Conductive composition, sintered compact thereof, laminated structure, electronic part, and semiconductor device

Abstract

The problem addressd by this invention is to provide a conductive composition that can be sintered at low temperature and has low resistance, the composition forming a conductive film having excellent flexibility and bend resistance.　Provided is a conductive composition comprising (A) surface-modified silver nanoparticles in which the surface is coated with a lower carboxylic acid, (B) a binder resin, and (C) an organic solvent, wherein the lower carboxylic acid of (A) the surface-modified silver nanoparticles present in the conductive composition starts desorption from the silver nanoparticles at 40 to 130 °C.

Description

Conductive composition, sintered body thereof, laminated structure, electronic component, and semiconductor device

[0001] The present invention relates to a conductive composition, a sintered body thereof, a laminated structure, an electronic component, and a semiconductor device.

[0002] In recent years, with the widespread use of high-performance communication devices such as smartphones and tablets, there has been an increasing demand for lighter, shorter, thinner, and smaller products. Furthermore, the market for the Internet of Things (IoT), in which all things are connected to the Internet, has been growing rapidly. Flexible electronic devices, such as bendable displays and solar cells, have attracted attention as essential devices for such high-performance communication devices and the IoT market. Flexible electronic devices refer to various electronic devices mounted on stretchable substrates such as plastic, metal foil, paper, and flexible glass. These devices can be bent, twisted, and stretched, allowing them to be incorporated into a variety of consumer and industrial products.

[0003] Such flexible electronic devices can be realized by fabricating an electronic device on a substrate such as plastic, followed by configuring the electronic device as a circuit. Because plastics have a low heat resistance, low-temperature processing, for example at temperatures below 150°C, is required to form the metal wiring necessary for circuit configuration. Furthermore, such metal wiring is required to have low resistance so as to provide good electrical properties even in thin films. Furthermore, such metal wiring is required to have flexibility that can follow the bending and stretching of the substrate, and durability (bending resistance) that can withstand repeated bending and stretching.

[0004] Conductive pastes for forming thin metal films are classified into resin-curing and sintering types. Resin-curing conductive pastes form conductive films by hardening the thermosetting resin in the conductive paste through heat treatment. This type has the advantage of low processing temperatures, but the conductive powders are only fixed in place by the thermosetting resin while in contact with each other, and the resin remains, resulting in a conductive film with a high specific resistance. On the other hand, sintering conductive pastes can achieve low-resistance conductive films because the metal is sintered (fused), but high-temperature processing at at least 200°C or higher is required to sinter the metal particles.

[0005] Patent Document 1 discloses a conductive composition that can be used to form a conductive circuit on a printed circuit board, the conductive composition comprising (A) fine silver particles having a number-average primary particle size of 40 nm to 400 nm, (B) a solvent, and (C) thermoplastic resin particles having a maximum endothermic peak in a DSC chart obtained by measurement using a differential scanning calorimeter in the range of 80° C. to 170° C. The conductive composition disclosed in Patent Document 1 is a sintered type, and is heat-treated at 200° C. to form a thin film.

[0006] International Publication No. 2016 / 063931

[0007] As described above, the conductive film of a resin-curing conductive paste that can be processed at low temperatures has a high resistivity, while a sintered conductive paste that provides a low-resistivity conductive film requires high-temperature processing. It has been difficult to provide a conductive paste that satisfies all of the following requirements: low-temperature processing, low resistance, good flexibility, and bending resistance. Furthermore, while conductive pastes that claim to be sinterable at low temperatures have been developed, they still require heat treatment at 150 to 200°C. An object of the present invention is to provide a conductive composition that can be sintered at low temperatures below 150°C and that forms a conductive film that has low resistance, good flexibility, and bending resistance.

[0008] Specific means for solving the above problems are as follows. A first embodiment of the present invention provides the following conductive composition. (1) A conductive composition comprising: (A) surface-modified silver nanoparticles whose surfaces are coated with a lower carboxylic acid; (B) a binder resin; and (C) an organic solvent, wherein the lower carboxylic acid of the (A) surface-modified silver nanoparticles present in the conductive composition begins to be released from the silver nanoparticles at 40°C to 130°C. (2) The conductive composition according to (1) above, wherein the lower carboxylic acid of the (A) surface-modified silver nanoparticles is at least one selected from acetic acid, butyric acid, lactic acid, methyl maleate, and hydroxyisobutyric acid. (3) The conductive composition according to (1) or (2) above, wherein the (C) organic solvent comprises an organic solvent having a boiling point of 180°C to 270°C. (4) The conductive composition according to any one of (1) to (3) above, wherein the average particle size of the (A) surface-modified silver nanoparticles is 20 nm to 600 nm. (5) The conductive composition according to any one of (1) to (4) above, wherein the weight-average molecular weight of the (B) binder resin is 5,000 to 200,000. (6) The conductive composition according to any one of (1) to (5) above, wherein the (B) binder resin is a cellulose-based resin. (7) The conductive composition according to any one of (1) to (6) above, wherein the mass ratio of the (A) surface-modified silver nanoparticles to the (B) binder resin (component (A):component (B)) is 90:10 to 99.7:0.3. (8) The conductive composition according to any one of (1) to (7) above, wherein the content of the (C) organic solvent is 10 parts by mass to 50 parts by mass relative to 100 parts by mass of the conductive composition. (9) The conductive composition according to any one of (1) to (7) above, wherein the specific resistance is 1.0 x 10 when heated at 120°C for 30 minutes. －５ The conductive composition according to any one of (1) to (8) above, which forms a sintered film having a resistivity of Ω cm or less. (10) The conductive composition according to any one of (1) to (9) above, which forms a sintered film having a rate of change in resistivity of 50% or less before and after 500 repeated bendings. (11) The conductive composition according to any one of (1) to (10) above, which forms a sintered film having a surface irregularity height difference of 6 μm or less when heated at 120° C. for 30 minutes.

[0009] A second embodiment of the present invention is (12) a sintered body of the conductive composition according to any one of (1) to (11) above. A third embodiment of the present invention is (13) a laminate structure having the sintered body according to (12) above on a substrate. A fourth embodiment of the present invention is (14) an electronic component or semiconductor device having the sintered body according to (12) above.

[0010] According to a first embodiment of the present invention, a conductive composition can be obtained that can be sintered at a low temperature and that forms a conductive film having low resistance and excellent flexibility and bending resistance. According to a second embodiment of the present invention, a sintered body having low resistance and excellent flexibility and bending resistance can be obtained. Furthermore, according to a third embodiment of the present invention, a laminate structure having a sintered body having low resistance and excellent flexibility and bending resistance on a substrate can be obtained. According to a fourth embodiment of the present invention, an electronic component or semiconductor device including a sintered body having low resistance and excellent flexibility and bending resistance can be obtained.

[0011] 1 is a graph showing TG-MS measurements of the conductive composition of the present invention. 2 is a scanning electron microscope (SEM) photograph of the cross section of a conductive film formed by screen-printing the conductive composition of the present invention and a conventional conductive composition on a polycarbonate film and heating the film at 120°C for 30 minutes. 3 is a photograph of a wiring pattern of the conductive composition used as a test piece.

[0012] In this specification, "low temperature sintering" of the conductive composition means that silver nanoparticles are fused to form a continuous silver film at a temperature of less than 150°C, preferably at a temperature of 120°C. In this specification, "low resistance" means that the conductive film has a resistance of 1.0 x 10 －５ "Excellent flexibility" of a sintered body means that, when the sintered body is formed on a substrate, the sintered body has flexibility sufficient to follow the extension and bending of the substrate. "Excellent bending resistance" of a sintered body means that the sintered body does not break and the change in resistivity is small even when the sintered body is bent repeatedly (for example, 500 times).

[0013] [Conductive Composition] The conductive composition of the first embodiment of the present invention comprises: (A) surface-modified silver nanoparticles whose surfaces are coated with a lower carboxylic acid; (B) a binder resin; and (C) an organic solvent, wherein the lower carboxylic acid of the (A) surface-modified silver nanoparticles present in this conductive composition begins to desorb from the silver nanoparticles at 40° C. to 130° C. According to this embodiment, it is possible to obtain a conductive composition that can be sintered at a low temperature and that forms a conductive film that has low resistance and good flexibility and bending resistance.

[0014] (A) Surface-modified silver nanoparticles whose surfaces are coated with a lower carboxylic acid The conductive composition of this embodiment contains (A) surface-modified silver nanoparticles whose surfaces are coated with a lower carboxylic acid (hereinafter also referred to as "(A) surface-modified silver nanoparticles" or "component (A)"). (A) Surface-modified silver nanoparticles whose surfaces are coated with a lower carboxylic acid can be made conductive by sintering.

[0015] Because metal nanoparticles have extremely high activity, most nanoparticles have a protective layer made of an organic substance formed on the particle surface to ensure particle independence and prevent particle aggregation. While such a protective layer effectively contributes to particle preservation, high-temperature processing is required to decompose the protective layer and fuse the metal particles. Even if a conductive film could be formed by low-temperature processing, the desired low resistance could not be obtained. In the silver nanoparticles of this embodiment, the surface of the silver nanoparticles is coated with a lower carboxylic acid, which acts as a protective layer. It has been discovered that by selecting a lower carboxylic acid as the protective layer for the silver nanoparticles and combining it with an organic solvent (C) described below, it is possible to sinter the silver nanoparticles at a low processing temperature of less than 150°C, thereby obtaining a low-resistance conductive film.

[0016] In this embodiment, by combining (A) surface-modified silver nanoparticles whose surfaces are coated with a lower carboxylic acid with (C) an organic solvent, the lower carboxylic acid of the surface-modified silver nanoparticles (A) present in this conductive composition begins to desorb from the silver nanoparticles at 40 to 130° C. The desorption initiation temperature is preferably 50 to 120° C., more preferably 50 to 110° C. The desorption initiation temperature of the organic protection layer containing a lower carboxylic acid from the silver nanoparticles can be measured by thermogravimetry-mass spectrometry (hereinafter referred to as TG-MS analysis).

[0017] TG-MS analysis is a method in which gases evolved from a sample by heating in a TG are introduced online into a mass spectrometer (MS) to obtain a mass spectrum. While TG alone cannot identify the components evolved during weight loss, MS can track changes in the chemical species and amount of components produced by volatilization or thermal decomposition over time. When measuring the desorption onset temperature of an organic protective layer from silver nanoparticles, a conductive composition is used as the sample. When the organic protective layer is a carboxylic acid, carboxylic acids are difficult to detect using GCMS analysis. Therefore, a methylation reaction pyrolysis method is used in which a methylation reagent (e.g., tetramethylammonium hydroxide (TMAH), trimethylsulfonium hydroxide (TMSH), trimethyl(α,α,α-trifluoro-m-tolyl)ammonium hydroxide (TMTFTH), tetramethylammonium acetate (TMAAc), etc.) is added to the sample to detect the methylated carboxylic acid. TG-MS analysis can produce a mass spectrum, such as that shown in Figure 1. In FIG. 1, a mass spectrum peak for lactic acid begins to appear at around 100°C, which indicates that lactic acid begins to desorb from the silver nanoparticles at approximately 100°C.

[0018] The lower carboxylic acid is preferably a carboxylic acid having 5 or less carbon atoms, more preferably a carboxylic acid having 2 to 5 carbon atoms. The lower carboxylic acid may be either a saturated carboxylic acid or an unsaturated carboxylic acid. The lower carboxylic acid may be either a monocarboxylic acid or a dicarboxylic acid, with monocarboxylic acids being preferred, and examples thereof include lower monocarboxylic acids and monoesters of lower dicarboxylic acids. The lower carboxylic acid may also be a hydroxycarboxylic acid in which the hydrocarbon group is substituted with a hydroxyl group. Specific examples of lower carboxylic acids include formic acid, acetic acid, propionic acid, butyric acid (butanoic acid), isobutyric acid (2-methylpropionic acid), 2-hydroxyisobutyric acid, valeric acid (pentanoic acid), isovaleric acid (3-methylbutanoic acid), lactic acid, maleic acid, monomethyl maleate, fumaric acid, monomethyl fumarate, methylmalonic acid, dimethylmalonic acid, methylsuccinic acid, malic acid, 1-methyl D-malate, tartaric acid, 2-methyltartaric acid, acrylic acid, and methacrylic acid, and among these, acetic acid, butyric acid, lactic acid, monomethyl maleate, and 2-hydroxyisobutyric acid are preferred. Any one of the lower carboxylic acids may be used, or two or more may be used in combination.

[0019] The lower carboxylic acid can be attached to the surface of the silver nanoparticles by using it during the synthesis of the silver nanoparticles, or by adding the lower carboxylic acid to a composition containing the silver nanoparticles.

[0020] (A) The surface-modified silver nanoparticles may have on their surfaces organic substances other than lower carboxylic acids, as long as the effects of the present invention are not impaired. Examples of such organic substances include medium-sized carboxylic acids having 6 to 12 carbon atoms, higher carboxylic acids having 13 or more carbon atoms, and alkylamines.

[0021] The conductive composition of this embodiment may contain surface-modified silver nanoparticles other than component (A) as long as the effects of the present invention are not impaired. Examples of such surface-modified silver nanoparticles include surface-modified silver nanoparticles whose surfaces are coated with a medium-chain carboxylic acid, a higher carboxylic acid, and / or an alkylamine. The conductive composition preferably contains 15 to 100 parts by mass, and more preferably 20 to 100 parts by mass, of the surface-modified silver nanoparticles (A) per 100 parts by mass of the total amount of silver nanoparticles. The total amount of silver nanoparticles in the conductive composition is preferably 40 to 89.7 parts by mass, more preferably 55 to 89.6 parts by mass, and even more preferably 67 to 84.5 parts by mass per 100 parts by mass of the conductive composition.

[0022] In this embodiment, the average particle size of the silver nanoparticles is preferably 20 to 600 nm, more preferably 50 to 550 nm, and even more preferably 80 to 500 nm. Having an average particle size within the above range allows for an appropriate amount of lower carboxylic acid to adhere to the surface of the silver nanoparticles, and also promotes sintering (fusion) of the silver nanoparticles. One type of silver nanoparticle having an average particle size within the above range may be used, or two or more types may be used in combination. In this embodiment, the average particle size of the silver nanoparticles is the average value of the long side lengths of 30 or more particles contained in an image observed with a scanning electron microscope, or the value obtained by measuring the average particle size by a flow method using a laser diffraction particle size distribution analyzer (Partica LA-950V2, manufactured by Horiba, Ltd.).

[0023] In this embodiment, the silver nanoparticles can be produced by a known method. Examples of known production methods include, but are not limited to, those described in International Publication No. 2012 / 059974, JP 2015-40319 A, and International Publication No. 2017 / 169534. Furthermore, the silver nanoparticles can be produced, for example, as follows, but are not limited to this production method.

[0024] First, a composition for producing silver nanoparticles (silver nanoparticle preparation composition) is prepared. The silver nanoparticle preparation composition contains a silver compound that serves as the raw material for the silver nanoparticles, a lower carboxylic acid to be attached to the surface of the silver nanoparticles as needed, and an optional organic solvent. Preferred silver compounds include silver nitrate and silver oxalate, with silver oxalate being particularly preferred. Any organic solvent that can disperse the silver compound may be used, including, for example, alcohol-based solvents, glycol ether-based solvents, ether-based solvents, ester-based solvents, amine-based solvents, and ketone-based solvents.

[0025] These components are mixed to obtain a composition for preparing silver nanoparticles. The proportions of each component in the composition can be adjusted as appropriate. For example, the content of the silver compound in the composition is preferably 20 to 70 parts by mass, based on the total amount of the composition. Furthermore, if a lower carboxylic acid is attached to the surface of silver nanoparticles during synthesis, the content of the lower carboxylic acid is preferably 0.1 to 20% by mass, more preferably 0.1 to 15% by mass, based on the total amount of the composition. The content of the organic solvent can be adjusted depending on the viscosity of the composition. The means for mixing the components is not particularly limited, and they can be mixed using general-purpose equipment such as a mechanical stirrer, magnetic stirrer, vortex mixer, planetary mill, ball mill, three-roll mill, line mixer, planetary mixer, or dissolver. To avoid a rise in the temperature of the composition due to the effects of heat of dissolution and frictional heat during mixing, which could lead to the initiation of a thermal decomposition reaction of the silver particles, it is preferable to mix the composition while maintaining the temperature at, for example, 60°C or below, preferably 40°C or below.

[0026] The composition for preparing silver nanoparticles is then subjected to a reaction, usually by heating, in a reaction vessel, whereby a thermal decomposition reaction of the silver compound occurs to produce silver nanoparticles. The reaction by heating may be carried out by introducing the composition into a preheated reaction vessel, or by introducing the composition into the reaction vessel and then heating it.

[0027] The reaction temperature may be any temperature at which the thermal decomposition reaction of the silver compound proceeds and silver nanoparticles are produced, and is, for example, 50 to 250°C. The reaction time can be appropriately selected depending on the desired average particle size and the composition of the composition corresponding to that size. The reaction time is, for example, 1 minute to 100 hours.

[0028] Since silver nanoparticles produced by the thermal decomposition reaction of a silver compound are obtained as a mixture containing unreacted raw materials, it is preferable to purify the silver nanoparticles. Purification methods include solid-liquid separation and precipitation methods that utilize the difference in specific gravity between the silver nanoparticles and unreacted raw materials such as organic solvents. To facilitate handling during purification, the mixture containing silver nanoparticles may be diluted with a low-boiling point solvent such as acetone or methanol to adjust its viscosity. After purification, the mixture can be washed as needed and separated by filtration, centrifugation, or the like to obtain silver nanoparticles.

[0029] The average particle size of the resulting silver nanoparticles can be adjusted by adjusting the composition of the composition for producing silver nanoparticles and the reaction conditions.

[0030] The silver nanoparticles obtained as described above are usually provided in the form of a slurry in which the silver nanoparticles are dispersed in an organic solvent, from the viewpoint of storage stability. The organic solvent for the slurry is not particularly limited as long as it can disperse silver nanoparticles, but for example, it is preferably the (C) organic solvent blended in the conductive composition described below. The organic solvent for the slurry may be any one of the organic solvents used alone or in combination of two or more. Note that when a silver nanoparticle slurry is used to produce the conductive composition of this embodiment, the organic solvent in the slurry is treated as the (C) organic solvent of the conductive composition, and the amount of the organic solvent in the slurry is also included in the amount of the (C) organic solvent in the conductive composition of this embodiment.

[0031] (B) Binder Resin The conductive composition of this embodiment contains (B) binder resin (hereinafter also referred to as "component (B)"). The (B) binder resin imparts flexibility and bending resistance to a sintered body of the conductive composition. In addition, the (B) binder resin improves the wettability of the conductive composition to a substrate when forming a coating film, thereby improving adhesion to the substrate and the surface smoothness of the coating film.

[0032] The weight-average molecular weight of the (B) binder resin is preferably 5,000 to 200,000, more preferably 10,000 to 195,000, and even more preferably 15,000 to 190,000. Here, the weight-average molecular weight (Mw) refers to the weight-average molecular weight calculated in terms of polystyrene using a calibration curve based on standard polystyrene by gel permeation chromatography (GPC). By setting the weight-average molecular weight of the (B) binder resin within this range, it is possible to impart superior flexibility and bending resistance to a sintered body of the conductive composition.

[0033] The (B) binder resin can be a known binder resin, for example, cellulose-based resins such as ethyl cellulose, hydroxyethyl cellulose, ethylhydroxycellulose, hydroxypropyl cellulose, methyl cellulose, cellulose acetate, and cellulose butyrate; vinyl-based resins such as polyvinyl alcohol, polyvinyl acetate, polyvinyl butyral, polyvinyl acetal, polyvinylpyrrolidone, polyacrylamide, and polyvinyl chloride; styrene-based resins such as polystyrene, styrene-maleic anhydride copolymer, styrene-acrylic copolymer, and styrene-butadiene copolymer; polyolefin-based resins such as polyethylene, polypropylene, polybutadiene, and polyisoprene; polyurethane-based resins; polyester-based resins; polyamide-based resins; copolymers thereof; hydrogenated products thereof; modified products thereof; and hydrogenated modified copolymers thereof. The binder resin may be any one type, or two or more types may be used in combination. From the viewpoint of further improving the surface smoothness of the coating film, the binder resin is preferably a cellulose-based resin, and more preferably ethyl cellulose.

[0034] From the viewpoint of achieving both low resistance and flexibility and bending resistance, the content of the (B) binder resin in the conductive composition is preferably 0.3 to 10 parts by mass, more preferably 0.4 to 5 parts by mass, and even more preferably 0.5 to 3 parts by mass, relative to 100 parts by mass of the conductive composition.

[0035] In this embodiment, the mass ratio of the (A) surface-modified silver nanoparticles to the (B) binder resin (component (A):component (B)) is preferably 90:10 to 99.7:0.3, and more preferably 91:9 to 99.6:0.4.

[0036] (C) Organic Solvent The conductive composition of this embodiment contains (C) an organic solvent (hereinafter also referred to as "component (C)"). The (C) organic solvent disperses the (A) surface-modified silver nanoparticles and dissolves the (B) binder resin.

[0037] The (C) organic solvent may be any organic solvent that, when combined with (A) surface-modified silver nanoparticles whose surfaces are coated with a lower carboxylic acid, can cause the lower carboxylic acid of the (A) surface-modified silver nanoparticles present in the conductive composition to begin to desorb from the silver nanoparticles at 40°C to 130°C.

[0038] The (C) organic solvent preferably contains an organic solvent having a boiling point of 180°C to 270°C, and more preferably contains an organic solvent having a boiling point of 200°C to 240°C. Having a boiling point of 180°C or higher allows the organic solvent to remain appropriately until the lower carboxylic acid of the (A) surface-modified silver nanoparticles begins to detach, facilitating the detachment of the lower carboxylic acid. This also improves the workability of the conductive composition. On the other hand, having a boiling point of 270°C or lower promotes the detachment of the lower carboxylic acid and allows the organic solvent to be sufficiently removed in the low-temperature heating step.

[0039] From the viewpoints of the dispersibility of the (A) surface-modified silver nanoparticles and the compatibility with the (B) binder resin, the (C) organic solvent preferably contains a polar organic solvent, and more preferably contains a polar organic solvent having a boiling point of 180°C to 270°C. Examples of polar solvents having a boiling point of 180°C to 270°C include glycol ether-based solvents such as diethylene glycol monomethyl ether, diethylene glycol diethyl ether, diethylene glycol monobutyl ether (common name: butyl carbitol), diethylene glycol dibutyl ether, diethylene glycol butyl methyl ether, diethylene glycol monobutyl ether acetate, dipropylene glycol monomethyl ether, triethylene glycol monomethyl ether, triethylene glycol butyl methyl ether, triethylene glycol dimethyl ether, tripropylene glycol dimethyl ether, and ethylene glycol monophenyl ether; or terpineol-based solvents such as terpineol and dihydroterpineol. The (C) organic solvent may be used alone or in combination of two or more. In particular, glycol ether-based solvents having a boiling point of 180°C to 270°C have a polarity similar to that of lower carboxylic acids, and can therefore further promote the elimination of lower carboxylic acids from the (A) surface-modified silver nanoparticles. In this embodiment, the (C) organic solvent preferably contains a glycol ether-based solvent having a boiling point of 180°C to 270°C. Among these, diethylene glycol monobutyl ether (common name: butyl carbitol) is more preferred. The content of the glycol ether-based solvent having a boiling point of 180°C to 270°C in the (C) organic solvent is preferably 20 to 100 parts by mass, more preferably 30 to 100 parts by mass, and even more preferably 40 to 100 parts by mass, per 100 parts by mass of the (C) organic solvent.

[0040] The conductive composition of this embodiment may contain an organic solvent having a boiling point of less than 180°C, an organic solvent having a boiling point of more than 270°C, or a non-polar organic solvent, as long as the lower carboxylic acid of the surface-modified silver nanoparticles (A) present in the conductive composition can begin to be released from the silver nanoparticles at 40°C to 130°C.

[0041] The content of the (C) organic solvent is not particularly limited, but from the viewpoint of viscosity adjustment and coating film formability, it is preferably 10 to 50 parts by mass, more preferably 10 to 40 parts by mass, and even more preferably 15 to 30 parts by mass relative to 100 parts by mass of the conductive composition.

[0042] The conductive composition of the present embodiment may contain additives such as inorganic pigments, organic pigments, coupling agents such as silane coupling agents, leveling agents, thixotropic agents, insulating particles, interface treatment agents, dyes, plasticizers, antifoaming agents, foam breakers, and antioxidants, as needed, within a range that does not impair the effects of the present invention.

[0043] The method for producing the conductive composition of this embodiment is not particularly limited, and can be produced, for example, by blending components (A) to (C) and, if necessary, additives in predetermined ratios and stirring and mixing them. Known devices can be used as stirring and mixing means, and examples include a Henschel mixer, planetary mixer, dissolver, bead mill, Raikai mixer, pot mill, roll mill, triple roll mill, rotary mixer, and twin-screw mixer. Components (A) to (C) and any additives may be mixed simultaneously, or some of them may be mixed first and the rest may be mixed later.

[0044] The method for applying the conductive composition of this embodiment is not particularly limited, and for example, the composition can be applied to a desired portion of a substrate or the like by a known printing method, dispensing method, or coating method. Printing methods include, but are not limited to, screen printing, lithographic printing, carton printing, metal printing, offset printing, gravure printing, flexographic printing, and inkjet printing. Dispensing methods include, but are not limited to, jet dispensers and air dispensers. Coating methods include, but are not limited to, dip coating, spray coating, bar coater coating, gravure coating, reverse gravure coating, and spin coater coating.

[0045] The conductive composition of this embodiment is a sintered conductive composition. By heating and baking at a predetermined temperature, the lower carboxylic acid of the surface-modified silver nanoparticles (A) is eliminated, and the silver nanoparticles are fused together to form a conductive film that is a sintered body. The heating temperature can be 100°C to 300°C. However, when used in the manufacture of flexible electronic devices, the heating temperature is preferably less than 150°C, for example, 100°C or higher but less than 150°C, more preferably 100°C to 140°C, even more preferably 110°C to 130°C, and particularly preferably 120°C, from the viewpoint of not damaging substrates such as plastics. The heating time varies depending on the heating temperature, but is preferably 0.25 hours to 4 hours, more preferably 0.5 hours to 2 hours.

[0046] The conductive composition of this embodiment can produce a sintered body with low resistance even when subjected to a heat treatment at a low temperature of less than 150° C. For example, the conductive composition of this embodiment has a specific resistance of 1.0×10 when heated at 120° C. for 30 minutes. －５ This is because the silver nanoparticles are fused to form a continuous silver film, even by heat treatment at a low temperature of less than 150°C, and numerous conductive paths are formed (see the photograph on the right in Figure 2). On the other hand, with conventional conductive compositions, the silver nanoparticles cannot be fused by low-temperature heat treatment, and the conductive paths are limited to the contact points of the silver nanoparticles, resulting in a sintered film with a resistivity of 1.0 x 10 －５It was not possible to achieve a resistivity value of Ω·cm or less. The resistivity measurement method is not particularly limited, but may be, for example, the method described in the "Measurement of resistivity after heating at 120°C for 30 minutes" section of the Examples below. A specific example of the resistivity measurement method is as follows: A polycarbonate resin film (product name: Makrofol (registered trademark) DE 1-1 000000, manufactured by Covestro) is used as the organic substrate. The substrate measures 100 mm x 148 mm and has a thickness of 250 μm. Five types of wiring patterns (electrode length: 60 mm, electrode widths: 0.2 mm, 0.5 mm, 1 mm, 2 mm, 3 mm) made of a conductive composition as shown in FIG. 3 are printed on the surface of this substrate using a screen printer. A screen mask with SUS 500 mesh, emulsion thickness of 5 μm, and calendering treatment is used. After printing, the substrate is heated and dried at 120°C for 30 minutes in a constant temperature dryer. The film thickness of the resulting cured wiring pattern (hereinafter simply referred to as "wiring pattern") is measured. The film thickness is measured, for example, using a surface roughness and shape measuring instrument (model number: Surfcom 1500SD-2) manufactured by Tokyo Seimitsu Co., Ltd. The resistance values ​​at both ends of the cured wiring pattern are measured by the four-terminal method using a resistance measuring device RM3545-02 manufactured by HIOKI. The specific resistance value is calculated from the following formula (1): ρ = R × A / L Formula (1) Here, ρ is the specific resistance value, R is the measured resistance value (Ω) at both ends of the wiring pattern, and A is the cross-sectional area (cm ２ ), L is the length of the wiring pattern (cm).

[0047] By heat-treating the conductive composition of this embodiment, a sintered body with excellent flexibility and bending resistance can be obtained. For example, the conductive composition of this embodiment can form a sintered film in which the rate of change in resistivity before and after 500 repeated bending is 50% or less, more preferably 40% or less, and even more preferably 35% or less. The bending method and the method for measuring the rate of change in resistivity are, for example, the same as those described in the "Rate of Change in Resistivity Before and After Bending Test" section of the Examples below. A specific example of the method for measuring the rate of change in resistivity before and after a bending test is as follows: A wiring pattern (electrode length: 60 mm, electrode width: 1 mm) is printed on a polycarbonate resin film using a screen printer and then heated and dried in a constant temperature dryer at 120°C for 30 minutes to prepare a test specimen. A bending test is performed up to 500 times using a 4 mmφ rod in accordance with ASTM D1327 (JIS K-5600-5-1) so that the electrode-printed surface forms a mountain fold. The resistivity of the test piece after the bending test is calculated, and the rate of change (%) in the resistivity relative to the resistivity before the bending test is determined. The resistivity is calculated using the above formula (1).

[0048] When the conductive composition of this embodiment is formed into a coating film, the coating film has small surface irregularities and excellent surface smoothness, and the sintered film obtained by heat-treating the coating film also has high surface smoothness. For example, the conductive composition of this embodiment can form a sintered film having a surface irregularity difference of 6 μm or less, more preferably 5 μm or less, and even more preferably 3 μm or less, when heated at 120°C for 30 minutes. The surface irregularity difference can be measured, for example, according to the method described in the "Coating Film Surface Smoothness Measurement" section of the Examples below. A specific example of measuring the coating film surface smoothness is as follows. A wiring pattern (electrode length: 60 mm, electrode width: 1 mm) is printed on a polycarbonate resin film using a screen printer and then heated and dried in a constant temperature dryer at 120°C for 30 minutes to prepare a test piece. 2D cross-sectional profiles and 3D images are obtained using a confocal microscope (Lasertec Corporation, OPTELICS H1200) to confirm the irregularity difference on the coating film surface. In this specification, the unevenness height difference is defined as the maximum width of the unevenness on the coating film surface. The unevenness height difference on the coating film surface of the present conductive composition can be adjusted, for example, by the structure, molecular weight, and blending amount of (B) binder resin, and the blending amount of (C) organic solvent. Specifically, the fewer polar groups in the binder resin, the better the wettability to organic substrates, and the smaller the unevenness height difference on the coating film surface tends to be. Furthermore, the use of a high molecular weight binder resin reduces thixotropy, improves wettability to organic substrates, and tends to reduce the unevenness height difference on the coating film surface.

[0049] The conductive composition of this embodiment can be used to form conductive circuits on printed circuit boards, electrodes of capacitors, and the like, and is particularly suitable for forming conductive circuits and electrodes on flexible substrates. The conductive composition of this embodiment can also be used to form electrodes and heating wires of printable devices such as printable heaters. The conductive composition of this embodiment can also be used to bond components of electronic components or semiconductor devices, or to bond components to substrates, etc.

[0050] [Sintered body] The sintered body according to the second embodiment of the present invention is a sintered body of the conductive composition according to the first embodiment. The sintered body according to this embodiment has low resistance and excellent flexibility and bending resistance.

[0051] [Laminated Structure] A laminated structure according to a third embodiment of the present invention has the sintered body of the second embodiment described above on a substrate. The laminated structure according to this embodiment has a sintered body having low resistance and excellent flexibility and bending resistance on a substrate, and is therefore suitable for use in flexible electronic devices, but is not limited thereto. The substrate may be a flexible substrate such as a plastic film, or a hard substrate such as metal, glass, or ceramic. Examples of plastic films include, but are not limited to, polyimide films, PET films, and polycarbonate films.

[0052] [Electronic Component or Semiconductor Device] An electronic component or semiconductor device according to a fourth embodiment of the present invention has the sintered body of the second embodiment described above. Because the sintered body has low resistance and excellent flexibility and bending resistance, it is useful as a flexible electronic device, but is not limited thereto. Flexible electronic devices include, but are not limited to, flexible touch panels, flexible lighting, flexible batteries, flexible printed circuit boards, flexible color filters, surface cover lenses for smartphones, printable heaters, flexible sensors, and flexible actuators.

[0053] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. In the following examples, parts and % represent parts by mass and % by mass unless otherwise specified.

[0054] [Examples 1 to 21, Comparative Examples 1 to 3] The components shown in Table 1 were stirred and mixed using a hybrid mixer according to the formulation shown in Table 1, and then uniformly dispersed using a three-roll mill to prepare conductive compositions of the examples and comparative examples. In Table 1, the amount of each component is expressed in parts by mass (unit: g). The components used in the examples and comparative examples are as follows.

[0055] The following components (A) and (A') were produced using a method conforming to the above-described silver nanoparticle production method. Various carboxylic acids or alkylamines (8.2 g) and butanol (37.5 g) or a mixture of butanol (8.75 g) and ethylene glycol (28.75 g) were added to a 50 mL glass centrifuge tube containing a magnetic stirrer and stirred for approximately 1 minute. Then, silver oxalate (25.0 g) was added and stirred for approximately 10 minutes to obtain a composition for preparing silver nanoparticles. The glass centrifuge tubes were then placed upright on a hot stirrer (HHE-19G-U, manufactured by Koike Precision Machinery Co., Ltd.) equipped with an aluminum block, and the mixture was stirred at 40°C for 30 minutes, followed by stirring at 90°C for 30 minutes. After cooling, the magnetic stirrer was removed, and 15 g of methanol was added to each composition. The mixture was stirred using a vortex mixer, then centrifuged for 1 minute at 3,000 rpm (approximately 1,600 x G) using a Hitachi CF7D2 centrifuge, and the supernatant was removed. The process of adding 15 g of methanol, stirring, centrifuging, and removing the supernatant was repeated twice to recover the surface-modified silver nanoparticles. Diethylene glycol monobutyl ether (common name: butyl carbitol) was added to the mixture to obtain a slurry of surface-modified silver nanoparticles in diethylene glycol monobutyl ether. The organic solvent in the slurry was treated as the (C) organic solvent of the conductive composition.

[0056] (A) Surface-modified silver nanoparticles coated with a lower carboxylic acid (A-1): Surface-modified silver nanoparticles coated with acetic acid (average particle size: 100 nm, number of carbon atoms: 2) (A-2): Surface-modified silver nanoparticles 1 coated with lactic acid (average particle size: 100 nm, number of carbon atoms: 3) (A-3): Surface-modified silver nanoparticles 2 coated with lactic acid (average particle size: 500 nm, number of carbon atoms: 3) (A-4): Surface-modified silver nanoparticles coated with butyric acid (average particle size: 100 nm, number of carbon atoms: 4) (A-5): Surface-modified silver nanoparticles coated with methyl maleate (average particle size: 100 nm, number of carbon atoms: 5) (A') Surface-modified silver nanoparticles other than component (A) (A'-1): Surface-modified silver nanoparticles coated with octylamine (average particle size: 100 nm, number of carbon atoms: 8)

[0057] (B) Binder Resin (B-1): Polyvinyl butyral resin 1 (product name: BX-L, manufactured by Sekisui Chemical Co., Ltd., weight average molecular weight: 18,000) (B-2): Polyvinyl butyral resin 2 (product name: KS-5Z, manufactured by Sekisui Chemical Co., Ltd., weight average molecular weight: 130,000) (B-3): Ethyl cellulose resin 1 (product name: N14, manufactured by ASHLAND, weight average molecular weight: 87,100) (B-4): Ethyl cellulose resin 2 (product name: N50, manufactured by ASHLAND, weight average molecular weight: 135,000) (B-5): Ethyl cellulose resin 3 (product name: N200, manufactured by ASHLAND, weight average molecular weight: 187,800)

[0058] (C) Organic Solvent (C-1): Diethylene glycol diethyl ether (manufactured by Toho Chemical Industry Co., Ltd., boiling point: 189°C) (C-2): Dihydroterpineol (manufactured by Nippon Terpene Chemical Co., Ltd., boiling point: 207°C) (C-3): Terpineol (manufactured by Kobayashi Perfume Co., Ltd., boiling point: 219°C) (C-4): Diethylene glycol monobutyl ether (trade name: butyl carbitol) (manufactured by Taishin Chemical Co., Ltd., boiling point: 230°C) (C-5): Diethylene glycol dibutyl ether (manufactured by Toho Chemical Industry Co., Ltd., boiling point: 256°C) (C-6): Tetraethylene glycol dimethyl ether (manufactured by Taishin Chemical Co., Ltd., boiling point: 230°C) (C-7): Diethylene glycol monobutyl ether (trade name: butyl carbitol) contained in the component (A) or component (A') slurry

[0059] [Measurement of Desorption Initiation Temperature of Protective Layer] For each of the conductive compositions of the Examples and Comparative Examples, TG-MS analysis was performed to measure the desorption initiation temperature of the protective layer of the surface-modified silver nanoparticles. Tetramethylammonium hydroxide (TMAH), a methylation reagent, was added to each of the conductive compositions of the Examples and Comparative Examples to prepare a measurement sample. Measurement was performed using a TG-MS analyzer (NETZSCH STA 449F3, manufactured by NETZSCH) under the following measurement conditions: a measurement sample weight of 90 mg, a measurement temperature of 30°C to 320°C, and a helium atmosphere. The desorption initiation temperature of the protective layer was evaluated as ⊚ when it was between 40°C and 80°C, ◯ when it was between 80°C and 130°C, and × when it was above 130°C. The results are shown in Table 1.

[0060] [Measurement of specific resistance after heating at 120°C for 30 minutes] A polycarbonate resin film (product name: Makrofol (registered trademark) DE 1-1 000000, manufactured by Covestro) was used as the organic substrate. The substrate had a size of 100 mm x 148 mm and a thickness of 250 μm. Five types of wiring patterns (electrode length: 60 mm, electrode width: 0.2 mm, 0.5 mm, 1 mm, 2 mm, 3 mm) of the conductive composition as shown in FIG. 3 were printed on the surface of this substrate using a screen printer. The screen mask used was SUS 500 mesh, emulsion thickness of 5 μm, and calendared. After printing, the substrate was heated and dried at 120°C for 30 minutes in a constant temperature dryer. The film thickness of the resulting cured wiring pattern (hereinafter simply referred to as "wiring pattern") was 2 to 10 μm. The film thickness was measured using a surface roughness and shape measuring instrument (model: Surfcom 1500SD-2) manufactured by Tokyo Seimitsu Co., Ltd. The resistance values ​​at both ends of the cured wiring pattern were measured by the four-terminal method using a resistance measuring device RM3545-02 manufactured by HIOKI. The specific resistance value was calculated from the following formula (1): ρ = R × A / L Formula (1) where ρ is the specific resistance value, R is the measured resistance value (Ω) at both ends of the wiring pattern, and A is the cross-sectional area of ​​the wiring pattern (cm ２ ), and L is the length of the wiring pattern (cm). The results are shown in Table 1.

[0061] [Rate of change in resistivity before and after bending test] A wiring pattern with an electrode width of 1 mm was cut out from the wiring pattern prepared for the resistivity measurement described above to prepare a test specimen for a 500-fold bending test. The test method was in accordance with ASTM D1327 (JIS K-5600-5-1), in which a bending test was performed up to 500 times using a 4 mmφ rod so that the electrode printed surface formed a mountain fold. The resistivity of the test specimen after the bending test was calculated, and the rate of change in resistivity (%) relative to the resistivity value before the bending test was determined. The results are shown in Table 1.

[0062] [Measurement of Coating Surface Smoothness] A wiring pattern with an electrode width of 1 mm was cut out from the wiring pattern prepared for the resistivity measurement described above to prepare a test piece. A confocal microscope (Lasertec Corporation, OPTELICS H1200) was used to obtain 2D cross-sectional profiles and 3D images, and the unevenness height difference on the coating surface was confirmed. In this specification, the unevenness height difference is defined as the maximum width of the unevenness on the coating surface. The results are shown in Table 1.

[0063]

[0064]

[0065]

[0066] The conductive films (sintered films) obtained by heat treating the conductive compositions of Examples 1 to 21 at 120°C for 30 minutes all had a specific resistance of 1.0 x 10 －５ The resistivity was Ω cm or less. Furthermore, the sintered films of the conductive compositions of Examples 1 to 21 all had a rate of change in resistivity before and after a 500-fold bending test of 50% or less. Furthermore, the sintered films of the conductive compositions of Examples 1 to 21 all had a surface irregularity height difference of 6 μm or less.

[0067] On the other hand, the conductive film obtained from the conductive composition of Comparative Example 1, which did not contain (A) surface-modified silver nanoparticles the surface of which was coated with a lower carboxylic acid, but contained (A'-1): surface-modified silver nanoparticles coated with octylamine, had a specific resistance of 15 × 10 －５ The conductive composition of Comparative Example 2, in which the temperature at which the protective layer of the surface-modified silver nanoparticles began to be detached exceeded 130°C, had a specific resistance of 8 × 10 －５ (B) The sintered film of the conductive composition of Comparative Example 3, which did not contain a binder resin, broke in the 500-fold bending test, and was not found to have sufficient bending resistance. In addition, the height difference of the surface irregularities exceeded 6 μm.

[0068] The present invention provides a conductive composition that can be sintered at low temperatures and forms a conductive film with low resistance and excellent flexibility and bending resistance, and is particularly suitable for producing conductive circuits and electrodes on flexible substrates.

[0069] The disclosure of Japanese Patent Application No. 2022-153954 (filing date: September 27, 2022) is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. (A) Surface-modified silver nanoparticles coated with a lower carboxylic acid, (B) Binder resin and (C) Organic solvents and A conductive composition comprising, A conductive composition in which the lower carboxylic acid of the (A) surface-modified silver nanoparticles present in the conductive composition begins to detach from the silver nanoparticles at a temperature of 40°C to 130°C.

2. The conductive composition according to claim 1, wherein the lower carboxylic acid in the (A) surface-modified silver nanoparticles is at least one selected from acetic acid, butyric acid, lactic acid, methyl maleate, and hydroxyisobutyric acid.

3. The conductive composition according to claim 1, wherein the (C) organic solvent comprises an organic solvent having a boiling point of 180°C to 270°C.

4. The conductive composition according to claim 1, wherein the average particle size of the (A) surface-modified silver nanoparticles is 20 nm to 600 nm.

5. (B) The conductive composition according to claim 1, wherein the weight-average molecular weight of the binder resin is 5,000 to 200,000.

6. The conductive composition according to claim 1, wherein the (B) binder resin is a cellulose-based resin.

7. The conductive composition according to claim 1, wherein the mass ratio (component (A):component (B)) of (A) surface-modified silver nanoparticles to (B) binder resin is 90:10 to 99.7:0.

3.

8. The conductive composition according to claim 1, wherein the content of the (C) organic solvent is 10 to 50 parts by mass per 100 parts by mass of the conductive composition.

9. Under heating conditions of 120°C for 30 minutes, the resistivity is 1.0 × 10⁻⁶. －５ The conductive composition according to claim 1, which forms a sintered film with a density of Ω·cm or less.

10. The conductive composition according to claim 1, which forms a sintered film in which the rate of change in resistivity before and after 500 repeated bending cycles is 50% or less.

11. The conductive composition according to claim 1, wherein a sintered film having a surface unevenness height difference of 6 μm or less is formed under heating conditions of 120°C for 30 minutes.

12. A sintered body of a conductive composition according to any one of claims 1 to 11.

13. A laminated structure having the sintered body described in claim 12 on a substrate.

14. An electronic component or semiconductor device having the sintered body described in claim 12.