ltd.) was not added as a metal oxide. A silver fine particle dispersion 8 was obtained in the same manner as in.

(Comparative example 2)
The silver fine particles obtained in Synthesis Example 1 was changed from 76 parts by mass to 79 parts by mass, and the metal oxide to be added was changed from 4 parts by mass to 1 part by mass of antimony-doped tin oxide (product name SN-100P manufactured by Ishihara Sangyo Co., Ltd.). A silver fine particle dispersion 9 was obtained in the same manner as in Example 1 except for the above.

(Comparative example 3)
The silver fine particles obtained in Synthesis Example 1 were changed from 76 parts by mass to 55.2 parts by mass, and the metal oxide added was changed from 4 parts by mass to 24.8 parts by mass of antimony-doped tin oxide (product name SN-100P manufactured by Ishihara Sangyo Co., Ltd.). A silver fine particle dispersion 10 was obtained in the same manner as in Example 1 except that the amount was changed to parts by weight.

(Comparative example 4)
With respect to 76 parts by mass of the silver fine particles obtained in Synthesis Example 1, the metal oxide added was changed from 4 parts by mass of antimony-doped tin oxide (product name SN-100P manufactured by Ishihara Sangyo Co., Ltd.) to 4 parts by mass of silica. A fine silver particle dispersion 11 was obtained in the same manner as in Example 1.

The metal oxides used in Examples and Comparative Examples and the inorganic additives used in Comparative Examples are shown in Table 1 below.

[Evaluation test]
With respect to the conductive pastes obtained in the above Examples and Comparative Examples, (1) printability in gravure offset printing and (3) dispersibility were evaluated. Further, with respect to the conductive pattern formed of the obtained conductive fine particle dispersion, (2) shrinkage of line width, (4) volume resistance value, and (5) adhesiveness were measured. The results of each evaluation test are shown in Table 2 below.

(1) Printability The printability was evaluated by the following method using a simple gravure offset printing method by hand printing. As the gravure plate, a rubber roller in which each conductive paste is inked with a doctor blade and then a silicone blanket is wound on a flat plate ballad plating intaglio plate provided with grooves (grooves) having a groove line width of 30 μm and a groove depth of 5 μm The layers were brought into contact with each other to transfer the desired pattern onto the blanket. After that, the coating film on the blanket was pressed and transferred onto a sheet of glaze-processed alumina ceramic, and printed to form a print pattern having a line width of about 30 μm. Thus, a printed pattern having a printed line width of about 30 μm was obtained. Especially excellent in the linearity of the wire, "◎" without breakage, "○" with excellent linearity and no breakage, "△" with poor linearity and no breakage. "," The linearity of the line was inferior and there was a disconnection point was evaluated as "x".

(2) Shrinkage of line width It was evaluated by simple gravure offset printing by hand printing. After inking each conductive paste with a doctor blade into a flat plate ballad plating intaglio plate having a groove line width of 30 μm and a groove depth of 5 μm, press it into contact with a rubber roller wrapped with a silicone blanket. The desired pattern was transferred onto the blanket. After that, the coating film on the blanket was pressed and transferred onto a sheet of glaze-processed alumina ceramic, and printed to form a print pattern having a line width of about 30 μm. Thus, a printed pattern having a printed line width of about 30 μm was obtained. The obtained printed matter was heated to 900 ° C. at a heating rate of 8 ° C./min and then returned to room temperature. The line width was measured with a laser microscope, and the shrinkage ratio from the width during printing was measured. It was measured. A line shrinkage of 5% or less was evaluated as “◯”, a line shrinkage of 20% or less was evaluated as “Δ”, and a line shrinkage of 21% or more was evaluated as “x”.

(3) Dispersion The conductive paste is diluted 2-fold with a dispersion solvent, allowed to stand in a container, allowed to stand at room temperature for 1 day, and then visually observed for the presence or absence of precipitation and the state of the supernatant. The dispersibility of the paste was evaluated. When there is almost no sediment under the container, it is "○", when a small amount of sediment is observed, it is "△", when there is a clear difference in concentration between the top and bottom of the container, and when sediment is clearly visible, it is "X". Was evaluated.

(4) Volume resistance Gravure offset printing was used to coat a coating film with an applicator on a 2.5 cm square glaze-processed alumina ceramic using the conductive pastes obtained in Examples and Comparative Examples, aiming at a wet film thickness of 30 μm. A conductive pattern was formed by forming the conductive pattern and sintering it in a muffle furnace at a temperature rising rate of 8 ° C./min to 900 ° C. and then heating and firing under conditions of cooling to room temperature. The surface resistance (R) of this pattern was measured using Loresta GP MCP-T610 manufactured by Mitsubishi Chemical Anateric Co., Ltd., and the volume resistance value was calculated by multiplying this by the film thickness (t). When the volume resistance value is 5 μΩ · cm or less, it is “◎”, when it is 10 μΩ · cm or less, it is “○”, when it is 20 μΩ · cm or less, it is “△”, and when it is more than 20 μΩ · cm, it is “X”. evaluated. The results are shown in Table 1.
Formula (1): (volume resistance value ρv) = (surface resistance value R) × (pattern thickness t)

(5) Adhesion test Using the conductive pastes obtained in Examples and Comparative Examples by gravure offset printing, a 2.5 cm square glaze-processed alumina ceramic was coated with an applicator to a wet film thickness of 30 μm. The film was formed, heated to 900 ° C. at a heating rate of 8 ° C./min in a muffle furnace, and then sintered by heating and firing under conditions of cooling to room temperature to form a conductive film. As an adhesion test, tape peeling was performed by a cross-cut test. Evaluation was performed according to ASTM D3359-09. Using a cutter knife, 6 vertical and 6 horizontal cuts were made on the test surface to reach the substrate, and the intervals of the cuts were 1 mm, and 25 grids were made. Using Nichiban tape CT-24, the tape was strongly pressure-bonded to the cross-cut portion, and the end of the tape was held and peeled off at once, and the peeled state of the cross-cut was evaluated. The criteria for judgment are as follows. In all the base materials, those having a rating of 4B or higher are marked with “◯”, those having a rating of 3B or higher are marked with “Δ”, and any one of the base materials having a rating of 2B or lower is marked with “x”.
<Judgment criteria>
5B: No peeling 4B: Peeled portion clearly does not exceed 5% 3B: Peeled portion is 5% or more and less than 15% 2B: Peeled portion is 15% or more and less than 35% 1B: Peeled portion Is 35% or more and less than 65% 0B: The peeled portion is 65% or more

All of the silver fine particle dispersions 1 to 3 according to Examples 1 to 3 were excellent in volume resistance value by suppressing the shrinkage of the line width. Further, the silver fine particle dispersions 4 to 6 according to Examples 4 to 6 have a volume resistance value of more than 10 μΩ · cm and 20 μΩ · cm or less, which is higher than that of the other silver fine particle dispersions 1 to 3. It was slightly higher and slightly inferior, but showed good conductivity, and was excellent in suppressing the shrinkage of the line width. The fine silver particle dispersion 7 according to Example 7 was slightly inferior in the suppression of the line width shrinkability, but was low in volume resistance and excellent in conductivity.
Therefore, using the silver fine particle dispersions of Examples 1 to 7, a conductive pattern having a width of 30 μm could be formed by gravure offset printing by high temperature firing at a sintering temperature of 900 ° C. Further, from the results of Examples 1 to 7, by adding the doped metal oxide as a metal oxide in the silver fine particle dispersion, not only the shrinkage of the line width is suppressed but also the conductivity is excellent. It was possible to form a pattern. From the results of Examples 1, 2 and 7 and Examples 3 and 6, the metal oxides were antimony-doped tin oxide and tin oxide-doped indium oxide, so that the conductivity was particularly excellent. It was confirmed that a conductive pattern could be formed.

On the other hand, from the results of Comparative Examples 1, 2 and 4, when the metal oxide is not contained or the content of the metal oxide is less than 2% by mass with respect to the total metal components, shrinkage of the line width is caused. It was found that the suppressing effect could not be obtained. Further, from the results of Comparative Example 3, when the content of the metal oxide exceeds 30% by mass with respect to the total metal components, the shrinkage of the line width can be suppressed, but the volume resistance value is increased to 20 μΩ · cm. It exceeded 134.5 μΩ · cm, and was extremely inferior in conductivity. Further, from Comparative Example 4, it was difficult to obtain the effect of suppressing the shrinkage of the line width even when an additive other than the metal oxide was used, and the printability was poor, and the resistance value could not be measured.

10 Conductive Paste for Gravure Offset Printing 20 Pickup Roll 30 Blade 40 Gravure Plate 41 Recess 50 Blanket 60 Base Material (Adherend)
100 Printing device for gravure offset printing

Claims (11)

Containing conductive fine particles, a metal oxide, and a dispersion medium,
The conductive fine particle dispersion is characterized in that the content ratio of the conductive fine particles and the metal oxide (conductive fine particles: metal oxide) is 75:25 to 98: 2. The conductive fine particle dispersion according to claim 1, wherein the average particle diameter of the metal oxide is 700 nm or less. The conductive fine particle dispersion according to claim 1 or 2, wherein the conductive fine particles are at least one selected from silver, copper, and gold. The conductive fine particle dispersion according to claim 1, wherein the metal oxide is a doped metal oxide and / or a single metal oxide. The doped metal oxide comprises antimony-doped tin oxide, phosphorus-doped tin oxide, antimony-doped titanium oxide, tin oxide-doped indium oxide, zinc oxide-doped indium oxide, tin oxide-zinc oxide-doped indium oxide, and gallium oxide-doped zinc oxide. The conductive fine particle dispersion according to claim 4, which is at least one selected from the group. The conductive material according to claim 4, wherein the single metal oxide is at least one selected from the group consisting of tin oxide, indium oxide, aluminum oxide, titanium oxide, zinc oxide, and nickel oxide. Fine particle dispersion. The conductive fine particle dispersion according to any one of claims 1 to 6, wherein the conductive fine particle dispersion is a conductive paste for offset printing. A first step of applying the conductive fine particle dispersion according to any one of claims 1 to 7 to at least a part of the substrate;
A second step of sintering the conductive fine particles contained in the conductive fine particle dispersion by external heating to form a conductive pattern,
The method for forming a conductive pattern, wherein the sintering temperature in the second step is 650 ° C. or higher. The method for forming a conductive pattern according to claim 8, wherein in the first step, the conductive fine particle dispersion according to claim 7 is applied by a gravure offset printing method using a gravure plate. The gravure plate has a concave portion filled with a conductive fine particle dispersion for gravure offset printing on the printing surface,
The method for forming a conductive pattern according to claim 9, wherein the width of the recess is 50 μm or less. A method for producing a conductive substrate, which comprises drawing a conductive pattern on a base material using the method for forming a conductive pattern according to claim 8.

Images